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

Type 2N von Willebrand disease: genotype drives different bleeding phenotypes and treatment needs

BACKGROUND

Type 2 Normandy von Willebrand disease (VWD2N) is usually perceived as a mild bleeding disorder that can be treated with desmopressin (DDAVP). However, VWD2N patients can be compound heterozygous or homozygous for different variants, with p.Arg854Gln (R854Q) being the most frequent causative one. There are limited data about the impact of 2N variants on VWD2N phenotype and DDAVP response.

OBJECTIVES

This study aims to describe the phenotype of VWD2N, including DDAVP response, according to genotype.

METHODS

VWD2N patients with a complete genotype/phenotype characterization by the French reference center for VWD, including MCMDM-1VWD bleeding score, were eligible to be included in the study. Results of the DDAVP trial were also collected.

RESULTS

A total of 123 VWD2N patients from the French registry were included in this study. Results were stratified according to the presence (R854QPos, n = 114) or absence (R854QNeg, n = 9) of at least 1 R854Q allele. Three R854QPos subgroups were further individualized: patients homozygous (R854QHmz, n = 55), compound heterozygous for R854Q and a null allele (R854Q/3, n = 48), or compound heterozygous for R854Q and another 2N variant (R854Q/2N, n = 11).

FVIII

C levels were significantly lower in R854QNeg and R854Q/3 patients compared with R854QHmz ones (P < .001 and P < .0001, respectively). R854QNeg patients were diagnosed earlier due to bleeding symptoms and had a higher bleeding score than R854QPos patients (P < .001). In DDAVP trial, FVIII:C survival was lower in VWD type 2N than in type 1 patients. R854QPos patients had a heterogeneous DDAVP response, which was best predicted by baseline FVIII:C level.

CONCLUSION

The heterogeneous genetic background of VWD2N drives different bleeding phenotypes and response patterns to DDAVP, underlining the clinical relevance of DDAVP trial to identify patients potentially eligible to alternative therapeutic options.

Hydrodynamic Delivery: Characteristics, Applications, and Technological Advances

The principle of hydrodynamic delivery was initially used to develop a method for the delivery of plasmids into mouse hepatocytes through tail vein injection and has been expanded for use in the delivery of various biologically active materials to cells in various organs in a variety of animal species through systemic or local injection, resulting in significant advances in new applications and technological development. The development of regional hydrodynamic delivery directly supports successful gene delivery in large animals, including humans. This review summarizes the fundamentals of hydrodynamic delivery and the progress that has been made in its application. Recent progress in this field offers tantalizing prospects for the development of a new generation of technologies for broader application of hydrodynamic delivery.

α1-Adrenergic Stimulation Increases Platelet Adhesion to Endothelial Cells Mediated by TRPC6

Stimulation of a1-adrenergic nervous system is increased during systemic inflammation and other pathological conditions with the consequent adrenergic receptors (ARs) activation. It has been reported that a1-stimulation contributes to coagulation since a1-AR blockers inhibit coagulation and its organic consequences. Also, coagulation induced by a1-AR stimulation can be greatly decreased using a1-AR blockers. In health, endothelial cells (ECs) perform anticoagulant actions at cellular and molecular level. However, during inflammation, ECs turn dysfunctional promoting a procoagulant state. Endothelium-dependent coagulation progresses at cellular and molecular levels, promoting endothelial acquisition of procoagulant properties to potentiate coagulation by means of prothrombotic and antifibrinolytic proteins expression increase in ECs releasing them to circulation, the thrombus formation is strengthened. Calcium signaling is a main feature of coagulation. Inhibition of ion channels involved in Ca²⁺ entry severely decreases coagulation. The transient receptor potential canonical 6 (TRPC6) is a non-selective Ca²⁺-permeable ion channel. TRPC6 activity is induced by diacylglycerol, suggesting that is regulated by a1-ARs. Furthermore, a1-ARs stimulation elicits a TRPC-like current in rat mesenteric artery smooth muscle and mesangial cells. However, whether TRPC6 could promote an ECs-mediated platelet adhesion induced by a1-adrenergic stimulation is currently not known. Therefore, the aim of this study was to examine if the TRPC6 calcium channel mediates platelet adhesion induced by a1-adrenergic stimulation. Our results suggest that platelet adhesion to ECs is enhanced by the a1-adrenergic stimulation evoked by phenylephrine mediated by TRPC6 activity. We conclude that TRPC6 is a molecular determinant in platelet adhesion to ECs with implications in systemic inflammatory diseases treatment.

