Factor XI in Thrombosis

项目总结 凝血酶FXIa的酶原因子(F)XI在正常的血液凝结中的作用有限 (止血)，因为FXI缺乏与相对轻微的出血倾向有关。尽管如此，在 在人类种群数据的支持下，狒狒、兔子和老鼠强烈表明FXI使 对病理性凝血(血栓栓塞症)的贡献。在经典的凝血模型中，FXI被转换为 FXIa通过FXII(FXIIa)被激活，这一过程称为接触激活，这也需要蛋白质前激肽释放酶 (PK)和高分子量激肽原(HK)。接触性激活与止血的相关性已经被 有理由质疑，因为缺乏FXII、PK或HK的患者不会异常出血。在此基础上，在更新的版本中 止血模型FXI通过不同于接触性激活的机制被激活。然而，老鼠 缺乏FXII的人，类似于缺乏FXI的人，对血栓形成具有抵抗力，这意味着接触激活(或过程 与之类似)有助于病理性凝血。虽然现有的流行病学数据在以下方面相互矛盾 接触激活对人类血栓形成的重要性，我们注意到FXII有助于纤维蛋白的形成 和人体血液中的血小板聚集在体外流动模型中。我们假设FXII通过 接触激活或相关过程有助于小鼠病理性血栓的形成和稳定 抑制这一过程可以产生抗血栓作用。在本提案的目标1中，我们 我将提出这样的假设，即FXI必须与血小板相互作用，通过使用 允许蛋白质在体内瞬时表达的转基因技术。我们还将调查 FXIa可能通过不同于其经典功能的过程促进凝血 激活因子IX。Aim 2中的研究将使用嵌合体和 突变重组蛋白、常规凝血试验和全血流模型。我们还将 研究FXI-HK相互作用的重要性以及PK缺乏对血栓形成的影响 老鼠。此前，我们已经证明，在细菌性肺炎模型中，FXI缺乏赋予小鼠生存优势 感染。在目标3中，我们将比较FXI缺乏对存活率的影响，弥漫性血管内 多菌败血症模型中凝血和炎症对FXII、HK和PK缺乏的影响 老鼠。我们已经证明，用抗体抑制FXI对血管内皮细胞生长有显著影响 狒狒血管移植物血栓形成模型中的富含血小板血栓。在目标4中，我们将比较FXI的效果 并在此模型中抑制FXII以确定FXII是否在病理性血栓的生长中起重要作用 灵长类动物。这些研究的结果将使我们更好地了解 FXI在病理性凝血中的激活，并可能识别可以靶向的新靶点或途径 具有治疗或预防血栓栓塞性疾病的新的治疗策略。

PROJECT SUMMARY 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.