Correcting dominant-negative von Willebrand disease

In this issue of the Journal of Thrombosis and Haemostasis, Campioni et al report correction of dominant-negative von Willebrand disease (VWD) in vivo for the first time. In particular, they demonstrate that targeted inhibition of a mutant VWF allele can significantly improve bleeding phenotype in a Type 2A VWD murine model. Collectively, these data move us another step closer to developing personalized approaches for the treatment of VWD patients that extend beyond traditional von Willebrand factor (VWF) infusion therapy

O-glycan determinants regulate VWF trafficking to Weibel-Palade bodies.

Von Willebrand factor (VWF) undergoes complex post-translational modification within endothelial cells (EC) prior to secretion. This includes significant N- and O-linked glycosylation. Previous studies have demonstrated that changes in N-linked glycan structures significantly influence VWF biosynthesis. In contrast, although abnormalities in VWF O-linked glycans (OLG) have been associated with enhanced VWF clearance, their effect on VWF biosynthesis remains poorly explored. Herein, we report a novel role for OLG determinants in regulating VWF biosynthesis and trafficking within EC. We demonstrate that alterations in OLG (notably reduced terminal sialylation) lead to activation of the A1 domain of VWF within EC. In the presence of altered OLG, VWF multimerization is reduced and Weibel-Palade body (WPB) formation significantly impaired. Consistently, the amount of VWF secreted from WPB following EC activation was significantly reduced in the context of O-glycosylation inhibition. Finally, altered OLG on VWF not only reduced the amount of VWF secreted following EC activation, but also affected its hemostatic efficacy. Notably, VWF secreted following WPB exocytosis consisted predominantly of low molecular weight multimers and the length of tethered VWF string formation on the surface of activated ECs was significantly reduced. In conclusion, our data therefore support the hypothesis that alterations in O-glycosylation pathways directly impact VWF trafficking within human EC. These findings are interesting given that previous studies have reported altered OLG on plasma VWF (notably increased T antigen expression) in patients with von Willebrand disease

Persistent endotheliopathy in the pathogenesis of long COVID syndrome - reply to comment from von Meijenfeldt et al.

We are grateful for the comments and the interesting additional novel data presented by von Meijenfeldt et al. These findings provide further evidence that sustained endotheliopathy and coagulopathy are both common in patients following acute COVID-19. The longitudinal data presented provide additional insights into the duration of specific aspects of COVID-19–induced hemostatic dysfunction. Previous studies have reported elevated D-dimer levels in 25% of patients in the first few months after SARS-CoV-2 infection. Notwithstanding differences in patient cohorts and study design, von Meijenfeldt et al. show that these elevated D-dimer levels after acute COVID appear to normalize by 4 months. Given that convalescent COVID-19 patients commonly present with respiratory symptoms, this observation has important clinical implications with respect to the utility of D-dimer testing in pulmonary embolism testing algorithms.</p

Elevated von Willebrand factor levels in multiple myeloma: dysregulated mechanisms of both secretion and clearance

We read with great interest the recent publication by Ghansah et al whose work demonstrating increased thrombin generation and differential sensitivity to activated protein C (APC) in samples from patients with monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM) is an important addition to our growing understanding of the critical factors behind the high rate of thrombosis in MM.1 In particular, we noted that these authors also found raised von Willebrand Factor (VWF) antigen and Factor VIII (FVIII) levels in patients with newly diagnosed MM and, to a lesser extent in patients with MGUS. However, they concluded that the biological mechanisms underpinning raised VWF:Ag levels in MM and MGUS remain unresolved with the authors suggesting endothelial damage may be a key contributing factor. In fact, following on from the work of Ghansah et al, here, we show for the first time that not only is VWF synthesis increased in MM but that VWF circulatory clearance is also reduced in this disease. Furthermore, we also report the novel finding of raised VWF propeptide in precursor MM disease, incorporating both MGUS and smouldering MM (SM), which strengthens the evidence of a hypercoagulable profile in these premalignant conditions.</div

Elevated von Willebrand factor levels in multiple myeloma: dysregulated mechanisms of both secretion and clearance

