Essential roles of 11β-HSD1 in regulating brown adipocyte function

Transcripts with high distal heritability mediate genetic effects on complex metabolic traits

Although many genes are subject to local regulation, recent evidence suggests that complex distal regulation may be more important in mediating phenotypic variability. To assess the role of distal gene regulation in complex traits, we combined multi-tissue transcriptomes with physiological outcomes to model diet-induced obesity and metabolic disease in a population of Diversity Outbred mice. Using a novel high-dimensional mediation analysis, we identified a composite transcriptome signature that summarized genetic effects on gene expression and explained 30% of the variation across all metabolic traits. The signature was heritable, interpretable in biological terms, and predicted obesity status from gene expression in an independently derived mouse cohort and multiple human studies. Transcripts contributing most strongly to this composite mediator frequently had complex, distal regulation distributed throughout the genome. These results suggest that trait-relevant variation in transcription is largely distally regulated, but is nonetheless identifiable, interpretable, and translatable across species.

Knockdown of 11β-hydroxysteroid dehydrogenase type 1 alleviates LPS-induced myocardial dysfunction through the AMPK/SIRT1/PGC-1α pathway

Sepsis-induced myocardial dysfunction is primarily accompanied by severe sepsis, which is associated with high morbidity and mortality. 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), encoded by Hsd11b1, is a reductase that can convert inactive cortisone into metabolically active cortisol, but the role of 11β-HSD1 in sepsis-induced myocardial dysfunction remains poorly understood. The current study aimed to investigate the effects of 11β-HSD1 on a lipopolysaccharide (LPS)-induced mouse model, in which LPS (10 mg/kg) was administered to wild-type C57BL/6J mice and 11β-HSD1 global knockout mice. We asscessed cardiac function by echocardiography, performed transmission electron microscopy and immunohistochemical staining to analyze myocardial mitochondrial injury and histological changes, and determined the levels of reactive oxygen species and biomarkers of oxidative stress. We also employed polymerase chain reaction analysis, Western blotting, and immunofluorescent staining to determine the expression of related genes and proteins. To investigate the role of 11β-HSD1 in sepsis-induced myocardial dysfunction, we used LPS to induce lentivirus-infected neonatal rat ventricular cardiomyocytes. We found that knockdown of 11β-HSD1 alleviated LPS-induced myocardial mitochondrial injury, oxidative stress, and inflammation, along with an improved myocardial function; furthermore, the depletion of 11β-HSD1 promoted the phosphorylation of adenosine 5'-monophosphate-activated protein kinase (AMPK), peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), and silent information regulator 1 (SIRT1) protein levels both in vivo and in vitro. Therefore, the suppression of 11β-HSD1 may be a viable strategy to improve cardiac function against endotoxemia challenges.

Fresh insights into glucocorticoid-induced diabetes mellitus and new therapeutic directions

Glucocorticoid hormones were discovered to have use as potent anti-inflammatory and immunosuppressive therapeutics in the 1940s and their continued use and development have successfully revolutionized the management of acute and chronic inflammatory diseases. However, long-term use of glucocorticoids is severely hampered by undesirable metabolic complications, including the development of type 2 diabetes mellitus. These effects occur due to glucocorticoid receptor activation within multiple tissues, which results in inter-organ crosstalk that increases hepatic glucose production and inhibits peripheral glucose uptake. Despite the high prevalence of glucocorticoid-induced hyperglycaemia associated with their routine clinical use, treatment protocols for optimal management of the metabolic adverse effects are lacking or underutilized. The type, dose and potency of the glucocorticoid administered dictates the choice of hypoglycaemic intervention (non-insulin or insulin therapy) that should be provided to patients. The longstanding quest to identify dissociated glucocorticoid receptor agonists to separate the hyperglycaemic complications of glucocorticoids from their therapeutically beneficial anti-inflammatory effects is ongoing, with selective glucocorticoid receptor modulators in clinical testing. Promising areas of preclinical research include new mechanisms to disrupt glucocorticoid signalling in a tissue-selective manner and the identification of novel targets that can selectively dissociate the effects of glucocorticoids. These research arms share the ultimate goal of achieving the anti-inflammatory actions of glucocorticoids without the metabolic consequences.

Equisetin is an anti-obesity candidate through targeting 11β-HSD1

Obesity is increasingly prevalent globally, searching for therapeutic agents acting on adipose tissue is of great importance. Equisetin (EQST), a meroterpenoid isolated from a marine sponge-derived fungus, has been reported to display antibacterial and antiviral activities. Here, we revealed that EQST displayed anti-obesity effects acting on adipose tissue through inhibiting adipogenesis in vitro and attenuating HFD-induced obesity in mice, doing so without affecting food intake, blood pressure or heart rate. We demonstrated that EQST inhibited the enzyme activity of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), a therapeutic target of obesity in adipose tissue. Anti-obesity properties of EQST were all offset by applying excessive 11β-HSD1's substrates and 11β-HSD1 inhibition through knockdown in vitro or 11β-HSD1 knockout in vivo. In the 11β-HSD1 bypass model constructed by adding excess 11β-HSD1 products, EQST's anti-obesity effects disappeared. Furthermore, EQST directly bond to 11β-HSD1 protein and presented remarkable better intensity on 11β-HSD1 inhibition and better efficacy on anti-obesity than known 11β-HSD1 inhibitor. Therefore, EQST can be developed into anti-obesity candidate compound, and this study may provide more clues for developing higher effective 11β-HSD1 inhibitors.

