细胞极性蛋白Pard3在血小板中的表达和功能研究

Platelet activation plays a pivotal role in physiological hemostasis and pathological thrombosis. Platelet activation induces cytoskeletal reorganization that results in a change from discoid to spheric shape of the cell, and eventually adhesion and spreading on immobilized ligands. Furthermore, rearrangements of the cytoskeleton are crucial for the secretion of intracellularly stored granules by activated platelets. Though cytoskeletal reorganization is a critical driving force for platelet activation, little is know about the upstream regulatory molecule for the cytoskeletal reorganization in platelets. Here we reported that Pard3, a key regulator of the cytoskeleton and cell polarity, was highly expressed in the platelets of healthy people while low in platelets of Acute Coronary Syndrome (ACS) patients. Pard3 was able to relieve the intra-molecular interaction and thereby promote microtubule bundling and stabilization. We characterized platelet-specific Pard3 deficiency mice to elucidate the effect of Pard3 on platelet function. We found that Pard3 deficiency led to mild thrombocytopenia and decreased bleeding time. Functional analysis revealed that Pard3 deficiency potentiated platelet aggregation, secretion and spreading. We hence proposed that Pard3 may potentiated platelet activation by regulation of cytoskeletal reorganization. We plan to study the effects of Pard3 on platelet activation (aggregation, adhesion, spreading and retraction), cytoskeletal reorganization (microtubule stability and polarity), thrombus formation and signalling pathway by using knockout mice model. We also plan to evaluate the expression and clinical significance of platelet Pard3 in ACS patients. By implementing this project, we may not only reveal the role of Pard3 in platelet activation, but also may represent a new strategy for antiplatelet therapy.

血小板异常激活引起的血栓形成是动脉血栓性疾病的重要病理基础，而驱动血小板激活的动力是细胞骨架的重构。极性蛋白Pard3与细胞骨架密切相关，但其在血小板的功能未见报道。我们前期工作首次发现，1 血小板表达高水平的Pard3, 而急性冠脉综合征（ACS）患者血小板Pard3显著下调；2血小板Pard3与微管骨架存在动态相互作用；3血小板Pard3特异性基因敲除引起小鼠血小板减少，但出血时间缩短，血小板聚集、铺展、释放能力增强。本项目拟使用基因敲除小鼠、血栓动物模型、ACS患者血小板，深入研究Pard3对血小板激活的影响、对微管骨架特征（稳定性和极性）和动态变化（延伸和卷曲）的调控、对血小板重要受体和激酶信号的作用，并评估Pard3在ACS患者血小板中的表达和临床意义。本项目的完成不仅能够揭示极性蛋白对于血小板功能的调控作用，还可能为ACS患者抗血小板治疗提供新的策略—纠正异常的极性。

血小板活化受复杂的信号网络调控，本课题旨在探究Pard3调控血小板活化和血栓形成的分子机制，为抗血栓治疗的新药研发提供可能的作用靶点和理论依据。我们发现稳定型心绞痛患者Pard3表达较健康人显著下降，急性冠脉综合征患者Pard3表达较稳定型心绞痛患者更低。Pard3表达较低的患者出院1年内心绞痛复发率更高,提示Pard3低表达水平是急性冠脉综合征的预后不良的关键因素。在动物模型中，Par3缺失不改变小鼠血小板计数与平均容积，和血小板内容物α颗粒和致密颗粒的数量，但促进血小板活化，增强血小板聚集、释放、铺展和凝块回缩功能。此外，Pard3缺失缩短出血时间，加快血栓形成。血小板Pard3基因敲除小鼠心肌梗死后，心功能较对照组小鼠恶化加重，梗死面积增大，微循环血栓形成增多，提示血小板Pard3表达降低促进心肌梗死恶化。分子机制研究显示：Par3通过调控talin与整合素β3亚基的相互作用参与血小板活化。本项目的完成不仅能够揭示极性蛋白对于血小板功能的调控作用，还为ACS患者抗血小板治疗提供新的策略—纠正异常极性，恢复Pard3表达。

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