SIRT2 regulates adipocyte differentiation through FoxO1 acetylation/deacetylation

AGK2, a SIRT2 inhibitor, ameliorates D-galactose-induced liver fibrosis by inhibiting fibrogenic factors

In our study, we aimed to investigate the effect of SIRT2 inhibition on function, fibrosis and inflammation in liver fibrosis induced by D-Galactose (D-Gal) administration. A total of 32 3-month-old Sprague Dawley rats were used in the study. Rats were divided into 4 groups as Control, d-Gal, Solvent+d-Gal, d-Gal+AGK2+Solvent. d-Gal (150 mg/kg/day), AGK-2 (10 µM/bw) as a specific SIRT2 inhibitor, 4%DMSO + PBS as a solvent was applied to the experimental groups and physiological saline was applied to the control group for 10 weeks. All applications were performed subcutaneously. Histological fibrotic changes were studied in the liver tissues by Masson's trichrome staining, hematoxylin and eosin staining and immunohistochemistry and the levels of selected factors were determined by quantitative reverse transcription-polymerase chain reaction, western blot analysis, and immunohistochemical analysis. Biochemical parameters and Paraoxonase levels were determined in the plasma. d-Galactose administration increased AST, AST-ALT Ratio, APRI, SIRT2 protein expression, IL1β, TGF β, β-catenin, Type I collagen, Type III collagen and α-SMA, collagen fiber density and histopathological score. ALT and lipid panels were not changed and paraxonase plasma level was shown to decrease. These effects were largely blocked by the SIRT2 inhibitor AGK2. These findings suggest that SIRT2 inhibition attenuates d-Gal-induced liver injury and that this protection may be due to its antifibrotic and anti-inflammatory activities.

Deciphering adipose development: Function, differentiation and regulation

The overdevelopment of adipose tissues, accompanied by excess lipid accumulation and energy storage, leads to adipose deposition and obesity. With the increasing incidence of obesity in recent years, obesity is becoming a major risk factor for human health, causing various relevant diseases (including hypertension, diabetes, osteoarthritis and cancers). Therefore, it is of significance to antagonize obesity to reduce the risk of obesity-related diseases. Excess lipid accumulation in adipose tissues is mediated by adipocyte hypertrophy (expansion of pre-existing adipocytes) or hyperplasia (increase of newly-formed adipocytes). It is necessary to prevent excessive accumulation of adipose tissues by controlling adipose development. Adipogenesis is exquisitely regulated by many factors in vivo and in vitro, including hormones, cytokines, gender and dietary components. The present review has concluded a comprehensive understanding of adipose development including its origin, classification, distribution, function, differentiation and molecular mechanisms underlying adipogenesis, which may provide potential therapeutic strategies for harnessing obesity without impairing adipose tissue function.

ACAT1/SOAT1 maintains adipogenic ability in preadipocytes by regulating cholesterol homeostasis

Maintaining cholesterol homeostasis is critical for preserving adipocyte function during the progression of obesity. Despite this, the regulatory role of cholesterol esterification in governing adipocyte expandability has been understudied. Acyl-coenzyme A (CoA):cholesterol acyltransferase / Sterol O-acyltransferase 1 (ACAT1/SOAT1) is the dominant enzyme to synthesize cholesteryl ester in most tissues. Our previous study demonstrated that knockdown of either ACAT1 or ACAT2 impaired adipogenesis. However, the underlying mechanism of how ACAT1 mediates adipogenesis remains unclear. Here, we reported that ACAT1 is the dominant isoform in white adipose tissue of both humans and mice and knocking out ACAT1 reduced fat mass in mice. Furthermore, ACAT1-deficiency inhibited the early stage of adipogenesis via attenuating PPARγ pathway. Mechanistically, ACAT1 deficiency inhibited SREBP2-mediated cholesterol uptake and thus reduced intracellular and plasma membrane cholesterol level during adipogenesis. While replenishing cholesterol could rescue adipogenic master gene - Pparγ's transcription in ACAT1 deficient cells during adipogenesis. Finally, overexpression of catalytically functional ACAT1, not the catalytic-dead ACAT1, rescued cholesterol level and efficiently rescued the transcription of PPARγ, as well as the adipogenesis in ACAT1-deficient preadipocytes. In summary, our study revealed the indispensable role of ACAT1 in adipogenesis via regulating intracellular cholesterol homeostasis.

Discovery of Novel Thiazole-Based SIRT2 Inhibitors as Anticancer Agents: Molecular Modeling, Chemical Synthesis and Biological Assays

The search and development of effective sirtuin small molecule inhibitors (SIRTIs) continues to draw great attention due to their wide range of pharmacological applications. Based on SIRTs' involvement in different biological pathways, their ligands were investigated for many diseases, such as cancer, neurodegenerative disorders, diabetes, cardiovascular diseases and autoimmune diseases. The elucidation of a substantial number of SIRT2-ligand complexes is steering the identification of novel and more selective modulators. Among them, SIRT2 in the presence of the SirReal2 analog series was the most studied. On this basis, we recently reported structure-based analyses leading to the discovery of thiazole-based compounds acting as SIRT2 inhibitors (T1, SIRT2 IC50 = 17.3 µM). Herein, ligand-based approaches followed by molecular docking simulations allowed us to evaluate in silico a novel small series of thiazoles (3a-3d and 5a, 5d) as putative SIRT2 inhibitors. Results from the computational studies revealed comparable molecular interaction fields (MIFs) and docking positionings of most of these compounds with respect to reference SIRT2Is. Biochemical and biological assays validated this study and pointed to compound 5a (SIRT2 IC50 = 9.0 µM) as the most interesting SIRT2I that was worthy of further development as an anticancer agent.

Mitochondrial Function and Dysfunction in White Adipocytes and Therapeutic Implications

For a long time, white adipocytes were thought to function as lipid storages due to the sizeable unilocular lipid droplet that occupies most of their space. However, recent discoveries have highlighted the critical role of white adipocytes in maintaining energy homeostasis and contributing to obesity and related metabolic diseases. These physiological and pathological functions depend heavily on the mitochondria that reside in white adipocytes. This article aims to provide an up-to-date overview of the recent research on the function and dysfunction of white adipocyte mitochondria. After briefly summarizing the fundamental aspects of mitochondrial biology, the article describes the protective role of functional mitochondria in white adipocyte and white adipose tissue health and various roles of dysfunctional mitochondria in unhealthy white adipocytes and obesity. Finally, the article emphasizes the importance of enhancing mitochondrial quantity and quality as a therapeutic avenue to correct mitochondrial dysfunction, promote white adipocyte browning, and ultimately improve obesity and its associated metabolic diseases. © 2024 American Physiological Society. Compr Physiol 14:5581-5640, 2024.

