Abstract 13213: Tissue Inhibitor of Metalloproteinase (TIMP)-2 Regulates Macrophage Invasion by Modulating MMP-14 Expression and Retards Plaque Progression
Matrix metalloproteinases (MMP) are proposed to precipitate atherosclerotic plaque progression and instability. However, the role of their endogenous inhibitors, tissue inhibitor of metalloproteinases (TIMP) remains unclear. In an attempt to address this issue, circulating monocytes were isolated from mice with a single deficiency of apolipoprotein E (apoE) and either TIMP-1 or TIMP-2. TIMP-2 deficient monocytes and monocyte-derived macrophages demonstrated significantly (p<0.05) increased MMP-14 protein expression. Add back of recombinant TIMP-2 to TIMP-2 deficient macrophages decreased MMP-14 expression by 52% (p<0.05) but had no effect in TIMP-1 deficient macrophages. Conversely, siRNA for TIMP-2 but not TIMP-1 in wild-type macrophages increased MMP-14 expression 3-fold (p<0.05). Accordingly, monocyte/macrophage invasion was increased both in vitro (94%, p<0.01) and in vivo (77%, p<0.001) in TIMP-2 deficient mice compared to wild-type controls. Concomitantly, addition of exogenous TIMP-2 to TIMP-2 knockout monocyte/macrophages reduced invasion both in vitro (81%, p<0.01) and in vivo (70%, p<0.001) and also decreased macrophage expression by 69% (p<0.05). Analysis of brachiocephalic artery plaques revealed that loss of TIMP-1 or TIMP-2 had no effect on lesion area, compared with age-matched, strain-matched apoE knockout controls after 8 weeks of high-fat feeding. However, lesions from apoE/TIMP-2 double knockout animals exhibited a reduced number (p<0.001) of plaques with a layered phenotype (a marker of plaque progression and complexity), compared to apoE single knockout controls. Moreover, intra-plaque macrophage MMP-14 expression was increased by 74% (p<0.05) in TIMP-2 deficient mice compared to wild-type controls. Despite a significant reduction in SMC content (p<0.01), lesions from apoE/TIMP-1 double knockouts did not differ in any other parameters compared to control animals. These data suggest that TIMP-2 retards monocyte/macrophage accumulation in atherosclerotic lesions and thus promotes plaque stability possibly through modulating both MMP-14 protein expression and activity.
- © 2010 by American Heart Association, Inc.