101
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Filhoulaud G, Guilmeau S, Dentin R, Girard J, Postic C. Novel insights into ChREBP regulation and function. Trends Endocrinol Metab 2013; 24:257-68. [PMID: 23597489 DOI: 10.1016/j.tem.2013.01.003] [Citation(s) in RCA: 144] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Revised: 12/23/2012] [Accepted: 01/03/2013] [Indexed: 12/17/2022]
Abstract
Glucose is an energy source that also controls the expression of key genes involved in energetic metabolism through the glucose-signaling transcription factor carbohydrate response element-binding protein (ChREBP). ChREBP has recently emerged as a central regulator of glycolysis and de novo fatty acid synthesis in liver, but new evidence shows that it plays a broader and crucial role in various processes, ranging from glucolipotoxicity to apoptosis and/or proliferation in specific cell types. However, several aspects of ChREBP activation by glucose metabolites are currently controversial, as well as the effects of activating or inhibiting ChREBP, on insulin sensitivity, which might depend on genetic, dietary or environmental factors. Thus, much remains to be elucidated. Here, we summarize our current understanding of the regulation and function of this fascinating transcription factor.
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102
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Lai L, Yan L, Gao S, Hu CL, Ge H, Davidow A, Park M, Bravo C, Iwatsubo K, Ishikawa Y, Auwerx J, Sinclair DA, Vatner SF, Vatner DE. Type 5 adenylyl cyclase increases oxidative stress by transcriptional regulation of manganese superoxide dismutase via the SIRT1/FoxO3a pathway. Circulation 2013; 127:1692-701. [PMID: 23536361 DOI: 10.1161/circulationaha.112.001212] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
BACKGROUND For reasons that remain unclear, whether type 5 adenylyl cyclase (AC5), 1 of 2 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 in AC5 transgenic (Tg) mice and the signaling mechanisms involved. METHODS AND RESULTS Chronic isoproterenol increased oxidative stress and induced more severe cardiomyopathy in AC5 Tg, as left ventricular ejection fraction fell 1.9-fold more than wild type, along with greater left ventricular dilation and increased fibrosis, apoptosis, and hypertrophy. Oxidative stress induced by chronic isoproterenol, detected by 8-OhDG was 15% greater, P=0.007, in AC5 Tg hearts, whereas protein expression of manganese superoxide dismutase (MnSOD) was reduced by 38%, indicating that the susceptibility of AC5 Tg to cardiomyopathy may be attributable 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 knockout (KO) was lost in AC5 KO×MnSOD heterozyous KO 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. CONCLUSIONS 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.
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Affiliation(s)
- Lo Lai
- Department of Cell Biology & Molecular Medicine, University of Medicine & Dentistry of New Jersey, New Jersey Medical School, 185 South Orange Avenue, Newark, NJ 07103, USA.
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103
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Morris BJ. Seven sirtuins for seven deadly diseases of aging. Free Radic Biol Med 2013; 56:133-71. [PMID: 23104101 DOI: 10.1016/j.freeradbiomed.2012.10.525] [Citation(s) in RCA: 276] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 08/31/2012] [Accepted: 10/05/2012] [Indexed: 12/14/2022]
Abstract
Sirtuins are a class of NAD(+)-dependent deacetylases having beneficial health effects. This extensive review describes the numerous intracellular actions of the seven mammalian sirtuins, their protein targets, intracellular localization, the pathways they modulate, and their role in common diseases of aging. Selective pharmacological targeting of sirtuins is of current interest in helping to alleviate global disease burden. Since all sirtuins are activated by NAD(+), strategies that boost NAD(+) in cells are of interest. While most is known about SIRT1, the functions of the six other sirtuins are now emerging. Best known is the involvement of sirtuins in helping cells adapt energy output to match energy requirements. SIRT1 and some of the other sirtuins enhance fat metabolism and modulate mitochondrial respiration to optimize energy harvesting. The AMP kinase/SIRT1-PGC-1α-PPAR axis and mitochondrial sirtuins appear pivotal to maintaining mitochondrial function. Downregulation with aging explains much of the pathophysiology that accumulates with aging. Posttranslational modifications of sirtuins and their substrates affect specificity. Although SIRT1 activation seems not to affect life span, activation of some of the other sirtuins might. Since sirtuins are crucial to pathways that counter the decline in health that accompanies aging, pharmacological agents that boost sirtuin activity have clinical potential in treatment of diabetes, cardiovascular disease, dementia, osteoporosis, arthritis, and other conditions. In cancer, however, SIRT1 inhibitors could have therapeutic value. Nutraceuticals such as resveratrol have a multiplicity of actions besides sirtuin activation. Their net health benefit and relative safety may have originated from the ability of animals to survive environmental changes by utilizing these stress resistance chemicals in the diet during evolution. Each sirtuin forms a key hub to the intracellular pathways affected.
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Affiliation(s)
- Brian J Morris
- Basic & Clinical Genomics Laboratory, School of Medical Sciences and Bosch Institute, Building F13, University of Sydney, NSW 2006, Australia.
