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Sirtuin 6 (SIRT6) regulation is involved in carcinogenesis. However, its role in breast cancer (BC) metastasis remains unclear. We investigated the effects of SIRT6 on protein kinase C activator- and cytokine-mediated cancer cell invasion and migration in MCF-7 and MDA-MB-231 cells and the association between SIRT6 and matrix metalloproteinase-9 (MMP-9) expression. To assess MMP-9 and SIRT6 expression in patients, protein levels in BC tissues were analyzed. MCF-7 and MDA-MB-231 cell viability was analyzed using MTT assays. SIRT6 was silenced in both cell lines and protein secretion, expression, and mRNA levels were analyzed. Transcription factor DNA activity was investigated using luciferase assays. Matrigel invasion assays were used to assess the effects of SIRT6 in both cell lines. SIRT6 and MMP-9 expression in cancer tissues was significantly higher than in paired normal breast tissues. 12-O-tetradecanoylphorbol-13-acetate (TPA) or tumor necrosis factor-α (TNF-α) increased MMP-9 expression and cell invasion and migration, but SIRT6 knockdown abolished these effects. SIRT6 overexpression additively increased TPA- and TNF-α-induced MMP-9 expression. SIRT6 knockdown suppressed the mitogen-activated protein kinase (MAPK) signaling pathway and thus TPA- and TNF-α-induced MMP-9 expression. SIRT6 silencing suppressed TPA- and TNF-α-induced nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) expressions in both cell lines, and treatment with MAPK, NF-κB, and AP-1 inhibitors reduced MMP-9 expression. The anti-invasive effects of SIRT6 in BC cells might be mediated by suppression of MAPK phosphorylation and reduction in NF-κB and AP-1 DNA activities, leading to MMP-9 downregulation, suggesting that SIRT6 modulation has the potential to target BC metastasis., (© 2022. The Author(s).)

In response to hypoxic-ischemic brain damage (HIBD), microglia activation and its mediated inflammation contribute to neuronal damage. Inhibition of over-activated microglia is deemed to be a potential therapeutic strategy. Our previous studies showed that gastrodin efficiently depressed the neuroinflammation mediated by activated microglia in HIBD neonatal rats. The underlying mechanisms through which gastrodin acts on activated microglia have not been fully elucidated. This study is designed to determine whether gastrodin would regulate the Notch signaling pathway and Sirtuin3 (Sirt3), which are implicated in regulating microglia activation. The present results showed that gastrodin markedly suppressed the expression of members of Notch signaling pathway (Notch-1, NICD, RBP-JK and Hes-1) in activated microglia both in vivo and in vitro. Conversely, Sirt3 expression was enhanced. In BV-2 microglia treated with a γ-secretase inhibitor of Notch pathway- DAPT, the expression of RBP-JK, Hes-1, and NICD was suppressed in activated microglia. Treatment with DAPT and gastrodin further decreased NICD and Hes-1 expression. Sirt3 expression was also decreased after DAPT treatment. However, Sirt3 expression in activated BV-2 microglia given a combined DAPT and gastrodin treatment was not further increased. In addition, combination of DAPT and Gastrodin cumulatively decreased tumor necrosis factor-α (TNF-α) expression. The results suggest that gastrodin regulates microglia activation via the Notch signaling pathway and Sirt3. More importantly, interference of the Notch signaling pathway inhibited Sirt3 expression, indicating that Sirt3 is a downstream gene of the Notch signaling pathway. It is suggested that Notch and Sirt3 synergistically regulate microglia activation such as in TNF-α production., (© 2020. Springer Science+Business Media, LLC, part of Springer Nature.)

Although periprosthetic osteolysis induced by wear debris particles is significantly elevated in senior (65+ years old) patients, most of the published pre-clinical studies were performed using young (less than three-month old) mice indicating the critical need to employ experimental models of particle-induced osteolysis involving mice with advanced age. Emerging evidence indicates that currently available antiresorptive bone therapies have serious age-dependent side effects. However, a resurgence of healthcare interest has occurred in glycyrrhizin (GLY), a natural extract from the licorice roots, as alternative sources of drugs for treating inflammatory bone lytic diseases and prevention of cellular senescence. This study investigated the effects of GLY on inflammatory bone loss as well as expression patterns of senescence-associated secretory phenotype and senescence-protective markers using an experimental calvarium osteolytic model induced in aged (twenty-four-month-old) mice by polymethylmethacrylate (PMMA) particles. Our results indicate that local treatment with GLY significantly diminished the size of inflammatory osteolytic lesions in aged mice via the number of CXCR4+OCPs and Tartrate-resistant acid phosphatase positive (TRAP+) osteoclasts. Furthermore, GLY dramatically decreased the amounts of senescence-associated secretory phenotype markers, including pro-inflammatory macrophage migration inhibitory factor (MIF) chemokine, and cathepsins B and K in the bone lesions of aged mice. By contrast, GLY significantly elevated expression patterns of senescence-protective markers, including homeostatic stromal derived factor-1 (SDF-1) chemokine, and sirtuin-1, and sirtuin-6, in the PMMA particle-induced calvarial lesions of aged mice. Collectively, these data suggest that GLY can be used for the development of novel therapies to control bone loss and tissue aging in senior patients with periprosthetic osteolysis., (Copyright © 2021 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Sirtuin 6 (SIRT6), a member of the Sirtuin family, acts as nicotinamide adenine dinucleotide (NAD)-dependent protein deacetylase, mono-adenosine diphosphate (ADP)-ribosyltransferase, and fatty acid deacylase, and plays critical roles in inflammation, aging, glycolysis, and DNA repair. Accumulating evidence has suggested that SIRT6 is involved in brain functions such as neuronal differentiation, neurogenesis, and learning and memory. However, the precise molecular roles of SIRT6 during neuronal circuit formation are not yet well understood. In this study, we tried to elucidate molecular roles of SIRT6 on neurite development by using primary-cultured hippocampal neurons. We observed that SIRT6 was abundantly localized in the nucleus, and its expression was markedly increased during neurite outgrowth and synaptogenesis. By using shRNA-mediated SIRT6-knockdown, we show that both dendritic length and the number of dendrite branches were significantly reduced in the SIRT6-knockdown neurons. Microarray and subsequent gene ontology analysis revealed that reducing SIRT6 caused the downregulation of immediate early genes (IEGs) and alteration of several biological processes including MAPK (ERK1/2) signaling. We found that nuclear accumulation of phosphorylated ERK1/2 was significantly reduced in SIRT6-knockdown neurons. Overexpression of SIRT6 promoted dendritic length and branching, but the mutants lacking deacetylase activity had no significant effect on the dendritic morphology. Collectively, the presented findings reveal a role of SIRT6 in dendrite morphogenesis, and suggest that SIRT6 may act as an important regulator of ERK1/2 signaling pathway that mediates IEG expression, which leads to dendritic development., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Periodic fasting (PF) is an increasingly popular approach that assists in the management of metabolic and inflammatory diseases as well as in preventing mechanisms involved in aging. However, little is known about the effects of fasting on gut microbiota and its impact on the epigenetic regulation of metabolically relevant enzymes, especially sirtuins (SIRTs). We analyzed the effect of periodic fasting on the human gut microbiota, SIRTs expression, and mitochondrial content in 51 males and females. The participants fasted under supervision for five consecutive days following the Buchinger fasting guidelines. Ketogenesis, selected mRNAs, miRNAs, mitochondrial (mt) DNA, and gut composition were analyzed before and after PF. PF triggered a significant switch in metabolism, as indicated by the increase in ß-hydroxybutyrate (BHB) and pyruvate dehydrogenase kinase isoform 4 ( PDK4) expression in the capillary blood. MtDNA, SIRT1 , SIRT3 , and miRlet7b-5p expression in blood cells were elevated, whereas SIRT6 and miR125b-5p were not affected. Following fasting, gut microbiota diversity increased, and a statistically significant correlation between SIRT1 gene expression and the abundance of Prevotella and Lactobacillus was detected. The abundance of longevity related Christensenella species increased after fasting and inversely correlated with age as well as body mass index (BMI). Thus, this represents the first study that showing that fasting not only changes the composition of the gut microbiota, making it more diverse, but also affects SIRT expression in humans.

