vWF Secretion Research Articles

Von Willebrand Factor in Health and Disease

—Von Willebrand factor (vWF), the key component of hemostasis, is synthesized in endothelial cells and megakaryocytes and released into the blood as high molecular weight multimeric glycoproteins weighing up to 20 million Daltons. Blood plasma metalloprotease ADAMTS13 cleaves ultra-large vWF multimers to smaller multimeric and oligomeric molecules. The vWF molecules attach to the sites of damage at the surface of arterioles and capillaries and unfold under conditions of shear stress. On the unfolded vWF molecule, the regions interacting with receptors on the platelet membrane are exposed. After binding to the vWF filaments, platelets are activated; platelets circulating in the vessels are additionally attached to them, leading to thrombus formation, blocking of microvessels, and cessation of bleeding. This review describes the history of the discovery of vWF, presents data on the mechanisms of vWF secretion and its structure, and characterizes the processes of vWF metabolism in the body under normal and pathological conditions.

Characterization of the Pathogenicity of Novel Sequence Variants Identified in Type 1 VWD Subjects in the Zimmerman Program for the Molecular and Clinical Biology Study

Von Willebrand Disease (VWD) is the most prevalent inherited bleeding disorder. Von Willebrand factor's (VWF) complex intracellular processing may result in variable VWF expression which requires exploring the underlying mechanism related to individual variants. The mechanisms underlying type 1 VWD are not fully understood, although reduced secretion and increased clearance have been implicated. We aimed to characterize novel sequence variants (SV) identified in the VWF gene in type 1 VWD patients recruited through the Zimmerman Program in order to (1) define the underlying mechanism, (2) explore if mutations in a particular domain are mechanistically similar, and (3) correlate expression study data to patient phenotype.Homozygous and heterozygous expression in mammalian cells was used to study the effect of SV on VWF secretion, intracellular retention, function, and multimerization. Novel SV identified throughout the entire VWF protein were introduced into VWF-mycHis plasmid vector: V86M, W199X, C524Y, M947V, R960P, G994D, C996W, R1204W, Q1353X, E1660X, R1763Q, C2199Y, Q2256H, T2282I, P2524L, A2569E, C2693F, C2701Y, and C2754Y. Variant VWF cDNA was transfected homozygously and cotransfected heterozygously 1:1 with wild type (WT) VWF pCIneo into Human Embryonic Kidney cells (HEK293T). Supernatants (sup) and cell lysates from 3 separate transfections were collected and analyzed by ELISA for VWF:Ag, VWF binding to platelet glycoprotein 1b (VWF:GPIbM), VWF binding to collagen type III (VWF:CB). Typically VWF:GP1bM/VWF:Ag > 0.7 indicates normal platelet binding and VWF:CB/VWF:Ag > 0.7 indicates normal multimer structure. VWF multimer structure is analyzed by SDS-agarose electrophoresis and western blotting with differential staining of the VWF secreted from variant and WT alleles.V86M, M947V, R1204W, R1763Q, Q2256H, T2282I, P2524L, and A2569E demonstrated secretion of VWF in sup comparable to that of WT-VWF both when transfected homozygously and hetereozygously, normal VWF:GPIbM/VWF:Ag, VWF:CB/VWF:Ag and normal multimer structure. Two of the stop codon SV W199X and E1660X were not expressed homozgyously (as expected) but demonstrated normal secretion, function, and multimerization when cotransfected 1:1 with WT. Homozygous expression of R960P and C2693F demonstrated reduced VWF secretion, VWF:GPIbM/VWF:Ag, VWF:CB/VWF:Ag and abnormal multimerization. Heterozygous transfection with WT improved VWF secretion, but not multimer defects,reflected by a reduced VWF:CB/VWF:Ag. Homozygous expression of C524Y, G994D, C996W, Q1353X, C2199Y, C2701Y, and C2754Y resulted in absent or greatly reduced secretion with increased intracellular retention. Heterozygous expression resulted in reduced VWF secretion (<50% of WT) for all 7 variants. Q1353X, C2199Y, C2701Y, and C2754Y had normal VWF:CB/VWF:Ag, VWF:GPIbM/VWF:Ag, and multimer structure, but consisted primarily of secreted WT-VWF. G994D had VWF:CB/VWF:Ag ˂ 0.7 and reduced high molecular weight (HMW) multimers. Co-expression of C524Y and C996W with WT-VWF demonstrated nearly absent VWF secretion, indicating a strong dominant negative effect. The very low VWF:Ag levels precluded assessment of VWF function and multimerization.The VWF:CB/VWF:Ag ratio < 0.7 proved a reliable indicator of multimer structure. No clear domain-specific correlation of VWF secretion or multimer abnormality was observed. Co-expression results of Q1353X, C2199Y, C2701Y, C2754Y, C524Y, G994D, and C996W are consistent with the patient's phenotype, except that patients with C2701Y, and C524Y had slight defect in multimers. In contrast, the in-vitro G994D showed low VWF:CB/VWF:Ag and abnormal multimers but were normal in the patient. C2693F showed consistently abnormal multimer structure in both in vitro and in the patient while R960P had abnormal multimer structure in vitro only.In sum, 52.6% of the 19 SV theoretically are not causative of the VWD phenotype observed in the patients. These subjects had normal VWF propeptide/VWF:Ag suggesting reduced plasma survival is unlikely to be the causative mechanism. The VWD mechanism in these subjects remains undefined. Variants R960P, C2693F, and G994D (15.7%) behaved like Type 2 VWD SV with loss of HMW multimers. We identified 31.6% of the 19 VWF SV as likely to cause the type 1 VWD phenotype with reduced secretion. DisclosuresNo relevant conflicts of interest to declare.

