Department of Biochemistry, CARIM, Maastricht University, the Netherlands (G.P., J.H., I.P., F.S., P.E.J.v.d.M., R.A.S.A., S.P.W., J.W.M.H.).
Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, United Kingdom (G.P., M.T., S.P.W.).
Arterioscler Thromb Vasc Biol. 2021 Feb;41(2):e97-e111. doi: 10.1161/ATVBAHA.120.314641. Epub 2020 Dec 3.
Fibrin is considered to strengthen thrombus formation via integrin αIIbβ3, but recent findings indicate that fibrin can also act as ligand for platelet glycoprotein VI. Approach and Results: To investigate the thrombus-forming potential of fibrin and the roles of platelet receptors herein, we generated a range of immobilized fibrin surfaces, some of which were cross-linked with factor XIIIa and contained VWF-BP (von Willebrand factor-binding peptide). Multicolor microfluidics assays with whole-blood flowed at high shear rate (1000 s) indicated that the fibrin surfaces, regardless of the presence of factor XIIIa or VWF-BP, supported platelet adhesion and activation (P-selectin expression), but only microthrombi were formed consisting of bilayers of platelets. Fibrinogen surfaces produced similar microthrombi. Markedly, tiggering of coagulation with tissue factor or blocking of thrombin no more than moderately affected the fibrin-induced microthrombus formation. Absence of αIIbβ3 in Glanzmann thrombasthenia annulled platelet adhesion. Blocking of glycoprotein VI with Fab 9O12 substantially, but incompletely reduced platelet secretion, Ca signaling and aggregation, while inhibition of Syk further reduced these responses. In platelet suspension, glycoprotein VI blockage or Syk inhibition prevented fibrin-induced platelet aggregation. Microthrombi on fibrin surfaces triggered only minimal thrombin generation, in spite of thrombin binding to the fibrin fibers.
Together, these results indicate that fibrin fibers, regardless of their way of formation, act as a consolidating surface in microthrombus formation via nonredundant roles of platelet glycoprotein VI and integrin αIIbβ3 through signaling via Syk and low-level Ca rises.
纤维蛋白被认为通过整合素αIIbβ3增强血栓形成，但最近的研究结果表明，纤维蛋白也可以作为血小板糖蛋白 VI 的配体。
为了研究纤维蛋白的血栓形成潜力及其在此过程中血小板受体的作用，我们生成了一系列固定化纤维蛋白表面，其中一些用因子 XIIIa 交联并含有 VWF-BP（血管性血友病因子结合肽）。全血在高剪切率（1000s）下的多色微流控分析表明，无论是否存在因子 XIIIa 或 VWF-BP，纤维蛋白表面均支持血小板黏附和激活（P-选择素表达），但仅形成由双层血小板组成的微血栓。纤维蛋白原表面产生类似的微血栓。值得注意的是，用组织因子触发凝血或仅适度阻断凝血酶对纤维蛋白诱导的微血栓形成的影响不大。在 Glanzmann 血小板无力症中缺乏αIIbβ3 可使血小板黏附失效。用 Fab 9O12 阻断糖蛋白 VI 可显著但不完全地减少血小板分泌、Ca 信号和聚集，而抑制 Syk 则进一步降低这些反应。在血小板悬浮液中，糖蛋白 VI 阻断或 Syk 抑制可防止纤维蛋白诱导的血小板聚集。尽管纤维蛋白纤维与纤维蛋白纤维结合，但纤维蛋白表面上的微血栓仅触发最小程度的凝血酶生成。
总之，这些结果表明，纤维蛋白纤维，无论其形成方式如何，通过糖蛋白 VI 和整合素αIIbβ3 的非冗余作用，通过 Syk 信号和低水平 Ca 升高，在微血栓形成中充当巩固表面。