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104
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Oldknow KJ, Seebacher J, Goswami T, Villen J, Pitsillides AA, O'Shaughnessy PJ, Gygi SP, Schneyer AL, Mukherjee A. Follistatin-like 3 (FSTL3) mediated silencing of transforming growth factor β (TGFβ) signaling is essential for testicular aging and regulating testis size. Endocrinology 2013; 154:1310-20. [PMID: 23407452 PMCID: PMC3578998 DOI: 10.1210/en.2012-1886] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Follistatin-like 3 (FSTL3) is a glycoprotein that binds and inhibits the action of TGFβ ligands such as activin. The roles played by FSTL3 and activin signaling in organ development and homeostasis are not fully understood. The authors show mice deficient in FSTL3 develop markedly enlarged testes that are also delayed in their age-related regression. These FSTL3 knockout mice exhibit increased Sertoli cell numbers, allowing for increased spermatogenesis but otherwise showing normal testicular function. The data show that FSTL3 deletion leads to increased AKT signaling and SIRT1 expression in the testis. This demonstrates a cross-talk between TGFβ ligand and AKT signaling and leads to a potential mechanism for increased cellular survival and antiaging. The findings identify crucial roles for FSTL3 in limiting testis organ size and promoting age-related testicular regression.
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Affiliation(s)
- Karla J Oldknow
- Lifestyle Research Group, Comparative Biomedical Sciences, Royal Veterinary College, London, United Kingdom
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105
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Revollo JR, Li X. The ways and means that fine tune Sirt1 activity. Trends Biochem Sci 2013; 38:160-7. [PMID: 23394938 DOI: 10.1016/j.tibs.2012.12.004] [Citation(s) in RCA: 118] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 11/13/2012] [Accepted: 12/11/2012] [Indexed: 12/25/2022]
Abstract
Sirt1 is the most evolutionarily conserved mammalian sirtuin. It plays a vital role in the regulation of metabolism, stress responses, genome stability, and ultimately aging. Although much attention has focused on the identification of the cellular targets and functional networks controlled by Sirt1, the mechanisms that regulate Sirt1 activity by biological stimuli have only recently begun to emerge. As an enzyme, the activity of Sirt1 can be controlled by the availability of its substrates, post-translational modifications, interactions with other proteins, or changes in its expression levels. In this review, we briefly discuss the ways and means by which the activity of Sirt1 is fine-tuned under different conditions.
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Affiliation(s)
- Javier R Revollo
- Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, 111 T.W. Alexander Drive, Research Triangle Park, NC, USA.
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106
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Cantó C, Sauve AA, Bai P. Crosstalk between poly(ADP-ribose) polymerase and sirtuin enzymes. Mol Aspects Med 2013; 34:1168-201. [PMID: 23357756 DOI: 10.1016/j.mam.2013.01.004] [Citation(s) in RCA: 168] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Revised: 01/07/2013] [Accepted: 01/17/2013] [Indexed: 01/08/2023]
Abstract
Poly(ADP-ribose) polymerases (PARPs) are NAD(+) dependent enzymes that were identified as DNA repair proteins, however, today it seems clear that PARPs are responsible for a plethora of biological functions. Sirtuins (SIRTs) are NAD(+)-dependent deacetylase enzymes involved in the same biological processes as PARPs raising the question whether PARP and SIRT enzymes may interact with each other in physiological and pathophysiological conditions. Hereby we review the current understanding of the SIRT-PARP interplay in regard to the biochemical nature of the interaction (competition for the common NAD(+) substrate, mutual posttranslational modifications and direct transcriptional effects) and the physiological or pathophysiological consequences of the interactions (metabolic events, oxidative stress response, genomic stability and aging). Finally, we give an overview of the possibilities of pharmacological intervention to modulate PARP and SIRT enzymes either directly, or through modulating NAD(+) homeostasis.
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Affiliation(s)
- Carles Cantó
- Nestlé Institute of Health Sciences, Lausanne CH-1015, Switzerland
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107
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Abstract
Carbohydrate response element binding protein (ChREBP) is a transcription factor activated by glucose that is highly expressed in liver, pancreatic β-cells, brown and white adipose tissues, and muscle. We reported that hepatic suppression of the Chrebp gene improves hepatic steatosis, glucose intolerance, and obesity in genetically obese mice. Moreover, we have studied the role of ChREBP with special reference to feedforward and feedback looping in liver and pancreatic β-cells. Recently, several groups reported that (1) glucose activates ChREBP-α transactivity and in turn ChREBP-α induces ChREBP-β on both transcriptional and translational levels in adipose tissues, and (2) ChREBP regulates glucose transporter type 4 mRNA levels, which may affect glucose uptake in adipose tissues. Moreover, in adipose tissues of obese patients, Chrebpb mRNA levels were much lower than those in lean subjects, while the levels were much higher in liver of obese patients than those in lean subjects. These findings suggest that Chrebpb mRNA levels are different in various tissues and probably in the stages of diabetes mellitus. Herein, we review recent progress in the study of ChREBP with special references to (1) the mechanisms regulating ChREBP transactivity (posttranslational modifications, intramolecular glucose sensing module, feedforward mechanism, and the feedback loop between ChREBP and its target genes), and (2) the role of ChREBP in liver, pancreatic islets and adipose tissues. Understanding the role of ChREBP in each tissue will provide important insight into the pathogenesis of metabolic syndrome.
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Affiliation(s)
- Katsumi Iizuka
- University Hospital Center for Nutritional Support and Infection Control, Gifu University, Gifu 501-1194, Japan.
