Probing single-molecular activation states of soluble von Willebrand factor multimer in sheared whole blood*

The multimeric glycoprotein von Willebrand factor (VWF) mechanosensitively activated by high shear flows is crucial for primary hemostasis and thrombosis. At the molecular level, VWF activation relies on unfolding the A1 subdomain under tensile forces exceeding 20 pN. Existing flow chamber studies reveal a critical shear threshold exists for conformational elongation and activation of soluble VWF, although most experiments depleted red blood cells (RBCs) from the solution for visualization convenience.

 

There exists a knowledge gap connecting how macroscale hemodynamic and hemorheological conditions translate to molecular-level VWF activation, particularly given blood as a concentrated RBC suspension. To address this gap, we have developed a multiscale computational model to probe the elongation, tension distribution, and activation states of soluble VWF in whole blood under shear.

 

Our findings demonstrate that RBCs at physiological concentrations (~40%) significantly enhance the tension-dependent activation of soluble VWF under shear. Furthermore, we discovered that VWF conformational elongation, previously considered an activation indicator, does not necessarily cause tension-dependent VWF activation even under pathologically high shear rates without RBCs. Finally, we map the spatiotemporal activation states of soluble VWF across various pathophysiological conditions. Our work quantitatively illustrates how freely suspended VWF activates in whole blood and highlights the often-overlooked role of RBCs in facilitating VWF activation.