Patent Application
20240301030
The present invention relates to a vector comprising a polynucleotide, which encodes the FnIII cassette domains, the transmembrane domain and the cytoplasmic tail of the protein SORLA (Sortilin-related Receptor with A Type Repeats). The vector can be used for gene therapy in the treatment, prevention and/or alleviation of Alzheimer's Disease (AD).
The protein SORLA (Sortilin-related Receptor with A Type Repeats) is well known to be associated with Alzheimer's disease (AD). The protein is important for Amyloid Precursor Protein (APP) transport out of the endosomes where amyloidogenic processing of APP into pathogenic fragments (i.e. the Amyloid β-peptide (Aβ)) occurs. This SORLA-assisted transport of APP ensures a decreased cleavage of APP by the β-secretase, thereby reducing the production of the amyloid beta (Aβ) peptides. In AD, Aβ accumulates and forms damaging amyloid plaques within the brain. The ability of SORLA to engage in endosomal recycling is linked to a motif in its cytoplasmic tail (i.e. the FANSHY motif) that is important for interaction with the retromer complex (Fjorback et al. 2012) and which assists to traffics cargo out of endosomes.
The SORL1 gene that encodes SORLA is strongly associated with AD, and loss-of-function gene variants are considered causal for the development of AD (Scheltens et al. 2021). Further, SORLA is important for proper endosomal recycling. AD patients generally exhibit endosomal defects independently of the SORL1 gene status. However, due to the large size of the SORL1 gene, therapy approaches using SORLA are not feasible.
Instead, current pharmacological strategies aim to increase retromer function, in part by using small molecules that stabilize the retromer complex (Mecozzi et al. 2014). Increased retromer stability and thus activity has been demonstrated to decrease the amyloidogenic cleavage of APP, with a concomitant increase in the generation of the non-amyloidogenic product soluble APPα (sAPPα) (Mecozzi et al. 2014).
However, no feasible treatment for AD is available to date and AD remains to be an immense burden to patients and the health care system.
Due to its involvement in endosomal processes, increased expression of SORLA would be beneficial for AD patients, as well as for individuals at risk of developing AD. However, due to the large size of the SORL1 gene, any increased expression of the protein cannot be introduced by feasible gene therapy approaches available today, for example using an adeno-associated virus (AAV) vector with limited packaging capacity.
The inventors of the present invention have surprisingly discovered that a truncated version of SORLA can be used in gene therapy approaches to treat AD. Full-length SORLA is unsuitable for gene therapy approaches since the gene encoding full-length SORLA (SORL1) is too large to be inserted into suitable vectors for gene therapy. The inventors of the present invention have achieved to generate a SORLA mini-gene encoding a SORLA mini-receptor compatible with viral gene therapy. The length of the genetic sequence required for expression of said SORLA mini-receptor is small enough to be inserted into vectors suitable for gene therapy and may be referred to as a SORLA mini-gene. Most importantly, the SORLA mini-receptor at the same time retains functions beneficial for the treatment of AD, such as participation in endosomal recycling and the ability to decrease the amyloidogenic processing of APP.
The present invention discloses a mini-receptor of SORLA that comprises a cytoplasmic tail, a transmembrane domain and a part of the luminal region, namely the FNIII cassette domain of SORLA.
The inventors of the present invention have realized that the developed mini-receptor mimics the profile of an endosomal enhancer. In other words, SORLA may be regarded as an endosomal enhancer, and the inventors have realized that the herein disclosed mini-receptor may likewise be regarded as an endosomal enhancer. Most importantly, several advantages are associated with the mini-receptor compared to the full length receptor. Firstly, the mini-receptor does not decrease sAPPα, which is a beneficial property since sAPPα is a non-amyloidogenic product (see Example 2). Secondly, the nucleotide sequence for the mini-receptor (i.e. the mini-gene) is small enough to be packaged into a feasible vector for gene therapy, for example an AAV vector. Thirdly, it is speculated that the effect of retromer-enhancing compounds is through SORLA activity, and using a SORLA mini-receptor for gene therapy might therefore be more specific than broader application of retromer enhancing compounds. It might also be feasible to combine applications of both retromer and SORL1 gene therapies such as the herein disclosed SORLA mini-receptor, possibly in combination with other therapies such as small molecule therapies.
In one aspect, the present invention relates to a polynucleotide construct encoding upon expression a polypeptide P, wherein the polynucleotide comprises or consists of
In another aspect, the present invention relates to a polypeptide P, comprising or consisting of
In another aspect, the present invention relates to a vector comprising said polynucleotide construct and/or encoding said polypeptide P.
In a further aspect, the present invention relates to a cell comprising said construct and/or said polypeptide P and/or vector.
In a further aspect, the present invention relates to a composition comprising said construct, polypeptide P, vector and/or cell.
In a further aspect, the present invention relates to said construct, polypeptide P, vector, cell and/or composition for use in medicine.
In a further aspect, the present invention relates to said construct, polypeptide P, vector, cell and/or composition for use in treatment, prevention and/or alleviation of Alzheimer's Disease or a disease or disorder associated with Alzheimer's Disease.
In a further aspect, the present invention relates to a method of treating Alzheimer's Disease or a disease or disorder associated with Alzheimer's Disease, the method comprising administering to an individual in need thereof said construct, polypeptide P, vector, cell and/or composition.
In a further aspect, the present invention relates to the use of said construct, polypeptide P, vector, cell and/or composition for the manufacture of a medicament for the treatment, prevention and/or alleviation of Alzheimer's Disease, or a disease or disorder associated with Alzheimer's Disease.
In a further aspect, the present invention relates to the a method of increasing sAPPα in a cell, the method comprising introducing into a cell the polynucleotide construct of the invention, the vector of the invention, the polypeptide P of the invention and/or the composition of the invention, thus increasing sAPPα in said cell.
In a further aspect, the present invention relates to the a method of decreasing Aβ38, Aβ40, and/or Aβ42 in a cell, the method comprising introducing into a cell the polynucleotide construct of the invention, the vector of the invention, the polypeptide P of the invention and/or the composition of the invention,
thus decreasing Aβ38, Aβ40, and/or Aβ42 in said cell.
Schematic representation of full-length (SORLA-wt) expressed from SORL1-wt and the SorLA minireceptor (“3Fn mini-receptor” or SORLA-3Fn) expressed from SORL1-3Fn (“mini-gene”) showing domain architectures of both constructs (wt=wild-type). The minireceptor comprises or consists of a polypeptide Q1 comprising one or more than one or all FnIII domains of SORLA, a polypeptide Q2 comprising or consisting of a transmembrane domain of SORLA, and a polypeptide Q3 comprising or consisting of a cytoplasmic tail domain of SORLA, which together may be referred to as polypeptide P. Optionally, the mini-receptor may comprise a tag, for example a FLAG-tag.
Schematic representation of the vector construct.
(A) Secondary structure of a 3Fn domain; solution structure.
(B) Schematic structure of folding topology with conserved amino acids.
(C-E) Predicted secondary-structure-based alignment of the 6 3Fn domains of SORLA. Arrows (a-g) represent predicted β-strands and bold amino acids are conserved across the 3Fn domains. Only few amino acids are strictly conserved among different 3Fn domains indicating strong sequence variability. The alignment in panel (C) is continued in panel (D) and further in panel (E), together showing an alignment of the six 3Fn domains of SORLA.
The letters below conserved positions (letters in bold) correspond to p/P (=Pro), W (=Trp), Y (=Tyr), N(=Asn), T (=Thr), L (=Leu), and g (=Gly) at positions with a given amino acid conserved in 5-6 of the domains (capital letters used) or less often conserved (lower case letters used). The symbol ϕ is used to represent an amino acid with a hydrophobic side chain at the given position of the domain sequence (=L/Leu; V/Val; A/Ala; I/IIe; M/Met; F/Phe).
Representative Western Blot (WB) analysis of cell lysates (A) and conditioned medium (B) from N2a cells transfected with APP in the absence (APP+pcDNA) or in the presence of SORLA-wt (APP+SORLA-wt, transcribed from APP+SORL1-wt) or SORLA-3Fn (APP+SORLA-3Fn, transcribed from APP+SORL1-3Fn). Blots from SDS-PAGE separation of proteins from cell lysates were probed with an antibody against for SORLA (targeting the respective protein product of SORL1-WT including the SORL1-3Fn region; as such targeting both full-length SORLA and the mini-receptor), APP (recognized by an anti-myc antibody against the myc-tag on APP), and β-actin, whereas WBs for conditioned medium samples were probed with an antibody against sAPPα. Each condition was tested in duplicates in at least five independent experiments.
