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

Summary 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 αIIbβ3 antagonist GR144053. Conclusions We report VWF fiber‐contact pathway crosstalk and mechanisms of thrombolytic resistance in hemodynamic settings of myocardial infarction.