Polyphenol-rich green tea extract induces thermogenesis in mice by a mechanism dependent on adiponectin signaling

Adiponectin is downregulated in obesity negatively impacting the thermogenesis and impairing white fat browning. Despite the notable effects of green tea (GT) extract in the enhancement of thermogenesis, if its effects are being mediated by adiponectin has been scarcely explored. For this purpose, we investigated the role of adiponectin in the thermogenic actions of GT extract by using an adiponectin-knockout mice model. Male wild-type (WT) and knockout (AdipoKO) C57Bl/6 mice (3 months) were divided into 6 groups: mice fed a standard diet+gavage with water (SD WT, and SD AdipoKO), high-fat diet (HFD)+gavage with water (HFD WT, and HFD AdipoKO), and HFD + gavage with 500 mg/kg of body weight (BW) of GT extract (HFD + GT WT, and HFD + GT AdipoKO). After 20 weeks of experimentation, mice were euthanized and adipose tissue was properly removed. Our findings indicate that treatment with GT extract reversed complications of obesity in WT mice by decreasing final BW gain, adiposity index, adipocyte size and insulin resistance (IR). However, the action of the GT extract was not effective in reversing those markers in the AdipoKO mice, although GT acts independently in the reversal of IR. GT-treatment induced enhancement in energy expenditure (EE), BAT thermogenesis, and promoted browning phenotype in the subcutaneous WAT (scWAT) of WT mice. On the other hand, the thermogenic program was markedly impaired in BAT and scWAT of AdipoKO mice. Our outcomes unveiled adiponectin as a key direct signal for GT extract inducing adaptive thermogenesis and browning in scWAT.     

A polyphenolic extract from green tea leaves activates fat browning in high-fat-diet-induced obese mice

Fat browning has emerged as an attractive target for the treatment of obesity and related metabolic disorders. Its activation leads to increased energy expenditure and reduced adiposity, thus contributing to a better energy homeostasis. Green tea extracts (GTEs) were shown to attenuate obesity and low-grade inflammation and to induce the lipolytic pathway in the white adipose tissue (WAT) of mice fed a high-fat diet. The aim of the present study was to determine whether the antiobesity effect of an extract from green tea leaves was associated with the activation of browning in the WAT and/or the inhibition of whitening in the brown adipose tissue (BAT) in HF-diet induced obese mice. Mice were fed a control diet or an HF diet supplemented with or without 0.5% polyphenolic GTE for 8 weeks. GTE supplementation significantly reduced HF-induced adiposity (WAT and BAT) and HF-induced inflammation in WAT. Histological analysis revealed that GTE reduced the adipocyte size in the WAT and the lipid droplet size in the BAT. Markers of browning were induced in the WAT upon GTE treatment, whereas markers of HF-induced whitening were reduced in the BAT. These results suggest that browning activation in the WAT and whitening reduction in the BAT by the GTE could participate to the improvement of metabolic and inflammatory disorders mediated by GTE upon HF diet. Our study emphasizes the importance of using GTE as a nutritional tool to activate browning and to decrease fat storage in all adipose tissues, which attenuate obesity.     

Aging and caloric restriction impact adipose tissue,adiponectin, and circulating lipids

Adipose tissue expansion has been associated with system‐wide metabolic dysfunction and increased vulnerability to diabetes, cancer, and cardiovascular disease. A reduction in adiposity is a hallmark of caloric restriction (CR), an intervention that extends longevity and delays the onset of these same age‐related conditions. Despite these parallels, the role of adipose tissue in coordinating the metabolism of aging is poorly defined. Here, we show that adipose tissue metabolism and secretory profiles change with age and are responsive to CR. We conducted a cross‐sectional study of CR in adult, late‐middle‐aged, and advanced‐aged mice. Adiposity and the relationship between adiposity and circulating levels of the adipose‐derived peptide hormone adiponectin were age‐sensitive. CR impacted adiposity but only levels of the high molecular weight isoform of adiponectin responded to CR. Activators of metabolism including PGC‐1a, SIRT1, and NAMPT were differentially expressed with CR in adipose tissues. Although age had a significant impact on NAD metabolism, as detected by biochemical assay and multiphoton imaging, the impact of CR was subtle and related to differences in reliance on oxidative metabolism. The impact of age on circulating lipids was limited to composition of circulating phospholipids. In contrast, the impact of CR was detected in all lipid classes regardless of age, suggesting a profound difference in lipid metabolism. These data demonstrate that aspects of adipose tissue metabolism are life phase specific and that CR is associated with a distinct metabolic state, suggesting that adipose tissue signaling presents a suitable target for interventions to delay aging.     

