Targeting thermogenesis in brown fat and muscle to treat obesity and metabolic disease

Proteomics reveals genetic mechanisms of cold resistance in Hezuo pig liver tissue

Cold stress poses a significant challenge to pig farming in northern China, leading to reduced productivity and, in severe cases, even mortality. However, the mechanisms underlying cold resistance in pigs are not well understood. To explore the genetic mechanism of cold resistance in pigs under low-temperature conditions, the cold-tolerant Hezuo pig was selected as a model. DIA proteomics analysis was performed on liver tissues from Hezuo pigs after 24 h of exposure to low-temperature treatments. The results showed that approximately 149 differential abundance proteins (DAPs) were detected (95 up-regulated and 54 down-regulated). GO analysis showed that these DAPs were mainly associated with lipid metabolism, vesicle fusion, and membrane function. KEGG analysis showed that these DAPs were primarily enriched in lipid metabolism-related pathways such as cholesterol metabolism and vitamin digestion and absorption. Comprehensive analysis identified APOA4, APOA2, SREBF2, ATP23, STX2, USO1, ETFA, RAB11FIP1, ETNPPL, and SGMS1 as potential key proteins involved in cold resistance mechanisms. The mRNA expression of the genes for two key candidate proteins (APOA4 and SREBF2), which are involved in lipid metabolism, was analyzed using qRT-PCR, revealing a significant up-regulation after low-temperature treatment. These findings provide significant insights into the mechanisms of cold resistance in animals and may serve as candidate markers for further studies on cold tolerance. SIGNIFICANCE: Cold resistance is one of the key traits in pigs and involves multiple complex coordinated regulatory mechanisms. However, its genetic mechanisms are not completely understood. In this study, a DIA proteomics approach was used to identify proteins and pathways associated with cold resistance in the liver of low-temperature-treated Hezuo pigs. These findings offer novel candidate proteins and key pathways for investigating the molecular mechanisms of cold resistance in Hezuo pigs, providing a base for further elucidating the mechanisms of cold tolerance in pigs.

Energy intake and energy expenditure are minimally impacted by acute cold exposure in individuals living with obesity

CONTEXT

Cold exposure (CE) has been purported to be a possible weight loss strategy and to be anorexigenic, however, the impacts of CE on appetite and energy intake have not been fully explored, more so in individuals living with obesity.

OBJECTIVE

Determine the effects of a single dose of moderate CE on energy expenditure, intake, and appetite regulation in individuals living with obesity.

DESIGN

Forty-seven individuals living with obesity (18 males) underwent two experimental sessions, one 90-min CE (10 °C fluid using a liquid conditioned suit) and one control. Energy expenditure (indirect calorimetry), energy intake (food menu), subjective appetite (Visual analogue scales), food reward (Leeds Food Preference Questionnaire), appetite-related peptides (ELISA), skin temperature (Thermocouples), thermal comfort and thermal sensation (Likert scales) were assessed.

RESULTS

CE produced a small (18%) but significant increase in energy expenditure over 90 min (p < 0.001). Energy intake during lunch increased slightly (10%), yet significantly following CE (p = 0.008) before decreasing for the remainder of the day (p = 0.049). There were no differences in subjective appetite (p > 0.05), but there was a decrease in the rewarding value of low-fat sweet foods (p < 0.05). Leptin concentrations decreased significantly (p = 0.004), whereas GLP-1 concentrations were increased (p = 0.003) in response to CE. Thermal comfort and sensation also both decreased significantly during exposure (p < 0.001).

CONCLUSION

Although both energy expenditure and intake significantly changed, CE caused minimal impacts to energy balance in individuals living with obesity. When combined with the high levels of discomfort, these results question the efficiency of CE as an intervention able to produce meaningful changes in body weight and composition in individuals living with obesity.

STRA13 exacerbates T2DM-induced diabetic cardiomyopathy by regulating the RXRα/UCP-1 signaling pathway

STRA13, a basic helix-loop-helix protein superfamily member, is a CLOCK gene. Previous studies have reported the role of STRA13 in regulating blood pressure. However, the role of STRA13 in diabetic cardiomyopathy (DCM) has not been fully elucidated. In this study, STRA13 full knockout mice were subjected to a high-fat diet (HFD) to induce DCM. We found that STRA13 was upregulated in both heart tissue and cardiomyocytes undergoing metabolic disorders. STRA13 knockout ameliorated HFD-induced cardiac dysfunction, fibrosis, mitochondrial dysfunction and cell apoptosis. STRA13 deficiency also protected against HFD-induced glucose and lipid metabolism disorders. STRA13 overexpression in mice worsened HFD-induced cardiac dysfunction, fibrosis, and injury. STRA13 overexpression in cardiomyocytes worsened high glucose-induced cell injury, mitochondrial dysfunction and oxidative stress. STRA13 silencing in cardiomyocytes protected against the high glucose (HG)-induced alterations described above. Moreover, STRA13 was found to downregulate retinoid X receptor alpha (RXRα), resulting in reduced expression of uncoupling protein 1 (UCP-1). Co-IP confirmed that STRA13 interacted with RXRα. A luciferase assay confirmed that RXRα regulated the transcription of UCP-1. Silencing of STRA13 did not protect cardiomyocytes from HG-induced injury caused by RXRα or UCP-1 knockdown. Cardiac overexpression of UCP-1 also blunted the deteriorating effects of STRA13. However, STRA13 inhibited RXRα nuclear expression, which hampered the protective effects of RXRα overexpression in vivo. Taken together, our findings demonstrate that STRA13 exacerbates diabetic cardiomyopathy by impairing mitochondrial function through the disruption of RXRα-UCP-1 signaling. Therefore, targeting the STRA13-RXRα-UCP-1 axis may represent a promising therapeutic strategy for mitigating mitochondrial dysfunction and cardiac injury in the context of DCM.

Myriocin Restores Metabolic Homeostasis in dAGE-Exposed Mice via AMPK-PGC1α-Mediated Mitochondrial Activation and Systemic Lipid/Glucose Regulation

Background: Diet-derived advanced glycation end products (dAGEs) are closely associated with obesity and metabolic disorders. This study investigates the therapeutic potential of myriocin (Myr), a sphingolipid synthesis inhibitor, in counteracting dAGE-induced obesity and its underlying mechanisms. Methods: Male C57BL/6J wild-type mice were randomly assigned to receive either a low-AGE diet or a high-AGE diet with or without the administration of myriocin for a duration of 24 weeks. At the end of the experimental period, blood samples, whole livers, and adipose tissues were harvested for subsequent biochemical, histological, and molecular analyses. Results: Using a 24-week high-AGE diet mouse model, we demonstrate that Myr significantly reduces body weight gain (by 76%) and adipose tissue accumulation, while alleviating hepatic steatosis. Myr improves glucose homeostasis by lowering fasting blood glucose (a 44.5% reduction), enhancing oral glucose tolerance, and restoring hepatic glycolysis/gluconeogenesis balance via upregulating glucokinase and suppressing G6pc. Notably, Myr reduces serum LDL-C, TG, and TC levels by 52.3%, 51.8%, and 48.8%, respectively, and ameliorates liver dysfunction as evidenced by normalized ALT/AST activities. Metabolomics reveal Myr reshapes amino acid, carbohydrate, and lipid metabolism pathways. Mechanistically, Myr suppresses lipogenesis by downregulating Srebp1, Fasn, and Acc, while activating AMPK-PGC1α signaling to enhance mitochondrial biogenesis (a 2.1-fold increase in mtDNA) and thermogenesis via Ucp1 upregulation in brown and white adipose tissues. Conclusions: Our findings unveil Myr as a novel dual regulator of lipid and glucose metabolism through AMPK-PGC1α-mediated mitochondrial activation, providing the first evidence of sphingolipid inhibition as a therapeutic strategy against dAGE-induced metabolic syndrome. This study establishes a multifaceted mechanism involving hepatic lipid regulation, adipose browning, and systemic metabolic reprogramming, advancing potential clinical applications for obesity-related disorders.

PGC-1α Activation by Polyphenols: A Pathway to Thermogenesis

This review investigates the role of polyphenols, abundant natural compounds found in food, to influence the metabolic pathways involved in the thermogenesis and browning of white adipose tissue (WAT). Numerous proteins demonstrate altered expression patterns following prolonged polyphenol consumption, with peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) recognized as a key regulator, contributing to increased thermogenicity of adipose tissues. Polyphenols may enhance PGC-1α activity, stimulating WAT browning, and elevating brown adipose tissue (BAT) thermogenesis. Various classes of polyphenols are explored, along with extensive protein signaling and the physiological implications of these findings. A comprehensive understanding of the myriad proteins and pathways implicated in browning studies can provide readers with a broader perspective on the modulated response of adipose tissue to polyphenols and guide them to innovative therapeutic strategies for lipid metabolism, obesity, and associated metabolic disorders.

