COAT-Platelets

血小板与胶原蛋白和凝血酶共同刺激显示出许多不寻常的特征。正如最初所描述的，这些双重活化的血小板，被称为coat血小板（胶原蛋白和凝血酶刺激的血小板），表达高水平的表面结合因子v。这种血小板亚群约占总数的30%，在年轻血小板中最为突出。凝血酶加惊厥素（一种糖蛋白VI的激动剂）激活后，也观察到coat -血小板；然而，没有一种单一的激动剂能够产生coat血小板。FV对coat -血小板的功能意义表现为高因子V活性、因子Xa的优先结合和显著的凝血酶原活性。此外，我们还发现，coat血小板中含有其他几种高水平的α颗粒蛋白，包括血管性血友病因子、纤维蛋白原、纤维连接蛋白、血栓反应蛋白和α 2抗纤溶蛋白。出乎意料的是，转谷氨酰胺酶抑制剂（包括丹酰尸体碱、腐胺和乙酰酪蛋白）可以阻止COAT-血小板的形成，并且在COAT-血小板中加入了转谷氨酰胺酶的合成肽底物。作为转谷氨酰胺酶反应酰基受体的血小板成分被发现是5 -羟色胺，白蛋白的多价5 -羟色胺加合物是coat -血小板形成的有效抑制剂。从coat血小板中分离的纤维蛋白原也被发现有结合的血清素。本研究将通过鉴定在COAT-血小板上发现的其他α颗粒蛋白的血清素加合物，表征COAT-血小板上的血清素结合位点，以及在实验动物中评估COAT-血小板的生理操作来进一步表征COAT-血小板。

Platelets co-stimulated with collagen and thrombin display a number of unusual features. As initially described, these dual activated platelets, referred to a COAT-platelets (collagen and thrombin stimulated-platelets), express high levels of surface-bound factor V. This sub-population of platelets represents approximately 30 percent of the total and is most prominent among young platelets. COAT-platelets are also observed upon activation with thrombin plus convulxin, an agonist for glycoprotein VI; however, no single agonist examined was able to produce COAT-platelets. The functional significance of FV on COAT-platelets was shown by demonstrating high factor V activity, preferential binding of factor Xa and significant prothrombinase activity. In addition, COAT-platelets were found to have several other alpha-granule proteins including von Willebrand factor, fibrinogen, fibronectin, thrombospondin and alpha2-antiplasmin, bound at high levels. Unexpectedly, COAT-platelet formation is prevented by transglutaminase inhibitors including dansyl cadaverine, putrescine, and acetyl-casein, and a synthetic peptide substrate for transglutaminases is incorporated in COAT- platelets. The platelet component serving as the acyl acceptor for the transglutaminase reaction was found to be serotonin, and multi-valent serotonin-adducts of albumin were effective inhibitors of COAT-platelet formation. Fibrinogen isolated from COAT-platelets was also found to have conjugated serotonin. This proposal will further characterize COAT-platelets by identifying serotonin-adducts of other alpha-granule proteins found on COAT- platelets, by characterizing the serotonin binding sites present on COAT-platelets, and by evaluating the physiological manipulation of COAT-platelets in experimental animals.