Aging leads to a programmed loss of brown adipocytes in murine subcutaneous white adipose tissue

Insulin sensitivity deteriorates with age, but mechanisms remain unclear. Age‐related changes in the function of subcutaneous white adipose tissue (sWAT) are less characterized than those in visceral WAT. We hypothesized that metabolic alterations in sWAT, which in contrast to epididymal WAT, harbors a subpopulation of energy‐dissipating UCP1+ brown adipocytes, promote age‐dependent progression toward insulin resistance. Indeed, we show that a predominant consequence of aging in murine sWAT is loss of ‘browning’. sWAT from young mice is histologically similar to brown adipose tissue (multilocular, UCP1+), but becomes morphologically white by 12 months of age. Correspondingly, sWAT expression of ucp1 precipitously declines (~300‐fold) between 3 and 12 months. Loss continues into old age (24 months) and is inversely correlated with the development of insulin resistance. Additional age‐dependent changes in sWAT include lower expression of adbr3 and higher expression of maoa, suggesting reduced local adrenergic tone as a potential mechanism. Indeed, treatment with a β3‐adrenergic agonist to compensate for reduced tone rescues the aged sWAT phenotype. Age‐related changes in sWAT are not explained by the differences in body weight; mice subjected to 40% caloric restriction for 12 months are of body weight similar to 3‐month‐old ad lib fed mice, but display sWAT resembling that of age‐matched ad lib fed mice (devoid of brown adipose‐like morphology). Overall, findings identify the loss of ‘browning’ in sWAT as a new aging phenomenon and provide insight into the pathogenesis of age‐associated metabolic disease by revealing novel molecular changes tied to systemic metabolic dysfunction.     

Effects of exercise on brown and beige adipocytes

Physical exercise leads to beneficial effects in numerous tissues and organ systems and offers protection against obesity and type 2 diabetes. Recent studies have investigated the role of exercise on brown adipose tissue (BAT) and white adipose tissue (WAT), and have indicated marked adaptations to each tissue with exercise. Studies investigating the effects of exercise on BAT have produced conflicting results, with some showing an increase in the thermogenic activity of BAT and some demonstrating a decrease in the thermogenic activity of BAT. Human studies have observed a down-regulation of BAT activity (measured by a reduction in glucose uptake) in response to exercise. In WAT, exercise decreases adipocyte size, alters gene expression, and increases mitochondrial activity. Transplantation of exercise-trained subcutaneous WAT (scWAT) improves whole-body metabolic health. In rodents, exercise also results in a beiging of scWAT. Thus, exercise-induced changes to adipose tissue may be part of the mechanism by which exercise improves metabolic health.     

Opposing effects on cardiac function by calorie restriction in different‐aged mice

