Neuronal Control of Brown Fat Activity

Analysis of Heart Rate Variability in Newborns Dogs with Different Types of Delivery during the First 35 Days of Life

The present study aimed to evaluate the influence of the autonomic nervous system on cardiovascular function during the first 35 days of life in different types of delivery, using heart rate variability (HRV) indices. Thirty newborns were equally divided into two groups based on delivery type: eutocic delivery (EG) and emergency cesarean section (CG). Electrocardiographic evaluation was performed at birth (T0), 24 h postpartum (T1), and at 7, 14, 21, 28, and 35 days of life (T2 to T6). Physical parameters, neonatal reflexes, and Apgar scores were recorded. Over 35 days, the values of the time domain indices were higher in the GE group and increased with age. In the frequency domain, the low frequency (LF) index was higher in the CG, and the opposite occurred for the high frequency (HF) index. Since the CG presented lower HRV than the EG, it was shown that the type of delivery should be considered for the assessment of autonomic nervous system activity in neonates. Thus, as predictive factors of vitality, HRV and Apgar scores can help in the face of neonatal depression, demonstrating that delivery by emergency cesarean section can predispose newborns to delays in the autonomic influence on the heart.

Betanin from Beetroot (Beta vulgaris L.) Regulates Lipid Metabolism and Promotes Fat Browning in 3T3-L1 Adipocytes

Fat browning, which converts white adipose tissue to brown, has attracted attention as a promising strategy for the treatment of obesity. Betanin (BT) has been reported to have potential anti-obesity activity. 3T3-L1 cells were differentiated for 7 days during BT treatment. The BT concentration range for the study was determined using an MTT assay, and lipid accumulation was evaluated by Oil-Red-O staining. The expression of protein level was analyzed by Western blot. Immunofluorescence images were performed with confocal microscopy to visually show the amount and location of thermogenesis factor uncoupling protein1 (UCP1) and mitochondria. qRT-PCR was performed to evaluate mRNA expression. BT inhibited lipid accumulation and increased the expression of UCP1, peroxisome-proliferator-activated receptor gamma (PPARγ), and PPARγ coactivator-1 alpha (PGC-1α). In addition, the increases in beige adipocyte-specific markers were observed, supporting BT-mediated browning of the fat tissue. The UCP1 was localized in the inner membrane of the mitochondria, and its expression was associated with mitochondrial activation. Consistent with this, the mRNA expression of mitochondrial biogenesis markers increased in 3T3-L1 cells after BT treatment. Immunofluorescence staining also indicated an increased number of mitochondria and UCP1, respectively. Moreover, BT inhibited lipogenesis and enhanced lipolysis and fatty acid oxidation. This mechanism has been suggested to be mediated by an adenosine monophosphate-activated protein kinase (AMPK) pathway. BT induces fat browning and regulates lipid metabolism via the AMPK-mediated pathway in 3T3-L1 cells, suggesting that BT can be a promising candidate for controlling obesity.

Adipocyte G Protein-Coupled Receptors as Potential Targets for Novel Antidiabetic Drugs

The functional state of adipocytes plays a central role in regulating numerous important metabolic functions, including energy and glucose homeostasis. While white adipocytes store excess calories as fat (triglycerides) and release free fatty acids as a fuel source in times of need, brown and beige adipocytes (so-called thermogenic adipocytes) convert chemical energy stored in substrates (e.g., fatty acids or glucose) into heat, thus promoting energy expenditure. Like all other cell types, adipocytes express many G protein-coupled receptors (GPCRs) that are linked to four major functional classes of heterotrimeric G proteins (Gs, Gi/o, Gq/11, and G12/13). During the past few years, novel experimental approaches, including the use of chemogenetic strategies, have led to a series of important new findings regarding the metabolic consequences of activating or inhibiting distinct GPCR/G protein signaling pathways in white, brown, and beige adipocytes. This novel information should guide the development of novel drugs capable of modulating the activity of specific adipocyte GPCR signaling pathways for the treatment of obesity, type 2 diabetes, and related metabolic disorders.

Temperature dysregulation during therapeutic hypothermia predicts long-term outcome in neonates with HIE

Few reliable or easily obtainable biomarkers to predict long-term outcome in infants with hypoxic-ischemic encephalopathy (HIE) have been identified. We previously showed that mattress temperature (MT), as proxy for disturbed temperature regulation during therapeutic hypothermia (TH), predicts injury on early MRI and holds promise as physiologic biomarker. To determine whether MT in neonates treated with TH for moderate-severe HIE is associated with long-term outcome at 18-22 months, we performed a secondary analysis of the Optimizing Cooling trial using MT data from 167 infants treated at a core temperature of 33.5°C. Median MTs from four time-epochs (0-6 h, 6-24 h, 24-48 h, and 48-72 h of TH) were used to predict death or moderate-severe neurodevelopmental impairment (NDI), using epoch-specific derived and validated MT cutoffs. Median MT of infants who died or survived with NDI was consistently 1.5-3.0°C higher throughout TH. Infants requiring a median MT above the derived cut-offs had a significantly increased odds of death or NDI, most notably at 0-6 h (aOR 17.0, 95%CI 4.3-67.4). By contrast, infants who remained below cut-offs across all epochs had 100% NDI-free survival. MTs in neonates with moderate-severe HIE during TH are highly predictive of long-term outcome and can be used as physiologic biomarker.

Fibroblastic reticular cells in lymph node potentiate white adipose tissue beiging through neuro-immune crosstalk in male mice

Lymph nodes (LNs) are always embedded in the metabolically-active white adipose tissue (WAT), whereas their functional relationship remains obscure. Here, we identify fibroblastic reticular cells (FRCs) in inguinal LNs (iLNs) as a major source of IL-33 in mediating cold-induced beiging and thermogenesis of subcutaneous WAT (scWAT). Depletion of iLNs in male mice results in defective cold-induced beiging of scWAT. Mechanistically, cold-enhanced sympathetic outflow to iLNs activates β1- and β2-adrenergic receptor (AR) signaling in FRCs to facilitate IL-33 release into iLN-surrounding scWAT, where IL-33 activates type 2 immune response to potentiate biogenesis of beige adipocytes. Cold-induced beiging of scWAT is abrogated by selective ablation of IL-33 or β1- and β2-AR in FRCs, or sympathetic denervation of iLNs, whereas replenishment of IL-33 reverses the impaired cold-induced beiging in iLN-deficient mice. Taken together, our study uncovers an unexpected role of FRCs in iLNs in mediating neuro-immune interaction to maintain energy homeostasis.

4D-Printed Soft and Stretchable Self-Folding Cuff Electrodes for Small-Nerve Interfacing

Peripheral nerve interfacing (PNI) has a high clinical potential for treating various diseases, such as obesity or diabetes. However, currently existing electrodes present challenges to the interfacing procedure, which limit their clinical application, in particular, when targeting small peripheral nerves (<200 µm). To improve the electrode handling and implantation, a nerve interface that can fold itself to a cuff around a small nerve, triggered by the body moisture during insertion, is fabricated. This folding is achieved by printing a bilayer of a flexible polyurethane printing resin and a highly swelling sodium acrylate hydrogel using photopolymerization. When immersed in an aqueous liquid, the hydrogel swells and folds the electrode softly around the nerve. Furthermore, the electrodes are robust, can be stretched (>20%), and bent to facilitate the implantation due to the use of soft and stretchable printing resins as substrates and a microcracked gold film as conductive layer. The straightforward implantation and extraction of the electrode as well as stimulation and recording capabilities on a small peripheral nerve in vivo are demonstrated. It is believed that such simple and robust to use self-folding electrodes will pave the way for bringing PNI to a broader clinical application.

