Endothelial Cells Modulate Platelet Response to Dynamic Shear Stress

The goal of this study was to investigate how endothelial cells affect platelet response to physiologically relevant dynamic shear stress. In a cone and plate shearing device, washed platelets were exposed to constant (0.1, 0.3, 1, and 3 Pa) or dynamic (normal, low and temporally elevated) shear stress waveforms with or without the presence of endothelial cells. Platelet surface CD62P, CD42b and CD41a expression was measured using flow cytometry. Endothelial cell surface ICAM-1 and vWF expression was measured using ELISA, endothelial cell surface PECAM-1 expression was measured using fluorescence microscopy and endothelial cell derived microparticle generation was measured using flow cytometry. Elevated constant shear stress significantly increased platelet surface CD62P expression, and reduced platelet surface CD42b and CD41a expression. However, under dynamic flow conditions, low or elevated shear stress did not cause significant changes in platelets. But with the presence of endothelial cells, dynamic shear stress induced a significant increase in platelet surface CD62P expression and reduced platelet surface CD42b and CD41a expression. A significant increase in soluble vWF and the number of endothelial cell microparticles was observed, suggesting that soluble vWF and endothelial microparticle may be the mediators that induced platelet activation under pathological dynamic flow. These results suggest that pathological dynamic shear stress may not activate platelets directly. Through shear stress stimulated endothelial cells, platelets may become activated. As a protective mechanism, following cell activation, platelet adhesion protein expression is reduced to restrain platelet adhesion, aggregation and thrombus formation.