Metabolic mechanisms orchestrated by Sirtuin family to modulate inflammatory responses

Maintaining metabolic homeostasis is crucial for cellular and organismal health throughout their lifespans. The intricate link between metabolism and inflammation through immunometabolism is pivotal in maintaining overall health and disease progression. The multifactorial nature of metabolic and inflammatory processes makes study of the relationship between them challenging. Homologs of Saccharomyces cerevisiae silent information regulator 2 protein, known as Sirtuins (SIRTs), have been demonstrated to promote longevity in various organisms. As nicotinamide adenine dinucleotide-dependent deacetylases, members of the Sirtuin family (SIRT1-7) regulate energy metabolism and inflammation. In this review, we provide an extensive analysis of SIRTs involved in regulating key metabolic pathways, including glucose, lipid, and amino acid metabolism. Furthermore, we systematically describe how the SIRTs influence inflammatory responses by modulating metabolic pathways, as well as inflammatory cells, mediators, and pathways. Current research findings on the preferential roles of different SIRTs in metabolic disorders and inflammation underscore the potential of SIRTs as viable pharmacological and therapeutic targets. Future research should focus on the development of promising compounds that target SIRTs, with the aim of enhancing their anti-inflammatory activity by influencing metabolic pathways within inflammatory cells.

Rhein targets macrophage SIRT2 to promote adipose tissue thermogenesis in obesity in mice

Rhein, a component derived from rhubarb, has been proven to possess anti-inflammatory properties. Here, we show that rhein mitigates obesity by promoting adipose tissue thermogenesis in diet-induced obese mice. We construct a macrophage-adipocyte co-culture system and demonstrate that rhein promotes adipocyte thermogenesis through inhibiting NLRP3 inflammasome activation in macrophages. Moreover, clues from acetylome analysis identify SIRT2 as a potential drug target of rhein. We further verify that rhein directly interacts with SIRT2 and inhibits NLRP3 inflammasome activation in a SIRT2-dependent way. Myeloid knockdown of SIRT2 abrogates adipose tissue thermogenesis and metabolic benefits in obese mice induced by rhein. Together, our findings elucidate that rhein inhibits NLRP3 inflammasome activation in macrophages by regulating SIRT2, and thus promotes white adipose tissue thermogenesis during obesity. These findings uncover the molecular mechanism underlying the anti-inflammatory and anti-obesity effects of rhein, and suggest that rhein may become a potential drug for treating obesity.

The role of sirtuins and uncoupling proteins on vascular aging: The Northern Manhattan Study experience

Aging affects all organs. Arteries, in particular, are among the most affected. Vascular aging (VA) is defined as age-associated changes in function and structure of vessels. Classical VA phenotypes are carotid intima-media thickness (IMT), carotid plaque (CP), and arterial stiffness (STIFF). Individuals have different predisposition to these VA phenotypes and their associated risk of cardiovascular events. Some develop an early vascular aging (EVA), and others are protected and identified as having supernormal vascular aging (SUPERNOVA). The mechanisms leading to these phenotypes are not well understood. In the Northern Manhattan Study (NOMAS), we found genetic variants in the 7 Sirtuins (SIRT) and 5 Uncoupling Proteins (UCP) to be differently associated with risk to developing VA phenotypes. In this article, we review the results of genetic-epidemiology studies to better understand which of the single nucleotide polymorphisms (SNPs) in SIRT and UCP are responsible for both EVA and SUPERNOVA.

The Roles of White Adipose Tissue and Liver NADPH in Dietary Restriction-Induced Longevity

Dietary restriction (DR) protocols frequently employ intermittent fasting. Following a period of fasting, meal consumption increases lipogenic gene expression, including that of NADPH-generating enzymes that fuel lipogenesis in white adipose tissue (WAT) through the induction of transcriptional regulators SREBP-1c and CHREBP. SREBP-1c knockout mice, unlike controls, did not show an extended lifespan on the DR diet. WAT cytoplasmic NADPH is generated by both malic enzyme 1 (ME1) and the pentose phosphate pathway (PPP), while liver cytoplasmic NADPH is primarily synthesized by folate cycle enzymes provided one-carbon units through serine catabolism. During the daily fasting period of the DR diet, fatty acids are released from WAT and are transported to peripheral tissues, where they are used for beta-oxidation and for phospholipid and lipid droplet synthesis, where monounsaturated fatty acids (MUFAs) may activate Nrf1 and inhibit ferroptosis to promote longevity. Decreased WAT NADPH from PPP gene knockout stimulated the browning of WAT and protected from a high-fat diet, while high levels of NADPH-generating enzymes in WAT and macrophages are linked to obesity. But oscillations in WAT [NADPH]/[NADP+] from feeding and fasting cycles may play an important role in maintaining metabolic plasticity to drive longevity. Studies measuring the WAT malate/pyruvate as a proxy for the cytoplasmic [NADPH]/[NADP+], as well as studies using fluorescent biosensors expressed in the WAT of animal models to monitor the changes in cytoplasmic [NADPH]/[NADP+], are needed during ad libitum and DR diets to determine the changes that are associated with longevity.

Forkhead box O1 in metabolic dysfunction-associated fatty liver disease: molecular mechanisms and drug research

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a chronic liver disease that progresses from hepatic steatosis to non-alcoholic steatohepatitis, cirrhosis, and liver cancer, posing a huge burden on human health. Existing research has confirmed that forkhead box O1 (FOXO1), as a member of the FOXO transcription factor family, is upregulated in MAFLD. Its activity is closely related to nuclear-cytoplasmic shuttling and various post-translational modifications including phosphorylation, acetylation, and methylation. FOXO1 mediates the progression of MAFLD by regulating glucose metabolism, lipid metabolism, insulin resistance, oxidative stress, hepatic fibrosis, hepatocyte autophagy, apoptosis, and immune inflammation. This article elaborates on the regulatory role of FOXO1 in MAFLD, providing a summary and new insights for the current status of drug research and targeted therapies for MAFLD.

Unveiling the dynamics of acetylation and phosphorylation in SGBS and 3T3-L1 adipogenesis

Obesity, characterized by enlarged and dysfunctional adipose tissue, is among today's most pressing global public health challenges with continuously increasing prevalence. Despite the importance of post-translational protein modifications (PTMs) in cellular signaling, knowledge of their impact on adipogenesis remains limited. Here, we studied the temporal dynamics of transcriptome, proteome, central carbon metabolites, and the acetyl- and phosphoproteome during adipogenesis using LC-MS/MS combined with PTM enrichment strategies on human (SGBS) and mouse (3T3-L1) adipocyte models. Both cell lines exhibited unique PTM profiles during adipogenesis, with acetylated proteins being enriched for central energy metabolism, while phosphorylated proteins related to insulin signaling and organization of cellular structures. As candidates with strong correlation to the adipogenesis timeline we identified CD44 and the acetylation sites FASN_K673 and IDH_K272. While results generally aligned between SGBS and 3T3-L1 cells, details appeared cell line specific. Our datasets on SGBS and 3T3-L1 adipogenesis dynamics are accessible for further mining.