A novel mouse model of type 2N VWD was developed by CRISPR/Cas9 gene editing and recapitulates human type 2N VWD

A novel type 2N VWD mouse model was established in which VWF is incapable of binding FVIII but is otherwise fully functional.

VWF^2N/2N mice exhibited a severe bleeding phenotype after tail tip amputation but not in lateral tail vein or ventral artery injury models.

Type 2N von Willebrand disease is caused by mutations in the factor VIII (FVIII) binding site of von Willebrand factor (VWF), resulting in dysfunctional VWF with defective binding capacity for FVIII. We developed a novel type 2N mouse model using CRISPR/Cas9 technology. In homozygous VWF^2N/2N mice, plasma VWF levels were normal (1167 ± 257 mU/mL), but the VWF was completely incapable of binding FVIII, resulting in 53 ± 23 mU/mL of plasma FVIII levels that were similar to those in VWF-deficient (VWF^−/−) mice. When wild-type human or mouse VWF was infused into VWF^2N/2N mice, endogenous plasma FVIII was restored, peaking at 4 to 6 hours post-infusion, demonstrating that FVIII expressed in VWF^2N mice is viable but short-lived unprotected in plasma due to dysfunctional 2N VWF. The whole blood clotting time and thrombin generation were impaired in VWF^2N/2N but not in VWF^−/− mice. Bleeding time and blood loss in VWF^2N/2N mice were similar to wild-type mice in the lateral tail vein or ventral artery injury model. However, VWF^2N/2N mice, but not VWF^−/− mice, lost a significant amount of blood during the primary bleeding phase after a tail tip amputation injury model, indicating that alternative pathways can at least partially restore hemostasis when VWF is absent. In summary, we have developed a novel mouse model by gene editing with both the pathophysiology and clinical phenotype found in severe type 2N patients. This unique model can be used to investigate the biological properties of VWF/FVIII association in hemostasis and beyond.

Molecular coevolution of coagulation factor VIII and von Willebrand factor

Ancestral sequence reconstruction provides a unique platform for investigating the molecular evolution of single gene products and recently has shown success in engineering advanced biological therapeutics. To date, the coevolution of proteins within complexes and protein-protein interactions is mostly investigated in silico via proteomics and/or within single-celled systems. Herein, ancestral sequence reconstruction is used to investigate the molecular evolution of 2 proteins linked not only by stabilizing association in circulation but also by their independent roles within the primary and secondary hemostatic systems of mammals. Using sequence analysis and biochemical characterization of recombinant ancestral von Willebrand factor (VWF) and coagulation factor VIII (FVIII), we investigated the evolution of the essential macromolecular FVIII/VWF complex. Our data support the hypothesis that these coagulation proteins coevolved throughout mammalian diversification, maintaining strong binding affinities while modulating independent and distinct hemostatic activities in diverse lineages.

Von Willebrand disease type 2N: An update

Quantitative or qualitative defects of von Willebrand factor (VWF) are responsible for the most common inherited bleeding disorder, von Willebrand disease (VWD). Type 2N VWD is an uncommon recessive disorder that results from gene mutations located in the region coding for the binding site of VWF for factor VIII (FVIII). This narrative review describes the pathophysiology, diagnostic procedures and treatment as well as the molecular biology of type 2N VWD. Although other VWF-dependent functions like binding to platelets and collagen are preserved, FVIII plasma levels are low due to the rapid clearance of this moiety in the absence or reduction of its binding to VWF. The diagnosis of type 2N should be considered in patients with low FVIII coagulant activity (FVIII:C) and disproportionally higher VWF antigen, especially when they present with an autosomal recessive pattern of inheritance. Because an accurate diagnosis is essential for genetic counseling and optimal treatment, type 2N must be distinguished from mild/moderate hemophilia A and its carrier state. This differential diagnosis can be obtained by using the laboratory assay of the FVIII binding capacity of VWF (VWF:FVIIIB) or analysis of the FVIII binding site on the VWF gene.