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108
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Kemper JK, Choi SE, Kim DH. Sirtuin 1 deacetylase: a key regulator of hepatic lipid metabolism. VITAMINS AND HORMONES 2013; 91:385-404. [PMID: 23374725 DOI: 10.1016/b978-0-12-407766-9.00016-x] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Obesity is a serious medical problem worldwide and disruption of metabolic/energy homeostasis plays a pivotal role in this global epidemic. In obese people, fatty liver (steatosis) develops, which increases the risk for diabetes, cardiovascular disease, and even, liver cancer. Sirtuin 1 (SIRT1) is a NAD+-dependent deacetylase that functions as a key metabolic/energy sensor and mediates homeostatic responses to nutrient availability. Accumulating evidence indicates that SIRT1 is a master regulator of the transcriptional networks that control hepatic lipid metabolism. During energy-deprived conditions, SIRT1 deacetylates and alters the expression and activities of key transcriptional regulators involved in hepatic lipogenesis, fatty acid β-oxidation, and cholesterol/bile acid metabolism. This review will discuss the latest advances in this field, focusing on beneficial roles of SIRT1 in hepatic lipid metabolism including its potential as a therapeutic target for treatment of steatosis and other obesity-related metabolic diseases.
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Affiliation(s)
- Jongsook Kim Kemper
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana, Urbana, Illinois, USA.
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109
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Liu D, Pitta M, Jiang H, Lee JH, Zhang G, Chen X, Kawamoto EM, Mattson MP. Nicotinamide forestalls pathology and cognitive decline in Alzheimer mice: evidence for improved neuronal bioenergetics and autophagy procession. Neurobiol Aging 2012; 34:1564-80. [PMID: 23273573 DOI: 10.1016/j.neurobiolaging.2012.11.020] [Citation(s) in RCA: 163] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2012] [Revised: 11/17/2012] [Accepted: 11/25/2012] [Indexed: 12/31/2022]
Abstract
Impaired brain energy metabolism and oxidative stress are implicated in cognitive decline and the pathologic accumulations of amyloid β-peptide (Aβ) and hyperphosphorylated tau in Alzheimer's disease (AD). To determine whether improving brain energy metabolism will forestall disease progress in AD, the impact of the β-nicotinamide adenine dinucleotide precursor nicotinamide on brain cell mitochondrial function and macroautophagy, bioenergetics-related signaling, and cognitive performance were studied in cultured neurons and in a mouse model of AD. Oxidative stress resulted in decreased mitochondrial mass, mitochondrial degeneration, and autophagosome accumulation in neurons. Nicotinamide preserved mitochondrial integrity and autophagy function, and reduced neuronal vulnerability to oxidative/metabolic insults and Aβ toxicity. β-Nicotinamide adenine dinucleotide biosynthesis, autophagy, and phosphatidylinositol-3-kinase signaling were required for the neuroprotective action of nicotinamide. Treatment of 3xTgAD mice with nicotinamide for 8 months resulted in improved cognitive performance, and reduced Aβ and hyperphosphorylated tau pathologies in hippocampus and cerebral cortex. Nicotinamide treatment preserved mitochondrial integrity, and improved autophagy-lysosome procession by enhancing lysosome/autolysosome acidification to reduce autophagosome accumulation. Treatment of 3xTgAD mice with nicotinamide resulted in elevated levels of activated neuroplasticity-related kinases (protein kinase B [Akt] and extracellular signal-regulated kinases) and the transcription factor cyclic adenosine monophosphate (AMP) response element-binding protein in the hippocampus and cerebral cortex. Thus, nicotinamide suppresses AD pathology and cognitive decline in a mouse model of AD by a mechanism involving improved brain bioenergetics with preserved functionality of mitochondria and the autophagy system.
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Affiliation(s)
- Dong Liu
- Laboratory of Neurosciences, National Institute on Aging Intramural Research Program, Baltimore, MD, USA
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110
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Abstract
The maintenance of metabolic homeostasis requires the well-orchestrated network of several pathways of glucose, lipid and amino acid metabolism. Mitochondria integrate these pathways and serve not only as the prime site of cellular energy harvesting but also as the producer of many key metabolic intermediates. The sirtuins are a family of NAD(+)-dependent enzymes, which have a crucial role in the cellular adaptation to metabolic stress. The mitochondrial sirtuins SIRT3, SIRT4 and SIRT5 together with the nuclear SIRT1 regulate several aspects of mitochondrial physiology by controlling post-translational modifications of mitochondrial protein and transcription of mitochondrial genes. Here we discuss current knowledge how mitochondrial sirtuins and SIRT1 govern mitochondrial processes involved in different metabolic pathways.
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Affiliation(s)
- Eija Pirinen
- Laboratory for Integrative and Systems Physiology, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
- Biotechnology and Molecular Medicine, A.I. Virtanen Institute for Molecular Sciences, Biocenter Kuopio, University of Eastern Finland, Kuopio, Finland
| | - Giuseppe Lo Sasso
- Laboratory for Integrative and Systems Physiology, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
| | - Johan Auwerx
- Laboratory for Integrative and Systems Physiology, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
- To whom correspondence should be addressed:
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111
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Abstract
The silencer information regulator (Sir) family of proteins has attracted much attention during the past decade due to its prominent role in metabolic homeostasis in mammals. The Sir1-4 proteins were first discovered in yeast as nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylases, which through a gene silencing effect promoted longevity. The subsequent discovery of a homologous sirtuin (Sirt) family of proteins in the mammalian systems soon led to the realization that these molecules have beneficial effects in metabolism- and aging-related diseases. Through their concerted functions in the central nervous system, liver, pancreas, skeletal muscle, and adipose tissue, they regulate the body's metabolism. Sirt1, -6, and -7 exert their functions, predominantly, through a direct effect on nuclear transcription of genes involved in metabolism, whereas Sirt3-5 reside in the mitochondrial matrix and regulate various enzymes involved in the tricarboxylic acid and urea cycles, oxidative phosphorylation, as well as reactive oxygen species production. An interesting aspect of the functionality of sirtuin involves their regulation by the circadian rhythm, which affects their function via cyclically regulating systemic NAD(+) availability, further establishing the link of these proteins to metabolism. In this review, we will discuss the relation of sirtuins to NAD(+) metabolism, their mechanism of function, and their role in metabolism and mitochondrial functions. In addition, we will describe their effects in the cardiovascular and central nervous systems.
