Mitochondrial Sirtuins and Molecular Mechanisms of Aging

A Multi-Target Pharmacological Correction of a Lipoyltransferase LIPT1 Gene Mutation in Patient-Derived Cellular Models

Mutations in the lipoyltransferase 1 (LIPT1) gene are rare inborn errors of metabolism leading to a fatal condition characterized by lipoylation defects of the 2-ketoacid dehydrogenase complexes causing early-onset seizures, psychomotor retardation, abnormal muscle tone, severe lactic acidosis, and increased urine lactate, ketoglutarate, and 2-oxoacid levels. In this article, we characterized the disease pathophysiology using fibroblasts and induced neurons derived from a patient bearing a compound heterozygous mutation in LIPT1. A Western blot analysis revealed a reduced expression of LIPT1 and absent expression of lipoylated pyruvate dehydrogenase E2 (PDH E2) and alpha-ketoglutarate dehydrogenase E2 (α-KGDH E2) subunits. Accordingly, activities of PDH and α-KGDH were markedly reduced, associated with cell bioenergetics failure, iron accumulation, and lipid peroxidation. In addition, using a pharmacological screening, we identified a cocktail of antioxidants and mitochondrial boosting agents consisting of pantothenate, nicotinamide, vitamin E, thiamine, biotin, and α-lipoic acid, which is capable of rescuing LIPT1 pathophysiology, increasing the LIPT1 expression and lipoylation of mitochondrial proteins, improving cell bioenergetics, and eliminating iron overload and lipid peroxidation. Furthermore, our data suggest that the beneficial effect of the treatment is mainly mediated by SIRT3 activation. In conclusion, we have identified a promising therapeutic approach for correcting LIPT1 mutations.

Mitochondrial protein deacetylation by SIRT3 in osteoclasts promotes bone resorption with aging in female mice

OBJECTIVES

The mitochondrial deacetylase sirtuin-3 (SIRT3) is necessary for the increased bone resorption and enhanced function of mitochondria in osteoclasts that occur with advancing age; how SIRT3 drives bone resorption remains elusive.

METHODS

To determine the role of SIRT3 in osteoclast mitochondria, we used mice with conditional loss of Sirt3 in osteoclast lineage and mice with germline deletion of either Sirt3 or its known target Pink1.

RESULTS

SIRT3 stimulates mitochondrial quality in osteoclasts in a PINK1-independent manner, promoting mitochondrial activity and osteoclast maturation and function, thereby contributing to bone loss in female but not male mice. Quantitative analyses of global proteomes and acetylomes revealed that deletion of Sirt3 dramatically increased acetylation of osteoclast mitochondrial proteins, particularly ATPase inhibitory factor 1 (ATPIF1), an essential protein for mitophagy. Inhibition of mitophagy via mdivi-1 recapitulated the effect of deletion of Sirt3 or Atpif1 in osteoclast formation and mitochondrial function.

CONCLUSIONS

Decreasing mitophagic flux in osteoclasts may be a promising pharmacotherapeutic approach to treat osteoporosis in older adults.

SIRTUIN 5 ALLEVIATES EXCESSIVE MITOCHONDRIAL FISSION VIA DESUCCINYLATION OF ATPASE INHIBITORY FACTOR 1 IN SEPSIS-INDUCED ACUTE KIDNEY INJURY

ABSTRACT

Sepsis-induced acute kidney injury (SAKI) poses a significant clinical challenge with high morbidity and mortality. Excessive mitochondrial fission has been identified as the central pathogenesis of sepsis-associated organ damage, which is also implicated in the early stages of SAKI. Sirtuin 5 (SIRT5) has emerged as a central regulator of cellular mitochondrial function; however, its role in the regulation of sepsis-induced excessive mitochondrial fission in kidney and the underlying mechanism remains unclear. In this study, SAKI was modeled in mice through cecal ligation and puncture, and in human renal tubular epithelial (HK-2) cells stimulated with lipopolysaccharide (LPS), to mimic the cell SAKI model. Our findings revealed that septic mice with a SIRT5 knockout exhibited shortened survival times and elevated levels of renal injury compared to wild-type mice, suggesting the significant involvement of SIRT5 in SAKI pathophysiology. Additionally, we observed that SIRT5 depletion led to increased renal mitochondrial fission, while the use of a mitochondrial fission inhibitor (Mdivi-1) reversed the detrimental effects caused by SIRT5 depletion, emphasizing the pivotal role of SIRT5 in preventing excessive mitochondrial fission. In vitro experiments demonstrated that the overexpression of SIRT5 effectively mitigated the adverse effects of LPS on HK-2 cells viability and mitochondrial fission. Conversely, downregulation of SIRT5 decreased HK-2 cells viability and exacerbated LPS-induced mitochondrial fission. Mechanistically, the protective function of SIRT5 may be in part, ascribed to its desuccinylating action on ATPase inhibitory factor 1. In conclusion, this study provides novel insights into the underlying mechanisms of SAKI, suggesting the possibility of identifying future drug targets in terms of improved mitochondrial dynamics by SIRT5.

The AKT2/SIRT5/TFEB pathway as a potential therapeutic target in non-neovascular AMD

Non-neovascular or dry age-related macular degeneration (AMD) is a multi-factorial disease with degeneration of the aging retinal-pigmented epithelium (RPE). Lysosomes play a crucial role in RPE health via phagocytosis and autophagy, which are regulated by transcription factor EB/E3 (TFEB/E3). Here, we find that increased AKT2 inhibits PGC-1α to downregulate SIRT5, which we identify as an AKT2 binding partner. Crosstalk between SIRT5 and AKT2 facilitates TFEB-dependent lysosomal function in the RPE. AKT2/SIRT5/TFEB pathway inhibition in the RPE induced lysosome/autophagy signaling abnormalities, disrupted mitochondrial function and induced release of debris contributing to drusen. Accordingly, AKT2 overexpression in the RPE caused a dry AMD-like phenotype in aging Akt2 KI mice, as evident from decline in retinal function. Importantly, we show that induced pluripotent stem cell-derived RPE encoding the major risk variant associated with AMD (complement factor H; CFH Y402H) express increased AKT2, impairing TFEB/TFE3-dependent lysosomal function. Collectively, these findings suggest that targeting the AKT2/SIRT5/TFEB pathway may be an effective therapy to delay the progression of dry AMD.

An integrated bioinformatics analysis to identify the shared biomarkers in patients with obstructive sleep apnea syndrome and nonalcoholic fatty liver disease

Background

Obstructive sleep apnea (OSA) syndrome and nonalcoholic fatty liver disease (NAFLD) have been shown to have a close association in previous studies, but their pathogeneses are unclear. This study explores the molecular mechanisms associated with the pathogenesis of OSA and NAFLD and identifies key predictive genes.

Methods

Using the Gene Expression Omnibus (GEO) database, we obtained gene expression profiles GSE38792 for OSA and GSE89632 for NAFLD and related clinical characteristics. Mitochondrial unfolded protein response-related genes (UPRmtRGs) were acquired by collating and collecting UPRmtRGs from the GeneCards database and relevant literature from PubMed. The differentially expressed genes (DEGs) associated with OSA and NAFLD were identified using differential expression analysis. Gene Set Enrichment Analysis (GSEA) was conducted for signaling pathway enrichment analysis of related disease genes. Based on the STRING database, protein-protein interaction (PPI) analysis was performed on differentially co-expressed genes (Co-DEGs), and the Cytoscape software (version 3.9.1) was used to visualize the PPI network model. In addition, the GeneMANIA website was used to predict and construct the functional similar genes of the selected Co-DEGs. Key predictor genes were analyzed using the receiver operating characteristic (ROC) curve.

Results

The intersection of differentially expressed genes shared between OSA and NAFLD-related gene expression profiles with UPRmtRGs yielded four Co-DEGs: ASS1, HDAC2, SIRT3, and VEGFA. GSEA obtained the relevant enrichment signaling pathways for OSA and NAFLD. PPI network results showed that all four Co-DEGs interacted (except for ASS1 and HDAC2). Ultimately, key predictor genes were selected in the ROC curve, including HDAC2 (OSA: AUC = 0.812; NAFLD: AUC = 0.729), SIRT3 (OSA: AUC = 0.775; NAFLD: AUC = 0.750), and VEGFA (OSA: AUC = 0.812; NAFLD: AUC = 0.861) (they have a high degree of accuracy in predicting whether a subject will develop two diseases).

Conclusion

In this study, four co-expression differential genes for OSA and NAFLD were obtained, and they can predict the occurrence of both diseases. Transcriptional mechanisms involved in OSA and NAFLD interactions may be better understood by exploring these key genes. Simultaneously, this study provides potential diagnostic and therapeutic markers for patients with OSA and NAFLD.

