SIRT1: linking adaptive cellular responses to aging-associated changes in organismal physiology

S-Propargyl-Cysteine Ameliorates Peripheral Nerve Injury through Microvascular Reconstruction

Microvascular reconstruction is essential for peripheral nerve repair. S-Propargyl-cysteine (SPRC), the endogenous hydrogen sulfide (H₂S) donor, has been reported to promote angiogenesis. The aim of this study is to utilize the pro-angiogenic ability of SPRC to support peripheral nerve repair and to explore the potential mechanisms. The effects and mechanisms of SPRC on angiogenesis and peripheral nerve repair were examined under hypoxic condition by establishing a sciatic nerve crushed injury model in mice and rats, and a hypoxia model in human umbilical vascular endothelial cells (HUVECs) in vitro. We found that SPRC accelerated the function recovery of the injured sciatic nerve and alleviated atrophy of the gastrocnemius muscle in mice. It facilitated the viability of Schwann cells (SCs), the outgrowth and myelination of regenerated axons, and angiogenesis in rats. It enhanced the viability, proliferation, adhesion, migration, and tube formation of HUVECs under hypoxic condition. SPRC activated sirtuin1 (SIRT1) expression by promoting the production of endogenous H₂S, and SIRT1 negatively regulated Notch signaling in endothelial cells (ECs), thereby promoting angiogenesis. Collectively, our study has provided important evidence that SPRC has an effective role in peripheral nerve repair through microvascular reconstruction, which could be a potentially effective medical therapy for peripheral nerve injury.

Dipeptide IF and Exercise Training Attenuate Hypertension in SHR Rats by Inhibiting Fibrosis and Hypertrophy and Activating AMPKα1, SIRT1, and PGC1α

Bioactive peptides are physiologically active peptides produced from proteins by gastrointestinal digestion, fermentation, or hydrolysis by proteolytic enzymes. Bioactive peptides are resorbed in their whole form and have a preventive effect against various disease conditions, including hypertension, dyslipidemia, inflammation, and oxidative stress. In recent years, there has been a growing body of evidence showing that physiologically active peptides may have a function in sports nutrition. The present study aimed to evaluate the synergistic effect of dipeptide (IF) from alcalase potato protein hydrolysates and exercise training in hypertensive (SHR) rats. Animals were divided into five groups. Bioactive peptide IF and swimming exercise training normalized the blood pressure and decreased the heart weight. Cardiac, hepatic, and renal functional markers also normalized in SHR rats. The combined administration of IF peptide and exercise offer better protection in SHR rats by downregulating proteins associated with myocardial fibrosis, hypertrophy, and inflammation. Remarkably, peptide treatment alongside exercise activates the PI3K/AKT cell survival pathway in the myocardial tissue of SHR animals. Further, the mitochondrial biogenesis pathway (AMPKα1, SIRT1, and PGC1α) was synergistically activated by the combinatorial treatment of IF and exercise. Exercise training along with IF administration could be a possible approach to alleviating hypertension.

SIRT1 provides new pharmacological targets for polydatin through its role as a metabolic sensor

The SIRT family of proteins constitutes highly conserved deacetylases with diverse and extensive functions. These proteins have specific biological functions, including regulation of transcription, cell cycle, cell differentiation, apoptosis, stress, metabolism, and genomic stability. Polydatin is a monocrystalline compound isolated from a Chinese herb, Polygonum cuspidatum. The pharmacological mechanisms of polydatin are mostly unclear but involve members of the SIRT protein family, among which SIRT1 plays a vital role. Polydatin is usually considered a potential SIRT1 activator. This review summarizes the signaling mechanism of polydatin involving SIRT1 and discusses the roles of related signal molecules such as PGC-1α, Nrf2, p38-MAPK, NLPR3 inflammasome, and p53. Further, we describe the metabolic regulation of related biological macromolecules and demonstrate that SIRT1, as a metabolic sensor, may act as a new pharmacological target for polydatin.

IL-1β induces expression of proinflammatory cytokines and migration of human colon cancer cells through upregulation of SIRT1

SIRT1 is a mammalian NAD⁺-dependent deacetylase, which is known to be involved in various physiological events, such as adaptive response to environmental stresses including caloric restriction, as well as in aging and cellular senescence. However, recent studies have revealed overexpression of SIRT1 in many different types of human malignancies, particularly colon cancer. Interleukin-1β (IL-1β) is a proinflammatory cytokine that plays a major role in invasiveness, stemness and progression of colon cancer. However, the interaction between IL-1β and SIRT1 in the tumor development and progression remains elusive. In this study, we found that IL-1β induces SIRT1 protein expression in human colon cancer HCT-116 cells. IL-1β-induced SIRT1 upregulation led to enhanced expression of mRNA transcripts of pro-inflammatory cytokines, IL-6 and IL-8 as well as that of IL-1β. Knockdown of SIRT1 prevented IL-1β-induced phosphorylation and nuclear accumulation of c-Jun. Furthermore, pharmacologic inhibition of SIRT1 abrogated clonogenicity and migrative capability of human colon cancer cells stimulated with IL-1β. In summary, IL-1β-induced SIRT1 upregulation stimulates production of proinflammatory cytokines via a nuclear accumulation of c-Jun, leadng to colon cancer growth and progression.

Nicotinamide Mononucleotide Restores the Meiotic Competency of Porcine Oocytes Exposed to Ethylene Glycol Butyl Ether

Ethylene glycol butyl ether (EGBE), a type of glycol ethers, is a common chemical used in both industrial and household products. Increasing animal studies have indicated that it produces reproductive problems, such as testicular damage, reduced female fertility, death of embryos, and birth defects. However, how it influences the female germ cells has not yet determined. Here, we found that EGBE exposure resulted in the defective porcine oocyte maturation via disruption of cytoskeleton dynamics, showing the abnormal spindle assembly, chromosome alignment, and actin organization. Meanwhile, EGBE exposure perturbed the mitochondrial distribution and function, leading to the accumulation of reactive oxygen species (ROS) and generation of DNA damage and apoptosis. Of note, nicotinamide mononucleotide (NMN) supplementation rescued the meiotic defects caused by EGBE exposure via restoring NAD⁺ level and mitochondrial function and thus eliminating the excessive ROS. Taken together, our observations illustrate that NMN supplementation is an effective strategy to protect oocyte quality against environmental pollutant-induced deterioration, contributing to improve the animal and human fertility.

Dilated cardiomyopathy impairs mitochondrial biogenesis and promotes inflammation in an age- and sex-dependent manner

Dilated cardiomyopathy (DCM) belongs to the myocardial diseases associated with a severe impairment of cardiac function, but the question of how sex and age affect this pathology has not been fully explored. Impaired energy homeostasis, mitochondrial dysfunction, and systemic inflammation are well-described phenomena associated with aging. In this study, we investigated if DCM affects these phenomena in a sex- and age-related manner. We analyzed the expression of mitochondrial and antioxidant proteins and the inflammatory state in DCM heart tissue from younger and older women and men. A significant downregulation of Sirt1 expression was detected in older DCM patients. Sex-related differences were observed in the phosphorylation of AMPK that only appeared in older males with DCM, possibly due to an alternative Sirt1 regulation mechanism. Furthermore, reduced expression of several mitochondrial proteins (TOM40, TIM23, Sirt3, and SOD2) and genes (cox1, nd4) was only detected in old DCM patients, suggesting that age has a greater effect than DCM on these alterations. Finally, an increased expression of inflammatory markers in older, failing hearts, with a stronger pro-inflammatory response in men, was observed. Together, these findings indicate that age- and sex-related increased inflammation and disturbance of mitochondrial homeostasis occurs in male individuals with DCM.

