SIRT5 deficiency suppresses mitochondrial ATP production and promotes AMPK activation in response to energy stress

Sirtuin 5 alleviates apoptosis and autophagy stimulated by ammonium chloride in bovine mammary epithelial cells

Ammonia (NH3) is an irritating and harmful gas that affects cell apoptosis and autophagy. Sirtuin 5 (SIRT5) has multiple enzymatic activities and regulates NH3-induced autophagy in tumor cells. In order to determine whether SIRT5 regulates NH3-induced bovine mammary epithelial cell apoptosis and autophagy, cells with SIRT5 overexpression or knockdown were generated and in addition, bovine mammary epithelial cells were treated with SIRT5 inhibitors. The results showed that SIRT5 overexpression reduced the content of NH3 and glutamate in cells by inhibiting glutaminase activity in glutamine metabolism, and reduced the ratio of ADP/ATP. The results in the SIRT5 knockdown and inhibitor groups were comparable, including increased content of NH3 and glutamate in cells by activating glutaminase activity, and an elevated ratio of ADP/ATP. It was further confirmed that SIRT5 inhibited the apoptosis and autophagy of bovine mammary epithelial cells through reverse transcription-quantitative PCR, western blot, flow cytometry with Annexin V FITC/PI staining and transmission electron microscopy. In addition, it was also found that the addition of LY294002 or Rapamycin inhibited the PI3K/Akt or mTOR kinase signal, decreasing the apoptosis and autophagy activities of bovine mammary epithelial cells induced by SIRT5-inhibited NH3. In summary, the PI3K/Akt/mTOR signal involved in NH3-induced cell autophagy and apoptosis relies on the regulation of SIRT5. This study provides a new theory for the use of NH3 to regulate bovine mammary epithelial cell apoptosis and autophagy, and provides guidance for improving the health and production performance of dairy cows.

SIRT6 in Regulation of Mitochondrial Damage and Associated Cardiac Dysfunctions: A Possible Therapeutic Target for CVDs

Cardiovascular diseases (CVDs) can be described as a global health emergency imploring possible prevention strategies. Although the pathogenesis of CVDs has been extensively studied, the role of mitochondrial dysfunction in CVD development has yet to be investigated. Diabetic cardiomyopathy, ischemic-reperfusion injury, and heart failure are some of the CVDs resulting from mitochondrial dysfunction Recent evidence from the research states that any dysfunction of mitochondria has an impact on metabolic alteration, eventually causes the death of a healthy cell and therefore, progressively directing to the predisposition of disease. Cardiovascular research investigating the targets that both protect and treat mitochondrial damage will help reduce the risk and increase the quality of life of patients suffering from various CVDs. One such target, i.e., nuclear sirtuin SIRT6 is strongly associated with cardiac function. However, the link between mitochondrial dysfunction and SIRT6 concerning cardiovascular pathologies remains poorly understood. Although the Role of SIRT6 in skeletal muscles and cardiomyocytes through mitochondrial regulation has been well understood, its specific role in mitochondrial maintenance in cardiomyocytes is poorly determined. The review aims to explore the domain-specific function of SIRT6 in cardiomyocytes and is an effort to know how SIRT6, mitochondria, and CVDs are related.

Yiqigubiao pill treatment regulates Sirtuin 5 expression and mitochondrial function in chronic obstructive pulmonary disease

Background

Chronic obstructive pulmonary disease (COPD) is a heterogeneous group of pathophysiological bases of airway inflammation and its anti-inflammatory response. Aberrant mitochondrial signaling and mitochondrial dysfunction underlie the pathomechanisms leading to COPD. This study aims to investigate the effects of the Yiqigubiao (YQGB) pill, a traditional Chinese medicine (TCM), on Sirtuin 5 (SIRT5) and mitochondrial function in patients with COPD.

Methods

Thirty-four patients with COPD were randomized into oral YQGB or placebo groups concurrent with a 24-week routine treatment. The pulmonary function was assessed by examining the levels of forced expiratory volume in one second (FEV1)/forced vital capacity (FVC), FEV1, and FVC. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot were used to detect SIRT5 expression in mitochondria isolated from peripheral blood. Flow cytometry was used to detect changes in mitochondrial membrane potential and reactive oxygen species (ROS) in peripheral blood lymphocytes. Human bronchial epithelial (HBE) cells stimulated by cigarette smoke extract (CSE) were treated with YQGB. After SIRT5 was knocked down in cells, the changes in mitochondrial membrane potential, levels of adenosine triphosphate (ATP), and ROS were detected.

Results

YQGB treatment significantly improved lung function in patients with COPD. The expression of SIRT5 and the mitochondrial membrane potential significantly increased and ROS decreased in patients with COPD after YQGB treatment. The CSE decreased cell proliferation and SIRT5 expression, which was alleviated after YQGB treatment. Furthermore, SIRT5 was knocked down in CSE-stimulated HBE cells, and its expression was elevated upon YQGB treatment. The knockdown of SIRT5 significantly altered the CSE-stimulation-induced dysregulation of mitochondrial membrane potential, ATP levels, and ROS. This was also restored after YQGB treatment.

Conclusions

YQGB treatment can elevate SIRT5 expression, restore mitochondrial function in COPD, and exert protective effects.