Stimulation of the beta-2-adrenergic receptor with salbutamol activates human brown adipose tissue

While brown adipose tissue (BAT) is activated by the beta-3-adrenergic receptor (ADRB3) in rodents, in human brown adipocytes, the ADRB2 is dominantly present and responsible for noradrenergic activation. Therefore, we performed a randomized double-blinded crossover trial in young lean men to compare the effects of single intravenous bolus of the ADRB2 agonist salbutamol without and with the ADRB1/2 antagonist propranolol on glucose uptake by BAT, assessed by dynamic 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography-computed tomography scan (i.e., primary outcome). Salbutamol, compared with salbutamol with propranolol, increases glucose uptake by BAT, without affecting the glucose uptake by skeletal muscle and white adipose tissue. The salbutamol-induced glucose uptake by BAT positively associates with the increase in energy expenditure. Notably, participants with high salbutamol-induced glucose uptake by BAT have lower body fat mass, waist-hip ratio, and serum LDL-cholesterol concentration. In conclusion, specific ADRB2 agonism activates human BAT, which warrants investigation of ADRB2 activation in long-term studies (EudraCT: 2020-004059-34).

Light modulates glucose metabolism by a retina-hypothalamus-brown adipose tissue axis

Public health studies indicate that artificial light is a high-risk factor for metabolic disorders. However, the neural mechanism underlying metabolic modulation by light remains elusive. Here, we found that light can acutely decrease glucose tolerance (GT) in mice by activation of intrinsically photosensitive retinal ganglion cells (ipRGCs) innervating the hypothalamic supraoptic nucleus (SON). Vasopressin neurons in the SON project to the paraventricular nucleus, then to the GABAergic neurons in the solitary tract nucleus, and eventually to brown adipose tissue (BAT). Light activation of this neural circuit directly blocks adaptive thermogenesis in BAT, thereby decreasing GT. In humans, light also modulates GT at the temperature where BAT is active. Thus, our work unveils a retina-SON-BAT axis that mediates the effect of light on glucose metabolism, which may explain the connection between artificial light and metabolic dysregulation, suggesting a potential prevention and treatment strategy for managing glucose metabolic disorders.

Chronic Intermittent Hypoxia during Sleep Causes Browning of Interscapular Adipose Tissue Accompanied by Local Insulin Resistance in Mice

Obstructive sleep apnea (OSA) is a highly prevalent condition, characterized by intermittent hypoxia (IH), sleep disruption, and altered autonomic nervous system function. OSA has been independently associated with dyslipidemia, insulin resistance, and metabolic syndrome. Brown adipose tissue (BAT) has been suggested as a modulator of systemic glucose tolerance through adaptive thermogenesis. Reductions in BAT mass have been associated with obesity and metabolic syndrome. No studies have systematically characterized the effects of chronic IH on BAT. Thus, we aimed to delineate IH effects on BAT and concomitant metabolic changes. C57BL/6J 8-week-old male mice were randomly assigned to IH during sleep (alternating 90 s cycles of 6.5% F_IO₂ followed by 21% F_IO₂) or normoxia (room air, RA) for 10 weeks. Mice were subjected to glucose tolerance testing and ¹⁸F-FDG PET-MRI towards the end of the exposures followed by BAT tissues analyses for morphological and global transcriptomic changes. Animals exposed to IH were glucose intolerant despite lower total body weight and adiposity. BAT tissues in IH-exposed mice demonstrated characteristic changes associated with "browning"-smaller lipids, increased vascularity, and a trend towards higher protein levels of UCP1. Conversely, mitochondrial DNA content and protein levels of respiratory chain complex III were reduced. Pro-inflammatory macrophages were more abundant in IH-exposed BAT. Transcriptomic analysis revealed increases in fatty acid oxidation and oxidative stress pathways in IH-exposed BAT, along with a reduction in pathways related to myogenesis, hypoxia, and IL-4 anti-inflammatory response. Functionally, IH-exposed BAT demonstrated reduced absorption of glucose on PET scans and reduced phosphorylation of AKT in response to insulin. Current studies provide initial evidence for the presence of a maladaptive response of interscapular BAT in response to chronic IH mimicking OSA, resulting in a paradoxical divergence, namely, BAT browning but tissue-specific and systemic insulin resistance. We postulate that oxidative stress, mitochondrial dysfunction, and inflammation may underlie these dichotomous outcomes in BAT.

Brain-to-BAT - and Back?: Crosstalk between the Central Nervous System and Thermogenic Adipose Tissue in Development and Therapy of Obesity

The body of mammals harbors two distinct types of adipose tissue: while cells within the white adipose tissue (WAT) store surplus energy as lipids, brown adipose tissue (BAT) is nowadays recognized as the main tissue for transforming chemical energy into heat. This process, referred to as 'non-shivering thermogenesis', is facilitated by the uncoupling of the electron transport across mitochondrial membranes from ATP production. BAT-dependent thermogenesis acts as a safeguarding mechanism under reduced ambient temperature but also plays a critical role in metabolic and energy homeostasis in health and disease. In this review, we summarize the evolutionary structure, function and regulation of the BAT organ under neuronal and hormonal control and discuss its mutual interaction with the central nervous system. We conclude by conceptualizing how better understanding the multifaceted communicative links between the brain and BAT opens avenues for novel therapeutic approaches to treat obesity and related metabolic disorders.

Decreased Frequency of Mental Workload-Induced Subjective Hot Flashes Through Gum Massage: An Open-Label, Self-Controlled Crossover Trial

Objective:

Hot flashes, a symptom of menopause, can decrease women's quality of life. Sympathetic nervous system activation has been identified as an important factor in the occurrence of hot flashes. Given that somatosensory stimulation of the oral cavity can affect autonomic nervous activity, we aimed to investigate the possibility that somatosensory stimulation of the gums (i.e., gum massage) could improve hot flashes.

Materials and Methods:

Nineteen women experiencing at least one hot flash per day were instructed to perform a gum massage on themselves before undertaking mental workload, using arithmetic task, and the frequency of hot flashes experienced during this task was measured. Changes in autonomic nervous activity were assessed based on heart rate variability.

Results:

Massage conditions promoted a significantly lower arithmetic task-induced hot flash frequency compared with nonmassage conditions (p < 0.05). During gum massage, the ratio between low and high frequency (LF/HF) values decreased significantly under massage conditions compared with nonmassage conditions (p < 0.01). During the arithmetic task, the gum massage-induced reduction in LF/HF, which changed from baseline, was significantly correlated with the gum massage-induced reduction in hot flash frequency.

Conclusions:

The results of this study indicate that gum massage can reduce the subjective frequency of hot flashes over a certain period under mental workload. Our study also indicates that gum massage can potentially decrease sympathetic nerve activity, which is known to be involved in the occurrence of hot flashes.

Clinical Trial Registration number 328 (the institutional review board of Lion Corporation).

