Sex Differences in Brown Adipose Tissue Thermogenic Features During Caloric Restriction

The response of grey mouse lemurs to acute caloric restriction before reproduction supports the 'thrifty female hypothesis'

The 'thrifty female hypothesis' states that females preserve more of their energy reserves during winter than males because of the sex-specific time frame of energy allocation for reproduction. As males reactivate their reproductive axis before the mating period, while females mainly allocate energy during gestation and lactation, we hypothesized that males would have to use shorter torpor bouts and longer periods of normothermic activity to promote spermatogenesis during winter, a period of low food availability. Here, we applied an acute 2 week 80% caloric restriction in male and female grey mouse lemurs shortly before the mating period. We found evidence of thriftier phenotypes in wintering females, which performed deeper and longer torpor bouts than males and ultimately lost less body mass. Our results thus support the 'thrifty female hypothesis' in a seasonally breeding primate and reinforce the concept of a sex-biased trade-off in using torpor, which might ultimately benefit reproduction and survival.

Effects of the Fungicide Prothioconazole on Lipid Metabolism in Mice: Whitening Alterations of Brown Adipose Tissue

With considerable concerns about the associations between metabolic disorders and agricultural biocides, there are scattered data suggesting that the triazole fungicide prothioconazole (PTC) at lower doses than the no observed adverse effect level of 5000 μg/kg/d possibly has the potential to disrupt glycolipid metabolism in mammals. Here, we investigated the effects of 50, 500, and 5000 μg/kg/d of PTC on glycolipid metabolism in mice following 8 weeks of administration via drinking water, with specific attention on brown adipose tissue (BAT) and white adipose tissue (WAT) in addition to the liver. We found that along with the increased serum triglyceride level in the 5000 μg/kg/d group, small fatty vacuoles occurred in livers in all treatment groups, indicating lipid accumulation. No change in WAT was observed, but PTC caused BAT whitening, characterized by adipocyte hypertrophy, more unilocular adipocytes with enlarged lipid droplets, reduced UCP1 levels, and down-regulated Doi2 expression, and even the dose of 50 μg/kg/d was effective. Transcriptomic analysis revealed immune inhibition and circadian rhythm disturbance in BAT from the 5000 μg/kg/d group, which are in agreement with BAT whitening and inactivation. On employing the C3H10T1/2 cells in vitro, we found that PTC treatment concentration-dependently promoted lipid accumulation in brown adipocytes, along with altered expression of thermogenesis-related and circadian genes. Taken together, our study shows that low doses of PTC caused BAT whitening, calling for much attention to the new target by pollutants.

UCP1-dependent brown adipose activation accelerates cardiac metabolic remodeling and reduces initial hypertrophic and fibrotic responses to pathological stress

Brown adipose tissue (BAT) is correlated to cardiovascular health in rodents and humans, but the physiological role of BAT in the initial cardiac remodeling at the onset of stress is unknown. Activation of BAT via 48 h cold (16°C) in mice following transverse aortic constriction (TAC) reduced cardiac gene expression for LCFA uptake and oxidation in male mice and accelerated the onset of cardiac metabolic remodeling, with an early isoform shift of carnitine palmitoyltransferase 1 (CPT1) toward increased CPT1a, reduced entry of long chain fatty acid (LCFA) into oxidative metabolism (0.59 ± 0.02 vs. 0.72 ± 0.02 in RT TAC hearts, p < .05) and increased carbohydrate oxidation with altered glucose transporter content. BAT activation with TAC reduced early hypertrophic expression of β-MHC by 61% versus RT-TAC and reduced pro-fibrotic TGF-β1 and COL3α1 expression. While cardiac natriuretic peptide expression was yet to increase at only 3 days TAC, Nppa and Nppb expression were elevated in Cold TAC versus RT TAC hearts 2.7- and 2.4-fold, respectively. Eliminating BAT thermogenic activation with UCP1 KO mice eliminated differences between Cold TAC and RT TAC hearts, confirming effects of BAT activation rather than autonomous cardiac responses to cold. Female responses to BAT activation were blunted, with limited UCP1 changes with cold, partly due to already activated BAT in females at RT compared to thermoneutrality. These data reveal a previously unknown physiological mechanism of UCP1-dependent BAT activation in attenuating early cardiac hypertrophic and profibrotic signaling and accelerating remodeled metabolic activity in the heart at the onset of cardiac stress.

The role of oestrogen in determining sexual dimorphism in energy balance

Energy balance is determined by caloric intake and the rate at which energy is expended, with the latter comprising resting energy expenditure, physical activity and adaptive thermogenesis. The regulation of both energy intake and expenditure exhibits clear sexual dimorphism, with young women being relatively protected against weight gain and the development of cardiometabolic diseases. Preclinical studies have indicated that females are more sensitive to the satiety effects of leptin and insulin compared to males. Furthermore, females have greater thermogenic activity than males, whereas resting energy expenditure is generally higher in males than females. In addition to this, in post-menopausal women, the decline in sex steroid concentration, particularly in oestrogen, is associated with a shift in the distribution of adipose tissue and overall increased propensity to gain weight. Oestrogens are known to regulate energy balance and weight homeostasis via effects on both food intake and energy expenditure. Indeed, 17β-oestradiol treatment increases melanocortin signalling in the hypothalamus to cause satiety. Furthermore, oestrogenic action at the ventromedial hypothalamus has been linked with increased energy expenditure in female mice. We propose that oestrogen action on energy balance is multi-faceted and is fundamental to determining sexual dimorphism in weight control. Furthermore, evidence suggests that the decline in oestrogen levels leads to increased risk of weight gain and development of cardiometabolic disease in women across the menopausal transition.

From Beneath the Skin to the Airway Wall: Understanding the Pathological Role of Adipose Tissue in Comorbid Asthma-Obesity

This article provides a contemporary report on the role of adipose tissue in respiratory dysfunction. Adipose tissue is distributed throughout the body, accumulating beneath the skin (subcutaneous), around organs (visceral), and importantly in the context of respiratory disease, has recently been shown to accumulate within the airway wall: "airway-associated adipose tissue." Excessive adipose tissue deposition compromises respiratory function and increases the severity of diseases such as asthma. The mechanisms of respiratory impairment are inflammatory, structural, and mechanical in nature, vary depending on the anatomical site of deposition and adipose tissue subtype, and likely contribute to different phenotypes of comorbid asthma-obesity. An understanding of adipose tissue-driven pathophysiology provides an opportunity for diagnostic advancement and patient-specific treatment. As an exemplar, the potential impact of airway-associated adipose tissue is highlighted, and how this may change the management of a patient with asthma who is also obese. © 2023 American Physiological Society. Compr Physiol 13:4321-4353, 2023.

