Glutathione peroxidase induced in rat retinas to counteract photic injury.

PURPOSE To examine the hypothesis that glutathione peroxidase (GPX) is induced at different time points after retinal exposure to light and localizes in different retinal cells. METHODS The rats were kept in cyclic light for 2 weeks before the experiments. The animals were maintained in 12-hour light-dark cycles, before and after exposure to intense white fluorescent light, for as long as 24 hours and then returned to cyclic light. Expression of GPX was measured by immunohistocytochemistry and Western and Northern blot analyses. Light-induced retinal damage was determined by the thickness of the outer nuclear layer (ONL) thickness in relation to total retinal thickness. RESULTS GPX labeling did not appear in the photoreceptor inner segments, and slight labeling was observed in the photoreceptor outer segments or the retinal pigment epithelial (RPE) cells in the normal retina kept in cyclic light. In retinal specimens maintained in light for 12 and 24 hours, GPX labeling was induced in the photoreceptor outer segments and RPE cells. High expression of GPX in the RPE was sustained until day 7 after challenge. In contrast, GPX expression in the photoreceptor outer segments decreased on day 1 and disappeared on days 3 and 7 after exposure. Intense GPX labeling was seen from the internal limiting membrane to the ganglion cell layer. GPX labeling was constantly localized in both high-intensity white light and cyclic conditions, suggesting no induction of GPX in those areas. In addition, GPX labeling was apparent at the posterior retinal pole but not at the peripheral retina. We observed marked upregulation of GPX mRNA in rats kept in high-intensity white light. One, 3, and 7 days after exposure to high-intensity white light, there was a significant difference (P < 0.0001) between the control and experimental groups in the ratio of the outer nuclear layer thickness to the entire retina. CONCLUSIONS GPX was induced at different time points after exposure to high-intensity white light and localized in different retinal cells. Changes in expression of GPX after exposure to light may be related to the difference in susceptibility of the retina to damage by light.