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Brown adipose tissue (BAT) has abundant mitochondria with the unique capability of generating heat via uncoupled respiration. Mitochondrial uncoupling protein 1 (UCP1) is activated in BAT during cold stress and dissipates mitochondrial proton motive force generated by the electron transport chain to generate heat. However, other mitochondrial factors required for brown adipocyte respiration and thermogenesis under cold stress are largely unknown. Here, we show LETM1 domain-containing protein 1 (LETMD1) is a BAT-enriched and cold-induced protein required for cold-stimulated respiration and thermogenesis of BAT. Proximity labeling studies reveal that LETMD1 is a mitochondrial matrix protein. Letmd1 knockout male mice display aberrant BAT mitochondria and fail to carry out adaptive thermogenesis under cold stress. Letmd1 knockout BAT is deficient in oxidative phosphorylation (OXPHOS) complex proteins and has impaired mitochondrial respiration. In addition, BAT-specific Letmd1 deficient mice exhibit phenotypes identical to those observed in Letmd1 knockout mice. Collectively, we demonstrate that the BAT-enriched mitochondrial matrix protein LETMD1 plays a tissue-autonomous role that is essential for BAT mitochondrial function and thermogenesis., (© 2023. The Author(s).)

Brown adipose tissue plays a central role in the regulation of the energy balance by expending energy to produce heat. NAD + -dependent deacylase sirtuins have widely been recognized as positive regulators of brown adipose tissue thermogenesis. However, here we reveal that SIRT7, one of seven mammalian sirtuins, suppresses energy expenditure and thermogenesis by regulating brown adipose tissue functions. Whole-body and brown adipose tissue-specific Sirt7 knockout mice have higher body temperature and energy expenditure. SIRT7 deficiency increases the protein level of UCP1, a key regulator of brown adipose tissue thermogenesis. Mechanistically, we found that SIRT7 deacetylates insulin-like growth factor 2 mRNA-binding protein 2, an RNA-binding protein that inhibits the translation of Ucp1 mRNA, thereby enhancing its inhibitory action on Ucp1. Furthermore, SIRT7 attenuates the expression of batokine genes, such as fibroblast growth factor 21. In conclusion, we propose that SIRT7 serves as an energy-saving factor by suppressing brown adipose tissue functions., (© 2022. The Author(s).)

Organic elements make up 99% of an organism but without the remaining inorganic bioessential elements, termed the metallome, no life could be possible. The metallome is involved in all aspects of life, including charge balance and electrolytic activity, structure and conformation, signaling, acid-base buffering, electron and chemical group transfer, redox catalysis energy storage and biomineralization. Here, we report the evolution with age of the metallome and copper and zinc isotope compositions in five mouse organs. The aging metallome shows a conserved and reproducible fingerprint. By analyzing the metallome in tandem with the phenome, metabolome and proteome, we show networks of interactions that are organ-specific, age-dependent, isotopically-typified and that are associated with a wealth of clinical and molecular traits. We report that the copper isotope composition in liver is age-dependent, extending the existence of aging isotopic clocks beyond bulk organic elements. Furthermore, iron concentration and copper isotope composition relate to predictors of metabolic health, such as body fat percentage and maximum running capacity at the physiological level, and adipogenesis and OXPHOS at the biochemical level. Our results shed light on the metallome as an overlooked omic layer and open perspectives for potentially modulating cellular processes using careful and selective metallome manipulation., (© 2022. The Author(s).)

Sustained ryanodine receptor (RyR) Ca 2+ leak is associated with pathological conditions such as heart failure or skeletal muscle weakness. We report that a single session of sprint interval training (SIT), but not of moderate intensity continuous training (MICT), triggers RyR1 protein oxidation and nitrosylation leading to calstabin1 dissociation in healthy human muscle and in in vitro SIT models (simulated SIT or S-SIT). This is accompanied by decreased sarcoplasmic reticulum Ca 2+ content, increased levels of mitochondrial oxidative phosphorylation proteins, supercomplex formation and enhanced NADH-linked mitochondrial respiratory capacity. Mechanistically, (S-)SIT increases mitochondrial Ca 2+ uptake in mouse myotubes and muscle fibres, and decreases pyruvate dehydrogenase phosphorylation in human muscle and mouse myotubes. Countering Ca 2+ leak or preventing mitochondrial Ca 2+ uptake blunts S-SIT-induced adaptations, a result supported by proteomic analyses. Here we show that triggering acute transient Ca 2+ leak through RyR1 in healthy muscle may contribute to the multiple health promoting benefits of exercise., (© 2021. The Author(s).)

