Patent Application
20060024278
The invention relates to the generation of hair cells of the ear through the control of the genes involved in the retinoblastoma pathway, particularly Rb family proteins, and/or their protein expression products, related methods and compositions.
Inner ear hair cells play a crucial role in hearing and balance. The essential function and delicate structure of the hair cells make them particularly prone to damage. Millions of people suffer from permanent hearing impairment as the result of hair cell loss (Corwin, 1998).
Both environmental and genetic factors are involved in hair cell death. For instance, otoxic drugs, noise, as well as mutations in many genes can cause hair cell death (Schacht, 1999; Wu, 2002; Morton, 2002; Duan, 2002). For example, genes involved in the function of hair cells, such as myosin 15, can cause deafness when mutated (Self et al., 1998; Wang et al., 1998). Noise and viral infection are other leading causes of hair cell death (Duan et al., 2002; Morton, 2002). Moreover, like the majority of neurons, mammalian hair cells in general do not undergo spontaneous regeneration after damage, further complicating the process of functional recovery of hearing. Therefore, any therapy aimed at regenerating hair cells will require an understanding of hair cell development.
Hair cell development involves permanent exit of the cell cycle by the progenitor cells and the initiation of fate determination and terminal differentiation of the hair cell. A bHLH transcription factor, Math1, has been identified as the gene controlling hair cell fate, and expression of Math1 can trigger downstream hair cell terminal differentiation in the supporting cells, although the mechanism involved is not known (Bermingham et al., 1999; Kawamoto et al., 2003; Zheng and Gao, 2000). Other pathways, most notably, the retinoic acid and Notch pathways, are involved in the induction of hair cells either from the progenitor cell pool or from the supporting cells at early stages of development. (Bryant et al. 2002; Kiernan et al., 2001; Lanford et al., 1999; Raz and Kelley 1999; Zhang et al., 2000; Zine et al., 2000). One of the key questions in hair cell development is the identity of the genes and the pathways that regulate permanent cell cycle exit for the sensory progenitor cells, as well as the maintenance of the quiescent postmitotic hair cells and supporting cells. It is possible that perturbations of the pathways involved may force the postmitotic sensory epithelial cells to re-enter the cell cycle, an important implication for hair cell regeneration.
It has been recently demonstrated that cell cycle exit of the progenitor cell is a key event prior to the differentiation of hair cells and supporting cells. Negative cell cycle regulators have been increasingly recognized for their important roles in maintaining the postmitotic status of the hair cells. During embryonic development, both the cochlea and the vestibule are derived from the pro-sensory patch of the otocyst which forms through invagination of the otic placode (Bryant et al., 2002). The cochlear progenitor cells are in an active cell cycle that progresses through E12.2-13.5 when a zone of non-proliferating cells (ZNPC) is defined by the expression of p27kip1, a cyclin dependent kinase inhibitor (Chen et al., 2002; Chen and Segil, 1999; Lowenheim et al., 1999) that is highly expressed in the cochlear hair cell progenitor cells but completely absent in the hair cells. It has been established that the function of p27kip1 is necessary for the cell cycle exit in the supporting cells, as in p27kip1 knockout mice both the embryonic and adult supporting cells can re-enter the cell cycle. Subsequently, the expression of p27kip1 is downregulated in the cells within the ZNPC that are destined to become the hair cells, whereas its expression is maintained in the supporting cells. Supernumerary hair cells and supporting cells are generated in p27kip1 mouse cochlea, presumably by increasing the number of progenitor cells (Chen and Segil, 1999; Lowenheim et al., 1999). p27kip1 is the only negative cell cycle regulator known to be involved in early developmental control of the sensory cells in the cochlea.
Another cyclin dependent kinase inhibitor, p19ink4d, is expressed as early as E14 in the hair cells and has been implicated in the apoptotic pathway. The hair cells in the p19ink4d null mice start to re-enter the cell cycle at P5 and those cells subsequently die through apoptosis, causing progressive hearing loss in the mouse mutant (Chen et al., 2003). Therefore, in the inner ear, the function of p27kip1 is primarily involved in the postmitotic status of the supporting cells, whereas the function of p19ink4d is involved in protecting the hair cells from apoptosis. However, no gene has been identified that is required for cell cycle arrest in the fully differentiated hair cells, or that can be manipulated in the fully differentiated hair cells to lead to regeneration of healthy and functional hair cells. From the small number of hair cells being affected in the p19ink4d cochlea it is suggestive that some other negative cell cycle controllers may also be involved in the exit of the cell cycle, similar to the role of p27kip1 in the hair cells.
The cycling of proliferating cells through the different phases of the cell cycle is mainly controlled by different types of cyclin-dependent kinases (Classon and Harlow, 2002). To exit the cell cycle the expression of the cyclin-dependent kinases has to be downregulated through inhibitory functions of different types of cyclin dependent kinase inhibitors such as p27kip1, for Cdk2. In order to keep the cells, such as hair cells and a majority of neurons, in permanent cell cycle arrest, negative cell growth control genes are required. In addition, some growth factors, such as TGF-β, can be effective growth inhibitors (Hu and Zuckerman, 2000). It is, therefore, necessary to identify those cell cycle regulators, in particular the negative growth control genes, to understand how the postmitotic status of the sensory epithelial cell is maintained. Understanding the process could shed light on the possibility of re-entering the cell cycle by quiescent cells, through relieving the negative controls.
Avian, fish and chick sensory hair cells can be regenerated after being damaged by trauma (Corwin and Cotanche, 1988; Ryals and Rubel, 1988). In addition in the avian vestibular epithelium, new hair cells are generated through supporting cell division (Jorgensen and Mathiesen, 1988). The hair cells in the mammalian inner ear, however, do not undergo spontaneous regeneration despite the fact that the vestibular system retains very limited cell division capacity (Forge et al., 1993; Warchol et al., 1993). As a consequence damage to the hair cells leads to permanent hearing impairment since new hair cells cannot be formed. Irreversible damage to the hair cells is, therefore, the main cause of hearing loss and balance problems.
Cell cycle regulators, in particular negative cell growth control genes, have been implicated in the re-entry into the cell cycle of the inner ear sensory cells. Using a functional genomics approach, the expression profiles of the developing mouse utricle were studied. To identify critical molecules involved in the cell cycle regulation in hair cell development, microarray analysis was employed. Retinoblastoma protein (pRb) family members were implicated by their distinct expression pattern in the inner ear. Using mice bearing targeted deletion of Rb1, it was demonstrated that pRb is essential for cell cycle exit and maintenance of the postmitotic status in all hair cells. Hair cells without pRb are undergoing cell division, and are differentiated and functional, indicating a pRb independent differentiation process. Identification of the pRb family members and subsequent characterization of pRb conditional knockout mice revealed a pivotal role of retinoblastoma (Rb) in the maintenance of the quiescent state of differentiated hair cells. The capacity of differentiated, pRb-null hair cells to remain in the cell cycle, therefore, leads to hair cell regeneration by regulation of the Rb pathway.
Therefore, in one aspect a method for generating or regenerating functional, differentiated inner ear hair cells is provided. In some embodiments this method is for in vivo purposes. In other embodiments this method is for in vitro purposes. In one aspect of the invention the method for generating or regenerating functional, differentiated inner ear hair cells includes the step of eliminating or reducing the expression level or function of the retinoblastoma gene and/or retinoblastoma protein (pRb) in inner ear sensory cells by an amount effective to generate functional, differentiated inner ear hair cells.
The elimination or reduction can be accomplished either directly or indirectly. It has been demonstrated that deletion of the Rb gene leads to proliferation of the cells in which the Rb gene was deleted. This can be accomplished in, for example, progenitor cells, supporting cells or hair cells. It was found, for example, that postnatal mature hair cells proliferated after the acute elimination of the Rb1 gene. In addition, the deletion of Rb1 gave rise to proliferation of sensory progenitor cells.
Proliferation can, however, be accomplished by indirect means. For instance the elimination or reduction of Rb expression or function can be performed in one type of sensory epithelial cell in order to lead to the proliferation of another type of inner ear sensory epithelial cell. For example, it was found that supporting cells can be induced into the cell cycle when hair cells are cycling. Therefore, Rb expression or function can be reduced or eliminated, for example, in one type of sensory cell (e.g., hair cells) to result in the regeneration of another type of cell (e.g., supporting cell). Although not wishing to be bound by any theory, it is thought that this is the result of the action of signaling molecules of the cells with reduced or eliminated Rb expression or function. Therefore, one aspect of the invention provides a method of generating or regenerating an inner ear sensory cell by contacting the cell with another type of inner ear sensory cell in which the expression level or function of a Rb gene and/or its protein has been eliminated or reduced. In some embodiments the cell in which Rb expression or function has been eliminated or reduced is an intact cell. In another embodiment some portion of the cell is collected (e.g., a cell fraction subsequent to cell lysis) and used in the methods provided. In one embodiment of the invention a method is provided to generate or regenerate inner ear supporting cells by eliminating or reducing the expression level or function of a Rb gene and/or its protein in a hair cell and contacting a supporting cell with the hair cell to generate or regenerate the supporting cell.
In another aspect of the invention a method for restoring hearing or balance to a subject is provided. The subject can be any subject who suffers from or is at risk of suffering from hearing damage, loss of hair cells and/or the symptoms of hearing damage or loss of hair cells. Such a method includes the step of eliminating or reducing the expression level or function of pRb in the inner ear sensory cells of the subject by an amount effective to generate functional, differentiated inner ear hair cells and thereby to restore hearing or balance to the subject. In some embodiments the subject suffers from hearing damage due to a viral infection, noise, a mutation in a gene which causes hair cell death, or ototoxic drug exposure. In some embodiments this method is performed in vivo, while in other embodiments the cells are manipulated in vitro and then provided to the inner ear of the subject. Therefore, in another aspect of the invention a method for restoring hearing or balance to a subject by providing to the subject in need thereof functional, differentiated inner ear hair cells generated by the elimination or reduction of the expression level or function of Rb in inner ear sensory epithelial cells is also provided.
Inner ear sensory cells include any cell that can generate a functional, differentiated hair cell. Inner ear sensory cells include progenitor cells, supporting cells and hair cells. In some embodiments the supporting cells and/or hair cells are cells of the vestibular or auditory system. Cells of the vestibular system include cells of the utricle, saccule maculae and three crista. In other embodiments the supporting and/or hair cells are the cells of the auditory system. Cells of the auditory system include the cells of the cochlea.
The compositions and methods of the invention can also be used to generate or regenerate neuronal cells. In one aspect of the invention, therefore, a method for generating or regenerating neuronal cells is provided wherein the expression level or function of a Rb gene and/or its protein is reduced or eliminated in the neuronal cells. In one embodiment the neuronal cell is an inner ear neuronal cell. In another embodiment the neuronal cell is of the central nervous system. In another embodiment the neuronal cell is of the peripheral nervous system.
The retinoblastoma gene and/or retinoblastoma protein includes any of the genes and/or proteins that are part of the retinoblastoma family. In one embodiment the retinoblastoma gene and/or retinoblastoma protein is Rb1/Rb/p105. In another embodiment the retinoblastoma gene and/or retinoblastoma protein is Rbl1/p107. In yet another embodiment the retinoblastoma gene and/or retinoblastoma protein is RB2/Rbl2/p130. The retinoblastoma gene and/or retinoblastoma protein also includes any of the genes and/or proteins that are involved in the retinoblastoma pathway.
The reduction or elimination of the expression level or function of a retinoblastoma gene and/or its protein can be accomplished with a variety of agents. In some embodiments the agents are Rb-binding molecules. Rb-binding molecules are molecules that bind to the retinoblastoma gene or the retinoblastoma protein. Such molecules include, in some embodiments, antisense oligonucleotides, RNAi or siRNA molecules, intrabodies, adenovirus E1A or SV40 T-antigen. In some embodiments the molecules are Rb-binding polypeptides, such anti-Rb antibodies or anti-Rb antibody fragments. In one embodiment the elimination or reduction of the expression level or function of retinoblastoma gene and/or its protein can be accomplished by eliminating the Rb gene. In another embodiment the Rb gene and/or its transcripts are bound by a Rb-binding molecule, e.g., Rb-binding nucleic acids. In still another embodiment methods and compositions are contemplated whereby nucleic acids that eliminate or reduce the expression level of Rb are produced through the use of hair cell specific promoters. In one embodiment, the production of antisense oligonucleotides, RNAi or siRNA molecules can be placed under the control of the hair cell specific promoter. Hair cell specific promoters include, but are not limited to Brn 3.1, Math-1, myosin VIIa and Lhx3. In one embodiment of the invention an expression vector or plasmid which contains a hair cell specific promoter is provided. In still another embodiment a method of administering the expression vector or plasmid containing a hair cell promoter in order to generate or regenerate inner ear sensory cells is also provided. In yet a further embodiment in vitro methods for using expression vectors or plasmids containing a hair cell promoter for generating or regenerating inner ear sensory cells are also provided.
The reduction or elimination of the expression level or function of retinoblastoma gene and/or its protein can also be accomplished in yet other embodiments with kinase activators, cyclin-dependent kinases (CDKs), and/or agents that inhibit the activity of kinase inhibitors (e.g., histone acetyltransferase (HAT) inhibitors). In another aspect of the invention compositions of the agents provided herein and a pharmaceutically acceptable carrier are provided. The methods and compositions provided herein can, in some embodiments, include at least 2, 3, 4, 5, 6, or more different agents that reduce or eliminate the expression level or function of a Rb gene and/or its protein product.
The methods provided herein can also further include eliminating or reducing the expression level or function of other molecules, such as other cell cycle regulators. In some embodiments the expression level or function of p27kip1, p57kip2, Isl-1, a Notch family protein or a MAPK-JNK family protein is reduced or eliminated in these methods.
In another aspect of the invention a functional, differentiated inner ear hair cell line is provided. In some embodiments the functional, differentiated inner ear hair cell line is composed of functional, differentiated inner ear hair cells with reduced or eliminated expression level or function of Rb. The functional, differentiated inner ear hair cells in other embodiments can further have reduced or eliminated expression level or function of p27kip1, p57kip2, Isl-1, a Notch family protein or a MAPK-JNK family protein.
In still another aspect of the invention an inner ear sensory epithelial cell line, wherein the expression level or function of Rb is eliminated or reduced is also provided. In some embodiments the inner ear sensory epithelial cell line is an inner ear progenitor, supporting or hair cell line. In some embodiments the cell line lacks a thermolabile variant of the large T antigen that is stable at 33° C. The inner ear sensory epithelial cell line in some embodiments also can further have reduced or eliminated expression level or function of p27kip1, p57kip2, Isl-1, a Notch family protein or a MAPK-JNK family protein.
In yet another aspect of the invention an inner ear sensory epithelial cell, wherein the expression level or function of pRb is reduced or eliminated, is also provided. In some embodiments the inner ear sensory epithelial cell is a functional, differentiated inner ear hair cell. In other embodiments the inner ear sensory epithelial cell is a supporting cell. In yet other embodiments the inner ear sensory epithelial cell is a progenitor cell. In still other aspects of the invention compositions of inner ear sensory epithelial cells with reduced or eliminated Rb expression level or function and a pharmaceutically acceptable carrier are provided. Compositions provided herein, in some embodiments, can further comprise a therapy for treating hearing damage or ameliorating the symptoms of hearing damage. In some embodiments the therapy is a hearing aid or cochlear implant.
In still another aspect of the invention a screening method for identifying compounds for generating, regenerating or protecting hair cells by contacting a candidate compound with a sample containing cells of a functional, differentiated inner ear hair cell line, and determining if the candidate compound affects the production of or protects the functional, differentiated inner ear hair cells is provided. In other aspects a screening method for identifying compounds for inducing supporting cells or progenitor cells to become hair cells by contacting a candidate compound with a sample containing cells of an inner ear supporting or progenitor cell line, and determining if the candidate compound induces the supporting cells to become hair cells is also provided. In some embodiments the supporting cells are cells where the expression level or function of Rb is eliminated or reduced. In still other embodiments the cells lack a thermolabile variant of the large T antigen that is stable at 33° C.
