Targeting Sirtuin Research Articles

The anti-atherogenic effects of berberine on foam cell formation are mediated through the upregulation of sirtuin 1.

Berberine (BBR) is a botanical alkaloid that has been reported to have effects in cardiovascular diseases; however, the mechanisms involved are not yet fully understood. In the present study, the protective effects of BBR were evaluated, and the underlying molecular mechanisms were investigated. The effects of a combination of atorvastatin and BBR on foam cell formation were also investigated. THP-1-derived macrophages were pre-treated with BBR (5, 10 and 20 mg/l) for 2 h prior to the addition of oxidized low density lipoprotein (ox-LDL; 50 mg/l). Small interfering RNA (siRNA) targeting sirtuin 1 (SIRT1) and the adenosine 5'-monophosphate-activated protein kinase (AMPK) inhibitor, compound C, were used to investigate the mechanisms through which BBR exerts its effects. To determine the effect of a combination of atorvastatin and BBR, the macrophages were treated with atorvastatin and BBR separately or jointly for 2 h, and then treated with ox-LDL (50 mg/l) or lipopolysaccharide (LPS; 10 µM) for 12 h. Oil Red O staining was used to detect foam cell formation. Lipid amounts were assessed by high-performance liquid chromatography (HPLC). Gene and protein expression was evaluated by RT-qPCR, western blot analysis and enzyme-linked immunosorbent assay (ELISA) carried out separately or jointly. The results from Oil Red O staining and HPLC revealed that BBR effectively suppressed foam cell formation and lipid and cholesterol accumulation. Furthermore, BBR upregulated the expression of SIRT1 and AMPK and downregulated the expression of peroxisome proliferator-activated receptor-γ (PPAR-γ). Pre-treatment of the cells with SIRT1-siRNA or compound C attenuated the anti-atherosclerotic effects of BBR. The results obtained in the present study demonstrate that the combination of atorvastatin and BBR is more effective in inhibiting foam cell formation than using atorvastatin alone. These data suggest that BBR suppresses foam cell formation by activating the AMPK-SIRT1-PPAR-γ pathway and diminishing the uptake of ox-LDL. Combination therapy with BBR and atorvastatin was more effective in preventing atherosclerotic processes than atorvastatin alone.

SIRT1 prevents genotoxic stress-induced p53 activation in acute myeloid leukemia

AbstractSIRT1 is an important regulator of cellular stress response and genomic integrity. Its role in tumorigenesis is controversial. Whereas sirtuin 1 (SIRT1) can act as a tumor suppressor in some solid tumors, increased expression has been demonstrated in many cancers, including hematologic malignancies. In chronic myeloid leukemia, SIRT1 promoted leukemia development, and targeting SIRT1 sensitized chronic myeloid leukemia progenitors to tyrosine kinase inhibitor treatment. In this study, we investigated the role of SIRT1 in acute myeloid leukemia (AML). We show that SIRT1 protein, but not RNA levels, is overexpressed in AML samples harboring activating mutations in signaling pathways. In FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD)+-cells protein, expression of SIRT1 is regulated by FLT3 kinase activity. In addition, SIRT1 function is modulated via the ATM-DBC1-SIRT1 axis in a FLT3-ITD-dependent manner. In murine leukemia models driven by MLL-AF9 or AML1-ETO coexpressing FLT3-ITD, SIRT1 acts as a safeguard to counteract oncogene-induced stress, and leukemic blasts become dependent on SIRT1 activity. Pharmacologic targeting or RNAi-mediated knockdown of SIRT1 inhibited cell growth and sensitized AML cells to tyrosine kinase inhibitor treatment and chemotherapy. This effect was a result of the restoration of p53 activity. Our data suggest that targeting SIRT1 represents an attractive therapeutic strategy to overcome primary resistance in defined subsets of patients with AML.

