Metabolic homeostasis requires that cellular energy levels are adapted to environmental cues. This adaptation is largely regulated at the transcriptional level, through the interaction between transcription factors, coregulators, and the basal transcriptional machinery. Coregulators, which function both as metabolic sensors and transcriptional effectors, are ideally positioned to synchronize metabolic pathways to environmental stimuli. The balance between inhibitory actions of corepressors and stimulatory effects of coactivators enables the fine-tuning of metabolic processes. The tight regulation opens therapeutic opportunities to manage metabolic dysfunction, by directing the activity of cofactors towards specific transcription factors, pathways, or cells/tissues, thereby restoring whole body metabolic homeostasis.
We previously demonstrated that the deletion of the poly(ADP-ribose)polymerase (Parp)-1 gene in mice enhances oxidative metabolism, thereby protecting against diet-induced obesity. However, the therapeutic use of PARP inhibitors to enhance mitochondrial function remains to be explored. Here, we show tight negative correlation between Parp-1 expression and energy expenditure in heterogeneous mouse populations, indicating that variations in PARP-1 activity have an impact on metabolic homeostasis. Notably, these genetic correlations can be translated into pharmacological applications. Long-term treatment with PARP inhibitors enhances fitness in mice by increasing the abundance of mitochondrial respiratory complexes and boosting mitochondrial respiratory capacity. Furthermore, PARP inhibitors reverse mitochondrial defects in primary myotubes of obese humans and attenuate genetic defects of mitochondrial metabolism in human fibroblasts and C. elegans. Overall, our work validates in worm, mouse and human models that PARP inhibition may be used to treat both genetic and acquired muscle dysfunction linked to defective mitochondrial function.
Studies of the real-time dynamics of embryonic development require a gentle embryo
handling method, the possibility of long-term live imaging during the complete
embryogenesis, as well as of parallelization providing a population’s
statistics, while keeping single embryo resolution. We describe an automated
approach that fully accomplishes these requirements for embryos of Caenorhabditis
elegans, one of the most employed model organisms in biomedical research. We
developed a microfluidic platform which makes use of pure passive hydrodynamics to
run on-chip worm cultures, from which we obtain synchronized embryo populations, and
to immobilize these embryos in incubator microarrays for long-term high-resolution
optical imaging. We successfully employ our platform to investigate morphogenesis
and mitochondrial biogenesis during the full embryonic development and elucidate the
role of the mitochondrial unfolded protein response (UPRmt) within
C. elegans embryogenesis. Our method can be generally used for protein
expression and developmental studies at the embryonic level, but can also provide
clues to understand the aging process and age-related diseases in particular.
Primary brain tumors are presently classified based on imaging and histopathological
techniques, which remains unsatisfaying. We profiled here by quantitative real time
PCR (qRT-PCR) the transcripts of eighteen histone deacetylases (HDACs) and a subset
of transcriptional co-factors in non-tumoral brain samples from 15 patients operated
for epilepsia and in brain tumor samples from 50 patients diagnosed with grade II
oligodendrogliomas (ODII, n = 9), grade III oligodendrogliomas (ODIII, n = 22) and
glioblastomas (GL, n = 19). Co-factor transcripts were significantly different in
tumors as compared to non-tumoral samples and distinguished different molecular
subgroups of brain tumors, regardless of tumor grade. Among all patients studied,
the expression of HDAC1 and HDAC3 was inversely correlated with
survival, whereas the expression of HDAC4, HDAC5, HDAC6,
HDAC11 and SIRT1 was significantly and positively correlated with
survival time of patients with gliomas. 1H-HRMAS technology revealed
metabolomically distinct groups according to the expression of HDAC1, HDAC4 and
SIRT1, suggesting that these genes may play an important role in regulating brain
tumorigenesis and cancer progression. Our study hence identified different molecular
fingerprints for subgroups of histopathologically similar brain tumors that may
enable the prediction of outcome based on the expression level of co-factor genes
and could allow customization of treatment.