Purpose of Review: Sirtuins are a family of nicotinamide adenine dinucleotide+-dependent enzymes catalyzing target protein deacetylation to modulate cellular metabolism, response to oxidative stress and inflammation, senescence, autophagy and apoptosis. In this review, we provide an overview of recent studies regarding the alterations and roles of sirtuins in a variety of renal and cardiovascular diseases. We are also going to highlight activators and inhibitors of sirtuins in the prevention of these diseases. This will help us to understand how this field may change in the future., Recent Finding: Recent studies have elucidated how physical or diseased conditions alter the expressions and enzyme activity of sirtuins and expounded sexual differences in sirtuins functions. In addition, interventions by targeting sirtuins have been applied in preclinical and clinical studies to prevent or slow the development of related diseases., Summary: The advantages of female sex in renal and cardiovascular diseases are partially due to the expression and function of sirtuins. Estrogen activates sirtuins and in turn sirtuins promote estrogen receptor signaling. In addition, the hypoglycemic agents, sodium-glucose cotransporter 2 inhibitors protect against diabetic nephropathy at least in part via activating SIRT-1. Although several compounds targeted sirtuins are promising drug candidates in a variety of renal and cardiovascular diseases, well designed large clinical trials are still required to identify their efficacy and safety.

Autophagy is a major cause of pathological vascular remodeling under hypoxic pulmonary hypertension (PH). Sirtuin 3 (Sirt 3) has recently been reported to be involved in the regulation of autophagy, however, its role as an autophagy regulator during hypoxic PH, particularly the molecular mechanism, remains poorly understood. In the present study, Western blot, immunohistochemistry, immunofluorescence, bromodeoxyuridine incorporation and cell cycle analyses were performed to elucidate the underlying mechanism of hypoxia-induced autophagy and cell proliferation with respect to Sirt 3. We observed that the Sirt 3 expression was decreased under hypoxia and that Sirt 3 overexpression significantly inhibited the effects of hypoxia on autophagy. Next, we investigated the mechanistic role of microRNAs in Sirt 3-associated autophagy under hypoxic conditions, with luciferase reporter, microscale thermophoresis and RNA immunoprecipitation assays, results confirming that Sirt 3 is a direct target of miR-874-5p. Furthermore, miR-874-5p was upregulated following hypoxia, and miR-874-5p depletion in turn inhibited autophagy and consequently suppressed abnormal smooth muscle cell proliferation. These findings provide insight into the contribution of the miR-874-5p/Sirt 3 cascade with regard to changes in autophagy and proliferation associated with PH., (Copyright © 2020. Published by Elsevier B.V.)

Hepatocellular carcinoma (HCC) is the most common primary liver cancer. Sirtuins are NAD+-dependent histone deacetylases that regulate many cellular processes such as proliferation, apoptosis, and metabolism. SIRT (silent information regulator)-1, 5, 6 and 7, members of the mammalian Sirtuin family of proteins (SIRT1-SIRT7), are involved in carcinogenesis, prognosis, metastasis, and chemical resistant of HCC. These proteins act through the deacetylation of tumor suppressor or oncogenic factors. MicroRNAs (miRNAs) are a group of small non-coding RNAs that down regulate gene expression by targeting the 3'-untranslated region of miRNAs. MiRNAs can function as tumor suppressors or as oncogenes and are involved in progression, differentiation, apoptosis and drug resistance of tumor cells. The focus of this review is to delineate the relationship between some microRNAs and their target, Sirtuins, and to present an overview of their function in HCC as currently understood.

Accumulating evidence supports that Sirtuin 6 (SIRT6) may play a vital role in the pathogenesis of spinal cord injury. The current study was designed to investigate the specific effects of SIRT6 on spinal cord injury (SCI). HE and Nissl staining were performed for pathological analysis in SCI rats. SIRT6 expression was detected by RT-qPCR. CCK8 assay was applied for the detection of cell viability of LPS-injured PC12 cells. TNF-a, IL-1β, IL-6, MCP-1 levels and ROS, MPO, SOD levels were assessed to evaluate inflammation and oxidative stress in spinal cord injury. Cell apoptosis were evaluated by morphological examination using AO/EB fluorescent staining methods and key proteins related to apoptosis were explored via western blot. HE staining revealed increased cavity involving the dorsal white matter and central gray matter, and Nissl staining discovered the loss of motor neurons in the ventral horn in SCI rats. SIRT6 had lower expression in SCI rats. Lipopolysaccharide (LPS) exposure induced cell apoptosis and reduced the expression of SIRT6. Mechanistically, we revealed that up-regulation of SIRT6 alleviated inflammation and oxidative stress and inhibited cell apoptosis in spinal cord injury. Together, our findings indicated that SIRT6 attenuated spinal cord injury by suppressing inflammation, oxidative stress, and cell apoptosis. This study demonstrates that SIRT6 may represent a protective effect against spinal cord injury.

Sirtuin 6 (SIRT6), as a NAD + -dependent deacetylase, plays an indispensable role in the regulation of health and physiology. Loss of SIRT6 causes spontaneous colitis in mice and makes intestinal epithelial cells prone to stress. However, whether SIRT6 overexpression increases resistance to colitis remains unknown. Here, in vivo results demonstrated that SIRT6 overexpression attenuates DSS-induced colitis in terms of clinical manifestations, histopathological damage, loss of tight junction function and imbalanced intestinal microenvironment. Additionally, we also found that the activation of NF-κB and c-Jun induced by DSS is diminished by SIRT6 overexpression. Furthermore, SIRT6 may regulate TAK1 to inhibit NF-κB and c-Jun signaling. Thus, our findings highlight the protective effect of SIRT6 on colon, further supporting the perspective that SIRT6 may be a therapeutic target for intestine injury under stress.

Sepsis is a life-threatening condition. Polydatin (PD), a small natural compound from Polygonum cuspidatum, possesses antioxidant and anti-inflammatory properties. However, the protective mechanism of PD on sepsis-induced acute myocardial damage is still unclear. The aim of this study was to investigate the effect and mechanism of action of PD on lipopolysaccharide (LPS)-induced H9c2 cells and in a rat model of sepsis, and explored the role of PD-upregulated sirtuin (SIRT)6. LPS-induced H9c2 cells were used to simulate sepsis. Cecal ligation and puncture (CLP)-induced sepsis in rats were used to verify the protective effect of PD. ELISA, western blotting, immunofluorescence, immunohistochemistry, and flow cytometry were used to study the protective mechanism of PD against septic myocardial injury. PD pretreatment suppressed LPS-induced H9c2 cell apoptosis by promotion of SIRT6-mediated autophagy. Downregulation of SIRT6 or inhibition of autophagy reversed the protective effect of PD on LPS-induced apoptosis. PD pretreatment also suppressed LPS-induced inflammatory factor expression. CLP-induced sepsis in rats showed that PD pretreatment decreased CLP-induced myocardial apoptosis and serum tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 expression. 3-Methyladenine (autophagy inhibitor) pretreatment prevented the protective effect of PD on septic cardiomyopathy. SIRT6 expression was increased with PD treatment, which confirmed that PD attenuates septic cardiomyopathy by promotion of SIRT6-mediated autophagy. All these results indicate that PD has potential therapeutic effects that alleviate septic myocardial injury by promotion of SIRT6-mediated autophagy.

BACKGROUND Sirtuin (Sirt) 3 could promote autophagy by downregulating the expression of genes related to neovascularization in retinal endothelial cells. In this study, we aimed to investigate the effect of Sirt3 overexpression on retinopathy in streptozotocin (STZ)-induced diabetic rats, and to assess its mechanisms. MATERIAL AND METHODS Ntraperitoneal injection of STZ in rats was used to produce a diabetic model. The study rats were divided into 4 groups (n=6 for each group): a control group; a model group; a model+scrambled adenovirus group; and a model+Sirt3 overexpression group. Hematoxylin and eosin (H&E) staining determined the pathological changes of retina tissues. Immunohistochemistry, fluorescence quantitative polymerase chain reaction, and western blotting were used to detect the expression of Sirt3, vascular endothelial growth factor (VEGF), and microtubule-associated protein 1A/1B-light chain 3 (LC3). RESULTS In the model group, the inner limiting membrane was swollen, uneven and thickened, and the capillary endothelial cells occasionally protruded into the inner limiting membrane. These abnormalities were prevented by Sirt3 overexpression. Compared with the control group, the expression of Sirt3 at both mRNA and protein levels in the model group was significantly reduced, while the expression of VEGF was increased versus the control group (P.

