An endocrine role for brown adipose tissue?

Effect of rhGH treatment on lipidome and brown fat activity in prepuberal small for gestational age children: a pilot study

Recombinant human growth hormone (rhGH) therapy is the primary treatment for children born small for gestational age (SGA) who fail to show spontaneous catch-up growth by two or four years. While its effects on white adipose tissue are well-documented, this pilot study aimed to investigate its impact on the lipidome and the thermogenic and endocrine activities of brown adipose tissue (BAT) in SGA children following rhGH treatment. The study involved 11 SGA children divided into two groups: (a) SGA children who were not treated with rhGH (n = 4) and (b) SGA children who received rhGH treatment with Saizen® (n = 7). This second group of seven SGA children was followed for 12 months after initiating rhGH treatment. Interventions included 12-hour fasting blood extraction and infrared thermography at baseline and 3 and 12 months post-treatment. Five appropriate-for-gestational-age (AGA) children served as controls. Exclusion criteria included endocrinological, genetic, or chronic diseases. Untargeted lipidomics analysis was performed using liquid chromatography-mass spectrometry (LC-MS), and serum biomarker levels were measured using ELISA assays. Serum lipidomic analysis revealed that free fatty acids (FFAs) increased to levels close to those of the AGA group after three months of rhGH administration, including polyunsaturated fatty acids, correlating with reduced leptin levels. Elevated levels of 1a,1b-dihomo-PGJ2 and adrenic acid suggested potential aging markers. rhGH treatment also significantly reduced meteorin-like (METRNL) and monocyte chemoattractant protein-1 (MCP1) serum levels to control levels. rhGH influences the serum lipidome, promoting changes in maturation and metabolism. Further research is required to clarify the direct effects of rhGH on specific lipid species and batokines, potentially addressing metabolic disturbances linked to obesity and aging.

Sarcopenia and cachexia: molecular mechanisms and therapeutic interventions

Sarcopenia is defined as a muscle-wasting syndrome that occurs with accelerated aging, while cachexia is a severe wasting syndrome associated with conditions such as cancer and immunodeficiency disorders, which cannot be fully addressed through conventional nutritional supplementation. Sarcopenia can be considered a component of cachexia, with the bidirectional interplay between adipose tissue and skeletal muscle potentially serving as a molecular mechanism for both conditions. However, the underlying mechanisms differ. Recognizing the interplay and distinctions between these disorders is essential for advancing both basic and translational research in this area, enhancing diagnostic accuracy and ultimately achieving effective therapeutic solutions for affected patients. This review discusses the muscle microenvironment's changes contributing to these conditions, recent therapeutic approaches like lifestyle modifications, small molecules, and nutritional interventions, and emerging strategies such as gene editing, stem cell therapy, and gut microbiome modulation. We also address the challenges and opportunities of multimodal interventions, aiming to provide insights into the pathogenesis and molecular mechanisms of sarcopenia and cachexia, ultimately aiding in innovative strategy development and improved treatments.

[18F]F-AraG imaging reveals association between neuroinflammation and brown- and bone marrow adipose tissue

Brown and brown-like adipose tissues have attracted significant attention for their role in metabolism and therapeutic potential in diabetes and obesity. Despite compelling evidence of an interplay between adipocytes and lymphocytes, the involvement of these tissues in immune responses remains largely unexplored. This study explicates a newfound connection between neuroinflammation and brown- and bone marrow adipose tissue. Leveraging the use of [18F]F-AraG, a mitochondrial metabolic tracer capable of tracking activated lymphocytes and adipocytes simultaneously, we demonstrate, in models of glioblastoma and multiple sclerosis, the correlation between intracerebral immune infiltration and changes in brown- and bone marrow adipose tissue. Significantly, we show initial evidence that a neuroinflammation-adipose tissue link may also exist in humans. This study proposes the concept of an intricate immuno-neuro-adipose circuit, and highlights brown- and bone marrow adipose tissue as an intermediary in the communication between the immune and nervous systems. Understanding the interconnectedness within this circuitry may lead to advancements in the treatment and management of various conditions, including cancer, neurodegenerative diseases and metabolic disorders.

The role of brown adipose tissue in mediating healthful longevity

There are two major subtypes of adipose tissue, i.e., white adipose tissue (WAT) and brown adipose tissue (BAT). It has been known for a long time that WAT mediates obesity and impairs healthful longevity. More recently, interest has focused on BAT, which, unlike WAT, actually augments healthful aging. The goal of this review is to examine the role of BAT in mediating healthful longevity. A major role for BAT and its related beige adipose tissue is thermogenesis, as a mechanism to maintain body temperature by producing heat through uncoupling protein 1 (UCP1) or through UCP1-independent thermogenic pathways. Our hypothesis is that healthful longevity is, in part, mediated by BAT. BAT protects against the major causes of impaired healthful longevity, i.e., obesity, diabetes, cardiovascular disorders, cancer, Alzheimer's disease, reduced exercise tolerance, and impaired blood flow. Several genetically engineered mouse models have shown that BAT enhances healthful aging and that their BAT is more potent than wild-type (WT) BAT. For example, when BAT, which increases longevity and exercise performance in mice with disruption of the regulator of G protein signaling 14 (RGS14), is transplanted to WT mice, their exercise capacity is enhanced at 3 days after BAT transplantation, whereas BAT transplantation from WT to WT mice also resulted in increased exercise performance, but only at 8 weeks after transplantation. In view of the ability of BAT to mediate healthful longevity, it is likely that a pharmaceutical analog of BAT will become a novel therapeutic modality.

An update on the secretory functions of brown, white, and beige adipose tissue: Towards therapeutic applications

Adipose tissue, including white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue, is vital in modulating whole-body energy metabolism. While WAT primarily stores energy, BAT dissipates energy as heat for thermoregulation. Beige adipose tissue is a hybrid form of adipose tissue that shares characteristics with WAT and BAT. Dysregulation of adipose tissue metabolism is linked to various disorders, including obesity, type 2 diabetes, cardiovascular diseases, cancer, and infertility. Both brown and beige adipocytes secrete multiple molecules, such as batokines, packaged in extracellular vesicles or as soluble signaling molecules that play autocrine, paracrine, and endocrine roles. A greater understanding of the adipocyte secretome is essential for identifying novel molecular targets in treating metabolic disorders. Additionally, microRNAs show crucial roles in regulating adipose tissue differentiation and function, highlighting their potential as biomarkers for metabolic disorders. The browning of WAT has emerged as a promising therapeutic approach in treating obesity and associated metabolic disorders. Many browning agents have been identified, and nanotechnology-based drug delivery systems have been developed to enhance their efficacy. This review scrutinizes the characteristics of and differences between white, brown, and beige adipose tissues, the molecular mechanisms involved in the development of the adipocytes, the significant roles of batokines, and regulatory microRNAs active in different adipose tissues. Finally, the potential of WAT browning in treating obesity and atherosclerosis, the relationship of BAT with cancer and fertility disorders, and the crosstalk between adipose tissue with circadian system and circadian disorders are also investigated.

Dysfunction of the Brown Adipose Organ in HFD-Obese Rats and Effect of Tart Cherry Supplementation

Obesity has a great impact on adipose tissue biology, based on its function as a master regulator of energy balance. Brown adipose tissue (BAT) undergoes remodeling, and its activity declines in obese subjects due to a whitening process. The anti-obesity properties of fruit extracts have been reported. The effects of tart cherry against oxidative stress, inflammation, and the whitening process in the BAT of obese rats were investigated. Intrascapular BAT (iBAT) alterations and effects of Prunus cerasus L. were debated in rats fed for 17 weeks with a high-fat diet (DIO), in DIO supplemented with seed powder (DS), and with seed powder plus the juice (DJS) of tart cherry compared to CHOW rats fed with a normo-caloric diet. iBAT histologic observations revealed a whitening process in DIO rats that was reduced in the DS and DJS groups. A modulation of uncoupling protein-1 (UCP-1) protein and gene expression specifically were detected in the obese phenotype. An upregulation of UCP-1 and related thermogenic genes after tart cherry intake was detected compared to the DIO group. Metabolic adjustment, endoplasmic reticulum stress, protein carbonylation, and the inflammatory microenvironment in the iBAT were reported in DIO rats. The analysis demonstrated an iBAT modulation that tart cherry promoted. In addition to our previous results, these data confirm the protective impact of tart cherry consumption on obesity.

Brown adipose tissue evaluation using water and triglyceride as indices by diffuse reflectance spectroscopy

Brown adipose tissue (BAT) is related to lipid and glucose metabolism, and BAT evaluation is expected to contribute to disease prevention and treatment. We aimed to establish a BAT evaluation method using simple and non-invasive diffuse reflectance spectroscopy (DRS). We acquired diffuse reflectance spectra of BAT using DRS from rats with cold stimulation and analyzed the second-derivative spectra. To predict the amount of triglyceride in BAT from the second-derivative spectra, partial least-squares regression analysis was performed, and we examined whether BAT weight can be predicted from the amount of triglyceride by single regression analysis. By focusing on changes in the amount of triglyceride in BAT with cold stimulation, it was suggested that this amount could be predicted spectroscopically, and the predicted amount of triglyceride could be used to estimate the BAT weight with cold stimulation. If these results can be translated into humans, they may contribute to preventing metabolic disorders.