Non-alcoholic fatty liver disease (NAFLD) affects up to 30% of the adult population in Western societies, yet the underlying molecular pathways remain poorly understood. Here, we identify the dimeric Activator Protein 1 as a regulator of NAFLD. The Fos-related antigen 1 (Fra-1) and 2 (Fra-2) prevent dietary NAFLD by inhibiting pro-steatotic PPARγ signaling. Moreover, established NAFLD and the associated liver damage can be efficiently reversed by hepatocyte-specific Fra-1 expression. In contrast, c-Fos promotes PPARγ expression, while c-Jun exerts opposing, dimer-dependent functions. Interestingly, JunD was found to be essential for PPARγ signaling and NAFLD development. This unique antagonistic regulation of PPARγ by distinct AP-1 dimers occurs at the transcriptional level and establishes AP-1 as a link between obesity, hepatic lipid metabolism and NAFLD.
NAFLD; Steatosis; Activator Protein 1; PPARγ; Lipids; Transcription
TGR5 is a G-protein-coupled receptor
(GPCR) mediating cellular
responses to bile acids (BAs). Although some efforts have been devoted
to generate homology models of TGR5 and draw structure–activity
relationships of BAs, none of these studies has hitherto described
how BAs bind to TGR5. Here, we present an integrated computational,
chemical, and biological approach that has been instrumental to determine
the binding mode of BAs to TGR5. As a result, key residues have been
identified that are involved in mediating the binding of BAs to the
receptor. Collectively, these results provide new hints to design
potent and selective TGR5 agonists.
Bile acids; TGR5; diabetes; GPCR; site-directed mutagenesis; homology modeling; molecular docking
PPARγ-dependent gene expression during adipogenesis is facilitated by ADP-ribosyltransferase D-type 1 (ARTD1; PARP1)-catalyzed poly-ADP-ribose (PAR) formation. Adipogenesis is accompanied by a dynamic modulation of the chromatin landscape at PPARγ target genes by ligand-dependent co-factor exchange. However, how endogenous PPARγ ligands, which have a low affinity for the receptor and are present at low levels in the cell, can induce sufficient co-factor exchange is unknown. Moreover, the significance of PAR formation in PPARγ-regulated adipose tissue function is also unknown. Here, we show that inhibition of PAR formation in mice on a high-fat diet reduces weight gain and cell size of adipocytes, as well as PPARγ target gene expression in white adipose tissue. Mechanistically, topoisomerase II activity induces ARTD1 recruitment to PPARγ target genes, and ARTD1 automodification enhances ligand binding to PPARγ, thus promoting sufficient transcriptional co-factor exchange in adipocytes. Thus, ARTD1-mediated PAR formation during adipogenesis is necessary to adequately convey the low signal of endogenous PPARγ ligand to effective gene expression. These results uncover a new regulatory mechanism of ARTD1-induced ADP-ribosylation and highlight its importance for nuclear factor-regulated gene expression.
In recent years the role of acetylation has gained ground as an essential modulator of intermediary metabolism in skeletal muscle. Imbalance in energy homeostasis or chronic cellular stress, due to diet, aging or disease, translate into alterations in the acetylation levels of key proteins which governs bioenergetics, cellular substrate use and/or changes in mitochondrial content and function. For example, cellular stress induced by exercise or caloric restriction can alter the coordinated activity of acetyltransferases and deacetylases to increase mitochondrial biogenesis and function in order to adapt to low energetic levels. The natural duality of these enzymes, as metabolic sensors and effector proteins, have helped biologists understand how the body can integrate seemingly distinct signaling pathways to control mitochondrial biogenesis, insulin sensitivity, glucose transport, reactive oxygen species handling, angiogenesis and muscle satellite cell proliferation/differentiation. Our review will summarize the recent developments related to acetylation dependent responses following metabolic stress in skeletal muscle.
Acetylation; Sirtuins; Muscle adaptation; Energy stress; Oxidative Metabolisms; glucose homeostasis
Macrophage-mediated inflammation is a major contributor to obesity-associated insulin resistance. The co-repressor NCoR interacts with inflammatory pathway genes in macrophages, suggesting that its removal would result in increased activity of inflammatory responses. Surprisingly, we find that macrophage-specific deletion of NCoR instead results in an anti-inflammatory phenotype along with robust systemic insulin sensitization in obese mice. We present evidence that de-repression of LXRs contributes to this paradoxical anti-inflammatory phenotype by causing increased expression of genes that direct biosynthesis of palmitoleic acid and ω3 fatty acids. Remarkably, the increased ω3 fatty acid levels primarily inhibit NF-κB-dependent inflammatory responses by uncoupling NF-κB binding and enhancer/promoter histone acetylation from subsequent steps required for pro-inflammatory gene activation. This provides a mechanism for the in vivo anti-inflammatory insulin sensitive phenotype observed in mice with macrophage-specific deletion of NCoR. Therapeutic methods to harness this mechanism could lead to a new approach to insulin sensitizing therapies.
