AMP-activated Protein Kinase Inhibits Transforming Growth Factor-β-induced Smad3-dependent Transcription and Myofibroblast Transdifferentiation

In wound healing, myofibroblast transdifferentiation (MFT) is a metaplastic change in phenotype producing profibrotic effector cells that secrete and remodel the extracellular matrix. Unlike pathways that induce MFT, the molecular mechanisms that negatively regulate MFT are poorly understood. Here, we report that AMP-activated protein kinase (AMPK) blocks MFT in response to transforming growth factor-β (TGFβ). Pharmacological activation of AMPK inhibited TGFβ-induced secretion of extracellular matrix proteins collagen types I and IV and fibronectin. AMPK activation also prevented induction of the myofibroblast phenotype markers α-smooth muscle actin and the ED-A fibronectin splice variant. AMPK activators did not prevent MFT in cells transduced with an adenovirus expressing dominant negative, kinase-dead AMPKα2. Moreover, AMPK activators did not inhibit MFT induction in AMPKα1,2–/– fibroblasts, demonstrating a requirement for AMPKα expression. Adenoviral transduction of constitutively active AMPKα2 was sufficient to prevent TGFβ-induced collagen I, α-smooth muscle actin, and ED-A fibronectin. AMPK did not reduce TGFβ-stimulated Smad3 COOH-terminal phosphorylation and nuclear translocation, which are necessary for MFT. However, AMPK activation inhibited TGFβ-induced transcription driven by Smad3-binding cis-elements. Consistent with a role for AMPK in transcriptional regulation, nuclear translocation of AMPKα2 correlated with the appearance of active AMPKα in the nucleus. Collectively, these results demonstrate that AMPK inhibits TGFβ-induced transcription downstream of Smad3 COOH-terminal phosphorylation and nuclear translocation. Furthermore, activation of AMPK is sufficient to negatively regulate MFT in vitro.