SIRT1 enhances glucose tolerance by potentiating brown adipose tissue function

Gut microbiota-derived 4-hydroxyphenylacetic acid from resveratrol supplementation prevents obesity through SIRT1 signaling activation

Resveratrol (RSV), a natural polyphenol, has been suggested to influence glucose and lipid metabolism. However, the underlying molecular mechanism of its action remains largely unknown due to its multiple biological targets and low bioavailability. In this study, we demonstrate that RSV supplementation ameliorates high-fat-diet (HFD)-induced gut microbiota dysbiosis, enhancing the abundance of anti-obesity bacterial strains such as Akkermansia, Bacteroides and Blautia. The critical role of gut microbiota in RSV-mediated anti-obesity effects was confirmed through antibiotic-induced microbiome depletion and fecal microbiota transplantation (FMT), which showed that RSV treatment effectively mitigates body weight, histopathological damage, glucose dysregulation and systematic inflammation associated with HFD. Metabolomics analysis revealed that RSV supplementation significantly increases the levels of the gut microbial flavonoid catabolite 4-hydroxyphenylacetic acid (4-HPA). Notably, 4-HPA was sufficient to reverse obesity and glucose intolerance in HFD-fed mice. Mechanistically,4-HPA treatment markedly regulates SIRT1 signaling pathways and induces the expression of beige fat and thermogenesis-specific markers in white adipose tissue (WAT). These beneficial effects of 4-HPA are partially abolished by EX527, a known SIRT1 inhibitor. Collectively, our findings indicate that RSV improve obesity through a gut microbiota-derived 4-HPA-SIRT1 axis, highlighting gut microbiota metabolites as a promising target for obesity prevention.

Glucagon-like peptide-1: a new potential regulator for mesenchymal stem cells in the treatment of type 2 diabetes mellitus and its complication

Glucagon-like peptide-1 is an enteric proinsulin hormone secreted by intestinal L-cells that orchestrates insulin secretion in a glucose-dependent manner. Renowned for preserving pancreatic β-cell mass, glucagon-like peptide-1 facilitates β-cell proliferation and inhibits apoptosis, while concurrently suppressing glucagon secretion from pancreatic α-cells, thereby exerting hypoglycemic effects.Recent in vitro and in vivo studies have clarified the benefits of combination therapy with glucagon-like peptide-1 and stem cells in Type 2 diabetes mellitus. Glucagon-like peptide-1 enhances the repair of type 2 diabetes mellitus-afflicted tissues and organs by modulating sourced mesenchymal stem cell differentiation, proliferation, apoptosis, and migration. Importantly, glucagon-like peptide-1 overcomes the detrimental effects of the diabetic microenvironment on transplanted mesenchymal stem cells by increasing the number of localized cells in stem cell therapy and the unstable efficacy of stem cell therapy.This review elucidates the molecular and cellular mechanisms through which glucagon-like peptide-1 regulates mesenchymal stem cells in the type 2 diabetes mellitus context and discuss its therapeutic prospects for type 2 diabetes mellitus and its associated complications, proposing a novel and comprehensive treatment paradigm.

A human omentum-specific mesothelial-like stromal population inhibits adipogenesis through IGFBP2 secretion

Adipose tissue plasticity is orchestrated by molecularly and functionally diverse cells within the stromal vascular fraction (SVF). Although several mouse and human adipose SVF cellular subpopulations have by now been identified, we still lack an understanding of the cellular and functional variability of adipose stem and progenitor cell (ASPC) populations across human fat depots. To address this, we performed single-cell and bulk RNA sequencing (RNA-seq) analyses of >30 SVF/Lin- samples across four human adipose depots, revealing two ubiquitous human ASPC (hASPC) subpopulations with distinct proliferative and adipogenic properties but also depot- and BMI-dependent proportions. Furthermore, we identified an omental-specific, high IGFBP2-expressing stromal population that transitions between mesothelial and mesenchymal cell states and inhibits hASPC adipogenesis through IGFBP2 secretion. Our analyses highlight the molecular and cellular uniqueness of different adipose niches, while our discovery of an anti-adipogenic IGFBP2+ omental-specific population provides a new rationale for the biomedically relevant, limited adipogenic capacity of omental hASPCs.

Glucagon-Like Peptide-1: New Regulator in Lipid Metabolism

Glucagon-like peptide-1 (GLP-1) is a 30-amino acid peptide hormone that is mainly expressed in the intestine and hypothalamus. In recent years, basic and clinical studies have shown that GLP-1 is closely related to lipid metabolism, and it can participate in lipid metabolism by inhibiting fat synthesis, promoting fat differentiation, enhancing cholesterol metabolism, and promoting adipose browning. GLP-1 plays a key role in the occurrence and development of metabolic diseases such as obesity, nonalcoholic fatty liver disease, and atherosclerosis by regulating lipid metabolism. It is expected to become a new target for the treatment of metabolic disorders. The effects of GLP-1 and dual agonists on lipid metabolism also provide a more complete treatment plan for metabolic diseases. This article reviews the recent research progress of GLP-1 in lipid metabolism.

Guanidinoacetic acid ameliorates hepatic steatosis and inflammation and promotes white adipose tissue browning in middle-aged mice with high-fat-diet-induced obesity

Guanidinoacetic acid (GAA) is a naturally occurring amino acid derivative that plays a critical role in energy metabolism. In recent years, a growing body of evidence has emerged supporting the importance of GAA in metabolic dysfunction. Hence, we aimed to investigate the effects of GAA on hepatic and adipose tissue metabolism, as well as systemic inflammatory responses in obese middle-aged mice models and attempted to explore the underlying mechanism. We found that dietary supplementation of GAA inhibited inguinal white adipose tissue (iWAT) hypertrophy in high-fat diet (HFD)-fed mice. In addition, GAA supplementation observably decreased the levels of some systemic inflammatory factors, including IL-4, TNF-α, IL-1β, and IL-6. Intriguingly, GAA supplementation ameliorated hepatic steatosis and lipid deposition in HFD-fed mice, which was revealed by decreased levels of TG, TC, LDL-C, PPARγ, SREBP-1c, FASN, ACC, FABP1, and APOB and increased levels of HDL-C in the liver. Moreover, GAA supplementation increased the expression of browning markers and mitochondrial-related genes in the iWAT. Further investigation showed that dietary GAA promoted the browning of the iWAT via activating the AMPK/Sirt1 signaling pathway and might be associated with futile creatine cycling in obese mice. These results indicate that GAA has the potential to be used as an effective ingredient in dietary interventions and thus may play an important role in ameliorating and preventing HFD-induced obesity and related metabolic diseases.

The Emerging Role of SIRT7 in Glucose and Lipid Metabolism

Sirtuins (SIRT1-7 in mammals) are a family of NAD+-dependent lysine deacetylases and deacylases that regulate diverse biological processes, including metabolism, stress responses, and aging. SIRT7 is the least well-studied member of the sirtuins, but accumulating evidence has shown that SIRT7 plays critical roles in the regulation of glucose and lipid metabolism by modulating many target proteins in white adipose tissue, brown adipose tissue, and liver tissue. This review focuses on the emerging roles of SIRT7 in glucose and lipid metabolism in comparison with SIRT1 and SIRT6. We also discuss the possible implications of SIRT7 inhibition in the treatment of metabolic diseases such as type 2 diabetes and obesity.

