Hypoxia-inducible factor prolyl-hydroxylase-2 mediates transforming growth factor beta 1-induced epithelial-mesenchymal transition in renal tubular cells

Transforming growth factor beta 1 (TGF-beta 1)-induced epithelial-mesenchymal transition (EMT) in kidney epithelial cells plays a key role in renal tubulointerstitial fibrosis in chronic kidney diseases. As hypoxia-inducible factor (HIF)-1 alpha is found to mediate TGF-beta 1-induced signaling pathway, we tested the hypothesis that HIF-1 alpha and its upstream regulator prolyl hydroxylase domain-containing proteins (PHDs) are involved in TGF-beta 1-induced EMT using cultured renal tubular cells. Our results showed that TGF-beta 1 stimulated EMT in renal tubular cells as indicated by the significant decrease in epithelial marker P-cadherin, and the increase in mesenchymal markers alpha-smooth muscle actin (alpha-SMA) and fibroblast-specific protein 1 (FSP-1). Meanwhile, we found that TGF-beta 1 time-dependently increased HIF-1 alpha and that HIF-1 alpha siRNA significantly inhibited TGF-beta 1-induced EMT, suggesting that HIF-1 beta mediated TGF-beta 1 induced-EMT. Real-time PCR showed that PHD1 and PHD2, rather than PHD3, could be detected, with PHD2 as the predominant form of PHDs (PHD1:PHD2 = 0.21:1.0). Importantly, PHD2 mRNA and protein, but not PHD1, were decreased by TGF-beta 1. Furthermore, over-expression of PHD2 transgene almost fully prevented TGF-beta 1-induced HIF-1 alpha accumulation and EMT marker changes, indicating that PHD2 is involved in TGF-beta 1-induced EMT. Finally, Smad2/3 inhibitor SB431542 prevented TGF-beta 1-induced PHD2 decrease, suggesting that Smad2/3 may mediate TGF-beta 1-induced EMT through PHD2/HIF-1 alpha pathway. It is concluded that TGF-beta 1 decreased PHD2 expression via an Smad-dependent signaling pathway, thereby leading to HIF-1 alpha accumulation and then EMT in renal tubular cells. The present study suggests that PHD2/HIF-1 alpha is a novel signaling pathway mediating the fibrogenic effect of TGF-beta 1, and may be a new therapeutic target in chronic kidney diseases. (c) 2013 Elsevier B.V. All rights reserved.