The Versatility of Sirtuin-1 in Endocrinology and Immunology

Sirtuins belong to the class III family of NAD-dependent histone deacetylases (HDAC) and are involved in diverse physiological processes that range from regulation of metabolism and endocrine function to coordination of immunity and cellular responses to stress. Sirtuin-1 (SIRT1) is the most well-studied family member and has been shown to be critically involved in epigenetics, immunology, and endocrinology. The versatile roles of SIRT1 include regulation of energy sensing metabolic homeostasis, deacetylation of histone and non-histone proteins in numerous tissues, neuro-endocrine regulation via stimulation of hypothalamus-pituitary axes, synthesis and maintenance of reproductive hormones via steroidogenesis, maintenance of innate and adaptive immune system via regulation of T- and B-cell maturation, chronic inflammation and autoimmune diseases. Moreover, SIRT1 is an appealing target in various disease contexts due to the promise of pharmacological and/or natural modulators of SIRT1 activity within the context of endocrine and immune-related disease models. In this review we aim to provide a broad overview on the role of SIRT1 particularly within the context of endocrinology and immunology.

Exercise and Sirtuins: A Way to Mitochondrial Health in Skeletal Muscle

The sirtuins form a family of evolutionarily conserved nicotinamide adenine dinucleotide (NAD)-dependent deacetylases. Seven sirtuins (SIRT1–SIRT7) have been described in mammals, with specific intracellular localization and biological functions associated with mitochondrial energy homeostasis, antioxidant activity, proliferation and DNA repair. Physical exercise affects the expression of sirtuin in skeletal muscle, regulating changes in mitochondrial biogenesis, oxidative metabolism and the cellular antioxidant system. In this context, sirtuin 1 and sirtuin 3 have been the most studied. This review focuses on the effects of different types of exercise on these sirtuins, the molecular pathways involved and the biological effect that is caused mainly in healthy subjects. The reported findings suggest that an acute load of exercise activates SIRT1, which in turn activates biogenesis and mitochondrial oxidative capacity. Additionally, several sessions of exercise (training) activates SIRT1 and also SIRT3 that, together with the biogenesis and mitochondrial oxidative function, jointly activate ATP production and the mitochondrial antioxidant function.

Sirt1 promotes autophagy and inhibits apoptosis to protect cardiomyocytes from hypoxic stress

Sirtuin 1 (Sirt1) exerts its cardioprotective effects in various cardiovascular diseases via multiple cellular activities. However, the therapeutic implications of Sirt1 in hypoxic cardiomyocytes and the underlying mechanisms remain elusive. The present study investigated whether Sirt1 regulates autophagy and apoptosis in hypoxic H9C2 cardiomyocytes and in an experimental hypoxic mouse model. Right ventricular outflow tract biopsies were obtained from patients with cyanotic or acyanotic congenital heart diseases. Adenovirus Ad‑Sirt1 was used to activate Sirt1 and Ad‑Sh‑Sirt1 was used to inhibit Sirt1 expression in H9C2 cells, in order to investigate the effect of Sirt1 on cellular autophagy and apoptosis. SRT1720, a pharmacological activator of Sirt1 and EX‑527, a Sirt1 antagonist, were administered to mice to explore the role of Sirt1 in hypoxic cardiomyocytes in vivo. The levels of autophagy and apoptosis‑related proteins were evaluated using western blotting. Apoptosis was investigated by TUNEL staining and Annexin V/7‑aminoactinomycin D flow cytometry analysis. Heart tissue samples from cyanotic patients exhibited increased autophagy and apoptosis, as well as elevated Sirt1 levels, compared with the noncyanotic control samples. The data from the western blot analysis revealed that Sirt1 promoted autophagic flux and reduced apoptosis in hypoxic H9C2 cells. In addition, Sirt1 activated AMP‑activated protein kinase (AMPK), and the AMPK inhibitor Compound C abolished the effect of Sirt1 on autophagy activation. Further exploration of the mechanism revealed that Sirt1 protects hypoxic cardiomyocytes from apoptosis, at least in part, through inositol requiring kinase enzyme 1α (IRE1α). Consistent with the in vitro results, treatment with the Sirt1 activator SRT1720 activated AMPK, inhibited IRE1α, enhanced autophagy, and decreased apoptosis in the heart tissues of normoxic mice compared with the hypoxia control group. Opposite changes were observed in hypoxic mice treated with the Sirt1 inhibitor EX‑527. These results suggested that Sirt1 promoted autophagy via AMPK activation and reduced hypoxia‑induced apoptosis via the IRE1α pathway, to protect cardiomyocytes from hypoxic stress.

Tumor-suppressive function of SIRT4 in neuroblastoma through mitochondrial damage

Background

SIRT4 is a member of the sirtuin family of nicotinamide adenine dinucleotide-dependent enzymes located in the mitochondria, and is involved in regulating energy metabolism, stress response, and cellular lifespan in mammalian cells. However, its function in human neuroblastoma (NB) remains unexplored.

Methods

Expression of SIRT4 in 158 pairs of human NB tumor tissues and adjacent normal tissues collected from March 2009 to October 2012 was analyzed by immunohistochemistry, Western blotting, and real-time fluorescence quantitative PCR. For in vitro study, SIRT4 was overexpressed in SH-SY5Y, SK-N-BE, and IMR-32 cells to study the effects of SIRT4 expression on proliferation, invasion, and migration of human NB cells and on mitochondrial function.

Results

SIRT4 gene expression in human NB tumor tissues was significantly lower than that in adjacent normal tissues (P<0.001). SIRT4 expression was lower in NB patients with higher International Neuroblastoma Staging System stage (P=0.018), with lymph node metastasis, than patients without lymph node metastasis (P<0.001). Survival times of NB patients with low expression of SIRT4 were significantly shorter than those of patients with high expression of SIRT4 (P=0.0036). Overexpression of SIRT4 significantly reduced the proliferation, invasion, and migration ability of NB cells as well as mitochondrial energy production, and caused SIRT1 upregulation and mitochondrial damage in NB cells.

Conclusion

SIRT4 exhibits a tumor suppressor function in human NB and inhibits mitochondrial metabolism and SIRT1 expression in tumor cells, thereby reducing the energy metabolism of tumor cells. These results suggest that SIRT4 may be a new therapeutic target for human NB.

Amelioration of Huntington's disease phenotypes by Beta-Lapachone is associated with increases in Sirt1 expression, CREB phosphorylation and PGC-1α deacetylation

Huntington’s disease (HD) is one of the most devastating genetic neurodegenerative disorders with no effective medical therapy. β-Lapachone (βL) is a natural compound obtained from the bark of the Lapacho tree and has been reported to have beneficial effects on various diseases. Sirt1 is a deacetylase of the sirtuin family and deacetylates proteins including the peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) which is associated with mitochondrial respiration and biogenesis. To examine the effectiveness of βL on HD, βL was orally applied to R6/2 HD mice and behavioral phenotypes associated with HD, such as impairment of rota-rod performance and increase of clasping behavior, as well as changes of Sirt1 expression, CREB phosphorylation and PGC-1α deacetylation were examined. Western blot results showed that Sirt1 and p-CREB levels were significantly increased in the brains of βL-treated R6/2 mice. An increase in deacetylation of PGC-1α, which is thought to increase its activity, was observed by oral administration of βL. In an in vitro HD model, βL treatment resulted in an attenuation of MitoSOX red fluorescence intensity, indicating an amelioration of mitochondrial reactive oxygen species by βL. Furthermore, improvements in the rota-rod performance and clasping score were observed in R6/2 HD mice after oral administration of βL compared to that of vehicle control-treated mice. Taken together, our data show that βL is a potential therapeutic candidate for the treatment of HD-associated phenotypes, and increases in Sirt1 level, CREB phosphorylation and PGC-103B1 deacetylation can be the possible underlying mechanism of the effects of βL.

Activation of silent mating type information regulation 2 homolog 1 by human chorionic gonadotropin exerts a therapeutic effect on hepatic injury and inflammation

Incidence and prevalence of inflammatory liver diseases has increased over the last years, but therapeutic options are limited. Pregnancy induces a state of immune tolerance, which can result in spontaneous improvement of clinical symptoms of certain autoimmune diseases including autoimmune hepatitis (AIH). We investigated the immune-suppressive mechanisms of the human pregnancy hormone, chorionic gonadotropin (hCG), in the liver. hCG signaling activates silent mating type information regulation 2 homolog 1 (SIRT1), which deacetylates forkhead box o3 (FOXO3a), leading to repression of proapoptotic gene expression, because the immunosuppressive consequence attributed to the absence of caspase-3 activity of hepatocellular interleukin 16 (IL-16) is no longer processed and released. Thus, serum levels of IL-16, a key chemotactic factor for CD4⁺ lymphocytes, were reduced and migration to injured hepatocytes prevented. Furthermore, elevated IL-16 levels are found in the sera from patients with AIH, hepatitis B virus, hepatitis C virus, and nonalcoholic steatohepatitis.

