The combination of Asp519Val/Glu665Val and Lys1813Ala mutations in FVIII markedly increases coagulation potential

Abstract

The A2 domain dissociation in activated factor (F)VIII (FVIIIa) results in reduced activity. Previous studies demonstrated that some FVIII mutants (D519V/E665V and K1813A) with delayed A2 dissociation enhanced coagulation potential. We speculated, therefore, that FVIII encompassing a combination of these mutations might further enhance coagulant activity. Aim is to assess the D519V/E665V/K1813A-FVIII mutation as a gain-of-function. The FVIII mutants, D519V/E665V/K1813A, D519V/E665V, and K1813A were expressed in a BHK cell system, and global coagulation potential of these mutants was compared with WT FVIII in vitro and in hemophilia A mice in vivo. Kinetic analyses indicated that the apparent Kd for FIXa on the tenase assembly with D519V/E665V and D519V/E665V/K1813A mutants were lower, and that the generated FXa for D519V/E665V/K1813A was significantly greater than WT. The WT-FVIII activity after thrombin activation increased by ~12-fold within 5 minutes, and returned to initial levels within 30 minutes. In contrast, The FVIII-related activity of D519V/E665V/K1813A increased further with time after thrombin activation, and showed an ~25-fold increase at 2 hours. The A2 dissociation rate of D519V/E665V/K1813A was ~50-fold slower than WT in a one-stage clotting assay. Thrombin generation assays demonstrated that D519V/E665V/K1813A (0.125 nM) exhibited coagulation potential comparable to WT (1 nM). In animal studies, rotational thromboelastometry and tail-clip assays showed that the coagulation potential of D519V/E665V/K1813A (0.25 µg/kg) was equal to WT (2 µg/kg). FVIII-D519V/E665V/K1813A mutant could provide an ~8-fold increase in hemostatic function of WT FVIII, due to increased FVIIIa stability and the association between FVIIIa and FIXa.