NAD in pathological cardiac remodeling: Metabolic regulation and beyond

Nicotinamide adenine dinucleotide (NAD) coenzymes are carriers of high energy electrons in metabolism and also play critical roles in numerous signaling pathways. NAD metabolism is decreased in various cardiovascular diseases. Importantly, stimulation of NAD biosynthesis protects against heart disease under different pathological conditions. In this review, we describe pathways for both generation and catabolism of NAD coenzymes and the respective changes of these pathways in the heart under cardiac diseases, including pressure overload, myocardial infarction, cardiometabolic disease, cancer treatment cardiotoxicity, and heart failure. We next provide an update on the strategies and treatments to increase NAD levels, such as supplementation of NAD precursors, in the heart that prevent or reverse cardiomyopathy. We also introduce the approaches to manipulate NAD consumption enzymes to ameliorate cardiac disease. Finally, we discuss the mechanisms associated with improvements in cardiac function by NAD coenzymes, differentiating between mitochondria-dependent effects and those independent of mitochondrial metabolism.

Mexidol, Cytoflavin, and succinic acid derivatives as antihypoxic, anti-ischemic metabolic modulators, and ergogenic aids in athletes and consideration of their potential as performance enhancing drugs

Emoxypine (ethylmethylhydroxypyridine) is a synthetic derivative of vitamin B6 . Emoxypine succinate is a registered drug in Russia and Ukraine under various trade names including Mexidol, Mexicor, and Armadin Long. Mexidol demonstrates antihypoxic and anti-ischemic effects and also modulates metabolism. The use of Mexidol by Russian athletes has been confirmed in the past. Current use by athletes is unknown as this drug is not monitored or included in drug testing protocol. Metabotropic and antihypoxic effects of Mexidol were compared to the effects of meldonium or trimetazidine, both of which are included on the World Anti-Doping Agency (WADA) Prohibited List in category S4.4. Metabolic Modulators. The conjugation of emoxypine with succinate elevates the therapeutic effectiveness of the Mexidol formulation as succinic acid itself has important impacts to consider despite being a common food additive and drug excipient. Other succinic acid salts like ammonium succinate, found as dietary supplement, have been patented as performance enhancers. Available research on healthy subjects suggests that combinations of selected 3-substituted pyridine derivatives with succinate including Mexidol and a related drug Cytoflavin can enhance the performance of athletes. Cytoflavin is a multi-component formula containing meglumine sodium succinate, nicotinamide (vitamin B3 ), inosine (riboxin), and riboflavin. Other related succinate-based drugs include Remaxol, Reamberin, and Cogitum. Mexidol and Cytoflavin and related substances exhibit similar biological effects as drugs on the WADA Prohibited List, and if they are used for performance enhancement by athletes, they could be worthy of consideration as prohibited substances in sport.

Impact of Lysine Succinylation on the Biology of Fungi

Post-translational modifications (PTMs) play a crucial role in protein functionality and the control of various cellular processes and secondary metabolites (SMs) in fungi. Lysine succinylation (Ksuc) is an emerging protein PTM characterized by the addition of a succinyl group to a lysine residue, which induces substantial alteration in the chemical and structural properties of the affected protein. This chemical alteration is reversible, dynamic in nature, and evolutionarily conserved. Recent investigations of numerous proteins that undergo significant succinylation have underscored the potential significance of Ksuc in various biological processes, encompassing normal physiological functions and the development of certain pathological processes and metabolites. This review aims to elucidate the molecular mechanisms underlying Ksuc and its diverse functions in fungi. Both conventional investigation techniques and predictive tools for identifying Ksuc sites were also considered. A more profound comprehension of Ksuc and its impact on the biology of fungi have the potential to unveil new insights into post-translational modification and may pave the way for innovative approaches that can be applied across various clinical contexts in the management of mycotoxins.

Mitochondria and Brain Disease: A Comprehensive Review of Pathological Mechanisms and Therapeutic Opportunities

Mitochondria play a vital role in maintaining cellular energy homeostasis, regulating apoptosis, and controlling redox signaling. Dysfunction of mitochondria has been implicated in the pathogenesis of various brain diseases, including neurodegenerative disorders, stroke, and psychiatric illnesses. This review paper provides a comprehensive overview of the intricate relationship between mitochondria and brain disease, focusing on the underlying pathological mechanisms and exploring potential therapeutic opportunities. The review covers key topics such as mitochondrial DNA mutations, impaired oxidative phosphorylation, mitochondrial dynamics, calcium dysregulation, and reactive oxygen species generation in the context of brain disease. Additionally, it discusses emerging strategies targeting mitochondrial dysfunction, including mitochondrial protective agents, metabolic modulators, and gene therapy approaches. By critically analysing the existing literature and recent advancements, this review aims to enhance our understanding of the multifaceted role of mitochondria in brain disease and shed light on novel therapeutic interventions.

