Sirtuin Activity Research Articles

Uncovering the roles of sirtuin activity and food availability during the onset of the heat shock response in the California mussel (Mytilus californianus): Implications for antioxidative stress responses.

Sirtuins are a class of NAD+-dependent deacylases, with known regulatory roles in energy metabolism and cellular stress responses in vertebrates. Previous work using marine mussels have suggested a similar role in invertebrates, providing a potential mechanism linking food availability and thermal sensitivity in Mytilids. Sirtuin inhibitors affect mussels' recovery from environmental stressors, including acute heat shock and well-fed mussels exposed to sirtuin inhibitors and/or acute heat shock respond differently than poorly fed mussels, at the protein and whole-organism levels. While this implies a relationship between sirtuins, food availability, and temperature, the direct effects of sirtuin inhibitors (nicotinamide and suramin) on sirtuin activity or their putative effectors have not been explicitly tested. In this study, adult Mytilus californianus were acclimated to a low or high food availability and exposed to one of the following treatments: control, acute heat shock, sirtuin inhibitors, or acute heat shock and sirtuin inhibitors. Mussels increased sirtuin activity during early recovery (5h) from sirtuin inhibition and acute heat shock, but only if acclimated to a high food availability. Redox balance was also impacted in mussels acclimated to high food availability and exposed to sirtuin inhibitors, signifying interactions between ration, acute heat shock, and sirtuin inhibitors. Additionally, we found a correlation between sirtuin and superoxide dismutase activities, suggesting a potential regulatory role of oxidative stress by sirtuins. Following prolonged recovery (17h), we found increased sirtuin activity in mussels acclimated to low food availability, indicating that endogenous sirtuin activity may be related to food availability in mussels.

Metadichol® induced expression of Sirtuin family 1-7 in somatic and cancer cells

The Sirtuins 1-7 family and Klotho (KL), Forkhead box protein O1 (FOXO1), telomerase reverse transcriptase (TERT), tumor suppressor p53 (TP53) and growth differentiation factor 11 (GDF11) regulate aging, metabolism, and DNA repair and are involved in age-related diseases such as cancer, cardiovascular disease, and diabetes. Seven sirtuin genes in humans encode seven sirtuin enzymes (SIRT1–7), each of which has unique functions and subcellular locations. Sirtuins are nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases that play a significant role in physiological processes such as energy metabolism, stress responses, DNA repair, and gene expression and are potential targets for age-related diseases such as type 2 diabetes, inflammatory diseases, and neurodegenerative disorders. They also play a role in cancer by regulating critical cellular processes such as DNA repair and energy metabolism. Other genes, such as Klotho (KL), Forkhead box protein O1 (FOXO1), telomerase reverse transcriptase (TERT), tumor suppressor p53 (TP53) and growth differentiation factor 11 (GDF11), also regulate aging, metabolism, and DNA repair and are involved in age-related diseases such as cancer, cardiovascular disease, and diabetes. In addition, these proteins are closely related to sirtuins. A single molecule that can activate these five genes and sirtuin genes is challenging because each isoform has a unique structure, substrate, and regulatory mechanism. Most known sirtuin activators are specific for Sirtuin 1, the most studied isoform of the sirtuin family. This study was initiated based on previous work in which we showed that metadichol can express all nuclear receptors if it is possible to express all seven sirtuin families 1-7 using metadichol as a small molecule inducer. Herein, we report that at concentrations ranging from 1 pg/mL to 100 ng/mL, Metadichol®, a nanoemulsion of long-chain alcohols, induced the expression of the human Sirtuin 1-7 gene in dermal fibroblasts and a variety of cancer cells in a concentration-dependent manner and that KL, GDF11, telomerase, Foxo1 and P53 could have significant beneficial effects on mitigating age-related diseases. The results were quantified by using qRT‒PCR, and proteins were characterized using western blot techniques. The experimental procedure used is unique in that it did not involve the use of viruses or other gene insertion technique.

