Rat Model Of Retinitis Pigmentosa Research Articles

The impacts of resveratrol on the retinal degeneration in a rat model of retinitis pigmentosa induced by alkylation: an in-vivo study

ABSTRACT Upregulation of Sirtuin Type 1 (SIRT1), a nicotinamide adeninedinucleotide (NAD+)-dependent deacetylase, has been proved to protect against ample ocular diseases, while its effect on retinitis pigmentosa (RP) has not been illustrated. The study was aimed to explore the impacts of resveratrol (RSV), a SIRT1 activator, on the photoreceptor degeneration in a rat model of RP induced by N-methyl-N-nitrosourea (MNU), an alkylation. The rats were induced RP phenotypes via the intraperitoneal injection of MNU. The electroretinogram was conducted and revealed that RSV could not prevent the decline of retinal function in the RP rats. The optical coherence tomography (OCT) and the retinal histological examination were performed and showed that the reduced thickness of the outer nuclear layer (ONL) was not preserved by RSV intervention. The immunostaining technique was applied. Afther the MNU administration, the number of the apoptotic photoreceptors in the ONL throughout the retinasand the number of microglia cells present among the outer part throughout the retinas were not significantly reduced by RSV. Western blotting was also performed. The data showed that the level of SIRT1 protein was decreased after MNU administration, while RSV was not able to obviously alleviate the downregulation. Our data together indicated that RSV was not able to rescue the photoreceptor degeneration in the MNU-induced RP rats, which might be due to the MNU-induced consumption of the NAD+.

P3ht‐Graphene Device for the Restoration of Visual Properties in a Rat Model of Retinitis Pigmentosa

AbstractRetinal degeneration is one of the prevalent causes of blindness worldwide, for which no effective treatment has yet been identified. Inorganic photovoltaic devices have been investigated for visual restoration in advanced stage Retinitis pigmentosa (RP), although lack of implant flexibility and foreign‐object reactions have limited their application. Organic photoactive retinal prostheses may overcome these limitations, being biomimetic and tissue friendly. Inspired by organic photovoltaic strategies involving graphene, a hybrid retinal prosthesis is recently engineered consisting of a dual poly‐3‐hexylthiophene (P3HT) and graphene layer onto a flexible substrate. Here, this hybrid prosthesis is subretinally implanted in vivo in 5‐month‐old Royal College of Surgeons (RCS) rats, a rodent model of RP. Implanted dystrophic rats restored visual performances at both subcortical and cortical levels in response to light stimuli, in the absence of marked inflammatory responses. Moreover, the analysis of the physical‐mechanical properties after prolonged permanence in the eye showed excellent biocompatibility and robustness of the device. Overall, the results demonstrate that graphene‐enhanced organic photovoltaic devices can be suitably employed for the rescue of retinal dystrophies and supports the translation of the organic strategy into medical practice.

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.

Effect of NK-5962 on Gene Expression Profiling of Retina in a Rat Model of Retinitis Pigmentosa.

