Matrix metalloproteinase-2 degrades the cytoskeletal protein alpha-actinin in peroxynitrite mediated myocardial injury.

Matrix metalloproteinase (MMP)-2 mediates myocardial ischemia-reperfusion injury which is characterized by enhanced peroxynitrite biosynthesis during early reperfusion. Direct infusion of peroxynitrite into isolated hearts activates MMP-2 prior to the loss in mechanical function. The mechanical dysfunction is prevented by MMPs inhibitors. MMP-2 is also found in the sarcomere of cardiomyocytes where it cleaves troponin I and myosin light chain I. Cytoskeletal proteins such as alpha-actinin, desmin and spectrin are found in close association with the sarcomere and are known to be degraded in ischemia-reperfusion injury. It remains unknown whether these proteins are degraded in peroxynitrite-induced myocardial injury and if cytoskeletal proteins are also targets for MMP-2. Peroxynitrite (80 microM) was infused into isolated rat hearts which led to a delayed onset but rapidly developing decline in mechanical function. The MMPs inhibitor PD-166793 or the peroxynitrite scavenger glutathione prevented the decline in cardiac function. At the end of perfusion, alpha-actinin levels were decreased by 45+/-3% in peroxynitrite-infused hearts as compared to control hearts; however, this was normalized to that of control hearts with either PD-166793 or glutathione. Cardiac desmin and alphaII spectrin levels were unaltered following peroxynitrite infusion. alpha-Actinin and to a lesser extent desmin are susceptible to in vitro proteolysis by MMP-2 whereas spectrin is resistant. Cardiac dysfunction induced by peroxynitrite involves degradation of alpha-actinin that may be mediated by the proteolytic action of MMP-2.

MMP-2 and MMP-9 and their tissue inhibitors in the plasma of preterm and term neonates.

Matrix metalloproteinases (MMP) and their tissue inhibitors (TIMP) are involved in a variety of physiologic growth and development and pathophysiologic inflammatory conditions. We hypothesized that 1) MMP-2 and -9 plasma activities and TIMP-1 and -2 plasma concentrations in preterm and term neonates were dependent on the gestational and postnatal age; and 2) the respective MMP and their inhibitors were deranged in the development of bronchopulmonary dysplasia (BPD) and intraventricular hemorrhage (IVH) in preterm neonates. From 1998 to 1999, blood samples were collected from preterm neonates (25-36 wk gestation) with or without BPD and/or IVH as well as from healthy term (37-40 wk gestation) neonates during the first 28 d of life. MMP-2 and MMP-9 plasma activities were measured by zymography; TIMP-1 and TIMP-2 plasma concentrations were determined by ELISA. In neonates without BPD or IVH (n = 50), MMP-2 and MMP-9 plasma activities both appeared to be gestational age dependent, with the highest levels observed in neonates of 33-36 wk gestation. TIMP-1 plasma concentration was highest in term neonates but no gestational difference was found in TIMP-2. Only MMP-9 showed a 50% decrease after d 1 in the first postnatal month. Twelve preterm infants with BPD and/or IVH had significantly lower MMP-2 but higher MMP-9 activity and higher TIMP-1 concentration than those of corresponding neonates without BPD or IVH. These findings show the gestational age-dependent expression of plasma MMP activities and their inhibitors. MMP and TIMP may be involved in the feto-neonatal development and may contribute to the pathogenesis of BPD and/or IVH in critically ill preterm neonates.