Mitochondrial impairment, decreased sirtuin activity and protein acetylation in dorsal root ganglia in Friedreich Ataxia models

Friedreich ataxia (FA) is a rare, recessive neuro-cardiodegenerative disease caused by deficiency of the mitochondrial protein frataxin. Mitochondrial dysfunction, a reduction in the activity of iron-sulfur enzymes, iron accumulation, and increased oxidative stress have been described. Dorsal root ganglion (DRG) sensory neurons are among the cellular types most affected in the early stages of this disease. However, its effect on mitochondrial function remains to be elucidated. In the present study, we found that in primary cultures of DRG neurons as well as in DRGs from the FXNI151F mouse model, frataxin deficiency resulted in lower activity and levels of the electron transport complexes, mainly complexes I and II. In addition, altered mitochondrial morphology, indicative of degeneration was observed in DRGs from FXNI151F mice. Moreover, the NAD+/NADH ratio was reduced and sirtuin activity was impaired. We identified alpha tubulin as the major acetylated protein from DRG homogenates whose levels were increased in FXNI151F mice compared to WT mice. In the mitochondria, superoxide dismutase (SOD2), a SirT3 substrate, displayed increased acetylation in frataxin-deficient DRG neurons. Since SOD2 acetylation inactivates the enzyme, and higher levels of mitochondrial superoxide anion were detected, oxidative stress markers were analyzed. Elevated levels of hydroxynonenal bound to proteins and mitochondrial Fe2+ accumulation was detected when frataxin decreased. Honokiol, a SirT3 activator, restores mitochondrial respiration, decreases SOD2 acetylation and reduces mitochondrial superoxide levels. Altogether, these results provide data at the molecular level of the consequences of electron transport chain dysfunction, which starts negative feedback, contributing to neuron lethality. This is especially important in sensory neurons which have greater susceptibility to frataxin deficiency compared to other tissues.

LONG-TERM NMN TREATMENT INCREASES LIFESPAN AND HEALTHSPAN IN MICE IN A SEX DEPENDENT MANNER

Abstract Levels of nicotinamide adenine dinucleotide (NAD+) decline by up to 50% in aging. NAD+ is an essential co-factor for many metabolic processes, including the deacetylase activity of sirtuins, and previous studies have demonstrated that supplementing NAD+ levels has a range of health benefits in both mice and humans. Here we investigate the effect of long-term (from 13 months of age) administration of the NAD+ precursor nicotinamide mononucleotide (NMN) on frailty and lifespan in male and female mice. NMN treatment delayed the onset of frailty in both sexes, improved metabolic health in male mice, and increased median lifespan by 8.5% in female mice. Exploration of the potential mechanisms of this protection showed that NMN treatment prevented age-related gene expression changes in skeletal muscle and led to a large increase in levels of Anaerotruncus colihominis, a microbe associated with reduced inflammation, in the gut. A thorough characterization of NMN metabolism across age, sex and tissues shows context-specific sex differences in metabolic pathways, including greater Preiss-Handler pathway metabolism in females than males, which may contribute to observed sex differences in health and lifespan. Overall, this data provides preclinical evidence that chronic NMN treatment increases lifespan and improves frailty and metabolic health in aging, and highlights the importance of using both sexes for interventional lifespan studies.

A Sirtuin-Dependent T7 RNA Polymerase Variant.

Transcriptional regulation is of great significance for cells to maintain homeostasis and, meanwhile, represents an innovative but less explored means to control biological processes in synthetic biology and bioengineering. Herein we devised a T7 RNA polymerase (T7RNAP) variant through replacing an essential lysine located in the catalytic core (K631) with Nε-acetyl-l-lysine (AcK) via genetic code expansion. This T7RNAP variant requires the deacetylase activity of NAD-dependent sirtuins to recover its enzymatic activities and thereby sustains sirtuin-dependent transcription of the gene of interest in live cells including bacteria and mammalian cells as well as in in vitro systems. This T7RNAP variant could link gene transcription to sirtuin expression and NAD availability, thus holding promise to support some relevant research.

Fucoxanthin Abrogates Ionizing Radiation-Induced Inflammatory Responses by Modulating Sirtuin 1 in Macrophages.