CONCLUSION

Here, we report that hCG regulates the SIRT1/FOXO3a axis in hepatocytes, resulting in immune suppression by attenuating caspase-3-dependent IL-16 processing and release, which concomitantly prevents autoaggressive T-cell infiltration of the liver. Considering the low toxicity profile of hCG in humans, interrupting the inflammatory cycle by hCG opens new perspectives for therapeutic intervention of inflammatory liver diseases. (Hepatology 2017;65:2074-2089).

Metformin ameliorates hypoxia/reoxygenation-induced cardiomyocyte apoptosis based on the SIRT3 signaling pathway

Myocardial hypoxia/reoxygenation (H/R) injury is one of the main causes of death and disability worldwide. However, a limited number of therapies are available to minimize the detrimental effects of this injury. Recently, researchers have demonstrated that metformin exerts direct cardioprotective effects against H/R. The aim of this study was to investigate the underlying mechanisms of how metformin affects myocardial hypoxia/reoxygenation (H/R) injury. In our study, the activities of lactate dehydrogenase (LDH) and superoxide dismutase (SOD) as well as the levels of malondialdehyde (MDA) were measured. Following H/R injury, LDH activity and MDA levels were evidently increased, while SOD activity and cell viability significantly decreased. Surprisingly, metformin downregulated the levels of relative reactive oxygen species (ROS) and upregulated the levels of relative SOD following H/R injury. Furthermore, metformin-treated cells exhibited reduced cell death, which was demonstrated to be associated with increased SIRT3 expression compared to that in the control group, as evidenced by blocking of the protective effects of metformin on cell apoptosis by the SIRT3 inhibitor Nicotinamide (NAM). Therefore, our results demonstrate that metformin improves cells viability following H/R, and this cardioprotective effect is partly mediated by the SIRT3 signaling pathway.

Molecular and Cellular Changes During Cancer Progression Resulting From Genetic and Epigenetic Alterations

Tumorigenesis is a complex process that involves a persistent dismantling of cellular safeguards and checkpoints. These molecular and cellular changes that accumulate over months or decades lead to a change in the fundamental identity of a cell as it transitions from normal to malignant. In this chapter, we will examine some of the molecular changes in the evolving relationship between the genome and epigenome and highlight some of the key changes that occur as normal cells progress to tumor cells. For many years tumorigenesis was almost exclusively attributed to mutations in protein-coding genes. This notion that mutations in protein-coding genes were a fundamental driver of tumorigenesis enabled the development of several novel therapeutics that targeted the mutant protein or overactive pathway responsible for driving a significant portion of the tumor growth. However, because many therapeutic challenges remained in the face of these advances, it was clear that other pieces to the puzzle had yet to be discovered. Advances in molecular and genomics techniques continued and the study of epigenetics began to expand and helped reshape the view that drivers of tumorigenesis extended beyond mutations in protein-coding genes. Studies in the field of epigenetics began to identify aberrant epigenetic marks which created altered chromatin structures and enabled protein expression in tissues that defied rules governing tissue-specificity. Not only were epigenetic alterations found to enable overexpression of proto-oncogenes, they also led to the silencing of tumor suppressor genes. With these discoveries, it became clear that tumor growth could be stimulated by much more than mutations in protein-coding genes. In fact, it became increasingly clear that much of the human genome, while transcribed, did not lead to proteins. This discovery further led to studies that began to uncover the role of noncoding RNAs in regulating chromatin structure, gene transcription, and tumor biology. In this chapter, some of the key alterations in the genome and epigenome will be explored, and some of the cancer therapies that were developed as a result of these discoveries will be discussed.

Sirtuin 1 evaluation with a novel immunoassay approach based on TiO2-Au label and hyperbranched polymer hybrid

Accurate and highly sensitive evaluation of the sirtuin 1 (SirT1) level is becoming increasingly important for understanding the contribution of SirT1 in metabolism pathways. Here, a novel electrochemical immunoassay of SirT1 based on crosslinked hyperbranched azo-polymer decorated with gold colloids (Au-HAP) as sensing platform and titanium dioxide (TiO2)-Au nanocomposites to immobilize secondary antibody-horseradish peroxidase (Ab2-HRP) as electrochemical labels has been designed. Greatly enhanced sensitivity was achieved by exploiting the excellent conductivity of Au nanoparticle, the amplification effect of Au-HAP and TiO2-Au, and the favorable catalytic ability of HRP. The nanocomposites of Au-HAP and TiO2-Au could attach numerous capture antibodies on the surface for significant immune recognition efficiency. Meanwhile, the TiO2-Au-labeled Ab2-HRP using an HRP-thionine-H2O2 (hydrogen peroxide) detection system could further induce signal readout. Under optimal conditions, the signal intensity was linearly related to the concentration of SirT1 in the range of 1-500 ng ml(-1), and the limit of detection was 0.28 ng ml(-1). The developed biosensor exhibits attractive performance for the analysis of SirT1, with rapid response, high sensitivity, and high accuracy, and could become a promising technique for protein detection.

Neurodegeneration Alters Metabolic Profile and Sirt 1 Signaling in High-Fat-Induced Obese Mice

Different factors may contribute to the development of neurodegenerative diseases. Among them, metabolic syndrome (MS), which has reached epidemic proportions, has emerged as a potential element that may be involved in neurodegeneration. Furthermore, studies have shown the importance of the sirtuin family in neuronal survival and MS, which opens the possibility of new pharmacological targets. This study investigates the influence of sirtuin metabolic pathways by examining the functional capacities of glucose-induced obesity in an excitotoxic state induced by a quinolinic acid (QA) animal model. Mice were divided into two groups that received different diets for 8 weeks: one group received a regular diet, and the other group received a high-fat diet (HF) to induce MS. The animals were submitted to a stereotaxic surgery and subdivided into four groups: Standard (ST), Standard-QA (ST-QA), HF and HF-QA. The QA groups were given a 250 nL quinolinic acid injection in the right striatum and PBS was injected in the other groups. Obese mice presented with a weight gain of 40 % more than the ST group beyond acquiring an insulin resistance. QA induced motor impairment and neurodegeneration in both ST-QA and HF-QA, although no difference was observed between these groups. The HF-QA group showed a reduction in adiposity when compared with the groups that received PBS. Therefore, the HF-QA group demonstrated a commitment-dependent metabolic pathway. The results suggest that an obesogenic diet does not aggravate the neurodegeneration induced by QA. However, the excitotoxicity induced by QA promotes a sirtuin pathway impairment that contributes to metabolic changes.

The role and potential mechanism of resveratrol in the prevention and control of epilepsy

Epilepsy is one of the most common diseases affecting the nervous system, with more than 50 million patients suffering from epilepsy worldwide. Although epilepsy has been prevalent for thousands of years, it is still not possible to completely control the disease. Despite an increase in the number of available antiepileptic drugs, the incidence of epilepsy and its cure rate have not been substantially improved; thus, there is an urgent need to identify new drugs that treat, cure or protect against epilepsy. Resveratrol is a polyphenol compound with a broad range of biological activity; not only it has considerable antiepileptic effects, but it is also neuroprotective and has functions to counter epileptic depression. Resveratrol has the potential to be a new antiepileptic drug, thus further studies are needed to better investigate its potential.

