Endothelial progenitor cells in smokers are dysfunctional because of increased DNA damage and senescence

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BackgroundCardiovascular disease (CVD) is a major cause of death in smokers, especially in patients with chronic obstructive pulmonary disease (COPD). The molecular pathways that lead to endothelial dysfunction and CVD due to cigarette smoke remain unclear. DNA damage has been recognised as an important contributor in ageing disorders, including CVD. Circulating endothelial progenitor cells (EPC) are required for endothelial homoeostasis, and their dysfunction contributes to CVD. This study aimed to examine whether circulating EPC (also called blood outgrowth endothelial cells [BOEC]) from smokers and COPD patients are dysfunctional, and to investigate the role of DNA damage pathways in mediating endothelial dysfunction in these patients. MethodsBOEC were isolated from peripheral blood samples received from 16 healthy non-smokers (five men, 11 women; mean age 57 years [SE 2·7]), ten healthy smokers (five men, five women; 57 years [2·6]), and 16 COPD patients (11 men, five women; 67 years [1·6]). Endothelial senescence was measured by senescence-associated β-galactosidase (SA-β-gal) activity. Protein levels of sirtuin 1 (SIRT1) were measured by western blotting, expression of p16, γ-H2AX, and 53BP1 by immunofluorescence, and p21 by western blotting and immunofluorescence. SIRT1 activity was measured with a SIRT1 fluorescent activity assay kit. FindingsBOEC from smokers and COPD patients showed evidence of increased DNA double-strand breaks (increased γ-H2AX, 53BP1) compared with non-smokers. BOEC from healthy smokers and COPD patients displayed increased senescence (measured by SA-β-gal activity, p16, and p21) and decreased SIRT1 expression and activity compared with controls. SIRT1 protein levels and activity negatively correlated with senescence, indicating a regulatory role of SIRT1 on senescence. Interestingly, treatment of BOEC from COPD patients with a SIRT1 activator (resveratrol) rescued the senescent phenotype. InterpretationThe results from our study demonstrate that BOEC from smokers and COPD patients display increased DNA damage and senescence, associated with reduced SIRT1 expression and activity. These defects may contribute to endothelial dysfunction and cardiovascular events in people who smoke and could potentially constitute therapeutic targets for intervention. FundingImperial College London.