Note the substantial difference in how SORLA-wt and the mini-receptor effect the levels of sAPPα (B; *). The mini-receptor is superior to SORLA-wt in leading to cleaved APP, thus leading to increased sAPPα, and in not decreasing sAPPα. This is beneficial for the AD patient as sAPPα has been reported to be a trophic factor and as such to be important for neuronal survival.
Quantification of sAPPα production in cells transfected with SORL1-WT (leading to SORLA-wt expression), relating to the Western Blot in
Using mesoscale discovery (MSD) immunoassay, sAPPα (A) and sAPPβ (B) were quantified, further validating that sAPPα is reduced by the presence of wild-type SORLA (via transfection with SORL1-WT) but is not affected or instead rather increased by the presence of the mini-receptor SORLA-3Fn (via transfection with SORL1-3Fn) (A), compared to the sAPPβ level which was both reduced in the presence of wild-type SORLA (via transfection with SORL1-WT) and in the presence of the mini-receptor (via transfection with SORL1-3Fn).
Aβ40 ELISA assay on conditioned medium from five samples from three independent experiments. Both SORLA-wt (via transfection with SORL1-wt) and the mini-receptor SORLA-3Fn (via transfection with SORL1-3Fn) significantly decreased the level of Aβ40 compared to cells not transfected with any exogenous SORLA protein.
Aβ38 (A), Aβ40 (B), and Aβ42 (C) quantification of conditioned medium using Meso Scale Discovery (MSD) immunoassay. Aβ production of all three Aβ forms were significantly decreased in the presence of both SORLA-wt (via transfection with SORL1-wt) and the mini-receptor SORLA-3Fn (via transfection with SORL1-3Fn) compared to samples without exogenous SORLA (Blank).
A) Schematic representation of the core retromer units forming an arch that dimerizes by the VPS29 subunit at the top, and where two VPS26 subunits are also in close contact at the bottom.
B) Dimerizing SORLA mini-receptor stabilizes the retromer complex.
A) Western blot analysis of lysates from cells transfected with FLAG-mini-WT or FLAG-mini-FANSHY indicated similar expression levels of both variants (representative blots and bar graphs from quantifications of five independent experiments).
B) In contrast, Western blot analysis of lysates from cells transfected with FLAG-mini-WT or FLAG-mini-FANSHY showed that significantly more FLAG-mini-FANSHY is secreted into the medium (lanes 5 and 6) compared to FLAG-mini-WT (lanes 3 and 4) (representative blots and bar graphs from quantifications of five independent experiments). Empty vector without any mini-receptor construct (pcDNA) was included as a negative control.
C) Quantification of the Western Blot of B).
D-E) FACS analysis comparing the cell surface distribution of FLAG-mini-WT and FLAG-mini-FANSHY in transfected cells. For example, whereas the number of positive cells as defined reaching a predefined threshold of the antibody signal was 321 and 347 for two experiments for FLAG-mini-WT (upper panels in D and E, respectively), this number was increased to 592 and 509 for cells transfected with FLAG-mini-FANSHY (lower panels in D and E, respectively). Moreover, the signal was lower for cells expressing FLAG-mini-WT (Mean signals 4.635.522 and 4.736.355; upper panels in D and E respectively) in comparison to FLAG-mini-FANSHY (Mean signals 5.286.295 and 5.285.501; lower panels in D and E, respectively).
F) Immunocytochemistry detection of FLAG-mini-WT and FLAG-mini-FANSHY at the cell surface (stained in the absence of detergent/TritonX-100) of transfected cells. Clearly, there is a stronger accumulation of FLAG-mini-FANSHY at the cell surface compared to FLAG-mini-WT (arrows).
A) Schematic representations showing domain architectures of the SORLA-WT protein with all its natural domains (VPS10p, YWTD, CR domains, FnIII domains), variants of the 3Fn minireceptor with different tags (mini-myc and FLAG-mini, respectively) and the soluble 3Fn minireceptors used in Example 8.
Vps10p, Vacuolar Protein Sorting 10 Protein; YWTD, Tyrosine Tryptophan Threonine Aspartate; CR, complement-type repeats; 3Fn, Fibronectin-type-III domain; TM, transmembrane; 10CC, 10 conserved cysteines; EGF, Epidermal Growth Factor. B) Co-immunoprecipitation of lysates from HEK293 cells transiently transfected with the FLAG-tagged minireceptor and SORL1-WT using FLAG antibody. Proteins present in the eluates were analyzed by WB using a polyclonal SORL1 antibody (sol-SORLA).
C) Co-immunoprecipitation analysis of lysates from HEK293 cells transiently transfected with FLAG-tagged minireceptor and Myc-tagged minireceptor. Proteins were precipitated using a FLAG antibody and detected by WB using a myc antibody.
D) WB analysis of lysates and media from CHO cells transiently transfected with soluble 3Fn minireceptor (without the transmembrane or tail domain) treated with either 0 or 5% (+β-Mercaptoethanol) reducing agent. An anti-FLAG antibody is used for detection of the soluble 3Fn minireceptor constructs containing an N-terminal 3× FLAG-tag.
A) Schematics showing the principle behind the proximity ligation assay (PLA). When the two SORL1 constructs with a C-terminal FLAG-tag (SORL1-FLAG) or GFP-tag (SORL1-GFP) interact (i.e. dimerize) a red PLA signal develops in a number of steps.
B) Representative confocal microscopy images of HEK293 cells transiently co-transfected with SORL1-GFP (*) and SORL1-FLAG. Cells were immunostained for SorLA using FLAG antibody (arrow) and nuclear counterstained with DAPI (blue). Scale bars 5 μm. We tested whether the two different tags affected the localization of the tagged receptor forms using double transfected HEK293 cells and determination of their degree of co-localization. From this experiment we observed no indication that the tags lead to differences in cellular localization as they showed a strong overlap and Mander's coefficient of 0.71.
C-D) Next, we performed control experiments for the PLA setup but leaving out either the anti-FLAG (C) or anti-GFP (D) that in both settings abolished formation of the PLA signal.
E) Representative images from PLA analysis of the interaction between SORL1-GFP (*) and SORL1-FLAG in transiently transfected HEK293 cells. PLA signals are represented by dots (see arrows). Scale bars 5 μm. Quantification of colocalization between GFP (*) and PLA (arrows) signals using Mander's Correlation Coefficient. In the presence of both antibodies, we observed a strong PLA signal confirming that two full-length SORLA proteins can form a dimer within cells. However, when we determined the degree of co-localization between the PLA signal (representing SORLA dimers) and SORLA-GFP (representing both monomers and dimers), we noticed a clear lack of co-localization for several PLA signals and Mander's coefficient confirmed an overlap of only 0.35, suggesting that only a fraction of the cellular pool of SORLA protein exist as dimers.
F) Co-staining for the PLA signal representing dimers and the VPS35 subunit of the retromer core showed a high degree of co-localization with Mander's coefficient of 0.70, confirming that the majority of SORLA dimers are located together with retromer.
(A) Schematic depiction of SORL1 constructs containing C-terminal fusions of either the N-terminal (SORL1-V1) or C-terminal (SORL1-V2) fragment of the venus fluorescent protein. Upon interaction between the two SORL1 molecules the venus fragments get into close proximity enabling them to form a fluorescent beta-barrel structure
B) Retromer interacts specifically with SORL1 dimers. HEK293 cells were transfected with an empty vector SORL1-GFP, SORL1-V1, SORL1-V2, both SORL1-V1 and SORL1-V2 (expressing the various SORLA variants), or SORL1-WT, followed by immunoprecipitation with GFP-trap. Protein in the eluates were analyzed by WB using the indicated antibodies for detection of SORLA and VPS26B.
C) Representative immunofluorescence images of BiFC signals (*) from HEK293 cells transiently transfected with either SORL1-V1 (upper row), SORL1-V2 (middle row) or co-transfected with both SORL1-V1 and SORL1-V2 (lower row). The cells were counter-immunostained with a SORL1 antibody (arrow) and nuclei were stained with DAPI. Scale bars 5 μm.
D) Quantification of colocalization of venus signal with total SORL1 using Mander's Correlation Coefficient.
As used herein, the singular forms “a”, “an” and “the” include plural referents unless the context clearly states otherwise.
The term “some embodiments” can include one, or more than one embodiment.
The use of the word “a” or “an” when used throughout the text or in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” Thus, for example, reference to “mini-receptor” includes a plurality of such mini-receptors, such as one or more mini-receptors, at least one mini-receptor, or two or more mini-receptors.
