Factor Xl in Vascular Thrombosis

描述（由申请人提供）：蛋白酶因子Xla （fXIa）在血液凝固开始后通过维持凝血酶的生成来促进止血。除了促进纤维蛋白的形成外，fXIa还在一个涉及蛋白酶TAFI的过程中促进凝块对纤维蛋白溶解的抵抗。一些证据表明fXIa有助于病理性凝血。血浆fXIa前体fXI水平升高与人类动脉和静脉血栓形成风险增加有关。我们观察到，在动脉损伤模型中，fXI缺陷小鼠对血管闭塞具有抵抗性，这表明fXIa有助于血小板丰富的血栓形成。FXI在体外与血小板结合，并通过凝血酶或因子XI la （fXlla）转化为fXIa。这些相互作用在体内或复杂的体外系统中的重要性尚不清楚，凝血酶和fxla对fXI激活的相对重要性也不清楚。FXI I缺乏不会引起出血异常，表明FXI在体内被其他蛋白酶激活。然而，fXII缺陷小鼠对动脉闭塞有抵抗力，这增加了病理性闭塞性血栓形成的可能性，其过程与正常止血不同。在本提案的目的1中，我们将使用fXI， fXII和TAFI缺乏的小鼠来研究这些蛋白质在病理性凝血模型中的重要性。使用一组新的重组fXI变体来重建fXI缺陷小鼠，我们将确定fXI与血小板、凝血酶和fXlla相互作用对这些模型的重要性，并寻找与经典凝血途径无关的fXI和fXII的替代功能。在Aim 2中，将使用小鼠fXI依赖性出血模型来确定fXI是否需要与血小板、凝血酶和fXlla相互作用来止血。在Aim 3中，我们将使用人类和小鼠富血小板血浆系统来检验fXI和fXII对体外凝血酶生成和血小板激活的重要性，主要目的是确定两个物种之间是否存在差异。这些研究将使我们能够比较fXI、fXII和TAFI对正常止血和病理性凝血的重要性，并将为复杂系统中fXI激活的机制提供有价值的信息。最终，这项工作可能证明fXI和/或fXII对血管阻塞有实质性的作用，因此，它是治疗或预防人类血管血栓栓塞的新型研究性疗法的合法靶点。相关性：抗凝药物对治疗各种疾病中的异常血凝块非常有益，但其缺点是使患者容易发生严重出血。我们正在寻找血液中抗凝治疗的新靶点，这些靶点不会与高出血风险相关。

DESCRIPTION (provided by applicant): The protease factor Xla (fXIa) contributes to hemostasis by sustaining thrombin generation after initiation of blood coagulation. In addition to contributing to fibrin formation, fXIa promotes clot resistance to fibrinolysis in a process involving the proteinase TAFI. Several lines of evidence indicate fXIa contributes to pathologic coagulation. Elevated plasma levels of the fXIa precursor fXI are associated with increased risks for arterial and venous thrombosis in humans. We observed that fXI deficient mice are resistant to vascular occlusion in arterial injury models, indicating fXIa contributes to platelet rich thrombus formation. FXI binds to platelets in vitro, and is converted to fXIa by thrombin or factor XI la (fXlla). The importance of these interactions in vivo or in complex in vitro systems is not known, and the relative importance of thrombin and fXlla to fXI activation is not clear. FXI I deficiency does not cause a bleeding abnormality, indicating fXI is activated in vivo by other proteases. However, fXII deficient mice are resistant to arterial occlusion, raising the possibility that formation of a pathologic occlusive thrombus involves processes distinct from those involved in normal hemostasis. In Aim 1 of this proposal, we will use mice with deficiencies of fXI, fXII, and TAFI to investigate the importance of these proteins in models of pathologic coagulation. Using a panel of novel recombinant fXI variants to reconstitute fXI deficient mice, we will determine the importance of fXI interactions with platelets, thrombin and fXlla to these models, and look for alternative functions for fXI and fXII unrelated to classical coagulation pathways. In Aim 2, a murine fXI-dependent bleeding model will be used to determine if fXI interactions with platelets, thrombin and fXlla are required for hemostasis. In Aim 3 we will use human and murine platelet rich plasma systems to examine the importance of fXI and fXII to thrombin generation and platelet activation in vitro, with the primary goal of determining if there are differences between the two species. These studies will allow us to compare the importance of fXI, fXII and TAFI to normal hemostasis and to pathologic coagulation, and will provide valuable information regarding the mechanism(s) for fXI activation in complex systems. Ultimately, the work may demonstrate that fXI and/or fXII contribute in a substantive way to blood vessel occlusion, and are therefore, legitimate targets for novel investigative therapies to treat or prevent vascular thromboembolism in humans. Relevance: Anticoagulant drugs have been very beneficial for treating abnormal blood clots in a variety of diseases, but have the disadvantage of leaving the patient prone to serious bleeding. We are looking for new targets in blood for anticoagulation therapy that will not be associated with high bleeding risk.