Mulberry leaf flavonoids activate BAT and induce browning of WAT to improve type 2 diabetes via regulating the AMPK/SIRT1/PGC-1α signaling pathway

Mulberry (Morus alba L.) leaf is a well-established traditional Chinese botanical and culinary resource. It has found widespread application in the management of diabetes. The bioactive constituents of mulberry leaf, specifically mulberry leaf flavonoids (MLFs), exhibit pronounced potential in the amelioration of type 2 diabetes (T2D). This potential is attributed to their ability to safeguard pancreatic β cells, enhance insulin resistance, and inhibit α-glucosidase activity. Our antecedent research findings underscore the substantial therapeutic efficacy of MLFs in treating T2D. However, the precise mechanistic underpinnings of MLF's anti-T2D effects remain the subject of inquiry. Activation of brown/beige adipocytes is a novel and promising strategy for T2D treatment. In the present study, our primary objective was to elucidate the impact of MLFs on adipose tissue browning in db/db mice and 3T3-L1 cells and elucidate its underlying mechanism. The results manifested that MLFs reduced body weight and food intake, alleviated hepatic steatosis, improved insulin sensitivity, and increased lipolysis and thermogenesis in db/db mice. Moreover, MLFs activated brown adipose tissue (BAT) and induced the browning of inguinal white adipose tissue (IWAT) and 3T3-L1 adipocytes by increasing the expressions of brown adipocyte marker genes and proteins such as uncoupling protein 1 (UCP1) and beige adipocyte marker genes such as transmembrane protein 26 (Tmem26), thereby promoting mitochondrial biogenesis. Mechanistically, MLFs facilitated the activation of BAT and the induction of WAT browning to ameliorate T2D primarily through the activation of AMP-activated protein kinase (AMPK)/sirtuin 1 (SIRT1)/peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α) signaling pathway. These findings highlight the unique capacity of MLF to counteract T2D by enhancing BAT activation and inducing browning of IWAT, thereby ameliorating glucose and lipid metabolism disorders. As such, MLFs emerge as a prospective and innovative browning agent for the treatment of T2D.

Adipocyte NMNAT1 expression is essential for nuclear NAD+ biosynthesis but dispensable for regulating thermogenesis and whole-body energy metabolism

Nicotinamide adenine dinucleotide (NAD+) functions as an essential cofactor regulating a variety of biological processes. The purpose of the present study was to determine the role of nuclear NAD+ biosynthesis, mediated by nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1), in thermogenesis and whole-body energy metabolism. We first evaluated the relationship between NMNAT1 expression and thermogenic activity in brown adipose tissue (BAT), a key organ for non-shivering thermogenesis. We found that reduced BAT NMNAT1expression was associated with inactivation of thermogenic gene program induced by obesity and thermoneutrality. Next, we generated and characterized adiponectin-Cre-driven adipocyte-specific Nmnat1 knockout (ANMT1KO) mice. Loss of NMNAT1 markedly reduced nuclear NAD+ concentration by approximately 70% in BAT. Nonetheless, adipocyte-specific Nmnat1 deletion had no impact on thermogenic (rectal temperature, BAT temperature and whole-body oxygen consumption) responses to β-adrenergic ligand norepinephrine administration and acute cold exposure, adrenergic-mediated lipolytic activity, and metabolic responses to obesogenic high-fat diet feeding. In addition, loss of NMNAT1 did not affect nuclear lysine acetylation or thermogenic gene program in BAT. These results demonstrate that adipocyte NMNAT1 expression is required for maintaining nuclear NAD+ concentration, but not for regulating BAT thermogenesis or whole-body energy homeostasis.

Maresin 1 activates brown adipose tissue and promotes browning of white adipose tissue in mice

OBJECTIVE

Maresin 1 (MaR1) is a docosahexaenoic acid-derived proresolving lipid mediator with insulin-sensitizing and anti-steatosis properties. Here, we aim to unravel MaR1 actions on brown adipose tissue (BAT) activation and white adipose tissue (WAT) browning.

METHODS

MaR1 actions were tested in cultured murine brown adipocytes and in human mesenchymal stem cells (hMSC)-derived adipocytes. In vivo effects of MaR1 were tested in diet-induced obese (DIO) mice and lean WT and Il6 knockout (Il6-/-) mice.

RESULTS

In cultured differentiated murine brown adipocytes, MaR1 reduces the expression of inflammatory genes, while stimulates glucose uptake, fatty acid utilization and oxygen consumption rate, along with the upregulation of mitochondrial mass and genes involved in mitochondrial biogenesis and function and the thermogenic program. In Leucine Rich Repeat Containing G Protein-Coupled Receptor 6 (LGR6)-depleted brown adipocytes using siRNA, the stimulatory effect of MaR1 on thermogenic genes was abrogated. In DIO mice, MaR1 promotes BAT remodeling, characterized by higher expression of genes encoding for master regulators of mitochondrial biogenesis and function and iBAT thermogenic activation, together with increased M2 macrophage markers. In addition, MaR1-treated DIO mice exhibit a better response to cold-induced BAT activation. Moreover, MaR1 induces a beige adipocyte signature in inguinal WAT of DIO mice and in hMSC-derived adipocytes. MaR1 potentiates Il6 expression in brown adipocytes and BAT of cold exposed lean WT mice. Interestingly, the thermogenic properties of MaR1 were abrogated in Il6-/- mice.

CONCLUSIONS

These data reveal MaR1 as a novel agent that promotes BAT activation and WAT browning by regulating thermogenic program in adipocytes and M2 polarization of macrophages. Moreover, our data suggest that LGR6 receptor is mediating MaR1 actions on brown adipocytes, and that IL-6 is required for the thermogenic effects of MaR1.

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.

Nicotinamide riboside kinase 1 protects against diet and age-induced pancreatic β-cell failure

OBJECTIVE

Disturbances in NAD⁺ metabolism have been described as a hallmark for multiple metabolic and age-related diseases, including type 2 diabetes. While alterations in pancreatic β-cell function are critical determinants of whole-body glucose homeostasis, the role of NAD⁺ metabolism in the endocrine pancreas remains poorly explored. Here, we aimed to evaluate the role of nicotinamide riboside (NR) metabolism in maintaining NAD⁺ levels and pancreatic β-cell function in pathophysiological conditions.

METHODS

Whole body and pancreatic β-cell-specific NRK1 knockout (KO) mice were metabolically phenotyped in situations of high-fat feeding and aging. We also analyzed pancreatic β-cell function, β-cell mass and gene expression.

RESULTS

We first demonstrate that NRK1, the essential enzyme for the utilization of NR, is abundantly expressed in pancreatic β-cells. While NR treatment did not alter glucose-stimulated insulin secretion in pancreatic islets from young healthy mice, NRK1 knockout mice displayed glucose intolerance and compromised β-cells response to a glucose challenge upon high-fat feeding or aging. Interestingly, β cell dysfunction stemmed from the functional failure of other organs, such as liver and kidney, and the associated changes in circulating peptides and hormones, as mice lacking NRK1 exclusively in β-cells did not show altered glucose homeostasis.

CONCLUSIONS

This work unveils a new physiological role for NR metabolism in the maintenance of glucose tolerance and pancreatic β-cell function in high-fat feeding or aging conditions.

Balancing NAD+ deficits with nicotinamide riboside: therapeutic possibilities and limitations

Alterations in cellular nicotinamide adenine dinucleotide (NAD+) levels have been observed in multiple lifestyle and age-related medical conditions. This has led to the hypothesis that dietary supplementation with NAD+ precursors, or vitamin B3s, could exert health benefits. Among the different molecules that can act as NAD+ precursors, Nicotinamide Riboside (NR) has gained most attention due to its success in alleviating and treating disease conditions at the pre-clinical level. However, the clinical outcomes for NR supplementation strategies have not yet met the expectations generated in mouse models. In this review we aim to provide a comprehensive view on NAD+ biology, what causes NAD+ deficits and the journey of NR from its discovery to its clinical development. We also discuss what are the current limitations in NR-based therapies and potential ways to overcome them. Overall, this review will not only provide tools to understand NAD+ biology and assess its changes in disease situations, but also to decide which NAD+ precursor could have the best therapeutic potential.

Seabuckthorn Reverses High-Fat-Diet-Induced Obesity and Enhances Fat Browning via Activation of AMPK/SIRT1 Pathway

Seabuckthorn possesses various bioactive compounds and exhibits several positive pharmacological activities. The present trial aims to determine the effect of seabuckthorn powder intake on high-fat diet (HFD)-induced obesity prevention in mice. The results suggest that seabuckthorn powder intake decreased body weight, fat mass, and circulating lipid levels, and improved insulin sensitivity in HFD-fed mice. Moreover, dietary seabuckthorn powder alleviated hepatic steatosis and hepatic lipid accumulation induced by the HFD. Furthermore, seabuckthorn exhibited obvious anti-inflammatory capacity in white adipose tissue (WAT) by regulating the abundance of inflammation-related cytokines, such as interleukins 4, 6, and 10; tumor necrosis factor α; and interferon-γ. More importantly, dietary seabuckthorn powder promoted a thermogenic program in BAT and induced beige adipocyte formation in iWAT in HFD-fed mice. Interestingly, we found that seabuckthorn powder effectively restored AMPK and SIRT1 activities in both BAT and iWAT in HFD-fed mice. Collectively, these results potentiate the application of seabuckthorn powder as a nutritional intervention strategy to prevent obesity and related metabolic diseases by promoting thermogenesis in BAT and improving beige adipocyte formation in WAT.

