Retinal Photoreceptor Degeneration Research Articles

Photoreceptor cell death by apoptosis in dogs with sudden acquired retinal degeneration syndrome

SUMMARY Objective To examine the role of apoptosis in retinal photoreceptor degeneration in dogs with sudden acquired retinal degeneration syndrome (SARDS). Sample Population Retinas from 3 dogs with SARDS and from 2 clinically normal adult dogs. Procedure Apoptosis was identified by in situ endlabeling and observation of characteristic morphologic changes by light microscopy. Results The degree of photoreceptor degeneration varied with duration of vision loss in SARDS-affected eyes. The retina of all 3 SARDS-affected eyes had numerous (34, 61, and 70) apoptotic nuclei per section that were overwhelmingly located in the outer nuclear layer. Apoptotic nuclei were not detected, or were rare in similarly sized retinal sections from normal dogs. Inflammation was not an important feature of SARDS. Conclusions Apoptosis appears to be at least 1 mechanism of photoreceptor cell death in dogs with SARDS. Clinical Relevance Because apoptosis appears to be a final common pathway in many retinal degeneration syndromes, future treatment strategies that control apoptosis in other diseases may be applicable to dogs with SARDS. Halting this pathway may allow some photoreceptors to survive and, perhaps, preserve vision. (Am J Vet Res 1998;59:149–152)

Carcinoma-associated retinopathy in breast carcinoma and carcinoid tumor

Carcinoma-associated retinopathy (CAR) is a rare paraneoplastic syndrome characterized by diffuse retinal photoreceptor degeneration in the presence of an epithelial tumor. We report on three patients, who developed paraneoplastic retinopathy in the presence of breast carcinoma and a cervical carcinoid tumor. In addition to biomicroscopic, psychophysical, electrophysiological and angiographic examinations, serum samples were obtained for immunohistochemical staining of human retina. Ring-shaped visual field defects with statokinetic dissociation and abnormal rod and cone responses were found. Immunohistochemical findings included reactions at the level of the inner segments of the photoreceptors, the outer nuclear layer and the outer plexiform layer in absence of anti-recoverin antibodies. CAR should be considered in the differential diagnosis of visual loss in presence of tumors other than small-cell carcinoma of the lung. The presence of antiretinal antibodies is compatible with a tumor-induced immune response to epitopes shared by both the tumor and retinal tissue. Apparently, various retinal proteins may function as autoantigens.

Basic Fibroblast Growth Factor (bFGF) and Transforming Growth Factor Beta (TGF-β) Act as Stop and Go Signals to Modulate Postnatal Ocular Growth in the Chick

Occlusion of the eye (form deprivation) during post-natal development leads to ocular enlargement and myopia. The chick model of form deprivation myopia (FDM) has been used to identify candidate factors that underly the control of ocular growth. The major biochemical change associated with eye enlargement is an increase in scleral cartilage proteoglycan production (Rada et al., 1991) which is reduced in recovering eyes. Thus increasing evidence suggests that in the chicken eye, two different signals are involved, one for stop (occluder off) and one for go (occluder on). Because transforming growth factor-beta (TGF-β) and basic fibroblast growth factor (bFGF) are known to act in a push-pull manner in regulating extracellular matrix, their possible roles in FDM were tested. Chicks were occluded monocularly for 8 days, after which axial dimensions were assessed using A-scan ultrasonography, and refractive errors using streak retinoscopy. Under light halothane anesthesia, the control group received daily vehicle injections into both eyes whereas the experimental groups were treated with growth factors in the occluded eye and vehicle in the unoccluded eye.It was shown that: (1) bFGF reduced FDM in a dose-dependent manner, with a 50% effective dose (ED50) of 1·05 and 1·67 ng for subconjunctival and intravitreal delivery, respectively. Both axial eye length and refraction were similarly affected. The effects were mainly confined to a decrease in vitreous chamber depth. The anterior chamber was less deep but only after intravitreal injections, whereas lens thickness was not affected at all. At maximum effect, after subconjunctival applications the bFGF-treated occluded eyes were only 0·09 ± 0·16 mm longer than controls, which corresponded to a refractive error of - 0·67 ± 0·82 diopters (D), whereas after intravitreal applications the difference in axial eye length was - 0·07 ± 0·19 mm, corresponding to - 0·3 ± 0·52 D. (2) This effect could be mimicked by a FGF, but with a potency ∼ 160 times less than that of bFGF. The aFGF rescue effect could only be demonstrated for subconjunctival delivery; high intravitreal doses (≥ 300 ng per injection) induced retinal detachment and photoreceptor degeneration, while doses of aFGF close to the ED50 for bFGP (3 ng per injection) were completely ineffective. (3) TGF-β1 was not found to induce myopia in unoccluded eyes, or to increase myopia in occluded eyes. It was, however, a potent inhibitor of the bFGF rescue effect, if administered together with bFGF in the subconjunctival space. The addition of 50 pg of TGF-β1 resulted in increased axial eye lengths (0·65 ±0·24 mm) and higher myopic refractions (-3·67 ± 2·07 D), compared to eyes treated with bFGF alone (axial eye length: 0·09 ± 016 mm; refractive error: -0·67 ± 0·82 D).The observations show that bFGF and TGF-β1 are candidates for stop and go signals in the control of ocular growth. The possible roles and targets of these factors in the eye are discussed.