Myeloid sirtuin 6 deficiency causes obesity in mice by inducing norepinephrine degradation to limit thermogenic tissue function

Brown and beige adipocytes dissipate energy to generate heat through uncoupled respiration, and the hormone norepinephrine plays an important role in stimulating brown fat thermogenesis and beige adipocyte development in white adipose depots. Increasing energy expenditure by promoting the function and development of brown and beige fat is a potential approach to treat obesity and diabetes. Here, we investigated the effects of macrophage sirtuin 6 (SIRT6) on the regulation of the norepinephrine content of brown adipose tissue (BAT) and on obesity in mice. Myeloid SIRT6 deficiency impaired the thermogenic function of BAT, thereby decreasing core body temperatures because of reduced norepinephrine concentrations in BAT and subsequently leading to cold sensitivity. In addition, the oxygen consumption rate was reduced, resulting in severe insulin resistance and obesity. Furthermore, macrophage SIRT6 deficiency inhibited BAT thermogenesis after cold exposure or norepinephrine treatment and cold exposure-induced increases in markers of lipid metabolism and thermogenesis in white adipose tissue. Myeloid-specific SIRT6 deficiency promoted H3K9 acetylation in the promoter regions and the expression of genes encoding the norepinephrine-degrading enzyme MAOA and the norepinephrine transporter SLC6A2 in macrophages in BAT, leading to norepinephrine degradation and obesity. Our findings indicate that SIRT6 in macrophages is essential for maintaining norepinephrine concentrations in BAT in mice.

Loss of Skeletal Muscle Inositol Polyphosphate Multikinase Disrupts Glucose Regulation and Limits Exercise Capacity

Inositol phosphates are critical signaling messengers involved in a wide range of biological pathways, and inositol polyphosphate multikinase (IPMK) functions as a rate-limiting enzyme for inositol polyphosphate metabolism. IPMK has been implicated in cellular metabolism, but its function at the systemic level is still poorly understood. Since skeletal muscle is a major contributor to energy homeostasis, we have developed a mouse model in which skeletal muscle IPMK is specifically deleted and examined how a loss of IPMK affects whole-body metabolism. Here, we report that skeletal-muscle-specific IPMK knockout mice exhibited a ~12% increase in body weight compared to WT controls (p < 0.05). These mice also showed a significantly impaired glucose tolerance, as indicated by their ~50% higher blood glucose levels during GTT. Additionally, exercise capacity was reduced by ~45% in IPMK-MKO mice, demonstrating a decline in endurance. Moreover, these metabolic alterations were accompanied by a 2.5-fold increase in skeletal muscle triglyceride accumulation, suggesting impaired lipid metabolism. Further analysis revealed that IPMK-deficient myocytes exhibited 30% lower β-oxidation rates. Thus, our results suggest that IPMK mediates whole-body metabolism by regulating muscle metabolism and may be potentially targeted for the treatment of metabolic syndromes.

Metformin delays the decline in thermogenic function of brown adipose tissue in a mouse model of Hutchinson-Gilford progeria syndrome

Brown adipose tissue (BAT) is the primary site for non-shivering thermogenesis in the body and plays a crucial role in maintaining core body temperature. However, its function gradually declines with age. To mitigate the age-related decline in BAT thermogenic capacity, we treated progeroid mice with metformin to investigate the potential mechanisms by which metformin can slow the reduction in BAT thermogenic function. We found that progeroid mice, after receiving metformin treatment, showed significant improvement in the senescent state of brown adipocytes through the activation of SIRT1, and effectively reduced mitochondrial oxidative stress. Additionally, metformin slowed the age-related decline in UCP1 expression levels in brown adipose tissue, thereby maintaining the thermogenic capacity of the progeroid mice. Moreover, metformin reduced inflammatory responses around senescent cells, further improving the overall senescent state of the tissue. These findings suggest that metformin can slow down the aging process in brown adipose tissue by targeting SIRT1, thereby enhancing its thermogenic capacity.

Blocking Adipocyte YY1 Decouples Thermogenesis From Beneficial Metabolism by Promoting Spermidine Production

The accumulation of mitochondria in thermogenic adipose tissue (i.e., brown and beige fat) increases energy expenditure, which can aid in alleviating obesity and metabolic disorders. However, recent studies have shown that knocking out key proteins required to maintain mitochondrial function inhibits the energy expenditure in thermogenic fat, and yet the knockout (KO) mice are unexpectedly protected from developing obesity or metabolic disorders when fed a high-fat diet (HFD). In the current study, nonbiased sequencing-based screening revealed the importance of Yin Yang 1 (YY1) in the transcription of electron transport chain genes and the enhancement of mitochondrial function in thermogenic adipose tissue. Specifically, YY1 adipocyte-null (YAKO) mice showed lower energy expenditure and were intolerant to cold stress. Interestingly, YAKO mice showed alleviation of HFD-induced metabolic disorders, which can be attributed to a suppression of adipose tissue inflammation. Metabolomic analysis revealed that blocking YY1 directed glucose metabolism toward lactate, enhanced the uptake of glutamine, and promoted the production of anti-inflammatory spermidine. Conversely, blocking spermidine production in YAKO mice reversed their resistance to HFD-induced disorders. Thus, although blocking adipocyte YY1 impairs the thermogenesis, it promotes spermidine production, alleviates adipose tissue inflammation, and therefore leads to an uncoupling of adipose tissue energy expenditure from HFD-induced metabolic disorders.

ARTICLE HIGHLIGHTS

Chromatin open atlas profiling in white, beige, and brown adipocytes identified Yin Yang 1 (YY1) as a key transcription factor governing electron transport chain gene expression and mitochondrial function in thermogenic adipocytes. Knocking out adipocyte YY1 leads to impaired thermogenesis under cold stress while protecting the mice from diet-induced obesity and metabolic disorders. YY1-null adipocytes undergo metabolic reprogramming, with increased glutamine use and spermidine generation that combat adipose tissue inflammation and insulin resistance, resulting in an uncoupling of thermogenic capacity and metabolic benefits.

Role of pancreatic lipase inhibition in obesity treatment: mechanisms and challenges towards current insights and future directions

The worldwide health emergency of obesity is closely connected to how dietary fats are metabolized, whereas the process is significantly influenced by pancreatic lipase (PL), an enzyme critical for lipid hydrolysis into fatty acids. This narrative review employs a methodological approach utilizing literature searches of PubMed data up to March 2024. The search term criteria encompasses keywords related to the role, mechanism, challenges, and current and future treatments of pancreatic lipase in obesity with an overall references is 106. This paper offers a comprehensive explanation of the role of PL, underlining its significance in the digestive process and lipid imbalances that contribute to obesity and by extension, its impact on obesity development and progression. Additionally, it delves into the dual functionality of the pancreas, emphasizing its impact on metabolism and energy utilization which, when dysregulated, promotes obesity. A focal point of this review is the investigation into the efficacy, challenges, and adverse effects of current pancreatic lipase inhibitors, with orlistat being highlighted as a primary current drug delivery. By discussing advanced obesity treatments, including the exploration of novel anti-obesity medications that target specific biological pathways, this review underscores the complexity of obesity treatment and the necessity for a multifaceted approach. In conclusion, this paper emphasizing the importance of understanding the role of enzymes like pancreatic lipase mechanistic and adopting a multidisciplinary approach to treatment and side effects of current obesity drugs and explore new emerging therapeutic strategies for more effective obesity management.

Graphene-Based Far-Infrared Therapy Promotes Adipose Tissue Thermogenesis and UCP1 Activation to Combat Obesity in Mice

Hyperthermia (HT) has broad potential for disease treatment and health maintenance. Previous studies have shown that far-infrared rays (FIRs) at 8-10 μm can potentially reduce inflammation, oxidative stress, and gut microbiota imbalance. However, the effects of FIR HT on energy metabolism require further investigation. To investigate the effects of graphene-FIR HT therapy on diet-induced obesity and their regulatory mechanisms in energy metabolism disorders. After 8 weeks of hyperthermia, mice fed standard chow or a high-fat diet (HFD) underwent body composition analysis. Energy expenditure was measured using metabolic cages. The protein changes in adipose tissue were detected by molecular technology. Graphene-FIR therapy effectively mitigated body fat accumulation, improved dyslipidemia, and impaired liver function while enhancing insulin sensitivity. Furthermore, graphene-FIR therapy increased VO2, VCO2, and EE levels in HFD mice to exhibit enhanced metabolic activity. The therapy activated the AMPK/PGC-1α/SIRT1 pathway in adipose tissue, increasing the expression of uncoupling protein 1 (UCP1) and glucose transporter protein four (GLUT4), activating the thermogenic program in adipose tissue, and improving energy metabolism disorder in HFD mice. In short, graphene-FIR therapy represents a comprehensive approach to improving the metabolic health of HFD mice.

