ACTIVATION OF SERPINS AND THEIR COGNATE PROTEASES IN MUSCLE AFTER CRUSH INJURY

Direct muscle injury was induced in rats in order to evaluate alterati ons in the balance of serine proteases and inhibitors (serpins) as a r esponse to tissue damage. It was previously found that certain proteas es, specifically urokinase-like plasminogen activator (uPA) and others , required activation in order to effect regeneration. We hypothesized that the magnitude and temporal sequence of serpin activation would f ollow, pari passu, activation of their cognate proteases. In addition to uPA, tissue PA (tPA) and tissue kallikrein were the proteases studi ed. The serpins we analyzed were protease nexin I (PNI), PA inhibitor 1 (PAI-1), and the kallikrein-binding protein (KBP). uPA nearly double d 48 h after injury, while there was no change in amidolytic activity after addition of fibrin monomer as an estimation of tPA activity. Tis sue kallikrein activity, barely detectable in normal muscle, slowly in creased, nearly tripling at 7 days after injury. Greater magnitude and more rapid changes in muscle serpins occurred over the same post-inju ry time course. By 24 h PNI increased threefold, while PAI-1 increased more slowly, reaching double the control values by 5 days after injur y. Surprisingly, KBP, the serpin-class inhibitor of tissue kallikrein, had the most robust response, increasing tenfold over control 48 h af ter crush injury of muscle. These results further implicate the serpin :protease balance in tissue injury. Participation of complex receptors , such as the alpha2-macroglobulin receptor/low density lipoprotein re ceptor-related protein (LRP) various growth factors, cytokines, and ot her molecules, in regulating this balance is implicated by these data. (C) 1994 Wiley-Liss, Inc.