Guerrero J A, Shafirstein G, Russell S, Varughese K I, Kanaji T, Liu J, Gartner T K, Bäumler W, Jarvis G E, Ware J
Department of Physiology & Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR, USA.
J Thromb Haemost. 2008 Apr;6(4):684-91. doi: 10.1111/j.1538-7836.2008.02916.x.
Platelet glycoprotein (GP) Ib-IX-V supports platelet adhesion on damaged vascular walls by binding to von Willebrand factor (VWF). For several decades it has been recognized that the alpha-subunit of GP (GPIbalpha) also binds thrombin but the physiological relevance, if any, of this interaction was unknown. Previous studies have shown that a sulfated tyrosine 276 (Tyr276) is essential for thrombin binding to GPIbalpha.
This study investigated the in vivo relevance of GPIbalpha residue Tyr276 in hemostasis and thrombosis.
Transgenic mouse colonies expressing the normal human GPIbalpha subunit or a mutant human GPIbalpha containing a Phe substitution for Tyr276 (hTg(Y276F)) were generated. Both colonies were bred to mice devoid of murine GPIbalpha.
Surface-expressed GPIbalpha levels and platelet counts were similar in both colonies. hTg(Y276F) platelets were significantly impaired in binding alpha-thrombin but displayed normal binding to type I fibrillar collagen and human VWF in the presence of ristocetin. In vivo thrombus formation as a result of chemical damage (FeCl(3)) demonstrated that hTg(Y276F) mice have a delayed time to occlusion followed by unstable blood flow indicative of embolization. In models of laser-induced injury, thrombi developing in hTg(Y276F) animals were also less stable.
The results demonstrate that GPIbalpha residue Tyr276 is physiologically important, supporting stable thrombus formation in vivo.
血小板糖蛋白（GP）Ib-IX-V通过与血管性血友病因子（VWF）结合来支持血小板在受损血管壁上的黏附。几十年来，人们已经认识到GP的α亚基（GPIbalpha）也能结合凝血酶，但这种相互作用的生理相关性（如果存在的话）尚不清楚。先前的研究表明，硫酸化的酪氨酸276（Tyr276）对于凝血酶与GPIbalpha的结合至关重要。
本研究调查了GPIbalpha残基Tyr276在体内止血和血栓形成中的相关性。
构建了表达正常人GPIbalpha亚基或含有Tyr276被苯丙氨酸取代的突变型人GPIbalpha（hTg(Y276F)）的转基因小鼠群体。将这两个群体与缺乏小鼠GPIbalpha的小鼠进行杂交。
两个群体中表面表达的GPIbalpha水平和血小板计数相似。hTg(Y276F)血小板在结合α-凝血酶方面明显受损，但在存在瑞斯托霉素的情况下，与I型纤维状胶原和人VWF的结合正常。化学损伤（FeCl(3)）导致的体内血栓形成表明，hTg(Y276F)小鼠的闭塞时间延迟，随后血流不稳定，提示有栓塞形成。在激光诱导损伤模型中，hTg(Y276F)动物形成的血栓也较不稳定。
结果表明，GPIbalpha残基Tyr276在生理上具有重要意义，支持体内稳定血栓的形成。
