Activity In White Adipose Tissue Research Articles

Sulfonylureas exert antidiabetic action on adipocytes by inhibition of PPARγ serine 273 phosphorylation

ObjectiveSulfonylureas (SUs) are still among the mostly prescribed antidiabetic drugs with an established mode of action: release of insulin from pancreatic β-cells. In addition, effects of SUs on adipocytes by activation of the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) have been described, which might explain their insulin-sensitizing potential observed in patients. However, there is a discrepancy between the impact of SUs on antidiabetic action and their rather moderate in vitro effect on PPARγ transcriptional activity. Recent studies have shown that some PPARγ ligands can improve insulin sensitivity by blocking PPARγ Ser-273 phosphorylation without having full agonist activity. It is unknown if SUs elicit their antidiabetic effects on adipocytes by inhibition of PPARγ phosphorylation. Here, we investigated if binding of SUs to PPARγ can interfere with PPARγ Ser-273 phosphorylation and determined their antidiabetic actions in vitro in primary human white adipocytes and in vivo in high-fat diet (HFD) obese mice. MethodsPrimary human white preadipocytes were differentiated in the presence of glibenclamide, glimepiride and PPARγ ligands rosiglitazone and SR1664 to compare PPARγ Ser-273 phosphorylation, glucose uptake and adipokine expression. Transcriptional activity at PPARγ was determined by luciferase assays, quantification of PPARγ Ser-273 phosphorylation was determined by Western blotting and CDK5 kinase assays. In silico modelling was performed to gain insight into the binding characteristics of SUs to PPARγ. HFD mice were administered SUs and rosiglitazone for 6 days. PPARγ Ser-273 phosphorylation in white adipose tissue (WAT), body composition, glucose tolerance, adipocyte morphology and expression levels of genes involved in PPARγ activity in WAT and brown adipose tissue (BAT) were evaluated. ResultsSUs inhibit phosphorylation of PPARγ at Ser-273 in primary human white adipocytes and exhibit a positive antidiabetic expression profile, which is characterized by up regulation of insulin-sensitizing and down regulation of insulin resistance-inducing adipokines. We demonstrate that SUs directly bind to PPARγ by in silico modelling and inhibit phosphorylation in kinase assays to a similar extend as rosiglitazone and SR1664. In HFD mice SUs reduce PPARγ phosphorylation in WAT and have comparable effects on gene expression to rosiglitazone. In BAT SUs increase UCP1 expression and reduce lipid droplets sizes. ConclusionsOur findings indicate that a part of SUs extra-pancreatic effects on adipocytes in vitro and in vivo is probably mediated via their interference with PPARγ phosphorylation rather than via classical agonistic activity at clinical concentrations.

P2Y13 receptor deficiency favors adipose tissue lipolysis and worsens insulin resistance and fatty liver disease.

Excessive lipolysis in white adipose tissue (WAT) leads to insulin resistance (IR) and ectopic fat accumulation in insulin-sensitive tissues. However, the impact of Gi-coupled receptors in restraining adipocyte lipolysis through inhibition of cAMP production remained poorly elucidated. Given that the Gi-coupled P2Y13 receptor (P2Y13-R) is a purinergic receptor expressed in WAT, we investigated its role in adipocyte lipolysis and its effect on IR and metabolic dysfunction-associated steatotic liver disease (MASLD). In humans, mRNA expression of P2Y13-R in WAT was negatively correlated to adipocyte lipolysis. In mice, adipocytes lacking P2Y13-R displayed higher intracellular cAMP levels, indicating impaired Gi signaling. Consistently, the absence of P2Y13-R was linked to increased lipolysis in adipocytes and WAT explants via hormone-sensitive lipase activation. Metabolic studies indicated that mice lacking P2Y13-R showed a greater susceptibility to diet-induced IR, systemic inflammation, and MASLD compared with their wild-type counterparts. Assays conducted on precision-cut liver slices exposed to WAT conditioned medium and on liver-specific P2Y13-R-knockdown mice suggested that P2Y13-R activity in WAT protects from hepatic steatosis, independently of liver P2Y13-R expression. In conclusion, our findings support the idea that targeting adipose P2Y13-R activity may represent a pharmacological strategy to prevent obesity-associated disorders, including type 2 diabetes and MASLD.

Tgr5-/- mice are protected from ethanol-induced metabolic alterations through enhanced leptin and Fgf21 signaling.