Nicotinamide Riboside and Dihydronicotinic Acid Riboside Synergistically Increase Intracellular NAD+ by Generating Dihydronicotinamide Riboside

Through evolution, eukaryote organisms have developed the ability to use different molecules as independent precursors to generate nicotinamide adenine dinucleotide (NAD⁺), an essential molecule for life. However, whether these different precursors act in an additive or complementary manner is not truly well understood. Here, we have evaluated how combinations of different NAD⁺ precursors influence intracellular NAD⁺ levels. We identified dihydronicotinic acid riboside (NARH) as a new NAD⁺ precursor in hepatic cells. Second, we demonstrate how NARH, but not any other NAD⁺ precursor, can act synergistically with nicotinamide riboside (NR) to increase NAD⁺ levels in cultured cells and in mice. Finally, we demonstrate that the large increase in NAD⁺ prompted by the combination of these two precursors is due to their chemical interaction and conversion to dihydronicotinamide riboside (NRH). Altogether, this work demonstrates for the first time that NARH can act as a NAD⁺ precursor in mammalian cells and how different NAD⁺ precursors can interact and influence each other when co-administered.

Dihydromyricetin ameliorates diet-induced obesity and promotes browning of white adipose tissue by upregulating IRF4/PGC-1α

BACKGROUND

Promoting the browning of white adipose tissue (WAT) is a promising approach for the treatment of obesity and related comorbidities because it increases energy expenditure. In this study, we investigated whether Dihydromyricetin (DHM), a flavonoid component, could ameliorate diet-induced obesity through promoting the browning of WAT.

METHODS

Male C57BL/6 J mice were received a high-fat diet (HFD) to induce obesity and subsequently were treated with DHM (100 mg/kg/day) or vehicle for 4 weeks. The effects of DHM on weight reduction and metabolic phenotype improvement were observed in the mice. The expression of genes and protein involved in browning of WAT were assessed in inguinal WAT (iWAT) of the mice. Then, the effect of DHM on the inducing browning program was verified in adipocytes differentiated from stromal vascular fraction (SVF) cells of mouse iWAT. Finally, the mechanism by which DHM improves the browning of WAT was explored using RNA-seq and luciferase reporter assay.

RESULTS

We find that DHM reduces body weight, decreases WAT mass, improves glucose and lipid metabolic disorders, and ameliorates hepatic steatosis in diet-induced obese (DIO) mice. Further studies show that DHM induces WAT browning, which is manifested by increased expression of uncoupling protein 1 (UCP1) and peroxisome proliferator-activated receptor gamma coactivator (PGC)-1α and enhanced mitochondrial activity in iWAT and primary adipocytes. In addition, we also find that DHM enhances interferon regulatory factor 4 (IRF4) expression, which is a key transcriptional regulator of PGC-1α.

CONCLUSION

Our findings identify that DHM prevents obesity by inducing the browning of WAT through the upregulation of IRF4/PGC-1α, which may have potential therapeutic implications for the treatment of obesity.

Progressive brown adipocyte dysfunction: whitening and impaired nonshivering thermogenesis as long-term obesity complications

Chronic obesity damages the cytoarchitecture of brown adipose tissue (BAT), leading to whitening of brown adipocytes and impaired thermogenesis, characterizing BAT dysfunction. Understanding the pathways of whitening progression can bring new targets to counter obesity. This study aimed to evaluate the chronic effect (12, 16, and 20 weeks) of a high-fat diet (50% energy as fat) upon energy expenditure, thermogenic markers, and pathways involved in BAT whitening in C57BL/6J mice. Sixty adult male mice comprised six nutritional groups, where the letters refer to the diet type (control, C or high-fat, HF), and the numbers refer to the period (in weeks) of diet administration: C12, HF12, C16, HF16, C20, and HF20. After sacrifice, biochemical, molecular, and stereological analyses addressed the outcomes. The HF groups had overweight, oral glucose intolerance, and hyperleptinemia, resulting in progressive whitening of BAT and decreased numerical density of nuclei per area of tissue compared to age-matched control groups. In addition, the whitening maximization was related to altered batokines gene expression, decreased nonshivering thermogenesis, and body temperature, resulting in low energy expenditure. The HF20 group showed enlarged adipocytes with stable and dysfunctional lipid droplets, followed by inflammation and ER stress. In conclusion, chronic HF diet intake caused time-dependent maximization of whitening with defective nonshivering thermogenesis. Long-term BAT dysfunction includes down-regulated vascularization markers, upregulated inflammasome activation, and ER stress markers.

LETMD1 is required for mitochondrial structure and thermogenic function of brown adipocytes

Obesity and metabolic disorders caused by energy surplus pose an increasing concern within the global population. Brown adipose tissue (BAT) dissipates energy through mitochondrial non-shivering thermogenesis, thus representing a powerful agent against obesity. Here we explore the novel role of a mitochondrial outer membrane protein, LETM1-domain containing 1 (LETMD1), in BAT. We generated a knockout (Letmd1KO ) mouse model and analyzed BAT morphology, function and gene expression under various physiological conditions. While the Letmd1KO mice are born normally and have normal morphology and body weight, they lose multilocular brown adipocytes completely and have diminished mitochondrial abundance, DNA copy number, cristae structure, and thermogenic gene expression in the intrascapular BAT, associated with elevated reactive oxidative stress. In consequence, the Letmd1KO mice fail to maintain body temperature in response to acute cold exposure without food and become hypothermic within 4 h. Although the cold-exposed Letmd1KO mice can maintain body temperature in the presence of food, they cannot upregulate expression of uncoupling protein 1 (UCP1) and convert white to beige adipocytes, nor can they respond to adrenergic stimulation. These results demonstrate that LETMD1 is essential for mitochondrial structure and function, and thermogenesis of brown adipocytes.

Role of CD38 in Adipose Tissue: Tuning Coenzyme Availability?

Nicotinamide adenine dinucleotide (NAD⁺) is a fundamental molecule in the regulation of energy metabolism, representing both a coenzyme and a substrate for different NAD⁺ degrading enzymes. Among these enzymes, CD38 can be seen under two perspectives: as the enzyme synthesizing Ca²⁺-mobilizing second messenger, starting from NAD⁺, and as the major NAD⁺-consumer, to be inhibited to increase NAD⁺ levels. Indeed, the regulation of NAD⁺ availability is a key event during different processes. In this review, we examine the recent studies related to the modulation of CD38 expression and activity, and the consequent changes in NAD(P)(H), in adipose tissue, during inflammation and cold-induced thermogenesis.

Crosstalk between Drp1 phosphorylation sites during mitochondrial remodeling and their impact on metabolic adaptation

Mitochondria constantly undergo fusion and fission events, referred as mitochondrial dynamics, which determine mitochondrial architecture and bioenergetics. Cultured cell studies demonstrate that mitochondrial dynamics are acutely regulated by phosphorylation of the mitochondrial fission orchestrator dynamin-related protein 1 (Drp1) at S579 or S600. However, the physiological impact and crosstalk of these phosphorylation sites is poorly understood. Here, we describe the functional interrelation between S579 and S600 phosphorylation sites in vivo and their role on mitochondrial remodeling. Mice carrying a homozygous Drp1 S600A knockin (Drp1 KI) mutation display larger mitochondria and enhanced lipid oxidation and respiratory capacities, granting improved glucose tolerance and thermogenic response upon high-fat feeding. Housing mice at thermoneutrality blunts these differences, suggesting a role for the brown adipose tissue in the protection of Drp1 KI mice against metabolic damage. Overall, we demonstrate crosstalk between Drp1 phosphorylation sites and provide evidence that their modulation could be used in the treatment and prevention of metabolic diseases.