The term “construct” as used herein refers to a polynucleotide construct, for example as described in the Examples below or in the claims. For example, this construct refers to the SORL1 mini-gene, encoding the SORLA mini-receptor.
The term “sorLA” as used herein is synonymous to the terms SORLA, Sortilin-related receptor, sortilin related receptor 1, Low-density lipoprotein receptor relative with 11 ligand-binding repeats, LDLR relative with 11 ligand-binding repeats, LR11, SorLA-1, Sorting protein-related receptor containing LDLR class A repeats and gp250. Human sorLA is annotated in UniProt under the accession number Q92673.
The term “wildtype” (WT) is generally understood as an unmodified protein or protein fragment compared to a protein or protein fragment where a modification has been introduced.
The term “wildtype” (WT) for example used in Examples 1 and 2 is understood to describe a naturally occurring protein, i.e. naturally occurring sorLA, and may be understood as full-length sorLA.
The term “wildtype” (WT) as used in some instances in Example 8 is understood to describe non-mutated variant of the minireceptor (FLAG-mini-WT=SORLA-3Fn mini-receptor) in comparison to a mutant variant of the mini-receptor with substitution of the FANSHY motif by Alanine residues (FLAG-mini-FANSHY).
The understanding of the term “wildtype” is further clarified in the respective Examples 1-8 below.
The protein encoded by SORL1 is called SORLA, also known as Sortilin-related receptor, sortilin related receptor 1, Low-density lipoprotein receptor relative with 11 ligand-binding repeats, LDLR relative with 11 ligand-binding repeats, LR11, SorLA-1,
Sorting protein-related receptor containing LDLR class A repeats, gp250. Human SORLA is, for example, annotated under the accession number Q92673 at the UniProt database (UniProtKB-Q92673, SORL_HUMAN). SORLA is a type-1 membrane protein that is, for example, expressed in neurons. SORLA is known to play roles in endocytosis and sorting.
The by SORL1 encoded protein SORLA comprises
Throughout this disclosure, the term 3Fn may also be expressed as FNIII or FN3 (Fn=fibronectin).
The terms homology, identity and similarity, with respect to a polynucleotide (or polypeptide), as defined herein are used interchangeably and refer to the percentage of nucleic acids (or amino acids) in the candidate sequence that are, homolog, identical or similar, respectively, to the residues of a corresponding native nucleic acids (or amino acids), after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent identity/similarity, and considering any conservative substitutions according to the NCIUB rules (hftp://www.chem.qmul.ac.uk/iubmb/misc/naseq.html; NC-IUB, Eur J Biochem (1985)) as part of the sequence identity. In particular, the percentage of similarity refers to the percentage of residues conserved with similar physiochemical properties. Neither 5′ or 3′ extensions nor insertions (for nucleic acids) or N′ or C′ extensions nor insertions (for polypeptides) result in a reduction of identity or similarity. Methods and computer programs for the alignments are well known in the art. Generally, a given similarity between two sequences implies that the identity between these sequences is at least equal to the similarity; for example, if two sequences are 80% similar to one another, they cannot be less than 80% identical to one another—but could be sharing 90% identity.
As defined herein the term “at least 70% homology, similarity or identity” means at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98% or at least 99% homology, similarity or identity throughout the present disclosure.
The terms “identity” and “homology” may be understood interchangeably herein.
The SORLA mini-receptor described herein comprises a cytoplasmic tail, a transmembrane region and a part of the luminal region, namely the FNIII cassette domain of SORLA.
As depicted in
Optionally, the mini-receptor may comprise a tag, for example a FLAG-tag.
The FNIII cassette, being in the luminal region and such interacting with other luminal proteins, is important for the functional properties of the SORLA mini-receptor. Thus, the SORLA mini-receptor may be referred to as the SORLA-3Fn mini-receptor (wherein 3FN is an abbreviation for FNIII cassette), as for example in Examples 1 to 6. The respective nucleotide sequence for expressing the SORLA mini-receptor may be referred to as SORL1-3Fn and may be referred to as the SORL1 mini-gene. Further, throughout the text and in relation to the present disclosure, SORLA mini-receptor may be referred to as mini-receptor only. In Examples 1 to 6, the denotation SORL1-WT or SorLA-wt refers to the full-length SORL1 nucleotide sequence or to the full-length SorLA protein. As such, the mini-receptor or mini-gene is compared to the full-length receptor or gene.
Alternatively, above described SORLA mini-receptor may, in the present disclosure, also be referred to as FLAG-mini-WT, as for example in Examples 7 to 8. In Examples 7 to 8, the established mini-receptor or mini-receptors (denoted FLAG-mini-WT) are compared to a mutated mini-receptor variant (denoted FLAG-mini-FANSHY), where mutations have been introduced to the FANSHY motif in the cytoplasmic tail.
In one aspect, the present invention relates to a polynucleotide construct encoding upon expression a polypeptide P, wherein the polynucleotide comprises or consists of
The person skilled in the art will appreciate that a number of nucleotides may be added upstream and/or downstream (at the 5′ end of the polynucleotide and/or at the 3′ end of the polynucleotide, respectively) of the first polynucleotide, the second polynucleotide and/or the third nucleotide. This may be done to optimize the construct, for example to optimize transcription and/or translation, packaging efficiency or properties of the encoded polynucleotide (i.e. polynucleotide P of the invention). As the polypeptide P of the invention comprises no more than 700 amino acids, the amount of additional nucleotides in the polynucleotide construct is limited to a total number of 2100 nucleotides.
In some embodiments of the present disclosure, the first polynucleotide, the second polynucleotide and/or the third polynucleotide comprise further nucleotides at the 3′ end and/or at the 5′ end, such as 1 further nucleotide, such as 2 further nucleotides, such as 3 further nucleotides, such as 4 further nucleotides, such as 5 further nucleotides, such as 6 further nucleotides, such as 7 further nucleotides, such as 8 further nucleotides, such as 9 further nucleotides, such as 10 further nucleotides, such as 11 further nucleotides, such as 12 further nucleotides, such as 13 further nucleotides, such as 14 further nucleotides, such as 15 further nucleotides, such as 16 further nucleotides, such as 17 further nucleotides, such as 18 further nucleotides, such as 19 further nucleotides, such as 20 further nucleotides, such as 21 further nucleotides, such as 22 further nucleotides, such as 23 further nucleotides, such as 24 further nucleotides, such as 25 further nucleotides, such as 26 further nucleotides, such as 27 further nucleotides, such as 28 further nucleotides, such as 29 further nucleotides, such as 30 further nucleotides, such as 31 further nucleotides, such as 32 further nucleotides, such as 33 further nucleotides.
The one or more further nucleotide may be any known type of nucleotide.
In some embodiments of the present invention the polynucleotide construct encodes upon expression a fusion protein comprising a first polypeptide Q1, a second polypeptide Q2 and a third polypeptide Q3.
In an alternative aspect, the present invention relates to a polynucleotide construct comprising
In some embodiments of the present disclosure, P comprises or consists of
In some embodiments of the present disclosure, P is no longer than 685 amino acids.
In some cases, it may be beneficial to express the mini-receptor construct of the invention comprising a tag. The person skilled in the art will be able to select the most appropriate tag, as well as the localization of the tag. A tag may be, for example, a FLAG tag (e.g. referred to as FLAG-mini in Examples 7 to 8) or a myc tag (e.g. referred to as mini-myc in Examples 7 to 8) or a GFP-tag or a venus fluorescent protein-tag (e.g. used in Example 8).
The tag may, for example, be localized N-terminal or C-terminal on the construct. In some instances, it may be beneficial to localize the tag on the N-terminal of the construct so as to leave the C-terminal unmodified and thus not potentially affecting any binding with other molecules binding to the C-terminal region of the construct, for example retromer binding to the cytoplasmic tail.
Usage of a tag may be beneficial in tracking the construct in-vitro or in-vivo to confirm the localisation of the construct. In other cases, for example in a clinical setting when transfection patient cells with the construct, e.g. Adeno-associated virus (AAV)-mediated, it may be beneficial to omit any tag with the aim of not introducing any non-essential protein parts that may potentially trigger an immunogenic response.
In some preferred embodiments of the disclosure, the mini-receptor does not comprise any tag.
In some embodiments of the present disclosure, P further comprises the amino acid sequence of SEQ ID NO: 21.
In some embodiments of the present disclosure, P comprises or consists of the amino acid sequences of SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17 and SEQ ID NO: 18.
