Sirtuins are a family of NAD+-dependent deacetylase enzymes (SIRT1-7 in mammals) that regulate gene expression, metabolism, stress resistance, and aging through removal of acetyl groups from histones and non-histone proteins. They function as metabolic sensors linking cellular energy status (NAD+/NADH ratio) to transcriptional programs. Sirtuins are activated by caloric restriction, exercise, and fasting, promoting mitochondrial biogenesis, autophagy, and stress resistance.
Sirtuins use NAD+ as a cofactor to remove acetyl groups from lysine residues on target proteins, releasing nicotinamide and O-acetyl-ADP-ribose. SIRT1 (nuclear) deacetylates histones, PGC-1α (promoting mitochondrial biogenesis), FOXO transcription factors (activating stress resistance genes), and p53 (modulating apoptosis). SIRT3 (mitochondrial) deacetylates and activates enzymes involved in fatty acid oxidation, ketogenesis, and antioxidant defense. During fasting or exercise, the NAD+/NADH ratio increases, activating sirtuins. SIRT1 deacetylates PGC-1α, initiating transcription of mitochondrial genes and promoting oxidative metabolism. Sirtuins also regulate inflammation by deacetylating NF-κB subunits, reducing inflammatory gene transcription.
Sirtuins represent the mechanistic link between lifestyle interventions (fasting, exercise, caloric restriction) and their anti-aging, anti-inflammatory effects. Activating sirtuins through these interventions promotes metabolic flexibility, mitochondrial health, and stress resistance. NAD+ availability becomes rate-limiting with age, explaining declining sirtuin activity in aging. Interventions to maintain NAD+ levels (niacin, NMN, reducing chronic inflammation) support sirtuin function.
- SIRT1 is the most studied, regulating nuclear gene expression and metabolism
- SIRT3 is mitochondrial, regulating oxidative metabolism and ROS defense
- Activity depends on NAD+/NADH ratio (activated when NAD+ is high)
- Caloric restriction increases sirtuin activity by raising NAD+ levels
- Resveratrol indirectly activates SIRT1 (though direct activation is debated)
- SIRT1 deacetylates PGC-1α promoting mitochondrial biogenesis
- SIRT3 deacetylates SOD2 increasing antioxidant capacity
- NAD+ — sirtuins require NAD+ as cofactor for deacetylation reactions
- histone deacetylases — sirtuins are class III HDACs with NAD+ dependence
- histone modification — sirtuins deacetylate histones affecting chromatin structure and gene expression
- caloric restriction — caloric restriction activates sirtuins by increasing NAD+/NADH ratio
- fasting — fasting increases NAD+ availability activating sirtuins
- exercise — exercise activates sirtuins through NAD+ and AMPK signaling
- PGC-1alpha — SIRT1 deacetylates and activates PGC-1α promoting mitochondrial biogenesis
- mitochondrial biogenesis — sirtuins promote mitochondrial biogenesis through PGC-1α activation
- FOXO — SIRT1 deacetylates FOXO transcription factors activating stress resistance genes
- autophagy — sirtuins promote autophagy through multiple deacetylation targets
- inflammation — sirtuins reduce inflammation by deacetylating NF-κB
- NF-κB — SIRT1 deacetylates NF-κB p65 subunit reducing inflammatory gene transcription
- fatty acid oxidation — SIRT3 deacetylates enzymes in beta-oxidation pathway
- ketogenesis — SIRT3 activates ketogenic enzymes in liver during fasting
- antioxidant defense — SIRT3 deacetylates SOD2 enhancing mitochondrial antioxidant capacity
- resveratrol — resveratrol is claimed to activate SIRT1 though mechanism is debated
- aging — declining sirtuin activity contributes to aging phenotypes
- metabolic flexibility — sirtuins promote metabolic flexibility by coordinating fuel utilization
- nicotinamide — nicotinamide is a product of sirtuin reactions and can inhibit sirtuins at high doses
- epigenetic — sirtuins regulate epigenetic marks through histone deacetylation