SIRT2 regulates oxidative stress-induced cell death through deacetylation of c-Jun NH2-terminal kinase

Trilobatin suppresses aging-induced cognitive impairment by targeting SIRT2: Involvement of remodeling gut microbiota to mediate the brain-gut axis

BACKGROUND

Aging is associated with learning and memory disorder, affecting multiple brain areas, especially the hippocampus. Previous studies have demonstrated trilobatin (TLB), as a natural food additive, can extend the life of Caenorhabditis elegans and exhibit neuroprotection in Alzheimer's disease mice. However, the possible significance of TLB in anti-aging remains elusive.

PURPOSE

This study aimed to delve into the physiological mechanism by which TLB ameliorated aging-induced cognitive impairment in senescence-accelerated mouse prone 8 (SAMP8) mice.

METHODS

6-month-old SAMP8 mice were administrated with TLB (5, 10, 20 mg/kg/day, i.g.) for 3 months. The therapeutic effect of TLB on aging-induced cognitive impairment was assessed in mice using behavioral tests and aging score. The gut microbiota composition in fecal samples was analyzed by metagenomic analysis. The protective effects of TLB on blood-brain barrier (BBB) and intestinal barrier were detected by transmission electron microscope, H&E staining and western blot (WB) assay. The inhibitive effects of TLB on inflammation in brain and intestine were assessed using immunofluorescence, WB and ELISA assay. Molecular docking and surface plasma resonance (SPR) assay were utilized to investigate interaction between TLB and sirtuin 2 (SIRT2).

RESULTS

Herein, the findings exhibited TLB mitigated aging-induced cognitive impairment, neuron injury and neuroinflammation in hippocampus of aged SAMP8 mice. Moreover, TLB treatment repaired imbalance of gut microbiota in aged SAMP8 mice. Furthermore, TLB alleviated the damage to BBB and intestinal barrier, concomitant with reducing the expression of SIRT2, phosphorylated levels of c-Jun NH2 terminal kinases (JNK) and c-Jun, and expression of MMP9 protein in aged SAMP8 mice. Molecular docking and SPR unveiled TLB combined with SIRT2 and down-regulated SIRT2 protein expression. Mechanistically, the potential mechanism of SIRT2 in TLB that exerted anti-aging effect was validated in vitro. As expected, SIRT2 deficiency attenuated phosphorylated level of JNK in HT22 cells treated with d-galactose.

CONCLUSION

These findings reveal, for the first time, SIRT2-mediated brain-gut barriers contribute to aging and aging-related diseases, and TLB can rescue aging-induced cognitive impairment by targeting SIRT2 and restoring gut microbiota disturbance to mediate the brain-gut axis. Overall, this work extends the potential application of TLB as a natural food additive in aging-related diseases.

Sirtuin 2 regulates neutrophil functions through NAD+ synthesis pathway in virus infection

Neutrophils play an important role in antiviral immunity, but the underlying mechanisms remain unclear. Here, we found that SIRT2 deficiency inhibited the infiltration of neutrophils, as well as the secretion of inflammatory cytokines and the formation of neutrophil extracellular traps (NETs), ameliorating disease symptoms during acute respiratory virus infection. Mechanistically, SIRT2 deficiency upregulates quinolinic acid (QA)-producing enzyme 3-hydroxyanthranilate oxygenase (3-HAO) and leads to expression of quinolinate phosphoribosyltransferase (QPRT), which promotes the synthesis of QA for NAD+ and limits viral infection when de novo NAD+ synthesis is blocked. Tryptophan-2,3-oxygenase expressed in epithelial cells metabolizes tryptophan to produce kynurenine and 3-hydroxyaminobenzoic acid, which is a source of intracellular QA in neutrophils. Thus, our findings reveal a previously unrecognized QPRT-mediated switch in NAD+ metabolism by exploiting neutrophil-derived QA as an alternative source of replenishing intracellular NAD+ pools induced by SIRT2 to regulate neutrophil functions during virus infection, with implications for future immunotherapy approaches.

Multiple Functional Protein-Protein Interaction Interfaces Allosterically Regulate ATP-Binding in Cyclin-Dependent Kinase-1

The ATP-dependent phosphorylation activity of cyclin-dependent kinase 1 (CDK1), an essential enzyme for cell cycle progression, is regulated by interactions with Cyclin-B, substrate, and Cks proteins. We have recently shown that active site acetylation in CDK1 abrogated binding to Cyclin-B which posits an intriguing long-range communication between the catalytic site and the protein-protein interaction (PPI) interface. Now, we demonstrate a general allosteric link between the CDK1 active site and all three of its PPI interfaces through atomistic molecular dynamics (MD) simulations. Specifically, we examined ATP binding free energies to CDK1 in native nonacetylated (K33wt) and acetylated (K33Ac) forms as well as the acetyl-mimic K33Q and the acetyl-null K33R mutant forms, which are accessible in vitro. In agreement with experiments, ATP binding is stronger in K33wt relative to the other three perturbed states. Free energy decomposition reveals, in addition to expected local changes, significant and selective nonlocal entropic responses to ATP binding/perturbation of K33 from theαC $$ \alpha C $$ -helix, activation loop (A-loop), andαG $$ \alpha G $$ -α $$ \alpha $$ H segments in CDK1 which interface with Cyclin-B, substrate, and Cks proteins, respectively. Statistical analysis reveals that while entropic responses of protein segments to active site perturbations are on average correlated with their dynamical changes, such correlations are lost in about 9%-48% of the dataset depending on the segment. Besides proving the bi-directional communication between the active site and the CDK1:Cyclin-B interface, our study uncovers a hitherto unknown mode of ATP binding regulation by multiple PPI interfaces in CDK1.

Advances in development of biomarkers for brain damage and ischemia

Acquired brain injury is an urgent situation that requires rapid diagnosis and treatment. Magnetic resonance imaging (MRI) and computed tomography (CT) are required for accurate diagnosis. However, these methods are costly and require substantial infrastructure and specialized staff. Circulatory biomarkers of acute brain injury may help in the management of patients with acute cerebrovascular events and prevent poor outcome and mortality. The purpose of this review is to provide an overview of the development of potential biomarkers of brain damage to increase diagnostic possibilities. For this purpose, we searched the PubMed database of studies on the diagnostic potential of brain injury biomarkers. We also accessed information from Clinicaltrials.gov to identify any clinical trials of biomarker measurements for the diagnosis of brain damage. In total, we present 41 proteins, enzymes and hormones that have been considered as biomarkers for brain injury, of which 20 have been studied in clinical trials. Several microRNAs have also emerged as potential clinical biomarkers for early diagnosis. Combining multiple biomarkers in a panel, along with other parameters, is yielding promising outcomes.