Inosine: novel activator of brown adipose tissue and energy homeostasis

Extracellular purinergic molecules act as signaling molecules that bind to cellular receptors and regulate signaling pathways. Growing evidence suggests that purines regulate adipocyte function and whole-body metabolism. Here, we focus on one specific purine: inosine. Brown adipocytes, which are important regulators of whole-body energy expenditure (EE), release inosine when they are stressed or become apoptotic. Unexpectedly, inosine activates EE in neighboring brown adipocytes and enhances differentiation of brown preadipocytes. Increasing extracellular inosine, either directly by increasing inosine intake or indirectly via pharmacological inhibition of cellular inosine transporters, increases whole-body EE and counteracts obesity. Thus, inosine and other closely related purines might be a novel approach to tackle obesity and associated metabolic disorders by enhancing EE.

Next-Cell Hypothesis: Mechanism of Obesity-Associated Carcinogenesis

Higher body fat content is related to a higher risk of mortality, and obesity-related cancer represents approximately 40% of all cancer patients diagnosed each year. Furthermore, epigenetic mechanisms are involved in cellular metabolic memory and can determine one's predisposition to being overweight. Low-grade chronic inflammation, a well-established characteristic of obesity, is a central component of tumor development and progression. Cancer-associated adipocytes (CAA), which enhance inflammation- and metastasis-related gene sets within the cancer microenvironment, have pro-tumoral effects. Adipose tissue is a major source of the exosomal micro ribonucleic acids (miRNAs), which modulate pathways involved in the development of obesity and obesity-related comorbidities. Owing to their composition of cargo, exosomes can activate receptors at the target cell or transfer molecules to the target cells and thereby change the phenotype of these cells. Exosomes that are released into the extracellular environment are internalized with their cargo by neighboring cells. The tumor-secreted exosomes promote organ-specific metastasis of tumor cells that normally lack the capacity to metastasize to a specific organ. Therefore, the communication between neighboring cells via exosomes is defined as the "next-cell hypothesis." The reciprocal interaction between the adipocyte and tumor cell is realized through the adipocyte-derived exosomal miRNAs and tumor cell-derived oncogenic miRNAs. The cargo molecules of adipocyte-derived exosomes are important messengers for intercellular communication involved in metabolic responses and have very specific signatures that direct the metabolic activity of target cells. RNA-induced silencing regulates gene expression through various mechanisms. Destabilization of DICER enzyme, which catalyzes the conversion of primary miRNA (pri-miRNA) to precursor miRNA (pre-miRNA), is an important checkpoint in cancer development and progression. Interestingly, adipose tissue in obesity and tumors share similar pathogenic features, and the local hypoxia progress in both. While hypoxia in obesity leads to the adipocyte dysfunction and metabolic abnormalities, in obesity-related cancer cases, it is associated with worsened prognosis, increased metastatic potential, and resistance to chemotherapy. Notch-interleukin-1 (IL-1)-Leptin crosstalk outcome is referred to as "NILCO effect." In this chapter, obesity-related cancer development is discussed in the context of "next-cell hypothesis," miRNA biogenesis, and "NILCO effect."

Regulatory mechanisms underlying interleukin-6 expression in murine brown adipocytes

Three types of adipocytes, white, brown, and beige, regulate the systemic energy balance through the storage and expenditure of chemical energy. In addition, adipocytes produce various bioactive molecules known as adipokines. In contrast to white adipocyte-derived molecules, less information is available on the adipokines produced by brown adipocytes (batokine). This study explored the regulatory expression of interleukin (IL)-6 in cell culture studies. Norepinephrine or a nonselective β-adrenergic receptor agonist increased the expression of IL-6 in primary brown adipocytes and HB2 brown adipocytes. Treatment with forskolin (Fsk), an activator of the cAMP-dependent protein kinase (PKA) pathway (downstream signaling of the β-adrenergic receptor), efficiently stimulated IL-6 expression in brown adipocytes and myotubes. Phosphorylated CREB and phosphorylated p38 MAP kinase levels were increased in Fsk-treated brown adipocytes within 5 min. In contrast, a long-term (∼60 min and ∼4 h) treatment with Fsk was required for increase in STAT3 phosphorylation and C/EBPβ expression, respectively. The PKA, p38 MAP kinase, STAT3, and C/EBPβ pathways are required for the maximal IL-6 expression induced by Fsk, which were verified by use of various inhibitors of these signal pathways. Vitamin C enhanced Fsk-induced IL-6 expression through the extracellular signal-regulated kinase activity. The present study provides basic information on the regulatory expression of IL-6 in activated brown adipocytes.

Polarized macrophages regulate fibro/adipogenic progenitor (FAP) adipogenesis through exosomes

BACKGROUND

Macrophage polarization has been observed in the process of muscle injuries including rotator cuff (RC) muscle atrophy and fatty infiltration after large tendon tears. In our previous study, we showed that fibrogenesis and white adipogenesis of muscle residential fibro/adipogenic progenitors (FAPs) cause fibrosis and fatty infiltration and that brown/beige adipogenesis of FAPs promotes rotator cuff muscle regeneration. However, how polarized macrophages and their exosomes regulate FAP differentiation remains unknown.

METHODS

We cultured FAPs with M0, M1, and M2 macrophages or 2 × 109 exosomes derived from M0, M1 and M2 with and without GW4869, an exosome inhibitor. In vivo, M0, M1, and M2 macrophages were transplanted or purified macrophage exosomes (M0, M1, M2) were injected into supraspinatus muscle (SS) after massive tendon tears in mice (n = 6). SS were harvested at six weeks after surgery to evaluate the level of muscle atrophy and fatty infiltration.

RESULTS

Our results showed that M2 rather than M0 or M1 macrophages stimulates brown/beige fat differentiation of FAPs. However, the effect of GW4869, the exosome inhibitor, diminished this effect. M2 exosomes also promoted FAP Beige differentiation in vitro. The transplantation of M2 macrophages reduced supraspinatus muscle atrophy and fatty infiltration. In vivo injections of M2 exosomes significantly reduced muscle atrophy and fatty infiltration in supraspinatus muscle.

CONCLUSION

Results from our study demonstrated that polarized macrophages directly regulated FAP differentiation through their exosomes and M2 macrophage-derived exosomes may serve as a novel treatment option for RC muscle atrophy and fatty infiltration.

Understanding the relationship between cancer associated cachexia and hypoxia-inducible factor-1

Cancer-associated cachexia (CAC) is a multifactorial disorder characterized by an unrestricted loss of body weight as a result of muscle and adipose tissue atrophy. Cachexia is influenced by several factors, including decreased metabolic activity and food intake, an imbalance between energy uptake and expenditure, excessive catabolism, and inflammation. Cachexia is highly associated with all types of cancers responsible for more than half of cancer-related mortalities worldwide. In healthy individuals, adipose tissue significantly regulates energy balance and glucose homeostasis. However, in metastatic cancer patients, CAC occurs mainly because of an imbalance between muscle protein synthesis and degradation which are organized by certain extracellular ligands and associated signaling pathways. Under hypoxic conditions, hypoxia-inducible factor-1 (HIF-1α) accumulated and translocated to the nucleus and activate numerous genes involved in cell survival, invasion, angiogenesis, metastasis, metabolic reprogramming, and cancer stemness. On the other hand, the ubiquitination proteasome pathway is inhibited during low O2 levels which promote muscle wasting in cancer patients. Therefore, understanding the mechanism of the HIF-1 pathway and its metabolic adaptation to biomolecules is important for developing a novel therapeutic method for cancer and cachexia therapy. Even though many HIF inhibitors are already in a clinical trial, their mechanism of action remains unknown. With this background, this review summarizes the basic concepts of cachexia, the role of inflammatory cytokines, pathways connected with cachexia with special reference to the HIF-1 pathway and its regulation, metabolic changes, and inhibitors of HIFs.

Adipose Tissue Remodeling in Obesity: An Overview of the Actions of Thyroid Hormones and Their Derivatives

Metabolic syndrome and obesity have become important health issues of epidemic proportions and are often the cause of related pathologies such as type 2 diabetes (T2DM), hypertension, and cardiovascular disease. Adipose tissues (ATs) are dynamic tissues that play crucial physiological roles in maintaining health and homeostasis. An ample body of evidence indicates that in some pathophysiological conditions, the aberrant remodeling of adipose tissue may provoke dysregulation in the production of various adipocytokines and metabolites, thus leading to disorders in metabolic organs. Thyroid hormones (THs) and some of their derivatives, such as 3,5-diiodo-l-thyronine (T2), exert numerous functions in a variety of tissues, including adipose tissues. It is known that they can improve serum lipid profiles and reduce fat accumulation. The thyroid hormone acts on the brown and/or white adipose tissues to induce uncoupled respiration through the induction of the uncoupling protein 1 (UCP1) to generate heat. Multitudinous investigations suggest that 3,3',5-triiodothyronine (T3) induces the recruitment of brown adipocytes in white adipose depots, causing the activation of a process known as "browning". Moreover, in vivo studies on adipose tissues show that T2, in addition to activating brown adipose tissue (BAT) thermogenesis, may further promote the browning of white adipose tissue (WAT), and affect adipocyte morphology, tissue vascularization, and the adipose inflammatory state in rats receiving a high-fat diet (HFD). In this review, we summarize the mechanism by which THs and thyroid hormone derivatives mediate adipose tissue activity and remodeling, thus providing noteworthy perspectives on their efficacy as therapeutic agents to counteract such morbidities as obesity, hypercholesterolemia, hypertriglyceridemia, and insulin resistance.

