Model Of Retinitis Pigmentosa Research Articles

Preclinical Models of Retinitis Pigmentosa.

Retinitis pigmentosa (RP) is the name for a group of phenotypically-related heritable retinal degenerative disorders. Many genes have been implicated as causing variants of RP, and while the clinical phenotypes are remarkably similar, they may differ in age of onset, progression, and severity. Common inheritance patterns for specific genes connected with the development of the disorder include autosomal dominant, autosomal recessive, and X-linked. Modeling the disease in animals and other preclinical systems offers a cost-conscious, ethical, and time-efficient method for studying the disease subtypes. The history of RP models is briefly examined, and both naturally occurring and transgenic preclinical models of RP in many different organisms are discussed. Syndromic forms of RP and models thereof are reviewed as well.

Large Animal Models of Retinitis Pigmentosa in Therapy Development and Preclinical Testing.

Large animal models are valuable for developing and testing translational therapies for inherited retinal dystrophies such as retinitis pigmentosa (RP). Gene augmentation therapy has been developed utilizing such models. Adeno-associated viral (AAV) vectors have been frequently utilized and delivered by intravitreal or subretinal injection. In vivo longitudinal assessments of therapeutic outcomes are essential. These include regular ophthalmic examinations as well as detailed fundus assessments including confocal scanning laser ophthalmoscopy (cSLO) and high-resolution cross-sectional imaging of the retina by spectral domain-optical coherence tomography (SD-OCT). Retinal function assessment includes vision testing and electroretinography (ERG).

Tlr4 gene deletion accelerates retinal degeneration in rd10 and P23H/+ murine models of retinitis pigmentosa

AbstractPurpose: The photoreceptor degeneration associated to retinitis pigmentosa (RP) is caused by a wide variety of genetic mutations, which greatly complicates the development of a universal effective treatment. As a process independent of the causative mutation, the inflammatory response resulting from neuronal death could represent a potential candidate for a general treatment for RP. In this context, we studied the role of TLR4, one of the main mediators of innate immunity, on the retinal degenerative process in two murine models of RP.Methods: rd10 and P23H/+ mice were used to evaluate the consequences of Tlr4 haploinsufficiency and complete deletion on retinal degeneration. Visual function was evaluated by electroretinographic recordings and optomotor test and retinal cytoarchitecture by immunohistology. The myeloid cell population (main mediators of the innate immune response) reactivity was studied by immunohistology and flow cytometry. Gene expression was assessed by RT‐quantitative PCR.Results: We found that Tlr4 expression was significantly increased in the retina of both RP models. To assess the effect of Tlr4 deletion in PR progression first we confirmed that abrogation of Tlr4 expression did not impair visual function in wild‐type animals. However, Tlr4 deficiency accelerated RP progression in both rd10 and P23H/+ mice. Deletion of a single Tlr4 allele reduced the retinal electroretinographic response and photoreceptor survival in both RP models. Moreover, complete abrogation of Tlr4 further exacerbates this phenotype. These results were confirmed by assessing visual acuity by optomotor test in P23H/+ mice. Microglia analysis showed higher proportion of phagocytic microglia and lower of homeostatic microglia in the photoreceptor layers upon Tlr4 total deletion.Conclusions: The TLR4 receptor exerts a neuroprotective effect on the retinal neurodegenerative process in RP, thus suggesting a potential therapeutic target for the disease.

The role of autophagy in disease

AbstractDefective proteostasis is one of the hallmarks neurodegenerative diseases. Of the different components of the proteostasis network, we are interested in autophagy and its changes with age. We have previously shown that, out of the different autophagic pathways that co‐exist in all mammalian cells, macroautophagy is the first that declines with age in the retina, A crosstalk between macroautophagy and chaperone mediated autophagy (CMA) has been described whereby, in aged mice retinas, the decrease in macroautophagy correlates with increased CMA. Our working hypothesis is that in aged and degenerated retinal cells increase CMA to compensate for macroautophagy loss, in an attempt to maintain cell viability. Here, I will present our latest data showing how CMA upregulation can protect photoreceptor cells in retinitis pigmentosa models.