Ionizing radiation (IR) triggers an overproduction of reactive oxygen species (ROS), disrupting the normal function of both immune and metabolic systems, leading to inflammation and metabolic disturbances. To address the pressing requirement for protection against IR, fucoxanthin (FX), a naturally occurring compound extracted from algae, was utilized as an efficient radioprotective agent in macrophages. In this study, we cultured murine RAW 264.7 macrophages and treated them with FX, along with agents influencing the activity of sirtuin 1 (SIRT1) and estrogen receptor α (ERα), to investigate their impact on IR-induced cellular responses. FX significantly attenuated IR-induced upregulation of pro-inflammatory genes (Il1b, Tnf, and Ccl2) and inhibited macrophage polarization toward the pro-inflammatory M1 phenotype. Additionally, FX regulated IR-induced metabolic genes mediating glycolysis and mitochondrial biogenesis. The ability of FX to mitigate IR-induced inflammation and glycolysis was ascribed to the expression and activity of SIRT1 and ERα in macrophages. This study not only uncovers the underlying mechanisms of FX's radioprotective properties but also highlights its potential as a protective agent against the detrimental effects of IR, thus offering new opportunities for enhancing radiation protection in the future.

Glycogen storage disease type Ib: modern understanding of the pathogenesis of neutropenia and prospects for its treatment with empagliflozin

Glycogen storage disease type Ib (GSD Ib) — is a disease from the group of hereditary metabolic diseases caused by insufficiency of the glucose-6-phosphate transporter (G6PT, SLC37A4), which leads to a violation of both glycogenolysis and gluconeogenesis and, as a consequence, to excessive accumulation of glycogen and fat in the liver, kidneys and intestinal mucosa. The main clinical manifestations and laboratory data include growth retardation, hepatomegaly, hypoglycemia, lactic acidosis, hyperuricemia and hyperlipidemia. Complications of this disease are hepatocellular adenoma with a possible risk of malignancy, nephropathy and osteoporosis. A specific sign of GSD Ib is neutropenia with impaired neutrophil function, which creates prerequisites for recurrent infections and the development of inflammatory bowel disease. Until the present, enzyme replacement therapy of GSD Ib has not been developed, therefore, the main methods of treatment are a specialized diet with the addition of raw corn starch (for relief of hypoglycemia) and the use of granulocyte colony stimulating factor (for relief of neutropenia). However, the recent establishment of the role of 1,5-anhydroglucitol in the pathogenesis of neutrophil dysfunction in GSD Ib has led to a reprofiling of indications for the use of empagliflozin, a type 2 renal sodium—glucose cotransporter inhibitor (SGLT2). In the modern literature, it is reported about a minor, but very successful experience of its use in patients with GSD Ib (outside the framework of official indications for use) and a beneficial effect on neutrophil dysfunction and its clinical consequences. Oddly enough, this hypoglycemic drug improved not only metabolic, but also glycemic control in patients with GSD Ib, despite the fact that the pathology is based on chronic hypoglycemia. More and more evidence points to the role of empagliflozin in the regulation of cellular homeostasis (for example, fatty acid metabolism, glucose, cholesterol, apoptosis and cell proliferation, in particular in the liver) by influencing the activity of sirtuin 1 (SIRT1), AMP-activated protein kinase (AMPK) and signal molecules such as -serine/threonine protein kinase (Akt) and a mechanical target of rapamycin (mTOR), which leads to an improvement in the structure and function of mitochondria, stimulation of autophagy, reducing oxidative stress and suppressing inflammation. Modulation of these pathways shifts oxidative metabolism from carbohydrates to lipids and leads to a key decrease in insulin levels, resistance to it, glucose and lipotoxicity. This review presents current data on the pathogenesis of neutropenia and the possibility of using empagliflozin for its relief in patients with GSD Ib.

Cardioprotective Action of a Novel Synthetic 19,20-EDP Analog Is Sirt Dependent.

