Factor XI in Thrombosis

 描述（由申请人提供）因子Xi（FXi）和因子XII（FXII）是血浆蛋白酶（FXIa和FXIIa）的酶原，所述血浆蛋白酶是经典血浆接触活化系统的组分。虽然这些蛋白质被认为是凝血蛋白酶，但FXI缺乏症与相对轻度的出血素质相关，而FXII缺乏症不会引起异常出血。尽管它们对止血的贡献有限，但越来越多的证据表明FXI和FXII对血栓性疾病有实质性贡献。这两种蛋白质都是啮齿动物、兔和灵长类动物模型中血栓形成所需的。流行病学证据表明，FXI可导致静脉血栓形成、卒中，可能还有心肌梗死。FXII与血液暴露于体外装置（例如心肺转流术期间）时触发的血栓形成有关。肝素、华法林和较新的直接口服抗凝剂等药物的有益效果是以增加出血为代价的，因为它们靶向止血和血栓形成所需的血浆成分。预期靶向FXI和FXII的治疗将产生抗血栓形成作用，而不会显著影响止血。一项II期试验证明，降低血浆FXI水平可有效且安全地预防膝关节置换术患者的静脉血栓形成，为这一前提提供了概念证明。本提案的目的是确定和理解将FXI和FXII招募到血栓形成和炎症过程中的机制。这项工作的核心是假设FXI和FXII的激活是通过血液暴露于某些类型的聚阴离子或人工表面来促进的。在目的1中，我们将建立无机多磷酸盐、DNA和RNA增强FXI、FXII和相关接触蛋白前激肽释放酶（PK）活化的机制。这将通过在纯化系统和血浆中使用重组蛋白和抗体的新组来实现。FXII分子的结构-功能关系知之甚少。在目标2中，我们将研究FXII的结构，以确定它如何与聚阴离子和人工表面相互作用。心室患者 用于晚期心力衰竭的辅助装置（VAD）具有与装置和抗凝治疗相关的血栓形成和出血倾向的复杂组合。我们将确定VAD是否诱导接触激活，以及靶向FXIIa或FXIa是否可以减弱该过程。最后，已知接触系统有助于炎症。之前，我们发现FXI缺乏通过减弱感染后最初几小时内发生的细胞因子风暴，增加了脓毒症模型小鼠的存活率。在目标3中，我们将确定这是否与 通过在多微生物败血症模型中研究FXI、FXII和PK缺陷小鼠对接触活化的影响。我们还将检测治疗诱导的FXI减少患者的血浆样本，以观察其对炎症标志物的影响。通过这项工作，我们希望更好地了解FXI和FXII导致血栓性和炎症性疾病的机制，以更好地为开发不影响止血的新型抗血栓治疗提供信息。

 DESCRIPTION (provided by applicant) Factor XI (FXI) and Factor XII (FXII) are the zymogens of plasma proteases (FXIa and FXIIa) that are components of the classic plasma contact activation system. While the proteins are considered coagulation proteases, FXI deficiency is associated with a relatively mild bleeding diathesis, and FXII deficiency does not cause abnormal bleeding. Despite their limited contributions to hemostasis, there is mounting evidence that FXI and FXII contribute substantively to thrombotic diseases. Both proteins are required for thrombosis in rodent, rabbit and primate models. Epidemiologic evidence indicates that FXI contributes to venous thrombosis, stroke, and perhaps myocardial infarction in humans. FXII is implicated in thrombosis triggered when blood is exposed to extracorporeal devices, such as during cardiopulmonary bypass. The beneficial effects of drugs such as heparin, warfarin and the newer direct oral anticoagulants come at a cost of increased bleeding, because they target plasma components required for hemostasis as well as thrombosis. It is anticipated that therapies targeting FXI and FXII would produce an antithrombotic effect without significantly compromising hemostasis. A phase 2 trial demonstrating that lowering the plasma FXI level effectively and safely prevents venous thrombosis in patients undergoing knee replacement surgery provides proof of concept for this premise. The goal of this proposal is to identify and understand mechanisms that recruit FXI and FXII into thrombotic and inflammatory processes. Central to this work is the hypothesis that FXI and FXII activation are promoted by blood exposure to certain types of polyanions or artificial surfaces. In Aim 1 we will establish the mechanisms by which inorganic polyphosphate; DNA and RNA enhance activation of FXI, FXII, and the related contact protein prekallikrein (PK). This will be achieved using novel panels of recombinant proteins and antibodies in purified systems and in plasma. Structure-function relationships are poorly understood for the FXII molecule. In Aim 2 we will study the structure of FXII to determine how it interacts with polyanions and artificial surfaces. Patients on ventricular assist devices (VADs) for advanced heart failure have a complex constellation of thrombotic and bleeding tendencies related to the device and to anticoagulation therapy. We will determine if VADs induce contact activation, and if targeting FXIIa or FXIa can attenuate this process. Finally, the contact system is known to contribute to inflammation. Previously, we showed that FXI deficiency increases survival in mice in sepsis models, by blunting the cytokine storm that occurs within the first few hours after infection. In Aim 3 we will determine if this is related to effects on contact activation by studying FXI, FXII and PK deficient mice in a model of polymicrobial sepsis. We will also test plasma samples from patients with therapy-induced reduction in FXI to see it affects markers of inflammation. Through this work we hope to better understand mechanisms by which FXI and FXII contribute to thrombotic and inflammatory disease, to better inform efforts to develop novel antithrombotic therapies that do not compromise hemostasis.