EXPRESSION OF MEMBRANE-TYPE MATRIX METALLOPROTEINASE IN RABBIT NEOINTIMAL TISSUE AND ITS CORRELATION WITH MATRIX-METALLOPROTEINASE-2 ACTIVATION

Smooth muscle cell (SMC) phenotypic alteration, followed by migration and proliferation, is a prominent feature of atherogenesis and vascula r neointimal formation. Despite extensive research, mechanism(s) respo nsible for this alteration remain unclear. Recently, matrix metallopro teinases (MMP), a family of potent proteinases, have been implicated i n vascular diseases by way of extracellular matrix degradation. Of par ticular interest is that expression of a 72-kD MMP (MMP-2) is elevated in neointima, and inhibition of this MMP results in reduced SMC migra tion and proliferation, suggesting a role for MMP-2 in neointimal deve lopment. However, MMP-2 needs activation before digesting protein; the mechanism of this activation in the arterial wall is largely unexplor ed. A novel membrane-type MMP termed MT-MMP-1 has recently been identi fied, and its expression in tumor cells is concomitant with MMP-2 acti vation. Transfection of this MMP cDNA into mammalian cells results in activation of MMP-2. However, the importance of this MMP in various pa thological situations is not clear. The present study was designed to explore the relationship between MT-MMP-1 expression and MMP-2 activat ion during rabbit neointimal development. Using polymerase chain react ion, we isolated a rabbit cDNA from arterial SMC; sequence analysis in dicated that it is a rabbit form of MT-MMP-1. A segment of this cDNA w as subcloned into pGEM-3 and employed to synthesize a DIG-labeled RNA probe. This probe was then used in the Northern blot analysis for MT-M MP-1 mRNA expression both in aortic tissue and in neointimal tissues d eveloped 3, 7, 14 and 21 days after balloon catheter de-endothelializa tion. The results show low-level expression of MT-MMP-1 in the normal aortic wall; expression is significantly increased in the neointimal t issues, with peak expression observed in tissues 3 days after injury. Expression of active MMP-2 was also determined using gel zymography. A close temporal expression pattern was observed between MT-MMP-1 and a ctive MMP-2. These data verify the expression of MT-MMP-1 in arterial SMC and suggest its importance in MMP-2 activation after balloon cathe ter de-endothelialization.