Obesity and type 2 diabetes (T2D) are metabolic disorders influenced by lifestyle and genetic factors that are characterized by insulin resistance in skeletal muscle, a prominent site of glucose disposal. Numerous genetic variants have been associated with obesity and T2D, of which the majority are located in non-coding DNA regions. This suggests that most variants mediate their effect by altering the activity of gene-regulatory elements, including enhancers. Here, we map skeletal muscle genomic enhancer elements that are dynamically regulated after exposure to the free fatty acid palmitate or the inflammatory cytokine TNFα. By overlapping enhancer positions with the location of disease-associated genetic variants, and resolving long-range chromatin interactions between enhancers and gene promoters, we identify target genes involved in metabolic dysfunction in skeletal muscle. The majority of these genes also associate with altered whole-body metabolic phenotypes in the murine BXD genetic reference population. Thus, our combined genomic investigations identified genes that are involved in skeletal muscle metabolism.

Selective autophagy ensures the removal of specific soluble proteins, protein aggregates, damaged mitochondria, and invasive bacteria from cells. Defective autophagy has been directly linked to metabolic disorders. However how selective autophagy regulates metabolism remains largely uncharacterized. Here we show that a deficiency in selective autophagy is associated with suppression of lipid oxidation. Hepatic loss of Atg7 or Atg5 significantly impairs the production of ketone bodies upon fasting, due to decreased expression of enzymes involved in β-oxidation following suppression of transactivation by PPARα. Mechanistically, nuclear receptor co-repressor 1 (NCoR1), which interacts with PPARα to suppress its transactivation, binds to the autophagosomal GABARAP family proteins and is degraded by autophagy. Consequently, loss of autophagy causes accumulation of NCoR1, suppressing PPARα activity and resulting in impaired lipid oxidation. These results suggest that autophagy contributes to PPARα activation upon fasting by promoting degradation of NCoR1 and thus regulates β-oxidation and ketone bodies production.

Ongoing studies in many species seek to understand the origins, architecture and consequences of phenotypic variation under normal and dysfunctional conditions, with the aim of identifying targets for intervention that can prevent, stabilize or reverse disease. Some suggest that only humans are appropriate for studying these questions and argue that candidate drug targets identified in mouse models are largely unreliable. Here, we review the vast evidence showing that mouse models continue to make fundamental contributions to our understanding of genetic principles, pathogenic mechanisms and therapeutic modalities. We propose a virtuous cycle in which the power of observational studies and natural experiments in humans are closely integrated with the rigour of true experiments in model organisms.

Oxidative functions of adipose tissue macrophages control the polarization of M1-like and M2-like phenotypes, but whether reduced macrophage oxidative function causes systemic insulin resistance in vivo is not clear. Here, we show that mice with reduced mitochondrial oxidative phosphorylation (OxPhos) due to myeloid-specific deletion of CR6-interacting factor 1 (Crif1), an essential mitoribosomal factor involved in biogenesis of OxPhos subunits, have M1-like polarization of macrophages and systemic insulin resistance with adipose inflammation. Macrophage GDF15 expression is reduced in mice with impaired oxidative function, but induced upon stimulation with rosiglitazone and IL-4. GDF15 upregulates the oxidative function of macrophages, leading to M2-like polarization, and reverses insulin resistance in ob/ob mice and HFD-fed mice with myeloid-specific deletion of Crif1. Thus, reduced macrophage oxidative function controls systemic insulin resistance and adipose inflammation, which can be reversed with GDF15 and leads to improved oxidative function of macrophages.

Age-associated changes in chromatin structure have a major impact on organismal longevity. Despite being a central part of the ageing process, the organismal responses to the changes in chromatin organization remain unclear. Here we show that moderate disturbance of histone balance during C. elegans development alters histone levels and triggers a stress response associated with increased expression of cytosolic small heat-shock proteins. This stress response is dependent on the transcription factor, HSF-1, and the chromatin remodeling factor, ISW-1. In addition, we show that mitochondrial stress during developmental stages also modulates histone levels, thereby activating a cytosolic stress response similar to that caused by changes in histone balance. These data indicate that histone and mitochondrial perturbations are both monitored through chromatin remodeling and involve the activation of a cytosolic response that affects organismal longevity. HSF-1 and ISW-1 hence emerge as a central mediator of this multi-compartment proteostatic response regulating longevity.