Effect of Glucocorticoid and 11β-Hydroxysteroid-Dehydrogenase Type 1 (11β-HSD1) in Neurological and Psychiatric Disorders

11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) activity is implicated as a moderator of the progression of multiple diseases and disorders in medicine and is actively subject to investigation as a therapeutic target. Here we summarize the mechanisms of the enzyme and detail the novel agents under investigation. Such agents modulate peripheral cortisol and cortisone levels in hypertension, type 2 diabetes, metabolic disorders, and Alzheimer's disease models, but there is mixed evidence for transduction into symptom management. There is inchoate evidence that 11β-HSD1 modulators may be useful pharmacotherapies for clinical improvement in psychiatry and neurology; however, more research is required.

Effects of Salvianolic acid B on RNA expression and co-expression network of lncRNAs in brown adipose tissue of obese mice

ETHNOPHARMACOLOGICAL RELEVANCE

Salvianolic acid B (SalB) is a polyphenolic compound in Salvia miltiorrhiza Bunge ("Danshen"), which has been largely used in Traditional Chinese Medicine for the treatment of metabolic syndrome, obesity, diabetes, among others.

AIM OF STUDY

This study was to investigate the effects of Salvianolic acid B (SalB) on mRNA, lncRNA and circRNA's expression profile in brown adipose tissue (BAT) of obese mice.

MATERIALS AND METHODS

High-fat-diet induced obese C57BL/6J mice were treated with SalB (100 mg/kg/day) for 8 weeks. Then, BAT was harvested for RNA-Seq analysis. Differentially expressed mRNAs, lncRNAs and circRNAs were analyzed using the Illumina Hiseq 4000. Following this procedure, bioinformatic tools including Gene ontology (GO), KEGG pathway and lncRNA-mRNA co-network analysis were utilized. Finally, RT-qPCR was performed to validate the differentially expressed RNAs.

RESULTS

Compared with control group, 2532 mRNAs, 774 lncRNAs and 25 circRNAs were differentially expressed in SalB group. Additionally, 40 upregulated and 109 downregulated gene-related pathways were identified in the SalB group. Among them, metabolic pathways showed the highest enrichment coefficient in upregulated genes. Moreover, 54 up-regulated and 626 down-regulated coding mRNAs associated with lncRNA-Hsd11b1 and lncRNA-Vmp1.

CONCLUSIONS

SalB may play an anti-obesity role by adjusting the expression of mRNAs correlated with inflammatory response and energy metabolism through regulating the expression of lncRNA-Hsd11b1. The findings of this research provide new directions to study the mechanisms of SalB, and would open therapeutic avenues for the treatment of obesity.

Genomic and Non-Genomic Actions of Glucocorticoids on Adipose Tissue Lipid Metabolism

Glucocorticoids (GCs) are hormones that aid the body under stress by regulating glucose and free fatty acids. GCs maintain energy homeostasis in multiple tissues, including those in the liver and skeletal muscle, white adipose tissue (WAT), and brown adipose tissue (BAT). WAT stores energy as triglycerides, while BAT uses fatty acids for heat generation. The multiple genomic and non-genomic pathways in GC signaling vary with exposure duration, location (adipose tissue depot), and species. Genomic effects occur directly through the cytosolic GC receptor (GR), regulating the expression of proteins related to lipid metabolism, such as ATGL and HSL. Non-genomic effects act through mechanisms often independent of the cytosolic GR and happen shortly after GC exposure. Studying the effects of GCs on adipose tissue breakdown and generation (lipolysis and adipogenesis) leads to insights for treatment of adipose-related diseases, such as obesity, coronary disease, and cancer, but has led to controversy among researchers, largely due to the complexity of the process. This paper reviews the recent literature on the genomic and non-genomic effects of GCs on WAT and BAT lipolysis and proposes research to address the many gaps in knowledge related to GC activity and its effects on disease.

HAND2 is a novel obesity-linked adipogenic transcription factor regulated by glucocorticoid signalling

AIMS/HYPOTHESIS

Adipocytes are critical cornerstones of energy metabolism. While obesity-induced adipocyte dysfunction is associated with insulin resistance and systemic metabolic disturbances, adipogenesis, the formation of new adipocytes and healthy adipose tissue expansion are associated with metabolic benefits. Understanding the molecular mechanisms governing adipogenesis is of great clinical potential to efficiently restore metabolic health in obesity. Here we investigate the role of heart and neural crest derivatives-expressed 2 (HAND2) in adipogenesis.

METHODS

Human white adipose tissue (WAT) was collected from two cross-sectional studies of 318 and 96 individuals. In vitro, for mechanistic experiments we used primary adipocytes from humans and mice as well as human multipotent adipose-derived stem (hMADS) cells. Gene silencing was performed using siRNA or genetic inactivation in primary adipocytes from loxP and or tamoxifen-inducible Cre-ERT2 mouse models with Cre-encoding mRNA or tamoxifen, respectively. Adipogenesis and adipocyte metabolism were measured by Oil Red O staining, quantitative PCR (qPCR), microarray, glucose uptake assay, western blot and lipolysis assay. A combinatorial RNA sequencing (RNAseq) and ChIP qPCR approach was used to identify target genes regulated by HAND2. In vivo, we created a conditional adipocyte Hand2 deletion mouse model using Cre under control of the Adipoq promoter (Hand2AdipoqCre) and performed a large panel of metabolic tests.