nuclear co-repressor; insulin resistance; obesity; macrophage; inflammation
The BXD genetic reference population is a recombinant inbred panel descended from crosses between the C57BL/6 (B6) and DBA/2 (D2) strains of mice, which segregate for about 5 million sequence variants. Recently, some of these variants have been established with effects on general metabolic phenotypes such as glucose response and bone strength. Here we phenotype 43 BXD strains and observe they have large variation (∼5-fold) in their spontaneous activity during waking hours. QTL analyses indicate that ∼40% of this variance is attributable to a narrow locus containing the aryl hydrocarbon receptor (Ahr), a basic helix-loop-helix transcription factor with well-established roles in development and xenobiotic metabolism. Strains with the D2 allele of Ahr have reduced gene expression compared to those with the B6 allele, and have significantly higher spontaneous activity. This effect was also observed in B6 mice with a congenic D2 Ahr interval, and in B6 mice with a humanized AHR allele which, like the D2 allele, is expressed much less and has less enzymatic activity than the B6 allele. Ahr is highly conserved in invertebrates, and strikingly inhibition of its orthologs in D. melanogaster and C. elegans (spineless and ahr-1) leads to marked increases in basal activity. In mammals, Ahr has numerous ligands, but most are either non-selective (e.g. resveratrol) or highly toxic (e.g., 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)). Thus, we chose to examine a major environmental influence—long term feeding with high fat diet (HFD)—to see if the effects of Ahr are dependent on major metabolic differences. Interestingly, while HFD robustly halved movement across all strains, the QTL position and effects of Ahr remained unchanged, indicating that the effects are independent. The highly consistent effects of Ahr on movement indicate that changes in its constitutive activity have a role on spontaneous movement and may influence human behavior.
Using 43 strains from the BXD mouse reference population, we observed a 5-fold difference in spontaneous activity. QTL analysis indicated that ∼40% of this variance is due to the aryl hydrocarbon receptor (Ahr). Ahr is a conserved transcription factor found in nearly all multicellular organisms and implicated in a multitude of functions, ranging across development, liver metabolism, and neuronal health. This gene is highly variant in the BXDs, and strains with the low-active Ahr allele have significantly higher voluntary locomotion. This increase is also observed in independent mouse models, which have reduced Ahr activity, including in transgenic mice with humanized AHR. Furthermore, decreasing Ahr expression in C. elegans and Drosophila causes similar, robust increases in spontaneous movement. This link is independent of major environmental perturbations as well: BXD strains fed high fat diet long-term move only half as much as their chow-fed brethren, yet the effects of Ahr were consistent and equally strong in both dietary cohorts. While Ahr is a highly liganded transcription factor in mammals, these data indicate that modifications to its constitutive activity are sufficient to control movement. However, certain ligands may be able to specifically act on this phenotypic aspect of the gene.
Sirtuins can promote deacetylation of a wide range of substrates in diverse cellular compartments and regulate many cellular processes1,2. Recently Narayan et al., reported that SIRT2 was required for necroptosis based on their findings that SIRT2 inhibition, knock-down or knock-out prevented necroptosis. We sought to confirm and explore the role of SIRT2 in necroptosis and tested four different sources of the SIRT2 inhibitor AGK2, three independent siRNAs against SIRT2, and cells from two independently generated Sirt2−/− mouse strains, however we were unable to show that inhibiting or depleting SIRT2 protected cells from necroptosis. Furthermore, Sirt2−/− mice succumbed to TNF induced Systemic Inflammatory Response Syndrome (SIRS) more rapidly than wild type mice while Ripk3−/− mice were resistant. Our results therefore question the importance of SIRT2 in the necroptosis cell death pathway.
