Endothelial P2X7 promotes venous thromboembolism

Abstract

Venous thromboembolism (VTE) affects 117 people per 100,000 each year and is an important cause of morbidity and mortality. VTE can lead to 1) death through pulmonary embolism, 2) the post-thrombotic syndrome, or 3) chronic pulmonary hypertension resulting in significant chronic respiratory compromise. Inflammatory pathways are intricately involved in thrombus formation and therefore in VTE mechanisms. In pathological conditions, adenosine triphosphate (ATP) is released in the extracellular compartment and is recognized as a danger signal by several cell types including endothelial cells. Recent data indicated that the CD39/CD73 system involved in the metabolism of ATP into AMP might protects against thrombosis by downregulating the pro-inflammatory pathway of the inflammasome. ATP can also interact with the P2X7 receptor involved in inflammation causing a wide range of responses. To determine how the endothelial P2X7 receptor contributes to venous thromboembolism. HUVECs were incubated with BzATP, thrombin or both. HUVECs were primed with TNF-alpha prior to stimulation. We used immunofluorescence, western blot and real-time quantitative PCR analyses to assess P2X7 expression by endothelial cells, activation of p38 and NFκB activation and expression of pro-inflammatory and pro-coagulant genes. We confirmed that endothelial cells expressed P2X7 in vitro in HUVECs and in vivo after induction of venous thrombosis by ligation of the inferior vena cava. Treatment of endothelial cells with BzATP and thrombin induced the activation of p38 and NFκB signaling pathways. This appears to be associated with an increased expression of IL-1β and downregulation of thrombomodulin expression. The expression of adhesion molecules, ICAM-1 and VCAM-1, tends to increase. Our data suggest that ATP released in the extracellular space following cell damage or activation induced a pro-inflammatory response in endothelial cells through P2X7 activation. P2X7 might have a pro-thrombotic role exacerbating venous thromboembolism.