Ferrostatin-1 specifically targets mitochondrial iron-sulfur clusters and aconitase to improve cardiac function in Sirtuin 3 cardiomyocyte knockout mice

AIMS

Ferroptosis is a form of iron-regulated cell death implicated in ischemic heart disease. Our previous study revealed that Sirtuin 3 (SIRT3) is associated with ferroptosis and cardiac fibrosis. In this study, we tested whether the knockout of SIRT3 in cardiomyocytes (SIRT3cKO) promotes mitochondrial ferroptosis and whether the blockade of ferroptosis would ameliorate mitochondrial dysfunction.

METHODS AND RESULTS

Mitochondrial and cytosolic fractions were isolated from the ventricles of mice. Cytosolic and mitochondrial ferroptosis were analyzed by comparison to SIRT3loxp mice. An echocardiography study showed that SIRT3cKO mice developed heart failure as evidenced by a reduction of EF% and FS% compared to SIRT3loxp mice. Comparison of mitochondrial and cytosolic fractions of SIRT3cKO and SIRT3loxp mice revealed that, upon loss of SIRT3, mitochondrial, but not cytosolic, total lysine acetylation was significantly increased. Similarly, acetylated p53 was significantly upregulated only in the mitochondria. These data demonstrate that SIRT3 is the primary mitochondrial deacetylase. Most importantly, loss of SIRT3 resulted in significant reductions of frataxin, aconitase, and glutathione peroxidase 4 (GPX4) in the mitochondria. This was accompanied by a significant increase in levels of mitochondrial 4-hydroxynonenal. Treatment of SIRT3cKO mice with the ferroptosis inhibitor ferrostatin-1 (Fer-1) for 14 days significantly improved preexisting heart failure. Mechanistically, Fer-1 treatment significantly increased GPX4 and aconitase expression/activity, increased mitochondrial iron‑sulfur clusters, and improved mitochondrial membrane potential and Complex IV activity.

CONCLUSIONS

Inhibition of ferroptosis ameliorated cardiac dysfunction by specifically targeting mitochondrial aconitase and iron‑sulfur clusters. Blockade of mitochondrial ferroptosis may be a novel therapeutic target for mitochondrial cardiomyopathies.

Acylspermidines are conserved mitochondrial sirtuin-dependent metabolites

Sirtuins are nicotinamide adenine dinucleotide (NAD+)-dependent protein lysine deacylases regulating metabolism and stress responses; however, characterization of the removed acyl groups and their downstream metabolic fates remains incomplete. Here we employed untargeted comparative metabolomics to reinvestigate mitochondrial sirtuin biochemistry. First, we identified N-glutarylspermidines as metabolites downstream of the mitochondrial sirtuin SIR-2.3 in Caenorhabditis elegans and demonstrated that SIR-2.3 functions as a lysine deglutarylase and that N-glutarylspermidines can be derived from O-glutaryl-ADP-ribose. Subsequent targeted analysis of C. elegans, mouse and human metabolomes revealed a chemically diverse range of N-acylspermidines, and formation of N-succinylspermidines and/or N-glutarylspermidines was observed downstream of mammalian mitochondrial sirtuin SIRT5 in two cell lines, consistent with annotated functions of SIRT5. Finally, N-glutarylspermidines were found to adversely affect C. elegans lifespan and mammalian cell proliferation. Our results indicate that N-acylspermidines are conserved metabolites downstream of mitochondrial sirtuins that facilitate annotation of sirtuin enzymatic activities in vivo and may contribute to sirtuin-dependent phenotypes.

Targeting mitochondria for ovarian aging: new insights into mechanisms and therapeutic potential

Ovarian aging is a complex process characterized by a decline in oocyte quantity and quality, directly impacting fertility and overall well-being. Recent researches have identified mitochondria as pivotal players in the aging of ovaries, influencing various hallmarks and pathways governing this intricate process. In this review, we discuss the multifaceted role of mitochondria in determining ovarian fate, and outline the pivotal mechanisms through which mitochondria contribute to ovarian aging. Specifically, we emphasize the potential of targeting mitochondrial dysfunction through innovative therapeutic approaches, including antioxidants, metabolic improvement, biogenesis promotion, mitophagy enhancement, mitochondrial transfer, and traditional Chinese medicine. These strategies hold promise as effective means to mitigate age-related fertility decline and preserve ovarian health. Drawing insights from advanced researches in the field, this review provides a deeper understanding of the intricate interplay between mitochondrial function and ovarian aging, offering valuable perspectives for the development of novel therapeutic interventions aimed at preserving fertility and enhancing overall reproductive health.

The Expansion of Sirtuin Gene Family in Gilthead Sea Bream (Sparus aurata)-Phylogenetic, Syntenic, and Functional Insights across the Vertebrate/Fish Lineage

The Sirtuin (SIRT1-7) family comprises seven evolutionary-conserved enzymes that couple cellular NAD availability with health, nutrition and welfare status in vertebrates. This study re-annotated the sirt3/5 branch in the gilthead sea bream, revealing three paralogues of sirt3 (sirt3.1a/sirt3.1b/sirt3.2) and two of sirt5 (sirt5a/sirt5b) in this Perciform fish. The phylogeny and synteny analyses unveiled that the Sirt3.1/Sirt3.2 dichotomy was retained in teleosts and aquatic-living Sarcopterygian after early vertebrate 2R whole genome duplication (WGD). Additionally, only certain percomorphaceae and gilthead sea bream showed a conserved tandem-duplicated synteny block involving the mammalian-clustered sirt3.1 gene (psmd13-sirt3.1a/b-drd4-cdhr5-ctsd). Conversely, the expansion of the Sirt5 branch was shaped by the teleost-specific 3R WGD. As extensively reviewed in the literature, human-orthologues (sirt3.1/sirt5a) showed a high, conserved expression in skeletal muscle that increased as development advanced. However, recent sirt3.2 and sirt5b suffered an overall muscle transcriptional silencing across life, as well as an enhanced expression on immune-relevant tissues and gills. These findings fill gaps in the ontogeny and differentiation of Sirt genes in the environmentally adaptable gilthead sea bream, becoming a good starting point to advance towards a full understanding of its neo-functionalization. The mechanisms originating from these new paralogs also open new perspectives in the study of cellular energy sensing processes in vertebrates.

Redox signaling and skeletal muscle adaptation during aerobic exercise

Redox regulation is a fundamental physiological phenomenon related to oxygen-dependent metabolism, and skeletal muscle is mainly regarded as a primary site for oxidative phosphorylation. Several studies have revealed the importance of reactive oxygen and nitrogen species (RONS) in the signaling process relating to muscle adaptation during exercise. To date, improving knowledge of redox signaling in modulating exercise adaptation has been the subject of comprehensive work and scientific inquiry. The primary aim of this review is to elucidate the molecular and biochemical pathways aligned to RONS as activators of skeletal muscle adaptation and to further identify the interconnecting mechanisms controlling redox balance. We also discuss the RONS-mediated pathways during the muscle adaptive process, including mitochondrial biogenesis, muscle remodeling, vascular angiogenesis, neuron regeneration, and the role of exogenous antioxidants.

Deletion of the Clock Gene Bmal2 Leads to Alterations in Hypothalamic Clocks, Circadian Regulation of Feeding, and Energy Balance

BMAL2 (ARNTL2) is a paralog of BMAL1 that can form heterodimers with the other circadian factors CLOCK and NPAS2 to activate transcription of clock and clock-controlled genes. To assess a possible role of Bmal2 in the circadian regulation of metabolism, we investigated daily variations of energy metabolism, feeding behavior, and locomotor behavior, as well as ability to anticipate restricted food access in male mice knock-out for Bmal2 (B2KO). While their amount of food intake and locomotor activity were normal compared with wild-type mice, B2KO mice displayed increased adiposity (1.5-fold higher) and fasted hyperinsulinemia (fourfold higher) and tended to have lower energy expenditure at night. Impairment of the master clock in the suprachiasmatic nuclei was evidenced by the shorter free-running period (-14 min/cycle) of B2KO mice compared with wild-type controls and by a loss of daily rhythmicity in expression of intracellular metabolic regulators (e.g., Lipoprotein lipase and Uncoupling protein 2). The circadian window of eating was longer in B2KO mice. The circadian patterns of food intake and meal numbers were bimodal in control mice but not in B2KO mice. In response to restricted feeding, food-anticipatory activity was almost prevented in B2KO mice, suggesting altered food clock that controls anticipation of food availability. In the mediobasal hypothalamus of B2KO mice, expression of genes coding orexigenic neuropeptides (including Neuropeptide y and Agouti-Related Peptide) was downregulated, while Lipoprotein lipase expression lost its rhythmicity. Together, these data highlight that BMAL2 has major impacts on brain regulation of metabolic rhythms, sleep-wake cycle, and food anticipation.

