Patent Application
20070003552
The invention relates to the field of biochemistry, molecular biology, structural biology and medicine. More in particular, the invention relates to cross-β structure, their binding proteins and their biological roles.
An increasing body of evidence suggests that unfolding of globular proteins can lead to toxicity.1 Unfolded proteins can initiate protein aggregation and fibrillization by adopting a partially structured conformation. Such fibrillar aggregates can (slowly) accumulate in various tissue types and are associated with a variety of degenerative diseases. The term “amyloid” is used to describe these fibrillar deposits (or plaques). Diseases characterized by anyloid are referred to as amyloidosis and include Alzheimer disease (AD), light-chain amyloidosis, type II diabetes and spongiform encephalopathies. It has been found recently that toxicity is an inherent property of misfolded proteins. According to the present invention this common mechanism for these conformational diseases.1
A cross-β structure is a secondary structural element in peptides or proteins. A cross-β structure can be formed upon denaturation, proteolysis or unfolding of proteins.2 These secondary structure elements are typically absent in globular regions of proteins. The cross-β structure is found in amyloid fibrils. Amyloid peptides or proteins are cytotoxic to cells. A cross-β structure is composed of stacked β-sheets. In a cross-β structure the individual β-strands, run either perpendicular to the long axis of a fibril, or the β-strands run in parallel to the long axis of a fiber. The direction of the stacking of the β-sheets in cross-β structures is perpendicular to the long fiber axis.
We report here that glycation of proteins also induces the formation of the cross-β structure. Our results, combined with existing literature information indicate that a common structure is induced upon unfolding of globular proteins. Therefore, the present invention discloses a novel pathway involving cross-β structure, which pathway will be called “cross-β structure pathway.” This pathway consists of several cross-β structure binding proteins, including so-called multiligand receptors and is involved in protein degradation and/or protein clearance. We also report the identification of novel cross-β binding proteins that contain a cross-β structure binding module. These findings support the identification of a cross-β structure pathway. Multiple aspects of this novel pathway are outlined below.
For example, the present invention discloses that proteolysed, denatured, unfolded, glycated, oxidized, acetylated or otherwise structurally altered proteins adopt cross-β structures. Examples of known cross-β structure forming proteins are all proteins that cause amyloidosis or proteins that are found in disease related amyloid depositions, for example, but not restricted to, Alzheimer β-amyloid (Aβ) and Islet Amyloid PolyPeptide (IAPP). The present invention discloses that fibrin, glycated proteins (for example glycated albumin and glycated hemoglobin) and endostatin are also capable of adopting a cross-β structure.
The invention furthermore discloses the identification of the formation of a cross-β structure as a signal for protein degradation and/or protein clearance.
The serine protease tissue plasminogen activator (tPA) induces the formation of plasmin through cleavage of plasminogen. Plasmin cleaves fibrin and this occurs during lysis of a blood clot. Although not essential for fibrinolysis in mice,3; 4 tPA has been recognized for its role in fibrinolysis for a long time. 5; 6 Activation of plasminogen by tPA is stimulated by fibrin or fibrin fragments, but not by its precursor, fibrinogen.7-10 This can be in part explained by the strong binding of tPA to fibrin and weak binding to fibrinogen. The binding sites in fibrin and in tPA responsible for binding and activation of tPA have been mapped and studied in detail.8-21 However the exact structural basis for the interaction of tPA with fibrin was unknown. In addition to fibrin and fibrin fragments, many other proteins have been described that are similarly capable of binding tPA and stimulating tPA-mediated plasmin formation.22-36 Like with fibrin and fibrin fragments, the exact nature of the interaction(s) between these ligands for tPA and tPA were not known. Moreover, it was unknown why and how all these proteins, which lack primary sequence homology, bind tPA. The invention now discloses tissue type plasminogen activator (tPA) as a protein capable of binding cross-β structures. Furthermore, the invention discloses the finger domain (also named fibronectin type I domain) and other comparable finger-domains as a cross-β structure binding module. The present invention further discloses that proteins which bind to these fingers will be typically capable of forming cross-β structures.
Since fibrin contains the cross-β structure, the present invention also discloses that the generation of cross-β structures plays a role in physiological processes. The invention discloses that the generation of cross-β structures is part of a signaling pathway, the “cross-β structure pathway,” that regulates protein degradation and/or protein clearance. Inadequate function of this pathway may result in the development of diseases, such as conformational diseases37 and/or amyloidosis.
The present invention furthermore discloses that the cross-β structure is a common denominator in ligands for multiligand receptors.38 The invention discloses therefore that multiligand receptors belong to the “cross-β structure pathway.”
The best studied example of a receptor for a cross-β structure is RAGE.39-44 Examples of ligands for RAGE are Aβ, protein-advanced glycation end-products (AGE) adducts (including glycated-BSA), amphoterin and S100. RAGE is a member of a larger family of multiligand receptors,38 that includes several other receptors, some of which, including CD36 are known to bind cross-β structure containing proteins (see also
Especially the role of FXII is important, since it activates the intrinsic coagulation pathway. Activation of the intrinsic pathway, and the resulting formation of vasoactive peptides and the activation of other important proteins contribute to the process of protection and/or clearance of undesired proteins or agents. The “cross-β structure pathway” is modulated in many ways. Factors that regulate the pathway include modulators of synthesis and secretion, as well as modulators of activity. The pathway is involved in many physiological and pathological processes. Therefore, the invention furthermore provides a method for modulating extracellular protein degradation and/or protein clearance comprising modulating the activity of a receptor for cross-β structure forming proteins. Examples of receptors for cross-β structure forming proteins include RAGE, CD36, Low density lipoprotein Related Protein (LRP), Scavenger Receptor B-1 (SR-BI), SR-A. The invention discloses that FXII, HGFa and fibronectine are also receptors for cross-β structure.
The present invention discloses that tissue-type plasminogen activator (tPA) is a cross-β structure binding protein, a multiligand receptor and a member of the “cross-β structure pathway.” The invention discloses that tPA mediates cross-β structure induced cell dysfunction and/or cell toxicity. The invention discloses that tPA mediates at least in part cell dysfunction and/or toxicity through activation of plasminogen. The plasminogen dependent effects are inhibited by B-type carboxypeptidase activity B and thereby a role for carboxyterminal lysine residues in the cross-β structure pathway is disclosed.
The present invention relates, amongst others, to the structure(s) in fibrin and other proteins that bind tPA, to the binding domain in tPA and to the pathway(s) regulated by this structure. The present invention discloses a presence of cross-β structures in proteins and peptides that are capable of binding tPA. The herein disclosed results indicate a strong correlation between the presence of a cross-β structure and the ability of a molecule to bind tPA. Furthermore, the results indicate the presence of an amyloid structure in fibrin. This indicates that under physiological conditions a cross-β structure can form, a phenomenon that has been previously unrecognized. The formation of cross-β structures has thus far only been associated with severe pathological disorders. tPA binds denatured proteins, which indicates that a large number of proteins, if not all proteins, can adopt a conformation containing cross-β structure or cross-β-like structure(s). Taken together, the formation of cross-β structures is likely to initiate and/or participate in a physiological cascade of events, necessary to adequately deal with removal of unwanted molecules, i.e., misfolded proteins, apoptotic cells or even pathogens.
Thus in a first embodiment the invention provides a method for modulating extracellular protein degradation and/or protein clearance comprising modulating cross-β structure formation (and/or cross-β structure-mediated activity) of the protein present in the circulation.
There are two major regular protein-folding patterns, which are known as the β-sheet and the a-helix. An antiparallel β-sheet is formed when an extended polypeptide chain folds back and forth upon itself, with each section of the chains running in the direction opposite to that of its immediate neighbours. This gives a structure held together by hydrogen bonds that connect the peptide bonds in neighbouring chains. Regions of a polypeptide chain that run in the same direction form a parallel β-sheet. A cross-β structure is composed of stacked β-sheets. In a cross-β structure the individual β-strands, run either perpendicular to the long axis of a fibril, or the β-strands run in parallel to the long axis of a fiber. The direction of the stacking of the β-sheets in cross-β structures is perpendicular to the long fiber axis. As disclosed herein within the experimental part, a broad range of proteins is capable of adopting a cross-β structure and moreover these cross-β structure comprising proteins are all capable of binding and stimulating tPA and thereby promoting destruction of unwanted or damaging proteins or agents.
An extracellular protein includes a protein present outside a cell or cells.
Protein degradation and/or protein clearance includes the breakdown and removal of unwanted proteins, for example unwanted and/or destroyed (for example denatured) protein. Also included is the removal of unwanted biomolecules during several processes, including fibrinolysis, formation of neuronal synaptic networks, clearance of used, unwanted and/or destroyed (denatured) proteins, induction of apoptosis and clearance of apoptotic cells and pathogens.
The term “in the circulation” is herein defined as a circulation outside a cell or cells, for example, but not restricted to, the continuous movement of blood.
In yet another embodiment the invention provides a method for increasing extracellular protein degradation and/or protein clearance comprising increasing cross-β structure formation and/or cross-β structure-mediated activity of the protein present in the circulation. Increase of cross-β structure formation of a particular protein leads, for example to activation of tPA which in turn induces the formation of plasmin through cleavage of plasminogen and thus results in an increase in the degradation and/or protein clearance.
In a preferred embodiment the invention provides a method for increasing extracellular protein degradation and/or protein clearance comprising providing a compound capable of increasing cross-β structure formation (and/or cross-β structure-mediated activity) of the protein present in the circulation. In an even more preferred embodiment the compound capable of increasing cross-β structure formation is glucose. Under certain circumstances the addition of glucose to a protein leads to an irreversible, non-enzymatic glycation reaction in which predominantly a glucose molecule is attached to the free amino groups of lysine residues in a protein. In addition, N-termini and free amino groups of arginine residues are prone to glycation. It is disclosed herein within the experimental part that glycation leads to cross-β structure formation. Hence, the invention provides a method for increasing extracellular protein degradation and/or protein clearance comprising providing a compound capable of increasing cross-β structure formation of the protein present in the circulation.
Other examples of compounds capable of increasing (or mimicking) cross-β structure formation in a protein are apolar solutions, urea (as disclosed herein within the experimental part), ions (for example Zn2+). However, it is clear that there are also other ways to increase or mimic cross-β structure formation for example by denaturation, low pH, temperature, mutations or protein modification in general (for example oxidation).
Besides, a method for increasing extracellular protein degradation and/or protein clearance comprising increasing cross-β structure formation of the protein present in the circulation via any of the above described methods to degrade and/or remove, preferably, the protein which comprises the cross-β structure, it is also possible to degrade and/or remove a protein which does not comprise a cross-β structure. This is for example accomplished by providing a compound comprising a cross-β structure and a compound comprising tPA-like activity at or near the protein which needs to be degraded and/or removed. An example of a compound comprising a cross-β structure is fibrin or a fragment thereof comprising the cross-β structure and an example of a compound comprising tPA-like activity is tPA.
In another embodiment the invention provides a method for decreasing extracellular protein degradation and/or protein clearance comprising decreasing cross-β structure formation of the protein present in the circulation. More preferably, the invention provides a method for decreasing extracellular protein degradation and/or protein clearance comprising providing a compound capable of decreasing cross-β structure formation of the protein present in the circulation. Decreasing of cross-β structure formation is for example accomplished by shielding or blocking of the groups involved in the formation of a cross-β structure. Examples of compounds capable of decreasing cross-β structure formation are Congo red, antibodies, β-breakers, phosphonates, heparin, amino-guanidine or laminin.45 Yet another way to decrease cross-β structure formation in a protein is by removal of a glucose group involved in the glycation of the protein.
In yet another embodiment the invention provides a method for modulating extracellular protein degradation and/or protein clearance comprising modulating tPA, or tPA-like activity. tPA induces the formation of plasmin through cleavage of plasminogen. Plasmin cleaves fibrin and this occurs during lysis of a blood clot. Activation of plasminogen by tPA is stimulated by fibrin or fibrin fragments, but not by its precursor fibrinogen. The term “tPA-like activity” is herein defined as a compound capable of inducing the formation of plasmin, possibly in different amounts, and/or other tPA mediated activities. Preferably, tPA-like activity is modified such that it has a higher activity or affinity towards its substrate and/or a cofactor. This is for example accomplished by providing the tPA-like activity with multiple binding domains for cross-β structure comprising proteins. Preferably, the tPA-like activity is provided with multiple finger domains. It is herein disclosed that the three-dimensional structures of the tPA finger-domain and the fibronectin finger-domains 4-5 reveals striking structural homology with respect to local charge-density distribution. Both structures contain a similar solvent exposed stretch of five amino-acid residues with alternating charge; for tPA Arg7, Glu9, Arg23, Glu32, Arg30, and for fibronectin Arg83, Glu85, Lys87, Glu89, Arg90, located at the fifth finger domain, respectively. The charged-residue alignments are located at the same side of the finger module. Hence, preferably, the tPA-like activity is provided with one or more extra finger domain(s) which comprise(s) ArgXGlu(X)13Arg(X)8GluXArg or ArgXGluXLysXGluArg.
The activity of tPA and/or the tPA mediated activation of plasminogen is increased by the binding to fibrin fragments, or other protein fragments that have a lysine or an arginine at the carboxy-terminal end. B-type carboxypeptidases, including but not limited to carboxypeptidase B (CpB) or Thrombin Activatable Fibinolysis Inhibitor (TAFI, also named carboxypeptidase U or carboxypeptidase R), are enzymes that cleave off carboxy-terminal lysine and arginine residues of fibrin fragments that would otherwise bind to tPA and/or plasminogen and stimulate plasmin formation.
In a preferred embodiment the invention provides a method for increasing extracellular protein degradation and/or protein clearance comprising providing a compound capable of increasing tPA-like and/or tPA mediated activity or activities. In an even more preferred embodiment the invention provides a method for increasing extracellular protein degradation and/or protein clearance comprising providing a compound capable of increasing tPA-like activity, wherein the compound comprises a cross-β structure. In another embodiment, the invention provides a method for increasing extracellular protein degradation and/or protein clearance comprising providing a compound capable of inhibiting B-type carboxypeptidase activity. In a more preferred embodiment the compound comprises carboxypeptidase inhibitor (CPI) activity.
In yet another embodiment the invention provides a method for decreasing extracellular protein degradation and/or protein clearance comprising providing a compound capable of decreasing tPA-like activity. More preferably, the invention provides a method for decreasing extracellular protein degradation and/or protein clearance comprising providing a compound capable of decreasing tPA-like activity or tPA-mediated activity or activities, wherein the compound is a protein and/or a functional equivalent and/or a fimctional fragment thereof. For example, such a compound capable of decreasing tPA-like activity is an inhibitor of tPA or a substrate of tPA which binds and does not let go. Examples of a compound capable of decreasing tPA-like activity or tPA-mediated activity include but are not limited to, lysine, arginine, e-amino-caproic acid or tranexamic acid, serpins (for example neuroserpin, PAI-1), tPA-Pevabloc, antibodies that inhibit tPA-like activity or tPA-mediated activity or B-type carboxypeptidase(s). For example, providing lysine results in the prevention or inhibition of binding of a protein comprisiung a C-terminal lysine-residue to the Kringle domain of plasminogen. Hence, tPA activation is prevented or inhibited. Preferably, the compound capable of decreasing tPA-like activity or tPA-mediated activity or activities reduce the tPA-like activity or tPA-mediated activity or activities and even more preferably, the tPA-like activity or tPA-mediated activity or activities is completely inhibited.
A functional fragment and/or a functional equivalent is typically defined as a fragment and/or a equivalent capable of performing the same function, possibly in different amounts. For example, a functional fragment of an antibody capable of binding to a cross-β structure would be the Fab' fragment of the antibody.
In yet another embodiment the invention provides a method for modulating extracellular protein degradation and/or protein clearance comprising modulating an interaction between a compound comprising a cross-β structure and a compound comprising tPA-like activity. In another embodiment the invention provides a method for decreasing extracellular protein degradation and/or protein clearance comprising decreasing an interaction between a compound comprising a cross-β structure and a compound comprising tPA-like activity. Such a compound is for example a chemical, a proteinaceous substance or a combination thereof. In a more preferred embodiment the invention provides a method for decreasing extracellular protein degradation and/or protein clearance comprising providing a compound capable of decreasing an interaction between a compound comprising a cross-β structure and a compound comprising tPA-like activity. Even more preferably, the invention provides a method for decreasing extracellular protein degradation and/or protein clearance according to the invention, wherein the compound is a protein and/or a functional equivalent and/or a functional fragment thereof. Even more preferably, the protein is an antibody and/or a functional equivalent and/or a functional fragment thereof. Other examples are Congo red or Thioflavin. The invention also provides a method for decreasing extracellular protein degradation and/or protein clearance comprising decreasing an interaction between a compound comprising a cross-β structure and a compound comprising tPA-like activity, wherein the interaction is decreased by providing a compound capable of competing with the interaction. More in particular, the compound capable of competing with the interaction comprises a finger domain and even more preferably, the finger domain comprises a stretch of at least 5 amino acid residues with alternating charge, for example ArgXGlu(X)13Arg(X)8GluXArg or ArgXGluXLysXGluArg. Preferably, the compound is fibronectin, FXII, HGFa or tPA. It is clear that the invention also comprises a method for increasing extracellular protein degradation and/or protein clearance comprising increasing an interaction between a compound comprising a cross-β structure and a compound comprising tPA-like activity. This is for example accomplished by providing a compound capable of increasing an interaction between a compound comprising a cross-pstructure and a compound comprising tPA-like activity. Preferably, the compound capable of increasing an interaction between a compound comprising a cross-β structure and a compound comprising tPA-like activity is a protein and/or a functional equivalent and/or a finctional fragment thereof. For example an antibody which stabilizes the interaction between a compound comprising cross-β structure and a compound comprising tPA-like activity, rendering the tPA-like activity in a continuous activated state, hence protein degradation and/or protein clearance is increased. However it is appreciated that increasing an interaction between a compound comprising a cross-β structure and a compound comprising tPA-like activity is also accomplished by mutations in either the compound comprising a cross-β structure or in the compound comprising tPA-like activity, like swapping of domains (for example by providing the compound comprising tPA-like activity with other or more finger domains (obtainable from tPA, fibronectin, FXII or HGFa) or by including binding domains of for example RAGE or CD36.