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Drp1 phosphorylation at S600 promotes the phosphorylation at the S579 site

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Both Drp1 P-S600 and P-S579 are required for maximal mitochondrial fragmentation

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Drp1 S600A knockin mice are protected against diet-induced metabolic damage

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Drp1 phosphorylation controls brown adipose tissue thermogenic capacity in mice

Impaired brown adipose tissue is differentially modulated in insulin-resistant obese wistar and type 2 diabetic Goto-Kakizaki rats

Brown adipose tissue (BAT) is a potential target to treat obesity and diabetes, dissipating energy as heat. Type 2 diabetes (T2D) has been associated with obesogenic diets; however, T2D was also reported in lean individuals to be associated with genetic factors. We aimed to investigate the differences between obese and lean models of insulin resistance (IR) and elucidate the mechanism associated with BAT metabolism and dysfunction in different IR animal models: a genetic model (lean GK rats) and obese models (diet-induced obese Wistar rats) at 8 weeks of age fed a high-carbohydrate (HC), high-fat (HF) diet, or high-fat and high-sugar (HFHS) diet for 8 weeks. At 15 weeks of age, BAT glucose uptake was evaluated by 18F-FDG PET under basal (saline administration) or stimulated condition (CL316,243, a selective β3-AR agonist). After CL316, 243 administrations, GK animals showed decreased glucose uptake compared to HC animals. At 16 weeks of age, the animals were euthanized, and the interscapular BAT was dissected for analysis. Histological analyses showed lower cell density in GK rats and higher adipocyte area compared to all groups, followed by HFHS and HF compared to HC. HFHS showed a decreased batokine FGF21 protein level compared to all groups. However, GK animals showed increased expression of genes involved in fatty acid oxidation (CPT1 and CPT2), BAT metabolism (Sirt1 and Pgc1-α), and obesogenic genes (leptin and PAI-1) but decreased gene expression of glucose transporter 1 (GLUT-1) compared to other groups. Our data suggest impaired BAT function in obese Wistar and GK rats, with evidence of a whitening process in these animals.

Sirt1 coordinates with ERα to regulate autophagy and adiposity

Sex difference in adiposity has long been recognized but the mechanism remains incompletely understood. Previous studies suggested that adiposity was regulated by autophagy in response to energy status change. Here, we show that the energy sensor Sirt1 mediates sex difference in adiposity by regulating autophagy and adipogenesis in partnership with estrogen receptor α (ERα). Autophagy and adipogenesis were suppressed by Sirt1 activation or overexpression, which was associated with reduced sex difference in adiposity. Mechanistically, Sirt1 deacetylated and activated AKT and STAT3, resulting in suppression of autophagy and adipogenesis via mTOR-ULK1 and p55 cascades. ERα induced Sirt1 expression and inhibited autophagy in adipocytes, while silencing Sirt1 reversed the effects of ERα on autophagy and promoted adipogenesis. Moreover, Sirt1 deacetylated ERα, which constituted a positive feedback loop in the regulation of autophagy and adiposity. Our results revealed a new mechanism of Sirt1 regulating autophagy in adipocytes and shed light on sex difference in adiposity.

Sirtuins-Mediated System-Level Regulation of Mammalian Tissues at the Interface between Metabolism and Cell Cycle: A Systematic Review

Sirtuins are a family of highly conserved NAD+-dependent proteins and this dependency links Sirtuins directly to metabolism. Sirtuins' activity has been shown to extend the lifespan of several organisms and mainly through the post-translational modification of their many target proteins, with deacetylation being the most common modification. The seven mammalian Sirtuins, SIRT1 through SIRT7, have been implicated in regulating physiological responses to metabolism and stress by acting as nutrient sensors, linking environmental and nutrient signals to mammalian metabolic homeostasis. Furthermore, mammalian Sirtuins have been implicated in playing major roles in mammalian pathophysiological conditions such as inflammation, obesity and cancer. Mammalian Sirtuins are expressed heterogeneously among different organs and tissues, and the same holds true for their substrates. Thus, the function of mammalian Sirtuins together with their substrates is expected to vary among tissues. Any therapy depending on Sirtuins could therefore have different local as well as systemic effects. Here, an introduction to processes relevant for the actions of Sirtuins, such as metabolism and cell cycle, will be followed by reasoning on the system-level function of Sirtuins and their substrates in different mammalian tissues. Their involvement in the healthy metabolism and metabolic disorders will be reviewed and critically discussed.

Corylin reduces obesity and insulin resistance and promotes adipose tissue browning through SIRT-1 and β3-AR activation

Brown adipose tissue (BAT) activation or beige adipocytes in white adipocytes (WAT) (browning) is a novel strategy against obesity. Corylin, a flavonoid compound extract from Psoralea corylifolia L., has been shown to exert anti-inflammatory, anticancer, and anti-atherosclerotic effects and ameliorate hyperlipidemia and insulin resistance. However, the therapeutic effect of corylin on obesity remains unknown. The objective of this study was to evaluate the effect of corylin on browning or obesity. Here, we report that corylin induced browning by elevating the expression levels of beige- or browning-specific marker genes, including cited1, hoxc9, pgc1α, prdm16, and ucp1, in 3T3-L1 adipocytes, WAT and BAT. Moreover, corylin also strikingly reduced body weight and fat accumulation and increased insulin sensitivity, mitochondrial biogenesis, and β-oxidation in HFD- and DIO-treated mice. The browning and lipolysis effects of corylin were abolished by sirtuin 1 (SIRT1) inhibitor (EX527) and β3-adrenergic receptor (β3-AR) antagonist (L-748,337) treatment. The possible molecular mechanism of corylin on the browning and lipolysis of adipocytes is through SIRT1- or β3-AR-dependent pathways. The study suggested that corylin exerts anti-obesity effects through the browning of white adipocytes, activating of BAT and promoting of lipid metabolism. Therefore, corylin may be a helpful therapeutic candidate for treating obesity.

Understanding Dietary Intervention-Mediated Epigenetic Modifications in Metabolic Diseases

The global prevalence of metabolic disorders, such as obesity, diabetes and fatty liver disease, is dramatically increasing. Both genetic and environmental factors are well-known contributors to the development of these diseases and therefore, the study of epigenetics can provide additional mechanistic insight. Dietary interventions, including caloric restriction, intermittent fasting or time-restricted feeding, have shown promising improvements in patients' overall metabolic profiles (i.e., reduced body weight, improved glucose homeostasis), and an increasing number of studies have associated these beneficial effects with epigenetic alterations. In this article, we review epigenetic changes involved in both metabolic diseases and dietary interventions in primary metabolic tissues (i.e., adipose, liver, and pancreas) in hopes of elucidating potential biomarkers and therapeutic targets for disease prevention and treatment.

Moderate SIRT1 overexpression protects against brown adipose tissue inflammation

OBJECTIVE

Metainflammation is a chronic low-grade inflammatory state induced by obesity and associated comorbidities, including peripheral insulin resistance. Brown adipose tissue (BAT), a therapeutic target against obesity, is an insulin target tissue sensitive to inflammation. Therefore, it is necessary to find strategies to protect BAT against the effects of inflammation in energy balance. In this study, we explored the impact of moderate sirtuin 1 (SIRT1) overexpression on insulin sensitivity and β-adrenergic responses in BAT and brown adipocytes (BA) under pro-inflammatory conditions.

METHODS

The effect of inflammation on BAT functionality was studied in obese db/db mice and lean wild-type (WT) mice or mice with moderate overexpression of SIRT1 (SIRT1^Tg+) injected with a low dose of bacterial lipopolysaccharide (LPS) to mimic endotoxemia. We also conducted studies on differentiated BA (BA-WT and BA-SIRT1^Tg+) exposed to a macrophage-derived pro-inflammatory conditioned medium (CM) to evaluate the protection of SIRT1 overexpression in insulin signaling and glucose uptake, mitochondrial respiration, fatty acid oxidation (FAO), and norepinephrine (NE)-mediated-modulation of uncoupling protein-1 (UCP-1) expression.