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Affiliation(s)
- Maha Abdellatif
- Cardiovascular Research Institute, Department of Cell Biology and Molecular Medicine, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
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112
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Feldman JL, Dittenhafer-Reed KE, Denu JM. Sirtuin catalysis and regulation. J Biol Chem 2012; 287:42419-27. [PMID: 23086947 DOI: 10.1074/jbc.r112.378877] [Citation(s) in RCA: 167] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sirtuins are a family of NAD(+)-dependent protein deacetylases/deacylases that dynamically regulate transcription, metabolism, and cellular stress response. Their general positive link with improved health span in mammals, potential regulation of pathways mediated by caloric restriction, and growing links to human disease have spurred interest in therapeutics that target their functions. Here, we review the current understanding of the chemistry of catalysis, biological targets, and endogenous regulation of sirtuin activity. We discuss recent efforts to generate small-molecule regulators of sirtuin activity.
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Affiliation(s)
- Jessica L Feldman
- Department of Biomolecular Chemistry and the Wisconsin Institute for Discovery, University of Wisconsin, Madison, Wisconsin 53715, USA.
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113
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Qui G, Spangler E, Wan R, Miller M, Mattson M, So KF, de Cabo R, Zou S, Ingram D. Neuroprotection provided by dietary restriction in rats is further enhanced by reducing glucocortocoids. Neurobiol Aging 2012; 33:2398-410. [PMID: 22226488 PMCID: PMC3374050 DOI: 10.1016/j.neurobiolaging.2011.11.025] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Revised: 10/21/2011] [Accepted: 11/20/2011] [Indexed: 12/24/2022]
Abstract
Glucocorticoids (GC)--corticosterone (CORT) in rodents and cortisol in primates--are stress-induced hormones secreted by adrenal glands that interact with the hypothalamic pituitary axis. High levels of cortisol in humans are observed in neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD), as well as in diabetes, post-traumatic stress syndrome, and major depression. Experimental models of diabetes in rats and mice have demonstrated that reduction of CORT reduces learning and memory deficits and attenuates loss of neuronal viability and plasticity. In contrast to the negative associations of elevated GC levels, CORT is moderately elevated in dietary restriction (DR) paradigms which are associated with many healthy anti-aging effects including neuroprotection. We demonstrate here in rats that ablating CORT by adrenalectomy (ADX) with replenishment to relatively low levels (30% below that of controls) prior to the onset of a DR regimen (ADX-DR) followed by central administration of the neurotoxin, kainic acid (KA), significantly attenuates learning deficits in a 14-unit T-maze task. The performance of the ADX-DR KA group did not differ from a control group (CON) that did not receive KA and was fed ad libitum (AL). By contrast, the sham-operated DR (SHAM-DR KA) group, SHAM-AL KA group, and ADX-AL KA group demonstrated poorer learning behavior in this task compared to the CON group. Stereological analysis revealed equivalent DR-induced neuroprotection in the SH-DR KA and ADX-DR KA groups, as measured by cell loss in the CA2/CA3 region of the hippocampus, while substantial cell loss was observed in SH-AL and ADX-AL rats. A separate set of experiments was conducted with similar dietary and surgical treatment conditions but without KA administration to examine markers of neurotrophic activity, brain-derived neurotrophic factor (BDNF), transcriptions factors (pCREB), and chaperone proteins (HSP-70). Under these conditions, we noted elevations in both BDNF and pCREB in ADX DR rats compared to the other groups; whereas, HSP-70, was equivalently elevated in ADX-DR and SH-DR groups and was higher than observed in both SH-AL and ADX-AL groups. These results support findings that DR protects hippocampal neurons against KA-induced cellular insult. However, this neuroprotective effect was further enhanced in rats with a lower-than control level of CORT resulting from ADX and maintained by exogenous CORT supplementation. Our results then suggest that DR-induced physiological elevation of GC may have negative functional consequences to DR-induced beneficial effects. These negative effects, however, can be compensated by other DR-produced cellular and molecular protective mechanisms.
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Affiliation(s)
| | - Edward Spangler
- Laboratory of Experimental Gerontology, Gerontology Research Center, National Institute on Aging, Baltimore, MD 21043
| | - Ruiqian Wan
- Laboratory of Neurosciences, Gerontology Research Center, National Institute on Aging, Baltimore, MD 210434
| | | | - Mark Mattson
- Laboratory of Neurosciences, Gerontology Research Center, National Institute on Aging, Baltimore, MD 210434
| | - Kwi-fok So
- Department of Anatomy, Li Ka Shing Medicine, The University of Hong Kong, 21 Sassoon Road, Pokfulam, Hong Kong SAR, PR China
| | - Rafael de Cabo
- Laboratory of Experimental Gerontology, Gerontology Research Center, National Institute on Aging, Baltimore, MD 21043
| | - Sige Zou
- Laboratory of Experimental Gerontology, Gerontology Research Center, National Institute on Aging, Baltimore, MD 21043
| | - Donald Ingram
- Correspondence should be sent to Donald K. Ingram at the Nutritional Neuroscience and Aging Laboratory, Pennington Biomedical Research Center, Louisiana State University System, 6400 Perkins Road, Baton Rouge, LA 70808.
