Signaling mechanisms of platelet GPIb-IX

血小板 GPIb-IX 的信号传导机制

• 批准号: 8786806
• 负责人: Xiaoping Du
• 金额: $ 39.95万
• 依托单位: UNIVERSITY OF ILLINOIS AT CHICAGO
• 依托单位国家: 美国
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-07-01 至 2018-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8786806
• 关键词: Adhesions; Agonist; Antibiotic A23187; Binding; Biological Assay; Biomechanics; Blood Platelets; Blood Vessels; Blood flow; Calcium; Coagulants; Coagulation Process; Collagen; Cyclic GMP; Cytoplasmic Granules; Cytoplasmic Tail; Data; Disease; Docking; Dose; Funding; Glycoprotein Ib; Grant; Hemorrhage; Hemostatic function; In Vitro; Inflammatory; Injury; Integrins; Ionophores; LIM Domain Kinase 1; Mediating; Membrane; Mitogen-Activated Protein Kinases; Myocardial Infarction; Names; Phosphatidylinositols; Phosphotransferases; Physiological; Platelet Activation; Platelet Glycoprotein GPIb-IX Complex; Platelet aggregation; Play; Process; Proteinase-Activated Receptors; Research Project Grants; Role; Sepsis; Signal Pathway; Signal Transduction; Site; Stroke; Surface; Testing; Thrombin; Thrombosis; Thromboxane A2; Thrombus; Vascular Endothelium; Vesicle; base; in vivo; inhibitor/antagonist; injured; oligomycin sensitivity-conferring protein; prevent; public health relevance; receptor; receptor function; response; shear stress; von Willebrand Factor; von Willebrand factor receptor

DESCRIPTION (provided by applicant): The platelet receptor for von Willebrand factor (VWF), the glycoprotein (GP) Ib-IX-V complex (GPIb-IX), is vital for initial platelet adhesion to injured blood vessel wall, especially under shear stress. VWF binding to GPIb-IX also initiates signaling resulting in the activation of the platelet integrin aIIbb3, which mediates stable platelet adhesio, platelet aggregation, and thrombus formation. In the current funding periods, we have made significant progress in understanding the signaling mechanisms that regulates the receptor function of GPIb and VWF-induced GPIb signaling leading to platelet activation. In particular, we have demonstrated an important role for Rac1 in mediating VWF/GPIb-IX-mediated early signaling. We also demonstrated an unexpected role of a potential downstream Rac1 effector, LIM kinase 1 (LIMK1) in selectively stimulating GPIb- IX-dependent thromboxane (TX) A2 synthesis and signal amplification. GPIb-IX also interacts with thrombin, and is important in low dose thrombin-induced platelet activation. However, it is unclear whether GPIb-IX serves facilitate more efficient thrombin cleavage of protease-activated receptors (PAR), or GPIb signaling promote thrombin-induced platelet activation. Based on our preliminary data, we hypothesize that the Rac1- and LIMK1-mediated GPIb-IX signaling pathways promotes PAR-dependent platelet response to low dose thrombin. In Aim 1 of this competitive renewal application, we will investigate the role of GPIb-IX signaling in promoting thrombin-induced platelet activation and the Rac1 and LIMK1 signaling pathways that mediates VWF- and thrombin-induced GPIb-IX signaling. Activated platelets play an important role in facilitating coagulation, mainly by providing externalized phosphotidylserine (PS). However, under currently accepted assay conditions, even extremely high concentrations of physiological platelet agonists collagen and thrombin only induce a small fraction of platelets to externalize PS, the reason for this paradox remains unclear. We show that under the shear force relevant to normal blood flow, platelets do not express procoagulant activity (although the extremely high shear stress may induce platelet procoagulant MP release that requires GPIb-IX- VWF interaction). However, physiological levels of shear stress are required for agonists to efficiently induce PS externalization and MP release from platelets. Importantly, we discovered that Rac1 plays a critical role in shear-dependent platelet PS externalization and MP release induced by GPIb-independent platelet agonists. Thus, we hypothesize that activation of platelet procoagulant function requires shear force-induced signaling in which Rac1 plays an important role. Therefore, in Aim 2, we will investigate the role of shear force, Rac1 and GPIb-IX signaling in the activation of platelet procoagulant function. These study should facilitate our understanding how low concentrations of agonists thrombin or initial platelet adhesion will elicit strong platele response leading to not only platelet thrombus formation but also clotting at the site of vascular injury, and help develop new inhibitor for treating thrombotic diseases.

描述（由申请方提供）：血管性血友病因子（VWF）的血小板受体，即糖蛋白（GP）Ib-IX-V复合物（GPIb-IX），对于血小板最初粘附至受损血管壁至关重要，尤其是在剪切应力下。VWF与GPIb-IX的结合还启动信号传导，导致血小板整联蛋白aIIbb 3的活化，其介导稳定的血小板粘附、血小板聚集和血栓形成。在目前的资助期间，我们在理解调节GPIb受体功能的信号传导机制和VWF诱导的GPIb信号传导导致血小板活化方面取得了重大进展。特别是，我们已经证明了Rac 1在介导VWF/GPIb-IX介导的早期信号传导中的重要作用。我们还证明了潜在的下游Rac 1效应子LIM激酶1（LIMK 1）在选择性刺激GPIb-IX依赖性血栓烷（TX）A2合成和信号放大中的意想不到的作用。GPIb-IX还与凝血酶相互作用，并且在低剂量凝血酶诱导的血小板活化中是重要的。然而，目前尚不清楚GPIb-IX是否有助于蛋白酶激活受体（PAR）的更有效的凝血酶切割，或者GPIb-IX信号传导是否促进凝血酶诱导的血小板活化。基于我们的初步数据，我们假设Rac 1和LIMK 1介导的GPIb-IX信号通路促进PAR依赖性血小板对低剂量凝血酶的反应。在本竞争性更新申请的目标1中，我们将研究GPIb-IX信号传导在促进凝血酶诱导的血小板活化中的作用，以及介导VWF和凝血酶诱导的GPIb-IX信号传导的Rac 1和LIMK 1信号传导途径。活化的血小板在促进凝血中起重要作用，主要是通过提供外部化的磷脂酰丝氨酸（PS）。然而，在目前公认的测定条件下，即使是极高浓度的生理性血小板激动剂胶原蛋白和凝血酶也仅诱导一小部分血小板外化PS，这种矛盾的原因仍不清楚。我们表明，在与正常血流相关的剪切力下，血小板不表达促凝血活性（尽管极高的剪切力可能诱导血小板促凝血MP释放，这需要GPIb-IX- VWF相互作用）。然而，生理水平的剪切应力是激动剂有效诱导PS外化和MP从血小板释放所必需的。重要的是，我们发现Rac 1在GPib非依赖性血小板激动剂诱导的剪切依赖性血小板PS外化和MP释放中发挥关键作用。因此，我们假设血小板促凝功能的激活需要剪切力诱导的信号传导，其中Rac 1起着重要作用。因此，在目标2中，我们将研究剪切力，Rac 1和GPIb-IX信号在血小板促凝功能激活中的作用。这些研究将有助于我们了解低浓度激动剂凝血酶或初始血小板粘附如何引起强烈的血小板反应，不仅导致血小板血栓形成，而且还导致血管损伤部位的凝血，并有助于开发新的抑制剂用于治疗血栓性疾病。