FoxO1 mediates TGF-beta1-dependent cardiac myofibroblast differentiation.

Cardiac fibroblast differentiation to myofibroblast is a crucial process in the development of cardiac fibrosis and is tightly dependent on transforming growth factor beta-1 (TGF-β1). The transcription factor forkhead box O1 (FoxO1) regulates many cell functions, including cell death by apoptosis, proliferation, and differentiation. However, several aspects of this process remain unclear, including the role of FoxO1 in cardiac fibroblast differentiation and the regulation of FoxO1 by TGF-β1. Here, we report that TGF-β1 stimulates FoxO1 expression, promoting its dephosphorylation, nuclear localization and transcriptional activity in cultured cardiac fibroblasts. TGF-β1 also increases differentiation markers such as α-smooth muscle actin, connective tissue growth factor, and pro-collagen I, whereas it decreases cardiac fibroblast proliferation triggered by fetal bovine serum. TGF-β1 also increases levels of p21waf/cip-cycle inhibiting factor protein, a cytostatic factor promoting cell cycle arrest and cardiac fibroblast differentiation. In addition, TGF-β1 increases cardiac fibroblast contractile capacity as assessed by collagen gel contraction assay. The effect of TGF-β1 on cardiac fibroblast differentiation was prevented by FoxO1 down-regulation and enhanced by FoxO1 overexpression. Thus, our findings reveal that FoxO1 is regulated by TGF-β1 and plays a critical role in cardiac fibroblast differentiation. We propose that FoxO1 is an attractive new target for anti-fibrotic therapy.