Myeloid-specific SIRT1 Deletion Aggravates Hepatic Inflammation and Steatosis in High-fat Diet-fed Mice

Sirtuin 1 (SIRT1) is a mammalian NAD⁺-dependent protein deacetylase that regulates cellular metabolism and inflammatory response. The organ-specific deletion of SIRT1 induces local inflammation and insulin resistance in dietary and genetic obesity. Macrophage-mediated inflammation contributes to insulin resistance and metabolic syndrome, however, the macrophage-specific SIRT1 function in the context of obesity is largely unknown. C57/BL6 wild type (WT) or myeloid-specific SIRT1 knockout (KO) mice were fed a high-fat diet (HFD) or normal diet (ND) for 12 weeks. Metabolic parameters and markers of hepatic steatosis and inflammation in liver were compared in WT and KO mice. SIRT1 deletion enhanced HFD-induced changes on body and liver weight gain, and increased glucose and insulin resistance. In liver, SIRT1 deletion increased the acetylation, and enhanced HFD-induced nuclear translocation of nuclear factor kappa B (NF-κB), hepatic inflammation and macrophage infiltration. HFD-fed KO mice showed severe hepatic steatosis by activating lipogenic pathway through sterol regulatory element-binding protein 1 (SREBP-1), and hepatic fibrogenesis, as indicated by induction of connective tissue growth factor (CTGF), alpha-smooth muscle actin (α-SMA), and collagen secretion. Myeloid-specific deletion of SIRT1 stimulates obesity-induced inflammation and increases the risk of hepatic fibrosis. Targeted induction of macrophage SIRT1 may be a good therapy for alleviating inflammation-associated metabolic syndrome.

Differential expression of sirtuins in the aging rat brain

Although there are seven mammalian sirtuins (SIRT1-7), little is known about their expression in the aging brain. To characterize the change(s) in mRNA and protein expression of SIRT1-7 and their associated proteins in the brain of “physiologically” aged Wistar rats. We tested mRNA and protein expression levels of rat SIRT1-7, and the levels of associated proteins in the brain using RT-PCR and western blotting. Our data shows that SIRT1 expression increases with age, concurrently with increased acetylated p53 levels in all brain regions investigated. SIRT2 and FOXO3a protein levels increased only in the occipital lobe. SIRT3-5 expression declined significantly in the hippocampus and frontal lobe, associated with increases in superoxide and fatty acid oxidation levels, and acetylated CPS-1 protein expression, and a reduction in MnSOD level. While SIRT6 expression declines significantly with age acetylated H3K9 protein expression is increased throughout the brain. SIRT7 and Pol I protein expression increased in the frontal lobe. This study identifies previously unknown roles for sirtuins in regulating cellular homeostasis and healthy aging.

Regulation of (pro)renin receptor expression in mIMCD via the GSK-3β-NFAT5-SIRT-1 signaling pathway

The localization and regulation of (pro)renin receptor (PRR) expression in kidney collecting duct cells are not well established. We hypothesized that low salt (LS) contributes to the regulation of PRR expression in these cells via the GSK-3β-NFAT5-sirtuin1 (SIRT-1) signaling pathway. Mouse inner medullary collecting duct (mIMCD) cells were treated with NaCl at 130 (normal salt; NS), 63 (LS), or 209 mM (high salt; HS) alone or in combination with NFAT5 scrambled small interfering (si) RNA, NFAT5 siRNA, or the SIRT-1 inhibitor EX-527. Compared with NS, LS increased the mRNA and protein expression of PRR by 71% and 69% (P < 0.05), and reduced phosphorylation of GSK-3β by 62% (P < 0.01), mRNA and protein expressions of NFAT5 by 65% and 45% (P < 0.05), and SIRT-1 by 44% and 50% (P < 0.01), respectively. LS also enhanced p65 NF-κB by 102% (P < 0.01). Treatment with HS significantly reduced the mRNA and protein expression of PRR by 32% and 23% (P < 0.05), and increased the mRNA and protein expression of NFAT5 by 39% and 45% (P < 0.05) and SIRT-1 by 51% and 56% (P < 0.05), respectively. HS+NFAT5 siRNA reduced the mRNA and protein expression of NFAT5 by 51% and 35% (P < 0.01) and increased the mRNA and protein expression of PRR by 148% and 70% (P < 0.01), respectively. HS+EX-527 significantly increased the mRNA and protein expression of PRR by 96% and 58% (P < 0.05), respectively. We conclude that expression of PRR in mIMCD cells is regulated by the GSK-3β-NFAT5- SIRT-1 signaling pathway.

SIRT1 inhibits apoptosis of degenerative human disc nucleus pulposus cells through activation of Akt pathway

Many studies have demonstrated that SIRT1, an NAD(+)-dependent deacetylase, reduces apoptosis in several different cells. However, the role of SIRT1 in apoptosis of disc nucleus pulposus (NP) cells remains unclear. The present study was performed to determine whether degenerative human NP would express SIRT1, and to investigate the role of SIRT1 in NP cells apoptosis. The expression of SIRT1 in disc NP of patients (>55 years) with lumbar disc degenerative disease (DDD) and the disc NP of patients (<25 years) with lumbar vertebra fracture (LVF) was assessed by immunohistochemistry, reverse transcription polymerase chain reaction, and Western blot analysis. The results showed that SIRT1 mRNA and protein levels were greater in LVF disc NP than those in DDD disc NP. Degenerative human NP cells were treated in culture with activator or inhibitor of SIRT1, resveratrol or nicotinamide, or SIRT1 small interfering RNA (siRNA), and cell apoptosis was quantified via flow cytometry. The rate of apoptosis was far fewer in resveratrol-treated NP cells than in SIRT1 siRNA-transfected or nicotinamide-treated NP cells. After SIRT1 siRNA was transfected, NP cells decreased phosphorylation of Akt, while resveratrol phosphorylated Akt. Treatment with LY294002 or Akt siRNA increased the rate of apoptosis. Our results suggested that SIRT1 plays a critical role in survival of degenerative human NP cells through the Akt anti-apoptotic signaling pathway.

Exercise training attenuates aging-associated mitochondrial dysfunction in rat skeletal muscle: role of PGC-1α

Aged skeletal muscle demonstrates declines in muscle mass and deterioration of mitochondrial content and function. Peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) plays an important role in promoting muscle mitochondrial biogenesis in response to exercise training, but its role in senescent muscle is not clear. In the present study we hypothesize that a downregulation of the PGC-1α signaling pathway contributes to mitochondrial deterioration in aged muscle whereas endurance training ameliorates the deficits. Three groups of Fischer 344/BNF1 rats were used: young, sedentary (Y, 4 months); old, sedentary (O, 22 months); and old trained (OT, 22 months), subjected to treadmill running at 17.5 m/min, 10% grade for 45 min/day, 5 days/week for 12-weeks. PGC-1α mRNA and nuclear PGC-1α protein content in the soleus muscle were both decreased in O vs. Y rats, whereas OT rats showed a 2.3 and 1.8-fold higher PGC-1α content than O and Y rats, respectively (P<0.01). Mitochondrial transcription factor A (Tfam), cytochrome c (Cyt c) and mitochondrial (mt) DNA contents were significantly decreased in O vs. Y rats, but elevated by 2.2 (P<0.01), 1.4 (P<0.05) and 2.4-fold (P<0.01), respectively, in OT vs. O rats. In addition, Tfam and mtDNA showed 1.6 and 1.8-fold (P<0.01) higher levels, respectively, in OT vs. Y rats. These adaptations were accompanied by significant increases in the expression of the phosphorylated form of AMP-activated kinase (AMPK) (P<0.01), p38 mitogen-activated kinase (MAPK) (P<0.05) and silent mating type information regulator 2 homolog 1 (SIRT1) (P<0.01) in OT rats. Furthermore, OT rats showed great levels of phosphorylation in cAMP responsive element binding protein (p-CREB) and DNA binding compared to O and Y rats. These data indicate that endurance training can attenuate aging-associated decline in mitochondrial protein synthesis in skeletal muscle partly due to upregulation of PGC-1α signaling.