Molecular determinants of the factor VIII/von Willebrand factor complex revealed by BIVV001 cryo-electron microscopy

Interaction of factor VIII (FVIII) with von Willebrand factor (VWF) is mediated by the VWF D'D3 domains and thrombin-mediated release is essential for hemostasis after vascular injury. VWF-D'D3 mutations resulting in loss of FVIII binding are the underlying cause of von Willebrand disease (VWD) type 2N. Furthermore, the FVIII-VWF interaction has significant implications for the development of therapeutics for bleeding disorders, particularly hemophilia A, in which endogenous VWF clearance imposes a half-life ceiling on replacement FVIII therapy. To understand the structural basis of FVIII engagement by VWF, we solved the structure of BIVV001 by cryo-electron microscopy to 2.9 Å resolution. BIVV001 is a bioengineered clinical-stage FVIII molecule for the treatment of hemophilia A. In BIVV001, VWF-D'D3 is covalently linked to an Fc domain of a B domain-deleted recombinant FVIII (rFVIII) Fc fusion protein, resulting in a stabilized rFVIII/VWF-D'D3 complex. Our rFVIII/VWF structure resolves BIVV001 architecture and provides a detailed spatial understanding of previous biochemical and clinical observations related to FVIII-VWF engagement. Notably, the FVIII acidic a3 peptide region (FVIII-a3), established as a critical determinant of FVIII/VWF complex formation, inserts into a basic groove formed at the VWF-D'/rFVIII interface. Our structure shows direct interaction of sulfated Y1680 in FVIII-a3 and VWF-R816 that, when mutated, leads to severe hemophilia A or VWD type 2N, respectively. These results provide insight on this key coagulation complex, explain the structural basis of many hemophilia A and VWD type 2N mutations, and inform studies to further elucidate how VWF dissociates rapidly from FVIII upon activation.

Activated factor VIII-mimicking effect by emicizumab on thrombus formation in type 2N von Willebrand disease under high shear flow conditions

INTRODUCTION

Type 2N von Willebrand disease (2NVWD) is characterized by a mild to moderate reduction in plasma levels of factor (F)VIII associated with defective binding of von Willebrand factor (VWF) to FVIII and accelerated proteolysis and clearance of FVIII. The clinical phenotype in 2NVWD is often indistinguishable from mild/moderate hemophilia (H)A. Emicizumab is a bispecific antibody to FIX/FIXa and FX/FXa that mimics FVIIIa cofactor function, and emicizumab prophylaxis significantly reduces bleeding events in patients with severe HA.

AIM

We investigated the potential benefits of emicizumab in the hemostatic management of 2NVWD.

PATIENTS/METHODS

Perfusion chamber experiments were performed using whole blood from three 2NVWD patients with different clinical phenotypes (bleeding scores: 0, 6 and 20; mutations: p.R816W, p.R816W, and p.R365X/p.T791M, respectively). Furthermore, the impact of specific FVIII-VWF interactions on thrombus formation was investigated.

RESULTS

Defective thrombus formation that correlated with bleeding phenotype was evident in these 2NVWD patients. Emicizumab improved surface coverage and thrombus height in all cases. Multi-color immunostaining of thrombi further demonstrated that emicizumab enhanced thrombin generation and fibrin formation. The addition of FVIII alone to 2NVWD whole blood did not augment thrombus formation, while supplementation with FVIII/VWF complex enhanced platelet-fibrin interactions. Furthermore, an anti-FVIII monoclonal antibody known to interrupt the release of FVIIIa from VWF depressed these effects.

