SIRT3 mediates multi-tissue coupling for metabolic fuel switching

Sirtuin 3 regulates astrocyte activation by reducing Notch1 signaling after status epilepticus

Sirtuin3 (Sirt3) is a nicotinamide adenine dinucleotide enzyme that contributes to aging, cancer, and neurodegenerative diseases. Recent studies have reported that Sirt3 exerts anti-inflammatory effects in several neuropathophysiological disorders. As epilepsy is a common neurological disease, in the present study, we investigated the role of Sirt3 in astrocyte activation and inflammatory processes after epileptic seizures. We found the elevated expression of Sirt3 within reactive astrocytes as well as in the surrounding cells in the hippocampus of patients with temporal lobe epilepsy and a mouse model of pilocarpine-induced status epilepticus (SE). The upregulation of Sirt3 by treatment with adjudin, a potential Sirt3 activator, alleviated SE-induced astrocyte activation; whereas, Sirt3 deficiency exacerbated astrocyte activation in the hippocampus after SE. In addition, our results showed that Sirt3 upregulation attenuated the activation of Notch1 signaling, nuclear factor kappa B (NF-κB) activity, and the production of interleukin-1β (IL1β) in the hippocampus after SE. By contrast, Sirt3 deficiency enhanced the activity of Notch1/NF-κB signaling and the production of IL1β. These findings suggest that Sirt3 regulates astrocyte activation by affecting the Notch1/NF-κB signaling pathway, which contributes to the inflammatory response after SE. Therefore, therapies targeting Sirt3 may be a worthy direction for limiting inflammatory responses following epileptic brain injury.

Mitochondrial Chaperone Code: Just warming up

More than 99% of the mitochondrial proteome is encoded by the nucleus and requires refolding following import. Therefore, mitochondrial proteins require the coordinated action of molecular chaperones for their folding and activation. Several heat shock protein (Hsp) molecular chaperones, including members of the Hsp27, Hsp40/70, and Hsp90 families, as well as the chaperonin complex Hsp60/10 have an established role in mitochondrial protein import and folding. The "Chaperone Code" describes the regulation of chaperone activity by dynamic post-translational modifications; however, little is known about the post-translational regulation of mitochondrial chaperones. Dissecting the regulation of chaperone function is essential for understanding their differential regulation in pathogenic conditions and the potential development of efficacious therapeutic strategies. Here, we summarize the recent literature on post-translational regulation of mitochondrial chaperones, the consequences for mitochondrial function, and potential implications for disease.

KN-93 promotes HDAC4 nucleus translocation to promote fatty acid oxidation in myocardial infarction

Myocardial infarction (MI) is a potentially fatal disease that causes a significant number of deaths worldwide. The strategy of increasing fatty acid oxidation in myocytes is considered a therapeutic avenue to accelerate metabolism to meet energy demands. We conducted the study aiming to investigate the effect of KN-93, which induces histone deacetylase (HDAC)4 shuttling to the nucleus, on fatty acid oxidation and the expression of related genes. A mouse model of myocardial infarction was induced by isoprenaline administration. Heart damage was assessed by the detection of cardiac injury markers. The level of fatty acid oxidation level was evaluated by testing the expression of related genes. Both immunofluorescence and immunoblotting in the cytosol or nucleus were utilized to observe the distribution of HDAC4. The interaction between HDAC4 and specificity protein (SP)1 was confirmed by co-immunoprecipitation. The acetylation level of SP1 was tested after KN-93 treatment and HDAC4 inhibitor. Oxygen consumption rate and immunoblotting experiments were used to determine whether the effect of KN-93 on increasing fatty acid oxidation is through HDAC4 and SP1. Administration of KN-93 significantly reduced cardiac injury in myocardial infarction and promoted fatty acid oxidation both in vitro and in vivo. KN-93 was shown to mediate nuclear translocation of HDAC4. HDAC4 was found to interact with SP1 and reduce SP1 acetylation. HDAC4 or SP1 inhibitors attenuated the effect of KN-93 on fatty acid oxidation. In conclusion, KN-93 promotes HDAC4 translocation to the nucleus, thereby potentially enhancing fatty acid oxidation by SP1.

SIRT3: A potential therapeutic target for liver fibrosis

Sirtuin3 (SIRT3) is a nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylase located in the mitochondria, which mainly regulates the acetylation of mitochondrial proteins. In addition, SIRT3 is involved in critical biological processes, including oxidative stress, inflammation, DNA damage, and apoptosis, all of which are closely related to the progression of liver disease. Liver fibrosis characterized by the deposition of extracellular matrix is a result of long termed or repeated liver damage, frequently accompanied by damaged hepatocytes, the recruitment of inflammatory cells, and the activation of hepatic stellate cells. Based on the functions and pharmacology of SIRT3, we will review its roles in liver fibrosis from three aspects: First, the main functions and pharmacological effects of SIRT3 were investigated based on its structure. Second, the roles of SIRT3 in major cells in the liver were summarized to reveal its mechanism in developing liver fibrosis. Last, drugs that regulate SIRT3 to prevent and treat liver fibrosis were discussed. In conclusion, exploring the pharmacological effects of SIRT3, especially in the liver, may be a potential strategy for treating liver fibrosis.

Sirtuins in kidney health and disease

Sirtuins (SIRTs) are putative regulators of lifespan in model organisms. Since the initial discovery that SIRTs could promote longevity in nematodes and flies, the identification of additional properties of these proteins has led to understanding of their roles as exquisite sensors that link metabolic activity to oxidative states. SIRTs have major roles in biological processes that are important in kidney development and physiological functions, including mitochondrial metabolism, oxidative stress, autophagy, DNA repair and inflammation. Furthermore, altered SIRT activity has been implicated in the pathophysiology and progression of acute and chronic kidney diseases, including acute kidney injury, diabetic kidney disease, chronic kidney disease, polycystic kidney disease, autoimmune diseases and renal ageing. The renoprotective roles of SIRTs in these diseases make them attractive therapeutic targets. A number of SIRT-activating compounds have shown beneficial effects in kidney disease models; however, further research is needed to identify novel SIRT-targeting strategies with the potential to treat and/or prevent the progression of kidney diseases and increase the average human healthspan.

Cardiomyocyte-specific deletion of GCN5L1 reduces lysine acetylation and attenuates diastolic dysfunction in aged mice by improving cardiac fatty acid oxidation

Cardiac mitochondrial dysfunction is a critical contributor to the pathogenesis of aging and many age-related conditions. As such, complete control of mitochondrial function is critical to maintain cardiac efficiency in the aged heart. Lysine acetylation is a reversible post-translational modification shown to regulate several mitochondrial metabolic and biochemical processes. In the present study, we investigated how mitochondrial lysine acetylation regulates fatty acid oxidation (FAO) and cardiac function in the aged heart. We found a significant increase in mitochondrial protein acetylation in the aged heart which correlated with increased level of mitochondrial acetyltransferase-related protein GCN5L1. We showed that acetylation status of several fatty acid and glucose oxidation enzymes (long-chain acyl-coenzyme A dehydrogenase, hydroxyacyl-coA dehydrogenase, and pyruvate dehydrogenase) were significantly up-regulated in aged heart which correlated with decreased enzymatic activities. Using a cardiac-specific GCN5L1 knockout (KO) animal model, we showed that overall acetylation of mitochondrial proteins was decreased in aged KO animals, including FAO proteins which led to improved FAO activity and attenuated cardiac diastolic dysfunction observed in the aged heart. Together, these findings indicate that lysine acetylation regulates FAO in the aged heart which results in improved cardiac diastolic function and this is in part regulated by GCN5L1.

Sirt3 Protects Retinal Pigment Epithelial Cells From High Glucose-Induced Injury by Promoting Mitophagy Through the AMPK/mTOR/ULK1 Pathway

Purpose

The regulation of mitophagy by Sirt3 has rarely been studied in ocular diseases. In the present study, we determined the effects of Sirt3 on AMPK/mTOR/ULK1 signaling pathway-mediated mitophagy in retinal pigment epithelial (RPE) cells in a high glucose environment.

Methods

The mRNA expression levels of Sirt3, AMPK, mTOR, ULK1, and LC3B in RPE cells under varying glucose conditions were measured by real-time polymerase chain reaction (RT-PCR). The expressions of Sirt3, mitophagy protein, and AMPK/mTOR/ULK1 signaling pathway-related proteins were detected by Western blotting. Lentivirus (LV) transfection mediated the stable overexpression of Sirt3 in cell lines. The experimental groups were NG (5.5 mM glucose), hypertonic, HG (30 mM glucose), HG + LV-GFP, and HG + LV-Sirt3. Western blotting was performed to detect the expressions of mitophagy proteins and AMPK/mTOR/ULK1-related proteins in a high glucose environment during the overexpression of Sirt3. Reactive oxygen species (ROS) production in a high glucose environment was measured by DCFH-DA staining. Mitophagy was detected by labeling mitochondria and lysosomes with MitoTracker and LysoTracker probes, respectively. Apoptosis was detected by flow cytometry.

