Sirtuins in epigenetic regulation

The Structures, Functions, and Roles of Class III HDACs (Sirtuins) in Neuropsychiatric Diseases

Over the past two decades, epigenetic regulation has become a rapidly growing and influential field in biology and medicine. One key mechanism involves the acetylation and deacetylation of lysine residues on histone core proteins and other critical proteins that regulate gene expression and cellular signaling. Although histone deacetylases (HDACs) have received significant attention, the roles of individual HDAC isoforms in the pathogenesis of psychiatric diseases still require further research. This is particularly true with regard to the sirtuins, class III HDACs. Sirtuins have unique functional activity and significant roles in normal neurophysiology, as well as in the mechanisms of addiction, mood disorders, and other neuropsychiatric abnormalities. This review aims to elucidate the differences in catalytic structure and function of the seven sirtuins as they relate to psychiatry.

Symmetrical 2,7-disubstituted 9H-fluoren-9-one as a novel and promising scaffold for selective targeting of SIRT2

Sirtuin 2 (SIRT2) belongs to the family of silent information regulators (sirtuins), which comprises nicotinamide adenine dinucleotide (NAD+)-dependent protein lysine deacetylases. With a distribution across numerous tissues and organs of the human body, SIRT2 is involved in a wide range of physiological and pathological processes, such as regulating the cell cycle, energy metabolism, DNA repair, and tumorigenesis. Aberrant expression of SIRT2 has been closely associated with particular etiologies of human diseases, positioning SIRT2 as a promising therapeutic target. Herein, we detail the design overview and findings of novel symmetrical 2,7-disubstituted 9H-fluoren-9-one derivatives targeting SIRT2. SG3 displayed the most potent SIRT2-selective inhibitory profile, with an IC50 value of 1.95 μ M $\mu {\rm{M}}$ , and reduced the cell viability of human breast cancer MCF-7 cells accompanied by hyperacetylation of α-tubulin. Finally, molecular docking, molecular dynamics simulations, and binding free energy calculations using molecular mechanics/generalized born surface area method were performed to verify the binding ability of SG3 to SIRT2. Taken together, these results could enhance our understanding of the structural elements necessary for inhibiting SIRT2 and shed light on the mechanism of inhibition.

Multifaceted regulation of sirtuin 2 (Sirt2) deacetylase activity

Sirtuin 2 (Sirt2) is a member of the sirtuin family of NAD-dependent lysine deacylases and plays important roles in regulation of the cell cycle and gene expression. As a nucleocytoplasmic deacetylase, Sirt2 has been shown to target both histone and nonhistone acetylated protein substrates. The central catalytic domain of Sirt2 is flanked by flexible N and C termini, which vary in length and composition with alternative splicing. These termini are further subject to posttranslational modifications including phosphorylation. Here, we investigate the function of the N and C termini on deacetylation of nuclear substrates by Sirt2. Remarkably, we find that the C terminus autoinhibits deacetylation, while the N terminus enhances deacetylation of proteins and peptides, but not nucleosomes-a chromatin model substrate. Using protein semisynthesis, we characterize the effect of cell cycle-linked N-terminal phosphorylation at two major phosphorylation sites (Ser23/Ser25) and find that these further enhance protein/peptide deacetylation, with no effect on nucleosome deacetylation. Additionally, we find that VRK1, an established binding partner of both Sirt2 and nucleosomes, can stimulate deacetylation of nucleosomes by Sirt2, likely through an electrostatic mechanism. Taken together, these findings reveal multiple mechanisms regulating the activity of Sirt2, which allow for a broad range of activities across its multiple biological roles.

Activation and inhibition of sirtuins: From bench to bedside

The sirtuin family comprises seven NAD+-dependent enzymes which catalyze protein lysine deacylation and mono ADP-ribosylation. Sirtuins act as central regulators of genomic stability and gene expression and control key processes, including energetic metabolism, cell cycle, differentiation, apoptosis, and aging. As a result, all sirtuins play critical roles in cellular homeostasis and organism wellness, and their dysregulation has been linked to metabolic, cardiovascular, and neurological diseases. Furthermore, sirtuins have shown dichotomous roles in cancer, acting as context-dependent tumor suppressors or promoters. Given their central role in different cellular processes, sirtuins have attracted increasing research interest aimed at developing both activators and inhibitors. Indeed, sirtuin modulation may have therapeutic effects in many age-related diseases, including diabetes, cardiovascular and neurodegenerative disorders, and cancer. Moreover, isoform selective modulators may increase our knowledge of sirtuin biology and aid to develop better therapies. Through this review, we provide critical insights into sirtuin pharmacology and illustrate their enzymatic activities and biological functions. Furthermore, we outline the most relevant sirtuin modulators in terms of their modes of action, structure-activity relationships, pharmacological effects, and clinical applications.

Chromatin lysine acylation: On the path to chromatin homeostasis and genome integrity

The fundamental role of cells in safeguarding the genome's integrity against DNA double-strand breaks (DSBs) is crucial for maintaining chromatin homeostasis and the overall genomic stability. Aberrant responses to DNA damage, known as DNA damage responses (DDRs), can result in genomic instability and contribute significantly to tumorigenesis. Unraveling the intricate mechanisms underlying DDRs following severe damage holds the key to identify therapeutic targets for cancer. Chromatin lysine acylation, encompassing diverse modifications such as acetylation, lactylation, crotonylation, succinylation, malonylation, glutarylation, propionylation, and butyrylation, has been extensively studied in the context of DDRs and chromatin homeostasis. Here, we delve into the modifying enzymes and the pivotal roles of lysine acylation and their crosstalk in maintaining chromatin homeostasis and genome integrity in response to DDRs. Moreover, we offer a comprehensive perspective and overview of the latest insights, driven primarily by chromatin acylation modification and associated regulators.

Catalpol attenuates hepatic glucose metabolism disorder and oxidative stress in triptolide-induced liver injury by regulating the SIRT1/HIF-1α pathway

Triptolide (TP), known for its effectiveness in treating various rheumatoid diseases, is also associated with significant hepatotoxicity risks. This study explored Catalpol (CAT), an iridoid glycoside with antioxidative and anti-inflammatory effects, as a potential defense against TP-induced liver damage. In vivo and in vitro models of liver injury were established using TP in combination with different concentrations of CAT. Metabolomics analyses were conducted to assess energy metabolism in mouse livers. Additionally, a Seahorse XF Analyzer was employed to measure glycolysis rate, mitochondrial respiratory functionality, and real-time ATP generation rate in AML12 cells. The study also examined the expression of proteins related to glycogenolysis and gluconeogenesis. Using both in vitro SIRT1 knockout/overexpression and in vivo liver-specific SIRT1 knockout models, we confirmed SIRT1 as a mechanism of action for CAT. Our findings revealed that CAT could alleviate TP-induced liver injury by activating SIRT1, which inhibited lysine acetylation of hypoxia-inducible factor-1α (HIF-1α), thereby restoring the balance between glycolysis and oxidative phosphorylation. This action improved mitochondrial dysfunction and reduced glucose metabolism disorder and oxidative stress caused by TP. Taken together, these insights unveil a hitherto undocumented mechanism by which CAT ameliorates TP-induced liver injury, positioning it as a potential therapeutic agent for managing TP-induced hepatotoxicity.