SIRT2 belongs to a highly conserved family of NAD+-dependent deacylases, consisting of seven members (SIRT1–SIRT7), which vary in subcellular localizations and have substrates ranging from histones to transcription factors and enzymes. Recently SIRT2 was revealed to play an important role in inflammation, directly binding, deacetylating, and inhibiting the p65 subunit of NF-κB.
A Sirt2 deficient mouse line (Sirt2−/−) was generated by deleting exons 5–7, encoding part of the SIRT2 deacetylase domain, by homologous recombination. Age- and sex-matched Sirt2−/− and Sirt2+/+ littermate mice were subjected to dextran sulfate sodium (DSS)-induced colitis and analyzed for colitis susceptibility.
Sirt2−/− mice displayed more severe clinical and histological manifestations after DSS colitis compared to wild type littermates. Notably, under basal condition, Sirt2 deficiency does not affect the basal phenotype and intestinal morphology Sirt2 deficiency, however, affects macrophage polarization, creating a pro-inflammatory milieu in the immune cells compartment.
These data confirm a protective role for SIRT2 against the development of inflammatory processes, pointing out a potential role for this sirtuin as a suppressor of colitis. In fact, SIRT2 deletion promotes inflammatory responses by increasing NF-κB acetylation and by reducing the M2-associated anti-inflammatory pathway. Finally, we speculate that the activation of SIRT2 may be a potential approach for the treatment of inflammatory bowel disease.
NAD+ is an important co-factor regulating metabolic homeostasis and a rate-limiting substrate for sirtuin deacylase. We show that NAD+ levels are reduced in aged mice and C. elegans and that decreasing NAD+ levels results in a further reduction in worm lifespan. Conversely, genetic or pharmacological restoration of NAD+ prevents age-associated metabolic decline and promotes longevity in worms. These effects are dependent upon the protein deacetylase sir-2.1 and involve the induction of mitonuclear protein imbalance as well as activation of stress signaling via the mitochondrial unfolded protein response (UPRmt) and the nuclear translocation and activation of FOXO transcription factor DAF-16. Our data suggest that augmenting mitochondrial stress signaling through the modulation of NAD+ levels may be a target to improve mitochondrial function and prevent or treat age-associated decline.
Dysfunction of Paneth and goblet cells in the intestine contributes to inflammatory bowel disease (IBD) and colitis-associated colorectal cancer (CAC). Here, we report a role for the NAD+-dependent histone deacetylase SIRT1 in the control of anti-bacterial defense. Mice with an intestinal specific Sirt1 deficiency (Sirt1int−/−) have more Paneth and goblet cells with a consequent rearrangement of the gut microbiota. From a mechanistic point of view, the effects on mouse intestinal cell maturation are mediated by SIRT1-dependent changes in the acetylation status of SPDEF, a master regulator of Paneth and goblet cells. Our results suggest that targeting SIRT1 may be of interest in the management of IBD and CAC.
Macrophages are important for maintaining intestinal immune homeostasis. Here, we show that PPARβ/δ (peroxisome proliferator-activated receptor β/δ) directly regulates CD300a in macrophages that express the immunoreceptor tyrosine based-inhibitory motif (ITIM)-containing receptor. In mice lacking CD300a, high-fat diet (HFD) causes chronic intestinal inflammation with low numbers of intestinal lymph capillaries and dramatically expanded mesenteric lymph nodes. As a result, these mice exhibit triglyceride malabsorption and reduced body weight gain on HFD. Peritoneal macrophages from Cd300a−/− mice on HFD are classically M1 activated. Activation of toll-like receptor 4 (TLR4)/MyD88 signaling by lipopolysaccharide (LPS) results in prolonged IL-6 secretion in Cd300a−/− macrophages. Bone marrow transplantation confirmed that the phenotype originates from CD300a deficiency in leucocytes. These results identify CD300a-mediated inhibitory signaling in macrophages as a critical regulator of intestinal immune homeostasis.
