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2.  Mitochondria, Energetics, Epigenetics, and Cellular Responses to Stress 
Environmental Health Perspectives  2014;122(12):1271-1278.
Background: Cells respond to environmental stressors through several key pathways, including response to reactive oxygen species (ROS), nutrient and ATP sensing, DNA damage response (DDR), and epigenetic alterations. Mitochondria play a central role in these pathways not only through energetics and ATP production but also through metabolites generated in the tricarboxylic acid cycle, as well as mitochondria–nuclear signaling related to mitochondria morphology, biogenesis, fission/fusion, mitophagy, apoptosis, and epigenetic regulation.
Objectives: We investigated the concept of bidirectional interactions between mitochondria and cellular pathways in response to environmental stress with a focus on epigenetic regulation, and we examined DNA repair and DDR pathways as examples of biological processes that respond to exogenous insults through changes in homeostasis and altered mitochondrial function.
Methods: The National Institute of Environmental Health Sciences sponsored the Workshop on Mitochondria, Energetics, Epigenetics, Environment, and DNA Damage Response on 25–26 March 2013. Here, we summarize key points and ideas emerging from this meeting.
Discussion: A more comprehensive understanding of signaling mechanisms (cross-talk) between the mitochondria and nucleus is central to elucidating the integration of mitochondrial functions with other cellular response pathways in modulating the effects of environmental agents. Recent studies have highlighted the importance of mitochondrial functions in epigenetic regulation and DDR with environmental stress. Development and application of novel technologies, enhanced experimental models, and a systems-type research approach will help to discern how environmentally induced mitochondrial dysfunction affects key mechanistic pathways.
Conclusions: Understanding mitochondria–cell signaling will provide insight into individual responses to environmental hazards, improving prediction of hazard and susceptibility to environmental stressors.
Citation: Shaughnessy DT, McAllister K, Worth L, Haugen AC, Meyer JN, Domann FE, Van Houten B, Mostoslavsky R, Bultman SJ, Baccarelli AA, Begley TJ, Sobol RW, Hirschey MD, Ideker T, Santos JH, Copeland WC, Tice RR, Balshaw DM, Tyson FL. 2014. Mitochondria, energetics, epigenetics, and cellular responses to stress. Environ Health Perspect 122:1271–1278; http://dx.doi.org/10.1289/ehp.1408418
doi:10.1289/ehp.1408418
PMCID: PMC4256704  PMID: 25127496
3.  Measurement of Fatty Acid Oxidation Rates in Animal Tissues and Cell Lines 
Methods in enzymology  2014;542:391-405.
While much oncological research has focused on metabolic shifts in glucose and amino acid oxidation, recent evidence suggests that fatty acid oxidation (FAO) may also play an important role in the metabolic reprogramming of cancer cells. Here, we present a simple method for measuring FAO rates using radiolabeled palmitate, common laboratory reagents, and standard supplies. This protocol is broadly applicable for measuring FAO rates in cultured cancer cells as well as in both malignant and nontransformed animal tissues.
doi:10.1016/B978-0-12-416618-9.00020-0
PMCID: PMC4154315  PMID: 24862277
4.  Phosphoproteomic Profiling of Human Myocardial Tissues Distinguishes Ischemic from Non-Ischemic End Stage Heart Failure 
PLoS ONE  2014;9(8):e104157.
The molecular differences between ischemic (IF) and non-ischemic (NIF) heart failure are poorly defined. A better understanding of the molecular differences between these two heart failure etiologies may lead to the development of more effective heart failure therapeutics. In this study extensive proteomic and phosphoproteomic profiles of myocardial tissue from patients diagnosed with IF or NIF were assembled and compared.
Proteins extracted from left ventricular sections were proteolyzed and phosphopeptides were enriched using titanium dioxide resin. Gel- and label-free nanoscale capillary liquid chromatography coupled to high resolution accuracy mass tandem mass spectrometry allowed for the quantification of 4,436 peptides (corresponding to 450 proteins) and 823 phosphopeptides (corresponding to 400 proteins) from the unenriched and phospho-enriched fractions, respectively.
Protein abundance did not distinguish NIF from IF. In contrast, 37 peptides (corresponding to 26 proteins) exhibited a ≥2-fold alteration in phosphorylation state (p<0.05) when comparing IF and NIF. The degree of protein phosphorylation at these 37 sites was specifically dependent upon the heart failure etiology examined. Proteins exhibiting phosphorylation alterations were grouped into functional categories: transcriptional activation/RNA processing; cytoskeleton structure/function; molecular chaperones; cell adhesion/signaling; apoptosis; and energetic/metabolism.