Protein Kinase C-Dependent Von Willebrand Factor Secretion Is a Dual-Phased Process That Originates from 2 Distinct Intracellular Compartments

Introductionvon Willebrand factor (VWF) and VWF-propeptide (VWFpp) are stored for secretion within specialized endothelial cell secretory organelles called Weibel-Palade bodies (WPBs). Protein kinase C (PKC) is a key signaling intermediary for a number of endothelial agonists that trigger the release of VWF, such as Vascular Endothelial Growth Factor (VEGF) and Shiga toxin Stx1B. While both agonists elevate intracellular free Ca2+ ([Ca2+]i) and simultaneously either signal through the novel, Ca2+-independent PKCδ (VEGF) or utilize the classical, Ca2+-dependent PKCα (Stx1B), there has been speculation whether an additional effector pathway may be operating during PKC-mediated VWF secretion. Phorbol 12-myristate 13-acetate (PMA), an activator of both classical and novel protein kinase C (PKC) isoforms, is also a potent VWF secretagogue, and it is generally assumed that PMA-evoked VWF release arises from exocytosis of WPBs.ResultsHere we present evidence that PMA elicits a dual-phased secretory response with an early (0-15 minutes) and a late (>15 minutes) stage. A large fraction of the early phase of PMA-evoked VWF and VWFpp secretion arises from a cycloheximide (CHX)-sensitive (i.e., nascent or non-storage) compartment, and can be blocked by pre-treatment with the broad spectrum PKC inhibitor bisindolylmaleimide I (BIS I). Histamine-induced VWFpp secretion during the early phase is insensitive to CHX or BIS I. VEGF induced a sharp rise of VWFpp secretion in the early phase and a much slower increase in the later phase. The early phase was also substantially reduced by CHX and BIS I, suggesting release from the same non-storage pool that is mobilized by PMA.High speed imaging of WPB exocytosis and [Ca2+]i in cells expressing VWFpp-EGFP targeted to WPBs revealed that the majority of PMA- and VEGF-induced VWFpp secretion during the early phase did not originate from WPBs. Histamine stimulation was associated with a sharp rise in [Ca2+]i, followed by rapid exocytosis within seconds of 41.4±4.0% (mean±sem, n=12 cells, 322 fusion events) of fluorescent WPBs. PMA did not elevate [Ca2+]i, led to a slow gradual increase in fusion events after a long and highly variable delay (357±63 seconds) and resulted in release of 12.4±3.3% (n=13 cells, 133 fusion events) of VWFpp-EGFP labeled WPBs. VEGF induced a complex [Ca2+]i increase, and after considerable delay (37.8 ±5.9 seconds) this was followed by WPB release of 18.2±3.5% (n=14 cells, 181 fusion events) of fluorescent WPBs. Because all three stimuli release quantitatively similar amounts of VWFpp during the early phase, the discrepancy in the fractions of WPBs undergoing degranulation suggests that PKC signaling mobilizes VWFpp from a compartment other than WPBs.Analysis of PMA-evoked VWFpp secretion showed that pre-treatment with the potent phospholipase D1/2 inhibitor 5-fluoro-2-indolyl des-chlorohalopemide (FIPI) significantly reduced the early, CHX-sensitive component of PMA-evoked VWFpp secretion, which suggests that this pool originates from the trans -Golgi network. Silencing of syntaxin-6, which we identify as a novel immature WPB-SNARE, and the recycling endosome regulator Rab11 revealed that PMA-evoked VWFpp secretion does not traverse through a non-classical post-Golgi compartment such as the recycling endosome on its way out.During the late phase PMA leads to almost complete degranulation of WPBs, but the mechanism has so far remained elusive. Time-lapse imaging of PMA-, histamine- and VEGF-stimulated WPB degranulation showed that this was insensitive to CHX treatment. In support of a role in sensitizing WPB release towards [Ca2+]i we found that a short pre-treatment with PMA enhanced the ability of ionomycin to induce Ca2+-driven VWFpp secretion at sub-maximal but not maximal doses. PMA-potentiated, ionomycin-induced VWFpp secretion was insensitive to CHX, underscoring that this originated from WPBs.ConclusionsOur data show that two pathways operate for rapid regulated secretion of VWF, one involving WPB exocytosis and the other, regulated by PKC activation, that accesses VWF and VWFpp in a late biosynthetic compartment, most likely the trans -Golgi network. Our findings also have significant implications for the mechanistic interpretation of data obtained from biochemical studies of WPB exocytosis induced by PMA, where secreted VWF has been assumed to arise solely from WPBs. DisclosuresNo relevant conflicts of interest to declare.

Effects of Shear Stress on Production of FVIII and vWF in a Cell-Based Therapeutic for Hemophilia A.