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114
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Chung JH, Manganiello V, Dyck JRB. Resveratrol as a calorie restriction mimetic: therapeutic implications. Trends Cell Biol 2012; 22:546-54. [PMID: 22885100 PMCID: PMC3462230 DOI: 10.1016/j.tcb.2012.07.004] [Citation(s) in RCA: 146] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2012] [Revised: 06/28/2012] [Accepted: 07/06/2012] [Indexed: 11/26/2022]
Abstract
It is widely believed that calorie restriction (CR) can extend the lifespan of model organisms and protect against aging-related diseases. A potential CR mimetic is resveratrol, which may have beneficial effects against numerous diseases such as type 2 diabetes, cardiovascular diseases, and cancer in tissue culture and animal models. However, resveratrol in its current form is not ideal as therapy, because even at very high doses it has modest efficacy and many downstream effects. Identifying the cellular targets responsible for the effects of resveratrol and developing target-specific therapies will be helpful in increasing the efficacy of this drug without increasing its potential adverse effects. A recent discovery suggests that the metabolic effects of resveratrol may be mediated by inhibiting cAMP phosphodiesterases (PDEs), particularly PDE4. Here, we review the current literature on the metabolic and cardiovascular effects of resveratrol and attempt to shed light on the controversies surrounding its action.
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Affiliation(s)
- Jay H Chung
- Laboratory of Obesity and Aging Research, Genetics and Developmental Biology Center, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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115
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Libert S, Guarente L. Metabolic and neuropsychiatric effects of calorie restriction and sirtuins. Annu Rev Physiol 2012; 75:669-84. [PMID: 23043250 DOI: 10.1146/annurev-physiol-030212-183800] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Most living organisms, including humans, age. Over time the ability to do physical and intellectual work deteriorates, and susceptibility to infectious, metabolic, and neurodegenerative diseases increases, which leads to general fitness decline and ultimately to death. Work in model organisms has demonstrated that genetic and environmental manipulations can prevent numerous age-associated diseases, improve health at advanced age, and increase life span. Calorie restriction (CR) (consumption of a diet with fewer calories but containing all the essential nutrients) is the most robust manipulation, genetic or environmental, to extend longevity and improve health parameters in laboratory animals. However, outside of the protected laboratory environment, the effects of CR are much less certain. Understanding the molecular mechanisms of CR may lead to the development of novel therapies to combat diseases of aging and to improve the quality of life. Sirtuins, a family of NAD(+)-dependent enzymes, mediate a number of metabolic and behavioral responses to CR and are intriguing targets for pharmaceutical interventions. We review the molecular understanding of CR; the role of sirtuins in CR; and the effects of sirtuins on physiology, mood, and behavior.
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Affiliation(s)
- Sergiy Libert
- Glenn Laboratory for the Science of Aging, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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116
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Abstract
Sirt1, the closest mammalian homolog of the Sir2 yeast longevity protein, has been extensively investigated in the last few years as an avenue to understand the connection linking nutrients and energy metabolism with aging and related diseases. From this research effort the picture has emerged of an enzyme at the hub of a complex array of molecular interactions whereby nutrient-triggered signals are translated into several levels of adaptive cell responses, the failure of which underlies diseases as diverse as diabetes, neurodegeneration and cancer. Sirt1 thus connects moderate calorie intake to “healthspan,” and a decline of Sirt-centered protective circuits over time may explain the “catastrophic” nature of aging.
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Affiliation(s)
- Salvatore Fusco
- Institute of General Pathology, Catholic University Medical School, Rome, Italy
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117
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Shan J, Pang S, Wanyan H, Xie W, Qin X, Yan B. Genetic analysis of the SIRT1 gene promoter in ventricular septal defects. Biochem Biophys Res Commun 2012; 425:741-5. [DOI: 10.1016/j.bbrc.2012.07.145] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2012] [Accepted: 07/26/2012] [Indexed: 01/17/2023]
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118
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Epigenetic regulation of BACE1 in Alzheimer’s disease patients and in transgenic mice. Neuroscience 2012; 220:256-66. [DOI: 10.1016/j.neuroscience.2012.06.029] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Accepted: 06/11/2012] [Indexed: 12/30/2022]
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119
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Cui Y, Wang H, Chen H, Pang S, Wang L, Liu D, Yan B. Genetic analysis of the SIRT1 gene promoter in myocardial infarction. Biochem Biophys Res Commun 2012; 426:232-6. [PMID: 22935421 DOI: 10.1016/j.bbrc.2012.08.071] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2012] [Accepted: 08/15/2012] [Indexed: 12/13/2022]
Abstract
Myocardial infarction (MI) is a restrictive phenotype of coronary artery disease. To date, a group of genes and genetic loci have been associated to MI. However, the genetic causes and underlying molecular mechanisms for MI remain largely unknown. SIRT1, one of highly conserved NAD-dependent class III deacetylases, has been involved in several cellular processes and implicated in human diseases. Autophagy is one of major cellular degradative pathways, which plays important roles in lipid metabolism. Recent studies have shown that SIRT1 deacetylates autophagy-related genes, and the expressions of autophagic genes are altered in MI patients. Accordingly, we hypothesized that SIRT1 may be linked to the MI pathogenesis. In this study, the SIRT1 gene promoter were genetically analyzed in large cohorts of MI patients (n = 327) and controls (n = 358). The results showed that six single-nucleotide polymorphisms and 14 sequence variants were identified. Among these, five novel heterozygous variants (g.69643743Ins, g.69643840Ins, g.69643903G > C, g.69644235G > C and g.69644353G > T) and one single-nucleotide polymorphism (rs35706870) were identified in MI patients, but in none of controls. Moreover, five novel heterozygous variants (g.69643672G > A, g.69644226C > T, g.69644278A > G, g.69644408G > A and g.69644408G > T) were only found in controls. The rest variants were found in MI patients and controls with similar frequencies. Taken together, the variants identified in MI patients may alter the transcriptional activities of SIRT1 gene promoter, which may change SIRT1 levels, contributing to the MI pathogenesis as a risk factor.
