Fig. 1 | Elevated NADH drives the daytime dip in body temperature during time-restricted calorie restriction.
Fig. 2 | Daytime NADH elevation regulates genome-wide transcription of fatty acid and amino acid metabolism genes during TRF-CR
Fig. 3 | NADH inhibits SIRT1 in the morning during TRF-CR to regulate metabolism and body temperature.
Fig. 4 | LbNOX redox state in liver drives energy conservation during nocturnal CR feeding.
Although sirtuins have been associated with the beneficial effects of CR across a range of organisms7,22,64,65, and CR promotes longevity in yeast by increasing ySir2p activity and NAD+/NADH4,45, the situation is more complex in mammals, because CR exerts tissue-specific effects on NAD+ and NADH22,66,67. Our findings using SAMDI-MS indicate that NADH inhibits SIRT1 activity at physiologically relevant concentrations22,52–54, and our in vivo genetic analyses indicate that hepatic NADH inhibition of SIRT1 during the daytime plays an important role in energy-sparing in liver under a low-energy state. Whether redox regulation of other sirtuin isoforms (SIRT2–7) could also contribute to tissue-specific promotion of energy conservation during low-energy conditions remains to be explored. Future studies are necessary to elucidate whether other energy-sensing pathways influence the capacity of NADH to regulate the activity of SIRT1 or other sirtuin isoforms during low-energy states in vivo. Our finding that the cytonuclear form of LbNOX drives SIRT1 activity in the nucleus to affect the transcriptional, metabolic and physiological response to TRF-CR suggests that SIRT1 is sensitive to changes in cytosolic NADH and/or to metabolic conditions that cause export of mitochondrial NADH equivalents into the cytosol as occurs during gluconeogenesis32–35. Although recent reports suggest that SIRT1 may interact with NADH in the nucleus68, continued development of methods that can accurately report subcellular concentrations of reduced/oxidized NAD(H) in vivo will facilitate greater understanding of how redox state across the day under different nutrient conditions may regulate SIRT1 and other sirtuin isoforms16.
Metabolic homoeostasis in mammals is mediated by interlocked nutrient-sensing and temporal signals throughout the 24-h light/dark cycle.
The molecular clock network drives oscillations of a broad range of transcripts and metabolites that direct anabolic and catabolic metabolism in anticipation of the fasting/feeding–sleep/wake cycle1–3 .
Interactions between the core molecular clock and nutrient-responsive transcription factors (TFs) contribute to metabolic homoeostasis, yet how these pathways cooperate under long-term energy-deficient conditions has remained obscure.
In yeast, calorie restriction (CR) transcriptionally reprogrammes metabolic gene expression to shift oxidative fuel preference and maintain energetic homoeostasis of the cell4 .
In mammals, CR downregulates energy-intensive processes, such as thermogenesis during sleep, and upregulates anabolic processes within the liver that convert metabolite stores into energetic substrates for the brain5,6 .
NAD+ and the NAD+-dependent ySIR2p deacetylase are required for the transcriptional response to CR in yeast7 , although the role of NAD+ in the response to low-energy conditions in mammals remains less clear.
Transcriptomic studies have revealed robust oscillations in the expression of the rate-limiting enzyme involved in NAD+ biosynthesis across peripheral tissues, which in turn feedback to regulate metabolic transcription cycles through SIRT1-mediated deacetylation and inhibition of the circadian repressor PER2 (refs. 8–13).
Supplementation of NAD+ with the soluble precursor nicotinamide riboside in ageing mice reverts senescence of the sleep/wake and mitochondrial oxidative respiration cycles, suggesting that robustness of the NAD+–SIRT1-clock pathway may enhance fitness10.
NAD+ also functions as an electron shuttle in oxidoreductase equilibrium reactions that vary according to both nutrient availability and time of day14,15, yet whether metabolic control of rhythmic transcription is modulated by cyclic changes in NAD(H) balance remains unknown.
To investigate whether NAD(H) balance provides a signal to regulate transcriptional and metabolic cycles in vivo, we examined the effect of uncoupling nutrient state from NADH levels by tonically inducing NADH oxidation during CR through hepatic transduction of LbNOX16,17.
When NADH levels were dissociated from energy state using LbNOX, we observed transcriptional reprogramming of SIRT1- and BMAL1-mediated gene networks that regulate fatty acid and amino acid metabolism and thermogenesis.
Our studies reveal that NADH redox state drives energy conservation during sleep through rhythmic inhibition of SIRT1 and downstream circadian processes.
参考文献：https:///10.1038/s42255-021-00498-1
Data availability Data generated in this study are publicly available in the GEO repository (GSE151281). We also utilized publicly accessible RNA-seq data from GEO repositories GSE133989 and GSE118787. JASPAR databases are found at http://jaspar./search?q=&collection=CORE&tax_group=vertebrates. Correspondence and requests for materials should be addressed to Joseph Bass (j-bass@northwestern.edu). Source data are provided with this paper. Received: 11 August 2021; Accepted: 28 October 2021;