Osteoclasts and osteoarthritis: Novel intervention targets and therapeutic potentials during aging

Osteoarthritis (OA), a chronic degenerative joint disease, is highly prevalent among the aging population, and often leads to joint pain, disability, and a diminished quality of life. Although considerable research has been conducted, the precise molecular mechanisms propelling OA pathogenesis continue to be elusive, thereby impeding the development of effective therapeutics. Notably, recent studies have revealed subchondral bone lesions precede cartilage degeneration in the early stage of OA. This development is marked by escalated osteoclast-mediated bone resorption, subsequent imbalances in bone metabolism, accelerated bone turnover, and a decrease in bone volume, thereby contributing significantly to the pathological changes. While the role of aging hallmarks in OA has been extensively elucidated from the perspective of chondrocytes, their connection with osteoclasts is not yet fully understood. There is compelling evidence to suggest that age-related abnormalities such as epigenetic alterations, proteostasis network disruption, cellular senescence, and mitochondrial dysfunction, can stimulate osteoclast activity. This review intends to systematically discuss how aging hallmarks contribute to OA pathogenesis, placing particular emphasis on the age-induced shifts in osteoclast activity. It also aims to stimulate future studies probing into the pathological mechanisms and therapeutic approaches targeting osteoclasts in OA during aging.

SIRT3 alleviates painful diabetic neuropathy by mediating the FoxO3a-PINK1-Parkin signaling pathway to activate mitophagy

INTRODUCTION

Painful diabetic neuropathy (PDN) is a common complication of diabetes. Previous studies have implicated that mitochondrial dysfunction plays a role in the development of PDN, but its pathogenesis and mechanism have not been fully investigated.

METHODS

In this study, we used high-fat diet/low-dose streptozotocin-induced rats as a model of type 2 diabetes mellitus. Behavioral testing, whole-cell patch-clamp recordings of dorsal root ganglion (DRG) neurons, and complex sensory nerve conduction velocity studies were used to assess peripheral neuropathy. Mitochondrial membrane potential (MMP), ATP, tissue reactive oxygen species, and transmission electron microscopy were used to evaluate the function and morphology of mitochondria in DRG. Real-time PCR, western blot, and immunofluorescence were performed to investigate the mechanism.

RESULTS

We found that damaged mitochondria were accumulated and mitophagy was inhibited in PDN rats. The expression of sirtuin 3 (SIRT3), which is an NAD+-dependent deacetylase in mitochondria, was inhibited. Overexpression of SIRT3 in DRG neurons by intrathecally administered LV-SIRT3 lentivirus ameliorated neurological and mitochondrial dysfunctions. This was evidenced by the reversal of allodynia and nociceptor hyperexcitability, as well as the restoration of MMP and ATP levels. Overexpression of SIRT3 restored the inhibited mitophagy by activating the FoxO3a-PINK1-Parkin signaling pathway. The effects of SIRT3 overexpression, including the reversal of allodynia and nociceptor hyperexcitability, the improvement of impaired mitochondria and mitophagy, and the restoration of PINK1 and Parkin expression, were counteracted when FoxO3a siRNA was intrathecally injected.

CONCLUSION

These results showed that SIRT3 overexpression ameliorates PDN via activation of FoxO3a-PINK1-Parkin-mediated mitophagy, suggesting that SIRT3 may become an encouraging therapeutic strategy for PDN.

Enhancer of zeste homolog 2 (EZH2)-dependent sirtuin-3 determines sensitivity to glucose starvation in radioresistant head and neck cancer cells

Sirtuin 3 (SIRT3) regulates mitochondrial function as a mitochondrial deacetylase during oxidative stress. However, the specific regulatory mechanism and function of SIRT3 in radioresistant cancer cells are unclear. In this study, we aim to investigate how SIRT3 determines the susceptibility to glucose deprivation and its regulation in p53-based radioresistant head and neck cancer cells. We observed mitochondrial function using two established isogenic radioresistant subclones (HN3R-A [p53 null] and HN3R-B [p53 R282W]) with intratumoral p53 heterogeneity. Cell counting analysis was performed to evaluate cell proliferation and cell death. The correlation between the regulation of SIRT3 and enhancer of zeste homolog 2 (EZH2) was confirmed by immunoblotting and chromatin immunoprecipitation assay. p53-deficient radioresistant cells (HN3R-A) expression reduced SIRT3 levels and increased sensitivity to glucose deprivation due to mitochondrial dysfunction compared to other cells. In these cells, activation of SIRT3 significantly prevented glucose deprivation-induced cell death, whereas the loss of SIRT3 increased the susceptibility to glucose deficiency. We discovered that radiation-induced EZH2 directly binds to the SIRT3 promoter and represses the expression. Conversely, inhibiting EZH2 increased the expression of SIRT3 through epigenetic changes. Our findings indicate that p53-deficient radioresistant cells with enhanced EZH2 exhibit increased sensitivity to glucose deprivation due to SIRT3 suppression. The regulation of SIRT3 by EZH2 plays a critical role in determining the cell response to glucose deficiency in radioresistant cancer cells. Therefore, EZH2-dependent SIRT3 could be used as a predictive biomarker to select treatment options for patients with radiation-resistance.

The Effect of Short-Term NAD3® Supplementation on Circulating Adult Stem Cells in Healthy Individuals Aged 40-70 Years

Objective This study aimed to assess the impact of acute and short-term supplementation with NAD3®, a theacrine-containing supplement, on circulating adult stem cell numbers in a healthy male and female population aged 40-70 years. Methods This was a double-blind, placebo-controlled crossover study with 12 participants randomized to receive either NAD3® or a placebo for seven days. Blood samples were collected after an overnight fast, before and after the seven-day supplementation period, and one and two hours after the final supplement dose. Using flow cytometry, circulating stem cells, including lymphocytoid CD34+ stem cells (CD45dimCD34+), stem cells associated with vascular maintenance and repair (CD45dimCD34+CD309+), CD34+ stem cells linked to a progenitor phenotype (CD45dimCD34+CD309neg), circulating endothelial stem cells (CD45negCD31+CD309+), and mesenchymal stem cells (CD45negCD90+) were quantified. Results Acute NAD3® supplementation did not result in the mobilization of stem cells from the bone marrow. However, seven days of daily NAD3® supplementation resulted in selective changes in circulating stem cell numbers. A significant time*treatment interaction was observed for CD45dimCD34+ cells (p=0.04) and CD45dimCD34+CD309neg cells (p=0.04), indicating a decrease in cell numbers with supplementation. There was also a trend toward an increase in circulating endothelial cells (p=0.08) with seven days of NAD3®supplementation. Conclusion Short-term NAD3® supplementation demonstrated an effect on the quantity of bone marrow-derived stem cells in circulation. The study suggests that this theacrine-containing supplement may play a role in modulating adult stem cell populations, emphasizing the potential impact of NAD3® on regenerative processes. Further research with extended supplementation periods and larger sample sizes is warranted to elucidate the functional consequences of these changes and explore the therapeutic implications for age-related declines in stem cell function.

SIRT3 Activation a Promise in Drug Development? New Insights into SIRT3 Biology and Its Implications on the Drug Discovery Process

Sirtuins catalyze deacetylation of lysine residues with a NAD+-dependent mechanism. In mammals, the sirtuin family is composed of seven members, divided into four subclasses that differ in substrate specificity, subcellular localization, regulation, as well as interactions with other proteins, both within and outside the epigenetic field. Recently, much interest has been growing in SIRT3, which is mainly involved in regulating mitochondrial metabolism. Moreover, SIRT3 seems to be protective in diseases such as age-related, neurodegenerative, liver, kidney, heart, and metabolic ones, as well as in cancer. In most cases, activating SIRT3 could be a promising strategy to tackle these health problems. Here, we summarize the main biological functions, substrates, and interactors of SIRT3, as well as several molecules reported in the literature that are able to modulate SIRT3 activity. Among the activators, some derive from natural products, others from library screening, and others from the classical medicinal chemistry approach.

Sirtuins Affect Cancer Stem Cells via Epigenetic Regulation of Autophagy

Sirtuins (SIRTs) are stress-responsive proteins that regulate several post-translational modifications, partly by acetylation, deacetylation, and affecting DNA methylation. As a result, they significantly regulate several cellular processes. In essence, they prolong lifespan and control the occurrence of spontaneous tumor growth. Members of the SIRT family have the ability to govern embryonic, hematopoietic, and other adult stem cells in certain tissues and cell types in distinct ways. Likewise, they can have both pro-tumor and anti-tumor effects on cancer stem cells, contingent upon the specific tissue from which they originate. The impact of autophagy on cancer stem cells, which varies depending on the specific circumstances, is a very intricate phenomenon that has significant significance for clinical and therapeutic purposes. SIRTs exert an impact on the autophagy process, whereas autophagy reciprocally affects the activity of certain SIRTs. The mechanism behind this connection in cancer stem cells remains poorly understood. This review presents the latest findings that position SIRTs at the point where cancer cells and autophagy interact. Our objective is to highlight the various roles of distinct SIRTs in cancer stem cell-related functions through autophagy. This would demonstrate their significance in the genesis and recurrence of cancer and offer a more precise understanding of their treatment possibilities in relation to autophagy.

