Extent Of Retinal Degeneration Research Articles

The Role of Autophagy in Chemical Proteasome Inhibition Model of Retinal Degeneration.

We recently demonstrated that chemical proteasome inhibition induced inner retinal degeneration, supporting the pivotal roles of the ubiquitin–proteasome system in retinal structural integrity maintenance. In this study, using beclin1-heterozygous (Becn1-Het) mice with autophagic dysfunction, we tested our hypothesis that autophagy could be a compensatory retinal protective mechanism for proteasomal impairment. Despite the reduced number of autophagosome, the ocular tissue morphology and intraocular pressure were normal. Surprisingly, Becn1-Het mice experienced the same extent of retinal degeneration as was observed in wild-type mice, following an intravitreal injection of a chemical proteasome inhibitor. Similarly, these mice equally responded to other chemical insults, including endoplasmic reticulum stress inducer, N-methyl-D-aspartate, and lipopolysaccharide. Interestingly, in cultured neuroblastoma cells, we found that the mammalian target of rapamycin-independent autophagy activators, lithium chloride and rilmenidine, rescued these cells against proteasome inhibition-induced death. These results suggest that Becn1-mediated autophagy is not an effective intrinsic protective mechanism for retinal damage induced by insults, including impaired proteasomal activity; furthermore, autophagic activation beyond normal levels is required to alleviate the cytotoxic effect of proteasomal inhibition. Further studies are underway to delineate the precise roles of different forms of autophagy, and investigate the effects of their activation in rescuing retinal neurons under various pathological conditions.

Amplitude and Latency of Electroretinographical Peaks as a tool to Predict the Extent of Retinal Degeneration in Retinitis Pigmentosa Patients

Retinitis Pigmentosa (RP) is a disease of visual system which causes loss of vision. Proper diagnosis of this disease is important as far as ophthalmologists and patients are concerned. The aim of present study is to use amplitude and latency of Electroretinographical Peaks a and b to diagnose the extent of retinal degeneration in RP patients. A population of 100 subjects was selected for the purpose of this study. Fifty subjects with normal visual system mainly retina were considered as a control group. Along with control group, 50 patients pre-diagnosed as RP were selected as a case group. Electroretinography was examined in total population. The results obtained were compared together to look for the possible changes in two groups which showed changes in amplitude and latency of ERG a and b peaks of case group in comparison to control population. It can be concluded that amplitude and latency of ERG, a and b waves can be helpful to predict the extent of retinal degeneration in RP patients.

Retinal gene therapy.

Inherited retinal diseases are the leading cause of sight impairment in people of working age in England and Wales, and the second commonest in childhood. Gene therapy offers the potential for benefit. Pubmed and clinicaltrials.gov. Gene therapy can improve vision in RPE65-associated Leber Congenital Amaurosis (RPE65-LCA). Potential benefit depends on efficient gene transfer and is limited by the extent of retinal degeneration. The magnitude of vision improvement from RPE65-LCA gene therapy is suboptimal, and its durability may be limited by progressive retinal degeneration. The safety and potential benefit of gene therapy for inherited and acquired retinal diseases is being explored in a rapidly expanding number of trials. Developments in vector design and delivery will enable greater efficiency and safety of gene transfer. Optimization of trial design will accelerate reliable assessment of outcomes.

Spectral sensitivity measurements reveal partial success in restoring missing rod function with gene therapy

Rod visual function can be established with some certainty by demonstrating that dark-adapted visual spectral sensitivity has the shape of the rod (scotopic) spectral sensitivity function and that this scotopic shape collapses to a cone (photopic) shape when cones, but not rods, have recovered following an intense bleach. We used these tests to assess retinal function in eight young adult and child patients with early-onset severe retinal dystrophy enrolled in phase II of a clinical gene therapy trial for RPE65 deficiency, an isomerase, the lack of which disrupts the “visual cycle” upon which rods solely depend for regenerating visual pigment after light exposure. The trial involved subretinal delivery of a recombinant adeno-associated viral vector expressing RPE65. After gene therapy, substantial improvements in 1-Hz dark-adapted flicker sensitivity were found in two of the eight patients. One patient showed up to a 1000-fold improvement in sensitivity 4 months after treatment, and the second, up to a 100-fold improvement 6 months after treatment. In both cases, the spectral sensitivity after treatment was rod-like after normal periods of dark adaptation, but remained cone-like during the cone plateau after an intense bleach. The dark-adapted spectral sensitivities of the other six patients were cone-like both before and after treatment with only minimal sensitivity changes. It is not clear why restored rod function was evident in only some patients, but the response may be limited by the extent of retinal degeneration at the locus tested. Meeting abstract presented at VSS 2015

Effect of Para-Aminobenzoic Acid on the Course of Retinal Degeneration in the rd10 Mouse