Purpose: NK-5962 is a key component of photoelectric dye-coupled polyethylene film, designated Okayama University type-retinal prosthesis (OUReP™). Previously, we found that NK-5962 solution could reduce the number of apoptotic photoreceptors in the eyes of the Royal College of Surgeons (RCS) rats by intravitreal injection under a 12 h light/dark cycle. This study aimed to explore possible molecular mechanisms underlying the anti-apoptotic effect of NK-5962 in the retina of RCS rats. Methods: RCS rats received intravitreal injections of NK-5962 solution in the left eye at the age of 3 and 4 weeks, before the age of 5 weeks when the speed in the apoptotic degeneration of photoreceptors reaches its peak. The vehicle-treated right eyes served as controls. All rats were housed under a 12 h light/dark cycle, and the retinas were dissected out at the age of 5 weeks for RNA sequence (RNA-seq) analysis. For the functional annotation of differentially expressed genes (DEGs), the Metascape and DAVID databases were used. Results: In total, 55 up-regulated DEGs, and one down-regulated gene (LYVE1) were found to be common among samples treated with NK-5962. These DEGs were analyzed using Gene Ontology (GO) term enrichment, Kyoto Encyclopedia of Genes and Genomes (KEGG), and Reactome pathway analyses. We focused on the up-regulated DEGs that were enriched in extracellular matrix organization, extracellular exosome, and PI3K–Akt signaling pathways. These terms and pathways may relate to mechanisms to protect photoreceptor cells. Moreover, our analyses suggest that SERPINF1, which encodes pigment epithelium-derived factor (PEDF), is one of the key regulatory genes involved in the anti-apoptotic effect of NK-5962 in RCS rat retinas. Conclusions: Our findings suggest that photoelectric dye NK-5962 may delay apoptotic death of photoreceptor cells in RCS rats by up-regulating genes related to extracellular matrix organization, extracellular exosome, and PI3K–Akt signaling pathways. Overall, our RNA-seq and bioinformatics analyses provide insights in the transcriptome responses in the dystrophic RCS rat retinas that were induced by NK-5962 intravitreal injection and offer potential target genes for developing new therapeutic strategies for patients with retinitis pigmentosa.

The Effect of Cyanine Dye NK-4 on Photoreceptor Degeneration in a Rat Model of Early-Stage Retinitis Pigmentosa.

The present study aimed to evaluate the effects of NK-4 on the apoptosis of photoreceptors in a rat model of retinitis pigmentosa and explore the mechanism underlying anti-apoptosis activity. The Royal College of Surgeons (RCS) rats received an intravitreous injection of NK-4 solution in the left eye and vehicle control in the right eye. Apoptosis was detected by TUNEL method in frozen sections of the eyes. The retinal tissues of the rats were dissected for RNA-seq analysis. Functional and pathway enrichment analyses of differentially expressed genes (DEGs) were performed by using Metascape and DAVID software. The expression levels of DEGs were confirmed by real-time quantitative PCR (RT-qPCR). The number of apoptotic cells decreased in the outer nuclear layer (ONL) and the thickness of the ONL was significantly thicker in the retina of NK-4-injected eyes, compared with control eyes. Five DEGs were identified by RNA-seq analysis, and Hmox1, Mt1, Atf5, Slc7a11, and Bdh2 were confirmed to be up-regulated by RT-qPCR. Functional and pathway enrichment analysis of the up-regulated genes showed that anti-apoptosis effects of NK-4 in the retina of RCS rats may be related to the pathways of metal ion homeostasis, negative regulation of neuron death, response to toxic substance, and pigment metabolic process. We found a potential mechanism of NK-4, providing a new viewpoint for the development of more therapeutic uses of NK-4 in the future.

AAV-CRB2 protects against vision loss in an inducible CRB1 retinitis pigmentosa mouse model

Loss of Crumbs homolog 1 (CRB1) or CRB2 proteins in Müller cells or photoreceptors in the mouse retina results in a CRB dose-dependent retinal phenotype. In this study, we present a novel Müller cell-specific Crb1KOCrb2LowMGC retinitis pigmentosa mouse model (complete loss of CRB1 and reduced levels of CRB2 specifically in Müller cells). The Crb double mutant mice showed deficits in electroretinography, optokinetic head tracking, and retinal morphology. Exposure of retinas to low levels of dl-α-aminoadipate acid induced gliosis and retinal disorganization in Crb1KOCrb2LowMGC retinas but not in wild-type or Crb1-deficient retinas. Crb1KOCrb2LowMGC mice showed a substantial decrease in inner/outer photoreceptor segment length and optokinetic head-tracking response. Intravitreal application of rAAV vectors expressing human CRB2 (hCRB2) in Müller cells of Crb1KOCrb2LowMGC mice subsequently exposed to low levels of dl-α-aminoadipate acid prevented loss of vision, whereas recombinant adeno-associated viral (rAAV) vectors expressing human CRB1 (hCRB1) did not. Both rAAV vectors partially protected the morphology of the retina. The results suggest that hCRB expression in Müller cells is vital for control of retinal cell adhesion at the outer limiting membrane, and that the rAAV-cytomegalovirus (CMV)-hCRB2 vector is more potent than rAAV-minimal CMV (CMVmin)-hCRB1 in protection against loss of vision.