In yet another embodiment the invention provides a method for modulating extracellular protein degradation and/or protein clearance comprising modulating an interaction of a compound comprising tPA-like activity and the substrate of the activity. It is clear that there are multiple ways by which the interaction can either be increased or decreased. An increase in the interaction between a compound comprising tPA-like activity and the substrate of the activity is for example accomplished by providing the compound comprising tPA-like activity with a mutation or mutations which improve the affinity of the compound with tPA-like activity for its substrate.
In yet another embodiment the invention provides a method for removing cross-β structures from the circulation, using a compound comprising a cross-β structure binding domain. Preferably, the compound is tPA or the finger domain of tPA. It is clear that the invention also comprises other cross-β structure binding domains, including, but not limited to the finger domains of HGFa, FXII and fibronectin. It is clear that the invention also comprises antibodies that bind cross-β structures.
The present invention further discloses the use of a novel strategy to prevent the formation or to decrease/diminish (amyloid) plaques involved in a conformational disease, type II diabetes and/or ageing (e.g., Alzheimer's disease). Plaques are typically defined as extracellular fibrillar protein deposits (fibrillar aggregates) and are characteristic of degenerative diseases. The “native” properties of the constituent amyloid proteins may vary: some are soluble oligomers in vivo (e.g., transthyretin in familial amyloid polyneuropathy), whereas others are flexible peptides (e.g., amyloid-b in Alzheimer's disease (AD)). The basic pathogenesis of conformational diseases, for example neurodegenerative disorders (AD, prion disorders) is thought to be related to abnormal pathologic protein conformation, i.e the conversion of a normal cellular and/or circulating protein into an insoluble, aggregated, β-structure rich form which is deposited in the brain. These deposits are toxic and produce neuronal dysfunction and death. The formation of cross-β structures has thus far only been associated with severe pathological disorders. Our results, show that tPA and other receptors for cross-β structure forming proteins can bind denatured proteins, indicating that a large number of proteins are capable of adopting a conformation containing cross-β or cross-β-like structures. Taken together, the formation of a cross-β structure initiates or participates in a physiological cascade of events; necessary to adequately deal with removal of unwanted molecules, i.e., misfolded proteins, apoptotic cells or even pathogens. By increasing cross-β structure formation in a protein involved in a conformational disease, the pathway for protein degradation and/or protein clearance is activated and the protein is degraded, resulting in a decreasing plaque or more preferably, the plaque is completely removed. Hence, the effects of the conformational disease are diminished or more preferably, completely abolished.
In a further embodiment the invention provides the use of a compound capable of increasing cross-β structure formation for diminishing plaques involved in a conformational disease. In another embodiment the invention provides the use of a compound capable of binding to a cross-β structure for diminishing plaques and/or inhibiting cross-β structure mediated toxicity involved in a conformational disease. In a preferable use of the invention, the compound is a protein and/or a functional equivalent and/or a functional fragment thereof and even more preferably, the protein is tPA, a finger domain, an antibody and/or a functional equivalent and/or a functional fragment thereof. Examples of such antibodies are 4B5 or 3H7.
In yet a further embodiment the invention provides use of a compound capable of increasing tPA-like activity for diminishing plaques involved in a conformational disease. Preferably, the tPA-like activity is modified such that it has a higher activity or affinity towards its substrate and/or cofactor. This is for example accomplished by providing the tPA-like activity with multiple binding domains for cross-β structure comprising proteins. Preferably, the binding domain comprises a finger domain and even more preferably, the finger domain comprises a stretch of at least 5 amino acid residues with alternating charge, for example ArgXGlu(X)13Arg(X)8GluXArg or ArgXGluXLysXGluArg. Even more preferably, the finger domain is derived from fibronectin, FXII, HGFa or tPA.
In yet another embodiment the invention provides the use of a compound capable of binding to a cross-β structure for the removal of cross-β structures. Preferably, the compound is a protein and/or a functional equivalent and/or a functional fragment thereof. More preferably, the compound comprises tPA or tPA-like activity and/or a functional equivalent and/or a functional fragment thereof. Even more preferably, the functional fragment comprises a finger domain. Preferably, the finger domain comprises a stretch of at least 5 amino acid residues with alternating charge, for example ArgXGlu(X)13Arg(X)8GluXArg or ArgXGluXLysXGluArg. Even more preferably, the finger domain is derived from fibronectin, FXII, HGFa or tPA. In another preferred embodiment the protein is an antibody and/or a functional equivalent and/or a functional fragment thereof. With this use the invention provides for example a therapeutic method to remove cross-β structure comprising proteins from for example the circulation, preferably via extracorporeal dialysis. For example, a patient with sepsis is subjected to such use by dialysis of blood of the patient through means which are provided with for example, preferably immobilized, finger domains. One could for example couple the finger domains to a carrier or to the inside of the tubes used for the dialysis. In this way, all cross-β structure comprising proteins will be removed from the blood stream of the patient, thereby relieving the patients of the negative effects caused by the cross-β structure comprising proteins. Besides finger domain comprising compounds, it is also possible to use other cross-β structure binding compounds, like antibodies or Congo Red. It is also clear that the use could be applied in haemodialysis of kidney patients.
In yet another embodiment the invention provides the use of a compound capable of increasing or stabilising an interaction of a compound comprising a cross-β structure and a compound comprising tPA-like activity for diminishing plaques involved in a conformational disease. Examples of a compound capable of increasing or stabilising an interaction of a compound comprising a cross-β structure and a compound comprising tPA-like activity are given herein. A preferable use according to the invention is provided, wherein the conformational disease is Alzheimer or diabetes. It is clear that the invention not only provides a use to decrease/diminish plaques involved in a conformational disease but that the onset of the disease can also be inhibited or more preferably, completely prevented. Examples of diseases which can be prevented and/or treated according to the invention are conformational disease, amyloidosis type diseases, atherosclerosis, diabetes, bleeding, thrombosis, cancer, sepsis and other inflammatory diseases, Multiple Sclerosis, auto-immune diseases, disease associated with loss of memory or Parkinson and other neuronal diseases (epilepsy).
In another embodiment the invention provides the use of an antibody capable of recognizing a cross-β structure epitope for determining the presence of plaque involved in a conformational disease. In yet another embodiment the invention provides use of a cross-β structure binding domain (preferably, a finger domain from for example tPA) for determining the presence of a plaque involved in a conformational disease.
These uses of the invention provide a new diagnostic tool. It was not until the present invention that a universal b-structure epitope was disclosed and that a diagnostic assay could be based on the presence of the cross-β structure. Such use is particular useful for diagnostic identification of conformational diseases or diseases associated with amyloid formation, like Alzheimer or diabetes. It is clear that this diagnostic use is also useful for other diseases which involve cross-β structure formation, like all amyloidosis type diseases, atherosclerosis, diabetes, bleeding, cancer, sepsis and other inflammatory diseases, Multiple Sclerosis, auto-immune diseases, disease associated with loss of memory or Parkinson and other neuronal diseases (epilepsy). For example, one can use a finger domain (of for example tPA) and provide it with a label (radio active, fluorescent etc.). This labeled finger domain can then be used either in vitro or in vivo for the detection of cross-β structure comprising proteins, hence for determining the presence of a plaque involved in a conformational disease. One can for example use an ELISA assay to determine the amount of sepsis in a patient or one can localize a plaque involved in a conformational disease.
In yet another embodiment the invention provides a recombinant tPA comprising an improved cross-β structure binding domain or multiple cross-β structure binding domains. Preferably, the tPA is provided with multiple, possibly different, finger domains. A recombinant tPA comprising an improved cross-β structure binding domain or multiple cross-β structure binding domains is used for different purposes. For example in a method for the improved treatment of thrombolysis or for the removal of cross-β structure comprising proteins from the circulation of a patient in need thereof. Another use of a recombinant tPA comprising an improved cross-β structure binding domain or multiple cross-β structure binding domains is in diagnostic assays, for example in a BSE detection kit or in imaging experiments. This imaging with a recombinant tPA comprising an improved cross-β structure binding domain or multiple cross-β structure binding domains is for example useful for detection of apoptosis. For example, labelled tPA, for example but not limited to radio-labelled tPA, is inoculated in an individual, followed by detection and localization of the labelled tPA in the body. It is clear that the recombinant tPA comprising a cross-β structure binding domain or multiple cross-β structure binding domains are also useful in therapeutic applications.
Because this invention has made clear that the cross-β structure is harmful when present in certain parts of the body, like for example the brain, and the damage is effected by the combination of cross-β structures with tPA, a method is provided to inhibit cross-β structure-mediated effects comprising providing an effective amount of a protein comprising a finger domain to block the binding sites of the cross-β structure for tPA. The cross-β structure-mediated effects may even be further diminished comprising providing an effective amount of B-type carboxypeptidase activity to inhibit the tPA activity.
In another embodiment, the local cross-β structure-mediated effect can be used against tumors. To that effect, cross-β structure-mediated effects are locally induced to increase local cytotoxicity and/or fibrinolysis comprising locally administering an effective amount of cross-β structures and/or cross-β structure inducing compounds in conjunction with tPA or a compound with tPA-like activity and/or CPI or a compound with CPI-like activity.
The present invention provides, in a further embodiment a method according to to the invention which is carried out ex vivo, e.g., by dialysis. According to this embodiment the circulating fluid (blood) of a subject is brought in a system outside the body for clearing cross-β structures from the circulation. Preferably, such a system is a flow through system, connected to the body circulation with an inlet and an outlet. The cross-β structures are cleared by binding to a cross-β binding compound as defined herein before. It is very important that no elements, such as the cross-β binding compounds from the system are brought into the subject's circulation. Preferred systems are dialysis systems, for that reason among others. The invention further provides devices for carrying out methods as disclosed above. Thus the invention provides a separation device for carrying out a method according to the invention, whereby the apparatus comprises a system for transporting circulation fluids ex vivo, the system provided with means for connecting to a subject's circulation for entry into the system and return from the system to the subject's circulation, the system comprising a solid phase, the solid phase comprising at least one compound capable of binding cross-β structures. Compounds for binding cross-β structures have been disclosed herein. The preferred device is a dialysis apparatus.
The invention also provides for detection of cross-β structures in samples. Such samples may be tissue samples, biopsies and the like, body fluid sample, such as blood, serum, liquor, CSF, urine, and the like. The invention thus provides a method for detecting cross-β structures in a sample, comprising contacting the sample with a compound capable of binding cross-β structures, allowing for binding of cross-β structures to the compound and detecting the complex formed through binding.
Cross-β binding compounds have been defined herein before. Detection of the complex or one of its constituents can be done through any conventional means involving antibodies or other specific binding compounds, further cross-β binding compounds, etc. Detection can be direct, by labelling the complex or a binding partner for the complex or its constituents, or even by measuring a change in a physical or chemical parameter of the complex versus unbound material. It may also be indirect by further binding compounds provided with a label. A label may be a radioactive label, an enzyme, a fluorescent molecule, etc.
The invention further provides devices for carrying out the diagnostic methods. Thus the invention provides a diagnostic device for carrying out a method according to the invention, comprising a sample container, a means for contacting the sample with a cross-β binding compound, a cross-β binding compound and a means for detecting bound cross-β structures. Preferably, the device comprises a means for separating unbound cross-β structures from bound cross-β structures. This can be typically done by providing the cross-β binding compounds on a solid phase.
Several proteins are known to bind cross-β containing proteins (2). These proteins are part of the, herein disclosed, signalling cascade (“cross-β structure pathway”) that is triggered upon formation of a cross-β structure. The “cross-β structure pathway” is modulated in many ways (3,4,5). Factors that regulate the pathway include modulators of synthesis and secretion, including NO regulators, as well as modulators of activity, including protease inhibitors. The pathway is involved in many physiological and pathological processes, including but not limited to atherosclerosis, diabetes, amyloidosis, bleeding, inflammation, multiple sclerosis, Parkinson's disease, sepsis, haemolytic uremic syndrome (7). Given the established role for tPA in long term potentiation the “cross-β structure pathway” may also be involved in learning.
The invention discloses (i) the identification of a “cross-β structre pathway,” (ii) the identification of multiligand receptors as being cross-β structure receptors, (iii) the identification of the finger domain as a cross-β binding module and (iv) the identification of finger containing proteins, including tPA, FXII, HGFa and fibronectin as part of the “cross-β structure pathway.”
This invention further provides compounds not previously known to bind cross-β structure.
As disclosed herein the invention provides compounds and methods for the detection and treatment of diseases associated with the excessive formation of cross-β structure. Such diseases include known conformational diseases, including Alzheimer disease and other types of amyloidosis. However, our invention discloses also that other diseases, not yet known to be associated with excessive formation of cross-β structure are also caused by excessive formation of cross-β structure. Such diseases include atherosclerosis, sepsis, diffuse intravascular coagulation, hemolytic uremic syndrome, preeclampsia, rheumatoid arthritis, autoimmune diseases, thrombosis and cancer.
According to the invention the compound is a cross-β structure binding molecule, preferably, a finger domain or a molecule containing one or more finger domains, or is a peptidomimetic analog of one or more finger domains. The compound can also be an antibody or a functional fragment thereof directed to the cross-β structure.
According to the invention the compound may also be a multiligand receptor of fragment thereof. The compound may e.g., be RAGE, CD36, Low density lipoprotein Related Protein (LRP), Scavenger Receptor B-1 (SR-B1), SR-A or a fragment of one of these proteins.
The finger domains, finger containing molecules or antibodies may be human, mouse, rat or from any other species.
According to the invention amino acids of the respective proteins may be replaced by other amino acids which may increase/decrease the affinity, the potency, bioavailability and/or half-life of the peptide. Alterations include conventional replacements (acid-acid, bulky-bulky and the like), introducing D-amino acids, making peptides cyclic, etc.
Furthermore the the invention provides compounds and methods:
This invention provides methods for preparing an assay to measure cross-β structure in sample solutions.
This invention provides methods for detecting cross-β structure in tissue samples or other samples obtained from living cells or animals.
This invention provides compounds and methods for preparing a composition for inhibiting cross-β structure fibril formation.
This invention provides compounds and methods for preparing a composition for modulating cross-β structure induced toxicity.
Abbreviations: Aβ , beta-amyloid peptide; AD, Alzheimer disease; AGE, advanced glycation end-products; CpB, carboxypeptidase B; COI (carboxypeptidase inhibitor); ELISA, enzyme-linked immunosorbent assay (ELISA); FN, fibronectin; FXII, factor XII (Hageman factor); HGFa, hepatocyte growth factor activator; IAPP, islet amyloid polypeptide; PCR, polymerase chain reactions (PCR); RAGE, receptor for AGE; tPA, tissue-type plasminogen activator.
The invention provides compounds and methods for the detection and treatment of diseases associated with the excessive formation of cross-β structure.
The cross-β structure can be part of an Aβ fibril or part of another amyloid fibril. The cross-β structure can also be present in denatured proteins.
The invention provides methods to detect the cross-β structure. In one embodiment a cross-β structure binding compound, preferably, a finger domain or a molecule comprising one or more finger modules, is bound or affixed to a solid surface, preferably, a microtiter plate. The solid surfaces useful in this embodiment would be known to one of skill in the art. For example, one embodiment of a solid surface is a bead, a column, a plastic dish, a plastic plate, a microscope slide, a nylon membrane, etc. After blocking, the surface is incubated with a sample. After removal of unbound sample, bound molecules comprising the cross-β structure are subsequently detected using a second cross-β structure binding compound, preferably, an anti-cross-β structure antibody or a molecule containing a finger module. The second cross-β structure compound is bound to a label, preferably, an enzym, such as peroxidase. The detectable label may also be a fluorescent label, a biotin, a digoxigenin, a radioactive atom, a paramagnetic ion, and a chemiluminescent label. It may also be labeled by covalent means such as chemical, enzymatic or other appropriate means with a moiety such as an enzyme or radioisotope. Portions of the above mentioned compounds of the invention may be labeled by association with a detectable marker substance (e.g., radiolabeled with 125I or biotinylated) to provide reagents useful in detection and quantification of compound or its receptor bearing cells or its derivatives in solid tissue and fluid samples such as blood, cerebral spinal fluid, urine or other. Such samples may also include serum used for tissue culture or medium used for tissue culture.
In another embodiment the solid surface can be microspheres for for example agglutination tests.