Microfluidic technology enables recapitulation of organ-level physiology to answer pertinent questions regarding biological systems that otherwise would remain unanswered. We have previously reported on the development of a novel product consisting of human placental cells (PLC) engineered to overexpress a therapeutic factor VIII (FVIII) transgene, mcoET3 (PLC-mcoET3), to treat Hemophilia A (HA). Here, microfluidic devices were manufactured to model the physiological shear stress in liver sinusoids, where infused PLC-mcoET3 are thought to lodge after administration, to help us predict the therapeutic outcome of this novel biological strategy. In addition to the therapeutic transgene, PLC-mcoET3 also constitutively produce endogenous FVIII and von Willebrand factor (vWF), which plays a critical role in FVIII function, immunogenicity, stability, and clearance. While vWF is known to respond to flow by changing conformation, whether and how shear stress affects the production and secretion of vWF and FVIII has not been explored. We demonstrated that exposure of PLC-mcoET3 to physiological levels of shear stress present within the liver sinusoids significantly reduced mRNA levels and secreted FVIII and vWF when compared to static conditions. In contrast, mRNA for the vector-encoded mcoET3 was unaltered by flow. To determine the mechanism responsible for the observed decrease in FVIII and vWF mRNA, PCR arrays were performed to evaluate expression of genes involved in shear mechanosensing pathways. We found that flow conditions led to a significant increase in KLF2, which induces miRNAs that negatively regulate expression of FVIII and vWF, providing a mechanistic explanation for the reduced expression of these proteins in PLC under conditions of flow. In conclusion, microfluidic technology allowed us to unmask novel pathways by which endogenous FVIII and vWF are affected by shear stress, while demonstrating that expression of the therapeutic mcoET3 gene will be maintained in the gene-modified PLCs upon transplantation, irrespective of whether they engraft within sites that expose them to conditions of shear stress.

The Use of Fluorescently Labeled ARC1779 Aptamer for Assessing the Effect of H2O2 on von Willebrand Factor Exocytosis

Here, we propose a new approach for quantitative estimation of von Willebrand factor (vWF) exposed on the surface of endothelial cells (ECs) using the ARC1779 aptamer that interacts with the vWF A1 domain. To visualize complex formation between vWF and the aptamer, the latter was conjugated with the Cy5 fluorescent label. Cultured human umbilical vein endothelial cells (HUVEC) were stained with the ARC1779-Cy5 conjugate and imaged with a fluorescence microscope. The images were analyzed with the CellProfiler software. vWF released from the Weibel–Palade bodies was observed as bright dot-like structures of round and irregular shape, the number of which increased several times after HUVEC exposure to histamine or thrombin. Staining with ARC1779-Cy5 also revealed long filamentous vWF structures on the surface of activated HUVEC. vWF secretion by ECs is activated by the second messengers cAMP and Ca2+. There is evidence that hydrogen peroxide also acts as a second messenger in ECs. In addition, exogenous H2O2 formed in leukocytes can enter ECs. The aim of our study was to determine the effect of H2O2 on the vWF exposure at the surface of HUVEC using the proposed method. It was shown that hydrogen peroxide at concentration 100 µM, which is lower than the cytotoxicity threshold of H2O2 for cultured HUVEC, increased several times the number of dot-like structures and total amount of vWF exposed on plasma membrane of HUVEC, which suggest that H2O2 acts as a mediator that activates exocytosis of Weibel–Palade bodies and vWF secretion in the vascular endothelium during inflammation and upon elevated generation of endogenous reactive oxygen species in ECs.

Ruxolitinib Reduces Endothelial Pro-Adhesive Interactions: Implications for JAK2V617+ MPN Thrombosis

Introduction The JAK2V617F+ mutation occurs in up to 95% of patients with polycythemia vera (PV) and increases the risk of thrombosis 6-fold. Recent studies demonstrate that JAK2V617F+ endothelial cells express pro-adhesive proteins, suggesting that the endothelium may contribute to increased thrombosis.1-3 The targeted JAK1/JAK2 inhibitor ruxolitinib is an approved second-line therapy for PV patients and is effective in alleviating constitutional symptoms, lowering hematocrit, and reducing cell number. However, there is limited data regarding efficacy of ruxolitinib in reducing thrombosis. Although recent work has demonstrated ruxolitinib reduces neutrophil extracellular trap formation,4 the vascular effects of ruxolitinib are unknown. Therefore, we hypothesize that ruxolitinib reduces endothelial cell pro-adhesive activation leading to decreased rolling and adhesion of JAK2V617F+ samples. Methods To mimic JAK2V617F activation, primary human umbilical vein endothelial cells (HUVEC, passage 1-5) were treated with TNF-α (10 ng/mL) +/- ruxolitinib (400 nM-4 µM, Selleckchem) and characterized 4h later. For confocal microscopy, cells were fixed with paraformaldehyde, permeabilized and stained for either VWF, VCAM-1, or P-selectin along with 2-(4-amidinophenyl)-1H-indole-carboxamide (DAPI, Thermo Fisher). Images were captured on Olympus FluoView FV1000 IX2 Inverted Confocal microscope. Secretion of VWF, VCAM-1 and P-selectin into conditioned media was assessed with ELISA (Molecular Innovations; BioLegend). Citrated normal and JAK2V617F+whole blood was obtained per IRB and labeled with calcein AM (ThermoFisher). To quantify leukocyte and platelet velocity and adhesion, an endothelialized poly-di-methyl-siloxane (PDMS) microchannel was prepared and treated with TNF-α (10 ng/mL) +/- ruxolitinib (400 nM-4 µM). Samples were perfused through the microfluidic at a shear stress of 0.35 dynes/cm2, and 10 s images were captured using a fluorescence microscope (Olympus). Cell velocity and adhesion were quantified using FIJI (NIH). Results Compared to TNF-α treated HUVEC alone, the combination of ruxolitinib + TNF-α reduced expression of VWF, VCAM-1 and P-selectin using both immunofluorescence and ELISA. In endothelialized microfluidic devices treated with TNF-α alone, both normal (n=3) and JAK2V617F+ (n=9) leukocyte and platelet velocity was significantly decreased and cell adhesion increased. This result was independent of hematocrit and platelet levels. In normal controls (n=2), TNF-α+ruxolitinib lead to a trend toward normal leukocyte and platelet velocity with decreased cell adhesion. Lastly, in a small subset of JAK2V617F+ patients (n=4), addition of ruxolitinib increased cell velocity. Conclusions In conclusion, in TNF-α-activated endothelial cells, treatment with ruxolitinib decreases pro-adhesive VWF, VCAM-1, and P-selectin expression. Using normal controls and JAK2V617F+ MPN blood samples, our TNF-α-activated endothelialized microfluidics model demonstrates significant reduction in leukocyte and platelet velocity and increased cell adhesion. In normal and JAK2V617F+ MPN whole blood, treatment of TNF-α-stimulated endothelium with ruxolitinib improves cell velocity. Further evaluation using JAK2V617F+ endothelial cells is planned. Collectively, these results suggest that ruxolitinib may reduce JAK2V617F+ thrombotic risk through reduction of pro-adhesive endothelial activation. Disclosures Vercellotti: CSL Behring: Research Funding.