Yet another aspect of the invention provides a method for generating or regenerating inner ear sensory epithelial cells (e.g., functional, differentiated inner ear hair cells) by eliminating or reducing the expression level or function of Isl-1 in inner ear sensory epithelial cells by an amount effective to generate inner ear sensory epithelial cells. In another aspect the method is a method for restoring hearing or balance in a subject by eliminating or reducing the expression level or function of Isl-1 in inner ear sensory cells. These methods can be performed in vivo or in vitro. In other aspects of the invention inner ear sensory epithelial cell lines, wherein the expression level or function of Isl-1 is eliminated or reduced, are provided. The cells, compositions thereof and methods of screening with such cells are also provided in other aspects of the invention.
Use of the foregoing cells, cell lines and agents in the preparation of medicaments, particularly for the treatment of hearing loss or loss of balance, is also provided according to the invention.
Each of the limitations of the invention can encompass various embodiments of the invention. It is, therefore, anticipated that each of the limitations of the invention involving any one element or combinations of elements can be included in each aspect of the invention.
These and other aspects of the invention, as well as various advantages and utilities, will be more apparent with reference to the detailed description of the preferred embodiments.
Scale bars=50 μm.
Scale bars=50 μm.
Scale bars: 50 μm (Panels A-R); 10 μm (Panel S).
Scale bars: 25 μm.
Scale bars=50 μm.
Scale bars: 25 μm.
Scale bars=50 μm.
Scale bars: 50 μm.
Scale bars: 50 μm.
Scale bars: 50 μm.
Scale bars=25 μm.
Scale bars=25 μm.
Scale bars=25 μm.
Scale bars=25 μm (Panels A-N) and 10 μm (Panel O).
Scale bars=25 μm.
Scale bars=25 μm.
Scale bars=25 μm.
Scale bars=25 μm.
Scale bars=10 μm.
Scale bars=25 μm.
Scale bars=25 μm.
Scale bars=25 μm.
Scale bars=25 μm.
Scale bars=25 μm.
Scale bars=25 μm.
The retinoblastoma protein (pRb) is well studied for its multiple roles in tumorigenesis, terminal exit of cell cycle, protection from apoptosis and differentiation (Classon and Harlow, 2002; Lipinski and Jacks, 1999). More than 100 proteins have been shown to interact with pRb (Morris and Dyson, 2001). Underphosphorylated pRb interacts with its cellular targets, most notably, the E2F family of transcription factors (E2F1-E2F3) and suppresses their transcription activities.
Phosphorylation of pRb by cyclin-dependent kinases (CDKs) releases pRb from its binding to E2F members, enabling them to regulate cell proliferation by promoting transition from the G1 to S phase of the cell cycle (Dyson, 1998). Activity of CDK depends upon binding with cyclin partners and is inhibited by cyclin-dependent kinase inhibitors, such as p27kip1 (Dyson, 1998). Homozygous Rb1 knockout animals are embryonic lethal between E13-E15, with severe defects in lens development, hematopoiesis, myogenesis, osteogenesis and neurogenesis (Classon and Harlow, 2002; Ferguson and Slack, 2001; Thomas et al., 2001). It has been shown that pRb interacts with bHLH protein Id2, an important regulator for proliferation and differentiation (Lasorella, 2002; Lasorella, 2000). Furthermore the genomic sequence of the Jagged2 (a ligand for Notch1) promoter contains a potential binding site for E2F, suggesting pRb may also influence the Notch pathway (Deng, 2000).
Rb plays a key role in neurogenesis. In the nervous system of Rb null mice the neuronal differentiation of proliferating precursors was impaired as manifested by decreased expression of neuronal markers such as neurotrophin receptors TrkA, TrkB and βII tubulin. Ectopic mitoses were found in many regions of the brain and a large number of cells underwent apoptosis in both the central and peripheral nervous systems (Ferguson and Slack, 2001; Yoshikawa, 2000). In pRb null mice cells underwent ectopic mitoses and subsequent apoptosis in both the central and peripheral nervous systems (Jacks et al., 1992; Macleod et al., 1996). Transgenic studies, using neuron specific Ta1 α-tubulin promoter driving a lacZ reporter gene in Rb null mice, showed widespread abnormal neuronal development including the retina, the neocortex and the olfactory epithelium. It has also been shown that Rb becomes essential immediately after neuron fate determination and that lack of Rb causes virtually all neuron populations to undergo apoptosis (Gloster et al., 1999; Slack et al., 1998). However, recent studies using conditional mice that specifically deleted pRb in the CNS, showed an increase in neuronal populations due to aberrant S phase entry (Ferguson et al., 2002; MacPherson et al., 2003; Marino et al., 2003). Interestingly, there was normal differentiation for some neurons without apoptosis. Rb therefore, seems to have multi-functional roles in the CNS: it is required for the cell cycle arrest in many cell types in the CNS, and it is also necessary for the differentiation of sub-cell types. However, none of the Rb family members has been previously studied in the inner ear.
Molecules with the potential to control cell cycle arrest in inner ear sensory cells were identified with a functional genomics approach in combination with studies of developing utricles. This approach had distinct advantages. A functional genomics approach provided a global view of the expression profiles of the cell cycle regulators during inner ear development, enabling the identification of interesting candidates for in-depth characterization. Also, the selection of the utricle as the sample of choice, together with using the sensory utricular epithelium, greatly reduced the complexity of analysis and allowed the association of the expressed genes with the sensory epithelial cells. With this approach a list of genes with the potential to play a role in the maintenance of cell cycle arrest of inner ear sensory cells was defined.
The microarray expression profile analysis identified over 80 cell cycle regulators, including many negative cell growth controllers with expression in the utricle. Their presence in the developing utricular sensory epithelium and their distinct expression patterns from cluster analysis suggest their specific roles in the context of utricle development. For example, p19ink4d, Mxi1, Jun-B and c-fos are all associated with negative regulation of cell growth (Balsalobre and Jolicoeur, 1995; Schlingensiepen et al., 1993; Schreiber-Agus et al., 1998) and share an upregulated expression profile in the developing utricle (
The results of the studies presented herein indicate that there was a consistent expression pattern of pRb in the inner ear sensory hair cells, from embryo to adult, which strongly suggests that pRb is required throughout hair cell development. The examination of the conditional pRb knockout mouse with pRb expression abolished in the inner ear revealed the primary role of pRb in maintaining the postmitotic state of the hair cells. Also it was demonstrated that one copy of Rb was sufficient to restore full function, as all the analyses done with pRb−/+ mice did not reveal any obvious abnormality. This study demonstrated that not only is retinoblastoma protein a key regulator in cell cycle arrest of sensory epithelial cells in the mammalian inner ear, but surprisingly additional differentiated mammalian hair cells can be generated through hair cell division when Rb expression is abolished. The sensory epithelial cells regenerated are differentiated and functional. This is in agreement with recent studies showing that acute loss of pRb in quiescent or senescent mouse embryonic fibroblast cells (MEFs) resulted in cell cycle re-entry (Sage, 2003).
Therefore, by manipulating Rb, to reduce or eliminate its expression level or function, at the gene or protein level, inner ear sensory epithelial cells (both the hair cell and the supporting cell) can re-enter or remain in the cell cycle in vivo or in vitro, leading to the regeneration of sensory epithelial cells in the inner ear, in particular the progenitor, supporting and/or hair cells. Manipulation of Rb, as such, is applicable to developing and fully differentiated sensory epithelial cells. The regenerated functional hair cells have the potential to be used in therapy to restore hearing and balance associated with hair cell damage. Rb is the only gene identified that in its absence enable the highly differentiated and functional hair cells to remain in the cell cycle and produce more hair cells with the same characteristics. Lack of the Rb gene also leads to cycling supporting cells.
Therefore, methods of generating or regenerating sensory inner ear cells, progenitor, supporting, or hair cells that are functional and differentiated, are provided. These methods can be for use in vivo and/or in vitro. The sensory inner ear cells are generated, in such methods, through the elimination or reduction of the expression level or function of a retinoblastoma gene and/or retinoblastoma protein. A “retinoblastoma gene or retinoblastoma protein” refers to any of the members of the retinoblastoma family. The retinoblastoma family members include Rb1/Rb/p105, Rbl1/p107 and RB2/Rbl2/p130. As used herein, the use of “Rb” and like terms is intended to encompass all of the members of the retinoblastoma family, the gene and/or its protein, while the use of “Rb gene” and “pRb” refer specifically to the gene and its protein, respectively. The methods of the invention provided herein can include the elimination or reduction of the expression level or function of each of these retinoblastoma family members either singularly or in any combination. In some embodiments the methods are directed to the reduction or elimination of Rb1/Rb/p105 expression level or function. The methods of the invention provided herein can be performed in any of the inner ear sensory epithelial cells. Such cells include progenitor cells, supporting cells and hair cells. “Progenitor cells”, as used, herein are cells that are capable of self-renewal and can produce progeny cells that are more differentiated than itself. Progenitor cells, therefore, include stem cells. “Supporting cells”, as used herein, include cells that are in direct contact with and/or separate the hair cells. Supporting and hair cells include those of the auditory system (e.g., the ganglion cells of the cochlea) and of the vestibular organs of the inner ear (e.g., the utricle, saccule maculae and three crista).
As used herein “generating” or “regenerating” refers to producing the new desired cells and/or causing cells to re-enter the cell cycle.
The reduction or elimination of the expression level or function of a retinoblastoma gene and/or its protein can be accomplished using a variety of agents (called herein “Rb inhibiting agents”. It will be apparent to one of ordinary skill in the art that agents that reduce or eliminate the expression level or function of Rb include Rb-binding molecules. “Rb-binding molecules” are molecules that bind Rb, such as antisense oligonucleotides (e.g., the antisense oligonucleotides of Bredesen et al., U.S. Pat. No. 5,324,654), RNAi molecules, Rb-binding polypeptides, e.g., anti-Rb antibodies or anti-Rb antibody fragments, intrabodies, small molecules or any other compound that binds to Rb and inhibits its function of maintaining cell cycle arrest. In some embodiments the Rb-binding molecule is adenovirus E1A or SV40 T-antigen that form a complex with pRb between amino acids 393 and 572 and 646 and 772 (Hu et al., 1990). Rb-binding molecules may be isolated from natural sources or synthesized or produced by recombinant means. Methods for preparing or identifying molecules which bind to a particular target, in this instance to Rb, are well-known in the art and are described below. Rb-binding polypeptides, such as antibodies, may easily be prepared by generating antibodies to pRb (or obtained from commercial sources) or by screening libraries to identify peptides or other compounds which bind to pRb.
As provided herein, agents include any molecule that eliminates or reduces the expression level or function of Rb, preferably to generate functional, differentiated hair cells. Agents also include compounds which result in the phosphorylation of Rb, such compounds are kinases, kinase activators or agents that inhibit kinase inhibitor activity. Since unphosphorylated pRb is essential for its function, the proteins such as cyclin-dependent kinases (CDKs) that can phosphorylate pRb may also be used to inactivate pRb. In addition molecules with histone acetyltransferase (HAT) activities such as p300/CBP hinders the phosphorylation of pRb by cyclin-dependent kinases (Chan et al., 2001). Therefore any approach that interferes with HAT activity may reduce pRb activities.
In another aspect of the invention, methods for generating, regenerating or providing regenerated hair cells to a subject in need thereof are provided. Such “a subject in need thereof” is one that has or is at risk of having hair cell damage and/or the symptoms associated with hair cell damage, e.g., hearing loss or loss of balance. As described above, damaged hair cells and supporting cells can be the result of viral infection, overdose of ototoxic drugs, noise, aging, hereditary causes, etc. Therefore, a subject at risk is one who has had exposure to these and/or other risk factors associated with hair cell damage, hearing loss and/or loss of balance. A subject at risk can also be one of advanced age. In one embodiment the subject is 60, 70 80, 85, 90 or more years old. Therefore, a method is provided for restoring hearing or balance to a subject. In a preferred aspect, the method includes eliminating or reducing the expression level or function of Rb in sensory inner ear cells in vivo to cause them to re-enter the cell cycle and to produce new progenitor, supporting or, functional, differentiated hair cells. In another preferable aspect of the invention, the method includes eliminating or reducing the expression level or function of Rb in sensory inner ear cells in vitro and providing these cells to the subject. They can be used to replace the damaged hair cells and/or progenitor or supporting cells in the inner ear, to restore hearing and balance. As Rb is expressed in inner ear sensory epithelial cells from embryo to adult, the generation or regeneration of the sensory epithelial cells can be performed in both early developmental stages or in the adult. The manipulation of the expression level of Rb or the function of pRb can be of short or long duration. The methods provided herein include the use of any agent in an amount effective to reduce or eliminate the expression level or function of Rb. The methods can be performed in any cell of the sensory epithelia that can lead to the production of inner ear hair cells. The result is the generation or regeneration of sensory inner ear cells. The generated/regenerated cells can be the progenitor cells, hair cells, the supporting cells or some combination thereof.
The methods and compositions provided herein can be used alone or in combination with other medical treatments that are used to ameliorate the symptoms associated with hair cell damage and/or hair cell loss. Such treatments include the use of hearing aids and cochlear implants.
Subjects as used herein includes humans, non-human primates, dogs, cats, horses, sheep, goats, cows, rabbits, pigs and rodents.
The methods provided herein can further include reducing or eliminating the expression level or function of proteins that are involved in the Rb pathway. These proteins can be one or more of the proteins of the Rb family. These proteins also can be upstream or downstream of Rb. These proteins, therefore, can include p107(Rbl1), p130(Rbl2), p27kip1, p57kip2, Isl-1, a Notch family protein or a MAPK-JNK family protein.
In another aspect of the invention methods and compositions for the generation or regeneration of neuronal cells through the elimination or reduction of Rb expression or function are provided. Neuronal cells include the neuronal cells of the inner ear, central nervous system or peripheral nervous system. Neuronal cells are predominantly categorized based on their local/regional synaptic connections (e.g., local circuit intemeurons vs. longrange projection neurons) and receptor sets, and associated second messenger systems. There are many different neuronal cell types. Examples include, but are not limited to, sensory and sympathetic neurons, cholinergic neurons, dorsal root ganglion neurons, proprioceptive neurons (in the trigeminal mesencephalic nucleus), ciliary ganglion neurons (in the parasympathetic nervous system), etc. A person of ordinary skill in the art will be able to easily identify neuronal cells and distinguish them from non-neuronal cells such as glial cells, typically utilizing cell-morphological characteristics, expression of cell-specific markers, secretion of certain molecules, etc.
In another aspect of the invention it is the expression level or function of Isl-1 alone or in combination with another gene/protein, that is eliminated or reduced in the supporting or inner ear hair cells, preferably to result in the production of functional, differentiated hair cells. This aspect of the invention is intended to encompass in vitro and in vivo applications.
As one example, antisense oligonucleotides can be used to reduce or eliminate the expression level of Rb. As used herein, the term “antisense oligonucleotide” or “antisense” describes an oligonucleotide that is an oligoribonucleotide, oligodeoxyribonucleotide, modified oligoribonucleotide, or modified oligodeoxyribonucleotide which hybridizes under physiological conditions to DNA comprising a particular gene or to an mRNA transcript of that gene and, thereby, inhibits the transcription of that gene and/or the translation of that mRNA, respectively. The antisense molecules are designed so as to interfere with transcription or translation of a target gene upon hybridization with the target gene or transcript. Antisense oligonucleotides that selectively bind to either a nucleic acid molecule encoding Rb are particularly preferred. Those skilled in the art will recognize that the exact length of the antisense oligonucleotide and its degree of complementarity with its target will depend upon the specific target selected, including the sequence of the target and the particular bases which comprise that sequence.