Alcohol-associated liver disease (ALD) is caused by chronic use of alcohol and ranges from hepatic steatosis to fibrosis and cirrhosis. Bile acids are physiological detergents that also regulate hepatic glucose and lipid homeostasis by binding to several receptors. One such receptor, Takeda G protein-coupled receptor 5 (TGR5), may represent a therapeutic target for ALD. Here, we used a chronic 10-day + binge ethanol-feeding model in mice to study the role of TGR5 in alcohol-induced liver injury. Female C57BL/6J wild-type mice and Tgr5-/- mice were pair-fed Lieber-DeCarli liquid diet with ethanol (5% v/v) or isocaloric control diet for 10 days followed by a gavage of 5% ethanol or isocaloric maltose control, respectively, to represent a binge-drinking episode. Tissues were harvested 9 hours following the binge, and metabolic phenotypes were characterized through examination of liver, adipose, and brain mechanistic pathways. Tgr5-/- mice were protected from alcohol-induced accumulation of hepatic triglycerides. Interestingly, liver and serum levels of Fgf21 were significantly increased during ethanol feeding in Tgr5-/- mice, as was phosphorylation of Stat3. Parallel to Fgf21 levels, increased leptin gene expression in white adipose tissue and increased leptin receptor in liver were detected in Tgr5-/- mice fed ethanol diet. Adipocyte lipase gene expression was significantly increased in Tgr5-/- mice regardless of diet, whereas adipose browning markers were also increased in ethanol-fed Tgr5-/- mice, indicating potential for enhanced white adipose metabolism. Lastly, hypothalamic mRNA targets of leptin, involved in the regulation of food intake, were significantly increased in Tgr5-/- mice fed ethanol diet. Tgr5-/- mice are protected from ethanol-induced liver damage and lipid accumulation. Alterations in lipid uptake and Fgf21 signaling, and enhanced metabolic activity of white adipose tissue, may mediate these effects.

Fatty Acids as Potent Modulators of Autophagy Activity in White Adipose Tissue.

A high-fat diet is one of the causative factors of obesity. The dietary profile of fatty acids is also an important variable in developing obesity, as saturated fatty acids are more obesogenic than monounsaturated and polyunsaturated fatty acids. Overweight and obesity are inseparably connected with the excess of adipose tissue in the body, characterized by hypertrophy and hyperplasia of fat cells, which increases the risk of developing metabolic syndrome. Changes observed within hypertrophic adipocytes result in elevated oxidative stress, unfolded protein accumulation, and increased endoplasmic reticulum (ER) stress. One of the processes involved in preservation of cellular homeostasis is autophagy, which is defined as an intracellular lysosome-dependent degradation system that serves to recycle available macromolecules and eliminate damaged organelles. In obesity, activation of autophagy is increased and the process appears to be regulated by different types of dietary fatty acids. This review describes the role of autophagy in adipose tissue and summarizes the current understanding of the effects of saturated and unsaturated fatty acids in autophagy modulation in adipocytes.

48 Metformin Rescues the Aging-induced Failure of Post-burn White Adipose Browning

IntroductionSevere burns are responsible for an estimated 300,000 deaths per year worldwide. While modern burn care has markedly improved survival for pediatric and adult patients, this is sadly not the case for one population: the elderly. Despite being the fastest-growing demographic in North America, burn patients over the age of 60 years have the highest mortality and morbidity rates. Recent evidence suggests that progressive aging induces several structural and functional alterations which impair the capacity of older trauma patients to adequately respond to stress. Indeed, it was discovered that reduced survival in elderly burn patients is associated with the failure to initiate the browning of white adipose tissue (WAT) —a hallmark of the systemic response to injury commonly observed in adults. Interestingly, the widely used hypoglycemic drug metformin has been found to protect against aging-induced metabolic decline in various pathological conditions. Thus, we investigated the anti-aging effects of metformin on the metabolic deterioration of post-burn WAT responses in elderly patients and mice after injury.MethodsHuman WAT was obtained from elderly patients admitted to our burn center. Elderly (75-week) mice received a full-thickness scald burn and/or daily intraperitoneal injections of metformin (100 mg/kg) for 7 days. The inguinal WAT was harvested for histological analyses. Mitochondrial respiration was measured via Seahorse XF96. Gene and protein expression was assessed via RT-PCR and western blot, respectively.ResultsPost-burn metformin treatment restores the thermogenic activation of WAT in elderly patients and mice, reflected by the increased expression of key browning markers, UCP-1 and PGC-1α (p< 0.05). This was accompanied by higher mitochondrial respiration, improved lipolysis (p< 0.05) and increased fat wasting (p< 0.01) relative to control counterparts. The anti-aging effects of metformin appeared to be mediated by AMPK, which consequently increased [NAD+] (p< 0.01), thereby promoting activation of the longevity-specific enzyme Sirt-1 (p< 0.05).ConclusionsHere, we show that post-burn metformin treatment effectively rejuvenates adaptive metabolic responses in elderly WAT by targeting key longevity pathways which rescue the age-dependent loss of being back to youthful levels. Our findings support the potential of anti-aging modalities to improve care and outcomes in elderly burned patients.

