Metabolic Reprogramming of the Retinal Pigment Epithelium Drives TGFβ2‐Induced Epithelial‐Mesenchymal Transition

Abstract

Transforming growth factor-beta 2 (TGFβ2) is a key orchestrator of retinal wound healing through induction of epithelial-mesenchymal-transition (EMT) in retinal pigment epithelial cells (RPE). Here we describe a previously unrecognized function of TGFβ2 in modulating mitochondrial morphology and metabolic function in human RPE cells. Treating ARPE-19 (human RPE cell line) with TGFβ2 (10 ng/ml) induced defects in mitochondrial network integrity with increased sphericity and fragmentation. Correspondingly, TGFβ2 reduced expression of genes regulating mitochondrial dynamics, reduced citrate synthase activity and intracellular ATP content. High-resolution respirometry showed that TGFβ2 reduced mitochondrial oxidative phosphorylation (OXPHOS) levels consistent with reduced expression of NDUFB5, a key gene of Complex I of the electron transport chain. The reduced mitochondrial respiration was associated with a compensatory increase in gene expression of glycolytic enzymes (PFKFB3, PKM2, LDHA) and glycolytic reserve. TGFβ2 induced a severe suppression of PGC-1α gene expression and treatment with the selective small molecule activator of PGC-1α, ZLN005, blocked TGFβ2-induced upregulation of mesenchymal genes (αSMA, Snai1, CTGF, COL1A1) and TGFβ2-induced migration using the scratch wound assay. Our data show that EMT is accompanied by mitochondrial dysfunction and a profound metabolic shift towards reduced OXPHOS and increased glycolysis that may be driven by PGC-1α suppression. The PGC-1α promoter, ZLN005, effectively blocks EMT in RPE and thus serves as a novel therapeutic avenue for treatment for subretinal fibrosis.