It is preferred that the antisense oligonucleotide be constructed and arranged so as to bind selectively with the target under physiological conditions, i.e., to hybridize substantially more to the target sequence than to any other sequence in the target cell under physiological conditions. Based upon the nucleotide sequences of nucleic acid molecules encoding the retinoblastoma family or pathway members (e.g., Rb1, NCBI Accession Nos. M26460, NM—000321; Rbl1/p107, NCBI Accession Nos. L14812, BC069179; RB2/Rbl2/p130, NCBI Accession Nos. BC034490, BC020528) or upon allelic or homologous genomic and/or cDNA sequences, one of skill in the art can easily choose and synthesize any of a number of appropriate antisense molecules for use in accordance with the present invention. In order to be sufficiently selective and potent for inhibition, such antisense oligonucleotides should comprise at least about 10 and, more preferably, at least about 15 consecutive bases which are complementary to the target, although in certain cases modified oligonucleotides as short as 7 bases in length have been used successfully as antisense oligonucleotides. See Wagner et al., Nat. Med. 1(11): 1116-1118, 1995. Most preferably, the antisense oligonucleotides comprise a complementary sequence of 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 bases. Although oligonucleotides may be chosen which are antisense to any region of a gene or its mRNA transcripts, in preferred embodiments the antisense oligonucleotides correspond to N-terminal or 5′ upstream sites such as translation initiation, transcription initiation or promoter sites. In addition, 3′-untranslated regions may be targeted by antisense oligonucleotides. Targeting to mRNA splicing sites has also been used in the art but may be less preferred if alternative mRNA splicing occurs. In addition, the antisense is targeted, preferably, to sites in which mRNA secondary structure is not expected (see, e.g., Sainio et al., Cell Mol. Neurobiol. 14(5):439-457, 1994) and at which proteins are not expected to bind.
In one set of embodiments, the antisense oligonucleotides of the invention may be composed of “natural” deoxyribonucleotides, ribonucleotides, or any combination thereof. That is, the 5′ end of one native nucleotide and the 3′ end of another native nucleotide may be covalently linked, as in natural systems, via a phosphodiester internucleoside linkage. These oligonucleotides may be prepared by art recognized methods which may be carried out manually or by an automated synthesizer. They also may be produced recombinantly by vectors. In some embodiments the vectors contain a hair cell specific promoter.
In preferred embodiments, however, the antisense oligonucleotides of the invention also may include “modified” oligonucleotides. That is, the oligonucleotides may be modified in a number of ways which do not prevent them from hybridizing to their target but which enhance their stability or targeting or which otherwise enhance their therapeutic effectiveness.
The term “modified oligonucleotide” as used herein describes an oligonucleotide in which (1) at least two of its nucleotides are covalently linked via a synthetic internucleoside linkage (i.e., a linkage other than a phosphodiester linkage between the 5′ end of one nucleotide and the 3′ end of another nucleotide) and/or (2) a chemical group not normally associated with nucleic acid molecules has been covalently attached to the oligonucleotide. Preferred synthetic internucleoside linkages are phosphorothioates, alkylphosphonates, phosphorodithioates, phosphate esters, alkylphosphonothioates, phosphoramidates, carbamates, carbonates, phosphate triesters, acetamidates, carboxymethyl esters and peptides.
The term “modified oligonucleotide” also encompasses oligonucleotides with a covalently modified base and/or sugar. For example, modified oligonucleotides include oligonucleotides having backbone sugars which are covalently attached to low molecular weight organic groups other than a hydroxyl group at the 3′ position and other than a phosphate group at the 5′ position. Thus modified oligonucleotides may include a 2′-O-alkylated ribose group. In addition, modified oligonucleotides may include sugars such as arabinose instead of ribose.
The present invention, thus, contemplates pharmaceutical preparations containing modified antisense molecules that are complementary to and hybridizable with, under physiological conditions, nucleic acid molecules encoding retinoblastoma protein, together with pharmaceutically acceptable carriers. Antisense oligonucleotides may be administered as part of a pharmaceutical composition. In this latter embodiment, it is preferable that a slow intravenous administration be used. Such a pharmaceutical composition may include the antisense oligonucleotides in combination with any standard physiologically and/or pharmaceutically acceptable carriers which are known in the art. The compositions should be sterile and contain a therapeutically effective amount of the antisense oligonucleotides in a unit of weight or volume suitable for administration to a patient. In one embodiment it is the vectors that produce antisense oligonucleotides that are administered for the in vivo production of the antisense oligonucleotides.
A reduction or elimination of the expression level of Rb in another method may be achieved by using the technique of RNA interference (RNAi). The use of RNAi involves the use of double-stranded RNA (dsRNA) to block gene expression. (See: Sui, G, et al, 2002, Proc Natl. Acad. Sci U.S.A. 99:5515-5520). The application of RNAi strategies for reducing gene expression specifically is understood by one of ordinary skill in the art.
In one aspect of the invention, a method is provided in which siRNA molecules are used to eliminate or reduce the expression level of Rb. In one embodiment, a cell is contacted with a small interfering RNA (siRNA) molecule to produce RNA interference (RNAi) that reduces expression of one or more Rb molecules. The siRNA molecule is directed against nucleic acids coding for Rb (e.g., RNA transcripts including untranslated and/or translated regions). In a preferred aspect of the invention Rb is Rb1. The expression level of the targeted Rb molecule(s) can be determined using well known methods such as Western blotting for determining the level of protein expression and Northern blotting or RT-PCR for determining the level of mRNA transcript of the target gene.
As used herein, a “siRNA molecule” is a double stranded RNA molecule (dsRNA) consisting of a sense and an antisense strand, which are complementary (Tuschl, T. et al., 1999, Genes & Dev., 13:3191-3197; Elbashir, S. M. et al., 2001, EMBO J., 20:6877-6888). In one embodiment the last nucleotide at the 3′ end of the antisense strand may be any nucleotide and is not required to be complementary to the region of the target gene. The siRNA molecule may be 19-23 nucleotides in length in some embodiments. In other embodiments, the siRNA is longer but forms a hairpin structure of 19-23 nucleotides in length. In still other embodiments, the siRNA is formed in the cell by digestion of double stranded RNA molecule that is longer than 19-23 nucleotides. The siRNA molecule preferably includes an overhang on one or both ends, preferably a 3′ overhang, and more preferably a two nucleotide 3′ overhang on the sense strand. In another preferred embodiment, the two nucleotide overhang is thymidine-thymidine (TT). The siRNA molecule corresponds to at least a portion of a target gene. In one embodiment the siRNA molecule corresponds to a region selected from a cDNA target gene beginning between 50 to 100 nucleotides downstream of the start codon. In a preferred embodiment the first nucleotide of the siRNA molecule is a purine. Many variations of siRNA and other double stranded RNA molecules useful for RNAi inhibition of gene expression will be known to one of ordinary skill in the art.
The siRNA molecules can be plasmid-based. In a preferred method, a polypeptide encoding sequence of Rb is amplified using the well known technique of polymerase chain reaction (PCR). The use of the entire polypeptide encoding sequence is not necessary; as is well known in the art, a portion of the polypeptide encoding sequence is sufficient for RNA interference. For example, the PCR fragment can be inserted into a vector using routine techniques well known to those of skill in the art. The insert can be placed between two promoters oriented in opposite directions, such that two complementary RNA molecules are produced that hybridize to form the siRNA molecule. Alternatively, the siRNA molecule is synthesized as a single RNA molecule that self-hybridizes to form a siRNA duplex, preferably with a non-hybridizing sequence that forms a “loop” between the hybridizing sequences. In one embodiment the siRNA is synthesized with plasmids that are controlled by a tissue-specific promoter. Preferably the tissue specific promoter is specific for the inner ear sensory epithelia. In one embodiment the tissue specific promoters are Brn-3.1, Math-1, myosin VIIa and Lhx3.
In one aspect of the invention a vector comprising any of the nucleotide coding Rb is provided, preferably one that includes promoters active in mammalian cells. Non-limiting examples of vectors are the pSUPER RNAi series of vectors (Brummelkamp, T. R. et al., 2002, Science, 296:550-553; available commercially from OligoEngine, Inc., Seattle, Wash.). In one embodiment a partially self-complementary nucleotide coding sequence can be inserted into the mammalian vector using restriction sites, creating a stem-loop structure. In a preferred embodiment, the mammalian vector comprises the polymerase-III H1-RNA gene promoter. The polymerase-III H1-RNA promoter produces a RNA transcript lacking a polyadenosine tail and has a well-defined start of transcription and a termination signal consisting of five thymidines (T5) in a row. The cleavage of the transcript at the termination site occurs after the second uridine and yields a transcript resembling the ends of synthetic siRNAs containing two 3′ overhanging T or U nucleotides. Other promoters useful in siRNA vectors will be known to one of ordinary skill in the art.
Vector systems for siRNA expression in mammalian cells include pSUPER RNAi system described above. Other examples include but are not limited to pSUPER.neo, pSUPER.neo+gfp and pSUPER.puro (OligoEngine, Inc.); BLOCK-iT T7-TOPO linker, pcDNA1.2/V5-GW/lacZ, pENTR/U6, pLenti6-GW/U6-laminshrna and pLenti6/BLOCK-iT-DEST (Invitrogen). These vectors and others are available from commercial suppliers.
The term “high stringency conditions” as used herein refers to parameters with which the art is familiar. Nucleic acid hybridization parameters may be found in references that compile such methods, e.g. Molecular Cloning: A Laboratory Manual, J. Sambrook, et al., eds., Second Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1989, or Current Protocols in Molecular Biology, F. M. Ausubel, et al., eds., John Wiley & Sons, Inc., New York. One example of high-stringency conditions is hybridization at 65° C. in hybridization buffer (3.5×SSC, 0.02% Ficoll, 0.02% polyvinyl pyrrolidone, 0.02% Bovine Serum Albumin, 2.5 mM NaH2PO4(pH7), 0.5% SDS, 2mM EDTA). SSC is 0.15M sodium chloride/0.015M sodium citrate, pH7; SDS is sodium dodecyl sulphate; and EDTA is ethylenediaminetetracetic acid. After hybridization, a membrane upon which the nucleic acid is transferred is washed, for example, in 2×SSC at room temperature and then at 0.1-0.5×SSC/0.1×SDS at temperatures up to 68° C. There are other conditions, reagents, and so forth which can be used, which result in the same degree of stringency. A skilled artisan will be familiar with such conditions, and thus they are not given here.
The methods provided herein, in some embodiments, also encompass the use of other inhibitors of the function of Rb, such as, “dominant negative” molecules. A dominant negative polypeptide is an inactive variant of a protein, which, by interacting with the cellular machinery, displaces an active protein from its interaction with the cellular machinery or competes with the active protein, thereby reducing the effect of the active protein. For example, a dominant negative receptor which binds a ligand but does not transmit a signal in response to binding of the ligand can reduce the biological effect of expression of the ligand. Likewise, a dominant negative catalytically-inactive kinase which interacts normally with target proteins but does not phosphorylate the target proteins can reduce phosphorylation of the target proteins in response to a cellular signal. Similarly, a dominant negative transcription factor which binds to a promoter site in the control region of a gene but does not increase gene transcription can reduce the effect of a normal transcription factor by occupying promoter binding sites without increasing transcription.
The end result of the expression of a dominant negative polypeptide in a cell is a reduction in function of active proteins. One of ordinary skill in the art can assess the potential for a dominant negative variant of a protein, and using standard mutagenesis techniques to create one or more dominant negative variant polypeptides. For example, given the teachings contained herein of retinoblastoma proteins, one of ordinary skill in the art can modify the sequence of the retinoblastoma protein by site-specific mutagenesis, scanning mutagenesis, partial gene deletion or truncation, and the like. See, e.g., U.S. Pat. No. 5,580,723 and Sambrook et al., Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor Laboratory Press, 1989. The skilled artisan then can test the population of mutagenized polypeptides for diminution and/or for retention of an activity. Other similar methods for creating and testing dominant negative variants of a protein will be apparent to one of ordinary skill in the art.
Inhibitors of the function of Rb also include Rb-binding polypeptides. As used herein “Rb-binding polypeptides” are polypeptides which bind to the retinoblastoma protein and inhibit its maintenance of cell cycle arrest, allowing sensory inner ear cells to re-enter the cell cycle, and preferably generate supporting cells and hair cells. Most preferably the hair cells that are generated are functional and differentiated and undergo little or no apoptotic activity. Preferred Rb-binding polypeptides are antibodies, such as monoclonal antibodies, including chimeric, human, or humanized antibodies; single chain antibodies or antigen-binding fragments, such as F(ab′)2, Fab, Fd, or Fv fragment; and intrabodies.
Antibodies and methods of their production are well known to those of ordinary skill in the art. As used herein, the term “antibody” means not only intact antibody molecules but also fragments of antibody molecules retaining specific binding ability. Such fragments are also well known in the art and are regularly employed both in vitro and in vivo. In particular, as used herein, the term “antibody” means not only intact immunoglobulin molecules but also the well-known active fragments F(ab′)2, and Fab.
According to one embodiment, the molecule is an intact soluble monoclonal antibody in an isolated form or in a pharmaceutical preparation. An intact soluble monoclonal antibody, as is well known in the art, is an assembly of polypeptide chains linked by disulfide bridges. Two principle polypeptide chains, referred to as the light chain and heavy chain, make up all major structural classes (isotypes) of antibody. Both heavy chains and light chains are further divided into subregions referred to as variable regions and constant regions. As used herein the term “monoclonal antibody” refers to a homogenous population of immunoglobulins which specifically bind to an epitope (i.e. antigenic determinant) , e.g., of pRb.
Significantly, as is well-known in the art, only a small portion of an antibody molecule, the paratope, is involved in the binding of the antibody to its epitope (see, in general, Clark, W. R. (1986) The Experimental Foundations of Modem Immunology Wiley & Sons, Inc., New York; Roitt, I. (1991) Essential Immunology, 7th Ed., Blackwell Scientific Publications, Oxford). The pFc′ and Fc regions of the antibody, for example, are effectors of the complement cascade but are not involved in antigen binding. An antibody from which the pFc′ region has been enzymatically cleaved, or which has been produced without the pFc′ region, designated an F(ab′)2 fragment, retains both of the antigen binding sites of an intact antibody. An isolated F(ab′)2 fragment is referred to as a bivalent monoclonal fragment because of its two antigen binding sites. Similarly, an antibody from which the Fc region has been enzymatically cleaved, or which has been produced without the Fc region, designated an Fab fragment, retains one of the antigen binding sites of an intact antibody molecule. Proceeding further, Fab fragments consist of a covalently bound antibody light chain and a portion of the antibody heavy chain denoted Fd (heavy chain variable region). The Fd fragments are the major determinant of antibody specificity (a single Fd fragment may be associated with up to ten different light chains without altering antibody specificity) and Fd fragments retain epitope-binding ability in isolation.
The terms Fab, Fc, pFc′, F(ab′)2 and Fv are used consistently with their standard immunological meanings [Klein, Immunology (John Wiley, New York, N.Y., 1982); Clark, W. R. (1986) The Experimental Foundations of Modern Immunology (Wiley & Sons, Inc., New York); Roitt, I. (1991) Essential Immunology, 7th Ed., (Blackwell Scientific Publications, Oxford)].