Results

Sirt3 expression was reduced in the high glucose group, inhibiting the AMPK/mTOR/ULK1 pathway, with diminished mitophagy and increased intracellular ROS production. The overexpression of Sirt3, increased expression of p-AMPK/AMPK and p-ULK1/ULK1, and decreased expression of p-mTOR/mTOR inhibited cell apoptosis and enhanced mitophagy.

Conclusions

Sirt3 protected RPE cells from high glucose-induced injury by activating the AMPK/mTOR/ULK1 signaling pathway.

Translational Relevance

By identifying new targets of action, we aimed to establish effective therapeutic targets for diabetic retinopathy treatment.

Indole-3-Propionic Acid Protects Against Heart Failure With Preserved Ejection Fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is a common but poorly understood form of heart failure, characterized by impaired diastolic function. It is highly heterogeneous with multiple comorbidities, including obesity and diabetes, making human studies difficult.

METHODS

Metabolomic analyses in a mouse model of HFpEF showed that levels of indole-3-propionic acid (IPA), a metabolite produced by gut bacteria from tryptophan, were reduced in the plasma and heart tissue of HFpEF mice as compared with controls. We then examined the role of IPA in mouse models of HFpEF as well as 2 human HFpEF cohorts.

RESULTS

The protective role and therapeutic effects of IPA were confirmed in mouse models of HFpEF using IPA dietary supplementation. IPA attenuated diastolic dysfunction, metabolic remodeling, oxidative stress, inflammation, gut microbiota dysbiosis, and intestinal epithelial barrier damage. In the heart, IPA suppressed the expression of NNMT (nicotinamide N-methyl transferase), restored nicotinamide, NAD+/NADH, and SIRT3 (sirtuin 3) levels. IPA mediates the protective effects on diastolic dysfunction, at least in part, by promoting the expression of SIRT3. SIRT3 regulation was mediated by IPA binding to the aryl hydrocarbon receptor, as Sirt3 knockdown diminished the effects of IPA on diastolic dysfunction in vivo. The role of the nicotinamide adenine dinucleotide circuit in HFpEF was further confirmed by nicotinamide supplementation, Nnmt knockdown, and Nnmt overexpression in vivo. IPA levels were significantly reduced in patients with HFpEF in 2 independent human cohorts, consistent with a protective function in humans, as well as mice.

CONCLUSIONS

Our findings reveal that IPA protects against diastolic dysfunction in HFpEF by enhancing the nicotinamide adenine dinucleotide salvage pathway, suggesting the possibility of therapeutic management by either altering the gut microbiome composition or supplementing the diet with IPA.

SIRT3/6: an amazing challenge and opportunity in the fight against fibrosis and aging

Fibrosis is a typical aging-related pathological process involving almost all organs, including the heart, kidney, liver, lung, and skin. Fibrogenesis is a highly orchestrated process defined by sequences of cellular response and molecular signals mechanisms underlying the disease. In pathophysiologic conditions associated with organ fibrosis, a variety of injurious stimuli such as metabolic disorders, epigenetic changes, and aging may induce the progression of fibrosis. Sirtuins protein is a kind of deacetylase which can regulate cell metabolism and participate in a variety of cell physiological functions. In this review, we outline our current understanding of common principles of fibrogenic mechanisms and the functional role of SIRT3/6 in aging-related fibrosis. In addition, sequences of novel protective strategies have been identified directly or indirectly according to these mechanisms. Here, we highlight the role and biological function of SIRT3/6 focus on aging fibrosis, as well as their inhibitors and activators as novel preventative or therapeutic interventions for aging-related tissue fibrosis.

Bushen Tianjing Recipe inhibits human ovarian granulosa cell line KGN apoptosis induced by miR-23a through the regulation of the sirtuin family

ETHNOPHARMACOLOGICAL RELEVANCE

Bushen Tianjing Recipe (BTR) is a tonic-kidney formula of Traditional Chinese Medicine (TCM) with good therapeutic effects in clinical settings. It was mainly applied to inhibit the decrease of ovarian reserve function in patients. However, the anti-apoptosis mechanism of BTR remains unknown.

AIM OF THE STUDY

The formula of BTR is composed of prepared rehmannia root, debark peony root, carapax testudinis and asiatic cornelian cherry fruit. All four components contain the essences of nourishing yin and tonic-kidney. In the theory of TCM, the kidneys store the essence and are primarily responsible for reproduction and development. Hence, we speculated that BTR had some effect on women's reproductive system. In our research, rat serum contains BTR resolved into culture medium for incubation with miR-23a-induced KGN cells to test and determine our hypothesis.

MATERIALS AND METHODS

BTR was prepared by the traditional decoction method to collect concentrated liquids for oral administration to rats (15.00 g/kg) for 14 days. The group with miR-23a-induced KGN cells was selected as the positive control, while the mimic one was the control. Pro-apoptosis and anti-apoptosis biomarkers were detected and analyzed by western blot together with upstream transcription factors and intracellular apoptotic signal pathways.

RESULTS

The medium- and high-concentration of BRT greatly reduced the apoptosis of miR-23a-induced KGN cells both in mitochondria and cytoplasm. It showed the up-regulation of SIRT1 and SIRT3, the down-regulation of pro-apoptosis factor Bax and apoptotic-related proteins Caspase 3, 8, 9, and the reduction of phosphorylation of ERK1/2 and NF-κB. however, there was no consistency in the group with a low concentration of BTR, compared with those of other groups.

CONCLUSION

Our research verified that BTR had a positive effect on women's reproductive system under medium or high concentration, illuminated the intrinsic mechanism at molecular levels, and convinced its potential application values in clinical settings.

Sirtuin3 ensures the metabolic plasticity of neurotransmission during glucose deprivation

Neurotransmission is an energetically expensive process that underlies cognition. During intense electrical activity or dietary restrictions, the glucose level in the brain plummets, forcing neurons to utilize alternative fuels. However, the molecular mechanisms of neuronal metabolic plasticity remain poorly understood. Here, we demonstrate that glucose-deprived neurons activate the CREB and PGC1α transcriptional program, which induces expression of the mitochondrial deacetylase Sirtuin 3 (Sirt3) both in vitro and in vivo. We show that Sirt3 localizes to axonal mitochondria and stimulates mitochondrial oxidative capacity in hippocampal nerve terminals. Sirt3 plays an essential role in sustaining synaptic transmission in the absence of glucose by providing metabolic support for the retrieval of synaptic vesicles after release. These results demonstrate that the transcriptional induction of Sirt3 facilitates the metabolic plasticity of synaptic transmission.

Sirtuin 3 is required for the dexmedetomidine-mediated alleviation of inflammation and oxidative stress in nephritis

INTRODUCTION

Although sirtuin 3 (SIRT3) is known to be involved in dexmedetomidine (DEX)-mediated alleviation of renal ischemia and reperfusion injury, the influence of the association between DEX and SIRT3 on nephritis development remains unclear. In this study, the role of SIRT3 in DEX-mediated amelioration of inflammation and oxidative stress in nephritis as well as the possible underlying mechanism were explored in vivo and in vitro.

METHODS

An animal model of glomerulonephritis was generated by injecting mice with interferon-alpha (IFNα)-expressing adenoviruses, and periodic acid-Schiff staining was then used to reveal pathogenicity-related changes in the renal tissue. Additionally, human embryonic kidney cells (HEK293) and renal mesangial cells (RMCs) were treated with IFNα to establish cell models of inflammation in vitro.

RESULTS

DEX administration alleviated glomerulonephritis in the animal model and upregulated SIRT3 expression in the renal tissue. SIRT3 knockdown inhibited the renoprotective effects of DEX against nephritis. IFNα induced inflammation, oxidative stress, and apoptosis in the RMCs and HEK293 cells and reduced their growth, as evidenced by the evaluation of cytokine levels (enzyme-linked immunosorbent assay), reactive oxygen species generation, catalase and superoxide dismutase activities, nuclear factor-erythroid factor 2-related factor 2/heme oxygenase-1 signal transduction, apoptotic cell proportion, and cell viability. In addition to promoting SIRT3 expression, DEX inhibited IFNα-induced inflammation, oxidative stress, and apoptosis in these cells and promoted their viability. SIRT3 knockdown partially reversed the beneficial effects of DEX on RMCs and HEK293 cells.

CONCLUSIONS

Our results suggest that DEX exhibits renoprotective activity during nephritis progression, protecting renal cells against inflammatory injury by promoting SIRT3 expression.

Assessing the Role of Post-Translational Modifications of Mitochondrial RNA Polymerase

The mitochondrial proteome is subject to abundant post-translational modifications, including lysine acetylation and phosphorylation of serine, threonine, and tyrosine. The biological function of the majority of these protein modifications is unknown. Proteins required for the transcription and translation of mitochondrial DNA (mtDNA) are subject to modification. This suggests that reversible post-translational modifications may serve as a regulatory mechanism for mitochondrial gene transcription, akin to mechanisms controlling nuclear gene expression. We set out to determine whether acetylation or phosphorylation controls the function of mitochondrial RNA polymerase (POLRMT). Mass spectrometry was used to identify post-translational modifications on POLRMT. We analyzed three POLRMT modification sites (lysine 402, threonine 315, threonine 993) found in distinct structural regions. Amino acid point mutants that mimic the modified and unmodified forms of POLRMT were employed to measure the effect of acetylation or phosphorylation on the promoter binding ability of POLRMT in vitro. We found a slight decrease in binding affinity for the phosphomimic at threonine 315. We did not identify large changes in viability, mtDNA content, or mitochondrial transcript level upon overexpression of POLRMT modification mimics in HeLa cells. Our results suggest minimal biological impact of the POLRMT post-translational modifications studied in our system.