Phosphoproteomic analysis demonstrated profound post-translational differences in proteins that are involved in multiple cellular processes between different heart failure phenotypes. Understanding the roles these phosphorylation alterations play in the development of NIF and IF has the potential to generate etiology-specific heart failure therapeutics, which could be more effective than current therapeutics in addressing the growing concern of heart failure.
doi:10.1371/journal.pone.0104157
PMCID: PMC4130503  PMID: 25117565
5.  Targeting sirtuins for the treatment of diabetes 
SUMMARY
Sirtuins are a class of NAD+-dependent deacetylases, such as deacetylases, that have a wide array of biological functions. Recent studies have suggested that reduced sirtuin action is correlated with Type 2 diabetes. Both overnutrition and aging, which are two major risk factors for diabetes, lead to decreased sirtuin function and result in abnormal glucose and lipid metabolism. Therefore, restoring normal levels of sirtuin action in Type 2 diabetes may be a promising method of treating diabetes. This article reviews the biological functions of three of the seven mammalian sirtuins – SIRT1, SIRT3 and SIRT6 – that have demonstrated prominent metabolic roles and early potential for drug targeting. Clinical trials investigating the use of sirtuin activators for treating diabetes are already underway and show promise as alternatives to current diabetes therapies. Thus, further research into sirtuin activators is warranted and may lead to a new class of safe, effective diabetes treatments.
doi:10.2217/dmt.13.6
PMCID: PMC4110209  PMID: 25067957
7.  Mitochondrial protein acetylation regulates metabolism 
Essays in biochemistry  2012;52:10.1042/bse0520023.
Changes in cellular nutrient availability or energy status induce global changes in mitochondrial protein acetylation. Over one-third of all proteins in the mitochondria are acetylated, of which the majority are involved in some aspect of energy metabolism. Mitochondrial protein acetylation is regulated by SIRT3 (sirtuin 3), a member of the sirtuin family of NAD+-dependent protein deacetylases that has recently been identified as a key modulator of energy homoeostasis. In the absence of SIRT3, mitochondrial proteins become hyperacetylated, have altered function, and contribute to mitochondrial dysfunction. This chapter presents a review of the functional impact of mitochondrial protein acetylation, and its regulation by SIRT3.
doi:10.1042/bse0520023
PMCID: PMC3872051  PMID: 22708561
8.  Old Enzymes, New Tricks: Sirtuins Are NAD+-Dependent De-acylases 
Cell metabolism  2011;14(6):10.1016/j.cmet.2011.10.006.
Seven mammalian sirtuins are nicotinamide adenine dinucleotide (NAD)+-dependent deacetylases and are important modulators of energy metabolism and stress resistance. Two new studies by Du et al. (2011) and Peng et al. (2011) identify a new enzymatic activity for SIRT5, expanding the cellular repertoire of posttranslational modifications targeted by the sirtuins.
doi:10.1016/j.cmet.2011.10.006
PMCID: PMC3830953  PMID: 22100408
9.  Generating Mammalian Sirtuin Tools for Protein-Interaction Analysis 
Methods in molecular biology (Clifton, N.J.)  2013;1077:10.1007/978-1-62703-637-5_5.
The sirtuins are a family of NAD+-dependent deacylases with important effects on aging, cancer, and metabolism. Sirtuins exert their biological effects by catalyzing deacetylation and/or deacylation reactions in which Acyl groups are removed from lysine residues of specific proteins. A current challenge is to identify specific sirtuin target proteins against the high background of acetylated proteins recently identified by proteomic surveys. New evidence indicates that bona fide sirtuin substrate proteins form stable physical associations with their sirtuin regulator. Therefore, identification of sirtuin interacting proteins could be a useful aid in focusing the search for substrates. Described here is a method for identifying sirtuin protein interactors. Employing basic techniques of molecular cloning and immunochemistry, the method describes the generation of mammalian sirtuin protein expression plasmids and their use to overexpress and immunoprecipitate sirtuins with their interacting partners. Also described is the use of the Database for Annotation, Visualization, and Integrated Discovery for interpreting the sirtuin protein-interaction data obtained.
doi:10.1007/978-1-62703-637-5_5
PMCID: PMC3819116  PMID: 24014400
Sirtuin; SIRT3; Deacetylation; Protein–protein interaction; Immunoprecipitation; DAVID
10.  Oxygen Flux Analysis to Understand the Biological Function of Sirtuins 
Methods in molecular biology (Clifton, N.J.)  2013;1077:10.1007/978-1-62703-637-5_16.
