Losing Regulation of the Extracellular Matrix is Strongly Predictive of Unfavorable Prognostic Outcome after Acute Myocardial Infarction

This study tested the hypothesis that MMP-9(-/-)tPA(-/-)double knock out (i.e., MTDKO) plays a crucial role in the prognostic outcome after acute myocardial infarction (AMI by ligation of left-coronary-artery) in MT(DKO)mouse. Animals were categorized into sham-operated controls in MT(DKO)animals (group 1) and in wild type (B6: group 2), AMI-MTDKO(group 3) and AMI-B6 (group 4) animals. They were euthanized, and the ischemic myocardium was harvested, by day 60 post AMI. The mortality rate was significantly higher in group 3 than in other groups and significantly higher in group 4 than in groups 1/2, but it showed no difference in the latter two groups (allp< 0.01). By day 28, the left-ventricular (LV) ejection fraction displayed an opposite pattern, whereas by day 60, the gross anatomic infarct size displayed an identical pattern of mortality among the four groups (allp< 0.001). The ratio of heart weight to tibial length and the lung injury score exhibited an identical pattern of mortality (p< 0.01). The protein expressions of apoptosis (mitochondrial-Bax/cleaved-caspase3/cleaved-PARP), fibrosis (Smad3/T-GF-ss), oxidative stress (NOX-1/NOX-2/oxidized-protein), inflammation (MMPs(2,9)/TNF-alpha/p-NF-kappa B), heart failure/pressure overload (BNP/ss-MHC) and mitochondrial/DNA damage (cytosolic-cytochrome-C/gamma-H2AX) biomarkers displayed identical patterns, whereas the angiogenesis markers (small vessel number/CD31+cells in LV myocardium) displayed opposite patterns of mortality among the groups (allp< 0.0001). The microscopic findings of fibrotic/collagen deposition/infarct areas and inflammatory cell infiltration of LV myocardium were similar to the mortality among the four groups (allp< 0.0001). MT(DKO)strongly predicted unfavorable prognostic outcome after AMI.