Thymocytes must pass both positive and negative selections to become mature T cells. Negative selection purges thymocytes whose T-cell receptors (TCR) exhibit high affinity to self-peptide MHC complexes (self pMHC) to avoid autoimmune diseases, while positive selection ensures the survival and maturation of thymocytes whose TCRs display intermediate affinity to self pMHCs for effective immunity, but whether transcriptional regulation helps conserve positively selected thymocytes from being purged by negative selection remains unclear. Here we show that the specific deletion of nuclear receptor co-repressor 1 (NCoR1) in T cells causes excessive negative selection to reduce mature thymocyte numbers. Mechanistically, NCoR1 protects positively selected thymocytes from negative selection by suppressing Bim expression. Our study demonstrates a critical function of NCoR1 in coordinated positive and negative selections in the thymus.Thymocytes are screened by two processes, termed positive and negative selections, which are permissive only for immature thymocytes with intermediate avidity to the selecting ligands. Here the authors show that the nuclear receptor NCoR1 suppresses Bim1 to inhibit negative selection and promote thymocyte survival.

Nonalcoholic fatty liver disease is one of the most prevalent metabolic disorders and it tightly associates with obesity, type 2 diabetes, and cardiovascular disease. Reduced mitochondrial lipid oxidation contributes to hepatic fatty acid accumulation. Here, we show that the Fas cell surface death receptor (Fas/CD95/Apo-1) regulates hepatic mitochondrial metabolism. Hepatic Fas overexpression in chow-fed mice compromises fatty acid oxidation, mitochondrial respiration, and the abundance of mitochondrial respiratory complexes promoting hepatic lipid accumulation and insulin resistance. In line, hepatocyte-specific ablation of Fas improves mitochondrial function and ameliorates high-fat-diet-induced hepatic steatosis, glucose tolerance, and insulin resistance. Mechanistically, Fas impairs fatty acid oxidation via the BH3 interacting-domain death agonist (BID). Mice with genetic or pharmacological inhibition of BID are protected from Fas-mediated impairment of mitochondrial oxidation and hepatic steatosis. We suggest Fas as a potential novel therapeutic target to treat obesity-associated fatty liver and insulin resistance.Hepatic steatosis is a common disease closely associated with metabolic syndrome and insulin resistance. Here Item et al. show that Fas, a member of the TNF receptor superfamily, contributes to mitochondrial dysfunction, steatosis development, and insulin resistance under high fat diet.

The enormous variation in human lifespan is in part due to a myriad of sequence variants, only a few of which have been revealed to date. Since many life-shortening events are related to diseases, we developed a Mendelian randomization-based method combining 58 disease-related GWA studies to derive longevity priors for all HapMap SNPs. A Bayesian association scan, informed by these priors, for parental age of death in the UK Biobank study (n=116,279) revealed 16 independent SNPs with significant Bayes factor at a 5% false discovery rate (FDR). Eleven of them replicate (5% FDR) in five independent longevity studies combined; all but three are depleted of the life-shortening alleles in older Biobank participants. Further analysis revealed that brain expression levels of nearby genes (RBM6, SULT1A1 and CHRNA5) might be causally implicated in longevity. Gene expression and caloric restriction experiments in model organisms confirm the conserved role for RBM6 and SULT1A1 in modulating lifespan.

Haematopoietic stem cells (HSCs) differ from their committed progeny by relying primarily on anaerobic glycolysis rather than mitochondrial oxidative phosphorylation for energy production. However, whether this change in the metabolic program is the cause or the consequence of the unique function of HSCs remains unknown. Here we show that enforced modulation of energy metabolism impacts HSC self-renewal. Lowering the mitochondrial activity of HSCs by chemically uncoupling the electron transport chain drives self-renewal under culture conditions that normally induce rapid differentiation. We demonstrate that this metabolic specification of HSC fate occurs through the reversible decrease of mitochondrial mass by autophagy. Our data thus reveal a causal relationship between mitochondrial metabolism and fate choice of HSCs and also provide a valuable tool to expand HSCs outside of their native bone marrow niches., Competing Interests: N.V., M.P.L., J.A., O.N., M.G. are authors on a patent entitled ‘Methods compounds useful in hematopoietic stem cell medicine' patent number P1828EP00 (2016). The remaining authors declare no competing financial interests.