Liraglutide Activates Type 2 Deiodinase and Enhances β3-Adrenergic-Induced Thermogenesis in Mouse Adipose Tissue

Aims

Liraglutide is a long-acting glucagon-like peptide 1 (GLP-1) receptor agonist used as an anti-hyperglycemic agent in type 2 diabetes treatment and recently approved for obesity management. Weight loss is attributed to appetite suppression, but therapy may also increase energy expenditure. To further investigate the effect of GLP-1 signaling in thermogenic fat, we assessed adipose tissue oxygen consumption and type 2 deiodinase (D2) activity in mice treated with liraglutide, both basally and after β3-adrenergic treatment.

Methods

Male C57BL/6J mice were randomly assigned to receive liraglutide (400 μg/kg, n=12) or vehicle (n=12). After 16 days, mice in each group were co-treated with the selective β3-adrenergic agonist CL316,243 (1 mg/kg, n=6) or vehicle (n=6) for 5 days. Adipose tissue depots were assessed for gene and protein expression, oxygen consumption, and D2 activity.

Results

Liraglutide increased interscapular brown adipose tissue (iBAT) oxygen consumption and enhanced β3-adrenergic-induced oxygen consumption in iBAT and inguinal white adipose tissue (ingWAT). These effects were accompanied by upregulation of UCP-1 protein levels in iBAT and ingWAT. Notably, liraglutide increased D2 activity without significantly upregulating its mRNA levels in iBAT and exhibited additive effects to β3-adrenergic stimulation in inducing D2 activity in ingWAT.

Conclusions

Liraglutide exhibits additive effects to those of β3-adrenergic stimulation in thermogenic fat and increases D2 activity in BAT, implying that it may activate this adipose tissue depot by increasing intracellular thyroid activation, adding to the currently known mechanisms of GLP-1A-induced weight loss.

Sympathetic nerve-adipocyte interactions in response to acute stress

Psychological stress predisposes our body to several disorders. Understanding the cellular and molecular mechanisms involved in the physiological responses to psychological stress is essential for the success of therapeutic applications. New studies show, by using in vivo inducible Cre/loxP-mediated approaches in combination with pharmacological blockage, that sympathetic nerves, activated by psychological stress, induce brown adipocytes to produce IL-6. Strikingly, this cytokine promotes gluconeogenesis in hepatocytes, that results in the decline of tolerance to inflammatory organ damage. The comprehension arising from this research will be crucial for the handling of many inflammatory diseases. Here, we review recent advances in our comprehension of the sympathetic nerve-adipocyte axis in the tissue microenvironment.

Circadian control of brown adipose tissue

Disruption of circadian (~24 h) rhythms is associated with an increased risk of cardiometabolic diseases. Therefore, unravelling how circadian rhythms are regulated in different metabolic tissues has become a prominent research focus. Of particular interest is brown adipose tissue (BAT), which combusts triglyceride-derived fatty acids and glucose into heat and displays a circannual and diurnal rhythm in its thermogenic activity. In this review, the genetic, neuronal and endocrine generation of these rhythms in BAT is discussed. In addition, the potential risks of disruption or attenuation of these rhythms in BAT, and possible factors influencing these rhythms, are addressed.

Ablation of Sam68 in adult mice increases thermogenesis and energy expenditure

Genetic deletion of Src associated in mitosis of 68kDa (Sam68), a pleiotropic adaptor protein prevents high-fat diet-induced weight gain and insulin resistance. To clarify the role of Sam68 in energy metabolism in the adult stage, we generated an inducible Sam68 knockout mice. Knockout of Sam68 was induced at the age of 7-10 weeks, and then we examined the metabolic profiles of the mice. Sam68 knockout mice gained less body weight over time and at 34 or 36 weeks old, had smaller fat mass without changes in food intake and absorption efficiency. Deletion of Sam68 in mice elevated thermogenesis, increased energy expenditure, and attenuated core-temperature drop during acute cold exposure. Furthermore, we examined younger Sam68 knockout mice at 11 weeks old before their body weights deviate, and confirmed increased energy expenditure and thermogenic gene program. Thus, Sam68 is essential for the control of adipose thermogenesis and energy homeostasis in the adult.

Central nervous system regulation of organismal energy and glucose homeostasis

Growing evidence implicates the brain in the regulation of both immediate fuel availability (for example, circulating glucose) and long-term energy stores (that is, adipose tissue mass). Rather than viewing the adipose tissue and glucose control systems separately, we suggest that the brain systems that control them are components of a larger, highly integrated, 'fuel homeostasis' control system. This conceptual framework, along with new insights into the organization and function of distinct neuronal systems, provides a context within which to understand how metabolic homeostasis is achieved in both basal and postprandial states. We also review evidence that dysfunction of the central fuel homeostasis system contributes to the close association between obesity and type 2 diabetes, with the goal of identifying more effective treatment options for these common metabolic disorders.

Brown Adipose Tissue: New Challenges for Prevention of Childhood Obesity. A Narrative Review

Pediatric obesity remains a challenge in modern society. Recently, research has focused on the role of the brown adipose tissue (BAT) as a potential target of intervention. In this review, we revised preclinical and clinical works on factors that may promote BAT or browning of white adipose tissue (WAT) from fetal age to adolescence. Maternal lifestyle, type of breastfeeding and healthy microbiota can affect the thermogenic activity of BAT. Environmental factors such as exposure to cold or physical activity also play a role in promoting and activating BAT. Most of the evidence is preclinical, although in clinic there is some evidence on the role of omega-3 PUFAs (EPA and DHA) supplementation on BAT activation. Clinical studies are needed to dissect the early factors and their modulation to allow proper BAT development and functions and to prevent onset of childhood obesity.

Reduced brown adipose tissue activity during cold exposure is a metabolic feature of the human thrifty phenotype

BACKGROUND

We recently demonstrated that thrifty subjects, characterized by a greater decrease in 24 h energy expenditure (24hEE) during short-term fasting, have less capacity for cold-induced thermogenesis (CIT) during 24 h of mild cold exposure.

OBJECTIVE

As cold-induced brown adipose tissue activation (CIBA) is a determinant of CIT, we sought to investigate whether thrifty individuals also have reduced CIBA.

METHODS

Twenty-four healthy subjects (age: 29.8 ± 9.5y, body fat: 27.3 ± 12.4%, 63% male) were admitted to our clinical research unit and underwent two 24hEE assessments in a whole-room indirect calorimeter during energy balance and fasting conditions at thermoneutrality to quantify their degree of thriftiness. Positron emission tomography/computed tomography scans were performed after exposure to 16 °C for 2 h to quantify peak CIBA.

RESULTS

A greater decrease in 24hEE during fasting was associated with lower peak CIBA (r = 0.50, p = 0.01), such that a 100 kcal/day greater reduction in 24hEE related to an average 3.2 g/mL lower peak CIBA.

CONCLUSION

Our results indicate that reduced CIBA is a metabolic trait of the thrifty phenotype which might explain reduced CIT capacity and greater predisposition towards weight gain in individuals with a thrifty metabolism.