Tenovin-1, a Selective SIRT1/2 Inhibitor, Attenuates High-fat Diet-induced Hepatic Fibrosis via Inhibition of HSC Activation in ZDF Rats

Type 2 diabetes mellitus (T2DM) increases the risk of non-alcoholic fatty liver disease (NAFLD) progression to advanced stages, especially upon high-fat diet (HFD). HFD-induced hepatic fibrosis can be marked by oxidative stress, inflammation, and activation of hepatic stellate cells. Sirtuin 1/2 (SIRT1/2), NAD-dependent class III histone deacetylases, are involved in attenuation of fibrosis. In our conducted research, TGF-β1-activated LX-2 cells, free fatty acid (FFA)-treated simultaneous co-culture (SCC) cells, and HFD-induced hepatic fibrosis in Zucker diabetic fatty (ZDF) rats, a widely used animal model in the study of metabolic syndromes, were used to evaluate the protective effect of Tenovin-1, a SIRT1/2 inhibitor. ZDF rats were divided into chow diet, HFD, and HFD + Tenovin-1 groups. Tenovin-1 reduced hepatic damage, inhibited inflammatory cell infiltration, micro/ macro-vesicular steatosis and prevented collagen deposition HFD-fed rats. Tenovin-1 reduced serum biochemical parameters, triglyceride (TG) and malondialdehyde (MDA) levels but increased glutathione, catalase, and superoxide dismutase levels. Tenovin-1 mitigated proinflammatory cytokines IL-6, IL-1β, TNFα and fibrosis biomarkers in HFD rats, TGF-β1-activated LX-2 and FFA treated SCC cells. Additionally, Tenovin-1 suppressed SIRT1/2 expression and inhibited JNK-1 and STAT3 phosphorylation in HFD rats and FFA-treated SCC cells. In conclusion, Tenovin-1 attenuates hepatic fibrosis by stimulating antioxidants and inhibiting inflammatory cytokines under HFD conditions in diabetic rats.

SIRT2 promotes base excision repair by transcriptionally activating OGG1 in an ATM/ATR-dependent manner

Sirtuin 2 (SIRT2) regulates the maintenance of genome integrity by targeting pathways of DNA damage response and homologous recombination repair. However, whether and how SIRT2 promotes base excision repair (BER) remain to be determined. Here, we found that independent of its catalytic activity SIRT2 interacted with the critical glycosylase OGG1 to promote OGG1 recruitment to its own promoter upon oxidative stress, thereby enhancing OGG1 promoter activity and increasing BER efficiency. Further studies revealed that SIRT2 was phosphorylated on S46 and S53 by ATM/ATR upon oxidative stress, and SIRT2 phosphorylation enhanced the SIRT2-OGG1 interaction and mediated the stimulatory effect of SIRT2 on OGG1 promoter activity. We also characterized 37 cancer-derived SIRT2 mutants and found that 5 exhibited the loss of the stimulatory effects on OGG1 transcription. Together, our data reveal that SIRT2 acts as a tumor suppressor by promoting OGG1 transcription and increasing BER efficiency in an ATM/ATR-dependent manner.

The role of Sirtuin 2 in liver - An extensive and complex biological process

Liver disease has become one of the main causes of health issue worldwide. Sirtuin (Sirt) 2 is a nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase, and is expressed in multiple organs including liver, which plays important and complex roles by interacting with various substrates. Physiologically, Sirt2 can improve metabolic homeostasis. Pathologically, Sirt2 can alleviate inflammation, endoplasmic reticulum (ER) stress, promote liver regeneration, maintain iron homeostasis, aggravate fibrogenesis and regulate oxidative stress in liver. In liver diseases, Sirt2 can mitigate fatty liver disease (FLD) including non-alcoholic fatty liver disease (NAFLD) and alcoholic fatty liver disease (AFLD), but aggravate hepatitis B (HBV) and liver ischemia-reperfusion injury (LIRI). The role of Sirt2 in liver cancer and aging-related liver diseases, however, has not been fully elucidated. In this review, these biological processes regulated by Sirt2 in liver are summarized, which aims to update the function of Sirt2 in liver and to explore the potential role of Sirt2 as a therapeutic target for liver diseases.

Sirtuins and autophagy in lipid metabolism

Sirtuins are a family of NAD+ -dependent deacetylases that regulate some important biological processes, including lipid metabolism and autophagy, through their deacetylase function. Autophagy is a new discovery in the field of lipid metabolism, which may provide a new idea for the regulation of lipid metabolism. There are many tandem parts in the regulation process of lipid metabolism and autophagy of sirtuins protein family. This paper summarized these tandem parts and proposed the possibility of sirtuins regulating lipid autophagy, as well as the interaction and synergy between sirtuins protein family. Currently, some natural drugs have been reported to affect metabolism by regulating sirtuins, some of which regulate autophagy by targeting sirtuins.

Deacetylase sirtuin 2 negatively regulates myeloid-derived suppressor cell functions in allograft rejection

Although myeloid-derived suppressor cells (MDSCs) are critical for allograft survival, their regulatory mechanism remains unclear. Herein, our results showed that metabolism sensor sirtuin 2 (SIRT2) negatively regulates the functions of MDSCs in inducing allogeneic skin graft rejection. Genetic deletion of SIRT2 in myeloid cells (Sirt2Δmye) increased the number of CD11b+Gr1+ MDSCs in bone marrow, spleens, draining lymph nodes, and allografts, inhibited the production of proinflammatory cytokine tumor necrosis factor ɑ, enhanced the production of anti-inflammatory cytokine interleukin 10, and potentiated the suppressive activation of MDSCs in prolonging allograft skin survival. C-X-C motif chemokine receptor 2 is critical for mediating the recruitment and cytokine production of MDSCs induced by SIRT2. Mechanistically, Sirt2Δmye enhanced NAD+ levels, succinate dehydrogenase subunit A (SDHA) activities, and oxidative phosphorylation (OXPHOS) levels in MDSCs after transplantation. Pharmacologically blocking nicotinamide phosphoribosyltransferase effectively reverses the production of cytokines and suppressive activities of MDSC induced by Sirt2Δmye. Blocking OXPHOS with knockdown of SDHA or pharmacological blocking of SDHA significantly restores Sirt2Δmye-mediated stronger MDSC suppressive activity and inflammatory factor productions. Thus, our findings identify a previously unrecognized interplay between NAD+ and SDH-mediated OXPHOS metabolic pathways in regulating MDSC functions induced by the metabolic sensor SIRT2 in allogeneic transplantation.

Ginsenoside Rh2 and its octyl ester derivative inhibited invasion and metastasis of hepatocellular carcinoma via the c-Jun/COX2/PGE2 pathway

BACKGROUND

Liver cancer is a topical global health issue. The treatment of liver cancer meets significant challenges in the high recurrence rate and invasive incidence. Therefore, the treatment strategies that target epithelial-mesenchymal transition (EMT) induced by cyclooxygenase 2 (COX2)/ prostaglandin E2 (PGE2) pathway have become epidemic. Ginsenoside Rh2 has been proved to inhibit the EMT. However, the underlying mechanisms remain unclear. Moreover, the octyl ester derivative of Rh2 (Rh2-O) exhibited superior anti-proliferative and immunomodulatory effects than Rh2 in our previous researches, which indicated that Rh2-O might also exert inhibitory effects on invasion and metastasis.

PURPOSE

The aim of current study is to explore the inhibitory effects of Rh2 and Rh2-O on invasion and metastasis of hepatocellular carcinoma, and to investigate whether these effects are dependent on the c-Jun/COX2/PGE2 pathway.

STUDY DESIGN

The Huh-7 liver cancer cells and the H22 tumor-bearing mice were treated with Rh2 and Rh2-O.

METHOD

In this paper, the inhibitory effects of Rh2 and Rh2-O on invasion and metastasis were tested by wound healing, trans-well assay and tumor-bearing mice, and the involvement of c-Jun/COX2/PGE2 pathway were verified by exogenous PGE2, activation of COX2 and overexpression of c-Jun.

RESULTS

The results showed that Rh2 and Rh2-O could efficiently inhibit the invasion and metastasis in a dose-dependent manner (p < 0.05). And the Rh2-O showed stronger effects than Rh2. Moreover, the exogenous PGE2, activation of COX2 by exogenous LPS and the overexpression of c-Jun by transfection all reversed the inhibitory effects of Rh2 and Rh2-O on metastasis or EMT (p < 0.05).

CONCLUSION

Rh2 and Rh2-O could inhibit the invasion and metastasis of hepatocellular carcinoma via restraining the EMT, which was mediated by c-Jun/COX2/PGE2 pathway.