Targeting SIRT4/TET2 Signaling Alleviates Human Keratinocyte Senescence by Reducing 5-hydroxymethylcytosine Loss

Skin aging is characterized by wrinkle formation and increased frailty and laxity, leading to the risk of age-related skin diseases. Keratinocyte is an important component of the epidermis in skin structure, and keratinocyte senescence has been identified as a pivotal factor in skin aging development. Because epigenetic pathways play a vital role in the regulation of skin aging, we evaluated human skin samples for DNA hydroxymethylation (5-hydroxymethylcytosine; 5-hmC) and SIRT4 expressions. Results found that both 5-hmC and SIRT4 showed a significant decrease in aged human skin samples. To test the results in vitro, human keratinocytes were cultured in H2O2, which modulates skin aging in vivo. However, H2O2-induced keratinocytes showed senescence-associated protein expression and significant downregulation of 5-hmC and SIRT4 expressions. Moreover, 5-hmC-converting enzymes ten eleven translocation 2 (TET2) showed a decrease and enhanced TET2 acetylation level in H2O2-induced keratinocytes. However, the overexpression of SIRT4 in keratinocytes alleviates the senescence phenotype, such as senescence-associated protein expression, decreases the TET2 acetylation, but increases TET2 and 5-hmC expressions. Our results provide a novel relevant mechanism whereby the epigenetic regulation of keratinocytes in skin aging may be correlated with SIRT4 expression and TET2 acetylation in 5-hmC alteration. Our study may provide a potential strategy for antiskin aging, which targets the SIRT4/TET2 axis involving epigenetic modification in keratinocyte senescence.

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.

Qishen granule attenuates doxorubicin-induced cardiotoxicity by protecting mitochondrial function and reducing oxidative stress through regulation of Sirtuin3

ETHNOPHARMACOLOGICAL RELEVANCE

Doxorubicin (DOX) is one of the most potent chemotherapy drugs available today. However, the adverse effect of cardiotoxicity limits its clinical application. New approaches are being investigated for the treatment of doxorubicin-induced cardiotoxicity (DIC). Doxorubicin is enriched in mitochondria and it could induce imbalance of protein modification, including acetylation of mitochondria proteins, thereby inducing DIC. Restoration of mitochondria function is an effective way to attenuate DIC. The formula for traditional Chinese medicine Granules of Qishen (QSG) was derived from the classic formula "Zhen-Wu-Tang" which has been extensively used in the treatment of myocardial infarction. It consists of six traditional Chinese medicines, including Astragalus membranaceus var. mongholicus (Bunge) P.K.Hsiao (Fabaceae), Salvia miltiorrhiza Bunge (Lamiaceae), Lonicera japonica Thunb. (Caprifoliaceae), Aconitum carmichaelii Debeaux (Ranunculaceae), Scrophularia ningpoensis Hemsl. (Scrophulariaceae), and Glycyrrhiza uralensis Fisch. (Fabaceae). QSG is a potential anti-DIC formula. A better understanding of the effectiveness and pharmacological mechanisms of QSG will aid in the prevention and treatment of DIC.

AIM OF THE STUDY

The purpose of this research was to explore the effectiveness of QSG in the treatment of DIC and to explore whether QSG could protect mitochondrial function and reduce oxidative damage by activating Sirtuin3(SIRT3)/Acetylated-superoxide dismutase 2(Ac-SOD2) signaling pathway.

MATERIALS AND METHODS

DOX was injected into mice through the tail vein to construct a mouse model of DOX-induced cardiotoxicity to explore the therapeutic effect of QSG in animals. Meanwhile, the H9C2 cell model was used to study the mechanism of QSG. The cardiac function was evaluated by echocardiography, hematoxylin-eosin (H&E) staining and measurement of serum levels of creatine kinase isoenzymes (CK-MB) and lactate dehydrogenase (LDH). Oxidative damage was evaluated by 2',7'-dichlorodihydro fluorescein diacetate (DCFH-DA) staining and Mito-SOX Red staining. Levels of total superoxide dismutase (SOD) activity and malondialdehyde (MDA) content were measured by following the instructions of commercially available kits. In order to detect the changes in mitochondrial membrane potential, cells were stained using the mitochondrial membrane potential detection kit (JC-1). Western blot analysis was applied to detect protein expressions of SIRT3, Ac-SOD2, Acetylation Lysine (Ac-Lys), Bax and Bcl-2. H9C2 cells were treated with SIRT3 inhibitor, in order to determine if QSG had effects via the SIRT3/Ac-SOD2 pathway.

RESULTS

In vivo studies showed that QSG ameliorated doxorubicin-induced damage of cardiac function in DIC mice model. The ejection fraction (EF) and fractional shortening (FS) were all up-regulated by QSG treatment. QSG decreased MDA levels and increased SOD activity. Meanwhile, doxorubicin induced high level of protein acetylation and QSG restored the acetylated protein back to normal levels. In particular, QSG upregulated expression of SIRT3 and downregulated Ac-SOD level. In vitro study demonstrated that QSG restored mitochondrial membrane potential, increased ATP level and reduced mitochondrial ROS production. When H9C2 cells were co-incubated with SIRT3 inhibitor, the efficacies of QSG on mitochondrial function were abrogated. Meanwhile, the regulative effects of QSG on SIRT3/Ac-SOD2 pathway were also abolished.

CONCLUSION

This study demonstrates that QSG is effective in treating DIC. QSG ameliorates oxidative damage and protects mitochondrial function partly by restoring protein acetylation level and by activating the SIRT3/Ac-SOD2 pathway.

Contributing roles of mitochondrial dysfunction and hepatocyte apoptosis in liver diseases through oxidative stress, post-translational modifications, inflammation, and intestinal barrier dysfunction

This review provides an update on recent findings from basic, translational, and clinical studies on the molecular mechanisms of mitochondrial dysfunction and apoptosis of hepatocytes in multiple liver diseases, including but not limited to alcohol-associated liver disease (ALD), metabolic dysfunction-associated steatotic liver disease (MASLD), and drug-induced liver injury (DILI). While the ethanol-inducible cytochrome P450-2E1 (CYP2E1) is mainly responsible for oxidizing binge alcohol via the microsomal ethanol oxidizing system, it is also responsible for metabolizing many xenobiotics, including pollutants, chemicals, drugs, and specific diets abundant in n-6 fatty acids, into toxic metabolites in many organs, including the liver, causing pathological insults through organelles such as mitochondria and endoplasmic reticula. Oxidative imbalances (oxidative stress) in mitochondria promote the covalent modifications of lipids, proteins, and nucleic acids through enzymatic and non-enzymatic mechanisms. Excessive changes stimulate various post-translational modifications (PTMs) of mitochondrial proteins, transcription factors, and histones. Increased PTMs of mitochondrial proteins inactivate many enzymes involved in the reduction of oxidative species, fatty acid metabolism, and mitophagy pathways, leading to mitochondrial dysfunction, energy depletion, and apoptosis. Unique from other organelles, mitochondria control many signaling cascades involved in bioenergetics (fat metabolism), inflammation, and apoptosis/necrosis of hepatocytes. When mitochondrial homeostasis is shifted, these pathways become altered or shut down, likely contributing to the death of hepatocytes with activation of inflammation and hepatic stellate cells, causing liver fibrosis and cirrhosis. This review will encapsulate how mitochondrial dysfunction contributes to hepatocyte apoptosis in several types of liver diseases in order to provide recommendations for targeted therapeutics.

The Therapeutic Potential of Targeting Ferroptosis in the Treatment of Mitochondrial Cardiomyopathies and Heart Failure

ABSTRACT

Ferroptosis is a form of iron-regulated cell death implicated in a wide array of diseases, including heart failure, hypertension, and numerous cardiomyopathies. In addition, mitochondrial dysfunction has been associated with several of these same disease states. However, the role of the mitochondrion in ferroptotic cell death remains debated. As a major regulator of cellular iron levels, the mitochondria may very well play a crucial role in the mechanisms behind ferroptosis, but at this point, this has not been adequately defined. Emerging evidence from our laboratory and others indicates a critical role of mitochondrial Sirtuin 3, a deacetylase linked with longevity and protection against numerous conditions, in the prevention of cardiovascular diseases. Here, we provide a brief overview of the potential roles of Sirtuin 3 in mitochondrial iron homeostasis and its contribution to the mitochondrial cardiomyopathy of Friedreich's ataxia and diabetic cardiomyopathy. We also discuss the current knowledge of the involvement of ferroptosis and the mitochondria in these and other cardiovascular disease states, including doxorubicin-induced cardiomyopathy, and provide insight into areas requiring further investigation.

The immunometabolic reprogramming of microglia in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder (NDD). In the central nervous system (CNS), immune cells like microglia could reprogram intracellular metabolism to alter or exert cellular immune functions in response to environmental stimuli. In AD, microglia could be activated and differentiated into pro-inflammatory or anti-inflammatory phenotypes, and these differences in cellular phenotypes resulted in variance in cellular energy metabolism. Considering the enormous energy requirement of microglia for immune functions, the changes in mitochondria-centered energy metabolism and substrates of microglia are crucial for the cellular regulation of immune responses. Here we reviewed the mechanisms of microglial metabolic reprogramming by analyzing their flexible metabolic patterns and changes that occurred in their metabolism during the development of AD. Further, we summarized the role of drugs in modulating immunometabolic reprogramming to prevent neuroinflammation, which may shed light on a new research direction for AD treatment.