In one embodiment the compound , containing a finger module is, used to stain tissue samples. Preferably, the compound is fused to a protein, peptide, such as glutathion-S-tranferase. Alternatively, the compound is coupled to a label. The detectable label may be a fluorescent label, a biotin, a digoxigenin, a radioactive atom, a paramagnetic ion, and a chemiluminescent label. It may also be labeled by covalent means such as chemical, enzymatic or other appropriate means with a moiety such as an enzyme or radioisotope. Portions of the above mentioned compounds of the invention may be labeled by association with a detectable marker substance (e.g., radiolabeled with 125I 99mTc, 131I, chelated radiolabels, or biotinylated) to provide reagents useful in detection and quantification of compound or its receptor bearing cells or its derivatives in solid tissue and fluid samples such as blood, cerebral spinal fluid or urine. The compound is incubated with the sample and after washing visualized with antibodies directed against the fused protein or polypeptide, preferably, glutathion-S-transferase.
In an embodiment the above sample is tissue from patients with or expected to suffer from a conformational disease. Alternatively, the tissue is derived from animals or from cells cultured in vitro.
The methods of the invention provide a new diagnostic tool. It was not until the present invention that a universal β-structure epitope was disclosed and that a diagnostic assay could be based on the presence of the cross-β structure. Such use is particular useful for diagnostic identification of conformational diseases or diseases associated with amyloid formation, like Alzheimer or diabetes. It is clear that this diagnostic use is also useful for other diseases which involve cross-β structure formation, like all amyloidosis type diseases, atherosclerosis, diabetes, bleeding, cancer, sepsis and other inflammatory diseases, Multiple Sclerosis, auto-immune diseases, disease associated with loss of memory or Parkinson and other neuronal diseases (epilepsy). For example, one can use a finger domain (of for example tPA) and provide it with a label (radio active, fluorescent etc.). This labeled finger domain can then be used either in vitro or in vivo for the detection of cross-β structure comprising proteins, hence for determining the presence of a plaque involved in a conformational disease. One can for example use an ELISA assay to determine the amount of sepsis in a patient or one can localize a plaque involved in a conformational disease.
In another embodiment this invention provides a method for inhibiting the formation of amyloid fibrils or to modulate cross-β structure induced toxicity. The compound is a cross-β binding module, preferably, a finger domain, a finger domain containing molecule, a peptidomimetic analog, and/or an anti-cross-β structure antibody, and/or a multiligand receptor or a fragment thereof.
According to the invention, the inhibition of fibril formation preferably, has the consequence of decreasing the load of fibrils.
The inhibition of fibril formation or modulating cross-β strcuture toxicity may also have the consequence of modulating cell death. The cell can be any cell, but preferably, is a neuronal cell, an endothelial cell, or a tumor cell. The cell can be a human cell or a cell from any other species.
The cell may typically be present in a subject. The subject to which the compound is administered may be a mammal or preferably, a human.
The subject may be suffering from amyloidoses, from another conformational disease, from prion disease, from chronic renal failure and/or dialysis related amyloidosis, from atheroscleroses, from cardiovascular disease, from autoimmune disease, or the subject may be obese. The subject may also be suffering from inflammation, rheumatoid arthritis, diabetes, retinopathy, sepsis, diffuse intravascular coagulation, hemolytic uremic syndrome, and/or preeclampsia, The diseases which may be treated or prevented with the methods of the present invention include but are not limited to diabetes, Alzheimer disease, senility, renal failure, hyperlipidemic atherosclerosis, neuronal cytotoxicity, Down's syndrome, dementia associated with head trauma, amyotrophic lateral sclerosis, multiple sclerosis, amyloidosis, an autoimmune disease, inflammation, a tumor, cancer, male impotence, wound healing, periodontal disease, neuopathy, retinopathy, nephropathy or neuronal degeneration.
The administration of compounds according to the invention may be constant or for a certain period of time. The compound may be delivered hourly, daily, weekly, monthly (e.g., in a time release form) or as a one time delivery. The delivery may also be continuous, e.g., intravenous delivery.
A carrier may be used. The carrier may be a diluent, an aerosol, an aqeuous solution, a nonaqueous solution or a solid carrier. This invention also provides pharmaceutical compositions including therapeutically effective amounts of polypeptide compositions and compounds, together with suitable diluents, preservatives, solubilizers, emulsifiers, adjuvants and/or carriers. Such compositions may be liquids or lyophilized or otherwise dried formulations and include diluents of various buffer content (e.g., Tris-HCl., acetate, phosphate), pH and ionic strength, additives such as albumin or gelatin to prevent absorption to surfaces, detergents (e.g., Tween 20, Tween 80, Pluronic F68, bile acid salts), solubilizing agents (e.g., glycerol, polyethylene glycerol), antioxidants (e.g., ascorbic acid, sodium metabisulfite), preservatives (e.g., Thimerosal, benzyl alcohol, parabens), bulking substances or tonicity modifiers (e.g., lactose, mannitol), covalent attachment of polymers such as polyethylene glycol to the compound, complexation with metal ions, or incorporation of the compound into or onto particulate preparations of polymeric compounds such as polylactic acid, polglycolic acid, hydrogels, etc, or onto liposomes, micro emulsions, micelles, unilamellar or multi lamellar vesicles, erythrocyte ghosts, or spheroplasts.
The administration of compounds according to the invention may comprise intralesional, intraperitoneal, intramuscular or intravenous injection; infusion; liposome-mediated delivery; topical, intrathecal, gingival pocket, per rectum, intrabronchial, nasal, oral, ocular or otic delivery. In a further embodiment, the administration includes intrabronchial administration, anal, intrathecal administration or transdermal delivery.
According to the invention the compounds may be administered hourly, daily, weekly, monthly or annually. In another embodiment, the effective amount of the compound comprises from about 0.000001 mg/kg body weight to about 100 mg/kg body weight.
The compounds according to the invention may be delivered locally via a capsule which allows sustained release of the agent over a period of time. Controlled or sustained release compositions include formulation in lipophilic depots (e.g., fatty acids, waxes, oils). Also included in the invention are particulate compositions coated with polymers (e.g., poloxamers or poloxamines) and the agent coupled to antibodies directed against tissue-specific receptors, ligands or antigens or coupled to ligands of tissue-specific receptors. Other embodiments of the compositions of the invention incorporate particulate forms protective coatings, protease inhibitors or permeation enhancers for various routes of administration, including parenteral, pulmonary, nasal and oral.
The effective amount of the compounds according to the invention preferably, comprise 1 ng/kg body weight to about 1 gr/kg body weight. The actual effective amount will be based upon the size of the compound and its properties.
The activity of tPA and/or the tPA mediated activation of plasminogen is increased by the binding to fibrin fragments, or other protein fragments that have a lysine or an arginine at the carboxy-terminal end. B-type carboxypeptidases, including but not limited to carboxypeptidase B (CpB) or Thrombin Activatable Fibinolysis Inhibitor (TAFI, also named carboxypeptidase U or carboxypeptidase R), are enzymes that cleave off carboxy-terminal lysine and arginine residues of fibrin fragments that would otherwise bind to tPA and/or plasminogen and stimulate plasmin formation.
Because this invention has made clear that the cross-β structures are harmful when present in certain parts of the body, like for example the brain, and the damage is effected by the combination of cross-β structures with tPA, a method is provided to inhibit cross-β structure-mediated effects comprising providing an effective amount of a protein comprising a finger domain to block the binding sites of the cross-β structure for tPA. The cross-β structure-mediated effects may even be further diminished comprising providing an effective amount of B-type carboxypeptidase activity to inhibit the tPA activity.
The invention provides the use of a compound capable of binding to a cross-β structure for the removal of cross-β structures. The compound is a cross-β binding molecule, preferably, a protein and/or a functional equivalent and/or a functional fragment thereof. More preferably, the compound comprises a finger domain or a finger domain containing molecule or a functional equivalent or a functional fragment thereof. Even more preferably, the finger domain is derived from fibronectin, FXII, HGFa or tPA. It is clear that the invention also comprises antibodies that bind cross-β structures. In another preferred embodiment the protein is an antibody and/or a functional equivalent and/or a functional fragment thereof. With this use the invention provides for example a therapeutic method to remove cross-β structure comprising proteins from for example the circulation, preferably, via extracorporeal dialysis. For example, a patient with sepsis is subjected to such use by dialysis of blood of the patient through means which are provided with for example, preferably, immobilized, finger domains. One could for example couple the finger domains to a solid surface or to the inside of the tubes used for the dialysis. In this way, all cross-β structure comprising proteins will be removed from the blood stream of the patient, thereby relieving the patients of the negative effects caused by the cross-β structure comprising proteins. Besides finger domain comprising compounds, it is also possible to use other cross-β structure binding compounds, like antibodies or soluble multiligand receptors. It is also clear that the use could be applied in haemodialysis of kidney patients.
As used herein “finger” encompasses a sequence that fullfills the criteria outlined in
As mentioned before, factor XII contains a finger d6main and is part of the “cross-beta structure pathway.” Factor XII is important since it activates the intrinsic coagulation pathway. We now provide experimental evidence that factor XII is activated by kaolin and by peptide aggregates with cross-β structure conformation. This shows that the intrinsic route of coagulation is part of the cross-β pathway and that cross-β structure compounds activate coagulation via factor XII. Moreover, we also provide experimental evidence disclosing that blood platelets become activated by cross-β structures. In this way the cross-β structure contributes to coagulation via platelet aggregation and thrombosis. Cross-0 structures also contribute to coagulation via extrinsic pathway and thrombosis via induction of the expression of tissue factor (TF) and by stimulating its release. Cross-β structures induce TF after binding to receptors on the surface of endothelial cells, monocytes, macrophages or other cells (Khechia et al, 1997; Bochkov et al, 2002). Alternatively cross-β structures induce coagulation and/or thrombosis by the fact that fibrin, formed during blood coagulation, comprises cross-β structures, which subsequently activate blood coagulation (Kranenburg et al, 2002). Taken together, it is thus concluded that cross-β structures are important inducers of blood coagulation via activation of factor XII, via activation of platelets and/or via induction of TF expression .and secretion. Thus, blood coagulation is part of the “cross beta structure” pathway. Cross-0 structures bind to compounds of the blood coagulation cascade through a cross-β binding domain (also referred to as “a specific binding partner” or “a specific binding part”).
Cross-beta structures in blood are provided by for example glycated proteins (Bouma et al, 2003), oxidated proteins (Horiuchi et al, 2003; Ursini et al, 2002), unfolded or misfolded proteins (Bucciantini et al, 2002) or pathogenic micro-organisms (Chapman et al, 2002).
The invention provides a method for interfering in blood coagulation and/or thrombosis comprising providing to blood a binding molecule that either binds to a cross-β structure or to a specific cross-β structure binding part of a compound which is part of a blood coagulation cascade. The term blood is to be understood as blood in vivo, i.e., in the circulation of a living animal (or non-human animal) or in vitro, i.e as blood outside of a living animal, for example blood present in a tube. Moreover, the term blood also includes a product derived from blood but still capable of coagulating.
A binding molecule is preferably a bi-specific molecule, i.e., a molecule with two different binding specificities. In a preferred embodiment, the bi-specific molecule is capable of binding to cross-beta as well as to another part of the cross-beta structure and/or of a protein comprising a cross-beta structure. In another preferred embodiment, the bi-specific molecule is capable of binding to a specific binding partner as well as to another part of the same compound which is part of a blood-coagulating cascade. In an even more preferred embodiment of the invention, the bi-specific molecule is an antibody or a finctional part and/or derivative thereof Such a bi-specific antibody is produced as a recombinant molecule and is optionally adapted to the host in which the antibody is used.
In yet another embodiment, the binding molecule is mono-specific and binds to cross-beta structures, for example Congo Red, Thioflavin T, Thioflavin S, CD36, RAGE, scavenger receptor A, LRP, scavenger receptor B-1, C1q, serum amyloid P component, a finger domain comprising protein such as tPA, HGFA, fibronectin, Factor XII or a functional part and/or derivative thereof, i.e., a part or derivative capable of binding to cross-beta structures (Bouma et al, 2002; Horiuchi et al, 2003).
In general all compounds of a blood coagulation cascade that are activated through the binding of a cross-beta structure are suitable points of interfering. Preferred embodiments are a platelet or fibrin or Factor XII or a receptor present on an endothelial cell or a receptor present on a monocyte/macrophage or any other cell exposing multi-ligand receptors and comprising Tissue Factor.
For example, blood platelets are activated after binding of a cross-beta structure. Surprisingly, activated platelets expose cross-beta structures on their surface. The cross-beta structures play a role in the coagulation cascade, for example by enhancing activation of other platelets. Enhancement is artificially decreased by administration of a molecule binding to a cross-beta structure, such as tPA, Congo Red or ThioflavinT. This results in activated platelets that do not aggregate. Platelet activation is also accomplished by fibrin components or thrombin or small peptide compounds, for example TRAβ. These components also induce cross-beta structures on activated platelets. Preferably, activation of a platelet is accomplished by binding of a cross-beta structure to a scavenger/multi-ligand receptor, like for example CD36, LRP, apoER2', scavenger receptor A, scavenger receptor B-I.
Factor XII generally binds to exposed collagen at the site of vesicle wall injury. Factor XII is activated by high molecular weight kininogen and kallikrein. When activated Factor XII becomes a serine protease which activates Factor XI. Activated Factor XII also induces Bradykinin which influences the blood flow. Because cross-beta structures activate Factor XII, they initiate the blood coagulation cascade. Interfering in this pathway with for example the binding of a (mono or) bi-specific molecule to a cross beta structure results in decreased blood coagulation.
Another way of interfering in a blood coagulation cascade is by interfering the binding of cross-beta structures to a receptor present on an endothelial cell or a receptor present on a monocyte/macrophage or any other cell exposing multi-ligand receptors and comprising Tissue Factor. Examples of such receptors are CD36, LRP, scavenger receptor A, scavenger receptor B-I, RAGE, FEEL-1, LOX-1, stabilin-1, stabilin-2 (Bouma et al 2003; Horiuchi et al,
Tamura et al, 2003; Jono et al 2002; Chen et al 2003). We now present evidence that at least endothelial cells and macrophages/monocytes comprise a multi-ligand receptor as well as Tissue Factor. These examples disclose that any cell comprising the combination of a multi-ligand receptor as well as Tissue Factor is capable of initiating or enhancing a blood coagulation cascade.
A (mono or) bi-specific molecule, as described above is useful in the preparation of a medicament for the treatment of coagulation disorders, such as, but not limited to thrombosis.
A pharmaceutical comprising a (mono or) bi-specific molecule of the invention is very useful for treating a diverse range of blood coagulation disorders.
In another embodiment, the invention provides a method for initiating or increasing a blood-coagulating cascade by providing cross-beta structures to blood. For example, local blood clotting is induced in the case of blood loss through vascular disruption. An example of a cross-beta comprising protein is fibrin.
In yet another embodiment, the invention provides a bi-specific molecule capable of binding to a specific cross-beta structure binding part of a compound which is part of a blood-coagulating cascade as well as to another part of the compound or a (mono or) bi-specific molecule capable of binding to cross-beta as well as to another part of the same cross-beta structure. Preferably, such a (mono or) bi-specific molecule is an antibody.
The invention furthermore provides a pharmaceutical comprising a (mono or) bi-specific molecule as described above.
Reagents
Bovine serum albumin (BSA) fraction V pH 7.0 and D-glucose-6-phosphate di-sodium (g6p), D, L-glyceraldehyde, and chicken egg-white lysozyme were from ICN (Aurora, Ohio, USA). Rabbit anti-recombinant tissue-type plasminogen activator (tPA) 385R and mouse anti-recombinant tPA 374B were purchased from American Diagnostica (Veenendaal, The Netherlands). Anti-laminin (L9393) was from Sigma. Swine anti-rabbit immunoglobulins/HRP (SWARPO) and rabbit anti-mouse immunoglobulins/HRP (RAMPO) were from DAKO Diagnostics B.V. (The Netherlands). Alteplase (recombinant tissue type plasminogen activator, tPA) was obtained from Boehringer-Ingelheim (Germany). Reteplase (Rapilysin), a recombinant mutant tPA containing only kringle2 and the catalytic domain (K2P-tPA) was obtained from Roche, Hertfordshire, UK, and porcine pancreas carboxypeptidase B (CpB) was from Roche, Mannheim, Germany. Carboxypeptidase inhibitor (CPI) was from Calbiochem (La Jolla, Calif., USA). Tween20 was purchased from Merck-Schuchardt (Hohenbrunn, Germany). Congo red was obtained from Aldrich (Milwaukee, Wis., USA). Thioflavin T and lyophilized human haemoglobin (Hb) were from Sigma (St. Louis, Mo., USA). Lyophilized human fibrinogen was from Kordia (Leiden, The Netherlands). Chromogenic plasmin substrate S-2251 was purchased from Chromogenix (Milan, Italy). Oligonucleotides were purchased from Sigma-Genosys (U.K.). Boro glass-capillaries (0.5 mm Ø) were from Mueller (Berlin, Germany).
Synthetic Peptides
Peptide Aβ(1-40), containing amino acids as present in the described human Alzheimer peptide (DAEFRHDSGYEVHHQKLVFFAEDVGSNKGAIIGLMVGGVV), fibrin peptides 85 (or FP13) (KRLEVDIDIKIRS), 86 (or FP12) (KRLEVDIDIKIR) and 87 (or FP10) (KRLEVDIDIK), derived from the sequence of human fibrin(ogen) and the islet amyloid polypeptide (IAPP) peptide or derivatives
(fl-hIAPP: KCNTATCATQRLANFLVHSSNNFGAILSSTNVGSNTY, ΔhIAPP (SNNFGAILSS), AmIAPP (SNNLGPVLPP) were obtained from Pepscan, Inc. (The Netherlands) or from the peptide synthesis facility at the Netherlands Cancer Institute (NCI, Amsterdam, The Netherlands). The peptides were dissolved in phosphate buffered saline (PBS) to a final concentration of 1 mg ml−1 and stored for three weeks at room temperature (RT) to allow formation of fibrils. During this period, the suspension was vortexed twice weekly. After three weeks, the suspension was stored at 4° C. Freeze-dried Aβ(1-40) from the NCI allowed to form cross-β structure in the same way. Cross-β structure formation was followed in time by examination of Congo red binding and green birefringence under polarised light.
