FGF6 and FGF9 regulate UCP1 expression independent of brown adipogenesis.

Uncoupling protein-1 (UCP1) plays a central role in energy dissipation in brown adipose tissue (BAT). Using high-throughput library screening of secreted peptides, we identify two fibroblast growth factors (FGF), FGF6 and FGF9, as potent inducers of UCP1 expression in adipocytes and preadipocytes. Surprisingly, this occurs through a mechanism independent of adipogenesis and involves FGF receptor-3 (FGFR3), prostaglandin-E2 and interaction between estrogen receptor-related alpha, flightless-1 (FLII) and leucine-rich-repeat-(in FLII)-interacting-protein-1 as a regulatory complex for UCP1 transcription. Physiologically, FGF6/9 expression in adipose is upregulated by exercise and cold in mice, and FGF9/FGFR3 expression in human neck fat is significantly associated with UCP1 expression. Loss of FGF9 impairs BAT thermogenesis. In vivo administration of FGF9 increases UCP1 expression and thermogenic capacity. Thus, FGF6 and FGF9 are adipokines that can regulate UCP1 through a transcriptional network that is dissociated from brown adipogenesis, and act to modulate systemic energy metabolism.

TGF-ß2 is an exercise-induced adipokine that regulates glucose and fatty acid metabolism.

Exercise improves health and well-being across diverse organ systems, and elucidating mechanisms underlying the beneficial effects of exercise can lead to new therapies. Here, we show that transforming growth factor-ß2 (TGF-ß2) is secreted from adipose tissue in response to exercise and improves glucose tolerance in mice. We identify TGF-ß2 as an exercise-induced adipokine in a gene expression analysis of human subcutaneous adipose tissue biopsies after exercise training. In mice, exercise training increases TGF-ß2 in scWAT, serum, and its secretion from fat explants. Transplanting scWAT from exercise-trained wild type mice, but not from adipose tissue-specific Tgfb2-/- mice, into sedentary mice improves glucose tolerance. TGF-ß2 treatment reverses the detrimental metabolic effects of high fat feeding in mice. Lactate, a metabolite released from muscle during exercise, stimulates TGF-ß2 expression in human adipocytes. Administration of the lactate-lowering agent dichloroacetate during exercise training in mice decreases circulating TGF-ß2 levels and reduces exercise-stimulated improvements in glucose tolerance. Thus, exercise training improves systemic metabolism through inter-organ communication with fat via a lactate-TGF-ß2-signaling cycle.

PKA-RIIB Deficiency Induces Brown Fatlike Adipocytes in Inguinal WAT and Promotes Energy Expenditure in Male FVB/NJ Mice.

Obesity has become the most common metabolic disorder worldwide. Promoting brown adipose tissue (BAT) and beige adipose tissue formation, and therefore, a functional increase in energy expenditure, may counteract obesity. Mice lacking type IIß regulatory subunit of adenosine 3',5' cyclic monophosphate (cAMP)-dependent protein kinase A (PKA-RIIB) display reduced adiposity and resistance to diet-induced obesity. PKA-RIIB, encoded by the Prkar2b gene, is most abundant in BAT and white adipose tissue (WAT) and in the brain. In this study, we show that mice lacking PKA-RIIB have increased energy expenditure, limited weight gain, and improved glucose metabolism. PKA-RIIB deficiency induces brownlike adipocyte in inguinal WAT (iWAT). PKA-RIIB deficiency also increases the expression of uncoupling protein 1 and other thermogenic genes in iWAT and primary preadipocytes from iWAT through a mechanism involving increased PKA activity, which is represented by increased phosphorylation of PKA substrate, cAMP response element binding protein, and P38 mitogen-activated protein kinase. Our study provides evidence for the role of PKA-RIIB deficiency in regulating thermogenesis in WAT, which may potentially have therapeutic implications for the treatment of obesity and related metabolic disorders.

Loss of BMP receptor type 1A in murine adipose tissue attenuates age-related onset of insulin resistance.

