Tier 3 — preclinical

Restoration of energy homeostasis by SIRT6 extends healthy lifespan

Roichman A, Elhanati S, Aon MA, Abramovich I, Di Francesco A, Shahar Y, Avivi MY, Shurgi M, Rubinstein A, Wiesner Y, Shuchami A, Petrover Z, Lebenthal-Loinger I, Yaron O, Lyashkov A, Ubaida-Mohien C, Kanfi Y, Lerrer B, Fernández-Marcos PJ, Serrano M, Gottlieb E, de Cabo R, Cohen HY
Nature Communications 2021 Volume 12, Issue 1, Article 3208

Bibliography

PubMed
PMID 34050173
PubMed Central
PMC8163764
DOI
10.1038/s41467-021-23545-7
Funding
Israel Science Foundation (621/13 and 777/16), I-Core Foundation (41/11), ESFD, D-Cure, Israel Cancer Association (2016-0103), ICRF and BSF, SAGOL center of healthy human aging. A. Roichman supported by the Adams Fellowship Program of the Israel Academy of Sciences and Humanities. R.d.C., M.A.A., and C.U.M. supported by the Intramural Research Program of the National Institute on Aging, NIH. E.G. supported by the I-Core foundation (1775/12) and Laura and Isaac Perlmutter Foundation. M. Serrano's laboratory funded by the IRB and by grants from the Spanish Ministry of Economy co-funded by the European Regional Development Fund (SAF2017-82613-R), the European Research Council (ERC-2014-AdG/669622), and "La Caixa" Foundation.
Competing interests
H.Y.C. advises SirTLab Ltd. The remaining authors declare no competing interests.

Study snapshot

DesignInterventional lifespan and healthspan study using whole-body SIRT6- and SIRT1-transgenic C57BL/6JOlaHsd mice, with in vivo multi-omics (serum and hepatic metabolomics, liver RNA-seq and proteomics) and 13C-lactate isotope tracing.
ModelWhole-body SIRT1-, SIRT6-, and SIRT1+SIRT6-transgenic C57BL/6JOlaHsd mice compared to wild-type littermates; liver-specific SIRT6-transgenic control cohort; young (4–7 months) and old (20–25 months) age groups; both sexes.
SampleLifespan cohorts: WT n=52 males / n=50 females; SIRT6-tg n=51 males / n=41 females; SIRT1-tg n=47 males / n=30 females; SIRT1+6-tg n=47 males / n=44 females. Smaller cohorts of 5–10 mice per group for physiological, metabolomic, transcriptomic, and tracing experiments.
InterventionWhole-body genetic overexpression of SIRT6 (single line, #55) from birth; compared to SIRT1 overexpression, SIRT1+SIRT6 double overexpression, and liver-specific SIRT6 overexpression.
DurationLifetime for lifespan endpoints; targeted assays at young (4–7 mo) and old (20–25 mo) time points.
EndpointsMedian and maximum lifespan (both sexes); Frailty and healthspan (spontaneous wheel running, treadmill endurance, in-cage activity); Age-related pathology (neoplasia, cancer, gastrointestinal adenoma incidence); Whole-body metabolism (respiratory exchange ratio, O2/CO2, metabolic flexibility); Gluconeogenic capacity from lactate and glycerol; Gluconeogenic capacity from lactate and glycerol; Hepatic transcriptome (RNA-seq) and proteome (LC-MS/MS); Hepatic and serum metabolomics (glycolysis/GNG, TCA cycle, redox, lipids, amino acids); Hepatic NAD+ levels and de novo NAD+ biosynthesis gene expression; Adipose tissue lipolysis (HSL phosphorylation) and plasma glycerol

What the study showed, in plain terms

SIRT6 is a protein that becomes less active with age and has been implicated in DNA repair, metabolism, and longevity. Earlier work in mixed-background mice had shown that boosting SIRT6 extended lifespan in males only. This study asked whether overexpressing SIRT6 across the whole body would extend lifespan in a genetically clean inbred strain (C57BL/6JOlaHsd), in both sexes, and by what mechanism.

The answer to the first question is yes. Male SIRT6-transgenic mice lived 27% longer at the median and 11% longer at maximum lifespan than wild-type littermates. Females lived 15% longer at both median and maximum. Overexpressing SIRT1 alone did nothing. Combining SIRT1 with SIRT6 gave no benefit over SIRT6 alone. Old SIRT6 mice were also markedly less frail — they ran further on running wheels and treadmills, kept better red blood cell counts, and delayed the onset of gastrointestinal adenomas.