Therefore, antibodies of the invention may be single chain antibodies or may be single domain antibodies (intrabodies or intracellular antibodies). Intrabodies are generally known in the art as single chain Fv fragments with domains of the immunoglobulin heavy (VH) and light chains (VL). Well-known functionally active antibody fragments include but are not limited to F(ab′)2, Fab, Fv and Fd fragments of antibodies. These fragments which lack the Fc fragment of intact antibody, clear more rapidly from the circulation, and may have less non-specific tissue binding than an intact antibody (Wahl et al., J. Nuc. Med. 24:316-325 (1983)). For example, single-chain antibodies can be constructed in accordance with the methods described in U.S. Pat. No. 4,946,778 to Ladner et al. Such single-chain antibodies include the variable regions of the light and heavy chains joined by a flexible linker moiety. Methods for obtaining a single domain antibody (“Fd”) which comprises an isolated variable heavy chain single domain, also have been reported (see, for example, Ward et al., Nature 341:644-646 (1989), disclosing a method of screening to identify an antibody heavy chain variable region (VH single domain antibody) with sufficient affinity for its target epitope to bind thereto in isolated form). Methods for making recombinant Fv fragments based on known antibody heavy chain and light chain variable region sequences are known in the art and have been described, e.g., Moore et al., U.S. Pat. No. 4,462,334. Other references describing the use and generation of antibody fragments include e.g., Fab fragments (Tijssen, Practice and Theory of Enzyme Immunoassays (Elsevieer, Amsterdam, 1985)), Fv fragments (Hochman et al., Biochemistry 12: 1130 (1973); Sharon et al., Biochemistry 15: 1591 (1976); Ehrilch et al., U.S. Pat. No. 4,355,023) and portions of antibody molecules (Audilore-Hargreaves, U.S. Pat. No. 4,470,925). Thus, those skilled in the art may construct antibody fragments from various portions of intact antibodies without destroying the specificity of the antibodies for the their target, e.g., pRb.
As is well-known in the art, the complementarity determining regions (CDRs) of an antibody are the portions of the antibody which are largely responsible for antibody specificity. The CDRs directly interact with the epitope of the antigen. In both the heavy chain and the light chain variable regions of IgG immunoglobulins, there are four framework regions (FR1 through FR4) separated respectively by three complementarity determining regions (CDR1 through CDR3). The framework regions (FRs) maintain the tertiary structure of the paratope, which is the portion of the antibody which is involved in the interaction with the antigen. The CDRs, and in particular the CDR3 regions, and more particularly the heavy chain CDR3 contribute to antibody specificity. Because these CDR regions and in particular the CDR3 region confer antigen specificity on the antibody these regions may be incorporated into other antibodies or peptides to confer the identical specificity onto that antibody or molecule.
The molecule useful according to the methods of the present invention may be a human antibody (e.g., a human monoclonal antibody) or an intact humanized monoclonal antibody. A “humanized monoclonal antibody” as used herein is a monoclonal antibody or functionally active fragment thereof having human constant regions and an antigen-binding region (e.g., CDR3) from a mammal of a species other than a human. Humanized monoclonal antibodies may be made by any method known in the art. Humanized monoclonal antibodies, for example, may be constructed by replacing the non-CDR regions of a non-human mammalian antibody with similar regions of human antibodies while retaining the epitopic specificity of the original antibody. For example, non-human CDRs and optionally some of the framework regions may be covalently joined to human FR and/or Fc/pFc′ regions to produce a functional antibody. There are entities in the United States which will synthesize humanized antibodies from specific murine antibody regions commercially, such as Protein Design Labs (Mountain View Calif.). For instance, a humanized form of a murine anti-Rb antibody could be prepared and used according to the methods of the invention.
European Patent Application 0239400, the entire contents of which is hereby incorporated by reference, provides an exemplary teaching of the production and use of humanized monoclonal antibodies in which at least the CDR portion of a murine (or other non-human mammal) antibody is included in the humanized antibody. Briefly, the following methods are useful, as examples for constructing a humanized monoclonal antibody including at least a portion of a mouse CDR. A first replicable expression vector including a suitable promoter operably linked to a DNA sequence encoding a variable domain of an immunoglobulin (Ig) heavy or light chain and the variable domain comprising framework regions from an human antibody and a CDR region of a murine antibody is prepared. Optionally a second replicable expression vector is prepared which includes a suitable promoter operably linked to a DNA sequence encoding at least the variable domain of a complementary human Ig light or heavy chain, respectively. A cell line is then transformed with the vector(s). Preferably the cell line is an immortalized mammalian cell line of lymphoid origin, such as a myeloma, hybridoma, trioma, or quadroma cell line, or is a normal lymphoid cell which has been immortalized by transformation with a virus. The transformed cell line is then cultured under conditions known to those of skill in the art to produce the humanized antibody.
As set forth in European Patent Application 0239400 several techniques are well known in the art for creating the particular antibody domains to be inserted into the replicable vector. (Vectors and recombinant techniques are discussed in greater detail below.) For example, the DNA sequence encoding the domain may be prepared by oligonucleotide synthesis. Alternatively a synthetic gene lacking the CDR regions in which four framework regions are fused together with suitable restriction sites at the junctions, such that double stranded synthetic or restricted subcloned CDR cassettes with sticky ends could be ligated at the junctions of the framework regions. Another method involves the preparation of the DNA sequence encoding the variable CDR containing domain by oligonucleotide site-directed mutagenesis. Each of these methods is well known in the art. Therefore, those skilled in the art may construct humanized antibodies containing a murine CDR region without destroying the specificity of the antibody for its epitope.
Human monoclonal antibodies may be made by any of the methods known in the art, such as those disclosed in U.S. Pat. No. 5,567,610, issued to Borrebaeck et al., U.S. Pat. No. 5,565,354, issued to Ostberg, U.S. Pat. No. 5,571,893, issued to Baker et al, Kozber, J. Immunol. 133: 3001 (1984), Brodeur, et al., Monoclonal Antibody Production Techniques and Applications, p. 51-63 (Marcel Dekker, Inc, New York, 1987), and Boerner et al., J. Immunol., 147: 86-95 (1991). In addition to the conventional methods for preparing human monoclonal antibodies, such antibodies may also be prepared by immunizing transgenic animals that are capable of producing human antibodies (e.g., Jakobovits et al., PNAS USA, 90: 2551 (1993), Jakobovits et al., Nature, 362: 255-258 (1993), Bruggermann et al., Year in Immuno., 7:33 (1993) and U.S. Pat. No. 5,569,825 issued to Lonberg).
A pRb binding antibody can be used to identify pRb binding molecules. It is now routine to produce large numbers of molecules having inhibitory functions based on one or a few peptide sequences or sequence motifs. (See, e.g., Bromme, et al., Biochem. J. 315:85-89 (1996); Palmer, et al., J. Med. Chem. 38:3193-3196 (1995)). For example, an inhibitor of pRB-antibody interactions may be chosen or designed as a polypeptide or modified polypeptide having the same sequence as an Rb-binding portion of the antibody, or having structural similarity to such a sequence of the antibody. Thus, a plurality of these compounds chosen or designed may be produced, tested for inhibitory activity, and sequentially modified to optimize or alter activity, stability, and/or specificity.
The method is useful for designing a wide variety of biological mimics that are more stable than the natural counterpart, because they are typically prepared by the free radical polymerization of functional monomers, resulting in a compound with a non-biodegradable backbone. Thus, the created molecules would have the same binding properties as the anti-Rb antibody but be more stable in vivo, thus preventing Rb from interacting with components normally available in its native environment. Other methods for designing such molecules include, for example, drug design based on structure-activity relationships which require the synthesis and evaluation of a number of compounds and molecular modeling.
Binding molecules may also be identified by conventional screening methods, such as those described above. Additionally, Rb-binding molecules can be identified from combinatorial libraries. Many types of combinatorial libraries have been described. For instance, U.S. Pat. No. 5,712,171 (which describes methods for constructing arrays of synthetic molecular constructs by forming a plurality of molecular constructs having the scaffold backbone of the chemical molecule and modifying at least one location on the molecule in a logically-ordered array); U.S. Pat. No. 5,962,412 (which describes methods for making polymers having specific physiochemical properties); and U.S. Pat. No. 5,962,736 (which describes specific arrayed compounds).
By using the known anti-Rb monoclonal antibodies, it is also possible to produce anti-idiotypic antibodies which can be used to screen other antibodies to identify whether the antibody has the same binding specificity as the known monoclonal antibody. Such anti-idiotypic antibodies can be produced using well-known hybridoma techniques (Kohler and Milstein, Nature, 256:495, 1975). An anti-idiotypic antibody is an antibody which recognizes unique determinants present on the known monoclonal antibodies. These determinants are located in the hypervariable region of the antibody. It is this region which binds to a given epitope and, thus, is responsible for the specificity of the antibody. An anti-idiotypic antibody can be prepared by immunizing an animal with the known monoclonal antibodies. The immunized animal will recognize and respond to the idiotypic determinants of the immunizing known monoclonal antibodies and produce an antibody to these idiotypic determinants. By using the anti-idiotypic antibodies of the immunized animal, which are specific for the known monoclonal antibodies, it is possible to identify other clones with the same idiotype as the known monoclonal antibody used for immunization. Idiotypic identity between monoclonal antibodies of two cell lines demonstrates that the two monoclonal antibodies are the same with respect to their recognition of the same epitopic determinant. Thus, by using anti-idiotypic antibodies, it is possible to identify other hybridomas expressing monoclonal antibodies having the same epitopic specificity.
It is also possible to use the anti-idiotype technology to produce monoclonal antibodies which mimic an epitope. For example, an anti-idiotypic monoclonal antibody made to a first monoclonal antibody will have a binding domain in the hypervariable region which is the image of the epitope bound by the first monoclonal antibody.
Other Rb-binding molecules of the invention can be identified using routine assays, such as binding assays. The Rb-binding molecules of the invention are isolated molecules, e.g., isolated polypeptides. As used herein, with respect to Rb-binding molecules, “isolated” means molecules are substantially pure and are essentially free of other substances with which they may be found in nature or in vivo systems to an extent practical and appropriate for their intended use. In particular, the isolated molecules are sufficiently pure and are sufficiently free from other biological constituents of their hosts cells so as to be useful in, for example, producing pharmaceutical preparations. Because an isolated molecule of the invention may be admixed with a pharmaceutically acceptable carrier in a pharmaceutical preparation, the molecule may comprise only a small percentage by weight of the preparation. The molecule is nonetheless substantially pure in that it has been substantially separated from the substances with which it may be associated in living systems. The term isolated refers to molecules which are either naturally occurring or synthetic. Thus, in some embodiments the isolated molecules are derived from natural sources. The term “isolated” as used in conjunction with the other agents provided herein, has the same meaning.
In other embodiments the isolated molecules may be synthesized or produced by recombinant means by those of skill in the art. Methods for preparing or identifying molecules which bind to a particular target are well known in the art. Molecular imprinting, for instance, may be used for the de novo construction of macromolecular structures such as peptides which bind to a particular molecule. See for example Kenneth J. Shea, Molecular Imprinting of Synthetic Network Polymers: The De Novo synthesis of Macromolecular Binding and Catalytic Sites, TRIP Vol. 2, No. 5, May 1994; Klaus Mosbach, Molecular Imprinting, Trends in Biochem. Sci., 19(9) January 1994; and Wulff, G., in Polymeric Reagents and Catalysts (Ford, W. T., Ed.) ACS Symposium Series No. 308, pp 186-230, American Chemical Society (1986). One method for preparing mimics of Rb-binding molecules involves the steps of: (i) polymerization of functional monomers around a known Rb-binding peptide that exhibits a desired activity; (ii) removal of the template molecule; and then (iii) polymerization of a second class of monomers in the void left by the template, to provide a new molecule which exhibits one or more desired properties which are similar to that of the template. In addition to preparing peptides in this manner other Rb-binding molecules such as polysaccharides, nucleosides, drugs, nucleoproteins, lipoproteins, carbohydrates, glycoproteins, steroids, lipids, and other biologically active materials can also be prepared. This method is useful for designing a wide variety of biological mimics that are more stable than their natural counterparts, because they are typically prepared by the free radical polymerization of functional monomers, resulting in a compound with a nonbiodegradable backbone.
Molecules which bind to Rb may also be identified by conventional screening methods such as phage display procedures (e.g., methods described in Hart, et al., J. Biol. Chem. 269:12468 (1994)). Hart et al. report a filamentous phage display library for identifying novel peptide ligands for mammalian cell receptors. In general, phage display libraries using, e.g., M13 or fd phage, are prepared using conventional procedures such as those described in the foregoing reference. The libraries display inserts containing from 4 to 80 amino acid residues. The inserts optionally represent a completely degenerate or a biased array of peptides. Rb-binding molecules that bind selectively to Rb are obtained by selecting those phages which express on their surface a peptide that binds to Rb. These phages then are subjected to several cycles of reselection to identify the peptide ligand-expressing phages that have the most useful binding characteristics. Typically, phages that exhibit the best binding characteristics (e.g., highest affinity) are further characterized by nucleic acid analysis to identify the particular amino acid sequences of the peptides expressed on the phage surface and the optimum length of the expressed peptide to achieve optimum binding to Rb. Alternatively, such peptide ligands can be selected from combinatorial libraries of peptides containing one or more amino acids. Such libraries can further be synthesized which contain non-peptide synthetic moieties which are less subject to enzymatic degradation compared to their naturally-occurring counterparts.
Thus, according to another aspect of the invention, a method for optimizing a selected Rb-binding molecule for its ability to bind to Rb and/or inhibit its maintenance of cell cycle arrest is provided. “Optimizing” as used herein refers to an iterative process of introducing changes to an existing system or compound and evaluating the functional significance of each change, followed by selecting the resulting system or compound associated with a functional outcome that is most improved; these steps are repeated until a desired endpoint is achieved or it appears further changes will not improve the functional outcome. The sane objective can be achieved in a parallel manner by generating a library of closely related compounds and screening the library for the compound or compounds possessing the most favorable embodiment of the characteristic being optimized. In this particular instance, optimizing a selected Rb-binding molecule for Rb-binding activity involves testing a panel of structurally related Rb-binding molecules for their ability to bind to Rb. The screening method involves contacting at least one candidate optimized Rb-binding molecule selected from a group of candidate optimized Rb-binding molecules with Rb under conditions which, in the absence of a competitor, permit a reference Rb-binding molecule to bind or remain bound to Rb. The candidate optimized Rb-binding molecule is contacted with Rb before, after, or simultaneously with contact between the labeled reference Rb-binding molecule and Rb. The residual binding of the labeled reference Rb-binding molecule to Rb is then detected. Detection of a decrease in binding of the reference Rb-binding molecule indicates that the candidate optimized Rb-binding molecule interferes with the binding of the reference Rb-binding molecule to Rb. Candidate optimized Rb-binding molecules can be generated as members of a combinatorial library of compounds, for example using SELEX technology. Gold L et al. (1995) Annu Rev Biochem 64:763:797.
This assay can involve the separation of both unbound unlabeled candidate optimized Rb-binding molecules and unbound labeled reference Rb-binding molecules from the sample. The separation step can be accomplished in any way known in the art, in a manner similar to the separation method described above. Likewise, the detection of the remaining bound labeled reference Rb-binding molecule can be accomplished in any way known in the art, in a manner similar to the detection method described above.
The screening assay can also be performed as a competition between labeled candidate optimized Rb-binding molecules (e.g., anti-Rb antibodies or fragments thereof) and unlabeled reference Rb-binding molecules. In this format, binding of the labeled optimized Rb-binding molecule to Rb is then detected. Detection of bound optimized Rb-binding molecule indicates that the candidate optimized Rb-binding molecule interferes with the binding of the reference Rb-binding molecule to Rb.
The screening assay can also be performed by contacting labeled Rb to immobilized Rb-binding molecules. In this format a panel of candidate optimized Rb-binding molecules can be presented in an array fashion on a silicon chip or in a plastic multiwell microtiter or microarray plate. Alternatively, each candidate optimized Rb-binding molecule can be separately coupled to a bead, a resin, a filter, a slide, or a biomolecular interaction analysis (BIA) chip. After contacting Rb with the immobilized candidate Rb-binding molecules and, if indicated, washing away unbound Rb, detection of complexes formed between the immobilized Rb-binding molecule and Rb provides the basis for selecting particular Rb-binding molecules as optimized.
Other assays will be apparent to those of skill in the art, having read the present specification, which are useful for determining whether a Rb-binding molecule binds to Rb and also inhibits the maintenance of cell cycle arrest.