Adipose Tissue Immunomodulation: A Novel Therapeutic Approach in Cardiovascular and Metabolic Diseases

Adipose tissue is a critical regulator of systemic metabolism and bodily homeostasis as it secretes a myriad of adipokines, including inflammatory and anti-inflammatory cytokines. As the main storage pool of lipids, subcutaneous and visceral adipose tissues undergo marked hypertrophy and hyperplasia in response to nutritional excess leading to hypoxia, adipokine dysregulation, and subsequent low-grade inflammation that is characterized by increased infiltration and activation of innate and adaptive immune cells. The specific localization, physiology, susceptibility to inflammation and the heterogeneity of the inflammatory cell population of each adipose depot are unique and thus dictate the possible complications of adipose tissue chronic inflammation. Several lines of evidence link visceral and particularly perivascular, pericardial, and perirenal adipose tissue inflammation to the development of metabolic syndrome, insulin resistance, type 2 diabetes and cardiovascular diseases. In addition to the implication of the immune system in the regulation of adipose tissue function, adipose tissue immune components are pivotal in detrimental or otherwise favorable adipose tissue remodeling and thermogenesis. Adipose tissue resident and infiltrating immune cells undergo metabolic and morphological adaptation based on the systemic energy status and thus a better comprehension of the metabolic regulation of immune cells in adipose tissues is pivotal to address complications of chronic adipose tissue inflammation. In this review, we discuss the role of adipose innate and adaptive immune cells across various physiological and pathophysiological states that pertain to the development or progression of cardiovascular diseases associated with metabolic disorders. Understanding such mechanisms allows for the exploitation of the adipose tissue-immune system crosstalk, exploring how the adipose immune system might be targeted as a strategy to treat cardiovascular derangements associated with metabolic dysfunctions.

GADD45α drives brown adipose tissue formation through upregulating PPARγ in mice

Stress can lead to obesity and metabolic dysfunction, but the underlying mechanisms are unclear. Here we identify GADD45α, a stress-inducible histone folding protein, as a potential regulator for brown adipose tissue biogenesis. Unbiased transcriptomics data indicate a positive correlation between adipose Gadd45a mRNA level and obesity. At the cellular level, Gadd45a knockdown promoted proliferation and lipolysis of brown adipocytes, while Gadd45a overexpression had the opposite effects. Consistently, using a knockout (Gadd45a^−/−) mouse line, we found that GADD45α deficiency inhibited lipid accumulation and promoted expression of thermogenic genes in brown adipocytes, leading to improvements in insulin sensitivity, glucose uptake, energy expenditure. At the molecular level, GADD45α deficiency increased proliferation through upregulating expression of cell cycle related genes. GADD45α promoted brown adipogenesis via interacting with PPARγ and upregulating its transcriptional activity. Our new data suggest that GADD45α may be targeted to promote non-shivering thermogenesis and metabolism while counteracting obesity.

Dose threshold for radiation induced fetal programming in a mouse model at 4 months of age: Hepatic expression of genes and proteins involved in glucose metabolism and glucose uptake in brown adipose tissue

Exposure to ionizing radiation contributing to negative health outcomes is a widespread concern. However, the impact of low dose and sub-lethal dose radiation (SLDR) exposures remain contentious, particularly in pregnant women who represent a vulnerable group. The fetal programming hypothesis states that an adverse in utero environment or stress during development of an embryo or fetus can result in permanent physiologic changes often resulting in progressive metabolic dysfunction with age. To assess changes in gene expression profiles of glucose/insulin signaling and lipid metabolism caused by radiation exposure in utero, pregnant C57Bl/6J mice were irradiated using a dose response ranging from low dose to SLDR and compared to a Sham-irradiated group. mRNA expression analysis in 16 week old offspring (n = 84) revealed that genes involved in metabolic function including glucose metabolism, insulin signaling and lipid metabolism were unaffected by prenatal radiation exposures up to 300 mGy. However, female offspring of dams exposed to 1000 mGy had upregulated expression of genes contributing to insulin resistance and gluconeogenesis. In a second cohort of mice, the effects of SLDR on fetal programming of hepatic SOCS3 and PEPCK protein expression were assessed. 4 month old female offspring of dams irradiated at 1000 mGy had: 1) increased liver weights, 2) increased hepatic expression of proteins involved in glucose metabolism and 3) increased ¹⁸F-fluorodeoxyglucose (FDG) uptake in interscapular brown adipose tissue (IBAT) measured by positron emission tomography (PET) (n = 25). The results of this study indicate that prenatal radiation exposure does not affect metabolic function up to 300 mGy and 1000 mGy may be a threshold dose for sex-specific alterations in glucose uptake and hepatic gene and protein expression of SOCS3, PEPCK, PPARGC1A and PPARGC1B. These findings suggest that SLDR doses alter glucose uptake in IBAT and hepatic gene and protein expression of offspring and these changes may progress with age.

Sex differences on adipose tissue remodeling: from molecular mechanisms to therapeutic interventions

Sexual dimorphism greatly influences adipose tissue remodeling, which is characterized by changes in the activity, number, and/or size of adipocytes in response to distinct stimuli, including lifestyle and anti-obesity drugs. This sex dependence seems to be due to the anatomical and endocrine disparities between men and women. At the molecular level, sex hormones are believed to mediate such differences and involve estrogen and androgen receptor-induced gene expression. The signaling pathways that regulate adipose tissue metabolism and function include peroxisome proliferator-activated receptor gamma, uncoupling protein 1 (UCP1), 5' adenosine monophosphate-activated protein kinase (AMPK), and mitochondrial oxidative phosphorylation (OXPHOS), among other molecular players. Sex hormone-related pathways also interplay with adrenergic signaling, probably the most well-characterized molecular mechanism implicated in the remodeling of white adipose tissue. This review overviews and integrates the signaling pathways behind sexual dimorphism in adipose tissue remodeling, hoping to increase the knowledge on the pathogenesis of diseases, such as obesity and related comorbidities, and consequently, to drive future studies to investigate the regulation of this tissue homeostasis, either in men or women.

Role of Neuro-Immune Cross-Talk in the Anti-obesity Effect of Electro-Acupuncture

There is evidence to show that electro-acupuncture (EA) has a promotive effect on both lipolysis and thermogenesis, and that these mechanisms underlie the anti-obesity effect of EA. The sympathetic nervous system (SNS) is known to play a role in thermogenesis. Additionally, obesity is characterized by a chronic low-grade inflammatory state. Based on these findings, the aim of the present study is to investigate the potential neuro-immune mechanisms underlying the therapeutic effect of EA in obesity. In the experiment, we used a high fat diet (HFD) rats model to study the effect of EA in reducing body weight. EA increases the activity of sympathetic nerves in inguinal white adipose tissue (iWAT), especially in the HFD group. Compared to HFD rats, EA can decrease sympathetic associated macrophage (SAM) and the level of norepinephrine transporter protein (Slc6a2). The relative uncoupling protein 1 expression shows EA increases thermogenesis in iWAT, and increases β3 receptors. Interestingly, injecting β antagonist in iWAT increases Slc6a2 protein levels. Additionally, the SNS-macrophage cross-talk response to EA showed in iWAT but not in epididymis white adipose tissue. The results of the present study indicate that EA exerts its anti-obesity effect via three mechanisms: (1) inhibition of SAMs and the norepinephrine transporter protein SlC6a2, (2) promoting SNS activity and thermogenesis, and (3) regulating immunologic balance.