Background: Renal transplant surgical proceedings are known to elicit periods of hypoxia and consequent blood flow reestablishment triggering ischemia-reperfusion (I-R) injury. Kidney damage induced by I-R injury associates with a higher risk of graft dysfunction and rejection. Anesthetic preconditioning exerts a beneficial effect on I-R injury by reducing oxidative stress, inflammation and apoptosis. However, the degree of renoprotection stimulated by commonly used anesthetics, as well as their mechanisms of action, are largely unknown. Sirtuins are class III histone deacetylases that reduce cellular stress, promote genome stability and regulate senescence. So far, the relationship between sirtuins and anesthetic preconditioning in the context of renal I-R has not been studied. The main objective of the present work was to determine the renal expression of sirtuins after I-R damage in rats under different anesthetic preconditioning treatments., Methods: Unilateral ischemia was performed via occlusion of the left renal hilum for 45 min and followed by 24 hours of reperfusion. Anesthetic preconditioning schemes (morphine 0.5 mg/kg, fentanyl 10 µg/kg, propofol 7.5 mg/kg, or dexmedetomidine 25 µg/kg) were administered 1 hour before ischemia. Creatinine levels were determined in serum, and expression of kidney injury molecule 1 and sirtuin 1, 2, 3 and 7 in kidney tissue was quantified by RT-PCR., Results: Anesthetic preconditioning with morphine, fentanyl, propofol and dexmedetomidine reduced kidney injury markers after I-R and modulated sirtuin gene expression. Opioids or dexmedetomidine administration before ischemia increased sirtuin 2 expression and correlated with improved renal function., Conclusions: Anesthetic preconditioning is a promising strategy to prevent I-R injury associated with transplantation. Our results suggest that sirtuin 2 is involved in the protective mechanisms of some commonly used anesthetics against I-R damage.

Sirtuins are a family of deacetylases that modify structural proteins, metabolic enzymes, and histones to change cellular protein localization and function. In mammals, there are seven sirtuins involved in processes like oxidative stress or metabolic homeostasis associated with aging, degeneration or cancer. We studied gene expression of sirtuins by qRT-PCR in human mural granulosa-lutein cells (hGL) from IVF patients in different infertility diagnostic groups and in oocyte donors (OD; control group). Study 1: sirtuins genes' expression levels and correlations with age and IVF parameters in women with no ovarian factor. We found significantly higher expression levels of SIRT1, SIRT2 and SIRT5 in patients ≥40 years old than in OD and in women between 27 and 39 years old with tubal or male factor, and no ovarian factor (NOF). Only SIRT2, SIRT5 and SIRT7 expression correlated with age. Study 2: sirtuin genes' expression in women poor responders (PR), endometriosis (EM) and polycystic ovarian syndrome. Compared to NOF controls, we found higher SIRT2 gene expression in all diagnostic groups while SIRT3, SIRT5, SIRT6 and SIRT7 expression were higher only in PR. Related to clinical parameters SIRT1, SIRT6 and SIRT7 correlate positively with FSH and LH doses administered in EM patients. The number of mature oocytes retrieved in PR is positively correlated with the expression levels of SIRT3, SIRT4 and SIRT5. These data suggest that cellular physiopathology in PR's follicle may be associated with cumulative DNA damage, indicating that further studies are necessary., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

The prevalence of psoriasis is increasing, and poses a serious risk to human health and quality of life. Psoriasis, a chronic immune‑mediated skin disease with epidermal hyperkeratosis and parakeratosis, is associated with numerous complications, including metabolic syndromes that are regulated by sirtuins (SIRTs) via deacetylation. As they serve a necessary function in inflammation and metabolism, SIRTs are considered to link inflammation and metabolic syndrome. Previous studies have indicated that SIRTs serve a function in the pathophysiology of psoriasis, but to date no detailed research has been conducted investigating the expression levels and patterns of SIRTs in psoriasis. The present study investigated the abnormal expression of SIRTs in psoriasis and provided a theoretical foundation for the treatment and prognosis of psoriasis. Tumor necrosis factor (TNF)‑α‑stimulated HaCaT cells and an imiquimod‑induced psoriasis mouse model were used to produce in vitro and in vivo models, respectively. Psoriasis clinical specimens (psoriasis area and severity index >10; n=22) and normal group specimens (n=22) were obtained from human subjects. The mRNA and protein expression levels in human and mouse skin lesions and TNF‑α‑stimulated HaCaT cells were detected using reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blotting, and compared with the control groups. The expression patterns of SIRT proteins were investigated using immunofluorescence (IF) staining. The expression levels of SIRT1, SIRT2, SIRT3, SIRT4 and SIRT5 were downregulated while those of SIRT6 and SIRT7 were upregulated in skin lesions and TNF‑α‑stimulated HaCaT cells compared with the control group as determined by RT‑qPCR, western blotting and IF. Statistically significant differences were observed in vivo and in vitro. P‑values of SIRT1‑7 mRNA are less than 0.05 in RT‑qPCR, and the P‑values of SIRT1‑7 proteins are less than 0.05 except for SIRT4 in the western blot analysis. SIRTs serve notable functions in severe psoriasis dermatitis, with the overexpression of SIRT6 and SIRT7 potentially induced by the adaptive immune response, and the downregulation of SIRT1, SIRT2, SIRT3, SIRT4 and SIRT5 may be a result of an internal environment imbalance in vivo. Psoriasis is an inflammation and metabolism‑associated disease mediated by the SIRT family. The present results provide a novel potential mechanism and strategy for the treatment of psoriasis by modulating the function and expression of SIRTs.

Sirtuin1 (Sirt1) and Sirtuin3 (Sirt3) are known to participate in regulating mitochondrial function. However, whether Total Salvianolic Acid Injection (TSI) protects against myocardial ischemia/reperfusion (I/R) injury through regulating Sirt1, Sirt3, and mitochondrial respiratory chain complexes is unclear. The aim of this study was to explore the effects of TSI on I/R-induced myocardial injury and the underlying mechanism. Male Sprague-Dawley rats were subjected to 30 min occlusion of the left anterior descending coronary artery followed by 90 min reperfusion with or without TSI treatment (8 mg/kg/h). The results demonstrated that TSI attenuated I/R-induced myocardial injury by the reduced infarct size, recovery of myocardial blood flow, and decreased cardiac apoptosis. Moreover, TSI protected heart from oxidative insults, such as elevation of myeloperoxidase, malondialdehyde, hydrogen peroxide, ROS, as well as attenuated I/R-elicited downregulation of Sirt1, Sirt3, NADH dehydrogenase [ubiquinone] 1 alpha subcomplex 10 (NDUFA10), succinate dehydrogenase complex, subunit A, flavoprotein variant (SDHA), and restoring mitochondrial respiratory chain complexes activity. The in vitro study in H9c2 cells using siRNA transfection further confirmed the critical role of Sirt1 and Sirt3 in the effect of TSI on the expression of NDUFA10 and SDHA. These results demonstrated that TSI attenuated I/R-induced myocardial injury via inhibition of oxidative stress, which was related to the activation of NDUFA10 and SDHA through the upregulation of Sirt1 and Sirt3.

Acetylation of lysine residues occurs in lens proteins. Previous studies have shown an improvement in the chaperone activity of αA-crystallin upon acetylation. Sirtuins are NAD + -dependent enzymes that can deacylate proteins. The roles of sirtuins in regulating the acetylation of lens proteins and their impacts on the function of α-crystallin are not known. Here, we detected sirtuin activity in mouse lenses, and SIRT3 and SIRT5 were present primarily in the mitochondria of cultured primary mouse lens epithelial cells. Western blotting showed higher levels of protein acetylation in the lenses of SIRT3 KO and SIRT5 KO mice than in lenses of WT mice. Mass spectrometry analyses revealed a greater number of acetylated lysine residues in α-crystallin isolated from the SIRT3 and SIRT5 KO lenses than from WT lenses. α-Crystallin isolated from SIRT3 and SIRT5 KO lenses displayed a higher surface hydrophobicity and higher chaperone activity than the protein isolated from WT lenses. Thus, SIRTs regulate the acetylation levels of crystallins in mouse lenses, and acetylation in lenses enhances the chaperone activity of α-crystallin., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Introduction: Sirtuins regulate energy metabolism and insulin sensitivity through their ability to act as energy sensors and regulators in several metabolic tissues., Aim: To evaluate the expression levels of sirtuin genes SIRT1, SIRT2, SIRT3 and SIRT6 and their target genes (PPAR-α, PGC1-α, NRF1, DGAT1, PPAR-γ and FOXO3a) in subcutaneous adipose tissue collected from individuals with normoweight, overweight and obesity., Methods: Adipose tissue samples, obtained by lipoaspiration during liposuction surgery, were processed to obtain RNA, which was reverse-transcribed to cDNA. Then, we measured the expression levels of each gene by qPCR., Results: We found differences in the mRNA expression of SIRT1, SIRT2, SIRT3 and SIRT6 and their target genes (PPAR-α, PGC1-α, NRF1, DGAT1, PPAR-γ and FOXO3a) in adipose tissue from overweight or obese subjects when compared to normoweight subjects. All genes analyzed, except SIRT2, showed correlation with BMI., Conclusions: Our findings in human subcutaneous adipose tissue show that increased body mass index modifies the expression of genes encoding sirtuins and their target genes, which are metabolic regulators of adipose tissue. Therefore, these could be used as biomarkers to predict the ability of adipose tissue to gain mass of adipose tissue., (Copyright © 2018 Diabetes India. Published by Elsevier Ltd. All rights reserved.)

