Fasting Promotes the Expression of SIRT1, an NAD+ -dependent Protein Deacetylase, Via Activation of PPARalpha in Mice

Calorie restriction (CR) extends lifespans in a wide variety of species. CR induces an increase in the NAD(+)/NADH ratio in cells and results in activation of SIRT1, an NAD(+)-dependent protein deacetylase that is thought to be a metabolic master switch linked to the modulation of lifespans. CR also affects the expression of peroxisome proliferator-activated receptors (PPARs). The three subtypes, PPARalpha, PPARgamma, and PPARbeta/delta, are expressed in multiple organs. They regulate different physiological functions such as energy metabolism, insulin action and inflammation, and apparently act as important regulators of longevity and aging. SIRT1 has been reported to repress the PPARgamma by docking with its co-factors and to promote fat mobilization. However, the correlation between SIRT1 and other PPARs is not fully understood. CR initially induces a fasting-like response. In this study, we investigated how SIRT1 and PPARalpha correlate in the fasting-induced anti-aging pathways. A 24-h fasting in mice increased mRNA and protein expression of both SIRT1 and PPARalpha in the livers, where the NAD(+) levels increased with increasing nicotinamide phosphoribosyltransferase (NAMPT) activity in the NAD(+) salvage pathway. Treatment of Hepa1-6 cells in a low glucose medium conditions with NAD(+) or NADH showed that the mRNA expression of both SIRT1 and PPARalpha can be enhanced by addition of NAD(+), and decreased by increasing NADH levels. The cell experiments using SIRT1 antagonists and a PPARalpha agonist suggested that PPARalpha is a key molecule located upstream from SIRT1, and has a role in regulating SIRT1 gene expression in fasting-induced anti-aging pathways.