Three years with adult human brown adipose tissue

Brown Adipose Tissue, Batokines, and Bioactive Compounds in Foods: An Update

The discovery of metabolically active brown adipose tissue (BAT) in human adults and the worldwide increase in obesity and obesity-related chronic noncommunicable diseases (NCDs) has made BAT a therapeutic target in the last two decades. The potential of BAT to oxidize fatty acids rapidly and increase energy expenditure inversely correlates with adiposity, insulin and glucose resistance, and cardiovascular and metabolic diseases. Currently, BAT is recognized by a new molecular signature; several BAT-derived molecules that act positively on target tissues have been identified and collectively called batokines. Bioactive compounds present in foods are endowed with thermogenic properties that increase BAT activation signaling. Understanding the mechanisms that lead to BAT activation and the batokines secreted by it within the thermogenic state is fundamental for its recruitment and management of obesity and NCDs. This review contributes to recent updates on the morphophysiology of BAT, its endocrine role in obesity, and the main bioactive compounds present in foods involved in classical and nonclassical thermogenic pathways activation.

Exploring the Interplay between Bone Marrow Stem Cells and Obesity

Obesity, a complex disorder with rising global prevalence, is a chronic, inflammatory, and multifactorial disease and it is characterized by excessive adipose tissue accumulation and associated comorbidities. Adipose tissue (AT) is an extremely diverse organ. The composition, structure, and functionality of AT are significantly influenced by characteristics specific to everyone, in addition to the variability connected to various tissue types and its location-related heterogeneity. Recent investigation has shed light on the intricate relationship between bone marrow stem cells and obesity, revealing potential mechanisms that contribute to the development and consequences of this condition. Mesenchymal stem cells within the bone marrow, known for their multipotent differentiation capabilities, play a pivotal role in adipogenesis, the process of fat cell formation. In the context of obesity, alterations in the bone marrow microenvironment may influence the differentiation of mesenchymal stem cells towards adipocytes, impacting overall fat storage and metabolic balance. Moreover, bone marrow's role as a crucial component of the immune system adds another layer of complexity to the obesity-bone marrow interplay. This narrative review summarizes the current research findings on the connection between bone marrow stem cells and obesity, highlighting the multifaceted roles of bone marrow in adipogenesis and inflammation.

Brown adipose tissue: can it keep us slim? A discussion of the evidence for and against the existence of diet-induced thermogenesis in mice and men

The issue under discussion here is whether a decrease in the degree of UCP1 activity (and brown adipose tissue activity in general) could be a cause of obesity in humans. This possibility principally requires the existence of the phenomenon of diet-induced thermogenesis. Obesity could be a consequence of a reduced functionality of diet-induced thermogenesis. Experiments in mice indicate that diet-induced thermogenesis exists and is dependent on the presence of UCP1 and thus of brown adipose tissue activity. Accordingly, many (but not all) experiments indicate that in the absence of UCP1, mice become obese. Whether similar mechanisms exist in humans is still unknown. A series of studies have indicated a correlation between obesity and low brown adipose tissue activity, but it may be so that the obesity itself may influence the estimates of brown adipose tissue activity (generally glucose uptake), partly explaining the relationship. Estimates of brown adipose tissue catabolizing activity would seem to indicate that it may possess a capacity sufficient to help maintain body weight, and obesity would thus be aggravated in its absence. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part II)'.

Peroxisome proliferator-activated receptors as targets to treat metabolic diseases: Focus on the adipose tissue, liver, and pancreas

The world is experiencing reflections of the intersection of two pandemics: Obesity and coronavirus disease 2019. The prevalence of obesity has tripled since 1975 worldwide, representing substantial public health costs due to its comorbidities. The adipose tissue is the initial site of obesity impairments. During excessive energy intake, it undergoes hyperplasia and hypertrophy until overt inflammation and insulin resistance turn adipocytes into dysfunctional cells that send lipotoxic signals to other organs. The pancreas is one of the organs most affected by obesity. Once lipotoxicity becomes chronic, there is an increase in insulin secretion by pancreatic beta cells, a surrogate for type 2 diabetes mellitus (T2DM). These alterations threaten the survival of the pancreatic islets, which tend to become dysfunctional, reaching exhaustion in the long term. As for the liver, lipotoxicity favors lipogenesis and impairs beta-oxidation, resulting in hepatic steatosis. This silent disease affects around 30% of the worldwide population and can evolve into end-stage liver disease. Although therapy for hepatic steatosis remains to be defined, peroxisome proliferator-activated receptors (PPARs) activation copes with T2DM management. Peroxisome PPARs are transcription factors found at the intersection of several metabolic pathways, leading to insulin resistance relief, improved thermogenesis, and expressive hepatic steatosis mitigation by increasing mitochondrial beta-oxidation. This review aimed to update the potential of PPAR agonists as targets to treat metabolic diseases, focusing on adipose tissue plasticity and hepatic and pancreatic remodeling.

Isolation and Differentiation of Adipocyte Precursors Derived from Neonatal Murine Brown Adipose Tissue

Brown adipose tissue (BAT) is an important regulator of energy homeostasis. Primary brown adipocyte culture provides a powerful and physiologically relevant tool for in vitro studies related to BAT. Here, we describe a detailed procedure for isolation and differentiation of adipocyte precursors from neonatal murine interscapular BAT (iBAT).

Liposarcoma With Hibernoma-like Histology: A Clinicopathologic Study of 16 Cases

Hibernoma is an uncommon benign tumor of brown fat cells that consistently expresses uncoupling protein 1 (UCP1). Herein, we clinicopathologically characterized 16 liposarcomas, for which histology, at least focally, closely resembled that of hibernoma, including sheets of brown fat-like, finely multivacuolated-to-eosinophilic tumor cells with no or minimal nuclear atypia. The cohort consisted of 4 well-differentiated liposarcomas (WDLSs), 6 dedifferentiated liposarcomas with a concomitant WDLS component, and 6 myxoid liposarcomas (MLSs). For all dedifferentiated liposarcoma cases, hibernoma-like histology was present only in the WDLS component. All tumors presented as large, deep-seated masses. Hibernoma-like histology resembled the pale cell, mixed cell, eosinophilic cell, or spindle cell subtypes of hibernoma, and it was a focal observation, with conventional liposarcoma histology coexisting in all cases. However, a few biopsy samples were predominated by hibernoma-like patterns, and 1 case was initially interpreted as hibernoma. Hibernoma-like components in WDLS immunohistochemically coexpressed MDM2 and CDK4 in most cases and harboredMDM2amplification in tested cases, whereas half of the cases expressed UCP1. The hibernoma-like components of MLS expressed DDIT3, andDDIT3rearrangements were present in the tested cases, whereas only negative or equivocal UCP1 expression was observed. In summary, WDLS and MLS focally demonstrate hibernoma-like histology on rare occasions. These elements are neoplastic, and some such areas in WDLS likely represent true brown fat differentiation, as supported by UCP1 expression. This pattern requires recognition to avoid the misdiagnosis as hibernoma, especially in biopsies. A careful search for classic liposarcoma histology and additional work-ups for the MDM2/CDK4 or DDIT3 status will be helpful for an accurate diagnosis.

Effects of a short-term cold exposure on circulating microRNAs and metabolic parameters in healthy adult subjects

This discovery study investigated in healthy subjects whether a short‐term cold exposure may alter circulating microRNAs and metabolic parameters and if co‐expression networks between these factors could be identified. This open randomized crossover (cold vs no cold exposure) study with blind end‐ point evaluation was conducted at 1 center with 10 healthy adult male volunteers. Wearing a cooling vest perfused at 14°C for 2 h reduced the local skin temperature without triggering shivering, increased norepinephrine and blood pressure while decreasing copeptin, C‐peptide and heart rate. Circulating microRNAs measured before and after wearing the cooling vest twice (4 time points) identified 196 mature microRNAs with excellent reproducibility over 72 h. Significant correlations of microRNA expression with copeptin, norepinephrine and C‐peptide were found. A co‐expression‐based microRNA‐microRNA network, as well as microRNA pairs displaying differential correlation as a function of temperature were also detected. This study demonstrates that circulating miRNAs are differentially expressed and coregulated upon cold exposure in humans, supporting their use as predictive and dynamic biomarkers of cardio‐metabolic disorders.