Targeting sirtuin-1 alleviates experimental autoimmune colitis by induction of Foxp3+ T-regulatory cells (MUC2P.818)

Abstract Induced Foxp3+ T-regulatory cells (iTreg) are essential to gastrointestinal immune homeostasis and play an important role in preventing autoimmune colitis. We have previously shown that inhibiting sirtuin-1 (Sirt1) can augment Treg function and hypothesized that targeting of Sirt1 might enhance iTreg development and thereby represent a potential therapy for inflammatory bowel disease (IBD). We adoptively transferred CD4+CD25-Foxp3- T effector (TE) cells from wild-type (C57BL/6) or fl-Sirt1/CD4cre mice into B6/Rag1-/- mice and monitored the mice until they lost 10-15% of their weight. Adoptive transfer of TE cells lacking Sirt1 to B6/Rag1-/- mice resulted in increased iTreg formation compared to mice receiving wild-type TE cells (2.3 ±1.6%, vs. 6.2 ±3%, in wild type and fl-Sirt1/CD4cre TE recipients, respectively, p<0.001). This correlated with attenuated colitis and reduced weight loss in fl-Sirt1/CD4cre vs. wild type TE recipients (1.04 ±1.4% vs. 13.97 ±2.2%, respectively, p<0.001). In a second model of IBD, we used pharmacologic Sirt1 targeting of mice receiving multiple cycles of dextran sodium sulfate (DSS) in their drinking water, alternated with fresh water. Likewise, wild-type mice receiving cyclic DSS and a Sirt1 inhibitor, EX-527, had reduced weight loss (5.8 ±5.9% vs. 13.2 ±6.9%, p=0.03) and increased iTreg formation compared to controls. Sirt1 appears a promising target for pharmacologic therapy of IBD as a result of promoting iTreg development.

Novel PPAR pan agonist, ZBH ameliorates hyperlipidemia and insulin resistance in high fat diet induced hyperlipidemic hamster.

Effective and safe pharmacological interventions for hyperlipidemia remains badly needed. By incorporating the key pharmacophore of fibrates into the natural scaffold of resveratrol, a novel structural compound ZBH was constructed. In present study, we found ZBH reserved approximately one third of the sirtuin 1 (SIRT1) activation produced by resveratrol at in-vitro enzyme activity assay, directly bound to and activated all three peroxisome proliferator-activated receptor (PPAR) subtypes respectively in PPAR binding and transactivation assays. Moreover, ZBH (EC50, 1.75 µM) activate PPARα 21 fold more efficiently than the well-known PPAR pan agonist bezafibrate (EC50, 37.37 µM) in the cellular transactivation assays. In the high fat diet induced hyperlipidemic hamsters, 5-week treatment with ZBH significantly lowered serum triglyceride, total cholesterol, LDL-C, FFA, hyperinsulinemia, and improved insulin sensitivity more potently than bezafibrate. Meanwhile, serum transaminases, creatine phosphokinase and CREA levels were found not altered by ZBH intervention. Mechanism study indicated ZBH promoted the expression of PPARα target genes and SIRT1 mRNA. Hepatic lipogenesis was markedly decreased via down-regulation of lipogenic genes, and fatty acid uptake and oxidation was simultaneously increased in the liver and skeletal muscle via up-regulation of lipolysis genes. Glucose uptake and utilization was also significantly promoted in skeletal muscle. These results suggested that ZBH significantly lowered hyperlipidemia and ameliorated insulin resistance more efficiently than bezafibrate in the hyperlipidemic hamsters primarily by activating of PPARα, and SIRT1 promotion and activation. ZBH thus presents a potential new agent to combat hyperlipidemia.

Targeting sirtuin-1 alleviates experimental autoimmune colitis by induction of Foxp3+ T-regulatory cells.

