Abstract 191: Shear Stress-Induced Atherosclerotic Plaque Regression Is Reversed by Matrix Metalloproteinase Inhibition: Role of Macrophage Mobility

Abstract

Atherosclerotic plaques usually form in regions of low blood flow, whereas vessels exposed to high shear stress tend to remain lesion-free. We hypothesized that exposing established atherosclerotic plaques to elevated shear stress leads to lesion regression by facilitating inflammatory cell movement within the plaque. We developed a surgical procedure in mice, the arteriovenous fistula (AVF), where the right carotid artery is anastomosed into the right jugular vein. LDLR -/- mice were placed on a high-fat diet, then divided into control, sham and AVF groups. Sham and AVF groups were kept on a high-fat diet for a further 4 weeks post-surgery. This procedure increases the shear stress in the artery, leads to plaque regression and increases plaque matrix metalloproteinase (MMP) activity. To understand the mechanism of this regression, we assessed the role of MMPs. Plaque MMP-9 expression was increased in AVF vs. control and sham (10.8%±1.4, 3.9%±0.7, 4.6%±1.1, respectively; p<0.0001). MMP-3 expression was also increased in AVF vs. control (9.5%±1.5, 5.0%±0.8, respectively; p<0.05), whereas MMP-2 expression was decreased in AVF vs. sham (5.7%±0.5, 11.3%±1.6, respectively; p<0.05). In addition, we overexpressed the tissue inhibitor of metalloproteinase (Timp-1) in mice before surgery. Sham plaque size was not affected. However, elevated Timp-1 prevented the reduction in plaque size in the AVF group (0.096±0.013 vs. 0.047±0.008 mm 2 , p<0.05). All groups had comparable lipid levels. To further understand the role of MMPs, we devised an endothelial cell (EC)-macrophage co-culture system where the ECs were exposed to high (15 dynes/cm 2 ) or low (0.5 dynes/cm 2 ) shear stress. A scratch assay was performed to evaluate migration of macrophages exposed to EC effluent. There was a 2.6-fold increase in migration in the high flow condition compared to the low (p<0.05). When the cells were exposed to the MMP inhibitor drug, GM6001, migration was decreased 2 fold (p<0.05). Our findings suggest that MMPs play a role in shear stress-induced plaque regression with MMP-9 being a key player. Shear stress acting on ECs may influence the cells within the plaque by increasing MMP expression, allowing for better macrophage mobility and egress which are characteristics of regressing plaques.