Oxidized low-density lipoprotein regulates matrix metalloproteinase-9 and its tissue inhibitor in human monocyte-derived macrophages

Background-Macrophages in human atherosclerotic plaques produce a family of matrix metalloproteinases (MMPs), which may influence vascular remodeling and plaque disruption. Because oxidized LDL (ox-LDL) is implicated in many proatherogenic events, we hypothesized that ox-LDL would regulate expression of MMP-9 and tissue inhibitor of metalloproteinase-l (TIMP-1) in monocyte-derived macrophages. Methods ann Results-Mononuclear cells were isolated from normal human subjects with Ficoll-Paque density gradient centrifugation, and adherent cells were allowed to differentiate into macrophages during 7 days of culture in plastic dishes. On day 7, by use of serum-free medium, the macrophages were incubated with various concentrations of native LDL (n-LDL) and copper-oxidized LDL, Exposure to ox-LDL (10 to 50 mu g/mL) increased MMP-9 mRNA expression as analyzed by Northern blot, protein expression as measured by ELISA and Western blot, and gelatinolytic activity as determined by zymography. The increase in MMP-9 expression was associated with increased nuclear binding of transcription factor NF-KB and AP-1 complex on electromobility shift assay, in contrast, ox-LDL (10 to 50 mu g/mL) decreased TIMP-1 expression. Ox-LDL-induced increase in MMP-9 expression was abrogated by HDL (100 mu g/mL). n-LDL had no significant effect on MMP-9 or TIMP-1 expression. Conclusions-These data demonstrate that unlike n-LDL, ox-LDL upregulates MMP-9 expression while reducing TIMP-1 expression in monocyte-derived macrophages, Furthermore, HDL abrogates ox-LDL-induced MMP-9 expression. Thus, ox-LDL may contribute to macrophage-mediated matrix breakdown in the atherosclerotic plaques, thereby predisposing them to plaque disruption and/or vascular remodeling.