Age-Associated Changes of Sirtuin 2 Expression in CNS and the Periphery

Sirtuin 2 (SIRT2), one of the seven members of the sirtuin family, has emerged as a potential regulator of aging and age-related pathologies since several studies have demonstrated that it shows age-related changes in humans and different animal models. A detailed analysis of the relevant works published to date addressing this topic shows that the changes that occur in SIRT2 with aging seem to be opposite in the brain and in the periphery. On the one hand, aging induces an increase in SIRT2 levels in the brain, which supports the notion that its pharmacological inhibition is beneficial in different neurodegenerative diseases. However, on the other hand, in the periphery, SIRT2 levels are reduced with aging while keeping its expression is protective against age-related peripheral inflammation, insulin resistance, and cardiovascular diseases. Thus, systemic administration of any known modulator of this enzyme would have conflicting outcomes. This review summarizes the currently available information on changes in SIRT2 expression in aging and the underlying mechanisms affected, with the aim of providing evidence to determine whether its pharmacological modulation could be an effective and safe pharmacological strategy for the treatment of age-related diseases.

Lactylation of METTL16 promotes cuproptosis via m6A-modification on FDX1 mRNA in gastric cancer

Cuproptosis, caused by excessively high copper concentrations, is urgently exploited as a potential cancer therapeutic. However, the mechanisms underlying the initiation, propagation, and ultimate execution of cuproptosis in tumors remain unknown. Here, we show that copper content is significantly elevated in gastric cancer (GC), especially in malignant tumors. Screening reveals that METTL16, an atypical methyltransferase, is a critical mediator of cuproptosis through the m6A modification on FDX1 mRNA. Furthermore, copper stress promotes METTL16 lactylation at site K229 followed by cuproptosis. The process of METTL16 lactylation is inhibited by SIRT2. Elevated METTL16 lactylation significantly improves the therapeutic efficacy of the copper ionophore- elesclomol. Combining elesclomol with AGK2, a SIRT2-specific inhibitor, induce cuproptosis in gastric tumors in vitro and in vivo. These results reveal the significance of non-histone protein METTL16 lactylation on cuproptosis in tumors. Given the high copper and lactate concentrations in GC, cuproptosis induction becomes a promising therapeutic strategy for GC.

Bombesin receptor-activated protein exacerbates cisplatin-induced AKI by regulating the degradation of SIRT2

BACKGROUND

Acute kidney injury (AKI) is a public health problem with no specific therapies in the clinic and the underlying pathogenesis of AKI remains obscure. Bombesin receptor-activated protein (BRAP, C6ORF89 protein) was initially discovered as a ligand for a previously orphan G-protein-coupled receptor bombesin-like receptor-3. At present, accepted biological effects of BRAP include cell cycle progression, wound repair and the activation of histone deacetylases. However, its role in kidney disease is unknown. In this study we have investigated the role of BRAP and underlying mechanisms involved in cisplatin (CP)-induced AKI.

METHODS

Here we used Bc004004 (homologous of C6ORF89 in mice) knockout mice and HK2 cells to investigate the effect of BRAP on AKI in vitro and in vivo. We analyzed ChIP-Seq and RNA-Seq data to search for the upstream regulators of BRAP and downstream mediators of BRAP action in AKI. Immunostaining, real-time polymerase chain reaction (PCR), co-immunoprecipitation, a dual-luciferase reporter assay and ChIP-PCR assay were applied to reveal the upstream and downstream regulation mechanism of BRAP during cisplatin-induced AKI.

RESULTS

BRAP was downregulated in mice and human kidneys with AKI. Global Bc004004 deletion alleviated tubular cell apoptosis and necroptosis in CP-induced AKI mice, whereas local overexpression of BRAP in kidneys aggravated them. Pan-caspase inhibitor Z-VAD pretreatment attenuated CP-induced blood creatinine increase and kidney injury in wild-type mice but not in BRAP -/- mice. The activation of mixed lineage kinase like-domain was magnified by Z-VAD in CP-treated mice, especially in BRAP -/- mice. The cytoprotective effect of Z-VAD was more substantial than necrostatin-1 (Nec-1, an inhibitor of necroptosis) in CP-treated human kidney proximal tubular epithelial (HK2) cells. Furthermore, Nec-1 pretreatment reduced the CP-induced cell death in BRAP overexpression HK2 cells but did not work in cells with normal BRAP levels. We determined that CP treatment activated the nuclear factor-κB subunit P65 and inhibition of P65 increased the messenger RNA (mRNA) levels of BRAP in HK2 cells. The chromatin immunoprecipitation assay and dual-luciferase reporter gene assay verified P65 binding to the C6ORF89 promoter and reduced its mRNA expression upon CP treatment. Next we found that sirtuin 2 (SIRT2) was downregulated in CP-induced AKI and BRAP levels directly impacted the protein levels of SIRT2. Our findings further confirmed that BRAP regulates the SIRT2 protein levels by affecting SIRT2's interactions with E3 ubiquitin ligase HRD1 and subsequent proteasomal degradation.

CONCLUSIONS

Our results demonstrated that BRAP played an important role in tubular cell apoptosis and necroptosis during CP-induced AKI. Safe and efficient BRAP inhibitors might be effective therapeutic options for AKI.

Cold exposure-induced endoplasmic reticulum stress regulates autophagy through the SIRT2/FoxO1 signaling pathway

Cold is a factor affecting health in humans and animals. The liver, a major metabolic center, is highly susceptible to ambient air temperature. Recent studies have shown that endoplasmic reticulum (ER) stress is associated with the liver, and regulates the occurrence and development of liver injury and autophagy. However, the mechanism underlying the relationship between cold exposure and ER stress in the liver is not well understood. In this study, we investigated the effect of ER stress on liver autophagy and its mechanism under cold exposure. AML12 cells were treated with Tg to construct an ER stress model, and the level of autophagy increased. To further explore the mechanism through which ER stress regulates autophagy, we knocked down SIRT2 with shRNA in Tg-treated AML12 cells. Knockdown of SIRT2 significantly increased ER stress and autophagy, increased FoxO1 acetylation, and promoted its entry into the nucleus. To further verify the results of in vitro experiments, we exposed mice to 4°C for 3 h per day for 3 weeks to exacerbate the burden on the liver after cold exposure. Cold exposure damaged the structure and function of the liver and promoted the inflammatory response. It also activated ER stress and promoted autophagy. In addition, cold exposure inhibited the expression of SIRT2, promoted FoxO1 acetylation, and enhanced the interaction with autophagy. Our findings indicated that cold exposure induces liver damage, ER stress, and autophagy through the SIRT2/FoxO1 pathway. These findings suggest that SIRT2 may be a potential target for regulating health under cold exposure.

Multiple Roles of SIRT2 in Regulating Physiological and Pathological Signal Transduction

Sirtuin 2 (SIRT2), as a member of the sirtuin family, has representative features of evolutionarily highly conserved nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase activity. In addition, SIRT2, as the only sirtuin protein colocalized with tubulin in the cytoplasm, has its own functions and characteristics. In recent years, studies have increasingly shown that SIRT2 can participate in the regulation of gene expression and regulate signal transduction in the metabolic pathway mainly through its post-translational modification of target genes; thus, SIRT2 has become a key centre in the metabolic pathway and participates in the pathological process of metabolic disorder-related diseases. In this paper, it is discussed that SIRT2 can regulate all aspects of gene expression, including epigenetic modification, replication, transcription and translation, and post-translational modification, which enables SIRT2 to participate in energy metabolism in life activities, and it is clarified that SIRT2 is involved in metabolic process-specific signal transduction mechanisms. Therefore, SIRT2 can be involved in metabolic disorder-related inflammation and oxidative stress, thereby triggering the occurrence of metabolic disorder-related diseases, such as neurodegenerative diseases, tumours, diabetes, and cardiovascular diseases. Currently, although the role of SIRT2 in some diseases is still controversial, given the multiple roles of SIRT2 in regulating physiological and pathological signal transduction, SIRT2 has become a key target for disease treatment. It is believed that with increasing research, the clinical application of SIRT2 will be promoted.