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Affiliation(s)
- Yinghua Cui
- Shandong Provincial Key Laboratory of Cardiac Disease Diagnosis and Treatment, Jining Medical University Affiliated Hospital, Jining Medical University, Jining, Shandong 272029, China
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Alvarez Y, Rodríguez M, Municio C, Hugo E, Alonso S, Ibarrola N, Fernández N, Crespo MS. Sirtuin 1 is a key regulator of the interleukin-12 p70/interleukin-23 balance in human dendritic cells. J Biol Chem 2012; 287:35689-35701. [PMID: 22893703 DOI: 10.1074/jbc.m112.391839] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Stimulation of human dendritic cells with the fungal surrogate zymosan produces IL-23 and a low amount of IL-12 p70. Trans-repression of il12a transcription, which encodes IL-12 p35 chain, by proteins of the Notch family and lysine deacetylation reactions have been reported as the underlying mechanisms, but a number of questions remain to be addressed. Zymosan produced the location of sirtuin 1 (SIRT1) to the nucleus, enhanced its association with the il12a promoter, increased the nuclear concentration of the SIRT1 co-substrate NAD(+), and decreased chromatin accessibility in the nucleosome-1 of il12a, which contains a κB-site. The involvement of deacetylation reactions in the inhibition of il12a transcription was supported by the absence of Ac-Lys-14-histone H3 in dendritic cells treated with zymosan upon coimmunoprecipitation of transducin-like enhancer of split. In contrast, we did not obtain evidence of a possible effect of SIRT1 through the deacetylation of c-Rel, the central element of the NF-κB family involved in il12a regulation. These data indicate that an enhancement of SIRT1 activity in response to phagocytic stimuli may reduce the accessibility of c-Rel to the il12a promoter and its transcriptional activation, thus regulating the IL-12 p70/IL-23 balance and modulating the ongoing immune response.
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Affiliation(s)
- Yolanda Alvarez
- Instituto de Biología y Genética Molecular, Consejo Superior de Investigaciones Científicas, 47003 Valladolid, Spain
| | - Mario Rodríguez
- Instituto de Biología y Genética Molecular, Consejo Superior de Investigaciones Científicas, 47003 Valladolid, Spain
| | - Cristina Municio
- Instituto de Biología y Genética Molecular, Consejo Superior de Investigaciones Científicas, 47003 Valladolid, Spain
| | - Etzel Hugo
- Instituto de Biología y Genética Molecular, Consejo Superior de Investigaciones Científicas, 47003 Valladolid, Spain
| | - Sara Alonso
- Instituto de Biología y Genética Molecular, Consejo Superior de Investigaciones Científicas, 47003 Valladolid, Spain
| | - Nieves Ibarrola
- Instituto de Biología Molecular y Celular del Cáncer, 37007 Salamanca, Spain
| | - Nieves Fernández
- Departamento de Bioquímica y Biología Molecular, y Fisiología, Universidad de Valladolid, 47005 Valladolid, Spain
| | - Mariano Sánchez Crespo
- Instituto de Biología y Genética Molecular, Consejo Superior de Investigaciones Científicas, 47003 Valladolid, Spain.
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White AT, Schenk S. NAD(+)/NADH and skeletal muscle mitochondrial adaptations to exercise. Am J Physiol Endocrinol Metab 2012; 303:E308-21. [PMID: 22436696 PMCID: PMC3423123 DOI: 10.1152/ajpendo.00054.2012] [Citation(s) in RCA: 124] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Accepted: 03/15/2012] [Indexed: 12/21/2022]
Abstract
The pyridine nucleotides, NAD(+) and NADH, are coenzymes that provide oxidoreductive power for the generation of ATP by mitochondria. In skeletal muscle, exercise perturbs the levels of NAD(+), NADH, and consequently, the NAD(+)/NADH ratio, and initial research in this area focused on the contribution of redox control to ATP production. More recently, numerous signaling pathways that are sensitive to perturbations in NAD(+)(H) have come to the fore, as has an appreciation for the potential importance of compartmentation of NAD(+)(H) metabolism and its subsequent effects on various signaling pathways. These pathways, which include the sirtuin (SIRT) proteins SIRT1 and SIRT3, the poly(ADP-ribose) polymerase (PARP) proteins PARP1 and PARP2, and COOH-terminal binding protein (CtBP), are of particular interest because they potentially link changes in cellular redox state to both immediate, metabolic-related changes and transcriptional adaptations to exercise. In this review, we discuss what is known, and not known, about the contribution of NAD(+)(H) metabolism and these aforementioned proteins to mitochondrial adaptations to acute and chronic endurance exercise.
