Simvastatin protects photoreceptors from oxidative stress induced by all‐trans‐retinal, through the up‐regulation of interphotoreceptor retinoid binding protein

Background and Purpose Simvastatin is a 3‐hydroxy‐3‐methylglutaryl CoA reductase inhibitor with multiple targets and effects. It protects neurons in the brain, but its protective effects on photoreceptors are unclear. In this study, we evaluated the neuroprotective effect of simvastatin on photoreceptors exposed to stress induced by all‐trans‐retinal (atRAL). Experimental Approach AlamarBlue and LDH assays were used to evaluate the viability and metabolic activity of Y79 cells (a retinoblastoma cell line) exposed to atRAL‐induced stress with or without simvastatin pretreatment. Changes in cellular ROS were evaluated using flow cytometry and mitochondrial stress markers JC‐1 and HSP60. Changes in levels of two photoreceptor‐specific markers, cone‐rod homeobox protein (CRX) and interphotoreceptor retinoid binding protein (IRBP), were evaluated with western blot. The results were validated in ex vivo human retinal explants and a mouse model of photoreceptor degeneration. Key Results Simvastatin improved mitochondrial function, alleviated oxidative stress and up‐regulated the photoreceptor‐specific markers IRBP and its upstream regulator CRX in Y79 cells and ex vivo human retinal explants under atRAL‐induced stress. Simvastatin attenuated photoreceptor degeneration in association with up‐regulation of IRBP and CRX expression after knockdown of IRBP in a murine model. Conclusion and Implications Our findings suggest that simvastatin has a novel role in protecting photoreceptors from atRAL‐induced stress. Simvastatin treatment resulted in up‐regulation of IRBP and its upstream transcription factor CRX in Y79 cells, ex vivo human retinal explants, and murine retinas in vivo. Further studies of simvastatin to treat photoreceptor degeneration are warranted.