The sirtuins are a family of highly conserved NAD+-dependent lysine deacylases with important roles in metabolic regulation. Of the seven mammalian sirtuins, three localize to the mitochondria: SIRT3, SIRT4, and SIRT5. Mitochondrial sirtuins are crucial regulators of the metabolic network that controls energy homeostasis and impacts cancer, obesity, diabetes, mitochondrial diseases, metabolic disorders, and many other human diseases of aging. To best study the mitochondrial function of the sirtuins, we have employed an oxygen flux analyzer as a tool to track and record the extracellular oxygen consumption rate and acidification rate that reflects mitochondrial respiration and glycolysis, respectfully. Here we described the methods using this assay to study the substrate utilization and mitochondrial function in a human hepato-cellular carcinoma cell line, Huh7. Additionally, we have generated a stable SIRT4 knocked-down Huh7 cell line. With this cell line, we evaluated how the absence of SIRT4 affects mitochondrial function, glucose utilization, glutamine oxidation, and fatty acid oxidation in these cells.
doi:10.1007/978-1-62703-637-5_16
PMCID: PMC3817486  PMID: 24014411
Mitochondrial sirtuins; Seahorse XF extracellular flux analyzer; Oxygen consumption rate; Seahorse assay; Substrate utilization; Mitochondrial function; SIRT4
11.  Ethanol Metabolism Modifies Hepatic Protein Acylation in Mice 
PLoS ONE  2013;8(9):e75868.
Mitochondrial protein acetylation increases in response to chronic ethanol ingestion in mice, and is thought to reduce mitochondrial function and contribute to the pathogenesis of alcoholic liver disease. The mitochondrial deacetylase SIRT3 regulates the acetylation status of several mitochondrial proteins, including those involved in ethanol metabolism. The newly discovered desuccinylase activity of the mitochondrial sirtuin SIRT5 suggests that protein succinylation could be an important post-translational modification regulating mitochondrial metabolism. To assess the possible role of protein succinylation in ethanol metabolism, we surveyed hepatic sub-cellular protein fractions from mice fed a control or ethanol-supplemented diet for succinyl-lysine, as well as acetyl-, propionyl-, and butyryl-lysine post-translational modifications. We found mitochondrial protein propionylation increases, similar to mitochondrial protein acetylation. In contrast, mitochondrial protein succinylation is reduced. These mitochondrial protein modifications appear to be primarily driven by ethanol metabolism, and not by changes in mitochondrial sirtuin levels. Similar trends in acyl modifications were observed in the nucleus. However, comparatively fewer acyl modifications were observed in the cytoplasmic or the microsomal compartments, and were generally unchanged by ethanol metabolism. Using a mass spectrometry proteomics approach, we identified several candidate acetylated, propionylated, and succinylated proteins, which were enriched using antibodies against each modification. Additionally, we identified several acetyl and propionyl lysine residues on the same sites for a number of proteins and supports the idea of the overlapping nature of lysine-specific acylation. Thus, we show that novel post-translational modifications are present in hepatic mitochondrial, nuclear, cytoplasmic, and microsomal compartments and ethanol ingestion, and its associated metabolism, induce specific changes in these acyl modifications. These data suggest that protein acylation, beyond protein acetylation, contributes to the overall metabolic regulatory network and could play an important role in the pathogenesis of alcoholic liver disease.
doi:10.1371/journal.pone.0075868
PMCID: PMC3779192  PMID: 24073283
12.  Suppression of Oxidative Stress by β-Hydroxybutyrate, an Endogenous Histone Deacetylase Inhibitor 
Science (New York, N.Y.)  2012;339(6116):211-214.
Concentrations of acetyl–coenzyme A and nicotinamide adenine dinucleotide (NAD+) affect histone acetylation and thereby couple cellular metabolic status and transcriptional regulation. We report that the ketone body d-β-hydroxybutyrate (βOHB) is an endogenous and specific inhibitor of class I histone deacetylases (HDACs). Administration of exogenous βOHB, or fasting or calorie restriction, two conditions associated with increased βOHB abundance, all increased global histone acetylation in mouse tissues. Inhibition of HDAC by βOHB was correlated with global changes in transcription, including that of the genes encoding oxidative stress resistance factors FOXO3A and MT2. Treatment of cells with βOHB increased histone acetylation at the Foxo3a and Mt2 promoters, and both genes were activated by selective depletion of HDAC1 and HDAC2. Consistent with increased FOXO3A and MT2 activity, treatment of mice with βOHB conferred substantial protection against oxidative stress.
doi:10.1126/science.1227166
PMCID: PMC3735349  PMID: 23223453
13.  Whole-organism screening for gluconeogenesis identifies activators of fasting metabolism 
Nature chemical biology  2012;9(2):97-104.