Copy number variation introduced by a massive mobile element facilitates global thermal adaptation in a fungal wheat pathogen

Copy number variation (CNV) can drive rapid evolution in changing environments. In microbial pathogens, such adaptation is a key factor underpinning epidemics and colonization of new niches. However, the genomic determinants of such adaptation remain poorly understood. Here, we systematically investigate CNVs in a large genome sequencing dataset spanning a worldwide collection of 1104 genomes from the major wheat pathogen Zymoseptoria tritici. We found overall strong purifying selection acting on most CNVs. Genomic defense mechanisms likely accelerated gene loss over episodes of continental colonization. Local adaptation along climatic gradients was likely facilitated by CNVs affecting secondary metabolite production and gene loss in general. One of the strongest loci for climatic adaptation is a highly conserved gene of the NAD-dependent Sirtuin family. The Sirtuin CNV locus localizes to an ~68-kb Starship mobile element unique to the species carrying genes highly expressed during plant infection. The element has likely lost the ability to transpose, demonstrating how the ongoing domestication of cargo-carrying selfish elements can contribute to selectable variation within populations. Our work highlights how standing variation in gene copy numbers at the global scale can be a major factor driving climatic and metabolic adaptation in microbial species.

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.

Role of epigenetics in the regulation of skin aging and geroprotective intervention: A new sight

Multiple epigenetic factors play a regulatory role in maintaining the homeostasis of cutaneous components and are implicated in the aging process of the skin. They have been associated with the activation of the senescence program, which is the primary contributor to age-related decline in the skin. Senescent species drive a series of interconnected processes that impact the immediate surroundings, leading to structural changes, diminished functionality, and heightened vulnerability to infections. Geroprotective medicines that may restore the epigenetic balance represent valid therapeutic alliances against skin aging. Most of them are well-known Western medications such as metformin, nicotinamide adenine dinucleotide (NAD+), rapamycin, and histone deacetylase inhibitors, while others belong to Traditional Chinese Medicine (TCM) remedies for which the scientific literature provides limited information. With the help of the Geroprotectors.org database and a comprehensive analysis of the referenced literature, we have compiled data on compounds and formulae that have shown potential in preventing skin aging and have been identified as epigenetic modulators.

Gut microbiota and their derivatives in the progression of colorectal cancer: Mechanisms of action, genome and epigenome contributions

Gut microbiota interacts with host epithelial cells and regulates many physiological functions such as genetics, epigenetics, metabolism of nutrients, and immune functions. Dietary factors may also be involved in the etiology of colorectal cancer (CRC), especially when an unhealthy diet is consumed with excess calorie intake and bad practices like smoking or consuming a great deal of alcohol. Bacteria including Fusobacterium nucleatum, Enterotoxigenic Bacteroides fragilis (ETBF), and Escherichia coli (E. coli) actively participate in the carcinogenesis of CRC. Gastrointestinal tract with chronic inflammation and immunocompromised patients are at high risk for CRC progression. Further, the gut microbiota is also involved in Geno-toxicity by producing toxins like colibactin and cytolethal distending toxin (CDT) which cause damage to double-stranded DNA. Specific microRNAs can act as either tumor suppressors or oncogenes depending on the cellular environment in which they are expressed. The current review mainly highlights the role of gut microbiota in CRC, the mechanisms of several factors in carcinogenesis, and the role of particular microbes in colorectal neoplasia.

A Molecular Perspective and Role of NAD+ in Ovarian Aging

The decline in female fecundity is linked to advancing chronological age. The ovarian reserve diminishes in quantity and quality as women age, impacting reproductive efficiency and the aging process in the rest of the body. NAD+ is an essential coenzyme in cellular energy production, metabolism, cell signaling, and survival. It is involved in aging and is linked to various age-related conditions. Hallmarks associated with aging, diseases, and metabolic dysfunctions can significantly affect fertility by disturbing the delicate relationship between energy metabolism and female reproduction. Enzymes such as sirtuins, PARPs, and CD38 play essential roles in NAD+ biology, which actively consume NAD+ in their enzymatic activities. In recent years, NAD+ has gained much attention for its role in aging and age-related diseases like cancer, Alzheimer's, cardiovascular diseases, and neurodegenerative disorders, highlighting its involvement in various pathophysiological processes. However, its impact on female reproduction is not well understood. This review aims to bridge this knowledge gap by comprehensively exploring the complex interplay between NAD+ biology and female reproductive aging and providing valuable information that could help develop plans to improve women's reproductive health and prevent fertility issues.

Development and Characterization of a Novel Carbon-11 Labeled Positron Emission Tomography Radiotracer for Neuroimaging of Sirtuin 1 with Benzoxazine-Based Compounds

Introduction

Sirtuins (SIRTs) comprise a group of histone deacetylase enzymes crucial for regulating metabolic pathways and contributing significantly to various disease mechanisms. Sirtuin 1 (SIRT1), among the seven known mammalian homologs, is extensively investigated and understood, playing a key role in neurodegenerative disorders and cancer. This study focuses on potential as a therapeutic target for conditions such as Parkinson's disease (PD), Huntington's disease (HD), and Alzheimer's disease (AD).

Methods

Utilizing positron emission tomography (PET) as a noninvasive molecular imaging modality, we aimed to expedite the validation of a promising sirtuin 1 inhibitor for clinical trials. However, the absence of a validated sirtuin 1 PET radiotracer impedes clinical translation. We present the development of [11C]1, and 11C-labeled benzoxazine-based derivative, as a lead imaging probe. The radiosynthesis of [11C]1 resulted in a radiochemical yield of 31 ± 4%.

Results

Baseline studies demonstrated that [11C]1 exhibited excellent blood-brain barrier (BBB) penetration capability, with uniform accumulation throughout various brain regions. Self-blocking studies revealed that introducing an unlabeled compound 1, effectively blocking sirtuin 1, led to a substantial reduction in whole-brain uptake, emphasizing the in vivo specificity of [11C]1 for sirtuin 1.

Discussion

The development of [11C]1 provides a valuable tool for noninvasive imaging investigations in rodent models with aberrant sirtuin 1 expression. This novel radiotracer holds promise for advancing our understanding of sirtuin 1's role in disease mechanisms and may facilitate the validation of sirtuin 1 inhibitors in clinical trials.

Ergothioneine and its congeners: anti-ageing mechanisms and pharmacophore biosynthesis

Ergothioneine, Ovothiol, and Selenoneine are sulfur/selenium-containing histidine-derived natural products widely distributed across different organisms. They exhibit significant antioxidant properties, making them as potential lead compounds for promoting health. Increasing evidence suggests that Ergothioneine is positively correlated with healthy ageing and longevity. The mechanisms underlying Ergothioneine's regulation of the ageing process at cellular and molecular levels are beginning to be understood. In this review, we provide an in-depth and extensive coverage of the anti-ageing studies on Ergothioneine and discuss its possible intracellular targeting pathways. In addition, we highlight the recent efforts in elucidating the biosynthetic details for Ergothioneine, Ovothiol, and Selenoneine, with a particular focus on the study of their pharmacophore-forming enzymology.

