Biochemistry and Pathophysiology of Factor XI and Contact Activation

项目摘要 因子XIa（fXIa）是血浆蛋白因子Xi（fXi）的蛋白酶形式，有助于凝血酶的产生 主要通过催化因子IX（fIX）的活化。这似乎反映了在主机中的辅助作用 止血反应的损伤，因为fXI缺乏导致，最多，一个相对温和的出血性疾病。尽管 止血作用有限，来自人群研究和动物模型的越来越多的证据支持 前提是fXI实质上有助于静脉和动脉血栓形成。这导致了相当大的 在治疗性抑制fXIa的兴趣，希望这样的策略将产生有用的抗血栓形成 效果，对止血的影响小于目前使用的抗凝剂，如肝素，华法林和 新的直接口服抗凝剂。FXI在结构上不同于维生素K依赖性凝血 形成凝血酶生成机制核心的蛋白酶。事实上，fXI产生于 前激肽释放酶（PK）基因，蛋白酶β-激肽释放酶的前体。PK，沿着因子XII（fXII）和高 分子量激肽原（HK）形成激肽释放酶-激肽系统（KKS），其是先天性免疫的组分 产生促炎肽的反应。作为PK的同系物，fXI保留了 母体分子的活性。然而，fXI已经获得了独特的功能，促进其与 凝血酶生成机制我们目前的工作模型是，fXI作为一个双向 凝血酶生成和KKS之间的界面，这使得它能够影响效果 对血栓形成和炎症过程的影响。我们实验室的工作旨在建立一个 更好地了解fXI的生物化学，分子生物学和病理生理学及其关系 凝血酶生成和KKS。我们对这一问题采取了广泛的做法，这反映在 本申请中描述的三个重点领域。重点领域1研究重要的结构-功能 fXI分子中与其在流动血液中的活性相关的关系。重点领域2将调查 在小鼠模型中fXI、fXII、PK和HK对血栓形成和脓毒症的贡献。我们还将 研究fXI在缺乏因子IX的小鼠（血友病B模型）中调节出血倾向的作用， 并继续进行最近的观察，即脉管系统中的大多数fXI形成非循环池 与血管壁相连。最后，重点领域3的工作旨在更好地了解 fXII，一种蛋白酶（fXIIa）的前体，可激活fXI和PK，并有助于血栓炎性 流程.我们强烈认为，我们在范德比尔特大学实验室的专业知识，以及恒星集团的 与我们合作了十多年的学术界和工业界的合作者，使我们处于一个独特的 该职位为血栓形成研究领域做出重要贡献，其目标是更好地了解 努力开发新的抗血栓形成疗法。

PROJECT SUMMARY Factor XIa (fXIa), the protease form of the plasma protein factor XI (fXI), contributes to thrombin generation primarily by catalyzing activation of factor IX (fIX). This appears to reflect an ancillary role in the host hemostatic response to injury, as fXI deficiency causes, at most, a relatively mild bleeding disorder. Despite its limited role in hemostasis, mounting evidence from human population studies and animal models support the premise that fXI contributes substantively to venous and arterial thrombosis. This has lead to considerable interest in therapeutic inhibition of fXIa, with the hope that such a strategy will produce a useful antithrombotic effect, with a smaller impact on hemostasis than currently used anticoagulants such as heparin, warfarin and newer direct oral anticoagulants. FXI is structurally distinct from the vitamin K-dependent coagulation proteases that form the core of the thrombin generation mechanism. Indeed, fXI arose from a duplication of the gene for prekallikrein (PK), the precursor of the protease -kallikrein. PK, along with factor XII (fXII) and high molecular weight kininogen (HK) form the kallikrein-kinin system (KKS), a component of the innate immune response that generates proinflammatory peptides in response to injury. As a homolog of PK, fXI retains activities of the parent molecule. However, fXI has acquired unique features that facilitate its interactions with the thrombin generation mechanism. Our current working model is that fXI functions as a bi-directional interface between thrombin generation and the KKS, and that this places it in a position to influence the effects of both systems on thrombotic and inflammatory processes. Work in our laboratory is directed at establishing a better understanding of the biochemistry, molecular biology and pathophysiology of fXI, and its relationships with thrombin generation and the KKS. We take a broad approach to this problem, which is reflected in the three Focus Areas described in this application. Focus Area 1 investigates important structure-function relationships in the fXI molecule that are relevant to its activity in flowing blood. Focus Area 2 will investigate the contributions of fXI, fXII, PK and HK to thrombus formation and sepsis in mouse models. We will also investigate the role of fXI in modulating bleeding tendency in mice lacking factor IX (a model of hemophilia B), and pursue a recent observation that the majority of fXI in the vasculature forms a non-circulating pool associated with the blood vessel wall. Finally, work in Focus Area 3 is directed at a better understanding of fXII, the precursor of a protease (fXIIa), that activates fXI and PK, and that contributes to thrombo-inflammatory processes. We strongly feel that the expertise in our laboratory at Vanderbilt University, and the stellar group of collaborators in academia and industry that have worked with us for over a decade, place us in a unique position to make important contributions to the field of thrombosis research, with the goal of better informing efforts to develop novel antithrombotic therapies.