Pathological von Willebrand factor fibers resist tissue plasminogen activator and ADAMTS13 while promoting the contact pathway and shear-induced platelet activation.

BACKGROUND: Under severe stenotic conditions, von Willebrand factor (VWF) multimerizes into large insoluble fibers at pathological shear rates.

OBJECTIVE: Evaluate the mechanics and biology of VWF fibers without the confounding effects of endothelium or collagen.

METHODS: Within a micropost-impingement microfluidic device, > 100-μm long VWF fibers multimerized on the post within 10 min using EDTA-treated platelet-free plasma (PFP) perfused at wall shear rates > 5000 s(-1) .

RESULTS: von Willebrand factor fiber thickness increased to > 10 μm as a result of increasing the shear rate to 10,000 s(-1) . In a stress-strain test, fibrous VWF had an elastic modulus of ~50 MPa. The insoluble VWF fibers were non-amyloid because they rapidly dissolved in trypsin, plasmin or 2% SDS, but were resistant to 50 nm ADAMTS13 or 100 nm tissue plasminogen activator in plasma. Following fiber formation, perfusion of low corn trypsin inhibitor (CTI)-treated (4 μg mL(-1) ), recalcified citrated plasma at 1500 s(-1) caused fibrin formation on the VWF fibers, a result not observed with purified type 1 collagen or a naked micropost. During VWF fiber formation, contact pathway factors accumulated on VWF because the use of EDTA/D-Phe-Pro-Arg chloromethylketone (PPACK)/apixaban/high CTI-treated PFP during VWF fiber formation prevented the subsequent fibrin production from low-CTI, recalcified citrated PFP. VWF fibers displayed FXIIa-immunostaining. When PPACK-inhibited whole blood was perfused over VWF fibers, platelets rolled and arrested on the surface of VWF, but only displayed P-selectin if prevailing shear rates were pathological. Platelet arrest on VWF fibers was blocked with αIIb β3 antagonist GR144053.

CONCLUSIONS: We report VWF fiber-contact pathway crosstalk and mechanisms of thrombolytic resistance in hemodynamic settings of myocardial infarction.