Metabolic determinants of Alzheimer's disease: A focus on thermoregulation

Alzheimer's disease (AD) is a complex age-related neurodegenerative disease, associated with central and peripheral metabolic anomalies, such as impaired glucose utilization and insulin resistance. These observations led to a considerable interest not only in lifestyle-related interventions, but also in repurposing insulin and other anti-diabetic drugs to prevent or treat dementia. Body temperature is the oldest known metabolic readout and mechanisms underlying its maintenance fail in the elderly, when the incidence of AD rises. This raises the possibility that an age-associated thermoregulatory deficit contributes to energy failure underlying AD pathogenesis. Brown adipose tissue (BAT) plays a central role in thermogenesis and maintenance of body temperature. In recent years, the modulation of BAT activity has been increasingly demonstrated to regulate energy expenditure, insulin sensitivity and glucose utilization, which could also provide benefits for AD. Here, we review the evidence linking thermoregulation, BAT and insulin-related metabolic defects with AD, and we propose mechanisms through which correcting thermoregulatory impairments could slow the progression and delay the onset of AD.

Inhibition of a Novel CLK1-THRAP3-PPARγ Axis Improves Insulin Sensitivity

Increasing energy expenditure by promoting "browning" in adipose tissues is a promising strategy to prevent obesity and associated diabetes. To uncover potential targets of cold exposure, which induces energy expenditure, we performed phosphoproteomics profiling in brown adipose tissue of mice housed in mild cold environment at 16°C. We identified CDC2-like kinase 1 (CLK1) as one of the kinases that were significantly downregulated by mild cold exposure. In addition, genetic knockout of CLK1 or chemical inhibition in mice ameliorated diet-induced obesity and insulin resistance at 22°C. Through proteomics, we uncovered thyroid hormone receptor-associated protein 3 (THRAP3) as an interacting partner of CLK1, further confirmed by co-immunoprecipitation assays. We further demonstrated that CLK1 phosphorylates THRAP3 at Ser243, which is required for its regulatory interaction with phosphorylated peroxisome proliferator-activated receptor gamma (PPARγ), resulting in impaired adipose tissue browning and insulin sensitivity. These data suggest that CLK1 plays a critical role in controlling energy expenditure through the CLK1-THRAP3-PPARγ axis.

Melanin-concentrating hormone-producing neurons in the hypothalamus regulate brown adipose tissue and thus contribute to energy expenditure

KEY POINTS

Melanin-concentrating hormone (MCH) neuron-ablated mice exhibit increased energy expenditure and reduced fat weight. Increased brown adipose tissue (BAT) activity and locomotor activity-independent energy expenditure contributed to body weight reduction in MCH neuron-ablated mice. MCH neurons send inhibitory input to the medullary raphe nucleus to modulate BAT activity.

ABSTRACT

Hypothalamic melanin-concentrating hormone (MCH) peptide robustly affects energy homeostasis. However, it is unclear whether and how MCH-producing neurons, which contain and release a variety of neuropeptides/transmitters, regulate energy expenditure in the central nervous system and peripheral tissues. We thus examined the regulation of energy expenditure by MCH neurons, focusing on interscapular brown adipose tissue (BAT) activity. MCH neuron-ablated mice exhibited reduced body weight, increased oxygen consumption, and increased BAT activity, which improved locomotor activity-independent energy expenditure. Trans-neuronal retrograde tracing with the recombinant pseudorabies virus revealed that MCH neurons innervate BAT via the sympathetic premotor region in the medullary raphe nucleus (MRN). MRN neurons were activated by MCH neuron ablation. Therefore, endogenous MCH neuron activity negatively modulates energy expenditure via BAT inhibition. MRN neurons might receive inhibitory input from MCH neurons to suppress BAT activity.

Pharmacological modulation of RORα controls fat browning, adaptive thermogenesis, and body weight in mice

Beiging is an attractive therapeutic strategy to fight against obesity and its side metabolic complications. The loss of function of the nuclear transcription factor RORα has been related to a lean phenotype with higher thermogenesis in sg/sg mice lacking this protein. Here we show that pharmacological modulation of RORα activity exerts reciprocal and cell-autonomous effect on UCP1 expression ex vivo, in cellulo, and in vivo. The RORα inverse-agonist SR3335 upregulated UCP1 expression in brown and subcutaneous white adipose tissue (scWAT) explants of wild-type (WT) mice, whereas the RORα agonist SR1078 had the opposite effect. We confirmed the reciprocal action of these synthetic RORα ligands on gene expression, mitochondrial mass, and uncoupled oxygen consumption rate in cultured murine and human adipocytes. Time course analysis revealed stepwise variation in gene expression, first of TLE3, an inhibitor of the thermogenic program, followed by a reciprocal effect on PRDM16 and UCP1. Finally, RORα ligands were shown to be useful tools to modulate in vivo UCP1 expression in scWAT with associated changes in this fat depot mass. SR3335 and SR1078 provoked the opposite effects on the WT mice body weight, but without any effect on sg/sg mice. This slimming effect of SR3335 was related to an increased adaptive thermogenesis of the mice, as assessed by the rectal temperature of cold-stressed mice and induction of UCP1 in scWAT, as well as by indirect calorimetry in presence or not of a β3-adrenoceptor agonist. These data confirmed that RORα ligands could be useful tools to modulate thermogenesis and energy homeostasis.NEW & NOTEWORTHY The regulation of adipose tissue browning was not fully deciphered and required further studies explaining how the regulation of this process may be of interest for tackling obesity and related metabolic disorders. Our data confirmed the involvement of the transcription factor RORα in the regulation of nonshivering thermogenesis, and importantly, revealed the possibility to in vivo modulate its activity by synthetic ligands with beneficial consequences on fat mass and body weight of the mice.

Quantification of Lipoprotein Uptake in Vivo Using Magnetic Particle Imaging and Spectroscopy

Lipids are a major source of energy for most tissues, and lipid uptake and storage is therefore crucial for energy homeostasis. So far, quantification of lipid uptake in vivo has primarily relied on radioactive isotope labeling, exposing human subjects or experimental animals to ionizing radiation. Here, we describe the quantification of in vivo uptake of chylomicrons, the primary carriers of dietary lipids, in metabolically active tissues using magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS). We show that loading artificial chylomicrons (ACM) with iron oxide nanoparticles (IONPs) enables rapid and highly sensitive post hoc detection of lipid uptake in situ using MPS. Importantly, by utilizing highly magnetic Zn-doped iron oxide nanoparticles (ZnMNPs), we generated ACM with MPI tracer properties superseding the current gold-standard, Resovist, enabling quantification of lipid uptake from whole-animal scans. We focused on brown adipose tissue (BAT), which dissipates heat and can consume a large part of nutrient lipids, as a model for tightly regulated and inducible lipid uptake. High BAT activity in humans correlates with leanness and improved cardiometabolic health. However, the lack of nonradioactive imaging techniques is an important hurdle for the development of BAT-centered therapies for metabolic diseases such as obesity and type 2 diabetes. Comparison of MPI measurements with iron quantification by inductively coupled plasma mass spectrometry revealed that MPI rivals the performance of this highly sensitive technique. Our results represent radioactivity-free quantification of lipid uptake in metabolically active tissues such as BAT.

