Stretch-induced membrane type matrix metalloproteinase and tissue plasminogen activator in cardiac fibroblast cells

In the normal heart, cardiomyocytes are surrounded by extracellular matrix (ECM) and latent matrix metalloproteinases (MMPs), which are produced primarily by cardiac fibroblasts. An activator of latent MMPs might be induced by ischemic conditions or pressure‐induced stretching. To test the hypothesis that an activator of latent MMP is induced in the ischemic heart during transformation of a compensatory hypertrophic response to a decompensatory failing response in cardiac fibroblast cells, we stretched the human cardiac fibroblasts at 25 cycles/min in serum‐free or 5% serum culture condition. The membrane type (MT)‐MMP activity in stretched cells was measured by zymography and immuno‐blot analyses using MT‐MMP‐2 antibody. The MT‐MMP activity was further characterized by transverse‐urea gradient (TUG)‐zymography. The results suggested that stretch induced a membrane MMP in the fibroblasts that was similar to the MT‐MMP induced in ischemic heart. Furthermore, we observed that membrane MMP has distinct mobility in TUG‐zymography. To localize the MT‐MMP and tissue plasminogen activator (tPA) of latent MMPs, the membrane and cytosol were separated by a method employing a detergent and sedimentation. The MT‐MMP and tPA activities of cytosol and membrane fractions were measured by gelatin‐ and plasminogen‐zymography, respectively. Differential‐display mRNA analysis was performed on control and stretched cells. In situ immuno‐labelling was performed to localize the MT‐MMP. The results indicate that induction of MT‐MMP occurred in the membrane fractions. The secretion of tPA was elevated in the stretched cells. The MT‐MMP activity was inhibited by prior incubation with an antibody generated to membrane MMP. The tPA activity was inhibited by using tPA antibody. These results suggest that, under stretched conditions, neutral transmembrane matrix proteinases are induced in the cardiac fibroblasts. This may lead to activation of adverse ECM remodeling, cardiac dilatation, and failure. J. Cell. Physiol. 176:374–382, 1998. © 1998 Wiley‐Liss, Inc.