Revealing chromatin-specific functions of histone deacylases

Histone deacylases are erasers of Nε-acyl-lysine post-translational modifications and have been targeted for decades for the treatment of cancer, neurodegeneration and other disorders. Due to their relatively promiscuous activity on peptide substrates in vitro, it has been challenging to determine the individual targets and substrate identification mechanisms of each isozyme, and they have been considered redundant regulators. In recent years, biochemical and biophysical studies have incorporated the use of reconstituted nucleosomes, which has revealed a diverse and complex arsenal of recognition mechanisms by which histone deacylases may differentiate themselves in vivo. In this review, we first present the peptide-based tools that have helped characterize histone deacylases in vitro to date, and we discuss the new insights that nucleosome tools are providing into their recognition of histone substrates within chromatin. Then, we summarize the powerful semi-synthetic approaches that are moving forward the study of chromatin-associated factors, both in vitro by detailed single-molecule mechanistic studies, and in cells by live chromatin modification. We finally offer our perspective on how these new techniques would advance the study of histone deacylases. We envision that such studies will help elucidate the role of individual isozymes in disease and provide a platform for the development of the next generation of therapeutics.

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.

Progress in discovery and development of natural inhibitors of histone deacetylases (HDACs) as anti-cancer agents

The study of epigenetic translational modifications had drawn great interest for the last few decades. These processes play a vital role in many diseases and cancer is one of them. Histone acetyltransferase (HAT) and histone deacetylases (HDACs) are key enzymes involved in the acetylation and deacetylation of histones and ultimately in post-translational modifications. Cancer frequently exhibits epigenetic changes, particularly disruption in the expression and activity of HDACs. It includes the capacity to regulate proliferative signalling, circumvent growth inhibitors, escape cell death, enable replicative immortality, promote angiogenesis, stimulate invasion and metastasis, prevent immunological destruction, and genomic instability. The majority of tumours develop and spread as a result of HDAC dysregulation. As a result, HDAC inhibitors (HDACis) were developed, and they today stand as a very promising therapeutic approach. One of the most well-known and efficient therapies for practically all cancer types is chemotherapy. However, the efficiency and safety of treatment are constrained by higher toxicity. The same has been observed with the synthetic HDACi. Natural products, owing to many advantages over synthetic compounds for cancer treatment have always been a choice for therapy. Hence, naturally available molecules are of particular interest for HDAC inhibition and HDAC has drawn the attention of the research fraternity due to their potential to offer a diverse array of chemical structures and bioactive compounds. This diversity opens up new avenues for exploring less toxic HDAC inhibitors to reduce side effects associated with conventional synthetic inhibitors. The review presents comprehensive details on natural product HDACi, their mechanism of action and their biological effects. Moreover, this review provides a brief discussion on the structure activity relationship of selected natural HDAC inhibitors and their analogues which can guide future research to discover selective, more potent HDACi with minimal toxicity.

A Sirtuin-Dependent T7 RNA Polymerase Variant

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

Reduced SIRT1 and SIRT3 and Lower Antioxidant Capacity of Seminal Plasma Is Associated with Shorter Sperm Telomere Length in Oligospermic Men

Infertility affects millions of couples worldwide and has a profound impact not only on their families, but also on communities. Telomere attrition has been associated with infertility, DNA damage and fragmentation. Oxidative stress has been shown to affect sperm DNA integrity and telomere length. Sirtuins such as SIRT1 and SIRT3 are involved in aging and oxidative stress response. The aim of the present study is to determine the role of SIRT1 and SIRT3 in regulating oxidative stress, telomere shortening, and their association with oligospermia. Therefore, we assessed the protein levels of SIRT1 and SIRT3, total antioxidant capacity (TAC), superoxide dismutase (SOD), malondialdehyde (MDA) and catalase activity (CAT) in the seminal plasma of 272 patients with oligospermia and 251 fertile men. We also measured sperm telomere length (STL) and leukocyte telomere length (LTL) using a standard real-time quantitative PCR assay. Sperm chromatin and protamine deficiency were also measured as per standard methods. Our results for oligospermic patients demonstrate significant reductions in semen parameters, shorter STL and LTL, lower levels of SOD, TAC, CAT, SIRT1 and SIRT3 levels, and also significant protamine deficiency and higher levels of MDA and DNA fragmentation. We conclude that a shorter TL in sperms and leukocytes is associated with increased oxidative stress that also accounts for high levels of DNA fragmentation in sperms. Our results support the hypothesis that various sperm parameters in the state of oligospermia are associated with or caused by reduced levels of SIRT1 and SIRT3 proteins.

Role of sirtuins in attenuating plaque vulnerability in atherosclerosis

Atherosclerosis is characterized by the development of intimal plaque, thrombosis, and stenosis of the vessel lumen causing decreased blood flow and hypoxia precipitating angina. Chronic inflammation in the stable plaque renders it unstable and rupture of unstable plaques results in the formation of emboli leading to hypoxia/ischemia to the organs by occluding the terminal branches and precipitate myocardial infarction and stroke. Such delibitating events could be controlled by the strategies that prevent plaque development or plaque stabilization. Despite the use of statins to stabilize plaques, there is a need for novel targets due to continuously increasing cases of cardiovascular events. Sirtuins (SIRTs), a family of signaling proteins, are involved in sustaining genome integrity, DNA damage response and repair, modulating oxidative stress, aging, inflammation, and energy metabolism. SIRTs play a critical role in modulating inflammation and involves in the development and progression of atherosclerosis. The role of SIRTs in relation to atherosclerosis and plaque vulnerability is scarcely discussed in the literature. Since SIRTs regulate oxidative stress, inflammation, and aging, they may also regulate plaque progression and vulnerability as these molecular mechanisms underlie the pathogenesis of plaque development, progression, and vulnerability. This review critically discusses the role of SIRTs in plaque progression and vulnerability and the possibility of targeting SIRTs to attenuate plaque rupture, focusing on the highlights in genomics, molecular pathways, and cell types involved in the underlying pathophysiology.

