Abstract 1668: SIRT1 Regulates Human Vascular Smooth Muscle Cell Lifespan
Vascular smooth muscle cells (SMCs) in diseased arteries are prone to accelerated aging because of local atherosclerotic stresses and ongoing cell replication. This premature aging could limit the ability of SMCs to perform reparative functions essential to plaque stability. However, the molecular factors that regulate SMC aging are not well understood. The purpose of this study was to determine if the NAD+-dependent deacetylase, SIRT1, a protein implicated in aging but of unknown function in SMCs, regulates SMC lifespan. By Western blot analysis, we determined that SIRT1 expression in aged, late-passaged human SMCs had declined to 5% of that expressed in fresh SMC tissue outgrowths. Overexpression of SIRT1 through retrovirus-mediated gene delivery substantially reduced cellular senescence, as evidenced by a decrease in senescence-associated β-galactosidase activity (29 ± 3 vs. 54 ± 1% of cells, p<0.05). Furthermore, SIRT1-overexpressing primary SMCs exhibited a 1.6-fold extension in cumulative population doublings relative to vector-infected SMCs (p<0.05). Similar results were obtained when SIRT1 was overexpressed in clonal SMC populations. To target both SIRT1 protein abundance and enzyme activity, we co-overexpressed SIRT1 with nicotinamide phosphoribosyltransferase (NAmPRT), a NAD+ biosynthetic enzyme that both clears the physiological inhibitor of SIRT1 and provides its co-substrate. This yielded a striking extension of SMC lifespan compared to SMCs overexpressing either SIRT1 or NAmPRT alone (p<0.05), and a marked suppression of senescence-associated β-galactosidase activity (16 ± 1 vs. 36 ± 2% of cells, p<0.05).
Human vascular SMCs express SIRT1, and the level of this class III histone deacetylase declines strikingly during replicative aging;
SMC lifespan can be extended by increasing the gene dosage of SIRT1; and
combined expression of both SIRT1 and NAmPRT provides a novel and potent means of extending SMC longevity, with implications for the productive remodeling of aging and vulnerable atherosclerotic lesions.