Background—Blood flow characteristics influence endothelial cell apoptosis. However, little is known about the occurrence of endothelial cell apoptosis in human atherosclerosis and its relation to blood flow.

Methods and Results—A total of 42 human carotid atherosclerotic plaques were retrieved by endarterectomy; they were examined in the longitudinal axial direction. Plaques were included in this study when upstream and downstream parts were clearly visible, occlusion was absent, and immunostaining for luminal endothelium was present all along the plaque. Using these criteria, 13 plaques were processed for further immunohistochemical studies (using anti-CD31, anti-Ki-67, and anti-splicing factor antibodies) and in situ detection of apoptosis (terminal dUTP nick end-labeling and ligase assay). Eight plaques showed ≥1 apoptotic endothelial cell at the luminal surface. Quantitative analysis of endothelial cell apoptosis in these plaques showed a systematic preferential occurrence of apoptosis in the downstream parts of plaques, where low flow and low shear stress prevail, in comparison with the upstream parts (18.8±3.3% versus 2.7±1.2%, respectively, P<0.001). Endothelial cell apoptosis was barely detectable in plaque microvessels.

Conclusions—Our results suggest that in vivo local shear stress influences luminal endothelial cell apoptosis and may be a major determinant of plaque erosion and thrombosis.