Weight gain in patients with severe atopic dermatitis treated with dupilumab: a cohort study

BACKGROUND

Dupilumab, targeting the interleukin-4α receptor and inhibiting the action of interleukin-4 and interleukin-13, was recently approved for treatment of moderate to severe atopic dermatitis. There is limited data on long-term effects and safety among patients with severe atopic dermatitis treated with dupilumab. Weight gain was observed among patients treated with dupilumab in our clinic. The aim was to describe weight change in a cohort study of patients with severe atopic dermatitis treated with dupilumab from baseline to follow-up after 12 months, and to analyze if weight change was associated with effect of treatment, reported appetite, and/or disturbed night sleep due to itching.

METHODS

All patients with atopic dermatitis receiving systemic treatment at the Unit of Dermatology, Karolinska University Hospital, have been registered and monitored consecutively since January 2017. This cohort constituted all patients who started treatment on dupilumab or methotrexate between 10 January 2017 and 30 June 2019 with at least 6 months of follow-up within the study period. The following variables were monitored at start of and during treatment: Eczema Severity Score Index, Patient-Oriented Eczema Measure, visual analogue scale for pruritus 10 cm, Montgomery-Åsberg Depression Rating Scale, Dermatology Life Quality Index, and weight. Data analyses were performed using two-sample Wilcoxon-Mann-Whitney rank-sum test, or the Wilcoxon matched-pairs sign-rank test with a p-value < 0.05 considered as statistically significant.

RESULTS

Patients treated with dupilumab (n = 12) gained weight (mean 6.1 kg, range [0.1-18.0], p = 0.002) after 1 year on treatment. The majority of patients showed a good response to treatment with dupilumab (n = 11); at follow-up at 6, 9, or 12 months, they reached EASI-90 (n = 6), EASI-75 (n = 4), or EASI-50 (n = 1). There was no significant association between weight gain and treatment response, reported appetite, or disturbed night-sleep due to itch. Patients treated with methotrexate showed no significant weight change (n = 8).

CONCLUSIONS

To our knowledge, this is the first report on a possible association between weight gain and dupilumab treatment; the extent of the association is yet to be seen, as is the mechanism behind this finding.

Human thermogenic adipocyte regulation by the long noncoding RNA LINC00473

Human thermogenic adipose tissue mitigates metabolic disease, raising much interest in understanding its development and function. Here, we show that human thermogenic adipocytes specifically express a primate-specific long non-coding RNA, LINC00473 which is highly correlated with UCP1 expression and decreased in obesity and type-2 diabetes. LINC00473 is detected in progenitor cells, and increases upon differentiation and in response to cAMP. In contrast to other known adipocyte LincRNAs, LINC00473 shuttles out of the nucleus, colocalizes and can be crosslinked to mitochondrial and lipid droplet proteins. Up- or down- regulation of LINC00473 results in reciprocal alterations in lipolysis, respiration and transcription of genes associated with mitochondrial oxidative metabolism. Depletion of PLIN1 results in impaired cAMP-responsive LINC00473 expression and lipolysis, indicating bidirectional interactions between PLIN1, LINC00473 and mitochondrial oxidative functions. Thus, we suggest that LINC00473 is a key regulator of human thermogenic adipocyte function, and reveals a role for a LincRNA in inter-organelle communication and human energy metabolism.

Indirubin, a small molecular deriving from connectivity map (CMAP) screening, ameliorates obesity-induced metabolic dysfunction by enhancing brown adipose thermogenesis and white adipose browning

Background

Obesity occurs when the body’s energy intake is constantly greater than its energy consumption and the pharmacological enhancing the activity of brown adipose tissue (BAT) and (or) browning of white adipose tissue (WAT) has been considered promising strategies to treat obesity.

Methods

In this study, we took a multi-pronged approach to screen UCP1 activators, including in silico predictions, in vitro assays, as well as in vivo experiments.

Results

Base on Connectivity MAP (CMAP) screening, we obtained multiple drugs that possess a remarkably correlating gene expression pattern to that of enhancing activity in BAT and (or) sWAT signature. Particularly, we focused on a previously unreported drug-indirubin, a compound obtained from the Indigo plant, which is now mainly used for the treatment of chronic myelogenous leukemia (CML). In the current study, our results shown that indirubin could enhance the BAT activity, as evidenced by up-regulated Ucp1 expression and enhanced mitochondrial respiratory function in vitro cellular model. Furthermore, indirubin treatment restrained high-fat diet (HFD)-induced body weight gain, improved glucose homeostasis and ameliorated hepatic steatosis which were associated with the increase of energy expenditure in the mice model. Moreover, we revealed that indirubin treatment increased BAT activity by promoting thermogenesis and mitochondrial biogenesis in BAT and induced browning of subcutaneous inguinal white adipose tissue (sWAT) of mice under HFD. Besides, our results indicated that indirubin induced UCP1 expression in brown adipocytes, at least in part, via activation of PKA and p38MAPK signaling pathways.

Conclusions

Our results clearly show that as an effective BAT (as well as beige cells) activator, indirubin may have a protective effect on the prevention and treatment of obesity and its complications.

Aifm2, a NADH Oxidase, Supports Robust Glycolysis and Is Required for Cold- and Diet-Induced Thermogenesis

Brown adipose tissue (BAT) is highly metabolically active tissue that dissipates energy via UCP1 as heat, and BAT mass is correlated negatively with obesity. The presence of BAT/BAT-like tissue in humans renders BAT as an attractive target against obesity and insulin resistance. Here, we identify Aifm2, a NADH oxidoreductase domain containing flavoprotein, as a lipid droplet (LD)-associated protein highly enriched in BAT. Aifm2 is induced by cold as well as by diet. Upon cold or β-adrenergic stimulation, Aifm2 associates with the outer side of the mitochondrial inner membrane. As a unique BAT-specific first mammalian NDE (external NADH dehydrogenase)-like enzyme, Aifm2 oxidizes NADH to maintain high cytosolic NAD levels in supporting robust glycolysis and to transfer electrons to the electron transport chain (ETC) for fueling thermogenesis. Aifm2 in BAT and subcutaneous white adipose tissue (WAT) promotes oxygen consumption, uncoupled respiration, and heat production during cold- and diet-induced thermogenesis. Aifm2, thus, can ameliorate diet-induced obesity and insulin resistance.

A decrease in brown adipose tissue activity is associated with weight gain during chemotherapy in early breast cancer patients

Background

A decrease in thermogenesis is suspected to be implicated in the energy expenditure reduction during breast cancer treatment. This study aimed to investigate the impact of chemotherapy on the metabolic activity of brown adipose tissue (BAT) and the link with weight variation.

Methods

This was an ancillary analysis of a multicentre trial involving 109 HER2+ breast cancer patients treated with neoadjuvant chemotherapy. A centralised review of ¹⁸F-FDG uptake intensity (SUV_max) in specific BAT regions (cervical and supraclavicular) was conducted on two PET-CT scans for each patient (before and after the first course of chemotherapy).

Results

Overall, after one course of chemotherapy a significant decrease of 4.4% in ¹⁸F-FDG-uptake intensity was observed. It was not correlated to initial BMI, age or season. During chemotherapy, 10.1% (n = 11) of the patients lost weight (− 7.7 kg ± 3.8 kg; ie, − 9.4% ± 3.7%) and 29.4% (n = 32) gained weight (+ 5.1 kg ± 1.7 kg; ie, + 8.5% ± 2.6%). Among these subgroups, only the patients who had gained weight underwent a significant decrease (13.42%) in ¹⁸F-FDG uptake intensity (p = 0.042).

Conclusion

This study is the first to highlight in a large cohort of patients the negative impact of chemotherapy on brown adipose tissue activity. Weight gain during chemotherapy could thus potentially be explained in part by a decrease in brown adipose tissue activity.

Rain exacerbates cold and metabolic strain during high-intensity running

BACKGROUND

Outdoor exercise often proceeds in rainy conditions. However, there are very few studies reporting the physiological effects of cold with rain or wet-cold exposure on humans during exercise. The purpose of this study was to investigate the effects of rain on physiological responses during running exercise at 80% V̇Omax in the cold.