Thermogenic Capacity of Human Supraclavicular Brown Fat and Cold-Stimulated Brain Glucose Metabolism

Human brain metabolism is susceptible to temperature changes. It has been suggested that the supraclavicular brown adipose tissue (BAT) protects the brain from these fluctuations by regulating heat production through the presence of uncoupling protein 1 (UCP-1). It remains unsolved whether inter-individual variation in the expression of UCP-1, which represents the thermogenic capacity of the supraclavicular BAT, is linked with brain metabolism during cold stress. Ten healthy human participants underwent 18F-FDG PET scanning of the brain under cold stimulus to determine brain glucose uptake (BGU). On a separate day, an excision biopsy of the supraclavicular fat—the fat proximal to the carotid arteries supplying the brain with warm blood—was performed to determine the mRNA expression of the thermogenic protein UCP-1. Expression of UCP-1 in supraclavicular BAT was directly related to the whole brain glucose uptake rate determined under cold stimulation (rho = 0.71, p = 0.03). In sub-compartmental brain analysis, UCP-1 expression in supraclavicular BAT was directly related to cold-stimulated glucose uptake rates in the hypothalamus, medulla, midbrain, limbic system, frontal lobe, occipital lobe, and parietal lobe (all rho ≥ 0.67, p < 0.05). These relationships were independent of body mass index and age. When analysing gene expressions of BAT secretome, we found a positive correlation between cold-stimulated BGU and DIO2. These findings provide evidence of functional links between brain metabolism under cold stimulation and UCP-1 and DIO2 expressions in BAT in humans. More research is needed to evaluate the importance of these findings in clinical outcomes, for instance, in examining the supporting role of BAT in cognitive functions under cold stress.

Brown adipose tissue and alzheimer's disease

Alzheimer's disease (AD), the most common type of senile dementia, is a chronic neurodegenerative disease characterized by cognitive dysfunction and behavioral disability. The two histopathological hallmarks in this disease are the extraneuronal accumulation of amyloid-β (Aβ) and the intraneuronal deposition of neurofibrillary tangles (NFTs). Despite this, central and peripheral metabolic dysfunction, such as abnormal brain signaling, insulin resistance, inflammation, and impaired glucose utilization, have been indicated to be correlated with AD. There is solid evidence that the age-associated thermoregulatory deficit induces diverse metabolic changes associated with AD development. Brown adipose tissue (BAT) has been known as a thermoregulatory organ particularly vital during infancy. However, in recent years, BAT has been accepted as an endocrine organ, being involved in various functions that prevent AD, such as regulating energy metabolism, secreting hormones, improving insulin sensitivity, and increasing glucose utilization in adult humans. This review focuses on the mechanisms of BAT activation and the effect of aging on BAT production and signaling. Specifically, the evidence demonstrating the effect of BAT on pathological mechanisms influencing the development of AD, including insulin pathway, thermoregulation, and other hormonal pathways, are reviewed in this article.

The crosstalk between BAT thermogenesis and skeletal muscle dysfunction

Metabolic defects increase the risk of skeletal muscle diseases, and muscle impairment might worsen metabolic disruption, leading to a vicious cycle. Both brown adipose tissue (BAT) and skeletal muscle play important roles in non-shivering thermogenesis to regulate energy homeostasis. BAT regulates body temperature, systemic metabolism, and seretion of batokines that have positive or negative impacts on skeletal muscle. Conversely, muscle can secrete myokines that regulate BAT function. This review explained the crosstalk between BAT and skeletal muscle, and then discussed the batokines and highlighted their impact on skeletal muscle under physiological conditions. BAT is now considered a potential therapeutic target for obesity and diabetes treatment. Moreover, manipulation of BAT may be an attractive approach for the treatment of muscle weakness by correcting metabolic deficits. Therefore, exploring BAT as a potential treatment for sarcopenia could be a promising avenue for future research.

TFAM expression in brown adipocytes confers obesity resistance by secreting extracellular vesicles that promote self-activation

The occurrence of diet-induced obesity has been increasing worldwide and has become a major health concern. Mitochondria are densely distributed in brown adipose tissue and are involved in lipid consumption. Therefore, increasing energy expenditure through the activation of brown adipocytes may be a potential therapy for obesity. Our findings showed that mitochondrial transcription factor A (TFAM) homozygous transgenic (TgTg) mice had highly activated brown adipocytes and increased expression of oxidative phosphorylation, leading to resistance to obesity. Transplantation models of TFAM-expressing brown adipocytes could mimic the phenotype of TFAM TgTg mice, and proving their anti-obesity effect. We found that brown adipocytes secrete exosomes which enable self-activation in an autocrine and paracrine manner. The secretion was enhanced in TFAM TgTg brown adipocytes, resulting in a higher activation. These findings may lead to a promising treatment strategy for obesity through selective stimulation of exosome secretion.

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Human TFAM overexpression in BAT promotes strong anti-obesity effects

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Increasing mitochondrial function in hTFAM TgTg mice facilitates EVs secretion

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Enhanced EV released in TgTg brown adipocytes induce self-differentiation/activation

Calcium cycling as a mediator of thermogenic metabolism in adipose tissue

Canonical non-shivering thermogenesis (NST) in brown and beige fat relies on uncoupling protein 1 (UCP1)-mediated heat generation, although alternative mechanisms of NST have been identified, including sarcoplasmic reticulum (SR)-calcium cycling. Intracellular calcium is a crucial cell signaling molecule for which compartmentalization is tightly regulated, and the sarco-endoplasmic calcium ATPase (SERCA) actively pumps calcium from the cytosol into the SR. In this review, we discuss the capacity of SERCA-mediated calcium cycling as a significant mediator of thermogenesis in both brown and beige adipocytes. Here, we suggest two primary mechanisms of SR calcium mediated thermogenesis. The first mechanism is through direct uncoupling of the ATPase and calcium pump activity of SERCA, resulting in the energy of ATP catalysis being expended as heat in the absence of calcium transport. Regulins, a class of SR membrane proteins, act to decrease the calcium affinity of SERCA and uncouple the calcium transport function from ATPase activity, but remain largely unexplored in adipose tissue thermogenesis. A second mechanism is through futile cycling of SR calcium whereby SERCA-mediated SR calcium influx is equally offset by SR calcium efflux, resulting in ATP consumption without a net change in calcium compartmentalization. A fuller understanding of the functional and mechanistic role of calcium cycling as a mediator of adipose tissue thermogenesis and how manipulation of these pathways can be harnessed for therapeutic gain remains unexplored. Significance Statement Enhancing thermogenic metabolism in brown or beige adipose tissue may be of broad therapeutic utility to reduce obesity and metabolic syndrome. Canonical BAT-mediated thermogenesis occurs via uncoupling protein 1 (UCP1). However, UCP1-independent pathways of thermogenesis, such as sarcoplasmic (SR) calcium cycling, have also been identified, but the regulatory mechanisms and functional significance of these pathways remain largely unexplored. Thus, this mini-review discusses the state of the field with regard to calcium cycling as a thermogenic mediator in adipose tissue.

PET/MRI-evaluated brown adipose tissue activity may be related to dietary MUFA and omega-6 fatty acids intake

An investigation of new ways to activate brown adipose tissue (BAT) is highly valuable, as it is a possible tool for obesity prevention and treatment. The aim of our study was to evaluate the relationships between dietary intake and BAT activity. The study group comprised 28 healthy non-smoking males aged 21–42 years. All volunteers underwent a physical examination and 75-g OGTT and completed 3-day food intake diaries to evaluate macronutrients and fatty acid intake. Body composition measurements were assessed using DXA scanning. An FDG-18 PET/MR was performed to visualize BAT activity. Brown adipose tissue was detected in 18 subjects (67% normal-weight individuals and 33% overweight/obese). The presence of BAT corresponded with a lower visceral adipose tissue (VAT) content (p = 0.04, after adjustment for age, daily kcal intake, and DXA Lean mass). We noted significantly lower omega-6 fatty acids (p = 0.03) and MUFA (p = 0.02) intake in subjects with detected BAT activity after adjustment for age, daily average kcal intake, and DXA Lean mass, whereas omega-3 fatty acids intake was comparable between the two groups. BAT presence was positively associated with the concentration of serum IL-6 (p = 0.01) during cold exposure. Our results show that BAT activity may be related to daily omega-6 fatty acids intake.

White, beige and brown adipose tissue: structure, function, specific features and possibility formation and divergence in pigs

Introduction. Traditionally, mammalian adipose tissue is divided into white (white adipose tissue – WAT) and brown (brown adipose tissue – BAT). While the functions of WAT are well known as the triglyceride depot, the role of BAT in mammalian physiology has been under close investigation. The first description of the role of BAT in maintaining thermogenesis dates back to 1961. This article offers a review of structural and functional specificity of white, beige and brown adipose tissue. Results and discussion. The differences and descriptions of adipocytes and their impact on the maintenance of the main functions of the mammalian body are described in this manuscript. In particular, thermogenesis, stress response, obesity, type II diabetes. In addition to WAT and BAT, an intermediate form was also detected in the body – beige fat (BeAT or Brite). The opposite opinions regarding the presence of three types of adipose tissue in the human and animal bodies are presented. Studies on the identification of uncoupling proteins 1 and 3 and their role in the transformation of white fat into beige/brown are considered. Basically, the data on the factors of endogenous and exogenous nature on their formation are given on the example of the human body. Conclusion. With an abundance of publications on the keywords: “white, brown fat”, these studies, in the overwhelming majority, are devoted to the role of these fats in the formation of human thermogenesis, the assessment of the impact on obesity. Pigs have also been suggested to lack functional BAT, which is a major cause of neonatal death in the swine industry, therefore the focus on investigating role of different types of adipose tissue in pigs seems very promising in order to understand whether there is a compensating mechanism of thermogenesis.