The invention further provides detectably labeled, immobilized and conjugated forms of Rb and the molecules for use in the methods of the invention, as well as fragments and functional equivalents thereof. The Rb-binding molecules of the invention may be labeled using radiolabels, fluorescent labels, enzyme labels, free radical labels, avidin-biotin labels, or bacteriophage labels, using techniques known to the art (Chard, Laboratory Techniques in Biology, “An Introduction to Radioimmunoassay and Related Techniques,” North Holland Publishing Company (1978).
Typical fluorescent labels include fluorescein isothiocyanate, rhodamine, phycoerythrin, phycocyanin, allophycocyanin, and fluorescamine.
Typical chemiluminescent compounds include luminol, isoluminol, aromatic acridinium esters, imidazoles, and the oxalate esters.
Typical bioluminescent compounds include luciferin, and luciferase. Typical enzymes include alkaline phosphatase, β-galactosidase, glucose-6-phosphate dehydrogenase, maleate dehydrogenase, glucose oxidase, and peroxidase.
In some embodiments the Rb-binding molecule are functional equivalents of the Rb-binding molecules provided herein, e.g., anti-Rb antibodies or fragments thereof. Functional equivalents, therefore include Rb-binding polypeptides e.g., anti-Rb antibodies or fragments thereof which are different because they comprise conservative substitutions within their amino acid sequence. As used herein, “conservative substitution” refers to an amino acid substitution which does not alter the relative charge or size characteristics of the peptide in which the amino acid substitution is made. Conservative substitutions of amino acids include substitutions made amongst amino acids with the following groups: (1) M, I, L, V; (2) F, Y, W; (3) K, R, H; (4) A, G; (5) S, T; (6) Q, N; and, (7) E, D. Such substitutions can be made by a variety of methods known to one of ordinary skill in the art. For example, amino-acid substitutions may be made by PCR-directed mutation, site-directed mutagenesis according to the method of Kunkel (Kunkel, Proc. Nat. Acad. Sci. U.S.A. 82: 488-492, 1985), or by chemical synthesis of a gene. These and other methods are known to those of ordinary skill in the art and may be found in references which compile such methods, e.g. Sambrook. et al., Molecular Cloning: A Laboratory Manual, 2nd edition, Cold Spring Harbor Laboratory Press, 1989. The activity of functionally equivalent variants of the agents of the invention can be tested by the binding and activity assays discussed herein.
The invention, in one aspect, also permits the reduction or elimination of Rb expression level or function by the construction of Rb gene “knock-outs” or “knock-downs” in cells and in animals, providing materials for treating and studying certain aspects of hearing cell damage and its regeneration. For example, a knock-out mouse (gene disruption) or a knock-down mouse (reduced gene expression by e.g., siRNA) may be constructed and examined for clinical studies of hair cell regeneration.
Hearing research has been greatly hindered by the lack of hair cell or supporting cell lines for in vitro characterization. The proliferative capacity of progenitor cells, differentiated hair cells and supporting cells provides an excellent opportunity to create such cell lines. The diverse properties of hair cells, such as vestibular and auditory hair cells, can therefore be characterized in vitro. Manipulating Rb expression level and/or function allows the sensory epithelial cells to be cultured in large numbers in vitro indefinitely (normal hair cells cannot divide and be maintained indefinitely in a culture system). It is, therefore, now possible to establish cell lines with hair cell and/or supporting cell characteristics.
Such cell lines are provided herein. The cell lines can either be established using the sensory epithelial cells in which Rb has been deleted, or using the cells in which Rb is inhibited by reducing or eliminating the expression level or function of Rb as described herein. Sensory epithelial cells, such as progenitor, supporting or hair cells, can be isolated from a subject by the disaggregation of inner ear tissue, and forming cell suspensions. Disaggregation of a tissue or a population of cells can be readily accomplished using techniques known to those skilled in the art. For example, the tissue can be disaggregated mechanically and/or treated with digestive enzymes and/or chelating agents that weaken the connections between neighboring cells, making it possible to disperse the tissue into a suspension of individual cells without appreciable cell breakage. Enzymatic dissociation can be accomplished by mincing the tissue and treating the minced tissue with any of a number of digestive enzymes either alone or in combination. These include but are not limited to trypsin, chymotrypsin, collagenase, elastase, and/or hyaluronidase, DNase, pronase, dispase, etc. Mechanical disruption can also be accomplished by a number of methods including, but not limited to, the use of grinders, blenders, sieves, homogenizers, pressure cells, or insonators to name but a few. For a review of tissue disaggregation techniques, see Freshney, Culture of Animal Cells, A Manual of Basic Techniques, 2d Ed., A. R. Liss, Inc., New York, 1987, Ch. 9, pp. 107-126.
Once the tissue has been reduced to a suspension of individual cells, the suspension optionally can be fractionated into subpopulations from which the desired cells can be obtained. This may be accomplished using standard techniques for cell separation including, but not limited to, cloning and selection of specific cell types, selective destruction of unwanted cells (negative selection), separation based upon differential cell agglutinability in the mixed population, freeze-thaw procedures, differential adherence properties of the cells in the mixed population, filtration, conventional and zonal centrifugation, centrifugal elutriation (counter-streaming centrifugation), unit gravity separation, countercurrent distribution, electrophoresis and fluorescence-activated cell sorting. For a review of clonal selection and cell separation techniques, see Freshney, Culture of Animal Cells, A Manual of Basic Techniques, 2d Ed., A. R. Liss, Inc., New York, 1987, Ch. 11 and 12, pp. 137-168.
Cells can be cultured in an appropriate nutrient medium under conditions that are metabolically favorable for the growth of the cells. As used herein, the phrase “metabolically favorable conditions” refers to conditions that maintain cell viability. Such conditions include growth in nutrient medium at 37° C. in a 5% CO2 incubator with greater than 90% humidity. Many commercially available media, such as RPMI 1640, Fisher's, Iscove's, McCoy's, Dulbecco's Modified Eagle's Medium, etc., and the like, which may or may not be supplemented with serum, may be suitable for use as nutrient medium. Antibiotics such as penicillin may also be included. Fungizone may also be used. In preferred embodiments, the sensory epithelial inner ear cells are cultured first, for a brief period of time in the presence of 10% serum. The medium is then changed to a serum-free medium in order to minimize the number of extraneous agents present in the medium under continuous culture. In general, these cell suspensions can be cultured according to standard cell culture techniques. In small scale, the cultures can be contained in culture plates, flasks, and dishes. In larger scale, the cultures can be contained in roller bottles, spinner flasks and other large scale culture vessels such as fermenters. Culturing in a three-dimensional, porous, solid matrix may also be used.
The cell lines cultures can be used to screen for further targets related to hair cell and/or supporting cell regeneration and protection and the compounds which act on the targets, and to characterize genes and proteins participating in the Rb pathway. Methods, therefore, are provided to study the functions of the progenitor cells, hair cells and the supporting cells. Progenitor or supporting cell lines can also be used to screen for compounds which can induce progenitor or supporting cells to become hair cells. These screening methods are, therefore, provided herein. An example of such a method comprises the steps of contacting a sample containing progenitor, supporting or hair cells with a candidate compound and determining if the candidate compound causes the desired effect (e.g., if the candidate compound causes generation, regeneration or protection of the progenitor, supporting or hair cells or if the candidate compound induces progenitor or supporting cells to become hair cells, in particular functional and differentiated hair cells.) In some embodiments, the use of explanted organ culture of the inner ear tissues are provided. The explanted culture has similar properties as the cell lines and, therefore, can be used for all the purposes mentioned for the cell lines.
As used herein, a “vector” may be any of a number of nucleic acids into which a desired sequence may be inserted by restriction and ligation for transport between different genetic environments or for expression in a host cell. Vectors are typically composed of DNA although RNA vectors are also available. Vectors include, but are not limited to, plasmids and phagemids. A cloning vector is one which is able to replicate in a host cell, and which is further characterized by one or more endonuclease restriction sites at which the vector may be cut in a determinable fashion and into which a desired DNA sequence may be ligated such that the new recombinant vector retains its ability to replicate in the host cell. In the case of plasmids, replication of the desired sequence may occur many times as the plasmid increases in copy number within the host bacterium or just a single time per host before the host reproduces by mitosis. In the case of phage, replication may occur actively during a lytic phase or passively during a lysogenic phase. An expression vector is one into which a desired DNA sequence may be inserted by restriction and ligation such that it is operably joined to regulatory sequences and may be expressed as an RNA transcript. Vectors may further contain one or more marker sequences suitable for use in the identification of cells which have or have not been transformed or transfected with the vector. Markers include, for example, genes encoding proteins which increase or decrease either resistance or sensitivity to antibiotics or other compounds, genes which encode enzymes whose activities are detectable by standard assays known in the art (e.g., B-galactosidase or alkaline phosphatase), and genes which visibly affect the phenotype of transformed or transfected cells, hosts, colonies or plaques. Preferred vectors are those capable of autonomous replication and expression of the structural gene products present in the DNA segments to which they are operably joined.
As used herein, a coding sequence and regulatory sequences are said to be “operably joined” when they are covalently linked in such a way as to place the expression or transcription of the coding sequence under the influence or control of the regulatory sequences. As used herein, “operably joined” and “operably linked” are used interchangeably and should be construed to have the same meaning. If it is desired that the coding sequences be translated into a functional protein, two DNA sequences are said to be operably joined if induction of a promoter in the 5′ regulatory sequences results in the transcription of the coding sequence and if the nature of the linkage between the two DNA sequences does not (1) result in the introduction of a frame-shift mutation, (2) interfere with the ability of the promoter region to direct the transcription of the coding sequences, or (3) interfere with the ability of the corresponding RNA transcript to be translated into a protein. Thus, a promoter region is operably joined to a coding sequence if the promoter region is capable of effecting transcription of that DNA sequence such that the resulting transcript can be translated into the desired protein or polypeptide.
The precise nature of the regulatory sequences needed for gene expression may vary between species or cell types, but shall in general include, as necessary, 5′ non-transcribed and 5′ non-translated sequences involved with the initiation of transcription and translation respectively, such as a TATA box, capping sequence, CAAT sequence, and the like. Often, such 5′ non-transcribed regulatory sequences will include a promoter region which includes a promoter sequence for transcriptional control of the operably joined gene. Regulatory sequences may also include enhancer sequences or upstream activator sequences as desired. The vectors of the invention may optionally include 5′ leader or signal sequences. The choice and design of an appropriate vector is within the ability and discretion of one of ordinary skill in the art.
It will also be recognized that the invention embraces the use of the retinoblastoma (e.g., retinoblastoma inhibitory) nucleic acid molecules and genomic sequences in expression vectors, as well as to transfect host cells and cell lines, be these prokaryotic, e.g., E. coli, or eukaryotic, e.g., CHO cells, COS cells, yeast expression systems, and recombinant baculovirus expression in insect cells. Especially useful are mammalian cells such as human, mouse, hamster, pig, goat, primate, etc. They may be of a wide variety of tissue types, including mast cells, fibroblasts, oocytes, and lymphocytes, and may be primary cells and cell lines. The expression vectors require that the pertinent sequence, i.e., those nucleic acids described supra, be operably linked to a promoter.
The invention, in one aspect, also permits the construction of retinoblatoma gene “knock-outs” and “knock-ins” in cells and in animals, providing materials for studying hair cell generation and regeneration as well as hearing damage and loss.
Expression vectors containing all the necessary elements for expression are commercially available and known to those skilled in the art. See, e.g., Sambrook et al., Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor Laboratory Press, 1989. Cells are genetically engineered by the introduction into the cells of heterologous DNA or RNA encoding a retinoblastoma inhibitory nucleic acid, a mutant, fragment, or variant thereof. As used herein a “retinoblastoma inhibitory nucleic acid” is any nucleic acid that can be used to produce an agent that reduces or eliminates the expression or function of at least one retinoblastoma gene and/or protein. These nucleic acids include, for example, nucleic acids that are used to produce nucleic acids that can inhibit the transcription or translation of a retinoblastoma gene. In addition, nucleic acids that encode a protein that can inhibit retinoblastoma function are also included. For instance, the nucleic acid can encode a Rb-binding polypeptide. The heterologous DNA or RNA is placed under operable control of transcriptional elements to permit the expression of the heterologous DNA in the host cell.
Preferred systems for mRNA expression in mammalian cells are those such as pcDNA/V5-GW/D-TOPO® and pcDNA3.1 (Invitrogen) that contain a selectable marker (which facilitates the selection of stably transfected cell lines) and contain the human cytomegalovirus (CMV) enhancer-promoter sequences. Additionally, suitable for expression in primate or canine cell lines is the pCEP4 vector (Invitrogen), which contains an Epstein Barr virus (EBV) origin of replication, facilitating the maintenance of plasmid as a multicopy extrachromosomal element. Another expression vector is the pEF-BOS plasmid containing the promoter of polypeptide Elongation Factor 1, which stimulates efficiently transcription in vitro. The plasmid is described by Mizushima and Nagata (Nuc. Acids Res. 18:5322, 1990), and its use in transfection experiments is disclosed by, for example, Demoulin (Mol. Cell. Biol. 16:4710-4716, 1996). Still another preferred expression vector is an adenovirus, described by Stratford-Perricaudet, which is defective for E1 and E3 proteins (J. Clin. Invest. 90:626-630, 1992). The use of the adenovirus as an eAdeno.P1A recombinant is described by Warnier et al., in intradermal injection in mice for immunization against P1A (Int. J. Cancer, 67:303-310, 1996).
The Rb-binding polypeptides of the present invention may also, of course, be produced by eukaryotic cells such as CHO cells, human hybridomas, immortalized B-lymphoblastoid cells, and the like. In this case, a vector is constructed in which eukaryotic regulatory sequences are operably joined to the nucleotide sequences encoding the peptide. The design and selection of an appropriate eukaryotic vector is within the ability and discretion of one of ordinary skill in the art. The subsequent purification of the peptides may be accomplished by any of a variety of standard means known in the art.
In another embodiment, the present invention provides host cells, both prokaryotic and eukaryotic, transformed or transfected with, and therefore including, the vectors of the present invention.
According to the methods of the invention, the compositions may be administered in a pharmaceutically acceptable composition. In general, pharmaceutically-acceptable carriers for peptides and structurally-related small molecules are well-known to those of ordinary skill in the art. As used herein, a pharmaceutically-acceptable carrier means a non-toxic material that does not interfere with the effectiveness of the biological activity of the active ingredients, i.e., the ability of an agent, such as a Rb-binding molecule, to generate or regenerate hair cells of the inner ear, preferably to restore hearing or damage. Pharmaceutically acceptable carriers include diluents, fillers, salts, buffers, stabilizers, solubilizers and other materials which are well-known in the art. Exemplary pharmaceutically acceptable carriers for peptides in particular are described in U.S. Pat. No. 5,211,657. The compositions of the invention may be formulated into preparations in solid, semi-solid, liquid or gaseous forms such as tablets, capsules, powders, granules, ointments, solutions, depositories, inhalants (e.g., aerosols) and injections, and usual ways for oral, parenteral or surgical administration. The invention also embraces locally administering the compositions of the invention, including as implants.
According to the methods of the invention the compositions (of the agents or cells provided herein) can be administered directly to the inner ear of a subject. In some embodiments the compositions provided herein can be administered by injection by gradual infusion over time or by any other medically acceptable mode. The administration may, for example, be intravenous, intraperitoneal, intramuscular, intracavity, subcutaneous or transdermal. Preparations for parenteral administration includes sterile aqueous or nonaqueous solutions, suspensions and emulsions. Examples of nonaqueous solvents are propylene glycol, polyethylene glycol, vegetable oil such as olive oil, an injectable organic esters such as ethyloliate. Aqueous carriers include water, alcoholic/aqueous solutions, emulsions or suspensions, including saline and buffered media. Parenteral vehicles include sodium chloride solution, Ringer's dextrose, dextrose and sodium chloride, lactated Ringer's or fixed oils. Intravenous vehicles include fluid and nutrient replenishers, electrolyte replenishers, (such as those based on Ringer's dextrose), and the like. Preservatives and other additives may also be present such as, for example, antimicrobials, antioxidants, chelating agents, and inert gases and the like. Those of skill in the art can readily determine the various parameters for preparing these alternative pharmaceutical compositions without resort to undue experimentation.
