Transforming growth factor β2-induced myofibroblastic differentiation of human retinal pigment epithelial cells: Regulation by extracellular matrix proteins and hepatocyte growth factor

Retinal pigment epithelial (RPE) cells possess the potential to transdifferentiate into myofibroblasts after stimulation with transforming growth factor beta (TGFβ) and are implicated in the pathogenesis of proliferative vitreoretinopathy. In this study we evaluated how TGFβ2 and various extracellular matrix (ECM) proteins modulate the transdifferentiation of human fetal retinal pigment epithelial cells (RPE) cells into myofibroblast-like cells. Furthermore, we investigated whether hepatocyte growth factor (HGF) can suppress this transdifferentiation. RPE cells were cultured on ECM coated or uncoated surfaces in the presence or absence of TGFβ2. HGF was added to certain cultures only once or on a daily basis during the treatment. Transdifferentiation of RPE cells into myofibroblasts was assessed by the quantitation of α-smooth muscle actin (α-SMA) using immunocytochemistry, flow cytometry, real-time PCR and Western blotting. TGFβ2 induced a significant increase of α-SMA expression in a dose-dependent manner. Compared with growth on uncoated surfaces, RPE cultured on fibronectin (FN)-coated surfaces and stimulated with TGFβ2 showed a significantly higher α-SMA expression than untreated cells. This upregulation of α-SMA could be markedly reduced by daily treatment with HGF; however, a single HGF administration did not significantly reduce α-SMA. These findings are important for further understanding the interaction of cytokines, RPE cells and their environment in mesenchymal transformation as well as its possible modulation. Continuous or long-term treatment with HGF should be further investigated for its potential to prevent mesenchymal transdifferentiation of RPE cells, and ultimately, PVR in vivo.