METHODS

Twelve healthy men (age: 21.7±3.3 years; height: 1.760±0.085 m; body weight: 68.8±7.1 kg; maximal oxygen consumption: 67.3±5.00 mL/kg/min) exercised on a treadmill at 80% V̇Omax intensity for 60 minutes with rain (RAIN) or not (CON) at 5 °C.

RESULTS

Rectal temperature was significantly lower in RAIN than in CON at 10, 40, 50, and 60 minutes (P<0.05). Mean weighted skin temperature was significantly lower in RAIN than in CON during exercise (P<0.05). Oxygen consumption and rating of perceived exertion were significantly higher in RAIN than in CON at 50 and 60 minutes (P<0.05). Plasma lactate was significantly higher in RAIN than in CON at 10 minutes and from 40 to 60 minutes (P<0.05). Plasma norepinephrine levels were significantly higher in RAIN than in CON at 10 minutes and from 40 to 60 minutes (P<0.05).

CONCLUSIONS

These results suggest that rain increased heat loss during the early phase of exercise in the cold, then heat production increased and transiently suppressed cold stress. However, with time, body heat loss intensified due to increasing wet area, and then energy expenditure and plasma lactate increased due to cold stress. Therefore, rain may decrease exercise performance and affect sport safety.

Association of circulating exosomal miR-122 levels with BAT activity in healthy humans

Brown adipose tissue (BAT) plays an important role in body fat accumulation and the regulation of energy expenditure. Since the role of miRNAs in the pathogenesis of obesity and related metabolic diseases is contentious, we analyzed exosomal miRNAs in serum of healthy subjects with special references to BAT activity and body fat level. Forty male volunteers aged 20–30 years were recruited. Their BAT activity was assessed by fluorodeoxyglucose positron emission tomography and computed tomography after 2 h of cold exposure and expressed as a maximal standardized uptake value (SUVmax). Exosomal miRNA levels was analyzed using microarray and real-time PCR analyses. The miR-122-5p level in the high BAT activity group (SUV ≧ 3) was 53% lower than in the low BAT activity group (SUVmax <3). Pearson’s correlation analysis revealed that the serum miR-122-5p level correlated negatively with BAT activity and the serum HDL-cholesterol, and it correlated positively with age, BMI, body fat mass, and total cholesterol and triglyceride serum levels. Multivariate regression analysis revealed that BAT activity was associated with the serum miR-122-5p level independently of the other parameters. These results reveal the serum exosomal miR-122-5p level is negatively associated with BAT activity independently of obesity.

Bitter Orange (Citrus aurantium Linné) Improves Obesity by Regulating Adipogenesis and Thermogenesis through AMPK Activation

Obesity is a global health threat. Herein, we evaluated the underlying mechanism of anti-obese features of bitter orange (Citrus aurantium Linné, CA). Eight-week-administration of CA in high fat diet-induced obese C57BL/6 mice resulted in a significant decrease of body weight, adipose tissue weight and serum cholesterol. In further in vitro studies, we observed decreased lipid droplets in CA-treated 3T3-L1 adipocytes. Suppressed peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT/enhancer binding protein alpha indicated CA-inhibited adipogenesis. Moreover, CA-treated primary cultured brown adipocytes displayed increased differentiation associated with elevation of thermogenic factors including uncoupling protein 1 and PPARγ coactivator 1 alpha as well. The effects of CA in both adipocytes were abolished in AMP-activated protein kinase alpha (AMPKα)-suppressed environments, suggesting the anti-adipogenic and pro-thermogenic actions of CA were dependent on AMPKα pathway. In conclusion, our results suggest CA as a potential anti-obese agent which regulates adipogenesis and thermogenesis via AMPKα.

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

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

Vascular Endothelial Growth Factor-A Deficiency in Perivascular Adipose Tissue Impairs Macrovascular Function

Objective: Thoracic perivascular adipose tissue (PVAT) has been shown to release factors that influence the functioning of neighboring vascular tissue. Cardiovascular complications of obesity are on the rise; therefore, this study set out to determine if adipose-specific ablation of vascular endothelial growth factor-A (VEGF-A) plays a role in the maintenance of aortic structure and function.

Methods: Adipose-specific VEGF-A-deficient mice were previously generated. Fabp4cre(+). VEGF^flox/flox and Fabp4cre(−). VEGF^flox/flox mice were maintained on chow diet. PVAT gene expression was measured with real-time quantitative PCR. Aortic vasomotor response was assessed with isometric tension measurements. Collagen deposition was analyzed histologically in the vascular media and compared using ratiometric pigment density.

Results: PVAT-specific adiponectin expression was decreased in Fabp4cre(+). VEGF^flox/flox mice. Isometric tension measurements revealed a dose-dependent dysfunction in response to acetylcholine within the distal aortic segment of Fabp4cre(+). VEGF^flox/flox. Fabp4cre(+). VEGF^flox/flox mice exhibited increased aortic deposition of collagen within the thoracic adventitial and medial spaces.

Conclusion: These data demonstrate that decreased expression of VEGF-A within the surrounding adipose tissue microenvironment of the thoracic aorta has a detrimental effect on aortic integrity and vascular function. Modulation of angiogenic pathways within PVAT may offer an important avenue toward the treatment of adipose tissue dysfunction in obesity and its vascular complications.

MitoNEET in Perivascular Adipose Tissue Prevents Arterial Stiffness in Aging Mice

PURPOSE

Arterial stiffness is an inevitable consequence of the aging process and is considered an early stage in the development of cardiovascular diseases. The perivascular adipose tissue (PVAT) is a distinct functional integral layer of the vasculature actively involved in blood pressure regulation and atherosclerosis development via PVAT-derived paracrine/autocrine factors. However, there is little knowledge regarding the relationship between PVAT and arterial stiffness.

METHODS

Using unique mice lacking PVAT, high-fat diet-induced obesity, and in mice overexpressing brown adipocyte selective mitoNEET, we investigated the relationship between PVAT and arterial stiffness in mice.

RESULTS

We found that lack of PVAT enhanced arterial stiffness in aging mice. High-fat diet feeding of aging C57BL/6J wild-type mice significantly induced hypertrophic PVAT and enhanced arterial stiffness. Furthermore, the expression of mitoNEET, a mitochondrial membrane protein related to energy expenditure, was significantly increased by pioglitazone treatment, while reduced in the hypertrophic PVAT induced by high-fat diet. Overexpression of mitoNEET in PVAT reduced the expression of inflammatory genes and was associated with lower pulse wave velocity in aging mice.

CONCLUSIONS

These data indicate that local PVAT homeostasis especially inflammation in PVAT is associated with arterial stiffness development. Pioglitazone-induced mitoNEET in PVAT prevents PVAT inflammation and is negatively associated with arterial stiffness. These findings provide new experimental insight into the roles of pioglitazone on PVAT in arterial stiffness and indicate that PVAT might be a target to treat or prevent cardiovascular disease.

Eicosapentaenoic Acid Reduces Adiposity, Glucose Intolerance and Increases Oxygen Consumption Independently of Uncoupling Protein 1

SCOPE

Brown adipose tissue (BAT) dissipates energy through uncoupling protein 1 (UCP1) and has been proposed as an anti-obesity target. It was reported previously that a high-fat (HF) diet enriched in eicosapentaenoic acid (EPA) significantly increased UCP1 and other thermogenic markers in BAT. It is hypothesized that these effects are mediated through UCP1-dependent regulation.