RESULTS

BAT from the db/db mice was susceptible to metabolic inflammation manifested by the activation of pro-inflammatory signaling cascades, increased pro-inflammatory gene expression, tissue-specific insulin resistance, and reduced UCP-1 expression. Impairment of insulin and noradrenergic responses were also found in the lean WT mice upon LPS injection. In contrast, BAT from the mice with moderate overexpression of SIRT1 (SIRT1^Tg+) was protected against LPS-induced activation of pro-inflammatory signaling, insulin resistance, and defective thermogenic-related responses upon cold exposure. Importantly, the decline in triiodothyronine (T₃) levels in the circulation and intra-BAT after exposure of the WT mice to LPS and cold was markedly attenuated in the SIRT1^Tg+ mice. In vitro BA experiments in the two genotypes revealed that upon differentiation with a T₃-enriched medium and subsequent exposure to a macrophage-derived pro-inflammatory CM, only BA-SIRT1^Tg+ fully recovered insulin and noradrenergic responses.

CONCLUSIONS

This study has ascertained the benefit of the moderate overexpression of SIRT1 to confer protection against defective insulin and β-adrenergic responses caused by BAT inflammation. Our results have potential therapeutic value in combinatorial therapies for BAT-specific thyromimetics and SIRT1 activators to combat metainflammation in this tissue.

Pinealectomy increases thermogenesis and decreases lipogenesis

The present study was designed to determine the effects of pineal gland-derived melatonin on obesity by employing a rat pinealectomy (Pnx) model. After 10 weeks of a high-fat diet, rats received sham or Pnx surgery followed by a normal chow diet for 10 weeks. Reverse transcription-quantitative PCR, western blotting analysis, immunohistochemistry and ELISA were used to determine the effects of Pnx. Pnx decreased the expression of melatonin receptor (MTNR)1A and MTNR1B, in brown adipose tissues (BAT) and white adipose tissues (WAT). Pnx rats showed increased insulin sensitivity compared with those that received sham surgery. Leptin levels were significantly decreased in the serum of the Pnx group. In addition, Pnx stimulated thermogenic genes in BAT and attenuated lipogenic genes in both WAT and the liver. Histological analyses revealed a marked decrease in the size of lipid droplets and increased expression of uncoupling protein 1 in BAT. In the liver of the Pnx group, the size and number of lipid droplets had also decreased. In conclusion, the results presented in the current study suggested that Pnx increases thermogenesis in BAT and decreases lipogenesis in WAT and the liver.

LncRNA TUG1 reduces inflammation and enhances insulin sensitivity in white adipose tissue by regulating miR-204/SIRT1 axis in obesity mice

Prevalence of obesity becomes an important health issue worldwide, but the management of obesity remains unsatisfied. This study aimed to explore the mechanism of long non-coding RNA TUG/miR-204/SIRT1 axis, which was involved in the pathogenesis of obesity. Obesity mouse model was induced by high-fat diet and treated with taurine upregulated gene1 (TUG1) virus via tail intravenous injection. Then, body weight, serum glucose, insulin tolerance, testicular fat weight were detected, as well as the expression of TUG1, microRNA-204 (miR-204), sirtuin1 (SIRT1), and inflammation and fatty accumulation associated proteins and cytokines. Regulatory relationship between TUG1/SIRT1 and miR-204 was confirmed by dual-luciferase reporter activity assay. A high-glucose-induced 3T3-L1 cell model was also constructed to explore the regulatory mechanism of TUG/miR-204/SIRT1 axis in the pathogenesis of obesity at cell level after altering the expression of TUG1, miR-204, and SIRT1. Overexpression of TUG1 could significantly attenuate the weight, serum glucose, glucose, insulin tolerance, fatty accumulation, and inflammation in obesity mice, as well as the elevation of miR-204, but increase the expression of SIRT1, phosphorylated AKT (p-AKT), glucose transporter4 (GLUT4), and peroxisome proliferator activated receptorγ (PPARγ). Both TUG1 and SIRT1 were targets of miR-204 and could be negatively regulated by miR-204. Overexpression of TUG1 could suppress the inflammation in adipocytes via downregulating miR-204 and promote GLUT4/PPARγ/AKT pathway high-glucose-induced inflammation in 3T3-L1 cells. miR-204 inhibitors could also suppress high-glucose-induced inflammation in 3T3-L1 cells via promoting SIRT1/ GLUT4/PPARγ/AKT pathway. LncRNA TUG1 could negatively regulate miR-204 to alleviate inflammation and insulin tolerance via promoting SIRT1/GLUT4/PPARγ/AKT pathway.

Allicin Regulates Energy Homeostasis through Brown Adipose Tissue

Brown adipose tissue (BAT) is a promising potential therapeutic target for the treatment of obesity and related metabolic diseases. Allicin, a natural product in garlic, has multiple biological and pharmacological functions. However, the role of allicin in the regulation of metabolic organs, particularly BAT activation, has not been well studied. Here, we show that allicin imparts a significant effect by inhibiting body weight gain, decreasing adiposity, maintaining glucose homeostasis, improving insulin resistance, and ameliorating hepatic steatosis in obese mice. These observations strongly correlate with the activation of BAT. Notably, allicin plays a role in BAT activation, which may partly contribute to the Sirt1-PGC1α-Tfam pathway. In addition, allicin can significantly increase the succinylation levels of UCP1 in BAT by inhibiting sirt5, whereas excess allicin induces autophagy/mitophagy and mitochondrial dysfunction. Thus, our findings point to allicin as a promising therapeutic approach for the treatment of obesity and metabolic disorders.

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Allicin reduces adiposity and maintains glucose homeostasis

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Allicin activates the brown adipocytes and increases the energy expenditure

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Allicin enhances BAT activity partly through SIRT1-PGC1a-Tfam signaling pathway

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Allicin regulates mitophagy via suppressed sirt5-mediated succinylation accumulation

Epigenetic dynamics of the thermogenic gene program of adipocytes

Brown adipose tissue (BAT) is a metabolically beneficial organ capable of burning fat by dissipating chemical energy into heat, thereby increasing energy expenditure. Moreover, subcutaneous white adipose tissue can undergo so-called browning/beiging. The recent recognition of the presence of brown or beige adipocytes in human adults has attracted much attention to elucidate the molecular mechanism underlying the thermogenic adipose program. Many key transcriptional regulators critical for the thermogenic gene program centering on activating the UCP1 promoter, have been discovered. Thermogenic gene expression in brown adipocytes rely on co-ordinated actions of a multitude of transcription factors, including EBF2, PPARγ, Zfp516 and Zc3h10. These transcription factors probably integrate into a cohesive network for BAT gene program. Moreover, these transcription factors recruit epigenetic factors, such as LSD1 and MLL3/4, for specific histone signatures to establish the favorable chromatin landscape. In this review, we discuss advances made in understanding the molecular mechanism underlying the thermogenic gene program, particularly epigenetic regulation.

Comprehensive amelioration of high-fat diet-induced metabolic dysfunctions through activation of the PGC-1α pathway by probiotics treatment in mice

Although the beneficial effects of probiotics in the prevention or treatment of metabolic disorders have been extensively researched, the precise mechanisms by which probiotics improve metabolic homeostasis are still not clear. Given that probiotics usually exert a comprehensive effect on multiple metabolic disorders, defining a concurrent mechanism underlying the multiple effects is critical to understand the function of probiotics. In this study, we identified the SIRT1-dependent or independent PGC-1α pathways in multiple organs that mediate the protective effects of a strain of Lactobacillus plantarum against high-fat diet-induced adiposity, glucose intolerance, and dyslipidemia. L. plantarum treatment significantly enhanced the expression of SIRT1, PPARα, and PGC-1α in the liver and adipose tissues under HFD-fed condition. L. plantarum treated mice also exhibited significantly increased expressions of genes involved in bile acid synthesis and reverse cholesterol transport in the liver, browning and thermogenesis of adipose tissue, and fatty acid oxidation in the liver and adipose tissue. Additionally, L. plantarum treatment significantly upregulated the expressions of adiponectin in adipose tissue, irisin in skeletal muscle and subcutaneous adipose tissue (SAT), and FGF21 in SAT. These beneficial changes were associated with a significantly improved HFD-induced alteration of gut microbiota. Our findings suggest that the PGC-1α-mediated pathway could be regarded as a potential target in the development of probiotics-based therapies for the prevention and treatment of metabolic disorders.

