Summary
Recent in vitro studies have shown that the zymogen and activated form of factor (F)VII bind to endothelial
cell protein C receptor (EPCR). At present, there is no evidence that FVIIa binds
to EPCR on vascular endothelium in vivo in the presence of circulating protein C, a primary ligand for EPCR. The present
study was carried out to investigate the interaction of murine and human ligands with
murine EPCR both in vivo and in vitro. Measurement of endogenous plasma levels of FVII in wild-type, EPCR-deficient and
EPCR-over expressing mice showed slightly lower levels of FVII in EPCR-over expressing
mice. However, infusion of high concentrations of competing ligands, either human
APCi or FVIIai, to EPCR-over expressing mice failed to increase plasma levels of mouse
FVII whereas they increased the plasma levels of protein C by two- to three-fold.
Examining the association of exogenously administered mouse FVIIa or human FVIIa by
immunohistochemistry revealed that human, but not murine FVIIa, binds to the murine
endothelium in an EPCR-dependent manner. In vitro binding studies performed using surface plasmon resonance and endothelial cells revealed
that murine FVIIa binds murine EPCR negligibly. Human FVIIa binding to EPCR, particularly
to mouse EPCR, is markedly enhanced by availability of Mg2+ ions. In summary, our data show that murine FVIIa binds poorly to murine EPCR, whereas
human FVIIa binds efficiently to both murine and human EPCR. Our data suggest that
one should consider the use of human FVIIa in mouse models to investigate the significance
of FVIIa and EPCR interaction.
Keywords
Endothelial cell protein C receptor - factor VIIa - protein C