In some embodiments of the present disclosure, P comprises or consists of the amino acid sequence of SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 21.
In some embodiments of the present disclosure, and in contrast to full-length SORLA protein, the construct does not contain the CR-cluster domain, the YWTD domain, the Vps10p domain and/or the propeptide.
In some embodiments of the present disclosure, and in contrast to full-length SORLA protein the construct does not contain the CR-cluster domain.
In some embodiments of the present disclosure, and in contrast to full-length SORLA protein, the construct does not contain the YWTD domain.
In some embodiments of the present disclosure, and in contrast to full-length SORLA protein, the construct does not contain the Vps10p domain.
In some embodiments of the present disclosure, and in contrast to full-length SORLA protein, the construct does not contain the propeptide.
In another aspect, the present invention relates to a polypeptide P, comprising or consisting of
In some embodiments of the present disclosure, the first polypeptide Q1, the second polypeptide Q2 and/or the third polypeptide Q3 comprise further amino acids, such as 1 further amino acid, such as 2 further amino acids, such as 3 further amino acids, such as 4 further amino acids, such as 5 further amino acids, such as 6 further amino acids, such as 7 further amino acids, such as 8 further amino acids, such as 9 further amino acids, such as 10 further amino acids, such as 11 further amino acids, such as 12 further amino acids, such as 13 further amino acids, such as 14 further amino acids, such as 15 further amino acids, such as 16 further amino acids, such as 17 further amino acids, such as 18 further amino acids, such as 19 further amino acids, such as 20 further amino acids, such as 21 further amino acids, such as 22 further amino acids, such as 23 further amino acids, such as 24 further amino acids, such as 25 further amino acids, such as 26 further amino acids, such as 27 further amino acids, such as 28 further amino acids, such as 29 further amino acids, such as 30 further amino acids, such as 31 further amino acids, such as 32 further amino acids, such as 33 further amino acids.
The one or more further amino acid may be any known type of amino acid.
In some embodiments of the present disclosure, the polypeptide P is a fusion protein of polypeptide Q1, Q2 and/or Q3.
In some embodiments of the present disclosure, there is a linker, comprising of further amino acids, between polypeptide Q1, polypeptide Q2 and polypeptide Q3.
In some embodiments of the present disclosure polypeptide P comprises or consists of
In some embodiments of the present disclosure, P is no longer than 685 amino acids.
In some embodiments of the present disclosure polypeptide P further comprises the amino acid sequence of SEQ ID NO: 21.
In some embodiments of the present disclosure polypeptide P comprises or consists of the amino acid sequences of SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17 and SEQ ID NO: 18.
In some embodiments of the present disclosure polypeptide P comprises or consists of the amino acid sequence of SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18 and SEQ ID NO: 21.
In another aspect, the present invention relates to a vector comprising said polynucleotide construct and/or encoding said polypeptide P.
In some embodiments of the present disclosure, the vector is selected from the group comprising of viral vectors, plasmids, cosmids and artificial chromosomes.
In some embodiments of the present disclosure, the vector is a plasmid vector.
In some embodiments of the present disclosure, the vector is a viral vector.
In some embodiments of the present disclosure, the vector has a packaging capacity from 1 to 40 kb, for example from 1 to 30 kb, such as from 1 to 20 kb, for example from 1 to 15 kb, such as from 1 to 10, for example from 1 to 8 kb, such as from 2 to 7 kb, for example from 3 to 6 kb, such as from 4 to 5 kb.
In some embodiments of the present disclosure, the viral vector is selected from the group consisting of adeno-associated vector (AAV), lentiviral vector, adenoviral vector and retroviral vector.
In some embodiments of the present disclosure, the viral vector is an adeno associated vector (AAV).
In some embodiments of the present disclosure, the viral vector is an AAV9 vector.
In some preferred embodiments of the present disclosure, the viral vector is an AAV9 vector.
In some embodiments of the present disclosure, the vector is an adeno-associated vector (AAV) with a packing capacity of 4.7 kb.
In some embodiments of the present disclosure, the vector is an adeno-associated vector (AAV) with a packing capacity of less than 5 kb.
The person skilled in the art will appreciate that Adeno-associated virus (AAV) vectors have limited packaging capacity. Over-packaging is for example detrimental to expression or limited success of expression, and can lead to reduction in both viral titers and in vivo transduction. While efforts are undertaken to optimize AAV vector packaging, the herein disclosed invention offers a solution to the problem by establishing a SORL1 mini-gene, which can be packaged into an AAV vector, instead of the full-length SORL1 gene which is over 6000 nucleotides long. AAV vectors are generally regarded to have a packaging capacity between around 4700 nucleotides to 5000 nucleotides. Additionally, the SORLA mini-receptor, transcribed from the SORL1 mini-gene, has further beneficial properties, as described in the herein enclosed examples below.
Human SORLA is annotated in UniProt under the accession number Q92673 as a protein of 2214 amino acids. This corresponds to a minimum of 6642 nucleotides to express/encode the protein. Further upstream or downstream sequences may be needed for expression. As such, full-length SORL1 is too large to be packaged into an AAV vector. The mini-gene solves this problem.
In an alternative aspect, the present invention relates to an AAV vector comprising said polynucleotide construct.
In a further alternative aspect, the present invention relates to an AAV9 vector comprising said polynucleotide construct.
In a further aspect, the present invention relates to a cell comprising said construct and/or said polypeptide P and/or vector.
In some embodiments of the present disclosure, the cell is selected from the group consisting of eukaryotic cells, preferably mammalian cells, more preferably primate cells, more preferably human cells.
In some embodiments of the present disclosure, the cell is a mammalian cell.
In some embodiments of the present disclosure, the cell is a neural cell.
In a further aspect, the present invention relates to a composition comprising said construct, polypeptide P, vector and/or cell.
In some embodiments of the present disclosure the composition is a pharmaceutical composition.
In some embodiments of the present disclosure the composition further comprises a pharmaceutically acceptable carrier.
In a further aspect, the present invention relates to said construct, polypeptide P, vector, cell and/or composition for use in medicine.
In a further aspect, the present invention relates to said construct, polypeptide P, vector, cell and/or composition for use in treatment, prevention and/or alleviation of Alzheimer's Disease or a disease or disorder associated with Alzheimer's Disease.
In some embodiments of the present disclosure, the Alzheimer's disease is of a type selected from the group consisting of Early-Onset Alzheimer's Disease, Late-Onset Alzheimer's Disease and Familial Alzheimer's Disease.
The person skilled in the art will appreciate that the present invention can be used in the treatment of individuals at risk for developing AD. For example, an individual at risk for developing AD may be an individual having a relative being diagnosed or recognised as having AD.
In an alternative aspect, the present invention relates to said construct, polypeptide, vector, cell and/or composition for use in treatment and/or prevention Alzheimer's Disease or a disease or disorder associated with Alzheimer's Disease in an individual at risk of developing Alzheimer's Disease.
The person skilled in the art will appreciate that the herein disclosed invention can be used to prevent AD and/or treat AD and/or alleviate symptoms of AD in AD patients. AD is a devastative disease affecting the brain on a structural level. It may therefore be beneficial to provide the SORL1 mini-gene (expressing the SORLA mini-receptor, e.g. via an AAV-vector), at an early stage, e.g. prior to the onset of symptoms, or at an early AD stage, or prior to substantive structural brain remodeling. For example, the herein described approach would be applicable to treat family members of AD patients prior to disease development.
In some embodiments of the present disclosure, said construct, vector, cell and/or composition are administered to an individual prior to the onset of AD symptoms.
In some embodiments of the present disclosure, said construct, vector, cell and/or composition is administered to an individual prior to the onset of AD symptoms.
In some embodiments of the present disclosure, said construct, vector, cell and/or composition is administered to an individual when a family member is diagnosed with AD.
Alternatively, the herein disclosed invention would be applicable to treat patients with early symptoms.
In some embodiments of the present disclosure, said construct, vector, cell and/or composition is administered to an individual with early AD symptoms.
Alternatively, the herein disclosed invention would be applicable to treat patients at various disease stages of AD.
In some embodiments of the present disclosure, said construct, vector, cell and/or composition is administered to an individual with a varying degree of AD symptoms.
Further, the herein disclosed invention would, due to its nature of restoring physiologic SORLA function, by applicable to treat patients at late stages of AD.
In some embodiments of the present disclosure, said construct, vector, cell and/or composition is administered to a patient at late stage of AD.
In some embodiments of the present disclosure, said construct, vector, cell and/or composition is administered to an individual when a relative of said individual is diagnosed with Alzheimer's disease.
