Homozygous Deletion in the Coding Sequence of the c-mer Gene in RCS Rats Unravels General Mechanisms of Physiological Cell Adhesion and Apoptosis

Nandrot, Emeline F.; Dufour, Éric; Provost, Alexandra; Péquignot, Marie O.; Bonnel, S.; Gogat, Karïn; Marchant, Dominique; Rouillac, Christelle; Condé, Bertille Sépulchre de; Bihoreau, Marie-Thérèse; Shaver, Cindi; Dufier, Jean‐Louis; Marsac, Cécile; Lathrop, Mark; Ménasche, Maurice; Abitbol, Marc

doi:10.1006/nbdi.2000.0328

Cited by 123 publications

(102 citation statements)

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“…These features are never seen in RCS rats at the ages studied (4,38). Our findings provide conclusive evidence that Mertk is the gene corresponding to rdy and substantiate a previous conclusion that Mertk is essential for the normal functioning of the mammalian retina (23), made on the basis of the RCS Mertk null mutation (14,43) and discovery of MERTK mutations in individuals with retinitis pigmentosa (23). Our results suggest that treatment of patients with retinitis pigmentosa due to mutation of MERTK by viral-mediated gene therapy might be feasible; introduction of the gene into the eyes of juvenile rats, which already display significant pathology, resulted in areas of near normal-appearing retina.…”

Section: Discussionsupporting

confidence: 90%

Correction of the retinal dystrophy phenotype of the RCS rat by viral gene transfer of Mertk

Vollrath

Feng

Duncan

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

264

188

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The Royal College of Surgeons (RCS) rat is a widely studied animal model of retinal degeneration in which the inability of the retinal pigment epithelium (RPE) to phagocytize shed photoreceptor outer segments leads to a progressive loss of rod and cone photoreceptors. We recently used positional cloning to demonstrate that the gene Mertk likely corresponds to the retinal dystrophy (rdy) locus of the RCS rat. In the present study, we sought to determine whether gene transfer of Mertk to a RCS rat retina would result in correction of the RPE phagocytosis defect and preservation of photoreceptors. We used subretinal injection of a recombinant replication-deficient adenovirus encoding rat Mertk to deliver the gene to the eyes of young RCS rats. Electrophysiological assessment of animals 30 days after injection revealed an increased sensitivity of treated eyes to low-intensity light. Histologic and ultrastructural assessment demonstrated substantial sparing of photoreceptors, preservation of outer segment structure, and correction of the RPE phagocytosis defect in areas surrounding the injection site. Our results provide definitive evidence that mutation of Mertk underlies the RCS retinal dystrophy phenotype, and that the phenotype can be corrected by treatment of juvenile animals. To our knowledge, this is the first demonstration of complementation of both a functional cellular defect (phagocytosis) and a photoreceptor degeneration by gene transfer to the RPE. These results, together with the recent discovery of MERTK mutations in individuals with retinitis pigmentosa, emphasize the importance of the RCS rat as a model for gene therapy of diseases that arise from RPE dysfunction.T he Royal College of Surgeons (RCS) rat strain displays an unusual retinal phenotype in which shed photoreceptor (PR) outer segment (OS) debris accumulates in the subretinal space (1). PR disk shedding normally commences at postnatal day (P)12 in the rat (2), and an OS debris layer is readily apparent in the eyes of RCS animals at P20. Genetic chimera studies suggest that the defect is a cell-autonomous function of the RPE, not the PRs (3). Indeed, in vivo (4) and RPE cell culture studies (5) revealed a defect in the ability of RCS RPE to phagocytize shed OS membranes. Despite the RPE-specific nature of the defect, death strikes the PRs first, through the process of apoptosis (6). The time course of PR degeneration is rapid, beginning around P20, with few PR nuclei remaining in the outer nuclear layer (ONL) by P60. Thinning and atrophy of the RPE begins after onset of PR degeneration. The cause of PR cell death is not well understood; the debris zone acting as a diffusion barrier to metabolites (7), disruption of the interphotoreceptor matrix (8), and PR hypoxia due to diminished oxygen diffusion (9) have been proposed as explanations.In contrast to the extensively studied retinal phenotype of the RCS rat, the nature of the genetic defect has remained obscure until recently. Early genetic linkage studies showed that the phenotype is complet...