Endocannabinoids Produced by White Adipose Tissue Modulate Lipolysis in Lean but Not in Obese Rodent and Human.

White adipose tissue (WAT) possesses the endocannabinoid system (ECS) machinery and produces the two major endocannabinoids (ECs), arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG). Accumulating evidence indicates that WAT cannabinoid 1 receptors (CB1R) are involved in the regulation of fat storage, tissue remodeling and secretory functions but their role in controlling lipid mobilization is unclear. In the present study, we used different strategies to acutely increase ECS activity in WAT and tested the consequences on glycerol production as a marker of lipolysis. Treating lean mice or rat WAT explants with JLZ195, which inhibits ECs degrading enzymes, induced an increase in 2-AG tissue contents that was associated with a CB1R-dependent decrease in lipolysis. Direct treatment of rat WAT explants with AEA also inhibited glycerol production while mechanistic studies revealed it could result from the stimulation of Akt-signaling pathway. Interestingly, AEA treatment decreased lipolysis both in visceral and subcutaneous WAT collected on lean subjects suggesting that ECS also reduces fat store mobilization in Human. In obese mice, WAT content and secretion rate of ECs were higher than in control while glycerol production was reduced suggesting that over-produced ECs may inhibit lipolysis activating local CB1R. Strikingly, our data also reveal that acute CB1R blockade with Rimonabant did not modify lipolysis in vitro in obese mice and human explants nor in vivo in obese mice. Taken together, these data provide physiological evidence that activation of ECS in WAT, by limiting fat mobilization, may participate in the progressive tissue remodeling that could finally lead to organ dysfunction. The present findings also indicate that acute CB1R blockade is inefficient in regulating lipolysis in obese WAT and raise the possibility of an alteration of CB1R signaling in conditions of obesity.

Maternal nicotine exposure enhances adipose tissue angiogenic activity in offspring: Sex and age differences

Maternal nicotine exposure during pregnancy and lactation (NIC) is associated with dysfunction of white adipose tissue (WAT). We focused on the NIC-induced WAT angiogenesis and explored its sex and age differences. Pregnant rats were randomly assigned to NIC (1.0 mg/kg nicotine twice per day) or control groups. Distribution and density of blood vessels were observed. Angiogenesis-related genes were tested at 4, 12 and 26 weeks to estimate angiogenic activity. In vitro, nicotine concentration- and time-response experiments (0−50 μM) were conducted in 3T3-L1. Lipid accumulation and angiogenesis-related genes were tested. NIC increased the blood vessels in inguinal subcutaneous WAT (igSWAT) and gonadal WAT (gWAT) of 26-week-aged male and 4-week-aged female offspring. In males, nicotine showed higher angiogenic activity at 26 weeks than at 4 weeks in igSWAT and gWAT. In females, nicotine’s angiogenic activity was higher at 4 weeks than 26 weeks in igSWAT and gWAT. In vitro, nicotine promoted adipocyte differentiation, and increased the expression of angiogenesis-related genes in concentration- and time dependent manners. In conclusion, NIC-induced enhancement of angiogenic activity in WAT presented sex and age differences: nicotine showed higher angiogenic activity in adulthood than in childhood of male offspring, but the converse results were observed in female offspring.

