Vandendries Erik R, Hamilton Justin R, Coughlin Shaun R, Furie Bruce, Furie Barbara C
Division of Hemostasis and Thrombosis, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.
Proc Natl Acad Sci U S A. 2007 Jan 2;104(1):288-92. doi: 10.1073/pnas.0610188104. Epub 2006 Dec 26.
Thrombin, a central mediator of hemostasis and thrombosis, converts fibrinogen to fibrin and is a potent platelet activator. Activated platelets provide a surface for assembly of the tenase and prothrombinase complexes required for thrombin generation. The role of thrombin-induced platelet activation in platelet accumulation and its interplay with fibrin deposition during thrombus assembly has not been fully defined. We studied these processes during laser-induced thrombus formation by using real-time digital fluorescence microscopy in mice lacking protease-activated receptor-4 (Par4), which is necessary for thrombin responsiveness in mouse platelets. Juxtamural platelet accumulation immediately after laser injury was not different in wild-type and Par4(-/-) mice. However, subsequent growth of platelet thrombi was markedly diminished in Par4(-/-) mice. At the time of maximal thrombus size in wild type, platelet accumulation was more than 10-fold higher in wild type than in Par4(-/-) mice. P-selectin expression, a marker of platelet activation, was reduced and delayed in Par4(-/-) thrombi. In contrast to platelet activation and accumulation, the rate and amount of fibrin deposition, predominantly intramural and juxtamural in this model, were indistinguishable in Par4(-/-) and wild-type mice. These results suggest that platelet activation by thrombin is necessary for normal propagation of a platelet thrombus at a distance from the injured vessel wall and hence for normal thrombus growth. However, platelet activation by thrombin is unnecessary for initial and limited accumulation of platelets at or near the vessel wall, and this limited accumulation of platelets and/or platelet-independent mechanism(s) of thrombin generation are sufficient for normal fibrin deposition in this model.
凝血酶是止血和血栓形成的核心介质，它能将纤维蛋白原转化为纤维蛋白，并且是一种强效的血小板激活剂。活化的血小板为凝血酶生成所需的凝血活酶和凝血酶原酶复合物的组装提供了一个表面。凝血酶诱导的血小板激活在血小板聚集过程中的作用及其在血栓形成过程中与纤维蛋白沉积的相互作用尚未完全明确。我们通过实时数字荧光显微镜在缺乏蛋白酶激活受体-4（Par4）的小鼠中研究了激光诱导血栓形成过程中的这些过程，Par4对小鼠血小板中的凝血酶反应性是必需的。激光损伤后立即发生的壁旁血小板聚集在野生型和Par4(-/-)小鼠中没有差异。然而，Par4(-/-)小鼠中血小板血栓的后续生长明显减弱。在野生型血栓大小达到最大值时，野生型中的血小板聚集比Par4(-/-)小鼠高10倍以上。血小板激活标志物P-选择素的表达在Par4(-/-)血栓中减少且延迟。与血小板激活和聚集相反，在该模型中主要为壁内和壁旁的纤维蛋白沉积的速率和量在Par4(-/-)和野生型小鼠中没有区别。这些结果表明，凝血酶诱导的血小板激活对于血小板血栓在远离受损血管壁处的正常扩展是必要的，因此对于正常的血栓生长也是必要的。然而，凝血酶诱导的血小板激活对于血小板在血管壁处或附近的初始和有限聚集是不必要的，并且这种有限的血小板聚集和/或凝血酶生成的非血小板依赖性机制足以在该模型中实现正常的纤维蛋白沉积。