The mechanism the paper landed on is unexpected. As mice age, they lose the ability to make new glucose (gluconeogenesis) in the liver during fasting, and blood sugar drops earlier than in young mice. SIRT6-transgenic mice keep young-like liver gluconeogenesis into old age. They do this by preserving hepatic NAD+ levels, keeping the NAD+/NADH balance in the cytoplasm favourable for lactate-to-pyruvate conversion, activating fat and amino acid oxidation, and — crucially — driving glycerol release from adipose tissue that the liver then uses as gluconeogenic substrate. Liver-only SIRT6 overexpression is not enough to reproduce these effects, so at least two tissues need SIRT6 activity to preserve energy homeostasis.

Key findings

  • SIRT6 overexpression extended median lifespan by 27% in males (p = 7.1 × 10⁻⁶) and 15% in females (p = 1.1 × 10⁻⁶); maximum lifespan extended 11% in males and 15% in females. SIRT1 overexpression alone had no effect on median or maximum lifespan.
  • SIRT6-transgenic males maintained young-like spontaneous wheel-running and treadmill endurance at 15–22 months. Age-related decline in physical activity was significantly repressed.
  • Old SIRT6-transgenic mice preserved young-like respiratory exchange ratio (RER) oscillation, red blood cell count, hematocrit, hemoglobin, low LDL/HDL ratio, and low serum IGF-1.
  • Wild-type mice lose the ability to sustain blood glucose during fasting after 22 months; SIRT6-transgenic mice at the same age maintain young-like glucose curves. This is not explained by faster glucose clearance — glucose tolerance is preserved in both.
  • Gluconeogenic capacity from injected lactate and glycerol decreased significantly with age in wild-type mice but was preserved at young-like levels in old SIRT6-transgenic mice, in both sexes.
  • Hepatic RNA-seq showed SIRT6-transgenic mice upregulated fatty acid β-oxidation, TCA cycle, aerobic respiration, and amino-acid catabolism genes, and downregulated inflammatory pathways. Effects were markedly stronger in males than females.
  • Hepatic proteomics identified 185 differentially expressed proteins between genotypes; SIRT6-upregulated proteins enriched for metabolic pathways, SIRT6-downregulated proteins enriched for immunoproteasome subunits (PA28α, PA28β, β2i, β5i). Ubiquitinated protein levels fell in SIRT6-tg livers, consistent with improved proteostasis.
  • Old SIRT6-tg mice preserved young-like hepatic NAD+ and FAD levels. NAM (nicotinamide) levels were elevated. De novo NAD+ biosynthesis genes (Ido2, Tdo2, Haao, Nmnat1) were upregulated at both mRNA and protein levels. PARP1-mediated NAD+ consumption was unchanged, so increased production — not reduced consumption — drives the NAD+ preservation.
  • Under 13C-lactate isotope tracing, SIRT6-tg livers showed preserved incorporation of lactate carbons into TCA cycle intermediates (α-ketoglutarate, succinate, malate) and glucose (M+2, M+3) at old age. The hepatic lactate/pyruvate ratio was significantly lower in old SIRT6-tg, consistent with a more favourable cytosolic NAD+/NADH ratio driving lactate-to-pyruvate conversion.
  • Liver-specific SIRT6 overexpression alone did not rescue age-related decline in gluconeogenesis or hepatic GNG-related metabolites, indicating extra-hepatic SIRT6 activity is required. In old SIRT6-tg mice, plasma glycerol was preserved at young-like levels and adipose HSL phosphorylation (Ser563, active form) was increased, showing enhanced lipolysis feeding the liver with GNG substrate.

What this study can and cannot tell us

This is a preclinical study in mice with lifelong whole-body SIRT6 overexpression from a single transgenic line. Results do not translate directly to what a person could achieve by supplementation or lifestyle. The intervention is genetic overexpression from birth, not a drug given later in life — so the paper does not answer whether adult-onset SIRT6 activation would produce similar benefits.

The effect is stronger in males than females across lifespan (27% vs 15% median extension), hepatic transcriptome response, and treadmill endurance. The paper proposes lower baseline IGF-1 in females and a milder hepatic inflammatory baseline as partial explanations, but a full mechanism for the sex difference is not established.

Liver-specific overexpression alone did not reproduce the whole-body effect on gluconeogenesis. The paper concludes that at least two tissues — liver and adipose — must overexpress SIRT6 to drive the lifespan effect. This limits the interpretation of any future intervention that targets a single tissue.

The senior author (H.Y.C.) advises SirTLab Ltd, a company developing SIRT6-modulating compounds. This is disclosed but reader awareness is appropriate given the therapeutic implications drawn from the data.

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Dr. Khaled Mahmoud, MBBChCritical Care Medicine, Longevity Science & Editorial Direction Dr. Abdulla Mostafa, PhDCellular Senescence, Neurological, Mitochondrial & Brain-Ageing Biology Dr. Amr Yasser, PhDCardiometabolic, Musculoskeletal, Gut & Bioavailability