RESULTS

We found that HAND2 is an obesity-linked white adipocyte transcription factor regulated by glucocorticoids that was necessary but insufficient for adipocyte differentiation in vitro. In a large cohort of humans, WAT HAND2 expression was correlated to BMI. The HAND2 gene was enriched in white adipocytes compared with brown, induced early in differentiation and responded to dexamethasone (DEX), a typical glucocorticoid receptor (GR, encoded by NR3C1) agonist. Silencing of NR3C1 in hMADS cells or deletion of GR in a transgenic conditional mouse model results in diminished HAND2 expression, establishing that adipocyte HAND2 is regulated by glucocorticoids via GR in vitro and in vivo. Furthermore, we identified gene clusters indirectly regulated by the GR-HAND2 pathway. Interestingly, silencing of HAND2 impaired adipocyte differentiation in hMADS and primary mouse adipocytes. However, a conditional adipocyte Hand2 deletion mouse model using Cre under control of the Adipoq promoter did not mirror these effects on adipose tissue differentiation, indicating that HAND2 was required at stages prior to Adipoq expression.

CONCLUSIONS/INTERPRETATION

In summary, our study identifies HAND2 as a novel obesity-linked adipocyte transcription factor, highlighting new mechanisms of GR-dependent adipogenesis in humans and mice.

DATA AVAILABILITY

Array data have been submitted to the GEO database at NCBI (GSE148699).

Sex Differences in Brown Adipose Tissue Function: Sex Hormones, Glucocorticoids, and Their Crosstalk

Excessive fat accumulation in the body causes overweight and obesity. To date, research has confirmed that there are two types of adipose tissue with opposing functions: lipid-storing white adipose tissue (WAT) and lipid-burning brown adipose tissue (BAT). After the rediscovery of the presence of metabolically active BAT in adults, BAT has received increasing attention especially since activation of BAT is considered a promising way to combat obesity and associated comorbidities. It has become clear that energy homeostasis differs between the sexes, which has a significant impact on the development of pathological conditions such as type 2 diabetes. Sex differences in BAT activity may contribute to this and, therefore, it is important to address the underlying mechanisms that contribute to sex differences in BAT activity. In this review, we discuss the role of sex hormones in the regulation of BAT activity under physiological and some pathological conditions. Given the increasing number of studies suggesting a crosstalk between sex hormones and the hypothalamic-pituitary-adrenal axis in metabolism, we also discuss this crosstalk in relation to sex differences in BAT activity.

Maternal High-Sucrose Diet Affects Phenotype Outcome in Adult Male Offspring: Role of Zbtb16

Overnutrition in pregnancy and lactation affects fetal and early postnatal development, which can result in metabolic disorders in adulthood. We tested a hypothesis that variation of the Zbtb16 gene, a significant energy metabolism regulator, modulates the effect of maternal high-sucrose diet (HSD) on metabolic and transcriptomic profiles of the offspring. We used the spontaneously hypertensive rat (SHR) strain and a minimal congenic rat strain SHR-Zbtb16, carrying the Zbtb16 gene allele originating from the PD/Cub rat, a metabolic syndrome model. Sixteen-week-old SHR and SHR-Zbtb16 rat dams were fed either standard diet (control groups) or a high-sucrose diet (HSD, 70% calories as sucrose) during pregnancy and 4 weeks of lactation. In dams of both strains, we observed an HSD-induced increase of cholesterol and triacylglycerol concentrations in VLDL particles and a decrease of cholesterol and triacylglycerols content in medium to very small LDL particles. In male offspring, exposure to maternal HSD substantially increased brown fat weight in both strains, decreased triglycerides in LDL particles, and impaired glucose tolerance exclusively in SHR. The transcriptome assessment revealed networks of transcripts reflecting the shifts induced by maternal HSD with major nodes including mir-126, Hsd11b1 in the brown adipose tissue, Pcsk9, Nr0b2 in the liver and Hsd11b1, Slc2a4 in white adipose tissue. In summary, maternal HSD feeding during pregnancy and lactation affected brown fat deposition and lipid metabolism in adult male offspring and induced major transcriptome shifts in liver, white, and brown adipose tissues. The Zbtb16 variation present in the SHR-Zbtb16 led to several strain-specific effects of the maternal HSD, particularly the transcriptomic profile shifts of the adult male offspring.

Glucocorticoid-Induced Obesity Develops Independently of UCP1

An excess of glucocorticoids leads to the development of obesity in both mice and humans, but the mechanism for this is unknown. Here, we determine the extent to which decreased BAT thermogenic capacity (as a result of glucocorticoid treatment) contributes to the development of obesity. Contrary to previous suggestions, we show that only in mice housed at thermoneutrality (30°C) does corticosterone treatment reduce total BAT UCP1 protein. This reduction is reflected in reduced brown adipocyte cellular and mitochondrial UCP1-dependent respiration. However, glucocorticoid-induced obesity develops to the same extent in animals housed at 21°C and 30°C, whereas total BAT UCP1 protein levels differ 100-fold between the two groups. In corticosterone-treated wild-type and UCP1 knockout mice housed at 30°C, obesity also develops to the same extent. Thus, our results demonstrate that the development of glucocorticoid-induced obesity is not caused by a decreased UCP1-dependent thermogenic capacity.