Strategies for rescue of retinal photoreceptor cells

A variety of genetic and environmental factors cause degeneration of retinal photoreceptors. This review focuses on current strategies to rescue defective, but still viable, rods and cones, including transplantation of normal retinal pigment epithelium cells, corrective gene therapy, administration of survival/growth factors, protection from the damaging effects of light, and dietary supplementation of vitamin A.

Transgenic mice with a rhodopsin mutation (Pro23His): A mouse model of autosomal dominant retinitis pigmentosa

We inserted into the germline of mice either a mutant or wild-type allele from a patient with retinitis pigmentosa and a missense mutation (P23H) in the rhodopsin gene. All three lines of transgenic mice with the mutant allele developed photoreceptor degeneration; the one with the least severe retinal photoreceptor degeneration had the lowest transgene expression, which was one-sixth the level of endogenous murine rod opsin. Of two lines of mice with the wild-type allele, one expressed approximately equal amounts of transgenic and murine opsin and maintained normal retinal function and structure. The other expressed approximately 5 times more transgenic than murine opsin and developed a retinal degeneration similar to that found in mice carrying a mutant allele, presumably due to the overexpression of this protein. Our findings help to establish the pathogenicity of mutant human P23H rod opsin and suggest that overexpression of wild-type human rod opsin leads to a remarkably similar photoreceptor degeneration.

Sick photoreceptors attract activated microglia from the ganglion cell layer: a model to study the inflammatory cascades in rats with inherited retinal dystrophy

Understanding of neuron-glial interactions in neurodegenerative diseases remains limited, but is of crucial importance for unravelling the etiology of such disorders both in humans and in animals. The present work employed a new, function-dependent technique for examining the role of microglia in rats afflicted with inherited retinal photoreceptor degeneration (strain: royal college of surgeons, RCS). In this rat strain, which served as a surrogate for human inherited retinal photoreceptor dystrophy, the optic nerve was cut and the ganglion cells were retrogradely labelled with the fluorescent dye 4Di-10ASP. The experiment was performed under three different conditions: (1) at the 50th day of postnatal age (P50) when there is ongoing degeneration of photoreceptor cells, (2) at P110 when most photoreceptors were degenerated and (3) at P50 in non-dystrophic rats of the Sprague-Dawley strain. After axotomy-induced ganglion cell death and labelling of activated microglia by phagocytosis of the ganglion cell debris, this study monitored whether the labelled and therefore identifiable microglial cells within the severed ganglion cell layer (GCL) are prompted to migrate and to participate in phagocytosis of debris produced within the endogenously degenerating photoreceptor cell layer (PRL). Massive migration of microglial cells from the GCL to the PRL occurred in dystrophic animals with optic nerve transection at P50. Double-labelling of microglial cells with the fluorescent dye ingested within the GCL and with lipofuscin ingested within the PRL indicated the ability of these cells to perform double-phagocytosis. Translocation of microglial cells towards the PRL did not occur when: (a) optic nerve transection was performed at P110 in dystrophic rats with completed photoreceptor degradation and therefore lacking stimuli for migration; (b) when the experiment was performed in retinae of normal, non-dystrophic rats, in which microglial cells were confined to the ganglion cell and to the inner plexiform layers only, that is to the layers which degenerated after optic nerve transection. The results, as revealed by this double-labelling in younger dystrophic rats, demonstrated that microglial cells possess the ability to respond specifically to dystrophy-induced stimuli and to migrate throughout the retinal depth.