Honokiol, an inducer of sirtuin-3, protects against non-steroidal anti-inflammatory drug-induced gastric mucosal mitochondrial pathology, apoptosis and inflammatory tissue injury

BACKGROUND AND PURPOSE

Mitochondrial oxidative stress, inflammation and apoptosis primarily underlie gastric mucosal injury caused by the widely used non-steroidal anti-inflammatory drugs (NSAIDs). Alternative gastroprotective strategies are therefore needed. Sirtuin-3 pivotally maintains mitochondrial structural integrity and metabolism while preventing oxidative stress; however, its relevance to gastric injury was never explored. Here, we have investigated whether and how sirtuin-3 stimulation by the phytochemical, honokiol, could rescue NSAID-induced gastric injury.

EXPERIMENTAL APPROACH

Gastric injury in rats induced by indomethacin was used to assess the effects of honokiol. Next-generation sequencing-based transcriptomics followed by functional validation identified the gastroprotective function of sirtuin-3. Flow cytometry, immunoblotting, qRT-PCR and immunohistochemistry were used measure effects on oxidative stress, mitochondrial dynamics, electron transport chain function, and markers of inflammation and apoptosis. Sirtuin-3 deacetylase activity was also estimated and gastric luminal pH was measured.

KEY RESULTS

Indomethacin down-regulated sirtuin-3 to induce oxidative stress, mitochondrial hyperacetylation, 8-oxoguanine DNA glycosylase 1 depletion, mitochondrial DNA damage, respiratory chain defect and mitochondrial fragmentation leading to severe mucosal injury. Indomethacin dose-dependently inhibited sirtuin-3 deacetylase activity. Honokiol prevented mitochondrial oxidative damage and inflammatory tissue injury by attenuating indomethacin-induced depletion of both sirtuin-3 and its transcriptional regulators PGC1α and ERRα. Honokiol also accelerated gastric wound healing but did not alter gastric acid secretion, unlike lansoprazole.

CONCLUSIONS AND IMPLICATIONS

Sirtuin-3 stimulation by honokiol prevented and reversed NSAID-induced gastric injury through maintaining mitochondrial integrity. Honokiol did not affect gastric acid secretion. Sirtuin-3 stimulation by honokiol may be utilized as a mitochondria-based, acid-independent novel gastroprotective strategy against NSAIDs.

A global view of the human post-translational modification landscape

Post-translational modifications (PTMs) provide a rapid response to stimuli, finely tuning metabolism and gene expression and maintain homeostasis. Advances in mass spectrometry over the past two decades have significantly expanded the list of known PTMs in biology and as instrumentation continues to improve, this list will surely grow. While many PTMs have been studied in detail (e.g. phosphorylation, acetylation), the vast majority lack defined mechanisms for their regulation and impact on cell fate. In this review, we will highlight the field of PTM research as it currently stands, discussing the mechanisms that dictate site specificity, analytical methods for their detection and study, and the chemical tools that can be leveraged to define PTM regulation. In addition, we will highlight the approaches needed to discover and validate novel PTMs. Lastly, this review will provide a starting point for those interested in PTM biology, providing a comprehensive list of PTMs and what is known regarding their regulation and metabolic origins.

Mitochondrial heterogeneity in diseases

As key organelles involved in cellular metabolism, mitochondria frequently undergo adaptive changes in morphology, components and functions in response to various environmental stresses and cellular demands. Previous studies of mitochondria research have gradually evolved, from focusing on morphological change analysis to systematic multiomics, thereby revealing the mitochondrial variation between cells or within the mitochondrial population within a single cell. The phenomenon of mitochondrial variation features is defined as mitochondrial heterogeneity. Moreover, mitochondrial heterogeneity has been reported to influence a variety of physiological processes, including tissue homeostasis, tissue repair, immunoregulation, and tumor progression. Here, we comprehensively review the mitochondrial heterogeneity in different tissues under pathological states, involving variant features of mitochondrial DNA, RNA, protein and lipid components. Then, the mechanisms that contribute to mitochondrial heterogeneity are also summarized, such as the mutation of the mitochondrial genome and the import of mitochondrial proteins that result in the heterogeneity of mitochondrial DNA and protein components. Additionally, multiple perspectives are investigated to better comprehend the mysteries of mitochondrial heterogeneity between cells. Finally, we summarize the prospective mitochondrial heterogeneity-targeting therapies in terms of alleviating mitochondrial oxidative damage, reducing mitochondrial carbon stress and enhancing mitochondrial biogenesis to relieve various pathological conditions. The possibility of recent technological advances in targeted mitochondrial gene editing is also discussed.

Hepatic steatosis is associated with dysregulated cholesterol metabolism and altered protein acetylation dynamics in chickens

BACKGROUND

Hepatic steatosis is a prevalent manifestation of fatty liver, that has detrimental effect on the health and productivity of laying hens, resulting in economic losses to the poultry industry. Here, we aimed to systematically investigate the genetic regulatory mechanisms of hepatic steatosis in laying hens.

METHODS

Ninety individuals with the most prominent characteristics were selected from 686 laying hens according to the accumulation of lipid droplets in the liver, and were graded into three groups, including the control, mild hepatic steatosis and severe hepatic steatosis groups. A combination of transcriptome, proteome, acetylome and lipidome analyses, along with bioinformatics analysis were used to screen the key biological processes, modifications and lipids associated with hepatic steatosis.

RESULTS

The rationality of the hepatic steatosis grouping was verified through liver biochemical assays and RNA-seq. Hepatic steatosis was characterized by increased lipid deposition and multiple metabolic abnormalities. Integration of proteome and acetylome revealed that differentially expressed proteins (DEPs) interacted with differentially acetylated proteins (DAPs) and were involved in maintaining the metabolic balance in the liver. Acetylation alterations mainly occurred in the progression from mild to severe hepatic steatosis, i.e., the enzymes in the fatty acid oxidation and bile acid synthesis pathways were significantly less acetylated in severe hepatic steatosis group than that in mild group (P < 0.05). Lipidomics detected a variety of sphingolipids (SPs) and glycerophospholipids (GPs) were negatively correlated with hepatic steatosis (r ≤ -0.5, P < 0.05). Furthermore, the severity of hepatic steatosis was associated with a decrease in cholesterol and bile acid synthesis and an increase in exogenous cholesterol transport.

CONCLUSIONS

In addition to acquiring a global and thorough picture of hepatic steatosis in laying hens, we were able to reveal the role of acetylation in hepatic steatosis and depict the changes in hepatic cholesterol metabolism. The findings provides a wealth of information to facilitate a deeper understanding of the pathophysiology of fatty liver and contributes to the development of therapeutic strategies.

Sirtuin3 confers protection against acute pulmonary embolism through anti-inflammation, and anti-oxidative stress, and anti-apoptosis properties: participation of the AMP-activated protein kinase/mammalian target of rapamycin pathway

An increasing number of studies have suggested that oxidative stress and inflammation play momentous roles in acute pulmonary embolism (APE). Honokiol, a bioactive biphenolic phytochemical substance, is known for its strong anti-oxidative and anti-inflammatory effects, and it served as an activator of sirtuin3 (SIRT3) in the present study. The purposes of the study were to explore the effects of honokiol on APE rats and investigate whether the function of honokiol is mediated by SIRT3 activation. In the study, the rats received a right femoral vein injection of dextran gel G-50 particles (12 mg/kg) to establish the APE model and were subsequently administered honokiol and/or a selective SIRT3 inhibitor 3-(1H-1,2,3-triazol-4-yl)pyridine (3-TYP; 5 mg/kg) intraperitoneally. The results showed that SIRT3 activation by honokiol attenuated the loss in lung function, ameliorated the inflammatory response and oxidative damage, and inhibited apoptosis in lung tissues of the rats with APE but that this was reversed by 3-TYP. In addition, we found that the AMP-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway might be activated by honokiol but restrained by 3-TYP. These results indicated that honokiol was capable of suppressing the adverse effects of APE and that this was diminished by SIRT3 suppression, implying that activation of SIRT3 might serve as a therapeutic method for APE.

Transient changes to metabolic homeostasis initiate mitochondrial adaptation to endurance exercise

Endurance exercise is well established to increase mitochondrial content and function in skeletal muscle, a process termed mitochondrial biogenesis. Current understanding is that exercise initiates skeletal muscle mitochondrial remodeling via modulation of cellular nutrient, energetic and contractile stress pathways. These subtle changes in the cellular milieu are sensed by numerous transduction pathways that serve to initiate and coordinate an increase in mitochondrial gene transcription and translation. The result of these acute signaling events is the promotion of growth and assembly of mitochondria, coupled to a greater capacity for aerobic ATP provision in skeletal muscle. The aim of this review is to highlight the acute metabolic events induced by endurance exercise and the subsequent molecular pathways that sense this transient change in cellular homeostasis to drive mitochondrial adaptation and remodeling.