A modest change in housing temperature alters whole body energy expenditure and adipocyte thermogenic capacity in mice

Typical vivarium temperatures (20-26°C) induce facultative thermogenesis in mice, a process attributable in part to uncoupling protein-1 (UCP1). The impact of modest changes in housing temperature on whole body and adipose tissue energetics in mice remains unclear. Here, we determined the effects of transitioning mice from 24°C to 30°C on total energy expenditure and adipose tissue protein signatures. C57BL/6J mice were housed at 24°C for 2 wk and then either remained at 24°C (n = 16/group, 8M/8F) or were transitioned to 30°C (n = 16/group, 8M/8F) for 4 wk. Total energy expenditure and its components were determined by indirect calorimetry. Interscapular brown adipose tissue (iBAT) and inguinal white adipose tissue (iWAT) proteins were quantified by Western blot and quantitative proteomics. Transitioning from 24°C to 30°C reduced total energy expenditure in both male (-25%) and female (-16%) mice, which was attributable to lower basal energy expenditure in males (-36%) and females (-40%). Total iBAT UCP1 protein content was 50% lower at 30°C compared with 24°C, whereas iWAT UCP1 protein content was similar between conditions. iBAT UCP1 protein content remained 20-fold greater than iWAT at 30°C. In iBAT and iWAT, 183 and 41 proteins were differentially expressed between 24°C and 30°C, respectively. iWAT proteins (257) differentially expressed between sexes at 30°C were not differentially expressed at 24°C. Thus, 30°C housing lowers total energy expenditure of mice when compared with an ambient temperature (24°C) that falls within the National Research Council's guidelines for housing laboratory mice. Lower iBAT UCP1 content accompanied chronic housing at 30°C. Furthermore, housing temperature influences sexual dimorphism in the iWAT proteome. These data have implications regarding the optimization of preclinical models of human disease.NEW & NOTEWORTHY Housing mice at 30°C reduced the basal and total energy expenditure compared with 24°C, which was accompanied by a reduction in brown adipose tissue UCP1 content. Proteomic profiling demonstrated the brown adipose tissue and white adipose tissue proteomes were largely influenced by housing temperature and sex, respectively. Therefore, 30°C housing revealed sexual dimorphism in the white adipose tissue proteome that was largely absent in animals housed at 24°C.

Sexual Dimorphism in Brown Adipose Tissue Activation and White Adipose Tissue Browning

The present narrative review gathers the studies reported so far, addressing sex differences in the effects of cold exposure, feeding pattern and age on brown adipose tissue (BAT) thermogenesis and white adipose tissue (WAT) browning. In rodents, when exposed to decreasing temperatures, females activate thermogenesis earlier. Results obtained in humans go in the same line, although they do not provide results as solid as those obtained in rodents. Regarding the effects of overfeeding, interesting sex differences on BAT thermogenic capacity have been reported, and the greater or lower sensitivity of each sex to this dietary situation seems to be dependent on the type of feeding. In the case of energy restriction, females are more sensitive than males. In addition, sex differences have also been observed in thermogenesis changes induced by phenolic compound administration. During sexual development, an increase in BAT mass and BAT activity takes place. This phenomenon is greater in boys than in girls, probably due to its relation to muscle-mass growth. The opposite situation takes place during ageing, a lifespan period where thermogenic capacity declines, this being more acute in men than in women. Finally, the vast majority of the studies have reported a higher susceptibility to developing WAT browning amongst females. The scarcity of results highlights the need for further studies devoted to analysing this issue, in order to provide valuable information for a more personalised approach.

Skeletal Muscle Uncoupling Proteins in Mice Models of Obesity

Obesity and accompanying type 2 diabetes are among major and increasing worldwide problems that occur fundamentally due to excessive energy intake during its expenditure. Endotherms continuously consume a certain amount of energy to maintain core body temperature via thermogenic processes, mainly in brown adipose tissue and skeletal muscle. Skeletal muscle glucose utilization and heat production are significant and directly linked to body glucose homeostasis at rest, and especially during physical activity. However, this glucose balance is impaired in diabetic and obese states in humans and mice, and manifests as glucose resistance and altered muscle cell metabolism. Uncoupling proteins have a significant role in converting electrochemical energy into thermal energy without ATP generation. Different homologs of uncoupling proteins were identified, and their roles were linked to antioxidative activity and boosting glucose and lipid metabolism. From this perspective, uncoupling proteins were studied in correlation to the pathogenesis of diabetes and obesity and their possible treatments. Mice were extensively used as model organisms to study the physiology and pathophysiology of energy homeostasis. However, we should be aware of interstrain differences in mice models of obesity regarding thermogenesis and insulin resistance in skeletal muscles. Therefore, in this review, we gathered up-to-date knowledge on skeletal muscle uncoupling proteins and their effect on insulin sensitivity in mouse models of obesity and diabetes.

Hypothalamic Estrogen Signaling and Adipose Tissue Metabolism in Energy Homeostasis

Obesity has become a global epidemic, and it is a major risk factor for other metabolic disorders such as type 2 diabetes and cardiometabolic disease. Accumulating evidence indicates that there is sex-specific metabolic protection and disease susceptibility. For instance, in both clinical and experimental studies, males are more likely to develop obesity, insulin resistance, and diabetes. In line with this, males tend to have more visceral white adipose tissue (WAT) and less brown adipose tissue (BAT) thermogenic activity, both leading to an increased incidence of metabolic disorders. This female-specific fat distribution is partially mediated by sex hormone estrogens. Specifically, hypothalamic estrogen signaling plays a vital role in regulating WAT distribution, WAT beiging, and BAT thermogenesis. These regulatory effects on adipose tissue metabolism are primarily mediated by the activation of estrogen receptor alpha (ERα) in neurons, which interacts with hormones and adipokines such as leptin, ghrelin, and insulin. This review discusses the contribution of adipose tissue dysfunction to obesity and the role of hypothalamic estrogen signaling in preventing metabolic diseases with a particular focus on the VMH, the central regulator of energy expenditure and glucose homeostasis.

The good and the BAT of metabolic sex differences in thermogenic human adipose tissue

Thermogenic adipose tissue, which comprises classical brown and beige adipose tissue, has the ability to improve systemic metabolism. Its identification in adult humans has fostered extensive investigations on the therapeutic value to counteract obesity and metabolic disorders. Sex and gender differences of human thermogenic adipose tissue, however, are still understudied despite their importance for personalized treatment options. Here, we review studies reporting human sex differences of thermogenic adipose tissue and related potential improvements of systemic energy metabolism. An increasing body of evidence suggests higher prevalence, mass and activity of thermogenic adipose tissue in women, but the consequences for metabolic disease progression and mechanisms are largely unknown. Therefore, we also discuss observations on sex-specific adipose metabolism in experimental mouse and rat studies that may assist to establish molecular mechanisms and instruct future investigations in humans.

Differential Responses of White Adipose Tissue and Brown Adipose Tissue to Calorie Restriction During Aging

Age-related adipose tissue dysfunction is potentially important in the development of insulin resistance and metabolic disorder. Caloric restriction (CR) is a robust intervention to reduce adiposity, improve metabolic health, and extend healthy life span. Both white adipose tissue (WAT) and brown adipose tissue (BAT) are involved in energy homeostasis. CR triggers the beiging of WAT in young mice; however, the effects of CR on beiging of WAT and function of BAT during aging are unclear. This study aimed to investigate how age and CR impact the beiging of WAT, the function of BAT, and metabolic health in mice. C57BL/6 mice were fed CR diet (40% less than the ad libitum [AL] diet) for 3 months initiated in young (3 months), middle-aged (12 months), and old (19 months) stage. We found age-related changes in different types of adipose tissue, including adipocyte enlargement, declined beiging of WAT, and declined thermogenic and β-oxidational function of BAT. Moreover, CR attenuated age-associated adipocyte enlargement and prevented the age-related decline in beiging potential of WAT. These protective effects on the beiging potential were significant in inguinal WAT at all three ages, which were significant in epididymal WAT at young and old age. In contrast, thermogenic and β-oxidational function of BAT further declined after CR in the young age group. In conclusion, our findings reveal the contribution of WAT beiging decline to age-related metabolic disorder and suggest nutritional intervention, specifically targeting WAT beiging, as an effective approach to metabolic health during aging.