Jiang Gui Fang activated interscapular brown adipose tissue and induced epididymal white adipose tissue browning through the PPARγ/SIRT1-PGC1α pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Gui Zhi Tang, a well-known Chinese herbal formula recorded in the Eastern Han Dynasty, has been widely used to treat exogenous cold for thousands of years. Recent studies have shown that Gui Zhi Tang has the effect of regulating the body temperature. Because of its effect on heat production, protecting vital organs of the body and avoiding damage from the cold environment, Jiang Gui Fang (JG) was obtained from the Department of Traditional Chinese Medicine at the General Hospital of Northern Theatre Command where it has been used clinically for many years and has exhibited favourable efficacy. Based on research on Gui Zhi Tang, the principles of traditional Chinese medicine and survey of a large number of studies, this empirical formula was developed. The composition of JG included Dried ginger, Cassia twig, and Liquorice in Gui Zhi Tang, which play a major role in the treatment of exogenous cold, and combined these components with other Chinese medicines, such as Pueraria, Spatholobus, Acanthopanacis cortex, Evodiae fructus, and Codonopsis pilosula.

AIM OF THE STUDY

To promote the core body temperature and prevent invasion of the major organs from the cold environment, we studied the effect of JG on the core body temperature of mice and then explored its regulation of interscapular brown adipose tissue (iBAT) and epididymal white adipose tissue (eWAT) and the possible mechanism. Finally, we determined the phytochemical composition of JG that plays a role in heat production.

MATERIALS AND METHODS

In vivo study, we performed a 4-week treatment of JG in acute cold environment at -20 °C and chronic cold exposure at 4 °C. The core temperature, adipose tissue weight, serum parameters, and morphological observation of adipocytes, liver and kidney were measured. Then we investigated the expression levels of adipogenic factors, thermogenic factors and lipoprotein. In vitro, we determined the lipid droplet content, ATP content, and the maximum oxygen consumption of mitochondria.

RESULTS

JG treatment promoted core temperature, inhibited eWAT weight, protected liver, and reduced glucose and lipids in Kunming (KM) mice. JG also increased the expression of BAT-associated thermogenic factors, including uncoupling protein 1 (UCP1) and peroxisome proliferator-activated receptor γ coactivator-1α (PGC1α). The levels of the lipogenic factor peroxisome proliferate-activator receptor gamma (PPARγ) and the lipolytic protein hormone-sensitive triglyceride lipase (HSL) in eWAT were elevated. The results of H&E and immunohistochemistry showed that JG significantly reduced the size of iBAT and eWAT and increased the content of UCP1. In vitro, JG reduced the content of lipid droplets and ATP in brown fat cells. The maximum oxygen consumption capacity of mitochondria and the expression levels of UCP1, PGC1α and silent mating type information regulation 2 homologue 1 (SIRT1) were enhanced after JG treatment.

CONCLUSIONS

In vivo and in vitro studies, the results demonstrated that JG obviously increased the core temperature of mice by activating iBAT and inducing eWAT browning, which proved the mechanism is closely related to the PPARγ/SIRT1- PGC1α pathway. In this paper, we will provide a reference for further study of iBAT activation and eWAT browning.

Regulation of Thermogenic Adipocyte Differentiation and Adaptive Thermogenesis Through Histone Acetylation

Over the past decade, the increasing prevalence of obesity and its associated metabolic disorders constitutes one of the most concerning healthcare issues for countries worldwide. In an effort to curb the increased mortality and morbidity derived from the obesity epidemic, various therapeutic strategies have been developed by researchers. In the recent years, advances in the field of adipocyte biology have revealed that the thermogenic adipose tissue holds great potential in ameliorating metabolic disorders. Additionally, epigenetic research has shed light on the effects of histone acetylation on adipogenesis and thermogenesis, thereby establishing the essential roles which histone acetyltransferases (HATs) and histone deacetylases (HDACs) play in metabolism and systemic energy homeostasis. In regard to the therapeutic potential of thermogenic adipocytes for the treatment of metabolic diseases, herein, we describe the current state of knowledge of the regulation of thermogenic adipocyte differentiation and adaptive thermogenesis through histone acetylation. Furthermore, we highlight how different HATs and HDACs maintain the epigenetic transcriptional network to mediate the pathogenesis of various metabolic comorbidities. Finally, we provide insights into recent advances of the potential therapeutic applications and development of HAT and HDAC inhibitors to alleviate these pathological conditions.

Programming mediated by fatty acids affects uncoupling protein 1 (UCP-1) in brown adipose tissue

Brown adipose tissue (BAT) has recently been given more attention for the part it plays in obesity. BAT can generate great amounts of heat through thermogenesis by the activation of uncoupling protein 1 (UCP-1), which can be regulated by many environmental factors such as diet. Moreover, the build-up of BAT relates to maternal nutritional changes during pregnancy and lactation. However, at present, there is a limited number of studies looking at maternal nutrition and BAT development, and it seems that the research trend in this field has been considerably declining since the 1980s. There is much to discover yet about the role of different fatty acids on the development of BAT and the activation of UCP-1 during the fetal and the postnatal periods of life. A better understanding of the impact of nutritional intervention on the epigenetic regulation of BAT could lead to new preventive care for metabolic diseases such as obesity. It is important to know in which circumstances lipids could programme BAT during pregnancy and lactation. The modification of maternal dietary fatty acids, amount and composition, during pregnancy and lactation might be a promising strategy for the prevention of obesity in the offspring and future generations.

Nutritional and non-nutritional agents that stimulate white adipose tissue browning

Obesity is a public health problem present in both developed and developing countries. The white adipose tissue (WAT) is the main deposit of lipids when there is an excess of energy. Its pathological growth is directly linked to the development of obesity and to a wide number of comorbidities, such as insulin-resistance, cardiovascular disease, among others. In this scenario, it becomes imperative to develop new approaches to the treatment and prevention of obesity and its comorbidities. It has been documented that the browning of WAT could be a suitable strategy to tackle the obesity epidemic that is developing worldwide. Currently there is an intense search for bioactive compounds with anti-obesity properties, which present the particular ability to generate thermogenesis in the brown adipose tissue (BAT) or beige. The present study provide recent information of the bioactive nutritional compounds capable of inducing thermogenesis and therefore capable of generate positive effects on health.

Adipose Lipocalin 2 overexpression protects against age-related decline in thermogenic function of adipose tissue and metabolic deterioration

OBJECTIVES

Aging increases the risk for development of adipose tissue dysfunction, insulin resistance, dyslipidemia, and liver steatosis. Lipocalin 2 (Lcn2) deficient mice are more prone to diet-induced obesity and metabolic dysfunction, indicating a protective role for Lcn2 in younger mice. In this study, we determined whether overexpressing Lcn2 in adipose tissue can protect against age-related metabolic deterioration.

METHODS

We developed ap2-promoter-driven Lcn2 transgenic (Tg) mice and aged Lcn2 Tg mice for the metabolic assessments.

RESULTS

We found decreased adipocyte size in inguinal white adipose tissue (iWAT) from 10-month-old Lcn2 Tg mice relative to WT. This was accompanied by increased markers of adipogenesis in iWAT and attenuation of the age-related decline in AMP-activated protein kinase (AMPK) phosphorylation in adipose tissue depots. In addition to improvements in adipose tissue function, whole-body metabolic homeostasis was maintained in aged Lcn2 Tg mice. This included improved glucose tolerance and reduced serum triglycerides in older Lcn2 Tg mice relative to WT mice. Further, liver morphology and liver lipid levels were improved in older Lcn2 Tg mice, alongside a decrease in markers of liver inflammation and fibrosis.

CONCLUSIONS

We demonstrate that overexpression of Lcn2 in adipose tissue not only preserves adipose tissue function during aging but also promotes maintenance of glucose tolerance, decreases dyslipidemia, and prevents liver lipid accumulation and steatosis.

Identification of a rhodanine derivative BML-260 as a potent stimulator of UCP1 expression

Identification of proper agents to increase or activate UCP1⁺ cells in adipose tissues remains a potent therapeutic strategy to combat obesity. Screening systems for UCP1 activators have been previously established and allow for unbiased discovery of effective compound(s).

Methods: A previously established Ucp1-2A-GFP reporter system was applied to a chemical library containing 33 phosphatase inhibitors. Compounds that can significantly activate UCP1 expression were further tested in vivo in mouse adipose tissues. Possible underlying mechanism was explored via RNA profiling, CMAP analysis, CRISPR targeting as well as inhibitor treatments.

