Abstract 13: Suppression of Atherosclerosis by CD39

Atherosclerotic plaque rupture and thrombosis remains the leading cause of death in the United States. We investigated the role of CD39, a potent ecto-enzymatic regulator of platelet activation and leukocyte trafficking, in atherosclerosis. We generated mice deficient in CD39 on a hyperlipidemic, apoE -/- background and noted a two-fold higher plaque burden in when compared to apoE -/- controls ( P =0.003). We noted higher levels of circulating markers of platelet activation, soluble P-selectin (39%) and RANTES (60%), in the CD39-deficient mice ( P =0.003 and P =0.015, respectively, n=7-11). CD39-haploinsufficient mice had 1.8-fold greater enhanced platelet reactivity in response to ADP compared to controls ( P =0.03, n=3-8). Macrophages from CD39-deficient mice had significantly higher lipoprotein uptake in vitro . Correspondingly, CD39 overexpression in RAW cells inhibited scavenger receptor expression and lipoprotein uptake. Altered fluid mechanics contribute to atherosclerosis, with non-laminar shear stress enhancing regional plaque formation as seen in arterial bifurcations. We examined coronal sections of aortas from apoE −/− mice and observed that CD39 is poorly expressed in the endothelium in regions of turbulent blood flow, where plaque develops, supporting our hypothesis that endothelial CD39 can be induced by fluid phase shear forces. HUVEC treated with physiologic laminar shear stress (LS) (15 dynes/cm 2 ) had a 5.9-fold increase in CD39 protein ( P =0.004, N=3-7) and a concordant increase in nucleotidase activity ( P =0.03 N=3) compared to static controls (SS). We identified Krüppel like factor 2 (KLF2) as an upstream candidate for transcriptional regulation of CD39 induction by fluid shear forces. Silencing KLF2 in vitro led to a 55% decrease in CD39 mRNA induction with LS vs SS controls ( P =0.002, N=3-4). Chromatin immunoprecipitation revealed that KLF2 binds to the CD39 ( P =0.01, N=3) and this binding was further enhanced under laminar shear stress ( P =0.0007, N=3). These data show that CD39, an anti-thrombotic, anti-inflammatory enzyme is a critical regulator of atherosclerosis by modulating platelet, macrophage and endothelial function and mechanistically identify KLF2 as a direct, upstream regulator of CD39 expression.