Creatine Supplementation Exhibits Sex Differences in White Adipose Tissue and Increases Mitochondrial Markers in Female Rats

Activation of white adipose tissue (WAT) thermogenesis, known as WAT browning, has emerged as an attractive approach to treat obesity and obesity‐related diseases. Traditionally BAT or browning WAT has been defined by the expression of uncoupling protein 1 (UCP1), a mitochondrial protein that uncouples respiration from ATP production. However, recent work has highlighted creatine metabolism or futile cycling as a potential thermogenic pathway. Creatine‐driven futile cycling is a catabolic process which results in ATP oxidation by mitochondrial creatine kinase, resulting in the phosphorylation of creatine and increases in ADP concentrations that drive thermogenic respiration. The purpose of the present study was two‐fold: 1) to determine the effects of creatine supplementation on markers of WAT browning, and 2) to determine if creatine supplementation exhibits sex differences. Thirty‐two Sprague‐Dawley rats (16 male, 16 female) were randomly assigned to one of four experimental groups: control, 2.5g/L, 5g/L and 10g/L of creatine monohydrate (CM) and 1% sucrose via drinking water. Rats had ad libitum access to their drinking water and a standard chow diet (AIN‐93G) throughout the study. Following the 8‐week intervention, brown interscapular adipose (BAT) and white subcutaneous inguinal (iWAT) fat depots were collected. Western blotting analysis demonstrated no significant changes in BAT samples for both males and females. Males had lower cytochrome C than females with 10g/L of creatine monohydrate (p&lt;0.05). In iWAT, mitochondrial markers (COXIV, PDH, citrate synthase, and cytochrome C) and GAMT exhibit no changes in males, however, a decrease in UCP‐1 at 5g/L compared to control was observed (p&lt;0.05). Females exhibit a lower control PDH content than males (p&lt;0.01) in iWAT, accompanied by an increase in PDH levels at all doses of CM compared to control (p&lt;0.05). Furthermore, in females COXIV and cytochrome C presented significant increases with 5g/L and 10g/L, respectively (p&lt;0.05). Both males and females did not present with body weight differences despite dose differences. This study presents novel work demonstrating that female WAT exhibits less mitochondrial markers than males under control conditions, however it demonstrates the potential for CM supplementation to increase female adipose thermogenicity to a similar level observed in males.Support or Funding InformationSupported by NSERC, Canada

46 Inhibition of Lipolysis with Acipimox Targets Post-burn White Adipose Browning by Altering Macrophage Polarity

Abstract Introduction Severe burns are accompanied by a detrimental hypermetabolic stress response that can persist for years post-injury. Our previous work revealed that, under prolonged stress, white adipose tissue (WAT) adopts brown adipose-like traits in a process termed ‘browning’. This switch, characterized by the presence of uncoupling protein 1 (UCP1), is driven by the polarization of macrophages towards an M2 phenotype. Recently, we demonstrated that inhibiting lipolysis with the clinically approved drug, Acipimox, represses the burn-induced thermogenic activation of WAT. These findings raise the possibility that elevated rates of lipolysis may play a role in regulating the macrophage polarization state after major burn. However, the interconnection between post-burn lipolysis and inflammation remains unclear. In the present study, we investigated the mechanism underlying Acipimox’s inhibitory effects on burn-induced browning. Using a mouse model of thermal injury, we determine the metabolic effects of reducing WAT lipolysis on burn-induced macrophage recruitment and M2-polarization. Methods Adult C57BL/6 mice received a 30% total body surface area scald burn. Mice were then given daily intraperitoneal injections of APX (50 mg/Kg). On day 7 post-burn, the inguinal adipose tissue depot (iWAT) was harvested for histological analyses. Flow cytometry and F4/80 staining were used to assess adipose macrophage distribution and profile, and gene expression was analyzed via qPCR. Results APX administration significantly increased mitochondrial coupling, reflected by the decrease in UCP-1 (p&amp;lt; 0.05) and PGC-1a (p&amp;lt; 0.01) levels relative to the iWAT of untreated burn mice. F4/80 immunostaining of iWAT demonstrated decreased macrophage recruitment in Acipimox treated mice (p&amp;lt; 0.05). Flow cytometric analysis indicated decreased macrophage infiltration at 7 days in Acipimox treated mice (p&amp;lt; 0.05). Furthermore, iWAT from Acipimox treated mice demonstrated a pro-inflammatory profile, indicated by a greater distribution of TLR4 positive macrophages (p&amp;lt; 0.05). Conclusions Previously, we showed that the administration of Acipimox effectively suppressed PKA-mediated lipolysis and improved mitochondrial coupling in adipose tissue post-burn. Here, we elucidate the mechanism underlying these metabolic changes. Importantly, we show Acipimox exerts its inhibitory effects on burn-induced WAT browning by directly modulating macrophage recruitment and the M2-polarization state. Applicability of Research to Practice Our study highlights the critical role of lipolysis in mediating the key post-burn metabolic phenomena browning and inflammation. The data presented herein validate the pharmacological inhibition of lipolysis as a potentially powerful therapeutic strategy to counteract the detrimental metabolic effects induced by burn.

