COAT-Platelets

在胶原蛋白和凝血酶的共同刺激下，血小板表现出许多不寻常的特征。正如最初所描述的，这些双重激活的血小板，指的是被包裹的血小板(胶原和凝血酶刺激的血小板)，表达高水平的表面结合因子V。这一亚群的血小板约占总数的30%，在年轻的血小板中最为突出。当用凝血酶和惊厥毒素(一种糖蛋白VI的激动剂)激活时，也可以观察到包裹-血小板；然而，没有一种单一的激动剂能够产生包裹-血小板。Fv具有较高的凝血因子V活性、Xa因子的优先结合活性和显著的凝血酶原酶活性，具有重要的功能意义。此外，包被血小板还发现了其他几种α颗粒蛋白，包括von Willebrand因子、纤维蛋白原、纤维连接蛋白、凝血酶反应蛋白和α2-抗纤溶酶，它们都是高水平结合的。出乎意料的是，转谷氨酰胺酶抑制剂包括丹西尔·卡维林、腐胺和乙酰酪蛋白可以防止涂层-血小板的形成，并且转谷氨酰胺酶的合成肽底物被结合到涂层-血小板中。作为转谷氨酰胺酶反应的酰基受体的血小板成分是5-羟色胺，而白蛋白的多价5-羟色胺加合物是有效的外套-血小板形成的抑制物。从包被血小板中分离出的纤维蛋白原也被发现具有结合的5-羟色胺。这项建议将通过鉴定被膜血小板上发现的其他α颗粒蛋白的5-羟色胺加合物，通过表征被膜血小板上存在的5-羟色胺结合位点，以及通过评估实验动物对被膜血小板的生理操作来进一步表征被膜血小板。

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.