Factor Xl in Vascular Thrombosis

描述（由申请方提供）：蛋白酶因子Xla（fXIa）通过在血液凝固开始后维持凝血酶生成来促进止血。除了有助于纤维蛋白形成之外，fXIa在涉及蛋白酶TAFI的过程中促进凝块对纤维蛋白溶解的抗性。一些证据表明fXIa有助于病理性凝血。fXIa前体fXI的血浆水平升高与人体动脉和静脉血栓形成风险增加相关。我们观察到fXI缺陷小鼠在动脉损伤模型中对血管闭塞具有抗性，表明fXIa有助于富含血小板的血栓形成。FXi在体外与血小板结合，并通过凝血酶或因子Xi Ia（fXIIa）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fXIIa对fXI活化的相对重要性尚不清楚。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缺陷型小鼠对动脉闭塞具有抗性，这提高了病理性闭塞性血栓的形成涉及与正常止血中所涉及的过程不同的过程的可能性。在本提案的目标1中，我们将使用fXI、fXII和TAFI缺陷的小鼠来研究这些蛋白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fXIIa的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。在目的2中，将使用鼠fXI依赖性出血模型来确定止血是否需要fXI与血小板、凝血酶和fXIIa的相互作用。在目标3中，我们将使用人和鼠富血小板血浆系统来检查fXI和fXII对体外凝血酶生成和血小板活化的重要性，主要目标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，并将提供有关复杂系统中fXI激活机制的有价值信息。最终，这项工作可以证明fXI和/或fXII以实质性的方式促进血管闭塞，因此是治疗或预防人类血管血栓栓塞的新型研究疗法的合理靶点。相关性：抗凝血剂药物对于治疗各种疾病中的异常血凝块非常有益，但具有使患者易于严重出血的缺点。我们正在寻找新的抗凝治疗靶点，这些靶点不会导致高出血风险。

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.