Direct evidence of brown adipocytes in different fat depots in children

Key questions and gaps in understanding adipose tissue macrophages and early-life metabolic programming

The global obesity epidemic, with its associated comorbidities and increased risk of early mortality, underscores the urgent need for enhancing our understanding of the origins of this complex disease. It is increasingly clear that metabolism is programmed early in life and that metabolic programming can have life-long health consequences. As a critical metabolic organ sensitive to early-life stimuli, proper development of adipose tissue (AT) is crucial for life-long energy homeostasis. Early-life nutrients, especially fatty acids (FAs), significantly influence the programming of AT and shape its function and metabolism. Of growing interest are the dynamic responses during pre- and postnatal development to proinflammatory omega-6 (n6) and anti-inflammatory omega-3 (n3) FA exposures in AT. In the US maternal diet, the ratio of "pro-inflammatory" n6- to "anti-inflammatory" n3-FAs has grown dramatically due to the greater prevalence of n6-FAs. Notably, AT macrophages (ATMs) form a significant population within adipose stromal cells, playing not only an instrumental role in AT formation and maintenance but also acting as key mediators of cell-to-cell lipid and cytokine signaling. Despite rapid advances in ATM and immunometabolism fields, research has focused on responses to obesogenic diets and during adulthood. Consequently, there is a significant gap in identifying the mechanisms contributing metabolic health, especially regarding lipid exposures during the establishment of ATM physiology. Our review highlights the current understanding of ATM diversity, their critical role in AT, their potential role in early-life metabolic programming, and the broader implications for metabolism and health.

Alternative isoform expression of key thermogenic genes in human beige adipocytes

Background

The beneficial effect of thermogenic adipocytes in maintaining body weight and protecting against metabolic disorders has raised interest in understanding the regulatory mechanisms defining white and beige adipocyte identity. Although alternative splicing has been shown to propagate adipose browning signals in mice, this has yet to be thoroughly investigated in human adipocytes.

Methods

We performed parallel white and beige adipogenic differentiation using primary adipose stem cells from 6 unrelated healthy subjects and assessed differential gene and isoform expression in mature adipocytes by RNA sequencing.

Results

We find 777 exon junctions with robust differential usage between white and beige adipocytes in all 6 subjects, mapping to 562 genes. Importantly, only 10% of these differentially spliced genes are also differentially expressed, indicating that alternative splicing constitutes an additional layer of gene expression regulation during beige adipocyte differentiation. Functional classification of alternative isoforms points to a gain of function for key thermogenic transcription factors such as PPARG and CITED1, and enzymes such as PEMT, or LPIN1. We find that a large majority of the splice variants arise from differential TSS usage, with beige-specific TSSs being enriched for PPARγ and MED1 binding compared to white-specific TSSs. Finally, we validate beige specific isoform expression at the protein level for two thermogenic regulators, PPARγ and PEMT.

Discussion

These results suggest that differential isoform expression through alternative TSS usage is an important regulatory mechanism for human adipocyte thermogenic specification.

Interleukin-6: An Under-Appreciated Inducer of Thermogenic Adipocyte Differentiation

Adipose tissue inflammation is a key factor leading to obesity-associated immune disorders, such as insulin resistance, beta cell loss in the pancreatic islets, meta-inflammation, and autoimmunity. Inhibiting adipose tissue inflammation is considered a straightforward approach to abrogate these diseases. However, recent findings show that certain pro-inflammatory cytokines are essential for the proper differentiation and functioning of adipocytes. Lipolysis is stimulated, and the thermogenic competence of adipocytes is unlocked by interleukin-6 (IL-6), a cytokine that was initially recognized as a key trigger of adipose tissue inflammation. Coherently, signal transducer and activator of transcription 3 (STAT3), which is a signal transducer for IL-6, is necessary for thermogenic adipocyte development. Given the impact of thermogenic adipocytes in increasing energy expenditure and reducing body adiposity, functions of IL-6 in the adipose tissue have gained attention recently. In this review, we show that IL-6 signaling may protect from excess fat accumulation by stimulating thermogenesis in adipocytes.

Loss of Uncoupling Protein 1 Expression in the Subcutaneous Adipose Tissue Predicts Childhood Obesity

Stimulation of thermogenesis by inducing uncoupling protein 1 (UCP1) expression in adipocytes is thought to promote weight loss by increasing energy expenditure, and it is postulated that the human newborn has thermogenic subcutaneous fat depots. However, it remains unclear whether a relevant number of UCP1-expressing (UCP1+) adipocytes exist in the early postnatal life. Here we studied the distribution of UCP1 and the expression of thermogenic genes in the subcutaneous adipose tissues of the human fetus, infant and child. We show that the deep layer of human fetal and neonatal subcutaneous fat, particularly the abdominal wall, is rich in UCP1+ adipocytes. These adipocytes develop in the late third trimester and persist throughout childhood, expressing a panel of genes linked to mitochondrial biogenesis and thermogenesis. During the early childhood adiposity rebound-a critical phase that determines obesity risk later in life-the absence of adipose tissue UCP1 expression in children with normal body mass index (BMI) correlates with an obesity-associated gene expression signature. Finally, UCP1 expression is negatively correlated with BMI z-score and adipocyte size in infants and children. Overall, our results show that the absence of UCP1 expression in adipose tissue is an early indicator of adipose tissue expansion in children.

Brown Fat and Nutrition: Implications for Nutritional Interventions

Brown and beige adipocytes are renowned for their unique ability to generate heat through a mechanism known as thermogenesis. This process can be induced by exposure to cold, hormonal signals, drugs, and dietary factors. The activation of these thermogenic adipocytes holds promise for improving glucose metabolism, reducing fat accumulation, and enhancing insulin sensitivity. However, the translation of preclinical findings into effective clinical therapies poses challenges, warranting further research to identify the molecular mechanisms underlying the differentiation and function of brown and beige adipocytes. Consequently, research has focused on the development of drugs, such as mirabegron, ephedrine, and thyroid hormone, that mimic the effects of cold exposure to activate brown fat activity. Additionally, nutritional interventions have been explored as an alternative approach to minimize potential side effects. Brown fat and beige fat have emerged as promising targets for addressing nutritional imbalances, with the potential to develop strategies for mitigating the impact of metabolic diseases. Understanding the influence of nutritional factors on brown fat activity can facilitate the development of strategies to promote its activation and mitigate metabolic disorders.

ZIC1 Dictates Osteogenesis Versus Adipogenesis in Human Mesenchymal Progenitor Cells Via a Hedgehog Dependent Mechanism

Numerous intrinsic factors regulate mesenchymal progenitor commitment to a specific cell fate, such as osteogenic or adipogenic lineages. Identification and modulation of novel intrinsic regulatory factors represent an opportunity to harness the regenerative potential of mesenchymal progenitors. In the present study, the transcription factor (TF) ZIC1 was identified to be differentially expressed among adipose compared with skeletal-derived mesenchymal progenitor cells. We observed that ZIC1 overexpression in human mesenchymal progenitors promotes osteogenesis and prevents adipogenesis. ZIC1 knockdown demonstrated the converse effects on cell differentiation. ZIC1 misexpression was associated with altered Hedgehog signaling, and the Hedgehog antagonist cyclopamine reversed the osteo/adipogenic differentiation alterations associated with ZIC1 overexpression. Finally, human mesenchymal progenitor cells with or without ZIC1 overexpression were implanted in an ossicle assay in NOD-SCID gamma mice. ZIC1 overexpression led to significantly increased ossicle formation in comparison to the control, as assessed by radiographic and histologic measures. Together, these data suggest that ZIC1 represents a TF at the center of osteo/adipogenic cell fate determinations-findings that have relevance in the fields of stem cell biology and therapeutic regenerative medicine.

