Abstract-Aging is associated with dysfunction of endothelial progenitor cells (EPCs), and shear stress has a beneficial impact on EPC function; however, the effects of aging and shear stress on the endothelial repair capacity of EPCs after arterial injury have not been reported. Here we investigated the influence of aging and shear stress on the reendothelialization capacity of human EPCs and the related molecular mechanism. Compared with EPCs isolated from young subjects, EPCs from the elderly displayed an impaired migration and adhesion in vitro and demonstrated a significantly reduced reendothelialization capacity in vivo after transplantation into nude mice with carotid artery denudation injury. Shear stress pretreatment enhances the migration, adhesion, and reendothelialization capacity in both young and elderly EPCs; however, it was to a greater extent in EPCs from the elderly. Although basal CXC chemokine receptor 4 (CXCR4) expression was similar in EPCs from the 2 age groups, the stromal cell derived factor 1-induced CXCR4 and Janus kinase 2 phosphorylations were much lower in the elderly than in young EPCs. Shear stress treatment upregulated CXCR4 expression and phosphorylation and, importantly, restored the stromal cell-derived factor 1/CXCR4-dependent Janus kinase 2 phosphorylation in the elderly EPCs. Furthermore, short hairpin RNA-mediated knockdown of CXCR4 expression or pretreatment with Janus kinase 2 inhibitor diminished the enhancement in the migration, adhesion, and reendothelialization capacity of the elderly EPCs from shear stress treatments. Thus, our study demonstrates that upregulation of the CXCR4/Janus kinase 2 pathway by shear stress contributes to the enhanced reendothelialization capacity of EPCs from elderly men. A ging is a well-recognized risk factor for cardiovascular disease. 1,2 The impact of aging, a traditional detrimental factor, for the increased development of cardiovascular disease is initiated by abnormalities in structure and function of the vascular endothelium.3-5 Thus, it is of particular importance to maintain the integrity of the vascular endothelium after arterial injury with aging.Accelerated reendothelialization is an important therapeutic means for repair of injured artery. Accumulating evidence indicates that circulating endothelial progenitor cells (EPCs) provide an endogenous repair mechanism to counteract ongoing risk factor-induced endothelial injury and to replace dysfunctional endothelium, 6-10 thus suggesting an important role of circulating EPCs for restoration of the integrity of the vascular endothelium with aging. Previous studies showed that aging leads to a reduction in the number of circulating EPCs, and aging is associated with dysfunctional EPCs in both healthy persons and patients with cardiovascular disease, [11][12][13][14][15][16] which is, at least in part, responsible for the development of age-related endothelial injury in humans. [17][18][19] However, the mechanism underlying age-related EPC dysfunction is not fully understood. It is, t...

Endothelial dysfunction is related to reduced arterial elasticity in patients with essential hypertension. Circulating endothelial progenitor cells (EPCs), an important endogenous repair approach for endothelial injury, is altered in hypertensive patients. However, the association between alteration in circulating EPCs and hypertension-related reduced arterial elasticity has not been reported. The purpose of this study is to investigate the association between alteration in circulating EPCs and hypertension-related reduced arterial elasticity. We measured the artery elasticity profiles including brachial-ankle PWV (baPWV) and C1 large and C2 small artery elasticity indices in patients with essential hypertension (n = 20) and age-matched normotensive subjects (n = 21). The number and activity of circulating EPCs isolated from peripheral blood were determined. Compared to normotensive subjects, the patients with hypertension exhibited decreased C1 large and C2 small artery elasticity indices, as well as increased baPWV. The number of circulating EPCs did not differ between the two groups. The migratory and proliferative activities of circulating EPCs in hypertensive patients were lower than those in normotensive subjects. Both proliferatory and migratory activities of circulating EPCs closely correlated with arterial elasticity profiles, including baPWV and C1 large and C2 small artery elasticity indices. Multivariate analysis identified both proliferative and migratory activities of circulating EPCs as independent predictors of the artery elasticity profiles. The present study demonstrates for the first time that impaired activity of circulating EPCs is associated with reduced arterial elasticity in patients with hypertension. The fall in endogenous repair capacity of vascular endothelium may be involved in the pathogenesis of hypertension-related vascular injury.