Serum von Willebrand factor for early diagnosis of lung adenocarcinoma in patients with type 2 diabetes mellitus.

BACKGROUNDThe elevation of plasma von Willebrand factor (vWF) has been proposed to be a predictor of lung cancer. Type 2 diabetes mellitus (T2DM) causes endothelial activation, resulting in the secretion of vWF. However, the role of vWF in patients with T2DM complicated with lung cancer remains unclear.AIMTo investigate the clinical value of serum vWF as a tumor marker in patients with T2DM combined with lung adenocarcinoma in situ (AIS).METHODSThis study enrolled 43 patients with T2DM combined with lung AIS (T2DM + AIS group), 43 patients with T2DM alone (T2DM group), 43 patients with lung AIS alone (AIS group), and 43 healthy volunteers (control group). The serum levels of vWF, insulin-like growth factor 1, and insulin-like growth factor binding protein 3 were determined. Multiple linear stepwise regression was performed to determine the correlations among variables.RESULTSSerum concentration of vWF in the T2DM + AIS group was significantly higher than those in the T2DM, AIS, and control groups (P < 0.05). Serum vWF levels in the T2DM and AIS groups were significantly higher than that in the control group (P < 0.05). There was no significant difference in serum vWF level between the T2DM and AIS groups. In the T2DM + AIS group, serum vWF was independently associated and positively correlated with serum levels of insulin-like growth factor 1 and insulin-like growth factor binding protein 3 (P < 0.05).CONCLUSIONSerum vWF level may represent a novel biomarker for the early diagnosis of lung AIS.

Hydrogen sulfide reduces the activity of human endothelial cells.

The volatile endogenous mediator hydrogen sulfide (H2S) is known to impair thrombus formation by affecting the activity of human platelets. Beside platelets and coagulation factors the endothelium is crucial during thrombogenesis. This study evaluates the effect of the H2S donor GYY4137 (GYY) on human umbilical vein endothelial cells (HUVECs) in vitro. Flow cytometry of resting, stimulated or GYY-treated and subsequently stimulated HUVECs was performed to analyse the expression of E-selectin, ICAM-1 and VCAM-1. To study a potential reversibility of the GYY action, E-selectin expression was further assessed on HUVECs that were stimulated 24 h after GYY exposure. A WST-1 assay was performed to study toxic effects of the H2S donor. By using the biotin switch assay, protein S-sulfhydration of GYY-exposed HUVECs was assessed. Further on, the effects of GYY on HUVEC migration and von Willebrand factor (vWF) secretion were assessed. GYY treatment significantly reduced the expression of E-selectin and ICAM-1 but not of VCAM-1. When HUVECs were stimulated 24 h after GYY treatment, E-selectin expression was no longer affected. The WST-1 assay revealed no effects of GYY on endothelial cell viability. Furthermore, GYY impaired endothelial migration, reduced vWF secretion and increased protein S-sulfhydration. Summarizing, GYY dose dependently and reversibly reduces the activity of endothelial cells.

VWF Exocytosis and Biogenesis of Weibel Palade Bodies in Endothelial Cells Are Differentially Controlled By Interactions between Bloc-2 and the Exocyst Complex

Italiano: Platelet Biogenesis: Employment, Equity Ownership; Ionis Research Funding: Research Funding. Flaumenhaft:PlateletDiagnostics: Consultancy, Other: Founder; Relay Therapeutics: Consultancy.

Effect of Autophagy Regulated by Sirt1/FoxO1 Pathway on the Release of Factors Promoting Thrombosis from Vascular Endothelial Cells.