Improving the control of energy homeostasis can lower cardiovascular risk in metabolically compromised individuals. To identify new regulators of whole-body energy control, we conducted a high-throughput screen in transgenic reporter zebrafish for small molecules that modulate the expression of the fasting-inducible gluconeogenic gene pck1. We show that this in vivo strategy identified several drugs that impact gluconeogenesis in humans, as well as metabolically uncharacterized compounds. Most notably, we find that the Translocator Protein (TSPO) ligands PK 11195 and Ro5-4864 are glucose lowering agents despite a strong inductive effect on pck1 expression. We show that these drugs are activators of a fasting-like energy state, and importantly that they protect high-fat diet induced obese mice from hepatosteatosis and glucose intolerance, two pathological manifestations of metabolic dysregulation. Thus, using a whole-organism screening strategy, this study has identified new small molecule activators of fasting metabolism.
doi:10.1038/nchembio.1136
PMCID: PMC3552031  PMID: 23201900
14.  Mitochondrial Acetylome Analysis in a Mouse Model of Alcohol-Induced Liver Injury Utilizing SIRT3 Knockout Mice 
Journal of Proteome Research  2012;11(3):1633-1643.
Mitochondrial protein hyperacetylation is a known consequence of sustained ethanol consumption and has been proposed to play a role in the pathogenesis of alcoholic liver disease (ALD). The mechanisms underlying this altered acetylome, however, remain unknown. The mitochondrial deacetylase sirtuin 3 (SIRT3) is reported to be the major regulator of mitochondrial protein deacetylation and remains a central focus for studies on protein acetylation. To investigate the mechanisms underlying ethanol-induced mitochondrial acetylation, we employed a model for ALD in both wild-type (WT) and SIRT3 knockout (KO) mice using a proteomics and bioinformatics approach. Here, WT and SIRT3 KO groups were compared in a mouse model of chronic ethanol consumption, revealing pathways relevant to ALD, including lipid and fatty acid metabolism, antioxidant response, amino acid biosynthesis and the electron-transport chain, each displaying proteins with altered acetylation. Interestingly, protein hyperacetylation resulting from ethanol consumption and SIRT3 ablation suggests ethanol-induced hyperacetylation targets numerous biological processes within the mitochondria, the majority of which are known to be acetylated through SIRT3-dependent mechanisms. These findings reveal overall increases in 91 mitochondrial targets for protein acetylation, identifying numerous critical metabolic and antioxidant pathways associated with ALD, suggesting an important role for mitochondrial protein acetylation in the pathogenesis of ALD.
doi:10.1021/pr2008384
PMCID: PMC3324946  PMID: 22309199
15.  The sirtuins, oxidative stress and aging: an emerging link 
Aging (Albany NY)  2013;5(3):144-150.
Reactive oxygen species (ROS) are a family of compounds that can oxidatively damage cellular macromolecules and may influence lifespan. Sirtuins are a conserved family of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases that regulate lifespan in many model organisms including yeast and mice. Recent work suggests that sirtuins can modulate ROS levels notably during a dietary regimen known as calorie restriction which enhances lifespan for several organisms. Although both sirtuins and ROS have been implicated in the aging process, their precise roles remain unknown. In this review, we summarize current thinking about the oxidative stress theory of aging, discuss some of the compelling data linking the sirtuins to ROS and aging, and propose a conceptual model placing the sirtuins into an ROS-driven mitochondria-mediated hormetic response.
PMCID: PMC3629286  PMID: 23474711
sirtuins; SIRT1; SIRT3; oxidative stress; mitohormesis; acetylation
16.  SIRT3 Deficiency and Mitochondrial Protein Hyperacetylation Accelerate the Development of the Metabolic Syndrome 
Molecular cell  2011;44(2):177-190.