Uncoupling protein 1-independent effects of eicosapentaenoic acid in brown adipose tissue of diet-induced obese female mice

Brown adipose tissue (BAT) plays a key role in energy expenditure through its thermogenic function, making its activation a popular target to reduce obesity. We recently reported that male mice housed at thermoneutrality with uncoupling protein 1 (UCP1) deficiency had increased weight gain and glucose intolerance, but eicosapentaenoic acid (EPA) ameliorated these effects. Whether female mice respond similarly to lack of UCP1 and to EPA remains unknown. We hypothesize that the effects of EPA on BAT activation are independent of UCP1 expression. We used female wild type (WT) and UCP1 knockout (KO) mice housed at thermoneutrality (30°C) as an obesogenic environment and fed them high fat (HF) diets with or without EPA for up to 14 weeks. Body weight (BW), body composition, and insulin and glucose tolerance tests were performed during the feeding trial. At termination, serum and BAT were harvested for further analyses. Mice in the KO-EPA group had significantly lower BW than KO-HF mice. In addition, KO-HF mice displayed significantly impaired glucose tolerance compared to their WT-HF littermates. However, EPA significantly enhanced glucose clearance in the KO mice compared to KO-HF mice. Protein levels of the mitochondrial cytochrome C oxidase subunits I, II, and IV were significantly lower in KO mice compared to WT. Our findings support that ablation of UCP1 is detrimental to energy metabolism of female mice in thermoneutral conditions. However, unexpectedly, EPA's protective effects against diet-induced obesity and glucose intolerance in these mice were independent of UCP1.

Sex differences and aging: Is there a role of brown adipose tissue?

In every population across the world, women live significantly longer than men; however, the underlying physiological processes that drive these sex differences in age-specific mortality are largely unknown. Recently, the role of adipose tissue in aging and longevity has been a focus of biomedical research in both humans and rodent models. Specifically, brown adipose tissue, a thermoregulatory tissue originally thought to not exist past infancy in humans, has been shown to potentially play a role in health throughout the lifespan. Females have larger adult brown adipose depots that are not just larger in size but also more efficient in non-shivering thermogenesis. This improved functioning of the brown adipose tissue may potentially lead to improved female health, and we hypothesize that this advantage may be of even bigger significance in the older population. Here, we briefly review what is known about sex differences in aging and how sex differences in brown adipose tissue may be contributing to the female lifespan advantage. These questions have usually been addressed in large experimental studies in rodents as a translational model of human aging. Overall, we propose that a better understanding of the thermogenesis-metabolism nexus is necessary in biomedical research, and sex differences in these factors may contribute to the female longevity bias seen in human populations.

The transcriptional co-regulator LDB1 is required for brown adipose function

Objective

Brown adipose tissue (BAT) is critical for thermogenesis and glucose/lipid homeostasis. Exploiting the energy uncoupling capacity of BAT may reveal targets for obesity therapies. This exploitation requires a greater understanding of the transcriptional mechanisms underlying BAT function. One potential regulator of BAT is the transcriptional co-regulator LIM domain-binding protein 1 (LDB1), which acts as a dimerized scaffold, allowing for the assembly of transcriptional complexes. Utilizing a global LDB1 heterozygous mouse model, we recently reported that LDB1 might have novel roles in regulating BAT function. However, direct evidence for the LDB1 regulation of BAT thermogenesis and substrate utilization has not been elucidated. We hypothesize that brown adipocyte-expressed LDB1 is required for BAT function.

Methods

LDB1-deficient primary cells and brown adipocyte cell lines were assessed via qRT-PCR and western blotting for altered mRNA and protein levels to define the brown adipose-specific roles. We conducted chromatin immunoprecipitation with primary BAT tissue and immortalized cell lines. Potential transcriptional partners of LDB1 were revealed by conducting LIM factor surveys via qRT-PCR in mouse and human brown adipocytes. We developed a Ucp1-Cre-driven LDB1-deficiency mouse model, termed Ldb1^ΔBAT, to test LDB1 function in vivo. Glucose tolerance and uptake were assessed at thermoneutrality via intraperitoneal glucose challenge and glucose tracer studies. Insulin tolerance was measured at thermoneutrality and after stimulation with cold or the administration of the β3-adrenergic receptor (β3-AR) agonist CL316,243. Additionally, we analyzed plasma insulin via ELISA and insulin signaling via western blotting. Lipid metabolism was evaluated via BAT weight, histology, lipid droplet morphometry, and the examination of lipid-associated mRNA. Finally, energy expenditure and cold tolerance were evaluated via indirect calorimetry and cold challenges.

Results

Reducing Ldb1 in vitro and in vivo resulted in altered BAT-selective mRNA, including Ucp1, Elovl3, and Dio2. In addition, there was reduced Ucp1 induction in vitro. Impacts on gene expression may be due, in part, to LDB1 occupying Ucp1 upstream regulatory domains. We also identified BAT-expressed LIM-domain factors Lmo2, Lmo4, and Lhx8, which may partner with LDB1 to mediate activity in brown adipocytes. Additionally, we observed LDB1 enrichment in human brown adipose. In vivo analysis revealed LDB1 is required for whole-body glucose and insulin tolerance, in part through reduced glucose uptake into BAT. In Ldb1^ΔBAT tissue, we found significant alterations in insulin-signaling effectors. An assessment of brown adipocyte morphology and lipid droplet size revealed larger and more unilocular brown adipocytes in Ldb1^ΔBAT mice, particularly after a cold challenge. Alterations in lipid handling were further supported by reductions in mRNA associated with fatty acid oxidation and mitochondrial respiration. Finally, LDB1 is required for energy expenditure and cold tolerance in both male and female mice.

Conclusions

Our findings support LDB1 as a regulator of BAT function. Furthermore, given LDB1 enrichment in human brown adipose, this co-regulator may have conserved roles in human BAT.

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The transcriptional co-regulator LDB1 is required for brown adipocyte gene expression, including Ucp1.

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Several LIM-domain factors, including Lmo2, Lmo4, and Lhx8, are expressed in BAT and may be potential LDB1 partners.

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Male Ldb1 BAT knockouts are glucose and insulin intolerant, have lower glucose uptake and altered insulin signaling.

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LDB1 impacts brown adipocyte morphology, lipid droplet size, and mRNA associated with lipid utilization.

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BAT-expressed LDB1 is required for energy expenditure and cold tolerance.