Factors promoting thrombosis such as von Willebrand factor (vWF) and P-selectin are essential for the development of atherosclerosis (AS) and arterial thrombosis. The processing, maturation and release of vWF are regulated by autophagy of vascular endothelial cells. The Sirt1/FoxO1 pathway is an important pathway to regulate autophagy of endothelial cells, therefore the Sirt1/FoxO1 pathway may be an important target for the prevention of thrombosis. We investigated the role of ox-LDL in the release of vWF and P-selectin and the expression of Sirt1 and FoxO1 by Western Blot, Flow Cytometry, ELISA, and tandem fluorescent mRFP-GFP-LC3. We found that vWF and P-selectin secretion increased and Sirt1/FoxO1 pathway was depressed in human umbilical vein endothelial cells (HUVEC) when treated with ox-LDL. Moreover, the expression of autophagy-related protein LC3-II/I and p62 increased. Then, we explored the relationship between autophagy regulated by the Sirt1/FoxO1 pathway and the secretion of vWF and P-selectin. We found that Sirt1/FoxO1, activated by the Sirt1 activators resveratrol (RSV) and SRT1720, decreased the secretion of vWF and P-selectin, which can be abolished by the autophagy inhibitor 3-MA. The expression of Rab7 increased when Sirt1/FoxO1 pathway was activated, and the accumulation of p62 was decreased. Autophagy flux was inhibited by ox-LDL and Sirt1/FoxO1 pathway might enhance autophagy flux through the promotion of the Rab7 expression. Taken together, our data suggest that by enhancing autophagy flux and decreasing the release of vWF and P-selectin, the Sirt1/FoxO1 pathway may be a promising target to prevent AS and arterial thrombosis.

Weibel-Palade Bodies Orchestrate Pericytes During Angiogenesis

Objective Weibel-Palade bodies (WPBs) are endothelial cell (EC)-specific organelles formed by vWF (von Willebrand factor) polymerization and that contain the proangiogenic factor Ang-2 (angiopoietin-2). WPB exocytosis has been shown to be implicated for vascular repair and inflammatory responses. Here, we investigate the role of WPBs during angiogenesis and vessel stabilization. Approach and Results WPB density in ECs decreased at the angiogenic front of retinal vascular network during development and neovascularization compared with stable vessels. In vitro, VEGF (vascular endothelial growth factor) induced a VEGFR-2 (vascular endothelial growth factor receptor-2)-dependent exocytosis of WPBs that contain Ang-2 and consequently the secretion of vWF and Ang-2. Blocking VEGF-dependant WPB exocytosis and Ang-2 secretion promoted pericyte migration toward ECs. Pericyte migration was inhibited by adding recombinant Ang-2 or by silencing Ang-1 (angiopoietin-1) or Tie2 (angiopoietin-1 receptor) in pericytes. Consistently, in vivo anti-VEGF treatment induced accumulation of WPBs in retinal vessels because of the inhibition of WPB exocytosis and promoted the increase of pericyte coverage of retinal vessels during angiogenesis. In tumor angiogenesis, depletion of WPBs in vWF knockout tumor-bearing mice promoted an increase of tumor angiogenesis and a decrease of pericyte coverage of tumor vessels. By another approach, normalized tumor vessels had higher WPB density. Conclusions We demonstrate that WPB exocytosis and Ang-2 secretion are regulated during angiogenesis to limit pericyte coverage of remodeling vessels by disrupting Ang-1/Tie2 autocrine signaling in pericytes.

Novel Endothelial Cell Targeted Peptide Nanoformulation for Inhibiting von Willebrand Factor Secretion to Reduce Thrombotic Complications in Sepsis

RationaleMicrovascular thrombosis and disseminated intravascular coagulation (DIC) are primary determinants of ischemia, organ failure and mortality/morbidity in sepsis. Interestingly, elevated plasma level of von Willebrand factor (vWF), the glue to which platelets adhere to form a clot, is associated with reduced survival and poor outcome in septic patients. Previously, we demonstrated that endothelial cell (EC) Gα12 is required for soluble N‐ethylmaleimide‐sensitive‐fusion factor attachment protein α (αSNAP)‐dependent vWF secretion from Weibel Palade bodies. Here, we report that sterically stabilized simple micelles (SSM) containing cell‐permeable myristoylated αSNAP binding domain (Myr‐SBD) peptide based on the unique N‐terminal Gα12 sequence that binds to αSNAP, inhibits vWF secretion.MethodsStructural complex of αSNAP/SBD was determined by blind‐ and data‐driven docking using AutoDock and HADDOCK, respectively. After incorporating Myr‐SBD into SSM (Myr‐SBD‐SSM) by film hydration method, micelle size and shape were confirmed by dynamic light scattering and transmission electron microscopy (TEM), respectively. Intracellular delivery of Myr‐SBD‐SSM was evaluated by fluorescence microscopy and fluorometry in cultured ECs. Cecal ligation and puncture (CLP) in C57BL/6 mice (14–16 wks, 25 g) was used to induce severe inflammation, microvascular thrombosis and DIC, and blood was collected 6 h and 24 h post CLP. The effect of Myr‐SBD‐SSM on plasma vWF, platelet count and inflammatory cytokines was assessed following addition of 0, 2 or 4 μmol Myr‐SBD/kg given i.v. at the time of surgery. Bleeding was assessed by tail‐snip assay. Glomerular fibrin deposition was scored by IHC analysis at 24 h post CLP.ResultsThe αSNAP/SBD structure showed the potential interaction between Arg of SBD peptide and Glu139 of αSNAP by H‐bond. Spherical shape of Myr‐SBD‐SSM (14.1 ± 2.7 nm in diameter) was confirmed by negative staining TEM. Addition of Myr‐SBD‐SSM to ECs resulted in the intracellular accumulation of Myr‐SBD which blocked thrombin‐induced vWF secretion. Intravenous delivery of Myr‐SBD‐SSM to mice at the time of CLP blunted the increase in plasma vWF and associated microvascular thrombosis in the kidney glomerulus. Importantly, Myr‐SBD‐SSM treatment resulted in increased platelet and WBC counts 6 h after surgery and improved survival compared to untreated or scrambled peptide treated mice with severe vascular inflammation suggesting Myr‐SBD‐SSM reduced clotting, platelet consumption and systemic inflammation in intraperitoneal sepsis. Moreover, Myr‐SBD‐SSM treatment did not increase tail‐snip bleeding time suggesting it did not prevent hemostasis.ConclusionOur studies demonstrate that Myr‐SBD‐SSM nanoformulation reduces vWF secretion and attenuates the thrombotic complications of severe inflammation.Support or Funding InformationThis work was supported by MPI R01 HL125356 (RDM, XD), Michael Reese Research and Education Foundation (RDM) and American Heart Association (MB, LR).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