The compositions of the invention are administered in therapeutically effective amounts. As used herein, an “effective amount” of the invention is a dosage which is sufficient to generate or regenerate progenitor cells, supporting cells and/or hair cells or to treat or prevent hearing damage and/or loss of balance. Preferably an effective amount of an agent is an effective amount for regenerating supporting and/or hair cells and restoring hearing or balance. Generally, a therapeutically effective amount may vary with the subject's age, condition, and sex, as well as the extent of the disease in the subject and can be determined by one of skill in the art. The dosage may be adjusted by the individual physician or veterinarian in the event of any complication. A therapeutically effective amount typically will vary from about 0.01 mg/kg to about 500 mg/kg, were typically from about 0.1 mg/kg to about 200 mg/kg, and often from about 0.2 mg/kg to about 20 mg/kg, in one or more dose administrations daily, for one or several days (depending of course of the mode of administration and the factors discussed above). For administering inner ear sensory cells, as provided herein, the dosage and administration regimen can also be determined by one of skill in the art. In general, the amount of cells that can be administered for the desired effect can be on the order of 102-104 or more cells, in one or more dose administrations. In one example, approximately 102 cells can be administered. In other examples approximately 103 or 104 cells can be administered.
The present invention is further illustrated by the following Examples, which in no way should be construed as further limiting. The entire contents of all of the references (including literature references, issued patents, published patent applications, and co-pending patent applications) cited throughout this application are hereby expressly incorporated by reference.
Isolation of utricular sensory epithelia
Timed-pregnant CbA/CaJ mice at various gestation stages (E14.5, E15.5, E17.5, P0, P2, P6 and P12) were anesthetized with CO2, their peritoneal cavity opened and the uterus removed and placed in cold DMEM/F12. Following isolation of embryos from the uterus, each embryo was decapitated and the utricles dissected from the temporal bone. The membranous roof of each utricle, the otoconia, and the otolithic membrane were removed (otoconia and otolithic membranes were present at E15.5, but not earlier). The utricles from each mouse were stored in RNAlater solution (Ambion, Houston, Tex.) in individual tubes at 4° C. An average of 40 utricles were used for each stage.
To separate the utricle epithelial sheets from the underlying basement membrane, utricles were incubated for one hour at 37° C. in a DMEM/F12 solution containing 500 μg/ml thermolysin (Sigma, St. Louis, Mo.). At the end of this incubation period, the utricles were transferred to an ice-cold solution of DMEM/F12/BSA without thermolysin. The sensory epithelia were delaminated from the underlying non-sensory tissue by the use of fine forceps.
Mouse utricle preparation
Semi-intact preparations of the mouse utricle were made as described previously (J. R. Holt, D. P. Corey, R. A. Eatock, J Neurosci 17, 8739 (1997); A. Rusch, R. A. Eatock, Ann NY Acad Sci 781, 71 (1996)). Temporal bones were removed from Col1A1-pRb+/− and Col1A1-pRb−/− embryos at E18.5. The utricles were exposed and bathed in standard extracellular solution containing 100 μg/ml protease type XXIV (Sigma, St. Louis, Mo.) for 20 minutes at room temperature to facilitate removal of the otolithic membrane. Extracellular solution contained (in mM): 144 NaCl, 0.7 NaH2PO4, 5.8 KCl, 1.3 CaCl2, 0.9 MgCl2, 5.6 D-glucose, 10 HEPES-NaOH, vitamins and minerals as in Eagle's MEM; pH 7.4, ˜320 mmol/kg.
GeneChip analysis of developing utricle
The extraction of total RNA, synthesis of cRNA, GeneChip hybridization and scanning were as described (Chen and Corey, 2002). The Microarray Analysis Suite V5 (MAS5, Affymetrix, Santa Clara, Calif.) was used to analyze the data. The data was then exported to an Excel file to be further analyzed with GeneSpring (Silicon Genetics, Redwood City, Calif.).
Using GeneSpring, MAS5 data was normalized before being further filtered by P (presence), M (marginal) and A (absence) and by fold change. Only the genes, classified as P or M, and with a 2-fold expression change in at least one of the conditions, were used for cluster analysis. The inclusion of non-ear samples such as from the heart and retina as well as cell lines served to identify the genes enriched in the utricle. Best K-mean was used to identify the number of clusters with the highest explained variability. K-mean analysis classified the genes into 15 clusters. Using the GO (Gene Ontology) classification, the cell cycle regulators were assigned to different clusters. To identify the genes primarily expressed in the sensory epithelium, RMA (robust multi-array average) (Irizarry et al., 2003) (http://www.bioconductor.org) was used to normalize all the data. The genes derived from the sensory epithelium, the stroma, or likely induced by thermolysin treatment were identified.
Analysis of pRb−/− conditional mice
Rbloxp/loxp mice, with the Rb1 exon 19 flanked by loxP sites (provided by Dr. Anton Berns, Netherlands Cancer Institute, Amsterdam, The Netherlands), were crossed with Rbloxp/+-cre mice (Collagen1A1-cre mice (Col-cre; provided by Dr. Barbara Kream, University of Connecticut Health Center, Farmington Conn.)) (F. Liu et al., Int J Dev Biol 48, 645 (2004)) to produce Col1A1-Rb−/− embryos (pRb−/− embryos). The genotyping of embryos was as described (Dr. Phil Hinds, Tufts University, Boston, Mass., personal communication and (R. Dacquin, M. Starbuck, T. Schinke, G. Karsenty, Dev Dyn 224, 245 (2002)). All animal work was conducted using procedures reviewed and approved by the institutional animal care and use committee of Massachusetts General Hospital, and were conducted in accordance with the NIH Guide for the Care and Use of Laboratory Research Animals.
BrdU labeling
Timed pregnant mice at E13.5 and E16.5 were injected with 5-bromo-2-deoxyuridine (BrdU, Sigma) (prepared in 1×PBS, pH 7.0). For E13.5 pregnant mice the injection was done once for 4 hours before the embryos were harvested, and for E16.5 pregnant mice the injection was done twice at 6-hour interval, and the embryos were harvested at E18.5. The final concentration was 50 μg BrdU per gram of body weight. The mice were sacrificed at E18.5, and the inner ear tissues were harvested and fixed with fresh 4% paraformaldehyde in PBS.
Immunohistochemistry
Frozen sections of the inner ear tissues were prepared for immunolabeling. Inner ear slides were dried for 15 minutes at 37° C. and rehydrated in 1×PBS for 5 minutes. Then the sections were subjected to an antigen unmasking treatment using the Antigen Unmasking Solution (Vector laboratories, Burlingame, Calif., Cat#h-3300), according to the protocol provided by the manufacturer. For the slides used for DAB staining, endogenous peroxidase was quenched with 1.5% H2O2 in methanol for 10 minutes then washed twice in 1×PBS. The blocking, primary antibody and second primary antibody incubation followed the standard protocol (Harlow and Lane, Using Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory Press, 1999). The secondary antibodies were anti-rabbit Alexa 594 and/or anti-mouse Alexa 488 for fluorescent labeling (Molecular Probes, Eugene, Oreg.) and anti-rabbit Biotinylated (Vector Laboratories, Burlingame, Calif.). Data visualization and acquisition were performed using a regular fluorescent microscope (Zeiss Axioscope 2) or a confocal microscope (Biorad, Hercules, Calif.).
Other reagents used were the following: DAPI and rhodamine-phalloidin (Molecular Probes, Eugene, Oreg.); anti-Rb (Pharmingen, San Diego, Calif.); anti-Math1 (provided by Dr. J. Johnson, University of Texas Southwestern Medical Center, Dallas, Tex.), anti-Brn-3.1 (provided by Dr. M Xiang, UMDNJ-Robert Wood Johnson Medical School, Piscataway, N.J.), anti-myo7a (Dr. T. Hasson, University of San Diego, San Diego, Calif.); anti-espin (provided by Dr. S. Heller, Massachusetts Eye and Ear Infirmary, Boston, Mass.); anti-Lhx3, -Isl-1 (DSHB, University of Iowa, Iowa City, Iowa); anti-BrdU (Accurate Chemical, Westbury, N.Y.); anti-p27kip1 (LabVision Corp., Fremont, Calif.); anti-p130 (Santa Cruz Biotech., Santa Cruz, Calif.); anti-p75ntr (Chemicon International, Temecula, Calif.); anti-Ptprq (provided by Dr. D. F. Bowen-Pope, University of Washington, Seattle, Wash.); anti-activated caspase 3 (R&D Research Systems, Minneapolis, Minn.); anti-tubulin (Sigma); anti-S100A1 (LabVision Corp.); anti-synaptophysin (provided by Dr. Jeff Macklis, Massachusetts General Hospital and Harvard Medical School, Boston Mass. 02114).
In situ analysis
Primers specific for each gene, with built-in T7 and SP6 promoter sequences, were used to amplify cDNA fragments from the inner ear cDNA pool. The PCR products were sequenced to ensure that the right genes were amplified. After purification, 1 μg of DNA template was used for making antisense and sense riboprobes, respectively, using the digoxigenin RNA labeling kit (SP6/T7) (Roche Diagnostics, Nutley, N.J.). Synthesis of the riboprobes was performed following the manufacturer's protocol.
Cryosectioned slides containing the inner ear tissues were used for in situ hybridization. The protocol for in situ hybridization was similar to what has been described previously with minor modifications (Birren et al., 1993; Tiveron et al., 1996). Briefly, thawed sections were fixed in 4% paraformaldehyde for 15 min at room temperature followed by a brief wash in PBS. The sections were then treated with Proteinase K (10 μg/ml) for 10 min followed by fixation in 4% paraformaldehyde for 15 min at room temperature. The slides were treated with 100 mM triethanolamine, pH 8.0, acetylated for 10 min at room temperature by adding dropwise acetic anhydride (0.25% final concentration) while being rocked, and washed with PBS. The slides were prehybridized for 1 hr with hybridization solution (50% formamide, 5×SSC, 1×Denhardt's, 0.1 mg/ml heparin, 0.3 mg/ml yeast RNA, 0.1% Tween 20, 5 mM EDTA) in plastic slide mailers. Hybridizations were carried out at 65° C. for 12-16 hours with the same solution in the presence of 1-2 μg/ml of probe. The slides were washed in 2×SSC at 65° C. for 15 min, then treated with 1 μg/ml RNase A at 37° C. for 30 min, followed by wash in 2×SSC and 0.2×SSC twice. The final washes included twice in 0.2×SSC for 30 min at 65° C. followed by in PBT at room temperature for 20 min.
For the labeling, slides were blocked for 1 hr at room temperature in PBT with 10% heat-inactivated sheep serum and incubated for 1.5 hr at room temperature with alkaline phosphatase-coupled anti-DIG antibody (Roche) diluted 1:2000 in PBT with 1% heat-inactivated sheep serum. The slides were washed for 5 min in AP buffer (100 mM Tris, pH 9.5, 100 mM NaCl, 50 mM MgCl2, 0.1% Tween 20) and equilibrated for 5 min in AP buffer with 5 mM Levamisol (Sigma) to block endogenous phosphatase activity. The signals were visualized by a color reaction using the NBT/BCIP reagents (NEN Life Science, Boston, Mass.). The color reaction was allowed to develop in the dark at room temperature and stopped with PBS.
FM1-43
To determine if the newly generated hair cells in the Rb−/− mice were functional, the uptake of FM1-43 with fluorescent microscopy was measured after applying FM1-43 (5 μm) to the medium bathing freshly dissected E18.5 Rb+/− and Rb−/− utricles (E18.5 Col1A1-pRb+/− and Col1A1-pRb−/− utricles) for 4 minutes or 1 minute at room temperature. Dye that partitioned into the outer leaflet of the membrane was subsequently washed out with fresh bath replacements. The samples were visualized and reordered using DIC (Gale et al., 2001; Geleoc and Holt, 2003; Meyers et al., 2003) and fluorescence microscopy with identical settings for control and pRb−/− utricles.
Patch Clamping
Semi-intact preparations of the mouse utricle were made as described previously (Holt et al., 1997; Rusch and Eatock, 1996). The utricles were bathed in standard extracellular solution containing 100 μg/ml protease type XXIV (Sigma, St. Louis, Mo.) for 20 minutes at room temperature (22-25° C.) to facilitate removal of the otolithic membrane.
Extracellular solution contained (in mM): 144 NaCl, 0.7 NaH2PO4, 5.8 KCl, 1.3 CaCl2, 0.9 MgCl2, 5.6 D-glucose, 10 HEPES-NaOH, vitamins and minerals as in Eagle's MEM; pH 7.4, ˜320 mmol/kg. Recording pipettes contained (in mM): 140 KCl, 0.1 CaCl2, 10 EGTA-KOH, 3.5 MgCl2, 2.5 Na2ATP, 5 HEPES-KOH, 0.1 Li-GTP, 0.1 Na-cAMP; pH 7.4, ˜290 mmol/kg.
Recording pipettes were pulled from R6 glass (Garner Glass, Claremont, Calif.) and had resistances in standard solutions of 4-5 M{tilde over (•)}. Recording pipettes contained (in mM): 140 KCl, 0.1 CaCl2, 10 EGTA-KOH, 3.5 MgCl2, 2.5 Na2ATP, 5 HEPES-KOH, 0.1 Li-GTP, 0.1 Na-cAMP; pH 7.4, ˜290 mmol/kg. Transduction currents were recorded in the whole-cell ruptured-patch mode with an Axopatch 200B amplifier (Axon Instruments, Union City, Calif.). Hair cells were voltage clamped at −64 mV. Transduction currents were low-pass-filtered at a corner frequency, fc, of 1-5 kHz (8-pole Bessel filter) and digitized >2×fc with a 12-bit data acquisition board (Digidata 1200, Axon Instruments) and stored on disk. Analysis was done with Origin 6.0 (Microcal Software, Northampton, Mass.).
Transduction currents were elicited by hair bundle displacements effected with a stiff probe. Glass pipettes were pulled to a final diameter of 1-2 μm and mounted on a piezoelectric bimorph (Corey and Hudspeth, 1980). The stimulus probe was driven by voltage protocols generated with pClamp 8.0 and the Digidata 1200 and low-pass-filtered by an 8-pole Bessel filter (Model 3382, Krohn-Hite, Brockton, Mass.), with fc below the probe's resonant frequency. Probe displacement as a function of applied voltage was calibrated off-line from videotaped images.
Adenovirus infection of culture utricles
Whole utricles from E17.5 and P10 flox-P-Rb mice were dissected and cultured in the medium as described (J. R. Holt et al., J Neurophysiol 81, 1881 (1999)). Hair cells are postmitotic at both stages and highly mature at P10 (A. Rusch, A. Lysakowski, R. A. Eatock, J Neurosci 18, 7487 (1998)). One day after culture, adenovirus-Cre/GFP and control adenovirus-GFP (obtained from Gene Transfer Vector Core, University of Iowa, Iowa City, Iowa) was added to the culture at a titer of 108 pfu/ml, respectively. 24 hours after virus infection, the medium was replaced with fresh medium supplemented BrdU (3 μg/ml) and the cultures were continued for 9 days. The medium was changed twice during the 9-day period. The utricles were subsequently fixed and cryosectioned as described. In general adenovirus-GFP had a higher infection rate than adenovirus-Cre/GFP, and a much higher infection rate was observed for E17.5 utricles than for P10 utricles.