Doxorubicin-Induced Cardiac Senescence Is Alleviated Following Treatment with Combined Polyphenols and Micronutrients through Enhancement in Mitophagy

Oxidative stress and impaired mitophagy are the hallmarks of cardiomyocyte senescence. Specifically, a decrease in mitophagic flux leads to the accumulation of damaged mitochondria and the development of senescence through increased ROS and other mediators. In this study, we describe the preventive role of A5+, a mix of polyphenols and other micronutrients, in doxorubicin (DOXO)-induced senescence of H9C2 cells. Specifically, H9C2 cells exposed to DOXO showed an increase in the protein expression proteins of senescence-associated genes, p21 and p16, and a decrease in the telomere binding factors TRF1 and TRF2, indicative of senescence induction. Nevertheless, A5+ pre-treatment attenuated the senescent-like cell phenotype, as evidenced by inhibition of all senescent markers and a decrease in SA-β-gal staining in DOXO-treated H9C2 cells. Importantly, A5+ restored the LC3 II/LC3 I ratio, Parkin and BNIP3 expression, therefore rescuing mitophagy, and decreased ROS production. Further, A5+ pre-treatment determined a ripolarization of the mitochondrial membrane and improved basal respiration. A5+-mediated protective effects might be related to its ability to activate mitochondrial SIRT3 in synergy with other micronutrients, but in contrast with SIRT4 activation. Accordingly, SIRT4 knockdown in H9C2 cells further increased MnSOD activity, enhanced mitophagy, and reduced ROS generation following A5+ pre-treatment and DOXO exposure compared to WT cells. Indeed, we demonstrated that A5+ protects H9C2 cells from DOXO-induced senescence, establishing a new specific role for A5+ in controlling mitochondrial quality control by restoring SIRT3 activity and mitophagy, which provided a molecular basis for the development of therapeutic strategies against cardiomyocyte senescence.

Cyclovirobuxine D alleviates aldosterone-induced myocardial hypertrophy by protecting mitochondrial function depending on the mutual regulation of Nrf2-SIRT3

BACKGROUND

Cyclovirobuxine D (CVB-D) is a natural alkaloid that exhibits multiple pharmacological activities, such as anti-inflammatory, anti-oxidative stress, and anti-cancer properties. However, its specific protective mechanism of action for myocardial hypertrophy remains unresolved.

PURPOSE

This work was to investigate the ameliorative impact of CVB-D in myocardial hypertrophy, and to elucidate aldosterone (ALD)-induced myocardial hypertrophy by inhibiting the SIRT3 mediated Nrf2 activation.

METHODS

The myocardial hypertrophy model was reproduced by ALD both in vitro and in vivo, and the protective effect of CVB-D on myocardium and mitochondria was evaluated by TEM, H&E, qPCR, Western blot and ChIP. An immunoprecipitation experiment was adopted to evaluate the acetylation level of Nrf2 and the binding between SIRT3 and Nrf2. Additionally, bardoxolone-methyl (BAR, an Nrf2 agonist), ML385 (an Nrf2 inhibitor), resveratrol (RES, a SIRT3 agonist), and 3-TYP (a SIRT3 inhibitor) were used to confirm the molecular mechanism of CVB-D. Lastly, a molecular docking technique was employed to predict the binding site of SIRT3 and Nrf2 proteins.

RESULTS

Our findings suggested that CVB-D improved mitochondrial function, leading to a reduction in ALD-induced cardiomyocyte hypertrophy. By CVB-D treatment, there was an activation of mutual regulation between Nrf2 and SIRT3. Specifically, CVB-D resulted in the increase of Nrf2 protein in the nucleus and activated Nrf2 signaling pathway, thus up-regulating SIRT3. The activation of SIRT3 and the protective action of mitochondrion disappeared because of the intervention of ML385. After CVB-D activated SIRT3, the acetylation level of Nrf2 decreased, followed by activating the Nrf2 pathway. The activation of Nrf2 and mitochondrial protection by CVB-D were reversed by 3-TYP. Our results are also supported by Co-IP and molecular docking analysis, revealing that CVB-D promotes SIRT3-mediated Nrf2 activation.

CONCLUSION

Thus, CVB-D ameliorates ALD-induced myocardial hypertrophy by recovering mitochondrial function by activating the mutual regulation of Nrf2 and SIRT3. Thus, CVB-D could be a beneficial drug for myocardial hypertrophy.

Parkinson's disease pathology is directly correlated to SIRT3 in human subjects and animal models: Implications for AAV.SIRT3-myc as a disease-modifying therapy

In Parkinson's disease (PD), post-mortem studies in affected brain regions have demonstrated a decline in mitochondrial number and function. This combined with many studies in cell and animal models suggest that mitochondrial dysfunction is central to PD pathology. We and others have shown that the mitochondrial protein deacetylase, SIRT3, has neurorestorative effects in PD models. In this study, to determine whether there is a link between PD pathology and SIRT3, we analysed SIRT3 levels in human subjects with PD, and compared to age-matched controls. In the SNc of PD subjects, SIRT3 was reduced by 56.8 ± 15.5% compared to control, regardless of age (p < 0.05, R = 0.6539). Given that age is the primary risk factor for PD, this finding suggests that reduced SIRT3 may contribute to PD pathology. Next, we measured whether there was a correlation between α-synuclein and SIRT3. In a parallel study, we assessed the disease-modifying potential of SIRT3 over-expression in a seeding model of α-synuclein. In PFF rats, infusion of rAAV1.SIRT3-myc reduced abundance of α-synuclein inclusions by 30.1 ± 18.5%. This was not observed when deacetylation deficient SIRT3H248Y was transduced, demonstrating the importance of SIRT3 deacetylation in reducing α-synuclein aggregation. These studies confirm that there is a clear difference in SIRT3 levels in subjects with PD compared to age-matched controls, suggesting a link between SIRT3 and the progression of PD. We also demonstrate that over-expression of SIRT3 reduces α-synuclein aggregation, further validating AAV.SIRT3-myc as a potential disease-modifying solution for PD.

Outcomes of hypothalamic oxytocin neuron-driven cardioprotection after acute myocardial infarction

Altered autonomic balance is a hallmark of numerous cardiovascular diseases, including myocardial infarction (MI). Although device-based vagal stimulation is cardioprotective during chronic disease, a non-invasive approach to selectively stimulate the cardiac parasympathetic system immediately after an infarction does not exist and is desperately needed. Cardiac vagal neurons (CVNs) in the brainstem receive powerful excitation from a population of neurons in the paraventricular nucleus (PVN) of the hypothalamus that co-release oxytocin (OXT) and glutamate to excite CVNs. We tested if chemogenetic activation of PVN-OXT neurons following MI would be cardioprotective. The PVN of neonatal rats was transfected with vectors to selectively express DREADDs within OXT neurons. At 6 weeks of age, an MI was induced and DREADDs were activated with clozapine-N-oxide. Seven days following MI, patch-clamp electrophysiology confirmed the augmented excitatory neurotransmission from PVN-OXT neurons to downstream nuclei critical for parasympathetic activity with treatment (43.7 ± 10 vs 86.9 ± 9 pA; MI vs. treatment), resulting in stark improvements in survival (85% vs. 95%; MI vs. treatment), inflammation, fibrosis assessed by trichrome blue staining, mitochondrial function assessed by Seahorse assays, and reduced incidence of arrhythmias (50% vs. 10% cumulative incidence of ventricular fibrillation; MI vs. treatment). Myocardial transcriptomic analysis provided molecular insight into potential cardioprotective mechanisms, which revealed the preservation of beneficial signaling pathways, including muscarinic receptor activation, in treated animals. These comprehensive results demonstrate that the PVN-OXT network could be a promising therapeutic target to quickly activate beneficial parasympathetic-mediated cellular pathways within the heart during the early stages of infarction.

