Early Activation of Metalloproteinases after Experimental Myocardial Infarction Occurs in Infarct and Non-infarct Zones.

The collagen matrix of the heart forms a network linking muscle fibers, muscle bundles, and intramyocardial blood vessels. Collagen turnover in the heart is normally a dynamic process that involves both collagen synthesis and degradation. Collagen breakdown generally involves its chemical digestion by matrix metalloproteinases (MMPs) which are activated in tissue repair, wound healing, and myocardial ischemia. We studied activation of MMPs by zymography in infarct (anterolateral wall) and non-infarct (septum) zones of rat hearts following coranary artery ligation, as well as in sham operated rats. Rats were sacrificed at 30 minutes, 1 hour, 2 hours, 4 hours, and 24 hours post infarction (six hearts for each time period). MMP activity was detected at different molecular weights, with bands at 54 kDa (MMP-1), 62 kDa (MMP-2), and 92 kDa (MMP-9) being the most prominent. MMP activities were indexed by densitometer optical reading. Activity was detected as early as 1 hour post infarct in the MI and remote zones at the 54 kDa (MMP-1) ( p < 0.01) and 62 kDa bands (MMP-2) ( p < 0.001), and at 2 hours post infarct in the infarct zone only at 92 kDa (MMP-9) ( p < 0.05). MMPs are activated early after infarction both in the infarct and importantly, non-infarct zones. This may contribute to collagen breakdown, infarct expansion, and left ventricular remodeling, known to occur early after infarction in experimental and clinical settings.