Abstract Number: LPB0084
Meeting: ISTH 2021 Congress
Background: Factor VIII (FVIII) is an essential actor in the intrinsic coagulation pathway, where it acts as a cofactor for activated FIX to form the tenase complex that anchors at the surface of activated platelets. Binding partners for FVIII on platelets include phosphatidylserine and platelet-bound fibrin. GPVI is a platelet-specific glycoprotein, the cross-linking of which by collagen, activates platelets. Upon screening for FVIII interactions with platelet-expressed glycoproteins, we observed FVIII binding to GPVI.
Aims: To characterize the FVIII/GPVI interaction at the molecular level and decipher its potential biological relevance on platelet functions.
Methods: Binding of human full-length and B domain-deleted (BDD) FVIII (Advate, Novoeight, Factane, FVIIIHSQ) was investigated on immobilized human recombinant GPVI (R&D) or home-made Fc-fused GPVI. FVIII was pre-incubated alone or with varying amounts of von Willebrand factor (VWF, Wilfactin), or human monovalent monoclonal anti-A2 (BOIIB2), anti-C1 (KM33) or anti-C2 (BO2C11) IgG. Binding of the FVIII C1R2090A/K2092A/F2093A and C2R2215A/R2220A variants was also investigated. Bound FVIII was revealed using SAF8C, a FVIII-specific polyclonal sheep IgG.
Results: Full-length and BDD FVIII, but not plasma-derived FVIII, bound in a dose-dependent manner to recombinant GPVI and GPVI-Fc. VWF inhibited FVIII binding to GPVI. Interestingly, C1 and C2-specific, but not A2-specific, monovalent IgG also inhibited the interaction. Accordingly, FVIII variants mutated in the target epitopes of BO2C11 or KM33 lost binding capacity to GPVI.
Conclusions: Phosphatidylserine and αIIbß3 integrin-bound fibrin have been identified as binding sites on platelets for the light chain of FVIII. The present findings identify GPVI as a novel binding partner for FVIII light chain on platelets; the interaction is however prevented in the presence of VWF. Future work will decipher the domains of GPVI implicated in FVIII binding and the potential biological significance of the interaction.
To cite this abstract in AMA style:Sekar R, Proulle V, Loyau S, Boulaftali Y, Mimoun A, Jandrot-Perrus M, Lacroix-Desmazes S. GPVI, a New Binding Partner for pro-coagulant Factor VIII on Platelets [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 2). https://abstracts.isth.org/abstract/gpvi-a-new-binding-partner-for-pro-coagulant-factor-viii-on-platelets/. Accessed December 7, 2021.
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