Mitochondria in endothelial cells angiogenesis and function: current understanding and future perspectives

Endothelial cells (ECs) angiogenesis is the process of sprouting new vessels from the existing ones, playing critical roles in physiological and pathological processes such as wound healing, placentation, ischemia/reperfusion, cardiovascular diseases and cancer metastasis. Although mitochondria are not the major sites of energy source in ECs, they function as important biosynthetic and signaling hubs to regulate ECs metabolism and adaptations to local environment, thus affecting ECs migration, proliferation and angiogenic process. The understanding of the importance and potential mechanisms of mitochondria in regulating ECs metabolism, function and the process of angiogenesis has developed in the past decades. Thus, in this review, we discuss the current understanding of mitochondrial proteins and signaling molecules in ECs metabolism, function and angiogeneic signaling, to provide new and therapeutic targets for treatment of diverse cardiovascular and angiogenesis-dependent diseases.

Aberrant SENP1-SUMO-Sirt3 Signaling Causes the Disturbances of Mitochondrial Deacetylation and Oxidative Phosphorylation in Prion-Infected Animal and Cell Models

Post-translational modifications of proteins, such as acetylation and SUMOylation, play important roles in regulation of protein functions and pathophysiology of different diseases including neurodegenerative diseases. Our previous studies have identified aberrant acetylation profiles and reduced deacetylases Sirt3 and Sirt1 in the brains of prion-infected mouse models. In this study, we have found that the levels of acetylated forms of AceCS2 and LCAD, the key enzymes regulating lipid metabolism, CS and IHD2, the key enzymes regulating complete oxidative metabolism, GDH, the key enzyme regulating the oxidative decomposition of glutamate into the tricarboxylic acid (TCA) cycle, and NDUFA9, the essential component in the complex I of respiratory chain activity, were significantly upregulated in the prion-infected animal and cell models, along with the decrease of Sirt3 activity and mitochondrial cytochrome c oxidase activity. Meanwhile, the increases of SUMO1 modifications and SUMO1-Sirt3 and decrease of SENP1 were identified in the brains and the cultured cells with prion infections. Removal of prion propagation in the cultured cells partially, but significantly, reversed the aberrant situations. Moreover, similar abnormal phenomena were also observed in the cultured 293 T cells transiently expressing cytosolic form PrP (Cyto-PrP), including decreased SENP1, increased SUMO1, decreased Sirt3 activity, increased acetylated forms of the key enzymes, and decreased cytochrome c oxidase activity. Attenuation of the accumulation of Cyto-PrP by co-expression of the p62 protein sufficiently diminished those abnormalities. The data here strongly indicate that deposits of prions in brains or accumulations of Cyto-PrP in cells trigger dysregulation of the SENP1-SUMO1-Sirt pathway and subsequently induce aberrant mitochondrial deacetylation and the mitochondrial respiratory chain.

Ketones and the Heart: Metabolic Principles and Therapeutic Implications

The ketone bodies beta-hydroxybutyrate and acetoacetate are hepatically produced metabolites catabolized in extrahepatic organs. Ketone bodies are a critical cardiac fuel and have diverse roles in the regulation of cellular processes such as metabolism, inflammation, and cellular crosstalk in multiple organs that mediate disease. This review focuses on the role of cardiac ketone metabolism in health and disease with an emphasis on the therapeutic potential of ketosis as a treatment for heart failure (HF). Cardiac metabolic reprogramming, characterized by diminished mitochondrial oxidative metabolism, contributes to cardiac dysfunction and pathologic remodeling during the development of HF. Growing evidence supports an adaptive role for ketone metabolism in HF to promote normal cardiac function and attenuate disease progression. Enhanced cardiac ketone utilization during HF is mediated by increased availability due to systemic ketosis and a cardiac autonomous upregulation of ketolytic enzymes. Therapeutic strategies designed to restore high-capacity fuel metabolism in the heart show promise to address fuel metabolic deficits that underpin the progression of HF. However, the mechanisms involved in the beneficial effects of ketone bodies in HF have yet to be defined and represent important future lines of inquiry. In addition to use as an energy substrate for cardiac mitochondrial oxidation, ketone bodies modulate myocardial utilization of glucose and fatty acids, two vital energy substrates that regulate cardiac function and hypertrophy. The salutary effects of ketone bodies during HF may also include extra-cardiac roles in modulating immune responses, reducing fibrosis, and promoting angiogenesis and vasodilation. Additional pleotropic signaling properties of beta-hydroxybutyrate and AcAc are discussed including epigenetic regulation and protection against oxidative stress. Evidence for the benefit and feasibility of therapeutic ketosis is examined in preclinical and clinical studies. Finally, ongoing clinical trials are reviewed for perspective on translation of ketone therapeutics for the treatment of HF.

ALDH2 attenuates myocardial pyroptosis through breaking down Mitochondrion-NLRP3 inflammasome pathway in septic shock

Cell survival or death is critical for cardiac function. Myocardial pyroptosis, as a newly recognized programmed cell death, remains poorly understood in sepsis. In this study, we evaluated the effect of aldehyde dehydrogenase (ALDH2) on myocardial pyroptosis and revealed the underlying mechanisms in sepsis. We established a septic shock mice model by intraperitoneal injection of Lipopolysaccharide (LPS, 15 mg/kg) 12 h before sacrifice. It was found that aldehyde dehydrogenase significantly inhibited NOD-like receptor protein 3 (NLRP3) inflammasome activation and Caspase-1/GSDMD-dependent pyroptosis, which remarkably improved survival rate and septic shock-induced cardiac dysfunction, relative to the control group. While aldehyde dehydrogenase knockout or knockdown significantly aggravated these phenomena. Intriguingly, we found that aldehyde dehydrogenase inhibited LPS-induced deacetylation of Hydroxyacyl-CoA dehydrogenase trifunctional multienzyme complex α subunit (HADHA) by suppressing the translocation of Histone deacetylase 3 (HDAC3) from nuclei to mitochondria. Acetylated HADHA is essential for mitochondrial fatty acid β-oxidation, and its interruption can result in accumulation of toxic lipids, induce mROS and cause mtDNA and ox-mtDNA release. Our results confirmed the role of Histone deacetylase 3 and HADHA in NOD-like receptor protein 3 inflammasome activation. Hdac3 knockdown remarkedly suppressed NOD-like receptor protein 3 inflammasome and pyroptosis, but Hadha knockdown eliminated the effect. aldehyde dehydrogenase inhibited the translocation of Histone deacetylase 3, protected ac-HADHA from deacetylation, and significantly reduced the accumulation of toxic aldehyde, and inhibited mROS and ox-mtDNA, thereby avoided NOD-like receptor protein 3 inflammasome activation and pyroptosis. This study provided a novel mechanism of myocardial pyroptosis through mitochondrial Histone deacetylase 3/HADHA- NOD-like receptor protein 3 inflammasome pathway and demonstrated a significant role of aldehyde dehydrogenase as a therapeutic target for myocardial pyroptosis in sepsis.

Sirtuin3 ensures the metabolic plasticity of neurotransmission during glucose deprivation

Neurotransmission is an energetically expensive process that underlies cognition. During intense electrical activity or dietary restrictions, glucose levels in the brain plummet, forcing neurons to utilize alternative fuels. However, the molecular mechanisms of neuronal metabolic plasticity remain poorly understood. Here, we demonstrate that glucose-deprived neurons activate the CREB and PGC1α transcriptional program that induces the expression of the mitochondrial deacetylase Sirtuin 3 (Sirt3) both in vitro and in vivo . We show that Sirt3 localizes to axonal mitochondria and stimulates mitochondrial oxidative capacity in hippocampal nerve terminals. Sirt3 plays an essential role in sustaining synaptic transmission in the absence of glucose by powering the retrieval of synaptic vesicles after release. These results demonstrate that the transcriptional induction of Sirt3 ensures the metabolic plasticity of synaptic transmission.

Highlights

Glucose deprivation drives transcriptional reprogramming of neuronal metabolism via CREB and PGC1α. Glucose or food deprivation trigger the neuronal expression of mitochondrial deacetylase sirtuin 3 (Sirt3) both in vitro and in vivo . Sirt3 stimulates oxidative ATP synthesis in nerve terminals.Sirt3 sustains the synaptic vesicle cycle in the absence of glucose.

