The increases in physiological levels of fluid shear stress have beneficial effects on vascular homeostasis. Endothelial progenitor cells (EPCs) play an important role in the maintenance of endothelial integrity. We hypothesized that shear stress-mediated vascular protection is related to the upregulation of endothelial nitric oxide synthase expression in EPCs. The human EPCs exposed to in vitro shear stress levels of 5, 15 and 25 dyn/cm2 for 4 h. In vitro shear stress, in a dose-dependent fashion, increased the endothelial nitric oxide synthase mRNA expression and the nitric oxide production in human EPCs. The present findings for the first time provide novel insights into the mechanisms of the physiological levels of fluid shear stress on the regulation of human EPC biologic phenotype as a potential factor, which might contribute to vascular protective activities in humans although evidence is indirect.

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