COBL, MKX and MYOC Are Potential Regulators of Brown Adipose Tissue Development Associated with Obesity-Related Metabolic Dysfunction in Children

Obesity is already accompanied by adipose tissue (AT) dysfunction and metabolic disease in children and increases the risk of premature death. Due to its energy-dissipating function, brown AT (BAT) has been discussed as being protective against obesity and related metabolic dysfunction. To analyze the molecular processes associated with BAT development, we investigated genome-wide expression profiles in brown and white subcutaneous and perirenal AT samples of children. We identified 39 upregulated and 26 downregulated genes in uncoupling protein 1 (UCP1)-positive compared to UCP1-negative AT samples. We prioritized for genes that had not been characterized regarding a role in BAT biology before and selected cordon-bleu WH2 repeat protein (COBL), mohawk homeobox (MKX) and myocilin (MYOC) for further functional characterization. The siRNA-mediated knockdown of Cobl and Mkx during brown adipocyte differentiation in vitro resulted in decreased Ucp1 expression, while the inhibition of Myoc led to increased Ucp1 expression. Furthermore, COBL, MKX and MYOC expression in the subcutaneous AT of children is related to obesity and parameters of AT dysfunction and metabolic disease, such as adipocyte size, leptin levels and HOMA-IR. In conclusion, we identify COBL, MKX and MYOC as potential regulators of BAT development and show an association of these genes with early metabolic dysfunction in children.

Thermogenic Adipose Redox Mechanisms: Potential Targets for Metabolic Disease Therapies

Metabolic diseases, such as diabetes and non-alcoholic fatty liver disease (NAFLD), have several negative health outcomes on affected humans. Dysregulated energy metabolism is a key component underlying the pathophysiology of these conditions. Adipose tissue is a fundamental regulator of energy homeostasis that utilizes several redox reactions to carry out the metabolism. Brown and beige adipose tissues, in particular, perform highly oxidative reactions during non-shivering thermogenesis to dissipate energy as heat. The appropriate regulation of energy metabolism then requires coordinated antioxidant mechanisms to counterbalance the oxidation reactions. Indeed, non-shivering thermogenesis activation can cause striking changes in concentrations of both oxidants and antioxidants in order to adapt to various oxidative environments. Current therapeutic options for metabolic diseases either translate poorly from rodent models to humans (in part due to the challenges of creating a physiologically relevant rodent model) or tend to have numerous side effects, necessitating novel therapies. As increased brown adipose tissue activity results in enhanced energy expenditure and is associated with beneficial effects on metabolic health, such as decreased obesity, it has gathered great interest as a modulator of metabolic disease. One potential reason for the beneficial health effects may be that although non-shivering thermogenesis is enormously oxidative, it is also associated with decreased oxidant formation after its activation. However, targeting its redox mechanisms specifically to alter metabolic disease remains an underexplored area. Therefore, this review will discuss the role of adipose tissue in energy homeostasis, non-shivering thermogenesis in adults, and redox mechanisms that may serve as novel therapeutic targets of metabolic disease.

Mitochondrial RNA stimulates beige adipocyte development in young mice

Childhood obesity is a serious public health crisis and a critical factor that determines future obesity prevalence. Signals affecting adipocyte development in early postnatal life have a strong potential to trigger childhood obesity; however, these signals are still poorly understood. We show here that mitochondrial (mt)RNA efflux stimulates transcription of nuclear-encoded genes for mitobiogenesis and thermogenesis in adipocytes of young mice and human infants. While cytosolic mtRNA is a potential trigger of the interferon (IFN) response, young adipocytes lack such a response to cytosolic mtRNA due to the suppression of IFN regulatory factor (IRF)7 expression by vitamin D receptor signalling. Adult and obese adipocytes, however, strongly express IRF7 and mount an IFN response to cytosolic mtRNA. In turn, suppressing IRF7 expression in adult adipocytes restores mtRNA-induced mitobiogenesis and thermogenesis and eventually mitigates obesity. Retrograde mitochondrion-to-nucleus signalling by mtRNA is thus a mechanism to evoke thermogenic potential during early adipocyte development and to protect against obesity.

The Sexual Dimorphism of Human Adipose Depots

The amount and the distribution of body fat exhibit trajectories that are sex- and human species-specific and both are determinants for health. The enhanced accumulation of fat in the truncal part of the body as a risk factor for cardiovascular and metabolic diseases is well supported by epidemiological studies. In addition, a possible independent protective role of the gluteofemoral fat compartment and of the brown adipose tissue is emerging. The present narrative review summarizes the current knowledge on sexual dimorphism in fat depot amount and repartition and consequences on cardiometabolic and reproductive health. The drivers of the sex differences and fat depot repartition, considered to be the results of complex interactions between sex determination pathways determined by the sex chromosome composition, genetic variability, sex hormones and the environment, are discussed. Finally, the inter- and intra-depot heterogeneity in adipocytes and progenitors, emphasized recently by unbiased large-scale approaches, is highlighted.

Factors Associated with White Fat Browning: New Regulators of Lipid Metabolism

Mammalian adipose tissue can be divided into white and brown adipose tissue based on its colour, location, and cellular structure. Certain conditions, such as sympathetic nerve excitement, can induce the white adipose adipocytes into a new type of adipocytes, known as beige adipocytes. The process, leading to the conversion of white adipocytes into beige adipocytes, is called white fat browning. The dynamic balance between white and beige adipocytes is closely related to the body’s metabolic homeostasis. Studying the signal transduction pathways of the white fat browning might provide novel ideas for the treatment of obesity and alleviation of obesity-related glucose and lipid metabolism disorders. This article aimed to provide an overview of recent advances in understanding white fat browning and the role of BAT in lipid metabolism.

Brown Adipose Tissue in Children and Its Metabolic Function

BACKGROUND

To regulate body temperature, mammals possess brown adipose tissue (BAT), which converts significant amounts of chemical energy into heat. Due to its remarkable energy demand, BAT is currently discussed as a target organ to treat obesity and obesity-related disorders.

SUMMARY

Although BAT is predominantly present in infants and its relative mass declines with age, new findings suggest that BAT has a relevant role in the regulation of energy homeostasis as well as in the regulation of the energy substrates glucose and lipids in older children, adolescents, and adults. In this overview, we will outline basic mechanisms of BAT thermogenesis and the recently described physiological relevance of BAT in metabolism in children and adolescents.

KEY MESSAGE

The connection of BAT activity with glucose metabolism and insulin sensitivity seems to be evident from recent studies, implicating BAT as an important influencing factor in the context of metabolic syndrome.

Impact of brown adipose tissue vascular density on body adiposity in healthy Japanese infants and children

Background and Objective

The importance of brown adipose tissue (BAT) is well recognized in healthy infants and children. However, information regarding age-related changes in BAT vascular density (BAT-d) and the impact of BAT-d on body adiposity are lacking. This study aimed to evaluate the normal values of BAT-d, factors influencing BAT-d, and the impact of BAT-d on body adiposity in healthy infants and children.

Methods

This study included 240 participants (127 girls and 113 boys) aged 1 month to 5 years. The tissue total hemoglobin concentration in the supraclavicular region adjusted according to the subcutaneous adipose tissue thickness (SAT) ([total-Hb-Adj]sup) as BAT-d. SAT in the deltoid and interscapular regions (SATdel+int), the Kaup index (body weight [g]/height or length [cm]/height or length [cm] × 10) as body adiposity, and fertilization season were also measured.

Results

The [total-Hb-Adj]sup of boys was higher than that of girls (r = 0.277, p = 0.009). Younger children had a significantly higher Kaup index (r = 0.495, p < 0.001) and SATdel+int (r = 0.614, p < 0.001) than older children. Children who had higher [total-Hb-Adj]sup had a significantly lower Kaup index (r = 0.495, p = 0.037) and SATdel+int (r = 0.614, p < 0.001).