Induced Foxp3+ T-regulatory cells (iTreg) are essential to gastrointestinal immune homeostasis and loss of the ability to develop iTregs may lead to autoimmune colitis. We previously showed a role for Sirtuin-1 (Sirt1) in control of Treg function and hypothesized that targeting of Sirt1 might enhance iTreg development and thereby represent a potential therapy for inflammatory bowel disease (IBD). We adoptively transferred CD4+CD25−Foxp3− T effector (TE) cells from wild-type (C57BL/6) or fl-Sirt1/CD4cre mice into B6/Rag1−/− mice and monitored the mice until they lost 10-15% of their weight. Adoptive transfer of TE cells lacking Sirt1 to B6/Rag1−/− mice resulted in a 2.8-fold increase in iTreg formation compared to mice receiving wild-type TE cells and correlated with attenuated colitis and reduced weight loss (1.04±1.4% vs. 13.97±2.2%, respectively, p<0.001). In a second model of IBD, we used pharmacologic Sirt1 targeting of mice receiving multiple cycles of dextran sodium sulfate (DSS) in their drinking water, alternated with fresh water. Likewise, wild-type mice receiving cyclic DSS and a Sirt1 inhibitor, EX-527, had reduced weight loss (5.8±5.9% vs. 13.2±6.9%, p=0.03) and increased iTreg formation compared to controls. Sirt1 appears a promising target for pharmacologic therapy of IBD as a result of promoting iTreg development.

Long-Term Effects of Peripubertal Binge EtOH Exposure on Hippocampal microRNA Expression in the Rat

Adolescent binge alcohol abuse induces long-term changes in gene expression, which impacts the physiological stress response and memory formation, two functions mediated in part by the ventral (VH) and dorsal (DH) hippocampus. microRNAs (miRs) are small RNAs that play an important role in gene regulation and are potential mediators of long-term changes in gene expression. Two genes important for regulating hippocampal functions include brain-derived neurotrophic factor (BDNF) and sirtuin-1 (SIRT1), which we identified as putative gene targets of miR-10a-5p, miR-26a, miR-103, miR-495. The purpose of this study was to quantify miR-10a-5p, miR-26a, miR-103, miR-495 expression levels in the dorsal and ventral hippocampus of male Wistar rats during normal pubertal development and then assess the effects of repeated binge-EtOH exposure. In addition, we measured the effects of binge EtOH-exposure on hippocampal Drosha and Dicer mRNA levels, as well as the putative miR target genes, BDNF and SIRT1. Overall, mid/peri-pubertal binge EtOH exposure altered the normal expression patterns of all miRs tested in an age- and brain region-dependent manner and this effect persisted for up to 30 days post-EtOH exposure. Moreover, our data revealed that mid/peri-pubertal binge EtOH exposure significantly affected miR biosynthetic processing enzymes, Drosha and Dicer. Finally, EtOH-induced significant changes in the expression of a subset of miRs, which correlated with changes in the expression of their predicted target genes. Taken together, these data demonstrate that EtOH exposure during pubertal development has long-term effects on miRNA expression in the rat hippocampus.

Targeting sirtuins for the treatment of diabetes.

Sirtuins are a class of NAD+-dependent deacetylases, such as deacetylases, that have a wide array of biological functions. Recent studies have suggested that reduced sirtuin action is correlated with Type 2 diabetes. Both overnutrition and aging, which are two major risk factors for diabetes, lead to decreased sirtuin function and result in abnormal glucose and lipid metabolism. Therefore, restoring normal levels of sirtuin action in Type 2 diabetes may be a promising method of treating diabetes. This article reviews the biological functions of three of the seven mammalian sirtuins - SIRT1, SIRT3 and SIRT6 - that have demonstrated prominent metabolic roles and early potential for drug targeting. Clinical trials investigating the use of sirtuin activators for treating diabetes are already underway and show promise as alternatives to current diabetes therapies. Thus, further research into sirtuin activators is warranted and may lead to a new class of safe, effective diabetes treatments.

Sirtuins Family- Recent Development as a Drug Target for Aging, Metabolism, and Age Related Diseases

Silent information regulator 2 (Sir2) proteins, or sirtuins, are a family of proteins which influence several physiological responses and have implications for treating diseases of ageing. In this context, we have presented a summarized view on the discovery of Sir2 family proteins, the enzymatic activities, the role of sirtuins in aging, lifespan and onset of age-related symptoms. In addition, we have described the roles of mammalian sirtuins-with particular emphasis on their associations to aging, metabolism, and age related diseases with recent references. Current findings provide an understanding about mammalian sirtuins and their target diseases, small molecules discovery or drug discovery targeting sirtuin to tackle the serious diseases of aging.

