The contribution of TFPIα to the hemostatic response to injury in mice

Background: Tissue factor pathway inhibitor (TFPI) is an essential regulator of coagulation, limiting thrombin generation and preventing thrombosis. In humans and mice, TFPIα is the sole isoform present in platelets.

Objective: Here, we asked whether TFPIα, because of its release from platelets at sites of injury, has a unique role in limiting the hemostatic response.

Methods: TFPIα-mutant (Tfpi^Δα/Δα ) mice were generated by introducing a stop codon in the C-terminus. Platelet accumulation, platelet activation, and fibrin accumulation were measured following penetrating injuries in the jugular vein and cremaster muscle arterioles, and imaged by fluorescence and scanning electron microscopy. Time to bleeding cessation was recorded in the jugular vein studies.

Results: Tfpi^Δα/Δα mice were viable and fertile. Plasma TFPI levels were normal in the Tfpi^Δα/Δα mice, no TFPI protein or activity was present in their platelets and thrombin-antithrombin complex levels were indistinguishable from Tfpi^+/+ littermates. There was a small, but statistically significant reduction in the time to bleeding cessation following jugular vein puncture injury in the Tfpi^Δα/Δα mice, but no measurable changes in platelet or fibrin accumulation or in hemostatic plug architecture following injury of the micro- or macrovasculature.

Conclusion: Loss of TFPIα expression does not produce a global prothrombotic state in mice. Platelet TFPIα is expected to be released or displayed in a focal manner at the site of injury, potentially accumulating to high concentrations in the narrow gaps between platelets. If so, the data from the vascular injury models studied here indicate this is not essential for a normal hemostatic response in mice.