Congo Red Binding and Thioflavin T Fluorescence of a Fibrin Clot
For Thioflavin T-fluorescence measurements 1 mg ml−1 of fibrinogen was incubated at 37° C. with 2 U ml−1 of factor IIa in 150 mM NaCl, 20 mM Tris-HCl pH 7.5, 10 mM CaCl2, 50 μM Thioflavin T. Background fluorescence of a clot was recorded in the absence of Thioflavin T and background Thioflavin T fluorescence was measured in the absence of factor IIa. Fluorescence was measured on a Hitachi F-4500 fluorescence spectrophotometer (Ltd., Tokyo, Japan), using Sarstedt REF67.754 cuvettes. Apparatus settings: excitation at 435 nm (slit 10 nm), emission at 485 nm (slit 10 nm), PMT voltage 950 V, measuring time 10 seconds, delay 0 seconds. For detection of Congo red binding a fibrin clot was formed at room temperature as described above (Thioflavin T was omitted in the buffer). The clot was incubated with Congo red solution and washed according to the manufacturer's recommendations (Sigma Diagnostics, Mo., USA). The clot was analysed under polarised light.
Initial Preparation of Glycated Albumin, Haemoglobin (Hb) and Lysozyme
For preparation of advanced glycation end-product modified bovine serum albumin (albumin-g6p), 100 mg ml−1 of albumin was incubated with PBS containing 1 M of g6p and 0.05% m/v NaN3, at 37° C. in the dark. One albumin solution was glycated for two weeks, a different batch of albumin was glycated for four weeks. Glycation was prolonged up to 23 weeks with part of the latter batch. Human Hb at 5 mg ml−1 was incubated for 10 weeks at 37° C. with PBS containing 1 M of g6p and .05% m/v of NaN3. In Addition, a Hb solution of 50 mg ml−1 was incubated for eight weeks with the same buffer. For preparation of glyceraldehyde-modified albumin (albumin-glyceraldehyde) and chicken egg-white lysozyme (lysozyme-glyceraldehyde), filter-sterilized protein solutions of 15 mg ml−1 were incubated for two weeks with PBS containing 10 mM of glyceraldehyde. In controls, g6p or glyceraldehyde was omitted in the solutions. After incubations, albumin and lysozyme solutions were extensively dialysed against distilled water and, subsequently, stored at −20° C. Protein concentrations were determined with Advanced protein-assay reagent ADV01 (Cytoskeleton, Denver, Colo., USA). Glycation was confirmed by measuring intrinsic fluorescent signals from advanced glycation end-products; excitation wavelength 380 nm, emission wavelength 435 nm.
Further Experiment Involving Glycation
For preparation of albumin-AGE, 100 mg ml−1 bovine serum albumin (fraction V, catalogue # A-7906, initial fractionation by heat shock, purity ≧98% (electrophoresis), remainder mostly globulins, Sigma-Aldrich, St. Louis, Mo., USA) was incubated at 37° C. in the dark, with phosphate-buffered saline (PBS, 140 mM sodium chloride, 2.7 mM potassium chloride, 10 mM disodium hydrogen phosphate, 1.8 mM potassium di-hydrogen phosphate, pH 7.3) 1M D-glucose-6-phosphate disodium salt hydrate (anhydrous) (ICN, Aurora, Ohio, USA) and 0.05% (m/v) NaN3. Bovine albumin has 83 potential glycation sites (59 lysine and 23 arginine residues, N-terminus). Albumin was glycated for two weeks (albumin-AGE:2), four weeks (albumin-AGE:4) or 23 weeks (albumin-AGE:23). In controls, g6p was omitted. After incubation, solutions were extensively dialysed against distilled water and, subsequently, stored at 4° C. Protein concentrations were determined with advanced protein-assay reagent ADV01 (Cytoskeleton, CO, USA). Alternatively, albumin was incubated for 86 weeks with 1 M g6p, 250 mM DL-glyceraldehyde (ICN, Aurora, Ohio, USA)/100 mM NaCNBH3, 1 M β-D-(-)-fructose (ICN, Aurora, Ohio, USA), 1 M D(+)-glucose (BDH, Poole, England), 500 mM glyoxylic acid monohydrate (ICN, Aurora, Ohio, USA)/100 mM NaCNBH3, and corresponding PBS and PBS/NaCNBH3 buffer controls. Glycation was confirmed (i.) by observation of intense brown staining, (ii.) by the presence of multimers on SDS-polyacrylamide gels, (iii) by assaying binding of AGE-specific antibodies moab anti-albumin-g6p 4B546 and poab anti-fibronectin-g6p (Ph. De Groot/I. Bobbink, UMC Utrecht; unpublished data), and (iv.) by measuring intrinsic fluorescent signals from AGE (excitation wavelength 380 nr, emission wavelength 445 nm). Autofluorescent signals of albumin-controls were less than 4% of the signals measured for albumin-AGE and were used for background corrections.
Isolation of Hb from Human Erythrocytes
Human Hb was isolated from erythrocytes in EDTA-anticoagulated blood of 3 healthy individuals and of 16 diabetic patients. 100 μl of whole blood was diluted in 5 ml of physiological salt (154 mM NaCl), cells were gently spun down, and resuspended in 5 ml of physiological salt. After a 16-h incubation at room temp., cells were again spun down. Pelleted cells were lysed by adding 2 ml of 0.1 M of boric acid, pH 6.5 and subsequently, cell debris was spun down. Supernatant was collected and stored at −20° C.
Determination of GlycoHb Concentrations
Concentrations of glycated Hb, also named glycohaemoglobin, or named HbAlc, in EDTA-blood of human healthy donors or diabetic patients, were determined using a turbidimetric inhibition immunoassay with haemolysed whole blood, according to the manufacturer's recommendations (Roche Diagnostics, Mannheim, Germany). Standard deviations are 2.3% of the measured HbAlc concentrations.
Binding of Congo Red to Glycated Albumin
Binding of Congo red to albumin-AGE glycated for 86 weeks with carbohydrates glucose, fructose and glucose-6-phosphate, or with carbohydrate derivatives glyceraldehyde and glyoxylic acid, was tested using air-dried samples. For this purpose, 5 μg albumin was applied to a glass cover slip and air-dried. Samples were incubated with Congo red and subsequently washed according to the manufacturer's recommendations (Sigma Diagnostics, St Louis, M0., USA). Pictures were taken on a Leica DMIRBE fluorescence microscope (Rijswijk, The Netherlands) using 596 nm and 620 nm excitation- and emission wavelengths, respectively.
Endostatin Preparations
Endostatin was purified from Escherichia coli essentially as described.47 In short, B121.DE3 bacteria expressing endostatin were lysed in a buffer containing 8 M urea, 10 mM Tris (pH 8.0), 10 mM imidazole and 10 mM β-mercapto-ethanol. Following purification over Ni2+-agarose, the protein sample was extensively dialysed against H2O. During dialysis endostatin precipitates as a fine white solid. Aliquots of this material were either stored at −80° C. for later use, or were freeze-dried prior to storage. Soluble endostatin produced in the yeast strain Pichia pastoris was kindly provided by Dr. Kim Lee Sim (EntreMed, Inc.,Rockville, Mass.). Aggregated endostatin was prepared from soluble endostatin as follows. Soluble yeast endostatin was dialysed overnight in 8 M urea and subsequently three times against H2O. Like bacterial endostatin, yeast endostatin precipitates as a fine white solid.
Congo Red Staining
Freeze-dried bacterial endostatin was resuspended in, either 0.1% formic acid (FA), or in dimethyl-sulfoxide and taken up in a glass capillary. The solvent was allowed to evaporate and the resulting endostatin material was stained with Congo red according to the manufacturer's protocol (Sigma Diagnostics, St. Louis, Mo., USA).
Circular Dichroism Measurements
UV circular dichroism (CD) spectra of peptide and protein solutions (100 μg ml−1 in H2O) were measured on a JASCO J-810 CD spectropolarimeter (Tokyo, Japan). Averaged absorption spectra of 5 or 10 single measurements from 190-240 nm or from 190-250 nm, for fibrin peptides 85, 86, 87 or for albumin, glycated albumin and human Aβ(16-22), respectively, are recorded. The CD spectrum of Aβ(16-22) was measured as a positive control. Aβ(16-22) readily adopts amyloid fibril conformation with cross-β structure, when incubated in H2O.45 For albumin and Aβ(16-22) relative percentage of the secondary structure elements present was estimated using k2d software.48
X-ray Fibre Diffraction
Aggregated endostatin was solubilized in 0.1% FA, lyophilized fibrin peptides were dissolved in H2O and glycated albumin was extensively dialysed against water. Samples were taken up in a glass capillary. The solvent was then allowed to evaporate over a period of several days. Capillaries containing the dried samples were placed on a Nonius kappaCCD diffractometer (Bruker-Nonius, Delft, The Netherlands). Scattering was measured using sealed tube MoKa radiation with a graphite monochromator on the CCD area detector during 16 hours. Scattering from air and the glass capillary wall were subtracted using in-house software (VIEW/EVAL, Dept. of Crystal- and Structural Chemistry, Utrecht University, The Netherlands).
Transmission Electron Microscopy
Endostatin-, haemoglobin- and albumin samples were applied to 400 mesh specimen grids covered with carbon-coated collodion films. After 5 minutes, the drops were removed with filter paper and the preparations were stained with 1% methylcellulose and 1% uranyl acetate. After washing in H2O, the samples were dehydrated in a graded series of EtOH and hexanethyldisilazane. Transmission electron microscopy (TEM) images were recorded at 60 kV on a JEM-1200EX electron microscope (JEOL, Japan).
Enzyme-linked Immunosorbent Assay: Binding of tPA to Glycated Albumin, Hb and Aβ(1-40)
Binding of tPA to albumin-g6p (four-weeks and 23-weeks incubations), albumin-glyceraldehyde, control albumin, human Hb-g6p (ten-weeks incubation), Hb control, or to Aβ(1-40) was tested using an enzyme-linked immunosorbent assay (ELISA) set-up. Albumin-g6p and control albumin (2.5 μg ml−1 in coat buffer, 50 mM Na2CO3/NaHCO3 pH 9.6, 0.02% m/v NaN3, 50 μl/well) were immobilized for 1 hour at room temperature in 96-well protein Immobilizer plates (Exiqon, Vedbaek, Denmark). Aβ(1-40) (10 tug ml−1 in coat buffer) was immobilized for 75 minutes at room temperature in a 96-well peptide Immobilizer plate (Exiqon, Vedbaek, Denmark). Control wells were incubated with coat buffer, only. After a wash step with 200 μl of PBS/0.1% v/v Tween20, plates were blocked with 300 μl of PBS/1% v/v Tween20, for 2 hours at room temperature, while shaking. All subsequent incubations were performed in PBS/0.1% v/v Tween20 for 1 hour at room temperature while shaking, with volumes of 50 μl per well. After each incubation wells were washed five times with 200 μl of PBS/0.1% v/v Tween20. Increasing amounts of f.l. tPA or K2-P tPA was added in triplicate to coated wells and to control wells. Antibody 385R and, subsequently, SWARPO, or antibody 374B and, subsequently, RAMPO were added to the wells at a concentration of 1 μg ml−1. Bound peroxidase-labeled antibody was visualised using 100 μl of a solution containing 8 mg of ortho-phenylene-diamine and 0.0175% v/v of H2O2 in 20 ml of 50 mM citric acid/100 mM Na2HPO4 pH 5.0. Staining was stopped upon adding 50 μl of a 2-M H2SO4 solution. Absorbance was read at 490 nm on a Vmax. kinetic microplate reader (Molecular Devices, Sunnyvale, Calif., USA).
Competition experiments were performed with 20 or 40 nM of tPA, with respectively albumin-g6p or Aβ(1-40) and with increasing amounts of Congo red in PBS/0.08% v/v Tween20/2% v/v EtOH.
ELISA: Binding of tPA to Albumin-AGE
Binding of the cross-β structure-marker tPA to albumin-AGE was tested using an ELISA setup. We showed that tPA binds to prototype amyloid peptides human Aβ(1-40) and human IAPP49 (this application). Therefore, we used tPA binding to these two peptides as positive control. The 86-weeks glycated samples and controls were coated to Greiner microlon plates (catalogue # 655092, Greiner, Frickenhausen, Germany). Wells were blocked with Superblock (Pierce, Rockford, Ill., USA). All subsequent incubations were performed in PBS/0.1% (v/v) Tween20 for 1 hour at room temperature while shaking, with volumes of 50 μl per well. After incubation, wells were washed five times with 300 μl PBS/0.1% (v/v) Tween20. Increasing concentrations of tPA were added in triplicate to coated wells as well as to control wells. During tPA incubations of 86-weeks incubated samples, at least a 123,000 times molar excess of ε-amino caproic acid (εACA, 10 mM) was added to the solutions. MACA is a lysine analogue and is used to avoid potential binding of tPA to albumin via its kringle2 domain.50 Monoclonal antibody 374b (American Diagnostica, Instrumentation laboratory, Breda, The Netherlands) and, subsequently, RAMPO (Dako diagnostics, Glostrup, Denmark) was added to the wells at a concentration of 0.3 μl ml−1. Bound peroxidase-labeled antibody was visualised using 100 μl of a solution containing 8 mg ortho-phenylene-diamine in 20 ml 50 mM citric acid/100 mM Na2HPO4 pH 5.0 with 0.0175% (v/v) H2O2. Staining was stopped upon adding 50 μl of a 2 M H2SO4 solution. Absorbance was read at 490 nm on a Vman kinetic microplate reader (Molecular Devices, Calif., USA). Background signals from non-coated control wells were substracted from corresponding coated wells.
Initially, Thioflavin T fluorescence of glycated albumin and lysozyme, and tPA
For fluorescence measurements, 500 nM of albumin-g6p, albumin-glyceraldehyde, control albumin, lysozyme-glyceraldehyde, or control lysozyme were incubated with increasing amounts of Thioflavin T, in 50 mM of glycine-NaOH, pH 9. For blank readings, an identical Thioflavin T dilution range was prepared without protein, or Thioflavin T was omitted in the protein solutions. Samples were prepared in triplicate.
Thioflavin T Fluorescence
In further experiments fluorescence measurements, albumin-g6p:2, albumin-g6p:4, albumin-g6p:23 and controls in 50 mM glycine-NaOH, pH 9 were incubated with increasing amounts of ThT (Sigma-Aldrich Chemie, Steinheim, Germany), a marker for amyloid cross-β structure.51 Albumin-AGE:4 concentration was 175 nM, other protein concentrations were 500 nM. For fluorescence measurements with 86-weeks glycated samples, 140 nM of protein was incubated with a fixed concentration of 20 μThT. Fluorescence was measured in triplicate on a Hitachi F-4500 fluorescence spectrophotometer (Ltd., Tokyo, Japan), after 1 hour incubation at room temperature. Excitation- and emission wavelengths were 435 nm (slit 10 nm) and 485 nm (slit 10 nm), respectively. Background signals from buffer and protein solution without ThT were substracted from corresponding measurements with protein solution incubated with ThT.
Fluorescence: Competitive Binding of Thioflavin T and tPA to Albumin-g6p
A solution of 430 nM albumin-g6p and 19 μM of Thioflavin T was incubated with increasing amounts of tPA, for 1 hour at room temperature. For blank readings, albumin-g6p was omitted. Samples were prepared in four-fold in 50 mM glycine-NaOH pH 9. Emission measurements were performed as described above.
Absorbance: Competitive Binding of Thioflavin T and tPA to Albumin-g6p
Albumin-g6p (500 nM) and Thioflavin T (10 μM) were incubated with increasing amounts of tPA, in 50 mM glycine-NaOH pH 9, for 1 hour at room temperature. Absorbance measurements were performed at the albumin-g6p Thioflavin T absorbance maximum at 420 nm. Samples were prepared in four-fold. For blank readings, albumin-g6p was omitted in the solutions. Absorbance was read in a quartz cuvette on a Pharmacia Biotech Ultrospec 3000 UV/visible spectrophotometer (Cambridge, England).
Plasminogen Activation Assay.
Plasminogen (200 μl ml−1) was incubated with tPA (200 μM) in the presence or the absence of a cofactor (5 μM of either endostatin, Aβ(1-40) or one the fibrin-derived peptides 85, 86 and 87). At the indicated time intervals samples were taken and the reaction was stopped in a buffer containing 5 mM EDTA and 150 mM εACA. After collection of the samples a chromogenic plasmin substrate S-2251 was added and plasmin activity was determined kinetically in a spectrophotometer at 37° C.
