Role of the Fas-Signaling Pathway in Photoreceptor Neuroprotection

OBJECTIVE: To determine whether inhibiting the Fas proapoptosis pathway will result in increased photoreceptor survival after separation of the retina from the retinal pigment epithelium (RPE). METHODS: Retina/RPE separation was induced in rat and mouse eyes by the subretinal injection of hyaluronic acid, 1%. Fas-pathway signaling was inhibited by the concomitant injection of a Fas receptor-neutralizing antibody, small inhibitory RNA against the Fas-receptor transcript (siFAS), or the use of the Fas-receptor defective mouse strain LPR. Indices of photoreceptor death included terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) staining, cell counts, and retinal thickness measurements. Retinas were immunostained with antibodies against rhodopsin and cone opsin to evaluate rod and cone photopigment production, respectively. RESULTS: Inhibition of Fas signaling using Fas receptor-neutralizing antibody, siFas, or LPR mice resulted in a significant reduction in the number of TUNEL-positive photoreceptor cells as well as in a significant preservation of outer nuclear layer cell counts and thickness as compared with retina/RPE separation in eyes with intact Fas signaling. Fas-pathway inhibition resulted in preservation of both rhodopsin- and cone opsin-positive cells. CONCLUSIONS: Inhibition of the Fas proapoptosis pathway results in significant photoreceptor preservation after retinal separation from the RPE. CLINICAL RELEVANCE: Fas-pathway inhibition might serve as a novel mechanism for preserving photoreceptor cells during retinal disease.