METHODS AND RESULTS

Wild-type (WT) and UCP1 knockout (KO) B6 male mice were housed at thermoneutrality and fed a HF diet, without or with eicosapentaenoic acid (EPA)-enriched fish oil. HF-fed KO mice were heavier and had higher BAT lipid content than other groups. Protective effects of EPA in WT, previously observed at 22 °C (reduced adiposity, improved glucose tolerance, and increased UCP1), disappeared at thermoneutrality. Mitochondrial proteins, cytochrome c oxidase subunit 1 (COX I), COX I, II, and IV were reduced in the KO mice compared to WT. Unexpectedly, EPA attenuated weight and fat mass gain and improved glucose tolerance in the KO mice. Finally, EPA increased BAT peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1α) protein and gene expression, and whole-body oxygen consumption in KO mice, consistent with increased mitochondria DNA (mtDNA)/nuclear DNA (nucDNA) ratio.

CONCLUSIONS

EPA rescued the weight gain and glucose intolerance in UCP1 KO mice at thermoneutrality, independent of UCP1; these effects may be mediated in part via increased oxygen consumption and BAT PGC1α.

STK25 regulates oxidative capacity and metabolic efficiency in adipose tissue

Whole-body energy homeostasis at over-nutrition critically depends on how well adipose tissue remodels in response to excess calories. We recently identified serine/threonine protein kinase (STK)25 as a critical regulator of ectopic lipid storage in non-adipose tissue and systemic insulin resistance in the context of nutritional stress. Here, we investigated the role of STK25 in regulation of adipose tissue dysfunction in mice challenged with a high-fat diet. We found that overexpression of STK25 in high-fat-fed mice resulted in impaired mitochondrial function and aggravated hypertrophy, inflammatory infiltration and fibrosis in adipose depots. Reciprocally, Stk25-knockout mice displayed improved mitochondrial function and were protected against diet-induced excessive fat storage, meta-inflammation and fibrosis in brown and white adipose tissues. Furthermore, in rodent HIB-1B cell line, STK25 depletion resulted in enhanced mitochondrial activity and consequently, reduced lipid droplet size, demonstrating an autonomous action for STK25 within adipocytes. In summary, we provide the first evidence for a key function of STK25 in controlling the metabolic balance of lipid utilization vs lipid storage in brown and white adipose depots, suggesting that repression of STK25 activity offers a potential strategy for establishing healthier adipose tissue in the context of chronic exposure to dietary lipids.

Brown Adipose Tissue Energy Metabolism in Humans

The demonstration of metabolically active brown adipose tissue (BAT) in humans primarily using positron emission tomography coupled to computed tomography (PET/CT) with the glucose tracer 18-fluorodeoxyglucose (18FDG) has renewed the interest of the scientific and medical community in the possible role of BAT as a target for the prevention and treatment of obesity and type 2 diabetes (T2D). Here, we offer a comprehensive review of BAT energy metabolism in humans. Considerable advances in methods to measure BAT energy metabolism, including nonesterified fatty acids (NEFA), chylomicron-triglycerides (TG), oxygen, Krebs cycle rate, and intracellular TG have led to very good quantification of energy substrate metabolism per volume of active BAT in vivo. These studies have also shown that intracellular TG are likely the primary energy source of BAT upon activation by cold. Current estimates of BAT's contribution to energy expenditure range at the lower end of what would be potentially clinically relevant if chronically sustained. Yet, 18FDG PET/CT remains the gold-standard defining method to quantify total BAT volume of activity, used to calculate BAT's total energy expenditure. Unfortunately, BAT glucose metabolism better reflects BAT's insulin sensitivity and blood flow. It is now clear that most glucose taken up by BAT does not fuel mitochondrial oxidative metabolism and that BAT glucose uptake can therefore be disconnected from thermogenesis. Furthermore, BAT thermogenesis is efficiently recruited upon repeated cold exposure, doubling to tripling its total oxidative capacity, with reciprocal reduction of muscle thermogenesis. Recent data suggest that total BAT volume may be much larger than the typically observed 50-150 ml with 18FDG PET/CT. Therefore, the current estimates of total BAT thermogenesis, largely relying on total BAT volume using 18FDG PET/CT, may underestimate the true contribution of BAT to total energy expenditure. Quantification of the contribution of BAT to energy expenditure begs for the development of more integrated whole body in vivo methods.

Adipose tissue depots and inflammation: effects on plasticity and resident mesenchymal stem cell function

Adipose tissue (AT) is a highly heterogeneous organ. Beside the heterogeneity associated to different tissue types (white, brown, and 'brite') and its location-related heterogeneity (subcutaneous, visceral, epicardial, and perivascular, etc.), AT composition, structure, and functionality are highly dependent on individual-associated factors. As such, the pro-inflammatory state associated to the presence of obesity and other cardiovascular risk factors (CVRFs) directly affects AT metabolism. Furthermore, the adipose-derived stem cells (ASCs) that reside in the stromal vascular fraction of AT, besides being responsible for most of the plasticity attributed to AT, is an additional source of heterogeneity. Thus, ASCs directly contribute to AT homeostasis, cell renewal, and spontaneous repair. These ASCs share many properties with the bone-marrow mesenchymal stem cells (i.e. potential to differentiate towards multiple tissue lineages, and angiogenic, antiapoptotic, and immunomodulatory properties). Moreover, ASCs show clear advantages in terms of accessibility and quantity of available sample, their easy in vitro expansion, and the possibility of having an autologous source. All these properties point out towards a potential use of ASCs in regenerative medicine. However, the presence of obesity and other CVRFs induces a pro-inflammatory state that directly impacts ASCs proliferation and differentiation capacities affecting their regenerative abilities. The focus of this review is to summarize how inflammation affects the different AT depots and the mechanisms by which these changes further enhance the obesity-associated metabolic disturbances. Furthermore, we highlight the impact of obesity-induced inflammation on ASCs properties and how those effects impair their plasticity.

Ablation of PPARγ in subcutaneous fat exacerbates age-associated obesity and metabolic decline

It is well established that aging is associated with metabolic dysfunction such as increased adiposity and impaired energy dissipation; however, the transcriptional mechanisms regulating energy balance during late life stages have not yet been fully elucidated. Here, we show that ablation of the nuclear receptor PPARγ specifically in inguinal fat tissue in aging mice is associated with increased fat tissue expansion and insulin resistance. These metabolic effects are accompanied by decreased thermogenesis, reduced levels of brown fat genes, and browning of subcutaneous adipose tissue. Comparative studies of the effects of PPARγ downregulation in young and mid‐aged mice demonstrate a preferential regulation of brown fat gene programs in inguinal fat in an age‐dependent manner. In conclusion, our study uncovers an essential role for PPARγ in maintaining energy expenditure during the aging process and suggests the possibility of targeting PPARγ to counteract age‐associated metabolic dysfunction.

MitoNEET in Perivascular Adipose Tissue Blunts Atherosclerosis under Mild Cold Condition in Mice

Background: Perivascular adipose tissue (PVAT), which surrounds most vessels, is de facto a distinct functional vascular layer actively contributing to vascular function and dysfunction. PVAT contributes to aortic remodeling by producing and releasing a large number of undetermined or less characterized factors that could target endothelial cells and vascular smooth muscle cells, and herein contribute to the maintenance of vessel homeostasis. Loss of PVAT in mice enhances atherosclerosis, but a causal relationship between PVAT and atherosclerosis and the possible underlying mechanisms remain to be addressed. The CDGSH iron sulfur domain 1 protein (referred to as mitoNEET), a mitochondrial outer membrane protein, regulates oxidative capacity and adipose tissue browning. The roles of mitoNEET in PVAT, especially in the development of atherosclerosis, are unknown.

Methods: The brown adipocyte-specific mitoNEET transgenic mice were subjected to cold environmental stimulus. The metabolic rates and PVAT-dependent thermogenesis were investigated. Additionally, the brown adipocyte-specific mitoNEET transgenic mice were cross-bred with ApoE knockout mice. The ensuing mice were subsequently subjected to cold environmental stimulus and high cholesterol diet challenge for 3 months. The development of atherosclerosis was investigated.

