Histone Deacetylase 4 is Required for TGFbeta1-induced Myofibroblastic Differentiation

Transforming Growth Factor beta1 (TGFbeta1) is a crucial cytokine triggering myofibroblastic (MF) differentiation, a process involved in tissue healing as well as in pathologic conditions such as fibrosis and cancer. Together with cell shape modifications, TGFbeta1-mediated differentiation of fibroblasts into myofibroblasts is characteristically associated with the neo-expression of smooth muscle alpha-actin (alpha-SMA), a cytoskeletal protein that enhances their contractile activity. Several cellular differentiation programs have been linked to epigenetic regulation of gene expression, including gene methylation and histone acetylation. Herein, we sought to investigate the role of histone deacetylases (HDAC) in TGFbeta1-induced MF differentiation. We found that TSA, a global inhibitor of class I and class II HDACs, prevented alpha-SMA transcript and protein expression and morphological changes mediated by TGFbeta1 in cultured human skin fibroblasts. In order to identify the HDAC(s) participating in MF differentiation, the impact of specific HDAC silencing (HDAC1 through HDAC8) using RNA interference was investigated in fibroblasts exposed to TGFbeta1. Among the eight HDACs tested, silencing of HDAC4, HDAC6, and HDAC8 expression impaired TGFbeta1-induced alpha-SMA expression. HDAC4 silencing most efficiently abrogated alpha-SMA expression and also prevented TGFss1-mediated morphological changes. Forced down-regulation of HDAC4 stimulated the expression of 5'-TG-3'-Interacting Factor (TGIF) and TGIF2 homeoproteins, two known endogenous repressors of the TGFbeta signaling pathway, but not of the inhibitory Smad7. Collectively, these data suggest that HDAC4 is an essential epigenetic regulator of MF differentiation and unveil HDAC4 as a potential target for treating MF-related disorders.