Persistent low body weight in humans is associated with higher mitochondrial activity in white adipose tissue

ABSTRACTBackgroundConstitutional thinness (CT) is a state of low but stable body weight (BMI ≤18 kg/m2). CT subjects have normal-range hormonal profiles and food intake but exhibit resistance to weight gain despite living in the modern world's obesogenic environment.ObjectiveThe goal of this study is to identify molecular mechanisms underlying this protective phenotype against weight gain.MethodsWe conducted a clinical overfeeding study on 30 CT subjects and 30 controls (BMI 20–25 kg/m2) matched for age and sex. We performed clinical and integrative molecular and transcriptomic analyses on white adipose and muscle tissues.ResultsOur results demonstrate that adipocytes were markedly smaller in CT individuals (mean ± SEM: 2174 ± 142 μm 2) compared with controls (3586 ± 216 μm2) (P < 0.01). The mitochondrial respiratory capacity was higher in CT adipose tissue, particularly at the level of complex II of the electron transport chain (2.2-fold increase; P < 0.01). This higher activity was paralleled by an increase in mitochondrial number (CT compared with control: 784 ± 27 compared with 675 ± 30 mitochondrial DNA molecules per cell; P < 0.05). No evidence for uncoupled respiration or “browning” of the white adipose tissue was found. In accordance with the mitochondrial differences, CT subjects had a distinct adipose transcriptomic profile [62 differentially expressed genes (false discovery rate of 0.1 and log fold change >0.75)], with many differentially expressed genes associating with positive metabolic outcomes. Pathway analyses revealed an increase in fatty acid oxidation ( P = 3 × 10−04) but also triglyceride biosynthesis (P = 3.6 × 10−04). No differential response to the overfeeding was observed in the 2 groups.ConclusionsThe distinct molecular signature of the adipose tissue in CT individuals suggests the presence of augm ented futile lipid cycling, rather than mitochondrial uncoupling, as a way to increase energy expenditure in CT individuals. We propose that increased mitochondrial function in adipose tissue is an important mediator in sustaining the low body weight in CT individuals. This knowledge could ultimately allow more targeted approaches for weight management treatment strategies. This trial was registered at clinicaltrials.gov as NCT02004821.

ApoC-III ASO promotes tissue LPL activity in the absence of apoE-mediated TRL clearance

Hypertriglyceridemia results from accumulation of triglyceride (TG)-rich lipoproteins (TRLs) in the circulation and is associated with increased CVD risk. ApoC-III is an apolipoprotein on TRLs and a prominent negative regulator of TG catabolism. We recently established that in vivo apoC-III predominantly inhibits LDL receptor-mediated and LDL receptor-related protein 1-mediated hepatic TRL clearance and that apoC-III-enriched TRLs are preferentially cleared by syndecan-1 (SDC1). In this study, we determined the impact of apoE, a common ligand for all three receptors, on apoC-III metabolism using apoC-III antisense oligonucleotide (ASO) treatment in mice lacking apoE and functional SDC1 (Apoe−/−Ndst1f/fAlb-Cre+). ApoC-III ASO treatment significantly reduced plasma TG levels in Apoe−/−Ndst1f/fAlb-Cre+ mice without reducing hepatic VLDL production or improving hepatic TRL clearance. Further analysis revealed that apoC-III ASO treatment lowered plasma TGs in Apoe−/−Ndst1f/fAlb-Cre+ mice, which was associated with increased LPL activity in white adipose tissue in the fed state. Finally, clinical data confirmed that ASO-mediated lowering of APOC-III via volanesorsen can reduce plasma TG levels independent of the APOE isoform genotype. Our data indicate that apoE determines the metabolic impact of apoC-III as we establish that apoE is essential to mediate inhibition of TRL clearance by apoC-III and that, in the absence of functional apoE, apoC-III inhibits tissue LPL activity.