Subretinally injected semiconducting polymer nanoparticles rescue vision in a rat model of retinal dystrophy.

Inherited retinal dystrophies and late-stage age-related macular degeneration, for which treatments remain limited, are among the most prevalent causes of legal blindness. Retinal prostheses have been developed to stimulate the inner retinal network; however, lack of sensitivity and resolution, and the need for wiring or external cameras, have limited their application. Here we show that conjugated polymer nanoparticles (P3HT NPs) mediate light-evoked stimulation of retinal neurons and persistently rescue visual functions when subretinally injected in a rat model of retinitis pigmentosa. P3HT NPs spread out over the entire subretinal space and promote light-dependent activation of spared inner retinal neurons, recovering subcortical, cortical and behavioural visual responses in the absence of trophic effects or retinal inflammation. By conferring sustained light sensitivity to degenerate retinas after a single injection, and with the potential for high spatial resolution, P3HT NPs provide a new avenue in retinal prosthetics with potential applications not only in retinitis pigmentosa, but also in age-related macular degeneration.

Longitudinal Structural and Microvascular Observation in RCS Rat Eyes Using Optical Coherence Tomography Angiography.

PurposeTo evaluate the change of retinal thickness and ocular microvasculature in a rat model of retinitis pigmentosa using swept source optical coherence tomography angiography (SS-OCTA)MethodsThree-weeks-old Royal College of Surgeons (RCS) rats (n = 8) and age-matched control rats (n = 14) were imaged by a prototype SS-OCTA system. Follow-up measurements occurred every three weeks on six RCS rats until week 18, and cross-sectional measurements were conducted on control rats. Thicknesses of different retinal layers and the total retina were measured. The enface angiograms from superficial vascular plexiform (SVP) and deep capillary plexiform (DCP) were analyzed, and the image sharpness was also extracted from the choroidal angiograms. Immunohistochemical analysis was done in the RCS rats after week 18, as well as in three-week-old RCS rats and age-matched controls.ResultsIn RCS rats, the thicknesses of the ganglion cell complex, the nuclear layer, the debris/photoreceptor layer and the total retina decreased over the weeks (P < 0.001). The SVP metrics remained unchanged whereas the DCP metrics decreased significantly over the weeks (P < 0.001). The immunohistochemical analysis confirmed our OCTA findings of capillary dropout in the DCP. The choroidal plexus appeared indistinct initially due to scattering of light at the intact retinal pigment epithelium (RPE) and became more visible after week nine probably due to RPE degeneration. Loss of choriocapillaris was visualized at week 18. In control rats, no vascular change was detected, but nuclear layers, photoreceptor layers and total retina showed slight thinning with age (P < 0.001).ConclusionsPhotoreceptor degeneration in RCS rats was associated with the loss of capillaries in DCP, but not in SVP. The OCTA imaging allows for the characterization of structural and angiographic changes in rodent models.

Differential effects of antipsychotic drugs on contrast response functions of retinal ganglion cells in wild-type Sprague-Dawley rats and P23H retinitis pigmentosa rats.