Aging, oxidative stress and degenerative diseases: mechanisms, complications and emerging therapeutic strategies

Aging accompanied by several age-related complications, is a multifaceted inevitable biological progression involving various genetic, environmental, and lifestyle factors. The major factor in this process is oxidative stress, caused by an abundance of reactive oxygen species (ROS) generated in the mitochondria and endoplasmic reticulum (ER). ROS and RNS pose a threat by disrupting signaling mechanisms and causing oxidative damage to cellular components. This oxidative stress affects both the ER and mitochondria, causing proteopathies (abnormal protein aggregation), initiation of unfolded protein response, mitochondrial dysfunction, abnormal cellular senescence, ultimately leading to inflammaging (chronic inflammation associated with aging) and, in rare cases, metastasis. RONS during oxidative stress dysregulate multiple metabolic pathways like NF-κB, MAPK, Nrf-2/Keap-1/ARE and PI3K/Akt which may lead to inappropriate cell death through apoptosis and necrosis. Inflammaging contributes to the development of inflammatory and degenerative diseases such as neurodegenerative diseases, diabetes, cardiovascular disease, chronic kidney disease, and retinopathy. The body's antioxidant systems, sirtuins, autophagy, apoptosis, and biogenesis play a role in maintaining homeostasis, but they have limitations and cannot achieve an ideal state of balance. Certain interventions, such as calorie restriction, intermittent fasting, dietary habits, and regular exercise, have shown beneficial effects in counteracting the aging process. In addition, interventions like senotherapy (targeting senescent cells) and sirtuin-activating compounds (STACs) enhance autophagy and apoptosis for efficient removal of damaged oxidative products and organelles. Further, STACs enhance biogenesis for the regeneration of required organelles to maintain homeostasis. This review article explores the various aspects of oxidative damage, the associated complications, and potential strategies to mitigate these effects.

Targeting Mitochondrial Sirtuins in Age-Related Neurodegenerative Diseases and Fibrosis

Aging is a natural and complex biological process that is associated with widespread functional declines in numerous physiological processes, terminally affecting multiple organs and tissues. Fibrosis and neurodegenerative diseases (NDs) often occur with aging, imposing large burdens on public health worldwide, and there are currently no effective treatment strategies for these diseases. Mitochondrial sirtuins (SIRT3-5), which are members of the sirtuin family of NAD+-dependent deacylases and ADP-ribosyltransferases, are capable of regulating mitochondrial function by modifying mitochondrial proteins that participate in the regulation of cell survival under various physiological and pathological conditions. A growing body of evidence has revealed that SIRT3-5 exert protective effects against fibrosis in multiple organs and tissues, including the heart, liver, and kidney. SIRT3-5 are also involved in multiple age-related NDs, including Alzheimer's disease, Parkinson's disease, and Huntington's disease. Furthermore, SIRT3-5 have been noted as promising targets for antifibrotic therapies and the treatment of NDs. This review systematically highlights recent advances in knowledge regarding the role of SIRT3-5 in fibrosis and NDs and discusses SIRT3-5 as therapeutic targets for NDs and fibrosis.

Immunomodulatory Effects of SGLT2 Inhibitors-Targeting Inflammation and Oxidative Stress in Aging

Given that the increase in the aging population has grown into one of the largest public health issues, inflammation and oxidative stress, which are closely associated with the aging process, became a focus of recent research. Sodium-glucose co-transporter 2 (SGLT2) inhibitors, a group of drugs initially developed as oral antidiabetics, have shown many beneficial effects over time, including improvement in renal function and cardioprotective effects. It has been shown that SGLT2 inhibitors, as a drug class, have an immunomodulatory and antioxidative effect, affecting endothelial function as well as metabolic parameters. Therefore, it is not surprising that various studies have investigated the potential mechanisms of action of SGLT2 inhibitors in age-related diseases. The proposed mechanisms by which SGLT2 inhibitors can achieve their anti-inflammatory effects include influence on AMPK/SIRT1/PGC-1α signaling, various cytokines, and the NLRP3 inflammasome. The antioxidative effect is related to their action on mitochondria and their influence on the signaling pathways of transforming growth factor β and nuclear erythroid 2-related factor 2/antioxidant response element. Also, SGLT2 inhibitors achieve their anti-inflammatory and antioxidative effects by affecting metabolic parameters, such as uric acid reduction, stimulation of ketogenesis, reduction of body weight, lipolysis, and epicardial fat tissue. Finally, SGLT2 inhibitors display anti-atherosclerotic effects that modulate inflammatory reactions, potentially resulting in improvement in endothelial function. This narrative review offers a complete and comprehensive overview of the possible pathophysiologic mechanisms of the SGLT2 inhibitors involved in the aging process and development of age-related disease. However, in order to use SGLT2 inhibitor drugs as an anti-aging therapy, further basic and clinical research is needed to elucidate the potential effects and complex mechanisms they have on inflammation processes.

Sirtuin 1 Expression in Canine Mammary Tumors: A Pilot Study

Sirtuin 1 (SIRT1) is a protein involved in aging, cell protection, and energy metabolism in mammals. Recently, SIRT1 has been intensively studied in medical oncology, but the role of SIRT1 is still controversial, as it has been proposed as both an oncogene and a tumor suppressor. The aim of this study is to investigate the expression of SIRT1 by immunohistochemistry in canine mammary tissues, and by Western blot and immunofluorescence analysis in different canine mammary cell lines. Our results showed a decrease in SIRT1 expression from normal mammary gland tissue, and from benign and well-differentiated malignant tumors (G1) to less differentiated ones (G2-G3). Furthermore, a shift in the subcellular localization of SIRT1 from the nucleus to the cytoplasm was observed in less differentiated malignant tumors. However, further studies are needed to investigate the subcellular localization of SIRT1 in canine cancer cells and the role it may play in oncogenesis in animals.

The AKT2/SIRT5/TFEB pathway as a potential therapeutic target in atrophic AMD

Age-related macular degeneration (AMD), the leading cause of geriatric blindness, is a multi-factorial disease with retinal-pigmented epithelial (RPE) cell dysfunction as a central pathogenic driver. With RPE degeneration, lysosomal function is a core process that is disrupted. Transcription factors EB/E3 (TFEB/E3) tightly control lysosomal function; their disruption can cause aging disorders, such as AMD. Here, we show that induced pluripotent stem cells (iPSC)-derived RPE cells with the complement factor H variant [ CFH (Y402H)] have increased AKT2, which impairs TFEB/TFE3 nuclear translocation and lysosomal function. Increased AKT2 can inhibit PGC1α, which downregulates SIRT5, an AKT2 binding partner. SIRT5 and AKT2 co-regulate each other, thereby modulating TFEB-dependent lysosomal function in the RPE. Failure of the AKT2/SIRT5/TFEB pathway in the RPE induced abnormalities in the autophagy-lysosome cellular axis by upregulating secretory autophagy, thereby releasing a plethora of factors that likely contribute to drusen formation, a hallmark of AMD. Finally, overexpressing AKT2 in RPE cells in mice led to an AMD-like phenotype. Thus, targeting the AKT2/SIRT5/TFEB pathway could be a potential therapy for atrophic AMD.

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.

Changes in the Mitochondria in the Aging Process-Can α-Tocopherol Affect Them?

Aerobic organisms use molecular oxygen in several reactions, including those in which the oxidation of substrate molecules is coupled to oxygen reduction to produce large amounts of metabolic energy. The utilization of oxygen is associated with the production of ROS, which can damage biological macromolecules but also act as signaling molecules, regulating numerous cellular processes. Mitochondria are the cellular sites where most of the metabolic energy is produced and perform numerous physiological functions by acting as regulatory hubs of cellular metabolism. They retain the remnants of their bacterial ancestors, including an independent genome that encodes part of their protein equipment; they have an accurate quality control system; and control of cellular functions also depends on communication with the nucleus. During aging, mitochondria can undergo dysfunctions, some of which are mediated by ROS. In this review, after a description of how aging affects the mitochondrial quality and quality control system and the involvement of mitochondria in inflammation, we report information on how vitamin E, the main fat-soluble antioxidant, can protect mitochondria from age-related changes. The information in this regard is scarce and limited to some tissues and some aspects of mitochondrial alterations in aging. Improving knowledge of the effects of vitamin E on aging is essential to defining an optimal strategy for healthy aging.

TFEB is a central regulator of the aging process and age-related diseases

Old age is associated with a greater burden of disease, including neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease, as well as other chronic diseases. Coincidentally, popular lifestyle interventions, such as caloric restriction, intermittent fasting, and regular exercise, in addition to pharmacological interventions intended to protect against age-related diseases, induce transcription factor EB (TFEB) and autophagy. In this review, we summarize emerging discoveries that point to TFEB activity affecting the hallmarks of aging, including inhibiting DNA damage and epigenetic modifications, inducing autophagy and cell clearance to promote proteostasis, regulating mitochondrial quality control, linking nutrient-sensing to energy metabolism, regulating pro- and anti-inflammatory pathways, inhibiting senescence and promoting cell regenerative capacity. Furthermore, the therapeutic impact of TFEB activation on normal aging and tissue-specific disease development is assessed in the contexts of neurodegeneration and neuroplasticity, stem cell differentiation, immune responses, muscle energy adaptation, adipose tissue browning, hepatic functions, bone remodeling, and cancer. Safe and effective strategies of activating TFEB hold promise as a therapeutic strategy for multiple age-associated diseases and for extending lifespan.