Calorie restriction (CR) increases average and maximum lifespan and exhibits an apparent beneficial impact on age‐related diseases. Several studies have shown that CR initiated either in middle or old age could improve ischemic tolerance and rejuvenate the aging heart; however, the data are not uniform when initiated in young. The accurate time to initiate CR providing maximum benefits for cardiac remodeling and function during aging remains unclear. Thus, whether a similar degree of CR initiated in mice of different ages could exert a similar effect on myocardial protection was investigated in this study. C57BL/6 mice were subjected to a calorically restricted diet (40% less than the ad libitum diet) for 3 months initiated in 3, 12, and 19 months. It was found that CR significantly reversed the aging phenotypes of middle‐aged and old mice including cardiac remodeling (cardiomyocyte hypertrophy and cardiac fibrosis), inflammation, mitochondrial damage, telomere shortening, as well as senescence‐associated markers but accelerated in young mice. Furthermore, whole‐genome microarray demonstrated that the AMP‐activated protein kinase (AMPK)–Forkhead box subgroup ‘O’ (FOXO) pathway might be a major contributor to contrasting regulation by CR initiated in different ages; thus, increased autophagy was seen in middle‐aged and old mice but decreased in young mice. Together, the findings demonstrated promising myocardial protection by 40% CR should be initiated in middle or old age that may have vital implications for the practical nutritional regimen.     

Brown and beige fat: From molecules to physiology

The recent re-discovery of brown adipose tissue (BAT) and even more recent discovery of the browning of white adipose tissue (WAT) in humans have generated intense scientific interest in the role of adipose tissue as potential target against obesity and its metabolic complications. The purpose of this review is to: i) critically evaluate the current evidence on the physiological significance of BAT and the browning of WAT in metabolic function in humans and ii) discuss factors that have been reported to regulate BAT and/or the browning of WAT in humans. The current literature supports that BAT and the browning of WAT constitute promising emerging targets for interventions aiming to prevent and/or treat of obesity and its metabolic complications. Further research is needed to better understand the physiological significance of BAT and browning of WAT in health and disease along with the factors modulating their metabolic function in humans.     

Lipocalin prostaglandin D synthase and PPARγ2 coordinate to regulate carbohydrate and lipid metabolism in vivo

Mice lacking Peroxisome Proliferator-Activated Receptor γ2 (PPARγ2) have unexpectedly normal glucose tolerance and mild insulin resistance. Mice lacking PPARγ2 were found to have elevated levels of Lipocalin prostaglandin D synthase (L-PGDS) expression in BAT and subcutaneous white adipose tissue (WAT). To determine if induction of L-PGDS was compensating for a lack of PPARγ2, we crossed L-PGDS KO mice to PPARγ2 KO mice to generate Double Knock Out mice (DKO). Using DKO mice we demonstrated a requirement of L-PGDS for maintenance of subcutaneous WAT (scWAT) function. In scWAT, DKO mice had reduced expression of thermogenic genes, the de novo lipogenic program and the lipases ATGL and HSL. Despite the reduction in markers of lipolysis in scWAT, DKO mice had a normal metabolic rate and elevated serum FFA levels compared to L-PGDS KO alone. Analysis of intra-abdominal white adipose tissue (epididymal WAT) showed elevated expression of mRNA and protein markers of lipolysis in DKO mice, suggesting that DKO mice may become more reliant on intra-abdominal WAT to supply lipid for oxidation. This switch in depot utilisation from subcutaneous to epididymal white adipose tissue was associated with a worsening of whole organism metabolic function, with DKO mice being glucose intolerant, and having elevated serum triglyceride levels compared to any other genotype. Overall, L-PGDS and PPARγ2 coordinate to regulate carbohydrate and lipid metabolism.     

Autophagy in Myf5+ progenitors regulates energy and glucose homeostasis through control of brown fat and skeletal muscle development

Macroautophagy (MA) regulates cellular quality control and energy balance. For example, loss of MA in aP2‐positive adipocytes converts white adipose tissue (WAT) into brown adipose tissue (BAT)‐like, enhancing BAT function and thereby insulin sensitivity. However, whether MA regulates early BAT development is unknown. We report that deleting Atg7 in myogenic Myf5+ progenitors inhibits MA in Myf5‐cell‐derived BAT and muscle. Knock out (KO) mice have defective BAT differentiation and function. Surprisingly, their body temperature is higher due to WAT lipolysis‐driven increases in fatty acid oxidation in ‘Beige’ cells in inguinal WAT, BAT and muscle. KO mice also present impaired muscle differentiation, reduced muscle mass and glucose intolerance. Our studies show that ATG7 in Myf5+ progenitors is required to maintain energy and glucose homeostasis through effects on BAT and muscle development. Decreased MA in myogenic progenitors with age and/or overnutrition might contribute to the metabolic defects and sarcopenia observed in these conditions.     