SUMMARY
Acetylation is increasingly recognized as an important metabolic regulatory post-translational protein modification, yet the metabolic consequence of mitochondrial protein hyperacetylation is unknown. We find that high-fat diet (HFD) feeding induces hepatic mitochondrial protein hyperacetylation in mice and downregulation of the major mitochondrial protein deacetylase SIRT3. Mice lacking SIRT3 (SIRT3KO) placed on a HFD show accelerated obesity, insulin resistance, hyperlipidemia, and steatohepatitis compared to wild-type (wt) mice. The lipogenic enzyme stearoyl-CoA desaturase 1 is highly induced in SIRT3KO mice, and its deletion rescues both wt and SIRT3KO mice from HFD-induced hepatic steatosis and insulin resistance. We further identify a single nucleotide polymorphism in the human SIRT3 gene that is suggestive of a genetic association with the metabolic syndrome. This polymorphism encodes a point-mutation in the SIRT3 protein, which reduces its overall enzymatic efficiency. Our findings show loss of SIRT3 and dysregulation of mitochondrial protein acetylation contribute to the metabolic syndrome.
doi:10.1016/j.molcel.2011.07.019
PMCID: PMC3563434  PMID: 21856199
17.  SIRT3 Deacetylates Mitochondrial 3-Hydroxy-3-Methylglutaryl CoA Synthase 2 and Regulates Ketone Body Production 
Cell Metabolism  2010;12(6):654-661.
SUMMARY
The mitochondrial sirtuin SIRT3 regulates metabolic homeostasis during fasting and calorie restriction. We identified mitochondrial 3-hydroxy-3-methylglutaryl CoA synthase 2 (HMGCS2) as an acetylated protein and a possible target of SIRT3 in a proteomics survey in hepatic mitochondria from Sirt3−/− (SIRT3KO) mice. HMGCS2 is the rate-limiting step in β-hydroxybutyrate synthesis and is hyperacetylated at lysines 310, 447, and 473 in the absence of SIRT3. HMGCS2 is deacetylated by SIRT3 in response to fasting in wild-type mice, but not in SIRT3KO mice. HMGCS2 is deacetylated in vitro when incubated with SIRT3 and in vivo by overexpression of SIRT3. Deacetylation of HMGCS2 lysines 310, 447, and 473 by incubation with wild-type SIRT3 or by mutation to arginine enhances its enzymatic activity. Molecular dynamics simulations show that in silico deacetylation of these three lysines causes conformational changes of HMGCS2 near the active site. Mice lacking SIRT3 show decreased β-hydroxybutyrate levels during fasting. Our findings show SIRT3 regulates ketone body production during fasting and provide molecular insight into how protein acetylation can regulate enzymatic activity.
doi:10.1016/j.cmet.2010.11.003
PMCID: PMC3310379  PMID: 21109197
18.  Deficiency of the lipid synthesis enzyme, DGAT1, extends longevity in mice 
Aging (Albany NY)  2012;4(1):13-27.
Calorie restriction results in leanness, which is linked to metabolic conditions that favor longevity. We show here that deficiency of the triglyceride synthesis enzyme acyl CoA:diacylglycerol acyltransferase 1 (DGAT1), which promotes leanness, also extends longevity without limiting food intake. Female DGAT1-deficient mice were protected from age-related increases in body fat, tissue triglycerides, and inflammation in white adipose tissue. This protection was accompanied by increased mean and maximal life spans of ~25% and ~10%, respectively. Middle-aged Dgat1−/− mice exhibited several features associated with longevity, including decreased levels of circulating insulin growth factor 1 (IGF1) and reduced fecundity. Thus, deletion of DGAT1 in mice provides a model of leanness and extended lifespan that is independent of calorie restriction.
PMCID: PMC3292902  PMID: 22291164
DGAT1; adipose tissue; longevity; triglycerides; calorie restriction
19.  Sirtuin Regulation of Mitochondria - Energy Production, Apoptosis, and Signaling 
Trends in biochemical sciences  2010;35(12):669-675.
Sirtuins are a highly conserved family of proteins whose activity can extend lifespan in model organisms such as yeast, worms, and flies. Mammals contain seven sirtuins (SIRT1-7) that modulate distinct metabolic and stress response pathways. Three sirtuins, SIRT3, SIRT4 and SIRT5, are located in the mitochondrion, a dynamic organelle that functions as the primary site of oxidative metabolism and plays critical roles in apoptosis and intracellular signaling. Recent findings have shed light on how the mitochondrial sirtuins function in the control of basic mitochondrial biology, including energy production, metabolism, apoptosis, and intracellular signaling.
doi:10.1016/j.tibs.2010.07.003
PMCID: PMC2992946  PMID: 20863707
20.  SIRT1 and SIRT3 Deacetylate Homologous Substrates: AceCS1,2 and HMGCS1,2 
Aging (Albany NY)  2011;3(6):635-642.