Targeting Sirtuin-1 in Huntington’s Disease: Rationale and Current Status

Huntington's disease (HD) is an autosomal dominant hereditary disease caused by a trinucleotide repeat mutation in the huntingtin gene that results in an increased number of glutamine residues in the N terminus of huntingtin protein. Mutant huntingtin leads to progressive impairment of motor function, cognitive dysfunction, and neuropsychiatric disturbance. There are no disease-modifying treatments available. During the past decade, sirtuin-1 (SIRT1) has been the focus of intense investigation and discussion because it regulates longevity in multiple organisms and has shown beneficial effects in a variety of models of neurodegenerative disorders. Studies in different animal models provide convincing evidence that SIRT1 protects neurons in mouse models of HD as well as in Caenorhabditis elegans, although controversial results were reported in a fly model. Indeed, many connections exist between the deacetylation function of SIRT1 and its role in neuroprotection. As a result, pharmacological interventions targeting SIRT1 might become promising strategies to combat HD. This review summarizes recent progress in SIRT1 research, with a focus on the specificity of this protein as a potential therapeutic target for HD, as well as existing challenges for developing SIRT1 modulators for clinical use.

Emerging Roles of SIRT1 in Cancer Drug Resistance

Innate resistance to various therapeutic interventions is a hallmark of cancer. In recent years, acquired resistance has emerged as a daunting challenge to targeted cancer therapy, which abolishes the efficacy of otherwise successful targeting drugs. Cancer cells gain the resistance property through a variety of mechanisms in primary and metastatic cancers, involving cellular intrinsic and extrinsic factors. Increasing evidence suggests that the mammalian stress response gene sirtuin 1 (SIRT1) plays a critical role in multiple aspects of cancer drug resistance. SIRT1 decreases drug penetration, confers proliferation and antiapoptotic survival advantages to cancer cells, facilitates acquired resistance through genetic mutations, promotes the survival of cancer stem cells, and changes the tumor microenvironment for resistance in cell-autonomous and -nonautonomous manners. This article provides an overview of research advances in the roles of SIRT1 in cancer drug resistance and highlights the prospect of targeting SIRT1 as a new strategy to overcome cancer drug resistance and improve therapeutic outcomes.

Sirtuin 1 (SIRT1): a potential immunohistochemical marker and therapeutic target in soft tissue neoplasms with myoid differentiation

Sirtuin, silent mating-type information regulation 2 homolog Saccharomyces cerevisiae 1 (SIRT1), is a protein that has been implicated in multiple mammalian functions including cell aging, stress resistance, and differentiation. SIRT1 has also been shown to be involved in multiple tumors. In addition, new pharmacotherapies have recently been approved that target SIRT1. The purpose of this study was to use immunohistochemistry to characterize SIRT1 protein expression in human soft tissue neoplasms with the hopes of finding new diagnostic and therapeutic modalities. SIRT1 immunoreactivity was reviewed in a series of 164 soft tissue tumors including alveolar soft part sarcoma, angiomyolipoma, clear cell sarcoma, desmoid/fibromatosis, desmoplastic small round cell tumor, Ewing sarcoma, gastrointestinal stromal tumor, glomus tumor, leiomyoma, leiomyosarcoma, lipoma, liposarcoma, malignant peripheral nerve sheath tumor, nodular fasciitis, osteosarcoma, rhabdomyosarcoma, schwannoma, solitary fibrous tumor, synovial sarcoma, undifferentiated pleomorphic sarcoma, and Wilms tumor. In addition, numerous benign tissues were tested for SIRT1 reactivity. In nonneoplastic tissue, strong cytoplasmic SIRT1 reactivity was observed in all prostate stroma, smooth muscle, and striated muscle. A similar pattern of cytoplasmic SIRT1 expression was observed in soft tissue neoplasms with myoid differentiation, namely, angiomyolipoma (100%), glomus tumor (100%), leiomyoma (90%), leiomyosarcoma (76.5%), and rhabdomyosarcoma (87%). The other lesions examined were negative. Although the physiologic role of SIRT1 remains to be clarified in myoid tissues and neoplasms differentiating along these lines, this observation points to a potential role for this marker in diagnostic immunohistochemistry. Furthermore, the recent emergence of drugs capable of selectively inhibiting SIRT1 raises the possibility of a potential application for targeted therapy. Additional studies are necessary to further characterise the role of SIRT1 in myoid tissues and neoplasms.

