Endothelin-1 Induces Cell Proliferation and Myofibroblast Differentiation through the ET(A)R/G(αq)/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 α-smooth muscle actin (α-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 α-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, α-SMA, and collagen I through the ET(A)R subtype. Inhibition of G(αq) protein, not G(αi) or G(βγ), inhibited these effects of ET-1, indicating the essential role of G(αq) protein-mediated ET(A)R signaling. In addition, ERK1/2 was required for ET(A)R/G(αq) 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 α-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 α-SMA synthesis, confirming the restorative effects of ERAs. This novel work reports on the ET(A)R/G(αq)/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.