Sirtuins and cognition: implications for learning and memory in neurological disorders

Sirtuins are an evolutionarily conserved family of regulatory proteins that function in an NAD+ -dependent manner. The mammalian family of sirtuins is composed of seven histone deacetylase and ADP-ribosyltransferase proteins (SIRT1-SIRT7) that are found throughout the different cellular compartments of the cell. Sirtuins in the brain have received considerable attention in cognition due to their role in a plethora of metabolic and age-related diseases and their ability to induce neuroprotection. More recently, sirtuins have been shown to play a role in normal physiological cognitive function, and aberrant sirtuin function is seen in pathological cellular states. Sirtuins are believed to play a role in cognition through enhancing synaptic plasticity, influencing epigenetic regulation, and playing key roles in molecular pathways involved with oxidative stress affecting mitochondrial function. This review aims to discuss recent advances in the understanding of the role of mammalian sirtuins in cognitive function and the therapeutic potential of targeting sirtuins to ameliorate cognitive deficits in neurological disorders.

Hepatic SIRT6 Modulates Transcriptional Activities of FXR to Alleviate Acetaminophen-induced Hepatotoxicity

BACKGROUND & AIMS

Excessive acetaminophen (APAP) intake causes oxidative stress and inflammation, leading to fatal hepatotoxicity; however, the mechanism remains unclear. This study aims to explore the protective effects and detailed mechanisms of sirtuin 6 (SIRT6) in the defense against APAP-induced hepatotoxicity.

METHODS

Hepatocyte-specific SIRT6 knockout mice, farnesoid X receptor (FXR) knockout mice, and mice with genetic or pharmacological activation of SIRT6 were subjected to APAP to evaluate the critical role of SIRT6 in the pathogenesis of acute liver injury. RNA sequences were used to investigate molecular mechanisms underlying this process.

RESULTS

Hepatic SIRT6 expression was substantially reduced in the patients and mice with acute liver injury. The deletion of SIRT6 in mice and mice primary hepatocytes led to high N-acetyl-p-benzo-quinoneimine and low glutathione levels in the liver, thereby enhancing APAP overdose-induced liver injury, manifested as increased hepatic centrilobular necrosis, oxidative stress, and inflammation. Conversely, overexpression or pharmacological activation of SIRT6 enhanced glutathione and decreased N-acetyl-p-benzo-quinoneimine, thus alleviating APAP-induced hepatotoxicity via normalization of liver damage, inflammatory infiltration, and oxidative stress. Our molecular analysis revealed that FXR is regulated by SIRT6, which is associated with the pathological progression of ALI. Mechanistically, SIRT6 deacetylates FXR and elevates FXR transcriptional activity. FXR ablation in mice and mice primary hepatocytes prominently blunted SIRT6 overexpression and activation-mediated ameliorative effects. Conversely, pharmacological activation of FXR mitigated APAP-induced hepatotoxicity in SIRT6 knockout mice.

CONCLUSIONS

Our current study suggests that SIRT6 plays a crucial role in APAP-induced hepatotoxicity, and pharmacological activation of SIRT6 may represent a novel therapeutic strategy for APAP overdose-induced liver injury.

OUP accepted manuscript

Reactive oxygen species (ROS) are constantly produced in cells, an excess of which causes oxidative stress. ROS has been linked to regulation of the Hippo pathway; however, the underlying detailed mechanisms remain unclear. Here, we report that MOB1, a substrate of MST1/2 and co-activator of LATS1/2 in the canonical Hippo pathway, interacts with and is acetylated at lysine 11 by acetyltransferase CBP and deacetylated by HDAC6. MOB1-K11 acetylation stabilizes itself by reducing its binding capacity with E3 ligase Praja2 and subsequent ubiquitination. MOB1-K11 acetylation increases its phosphorylation and activates LATS1. Importantly, upstream oxidative stress signals promote MOB1 acetylation by suppressing CBP degradation, independent of MST1/2 kinase activity and HDAC6 deacetylation effect, thereby linking oxidative stress to activation of the Hippo pathway. Functionally, the acetylation-deficient mutant MOB1-K11R promotes lung cancer cell proliferation, migration and invasion in vitro and accelerates tumor growth in vivo, compared to the wild-type MOB1. Clinically, acetylated MOB1 corresponds to better prediction of overall survival in patients with non-small cell lung cancer. Therefore, as demonstrated, an oxidative stress-CBP regulatory axis controls MOB1-K11 acetylation and activates LATS1, thereby activating the Hippo pathway and suppressing YAP/TAZ nuclear translocation and tumor progression.

Nicotinamide Mononucleotide Prevents Free Fatty Acid-Induced Reduction in Glucose Tolerance by Decreasing Insulin Clearance

The NAD-dependent deacetylase SIRT1 improves β cell function. Accordingly, nicotinamide mononucleotide (NMN), the product of the rate-limiting step in NAD synthesis, prevents β cell dysfunction and glucose intolerance in mice fed a high-fat diet. The current study was performed to assess the effects of NMN on β cell dysfunction and glucose intolerance that are caused specifically by increased circulating free fatty acids (FFAs). NMN was intravenously infused, with or without oleate, in C57BL/6J mice over a 48-h-period to elevate intracellular NAD levels and consequently increase SIRT1 activity. Administration of NMN in the context of elevated plasma FFA levels considerably improved glucose tolerance. This was due not only to partial protection from FFA-induced β cell dysfunction but also, unexpectedly, to a significant decrease in insulin clearance. However, in conditions of normal FFA levels, NMN impaired glucose tolerance due to decreased β cell function. The presence of this dual action of NMN suggests caution in its proposed therapeutic use in humans.

Multifaced role of protein deacetylase sirtuins in neurodegenerative disease

Sirtuins, a class III histone/protein deacetylase, is a central regulator of metabolic function and cellular stress response. This plays a pivotal role in the pathogenesis and progression of diseases such as cancer, neurodegeneration, metabolic syndromes, and cardiovascular disease. Sirtuins regulate biological and cellular processes, for instance, mitochondrial biogenesis, lipid and fatty acid oxidation, oxidative stress, gene transcriptional activity, apoptosis, inflammatory response, DNA repair mechanism, and autophagic cell degradation, which are known components for the progression of the neurodegenerative diseases (NDDs). Emerging evidence suggests that sirtuins are the useful molecular targets against NDDs like, Alzheimer's Disease (AD), Parkinson's Disease (PD), Huntington's Disease (HD), and Amyotrophic Lateral Sclerosis (ALS). However, the exact mechanism of neuroprotection mediated through sirtuins remains unsettled. The manipulation of sirtuins activity with its modulators, calorie restriction (CR), and micro RNAs (miR) is a novel therapeutic approach for the treatment of NDDs. Herein, we reviewed the current putative therapeutic role of sirtuins in regulating synaptic plasticity and cognitive functions, which are mediated through the different molecular phenomenon to prevent neurodegeneration. We also explained the implications of sirtuin modulators, and miR based therapies for the treatment of life-threatening NDDs.

