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Magali Saint-Geniez, Jared Iacovelli, Glenn Rowe, Zoltan Arany; Control of human RPE differentiation and metabolism by PGC-1α: implications for AMD. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):830.
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Regulation of RPE metabolism is critical for their functional maturation as photoreceptor outer-segment phagocytosis requires robust generation of ATP by mitochondrial oxidative phophorylation (OXPHOS). Alternatively, mitochondrial dysfunction in RPE has been shown to induce progressive retinal degeneration characterized by RPE dedifferentiation. Despite their significant implications, the molecular regulation of RPE oxidative metabolism under normal and pathological conditions remains unknown. The transcriptional co-activators, PGC-1α and PGC-1β, are powerful master regulators of mitochondrial biogenesis and oxidative metabolism in many tissues. This study examines the role of PGC-1 isoforms in controlling human RPE mitochondria biogenesis, metabolism, and differentiation.
Human fetal RPE (hfRPE) were isolated and differentiated using standard procedures. Gene expression of PGC-1s, mitochondrial dynamics, and RPE signature genes was analyzed by qPCR. PGC-1α expression was increased using adenoviral delivery. Mitochondrial respiration and fatty acid oxidation was monitored using the Seahorse extracellular flux analyzer. Barrier function was determined by measuring transepithelial resistance. Phagocytic activity was evaluated by quantifying bovine outer-segment uptake and degradation.
In vitro maturation of hfRPE cells is associated with increased mitochondrial abundance, increased expression of PGC-1α (p<0.01, n=3) but not PGC-1β and OXPHOS genes. High resolution respirometry reveals that respiration in hfRPE cells is significantly higher than ARPE-19 cells, >90% mitochondrial and highly coupled. Overexpression of PGC-1α in hfRPE significantly increases the expression of OXPHOS genes (p<0.05 ATP5O and COX5B; p<0.01 COX4I and NDUFB5), fatty acid beta-oxidation genes (p<0.05), ultimately leading to potent induction of mitochondrial respiration and fatty acid oxidation. Interestingly PGC-1α expression also induces RPE signature genes including BEST1 (p<0.05), TFEB (p<0.05) and MITF (p<0.01) but does not alter the cells’ barrier function and phagocytic activity.
Our results confirm that human RPE metabolism is highly dependent on mitochondrial respiration controlled by PGC-1α. We also demonstrate that RPE metabolic activity is concurrently regulated with cell maturation. Modulation of PGC-1a could represent a new therapeutic tool to regulate RPE metabolism and function in vivo.
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