The Action of Vitamin D in Adipose Tissue: Is There the Link between Vitamin D Deficiency and Adipose Tissue-Related Metabolic Disorders?

Adipose tissue plays an important role in systemic metabolism via the secretion of adipocytokines and storing and releasing energy. In obesity, adipose tissue becomes dysfunctional and characterized by hypertrophied adipocytes, increased inflammation, hypoxia, and decreased angiogenesis. Although adipose tissue is one of the major stores of vitamin D, its deficiency is detective in obese subjects. In the presented review, we show how vitamin D regulates numerous processes in adipose tissue and how their dysregulation leads to metabolic disorders. The molecular response to vitamin D in adipose tissue affects not only energy metabolism and adipokine and anti-inflammatory cytokine production via the regulation of gene expression but also genes participating in antioxidant defense, adipocytes differentiation, and apoptosis. Thus, its deficiency disturbs adipocytokines secretion, metabolism, lipid storage, adipogenesis, thermogenesis, the regulation of inflammation, and oxidative stress balance. Restoring the proper functionality of adipose tissue in overweight or obese subjects is of particular importance in order to reduce the risk of developing obesity-related complications, such as cardiovascular diseases and diabetes. Taking into account the results of experimental studies, it seemed that vitamin D may be a remedy for adipose tissue dysfunction, but the results of the clinical trials are not consistent, as some of them show improvement and others no effect of this vitamin on metabolic and insulin resistance parameters. Therefore, further studies are required to evaluate the beneficial effects of vitamin D, especially in overweight and obese subjects, due to the presence of a volumetric dilution of this vitamin among them.

Brown Adipose Tissue: A Short Historical Perspective

Brown adipose tissue (BAT) was first identified by Conrad Gessner in 1551, but it was only in 1961 that it was firmly identified as a thermogenic organ. Key developments in the subsequent two decades demonstrated that: (1) BAT is quantitatively important to non-shivering thermogenesis in rodents, (2) uncoupling of oxidative phosphorylation through a mitochondrial proton conductance pathway is the central mechanism by which heat is generated, (3) uncoupling protein-1 is the critical factor regulating proton leakage in BAT mitochondria. Following pivotal studies on cafeteria-fed rats and obese ob/ob mice, BAT was then shown to have a central role in the regulation of energy balance and the etiology of obesity. The application of fluorodeoxyglucose positron emission tomography in the late 2000s confirmed that BAT is present and active in adults, resulting in renewed interest in the tissue in human energetics and obesity. Subsequent studies have demonstrated a broad metabolic role for BAT, the tissue being an important site of glucose disposal and triglyceride clearance, as well as of insulin action. BAT continues to be a potential target for the treatment of obesity and related metabolic disorders.

Beta-klotho in type 2 diabetes mellitus: From pathophysiology to therapeutic strategies

Type 2 diabetes mellitus (T2DM) has become a global health problem with no cure. Despite lifestyle modifications and various pharmaceutical options, the achievement of stable and durable glucose control along with effective prevention of T2DM-related cardiovascular complications remains a challenging task in clinical management. With its selective high abundance in metabolic tissues (adipose tissue, liver, and pancreas), β-Klotho is the essential component of fibroblast growth factor (FGF) receptor complexes. It is essential for high-affinity binding of endocrine FGF19 and FGF21 to evoke the signaling cascade actively involved in homeostatic maintenance of glucose metabolism and energy expenditure. In this Review, we discuss the biological function of β-Klotho in the regulation of glucose metabolism and offer mechanistic insights into its involvement in the pathophysiology of T2DM. We review our current understanding of the endocrine axis comprised of β-Klotho and FGFs (FGF19 and FGF21) and its regulatory effects on glucose metabolism under physiological and T2DM conditions. We also highlight advances in the development and preclinical validation of pharmacological compounds that target β-Klotho and/or the β-Klotho-FGFRs complex for the treatment of T2DM. Given the remarkable advances in this field, we also discuss outstanding research questions and the many challenges in the clinical development of β-Klotho-based therapies.

Impaired brown adipose tissue is differentially modulated in insulin-resistant obese wistar and type 2 diabetic Goto-Kakizaki rats

Brown adipose tissue (BAT) is a potential target to treat obesity and diabetes, dissipating energy as heat. Type 2 diabetes (T2D) has been associated with obesogenic diets; however, T2D was also reported in lean individuals to be associated with genetic factors. We aimed to investigate the differences between obese and lean models of insulin resistance (IR) and elucidate the mechanism associated with BAT metabolism and dysfunction in different IR animal models: a genetic model (lean GK rats) and obese models (diet-induced obese Wistar rats) at 8 weeks of age fed a high-carbohydrate (HC), high-fat (HF) diet, or high-fat and high-sugar (HFHS) diet for 8 weeks. At 15 weeks of age, BAT glucose uptake was evaluated by 18F-FDG PET under basal (saline administration) or stimulated condition (CL316,243, a selective β3-AR agonist). After CL316, 243 administrations, GK animals showed decreased glucose uptake compared to HC animals. At 16 weeks of age, the animals were euthanized, and the interscapular BAT was dissected for analysis. Histological analyses showed lower cell density in GK rats and higher adipocyte area compared to all groups, followed by HFHS and HF compared to HC. HFHS showed a decreased batokine FGF21 protein level compared to all groups. However, GK animals showed increased expression of genes involved in fatty acid oxidation (CPT1 and CPT2), BAT metabolism (Sirt1 and Pgc1-α), and obesogenic genes (leptin and PAI-1) but decreased gene expression of glucose transporter 1 (GLUT-1) compared to other groups. Our data suggest impaired BAT function in obese Wistar and GK rats, with evidence of a whitening process in these animals.

Aging adipose: Depot location dictates age-associated expansion and dysfunction

Adipose tissue has a variety of diverse functions that maintain energy homeostasis. In conditions of excess energy availability, adipose tissue increases its lipid storage and communicates the nutritional abundance to various organs in the body. In conditions of energy depletion, such as fasting, cold exposure, or prolonged exercise, triglycerides stored in adipose tissue are released as free fatty acids to support the shift to catabolic metabolism. These diverse functions of storage, communication, and energy homeostasis are shared between numerous adipose depots including subcutaneous, visceral, brown, beige, intramuscular, marrow, and dermal adipose tissue. As organisms age, the cellular composition of these depots shifts to facilitate increased inflammatory cell infiltration, decreased vasculature, and increased adipocyte quantity and lipid droplet size. The purpose of this review is to give a comprehensive overview of the molecular and cellular changes that occur in various aged adipose depots and discuss their impact on physiology. The molecular signature of aged adipose leads to higher prevalence of metabolic disease in aged populations including type 2 diabetes, cardiovascular disease, Alzheimer's disease, and certain types of cancer.

Overexpression of translationally controlled tumor protein ameliorates metabolic imbalance and increases energy expenditure in mice

Background/Objectives

Translationally controlled tumor protein (TCTP) exhibits numerous biological functions. It has been shown to be involved in the regulation of glucose. However, its specific role in metabolism has not yet been clearly elucidated. Here, we aimed to assess the effect of TCTP overexpression on metabolic tissues and systemic energy metabolism.

Subjects/Methods

We investigated whether TCTP can ameliorate the metabolic imbalance that causes obesity using TCTP-overexpressing transgenic (TCTP TG) mice. The mice were subjected to biochemical, morphological, physiological and protein expression studies to define the role of TCTP in metabolic regulation in response to normal chow diet (NCD) compared to high-fat diet (HFD) conditions, and cold environment.

Results

We found that TCTP TG mice show improved metabolic homeostasis under both of NCD and HFD conditions with simultaneous enhancements in glucose tolerance and insulin sensitivity. In particular, we found coincident increases in energy expenditure with significant upregulation of uncoupling protein 1 (UCP1) in the brown adipose tissue (BAT). Moreover, TCTP overexpressing mice exhibit significantly enhanced adaptive thermogenesis of BAT in response to cold exposure.

Conclusions

Overexpression of TCTP ameliorated systemic metabolic homeostasis by stimulating UCP1-mediated thermogenesis in the BAT. This suggests that TCTP may function as a modulator of energy expenditure. This study suggests TCTP may serve as a therapeutic target for obesity and obesity-associated metabolic disorders including type 2 diabetes.

Use of Infrared Thermography to Estimate Brown Fat Activation After a Cooling Protocol in Patients with Severe Obesity That Underwent Bariatric Surgery

BACKGROUND

In contrast to the energy-storing role of white adipose tissue (WAT), brown adipose tissue (BAT) acts as the main site of non-shivering thermogenesis in mammals and has been reported to play a role in protection against obesity and associated metabolic alterations in rodents. Infrared thermography (IRT) has been proposed as a novel non-invasive, safe, and quick method to estimate BAT thermogenic activation in humans. The aim of this study is to determine whether the IRT could be a potential new tool to estimate BAT thermogenic activation in patients with severe obesity in response to bariatric surgery.

METHODS

Supraclavicular BAT thermogenic activation was evaluated using IRT in a cohort of 31 patients (50 ± 10 years old, BMI = 44.5 ± 7.8; 15 undergoing laparoscopy sleeve gastrectomy and 16 Roux-en-Y gastric bypass) at baseline and 6 months after a bariatric surgery. Clinical parameters were determined at these same time points.