Methionine restriction restores a younger metabolic phenotype in adult mice with alterations in fibroblast growth factor 21

Methionine restriction (MR) decreases body weight and adiposity and improves glucose homeostasis in rodents. Similar to caloric restriction, MR extends lifespan, but is accompanied by increased food intake and energy expenditure. Most studies have examined MR in young animals; therefore, the aim of this study was to investigate the ability of MR to reverse age‐induced obesity and insulin resistance in adult animals. Male C57BL/6J mice aged 2 and 12 months old were fed MR (0.172% methionine) or control diet (0.86% methionine) for 8 weeks or 48 h. Food intake and whole‐body physiology were assessed and serum/tissues analyzed biochemically. Methionine restriction in 12‐month‐old mice completely reversed age‐induced alterations in body weight, adiposity, physical activity, and glucose tolerance to the levels measured in healthy 2‐month‐old control‐fed mice. This was despite a significant increase in food intake in 12‐month‐old MR‐fed mice. Methionine restriction decreased hepatic lipogenic gene expression and caused a remodeling of lipid metabolism in white adipose tissue, alongside increased insulin‐induced phosphorylation of the insulin receptor (IR) and Akt in peripheral tissues. Mice restricted of methionine exhibited increased circulating and hepatic gene expression levels of FGF21, phosphorylation of eIF2a, and expression of ATF4, with a concomitant decrease in IRE1α phosphorylation. Short‐term 48‐h MR treatment increased hepatic FGF21 expression/secretion and insulin signaling and improved whole‐body glucose homeostasis without affecting body weight. Our findings suggest that MR feeding can reverse the negative effects of aging on body mass, adiposity, and insulin resistance through an FGF21 mechanism. These findings implicate MR dietary intervention as a viable therapy for age‐induced metabolic syndrome in adult humans.     

Conjugated linoleic acid reduces adiposity and increases markers of browning and inflammation in white adipose tissue of mice

The objective of this study was to examine the mechanism by which conjugated linoleic acid (CLA) reduces body fat. Young male mice were fed three combinations of fatty acids at three doses (0.06%, 0.2%, and 0.6%, w/w) incorporated into AIN76 diets for 7 weeks. The types of fatty acids were linoleic acid (control), an equal mixture of trans-10, cis-12 (10,12) CLA plus linoleic acid, and an equal isomer mixture of 10,12 plus cis-9, trans-11 (9,11) CLA. Mice receiving the 0.2% and 0.6% dose of 10,12 CLA plus linoleic acid or the CLA isomer mixture had decreased white adipose tissue (WAT) and brown adipose tissue (BAT) mass and increased incorporation of CLA isomers in epididymal WAT and liver. Notably, in mice receiving 0.2% of both CLA treatments, the mRNA levels of genes associated with browning, including uncoupling protein 1 (UCP1), UCP1 protein levels, and cytochrome c oxidase activity, were increased in epididymal WAT. CLA-induced browning in WAT was accompanied by increases in mRNA levels of markers of inflammation. Muscle cytochrome c oxidase activity and BAT UCP1 protein levels were not affected by CLA treatment. These data suggest a linkage between decreased adiposity, browning in WAT, and low-grade inflammation due to consumption of 10,12 CLA.     

The dark side of browning

The induction of brown-like adipocyte development in white adipose tissue (WAT) confers numerous metabolic benefits by decreasing adiposity and increasing energy expenditure. Therefore, WAT browning has gained considerable attention for its potential to reverse obesity and its associated co-morbidities. However, this perspective has been tainted by recent studies identifying the detrimental effects of inducing WAT browning. This review aims to highlight the adverse outcomes of both overactive and underactive browning activity, the harmful side effects of browning agents, as well as the molecular brake-switch system that has been proposed to regulate this process. Developing novel strategies that both sustain the metabolic improvements of WAT browning and attenuate the related adverse side effects is therefore essential for unlocking the therapeutic potential of browning agents in the treatment of metabolic diseases.     