Age-associated changes in oxidative stress and NAD+ metabolism in human tissue

Nicotinamide adenine dinucleotide (NAD⁺) is an essential electron transporter in mitochondrial respiration and oxidative phosphorylation. In genomic DNA, NAD⁺ also represents the sole substrate for the nuclear repair enzyme, poly(ADP-ribose) polymerase (PARP) and the sirtuin family of NAD-dependent histone deacetylases. Age associated increases in oxidative nuclear damage have been associated with PARP-mediated NAD⁺ depletion and loss of SIRT1 activity in rodents. In this study, we further investigated whether these same associations were present in aging human tissue. Human pelvic skin samples were obtained from consenting patients aged between 15–77 and newborn babies (0–1 year old) (n = 49) previously scheduled for an unrelated surgical procedure. DNA damage correlated strongly with age in both males (p = 0.029; r = 0.490) and females (p = 0.003; r = 0.600) whereas lipid oxidation (MDA) levels increased with age in males (p = 0.004; r = 0.623) but not females (p = 0.3734; r = 0.200). PARP activity significantly increased with age in males (p<0.0001; r = 0.768) and inversely correlated with tissue NAD⁺ levels (p = 0.0003; r = −0.639). These associations were less evident in females. A strong negative correlation was observed between NAD⁺ levels and age in both males (p = 0.001; r = −0.706) and females (p = 0.01; r = −0.537). SIRT1 activity also negatively correlated with age in males (p = 0.007; r = −0.612) but not in females. Strong positive correlations were also observed between lipid peroxidation and DNA damage (p<0.0001; r = 0.4962), and PARP activity and NAD⁺ levels (p = 0.0213; r = 0.5241) in post pubescent males. This study provides quantitative evidence in support of the hypothesis that hyperactivation of PARP due to an accumulation of oxidative damage to DNA during aging may be responsible for increased NAD⁺ catabolism in human tissue. The resulting NAD⁺ depletion may play a major role in the aging process, by limiting energy production, DNA repair and genomic signalling.

Activation of the stress proteome as a mechanism for small molecule therapeutics

Various small molecule pharmacologic agents with different known functions produce similar outcomes in diverse Mendelian and complex disorders, suggesting that they may induce common cellular effects. These molecules include histone deacetylase inhibitors, 4-phenylbutyrate (4PBA) and trichostatin A, and two small molecules without direct histone deacetylase inhibitor activity, hydroxyurea (HU) and sulforaphane. In some cases, the therapeutic effects of histone deacetylase inhibitors have been attributed to an increase in expression of genes related to the disease-causing gene. However, here we show that the pharmacological induction of mitochondrial biogenesis was necessary for the potentially therapeutic effects of 4PBA or HU in two distinct disease models, X-linked adrenoleukodystrophy and sickle cell disease. We hypothesized that a common cellular response to these four molecules is induction of mitochondrial biogenesis and peroxisome proliferation and activation of the stress proteome, or adaptive cell survival response. Treatment of human fibroblasts with these four agents induced mitochondrial and peroxisomal biogenesis as monitored by flow cytometry, immunofluorescence and/or western analyses. In treated normal human fibroblasts, all four agents induced the adaptive cell survival response: heat shock, unfolded protein, autophagic and antioxidant responses and the c-jun N-terminal kinase pathway, at the transcriptional and translational levels. Thus, activation of the evolutionarily conserved stress proteome and mitochondrial biogenesis may be a common cellular response to such small molecule therapy and a common basis of therapeutic action in various diseases. Modulation of this novel therapeutic target could broaden the range of treatable diseases without directly targeting the causative genetic abnormalities.

Resveratrol stimulates cortisol biosynthesis by activating SIRT-dependent deacetylation of P450scc

In the human adrenal cortex, cortisol is synthesized from cholesterol by members of the cytochrome P450 superfamily and hydroxysteroid dehydrogenases. Both the first and last steps of cortisol biosynthesis occur in mitochondria. Based on our previous findings that activation of ACTH signaling changes the ratio of nicotinamide adenine dinucleotide (NAD) phosphate to reduced NAD phosphate in adrenocortical cells, we hypothesized that pyridine nucleotide metabolism may regulate the activity of the mitochondrial NAD(+)-dependent sirtuin (SIRT) deacetylases. We show that resveratrol increases the protein expression and half-life of P450 side chain cleavage enzyme (P450scc). The effects of resveratrol on P450scc protein levels and acetylation status are dependent on SIRT3 and SIRT5 expression. Stable overexpression of SIRT3 abrogates the cellular content of acetylated P450scc, concomitant with an increase in P450scc protein expression and cortisol secretion. Mutation of K148 and K149 to alanine stabilizes the expression of P450scc and results in a 1.5-fold increase in pregnenolone biosynthesis. Finally, resveratrol also increases the protein expression of P450 11β, another mitochondrial enzyme required for cortisol biosynthesis. Collectively, this study identifies a role for NAD(+)-dependent SIRT deacetylase activity in regulating the expression of mitochondrial steroidogenic P450.

NAD+ metabolism and oxidative stress: the golden nucleotide on a crown of thorns

In the twentieth century, NAD+ research generated multiple discoveries. Identification of the important role of NAD+ as a cofactor in cellular respiration and energy production was followed by discoveries of numerous NAD+ biosynthesis pathways. In recent years, NAD+ has been shown to play a unique role in DNA repair and protein deacetylation. As discussed in this review, there are close interactions between oxidative stress and immune activation, energy metabolism, and cell viability in neurodegenerative disorders and ageing. Profound interactions with regard to oxidative stress and NAD+ have been highlighted in the present work. This review emphasizes the pivotal role of NAD+ in the regulation of DNA repair, stress resistance, and cell death, suggesting that NAD+ synthesis through the kynurenine pathway and/or salvage pathway is an attractive target for therapeutic intervention in age-associated degenerative disorders. NAD+ precursors have been shown to slow down ageing and extend lifespan in yeasts, and protect severed axons from degeneration in animal models neurodegenerative diseases.

Porphyromonas gingivalis lipopolysaccharide regulates interleukin (IL)-17 and IL-23 expression via SIRT1 modulation in human periodontal ligament cells

Increased interleukin (IL)-17 and IL-23 levels exist in the gingival tissue of periodontitis patients, but the precise molecular mechanisms that regulate IL-17 and IL-23 production remain unknown. The aim of this study was to explore the role of SIRT1 signaling on Porphyromonas gingivalis lipopolysaccharide (LPS)-induced IL-17 and IL-23 production in human periodontal ligament cells (hPDLCs). IL-17 and IL-23 production was significantly increased in LPS-treated cells. LPS treatment also led to the upregulation of SIRT1 mRNA and protein expression. LPS-induced IL-17 and IL-23 upregulation was attenuated by pretreatment with inhibitors of phosphoinositide 3-kinase (PI3K), p38, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), mitogen-activated protein kinase (MAPK), and NF-κB, as well as neutralizing antibodies against Toll-like receptors (TLRs) 2 and 4. Sirtinol treatment (a known SIRT1 inhibitor) or SIRT1 knockdown by small interfering RNA blocked LPS-stimulated IL-17 and IL-23 expression. Further investigation showed that LPS decreased osteoblast markers (i.e., ALP, OPN, and BSP) and concomitantly increased osteoclast markers (i.e., RANKL and M-CSF). This response was attenuated by inhibitors of the PI3K, p38, ERK, JNK, NF-κB, and SIRT1 pathways. These findings, for the first time, suggest that human periodontopathogen P. gingivalis LPS is implicated in periodontal disease bone destruction and may mediate IL-17 and IL-23 release from hPDLCs. This process is dependent, at least in part, on SIRT1-Akt/PI3K-MAPK-NF-κB signaling.