Microglial alterations as a possible treatment target in retinitis pigmentosa

AbstractPurpose: The term retinitis pigmentosa (RP) describes a group of hereditary retinopathies. The first clinical signs of RP are night blindness and loss of peripheral vision. Central vision remains preserved until advanced stages of the disease. At a cellular level, the rods are the first to degenerate. Subsequently, there is degeneration of the cones. Inflammation plays a fundamental role in RP. The microglia respond quickly to alterations, acquiring amoeboid morphology; migrating to damage focus; acquiring macrophages functions; phagocytosing cellular debris; secreting molecules that initiate tissue repair; and favouring neuroprotection. However, if the activation is excessive, the constant secretion of nitric oxide and proinflammatory cytokines lead to pathological side effects. The purpose of this work was to review published studies in order to know if the inhibition of micloglial activation may be a good option to increase photoreceptor protection.Methods: A systematic literature review was conducted, in accordance with PRISMA criteria, in different bibliographic databases: Medline, Embase, SCOPUS and Web of Science. We searched human and animal reviews, published in English in the past 10 years. Initial search terms were ‘retina’, ‘retinitis pigmentosa’, ‘retinal degeneration’ and ‘therapeutics. Duplicate studies were removed, and the remaining articles were assessed for eligibility by full‐text review.Results: Understanding the mechanisms leading to photoreceptor death is essential for the development of new treatments in RP. It has been shown increased retinal infiltration of activated microglia in many animal models of RP. Different works have studied the clinical efficacy of antioxidants, minocycline, transforming growth factor beta or tamoxifen. However, the complete efficacy in RP has not been fully established.Conclusions: Pharmacological inhibition of microglial activation may be a good therapeutic target to reduce photoreceptor cell death in RP.

Biodistribution of progesterone in the eye after topical ocular administration via drops or inserts

Progesterone (PG) has been shown to have a slowing effect on photoreceptor cell death in mouse models of retinitis pigmentosa when administered orally. The aim of this study was to investigate whether ophthalmically administered progesterone was able to reach neuroretina and thus, the distribution through ocular tissues of different PG formulations was studied. The effect of different initial PG concentration was also investigated. Different formulations with PG in their composition (drops, a corneal/scleral-insert and scleral-inserts) were prepared and assayed. Using whole porcine eyes, the different formulations were topically administered to the ocular surface. Frozen eyes were dissected, the PG in each tissue was extracted in acetonitrile and the amount of PG quantified by UHPLC-MS/MS. Our results show that after topical administration, PG diffuses from the ocular surface and distributes throughout all tissues of the eye. Lower levels of PG were found in sclera, choroid and neuroretina when PG was applied as drops compared to inserts. Our results also show that an increase in the initial PG concentrations applied, resulted in a statistically significant increase in the amounts of PG in aqueous humour, sclera, choroid and neuroretina.

Trans-Sclera Electrical Stimulation Improves Retinal Function in a Mouse Model of Retinitis Pigmentosa.

Retinitis pigmentosa (RP) is a photoreceptor-degenerating disease with no effective treatment. Trans-corneal electrical stimulation has neuroprotective effects in degenerating retinas, but repeated applications cause corneal injury. To avoid the risk of corneal damage, here we tested whether repetitive trans-sclera electrical stimulation (TsES) protects degenerating retinas in rd10 mice, a model of RP. At postnatal day 20 (P20), the right eyes of rd10 mice were exposed to 30 min of TsES daily or every other day till P25, at the amplitude of 50 or 100 μA, with zero current as the sham. Immunostaining, multi-electrode-array (MEA) recording, and a black-and-white transition box were applied to examine the morphological and functional changes of the treated retina. Functionally, TsES modified the retinal light responses. It also reduced the high spontaneous firing of retinal ganglion cells. TsES at 100 μA but not 50 μA increased the light sensitivities of ganglion cells as well as their signal-to-noise ratios. TsES at 100 μA increased the survival of photoreceptors without improving the visual behavior of rd10 mice. Our data suggest that repetitive TsES improves the retinal function of rd10 mice at the early degenerating stage, therefore, it might be an effective long-term strategy to delay retinal degeneration in RP patients.