A photoreceptor calcium binding protein is recognized by autoantibodies obtained from patients with cancer-associated retinopathy.

Cancer-associated retinopathy (CAR), a paraneoplastic syndrome, is characterized by the degeneration of retinal photoreceptors under conditions where the tumor and its metastases have not invaded the eye. The retinopathy often is apparent before the diagnosis of cancer and may be associated with autoantibodies that react with specific sites in the retina. We have examined the sera from patients with CAR to further characterize the retinal antigen. Western blot analysis of human retinal proteins reveals a prominent band at 26 kD that is labeled by the CAR antisera. Antibodies to the 26-kD protein were affinity-purified from complex CAR antisera and used for EM-immunocytochemical localization of the protein to the nuclei, inner and outer segments of both rod and cone cells. Other antibodies obtained from the CAR sera did not label photoreceptors. Using the affinity-purified antibodies for detection, the 26-kD protein, designated p26, was purified to homogeneity from the outer segments of bovine rod photoreceptor cells by Phenyl-Sepharose and ion exchange chromatography. Partial amino acid sequence of p26 was determined by gas phase Edman degradation and revealed extensive homology with a cone-specific protein, visinin. Based upon structural relatedness, both the p26 rod protein and visinin are members of the calmodulin family and contain calcium binding domains of the E-F hand structure.

Blindness in goats following ingestion of Stypandra glauca

Twenty-seven of 427 Angora goats of mixed age became blind within a week of consuming large amounts of Stypandra glauca ("nodding blue lily"). A further 200 goats were depressed for several weeks, but most subsequently recovered. Blindness was associated with optic nerve neuropathy which is postulated to have followed compression of the optic nerves within the bony optic canals as a result of severe myelin oedema. Histologically, the intracanalicular portion of the optic nerve was sclerotic, while the intracranial portion of the optic nerve and the optic tracts were degenerating. The retrobulbar portion of the optic nerve was relatively unaffected. In addition, multifocal retinal photoreceptor degeneration was found ophthalmoscopically and histologically. The syndrome was not reproduced during a trial in which 2 goats were fed 4 and 20 kg of S. glauca harvested after it had finished flowering, more than 3 weeks after the first natural cases of blindness. Based on epidemiological and pathological data we propose that S. glauca is toxic to stock, but only for a short period while flowering in spring.

Uveoretinitis in rabbits following immunization with interphotoreceptor retinoid-binding protein

Interphotoreceptor retinoid-binding protein (IRBP) is a glycoprotein found in the interphotoreceptor matrix between the neurosensory retina and the retinal pigment epithelium and is thought to shuttle retinol among cells that border the interphotoreceptor space. Immunization of rabbits with bovine IRBP caused subsequent photoreceptor degeneration, as documented by light- and electron microscopy. Beginning on post-injection day 18, scattered regions had photoreceptor outer segments that were disorganized and shortened or absent. Macrophages were found between the retinal pigment epithelium and neurosensory retina and within choroidal interstitium and blood vessels. Labeling of these cells with a marker specific for monocytic macrophages (RAM11) and absence of labeling with a marker for retinal pigment epithelium (rabbit anti-bovine cellular retinaldehyde-binding protein) suggest that these macrophages were hematogenous in origin. Staining of retinas with fluorescein isothiocyanate (FITC)-conjugated sheep anti-rabbit IgG revealed leakage of rabbit IgG into the interphotoreceptor matrix on and after day 18 in experimental animals but not in controls, suggesting breakdown of the outer blood-retinal barrier. Indirect immunofluorescence with anti-glial fibrillary acidic protein revealed labeling of Müller cells in experimental retinas on and after day 18, but not in control or shorter survival experimental retinas. There were foci of increased cellularity in the choroid on days 18, 26 and 39. From days 26 through 67, the retinal pathology became more widespread. Varying degrees of outer-segment degeneration were present in all parts of the retina and in many areas there was total loss of outer segments and loss of some photoreceptor-cell bodies. The inner retina appeared unaffected in all experimental and control retinas. These results demonstrate that injection of rabbits with bovine IRBP causes retinal photoreceptor degeneration as anti-IRBP titers increase and breakdown of the outer blood-retinal barrier ensues. Further studies will be required to elucidate factor(s) that control accessibility of the neurosensory retina to circulating antibodies against IRBP and other intrinsic retinal proteins.

