Abstract
Abstract: :
Purpose: Mutations in a number of genes involved in the visual cycle result in various forms of inherited retinal degeneration, but it is not yet known whether genetic defects expressed in the retinal pigment epithelium induce apoptosis in the retina; the common pathway of photoreceptor cell death triggered by various external stimuli and other genetic defects. We therefore examined eyes from Rpe65 knockout mice for evidence of apoptotic retinal cell death, evaluated in comparison with Rho knockout mice. Methods: Eyes from Rpe65–/–, Rho–/–, and wild type mice were harvested at postnatal days 8, 25, 35, 50, 70, and 100. DNA fragmentation was visualized in paraffin embedded tissue sections by detection with TdT–FragELTM. Assays of Bax, Bcl–2, c–fos, and c–jun transcript abundance were performed using quantitative RT–PCR. Results: In Rpe65–/–, Rho–/–, and wild type mice, apoptotic retinal cell death was most pronounced at postnatal day 8, occurring in the inner nuclear layer at a time corresponding to developmental remodeling of the retina. Expression of the pro–apoptotic factor, Bax, was also at its highest level at this time. At postnatal day 25, in Rpe65–/– and Rho–/– mice but not wild type mice, a second less pronounced burst of apoptotic retinal cell death was seen in the outer nuclear layer. At older ages, the number of apoptotic retinal cells in mutant mice was significantly reduced to a level only slightly greater than in wild type. Analysis of the role of individual caspases potentially involved in the apoptotic mechanism is underway. Conclusions: Apoptotic retinal cell death occurs in both Rpe65–/– and Rho–/– mice with apparently similar timing and intensity. However, as photoreceptor cell degeneration in Rho–/– mice occurs at earlier ages and with greater severity than in Rpe65–/– mice, the extent of photoreceptor cell death may be determined by different factors or mechanisms in each case.
Keywords: retinal degenerations: hereditary • retinal pigment epithelium • apoptosis/cell death