Antipsychotic drugs haloperidol and clozapine have been reported to increase the sensitivity of retinal ganglion cells (RGCs) to flashes of light in the P23H rat model of retinitis pigmentosa. In order to better understand the effects of these antipsychotic drugs on the visual responses of P23H rat RGCs, I examined the responses of RGCs to a drifting sinusoidal grating of various contrasts. In-vitro multielectrode array recordings were made from P23H rat RGCs and healthy Sprague-Dawley (SD) rat RGCs. Retinas were stimulated with a drifting sinusoidal grating with eight values of contrast (0, 4, 6, 8.5, 13, 26, 51, and 83%). Contrast response functions based on response amplitudes were fitted with a hyperbolic ratio function and contrast thresholds were determined from the fitted curves. SD rat RGCs were divided into two categories, saturating and non-saturating cells, based on whether they showed saturation of responses at high contrast levels. Most SD rat RGCs (58%) were saturating cells. Haloperidol and clozapine decreased the responses of saturating SD rat RGCs to all grating contrasts, except for the highest contrast tested. Clozapine also decreased the responses of non-saturating SD rat RGCs to all grating contrasts, except for the highest contrast tested. Haloperidol did not however significantly affect the responses of non-saturating SD rat RGCs. Haloperidol and clozapine increased the contrast thresholds of both saturating and non-saturating cells in SD rat retinas. Most (73%) P23H rat RGCs could be categorized as either saturating or non-saturating cells. The remaining ‘uncategorized’ cells were poorly responsive to the drifting grating and were analyzed separately. Haloperidol and clozapine increased the responses of non-saturating and uncategorized P23H rat RGCs to most grating contrasts, including the highest contrast tested. Haloperidol and clozapine also increased the responses of saturating P23H rat RGCs to most grating contrasts but these increases were not statistically significant. Haloperidol and clozapine decreased the contrast thresholds of saturating cells, non-saturating cells and uncategorized cells in P23H rat retinas, although the decrease in contrast thresholds of saturating cells was not found to be statistically significant. Overall, the findings show that haloperidol and clozapine have differential effects on the contrast response functions of SD and P23H rat RGCs. In contrast to the effects observed on SD rat RGCs, both haloperidol and clozapine increased the responsiveness of P23H rat RGCs to both low and high contrast visual stimuli and decreased contrast thresholds.

Long-term Rescue of Photoreceptors in a Rodent Model of Retinitis Pigmentosa Associated with MERTK Mutation

MERTK mutation reduces the ability of retinal pigment epithelial (RPE) cells to phagocytize the photoreceptor outer segments, which leads to accumulation of debris separating photoreceptors from RPE cells, resulting in their degeneration and loss of vision. In a rat model of Retinitis Pigmentosa due to MERTK mutation, we demonstrate that surgical removal of debris performed when about half of photoreceptors are lost (P38), allows the remaining photoreceptor cells to renew their outer segments and survive for at least 6 months – 3 times longer than in untreated eyes. In another set of experiments, patterned laser photocoagulation was performed before the debris formation (P19-25) to destroy a fraction of photoreceptors and thereby reduce the phagocytic load of shed outer segment fragments. This treatment also delayed the degeneration of the remaining photoreceptors. Both approaches were assessed functionally and morphologically, using electroretinography, optical coherence tomography, and histology. The long-term preservation of photoreceptors we observed indicates that MERTK-related form of inherited retinal degeneration, which has currently no cure, could be amenable to laser therapy or subretinal surgery, to extend the visual function, potentially for life.

Protective effect of clusterin on rod photoreceptor in rat model of retinitis pigmentosa.

Retinitis Pigmentosa (RP) begins with the death of rod photoreceptors and is slowly followed by a gradual loss of cones and a rearrangement of the remaining retinal neurons. Clusterin is a chaperone protein that protects cells and is involved in various pathophysiological stresses, including retinal degeneration. Using a well-established transgenic rat model of RP (rhodopsin S334ter), we investigated the effects of clusterin on rod photoreceptor survival. To investigate the role of clusterin in S334ter-line3 retinas, Voronoi analysis and immunohistochemistry were used to evaluate the geometry of rod distribution. Additionally, immunoblot analysis, Bax activation, STAT3 and Akt phosphorylation were used to evaluate the pathway involved in rod cell protection. In this study, clusterin (10μg/ml) intravitreal treatment produced robust preservation of rod photoreceptors in S334ter-line3 retina. The mean number of rods in 1mm2 was significantly greater in clusterin injected RP retinas (postnatal (P) 30, P45, P60, & P75) than in age-matched saline injected RP retinas (P<0.01). Clusterin activated Akt, STAT3 and significantly reduced Bax activity; in addition to inducing phosphorylated STAT3 in Müller cells, which suggests it may indirectly acts on photoreceptors. Thus, clusterin treatment may interferes with mechanisms leading to rod death by suppressing cell death through activation of Akt and STAT3, followed by Bax suppression. Novel insights into the pathway of how clusterin promotes the rod cell survival suggest this treatment may be a potential therapeutic strategy to slow progression of vision loss in human RP.