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Affiliation(s)
- Amanda T White
- Biomedical Sciences Graduate Program, University of California, San Diego, La Jolla, CA 92093, USA
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122
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White AT, Schenk S. NAD(+)/NADH and skeletal muscle mitochondrial adaptations to exercise. AMERICAN JOURNAL OF PHYSIOLOGY. ENDOCRINOLOGY AND METABOLISM 2012. [PMID: 22436696 DOI: 10.1152/ajpendo.00054.2012.] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The pyridine nucleotides, NAD(+) and NADH, are coenzymes that provide oxidoreductive power for the generation of ATP by mitochondria. In skeletal muscle, exercise perturbs the levels of NAD(+), NADH, and consequently, the NAD(+)/NADH ratio, and initial research in this area focused on the contribution of redox control to ATP production. More recently, numerous signaling pathways that are sensitive to perturbations in NAD(+)(H) have come to the fore, as has an appreciation for the potential importance of compartmentation of NAD(+)(H) metabolism and its subsequent effects on various signaling pathways. These pathways, which include the sirtuin (SIRT) proteins SIRT1 and SIRT3, the poly(ADP-ribose) polymerase (PARP) proteins PARP1 and PARP2, and COOH-terminal binding protein (CtBP), are of particular interest because they potentially link changes in cellular redox state to both immediate, metabolic-related changes and transcriptional adaptations to exercise. In this review, we discuss what is known, and not known, about the contribution of NAD(+)(H) metabolism and these aforementioned proteins to mitochondrial adaptations to acute and chronic endurance exercise.
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Affiliation(s)
- Amanda T White
- Biomedical Sciences Graduate Program, University of California, San Diego, La Jolla, CA 92093, USA
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123
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Zhang A, Wang H, Qin X, Pang S, Yan B. Genetic analysis of SIRT1 gene promoter in sporadic Parkinson's disease. Biochem Biophys Res Commun 2012; 422:693-6. [PMID: 22613205 DOI: 10.1016/j.bbrc.2012.05.059] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2012] [Accepted: 05/11/2012] [Indexed: 01/28/2023]
Abstract
Parkinson's disease (PD) is one of the most common neurodegenerative diseases. To date, genetic causes and underlying molecular mechanisms for sporadic PD remain largely unknown. Sirtuis are highly conserved NAD-dependent class III deacetylases. SIRT1, the closest to yeast Sir2, has deacetylase activity and ADP-ribosyltransferase activity. SIRT1 gene has been connected to many cellular processes and implicated in human diseases, such as obesity, type 2 diabetes, cancer and neurodegenerative diseases. Studies in animal model have also associated SIRT1 with aggregation of alpha-synuclein, a critical protein in the PD pathogenesis. We hypothesized that the genetic variants within the regulatory regions of SIRT1 gene that repress its gene expression, rather than mutations in its coding region that abolish SIRT1 function, may contribute to PD as a risk factor. In this study, we genetically analyzed the promoter region of SIRT1 gene in sporadic PD patients and ethic-matched healthy controls. Three novel heterozygous sequence variants, g.69644133C>G, g.69644213G>A and g.69644351G>A, were identified in PD patients, but in none of controls, which may alter the transcriptional activities of SIRT1 gene promoter, resulting in reduced SIRT1 levels. One novel heterozygous variant, g.69644219G>A, linked with single-nucleotide polymorphism - g.69644217A>C (rs932658), was only found in one control, which may have no functional activity. Therefore, our results suggested that genetic variants within the SIRT1 gene promoter may repress SIRT1 gene expression, contributing to PD as a risk factor.
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Affiliation(s)
- Aimei Zhang
- Division of Neurology, Jining Medical College Affiliated Hospital, Jining Medical College, Jining, Shandong 272029, China
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Benhamed F, Denechaud PD, Lemoine M, Robichon C, Moldes M, Bertrand-Michel J, Ratziu V, Serfaty L, Housset C, Capeau J, Girard J, Guillou H, Postic C. The lipogenic transcription factor ChREBP dissociates hepatic steatosis from insulin resistance in mice and humans. J Clin Invest 2012; 122:2176-94. [PMID: 22546860 DOI: 10.1172/jci41636] [Citation(s) in RCA: 295] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2009] [Accepted: 02/15/2012] [Indexed: 12/12/2022] Open
Abstract
Nonalcoholic fatty liver disease (NAFLD) is associated with all features of the metabolic syndrome. Although deposition of excess triglycerides within liver cells, a hallmark of NAFLD, is associated with a loss of insulin sensitivity, it is not clear which cellular abnormality arises first. We have explored this in mice overexpressing carbohydrate responsive element-binding protein (ChREBP). On a standard diet, mice overexpressing ChREBP remained insulin sensitive, despite increased expression of genes involved in lipogenesis/fatty acid esterification and resultant hepatic steatosis (simple fatty liver). Lipidomic analysis revealed that the steatosis was associated with increased accumulation of monounsaturated fatty acids (MUFAs). In primary cultures of mouse hepatocytes, ChREBP overexpression induced expression of stearoyl-CoA desaturase 1 (Scd1), the enzyme responsible for the conversion of saturated fatty acids (SFAs) into MUFAs. SFA impairment of insulin-responsive Akt phosphorylation was therefore rescued by the elevation of Scd1 levels upon ChREBP overexpression, whereas pharmacological or shRNA-mediated reduction of Scd1 activity decreased the beneficial effect of ChREBP on Akt phosphorylation. Importantly, ChREBP-overexpressing mice fed a high-fat diet showed normal insulin levels and improved insulin signaling and glucose tolerance compared with controls, despite having greater hepatic steatosis. Finally, ChREBP expression in liver biopsies from patients with nonalcoholic steatohepatitis was increased when steatosis was greater than 50% and decreased in the presence of severe insulin resistance. Together, these results demonstrate that increased ChREBP can dissociate hepatic steatosis from insulin resistance, with beneficial effects on both glucose and lipid metabolism.
