The cGMP-dependent protein kinase pathway in platelets

血小板活化在心脏病发作和中风等血栓性疾病的发展中起着关键作用。这个 血小板在血栓形成中的作用主要涉及两个方面：第一，血小板的黏附、聚集和分泌 颗粒含量在动脉粥样硬化的发展过程中起着重要作用，动脉粥样硬化可导致慢性血管损伤。第二， 血管损伤部位的血小板活化是引发动脉血栓形成的关键。一种细胞内次要的 信使分子cGMP是在血小板活化过程中合成的。CGMP在血小板活化中的作用 自从cGMP被发现以来就一直备受争议。在过去的30年里，cGMP一直是一个流行的概念， 激活cGMP依赖的蛋白激酶(PKG)，抑制血小板的激活。然而，这个概念一直是 我们最近发现cGMP和PKG在血小板激活中起着双相作用，我们对此提出了挑战，我们发现cGMP 当低浓度的cGMP在血小板激动剂刺激下产生时起刺激作用，但 在高cGMP浓度下有抑制作用。在上一次筹资期间，我们在以下方面取得了重大进展 了解cGMP途径在血小板活化中的双相作用机制。我们发现， CGMP-PKG途径在刺激血小板分泌和分泌依赖的血小板聚集中起普遍作用 由大多数血小板激动剂诱导。我们已经获得证据支持cGMP的一个新的上游信号通路。 在涉及磷脂酰肌醇3-激酶、各种形式的Akt和一氧化氮合酶(NO)的血小板激活过程中。我们 还获得了证据支持cGMP的一种新的下行信号机制，涉及各种异构体 PKG和依赖于PKG的p38和ERK丝裂原活化蛋白激酶通路的顺序激活。这些 这些发现使我们能够假设一种刺激血小板分泌的新的信号通路。在这一途径中，血小板 激动剂通过激活不同亚型的PI3K、Akt、NOS3、可溶性鸟苷酸环化酶和PKG，并通过p38和 ERK途径，诱导血小板分泌，从而放大和稳定血小板聚集。为了检验这一假设，我们 提出以下具体目标：1.研究不同Akt亚型作为cGMP上游激活剂的作用 在血小板激活过程中的途径。2.为确定激动剂诱导血小板产生NO的机制，其 调节，以及它在血小板分泌和聚集中的作用。3.确定角色和信号机制的特征 不同亚型PKG在血小板分泌和聚集中的作用。

Platelet activation play critical roles in the development of thrombotic diseases such as heart attack and stroke. The roles of platelets in thrombosis involves two major aspects: Firstly, platelet adhesion, aggregation and secretion of granule contents are important in the development of atherosclerosis, which causes chronic vascular injury. Secondly, platelet activation at the site of vascular injury is critical in initiating arterial thrombosis. An intracellular secondary messenger molecule, cGMP, is synthesized during platelet activation. The role of cGMP in platelet activation has been controversial since the discovery of cGMP. It has been a prevailing concept in the past 30 years that cGMP, by activating the cGMP-dependent protein kinase (PKG), inhibits platelet activation. This concept, however, has been challenged by our recent finding that cGMPand PKG play a biphasic role in platelet activation, We show that cGMP plays a stimulatory role when low concentrations of cGMP is produced upon platelet agonist stimulation, but becomes inhibitory at high cGMP concentrations. During the last funding period, we have made significant progress in understanding the mechanisms of the biphasic roles of the cGMP pathway in platelet activation. We have found that the cGMP-PKG pathway plays a general role in stimulating platelet secretion and secretion-dependent platelet aggregation induced by most platelet agonists. We have obtained evidence supporting a new upstream signaling pathway of cGMP during platelet activation involving phosphoinositide 3-kinase, various forms of Akt and nitric oxide (NO) synthase. We have also obtained evidence supporting a novel downstreamsignaling mechanism of cGMP involving various isoforms of PKG and PKG-dependent sequentially activation of p38 and ERK mitogen-activated protein kinase pathways. These discoveries allow us to hypothesize a novel signaling pathwaythat stimulates platelet secretion. In this pathway, platelet agonists, by activating different isoforms of PI3K, Akt, NOS3,soluble guanylyl cyclase, and PKG, and via the p38 and ERK pathways, induce platelet secretion, which amplifies and stabilizes platelet aggregation. To test this hypothesis, we propose following specific aims: 1.To investigate the role of different Akt isoforms as upstream activators of the cGMP pathway during platelet activation. 2. To determine mechanisms of agonist-induced platelet NO production, its regulation, and its role in platelet secretion and aggregation. 3.To characterize the roles and the signaling mechanisms of different isoforms of PKGin platelet secretion and aggregation.