G Alpha 12-Dependent Constitutive Ec-Specific Vwf Secretion

A poorly understood component of hemostasis and thrombosis is von Willebrand factor (vWF) secretion by endothelial cells (EC). Here, we used genetic approaches in vitro and in vivo to determine the role of G proteins, RhoA, and αSNAP in constitutive vs. evoked vWF secretion. As expected, αSNAP siRNA completely abolished constitutive and evoked vWF secretion by HUVECs. In addition, siRNA‐mediated depletion of G protein 12 α subunit (GNA12) inhibited both constitutive and thrombin‐induced vWF secretion, while over‐expression of activated GNA12 promoted vWF secretion. In GNAq, p115 RhoGEF and RhoA‐depleted HUVECs, thrombin‐induced vWF secretion was reduced by 40% whereas basal vWF levels were unchanged. GNA12 −/− mice showed increased tail‐snip clotting time, reduced laser‐injury arterial clot formation, and reduced vWF levels in blood and in thrombin‐stimulated blood‐free mouse lung perfusate. Finally, in vitro binding assays revealed a novel role of the GNA12 N‐terminal domain in binding and activation of αSNAP. Taken together, these studies uncover obligatory and complementary roles of GNA12 and GNAq/11 in constitutive vs. evoked EC vWF secretion. Supported by :NIH P01 HL60678, R01 HL109435, and P30 HL101302