Department of Biochemistry, Maastricht University, Maastricht, The Netherlands.
J Thromb Haemost. 2015 Jan;13(1):92-100. doi: 10.1111/jth.12766. Epub 2014 Nov 29.
Tissue factor pathway inhibitor-α (TFPIα) inhibits factor Xa by forming a binary TFPI-FXa complex in a reaction that is stimulated by protein S. TF-FVIIa forms a quaternary complex with TFPIα and FXa, which shuts off the initiation of coagulation via the extrinsic pathway.
To investigate whether direct inhibition of FXa by TFPIα independently of TF plays a role in downregulating coagulation.
Inhibition of FXa by TFPIα in plasma was determined by measuring thrombin generation triggered with FXa, the FX activator from Russell's viper venom (RVV-X), FXIa, or FIXa. TF-independent anticoagulant activities of TFPIα and its cofactor, protein S, were quantified: (i) after neutralization of TFPIα and protein S with anti-TFPI or anti-protein S antibodies; and (ii) in TFPI-depleted or protein S-depleted plasmas supplemented with varying amounts of TFPIα or protein S.
Both anti-TFPI and anti-protein S antibodies enhanced thrombin generation in plasma triggered with RVV-X, FXa, FIXa, or FXIa. Anti-TFPI and anti-protein S antibodies decreased the lag time and increased the peak height of thrombin generation to the same extent, indicating that inhibition of FXa by TFPIα requires the presence of protein S. TFPIα and protein S titrations in TFPI-depleted or protein S-depleted plasma in which thrombin formation was initiated with triggers other than TF also revealed TF-independent anticoagulant activity of TFPIα, which was completely dependent on the presence of protein S.
Direct inhibition of FXa by TFPIα contributes to the downregulation of coagulation.
组织因子途径抑制剂-α（TFPIα）通过与蛋白 S 共同作用形成一个二元 TFPI-FXa 复合物来抑制因子 Xa 的活性，该反应受到蛋白 S 的刺激。TF-FVIIa 与 TFPIα 和 FXa 形成一个四元复合物，通过外源性途径关闭凝血的起始。
研究 TFPIα 对 FXa 的直接抑制作用是否独立于 TF 在下调凝血中的作用。
通过测量 FXa 引发的凝血酶生成来确定 TFPIα 在血浆中对 FXa 的抑制作用，FXa 的 FX 激活剂来自罗素蝰蛇毒液（RVV-X）、FXIa 或 FIXa。TFPIα 及其辅助因子蛋白 S 的 TF 非依赖性抗凝活性通过以下两种方法进行量化：(i) 用抗 TFPI 或抗蛋白 S 抗体中和 TFPIα 和蛋白 S 后；(ii) 在 TFPI 耗尽或蛋白 S 耗尽的血浆中补充不同量的 TFPIα 或蛋白 S。
抗 TFPI 和抗蛋白 S 抗体均增强了 RVV-X、FXa、FIXa 或 FXIa 引发的血浆中凝血酶的生成。抗 TFPI 和抗蛋白 S 抗体降低了凝血酶生成的延迟时间并同等程度地增加了凝血酶生成的峰值高度，表明 TFPIα 对 FXa 的抑制作用需要蛋白 S 的存在。TFPIα 和蛋白 S 在 TFPI 耗尽或蛋白 S 耗尽的血浆中的滴定，其中凝血酶形成的触发物不是 TF，也揭示了 TFPIα 的 TF 非依赖性抗凝活性，该活性完全依赖于蛋白 S 的存在。
TFPIα 对 FXa 的直接抑制作用有助于下调凝血。