Mitochondria are semi-autonomous organelles regulated by a complex network of proteins that are vital for many cellular functions. Because mitochondrial modulators can impact many aspects of cellular homeostasis, their identification and validation has proven challenging. It requires the measurement of multiple parameters in parallel to understand the exact nature of the changes induced by such compounds. We developed a platform of assays scoring for mitochondrial function in two complementary models systems, mammalian cells and C. elegans. We first optimized cell culture conditions and established the mitochondrial signature of 1,200 FDA-approved drugs in liver cells. Using cell-based and C. elegans assays, we further defined the metabolic effects of two pharmacological classes that emerged from our hit list, i.e. imidazoles and statins. We found that these two drug classes affect respiration through different and cholesterol-independent mechanisms in both models. Our screening strategy enabled us to unequivocally identify compounds that have toxic or beneficial effects on mitochondrial activity. Furthermore, the cross-species approach provided novel mechanistic insight and allowed early validation of hits that act on mitochondrial function.
We identified a mutation in the Diet1 gene in a mouse strain that is resistant to hyperlipidemia and atherosclerosis. Diet1 encodes a 236 kD protein consisting of tandem low density lipoprotein receptor and MAM (meprin-A5-protein tyrosine phosphatase mu) domains, and is expressed in enterocytes of the small intestine. Diet1-deficient mice exhibited an elevated bile acid pool size and impaired feedback regulation of hepatic Cyp7a1, which encodes the rate-limiting enzyme in bile acid synthesis. In mouse intestine and in cultured human intestinal cells, Diet1 expression levels influenced the production of fibroblast growth factor 15/19 (FGF15/19), a hormone that signals from the intestine to liver to regulate Cyp7a1. Transgenic expression of Diet1, or adenoviral-mediated Fgf15 expression, restored normal Cyp7a1 regulation in Diet-1–deficient mice. Diet1 and FGF19 proteins exhibited overlapping subcellular localization in cultured intestinal cells. These results establish Diet1 as a control point in enterohepatic bile acid signaling and lipid homeostasis.
Mitochondrial disorders are highly heterogeneous conditions characterized by defects of the mitochondrial respiratory chain. Pharmacological activation of mitochondrial biogenesis has been proposed as an effective means to correct the biochemical defects and ameliorate the clinical phenotype in these severely disabling, often fatal, disorders. Pathways related to mitochondrial biogenesis are targets of Sirtuin1, a NAD+-dependent protein deacetylase. As NAD+ boosts the activity of Sirtuin1 and other sirtuins, intracellular levels of NAD+ play a key role in the homeostatic control of mitochondrial function by the metabolic status of the cell. We show here that supplementation with nicotinamide riboside, a natural NAD+ precursor, or reduction of NAD+ consumption by inhibiting the poly(ADP-ribose) polymerases, leads to marked improvement of the respiratory chain defect and exercise intolerance of the Sco2 knockout/knockin mouse, a mitochondrial disease model characterized by impaired cytochrome c oxidase biogenesis. This strategy is potentially translatable into therapy of mitochondrial disorders in humans.
•NAD+ is a substrate activator of Sirtuin 1, a key player of mitochondrial biogenesis•Parp1 inhibitors and nicotinamide riboside increase the NAD+ content in tissues•These compounds improve the phenotype of a mitochondrial disease mouse model•These are potential therapies for human mitochondrial disorders
Human mitochondrial disorders are heterogenous in nature and are crippling. Cerutti et al. correct the respiratory chain defect and exercise intolerance of the Sco2 knockout/knockin model through pharmacological activation of Sirt1-dependent mitochondrial biogenesis. Their results highlight the concept of a potential general therapeutic strategy in genetically diverse mitochondrial disorders.
Nutrient availability is the major regulator of life and reproduction, and a complex cellular signaling network has evolved to adapt organisms to fasting. These sensor pathways monitor cellular energy metabolism, especially mitochondrial ATP production and NAD+/NADH ratio, as major signals for nutritional state. We hypothesized that these signals would be modified by mitochondrial respiratory chain disease, because of inefficient NADH utilization and ATP production. Oral administration of nicotinamide riboside (NR), a vitamin B3 and NAD+ precursor, was previously shown to boost NAD+ levels in mice and to induce mitochondrial biogenesis. Here, we treated mitochondrial myopathy mice with NR. This vitamin effectively delayed early- and late-stage disease progression, by robustly inducing mitochondrial biogenesis in skeletal muscle and brown adipose tissue, preventing mitochondrial ultrastructure abnormalities and mtDNA deletion formation. NR further stimulated mitochondrial unfolded protein response, suggesting its protective role in mitochondrial disease. These results indicate that NR and strategies boosting NAD+ levels are a promising treatment strategy for mitochondrial myopathy.
