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Repair of the infarcted heart requires TGF-β/Smad3 signaling in cardiac myofibroblasts and formation of an organized myofibroblast-populated scar. However, TGF-β-driven myofibroblast activation needs to be tightly regulated to prevent excessive fibrosis and adverse remodeling that may precipitate heart failure. We hypothesized that induction of endogenous suppressive signals, such as the inhibitory Smad7; may restrain infarct myofibroblast activation, protecting from adverse remodeling and fibrosis, and we examined the molecular mechanisms of Smad7 actions. In a mouse model of non-reperfused infarction, Smad3 activation triggered Smad7 synthesis in α-SMA+ infarct myofibroblasts, but not in α-SMA-negative fibroblasts. Mice with myofibroblast-specific Smad7 loss had increased heart failure-related mortality, worse dysfunction, and accentuated fibrosis in the infarct border zone and papillary muscles. In …