Changes in brown adipose tissue lipid mediator signatures with aging, obesity, and DHA supplementation in female mice

Brown adipose tissue (BAT) dysfunction in aging and obesity has been related to chronic unresolved inflammation, which could be mediated by an impaired production of specialized proresolving lipid mediators (SPMs), such as Lipoxins-LXs, Resolvins-Rvs, Protectins-PDs, and Maresins-MaRs. Our aim was to characterize the changes in BAT SPMs signatures and their association with BAT dysfunction during aging, especially under obesogenic conditions, and their modulation by a docosahexaenoic acid (DHA)-rich diet. Lipidomic, functional, and molecular studies were performed in BAT of 2- and 18-month-old lean (CT) female mice and in 18-month-old diet-induced obese (DIO) mice fed with a high-fat diet (HFD), or a DHA-enriched HFD. Aging downregulated Prdm16 and UCP1 levels, especially in DIO mice, while DHA partially restored them. Arachidonic acid (AA)-derived LXs and DHA-derived MaRs and PDs were the most abundant SPMs in BAT of young CT mice. Interestingly, the sum of LXs and of PDs were significantly lower in aged DIO mice compared to young CT mice. Some of the SPMs most significantly reduced in obese-aged mice included LXB4 , MaR2, 4S,14S-diHDHA, 10S,17S-diHDHA (a.k.a. PDX), and RvD6. In contrast, DHA increased DHA-derived SPMs, without modifying LXs. However, MicroPET studies showed that DHA was not able to counteract the impaired cold exposure response in BAT of obese-aged mice. Our data suggest that a defective SPMs production could underlie the decrease of BAT activity observed in obese-aged mice, and highlight the relevance to further characterize the physiological role and therapeutic potential of specific SPMs on BAT development and function.

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

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

Chronic stress inhibits hypothalamus-pituitary-thyroid axis and brown adipose tissue responses to acute cold exposure in male rats

PURPOSE

Cold exposure activates the hypothalamus-pituitary-thyroid (HPT) axis, response blunted by previous acute stress or corticosterone administration. Chronic stressors can decrease serum T3 concentration, and thyrotropin-releasing hormone (Trh) expression in the paraventricular nucleus (PVN), but impact on the response to cold is unknown; this was studied in rats submitted to daily repeated restraint (rRes) that causes habituation of hypothalamus-pituitary-adrenal (HPA) axis response, or to chronic variable stress (CVS) that causes sensitization and hyperreactivity.

METHODS

Wistar male adult rats were submitted to rRes 30 min/day, or to CVS twice a day, for 15 days. On day 16, rats were exposed 1 h to either 5 or 21 °C. Parameters of HPT and HPA axes activity and of brown adipose tissue (BAT) cold response were measured; gene expression in PVN and BAT, by RT-PCR; serum hormone concentration by radioimmunoassay or ELISA.

RESULTS

Compared to naïve animals, Crh and corticosterone concentrations were attenuated at the end of rRes, but increased at the end of CVS treatments. Cold exposure increased mRNA levels of Crh, Trh, and serum concentration of thyrotropin in naïve, but not in rRes or CVS rats; corticosterone increased in all groups. Cold induced expression of thermogenic genes in BAT (Dio2 and Ucp1) in naïve but not in stressed rats; Adrb3 expression was differentially regulated.

CONCLUSION

Both types of chronic stress blunted HPT and BAT responses to cold. Long-term stress effects on noradrenergic and/or hormonal signaling are likely responsible for HPT dysfunction and not the type of chronic stressor.

Maternal High Fat Diet Consumption Exaggerates Metabolic Disorders in Mice With Cigarette-Smoking Induced Intrauterine Undernutrition

Objectives: Maternal smoking causes fetal underdevelopment and results in births which are small for gestation age due to intrauterine undernutrition, leading to various metabolic disorders in adulthood. Furthermore, postnatal high fat diet (HFD) consumption is also a potent obesogenic factor, which can interact with maternal smoking. In this study, we aimed to determine whether maternal HFD consumption during pregnancy can reverse the adverse impact of maternal smoking and change the response to postnatal HFD consumption.

Methods: Female mice were exposed to cigarette smoke (SE, 2 cigarettes/day) or sham exposed for 5 weeks before mating, with half of the SE dams fed HFD (43% fat, SE+HFD). The same treatment continued throughout gestation and lactation. Male offspring from each maternal group were fed the same HFD or chow after weaning and sacrificed at 13 weeks.

Results: Maternal SE alone increased body weight and fat mass in HFD-fed offspring, while SE+HFD offspring showed the highest energy intake and glucose metabolic disorder in adulthood. In addition, postnatal HFD increased the body weight and aggravated the metabolic disorder caused by maternal SE and SE+HFD.

Conclusions: Maternal HFD consumption could not ameliorate the adverse effect of maternal SE but exaggerate metabolic disorders in adult offspring. Smoking cessation and a healthy diet are needed during pregnancy to optimize the health outcome in the offspring.

Sex Differences in Brown Adipose Tissue Function: Sex Hormones, Glucocorticoids, and Their Crosstalk

Excessive fat accumulation in the body causes overweight and obesity. To date, research has confirmed that there are two types of adipose tissue with opposing functions: lipid-storing white adipose tissue (WAT) and lipid-burning brown adipose tissue (BAT). After the rediscovery of the presence of metabolically active BAT in adults, BAT has received increasing attention especially since activation of BAT is considered a promising way to combat obesity and associated comorbidities. It has become clear that energy homeostasis differs between the sexes, which has a significant impact on the development of pathological conditions such as type 2 diabetes. Sex differences in BAT activity may contribute to this and, therefore, it is important to address the underlying mechanisms that contribute to sex differences in BAT activity. In this review, we discuss the role of sex hormones in the regulation of BAT activity under physiological and some pathological conditions. Given the increasing number of studies suggesting a crosstalk between sex hormones and the hypothalamic-pituitary-adrenal axis in metabolism, we also discuss this crosstalk in relation to sex differences in BAT activity.

Absence of uncoupling protein 3 at thermoneutrality influences brown adipose tissue mitochondrial functionality in mice

The physiological role played by uncoupling protein 3 (UCP3) in brown adipose tissue (BAT) has not been fully elucidated so far. In the present study, we evaluated the impact of the absence of UCP3 on BAT mitochondrial functionality and morphology. To this purpose, wild type (WT) and UCP3 Knockout (KO) female mice were housed at thermoneutrality (30°C), a condition in which BAT contributes to energy homeostasis independently of its cold-induced thermogenic function. BAT mitochondria from UCP3 KO mice presented a lower ability to oxidize the fatty acids and glycerol-3-phosphate, and an enhanced oxidative stress as revealed by enhanced mitochondrial electron leak, lipid hydroperoxide levels, and induction of antioxidant mitochondrial enzymatic capacity. The absence of UCP3 also influenced the mitochondrial super-molecular protein aggregation, an important feature for fatty acid oxidation rate as well as for adequate cristae organization and mitochondrial shape. Indeed, electron microscopy revealed alterations in mitochondrial morphology in brown adipocytes from KO mice. In the whole, data here reported show that the absence of UCP3 results in a significant alteration of BAT mitochondrial physiology and morphology. These observations could also help to clarify some aspects of the association between metabolic disorders associated with low UCP3 levels, as previously reported in human studies.