A review on drug repurposing applicable to obesity

Obesity is a major public health concern and burden on individuals and healthcare systems. Due to the challenges and limitations of lifestyle adjustments, it is advisable to consider pharmacological treatment for people affected by obesity. However, the side effects and limited efficacy of available drugs make the obesity drug market far from sufficient. Drug repurposing involves identifying new applications for existing drugs and offers some advantages over traditional drug development approaches including lower costs and shorter development timelines. This review aims to provide an overview of drug repurposing for anti-obesity medications, including the rationale for repurposing, the challenges and approaches, and the potential drugs that are being investigated for repurposing. Through advanced computational techniques, researchers can unlock the potential of repurposed drugs to tackle the global obesity epidemic. Further research, clinical trials, and collaborative efforts are essential to fully explore and leverage the potential of drug repurposing in the fight against obesity.

Butyrate Prevents Obesity Accompanied by HDAC9-Mediated Browning of White Adipose Tissue

BACKGROUND/OBJECTIVES

Mounting evidence indicates that the short-chain fatty acid butyrate protects against obesity and associated comorbidities, partially through the induction of adipose tissue thermogenesis. However, the effects of butyrate on white adipose tissue (WAT) browning and its molecular mechanism are still elusive. The objective of this study was to investigate butyrate-induced thermogenesis in white adipose tissue and its underlying mechanism.

METHODS

We studied the effects of butyrate on diet-induced obesity in the humanized APOE*3-Leiden.CETP transgenic mouse model and explored factors related to white adipose browning. Specifically, mice were challenged with a high-fat diet supplemented with butyrate. Adiposity was measured to assess obesity development. Energy metabolism was detected using an indirect calorimetry system. RNA-seq analysis was conducted to analyze the transcription landscape of WAT and responsible targets. Furthermore, the revealed molecular mechanism was verified in vitro.

RESULTS

Butyrate alleviated high-fat diet-induced obesity and promoted energy expenditure accompanied by brown adipose tissue activation and WAT browning. Mechanistically, RNA-seq analysis revealed that butyrate downregulated HDAC9 in WAT. Additionally, butyrate decreased HDAC9 while increasing thermogenesis in vitro. Inhibition of HDAC9 with TMP269 promoted thermogenic gene expression, mimicking the effects of butyrate.

CONCLUSIONS

Butyrate protects against diet-induced obesity accompanied by decreasing the expression of HDAC9 in white adipose tissue and inducing browning. This study reveals a new mechanism whereby butyrate activates adaptive thermogenesis and provides new insights for the development of weight-loss drugs targeting adipose HDAC9.

Acute exercise promotes WAT browning by remodeling mRNA m6A methylation

AIMS

Regular exercise promotes the beiging and metabolic adaptations of white adipose tissue (WAT) through the cumulative transcriptional responses that occur after each exercise session. However, the effects of a single bout of acute exercise and the role of N6-methyladenosine (m6A) in these adaptations remain unclear. We aim to investigate this further.

MATERIALS AND METHODS

We constructed mouse models for chronic (8 weeks of running) and acute (single 1-hour run) exercise to study the effects on white adipose tissue (WAT) metabolism and beiging through metabolic phenotyping and transcriptome sequencing. Additionally, we explored the impact of acute exercise on WAT m6A modification and target genes, combining m6A regulators with cell models to elucidate the role of m6A in WAT exercise adaptation.

KEY FINDINGS

Here, we reveal that upregulated m6A modification after acute exercise induces the formation of glycolytic beige fat (g-beige fat) in WAT. Mechanistically, the metabolite β-hydroxybutyrate (BHBA) secreted after acute exercise upregulates m6A modification in WAT. This enhances m6A-dependent translation of the histone acetyltransferase CREBBP, promoting the transcription of key beiging genes by increasing chromatin accessibility. Pharmacologically elevating circulating BHBA mimics the metabolic response induced by acute exercise, upregulating m6A modification and its downstream signals. Additionally, BHBA exhibits long-term effects, improving metabolic homeostasis in obesity by promoting thermogenesis in WAT.

SIGNIFICANCE

Our results reveal the role of metabolites in WAT metabolic adaptation through m6A-mediated chromatin accessibility after acute exercise, providing a novel therapeutic target for regulating WAT metabolism from a nutritional epigenetics perspective.

Pachymic acid promotes brown/beige adipocyte differentiation and lipid metabolism in preadipocytes 3T3-L1 MBX

OBJECTIVES

To investigate the effect of pachymic acid on brown/beige adipocyte differentiation and lipid metabolism in preadipocytes 3T3-L1 MBX.

METHODS

The brown cocktail method was employed to induce 3T3-L1 MBX cells to differentiate into beige adipocytes. The impact of pachymic acid on the viability of 3T3-L1 MBX preadipocytes was evaluated using the CCK-8 assay. The formation of lipid droplets following treatment with pachymic acid was observed through oil red O staining, and the content of lipids in differentiated cells was determined. The expression levels of key browning genes, including uncoupling protein (Ucp) 1, the peroxisome proliferation-activating receptor gamma coactivator (Pgc)-1α, and the transcription factor containing PR domain 16 (Prdm16) were detected by quantitative reverse transcription polymerase chain reaction. The expression of sterol regulatory element binding protein (Srebp) 1c, acetyl-CoA carboxylase (Acc), fatty acid synthetase (Fas), and steroid-sensitive lipase (Hsl), fatty triglyceride hydrolase (Atgl), and carnitine palmitoyl transferase (Cpt) 1 of lipolysis-related genes were also examined.

RESULTS

The 3T3-L1 MBX was induced in vitro to form beige adipocytes with high expression of key browning genes, including Ucp1, Pgc-1α, Prdm16, and beige adipose-marker genes, including Cd137, Tbx1, and Tmem26. The concentration range of 0-80 μM pachymic acid was non-cytotoxic to 3T3-L1 MBX. Pachymic acid treatment significantly inhibited the differentiation of 3T3-L1 MBX, resulting in a notable decrease in lipid accumulation content (P<0.01). Additionally, there was a marked increase in the expression of key browning genes and their proteins, such as Ucp1, Pgc-1α, and Prdm16, while the expressions of fat synthesis-related genes Srebp1c, Acc and Fas were significantly decreased (all P<0.05). The expressions of lipolysis-related genes, including Hsl, Atgl, and Cpt1, were significantly increased (all P<0.05). Besides, treating with 20 μmol/L pachymic acid showed the most pronounced effect.

CONCLUSIONS

Pachymic acid can inhibit fat synthesis and promote lipid decomposition by regulating the brown formation and lipid differentiation of 3T3-L1 MBX preadipocytes.

Senescent cell depletion alleviates obesity-related metabolic and cardiac disorders

Obesity is a major contributor to metabolic and cardiovascular disease. Although senescent cells have been shown to accumulate in adipose tissue, the role of senescence in obesity-induced metabolic disorders and in cardiac dysfunction is not yet clear; therefore, the therapeutic potential of managing senescence in obesity-related metabolic and cardiac disorders remains to be fully defined.

OBJECTIVE

We investigated the beneficial effects of a senolytic cocktail (dasatinib and quercetin) on senescence and its influence on obesity-related parameters.

METHODS AND RESULTS

We found that the increase in body weight and adiposity, glucose intolerance, insulin resistance, dyslipidemia, hyperleptinemia, and hepatic disorders which were induced by an obesogenic diet were alleviated by senolytic cocktail treatment in mice. Treatment with senolytic compounds eliminated senescent cells, counteracting the activation of the senescence program and DNA damage in white adipose tissue (WAT) observed with an obesogenic diet. Moreover, the senolytic cocktail prevented the brown adipose tissue (BAT) whitening and increased the expression of the thermogenic gene profile in BAT and pWAT. In the hearts of obese mice, senolytic combination abolished myocardial maladaptation, reducing the senescence-associated secretory phenotype (SASP) and DNA damage, repressing cardiac hypertrophy, and improving diastolic dysfunction. Additionally, we showed that treatment with the senolytic cocktail corrected gene expression programs associated with fatty acid metabolism, oxidative phosphorylation, the P53 pathway, and DNA repair, which were all downregulated in obese mice.

CONCLUSIONS

Collectively, these data suggest that a senolytic cocktail can prevent the activation of the senescence program in the heart and WAT and activate the thermogenic program in BAT. Our results suggest that targeting senescent cells may be a novel therapeutic strategy for alleviating obesity-related metabolic and cardiac disorders.