2-(Methyl(phenyl)amino)-N-(phenyloxyphenyl)acetamide structural motif representing a framework for selective SIRT2 inhibition

The mammalian cytoplasmic protein SIRT2, a class III histone deacetylase family member, possesses NAD+-dependent lysine deacetylase/deacylase activity. Dysregulation of SIRT2 has been implicated in the pathogenesis of several diseases, including neurological and metabolic disorders and cancer; thus, SIRT2 emerges as a potential therapeutic target. Herein, we identified a series of diaryl acetamides (ST61-ST90) by the structural optimization of our hit STH2, followed by enhanced SIRT2 inhibitory potency and selectivity. Among them, ST72, ST85, and ST88 selectively inhibited SIRT2 with IC50 values of 9.97, 5.74, and 8.92 μM, respectively. Finally, the entire study was accompanied by in silico prediction of binding modes of docked compounds and the stability of SIRT2-ligand complexes. We hope our findings will provide substantial information for designing selective inhibitors of SIRT2.

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

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

Research progress on Sirtuins (SIRTs) family modulators

Sirtuins (SIRTs) represent a class of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases that exert a crucial role in cellular signal transduction and various biological processes. The mammalian sirtuins family encompasses SIRT1 to SIRT7, exhibiting therapeutic potential in counteracting cellular aging, modulating metabolism, responding to oxidative stress, inhibiting tumors, and improving cellular microenvironment. These enzymes are intricately linked to the occurrence and treatment of diverse pathological conditions, including cancer, autoimmune diseases, and cardiovascular disorders. Given the significance of histone modification in gene expression and chromatin structure, maintaining the equilibrium of the sirtuins family is imperative for disease prevention and health restoration. Mounting evidence suggests that modulators of SIRTs play a crucial role in treating various diseases and maintaining physiological balance. This review delves into the molecular structure and regulatory functions of the sirtuins family, reviews the classification and historical evolution of SIRTs modulators, offers a systematic overview of existing SIRTs modulation strategies, and elucidates the regulatory mechanisms of SIRTs modulators (agonists and inhibitors) and their clinical applications. The article concludes by summarizing the challenges encountered in SIRTs modulator research and offering insights into future research directions.

Sirtuin dysregulation in Parkinson's disease: Implications of acetylation and deacetylation processes

Parkinson's disease (PD) is a progressive neurodegenerative condition that primarily affects motor function and is caused by a gradual decline of dopaminergic neurons in the brain's substantia pars compacta (Snpc) region. Multiple molecular pathways are involved in the pathogenesis, which results in impaired cellular functions and neuronal degeneration. However, the role of sirtuins, a type of NAD+-dependent deacetylase, in the pathogenesis of Parkinson's disease has recently been investigated. Sirtuins are essential for preserving cellular homeostasis because they control a number of biological processes, such as metabolism, apoptosis, and DNA repair. This review shed lights on the dysregulation of sirtuin activity in PD, highlighting the role that acetylation and deacetylation processes play in the development of the disease. Key regulators of protein acetylation, sirtuins have been found to be involved in the aberrant acetylation of vital substrates linked to PD pathology when their balance is out of balance. The hallmark characteristics of PD such as neuroinflammation, oxidative stress, and mitochondrial dysfunction have all been linked to the dysregulation of sirtuin expression and activity. Furthermore, we have also explored how the modulators of sirtuins can be a promising therapeutic intervention in the treatment of PD.

How mesenchymal stem cells transform into adipocytes: Overview of the current understanding of adipogenic differentiation

Mesenchymal stem cells (MSCs) are stem/progenitor cells capable of self-renewal and differentiation into osteoblasts, chondrocytes and adipocytes. The transformation of multipotent MSCs to adipocytes mainly involves two subsequent steps from MSCs to preadipocytes and further preadipocytes into adipocytes, in which the process MSCs are precisely controlled to commit to the adipogenic lineage and then mature into adipocytes. Previous studies have shown that the master transcription factors C/enhancer-binding protein alpha and peroxisome proliferation activator receptor gamma play vital roles in adipogenesis. However, the mechanism underlying the adipogenic differentiation of MSCs is not fully understood. Here, the current knowledge of adipogenic differentiation in MSCs is reviewed, focusing on signaling pathways, noncoding RNAs and epigenetic effects on DNA methylation and acetylation during MSC differentiation. Finally, the relationship between maladipogenic differentiation and diseases is briefly discussed. We hope that this review can broaden and deepen our understanding of how MSCs turn into adipocytes.

Skin keratinocyte-derived SIRT1 and BDNF modulate mechanical allodynia in mouse models of diabetic neuropathy

Diabetic neuropathy is a debilitating disorder characterized by spontaneous and mechanical pain. The role of skin mechanoreceptors in the development of mechanical pain (allodynia) is unclear. We discovered that mice with diabetic neuropathy had decreased sirtuin 1 (SIRT1) deacetylase activity in foot skin, leading to reduced expression of brain-derived neurotrophic factor (BDNF) and subsequent loss of innervation in Meissner corpuscles, a mechanoreceptor expressing the BDNF receptor TrkB. When SIRT1 was depleted from skin, the mechanical allodynia worsened in diabetic neuropathy mice, likely due to retrograde degeneration of the Meissner-corpuscle innervating Aβ axons and aberrant formation of Meissner corpuscles which may have increased the mechanosensitivity. The same phenomenon was also noted in skin BDNF knockout mice. Furthermore, overexpression of SIRT1 in skin induced Meissner corpuscle reinnervation and regeneration, resulting in significant improvement of diabetic mechanical allodynia. Overall, the findings suggested that skin-derived SIRT1 and BDNF function in the same pathway in skin sensory apparatus regeneration and highlighted the potential of developing topical SIRT1-activating compounds as a novel treatment for diabetic mechanical allodynia.

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

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

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.

Effects of resistance training on alleviating hypoxia-induced muscle atrophy: Focus on acetylation of FoxO1

This study aims to explore the role of FoxO1 and its acetylation in the alleviation of hypoxia-induced muscle atrophy by resistance training. Forty male Sprague-Dawley rats were randomly divided into four groups: normoxic control group (C), normoxic resistance training group (R), hypoxic control group (H) and hypoxic resistance training group (HR). Rats in R and HR groups were trained on an incremental weight-bearing ladder every other day, while those in H and HR groups were kept in an environment containing 12.4% O2 . After 4 weeks, muscles were collected for analysis. Differentiated L6 myoblasts were analysed in vitro after hypoxia exposure and plasmids transfection (alteration in FoxO1 acetylation). The lean body mass loss, wet weight and fibre cross-sectional area of extensor digitorum longus of rats were decreased after 4 weeks hypoxia, and the adverse reactions above was reversed by resistance training. At the same time, the increase in hypoxia-induced autophagy was suppressed, which was accompanied by a decrease in the expression of nuclear FoxO1 and cytoplasmic Ac-FoxO1 by resistance training. The L6 myotube diameter increased and the expression of autophagic proteins were inhibited under hypoxia via intervening by FoxO1 deacetylation. Overall, resistance training alleviates hypoxia-induced muscle atrophy by inhibiting nuclear FoxO1 and cytoplasmic Ac-FoxO1-mediated autophagy.

