Platelets modulate endothelial cell response to dynamic shear stress through PECAM-1.

INTRODUCTION: Both vascular endothelial cells and platelets are sensitive to blood flow induced shear stress. We have recently reported that platelet-endothelial cell interaction could greatly affect platelet activation under flow. In the present study, we aimed to investigate how platelet-endothelial cell interaction affected endothelial cell inflammatory responses under flow.

MATERIALS AND METHODS: Human coronary artery endothelial cells were exposed to normal or low pulsatile shear stress with or without the presence of platelets. Following shear exposure, endothelial cell ICAM-1 expression was measured using ELISA, Western blot and PCR; cell surface PECAM-1 expression/phosphorylation was measured using ELISA. Platelet adhesion to endothelial cells was quantified using immunofluorescence microscopy. To determine the role of PECAM-1 in platelet-endothelial cell interaction, endothelial cell PECAM-1 expression was suppressed using siRNA.

RESULTS: Pathological low shear stress induced a significant increase in endothelial cell ICAM-1 expression, at both protein and mRNA levels. Platelet adhesion to endothelial cells increased significantly under low shear stress, co-localizing with PECAM-1 at endothelial cell junctions. The presence of platelets inhibited low shear stress-induced ICAM-1 upregulation. When endothelial cell PECAM-1 expression was suppressed, platelet adhesion to endothelial cells under low shear stress decreased significantly; endothelial cell ICAM-1 expression was not affected by shear stress, with or without platelets.

CONCLUSIONS: These results suggested that PECAM-1 could mediate platelet adhesion to endothelial cells under shear stress. Platelets binding to endothelial cells interfered with endothelial cell mechanotransduction through PECAM-1, affecting endothelial cell inflammatory responses towards pathological shear flow.