Sirtuins: Promising Therapeutic Targets to Treat Ischemic Stroke

Stroke is a major cause of mortality and disability globally, with ischemic stroke (IS) accounting for over 80% of all stroke cases. The pathological process of IS involves numerous signal molecules, among which are the highly conserved nicotinamide adenine dinucleotide (NAD+)-dependent enzymes known as sirtuins (SIRTs). SIRTs modulate various biological processes, including cell differentiation, energy metabolism, DNA repair, inflammation, and oxidative stress. Importantly, several studies have reported a correlation between SIRTs and IS. This review introduces the general aspects of SIRTs, including their distribution, subcellular location, enzyme activity, and substrate. We also discuss their regulatory roles and potential mechanisms in IS. Finally, we describe the current therapeutic methods based on SIRTs, such as pharmacotherapy, non-pharmacological therapeutic/rehabilitative interventions, epigenetic regulators, potential molecules, and stem cell-derived exosome therapy. The data collected in this study will potentially contribute to both clinical and fundamental research on SIRTs, geared towards developing effective therapeutic candidates for future treatment of IS.

Sirtuin family in autoimmune diseases

In recent years, epigenetic modifications have been widely researched. As humans age, environmental and genetic factors may drive inflammation and immune responses by influencing the epigenome, which can lead to abnormal autoimmune responses in the body. Currently, an increasing number of studies have emphasized the important role of epigenetic modification in the progression of autoimmune diseases. Sirtuins (SIRTs) are class III nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylases and SIRT-mediated deacetylation is an important epigenetic alteration. The SIRT family comprises seven protein members (namely, SIRT1-7). While the catalytic core domain contains amino acid residues that have remained stable throughout the entire evolutionary process, the N- and C-terminal regions are structurally divergent and contribute to differences in subcellular localization, enzymatic activity and substrate specificity. SIRT1 and SIRT2 are localized in the nucleus and cytoplasm. SIRT3, SIRT4, and SIRT5 are mitochondrial, and SIRT6 and SIRT7 are predominantly found in the nucleus. SIRTs are key regulators of various physiological processes such as cellular differentiation, apoptosis, metabolism, ageing, immune response, oxidative stress, and mitochondrial function. We discuss the association between SIRTs and common autoimmune diseases to facilitate the development of more effective therapeutic strategies.

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.

Ageing in the brain: mechanisms and rejuvenating strategies

Ageing is characterized by the progressive loss of cellular homeostasis, leading to an overall decline of the organism's fitness. In the brain, ageing is highly associated with cognitive decline and neurodegenerative diseases. With the rise in life expectancy, characterizing the brain ageing process becomes fundamental for developing therapeutic interventions against the increased incidence of age-related neurodegenerative diseases and to aim for an increase in human life span and, more importantly, health span. In this review, we start by introducing the molecular/cellular hallmarks associated with brain ageing and their impact on brain cell populations. Subsequently, we assess emerging evidence on how systemic ageing translates into brain ageing. Finally, we revisit the mainstream and the novel rejuvenating strategies, discussing the most successful ones in delaying brain ageing and related diseases.

Dammarane-type saponins from Gynostemma pentaphyllum and their anti-aging activities via up-regulating mitochondria related proteins

The importance of mitochondria in regulation of aging has been extensively recognized and confirmed. Gynostemma pentaphyllum (Thunb.) Makino, a homology of medicine and food, has been widely utilized as dietary supplement. In this study, the transcriptome of normal cells (wild type mouse embryo fibroblasts) regulated by the 30% aqueous EtOH extract of G. pentaphyllum was firstly evaluated by RNA sequencing and the results revealed that the G. pentaphyllum could up-regulate the genes involved in oxidative phosphorylation (OXPHOS) and sirtuin (SIRT) signaling pathways, indicating its effect in promoting cell viability might be attributed to the role of improving mitochondrial functions. To further discover the bioactive compounds, sixteen undescribed dammarane-type saponins along with twenty-eight known analogues were isolated from the active extract of G. pentaphyllum. Their structures were elucidated by means of comprehensive analysis of NMR and HRMS spectroscopic data. All isolates were evaluated for the regulatory effects on SIRT3 and translocase of the outer membrane 20 (TOM20), and thirteen of them exhibited satisfactory agonist activities on both SIRT3 and TOM20 at 5 μM. Furthermore, the preliminary structure-activity relationships analysis demonstrated the additional hydroxymethyl and carbonyl groups or less sugar residues in saponins could contribute positively to the up-regulatory effect on SIRT3 and TOM20. These findings encouraged the potential roles of G. pentaphyllum and its bioactive saponins in the development of natural drugs for the treatment of aging-related diseases.

Curcumin supplementation increases longevity and antioxidant capacity in Caenorhabditis elegans

Curcumin is well known as a potent antioxidant and free radical scavenger and has great potential for anti-aging applications. In this study, we investigate the molecular mechanism of curcumin in prolonging the lifespan of C. elegans. Four concentrations of curcumin (10, 25, 50, and 100 µM) were administered, and the optimal treatment concentration was determined by analyzing the nematode lifespan, physiology, and biochemistry. Additionally, RNA-seq and qRT-PCR were performed to explore the antioxidant effect of curcumin and its underlying mechanism. Results revealed that curcumin could significantly improve the survival capacity of C. elegans without influencing its growth. Curcumin was observed to significantly decrease the levels of reactive oxygen species (ROS) under extreme conditions such as heat stress and paraquat stress. In addition, curcumin increased the amount of nematode mitochondrial DNA (mtDNA) replication. RNA-seq results revealed that the underlying mechanism of curcumin in C. elegans is related to the mitogen-activated protein kinase (MAPK) pathway. qRT-PCR results confirmed that the expression of oxidative stress-related genes (sod-1, sod-2, sod-3, gst-4) was increased, and the expression of MAPK signaling pathway-related genes (sek-1, pmk-1, nsy-1) was significantly downregulated. Furthermore, the administration of curcumin extended the lifespan of nematodes, potentially through the enhancement of oxidative stress resistance and the downregulation of the MAPK signaling pathway. These findings improve our understanding of both lifespan extension and the potential mechanism of curcumin in C. elegans.

Microglia-derived TNF-α contributes to RVLM neuronal mitochondrial dysfunction via blocking the AMPK-Sirt3 pathway in stress-induced hypertension

BACKGROUND

Neuroinflammation in the rostral ventrolateral medulla (RVLM) has been associated with the pathogenesis of stress-induced hypertension (SIH). Neuronal mitochondrial dysfunction is involved in many pathological and physiological processes. However, the impact of neuroinflammation on neuronal mitochondrial homeostasis and the involved signaling pathway in the RVLM during SIH are largely unknown.

METHODS

The morphology and phenotype of microglia and the neuronal mitochondrial injury in vivo were analyzed by immunofluorescence, Western blot, RT-qPCR, transmission electron microscopy, and kit detection. The underlying mechanisms of microglia-derived tumor necrosis factor-α (TNF-α) on neuronal mitochondrial function were investigated through in vitro and in vivo experiments such as immunofluorescence and Western blot. The effect of TNF-α on blood pressure (BP) regulation was determined in vivo via intra-RVLM microinjection of TNF-α receptor antagonist R7050.

RESULTS

The results demonstrated that BP, heart rate (HR), renal sympathetic nerve activity (RSNA), plasma norepinephrine (NE), and electroencephalogram (EEG) power increased in SIH rats. Furthermore, the branching complexity of microglia in the RVLM of SIH rats decreased and polarized into M1 phenotype, accompanied by upregulation of TNF-α. Increased neuronal mitochondria injury was observed in the RVLM of SIH rats. Mechanistically, Sirtuin 3 (Sirt3) and p-AMPK expression were markedly downregulated in both SIH rats and TNF-α-treated N2a cells. AMPK activator A769662 upregulated AMPK-Sirt3 signaling pathway and consequently reversed TNF-α-induced mitochondrial dysfunction. Microinjection of TNF-α receptor antagonist R7050 into the RVLM of SIH rats significantly inhibited the biological activities of TNF-α, increased p-AMPK and Sirt3 levels, and alleviated neuronal mitochondrial injury, thereby reducing c-FOS expression, RSNA, plasma NE, and BP.

CONCLUSIONS

This study revealed that microglia-derived TNF-α in the RVLM impairs neuronal mitochondrial function in SIH possibly through inhibiting the AMPK-Sirt3 pathway. Therefore, microglia-derived TNF-α in the RVLM may be a possible therapeutic target for the intervention of SIH.

Cellular and molecular biology of sirtuins in cardiovascular disease

Sirtuins (SIRTs) are a nicotinic adenine dinucleotide (+) -dependent histone deacetylase that regulates critical signaling pathways in prokaryotes and eukaryotes. Studies have identified seven mammalian homologs of the yeast SIRT silencing message regulator 2, namely, SIRT1-SIRT7. Recent in vivo and in vitro studies have successfully demonstrated the involvement of SIRTs in key pathways for cell biological function in physiological and pathological processes of the cardiovascular system, including processes including cellular senescence, oxidative stress, apoptosis, DNA damage, and cellular metabolism. Emerging evidence has stimulated a significant evolution in preventing and treating cardiovascular disease (CVD). Here, we review the important roles of SIRTs for the regulatory pathways involved in the pathogenesis of cardiovascular diseases and their molecular targets, including novel protein post-translational modifications of succinylation. In addition, we summarize the agonists and inhibitors currently identified to target novel specific small molecules of SIRTs. A better understanding of the role of SIRTs in the biology of CVD opens new avenues for therapeutic intervention with great potential for preventing and treating CVD.