Acetylation and deacetylation of histone in adipocyte differentiation and the potential significance in cancer

Adipocytes are derived from pluripotent mesenchymal stem cells and can develop into several cell types including adipocytes, myocytes, chondrocytes, and osteocytes. Adipocyte differentiation is regulated by a variety of transcription factors and signaling pathways. Various epigenetic factors, particularly histone modifications, play key roles in adipocyte differentiation and have indispensable functions in altering chromatin conformation. Histone acetylases and deacetylases participate in the regulation of protein acetylation, mediate transcriptional and post-translational modifications, and directly acetylate or deacetylate various transcription factors and regulatory proteins. The adipocyte differentiation of stem cells plays a key role in various metabolic diseases. Cancer stem cells(CSCs) play an important function in cancer metastasis, recurrence, and drug resistance, and have the characteristics of stem cells. They are expressed in various cell lineages, including adipocytes. Recent studies have shown that cancer stem cells that undergo epithelial-mesenchymal transformation can undergo adipocytic differentiation, thereby reducing the degree of malignancy. This opens up new possibilities for cancer treatment. This review summarizes the regulation of acetylation during adipocyte differentiation, involving the functions of histone acetylating and deacetylating enzymes as well as non-histone acetylation modifications. Mechanistic studies on adipogenesis and acetylation during the differentiation of cancer cells into a benign cell phenotype may help identify new targets for cancer treatment.

In silico approach reveals N-(5-phenoxythiophen-2-yl)-2-(arylthio)acetamides as promising selective SIRT2 inhibitors: the case of structural optimization of virtual screening-derived hits

Epigenetic modifications play an essential role in tumor suppression and promotion. Among the diverse range of epigenetic regulators, SIRT2, a member of NAD+-dependent protein deacetylates, has emerged as a crucial regulator of cellular processes, including cell cycle progression, DNA repair, and metabolism, impacting tumor growth and survival. In the present work, a series of N-(5-phenoxythiophen-2-yl)-2-(arylthio)acetamide derivatives were identified following a structural optimization of previously reported virtual screening hits, accompanied by enhanced SIRT2 inhibitory potency. Among the compounds, ST44 and ST45 selectively inhibited SIRT2 with IC50 values of 6.50 and 7.24 μM, respectively. The predicted binding modes of the two compounds revealed the success of the optimization run. Moreover, ST44 displayed antiproliferative effects on the MCF-7 human breast cancer cell line. Further, the contribution of SIRT2 inhibition in this effect of ST44 was supported by western blotting, affording an increased α-tubulin acetylation. Furthermore, molecular dynamics (MD) simulations and binding free energy calculations using molecular mechanics/generalized born surface area (MM-GBSA) method evaluated the accuracy of predicted binding poses and ligand affinities. The results revealed that ST44 exhibited a remarkable level of stability, with minimal deviations from its initial docking conformation. These findings represented a significant improvement over the virtual screening hits and may contribute substantially to our knowledge for further selective SIRT2 drug discovery.Communicated by Ramaswamy H. Sarma.

SIRT2 negatively regulates the cGAS-STING pathway by deacetylating G3BP1

SIRT2, a cytoplasmic member of the Sirtuin family, has important roles in immunity and inflammation. However, its function in regulating the response to DNA virus infection remains elusive. Here, we find that SIRT2 is a unique regulator among the Sirtuin family that negatively modulates the cGAS-STING-signaling pathway. SIRT2 is down-regulated after Herpes simplex virus-1 (HSV-1) infection, and SIRT2 deficiency markedly elevates the expression levels of type I interferon (IFN). SIRT2 inhibits the DNA binding ability and droplet formation of cGAS by interacting with and deacetylating G3BP1 at K257, K276, and K376, leading to the disassembly of the cGAS-G3BP1 complex, which is critical for cGAS activation. Administration of AGK2, a selective SIRT2 inhibitor, protects mice from HSV-1 infection and increases the expression of IFN and IFN-stimulated genes. Our study shows that SIRT2 negatively regulates cGAS activation through G3BP1 deacetylation, suggesting a potential antiviral strategy by modulating SIRT2 activity.

Research progress of intramuscular fat formation based on co-culture

Intramuscular fat (IMF) is closely related to the meat quality of livestock and poultry. As a new cell culture technique in vitro, cell co-culture has been gradually applied to the related research of IMF formation because it can simulate the changes of microenvironment in vivo during the process of IMF cell formation. In the co-culture model, in addition to studying the effects of skeletal muscle cells on the proliferation and differentiation of IMF, we can also consider the role of many secretion factors in the formation of IMF, thus making the cell research in vitro closer to the real level in vivo. This paper reviewed the generation and origin of IMF, summarized the existing co-culture methods and systems, and discussed the advantages and disadvantages of each method as well as the challenges faced in the establishment of the system, with emphasis on the current status of research on the formation of IMF for human and animal based on co-culture technology.

Insertion/deletions within the bovine FoxO1 gene and their association analysis with growth traits in three Chinese cattle breeds

FOXO1 (FKHR) gene, as a transcription factor, plays a vital role in animal growth and development, participating in many biological processes. The aim of this study was to ascertain Insertion/deletions (Indels) polymorphism within bovine FoxO1 gene in 679 Chinese adult cows and associate them with stature traits. Two Indels (named as Indel-3 and Indel-4, recorded as rs383545622 and rs525318770 in NCBI, respectively) were successfully genotyped by the Once PCR method, which was reliable, rapid and cost effective for simultaneous detection of two or more Indels. Indel-3 and Indel-4 were located at the second intron. All four different haplotypes (H1: D3D4, H2: I3D4, H3: D3I4, H4: I3I4) could be identified, and the D (del-) allele, DD (del-/del-) genotype and D3D4 haplotype retained the highest frequency. However, individuals with DI (D3I3, D4I4 or H1H4/H2H3 genotype) showed significantly better phenotypic traits than those with the other genotypes in Nanyang cattle, showing a hybrid vigor. The results implied that this DI genotype can be applied to early selective breeding to improve the productivity of Nanyang cattle. Our results suggested that these two Indels within the bovine FoxO1 gene might be used as genetic markers for marker-assisted selection (MAS) in cattle breeding and genetics.

Acetyltransferases CBP/p300 Control Transcriptional Switch of β-Catenin and Stat1 Promoting Osteoblast Differentiation

CREB-binding protein (CBP) (CREBBP) and p300 (EP300) are multifunctional histone acetyltransferases (HATs) with extensive homology. Germline mutations of CBP or p300 cause skeletal abnormalities in humans and mice. However, the precise roles of CBP/p300 in bone homeostasis remain elusive. Here, we report that conditional knockout of CBP or p300 in osteoblasts results in reduced bone mass and strength due to suppressed bone formation. The HAT activity is further confirmed to be responsible for CBP/p300-mediated osteogenesis using A-485, a selective inhibitor of CBP/p300 HAT. Mechanistically, CBP/p300 HAT governs osteogenic gene expression in part through transcriptional activation of β-catenin and inhibition of Stat1. Furthermore, acetylation of histone H3K27 and the transcription factor Foxo1 are demonstrated to be involved in CBP/p300 HAT-regulated β-catenin and Stat1 transcription, respectively. Taken together, these data identify acetyltransferases CBP/p300 as critical regulators that promote osteoblast differentiation and reveal an epigenetic mechanism responsible for maintaining bone homeostasis. © 2023 American Society for Bone and Mineral Research (ASBMR).

