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

Abstract

PURPOSE. RP is a retinal degeneration disorder that is caused by mutations of various genes, including semaphorin-4A (SEM-A4A). 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.METHODS. 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.RESULTS. 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. CONCLUSIONS.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. (Invest Ophthalmol Vis Sci. 2012;53:6729-6737)

TUDCA Promotes Phagocytosis by Retinal Pigment Epithelium via MerTK Activation

“…46 Previously, we revealed that mutant semaphorin-4A, which is implicated in RP, caused ER stress and phagocytic dysfunction under the light-irradiated condition in ARPE-19 cells. 26 However, TUDCA did not reduce the increase of ER stress marker ( Supplementary Fig. S1).…”

“…[21][22][23][24] Our prior findings showed that white light irradiation leads to the phagocytic dysfunction of RPE cells. 25,26 Tauroursodeoxycholic acid (TUDCA) is present in human bile and has been used in Chinese medicine for a long time for a variety of biliary and liver diseases. It is known to enhance phagocytosis in cultured rat Küpffer cells.…”

A point mutation in Semaphorin 4A associates with defective endosomal sorting and causes retinal degeneration

“…Third, slight amino-acid differences between human and mouse Sema4A might contribute to the fragility of the human Sema4A protein structure with a D345H mutation. It has been recently reported that transiently expressed human Sema4A D345H mutant protein showed altered intracellular localization in human RPE cell lines22. Additionally, as large-scale sequential analyses of patient DNA have not been performed except for Pakistani individuals11, further studies will be required to determine whether patients in other racial groups possess the same mutation.…”

S-nitrosylation regulates mitochondrial quality control via activation of parkin

“…Zebrafish (AB line, Zebrafish International Resource Center, Oregon, USA) were bred and maintained according to the methods described by Westerfield with some modification2425. Briefly, zebrafish were raised at 28.5 ± 0.5°C with a 14 h/10 h light/dark cycle.…”