Time-Course Changes in Oxidative Stress and Inflammation in the Retinas of rds Mice: A Retinitis Pigmentosa Model

(1) Background: Retinitis pigmentosa (RP) is characterized by progressive photoreceptor death. A Prph2Rd2 or an rds mouse is an RP model that closely reflects human RP. The objective of this study was to investigate the relationship of rod and cone death with oxidative stress and inflammation in rds mice. (2) Methods: The retinas of control and rds mice on postnatal days (PN) 11, 17, 21, 28, 35, and 42 were used. Oxidative damage to macromolecules, glutathione (GSH and GSSG), GSH synthesis enzymes, glial fibrillar acidic protein (GFAP), ionized calcium-binding adapter molecule 1 (Iba1), and cluster of differentiation 68 (CD68) was studied. (3) Results: The time sequence of oxidative stress and inflammation changes in rds mice occurs as follows: (i) At PN11, there is a small increase in photoreceptor death and in the microglial cells; (ii) at PN17, damage to the macromolecules is observed; (iii) at PN21, the maximum photoreceptor death rate is detected and there is an increase in GSH-GSSG and GFAP; (iv) at PN21, the microglial cells are activated; and(v) at PN28, there is a decrease in GSH synthesis enzymes. (4) Conclusions: These findings contribute to the understanding of RP physiopathology and help us to understand whether oxidative stress and inflammation are therapeutic targets. These findings contribute to our understanding that, in RP, oxidative stress and inflammation evolution and their relationship are time-dependent. In this sense, it is important to highlight that both processes are potential therapeutic targets in this disease.

Development of a novel knockout model of retinitis pigmentosa using Pde6b-knockout Long-Evans rats.

Although rats with melanin-pigmentated retinal pigment epithelial (RPE) cells are physiologically more appropriate models for human eye research than their albino counterparts, reliable models from the former strain are not available to study retinal degeneration. Here, we describe the development of a novel Pde6b-knockout Long–Evans (LE Pde6b KO) rat model that recapitulates key features of human retinitis pigmentosa (RP). After the generation of the Pde6b-knockout Sprague–Dawley rats with the CRISPR-Cpf1 system, the LE rat was back-crossed over 5 generations to develop the pigmented LE Pde6b KO strain. Interestingly, LE Pde6b KO displayed well-developed bone-spicule pigmentation; a hallmark of fundus in patients with RP which cannot be observed in non-pigmented albino rats. Moreover, the rat model showed progressive thinning of the retina, which was evident by intravital imaging with optical coherence tomography. Histologically, significant atrophy was observed in the outer nuclear layer. Functionally, LE Pde6b KO presented a marked decrease of amplitude level during electroretinogram testing, demonstrating significant loss of visual function. Therefore, these findings suggest that the LE Pde6b KO model robustly recapitulates the hallmark phenotype of RP. We believe that the LE Pde6b KO model may be used effectively for preclinical translational research to further study retinal degeneration.

Microtubule modification defects underlie cilium degeneration in cell models of retinitis pigmentosa associated with pre-mRNA splicing factor mutations

