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Direct observation of von Willebrand factor elongation and fiber formation on collagen during acute whole blood exposure to pathological flow.

ABSTRACT: In severe stenosis, von Willebrand factor (vWF) experiences millisecond exposures to pathological wall shear rates (?(w)). We sought to evaluate the deposition of vWF onto collagen surfaces under flow in these environments.Distinct from viscometry experiments that last many seconds, we deployed microfluidic devices for single-pass perfusion of whole blood or platelet-free plasma over fibrillar type 1 collagen (<50 ms transit time) at pathological ?(w) or spatial wall shear rate gradients (grad ?(w)). Using fluorescent anti-vWF, long thick vWF fibers (>20 ?m) bound to collagen were visualized at constant ?(w)>30000 s(-1) during perfusion of platelet-free plasma, a process enhanced by EDTA. Rapid acceleration or deceleration of EDTA platelet-free plasma at grad ?(w)=±1.1×10(5) to ±4.3×10(7) s(-1)/cm did not promote vWF deposition. At 19400 s(-1), EDTA blood perfusion resulted in rolling vWF-platelet nets, although blood perfusion (normal Ca(2+)) generated large vWF/platelet deposits that repeatedly embolized and were blocked by anti-glycoprotein Ib or the ?(IIb)?(3) inhibitor GR144053 and did not require grad ?(w). Blood perfusion at venous shear rate (200 s(-1)) produced a stable platelet deposit that was a substrate for massive but unstable vWF-platelet aggregates when flow was increased to 7800 s(-1).Triggered by collagen and enhanced by platelet glycoprotein Ib and ?(IIb)?(3), vWF fiber formation occurred during acute exposures to pathological ?(w) and did not require gradients in wall shear rate.

SUBMITTER: Colace TV

PROVIDER: S-EPMC3595169 | biostudies-literature | 2013 Jan

REPOSITORIES: biostudies-literature

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Direct observation of von Willebrand factor elongation and fiber formation on collagen during acute whole blood exposure to pathological flow.

Colace Thomas V TV Diamond Scott L SL

Arteriosclerosis, thrombosis, and vascular biology 20121025 1

<h4>Objective</h4>In severe stenosis, von Willebrand factor (vWF) experiences millisecond exposures to pathological wall shear rates (γ(w)). We sought to evaluate the deposition of vWF onto collagen surfaces under flow in these environments.<h4>Methods and results</h4>Distinct from viscometry experiments that last many seconds, we deployed microfluidic devices for single-pass perfusion of whole blood or platelet-free plasma over fibrillar type 1 collagen (<50 ms transit time) at pathological γ(w ...[more]

PMID: 23104847

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Project description:Essentials von Willebrand factor (VWF) function is shear stress dependent. Platelet accumulation in a microfluidic assay correlates with VWF levels. The microfluidic assay discriminates type 1 von Willebrand disease from healthy controls. The microfluidic flow assay detects responses to therapeutic intervention (DDAVP).SUMMARYBackground von Willebrand disease (VWD) is a mucocutaneous bleeding disorder with a reported prevalence of 1 in 10 000. von Willebrand factor (VWF) function and platelet adhesion are regulated by hemodynamic forces that are not integrated into most current clinical assays. Objective We evaluated whether a custom microfluidic flow assay (MFA) can screen for deficiencies in VWF in patients presenting with mucocutaneous bleeding. Methods Whole blood from individuals with mucocutaneous bleeding was assayed in a custom MFA. Results Thirty-two patients with type 1 VWD (10/32) or reported mucocutaneous bleeding were enrolled. The platelet adhesion velocity (r = 0.5978 for 750 s-1 and 0.6895 for 1500 s-1 ) and the maximum platelet surface area coverage (r = 0.5719 for 750 s-1 and 0.6633 for 1500 s-1 ) in the MFA correlated with VWF levels. Furthermore, the platelet adhesion velocity at 750 s-1 (type 1 VWD, mean 0.0009761, 95% confidence interval [CI] 0.0003404-0.001612; control, mean 0.003587, 95% CI 0.002455-0.004719) and at 1500 s-1 (type 1 VWD, mean 0.0003585, 95% CI 0.00003914-0.0006778; control, mean 0.003132, 95% CI 0.001565-0.004699) differentiated type 1 VWD from controls. Maximum platelet surface area coverage at 750 s-1 (type 1 VWD, mean 0.1831, 95% CI 0.03816-0.3281; control, mean 0.6755, 95% CI 0.471-0.88) and at 1500 s-1 (type 1 VWD, mean 0.07873, 95% CI 0.01689-0.1406; control, mean 0.6432, 95% CI 0.3607-0.9257) also differentiated type 1 VWD from controls. We also observed an improvement in platelet accumulation after 1-desamino-8-d-arginine vasopressin (DDAVP) treatment at 1500 s-1 (pre-DDAVP, mean 0.4784, 95% CI 0.1777-0.7791; post-DDAVP, mean 0.8444, 95% CI 0.7162-0.9726). Conclusions These data suggest that this approach can be used as a screening tool for VWD.

Project description:Streptococcus pneumoniae is a major cause of community acquired pneumonia and septicaemia in humans. These diseases are frequently associated with thromboembolic cardiovascular complications. Pneumococci induce the exocytosis of endothelial Weibel-Palade Bodies and thereby actively stimulate the release of von Willebrand factor (VWF), which is an essential glycoprotein of the vascular hemostasis. Both, the pneumococcus induced pulmonary inflammation and the thromboembolytic complications are characterized by a dysbalanced hemostasis including a marked increase in VWF plasma concentrations. Here, we describe for the first time VWF as a novel interaction partner of capsulated and non-encapsulated pneumococci. Moreover, cell culture infection analyses with primary endothelial cells characterized VWF as bridging molecule that mediates bacterial adherence to endothelial cells in a heparin-sensitive manner. Due to the mechanoresponsive changes of the VWF protein conformation and multimerization status, which occur in the blood stream, we used a microfluidic pump system to generate shear flow-induced multimeric VWF strings on endothelial cell surfaces and analyzed attachment of RFP-expressing pneumococci in flow. By applying immunofluorescence visualization and additional electron microscopy, we detected a frequent and enduring bacterial attachment to the VWF strings. Bacterial attachment to the endothelium was confirmed in vivo using a zebrafish infection model, which is described in many reports and acknowledged as suitable model to study hemostasis mechanisms and protein interactions of coagulation factors. Notably, we visualized the recruitment of zebrafish-derived VWF to the surface of pneumococci circulating in the blood stream and detected a VWF-dependent formation of bacterial aggregates within the vasculature of infected zebrafish larvae. Furthermore, we identified the surface-exposed bacterial enolase as pneumococcal VWF binding protein, which interacts with the VWF domain A1 and determined the binding kinetics by surface plasmon resonance. Subsequent epitope mapping using an enolase peptide array indicates that the peptide 181YGAEIFHALKKILKS195 might serve as a possible core sequence of the VWF interaction site. In conclusion, we describe a VWF-mediated mechanism for pneumococcal anchoring within the bloodstream via surface-displayed enolase, which promotes intravascular bacterial aggregation.

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Direct observation of von Willebrand factor elongation and fiber formation on collagen during acute whole blood exposure to pathological flow.

Publications

Direct observation of von Willebrand factor elongation and fiber formation on collagen during acute whole blood exposure to pathological flow.

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