Mounting evidence suggests that cytochrome P450 epoxygenase-derived metabolites of docosahexaenoic acid, called epoxydocosapentaenoic acids (EDPs), limit mitochondrial damage after cardiac injury. In particular, the 19,20-EDP regioisomer has demonstrated potent cardioprotective action. Thus, we investigated our novel synthetic 19,20-EDP analog SA-22 for protection against cardiac ischemia-reperfusion (IR) injury. Isolated C57BL/6J mouse hearts were perfused through Langendorff apparatus for 20 minutes to obtain baseline function, followed by 30 minutes of global ischemia. Hearts were then treated with vehicle, 19,20-EDP, SA-22, or SA-22 with the pan-sirtuin inhibitor nicotinamide or the SIRT3-selective inhibitor 3-(1H-1,2,3-triazol-4-yl) pyridine (3-TYP) at the start of 40 minutes reperfusion (N = 5-8). We assessed IR injury-induced changes in recovery of myocardial function, using left ventricular developed pressure and systolic and diastolic pressure change. Tissues were assessed for electron transport chain function, SIRT1 and SIRT3, optic atrophy type 1, and caspase-1. We also used H9c2 cells in an in vitro model of hypoxia/reoxygenation injury (N = 3-6). Hearts perfused with SA-22 had significantly improved postischemic left ventricular developed pressure, systolic and diastolic recovery (64% of baseline), compared with vehicle control (15% of baseline). In addition, treatment with SA-22 led to better catalytic function observed in electron transport chain and SIRT enzymes. The protective action of SA-22 resulted in reduced activation of pyroptosis in both hearts and cells after injury. Interestingly, although nicotinamide cotreatment worsened functional outcomes, cell survival, and attenuated sirtuin activity, it failed to completely attenuate SA-22-induced protection against pyroptosis, possibly indicating EDPs exert cytoprotection through pleiotropic mechanisms. In short, these data demonstrate the potential of our novel synthetic 19,20-EDP analog, SA-22, against IR/hypoxia-reoxygenation injury and justify further development of therapeutic agents based on 19,20-EDP.

Zymograph profiling reveals a divergent evolution of sirtuin that may originate from class III enzymes

Sirtuins are a group of NAD+-dependent deacylases that conserved in three domains of life and comprehensively involved in the regulation of gene transcription, chromosome segregation, RNA splicing, apoptosis, and aging. Previous studies in mammalian cells have revealed that sirtuins not only exist as multiple copies, but also show distinct deacylase activities in addition to deacetylation. However, the understanding of sirtuin zymographs in other organisms with respect to molecular evolution remains at an early stage. Here, we systematically analyze the sirtuin activities in representative species from archaea, bacteria, and eukaryotes, using both the HPLC assay and a 7-amino-4-methylcoumarin-based fluorogenic method. Global profiling suggests that the deacylase activities of sirtuins could be divided into three categories and reveals undifferentiated zymographs of class III sirtuins, especially for those from bacteria and archaea. Nevertheless, initial differentiation of enzymatic activity was also observed for the class III sirtuins at both paralog and ortholog levels. Further phylogenetic analyses support a divergent evolution of sirtuin that may originate from class III sirtuins. Together, this work demonstrates a comprehensive panorama of sirtuin zymographs and provides new insights into the cellular specific regulation and molecular evolution of sirtuins.

A systematic review and meta-analysis of the SIRT1 response to exercise

Sirtuin 1 (SIRT1) is a key physiological regulator of metabolism and a target of therapeutic interventions for cardiometabolic and ageing-related disorders. Determining the factors and possible mechanisms of acute and adaptive SIRT1 response to exercise is essential for optimising exercise interventions aligned to the prevention and onset of disease. Exercise-induced SIRT1 upregulation has been reported in animals, but, to date, data in humans have been inconsistent. This exploratory systematic review and meta-analysis aims to assess various exercise interventions measuring SIRT1 in healthy participants. A total of 34 studies were included in the meta-analysis (13 single bout exercise, 21 training interventions). Studies were grouped according to tissue sample type (blood, muscle), biomarkers (gene expression, protein content, enzyme level, enzyme activity), and exercise protocols. A single bout of high-intensity or fasted exercise per se increases skeletal muscle SIRT1 gene expression as measured by qPCR or RT-PCR, while repeated resistance training alone increases blood SIRT1 levels measured by ELISA. A limited number of studies also show a propensity for an increase in muscle SIRT1 activity as measured by fluorometric or sirtuin activity assay. In conclusion, exercise acutely upregulates muscle SIRT1 gene expression and chronically increases SIRT1 blood enzyme levels.

Succinylation modification: a potential therapeutic target in stroke.