Rhabdomyosarcoma: Current Therapy, Challenges, and Future Approaches to Treatment Strategies

Rhabdomyosarcoma is a rare cancer arising in skeletal muscle that typically impacts children and young adults. It is a worldwide challenge in child health as treatment outcomes for metastatic and recurrent disease still pose a major concern for both basic and clinical scientists. The treatment strategies for rhabdomyosarcoma include multi-agent chemotherapies after surgical resection with or without ionization radiotherapy. In this comprehensive review, we first provide a detailed clinical understanding of rhabdomyosarcoma including its classification and subtypes, diagnosis, and treatment strategies. Later, we focus on chemotherapy strategies for this childhood sarcoma and discuss the impact of three mechanisms that are involved in the chemotherapy response including apoptosis, macro-autophagy, and the unfolded protein response. Finally, we discuss in vivo mouse and zebrafish models and in vitro three-dimensional bioengineering models of rhabdomyosarcoma to screen future therapeutic approaches and promote muscle regeneration.

The Emerging Importance of Mitochondria in White Adipocytes: Neither Last nor Least

The growing recognition of mitochondria's crucial role in the regulation of white adipose tissue remodeling and energy balance underscores its significance. The marked metabolic diversity of mitochondria provides the molecular and cellular foundation for enabling adipose tissue plasticity in response to various metabolic cues. Effective control of mitochondrial function at the cellular level, not only in thermogenic brown and beige adipocytes but also in energy-storing white adipocytes, exerts a profound influence on adipose homeostasis. Furthermore, mitochondria play a pivotal role in intercellular communication within adipose tissue via production of metabolites with signaling properties. A more comprehensive understanding of mitochondrial regulation within white adipocytes will empower the development of targeted and efficacious strategies to enhance adipose function, leading to advancements in overall metabolic health.

A metabolite from commensal Candida albicans enhances the bactericidal activity of macrophages and protects against sepsis

The gut microbiome is recognized as a key modulator of sepsis development. However, the contribution of the gut mycobiome to sepsis development is still not fully understood. Here, we demonstrated that the level of Candida albicans was markedly decreased in patients with bacterial sepsis, and the supernatant of Candida albicans culture significantly decreased the bacterial load and improved sepsis symptoms in both cecum ligation and puncture (CLP)-challenged mice and Escherichia coli-challenged pigs. Integrative metabolomics and the genetic engineering of fungi revealed that Candida albicans-derived phenylpyruvate (PPA) enhanced the bactericidal activity of macrophages and reduced organ damage during sepsis. Mechanistically, PPA directly binds to sirtuin 2 (SIRT2) and increases reactive oxygen species (ROS) production for eventual bacterial clearance. Importantly, PPA enhanced the bacterial clearance capacity of macrophages in sepsis patients and was inversely correlated with the severity of sepsis in patients. Our findings highlight the crucial contribution of commensal fungi to bacterial disease modulation and expand our understanding of the host-mycobiome interaction during sepsis development.

Mitochondria in health, disease, and aging

Mitochondria are well known as organelles responsible for the maintenance of cellular bioenergetics through the production of ATP. Although oxidative phosphorylation may be their most important function, mitochondria are also integral for the synthesis of metabolic precursors, calcium regulation, the production of reactive oxygen species, immune signaling, and apoptosis. Considering the breadth of their responsibilities, mitochondria are fundamental for cellular metabolism and homeostasis. Appreciating this significance, translational medicine has begun to investigate how mitochondrial dysfunction can represent a harbinger of disease. In this review, we provide a detailed overview of mitochondrial metabolism, cellular bioenergetics, mitochondrial dynamics, autophagy, mitochondrial damage-associated molecular patterns, mitochondria-mediated cell death pathways, and how mitochondrial dysfunction at any of these levels is associated with disease pathogenesis. Mitochondria-dependent pathways may thereby represent an attractive therapeutic target for ameliorating human disease.

Sirtuin Inhibitor Cambinol Induces Cell Differentiation and Differently Interferes with SIRT1 and 2 at the Substrate Binding Site

Epigenetic mechanisms finely regulate gene expression and represent potential therapeutic targets. Cambinol is a synthetic heterocyclic compound that inhibits class III histone deacetylases known as sirtuins (SIRTs). The acetylating action that results could be crucial in modulating cellular functions via epigenetic regulations. The main aim of this research was to investigate the effects of cambinol, and its underlying mechanisms, on cell differentiation by combining wet experiments with bioinformatics analyses and molecular docking simulations. Our in vitro study evidenced the ability of cambinol to induce the differentiation in MCF-7, NB4, and 3T3-L1 cell lines. Interestingly, focusing on the latter that accumulated cytoplasmic lipid droplets, the first promising results related to the action mechanisms of cambinol have shown the induction of cell cycle-related proteins (such as p16 and p27) and modulation of the expression of Rb protein and nuclear receptors related to cell differentiation. Moreover, we explored the inhibitory mechanism of cambinol on human SIRT1 and 2 performing in silico molecular simulations by protein-ligand docking. Cambinol, unlike from other sirtuin inhibitors, is able to better interact with the substrate binding site of SIRT1 than with the inhibition site. Additionally, for SIRT2, cambinol partially interacts with the substrate binding site, although the inhibition site is preferred. Overall, our findings suggest that cambinol might contribute to the development of an alternative to the existing epigenetic therapies that modulate SIRTs.

Cellular and Mitochondrial NAD Homeostasis in Health and Disease

The mitochondrion has a unique position among other cellular organelles due to its dynamic properties and symbiotic nature, which is reflected in an active exchange of metabolites and cofactors between the rest of the intracellular compartments. The mitochondrial energy metabolism is greatly dependent on nicotinamide adenine dinucleotide (NAD) as a cofactor that is essential for both the activity of respiratory and TCA cycle enzymes. The NAD level is determined by the rate of NAD synthesis, the activity of NAD-consuming enzymes, and the exchange rate between the individual subcellular compartments. In this review, we discuss the NAD synthesis pathways, the NAD degradation enzymes, and NAD subcellular localization, as well as NAD transport mechanisms with a focus on mitochondria. Finally, the effect of the pathologic depletion of mitochondrial NAD pools on mitochondrial proteins' post-translational modifications and its role in neurodegeneration will be reviewed. Understanding the physiological constraints and mechanisms of NAD maintenance and the exchange between subcellular compartments is critical given NAD's broad effects and roles in health and disease.