mitochondrial myopathy; NAD+; nicotinamide riboside; treatment; unfolded protein response
For reasons that remain unclear, whether type 5 AC (AC5), one of two major AC isoforms in heart, is protective or deleterious in response to cardiac stress is controversial. To reconcile this controversy we examined the cardiomyopathy induced by chronic isoproterenol (ISO) in AC5 transgenic (Tg) mice and the signaling mechanisms involved.
Methods and Results
Chronic ISO increased oxidative stress and induced more severe cardiomyopathy in AC5 Tg, as left ventricular (LV) ejection fraction fell 1.9 fold more than wild type (WT), along with greater LV dilation and increased fibrosis, apoptosis and hypertrophy. Oxidative stress induced by chronic ISO, detected by 8-OhDG was 15% greater, p=0.007, in AC5 Tg hearts, while protein expression of MnSOD was reduced by 38%, indicating that the susceptibility of AC5 Tg to cardiomyopathy may be due to decreased MnSOD expression. Consistent with this, susceptibility of the AC5 Tg to cardiomyopathy was suppressed by overexpression of MnSOD, whereas protection afforded by the AC5 KO was lost in AC5 KO×MnSOD+/− mice. Elevation of MnSOD was eliminated by both sirtuin and MEK inhibitors, suggesting both the SIRT1/FoxO3a and MEK/ERK pathway are involved in MnSOD regulation by AC5.
Overexpression of AC5 exacerbates the cardiomyopathy induced by chronic catecholamine stress by altering regulation of SIRT1/FoxO3a, MEK/ERK and MnSOD, resulting in oxidative stress intolerance, thereby shedding light on new approaches for treatment of heart failure.
Adenylyl cyclase; Adrenergic; Cardiomyopathy; Oxidative Stress
The deacetylase sirtuin 1 (Sirt1) exerts beneficial effects on lipid metabolism, but its roles in plasma LDL-cholesterol regulation and atherosclerosis are controversial. Thus, we applied the pharmacological Sirt1 activator SRT3025 in a mouse model of atherosclerosis and in hepatocyte culture.
Methods and results
Apolipoprotein E-deficient (Apoe−/−) mice were fed a high-cholesterol diet (1.25% w/w) supplemented with SRT3025 (3.18 g kg−1 diet) for 12 weeks. In vitro, the drug activated wild-type Sirt1 protein, but not the activation-resistant Sirt1 mutant; in vivo, it increased deacetylation of hepatic p65 and skeletal muscle Foxo1. SRT3025 treatment decreased plasma levels of LDL-cholesterol and total cholesterol and reduced atherosclerosis. Drug treatment did not change mRNA expression of hepatic LDL receptor (Ldlr) and proprotein convertase subtilisin/kexin type 9 (Pcsk9), but increased their protein expression indicating post-translational effects. Consistent with hepatocyte Ldlr and Pcsk9 accumulation, we found reduced plasma levels of Pcsk9 after pharmacological Sirt1 activation. In vitro administration of SRT3025 to cultured AML12 hepatocytes attenuated Pcsk9 secretion and its binding to Ldlr, thereby reducing Pcsk9-mediated Ldlr degradation and increasing Ldlr expression and LDL uptake. Co-administration of exogenous Pcsk9 with SRT3025 blunted these effects. Sirt1 activation with SRT3025 in Ldlr−/− mice reduced neither plasma Pcsk9, nor LDL-cholesterol levels, nor atherosclerosis.
We identify reduction in Pcsk9 secretion as a novel effect of Sirt1 activity and uncover Ldlr as a prerequisite for Sirt1-mediated atheroprotection in mice. Pharmacological activation of Sirt1 appears promising to be tested in patients for its effects on plasma Pcsk9, LDL-cholesterol, and atherosclerosis.
Sirt1; LDL-cholesterol; Pcsk9; LDL receptor; Atherogenesis
Mitochondrial dysfunction is not only a hallmark of rare inherited mitochondrial disorders, but is 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 a range of diseases, which has spurred active drug discovery efforts in this area.