Downregulation of miR-181a upregulates sirtuin-1 (SIRT1) and improves hepatic insulin sensitivity

Sirtuin-1 (SIRT1) is a potential therapeutic target to combat insulin resistance and type 2 diabetes. This study aims to identify a microRNA (miRNA) targeting SIRT1 to regulate hepatic insulin sensitivity. Luciferase assay combined with mutation and immunoblotting was used to screen and verify the bioinformatically predicted miRNAs. miRNA and mRNA levels were measured by real-time PCR. Insulin signalling was detected by immunoblotting and glycogen synthesis. Involvement of SIRT1 was studied with adenovirus, inhibitor and SIRT1-deficient hepatocytes. The role of miR-181a in vivo was explored with adenovirus and locked nucleic acid antisense oligonucleotides. miR-181a targets the 3' untranslated region (3'UTR) of Sirt1 mRNA through a miR-181a binding site, and downregulates SIRT1 protein abundance at the translational level. miR-181a is increased in insulin-resistant cultured hepatocytes and liver, and in the serum of diabetic patients. Overexpression of miR-181a decreases SIRT1 protein levels and activity, and causes insulin resistance in hepatic cells. Inhibition of miR-181a by antisense oligonucleotides increases SIRT1 protein levels and activity, and improves insulin sensitivity in hepatocytes. Ectopic expression of SIRT1 abrogates the effect of miR-181a on insulin sensitivity, and inhibition of SIRT1 activity or SIRT1 deficiency markedly attenuated the improvement in insulin sensitivity induced by antisense miR-181a. In addition, overexpression of miR-181a by adenovirus impairs hepatic insulin signalling, and intraperitoneal injection of locked nucleic acid antisense oligonucleotides for miR-181a improves glucose homeostasis in diet-induced obesity mice. miR-181a regulates SIRT1 and improves hepatic insulin sensitivity. Inhibition of miR-181a might be a potential new strategy for treating insulin resistance and type 2 diabetes.

Sirtuin activators

Background: Sirtuin 1 – 7 (SIRT1 – 7) are deacetylases that are dependent on NAD+ for their activity. SIRT1 down-regulates p53 activity, increasing lifespan, cell survival, and neuroprotection; it also deacetylates peroxisome proliferator-activated receptor-γ and its coactivator 1α, promoting fat mobilization, increasing mitochondrial size and number, and positively regulating insulin secretion. Sirtuins link nutrient availability and energy metabolism. Calorie restriction, which increases lifespan and is beneficial in age-related disorders, activates sirtuin. Major efforts are thus focused to developing sirtuin activators. Objective: After discussing the potential involvement of sirtuins in pathophysiological processes, this review looks at new, synthetic sirtuin activators. Conclusions: To date, resveratrol is the most potent natural compound able to activate SIRT1, mimicking the positive effect of calorie restriction. Resveratrol might help in the treatment or prevention of obesity and in preventing the aging-related decline in heart function and neuronal loss. As resveratrol has low bioavailability and interacts with multiple molecular targets, the development of new molecules with better bioavailability and targeting sirtuin at lower concentrations is a promising field of the medicinal chemistry. New SIRT1 activators that are up to 1000 times more effective than resveratrol have recently been identified. These improve the response to insulin and increase the number and activity of mitochondria in obese mice. Human trials with a formulation of resveratrol with improved bioavailability and with a synthetic SIRT1 activator are in progress.