Conclusion

The [total-Hb-Adj]sup, as a parameter of BAT-d, is negatively correlated with body adiposity in children aged 1 month to 5 years, and BAT might affect human obesity to a much greater extent than expected. To prevent or treat obesity in early childhood, the level of BAT-d should be considered when using a dietary intervention.

Iron chelation increases beige fat differentiation and metabolic activity, preventing and treating obesity

Beige and brown fat consume glucose and lipids to produce heat, using uncoupling protein 1 (UCP1). It is thought that full activation of brown adipose tissue (BAT) may increase total daily energy expenditure by 20%. Humans normally have more beige and potentially beige-able fat than brown fat. Strategies to increase beige fat differentiation and activation may be useful for the treatment of obesity and diabetes. Mice were fed chow or high-fat diet (HFD) with or without the iron chelator deferasirox. Animals fed HFD + deferasirox were markedly lighter than their HFD controls with increased energy expenditure (12% increase over 24 h, p < 0.001). Inguinal fat from HFD + deferasirox mice showed increased beige fat quantity with greater Ucp1 and Prdm16 expression. Inguinal adipose tissue explants were studied in a Seahorse bioanalyser and energy expenditure was significantly increased. Deferasirox was also effective in established obesity and in ob/ob mice, indicating that intact leptin signalling is not needed for efficacy. These studies identify iron chelation as a strategy to preferentially activate beige fat. Whether activating brown/beige fat is effective in humans is unproven. However, depleting iron to low-normal levels is a potential therapeutic strategy to improve obesity and related metabolic disorders, and human studies may be warranted.

Role of Distinct Fat Depots in Metabolic Regulation and Pathological Implications

People suffering from obesity and associated metabolic disorders including diabetes are increasing exponentially around the world. Adipose tissue (AT) distribution and alteration in their biochemical properties play a major role in the pathogenesis of these diseases. Emerging evidence suggests that AT heterogeneity and depot-specific physiological changes are vital in the development of insulin resistance in peripheral tissues like muscle and liver. Classically, AT depots are classified into white adipose tissue (WAT) and brown adipose tissue (BAT); WAT is the site of fatty acid storage, while BAT is a dedicated organ of metabolic heat production. The discovery of beige adipocyte clusters in WAT depots indicates AT heterogeneity has a more central role than hither to ascribed. Therefore, we have discussed in detail the current state of understanding on cellular and molecular origin of different AT depots and their relevance toward physiological metabolic homeostasis. A major focus is to highlight the correlation between altered WAT distribution in the body and metabolic pathogenesis in animal models and humans. We have also underscored the disparity in the molecular (including signaling) changes in various WAT tissues during diabetic pathogenesis. Exercise-mediated beneficial alteration in WAT physiology/distribution that protects against metabolic disorders is evolving. Here we have discussed the depot-specific biochemical adjustments induced by different forms of exercise. A detailed understanding of the molecular details of inter-organ crosstalk via substrate utilization/storage and signaling through chemokines provide strategies to target selected WAT depots to pharmacologically mimic the benefits of exercise countering metabolic diseases including diabetes.

The evolutionary significance of human brown adipose tissue: Integrating the timescales of adaptation

While human adaptability is regarded as a classical topic in anthropology, recent work provides new insight into metabolic adaptations to cold climates and the role of phenotypic plasticity in human evolution. A growing body of literature demonstrates that adults retain brown adipose tissue (BAT) which may play a role in non-shivering thermogenesis. In this narrative review, we apply the timescales of adaptation framework in order to explore the adaptive significance of human BAT. Human variation in BAT is shaped by multiple adaptive modes (i.e., allostasis, acclimatization, developmental adaptation, epigenetic inheritance, and genetic adaptation), and together the adaptive modes act as an integrated system. We hypothesize that plasticity in BAT facilitated the successful expansion of human populations into circumpolar regions, allowing for selection of genetic adaptations to cold climates to take place. Future research rooted in human energetics and biocultural perspectives is essential for understanding BAT's adaptive and health significance.

Co-Evolution of Breast Milk Lipid Signaling and Thermogenic Adipose Tissue

Breastfeeding is a unique and defining behavior of mammals and has a fundamental role in nourishing offspring by supplying a lipid-rich product that is utilized to generate heat and metabolic fuel. Heat generation from lipids is a feature of newborn mammals and is mediated by the uncoupling of mitochondrial respiration in specific fat depots. Breastfeeding and thermogenic adipose tissue have a shared evolutionary history: both have evolved in the course of homeothermy evolution; breastfeeding mammals are termed "thermolipials", meaning "animals with warm fat". Beyond its heat-producing capacity, thermogenic adipose tissue is also necessary for proper lipid metabolism and determines adiposity in offspring. Recent advances have demonstrated that lipid metabolism in infants is orchestrated by breast milk lipid signals, which establish mother-to-child signaling and control metabolic development in the infant. Breastfeeding rates are declining worldwide, and are paralleled by an alarming increase in childhood obesity, which at least in part may have its roots in the impaired metabolic control by breast milk lipid signals.

Transcriptional Landscaping Identifies a Beige Adipocyte Depot in the Newborn Mouse

The present study sought to identify gene networks that are hallmarks of the developing inguinal subcutaneous adipose tissue (iWAT) and the interscapular brown adipose tissue (BAT) in the mouse. RNA profiling revealed that the iWAT of postnatal (P) day 6 mice expressed thermogenic and lipid catabolism transcripts, along with the abundance of transcripts associated with the beige adipogenesis program. This was an unexpected finding, as thermogenic BAT was believed to be the only site of nonshivering thermogenesis in the young mouse. However, the transcriptional landscape of BAT in P6 mice suggests that it is still undergoing differentiation and maturation, and that the iWAT temporally adopts thermogenic and lipolytic potential. Moreover, P6 iWAT and adult (P56) BAT were similar in their expression of immune gene networks, but P6 iWAT was unique in the abundant expression of antimicrobial proteins and virus entry factors, including a possible receptor for SARS-CoV-2. In summary, postnatal iWAT development is associated with a metabolic shift from thermogenesis and lipolysis towards fat storage. However, transcripts of beige-inducing signal pathways including β-adrenergic receptors and interleukin-4 signaling were underrepresented in young iWAT, suggesting that the signals for thermogenic fat differentiation may be different in early postnatal life and in adulthood.

Emerging evidence for the opposite role of circulating irisin levels and brown adipose tissue activity measured by infrared thermography in anthropometric and metabolic profile during childhood

Irisin is an adipomyokine that increases browning of adipose tissue and thermogenesis, thereby protecting against obesity and insulin resistance. However, the correlation between irisin, brown adipose tissue (BAT), and childhood obesity, as well as its association with an increased risk of developing metabolic diseases, has not been completely elucidated. This study aimed to investigate the association between irisin levels and BAT activity measured by infrared thermography among children and verify their correlation with anthropometric and metabolic parameters. This study included 42 children with normal weight and 18 overweight/obese children. Anthropometric data, irisin levels, lipid and glucose profile were evaluated. The percentage of the thermally active portion of the supraclavicular area (%Area_SCR) before and after a cold stimulus was measured by infrared thermography, and the differences between the percentages of thermally active (Δ%Area_SCR) was calculated as an index of BAT activation. The results were correlated with anthropometric and metabolic parameters. Circulating irisin levels was positive correlated with age (rho=0.327, P= 0.011), body mass index (BMI) (rho=0.707, P<0.001), waist circumference (rho=0.624, P<0.001), total cholesterol (rho=0.361, P=0.044), triglycerides (rho=0.419, P=0.001), and low-density lipoprotein cholesterol (LDLc) (rho=0.381, P= 0.003). Active BAT was negatively correlated with BMI, waist circumference, triglycerides, LDLc and irisin levels. We observed that normal weight children increased significantly the Δ% Area_SCR as compared to overweight/obese children. In conclusion, circulating irisin levels and BAT activity appear to have opposing roles, since normal weight children had greater BAT activity and lower circulating levels of irisin.