A comparative assessment of reference genes in mouse brown adipocyte differentiation and thermogenesis in vitro

Adipogenic differentiation and thermogenesis in brown adipose tissue (BAT) undergo dynamic processes, altering phenotypes and gene expressions. Proper reference genes in gene expression analysis are crucial to mitigate experimental variances and ensure PCR efficacy. Unreliable reference genes can lead to erroneous gene expression quantification, resulting in data misinterpretation. This study focused on identifying suitable reference genes for mouse brown adipocyte research, utilizing brown adipocytes from the Ucp1-luciferase ThermoMouse model. Comparative analysis of gene expression data under adipogenesis and thermogenesis conditions was conducted, validating 13 housekeeping genes through various algorithms, including DeltaCq, BestKeeper, geNorm, Normfinder, and RefFinder. Tbp and Rer1 emerged as optimal references for Ucp1 and Pparg expression in brown adipogenesis, while Tbp and Ubc were ideal for the expression analysis of these target genes in thermogenesis. Conversely, certain conventional references, including Actb, Tubb5, and Gapdh, proved unstable as reference genes under both conditions. These findings stress the critical consideration of reference gene selection in gene expression analysis within specific biological systems to ensure accurate conclusions.

Spop deficiency impairs adipogenesis and promotes thermogenic capacity in mice

As the adaptor protein that determines substrate specificity of the Cul3-SPOP-Rbx1 E3 ligase complex, SPOP is involved in numerous biological processes. However, its physiological connections with adipogenesis and thermogenesis remain poorly understood. In the current study, we report that the conditional knockout of Spop in mice results in substantial changes in protein expression, including the upregulation of a critical factor associated with thermogenesis, UCP1. Loss of SPOP also led to defects in body weight gain. In addition, conditional knockout mice exhibited resistance to high-fat-diet-induced obesity. Proteomics analysis found that proteins upregulated in the knockout mice are primarily enriched for functions in glycolysis/gluconeogenesis, oxidative phosphorylation, and thermogenesis. Furthermore, Spop knockout mice were more resilient during cold tolerance assay compared with the wild-type controls. Finally, the knockout of SPOP efficiently impaired adipogenesis in primary preadipocytes and the expression of associated genes. Collectively, these findings demonstrate the critical roles of SPOP in regulating adipogenesis and thermogenic capacity in mice.

Rapid modulation of interscapular brown adipose tissue mitochondrial activity by ketosis induced by 1,3-butanediol administration to rats

Some studies indicate that brown adipose tissue (BAT) represents a promising target in the fight against dysmetabolic diseases, with indications suggesting it as a potential target for the effects of ketone bodies. We investigate whether the elevation of plasma levels of the ketone body β-hydroxybutyrate, achieved through the in vivo administration of its precursor 1,3-butanediol (BD) to rats, could impact interscapular BAT (iBAT) mitochondrial biochemistry and functionality. We examined the effects induced by BD within 3 h and after 2 weeks of treatment. A large-scale quantitative proteomics approach, coupling liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis, and Western blot associated with functional studies by respirometry allowed us to evaluate the changes in iBAT mitochondrial protein expression and bioenergetics induced by BD. BD administration increased β-hydroxybutyrate plasma levels, which correlated with an enhancement in iBAT mitochondrial respiration rate, likely due to the activation of the respiratory chain and uncoupling protein-1. The proteomic analysis demonstrated that BD influenced the mitochondrial levels of specific subunits belonging to the five respiratory complexes, uncoupling protein-1, and proteins involved in propanoate metabolism. BD administration also induced lysine β-hydroxybutyrylation of mitochondrial proteins, including specific subunits of the respiratory chain complexes and uncoupling protein-1. Most of the BD-induced effects were observed within 3 h of its administration and persisted/increased after 2 weeks of treatment. In conclusion, by using BD to increase β-hydroxybutyrate levels, we provide evidence supporting the role of β-hydroxybutyrate as a signaling molecule capable of rapidly modulating BAT physiology by acting at the mitochondrial level.

GRAF1 deficiency leads to defective brown adipose tissue differentiation and thermogenic response

Adipose tissue, which is crucial for the regulation of energy within the body, contains both white and brown adipocytes. White adipose tissue (WAT) primarily stores energy, while brown adipose tissue (BAT) plays a critical role in energy dissipation as heat, offering potential for therapies aimed at enhancing metabolic health. Regulation of the RhoA/ROCK pathway is crucial for appropriate specification, differentiation and maturation of both white and brown adipocytes. However, our knowledge of how this pathway is controlled within specific adipose depots remains unclear, and to date a RhoA regulator that selectively controls adipocyte browning has not been identified. Our study shows that GRAF1, a RhoGAP, is highly expressed in metabolically active tissues, and closely correlates with brown adipocyte differentiation in culture and in vivo. Mice with either global or adipocyte-specific GRAF1 deficiency exhibit impaired BAT maturation and compromised cold-induced thermogenesis. Moreover, defects in differentiation of human GRAF1-deficient brown preadipocytes can be rescued by treatment with a Rho kinase inhibitor. Collectively, these studies indicate that GRAF1 can selectively induce brown adipocyte differentiation and suggest that manipulating GRAF1 activity may hold promise for the future treatment of diseases related to metabolic dysfunction.

A novel selenoglycoside compound GlcSeCys alleviates diets-induced obesity and metabolic dysfunctions with the modulation of Galectin-1 and selenoproteins

Selenium, an essential trace element in human, has been shown to play protective roles in obesity and metabolic disorders despite insufficient understanding of mechanisms. Moreover, it's well known that biological actions of selenium compounds differed greatly due to divergent chemical forms. Selenoglycoside is a type of organoselenium compounds with excellent hydrophilicity, but biological activity of which in vivo are almost unknown. We have designed and synthesized Se-β-d-glucopyranosyl-D-selenocysteine, a novel selenoglycoside compound named GlcSeCys. Herein, GlcSeCys was given to high fat high cholesterol (HFHC) fed mice to determine its actions as well as relevant molecular mechanisms using transcriptome and multiple molecular biological methods. It was revealed that GlcSeCys displayed pronounced anti-obesity effect and significantly alleviated hyperglycemia, hyperinsulinemia along with hepatic steatosis in HFHC diets-induced mice. Mechanistically, GlcSeCys was found to inhibit lipogenesis, lipid uptake and inflammation in liver, along with attenuation of Galectin-1 and induction of selenoprotein S (SELENOS). With regard to adipose tissues, GlcSeCys ameliorated hypertrophy of adipocytes, suppressed lipids biosynthesis and stimulated WAT browning along with abrogated WAT inflammation activation, which were in line with repression of Galectin-1 and increase of GPx3. Collectively, our results uncovered, for the first time, that selenoglycoside compound GlcSeCys possessed excellent protective effects against obesity and metabolic disorders, and the mechanisms were correlated with modulation of Galectin-1 and selenoproteins, shedding lights upon molecular biology of selenium and novel therapeutic for obesity and relevant metabolic disorders.

Hypoxia-inducible factor-1α-deficient adipose-tissue macrophages produce the heat to mediate lipolysis of white adipose tissue through uncoupling protein-1

BACKGROUND

Uncoupling protein 1 (UCP1) is a proton uncoupler located across the mitochondrial membrane generally involved in thermogenesis of brown adipose tissues. Although UCP1 is known to be strongly expressed in brown adipocytes, recent evidence suggest that white adipocytes can also express UCP1 under certain circumstances such as cold- or β-adrenergic receptor-stimulation, allowing them to acquire brown adipocyte-like features thereby becoming 'beige' adipocytes.

RESULTS

In this study, we report that UCP1 can be expressed in adipose-tissue macrophages (ATM) lacking functional hypoxia-inducible factor-1 (HIF-1) and this does not require cold- nor β-adrenergic receptor activation. By using myeloid-specific Hif-1α knockout (KO) mice, we observed that these mice were protected from diet-induced obesity and exhibited an improved thermogenic tolerance upon cold challenge. ATM isolated from white adipose tissues (WAT) of these mice fed with high fat diet exhibited significantly higher M2-polarization, decreased glycolysis, increased mitochondrial functions and acetyl-CoA levels, along with increased expression of Ucp1, peroxisome proliferator activated receptor-gamma co-activator-1a, and others involved in histone acetylation. Consistent with the increased Ucp1 gene expression, these ATM produced a significant amount of heat mediating lipolysis of co-cultured adipocytes liberating free fatty acid. Treating ATM with acetate, a substrate for acetyl-CoA synthesis was able to boost the heat production in wild-type or Hif-1α-deficient but not UCP1-deficient macrophages, indicating that UCP1 was necessary for the heat production in macrophages. Lastly, we observed a significant inverse correlation between the number of UCP1-expressing ATM in WAT and the body mass index of human individuals.

CONCLUSIONS

UCP1-expressing ATM produce the heat to mediate lipolysis of adipocytes, indicating that this can be a novel strategy to treat and prevent diet-induced obesity.

