High glucose-induced epithelial-mesenchymal transition contributes to the upregulation of fibrogenic factors in retinal pigment epithelial cells.

It has been reported that epithelial-mesenchymal transition (EMT) mediates multiple physiological and pathological processes. However, the occurrence and the pathogenic role of high glucose-induced EMT in retinal pigment epithelial cells (RPE cells) is unknown. The aim of this study was to examine the effects of high glucose on EMT in RPE cells. Cultured RPE cells were exposed to 25 mM D-glucose. A vector encoding the Snail gene and siRNA targeting Snail (Snail siRNA) were transfected into the cells to induce the overexpression or silencing of Snail, respectively. AKT and extracellular signal-regulated kinase (ERK) inhibitors were used to block the activation of AKT and ERK, respectively. The levels of EMT markers, fibrogenic factors, phosphorylated ERK and phosphorylated AKT were determined by western blot analysis and immunofluorescence staining. Cell migration was evaluated by wound healing assay. Our results revealed that high glucose elevated the expression of the key EMT transcriptional factor, Snail, and that of other mesenchymal makers, and promoted cell migration. Moreover, the overexpression of Snail elevated the levels of fibronectin and connective tissue growth factor (CTGF), whereas the silencing of Snail decreased the expression of fibronectin and CTGF induced by high glucose in the cells. Mechanistically, the AKT inhibitor (AKT inhibitor IV) and ERK inhibitor (U0126) significantly decreased the expression of Snail, as well as the levels of fibronectin and CTGF which were induced by high glucose. On the whole, and to the best of our knowedge, the present study is the first to demonstrate the upregulation of mesenchymal markers in RPE cells induced by high glucose, and suggest that mesenchymal transition may be involved in the pathological processes of retinal diseases.