To identify cell cycle regulators with potential roles in hair cell development GeneChip analysis was used to study the gene expression patterns of the developing mouse utricle. The whole utricle is a relatively simple sensory organ, consisting of the hair cells, the supporting cells and the stromal tissues (
The murine 6.5k chipset with ˜6500 genes and ESTs was used for hybridization. The data were first generated using MAS5 and then were further analyzed with K-mean cluster using GeneSpring (Silicon Genetics) to identify the genes with coregulation during development. RMA was used to compare the expression of the thermolysin treated samples to the whole utricles, and the genes primarily expressed in the sensory epithelia (for instance myosin VI and Math1) and the stroma (Norrie gene and peripheral myelin protein) were identified (
Using GO classification all the cell cycle regulators (144 in total) that passed the data filtering were first identified. 81 cell cycle regulators were identified (i.e. the genes expressed in at least one of the samples with an expression level that changed over 2-fold in at least one of the conditions). By K-mean analysis they were clustered into 15 groups (
Many negative cell growth regulators were identified in clusters 11 and 12. Cluster 11 included many genes that are upregulated during development such as Max interacting protein 1 (Mxi1) and Cdk4 inhibitor p19 (p19ink4d), whereas cluster 12 contained the genes with consistent expression throughout development including retinoblastoma and growth arrest specific protein 1 (gas1). In total, 13 genes known to be negative cell cycle regulators are in the two clusters (Table 1), and with the exception of p19ink4d, most of these genes have not been characterized in the inner ear. Taken together this group of cell cycle regulator genes represents the potential candidates in controlling growth arrest in the developing utricle.
To provide further evidence to show that the genes from the thermolysin treated samples were indeed of sensory epithelia origin, the expression of a selected group of the cell cycle regulators were studied in the inner ear using in situ hybridization. All the genes tested, including Jun-B, Abelson murine leukemia oncogene (Abl1) and Max interacting protein Mxi1, were expressed in the sensory epithelium, in particular in hair cells (
The retinoblastoma gene (Rb) is expressed in the sensory epithelial cells of the mouse inner ear
Of the negative cell growth genes the retinoblastoma family members showed interesting expression patterns: Rb1 maintained a constant level of expression throughout development, Rbl1 (p107) showed downregulation whereas Rbl2 (p130) exhibited upregulation during development (
Using both GeneChip and immunohistochemistry, the retinoblastoma gene (Rb) was detected in the sensory epithelial cells including the hair cells and the supporting cells, in the developing mouse inner ear. The GeneChip analysis of the expression of the Rb family members in the developing utricle correlates with the current understanding of their roles during the cell cycle, i.e. the level of p107 is highest between G1-S phase and the p130 level is highest during G0-G1 phase (
Using immunostaining, pRb was detected at an early stage of development. At E12.5 the expression of pRb was detected ubiquitously in the otocyst at a moderate level (
The expression pattern of the Rb family members, therefore, strongly suggested their potential roles in inner ear development, in particular the sensory epithelial cells. As a first step to comprehensively characterizing their inner ear functions, conditional Rb knockout mice were studied.
Rb is known to suppress the function of the E2f family, especially E2f1-E2f3. p130 and p107 are thought to participate in the Rb pathway (Classon and Dyson, 2001). The expression of p130 or E2f5 is not altered in the pRb−/− inner ear sensory cells. It has also been shown that in general p107 will be upregulated when pRb is deleted, to compensate for pRb function (Berns, 2003). Given the distinct expression pattern of p107 during utricle development it is likely that p107 will participate in a compensatory mechanism after loss of Rb. It is unlikely, however, that any change in p107 expression is adequate to compensate for the loss of pRb function, as demonstrated by continuous hair cell and supporting cell division.
Rb conditional knockout mice
Since germline Rb1 knockout mice are embryonic lethal between E13-E15 when most of the hair cells are not fully developed (Jacks, 1992), the conditional Rb knockout model provided by Dr. Phil Hinds (Tufts University, Boston, Mass.) was used for this study. Mice with loxP sites flanking exon 19 of the Rb1 gene were obtained as were mice with cre-recombinase under the control of collagen 1A1 promoter (Dr. Barbara Kream, University of Connecticut Health Center, Farmington, Conn.). The Rb1loxp/loxp mice were crossed with the Col-cre mice (Dacquin et al., 2002) to create pRb−/− mice. The 3.6 kb Col1A1 promoter driving cre results in the expression of cre-recombinase in a pattern similar to endogenous Col1A1 expression. The pRb conditional knockout mice produced from this cross were perinatal lethal, due to respiratory failure (G. Gutierrez and P. Hinds, unpublished observations), and therefore, the analysis focused on mouse embryos.
The expression of collagen1A1 (Col1A1) in the developing utricle was examined. GeneChip analysis showed that Col1A1 is expressed in the utricle, with the main expression being derived from the stroma. In situ hybridization confirmed the expression of Col1A1 in the developing otic placode as early as E10.5 and, subsequently, in the hair cells and supporting cells (
The expression of pRb in the pRb−/− mice was studied using the anti-Rb antibody. pRb was found to be completely absent in the sensory epithelial cells in both the pRb−/− inner ear at E13.5 (the earliest stage examined) and E18.5 (
Rb controls cell cycle exit in the hair cells and to a lesser extent in the supporting cells
a) Increased hair cell number in the pRb−/− mouse inner ear
If pRb is critical in regulating the cell cycle exit control during hair cell development, loss of pRb could allow hair cells to remain in the cell cycle, thereby producing more hair cells. Using confocal microscopy the number of utricular hair cells of pRb−/− mice at E18.5 was counted, after rhodamine-phalloidin staining of the hair bundles. The hair bundles were clearly labeled in the pRb−/− utricle, which exhibited normal morphology, as in the controls. The overall hair bundle morphology of the knockout and control mice was similar, judging from confocal microscopy. Compared to the control littermates there was a 40% increase in the number of hair bundles in the pRb−/− mice: pRb−/−, 1406±73 (mean±SD), n=3; pRb+/−, 987±62 (mean±SD), n=5; P<0.05. It was evident from the confocal study that the distribution of the hair cells in the pRb−/− mice was abnormal (
b) The hair cells in the pRb−/− mice undergo cell division
To investigate if the differentiated hair cells can still enter the cell cycle, anti-PCNA antibody was used to localize the dividing cells together with the hair cell marker myosin VIIa (myo7a). During normal development the progenitor cells differentiate to hair cells after they become postmitotic. At E13.5 in the pRb−/− utricle, double-labeling showed that all of the hair cells stained strongly for PCNA, whereas the control hair cells were PCNA negative (
At E18.5 most of the pRb−/− cochlear hair cells stained intensely for PCNA, similar to the labeling in the pRb−/− utricle hair cells. No labeling was observed in the control cochlear hair cells. The large number of hair cells in the pRb−/− cochlea also confirmed the observations made in the confocal study. In addition, some of the supporting cells in the pRb−/− cochlea were also stained strongly for PCNA, yet in the control, PCNA labeling in the supporting cells was completely absent (
In further support of the observation of cycling hair cells, dividing hair cells in the M phase were observed in the pRb−/− utricle (
The proliferation of the hair cells was further studied by injecting BrdU into pregnant mice at E16.5 twice at 6-hour intervals. The embryos were then harvested at E18.5, 48 hours after initial injection. During normal development, at E16.5 the hair cells are postmitotic and have started to express many hair cell marker genes. This was clearly demonstrated in the control pRb+/− mice since there were no BrdU labeled hair cells (
Although some pRb−/− hair cells were not labeled with BrdU, it is likely that these hair cells are dividing hair cells in the S-phase, outside the time frame when BrdU was available, i.e. the first 12 of 48 hours. This was supported by the PCNA labeling experiment where a majority of the E18.5 hair cells were PCNA positive, indicating that given a longer time frame most of hair cells would be labeled as PCNA measures the activity between G1-S phases of the cell cycle (Woods et al., 1991). Therefore, it is likely that all the hair cells in the pRb−/− mice were actively dividing.
c) p27kip1 and p57kip2 are likely to be involved in the pRb pathway
To further understand how the supporting cells re-enter the cell cycle in the pRb−/− cochlea, the expression of p27kip1 was studied, a Cdk4 kinase inhibitor with prominent expression in the cochlear supporting cells. Downregulation of p27kip1 in the cochlea hair cell precursors correlated with upregulation of pRb in the same cells, during early development (
Loss of p27kip1 leads to proliferation of the cochlear supporting cells, suggesting that both pRb and p27kip1 control the postmitotic status of the supporting cells. Interestingly, there is a general reduction of p27kip1 expression in the pRb−/− supporting cells, and in some supporting cells p27kip1 is completely absent (
At E14 when p27kip1 has established ZNPC within the sensory patch of the primordial organ of Corti, the Rb expression is maintained in both the sensory and non-sensory cells. It is therefore likely that the exit of the cell cycle of the sensory precursor cells may be initiated primarily by p27kip1, which occurs prior to the differentiation of the hair cells. This is supported by studies which showed that upregulation of p27kip1 and cell cycle withdrawal proceed the differentiation of neurons (Farah, 2000). Immediately after the initiation of hair cell differentiation, Rb is upregulated in the hair cell whose p27kip1 is downregulated. Therefore there appears to be a coordinated expression control between p27kip1 and Rb, to ensure that the cell cycle arrest is maintained in the differentiating hair cells.
During normal development the sensory precursor cells become postmitotic prior to differentiation which involves patterning of hair cells and supporting cells. This study showed that loss of Rb leads to re-entry to the cell cycle of primarily the hair cells, and the massive increase in hair cell number clearly disrupted the regular hair cell/supporting cell pattern. Therefore the correct number of postmitotic cells is largely maintained by Rb in the cochlea, together with p27kip1. The particular role of pRb in the maintenance of postmitotic hair cells helps to explain the observation that in the p27kip1 mouse cochlea only one additional row of inner and outer hair cells is produced. It is possible that deletion of p27kip1 leads to increased number of hair cell precursors, and differentiation of the precursor cells to the hair cells results in the upregulation of the Rb gene, thereby blocking the differentiated hair cells from re-entering the cell cycle. In the cochlear supporting cells however, both pRb and p27kip1 are expressed and loss of function for either one can lead to cell cycle re-entry. Therefore unlike the hair cells where the function of pRb is likely to replace that of p27kip1, functions of both molecules are required for the maintenance of quiescent supporting cells. However, the rate of cell division in the pRb−/− supporting cells is considerably lower than that in the hair cells. This is likely due to the presence of p27kip1 in the supporting cells, thereby partially compensating the function of pRb. The compensation by p27kip1 may not be complete, however, as the re-entry of cell cycle and downregulation of p27kip1 are observed in some supporting cells. There is, therefore, likely a genetic mechanism, which is different from that in the hair cells, by which the functions of p27kip1 and pRb are coordinated in the supporting cells.
To further test if some other negative cell cycle regulators, identified through GeneChip analysis, are involved in the Rb controlled pathway, the expression patterns of p57kip2, Mxi1, Abl1 and Jun-B were studied. Immunostaining with anti-p57kip2 antibody showed that at E18.5 p57kip2 was normally expressed in the outer hair cells in the cochlea, and in some of the utricular hair cells. However p57kip2 was markedly reduced in the pRb−/− cochlear hair cells (
d) The newly derived hair cells are differentiated and functional
The Rb gene is involved in the differentiation of different cell types. For example Rb is required for the differentiation of the osteoblast by physically interacting and activating osteoblast transcription factor CBFA1 (Thomas, 2001). Increasing evidence has indicated that pRb has a role in neural development, is required for cell cycle exit in some neurons, and is required for differentiation in other neurons (Ferguson, 2002; Marino, 2003). The observation of cell division of hair cells in the pRb−/− mice at E18.5 indicated that the genetic program for the hair cell differentiation was intact in the pRb−/− hair cells, and that pRb primarily functions as a suppressor of cell cycle re-entry.
Only the hair cells on the apical surface of the pRb−/− utricle appeared to have normal structure. The stereocilia were intact, and the cells bore the normal pear-like appearance of hair cells. Also, the hair bundles were labeled with actin-cross linking protein, espin (
Generally, hair cells form synapses with axons of ganglion neurons, which can be labeled with acetylated tubulin. Therefore, the tubulin distribution in the pRb−/− utricle was studied. Indeed labeling with anti-tubulin antibody showed, similar to the controls, that most of the hair cells in the pRb−/− mice were surrounded by nerve fibers with tubulin labeling (
In addition, recent studies have shown that the hair cells can take up FM1-43, a small styryl dye, through the open mechanotransduction channel (Gale, 2001; Geleoc, 2003; Meyers, 2003). The uptake of FM1-43 is an indication of the presence of the functional mechanotransduction channels, a hallmark for a functional hair cell. To determine if the newly generated hair cells in the pRb−/− mice were functional, the uptake of FM1-43 was measured. DIC was used to visualize the hair bundles.
To further illustrate that the transduction apparatus in the pRb−/− hair cells are functional, patch clamping was performed to measure transduction currents of the utricular hair cells. The results showed that transduction currents were elicited in both pRb−/− and pRb+/− hair cells (
Deletion of the pRb in the hair cell did not seem to elicit an abnormal differentiation process, judging by the labeling of various hair cell markers, the overall normal structure of the stereocilia and the FM1-43 uptake through functional channels. In fact, all the hair cell markers tested were expressed by the Rb−/− hair cells, similar to the controls. The overall architecture of the hair cells is relatively normal with properly formed stereocilia. The assay with dye FM1-43 uptake experiment also showed the newly derived hair cells were functional, in agreement with a recent study which demonstrated that between embryonic days E16-E17 the inner ear hair cells have acquired the necessary components for the assembly of functional transduction channels (Geleoc, 2003). The study showed that the differentiation and proliferation processes appear to be decoupled in the pRb−/− hair cells, and the differentiation of the hair cells is, therefore, likely pRb independent.
e) There is no evidence of apoptosis in the sensory epithelial cells of the pRb−/− inner ear
Germline Rb−/− mice die between E13-E15 with hematopoietic and neurological defects. In the CNS in germline pRb−/− mice, there is extensive apoptosis as the result of aberrant entry of S phase in differentiating cells (Slack, 1998; Gloster, 1999). During normal development apoptosis has been observed in the spiral ganglion cells and the greater epithelial ridge (GER, located around the inner hair cells), in C3H/HeJ mice (Kamiya, 2001). Since one of the main functions of pRb during development is to protect cells from apoptosis whether programmed cell death occurred in pRb−/− inner ear differentiated hair cells, after re-entry into the cell cycle was examined. Generally, when hair cells die they are extruded through the apical surface of the sensory epithelium, leaving a temporary space in the lumen. The examination of the utricles at all stages (multiple samples from E13.5 and E18.5) did not identify such an event, suggesting that pRb is not involved in the cell death pathway during normal development.
Cell death was further studied with anti-active caspase3 antibody in the pRb−/− utricle and the cochlea. Significant labeling was not observed. However, in a positive control, the Brn-3.1 knockout mouse cochlea showed numerous caspase3 positive cells. Altogether, the data show that the absence of pRb does not lead to increased cell death in the inner ear. The hair cell apoptotic pathway in development is therefore pRb independent. Therefore, it is possible to manipulate the expression, level or function of pRb in hair cells and supporting cells to induce their re-entry into the cell cycle. The newly generated hair cells thus manipulated are fully differentiated and functional and do not undergo apoptosis. It is possible, therefore, to regenerate differentiated and functional hair cells in the mammalian (e.g., in the human) inner ear.
Different molecules and mechanisms are likely involved in hair cell apoptosis, such as p19ink4d during development and MAPK-JNK signal pathway in stress induced cell death (Chen, 2003; Wang, 2003). Inhibition of MAPK-JNK pathway protects the hair cells from ototoxic drugs and acoustic trauma induced cell death. Interestingly a recent study showed that Rb physically interacts with c-Jun NH(2)-terminal kinase/stress-activated protein kinase (JNK/SAPK), a member of the mammalian MAPK family, thereby inhibiting JNK/SAPK mediated apoptotic cell death induced by ultraviolet radiation or cytotoxic effect of topoisomerase I inhibitor camptothecin (Shim, 2000; Lauricella, 2001). pRb may have an additional protective role in preventing trauma induced hair cell death.
