Novel strategies to prevent FcgRIIA-dependent platelet activation and thrombosis

描述（由申请人提供）：活化血小板Fc受体，Fc？RIIA是几种免疫介导的血小板减少和血栓形成（ITT）综合征的发病机制的核心，包括肝素诱导的血小板减少/血栓形成。成功治疗这些血栓性综合征的障碍之一是，针对血小板活化途径预防血栓形成的治疗要么无效，要么具有出血并发症的固有风险。本提案的目的是a)确定优先促进Fc？RIIA介导的血小板活化和b)制定治疗性抗血小板策略，以预防ITT的病理性血栓形成，同时尽量减少出血并发症。我们的初步研究发现酪氨酸激酶Syk、丝氨酸/苏氨酸激酶Akt和Ca2+传感器CalDAG-GEFI是ITT环境下抗血小板治疗的有希望的新靶点。itam偶联受体如Fc？RIIA， Syk对磷脂酶C的激活很重要。从而产生第二信使Ca2+和二酰基甘油。CalDAG-GEFI将细胞内Ca2+的增加与调节整合素激活、血栓素生成和颗粒释放的信号通路联系起来。对Akt的初步研究表明，它对Fc？riia诱导钙通量和整合素激活，从而将其与Syk和CalDAG-GEFI联系起来。初步结果以及我们和其他人的工作进一步表明，Syk、CalDAG- GEFI和Akt对Fc？RIIA/ itam介导的血小板活化。通过提出的研究，我们将提高我们对CalDAG-GEFI（目标1）和Akt（目标2）参与Fc？riia介导的血小板活化。在目标3中，我们将验证Syk和Akt，并探索CalDAG-GEFI作为ITT的治疗靶点。药物抑制Syk和Akt治疗和预防ITT的安全性和有效性将在我们建立的小鼠模型中进行测试。CalDAG-GEFI或Akt2作为治疗ITT的治疗靶点的效用将在转基因人类Fc？RIIA和小鼠敲除CalDAG-GEFI或Akt2。这一建议的成功完成将加速免疫介导的血小板疾病新疗法的合理设计。

DESCRIPTION (provided by applicant): Activation of the platelet Fc receptor, Fc?RIIA, is central to the pathogenesis of several immune- mediated thrombocytopenia and thrombosis (ITT) syndromes, including heparin-induced thrombocytopenia/thrombosis. One of the barriers to successful treatment of these thrombotic syndromes is that therapeutic targeting of platelet activation pathways to prevent thrombosis is either not effective or comes with an inherent risk of bleeding complications. The purpose of this proposal is a) to identify critical signaling molecules, which preferentially contribute to Fc?RIIA- mediated platelet activation and b) to develop therapeutic anti-platelet strategies to prevent pathologic thrombosis in ITT while minimizing bleeding complications. Our preliminary studies identify the tyrosine kinase Syk, the Ser/Thr kinase Akt, and the Ca2+ sensor CalDAG-GEFI as promising new targets for antiplatelet therapy in the setting of ITT. Downstream of ITAM-coupled receptors like Fc?RIIA, Syk is important for the activation of phospholipase C?2 and thus the generation of the second messengers Ca2+ and diacylglycerol. CalDAG-GEFI links an increase in intracellular Ca2+ to the signaling pathways regulating integrin activation, thromboxane generation, and granule release. Preliminary studies on Akt demonstrate that it is important for Fc?RIIA-induced calcium flux and integrin activation, thus linking it to Syk and CalDAG-GEFI. Preliminary results as well as work by us and others further demonstrate that Syk, CalDAG- GEFI, and Akt are particularly important for Fc?RIIA/ITAM-mediated platelet activation. With the proposed studies, we will improve our understanding of the molecular mechanisms by which CalDAG-GEFI (aim 1) and Akt (aim 2) contribute to Fc?RIIA-mediated platelet activation. In aim 3, we will validate Syk and Akt and explore CalDAG-GEFI as therapeutic targets in ITT. The safety and efficacy of pharmacologic inhibition of Syk and Akt for the treatment and prevention of ITT will be tested in our established mouse models. The utility of CalDAG-GEFI or Akt2 as therapeutic targets for the treatment of ITT will be evaluated in crosses between mice transgenic for the human Fc?RIIA and mice knockout for CalDAG-GEFI or Akt2. The successful completion of this proposal will accelerate the rational design of novel therapeutics for immune-mediated platelet disorders. PUBLIC HEALTH RELEVANCE: The human platelet Fc receptor, Fc?RIIA, has been implicated in several hematological disorders characterized by immune-mediated thrombocytopenia and/or thrombosis (ITT). We have identified 3 signaling molecules, which preferentially mediate Fc?RIIA- dependent platelet activation and thus may make effective targets for the treatment or prevention of ITT. The successful completion of this proposal will accelerate the rational design of novel therapeutics for immune-mediated platelet disorders.