We read with great interest the recent publication by Ghansah et al whose work demonstrating increased thrombin generation and differential sensitivity to activated protein C (APC) in samples from patients with monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM) is an important addition to our growing understanding of the critical factors behind the high rate of thrombosis in MM.1 In particular, we noted that these authors also found raised von Willebrand Factor (VWF) antigen and Factor VIII (FVIII) levels in patients with newly diagnosed MM and, to a lesser extent in patients with MGUS. However, they concluded that the biological mechanisms underpinning raised VWF:Ag levels in MM and MGUS remain unresolved with the authors suggesting endothelial damage may be a key contributing factor. In fact, following on from the work of Ghansah et al, here, we show for the first time that not only is VWF synthesis increased in MM but that VWF circulatory clearance is also reduced in this disease. Furthermore, we also report the novel finding of raised VWF propeptide in precursor MM disease, incorporating both MGUS and smouldering MM (SM), which strengthens the evidence of a hypercoagulable profile in these premalignant conditions.</div

Aptamer BT200 blocks interaction of K1405-1408 in the VWF-A1 domain with macrophage LRP1

Rondaptivan pegol (previously BT200) is a PEGylated RNA aptamer that binds to the A1 domain of VWF. Recent clinical trials demonstrated that BT200 significantly increased plasma VWF-FVIII levels by attenuating VWF clearance. The biological mechanism(s) through which BT200 attenuates in vivo clearance of VWF have not been defined. We hypothesized that BT200 interaction with the VWF-A1 domain may increase plasma VWF levels by attenuating macrophage-mediated clearance. We observed that full length- and VWF-A1A2A3 binding to macrophages, and VWF-A1 domain binding to LRP1 cluster II and cluster IV, were concentration-dependently inhibited by BT200. Additionally, full length VWF binding to LRP1 expressed on HEK293T (HEK-LRP1) cells was also inhibited by BT200. Importantly, BT200 interacts with the VWF-A1 domain in proximity to a conserved cluster of four lysine residues (K1405, K1406, K1407 and K1408). Alanine mutagenesis of this K1405-K1408 cluster (VWF-4A) significantly (p<0.001) attenuated binding of VWF to both LRP1 clusters II and IV. Furthermore, in vivo clearance of VWF-4A was significantly (p<0.001) reduced compared to wild type VWF. BT200 did not significantly inhibit binding of VWF-4A to LRP1 cluster IV or HEK-LRP1 cells. Finally, BT200 interaction with the VWF-A1 domain also inhibited binding to macrophage galactose lectin (MGL) and the SR-AI scavenger receptor. Collectively, our findings demonstrate that BT200 prolongs VWF half-life by attenuating macrophage-mediated clearance and specifically the interaction of K1405-1408 in the VWF-A1 domain with macrophage LRP1. These data support the concept that targeted inhibition of VWF clearance pathways represent a novel therapeutic approach for VWD and hemophilia A

Endothelial cell activation, Weibel-Palade body secretion, and enhanced angiogenesis in severe COVID-19

Background: Severe COVID-19 is associated with marked endothelial cell (EC) activation that plays a key role in immunothrombosis and pulmonary microvascular occlusion. However, the biological mechanisms through which SARS-CoV-2 causes EC activation and damage remain poorly defined. Objectives: We investigated EC activation in patients with acute COVID-19, and specifically focused on how proteins stored within Weibel-Palade bodies may impact key aspects of disease pathogenesis. Methods: Thirty-nine patients with confirmed COVID-19 were recruited. Weibel-Palade body biomarkers (von Willebrand factor [VWF], angiopoietin-2 [Angpt-2], and osteoprotegerin) and soluble thrombomodulin (sTM) levels were determined. In addition, EC activation and angiogenesis were assessed in the presence or absence of COVID-19 plasma incubation. Results: Markedly elevated plasma VWF antigen, Angpt-2, osteoprotegerin, and sTM levels were observed in patients with acute COVID-19. The increased levels of both sTM and Weibel-Palade body components (VWF, osteoprotegerin, and Angpt-2) correlated with COVID-19 severity. Incubation of COVID-19 plasma with ECs triggered enhanced VWF secretion and increased Angpt-2 expression, as well as significantly enhanced in vitro EC tube formation and angiogenesis. Conclusion: We propose that acute SARS-CoV-2 infection leads to a complex and multifactorial EC activation, progressive loss of thrombomodulin, and increased Angpt-2 expression, which collectively serve to promote a local proangiogenic state.</p

VWF–ADAMTS13 axis dysfunction in children with sickle cell disease treated with hydroxycarbamide vs blood transfusion