Retinitis pigmentosa (RP) is the most common cause of hereditary blindness, and may occur in isolation as a non-syndromic condition or alongside other features in a syndromic presentation. Biallelic or monoallelic mutations in one of eight genes encoding pre-mRNA splicing factors are associated with non-syndromic RP. The molecular mechanism of disease remains incompletely understood, limiting opportunities for targeted treatment. Here we use CRISPR and base edited PRPF6 and PRPF31 mutant cell lines, and publicly-available data from human PRPF31 +/− patient derived retinal organoids and PRPF31 siRNA-treated organotypic retinal cultures to confirm an enrichment of differential splicing of microtubule, centrosomal, cilium and DNA damage response pathway genes in these cells. We show that genes with microtubule/centrosome/centriole/cilium gene ontology terms are enriched for weak 3′ and 5′ splice sites, and that subtle defects in spliceosome activity predominantly affect efficiency of splicing of these exons. We suggest that the primary defect in PRPF6 or PRPF31 mutant cells is microtubule and centrosomal defects, leading to defects in cilium and mitotic spindle stability, with the latter leading to DNA damage, triggering differential splicing of DNA damage response genes to activate this pathway. Finally, we expand understanding of “splicing factor RP” by investigating the function of TTLL3, one of the most statistically differentially expressed genes in PRPF6 and PRPF31 mutant cells. We identify that TTLL3 is the only tubulin glycylase expressed in the human retina, essential for monoglycylation of microtubules of the cilium, including the retinal photoreceptor cilium, to prevent cilium degeneration and retinal degeneration. Our preliminary data suggest that rescue of tubulin glycylation through overexpression of TTLL3 is sufficient to rescue cilium number in PRPF6 and PRPF31 mutant cells, suggesting that this defect underlies the cellular defect and may represent a potential target for therapeutic intervention in this group of disorders.

Mesenchymal stem cell-derived extracellular vesicles protect retina in a mouse model of retinitis pigmentosa by anti-inflammation through miR-146a-Nr4a3 axis

BackgroundRetinitis pigmentosa is a rod-cone degenerative disease that induces irreversible vision loss. This study probed the protective capacity of mesenchymal stem cell-derived small EVs (MSC-EVs) on the retinas of rd10 mice and the underlying mechanism.MethodsMSC-EVs were injected into the vitreous of rd10 mice at postnatal day 14 and P21; morphology and function were examined at P28. The mechanism of action was explored by using co-culture of photoreceptor cell line 661 W and microglia cell line BV2.ResultsTreatment with MSC-EVs increased the survival of photoreceptors and preserved their structure. Visual function, as reflected by optomotor and electroretinogram responses, was significantly enhanced in MSC-EVs-treated rd10 mice. Mechanistically, staining for Iba1, GFAP, F4/80, CD68 and CD206 showed that MSC-EVs suppressed the activation of microglial, Müller glial and macrophages. Furthermore, western blotting showed that the treatment inhibited the NF-κB pathway. RNA-seq and qPCR showed that MSC-EVs upregulated anti-inflammatory cytokines while downregulating pro-inflammatory cytokines. MSC-EVs application in vitro decreased the number of TUNEL-positive 661 W cells co-cultured with LPS-stimulated BV2, with similar impact on the cytokine expression as in vivo study. Genetic screening predicted miR-146a to be the downstream target of MSC-EVs, which was detected in MSC-EVs and upregulated in co-cultured 661 W cells and BV2 cells after MSC-EVs treatment. Upregulation of miR-146a by using its mimic decreased the expression of the transcription factor Nr4a3, and its downregulation inhibition promoted Nr4a3 expression in both 661 W and BV2 cells. Nr4a3 was further identified as the target gene of miR-146a by dual-luciferase assay. Furthermore, overexpressing miR-146a significantly decreased the expression of LPS-induced pro-inflammatory cytokines in BV2 cells.ConclusionsMSC-EVs delays retinal degeneration in rd10 mice mainly by its anti-inflammatory effect via the miR-146a-Nr4a3axis. Hence, MSC-EVs may be used in the treatment of neurodegenerative diseases.

A Potential Role of Cyclic Dependent Kinase 1 (CDK1) in Late Stage of Retinal Degeneration.