LETMD1 regulates mitochondrial protein synthesis and import to guard brown fat mitochondrial integrity and function

Thermogenic brown adipocytes (BAs) catabolize lipids to generate heat, representing powerful agents against the growing global obesity epidemic. We and others reported recently that LETMD1 is a BA-specific protein essential for mitochondrial structure and function, but the mechanisms of action remain unclear. We performed sequential digestion to demonstrate that LETMD1 is a trans-inner mitochondrial membrane protein. We then generated UCP1Cre-driven BA-specific Letmd1 knockout (Letmd1 UKO ) mice to show that Letmd1 UKO leads to protein aggregation, reactive oxidative stress, hyperpolarization, and mitophagy in BAs. We further employed TurboID proximity labeling to identify LETMD1-interacting proteins. Many candidate proteins are associated with mitochondrial ribosomes, protein import machinery, and electron transport chain complexes (ETC-I and ETC-IV). Using quantitative proteomics, we confirmed the elevated aggregations of ETC and mitochondrial ribosomal proteins, impairing mitochondrial protein synthesis in the Letmd1 UKO BAs. Therefore, LETMD1 may function to maintain mitochondrial proteostasis through regulating import of nuclear-encoded proteins and local protein translation in brown fat mitochondria.

A novel long noncoding RNA AK029592 contributes to thermogenic adipocyte differentiation

Exploration of factors originating from brown adipose tissue that govern the thermogenic adipocyte differentiation is imperative for comprehending the regulatory framework underlying brown fat biogenesis and for devising therapeutic approaches for metabolic disorders associated with obesity. Prior evidence has illuminated the pivotal role of long noncoding RNAs (lncRNAs) in orchestrating thermogenesis within adipose tissue. Here, we aimed to explore and identify the critical lncRNA that could promote thermogenic adipocyte differentiation and to provide a novel strategy to treat obesity-related metabolic diseases in the future. In this study, through amalgamation with our previous lncRNA microarray data from small extracellular vesicles derived from BAT (sEV-BAT), we have identified sEV-BAT-enriched lncRNA AK029592 as a critical constituent of the thermogenic program, which actively fostered beige adipocyte differentiation and enhanced the thermogenic capacities of adipose tissue. Moreover, lncRNA AK029592 could sponge miR-199a-5p in adipocytes to stimulate thermogenic gene expression. Consequently, we concluded lncRNA AK029592 as a crucial lncRNA component of the thermogenic program that regulated beige adipocyte differentiation and white adipose tissue browning, thereby providing a novel therapeutic target and strategy in combating obesity and related metabolic diseases.

A review: Polysaccharides targeting mitochondria to improve obesity

Polysaccharides are one of the most important and widely used bioactive components of natural products, which can be used to treat metabolic diseases. Natural polysaccharides (NPs) have been the subject of much study and research in the field of treating obesity in recent years. Studies in the past have demonstrated that mitochondria are important for the initiation, progression, and management of obesity. Additionally, NPs have the ability to improve mitochondrial dysfunction via a variety of mechanisms. This review summarized the relationship between the structure of NPs and their anti-obesity activity, focusing on the anti-obesity effects of these compounds at the mitochondrial level. We discussed the association between the structure and anti-obesity action of NPs, including molecular weight, monosaccharide composition, glycosidic linkage, conformation and extraction methods. Furthermore, NPs can demonstrate a range of functions in adipose tissue, including but not limited to improving the mitochondrial oxidative respiratory chain, inhibiting oxidative stress, and maintaining mitochondrial mass homeostasis. The purpose of this work is to acquire a thorough understanding of the function that mitochondria play in the anti-obesity effects of NPs and to offer fresh insights for the investigation of how NPs prevent obesity and the creation of natural anti-obesity medications.

Keys to the switch of fat burning: stimuli that trigger the uncoupling protein 1 (UCP1) activation in adipose tissue

As one of the main pathogenic factors of cardiovascular and cerebrovascular diseases, the incidence of metabolic diseases such as adiposity and metabolic dysfunction-associated steatotic liver disease (MASLD) is increasing annually. It is urgent and crucial to find more therapeutic targets to treat these diseases. Mainly expressed in brown adipocytes, mitochondrial uncoupling protein 1 (UCP1) is key to the thermogenesis of classical brown adipose tissue (BAT). Furthermore, white adipose tissue (WAT) is likely to express more UCP1 and subsequently acquire the ability to undergo thermogenesis under certain stimuli. Therefore, targeting and activating UCP1 to promote increased BAT thermogenesis and browning of WAT are helpful in treating metabolic diseases, such as adiposity and MASLD. In this case, the stimuli that activate UCP1 are emerging. Therefore, we summarize the thermogenic stimuli that have activated UCP1 in recent decades, among which cold exposure is one of the stimuli first discovered to activate BAT thermogenesis. As a convenient and efficient therapy with few side effects and good metabolic benefits, physical exercise can also activate the expression of UCP1 in adipose tissue. Notably, for the first time, we have summarized and demonstrated the stimuli of traditional Chinese medicines that can activate UCP1, such as acupuncture, Chinese herbal formulas, and Chinese medicinal herbs. Moreover, pharmacological agents, functional foods, food ingredients, and the gut microbiota are also commonly associated with regulating and activating UCP1. The identification and analysis of UCP1 stimuli can greatly facilitate our understanding of adipose tissue thermogenesis, including the browning of WAT. Thus, it is more conducive to further research and therapy for glucose and lipid metabolism disorders.

Genetic Deletion of Skeletal Muscle Inositol Polyphosphate Multikinase Disrupts Glucose Homeostasis and Impairs Exercise Tolerance

Inositol phosphates are critical signaling messengers involved in a wide range of biological pathways in which inositol polyphosphate multikinase (IPMK) functions as a rate-limiting enzyme for inositol polyphosphate metabolism. IPMK has been implicated in cellular metabolism, but its function at the systemic level is still poorly understood. Since skeletal muscle is a major contributor to energy homeostasis, we have developed a mouse model in which skeletal muscle IPMK is specifically deleted and examined how a loss of IPMK affects whole-body metabolism. Here, we report that mice in which IPMK knockout is deleted, specifically in the skeletal muscle, displayed an increased body weight, disrupted glucose tolerance, and reduced exercise tolerance under the normal diet. Moreover, these changes were associated with an increased accumulation of triglyceride in skeletal muscle. Furthermore, we have confirmed that a loss of IPMK led to reduced beta-oxidation, increased triglyceride accumulation, and impaired insulin response in IPMK-deficient muscle cells. Thus, our results suggest that IPMK mediates the whole-body metabolism via regulating muscle metabolism and may be potentially targeted for the treatment of metabolic syndromes.

The effects of ghrelin and LEAP-2 in energy homeostasis are modulated by thermoneutrality, high-fat diet and aging

PURPOSE

Liver-expressed antimicrobial peptide 2 (LEAP-2) has been recently identified as the endogenous non-competitive allosteric antagonist of the growth hormone secretagogue receptor 1a (GHSR1a). In rodents, LEAP-2 blunts ghrelin-induced feeding and its plasma levels are modulated in response to nutritional status, being decreased upon fasting and increased in high-fat diet (HFD) fed mice. Clinical data support the regulation of circulating LEAP-2 by nutrient availability in humans. In this work, our primary objective was to examine the chronic effects of ghrelin and LEAP-2 administration on food intake, adiposity, and energy expenditure in young mice subjected to standard and HFD at both room temperature and at thermoneutrality. Furthermore, we aimed to assess the impact of these two hormones on aging mice.

RESULTS

Our results indicate that LEAP-2 produces a significant decrease of body weight and adiposity, an increase in energy expenditure, and activation of the thermogenic program in white and brown adipose tissue depots. However, this effect is not maintained under HFD or under thermoneutral conditions and is only partially observed in aging mice.

CONCLUSION

In summary our studies describe the central effects of LEAP-2 within distinct experimental contexts, and contribute to the comprehension of LEAP-2's role in energy metabolism.

Energy Expenditure in Humans: Principles, Methods, and Changes Throughout the Life Course

Humans require energy to sustain their daily activities throughout their lives. This narrative review aims to (a) summarize principles and methods for studying human energy expenditure, (b) discuss the main determinants of energy expenditure, and (c) discuss the changes in energy expenditure throughout the human life course. Total daily energy expenditure is mainly composed of resting energy expenditure, physical activity energy expenditure, and the thermic effect of food. Total daily energy expenditure and its components are estimated using variations of the indirect calorimetry method. The relative contributions of organs and tissues determine the energy expenditure under different physiological conditions. Evidence shows that energy expenditure varies along the human life course, at least in part due to changes in body composition, the mass and specific metabolic rates of organs and tissues, and levels of physical activity. This information is crucial to estimate human energy requirements for maintaining health throughout the life course.

Deletion of miPEP in adipocytes protects against obesity and insulin resistance by boosting muscle metabolism

Mitochondria facilitate thousands of biochemical reactions, covering a broad spectrum of anabolic and catabolic processes. Here we demonstrate that the adipocyte mitochondrial proteome is markedly altered across multiple models of insulin resistance and reveal a consistent decrease in the level of the mitochondrial processing peptidase miPEP.

OBJECTIVE

To determine the role of miPEP in insulin resistance.

METHODS

To experimentally test this observation, we generated adipocyte-specific miPEP knockout mice to interrogate its role in the aetiology of insulin resistance.