Dysmetabolic adipose tissue in obesity: morphological and functional characteristics of adipose stem cells and mature adipocytes in healthy and unhealthy obese subjects

The way by which subcutaneous adipose tissue (SAT) expands and undergoes remodeling by storing excess lipids through expansion of adipocytes (hypertrophy) or recruitment of new precursor cells (hyperplasia) impacts the risk of developing cardiometabolic and respiratory diseases. In unhealthy obese subjects, insulin resistance, type 2 diabetes, hypertension, and obstructive sleep apnoea are typically associated with pathologic SAT remodeling characterized by adipocyte hypertrophy, as well as chronic inflammation, hypoxia, increased visceral adipose tissue (VAT), and fatty liver. In contrast, metabolically healthy obese individuals are generally associated with SAT development characterized by the presence of smaller and numerous mature adipocytes, and a lower degree of VAT inflammation and ectopic fat accumulation. The remodeling of SAT and VAT is under genetic regulation and influenced by inherent depot-specific differences of adipose tissue-derived stem cells (ASCs). ASCs have multiple functions such as cell renewal, adipogenic capacity, and angiogenic properties, and secrete a variety of bioactive molecules involved in vascular and extracellular matrix remodeling. Understanding the mechanisms regulating the proliferative and adipogenic capacity of ASCs from SAT and VAT in response to excess calorie intake has become a focus of interest over recent decades. Here, we summarize current knowledge about the biological mechanisms able to foster or impair the recruitment and adipogenic differentiation of ASCs during SAT and VAT development, which regulate body fat distribution and favorable or unfavorable metabolic responses.

Reduced brown adipose tissue-associated skin temperature following cold stimulation in children and adolescents with type 1 diabetes

BACKGROUND

Brown adipose tissue (BAT) is essential to maintain body temperature. Its ability to convert chemical energy in glucose and free fatty acids to heat is conferred by a unique protein, UCP-1. BAT activity is greatest in children and adolescents, declining through adulthood. Blood glucose concentrations outside the normal nondiabetic range are common in type 1 diabetes and hyperglycaemia leads to insulin resistance in muscle and white adipose tissue, but whether this applies to BAT, is not known.

METHOD

To investigate the effect of type 1 diabetes on BAT activity, we measured the supraclavicular temperature of 20 children with type 1 diabetes and compared them to 20 age-matched controls, using infrared thermography.

RESULTS

The diabetes group had lower stimulated supraclavicular temperatures (diabetes group: 35.03 (34.76-35.30)°C; control group: 35.42 (35.16-35.69)°C; p = 0.037) and a reduced response in relative temperature following cold stimulation, after adjusting for BMI (diabetes group: 0.11 (0.03-0.18)°C; control group: 0.22 (0.15-0.29)°C; p = 0.034). In the diabetes group, there was no association between glycaemic measures and supraclavicular temperatures, but the method of insulin delivery may significantly affect the change in supraclavicular temperature with stimulation (injections: 0.01 (-0.07-0.09)°C; pump: 0.15 (0.04-0.26)°C; p = 0.028).

CONCLUSIONS

While further work is needed to better understand the glucose-insulin-BAT relationship, one possible explanation for the reduced supraclavicular temperature is that exogenous, unlike endogenous, insulin, is not suppressed by the activity of the sympathetic nervous system, preventing lipolysis-driven activation of BAT.

Evidence for a sensitive period of plasticity in brown adipose tissue during early childhood among indigenous Siberians

OBJECTIVES

Evolutionary theorists have debated the adaptive significance of developmental plasticity in organisms with long lifespans such as humans. This debate in part stems from uncertainty regarding the timing of sensitive periods. Does sensitivity to environmental signals fluctuate across development or does it steadily decline? We investigated developmental plasticity in brown adipose tissue (BAT) among indigenous Siberians in order to explore the timing of phenotypic sensitivity to cold stress.

METHODS

BAT thermogenesis was quantified using infrared thermal imaging in 78 adults (25 men; 33 women). Cold exposure during gestation, infancy, early childhood, middle childhood, and adolescence was quantified using: (1) the average ambient temperature across each period; (2) the number of times daily temperature dropped below -40°F during each period. We also assessed past cold exposure with a retrospective survey of participation in outdoor activities.

RESULTS

Adult BAT thermogenesis was significantly associated with the average temperature (p = 0.021), the number of times it was below -40°F (p = 0.026), and participation in winter outdoor activities (p = 0.037) during early childhood.

CONCLUSIONS

Our results suggest that early childhood represents an important stage for developmental plasticity, and that culture may play a critical role in shaping the timing of environmental signals. The findings highlight a new pathway through which the local consequences of global climate change may influence human biology, and they suggest that ambient temperature may represent an understudied component of the developmental origins of health and disease.

Human Milk Drives the Intimate Interplay Between Gut Immunity and Adipose Tissue for Healthy Growth

As the physiological food for the developing child, human milk is expected to be the diet that is best adapted for infant growth needs. There is also accumulating evidence that breastfeeding influences long-term metabolic outcomes. This review covers the potential mechanisms by which human milk could regulate healthy growth. We focus on how human milk may act on adipose tissue development and its metabolic homeostasis. We also explore how specific human milk components may influence the interplay between the gut microbiota, gut mucosa immunity and adipose tissue. A deeper understanding of these interactions may lead to new preventative and therapeutic strategies for both undernutrition and other metabolic diseases and deserves further exploration.

Brown Fat-Activating Lipokine 12,13-diHOME in Human Milk Is Associated With Infant Adiposity

CONTEXT

Little is known about the specific breastmilk components responsible for protective effects on infant obesity. Whether 12,13-dihydroxy-9Z-octadecenoic acid (12,13-diHOME), an oxidized linoleic acid metabolite and activator of brown fat metabolism, is present in human milk, or linked to infant adiposity, is unknown.

OBJECTIVE

To examine associations between concentrations of 12,13-diHOME in human milk and infant adiposity.

DESIGN

Prospective cohort study from 2015 to 2019, following participants from birth to 6 months of age.

SETTING

Academic medical centers.

PARTICIPANTS

Volunteer sample of 58 exclusively breastfeeding mother-infant pairs; exclusion criteria included smoking, gestational diabetes, and health conditions with the potential to influence maternal or infant weight gain.

MAIN OUTCOME MEASURES

Infant anthropometric measures including weight, length, body mass index (BMI), and body composition at birth and at 1, 3, and 6 months postpartum.

RESULTS

We report for the first time that 12,13-diHOME is present in human milk. Higher milk 12,13-diHOME level was associated with increased weight-for-length Z-score at birth (β = 0.5742, P = 0.0008), lower infant fat mass at 1 month (P = 0.021), and reduced gain in BMI Z-score from 0 to 6 months (β = -0.3997, P = 0.025). We observed similar associations between infant adiposity and milk abundance of related oxidized linoleic acid metabolites 12,13-Epoxy-9(Z)-octadecenoic acid (12,13-epOME) and 9,10-Dihydroxy-12-octadecenoic acid (9,10-diHOME), and metabolites linked to thermogenesis including succinate and lyso-phosphatidylglycerol 18:0. Milk abundance of 12,13-diHOME was not associated with maternal BMI, but was positively associated with maternal height, milk glucose concentration, and was significantly increased after a bout of moderate exercise.

CONCLUSIONS

We report novel associations between milk abundance of 12,13-diHOME and adiposity during infancy.