Cyclin dependent kinase 1 (CDK1) has long been known to drive the cell cycle and to regulate the division and differentiation of cells. Apart from its role in mitosis regulation, it also exerts multiple functions as a protein kinase, including engagement in cell death, possibly via a cell cycle-independent mechanism. The latter is suggested, since CDK1 re-expression can be found in non-dividing and terminally differentiated neurons in several neurodegeneration models. However, the details of if and how CDK1 might be involved in the neurodegenerative condition, retinitis pigmentosa (RP), which displays progressive vision loss, are unclear. In the present study, we investigated CDK1 in degenerating RP photoreceptors of the rd1 RP model, including whether there is a link between this kinase and the cGMP-PKG system, which is regarded as a disease driver. With experiments performed using either in vivo retinal tissue or in vitro material, via organotypic retinal explants, our results showed that CDK1 appears in the photoreceptors at a late stage of their degeneration, and in such a position, it may be associated with the cGMP-PKG network.

Epigenetics and Degenerative Retinal Diseases: Prospects for New Therapeutic Approaches.

There is growing evidence that retinal degenerative diseases are accompanied by epigenetic changes in both deoxyribonucleic acid methylation and histone modification. Even in the monogenic disease retinitis pigmentosa, there is a cascade of changes in gene expression that correlate with epigenetic changes, suggesting that many of the symptoms, and degenerative changes, may be a result of epigenetic changes downstream from the genetic mutation. This is supported by data from studies of diabetic retinopathy and macular degeneration, 2 diseases where it has been difficult to define a single causative change. Initial studies with modifiers of deoxyribonucleic acid methylation suggest that they can provide therapeutic benefit. A number of drugs are available to inhibit specific epigenetic histone modifier enzymes, and these offer the possibility of new therapeutic approaches to retinal disease. Systemic treatment with inhibitors of histone demethylases and histone deacetylases have arrested rod degeneration in rodent models of retinitis pigmentosa. Some evidence has suggested that similar treatments may provide benefits for patients with diabetic retinopathy. Because differentiation of retinal stem cells is regulated in part by epigenetic mechanisms, it may also be possible to direct stem cell differentiation pathways through the use of selective epigenetic modifiers. This is predicted to provide a valuable avenue to accelerate the introduction of regenerative approaches to retinal disease. Epigenetic modifiers are poised to become a powerful new approach to treat retinal degenerative diseases.

Light-induced charge generation in polymeric nanoparticles restores vision in advanced-stage retinitis pigmentosa rats

Retinal dystrophies such as Retinitis pigmentosa are among the most prevalent causes of inherited legal blindness, for which treatments are in demand. Retinal prostheses have been developed to stimulate the inner retinal network that, initially spared by degeneration, deteriorates in the late stages of the disease. We recently reported that conjugated polymer nanoparticles persistently rescue visual activities after a single subretinal injection in the Royal College of Surgeons rat model of Retinitis pigmentosa. Here we demonstrate that conjugated polymer nanoparticles can reinstate physiological signals at the cortical level and visually driven activities when microinjected in 10-months-old Royal College of Surgeons rats bearing fully light-insensitive retinas. The extent of visual restoration positively correlates with the nanoparticle density and hybrid contacts with second-order retinal neurons. The results establish the functional role of organic photovoltaic nanoparticles in restoring visual activities in fully degenerate retinas with intense inner retina rewiring, a stage of the disease in which patients are subjected to prosthetic interventions.

DNA and RNA oxidative damage in the retina is associated with ganglion cell mitochondria

This study examines retinas from a rat glaucoma model for oxidized nucleosides 8OHdG and 8OHG, biomarkers for oxidative damage of DNA and RNA, respectively. Immunohistochemical data indicate a predominant localization of 8OHdG/8OHG in retinal ganglion cells (RGCs). The levels for these oxidized DNA/RNA products were 3.2 and 2.8 fold higher at 1 and 2 weeks after intraocular pressure elevation compared to control retinas, respectively. 8OHdG/8OHG were almost exclusively associated with mitochondrial DNA/RNA: ~ 65% of 8OHdG/8OHG were associated with RNA isolated from mitochondrial fraction and ~ 35% with DNA. Furthermore, we analyzed retinas of the rd10 mouse, a model for retinitis pigmentosa, with severe degeneration of photoreceptors to determine whether high levels of 8OHdG/8OHG staining intensity in RGCs of control animals is related to the high level of mitochondrial oxidative phosphorylation necessary to support light-evoked RGC activity. No significant difference in 8OHdG/8OHG staining intensity between control and rd10 mouse retinas was observed. The results of this study suggest that high levels of 8OHdG/8OHG in RGCs of wild-type animals may lead to cell damage and progressive loss of RGCs observed during normal aging, whereas ocular hypertension-induced increase in the level of oxidatively damaged mitochondrial DNA/RNA could contribute to glaucomatous neurodegeneration.

