Epigallocatechin-3-gallate prevents TGF-β1-induced epithelial-mesenchymal transition and fibrotic changes of renal cells via GSK-3β/β-catenin/Snail1 and Nrf2 pathways

Several lines of evidence have demonstrated anti-fibrotic property of epigallocatechin-3-gallate (EGCG) in many tissues/organs but with unclear mechanisms. This study thus aimed to define cellular mechanisms underlying such protective effect of EGCG. HK-2 renal cells were treated with 5 ng/ml TGF-β1 for 24 h with/without pretreatment by 5 μM EGCG for 1 h. The cells were then evaluated by morphological examination, immunofluorescence study, semi-quantitative RT-PCR, Western blotting, and atomic force microscopy (AFM). The results showed that TGF-β1-treated cells underwent epithelial mesenchymal transition (EMT) as evidenced by morphological change into fibroblast-like and increases in spindle index, mesenchymal markers (Snail1 and vimentin), extracellular matrix (fibronectin), cell stiffness (by AFM measurement) and actin stress fibers, whereas the epithelial markers (E-cadherin and ZO-1) were decreased. All of these features were abolished by EGCG pretreatment. Functional studies revealed that the anti-fibrotic property of EGCG was, at least in part, due to de-activation/stabilization of GSK-3β/β-catenin/Snail1 (EMT-triggering) signaling pathway that was activated by TGF-β1 as shown by maintaining phosphorylated GSK-3β, β-catenin and Snail1 to their basal levels. Additionally, Nrf2 knockdown by small interfering RNA could abolish the EGCG effect on β-catenin expression. These data indicate that EGCG attenuates TGF-β1-induced EMT in renal tubular cells through GSK-3β/β-catenin/Snail1 and Nrf2 pathways.