Results: We identified BML-260, a known potent inhibitor of the dual-specific phosphatase JSP-1, that significantly increased UCP1 expression in both brown and white adipocytes. BML-260 treatment also activated oxidative phosphorylation genes, increased mitochondrial activity as well as heat generation in vitro and in vivo. Mechanistic studies revealed that effect of BML-260 on adipocytes was partly through activated CREB, STAT3 and PPAR signaling pathways, and was unexpectedly JSP-1 independent.

Conclusion: The rhodanine derivate BML-260 was previously identified to be a JSP-1 inhibitor, and thus was proposed to treat inflammatory and proliferative disorders associated with dysfunctional JNK signaling. This work provides evidences that BML-260 can also exert a JSP-1-independent effect in activating UCP1 and thermogenesis in adipocytes, and be potentially applied to treat obesity.

Sinomenine Induces G1-Phase Cell Cycle Arrest and Apoptosis in Malignant Glioma Cells Via Downregulation of Sirtuin 1 and Induction of p53 Acetylation

Sinomenine, a bioactive alkaloid isolated from the traditional Chinese herb Sinomenium acutum, possesses antiinflammatory, antinociceptive, antifibrotic, and antitumorigenic properties. In this work, we sought to explore the biological effects of sinomenine on glioma cells. It was found that sinomenine caused a concentration-dependent inhibition of viability in both U87 and U251 glioma cells. Sinomenine at 16 μmol/L caused 55% to 60% reduction in the proliferation of U87 and U251 cells. Moreover, sinomenine treatment induced a G0/G1 cell cycle arrest and apoptosis. Mechanistically, sinomenine promoted p53 expression and acetylation and reduced the expression of sirtuin 1. Ectopic expression of sirtuin 1 significantly prevented sinomenine-induced p53 acetylation and growth suppression in glioma cells. Moreover, sinomenine inhibited the growth of U87 xenograft tumors in vivo and raised the p53 protein expression. Collectively, sinomenine shows antiproliferative effects against glioma cells which is mediated through downregulation of sirtuin 1 and induction of p53 activity.

Metformin enhances mitochondrial biogenesis and thermogenesis in brown adipocytes of mice

AIMS

We studied the effect of metformin on the brown adipose tissue (BAT) in a fructose-rich-fed model, focusing on BAT proliferation, differentiation, and thermogenic markers.

MAIN METHODS

C57Bl/6 mice received isoenergetic diets for ten weeks: control (C) or high-fructose (F). For additional eight weeks, animals received metformin hydrochloride (M, 250 mg/kg/day) or saline. After sacrifice, BAT and white fat pads were prepared for light microscopy and molecular analyses.

KEY FINDINGS

Body mass gain, white fat pads, and adiposity index were not different among the groups. There was a reduction in energy intake in the F group and energy expenditure in the F and FM groups. Metformin led to a more massive BAT in both groups CM and FM, associated with a higher adipocyte proliferation (β1-adrenergic receptor, proliferating cell nuclear antigen, and vascular endothelial growth factor), and differentiation (PR domain containing 16, bone morphogenetic protein 7), in part by activating 5' adenosine monophosphate-activated protein kinase. Metformin also enhanced thermogenic markers in the BAT (uncoupling protein type 1, peroxisome proliferator-activated receptor gamma coactivator-1 alpha) through adrenergic stimuli and fibroblast growth factor 21. Metformin might improve mitochondrial biogenesis in the BAT (nuclear respiratory factor 1, mitochondrial transcription factor A), lipolysis (perilipin, adipose triglyceride lipase, hormone-sensitive lipase), and fatty acid uptake (lipoprotein lipase, cluster of differentiation 36, adipocyte protein 2).

SIGNIFICANCE

Metformin effects are not linked to body mass changes, but affect BAT thermogenesis, mitochondrial biogenesis, and fatty acid uptake. Therefore, BAT may be a metformin adjuvant target for the treatment of metabolic disorders.

Thyroid hormone (T3) stimulates brown adipose tissue activation via mitochondrial biogenesis and MTOR-mediated mitophagy

The thyroid hormone triiodothyronine (T3) activates thermogenesis by uncoupling electron transport from ATP synthesis in brown adipose tissue (BAT) mitochondria. Although T3 can induce thermogenesis by sympathetic innervation, little is known about its cell autonomous effects on BAT mitochondria. We thus examined effects of T3 on mitochondrial activity, autophagy, and metabolism in primary brown adipocytes and BAT and found that T3 increased fatty acid oxidation and mitochondrial respiration as well as autophagic flux, mitophagy, and mitochondrial biogenesis. Interestingly, there was no significant induction of intracellular reactive oxygen species (ROS) despite high mitochondrial respiration and UCP1 induction by T3. However, when cells were treated with Atg5 siRNA to block autophagy, induction of mitochondrial respiration by T3 decreased, and was accompanied by ROS accumulation, demonstrating a critical role for autophagic mitochondrial turnover. We next generated an Atg5 conditional knockout mouse model (Atg5 cKO) by injecting Ucp1 promoter-driven Cre-expressing adenovirus into Atg5Flox/Flox mice to examine effects of BAT-specific autophagy on thermogenesis in vivo. Hyperthyroid Atg5 cKO mice exhibited lower body temperature than hyperthyroid or euthyroid control mice. Metabolomic analysis showed that T3 increased short and long chain acylcarnitines in BAT, consistent with increased β-oxidation. T3 also decreased amino acid levels, and in conjunction with SIRT1 activation, decreased MTOR activity to stimulate autophagy. In summary, T3 has direct effects on mitochondrial autophagy, activity, and turnover in BAT that are essential for thermogenesis. Stimulation of BAT activity by thyroid hormone or its analogs may represent a potential therapeutic strategy for obesity and metabolic diseases. Abbreviations: ACACA: acetyl-Coenzyme A carboxylase alpha; AMPK: AMP-activated protein kinase; Acsl1: acyl-CoA synthetase long-chain family member 1; ATG5: autophagy related 5; ATG7: autophagy related 7; ATP: adenosine triphosphate; BAT: brown adipose tissue; cKO: conditional knockout; COX4I1: cytochrome c oxidase subunit 4I1; Cpt1b: carnitine palmitoyltransferase 1b, muscle; CQ: chloroquine; DAPI: 4',6-diamidino-2-phenylindole; DIO2: deiodinase, iodothyronine, type 2; DMEM: Dulbecco's modified Eagle's medium; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; Fabp4: fatty acid binding protein 4, adipocyte; FBS: fetal bovine serum; FCCP: carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone; FGF: fibroblast growth factor; FOXO1: forkhead box O1; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; Gpx1: glutathione peroxidase 1; Lipe: lipase, hormone sensitive; MAP1LC3B: microtubule-associated protein 1 light chain 3; mRNA: messenger RNA; MTORC1: mechanistic target of rapamycin kinase complex 1; NAD: nicotinamide adenine dinucleotide; Nrf1: nuclear respiratory factor 1; OCR: oxygen consumption rate; PBS: phosphate-buffered saline; PCR: polymerase chain reaction; PPARGC1A: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; Pnpla2: patatin-like phospholipase domain containing 2; Prdm16: PR domain containing 16; PRKA: protein kinase, AMP-activated; RPS6KB: ribosomal protein S6 kinase; RFP: red fluorescent protein; ROS: reactive oxygen species; SD: standard deviation; SEM: standard error of the mean; siRNA: small interfering RNA; SIRT1: sirtuin 1; Sod1: superoxide dismutase 1, soluble; Sod2: superoxide dismutase 2, mitochondrial; SQSTM1: sequestosome 1; T3: 3,5,3'-triiodothyronine; TFEB: transcription factor EB; TOMM20: translocase of outer mitochondrial membrane 20; UCP1: uncoupling protein 1 (mitochondrial, proton carrier); ULK1: unc-51 like kinase 1; VDAC1: voltage-dependent anion channel 1; WAT: white adipose tissue.