SIRT2 and FOXO3a expressions in the cerebral cortex and hippocampus of young and aged male rats: antioxidant and anti-apoptotic effects of melatonin

Melatonin has antioxidant, anti-apoptotic and anti-aging effects in the brain. Sirtuin2 (SIRT2) accumulates in the central nervous system with aging, and its inhibition appears to be protective in aging and aging-related neurodegenerative diseases. Forkhead Box-class O3a (FOXO3a) transcription factor is one of the main targets of SIRT2, and SIRT2-mediated FOXO3a deacetylation is closely related to aging, oxidative stress, and apoptosis. This study aimed to investigate the effects of melatonin on SIRT2 and FOXO3a expressions in the cerebral cortex and hippocampus of aged rats. Young (3 months, n = 18) and aged (22 months, n = 18) male Wistar rats were divided into control (4% DMSO-PBS, sc, for 21 days), melatonin (10 mg/kg, sc, for 21 days) and salermide (1 mM; 25 μl/100 g bw, ip, for 21 days) groups. SIRT2, FOXO3a, Bcl-2, Bax and Bim expressions in the cerebral cortex and hippocampus were demonstrated by Western blotting. SIRT2 and FOXO3a protein levels were also measured by a sandwich ELISA method. Oxidative stress index (OSI) was calculated by measuring total oxidant status (TOS) and total antioxidant status (TAS). Aging increased SIRT2, FOXO3a, Bim (only in the cerebral cortex), Bax (only in the hippocampus), TOS, and OSI, while decreasing Bcl-2, Bcl-2/Bax and TAS in both brain regions. Melatonin decreased SIRT2, FOXO3a, oxidative stress parameters and pro-apoptotic proteins, while increasing TAS, Bcl-2 and Bcl-2/Bax, more specifically in the hippocampus of the aged brain. Our results indicate that inhibition of SIRT2 and FOXO3a expressions appears to be involved in the protective effects of melatonin in the hippocampus of aged rats.

SIRT2-mediated deacetylation and deubiquitination of C/EBPβ prevents ethanol-induced liver injury

Protein acetylation has emerged to play pivotal roles in alcoholic liver disease (ALD). Sirutin 2 (SIRT2) is a nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase involved in the regulation of aging, metabolism, and stress. However, the role of SIRT2 in ALD remains unclear. Here, we report that the SIRT2-mediated deacetylation-deubiquitination switch of CCAAT/enhancer-binding protein beta (C/EBPβ) prevents ALD. Our results showed that hepatic SIRT2 protein expression was negatively correlated with the severity of alcoholic liver injury in ALD patients. Liver-specific SIRT2 deficiency sensitized mice to ALD, whereas transgenic SIRT2 overexpression in hepatocytes significantly prevented ethanol-induced liver injury via normalization of hepatic steatosis, lipid peroxidation, and hepatocyte apoptosis. Mechanistically, we identified C/EBPβ as a critical substrate of SIRT2 implicated in ALD. SIRT2-mediated deacetylation at lysines 102 and 211 decreased C/EBPβ ubiquitination, resulting in enhanced protein stability and subsequently increased transcription of C/EBPβ-target gene LCN2. Importantly, hepatic deacetylated C/EBPβ and LCN2 compensation reversed SIRT2 deletion-induced ALD aggravation in mice. Furthermore, C/EBPβ protein expression was positively correlated with SIRT2 and LCN2 expression in the livers of ALD patients and was inversely correlated with ALD development. Therefore, activating SIRT2-C/EBPβ-LCN2 signaling pathway is a potential therapy for ALD.

Emerging roles of Sirtuin 2 in cardiovascular diseases

Sirtuins are a family of NAD⁺ -dependent deacetylases implicated in a wide variety of age-associated pathologies, including cardiovascular disorders. Among the seven mammalian sirtuins, SIRT2 modulates various cellular processes through the deacetylation or deacylation of their target proteins. Notably, the levels of SIRT2 in the heart decline with age and other pathological conditions, leading to cardiovascular dysfunction. In the present review, we discuss the emerging roles of SIRT2 in cardiovascular dysfunction and heart failure associated with factors like age, hypertension, oxidative stress, and diabetes. We also discuss the potential of using inhibitors to study the unexplored role of SIRT2 in the heart. While SIRT2 undoubtedly plays a crucial role in the cardiovascular system, its functions are only beginning to be understood, making it an attractive candidate for further research in the field.

Emerging role of SIRT2 in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is one of the most devastating cancer types, accounting for >80% of lung cancer cases. The median relative survival time of patients with NSCLC is <1 year. Lysine acetylation is a major post-translational modification that is required for various biological processes, and abnormal protein acetylation is associated with various diseases, including NSCLC. Protein deacetylases are currently considered cancer permissive partly due to malignant cells being sensitive to deacetylase inhibition. Sirtuin 2 (SIRT2), a primarily cytosolic nicotinamide adenine dinucleotide-dependent class III protein deacetylase, has been shown to catalyze the removal of acetyl groups from a wide range of proteins, including tubulin, ribonucleotide reductase regulatory subunit M2 and glucose-6-phosphate dehydrogenase. In addition, SIRT2 is also known to possess lysine fatty deacylation activity. Physiologically, SIRT2 serves as a regulator of the cell cycle and of cellular metabolism. It has been shown to play important roles in proliferation, migration and invasion during carcinogenesis. It is notable that both oncogenic and tumor suppressive functions of SIRT2 have been described in NSCLC and other cancer types, suggesting a context-specific role of SIRT2 in cancer progression. In addition, inhibition of SIRT2 exhibits a broad anticancer effect, indicating its potential as a therapeutic for NSCLC tumors with high expression of SIRT2. However, due to the diverse molecular and genetic characteristics of NSCLC, the context-specific function of SIRT2 remains to be determined. The current review investigated the functions of SIRT2 during NSCLC progression with regard to its regulation of metabolism, stem cell-like features and autophagy.

The Performance of HepG2 and HepaRG Systems through the Glass of Acetaminophen-Induced Toxicity

Investigation of drug-induced liver injuries requires appropriate in vivo and in vitro toxicological model systems. In our study, an attempt was made to compare the hepatocarcinoma HepG2 and the stem cell-derived HepaRG cell lines both in two- and three-dimensional culture conditions to find the most suitable model. Comparison of the liver-specific characteristics of these models was performed via the extent and mechanism of acetaminophen (APAP)-induced hepatotoxicity. Investigating the detailed mechanism of APAP-induced hepatotoxicity, different specific cell death inhibitors were used: the pan-caspase inhibitor zVAD-fmk and dabrafenib significantly protected both cell lines from APAP-induced cell death. However, the known specific inhibitors of necroptosis (necrostatin-1 and MDIVI) were only effective in differentiated HepaRG, which suggest a differential execution of activated pathways in the two models. By applying 3D culture methods, CYP2E1 mRNA levels could be elevated, but we failed to achieve a significant increase in hepatocyte function; hence, the 3D cultivation especially in APAP toxicity studies is not necessarily worth the complicated maintenance. Based on our findings, the hepatocyte functions of HepaRG may stand between the properties of HepG2 cells and primary hepatocytes (PHHs). However, it should be noted that in contrast to PHHs having many limitations, HepaRG cells are relatively immortal, having a stable phenotype and CYP450 expression.

Parasitic sirtuin 2 as an opportunity in drug discovery

Infections caused by protozoans remain a public health issue, especially in tropical countries. Serious adverse events, lack of efficacy at the different stages of the infection and routes of administration that have a negative impact on treatment adherence are some of the problems with currently available therapy against these diseases. Here we describe an epigenetic target, sirtuin 2 and its related proteins, that is promising given the results in phenotypic assays and in vivo models against Sir2 of Plasmodium falciparum, Leishmania donovani, Leishmania infantum, Schistosoma mansoni, Trypanosoma brucei and Trypanosoma cruzi parasites. The results we present highlight how this target can be extensively explored and how its inhibitors might be employed in the clinic.