Effects of Dimerization on the Deacylase Activities of Human SIRT2

Human sirtuin isoform 2 (SIRT2) is an NAD+-dependent enzyme that functions as a lysine deacetylase and defatty-acylase. Here, we report that SIRT2 readily dimerizes in solution and in cells and that dimerization affects its ability to remove different acyl modifications from substrates. Dimerization of recombinant SIRT2 was revealed with analytical size exclusion chromatography and chemical cross-linking. Dimerized SIRT2 dissociates into monomers upon binding long fatty acylated substrates (decanoyl-, dodecanoyl-, and myristoyl-lysine). However, we did not observe dissociation of dimeric SIRT2 in the presence of acetyl-lysine. Analysis of X-ray crystal structures led us to discover a SIRT2 double mutant (Q142A/E340A) that is impaired in its ability to dimerize, which was confirmed with chemical cross-linking and in cells with a split-GFP approach. In enzyme assays, the SIRT2(Q142A/E340A) mutant had normal defatty-acylase activity and impaired deacetylase activity compared with the wild-type protein. These results indicate that dimerization is essential for optimal SIRT2 function as a deacetylase. Moreover, we show that SIRT2 dimers can be dissociated by a deacetylase and defatty-acylase inhibitor, ascorbyl palmitate. Our finding that its oligomeric state can affect the acyl substrate selectivity of SIRT2 is a novel mode of activity regulation by the enzyme that can be altered genetically or pharmacologically.

Impact of NAD+ metabolism on ovarian aging

Nicotinamide adenine dinucleotide (NAD+), a crucial coenzyme in cellular redox reactions, is closely associated with age-related functional degeneration and metabolic diseases. NAD exerts direct and indirect influences on many crucial cellular functions, including metabolic pathways, DNA repair, chromatin remodeling, cellular senescence, and immune cell functionality. These cellular processes and functions are essential for maintaining tissue and metabolic homeostasis, as well as healthy aging. Causality has been elucidated between a decline in NAD levels and multiple age-related diseases, which has been confirmed by various strategies aimed at increasing NAD levels in the preclinical setting. Ovarian aging is recognized as a natural process characterized by a decline in follicle number and function, resulting in decreased estrogen production and menopause. In this regard, it is necessary to address the many factors involved in this complicated procedure, which could improve fertility in women of advanced maternal age. Concerning the decrease in NAD+ levels as ovarian aging progresses, promising and exciting results are presented for strategies using NAD+ precursors to promote NAD+ biosynthesis, which could substantially improve oocyte quality and alleviate ovarian aging. Hence, to acquire further insights into NAD+ metabolism and biology, this review aims to probe the factors affecting ovarian aging, the characteristics of NAD+ precursors, and the current research status of NAD+ supplementation in ovarian aging. Specifically, by gaining a comprehensive understanding of these aspects, we are optimistic about the prominent progress that will be made in both research and therapy related to ovarian aging.

On the wake of metformin: Do anti-diabetic SGLT2 inhibitors exert anti-aging effects?

Here we propose that SGLT2 inhibitors (SGLT2i), a class of drugs primarily used to treat type 2 diabetes, could also be repositioned as anti-aging senomorphic drugs (agents that prevent the extrinsic harmful effects of senescent cells). As observed for metformin, another anti-diabetic drug with established anti-aging potential, increasing evidence suggests that SGLT2i can modulate some relevant pathways associated with the aging process, such as free radical production, cellular energy regulation through AMP-activated protein kinase (AMPK), autophagy, and the activation of nuclear factor (NF)-kB/inflammasome. Some interesting pro-healthy effects were also observed on human microbiota. All these mechanisms converge on fueling a systemic proinflammatory condition called inflammaging, now recognized as the main risk factor for accelerated aging and increased risk of age-related disease development and progression. Inflammaging can be worsened by cellular senescence and immunosenescence, which contributes to the increased burden of senescent cells during aging, perpetuating the proinflammatory condition. Interestingly, increasing evidence suggested the direct effects of SGLT-2i against senescent cells, chronic activation of immune cells, and metabolic alterations induced by overnutrition (meta-inflammation). In this framework, we analyzed and discussed the multifaceted impact of SGLT2i, compared with metformin effects, as a potential anti-aging drug beyond diabetes management. Despite promising results in experimental studies, rigorous investigations with well-designed cellular and clinical investigations will need to validate SGLT2 inhibitors' anti-aging effects.

Telomere maintenance in African trypanosomes

Telomere maintenance is essential for genome integrity and chromosome stability in eukaryotic cells harboring linear chromosomes, as telomere forms a specialized structure to mask the natural chromosome ends from DNA damage repair machineries and to prevent nucleolytic degradation of the telomeric DNA. In Trypanosoma brucei and several other microbial pathogens, virulence genes involved in antigenic variation, a key pathogenesis mechanism essential for host immune evasion and long-term infections, are located at subtelomeres, and expression and switching of these major surface antigens are regulated by telomere proteins and the telomere structure. Therefore, understanding telomere maintenance mechanisms and how these pathogens achieve a balance between stability and plasticity at telomere/subtelomere will help develop better means to eradicate human diseases caused by these pathogens. Telomere replication faces several challenges, and the "end replication problem" is a key obstacle that can cause progressive telomere shortening in proliferating cells. To overcome this challenge, most eukaryotes use telomerase to extend the G-rich telomere strand. In addition, a number of telomere proteins use sophisticated mechanisms to coordinate the telomerase-mediated de novo telomere G-strand synthesis and the telomere C-strand fill-in, which has been extensively studied in mammalian cells. However, we recently discovered that trypanosomes lack many telomere proteins identified in its mammalian host that are critical for telomere end processing. Rather, T. brucei uses a unique DNA polymerase, PolIE that belongs to the DNA polymerase A family (E. coli DNA PolI family), to coordinate the telomere G- and C-strand syntheses. In this review, I will first briefly summarize current understanding of telomere end processing in mammals. Subsequently, I will describe PolIE-mediated coordination of telomere G- and C-strand synthesis in T. brucei and implication of this recent discovery.

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

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

Pachymic acid suppresses the inflammatory response of chondrocytes and alleviates the progression of osteoarthritis via regulating the Sirtuin 6/NF-κB signal axis

Articular cartilage degeneration is a characteristic pathological change of osteoarthritis (OA). Pachymic acid (PA) is an active ingredient found in Poria cocos. Previous studies have shown that PA has anti-inflammatory effects on a variety of diseases. However, the role of PA in OA and its underlying mechanisms has not been clearly elucidated. In this study, we investigated potential protective effect of PA on OA through cell experiments in vitro and animal experiments in vivo. PA inhibited interleukin-1β-induced inflammatory mediator production in chondrocytes, which includes nitric oxide, inducible nitric oxide synthase, prostaglandin E2, cyclooxygenase-2, tumor necrosis factor alpha and interleukin-6. Meanwhile, PA also reversed the up-regulation of matrix metalloproteinase-3 and thrombospondin motifs 5, and the down-regulation of collagen type II and aggrecan in IL-1β-treated chondrocytes. Mechanistically, our findings revealed that PA-mediated overexpression of SIRT6 inhibited the NF-κB signaling pathway. In vivo, PA contributes to improve cartilage damage in the mouse OA model. In summary, PA inhibited IL-1β-induced inflammation and extracellular matrix degeneration by promoting SIRT6 expression and inhibiting the NF-κB signaling pathway, which indicates that PA is beneficial for the treatment of OA.

