Extension of Human Cell Lifespan by Nicotinamide Phosphoribosyltransferase

Abstract

Extending the productive lifespan of human cells could have major implications for diseases of aging, such as atherosclerosis. We identified a relationship between aging of human vascular smooth muscle cells (SMCs) and nicotinamide phosphoribosyltransferase (Nampt/PBEF/Visfatin), the rate-limiting enzyme for NAD ؉ salvage from nicotinamide. Replicative senescence of SMCs was preceded by a marked decline in the expression and activity of Nampt. Furthermore, reducing Nampt activity with the antagonist FK866 induced premature senescence in SMCs, assessed by serial quantification of the proportion of cells with senescence-associated ␤-galactosidase activity. In contrast, introducing the Nampt gene into aging human SMCs delayed senescence and substantially lengthened cell lifespan, together with enhanced resistance to oxidative stress. Nampt-mediated SMC lifespan extension was associated with increased activity of the NAD ؉ -dependent longevity enzyme SIRT1 and was abrogated in Nampt-overexpressing cells transduced with a dominant-negative form of SIRT1 (H363Y). Nampt overexpression also reduced the fraction of p53 that was acetylated on lysine 382, a target of SIRT1, suppressed an age-related increase in p53 expression, and increased the rate of p53 degradation. Moreover, add-back of p53 with recombinant adenovirus blocked the anti-aging effects of Nampt. These data indicate that Nampt is a longevity protein that can add stress-resistant life to human SMCs by optimizing SIRT1-mediated p53 degradation.Age is the greatest risk factor for myocardial infarctions and strokes (1). This risk is partly attributable to an age-related decline in the ability of vascular cells to resist stress and effectively remodel the arterial wall. Vascular smooth muscle cells (SMCs) 3 are especially important in this regard; the efficiency with which SMCs stabilize a developing atherosclerotic lesion determines whether the lesion will rupture, a potentially fatal event. Strategies to prevent the premature senescence of SMCs could be a promising approach for reducing vascular disease if molecular targets can be identified.Nicotinamide phosphoribosyltransferase (Nampt, also known as Pre-B-cell colony-enhancing factor and Visfatin (2)) is the rate-limiting enzyme for NAD ϩ biosynthesis from nicotinamide. The intracellular levels of NAD ϩ and nicotinamide have recently been identified as important for certain cell survival reactions, including those linked to the sirtuin family of protein deacetylases (3, 4). Sirtuins, such as Sir2 and its mammalian homolog SIRT1, consume NAD ϩ and generate nicotinamide as they hydrolytically remove a targeted acetyl group (3). Nicotinamide is a known inhibitor of NAD ϩ -dependent deacetylation reactions. Therefore, pathways that both replenish NAD ϩ and clear nicotinamide could be vital to SIRT1 activity.Recently, we discovered that Nampt was substantially upregulated when a uniquely long-lived human vascular SMC line was subjected to the stress of complete serum withdrawal (5). Here, we report that Nampt i...

SirT1-null mice develop tumors at normal rates but are poorly protected by resveratrol

“…In cultured cancer cells, SirT1 can inhibit apoptosis but also has an inhibitory effect on proliferation of certain cancer cell types (Fu et al, 2006). Several reports show data consistent with SirT1 having an inhibitory effect (Langley et al, 2002;Ota et al, 2006;Abdelmohsen et al, 2007;van der Veer et al, 2007;Huang et al, 2008), a promoting effect (Chua et al, 2005) or no effect (Michishita et al, 2005;Kamel, Boily and McBurney, unpublished data) on cellular senescence. SirT1 expression can be repressed by HIC1 (Chen et al, 2005b), activated by BRCA1 (Wang et al, 2008b), and both suppressed (in fed cells) and activated (with FoxO3a in starved cells) by p53 (Nemoto et al, 2004), three tumorsuppressor proteins.…”

Sirtuins: critical regulators at the crossroads between cancer and aging

“…Overexpression of SIRT1 alone does not affect replicative lifespan (Michishita et al, 2005), but Nampt overexpression, which increases SIRT1 activity through enhanced production of NAD þ , promotes p53 deacetylation and extends replicative lifespan of human smooth muscle cells (van der Veer et al, 2007). These results suggest that increased NAD þ levels regulate SIRT1 and at least one other factor to promote longevity, or that increased SIRT1 levels are not sufficient and SIRT1 must be activated to extend replicative lifespan.…”

“…Overexpression of Nampt increases NAD þ levels and induces SIRT1 activity, with changes in gene expression paralleling those in cells overexpressing SIRT1 (Revollo et al, 2004). Nampt decreases as primary cells age and undergo replicative senescence, which lowers NAD þ levels and SIRT1 activity (van der Veer et al, 2007). Inhibition of Nampt activity induces premature senescence in early-passage primary cells, while overexpression of Nampt delays senescence and increases survival after oxidative stress in late-passage primary cells (van der Veer et al, 2007).…”

“…Inhibition of Nampt activity induces premature senescence in early-passage primary cells, while overexpression of Nampt delays senescence and increases survival after oxidative stress in late-passage primary cells (van der Veer et al, 2007). These effects of Nampt are dependent on SIRT1, as overexpression of a catalytically inactive SIRT1 blocks lifespan extension and accelerates senescence (van der Veer et al, 2007).…”

“…A decrease in HuR during senescence destabilizes the SIRT1 mRNA (Abdelmohsen et al, 2007). SIRT1 enzymatic activity also decreases as NAD þ levels fall due to a decrease in Nampt activity (van der Veer et al, 2007).…”