Metabolic alterations in the visual pathway of retinitis pigmentosa rats: A longitudinal multimodal magnetic resonance imaging study with histopathological validation.

Because retinitis pigmentosa (RP) has been shown to cause degenerative changes in the entire visual pathway, there is an urgent need to perform longitudinal assessments of RP-induced degeneration and identify imaging protocols to detect this degeneration as early as possible. In this study, we assessed a transgenic rat model of RP by using complementary noninvasive magnetic resonance imaging techniques, namely, proton magnetic resonance spectroscopy (1 H-MRS), to investigate the metabolic changes in RP. Our study demonstrated decreased concentrations and ratios to creatine (Cr) of N-acetylaspartate (NAA), glutamate (Glu), γ-aminobutyric acid (GABA), and taurine (Tau), whereas myo-inositol (Ins) and choline (Cho) were increased in the visual cortex of Royal College of Surgeons (RCS) rats compared with control rats (p < 0.05). Furthermore, with the progression of RP, the concentrations of NAA, Glu, GABA, and Tau, and the ratios of GABA/Cr and Tau/Cr significantly decreased over time, whereas the concentrations of Ins and Cho and the ratio of Ins/Cr significantly increased over time (p < 0.05). In addition, in RCS rats, NAA/Cr decreased significantly from 3 to 4 months postnatal (p < 0.001), and Cho/Cr increased significantly from 4 to 5 months postnatal (p = 0.005). Meanwhile, the 1 H-MRS indicators in 5-month postnatal RCS rats could be confirmed by immunohistochemical staining. In conclusion, with the progression of RP, the metabolic alterations in the visual cortex indicated progressive reprogramming with the decrease of neurons and axons, accompanied by the proliferation of gliocytes.

Possible Role of Insulin-Degrading Enzyme in the Physiopathology of Retinitis Pigmentosa.

Insulin-degrading enzyme (IDE) was named after its role as a proteolytic enzyme of insulin. However, recent findings suggest that IDE is a widely expressed, multitask protein, with both proteolytic and non-proteolytic functions. Here, we characterize the expression of IDE in the mammalian retina in both physiological and pathological conditions. We found that IDE was enriched in cone inner segments. IDE levels were downregulated in the dystrophic retina of several mouse models of retinitis pigmentosa carrying distinct mutations. In rd10 mice, a commonly studied mouse model of retinitis pigmentosa, treatment with an IDE activator (a synthetic peptide analog of preimplantation factor) delayed loss of visual function and preserved photoreceptor cells. Together, these results point to potential novel roles for IDE in retinal physiology and disease, further extending the list of diverse functions attributed to this enzyme.

Inverse Problem Reveals Conditions for Characteristic Retinal Degeneration Patterns in Retinitis Pigmentosa Under the Trophic Factor Hypothesis.

Retinitis pigmentosa (RP) is the most common inherited retinal dystrophy with a prevalence of about 1 in 4,000, affecting approximately 1.5 million people worldwide. Patients with RP experience progressive visual field loss as the retina degenerates, destroying light-sensitive photoreceptor cells (rods and cones), with rods affected earlier and more severely than cones. Spatio-temporal patterns of retinal degeneration in human RP have been well characterised; however, the mechanism(s) giving rise to these patterns have not been conclusively determined. One such mechanism, which has received a wealth of experimental support, is described by the trophic factor hypothesis. This hypothesis suggests that rods produce a trophic factor necessary for cone survival; the loss of rods depletes this factor, leading to cone degeneration. In this article, we formulate a partial differential equation mathematical model of RP in one spatial dimension, spanning the region between the retinal centre (fovea) and the retinal edge (ora serrata). Using this model we derive and solve an inverse problem, revealing for the first time experimentally testable conditions under which the trophic factor mechanism will qualitatively recapitulate the spatio-temporal patterns of retinal regeneration observed in human RP.