Identification of SIRT3 as an eraser of H4K16la

Lysine lactylation (Kla) is a novel histone post-translational modification discovered in late 2019. Later, HDAC1-3, were identified as the robust Kla erasers. While the Sirtuin family proteins showed weak eraser activities toward Kla, as reported. However, the catalytic mechanisms and physiological functions of HDACs and Sirtuins are not identical. In this study, we observed that SIRT3 exhibits a higher eraser activity against the H4K16la site than the other human Sirtuins. Crystal structures revealed the detailed binding mechanisms between lactyl-lysine peptides and SIRT3. Furthermore, a chemical probe, p-H4K16laAlk, was developed to capture potential Kla erasers from cell lysates. SIRT3 was captured by this probe and detected via proteomic analysis. And another chemical probe, p-H4K16la-NBD, was developed to detect the eraser-Kla delactylation processes directly via fluorescence indication. Our findings and chemical probes provide new directions for further investigating Kla and its roles in gene transcription regulation.

SIRT-1 is required for release of enveloped enteroviruses

Enterovirus D68 (EV-D68) is a re-emerging enterovirus that causes acute respiratory illness in infants and has recently been linked to Acute Flaccid Myelitis. Here, we show that the histone deacetylase, SIRT-1, is essential for autophagy and EV-D68 infection. Knockdown of SIRT-1 inhibits autophagy and reduces EV-D68 extracellular titers. The proviral activity of SIRT-1 does not require its deacetylase activity or functional autophagy. SIRT-1's proviral activity is, we demonstrate, mediated through the repression of endoplasmic reticulum stress (ER stress). Inducing ER stress through thapsigargin treatment or SERCA2A knockdown in SIRT-1 knockdown cells had no additional effect on EV-D68 extracellular titers. Knockdown of SIRT-1 also decreases poliovirus and SARS-CoV-2 titers but not coxsackievirus B3. In non-lytic conditions, EV-D68 is primarily released in an enveloped form, and SIRT-1 is required for this process. Our data show that SIRT-1, through its translocation to the cytosol, is critical to promote the release of enveloped EV-D68 viral particles.

Lactate-induced protein lactylation: A bridge between epigenetics and metabolic reprogramming in cancer

Lactate is not only an endpoint of glycolysis but is gradually being discovered to play the role of a universal metabolic fuel for energy via the 'lactate shuttle' moving between cells and transmitting signals. The glycolytic-dependent metabolism found in tumours and fast-growing cells has made lactate a pivotal player in energy metabolism reprogramming, which enables cells to obtain abundant energy in a short time. Moreover, lactate can provide favourable conditions for tumorigenesis by shaping the acidic tumour microenvironment, recruiting immune cells, etc. and the recently discovered lactate-induced lactylation moves even further on pro-tumorigenesis mechanisms of lactate production, circulation and utilization. As with other epigenetic modifications, lactylation can modify histone proteins to alter the spatial configuration of chromatin, affect DNA accessibility and regulate the expression of corresponding genes. What's more, the degree of lactylation is inseparable from the spatialized lactate concentration, which builds a bridge between epigenetics and metabolic reprogramming. Here, we review the important role of lactate in energy reprogramming, summarize the latest finding of lactylation in tumorigenesis and try to explore therapeutic strategies in oncotherapy that can kill two birds with one stone.

Histone Deacetylase UvHST2 Is a Global Regulator of Secondary Metabolism in Ustilaginoidea virens

Ustilaginoidea virens, the causal agent of rice false smut, produces a large amount of mycotoxins, including ustilaginoidins and sorbicillinoids. However, little is known about the regulatory mechanism of mycotoxin biosynthesis inU. virens. Here, we demonstrate that the NAD+-dependent histone deacetylase UvHST2 negatively regulates ustilaginoidin biosynthesis. UvHst2 knockout caused retarded hypha growth and reduced conidiation and pathogenicity inU. virens. Transcriptome analysis revealed that the transcription factor genes, transporter genes, and other tailoring genes in eight biosynthetic gene clusters (BGCs) including ustilaginoidin and sorbicillinoid BGCs were upregulated in ΔUvhst2. Interestingly, the UvHst2 deletion affects alternative splicing. Metabolomics revealed that UvHST2 negatively regulates the biosynthesis of various mycotoxins including ustilaginoidins, sorbicillin, ochratoxin B, zearalenone, and O-M-sterigmatocystin. Combined transcriptome and metabolome analyses uncover that UvHST2 positively regulates pathogenicity but negatively modulates the expression of BGCs involved in secondary metabolism. Collectively, UvHST2 functions as a global regulator of secondary metabolism inU. virens.

Relating aging and autophagy: a new perspective towards the welfare of human health

The most common factor that contributes to aging is the loss of proteostasis, resulting in an excess amount of non-functional/damaged proteins. These proteins lead to various age-associated phenotypes such as cellular senescence and dysfunction in the nutrient-sensing pathways. Despite the various factors that can contribute to aging, it is still a process that can be changed. According to recent advances in the field of biology, the ability to alter the pathways that are involved in aging can improve the lifespan of a person. Autophagy is a process that helps in preserving survival during stressful situations, such as starvation. It is a common component of various anti-aging interventions, including those that target the insulin/IGF-1 and rapamycin signaling pathways. It has been shown that altered autophagy is a common feature of old age and its impaired regulation could have significant effects on the aging process. This review aims to look into the role of autophagy in aging and how it can be used to improve one's health.

The Role of Increased Expression of Sirtuin 6 in the Prevention of Premature Aging Pathomechanisms

Sirtuins, in mammals, are a group of seven enzymes (SIRT1-SIRT7) involved in the post-translational modification of proteins-they are considered longevity proteins. SIRT6, classified as class IV, is located on the cell nucleus; however, its action is also connected with other regions, e.g., mitochondria and cytoplasm. It affects many molecular pathways involved in aging: telomere maintenance, DNA repair, inflammatory processes or glycolysis. A literature search for keywords or phrases was carried out in PubMed and further searches were carried out on the ClinicalTrials.gov website. The role of SIRT6 in both premature and chronological aging has been pointed out. SIRT6 is involved in the regulation of homeostasis-an increase in the protein's activity has been noted in calorie-restriction diets and with significant weight loss, among others. Expression of this protein is also elevated in people who regularly exercise. SIRT6 has been shown to have different effects on inflammation, depending on the cells involved. The protein is considered a factor in phenotypic attachment and the migratory responses of macrophages, thus accelerating the process of wound healing. Furthermore, exogenous substances will affect the expression level of SIRT6: resveratrol, sirtinol, flavonoids, cyanidin, quercetin and others. This study discusses the importance of the role of SIRT6 in aging, metabolic activity, inflammation, the wound healing process and physical activity.