Sex-Specific Response to Caloric Restriction After Reproductive Investment in Microcebus murinus: An Integrative Approach

In seasonal environments, males and females usually maintain high metabolic activity during the whole summer season, exhausting their energy reserves. In the global warming context, unpredictability of food availability during summer could dramatically challenge the energy budget of individuals. Therefore, one can predict that resilience to environmental stress would be dramatically endangered during summer. Here, we hypothesized that females could have greater capacity to survive harsh conditions than males, considering the temporal shift in their respective reproductive energy investment, which can challenge them differently, as well as enhanced flexibility in females' physiological regulation. We tackled this question on the gray mouse lemur (Microcebus murinus), focusing on the late summer period, after the reproductive effort. We monitored six males and six females before and after a 2-weeks 60% caloric restriction (CR), measuring different physiological and cellular parameters in an integrative and comparative multiscale approach. Before CR, females were heavier than males and mostly characterized by high levels of energy expenditure, a more energetic mitochondrial profile and a downregulation of blood antioxidants. We observed a similar energy balance between sexes due to CR, with a decrease in metabolic activity over time only in males. Oxidative damage to DNA was also reduced by different pathways between sexes, which may reflect variability in their physiological status and life-history traits at the end of summer. Finally, females' mitochondria seemed to exhibit greater flexibility and greater metabolic potential than males in response to CR. Our results showed strong differences between males and females in response to food shortage during late summer, underlining the necessity to consider sex as a factor for population dynamics in climate change models.

Feeding brown fat: dietary phytochemicals targeting non-shivering thermogenesis to control body weight

Excessive adipose accumulation, which is the main driver for the development of secondary metabolic complications, has reached epidemic proportions and combined pharmaceutical, educational and nutritional approaches are required to reverse the current rise in global obesity prevalence rates. Brown adipose tissue (BAT) is a unique organ able to dissipate energy and thus a promising target to enhance BMR to counteract a positive energy balance. In addition, active BAT might support body weight maintenance after weight loss to prevent/reduce relapse. Natural products deliver valuable bioactive compounds that have historically helped to alleviate disease symptoms. Interest in recent years has focused on identifying nutritional constituents that are able to induce BAT activity and thereby enhance energy expenditure. This review provides a summary of selected dietary phytochemicals, including isoflavones, catechins, stilbenes, the flavonoids quercetin, luteolin and resveratrol as well as the alkaloids berberine and capsaicin. Most of the discussed phytochemicals act through distinct molecular pathways e.g. sympathetic nerve activation, AMP-kinase signalling, SIRT1 activity or stimulation of oestrogen receptors. Thus, it might be possible to utilise this multitude of pathways to co-activate BAT using a fine-tuned combination of foods or combined nutritional supplements.

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

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

Uncovering the Role of p38 Family Members in Adipose Tissue Physiology

The complex functions of adipose tissue have been a focus of research interest over the past twenty years. Adipose tissue is not only the main energy storage depot, but also one of the largest endocrine organs in the body and carries out crucial metabolic functions. Moreover, brown and beige adipose depots are major sites of energy expenditure through the activation of adaptive, non-shivering thermogenesis. In recent years, numerous signaling molecules and pathways have emerged as critical regulators of adipose tissue, in both homeostasis and obesity-related disease. Among the best characterized are members of the p38 kinase family. The activity of these kinases has emerged as a key contributor to the biology of the white and brown adipose tissues, and their modulation could provide new therapeutic approaches against obesity. Here, we give an overview of the roles of the distinct p38 family members in adipose tissue, focusing on their actions in adipogenesis, thermogenic activity, and secretory function.

A nutritional memory effect counteracts benefits of dietary restriction in old mice

Dietary restriction (DR) during adulthood can greatly extend lifespan and improve metabolic health in diverse species. However, whether DR in mammals is still effective when applied for the first time at old age remains elusive. Here, we report results of a late-life DR switch experiment employing 800 mice, in which 24 months old female mice were switched from ad libitum (AL) to DR or vice versa. Strikingly, the switch from DR-to-AL acutely increases mortality, whereas the switch from AL-to-DR causes only a weak and gradual increase in survival, suggesting a memory of earlier nutrition. RNA-seq profiling in liver, brown (BAT) and white adipose tissue (WAT) demonstrate a largely refractory transcriptional and metabolic response to DR after AL feeding in fat tissue, particularly in WAT, and a proinflammatory signature in aged preadipocytes, which is prevented by chronic DR feeding. Our results provide evidence for a nutritional memory as a limiting factor for DR-induced longevity and metabolic remodeling of WAT in mammals.

Early weaning alters the thermogenic capacity of brown adipose tissue in adult male and female rats

PURPOSE

Early weaning (EW) is a risk factor for obesity development. Brown adipose tissue (BAT) hypofunction is related to obesity onset. Here, we evaluated whether sympathetic nervous system (SNS) activity in BAT and the thermogenic function of BAT are decreased in adulthood in obese rats from two EW models.

METHODS

At the time of birth, lactating Wistar rats and their pups (three males and three females) were separated into three groups: the control group, in which pups consumed milk throughout lactation; the non-pharmacological EW (NPEW) group, in which suckling was interrupted with a bandage during the last 3 days of lactation; and the pharmacological EW (PEW) group, in which dams were treated with bromocriptine (0.5 mg/twice a day) 3 days before weaning. The offspring were sacrificed on PN180.

RESULTS

Adult male rats from both EW models exhibited lower BAT SNS activity. Female rats from the PEW group showed a decrease in BAT SNS activity. The protein levels of UCP1 were lower in the NPEW males, while PGC1α levels were lower in both PEW and NPEW males. Both groups of EW females showed reductions in the levels of β3-AR, TRβ1, and PGC1α. The UCP1 protein level was reduced only in the NPEW females. The EW groups of both sexes had lower AMPK protein levels in BAT. In the hypothalamus, only the PEW females showed an increase in AMPK protein levels. In both groups of EW males, adrenal catecholamine was increased and tyrosine hydroxylase was decreased, while in EW females, adrenal catecholamine was decreased.

CONCLUSIONS

Early weaning alters the thermogenic capacity of BAT, which partially contributes to obesity in adulthood, and there are sex-related differences in these alterations.

Sex-dependent Differences in the Bioenergetics of Liver and Muscle Mitochondria from Mice Containing a Deletion for glutaredoxin-2

Our group recently published a study demonstrating that deleting the gene encoding the matrix thiol oxidoreductase, glutaredoxin-2 (GRX2), alters the bioenergetics of mitochondria isolated from male C57BL/6N mice. Here, we conducted a similar study, examining H₂O₂ production and respiration in mitochondria isolated from female mice heterozygous (GRX2+/−) or homozygous (GRX2−/−) for glutaredoxin-2. First, we observed that deleting the Grx2 gene does not alter the rate of H₂O₂ production in liver and muscle mitochondria oxidizing pyruvate, α-ketoglutarate, or succinate. Examination of the rates of H₂O₂ release from liver mitochondria isolated from male and female mice revealed that (1) sex has an impact on the rate of ROS production by liver and muscle mitochondria and (2) loss of GRX2 only altered ROS release in mitochondria collected from male mice. Assessment of the bioenergetics of these mitochondria revealed that loss of GRX2 increased proton leak-dependent and phosphorylating respiration in liver mitochondria isolated from female mice but did not alter rates of respiration in liver mitochondria from male mice. Furthermore, we found that deleting the Grx2 gene did not alter rates of respiration in muscle mitochondria collected from female mice. This contrasts with male mice where loss of GRX2 substantially augmented proton leaks and ADP-stimulated respiration. Our findings indicate that some fundamental sexual dimorphisms exist between GRX2-deficient male and female rodents.

