Blocking the RhoA/ROCK/cofilin/F-actin Pathway via Y27632 Protects Against MERTK-deficient Retinal Degeneration and Visual Function Impairment.

Retinitis pigmentosa (RP) is the most common inherited neurodegenerative retinal disease. Mer receptor tyrosine kinase (MERTK) mutations are associated with severe RP and dysfunction of the RPE. Previous studies have shown that MERTK and the Rho-associated coiled-coil-containing kinases (ROCK) pathway are involved in phagocytosis. However, the specific role of the ROCK pathway in the context of MERTK-associated RP needs to be revealed. We established an in vitro RP cellular model via MERTK depletion in human primary retinal pigment epithelium (HsRPE) cells by siRNAs, and RCS rats with spontaneous Mertk mutations were used as RP experimental animal models. Cell viability, apoptosis, phagocytosis, and visual function were measured by MTT, TUNEL and Annexin V/propidium iodide staining, phagocytosis assays and transmission electron microscopy, and electroretinography, respectively. The expression of RhoA, ROCK, Factin, and cofilin was determined by quantitative real-time PCR, western blotting, or immunofluorescence staining. MERTK knockdown substantially impaired cell survival, promoted apoptosis, and suppressed phagocytosis in HsRPE cells. In RCS rats, Mertk mutations impaired phagocytosis, promoted apoptosis of the RPE, and damaged visual functions. Silencing MERTK upregulated the phosphorylation of RhoA, ROCK2, and cofilin and decreased F-actin expression in HsRPE cells. Blocking the RhoA/ROCK axis by a selective ROCK inhibitor, Y27632, rescued the MERTK depletion-induced phagocytic dysfunction and apoptosis of HsRPE cells and rat RPE. Our results collectively indicate that MERTK maintains RPE survival and phagocytosis via regulating the RhoA/ROCK/cofilin/F-actin axis. This study demonstrates that MERTK deficiency impairs RPE phagocytosis and promotes cell apoptosis, leading to retinal degeneration and visual dysfunction. These findings provide new insight into RP pathogenesis and thereby offer valuable references for future drug development.