Tfpi-/- embryos have severe vascular pathology with associated cellular death in the central nervous system but not in other organs.
Removing FV from the Tfpi-/- embryos completely ameliorates the central nervous system pathology.
Tissue factor pathway inhibitor (TFPI) inhibits proteases in the blood coagulation cascade that lead to the production of thrombin, including prothrombinase (FXa/FVa), the catalytic complex that directly generates thrombin. Thus, TFPI and FV are directly linked in regulating the procoagulant response. Studies using knock-out mice indicate that TFPI and FV are necessary for embryogenesis, but their contributions to vascular development are unclear. We performed extensive histological analyses of Tfpi-/- and Tfpi-/-F5-/- mouse embryos to investigate the importance of the interplay between TFPI and FV in regulating hemostasis and vascular development during embryogenesis. We observed normal tissue development throughout Tfpi-/- embryos except in the central nervous system. The central nervous system displayed stunted brain growth, delayed development of the meninges, and severe vascular pathology characterized by the formation of glomeruloid bodies surrounding areas of cellular death, fibrin deposition, and hemorrhage. Removing FV from the Tfpi-/- embryos completely ameliorated their brain pathology, suggesting that TFPI dampens FV-dependent procoagulant activity in a manner that modulates cerebrovascular development. Thus, we have identified a previously unrecognized role for TFPI activity within the central nervous system. This TFPI activity likely diminishes an effect of excess thrombin activity on signaling pathways that control cerebral vascular development.