Abstract
Purpose::
The integrity of the Retinal Pigment Epithelium (RPE) layer is important for the survival of photoreceptors. RPE cell damage and photoreceptor loss are common features of retinal diseases such as age-related macular degeneration. In this study we investigate whether the presence of RPE cells in degenerating eyes may prevent the disruption of inner retinal circuitry and reduce the loss of interneurons.
Methods::
In this study we examined two animal models, the acute and chronic light damaged rat eyes. Acute light damage male Wistar rats (n=18) were exposed to bright light (10K Lux) for 3hrs and then kept in a 12hr light/dark cycle lighting conditions (approx 100 Lux) of a normal animal house for up to 6 months. Chronic light damage Wistar rats were maintained under normal animal house lighting conditions (approx 100Lux) for up to 2 years. Animals were euthanasied with an overdose of sodium pentobarbital (150mg/kg I.P.). Eyes were removed and fixed with either 4% paraformaldehyde for 1hr and embedded for paraffin wax sectioning or in 2.5% glutaraldehyde overnight and subsequently resin embedded. Immunohistochemistry was performed on sections using glial markers GLAST, GFAP and CRALBP and neuronal markers PKC alpha and Glyt-1.
Results::
In the acute-light damaged eyes, there was a rapid loss of photoreceptors associated with RPE loss and a breakdown of Bruch's Membrane (BM). In the chronic-light damage rat eyes, there was a slow progressive loss of photoreceptors. In some chronic-light damaged eyes, overt photoreceptor loss was associated with the loss of RPE and a breakdown of BM. In eyes with overt photoreceptor and RPE cell loss, there was disruption of the inner retina. Bipolar and amacrine cell numbers were reduced as a result of cell death and the migration of interneurons. Migrated bipolar and amacrine cells were observed in ectopic positions in the choroid or in the ganglion cell layer. In contrast in light damage eyes where photoreceptors were completely lost and RPE cell were still present, there was no significant reduction in bipolar and amacrine cells numbers in comparison to controls.
Conclusions::
We confirm that acute and chronic light damage causes the loss of photoreceptors and RPE cells. In eyes with overt photoreceptor loss, which retain their RPE cells, also preserve bipolar and amacrine cells and maintain inner retinal organization. These data suggest that RPE cells are not only important for photoreceptor survival but also important for interneuron health and organization. Our data suggests that preserving RPE cells may be important for cell based repair therapies in degenerating retinas.
Keywords: retinal degenerations: cell biology • retinal pigment epithelium • bipolar cells