RESULTS

We observed a strong phenotype characterised by enhanced insulin sensitivity and reduced adiposity, despite normal food intake and physical activity. Strikingly, these phenotypes vanished when mice were housed at thermoneutrality, suggesting that metabolic protection conferred by miPEP deletion hinges upon a thermoregulatory process. Tissue specific analysis of miPEP deficient mice revealed an increment in muscle metabolism, and upregulation of the protein FBP2 that is involved in ATP hydrolysis in the gluconeogenic pathway.

CONCLUSION

These findings suggest that miPEP deletion initiates a compensatory increase in skeletal muscle metabolism acting as a protective mechanism against diet-induced obesity and insulin resistance.

Consumption of dietary turmeric promotes fat browning and thermogenesis in association with gut microbiota regulation in high-fat diet-fed mice

This study was designed to verify the anti-obesity effect of dietary turmeric powder (TP) as a traditional cooking spice and its underlying mechanism. The HFD-fed C57BL/6J mice were supplemented with or without TP (8%) for 12 weeks. The results indicated that the glucolipid metabolism disorder of high-fat diet (HFD)-fed mice was significantly ameliorated through the supplementation of TP. The consumption of TP also induced beige-fat development and brown adipose tissue (BAT)-derived nonshivering thermogenesis in HFD-fed obese mice. 16S rDNA-based microbiota or targeted metabolomics analysis indicated that TP ameliorated the intestinal microbiota dysbiosis and microbial metabolism abnormality caused by HFD, reflected by dramatically increasing the relative abundance of Muribaculaceae, Candidatus_Saccharimonas, and Bifidobacterium and production of short-chain fatty acids (SCFAs) and succinate. Interestingly, TP-induced BAT thermogenesis and iWAT browning were highly correlated with the reconstruction of the gut microbiome and formation of SCFAs and succinate. Collectively, these findings manifest beneficial actions of TP on the promotion of adipose browning and thermogenesis in association with gut microbiota reconstruction, and our findings may provide a promising way for preventing obesity.

Hypothalamic neural circuits regulating energy expenditure

The hypothalamus plays a central role in regulating energy expenditure and maintaining energy homeostasis, crucial for an organism's survival. Located in the ventral diencephalon, it is a dynamic and adaptable brain region capable of rapid responses to environmental changes, exhibiting high anatomical and cellular plasticity and integrates a myriad of sensory information, internal physiological cues, and humoral factors to accurately interpret the nutritional state and adjust food intake, thermogenesis, and energy homeostasis. Key hypothalamic nuclei contain distinct neuron populations that respond to hormonal, nutrient, and neural inputs and communicate extensively with peripheral organs like the gastrointestinal tract, liver, pancreas, and adipose tissues to regulate energy production, storage, mobilization, and utilization. The hypothalamus has evolved to enhance energy storage for survival in famine and scarce environments but contribute to obesity in modern contexts of caloric abundance. It acts as a master regulator of whole-body energy homeostasis, rapidly adapting to ensure energy supplies for cellular functions. Understanding hypothalamic function, pertaining to energy expenditure, is crucial for developing targeted interventions to address metabolic disorders, offering new insights into the neural control of metabolic states and potential therapeutic strategies.

Chemogenetic Excitation of Ventromedial Hypothalamic Steroidogenic Factor 1 (SF1) Neurons Increases Muscle Thermogenesis in Mice

Allostatic adaptations to a perceived threat are crucial for survival and may tap into mechanisms serving the homeostatic control of energy balance. We previously established that exposure to predator odor (PO) in rats significantly increases skeletal muscle thermogenesis and energy expenditure (EE). Evidence highlights steroidogenic factor 1 (SF1) cells within the central and dorsomedial ventromedial hypothalamus (c/dmVMH) as a modulator of both energy homeostasis and defensive behavior. However, the brain mechanism driving elevated EE and muscle thermogenesis during PO exposure has yet to be elucidated. To assess the ability of SF1 neurons of the c/dmVMH to induce muscle thermogenesis, we used the combined technology of chemogenetics, transgenic mice, temperature transponders, and indirect calorimetry. Here, we evaluate EE and muscle thermogenesis in SF1-Cre mice exposed to PO (ferret odor) compared to transgenic and viral controls. We detected significant increases in muscle temperature, EE, and oxygen consumption following the chemogenetic stimulation of SF1 cells. However, there were no detectable changes in muscle temperature in response to PO in either the presence or absence of chemogenetic stimulation. While the specific role of the VMH SF1 cells in PO-induced thermogenesis remains uncertain, these data establish a supporting role for SF1 neurons in the induction of muscle thermogenesis and EE similar to what is seen after predator threats.

Walnut supplementation increases levels of UCP1 and CD36 in brown adipose tissue independently of diet type

Dietary interventions that modulate the brown adipose tissue (BAT) thermogenic activity could represent a promising therapy for metabolic disorders. In order to examine if dietary walnuts intake regulates the expression of BAT thermogenic markers levels in healthy and metabolically challenged (fructose fed) animals, rats were initially divided into the control and fructose-fed groups. After nine weeks, these groups were subdivided into the one kept on the original regimens and the other supplemented with walnuts. High-fructose diet resulted in an increased relative BAT mass and no change in UCP1 content, while the walnut supplementation increased the amount of UCP1 in BAT, but did not affect 5-HT, NA, DHPG content and DHPG/NA ratio regardless of the diet. Moreover, the CD36 levels were increased following the walnut consumption, unlike FATP1, GLUT1, GLUT4, and glycogen content which remained unchanged. Additionally, the BAT levels of activated IR and Akt were not affected by walnut consumption, while ERK signaling was decreased. Overall, we found that walnut consumption increased UCP1 and CD36 content in the BAT of both control and metabolically challenged rats, suggesting that FFAs represent the BAT preferred substrate under the previously described circumstances. This further implies that incorporating walnuts into the everyday diet may help to alleviate some symptoms of the metabolic disorder.

Molecular Regulation of Thermogenic Mechanisms in Beige Adipocytes

Adipose tissue is conventionally recognized as a metabolic organ responsible for storing energy. However, a proportion of adipose tissue also functions as a thermogenic organ, contributing to the inhibition of weight gain and prevention of metabolic diseases. In recent years, there has been significant progress in the study of thermogenic fats, particularly brown adipose tissue (BAT). Despite this progress, the mechanism underlying thermogenesis in beige adipose tissue remains highly controversial. It is widely acknowledged that beige adipose tissue has three additional thermogenic mechanisms in addition to the conventional UCP1-dependent thermogenesis: Ca2+ cycling thermogenesis, creatine substrate cycling thermogenesis, and triacylglycerol/fatty acid cycling thermogenesis. This paper delves into these three mechanisms and reviews the latest advancements in the molecular regulation of thermogenesis from the molecular genetic perspective. The objective of this review is to provide readers with a foundation of knowledge regarding the beige fats and a foundation for future research into the mechanisms of this process, which may lead to the development of new strategies for maintaining human health.

Optogenetic therapeutic strategies for diabetes mellitus

Diabetes mellitus (DM) is a common chronic disease affecting humans globally. It is characterized by abnormally elevated blood glucose levels due to the failure of insulin production or reduction of insulin sensitivity and functionality. Insulin and glucagon-like peptide (GLP)-1 replenishment or improvement of insulin resistance are the two major strategies to treat diabetes. Recently, optogenetics that uses genetically encoded light-sensitive proteins to precisely control cell functions has been regarded as a novel therapeutic strategy for diabetes. Here, we summarize the latest development of optogenetics and its integration with synthetic biology approaches to produce light-responsive cells for insulin/GLP-1 production, amelioration of insulin resistance and neuromodulation of insulin secretion. In addition, we introduce the development of cell encapsulation and delivery methods and smart bioelectronic devices for the in vivo application of optogenetics-based cell therapy in diabetes. The remaining challenges for optogenetics-based cell therapy in the clinical translational study are also discussed.

Inhibition of activin receptor 2 signalling ameliorates metabolic dysfunction-associated steatotic liver disease in western diet/L-NAME induced cardiometabolic disease

OBJECTIVE

Blockade of activin 2 receptor (ACVR2) signaling has been shown to improve insulin sensitivity and aid in weight loss. Inhibition of ACVR2 signaling restores cardiac function in multiple heart failure models. However, its potential in the treatment of obesity-related cardiometabolic disease remains unknown. Here, we investigated targeting ACVR2 signaling in cardiometabolic disease manifested with metabolic dysfunction-associated steatotic liver disease (MASLD).

METHODS

Mice were fed a high-fat, high-sugar diet combined with the administration of nitric oxide synthase inhibitor L-NAME in drinking water, which causes hypertensive stress. For the last eight weeks, the mice were treated with the soluble ACVR2B decoy receptor (sACVR2B-Fc).

