Abstract 10824: A Novel Role of Endothelial Autophagy in the Regulation of Thrombosis in vivo

Abstract

Background: Arterial thrombosis of native and graft vessels is the inciting event for acute coronary syndromes, and the cause of significant cardiovascular morbidity and mortality. Endothelial cell (EC) dysfunction is believed to play a central role in the pathobiology of thrombosis. ECs are activated upon atherosclerotic plaque rupture and induce the expression of tissue factor (TF) with resultant atherothrombotic sequelae. The molecular basis of how endothelial TF is unregulated remains unknown. We hypothesize that endothelial autophagy, a process involved in cellular homeostasis and stress responses, plays a causal role in the expression of TF, and via this mechanism modulates thrombosis. Methods: We generated EC-specific ATG7 knockout (EC-ATG7 -/- ) mice using CreLoxP technology. We used small interfering RNA (siRNA) to knockdown and characterize the effect of ATG7 inhibition in HUVECs. We also employed intravital microscopy in FeCl 3 -induced carotid and laser-induced cremaster artery injury to evaluate thrombosis. Results: siRNA-mediated knockdown of ATG7 in HUVEC resulted in decreased TF mRNA and protein expression by over 60% (N=3-5; p<0.05). Mean TF mRNA level in EC-ATG7 -/- mice was 43% lower (p<0.05) compared with WT mice, after FeCl 3 -induced carotid artery injury. Time to carotid artery occlusion was significantly prolonged in EC-ATG7 -/- mice compared with WT mice (15.5±2.0 and 31.0±4.0 min, respectively; N=10/group; p=0.003). The time to maximum platelet fluorescence intensity in EC-ATG7 -/- mice was significantly prolonged relative to that for WT mice (1.0±0.6 and 2.3±1.2 min, respectively; N=33-38 thrombi; p<0.0001). Thrombi size, as determined by platelet fluorescence intensity, were significantly smaller in EC-ATG7 -/- vs. WT mice, (1.8±0.7 and 8.2±2.9, respectively; x10 9 ; p=0.049). Conclusions: Knockdown of ATG7 resulted in reduced TF expression in vitro and in vivo. Compared to WT mice, EC-ATG7 -/- mice exhibited 2-fold greater occlusion times and reduced thrombi formation across all models of thrombosis. Taken together, these findings are evidence that endothelial autophagy regulates thrombosis in a TF-dependent manner, and underscores a novel and previously unrecognized target for antithrombotic drug development.