Involvement of SIRT1 in hypoxic down-regulation of c-Myc and β-catenin and hypoxic preconditioning effect of polyphenols

SIRT1 has been found to function as a Class III deacetylase that affects the acetylation status of histones and other important cellular nonhistone proteins involved in various cellular pathways including stress responses and apoptosis. In this study, we investigated the role of SIRT1 signaling in the hypoxic down-regulations of c-Myc and β-catenin and hypoxic preconditioning effect of the red wine polyphenols such as piceatannol, myricetin, quercetin and resveratrol. We found that the expression of SIRT1 was significantly increased in hypoxia-exposed or hypoxic preconditioned HepG2 cells, which was closely associated with the up-regulation of HIF-1α and down-regulation of c-Myc and β-catenin expression via deacetylation of these proteins. In addition, blockade of SIRT1 activation using siRNA or amurensin G, a new potent SIRT1 inhibitor, abolished hypoxia-induced HIF-1α expression but increased c-Myc and β-catenin expression. SIRT1 was also found to stabilize HIF-1α protein and destabilize c-Myc, β-catenin and PHD2 under hypoxia. We also found that myricetin, quercetin, piceatannol and resveratrol up-regulated HIF-1α and down-regulated c-Myc, PHD2 and β-catenin expressions via SIRT1 activation, in a manner that mimics hypoxic preconditioning. This study provides new insights of the molecular mechanisms of hypoxic preconditioning and suggests that polyphenolic SIRT1 activators could be used to mimic hypoxic/ischemic preconditioning.

SIRT1 associates with eIF2-alpha and regulates the cellular stress response

SIRT1 is a NAD+ dependent protein deacetylase known to increase longevity in model organisms. SIRT1 regulates cellular response to oxidative and/or genotoxic stress by regulating proteins such as p53 and FOXO. The eukaryotic initiation factor-2, eIF2, plays a critical role in the integrated stress response pathway. Under cellular stress, phosphorylation of the alpha subunit of eIF2 is essential for immediate shut-off of translation and activation of stress response genes. Here we demonstrate that SIRT1 interacts with eIF2α. Loss of SIRT1 results in increased phosphorylation of eIF2α. However, the downstream stress induced signaling pathway is compromised in SIRT1-deficient cells, indicated by delayed expression of the downstream target genes CHOP and GADD34 and a slower post-stress translation recovery. Finally, SIRT1 co-immunoprecipitates with mediators of eIF2α dephosphorylation, GADD34 and CreP, suggesting a role for SIRT1 in the negative feedback regulation of eIF2α phosphorylation.

Sirtuins: molecular traffic lights in the crossroad of oxidative stress, chromatin remodeling, and transcription

Transcription is regulated by acetylation/deacetylation reactions of histone and nonhistone proteins mediated by enzymes called KATs and HDACs, respectively. As a major mechanism of transcriptional regulation, protein acetylation is a key controller of physiological processes such as cell cycle, DNA damage response, metabolism, apoptosis, and autophagy. The deacetylase activity of class III histone deacetylases or sirtuins depends on the presence of NAD⁺ (nicotinamide adenine dinucleotide), and therefore, their function is closely linked to cellular energy consumption. This activity of sirtuins connects the modulation of chromatin dynamics and transcriptional regulation under oxidative stress to cellular lifespan, glucose homeostasis, inflammation, and multiple aging-related diseases including cancer. Here we provide an overview of the recent developments in relation to the diverse biological activities associated with sirtuin enzymes and stress responsive transcription factors, DNA damage, and oxidative stress and relate the involvement of sirtuins in the regulation of these processes to oncogenesis. Since the majority of the molecular mechanisms implicated in these pathways have been described for Sirt1, this sirtuin family member is more extensively presented in this paper.

Effects of Kynurenine Pathway Inhibition on NAD Metabolism and Cell Viability in Human Primary Astrocytes and Neurons

The kynurenine pathway (KP) is the principle route of L-Tryptophan (TRP) metabolism, producing several neurotoxic and neuroprotective metabolic precursors before complete oxidation to the essential pyridine nucleotide nicotinamide adenine dinucleotide (NAD⁺). KP inhibition may prove therapeutic in central nervous system (CNS) inflammation by reducing the production of excitotoxins such as quinolinic acid (QUIN). However, KP metabolism may also be cytoprotective through the de novo synthesis of intracellular NAD⁺. We tested the hypothesis that the KP is directly involved in the maintenance of intracellular NAD⁺ levels and SIRT1 function in primary astrocytes and neurons through regulation of NAD⁺ synthesis. Competitive inhibition of indoleamine 2,3 dioxygenase (IDO), and quinolinic acid phosphoribosyltransferase (QPRT) activities with 1-methyl-L-Tryptophan (1-MT), and phthalic acid (PA) respectively, resulted in a dose-dependent decrease in intracellular NAD⁺ levels and sirtuin deacetylase-1 (SIRT1) activity, and correlated directly with reduced cell viability. These results support the hypothesis that the primary role of KP activation during neuroinflammation is to maintain NAD⁺ levels through de novo synthesis from TRP. Inhibition of KP metabolism under these conditions can compromise cell viability, NAD-dependent SIRT1 activity and CNS function, unless alternative precursors for NAD⁺ synthesis are made available.

Nuclear SIRT1 activity, but not protein content, regulates mitochondrial biogenesis in rat and human skeletal muscle

Silent mating type information regulator 2 homolog 1 (SIRT1)-mediated peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) deacetylation is potentially key for activating mitochondrial biogenesis. Yet, at the whole muscle level, SIRT1 is not associated with mitochondrial biogenesis (Gurd, BJ, Yoshida Y, Lally J, Holloway GP, Bonen A. J Physiol 587: 1817-1828, 2009). Therefore, we examined nuclear SIRT1 protein and activity in muscle with varied mitochondrial content and in response to acute exercise. We also measured these parameters after stimulating mitochondrial biogenesis with chronic muscle contraction and 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) administration in rodents and exercise training in humans. In skeletal and heart muscles, nuclear SIRT1 protein was negatively correlated with indices of mitochondrial density (citrate synthase activity, CS; cytochrome oxidase IV, COX IV), but SIRT1 activity was positively correlated with these parameters (r > 0.98). Acute exercise did not alter nuclear SIRT1 protein but did induce a time-dependent increase in nuclear SIRT1 activity. This increase in SIRT1 activity was temporally related to increases in mRNA expression of genes activated by PGC-1α. Both chronic muscle stimulation and AICAR increased mitochondrial biogenesis and muscle PGC-1α, but not nuclear PGC-1α. Concomitantly, muscle and nuclear SIRT1 protein contents were reduced, but nuclear SIRT1 activity was increased. In human muscle, training-induced mitochondrial biogenesis did not alter muscle or nuclear SIRT1 protein content, but it did increase muscle and nuclear PGC-1α and SIRT1 activity. Thus, nuclear SIRT1 activity, but not muscle or nuclear SIRT1 protein content, is associated with contraction-stimulated mitochondrial biogenesis in rat and human muscle, possibly via AMPK activation.

Age related changes in NAD+ metabolism oxidative stress and Sirt1 activity in wistar rats

The cofactor nicotinamide adenine dinucleotide (NAD+) has emerged as a key regulator of metabolism, stress resistance and longevity. Apart from its role as an important redox carrier, NAD+ also serves as the sole substrate for NAD-dependent enzymes, including poly(ADP-ribose) polymerase (PARP), an important DNA nick sensor, and NAD-dependent histone deacetylases, Sirtuins which play an important role in a wide variety of processes, including senescence, apoptosis, differentiation, and aging. We examined the effect of aging on intracellular NAD+ metabolism in the whole heart, lung, liver and kidney of female wistar rats. Our results are the first to show a significant decline in intracellular NAD+ levels and NAD:NADH ratio in all organs by middle age (i.e.12 months) compared to young (i.e. 3 month old) rats. These changes in [NAD(H)] occurred in parallel with an increase in lipid peroxidation and protein carbonyls (o- and m- tyrosine) formation and decline in total antioxidant capacity in these organs. An age dependent increase in DNA damage (phosphorylated H2AX) was also observed in these same organs. Decreased Sirt1 activity and increased acetylated p53 were observed in organ tissues in parallel with the drop in NAD+ and moderate over-expression of Sirt1 protein. Reduced mitochondrial activity of complex I-IV was also observed in aging animals, impacting both redox status and ATP production. The strong positive correlation observed between DNA damage associated NAD+ depletion and Sirt1 activity suggests that adequate NAD+ concentrations may be an important longevity assurance factor.