Role of Mineralocorticoid Receptor in Adipogenesis and Obesity in Male Mice

Increased visceral adiposity and hyperglycemia, 2 characteristics of metabolic syndrome, are also present in conditions of excess glucocorticoids (GCs). GCs are hormones thought to act primarily via the glucocorticoid receptor (GR). GCs are commonly prescribed for inflammatory disorders, yet their use is limited due to many adverse metabolic side effects. In addition to GR, GCs also bind the mineralocorticoid receptor (MR), but there are many conflicting studies about the exact role of MR in metabolic disease. Using MR knockout mice (MRKO), we find that both white and brown adipose depots form normally when compared with wild-type mice at P5. We created mice with adipocyte-specific deletion of MR (FMRKO) to better understand the role of MR in metabolic dysfunction. Treatment of mice with excess GCs for 4 weeks, via corticosterone in drinking water, induced increased fat mass and glucose intolerance to similar levels in FMRKO and floxed control mice. Separately, when fed a high-fat diet for 16 weeks, FMRKO mice had reduced body weight, fat mass, and hepatic steatosis, relative to floxed control mice. Decreased adiposity likely resulted from increased energy expenditure since food intake was not different. RNA sequencing analysis revealed decreased enrichment of genes associated with adipogenesis in inguinal white adipose of FMRKO mice. Differentiation of mouse embryonic fibroblasts (MEFs) showed modestly impaired adipogenesis in MRKO MEFs compared with wild type, but this was rescued upon the addition of peroxisome proliferator-activated receptor gamma (PPARγ) agonist or PPARγ overexpression. Collectively, these studies provide further evidence supporting the potential value of MR as a therapeutic target for conditions associated with metabolic syndrome.

Inflammatory Signaling and Brown Fat Activity

Obesity is characterized by a state of chronic inflammation in adipose tissue mediated by the secretion of a range of inflammatory cytokines. In comparison to WAT, relatively little is known about the inflammatory status of brown adipose tissue (BAT) in physiology and pathophysiology. Because BAT and brown/beige adipocytes are specialized in energy expenditure they have protective roles against obesity and associated metabolic diseases. BAT appears to be is less susceptible to developing inflammation than WAT. However, there is increasing evidence that inflammation directly alters the thermogenic activity of brown fat by impairing its capacity for energy expenditure and glucose uptake. The inflammatory microenvironment can be affected by cytokines secreted by immune cells as well as by the brown adipocytes themselves. Therefore, pro-inflammatory signals represent an important component of the thermogenic potential of brown and beige adipocytes and may contribute their dysfunction in obesity.

Caulis Spatholobi Ameliorates Obesity through Activating Brown Adipose Tissue and Modulating the Composition of Gut Microbiota

Obesity is associated with disrupted energy homeostasis and intestinal dysbiosis. Caulis Spatholobi, traditional Chinese medicine for herbal therapy, contains a wide range of bioactive compounds and has a specific pharmacological function. However, its effects on obesity and related metabolic disorder have remained largely unexplored. In this study, we showed that the water extract of Caulis Spatholobi (WECS) has a significant effect in inhibiting body weight gain, decreasing adiposity, maintaining glucose homeostasis, reducing insulin resistance and improving hepatic steatosis in diet-introduced obesity (DIO) mice. Besides, the administration of WECS significantly increased the expression levels of genes involved in the brown adipose tissue (BAT) activation and thermogenesis in DIO mice. Also, the activation of BAT treated with WECS was also confirmed in BAT primary cells. Mechanisms, the improvement of glucose homeostasis and insulin resistance may be related to the upregulated MAPK and AMPK pathways in white adipose tissue (WAT) and BAT. Notably, WECS also improved the obesity-induced gut microbiota dysbiosis, which induced an increase of anti-obesity and anti-diabetes related bacteria genus. In conclusion, Caulis Spatholobi can ameliorate obesity through activating brown adipose tissue and modulating the composition of gut microbiota. Our findings provide a novel perspective on Chinese medicine applications and provide a promising therapeutic approach for the treatment of obesity and metabolic disorders.

Heart Failure With Preserved Ejection Fraction and Adipose Tissue: A Story of Two Tales

Heart failure with preserved ejection fraction (HFpEF) is characterized by signs and symptoms of heart failure in the presence of a normal left ventricular ejection fraction. Although it accounts for up to 50% of all clinical presentations of heart failure, there are no evidence-based therapies for HFpEF to reduce morbidity and mortality. Additionally there is a lack of mechanistic understanding about the pathogenesis of HFpEF. HFpEF is associated with many comorbidities (such as obesity, hypertension, type 2 diabetes, atrial fibrillation, etc.) and is coupled with both cardiac and extra-cardiac abnormalities. Large outcome trials and registries reveal that being obese is a major risk factor for HFpEF. There is increasing focus on investigating the link between obesity and HFpEF, and the role that the adipose tissue and the heart, and the circulating milieu play in development and pathogenesis of HFpEF. This review discusses features of the obese-HFpEF phenotype and highlights proposed mechanisms implicated in the inter-tissue communication between adipose tissue and the heart in obesity-associated HFpEF.

Distinct ipRGC subpopulations mediate light's acute and circadian effects on body temperature and sleep

The light environment greatly impacts human alertness, mood, and cognition by both acute regulation of physiology and indirect alignment of circadian rhythms. These processes require the melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs), but the relevant downstream brain areas involved remain elusive. ipRGCs project widely in the brain, including to the central circadian pacemaker, the suprachiasmatic nucleus (SCN). Here we show that body temperature and sleep responses to acute light exposure are absent after genetic ablation of all ipRGCs except a subpopulation that projects to the SCN. Furthermore, by chemogenetic activation of the ipRGCs that avoid the SCN, we show that these cells are sufficient for acute changes in body temperature. Our results challenge the idea that the SCN is a major relay for the acute effects of light on non-image forming behaviors and identify the sensory cells that initiate light's profound effects on body temperature and sleep.

Melatonin multiple effects on brown adipose tissue molecular machinery

Brown adipose tissue (BAT) influences energy balance through nonshivering thermogenesis, and its metabolism daily and seasonal variations are regulated by melatonin through partially known mechanisms. We evaluated the role of melatonin in BAT molecular machinery of male Control, pinealectomized (PINX), and melatonin-treated pinealectomized (PINX/Mel) adult rats. BAT was collected either every 3 hours over 24 hours or after cold or high-fat diet (HFD) acute exposure. HFD PINX animals presented decreased Dio2 expression, while HFD PINX/Mel animals showed increased Dio2, Ucp1, and Cidea expression. Cold-exposed PINX rats showed decreased Dio2 and Lhs expression, and melatonin treatment augmented Adrβ3, Dio2, Ucp1, and Cidea expression. Daily profiles analyses showed altered Dio2, Lhs, Ucp1, Pgc1α, and Cidea gene and UCP1 protein expression in PINX animals, leading to altered rhythmicity under sub-thermoneutral conditions, which was partially restored by melatonin treatment. The same was observed for mitochondrial complexes I, II, and IV protein expression and enzyme activity. Melatonin absence seems to impair BAT responses to metabolic challenges, and melatonin replacement reverses this effect, with additional increase in the expression of crucial genes, suggesting that melatonin plays an important role in several key points of the thermogenic activation pathway, influencing both the rhythmic profile of the tissue and its ability to respond to metabolic challenges, which is crucial for the organism homeostasis.

Brain to bone: What is the contribution of the brain to skeletal homeostasis?