Association of PPARG rs3856806 C>T polymorphism with body mass index, glycaemia and lipid parameters in Serbian adolescents

Background/Aim: Peroxisome proliferator-activated receptor gamma (PPARg) belongs to a family of nuclear hormone receptors and ligand-activated transcription factors. PPARG gene is expressed in many tissues including adipose tissue where it plays a crucial role in differentiation of adipocyte, insulin resistance, blood glucose levels and lipid metabolism. The aim of the study was to examine the association of rs3856806 polymorphism with the body mass index (BMI), fasting glucose levels and lipid parameters in Serbian adolescents. Methods: This research included 287 adolescents of both genders (143 boys and 144 girls), 14-15 years of age. Genotype detection was done by polymerase chain reaction-restriction fragment length polymorphism (RFLP) assay. Results: Results showed statistically significant difference in terms of fasting glucose levels among girls (p = 0.013) depending on their genotype. Female carriers of CC genotype had significantly higher level of fasting glucose levels. Also, results showed that in the group of overweight and obese girls, carriers of CT or TT genotype had statistically significant lower values of HDL cholesterol compared to girls - carriers of CC genotype (p = 0.000). However, this result was not confirmed by multiple regression analysis. Statistically significant association of rs3856806 polymorphism was not observed with BMI nor with other lipid parameters. Conclusion: This polymorphism is associated with fasting glucose level and HDL cholesterol among girls. To draw definite conclusions, further research should be conducted including non-genetic factors and other polymorphisms among this gene.

Transferrin Receptor Functionally Marks Thermogenic Adipocytes

Background

Thermogenic adipocytes, including beige and brown adipocytes, are critical for thermogenesis and energy homeostasis. Identification of functional cell surface markers of thermogenic adipocytes is of significance for potential application in biological and clinical practices.

Methods

With a combination of RNA-sequencing of in vivo and in vitro models, we identified transferrin receptor (Tfr1), a receptor specialized for cellular iron uptake, as a previously unappreciated cell surface molecule for thermogenic adipocytes compared to white adipocytes. The alternation of Tfr1 levels under physiological and pathological stimuli was assessed, and the mitochondria functionality, browning capacity, and iron metabolism of mature adipocytes were examined with Tfr1 knockdown.

Results

Tfr1 was expressed predominantly in thermogenic adipocytes versus white adipocyte, and its expression levels were tightly correlated with the activation or inhibition status of thermogenic adipocytes under external stimuli. Besides, Tfr1 gene deficiency in thermogenic adipocytes led to reduced thermogenic gene programs and mitochondrial integrity.

Conclusion

Tfr1 functionally marks thermogenic adipocytes and could serve as a potential thermogenic adipocyte surface marker.

The Obesity-Susceptibility Gene TMEM18 Promotes Adipogenesis through Activation of PPARG

TMEM18 is the strongest candidate for childhood obesity identified from GWASs, yet as for most GWAS-derived obesity-susceptibility genes, the functional mechanism remains elusive. We here investigate the relevance of TMEM18 for adipose tissue development and obesity. We demonstrate that adipocyte TMEM18 expression is downregulated in children with obesity. Functionally, downregulation of TMEM18 impairs adipocyte formation in zebrafish and in human preadipocytes, indicating that TMEM18 is important for adipocyte differentiation in vivo and in vitro. On the molecular level, TMEM18 activates PPARG, particularly upregulating PPARG1 promoter activity, and this activation is repressed by inflammatory stimuli. The relationship between TMEM18 and PPARG1 is also evident in adipocytes of children and is clinically associated with obesity and adipocyte hypertrophy, inflammation, and insulin resistance. Our findings indicate a role of TMEM18 as an upstream regulator of PPARG signaling driving healthy adipogenesis, which is dysregulated with adipose tissue dysfunction and obesity.

The omentum of obese girls harbors small adipocytes and browning transcripts

Severe obesity (SO) affects about 6% of youth in the United States, augmenting the risks for cardiovascular disease and type 2 diabetes. Herein, we obtained paired omental adipose tissue (omVAT) and abdominal subcutaneous adipose tissue (SAT) biopsies from girls with SO undergoing sleeve gastrectomy (SG), to test whether differences in cellular and transcriptomic profiles between omVAT and SAT depots affect insulin sensitivity differently. Following weight loss, these analyses were repeated in a subgroup of subjects having a second SAT biopsy. We found that omVAT displayed smaller adipocytes compared with SAT, increased lipolysis through adipose triglyceride lipase phosphorylation, reduced inflammation, and increased expression of browning/beiging markers. Contrary to omVAT, SAT adipocyte diameter correlated with insulin resistance. Following SG, both weight and insulin sensitivity improved markedly in all subjects. SAT adipocytes' size became smaller, showing increased lipolysis through perilipin 1 phosphorylation, decreased inflammation, and increased expression in browning/beiging markers. In summary, in adolescent girls with SO, both omVAT and SAT depots showed distinct cellular and transcriptomic profiles. Following weight loss, the SAT depot changed its cellular morphology and transcriptomic profiles into more favorable ones. These changes in the SAT depot may play a fundamental role in the resolution of insulin resistance.

Low expression of brown and beige fat genes in subcutaneous tissues in obese patients

INTRODUCTION

The molecular mechanisms behind obesity pathogenesis remain largely undefined. Impairment in the browning process of subcutaneous tissues proposed to contribute to obesity pathogenesis. In the current study, we aimed to assess whether the expression of brown fat genes in subcutaneous tissues in obese patients is altered as compared to non-obese patients.

MATERIAL AND METHODS

Participants were recruited from patients undergoing general surgeries. At the same site of surgery, biopsies were taken from the abdominal subcutaneous tissues from each participant, along with a venous blood sample. The expression of BAT genes was measured using a real-time PCR method. Serum FGF21 was measured using an ELISA kit, and the serum blood lipid profile was measured using the Dimension VistaTM 1500 System.

RESULTS

A total of 58 surgical patients was involved. A low expression of BAT genes was observed in the groups with higher body mass index (BMI) (< 30 kg/m²) as compared to the groups with lower BMI (> 30 kg/m²). The expression of CIDEA and CITED1 was significantly higher in the patients with normal weight as compared to obese (p = 0.01 and p = 0.02, respectively). A significant negative correlation was found between the expression of BAT genes and BMI in patients with BMI < 35 kg/m². However, the strongest negative correlation was observed in the expression of CIDEA (r = -0.5, p = 0.004), followed by TBX1 (r = -0.4, p = 0.01), CITED1, and ZIC1 (r = -0.4, p = 0.03). Whereas the correlation of UCP1 with BMI remained insignificant (r = -0.29, p = 0.08). When including patients with BMI > 35 kg/m², the correlation decreased and became insignificant (p = 0.08). No significant correlation was found between the expression of BAT genes and blood lipid profiles (p > 0.05). Serum FGF21 was positively and significantly correlated to the expression of UCP1 (r = 0.56, p = 0.02) and TBX1 (r = 0.62, p = 0.01), however, this correlation was missing in patients with severe obesity.

CONCLUSIONS

Our data suggested that brown and beige genes expression in abdominal subcutaneous tissues is dysregulated in patients with obesity. Further studies are needed to investigate the role of browning of subcutaneous tissues in regulating body weight and metabolism in human.

Sexual Dimorphism of Brown Adipose Tissue Function

OBJECTIVE

To determine whether brown adipose tissue (BAT) activity in school-age children differs between the sexes and to explore the impact of dietary intake, sedentary behavior, and picky/fussy eating.

STUDY DESIGN

Children aged 8.5-11.8 years of age (n = 36) underwent infrared thermography to determine the temperature of the skin overlying the main superficial BAT depot in the supraclavicular region before and after 5 minutes of mild cold exposure (single-hand immersion in cool tap water at about 20°C). The relationships between the supraclavicular region temperature and parental reports of food consumption, eating behavior, and inactivity were explored.

