Matrix metalloproteinase regulation of inflammatory proteins

Recruitment of leukocytes is a hallmark feature of inflammation, as is the dissipation of the infiltrate for healing. Continual recruitment and leukocyte activation results in host tissue damage that is pathognomonic of chronic inflammatory disease. Matrix metalloproteases (MMPs) are an important family of endopeptidases that are elevated and associated with inflammatory diseases. Historically considered to promote cellular invasion by degrading components of the extracellular matrix, it is now recognized that MMPs specifically process bioactive molecules to alter the function of these proteins. A novel substrate discovery method identified that MMP truncation of the first 4 amino acid residues of the monocyte chemoattractant cytokine (chemokine) CCL7 produced a receptor antagonist that is capable of reversing the inflammatory response in vivo. Since this first discovery, nearly half of all chemokines have been identified as MMP substrates, resulting in products that promote and inhibit neutrophil recruitment, and inhibit monocyte recruitment and so implicating MMPs as major regulators of innate immunity. I hypothesized that MMP processing of select chemokines would promote monocyte recruitment, and that neutrophil-specific membrane-type (MT)6-MMP processes chemokines and other inflammatory mediators during neutrophil migration through the endothelium and stroma. To identify chemokines activated by MMP-processing, I systematically evaluated all monocyte attracting CC chemokines, finding that all are cleaved by at least one MMP. Moreover, in vitro functional assays showed that MMP processing of CCL16 increases glycosaminoglycan binding of the chemokine, whereas CCL15 and CCL23 products have enhanced agonist activity. To identify substrates of MT6-MMP, chemokine cleavage was evaluated in vitro, and the proteomics method terminal amino isotopic labeling of substrates (TAILS) was applied to soluble and membrane-associated human lung fibroblast and human microendothelial cell proteomes. 14 chemokines, as well as vimentin, insulin-like growth factor binding protein-7, cystatin C, and galectin-1 were confirmed to be substrates of MT6-MMP. I propose that MT6-MMP has pleiotropic roles in inflammation by potentiating and then inhibiting neutrophil recruitment, contributing to monocyte recruitment, and promoting wound healing. Contributing to our understanding of the roles of MMPs in inflammation, my work also suggests new modalities whereby perturbing MMP regulation promotes inflammatory disease.Medicine, Faculty ofBiochemistry and Molecular Biology, Department ofGraduat