RESULTS

Supraclavicular BAT-related activity was detected in our patients by IRT after a cooling stimulus. The BAT thermogenic activation was higher at 6 months after laparoscopy sleeve gastrectomy (0.06 ± 0.1 vs 0.32 ± 0.1), while patients undergoing to a roux-en-Y gastric bypass did not change their thermogenic response using the same cooling stimulus (0.09 ± 0.1 vs 0.08 ± 0.1).

CONCLUSIONS

Our study postulates the IRT as a potential tool to evaluate BAT thermogenic activation in patients with obesity before and after a bariatric surgery. Further studies are needed to evaluate differences between LSG technique and RYGB on BAT activation.

Gab2 deficiency suppresses high-fat diet-induced obesity by reducing adipose tissue inflammation and increasing brown adipose function in mice

Obesity is caused by a long-term imbalance between energy intake and consumption and is regulated by multiple signals. This study investigated the effect of signaling scaffolding protein Gab2 on obesity and its relevant regulation mechanism. Gab2 knockout (KO) and wild-type (WT) mice were fed with a standard diet (SD) or high-fat diet (HFD) for 12 weeks. The results showed that the a high-fat diet-induced Gab2 expression in adipose tissues, but deletion of Gab2 attenuated weight gain and improved glucose tolerance in mice fed with a high-fat diet. White adipose tissue and systemic inflammations were reduced in HFD-fed Gab2 deficiency mice. Gab2 deficiency increased the expression of Ucp1 and other thermogenic genes in brown adipose tissue. Furthermore, the regulation of Gab2 on the mature differentiation and function of adipocytes was investigated in vitro using primary or immortalized brown preadipocytes. The expression of brown fat-selective genes was found to be elevated in differentiated adipocytes without Gab2. The mechanism of Gab2 regulating Ucp1 expression in brown adipocytes involved with its downstream PI3K (p85)-Akt-FoxO1 signaling pathway. Our research suggests that deletion of Gab2 suppresses diet-induced obesity by multiple pathways and Gab2 may be a novel therapeutic target for the treatment of obesity and associated complications.

Dark-Side of Exosomes

Exosomes are nanoscale extracellular vesicles that can transport cargos of proteins, lipids, DNA, various RNA species and microRNAs (miRNAs). Exosomes can enter cells and deliver their contents to recipient cell. Owing to their cargo exosomes can transfer different molecules to the target cells and change the phenotype of these cells. The fate of the contents of an exosome depends on its target destination. Various mechanisms for exosome uptake by target cells have been proposed, but the mechanisms responsible for exosomes internalization into cells are still debated. Exosomes exposed cells produce labeled protein kinases, which are expressed by other cells. This means that these kinases are internalized by exosomes, and transported into the cytoplasm of recipient cells. Many studies have confirmed that exosomes are not only secreted by living cells, but also internalized or accumulated by the other cells. The "next cell hypothesis" supports the notion that exosomes constitute communication vehicles between neighboring cells. By this mechanism, exosomes participate in the development of diabetes and its associated complications, critically contribute to the spreading of neuronal damage in Alzheimer's disease, and non-proteolysed form of Fas ligand (mFasL)-bearing exosomes trigger the apoptosis of T lymphocytes. Furthermore, exosomes derived from human B lymphocytes induce antigen-specific major histocompatibility complex (MHC) class II-restricted T cell responses. Interestingly, exosomes secreted by cancer cells have been demonstrated to express tumor antigens, as well as immune suppressive molecules. This process is defined as "exosome-immune suppression" concept. The interplay via the exchange of exosomes between cancer cells and between cancer cells and the tumor stroma promote the transfer of oncogenes and onco-miRNAs from one cell to other. Circulating exosomes that are released from hypertrophic adipocytes are effective in obesity-related complications. On the other hand, the "inflammasome-induced" exosomes can activate inflammatory responses in recipient cells. In this chapter protein kinases-related checkpoints are emphasized considering the regulation of exosome biogenesis, secretory traffic, and their impacts on cell death, tumor growth, immune system, and obesity.

β3-Adrenergic receptor agonist treats rotator cuff fatty infiltration by activating beige fat in mice

BACKGROUND

Rotator cuff (RC) muscle atrophy and fatty infiltration (FI) are independent factors correlated with failure of attempted tendon repair in larger RC tears. However, there is no effective treatment for RC muscle atrophy and FI at this time. The recent discovery of beige adipose tissue (BAT) in adults shed light on a new avenue in treating obesity and excessive fat deposition by promoting BAT activity. The goal of this study was to define the role of intramuscular BAT in RC muscle FI and the effect of β₃-adrenergic receptor agonists in treating RC muscle FI by promoting BAT activity.

MATERIALS AND METHODS

Three-month-old wild-type C57BL/6J, platelet derived growth factor receptor-alpha (PDGFRα) green fluorescent protein (GFP) reporter and uncoupling protein 1 (UCP-1) knockout mice underwent a unilateral RC injury procedure, which included supraspinatus (SS) and infraspinatus tendon resection and suprascapular nerve transection. To stimulate BAT activity, amibegron, a selective β₃-adrenergic receptor agonist, was administered to C57BL/6J mice either on the same day as surgery or 6 weeks after surgery through daily intraperitoneal injections. Gait analysis was conducted to measure forelimb function at 6 weeks or 12 weeks (in groups receiving delayed amibegron treatment) after surgery. Animals were killed humanely at 6 weeks (or 12 weeks for delayed amibegron groups) after surgery. SS muscles were harvested and analyzed histologically and biochemically.

RESULTS

Histologic analysis of SS muscles from PDGFRα-GFP reporter mice showed that PDGFRα-positive fibroadipogenic progenitors in RC muscle expressed UCP-1, a hallmark of BAT during the development of FI after RC tears. Impairing BAT activity by knocking out UCP-1 resulted in more severe muscle atrophy and FI with inferior forelimb function in UCP-1 knockout mice compared with wild-type mice. Promoting BAT activity with amibegron significantly reduced muscle atrophy and FI after RC tears and improved forelimb function. Delayed treatment with amibegron reversed muscle atrophy and FI in muscle.

CONCLUSIONS

Fat accumulated in muscle after RC tears possesses BAT characteristics. Impairing BAT activity results in worse RC muscle atrophy and FI. Amibegron reduces and reverses RC atrophy and FI by promoting BAT activity.

Associations Between Different Dietary Vitamins and the Risk of Obesity in Children and Adolescents: A Machine Learning Approach

BACKGROUNDS

Simultaneous dietary intake of vitamins is considered as a common and real scenario in daily life. However, limited prospective studies have evaluated the association between multivitamins intake and obesity in children and adolescents.

OBJECTIVES

This study aimed to evaluate the relationship between the intake of different dietary vitamins and the risk of obesity in children (6-11 years) and adolescents (12-19 years).

METHODS

We conducted a cross-sectional study based on data from U.S. National Health and Nutrition Examination Survey, 2013-2016. A total of 3634 children and adolescents were included who had available data on dietary vitamins, obesity and covariates. We analyzed the dietary intake levels of nine vitamins, including vitamin A, vitamin B₁, vitamin B₂, vitamin B₆, vitamin B₁₂, vitamin C, vitamin D, vitamin E, vitamin K. Multivariate logistic regression was used to model the associations between vitamins and obesity. Bayesian kernel machine regression (BKMR) was employed to explore the joint and independent effects of vitamins on obesity among children and adolescents.

RESULTS

In the multivariate logistic regression model, five vitamins (vitamin A, vitamin B₁, vitamin B₂, vitamin B₁₂, and vitamin D) were negatively associated with obesity in children and adolescents. BKMR analysis showed that when the concentration of the nine vitamins was at or above the 55th percentile compared with the median value, the combined intake of these vitamins could significantly reduce the risk of obesity in children and adolescents. Potential interactions between vitamin B₂ and vitamin B₁₂ in increasing the risk of obesity in children and adolescents were observed.

CONCLUSIONS

We determine the combined effects of multivitamins on obesity in children and adolescents, and observe a significant interaction between vitamin B₂ and vitamin B₁₂. Further cohort studies are needed to clarify the health effects of multivitamins intake in a larger population.

Moderate SIRT1 overexpression protects against brown adipose tissue inflammation

OBJECTIVE

Metainflammation is a chronic low-grade inflammatory state induced by obesity and associated comorbidities, including peripheral insulin resistance. Brown adipose tissue (BAT), a therapeutic target against obesity, is an insulin target tissue sensitive to inflammation. Therefore, it is necessary to find strategies to protect BAT against the effects of inflammation in energy balance. In this study, we explored the impact of moderate sirtuin 1 (SIRT1) overexpression on insulin sensitivity and β-adrenergic responses in BAT and brown adipocytes (BA) under pro-inflammatory conditions.

METHODS

The effect of inflammation on BAT functionality was studied in obese db/db mice and lean wild-type (WT) mice or mice with moderate overexpression of SIRT1 (SIRT1^Tg+) injected with a low dose of bacterial lipopolysaccharide (LPS) to mimic endotoxemia. We also conducted studies on differentiated BA (BA-WT and BA-SIRT1^Tg+) exposed to a macrophage-derived pro-inflammatory conditioned medium (CM) to evaluate the protection of SIRT1 overexpression in insulin signaling and glucose uptake, mitochondrial respiration, fatty acid oxidation (FAO), and norepinephrine (NE)-mediated-modulation of uncoupling protein-1 (UCP-1) expression.