RESULTS

The supraclavicular region temperature was higher in boys (n = 16) at baseline, and after cold exposure. Boys displayed a greater thermogenic response to cold. Strong negative correlations were observed between the supraclavicular region temperature and body mass index percentile, and differences in supraclavicular region temperature between girls and boys persisted after adjustment for body mass index percentile. A negative linear relationship was observed between protein and vegetable intake and supraclavicular region temperature in girls only, but did not persist after adjustment for multiple comparisons. There was no difference in the adjusted supraclavicular region temperature between active or inactive children, or picky and nonpicky eaters.

CONCLUSIONS

These findings indicate sexual dimorphism in BAT thermogenic activity and a sex-specific impact of diet. Future studies should aim to quantify the contribution of BAT to childhood energy expenditure, energy imbalance, and any role in the origins of childhood obesity.

Critical lipids link breastfeeding to healthy adipose tissue in infancy and adulthood

The study of beige adipose tissue (BeAT) has recently gained popularity because of its potential as a therapeutic target for the treatment of obesity and other metabolic disorders. While BeAT regulation is well understood in adults, the critical signals regulating BeAT during infant development need to be better defined. The bioactive components in breast milk have been primarily studied in the context of immunity. In this issue of the JCI, Yu and Dilbaz et al. identify how a class of breast milk-specific lipid mediators referred to as alkylglycerols (AKGs) maintain BeAT in infants and prevent the transdifferentiation of BeAT into lipid-storing white adipose tissue (WAT).

Breast milk alkylglycerols sustain beige adipocytes through adipose tissue macrophages

Prevalence of obesity among infants and children below 5 years of age is rising dramatically, and early childhood obesity is a forerunner of obesity and obesity-associated diseases in adulthood. Childhood obesity is hence one of the most serious public health challenges today. Here, we have identified a mother-to-child lipid signaling that protects from obesity. We have found that breast milk-specific lipid species, so-called alkylglycerol-type (AKG-type) ether lipids, which are absent from infant formula and adult-type diets, maintain beige adipose tissue (BeAT) in the infant and impede the transformation of BeAT into lipid-storing white adipose tissue (WAT). Breast milk AKGs are metabolized by adipose tissue macrophages (ATMs) to platelet-activating factor (PAF), which ultimately activates IL-6/STAT3 signaling in adipocytes and triggers BeAT development in the infant. Accordingly, lack of AKG intake in infancy leads to a premature loss of BeAT and increases fat accumulation. AKG signaling is specific for infants and is inactivated in adulthood. However, in obese adipose tissue, ATMs regain their ability to metabolize AKGs, which reduces obesity. In summary, AKGs are specific lipid signals of breast milk that are essential for healthy adipose tissue development.

Resting Energy Expenditure, Insulin Resistance and UCP1 Expression in Human Subcutaneous and Visceral Adipose Tissue of Patients With Obesity

Determinants of resting energy expenditure (REE) in humans are still under investigation, especially the association with insulin resistance. Brown adipose tissue (AT) regulates energy expenditure through the activity of the uncoupling protein 1 (UCP1). White AT browning is the process by which some adipocytes within AT depots acquire properties of brown adipocytes ("brite" adipocytes) and it correlates with metabolic improvement. We analyzed determinants of REE in patients with obesity and assessed UCP1 expression as a "brite" marker in abdominal subcutaneous AT (SAT) and visceral omental AT (VAT). Clinical data, REE, free fat mass (FFM), and fat mass (FM) were determined in 209 patients with obesity. UCP1, PPARG coactivator 1 alpha (PPARGC1A), transcription factor A, mitochondrial (TFAM), T-box transcription factor 1 (TBX1), and solute carrier family 27 member 1 (SLC27A1) expression was assayed in SAT and VAT samples, obtained during sleeve gastrectomy from 62 patients with obesity. REE and body composition data were also available for a subgroup of 35 of whom. In 209 patients with obesity a multiple regression model was computed with REE as the dependent variable and sex, waist, FFM, FM, homeostasis model assessment-insulin resistance (HOMA), interleukin-6 and High Density Lipoprotein-cholesterol as the independent variables. Only FFM, FM and HOMA were independently correlated with REE (r = 0.787, AdjRsqr = 0.602). In each patient VAT displayed a higher UCP1, PPARGC1A, TFAM, TBX1, and SLC27A1 expression than SAT and UCP1 expression in VAT (UCP1-VAT) correlated with Body Mass Index (BMI) (r = 0.287, p < 0.05). Introducing UCP1-VAT in the multivariate model, we showed that FFM, HOMA, interleukin-6, High Density Lipoprotein-cholesterol, and UCP1-VAT were independent factors correlated with REE (r = 0.736, AdjRsqr = 0.612). We confirmed that REE correlates with FFM, FM and HOMA in a large cohort of patients. Our results clearly showed that UCP1-VAT expression was significantly increased in severe human obesity (BMI > 50 kg/m²) and that it behaved as an independent predictor of REE. Lastly, we suggest that an increased REE and browning in metabolically complicated severe obesity could represent an effort to counteract further weight gain.

Brown adipose tissue development and function and its impact on reproduction

Although brown adipose tissue (BAT) is one of the smallest organs in the body, it has the potential to have a substantial impact on both heat production as well as fat and carbohydrate metabolism. This is most apparent at birth, which is characterised with the rapid appearance and activation of the BAT specific mitochondrial uncoupling protein (UCP)1 in many large mammals. The amount of brown fat then gradually declines with age, an adaptation that can be modulated by the thermal environment. Given the increased incidence of maternal obesity and its potential transmission to the mother's offspring, increasing BAT activity in the mother could be one mechanism to prevent this cycle. To date, however, all rodent studies investigating maternal obesity have been conducted at standard laboratory temperature (21°C), which represents an appreciable cold challenge. This could also explain why offspring weight is rarely increased, suggesting that future studies would benefit from being conducted at thermoneutrality (~28°C). It is also becoming apparent that each fat depot has a unique transcriptome and show different developmental pattern, which is not readily apparent macroscopically. These differences could contribute to the retention of UCP1 within the supraclavicular fat depot, the most active depot in adult humans, increasing heat production following a meal. Despite the rapid increase in publications on BAT over the past decade, the extent to which modifications in diet and/or environment can be utilised to promote its activity in the mother and/or her offspring remains to be established.

Adipose Tissue is a Potential Source of Hyperandrogenism in Obese Female Rats

OBJECTIVE

Obesity in females is often associated with metabolic complications and hyperandrogenism, but the sources of androgens are not completely understood. Therefore, this study investigated whether adipose tissue could be a source of androgens promoting hyperandrogenism development in obese female rats.

METHODS

Gene expression of steroidogenic enzymes and testosterone levels were determined in periovarian and inguinal adipose tissue and in the supernatant of cultured preadipocytes and adipocytes. The conversion of pregnenolone to androgens was analyzed by thin-layer chromatography.

RESULTS

Substantial amounts of testosterone in adipose tissue (25-153 ng/g tissue) and in the supernatant of adipocytes (0.33-0.69 ng/ten thousand cells]) were found. StAR and steroidogenic enzymes encoded by genes including Cyp11A1, Cyp17A1, Cyp19, Hsd3b2, Hsd17b3, and Srd5a2 were expressed in adipose tissue and cultured cells. Thin layer chromatography data revealed that preadipocytes and adipocytes were able to convert pregnenolone to testosterone. Higher levels for all steroidogenic enzymes were found in both depots of obese animals compared with lean animals, with significantly higher levels in inguinal tissue.

CONCLUSIONS

The whole steroidogenic machinery and capacity for testosterone biosynthesis were found in fat depots of female rats. These findings support the hypothesis that adipose tissue may contribute substantially to the hyperandrogenism in female obesity.

