Rapamycin Attenuates Visible Light-induced Injury In Retinal Photoreceptor Cells Via Inhibiting Endoplasmic Reticulum Stress

Purpose The objective of this study was to investigate the molecularmechanisms and signaling pathway that rapamycin protects661Wcells from visible light-induced injury.Metheds After661W cells were exposed to2600-Lux light, cell viability anddeath were monitored with MTT and propidium iodide staining. Thechanges of reactive oxygen species (ROS) in the661W cells wasdetected with a2’,7’-dichlorfluorescein-Diacetate(DCFH-DA) assay.We examined the morphology of the ER with transmission electronmicroscopy. We examined the changes of ER stress markers usingwestern blot and quantitative RT-PCR. Rapamycin pretreatmentsignificantly suppressed light-induced ER stress and all three majorbranches of the unfolded protein response (UPR), including PERK,IRE1and ATF6pathways both at the protein and mRNA levels.Additionally, the inhibition of ER stress by rapamycin was furtherconfirmed with adithiothreitol (DTT;a classical ER stressinducer)-damaged661W cell model.Results Light exposure lead to remarkable up-regulation of EIF2a, ATF4,CHOP, IRE1, BIP, and ATF6, both at the protein level and the mRNAlevel, which represent three sub signaling pathways, respectively.Rapamycin was able to remarkably inhibit the activation of mTOR andits downstream factors eukaryotic translation initiation factor4E-binding protein1(4EBP1), p-4EBP1, p70, p-p70, andphosphorylated ribosomal protein S6kinase (p-S6K) in the light-injured661W cells. Rapamycin treatment remarkably attenuated theboth visible light and DTT-induced up-regulation of ER stress markersusing western blot and quantitative RT-PCR.Conclusions Visible light induces ER stress in661W cells; The mTOR inhibitor,rapamycin effectively protects661W cells from light injury throughsuppressing the ER stress pathway. Rapamycin may have a potentialapplication in the treatment of retinal light injury as a novelneuroprotective drug.