Glucocorticoid gene regulation of aquaporin-7

AQP7 is the primary glycerol transporter in white (WAT) and brown (BAT) adipose tissues. There are immediate and quantitatively important actions of cortisone over the expression of AQP7 in murine and human adipocytes. Short-term response (minutes) of cortisone treatment result in an mRNA overexpression in white and brown differentiated adipocytes (between 1.5 and 6 folds). Conversely, long-term response (hours or days) result in decreased mRNA expression. The effects observed on AQP7 mRNA expression upon cortisone treatment in brown and white differentiated adipocytes are concordant with those observed for GK and HSD1B11.

Glucocorticoids and Brown Adipose Tissue: Do glucocorticoids really inhibit thermogenesis?

A reduction in the thermogenic activity of brown adipose tissue (BAT) is presently discussed as a possible determinant for the development of obesity in humans. One group of endogenous factors that could potentially affect BAT activity is the glucocorticoids (e.g. cortisol). We analyse here studies examining the effects of alterations in glucocorticoid signaling on BAT recruitment and thermogenic capacity. We find that irrespective of which manipulation of glucocorticoid signaling is examined, a seemingly homogeneous picture of lowered thermogenic capacity due to glucocorticoid stimulation is apparently obtained: e.g. lowered uncoupling protein 1 (UCP1) protein levels per mg protein, and an increased lipid accumulation in BAT. However, further analyses generally indicate that these effects result from a dilution effect rather than a true decrease in total capacity; the tissue may thus be said to be in a state of pseudo-atrophy. However, under conditions of very low physiological stimulation of BAT, glucocorticoids may truly inhibit Ucp1 gene expression and consequently lower total UCP1 protein levels, but the metabolic effects of this reduction are probably minor. It is thus unlikely that glucocorticoids affect organismal metabolism and induce the development of obesity through alterations of BAT activity.

Clonal derivation of white and brown adipocyte progenitor cell lines from human pluripotent stem cells

BACKGROUND

The role of brown fat in non-shivering thermogenesis and the discovery of brown fat depots in adult humans has made it the subject of intense research interest. A renewable source of brown adipocyte (BA) progenitors would be highly valuable for research and therapy. Directed differentiation of human pluripotent stem (hPS) cells to white or brown adipocytes is limited by lack of cell purity and scalability. Here we describe an alternative approach involving the identification of clonal self-renewing human embryonic progenitor (hEP) cell lines following partial hPS cell differentiation and selection of scalable clones.

METHODS

We screened a diverse panel of hPS cell-derived clonal hEP cell lines for adipocyte markers following growth in adipocyte differentiation medium. The transcriptome of the human hES-derived clonal embryonic progenitor cell lines E3, C4ELS5.1, NP88, and NP110 representing three class of definitive adipocyte progenitors were compared to the relatively non-adipogenic line E85 and adult-derived BAT and SAT-derived cells using gene expression microarrays, RT-qPCR, metabolic analysis and immunocytochemistry. Differentiation conditions were optimized for maximal UCP1 expression.

RESULTS

Many of the differentiated hEP cell lines expressed the adipocyte marker, FAPB4, but only a small subset expressed definitive adipocyte markers including brown adipocyte marker, UCP1. Class I cells (i.e., E3) expressed CITED1, ADIPOQ, and C19orf80 but little to no UCP1. Class II (i.e., C4ELS5.1) expressed CITED1 and UCP1 but little ADIPOQ and LIPASIN. Class III (i.e., NP88, NP110) expressed CITED1, ADIPOQ, C19orf80, and UCP1 in a similar manner as fetal BAT-derived (fBAT) cells. Differentiated NP88 and NP110 lines were closest to fBAT cells morphologically in adiponectin and uncoupling protein expression. But they were more metabolically active than fBAT cells, had higher levels of 3-hydroxybutyrate, and lacked expression of fetal/adult marker, COX7A1. The hEP BA progenitor lines were scalable to 17 passages without loss of differentiation capacity and could be readily rederived.

CONCLUSIONS

Taken together, these data demonstrate that self-renewing adipocyte progenitor cells can be derived from hES cells and that they are functionally like BAT cells but with unique properties that might be advantageous for basic research and for development of cell-based treatments for metabolic diseases.

Glucocorticoid Receptor and Adipocyte Biology

Glucocorticoids are steroid hormones that play a key role in metabolic adaptations during stress, such as fasting and starvation, in order to maintain plasma glucose levels. Excess and chronic glucocorticoid exposure, however, causes metabolic syndrome including insulin resistance, dyslipidemia, and hyperglycemia. Studies in animal models of metabolic disorders frequently demonstrate that suppressing glucocorticoid signaling improves insulin sensitivity and metabolic profiles. Glucocorticoids convey their signals through an intracellular glucocorticoid receptor (GR), which is a transcriptional regulator. The adipocyte is one cell type that contributes to whole body metabolic homeostasis under the influence of GR. Glucocorticoids' functions on adipose tissues are complex. Depending on various physiological or pathophysiological states as well as distinct fat depots, glucocorticoids can either increase or decrease lipid storage in adipose tissues. In rodents, glucocorticoids have been shown to reduce the thermogenic activity of brown adipocytes. However, in human acute glucocorticoid exposure, glucocorticoids act to promote thermogenesis. In this article, we will review the recent studies on the mechanisms underlying the complex metabolic functions of GR in adipocytes. These include studies of the metabolic outcomes of adipocyte specific GR knockout mice and identification of novel GR primary target genes that mediate glucocorticoid action in adipocytes.