Resveratrol is a natural compound that affects energy metabolism and mitochondrial function and serves as a calorie restriction mimetic, at least in animal models of obesity. Here we treated 11 healthy, obese men with placebo and 150 mg/day resveratrol in a randomized double-blind cross-over study for 30 days. Resveratrol significantly reduced sleeping- and resting metabolic rate. In muscle, resveratrol activated AMPK, increased SIRT1 and PGC-1α protein levels, increased citrate synthase activity without change in mitochondrial content, and improved muscle mitochondrial respiration on a fatty acid-derived substrate. Furthermore, resveratrol elevated intramyocellular lipid levels, and decreased intrahepatic lipid content, circulating glucose, triglycerides, alanine-aminotransferase, and inflammation markers. Systolic blood pressure dropped and HOMA index improved after resveratrol. In the postprandial state, adipose tissue lipolysis and plasma fatty acid and glycerol decreased. In conclusion, we demonstrate that 30 days of resveratrol supplementation induces metabolic changes in obese humans, mimicking the effects of calorie restriction.
Sirt3 is a mitochondrial NAD+-dependent deacetylase that governs mitochondrial metabolism and reactive oxygen species homeostasis. Sirt3 deficiency has been reported to accelerate the development of the metabolic syndrome. However, the role of Sirt3 in atherosclerosis remains enigmatic. We aimed to investigate whether Sirt3 deficiency affects atherosclerosis, plaque vulnerability, and metabolic homeostasis. Low-density lipoprotein receptor knockout (LDLR−/−) and LDLR/Sirt3 double-knockout (Sirt3−/−LDLR−/−) mice were fed a high-cholesterol diet (1.25 % w/w) for 12 weeks. Atherosclerosis was assessed en face in thoraco-abdominal aortae and in cross sections of aortic roots. Sirt3 deletion led to hepatic mitochondrial protein hyperacetylation. Unexpectedly, though plasma malondialdehyde levels were elevated in Sirt3-deficient mice, Sirt3 deletion affected neither plaque burden nor features of plaque vulnerability (i.e., fibrous cap thickness and necrotic core diameter). Likewise, plaque macrophage and T cell infiltration as well as endothelial activation remained unaltered. Electron microscopy of aortic walls revealed no difference in mitochondrial microarchitecture between both groups. Interestingly, loss of Sirt3 was associated with accelerated weight gain and an impaired capacity to cope with rapid changes in nutrient supply as assessed by indirect calorimetry. Serum lipid levels and glucose tolerance were unaffected by Sirt3 deletion in LDLR−/− mice. Sirt3 deficiency does not affect atherosclerosis in LDLR−/− mice. However, Sirt3 controls systemic levels of oxidative stress, limits expedited weight gain, and allows rapid metabolic adaptation. Thus, Sirt3 may contribute to postponing cardiovascular risk factor development.
Electronic supplementary material
The online version of this article (doi:10.1007/s00395-013-0399-0) contains supplementary material, which is available to authorized users.
SIRTUIN 3; Atherosclerosis; Metabolism; Oxidative stress
Nicotinamide adenine dinucleotide (NAD) is a central metabolic cofactor by virtue of its redox capacity, and as such regulates a wealth of metabolic transformations. However, the identification of the longevity protein Sir2, the founding member of the sirtuin protein family, as being NAD+-dependent reignited interest in this metabolite. The sirtuins (SIRT1-7 in mammals) utilize NAD+ to deacetylate proteins in different subcellular compartments with a variety of functions, but with a strong convergence on optimizing mitochondrial function. Since cellular NAD+ levels are limiting for sirtuin activity, boosting its levels is a powerful means to activate sirtuins as a potential therapy for mitochondrial, often age-related, diseases. Indeed, supplying excess precursors, or blocking its utilization by PARP enzymes or CD38/CD157, boosts NAD+ levels, activates sirtuins and promotes healthy aging. Here, we discuss the current state of knowledge of NAD+ metabolism, primarily in relation to sirtuin function. We highlight how NAD+ levels change in diverse physiological conditions, and how this can be employed as a pharmacological strategy.
Aging; Metabolism; Mitochondria; PARPs; Sirtuins