Sirt6 is a member of the sirtuin family involved in physiological and pathological processes including aging, cancer, obesity, diabetes, and energy metabolism. This study is aimed at evaluating the relationship between liver SIRT6 gene expression and the oxidative stress network depending on adiposity levels in Zucker rats, an animal model of metabolic syndrome. We observed that liver-specific SIRT6 expression is reduced in an in vivo model of spontaneous obesity and metabolic syndrome. We also observed that SIRT6 expression in the liver is positively associated with SIRT1 and GST-M2 expressions, two proteins involved in antioxidant protection pathways and inversely related to body weight and plasmatic oxidative status. Interestingly, the SIRT6 expression is upregulated after energy restriction-induced weight loss concomitantly with an improvement in oxidative stress markers. These results suggest that SIRT6 may be a potential therapeutic target for the treatment of obesity and associated metabolic disorders, such as liver disease.

Sirtuin 3 (SIRT3) mediates cellular resistance toward various forms of stress. SIRT3 expression in the developing brain, especially its localization in various glial cell types, has not been fully explored. This study aimed to determine SIRT3 expression in the brain of neonatal rats subjected to hypoxia. By immunohistochemistry, immunofluorescence and Western blotting, we show here that SIRT3 expression in the periventricular white matter was up-regulated in hypoxia group compared with the control group at the corresponding time points. Intense SIRT3 expression was detected in microglia at early time points after hypoxia whose cell number was increased with reduced ramifications in hypoxia group compared with the control group. Furthermore, SIRT3 immunoreactivity was obviously enhanced at 24 h, 3 and 7d, but was declined at 14d after hypoxia so that SIRT3 expression between the two groups was comparable. SIRT3 immunofluorescence was also localized in astrocytes labeled with GFAP which was augmented at different time points in hypoxia group. GPAP positive astrocytes exhibited long extending processes being most pronounced at 3d. SIRT3 was moderately expressed at 24 h, 3 and 7d, but was markedly increased at 14d after hypoxia. Moderate SIRT3 expression was also localized in oligodendrocytes labeled with CNPase in the control group. The incidence of CNPase positive oligodendrocytes showing colocalization of SIRT3 increased significantly at 24 h, 3 and 7d after hypoxia. In conclusion, SIRT3 expression was differentially up-regulated in all three major glial cell types following hypoxia. It is suggested that increased SIRT3 expression in the respective glial cell types following hypoxia is involved in different signaling pathways that protect against hypoxic stress in the developing brain., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Sirt family has been reported playing a significant role in the cancer development, especial its deacetylase activity plays a key function, but whether SIRT6 plays a role in mediating tumor epithelial-mesenchymal transition (EMT) and metastasis in colon cancer has not been explored. Here, the mass spectrometry and co-immunoprecipitation assays were utilized to detect that SIRT6 was physically associated with transcription factor snail. Most important, HCT116 cells transfected with SIRT6 shRNA reversed EMT, while increased the expression of TET1, and the HCT116 cells transfected with SIRT6 displayed the contrary tendency. Transwell invasion assay, soft agar assay, as well as colony formation together showed that SIRT6 promoted cell EMT and tumorigenesis in vitro. We also found SIRT6 is a reader of snail. ChIP as well as qChIP suggested H3K9 binding on the promoter of TET1 dependent on SIRT6. SIRT6 promoted EMT process through two different ways, one is as a reader of snail, and other way was the suppression of TET1 transcription. These two ways are all dependent on its H3K9 deacetylase activity. Further, patient samples collected showed that SIRT6 was significantly increased in colon cancer samples, and its higher expression was correlated with poor prognosis, worse overall survivals. Together, our experiments revealed the mechanism for SIRT6 in facilitating tumorigenesis and metastasis of colon cancer cells, suggesting that SIRT6 might be a potential therapeutic target for treating colon cancer., (© 2017 Wiley Periodicals, Inc.)

Acrolein is a ubiquitous dietary and environmental pollutant, which can also be generated endogenously during cellular stress. However, the molecular mechanisms underlying acrolein-induced neurotoxicity, especially in ototoxicity conditions, have not been fully determined. In this study, we investigated the mechanisms on acrolein-induced toxicity in primary cultured cochlear nucleus neurons with focus on Sirt3, a mitochondrial deacetylase. We found that acrolein treatment induced neuronal injury and programmed cell death (PCD) in a dose dependent manner in cochlear nucleus neurons, which was accompanied by increased intracellular reactive oxygen species (ROS) generation and lipid peroxidation. Acrolein exposure also significantly reduced the mitochondrial membrane potential (MMP) levels, promoted cytochrome c release and decreased mitochondrial ATP production. In addition, increased ER tracker fluorescence and activation of ER stress factors were observed after acrolein treatment, and the ER stress inhibitors were shown to attenuate acrolein-induced toxicity in cochlear nucleus neurons. The results of western blot and RT-PCR showed that acrolein markedly decreased the expression of Sirt3 at both mRNA and protein levels, and reduced the activity of downstream mitochondrial enzymes. Furthermore, overexpression of Sirt3 by lentivirus transfection partially prevented acrolein-induced neuronal injury in cochlear nucleus neurons. These results demonstrated that acrolein induces mitochondrial dysfunction and ER stress in cochlear nucleus neurons, and Sirt3 acts as an endogenous protective factor in acrolein-induced ototoxicity., (Copyright © 2017. Published by Elsevier Ltd.)

Treatment of intervertebral disc degeneration (IDD) seeks to prevent senescence and death of nucleus pulposus (NP) cells. Previous studies have shown that sirt6 exerts potent anti-senescent and anti-apoptotic effects in models of age-related degenerative disease. However, it is not known whether sirt6 protects against IDD. Here, we explored whether sirt6 influenced IDD. The sirt6 level was reduced in senescent human NP cells. Sirt6 overexpression protected against apoptosis and both replicative and stress-induced premature senescence. Sirt6 also activated NP cell autophagy both in vivo and in vitro. 3-methyladenine (3-MA) and chloroquine (CQ)-mediated inhibition of autophagy partially reversed the anti-senescent and anti-apoptotic effects of sirt6, which regulated the expression of degeneration-associated proteins. In vivo, sirt6 overexpression attenuated IDD. Together, the data showed that sirt6 attenuated cell senescence, and reduced apoptosis, by triggering autophagy that ultimately ameliorated IDD. Thus, sirt6 may be a novel therapeutic target for IDD treatment.

Objectives: Sirtuins (1-7) are evolutionarily conserved NAD-dependent deacetylases that play an important role in carcinogenesis. However, their role in renal cell carcinoma (RCC) remains unclear. The objective of the present study was to examine the role of SIRTs in RCC carcinogenesis and prognosis., Materials and Methods: Paraffin-embedded specimens from 102 patients who underwent extirpative renal surgeries for renal masses between January 2004 and December 2010 were examined. SIRT expression was compared between RCC and adjacent normal kidney tissues by immunohistochemical staining. Survival differences and cancer-specific survival were analyzed with the Kaplan-Meier log-rank test and univariate and multivariate Cox regression analyses, respectively., Results: SIRT1, SIRT3, and SIRT6 expression was significantly lower in RCC than in normal tissues (P = 0.001, P = 0.006, and P = 0.033, respectively), whereas the expression of other SIRT proteins did not differ significantly between the 2 tissues. SIRT3 expression was significantly associated with longer cancer-specific survival (HR = 0.133, P = 0.047), after adjusting for age, T stage, Fuhrman grade, Karnofsky performance status, and distant metastases. Kaplan-Meier analysis showed that patients with high-SIRT3 expression had relatively better survival than those with low-SIRT3 expression (P = 0.046, log-rank test)., Conclusions: Our results provide preliminary evidence suggesting that SIRT1, SIRT3, and SIRT6 function as tumor suppressors in RCC. In particular, SIRT3 seems to have a favorable influence on the survival of patients with clear cell RCC., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Sirtuin 6, a member of sirtuin family, is generally regarded as a tumor suppressor as it participates in suppressing hypoxia-inducible factor 1α and MYC transcription activity by deacetylating H3K9 (histone H3 lysine 9) and H3K56 (histone H3 lysine) at promoters of target genes, leading to the aerobic glycolysis inhibition and cell growth suppression. However, its expression has recently been reported to be highly elevated in a series of tumors, including prostate cancer, breast cancer, and non-small cell lung cancer, indicating that sirtuin 6 plays dual roles in tumorigenicity in a cell/tumor type-specific manner. To our knowledge, the biological roles of sirtuin 6 in esophageal cancer cells have still been underestimated. In the study, data from quantitative reverse transcriptase polymerase chain reaction-based assays and immunohistochemical assays revealed that sirtuin 6 was remarkably overexpressed in esophageal squamous tumor tissues. Moreover, its upregulation was closely related with clinical features, such as gender, pathology, tumor-node-metastasis, and cell differentiation. Subsequently, the biological tests showed that it promoted cell proliferation and induced the expression of Bcl2, a key anti-apoptotic factor, in esophageal carcinoma cells. Moreover, using the ratio of LC3II/I, a widely recognized autophagy biomarker, we showed that it apparently induced cell autophagy, which was further confirmed by the autophagy flux assays. In addition, results from western blotting assays and immunoprecipitation assays displayed that sirtuin 6 specifically interacted with ULK1 and positively regulated its activity by inhibiting its upstream factor mammalian target of rapamycin activity. In summary, our studies shed insights into the crucial functions of sirtuin 6 in esophageal carcinoma cells and provide evidence supporting sirtuin 6-based personalized therapies in esophageal carcinoma cell patients.