Stroke is a leading cause of mortality and disability worldwide. Ischemic cell death triggered by the compromised supply of blood oxygen and glucose is one of the major pathophysiology of stroke-induced brain injury. Impaired mitochondrial energy metabolism is observed minutes after stroke and is closely associated with the progression of neuropathology. Recently, a new type of post-translational modification, known as lysine succinylation, has been recognized to play a significant role in mitochondrial energy metabolism after ischemia. However, the role of succinylation modification in cell metabolism after stroke and its regulation are not well understood. We aimed to review the effects of succinylation on energy metabolism, reactive oxygen species generation, and neuroinflammation, as well as Sirtuin 5 mediated desuccinylation after stroke. We also highlight the potential of targeting succinylation/desuccinylation as a promising strategy for the treatment of stroke. The succinylation level is dynamically regulated by the nonenzymatic or enzymatic transfer of a succinyl group to a protein on lysine residues and the removal of succinyl catalyzed by desuccinylases. Mounting evidence has suggested that succinylation can regulate the metabolic pathway through modulating the activity or stability of metabolic enzymes. Sirtuins, especially Sirtuin 5, are characterized for their desuccinylation activity and have been recognized as a critical regulator of metabolism through desuccinylating numerous metabolic enzymes. Imbalance between succinylation and desuccinylation has been implicated in the pathophysiology of stroke. Pharmacological agents that enhance the activity of Sirtuin 5 have been employed to promote desuccinylation and improve mitochondrial metabolism, and neuroprotective effects of these agents have been observed in experimental stroke studies. However, their therapeutic efficacy in stroke patients should be validated.

Nicotinamide Adenine Dinucleotide (NAD+)-Dependent Signaling in Neurological Disorders.

Significance: Nicotinamide adenine dinucleotide (NAD+) participates in redox reactions and NAD+-dependent signaling processes, which couples the enzymatic degradation of NAD+ to posttranslational modifications of proteins or the production of second messengers. Cellular NAD+ levels are dynamically controlled by synthesis and degradation, and dysregulation of this balance has been associated with acute and chronic neuronal dysfunction. Recent Advances: A decline in NAD+ has been observed during normal aging and since aging is the primary risk factor for many neurological disorders, NAD+ metabolism has become a promising therapeutic target and prolific research field in recent years. Critical Issues: In many neurological disorders, either as a primary feature or as consequence of the pathological process, neuronal damage is accompanied by dysregulated mitochondrial homeostasis, oxidative stress, or metabolic reprogramming. Modulating NAD+ availability appears to have a protective effect against such changes observed in acute neuronal damage and age-related neurological disorders. Such beneficial effects could be, at least in part, due to the activation of NAD+-dependent signaling processes. Future Directions: While in many instances the protective effect has been ascribed to the activation of sirtuins, approaches that directly test the role of sirtuins or that target the NAD+ pool in a cell-type-specific manner may be able to provide further mechanistic insight. Likewise, these approaches may afford greater efficacy to strategies aimed at harnessing the therapeutic potential of NAD+-dependent signaling in neurological disorders. Antioxid. Redox Signal. 39, 1150-1166.

Natural Phytochemicals as SIRT Activators-Focus on Potential Biochemical Mechanisms.

Sirtuins are a family of proteins with enzymatic activity. There are seven mammalian sirtuins (SIRT1-SIRT7) that are found in different cellular compartments. They are a part of crucial cellular pathways and are regulated by many factors, such as chemicals, environmental stress, and phytochemicals. Several in vitro and in vivo studies have presented their involvement in anti-inflammatory, antioxidant, and antiapoptotic processes. Recent findings imply that phytochemicals such as resveratrol, curcumin, quercetin, fisetin, berberine, and kaempferol may regulate the activity of sirtuins. Resveratrol mainly activates SIRT1 and indirectly activates AMPK. Curcumin influences mainly SIRT1 and SIRT3, but its activity is broad, and many pathways in different cells are affected. Quercetin mainly modulates SIRT1, which triggers antioxidant and antiapoptotic responses. Fisetin, through SIRT1 regulation, modifies lipid metabolism and anti-inflammatory processes. Berberine has a wide spectrum of effects and a significant impact on SIRT1 signaling pathways. Finally, kaempferol triggers anti-inflammatory and antioxidant effects through SIRT1 induction. This review aims to summarize recent findings on the properties of phytochemicals in the modulation of sirtuin activity, with a particular focus on biochemical aspects.

A secreted sirtuin from Campylobacter jejuni contributes to neutrophil activation and intestinal inflammation during infection.

