Platelet surface P-selectin molecules increased after exposing platelet to a high shear flow

Background. P-selectin is known to play a crucial role in leucocyte recruitment at sites of vascular injury. Although platelet surface expression of P-selectin molecules are well known to occur after platelet stimulation by chemical agonists such as α-thrombin, it is still uncertain whether P-selectin expression occurs in the process of the more physiological platelet activation pathway mediated by interaction between von Willebrand factor (vWF) and platelet receptor proteins, including glycoprotein (GP) Ibα and GP IIb/IIIa, occurring under high shear rates generated by blood flow. Methods. We have developed a method to detect P-selectin molecules expressed on platelet surface with flow-cytometer and monoclonal antibody, which can bind exclusively to P-selectin (WGA1), directly conjugated with fluorescein isothiocynate. This method allowed us to measure platelet surface P-selectin molecules semiquantitatively. Results. We demonstrated that a significant increase in platelet surface P-selectin molecules occur after exposing platelets to a relatively high shear rate of 10,800 s^-1. We have also demonstrated that shear-induced surface expression of P-selectin as well as microparticle release from platelets depended at least on the interaction between von Willebrand factor and glycoprotein Ibα, a platelet surface receptor for the former. Conclusions. Shear-induced von Willebrand-mediated surface expression of P-selectin may play a role in leucocyte recruitment in platelet thrombi at vascular injury sites.