Transcriptional analysis of adipose tissue during development reveals depot-specific responsiveness to maternal dietary supplementation

Brown adipose tissue (BAT) undergoes pronounced changes after birth coincident with the loss of the BAT-specific uncoupling protein (UCP)1 and rapid fat growth. The extent to which this adaptation may vary between anatomical locations remains unknown, or whether the process is sensitive to maternal dietary supplementation. We, therefore, conducted a data mining based study on the major fat depots (i.e. epicardial, perirenal, sternal (which possess UCP1 at 7 days), subcutaneous and omental) (that do not possess UCP1) of young sheep during the first month of life. Initially we determined what effect adding 3% canola oil to the maternal diet has on mitochondrial protein abundance in those depots which possessed UCP1. This demonstrated that maternal dietary supplementation delayed the loss of mitochondrial proteins, with the amount of cytochrome C actually being increased. Using machine learning algorithms followed by weighted gene co-expression network analysis, we demonstrated that each depot could be segregated into a unique and concise set of modules containing co-expressed genes involved in adipose function. Finally using lipidomic analysis following the maternal dietary intervention, we confirmed the perirenal depot to be most responsive. These insights point at new research avenues for examining interventions to modulate fat development in early life.

Perilipin-2 deletion promotes carbohydrate-mediated browning of white adipose tissue at ambient temperature

Mice lacking perilipin-2 (Plin2-null) are resistant to obesity, insulin resistance, and fatty liver induced by Western or high-fat diets. In the current study, we found that, compared with WT mice on Western diet, Plin2-null adipose tissue was more insulin sensitive and inguinal subcutaneous white adipose tissue (iWAT) exhibited profound browning and robust induction of thermogenic and carbohydrate-responsive genetic programs at room temperature. Surprisingly, these Plin2-null responses correlated with the content of simple carbohydrates, rather than fat, in the diet, and were independent of adipose Plin2 expression. To define Plin2 and sugar effects on adipose browning, WT and Plin2-null mice were placed on chow diets containing 20% sucrose in their drinking water for 6 weeks. Compared with WT mice, iWAT of Plin2-null mice exhibited pronounced browning and striking increases in the expression of thermogenic and insulin-responsive genes on this diet. Significantly, Plin2-null iWAT browning was associated with reduced sucrose intake and elevated serum fibroblast growth factor (FGF)21 levels, which correlated with greatly enhanced hepatic FGF21 production. These data identify Plin2 actions as novel mediators of sugar-induced adipose browning through indirect effects of hepatic FGF21 expression, and suggest that adipose browning mechanisms may contribute to Plin2-null resistance to obesity.

Long-chain polyunsaturated fatty acids and extensively hydrolyzed casein-induced browning in a Ucp-1 reporter mouse model of obesity

Browning in adipose tissues, which can be affected by diet, may mitigate the detrimental effects of adiposity and improve longer-term metabolic health. Here, browning-inducing effects of long-chain polyunsaturated fatty acids, e.g., arachidonic acid (ARA)/docosahexaenoic acid (DHA) and extensively hydrolyzed casein (eHC) were investigated in uncoupling protein 1 (Ucp-1) reporter mice. To address the overall functionality, their potential role in supporting a healthy metabolic profile under obesogenic dietary challenges later in life was evaluated. At weaning Ucp1+/LUC reporter mice were fed a control low fat diet (LFD) with or without ARA + DHA, eHC or eHC + ARA + DHA for 8 weeks until week 12 after which interventions continued for another 12 weeks under a high-fat diet (HFD) challenge. Serology (metabolic responses and inflammation) and in vivo and ex vivo luciferase activity were determined; in the meantime browning-related proteins UCP-1 and the genes peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α), PR domain containing 16 (PRDM16) and Ucp-1 were examined. ARA + DHA, eHC or their combination reduced body weight gain and adipose tissue weight compared to the HFD mice. The interventions induced Ucp-1 expression in adipose tissues prior to and during the HFD exposure. Ucp-1 induction was accompanied by higher PGC1a and PRDM16 expression. Glucose tolerance and insulin sensitivity were improved coinciding with lower serum cholesterol, triglycerides, free fatty acids, insulin, leptin, resistin, fibroblast growth factor 21, alanine aminotransferase, aspartate aminotransferase and higher adiponectin than the HFD group. HFD-associated increased systemic (IL-1β and TNF-α) and adipose tissue inflammation (F4/80, IL-1β, TNF-α, IL-6) was reduced. Studies in a Ucp-1 reporter mouse model revealed that early intervention with ARA/DHA and eHC improves metabolic flexibility and attenuates obesity during HFD challenge later in life. Increased browning is suggested as, at least, part of the underlying mechanism.

Update on endocrine aspects of childhood obesity

PURPOSE OF REVIEW

Although childhood obesity has leveled off in the last decade, 'severe obesity' continues to be on the rise. Various genetic, environmental and hormonal factors contribute to obesity. This article reviews the most current understanding of obesity's multifactorial origin and recent recommendations for its management in childhood and adolescence.

RECENT FINDINGS

Epigenetics plays a key role in transmitting obesity risk to offspring. Single-nucleotide polymorphisms at genetic loci for adipokines and their receptors are associated with obesity. Gut microbiota is an important regulator of weight status, and Bifidobacterium species improves metabolic status. The incidence of comorbidities including prediabetes and type 2 diabetes has increased. Novel biomarkers such as alpha-hydroxybutyrate and branched-chain amino acids correlate with insulin sensitivity and predict glycemic control in adolescents. Lifestyle modifications and pharmacotherapy can produce small BMI changes. Bariatric surgery induces substantial weight loss and remission of comorbidities.

SUMMARY

Alterations in genetics, epigenetics and microbiota influence childhood obesity. Lifestyle modification remains the mainstay of management and pharmacotherapy with Food and Drug Administration approved medications is recommended only for patients resistant to lifestyle changes and for comorbidities. Bariatric surgery produces sustained weight loss and cardiovascular benefits and is an effective option for adolescents with severe obesity.

Brown adipogenic potential of brown adipocytes and peri-renal adipocytes from human embryo

Both brown adipocytes (BAC) and beige cells hold therapeutic potential for the treatment of metabolic disorders. Unfortunately, the amount and activity of these cells are limited in adults. Although BAC marker expression has been shown in peri-renal adipose tissues in children and adults, functional assessment is lacking. Furthermore, it is entirely unknown whether adipose progenitors are present in human embryo and able to give rise to BAC in situ during evolution. Therefore, adipose tissues in the interscapular and peri-renal regions were dissected from human embryo and subcutaneous white adipose tissues (sWAT) were obtained from an adult. After subjected to differentiation in vitro, adipocyte progenitors were detected present in all these adipose tissues. When stimulated for adipogenesis, differentiated adipocytes in the intercapular and peri-renal regions showed similar features: (1) induced BAC and beige cell marker expression including UCP1 and PRDM16 and comparable mitochondrion copy number; (2) similar gene expression patterns by RNA-Seq analysis; and (3) similar maximal oxygen consumption rates examined by respirometry. Nevertheless, stimulation of adipocyte progenitors in sWAT induces neither BAC and beige cell marker expression nor any change of oxygen consumption. In conclusion, peri-renal adipocyte progenitors in human embryo hold browning potential for BAC production.

FTO Obesity Risk Variants Are Linked to Adipocyte IRX3 Expression and BMI of Children - Relevance of FTO Variants to Defend Body Weight in Lean Children?

BACKGROUND

Genome-wide association studies have identified variants within the FTO (fat mass and obesity associated) locus as the strongest predictors of obesity amongst all obesity-associated gene loci. Recent evidence suggests that variants in FTO directly affect human adipocyte function through targeting IRX3 and IRX5 and thermogenesis regulation.

AIM

We addressed the relevance of this proposed FTO-IRX pathway in adipose tissue (AT) of children.