Isl-1 is downregulated in the Rb−/− hair cells
In a separate study, two homeodomain transcription factors of the LIM family, Lim-3 transcription factor (Lhx3) and Isl-1, both with inner ear sensory cell expression patterns were identified and characterized. In the inner ear it was found that Lhx3 had hair cell specific expression starting at E13.5, whereas Isl-1 showed expression in the otocyst as early as E11.5. The expression of Lhx3 remained hair cell specific while Isl-1 expression remained predominantly in the supporting cells, with downregulated expression in the hair cells. The timing of expression of Lhx3 is very similar to that of myosin VIIa, indicating that it can be used as a relatively late hair cell marker (compared to Math1 or Brn-3.1 expression), whereas Isl-1 can be used to primarily label the supporting cells. Both Lhx3 and Isl1 maintain their expression in the adult sensory epithelial cells.
In the E13.5 utricle, Isl-1 labeled 3-4 layers of supporting cells in the pRb−/− and control mice. In the hair cells, there was little Isl-1 labeling in the pRb−/− samples but strong labeling in the control (
Evidence that the supporting cells are induced to become hair cells
Many pRb−/− hair cell nuclei appeared along the base of the utricle epithelium, among the supporting cells. This indicates that these cells may either be newly generated hair cells migrating from the apical region or supporting cells induced to become hair cells, or both.
In the normal utricle, the hair cells and the supporting cells have very different nuclear shapes; the hair cell nucleus is round (from Brn-3.1 and Lhx3 staining) and the supporting cell nucleus is cylindrical (Isl-1 staining). Some pRb−/− hair cells in the base of the utricle have the same cylindrical nuclei as the supporting cells, whereas the hair cells above the basal lumen have, in general, a round shape (
The induction of the supporting cell to hair cell is also supported by the expression of the hair cell markers that recapitulates the sequential expression patterns during development. During normal inner ear development the presumptive hair cells will first express the bHLH transcription factor Math1 at E12.5. Math1 expression is followed by the expression of another transcription factor Brn-3.1. Subsequently the hair cells express other hair cell markers such as myosin VIIa and Lhx3 at E14.5 in the cochlea. If, the supporting cells in the pRb−/− utricle are to become hair cells, they are expected to express Math1 and Brn-3.1, before they express myosin VIIa or Lhx3.
The E18.5 pRb−/− utricle was studied using Brn-3.1 and Lhx3 double-labeling (during normal hair cell development Brn-3.1 is expressed earlier than Lhx3). While the majority of the hair cells were double-labeled with both Brn-3.1 and Lhx3, some hair cells were only labeled with Brn-3.1 and not Lhx3 (
The expression of hair cell marker in the Rb−/− cochlear supporting cell zone
The possibility that the supporting cells can be induced to become hair cells in the E18.5 pRb−/− cochlea was further investigated. As has been shown previously, the initiation of hair cell differentiation coincides with the downregulation of p27kip1. By E16.5, p27kip1 is only expressed in the cochlear supporting cells (
Notch pathway may play a role in supporting cell to hair cell induction
Notch pathway plays a major role in generating the mosaic patterns of the hair cell and supporting cell, through interactions between Notch1 and its ligands (Kiernan et al., 2001; Lanford et al., 1999; Zine and de Ribaupierre, 2002; Zine et al., 2000). Previous studies have shown that perturbation of Notch pathway, either in vivo or in vitro (Zhang, 2000; Zine, 2000; Lanford, 1999), can produce supernumerary hair cells via dedifferentiation of the supporting cells.
To determine if the Notch pathway plays any role in the supporting cell to hair cell induction in the pRb−/− inner ear, the expression of the major components in the Notch pathway including Notch1, jag1, jag2, delta1 and numb using in situ hybridization was studied. The analysis showed a marked reduction in Notch1 expression in the supporting cells of pRb−/− mice, whereas the expression of the ligands was largely unaffected. Since Rb is expressed in normal supporting cells, the deletion of the Rb gene in the pRb−/− supporting cells likely resulted in the reduced expression of Notch1, potentiating them to become hair cells. Therefore disruption of the Notch pathway may have contributed to the supporting cell to hair cell induction in the pRb−/− mice, although it is not clear if the reduction of Notch1 is directly the result of Rb deletion in the supporting cells or is a consequence of overproduction of the neighboring hair cells. This question can be better addressed using the conditional Rb−/− mice with Rb being specifically abolished in the hair cell (for example with Brn-3.1-Cre mice). Such a model should provide a clear view of supporting cell to hair cell conversion, as a continuous induction process should deplete or severely reduce the number of the supporting cells in the postnatal mice.
In fish, amphibians and birds, regeneration of sensory hair cells through asymmetric cell divisions of supporting cells can contribute to recovery of hearing and balance after hair cell loss caused by trauma or toxicity (J. T. Corwin, D. A. Cotanche, Science 240, 1772 (1988); B. M. Ryals, E. W. Rubel, Science 240, 1774 (1988)). Mammalian hair cells do not spontaneously regenerate, even though supporting cells in vestibular sensory epithelia retain a limited ability to divide (A. Forge, L. Li, J. T. Corwin, G. Nevill, Science 259, 1616 (1993); M. E. Warchol, P. R. Lambert, B. J. Goldstein, A. Forge, J. T. Corwin, Science 259, 1619 (1993)). Consequently, hair cell death in mammals often leads to permanent hearing and balance impairment.
As the inner ear develops, hair cell progenitor cells exit from the cell cycle and, like neurons, terminally differentiate. Negative cell-cycle regulators apparently maintain the postmitotic status of hair cells and contribute to their terminal differentiation. Cyclin-dependent-kinase inhibitors, p27Kip1 and p19Ink4d, participate in cell-cycle exit of hair cell progenitors and in hair cell apoptosis, respectively (H. Lowenheim et al., Proc Natl Acad Sci USA 96, 4084 (1999); P. Chen et al., Nat Cell Biol 5, 422 (2003)). However the key regulators of cell-cycle exit and concomitant hair cell terminal differentiation remain elusive. The retinoblastoma protein, pRb, encoded by the retinoblastoma gene, Rb1, functions in cell-cycle exit, differentiation and survival (M. Classon, E. Harlow, Nat Rev Cancer 2, 910 (2002); M. M. Lipinski, T. Jacks, Oncogene 18, 7873 (1999)). pRb is a member of the pocket protein family, which includes p107 (encoded by Rbl1, BC069179) and p130 (encoded by Rbl2, BC020528). Like pRb, p107 and p130 cause cell-cycle arrest when overexpressed (M. Classon, N. Dyson, Exp Cell Res 264, 135 (2001)). Germline pRb−/− animals die in utero around E13.5, with severe defects in lens development, hematopoiesis, myogenesis, osteogenesis and neurogenesis (M. Classon, E. Harlow, Nat Rev Cancer 2, 910 (2002); T. Jacks et al., Nature 359, 295 (1992); K. L. Ferguson, R. S. Slack, Neuroreport 12, A55 (2001); D. M. Thomas et al., Mol Cell 8, 303 (2001)). In both the central and peripheral nervous systems, neurons undergo ectopic mitoses and subsequent apoptosis (K. L. Ferguson, R. S. Slack, Neuroreport 12, A55 (2001), R. S. Slack, H. El-Bizri, J. Wong, D. J. Belliveau, F. D. Miller, J Cell Biol 140, 1497 (1998)). Mice with Rb1 conditionally deleted in the central nervous system show an increase in neuronal number due to aberrant S-phase entry, without apoptosis (K. L. Ferguson et al., Embo J 21, 3337 (2002); D. MacPherson et al., Mol Cell Biol 23, 1044 (2003); S. Marino, D. Hoogervoorst, S. Brandner, A. Berns, Development 130, 3359 (2003)). However, it is not clear whether these supernumerary neurons are highly differentiated or functional.
To identify molecules involved in cell-cycle regulation during hair cell development oligonucleotide microarrays were used to study gene expression in the developing mouse utricle, a balance organ of the inner ear. It was noticed that retinoblastoma family members show a suggestive pattern: from E14.5 to P12, Rb1 expression was constant, Rbl1 showed downregulation, and Rbl2 exhibited upregulation. An anti-pRb antibody weakly labeled all cells in the E12.5 otocyst (
Because germline pRb−/− mice die around E13.5 (T. Jacks et al., Nature 359, 295 (1992)), when hair cells are extremely immature, a conditional pRb knockout was studied. Mice with lox-P sites flanking exon 19 of the Rb1 gene (Rbl1oxp) (M. Vooijs, H. te Riele, M. van der Valk, A. Berns, Oncogene 21, 4635 (2002)) were crossed with mice carrying cre under the control of the 3.6 kb collagen1A1 (Col1A1) promoter, which express cre-recombinase in a pattern similar to endogenous Col1A1 (F. Liu et al., Int J Dev Biol 48, 645 (2004)). Because these pRb conditional knockout mice (Col1A1-pRb−/−) die perinatally, embryos were studied. By in situ hybridization, Col1A1 was detected ubiquitously in the E11.5 otocyst, but later reduced in hair cells and supporting cells (
Hair bundle numbers were increased in pRb−/− utricles and cochleas
Cells with hair bundles in E18.5 Col1A1-pRb−/− utricles were counted. Col1A1-pRb−/− utricles had 40% more cells with bundles than littermate controls (Col1A1-pRb−/−: 1406±73 (mean±SD), N=3; Col1A1-pRb−/−: 987±62, N=5; P<0.05) (
Loss of pRb leads to proliferation and differentiation
To test hair-cell proliferation specifically, E16.5 pregnant mothers were injected with BrdU and embryos harvested at E18.5. During normal development, mouse hair cells become postmitotic as early as E12.5 (M. Xiang, W. Q. Gao, T. Hasson, J. J. Shin, Development 125, 3935 (1998)). As expected, no hair cells or cochlear supporting cells were BrdU-positive in control mice (
Dividing cells were also identified with an anti-PCNA antibody (A. L. Woods et al., Histopathology 19, 21 (1991)). In E13.5 and E18.5 Col1A1-pRb−/− utricles but not in controls, most hair cells stained strongly for PCNA (
Most apical hair cells in E18.5 Col1A1-pRb−/− utricles showed highly differentiated morphology, including pear-shaped cell bodies and intact hair bundles. Hair bundles were labeled with antibodies to espin (an actin crosslinker) and Ptprq (present in highly-differentiated cochlear hair bundles) (
Loss of pRb does not eliminate hair cell function
The sine qua non of hair cell function is mechanosensitivity. FM1-43, a fluorescent dye, enters hair cells through open mechanotransduction channels and so serves as a vital optical assay for mechanosensitivity (J. E. Gale, W. Marcotti, H. J. Kennedy, C. J. Kros, G. P. Richardson, J Neurosci 21, 7013 (2001); J. R. Meyers et al., J Neurosci 23, 4054 (2003)). FM1-43 labeling was observed in bundles and cell bodies of most hair cells in both control (
Loss of pRb does not lead to apoptosis
To determine whether apoptosis occurs in Col1A1-pRb−/− hair cells, activated caspase-3 was assayed. Caspase-3-positive cells in Col1A1-pRb−/− was not detected in sensory epithelium, nor in controls (
Evidence of postmitotic and mature hair cells can re-enter the cell cycle, after acute deletion of Rb1 gene
The prominent expression of Rb1 in postnatal hair cells and the fact that acute loss of pRb causes cell-cycle re-entry in quiescent or senescent cells ( J. Sage, A. L. Miller, P. A. Perez-Mancera, J. M. Wysocki, T. Jacks, Nature 424, 223 (Jul. 10, 2003)) are suggestive of a role for pRb in maintaining hair cells' non-proliferative status. To test this hypothesis, floxP-pRb utricles were cultured and infected with adenovirus carrying cre-recombinase, acutely deleting the Rb1 gene in infected hair cells (J. R. Holt et al., J Neurophysiol 81, 1881 (1999).) Utricular hair cells are mature at P10 and postmitotic at both stages studied (E17.5 and P10). After continuous culture in the presence of BrdU, no labeling was detected in adeno-GFP-infected (
Inner ear hair cells can continue to cell cycle in postnatal mice in vivo and are functional
To test if proliferating hair cells can be maintained in the postnatal mice, a new pRb conditional knockout was created by breeding Brn-Cre and floxp-Rb mice. Brn-3.1 is a hair cell specific transcription factor. Brn-Cre-pRb mice survived postnatally because Brn-3.1 is only expressed in the hair cells and retinal ganglion cells. The hair cells of Brn-Cre-pRb mice were studied for their proliferation, hair bundle integrity and function. Hair cells in 3-month-old Brn-Cre-pRb mouse utricles were labeled with BrdU and PCNA (
pRb is also involved in cell cycle exit control of the sensory progenitor cells in the inner ear
To study progenitor cell proliferation, E13.5 pregnant mice were injected with BrdU, 4 hours prior to embryo harvest. In the primordial organ of Corti, the p27Kip1-positive “zone of non-proliferating cells (ZPNC)” harbors postmitotic sensory precursor cells (P. Chen, J. E. Johnson, H. Y. Zoghbi, N. Segil, Development 129, 2495 (May, 2002).) BrdU-positive cells were found in the p27Kip1-positive region of Col1A1-pRb−/− mice (
Supporting cell to hair cell conversion
Cochleas in Col1A1-pRb−/− mice were studied for supporting-cell to hair-cell conversion. If this was the main pathway for increased hair cell number, it was expected p27Kip1-labeled supporting cells would label with Math1, the earliest hair cell marker; or Math1-positive cells would appear in supporting cell regions outside the hair-cell region. No p27Kip1 and Math1 double-positive cells, or Math1-positive cells in the supporting cell region were found. While cell fate conversion cannot be completely excluded, it is most likely that increased hair cell precursors and subsequent hair cell division are primarily responsible for the overproduction of hair cells.
From these studies it has been found that pRb regulates cell-cycle exit in hair cells, its loss permits cell-cycle re-entry and an increase hair cell numbers. These studies also demonstrate that differentiated mammalian hair cells can continue to cycle and divide in the absence of pRb, so that functional hair cells can be generated through divisions of preexisting hair cells. Furthermore, acute ablation of pRb in differentiated hair cells led to cell-cycle re-entry. Demonstration that pRb critically regulates hair cell division opens new opportunities, both for hair cell regeneration and for creating cell lines for hearing research. For hair cell regeneration, a reversible block of pRb function in hair cells could be used in place of permanent deletion of the Rb1 gene. Thus, regulated inactivation of pRb through use of, for example, siRNA, a small molecule inhibitor of pRb or reversible manipulation of pRb-modifying kinases could result in production of functional hair cells followed by restoration of normal cell-cycle exit.
These results also show that an irreversible switch from proliferation is not required for “terminal” differentiation, since cycling cells in the absence of pRb are highly differentiated and functional. These findings have implications for regenerating other functional cells (e.g., neuronal cells in the central nervous system (CNS), peripheral nervous system and inner ear) through manipulation of negative cell growth control genes.
Each of the foregoing patents, patent applications and references that are recited in this application are herein incorporated in their entirety by reference. Having described the presently preferred embodiments, and in accordance with the present invention, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the teachings set forth herein. It is, therefore, to be understood that all such variations, modifications, and changes are believed to fall within the scope of the present invention as defined by the appended claims.
This application claims priority under 35 U.S.C. §119 from U.S. provisional application serial No. 60/538,917, filed Jan. 23, 2004, the entire contents of which is herein incorporated by reference.
Aspects of the invention may have been made using funding from National Institute on Deafness and Other Communication Disorders Grant DC04546. Accordingly, the Government may have rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 60538917 | Jan 2004 | US |