Previous studies have reported elevated von Willebrand factor (VWF) levels in patients with sickle cell disease (SCD) and demonstrated a key role for the VWF-ADAMTS13 axis in the pathobiology of SCD vaso-occlusion. Although blood transfusion is the gold standard for stroke prevention in SCD, the biological mechanisms underpinning its improved efficacy compared with hydroxycarbamide are not fully understood. We hypothesized that the improved efficacy of blood transfusion might relate to differences in VWF–ADAMTS13 axis dysfunction. In total, 180 children with a confirmed diagnosis of SCD (hemoglobin SS) on hydroxycarbamide (n = 96) or blood transfusion (n = 84) were included. Despite disease-modifying treatment, plasma VWF and VWF propeptide were elevated in a significant proportion of children with SCD (33% and 47%, respectively). Crucially, all VWF parameters were significantly higher in the hydroxycarbamide compared with the blood transfusion cohort (P </p

ADAMTS13 regulation of VWF multimer distribution in severe COVID-19

Background: Consistent with fulminant endothelial cell activation, elevated plasma von Willebrand factor (VWF) antigen levels have been reported in patients with COVID-19. The multimeric size and function of VWF are normally regulated through A Disintegrin And Metalloprotease with ThrombSpondin Motif type 1 motif, member 13 (ADAMTS-13)--mediated proteolysis.Objectives: This study investigated the hypothesis that ADAMTS-13 regulation of VWF multimer distribution may be impaired in severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection contributing to the observed microvascular thrombosis.Patients and methods: Patients with COVID-19 (n = 23) were recruited from the Beaumont Hospital Intensive Care Unit (ICU) in Dublin. Plasma VWF antigen, multimer distribution, ADAMTS-13 activity, and known inhibitors thereof were assessed.Results: We observed markedly increased VWF collagen-binding activity in patients with severe COVID-19 compared to controls (median 509.1 versus 94.3 IU/dl). Conversely, plasma ADAMTS-13 activity was significantly reduced (median 68.2 IU/dl). In keeping with an increase in VWF:ADAMTS-13 ratio, abnormalities in VWF multimer distribution were common in patients with COVID-19, with reductions in high molecular weight VWF multimers. Terminal sialylation regulates VWF susceptibility to proteolysis by ADAMTS-13 and other proteases. We observed that both N- and O-linked sialylation were altered in severe COVID-19. Furthermore, plasma levels of the ADAMTS-13 inhibitors interleukin-6, thrombospondin-1, and platelet factor 4 were significantly elevated.Conclusions: These findings support the hypothesis that SARS-CoV-2 is associated with profound quantitative and qualitative increases in plasma VWF levels, and a multifactorial down-regulation in ADAMTS-13 function. Further studies will be required to determine whether therapeutic interventions to correct ADAMTS-13-VWF multimer dysfunction may be useful in COVID-microvascular thrombosis and angiopathy.</p

Von Willebrand factor propeptide in severe coronavirus disease 2019 (COVID-19): evidence of acute and sustained endothelial cell activation

Endothelial cell (EC) activation plays a key role in the pathogenesis of pulmonary microvascular occlusion, which is a hallmark of severe coronavirus disease 2019 (COVID-19). Consistent with EC activation, increased plasma von Willebrand factor antigen (VWF:Ag) levels have been reported in COVID-19. Importantly however, studies in other microangiopathies have shown that plasma VWF propeptide (VWFpp) is a more sensitive and specific measure of acute EC activation. In the present study, we further investigated the nature of EC activation in severe COVID-19. Markedly increased plasma VWF:Ag [median (interquatile range, IQR) 608·8 (531–830)iu/dl] and pro-coagulant factor VIII (FVIII) levels [median (IQR) 261·9 (170–315) iu/dl] were seen in patients with severe severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection. Sequential testing showed that these elevated VWF–FVIII complex levels remained high for up to 3 weeks. Similarly, plasma VWFpp levels were also markedly elevated [median (IQR) 324·6 (267–524) iu/dl]. Interestingly however, the VWFpp/VWF:Ag ratio was reduced, demonstrating that decreased VWF clearance contributes to the elevated plasma VWF:Ag levels in severe COVID-19. Importantly, plasma VWFpp levels also correlated with clinical severity indices including the Sequential Organ Failure Assessment (SOFA) score, Sepsis-Induced Coagulopathy (SIC) score and the ratio of arterial oxygen partial pressure to fractional inspired oxygen (P/F ratio). Collectively, these findings support the hypothesis that sustained fulminant EC activation is occurring in severe COVID-19, and further suggest that VWFpp may have a role as a biomarker in this setting