Lower oxidative DNA damage despite greater ROS production in muscles from rats selectively bred for high running capacity

Artificial selection in rat has yielded high-capacity runners (HCR) and low-capacity runners (LCR) that differ in intrinsic (untrained) aerobic exercise ability and metabolic disease risk. To gain insight into how oxygen metabolism may have been affected by selection, we compared mitochondrial function, oxidative DNA damage (8-dihydroxy-guanosine; 8dOHG), and antioxidant enzyme activities in soleus muscle (Sol) and gastrocnemius muscle (Gas) of adult and aged LCR vs. HCR rats. In Sol of adult HCR rats, maximal ADP-stimulated respiration was 37% greater, whereas in Gas of adult HCR rats, there was a 23% greater complex IV-driven respiratory capacity and 54% greater leak as a fraction of electron transport capacity (suggesting looser mitochondrial coupling) vs. LCR rats. H(2)O(2) emission per gram of muscle was 24-26% greater for both muscles in adult HCR rats vs. LCR, although H(2)O(2) emission in Gas was 17% lower in HCR, after normalizing for citrate synthase activity (marker of mitochondrial content). Despite greater H(2)O(2) emission, 8dOHG levels were 62-78% lower in HCR rats due to 62-96% higher superoxide dismutase activity in both muscles and 47% higher catalase activity in Sol muscle in adult HCR rats, with no evidence for higher 8 oxoguanine glycosylase (OGG1; DNA repair enzyme) protein expression. We conclude that genetic segregation for high running capacity has generated a molecular network of cellular adaptations, facilitating a superior response to oxidative stress.

Aging changes the chromatin configuration and histone methylation of mouse oocytes at germinal vesicle stage

Aging decreases the fertility of mammalian females. In old oocytes at metaphase II stage (MII) there are alterations of the chromatin configuration and chromatin modifications such as histone acetylation. Recent data indicate that alterations of histone acetylation at MII initially arise at germinal vesicle stage (GV). Therefore, we hypothesized that the chromatin configuration and histone methylation could also change in old GV oocytes. In agreement with our hypothesis, young GV oocytes had non-surrounded nucleolus (NSN) and surrounded nucleolus (SN) chromatin configurations, while old GV oocytes also had chromatin configurations that could not be classified as NSN or SN. Regarding histone methylation, young GV and MII oocytes showed dimethylation of lysines 4, 9, 36 and 79 in histone 3 (H3K4me2, H3K9me2, H3K36me2, H3K79me2), lysine 20 in histone H4 (H4K20me2) and trimethylation of lysine 9 in histone 3 (H3K9me3) while a significant percentage of old GV and MII oocytes lacked H3K9me3, H3K36me2, H3K79me2 and H4K20me2. The percentage of old oocytes lacking histone methylation was similar at GV and MII suggesting that alterations of histone methylation in old MII oocytes initially arise at GV. Besides, the expression of the histone methylation-related factors Cbx1 and Sirt1 was also found to change in old GV oocytes. In conclusion, our study reports changes of chromatin configuration and histone methylation in old GV oocytes, which could be very useful for further understanding of human infertility caused by aging.

Energy balance, host-related factors, and cancer progression

Obesity is associated with an increased risk and worsened prognosis for many types of cancer, but the mechanisms underlying the obesity-cancer progression link are poorly understood. Several energy balance-related host factors are known to influence tumor progression and/or treatment responsiveness after cancer develops, and these have been implicated as key contributors to the complex effects of obesity on cancer outcome. These host factors include leptin, adiponectin, steroid hormones, reactive oxygen species associated with inflammation, insulin, insulin-like growth factor-1, and sirtuins. Each of these host factors is considered in this article in the context of energy balance and cancer progression. In addition, future research directions in this field are discussed, including the importance of study designs addressing energy balance across the life course, the development and application of highly relevant animal models, potential roles of cancer stem cells in the response to energy balance modulation, and emerging pharmacologic approaches that target energy balance-related pathways.

Sirtuin 3, a new target of PGC-1alpha, plays an important role in the suppression of ROS and mitochondrial biogenesis

Background

Sirtuin 3 (SIRT3) is one of the seven mammalian sirtuins, which are homologs of the yeast Sir2 gene. SIRT3 is the only sirtuin with a reported association with the human life span. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) plays important roles in adaptive thermogenesis, gluconeogenesis, mitochondrial biogenesis and respiration. PGC-1α induces several key reactive oxygen species (ROS)-detoxifying enzymes, but the molecular mechanism underlying this is not well understood.

Results

Here we show that PGC-1α strongly stimulated mouse Sirt3 gene expression in muscle cells and hepatocytes. Knockdown of PGC-1α led to decreased Sirt3 gene expression. PGC-1α activated the mouse SIRT3 promoter, which was mediated by an estrogen-related receptor (ERR) binding element (ERRE) (−407/−399) mapped to the promoter region. Chromatin immunoprecipitation and electrophoretic mobility shift assays confirmed that ERRα bound to the identified ERRE and PGC-1α co-localized with ERRα in the mSirt3 promoter. Knockdown of ERRα reduced the induction of Sirt3 by PGC-1α in C₂C₁₂ myotubes. Furthermore, Sirt3 was essential for PGC-1α-dependent induction of ROS-detoxifying enzymes and several components of the respiratory chain, including glutathione peroxidase-1, superoxide dismutase 2, ATP synthase 5c, and cytochrome c. Overexpression of SIRT3 or PGC-1α in C₂C₁₂ myotubes decreased basal ROS level. In contrast, knockdown of mSIRT3 increased basal ROS level and blocked the inhibitory effect of PGC-1α on cellular ROS production. Finally, SIRT3 stimulated mitochondrial biogenesis, and SIRT3 knockdown decreased the stimulatory effect of PGC-1α on mitochondrial biogenesis in C₂C₁₂ myotubes.

Conclusion

Our results indicate that Sirt3 functions as a downstream target gene of PGC-1α and mediates the PGC-1α effects on cellular ROS production and mitochondrial biogenesis. Thus, SIRT3 integrates cellular energy metabolism and ROS generation. The elucidation of the molecular mechanisms of SIRT3 regulation and its physiological functions may provide a novel target for treating ROS-related disease.

Myeloid deletion of SIRT1 induces inflammatory signaling in response to environmental stress

Macrophage activation and infiltration into resident tissues is known to mediate local inflammation and is a hallmark feature of metabolic syndrome. Members of the sirtuin family of proteins regulate numerous physiological processes, including those involved in nutrient regulation and the promotion of longevity. However, the important role that SIRT1, the leading sirtuin family member, plays in immune response remains unclear. In this study, we demonstrate that SIRT1 modulates the acetylation status of the RelA/p65 subunit of NF-κB and thus plays a pivotal role in regulating the inflammatory, immune, and apoptotic responses in mammals. Using a myeloid cell-specific SIRT1 knockout (Mac-SIRT1 KO) mouse model, we show that ablation of SIRT1 in macrophages renders NF-κB hyperacetylated, resulting in increased transcriptional activation of proinflammatory target genes. Consistent with increased proinflammatory gene expression, Mac-SIRT1 KO mice challenged with a high-fat diet display high levels of activated macrophages in liver and adipose tissue, predisposing the animals to development of systemic insulin resistance and metabolic derangement. In summary, we report that SIRT1, in macrophages, functions to inhibit NF-κB-mediated transcription, implying that myeloid cell-specific modulation of this sirtuin may be beneficial in the treatment of inflammation and its associated diseases.

Dietary restriction and brain health

The benefits of dietary restriction (DR) on health and aging prevention have been well recognized. Recent studies suggest that DR may enhance brain functions including learning and memory, synaptic plasticity, and neurogenesis, all of which are associated with brain health. Under the stress stimulated by DR, a favorable environment is established for facilitating neuronal plasticity, enhancing cognitive function, stimulating neurogenesis and regulating inflammatory response. DR-induced expressions of factors such as heat shock proteins (HSPs), neurotrophic factors, and Sirtuin1 (SIRT1) are responsible for the effect of DR on the brain. Due to the difficulty in practising long-term DR in human, the potential mimics of DR are also discussed.