Circulating blood eNAMPT drives the circadian rhythms in locomotor activity and energy expenditure

Nicotinamide adenine dinucleotide (NAD⁺) is an essential cofactor of critical enzymes including protein deacetylase sirtuins/SIRTs and its levels in mammalian cells rely on the nicotinamide phosphoribosyltransferase (NAMPT)-mediated salvage pathway. Intracellular NAMPT (iNAMPT) is secreted and found in the blood as extracellular NAMPT (eNAMPT). In the liver, the iNAMPT-NAD⁺ axis oscillates in a circadian manner and regulates the cellular clockwork. Here we show that the hypothalamic NAD⁺ levels show a distinct circadian fluctuation with a nocturnal rise in lean mice. This rhythm is in phase with that of plasma eNAMPT levels but not with that of hypothalamic iNAMPT levels. Chemical and genetic blockade of eNAMPT profoundly inhibit the nighttime elevations in hypothalamic NAD⁺ levels as well as those in locomotor activity (LMA) and energy expenditure (EE). Conversely, elevation of plasma eNAMPT by NAMPT administration increases hypothalamic NAD⁺ levels and stimulates LMA and EE via the hypothalamic NAD⁺-SIRT-FOXO1-melanocortin pathway. Notably, obese animals display a markedly blunted circadian oscillation in blood eNAMPT-hypothalamic NAD⁺-FOXO1 axis as well as LMA and EE. Our findings indicate that the eNAMPT regulation of hypothalamic NAD⁺ biosynthesis underlies circadian physiology and that this system can be significantly disrupted by obesity.

Effect of the Ketone Body, D-β-Hydroxybutyrate, on Sirtuin2-Mediated Regulation of Mitochondrial Quality Control and the Autophagy-Lysosomal Pathway

Mitochondrial activity and quality control are essential for neuronal homeostasis as neurons rely on glucose oxidative metabolism. The ketone body, D-β-hydroxybutyrate (D-BHB), is metabolized to acetyl-CoA in brain mitochondria and used as an energy fuel alternative to glucose. We have previously reported that D-BHB sustains ATP production and stimulates the autophagic flux under glucose deprivation in neurons; however, the effects of D-BHB on mitochondrial turnover under physiological conditions are still unknown. Sirtuins (SIRTs) are NAD⁺-activated protein deacetylases involved in the regulation of mitochondrial biogenesis and mitophagy through the activation of transcription factors FOXO1, FOXO3a, TFEB and PGC1α coactivator. Here, we aimed to investigate the effect of D-BHB on mitochondrial turnover in cultured neurons and the mechanisms involved. Results show that D-BHB increased mitochondrial membrane potential and regulated the NAD⁺/NADH ratio. D-BHB enhanced FOXO1, FOXO3a and PGC1α nuclear levels in an SIRT2-dependent manner and stimulated autophagy, mitophagy and mitochondrial biogenesis. These effects increased neuronal resistance to energy stress. D-BHB also stimulated the autophagic-lysosomal pathway through AMPK activation and TFEB-mediated lysosomal biogenesis. Upregulation of SIRT2, FOXOs, PGC1α and TFEB was confirmed in the brain of ketogenic diet (KD)-treated mice. Altogether, the results identify SIRT2, for the first time, as a target of D-BHB in neurons, which is involved in the regulation of autophagy/mitophagy and mitochondrial quality control.

Human sirtuin 2 inhibitors, their mechanisms and binding modes

The silent information regulator (sirtuin) is a family of enzymes involved in epigenetic processes with lysine deacetylase activity, having as substrates histones and other proteins. They participate in a wide range of cellular and pathologic processes, such as gene expression, cell division and motility, oxidative-induced stress management, metabolic control and carcinogenesis, among others, thus presenting as interesting therapeutic targets. In this article, the authors describe the inhibitory mechanisms and binding modes of the human sirtuin 2 (hSIRT2) inhibitors, which had their complexes with the enzyme structurally characterized. The results help pave the way for the rational designing of new hSIRT2 inhibitors and the development of novel therapeutic agents targeting this epigenetic enzyme.

FOXOs: masters of the equilibrium

Forkhead box O (FOXO) transcription factors (TFs) are a subclass of the larger family of forkhead TFs. Mammalians express four members FOXO1, FOXO3, FOXO4, and FOXO6. The interest in FOXO function stems mostly from their observed role in determining lifespan, where in model organisms, increased FOXO activity results in extended lifespan. FOXOs act as downstream of several signaling pathway and are extensively regulated through post-translational modifications. The transcriptional program activated by FOXOs in various cell types, organisms, and under various conditions has been described and has shed some light on what the critical transcriptional targets are in mediating FOXO function. At the cellular level, these studies have revealed a role for FOXOs in cell metabolism, cellular redox, cell proliferation, DNA repair, autophagy, and many more. The general picture that emerges hereof is that FOXOs act to preserve equilibrium, and they are important for cellular homeostasis. Here, we will first briefly summarize the general knowledge of FOXO regulation and possible functions. We will use genomic stability to illustrate how FOXOs ensure homeostasis. Genomic stability is critical for maintaining genetic integrity, and therefore preventing disease. However, genomic mutations need to occur during lifetime to enable evolution, yet their accumulation is believed to be causative to aging. Therefore, the role of FOXO in genomic stability may underlie its role in lifespan and aging. Finally, we will come up with questions on some of the unknowns in FOXO function, the answer(s) to which we believe will further our understanding of FOXO function and ultimately may help to understand lifespan and its consequences.

Sirtuins: Key players in obesity-associated adipose tissue remodeling

Obesity, a complex disease involving an excessive amount of body fat and a major threat to public health all over the world, is the determining factor of the onset and development of metabolic disorders, including type 2 diabetes, cardiovascular diseases, and non-alcoholic fatty liver disease. Long-term overnutrition results in excessive expansion and dysfunction of adipose tissue, inflammatory responses and over-accumulation of extracellular matrix in adipose tissue, and ectopic lipid deposit in other organs, termed adipose tissue remodeling. The mammalian Sirtuins (SIRT1-7) are a family of conserved NAD⁺-dependent protein deacetylases. Mounting evidence has disclosed that Sirtuins and their prominent substrates participate in a variety of physiological and pathological processes, including cell cycle regulation, mitochondrial biogenesis and function, glucose and lipid metabolism, insulin action, inflammatory responses, and energy homeostasis. In this review, we provided up-to-date and comprehensive knowledge about the roles of Sirtuins in adipose tissue remodeling, focusing on the fate of adipocytes, lipid mobilization, adipose tissue inflammation and fibrosis, and browning of adipose tissue, and we summarized the clinical trials of Sirtuin activators and inhibitors in treating metabolic diseases, which might shed light on new therapeutic strategies for obesity and its associated metabolic diseases.