RESULTS

BAT from the db/db mice was susceptible to metabolic inflammation manifested by the activation of pro-inflammatory signaling cascades, increased pro-inflammatory gene expression, tissue-specific insulin resistance, and reduced UCP-1 expression. Impairment of insulin and noradrenergic responses were also found in the lean WT mice upon LPS injection. In contrast, BAT from the mice with moderate overexpression of SIRT1 (SIRT1^Tg+) was protected against LPS-induced activation of pro-inflammatory signaling, insulin resistance, and defective thermogenic-related responses upon cold exposure. Importantly, the decline in triiodothyronine (T₃) levels in the circulation and intra-BAT after exposure of the WT mice to LPS and cold was markedly attenuated in the SIRT1^Tg+ mice. In vitro BA experiments in the two genotypes revealed that upon differentiation with a T₃-enriched medium and subsequent exposure to a macrophage-derived pro-inflammatory CM, only BA-SIRT1^Tg+ fully recovered insulin and noradrenergic responses.

CONCLUSIONS

This study has ascertained the benefit of the moderate overexpression of SIRT1 to confer protection against defective insulin and β-adrenergic responses caused by BAT inflammation. Our results have potential therapeutic value in combinatorial therapies for BAT-specific thyromimetics and SIRT1 activators to combat metainflammation in this tissue.

Age-Dependent Changes of Adipokine and Cytokine Secretion From Rat Adipose Tissue by Endogenous and Exogenous Toll-Like Receptor Agonists

White adipose tissue but recently also brown adipose tissue have emerged as endocrine organs. Age-associated obesity is accompanied by prolonged and elevated lipopolysaccharide (LPS)-induced sickness symptoms and increased cytokine and adipokine levels in the circulation partially originating from adipose tissue. In the present study, ex vivo fat explants were used to investigate how the exogenous pathogen-associated molecular pattern (PAMP) LPS or the endogenous danger-associated molecular patterns (DAMPs) high mobility group box-1 protein (HMGB1) and biglycan modulate the release of cytokines and adipokines/batokines and, thus, could influence systemic and/or local inflammation. The response of adipose tissue (epididymal, retroperitoneal, subcutaneous, and brown) was compared between young lean and old obese rats (2 vs. 24 months old). LPS induced a strong interleukin (IL)-6 and tumor necrosis factor (TNF) alpha release into the supernatant of all adipose tissue types investigated. HMGB1 (subcutaneous) and biglycan (retroperitoneal) led to an increased release of IL-6 and TNFalpha (HMGB1) and decreased visfatin and adiponectin (biglycan) secretion from epididymal adipose tissue (young rats). Visfatin was also decreased by HMGB1 in retroperitoneal adipose tissue of old rats. We found significantly higher leptin (all fat pads) and adiponectin (subcutaneous) levels in supernatants of adipose tissue from old compared to young rats, whereas visfatin secretion showed the opposite. The expression of the biglycan receptor Toll-like receptor (TLR) 2 as well as the LPS and HMGB1 receptors TLR4 and receptor for advanced glycation end products (RAGE) were reduced with age (TLR4/RAGE) and by stimulation with their ligands (subcutaneous). Overall, we revealed that adipokines/adipose-tissue released cytokines show some modulation of their release caused by mediators of septic (batokines) and sterile inflammation with potential implication for acute and chronic disease. Moreover, aging may increase or decrease the release of fat-derived mediators. These data show that DAMPS and LPS locally modulate cytokine secretion while only DAMPS but not LPS can locally alter adipokine secretion during inflammation.

Elevated Levels of Circulating miR-92a Are Associated with Impaired Glucose Homeostasis in Patients with Obesity and Correlate with Metabolic Status After Bariatric Surgery

INTRODUCTION

miRNAs are small non-coding RNAs, some of which are expressed in adipose tissues, are present in the circulation, and are regulated in obesity. Bariatric surgery (BS) has been proposed to lead to activation of brown adipose tissue, an effect that may be related to beneficial effects of BS on systemic metabolism. Here, we evaluated circulating levels of miR-92a and miR-99b, two miRNAs proposed as biomarkers of brown fat activity, in a cohort of patients with severe obesity before and after BS, and studied their potential relationship with BS-associated improvements in metabolic parameters.

METHODS

Circulating levels of miR-92a and miR-99b were quantified in a cohort of 26 patients (age, 48 ± 10 years; BMI, 45 ± 7 kg/m²) before and 6 months after BS. Clinical parameters were determined at different time points and correlations among them were studied.

RESULTS

Basal levels of miR-92a were significantly increased in patients with obesity relative to lean controls. Serum miR-92a levels were strongly reduced at 6 months after BS, reaching levels similar to those in controls. Serum miR-99b levels were unchanged in relation to both the obese condition and BS. Elevated levels of miR-92a were directly correlated with worsened glucose homeostasis parameters and poor BS outcome.

CONCLUSIONS

Our findings show that miR-92a is elevated in conditions of obesity, and its reduction after BS correlates with metabolic improvement. Further studies would be necessary to establish miR-92a as serum biomarker and potential predictor of the BS success in improving the metabolic status of patients with obesity.

Adipogenesis: A Complex Interplay of Multiple Molecular Determinants and Pathways

The formation of adipocytes during embryogenesis has been largely understudied. However, preadipocytes appear to originate from multipotent mesenchymal stromal/stem cells which migrate from the mesoderm to their anatomical localization. Most studies on adipocyte formation (adipogenesis) have used preadipocytes derived from adult stem/stromal cells. Adipogenesis consists of two phases, namely commitment and terminal differentiation. This review discusses the role of signalling pathways, epigenetic modifiers, and transcription factors in preadipocyte commitment and differentiation into mature adipocytes, as well as limitations in our understanding of these processes. To date, a limited number of transcription factors, genes and signalling pathways have been described to regulate preadipocyte commitment. One reason could be that most studies on adipogenesis have used preadipocytes already committed to the adipogenic lineage, which are therefore not suitable for studying preadipocyte commitment. Conversely, over a dozen molecular players including transcription factors, genes, signalling pathways, epigenetic regulators, and microRNAs have been described to be involved in the differentiation of preadipocytes to adipocytes; however, only peroxisome proliferator-activated receptor gamma has proven to be clinically relevant. A detailed understanding of how the molecular players underpinning adipogenesis relate to adipose tissue function could provide new therapeutic approaches for addressing obesity without compromising adipose tissue function.

New Role for Growth/Differentiation Factor 15 in the Survival of Transplanted Brown Adipose Tissues in Cooperation with Interleukin-6

To identify factors involved in the earliest phase of the differentiation of human embryonic stem cells (hESCs) into brown adipocytes (BAs), we performed multi-time point microarray analyses. We found that growth/differentiation factor 15 (GDF15) expressions were specifically upregulated within three days of differentiation, when expressions of immature hESC markers were sustained. Although GDF15 expressions continued to increase in the subsequent differentiation phases, GDF15-deficient hESCs differentiated into mature BAs (Day 10) without apparent abnormalities. In addition, GDF15-deficient mice had normal brown adipose tissue (BAT) and were metabolically healthy. Unexpectedly, we found that interleukin-6 (IL6) expression was significantly lowered in the BAT of GDF15^-/- mice. In addition, GDF15^-/- hESCs showed abortive IL6 expressions in the later phase (>Day 6) of the differentiation. Interestingly, GDF15 expression was markedly repressed throughout the whole course of the differentiation of IL6^-/- hESCs into BAs, indicating IL6 is essential for the induction of GDF15 in the differentiation of hESCs. Finally, intraperitoneally transplanted BAT grafts of GDF15^-/- donor mice, but not those of wild-type (WT) mice, failed in the long-term survival (12 weeks) in GDF15^-/- recipient mice. Collectively, GDF15 is required for long-term survival of BAT grafts by creating a mutual gene induction loop with IL6.

Mechanisms linking adipose tissue inflammation to cardiac hypertrophy and fibrosis

Adipose tissue is classically recognized as the primary site of lipid storage, but in recent years has garnered appreciation for its broad role as an endocrine organ comprising multiple cell types whose collective secretome, termed as adipokines, is highly interdependent on metabolic homeostasis and inflammatory state. Anatomical location (e.g. visceral, subcutaneous, epicardial etc) and cellular composition of adipose tissue (e.g. white, beige, and brown adipocytes, macrophages etc.) also plays a critical role in determining its response to metabolic state, the resulting secretome, and its potential impact on remote tissues. Compared with other tissues, the heart has an extremely high and constant demand for energy generation, of which most is derived from oxidation of fatty acids. Availability of this fatty acid fuel source is dependent on adipose tissue, but evidence is mounting that adipose tissue plays a much broader role in cardiovascular physiology. In this review, we discuss the impact of the brown, subcutaneous, and visceral white, perivascular (PVAT), and epicardial adipose tissue (EAT) secretome on the development and progression of cardiovascular disease (CVD), with a particular focus on cardiac hypertrophy and fibrosis.