Cryopreservation Induces Acetylation of Metabolism-Related Proteins in Boar Sperm

Cryodamage affects the normal physiological functions and survivability of boar sperm during cryopreservation. Lysine acetylation is thought to be an important regulatory mechanism in sperm functions. However, little is known about protein acetylation and its effects on cryotolerance or cryodamage in boar sperm. In this study, the characterization and protein acetylation dynamics of boar sperm during cryopreservation were determined using liquid chromatography-mass spectrometry (LC-MS). A total of 1440 proteins were identified out of 4705 modified proteins, and 2764 quantifiable sites were elucidated. Among the differentially modified sites, 1252 were found to be upregulated compared to 172 downregulated sites in fresh and frozen sperms. Gene ontology indicated that these differentially modified proteins are involved in metabolic processes and catalytic and antioxidant activities, which are involved in pyruvate metabolism, phosphorylation and lysine degradation. In addition, the present study demonstrated that the mRNA and protein expressions of SIRT5, IDH2, MDH2 and LDHC, associated with sperm quality parameters, are downregulated after cryopreservation. In conclusion, cryopreservation induces the acetylation and deacetylation of energy metabolism-related proteins, which may contribute to the post-thawed boar sperm quality parameters.

Sirtuin-dependent metabolic and epigenetic regulation of macrophages during tuberculosis

Macrophages are the preeminent phagocytic cells which control multiple infections. Tuberculosis a leading cause of death in mankind and the causative organism Mycobacterium tuberculosis (MTB) infects and persists in macrophages. Macrophages use reactive oxygen and nitrogen species (ROS/RNS) and autophagy to kill and degrade microbes including MTB. Glucose metabolism regulates the macrophage-mediated antimicrobial mechanisms. Whereas glucose is essential for the growth of cells in immune cells, glucose metabolism and its downsteam metabolic pathways generate key mediators which are essential co-substrates for post-translational modifications of histone proteins, which in turn, epigenetically regulate gene expression. Herein, we describe the role of sirtuins which are NAD+-dependent histone histone/protein deacetylases during the epigenetic regulation of autophagy, the production of ROS/RNS, acetyl-CoA, NAD+, and S-adenosine methionine (SAM), and illustrate the cross-talk between immunometabolism and epigenetics on macrophage activation. We highlight sirtuins as emerging therapeutic targets for modifying immunometabolism to alter macrophage phenotype and antimicrobial function.

ADENOSINE MONOPHOSPHATE-ACTIVATED PROTEIN KINASE PHOSPHORYLATION MEDIATED BY SIRTUIN 5 ALLEVIATES SEPTIC ACUTE KIDNEY INJURY

ABSTRACT

Background : Our previous studies have shown that ameliorating mitochondrial damage in renal tubular epithelial cells (RTECs) can alleviate septic acute kidney injury (SAKI). It is reported that AMPK phosphorylation (p-AMPK) could ameliorate mitochondrial damage in renal tissue and Sirtuin 5 (SIRT5) overexpression significantly enhanced the level of p-AMPK in bovine preadipocytes. However, the role of SIRT5-mediated phosphorylation of AMPK in SAKI needs to be clarified. Methods : WT/SIRT5 gene knockout mouse model of cecal ligation and puncture-induced SAKI and a human kidney 2 cell model of LPS-induced SAKI were constructed. An AMPK chemical activator and SIRT5 overexpression plasmid were used. Indexes of mitochondrial structure and function, level of p-AMPK, and expression of SIRT5 protein in renal tissue and RTECs were measured. Results : After sepsis stimulation, the p-AMPK level was decreased, mitochondrial structure was disrupted, and ATP content was decreased. Notably, an AMPK activator alleviated SAKI. Sirtuin 5 gene knockout significantly aggravated SAKI, while SIRT5 overexpression alleviated mitochondrial dysfunction after LPS stimulation, as manifested by the increase of p-AMPK level, the alleviation of mitochondrial structure damage, the restoration of ATP content, the decrease of proapoptotic protein expression, as well as the reduction of reactive oxygen species generation. Conclusions : Upregulation of SIRT5 expression can attenuate mitochondrial dysfunction in RTECs and alleviate SAKI by enhancing the phosphorylation of AMPK.

Histone Deacetylases: Molecular Mechanisms and Therapeutic Implications for Muscular Dystrophies

Histone deacetylases (HDACs) are enzymes that regulate the deacetylation of numerous histone and non-histone proteins, thereby affecting a wide range of cellular processes. Deregulation of HDAC expression or activity is often associated with several pathologies, suggesting potential for targeting these enzymes for therapeutic purposes. For example, HDAC expression and activity are higher in dystrophic skeletal muscles. General pharmacological blockade of HDACs, by means of pan-HDAC inhibitors (HDACi), ameliorates both muscle histological abnormalities and function in preclinical studies. A phase II clinical trial of the pan-HDACi givinostat revealed partial histological improvement and functional recovery of Duchenne Muscular Dystrophy (DMD) muscles; results of an ongoing phase III clinical trial that is assessing the long-term safety and efficacy of givinostat in DMD patients are pending. Here we review the current knowledge about the HDAC functions in distinct cell types in skeletal muscle, identified by genetic and -omic approaches. We describe the signaling events that are affected by HDACs and contribute to muscular dystrophy pathogenesis by altering muscle regeneration and/or repair processes. Reviewing recent insights into HDAC cellular functions in dystrophic muscles provides new perspectives for the development of more effective therapeutic approaches based on drugs that target these critical enzymes.