Histone modifications control numerous processes in eukaryotes, including inflammation. Some bacterial pathogens alter the activity or expression of host-derived factors, including sirtuins, to modify histones and induce responses that promote infection. In this study, we identified a deacetylase encoded by Campylobacter jejuni which has sirtuin activities and contributes to activation of human neutrophils by the pathogen. This sirtuin is secreted from the bacterium into neutrophils, where it associates with and deacetylates host histones to promote neutrophil activation and extracellular trap production. Using the murine model of campylobacteriosis, we found that a mutant of this bacterial sirtuin efficiently colonized the gastrointestinal tract but was unable to induce cytokine production, gastrointestinal inflammation, and tissue pathology. In conclusion, these results suggest that secreted bacterial sirtuins represent a previously unreported class of bacterial effector and that bacterial-mediated modification of host histones is responsible for the inflammation and pathology that occurs during campylobacteriosis.

Effects of follicle-stimulating hormone, insulin-like growth factor 1, fibroblast growth factor 2, and fibroblast growth factor 9 on sirtuins expression and histone deacetylase activity in bovine granulosa cells

Granulosa cells (GC) are critical regulators of fertility. During the process of ovarian folliculogenesis, these cells undergo profound changes while producing steroid hormones that are important to control follicular growth, oocyte maturation, and ovulation. Sirtuins are enzymes that regulate several biological processes and have been associated with control of GC function. However, how sirtuins are regulated in GC during ovarian folliculogenesis remains to be unveiled. The present study was designed to investigate effects of hormones that control GC proliferation, differentiation, and steroidogenesis on expression of the seven members of the mammalian sirtuins family (SIRT1-7) and on histone deacetylase activity of nuclear sirtuins (SIRT1, 6, and 7) in GC. Bovine granulosa cells were isolated from small antral follicles (1–5 mm) and were treated with or without follicle-stimulating hormone (FSH), insulin-like growth factor 1 (IGF-1), and fibroblast growth factors 2 (FGF2) and 9 (FGF9). Following treatments, cell proliferation was determined via a cell analyzer, estradiol synthesis and histone deacetylase activity were determined via ELISA, and sirtuins mRNA expression was determined via qPCR. Treatments with FSH and IGF-1 stimulated cell proliferation while addition of FGF2 or FGF9 suppressed estradiol production stimulated by FSH plus IGF-1. In terms of treatments that regulated sirtuins expression in GC, fibroblast growth factors were the most impactful: FGF2 alone increased SIRT1 mRNA expression in comparison to several treatments and increased mRNA abundance of SIRT2 and SIRT7 when added to the combination of FSH and IGF-1; the addition of FGF9 to the combination of FSH and IGF-1 increased mRNA expression of SIRT2, SIRT3, SIRT4, SIRT6, and SIRT7 and increased mRNA expression of SIRT5 in comparison to the negative control group that received no treatment. Also, FGF2 alone increased histone deacetylase activity of sirtuins in comparison to all treatments that contained FSH and/or IGF-1. Furthermore, several correlations were observed between treatments and sirtuins expression and activity, between estradiol or GC numbers and sirtuins expression, and between expression of sirtuins. As FGF2 and FGF9 are considered anti-differentiation factors of GC that stimulate GC proliferation while suppressing estradiol production in combination with FSH and IGF-1, data of this study suggest that sirtuins are associated with control of differentiation of bovine GC.

Insight from sirtuins interactome: topological prominence and multifaceted roles of SIRT1 in modulating immunity, aging and cancer.

The mammalian sirtuin family, consisting of SIRT1-SIRT7, plays a vital role in various biological processes, including cancer, diabetes, neurodegeneration, cardiovascular disease, cellular metabolism, and cellular homeostasis maintenance. Due to their involvement in these biological processes, modulating sirtuin activity seems promising to impact immune- and aging-related diseases, as well as cancer pathways. However, more understanding is required regarding the safety and efficacy of sirtuin-targeted therapies due to the complex regulatory mechanisms that govern their activity, particularly in the context of multiple targets. In this study, the interaction landscape of the sirtuin family was analyzed using a systems biology approach. A sirtuin protein-protein interaction network was built using the Cytoscape platform and analyzed using the NetworkAnalyzer and stringApp plugins. The result revealed the sirtuin family's association with numerous proteins that play diverse roles, suggesting a complex interplay between sirtuins and other proteins. Based on network topological and functional analysis, SIRT1 was identified as the most prominent among sirtuin family members, demonstrating that 25 of its protein partners are involved in cancer, 22 in innate immune response, and 29 in aging, with some being linked to a combination of two or more pathways. This study lays the foundation for the development of novel therapies that can target sirtuins with precision and efficacy. By illustrating the various interactions among the proteins in the sirtuin family, we have revealed the multifaceted roles of SIRT1 and provided a framework for their possible roles to be precisely understood, manipulated, and translated into therapeutics in the future.