In some embodiments of the present disclosure, said construct, vector, cell and/or composition is administered to an individual when it becomes known that a relative of said individual is suffering or has suffered from Alzheimer's disease.
It may, for example, become known that a relative of an individual is suffering from AD when said relative is diagnosed by a clinician. Alternatively, it may, for example become known that a relative of said individual is suffering or has suffered from Alzheimer's disease by obtaining information from other sources, such as family records or memories.
A relative of an individual may be understood as a family member of an individual.
A relative of an individual may be understood as a person sharing genetic material with said individual.
For example, a relative of an individual is a great-grandmother.
For example, a relative of an individual is a great-grandfather.
For example, a relative of an individual is a grandmother.
For example, a relative of an individual is a grandfather.
For example, a relative of an individual is a mother.
For example, a relative of an individual is a father.
For example, a relative of an individual is a sibling.
For example, a relative of an individual is a brother.
For example, a relative of an individual is a daughter.
For example, a relative of an individual is a son.
In some embodiments of the present disclosure, said construct, vector, cell and/or composition is administered to an individual once it is established that one or more family members of said individual suffer from Alzheimer's disease.
In some embodiments of the present disclosure said construct, vector, cell and/or composition is administered to an individual once it is established that one or more family members of said individual suffer from Alzheimer's disease.
The person skilled in the art will appreciate a potential genetic inherence of a risk to develop AD. The person skilled in the art will appreciate that administration of said construct, vector, cell and/or composition to an individual at risk for developing AD, e.g. having a risk when being a relative of a person diagnosed with AD, will offer, for example, the possibility of preventing AD prior to disease onset, or of reducing symptoms of AD.
In a further aspect, the present invention relates to a method of treating Alzheimer's Disease or a disease or disorder associated with Alzheimer's Disease, the method comprising administering to an individual in need thereof said construct, polypeptide P, vector, cell and/or composition.
In a further aspect, the present invention relates to the use of said construct, polypeptide P, vector, cell and/or composition for the manufacture of a medicament for the treatment, prevention and/or alleviation of Alzheimer's Disease, or a disease or disorder associated with Alzheimer's Disease.
In a further aspect, the present invention relates to the a method of increasing sAPPα in a cell, the method comprising introducing into a cell the polynucleotide construct of the invention, the vector of the invention, the polypeptide P of the invention and/or the composition of the invention, thus increasing sAPPα in said cell.
In a further aspect, the present invention relates to the a method of decreasing Aβ38, Aβ40, and/or Aβ42 in a cell, the method comprising introducing into a cell the polynucleotide construct of the invention, the vector of the invention, the polypeptide P of the invention and/or the composition of the invention, thus decreasing Aβ38, Aβ40, and/or Aβ42 in said cell.
The person skilled in the art will be able to select the available option for introducing the polynucleotide construct of the invention, the vector of the invention, the polypeptide P of the invention and/or the composition of the invention into a cell. For example, viral transfection may be used.
In some embodiments of the invention, said cell is a neuronal cell.
In some embodiments of the invention, said methods are in-vivo methods.
In some embodiments of the invention, said methods are in-vitro methods.
This example illustrates the generation of the SORLA-3Fn mini-receptor.
The mini-receptor construct was generated by a single PCR reaction (Herculase II Fusion) followed by restriction enzyme digestion and subsequent ligation. The primer pair (Fwd: 5′-CAGGATCCGACTACAAGGACCACGACGGCGACTACAAGGACCACGACATCGACT ACAAGGACGACGACGACAAGGAGTTGACTGTGTACAAAGTACAG-3′ and rev: 5′-GTGAATTCTCAGGCTATCACCATGG-3′) was used to amplify a human SORL1 fragment downstream of Glu1552 to the stop codon. Thus, the final amplicon encompassed a 5′ BamHI and a 3′ EcoRI restriction site flanking sequences for the FLAG-tag (3×), the 3Fn cassette (of six Fibronectin type III (FNIII or FN3) repeats, the transmembrane region and the cytoplasmic tail. Lastly, the mini-receptor PCR product was cloned into a Psectag2B expression vector (Invitrogen) between the BamHI and EcoRI restriction sites to be in frame with the murine lg κ-chain V-J2-C signal peptide. The expression product of the amplicon (the SORLA mini-receptor) is illustrated in
Next, N2a cells were transfected with the vector encoding the mini-receptor to verify correct expression of the construct. Lysates from the transfected N2a cells were then harvested and proteins were analyzed by WB using antibodies recognizing the SORLA ectodomain (extracellular domain; targeting the respective protein product of SORL1-WT or SORL1-3Fn) and β-actin (
Additionally, the domain boundaries of the individual SORLA 3Fn modules were determined in-silico using several softwares (PsiPred, SSpro Scratch and Yaspin) to predict secondary structures. Subsequently, an alignment of the six 3Fn domains was generated based upon their highly conserved secondary structures and few conserved amino acids (
Note that during the herein described example, the mini-receptor has been constructed comprising a FLAG-tag, for example to be able to in a convenient way to trace the mini-receptor during the initial establishment and proof-of-concept phase. The person skilled in the art will be able to use the methodology described herein to establish a mini-receptor without any tag (or with an alternative tag) for use in a setting where a tag would not be needed or wanted, e.g. when using the mini-receptor in a therapeutical setting, e.g. when being expressed via a viral vector in patient cells.
This cloning experiment demonstrates the successful generation of a SORL1 mini-gene and expression of a SORLA mini-receptor consisting of a FLAG-tag (3×), six 3Fn modules, a transmembrane domain and the cytoplasmic tail. A schematic overview of the produced mini-receptor, in comparison with SORLA-wt (transcribed from SORL1-WT), is depicted in
In summary, we demonstrated for the first time the successful production and expression of a SORLA-3Fn mini-receptor encompassing the 3Fn-cassette, the transmembrane region and the cytoplasmic tail. This mini-receptor is used in the following examples to functionally characterize the invention.
This example aimed to investigate how the SORLA mini-receptor affects key proteins and pathways involved in Alzheimer's disease. We have previously shown how the full-length SORLA protein decreases APP trafficking in the secretory pathway and increases APP recycling out of the endosome resulting in a decrease of both sAPPα and sAPPb/Ab-peptide products (Andersen et al. 2005). However, as the mini-receptor does not harbor the CR-domains required for the direct binding of the APP protein (Mehmedbasic et al. 2015), nor the VPS10p-domain suggested to bind the amyloid-β (Aβ) peptide (Kitago et al. 2015), it is not known whether the remaining part of SORLA that constitute the mini-receptor also has an impact on APP biology.
To address this, we transfected Murine neuroblastoma-2a cells (N2a) cells with either a construct for human APP-myc for expression of the human APP protein (together with a pcDNA plasmid without insert) or co-transfected cells with APP-myc together with plasmids encoding SORLA-wt or SORLA-3Fn (SORLA mini-receptor, as described in Example 1, or also referred to as FLAG-mini in Example 8) and analyzed APP proteolysis using a western blot approach and quantification of specific APP metabolites by mesoscale discovery (MSD) assays specific for human-sequence APP fragments (
As previously shown (Andersen et al. 2005), SORLA-wt (transcribed from SORL1-WT) inhibits cleavage of APP into sAPPα (lanes 5 and 6) leading to a strong reduction of the signal for sAPPα in conditioned medium from SORLA-wt transfected cells (
However, cells transfected with SORLA-3Fn (transcribed from SORL1-3Fn) did not show any obvious reduction of sAPPα levels in conditioned medium (lanes 7 and 8) based on inspection of the Western Blots (Wb) (
Consequently, there is a substantial difference in how SORLA-wt and the mini-receptor effect the levels of sAPPα. The mini-receptor is superior to SORLA-wt in leading to cleaved APP—leading to increased sAPPα, and in not decreasing sAPPα. This is beneficial for the AD patient.
These results were further confirmed by quantification of band intensities from all five Wb membranes, showing that no decrease of sAPPα could be detected in cells transfected with mini-receptor. The level of sAPPα was even higher than for control cells (
This finding was validated by measuring sAPPα with the more quantitative MSD analysis (
Accordingly, besides the size of the mini-receptor construct enabling viral delivery (i.e. gene therapy), the specific decrease of the amyloidogenic processing is an advantage as the non-amyloidogenic sAPPα fragment is considered to have neurotrophic/beneficial effects.
