Abstract: 【Objective】 To investigate the effects of shear stress on the endothelial repair capacity of endothelial progenitor cells (EPC) and underlying molecular mechanism. 【Methods】Young (25.4 ± 6.6 years old

n = 10) healthy male subjects without clinical evidence of cardiovascular risk factors and significant medical history were enrolled into the study. EPC were isolated from peripheral blood of 10 young subjects by density gradient centrifugation method. EPC migration and adhesion in vitro were investigated after exposure to 15 dyn/cm2 of shear stress for 6

12 or 24 hours. To determine the effect of shear stress on EPC-mediated re-endothelialization in vivo

EPC were exposed to 15 dyn/cm2 of shear stress for 12 hours and then intravenously injected (separately) into nude mice 3 hours after surgical carotid artery denudation. The expression of genes and proteins of interest on surface of EPC were analyzed by Realtime RT-PCR or Western-blot. 【Results】 Pretreatment with shear stress significantly increased EPC migration

adhesion function in vitro and enhanced the re-endothelialization capacity of EPC from young subjects(before shear stress treatment:34%± 6%;after shear stress treatment:51% ± 8%; P < 0.01). CXC chemokine receptor 4 (CXCR4) expression were markedly upregulated by shear stress pretreatment in vitro (before shear stress treatment: 1.0; after shear stress treatment:2.8 ± 0.3; P < 0.01). 【Conclusion】Fluid shear stress improves endothelial repair capacity of endothelial progenitor cells

which may be partly related to CXCR4-induced signaling pathway.