Neuronal SIRT3 Deletion Predisposes to Female-Specific Alterations in Cellular Metabolism, Memory, and Network Excitability

Mitochondrial dysfunction is an early event in the pathogenesis of neurologic disorders and aging. Sirtuin 3 (SIRT3) regulates mitochondrial function in response to the cellular environment through the reversible deacetylation of proteins involved in metabolism and reactive oxygen species detoxification. As the primary mitochondrial deacetylase, germline, or peripheral tissue-specific deletion of SIRT3 produces mitochondrial hyperacetylation and the accelerated development of age-related diseases. Given the unique metabolic demands of neurons, the role of SIRT3 in the brain is only beginning to emerge. Using mass spectrometry-based acetylomics, high-resolution respirometry, video-EEG, and cognition testing, we report targeted deletion of SIRT3 from select neurons in the cortex and hippocampus produces altered neuronal excitability and metabolic dysfunction in female mice. Targeted deletion of SIRT3 from neuronal helix-loop-helix 1 (NEX)-expressing neurons resulted in mitochondrial hyperacetylation, female-specific superoxide dismutase-2 (SOD2) modification, increased steady-state superoxide levels, metabolic reprogramming, altered neuronal excitability, and working spatial memory deficits. Inducible neuronal deletion of SIRT3 likewise produced female-specific deficits in spatial working memory. Together, the data demonstrate that deletion of SIRT3 from forebrain neurons selectively predisposes female mice to deficits in mitochondrial and cognitive function.SIGNIFICANCE STATEMENT Mitochondrial SIRT3 is an enzyme shown to regulate energy metabolism and antioxidant function, by direct deacetylation of proteins. In this study, we show that neuronal SIRT3 deficiency renders female mice selectively vulnerable to impairment in redox and metabolic function, spatial memory, and neuronal excitability. The observed sex-specific effects on cognition and neuronal excitability in female SIRT3-deficient mice suggest that mitochondrial dysfunction may be one factor underlying comorbid neuronal diseases, such as Alzheimer's disease and epilepsy. Furthermore, the data suggest that SIRT3 dysfunction may predispose females to age-related metabolic and cognitive impairment.

Changes of energy metabolism in failing heart and its regulation by SIRT3

Heart failure (HF) is the leading cause of hospitalization in elderly patients and a disease with extremely high morbidity and mortality rate worldwide. Although there are some existing treatment methods for heart failure, due to its complex pathogenesis and often accompanied by various comorbidities, there is still a lack of specific drugs to treat HF. The mortality rate of patients with HF is still high, highlighting an urgent need to elucidate the pathophysiological mechanisms of HF and seek new therapeutic approaches. The heart is an organ with a very high metabolic intensity, mainly using fatty acids, glucose, ketone bodies, and branched-chain amino acids as energy substrates to supply energy for the heart. Loss of metabolic flexibility and metabolic remodeling occurs with HF. Sirtuin3 (SIRT3) is a member of the NAD⁺-dependent Sirtuin family located in mitochondria, and can participate in mitochondrial physiological functions through the deacetylation of metabolic and respiratory enzymes in mitochondria. As the center of energy metabolism, mitochondria are involved in many physiological processes. Maintaining stable metabolic and physiological functions of the heart depends on normal mitochondrial function. The damage or loss of SIRT3 can lead to various cardiovascular diseases. Therefore, we summarize the recent progress of SIRT3 in cardiac mitochondrial protection and metabolic remodeling.

A Promising Strategy to Treat Neurodegenerative Diseases by SIRT3 Activation

SIRT3, the primary mitochondrial deacetylase, regulates the functions of mitochondrial proteins including metabolic enzymes and respiratory chain components. Although SIRT3's functions in peripheral tissues are well established, the significance of its downregulation in neurodegenerative diseases is beginning to emerge. SIRT3 plays a key role in brain energy metabolism and provides substrate flexibility to neurons. It also facilitates metabolic coupling between fuel substrate-producing tissues and fuel-consuming tissues. SIRT3 mediates the health benefits of lifestyle-based modifications such as calorie restriction and exercise. SIRT3 deficiency is associated with metabolic syndrome (MetS), a precondition for diseases including obesity, diabetes, and cardiovascular disease. The pure form of Alzheimer's disease (AD) is rare, and it has been reported to coexist with these diseases in aging populations. SIRT3 downregulation leads to mitochondrial dysfunction, neuroinflammation, and inflammation, potentially triggering factors of AD pathogenesis. Recent studies have also suggested that SIRT3 may act through multiple pathways to reduce plaque formation in the AD brain. In this review, we give an overview of SIRT3's roles in brain physiology and pathology and discuss several activators of SIRT3 that can be considered potential therapeutic agents for the treatment of dementia.

Arabidopsis thaliana sirtuins control proliferation and glutamate dehydrogenase activity

Sirtuins are part of a gene family of NAD-dependent deacylases that act on histone and non-histone proteins and control a variety of activities in all living organisms. Their roles are mainly related to energy metabolism and include lifetime regulation, DNA repair, stress resistance, and proliferation. A large amount of knowledge concerning animal sirtuins is available, but data about their plant counterparts are scarce. Plants possess few sirtuins that have, like in animals, a recognized role in stress defense and metabolism regulation. However, engagement in proliferation control, which has been demonstrated for mammalian sirtuins, has not been reported for plant sirtuins so far. In this work, srt1 and srt2 Arabidopsis mutant seedlings have been used to evaluate in vivo the role of sirtuins in cell proliferation and regulation of glutamate dehydrogenase, an enzyme demonstrated to be involved in the control of cell cycle in SIRT4-defective human cells. Moreover, bioinformatic analyses have been performed to elucidate sequence, structure, and function relationships between Arabidopsis sirtuins and between each of them and the closest mammalian homolog. We found that cell proliferation and GDH activity are higher in mutant seedlings, suggesting that both sirtuins exert a physiological inhibitory role in these processes. In addition, mutant seedlings show plant growth and root system improvement, in line with metabolic data. Our data also indicate that utilization of an easy to manipulate organism, such as Arabidopsis plant, can help to shed light on the molecular mechanisms underlying the function of genes present in interkingdom species.

SIRT3 deficiency decreases oxidative metabolism capacity but increases lifespan in male mice under caloric restriction

Mitochondrial NAD⁺ -dependent protein deacetylase Sirtuin3 (SIRT3) has been proposed to mediate calorie restriction (CR)-dependent metabolic regulation and lifespan extension. Here, we investigated the role of SIRT3 in CR-mediated longevity, mitochondrial function, and aerobic fitness. We report that SIRT3 is required for whole-body aerobic capacity but is dispensable for CR-dependent lifespan extension. Under CR, loss of SIRT3 (Sirt3^-/- ) yielded a longer overall and maximum lifespan as compared to Sirt3^+/+ mice. This unexpected lifespan extension was associated with altered mitochondrial protein acetylation in oxidative metabolic pathways, reduced mitochondrial respiration, and reduced aerobic exercise capacity. Also, Sirt3^-/- CR mice exhibit lower spontaneous activity and a trend favoring fatty acid oxidation during the postprandial period. This study shows the uncoupling of lifespan and healthspan parameters (aerobic fitness and spontaneous activity) and provides new insights into SIRT3 function in CR adaptation, fuel utilization, and aging.

Molecular Mechanisms for Ketone Body Metabolism, Signaling Functions, and Therapeutic Potential in Cancer

The ketone bodies (KBs) β-hydroxybutyrate and acetoacetate are important alternative energy sources for glucose during nutrient deprivation. KBs synthesized by hepatic ketogenesis are catabolized to acetyl-CoA through ketolysis in extrahepatic tissues, followed by the tricarboxylic acid cycle and electron transport chain for ATP production. Ketogenesis and ketolysis are regulated by the key rate-limiting enzymes, 3-hydroxy-3-methylglutaryl-CoA synthase 2 and succinyl-CoA:3-oxoacid-CoA transferase, respectively. KBs participate in various cellular processes as signaling molecules. KBs bind to G protein-coupled receptors. The most abundant KB, β-hydroxybutyrate, regulates gene expression and other cellular functions by inducing post-translational modifications. KBs protect tissues by regulating inflammation and oxidative stress. Recently, interest in KBs has been increasing due to their potential for treatment of various diseases such as neurological and cardiovascular diseases and cancer. Cancer cells reprogram their metabolism to maintain rapid cell growth and proliferation. Dysregulation of KB metabolism also plays a role in tumorigenesis in various types of cancer. Targeting metabolic changes through dietary interventions, including fasting and ketogenic diets, has shown beneficial effects in cancer therapy. Here, we review current knowledge of the molecular mechanisms involved in the regulation of KB metabolism and cellular signaling functions, and the therapeutic potential of KBs and ketogenic diets in cancer.

SIRT3 alleviates mitochondrial dysfunction induced by recurrent low glucose and improves the supportive function of astrocytes to neurons

Hypoglycemia is an independent risk factor of cognitive impairment in patients with diabetes. Our previous study indicated that dysfunction of astrocytic mitochondria induced by recurrent low glucose (RLG) may account for hypoglycemia-associated neuronal injury and cognitive decline. Sirtuin 3 (SIRT3) is a key deacetylase for mitochondrial proteins and has recently been demonstrated to be an important regulator of mitochondrial function. However, whether mitochondrial dysfunction due to hypoglycemia is associated with astrocytic SIRT3 remains unclear, and few studies have focused on the impact of astrocytic SIRT3 on neuronal survival. In the present work, primary mouse cortical astrocytes cultured in normal glucose (5.5 mM) and high glucose (16.5 mM) were treated with five rounds of RLG (0.1 mM). The results showed that RLG suppressed SIRT3 expression in a glucose-dependent manner. High-glucose culture considerably increased the vulnerability of SIRT3 to RLG, leading to disrupted mitochondrial morphology in astrocytes. Overexpression of SIRT3 markedly improved astrocytic mitochondrial function and reduced RLG-induced oxidative stress. Moreover, SIRT3 suppressed a shift towards a neuroinflammatory A1-like reactive phenotype of astrocytes in response to RLG with reduced IL-1β, IL-6, and TNFα levels. Furthermore, it elevated brain-derived neurotrophic factor (BDNF) levels and promoted neurite growth by activating BDNF/TrkB signaling in the co-cultured neurons. The present study reveals the probable crosstalk between neurons and astrocytes after hypoglycemic exposure and provides a potential target in treating hypoglycemia-associated neuronal injury.