We therefore next determined the level of Aβ40 in the medium from the transfected N2a cells using a standard ELISA protocol (five samples selected from three independent experiments). As shown previously (Andersen et al. 2005), the level of Aβ40 is strongly reduced in the presence of SORLA-wt (
This finding was substantiated by MSD quantification of the three Amyloid β-peptide species Aβ38, Aβ40, and Aβ42 where we found a significant decrease of all three Aβ forms in the presence of SORLA-3Fn compared to control cells, to a similar low level as seen for cells transfected with SORLA-wt (
In summary, in line with previous findings, the presence of SORLA-wt decreased both non-amyloidogenic and amyloidogenic processing, as evidenced by significantly reduced levels of sAPPα, sAPPb, and Ab-peptides of 38, 40, and 42 amino acids in length (
Whereas SORLA-wt decreases both the amyloidogenic and the non-amyloidogenic processing of APP, the mini-receptor SORLA-3Fn has no effect on the non-amyloidogenic processing (as sAPPα is not altered). However, the mini-receptor can specifically decrease the level of the amyloidogenic products (sAPPβ and Aβ). This profile is similar to the situation observed for cells treated with retromer enhancing drugs (Mecozzi et al. 2014) since retromer function is related to trafficking cargo (i.e. APP) out of the endosome which is the main cellular site for the amyloidogenic processing (Haass 2012). As the mini-receptor shares the same cytoplasmic domain as SORLA-wt, the mini-receptor is likely to also engage in retromer-dependent endosomal recycling similar to SORLA-wt (Fjorback et al. 2012). The SORLA-dependent reduction in non-amyloidogenic processing of APP into sAPPα relies on SORLA-wt (containing the CR-cluster) activity in the secretory pathway (Mehmedbasic et al. 2015). Taken together this provides a model that suggest independent roles of SORLA in these two processing pathways. This is the optimal profile for a drug as sAPPα is speculated to have a neurotrophic/beneficial function, and thus pharmacological interventions would optimally be designed not to affect the generation of this APP fragment.
It is a surprise and unexpected benefit that the minireceptor SORLA-3Fn is able to decrease the amyloidogenic processing of APP (via decrease of sAPPβ) as a previous study showed how SORLA deleted of its 11 CR-domains, but with an intact 3Fn-region, did not interact with APP nor its processing (Mehmedbasic et al. 2015). The herein presented data supports a promising therapeutic effect of delivering the minireceptor to the brain of AD patients.
We speculate that the mini-receptor forms a complex with APP and BACE1 as previously described for SORLA-wt (Spoelgen et al. 2006), where we also found that the cytoplasmic domain of SORLA was able to decrease formation of this ternary complex.
We will provide proof-of-concept that some mutations in the FANSHY sequence can increase complex-formation with retromer, and that such mutated constructs have improved ability to undergo endosomal trafficking and to further decrease APP amyloidogenic processing.
We will use a panel of peptides comprising the FANSHY motif. The peptides will either carry the wildtype FANSHY sequence, or substitution(s) of single amino acid(s) that, based on in silico analysis, are predicted to increase affinity for retromer.
Such peptides will be tested for interaction with retromer using isothermal titration calorimetry.
Mutations that lead to increased retromer binding of peptides will be introduced in constructs for SORLA-3Fn for subsequent testing of effects on APP processing in cultured (N2a) cells and/or primary murine neuronal cultures.
We expect to identify a variant or several variants of the mini-receptor that bind(s) stronger to retromer, and that decreases APP amyloidogenic processing even more than the mini-receptor without the above described modifications (i.e. substitutions).
2nd generation mini-receptor(s) will have improved translational value as they increase endosomal recycling even more and show an even stronger reduction in Aβ levels as compared to the mini-receptor without the above described modifications (i.e. substitutions).
Providing evidence that viral delivery of the mini-receptor reduces amyloidogenic processing in neuronal cultures as it does in cultured cell lines.
First we will prepare a AAV9-based viral vector with the SORLA-3Fn insert (with or without any tag). Next, we will isolate primary cortical (or hippocampal) neurons from wild-type mice, and compare APP processing in infected versus non-infected neurons using Western blotting and mesoscale discovery assays for the endogenous mouse APP fragments.
We expect to find decreased Aβ secretion of infected neurons compared to non-infected neurons, but similar levels of sAPPα. The successful delivery of SORLA-3Fn to primary neurons will be shown by Western blot of cell lysates using an antibody for the SORLA extracellular domain.
We expect to show that the mini-receptor can be used to decrease Aβ levels in primary neurons.
To demonstrate that the SORLA mini-receptor can reduce the enlarged endosomes observed in SORL1 deficient neuronal cultures similar to previous findings relating to retromer-enhancing compounds (Jessica Young, unpublished).
We will investigate, using iPSC-derived neurons with SORL1 knockout (as published by Knupp et al, 2020), if mini-receptor treatment will rescue endosome enlargement. If so, we would next apply similar “rescue-experiments” to iPSC-derived neurons carrying disease alleles for APP and/or PSEN1 that also show increased (i.e. pathogenic) endosome size (Kwart et al. 2019).
The iPSC line with targeted deletion of SORL1 has been instablished (Knupp et al. 2020) (8). We will determine endosome size using Rab5 immunocytochemistry in SORL1-deficient neurons that has been infected with SORLA-3Fn mini-receptor, and compare to non-infected neurons. Subsequently, iPSC-derived neurons with other AD-related mutations will be infected with the SORLA-3Fn mini-receptor.
We expect to find that SORLA-3Fn reduces the size of endosomes of SORL1-deficient iPSC-derived neurons to a similar size of wildtype iPSC-derived neurons (i.e. rescue). In iPSC-derived neurons with causal variants in the genes of APP or PSEN1, infection with SORLA-3Fn similarly restores normal endosome size.
We expect to find that delivery of the gene for the SORLA mini-receptor can reduce pathologically enlarged endosomes in neurons that are genetically similar to causal variants, i.e. deficient of SORL1 or with mutations in APP and PSEN1.
Further development of the mini-receptor.
Structures elucidated by cryoEM of the retromer complex assembled at endosomal tubule membranes have identified a coat of retromer at the cytosolic site, where two core retromer units form an arch that dimerizes by the VPS29 subunit at the top, and where two VPS26 subunits are also in close contact at the bottom (
Methods to increase dimerization of the mini-receptor will be tested for the ability to increase its protective activity against AD. In one setting, aimed for gene therapy with the mini-receptor, a mini-receptor version with engineered mutations that increase the strength of the dimer will established. This version will be superior in activity compared to the non-engineered mini-receptor. Such mutations may be identified based on the structure of the mini-receptor dimer complex.
Compounds (small molecule chaperones or antibodies) that enter the endosomal lumen by endocytic uptake, and that can increase the SORLA 3Fn-dimer interaction, may further increase the strength of the mini-receptor dimer. This will be tested.
We will further optimize the mini-receptor.
Different versions of the mini-receptor will be established, with different fine-tuned properties.
To demonstrate that the FANSHY-motif in the SORLA cytoplasmic tail, previously shown to be involved in binding to Retromer, is also important for the intracellular trafficking of the SORLA minireceptor.
A construct for FLAG-mini-WT (as referred to as SORLA-3Fn mini-receptor in Examples 1 and 2, comprising an N-terminal FLAG tag, WT=wildtype indicating the non-mutated variant of the minireceptor in Example 7) was used as template for site-directed mutagenesis to generate a mutant construct (FLAG-mini-FANSHY) with the six amino acid FANSHY-motif being substituted by alanine residues, using standard methods and primers.