Controlled delivery of tauroursodeoxycholic acid from biodegradable microspheres slows retinal degeneration and vision loss in P23H rats.

Successful drug therapies for treating ocular diseases require effective concentrations of neuroprotective compounds maintained over time at the site of action. The purpose of this work was to assess the efficacy of intravitreal controlled delivery of tauroursodeoxycholic acid (TUDCA) encapsulated in poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres for the treatment of the retina in a rat model of retinitis pigmentosa. PLGA microspheres (MSs) containing TUDCA were produced by the O/W emulsion-solvent evaporation technique. Particle size and morphology were assessed by light scattering and scanning electronic microscopy, respectively. Homozygous P23H line 3 rats received a treatment of intravitreal injections of TUDCA-PLGA MSs. Retinal function was assessed by electroretinography at P30, P60, P90 and P120. The density, structure and synaptic contacts of retinal neurons were analyzed using immunofluorescence and confocal microscopy at P90 and P120. TUDCA-loaded PLGA MSs were spherical, with a smooth surface. The production yield was 78%, the MSs mean particle size was 23 μm and the drug loading resulted 12.5 ± 0.8 μg TUDCA/mg MSs. MSs were able to deliver the loaded active compound in a gradual and progressive manner over the 28-day in vitro release study. Scotopic electroretinografic responses showed increased ERG a- and b-wave amplitudes in TUDCA-PLGA-MSs-treated eyes as compared to those injected with unloaded PLGA particles. TUDCA-PLGA-MSs-treated eyes showed more photoreceptor rows than controls. The synaptic contacts of photoreceptors with bipolar and horizontal cells were also preserved in P23H rats treated with TUDCA-PLGA MSs. This work indicates that the slow and continuous delivery of TUDCA from PLGA-MSs has potential neuroprotective effects that could constitute a suitable therapy to prevent neurodegeneration and visual loss in retinitis pigmentosa.

Effects of Antipsychotic Drugs Haloperidol and Clozapine on Visual Responses of Retinal Ganglion Cells in a Rat Model of Retinitis Pigmentosa.

In the P23H rat model of retinitis pigmentosa, the dopamine D2 receptor antagonists sulpiride and eticlopride appear to improve visual responses of retinal ganglion cells (RGCs) by increasing light sensitivity of RGCs and transforming abnormal, long-latency ON-center RGCs into OFF-center cells. Antipsychotic drugs are believed to mediate their therapeutic benefits by blocking D2 receptors. This investigation was conducted to test whether haloperidol (a typical antipsychotic drug) and clozapine (an atypical antipsychotic drug) could similarly alter the light responses of RGCs in the P23H rat retina. Extracellular recordings were made from RGCs in isolated P23H rat retinas. Responses of RGCs to flashes of light were evaluated before and during bath application of a drug. Both haloperidol and clozapine increased light sensitivity of RGCs on average by ∼0.3 log unit. For those ON-center RGCs that exhibit an abnormally long-latency response to the onset of a small spot of light, both haloperidol and clozapine brought out a short-latency OFF response and markedly reduced the long-latency ON response. The selective serotonin 5-HT2A antagonist MDL 100907 had similar effects on RGCs. The effects of haloperidol on light responses of RGCs can be explained by its D2 receptor antagonism. The effects of clozapine on light responses of RGCs on the other hand may largely be due to its 5-HT2A receptor antagonism. Overall, the results suggest that antipsychotic drugs may be useful in improving vision in patients with retinitis pigmentosa.