Quantitative acetylated proteomics on left atrial appendage tissues revealed atrial energy metabolism and contraction status in patients with valvular heart disease with atrial fibrillation

Background

Numerous basic studies have demonstrated critical roles of metabolic and contractile remodeling in pathophysiological changes of atrial fibrillation (AF), but acetylation changes underlying atrial remodeling have not been fully elucidated. Quantitative acetylated proteomics enables researchers to identify a comprehensive map of protein alterations responsible for pathological development and progression of AF in the heart of patients.

Materials and methods

In this study, 18 samples (9 with chronic AF and 9 with sinus rhythm) of left atrial appendage (LAA) tissues were obtained during mitral valve replacement surgery. Changes in the quantitative acetylated proteome between the AF and sinus rhythm (SR) groups were studied by dimethyl labeling, acetylation affinity enrichment, and high-performance liquid chromatography-tandem mass spectrometry analysis.

Results

We identified a total of 5,007 acetylated sites on 1,330 acetylated proteins, among which 352 acetylated sites on 193 acetylated proteins were differentially expressed between the AF and SR groups by setting a quantification ratio of 1.3 for threshold value and P < 0.05 for significant statistical difference. The bioinformatics analysis showed that the differentially expressed acetylated proteins were mainly involved in energy metabolism and cellular contraction and structure function-related biological processes and pathways. Among 87 differentially expressed energy metabolism acetylated proteins related to the processes of fatty acid, carbohydrate, ketone body metabolism, and oxidative phosphorylation, nearly 87.1% Kac sites were upregulated (148 Kac sites among 170) in the AF group. Besides, generally declining acetylation of cardiac muscle contraction-related proteins (88.9% Kac sites of myosin) was found in the LAA of patients with AF. Immune coprecipitation combined with Western blotting was conducted to validate the differential expression of acetylated proteins.

Conclusion

Many differentially expressed energy metabolism and cellular contraction acetylated proteins were found in the LAA tissues of patients with chronic AF, and may reflect the impaired ATP production capacity and decreased atrial muscle contractility in the atrium during AF. Thus, acetylation may play an important regulatory role in metabolic and contractile remodeling of the atrium during AF. Moreover, the identified new acetylated sites and proteins may become promising targets for prevention and treatment of AF.

Lysine acetylome profiling in mouse hippocampus and its alterations upon FMRP deficiency linked to abnormal energy metabolism

Loss of fragile X retardation protein (FMRP) leads to fragile X syndrome (FXS), a common cause of inherited intellectual disability. Protein lysine acetylation (K-ac), a reversible post-translational modification of proteins, is associated with the regulation of brain development and neuropathies. However, a comprehensive hippocampal K-ac protein profile in response to FMRP deficiency has not been reported until now. Using LC-MS/MS to analyze the enriched K-ac peptides, this study identified 1629 K-ac hits across 717 proteins in the mouse hippocampus, and these proteins were enriched in several metabolic processes. Of them, 51 K-ac hits across 45 proteins were significantly changed upon loss of FMRP. These altered K-ac proteins were enriched in energy metabolic processes including carboxylic acid metabolism process, aerobic respiration and citrate cycle, linking with several neurological disorders such as lactic acidosis, Lewy body disease, Leigh disease and encephalopathies. In the mouse hippocampus and the hippocampal HT-22 cells, FMRP deficiency could induce altered K-ac modification of several key enzymes, decrease in ATP and increase in lactate. Thus, this study identified a global hippocampal lysine acetylome and an altered K-ac protein profile upon loss of FMRP linked to abnormal energy metabolism, implicating in the pathogenesis of FXS. SIGNIFICANCE: Fragile X syndrome (FXS) is a common inherited neurodevelopment disorder characterized by intellectual disability and an increased risk for autism spectrum disorder. FXS is resulted from silencing of the FMR1 gene, which induces loss of its encoding protein FMRP. Molecular and metabolic changes of Fmr1-null animal models of FXS have been identified to potentially contribute to the pathogenesis of FXS. Here, we used a TMT-labeled quantitative proteomic analysis of the peptides enriched by anti-K-ac antibodies and identified a global K-ac protein profile in the mouse hippocampus with a total of 1629 K-ac peptides on 717 proteins. Of them, 51 K-ac peptides regarding 45 proteins altered in response to loss of FMRP, which were enriched in energy metabolic processes and were implicated in several neurological disorders. Thus this study for the first time provides a global hippocampal lysine acetylome upon FMRP deficiency linked to abnormal metabolic pathways, which may contribute to pathogenic mechanism of FXS.

A comprehensive mouse brain acetylome-the cellular-specific distribution of acetylated brain proteins

Nε-lysine acetylation is a reversible posttranslational modification (PTM) involved in multiple physiological functions. Genetic and animal studies have documented the critical roles of protein acetylation in brain development, functions, and various neurological disorders. However, the underlying cellular and molecular mechanism are still partially understood. Here, we profiled and characterized the mouse brain acetylome and investigated the cellular distribution of acetylated brain proteins. We identified 1,818 acetylated proteins, including 5,196 acetylation modification sites, using a modified workflow comprising filter-aided sample preparation (FSAP), acetylated peptides enrichment, and MS analysis without pre- or post-fraction. Bioinformatics analysis indicated these acetylated mouse brain proteins were mainly located in the myelin sheath, mitochondrial inner membrane, and synapse, as well as their involvement in multiple neurological disorders. Manual annotation revealed that a set of brain-specific proteins were acetylation-modified. The acetylation of three brain-specific proteins was verified, including neurofilament light polypeptide (NEFL), 2’,3’-cyclic-nucleotide 3’-phosphodiesterase (CNP), and neuromodulin (GAP43). Further immunofluorescence staining illustrated that acetylated proteins were mainly distributed in the nuclei of cortex neurons and axons of hippocampal neurons, sparsely distributed in the nuclei of microglia and astrocytes, and the lack of distribution in both cytoplasm and nuclei of cerebrovascular endothelial cells. Together, this study provided a comprehensive mouse brain acetylome and illustrated the cellular-specific distribution of acetylated proteins in the mouse brain. These data will contribute to understanding and deciphering the molecular and cellular mechanisms of protein acetylation in brain development and neurological disorders. Besides, we proposed some problems that need to be solved in future brain acetylome research.

The Role of SIRT3 in Exercise and Aging

The health benefits of regular exercise are well established. Nonetheless, the molecular mechanism(s) responsible for exercise-induced health benefits remain a topic of debate. One of the key cell-signaling candidates proposed to provide exercise-induced benefits is sirtuin 3 (SIRT3). SIRT3, an NAD+ dependent mitochondrial deacetylase, positively modulates many cellular processes, including energy metabolism, mitochondrial biogenesis, and protection against oxidative stress. Although the exercise-induced change in SIRT3 signaling is a potential mechanism contributing to the health advantages of exercise on aging, studies investigating the impact of exercise on SIRT3 abundance in cells provide conflicting results. To resolve this conundrum, this narrative review provides a detailed analysis of the role that exercise-induced changes in SIRT3 play in providing the health and aging benefits associated with regular physical activity. We begin with an overview of SIRT3 function in cells followed by a comprehensive review of the impact of exercise on SIRT3 expression in humans and other mammalians. We then discuss the impact of SIRT3 on aging, followed by a thorough analysis of the cell-signaling links between SIRT3 and exercise-induced adaptation. Notably, to stimulate future research, we conclude with a discussion of key unanswered questions related to exercise, aging, and SIRT3 expression.

NAD+ centric mechanisms and molecular determinants of skeletal muscle disease and aging

The nicotinamide adenine dinucleotide (NAD+) is an essential redox cofactor, involved in various physiological and molecular processes, including energy metabolism, epigenetics, aging, and metabolic diseases. NAD+ repletion ameliorates muscular dystrophy and improves the mitochondrial and muscle stem cell function and thereby increase lifespan in mice. Accordingly, NAD+ is considered as an anti-oxidant and anti-aging molecule. NAD+ plays a central role in energy metabolism and the energy produced is used for movements, thermoregulation, and defense against foreign bodies. The dietary precursors of NAD+ synthesis is targeted to improve NAD+ biosynthesis; however, studies have revealed conflicting results regarding skeletal muscle-specific effects. Recent advances in the activation of nicotinamide phosphoribosyltransferase in the NAD+ salvage pathway and supplementation of NAD+ precursors have led to beneficial effects in skeletal muscle pathophysiology and function during aging and associated metabolic diseases. NAD+ is also involved in the epigenetic regulation and post-translational modifications of proteins that are involved in various cellular processes to maintain tissue homeostasis. This review provides detailed insights into the roles of NAD+ along with molecular mechanisms during aging and disease conditions, such as the impacts of age-related NAD+ deficiencies on NAD+-dependent enzymes, including poly (ADP-ribose) polymerase (PARPs), CD38, and sirtuins within skeletal muscle, and the most recent studies on the potential of nutritional supplementation and distinct modes of exercise to replenish the NAD+ pool.