NAD + is a vital redox cofactor and a substrate required for activity of various enzyme families, including sirtuins and poly(ADP-ribose) polymerases. Supplementation with NAD + precursors, such as nicotinamide mononucleotide (NMN) or nicotinamide riboside (NR), protects against metabolic disease, neurodegenerative disorders and age-related physiological decline in mammals. Here we show that nicotinamide riboside kinase 1 (NRK1) is necessary and rate-limiting for the use of exogenous NR and NMN for NAD + synthesis. Using genetic gain- and loss-of-function models, we further demonstrate that the role of NRK1 in driving NAD + synthesis from other NAD + precursors, such as nicotinamide or nicotinic acid, is dispensable. Using stable isotope-labelled compounds, we confirm NMN is metabolized extracellularly to NR that is then taken up by the cell and converted into NAD + . Our results indicate that mammalian cells require conversion of extracellular NMN to NR for cellular uptake and NAD + synthesis, explaining the overlapping metabolic effects observed with the two compounds.

Mitochondrial dysfunction is at the core of many diseases ranging from inherited metabolic diseases to common conditions that are associated with aging. Although associations between aging and mitochondrial function have been identified using mammalian models, much of the mechanistic insight has emerged from Caenorhabditis elegans. Mitochondrial respiration is recognized as an indicator of mitochondrial health. The Seahorse XF96 respirometer represents the state-of-the-art platform for assessing respiration in cells, and we adapted the technique for applications involving C. elegans. Here we provide a detailed protocol to optimize and measure respiration in C. elegans with the XF96 respirometer, including the interpretation of parameters and results. The protocol takes ∼2 d to complete, excluding the time spent culturing C. elegans, and it includes (i) the preparation of C. elegans samples, (ii) selection and loading of compounds to be injected, (iii) preparation and execution of a run with the XF96 respirometer and (iv) postexperimental data analysis, including normalization. In addition, we compare our XF96 application with other existing techniques, including the eight-well Seahorse XFp. The main benefits of the XF96 include the limited number of worms required and the high throughput capacity due to the 96-well format., Competing Interests: The authors declare that they have no competing financial interests.

Mitochondria participate in crucial cellular processes such as energy harvesting and intermediate metabolism. Although mitochondria possess their own genome--a vestige of their bacterial origins and endosymbiotic evolution--most mitochondrial proteins are encoded in the nucleus. The expression of the mitochondrial proteome hence requires tight coordination between the two genomes to adapt mitochondrial function to the ever-changing cellular milieu. In this Review, we focus on the pathways that coordinate the communication between mitochondria and the nucleus during homeostasis and mitochondrial stress. These pathways include nucleus-to-mitochondria (anterograde) and mitochondria-to-nucleus (retrograde) communication, mitonuclear feedback signalling and proteostasis regulation, the integrated stress response and non-cell-autonomous communication. We discuss how mitonuclear communication safeguards cellular and organismal fitness and regulates lifespan.

Phenome-wide association is a novel reverse genetic strategy to analyze genome-to-phenome relations in human clinical cohorts. Here we test this approach using a large murine population segregating for ∼5 million sequence variants, and we compare our results to those extracted from a matched analysis of gene variants in a large human cohort. For the mouse cohort, we amassed a deep and broad open-access phenome consisting of ∼4,500 metabolic, physiological, pharmacological and behavioural traits, and more than 90 independent expression quantitative trait locus (QTL), transcriptome, proteome, metagenome and metabolome data sets--by far the largest coherent phenome for any experimental cohort (www.genenetwork.org). We tested downstream effects of subsets of variants and discovered several novel associations, including a missense mutation in fumarate hydratase that controls variation in the mitochondrial unfolded protein response in both mouse and Caenorhabditis elegans, and missense mutations in Col6a5 that underlies variation in bone mineral density in both mouse and human.