N1E-115 Cell Culture and Differentiation
N1E-115 mouse neuroblastoma cells were routinely cultured in DMEM containing 5% FCS, supplemented with antibiotics. Cells were differentiated into post-mitotic neurons.52 The cells were exposed to Aβ(50 μg ml−1) for 24 hours in the presence or absence of 20 μg ml−1 lasminogen in the presence or absence of 50 μg ml−1CpB. Cells were photographed, counted and lysed by the addition of 4× sample buffer (250 mM Tris pH 6.8, 8% SDS, 10% glycerol, 100 mM DTT, 0.01% w/v bromophenol blue) to the medium. The lysate, containing both adherent and floating (presumably dying and/or dead) cells as well as the culture medium were analysed for the presence of plasminogen and plasmin as well as for laminin by Western blot analysis using specific antibodies against plasminogen (MoAb 3642, American Diagnostics), laminin (PoAb L9393, Sigma).
Binding of Human Factor XII to Amyloid Peptides and Proteins, that Contain the cross-β Structure Fold
We tested the binding of human FXII (Calbiochem, La Jolla, Calif., USA, catalogue #233490) to amyloid (poly)peptides. Prototype amyloid peptides human amyloid-β(1-40) (hA(1-40)) and human fibrin fragment α147-159 FP13, and glucose-6-phosphate glycated bovine albumin (albumin-advanced glycation endproduct (AGE)) and glucose-6-phosphate glycated human haemoglobin (Hb-AGE), that all contain cross-β structure, as well as negative controls mouse A islet amyloid polypeptide (ΔmIAPP), albumin-control and Hb-control, that all three lack the amyloid-specific structure, were coated to ELISA plates and overlayed with a concentration series of human factor XII. Binding of FXII was detected using a rabbit polyclonal anti-FXII antibody (Calbiochem, La Jolla, Calif., USA, catalogue #233504) and peroxidase-labeled swine anti-rabbit IgG. Wells were coated in triplicate. The FXII binding buffer consisted of 10 mM HEPES pH 7.3, 137 mM NaCl, 11 mM D-glucose, 4 mM KCl, 1 mg ml−1 albumin, 50 μM ZnCl2, 0.02% (m/v) NaN3 and 10 mM ε-amino caproic acid (εACA). Lysine analogue εACA was added to avoid putative binding of FXII to cross-β structure via the FXII kringle domain. In addition, binding of FXII to hAβ(1-40) and the prototype amyloid human amylin fragment hΔIAPP was tested using dot blot analysis. 10 μg of the peptides, that contain cross-β structure, as wells as the negative control peptide mΔIAPP and phosphate-buffered saline (PBS) were spotted in duplicate onto methanol-activated nitrocellulose. Spots were subsequently incubated with 2 nM FXII in FXII buffer or with FXII buffer alone, anti-FXII antibody, and SWARPO. Binding of FXII was visualized by chemiluminescence upon incubation with enhanced luminol reagent (PerkinElmer Life Sciences, Boston, Mass., USA). To test whether FXII and tPA, which is known for its capacity to bind to polypeptides that contain the cross-β structure fold,49 bind to overlapping binding sites on amyloid (poly)peptides, we performed competitive ELISA's. Coated hAβ(1-40) or amyloid albumin-AGE were incubated with 2.5 nM or 15 nM FXII in binding buffer, in the presence of a concentration series of human recombinant tissue-type plasminogen activator (Actilyse®, full-length tPA), or Reteplase® (K2P-tPA). Reteplase is a truncated form of tPA, that consists of the second kringle domain and the protease domain. The f.l. tPA- and K2P-tPA concentration was at maximum 135 times the kD for tPA binding to hAβ(l-40) (50 nM) or 150 times the kD for tPA binding to albumin-AGE (1 nM).
Cloning Procedure
Cloning of the amino-terminal finger domain (F) of human tPA, residues Ser1-Ser50, preceded by the pro-peptide (residues Met-35-Arg-1) and a BglII restriction site, was performed by using PCR and standard recombinant DNA techniques. In brief, the propeptide-finger region was amplified by PCR using 1 ng of plasmin Zpl7,53 containing the cDNA encoding tPA as a template. Oligonucleotides used were 5′-AAAAGTCGACAGCCGCCACCATGGATGCAATGAAGAGA (1) and 3′-AAAAGCGGCCGCCCACTTTTGACAGGCACTGAG (2) comprising a SalI- or a NotI restriction-site, respectively (underlined). The PCR product was cloned in a SalI/NotI-digested expression vector, pMT2-GST.54 As a results a construct is generated that contains a SalI restriction site, the coding sequence for the finger domain of tPA, a NotI and a KpnI restriction site, a thrombin cleavage-site (TCS), a glutathion-S-transferase (GST) tag and an EcoRI restriction site. The appropriate sequence of the construct was confirmed by sequence analysis. In a similar way a construct consisting of the tPA F-EGF domains was prepared. Next, the constructs were ligated SalI-EcoRI in pGEM3Zf(−) (Promega, Madison, Wis., USA). The HindIII-SalI-tPA propeptide-BglII-F-NotI-KpnI-TCS-GST-EcoRI construct was used as a cloning cassette for preparation of constructs containing tPA KI, F-EGF-K1, EGF, as wells as human hepatocyte growth factor activator F and F-EGF, human factor XII F and F-EGF, and human fibronectin F4, F5, F4-5 and F10-12. Subsequently, constructs were ligated HindIII-EcoRI in the pcDNA3 expression vector (Invitrogen, Breda, The Netherlands). In addition, the GST tag alone was cloned into pcDNA3, preceded by the tPA propeptide. Primers used for constructs were:
Transient Expression of tPA-F-GST in 293T Cells
Initially 293T cells were grown in RPMI1640 medium (Invitrogen, Scotland, U.K.) supplemented with 5% v/v fetal calf-serum, penicillin, streptomycin and guanidine, to 15% confluency. Cells were transiently transfected using Fugene-6, according to the manufacturer's recommendations (Roche, Ind., USA). pMT2-tPA-F-GST containing the tPA fragment, or a control plasmid, pMT2-RPTPp-GST, containing the extracellulair domain of receptor-like protein tyrosine phosphatase μ (RPTPμ)54 were transfected, and medium was harvested after 48 hours transfection. Expression of tPA-F-GST and RPTPμ-GST in 293T medium was verified by immunoblotting. Collected samples were run out on SDS-PAA gels after the addition of 2× sample buffer. Gels were blotted on nitrocellulose membranes. Membranes were blocked in 1% milk (Nutricia) and incubated with primary monoclonal anti-GST antibody 2F3,54 and secondary HRP-conjugated rabbit anti-mouse IgG (RAMPO). The blots were developed using Western Lightning Chemiluminescence Reagent Plus (PerkinElmer Life Sciences, Mass., USA).
Stable Expression of Finger Constructs in BHK Cells
Baby hamster kidney cells were seeded in DMEM/NUT mix F-12(HAM) medium (Invitrogen, U.K.) supplemented with 5% v/v fetal calf-serum (FCS), penicillin, streptomycin and guanidine, to 1% confluency. Cells were stably transfected by using the Ca3(PO4)2-DNA precipitation method. After 24 hours, medium was supplemented with 1 mg ml−1 geneticin G-418 sulphate (Gibco, U.K.). Medium with G-418 was refreshed several times during 10 days, to remove dead cells. After this period of time, stable single colonies were transferred to new culture flasks and cells were grown to confluency. Expression of constructs was then verified by immunoblotting. Collected samples were run out on SDS-PAA gels after the addition of 2× sample buffer. Gels were blotted on nitrocellulose membranes. Membranes were blocked in 5% milk (Nutricia) with 1.5% m/v BSA and incubated with primary monoclonal anti-GST antibody (Santa Cruz Biotechnology, Santa Cruz, Calif., USA, catalogue # Z-5), and secondary HRP-conjugated rabbit anti-mouse IgG (RAMPO). The blots were developed using Western Lightning Chemiluminescence Reagent Plus (PerkinElmer Life Sciences, Mass., USA). Stable clones were from now on grown in the presence of 250 μg ml−1 G-418. For pull-down experiments, conditioned medium with 5% FCS of stable clones that produce constructs of interest was used. For purification purposes, cells of a stable clone of tPA F-EGF-GST were transferred to triple-layered culture flasks and grown in medium with 0.5% v/v Ultroser G (ITK Diagnostics, Uithoorn, The Netherlands). Medium was refreshed every three to four days. TPA F-EGF-GST was isolated from the medium on a Glutathione Sepharose 4B (Amersham Biosciences, Uppsala, Sweden) column and eluted with 100 mM reduced glutathione (Roche Diagnostics, Mannheim, Germany). Purity of the construct was checked with SDS-PAGE followed by Coomassie staining or Western blotting. From these analyses it is clear that some GST is present in the preparation. Purified tPA F-EGF-GST was dialyzed against PBS and stored at −20° C.
Purification of GST-tagged tPA-F-GST and RPTPμ-GST
Medium was concentrated twenty-fold using Nanosep 10K Ω centrifugal devices (Pall Gelman Laboratory, Miss., USA) and incubated with glutathione coupled to Sepharose 4B, according to the manufacturer's recommendations (Pharmacia Biotech, Uppsala, Sweden). Bound constructs were washed with PBS and eluted with 10 mM of glutathione in 50 mM Tris-HCl pH 8.0. Constructs were stored at −20° C., before use.
Amyloid Pull-down
Conditioned medium of BHK cells expressing GST-tagged tPA F, F-EGF, EGF, K1, F-EGF-K1, FXII F, HGFa F, Fn F4, Fn F5, Fn F4-5 and GST was used for amyloid binding assays. At first, constructs were adjusted to approximately equal concentration using Western blots. Qualitative binding of the recombinant fragments are evaluated using a “pull-down” assay. To this end, the recombinantly made fragments, are incubated with either Aβ or IAPP fibrils. Since these peptides form insoluble fibers, unbound proteins can be easily removed from the fibers following centrifugation. The pellets, containing the bound fragments are subsequently washed several times. Bound fragments are solubilized in SDS-sample buffer and analyzed by PAGE, as well as unbound proteins in the supernatant fraction and starting material. The gels are analyzed using immunoblotting analysis with the anti-GST antibody Z-5.
Amyloid ELISA with tPA F-EGF-GST
In order to define the affinity of the purified tPA F-EGF-GST recombinant protein we performed ELISA's with immobilized amyloid (poly)peptides and non-amyloid control ΔmIAPP. Twenty-five μg ml−1 of Aβ , FP13, IAPP or ΔmIAPP was immobilized on Exiqon peptide immoblizer plates. A concentration series of tPA F-EGF-GST in the presence of excess εACA, was added to the wells and binding was assayed using anti-GST antibody Z-5. As a control GST (Sigma-Aldrich, St. Louis, Mo., USA, catalogue # G-5663) was used at the same concentrations.
Immunohistochemistry: Binding of tPA F-EGF to Human AD Brain
Paraffin brain sections of a human inflicted with AD was a kind gift of Prof. Slootweg (Dept. of Pathology, UMC Utrecht). Sections were deparaffinized in a series of xylene-ethanol. Endogenous peroxidases were blocked with methanol/1.5% H2O2 for 15 minutes. After rinsing in H2O, sections were incubated with undiluted formic acid for 10 minutes, followed by incubation in PBS for 5 minutes. Sections were blocked in 10% HPS in PBS for 15 minutes. Sections were exposed for 2 hours with 7 nM of tPA F-EGF-GST or GST in PBS/0.3% BSA. After three wash steps with PBS, sections were overlayed with 200 ng ml−1 anti-GST antibody Z-5, for 1 hour. After washing, ready-to-use goat anti-rabbit Powervision (Immunologic, Duiven, The Netherlands, catalogue # DPVR-55AP) was applied and incubated for 1 hour. After washing, sections were stained for 10 minutes with 3,3′-diamino benzidine (Sigma-Aldrich, St Louis, Mo., USA, catalogue # D-5905), followed by haematoxylin staining for 10 seconds. After washing with H2O, sections were incubated with Congo red according to the manufacturer's recommendations (Sigma Diagnostics, St Louis, Mo., USA). Sections were cleared in xylene and mounted with D.P.X. Mounting Medium (Nustain, Nottingham, U.K.). Analysis of sections was performed on a Leica DMIRBE fluorescence microscope (Rijswijk, The Netherlands). Fluorescence of Congo red was analysed using an excitation wavelength of 596 nm and an emission wavelength of 620 nm.
ELISA: Binding of tPA-F-GST and RPTPl-GST to Human Ab(1-40) and Glycated Albumin
Binding of tPA-F-GST and RPTPl-GST to fibrous amyloids human Aβ (1-40) and albumin-g6p was assayed with an ELISA. In brief, human Aβ (1-40), albumin-g6p, or buffer only, were coated on a peptide I Immobilizer, or a protein I Immobilizer, respectively. Wells were incubated with the purified GST-tagged constructs or control medium, and binding was detected using primary anti-GST monoclonal antibody 2F3 and RAMPO. The wells were also incubated with 500 nM of tPA in the presence of 10 mM of eACA. Binding of tPA is then independent of the lysyl binding-site located at the kringle2 domain. Binding of tPA was measured using primary antibody 374B and RAMPO. Experiments were performed in triplicate and blank readings of non-coated wells were substracted.
Anti-AGE Antibodies
Antibodies against glucose-6-phosphate glycated bovine serum albumin were elicited in rabbits using standard immunization schemes. Anti-AGE1 was obtained after immunization with two-weeks glycated albumin-AGE (Prof. Dr. Ph. G. de Groot/Dr. I. Bobbink; unpublished data). The antibody was purified from serum using a Protein G column. Anti-AGE2 was developed by Davids Biotechnologie (Regensburg, Germany). After immunization with albumin-AGE:23, antibodies were affinity purified on human Aβ(1-40) conjugated to EMD-Epoxy activated beads (Merck, Darmstadt, Germany). Polyclonal mouse anti-AGE antibody was obtained after immunization with albumin-AGE:23 and human Aβ(1-40), in a molar ratio of 9:1. Polyclonal serum was obtained using standard immunization procedures, which were performed by the Academic Biomedical Cluster Hybridoma Facility (Utrecht University, The Netherlands). Subsequently monoclonal antibodies were generated using standard procedures.
ELISA: Binding of Antibodies Against Amyloid Peptides or Glycated Protein to Protein-AGE and Amyloid Fibrils
For ELISA's, amnyloid compounds were immobilized on Exiqon peptide or protein Immobilizers (Vedbaek, Denmark), as described before. Anti-AGE antibodies and commercially available anti-Aβ(1-42) H-43 (Santa Cruz Biotechnology, Santa Cruz, Calif., USA) were diluted in PBS with 0.1% v/v Tween20. Rabbit anti-human vitronectin K9234 was a kind gift of Dr. H. de Boer (UMC Utrecht), and was used as a negative control. For ELISA's with mouse polyclonal anti-albumin-AGE/Aβ, control serum with antibody elicited against an unrelated protein was used. Binding of mouse polyclonal anti-albumin-AGE/Aβwas performed using a dilution series of serum in PBS/0.1% Tween20. For competitive binding assays with IAPP, anti-AGE1 was pre-incubated with varying IAPP concentrations. The IAPP fibrils were spun down and the supernatant was applied in triplicate to wells of an ELISA plate coated with Aβ. Competitive binding assays with multiligand cross-β structure binding serine protease tPA were performed in a slightly different way. Coated Aβ and IAPP are overlayed with a anti-AGE1 or anti-Aβ(1-42) H-43 concentration related to the kD, together with a concentration series of tPA. A 107-104 times molar excess of lysine analogue εACA (10 mM) was present in the binding buffer in order to avoid binding of tPA to lysine residues of Aβ and IAPP, which would be independent of the presence of amyloid structures.
Pull-down Assay with Amyloid Peptides and Rabbit Anti-AGE1 Antibody
Anti-AGE1 was incubated with amyloid aggregates of Aβ(16-22), Aβ(1-40) and IAPP. After centrifugation, pellets were washed three times with PBS/0.1% Tween20, dissolved in non-reducing sample buffer (1.5% (m/v) sodium dodecyl sulphate, 5% (v/v) glycerol, 0.01% (m/v) bromophenol blue, 30 mM Tris-HCl pH 6.8). Supernatant after pelleting of the amyloid fibrils was diluted 1:1 with 2× sample buffer. Samples were applied to a polyacrylamide gel and after Western blotting, anti-AGE1 was detected with SWARPO.
Immunohistochemical Analysis of the Binding of Anti-AGE2 to an Amyloid Plaque in a Section of a Human Brain Inflicted by AD.
Rabbit anti-AGE2, affinity purified on an Aβ column, was used for assaying binding properties towards amyloid plaques in brain sections of a human with AD. The procedure was performed essentially as described above. To avoid eventual binding of 11 μg ml−1 anti-AGE2 to protein-AGE adducts or to human albumin in the brain section, 300 nM of g6p-glycated dipeptide Gly-Lys was added to the binding buffer, together with 0.3% m/v BSA. After the immunohistochemical stain, the section was stained with Congo red.
Sandwich ELISA for Detection of Amyloid Albumin-AGE in Solution
For detection of amyloid cross-β structure in solutions we used the sandwich ELISA approach. Actilyse tPA was immoblized at a concentration of 10 μg ml−1 to wells of a 96-wells protein Immobilizer plate (Exiqon, Vedbaek, Denmark). Concentration series of albumin-AGE:23 and albumin-control:23 were added to the tPA-coated wells, as well as to non-coated control wells. Binding of amyloid structures was detected upon incubation with 1 μg ml−1 anti-Aβ(1-42) H-43 (Santa Cruz Biotechnology, Santa Cruz, Calif., USA) and subsequently 0.3 μg ml−1 SWARPO, followed by ortho-phenylene-diamine/H2O2/H2SO4 stain.