Posttranslational modifications in diabetes: Mechanisms and functions

As one of the most widespread chronic diseases, diabetes and its accompanying complications affect approximately one tenth of individuals worldwide and represent a growing cause of morbidity and mortality. Accumulating evidence has proven that the process of diabetes is complex and interactive, involving various cellular responses and signaling cascades by posttranslational modifications (PTMs). Therefore, understanding the mechanisms and functions of PTMs in regulatory networks has fundamental importance for understanding the prediction, onset, diagnosis, progression, and treatment of diabetes. In this review, we offer a holistic summary and illustration of the crosstalk between PTMs and diabetes, including both types 1 and 2. Meanwhile, we discuss the potential use of PTMs in diabetes treatment and provide a prospective direction for deeply understanding the metabolic diseases.

Role of Post-translational Modification of Silent Mating Type Information Regulator 2 Homolog 1 in Cancer and Other Disorders

Silent mating type information regulator 2 homolog 1 (SIRT1), an NAD⁺-dependent histone/protein deacetylase, has multifarious physiological roles in development, metabolic regulation, and stress response. Thus, its abnormal expression or malfunction is implicated in pathogenesis of various diseases. SIRT1 undergoes post-translational modifications, including phosphorylation, oxidation/reduction, carbonylation, nitrosylation, glycosylation, ubiquitination/deubiquitination, SUMOylation etc. which can modulate its catalytic activity, stability, subcellular localization, and also binding affinity for substrate proteins. This short review highlights the regulation of SIRT1 post-translational modifications and their pathophysiologic implications.

Sirtfoods: New Concept Foods, Functions, and Mechanisms

Sirtfood is a new concept food that compounds diets that can target sirtuins (SIRTs). SIRTs are nicotinamide adenine dinucleotide (NAD⁺)-dependent deacylases and ADP-ribosyltransferases (enzymes). SIRTs are mediators of calorie restriction (CR) and their activation can achieve some effects similar to CR. SIRTs play essential roles in ameliorating obesity and age-related metabolic diseases. Food ingredients such as resveratrol, piceatannol, anthocyanidin, and quinine are potential modulators of SIRTs. SIRT modulators are involved in autophagy, apoptosis, aging, inflammation, and energy homeostasis. Sirtfood proponents believe that natural Sirtfood recipes exert significant health effects.

Novel prospects for scarless wound healing: The roles of myofibroblasts and adipocytes

Disturbances or defects in the process of wound repair can disrupt the delicate balance of cells and molecules necessary for complete wound healing, thus leading to chronic wounds or fibrotic scars. Myofibroblasts are one of the most important cells involved in fibrotic scars, and reprogramming provides a potential avenue to increase myofibroblast clearance. Although myofibroblasts have long been recognized as terminally differentiated cells, recent studies have shown that myofibroblasts have the capacity to be reprogrammed into adipocytes. This review intends to summarize the potential of reprogramming myofibroblasts into adipocytes. We will discuss myofibroblast lineage tracing, as well as the known mechanisms underlying adipocyte regeneration from myofibroblasts. In addition, we investigated different changes in myofibroblast gene expression, transcriptional regulators, signalling pathways and epigenetic regulators during skin wound healing. In the future, myofibroblast reprogramming in wound healing will be better understood and appreciated, which may provide new ideas for the treatment of scarless wound healing.

Virtual Screening in the Identification of Sirtuins’ Activity Modulators

Sirtuins are NAD⁺-dependent deac(et)ylases with different subcellular localization. The sirtuins’ family is composed of seven members, named SIRT-1 to SIRT-7. Their substrates include histones and also an increasing number of different proteins. Sirtuins regulate a wide range of different processes, ranging from transcription to metabolism to genome stability. Thus, their dysregulation has been related to the pathogenesis of different diseases. In this review, we discussed the pharmacological approaches based on sirtuins’ modulators (both inhibitors and activators) that have been attempted in in vitro and/or in in vivo experimental settings, to highlight the therapeutic potential of targeting one/more specific sirtuin isoform(s) in cancer, neurodegenerative disorders and type 2 diabetes. Extensive research has already been performed to identify SIRT-1 and -2 modulators, while compounds targeting the other sirtuins have been less studied so far. Beside sections dedicated to each sirtuin, in the present review we also included sections dedicated to pan-sirtuins’ and to parasitic sirtuins’ modulators. A special focus is dedicated to the sirtuins’ modulators identified by the use of virtual screening.

Multiple Roles of SIRT2 in Regulating Physiological and Pathological Signal Transduction

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

Sirt2 promotes white matter oligodendrogenesis during development and in models of neonatal hypoxia

Delayed oligodendrocyte (OL) maturation caused by hypoxia (Hx)-induced neonatal brain injury results in hypomyelination and leads to neurological disabilities. Previously, we characterized Sirt1 as a crucial regulator of OL progenitor cell (OPC) proliferation in response to Hx. We now identify Sirt2 as a critical promoter of OL differentiation during both normal white matter development and in a mouse model of Hx. Importantly, we find that Hx reduces Sirt2 expression in mature OLs and that Sirt2 overexpression in OPCs restores mature OL populations. Reduced numbers of Sirt2+ OLs were also observed in the white matter of preterm human infants. We show that Sirt2 interacts with p27Kip1/FoxO1, p21Cip1/Cdk4, and Cdk5 pathways, and that these interactions are altered by Hx. Furthermore, Hx induces nuclear translocation of Sirt2 in OPCs where it binds several genomic targets. Overall, these results indicate that a balance of Sirt1 and Sirt2 activity is required for developmental oligodendrogenesis, and that these proteins represent potential targets for promoting repair following white matter injury.

Progress in Nonalcoholic Fatty Liver Disease: SIRT Family Regulates Mitochondrial Biogenesis

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis, insulin resistance, mitochondrial dysfunction, inflammation, and oxidative stress. As a group of NAD+-dependent III deacetylases, the sirtuin (SIRT1-7) family plays a very important role in regulating mitochondrial biogenesis and participates in the progress of NAFLD. SIRT family members are distributed in the nucleus, cytoplasm, and mitochondria; regulate hepatic fatty acid oxidation metabolism through different metabolic pathways and mechanisms; and participate in the regulation of mitochondrial energy metabolism. SIRT1 may improve NAFLD by regulating ROS, PGC-1α, SREBP-1c, FoxO1/3, STAT3, and AMPK to restore mitochondrial function and reduce steatosis of the liver. Other SIRT family members also play a role in regulating mitochondrial biogenesis, fatty acid oxidative metabolism, inflammation, and insulin resistance. Therefore, this paper comprehensively introduces the role of SIRT family in regulating mitochondrial biogenesis in the liver in NAFLD, aiming to further explain the importance of SIRT family in regulating mitochondrial function in the occurrence and development of NAFLD, and to provide ideas for the research and development of targeted drugs. Relatively speaking, the role of some SIRT family members in NAFLD is still insufficiently clear, and further research is needed.