Transcription Regulators and Hormones Involved in the Development of Brown Fat and White Fat Browning: Transcriptional and Hormonal Control of Brown/Beige Fat Development

The high prevalence of obesity and related metabolic complications has inspired research on adipose tissues. Three kinds of adipose tissues are identified in mammals: brown adipose tissue (BAT), beige or brite adipose tissue and white adipose tissue (WAT). Beige adipocytes share some characteristics with brown adipocytes such as the expression of UCP1. Beige adipocytes can be activated by environmental stimuli or pharmacological treatment, and this change is accompanied by an increase in energy consumption. This process is called white browning, and it facilitates the maintenance of a lean and healthy phenotype. Thus, promoting beige adipocyte development in WAT shows promise as a new strategy in treating obesity and related metabolic consequences. In this review, we summarized the current understanding of the regulators and hormones that participate in the development of brown fat and white fat browning.

Glucocorticoids Suppress the Browning of Adipose Tissue via miR-19b in Male Mice

Physiological levels of glucocorticoids (GCs) are required for proper metabolic control, and excessive GC action has been linked to a variety of pandemic metabolic diseases. MicroRNA (miRNA)-19b plays a critical role in the pathogenesis of GC-induced metabolic diseases. This study explored the potential of miRNA-based therapeutics targeting adipose tissue. Our results showed that overexpressed miR-19b in stromal vascular fraction (SVF) cells derived from subcutaneous adipose tissue had the same effects as dexamethasone (DEX) treatment on the inhibition of adipose browning and oxygen consumption rate. The inhibition of miR-19b blocked DEX-mediated suppression of the expression of browning marker genes as well as the oxygen consumption rate in differentiated SVF cells derived from subcutaneous and brown adipose tissue. Overexpressed miR-19b in SVF cells derived from brown adipose tissue had the same effects as DEX treatment on the inhibition of brown adipose differentiation and energy expenditure. Glucocorticoids transcriptionally regulate the expression of miR-19b via a GC receptor-mediated direct DNA binding mechanism. This study confirmed that miR-19b is an essential target for GC-mediated control of adipose tissue browning. It is hoped that the plasticity of the adipose organ can be exploited in the next generation of therapeutic strategies to combat the increasing incidence of metabolic diseases, including obesity and diabetes.

LSD1-a pivotal epigenetic regulator of brown and beige fat differentiation and homeostasis

This Outlook discusses the finding by Zeng et al. that LSD1, a histone demethylase, regulates brown adipocyte metabolism in two distinct ways.

In this issue of Genes & Development, Zeng and colleagues (pp. 1822–1836) identify lysine-specific demethylase 1 (LSD1) as a pivotal regulator of whole-body energy expenditure by controlling the oxidative and thermogenic activity of brown adipose tissue (BAT). They show that LSD1 interacts with PRDM16 to repress select white adipose tissue (WAT) genes but also represses hydroxysteroid 11-β-dehydrogenase 1 (HSD11B1) independently of PRDM16 to prevent production of glucocorticoids that impair BAT functions. Their study provides important insight into epigenetic mechanisms regulating the function of BAT.

Human brown adipose tissue-function and therapeutic potential in metabolic disease

There has been a resurgence of interest in brown adipose tissue (BAT) over the last decade. Key to this has been our ability to accurately image it, which has improved significantly. The role of BAT in regulating energy expenditure is important, and its pharmacological manipulation may hold therapeutic potential in metabolic disease. There is ample evidence of BAT activation by cold exposure, and pharmacological utilisation of similar pathways, using B3 receptor agonists holds promise since the development of selective agonists with limited cross-reactivity has rekindled interest. Endogenous agents like irisin, FGF21 and certain gut hormones may hold value as BAT activators. Other agents such as steroid hormones may also hold therapeutic potential, although short-term worsening of metabolic profile remains problematic. Clearly, pharmacological manipulation of BAT is important, and thanks to recent advances we may one day be able to add such agents to our anti-obesity arsenal.

Nuclear Receptor Function through Genomics: Lessons from the Glucocorticoid Receptor

Unlocking the therapeutic potential of the glucocorticoid receptor (GR) has motivated a search for small molecules that selectively modulate its ability to activate or repress gene transcription. Recently, breakthrough studies in the field of genomics have reinvigorated debate over longstanding transcriptional models explaining how GR controls tissue-specific gene expression. Here, we highlight these genomic studies with the dual goals of advancing understanding of nuclear receptor-mediated transcription and stimulating thought on the development of anti-inflammatory and immunosuppressive ligands for GR that have reduced harmful effects on metabolism.

