Biochemistry and Pathophysiology of Factor XI and Contact Activation

项目概要 XIa 因子 (fXIa) 是血浆蛋白 XI 因子 (fXI) 的蛋白酶形式，有助于凝血酶的生成 主要通过催化因子 IX (fIX) 的激活。这似乎反映了主机中的辅助角色 对损伤的止血反应，因为 fXI 缺乏最多会导致相对轻微的出血性疾病。尽管其 在止血方面的作用有限，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 对静脉和动脉血栓形成有实质性贡献。这导致了相当大的 对 fXIa 的治疗性抑制感兴趣，希望这种策略能够产生有用的抗血栓药物 与目前使用的抗凝剂如肝素、华法林等相比，对止血的影响更小 较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 源于复制 前激肽释放酶 (PK) 基因，是蛋白酶 α-激肽释放酶的前体。 PK，以及因子 XII (fXII) 和高 激肽释放酶-激肽系统 (KKS) 的分子量激肽原 (HK)，是先天免疫的一个组成部分 因损伤而产生促炎肽的反应。作为 PK 的同系物，fXI 保留 母体分子的活性。然而，fXI 已经获得了独特的功能，可以促进其与 凝血酶生成机制。我们当前的工作模型是 fXI 充当双向 凝血酶生成和 KKS 之间的界面，这使其能够影响效果 两个系统对血栓和炎症过程的影响。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。我们对这个问题采取了广泛的方法，这反映在 本申请中描述了三个重点领域。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 将进行调查 fXI、fXII、PK 和 HK 对小鼠模型中血栓形成和败血症的贡献。我们还将 研究 fXI 在调节缺乏 IX 因子的小鼠（血友病 B 模型）出血倾向中的作用， 并进行最近的观察，即脉管系统中的大多数 fXI 形成非循环池 与血管壁有关。最后，重点领域 3 的工作旨在更好地理解 fXII 是蛋白酶 (fXIIa) 的前体，可激活 fXI 和 PK，并有助于血栓炎症 流程。我们强烈认为范德比尔特大学实验室的专业知识以及一流的团队 学术界和工业界的合作者与我们合作了十多年，使我们处于独特的地位 为血栓研究领域做出重要贡献，目标是更好地提供信息 努力开发新型抗血栓疗法。

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.