Male and female cats have different regional body compositions and energy requirements for weight loss and weight maintenance

Body composition and energy requirements are different between males and females in several species, and both interfere with weight loss. The aim of this study was to compare the total and regional body composition and energy requirements in obese male (n = 8) and female (n = 8) cats, during weight loss and weight maintenance over 17 subsequent weeks after regimen. The total and regional (thoracic and pelvic limbs, and trunk) body composition was assessed by dual-energy X-ray absorptiometry (DXA). Females exhibited a higher fat mass (FM) than males (p < 0.05), and the trunk was the site with greater fat accumulation regardless of gender. A 23.0 ± 2.8% reduction in body weight was followed by a 50.3 ± 9.4% and a 37.0 ± 8.9% reduction in fat in the trunk region in males and females respectively. Lean mass (LM) mobilization was also increased in the trunk (p < 0.05), and the loss of LM was associated with a reduction in bone mass. The energy intake to achieve the same rate of weight loss was 12.9 ± 3.4% higher in males (p < 0.05). The cats exhibited a gradual increase in energy requirements to maintain their body weight after weight loss (p < 0.05). It was concluded that obese cats mainly accumulate fat in the trunk. The reduction in lean mass after the regimen also occurred in the trunk, with no modifications in the skeletal muscle mass of the limbs. Neutered male cats have higher energy requirements than neutered females, and gender should be considered during obesity management in cats.

Individual differences in early body mass affect thermogenic performance and sibling interactions in litter huddles of the house mouse

We asked whether within-litter differences in early body mass are associated with differences in house mouse pups' thermogenic performance and whether such variation predicts individual differences in competitive interactions for thermally more advantageous positions in the huddle. We explored pups' thermogenic performance in isolation by measuring changes in (maximal) peripheral body temperatures during a 5-min thermal challenge using infrared thermography. Changes in peripheral body temperature were significantly explained by individual differences in body mass within a litter; relatively lighter individuals showed an overall quicker temperature decrease leading to lower body temperatures toward the end of the thermal challenge compared to heavier littermates. Within the litter huddle, relatively lighter pups with a lower thermogenic performance showed consistently more rooting and climbing behavior, apparently to reach the thermally advantageous center of the huddle. This suggests that within-litter variation in starting body mass affects the pups' thermal and behavioral responses to environmental challenges.

Neonatal tobacco smoke reduces thermogenesis capacity in brown adipose tissue in adult rats

Maternal smoking is a risk factor for progeny obesity. We have previously shown, in a rat model of neonatal tobacco smoke exposure, a mild increase in food intake and a considerable increase in visceral adiposity in the adult offspring. Males also had secondary hyperthyroidism, while females had only higher T4. Since brown adipose tissue (BAT) hypofunction is related to obesity, here we tested the hypothesis that higher levels of thyroid hormones are not functional in BAT, suggesting a lower metabolic rate. We evaluated autonomic nerve activity in BAT and its function in adult rats that were exposed to tobacco smoke during lactation. At birth, litters were adjusted to 3 male and 3 female pups/litter. From postnatal day (PND) 3 to 21, Wistar lactating rats and their pups were divided into SE group, smoke-exposed in a cigarette smoking machine (4 times/day) and C group, exposed to filtered air. Offspring were sacrificed at PND180. Adult SE rats of both genders had lower interscapular BAT autonomic nervous system activity, with higher BAT mass but no change in morphology. BAT UCP1 and CPT1a protein levels were decreased in the SE groups of both genders. Male SE rats had lower β3-AR, TRα1, and TRβ1 expression while females showed lower PGC1α expression. BAT Dio2 mRNA and hypothalamic POMC and MC4R levels were similar between groups. Hypothalamic pAMPK level was higher in SE males and lower in SE females. Thus, neonatal cigarette smoke exposure induces lower BAT thermogenic capacity, which can be obesogenic at adulthood.

Influence of previous body mass index and sex on regional fat changes in a weight loss intervention

OBJECTIVES

Men and women may lose weight in a different fashion. This study compares the changes in different anatomical regions after a well-controlled weight loss program by sex and initial BMI.

METHODS

A total of 180 subjects (48 overweight women, 36 overweight men, and 48 obese women and 48 obese men) were recruited to participate in a 22-week weight loss programme (diet + exercise).

RESULTS

Regarding percentage body weight change from baseline, there was no triple interaction (BMI, sex and anatomical region), but there was interaction between BMI and anatomical region (F2,840 = 34.5; p < 0.001), and between sex and anatomical region (F2,840 = 98.8; p < 0.001). Usually, the arms and legs are the regions that lose more weight in obese participants, but men lose the highest percentage of mass from the trunk. There were differences between men and women for the areas of left trunk mass (750g), right trunk mass (700g), total mass of the trunk (1400g), android mass (350g), and finally in the total mass in overweight participants (1300g), with higher values for men than for women. The region that loses more weight and fat is the trunk, followed by the legs, and then the arms, when the loss is observed in function of the total weight or fat lost.

CONCLUSION

Both BMI and sex exert a definite influence fat loss, especially in some anatomical regions.

PRL2 links magnesium flux and sex-dependent circadian metabolic rhythms

Magnesium (Mg2+) plays pleiotropic roles in cellular biology, and it is essentially required for all living organisms. Although previous studies demonstrated intracellular Mg2+ levels were regulated by the complex of phosphatase of regenerating liver 2 (PRL2) and Mg2+ transporter of cyclin M (CNNMs), physiological functions of PRL2 in whole animals remain unclear. Interestingly, Mg2+ was recently identified as a regulator of circadian rhythm-dependent metabolism; however, no mechanism was found to explain the clock-dependent Mg2+ oscillation. Herein, we report PRL2 as a missing link between sex and metabolism, as well as clock genes and daily cycles of Mg2+ fluxes. Our results unveil that PRL2-null animals displayed sex-dependent alterations in body composition, and expression of PRLs and CNNMs were sex- and circadian time-dependently regulated in brown adipose tissues. Consistently, PRL2-KO mice showed sex-dependent alterations in thermogenesis and in circadian energy metabolism. These physiological changes were associated with an increased rate of uncoupled respiration with lower intracellular Mg2+ in PRL2-KO cells. Moreover, PRL2 deficiency causes inhibition of the ATP citrate lyase axis, which is involved in fatty acid synthesis. Overall, our findings support that sex- and circadian-dependent PRL2 expression alter intracellular Mg2+ levels, which accordingly controls energy metabolism status.

