Laboratory for Hemostasis, Inflammation & Thrombosis, Unité Mixed de Recherche 1176, Institut National de la Santé et de la Recherche Médicale, Université Paris-Saclay, Le Kremlin-Bicêtre, France.
Department of Clinical Chemistry and Haematology, Utrecht Medical Centre, Utrecht, The Netherlands.
J Thromb Haemost. 2022 Mar;20(3):755-766. doi: 10.1111/jth.15598. Epub 2021 Dec 3.
Platelet-binding Von Willebrand Factor (VWF) strings assemble upon stimulated secretion from endothelial cells.
To investigate the efficiency of platelet binding to multi-molecular VWF bundles secreted from endothelial cells and to investigate the role of osteoprotegerin, a protein located in Weibel-Palade bodies that interacts with the VWF platelet binding domain.
The nanobody VWF/AU-a11 that specifically binds to VWF in its active platelet-binding conformation was used to investigate the conformation of VWF.
Upon stimulated secretion from endothelial cells, VWF strings were only partially covered with platelets, while a VWD-type 2B mutation or ristocetin enhanced platelet binding by 2-3-fold. Osteoprotegrin, reduces platelet adhesion to VWF by 40% ± 18% in perfusion assays. siRNA-mediated down-regulation of endothelial osteoprotegerin expression resulted in a 1.8-fold increase in platelet adhesion to VWF strings. Upon viral infection, there is a concordant rise in VWF and osteoprotegerin plasma levels. Unexpectedly, no such increase was observed in plasma of desmopressin-treated hemophilia A-patients. In a mouse model, osteoprotegerin expression was low in liver endothelial cells of vehicle-treated mice, and concanavalin A-treatment increased VWF and osteoprotegerin expression 4- and 40-fold, respectively. This increase was translated in a 30-fold increased osteoprotegerin/VWF ratio in plasma.
Release of VWF from endothelial cells opens the platelet-binding site, irrespective of the presence of flow. However, not all available platelet-binding sites are being occupied, suggesting some extent of regulation. Part of this regulation involves endothelial proteins that are co-secreted with VWF, like osteoprotegerin. This regulatory mechanism may be of more relevance under inflammatory conditions.
血小板结合的血管性血友病因子 (VWF) 串在血管内皮细胞受刺激分泌时组装。
研究血小板结合从内皮细胞分泌的多分子 VWF 束的效率，并研究位于 Weibel-Palade 体中的与 VWF 血小板结合结构域相互作用的骨保护蛋白（osteoprotegerin）的作用。
使用特异性结合 VWF 其活性血小板结合构象的纳米抗体 VWF/AU-a11 来研究 VWF 的构象。
在内皮细胞受刺激分泌后，VWF 串仅部分被血小板覆盖，而 VWD 型 2B 突变或瑞斯托菌素增强了 2-3 倍的血小板结合。骨保护蛋白在灌注试验中可将血小板与 VWF 的黏附减少 40%±18%。内皮细胞骨保护蛋白表达的 siRNA 下调导致血小板与 VWF 串的黏附增加 1.8 倍。病毒感染后，VWF 和骨保护蛋白的血浆水平呈一致上升。出乎意料的是，在去氨加压素治疗的血友病 A 患者的血浆中未观察到这种增加。在小鼠模型中，骨保护蛋白在未处理小鼠的肝内皮细胞中表达水平较低，而刀豆球蛋白 A 处理分别使 VWF 和骨保护蛋白的表达增加 4 倍和 40 倍。这种增加转化为血浆中骨保护蛋白/VWF 比值增加 30 倍。
内皮细胞释放 VWF 会打开血小板结合位点，无论是否存在流动。然而，并非所有可用的血小板结合位点都被占据，这表明存在一定程度的调节。这种调节的一部分涉及与 VWF 共同分泌的内皮蛋白，如骨保护蛋白。这种调节机制在炎症条件下可能更为重要。