VAS2870 Inhibits Histamine-Induced Calcium Signaling and vWF Secretion in Human Umbilical Vein Endothelial Cells.

In this study, we investigated the effects of NAD(P)H oxidase (NOX) inhibitor VAS2870 (3-benzyl-7-(2-benzoxazolyl)thio-1,2,3-triazolo[4,5-d]pyrimidine) on the histamine-induced elevation of free cytoplasmic calcium concentration ([Ca2+]i) and the secretion of von Willebrand factor (vWF) in human umbilical vein endothelial cells (HUVECs) and on relaxation of rat aorta in response to histamine. At 10 μM concentration, VAS2870 suppressed the [Ca2+]i rise induced by histamine. Inhibition was not competitive, with IC50 3.64 and 3.22 μM at 1 and 100 μM concentrations of histamine, respectively. There was no inhibition of [Ca2+]i elevation by VAS2870 in HUVECs in response to the agonist of type 1 protease-activated receptor SFLLRN. VAS2870 attenuated histamine-induced secretion of vWF and did not inhibit basal secretion. VAS2870 did not change the degree of histamine-induced relaxation of rat aortic rings constricted by norepinephrine. We suggest that NOX inhibitors might be used as a tool for preventing thrombosis induced by histamine release from mast cells without affecting vasorelaxation.

Dengue Virus NS1 Exposure Affects von Willebrand Factor Profile and Platelet Adhesion Properties of Cultured Vascular Endothelial Cells.

Hematological abnormalities and altered vascular permeability are frequently encountered in Dengue virus infected patients, but the mechanisms that alter platelet-endothelium interactions remain incompletely understood. The DENV NS1 protein has been implicated in adverse disease outcomes. In the present study the role of NS1 protein in affecting the expression of vWF and platelet adhesion properties of endothelial cells was studied in vitro. The results suggest that vWF is down regulated in cultured endothelial cells 6 and 24h after exposure with increase in vWF levels in culture supernatants at corresponding time points. Ultrastructural studies showed distinct evidence of endothelial cell activation morphology and degranulation of Weibel-Palade bodies in NS1 exposed cells that also showed increased platelet activation physiology. The findings suggest that changes in vWF production and secretion may be induced in endothelial cells exposed to DENV NS1 protein; and play a role in bleeding complications of severe DENV disease.