Reshaping the Cone-Mosaic in a Rat Model of Retinitis Pigmentosa: Modulatory Role of ZO-1 Expression in DL-Alpha-Aminoadipic Acid Reshaping.

In S334ter-line-3 rat model of Retinitis Pigmentosa (RP), rod cell death induces the rearrangement of cones into mosaics of rings while the fibrotic processes of Müller cells remodel to fill the center of the rings. In contrast, previous work established that DL-alpha-aminoadipic-acid (AAA), a compound that transiently blocks Müller cell metabolism, abolishes these highly structured cone rings. Simultaneously, adherens-junction associated protein, Zonula occludens-1 (ZO-1) expression forms in a network between the photoreceptor segments and Müller cells processes. Thus, we hypothesized that AAA treatment alters the cone mosaic rings by disrupting the distal sealing formed by these fibrotic processes, either directly or indirectly, by down regulating the expression of ZO-1. Therefore, we examined these processes and ZO-1 expression at the outer retina after intravitreal injection of AAA and observed that AAA treatment transiently disrupts the distal glial sealing in RP retina, plus induces cones in rings to become more homogeneous. Moreover, ZO-1 expression is actively suppressed after 3 days of AAA treatment, which coincided with cone ring disruption. Similar modifications of glial sealing and cone distribution were observed after injection of siRNA to inhibit ZO-1 expression. These findings support our hypothesis and provide additional information about the critical role played by ZO-1 in glial sealing and shaping the ring mosaic in RP retina. These studies represent important advancements in the understanding of retinal degeneration’s etiology and pathophysiology.

Effects of Dopamine D2-Like Receptor Antagonists on Light Responses of Ganglion Cells in Wild-Type and P23H Rat Retinas.

In animal models of retinitis pigmentosa the dopaminergic system in the retina appears to be dysfunctional, which may contribute to the debilitated sight experienced by retinitis pigmentosa patients. Since dopamine D2-like receptors are known to modulate the activity of dopaminergic neurons, I examined the effects of dopamine D2-like receptor antagonists on the light responses of retinal ganglion cells (RGCs) in the P23H rat model of retinitis pigmentosa. Extracellular electrical recordings were made from RGCs in isolated transgenic P23H rat retinas and wild-type Sprague-Dawley rat retinas. Intensity-response curves to flashes of light were evaluated prior to and during bath application of a dopamine D2-like receptor antagonist. The dopamine D2/D3 receptor antagonists sulpiride and eticlopride and the D4 receptor antagonist L-745,870 increased light sensitivity of P23H rat RGCs but decreased light sensitivity in Sprague-Dawley rat RGCs. In addition, L-745,870, but not sulpiride or eticlopride, reduced the maximum peak responses of Sprague-Dawley rat RGCs. I describe for the first time ON-center RGCs in P23H rats that exhibit an abnormally long-latency (>200 ms) response to the onset of a small spot of light. Both sulpiride and eticlopride, but not L-745,870, reduced this ON response and brought out a short-latency OFF response, suggesting that these cells are in actuality OFF-center cells. Overall, the results show that the altered dopaminergic system in degenerate retinas contributes to the deteriorated light responses of RGCs.

Astrocytes and Müller Cell Alterations During Retinal Degeneration in a Transgenic Rat Model of Retinitis Pigmentosa.