SIRT1 and SIRT3 are NAD+-dependent protein deacetylases that are evolutionarily conserved across mammals. These proteins are located in the cytoplasm/nucleus and mitochondria, respectively. Previous reports demonstrated that human SIRT1 deacetylates Acetyl-CoA Synthase 1 (AceCS1) in the cytoplasm, whereas SIRT3 deacetylates the homologous Acetyl-CoA Synthase 2 (AceCS2) in the mitochondria. We recently showed that 3-hydroxy-3-methylglutaryl CoA synthase 2 (HMGCS2) is deacetylated by SIRT3 in mitochondria, and we demonstrate here that SIRT1 deacetylates the homologous 3-hydroxy-3-methylglutaryl CoA synthase 1 (HMGCS1) in the cytoplasm. This novel pattern of substrate homology between cytoplasmic SIRT1 and mitochondrial SIRT3 suggests that considering evolutionary relationships between the sirtuins and their substrates may help to identify and understand the functions and interactions of this gene family. In this perspective, we take a first step by characterizing the evolutionary history of the sirtuins and these substrate families.
PMCID: PMC3164371  PMID: 21701047
sirtuins; evolution; deacetylases; aging
21.  SIRT3 regulates fatty acid oxidation via reversible enzyme deacetylation 
Nature  2010;464(7285):121-125.
Sirtuins are NAD+-dependent protein deacetylases and mediate adaptive responses to a variety of stresses, including calorie restriction and metabolic stress. Sirtuin 3 (SIRT3) is localized in the mitochondrial matrix where it regulates the acetylation levels of metabolic enzymes, including acetyl coenzyme A synthetase 21,2. Mice lacking both SIRT3 alleles appear phenotypically normal under basal conditions, but show marked hyperacetylation of several mitochondrial proteins3. We report that SIRT3 expression is upregulated during fasting in liver and brown adipose tissues. Livers from mice lacking SIRT3 show higher levels of fatty acid oxidation intermediate products and triglycerides during fasting associated with decreased levels of fatty acid oxidation when compared to wild-type mice. Mass spectrometry analysis of mitochondrial proteins shows that long-chain acyl CoA dehydrogenase (LCAD) is hyperacetylated at lysine 42 in the absence of SIRT3. LCAD is deacetylated in wild-type mice under fasted conditions and by SIRT3 in vitro and in vivo, and hyperacetylation of LCAD reduces its enzymatic activity. Mice lacking SIRT3 exhibit hallmarks of fatty acid oxidation disorders during fasting including reduced ATP levels and intolerance to cold exposure. These findings identify acetylation as a novel regulatory mechanism for mitochondrial fatty acid oxidation and demonstrate that SIRT3 modulates mitochondrial intermediary metabolism and fatty acid utilization during fasting.
doi:10.1038/nature08778
PMCID: PMC2841477  PMID: 20203611
22.  Mammalian Sir2 Homolog SIRT3 Regulates Global Mitochondrial Lysine Acetylation▿ †  
Molecular and Cellular Biology  2007;27(24):8807-8814.
Homologs of the Saccharomyces cerevisiae Sir2 protein, sirtuins, promote longevity in many organisms. Studies of the sirtuin SIRT3 have so far been limited to cell culture systems. Here, we investigate the localization and function of SIRT3 in vivo. We show that endogenous mouse SIRT3 is a soluble mitochondrial protein. To address the function and relevance of SIRT3 in the regulation of energy metabolism, we generated and phenotypically characterized SIRT3 knockout mice. SIRT3-deficient animals exhibit striking mitochondrial protein hyperacetylation, suggesting that SIRT3 is a major mitochondrial deacetylase. In contrast, no mitochondrial hyperacetylation was detectable in mice lacking the two other mitochondrial sirtuins, SIRT4 and SIRT5. Surprisingly, despite this biochemical phenotype, SIRT3-deficient mice are metabolically unremarkable under basal conditions and show normal adaptive thermogenesis, a process previously suggested to involve SIRT3. Overall, our results extend the recent finding of lysine acetylation of mitochondrial proteins and demonstrate that SIRT3 has evolved to control reversible lysine acetylation in this organelle.
doi:10.1128/MCB.01636-07
PMCID: PMC2169418  PMID: 17923681

Results 1-22 (22)