The brain, which governs most, if not all, physiological functions in the body, from the complexities of cognition, learning and memory, to the regulation of basal body temperature, heart rate and breathing, has long been known to affect skeletal health. In particular, the hypothalamus - located at the base of the brain in close proximity to the medial eminence, where the blood-brain-barrier is not as tight as in other regions of the brain but rather "leaky", due to fenestrated capillaries - is exposed to a variety of circulating body cues, such as nutrients (glucose, fatty acids, amino acids), and hormones (insulin, glucagon, leptin, adiponectin) [1-3].Information collected from the body via these peripheral cues is integrated by hypothalamic sensing neurons and glial cells [4-7], which express receptors for these nutrients and hormones, transforming these cues into physiological outputs. Interestingly, many of the same molecules, including leptin, adiponectin and insulin, regulate both energy and skeletal homeostasis. Moreover, they act on a common set of hypothalamic nuclei and their residing neurons, activating endocrine and neuronal systems, which ultimately fine-tune the body to new physiological states. This review will focus exclusively on the brain-to-bone pathway, highlighting the most important anatomical sites within the brain, which are known to affect bone, but not covering the input pathways and molecules informing the brain of the energy and bone metabolic status, covered elsewhere [8-10]. The discussion in each section will present side by side the metabolic and bone-related functions of hypothalamic nuclei, in an attempt to answer some of the long-standing questions of whether energy is affected by bone remodeling and homeostasis and vice versa.

Membrane-Initiated Estrogen Receptor Signaling Mediates Metabolic Homeostasis via Central Activation of Protein Phosphatase 2A

Women gain weight and their diabetes risk increases as they transition through menopause; these changes can be partly reversed by hormone therapy. However, the underlying molecular mechanisms mediating these effects are unknown. A novel knock-in mouse line with the selective blockade of the membrane-initiated estrogen receptor (ER) pathway was used, and we found that the lack of this pathway precipitated excessive weight gain and glucose intolerance independent of food intake and that this was accompanied by impaired adaptive thermogenesis and reduced physical activity. Notably, the central activation of protein phosphatase (PP) 2A improved metabolic disorders induced by the lack of membrane-initiated ER signaling. Furthermore, the antiobesity effect of estrogen replacement in a murine menopause model was abolished by central PP2A inactivation. These findings define a critical role for membrane-initiated ER signaling in metabolic homeostasis via the central action of PP2A.

Genetic Targeting of GRP78 in the VMH Improves Obesity Independently of Food Intake

Recent data have demonstrated that the hypothalamic GRP78/BiP (glucose regulated protein 78 kDa/binding immunoglobulin protein) modulates brown adipose tissue (BAT) thermogenesis by acting downstream on AMP-activated protein kinase (AMPK). Herein, we aimed to investigate whether genetic over-expression of GRP78 in the ventromedial nucleus of the hypothalamus (VMH: a key site regulating thermogenesis) could ameliorate very high fat diet (vHFD)-induced obesity. Our data showed that stereotaxic treatment with adenoviruses harboring GRP78 in the VMH reduced hypothalamic endoplasmic reticulum ER stress and reversed vHFD-induced obesity. Herein, we also demonstrated that this body weight decrease was more likely associated with an increased BAT thermogenesis and browning of white adipose tissue (WAT) than to anorexia. Overall, these results indicate that the modulation of GRP78 in the VMH may be a target against obesity.

Butyrate reduces appetite and activates brown adipose tissue via the gut-brain neural circuit

OBJECTIVE

Butyrate exerts metabolic benefits in mice and humans, the underlying mechanisms being still unclear. We aimed to investigate the effect of butyrate on appetite and energy expenditure, and to what extent these two components contribute to the beneficial metabolic effects of butyrate.

DESIGN

Acute effects of butyrate on appetite and its method of action were investigated in mice following an intragastric gavage or intravenous injection of butyrate. To study the contribution of satiety to the metabolic benefits of butyrate, mice were fed a high-fat diet with butyrate, and an additional pair-fed group was included. Mechanistic involvement of the gut-brain neural circuit was investigated in vagotomised mice.

RESULTS

Acute oral, but not intravenous, butyrate administration decreased food intake, suppressed the activity of orexigenic neurons that express neuropeptide Y in the hypothalamus, and decreased neuronal activity within the nucleus tractus solitarius and dorsal vagal complex in the brainstem. Chronic butyrate supplementation prevented diet-induced obesity, hyperinsulinaemia, hypertriglyceridaemia and hepatic steatosis, largely attributed to a reduction in food intake. Butyrate also modestly promoted fat oxidation and activated brown adipose tissue (BAT), evident from increased utilisation of plasma triglyceride-derived fatty acids. This effect was not due to the reduced food intake, but explained by an increased sympathetic outflow to BAT. Subdiaphragmatic vagotomy abolished the effects of butyrate on food intake as well as the stimulation of metabolic activity in BAT.

CONCLUSION

Butyrate acts on the gut-brain neural circuit to improve energy metabolism via reducing energy intake and enhancing fat oxidation by activating BAT.

Chronic infusion of taurolithocholate into the brain increases fat oxidation in mice

Bile acids can function in the postprandial state as circulating signaling molecules in the regulation of glucose and lipid metabolism via the transmembrane receptor TGR5 and nuclear receptor FXR. Both receptors are present in the central nervous system, but their function in the brain is unclear. Therefore, we investigated the effects of intracerebroventricular (i.c.v.) administration of taurolithocholate (tLCA), a strong TGR5 agonist, and GW4064, a synthetic FXR agonist, on energy metabolism. We determined the effects of chronic i.c.v. infusion of tLCA, GW4064, or vehicle on energy expenditure, body weight and composition as well as tissue specific fatty acid uptake in mice equipped with osmotic minipumps. We found that i.c.v. administration of tLCA (final concentration in cerebrospinal fluid: 1 μM) increased fat oxidation (tLCA group: 0.083 ± 0.006 vs control group: 0.036 ± 0.023 kcal/h, F = 5.46, P = 0.04) and decreased fat mass (after 9 days of tLCA infusion: 1.35 ± 0.13 vs controls: 1.96 ± 0.23 g, P = 0.03). These changes were associated with enhanced uptake of triglyceride-derived fatty acids by brown adipose tissue and with browning of subcutaneous white adipose tissue. I.c.v. administration of GW4064 (final concentration in cerebrospinal fluid: 10 μM) did not affect energy metabolism, body composition nor bile acid levels, negating a role of FXR in the central nervous system in metabolic control. In conclusion, bile acids such as tLCA may exert metabolic effects on fat metabolism via the brain.

Brown Adipose Tissue in Human Infants

Adapting to the cold extrauterine environment after birth is a great challenge for the newborn. Due to their high surface area-to-volume ratio, infants tend to lose more heat to the environment as compared to adults. In addition, human newborns lack sufficiently developed skeletal muscle mass to maintain body temperature through shivering thermogenesis, an important source of heat in cold-exposed adults. Evolution has provided humans and other placental mammals with brown adipose tissue (BAT), a tissue that converts chemically stored energy, in the form of fatty acids and glucose, into heat through non-shivering thermogenesis. The thermogenic activity of this tissue is significant for the human infant's ability to maintain a sufficiently high core body temperature. Although BAT has been studied in human infants for more than a century, the literature covering different aspects of the tissue is rather limited. The aim of this review is to summarize the literature and describe what is actually known about the tissue and its importance for early human life.