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Section: Discussionsupporting

confidence: 90%

Correction of the retinal dystrophy phenotype of the RCS rat by viral gene transfer of Mertk

Vollrath

Feng

Duncan

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

264

188

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“…However, this was subsequently found -in rats, mice and humans -to be due to mutations of the Mer gene alone [37][38][39][40][41] . A long-studied inherited form of retinitis pigmentosa in rats [37][38][39] , and a more recently described inherited form of the disease in humans 40,41 , are both due to Mer gene mutations. MER and TYRO3 have been localized to the apical tips of the RPE cell processes that penetrate the photoreceptor outer segment layer and pinch off the distal ends of the outer segments 10 .…”

Section: Tam Regulation Of Phagocytosismentioning

confidence: 99%

Immunobiology of the TAM receptors

2008

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Recent studies have revealed that the TAM receptor protein tyrosine kinases -TYRO3, AXL and MER -have pivotal roles in innate immunity. They inhibit inflammation in dendritic cells and macrophages, promote the phagocytosis of apoptotic cells and membranous organelles, and stimulate the maturation of natural killer cells. Each of these phenomena may depend on a cooperative interaction between TAM receptor and cytokine receptor signalling systems. Although its importance was previously unrecognized, TAM signalling promises to have an increasingly prominent role in studies of innate immune regulation.Receptor protein tyrosine kinases (PTKs) are cell-surface transmembrane receptors that contain a regulated PTK activity within their cytoplasmic domains. They function as sensors for extracellular ligands, the binding of which triggers receptor dimerization and activation of the receptor's kinase. This leads to the recruitment, phosphorylation and activation of multiple downstream signalling proteins, which ultimately change the physiology of cells. Although there are only 58 receptor PTK genes in the human genome 1 (see the human kinome website), the signal transduction cascades initiated by receptor PTK activation control diverse cellular processes -from cell differentiation to cell death. Well-known receptor PTK subfamilies include the ERBB receptors, which have essential roles in cardiac and neural development and the progression of some forms of breast cancer 2 ; and the ephrin receptors, which are required for tissue morphogenesis and the patterning of neuronal connections in the developing brain 3 .The focus of this Review, the TAM group, was among the last receptor PTK subfamilies to be identified, and the biological roles of its three members -TYRO3, AXL and MERremained uncharacterized for several years. Largely through the analysis of engineered lossof-function mutants in mice, these roles have become increasingly apparent. They reflect a specific requirement for TAM signalling in settings in which fully differentiated cells, tissues and organs must be maintained in the face of continuous challenge, turnover and renewal. In humans, ongoing homeostatic regulation of this sort must be carried out, frequently on a daily basis, for decades. Although an essential role for TAM regulation of tissue homeostasis is evident in the adult nervous, reproductive and vascular systems, it is in In this Review, we highlight the central roles that TAM signalling has in the intrinsic inhibition of the inflammatory response to pathogens by dendritic cells (DCs) and macrophages; during phagocytosis of apoptotic cells by these same cells; and in the maturation and killing activity of natural killer (NK) cells. We also discuss how, in many or all of these settings, TAM receptors depend on and interact with cytokine receptors. TAM receptors and ligandsThe three TAM receptors, TYRO3, AXL and MER, were identified as a distinct receptor PTK subfamily in 1991 (REFS 4,5 ). Subsequent cloning of full-length cDNAs by multiple labo...

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“…5 Degeneration is virtually complete after 2-3 months when little electroretinographical activity is detectable and few photoreceptor cells remain. 6,7 Thinning and atrophy of the RPE begins after the onset of degeneration.…”

Section: Introductionmentioning

confidence: 99%

Long-term preservation of retinal function in the RCS rat model of retinitis pigmentosa following lentivirus-mediated gene therapy

et al. 2005

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The Royal College of Surgeons (RCS) rat is a wellcharacterized model of autosomal recessive retinitis pigmentosa (RP) due to a defect in the retinal pigment epithelium (RPE). It is homozygous for a null mutation in the gene encoding , a receptor tyrosine kinase found in RPE cells, that is required for phagocytosis of shed photoreceptor outer segments. The absence of Mertk results in accumulation of outer segment debris. This subsequently leads to progressive loss of photoreceptor cells. In order to evaluate the efficacy of lentiviral-mediated gene replacement therapy in the RCS rat, we produced recombinant VSV-G pseudotyped HIV-1-based lentiviruses containing a murine Mertk cDNA driven by a spleen focus forming virus (SFFV) promoter. The vector was subretinally injected into the right eye of 10-dayold RCS rats; the left eye was left untreated as an internal control. Here, we present a detailed assessment of the duration and extent of the morphological rescue and the resulting functional benefits. We examined animals at various time points over a period of 7 months by light and electron microscopy, and electroretinography. We observed correction of the phagocytic defect, slowing of photoreceptor cell loss and preservation of retinal function for up to 7 months. This study demonstrates the potential of gene therapy approaches for the treatment of retinal degenerations caused by defects specific to the RPE and supports the use of lentiviral vectors for the treatment of such disorders. Gene Therapy (2005) 12, 694-701.

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Homozygous Deletion in the Coding Sequence of the c-mer Gene in RCS Rats Unravels General Mechanisms of Physiological Cell Adhesion and Apoptosis

Cited by 123 publications

References 50 publications

Correction of the retinal dystrophy phenotype of the RCS rat by viral gene transfer of Mertk

Correction of the retinal dystrophy phenotype of the RCS rat by viral gene transfer of Mertk

Immunobiology of the TAM receptors

Long-term preservation of retinal function in the RCS rat model of retinitis pigmentosa following lentivirus-mediated gene therapy

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