Systemic Metabolism and Mitochondria in the Mechanism of Alzheimer's Disease: Finding Potential Therapeutic Targets

Elderly people over the age of 65 are those most likely to experience Alzheimer's disease (AD), and aging and AD are associated with apparent metabolic alterations. Currently, there is no curative medication against AD and only several drugs have been approved by the FDA, but these drugs can only improve the symptoms of AD. Many preclinical and clinical trials have explored the impact of adjusting the whole-body and intracellular metabolism on the pathogenesis of AD. The most recent evidence suggests that mitochondria initiate an integrated stress response to environmental stress, which is beneficial for healthy aging and neuroprotection. There is also an increasing awareness of the differential risk and potential targeting strategies related to the metabolic level and microbiome. As the main participants in intracellular metabolism, mitochondrial bioenergetics, mitochondrial quality-control mechanisms, and mitochondria-linked inflammatory responses have been regarded as potential therapeutic targets for AD. This review summarizes and highlights these advances.

Aging, cell senescence, the pathogenesis and targeted therapies of intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) refers to the aging and degenerative diseases of intervertebral disc components such as nucleus pulposus, annulus fibrosus, and cartilage endplate, and is the main cause of chronic low back pain. Over the past few years, many researchers around the world concerned that the degeneration of nucleus pulposus (NP) cells plays the main role in IVDD. The degeneration of NP cells is caused by a series of pathological processes, including oxidative stress, inflammatory response, apoptosis, abnormal proliferation, and autophagy. Interestingly, many studies have found a close relationship between the senescence of NP cells and the progression of NP degeneration. The classical aging pathways also have been confirmed to be involved in the pathological process of IVDD. Moreover, several anti-aging drugs have been used to treat IVDD by inhibiting NP cells senescence, such as proanthocyanidins, resveratrol and bone morphogenetic protein 2. Therefore, this article will systematically list and discuss aging, cell senescence, the pathogenesis and targeted therapies of IVDD, in order to provide new ideas for the treatment of IVDD in the future.

Cardioprotective effect of ultrasound-targeted destruction of Sirt3-loaded cationic microbubbles in a large animal model of pathological cardiac hypertrophy

Pathological cardiac hypertrophy occurs in response to numerous increased afterload stimuli and precedes irreversible heart failure (HF). Therefore, therapies that ameliorate pathological cardiac hypertrophy are urgently required. Sirtuin 3 (Sirt3) is a main member of histone deacetylase class III and is a crucial anti-oxidative stress agent. Therapeutically enhancing the Sirt3 transfection efficiency in the heart would broaden the potential clinical application of Sirt3. Ultrasound-targeted microbubble destruction (UTMD) is a prospective, noninvasive, repeatable, and targeted gene delivery technique. In the present study, we explored the potential and safety of UTMD as a delivery tool for Sirt3 in hypertrophic heart tissues using adult male Bama miniature pigs. Pigs were subjected to ear vein delivery of human Sirt3 together with UTMD of cationic microbubbles (CMBs). Fluorescence imaging, western blotting, and quantitative real-time PCR revealed that the targeted destruction of ultrasonic CMBs in cardiac tissues greatly boosted Sirt3 delivery. Overexpression of Sirt3 ameliorated oxidative stress and partially improved the diastolic function and prevented the apoptosis and profibrotic response. Lastly, our data revealed that Sirt3 may regulate the potential transcription of catalase and MnSOD through Foxo3a. Combining the advantages of ultrasound CMBs with preclinical hypertrophy large animal models for gene delivery, we established a classical hypertrophy model as well as a strategy for the targeted delivery of genes to hypertrophic heart tissues. Since oxidative stress, fibrosis and apoptosis are indispensable in the evolution of cardiac hypertrophy and heart failure, our findings suggest that Sirt3 is a promising therapeutic option for these diseases. STATEMENT OF SIGNIFICANCE: : Pathological cardiac hypertrophy is a central prepathology of heart failure and is seen to eventually precede it. Feasible targets that may prevent or reverse disease progression are scarce and urgently needed. In this study, we developed surface-filled lipid octafluoropropane gas core cationic microbubbles that could target the release of human Sirt3 reactivating the endogenous Sirt3 in hypertrophic hearts and protect against oxidative stress in a pig model of cardiac hypertrophy induced by aortic banding. Sirt3-CMBs may enhance cardiac diastolic function and ameliorate fibrosis and apoptosis. Our work provides a classical cationic lipid-based, UTMD-mediated Sirt3 delivery system for the treatment of Sirt3 in patients with established cardiac hypertrophy, as well as a promising therapeutic target to combat pathological cardiac hypertrophy.

Amino acids downregulate SIRT4 to detoxify ammonia through the urea cycle

Ammonia production via glutamate dehydrogenase is inhibited by SIRT4, a sirtuin that displays both amidase and non-amidase activities. The processes underlying the regulation of ammonia removal by amino acids remain unclear. Here, we report that SIRT4 acts as a decarbamylase that responds to amino acid sufficiency and regulates ammonia removal. Amino acids promote lysine 307 carbamylation (OTCCP-K307) of ornithine transcarbamylase (OTC), which activates OTC and the urea cycle. Proteomic and interactome screening identified OTC as a substrate of SIRT4. SIRT4 decarbamylates OTCCP-K307 and inactivates OTC in an NAD+-dependent manner. SIRT4 expression was transcriptionally upregulated by the amino acid insufficiency-activated GCN2-eIF2α-ATF4 axis. SIRT4 knockout in cultured cells caused higher OTCCP-K307 levels, activated OTC, elevated urea cycle intermediates and urea production via amino acid catabolism. Sirt4 ablation decreased male mouse blood ammonia levels and ameliorated CCl4-induced hepatic encephalopathy phenotypes. We reveal that SIRT4 safeguards cellular ammonia toxicity during amino acid catabolism.

Metformin regulates chondrocyte senescence and proliferation through microRNA-34a/SIRT1 pathway in osteoarthritis

BACKGROUND

Osteoarthritis (OA) is the most common degenerative disease in joints among elderly patients. Senescence is deeply involved in the pathogenesis of osteoarthritis. Metformin is widely used as the first-line drug for Type 2 diabetes mellitus (T2DM), and has great potential for the treatment of other aging-related disorders, including OA. However, the role of metformin in OA is not fully elucidated. Therefore, our aim here was to investigate the effects of metformin on human chondrocytes.

METHODS

After metformin treatment, expression level of microRNA-34a and SIRT1 in chondrocyte were detected with quantitative real-time PCR and immunofluorescence staining. Then, microRNA-34a mimic and small interfering RNA (siRNA) against SIRT1 (siRNA-SIRT1) were transfected into chondrocyte. Senescence-associated β-galactosidase (SA-β-gal) staining was performed to assess chondrocyte senescence. Chondrocyte viability was illustrated with MTT and colony formation assays. Western blot was conducted to detect the expression of P16, IL-6, matrix metalloproteinase-13 (MMP-13), Collagen type II (COL2A1) and Aggrecan (ACAN).

RESULTS

We found that metformin treatment (1 mM) inhibited microRNA-34a while promoted SIRT1 expression in OA chondrocytes. Both miR-34a mimics and siRNA against SIRT1 inhibited SIRT1 expression in chondrocytes. SA-β-gal staining assay confirmed that metformin reduced SA-β-gal-positive rate of chondrocytes, while transfection with miR-34a mimics or siRNA-SIRT1 reversed it. MTT assay and colony formation assay showed that metformin accelerated chondrocyte proliferation, while miR-34a mimics or siRNA-SIRT1 weakened this effect. Furthermore, results from western blot demonstrated that metformin suppressed expression of senescence-associated protein P16, proinflammatory cytokine IL-6 and catabolic gene MMP-13 while elevated expression of anabolic proteins such as Collagen type II and Aggrecan, which could be attenuated by transfection with miR-34a mimics.

CONCLUSION

Overall, our data suggest that metformin regulates chondrocyte senescence and proliferation through microRNA-34a/SIRT1 pathway, indicating it could be a novel strategy for OA treatment.

Trypanosoma cruzi Sirtuin 2 as a Relevant Druggable Target: New Inhibitors Developed by Computer-Aided Drug Design

Trypanosoma cruzi, the etiological agent of Chagas disease, relies on finely coordinated epigenetic regulation during the transition between hosts. Herein we targeted the silent information regulator 2 (Sir2) enzyme, a NAD+-dependent class III histone deacetylase, to interfere with the parasites’ cell cycle. A combination of molecular modelling with on-target experimental validation was used to discover new inhibitors from commercially available compound libraries. We selected six inhibitors from the virtual screening, which were validated on the recombinant Sir2 enzyme. The most potent inhibitor (CDMS-01, IC50 = 40 μM) was chosen as a potential lead compound.