11β-HSD1 Modulates the Set Point of Brown Adipose Tissue Response to Glucocorticoids in Male Mice

Glucocorticoids (GCs) are potent regulators of energy metabolism. Chronic GC exposure suppresses brown adipose tissue (BAT) thermogenic capacity in mice, with evidence for a similar effect in humans. Intracellular GC levels are regulated by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) activity, which can amplify circulating GC concentrations. Therefore, 11β-HSD1 could modulate the impact of GCs on BAT function. This study investigated how 11β-HSD1 regulates the molecular architecture of BAT in the context of GC excess and aging. Circulating GC excess was induced in 11β-HSD1 knockout (KO) and wild-type mice by supplementing drinking water with 100 μg/mL corticosterone, and the effects on molecular markers of BAT function and mitochondrial activity were assessed. Brown adipocyte primary cultures were used to examine cell autonomous consequences of 11β-HSD1 deficiency. Molecular markers of BAT function were also examined in aged 11β-HSD1 KO mice to model lifetime GC exposure. BAT 11β-HSD1 expression and activity were elevated in response to GC excess and with aging. 11β-HSD1 KO BAT resisted the suppression of uncoupling protein 1 (UCP1) and mitochondrial respiratory chain subunit proteins normally imposed by GC excess. Furthermore, brown adipocytes from 11β-HSD1 KO mice had elevated basal mitochondrial function and were able to resist GC-mediated repression of activity. BAT from aged 11β-HSD1 KO mice showed elevated UCP1 protein and mitochondrial content, and a favorable profile of BAT function. These data reveal a novel mechanism in which increased 11β-HSD1 expression, in the context of GC excess and aging, impairs the molecular and metabolic function of BAT.

Mouse aldehyde-oxidase-4 controls diurnal rhythms, fat deposition and locomotor activity

Aldehyde-oxidase-4 (AOX4) is one of the mouse aldehyde oxidase isoenzymes and its physiological function is unknown. The major source of AOX4 is the Harderian-gland, where the enzyme is characterized by daily rhythmic fluctuations. Deletion of the Aox4 gene causes perturbations in the expression of the circadian-rhythms gene pathway, as indicated by transcriptomic analysis. AOX4 inactivation alters the diurnal oscillations in the expression of master clock-genes. Similar effects are observed in other organs devoid of AOX4, such as white adipose tissue, liver and hypothalamus indicating a systemic action. While perturbations of clock-genes is sex-independent in the Harderian-gland and hypothalamus, sex influences this trait in liver and white-adipose-tissue which are characterized by the presence of AOX isoforms other than AOX4. In knock-out animals, perturbations in clock-gene expression are accompanied by reduced locomotor activity, resistance to diet induced obesity and to hepatic steatosis. All these effects are observed in female and male animals. Resistance to obesity is due to diminished fat accumulation resulting from increased energy dissipation, as white-adipocytes undergo trans-differentiation towards brown-adipocytes. Metabolomics and enzymatic data indicate that 5-hydroxyindolacetic acid and tryptophan are novel endogenous AOX4 substrates, potentially involved in AOX4 systemic actions.

Glucocorticoids Acutely Increase Brown Adipose Tissue Activity in Humans, Revealing Species-Specific Differences in UCP-1 Regulation

The discovery of brown adipose tissue (BAT) in adult humans presents a new therapeutic target for metabolic disease; however, little is known about the regulation of human BAT. Chronic glucocorticoid excess causes obesity in humans, and glucocorticoids suppress BAT activation in rodents. We tested whether glucocorticoids regulate BAT activity in humans. In vivo, the glucocorticoid prednisolone acutely increased (18)fluorodeoxyglucose uptake by BAT (measured using PET/CT) in lean healthy men during mild cold exposure (16°C-17°C). In addition, prednisolone increased supraclavicular skin temperature (measured using infrared thermography) and energy expenditure during cold, but not warm, exposure in lean subjects. In vitro, glucocorticoids increased isoprenaline-stimulated respiration and UCP-1 in human primary brown adipocytes, but substantially decreased isoprenaline-stimulated respiration and UCP-1 in primary murine brown and beige adipocytes. The highly species-specific regulation of BAT function by glucocorticoids may have important implications for the translation of novel treatments to activate BAT to improve metabolic health.

Lipopolysaccharide challenge significantly influences lipid metabolism and proteome of white adipose tissue in growing pigs

Background

White adipose tissue is recognized as a highly active organ, which is closely related to a large number of physiological and metabolic processes besides storing triglycerides. However, little is known regarding the response of adipose tissue to acute inflammation. Therefore, in this study we employed growing pigs to investigate the changes of lipid metabolism and proteome in white adipose tissue after lipopolysaccharide (LPS) stimulation as a model for bacterial infection.

Methods

The expression of lipid metabolism and inflammation related genes was determined by quantitative real-time polymerase chain reaction. Label-free proteomics analysis was used to investigate changes of the protein profile in white adipose tissue and western blot was used to verify changes of selected adipokines.

Results

The results indicated that LPS significantly increased the expression of toll-like receptor (TLR) 2/4 pathway-related genes and pro-inflammatory factors. Lipid metabolism related genes, including acetyl-CoA carboxylase 1 (ACACA), fatty acid synthase (FASN), stearoyl-CoA desaturase (SCD), uncoupling protein 2 (UCP2), and 11 β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), were down-regulated and the lipolytic enzyme activity was decreased after LPS injection. Proteome analysis revealed 47 distinct proteins with > 2-fold changes. The down-regulation of two proteins (cAMP-dependent protein kinase type II-alpha regulatory subunit and β-tubulin) has been verified by western blot analysis. In addition, the abundance of two adipokines (adiponectin and zinc-α2-glycoprotein) was significantly increased after LPS injection.