Influencing Factors of Thermogenic Adipose Tissue Activity

Obesity is an escalating public health challenge and contributes tremendously to the disease burden globally. New therapeutic strategies are required to alleviate the health impact of obesity-related metabolic dysfunction. Brown adipose tissue (BAT) is specialized for dissipating chemical energy for thermogenesis as a defense against cold environment. Intriguingly, the brown-fat like adipocytes that dispersed throughout white adipose tissue (WAT) in rodents and humans, called "brite" or "beige" adipocytes, share similar thermogenic characteristics to brown adipocytes. Recently, researchers have focused on cognition of these thermogenic adipose tissues. Some factors have been identified to regulate the development and function of thermogenic adipose tissues. Cold exposure, pharmacological conditions, and lifestyle can enhance non-shivering thermogenesis and metabolism via some mechanisms. However, environmental pollutants, such as ambient fine particulates and ozone, may impair the function of these thermogenic adipose tissues and thereby induce metabolic dysfunction. In this review, the origin, function and influencing factors of thermogenic adipose tissues were summarized and it will provide insights into identifying new therapeutic strategies for the treatment of obesity and obesity-related diseases.

Estradiol stimulates mitochondrial biogenesis and adiponectin expression in skeletal muscle

Sexual dimorphism has been found in mitochondrial features of skeletal muscle, with female rats showing greater mitochondrial mass and function compared with males. Adiponectin is an insulin-sensitizing adipokine whose expression has been related to mitochondrial function and that is also expressed in skeletal muscle, where it exerts local metabolic effects. The aim of this research was to elucidate the role of sex hormones in modulation of mitochondrial function, as well as its relationship with adiponectin production in rat skeletal muscle. An in vivo study with ovariectomized Wistar rats receiving or not receiving 17β-estradiol (E2) (10 μg/kg per 48 h for 4 weeks) was carried out, in parallel with an assay of cultured myotubes (L6E9) treated with E2 (10 nM), progesterone (Pg; 1 μM), or testosterone (1 μM). E2 upregulated the markers of mitochondrial biogenesis and dynamics, and also of mitochondrial function in skeletal muscle and L6E9. Although in vivo E2 supplementation only partially restored the decreased adiponectin expression levels induced by ovariectomy, these were enhanced by E2 and Pg treatment in cultured myotubes, whereas testosterone showed no effects. Adiponectin receptor 1 expression was increased by E2 treatment, both in vivo and in vitro, but testosterone decreased it. In conclusion, our results are in agreement with the sexual dimorphism previously reported in skeletal muscle mitochondrial function and indicate E2 to be its main effector, as it enhances mitochondrial function and diminishes oxidative stress. Moreover, our data support the idea of the existence of a link between mitochondrial function and adiponectin expression in skeletal muscle, which could be modulated by sex hormones.

Sex differences in thermogenesis structure behavior and contact within huddles of infant mice

Brown adipose tissue (BAT) is a thermogenic effector abundant in most mammalian infants. For multiparous species such as rats and mice, the interscapular BAT deposit provides both an emergency "thermal blanket" and a target for nestmates seeking warmth, thereby increasing the cohesiveness of huddling groups. Sex differences in BAT regulation and thermogenesis have been documented in a number of species, including mice (Mus musculus)--with females generally exhibiting relative upregulation of BAT. It is nonetheless unknown whether this difference affects the behavioral dynamics occurring within huddles of infant rodents. We investigated sex differences in BAT thermogenesis and its relation to contact while huddling in eight-day-old C57BL/6 mouse pups using infrared thermography, scoring of contact, and causal modeling of the relation between interscapular temperature relative to other pups in the huddle (T IS (rel)) and contacts while huddling. We found that females were warmer than their male siblings during cold challenge, under conditions both in which pups were isolated and in which pups could actively huddle in groups of six (3 male, 3 female). This difference garnered females significantly more contacts from other pups than males during cold-induced huddling. Granger analyses revealed a significant negative feedback relationship between contacts with males and T IS (rel) for females, and positive feedback between contacts with females and T IS (rel) for males, indicating that male pups drained heat from female siblings while huddling. Significant sex assortment nonetheless occurred, such that females made more contacts with other females than expected by chance, apparently outcompeting males for access to each other. These results provide further evidence of enhanced BAT thermogenesis in female mice. Slight differences in BAT can significantly structure the behavioral dynamics occurring in huddles, resulting in differences in the quantity and quality of contacts obtained by the individuals therein, creating sex differences in behavioral interactions beginning in early infancy.

Energy metabolism and biochemical features of adipose tissues in ICR mice after long-term calorie-restricted diet

Long-term calorie-restricted diet (8 weeks, 60% of control food intake) was followed by an increase in thermogenic activity of interscapular brown fat. The relative amount of DNA and protein and the rate of oxygen consumption increased and tissue-specific marker of brown fat (uncoupling protein UCP1) appeared in significantly reduced deep-pink abdominal adipose tissue.

Effects of neonatal overfeeding on juvenile and adult feeding and energy expenditure in the rat

Overfeeding during perinatal life leads to an overweight phenotype that persists throughout the juvenile stage and into adulthood, however, the mechanim(s) underlying this effect are poorly understood. We hypothesized that obesity due to neonatal overfeeding is maintained by changes in energy expenditure and that these changes differ between males and females. We investigated feeding, physical activity, hormonal and metabolic alterations that occur in adult rats made obese by having been nursed in small litters (SL) compared with those from control litters (CL). There were no differences in absolute food intake between the groups, and juvenile and adult SL rats ate less chow per gram body weight than the CL did in the dark (active) phase. Juvenile, but not adult SL rats did have reduced whole body energy expenditure, but there were no differences between the groups by the time they reached adulthood. Adult SL females (but not males) had reduced brown adipose tissue (BAT) temperatures compared with CL in the first half of the dark phase. Our results indicate a persistent overweight phenotype in rats overfed as neonates is not associated with hyperphagia at any stage, but is reflected in reduced energy expenditure into the juvenile phase. The reduced dark phase BAT activity in adult SL females is not sufficient to reduce total energy expenditure at this stage of life and there is an apparently compensatory effect that prevents SL and CL from continuing to diverge in weight that appears between the juvenile and adult stages.

Control and physiological determinants of sympathetically mediated brown adipose tissue thermogenesis

Brown adipose tissue (BAT) represents a remarkable heat-producing tissue. The thermogenic potential of BAT is conferred by uncoupling protein 1, a protein found uniquely in brown adipocytes. BAT activity and capacity is controlled by the sympathetic nervous system (SNS), which densely innervates brown fat depots. SNS-mediated BAT thermogenesis is essentially governed by hypothalamic and brainstem neurons. BAT activity is also modulated by brain energy balance pathways including the very significant brain melanocortin system, suggesting a genuine involvement of SNS-mediated BAT thermogenesis in energy homeostasis. The use of positron emission tomography/computed tomography scanning has revealed the presence of well-defined BAT depots in the cervical, clavicular, and paraspinal areas in adult humans. The prevalence of these depots is higher in subjects exposed to low temperature and is also higher in women compared to men. Moreover, the prevalence of BAT decreases with age and body fat mass, suggesting that BAT could be involved in energy balance regulation and obesity in humans. This short review summarizes recent progress made in our understanding of the control of SNS-mediated BAT thermogenesis and of the determinants of BAT prevalence or detection in humans.

