Suppression of Epithelial-Mesenchymal Transition in Retinal Pigment Epithelial Cells by an MRTF-A Inhibitor

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Abstract
Purpose: Epithelial-mesenchymal transition (EMT) in retinal pigment epithelial (RPE) cells is related to the pathogenesis of subretinal fibrosis such as that associated with macular degeneration. The role of myocardin-related transcription factor A (MRTF-A) in EMT of RPE cells and subretinal fibrosis was investigated. Methods: The migratory activity of human RPE-1 cells in culture was evaluated using a scratch assay. The subcellular distribution of MRTF-A in RPE-1 cells, as well as the extent of subretinal fibrosis in a mouse model, were determined by immunofluorescence analysis. Expression of α–smooth muscle actin (α-SMA), collagen type I (COL1), connective tissue growth factor (CTGF), and paxillin was examined by immunoblot analysis or reverse transcription and quantitative polymerase chain reaction analysis, whereas that of pro–matrix metalloproteinase-2 (MMP-2) was assessed by gelatin zymography. Results: The MRTF-A signaling inhibitor CCG-1423 suppressed RPE-1 cell migration in a concentration-dependent manner. Transforming growth factor-beta (TGF-β2) induced MRTF-A translocation from the cytoplasm to the nucleus of RPE-1 cells, and this effect was attenuated by CCG-1423. TGF-β2 up-regulated the abundance of α-SMA, paxillin, and pro–MMP-2 proteins as well as the amounts of α-SMA, COL1, and CTGF mRNAs in a manner sensitive to inhibition by CCG-1423. Finally, intravitreal injection of CCG-1423 markedly attenuated the development of subretinal fibrosis induced by photocoagulation in vivo. Conclusions: Our results implicate MRTF-A in EMT of RPE cells and in the development of subretinal fibrosis in vivo, suggesting that MRTF-A is a potential therapeutic target for retinal diseases characterized by subretinal fibrosis.

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