Selective Glucocorticoid Receptor Antagonist CORT125281 Activates Brown Adipose Tissue and Alters Lipid Distribution in Male Mice

Glucocorticoids influence a wide range of metabolic processes in the human body, and excessive glucocorticoid exposure is known to contribute to the development of metabolic disease. We evaluated the utility of the novel glucocorticoid receptor (GR) antagonist CORT125281 for its potential to overcome adiposity, glucose intolerance, and dyslipidemia and compared this head-to-head with the classic GR antagonist RU486 (mifepristone). We show that, although RU486 displays cross-reactivity to the progesterone and androgen receptor, CORT125281 selectively inhibits GR transcriptional activity. In a mouse model for diet-induced obesity, rhythmicity of circulating corticosterone levels was disturbed. CORT125281 restored this disturbed rhythmicity, in contrast to RU486, which further inhibited endogenous corticosterone levels and suppressed adrenal weight. Both CORT125281 and RU486 reduced body weight gain and fat mass. In addition, CORT125281, but not RU486, lowered plasma levels of triglycerides, cholesterol, and free fatty acids and strongly stimulated triglyceride-derived fatty acid uptake by brown adipose tissue depots. In combination with reduced lipid content in brown adipocytes, this indicates that CORT125281 enhances metabolic activity of brown adipose tissue depots. CORT125281 was also found to increase liver lipid accumulation. Taken together, CORT125281 displayed a wide range of beneficial metabolic activities that are in part distinct from RU486, but clinical utility may be limited due to liver lipid accumulation. This warrants further evaluation of GR antagonists or selective modulators that are not accompanied by liver lipid accumulation while preserving their beneficial metabolic activities.

Hypothalamic ΔFosB prevents age-related metabolic decline and functions via SNS

The ventral hypothalamus (VHT) integrates several physiological cues to maintain glucose homeostasis and energy balance. Aging is associated with increased glucose intolerance but the underlying mechanisms responsible for age-related metabolic decline, including neuronal signaling in the VHT, remain elusive. We have shown that mice with VHT-targeted overexpression of ∆FosB, a splice variant of the AP1 transcription factor FosB, exhibit increased energy expenditure, leading to decreased adiposity. Here, we show that VHT-targeted overexpression of ∆FosB also improves glucose tolerance, increases insulin sensitivity in target organs and thereby suppresses insulin secretion. These effects are also observed by the overexpression of dominant negative JunD, demonstrating that they occur via AP1 antagonism within the VHT. Furthermore, the improved glucose tolerance and insulin sensitivity persisted in aged animals overexpressing ∆FosB in the VHT. These beneficial effects on glucose metabolism were abolished by peripheral sympathectomy and α-adrenergic, but not β-adrenergic, blockade. Taken together, our results show that antagonizing AP1 transcription activity in the VHT leads to a marked improvement in whole body glucose homeostasis via activation of the SNS, conferring protection against age-related impairment in glucose metabolism. These findings may open novel avenues for therapeutic intervention in diabetes and age-related glucose intolerance.

The suprachiasmatic nucleus drives day-night variations in postprandial triglyceride uptake into skeletal muscle and brown adipose tissue

NEW FINDINGS

What is the central question of this study? What are the factors influencing day-night variations in postprandial triglycerides? What is the main finding and its importance? Rats show low postprandial plasma triglyceride concentrations early in the active period that are attributable to a higher uptake by skeletal muscle and brown adipose tissue. We show that these day-night variations in uptake are driven by the suprachiasmatic nucleus, probably via a Rev-erbα-mediated mechanism and independent of locomotor activity. These findings highlight that the suprachiasmatic nucleus has a major role in day-night variations in plasma triglycerides and that disturbances in our biological clock might be an important risk factor contributing to development of postprandial hyperlipidaemia. Energy metabolism follows a diurnal pattern, mainly driven by the suprachiasmatic nucleus (SCN), and disruption of circadian regulation has been linked to metabolic abnormalities. Indeed, epidemiological evidence shows that night work is a risk factor for cardiovascular disease, and postprandial hyperlipidaemia is an important contributor. Therefore, the aim of this work was to investigate the factors that drive day-night variations in postprandial triglycerides (TGs). Intact and SCN-lesioned male Wistar rats were subjected to an oral fat challenge during the beginning of the rest phase (day) or the beginning of the active phase (night). The plasma TG profile was evaluated and tissue TG uptake assayed. After the fat challenge, intact rats showed lower postprandial plasma TG concentrations early in the night when compared with the day. However, no differences were observed in the rate of intestinal TG secretion between day and night. Instead, there was a higher uptake of TG by skeletal muscle and brown adipose tissue early in the active phase (night) when compared with the rest phase (day), and these variations were abolished in rats bearing bilateral SCN lesions. Rev-erbα gene expression suggests this as a possible mediator of the mechanism linking the SCN and day-night variations in TG uptake. These findings show that the SCN has a major role in day-night variations in plasma TGs by promoting TG uptake into skeletal muscle and brown adipose tissue. Consequently, disturbance of the biological clock might be an important risk factor contributing to the development of hyperlipidaemia.

Perinatal maternal high-fat diet induces early obesity and sex-specific alterations of the endocannabinoid system in white and brown adipose tissue of weanling rat offspring

Perinatal maternal high-fat (HF) diet programmes offspring obesity. Obesity is associated with overactivation of the endocannabinoid system (ECS) in adult subjects, but the role of the ECS in the developmental origins of obesity is mostly unknown. The ECS consists of endocannabinoids, cannabinoid receptors (cannabinoid type-1 receptor (CB1) and cannabinoid type-2 receptor (CB2)) and metabolising enzymes. We hypothesised that perinatal maternal HF diet would alter the ECS in a sex-dependent manner in white and brown adipose tissue of rat offspring at weaning in parallel to obesity development. Female rats received standard diet (9 % energy content from fat) or HF diet (29 % energy content from fat) before mating, during pregnancy and lactation. At weaning, male and female offspring were killed for tissue harvest. Maternal HF diet induced early obesity, white adipocyte hypertrophy and increased lipid accumulation in brown adipose tissue associated with sex-specific changes of the ECS's components in weanling rats. In male pups, maternal HF diet decreased CB1 and CB2 protein in subcutaneous adipose tissue. In female pups, maternal HF diet increased visceral and decreased subcutaneous CB1. In brown adipose tissue, maternal HF diet increased CB1 regardless of pup sex. In addition, maternal HF diet differentially changed oestrogen receptor across the adipose depots in male and female pups. The ECS and oestrogen signalling play an important role in lipogenesis, adipogenesis and thermogenesis, and we observed early changes in their targets in adipose depots of the offspring. The present findings provide insights into the involvement of the ECS in the developmental origins of metabolic disease induced by inadequate maternal nutrition in early life.

Reduction of Hypothalamic Endoplasmic Reticulum Stress Activates Browning of White Fat and Ameliorates Obesity

The chaperone GRP78/BiP (glucose-regulated protein 78 kDa/binding immunoglobulin protein) modulates protein folding in reply to cellular insults that lead to endoplasmic reticulum (ER) stress. This study investigated the role of hypothalamic GRP78 on energy balance, with particular interest in thermogenesis and browning of white adipose tissue (WAT). For this purpose, we used diet-induced obese rats and rats administered thapsigargin, and by combining metabolic, histologic, physiologic, pharmacologic, thermographic, and molecular techniques, we studied the effect of genetic manipulation of hypothalamic GRP78. Our data showed that rats fed a high-fat diet or that were centrally administered thapsigargin displayed hypothalamic ER stress, whereas genetic overexpression of GRP78 specifically in the ventromedial nucleus of the hypothalamus was sufficient to alleviate ER stress and to revert the obese and metabolic phenotype. Those effects were independent of feeding and leptin but were related to increased thermogenic activation of brown adipose tissue and induction of browning in WAT and could be reversed by antagonism of β3 adrenergic receptors. This evidence indicates that modulation of hypothalamic GRP78 activity may be a potential strategy against obesity and associated comorbidities.