Recent evidence suggests that oxidative injury plays a significant role in the pathogenesis of retinal degenerative diseases. Para-aminobenzoic acid (PABA) is a cyclic amino acid, which may act to decrease lipid peroxidation and oxidative injury. Our aim was to evaluate the efficacy of PABA in attenuating oxidative injury and rate of retinal degeneration in the rd10 mouse. PABA (50 mg/kg) was administered intraperitoneally six times per week in 28 rd10 mice from postnatal day 3. Twenty-four littermate control mice were similarly injected with saline. At 3, 4.5, and 6 weeks of age, electrophysiological (full field electroretinogram-ERG), quantitative histological, and immunohistochemical techniques were used to assess the course and extent of retinal degeneration. Degree of lipid peroxidation was determined by the measurement of thiobarbituric acid reactive species (TBARS) and retinal carbonyl content was quantified using the 2,4-dinitrophenylhydrazine method. Dark adapted mixed rod-cone ERG responses at 3 weeks of age were higher in the PABA-treated group as compared to saline control (P < 0.05). By 4.5 weeks, this protective effect was largely abolished and by 6 weeks ERG was unrecordable in both groups. However, at both 3 and 4.5 weeks of age, light-adapted cone ERG amplitudes were better preserved in PABA-treated animals. At 4.5 weeks, thickness of the outer nuclear layer was 28.6% higher in the peripheral retina of PABA-treated mice as compared to controls (P < 0.05). Quantitative immunohistochemistry revealed 2.4-fold higher red/green cone opsin content in the retinas of PABA-treated mice (P < 0.005). At both 3 and 4.5 weeks, levels of TBARS and protein carbonyls were 49%-69% lower in PABA-treated retinas (P < 0.05-0.0005), suggesting less oxidative injury. PABA treatment may protect retinal function and attenuate the course of retinal degeneration in rd10 mice. Biochemical parameters indicate a lower degree of oxidative injury in PABA-treated retinas. PABA may potentially serve as an addition to antioxidative treatment for retinal and macular degenerations.

Docosahexaenoic acid attenuates microglial activation and delays early retinal degeneration

Microgliosis is a common phenomenon in neurodegenerative disorders including retinal dystrophies. We performed a detailed characterization of activated microglia in the retinoschisin (Rs1h)-deficient (Rs1h(-/Y)) mouse model of inherited retinal degeneration. To visualize and isolate microglia, we crossed Rs1h(-/Y) animals with transgenic MacGreen mice, which express green fluorescent protein under the control of the macrophage-specific csf1r promoter. Activated microglia were detected in retinal sections and whole-mounts of early postnatal MacGreen/Rs1h(-/Y) mice before the onset of overt neuronal cell death. These activated microglia contained prominent lipid droplets and analysis of the retinal lipid composition showed decreased docosahexaenoic acid (DHA) levels in Rs1h(-/Y) retinas. To establish a link between microglia activation, reduced DHA levels, and neurodegeneration, a dietary intervention study was performed. Female Rs1h(-/-) mice and their Rs1h(-/Y) litter were either subjected to a diet enriched with DHA, or a control chow lacking DHA. Supplementation with DHA enhanced photoreceptor survival and converted activated microglia to a quiescent phenotype. Furthermore, DHA, but not docosapentaenoic acid or adrenic acid reduced pro-inflammatory gene expression, migration, and lipid accumulation of cultured BV-2 microglia. We conclude that retinal DHA levels control the activity of microglia and thereby may affect the progression and extent of retinal degeneration.

Characterization of Rhodopsin P23H-Induced Retinal Degeneration in aXenopus laevisModel of Retinitis Pigmentosa

To investigate the pathogenic mechanisms that underlie retinal degeneration induced by the rhodopsin mutation P23H in a Xenopus laevis model of RP. Transgenic X. laevis were generated that expressed the rhodopsin mutants rhoP23H and rhoP23H/K29R (a variant incapable of transducin activation). Using quantitative dot blot assay, transgenic rhodopsin levels and the extent of retinal degeneration were determined. The contribution of rhodopsin signal transduction to cell death was assessed by comparison of rhoP23H and rhoP23H/K296R effects and by dark rearing of rhoP23H tadpoles. Intracellular localization and the oligomeric state of rhoP23H were determined by confocal immunofluorescence microscopy and Western blot analysis. RhoP23H induced retinal degeneration in a dose-dependent manner whereas expression of a control rhodopsin did not, indicating that rod photoreceptor death was specific to the P23H mutation and was not caused by the overexpression of rhodopsin. Neither abolishment of rhoP23H photosensitivity and ability to activate transducin nor dark rearing rescued rod viability. RhoP23H was localized primarily to the endoplasmic reticulum (ER) of inner segments. Western blot analysis of transgenic retinas showed that rhoP23H was prone to form dimers and higher molecular weight oligomers. However, aggresomes were not observed in rhoP23H transgenic retinal sections, despite their being reported in cultured cells expressing rhoP23H. These results support a role for rhoP23H misfolding and inner segment accumulation in rod death, possibly by ER overload or other cellular stress pathways rather than by altered rhodopsin signal transduction or aggresome formation.