Nicotinamide riboside activates SIRT5 deacetylation.

Human sirtuins play important roles in various cellular events including DNA repair, gene silencing, mitochondrial biogenesis, insulin secretion and apoptosis. They regulate a wide array of protein and enzyme targets through their NAD+ -dependent deacetylase activities. Sirtuins are also thought to mediate the beneficial effects of low-calorie intake to extend longevity in diverse organisms from yeast to mammals. Small molecules mimicking calorie restriction to stimulate sirtuin activity are attractive therapeutics against age-related disorders such as cardiovascular diseases, diabetes and neurodegeneration. Little is known about one of the mitochondrial sirtuins, SIRT5. SIRT5 has emerged as a critical player in maintaining cardiac health and neuronal viability upon stress and functions as a tumour suppressor in a context-specific manner. Much has been debated about whether SIRT5 has evolved away from being a deacetylase because of its weak catalytic activity, especially in the in vitro testing. We have, for the first time, identified a SIRT5-selective allosteric activator, nicotinamide riboside (NR). It can increase SIRT5 catalytic efficiency with different synthetic peptide substrates. The mechanism of action was further explored using a combination of molecular biology and biochemical strategies. Based on the existing structural biology information, the NR binding site was also mapped out. These activators are powerful chemical probes for the elucidation of cellular regulations and biological functions of SIRT5. The knowledge gained in this study can be used to guide the design and synthesis of more potent, isotype-selective SIRT5 activators and to develop them into therapeutics for metabolic disorders and age-related diseases.

Abstract A014: NFI-family transcriptional factors direct AR cistrome redistribution during prostate cancer tumorigenesis

Abstract Previous studies found AR cistrome reprogramming during transition from normal prostate to PCa, and progression to CRPC. AR binding sites (bs) in PCa were reported to be enriched for FOXA1 and HOXB13, in comparison to normal prostate where these are not enriched. However, mechanisms that may drive FOXA1 and HOXB13 to these sites and initiate this neoplastic transformation remain unclear. To address this, we first asked if there are other transcription factors (TFs) involved in tumor evolution. A motif enrichment analysis using patient data set (GSE130408) showed significant enrichment of NFI and NFI half motifs at AR bs in localized hormone sensitive PCa in comparison to normal prostate (0.07 vs 0.04, p=0.0001; and 0.27 vs 0.21, p=0.0044, respectively). Notably, NFI TFs were shown previously to be associated with AR bs in PCa cells, and to modulate AR-target gene expression and changes in chromatin accessibility. This suggested that NFI TFs may contribute to AR cistrome redistribution that drives PCa development. Next, we generated a CRPC cell model resistant to enzalutamide (ENZ), and found that AR activity in these cells was driven by the ARv7 splice variant. Notably, ATAC-seq identified in these cells a subset of sites with greatly increased chromatin accessibility, and ChIP-seq showed that these ATAC-up sites were associated with ARv7 binding and increased H3K27acetylation (H3K27ac, the mark of active enhancers). Significantly, these sites also were enriched for NFI and NFI half motifs (0.04, p<0.0001 and 0.1, p<0.0001, respectively). Notably, while AR is known as a transcriptional activator, it also has repressive functions. To study AR-direct repression, we examined the redistribution of H3K27ac mark in response to AR-inhibition (ENZ) or stimulation (DHT). We identified subsets of AR-bound regions with increased H3K27ac after ENZ that corresponded to regions with decreased H3K27ac after DHT. These regions were highly enriched for NFI and NFI-half motifs (0.04, p<0.0001 and 0.14, p<0.0001, respectively). As expected, these regions also were associated with DHT-repressed genes including UGT2B15, physiologically involved in steroid hormones metabolism. Notably, depletion of NFI-B and X (the most expressed NFI-family members in PCa) resulted in increased H3K27ac levels at UGT2B15, and impaired the suppressive effect of DHT on UGT2B15 expression. RNA-seq after NFIB and X knockdown then showed 212 up- and 119 downregulated genes, indicating NFI is a modulator of both AR-activated and repressed genes. Ingenuity Pathway Analysis demonstrated contribution of NFIs to androgen signaling and maintaining the activity of Sirtuin (SIRT) pathways. SIRTs possess deacetylase activity, including deacetylation of histones, and inhibition of SIRT1 resulted in dramatically increased UGT2B15 expression. Collectively, these data support a role for NFI TFs in directing the AR cistrome during PCa tumorigenesis, and in modulating its transcriptional activation versus repressive functions, with the latter being mediated by recruitment of SIRT1. Citation Format: Larysa Poluben, Joshua Russo, Olga Voznesensky, Mannan Nouri, Anastasia Stavridi, Xintao Qiu, Matthew Freedman, Henry W. Long, Steven P. Balk. NFI-family transcriptional factors direct AR cistrome redistribution during prostate cancer tumorigenesis [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A014.

