Myofibroblast-specific Smad7 Attenuates Fibrosis Of The Pressure- overloaded Heart By Inhibiting Mmp2-mediated Collagen Denaturation And By Restraining Macrophage Activation.

Expansion and activation of cardiac fibroblasts contributes to adverse remodeling, fibrosis and dysfunction in the pressure-overloaded heart. Although early fibroblast TGF-β/Smad3 activation protects the pressure overloaded heart by preserving the matrix, sustained TGF-β activation may be deleterious, accentuating fibrosis and dysfunction. We hypothesized that induction of the endogenous TGF-β inhibitory Smad, Smad7, may attenuate fibroblast activation and deposition of collagen, limiting myocardial fibrosis and dysfunction in the pressure-overloaded heart. In a mouse model of pressure overload induced through transverse aortic constriction (TAC), Smad7 was upregulated in cardiac fibroblasts and myofibroblasts. Mice with myofibroblast-specific loss of Smad7 had increased mortality, systolic dysfunction, dilative remodeling and accelerated diastolic dysfunction in response to TAC. Moreover, myofibroblast-specific Smad7 loss hearts had higher collagen deposition and denaturation, as well as increased deposition of the fibrogenic protein periostin. Secretomic analysis showed that fibroblast Smad7 loss accentuates secretion of matrix metalloproteinase-2 (MMP2), extracellular matrix proteins and structural collagens. In vitro, the antifibrotic effects of Smad7 on fibroblast-induced collagen denaturation and pad contraction were partly mediated via MMP2 downregulation. Ingenuity pathway analysis predicted the fibrogenic matricellular protein CCN2/CTGF to be activated in Smad7 null fibroblasts. Surprisingly, myofibroblast-specific Smad7 loss increased myocardial macrophage infiltration in the pressure-overloaded heart. In vitro experiments suggested paracrine effects of Smad7 KO fibroblasts on macrophage proliferation and fibrogenic activation that involved the fibroblast-secreted mediators CD5L, SPARC, CTGF and TGFBI. In summary, the anti-fibrotic effects of Smad7 in the pressure-overloaded heart involve not only reduction in collagen deposition, but also suppression of MMP2-mediated matrix denaturation and paracrine effects inducing fibrogenic activation of macrophages.