N2a cells were transfected with the two constructs using FuGene and, following standard protocols, lysates and medium were collected 48 hours after transfection and analysed by SDS-PAGE and Western blot (Wb) experiments using a polyclonal antibody that recognizes the extracellular fragment of full-length SORLA, and which is therefore also able to bind the extracellular part of the mini-receptors (
FACS analysis of transfected cells were conducted using standard protocols and the same primary polyclonal SORLA antibody as for Western blot analysis was used for cell staining, as well as a fluorescently labelled secondary anti-rabbit antibody coupled to fluorochrome 488 (
Immunocytochemical detection of cell surface expression of transfected cells was also performed using the polyclonal anti-SORLA antibody. Detergent has been left out of all solutions for incubation and washing to avoid penetration of antibodies across the cell membrane. Therefore, the antibody is expected to only bind receptor molecules located at the cell surface (
We generated a mutant mini-receptor, FLAG-mini-FANSHY, that is unable to bind Retromer as the FANSHY-motif has been replaced by alanine residues as previously described (Fjorback, 2012). We used lysates and conditioned medium from cells transfected with either FLAG-mini-WT (mini-receptor without any mutations in the tail region, equivalent to SORLA-3Fn mini-receptor referred to in Examples 1 and 2) or FLAG-mini-FANSHY (mini-receptor with mutations in the tail region) to determine how shedding from the cell surface was affected by lack of Retromer binding. Whereas we did not observe any difference on the cellular expression between the two mini-receptor variants (
In order to obtain support for a change in cellular distribution, we applied Fluorescence-activated cell sorting (FACS) analysis to determine the expression at the cell surface of FLAG-mini-WT and FLAG-mini-FANSHY. Using this method we analyzed the cell surface expression for two samples of transfected cells and found more cells with the mutant construct at the cell surface (WT: 321/347 vs FANSHY: 592/509) as well as much stronger signal (WT: 4.63E6/4.73E6 vs FANSHY: 5.29E6/5.29E6) for the mutated mini-receptor (
To visualize the stronger expression of FLAG-mini-FANSHY at the cell surface in comparison to FLAG-mini-WT, we also performed immunocytochemical analysis of transfected cells and determined cell surface localization by acquiring confocal microscopy pictures of cells stained with primary antibody for SORLA in the absence of a detergent allowing to identify only mini-receptor at the cell surface. Representative pictures show how the cell surface signal for the mutated variant FLAG-mini-FANSHY is stronger than for the non-mutated variant FLAG-mini-WT (
We have provided evidence that deletion of the Retromer binding site of the FLAG-mini-receptor decreases the intracellular localization of the construct, and increases its expression at the cell surface. This further confirms the ability of a mini-receptor construct (e.g. as described in Examples 1 and 2) to interact with retromer and to perform important functions needed to ensure physiological endosomal processing. As such the mini-receptor is expected to be functional and is expected to be beneficial in a therapeutic setting, e.g. via viral transfer to Alzheimer's Disease patients.
To further investigate SorLA as well as SorLA mini-receptor binding and dimerization capabilities.
The domain boundaries of the SORL1 3Fn cassette was determined in-silico using several online softwares (PsiPred, SSpro, Scratch and Yaspin) to predict secondary structures in the amino acid sequence. Subsequently, an alignment of the six SORL1 3Fn domains was generated based on their highly conserved pattern of secondary structures and few conserved amino acids.
The FLAG 3Fn minireceptor was generated by a single-step PCR reaction (Herculase=Fusion) using the primer pair (fwd: 5′-CAGGATCCGACTACAAGGACCACGACGGCGACTACAAGGACCACGACATCGACT ACAAGGACGACGACGACAAGGAGTTGACTGTGTACAAAGTACAG-3′ and rev: 5′-GTGAATTCTCAGGCTATCACCATGG-3′) amplifying a human SORL1 fragment downstream of Glu1552 (predicted beginning of 3Fn cassette) to the stop codon. Additionally, the forward primer adds a sequence encoding a 3×FLAG tag to the 5′ end of the amplicon. The PCR product was cloned into a Psectag2B expression vector (Invitrogen) using BamHI and EcoRI restriction enzymes utilizing the murine lg κ-chain V-J2-C signal peptide to drive expression.
The myc 3Fn minireceptor was produced similarly by using the primer pair (fwd: 5′-CAGGATCCGAGTTGACTGTGTACAAAGTAC-3′ and rev: 5′-GTGAATTCTCACAGATCCTCTTCTGAGATGAGTTTTTGTTCGGCTATCACCATGGG-3′) adding a myc-tag to the C-terminal.
The soluble 3Fn minireceptor with a FLAG-tag was generated by site-directed mutagenesis introducing a stop codon in the predicted C-terminal of the 3Fn cassette. Primers were designed following instructions from the manufacturer (fwd: 5′-CCTGCTGTACGATGAGTGAGGGTCTGGTGCAGATGC-3′, rev: 5′-GCATCTGCACCAGACCCTCACTCATCGTACAGCAGG-3′). Site-directed mutagenesis was performed on human cDNA (3Fn minireceptor) within the psectag2B vector using the Quickchange XL site-directed mutagenesis kit (Agilent).
HEK293, N2a and Hela cells were cultured in Dulbecco's Modified Eagles Medium (DMEM, Lonza) supplemented with 10% fetal bovine serum (FBS) and 5% penicillin/streptomycin (P/S) in a humidified 5% CO2 incubator at 37° C.
CHO cells were grown in Hyclone (Sigma) medium supplemented with 10% FBS and 5% P/S in a humidified 5% CO2 incubator at 37° C.
Transient transfections of cells with different SORL1 and minireceptor constructs were performed using Fugene 6 Transfection Reagent kit (Promega) and either 1 μg or 3 μg of DNA templates.
Approximately 5×105 N2a cells were seeded per well in a 6-well plate and grown for 24 hrs. Cells were then transiently co-transfected with plasmids encoding APP-myc together with either SORL1-WT, 3Fn minireceptor or an empty pcDNA3.1 vector. The medium was changed to serum-free medium (SFM) after 48 hrs and incubated for another 48 hrs before harvesting cell lysates and conditioned medium.
Cell supernatant was collected, and cell pellets were lysed on ice for 1 h in lysis buffer (1M Tris HCl pH 8.1, 0.5M EDTA, 1% Triton-X-100, 1% NP40) supplemented with Complete™ protease inhibitor (Roche). Total protein content in the lysates was measured using the BCA assay kit (Sigma).
Lysate and media samples were mixed with SDS and 5% β-mercaptoethanol (unless otherwise noted) followed by heating at 95° C. for 5 min. Proteins were separated by SDS-PAGE gel electrophoresis using precast 4-12% Bis-Tris gradient gels (Invitrogen) and transferred onto a nitrocellulose membrane (Amersham). The membranes were blocked for 1 h at RT in blocking buffer (Tris-Base 0.25M, NaCl 2.5M, skimmed milk 2%, tween-20 2%) followed by incubation in primary antibodies O.N. at 4° C. Membranes were incubated in HRP-conjugated secondary antibodies (1:1500) for 1 h at RT and finally the proteins were detected using SuperSignal West Femto Maximum Sensitivity Substrate (Thermofisher) on a Las-4000 Image Reader (Fujifilm).
Antibodies: anti-FLAG (M2, Sigma), anti-sAPPα (WO2) (MABN10, Merck), anti-myc (R951-25, Invitrogen), anti-LR11 (BD Transduction Laboratories), anti-SORLA generated to recognize the entire extracellular part of the SORLA proteins (5387, in house, Aarhus University), anti-VPS26b, anti-APP and anti-β-actin (A5441, Sigma).
The level of shed sAPPα and sAPPβ in supernatant from transfected N2a cells was measured using the sAPPα/sAPPβ duplex assay kit (Mesoscale Discovery).
A serial dilution of the sAPPα and sAPPβ calibrators was prepared following instructions from the manufacturer. The precoated 4-spot plate was incubated at RT in 3% blocker A solution for 1 h with shaking followed by 3 times washing in Tris wash buffer. Calibrators and undiluted cell supernatants (25 μl) were added to the plate and incubated for 1 h at RT with shaking and subsequently the plate was washed 3 times. Finally, the wells were incubated in 1× Read Buffer T for 10 min at RT followed by detection of electrochemilumiscent signals from the samples using a SECTOR® Imager (Mesoscale Discovery). Concentrations of sAPPα and sAPPβ were calculated on Microsoft excel by fitting to a standard curve generated from the calibrators.
Secreted Aβ38, Aβ40 and Aβ42 in cell supernatants from transfected N2a cells were quantified by the Aβ panel 1 V-plex assay kit (Mesoscale Discovery).
Aβ38, Aβ40 and Aβ42 calibrators were mixed and diluted in a 4-fold serial dilution as instructed from the manufacturer. Precoated wells of the multi-spot plate were blocked at RT in Diluent 35 for 1 h at RT and washed 3 times in 1×PBS+0.05% Tween-20. Detection antibody and calibrators/undiluted cell supernatants were added simultaneously to the plate and incubated for 2 hrs at RT with shaking. Lastly, the wells were washed 3 times and 2× Read Buffer T was added for immediate analysis of electrochemiluminescent signals on a SECTOR® Imager. Concentrations of Aβ38, Aβ40 and Aβ42 were calculated by Microsoft excel by fitting the samples to a standard curve.
HEK293 cells were transiently transfected followed by 48 hrs of incubation before harvesting cell lysates. Gammabind G sepharose beads/dynabeads were coated with 2.5 μg of anti-FLAG antibody (F1804, Sigma) for 2 hrs with end-over-end rotation at RT. Beads were washed 3 times and incubated in 70 μg of total protein from transfected HEK293 cells O.N. at 4° C. with end-over-end rotation. Next, beads were washed 5 times and bound proteins were eluted from the beads using SDS sample buffer supplemented with 5% β-mercaptoethanol. All washing steps were performed in PBS+0, 05% tween-20.