Nanoplastics induce epigenetic signatures of transgenerational impairments associated with reproduction in copepods under ocean acidification

Ocean acidification (OA) is one of many major global climate changes that pose a variety of risks to marine ecosystems in different ways. Meanwhile, there is growing concern about how nanoplastics (NPs) affect marine ecosystems. Combined exposure of marine organisms to OA and NPs is inevitable, but their interactive effects remain poorly understood. In this study, we investigated the multi- and transgenerational toxicity of NPs on copepods under OA conditions for ten generations. The findings revealed that OA and NPs have a synergistic negative effect on copepod reproduction across generations. In particular, the transgenerational groups showed reproductive impairments in the F1 and F2 generations (F1T and F2T), even though they were never exposed to NPs. Moreover, our epigenetic examinations demonstrated that the observed intergenerational reproductive impairments are associated with differential methylation patterns of specific genes, suggesting that the interaction of OA and NPs can pose a significant threat to the sustainability of copepod populations through epigenetic modifications. Overall, our findings provide valuable insight into the intergenerational toxicity and underlying molecular mechanisms of responses to NPs under OA conditions.

Macrocyclic Octapeptide Binding and Inferences on Protein Substrate Binding to Histone Deacetylase 6

Histone deacetylases (HDACs) are essential for the regulation of myriad biological processes, and their aberrant function is implicated in cancer, neurodegeneration, and other diseases. The cytosolic isozyme HDAC6 is unique among the greater family of deacetylases in that it contains two catalytic domains, CD1 and CD2. HDAC6 CD2 is responsible for tubulin deacetylase and tau deacetylase activities, inhibition of which is a key goal as new therapeutic approaches are explored. Of particular interest as HDAC inhibitors are naturally occurring cyclic tetrapeptides such as Trapoxin A or HC Toxin, or the cyclic depsipeptides Largazole and Romidepsin. Even more intriguing are larger, computationally designed macrocyclic peptide inhibitors. Here, we report the 2.0 Å resolution crystal structure of HDAC6 CD2 complexed with macrocyclic octapeptide 1. Comparison with the previously reported structure of the complex with macrocyclic octapeptide 2 reveals that a potent thiolate-zinc interaction made by the unnatural amino acid (S)-2-amino-7-sulfanylheptanoic acid contributes to nanomolar inhibitory potency for each inhibitor. Apart from this zinc-binding residue, octapeptides adopt strikingly different overall conformations and make few direct hydrogen bonds with the protein. Intermolecular interactions are dominated by water-mediated hydrogen bonds; in essence, water molecules appear to cushion the enzyme-octapeptide interface. In view of the broad specificity observed for protein substrates of HDAC6 CD2, we suggest that the binding of macrocyclic octapeptides may mimic certain features of the binding of macromolecular protein substrates.

Sirtuin1-p53: a potential axis for cancer therapy

Sirtuin1 (SIRT1) is a conserved nicotinamide adenine dinucleotide (NAD⁺)-dependent histone deacetylase that plays key roles in a range of cellular events, including the maintenance of genome stability, gene regulation, cell proliferation, and apoptosis. P53 is one of the most studied tumor suppressors and the first identified non-histone target of SIRT1. SIRT1 deacetylates p53 in a NAD⁺-dependent manner and inhibits its transcriptional activity, thus exerting action on a series of pathways related to tissue homeostasis and various pathological states. The SIRT1-p53 axis is thought to play a central role in tumorigenesis. Although SIRT1 was initially identified as a tumor promoter, evidence now indicates that SIRT1 may also act as a tumor suppressor. This seemingly contradictory evidence indicates that the functionality of SIRT1 may be dictated by different cell types and intracellular localization patterns. In this review, we summarize recent evidence relating to the interactions between SIRT1 and p53 and discuss the relative roles of these two molecules with regards to cancer-associated cellular events. We also provide an overview of current knowledge of SIRT1-p53 signaling in tumorigenesis. Given the vital role of the SIRT1-p53 pathway, targeting this axis may provide promising strategies for the treatment of cancer.

Structural Basis of Sirtuin 6-Catalyzed Nucleosome Deacetylation

The reversible acetylation of histone lysine residues is controlled by the action of acetyltransferases and deacetylases (HDACs), which regulate chromatin structure and gene expression. The sirtuins are a family of NAD-dependent HDAC enzymes, and one member, sirtuin 6 (Sirt6), influences DNA repair, transcription, and aging. Here, we demonstrate that Sirt6 is efficient at deacetylating several histone H3 acetylation sites, including its canonical site Lys9, in the context of nucleosomes but not free acetylated histone H3 protein substrates. By installing a chemical warhead at the Lys9 position of histone H3, we trap a catalytically poised Sirt6 in complex with a nucleosome and employ this in cryo-EM structural analysis. The structure of Sirt6 bound to a nucleosome reveals extensive interactions between distinct segments of Sirt6 and the H2A/H2B acidic patch and nucleosomal DNA, which accounts for the rapid deacetylation of nucleosomal H3 sites and the disfavoring of histone H2B acetylation sites. These findings provide a new framework for understanding how HDACs target and regulate chromatin.

Emerging Roles of SIRT5 in Metabolism, Cancer, and SARS-CoV-2 Infection

Sirtuin 5 (SIRT5) is a predominantly mitochondrial enzyme catalyzing the removal of glutaryl, succinyl, malonyl, and acetyl groups from lysine residues through a NAD+-dependent deacylase mechanism. SIRT5 is an important regulator of cellular homeostasis and modulates the activity of proteins involved in different metabolic pathways such as glycolysis, tricarboxylic acid (TCA) cycle, fatty acid oxidation, electron transport chain, generation of ketone bodies, nitrogenous waste management, and reactive oxygen species (ROS) detoxification. SIRT5 controls a wide range of aspects of myocardial energy metabolism and plays critical roles in heart physiology and stress responses. Moreover, SIRT5 has a protective function in the context of neurodegenerative diseases, while it acts as a context-dependent tumor promoter or suppressor. In addition, current research has demonstrated that SIRT5 is implicated in the SARS-CoV-2 infection, although opposing conclusions have been drawn in different studies. Here, we review the current knowledge on SIRT5 molecular actions under both healthy and diseased settings, as well as its functional effects on metabolic targets. Finally, we revise the potential of SIRT5 as a therapeutic target and provide an overview of the currently reported SIRT5 modulators, which include both activators and inhibitors.

Pyrazolone derivatives as potent and selective small-molecule SIRT5 inhibitors

Sirtiun 5 (SIRT5) is a NAD+-dependent protein lysine deacylase. It is emerging as a promising target for the development of drugs to treat cancer and metabolism-related diseases. In this study, we screened 5000 compounds and identified a hit compound 14 bearing a pyrazolone functional group as a novel SIRT5-selective inhibitor. Structure-based optimization of 14 resulted in compound 47 with an IC50 value of 0.21 ± 0.02 μM and a 100-fold improved potency. Compound 47 showed substantial selectivity for SIRT5 over SIRT1-3 and SIRT6. Biochemical studies suggest that 47 does not occupy the NAD + -binding pocket and acts as a substrate-competitive inhibitor. The identified potent and selective SIRT5 inhibitors allow further studies as research tools and therapeutic agents.

