Autophagy activation in the injured photoreceptor inhibits fas-mediated apoptosis.

Purpose: To examine the activation of autophagy and its relationship to Fas-mediated photoreceptor apoptosis during experimental retinal detachment.
Methods: Retina-retinal pigment epithelium (RPE) separation was created in Brown-Norway rats by subretinal injection of 1% hyaluronic acid and the intraretinal levels of the autophagy proteins LC3 and Atg5, the time course of LC3-I to LC3-II conversion, and the activation of cathepsins B and D were assayed with Western blot analysis and immunohistochemistry. We measured the ability of a Fas-activating antibody to induce LC3-I to LC3-II conversion in 661W cells, and the in vivo effect of Met12, a small molecule inhibitor of the Fas receptor, on LC3-I to LC3-II conversion and Atg5 expression. Autophagy activation was inhibited using 3-methyladenine (3-MA) or siRNA knockdown of Atg5 and the effect on apoptosis was measured using a caspase 8 activity assay, caspase 8 immunoblots, and photoreceptor TUNEL staining.
Results: Retina-RPE separation resulted in a Fas-dependent activation of autophagy, with increased Atg5 levels and intraphotoreceptor conversion of LC3-I to LC3-II. Detached retinas had increased levels of autophagosome-associated lysosomal proteases, cathepsins B and D. Inhibition of autophagy by 3-MA or siAtg5 accelerated the time course of caspase 8 activation and photoreceptor TUNEL staining.
Conclusions: Autophagy activation occurs in the photoreceptors after retina-RPE separation. This appears to be, at least in part, dependent on Fas receptor activation, and plays a role in regulating the level of photoreceptor apoptosis.