Diet‐induced Obese Mice Are Leptin Insufficient After Weight Reduction

Behavioral therapies aimed at reducing excess body fat result in limited fat loss after dieting. To understand the causes for maintenance of adiposity, high‐fat (HF) diet–induced obese (DIO) mice were switched to a low‐fat chow diet, and the effects of chow on histological and molecular alterations of adipose tissue and metabolic parameters were examined. DIO mice reduced and stabilized their body weights after being switched to chow (HF‐chow), but retained a greater amount of adiposity than chow‐fed mice. Reduction in adipocyte volume, not number, caused a decrease in fat mass. HF‐chow mice showed normalized circulating insulin and leptin levels, improved glucose tolerance, and reduced inflammatory status in white adipose tissue (WAT). Circulating leptin levels corrected for fat mass were lower in HF‐chow mice. Leptin administration was used to test whether reduced leptin level of HF‐chow mice inhibited further fat loss. Leptin treatment led to an additional reduction in adiposity. Finally, HF‐HF mice had lower mRNA levels of β₃ adrenergic receptor (β₃‐AR) in epididymal WAT (EWAT) compared to chow‐fed mice, and diet change led to an increase in the WAT β₃‐AR mRNA levels that were similar to the levels of chow‐fed mice, suggesting an elevation in sympathetic activation of WAT during diet switch relative to HF‐HF mice leading to the reduced leptin level and proinflammatory cytokine content. In summary, HF‐chow mice were resistant to further fat loss due to leptin insufficiency. Diet alteration from HF to low fat improved metabolic state of DIO mice, although their adiposity was defended at a higher level.     

Loss of DJ-1 promotes browning of white adipose tissue in diet-induced obese mice

The seminal discovery of browning of white adipose tissue (WAT) holds great promise for the treatment of obesity and metabolic syndrome. DJ-1 is evolutionarily conserved across species, and mutations in DJ-1 have been identified in Parkinson's disease. Higher levels of DJ-1 are associated with obesity, but the underlying mechanism is less understood. Here, we report the previously unappreciated role of DJ-1 in white adipocyte biology in mature models of obesity. We used DJ-1 knockout (KO) mouse models and wild-type littermates maintained on a normal diet or high-fat diet as well as in vitro cell models to show the direct effects of DJ-1 depletion on adipocyte phenotype, thermogenic capacity, fat metabolism, and microenvironment profile. Global DJ-1 KO mice show increased sympathetic input to WAT and β3-adrenergic receptor intracellular signaling, leading to a previously unrecognized compensatory mechanism through browning of WAT with associated characteristics, including high mitochondrial contents, reduced lipid accumulation, adequate vascularization and attenuated autophagy. DJ-1 KO mice had normal body weight, energy balance, and adiposity, which were associated with protective effects on healthy WAT expansion by hyperplasia. Our findings revealed that browning of inguinal WAT occurred in DJ-1 KO mice that do not show increased predisposition to obesity and suggest that such potential mechanism may overcome the adverse metabolic consequences of obesity independent of an effect on body weight. Here, we provide the first direct evidence that targeting DJ-1 in adipocyte metabolic health may offer a unique therapeutic strategy for the treatment of obesity.     