RESULTS

sACVR2B-Fc protected against the development of comorbidities associated with cardiometabolic disease. This was most pronounced in the liver where ACVR2 blockade attenuated the development of MASLD including cessation of pro-fibrotic activation. It also significantly reduced total plasma cholesterol levels, impeded brown adipose tissue whitening, and improved cardiac diastolic function. In vitro, ACVR2 ligands activin A, activin B and GDF11 induced profibrotic signaling and the proliferation of human cardiac fibroblasts.

CONCLUSIONS

Blockade of ACVR2B exerts broad beneficial effects for therapy of cardiometabolic disease. By reducing obesity, ameliorating cardiovascular deterioration and restraining MASLD, blockade of ACVR2B signaling proves a potential target in MASLD and its comorbidities.

Adipo-Epithelial Transdifferentiation in In Vitro Models of the Mammary Gland

Subcutaneous adipocytes are crucial for mammary gland epithelial development during pregnancy. Our and others' previous data have suggested that adipo-epithelial transdifferentiation could play a key role in the mammary gland alveolar development. In this study, we tested whether adipo-epithelial transdifferentiation occurs in vitro. Data show that, under appropriate co-culture conditions with mammary epithelial organoids (MEOs), mature adipocytes lose their phenotype and acquire an epithelial one. Interestingly, even in the absence of MEOs, extracellular matrix and diffusible growth factors are able to promote adipo-epithelial transdifferentiation. Gene and protein expression studies indicate that transdifferentiating adipocytes exhibit some characteristics of milk-secreting alveolar glands, including significantly higher expression of milk proteins such as whey acidic protein and β-casein. Similar data were also obtained in cultured human multipotent adipose-derived stem cell adipocytes. A miRNA sequencing experiment on the supernatant highlighted mir200c, which has a well-established role in the mesenchymal-epithelial transition, as a potential player in this phenomenon. Collectively, our data show that adipo-epithelial transdifferentiation can be reproduced in in vitro models where this phenomenon can be investigated at the molecular level.

Itaconate alleviates diet-induced obesity via activation of brown adipocyte thermogenesis

Despite medical advances, there remains an unmet need for better treatment of obesity. Itaconate, a product of the decarboxylation of the tricarboxylic acid cycle intermediate cis-aconitate, plays a regulatory role in both metabolism and immunity. Here, we show that itaconate, as an endogenous compound, counteracts high-fat-diet (HFD)-induced obesity through leptin-independent mechanisms in three mouse models. Specifically, itaconate reduces weight gain, reverses hyperlipidemia, and improves glucose tolerance in HFD-fed mice. Additionally, itaconate enhances energy expenditure and the thermogenic capacity of brown adipose tissue (BAT). Unbiased proteomic analysis reveals that itaconate upregulates key proteins involved in fatty acid oxidation and represses the expression of lipogenic genes. Itaconate may provoke a major metabolic reprogramming by inducing fatty acid oxidation and suppression of fatty acid synthesis in BAT. These findings highlight itaconate as a potential activator of BAT-mediated thermogenesis and a promising candidate for anti-obesity therapy.

BCAA-nitrogen flux in brown fat controls metabolic health independent of thermogenesis

Brown adipose tissue (BAT) is best known for thermogenesis. Rodent studies demonstrated that enhanced BAT thermogenesis is tightly associated with increased energy expenditure, reduced body weight, and improved glucose homeostasis. However, human BAT is protective against type 2 diabetes, independent of body weight. The mechanism underlying this dissociation remains unclear. Here, we report that impaired mitochondrial catabolism of branched-chain amino acids (BCAAs) in BAT, by deleting mitochondrial BCAA carriers (MBCs), caused systemic insulin resistance without affecting energy expenditure and body weight. Brown adipocytes catabolized BCAA in the mitochondria as nitrogen donors for the biosynthesis of non-essential amino acids and glutathione. Impaired mitochondrial BCAA-nitrogen flux in BAT resulted in increased oxidative stress, decreased hepatic insulin signaling, and decreased circulating BCAA-derived metabolites. A high-fat diet attenuated BCAA-nitrogen flux and metabolite synthesis in BAT, whereas cold-activated BAT enhanced the synthesis. This work uncovers a metabolite-mediated pathway through which BAT controls metabolic health beyond thermogenesis.

Remodeling Intestinal Microbiota Alleviates Severe Combined Hyperlipidemia-Induced Nonalcoholic Steatohepatitis and Atherosclerosis in LDLR-/- Hamsters

Combined hyperlipidemia (CHL) manifests as elevated cholesterol and triglycerides, associated with fatty liver and cardiovascular diseases. Emerging evidence underscores the crucial role of the intestinal microbiota in metabolic disorders. However, the potential therapeutic viability of remodeling the intestinal microbiota in CHL remains uncertain. In this study, CHL was induced in low-density lipoprotein receptor-deficient (LDLR-/-) hamsters through an 8-week high-fat and high-cholesterol (HFHC) diet or a 4-month high-cholesterol (HC) diet. Placebo or antibiotics were administered through separate or cohousing approaches. Analysis through 16S rDNA sequencing revealed that intermittent antibiotic treatment and the cohousing approach effectively modulated the gut microbiota community without impacting its overall abundance in LDLR-/- hamsters exhibiting severe CHL. Antibiotic treatment mitigated HFHC diet-induced obesity, hyperglycemia, and hyperlipidemia, enhancing thermogenesis and alleviating nonalcoholic steatohepatitis (NASH), concurrently reducing atherosclerotic lesions in LDLR-/- hamsters. Metabolomic analysis revealed a favorable liver lipid metabolism profile. Increased levels of microbiota-derived metabolites, notably butyrate and glycylglycine, also ameliorated NASH and atherosclerosis in HFHC diet-fed LDLR-/- hamsters. Notably, antibiotics, butyrate, and glycylglycine treatment exhibited protective effects in LDLR-/- hamsters on an HC diet, aligning with outcomes observed in the HFHC diet scenario. Our findings highlight the efficacy of remodeling gut microbiota through antibiotic treatment and cohousing in improving obesity, NASH, and atherosclerosis associated with refractory CHL. Increased levels of beneficial microbiota-derived metabolites suggest a potential avenue for microbiome-mediated therapies in addressing CHL-associated diseases.

The natural compounds, Magnolol or Honokiol, promote adipose tissue browning and resist obesity through modulating PPARα/γ activity

Non-alcoholic fatty liver disease (NAFLD) is closely associated with the body's energy metabolism. A potential strategy to regulate energy metabolism, combat obesity, and reduce NAFLD is by enhancing adipocyte thermogenesis and increasing energy expenditure. In this study, our objective was to examine the effects of phenolic extracts derived from Magnolia officinalis on the regulation of NAFLD. Specifically, we investigated the impact of Magnolol or Honokiol treatment on high-fat diet (HFD)-induced obese C57BL6/J male mice. Firstly, we monitored energy metabolism, dissected tissues, and analyzed tissue sections. Additionally, we conducted experiments on HepG2 and primary adipocytes to gain insights into the roles of Magnolol or Honokiol. To further understand the effects of these compounds on related signaling pathways and marker genes, we performed molecular docking, dual-luciferase assays, and interfered with target genes. Our findings revealed that Magnolol or Honokiol activate the peroxisome proliferator activated receptor alpha (PPARα) signaling pathway, leading to the alleviation of NAFLD. This activation promotes fatty acid oxidation, reduces lipogenesis, and enhances the expression and secretion of FGF21. Notably, Fibroblast growth factor 21 (FGF21), secreted by the liver, plays a crucial role in improving communication between the liver and adipocytes while also promoting the browning of adipose tissue. Additionally, Magnolol or Honokiol activate the peroxisome proliferator activated receptor gamma (PPARγ) signaling pathway, resulting in increased uncoupling protein 1 (UCP1) expression, heightened heat production in adipose tissue, and anti-obesity. Therefore, Magnolol or Honokiol alleviate NAFLD, promote adipose tissue browning and resist obesity through dual activation of PPARα/γ.

Dapagliflozin promotes white adipose tissue browning though regulating angiogenesis in high fat induced obese mice

Browning of white adipose tissue (WAT) is become an appealing target for therapeutics in the treatment of obesity and related metabolic diseases. Dapagliflozin is widely used in the treatment of type 2 diabetes, and it is also found that the drug exhibits regulate systemic metabolism such as obesity, insulin resistance and hepatic steatosis. However, the precise role of dapagliflozin on WAT remodeling remains to be elucidated. The current study aimed to explore the role of dapagliflozin on WAT browning in high-fat diet (HFD)-induced obese mice. Male C57BL/6J mice (n = 6 per group) were used to establish obesity model by following feeding with HFD for 6 weeks. The mice were randomly treated with or without dapagliflozin for the experimental observation. The volume and fat fraction of WAT were quantified, H&E, UCP-1 staining and immunohistochemistry were conducted to investigate the white-to-brown fat conversion and angiogenesis in WAT respectively. Quantitative real-time polymerase chain reaction (qPCR) was employed to explore the mRNA expression levels of genes related to fat browning and angiogenesis in WAT. Subsequently, 3T3-L1 cells were used to explore the effect of dapagliflozin on preadipocytes differentiation in vitro. Our results demonstrated that dapagliflozin could reduce body weight gain and promote WAT browning in HFD induced obese mice via regulating lipogenesis and angiogenesis in WAT. Furthermore, dapagliflozin reduce cells differentiation, up-regulate the expression of WAT browning and angiogenesis genes in 3T3-L1 adipocytes in vitro. In conclusion, dapagliflozin can potentially promote WAT browning in HFD induced obese mice via improving lipogenesis and angiogenesis in WAT.