Understanding the Function of Mammalian Sirtuins and Protein Lysine Acylation

Protein lysine acetylation is an important posttranslational modification that regulates numerous biological processes. Targeting lysine acetylation regulatory factors, such as acetyltransferases, deacetylases, and acetyl-lysine recognition domains, has been shown to have potential for treating human diseases, including cancer and neurological diseases. Over the past decade, many other acyl-lysine modifications, such as succinylation, crotonylation, and long-chain fatty acylation, have also been investigated and shown to have interesting biological functions. Here, we provide an overview of the functions of different acyl-lysine modifications in mammals. We focus on lysine acetylation as it is well characterized, and principles learned from acetylation are useful for understanding the functions of other lysine acylations. We pay special attention to the sirtuins, given that the study of sirtuins has provided a great deal of information about the functions of lysine acylation. We emphasize the regulation of sirtuins to illustrate that their regulation enables cells to respond to various signals and stresses.

The link between deacetylation and hepatotoxicity induced by exposure to hexavalent chromium

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Cr(VI) can induce inflammatory, oxidative stress, and apoptosis in rat liver.

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Cr(VI) induces inflammatory response in the liver by inhibiting deacetylation.

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Oxidative stress caused by Cr(VI) is related to the inhibition of deacetylation.

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Cr(VI) aggravates hepatocyte apoptosis by inhibiting deacetylation in rats.

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Cr(VI) induces liver injury via inhibition of the deacetylation of Sirt1.

Introduction

Hexavalent chromium (Cr(VI)), one of the toxic heavy metals, poses a serious threat to human and animal health. Protein acetylation regulates the structure and function of most proteins in a variety of ways. However, the hepatotoxicity of Cr(VI) and whether it is related to deacetylation remains largely unknown.

Objectives

We aimed to explore the link between the deacetylation of silent information regulator two ortholog 1 (Sirt1) and hepatotoxicity induced by Cr(VI) exposure, and to better clarify the biological mechanism of liver injury induced by Cr(VI).

Methods

We established a model of liver injury of K₂Cr₂O₇ by injecting rats intraperitoneally for 35 days continuously and adding resveratrol (Res) to further explore the link between deacetylation and hepatotoxicity.

Results

The results revealed that Cr(VI) induced inflammatory response and apoptosis in hepatocytes. Furthermore, Cr(VI) reduced Sirt1 expression and inhibited the deacetylation of Sirt1 to downstream key transcription factors, including nuclear factor erythroid 2-related factor 2 (Nrf2), Forkhead box O3 (FOXO3), and nuclear factor-kappa B (NF-κB). Conversely, when Res was administered as an activator of Sirt1, the deacetylation of Sirt1 was enhanced, and inflammatory response and apoptosis were significantly alleviated.

Conclusion

In summary, this work firstly demonstrates that Cr(VI) induces liver injury in rat by inhibiting the deacetylation of Sirt1, which is of positive significance for protecting the natural environment and animal health from chronic Cr poisoning.

Overexpression of sirtuin 2 and its association with prognosis in acute ischemic stroke patients

Background

This study aimed to investigate the correlation of sirtuin 2 (SIRT2) with acute ischemic stroke (AIS) risk, severity, inflammation, and prognosis.

Methods

A hundred and sixty‐four first episode AIS patients and 164 age and gender matched non‐AIS patients with high‐stroke‐risk factors (controls) were enrolled. Peripheral blood was collected and serum was separated for SIRT2 and pro‐inflammatory cytokines detection by enzyme‐linked immunosorbent assay. AIS patients were continually followed up to 36 months or death, then recurrence‐free survival (RFS) and overall survival (OS) were calculated.

Results

Serum SIRT2 expression was increased in AIS patients compared to controls (p < 0.001), then receiver operative characteristic curve disclosed that the serum SIRT2 expression could differentiate AIS patients from controls with a good area under curve of 0.890 (95%CI: 0.854–0.926), a sensitivity of 78.7% and a specificity of 91.5% at the best cut‐off point. Serum SIRT2 expression was positively correlated with National Institute of Health stroke scale score (p < 0.001), serum tumor necrosis factor‐α (p < 0.001), interleukin (IL)‐6 (p = 0.012) and IL‐17 (p < 0.001) expressions in AIS patients. In addition, serum SIRT2 expression was elevated in recurrent/dead AIS patients compared to non‐recurrent/dead AIS patients (p = 0.025), and was also increased in dead AIS patients compared to survivors (p = 0.006). Moreover, RFS (p = 0.029) and OS (p = 0.049) were both worse in AIS patients with SIRT2 high expression compared to AIS patients with SIRT2 low expression.

Conclusion

SIRT2 may serve as a marker for AIS risk and prognosis in clinical practice.

The extracellular lactate-to-pyruvate ratio modulates the sensitivity to oxidative stress-induced apoptosis via the cytosolic NADH/NAD+ redox state

The advantages of the Warburg effect on tumor growth and progression are well recognized. However, the relevance of the Warburg effect for the inherent resistance to apoptosis of cancer cells has received much less attention. Here, we show here that the Warburg effect modulates the extracellular lactate-to-pyruvate ratio, which profoundly regulates the sensitivity towards apoptosis induced by oxidative stress in several cell lines. To induce oxidative stress, we used the rapid apoptosis inducer Raptinal. We observed that medium conditioned by HepG2 cells has a high lactate-to-pyruvate ratio and confers resistance to Raptinal-induced apoptosis. In addition, imposing a high extracellular lactate-to-pyruvate ratio in media reduces the cytosolic NADH/NAD⁺ redox state and protects against Raptinal-induced apoptosis. Conversely, a low extracellular lactate-to-pyruvate ratio oxidizes the cytosolic NADH/NAD⁺ redox state and sensitizes HepG2 cells to oxidative stress-induced apoptosis. Mechanistically, a high extracellular lactate-to-pyruvate ratio decreases the activation of JNK and Bax under oxidative stress, thereby inhibiting the intrinsic apoptotic pathway. Our observations demonstrate that the Warburg effect of cancer cells generates an anti-apoptotic extracellular environment by elevating the extracellular lactate-to-pyruvate ratio which desensitizes cancer cells towards apoptotic insults. Consequently, our study suggests that the Warburg effect can be targeted to reverse the lactate-to-pyruvate ratios in the tumor microenvironment and thereby re-sensitize cancer cells to oxidative stress-inducing therapies.

Sustained Activation of AMPK Enhances Differentiation of Human iPSC-Derived Cardiomyocytes via Sirtuin Activation

Recent studies suggest that metabolic regulation may improve differentiation of cardiomyocytes derived from induced pluripotent stem cells (iPSCs). AMP-activated protein kinase (AMPK) is a master regulator of metabolic activities. We investigated whether AMPK participates in iPSC-derived cardiomyocyte differentiation. We observed that AMPK phosphorylation at Thr172 increased at day 9 but then decreased after day 11 of differentiation to cardiomyocytes. Inhibition of AMPK with compound C significantly reduced mRNA and protein expression of cardiac troponins TNNT2 and TNNI3. Moreover, sustained AMPK activation using AICAR from days 9 to 14 of differentiation increased mRNA and protein expression of both TNNT2 and TNNI3. AICAR decreased acetylation of histone 3 at Lys9 and 56 and histone 4 at Lys16 (known target sites for nuclear-localized sirtuins [SIRT1, SIRT6]), suggesting that AMPK activation enhances sirtuin activity. Sustained AMPK activation during days 9–14 of differentiation induces sirtuin-mediated histone deacetylation and may enhance cardiomyocyte differentiation from iPSCs.

