Anticoagulant Function of Arterial Endothelial Cells

血浆蛋白C是凝血不可缺少的调节因子。这种分子的缺乏与血栓性疾病有关，缺乏蛋白C的基因敲除小鼠在出生后24小时内出现致命的血栓。蛋白C是一种丝氨酸蛋白酶，以酶原形式循环，只有在转化为活性蛋白酶形式时才起作用。内皮细胞表面凝血酶可促进蛋白C的活化。已经确定了两个相关的内皮细胞表面分子。一种是凝血酶调节蛋白(TM)，它能够与凝血酶高亲和力特异性结合。我们发现了另一种与蛋白C激活机制有关的内皮细胞表面分子。内皮细胞蛋白C受体(EPCR)与蛋白C特异性结合，并通过凝血酶/TM复合体介导蛋白C的有效激活。EPCR或TM基因的敲除会导致胚胎死亡，并且不能在体内分析这些分子的抗凝血活性。在这里，我们产生了针对所有这些关键小鼠因子的功能性阻断单抗。抗蛋白C单抗，它专门阻止与EPCR的结合，在注射的小鼠中引起致命的血栓形成。一株抗EPCRmAb诱导严重血栓形成。我们还制备了针对小鼠TM的功能阻断mAb，该抗体再次引起致命性血栓形成。这些单抗将成为分析体内蛋白C途径功能的有力工具。

Plasma protein C is an indispensable regulator of blood coagulation. Deficiencies in this molecule are associated with thrombotic disease, and knockout mice lacking protein C suffered lethal thromboses within 24 hours after birth. Protein C is a serine protease that circulates as a zymogen form, and functions only when converted into the active protease form. Protein C activation is promoted by thrombin on the endothelial cell surface. Two associate endothelial cell surface molecules have been identified. One is thrombomodulin (TM), which is capable of high-affinity specific binding of thrombin. We identified another endothelial cell surface molecule involved in the activation mechanism of protein C.The endothelial cell protein C receptor (EPCR) specifically binds protein C, and enables effective protein C activation mediated by the thrombin/TM complex. Knockout of the gene for EPCR or TM caused embryonic lethality, and did not allow in vivo analysis of the anticoagulant activities of these molecules. Here, we generated function blocking monoclonal antibodies (mAbs) against all these key murine factors. Anti-protein C mAbs, which specifically prevent the binding to EPCR, caused lethal thrombosis in injected mice. An anti-EPCR mAb induced severe thrombosis. We also generated function-blocking mAb against murine TM.This antibody again caused lethal thrombosis. These mAbs will be powerful tools for analyzing in vivo protein C pathway function.