Adenosine A2A receptor activation prevents DOCA-salt induced hypertensive cardiac remodeling via iBAT

Hypertensive cardiac remodeling is a constellation of abnormalities that includes cardiomyocyte hypertrophy and death and tissue fibrosis. Adenosine is a long-known vasodilator, through interacting with its four cell surface receptor subtypes in cardiovascular system. However, it is unclear that whether adenosine A2A receptor (A2AR) activation is involved in the cardiac remodeling in hypertension. WT mice were utilized to induce DOCA-salt sensitive hypertension and received A2AR agonist CGS21680 or antagonist KW6002 treatment. Cardiac functional phenotyping measurement by echocardiography showed that CGS21680 improved cardiac dysfunction in DOCA-salt mice. Moreover, CGS21680 reduced cardiomyocyte hypertrophy, cardiac inflammation and fibrosis. However, iBAT depletion surgery induces dramatic cardiac remodeling in DOCA-salt mice, and the protective function of CGS21680 was blocked without intact iBAT. Mechanistically, A2AR agonist CGS21680 increased iBAT-derived fibroblast growth factor 21 (FGF21). Our data suggest that activation of A2AR could be a potential therapeutic strategy in preventing heart damage in hypertension.

Differential association between S100A4 levels and insulin resistance in prepubertal children and adult subjects with clinically severe obesity

OBJECTIVES

S100A4 has been recently identified as an adipokine associated with insulin resistance (IR) in adult subjects with obesity. However, no data about its levels in children with obesity and only a few approaches regarding its potential mechanism of action have been reported. To obtain a deeper understanding of the role of S100A4 in obesity, (a) S100A4 levels were measured in prepubertal children and adult subjects with and without obesity and studied the relationship with IR and (b) the effects of S100A4 in cultured human adipocytes and vascular smooth muscle cells (VSMCs) were determined.

METHODS

Sixty-five children (50 with obesity, age 9.0 ±1.1 years and 15 normal weight, age 8.4 ±0.8 years) and fifty-nine adults (43 with severe obesity, age 46 ±11 years and 16 normal weight, age 45 ±9 years) were included. Blood from children and adults and adipose tissue samples from adults were obtained and analysed. Human adipocytes and VSMC were incubated with S100A4 to evaluate their response to this adipokine.

RESULTS

Circulating S100A4 levels were increased in both children (P = .002) and adults (P < .001) with obesity compared with their normal-weight controls. In subjects with obesity, S100A4 levels were associated with homeostatic model assessment-insulin resistance (HOMA-IR) in adults (βstd = .42, P = .008) but not in children (βstd = .12, P = .356). Human adipocytes were not sensitive to S100A4, while incubation with this adipokine significantly reduced inflammatory markers in VSMC.

CONCLUSIONS

Our human data demonstrate that higher S100A4 levels are a marker of IR in adults with obesity but not in prepubertal children. Furthermore, the in vitro results suggest that S100A4 might exert an anti-inflammatory effect. Further studies will be necessary to determine whether S100A4 can be a therapeutic target for obesity.

A systematic review of the association of neuregulin 4, a brown fat-enriched secreted factor, with obesity and related metabolic disturbances

Neuregulin 4 (Nrg4), a novel brown fat-enriched hormone, plays a key role in the modulation of glucose and lipid metabolism and energy balance. Recent data have demonstrated that the expression of Nrg4 is substantially down-regulated in mouse and human obesity, making its regulatory aspect intriguing. Because of the close relationship between Nrg4, obesity, and associated metabolic diseases, this systematic review aimed to assess the association of Nrg4 with obesity and related metabolic disturbances, emphasizing its possible mechanisms of action in these disorders. We searched PubMed/Medline, ScienceDirect, Scopus, EMBASE, ProQuest, and Google Scholar up until June 2019. The evidence reviewed here indicates that Nrg4 may contribute to the prevention of obesity and related metabolic complications by elevating brown adipose tissue activity, increasing the expression of thermogenic markers, decreasing the expression of lipogenic/adipogenic genes, exacerbating white adipose tissue browning, increasing the number of brite/beige adipocytes, promoting hepatic fat oxidation and ketogenesis, inducing neurite outgrowth, enhancing blood vessels in adipose tissue, increasing the circulatory levels of healthy adipokines, and improving glucose homeostasis. Thus, Nrg4 appears to be a novel therapeutic strategy for the treatment of obesity and associated metabolic complications. However, prospective cohort studies are warranted to confirm these outcomes.

Glucose metabolism in brown adipose tissue determined by deuterium metabolic imaging in rats

BACKGROUND/OBJECTIVES

Brown adipose tissue (BAT) has gained growing interest as a potential target for treatment of obesity. Currently, the most widely used technique/method for in vivo measurements of BAT activity in humans is ¹⁸FDG PET/CT. To supplement these investigations novel radiation-free methods are warranted. Deuterium metabolic imaging (DMI) is a novel modality that combines magnetic resonance spectroscopic (MRS) imaging with deuterium-labelled glucose (²H-glucose). This allows for spatio-temporal and metabolic imaging beyond glucose uptake. We aimed to evaluate if DMI could discriminate glucose metabolism in BAT of cold-acclimatised and thermoneutral rats.

SUBJECTS/METHODS

Male Sprague-Dawley rats were housed in a cold environment (9 °C, n = 10) or at thermoneutrality (30 °C, n = 11) for 1 week. For imaging rats were anaesthetized, received a ²H-glucose (1 M, 1.95 g/kg) bolus and DMI was acquired at baseline followed by 20 min time intervals up to 2 h. Furthermore, Dixon MRI was performed for anatomical determination of the interscapular BAT (iBAT) depot along with dynamic contrast enhanced (DCE) MRI to evaluate perfusion.

RESULTS

²H-glucose signal was higher in cold-acclimatised rats compared with thermoneutral rats (p ≤ 0.001) indicating an overall increase in glucose uptake and metabolism. This was in line with a lower fat/water threshold, higher perfusion and increased UCP1 mRNA expression in iBAT (ninefold increment) of cold-acclimatised rats compared with thermoneutral rats.

CONCLUSIONS

We find that DMI can discriminate cold-acclimatised and thermoneutral BAT in rats. This is the first study to evaluate BAT activity by DMI, which may open up for the use of the non-radioactive DMI method for BAT measurements in humans.

Interaction between adipocytes and high-density lipoprotein:new insights into the mechanism of obesity-induced dyslipidemia and atherosclerosis

Obesity is the most common nutritional disorder worldwide and is associated with dyslipidemia and atherosclerotic cardiovascular disease. The hallmark of dyslipidemia in obesity is low high density lipoprotein (HDL) cholesterol (HDL-C) levels. Moreover, the quality of HDL is also changed in the obese setting. However, there are still some disputes on the explanations for this phenomenon. There is increasing evidence that adipose tissue, as an energy storage tissue, participates in several metabolism activities, such as hormone secretion and cholesterol efflux. It can influence overall reverse cholesterol transport and plasma HDL-C level. In obesity individuals, the changes in morphology and function of adipose tissue affect plasma HDL-C levels and HDL function, thus, adipose tissue should be the main target for the treatment of HDL metabolism in obesity. In this review, we will summarize the cross-talk between adipocytes and HDL related to cardiovascular disease and focus on the new insights of the potential mechanism underlying obesity and HDL dysfunction.

Single xenotransplant of rat brown adipose tissue prolonged the ovarian lifespan of aging mice by improving follicle survival

Prolonging the ovarian lifespan is attractive and challenging. An optimal clinical strategy must be safe, long-acting, simple, and economical. Allotransplantation of brown adipose tissue (BAT), which is most abundant and robust in infants, has been utilized to treat various mouse models of human disease. Could we use BAT to prolong the ovarian lifespan of aging mice? Could we try BAT xenotransplantation to alleviate the clinical need for allogeneic BAT due to the lack of voluntary infant donors? In the current study, we found that a single rat-to-mouse (RTM) BAT xenotransplantation did not cause systemic immune rejection but did significantly increase the fertility of mice and was effective for more than 5 months (equivalent to 10 years in humans). Next, we did a series of analysis including follicle counting; AMH level; estrous cycle; mTOR activity; GDF9, BMP15, LHR, Sirt1, and Cyp19a level; ROS and annexin V level; IL6 and adiponectin level; biochemical blood indices; body temperature; transcriptome; and DNA methylation studies. From these, we proposed that rat BAT xenotransplantation rescued multiple indices indicative of follicle and oocyte quality; rat BAT also improved the metabolism and general health of the aging mice; and transcriptional and epigenetic (DNA methylation) improvement in F0 mice could benefit F1 mice; and multiple KEGG pathways and GO classified biological processes the differentially expressed genes (DEGs) or differentially methylated regions (DMRs) involved were identical between F0 and F1. This study could be a helpful reference for clinical BAT xenotransplantation from close human relatives to the woman.

Renoprotective effects of brown adipose tissue activation in diabetic mice

BACKGROUND

Brown adipose tissue (BAT) has been regarded as a potential target organ to combat obesity and related metabolic disorders. However, the effect of BAT activation on the development of diabetic kidney disease (DKD) remains unclear.

METHODS

Diabetic mice were induced by streptozotocin (STZ) combined with a high-fat diet. To activate BAT, mice were administered 1 mg/kg per day, i.p., CL316,243, a β₃ -adrenergic receptor agonist, for 4 weeks. Blood glucose, serum lipids, adipokines, 24-hour urinary albumin, 8-hydroxydeoxyguanosine (8-OHdG), and circulating microRNA (miRNA) levels were analyzed, in addition to renal pathology. Histological changes (fibrosis, inflammation) were evaluated in the kidneys, as was the expression of oxidative stress-related genes. Renal signaling pathways (fibroblast growth factor [Fgf]21/β-klotho/FGF receptor 1c and AMP-activated protein kinase[AMPK]/sirtuin 1 [Sirt1]/peroxisome proliferator-activated receptor-γ coactivator-1α [Pgc1α]) were also evaluated.

