SEMA4A Mutations Lead to Susceptibility to Light Irradiation, Oxidative Stress, and ER Stress in Retinal Pigment Epithelial Cells

Abstract

RP is a retinal degeneration disorder that is caused by mutations of various genes, including semaphorin-4A (SEMA4A). A number of retinal diseases, including RP, are associated with light exposure, oxidative stress, and endoplasmic reticulum (ER) stress. In this study, we investigated whether mutant SEMA4A causes retinal dysfunction via light exposure, oxidative stress, and ER stress. Mutant SEMA4A (D345H or F350C) was overexpressed in a human retinal epithelium cell line ARPE19. Intracellular localization of mutant SEMA4A was investigated using confocal laser scanning microscopy. The ARPE-19 cells were also irradiated with white light, and expression of 78 kDa glucose-regulated protein (GRP78), a marker of ER stress, and phagocytosis were measured. The cells were treated with an ER stress inducer, tunicamycin, or an oxidative stressor, H(2)O(2), and cell death was measured. Human SEMA4A mutants were expressed in zebrafish embryos with tunicamycin and mRNA of DNA damage-inducible transcript 3 (ddit3) was measured as an ER stress marker. Mutant SEMA4A was localized in the ER, whereas wild type (WT) SEMA4A was observed in cell membranes. The expression of GRP78 was increased by mutant SEMA4A following light irradiation, and phagocytosis was suppressed in mutant SEMA4A-transfected cells. Mutant SEMA4A induced susceptibility to ER stress and oxidative stress. In zebrafish, human mutant SEMA4A increased ddit3 mRNA compared with WT under the ER stress condition. Our results suggest that mutations in SEMA4A may cause susceptibility to light exposure, oxidative stress, and ER stress, which may be involved in the progression and pathology of RP.