Purpose: Retinitis pigmentosa includes a group of progressive retinal degenerative diseases that affect the structure and function of photoreceptors. Secondarily to the loss of photoreceptors, there is a reduction in retinal vascularization, which seems to influence the cellular degenerative process. Retinal macroglial cells, astrocytes, and Müller cells provide support for retinal neurons and are fundamental for maintaining normal retinal function. The aim of this study was to investigate the evolution of macroglial changes during retinal degeneration in P23H rats.Methods: Homozygous P23H line-3 rats aged from P18 to 18 months were used to study the evolution of the disease, and SD rats were used as controls. Immunolabeling with antibodies against GFAP, vimentin, and transducin were used to visualize macroglial cells and cone photoreceptors.Results: In P23H rats, increased GFAP labeling in Müller cells was observed as an early indicator of retinal gliosis. At 4 and 12 months of age, the apical processes of Müller cells in P23H rats clustered in firework-like structures, which were associated with ring-like shaped areas of cone degeneration in the outer nuclear layer. These structures were not observed at 16 months of age. The number of astrocytes was higher in P23H rats than in the SD matched controls at 4 and 12 months of age, supporting the idea of astrocyte proliferation. As the disease progressed, astrocytes exhibited a deteriorated morphology and marked hypertrophy. The increase in the complexity of the astrocytic processes correlated with greater connexin 43 expression and higher density of connexin 43 immunoreactive puncta within the ganglion cell layer (GCL) of P23H vs. SD rat retinas.Conclusions: In the P23H rat model of retinitis pigmentosa, the loss of photoreceptors triggers major changes in the number and morphology of glial cells affecting the inner retina.

TIMP-1 affects the spatial distribution of dendritic processes of second-order neurons in a rat model of Retinitis Pigmentosa

Retinitis Pigmentosa (RP) is an inherited disorder that may lead to blindness. In the rhodopsin S334ter-line-3 rat model of RP, the death of rods induces spatial rearrangement of cones into regular ring mosaics. Using this model, we discovered that the ring mosaics are restored to a homogeneous distribution upon application of tissue inhibitor of metalloproteinase-1 (TIMP-1). In this study, we further investigated the cone migration and spatial distribution of second-order neurons and their connections to cones in the presence or absence of TIMP-1 using immunohistochemistry to identify retinal neurons and their connections with cones. M-opsin cell bodies and their outer segments were evaluated to determine whether TIMP-1 delays the degeneration of outer segments of cones. We observed that during cone rearrangement into ring mosaics in RP retina, dendritic processes of second-order neurons undergo remodeling to maintain their synaptic connections with the cones in the rings. TIMP-1 treatment induced the cones to rearrange and dendritic processes of second-order neurons to return to a more homogeneous spatial distribution. In addition, TIMP-1 treatment protected the outer segments of cones at later stages of retinal degeneration. Our findings clearly demonstrate that despite their dramatic spatial rearrangement, cones and second-order neuron processes maintain their synaptic connections before and after TIMP-1 treatment.

The effect of TIMP-1 on the cone mosaic in the retina of the rat model of retinitis pigmentosa.

The array of photoreceptors found in normal retinas provides uniform and regular sampling of the visual space. In contrast, cones in retinas of the S334ter-line-3 rat model for RP migrate to form a mosaic of rings, leaving large holes with few or no photoreceptors. Similar mosaics appear in human patients with other forms of retinal dystrophy. In the current study, we aimed to investigate the effect of tissue inhibitor of metalloproteinase-1 (TIMP-1) on the mosaic of cones in S334ter-line-3 rat retinas. We focused on TIMP-1 because it is one of the regulators of the extracellular matrix important for cellular migration. Immunohistochemistry was performed to reveal M-opsin cone cells (M-cone) and the results were quantified to test statistically whether or not TIMP-1 restores the mosaics to normal. In particular, the tests focused on the Voronoi and nearest-neighbor distance analyses. Our tests indicated that TIMP-1 led to significant disruption of the M-opsin cone rings in S334ter-line-3 rat retinas and resulted in almost complete homogeneous mosaics. In addition, TIMP-1 induced the M-cone spatial distribution to become closer to random with decreased regularity in S334ter-line-3 rat retinas. These findings confirm that TIMP-1 induced M-cone mosaics in S334ter-line-3 to gain homogeneity without reaching the degree of regularity seen in normal retinal mosaics. Even if TIMP-1 fails to promote regularity, the effects of this drug on homogeneity appear to be so dramatic that TIMP-1 may be a potential therapeutic agent. TIMP-1 improves sampling of the visual field simply by causing homogeneity.