RESULTS

Compared with untreated STZ-diabetic mice, CL316,243 treatment reduced blood glucose, albeit not significantly (20.58 ± 3.55 vs 23.60 ± 3.90 mM), and significantly decreased triglycerides and low-density lipoprotein cholesterol and increased high-density lipoprotein cholesterol. Simultaneously, BAT activation significantly decreased 24-hour urinary albumin (34.21 ± 6.28 vs 70.46 ± 15.81 μg/24 h; P < 0.05) and 8-OHdG, improved renal fibrosis, inflammation, and oxidative stress, and ameliorated renal morphological abnormalities. In addition to enhancing BAT activity, CL316,243 significantly increased serum adiponectin concentrations and renal Fgf21 sensitivity, and reactivated the renal AMPK/Sirt1/Pgc1α signaling pathway. Furthermore, CL316,243 treatment increased levels of some circulating miRNAs and downregulated expression of their target genes in the kidney.

CONCLUSIONS

Activating BAT could improve kidney injury in diabetic mice via metabolic improvements and renal AMPK activation by beneficial adipokines and miRNAs.

Chlorogenic Acid Stimulates the Thermogenesis of Brown Adipocytes by Promoting the Uptake of Glucose and the Function of Mitochondria

Brown adipose tissue (BAT) prevents obesity and related diseases by uncoupling oxidative phosphorylation with adenosine triphosphate. Previous studies have demonstrated that polyphenols can promote the thermogenesis of BAT in mice. Chlorogenic acid (CGA) is a common phenolic acid found in fruits and vegetables, as well as traditional Chinese medicine, which is responsible for a variety of physiological activities. However, it is still unclear whether CGA has positive effects on the thermogenesis of BAT. In this study, CGA enhances the thermogenesis and proton leak of brown adipocytes, however, no changes are evident regarding the differentiation of C₃ H₁₀ T_1/2 into brown adipocytes. Surprisingly, CGA promotes the uptake of glucose by upregulating the glucose transporter 2 and phosphofructokinase. Moreover, CGA increases the number and the function of mitochondrial. Taken together, CGA stimulates thermogenesis of brown adipocytes by promoting the uptake of glucose and the function of mitochondria. PRACTICAL APPLICATION: Chlorogenic acid (CGA) is widely found in fruits, vegetables, and traditional Chinese medicines, which has been considered to have antibacterial and anti-inflammatory function. However, whether it has the function of resisting obesity and promoting thermogenesis is still unclear. In this study, brown adipocyte was used to explore the function and mechanism of CGA on thermogenesis. It provides new ideas for the utilization of foods rich in CGA and traditional Chinese medicine.

Brown Adipose Tissue Development and Metabolism

Brown adipose tissue is well known to be a thermoregulatory organ particularly important in small rodents and human infants, but it was only recently that its existence and significance to metabolic fitness in adult humans have been widely realized. The ability of active brown fat to expend high amounts of energy has raised interest in stimulating thermogenesis therapeutically to treat metabolic diseases related to obesity and type 2 diabetes. In parallel, there has been a surge of research aimed at understanding the biology of rodent and human brown fat development, its remarkable metabolic properties, and the phenomenon of white fat browning, in which white adipocytes can be converted into brown like adipocytes with similar thermogenic properties. Here, we review the current understanding of the developmental and metabolic pathways involved in forming thermogenic adipocytes, and highlight some of the many unknown functions of brown fat that make its study a rich and exciting area for future research.

Annexins in Adipose Tissue: Novel Players in Obesity

Obesity and the associated comorbidities are a growing health threat worldwide. Adipose tissue dysfunction, impaired adipokine activity, and inflammation are central to metabolic diseases related to obesity. In particular, the excess storage of lipids in adipose tissues disturbs cellular homeostasis. Amongst others, organelle function and cell signaling, often related to the altered composition of specialized membrane microdomains (lipid rafts), are affected. Within this context, the conserved family of annexins are well known to associate with membranes in a calcium (Ca²⁺)- and phospholipid-dependent manner in order to regulate membrane-related events, such as trafficking in endo- and exocytosis and membrane microdomain organization. These multiple activities of annexins are facilitated through their diverse interactions with a plethora of lipids and proteins, often in different cellular locations and with consequences for the activity of receptors, transporters, metabolic enzymes, and signaling complexes. While increasing evidence points at the function of annexins in lipid homeostasis and cell metabolism in various cells and organs, their role in adipose tissue, obesity and related metabolic diseases is still not well understood. Annexin A1 (AnxA1) is a potent pro-resolving mediator affecting the regulation of body weight and metabolic health. Relevant for glucose metabolism and fatty acid uptake in adipose tissue, several studies suggest AnxA2 to contribute to coordinate glucose transporter type 4 (GLUT4) translocation and to associate with the fatty acid transporter CD36. On the other hand, AnxA6 has been linked to the control of adipocyte lipolysis and adiponectin release. In addition, several other annexins are expressed in fat tissues, yet their roles in adipocytes are less well examined. The current review article summarizes studies on the expression of annexins in adipocytes and in obesity. Research efforts investigating the potential role of annexins in fat tissue relevant to health and metabolic disease are discussed.

Adipose Tissue-Derived Signatures for Obesity and Type 2 Diabetes: Adipokines, Batokines and MicroRNAs

: Obesity is one of the main risk factors for type 2 diabetes mellitus (T2DM). It is closely related to metabolic disturbances in the adipose tissue that primarily functions as a fat reservoir. For this reason, adipose tissue is considered as the primary site for initiation and aggravation of obesity and T2DM. As a key endocrine organ, the adipose tissue communicates with other organs, such as the brain, liver, muscle, and pancreas, for the maintenance of energy homeostasis. Two different types of adipose tissues-the white adipose tissue (WAT) and brown adipose tissue (BAT)-secrete bioactive peptides and proteins, known as "adipokines" and "batokines," respectively. Some of them have beneficial anti-inflammatory effects, while others have harmful inflammatory effects. Recently, "exosomal microRNAs (miRNAs)" were identified as novel adipokines, as adipose tissue-derived exosomal miRNAs can affect other organs. In the present review, we discuss the role of adipose-derived secretory factors-adipokines, batokines, and exosomal miRNA-in obesity and T2DM. It will provide new insights into the pathophysiological mechanisms involved in disturbances of adipose-derived factors and will support the development of adipose-derived factors as potential therapeutic targets for obesity and T2DM.

Neuroendocrine Regulation of Energy Metabolism Involving Different Types of Adipose Tissues

Despite tremendous research efforts to identify regulatory factors that control energy metabolism, the prevalence of obesity has been continuously rising, with nearly 40% of US adults being obese. Interactions between secretory factors from adipose tissues and the nervous system innervating adipose tissues play key roles in maintaining energy metabolism and promoting survival in response to metabolic challenges. It is currently accepted that there are three types of adipose tissues, white (WAT), brown (BAT), and beige (BeAT), all of which play essential roles in maintaining energy homeostasis. WAT mainly stores energy under positive energy balance, while it releases fuels under negative energy balance. Thermogenic BAT and BeAT dissipate energy as heat under cold exposure to maintain body temperature. Adipose tissues require neural and endocrine communication with the brain. A number of WAT adipokines and BAT batokines interact with the neural circuits extending from the brain to cooperatively regulate whole-body lipid metabolism and energy homeostasis. We review neuroanatomical, histological, genetic, and pharmacological studies in neuroendocrine regulation of adipose function, including lipid storage and mobilization of WAT, non-shivering thermogenesis of BAT, and browning of BeAT. Recent whole-tissue imaging and transcriptome analysis of differential gene expression in WAT and BAT yield promising findings to better understand the interaction between secretory factors and neural circuits, which represents a novel opportunity to tackle obesity.

Beneficial Metabolic Effects of Mirabegron In Vitro and in High-Fat Diet-Induced Obese Mice

Mirabegron, a β3-adrenergic receptor agonist, has been shown to stimulate the activity of brown fat and increase the resting metabolic rate in humans. However, it is unknown whether mirabegron can reduce body weight and improve metabolic health. We investigated the antiobesity effects of mirabegron using both in vitro and in vivo models. Mouse brown preadipocytes and 3T3-L1 cells were treated with different concentrations of mirabegron (0.03-3 µg/ml), and the expression of brown fat-related genes was measured by quantitative real-time polymerase chain reaction. Furthermore, male C57BL/6J mice were fed a high-fat diet for 10 weeks, and mirabegron (2 mg/kg body weight) or a vehicle control was delivered to the interscapular brown adipose tissue (iBAT) using ALZET osmotic pumps from week 7 to 10. The metabolic parameters and tissues were analyzed. In both mouse brown preadipocytes and 3T3-L1 cells, mirabegron stimulated uncoupling protein 1 (UCP1) expression. In animal studies, mirabegron-treated mice had a lower body weight and adiposity. Lipid droplets in the iBAT of mirabegron-treated mice were fewer and smaller in size compared with those from vehicle-treated mice. H&E staining and immunohistochemistry indicated that mirabegron increased the abundance of beige cells in inguinal white adipose tissue (iWAT). Compared with vehicle-treated mice, mirabegron-treated mice had a higher gene expression of UCP1 (14-fold) and cell death-inducing DNA fragmentation factor alpha-like effector A (CIDEA) (4-fold) in iWAT. Furthermore, mirabegron-treated mice had improved glucose tolerance and insulin sensitivity. Taken together, mirabegron enhances UCP1 expression and promotes browning of iWAT, which are accompanied by improved glucose tolerance and insulin sensitivity and prevention from high-fat diet-induced obesity.