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Abstract
Carbohydrate-responsive element binding protein (ChREBP (MLXIPL)) is emerging as an important mediator of glucotoxity both in the liver and in the pancreatic β-cells. Although the regulation of its nuclear translocation and transcriptional activation by glucose has been the subject of intensive research, it is still not fully understood. We have recently uncovered a novel mechanism in the excitable pancreatic β-cell where ChREBP interacts with sorcin, a penta-EF-hand Ca(2)(+)-binding protein, and is sequestered in the cytosol at low glucose concentrations. Upon stimulation with glucose and activation of Ca(2)(+) influx, or application of ATP as an intracellular Ca(2)(+)-mobilising agent, ChREBP rapidly translocates to the nucleus. In sorcin-silenced cells, ChREBP is constitutively present in the nucleus, and both glucose and Ca(2)(+) are ineffective in stimulating further ChREBP nuclear shuttling. Whether an active Ca(2)(+)-sorcin element of ChREBP activation also exists in non-excitable cells is discussed.
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Affiliation(s)
- Isabelle Leclerc
- Division of Diabetes, Endocrinology and Metabolism, Section of Cell Biology, Department of Medicine, Imperial College London, SW7 2AZ London, UK.
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Nicotinamide, NAD(P)(H), and Methyl-Group Homeostasis Evolved and Became a Determinant of Ageing Diseases: Hypotheses and Lessons from Pellagra. Curr Gerontol Geriatr Res 2012; 2012:302875. [PMID: 22536229 PMCID: PMC3318212 DOI: 10.1155/2012/302875] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Accepted: 12/19/2011] [Indexed: 01/22/2023] Open
Abstract
Compartmentalized redox faults are common to ageing diseases. Dietary constituents are catabolized to NAD(H) donating electrons producing proton-based bioenergy in coevolved, cross-species and cross-organ networks. Nicotinamide and NAD deficiency from poor diet or high expenditure causes pellagra, an ageing and dementing disorder with lost robustness to infection and stress. Nicotinamide and stress induce Nicotinamide-N-methyltransferase (NNMT) improving choline retention but consume methyl groups. High NNMT activity is linked to Parkinson's, cancers, and diseases of affluence. Optimising nicotinamide and choline/methyl group availability is important for brain development and increased during our evolution raising metabolic and methylome ceilings through dietary/metabolic symbiotic means but strict energy constraints remain and life-history tradeoffs are the rule. An optimal energy, NAD and methyl group supply, avoiding hypo and hyper-vitaminoses nicotinamide and choline, is important to healthy ageing and avoids utilising double-edged symbionts or uncontrolled autophagy or reversions to fermentation reactions in inflammatory and cancerous tissue that all redistribute NAD(P)(H), but incur high allostatic costs.
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Abstract
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.
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128
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Havula E, Hietakangas V. Glucose sensing by ChREBP/MondoA-Mlx transcription factors. Semin Cell Dev Biol 2012; 23:640-7. [PMID: 22406740 DOI: 10.1016/j.semcdb.2012.02.007] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Accepted: 02/24/2012] [Indexed: 01/02/2023]
Abstract
The paralogous transcription factors ChREBP and MondoA, together with their common binding partner Mlx, have emerged as key mediators of intracellular glucose sensing. By regulating target genes involved in glycolysis and lipogenesis, they mediate metabolic adaptation to changing glucose levels. As disturbed glucose homeostasis plays a central role in human metabolic diseases and as cancer cells often display altered glucose metabolism, better understanding of cellular glucose sensing will likely uncover new therapeutic opportunities. Here we review the regulation, function and evolutionary conservation of the ChREBP/MondoA-Mlx glucose sensing system and discuss possible directions for future research.
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Affiliation(s)
- Essi Havula
- Institute of Biotechnology, University of Helsinki, Viikinkaari 1, 00014 Helsinki, Finland
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The cAMP/PKA pathway rapidly activates SIRT1 to promote fatty acid oxidation independently of changes in NAD(+). Mol Cell 2012; 44:851-63. [PMID: 22195961 DOI: 10.1016/j.molcel.2011.12.005] [Citation(s) in RCA: 270] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Revised: 12/01/2011] [Accepted: 12/06/2011] [Indexed: 01/08/2023]
Abstract
The NAD(+)-dependent deacetylase SIRT1 is an evolutionarily conserved metabolic sensor of the Sirtuin family that mediates homeostatic responses to certain physiological stresses such as nutrient restriction. Previous reports have implicated fluctuations in intracellular NAD(+) concentrations as the principal regulator of SIRT1 activity. However, here we have identified a cAMP-induced phosphorylation of a highly conserved serine (S434) located in the SIRT1 catalytic domain that rapidly enhanced intrinsic deacetylase activity independently of changes in NAD(+) levels. Attenuation of SIRT1 expression or the use of a nonphosphorylatable SIRT1 mutant prevented cAMP-mediated stimulation of fatty acid oxidation and gene expression linked to this pathway. Overexpression of SIRT1 in mice significantly potentiated the increases in fatty acid oxidation and energy expenditure caused by either pharmacological β-adrenergic agonism or cold exposure. These studies support a mechanism of Sirtuin enzymatic control through the cAMP/PKA pathway with important implications for stress responses and maintenance of energy homeostasis.
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