Adenosine triphosphate-induced photoreceptor death and retinal remodeling in rats.

Many common causes of blindness involve the death of retinal photoreceptors, followed by progressive inner retinal cell remodeling. For an inducible model of retinal degeneration to be useful, it must recapitulate these changes. Intravitreal administration of adenosine triphosphate (ATP) has recently been found to induce acute photoreceptor death. The aim of this study was to characterize the chronic effects of ATP on retinal integrity. Five-week-old, dark agouti rats were administered 50 mM ATP into the vitreous of one eye and saline into the other. Vision was assessed using the electroretinogram and optokinetic response and retinal morphology investigated via histology. ATP caused significant loss of visual function within 1 day and loss of 50% of the photoreceptors within 1 week. At 3 months, 80% of photoreceptor nuclei were lost, and total photoreceptor loss occurred by 6 months. The degeneration and remodeling were similar to those found in heritable retinal dystrophies and age-related macular degeneration and included inner retinal neuronal loss, migration, and formation of new synapses; Müller cell gliosis, migration, and scarring; blood vessel loss; and retinal pigment epithelium migration. In addition, extreme degeneration and remodeling events, such as neuronal and glial migration outside the neural retina and proliferative changes in glial cells, were observed. These extreme changes were also observed in the 2-year-old P23H rhodopsin transgenic rat model of retinitis pigmentosa. This ATP-induced model of retinal degeneration may provide a valuable tool for developing pharmaceutical therapies or for testing electronic implants aimed at restoring vision. J. Comp. Neurol. 522:2928–2950, 2014. © 2014 Wiley Periodicals, Inc.

Effects of a Metabotropic Glutamate 1 Receptor Antagonist on Light Responses of Retinal Ganglion Cells in a Rat Model of Retinitis Pigmentosa

BackgroundRetinitis pigmentosa (RP) is a progressive retinal degenerative disease that causes deterioration of rod and cone photoreceptors. A well-studied animal model of RP is the transgenic P23H rat, which carries a mutation in the rhodopsin gene. Previously, I reported that blocking retinal GABAC receptors in the P23H rat increases light responsiveness of retinal ganglion cells (RGCs). Because activation of metabotropic glutamate 1 (mGlu1) receptors may enhance the release of GABA onto GABAC receptors, I examined the possibility that blocking retinal mGlu1 receptors might in itself increase light responsiveness of RGCs in the P23H rat.Methodology/Principal FindingsElectrical recordings were made from RGCs in isolated P23H rat retinas. Spike activity of RGCs was measured in response to brief flashes of light over a range of light intensities. Intensity-response curves were evaluated prior to and during bath application of the mGlu1 receptor antagonist JNJ16259685. I found that JNJ16259685 increased light sensitivity of all ON-center RGCs and most OFF-center RGCs studied. RGCs that were least sensitive to light showed the greatest JNJ16259685-induced increase in light sensitivity. On average, light sensitivity increased in ON-center RGCs by 0.58 log unit and in OFF-center RGCs by 0.13 log unit. JNJ16259685 increased the maximum peak response of ON-center RGCs by 7% but had no significant effect on the maximum peak response of OFF-center RGCs. The effects of JNJ16259685 on ON-center RGCs were occluded by a GABAC receptor antagonist.ConclusionsThe results of this study indicate that blocking retinal mGlu1 receptors in a rodent model of human RP potentiates transmission of any, weak signals originating from photoreceptors. This augmentation of photoreceptor-mediated signals to RGCs occurs presumably through a reduction in GABAC-mediated inhibition.