Furukawa Shoko, Nogami Keiji, Ogiwara Kenichi, Shima Midori
Department of Pediatrics, Nara Medical University, 840 Shijo-cho, 634-8522, Kashihara, Nara, Japan.
Int J Hematol. 2019 Apr;109(4):390-401. doi: 10.1007/s12185-019-02611-3. Epub 2019 Feb 13.
Factor VIIa/tissue factor (FVIIa/TF) initiates blood coagulation by promoting FXa generation (extrinsic-Xa). Subsequent generation of intrinsic FXa (intrinsic-Xa) amplifies thrombin formation. Previous studies suggested that FVIIa/TF activates FVIII rapidly in immediate coagulation reactions, and FVIIa/TF/FXa activates FVIII prior to thrombin-dependent feedback. We investigated FVIII/FVIIa/TF/FXa relationships in early coagulation mechanisms. Total FXa generated by FVIIa/TF and FVIIa/TF-activated FVIII (FVIIIa) was 22.6 ± 1.7 nM (1 min); total FXa with FVIIa-inhibitor was 3.4 ± 0.7 nM, whereas FXa generated by FVIIa/TF or FVIII/TF was 10.4 ± 1.1 or 0.74 ± 0.14 nM, respectively. Little Xa was generated by FVIII alone, suggesting that intrinsic-Xa mechanisms were mediated by FVIIIa and FVIII/TF in the initiation phase. Intrinsic-Xa was delayed somewhat by von Willebrand factor (VWF). FVIII activation by FXa with FVIIa/TF was comparable to activation with Glu-Gly-Arg-inactivated-FVIIa/TF. TF counteracted the inhibitory effects of VWF on FXa-induced FVIII activation mediated by Arg cleavage. The FVIII-C2 domain bound to cytoplasmic domain-deleted TF (TF), and VWF blocked this binding by > 80%, indicating an overlap between VWF- and TF-binding site(s) on C2. Overall, these data suggest that FVIII-associated intrinsic-Xa, governed by both FVIIa/TF-induced and FXa-induced FVIII activation mediated by FVIII-TF interactions, together with FVIIa-dependent extrinsic-Xa mechanisms, may be central to the initiation phase of coagulation.
凝血因子VIIa/组织因子（FVIIa/TF）通过促进因子Xa（FXa）生成（外源性Xa）启动血液凝固。随后内源性FXa（内源性Xa）的生成会放大凝血酶的形成。先前的研究表明，在即时凝血反应中FVIIa/TF能迅速激活FVIII，并且在凝血酶依赖性反馈之前FVIIa/TF/FXa就能激活FVIII。我们研究了早期凝血机制中FVIII/FVIIa/TF/FXa之间的关系。FVIIa/TF和FVIIa/TF激活的FVIII（FVIIIa）产生的总FXa为22.6±1.7 nM（1分钟）；使用FVIIa抑制剂时总FXa为3.4±0.7 nM，而FVIIa/TF或FVIII/TF产生的FXa分别为10.4±1.1 nM或0.74±0.14 nM。单独的FVIII产生的Xa很少，这表明在内源性Xa机制在起始阶段是由FVIIIa和FVIII/TF介导的。内源性Xa会因血管性血友病因子（VWF）而有所延迟。FXa与FVIIa/TF一起对FVIII的激活与用Glu-Gly-Arg失活的FVIIa/TF激活相当。TF抵消了VWF对由精氨酸裂解介导的FXa诱导的FVIII激活的抑制作用。FVIII的C2结构域与缺失细胞质结构域的TF（TF）结合，并且VWF使这种结合减少了>80%，表明C2上VWF结合位点和TF结合位点存在重叠。总体而言，这些数据表明，由FVIIa/TF诱导和由FVIII-TF相互作用介导的FXa诱导的FVIII激活共同控制的FVIII相关内源性Xa，与FVIIa依赖性外源性Xa机制一起，可能是凝血起始阶段的核心。