Sirtuins and their influence on autophagy

Sirtuins and autophagy are well-characterized agents that can promote longevity and protect individual organisms from age-associated diseases like neurodegenerative disorders. In recent years, more and more data has been obtained that discerned potential overlaps and crosstalk between Sirtuin proteins and autophagic activity. This review aims to summarize the advances within the field for each individual Sirtuin in mammalian systems. In brief, most Sirtuins have been implicated in promoting autophagy, with Sirtuin 1 and Sirtuin 6 showing the highest immediate involvement, while Sirtuin 4 and Sirtuin 5 only demonstrate occasional influence. The way Sirtuins regulate autophagy, however, is very diverse, as they have been shown to regulate gene expression of autophagy-associated genes and posttranslational modifications of proteins, with consequences for the activity and cellular localization of these proteins. They have also been shown to determine specific proteins for autophagic degradation. Overall, much data has been accumulated over recent years, yet many open questions remain. Especially although the dynamic between Sirtuin proteins and the immediate regulation of autophagic players like Light Chain 3B has been confirmed, many of these proteins have various orthologues in mammalian systems, and research so far has not exceeded the bona fide components of autophagy.

Shedding light on structure, function and regulation of human sirtuins: a comprehensive review

Sirtuins play an important role in signalling pathways associated with various metabolic regulations. They possess mono-ADP-ribosyltransferase or deacylase activity like demalonylase, deacetylase, depalmitoylase, demyristoylase and desuccinylase activity. Sirtuins are histone deacetylases which depends upon nicotinamide adenine dinucleotide (NAD) that deacetylate lysine residues. There are a total of seven human sirtuins that have been identified namely, SIRT1, SIRT2, SIRT3, SIRT4, SIRT5, SIRT6 and SIRT7. The subcellular location of mammalian sirtuins, SIRT1, SIRT6, and SIRT7 are in the nucleus; SIRT3, SIRT4, and SIRT5 are in mitochondria, and SIRT2 is in cytoplasm. Structurally sirtuins contains a N-terminal, a C-terminal and a Zn+ binding domain. The sirtuin family has been found to be crucial for maintaining lipid and glucose homeostasis, and also for regulating insulin secretion and sensitivity, DNA repair pathways, neurogenesis, inflammation, and ageing. Based on the literature, sirtuins are overexpressed and play an important role in tumorigenicity in various types of cancer such as non-small cell lung cancer, colorectal cancer, etc. In this review, we have discussed about the different types of human sirtuins along with their structural and functional features. We have also discussed about the various natural and synthetic regulators of sirtuin activities like resveratrol. Our overall study shows that the correct regulation of sirtuins can be a good target for preventing and treating various diseases for improving the human lifespan. To investigate the true therapeutic potential of sirtuin proteins and their efficacy in a variety of pathological diseases, a better knowledge of the link between the structure and function of sirtuin proteins would be necessary.

An Epigenetic Role of Mitochondria in Cancer

Mitochondria are not only the main energy supplier but are also the cell metabolic center regulating multiple key metaborates that play pivotal roles in epigenetics regulation. These metabolites include acetyl-CoA, α-ketoglutarate (α-KG), S-adenosyl methionine (SAM), NAD⁺, and O-linked beta-N-acetylglucosamine (O-GlcNAc), which are the main substrates for DNA methylation and histone post-translation modifications, essential for gene transcriptional regulation and cell fate determination. Tumorigenesis is attributed to many factors, including gene mutations and tumor microenvironment. Mitochondria and epigenetics play essential roles in tumor initiation, evolution, metastasis, and recurrence. Targeting mitochondrial metabolism and epigenetics are promising therapeutic strategies for tumor treatment. In this review, we summarize the roles of mitochondria in key metabolites required for epigenetics modification and in cell fate regulation and discuss the current strategy in cancer therapies via targeting epigenetic modifiers and related enzymes in metabolic regulation. This review is an important contribution to the understanding of the current metabolic-epigenetic-tumorigenesis concept.

Delayed Impact of 2-Oxoadipate Dehydrogenase Inhibition on the Rat Brain Metabolism Is Linked to Protein Glutarylation

Background

The DHTKD1-encoded 2-oxoadipate dehydrogenase (OADH) oxidizes 2-oxoadipate—a common intermediate of the lysine and tryptophan catabolism. The mostly low and cell-specific flux through these pathways, and similar activities of OADH and ubiquitously expressed 2-oxoglutarate dehydrogenase (OGDH), agree with often asymptomatic phenotypes of heterozygous mutations in the DHTKD1 gene. Nevertheless, OADH/DHTKD1 are linked to impaired insulin sensitivity, cardiovascular disease risks, and Charcot-Marie-Tooth neuropathy. We hypothesize that systemic significance of OADH relies on its generation of glutaryl residues for protein glutarylation. Using pharmacological inhibition of OADH and the animal model of spinal cord injury (SCI), we explore this hypothesis.

Methods

The weight-drop model of SCI, a single intranasal administration of an OADH-directed inhibitor trimethyl adipoyl phosphonate (TMAP), and quantification of the associated metabolic changes in the rat brain employ established methods.

