Activation of AMP-Activated Protein Kinase Prevents TGF-beta 1-Induced Epithelial-Mesenchymal Transition and Myofibroblast Activation

Transforming growth factor (TGF)-beta contributes to tubulointerstitial fibrosis. We investigated the mechanism by which TGF-beta exerts its profibrotic effects and specifically the role of AMP-activated protein kinase (AMPK) in kidney tubular epithelial cells and interstitial fibroblasts. In proximal tubular epithelial cells, TGF-beta 1 treatment causes a decrease in AMPK phosphorylation and activation together with increased fibronectin and a-smooth muscle actin expression and decreased in E-cadherin. TGF-beta 1 causes similar changes in interstitial fibroblasts. Activation of AMPK with 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside, metformin, or overexpression of constitutively active AMPK markedly attenuated TGF-beta 1 functions. Conversely, inhibition of AMPK with adenine 9-beta-D-arabinofuranoside or siRNA-mediated knockdown of AMPK (official name PRKAA1) mimicked the effect of TGF-beta 1 and enhanced basal and TGF-beta 1 induced phenotypic changes. Importantly, we found that tuberin contributed to the protective effects of AMPK and that TGF-beta 1 promoted cell injury by blocking AMPK-mediated tuberin phosphorylation and activation. In the kidney cortex of TGF-beta transgenic mice, the significant decrease in AMPK phosphorylation and tuberin phosphorylation on its AMPK-dependent activating site was associated with an increase in mesenchymal markers and a decrease in E-cadherin. Collectively, the data indicate that TGF-beta exerts its profibrotic action in vitro and in vivo via inactivation of AMPK. AMPK and tuberin activation prevent tubulointerstitial injury induced by TGF-beta. Activators of AMPK provide potential therapeutic strategy to prevent kidney fibrosis and progressive kidney disease.