Injury to extracellular matrix components by matrix metalloproteinases (MMPs) derived from leukocytes is a pivotal pathogenetic event in disabling chronic diseases such as pulmonary emphysema, cystic fibrosis, acute respiratory distress syndrome, and rheumatoid arthritis. The prevailing concept of MMP-mediated tissue injury is that MMPs are freely secreted into the extracellular space as proenzymes. However, there is little information available about the mechanisms by which proMMPs are activated in vivo, or how they circumvent the effects of high- affinity inhibitors within the extracellular space. Our preliminary data indicate that MMP-7 (matrilysin), MMP-8 (neutrophil collagenase), and MMP-9 (92 kDa gelatinase; 92 kDa type IV collagenase; gelatinase B) are expressed on the cell surface of human leukocytes, and that their expression is upregulated by pro-inflammatory mediators. We propose to test the hypothesis that when MMPs are confined to the cell surface of leukocytes, they are focused and protected from naturally- occurring inhibitors. In doing so, we will pursue the following Specific Aims: 1. Determine which MMPs (MMP-7, -8, -9 and MMP- 12[macrophage metalloelastase]) are expressed on the cell surface of neutrophils and monocytes, quantify their expression in response to cellular activation, and investigate the possibility that coordinate expression of MMPs and adhesion molecules on activated cell membranes facilitates MMP-mediated extracellular proteolysis. 2. Examine the consequences of binding of MMPs to the cell surface of inflammatory cells with respect to proenzyme activation, catalytic activity and susceptibility to inhibition. 3. Investigate the mechanisms of binding of MMPs to leukocyte cell membranes. We anticipate that the proposed studies will provide novel insights into the mechanisms by which MMPs mediate tissue injury, and that this knowledge will facilitate rational development of effective therapeutic strategies for many chronic and disabling diseases in which MMP-mediated tissue injury is a critical event.
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