Results

The TMAP-induced metabolic changes in the brain of the control, laminectomized (LE) and SCI rats are long-term and (patho)physiology-dependent. Increased glutarylation of the brain proteins, proportional to OADH expression in the control and LE rats, represents a long-term consequence of the OADH inhibition. The proportionality suggests autoglutarylation of OADH, supported by our mass-spectrometric identification of glutarylated K155 and K818 in recombinant human OADH. In SCI rats, TMAP increases glutarylation of the brain proteins more than OADH expression, inducing a strong perturbation in the brain glutathione metabolism. The redox metabolism is not perturbed by TMAP in LE animals, where the inhibition of OADH increases expression of deglutarylase sirtuin 5. The results reveal the glutarylation-imposed control of the brain glutathione metabolism. Glutarylation of the ODP2 subunit of pyruvate dehydrogenase complex at K451 is detected in the rat brain, linking the OADH function to the brain glucose oxidation essential for the redox state. Short-term inhibition of OADH by TMAP administration manifests in increased levels of tryptophan and decreased levels of sirtuins 5 and 3 in the brain.

Conclusion

Pharmacological inhibition of OADH affects acylation system of the brain, causing long-term, (patho)physiology-dependent changes in the expression of OADH and sirtuin 5, protein glutarylation and glutathione metabolism. The identified glutarylation of ODP2 subunit of pyruvate dehydrogenase complex provides a molecular mechanism of the OADH association with diabetes.

Visualizing physiological parameters in cells and tissues using genetically encoded indicators for metabolites

The study of metabolism is undergoing a renaissance. Since the year 2002, over 50 genetically-encoded fluorescent indicators (GEFIs) have been introduced, capable of monitoring metabolites with high spatial/temporal resolution using fluorescence microscopy. Indicators are fusion proteins that change their fluorescence upon binding a specific metabolite. There are indicators for sugars, monocarboxylates, Krebs cycle intermediates, amino acids, cofactors, and energy nucleotides. They permit monitoring relative levels, concentrations, and fluxes in living systems. At a minimum they report relative levels and, in some cases, absolute concentrations may be obtained by performing ad hoc calibration protocols. Proper data collection, processing, and interpretation are critical to take full advantage of these new tools. This review offers a survey of the metabolic indicators that have been validated in mammalian systems. Minimally invasive, these indicators have been instrumental for the purposes of confirmation, rebuttal and discovery. We envision that this powerful technology will foster metabolic physiology.

Mitochondrial dynamics and biogenesis indicators may serve as potential biomarkers for diagnosis of myasthenia gravis

Due to challenges in diagnosing myasthenia gravis (MG), identifying novel diagnostic biomarkers for this disease is essential. Mitochondria are key organelles that regulate multiple physiological functions, such as energy production, cell proliferation and cell death. In the present study, Mfn1/2, Opa1, Drp1, Fis1, AMPK, PGC-1α, NRF-1 and TFAM were compared between patients with MG and healthy subjects to identify potential diagnostic biomarkers for MG. Blood samples were collected from 50 patients with MG and 50 healthy subjects. The participants' demographic information and routine blood test results were recorded. Mitochondrial dynamics were evaluated and levels of Mfn1/2, Opa1, Drp1, Fis1, AMPK, PGC-1α, NRF-1 and TFAM were determined in peripheral blood mononuclear cells using western blotting and reverse transcription-quantitative PCR, respectively. Receiver operating characteristic curve analysis was used to evaluate the diagnostic accuracy of these indicators. The areas under the curve values of Mfn1/2, Opa1, Drp1, Fis1,AMPK, PGC-1α, NRF-1 and TFAM were 0.5408-0.8696. Compared with control subjects, mRNA expression levels of Mfn1/2, Opa1, AMPK, PGC-1α, NRF-1 and TFAM were lower, while those of Drp1 and Fis1 were higher in patients with MG. The protein expression levels of all these molecules were lower in patients with MG than in control subjects. These results suggested that mitochondrial dynamics and biogenesis indicators may be diagnostic biomarkers for MG.

Sirtuin 5 promotes arterial thrombosis by blunting the fibrinolytic system

AIMS

Arterial thrombosis as a result of plaque rupture or erosion is a key event in acute cardiovascular events. Sirtuin 5 (SIRT5) belongs to the lifespan-regulating sirtuin superfamily and has been implicated in acute ischaemic stroke and cardiac hypertrophy. This project aims at investigating the role of SIRT5 in arterial thrombus formation.

METHODS AND RESULTS

Sirt5 transgenic (Sirt5Tg/0) and knock-out (Sirt5-/-) mice underwent photochemically induced carotid endothelial injury to trigger arterial thrombosis. Primary human aortic endothelial cells (HAECs) were treated with SIRT5 silencing-RNA (si-SIRT5) as well as peripheral blood mononuclear cells from acute coronary syndrome (ACS) patients and non-ACS controls (case-control study, total n = 171) were used to increase the translational relevance of our data. Compared to wild-type controls, Sirt5Tg/0 mice displayed accelerated arterial thrombus formation following endothelial-specific damage. Conversely, in Sirt5-/- mice, arterial thrombosis was blunted. Platelet function was unaltered, as assessed by ex vivo collagen-induced aggregometry. Similarly, activation of the coagulation cascade as assessed by vascular and plasma tissue factor (TF) and TF pathway inhibitor expression was unaltered. Increased thrombus embolization episodes and circulating D-dimer levels suggested augmented activation of the fibrinolytic system in Sirt5-/- mice. Accordingly, Sirt5-/- mice showed reduced plasma and vascular expression of the fibrinolysis inhibitor plasminogen activator inhibitor (PAI)-1. In HAECs, SIRT5-silencing inhibited PAI-1 gene and protein expression in response to TNF-α. This effect was mediated by increased AMPK activation and reduced phosphorylation of the MAP kinase ERK 1/2, but not JNK and p38 as shown both in vivo and in vitro. Lastly, both PAI-1 and SIRT5 gene expressions are increased in ACS patients compared to non-ACS controls after adjustment for cardiovascular risk factors, while PAI-1 expression increased across tertiles of SIRT5.

