MYOCARDIAL MATRIX METALLOPROTEINASE(S) - LOCALIZATION AND ACTIVATION

Matrix metalloproteinases (MMPs) and neutrophil elastase (NE) may each contribute to fibrillar collagen degradation in various disease state s. Little, however, is known about the activation and localization of MMP in the heart. Accordingly, we extracted MMP and examined mechanism s of proMMP activation in whole tissue extracts of the adult rat myoca rdium. Incubation of extracts with serine proteases (i.e., trypsin or neutrophil elastase) at 37 degrees C resulted in a time-dependent acti vation of proMMPs. Based on immunoblot and measurements of MMP activit y by zymography, the molecular weight of active MMP was deduced to be 52 kDa. The second-order rate constant for activation of proMMP by ser ine protease was 5.5 +/- 0.2 x 10(5) M(-1)min(-1) and for oxidized glu tathione (GSSG) 1.5 +/- 0.1 M(-1)min(-1). Incubation of the extract wi th both serine protease and GSSG increased the rate of activation 30-f old. Based on reverse zymographic analysis of collagenase inhibition, tissue inhibitors of metalloproteinases were identified. Indirect immu nofluorescence localized proMMPs/MMPs to the endothelium and subendoth elial space of the endocardium and throughout the interstitial space f ound between groups of muscle fibers. These results suggest that the m echanism of activation of MMPs by either a serine protease and by oxid izing, thiol-modifying reagents are mechanistically different and the presence of either a serine protease or GSSG synergestically increase the rate of activation of proMMPs. Our results also suggest that MMPs may be regulated by its own endogenous inhibitors. The contribution of this proteolytic enzyme to tissue remodeling and wound healing respon ses that occur in various diseases states remains to be established.