Up-regulation of the mu-opioid receptor gene is mediated through chromatin remodeling and transcriptional factors in differentiated neuronal cells

The effects of morphine are mediated mainly through the mu opioid receptor (MOR). Expression of the MOR is up-regulated during neuronal differentiation in P19 embryonal carcinoma cells and epigenetic changes play an important role in MOR up-regulation. This study investigates the basis for differentiation-dependent alterations of MOR chromatin by studying the recruitment or dissociation of several factors to the remodeled chromatin locus. Chromatin immunoprecipitation assays were used to demonstrate the recruitment of the transcriptional activator Sp1 and the chromatin remodeling factors Brg1 and BAF155 to this promoter, as well as the dissociation of repressors [histone deacetylases, mSin3A, Brm, and methyl-CpG-binding protein 2 (MeCP2)]. Histone modifications (acetylation, induction of histone H3-lys4 methylation, and reduction of H3-lys9 methylation) were consistently detected on this promoter. Overexpression of Sp1 strongly enhanced MOR promoter activity, and the histone deacetylase inhibitor trichostatin A also increased promoter activity. In vitro DNA CpG-methylation of the promoter partially blocked binding of the Sp1 factor but induced MeCP2 binding. Coimmunoprecipitation studies also found novel evidence of an endogenous MeCP2 interaction with Sp3 but a weaker interaction with Sp1. Overall, the results suggest that during neuronal differentiation, MeCP2 and DNA methylation mediate remodeling of the MOR promoter by chromatin remodeling factors (Brg1 and BAF155) from a compacted state to a conformation allowing access for transcriptional factors. Subsequent recruitment of the activating transcription factor Sp1 to the remodeled promoter results in MOR up-regulation.

[Molecular basis of photoaging]

As a result of the increase in life expectancy, the study of the organic process of aging has been stimulated. Skin ageing, which reflects the signs of time, is a time-dependent process of progressive deterioration that can be intensified by sun exposure, which is known as photoaging. The damage of radiation on various cell structures and on the skin results in molecular and morphological changes to these components. Many research studies are performed to try to minimize the effects of photoaging; however, the main strategy to manage it is still prevention, which will only be achieved once we learn about the mechanisms involved in the process.

Energy restriction as an antitumor target of thiazolidinediones

Cancer cells gain growth advantages in the microenvironment by shifting cellular metabolism to aerobic glycolysis, the so-called Warburg effect. There is a growing interest in targeting aerobic glycolysis for cancer therapy by exploiting the differential susceptibility of malignant versus normal cells to glycolytic inhibition, of which the proof-of-concept is provided by the in vivo efficacy of dietary caloric restriction and natural product-based energy restriction-mimetic agents (ERMAs) such as resveratrol and 2-deoxyglucose in suppressing carcinogenesis in animal models. Here, we identified thiazolidinediones as a novel class of ERMAs in that they elicited hallmark cellular responses characteristic of energy restriction, including transient induction of Sirt1 (silent information regulator 1) expression, activation of the intracellular fuel sensor AMP-activated protein kinase, and endoplasmic reticulum stress, the interplay among which culminated in autophagic and apoptotic death. The translational implications of this finding are multifold. First, the novel function of troglitazone and ciglitazone in targeting energy restriction provides a mechanistic basis to account for their peroxisome proliferator-activated receptor gamma-independent effects on a broad spectrum of signaling targets. Second, we demonstrated that Sirt1-mediated up-regulation of beta-transducin repeat-containing protein-facilitated proteolysis of cell cycle- and apoptosis-regulatory proteins is an energy restriction-elicited signaling event and is critical for the antitumor effects of ERMAs. Third, it provides a molecular rationale for using thiazolidinediones as scaffolds to develop potent ERMAs, of which the proof-of-principle is demonstrated by OSU-CG12. OSU-CG12, a peroxisome proliferator-activated receptor gamma-inactive ciglitazone derivative, exhibits 1- and 3-order of magnitude higher potency in eliciting starvation-like cellular responses relative to resveratrol and 2-deoxyglucose, respectively.

Calories and carcinogenesis: lessons learned from 30 years of calorie restriction research

Calorie restriction (CR) is arguably the most potent, broadly acting dietary regimen for suppressing the carcinogenesis process, and many of the key studies in this field have been published in Carcinogenesis. Translation of the knowledge gained from CR research in animal models to cancer prevention strategies in humans is urgently needed given the worldwide obesity epidemic and the established link between obesity and increased risk of many cancers. This review synthesizes the evidence on key biological mechanisms underlying many of the beneficial effects of CR, with particular emphasis on the impact of CR on growth factor signaling pathways and inflammatory processes and on the emerging development of pharmacological mimetics of CR. These approaches will facilitate the translation of CR research into effective strategies for cancer prevention in humans.

Sirtuins inhibitors: the approach to affinity and selectivity

Accumulating evidence has indicated the importance of sirtuins (class III histone deacetylases) in various biological processes. Their potential roles in metabolic and neurodegenerative diseases have encouraged scientists to seek potent and selective sirtuin inhibitors to investigate their biological functions with a view to eventual new therapeutic treatments. This article surveys current knowledge of sirtuin inhibitors including those discovered via high-throughput screening (HST) or via mechanism-based drug design from synthetic or natural sources. Their inhibitory affinity, selectivities, and possible inhibition mechanisms are discussed.

Exercise alters SIRT1, SIRT6, NAD and NAMPT levels in skeletal muscle of aged rats

Silent information regulators are potent NAD(+)-dependent protein deacetylases, which have been shown to regulate gene silencing, muscle differentiation and DNA damage repair. Here, changes in the level and activity of sirtuin 1 (SIRT1) in response to exercise in groups of young and old rats were studied. There was an age-related increase in SIRT1 level, while exercise training significantly increased the relative activity of SIRT1. A strong inverse correlation was found between the nuclear activity of SIRT1 and the level of acetylated proteins. Exercise training induced SIRT1 activity due to the positive effect of exercise on the activity of nicotinamide phosphoribosyltransferase (NAMPT) and thereby the production of sirtuin-fueling NAD(+). Exercise training normalized the age-associated shift in redox balance, since exercised animals had significantly lower levels of carbonylated proteins, expression of hypoxia-inducible factor-1 alpha and vascular endothelial growth factor. The age-associated increase in the level of SIRT6 was attenuated by exercise training. On the other hand, aging did not significantly increase the level of DNA damage, which was in line with the activity of 8-oxoguanine DNA glycosylase, while exercise training increased the level of this enzyme. Regular exercise decelerates the deleterious effects of the aging process via SIRT1-dependent pathways through the stimulation of NAD(+) biosynthesis by NAMPT.

SIRT1-dependent regulation of chromatin and transcription: linking NAD(+) metabolism and signaling to the control of cellular functions

Sirtuins comprise a family of NAD(+)-dependent protein deacetylases and ADP-ribosyltransferases. Mammalian SIRT1 - a homolog of yeast Sir2, the prototypical member of the sirtuin family - is an important regulator of metabolism, cell differentiation and senescence, stress response, and cancer. As an NAD(+)-dependent enzyme, SIRT1 regulates gene expression programs in response to cellular metabolic status, thereby coordinating metabolic adaptation of the whole organism. Several important mechanisms have emerged for SIRT1-dependent regulation of transcription. First, SIRT1 can modulate chromatin function through direct deacetylation of histones as well as by promoting alterations in the methylation of histones and DNA, leading to the repression of transcription. The latter is accomplished through the recruitment of other nuclear enzymes to chromatin for histone methylation and DNA CpG methylation, suggesting a broader role of SIRT1 in epigenetic regulation. Second, SIRT1 can interact and deacetylate a broad range of transcription factors and coregulators, thereby regulating target gene expression both positively and negatively. Cellular energy state, specifically NAD(+) metabolism, plays a major role in the regulation of SIRT1 activity. Recent studies on the NAD(+) biosynthetic enzymes in the salvage pathway, nicotinamide phosphoribosyltransferase (NAMPT) and nicotinamide mononucleotide adenylyltransferase 1 (NMNAT-1), have revealed important functions for these enzymes in SIRT1-dependent transcription regulation. The collective molecular actions of SIRT1 control specific patterns of gene expression that modulate a wide variety of physiological outcomes.