Results: Our data show that mitoNEET mRNA was downregulated in PVAT of both peroxisome proliferator-activated receptor gamma coactivator 1-alpha (Pgc1α)- and beta (Pgc1β)-knockout mice which are sensitive to cold. MitoNEET expression was higher in PVAT of wild type mice and increased upon cold stimulus. Transgenic mice with overexpression of mitoNEET in PVAT were cold resistant, and showed increased expression of thermogenic genes. ApoE knockout mice with mitoNEET overexpression in PVAT showed significant downregulation of inflammatory genes and showed reduced atherosclerosis development upon high fat diet feeding when kept in a 16°C environment.

Conclusion: mitoNEET in PVAT is associated with PVAT-dependent thermogenesis and prevents atherosclerosis development. The results of this study provide new insights on PVAT and mitoNEET biology and atherosclerosis in cardiovascular diseases.

Hibernoma: a rare case of adipocytic tumor in head and neck

Background

Hibernoma is a rare soft tissue tumor stem from persistent fetal brown fat tissue. This benign tumor may occasionally occur in head and neck area and, in most cases, is characterized by an asymptomatic slow growth.

Case presentation

We presented an uncommon case of hibernoma of the posterior cervical triangle occurring in a 30-year-old man referred to the department of otolaryngology. The patient suffered from a right, very painful, and rapidly growing mass since 3 months. MRI examination reported both an infiltrating mass and a homogenous enhancement of an underlying vascularization after the injection of intravenous contrast. According to the risk of sarcoma, a surgical procedure was made to completely excise the mass that was a hibernoma.

Conclusions

Hibernoma may occur with an uncommon clinical presentation imitating malignancy. MRI plays a key role in the differential diagnosis and surgery remains the better therapeutic approach.

Small non coding RNAs in adipocyte biology and obesity

Obesity has reached epidemic proportions world-wide and constitutes a substantial risk factor for hypertension, type 2 diabetes, cardiovascular diseases and certain cancers. So far, regulation of energy intake by dietary and pharmacological treatments has met limited success. The main interest of current research is focused on understanding the role of different pathways involved in adipose tissue function and modulation of its mass. Whole-genome sequencing studies revealed that the majority of the human genome is transcribed, with thousands of non-protein-coding RNAs (ncRNA), which comprise small and long ncRNAs. ncRNAs regulate gene expression at the transcriptional and post-transcriptional level. Numerous studies described the involvement of ncRNAs in the pathogenesis of many diseases including obesity and associated metabolic disorders. ncRNAs represent potential diagnostic biomarkers and promising therapeutic targets. In this review, we focused on small ncRNAs involved in the formation and function of adipocytes and obesity.

Shortcuts to a functional adipose tissue: The role of small non-coding RNAs

Metabolic diseases such as type 2 diabetes are a major public health issue worldwide. These diseases are often linked to a dysfunctional adipose tissue. Fat is a large, heterogenic, pleiotropic and rather complex tissue. It is found in virtually all cavities of the human body, shows unique plasticity among tissues, and harbors many cell types in addition to its main functional unit - the adipocyte. Adipose tissue function varies depending on the localization of the fat depot, the cell composition of the tissue and the energy status of the organism. While the white adipose tissue (WAT) serves as the main site for triglyceride storage and acts as an important endocrine organ, the brown adipose tissue (BAT) is responsible for thermogenesis. Beige adipocytes can also appear in WAT depots to sustain heat production upon certain conditions, and it is becoming clear that adipose tissue depots can switch phenotypes depending on cell autonomous and non-autonomous stimuli. To maintain such degree of plasticity and respond adequately to changes in the energy balance, three basic processes need to be properly functioning in the adipose tissue: i) adipogenesis and adipocyte turnover, ii) metabolism, and iii) signaling. Here we review the fundamental role of small non-coding RNAs (sncRNAs) in these processes, with focus on microRNAs, and demonstrate their importance in adipose tissue function and whole body metabolic control in mammals.

Growth Hormone's Effect on Adipose Tissue: Quality versus Quantity

Obesity is an excessive accumulation or expansion of adipose tissue (AT) due to an increase in either the size and/or number of its characteristic cell type, the adipocyte. As one of the most significant public health problems of our time, obesity and its associated metabolic complications have demanded that attention be given to finding effective therapeutic options aimed at reducing adiposity or the metabolic dysfunction associated with its accumulation. Growth hormone (GH) has therapeutic potential due to its potent lipolytic effect and resultant ability to reduce AT mass while preserving lean body mass. However, AT and its resident adipocytes are significantly more dynamic and elaborate than once thought and require one not to use the reduction in absolute mass as a readout of efficacy alone. Paradoxically, therapies that reduce GH action may ultimately prove to be healthier, in part because GH also possesses potent anti-insulin activities along with concerns that GH may promote the growth of certain cancers. This review will briefly summarize some of the newer complexities of AT relevant to GH action and describe the current understanding of how GH influences this tissue using data from both humans and mice. We will conclude by considering the therapeutic use of GH or GH antagonists in obesity, as well as important gaps in knowledge regarding GH and AT.

Impact of Growth Hormone on Regulation of Adipose Tissue

Increasing prevalence of obesity and obesity-related conditions worldwide has necessitated a more thorough understanding of adipose tissue (AT) and expanded the scope of research in this field. AT is now understood to be far more complex and dynamic than previously thought, which has also fueled research to reevaluate how hormones, such as growth hormone (GH), alter the tissue. In this review, we will introduce properties of AT important for understanding how GH alters the tissue, such as anatomical location of depots and adipokine output. We will provide an overview of GH structure and function and define several human conditions and cognate mouse lines with extremes in GH action that have helped shape our understanding of GH and AT. A detailed discussion of the GH/AT relationship will be included that addresses adipokine production, immune cell populations, lipid metabolism, senescence, differentiation, and fibrosis, as well as brown AT and beiging of white AT. A brief overview of how GH levels are altered in an obese state, and the efficacy of GH as a therapeutic option to manage obesity will be given. As we will reveal, the effects of GH on AT are numerous, dynamic and depot-dependent. © 2017 American Physiological Society. Compr Physiol 7:819-840, 2017.

Modern trends in lipomodeling

Lipomodeling is the process of relocating autologous fat to change the shape, volume, consistency, and profile of tissues, with the aim of reconstructing, rejuvenating, and regenerating body features. There have been several important advancements in lipomodeling procedures during the last thirty years. Four clinical steps are important for the success of engraftment: fat harvesting, fat processing, fat reinjection, and preconditioning of the recipient site. With the discovery of adipose derived stem cells and dedifferentiated cells, fat cells become a major tool of regenerative medicine. This article reviews recent trends in lipomodeling trying to understand most of the issues in this field.

The effect of temperature, gradient, and load carriage on oxygen consumption, posture, and gait characteristics

PURPOSE

The purpose of this experiment was to evaluate the effect of load carriage in a range of temperatures to establish the interaction between cold exposure, the magnitude of change from unloaded to loaded walking and gradient.

METHODS

Eleven participants (19-27 years) provided written informed consent before performing six randomly ordered walking trials in six temperatures (20, 10, 5, 0, -5, and -10 °C). Trials involved two unloaded walking bouts before and after loaded walking (18.2 kg) at 4 km · h-1, on 0 and 10% gradients in 4 min bouts.

RESULTS

The change in absolute oxygen consumption (V̇O2) from the first unloaded bout to loaded walking was similar across all six temperatures. When repeating the second unloaded bout, V̇O2 at both -5 and -10 °C was greater compared to the first. At -10 °C, V̇O2 was increased from 1.60 ± 0.30 to 1.89 ± 0.51 L · min-1. Regardless of temperature, gradient had a greater effect on V̇O2 and heart rate (HR) than backpack load. HR was unaffected by temperature. Stride length (SL) decreased with decreasing temperature, but trunk forward lean was greater during cold exposure.

