MMP9 production by human monocyte-derived macrophages is decreased on polymerized type I collagen

The production of matrix metalloproteinases (MMPs), such as MMP9, by macrophages may be a critical factor in the rupture of unstable atherosclerotic plaques and aortic aneurysms. Therefore, we studied the role of matrix and soluble cytokines in the regulation of monocyte/macrophage expression of MMP9. Although freshly isolated monocytes synthesize little MMP9, cells cultured on tissue-culture plastic differentiate into macrophages and synthesize maximal amounts of MMP9. Differentiated macrophages cultured on plastic are unresponsive to further stimulation by interleukin 1beta, tumor necrosis factor alpha, or platelet-derived growth factor BB. In contrast, monocytes cultured on polymerized collagen synthesize much less MMP9 than cells cultured on plastic and demonstrate a more than three-fold increase in MMP9 synthesis in response to interleukin 1beta, tumor necrosis factor alpha, and platelet-derived growth factor BB. To determine whether the physical state of the collagen was critical for the decrease in basal synthesis of MMP9, monocytes were cultured in suspension for 5 days to allow differentiation and then seeded onto monomer or polymerized collagen. Synthesis of MMP9 was significantly decreased in cells on polymerized collagen and modestly increased in macrophages seeded on monomer collagen. These results suggest that MMP9 synthesis by macrophages in the vessel wall may be under negative control by native, polymerized collagen and that disruption of this native conformation could increase MMP9 production. In addition, cells in contact with the collagen matrix are potentially more responsive to soluble mediators such as platelet-derived growth factor, interleukin 1beta, and tumor necrosis factor alpha.