Constitutive overexpression of human erythropoietin protects the mouse retina against induced but not inherited retinal degeneration.

Elevation of erythropoietin (Epo) concentrations by hypoxic preconditioning or application of recombinant human Epo (huEpo) protects the mouse retina against light-induced degeneration by inhibiting photoreceptor cell apoptosis. Because photoreceptor apoptosis is also the common path to cell loss in retinal dystrophies such as retinitis pigmentosa (RP), we tested whether high levels of huEpo would reduce apoptotic cell death in two mouse models of human RP. We combined the two respective mutant mouse lines with a transgenic line (tg6) that constitutively overexpresses huEpo mainly in neural tissues. Transgenic expression of huEpo caused constitutively high levels of Epo in the retina and protected photoreceptors against light-induced degeneration; however, the presence of high levels of huEpo did not affect the course or the extent of retinal degeneration in a light-independent (rd1) and a light-accelerated (VPP) mouse model of RP. Similarly, repetitive intraperitoneal injections of recombinant huEpo did not protect the retina in the rd1 and the VPP mouse. Lack of neuroprotection by Epo in the two models of inherited retinal degeneration was not caused by adaptational downregulation of Epo receptor. Our results suggest that apoptotic mechanisms during acute, light-induced photoreceptor cell death differ from those in genetically based retinal degeneration. Therapeutic intervention with cell death in inherited retinal degeneration may therefore require different drugs and treatments.

Histopathologic study of variation in severity of retinitis pigmentosa due to the dominant rhodopsin mutation Pro23His

PURPOSE: To compare histopathologic findings in an autopsy eye of an 87-year-old woman with retinitis pigmentosa and the rhodopsin mutation Pro23His with findings in an autopsy eye of a 77-year-old female relative (first cousin) with retinitis pigmentosa and the same mutation. DESIGN: Histopathologic study. METHODS: One eye from each patient was prepared for light and electron microscopy within 5 hours after death. Photoreceptor nuclear counts were performed. RESULTS: Photoreceptor degeneration and intraretinal bone spicule pigmentation were evident in both cases. The younger patient had more extensive photoreceptor loss and more intraretinal pigmentation than her older relative. CONCLUSION: A marked variation in the extent of retinal degeneration can be seen in two relatives with retinitis pigmentosa and rhodopsin, Pro23His. This study supports the idea that factors other than the primary gene defect are responsible for the severity of this condition.

Optokinetic nystagmus in progressive retinal degeneration.

Optokinetic nystagmus (OKN) was studied in both normally pigmented and delayed amelanotic (DAM) strains of domestic chicken. The DAM line is characterized by postnatal feather and ocular depigmentation accompanied by progressive retinal degeneration that occurs, initially and most severely, in the central retina. A close association exists between the extent of ocular pigment loss and relative reduction in OKN responsiveness in DAMs. The directional asymmetry of OKN responses, which normally occurs with monocular temporal-to-nasal (T-N) but not to nasal-to-temporal (N-T) stimulation, was altered in relation to the extent of ocular amelanosis among DAMs. In particular, T-N OKN responses were progressively reduced as amelanosis of the central retina increased in severity. In DAMs with moderate to severe reductions in T-N responsiveness, relatively little reduction occurred in N-T responsiveness. The central retina, therefore, appears to play a major role in mediating responses to T-N stimulation, whereas the peripheral retina mediates both directions of response. Optokinetic nystagmus also provides a useful index of the extent of retinal degeneration and the progressive loss of retinal pigment epithelium and photoreceptors which occurs in this mutant strain.

Postembryonic eye degeneration in the troglobitic salamander Typhlotriton spelaeus.

Comparative histological observations of the eyes of Typhlotriton spelaeus and several epigean, plethodontid species indicate that the principal postembryonic degenerative changes in the eyes of T. spelaeus involve the eyelids and cornea, visual cells, outer plexiform layer, and the pigment epithelium. Ordinarily these changes were initiated after metamorphosis, before attainment of sexual maturity, but a few larvae had degenerating retinae. The corneal epithelium becomes irregular and thin as eyelids develop during and after metamorphosis, but retains its larval structure in animals in which eyelid overlap is incomplete. Disruption and vacuolation of the lens sometimes occurs in postmetamorphic animals with degenerating visual cells. Retinal degeneration involves reduction of the inner and outer segments of visual cells, loss of the outer plexiform layer, and retraction of apical processes of the pigment epithelium. In its earliest stage, retinal reduction is first apparent at the retinal margin where visual cells are normally less well-differentiated, but in its terminal stage reduction has gone to completion over the entire retina. Extent of retinal degeneration in adults is directly related to postmetamorphic age but there is variability in each age group. Females generally have smaller eyes, and more extensive degeneration of visual cells than males. The loss of visual function in adults is correlated with extensive visual cell degeneration.