From the Department of Biomedical Engineering (C.P., A.T.P.N., J.P., M.W.H., M.T.H., A.G., Q.J.T.M.), School of Medicine, Oregon Health & Science University, Portland.
Division of Hematology/Medical Oncology (C.P., A.G., O.J.T.M.), School of Medicine, Oregon Health & Science University, Portland.
Arterioscler Thromb Vasc Biol. 2019 Jul;39(7):1390-1401. doi: 10.1161/ATVBAHA.119.312619. Epub 2019 May 23.
Objective- Activation of coagulation FXI (factor XI) by FXIIa (activated factor XII) is a prothrombotic process. The endothelium is known to play an antithrombotic role by limiting thrombin generation and platelet activation. It is unknown whether the antithrombotic role of the endothelium includes sequestration of FXIa (activated factor XI) activity. This study aims to determine the role of endothelial cells (ECs) in the regulation of the intrinsic pathway of coagulation. Approach and Results- Using a chromogenic assay, we observed that human umbilical veins ECs selectively blocked FXIa yet supported kallikrein and FXIIa activity. Western blotting and mass spectrometry analyses revealed that FXIa formed a complex with endothelial PAI-1 (plasminogen activator inhibitor-1). Blocking endothelial PAI-1 increased the cleavage of a chromogenic substrate by FXIa and the capacity of FXIa to promote fibrin formation in plasma. Western blot and immunofluorescence analyses showed that FXIa-PAI-1 complexes were either released into the media or trafficked to the early and late endosomes and lysosomes of ECs. When baboons were challenged with Staphylococcus aureus to induce a prothrombotic phenotype, an increase in circulating FXIa-PAI-1 complex levels was detected by ELISA within 2 to 8 hours postchallenge. Conclusions- PAI-1 forms a complex with FXIa on ECs, blocking its activity and inducing the clearance and degradation of FXIa. Circulating FXIa-PAI-1 complexes were detected in a baboon model of S. aureus sepsis. Although ECs support kallikrein and FXIIa activity, inhibition of FXIa by ECs may promote the clearance of intravascular FXIa. Visual Overview- An online visual overview is available for this article.
目的- FXIIa（激活的因子 XII）激活凝血 FXI（因子 XI）是一个促血栓形成的过程。已知内皮细胞通过限制凝血酶生成和血小板激活来发挥抗血栓作用。内皮细胞是否具有隔离 FXIa（激活的因子 XI）活性的抗血栓作用尚不清楚。本研究旨在确定内皮细胞（ECs）在调节内源性凝血途径中的作用。方法和结果- 使用显色测定法，我们观察到人脐静脉 ECs 选择性阻断 FXIa，同时支持激肽释放酶和 FXIIa 活性。Western 印迹和质谱分析显示，FXIa 与内皮细胞 PAI-1（纤溶酶原激活物抑制剂-1）形成复合物。阻断内皮细胞 PAI-1 增加了 FXIa 对显色底物的裂解以及 FXIa 在血浆中促进纤维蛋白形成的能力。Western blot 和免疫荧光分析显示，FXIa-PAI-1 复合物要么释放到培养基中，要么转运到 ECs 的早期和晚期内体和溶酶体中。当狒狒受到金黄色葡萄球菌的挑战以诱导促血栓形成表型时，通过 ELISA 在挑战后 2 至 8 小时内检测到循环 FXIa-PAI-1 复合物水平增加。结论- PAI-1 在 ECs 上与 FXIa 形成复合物，阻断其活性并诱导 FXIa 的清除和降解。在金黄色葡萄球菌脓毒症的狒狒模型中检测到循环 FXIa-PAI-1 复合物。尽管 ECs 支持激肽释放酶和 FXIIa 活性，但 ECs 对 FXIa 的抑制可能促进血管内 FXIa 的清除。