Reprogramming of Hepatic Metabolism and Microenvironment in Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD), a spectrum of metabolic liver disease associated with obesity, ranges from relatively benign hepatic steatosis to nonalcoholic steatohepatitis (NASH). The latter is characterized by persistent liver injury, inflammation, and liver fibrosis, which collectively increase the risk for end-stage liver diseases such as cirrhosis and hepatocellular carcinoma. Recent work has shed new light on the pathophysiology of NAFLD/NASH, particularly the role of genetic, epigenetic, and dietary factors and metabolic dysfunctions in other tissues in driving excess hepatic fat accumulation and liver injury. In parallel, single-cell RNA sequencing studies have revealed unprecedented details of the molecular nature of liver cell heterogeneity, intrahepatic cross talk, and disease-associated reprogramming of the liver immune and stromal vascular microenvironment. This review covers the recent advances in these areas, the emerging concepts of NASH pathogenesis, and potential new therapeutic opportunities. Expected final online publication date for the Annual Review of Nutrition, Volume 42 is August 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Variations of nitrogen-metabolizing enzyme activity and microbial community under typical loading conditions in full-scale leachate anoxic/aerobic system

Influent loading determines the performance of leachate treatment plant (LTP) facing the dynamic conditions, but enzyme expression in microbial community is unclear. Here, six nitrogen-metabolizing enzymes were detected during nitrification failures (NF), high loading (HL), low loading (LL), and low carbon/nitrogen (LCN) in a 500 m³/d LTP. Nitrogen removal in LL was 15 ± 5% higher than that in HL. The activity of hydroxylamine oxidoreductase decreased by 90% as the influent total nitrogen increased from 2450 mg/L to 3100 mg/L, which might be a critical enzyme causing the nitrification failure. Denitrifying enzyme abated by 1.3% as the carbon/nitrogen dropped by 1% in LCN. With the influent chemical oxygen demand decreased from 22000 mg/L to 12000 mg/L, the relative abundance of norank_f_Saprospiraceae dropped from 33.66% to 11.94%, and finally disappeared, which seems to be an indicator of the high load operation. These findings provide the basis for improving the efficiency of LTPs.

Mitochondrial Sirtuin-3 (SIRT3) Prevents Doxorubicin-Induced Dilated Cardiomyopathy by Modulating Protein Acetylation and Oxidative Stress

BACKGROUND

High doses of doxorubicin put cancer patients at risk for developing dilated cardiomyopathy. Previously, we showed that doxorubicin treatment decreases SIRT3 (sirtuin 3), the main mitochondrial deacetylase and increases protein acetylation in rat cardiomyocytes. Here, we hypothesize that SIRT3 expression can attenuate doxorubicin induced dilated cardiomyopathy in vivo by preventing the acetylation of mitochondrial proteins.

METHODS

Nontransgenic, M3-SIRT3 (truncated SIRT3; short isoform), and M1-SIRT3 (full-length SIRT3; mitochondrial localized) transgenic mice were treated with doxorubicin for 4 weeks (8 mg/kg body weight per week). Echocardiography was performed to assess cardiac structure and function and validated by immunohistochemistry and immunofluorescence (n=4-10). Mass spectrometry was performed on cardiac mitochondrial peptides in saline (n=6) and doxorubicin (n=5) treated hearts. Validation was performed in doxorubicin treated primary rat and human induced stem cell derived cardiomyocytes transduced with adenoviruses for M3-SIRT3 and M1-SIRT3 and deacetylase deficient mutants (n=4-10).

RESULTS

Echocardiography revealed that M3-SIRT3 transgenic mice were partially resistant to doxorubicin induced changes to cardiac structure and function whereas M1-SIRT3 expression prevented cardiac remodeling and dysfunction. In doxorubicin hearts, 37 unique acetylation sites on mitochondrial proteins were altered. Pathway analysis revealed these proteins are involved in energy production, fatty acid metabolism, and oxidative stress resistance. Increased M1-SIRT3 expression in primary rat and human cardiomyocytes attenuated doxorubicin-induced superoxide formation, whereas deacetylase deficient mutants were unable to prevent oxidative stress.

CONCLUSIONS

Doxorubicin reduced SIRT3 expression and markedly affected the cardiac mitochondrial acetylome. Increased M1-SIRT3 expression in vivo prevented doxorubicin-induced cardiac dysfunction, suggesting that SIRT3 could be a potential therapeutic target for mitigating doxorubicin-induced dilated cardiomyopathy.

Sirtuin 3 Dependent and Independent Effects of NAD+ to Suppress Vascular Inflammation and Improve Endothelial Function in Mice

Atherosclerosis is initiated by endothelial cell dysfunction and vascular inflammation under the condition of hyperlipidemia. Sirtuin 3 (SIRT3) is a nicotinamide adenine dinucleotide (NAD⁺)-dependent mitochondrial deacetylase, which plays a key role in maintaining normal mitochondrial function. The present study tested whether endothelial-selective SIRT3 deletion accelerates vascular inflammation and oxidative stress, and assessed the protective effect of NAD⁺ to alleviate these changes in endothelial cells and in mouse models of atherosclerosis. We found that the selective deletion of SIRT3 in endothelial cells further impaired endothelium-dependent vasodilatation in the aorta treated with IL-1β, which was accompanied by upregulation of vascular inflammation markers and mitochondrial superoxide overproduction. Excepting the dysfunction of endothelium-dependent vasodilatation, such effects could be attenuated by treatment with NAD⁺. In human umbilical vein endothelial cells, SIRT3 silencing potentiated the induction of inflammatory factors by IL-1β, including VCAM-1, ICAM-1, and MCP1, and the impairment of mitochondrial respiration, both of which were alleviated by NAD⁺ treatment. In ApoE-deficient mice fed with a high-cholesterol diet, supplementation with nicotinamide riboside, the NAD⁺ precursor, reduced plaque formation, improved vascular function, and diminished vascular inflammation. Our results support the SIRT3-dependent and -independent of NAD⁺ to improve endothelial function in atherosclerosis.

State of Knowledge on Molecular Adaptations to Exercise in Humans: Historical Perspectives and Future Directions

For centuries, regular exercise has been acknowledged as a potent stimulus to promote, maintain, and restore healthy functioning of nearly every physiological system of the human body. With advancing understanding of the complexity of human physiology, continually evolving methodological possibilities, and an increasingly dire public health situation, the study of exercise as a preventative or therapeutic treatment has never been more interdisciplinary, or more impactful. During the early stages of the NIH Common Fund Molecular Transducers of Physical Activity Consortium (MoTrPAC) Initiative, the field is well-positioned to build substantially upon the existing understanding of the mechanisms underlying benefits associated with exercise. Thus, we present a comprehensive body of the knowledge detailing the current literature basis surrounding the molecular adaptations to exercise in humans to provide a view of the state of the field at this critical juncture, as well as a resource for scientists bringing external expertise to the field of exercise physiology. In reviewing current literature related to molecular and cellular processes underlying exercise-induced benefits and adaptations, we also draw attention to existing knowledge gaps warranting continued research effort. © 2021 American Physiological Society. Compr Physiol 12:3193-3279, 2022.

Salt-Induced Hepatic Inflammatory Memory Contributes to Cardiovascular Damage Through Epigenetic Modulation of SIRT3

BACKGROUND

High salt intake is the leading dietary risk factor for cardiovascular diseases. Although clinical evidence suggests that high salt intake is associated with nonalcoholic fatty liver disease, which is an independent risk factor for cardiovascular diseases, it remains elusive whether salt-induced hepatic damage leads to the development of cardiovascular diseases.

METHODS

Mice were fed with normal or high-salt diet for 8 weeks to determine the effect of salt loading on liver histological changes and blood pressure, and salt withdrawal and metformin treatment were also conducted on some high-salt diet-fed mice. Adeno-associated virus 8, global knockout, or tissue-specific knockout mice were used to manipulate the expression of some target genes in vivo, including SIRT3 (sirtuin 3), NRF2 (NF-E2-related factor 2), and AMPK (AMP-activated protein kinase).