A DUAL MTOR/NAD+ ACTING GEROTHERAPY

The geroscience hypothesis states that a therapy that prevents the underlying aging process should prevent multiple aging related diseases. The mTOR (mechanistic target of rapamycin)/insulin and NAD+ (nicotinamide adenine dinucleotide) pathways are two of the most validated aging pathways. Yet, it's largely unclear how they might talk to each other in aging. In genome-wide CRISPRa screening with a novel class of N-O-Methyl-propanamide-containing compounds we named BIOIO-1001, we identified lipid metabolism centering on SIRT3 as a point of intersection of the mTOR/insulin and NAD+ pathways. In vivo testing indicated that BIOIO-1001 reduced high fat, high sugar diet-induced metabolic derangements, inflammation, and fibrosis, each being characteristic of non-alcoholic steatohepatitis (NASH). An unbiased screen of patient datasets suggested a potential link between the anti-inflammatory and anti-fibrotic effects of BIOIO-1001 in NASH models to those in amyotrophic lateral sclerosis (ALS). Directed experiments subsequently determined that BIOIO-1001 was protective in both sporadic and familial ALS models. Both NASH and ALS have no treatments and suffer from a lack of convenient biomarkers to monitor therapeutic efficacy. A potential strength in considering BIOIO-1001 as a therapy is that the blood biomarker that it modulates, namely plasma triglycerides, can be conveniently used to screen patients for responders. More conceptually, to our knowledge BIOIO-1001 is a first therapy that fits the geroscience hypothesis by acting on multiple core aging pathways and that can alleviate multiple conditions after they have set in.

The Role of Epigenetics in Neuroinflammatory-Driven Diseases

Neurodegenerative disorders are characterized by the progressive loss of central and/or peripheral nervous system neurons. Within this context, neuroinflammation comes up as one of the main factors linked to neurodegeneration progression. In fact, neuroinflammation has been recognized as an outstanding factor for Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and multiple sclerosis (MS). Interestingly, neuroinflammatory diseases are characterized by dramatic changes in the epigenetic profile, which might provide novel prognostic and therapeutic factors towards neuroinflammatory treatment. Deep changes in DNA and histone methylation, along with histone acetylation and altered non-coding RNA expression, have been reported at the onset of inflammatory diseases. The aim of this work is to review the current knowledge on this field.

Acetylation State of Lysine 14 of Histone H3.3 Affects Mutant Huntingtin Induced Pathogenesis

Huntington's Disease (HD) is a fatal neurodegenerative disorder caused by the expansion of a polyglutamine-coding CAG repeat in the Huntingtin gene. One of the main causes of neurodegeneration in HD is transcriptional dysregulation that, in part, is caused by the inhibition of histone acetyltransferase (HAT) enzymes. HD pathology can be alleviated by increasing the activity of specific HATs or by inhibiting histone deacetylase (HDAC) enzymes. To determine which histone's post-translational modifications (PTMs) might play crucial roles in HD pathology, we investigated the phenotype-modifying effects of PTM mimetic mutations of variant histone H3.3 in a Drosophila model of HD. Specifically, we studied the mutations (K→Q: acetylated; K→R: non-modified; and K→M: methylated) of lysine residues K9, K14, and K27 of transgenic H3.3. In the case of H3.3K14Q modification, we observed the amelioration of all tested phenotypes (viability, longevity, neurodegeneration, motor activity, and circadian rhythm defects), while H3.3K14R had the opposite effect. H3.3K14Q expression prevented the negative effects of reduced Gcn5 (a HAT acting on H3K14) on HD pathology, while it only partially hindered the positive effects of heterozygous Sirt1 (an HDAC acting on H3K14). Thus, we conclude that the Gcn5-dependent acetylation of H3.3K14 might be an important epigenetic contributor to HD pathology.

On the Potential Role of the Antioxidant Couple Vitamin E/Selenium Taken by the Oral Route in Skin and Hair Health

The relationship between oxidative stress and skin aging/disorders is well established. Many topical and oral antioxidants (vitamins C and E, carotenoids, polyphenols) have been proposed to protect the skin against the deleterious effect induced by increased reactive oxygen species production, particularly in the context of sun exposure. In this review, we focused on the combination of vitamin E and selenium taken in supplements since both molecules act in synergy either by non-enzymatic and enzymatic pathways to eliminate skin lipids peroxides, which are strongly implicated in skin and hair disorders.

Post-Translational Modifications by Lipid Metabolites during the DNA Damage Response and Their Role in Cancer

Genomic DNA damage occurs as an inevitable consequence of exposure to harmful exogenous and endogenous agents. Therefore, the effective sensing and repair of DNA damage are essential for maintaining genomic stability and cellular homeostasis. Inappropriate responses to DNA damage can lead to genomic instability and, ultimately, cancer. Protein post-translational modifications (PTMs) are a key regulator of the DNA damage response (DDR), and recent progress in mass spectrometry analysis methods has revealed that a wide range of metabolites can serve as donors for PTMs. In this review, we will summarize how the DDR is regulated by lipid metabolite-associated PTMs, including acetylation, S-succinylation, N-myristoylation, palmitoylation, and crotonylation, and the implications for tumorigenesis. We will also discuss potential novel targets for anti-cancer drug development.

The Pursuit of Enzyme Activation: A Snapshot of the Gold Rush

A range of enzymes drive human physiology, and their activities are tightly regulated through numerous signaling pathways. Depending on the context, these pathways may activate or inhibit an enzyme as a way to ensure proper execution of cellular functions. From a drug discovery and development perspective, pharmacological inhibition of enzymes has been a focus of interest, as many diseases are associated with the upregulation of enzyme function. On the other hand, however, pharmacological activation of enzymes such as kinases and phosphatases has been of increasing interest. In this review, we discuss seven case studies that highlight pharmacological activation strategy, describe the binding modes and pharmacology of the activators, and comment on how this on-demand activation strategy complements the commonly pursued inhibition strategy, thus jointly enabling bidirectional modulation of specific target of interest. Going forward, we expect activators to play important roles as chemical probes and drug leads.

Crosstalk between Sirtuins and Nrf2: SIRT1 activators as emerging treatment for diabetic neuropathy

About 50% of the diabetic patients worldwide suffer from Diabetic peripheral neuropathy (DPN) which is characterized by chronic pain and loss of sensation, frequent foot ulcerations, and risk for amputation. Numerous factors like hyperglycemia, oxidative stress (OS), impaired glucose signaling, inflammatory responses, neuronal cell death are known to be the various mechanisms underlying DACD and DPN. Development of tolerance, insufficient and inadequate relief and potential toxicity of classical antinociceptives still remains a challenge in the clinical setting. Therefore, there is an emerging need for novel treatments which are both without any potential side effects as well as which focus more on the pathophysiological mechanisms underlying the disease. Also, sirtuins are known to deacetylate Nrf2 and contribute to its action of reducing ROS by generation of anti-oxidant enzymes. Therefore, targeting sirtuins could be a favourable therapeutic strategy to treat diabetic neuropathy by reducing ROS and thereby alleviating OS in DPN. In the present review, we outline the potential use of SIRT1 activators as therapeutic alternatives in treating DPN. We have tried to highlight how sirtuins are interlinked with Nrf2 and NF-κB and put forth how SIRT activators could serve as potential therapy for DPN.