Tissue-specific functional interaction between apolipoproteins A1 and E in cold-induced adipose organ mitochondrial energy metabolism

White (WAT) and brown (BAT) adipose tissue, the two main types of adipose organ, are responsible for lipid storage and non-shivering thermogenesis, respectively. Thermogenesis is a process mediated by mitochondrial uncoupling protein 1 (UCP1) which uncouples oxidative phosphorylation from ATP production, leading to the conversion of free fatty acids to heat. This process can be triggered by exposure to low ambient temperatures, caloric excess, and the immune system. Recently mitochondrial thermogenesis has also been associated with plasma lipoprotein transport system. Specifically, apolipoprotein (APO) E3 is shown to have a bimodal effect on WAT thermogenesis that is highly dependent on its site of expression. Similarly, APOE2 and APOE4 differentially affect BAT and WAT mitochondrial metabolic activity in processes highly modulated by APOA1. Furthermore, the absence of classical APOA1 containing HDL (APOA1-HDL), is associated with no measurable non-shivering thermogenesis in WAT of mice fed high fat diet. Based on these previous observations which indicate important regulatory roles for both APOA1 and APOE in adipose tissue mitochondrial metabolic activity, here we sought to investigate the potential roles of these apolipoproteins in BAT and WAT metabolic activation in mice, following stimulation by cold exposure (7 °C). Our data indicate that APOA1-HDL promotes metabolic activation of BAT only in the presence of very low levels (virtually undetectable) of APOE3-containing HDL (APOE3-HDL), which acts as an inhibitor in this process. In contrast, induction of WAT thermogenesis is subjected to a more complicated regulation which requires the combined presence of both APOA1-HDL and APOE3-HDL.     

Withaferin A exerts an anti-obesity effect by increasing energy expenditure through thermogenic gene expression in high-fat diet-fed obese mice

BackgroundThe enhancement of energy expenditure has attracted attention as a therapeutic target for the management of body weight. Withaferin A (WFA), a major constituent of Withania somnifera extract, has been reported to possess anti-obesity properties, however the underlying mechanism remains unknown.PurposeTo investigate whether WFA exerts anti-obesity effects via increased energy expenditure, and if so, to characterize the underlying pathway.MethodsC57BL/6 J mice were fed a high-fat diet (HFD) for 10 weeks, and WFA was orally administered for 7 days. The oxygen consumption rate of mice was measured at 9 weeks using an OxyletPro™ system. Hematoxylin and eosin (H&E), immunohistochemistry, immunoblotting, and real-time PCR methods were used.ResultsTreatment with WFA ameliorated HFD-induced obesity by increasing energy expenditure by improving of mitochondrial activity in brown adipose tissue (BAT) and promotion of subcutaneous white adipose tissue (scWAT) browning via increasing uncoupling protein 1 levels. WFA administration also significantly increased AMP-activated protein kinase (AMPK) phosphorylation in the BAT of obese mice. Additionally, WFA activated mitogen-activated protein kinase (MAPK) signaling, including p38/extracellular signal-regulated kinase MAPK, in both BAT and scWAT.ConclusionWFA enhances energy expenditure and ameliorates obesity via the induction of AMPK and activating p38/extracellular signal-regulated kinase MAPK, which triggers mitochondrial biogenesis and browning-related gene expression.     

Ghrelin regulates adiposity in white adipose tissue and UCP1 mRNA expression in brown adipose tissue in mice

To examine the involvement of ghrelin in obesity, we investigated the effects of treatment with peripherally administered ghrelin on food intake, adiposity, and expression of uncoupling protein (UCP) mRNA in brown (BAT) and white (WAT) adipose tissue in mice. Acute bolus administration of ghrelin at a dose of 120 nmol/kg increased cumulative food intake over 4 and 24 h as compared to controls (p<0.05 for each), whereas 12 nmol/kg/day ghrelin showed no remarkable effect (p>0.1). Chronic repeated treatment with 12 nmol/kg/day ghrelin for 7 days increased body weight and adiposity assessed by the weight of adipose tissue, triglyceride content in WAT (p<0.05 for each versus control). In addition, the same treatment decreased and increased mRNA expression of BAT UCP1 and WAT UCP2, respectively (p<0.05 for each). In conclusion, ghrelin can regulate body weight, adiposity and UCPs mRNA expression in mice. The present results provide evidence for a new regulatory loop involving ghrelin and UCP, and add novel insights into the regulatory mechanisms of obesity.