Approximately 5×104 HEK293 cells were seeded on glass coverslips coated with poly-L-lysine 0.1% (Sigma) followed by 24 hrs of incubation before transfection. Cells were transfected with SORL1-FLAG and SORL1-GFP using Fugene (Promega) transfection reagent. After another 24 hrs cells were fixed in 4% PFA for 10 min at RT with subsequent washing in PBS. Coverslips were washed in PBS with 0.1% triton-x-100 and blocked in PBS supplemented with 10% FBS for 30 min at RT. After blocking, the cells were incubated O.N. at 4° C. with primary antibodies against the FLAG-tag (F1804 Sigma, 1:1000) and the GFP-tag (ab6556 Abcam, 1:2000). Next, cells were washed in PBS with 0.1% triton-x-100 and incubated in Alexa fluor secondary antibodies (Invitrogen, 1:500) for 1 hr at RT. Cells were then washed in PBS and nuclei were counterstained with Hoechst (Abcam, 1:50000) for 10 min at RT. Lastly, the coverslips were mounted on glass slides with DAKO fluorescence mounting medium (Agilent), and after drying stained cells were imaged using a Zeiss LSM780 confocal microscope.
Approximately 5×104 HEK293 cells were seeded on glass coverslips coated with poly-L-lysine 0.1% and grown for 24 hrs before transfection using Fugene (Promega). Cells were transfected with 500 ng of either SORL1-V1, SORL1-V2, SORL1-GFP or both SORL1-V1 and SORL1-V2. Transfected cells were incubated for another 24 hrs and fixed with 4% PFA for 10 min followed by washing in PBS. Counter-staining with SORLA antibody (sol-SORLA, 5367) diluted 1:100 and DAPI was performed as described for ICC above. The coverslips were mounted on glass slides using DAKO mounting medium (Agilent) and cells were visualized on a Zeiss LSM780 confocal microscope.
HEK293 cells were seeded on 0.1% poly-L-lysine coated glass coverslips and incubated for 24 hours before transfection using Fugene (Promega). The cells were co-transfected with 500 ng plasmids encoding either SORL1-FLAG or SORL1-GFP and incubated for 24 hours. The transfected cells were fixed in 4% PFA for 10 min and washed in PBS followed by incubation in primary antibodies. Cells were incubated overnight at 4° C. in either an anti-FLAG antibody (F1804 M2, Sigma) or an anti-GFP antibody (ab5665 rabbit, Abcam) or both diluted 1:1000 and 1:2000 respectively. The cells were then washed in PBS with 0.1% triton-x-100 and incubated in PLA probes (Sigma) for 1 hr at 37° C. Next, cells were washed in Wash buffer A and incubated in ligase (Sigma) for 30 min at 37° C. The coverslips were then washed in buffer A followed by incubation in polymerase (Sigma) for 100 min at 37° C. Subsequently, the cells were first washed in wash buffer B followed by washing in 0.01×wash buffer B for 1 min. Finally, coverslips were mounted on glass slides with Duolink® In Situ Mounting Medium with DAPI (Sigma) and imaged by confocal microscopy (LSM780, Zeiss).
SORL1 dimers formed by the interaction between C-terminal venus fragments (and SORL1-GFP as control) were immunoprecipitated using GFP-Trap Magnetic Particles (M-270, Chromotek) following the manufacturer's instructions. 500 ng of total lysate from transfected HEK293/Hela cells was incubated with 25 μl of magnetic bead slurry for 1 hr at 4° C. with end-over-end rotation. Subsequently, beads were washed 5 times in wash buffer (10 mM Tris/HCl PH 7.5, 150 mM NaCl, 0.05% Nonidet-P40, 0.5 mM EDTA) and eluated using SDS sample buffer.
To further delineate the dimer capacity of SORLA, we generated two SORLA minireceptor constructs comprising the six 3Fn-domains, the transmembrane region and the cytoplasmic tail with either an N-terminal FLAG tag (as also described in Examples 1 and 2) or with a C-terminal myc-tag (in Example 8 referred to as FLAG-mini and mini-myc, respectively;
First, we tested the ability of the two membrane-bound minireceptors to form a complex using co-immunoprecipitation analysis of cells transfected with FLAG-mini and mini-myc. We could clearly precipitate mini-myc using an anti-FLAG antibody, when both minireceptors were co-expressed, while cells that were only transfected with mini-myc but not expressing FLAG-mini showed no precipitation of mini-myc (
In a second set of experiments when testing the expression of the s3Fn1-6 construct, we observed a clear signal corresponding to a dimer in WB analysis after normal SDS-PAGE separation of proteins from both lysates and medium from cells transfected with the soluble, six-domain SORLA fragment (
Finally, we also tested whether the minireceptor could interact with the full-length form of SORLA, forming heterodimers. We co-transfected HEK293 cells with FLAG-mini and full-length SORLA, prepared cell lysates, and precipitated proteins using anti-FLAG antibody. WB analysis using detection by a polyclonal serum against the SORLA extracellular fragment clearly showed that FLAG-mini also precipitates full-length SORLA in cells (
We next turned our attention to study the cellular localization of SORLA dimer formation. We prepared constructs for full-length SORLA proteins with C-terminal FLAG- or GFP-tags (
An immunostaining was performed using secondary antibodies tagged with short oligonucleotides able to hybridize when the two target molecules get into close proximity (i.e. dimerizes) allowing for rolling-circle amplification. For visualization by confocal microscopy fluorescently labeled oligos are bound to complementary sequences on the amplicon represented by red dots. Strong PLA signals were detected by microscopy when staining with both a FLAG and a GFP antibody simultaneously indicating dimerization between the two SORLA molecules.
First, we tested whether the two different tags affected the localization of the tagged receptor forms using double transfected HEK293 cells and determination of their degree of co-localization. From this experiment we observed no indication that the tags lead to differences in cellular localization as they showed a strong overlap and Mander's coefficient of 0.71 (
We and others have previously demonstrated how SORLA associates with retromer in endosomes (Fjorback et al. 2012), and is has been shown how the related receptor Sortilin forms a dimer specifically in acidic compartments (Jauliene et al. 2017). We therefore hypothesized that also SORLA dimers are predominantly formed in the endosome. Co-staining for the PLA signal representing dimers and the VPS35 subunit of the retromer core showed a high degree of co-localization with Mander's coefficient of 0.70, confirming that the majority of SORLA dimers are located together with retromer (
We next wanted to confirm that cellular SORLA exists in equilibrium between monomer and dimer using the bimolecular fluorescence complementation (BiFC) assay as an independent approach.
This technique is based upon structural complementation between non-fluorescent N-terminal and C-terminal fragments of a split fluorescent protein (such as GFP) fused to bait and prey proteins, respectively. Upon interaction between the bait and prey proteins the split domains get into close proximity enabling them to refold into a functional β-barrel structure containing the fluorophore (
Accordingly, two SORLA constructs were engineered to contain C-terminal fusions of either the N-terminal (Met1-Gln157) or C-terminal (Lys158-Lys238) fragment of the venus fluorescent protein (a derivative of GFP). These two SORLA constructs were termed SORLA-V1 and SORLA-V2 containing either the N-terminal or C-terminal part of the venus fluorescent protein, respectively.
Transfection of HEK293T cells with each of the two SORLA BiFC constructs individually did not produce any green fluorescent signals (
We next wanted to test if retromer binds preferentially to the SORLA monomer or dimer. For that purpose, we applied the GFP-trap technique that rely on a nanobody that interacts with the venus protein (as well as GFP) in their folded state. However, the nanobody used for the GFP-trap does not bind neither the V1 nor the V2 with sufficient affinity to allow precipitation of these isolated parts of the venus protein.
We transfected cells with SORLA-GFP, SORLA-V1, SORLA-V2, combined SORLA-V1 and SORLA-V2, and full-length SORLA without tags, and confirmed that SORLA forms a dimer that can be precipitated with the GFP-trap (
Combined, our data provides the first evidence of SORLA dimer formation by its 3Fn-domains. Further, the data further supports that the minireceptor is sufficient, and even superior in certain regards compared to full-length SorLA (e.g. in regard to its effect on non-amyloidogenic and amyloidogenic processing) to interact with retromer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21183382.7 | Jul 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/068235 | 7/1/2022 | WO |
