RPGR^ORF15 mutations disrupt lysosomal lipid metabolism in retinal pigment epithelium cells and cause retinitis pigmentosa

PURPOSE: X-linked retinitis pigmentosa (XLRP) is a severely blinding retinal disease, most of which are due to mutations in retinitis pigmentosa GTPase regulator (RPGR). The patients with RPGR mutations exhibit severe retinal pigment epithelium (RPE) atrophy and photoreceptor degeneration. Previous research mainly focused on the role of RPGR in the connecting cilia of photoreceptors. However, the mechanism underlying RPE deficiency in patients remains unclear. Moreover, the function of RPGR in RPE cells has not been investigated.

METHODS: To investigate the mechanisms underlying RPE atrophy and the role of RPGR in RPE cells, the rpgra-/- zebrafish, human RPE cell line RPE-1, and ARPE-19 were utilized. Histological analysis, immunofluorescence, and lipid staining were used to investigate the morphology of photoreceptor and RPE cells, as well as the accumulation of lipid droplets (LDs) in RPE cells. FITC-labeled OS were used to evaluate the engulfment and degradation capabilities of RPE cells.

RESULTS: The zebrafish homolog of human RPGRORF15, rpgra, is expressed in RPE cells. The rpgra-/- zebrafish exhibits RPE atrophy, followed by photoreceptor degeneration. Loss of rpgra impairs lysosome formation in RPE cells, leading to defective RPE phagocytosis. This triggers lipid metabolism disorders, ultimately causing RPE and retinal degeneration.

CONCLUSIONS: RPGRORF15 is essential for maintaining lysosome function and lipid metabolism homeostasis in RPE cells. This finding elucidates the previously unrecognized role of RPGRORF15 in RPE cells. This study provides new insights into the mechanisms underlying RPGR-associated retinal diseases and offers potential therapeutic approaches.