It is well-established that in addition to its role in mediating platelet to platelet and platelet to matrix binding, VWF has a direct role in thrombin and fibrin generation by acting as a carrier molecule for the cofactor FVIII. Recent studies show that the interaction affects not only the biology of both FVIII and VWF, and the pathology of haemophilia and VWD, but also presents opportunities in the treatment of haemophilia. This review details the mechanisms and the molecular determinants of FVIII interaction with VWF, and the role of FVIII–VWF interaction in modulating FVIII interactions with other proteases, cell types and cellular receptors. The effect of

defective interaction of FVIII with VWF as a result of mutations in either protein is discussed. The introduction of cryoprecipitate as a useful treatment for GPCR Compound Library patients with constitutional bleeding disorders led to the identification of a novel protein complex containing both anti-haemophilia A activity, check details and platelet-binding properties. These discrete functions were subsequently shown to be mediated by two proteins circulating together in a single complex in normal plasma – namely anti-haemophilia factor VIII (FVIII) and FVIII-related antigen (FVIII-RAG) [1]. The FVIII component of this complex corrected bleeding in haemophilia A, whilst the FVIII-RAG (or von Willebrand factor; VWF) component could correct the bleeding phenotype

in patients with von Willebrand’s disease

(VWD). It is now well recognized that FVIII and VWF constitute independent gene products with distinct functions. Nevertheless, the haemostatic activities and life-cycles of these glycoproteins in the normal circulation remain inextricably linked. Consequently, understanding the biochemical basis underlying the interaction between FVIII and VWF in human plasma is of direct translational significance. Vascular injury leads to generation of a platelet plug at the site of injury, which is subsequently stabilized through activation of the coagulation cascade and formation of a cross-linked fibrin network. Platelet adhesion, activation, and aggregation, together with concurrent thrombin generation, are central events in this response. The FVIII–VWF complex plays critical through roles in regulating both platelet responses and the normal coagulation cascade. First, increased local shear stress at sites of vascular damage results in VWF adhesion to the sub-endothelial matrix. This bound VWF can then tether circulating platelets, to initiate formation of the platelet plug. Second, as VWF and FVIII circulate as a single complex in normal plasma, the ability of VWF to interact with exposed subendothelial tissues at sites of vascular injury, also serves to significantly increase the local concentration of FVIII [2]. Tissue-factor-initiated thrombin generation causes FVIII activation and release from VWF, as a result of limited proteolytic FVIII cleavage.