CASPASE-7 ABLATION PROTECTS THE T17M RHODOPSIN MICE FROM SEVERE RETINAL DEGENERATION THROUGH REPROGRAMING OF THE UPR AND INHIBITION OF TRAF2-JNK APOPTOSIS

Purpose: We previously demonstrated that misfolded T17M rhodopsin (RHO) activates the Unfolded Protein Response (UPR) in mouse rod photoreceptor cells eventually leading to Autosomal Dominant Retinitis Pigmentosa. We also have shown that the ablation of the UPR-induced CASP-7 in T17M RHO transgenic mice slows down the rate of retinal degeneration measured by ERG and SD-OCT. Therefore, the goal of this study is to elucidate the molecular mechanisms involved in the preservation of vision in T17MRHO CASP7-/- retinas to validate new therapeutic targets Methods: In vitro and in vivo studies were conducted to elucidate the pathway by which CASP-7 ablation promotes the ADRP photoreceptor cell survival. RNA and protein extracts were obtained from the 661W cells co-transfected with either wt or T17M RHO plasmid and control or CASP-7 siRNA. Retinas were harvested from C57/BL6, T17MRHO, T17MRHO CASP7-/- mice at P30 to perform qRT-PCR and western blot analysis. Results: The study of the cellular signaling in T17MRHO CASP7-/- retina demonstrated that the preservation of the structure and function of ADRP photoreceptors is occurred via down-regulation of the UPR-induced gene and protein expression. The ATF4, pATF6, mTor and Hif1 proteins were down regulated by 55%, 57%, 31%, 77% correspondingly and the level of pAKT was elevated by 60% in T17MRHO CASP7-/- retina. In addition, the inhibition of PARP1 and TNFa proteins in T17MRHO CASP7-/- retina was observed. All together these modifications lead to diminishing the TRAF2 and pc-Jun by 31%, 50% correspondingly. In vitro study also confirmed the modulation of cellular signaling observed in T17M RHO CASP7-/- retina. Conclusions: Both in vivo and in vitro studies indicated that the ablation of CASP-7 in the T17MRHO retina prevents the deterioration of retinal function and structure through reprograming of the UPR and modulation of TRAF2-JNK-induced apoptosis. This reduction is believed to occur through the down-regulation of the mTOR and Hif1a proteins. The inhibition of the PARP1 and TNFa proteins is also found to be responsible for diminishing the TRAF2-JNK apoptosis. In both scenarios, the reduction in c-Jun apoptosis leads to ADRP photoreceptor survival. This study points out c-Jun as a potential therapeutic targets for ADRP treatment.