The PI3K/Akt/mTOR pathway regulates the replicative senescence of human VSMCs.

Replicative senescence of vascular smooth muscle cells (VSMCs) contributes to aging as well as age-related cardiovascular diseases. Rapamycin can delay the onset of aging-related diseases via inhibition of the mammalian target of rapamycin (mTOR), but its role in vascular aging remains elusive. This study investigated the involvement of mTOR signaling in replicative senescence of VSMCs. Replicative senescence was induced by the extended passages of human VSMCs. Aging-related cell morphology was observed. The aging-related proteins and enzyme activity, and oxidative stress were measured. Significant increase in SA-ß-gal activity and protein expression, p53 and p16 protein expression, proliferation index (PI), malondialdehyde (MDA) concentration, superoxide dismutase (SOD) and glutathione peroxidase (GPX) activity, and significant decrease in telomerase activity was observed in aging VSMCs compared to young cells. Significant activation of PI3K/Akt/mTOR signaling was observed in aging cells but not young cells. Pretreatment of VSMCs with PI3K inhibitor blocked while PI3K activator increased the changes of the above replicative senescence-related parameters in VSMCs. Rapamycin and silencing of mTOR expression inhibited replicative senescence in VSMCs through decreasing the level of p-mTOR Ser2448, p-mTOR Thr2446, and S6K1 phosphorylation. This study for the first time demonstrated that the PI3K/Akt/mTOR/S6K1 signal pathway plays an important role in regulating replicative senescence of human VSMCs.

AMPK/TSC2/mTOR pathway regulates replicative senescence of human vascular smooth muscle cells.

Age-associated diseases, including vascular diseases, are on the rise with the increase in the aging population. However, the mechanisms of aging and age-associated vascular dysfunction remain to be fully elucidated. Replicative senescence of vascular smooth muscle cells (VSMCs) contributes to aging as well as age-associated vascular diseases. Rapamycin may delay aging-associated diseases via inhibition of the mammalian target of rapamycin (mTOR), but its role in VSMC aging has remained elusive. The present study investigated the involvement of mTOR signaling in replicative senescence of VSMCs. Replicative senescence was induced in human VSMCs by extended passages and identified by assessing the cell morphology, senescence-associated ß-galactosidase activity, and p53 and p21 protein expression. Protein expression and phosphorylation were determined by western blot analysis. Significant senescence of VSMCs was observed in cells subjected to extended passaging (until passage 15). Significant decreases in adenosine monophosphate-activated protein kinase (AMPK)/tuberous sclerosis complex 2 (TSC2) phosphorylation, but significant increases in mTOR/ribosomal protein S6 kinase 1 (S6K1) phosphorylation, were observed in cells with replicative senescence compared with those in young cells. Pre-treatment of VSMCs with AMPK activator and mTOR inhibitor delayed replicative senescence and reversed changes in AMPKα, TSC2, mTOR and S6K1 phosphorylation in senescent VSMCs. The AMPK/TSC2/mTOR/S6K1 signaling axis was found to have an important role in regulating replicative senescence of human VSMCs.