Conclusion

In conclusion, LPS challenge can cause acute inflammation in white adipose tissue. Concurrently, lipid metabolism was significantly suppressed and the abundance of several proteins changed in white adipose tissue. The results provide new clues to understand the adipose dysfunction during inflammation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-015-0067-5) contains supplementary material, which is available to authorized users.

Adipocyte glucocorticoid receptors mediate fat-to-brain signaling

Stress-related (e.g., depression) and metabolic pathologies (e.g., obesity) are important and often co-morbid public health concerns. Here we identify a connection between peripheral glucocorticoid receptor (GR) signaling originating in fat with the brain control of both stress and metabolism. Mice with reduced adipocyte GR hypersecrete glucocorticoids following acute psychogenic stress and are resistant to diet-induced obesity. This hypersecretion gives rise to deficits in responsiveness to exogenous glucocorticoids, consistent with reduced negative feedback via adipocytes. Increased stress reactivity occurs in the context of elevated hypothalamic expression of hypothalamic-pituitary-adrenal (HPA) axis-excitatory neuropeptides and in the absence of altered adrenal sensitivity, consistent with a central cite of action. Our results identify a novel mechanism whereby activation of the adipocyte GR promotes peripheral energy storage while inhibiting the HPA axis, and provide functional evidence for a fat-to-brain regulatory feedback network that serves to regulate not just homeostatic energy balance but also responses to psychogenic stimuli.

The brown fat secretome: metabolic functions beyond thermogenesis

Brown fat is highly active in fuel oxidation and dissipates chemical energy through uncoupling protein (UCP)1-mediated heat production. Activation of brown fat leads to increased energy expenditure, reduced adiposity, and lower plasma glucose and lipid levels, thus contributing to better homeostasis. Uncoupled respiration and thermogenesis have been considered to be responsible for the metabolic benefits of brown adipose tissue. Recent studies have demonstrated that brown adipocytes also secrete factors that act locally and systemically to influence fuel and energy metabolism. This review discusses the evidence supporting a thermogenesis-independent role of brown fat, particularly through its release of secreted factors, and their implications in physiology and therapeutic development.

Glucocorticoids transcriptionally regulate miR-27b expression promoting body fat accumulation via suppressing the browning of white adipose tissue

Long-term glucocorticoid (GC) treatment induces central fat accumulation and metabolic dysfunction. We demonstrate that microRNA-27b (miR-27b) plays a central role in the pathogenesis of GC-induced central fat accumulation. Overexpression of miR-27b had the same effects as dexamethasone (DEX) treatment on the inhibition of brown adipose differentiation and the energy expenditure of primary adipocytes. Conversely, antagonizing miR-27b function prevented DEX suppression of the expression of brown adipose tissue-specific genes. GCs transcriptionally regulate miR-27b expression through a GC receptor-mediated direct DNA-binding mechanism, and miR-27b suppresses browning of white adipose tissue (WAT) by targeting the three prime untranslated region of Prdm16. In vivo, antagonizing miR-27b function in DEX-treated mice resulted in the efficient induction of brown adipocytes within WAT and improved GC-induced central fat accumulation. Collectively, these results indicate that miR-27b functions as a central target of GC and as an upstream regulator of Prdm16 to control browning of WAT and, consequently, may represent a potential target in preventing obesity.

Effects of glucocorticoids on human brown adipocytes

Clinical cases of glucocorticoid (GC) excess are characterized by increased fat mass and obesity through the accumulation of white adipocytes. The effects of GCs on growth and function of brown adipose tissue are unknown and may contribute to the negative energy balance observed clinically. This study aims to evaluate the effect of GCs on proliferation, differentiation, and metabolic function of brown adipocytes. Human brown adipocytes sourced from supraclavicular fat biopsies were grown in culture and differentiated to mature adipocytes. Human white adipocytes sourced from subcutaneous abdominal fat biopsies were cultured as controls. Effects of dexamethasone on growth, differentiation (UCP1, CIDEA, and PPARGC1A expression), and function (oxygen consumption rate (OCR)) of brown adipocytes were quantified. Dexamethasone (1 μM) significantly stimulated the proliferation of brown preadipocytes and reduced that of white preadipocytes. During differentiation, dexamethasone (at 0.1, 1, and 10 μM) stimulated the expression of UCP1, CIDEA, and PPARGC1A in a concentration-dependent manner and enhanced by fourfold to sixfold the OCR of brown adipocytes. Isoprenaline (100 nM) significantly increased (P<0.05) expression of UCP1 and OCR of brown adipocytes. These effects were significantly reduced (P<0.05) by dexamethasone. Thus, we show that dexamethasone stimulates the proliferation, differentiation, and function of human brown adipocytes but inhibits adrenergic stimulation of the functioning of brown adipocytes. We conclude that GCs exert complex effects on development and function of brown adipocytes. These findings provide strong evidence for an effect of GCs on the biology of human brown adipose tissue (BAT) and for the involvement of the BAT system in the metabolic manifestation of Cushing's syndrome.