SIRT4 is well-known for its deacetylase activity in energy metabolism, but little is known about its roles in carcinogenesis. We demonstrated that SIRT4 was decreased in 70 out of 133 non-small cell lung cancer (NSCLC) cases by immunohistochemical staining and localized in the mitochondria using confocal microscopy. Low levels of SIRT4 expression was correlated with tumor node metastasis (TNM) stage, histological type of tumor (adenocarcinoma), lymph nodal status, Ki-67 (proliferation index) and poor overall survival. We also studied the biological role of SIRT4 in lung cancer cell lines transfected with SIRT4 plasmid or SIRT4-siRNA. SIRT4 inhibited lung cancer cell proliferation, blocked the cell cycle and repressed cell invasion and migration. Mitochondrial dynamics has been implicated in malignant properties of cells, particularly metastasis that is the major cause of death in patients diagnosed with cancer including lung cancer. This is the first study to identify an association between SIRT4 expression and decreased mitochondrial fission, which was driven by Drp1. SIRT4 inhibited Drp1 phosphorylation and weakened Drp1 recruitment to the mitochondrial membrane via an interaction with Fis-1. SIRT4 expression was lower in nodal metastatic tumor samples than their corresponding primary tumors, and cases with low expression of SIRT4 tended to have high p-Drp1 labeling. Also, MEK/ERK activity appeared to be hampered by SIRT4 expression, which may have implications for cells' invasive capacities. In conclusion, our findings suggest that SIRT4 functions as an important antitumor protein in NSCLC, and should be investigated further with respect to future anticancer strategies.

Sirtuin 6 (SIRT6) is a member of the SIRT family NAD+‑dependent deacetylases reported to function in controlling organism homeostasis, lifespan, and diseases. This study investigated the role of SIRT6 in papillary thyroid cancer (PTC). Data of 391 PTC patients was extracted from The Cancer Genome Atlas database to investigate the expression of SIRTs (SIRT1‑7) and their relationship with clinicopathological parameters. Additional 45 pairs of PTC tumor tissues and corresponding non‑tumor tissues were studied using microarray analysis for SIRT6 expression. Surgically resected, pathologically diagnosed tissues from 130 in‑house PTC patients were used for confirmation of SIRT6 expression. SIRT6 silenced K1 and TPC‑1 cells were generated to explore the influence of SIRT6 on cancer cell aggressiveness in vitro. SIRT6 mRNA and protein levels were upregulated in PTC tumor tissues and its overexpression was an independent biomarker for nodal metastasis (odds ratio=1.794, 95% confidence interval: 1.256‑1.920, p=0.012). SIRT6 expression was related to poor recurrence‑free survival, however, not significantly. Silencing SIRT6 downregulated PTC cell aggressiveness in vitro by suppressing ERK and Mcl‑1. In conclusion, these results suggest that SIRT6 enhances cell aggressiveness in PTC via BRAF/ERK/Mcl‑1 pathway, and thus may be a promising target in the treatment of the disease.

Virulence of Cryptococcus neoformans is regulated by a range of transcription factors, and is also influenced by the acquisition of adaptive mutations during infection. Beyond the temporal regulation of virulence factor production by transcription factors and these permanent microevolutionary changes, heritable epigenetic modifications such as histone deacetylation may also play a role during infection. Here we describe the first comprehensive analysis of the sirtuin class of NAD+ dependent histone deacetylases in the phylum Basidiomycota, identifying five sirtuins encoded in the C. neoformans genome. Each sirtuin gene was deleted and a wide range of phenotypic tests performed to gain insight into the potential roles they play. Given the pleiotropic nature of sirtuins in other species, it was surprising that only two of the five deletion strains revealed mutant phenotypes in vitro. However, cryptic consequences of the loss of each sirtuin were identified through whole cell proteomics, and mouse infections revealed a role in virulence for SIR2, HST3 and HST4. The most intriguing phenotype was the repeated inability to complement mutant phenotypes through the reintroduction of the wild-type gene. These data support the model that regulation of sirtuin activity may be employed to enable a drastic alteration of the epigenetic landscape and virulence of C. neoformans.

To extend our understanding of previous studies on the pathogenesis and mechanism of high mobility group box 1 (HMGB1) in chronic rhinosinusitis with nasal polyps (CRSwNP), here we show that Sirtuin 6 (Sirt6), one of the Sirtuin family members which are widely studied in aging, DNA repair, metabolism, inflammation and cancer, was expressed in normal nasal mucosa using immunohistochemical staining and Western blot assay. Sirt6 expression levels were decreased in CRSwNP tissue. Sirt6 expression levels were modulated by small interfering RNA transfection in human nasal epithelial cells (HNE). We found that depletion of Sirt6 suppressed the number of human nasal epithelial cell cilia, and dramatically induced HMGB1 translocation from nucleus to cytoplasm in the HNE cells. Glycyrrhizic acid (GA) and glycyrrhetinic acid (GTA) are specific chemical compounds that may be isolated from the licorice plant. GTA has been shown to have anti-inflammatory and anti-allergic activity: it binds selectively to HMGB1 protein released extra-cellularly and inhibits its cytokine activities through a scavenger mechanism on the protein accumulation. In an in vitro study we used the 18-β-stereoisomer of GTA to enhance Sirt6 expression levels, inhibiting through this mechanism the translocation of HMGB1 protein from nucleus and reversing its extracellular accumulation stimulated by lipopolysaccharides. These findings reveal a previously unknown role for nasal mucosa steady-state conditions in the control of Sirt6 activity, and provide evidence for a relationship between HMGB1 and Sirt6 in CRSwNP, and promising benefits of glycyrrhetinic acid for CRSwNP patients.

Astragaloside IV, the active component of Astragalus membranaceus, exhibits diverse biological roles including the anti-tumor activity. In this study, we evaluated the chemosensitive role of astragaloside IV in non-small cell lung cancer cells. Cell Counting Kit-8 analysis was performed to determine cell viability. Real-time polymerase chain reaction and western blot were used to measure the messenger RNA and protein expression. Results showed that astragaloside IV treatment could suppress the proliferation of non-small cell lung cancer cells. In addition, combined treatment with astragaloside IV remarkably enhanced the chemosensitivity to gefitinib in three non-small cell lung cancer cell lines including NCI-H1299, HCC827, and A549. Furthermore, compared with gefitinib-treated cells, the messenger RNA expression of SIRT6 was obviously increased in non-small cell lung cancer cells treated with gefitinib combined with astragaloside IV. In addition, downregulation of SIRT6 was accomplished using small interference RNA technology. As a result, SIRT6 inhibition abolished the sensitization role of astragaloside IV in non-small cell lung cancer cells. Taken together, these data demonstrated that astragaloside IV sensitized tumor cells to gefitinib via regulation of SIRT6, suggesting that astragaloside IV may serve as potential therapeutic approach for lung cancer.

