Abnormal von Willebrand factor secretion, factor VIII stabilization and thrombus dynamics in type 2N von Willebrand disease mice

Abstract

Background von Willebrand factor (VWF) and factor VIII (FVIII) circulate as a non-covalent complex, with VWF serving as the carrier for FVIII. VWF indirectly influences secondary hemostasis by stabilizing FVIII and transporting it to the site of primary hemostasis. Type 2N von Willebrand disease involves impaired binding of VWF to FVIII, resulting in decreased plasma levels of FVIII. Objectives In these studies, we characterize the impact of three type 2N VWD variants (R763A, R854Q, R816W) on VWF secretion, FVIII stabilization and thrombus formation in a murine model. Methods Type 2N VWD mice were generated by hydrodynamic injections of mutant murine VWF cDNAs and the influence of these variants on VWF secretion and FVIII binding was evaluated. In vivo hemostasis and the dynamics of thrombus formation and embolization were assessed using a murine tail vein transection hemostasis model and an intravital thrombosis model in the cremaster arterioles. Results Type 2N VWD variants were associated with decreased VWF secretion using cell and animal-based models. FVIII-binding to type 2N variants was impaired in vitro and was variably stabilized in vivo by expressed or infused 2N variant VWF protein. Both transgenic type 2N VWD and FVIII knockout (KO) mice demonstrated impaired thrombus formation associated with decreased thrombus stability. Conclusions The type 2N VWD phenotype can be recapitulated in a murine model and is associated with both quantitative and qualitative VWF deficiencies and impaired thrombus formation. Patients with type 2N VWD may have normal primary hemostasis formation but decreased thrombus stability related to ineffective secondary hemostasis.

Genetic regulation of plasma von Willebrand factor levels in health and disease

“…Although little is currently known regarding the mechanistic basis by which these variants regulate VWF half‐life, they may alter either the glycosylation or conformation of the VWF molecule, and probably enhance the affinity of VWF for one or more of its clearance receptors . Type 2 VWD, which is predominantly characterized by platelet, collagen or FVIII‐binding qualitative defects, may also be complicated by impaired VWF secretion or accelerated clearance of the VWF–platelet complex .…”

Increased von Willebrand factor levels in polycythemia vera and phenotypic differences with essential thrombocythemia

“…40 In fact, FVIII accelerates the formation of activated factor X (FXa) and thrombin. 43 Thus, our study suggests that the thrombotic diathesis of PV may be supported by high VWF and FVIII levels in addition to other known pathogenetic factors such as high hematocrit, 44 elevated blood viscosity, 45 platelet activation, 8,17 and leukocytosis. 46 Notably, patients with previous thrombosis had the degradation of the circulating VWF/FVIII complex.…”

“…High FVIII levels per se are associated with increased venous thromboembolism and may then contribute to venous thromboses in PV . In fact, FVIII accelerates the formation of activated factor X (FXa) and thrombin . Thus, our study suggests that the thrombotic diathesis of PV may be supported by high VWF and FVIII levels in addition to other known pathogenetic factors such as high hematocrit, elevated blood viscosity, platelet activation, and leukocytosis .…”

Von Willebrand disease type 2N: An update

“…Some type 2N variants (e.g., C858F and D879N) are associated with low VWF levels that tend to exacerbate the bleeding phenotype 51,66 . A defective secretion of VWF in association with impaired thrombus formation was also observed for the R854Q and R763A variants in mice with type 2N VWD, suggesting that primary hemostasis is normal in type 2N VWD but that secondary hemostasis is defective with decreased thrombus stability 67 . In practical terms, to ensure that patients have a post‐DDAVP response of a magnitude sufficient to increase FVIII at hemostatic levels and thus to avoid the use of plasma products containing both FVIII and VWF, an explorative trial is recommended, with blood samples taken at baseline, 1, and 4 h following administration in order to evaluate not only the peak but also and most importantly the clearance pattern of FVIII:C. Recently the definition of desmopressin response was proposed by the ASH ISTH NHF WFH 2021 guidelines and It was defined an increase of at least 2 times the baseline VWF activity level and the levels of both VWF and factor VIII (FVIII):C to > 0.50 IU/mL for at least 4 hours.…”