Nicotine-reduced endothelial progenitor cell senescence through augmentation of telomerase activity via the PI3K/Akt pathway.

BACKGROUND AIMS: Previous studies have shown that nicotine increases endothelial progenitor cell (EPC) numbers and functional activity. However, the mechanisms by which nicotine increases EPC numbers and activity remain to be determined. Recent studies have demonstrated that EPC numbers and activity are associated with EPC senescence, which involves telomerase activity. Therefore, we investigated whether nicotine might be able to prevent senescence of EPC through telomerase activation, leading to the potentiation of cellular function.
METHODS: After prolonged in vitro cultivation, EPC were incubated with or without nicotine. The senescence of EPC was determined by acidic beta-galactosidase staining. The bromo-deoxyuridine incorporation assay and colony assay were employed to assess proliferative capacity and clonal expansion potential, respectively. To examine further the underlying mechanisms of these effects, we measured telomerase activity and the phosphorylation of Akt by Western blotting.
RESULTS: Nicotine dose-dependently prevented the onset of EPC senescence in culture. Moreover, nicotine increased the proliferation of EPC and colony-forming capacity. Nicotine significantly increased telomerase activity and phosphorylation of Akt, a downstream effector of phosphoinositide 3-kinase (PI3K). Moreover, pre-treatment with PI3K blockers, either wortmannin or LY294002, significantly attenuated the nicotine-induced telomerase activity. In addition, mecamylamine, a non-selective antagonist of nicotinic acetylcholine receptors (nAchR), abrogated the effects of nicotine on EPC.
CONCLUSIONS: The results of the present study indicate that nicotine delays the onset of EPC senescence, which might be related to activation of telomerase through the PI3K/Akt pathway. In addition, the effects of nicotine might be specifically mediated by nAchR activation.