Molecular mechanisms of X‐linked retinitis pigmentosa

Purpose Retinitis Pigmentosa is a class of inherited retinal degeneration that causes progressive vision impairment even blindness. The mutations of Retinitis Pigmentosa GTPase Regulator (RPGR) gene account for up to 20% of RP cases. RPGR protein is highly expressed at the connecting cilium of vertebrates’ photoreceptors. RPGR protein has the function of regulating protein trafficking from basal body to axoneme. The trafficking is controlled by the protein complex formed by RPGR, RPGRIP1 and IFT proteins, although its precise function yet to be identified. RPGR−/− mice model was employed for investigating disease mechanisms during retinal degeneration. Methods Cell death pathway and protein trafficking were detected by immunohistochemistry. Results The retina of RPGR−/− mice started to undergo degeneration from 3M old. The caspase dependent cell death pathway was found to be activated during degeneration. The Apoptosis Inducing Factor existed in outer nuclear layer indicated that caspase‐independent apoptosis also contributed to cell death. The activated microglia, showed migration from outer plexiform layer to ONL in the retina of RPGR−/− mice and the downstream inflammation pathway were activated in RPGR−/− retina. Prior to the onset of retinal degeneration, the key elements involved in the phototransduction such as rhodopsin already mislocalized and accumulated in inner segment and outer nuclear layer. The mislocalization may result from the abnormal formation of the regulator of membrane trafficking Rab8 in RPGR−/− mice that controls the fusion of rhodopsin transport carrier and directs the cargo delivery across the CC. Conclusions In Conclusion, multi‐pathways were involved in the photoreceptor cell death and the deficiency of RPGR led to abnormal localization of the crucial proteins that participate in photoreceptor maintenance and phototransduction.