Preparation of Cross-β Structure Rich Compounds
Soluble endostatin produced in the yeast strain Pichia pastoris was kindly provided by Dr. Kim Lee Sim (EntreMed, Inc., Rockville, Mass., USA). Cross-β structure rich endostatin was prepared from soluble endostatin as follows. Soluble yeast endostatin was dialysed overnight in 8 M urea and subsequently three times against H2O. Endostatin precipitates as a fine white solid. The presence of cross-β structure was established by Congo red binding and X-ray fiber diffraction (Kranenburg, Bouma et al., 2002; Kranenburg, Kroon-Batenburg et al., 2003). Aggregated endostatin was solubilized in 0.1% formic acid, lyophilized fibrin peptides and Aβ were dissolved in H2O and glycated albumin was extensively dialysed against water. Samples were taken up in a glass capillary. The solvent was then allowed to evaporate over a period of days. Capillaries containing the dried samples were placed on a Nonius kappaCCD diffractometer (Bruker-Nonius, Delft, The Netherlands). Scattering was measured using sealed tube MoKa radiation with a graphite monochromator on the CCD area detector during 16 hours. Scattering from air and the glass capillary wall were subtracted using in-house software (VIEW/EVAL, Dept. of Crystal- and Structural Chemistry, Utrecht University, The Netherlands). For preparation of advanced glycation end-product modified bovine serum albumin (albumin-AGE), 100 mg ml−1 of albumin was incubated with PBS containing 1 M of glucose-6-phosphate (g6p) and 0.05% m/v NaN3, at 37° C. in the dark. Glycation was prolonged up to 23 weeks (Bouma, Kroon-Batenburg et al., 2003). Human haemoglobin (Hb) at 5 mg ml−1 was incubated for 32 weeks at 37° C. with PBS containing 1 M of g6p and 0.05% m/v of NaN3. In control solutions, g6p was omitted. After incubations, solutions were extensively dialyzed against distilled water and, subsequently, stored at 4° C. Protein concentrations were determined with Advanced protein-assay reagent ADV01 (Cytoskeleton, Denver, Colo., USA). Glycation and formation of advanced glycation end-products (AGE) was confirmed by measuring intrinsic fluorescent signals from advanced glycation end-products; excitation wavelength 380 nm, emission wavelength 435 nm. In addition, binding of AGE-specific antibodies was determined. Presence of cross-β structure in albumin-AGE was confirmed by Congo red binding, Thioflavin T binding, the presence of β-sheet secondary structure, as observed with circular dichroism spectropolarimetry (CD) analyzes, and by X-ray fiber diffraction experiments (Bouma, Kroon-Batenburg et al., 2003). Presence of cross-β structure in Hb-AGE was conformed by tPA binding, CD analyzes, transmission electron microscopy imaging of fibrillar structures and by Congo red fluorescence measurements. Amyloid preparations of human γ-globulins were made as follows. Lyophilized γ-globulins (Sigma-Aldrich) was dissolved in a 1(:)1 volume ratio of 1,1,1,3,3,3-hexafluoro-2-propanol and trifluoro-acetic acid and subsequently dried under an air stream. Dried γ-globulins was dissolved in H2O to an end-concentration of 1 mg/ml and kept at room temperature for at least three days. Aliquots were stored at −20° C. and analyzed for the presence of cross-β structure. Fluorescence of Congo red and Thioflavin T was assessed as well as tPA binding in an ELISA and tPA activating properties in the chromogenic plasmin assay.
Other peptide batches with amyloid-like properties were prepared as follows. Human Aβ(1-40) Dutch type (DAEFRHDSGYEVHHQKLVFFAQDVGSNKGAIIGLMVGGVV), islet amyloid polypeptide (IAPP, KCNTATCATQRLANFLVHSSNNFGAILSSTNVGSNTY), amyloid fragment of transthyretin (TTR11, YTIAALLSPYS) (Jaroniec, MacPhee et al., 2002), laminin α1-chain(2097-2108) amyloid core peptide (LAM12, AASIKVAVSADR) (Yamada, Kadoya et al., 2002), mouse non-amyloidogenic IAPP(20-29) core (mIAPP, SNNLGPVLPP), non-amyloid fragment FP10of human fibrin a-chain(148-157) (KRLEVDIDIK) (Schielen, Adams et al., 1191; Kranenburg, Bouma et al., 2002) and human fibrin α-chain(148-160) amyloid fragment with Lys157Ala mutation (FP13, KRLEVDIDIAIRS) (BB, unpublished and (Schielen, Adams et al., 1991; Kranenburg, Bouma et al., 2002)). For pull-down experiments Aβ and IAPP were dissolved in PBS, at 1 mg ml−1 and kept at room temperature for at least three weeks. Alternatively, amyloid Aβ, IAPP, FP13 and LAM12 were disaggregated in a 1:1 (v/v) mixture of 1,1,1,3,3,3-hexafluoro-2-isopropyl alcohol and trifluoroacetic acid, air-dried and dissolved in H2O (Aβ, IAPP, LAM12: 10 mg ml−1, FP13: 1 mg ml−1). After three days at 37° C., peptides were kept at room temperature for two weeks, before storage at 4° C. Freshly dissolved Aβ (10 mg ml−1) in 1,1,1,3,3,3-hexafluoro-2-isopropyl alcohol and trifluoroacetic acid was diluted in H2O prior to immobilization on ELISA plates. TTR11 (15 mg ml−1) was dissolved in 10% (v/v) acetonitrile in water, at pH 2 (HCl), and kept at 37° C. for three days and subsequently at room temperature for two weeks. mIAPP and FP10 were dissolved at a concentration of 1 mg ml−1in H2O and stored at 4° C. Peptide solutions were tested for the presence of amyloid conformation by Thioflavin T- (ThT) or Congo red fluorescence as described (Hoppener, Oosterwijk et al., 1999; Hoppener, Ahren et al., 2000; Bouma, Kroon-Batenburg et al., 2003). ThT and Congo red fluorescence was enhanced for amyloid peptides, and not for non-amyloid mIAPP, FP10 or freshly dissolved Aβ.
Plasmin-α2-anti-plasmin- and Factor XIIa Measurements
Factor XIIa and PAP levels in citrated plasma of 40 apparently healthy controls and of 40 patients with systemic amyloidosis were measured. Factor XIIa was measured with an ELISA (Axis-Shield Diagnostics, Dundee, UK). PAP complexes were measured with the ELISA of Technoclone (Vienna, Austria). The control group consisted of 19 male and 21 female subjects with an average age of 49.4 years (standard deviation 6.8 years). The patient population consisted of 17 male and 23 female subjects with an average age of 51.8 years (standard deviation 9.9 years). Patients diagnosis was biopsy proven. All patients have provided informed consent prior to inclusion in this study and the study was approved by the local ethical committee.
Cloning and Expression of Recombinant Fibronectin Type I Domains
Amino-acid sequences of recombinantly produced domains of tPA, fibronectin and factor XII, and the domain architecture of the recombinant constructs are depicted in
Alternatively, recombinant finger domains of fibronectin (F4-5) and tPA were expressed with a His-tag. Two fibronectin F4-5 constructs were cloned. One construct comprising the Igk signal sequence (vector 71, ABC-expression facility, Utrecht University/UMC Utrecht). With two designed primers (8, 9, see
Plasmin activity was assayed as described (Kranenburg, Bouma et al., 2002). Peptides and proteins that were tested for their stimulatory ability were regularly used at 100 μg ml−1. The tPA and plasminogen concentrations were 200 pM and 1.1 μM, respectively. Chromogenic substrate S-2251 (Chromogenix) was used to measure plasmin activity. Conversion of inactive zymogen factor XII to proteolytically active factor XII (factor XIIa) was assayed by measurement of the conversion of chromogenic substrate Chromozym-PK (Roche Diagnostics, Almere, The Netherlands) by kallikrein. Chromozym-PK was used at a concentration of 0.3 mM. Factor XII, human plasma prekallikrein (Calbiochem) and human plasma cofactor high-molecular weight kininogen (Calbiochem) were used at concentrations of 1 μg ml−1. The assay buffer contained HBS (10 mM HEPES, 4 mM KCl, 137 mM NaCl, 5 μM ZnCl2, 0.1% m/v BSA (A7906, Sigma, St. Louis, Mo., USA), pH 7.2). Assays were performed using microtiter plates (Costar, Cambridge, Mass., USA). Peptides and proteins were tested for their ability to activate factor XII. 150 μg ml−1 kaolin, an established activator of factor XII was used as positive control and solvent (H2O) as negative control. The conversion of Chromozym-PK was recorded kinetically at 37° C. for 60 minutes. Assays were done in duplicates. In control wells factor XII was omitted from the assay solutions and no conversion of Chromozym-PK was detected. In some assays albumin was omitted from the reaction mixture. In another type of factor XII activation assay, chromogenic substrate S-2222 (Chromogenix) was used to follow the activity of factor XII itself. With S-2222, activation of factor XII in plasma was established, using 60% v/v plasma, diluted with substrate and H2O with or without potential cofactor. Furthermore, auto-activation of factor XII was established by incubating 53 μg/ml purified factor XII in 50 mM Tris-HCl buffer pH 7.5 with 1 mM EDTA and
and H2O with or without potential cofactor.
Binding of tPA, Factor XII and the Fibronectin Type I Domains Thereof to Cross-β Structure Containing Protein Aggregates
Previously, we demonstrated that tPA specifically binds to any protein or peptide, as long as ligands have adopted amyloid-like cross-β structure conformation (Kranenburg, Bouma et al., 2002). Moreover, binding of tPA to aggregates with cross-β structure is accompanied by activation of tPA. Similar binding- and activation characteristics are indicated for factor XII, a serine protease with a similar domain architecture as tPA. Binding of factor XII to protein aggregates with cross-β structure is analyzed in an ELISA set-up. Activation of factor XII by aggregates comprising cross-β structure is analyzed according to the procedure described below. Next, binding of the fibronectin type I domain (F) of tPA and factor XII to amyloid-like aggregates was determined with ELISA's. Aggregates with cross-β structure are immobilized on Exiqon (Dahlback, Denmark) or Nunc (amino strips, catalogue #076901) Immobilizer plates, or Greiner microlon high-binding plates. Binding of tPA or factor XII was detected with specific antibodies; monoclonal 374b (American diagnostica) for tPA and polyclonal anti-factor XII antibody (Calbiochem). Binding of F domains was determined with F domains comprising a biotin tag, glutathione S transferase tag or His6-tag. F domains were obtained as described below. In control experiments, binding of K2P tPA, a tPA analogue that lacks the N-terminal F-EGF-like domain-kringle 1 domain (Reteplase, Boehringer-Ingelheim, Germany), was tested. Binding of tPA and K2P tPA was tested in the presence of 10 mM ε-amino caproic acid (εACA), a lysine analogue that abolishes the binding of the tPA kringle2 domain to solvent exposed lysine residues.
Thioflavin T Fluorescence
Fluorescence of Thioflavin T (ThT)-protein/peptide adducts was measured as follows. Solutions of 25 μl/ml of protein or peptide preparations were prepared in 50 mM glycine buffer pH 9.0 with 25 μM ThT. Fluorescence was measured at 485 nm upon excitation at 435 nm. Background signals from buffer, buffer with ThT and protein/peptide solution without ThT were subtracted from corresponding measurements with protein solution incubated with ThT. Regularly, fluorescence of Aβ was used as a positive control, and fluorescence of FP10, a non-amyloid fibrin fragment (Kranenburg, Bouma et al., 2002), was used as a negative control. Fluorescence was measured in triplicate on a Hitachi F-4500 fluorescence spectrophotometer (Ltd., Tokyo, Japan).
Thioflavin T fluorescence was determined for human blood platelets, that were isolated as described above. The washed platelets in HEPES-Tyrode buffer (200,000/μl) were kept at room temperature. ThT fluorescence was determined at t=0 and at t=72 h, after storage at room temperature. For the measurements the platelets were diluted in assay buffer. Appropriate background signal readings were measured and subtracted.
Effects of Protein Aggregates with Cross-β Structure Conformation on the p38MAPK Pathway
Freshly isolated human blood platelets were obtained following the procedure described below. Seventy five μl of the platelet stock was added to 25 μl of agonist solution and incubated at room temperature for 1 minute and 5 minutes. Cells were fixed with 3% v/v formaldehyde and incubated on ice for 15 minutes. Platelets were pelleted upon centrifugation for 1 minute at 8450*g, and pellets were resuspended in 60 pI reducing sample buffer. After 6 minutes, at 100° C. samples were applied to SDS-PA gels for finally Western blot analysis. Blots were first incubated with polyclonal anti-p38MAPK antibody (Cell Signalling Technology) and SWARPO. Then, blots were also incubated with monoclonal anti-actin antibody AC40 (Sigma) and RAMPO, for scaling purposes. The relative degree of p38MAPK phosphorylation was determined using densitometric analysis of the blots.
Influence of Protein Aggregates with Cross-β Structure Conformation on Blood Platelet Aggregation
The influence of protein and peptide aggregates with cross-β structure conformation on blood platelet aggregation was tested with washed platelets in an aggregometric assay. Freshly drawn human aspirin free blood was mixed gently with citrate buffer to avoid coagulation. Blood was spinned for 15 minutes at 150*g at 20° C. and supernatant was collected; platelet rich plasma (PRP). Buffer with 2.5% trisodium citrate, 1.5% citric acid and 2% glucose, pH 6.5 was added to a final volume ration of 1:10 (buffer-PRP). After spinning down the platelets upon centrifugation for 15 minutes at 330*g at 20° C., the pellet was resuspended in HEPES-Tyrode buffer pH 6.5. Prostacyclin was added to a final concentration of 10 ng/ml, and the solution was centrifuged for 15 minutes at 330*g at 20° C., with a soft brake. The pellet was resuspended in HEPES-Tyrode buffer pH 7.2 in a way that the final platelet number was adjusted to 200,000/μl. Platelets were kept at 37° C. for at least 30 minutes, before use in the assays, to ensure that they were in the resting state.
For the aggregometric assays, 400 μl platelet solution was added to a glass tube with 100 μl containing the agonist of interest, fibrinogen and CaCl2. Final concentrations of fibrinogen and CaCl2 were 0.5 mg/ml and 3 mM, respectively. A stirring magnet was added and the apparatus (Whole-blood aggregometer, Chrono-log, Havertown, Pa., USA) was blanked. Aggregation was followed in time by measuring the absorbance of the solution, that will decrease in time upon platelet aggregation. As a positive control, 0.5 U/ml thrombin was used. Aggregation was followed for 10 minutes.
Activation of tPA by β2-glycoprotein I and Binding of Factor XII and tPA to β2-glycoprotein I
Purification of β2-glycoprotein I (p2gpi) was performed according to established methods. Recombinant human β2gpi was expressed in insect cells and purified as described in de Laat et al. (de Laat, Derksen et al., 2004a). Plasma derived β2gpi as used in the factor XII ELISA, the chromogenic plasmin assay and in the anti-phospholipid syndrome antibody ELISA (see below), was purified from fresh human plasma as described in Horbach et al. (Horbach, van Oort et al., 1996). Alternatively, β2gpi was purified from either fresh human plasma or from frozen-thawed plasma on an anti-β2 gpi antibody affinity column(Horbach, van Oort et al., 1998).
Activation of tissue-type plasminogen activator (tPA) (Actilyse, Boehringer-Ingelheim) by β2gpi preparations was tested in a chromogenic plasmin assay (see above). 100 μg/ml plasma β2gpi or recombinant β2gpi were tested for their stimulatory co-factor activity in the tPA-mediated conversion of plasminogen to plasmin and were compared to the stimulatory activity of cross-β structure rich fibrin peptide FP13 (Kranenburg, Bouma et al., 2002).
Binding of purified human factor XII from plasma (Calbiochem) or of purified recombinant human tPA to β2gpi purified from human plasma or to recombinant human β2gpi was tested in an ELISA. Ten pg of factor XII or tPA in PBS was coated onto wells of a Costar 2595 ELISA plate and overlayed with concentration series of the two β2gpi preparations. Binding of β2 gpi was assessed with monoclonal antibody 2B2 (Horbach, van Oort et al., 1998).
From preparations of β2gpi purified from fresh plasma or purified from frozen-thawed plasma 33 μg was brought onto a 7.5% poly-acrylarnide gel. After Western blotting, the nitrocellulose was incubated with 1000× diluted anti-human factor XII antibody (Calbiochem) and subsequently 3000× diluted SWARPO (DAKO).
Purified β2gpi from human plasma (400 μg/ml final concentration) was incubated with 100 μM cardiolipin vesicles or with 250 μg/ml DXS500k. Fluorescence of β2gpi in buffer, cardiolipin or DXS500k in buffer, buffer and ThT alone, and of β2gpi-cardiolipin adducts and β2gpi-DXS500k adducts with or without ThT was recorded as described above.
Binding of Anti-β2gpi Autoantibodies from Antiphospholipid Syndrome Auto-immune Patients to Immobilized β2gpi is Inhibited by Recombinant β2gpi and not by Plasma Derived β2gpi
When plasma derived β2gpi is coated onto hydrophilic ELISA plates, anti-β2gpi autoantibodies isolated from plasma of antiphospholipid syndrome auto-immune patients can bind (de Laat, Derksen et al., 2004b) (data kindly provided by B. de Laat, UMC Utrecht). To study the influence of co-incubations of the coated β2gpi with antibodies together with plasma β2gpi or recombinant β2gpi, concentration series of β2gpi were added to the patient antibodies. Subsequently, binding of the antibodies to coated β2gpi was assayed.