Investigation of Some Angiogenic Factors Related to Aging in Brown and White Adipose Tissues of Rats

Aging is a biological phenomenon in which life force decreases, there is an increase in dysfunction, and activities at the level of tissue and cell with insufficient response to changes in internal and external environments decrease. In biological aging, there are deficiencies in the cell level, the cells and tissues are prevented from feeding with enough oxygen and hypoxic conditions can occur. Due to the loss of function in living organisms as a result of aging, the failure of the organelles to perform their functions may lead to the emergence of oxygen deficiency conditions in the tissues. The most common feature of aging is the change of physiological functions over time. Especially when oxygen deficiency appears in the tissues, the number of red blood cells increases, hormones and angiogenic factors releasing increase. Hypoxia may also occur in tissues due to environmental factors, obesity and various circulatory insufficiency, and the organism may activate angiogenic factors in response to this. Adequate oxygen must be provided for the normal functioning of the tissues. In the case of oxygen deficiency (hypoxia), matrix metallo proteinase, vascular endothelial growth factor, tumor necrosis factor, interleukin may play role such as angiogenic factors. In this study, the levels of vascular endothelial growth factor (VEGF), matrix metalloproteinase‐II, hypoxia‐inducible factor‐1α, adrenomedullin were investigated in 6 months and 24 months old rats. The vascularity function of the tissues is very important. Vein formation is required in both normal functional tissues and in tissues that are in neoplastic formation. Therefore, in this study, we investigated the angiogenic factors in rats' brown and white adipose tissue in cases by aging. In the study, 24 rats were divided into two groups; 12, 6‐month old young and 12, 24‐month‐old rats were evaluated as elderly group. In the study, angiogenic factors increased in the white adipose tissues of the elderly animals, whereas it was found that there was a greater increase in the brown adipose tissue that plays a role in the thermogenesis event in young rats. Decreasing physical activity in elderly animals and increased activity in white adipose tissue resulted in a significant increase in the weight of aged rats. Angiogenic factors play an important role in maintaining the oxygen demand of the organism in elderly animals, while it may cause an increase in the expanding of the white adipose tissue, which is effective on weight gain, which may lead to obesity.Support or Funding InformationThis research was funded by Inonu University, Department of Scientific Research Projects Project No: FYL‐2017‐748).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The Effects of Aging on Rho-Kinase and Insulin Signaling in Skeletal Muscle and White Adipose Tissue of Rats.

The insulin receptor substrate 1 regulates insulin-mediated glucose uptake and is a target of Rho-kinase (Rock); however, the relationship between age-related insulin resistance and Rock signaling specifically in skeletal muscle and adipose tissue is unknown. We evaluated the content and activity of Rock in C2C12 myotubes, and in skeletal muscle and white adipose tissue (WAT) from two rodent models that differ in their patterns of body fat accumulation during aging (Wistar and Fischer 344 rats). Body fat gain in the Wistar rats was greater than in Fischer rats and only Wistar rats had impairment of whole-body insulin sensitivity. Rock activity and insulin signaling were impaired in skeletal muscle in both rat models, but only middle-aged Wistar rats had higher Rock activity in WAT. These data are consistent with a positive role of Rock in regulating insulin signaling in both skeletal muscle and its negative role in the adipose tissue, suggesting that Rock activity in adipose tissue is important in age-related insulin resistance.

High phosphate diet suppresses lipogenesis in white adipose tissue.

Excessive phosphate intake has been positively associated with renal and vascular dysfunction, conversely negatively associated with body fat accumulation. We investigated the effect of a high-phosphate diet on the expression of lipid metabolic genes in white adipose tissue and liver. Male 8-week-old Sprague–Dawley rats were fed a control diet containing 0.6% phosphate or a high-phosphate diet containing 1.5% phosphate for 4 weeks. In comparison to the control group, the HP group showed a significantly lower body fat mass and fasting plasma insulin level alongside decreased lipogenic and increased lipolytic gene expression in visceral fat. Additionally, the expression of genes involved in hepatic lipogenesis, hepatic glycogenesis, and triglyceride accumulation decreased in the high-phosphate group. Exogenous phosphate, parathyroid hormone, and fibroblast growth factor 23 did not directly affect the expression of lipolytic or lipogenic genes in 3T3-L1 adipocytes and HepG2 hepatocytes. Thus, the high-phosphate diet suppressed the activity of white adipose tissue by increasing lipolytic gene expression and decreasing lipogenic gene expression. These effects could have been caused by the lowered fasting plasma insulin level that occurred in response to the high-phosphate diet, but were not directly caused by the increases in plasma phosphate or phosphaturic hormones.

