FoxO1 mediates TGF-beta1-dependent cardiac myofibroblast differentiation

Abstract

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.

Transforming growth factor-beta and Forkhead box O transcription factors as cardiac fibroblast regulators

“…In this cell model, TGF-β1 increases in a time and dose dependent manner FoxO1 mRNA and protein levels, induces FoxO1 dephosphorylation, increases FoxO1 nuclear translocation and increases FoxO1 target gene transcription (34). Moreover, FoxO1 overexpression enhances TGF-β1 effects on cardiac fibroblasts (34). Taken together, these data suggest that FoxO1 is required for TGF-β1 dependent fibroblast to myofibroblast differentiation.…”

“…In neonatal cardiac fibroblast TGF-β1 induces fibroblast to myofibroblast differentiation, which is completely prevented by FoxO1 inhibition (34). In this cell model, TGF-β1 increases in a time and dose dependent manner FoxO1 mRNA and protein levels, induces FoxO1 dephosphorylation, increases FoxO1 nuclear translocation and increases FoxO1 target gene transcription (34). Moreover, FoxO1 overexpression enhances TGF-β1 effects on cardiac fibroblasts (34).…”

“…A recent study in cardiac fibroblasts, Vivar et al demonstrated that TGF-β1 induces differentiation of fibroblast into myofibroblast in a FoxO1 dependent manner (34). The forkhead transcription factor superfamily is characterized by a winged-helix DNA binding motif and the forkhead domain (45).…”

“…Several line of evidences support the importance of TGF-β in the induction and maintenance of the fibrotic response. In cultured fibroblasts, TGF-β directly induces collagen production and contraction by fibroblasts, including those isolated from heart tissue (34). Subcutaneous injection of TGF-β results in enhanced deposition of extracellular matrix (35).…”

The role of α-smooth muscle actin in fibroblast-mediated matrix contraction and remodeling

“…Our group and other investigators have used experimental animal models and in vitro approaches to study the role of fibroblasts in the infarcted and remodeling myocardium [22],[23],[24],[25],[26],[27],[28],[29]. In vitro studies investigating myocardial fibrotic responses, have used either cardiac fibroblasts cultured and stimulated in plates, or cells enmeshed in collagen lattices [25],[30],[31],[32].…”