CONCLUSION

SIRT5 promotes arterial thrombosis by modulating fibrinolysis through endothelial PAI-1 expression. Hence, SIRT5 may be an interesting therapeutic target in the context of atherothrombotic events.

Preparation of Affinity Purified Antibodies against ε-Glutaryl-Lysine Residues in Proteins for Investigation of Glutarylated Proteins in Animal Tissues

The glutarylation of lysine residues in proteins attracts attention as a possible mechanism of metabolic regulation, perturbed in pathologies. The visualization of protein glutarylation by antibodies specific to ε-glutaryl-lysine residues may be particularly useful to reveal pathogenic mutations in the relevant enzymes. We purified such antibodies from the rabbit antiserum, obtained after sequential immunization with two artificially glutarylated proteins, using affinity chromatography on ε-glutaryl-lysine-containing sorbents. Employing these anti(ε-glutaryl-lysine)-antibodies for the immunoblotting analysis of rat tissues and mitochondria has demonstrated the sample-specific patterns of protein glutarylation. The study of the protein glutarylation in rat tissue homogenates revealed a time-dependent fragmentation of glutarylated proteins in these preparations. The process may complicate the investigation of potential changes in the acylation level of specific protein bands when studying time-dependent effects of the acylation regulators. In the rat brain, the protein glutarylation, succinylation and acetylation patterns obtained upon the immunoblotting of the same sample with the corresponding antibodies are shown to differ. Specific combinations of molecular masses of major protein bands in the different acylation patterns confirm the selectivity of the anti(ε-glutaryl-lysine)-antibodies obtained in this work. Hence, our affinity-purified anti(ε-glutaryllysine)-antibodies provide an effective tool to characterize protein glutarylation, revealing its specific pattern, compared to acetylation and succinylation, in complex protein mixtures.

Loss of the mitochondrial phosphate carrier SLC25A3 induces remodeling of the cardiac mitochondrial protein acylome

Mitochondria are recognized as signaling organelles because, under stress, mitochondria can trigger various signaling pathways to coordinate the cell's response. The specific pathway(s) engaged by mitochondria in response to mitochondrial energy defects in vivo and in high-energy tissues like the heart are not fully understood. Here, we investigated cardiac pathways activated in response to mitochondrial energy dysfunction by studying mice with cardiomyocyte-specific loss of the mitochondrial phosphate carrier (SLC25A3), an established model that develops cardiomyopathy as a result of defective mitochondrial ATP synthesis. Mitochondrial energy dysfunction induced a striking pattern of acylome remodeling, with significantly increased post-translational acetylation and malonylation. Mass spectrometry-based proteomics further revealed that energy dysfunction-induced remodeling of the acetylome and malonylome preferentially impacts mitochondrial proteins. Acetylation and malonylation modified a highly interconnected interactome of mitochondrial proteins, and both modifications were present on the enzyme isocitrate dehydrogenase 2 (IDH2). Intriguingly, IDH2 activity was enhanced in SLC25A3-deleted mitochondria, and further study of IDH2 sites targeted by both acetylation and malonylation revealed that these modifications can have site-specific and distinct functional effects. Finally, we uncovered a novel crosstalk between the two modifications, whereby mitochondrial energy dysfunction-induced acetylation of sirtuin 5 (SIRT5), inhibited its function. Because SIRT5 is a mitochondrial deacylase with demalonylase activity, this finding suggests that acetylation can modulate the malonylome. Together, our results position acylations as an arm of the mitochondrial response to energy dysfunction and suggest a mechanism by which focal disruption to the energy production machinery can have an expanded impact on global mitochondrial function.

SIRT5 Inhibition Induces Brown Fat-Like Phenotype in 3T3-L1 Preadipocytes

Brown adipose tissue (BAT) activity plays a key role in regulating systemic energy. The activation of BAT results in increased energy expenditure, making this tissue an attractive pharmacological target for therapies against obesity and type 2 diabetes. Sirtuin 5 (SIRT5) affects BAT function by regulating adipogenic transcription factor expression and mitochondrial respiration. We analyzed the expression of SIRT5 in the different adipose depots of mice. We treated 3T3-L1 preadipocytes and mouse primary preadipocyte cultures with the SIRT5 inhibitor MC3482 and investigated the effects of this compound on adipose differentiation and function. The administration of MC3482 during the early stages of differentiation promoted the expression of brown adipocyte and mitochondrial biogenesis markers. Upon treatment with MC3482, 3T3-L1 adipocytes showed an increased activation of the AMP-activated protein kinase (AMPK), which is known to stimulate brown adipocyte differentiation. This effect was paralleled by an increase in autophagic/mitophagic flux and a reduction in lipid droplet size, mediated by a higher lipolytic rate. Of note, MC3482 increased the expression and the activity of adipose triglyceride lipase, without modulating hormone-sensitive lipase. Our findings reveal that SIRT5 inhibition stimulates brown adipogenesis in vitro, supporting this approach as a strategy to stimulate BAT and counteract obesity.