Effects of ovariectomy and 17-β estradiol replacement on rat brown adipose tissue mitochondrial function

Taking into account the sexual dimorphism previously reported regarding mitochondrial function and biogenesis in brown adipose tissue, the aim of the present study was to go further into these differences by investigating the effect of ovariectomy and 17-β estradiol (E2) replacement on brown adipose tissue mitochondrial function. In this study, fourteen-week-old control female and ovariectomized female Wistar rats were used. Rats were ovariectomized at 5 weeks of age and were treated every 2 days with placebo (OVX group) or E2 (10 μg/kg) (OVX+E2 group) for 4 weeks before sacrifice. We studied the levels of oxidative capacity, antioxidant defence and oxidative damage markers in brown adipose tissue. Moreover, the levels of key elements of mitochondrial biogenesis as well as UCP1 protein levels, as an index of mitochondrial thermogenic capacity, were also determined. In response to ovariectomy, mitochondrial proliferation increased, resulting in less functional mitochondria, since oxidative capacity and antioxidant defences decreased. Although E2 supplementation was able to restore the serum levels of E2 shown by control rats, the treatment reverted the effects of the ovariectomy only in part, and oxidative and antioxidant capacities in OVX+E2 rats did not reach the levels shown by control females. Taking these results into account, we suggest that ovarian hormones are responsible, at least in part, for the sexual dimorphism in BAT mitochondrial function. However, other signals produced by ovary, rather than E2, would play an important role in the control of mitochondrial function in BAT.

Age and sex-related changes in rat brain mitochondrial oxidative status

Mitochondria are the main source of free radical species and the most direct target for their damaging effects, which especially affect the brain mitochondrial function, which is better maintained by females than males. The aim of this work was to investigate the age-related changes in rat brain mitochondrial oxidative status focusing on sex differences. Male and female rat brain from four different age groups (6, 12, 18 and 24 months old) were analyzed. Oxidative damage accumulates in rat brain throughout aging, related to the increasing activity of mitochondrial respiratory chain (MRC) and failure of several antioxidant defenses. The aging effect was less marked in females, which accumulated less oxidative damage than males due in part to their greater antioxidant capacity, such as higher GPx activity and higher UCP5 level. This sexual dimorphism gradually increased during aging.

The glucocorticoid contribution to obesity

Obesity is fast becoming the scourge of our time. It is one of the biggest causes of death and disease in the industrialized world, and affects as many as 32% of adults and 17% of children in the USA, considered one of the world's fattest nations. It can also cost countries billions of dollars per annum in direct and indirect care, latest estimates putting the USA bill for obesity-related costs at $147 billion in 2008. It is becoming clear that the pathophysiology of obesity is vastly more complicated than the simple equation of energy in minus energy out. A combination of genetics, sex, perinatal environment and life-style factors can influence diet and energy metabolism. In this regard, psychological stress can have significant long-term impact upon the propensity to gain and maintain weight. In this review, we will discuss the ability of psychological stress and ultimately glucocorticoids (GCs) to alter appetite regulation and metabolism. We will specifically focus on (i) GC regulation of appetite and adiposity, (ii) the apparent sexual dimorphism in stress effects on obesity and (iii) the ability of early life stress to programme obesity in the long term.

Long-term caloric restriction reduces metabolic rate and heart rate under cool and thermoneutral conditions in FBNF1 rats

The long-term metabolic and cardiovascular responses to caloric restriction (CR) are poorly understood. We examined the responses to one year of CR in FBNF1 rats housed in cool (COOL; T(a)=15 °C) or thermoneutral (TMN; T(a)=30 °C) conditions. Rats were acclimated to COOL or TMN for 2 months, instrumented for cardiovascular telemetry and studied in calorimeters. Baseline caloric intake, oxygen consumption (VO(2)), mean arterial blood pressure (MAP), and heart rate (HR) were determined prior to assignment to ad lib (AL) or CR groups (30-40% CR) within each T(a) (n = 8). Groups of rats were studied after 10 weeks CR, one year CR, and after 4 days of re-feeding. Both 10 weeks and one year of CR reduced HR and VO(2) irrespective of T(a). Evaluation of the relationship between metabolic organ mass (liver, heart, brain, and kidney mass) and energy expenditure revealed a clear shift induced by CR to reduce expenditure per unit metabolic mass in both COOL and TMN groups. Re-feeding resulted in prompt elevations of HR and VO(2) to levels observed in control rats. These findings are consistent with the hypothesis that long term CR produces sustained reductions in metabolic rate and heart rate in rats.

Age and sex-related changes in rat brain mitochondrial function

Aging is responsible for the decline in the function of mitochondria and their increase in size and number--adaptive mechanism to restore mitochondrial function. Estrogens increase mitochondrial function, especially in female rats. The aim of this study was to determine the age-related changes in rat brain mitochondrial function focusing on sex differences. Cellular and mitochondrial protein and DNA content, mitochondrial oxidative and phosphorylative function in male and female rat brain from four different age groups (6, 12, 18 and 24 months old) were analyzed. Mitochondria protein/DNA content decreased with aging shifting toward lesser mitochondrial functional capacity and the mitochondria number increased. A sex dimorphism was determined, with female rat brain showing mitochondria with greater functional capacity than males. These sex differences gradually increased during aging.

Outdoor temperature, age, sex, body mass index, and diabetic status determine the prevalence, mass, and glucose-uptake activity of 18F-FDG-detected BAT in humans

CONTEXT

In humans, the prevalence, mass, and glucose-uptake activity of (18)F-fluorodeoxyglucose ((18)F-FDG)-detected brown adipose tissue (BAT), which are expectedly enhanced by a cold stimulus, also appear modulated by other factors that still have to be disentangled.

OBJECTIVE

The objective of the study was to investigate the factors determining the prevalence, mass, and glucose-uptake activity of (18)F-FDG-detected BAT in humans.

RESEARCH DESIGN AND METHODS

We retrospectively analyzed all (18)F-FDG positron emission tomography/computed tomography examinations performed between January 2007 and December 2008 at our institution for (18)F-FDG uptake within the cervical/supraclavicular, mediastinal, paravertebral, and perirenal fat areas. The influence of outdoor temperature, sex, age, body mass index (BMI), plasma glucose level, diabetes diagnosis, day length, and cancer status on the prevalence, mass, and glucose-uptake activity of (18)F-FDG-detected BAT depots was investigated.

RESULTS

Three hundred twenty-eight of the 4842 patients (6.8%) had (18)F-FDG-detected BAT. The prevalence of (18)F-FDG BAT was negatively associated with outdoor temperature (P < 0.0001), age (P < 0.0001), BMI (P < 0.0001), and diabetes status (P = 0.0003). Moreover, there was a significant age × sex interaction for the prevalence of (18)F-FDG BAT (the younger the subjects, the greater the sex difference). The mass and glucose-uptake activity of (18)F-FDG-detected BAT also decreased with increasing outdoor temperature (P < 0.0001), age (P < 0.0001), and BMI (P < 0.0001). They were lower in men than in women (P < 0.001) and lower in diabetic than in nondiabetic patients (P = 0.0002).

CONCLUSIONS

The present study identifies outdoor temperature, age, sex, BMI, and diabetes status as determinants of the prevalence, mass, and glucose-uptake activity of (18)F-FDG-detected BAT.