Role of NAD+ and FAD in Ischemic Stroke Pathophysiology: An Epigenetic Nexus and Expanding Therapeutic Repertoire

The redox coenzymes viz., oxidized β-nicotinamide adenine dinucleotide (NAD⁺) and flavin adenine dinucleotide (FAD) by way of generation of optimal reducing power and cellular energy currency (ATP), control a staggering array of metabolic reactions. The prominent cellular contenders for NAD⁺ utilization, inter alia, are sirtuins (SIRTs) and poly(ADP-ribose) polymerase (PARP-1), which have been significantly implicated in ischemic stroke (IS) pathogenesis. NAD⁺ and FAD are also two crucial epigenetic enzyme-required metabolites mediating histone deacetylation and poly(ADP-ribosyl)ation through SIRTs and PARP-1 respectively, and demethylation through FAD-mediated lysine specific demethylase activity. These enzymes and post-translational modifications impinge on the components of neurovascular unit, primarily neurons, and elicit diverse functional upshots in an ischemic brain. These could be circumstantially linked with attendant cognitive deficits and behavioral outcomes in post-stroke epoch. Parsing out the contribution of NAD⁺/FAD-synthesizing and utilizing enzymes towards epigenetic remodeling in IS setting, together with their cognitive and behavioral associations, combined with possible therapeutic implications will form the crux of this review.

Novel epigenetic therapeutic strategies and targets in cancer

The critical role of dysregulated epigenetic pathways in cancer genesis, development, and therapy has typically been established as a result of scientific and technical innovations in next generation sequencing. RNA interference, histone modification, DNA methylation and chromatin remodelling are epigenetic processes that control gene expression without causing mutations in the DNA. Although epigenetic abnormalities are thought to be a symptom of cell tumorigenesis and malignant events that impact tumor growth and drug resistance, physicians believe that related processes might be a key therapeutic target for cancer treatment and prevention due to the reversible nature of these processes. A plethora of novel strategies for addressing epigenetics in cancer therapy for immuno-oncological complications are currently available - ranging from basic treatment to epigenetic editing. - and they will be the subject of this comprehensive review. In this review, we cover most of the advancements made in the field of targeting epigenetics with special emphasis on microbiology, plasma science, biophysics, pharmacology, molecular biology, phytochemistry, and nanoscience.

Harnessing conserved signaling and metabolic pathways to enhance the maturation of functional engineered tissues

The development of induced-pluripotent stem cell (iPSC)-derived cell types offers promise for basic science, drug testing, disease modeling, personalized medicine, and translatable cell therapies across many tissue types. However, in practice many iPSC-derived cells have presented as immature in physiological function, and despite efforts to recapitulate adult maturity, most have yet to meet the necessary benchmarks for the intended tissues. Here, we summarize the available state of knowledge surrounding the physiological mechanisms underlying cell maturation in several key tissues. Common signaling consolidators, as well as potential synergies between critical signaling pathways are explored. Finally, current practices in physiologically relevant tissue engineering and experimental design are critically examined, with the goal of integrating greater decision paradigms and frameworks towards achieving efficient maturation strategies, which in turn may produce higher-valued iPSC-derived tissues.

Dietary carbohydrates: Pathogenesis and potential therapeutic targets to obesity-associated metabolic syndrome

Metabolic syndrome (MetS) is a common feature in obesity, comprising a cluster of abnormalities including abdominal fat accumulation, hyperglycemia, hyperinsulinemia, dyslipidemia, and hypertension, leading to diabetes and cardiovascular diseases (CVD). Intake of carbohydrates (CHO), particularly a sugary diet that rapidly increases blood glucose, triglycerides, and blood pressure levels is the predominant determining factor of MetS. Complex CHO, on the other hand, are a stable source of energy taking a longer time to digest. In particular, resistant starch (RS) or soluble fiber is an excellent source of prebiotics, which alter the gut microbial composition, which in turn improves metabolic control. Altering maternal CHO intake during pregnancy may result in the child developing MetS. Furthermore, lifestyle factors such as physical inactivity in combination with dietary habits may synergistically influence gene expression by modulating genetic and epigenetic regulators transforming childhood obesity into adolescent metabolic disorders. This review summarizes the common pathophysiology of MetS in connection with the nature of CHO, intrauterine nutrition, genetic predisposition, lifestyle factors, and advanced treatment approaches; it also emphasizes how dietary CHO may act as a key element in the pathogenesis and future therapeutic targets of obesity and MetS.

Defined stereoisomers of 2″-amino NAD+ and their activity against human sirtuins and a bacterial (ADP-ribosyl) transferase

Nicotinamide adenine dinucleotide (NAD⁺) is an important biomolecule with essential roles at the intersection of energy metabolism, epigenetic regulation and cell signalling. Synthetic analogues of NAD⁺ are therefore of great interest as chemical tools for medicinal chemistry, chemical biology and drug discovery. Herein, we report the chemical synthesis and full analytical characterisation of three stereoisomers of 2″-amino NAD⁺, and their biochemical evaluation against two classes of NAD⁺-consuming enzymes: the human sirtuins 1-3, and the bacterial toxin TccC3. To rationalise the observed activities, molecular docking experiments were carried out with SIRT1 and SIRT2, which identified the correct orientation of the pyrophosphate linkage as a major determinant for activity in this series. These results, together with results from stability tests and a conformational analysis, allow, for the first time, a side-by-side comparison of the chemical and biochemical features, and analytical properties, of different 2″-amino NAD⁺ stereoisomers. Our findings provide insight into the recognition of co-substrate analogues by sirtuins, and will greatly facilitate the application of these important NAD⁺ analogues as chemical tool compounds for mechanistic studies with these as well as other NAD⁺-dependent enyzmes.

Adaptive and Pathological Outcomes of Radiation Stress-Induced Redox Signaling

Significance: Ionizing radiation can damage cells either directly or through oxidative damage caused by ionization. Although radiation exposure from natural sources is very limited, ionizing radiation in nuclear disaster zones and long spaceflights causes inconspicuous, yet measurable physiological effects in men and animals, whose significance remains poorly known. Understanding the physiological impacts of ionizing radiation has a wide importance due to the increased use of medical imaging and radiotherapy. Recent Advances: Radiation exposure has been traditionally investigated from the perspective of DNA damage and its consequences. However, recent studies from Chernobyl as well as spaceflights have provided interesting insights into oxidative stress-induced metabolic alterations and disturbances in the circadian regulation. Critical Issues: In this review, we discuss the physiological consequences of radiation exposure in the light of oxidative stress signaling. Radiation exposure likely triggers many converging or interconnecting signaling pathways, some of which mimic mitochondrial dysfunction and might explain the observed metabolic changes. Future Directions: Better understanding of the different radiation-induced signaling pathways might help to devise strategies for mitigation of the long-term effects of radiation exposure. The utility of fibroblast growth factor 21 (FGF21) as a radiation exposure biomarker and the use of radiation hormesis as a method to protect astronauts on a prolonged spaceflight, such as a mission to Mars, should be investigated. Antioxid. Redox Signal. 37, 336-348.