Constitutive and AP20187-induced Ret activation in photoreceptors does not protect from light-induced damage.

Delivery of glial cell-derived neurotrophic factor (GDNF), either as a recombinant protein or by retinal gene transfer results in photoreceptor (PR) neuroprotection in genetic models of retinitis pigmentosa (RP). The mechanism of GDNF action and its direct targets in the retina remain unknown. The goal of the present study was to test the neuroprotective effect of GDNF from light-induced damage, a commonly used stimulus of PR degeneration, and to determine whether protection occurs directly on PRs. METHODS: Adeno-associated viral vectors (AAV) were developed that expressed either GDNF or a constitutively (RetMen2A) or pharmacologically activated chimeric GDNF receptor (Fv2Ret). Fv2Ret homodimerization and activation are induced by the administration of the small dimerizer drug AP20187. AAV2/2 vectors and the cytomegalovirus (CMV) promoter were used to transduce GDNF in the retina, whereas RetMen2A and Fv2Ret were transduced by AAV2/5 vectors and their expression restricted to PRs by the rhodopsin promoter. In vivo GDNF levels were measured by ELISA, RetMen2A and Fv2Ret expression and activation in vitro and/or in vivo were assessed by Western blot and immunofluorescence analyses. E