Investigation of the role of von Willebrand factor in shear-induced platelet activation and functional alteration under high non-physiological shear stress

Backgroundvon Willebrand factor (vWF) plays a crucial role in physiological hemostasis through platelet and subendothelial collagen adhesion. However, its role in shear-induced platelet activation and functional alteration under non-physiological conditions common to blood-contacting medical devices (BCMDs) is not well investigated.MethodsFresh healthy human blood was treated with an anti-vWF antibody to block vWF-GPIb alpha interaction. Untreated blood was used as a control. They were exposed to three levels of non-physiological shear stress (NPSS) (75, 125, and 175 Pa) through a shearing device with an exposure time of 0.5 s to mimic typical shear conditions in BCMDs. Flow cytometric assays were used to measure the expression levels of PAC-1 and P-Selectin and platelet aggregates for platelet activation and the expression levels of GPIb alpha, GPIIb/IIIa, and GPVI for receptor shedding. Collagen/ristocetin-induced platelet aggregation capacity was characterized by aggregometry.ResultsThe levels of platelet activation and aggregates increased with increasing NPSS in the untreated blood. More receptors were lost with increasing NPSS, resulting in a decreased capacity of collagen/ristocetin-induced platelet aggregation. In contrast, the increase in platelet activation and aggregates after exposure to NPSS, even at the highest level of NPSS, was significantly lower in treated blood. Nevertheless, there was no notable difference in receptor shedding, especially for GPIIb/IIIa and GPVI, between the two blood groups at the same level of NPSS. The block of vWF exacerbated the decreased capacity of collagen/ristocetin-induced platelet aggregation.ConclusionsHigh NPSS activates platelets mainly by enhancing the vWF-GPIb alpha interaction. Platelet activation and receptor shedding induced by high NPSS likely occur through different pathways. Platelet activation and functional alteration under high NPSS were investigated with blocking of vWF-GPIb alpha interaction.High NPSS activates platelets mainly by enhancing the vWF-GPIb alpha interaction.Shear-induced platelet activation and receptor shedding have distinct pathways.image