A Unique Case of Type 3 Von Willebrand Disease

Background: Von Willebrand disease (vWD) is the most common inherited bleeding disorder worldwide. Genetic mutations in the von Willebrand gene may result in either quantitative (Types 1 and 3 vWD) or qualitative defects (Type 2 vWD) of von Willebrand Factor (vWF). Type 3 is the rarest and most severe form of vWD, resulting in a virtual absence of vWF. Type 3 vWD follows autosomal recessive inheritance and is most often reported in patients who are homozygous for the same gene mutation. We report a patient with type 3 vWD who inherited two different mutations, one from each parent, resulting in compound heterozygosity.Case:Our patient, now a 2 year old female, initially presented with prolonged bleeding lasting approximately 5 hours at the injection site of her 2 month immunizations. Labs on initial presentation showed a normal WBC count, hemoglobin, hematocrit, and platelet count, with normal levels of Factor IX, XI, and XII activity. PTT was prolonged at 59 (reference range 23.3-35.7) with a normal INR. Von Willebrand panel showed markedly decreased Factor VIII (2%), vWF antigen (6%), and vWF activity (8%). VWF multimers were absent, consistent with a diagnosis of type 3 vWD. VWF gene sequence analysis showed two pathologic variants, one on each allele: c2345delC in exon 18 and a deletion within exon 6. Her parents, both 27 years old and with no history of abnormal bleeding, are non-consanguineous. Analysis of parents for vWD revealed that mother is heterozygous for the c2345delC variant and the patient's father is heterozygous for the deletion within exon 6 of the VWF gene. The patient's older sibling who is now 4 years old developed unusual petechiae and bruising after an altercation at school, his testing was positive for only the maternal mutation, resulting in a diagnosis of Type 1 vWD, and a younger brother was negative for both mutations. Our patient has subsequently suffered recurrent episodes of bruising, gingival bleeding, and poor tissue healing and currently requires replacement therapy (prophylaxis) with Humate-P three times each week and additionally as needed.Discussion:Type 3 vWD is quite rare, with a prevalence ranging from 0.1-5.3 per million. Our case is especially interesting due to the unique inheritance pattern resulting in our patient's type 3 vWD phenotype. Type 3 vWD cases are often described in patients homozygous for a mutation in the VWF gene, frequently as a result of consanguinity. Our patient inherited a unique variant from each parent, resulting in heterozygous expression of two defective VWF alleles (compound heterozygosity). Our patient's maternally inherited defect c2435delC in exon 18 is the variant found in the original vWD family described by Dr. Erik von Willebrand in 1926. Less is understood about the paternally inherited defect of a deletion in exon 6 of VWF.In our patient's family, because each parent is heterozygous for a mutation in the VWF gene, future children have a 75% chance of inheriting at least one mutation, and a 25% chance of inheriting both mutations, leading to Type 3 vWD. Type 3 vWD patients have impaired endogenous synthesis of functional vWF, thus therapies such as desmopressin, used in other types of vWD to stimulate secretion of endogenous vWF, are ineffective. Instead, first-line treatment in Type 3 is replacement therapy with Humate-P as needed during bleeding episodes and/or as prophylaxis. Humate P is VWF/FVIII concentrate obtained from pooled human plasma from many carefully screened plasma donors and contains the clotting proteins VWF and FVIII. Humate-P has a VWF:FVIII ratio of approximately 2.4:1. Complications of therapy include the rare development of anti-vWF alloantibodies, which most often occurs in patients with partial or complete VWF gene deletions. Our patient has received aminocaproic acid for minimal bleeding episodes and due to her severe intensity of disease and age of increased risk of injuries had received plasma derived vWF/FVIII concentrates for multiple episodes of moderate bleeding. She has not developed antibodies yet, but is at high risk. The rWVF (recombinant von Willebrand factor) offers new perspective in treatment of vWD more so with type 3 disease. It is a homogenous protein synthesized by a genetically engineered Chinese hamster ovary (CHO) cell line, retains its intact multimer pattern because it is never exposed to proteases(ADAMTS13) which can degrade it. The rVWF is currently in phase 3 clinical trials DisclosuresNo relevant conflicts of interest to declare.

Increased SERUM VON Willebrand Levels in Chronic Lymphocytic Leukemia (CLL) Patients Are Related to a Shorter Time to Treatment

CLL is a frequent and usually indolent disease that require only follow-up in about 2/3 of patients while the rest 1/3 of patients are symptomatic, have a worse outcome and need to be treated. The role of angiogenesis in CLL prognosis remains unclear. It has been shown that CLL plasma promotes von Willebrand factor (vWF) secretion, and expression in human umbilical vein endothelial cell cultures (HUVECs) [1]. Therefore, we investigated whether serum vWF levels in CLL patients at diagnosis could provide prognostic information.Patients and methods: 33 CLL patients were studied of whom 55%, 32% and 13% were Binet staged A, B and C respectively. 45% never required treatment while 55% required treatment either at the time of diagnosis or during their follow-up. The time to first treatment (TFT) was 34 months. Serum vWF was measured by ELISA (R&D Quantiquine, duo Set) in frozen sera drawn at patients' diagnosis and in 10 healthy individuals (HI). Measurements were performed in duplicate according to the manufacturer's instructions. Statistical analysis was performed by conventional methods, using the SPSS v.22 software. P values below 0,05 were considered statistically significant.Results: Serum vWF levels ranged from 178,5 to 14353,5 pg/ml (median 1028,5) in patients and from 374,6 to 1141,3 pg/ml (median 528,5) in HI, the difference being statistically significant (p< 0,05). Patients with Serum vWF levels above 528,5 pg/ml (median normal value) had a significantly shorter TFT than the others (p=0,01) as shown in figure. Otherwise, serum vWF levels correlated only with hypogammaglobulinemia (p=0,04).Conclusion: Serum vWF levels were increased in CLL patients. Importantly, we showed for the first time, to our knowledge, that higher vWF levels correlated with a shorter TFT, suggesting that increased vWF levels reflect active neoangiogenesis that in turn, contributes to a more aggressive disease behavior.[1] Shahidi M et al, Induction of endothelial cell proliferation and von Willebrand factor expression and secretion by leukemic plasma of patients with chronic lymphocytic leukemia before and after inhibition of NF-κB. Blood Coagul Fibrinolysis. 2016 Sep;27(6):711-6. DisclosuresNo relevant conflicts of interest to declare.

Von Willebrand factor enhances microvesicle-induced vascular leakage and coagulopathy in mice with traumatic brain injury

Abstractvon Willebrand factor (VWF) is an adhesive ligand, and its activity is proteolytically regulated by the metalloprotease ADAMTS-13 (a disintegrin and metalloprotease with thrombospondin type 1 repeat 13). An elevated level of plasma VWF has been widely considered a marker for endothelial cell activation in trauma and inflammation, but its causal role in these pathological conditions remains poorly defined. Using a fluid percussion injury mouse model, we demonstrated that VWF released during acute traumatic brain injury (TBI) was activated and became microvesicle-bound. The VWF-bound microvesicles promoted vascular leakage and systemic coagulation. Recombinant ADAMTS-13 given either before or after TBI reduced the VWF reactivity with minimal influence on VWF secretion. rADAMTS-13 protected the integrity of endothelial cell barriers and prevented TBI-induced coagulopathy by enhancing VWF cleavage without impairing basal hemostasis. Promoting microvesicle clearance by lactadherin had efficacy similar to that of rADAMTS-13. This study uncovers a novel synergistic action between VWF and cellular microvesicles in TBI-induced vascular leakage and coagulopathy and demonstrates protective effects of rADAMTS-13.