Structural Analysis of Oxidized Low Density Lipoprotein
Low density lipoproteins (LDL) were isolated from fresh (<24 h) human plasma, obtained from the Dutch bloodbank, that was kept at 10° C. LDL was isolated essentially as earlier described. Plasma was centrifuged in an ultracentrifuge for three subsequent cycles. The LDL fraction was isolated and stored under N2, at 4° C. Before experiments, native LDL (nLDL) was dialyzed overnight at 4° C. against 0.9% w/v NaCl. To obtain oxidized LDL (oxLDL) with varying degrees of oxidation, native was first dialyzed against 0.15 M NaCl solution containing 1 mM NaNO3, overnight at 4 ° C. Then, nLDL was diluted to 3-5 mg/ml, and CuSO4 was added to a final concentration of 25 μM and incubated at 37 ° C. The degree of oxidation was followed by measurement of diene-formation at λ=234 nm (Ultrospec 3000 Spectrophotometer (Pharmacia Biotech)). To stop the oxidation reaction, LDL was dialyzed against 0.15 M NaCl, 1 mM NaNO3 and 1 mM EDTA.
In time, an increase of the oxidation of LDL, as measured by specific diene fluorescence at 243 nm, was completed with Thioflavin T fluorescence and Congo red fluorescence measurements. Fluorescence measurements were performed as described above. In addition, the ability of nLDL and oxLDL to induce tPA activation was tested in the chromogenic plasmin assay. For this purpose, 24% oxidized LDL was used. Finally, we tested the ability of oxLDL to activate factor XII in plasma, as determined by following the conversion of the substrate S-2222, that is cleaved when activated factor XII is present (see above). Activation assays were performed in the wells of 96-wells ELISA plates, at 37° C.
Binding of Amyloid-specific Dyes to a Fibrin Clot.
Pooled human plasma of healthy donors was clotted by adding either phospholipids, CaCl2 and kaolin when aPTT's are concerned, or tissue factor rich thromboplastin and CaCl2 when PT assays are concerned. APTT's and PT's are performed in the presence of concentration series of the amyloid-specific dyes Congo red, Thioflavin S (ThS) or Thioflavin T (ThT), accompanied by the appropriate buffer controls, i.e., Na2SO4 for Congo red and NH4Cl for ThS and ThT. Coagulation velocities under influence of amyloid-specific dyes were measured, or the binding of the dyes was established by visual inspection or by use of direct-light microscopy or fluorescence microscopy.
1. Structure is Present in Fibrin and in Synthetic Peptides Derived from Fibrin.
We have demonstrated that a fibrin clot stains with Congo red (not shown) and exhibits Thioflavin T fluorescence (
In conclusion, these data provide evidence for physiological occurrence/relevance for formation of cross-β structure and the role of this structural element in binding of tPA to fibrin.
2. Aβ Structure, Binds Plasmin(ogen) and tPA, Stimulates Plasminogen Activation, Induces Matrix Degradation and Induces Cell Detachment that is Aggravated by Plasminogen and Inhibited by CpB
To test whether tPA, plasminogen and plasmin bind Aβ we performed solid-phase binding assays. Aβ was coated onto plastic 96-well plates and binding of the peptide to either plasmin(ogen) or to tPA was assessed by overlaying the coated peptide with increasing concentrations of either tPA, plasminogen or plasmin. Binding was assessed using specific antibodies to either plasmin(ogen) or to tPA by performing ELISA.
We investigated the kinetics of plasminogen activation in the absence and the presence of Aβ. As has been published before by Kingston et al.24 we find that Aβ potently stimulates the activation of plasminogen by tPA (
We considered the possibility that the generation of free lysines during Aβ stimulated plasmin formation was responsible for the observed second order kinetics. To test this, we made use of carboxypeptidase B (CpB), an enzyme that cleaves of C-terminal lysine and arginine residues) and the CpB-inhibitor CPI.
3. Endostatin can Form Amyloid Fibrils Comprising Cross-β Structure.
Using Congo red staining (not shown), X-ray diffraction analysis and TEM we have demonstrated the presence of cross-β structure in aggregated endostatin from Escherichia coli, as wells as from Pichia pastoris, and the ability of endostatin to form amyloid fibrils (
Here we have demonstrated that endostatin is an example of a denatured protein that is able to stimulate the suggested cross-β pathway.
4. IAPP Binds tPA and Stimulates tPA-mediated Plasminogen Activation.
Amyloid deposits of IAPP are formed in the pancreas of type II diabetic patients.59 IAPP can cause cell death in vitro and is therefore thought to contribute to destruction of β-cells that is seen in vivo, which leads to insufficient insulin production. IAPP forms fibrils comprising cross-β structure.60
We tested whether IAPP could stimulate tPA-mediated plasminogen activation (
5. Glycated Albumin Binds Thioflavin T and tPA, and Aggregates as Amyloid Fibrils Comprising Cross-β Structure.
It has been demonstrated that glycation of several proteins can induce or increase the ability of these proteins to bind tPA and stimulate tPA-mediated plasmin formation.22; 61 We here show that glycation of albumin with g6p not only confers high affinity tPA binding to albumin (
Analyses with TEM of the g6p-modified albumin preparations revealed that after a four-weeks incubation amorphous albumin aggregates are formed (
X-ray fibre diffraction analyses revealed that albumin-g6p (23 weeks) comprises a significantly amount of crystalline fibres (FIGS. 8J,L), whereas diffraction patterns of albumin-g6p (2 weeks) and albumin-g6p (4 weeks) show features originating from amorphous precipitated globular protein, very similar to the patterns obtained for albumin controls (
These results show that due to incubation and/or modification with sugar moieties cross-β structures in albumin are formed that are able to support tPA binding.
6. Glycation of Haemoglobin Induces tPA Binding and Fibril Formation.
Incubation of human haemoglobin with g6p resulted in high-affinity tPA binding (
7. Amyloid Albumin is Formed Irrespective of the Original Carbohydrate (Derivative)
From the above listed observations it is clear that modification of —NH2 groups of albumin with g6p induces formation of amyloid cross-β structure. The next question we addressed was whether triggering of refolding of globular albumin into an amyloid fold was a restricted property of g6p, or whether amyloid formation occurs irrespective of the original carbohydrate or carbohydrate derivative used for AGE formation. Albumin solutions were incubated for 86 weeks at 37° C. with 1 M g6p, 250 mM DL-glyceraldehyde/100 mM NaCNBH3, 1 M β-D-(−)-fructose, 1 M D(+)-glucose, 500 mM glyoxylic acid/100 mM NaCNBH3, and corresponding PBS and PBS/NaCNBH3 buffer controls. Glyceraldehyde and glyoxylic acid are carbohydrate derivatives that are precursors of AGE in Maillard reactions.63; 64 After 86 weeks albumin-glyceraldehyde and albumin-fructose were light-yellow/brown suspensions. Controls were colorless and clear solutions. Albumin-glucose and albumin-glyoxylic acid were clear light-yellow to light-brown solutions. Albumin-g6p:86 was a clear and dark brown solution. AGE formation was confirmed by autofluorescence measurements using AGE-specific excitation/emission wavelengths (not shown), binding of moab anti-AGE 4B5 (not shown) and binding of poab anti-AGE (not shown). As expected, albumin-glyoxylic acid did not show an autofluorescent signal due to the fact that (mainly) non-fluorescent carboxymethyl-lysine (CML) adducts are formed.63
The autofluorescence data and the binding of AGE-specific antibodies listed above show that various carbohydrates and carbohydrate derivatives can lead to similar AGE structures. Using g6p as starting point for AGE formation, we showed that albumin adopted amyloid properties, similar to those observed in well-studied fibrils of Aβ and IAPP. Therefore, we tested for the presence of amyloid structures in the albumin-AGE adducts obtained with alternative carbohydrates and derivatives. We measured fluorescence of albumin-AGE—ThT solutions (
From the ThT, Congo red and tPA data, it is clear that inducing amyloid properties in albumin is not an exclusive property of g6p. Apparently, a spectrum of carbohydrates and carbohydrate derivatives, comprising g6p, glucose, fructose, glyceraldehyde, and likely more, has the capacity to trigger the switch from a globular native fold to the amyloid cross-β structure fold, upon their covalent binding to albumin.
8. Analysis of Congo Red Binding and tPA Binding to Aβ.
It has been demonstrated that Aβ can bind tPA and Congo red. We show that the binding of tPA to Aβ can be competed by Congo red (
9. Binding of Human FXII to Amyloid Peptides and Proteins, that Contain the Cross-β Structure Fold.
The graphs in
10. Binding of tPA to the Cross-β Structure Containing Molecules, Aβ and Glycated Albumin Requires the Presence of an N-terminal Region in tPA, which Contains the Finger Domain.
Several domains in tPA have been shown to mediate binding to fibrin or fibrin fragments.12; 53; 66; 67 However it is unknown which domain of tPA is needed for binding to Aβ or other cross-β structure-containing molecules. We show that a mutated tPA, termed reteplase, which lacks the N-terminal finger, EGF and kringle 1 domain (K2-tPA) is unable to bind cross-β structure comprising molecules (FIGS. 13A,B). These results suggest that the N-terminal region is required for binding of tPA to fibrils comprising cross-β structure.
Expression and Purification of tPA-F-GST and RPTP-GST
Purification of the GST-tagged constructs tPA-F-GST and RPTPIμ-GST(control) from 293T medium using glutathione coupled to Sepharose 4B beads resulted in single bands of approximately 35 kDa and 150 kDa, respectively (not shown). Traces of BSA, originating from the FCS used in the medium, were also present.
ELISA: Binding of tPA-F-GST and RPTP-GST to Human Aβ(1-40) and Glycated Albumin
In the ELISA, control tPA bound to both human Aβ(1-40) and albumin-g6p in the presence of excess εACA (
We prepared cDNA constructs in pcDNA3 of the F, F-EGF, EGF, F-EGF-K1 and K1fragments of human tPA. Recombinant proteins with a C-terminal GST tag were expressed in BHK cells and secreted to the medium. Medium from BHK cells expressing the GST tag alone was used as a control. Conditioned medium was used for pull-down assays using Aβ and IAPP fibrils, followed by Western blot analyses. Efficient binding to Aβ is evident for all three tPA mutants that contain the finger domain, i.e., F-GST, F-EGF-GST and F-EGF-K1-GST (
We compared binding of purified tPA F-EGF-GST, recombinant f.l. Actilyse tPA and a GST control to immobilized amyloid Aβ, amyloid fibrin fragment α148-160 FP13, amyloid IAPP and to non-amyloid mΔIAPP control (FIGS. 13E-G). Full-length tPA and tPA F-EGF-GST bind to all three amyloid peptides; for Aβ kD's for tPA and F-EGF are 2 and 2 nM, respectively, for FP13 5 and 2 nM, for IAPP 2 and 13 nM. No binding to non-amyloid mΔIAPP is observed (
With immunohistochemical analysis we tested binding of the purified recombinant tPA F-EGF-GST construct to paraffin sections of human brain inflicted by AD. Presence of amyloid depositions was confirmed by the Dept. of Pathology (UMC Utrecht) using standard techniques. In our experiments, these amyloid depositions were located using Congo red fluorescence (FIGS. 13I,K,M). In
At present, based on sequential and structural homology, next to tPA three proteins are known that contain one or more finger domains, i.e., HGFa (one F domain), FXII (one F domain, Fn (one stretch of six F domains, two stretches of three F domains). From the above listed results we concluded that the F domain of tPA plays a crucial role in binding of tPA to amyloid (poly)peptides. We hypothesized that the finger domain could be a general cross-β structure binding module. Presently 4 proteins, tPA, FXII, HGFa and fibroenctin, are known that contain a finger motif.
11. Amyloid-binding Domain of tPA
The finger domain of tPA has been shown to be of importance for high-affinity binding to fibrin.12; 66 Our present results using reteplase (K2-P tPA) and F-tPA, F-EGF-tPA and F-EGF-K1-tPA indicate an important role for the N-terminal finger domain of tPA in binding to stimulatory factors other than fibrin. Thus far all these factors bind Congo red and contain cross-β structure. Furthermore, the binding site of fibronectin for fibrin has been mapped to the finger-domain tandem F4-F5.68 It has been demonstrated that plasminogen activation by full-length tPA, in the presence of fibrin fragment FCB2, can be inhibited by fibronectin.69 Taken together, these observations suggest that tPA and fibronectin compete, via their finger domain, for the same or overlapping binding sites on fibrin. Our data, now, show that the F4-5 domains of Fn bind to amyloid Aβ.
12. Binding of Anti-AGE Antibodies to Amyloid (poly)Peptides and Binding of Anti-Aβ to Protein-AGE Adducts
Recently, O'Nuallain and Wetzel70 showed that antibodies elicited against a peptide with amyloid characteristics, can bind to any other peptide with similar amyloid properties, irrespective of amino-acid sequence. Based on these data and on our observations that tissue-type plasminogen activator and factor XII can bind to a family of sequence-unrelated polypeptides, that share the amyloid specific cross-β structure fold, we hypothesize that a broader class of proteins can display affinity towards this structural unit, rather than towards a linear or conformational epitope, built up by specific amino-acid residues. This hypothesis prompted us with the question whether antibodies elicited against albumin-AGE, that contains the amyloid cross-β structure fold, also display the broad-range specificity towards any (poly)peptide which bears this cross-β structure fold.
In an ELISA set-up α-AGE1, which was elicited against g6p-glycated albumin-AGE, binds to amyloid albumin-AGE:23 (Kd=66 nM) and Hb-AGE:32 (Kd=20 nM), as wells as to Aβ(1-40) (Kd=481 nM) and IAPP (Kd=18 nM) (FIGS. 15A-C). Negative controls were non-glycated albumin and Hb, non-amyloid peptide mouse ΔIAPP for IAPP and polyclonal anti-human vitronectin antibody α-hVn K9234 for Aβ. To test whether the same fraction of α-AGE1 binds to IAPP and Aβ, the antibody was pre-incubated with IAPP fibrils, followed by pelleting of the fibrils, together with the possible amyloid-binding fraction of α-AGE1. Binding of α-AGE1, left in the supernatant, to Aβ(1-40) was reduced (
Based on the above listed results obtained with anti-AGE1, we tested whether commercially available rabbit anti-human Aβ(1-42) H-43 also displays broad-range specificity towards any (poly)peptide with unrelated amino-acid sequence, though with amyloid characteristics. Indeed, with an ELISA we could show that H-43 not only binds to Aβ(1-40), but also to IAPP and albumin-AGE (
ELISA's with polyclonal mouse anti-albumin-AGE/Aβ show that the antibody not only binds to these antigens, but that it specifically binds to other amyloid peptides than those used for immunization (FIGS. 15J-L). Similar to the rabbit anti-AGE1 antibody and anti-Aβ(1-42) H-43, anti-albumin-AGE/Aβ displays affinity for the amyloid peptides tested, irrespective of amino-acid sequence. This suggests that also mouse anti-albumin-AGE/Aβ is a multiligand amyloid binding antibody.
Based on the amyloid binding characteristics of anti-AGE1, anti-Aβ(1-42) H-43 and anti-albumin-AGE/Aβ, we purified the amyloid-binding fraction of anti-AGE2, which is elicited against albumin-AGE:23, with Aβ fibrils irreversibly coupled to a column. This fraction was used for immunohistochemical analysis of a human brain section that is inflicted by Alzheimer's disease. In
Our finding that anti-amyloid and anti-AGE antibodies display affinity for a broad range of sequentially unrelated (poly)peptides, as long as the cross-β structure fold is present, is in agreement with the recently published data by O'Nuallain and Wetzel70 and Kayed et al.71 From several older reports in literature it can be distilled that anti-cross-β antibodies can be obtained. For example, cross-reactive antibodies against fibrin and Aβ and against Aβ and haemoglobin are described.72; 73 We indicated here that fibrinogen and haemoglobin-AGE adopt the cross-β structure fold, which suggests that the cross-reactivity observed for anti-Aβ antibodies was in fact binding of anti-cross-β structure antibodies to similar structural epitopes on Aβ, fibrinogen and haemoglobin.
Based on our results with the poly-clonal anti-AGE and amyloid antibodies we hypothesized that anti-cross-β structure antibodies could be obtained. We therefore fused the spleen of mice immunized with glycated BSA and Aβ with myeloma cells. We subsequently selected potential anti-cross-β structure antibodies by examining binding of hybridoma produced antibodies to glycated haemoglobin and IAPP. Using this procedure, we isolated a monoclonal antibody 3H7, that recognizes glycated haemoglobin as well as several peptides that contain the cross-β structure (
13. Sandwich ELISA: Fishing Amyloid Structures from Solution
Using a sandwich ELISA approach with coated tPA that was overlayed with amyloid albumin-AGE:23 in solution, followed by detection with broad-range anti-Aβ(1-42) H-43 (
It is herein disclosed that the three-dimensional structures of the tPA finger-domain74; 75 and the fibronectin finger-domains 4-575; 76 reveals striking structural homology with respect to local charge-density distribution. Both structures contain a similar solvent exposed stretch of five amino-acid residues with alternating charge; for tPA Arg7, Glu9, Arg23, Glu32, Arg30, and for fibronectin Arg83, Glu85, Lys87, Glu89, Arg90, located at the fifth finger domain, respectively. The charged-residue alignments are located at the same side of the finger module. These alignments may be essential for fibrin binding.