An Update on the Role and Potential Molecules in Relation to Ruminococcus gnavus in Inflammatory Bowel Disease, Obesity and Diabetes Mellitus

Ruminococcus gnavus (R. gnavus) is a gram-positive anaerobe commonly resides in the human gut microbiota. The advent of metagenomics has linked R. gnavus with various diseases, including inflammatory bowel disease (IBD), obesity, and diabetes mellitus (DM), which has become a growing area of investigation. The initial focus of research primarily centered on assessing the abundance of R. gnavus and its potential association with disease presentation, taking into account variations in sample size, sequencing and analysis methods. However, recent investigations have shifted towards elucidating the underlying mechanistic pathways through which R. gnavus may contribute to disease manifestation. In this comprehensive review, we aim to provide an updated synthesis of the current literature on R. gnavus in the context of IBD, obesity, and DM. We critically analyze relevant studies and summarize the potential molecular mediators implicated in the association between R. gnavus and these diseases. Across numerous studies, various molecules such as methylation-controlled J (MCJ), glucopolysaccharides, ursodeoxycholic acid (UDCA), interleukin(IL)-10, IL-17, and capric acid have been proposed as potential contributors to the link between R. gnavus and IBD. Similarly, in the realm of obesity, molecules such as hydrogen peroxide, butyrate, and UDCA have been suggested as potential mediators, while glycine ursodeoxycholic acid (GUDCA) has been implicated in the connection between R. gnavus and DM. Furthermore, it is imperative to emphasize the necessity for additional studies to evaluate the potential efficacy of targeting pathways associated with R. gnavus as a viable strategy for managing these diseases. These findings have significantly expanded our understanding of the functional role of R. gnavus in the context of IBD, obesity, and DM. This review aims to offer updated insights into the role and potential mechanisms of R. gnavus, as well as potential strategies for the treatment of these diseases.

Wiring the Brain for Wellness: Sensory Integration in Feeding and Thermogenesis: A Report on Research Supported by Pathway to Stop Diabetes

The recognition of sensory signals from within the body (interoceptive) and from the external environment (exteroceptive), along with the integration of these cues by the central nervous system, plays a crucial role in maintaining metabolic balance. This orchestration is vital for regulating processes related to both food intake and energy expenditure. Animal model studies indicate that manipulating specific populations of neurons in the central nervous system which influence these processes can effectively modify energy balance. This body of work presents an opportunity for the development of innovative weight loss therapies for the treatment of obesity and type 2 diabetes. In this overview, we delve into the sensory cues and the neuronal populations responsible for their integration, exploring their potential in the development of weight loss treatments for obesity and type 2 diabetes. This article is the first in a series of Perspectives that report on research funded by the American Diabetes Association Pathway to Stop Diabetes program.

ARTICLE HIGHLIGHTS

Microbial-Based Bioactive Compounds to Alleviate Inflammation in Obesity

The increased prevalence of obesity with several other metabolic disorders, including diabetes and non-alcoholic fatty liver disease, has reached global pandemic proportions. Lifestyle changes may result in a persistent positive energy balance, hastening the onset of these age-related disorders and consequently leading to a diminished lifespan. Although suggestions have been raised on the possible link between obesity and the gut microbiota, progress has been hampered due to the extensive diversity and complexities of the gut microbiota. Being recognized as a potential biomarker owing to its pivotal role in metabolic activities, the dysregulation of the gut microbiota can give rise to a persistent low-grade inflammatory state associated with chronic diseases during aging. This chronic inflammatory state, also known as inflammaging, induced by the chronic activation of the innate immune system via the macrophage, is controlled by the gut microbiota, which links nutrition, metabolism, and the innate immune response. Here, we present the functional roles of prebiotics, probiotics, synbiotics, and postbiotics as bioactive compounds by underscoring their putative contributions to (1) the reduction in gut hyperpermeability due to lipopolysaccharide (LPS) inactivation, (2) increased intestinal barrier function as a consequence of the upregulation of tight junction proteins, and (3) inhibition of proinflammatory pathways, overall leading to the alleviation of chronic inflammation in the management of obesity.

CD155 is essential for skeletal muscle regeneration by regulating satellite cell proliferation and differentiation

CD155, a member of the immunoglobulin superfamily, is closely related to cell proliferation, adhesion, and migration. CD155 is overexpressed on the surface of cancer cells to promote cell proliferation and is upregulated in damaged tissues as a stress-induced molecule. The process of skeletal muscle regeneration after injury is complex and involves injurious stimulation and subsequent satellite cell proliferation. However, the role of CD155 in this process remains unelucidated. This study aimed to explore the role of CD155 in injured skeletal muscle regeneration and to clarify its effect on satellite cell proliferation and differentiation. Here, quantitative real-time polymerase chain reaction (RT-qPCR) and immunofluorescence results indicated that CD155 expression in satellite cells increased after skeletal muscle injury. CD155 knockout in mice impaired the regeneration of skeletal muscle. A bone marrow transplantation mouse model was constructed and revealed that CD155 on skeletal muscle tissues, not immune cells, affected muscle regeneration. In vitro, CD155 knockdown in myoblasts inhibited their proliferation and differentiation. The transcriptomic analysis also indicated that CD155 absence can impair the biological proliferation and differentiation process of myoblasts. Our research demonstrates that CD155 directly promotes injured muscle regeneration by regulating satellite cell proliferation and differentiation, which may be a potential therapeutic molecule for skeletal muscle injury.

Neuregulin 4 mediates the metabolic benefits of mild cold exposure by promoting beige fat thermogenesis

Interorgan crosstalk via secreted hormones and metabolites is a fundamental aspect of mammalian metabolic physiology. Beyond the highly specialized endocrine cells, peripheral tissues are emerging as an important source of metabolic hormones that influence energy and nutrient metabolism and contribute to disease pathogenesis. Neuregulin 4 (Nrg4) is a fat-derived hormone that protects mice from nonalcoholic steatohepatitis (NASH) and NASH-associated liver cancer by shaping hepatic lipid metabolism and the liver immune microenvironment. Despite its enriched expression in brown fat, whether NRG4 plays a role in thermogenic response and mediates the metabolic benefits of cold exposure are areas that remain unexplored. Here we show that Nrg4 expression in inguinal white adipose tissue (iWAT) is highly responsive to chronic cold exposure. Nrg4 deficiency impairs beige fat induction and renders mice more susceptible to diet-induced metabolic disorders under mild cold conditions. Using mice with adipocyte and hepatocyte-specific Nrg4 deletion, we reveal that adipose tissue-derived NRG4, but not hepatic NRG4, is essential for beige fat induction following cold acclimation. Furthermore, treatment with recombinant NRG4-Fc fusion protein promotes beige fat induction in iWAT and improves metabolic health in mice with diet-induced obesity. These findings highlight a critical role of NRG4 in mediating beige fat induction and preserving metabolic health under mild cold conditions.

Metabolic flux analysis in adipose tissue reprogramming

Obesity is a growing epidemic in the United States and worldwide and is associated with insulin resistance and cardiovascular disease, among other comorbidities. Understanding of the pathology that links overnutrition to these disease processes is ongoing. Adipose tissue is a heterogeneous organ comprised of multiple different cell types and it is likely that dysregulated metabolism within these cell populations disrupts both inter- and intracellular interactions and is a key driver of human disease. In recent years, metabolic flux analysis, which offers a precise quantification of metabolic pathway fluxes in biological systems, has emerged as a candidate strategy for uncovering the metabolic changes that stoke these disease processes. In this mini review, we discuss metabolic flux analysis as an experimental tool, with a specific emphasis on mass spectrometry with isotope tracing as this is the technique most frequently used for metabolic flux analysis in adipocytes. Furthermore, we examine existing literature that uses metabolic flux analysis to further our understanding of adipose tissue biology. Our group has a specific interest in understanding the role of white adipose tissue inflammation in the progression of cardiometabolic disease, as we know that in obesity the accumulation of pro-inflammatory adipose tissue macrophages is associated with significant morbidity, so we use this as a paradigm throughout our review for framing the application of these experimental techniques. However, there are many other biological applications to which they can be applied to further understanding of not only adipose tissue biology but also systemic homeostasis.