ABSTRACT
BACKGROUND: Matrix metalloproteinases (MMPs) contribute to left ventricular remodeling after myocardial infarction (MI). Specific causative roles of particular MMPs, however, remain unclear. MMP-7 is abundant in cardiomyocytes and macrophages, but MMP-7 function after MI has not been defined. METHODS AND RESULTS: Wild-type (WT; n=55) and MMP-7-null (MMP-7-/-; n=32) mice underwent permanent coronary artery ligation for 7 days. MI sizes were similar, but survival was greatly improved in MMP-7-/- mice. The survival difference could not be attributed to differences in left ventricular dilation because end-diastolic volumes increased similarly. ECG analysis revealed a prolonged PR interval in WT but not in MMP-7-/- post-MI mice. Post-MI conduction velocity, determined by optically mapping electrical wavefront propagation, decreased to 78+/-6% of control for WT and was normalized in MMP-7-/- mice. In WT mice, slower conduction velocity correlated with a 53% reduction in the gap junction protein connexin-43. Direct binding of MMP-7 to connexin-43, determined by surface plasmon resonance technology, occurred in a dose-dependent manner. Connexin-43 processing by MMP-7 was confirmed by in silico and in vitro substrate analyses and MMP-7 infusion induced arrhythmias in vivo. CONCLUSIONS: MMP-7 deletion results in improved survival and myocardial conduction patterns after MI. This is the first report to implicate MMP-7 in post-MI remodeling and to demonstrate that connexin-43 is a novel MMP-7 substrate.
Subject(s)
Connexin 43/metabolism , Heart Conduction System/physiopathology , Matrix Metalloproteinase 7/physiology , Myocardial Infarction/mortality , Myocardial Infarction/physiopathology , Amino Acid Sequence , Animals , Cell Communication , Dose-Response Relationship, Drug , Electric Conductivity , Electrocardiography , Gap Junctions/chemistry , Gap Junctions/pathology , Gene Deletion , Heart Block/etiology , Heart Block/physiopathology , Immunohistochemistry , Macrophages/chemistry , Macrophages/cytology , Macrophages/pathology , Matrix Metalloproteinase 7/analysis , Matrix Metalloproteinase 7/genetics , Mice , Mice, Inbred C57BL , Molecular Sequence Data , Myocardial Infarction/pathology , Myocardium/chemistry , Myocardium/pathology , Myocytes, Cardiac/chemistry , Myocytes, Cardiac/cytology , Myocytes, Cardiac/pathology , Protein Binding/drug effects , Recombinant Proteins/pharmacology , Survival Analysis , Ventricular Remodeling/physiologyABSTRACT
Adequate wound healing and scar formation is an essential response to myocardial infarction (MI), and fibroblasts are primary cellular components regulating the process. How fibroblast functions are altered post-MI and to what extent these abnormalities persist in vitro is not well understood. Accordingly, we isolated myocardial fibroblasts from MI and non-MI (remote) regions at 7 days post-MI (n=35) and from the free wall and septum of unoperated control C57BL/6 mice (n=14). Proliferation was increased 182+/-28% in MI, but not in remote, fibroblasts compared with unoperated controls (P=0.01). Migration decreased 61+/-8%, adhesion to laminin decreased 79+/-8%, adhesion to collagen IV increased 196+/-27%, and collagen synthesis increased 169+/-24% in fibroblasts isolated from the MI region (all P<0.05). Migration, adhesion, and collagen synthesis changes were similar in remote fibroblasts, and the phenotypic differences were maintained through passage four. Transforming growth factor beta1 (TGFbeta1) is a bioactive molecule that has been shown to affect fibroblast function. Stimulation of unoperated control fibroblasts with 10 ng/ml TGFbeta(1) increased proliferation 137+/-7% (P=0.03 vs. unstimulated), increased adhesion to collagen IV 149+/-6% (P<0.01), and increased collagen I levels 187+/-10% (P=0.01). TGFbeta1 may, therefore, explain some of the changes in post-MI fibroblast phenotype. These data demonstrate for the first time region specific alterations in post-MI fibroblast biology that are maintained in vitro. Additionally, our model provides a novel in vitro template for examining the cellular mechanisms of wound healing and scar formation post-MI.