Neuronal SIRT1 Regulates Metabolic and Reproductive Function and the Response to Caloric Restriction

Sirt1 is an NAD-dependent, class III deacetylase that functions as a cellular energy sensor. In addition to its well-characterized effects in peripheral tissues, emerging evidence suggests that neuronal Sirt1 activity plays a role in the central regulation of energy balance and glucose metabolism. In this study, we generated mice expressing an enzymatically inactive form (N-MUT) or wild-type (WT) SIRT1 (N-OX) in mature neurons. N-OX male and female mice had impaired glucose tolerance, and N-MUT female, but not male, mice had improved glucose tolerance compared with that of WT littermates. Furthermore, glucose tolerance was improved in all mice with caloric restriction (CR) but was greater in the N-OX mice, who had better glucose tolerance than their littermates. At the reproductive level, N-OX females had impaired estrous cycles, with increased cycle length and more time in estrus. LH and progesterone surges were absent on the evening of proestrus in the N-OX mice, suggesting a defect in spontaneous ovulation, which was confirmed by the ovarian histology revealing fewer corpora lutea. Despite this defect, the mice were still fertile when mated to WT mice on the day of proestrus, indicating that the mice could respond to normal pheromonal or environmental cues. When subjected to CR, the N-OX mice went into diestrus arrest earlier than their littermates. Together, these results suggested that the overexpression of SIRT1 rendered the mice more sensitive to the metabolic improvements and suppression of reproductive cycles by CR, which was independent of circadian rhythms.

Dietary Isoliquiritigenin at a Low Dose Ameliorates Insulin Resistance and NAFLD in Diet-Induced Obesity in C57BL/6J Mice

Isoliquiritigenin (ILG) is a flavonoid constituent of Glycyrrhizae plants. The current study investigated the effects of ILG on diet-induced obesity and metabolic diseases. C57BL/6J mice were fed a normal diet (AIN-76 purified diet), high-fat diet (40 kcal% fat), and high-fat diet +0.02% (w/w) ILG for 16 weeks. Supplementation of ILG resulted in decreased body fat mass and plasma cholesterol level. ILG ameliorated hepatic steatosis by suppressing the expression of hepatic lipogenesis genes and hepatic triglyceride and fatty acid contents, while enhancing β-oxidation in the liver. ILG improved insulin resistance by lowering plasma glucose and insulin levels. This was also demonstrated by the intraperitoneal glucose tolerance test (IPGTT). Additionally, ILG upregulated the expression of insulin signaling-related genes in the liver and muscle. Interestingly, ILG elevated energy expenditure by increasing the expression of thermogenesis genes, which is linked to stimulated mitochondrial biogenesis and uncoupled cellular respiration in brown adipose tissue. ILG also suppressed proinflammatory cytokine levels in the plasma. These results suggest that ILG supplemented at 0.02% in the diet can ameliorate body fat mass, plasma cholesterol, non-alcoholic fatty liver disease, and insulin resistance; these effects were partly mediated by increasing energy expenditure in high-fat fed mice.

Screening of FDA-approved drugs identifies sutent as a modulator of UCP1 expression in brown adipose tissue

BACKGROUND

The pharmacological activation of thermogenesis in brown adipose tissue has long been considered promising strategies to treat obesity. However, identification of safe and effective agents remains a challenge. In this study, we addressed this challenge by developing a cellular system with a fluorescence readout, and applied in a high-throughput manner to screen for FDA-approved drugs that may activate endogenous UCP1 expression in adipocytes.

METHODS

We have generated a Ucp1-2A-GFP reporter mouse, in which GFP intensity serves as a surrogate of the endogenous expression level of UCP1 protein; and immortalized brown adipocytes were derived from this mouse model and applied in drug screening. Candidate drugs were further tested in mouse models either fed with normal chow or high fat diet to induce obesity.

FINDINGS

By using the cellular screening platform, we identified a group of FDA-approved drugs that can upregulate UCP1 expression in brown adipocyte, including previously known UCP1 activators and new candidate drugs. Further studies focusing on a previously unreported drug-sutent, revealed that sutent treatment could increase the energy expenditure and inhibit lipid synthesis in mouse adipose and liver tissues, resulting in improved metabolism and resistance to obesity.

INTERPRETATION

This study offered an easy-to-use cellular screening system for UCP1 activators, and provided a candidate list of FDA-approved drugs that can potentially treat obesity. Further study of these candidates may shed new light on the drug discovery towards obesity. FUND: National Key Research and Development Program and the Strategic Priority Research Program of the Chinese Academy of Sciences, etc. (250 words).

Trans-anethole ameliorates obesity via induction of browning in white adipocytes and activation of brown adipocytes

To treat obesity, suppression of white adipose tissue (WAT) expansion and activation of brown adipose tissue (BAT) are considered as potential therapeutic targets. Recent advances have been made in the induction of brown fat-like adipocytes (beige) in WAT, which represents an attractive potential strategy for the management and treatment of obesity. Use of natural compounds for browning of white adipocytes can be considered as a safe and novel strategy against obesity. Here, we report that trans-anethole (TA), a flavoring substance present in the essential oils of various plants, alleviated high fat diet (HFD)-induced obesity in mice models via elevation of the expression of beige-specific genes such as Ppargc1α, Prdm16, Ucp1, Cd137, Cited1, Tbx1, and Tmem26. TA also regulated lipid metabolism in white adipocytes via reduction of adipogenesis and lipogenesis as well as elevation of lipolysis and fat oxidation. Moreover, TA exhibited thermogenic activity by increasing mitochondrial biogenesis in white adipocytes and activating brown adipocytes. In addition, molecular docking analysis enabled us to successfully predict core proteins for fat browning such as β3-adrenergic receptor (β3-AR) and sirtuin1 (SIRT1) based on their low binding energy interactions with TA for promotion of regulatory mechanisms. Indeed, agonistic and antagonistic studies demonstrated that TA induced browning of 3T3-L1 adipocytes through activation of β3-AR as well as the AMPK-mediated SIRT1 pathway regulating PPARα and PGC-1α. In conclusion, TA possesses potential therapeutic implications for treatment of obesity by playing multiple modulatory roles in the induction of white fat browning, activation of brown adipocytes, and promotion of lipid catabolism.

Reducing Smad3/ATF4 was essential for Sirt1 inhibiting ER stress-induced apoptosis in mice brown adipose tissue

Sirtuin 1 (Sirt1) promotes adaptive thermogenesis by controlling the acetylation status of enzymes and transcriptional factors in interscapular brown adipose tissue (iBAT). However, the effects of Sirt1 on endoplasmic reticulum (ER) stress and apoptosis of iBAT remain elusive. In this study, the mRNA levels of Sirt1 and thermogenesis genes were reduced but the genes related with ER stress were elevated in iBAT of high-fat diet (HFD)-induced obese mice. Moreover, ER stress further inhibited mRNA level of Sirt1 and triggered brown adipocyte apoptosis in vitro and in vivo. Further analysis revealed that Sirt1 overexpression alleviated ER stress-induced brown adipocyte apoptosis by inhibiting Smad3 and ATF4. In addition, Smad3 bound to ATF4 promoter region and positively transcriptional regulation of ATF4. Our data also confirmed that Sirt1 reduced early apoptotic cells and blocked the mitochondrial apoptosis pathway by directly interacting with ATF4. Furthermore, Sirt1 attenuated tunicamycin-induced cold intolerance and elevating thermogenesis by inhibiting ER stress and apoptosis in iBAT. In summary, our data collectively revealed Sirt1 reduced ER stress and apoptosis of brown adipocyte in vivo and in vitro by inhibiting Smad3/ATF4 signal. These data reveal a novel mechanism that links Sirt1 to brown adipocyte apoptosis.

Sirtuins in glucose and lipid metabolism

Sirtuins are evolutionarily conserved protein, serving as nicotinamide adenine dinucleotide-dependent deacetylases or adenosine diphosphate-ribosyltransferases. The mammalian sirtuins family, including SIRT1~7, is involved in many biological processes such as cell survival, proliferation, senescence, stress response, genome stability and metabolism. Evidence accumulated over the past two decades has indicated that sirtuins not only serve as important energy status sensors but also protect cells against metabolic stresses. In this review, we summarize the background of glucose and lipid metabolism concerning sirtuins and discuss the functions of sirtuins in glucose and lipid metabolism. We also seek to highlight the biological roles of certain sirtuins members in cancer metabolism.