AIMS/HYPOTHESIS: Adipose tissue dysfunction is a prime risk factor for the development of metabolic disease. Bone morphogenetic proteins (BMPs) have previously been implicated in adipocyte formation. Here, we investigate the role of BMP signalling in adipose tissue health and systemic glucose homeostasis. METHODS: We employed the Cre/loxP system to generate mouse models with conditional ablation of BMP receptor 1A in differentiating and mature adipocytes, as well as tissue-resident myeloid cells. Metabolic variables were assessed by glucose and insulin tolerance testing, insulin-stimulated glucose uptake and gene expression analysis. RESULTS: Conditional deletion of Bmpr1a using the aP2 (also known as Fabp4)-Cre strain resulted in a complex phenotype. Knockout mice were clearly resistant to age-related impairment of insulin sensitivity during normal and high-fat-diet feeding and showed significantly improved insulin-stimulated glucose uptake in brown adipose tissue and skeletal muscle. Moreover, knockouts displayed significant reduction of variables of adipose tissue inflammation. Deletion of Bmpr1a in myeloid cells had no impact on insulin sensitivity, while ablation of Bmpr1a in mature adipocytes partially recapitulated the initial phenotype from aP2-Cre driven deletion. Co-cultivation of macrophages with pre-adipocytes lacking Bmpr1a markedly reduced expression of proinflammatory genes. CONCLUSIONS/INTERPRETATION: Our findings show that altered BMP signalling in adipose tissue affects the tissue's metabolic properties and systemic insulin resistance by altering the pattern of immune cell infiltration. The phenotype is due to ablation of Bmpr1a specifically in pre-adipocytes and maturing adipocytes rather than an immune cell-autonomous effect. Mechanistically, we provide evidence for a BMP-mediated direct crosstalk between pre-adipocytes and macrophages.

Genetic and functional characterization of clonally derived adult human brown adipocytes.

Brown adipose tissue (BAT) acts in mammals as a natural defense system against hypothermia, and its activation to a state of increased energy expenditure is believed to protect against the development of obesity. Even though the existence of BAT in adult humans has been widely appreciated, its cellular origin and molecular identity remain elusive largely because of high cellular heterogeneity within various adipose tissue depots. To understand the nature of adult human brown adipocytes at single cell resolution, we isolated clonally derived adipocytes from stromal vascular fractions of adult human BAT from two individuals and globally analyzed their molecular signatures. We used RNA sequencing followed by unbiased genome-wide expression analyses and found that a population of uncoupling protein 1 (UCP1)-positive human adipocytes possessed molecular signatures resembling those of a recruitable form of thermogenic adipocytes (that is, beige adipocytes). In addition, we identified molecular markers that were highly enriched in UCP1-positive human adipocytes, a set that included potassium channel K3 (KCNK3) and mitochondrial tumor suppressor 1 (MTUS1). Further, we functionally characterized these two markers using a loss-of-function approach and found that KCNK3 and MTUS1 were required for beige adipocyte differentiation and thermogenic function. The results of this study present new opportunities for human BAT research, such as facilitating cell-based disease modeling and unbiased screens for thermogenic regulators.

The effect of neuropeptide Y on brown-like adipocyte's differentiation and activation.

Despite its wide distribution in the central nervous system, the presence of Neuropeptide Y (NPY) in peripheral tissues has been detected. White adipose tissue (WAT) is a new site of NPY synthesis and secretion. The development of brown-like adipocytes in WAT is controlled by hypothalamic NPY neurons through interaction with sympathetic nervous system (SNS). However, whether peripheral NPY has a direct effect on induction of the Uncoupling protein1 (UCP1)-positive adipocytes is unknown. We have used adipocytes derived from C3H10T1/2 stem cells as a model of brown-like adipocyte, and investigated the role of NPY in their differentiation and activation. In general, NPY had no effect on brown adipogenesis of C3H10T1/2 stem cell, but suppressed db-cAMP activation of brown-like adipocytes, which was due to blunting brown fat-relevant gene expression and mitochondrial function. NPY showed suppression in a receptor-dependent manner, inhibition of endogenous cAMP production and cAMP-PKA-dependent pathways p38 MAPK and CREB phosphorylation were involved in the downstream mechanisms. A novel role of NPY in the peripheral is presented, which may help decrease energy expenditure in WAT of obese subjects.