Reversible acetylation was initially described as an epigenetic mechanism regulating DNA accessibility. Since then, this process has emerged as a controller of histone and nonhistone acetylation that integrates key physiological processes such as metabolism, circadian rhythm and cell cycle, along with gene regulation in various organisms. The widespread and reversible nature of acetylation also revitalized interest in the mechanisms that regulate lysine acetyltransferases (KATs) and deacetylases (KDACs) in health and disease. Changes in protein or histone acetylation are especially relevant for many common diseases including obesity, diabetes mellitus, neurodegenerative diseases and cancer, as well as for some rare diseases such as mitochondrial diseases and lipodystrophies. In this Review, we examine the role of reversible acetylation in metabolic control and how changes in levels of metabolites or cofactors, including nicotinamide adenine dinucleotide, nicotinamide, coenzyme A, acetyl coenzyme A, zinc and butyrate and/or β-hydroxybutyrate, directly alter KAT or KDAC activity to link energy status to adaptive cellular and organismal homeostasis.

The vitamin D endocrine system has many extraskeletal targets, including adipose tissue. 1,25-Dihydroxyvitamin D₃, the active form of vitamin D, not only increases adipogenesis and the expression of typical adipocyte genes but also decreases the expression of uncoupling proteins. Mice with disrupted vitamin D action--owing to gene deletion of the nuclear receptor vitamin D receptor (Vdr) or the gene encoding 1α-hydroxylase (Cyp27b1)--lose fat mass over time owing to an increase in energy expenditure, whereas mice with increased Vdr-mediated signalling in adipose tissue become obese. The resistance to diet-induced obesity in mice with disrupted Vdr signalling is caused at least partially by increased expression of uncoupling proteins in white adipose tissue. However, the bile acid pool is also increased in these animals, and bile acids are known to be potent inducers of energy expenditure through activation of several nuclear receptors, including Vdr, and G-protein-coupled receptors, such as GPBAR1 (also known as TGR5). By contrast, in humans, obesity is strongly associated with poor vitamin D status. A causal link has not been firmly proven, but most intervention studies have failed to demonstrate a beneficial effect of vitamin D supplementation on body weight. The reasons for the major discrepancy between mouse and human data are unclear, but understanding the link between vitamin D status and energy homeostasis could potentially be very important for the human epidemic of obesity and the metabolic syndrome.

Mitochondrial dysfunction is not only a hallmark of rare inherited mitochondrial disorders but also implicated in age-related diseases, including those that affect the metabolic and nervous system, such as type 2 diabetes and Parkinson's disease. Numerous pathways maintain and/or restore proper mitochondrial function, including mitochondrial biogenesis, mitochondrial dynamics, mitophagy and the mitochondrial unfolded protein response. New and powerful phenotypic assays in cell-based models as well as multicellular organisms have been developed to explore these different aspects of mitochondrial function. Modulating mitochondrial function has therefore emerged as an attractive therapeutic strategy for several diseases, which has spurred active drug discovery efforts in this area.

Since the beginning of the century, the mammalian sirtuin protein family (comprising SIRT1-SIRT7) has received much attention for its regulatory role, mainly in metabolism and ageing. Sirtuins act in different cellular compartments: they deacetylate histones and several transcriptional regulators in the nucleus, but also specific proteins in other cellular compartments, such as in the cytoplasm and in mitochondria. As a consequence, sirtuins regulate fat and glucose metabolism in response to physiological changes in energy levels, thereby acting as crucial regulators of the network that controls energy homeostasis and as such determines healthspan.

We present a consolidated view of the complexity and challenges of designing studies for measurement of energy metabolism in mouse models, including a practical guide to the assessment of energy expenditure, energy intake and body composition and statistical analysis thereof. We hope this guide will facilitate comparisons across studies and minimize spurious interpretations of data. We recommend that division of energy expenditure data by either body weight or lean body weight and that presentation of group effects as histograms should be replaced by plotting individual data and analyzing both group and body-composition effects using analysis of covariance (ANCOVA).

Bile acids are increasingly being appreciated as complex metabolic integrators and signalling factors and not just as lipid solubilizers and simple regulators of bile-acid homeostasis. It is therefore not surprising that a number of bile-acid-activated signalling pathways have become attractive therapeutic targets for metabolic disorders. Here, we review how the signalling functions of bile acids can be exploited in the development of drugs for obesity, type 2 diabetes, hypertriglyceridaemia and atherosclerosis, as well as other associated chronic diseases such as non-alcoholic steatohepatitis.