Bettoni Serena, Galbusera Miriam, Gastoldi Sara, Donadelli Roberta, Tentori Chiara, Spartà Giuseppina, Bresin Elena, Mele Caterina, Alberti Marta, Tortajada Agustin, Yebenes Hugo, Remuzzi Giuseppe, Noris Marina
IRCCS-Istituto di Ricerche Farmacologiche "Mario Negri," Centro di Ricerche Cliniche per le Malattie Rare "Aldo e Cele Daccò," 24020 Ranica Bergamo, Italy.
Department of Immunology, Complutense University, Research Institute Hospital 12 de Octubre, 28040 Madrid, Spain.
J Immunol. 2017 Aug 1;199(3):1021-1040. doi: 10.4049/jimmunol.1601121. Epub 2017 Jun 26.
von Willebrand factor (VWF), a multimeric protein with a central role in hemostasis, has been shown to interact with complement components. However, results are contrasting and inconclusive. By studying 20 patients with congenital thrombotic thrombocytopenic purpura (cTTP) who cannot cleave VWF multimers because of genetic deficiency, we investigated the mechanism through which VWF modulates complement and its pathophysiological implications for human diseases. Using assays of ex vivo serum-induced C3 and C5b-9 deposits on endothelial cells, we documented that in cTTP, complement is activated via the alternative pathway (AP) on the cell surface. This abnormality was corrected by restoring ADAMTS13 activity in cTTP serum, which prevented VWF multimer accumulation on endothelial cells, or by an anti-VWF Ab. In mechanistic studies we found that VWF interacts with C3b through its three type A domains and initiates AP activation, although assembly of active C5 convertase and formation of the terminal complement products C5a and C5b-9 occur only on the VWF-A2 domain. Finally, we documented that in the condition of ADAMTS13 deficiency, VWF-mediated formation of terminal complement products, particularly C5a, alters the endothelial antithrombogenic properties and induces microvascular thrombosis in a perfusion system. Altogether, the results demonstrated that VWF provides a platform for the activation of the AP of complement, which profoundly alters the phenotype of microvascular endothelial cells. These findings link hemostasis-thrombosis with the AP of complement and open new therapeutic perspectives in cTTP and in general in thrombotic and inflammatory disorders associated with endothelium perturbation, VWF release, and complement activation.
血管性血友病因子（VWF）是一种在止血过程中起核心作用的多聚体蛋白，已被证明可与补体成分相互作用。然而，结果却相互矛盾且尚无定论。通过研究20例因基因缺陷而无法裂解VWF多聚体的先天性血栓性血小板减少性紫癜（cTTP）患者，我们探究了VWF调节补体的机制及其对人类疾病的病理生理学影响。通过体外血清诱导的C3和C5b - 9在内皮细胞上沉积的检测，我们记录到在cTTP中，补体通过细胞表面的替代途径（AP）被激活。通过恢复cTTP血清中的ADAMTS13活性（可防止VWF多聚体在内皮细胞上积累）或使用抗VWF抗体，这种异常得以纠正。在机制研究中，我们发现VWF通过其三个A结构域与C3b相互作用并启动AP激活，尽管活性C5转化酶的组装以及终末补体产物C5a和C5b - 9的形成仅发生在VWF - A2结构域上。最后，我们记录到在ADAMTS13缺乏的情况下，VWF介导的终末补体产物，特别是C5a的形成，改变了内皮细胞的抗血栓形成特性，并在灌注系统中诱导微血管血栓形成。总之，结果表明VWF为补体替代途径的激活提供了一个平台，这深刻改变了微血管内皮细胞的表型。这些发现将止血 - 血栓形成与补体替代途径联系起来，并为cTTP以及一般与内皮细胞扰动、VWF释放和补体激活相关的血栓性和炎性疾病开辟了新的治疗前景。