Elevated glycolytic activity and redox imbalance induced by tissue hypoxia are common phenomena of chronic inflammation, including inflammatory bone diseases such as arthritis. However, relation between glycolysis and redox signaling in the inflammatory milieu is unclear. The histone deacetylase sirtuin 6 (SIRT6) is a crucial modulator of inflammation and glucose metabolism, and it is also involved in cellular protection against oxidative injury. The aims of the study were to examine the connection between glycolysis and reactive oxygen species (ROS) production in human osteoblastic cells (HOB) and whether SIRT6 modulates inflammatory response via regulation of glycolytic activity and ROS generation. In HOB cultured under hypoxia, expression of lactate dehydrogenase A (LDHA), lactate production and ROS generation were examined. The reciprocal effects between lactate and ROS production and their impact on inflammatory cytokine induction were assessed. The action of SIRT6 on the above reactions was determined. In a rat model of collagen-induced arthritis (CIA), the relation between inflammatory activity and osteoblastic expression of LDHA, level of oxidative lesions, Cyr61 synthesis and macrophage recruitment were examined in joints with or without lentiviral-SIRT6 gene therapy. Results showed that hypoxia stress enhanced lactate and LDHA production in HOB. ROS generation was also increased, and there was a positive feedback between glycolysis and ROS formation. Overexpression of SIRT6 attenuated hypoxia-enhanced glycolysis and ROS generation. Hypoxia-induced expressions of Cyr61, TNF-α, IL-1β, and IL-6 were suppressed by SIRT6 and the inhibitory effects overlapped with antiglycolytic and antioxidation mechanisms. In the model of CIA, forced expression of SIRT6 ameliorated disease progression, osteoblastic synthesis of Cyr61, and macrophage recruitment. More importantly, expression of LDHA and oxidative lesions were decreased in osteoblasts of SIRT6-treated joints. Our findings suggest that SIRT6 suppresses inflammatory response in osteoblasts via modulation of glucose metabolism and redox homeostasis. SIRT6-based strategy may possess therapeutic potential for inflammatory bone resorption. © 2016 BioFactors, 43(2):170-180, 2017., (© 2016 International Union of Biochemistry and Molecular Biology.)

Sirtuin7 (SIRT7) plays an important role in many cancer types, but its function in non-small cell lung cancer (NSCLC) remains unclear. This study investigated the biological role and underlying mechanism of SIRT7 in NSCLC. Results showed that SIRT7 was highly expressed in NSCLC cell lines, as detected by real-time quantitative polymerase chain reaction and western blot analysis. SIRT7 knockdown by small interfering RNA (siRNA) significantly inhibited the growth of NSCLC cells and induced their apoptosis. Bioinformatics algorithms indicated that SIRT7 was a putative target of microRNA-3666 (miR-3666). Dual-luciferase reporter assay demonstrated that miR-3666 could target the 3'-untranslated region of SIRT7. Western blot analysis revealed that miR-3666 could regulate the protein expression of SIRT7. The miR-3666 overexpression significantly inhibited NSCLC cell growth. The restoration of SIRT7 protein expression significantly abrogated the effect of the miR-3666 overexpression. Moreover, SIRT7 depletion induced by siRNA or miR-3666 overexpression promoted the expression of pro-apoptotic genes. Taken together, our study suggests that SIRT7 functions as an oncogene in NSCLC, and miR-3666 can target SIRT7 to inhibit NSCLC cell growth by promoting the pro-apoptotic signaling pathway. Thus, this study provides novel insights into the development of new and potential treatments for NSCLC.

Nicotinamide is both a reaction product and an inhibitor of the conserved sirtuin family of deacetylases, which have been implicated in a broad range of cellular functions in eukaryotes from yeast to humans. Phenotypes observed following treatment with nicotinamide are most often assumed to stem from inhibition of one or more of these enzymes. Here, we used this small molecule to inhibit multiple sirtuins at once during treatment with DNA damaging agents in the Saccharomyces cerevisiae model system. Since sirtuins have been previously implicated in the DNA damage response, we were surprised to observe that nicotinamide actually increased the survival of yeast cells exposed to the DNA damage agent MMS. Remarkably, we found that enhanced resistance to MMS in the presence of nicotinamide was independent of all five yeast sirtuins. Enhanced resistance was also independent of the nicotinamide salvage pathway, which uses nicotinamide as a substrate to generate NAD+, and of a DNA damage-induced increase in the salvage enzyme Pnc1 Our data suggest a novel and unexpected function for nicotinamide that has broad implications for its use in the study of sirtuin biology across model systems., (Copyright © 2016 by the Genetics Society of America.)

This study was aimed to further investigate the possible mechanisms by which the glucagon like peptide 1 analogue, exendin-4 (EX4), protects rat retinal cells at the early stage of diabetes. EX4 was injected intravitreally into normal and early-stage streptozotocin-diabetic rats. Cell death, reactive oxygen species (ROS), and electroretinogram (ERG) were measured. Sirtuin (Sirt) mRNA and protein were analyzed. In retinas of diabetic rats 1 month after diabetes onset, cell death and ROS level increased significantly, and the b-wave amplitudes and OPs were significantly reduced. Four days after intravitreal EX4 treatment, retinal cell death and ROS level in retinas reduced significantly, and visual function was recovered. In the retinas of early-stage diabetic rats, the expressions of Sirt1 and Sirt3 were also found to be significantly decreased, and both were back to normal levels after intravitreal injection of EX4. In R28 cells, hydrogen peroxide (H2O2) treatment increased ROS and cell death and decreased Sirt1 and Sirt3. With the addition of EX4 into the culture system, the expressions of Sirt1 and Sirt3 were increased, and the H2O2-induced ROS and cell death were significantly reduced. These results confirm a mechanism for EX4 to protect retinal cells from diabetic damage and oxidative injury. EX4 reduces retinal cell death and ROS generation by upregulating Sirt1 and Sirt3 expressions in the retina of early-stage diabetic rats as well as in H2O2-treated R28 cells., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Insufficient insulin produced by pancreatic β-cells in the control of blood sugar is a central feature of the etiology of diabetes. Reports have shown that endoplasmic reticulum (ER) stress is fundamentally involved in β-cell dysfunction. In this study, we hypothesized that NAD-dependent deacetylase sirtuin-3 (SIRT3), an important regulator of cell metabolism, protects pancreatic β-cells from ER stress-mediated apoptosis. To validate our hypothesis, a rat diabetic model was established by a high-fat diet (HFD). We found that SIRT3 expression was markedly decreased in NIT1 and INS1 cells incubated with palmitate. Palmitate treatment significantly decreased β-cell viability and insulin secretion, and promoted malondialdehyde (MDA) formation. However, SIRT3 overexpression in NIT1 and INS1 cells reversed these effects, resulting in higher insulin secretion, decreased β-cell apoptosis, and downregulation of the expression of ER stress-associated genes. Moreover, SIRT3 overexpression also inhibited calcium influx and the hyperacetylation of glucose-regulated protein of 78 kDa (GRP78). SIRT3 knockdown effectively enhanced the upregulation of phospho-extracellular regulated protein kinases (pERK), inositol-requiring enzyme-1 (IRE1), activating transcription factor 6 (ATF6), and C/EBP homologous protein (CHOP) induced by palmitate, and promoted palmitate-induced β-cell apoptosis and dysfunction. Taken together, our results suggest that SIRT3 is an integral regulator of ER function and that its depletion might result in the hyperacetylation of critical ER proteins that protect against islet lipotoxicity under conditions of nutrient excess.

The activation of signal transducer and activator of transcription 3 (STAT3) is critical for the development of cardiac hypertrophy and heart failure. Sirtuin 6 (SIRT6) protects cardiomyocytes from hypertrophy. This study focused on the association between SIRT6 and STAT3 in the regulation of cardiomyocyte hypertrophy. In the phenylephrine (PE)-induced hypertrophic cardiomyocyte model and in the hearts of isoprenaline-induced cardiac hypertrophic rat model, the mRNA and protein expressions of STAT3 and its phosphorylated level at tyrosine 705 (P-STAT3) were significantly increased. By contrast, the deacetylation activity of SIRT6 was weakened without altering its protein expression. In addition, the nuclear localization of STAT3 and P-STAT3 was enhanced by PE, suggesting that STAT3 was activated in cardiomyocyte hypertrophy. Adenovirus infection-induced SIRT6 overexpression repressed the activation of STAT3 by decreasing its mRNA and protein levels, by suppressing its transcriptional activity, and by hindering the expressions of its target genes. Moreover, the effect of SIRT6 overexpression on eliminating PE-induced expressions of hypertrophic biomarkers, such as atrial natriuretic factor and brain natriuretic peptide, was reversed by STAT3 overexpression. Likewise, SIRT6 knockdown-induced upregulation of atrial natriuretic factor and brain natriuretic peptide was reversed by STAT3 silencing. These observations suggest that the antihypertrophic effect of SIRT6 involves STAT3 suppression. In conclusion, SIRT6 prevents PE-induced activation of STAT3 in cardiomyocyte hypertrophy; the inhibitory effect of SIRT6 on STAT3 contributes to cardiac protection.

Hyperglycaemia in diabetes is either caused by reduced availability of insulin (type 1 diabetes, T1D) or insulin resistance to the cells (type 2 diabetes, T2D). In recent years, the prevalence of T2D has increased to an alarming proportion, encompassing 95 percent of the total diabetic burden, probably due to economy-driven changes in lifestyle. Recent epidemiological studies show comorbid depression, anxiety and related mental illness. To explore the molecular mechanisms underlying this comorbid conditions, we used Sprague-Dawley rats on high-fructose diet for 8 weeks to induce prediabetic condition. Rats with this metabolic syndrome also showed hyper-anxiety when they were subjected to anxiety-related behavioural assays. Rats were administered with resveratrol, an activator of sirtuins, and metformin, a standard antidiabetic drug, simultaneously with fructose. We observed that resveratrol was more effective in protecting from both the metabolic (prediabetic) and affective (anxiety) disorders than metformin. Molecular studies showed that recovery was associated with the upregulation of few nuclear sirtuins that act epigenetically - Sirt 1 and 7, which were significantly attenuated in the striatum of prediabetic rats. In conclusion, our study showed that hyper-anxiety associated with prediabetic condition is ameliorated by resveratrol through modulation of sirtuins, which is more or less similar to metformin.

