Abstract 257: Autophagy in Endothelial Cell Has an Important Role for Hemostasis and Thrombosis

Abstract

Autophagy has been reported to maintain intracellular homeostasis through lysosomal-mediated degradation of damaged organelles and proteins. Recent evidence suggests that autophagy regulates many physiological and pathological process including aging, reactive oxygen species levels, and inflammation. The role of autophagy in endothelial cell biology is poorly understood. Electron microscopic analysis of human umbilical vein endothelial cell (HUVEC) surprisingly demonstrated spontaneous fusion of autophagosomes with Weibel-Palade bodies, endothelial specific organelles containing abundant von Willebrand factor (VWF). Knockdown of the essential autophagy gene Atg7 resulted in a reduction in release of VWF from HUVECs after histamine (2.07±0.02 mU/mL vs. 1.30±0.02 mU/mL), or vascular endothelial growth factor (3.10±0.01 mU/mL vs. 1.22±0.03 mU/mL) stimulation. Pharmacological inhibition of autophagy showed similar results. We generated mice that have an endothelial specific deletion of Atg7. These mice have normal blood pressure (Control; 113±8/87±6 mmHg vs. Atg7 deficient; 119±7/88±4 mmHg) and normal vessel architecture. However, endothelial specific Atg7 deficient mice showed a reduction of plasma VWF and marked elevation of their bleeding times (The number of mice with bleeding time of more than 10min; Control=1/17, Atg7 deficient 6/9). Thus, an intact endothelial autophagy machinery is necessary for VWF secretion and hemostasis.