Abstract
Purpose: :
The retinal pigment epithelium (RPE) near the retinal margin proliferates slowly throughout life. Newly generated cells may move centrally to replace those lost with age. This is partly regulated by melanin, as albino animals exhibit a different proliferative capacity in comparison to pigmented animals. At a young age, albino RPE cells have a population of polyploidal cells, suggesting that cell cycle regulation may be abnormal. Here, we investigate the impact of ageing on the RPE and adjacent outer retina of both pigmentation phenotypes.
Methods: :
DA pigmented and albino Wistar rats aged 3 months and 20 months were used. Immunohistochemical analysis determined the RPE cell size, number of polyploidal cells, number of centrosomes and the effect of RPE65 on the RPE. Scanning electron microscopy (SEM) revealed the state of the overlying photoreceptors.
Results: :
Differences in pigmentation phenotype affect the ageing response of animals, with albinos having an accelerated form of ageing. First, albino animals have a greater increase in RPE cell loss with age. Second, there is a threefold increase in the number of polyploidal cells in the albino RPE. 40% of albino RPE cells are polyploidal with age, whilst less than 2% of DA RPE cells become polyploidal. Third, there is a significant decrease in the expression of RPE65 in the polyploidal cells. Fourth, the increased stress faced by the albino RPE leads to the marked deterioration of the overlying photoreceptor outer segments.
Conclusions: :
A culmination of factors results in the greater decline in the outer retina of the aged albino RPE. These results reveal that albinism is a progressive outer retinal disease.
Keywords: retinal pigment epithelium • aging