REGULATION OF G PROTEIN SIGNALING IN PLATLETS

人血小板在血管损伤部位被激动剂如胶原蛋白、凝血酶和AP快速激活。除了胶原蛋白之外，大多数激动剂通过与异源三聚体G蛋白偶联的细胞表面受体激活血小板。总的来说，G蛋白和G蛋白偶联受体提供了允许快速血小板活化的敏感机制。然而，这种敏感性也增加了不适当的血小板活化的风险，如果不加控制，将导致组织缺血和梗死。当进行性疾病如动脉粥样硬化使血管腔变窄时尤其如此。由于通过循环系统将可预见地使血小板暴露于可能引起不必要的活化的条件，因此合理地提出存在限制通过G蛋白的信号传导的机制。我们的假设是，在血小板中，这种调节机制针对受体和G蛋白，但在G蛋白水平上起作用的机制特别重要，并与内皮细胞协同工作，但在G蛋白水平上起作用的机制特别重要，并与内皮细胞PGI2、NO和CD 39协同工作，以防止不适当的血小板活化。本研究的目的是验证这一假设，并扩展目前关于血小板中G蛋白依赖性信号调节的信息。三个相关的问题将使用人类血小板和基因工程小鼠的血小板来解决。首先，血小板中至少有10种不同的G蛋白。在何种程度上，每一个都对信号做出了独特的贡献，在何种程度上它们是多余的？第二，离体血小板高活性中G蛋白的持续活化是否有助于体内血栓形成和动脉粥样硬化的进展。第三，RGS蛋白在限制血小板中G蛋白信号传导中的作用是什么，它们是否提供了防止不必要的血小板活化的手段？我们将解决这些问题，主要是使用转基因工程的血小板G蛋白信号功能的增益和损失。这些研究的结果应该是关于正常血小板生物学的新信息，确定治疗干预的潜在靶点，并建立模型系统，在其中可以研究和理解血小板活化失调的后果。

Human platelets are rapidly activated at sites of vascular injury by agonists such as collagen, thrombin and AP. With the notable exception of collagen, most agonists activate platelets via cell surface receptors coupled to heterotrimeric G proteins. Collectively, G proteins and G protein coupled receptors provide a sensitive mechanism that allows rapid platelet activation. However, this sensitivity also increases the risk that inappropriate platelet activation will, if unchecked, cause tissue ischemia and infarction. This is particularly true when progressive diseases such as atherosclerosis narrow the vascular lumen. Since passage through the circulatory system will predictably expose platelets to conditions that could cause unwanted activation, it is reasonable to propose that mechanisms exist to place limits on signaling through G proteins. It is our hypothesis that in platelets such regulatory mechanisms are directed towards both receptors and G proteins, but those working at the level of the G proteins are particularly important and work in concert with endothelial but those working at the level of the G proteins Are particularly important and work in concert with endothelial PGI2, NO and CD39 to prevent inappropriate platelet activation. The goal of the proposed studies is to test this hypothesis and to extend current information about the regulation of G protein-dependent signaling in platelets. Three related issues will be addressed using human platelets and platelets from genetically-engineered mice. First, there are at least 1o different G proteins in platelets. To what extend does each make a unique contribution to signaling and to what extent are they redundant? Second, will persistent activation of G proteins in platelet hyperactivity ex vivo and will it contribute to the development of thrombosis and the progression of atherosclerosis in vivo. Third, what are the roles of RGS proteins in limiting G protein signaling in platelets and do they provide a means of preventing unwarranted platelet activation? We will address these questions primarily using transgenic engineered for both a gain and loss of function of platelet G protein signaling. The results of these studies should new information about normal platelet biology, identify potential targets for therapeutic intervention, and create model systems in which the consequences of dysregulated platelet activation can be studied and understood.