Tacrolimus prevents von Willebrand factor secretion by allostimulated human glomerular endothelium.

Little is known about the endothelial injury caused directly by circulating donor-specific antibodies (DSAs) during antibody-mediated rejection. von Willebrand factor (vWF) is a highly thrombotic glycoprotein stored in Weibel-Palade bodies in endothelial cells. It has been shown that its secretion is triggered by allostimulation. Calcineurin-like phosphatases regulate pathways involved in vWF secretion. Therefore, we hypothesized that tacrolimus would prevent alloantibody-induced glomerular lesions, in part via inhibition of vWF secretion from endothelial cells. Here, we used a human in vitro model of glomerular endothelium expressing HLA class I and II antigens and demonstrated that anti-HLA class II antibodies elicit a higher endothelial release of vWF than do anti-HLA class I antibodies in cell supernatants. We observed that tacrolimus treatment decreased vWF secretion after stimulation with both classes of anti-HLA antibodies and decreased platelet adhesion on allostimulated endothelial cells in a microfluidic chamber. In kidney recipients, tacrolimus trough levels were negatively associated with vWF blood levels. These results indicate that direct disruption of hemostasis via vWF secretion is a potential mechanism of antibody-mediated injury in patients with DSAs. Our results further suggest that the targeting of microcirculation hemostasis may be beneficial to prevent the development of microangiopathic lesions in antibody-mediated rejection.

Sulodexide Slows Down the Senescence of Aortic Endothelial Cells Exposed to Serum from Patients with Peripheral Artery Diseases

Background/Aims: Aging of the arterial endothelial cells results in the appearance of their inflammatory phenotype, which may predispose patients to the acceleration of arteriosclerosis. We studied the effect of serum from patients with peripheral artery disease (PAD) on the senescence of human aortic endothelial cells (HAEC) and how that process is modulated by sulodexide. Methods: HAEC replicative aging in vitro was studied in the presence of 10% PAD-serum (PAD Group) or10%PAD serum and Sulodexide 0.5 LRU/mL (PAD-SUL group). In control group cells were cultured in medium supplemented with 10% fetal bovine serum. All studied parameters were evaluated at the beginning and at the end of the study, in all experimental groups. Population doubling time (PDT) was studied from the cells growth rate after repeated passages, and senescence-associated beta- galactosidase activity (SA-β gal activity) was measured with the fluorescence flow cytometry. Expression of IL6, vWF, p21 and p53 genes was measured with the real-time polymerase chain reaction (Real-Time PCR). Concentrations of IL6 and vWF were measured with the standard ELISA kits. Results: PAD serum accelerated the senescence of HAEC as reflected by increased, compared to control, expression of the IL6 gene (+43%, p<0.05) vWF gene (+443%, p<0.01), p21 gene (+ 124%, p<0.01) and p53 gene (+ 85%, p<0.01). Secretion of IL6 and vWF was higher in that group: + 101%, p<0.01 and + 78%, p<0.01, respectively, as compared to control. Also, SA-β gal activity was higher in the PAD group (+33%, p<0.05) than in the control group. In the PAD group PDT was longer (+108%, p<0.01) as compared to control. Simultaneous use of Sulodexide with PAD serum significantly reduced all the above described senescent changes in HAEC. Conclusions: PAD serum accelerates the aging of HAEC which may result in the faster progression of arteriosclerosis. Sulodexide reduces PAD induced senescence of HAEC, which results in lower inflammatory and thrombogenic activity of these cells.

Pattern of von Willebrand factor in hypertensive patients in Lagos, Nigeria

Background and Objective: Hypertension alone accounts for 50% of death from stroke. Its ability to induce endothelial dysfunction leads to the release of von Willebrand factor (vWF), a prothrombotic glycoprotein. The increase secretion of vWF may account for increased risk of stroke in hypertensive disorders. This study aimed to determine the vWF:antigen (Ag) levels among hypertensives and assess its relationship with blood pressure and occurrence of stroke in hypertensives. Subjects and Methods: The study included 66 hypertensives, 33 with stroke (HS) and 33 without stroke (HWS), and 33 controls matched for age and sex. Structured questionnaires were used to obtain biodata and clinical information. Blood pressure was taken after 15 min rest. Four milliliters of blood was collected into 0.1 ml of 3.2% trisodium citrate for vWF:Ag assay and 4 ml into K-ethylenediaminetetraacetic acid anticoagulant bottles for blood grouping and erythrocyte sedimentation rate. Data were analyzed with SPSS version 21. Confidence interval was set at 95%. Results: Mean vWF:Ag levels were significantly higher in hypertensives compared with nonhypertensives (P = 0.005), but no statistically significant difference was observed between HS and HWS (P = 0.874). A positive correlation of vWF with systolic blood pressure was observed (r = 0.335, P = 0.001). Conclusion: Our study suggests that higher systolic blood pressure is associated with higher levels of endothelial activation and release of vWF.