Myocardial infarction (MI) is a major cause of heart failure (HF). HF is associated with adverse cardiac remodeling that is primarily driven by Transforming growth factor beta (TGFb1) mediated fibrosis and myocyte hypertrophy. We previously reported that loss of bone morphogenetic protein 9 (BMP9) promotes cardiac fibrosis in pressure-overload induced HF. No studies have explored a role for BMP9 in post MI cardiac remodeling. We hypothesize that loss of BMP9 may promote cardiac healing by stabilizing LV scar formation. To test this hypothesis, we subjected whole body BMP9 knockout (-/-) mice to left coronary artery ligation for two weeks followed by PV loop analysis and studied indices of cardiac remodeling. Compared to wild type (WT) controls BMP9-/- mice had significantly lower survival (83% vs 61%, p<0.001, respectively) with a higher rate of cardiac rupture(15% vs 90%). Compared to WT controls, surviving BMP9-/- mice had higher LVEDP, reduced LV dP/dt, and higher lung weight. Compared to WT mice, BMP9-/- mice had significantly higher levels of Type I collagen (2 fold p<0.05). Compared to WT mice, BMP9-/- mice had increased matrix metalloproteinases (MMP)-2 and MMP-9 (2.5 fold p<0.05) activity levels in the LV. Treatment of cultured primary human cardiac fibroblasts with recombinant BMP9 attenuated TGFb1-mediated Type I collagen and MMP-9 protein expression. To assess collagen content and cross-linking, two-photon excitation fluorescence imaging was performed and identified an increase in collagen abundance, but a trend towards lower collagen cross-linking in the LV of BMP9-/- mice compared to WT mice 2 weeks after MI. Our central finding is that loss of BMP9 is associated with reduced survival, increased propensity towards cardiac rupture, and increased LV collagen abundance, but reduced collagen integrity in a murine model of acute MI. These identify a potentially important functional role for BMP9 in post-infarct cardiac remodeling.
Cardiac myofibroblasts isolated from the site of myocardial infarction express endothelin de novo