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iPSC-derived cardiomyocytes transiently increased AMPK phosphorylation at Thr172

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Chemical inhibition of AMPK with compound C decreased TNNI3 and TNNT2 expression

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Sustained activation of AMPK using AICAR increased expression of TNNT2 and TNNI3

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AICAR decreased acetylation of histones H3 (at Lys9 and Lys56) and H4 (at Lys16).

The role of SIRT2 in cancer: A novel therapeutic target

Sirtuin 2 (SIRT2) belongs to the sirtuins family. It exists in many tissues and organs of the human body and regulates a wide range of biological functions. Studies have found that the abnormal expression of SIRT2 was associated with a variety of malignant tumors. SIRT2 possesses an important role in tumorigenesis, with both tumor-promoting and tumor-suppressing function. However, the mechanisms in which SIRT2 plays the roles in cancer are still controversial. This article reviews the role and molecular mechanism of SIRT2 in tumor evolution, and provides ideas for future research in this field, to guide the targeted therapy and drug development of related malignancies.

Haplotypes of the Mutated SIRT2 Promoter Contributing to Transcription Factor Binding and Type 2 Diabetes Susceptibility

Genetic variability is an important causative factor for susceptibility and pathogenesis of type 2 diabetes (T2D). Histone deacetylase, sirtuin 2 (SIRT2), plays regulatory roles in glucose metabolism and insulin sensitivity. However, whether the SIRT2 variants or haplotypes contribute to T2D risk remain to be elucidated. In this study, we first detected three novel polymorphisms (P-MU1, P-MU2, and P-MU3) in the promoter of SIRT2 in the Chinese population. All pairwise sets of the three loci were strongly in linkage disequilibrium. Next, we constructed the haplotype block structure, and found H1-GGC and H2-CCA accounted for the most (total 91.8%) in T2D. The haplotype combination H1-H1-GGGGCC displayed a high risk for T2D (OR = 2.03, 95% CI = 1.12-3.72). By association analysis, we found the individuals carrying H1-H1-GGGGCC had significantly higher fasting plasma glucose and glycated hemoglobin. The haplotype H1-GGC presented a 6.74-fold higher promoter activity than H2-CCA, which was consistent with the correlation results. Furthermore, we clarified the mechanism whereby the C allele of both the P-MU1 and P-MU2 loci disrupted the signal transducer and activator of transcription 1 (STAT1) binding sites, leading to the attenuation of the SIRT2 transcription. Together, these data suggest that the linked haplotype GGC could be considered as a promising marker for T2D diagnosis and therapy assessment.

The Effects of Inhibition of MicroRNA-375 in a Mouse Model of Doxorubicin-Induced Cardiac Toxicity

BACKGROUND Doxorubicin-induced myocardial toxicity is associated with oxidative stress, cardiomyocyte, apoptosis, and loss of contractile function. Previous studies showed that microRNA-375 (miR-375) expression was increased in mouse models of heart failure and clinically, and that inhibition of miR-375 reduced inflammation and increased survival of cardiomyocytes. This study aimed to investigate the effects and mechanisms of inhibition of miR-375 in a mouse model of doxorubicin-induced cardiac toxicity in vivo and in doxorubicin-treated rat and mouse cardiomyocytes in vitro. MATERIAL AND METHODS The mouse model of doxorubicin-induced cardiac toxicity was developed using an intraperitoneal injection of doxorubicin (15 mg/kg diluted in 0.9% saline) for eight days. Treatment was followed by a single subcutaneous injection of miR-375 inhibitor. H9c2 rat cardiac myocytes and adult murine cardiomyocytes (AMCs) were cultured in vitro and treated with doxorubicin, with and without pretreatment with miR-375 inhibitor. RESULTS Doxorubicin significantly upregulated miR-375 expression in vitro and in vivo, and inhibition of miR-375 re-established myocardial redox homeostasis, prevented doxorubicin-induced oxidative stress and cardiomyocyte apoptosis, and activated the PDK1/AKT axis by reducing the direct binding of miR-375 to 3' UTR of the PDK1 gene. Inhibition of PDK1 and AKT abolished the protective role of miR-375 inhibition on doxorubicin-induced oxidative damage. CONCLUSIONS Inhibition of miR-375 prevented oxidative damage in a mouse model of doxorubicin-induced cardiac toxicity in vivo and in doxorubicin-treated rat and mouse cardiomyocytes in vitro through the PDK1/AKT signaling pathway.

AK-1, a Sirt2 inhibitor, alleviates carbon tetrachloride-induced hepatotoxicity in vivo and in vitro

Background/Aim: Acute liver injury (ALI) is a life-threatening clinical syndrome that is usually caused by toxic chemicals, drugs, or pathogen infections. Sirtuin2 (Sirt2), an NAD⁺-dependent deacetylase, appears to play detrimental roles in liver injury. Here, we evaluated the therapeutic application targeting Sirt2 in carbon tetrachloride (CCl₄)-induced ALI, by using AK-1 (a Sirt2 inhibitor).Methods: For in vivo experiments, a single injection of CCl₄ was used to induce ALI. One hour later, mice were intraperitoneally injected with AK-1 and were sacrificed 24 h after CCl₄ administration. For in vitro experiments, primary mouse hepatocytes were used to determine the effects of AK-1 on oxidative stress and hepatocellular death induced by CCl₄.Results: AK-1 alleviated CCl₄-induced ALI as confirmed by histopathologic analysis, and decreased levels of serum biochemicals and inflammatory cytokines. Although it barely affected the expression of hepatic cytochrome P450 enzymes, AK-1 attenuated CCl₄-induced oxidative stress and its related cell death. Mechanistically, Sirt2 inhibition significantly increased the nuclear protein level of nuclear factor erythroid 2-related factor 2 (Nrf2), and meanwhile decreased phosphorylation of c-Jun N-terminal kinases (JNK), in normal and injured livers. Similar results were observed in vitro. AK-1 significantly attenuated CCl₄-induced cytotoxicity and oxidative stress by up-regulating the activity of Nrf2, and down-regulating JNK signaling in hepatocytes.Conclusions: Our results suggest that AK-1 treatment attenuated oxidative stress and cell death in the ALI model, at least partially, via activating Nrf2 and inhibiting JNK signaling, and that Sirt2 inhibition might be a potential approach to cure ALI.

Dichotomous Sirtuins: Implications for Drug Discovery in Neurodegenerative and Cardiometabolic Diseases

Sirtuins (SIRT1-7), a class of NAD⁺-dependent deacylases, are central regulators of metabolic homeostasis and stress responses. While numerous salutary effects associated with sirtuin activation, especially SIRT1, are well documented, other reports show health benefits resulting from sirtuin inhibition. Furthermore, conflicting findings have been obtained regarding the pathophysiological role of specific sirtuin isoforms, suggesting that sirtuins act as 'double-edged swords'. Here, we provide an integrated overview of the different findings on the role of mammalian sirtuins in neurodegenerative and cardiometabolic disorders and attempt to dissect the reasons behind these different effects. Finally, we discuss how addressing these obstacles may provide a better understanding of the complex sirtuin biology and improve the likelihood of identifying effective and selective drug targets for a variety of human disorders.