Purpose: To characterize the functional role of SIRT6 in hepatocellular carcinoma (HCC)., Experimental Design: The expression of SIRT6 in 60 paired paraffin-embedded HCC tissues and adjacent nontumoral liver tissues was examined by immunohistochemistry. The expression of SIRT6 in 101 paired frozen HCC tissues and adjacent nontumoral liver tissues was analyzed by Western blotting analysis and qPCR. The biologic consequences of overexpression and knockdown of SIRT6 in HCC cell lines were studied in vitro and in vivo, Results: SIRT6 expression was frequently upregulated in clinical HCC samples, and its expression was highly associated with tumor grade (P = 0.02), tumor size (P = 0.02), vascular invasion (P = 0.004), and shorter survival (P = 0.024). Depletion of SIRT6 from multiple liver cancer cell lines inhibited their growth and induced apoptosis in vitro At the molecular level, we observed that the activation of the BCL2-associated X protein (Bax) signaling pathway, a major pathway that determines cancer cell apoptosis, is regulated by SIRT6 via its deacetylase activity. SIRT6 was recruited to the promoter of Bax, where it deacetylated histone 3 lysine 9 and suppressed its promoter activity. Binding of transcription factors (p53 and E2F-1) to Bax promoter was also generally increased in SIRT6-depleted cells. In mouse xenografts, SIRT6 suppression inhibited tumor growth and induced apoptosis. Finally, there is a negative correlation between SIRT6 and Bax mRNA expressions in human HCC samples., Conclusions: SIRT6 is an important protumorigenic factor in liver carcinogenesis. Thus, the therapeutic targeting of SIRT6 may offer options for HCC treatment. Clin Cancer Res; 22(13); 3372-82. ©2016 AACR., (©2016 American Association for Cancer Research.)

Aberrant epigenetic modifications are implicated in maternal diabetes-induced neural tube defects (NTDs). Because cellular stress plays a causal role in diabetic embryopathy, we investigated the possible role of the stress-resistant sirtuin (SIRT) family histone deacetylases. Among the seven sirtuins (SIRT1-7), pre-gestational maternal diabetes in vivo or high glucose in vitro significantly reduced the expression of SIRT 2 and SIRT6 in the embryo or neural stem cells, respectively. The down-regulation of SIRT2 and SIRT6 was reversed by superoxide dismutase 1 (SOD1) over-expression in the in vivo mouse model of diabetic embryopathy and the SOD mimetic, tempol and cell permeable SOD, PEGSOD in neural stem cell cultures. 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), a superoxide generating agent, mimicked high glucose-suppressed SIRT2 and SIRT6 expression. The acetylation of histone 3 at lysine residues 56 (H3K56), H3K14, H3K9, and H3K27, putative substrates of SIRT2 and SIRT6, was increased by maternal diabetes in vivo or high glucose in vitro, and these increases were blocked by SOD1 over-expression or tempol treatment. SIRT2 or SIRT6 over-expression abrogated high glucose-suppressed SIRT2 or SIRT6 expression, and prevented the increase in acetylation of their histone substrates. The potent sirtuin activator (SRT1720) blocked high glucose-increased histone acetylation and NTD formation, whereas the combination of a pharmacological SIRT2 inhibitor and a pan SIRT inhibitor mimicked the effect of high glucose on increased histone acetylation and NTD induction. Thus, diabetes in vivo or high glucose in vitro suppresses SIRT2 and SIRT6 expression through oxidative stress, and sirtuin down-regulation-induced histone acetylation may be involved in diabetes-induced NTDs. The mechanism underlying pre-gestational diabetes-induced neural tube defects (NTDs) is still elusive. Our study unravels a new epigenetic mechanism in which maternal diabetes-induced oxidative stress represses sirtuin deacetylase 2 (SIRT2) and 6 (SIRT6) expression leading to histone acetylation and gene expression. SIRT down-regulation mediates the teratogenicity of diabetes leading to (NTD) formation. The study provides a mechanistic basis for the development of natural antioxidants and SIRT activators as therapeutics for diabetic embryopathy., (© 2016 International Society for Neurochemistry.)

Sirtuin 6 (SIRT6) is a member of the mammalian NAD+‑dependent deacetylase sirtuin family that acts to maintain genomic stability and to repress genes. SIRT6 has recently been reported to be a tumor suppressor that controls cancer metabolism, although this effect of SIRT6 is still in dispute. Moreover, the role of SIRT6 in glioma is largely unknown. In the present study, we found that overexpression of SIRT6 using an adenovirus inhibited glioma cell growth and induced marked cell injury in two glioma cell lines (U87‑MG and T98G). Fluorescent terminal deoxyribonucleotidyl transferase (TdT)‑mediated biotin‑16‑dUTP nick‑end labelling (TUNEL) assay showed that SIRT6 overexpression induced obvious apoptosis in the T98G glioma cells. Immunoblotting and immunofluorescent staining demonstrated that SIRT6 overexpression promoted the mitochondrial-to‑nuclear translocation of apoptosis‑inducing factor (AIF), a potent apoptosis inducer. Moreover, we found that SIRT6 overexpression largely reduced oxidative stress and suppressed the activation of the JAK2/STAT3 signaling pathway in glioma cells. Finally, we showed that SIRT6 mRNA and protein levels in human glioblastoma multiforme tissues were significantly lower than the levels in peritumor tissues. In summary, our data suggest that SIRT6 suppresses glioma cell growth via induction of apoptosis, inhibition of oxidative stress and inhibition of the activation of the JAK2/STAT3 signaling pathway. These results indicate that SIRT6 may be a promising therapeutic target for glioma treatment.

Mammalian Sirtuin proteins (SIRTs) are homologs of yeast Sir2, and characterized as class III histone deacetylases of NAD(+) dependence. Unlike their lower counterparts that are directly involved in the extending of lifespan, mammalian SIRTs mainly function in metabolism and cellular homeostasis, among them, SIRT7 is the least understood. SIRT7 is localized in the nucleus and rich in nucleoli associated with RNA polymerase I, and correlated with cell proliferation. In contrast, SIRT7 has recently been demonstrated to specifically deacetylate H3K18ac in the chromatin, and in most cases represses proliferation. Although MicroRNA as miR-125b has been reported to down-regulate SIRT7 by binding to its 3'UTR, however, how SIRT7 gene is regulated remains unclear. Here, we identified the transcription initiation site of human SIRT7 gene at the upstream 23rd A nucleotide respective to the translational codon, and the SIRT7 is a TATA-less and initiator-less gene. The sequences in the upstream region between -256 and -129 bp are identical with important functions in the three species detected. A C/EBPα responding element is found that binds both C/EBPα and C/EBPβ in vitro. We showed TSA induced SIRT7 gene transcription and only the HDAC3, but not its catalytic domain depleted mutant, interacted with C/EBPα to occupy the C/EBPα element and repressed SIRT7 gene in the hepatocellular carcinoma cells. To our knowledge, this is the first report on the regulation mechanism of SIRT7 gene, in which, HDAC3 collaborated with C/EBPα to occupy its responding element in the upstream region of SIRT7 gene and repressed its expression in human cells., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Conclusion: The expression of sirtuin in vestibular end organs and cochlea responds differently to age-related changes. Down-regulation of SIRT1, 3, and 5 in the cochlea may weaken the protective activity regarding degeneration of the organ of Corti as well as of spiral ganglion cells, resulting in the development of age-related hearing loss. An increase in SIRT 1, 4, or 5 in vestibular tissue could indicate an increased need of detoxification of reactive oxygen species and an increased anti-ageing potential., Objective: To analyse the expression of sirtuins (SIRT1-7) in the normal young and old mouse inner ears., Methods: Young (8 weeks) and old (22 months) CBA/J mice were used in this study. Localization of SIRT1-7 in the inner ear, i.e. cochlea, vestibular end organs, and vestibular ganglion, was investigated using real-time PCR and immunohistochemistry., Results: In the vestibular end organs, the expression of SIRT1, 2, 4, 5 (both mRNA and protein), SIRT6, and 7 (only mRNA) was found to be increased, while a slightly decreased immunoreactivity was observed in SIRT3. In the cochlea, the expression of SIRT1, 3, and 5 (both mRNA and protein) was decreased in the old mice, whereas no noticeable difference was observed regarding SIRT2, 4, 6, or 7.