CONCLUSION

Decreased ambient temperature did not influence the magnitude of change in V̇O2 from unloaded to loaded walking. However, in cold temperatures, V̇O2 was significantly higher than in warm conditions. The increased V̇O2 in colder temperatures at the same exercise intensity is predicted to ultimately lead to earlier onset of fatigue and cessation of exercise. These results highlight the need to consider both appropriate clothing and fitness during cold exposure.

p107 Determines a Metabolic Checkpoint Required for Adipocyte Lineage Fates

We show that the transcriptional corepressor p107 orchestrates a metabolic checkpoint that determines adipocyte lineage fates for non-committed progenitors. p107 accomplishes this when stem cell commitment would normally occur in growth arrested cells. p107-deficient embryonic progenitors are characterized by a metabolic state resembling aerobic glycolysis that is necessary for their pro-thermogenic fate. Indeed, during growth arrest they have a reduced capacity for NADH partitioning between the cytoplasm and mitochondria. Intriguingly, this occurred despite an increase in the capacity for mitochondrial oxidation of non-glucose substrates. The significance of metabolic reprogramming is underscored by the disruption of glycolytic capacities in p107-depleted progenitors that reverted their fates from pro-thermogenic to white adipocytes. Moreover, the manipulation of glycolytic capacity on nonspecified embryonic and adult progenitors forced their beige fat commitment. These innovative findings introduce a new approach to increase pro-thermogenic adipocytes based on simply promoting aerobic glycolysis to manipulate nonspecified progenitor fate decisions. Stem Cells 2017;35:1378-1391.

Impaired adrenergic agonist-dependent beige adipocyte induction in aged mice

OBJECTIVE

There are two types of thermogenic adipocytes expressing uncoupling protein (UCP)-1: the brown adipocyte activated by adrenergic stimulation and the beige adipocyte that appears within the white adipose tissue (WAT) in response to chronic adrenergic stimulation. This study examined age-related changes in responses of both types of adipocytes to adrenergic stimulation in mice.

METHODS

Aged (age 20 months) and young (4 months) mice were injected daily with either saline or β3-adrenergic receptor agonist CL316,243 (CL; 0.1 mg/kg, once a day) for 1 week.

RESULTS

The body and WAT weight tended to be higher in aged mice. CL treatment increased UCP-1 protein amounts in both brown adipose tissue and inguinal WAT, suggesting activation of brown and beige adipocytes. However, induction of beige adipocytes was impaired in aged mice, whereas brown adipocyte activation was comparable to young mice. The number of platelet-derived growth factor receptor α-expressing progenitor cells, which were reported to differentiate into beige adipocytes, significantly decreased in inguinal WAT of aged mice compared with that of young mice.

CONCLUSIONS

Inductive ability of beige adipocytes in WAT declines with aging in mice. It may be partly because of a decreased number of progenitor cells associated with aging.

Active Brown Fat During 18F-FDG PET/CT Imaging Defines a Patient Group with Characteristic Traits and an Increased Probability of Brown Fat Redetection

Brown adipose tissue (BAT) provides a means of nonshivering thermogenesis. In humans, active BAT can be visualized by ¹⁸F-FDG uptake as detected by PET combined with CT. The retrospective analysis of clinical scans is a valuable source to identify anthropometric parameters that influence BAT mass and activity and thus the potential efficacy of envisioned drugs targeting this tissue to treat metabolic disease. Methods: We analyzed 2,854 ¹⁸F-FDG PET/CT scans from 1,644 patients and identified 98 scans from 81 patients with active BAT. We quantified the volume of active BAT depots (mean values in mL ± SD: total BAT, 162 ± 183 [n = 98]; cervical, 40 ± 37 [n = 53]; supraclavicular, 66 ± 68 [n = 71]; paravertebral, 51 ± 53 [n = 69]; mediastinal, 43 ± 40 [n = 51]; subphrenic, 21 ± 21 [n = 29]). Because only active BAT is detectable by ¹⁸F-FDG uptake, these numbers underestimate the total amount of BAT. Considering only 32 scans of the highest activity as categorized by a visual scoring strategy, we determined a mean total BAT volume of 308 ± 208 mL. In 30 BAT-positive patients with 3 or more repeated scans, we calculated a much higher mean probability to redetect active BAT (52% ± 25%) as compared with the overall prevalence of 4.9%. We calculated a BAT activity index (BFI) based on volume and intensity of individual BAT depots. Results: We detected higher total BFI in younger patients (P = 0.009), whereas sex, body mass index, height, mass, outdoor temperature, and blood parameters did not affect total or depot-specific BAT activity. Surprisingly, renal creatinine clearance as estimated from mass, age, and plasma creatinine was a significant predictor of BFI on the total (P = 0.005) as well as on the level of several individual depots. In summary, we detected a high amount of more than 300 mL of BAT tissue. Conclusion: BAT-positive patients represent a group with a higher than usual probability to activate BAT during a scan. Estimated renal creatinine clearance correlated with the extent of activated BAT in a given scan. These data imply an efficacy of drugs targeting BAT to treat metabolic disease that is at the same time higher and subject to a larger individual variation than previously assumed.

Isolation, Primary Culture, and Differentiation of Preadipocytes from Mouse Brown Adipose Tissue

Evolutionally, brown adipose tissue (BAT) is developed for nonshivering thermogenesis to prevent hypothermia. BAT has a high capacity to dissipate chemical energy generated from metabolism of nutrients for heat production. Therefore when BAT is activated, nutrients are "burned' instead of being stored. This feature makes BAT an attractive target for obesity treatment. To investigate BAT function and regulation, brown adipocyte culturing is indispensable. This chapter describes a detailed protocol for isolation, primary culture, and differentiation of preadipocytes from mouse BAT. The preadipocytes can be used for investigating the regulation of brown fat cell differentiation. The differentiated brown adipocytes maintain major BAT features including high expression of uncoupling protein-1 and can be used to study BAT biology and pharmacology.

Loss of UCP1 exacerbates Western diet-induced glycemic dysregulation independent of changes in body weight in female mice

We tested the hypothesis that female mice null for uncoupling protein 1 (UCP1) would have increased susceptibility to Western diet-induced "whitening" of brown adipose tissue (AT) and glucose intolerance. Six-week-old C57BL/6J wild-type (WT) and UCP1 knockout (UCP1^-/-) mice, housed at 25°C, were randomized to either a control diet (10% kcal from fat) or Western diet (45% kcal from fat and 1% cholesterol) for 28 wk. Loss of UCP1 had no effect on energy intake, energy expenditure, spontaneous physical activity, weight gain, or visceral white AT mass. Despite similar susceptibility to weight gain compared with WT, UCP1^-/- exhibited whitening of brown AT evidenced by a striking ~500% increase in mass and appearance of large unilocular adipocytes, increased expression of genes related to inflammation, immune cell infiltration, and endoplasmic reticulum/oxidative stress (P < 0.05), and decreased mitochondrial subunit protein (COX I, II, III, and IV, P < 0.05), all of which were exacerbated by Western diet (P < 0.05). UCP1^-/- mice also developed liver steatosis and glucose intolerance, which was worsened by Western diet. Collectively, these findings demonstrate that loss of UCP1 exacerbates Western diet-induced whitening of brown AT, glucose intolerance, and induces liver steatosis. Notably, the adverse metabolic manifestations of UCP1^-/- were independent of changes in body weight, visceral adiposity, and energy expenditure. These novel findings uncover a previously unrecognized metabolic protective role of UCP1 that is independent of its already established role in energy homeostasis.