A transcribed ultraconserved noncoding RNA, uc.417, serves as a negative regulator of brown adipose tissue thermogenesis

Brown adipose tissue (BAT) oxidizes fatty acids for thermogenesis and could therefore be considered as part of a new strategy in combating obesity and associated metabolic diseases. It is well established that aging is accompanied by a decline of brown adipocyte regenerative capacity. How aging contributes to this loss is poorly understood. Here, we identify a long noncoding RNA, uc.417, which is transcribed from an ultraconserved region in rodents. Expression of uc.417 increases with age. Ectopic expression of uc.417 impairs adipogenesis and the thermogenic program in brown adipocytes. However, uc.417 is not required for brown fat function. In vivo, uc.417 attenuates the cold-induced thermogenic program in mouse BAT. Moreover, we find that uc.417 moderately inhibits phosphorylation of p38MAPK without affecting the total protein level of p38MAPK. The p38MAPK pathway is essential for activating BAT to stimulate uncoupling protein 1 gene expression. The data point to uc.417 as being an important factor in an age-dependent loss of function of brown adipose tissue.-Cui, X., You, L., Li, Y., Zhu, L., Zhang, F., Xie, K., Cao, Y., Ji, C., Guo, X. A transcribed ultraconserved noncoding RNA, uc.417, serves as a negative regulator of brown adipose tissue thermogenesis.

A BAT-Centric Approach to the Treatment of Diabetes: Turn on the Brain

The marked (18)F-flurodeoxyglucose uptake by brown adipose tissue (BAT) enabled its identification in human positron emission tomography imaging studies. In this Perspective, we discuss how glucose extraction by BAT and beige adipose tissue (BeAT) sufficiently impacts on glycemic control. We then present a unique overview of the central circuits modulated by gluco-regulatory hormones, temperature, and glucose itself, which converge on sympathetic preganglionic neurons and whose activation syphon circulating glucose into BAT/BeAT. Targeted stimulation of the sympathetic nervous system at specific nodes to selectively recruit BAT/BeAT may represent a safe and effective means of treating diabetes.

Relevance of lipid metabolism for brown fat visualization and quantification

PURPOSE OF REVIEW

Brown adipose tissue (BAT) is an emerging target to combat cardiometabolic disorders as it can take up substantial amounts of glucose and lipids from the circulation for heat production. This review focuses on new concepts in BAT physiology and discusses the need for new techniques to determine BAT activity in humans.

RECENT FINDINGS

Mouse studies showed that BAT activation selectively increases oxidation of lipids over glucose, by recruiting fatty acids from intracellular triglycerides. To replenish these intracellular lipid stores, brown adipocytes take up both glucose and triglyceride-derived fatty acids, resulting in attenuation of dyslipidaemia, insulin resistance and atherosclerosis. Clinical studies identified the involvement of the β3-adrenergic receptor in BAT activation and demonstrated that human BAT activation also selectively increases lipid oxidation. Notably, insulin resistance during ageing or weight gain reduces the capacity of BAT to internalize glucose, without reducing fatty acid uptake or oxidative metabolism.

SUMMARY

Preclinical studies established BAT as an important target to combat cardiometabolic disorders and elucidated underlying mechanisms whereas clinical studies identified therapeutic handles. Development of novel lipid-based PET-CT tracers and identification of translational biomarkers of BAT activity are required as alternatives to [F]fluorodeoxyglucose PET-CT to accelerate clinical development of BAT-activating therapeutic strategies.

Reductions in hypothalamic Gfap expression, glial cells and α-tanycytes in lean and hypermetabolic Gnasxl-deficient mice

Background

Neuronal and glial differentiation in the murine hypothalamus is not complete at birth, but continues over the first two weeks postnatally. Nutritional status and Leptin deficiency can influence the maturation of neuronal projections and glial patterns, and hypothalamic gliosis occurs in mouse models of obesity. Gnasxl constitutes an alternative transcript of the genomically imprinted Gnas locus and encodes a variant of the signalling protein Gα_s, termed XLα_s, which is expressed in defined areas of the hypothalamus. Gnasxl-deficient mice show postnatal growth retardation and undernutrition, while surviving adults remain lean and hypermetabolic with increased sympathetic nervous system (SNS) activity. Effects of this knock-out on the hypothalamic neural network have not yet been investigated.

Results

RNAseq analysis for gene expression changes in hypothalami of Gnasxl-deficient mice indicated Glial fibrillary acid protein (Gfap) expression to be significantly down-regulated in adult samples. Histological analysis confirmed a reduction in Gfap-positive glial cell numbers specifically in the hypothalamus. This reduction was observed in adult tissue samples, whereas no difference was found in hypothalami of postnatal stages, indicating an adaptation in adult Gnasxl-deficient mice to their earlier growth phenotype and hypermetabolism. Especially noticeable was a loss of many Gfap-positive α-tanycytes and their processes, which form part of the ependymal layer that lines the medial and dorsal regions of the 3^rd ventricle, while β-tanycytes along the median eminence (ME) and infundibular recesses appeared unaffected. This was accompanied by local reductions in Vimentin and Nestin expression. Hypothalamic RNA levels of glial solute transporters were unchanged, indicating a potential compensatory up-regulation in the remaining astrocytes and tanycytes.

Conclusion

Gnasxl deficiency does not directly affect glial development in the hypothalamus, since it is expressed in neurons, and Gfap-positive astrocytes and tanycytes appear normal during early postnatal stages. The loss of Gfap-expressing cells in adult hypothalami appears to be a consequence of the postnatal undernutrition, hypoglycaemia and continued hypermetabolism and leanness of Gnasxl-deficient mice, which contrasts with gliosis observed in obese mouse models. Since α-tanycytes also function as adult neural progenitor cells, these findings might indicate further developmental abnormalities in hypothalamic formations of Gnasxl-deficient mice, potentially including neuronal composition and projections.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-016-0219-1) contains supplementary material, which is available to authorized users.

The role of innate immunity in the regulation of brown and beige adipogenesis

The adipose tissue (AT) is multifunctional, acting as an endocrine tissue and participating in the regulation of the organism's homeostasis. Metabolic, endocrine and inflammatory mechanisms are tightly intertwined within the AT, regulating its function. Disruption of the equilibrium among these mechanisms leads to pathologies, the most common being obesity-related insulin resistance. Two types of AT exist, the white and the brown AT. Traditionally the white AT (WAT) was thought to store energy in the form of lipids, while the brown AT (BAT) was known to mediate heat generation. Recently, the 'brite' or 'beige' AT was identified, which is localized predominantly in subcutaneous WAT, but shares functional features with the BAT and is capable of heat production. The major stimulus triggering beige and brown adipogenesis is cold exposure and catecholamine signalling. However, several further signals and mechanisms exist, which can orchestrate and fine-tune beige and brown AT function. Immune cells and inflammation have emerged as regulators of beige and brown AT function. The present review will focus on the recently identified crosstalk between innate immunity and the regulation of beige and brown adipogenesis.