Factor XI in Thrombosis

描述（由申请人提供）：因子(f) XI是凝血蛋白酶fXIa的酶原，在正常的血液凝固（止血）中起有限的作用，因为fXI缺乏与相对轻微的出血倾向相关。尽管如此，在狒狒、兔子和老鼠身上的研究，得到了人类种群数据的支持；强烈表明fXI在病理性凝血（血栓栓塞）中起重要作用。在经典的凝血模型中，fXI通过活化的fXII （fXIIa）转化为fXIa，这一过程被称为接触活化，这一过程还需要蛋白prekallikrein （PK）和高分子量激肽原（HK）。接触激活与止血的相关性受到质疑，这是合理的，因为缺乏fXII， PK或HK的患者不会异常出血。基于此，在较新的止血模型中，fXI通过不同于接触激活的机制被激活。然而，缺乏fXII的小鼠与缺乏fXI的小鼠一样，对血栓形成有抵抗力，这表明接触激活（或类似的过程）有助于病理性凝血。虽然现有的流行病学数据在接触激活对人类血栓形成的重要性方面存在矛盾，但我们注意到，在离体血流模型中，fXII有助于人血液中的纤维蛋白形成和血小板聚集。我们假设fXII通过接触激活或相关过程参与小鼠和灵长类动物的病理性血栓形成和稳定性，抑制这一过程可以产生抗血栓作用。在本提案的目的1中，我们将通过使用允许蛋白质在体内短暂表达的转染技术来解决fXI必须与血小板相互作用以促进血栓形成的假设。我们还将研究fXIa通过不同于其激活因子IX的经典功能的过程促进凝血的可能性。Aim 2的研究将使用嵌合和突变重组蛋白、常规凝血试验和全血流量模型来研究fXI与fXIIa的相互作用。我们还将研究fXI-HK相互作用的重要性以及PK缺乏对小鼠血栓形成的影响。以前我们已经证明，在细菌感染模型中，fXI缺乏赋予小鼠生存优势。在Aim 3中，我们将在小鼠多微生物脓毒症模型中比较fXI缺乏对生存、弥散性血管内凝血和炎症的影响与fXII、HK和PK缺乏的影响。我们已经证明，在狒狒血管移植血栓模型中，用抗体抑制fXI对富血小板血栓的生长有显著影响。在Aim 4中，我们将比较fXI和fXII抑制在该模型中的作用，以确定fXII是否在灵长类动物病理性血栓的生长中起重要作用。这些研究的结果将使我们对病理性凝血中fXI激活的机制有更深入的了解，并可能确定新的靶点或途径，从而可以采用新的治疗策略来治疗或预防血栓栓塞性疾病。

DESCRIPTION (provided by applicant): Factor (f) XI, the zymogen of the coagulation protease fXIa, serves a limited role in normal blood clotting (hemostasis), as fXI deficiency is associated with a relatively mild bleeding tendency. Despite this, work in baboons, rabbits, and mice, supported by human population data; strongly indicate that fXI makes important contributions to pathologic coagulation (thromboembolism). In classic coagulation models, fXI is converted to fXIa by activated fXII (fXIIa) in a process called contact activation, which also requires the proteins prekallikrein (PK) and high molecular weight kininogen (HK). The relevance of contact activation to hemostasis has been questioned, justifiably, as patients lacking fXII, PK or HK do not bleed abnormally. Based on this, in newer models of hemostasis fXI is activated through mechanisms distinct from contact activation. However, mice lacking fXII, similar to those lacking fXI, are resistant to thrombosis, suggesting contact activation (or a process similar to it) contributes to pathologic coagulation. While available epidemiologic data are conflicted regarding the importance of contact activation to thrombosis in humans, we noted that fXII contributes to fibrin formation and platelet aggregation in human blood in an ex vivo flow model. We hypothesize that fXII working through contact activation or a related process contributes to pathologic thrombus formation and stability in mice and primates, and that inhibiting this process can produce an anti-thrombotic effect. In Aim 1 of this proposal we will address the hypothesis that fXI must interact with platelets to contribute to thrombus formation by using transfection techniques that allow proteins to be transiently expressed in vivo. We will also investigate the possibility that fXIa can contribute to coagulation by processes distinct from those related to its classic function of activating factor IX. Studies in Aim 2 will investigate the interaction of fXI with fXIIa using chimeric and mutant recombinant proteins, conventional clotting assays, and whole blood flow models. We will also examine the importance of the fXI-HK interaction and the impact of PK deficiency on thrombus formation in mice. Previously we have shown that fXI deficiency confers a survival advantage in mice in models of bacterial infection. In Aim 3 we will compare the effects of fXI deficiency on survival, disseminated intravascular coagulation, and inflammation to those of deficiencies of fXII, HK, and PK in a model of polymicrobial sepsis in mice. We have demonstrated that inhibiting fXI with an antibody has a dramatic effect on the growth of platelet-rich thrombi in a baboon vascular graft thrombosis model. In Aim 4, we will compare the effects of fXI and fXII inhibition in this model to determine if fXII plays an important role in the growth of pathologic thrombi in primates. Results from these studies will give us a stronger understanding of the mechanisms involved in activation of fXI in pathologic coagulation, and may identify novel targets or pathways that could be targeted with novel therapeutic strategies to treat or prevent thromboembolic disease. PUBLIC HEALTH RELEVANCE: Factor XI is a plasma protein that serves a limited role in normal blood coagulation, but appears to make disproportionately greater contributions to thrombosis. We are investigating the mechanisms by which factor XI and related plasma proteins affect thrombotic disease.