RESULTS

Mice fed with a high-salt diet displayed obvious hepatic steatosis and inflammation, accompanied with hypertension and cardiac dysfunction. All these pathological changes persisted after salt withdrawal, displaying a memory phenomenon. Gene expression analysis and phenotypes of SIRT3 knockout mice revealed that reduced expression of SIRT3 was a chief culprit responsible for the persistent inflammation in the liver, and recovering SIRT3 expression in the liver effectively inhibits the sustained hepatic inflammation and cardiovascular damage. Mechanistical studies reveal that high salt increases acetylated histone 3 lysine 27 (H3K27ac) on SIRT3 promoter in hepatocytes, thus inhibiting the binding of NRF2, and results in the sustained inhibition of SIRT3 expression. Treatment with metformin activated AMPK, which inhibited salt-induced hepatic inflammatory memory and cardiovascular damage by lowering the H3K27ac level on SIRT3 promoter, and increased NRF2 binding ability to activate SIRT3 expression.

CONCLUSIONS

This study demonstrates that SIRT3 inhibition caused by histone modification is the key factor for the persistent hepatic steatosis and inflammation that contributes to cardiovascular damage under high salt loading. Avoidance of excessive salt intake and active intervention of epigenetic modification may help to stave off the persistent inflammatory status that underlies high-salt-induced cardiovascular damage in clinical practice.

Mitochondrial protein hyperacetylation underpins heart failure with preserved ejection fraction in mice

Over 50% of patients with heart failure have preserved ejection fraction (HFpEF), rather than reduced ejection fraction (HFrEF). The prevalence of HFpEF continues to increase, while the pathogenic mechanisms underlying HFpEF remain largely elusive and evidence-based therapies are still lacking. This study was designed to investigate the metabolic signature of HFpEF and test the potential therapeutic intervention in a mouse model. By utilizing a "3-Hit" HFpEF mouse model, we observed a global protein hyperacetylation in the HFpEF hearts as compared to the pressure overload-induced HFrEF and adult/aged non-heart failure (NHF) hearts. Acetylome analysis identified that a large proportion of the hyperacetylated proteins (74%) specific to the HFpEF hearts are in mitochondria, and enriched in tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS), and fatty acid oxidation. Further study showed that the elevated protein acetylation in the HFpEF hearts was correlated with reduced NAD⁺/NADH ratio, impaired mitochondrial function, and depleted TCA cycle metabolites. Normalization of NAD⁺/NADH ratio by supplementation of nicotinamide riboside (NR) for 30 days downregulated the acetylation level, improved mitochondrial function and ameliorated HFpEF phenotypes. Therefore, our study identified a distinct protein acetylation pattern in the HFpEF hearts, and proposed NR as a promising agent in lowering acetylation and mitigating HFpEF phenotypes in mice.

Protein acetylation effects on enzyme activity and metabolic pathway fluxes

Acetylation of proteins seems a widespread process found in the three domains of life. Several studies have shown that besides histones, acetylation of lysine residues also occurs in non-nuclear proteins. Hence, it has been suggested that this covalent modification is a mechanism that might regulate diverse metabolic pathways by modulating enzyme activity, stability, and/or subcellular localization or interaction with other proteins. However, protein acetylation levels seem to have low correlation with modification of enzyme activity and pathway fluxes. In addition, the results obtained with mutant enzymes that presumably mimic acetylation have frequently been over-interpreted. Moreover, there is a generalized lack of rigorous enzyme kinetic analysis in parallel to acetylation level determinations. The purpose of this review is to analyze the current findings on the impact of acetylation on metabolic enzymes and its repercussion on metabolic pathways function/regulation.

Transient Dexamethasone Loading Induces Prolonged Hyperglycemia in Male Mice With Histone Acetylation in Dpp-4 Promoter

Glucocorticoid causes hyperglycemia, which is common in patients with or without diabetes. Prolonged hyperglycemia can be experienced even after the discontinuation of glucocorticoid use. In the present study, we examined the time course of blood glucose level in hospital patients who received transient glucocorticoid treatment. In addition, the mechanism of prolonged hyperglycemia was investigated by using dexamethasone (Dexa)-treated mice and cultured cells. The blood glucose level in glucose tolerance tests, level of insulin and glucagon-like peptide 1 (GLP-1), and the activity of dipeptidyl peptidase 4 (DPP-4) were examined during and after Dexa loading in mice, with histone acetylation level of the promoter region. Mice showed prolonged hyperglycemia during and after transient Dexa loading accompanied by persistently lower blood GLP-1 level and higher activity of DPP-4. The expression level of Dpp-4 was increased in the mononuclear cells and the promoter region of Dpp-4 was hyperacetylated during and after the transient Dexa treatment. In vitro experiments also indicated development of histone hyperacetylation in the Dpp-4 promoter region during and after Dexa treatment. The upregulation of Dpp-4 in cultured cells was significantly inhibited by a histone acetyltransferase inhibitor. Moreover, the histone hyperacetylation induced by Dexa was reversible by treatment with a sirtuin histone deacetylase activator, nicotinamide mononucleotide. We identified persistent reduction in blood GLP-1 level with hyperglycemia during and after Dexa treatment in mice, associated with histone hyperacetylation of promoter region of Dpp-4. The results unveil a novel mechanism of glucocorticoid-induced hyperglycemia, and suggest therapeutic intervention through epigenetic modification of Dpp-4.

Overexpression of SIRT3 Suppresses Oxidative Stress-induced Neurotoxicity and Mitochondrial Dysfunction in Dopaminergic Neuronal Cells

Sirtuin 3 (SIRT3), a well-known mitochondrial deacetylase, is involved in mitochondrial function and metabolism under various stress conditions. In this study, we found that the expression of SIRT3 was markedly increased by oxidative stress in dopaminergic neuronal cells. In addition, SIRT3 overexpression enhanced mitochondrial activity in differentiated SH-SY5Y cells. We also showed that SIRT3 overexpression attenuated rotenone- or H₂O₂-induced toxicity in differentiated SH-SY5Y cells (human dopaminergic cell line). We further found that knockdown of SIRT3 enhanced rotenone- or H₂O₂-induced toxicity in differentiated SH-SY5Y cells. Moreover, overexpression of SIRT3 mitigated cell death caused by LPS/IFN-γ stimulation in astrocytes. We also found that the rotenone treatment increases the level of SIRT3 in Drosophila brain. We observed that downregulation of sirt2 (Drosophila homologue of SIRT3) significantly accelerated the rotenone-induced toxicity in flies. Taken together, these findings suggest that the overexpression of SIRT3 mitigates oxidative stress-induced cell death and mitochondrial dysfunction in dopaminergic neurons and astrocytes.

Sirtuin 3 (SIRT3) Pathways in Age-Related Cardiovascular and Neurodegenerative Diseases

Age-associated cardiovascular and neurodegenerative diseases lead to high morbidity and mortality around the world. Sirtuins are vital enzymes for metabolic adaptation and provide protective effects against a wide spectrum of pathologies. Among sirtuins, mitochondrial sirtuin 3 (SIRT3) is an essential player in preserving the habitual metabolic profile. SIRT3 activity declines as a result of aging-induced changes in cellular metabolism, leading to increased susceptibility to endothelial dysfunction, hypertension, heart failure and neurodegenerative diseases. Stimulating SIRT3 activity via lifestyle, pharmacological or genetic interventions could protect against a plethora of pathologies and could improve health and lifespan. Thus, understanding how SIRT3 operates and how its protective effects could be amplified, will aid in treating age-associated diseases and ultimately, in enhancing the quality of life in elders.

Structure-Guided Design of a Small-Molecule Activator of Sirtuin-3 that Modulates Autophagy in Triple Negative Breast Cancer

Sirtuin-3 (SIRT3) is an NAD⁺-dependent protein deacetylase localized primarily in the mitochondria with many links to different types of human cancers. Autophagy, which is a highly conserved lysosomal degradation process in eukaryotic cells, has been recently reported to be positively regulated by SIRT3 in cancer; therefore, activating SIRT3-modulated autophagy may be a promising strategy for drug discovery. In this study, we discovered a small-molecule activator of SIRT3 compound 33c (ADTL-SA1215) with specific SIRT3 deacetylase activity by structure-guided design and high-throughput screening. Subsequently, compound 33c inhibited the proliferation and migration of human breast carcinoma MDA-MB-231 cells by SIRT3-driven autophagy/mitophagy signaling pathways in vitro and in vivo. Collectively, these results demonstrate that pharmacological activation of SIRT3 is a potential therapeutic approach of triple negative breast cancer (TNBC). More importantly, compound 33c may be a first-in-class specific small-molecule activator of SIRT3 that would be utilized for future cancer drug development.

Metabolic and Signaling Roles of Ketone Bodies in Health and Disease

Ketone bodies play significant roles in organismal energy homeostasis, serving as oxidative fuels, modulators of redox potential, lipogenic precursors, and signals, primarily during states of low carbohydrate availability. Efforts to enhance wellness and ameliorate disease via nutritional, chronobiological, and pharmacological interventions have markedly intensified interest in ketone body metabolism. The two ketone body redox partners, acetoacetate and D-β-hydroxybutyrate, serve distinct metabolic and signaling roles in biological systems. We discuss the pleiotropic roles played by both of these ketones in health and disease. While enthusiasm is warranted, prudent procession through therapeutic applications of ketogenic and ketone therapies is also advised, as a range of metabolic and signaling consequences continue to emerge. Organ-specific and cell-type-specific effects of ketone bodies are important to consider as prospective therapeutic and wellness applications increase.