SIRT1 suppresses in vitro decidualization of human endometrial stromal cells through the downregulation of forkhead box O1 expression

SIRT1 regulates survival, DNA repair, and metabolism in human cells and has pleiotropic effects on age-related diseases through either deacetylating target proteins or inhibiting gene transcription. Forkhead box O1 (FOXO1) is one of the most important transcription factors during decidualization. Prolactin (PRL) and insulin-like growth factor-binding protein 1 (IGFBP1) are well-known FOXO1-dependent genes in decidualizing cells. To determine whether SIRT1 plays a role in decidualization, we investigated morphological changes in cells following artificially stimulated decidualization and expression levels of PRL, IGFBP1, and FOXO1 in the immortalized non-neoplastic human endometrial stromal cell line T HESCs. SIRT1 expression decreased in the decidualization condition and SIRT1 inhibited morphological changes caused by decidualization of T HESCs. SIRT1 suppressed PRL, IGFBP1, and FOXO1 expression; inhibited FOXO1, PRL, and IGFBP1 promoter activity; and decreased histone protein acetylation of the FOXO1 promoter. We found that FOXO1 expression increased in the secretory phase compared with the proliferative phase, whereas SIRT1 expression decreased in the secretory phase in the human endometrium. We also revealed that SIRT1 may inhibit embryo implantation according to the blastocyst-like spheroid implantation assay. Collectively, these results indicate that SIRT1 suppresses decidualization of human endometrial stromal cells by inhibiting FOXO1 expression.

Sirtuins as therapeutic targets for improving delayed wound healing in diabetes

Sirtuins are a vast family of histone deacetylases, which are NAD⁺ dependent enzymes, consisting of seven members, namely SIRT 1, SIRT 6 and SIRT 7 located within the nucleus, SIRT 2 in the cytoplasm and SIRT 3, SIRT 4, and SIRT 5 in the mitochondria. They have vital roles in regulating various biological functions such as age-related metabolic disorders, inflammation, stress response, cardiovascular and neuronal functions. Delayed wound healing is one of the complication of diabetes, which can lead to lower limb amputation if not treated timely. SIRT 1, 3 and 6 are potent targets for diabetic wound healing. SIRT 1 deficiency reduces recruitment of fibroblasts, macrophages, mast cells, neutrophils to wound site and delays wound healing; negatively expressing MMP-9. The SIRT 1 mediated signalling pathway in diabetic wound healing is the SIRT 1-foxo-C-Myc pathway. On the contrary SIRT 3 deficiency, impairs proliferation and migration of fibroblasts and SIRT 6 deficiency impairs wound closure rate and interrupts the vascular remodelling. This review focuses on the role of sirtuins in improving delayed wound healing in diabetes and its natural modulators with their specific functions towards healing diabetic wounds.

Phytochemicals targeting NAFLD through modulating the dual function of forkhead box O1 (FOXO1) transcription factor signaling pathways

Literature evidence reveals that natural compounds are potential candidates for ameliorating obesity-associated non-alcoholic fatty liver disease (NAFLD) by targeting forkhead box O1 (FOXO1) transcription factor. FOXO1 has a dual and complex role in regulating both increase and decrease in lipid accumulation in hepatocytes and adipose tissues (AT) at different stages of NAFLD. In insulin resistance (IR), it is constitutively expressed, resulting in increased hepatic glucose output and lipid metabolism irregularity. The studies on different phytochemicals indicate that dysregulation of FOXO1 causes disturbance in cellular nutrients homeostasis, and the natural entities have an enduring impact on the mitigation of these abnormalities. The current review communicates and evaluates certain phytochemicals through different search engines, targeting FOXO1 and its downstream cellular pathways to find lead compounds as potential therapeutic agents for treating NAFLD and related metabolic disorders. The findings of this review confirm that polyphenols, flavonoids, alkaloids, terpenoids, and anthocyanins are capable of modulating FOXO1 and associated signaling pathways, and they are potential therapeutic agents for NAFLD and related complications. HIGHLIGHTS: • FOXO1 has the potential to be targeted by novel drugs from natural sources for the treatment of NAFLD and obesity. • FOXO1 regulates cellular autophagy, inflammation, oxidative stress, and lipogenesis through alternative mechanisms. • Phytochemicals treat NAFLD by acting on FOXO1 or SREBP1c and PPARγ transcription factor signaling pathways.

SIRT2 Deficiency Exacerbates Hepatic Steatosis via a Putative Role of the ER Stress Pathway

Nonalcoholic fatty liver disease (NAFLD), a condition strongly associated with obesity and insulin resistance, is characterized by hepatic lipid accumulation and activation of the endoplasmic reticulum (ER) stress response. The sirtuin 2 (SIRT2) protein deacetylase is emerging as a new player in metabolic homeostasis, but its role in the development of hepatic steatosis and its link with ER stress activation remains unknown. SIRT2-knockout (SIRT2-KO) and wild-type mice were fed either a control or a high-fat diet (HFD) for 4 weeks. Genetic manipulation of SIRT2 levels was performed in human hepatic cells. Although apparently normal under a control diet, SIRT2-KO mice showed accelerated body weight gain and adiposity on a HFD, accompanied by severe insulin resistance. Importantly, SIRT2-KO mice exhibited worsened hepatic steatosis independently from diet, consistent with upregulated gene expression of lipogenic enzymes and increased expression of ER stress markers. Exposure of hepatic cells to palmitate induced lipid accumulation, increased ER stress, and decreased SIRT2 expression. Moreover, SIRT2-silenced cells showed enhanced lipid accumulation and ER stress activation under basal conditions, whereas SIRT2 overexpression abrogated palmitate-induced lipid deposition and ER stress activation. Our findings reveal a role for SIRT2 in the regulation of hepatic lipid homeostasis, potentially through the ER stress response, suggesting that SIRT2 activation might constitute a therapeutic strategy against obesity and its metabolic complications.

Mechanistic insights into the role of FOXO in diabetic retinopathy

Diabetes mellitus (DM), a metabolic disorder characterized by insulin-deficiency or insulin-resistant conditions. The foremost microvascular complication of diabetes is diabetic retinopathy (DR). This is a multifaceted ailment mainly caused by the enduring adverse effects of hyperglycaemia. Inflammation, oxidative stress, and advanced glycation products (AGES) are part and parcel of DR pathogenesis. In regulating many cellular and biological processes, the family of fork-head transcription factors plays a key role. The current review highlights that FOXO is a requisite regulator of pathways intricate in diabetic retinopathy on account of its effect on microvascular cells inflammatory and apoptotic gene expression, and FOXO also has the foremost province in regulating cell cycle, proliferation, apoptosis, and metabolism. Blockage of insulin turns into an exaggerated level of glucose in the bloodstream and can upshot into the exaggerated triggering of FOXO1, which can ultimately uplift the production of several factors of apoptosis and inflammation, such as TNF-α, NF-kB, and various others, as well as reactive oxygen species, which can also come up with diabetic retinopathy. The current review also focuses on various therapies which can be used in the future, like SIRT1 signalling, resveratrol, retinal VEGF, etc., which can be used to suppress FOXO over activation and can prevent the progression of diabetic complications viz. diabetic retinopathy.