A neuron-specific deletion of the microRNA-processing enzyme DICER induces severe but transient obesity in mice

MicroRNAs (miRNAs) are small, non-coding RNA molecules that regulate gene expression post-transcriptionally. MiRNAs are implicated in various biological processes associated with obesity, including adipocyte differentiation and lipid metabolism. We used a neuronal-specific inhibition of miRNA maturation in adult mice to study the consequences of miRNA loss on obesity development. Camk2a-CreERT2 (Cre⁺) and floxed Dicer (Dicer^lox/lox) mice were crossed to generate tamoxifen-inducible conditional Dicer knockouts (cKO). Vehicle- and/or tamoxifen-injected Cre⁺;Dicer^lox/lox and Cre⁺;Dicer^+/+ served as controls. Four cohorts were used to a) measure body composition, b) follow food intake and body weight dynamics, c) evaluate basal metabolism and effects of food deprivation, and d) assess the brain transcriptome consequences of miRNA loss. cKO mice developed severe obesity and gained 18 g extra weight over the 5 weeks following tamoxifen injection, mainly due to increased fat mass. This phenotype was highly reproducible and observed in all 38 cKO mice recorded and in none of the controls, excluding possible effects of tamoxifen or the non-induced transgene. Development of obesity was concomitant with hyperphagia, increased food efficiency, and decreased activity. Surprisingly, after reaching maximum body weight, obese cKO mice spontaneously started losing weight as rapidly as it was gained. Weight loss was accompanied by lowered O₂-consumption and respiratory-exchange ratio. Brain transcriptome analyses in obese mice identified several obesity-related pathways (e.g. leptin, somatostatin, and nemo-like kinase signaling), as well as genes involved in feeding and appetite (e.g. Pmch, Neurotensin) and in metabolism (e.g. Bmp4, Bmp7, Ptger1, Cox7a1). A gene cluster with anti-correlated expression in the cerebral cortex of post-obese compared to obese mice was enriched for synaptic plasticity pathways. While other studies have identified a role for miRNAs in obesity, we here present a unique model that allows for the study of processes involved in reversing obesity. Moreover, our study identified the cortex as a brain area important for body weight homeostasis.

Enzymatic intracrine regulation of white adipose tissue

Abdominal fat formation has become a permanent risk factor for metabolic syndrome and various cancers in one-third of the world's population of obese and even lean patients. Formation of abdominal fat involves additional mechanisms beyond an imbalance in energy intake and expenditure, which explains systemic obesity. In this review, we briefly summarized autonomous regulatory circuits that locally produce hormones from inactive precursors or nutrients for intra-/auto-/paracrine signaling in white adipose depots. Enzymatic pathways activating steroid and thyroid hormones in adipose depots were compared with enzymatic production of retinoic acid from vitamin A. We discussed the role of intracrine circuits in fat-depot functions and strategies to reduce abdominal adiposity through thermogenic adipocytes with interrupted generation of retinoic acid.

Mechanisms of glucocorticoid-induced insulin resistance: focus on adipose tissue function and lipid metabolism

Glucocorticoids (GCs) are critical in the regulation of the stress response, inflammation and energy homeostasis. Excessive GC exposure results in whole-body insulin resistance, obesity, cardiovascular disease, and ultimately decreased survival, despite their potent anti-inflammatory effects. This apparent paradox may be explained by the complex actions of GCs on adipose tissue functionality. The wide prevalence of oral GC therapy makes their adverse systemic effects an important yet incompletely understood clinical problem. This article reviews the mechanisms by which supraphysiologic GC exposure promotes insulin resistance, focusing in particular on the effects on adipose tissue function and lipid metabolism.

Nutritional manipulations in the perinatal period program adipose tissue in offspring

Epidemiological studies demonstrated initially that maternal undernutrition results in low birth weight with increased risk for long-lasting energy balance disorders. Maternal obesity and diabetes associated with high birth weight, excessive nutrition in neonates, and rapid catchup growth also increase the risk of adult-onset obesity. As stated by the Developmental Origin of Health and Disease concept, nutrient supply perturbations in the fetus or neonate result in long-term programming of individual body weight set point. Adipose tissue is a key fuel storage unit involved mainly in the maintenance of energy homeostasis. Studies in numerous animal models have demonstrated that the adipose tissue is the focus of developmental programming events in a sex- and depot-specific manner. In rodents, adipose tissue development is particularly active during the perinatal period, especially during the last week of gestation and during early postnatal life. In contrast to rodents, this process essentially takes place before birth in bigger mammals. Despite these different developmental time windows, altricial and precocial species share several mechanisms of adipose tissue programming. Offspring from malnourished dams present adipose tissue with a series of alterations: impaired glucose uptake, insulin and leptin resistance, low-grade inflammation, modified sympathetic activity with reduced noradrenergic innervations, and thermogenesis. These modifications reprogram adipose tissue metabolism by changing fat distribution and composition and by enhancing adipogenesis, predisposing the offspring to fat accumulation. Subtle adipose tissue circadian rhythm changes are also observed. Inappropriate hormone levels, modified tissue sensitivity (especially glucocorticoid system), and epigenetic mechanisms are key factors for adipose tissue programming during the perinatal period.