CONCLUSIONS

Emicizumab-induced enhancing effects of thrombus formation, independent on VWF, might be useful as an alternative therapy for 2NVWD patients. The extent of FVIII-VWF interaction should be optimal to deliver and release FVIII/FVIIIa on the activated platelet surface.

von Willebrand Factor Is a Critical Mediator of Deep Vein Thrombosis in a Mouse Model of Diet-Induced Obesity

OBJECTIVE

Obesity is characterized by chronic low-grade inflammation and consequentially a hypercoagulable state, associating with an increased incidence of venous thromboembolism. Increased VWF (von Willebrand factor) plasma concentration and procoagulant function are independent risk factors for venous thromboembolism and are elevated in obese patients. Here, we explore the pathobiological role of VWF in obesity-associated venous thrombosis using murine models. Approach and Results: We first showed that diet-induced obese mice have increased VWF plasma levels and FVIII (factor VIII) activity compared with littermate controls. Elevated VWF levels appeared to be because of both increased synthesis and impaired clearance. Diet-induced obesity-associated venous thrombosis was assessed using the inferior vena cava-stenosis model of deep vein thrombosis. Diet-induced obese mice developed larger venous thrombi that were rich in VWF, erythrocytes, and leukocytes. Administering a polyclonal anti-VWF antibody or an anti-VWF A1 domain nanobody was protective against obesity-mediated thrombogenicity. Delayed administration (3 hours post-inferior vena cava stenosis) similarly reduced thrombus weight in diet-induced obese mice.

CONCLUSIONS

This study demonstrates the critical role of VWF in the complex, thrombo-inflammatory state of obesity. It adds to the growing rationale for targeting VWF-specific interactions in thrombotic disease.

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

BACKGROUND

Acquired von Willebrand factor (VWF) deficiency was described in Philadelphia-negative myeloproliferative neoplasms, especially in essential thrombocythemia (ET). VWF phenotype in contemporary patients with polycythemia vera (PV) remains less explored.

OBJECTIVES

To characterize the VWF phenotype in PV and to compare VWF phenotype in PV with matched healthy subjects and ET patients.

PATIENTS/METHODS

We studied 48 PV patients, treated according to current recommendations (hematocrit ≤ 45%, on low-dose aspirin prophylaxis); 48 healthy and 41 subjects with ET, all sex, age, and blood group matched. We measured VWF antigen, activity, multimeric pattern, ADAMTS-13, and factor VIII (FVIII) antigen.

RESULTS

In patients with PV, VWF antigen and activity were significantly higher than in healthy subjects (antigen: 119[96-137] vs 93[79-107] IU/dL; activity: 114[95-128] vs 90[79-107] IU/dL, respectively, medians and interquartile, P < 0.01), with normal multimeric distribution. ADAMTS-13 levels were similar between patients with PV and healthy subjects. FVIII levels were higher in PV than in healthy subjects (141[119-169] versus 98[88-123] IU/dL, respectively, P < 0.01). By multivariable analysis, JAK2-p.V617F allelic burden, erythrocyte count, and male sex significantly predicted VWF antigen and activity levels. As compared to patients with ET, patients with PV showed similar VWF antigen levels but approximately 40% higher activity (79[49-104] vs 112[93-125] IU/dL, respectively, P < 0.01).

CONCLUSIONS

Patients with PV show increased VWF and FVIII levels, predicted by JAK2-p.V617F burden and erythrocyte count. At variance with ET, acquired VWF defect was not observed in PV. High VWF/FVIII levels may sustain the thrombotic diathesis of PV and may be investigated as biomarkers for risk stratification.

