Comparison of the inhibitory activities of human tissue factor pathway inhibitor (TFPI)a and TFPIß

Abstract

Background: Tissue factor pathway inhibitor (TFPI) is an alternatively spliced protein with two isoforms, TFPIa and TFPIß, which differ in their C-terminal structure and cellular localization. Detailed characterization of their inhibitory activity is needed to define potentially unique inhibitory roles in tissue factor (TF)-mediated thrombotic and inflammatory disease, and to understand how pharmaceuticals targeted to different structural regions of the TFPI isoforms alter hemostasis in hemophilia patients. Methods: The TF inhibitory activity of TFPIß localized to the surface of CHO cells was compared with that of soluble TFPIa by the use of in vitro and in vivo assays. Results: In TF-factor VIIa-mediated FXa generation assays, TFPIß was a slightly better inhibitor than TFPIa, which was approximately three-fold better than TFPI-160, a soluble, altered form of TFPI similar to TFPIß. In direct FXa inhibitory assays, TFPIß had an IC50 2.5-fold lower than that of TFPIa and 56-fold lower than that of TFPI-160. TFPIß inhibited TF-mediated CHO cell migration though Matrigel, whereas TFPIa and TFPI-160 were poor inhibitors, demonstrating that TFPIß effectively blocks TF-initiated signaling events during cellular migration through matrices that are not permeable to soluble forms of TFPI. Furthermore, TFPIß inhibited TF-dependent CHO cell infiltration into lung tissue following tail vein injection into SCID mice, and blocked the development of consumptive coagulopathy. Conclusions: TFPIß is a slightly better inhibitor of TF procoagulant activity than TFPIa. As a surface-associated protein, TFPIß is a much better inhibitor of TF-mediated cellular migration than soluble TFPIa, and may specifically act in the inhibition of TF-mediated signaling events on inflamed endothelium and/or monocytes. © 2013 International Society on Thrombosis and Haemostasis.