Sirtuin3 (SIRT3) is an important protein deacetylase which predominantly presents in mitochondria and exhibits broad bioactivities including regulating energy metabolism and counteracting inflammatory effect. Since inflammatory cascade was proved to be critical for pathological damage following subarachnoid hemorrhage (SAH), we investigated the overall expression and cell-specific distribution of SIRT3 in the cerebral cortex of Sprague-Dawley rats with experimental SAH induced by internal carotid perforation. Results suggested that SIRT3 was expressed abundantly in neurons and endothelia but rarely in gliocytes in normal cerebral cortex. After experimental SAH, mRNA and protein expressions of SIRT3 decreased significantly as early as 8 hours and dropped to the minimum value at 24 h after SAH. By contrast, SOD2 expression increased slowly as early as 12 hours after experimental SAH, rose up sharply at the following 12 hours, and then was maintained at a higher level. In conclusion, attenuated SIRT3 expression in cortical neurons was associated closely with enhanced reactive oxygen species generation and cellular apoptosis, implying that SIRT3 might play an important neuroprotective role during early brain injury following SAH., Competing Interests: The authors declare that they have no competing interests.

Sirtuin-2 (Sirt2) is a member of the NAD(+)-dependent protein deacetylase family. Various members of the sirtuin class have been found to be involved in processes related to longevity, regulation of inflammation, and neuroprotection. Induction of Sirt2 mRNA was found in the whole hemisphere after experimental stroke in a recent screening approach. Moreover, Sirt2 protein is highly expressed in myelin-rich brain regions after stroke. To examine the effects of Sirt2 on ischemic stroke, we induced transient focal cerebral ischemia in adult male Sirt2-knockout and wild-type mice. Two stroke models with different occlusion times were applied: a severe ischemia (45 minutes of middle cerebral artery occlusion (MCAO)) and a mild one (15 minutes of MCAO), which was used to focus on subcortical infarcts. Neurological deficit was determined at 48 hours after 45 minutes of MCAO, and up to 7 days after induction of 15 minutes of cerebral ischemia. In contrast to recent data on Sirt1, Sirt2(-/-) mice showed less neurological deficits in both models of experimental stroke, with the strongest manifestation after 48 hours of reperfusion. However, we did not observe a significant difference of stroke volumes or inflammatory cell count between Sirt2-deficient and wild-type mice. Thus we postulate that Sirt2 mediates myelin-dependent neuronal dysfunction during the early phase after ischemic stroke.

Activation of genes promoting aerobic glycolysis and suppression of mitochondrial oxidative phosphorylation is one of the hallmarks of cancer. The RUNX2 transcription factor mediates breast cancer (BC) metastasis to bone and is regulated by glucose availability. But, the mechanisms by which it regulates glucose metabolism and promotes an oncogenic phenotype are not known. RUNX2 expression in luminal BC cells correlated with lower estrogen receptor-α (ERα) levels, anchorage-independent growth, expression of glycolytic genes, increased glucose uptake, and sensitivity to glucose starvation, but not to inhibitors of oxidative phosphorylation. Conversely, RUNX2 knockdown in triple-negative BC cells inhibited mammosphere formation and glucose dependence. RUNX2 knockdown resulted in lower LDHA, HK2, and GLUT1 glycolytic gene expression, but upregulation of pyruvate dehydrogenase-A1 (PDHA1) mRNA and enzymatic activity, which was consistent with lower glycolytic potential. The NAD-dependent histone deacetylase, SIRT6, a known tumor suppressor, was a critical regulator of these RUNX2-mediated metabolic changes. RUNX2 expression resulted in elevated pAkt, HK2, and PDHK1 glycolytic protein levels that were reduced by ectopic expression of SIRT6. RUNX2 also repressed mitochondrial oxygen consumption rates (OCR), a measure of oxidative phosphorylation (respiration). Overexpression of SIRT6 increased respiration in RUNX2-positive cells, but knockdown of SIRT6 in cells expressing low RUNX2 decreased respiration. RUNX2 repressed SIRT6 expression at both the transcriptional and post-translational levels and endogenous SIRT6 expression was lower in malignant BC tissues or cell lines that expressed high levels of RUNX2. These results support a hypothesis whereby RUNX2-mediated repression of the SIRT6 tumor suppressor regulates metabolic pathways that promote BC progression., (© 2015 Wiley Periodicals, Inc.)

Background: Cardiac oxidative stress, bioenergetics and catecholamine play major roles in heart failure progression. However, the relationships between these three dominant heart failure factors are not fully elucidated. Caffeic acid ethanolamide (CAEA), a synthesized derivative from caffeic acid that exerted antioxidative properties, was thus applied in this study to explore its effects on the pathogenesis of heart failure., Results: In vitro studies in HL-1 cells exposed to isoproterenol showed an increase in cellular and mitochondria oxidative stress. Two-week isoproterenol injections into mice resulted in ventricular hypertrophy, myocardial fibrosis, elevated lipid peroxidation, cardiac adenosine triphosphate and left ventricular ejection fraction decline, suggesting oxidative stress and bioenergetics changes in catecholamine-induced heart failure. CAEA restored oxygen consumption rates and adenosine triphosphate contents. In addition, CAEA alleviated isoproterenol-induced cardiac remodeling, cardiac oxidative stress, cardiac bioenergetics and function insufficiency in mice. CAEA treatment recovered sirtuin 1 and sirtuin 3 activity, and attenuated the changes of proteins, including manganese superoxide dismutase and hypoxia-inducible factor 1-α, which are the most likely mechanisms responsible for the alleviation of isoproterenol-caused cardiac injury, Conclusion: CAEA prevents catecholamine-induced cardiac damage and is therefore a possible new therapeutic approach for preventing heart failure progression.

Sirtuins belong to the family of class III histone deacetylases; its role in neoplasia is controversial as both tumor-suppressive and promoting functions have been reported. There are very few reports available, where expressions of sirtuin isoforms are comprehensively analyzed during neoplasia. Therefore, in the present study, the expression of SIRT1, SIRT2, and SIRT7 during different stages of cervical cancer progression was analyzed. The normal cervical epithelium showed feeble expression of sirtuin isoforms, SIRT1, SIRT2, and SIRT7. A significant increase in SIRT1 expression was noted in the cytoplasm as well as in the nucleus of proliferative layers of cervical epithelium in squamous intraepithelial lesions (SIL); however, in the squamous cell carcinomas (SCC), a heterogeneous pattern of SIRT1 expression varying from low to high was noted. A progressive increase in the expression of both SIRT2 and SIRT7 was noted during cancer progression in the following order: normal < preneoplasia < cancer. Cervical cancer cell lines, HeLa and SiHa, showed higher levels of SIRT1 and SIRT2 in comparison to the immortalized cell counterpart, HaCaT. Specific inhibitors of SIRT1 (Ex527) and SIRT2 (AGK2) impaired the growth of the cervical cancer cells, SiHa, but not of the HaCaT cells. SIRT1 inhibition caused cell death, while SIRT2 inhibition resulted in cell cycle arrest. In conclusion, we report the overexpression of SIRT2 and SIRT7 proteins in cervical cancer and suggest probable application of sirtuin inhibitors as therapeutic targets. Further, a specific increase in the levels of SIRT1 in intraepithelial lesion makes it a promising candidate for identification of preneoplastic changes.

The most common feature of endothelial dysfunction is endothelial inflammation. A bunch of factors are associated with endothelial dysfunction. These include pro-inflammatory cytokines, cell adhesion molecules, and matrix degrading enzymes. SIRT4, a member of the sirtuin family, is a mitochondrial ADP-ribosyltransferase. The roles of SIRT4 in regulating inflammation in endothelial cells are unknown. In this study, we found that lipopolysaccharide treatment decreased the expression of SIRT4 in human umbilical vein endothelial cells. Silence of SIRT4 exacerbated the expression of pro-inflammatory cytokines (IL-1β, IL-6 and IL-8), COX-prostaglandin system (COX-2), ECM remodeling enzymes MMP-9, and the adhesion molecule ICAM-1. The upregulation of these genes are involved in inflammation, vascular remodeling, and angiogenesis. In contrast, overexpression of SIRT4 attenuated the induction of these factors. Mechanistically, SIRT4 was found to interfere with the NF-κB signaling pathway by preventing NF-κB nuclear translocation and thereby has an anti-inflammatory function. Loss of SIRT4 increased the nuclear translocation as well as the transcriptional activity of NF-κB. However, overexpression of SIRT4 mitigated the nuclear translocation and the transcriptional activity of NF-κB. Our data suggested that SIRT4 might be a potential pharmacological target for inflammatory vascular diseases.