Genetic determinants of VWF clearance and FVIII binding modify FVIII pharmacokinetics in pediatric hemophilia A patients

Factor VIII (FVIII) pharmacokinetic (PK) properties show high interpatient variability in hemophilia A patients. Although previous studies have determined that age, body mass index, von Willebrand factor antigen (VWF:Ag) levels, and ABO blood group status can influence FVIII PK, they do not account for all observed variability. In this study, we aim to describe the genetic determinants that modify the FVIII PK profile in a population of 43 pediatric hemophilia A patients. We observed that VWF:Ag and VWF propeptide (VWFpp)/VWF:Ag, but not VWFpp, were associated with FVIII half-life. VWFpp/VWF:Ag negatively correlated with FVIII half-life in patients with non-O blood type, but no correlation was observed for type O patients, suggesting that von Willebrand factor (VWF) half-life, as modified by the ABO blood group, is a strong regulator of FVIII PK. The FVIII-binding activity of VWF positively correlated with FVIII half-life, and the rare or low-frequency nonsynonymous VWF variants p.(Arg826Lys) and p.(Arg852Glu) were identified in patients with reduced VWF:FVIIIB but not VWF:Ag. Common variants at the VWF, CLEC4M, and STAB2 loci, which have been previously associated with plasma levels of VWF and FVIII, were associated with the FVIII PK profile. Together, these studies characterize the mechanistic basis by which VWF clearance and ABO glycosylation modify FVIII PK in a pediatric population. Moreover, this study is the first to identify non-VWF and non-ABO variants that modify FVIII PK in pediatric hemophilia A patients.

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

Plasma levels of the multimeric glycoprotein von Willebrand factor (VWF) constitute a complex quantitative trait with a continuous distribution and wide range in the normal population (50-200%). Quantitative deficiencies of VWF (< 50%) are associated with an increased risk of bleeding, whereas high plasma levels of VWF (> 150%) influence the risk of arterial and venous thromboembolism. Although environmental factors can strongly influence plasma VWF levels, it is estimated that approximately 65% of this variability is heritable. Interestingly, although variability in VWF can account for ~ 5% of the genetic influence on plasma VWF levels, other genetic loci also strongly modify plasma VWF levels. The identification of the additional sources of VWF heritability has been the focus of recent observational trait-mapping studies, including genome-wide association studies or linkage analyses, as well as hypothesis-driven research studies. Quantitative trait loci influencing VWF glycosylation, secretion and clearance have been associated with plasma VWF antigen levels in normal individuals, and may contribute to quantitative VWF abnormalities in patients with a thrombotic tendency or type 1 von Willebrand disease (VWD). The identification of genetic modifiers of plasma VWF levels may allow for better molecular diagnosis of type 1 VWD, and enable the identification of individuals at increased risk for thrombosis. Validation of trait-mapping studies with in vitro and in vivo methodologies has led to novel insights into the life cycle of VWF and the pathogenesis of quantitative VWF abnormalities.

The common VWF single nucleotide variants c.2365A>G and c.2385T>C modify VWF biosynthesis and clearance

Plasma levels of von Willebrand factor (VWF) vary considerably in the general population and this variation has been linked to several genetic and environmental factors. Genetic factors include 2 common single nucleotide variants (SNVs) located in VWF, rs1063856 (c.2365A>G) and rs1063857 (c.2385T>C), although to date the mechanistic basis for their association with VWF level is unknown. Using genotypic/phenotypic information from a European healthy control population, in vitro analyses of recombinant VWF expressing both SNVs, and in vivo murine models, this study determined the precise nature of their association with VWF level and investigated the mechanism(s) involved. Possession of either SNV corresponded with a significant increase in plasma VWF in healthy controls (P < .0001). In vitro expression confirmed this observation and highlighted an independent effect for each SNV (P < .0001 and P < .01, respectively), despite close proximity and strong linkage disequilibrium between them both. The influence of c.2365A>G on VWF levels was also confirmed in vivo. This increase in VWF protein corresponded to an increase in VWF messenger RNA (mRNA) resulting, in part, from prolonged mRNA half-life. In addition, coinheritance of both SNVs was associated with a lower VWF propeptide-to-VWF antigen ratio in healthy controls (P < .05) and a longer VWF half-life in VWF knockout mice (P < .0001). Both SNVs therefore directly increase VWF plasma levels through a combined influence on VWF biosynthesis and clearance, and may have an impact on disease phenotype in both hemostatic and thrombotic disorders.