Based on our observations, results and the herein disclosed similarities, we show that the same binding sites for tPA become present in all proteins that bind and activate tPA and that this binding site comprises cross-β structure.
Taken together, our data show that cross-β structure is a physiological relevant quarternary structure element which appearance is tightly regulated and which occurrence induces a normal physiological response, i.e., the removal of unwanted biomolecules. To our knowledge the existence of a general system, which we term “cross-β structure pathway” to remove unwanted biomolecules is, herein, dislcosed for the first time. Our results show that this mechanism is fundamental to nature and controls many physiological processes to protect organisms from induced damage or from accumulating useless or denatured biomolecules. If by whatever means deregulated, this system may cause severe problems. On the other hand, if properly used this system may be applicable for inducing cell death in specific target cells, like for example tumour cells.
The fibrinolytic cascade and the contact activation cascade of the haemostatic system are triggered by protein aggregates: Tissue-type plasminogen activator and factor XII interact with protein aggregates comprising amyloid-like cross-β structure, via their fibronectin type I domain. tPA, factor XII, fibronectin and the fibronectin type I domains of tPA, factor XII and fibronectin bind to protein aggregates with cross-β structure conformation
Previously, we established that tissue-type plasminogen activator interacts with protein and peptide aggregates that comprise the cross-β structure conformation, a structural element found in amyloid-like polypeptide assemblies (Kranenburg, Bouma et al., 2002; Bouma, Kroon-Batenburg et al., 2003). Now, we expanded this analysis to other proteins that resemble tPA domain architecture and to separate domains of tPA. Binding of full-length tPA, factor XII and fibronectin, as well as of fibronectin type I (finger, F) domains of tPA and factor XII and F4-5 of fibronectin, to protein and peptide aggregates with cross-β structure conformation was analyzed in an ELISA. In
Activation of Factor XII and tPA by Protein Aggregates with Amyloid-like Cross-β Structure
Contacting factor XII to artificial negatively charged surfaces results in its activation, as measured by the conversion of prekallikrein to kallikrein, which can convert chromogenic substrate Chromozyme PK (
The aforementioned observations show that both the contact system and the fibrinolytic system are activated in conformational diseases, or amyloidoses. We measured activation of these systems in patients with systemic amyloidoses. Increased activation of the fibrinolytic system is detected by measuring the levels of plasmin in complex with its circulating inhibitor α2-anti-plasmin (PAP). Increased activity of the contact system is detected by measuring the levels of activated factor XII. Both PAP levels (3192 ng ml−1 vs 217 ng ml−1) and factor XIIa levels (3.1 ng ml−1 vs 2.1 ng ml−1) were elevated in patient plasma (FIGS. 18H,I). Twelve out of 16 patients with elevated factor XIIa levels also had elevated PAP levels. These measurements show that systemic amyloidosis is accompanied by increased levels of activated serine proteases, and disclose a role for amyloid in activation of tPA and factor XII in vivo.
Factor XII, tPA, Fibronectin and their Recombinant Fibronectin Type I Domains Interact with Aggregates Comprising Cross-β Structure
Like tPA, factor XII, fibronectin, tPA F domain, factor XII F domain and fibronectin F4-5 domains bind to peptide aggregates with cross-β structure conformation. In addition, a chemically synthesized F domain of tPA (T. Hackeng, Academic hospital Maastricht, The Netherlands) the fibronectin F10-12 domains and the hepatocyte growth factor activator F domain bind to amyloid-like cross-β structure rich aggregates (B. Bouma, data not shown). Moreover, like tPA (Kranenburg, Bouma et al., 2002; Reijerkerk, Mosnier et al., 2003; Bouma, Kroon-Batenburg et al., 2003), factor XII becomes activated by amyloid-like aggregates. This has not only been established in an indirect way by measuring activated kallikrein from prekalikrein upon activation of factor XII, but also in a direct way by measuring auto-activation of factor XII upon exposure to amyloid-like protein aggregates (see
Our data show that both the fibrinolytic cascade and the contact system of blood coagulation become activated by activation of tPA and factor XII via protein aggregates with amyloid-like cross-β structure conformation, respectively. Moreover, the presence of amyloid-like protein conformation in the circulation or elsewhere in the body is a risk factor for inducing pathological activation of the fibrinolytic cascade and/or the contact activation system.
Our data on factor XII activation allow for a further analysis of the role of cross-β structure in factor XII activation. For example, factor XII auto-activation by cross-β structure is analyzed by contacting purified factor XII to cross-β structure in the presence of a chromogenic substrate that is converted when factor XII is activated. In addition, the influence of cross-β structure binding proteins and compounds on the activation of factor XII in the presence of cross-β structure is studied. Our observation that both tPA and factor XII become activated by proteins that are contacted to DXS500k further show that the fibrinolytic cascade and the contact activation cascade of the haemostatic system is activated by a common mechanism, in which protein aggregates comprising amyloid-like cross-β structure play an initiating role.
Our data show increased levels of PAP and fxIIa in amyloidosis patients. These results show a role for amyloid-like protein aggregates in the activation of tPA and factor XII in the amyloidosis patients. These results also provide a molecular explanation for bleeding diathesis and coagulation abnormalities that are recognised complications in amyloidosis patients. Dysregulation of the fibrinolytic system and the contact system by amyloid underlies this pathology directly by amyloid-mediated activation of tPA and indirectly by factor XII mediated formation of bradykinin which releases tPA. In addition to a role for fibronectin type I domain-comprising tPA and factor XII in amyloidosis, also a role for HGFA and fibronectin in conformational diseases is clear. Incorporation of fibronectin in amyloid deposits serves a function in neurite outgrowth in Alzheimer's disease, and represents a defense mechanism against amyloid deposition by shielding of toxic structures and by inhibiting fibril extension. Hepatocyte growth factor (HGF, scatter factor), a physiological substrate of HGFA, is increased in the brain of AD patients and HGF levels in plasma are elevated in amyloid A amyloidosis and light-chain amyloidosis. Our data, now, show that fibronectin type I—amyloid interactions are important for these activities.
Isolated blood platelets become activated via their p38MAPK pathway and aggregate upon exposure to polypeptides with cross-β structure conformation.
Blood platelets become activated and aggregate upon exposure to proteins with cross-β structure conformation, express amyloid-like structures and show increased binding of amyloid dye Thioflavin T upon aging.
Incubation of freshly isolated platelets with various compounds that contain cross-β structure conformation results in activation of the p38MAPK pathway, as determined by analysis of p38MAPK phosphorylation. Incubation of platelets with amyloid haemoglobin-AGE results in platelet activation similar to the positive control native low density lipoprotein after 1 minute (
Recent insights have indicated that the formation of amyloid is not necessarily the result of a defect in the normal folding or clearance pathway, but that amyloid is also formed through normal biological proteolytic processing. We found that (i) activation of platelets induce amyloid at their cell surface and (ii) that platelets adhered to von Willebrand Factor (vWF) or collagen surface under flow express amyloid domains (FIGS. 21A,B). Expression is at the cell body and areas of spreading are negative (vWF surface) and at tips of aggregates (collagen) suggesting that adhered and aggregated platelets express areas of rich and poor in amyloid. Platelets stimulated with TRAP (an activator of the PAR-1 receptor without proteolytic properties and incapable of converting released fibrinogen into fibrin) and thrombin (an activator of PAR-1 and PAR-4 through proteolysis and an activator of fibrin formation) express arnyloid as visualized using the fluorescent amyloid dyes Congo Red and ThT in a FACS analysis (FIGS. 21C,D). Resting platelets do not express arnyloid at the cell surface (
To test whether arnyloid may influence platelet aggregation by classical stimuli, we tested whether arnyloid specific dyes and the amyloid binding protein tPA affect platelet aggregation. Indeed, using optical aggregometry we observed that Congo Red, ThT as well as tPA inhibited platelet aggregation. Dose response studies show up to 30% inhibition by 200 ,μM Congo red and upto 45% inhibition by 200 μM ThT (
Cross-β Structure is Thrombogenic
Based on our observations that compounds which comprise cross-β structure induces activation in platelets of the p38MAPK pathway and induces platelet aggregation, we conclude that the exposure of platelets to proteins with cross-β structure in the circulation has similar effects. Platelets stored under conditions recommended by the blood bank show increased binding of an amyloid dye. Therefore, aging platelets themselves may contain proteins that have adopted the activating cross-β structure conformation. Isolating only those cells in donor blood which display relatively minimal ThT binding is beneficial for the acceptor of the platelets.
Our pilot studies have demonstrated the presence of amyloid on activated and adhered platelets. For the development of effective anti-thrombogenic agents, knowledge on which protein or proteins are forming amyloid-like structures on platelets is required. In addition, knowledge on which pathways are involved in extracellular exposure upon platelet activation of putatively intracellularly stored amyloid-like conformation rich proteins, is beneficial for the development of treatment strategies that prevent amyloid exposure on platelets. With this knowledge pathway inhibitors are developed solely or in addition to blockers/scavengers of amyloid-like aggregates.
Relationship Between the Structure of β-glycoprotein I, the Key Antigen in Patients with Antiphospholipid Synsdrome, and Antigenicity.
The Anti-phospholipid Syndrome and Conformationally Altered β-glycoprotein I
The anti-phospholipid syndrome (APS) is an auto-immune disease characterized by the presence of anti-β2-glycoprotein I auto-antibodies (de Groot and Derksen, 2004; de Laat, Derksen et al., 2004a; de Laat, Derksen et al., 2004b). Two of the major clinical concerns of the APS are the propensity of auto-antibodies to induce thrombosis and the risk for fetal resorption (de Groot, Horbach et al., 1996; Connor and Hunt, 2003). Little is known about the onset of the auto-immune disease. Recent work has demonstrated the need for conformational alterations in the main antigen in APS, β-glycoprotein I (β2gpi), before the initially hidden epitope for auto-antibodies is exposed (Matsuura, Igarashi et al., 1994; de Laat, Derksen et al., 2004a; de Laat, Derksen et al., 2004b). Binding of native β2gpi to certain types of ELISA plates mimicks the exposure of the cryptic epitopes that are apparently present in APS patients. It has been demonstrated that anti-β2gpi auto-antibodies do not bind to globular β2gpi in solution, but only then when β2gpi has been immobilized to certain types of ELISA plates (Matsuura, Igarashi et al., 1994; de Laat, Derksen et al., 2004a; de Laat, Derksen et al., 2004b). Thus, the globular and native form of the protein is not the primary antigen in the autoimmune disease. Auto-antibodies seem to be elicited against a conformationally altered form of autologous β2gpi, which would fit in the “danger” model of immunology (Matzinger, 2002a; Matzinger, 2002b). This proposed mechanism could explain the observed risk for thrombosis in APS patients. Auto-antibodies prevent clearance of conformationally altered β2gpi with exposed amyloid cross-β structure epitopes. This induces activation of the contact system, platelet activation and tissue factor expression on endothelial cells.
Factor XII and tPA Bind to Recombinant β2gpi and to β2gpi Purified from Frozen-thawed Plasma, and not to β2gpi Purified from Fresh Plasma
Recombinant β2gpi and not β2gpi purified from fresh plasma, stimulates effectively the tPA-mediated conversion of plasminogen to plasmin, as measured as the conversion of the plasmin specific chromogenic substrate S-2251 (
Epitopes for Auto-antibodies are Specifically Exposed on Non-native Conformations of β2gpi Comprising Cross-β Structure
With our observations that support the idea that cross-β structure in part build up an epitope recognized by autoimmune antibodies, our studies are expanded to other diseases and complications in which auto-antibodies play a role. For example, haemophilia patients with anti-factor VIII auto-antibodies are screened for the presence of antibodies in their plasma that recognize the cross-β structure conformation. A more detailed analysis reveals whether putative cross-β structure binding antibodies specifically bind in part to cross-β structure in the antigen, or whether the antibodies bind to cross-β structure present in any unrelated protein.
The Artherogenic Form of Low Density Lipoproteins, Oxidized LDL, Exhibits Amyloid-like Structural Properties
Oxidation of Low Density Lipoprotein Particles Contributes to the Pathogenesis of Artherogenesis
Misfolding and aggregation of the apoB protein fraction of LDL upon oxidation, its resistance to proteolysis and its cytotoxicity are motifs commonly seen for amyloid-like protein aggregates (Ursini, Davies et al., 2002). Moreover, multiligand receptors with affinity for amyloid-like structures, i.e., CD36, RAGE, scavenger receptor A and scavenger receptor B-I, are also receptors for oxidized adducts of lipoproteins (Horiuchi, Sakamoto et al., 2003; Korporaal, Gorter et al., 2005). Therefore, it has been suggested that the role of amyloid-like apoB in oxidized LDL particles during atherosclerosis is similar to the pathogenic role of amyloid-like aggregates in protein misfolding diseases.
Oxidized LDL Displays Amyloid-like Features Pointing to the Presence of Cross-β Structure Conformation
Freshly isolated low density lipoprotein (LDL) was oxidized upon incubation with 25 μM CuSO4, for various incubation times. In time, the degree of oxidation was determined by reading the absorbance of diene structures at 234 nm, as well as the fluorescence upon incubation of oxidized LDL (oxLDL) with Congo red or Thioflavin T (FIGS. 23A,B). With a 24% oxidized oxLDL preparation, the ability to activate tPA in the chromogenic plasmin activation assay was determined and compared to native LDL. It was clearly seen that upon oxidation LDL gains tPA activating properties (
The Pathological Role of oxLDL During Atherosclerosis is Related to the Presence of Amyloid-like Cross-β Structure Conformation in the apoB Fraction
Previous data show that oxLDL plays an important role in the pathological events seen during atherosclerosis. The role of the interaction between oxLDL particles and multiligand receptor CD36 on the surface of blood platelets has been demonstrated (Takahashi, Fuda et al., 1998). CD36 is one of the known cellular receptors with broad range ligand specificity, including specificity for amyloid-like structures (Coraci, Husemann et al., 2002; Bamberger, Harris et al., 2003). Our data, now, add to our idea that the cross-β structure conformation in oxLDL, as well as in amyloid-β (Bamberger, Harris et al., 2003) and in glycated proteins(Ohgami, Nagai et al., 2001; Bouma, Kroon-Batenburg et al., 2003), is the true ligand binding site, that is important in mediating signals outside-in the platelets. Activation of platelets by oxLDL results in platelet aggregation, that contributes to the thromogenic conditions seen during atherosclerosis. Our observations that amyloid-like protein aggregates with cross-β structure conformation are also able to activate platelets and to induce platelet aggregation fit in the idea that protein aggregates comprising amyloid-like structures, including oxLDL, play a pivotal role in the pathological conditions that come with thrombogenesis. Moreover, our data show that oxLDL contributes to pathological conditions via two additional ways. First, the fibrinolytic cascade is activated by inducing tPA activation. Second, oxLDL activates the contact system of blood coagulation, by inducing factor XII activation. The ability of oxLDL to both activate tPA and factor XII, is similar to what is observed with many of our amyloid-like peptides and proteins with cross-β structure. Therefore, this ability of oxLDL points to the presence of cross-β structure in the apoB protein part of the oxidized LDL particles.
A Fibrin Clot Comprises Amyloid-like Cross-β Structure Conformation.
A Fibrin Clot Binds Amyloid-specific Dyes Congo Red, Thioflavin T and Thioflavin S.
Incubation of a preformed fibrin clot with the amyloid-specific dyes Congo red (CR), Thioflavin S (ThS) or Thioflavin T (ThT) results in specific binding of the dyes, as assayed with direct-light microscopy and fluorescence microscopy (FIGS. 24A,B). In addition, formation of a fibrin clot is delayed in the presence of the amyloid-specific dyes, as established both in aPTT's (FIGS. 24C-E) and in PT's (FIGS. 24F-H). These data indicate that a fibrin clot is composed of aggregates comprising the amyloid-specific cross-β structure conformation. Moreover, the data show that formation of a three-dimensional fibrin polymer network is dependent on cross-β structure formation, as introduction of amyloid binding dyes inhibit fibrin assembly into clots. Our previously disclosed observations (see above) showed that platelet activation and aggregation is induced by cross-β structure rich activators (
‡Two-weeks incubated albumin was from a different batch than four- and 23-weeks incubated albumin.
†Percentage of amino-acid residues in β-sheets are given.
‡The HbAlc concentration is given as a percentage of the total amount of Hb present in erythrocytes of diabetes mellitus patients and of healthy controls. The s.d. is 2.3% of the values given.
†Presence of fibres as determined with TEM.
| Number | Date | Country | Kind |
|---|---|---|---|
| EP02077797.5 | Jul 2002 | EP | regional |
This application is a continuation-in-part of U.S. patent application Ser. No. 11/033,105, filed Jan. 10, 2005, pending, which application is a continuation of PCT International Patent Application PCT/NL2003/000501, filed Jul. 8, 2003, designating the United States of America, corresponding to PCT International Publication WO 2004/004698 A3 (published in English on Jan. 15, 2004), which claims priority from European Patent Application EP02077797.5, filed Jul. 9, 2002, the contents of the entirety of all of which are incorporated by this reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/NL03/00501 | Jul 2003 | US |
| Child | 11033105 | Jan 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11033105 | Jan 2005 | US |
| Child | 11087102 | Mar 2005 | US |