Hepatoprotective Effect of Myricetin following Lipopolysaccharide/DGalactosamine: Involvement of Autophagy and Sirtuin 1.

Acute liver injury (ALI) is a critical and fatal disorder associated with excessive oxidative stress and inflammation, ultimately leading to the death of hepatocytes. Myricetin is a bioflavonoid in some berries, including blueberries and strawberries, with anti-inflammatory, antioxidant and anti-apoptotic properties. In the current research, the hepatoprotective potential of myricetin was studied in the LPS/D-GalN model of ALI in C57BL/6 mice. For inducing liver injury, D-GalN (400 mg/kg) and LPS (50 µg/kg) were injected via intraperitoneal route and myricetin was orally administered (25 or 100 mg/kg/day) for two days before inducing injury. Functional indices of liver dysfunction along with hepatic apoptotic, autophagic, oxidative stress and inflammatory factors were measured. Myricetin (100 mg/kg) reduced the fatality rate of animals and pathological liver changes and suitably lowered serum levels of total bilirubin, 8-OH-dG, ALT, AST and ALP in addition to decreasing apoptotic, oxidative and inflammatory factors, NOX, NLRP3, caspase 3, MPO and enhancing some antioxidants. Besides, myricetin improved the hepatic level and activity of sirtuin 1 and reversed inappropriate alterations of autophagic parameters, including LC3 II, Beclin 1, and P62. The beneficial effects of myricetin were attenuated after co-treatment with the autophagy inhibitor 3- methyladenine. This study indicates the hepatoprotective potential of myricetin that can be ascribed to its down-regulation of oxidative, apoptotic, and inflammatory factors and upregulation of antioxidants besides its partial regulation of sirtuin 1 and autophagic pathway.

Influence of Polyphenols on Adipose Tissue: Sirtuins as Pivotal Players in the Browning Process.

Adipose tissue (AT) can be classified into two different types: (i) white adipose tissue (WAT), which represents the largest amount of total AT, and has the main function of storing fatty acids for energy needs and (ii) brown adipose tissue (BAT), rich in mitochondria and specialized in thermogenesis. Many exogenous stimuli, e.g., cold, exercise or pharmacological/nutraceutical tools, promote the phenotypic change of WAT to a beige phenotype (BeAT), with intermediate characteristics between BAT and WAT; this process is called "browning". The modulation of AT differentiation towards WAT or BAT, and the phenotypic switch to BeAT, seem to be crucial steps to limit weight gain. Polyphenols are emerging as compounds able to induce browning and thermogenesis processes, potentially via activation of sirtuins. SIRT1 (the most investigated sirtuin) activates a factor involved in mitochondrial biogenesis, peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), which, through peroxisome proliferator-activated receptor γ (PPAR-γ) modulation, induces typical genes of BAT and inhibits genes of WAT during the transdifferentiation process in white adipocytes. This review article aims to summarize the current evidence, from pre-clinical studies to clinical trials, on the ability of polyphenols to promote the browning process, with a specific focus on the potential role of sirtuins in the pharmacological/nutraceutical effects of natural compounds.