RESULTS

Expression of IRX3 was higher in adipocytes compared to SVF. We found increased adipocyte-specific expression of IRX3 and IRX5 with the presence of the FTO risk haplotype in lean children, whereas it was unaffected by risk variants in obese peers. We further show that IRX3 expression was elevated in isolated adipocytes and AT of lean compared to obese children, particularly in UCP1-negative adipocytes, and inversely correlated with BMI SDS. Independent of BMI, IRX3 expression in adipocytes was significantly related to adipocyte hypertrophy, and subsequent associations with AT inflammation and HOMA-IR in the children.

CONCLUSION

One interpretation of our observation of FTO risk variants linked to IRX3 expression and adipocyte size restricted to lean children, along with the decreased IRX3 expression in obese compared to lean peers, may reflect a defense mechanism for protecting body-weight, which is pertinent for lean children.

Gene pathway development in human epicardial adipose tissue during early life

Studies in rodents and newborn humans demonstrate the influence of brown adipose tissue (BAT) in temperature control and energy balance and a critical role in the regulation of body weight. Here, we obtained samples of epicardial adipose tissue (EAT) from neonates, infants, and children in order to evaluate changes in their transcriptional landscape by applying a systems biology approach. Surprisingly, these analyses revealed that the transition to infancy is a critical stage for changes in the morphology of EAT and is reflected in unique gene expression patterns of a substantial proportion of thermogenic gene transcripts (~10%). Our results also indicated that the pattern of gene expression represents a distinct developmental stage, even after the rebound in abundance of thermogenic genes in later childhood. Using weighted gene coexpression network analyses, we found precise anthropometric-specific correlations with changes in gene expression and the decline of thermogenic capacity within EAT. In addition, these results indicate a sequential order of transcriptional events affecting cellular pathways, which could potentially explain the variation in the amount, or activity, of BAT in adulthood. Together, these results provide a resource to elucidate gene regulatory mechanisms underlying the progressive development of BAT during early life.

Adipocyte nuclei captured from VAT and SAT

Background

Obesity-related comorbidities are thought to result from the reprogramming of the epigenome in numerous tissues and cell types, and in particular, mature adipocytes within visceral and subcutaneous adipose tissue, VAT and SAT. The cell-type specific chromatin remodeling of mature adipocytes within VAT and SAT is poorly understood, in part, because of the difficulties of isolating and manipulating large fragile mature adipocyte cells from adipose tissues.

Methods

We constructed MA-INTACT (Mature Adipocyte-Isolation of Nuclei TAgged in specific Cell Types) mice using the adiponectin (ADIPOQ) promoter (ADNp) to tag the surface of mature adipocyte nuclei with a reporter protein. The SUN1mRFP1Flag reporter is comprised of a fragment of the nuclear transmembrane protein SUN1, the fluorescent protein mRFP1, and three copies of the Flag epitope tag.

Results

Mature adipocyte nuclei were rapidly and efficiently immuno-captured from VAT and SAT (MVA and MSA nuclei, respectively), of MA-INTACT mice. MVA and MSA nuclei contained 1,000 to 10,000-fold higher levels of adipocyte-specific transcripts, ADIPOQ, PPARg2, EDNRB, and LEP, relative to uncaptured nuclei, while the latter expressed higher levels of leukocyte and endothelial cell markers IKZF1, RETN, SERPINF1, SERPINE1, ILF3, and TNFA. MVA and MSA nuclei differentially expressed several factors linked to adipogenesis or obesity-related health risks including CEBPA, KLF2, RETN, SERPINE1, and TNFA. The various nuclear populations dramatically differentially expressed transcripts encoding chromatin remodeler proteins regulating DNA cytosine methylation and hydroxymethylation (TETs, DNMTs, TDG, GADD45s) and nucleosomal histone modification (ARID1A, KAT2B, KDM4A, PRMT1, PRMT5, PAXIP1). Remarkably, MSA and MVA nuclei expressed 200 to 1000-fold higher levels of thermogenic marker transcripts PRDM16 and UCP1.

Conclusions

The MA-INTACT mouse enables a simple way to perform cell-type specific analysis of highly purified mature adipocyte nuclei from VAT and SAT and increases the statistical significance of data collected on adipocytes. Isolated VAT and SAT adipocyte nuclei expressed distinct patterns of transcripts encoding chromatin remodeling factors and proteins relevant to diabetes, cardiovascular disease, and thermogenesis. The MA-INTACT mouse is an useful model to test the impact of caloric intake, dietary nutrients, exercise, and pharmaceuticals on the epigenome-induced health risks of obesity.

Electronic supplementary material

The online version of this article (doi:10.1186/s40608-016-0112-6) contains supplementary material, which is available to authorized users.

Milk: an epigenetic amplifier of FTO-mediated transcription? Implications for Western diseases

Single-nucleotide polymorphisms within intron 1 of the FTO (fat mass and obesity-associated) gene are associated with enhanced FTO expression, increased body weight, obesity and type 2 diabetes mellitus (T2DM). The N⁶-methyladenosine (m⁶A) demethylase FTO plays a pivotal regulatory role for postnatal growth and energy expenditure. The purpose of this review is to provide translational evidence that links milk signaling with FTO-activated transcription of the milk recipient. FTO-dependent demethylation of m⁶A regulates mRNA splicing required for adipogenesis, increases the stability of mRNAs, and affects microRNA (miRNA) expression and miRNA biosynthesis. FTO senses branched-chain amino acids (BCAAs) and activates the nutrient sensitive kinase mechanistic target of rapamycin complex 1 (mTORC1), which plays a key role in translation. Milk provides abundant BCAAs and glutamine, critical components increasing FTO expression. CpG hypomethylation in the first intron of FTO has recently been associated with T2DM. CpG methylation is generally associated with gene silencing. In contrast, CpG demethylation generally increases transcription. DNA de novo methylation of CpG sites is facilitated by DNA methyltransferases (DNMT) 3A and 3B, whereas DNA maintenance methylation is controlled by DNMT1. MiRNA-29s target all DNMTs and thus reduce DNA CpG methylation. Cow´s milk provides substantial amounts of exosomal miRNA-29s that reach the systemic circulation and target mRNAs of the milk recipient. Via DNMT suppression, milk exosomal miRNA-29s may reduce the magnitude of FTO methylation, thereby epigenetically increasing FTO expression in the milk consumer. High lactation performance with increased milk yield has recently been associated with excessive miRNA-29 expression of dairy cow mammary epithelial cells (DCMECs). Notably, the galactopoietic hormone prolactin upregulates the transcription factor STAT3, which induces miRNA-29 expression. In a retrovirus-like manner milk exosomes may transfer DCMEC-derived miRNA-29s and bovine FTO mRNA to the milk consumer amplifying FTO expression. There is compelling evidence that obesity, T2DM, prostate and breast cancer, and neurodegenerative diseases are all associated with increased FTO expression. Maximization of lactation performance by veterinary medicine with enhanced miRNA-29s and FTO expression associated with increased exosomal miRNA-29 and FTO mRNA transfer to the milk consumer may represent key epigenetic mechanisms promoting FTO/mTORC1-mediated diseases of civilization.

Caring for children with NAFLD and navigating their care into adulthood

NAFLD is the most common chronic liver disease in children and adults, with its prevalence closely associated with obesity and other features of the metabolic syndrome. As young adults with NAFLD transition from the paediatric care environment to adult services, establishing a coordinated model of transition to ensure ongoing and appropriate care is critical. Enabling a smooth transfer begins with an understanding of the key differences between paediatric and adult NAFLD as well as the psychosocial factors that affect older adolescents. This Review summarizes the literature on paediatric NAFLD from the past two decades with a focus on the differences in epidemiology, pathology, pathophysiology and treatment that are relevant to clinicians who transition paediatric patients to adult care. An integrated model, which employs a team of adult and paediatric providers who can address the psychosocial, cognitive and logistical challenges of transition, provides the best opportunity for a seamless and coordinated transfer to adult care.