Role of complement regulator properdin in the interaction between platelets and l

描述(申请人提供)：在美国，心血管疾病是导致男性和女性死亡的主要原因。炎症性心血管疾病患者循环中活化的血小板和血小板/白细胞聚集物的数量增加，这两者在疾病的发生和发展中都起着核心作用。活化的血小板促进 补体系统在其表面的启动和繁殖，导致血管炎症和血栓形成。我们最近报道了补体替代途径的正性调节剂备解素与激活的血小板直接结合而不是与静止的血小板结合的分子机制，不依赖于C3b，并启动补体激活。我们的新的初步数据表明，在体外，人类备解素在剪应力作用下增加了血小板/白细胞聚集的形成和胶原诱导的全血血栓的形成。抑制备解素与C3b和细胞的结合显著减少了这两种结果。备解素如何刺激血小板和白细胞之间的相互作用的潜在机制尚不清楚，本提案的目的是定义这些机制。备解素主要由激活的白细胞产生。在炎性微环境中，激活的白细胞和血小板直接相互作用，白细胞衍生的备解素在高浓度下可供血小板使用。我们假设，备解素通过补体替代途径依赖的机制(至少部分包括备解素启动的补体激活)以及不依赖补体激活的机制(即充当细胞之间的桥梁)来增强血小板和白细胞之间的相互作用。为了解决这一假说，我们提出了以下目标：(1)确定如何抑制备解素与C3b以及与血小板和白细胞的相互作用，以防止在这些细胞上，备解素介导的转换酶或备解素启动的补体激活的稳定，和/或补体非依赖的备解素效应；(2)通过在体外分析人全血中血小板/白细胞聚集和血栓形成的方法，通过使用途径和效应特异性的补体抑制剂来表征备解素和替代途径对血小板和白细胞之间相互作用的贡献。总之，这些研究将通过定义一种新的血小板/白细胞相互作用的分子机制，极大地促进对人类备解素的功能和血管疾病发病机制中替代途径的理解。此外，通过确定备解素功能的候选抑制剂，这项研究将允许设计独特的治疗策略来调节血小板和白细胞之间的相互作用，以治疗心血管疾病，其中补体、血小板/白细胞聚集物和血栓在发病机制中发挥关键作用。

DESCRIPTION (provided by applicant): In the U.S., cardiovascular disease is the leading cause of mortality in men and women. Patients with inflammatory cardiovascular disease have an increased number of circulating activated platelets and platelet/leukocyte aggregates, both of which play a central role in the initiation and progression of disease. Activated platelets promote the initiation and propagation of the complement system on their surface, leading to vascular inflammation and thrombosis. We have recently reported a molecular mechanism by which properdin, a positive regulator of the alternative pathway of complement, binds directly to activated, but not to resting platelets, independently from C3b, and initiates complement activation. Our novel preliminary data demonstrate ex-vivo that human properdin increases platelet/leukocyte aggregate formation and the development of collagen-induced thrombi in whole blood subjected to shear stress. Inhibition of properdin binding to C3b and to cells significantly reduces both outcomes. The mechanisms underlying how properdin stimulates the interaction between platelets and leukocytes are unknown and the objective of this proposal is to define these mechanisms. Properdin is produced mainly by activated leukocytes. In inflammatory microenvironments, activated leukocytes and platelets directly interact with one another, and the leukocyte- derived properdin would be available to platelets at high concentrations. We hypothesize that properdin enhances the interaction between platelets and leukocytes via complement alternative pathway-dependent mechanisms including, at least in part, properdin-initiated complement activation, as well as via mechanisms that do not depend on complement activation (i.e. serving as a bridge between cells). To address this hypothesis we propose the following aims: (1) To determine how the interaction of properdin with C3b as well as with platelets and leukocytes can be inhibited in order to prevent, on these cells, properdin-mediated stabilization of convertases or properdin-initiated complement activation, and/or complement-independent properdin effects; (2) To characterize the contribution of properdin and of the alternative pathway to the interaction between platelets and leukocytes by using pathway- and effector-specific complement inhibitors in ex-vivo analyses of platelet/leukocyte aggregate and thrombi formation in human whole blood. Collectively, these studies will significantly advance the understanding of the functions of human properdin and the alternative pathway in the pathogenesis of vascular diseases by defining a new molecular mechanism for platelet/leukocyte interactions. In addition, by identifying candidate inhibitors of properdin functions, this study will allow the design of unique therapeutic strategies to modulate the interaction between platelet and leukocytes for treating cardiovascular diseases where complement, platelet/leukocyte aggregates, and thrombi play key roles in the pathogenesis.