SIRT2 and Lysine Fatty Acylation Regulate the Activity of RalB and Cell Migration

Protein lysine fatty acylation is increasingly recognized as a prevalent and important protein post-translation modification. Recently, it has been shown that K-Ras4a, R-Ras2, and Rac1 are regulated by lysine fatty acylation. Here, we investigated whether other members of the Ras superfamily could also be regulated by lysine fatty acylation. Several small GTPases exhibit hydroxylamine resistant fatty acylation, suggesting they may also have protein lysine fatty acylation. We further characterized one of these GTPases, RalB. We show that RalB has C-terminal lysine fatty acylation, with the predominant modification site being Lys200. The lysine acylation of RalB is regulated by SIRT2, a member of the sirtuin family of nicotinamide adenine dinucleotide (NAD)-dependent protein lysine deacylases. Lysine fatty acylated RalB exhibited enhanced plasma membrane localization and recruited its known effectors Sec5 and Exo84, members of the exocyst complex, to the plasma membrane. RalB lysine fatty acylation did not affect the proliferation or anchorage-independent growth but did affect the trans-well migration of A549 lung cancer cells. This study thus identified an additional function for protein lysine fatty acylation and the deacylase SIRT2.

The function of histone acetylation in cervical cancer development

Cervical cancer is the fourth most common female cancer in the world. It is well known that cervical cancer is closely related to high-risk human papillomavirus (HPV) infection. However, epigenetics has increasingly been recognized for its role in tumorigenesis. Epigenetics refers to changes in gene expression levels based on non-gene sequence changes, primarily through transcription or translation of genes regulation, thus affecting its function and characteristics. Typical post-translational modifications (PTMs) include acetylation, propionylation, butyrylation, malonylation and succinylation, among which the acetylation modification of lysine sites has been studied more clearly so far. The acetylation modification of lysine residues in proteins is involved in many aspects of cellular life activities, including carbon metabolism, transcriptional regulation, amino acid metabolism and so on. In this review, we summarize the latest discoveries on cervical cancer development arising from the aspect of acetylation, especially histone acetylation.

Allosteric Regulation of Cyclin-B Binding by the Charge State of Catalytic Lysine in CDK1 Is Essential for Cell-Cycle Progression

Cyclin-dependent kinase 1 (CDK1) is essential for cell-cycle progression. While dependence of CDK activity on cyclin levels is well established, molecular mechanisms that regulate their binding are less understood. Here, we report for the first time that CDK1:cyclin-B binding is not default but rather determined by the evolutionarily conserved catalytic residue, lysine-33 in CDK1. We demonstrate that the charge state of this lysine allosterically remodels the CDK1:cyclin-B interface. Cell cycle-dependent acetylation of lysine-33 or its mutation to glutamine, which mimics acetylation, abrogates cyclin-B binding. Using biochemical approaches and atomistic molecular dynamics simulations, we have uncovered both short-range and long-range effects of perturbing the charged state of the catalytic lysine, which lead to inhibition of kinase activity. Specifically, although loss of the charge state of catalytic lysine did not impact ATP binding significantly, it altered its orientation in the active site. In addition, the catalytic lysine also acts as an intra-molecular electrostatic tether at the active site to orient structural elements interfacing with cyclin-B. Physiologically, opposing activities of SIRT1 and P300 regulate acetylation and thus control the charge state of lysine-33. Importantly, cells expressing acetylation mimic mutant of Cdc2/CDK1 in yeast are arrested in G2 and fail to divide, indicating the requirement of the deacetylated state of the catalytic lysine for cell division. Thus, by illustrating the molecular role of the catalytic lysine and cell cycle-dependent deacetylation as a determinant of CDK1:cyclin-B interaction, our results redefine the current model of CDK1 activation and cell-cycle progression.

Anthocyanins from Lycium ruthenicum Murr. Ameliorated d-Galactose-Induced Memory Impairment, Oxidative Stress, and Neuroinflammation in Adult Rats

Lycium ruthenicum Murr. (LR) is a perennial shrub commonly used as a nutritional food and medicine. Herein, we identified 12 anthocyanins from LR, with petunidin derivatives constituting approximately 97% of the total anthocyanin content. Furthermore, the potential mechanism of anthocyanins exerting neuroprotective effects in d-galactose (d-gal)-treated rats was explored. Behavioral results showed that anthocyanins relieved d-gal-induced memory disorder. Additionally, anthocyanins reduced receptor for advanced glycation end products (RAGE) and suppressed oxidative stress caused by d-gal. Anthocyanins suppressed microgliosis and astrocytosis and reduced the overexpression of nuclear factor kappa B (NF-κB), interleukin-1-β (IL-1β), cyclooxygenase-2 (COX-2), and tumor necrosis factor-α (TNF-α). Moreover, anthocyanins lowered C-jun N-terminal kinase ( p-JNK), caspase-3 levels, and the B-cell lymphoma 2-associated X protein/B-cell lymphoma 2 (Bax/Bcl-2) ratio. Thus, anthocyanins from LR attenuated memory disfunction, neuroinflammation, and neurodegeneration caused by d-gal, possibly through the RAGE/NF-κB/JNK pathway, representing a promising, safe candidate for prevention and therapy of neurodegenerative diseases.

Updates on the epigenetic roles of sirtuins

Sirtuins are a class of enzyme with NAD⁺-dependent protein lysine deacylase activities. They were initially discovered to regulate transcription and life span via histone deacetylase activities. Later studies expanded their activities to other proteins and acyl lysine modifications. Through deacylating various substrate proteins, they regulate many biological processes, including transcription, DNA repair and genome stability, metabolism, and signal transduction. Here, we review recent understandings of the epigenetic functions (broadly defined to include transcriptional, post-transcriptional regulation, and DNA repair) of mammalian sirtuins. Because of the important functions of sirtuins, their own regulation is of great interest and is also discussed.

The Regulation of JNK Signaling Pathways in Cell Death through the Interplay with Mitochondrial SAB and Upstream Post-Translational Effects

c-Jun-N-terminal kinase (JNK) activity plays a critical role in modulating cell death, which depends on the level and duration of JNK activation. The kinase cascade from MAPkinase kinase kinase (MAP3K) to MAPkinase kinase (MAP2K) to MAPKinase (MAPK) can be regulated by a number of direct and indirect post-transcriptional modifications, including acetylation, ubiquitination, phosphorylation, and their reversals. Recently, a JNK-mitochondrial SH3-domain binding protein 5 (SH3BP5/SAB)-ROS activation loop has been elucidated, which is required to sustain JNK activity. Importantly, the level of SAB expression in the outer membrane of mitochondria is a major determinant of the set-point for sustained JNK activation. SAB is a docking protein and substrate for JNK, leading to an intramitochondrial signal transduction pathway, which impairs electron transport and promotes reactive oxygen species (ROS) release to sustain the MAPK cascade.

SIRT2 deacetylase regulates the activity of GSK3 isoforms independent of inhibitory phosphorylation

Glycogen synthase kinase 3 (GSK3) is a critical regulator of diverse cellular functions involved in the maintenance of structure and function. Enzymatic activity of GSK3 is inhibited by N-terminal serine phosphorylation. However, alternate post-translational mechanism(s) responsible for GSK3 inactivation are not characterized. Here, we report that GSK3α and GSK3β are acetylated at Lys246 and Lys183, respectively. Molecular modeling and/or molecular dynamics simulations indicate that acetylation of GSK3 isoforms would hinder both the adenosine binding and prevent stable interactions of the negatively charged phosphates. We found that SIRT2 deacetylates GSK3β, and thus enhances its binding to ATP. Interestingly, the reduced activity of GSK3β is associated with lysine acetylation, but not with phosphorylation at Ser9 in hearts of SIRT2-deficient mice. Moreover, GSK3 is required for the anti-hypertrophic function of SIRT2 in cardiomyocytes. Overall, our study identified lysine acetylation as a novel post-translational modification regulating GSK3 activity.