Mitochondrial sirtuins in stem cells and cancer

The mammalian sirtuin family consists of seven proteins, three of which (SIRT3, SIRT4, and SIRT5) localise specifically within mitochondria and preserve mitochondrial function and homeostasis. Mitochondrial sirtuins are involved in diverse functions such as deacetylation, ADP-ribosylation, demalonylation and desuccinylation, thus affecting various aspects of cell fate. Intriguingly, mitochondrial sirtuins are able to manage these delicate processes with accuracy mediated by crosstalk between the nucleus and mitochondria. Previous studies have provided ample information about their substrates and targets, whereas less is known about their role in cancer and stem cells. Here, we review and discuss recent advances in our understanding of the structural and functional properties of mitochondrial sirtuins, including their targets in cancer and stem cells. These advances could help to improve the understanding of their interplay with signalling cascades and pathways, leading to new avenues for developing novel drugs for sirtuin-related disease treatments. We also highlight the complex network of mitochondrial sirtuins in cancer and stem cells, which may be important in deciphering the molecular mechanism for their activation and inhibition.

The possible role of sirtuin 5 in the pathogenesis of apical periodontitis

OBJECTIVES

We investigated the relation between expression of sirtuin 5 (SIRT5) in osteoblastic cells and progression of apical periodontitis. The role of SIRT5 in hypoxia-induced reactive oxygen species (ROS) formation and osteoblast apoptosis was also examined.

MATERIALS AND METHODS

Progression of rat apical periodontitis was monitored by conventional radiography and microcomputed tomography. SIRT5 and oxidative stress biomarker 8-OHdG in bone-lining cells were assessed by immunohistochemistry. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling was used to demonstrate apoptosis. In primary human osteoblasts cultured under hypoxia, Western blot was used to analyze SIRT5 expression and cleavage of pro-caspase 3 and poly(ADP-ribose) polymerase (PARP). SIRT5 was overexpressed through lentiviral technique. ROS formation and mitochondrial membrane potential changes were assessed by MitoSOX-Red and JC-1 fluorescence, respectively. Immunofluorescence microscope was used to evaluate mitochondrial release of cytochrome c.

RESULTS

In rat apical periodontitis, disease progression was accompanied by decreased expression of SIRT5, increased oxidative stress, and enhanced apoptosis in bone-lining cells. SIRT5 was suppressed in cultured osteoblasts under hypoxia. SIRT5 overexpression ameliorated hypoxia-enhanced ROS formation, mitochondrial depolarization, cytochrome c leakage, activation of caspase-3, and PARP fragmentation.

CONCLUSIONS

SIRT5 is able to alleviate hypoxia-enhanced osteoblast apoptosis. SIRT5 augmentation may have therapeutic potential for apical periodontitis.

The Roles of Histone Deacetylases and Their Inhibitors in Cancer Therapy

Genetic mutations and abnormal gene regulation are key mechanisms underlying tumorigenesis. Nucleosomes, which consist of DNA wrapped around histone cores, represent the basic units of chromatin. The fifth amino group (Nε) of histone lysine residues is a common site for post-translational modifications (PTMs), and of these, acetylation is the second most common. Histone acetylation is modulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs), and is involved in the regulation of gene expression. Over the past two decades, numerous studies characterizing HDACs and HDAC inhibitors (HDACi) have provided novel and exciting insights concerning their underlying biological mechanisms and potential anti-cancer treatments. In this review, we detail the diverse structures of HDACs and their underlying biological functions, including transcriptional regulation, metabolism, angiogenesis, DNA damage response, cell cycle, apoptosis, protein degradation, immunity and other several physiological processes. We also highlight potential avenues to use HDACi as novel, precision cancer treatments.

AMPK, Mitochondrial Function, and Cardiovascular Disease

Adenosine monophosphate-activated protein kinase (AMPK) is in charge of numerous catabolic and anabolic signaling pathways to sustain appropriate intracellular adenosine triphosphate levels in response to energetic and/or cellular stress. In addition to its conventional roles as an intracellular energy switch or fuel gauge, emerging research has shown that AMPK is also a redox sensor and modulator, playing pivotal roles in maintaining cardiovascular processes and inhibiting disease progression. Pharmacological reagents, including statins, metformin, berberine, polyphenol, and resveratrol, all of which are widely used therapeutics for cardiovascular disorders, appear to deliver their protective/therapeutic effects partially via AMPK signaling modulation. The functions of AMPK during health and disease are far from clear. Accumulating studies have demonstrated crosstalk between AMPK and mitochondria, such as AMPK regulation of mitochondrial homeostasis and mitochondrial dysfunction causing abnormal AMPK activity. In this review, we begin with the description of AMPK structure and regulation, and then focus on the recent advances toward understanding how mitochondrial dysfunction controls AMPK and how AMPK, as a central mediator of the cellular response to energetic stress, maintains mitochondrial homeostasis. Finally, we systemically review how dysfunctional AMPK contributes to the initiation and progression of cardiovascular diseases via the impact on mitochondrial function.