Contributors to Metabolic Disease Risk Following Spinal Cord Injury

Spinal cord injury (SCI) induced changes in neurological function have significant impact on the metabolism and subsequent metabolic-related disease risk in injured individuals. This metabolic-related disease risk relationship is differential depending on the anatomic level and severity of the injury, with high level anatomic injuries contributing a greater risk of glucose and lipid dysregulation resulting in type 2 diabetes and cardiovascular disease risk elevation. Although alterations in body composition, particularly excess adiposity and its anatomical distribution in the visceral depot or ectopic location in non-adipose organs, is known to significantly contribute to metabolic disease risk, changes in fat mass and fat-free mass do not fully account for this elevated disease risk in subjects with SCI. There are other negative adaptations in body composition including reductions in skeletal muscle mass and alterations in muscle fiber type, in addition to significant reduction in physical activity, that contribute to a decline in metabolic rate and increased metabolic disease risk following SCI. Recent studies in adult humans suggest cold- and diet-induced thermogenesis through brown adipose tissue metabolism may be important for energy balance and substrate metabolism, and particularly sensitive to sympathetic nervous signaling. Considering the alterations that occur in the autonomic nervous system (SNS) (sympathetic and parasympathetic) following a SCI, significant dysfunction of brown adipose function is expected. This review will highlight metabolic alterations following SCI and integrate findings from brown adipose tissue studies as potential new areas of research to pursue.

A new method of infrared thermography for quantification of brown adipose tissue activation in healthy adults (TACTICAL): a randomized trial

The ability to alter the amount and activity of brown adipose tissue (BAT) in human adults is a potential strategy to manage obesity and related metabolic disorders associated with food, drug, and environmental stimuli with BAT activating/recruiting capacity. Infrared thermography (IRT) provides a non-invasive and inexpensive alternative to the current methods (e.g. ¹⁸F-FDG PET) used to assess BAT. We have quantified BAT activation in the cervical-supraclavicular (C-SCV) region using IRT video imaging and a novel image computational algorithm by studying C-SCV heat production in healthy young men after cold stimulation and the ingestion of capsinoids in a prospective double-blind placebo-controlled randomized trial. Subjects were divided into low-BAT and high-BAT groups based on changes in IR emissions in the C-SCV region induced by cold. The high-BAT group showed significant increases in energy expenditure, fat oxidation, and heat output in the C-SCV region post-capsinoid ingestion compared to post-placebo ingestion, but the low-BAT group did not. Based on these results, we conclude that IRT is a promising tool for quantifying BAT activity.

Modulation of energy balance by fibroblast growth factor 21

Fibroblast growth factors (FGFs) are a superfamily of 22 proteins related to cell proliferation and tissue repair after injury. A subgroup of three proteins, FGF19, FGF21, and FGF23, are major endocrine mediators. These three FGFs have low affinity to heparin sulfate during receptor binding; in contrast they have a strong interaction with the cofactor Klotho/β-Klotho. FGF21 has received particular attention because of its key role in carbohydrate, lipids, and energy balance regulation. FGF21 improves glucose and lipids metabolism as well as increasing energy expenditure in animal models and humans. Conditions that induce human physical stress such as exercise, lactation, obesity, insulin resistance, and type 2 diabetes influence FGF21 circulating levels. FGF21 also has an anti-oxidant function in human metabolic diseases which contribute to understanding the FGF21 compensatory increment in obesity, the metabolic syndrome, and type 2 diabetes. Interestingly, energy expenditure and weight loss is induced by FGF21. The mechanism involved is through "browning" of white adipose tissue, increasing brown adipose tissue activity and heat production. Therefore, clinical evaluation of therapeutic action of exogenous FGF21 administration is warranted, particularly to treat diabetes and obesity.

Seasonal influence on stimulated BAT activity in prospective trials: a retrospective analysis of BAT visualized on 18F-FDG PET-CTs and 123I-mIBG SPECT-CTs

Retrospective studies have shown that outdoor temperature influences the prevalence of detectable brown adipose tissue (BAT). Prospective studies use acute cold exposure to activate BAT. In prospective studies, BAT might be preconditioned in winter months leading to an increased BAT response to various stimuli. Therefore the aim of this study was to assess whether outdoor temperatures and other weather characteristics modulate the response of BAT to acute cold. To assess metabolic BAT activity and sympathetic outflow to BAT, 64 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET-CT) and 56 additional 123I- meta-iodobenzylguanidine (123I- mIBG) single-photon emission computed tomography-CT (SPECT-CT) scans, respectively, of subjects participating in previously executed trials were retrospectively included. BAT activity was measured in subjects after an overnight fast, following 2 h of cold exposure (∼17°C). The average daytime outdoor temperatures and other weather characteristics were obtained from the Dutch Royal Weather Institute. Forty-nine subjects were BAT positive. One week prior to the scan, outdoor temperature was significantly lower in the BAT-positive group compared with the BAT-negative group. Higher outdoor temperatures on preceding days resulted in lower stimulated metabolic BAT activity and volume (all P < 0.01). Outdoor temperatures did not correlate with sympathetic outflow to BAT. In conclusion, outdoor temperatures influence metabolic BAT activity and volume, but not sympathetic outflow to BAT, in subjects exposed to acute cold. To improve the consistency of the findings of future BAT studies in humans and to exclude bias introduced by outdoor temperatures, these studies should be planned in periods of similar outdoor temperatures.

Targeting adipose tissue in the treatment of obesity-associated diabetes

Adipose tissue regulates numerous physiological processes, and its dysfunction in obese humans is associated with disrupted metabolic homeostasis, insulin resistance and type 2 diabetes mellitus (T2DM). Although several US-approved treatments for obesity and T2DM exist, these are limited by adverse effects and a lack of effective long-term glucose control. In this Review, we provide an overview of the role of adipose tissue in metabolic homeostasis and assess emerging novel therapeutic strategies targeting adipose tissue, including adipokine-based strategies, promotion of white adipose tissue beiging as well as reduction of inflammation and fibrosis.

Brown adipose tissue: The heat is on the heart

The study of brown adipose tissue (BAT) has gained significant scientific interest since the discovery of functional BAT in adult humans. The thermogenic properties of BAT are well recognized; however, data generated in the last decade in both rodents and humans reveal therapeutic potential for BAT against metabolic disorders and obesity. Here we review the current literature in light of a potential role for BAT in beneficially mediating cardiovascular health. We focus mainly on BAT's actions in obesity, vascular tone, and glucose and lipid metabolism. Furthermore, we discuss the recently discovered endocrine factors that have a potential beneficial role in cardiovascular health. These BAT-secreted factors may have a favorable effect against cardiovascular risk either through their metabolic role or by directly affecting the heart.

Autocrine effect of vascular endothelial growth factor-A is essential for mitochondrial function in brown adipocytes

OBJECTIVE

The obesity epidemic in the United States, as well as the accompanying condition of type 2 diabetes, puts a majority of the population at an increased risk of developing cardiovascular diseases including coronary artery disease, stroke, and myocardial infarction. In contrast to white adipose tissue (WAT), brown adipose tissue (BAT) is well vascularized, rich in mitochondria, and highly oxidative. While it is known that the angiogenic factor VEGF-A is required for brown adipocyte development, the functional consequences and exact mechanism remain to be elucidated. Here, we show that VEGF-A plays an essential autocrine role in the function of BAT.

MATERIALS AND METHODS

Mouse models were generated with an adipose-specific and macrophage-specific ablation of VEGF-A. Adipose tissue characteristics and thermogenic response were analyzed in vivo, and mitochondrial morphology and oxidative respiration were analyzed in vitro to assess effects of endogenous VEGF-A ablation.

RESULTS

VEGF-A expression levels are highest in adipocyte precursors compared to immune or endothelial cell populations within both WAT and BAT. Loss of VEGF-A in adipocytes, but not macrophages, results in decreased adipose tissue vascularization, with remarkably diminished thermogenic capacity in vivo. Complete ablation of endogenous VEGF-A decreases oxidative capacity of mitochondria in brown adipocytes. Further, acute ablation of VEGF-A in brown adipocytes in vitro impairs mitochondrial respiration, despite similar mitochondrial mass compared to controls.

CONCLUSION

These data demonstrate that VEGF-A serves to orchestrate the acquisition of thermogenic capacity of brown adipocytes through mitochondrial function in conjunction with the recruitment of blood vessels.