Increased Expression of Membrane Type 3-Matrix Metalloproteinase in Human Atherosclerotic Plaque

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Abstract
Background— Matrix metalloproteinases (MMPs) are thought to play a prominent role in atherogenesis and destabilization of plaque. Pericellularly localized membrane-type (MT)-MMPs activate secreted MMPs. We investigated the hypothesis that MT3-MMP is expressed in human atherosclerotic plaques and is regulated by locally produced inflammatory cytokines and oxidized low-density lipoprotein (Ox-LDL). Methods and Results— Expression and cellular localization of MT3-MMP in normal and atherosclerotic human coronary arteries were examined using specific antibodies. Abundant MT3-MMP expression was noted in medial smooth muscle cells (SMCs) of normal arteries. In atherosclerotic arteries, MT3-MMP expression was observed within complex plaques and colocalized with SMCs and macrophages (Mφ). Cultured human monocyte-derived Mφ constitutively expressed MT3-MMP mRNA and proteolytically active protein, as demonstrated by mRNA analyses, immunoblotting, and gelatin zymography, respectively. Ox-LDL, tumor necrosis factor-α, or macrophage colony-stimulating factor caused dose- and time-dependent increases in steady-state levels of MT3-MMP mRNA in cultured Mφ. This correlated with a 2- to 4-fold increase in levels of MT3-MMP immunoreactive protein and enzymatic activity in Mφ membranes. Confocal microscopy and flow cytometry confirmed induction and spatial distribution of MT3-MMP protein from intracellular domains to the Mφ plasma membrane by Ox-LDL, tumor necrosis factor-α, or macrophage colony-stimulating factor. Conclusions— MT3-MMP is expressed by SMCs and Mφ in human atherosclerotic plaques. Proinflammatory molecules cause a progressive increase in the expression of MT3-MMP in cultured Mφ. Our results suggest a mechanism by which inflammatory molecules could promote Mφ-mediated degradation of extracellular matrix and thereby contribute to plaque destabilization.