First person - Michael Robichaux.

ABSTRACTFirst Person is a series of interviews with the first authors of a selection of papers published in Disease Models & Mechanisms, helping early-career researchers promote themselves alongside their papers. Michael Robichaux is first author on ‘ Subcellular localization of mutant P23H rhodopsin in an RFP fusion knock-in mouse model of retinitis pigmentosa’, published in DMM. Michael conducted the research described in this article while a postdoctoral fellow in Ted Wensel's lab at Baylor College of Medicine, Houston, TX, USA. He is now an assistant professor at West Virginia University, Morgantown, WV, USA, investigating the intricate subcellular processes in photoreceptor neurons that enable vision.

Myo/Nog Cells Migrate to Areas of Cell Death and are Phagocytic in a Murine Model of Retinitis Pigmentosa

IntroductionRetinitis Pigmentosa (RP) is a set of diseases that leads to progressive visual impairment, affecting over one million people worldwide. Despite the heterogeneity of the disease course and mechanism, the various forms of RP all involve progressive loss of retinal rod and cone cells. Myo/Nog cells have been shown to play a crucial role in ocular development. They have been implicated in neuroprotection in response to acute injuries and stress. In this study, we examined the behavior of Myo/Nog cells in a murine model of congenital retinitis pigmentosa (RP), determined the anatomical location of these cells as the degeneration progresses, and assessed their possible role of clearing out the debris caused by the degeneration.MethodsC3H/Hej (C3H) mice, which are homozygous for the cGMP phosphodiesterase 6B (PDE6) mutation (also known as the rd1 mutation), were used as the animal model of RP in this study. C3H and C57Bl/6J (C57) control mice were assessed at weeks 2.5, 3, 4, 5, and 6 using scotopic electroretinographs (ERG), ocular computer topography (OCT), and immunofluorescence microscopy. Enucleated eyes were fixed in paraformaldehyde and cryo‐sectioned. Sections were incubated in TUNEL reagent to detect and quantify cell death. Cryosections were labeled with a Myo/Nog specific monoclonal antibody to brain‐specific angiogenesis inhibitor (BAI1). Myo/Nog cell counts were performed by identifying the total number of BAI1+ cells, TUNEL+ cells, and the number of cells that were positive for both BAI1 and TUNEL. Myo/Nog cell counts, photoreceptor counts, outer nuclear layer (ONL), and inner nuclear layer (INL) thicknesses were all obtained using NIS elements software on a FluorScope microscope.ResultsERG showed decreased amplitudes of the A and B waves in C3H mice when compared to the C57 group. OCTs demonstrated a significant difference in retinal thickness between the two groups. Progressive thinning of the retina in the C3H mice was confirmed by microscopy. We observed early degeneration of the retina of C3H mice in the central and mid‐peripheral areas before week 2.5, which then progressed more significantly in the edge of the retina in later weeks. Myo/Nog cells were significantly more numerous in C3H mice compared to C57 mice at all time points. Most Myo/Nog cells of C3H mice were found in the outer nuclear layer (ONL) and within the neighboring choroid. Data obtained from ERG and histological demonstrated progressive photoreceptor loss over time, and a rapid decline in ONL/INL thickness between weeks 2.5‐4 in C3H mice. Myo/Nog cells appeared to have phagocytosed cell corpses as evidenced by the overlap in Myo/Nog cell labeling with the labeling of cellular debris (the depleted photoreceptors).ConclusionsThese findings are consistent with the behaviors of Myo/Nog cells in other forms of retinal stress and injury. Future studies will examine the importance of Myo/Nog cells in clearance in retinopathies.