High Expression of STAT3 in Subcutaneous Adipose Tissue Associates with Cardiovascular Risk in Women with Rheumatoid Arthritis.

Despite the predominance of female patients and uncommon obesity, rheumatoid arthritis (RA) is tightly connected to increased cardiovascular morbidity. The aim of this study was to investigate transcriptional activity in the subcutaneous white adipose tissue (WAT) with respect to this disproportionate cardiovascular risk (CVR) in RA. CVR was estimated in 182 female patients, using the modified Systematic Coronary Risk Evaluation scale, and identified 93 patients with increased CVR. The overall transcriptional activity in WAT was significantly higher in patients with CVR and was presented by higher serum levels of WAT products leptin, resistin and IL-6 (all, p < 0.001). CVR was associated with high WAT-specific transcription of the signal transducer and activator of transcription 3 (STAT3) and the nuclear factor NF-kappa-B p65 subunit (RELA), and with high transcription of serine-threonine kinase B (AKT1) in leukocytes. These findings suggest Interleukin 6 (IL-6) and leptin take part in WAT-specific activation of STAT3. The binary logistic regression analysis confirmed an independent association of CVR with IL-6 in serum, and with STAT3 in WAT. The study shows an association of CVR with transcriptional activity in WAT in female RA patients. It also emphasizes the importance of STAT3 regulatory circuits for WAT-related CVR in RA.

Body weight predicts Nicotinamide N-Methyltransferase activity in mouse fat

ABSTRACT Aim: Nicotinamide N-methyltransferase (NNMT) is a novel regulator of energy homeostasis in adipose tissue. NNMT expression is higher in obese mice than in lean mice, and NNMT knockdown prevents diet-induced obesity. Little is known about the regulation of enzyme activity during the development of obesity. The aim of this study was to analyze NNMT activity in tissues of mice with incipient and established obesity. Methods: A fluorescence-based, sensitive, low-volume, high-throughput method was developed to assay NNMT activity. C57BL/6 mice were fed a high-fat diet for 4 weeks (incipient obesity) and for 12 weeks (established obesity). Tissues and serum were harvested and analyzed. Results: NNMT activity was highest in subcutaneous white fat (55.0 µU/mg), followed by epididymal white fat (35.6 µU/mg), brown adipose tissue (7.8 µU/mg), liver (7.6 µU/mg), and lung (7.3 µU/mg). Little activity was detected in heart, skeletal muscle, and kidney. No activity was found in serum samples. Body weight predicted NNMT activity in white fat, but not in brown fat or any other tissue, and only in incipient obesity. With established obesity, this association was lost. Conclusions: As obesity develops, body weight predicts NNMT activity in white adipose tissue, but not in any other tissue, consistent with a specific role of adipose-tissue NNMT in the regulation of body weight.

CNS β3-adrenergic receptor activation regulates feeding behavior, white fat browning, and body weight

Pharmacological β3-adrenergic receptor (β3AR) activation leads to increased mitochondrial biogenesis and activity in white adipose tissue (WAT), a process commonly referred to as "browning", and transiently increased insulin release. These effects are associated with improved metabolic function and weight loss. It is assumed that this impact of β3AR agonists is mediated solely through activation of β3ARs in adipose tissue. However, β3ARs are also found in the brain, in areas such as the brain stem and the hypothalamus, which provide multisynaptic innervation to brown and white adipose depots. Thus, contrary to the current adipocentric view, the central nervous system (CNS) may also have the ability to regulate energy balance and metabolism through actions on central β3ARs. Therefore, this study aimed to elucidate whether CNS β3ARs can regulate browning of WAT and other aspects of metabolic regulation, such as food intake control and insulin release. We found that acute central injection of β3AR agonist potently reduced food intake, body weight, and increased hypothalamic neuronal activity in rats. Acute central β3AR stimulation was also accompanied by a transient increase in circulating insulin levels. Moreover, subchronic central β3AR agonist treatment led to a browning response in both inguinal (IWAT) and gonadal WAT (GWAT), along with reduced GWAT and increased BAT mass. In high-fat, high-sugar-fed rats, subchronic central β3AR stimulation reduced body weight, chow, lard, and sucrose water intake, in addition to increasing browning of IWAT and GWAT. Collectively, our results identify the brain as a new site of action for the anorexic and browning impact of β3AR activation.

