Regulation of Matrix Metalloproteinases and Plasminogen Activator Inhibitor-1 Synthesis by Plasminogen in Cultured Human Vascular Smooth Muscle Cells

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Abstract
Plasmin and matrix metalloproteinases (MMPs) both participate in extracellular matrix remodeling. This study examined the effects of tumor necrosis factor-α (TNF-α) and plasminogen on collagenase, stromelysin, and plasminogen activator inhibitor-1 (PAI-1) synthesis by cultured human vascular smooth muscle cells (SMCs). TNF-α induced the concentration-dependent synthesis of collagenase and stromelysin, which remained predominantly in proenzyme forms, as determined by Western analysis of culture media. In contrast, plasminogen and plasmin not only increased secretion of MMPs but also induced cleavage to their active forms. The serine protease inhibitor aprotinin inhibited this activation of MMPs by plasminogen and plasmin. TNF-α reduced plasminogen-induced activation of MMPs, suggesting induction of an inhibitor of plasmin generation, such as PAI-1. Enzyme-linked immunosorbent assay of culture media showed that TNF-α (10 ng/mL) increased PAI-1 secretion by 4.2-fold compared with control (105.5±9.6 versus 24.9±1.7 ng/mL, n=3). Surprisingly, plasminogen also increased PAI-1 secretion by vascular SMCs (3.6-fold over control). These results demonstrate coordination of cytokines and serine proteases in regulating MMP secretion and activation. In addition, the induction of PAI-1 by TNF-α and plasminogen suggests a negative-feedback mechanism to limit both plasmin-mediated and MMP-mediated matrix degradation.