Endothelin-1 Induces Cell Proliferation and Myofibroblast Differentiation through the ETAR/G(alpha q)/ERK Signaling Pathway in Human Cardiac Fibroblasts

Endothelin-1 (ET-1) has been implicated in the pathogenesis of cardiac fibrosis. Stimulation of endothelin receptors (ETR) with ET-1 leads to fibroblast activation and myofibroblast differentiation, which is mainly characterized by an overexpression of alpha-smooth muscle actin (alpha-SMA) and collagens. Although ET-1 is a potent profibrotic mediator, the signal transductions and subtype specificity of ETR contributing to cell proliferation, as well as alpha-SMA and collagen I synthesis in human cardiac fibroblasts are not well clarified. This study aimed to evaluate the subtype specificity and signal transduction of ETR on fibroblast activation and myofibroblast differentiation. Treatment with ET-1 induced fibroblast proliferation, and synthesis of myofibroblast markers, alpha-SMA, and collagen I through the ETAR subtype. Inhibition of G(alpha q) protein, not G(alpha i) or G(beta gamma), inhibited these effects of ET-1, indicating the essential role of G(alpha q) protein-mediated ETAR signaling. In addition, ERK1/2 was required for ETAR/G(alpha q) axis-induced proliferative capacity and overexpression of these myofibroblast markers. Antagonism of ETR with ETR antagonists (ERAs), ambrisentan and bosentan, inhibited ET-1-induced cell proliferation and synthesis of alpha-SMA and collagen I. Furthermore, ambrisentan and bosentan promoted the reversal of myofibroblasts after day 3 of treatment, with loss of proliferative ability and a reduction in alpha-SMA synthesis, confirming the restorative effects of ERAs. This novel work reports on the ETAR/G(alpha q)/ERK signaling pathway for ET-1 actions and blockade of ETR signaling with ERAs, representing a promising therapeutic strategy for prevention and restoration of ET-1-induced cardiac fibrosis.