Chronic l-menthol-induced browning of white adipose tissue hypothesis: A putative therapeutic regime for combating obesity and improving metabolic health

IntroductionObesity constitutes a serious global health concern reaching pandemic prevalence rates. The existence of functional brown adipose tissue (BAT) in adult humans has provoked intense research interest in the role of this metabolically active tissue in whole-body energy balance and body weight regulation. A number of environmental, physiological, pathological, and pharmacological stimuli have been proposed to induce BAT-mediated thermogenesis and functional thermogenic BAT-like activity in white adipose tissue (WAT), opening new avenues for therapeutic strategies based on enhancing the number of beige adipocytes in WAT. HypothesisRecent evidence support a role of l-menthol cooling, mediated by TRPM8 receptor, on UCP1-dependent thermogenesis and BAT-like activity in classical WAT depots along with the recruitment of BAT at specific anatomical sites. l-Menthol-induced BAT thermogenesis has been suggested to occur by a β-adrenergic-independent mechanism, avoiding potential side-effects due to extensive β-adrenergic stimulation mediated by available beta receptor agonists. l-Menthol has been also linked to the activation of the cold-gated ion channel TRPA1. However, its role in l-menthol-induced UCP1-dependent thermogenic activity in BAT and WAT remains undetermined. White adipose tissue plasticity has important clinical implications for obesity prevention and/or treatment because higher levels of UCP1-dependent thermogenesis can lead to enhanced energy expenditure at a considerable extent. We hypothesize that chronic dietary l-menthol treatment could induce TRPM8- and TRPA1-dependent WAT adaptations, resembling BAT-like activity, and overall improve whole-body metabolic health in obese and overweight individuals. ConclusionsThe putative impact of chronic l-menthol dietary treatment on the stimulation of BAT-like activity in classical WAT depots in humans remains unknown. A detailed experimental design has been proposed to investigate the hypothesized l-menthol-induced browning of WAT. If our hypothesis was to be confirmed, TRPM8/TRPA1-induced metabolic adaptations of WAT to BAT-like activity could provide a promising novel therapeutic approach for increasing energy expenditure, regulating body weight, and preventing obesity and its related co-morbidities in humans.

Brown Fat and Browning for the Treatment of Obesity and Related Metabolic Disorders.

Brown fat is a specialized fat depot that can increase energy expenditure and produce heat. After the recent discovery of the presence of active brown fat in human adults and novel transcription factors controlling brown adipocyte differentiation, the field of the study of brown fat has gained great interest and is rapidly growing. Brown fat expansion and/or activation results in increased energy expenditure and a negative energy balance in mice and limits weight gain. Brown fat is also able to utilize blood glucose and lipid and results in improved glucose metabolism and blood lipid independent of weight loss. Prolonged cold exposure and beta adrenergic agonists can induce browning of white adipose tissue. The inducible brown adipocyte, beige adipocyte evolving by thermogenic activation of white adipose tissue have different origin and molecular signature from classical brown adipocytes but share the characteristics of high mitochondria content, UCP1 expression and thermogenic capacity when activated. Increasing browning may also be an efficient way to increase whole brown fat activity. Recent human studies have shown possibilities that findings in mice can be reproduced in human, making brown fat a good candidate organ to treat obesity and its related disorders.

B-cell-activating factor deficiency attenuates high-fat diet-induced glucose intolerance by potentiating adipose tissue function

B-cell-activating factor (BAFF) has recently been demonstrated to be expressed in adipocytes and up-regulated by high-fat diet feeding, indicating a possible role in metabolic regulation. Here we show that glucose tolerance was significantly improved in high-fat diet-fed BAFF knockout (BAFF−/−) mice. BAFF−/− mice revealed higher levels of glucose transporter expression and insulin-stimulated Akt phosphorylation in brown adipose tissue compared to wild type controls. Expression levels of mitochondrial ND5 and genes involved in lipid metabolism were significantly elevated in brown adipose tissue of BAFF−/− mice, and this enhancement was found to be mediated by FGF21 and leptin. It was also observed that expression of IL-10 and foxp3 was increased in adipose tissues, as well as PPARγ activity in white adipose tissue. Our findings suggest that suppression of BAFF could have a therapeutic potential for prevention of type 2 diabetes.