STRETCH-INDUCED MEMBRANE TYPE MATRIX METALLOPROTEINASE AND TISSUE-PLASMINOGEN ACTIVATOR IN CARDIAC FIBROBLAST CELLS

in the normal heart, cardiomyocytes are surrounded by extracellular ma trix (ECM) and latent matrix metalloproteinases (MMPs), which are prod uced primarily by cardiac fibroblasts. An activator of latent MMPs mig ht be induced by ischemic conditions or pressure-induced stretching. T o test the hypothesis that an activator of latent MMP is induced in th e ischemic heart during transformation of a compensatory hypertrophic response to a decompensatory failing response in cardiac fibroblast ce lls, we stretched the human cardiac fibroblasts at 25 cycles/min in se rum-free or 5% serum culture condition. The membrane type (MT)-MMP act ivity in stretched cells was measured by zymography and immune-blot an alyses using MT-MMP-2 antibody. The MT-MMP activity was further charac terized by transverse-urea gradient (TUG)-zymography. The results sugg ested that stretch induced a membrane MMP in the fibroblasts that was similar to the MT-MMP induced in ischemic heart. Furthermore, we obser ved that membrane MMP has distinct mobility in TUC-zymography. To loca lize the MT-MMP and tissue plasminogen activator (tPA) of latent MMPs, the membrane and cytosol were separated by a method employing a deter gent and sedimentation. The MT-MMP and tPA activities of cytosol and m embrane fractions were measured by gelatin-and plasminogen-zymography, respectively. Differential-display mRNA analysis was performed on con trol and stretched cells. In situ immune-labelling was performed to lo calize the MT-MMP. The results indicate that induction of MT-MMP occur red in the membrane fractions. The secretion of tPA was elevated in th e stretched cells. The MT-MMP activity was inhibited by prior incubati on with an antibody generated to membrane MMP. The tPA activity was in hibited by using tPA antibody. These results suggest that, under stret ched conditions, neutral transmembrane matrix proteinases are induced in the cardiac fibroblasts. This may lead to activation of adverse ECM remodeling, cardiac dilatation, and failure. (C) 1998 Wiley-Liss, Inc .