Impacts of Aerobic Exercise on Depression-Like Behaviors in Chronic Unpredictable Mild Stress Mice and Related Factors in the AMPK/PGC-1α Pathway

This study was to study the impact of aerobic exercises on the chronic unpredictable mild stress (CUMS) in mice, and to discuss the possible mechanism from the skeletal muscle AMPK/PGC-1α energy metabolism signaling pathway. The healthy male mice were randomly divided into Control Group (CG), Model Group (MG), and Model Exercise Group (ME).Twelve stress methods were adopted for four weeks (28 days) to establish the depression model. ME was subject to aerobic training plan after the model was established. The weight of the mice was recorded weekly. After the experimental intervention, the three groups of mice were subjected to behavioral assessment tests. Western blotting, RT-PCR, and ELISA were performed to test AMPK, p-AMPK, PGC-1α, and ATP in skeletal muscle. There were no significant difference in body weight between the three groups. CUMS leaded to significant decline in behavioral scores. and the p-AMPK and PGC-1α decreased significantly. But boosted ATP content. Aerobic exercise enhanced the expressions of p-AMPK and PGC-1α, increased the ratio of p-AMPK/AMPK, boosted ATP content. And improved behavioral scores significantly. Chronic stress-induced depression-like behavior was improved significantly by Aerobic exercise. The mechanism of aerobic exercise for improving depressive symptoms in mice with chronic stress depression may be related to influence AMPK/PGC-1α pathway.

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.

Mitohormesis and metabolic health: The interplay between ROS, cAMP and sirtuins

The key role of mitochondria in oxidative metabolism and redox homeostasis explains the link between mitochondrial dysfunction and the development of metabolic disorders. Mitochondria's highly dynamic nature, based on alterations in biogenesis, mitophagy, fusion and fission, allows adjusting sequential redox reactions of the electron transport chain (ETC) and dissipation of the membrane potential by ATP synthase, to different environmental cues. With reactive oxygen species being an inevitable by-product of oxidative phosphorylation (OXPHOS), alterations on mitochondrial oxidative rate with a consequent excessive load of reactive oxygen species have been traditionally associated with pathological conditions. However, reactive oxygen species have also been suggested as promoters of mitohormesis, a process in which low, non-cytotoxic concentrations of reactive oxygen species promote mitochondrial homeostasis. Therefore, signaling systems involved in the regulation of mitochondrial homeostasis are attractive candidates for drug development for metabolic diseases triggered by mitochondrial dysfunction. Reversible phosphorylation downstream the cyclic AMP (cAMP) signaling cascade and deacetylation mediated by sirtuins are recognized as major mitochondrial regulators.

Gender Differences in Cardiac Hypertrophy

Cardiac hypertrophy is an adaptive response to abnormal physiological and pathological stimuli, which can be classified into concentric and eccentric hypertrophy, induced by pressure overload or volume overload, respectively. In both physiological and pathological scenarios, females generally show a more favorable form of hypertrophy compared with their male counterparts. However once established, cardiac hypertrophy is a stronger risk factor for heart failure in females. Pre-menopausal women are better protected against cardiac hypertrophy compared with men, but this protection is abolished following menopause and is partially restored after estrogen replacement therapy. Estrogen exerts its protection by counteracting pro-hypertrophy signaling pathways, whereas androgen mostly plays an opposite role in cardiac hypertrophy. We here summarize the progress in the understanding of sexual dimorphisms in cardiac hypertrophy and highlight recent breakthroughs in the regulatory role of sex hormones and their intricate molecular networks, in order to shed light on gender-oriented therapeutic efficacy for pathological hypertrophy.

Role of Phosphorylated AMP-Activated Protein Kinase (AMPK) in Myocardial Insulin Resistance After Myocardial Ischemia-Reperfusion During Cardiopulmonary Bypass Surgery in Dogs

Background

The aim of this study was to determine the role of AMP-activated protein kinase (AMPK) in myocardial insulin resistance after myocardial ischemia-reperfusion during cardiopulmonary bypass surgery in dogs.

Material/Methods

Twenty-four mongrel dogs were randomly assigned to 4 groups. The control group did not undergo aortic cross-clamping; the model group underwent 60 mins of aortic cross-clamping with 150 ml cardioplegic solution. The treatment group, the inhibition group respectively with 0.11mg/kg AICAR (AMPK agonist) in 150 ml cardioplegic solution and 0.11 mg/kg Compound C (AMPK inhibitor) in 150 ml cardioplegic solution. The blood flow was determined and left ventricular myocardial tissue were taken at pre-bypass, 15, 60, and 90 min after aorta declamping, respectively. Expression of AMPK mRNA, p-AMPK and GLUT-4 proteins was determined by RT-PCR, IHC and WB.

Results

Compared with the control group, receiving 60 min ischemia at 15 min after reperfusion, Myocardial Glucose Extraction Ratio were significantly decreased in the other 3 groups, it was significantly decreased from 20.0% to 1.2% at 60 min of reperfusion, and recovered to 6.1% after 90 min reperfusion in model group, while recovered to 4.1%, 12.0% after 90 min reperfusion respectively exposed to Compound C and AICAR. The expressions of p-AMPK, GLUT-4 protein and AMPK mRNA in myocardium were decreased in different experiment groups, but these changes occurred to a lesser extent in the treatment group.

Conclusions

The inability of GLUT-4 expression induced by the decreases in p-AMPK protein expression that may be one of the reasons for myocardial insulin resistance.