| Matrix metalloproteinases (MMPs) are best known for their roles in the long term remodeling of the extracellular matrix. Our group recently has demonstrated that MMP-2 is involved in acute myocardial ischemia-reperfusion injury. I studied the regulation and molecular action of MMP-2 in the oxidatively stressed heart. In such hearts, stressed either by the infusion of peroxynitrite or the NO (nitric oxide) synthase inhibitor, NG-nitro-L-arginine methyl ester, I found an increase in MMP-2 activity in the perfusate. An inhibitor of MMPs, PD-166793, protected the heart from peroxynitrite-induced injury. In another form of oxidative stress to the heart, ischemia and reperfusion, I found an imbalance between tissue inhibitors of metalloproteinases (TIMPs) and MMPs, resulting in an enhanced gelatinolytic activity. I also demonstrated that TIMP-4, the most abundant form of TIMP in the heart, is associated with sarcomeres in the normal heart but its content is reduced in ischemic-reperfused hearts.; The molecular mechanism of MMP-2-induced myocardial ischemia-reperfusion injury is unknown. The degradation of contractile proteins such as troponin I is suggested to be part of the pathophysiology of ischemia-reperfusion injury. I studied the role of MMP-2 in the proteolysis of troponin. MMP-2 was able to proteolyze troponin I and T but not troponin C in vitro. Only troponin I was susceptible to degradation by MMP-2 in the native troponin complex. In isolated perfused hearts, inhibitors of MMPs (o-phenanthroline and doxycycline) not only improved the recovery of mechanical function but also prevented the loss of troponin I. Immunoelectron microscopy revealed the colocalization of MMP-2 with sarcomeres. Immunoprecipitation and confocal microscopy studies demonstrated the association of MMP-2 and troponin I within cardiac myocytes. These data present novel, clear-cut evidence of the intracellular action of MMP-2 in the cardiac myocyte during ischemia-reperfusion injury.; In summary, I found a role of MMPs in the oxidatively stressed heart induced either by peroxynitrite infusion, by removal of basal NO generation or by subjecting the heart to ischemia-reperfusion. I also discovered a novel intracellular action of MMP-2 on troponin I within the cardiac myocyte. These data offer new insight in the pathology of oxidative stress injury to the heart and provide therapeutic strategy. |