IRF4 is a key thermogenic transcriptional partner of PGC-1α.

Brown fat can reduce obesity through the dissipation of calories as heat. Control of thermogenic gene expression occurs via the induction of various coactivators, most notably PGC-1α. In contrast, the transcription factor partner(s) of these cofactors are poorly described. Here, we identify interferon regulatory factor 4 (IRF4) as a dominant transcriptional effector of thermogenesis. IRF4 is induced by cold and cAMP in adipocytes and is sufficient to promote increased thermogenic gene expression, energy expenditure, and cold tolerance. Conversely, knockout of IRF4 in UCP1(+) cells causes reduced thermogenic gene expression and energy expenditure, obesity, and cold intolerance. IRF4 also induces the expression of PGC-1α and PRDM16 and interacts with PGC-1α, driving Ucp1 expression. Finally, cold, ß-agonists, or forced expression of PGC-1α are unable to cause thermogenic gene expression in the absence of IRF4. These studies establish IRF4 as a transcriptional driver of a program of thermogenic gene expression and energy expenditure.

The prevalence and predictors of active brown adipose tissue in Chinese adults.

OBJECTIVE: Previous studies have shown that active brown adipose tissue (BAT) is present in adults and may play important roles in the regulation of energy homeostasis. However, nearly every study has been carried out in patients undergoing scanning for cancer surveillance (CS), whose metabolism and BAT activity may not reflect those of healthy individuals. The objective of this study was to investigate the prevalence and predictors of active BAT in Chinese adults, particularly in healthy individuals. DESIGN: A total of 31,088 consecutive subjects aged ≥18 years who had undergone positron emission tomography/computed tomography (PET/CT) scanning of BAT were evaluated in this study. METHODS: We measured BAT activity via (18)F-fluorodeoxyglucose PET/CT in subjects who had undergone scanning for either a routine medical checkup (MC) or CS in Shanghai. Then, we investigated the predictors of active BAT, particularly in healthy individuals. RESULTS: In both groups, the prevalence of BAT was higher in women than in men. Using a multivariate logistic analysis, we found age, sex, BMI, and high thyroid glucose uptake to be significant predictors of BAT activity in the MC group. Similarly, we found age, sex, and BMI to be significant predictors of BAT activity, but not thyroid high glucose uptake, in the CS group. CONCLUSIONS: In Chinese adults, BAT activity inversely correlates with BMI and thyroid high glucose uptake, which reinforces the central role of brown fat in adult metabolism and provides clues to a potential means for treating the metabolic syndrome.

Differences in the metabolic status of healthy adults with and without active brown adipose tissue.

BACKGROUND: Previous studies have proven the existence of active brown adipose tissue (BAT) in adults; however, its effect on systematic metabolism remains unclear. AIM: The current study was designed to investigate the differences in the metabolic profiles of healthy adults with and without active BAT using positron emission tomography-computed tomography (PET-CT) scans in the un-stimulated state. METHODS: A cross-sectional analysis was performed to assess the health of adults using PET-CT whole-body scans at Huashan Hospital Medical Centre between November 2009 and May 2010. A total of 62 healthy adults with active BAT were enrolled in the BAT-positive group. For each positive subject, a same-gender individual who underwent PET-CT the same day and who had no detectable BAT was chosen as the negative control. Body composition was measured, and blood samples were collected for assays of metabolic profiles and other biomarkers. RESULTS: In both the male and female groups, BAT-positive individuals were younger and had lower body mass indexes, fasting insulin, insulin resistance, and leptin, but a greater level of high-density lipoprotein cholesterol compared with the negative controls. In the male group, body fat content and levels of tumor necrosis factor-α were significantly lower in the BAT-positive than in the negative control group. CONCLUSIONS: The healthy adults with active BAT in an un-stimulated state had favorable metabolic profiles suggesting that active BAT may be a potential target for preventing and treating obesity and other metabolic disorders.