Ovulatory function and retinal catecholamine concentrations in female rats with and without inherited retinal photoreceptor degeneration.

The timing of the critical period and LH surge during the afternoon of proestrus was unchanged in female rats with degenerated retinal photoreceptors (Hunter and Royal College of Surgeons strains), when compared to female rats with intact retinae (Piebald Virol Glaxo and Wistar strains). Both RCS and Wistar strains responded to constant light (LL) exposure by attaining persistent vaginal cornification at the same rate. In addition, both RCS and Wistar strains regained normal estrous cycles when moved from LL to control lighting (LD). Therefore, an intact retinal photoreceptor layer is not essential for normal ovulatory function. In addition, these results show that the effects of LL on gonadotrophin secretion are mediated through the brain and are not the result of retinal degeneration. Measurements of retinal concentrations of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (Dopac), in Wistar and RCS rats showed that concentrations of both compounds were reduced by LL, and then increased back to control values when animals were moved back into LD. Although the magnitude of the changes in retinal concentrations of DA and Dopac was greater in Wistar than in RCS rats (possibly related to the degeneration which occurs in Wistar but not RCS rats), these results suggest that dopaminergic cells, probably within the amacrine cell population of the retina, respond to different light regimes, perhaps by changes in activity.

An Ultrastructural Study of Retinal Photoreceptor Degeneration Associated with Bronchial Carcinoma

We studied both eyes of a 66-year-old man with retinal degeneration and oat cell carcinoma of the bronchus. Retinal degeneration was most marked peripheral to the parafovea where photoreceptor cells and their outer segments were absent. Within the parafovea, photoreceptor cells remained but rod outer segments were absent and cone outer segments were fragmented and disorganized. The retinal pigment epithelium contained many immature melanin granules within melanolysosomes, suggesting abnormal melanin synthesis and resorption. We suggest that a pharmacologically active substance resembling a hormone produced by the tumor increased melanin synthesis in the pigment epithelium and that the increased melanin content in these cells compromised their ability to phagocytose and maintain normal turnover of photoreceptor outer segments. We believe these changes led to photoreceptor outer segment loss and subsequent degeneration of the photoreceptor cells.

Experimental Klebsiella-induced endophthalmitis in the rabbit.

Klebsiella organisms have been reported in postoperative endophthalmitis. We describe an experimental model of endophthalmitis with anterior segment inflammation over the injection of Klebsiella oxytoca into the rabbit vitreous. Within 24 hours, polymorphonuclear leukocytes were found at the corneal limbus, adjacent to the endothelium, in the iris and ciliary body, throughout the vitreous, and in the optic nerve. Retinal photoreceptor degeneration was widespread within 48 hours. Mononuclear cells appeared in the vitreous within 72 hours. Increased pathologic manifestations concomitant with decreased numbers of recoverable, viable organisms implicate the endotoxins of K oxytoca in the observed pathologic condition. Our model may be useful in further studies on antibiotic therapy in Klebsiella ocular infections and in continuing work on the cross-reaction between Klebsiella and HLA-B27.

The effects of the pineal gland on light-induced retinal photoreceptor damage

Light-induced retinal photoreceptor degeneration was compared in pinealectomized and sham-pinealectomized rats at 40, 50 and 60 days of age. There was no significant difference in retinal damage between pinealectomized and sham-pinealectomized rats when they were subjected to light treatment at 40 or 50 days. However, 60-day-old pinealectomized rats showed less photoreceptor damage than did 60-day-old intact sham-pinealectomized rats when both groups were exposed to light treatment. The results suggest that the pineal gland plays a role in retinal metabolism. An hypothesis to explain the results is discussed; the effects of the pineal gland on the susceptibility of the retinal to photic damage is speculated to be endocrine in nature.

Continuous red light induces persistent estrus without retinal degeneration in the albino rat.

Female rats were exposed for 12 weeks to red (peak 660 nm) or Cool White continuous light (LL), or to 12 h per day (LD) of Cool White light, all at a flux density of 100 muw/cm2 (approximately 30 incident foot-candles). Either red or white LL produced significantly prolonged vaginal cornification and significantly reduced ovarian weight, as compared to LD exposure. White LL, but not red LL, produced degeneration of retinal photoreceptors.