Homocysteine rapidly increases matrix metalloproteinase-2 expression and activity in cultured human vascular smooth muscle cells

SummaryIn this study we aimed to test the hypothesis that in human vascular smooth muscle cells (VSMC) homocysteine influences synthesis and release of matrix metalloproteinase-2 (MMP-2), which is deeply involved in vascular remodeling and atherosclerotic plaque instabilization. Experiments were carried out in cultured human VSMC exposed to 50–500 μmol/l homocysteine after a 24-hour culture with MEM containing 0.1% BSA. Both in supernatants and cell lysates we evaluated MMP-2 activity (gelatin zimography), MMP-2 and TIMP-2 protein synthesis (Western immunoblotting). Homocysteine effects were investigated also after cell exposure to i) specific MEK inhibitor PD98059 (30 μmol/l) to evaluate the involvement of Mitogen-Activated Protein Kinase (MAPK) and ii) specific phosphatidylinositol 3-kinase (PI3-K) inhibitor LY294002 (100 μmol/l) to evaluate the involvement of PI3-K pathway. Gelatin zimography evidenced that MMP-2 activity is increased both in conditioned media and in cell lysates starting from 8-hour incubation with 100 μmol/l homocysteine. Western blot analysis evidenced increased MMP-2 levels in both conditioned media and cell lysates. Cell exposure to PD98059 and LY294002 prevented homocysteine effects on MMP-2 synthesis. Homocysteine, at concentrations associated with increased risk of cardiovascular events, increases MMP-2 activity, synthesis and secretion in VSMC through a mechanism involving the activation of MAPK and PI3-K pathways. These data suggest that homocysteine is directly involved in mechanisms leading to remodelling and instabilization of atherosclerotic plaques.