White to brown fat phenotypic switch induced by genetic and environmental activation of a hypothalamic-adipocyte axis

A simplified enriched environment increases body temperature and suppresses cancer progression in mice

Mice housed in an enriched environment (EE) have inhibited tumor development because of eustress (positive stress) stimulation. However, the mechanisms underlying increased cancer resistance in EEs remain unclear; this may be due to poor reproducibility of the results because of the complicated EE assembly requirements. In this study, we examined the effects of a simplified EE (sEE) model, consisting only of a nesting shelter and a running wheel, on cancer development in mice. We found that, similar to the complex EE, the sEE promoted motor function and alleviated anxiety in mice. Moreover, the mice housed in the sEE showed inhibited tumor growth and metastasis in addition to a higher average body temperature (especially at the point of transition from light to darkness). Furthermore, mice in the sEE had a decreased brown adipose tissue (BAT) mass, with a significant upregulation of the Ucp1 and Adrb3 genes (which encode uncoupling protein 1 and β-adrenergic receptor, respectively) observed in the BAT at the point of transition from light to darkness. An antibody against the immune checkpoint protein programmed cell death 1 was also found to have an additive effect with the sEE against tumor development. Our findings indicate that the established sEE model may be a useful tool for studying the antitumor effects of eustress and can potentially introduce new avenues for cancer prevention and treatment.

Breast cancer-released exosomes trigger cancer-associated cachexia to promote tumor progression

Cancer-secreted exosomes are emerging mediators of cancer-associated cachexia. Here, we show that miR-155 secreted by breast cancer cells is a potent role on the catabolism of adipocytes and muscle cells through targeting the PPARγ. After cocultivated with mature adipocytes or C2C12, tumour cells exhibit an aggressive phenotype via inducing epithelial-mesenchymal transition while breast cancer-derived exosomes increased catabolism and release the metabolites in adipocytes and muscle cells. In adipocytes, cancer cell-secreted miR-155 promotes beige/brown differentiation and remodel metabolism in resident adipocytes by downregulating the PPARγ expression, but does not significantly affect biological conversion in C2C12. Likewise, propranolol ameliorates tumour exosomes-associated cachectic wasting through upregulating the PPARγ expression. In summary, we have demonstrated that the transfer of miR-155 from exosomes acts as an oncogenic signal reprograming systemic energy metabolism and leading to cancer-associated cachexia in breast cancer.

Foxp1 controls brown/beige adipocyte differentiation and thermogenesis through regulating β3-AR desensitization

β-Adrenergic receptor (β-AR) signaling is a pathway controlling adaptive thermogenesis in brown or beige adipocytes. Here we investigate the biological roles of the transcription factor Foxp1 in brown/beige adipocyte differentiation and thermogenesis. Adipose-specific deletion of Foxp1 leads to an increase of brown adipose activity and browning program of white adipose tissues. The Foxp1-deficient mice show an augmented energy expenditure and are protected from diet-induced obesity and insulin resistance. Consistently, overexpression of Foxp1 in adipocytes impairs adaptive thermogenesis and promotes diet-induced obesity. A robust change in abundance of the β3-adrenergic receptor (β3-AR) is observed in brown/beige adipocytes from both lines of mice. Molecularly, Foxp1 directly represses β3-AR transcription and regulates its desensitization behavior. Taken together, our findings reveal Foxp1 as a master transcriptional repressor of brown/beige adipocyte differentiation and thermogenesis, and provide an important clue for its targeting and treatment of obesity.

Beta3-adrenergic receptor (b3-AR) signaling in response to cold activates adipose tissue thermogenesis. Here the authors identify the transcription factor FoxP1 as a direct negative regulator of b3-AR expression and show that loss of FoxP1 leads to enhanced development of thermogenic adipose tissue.

The Beige Adipocyte as a Therapy for Metabolic Diseases

Adipose tissue is traditionally categorized into white and brown relating to their function and morphology. The classical white adipose tissue builds up energy in the form of triglycerides and is useful for preventing fatigue during periods of low caloric intake and the brown adipose tissue more energetically active, with a greater number of mitochondria and energy production in the form of heat. Since adult humans possess significant amounts of active brown fat depots and its mass inversely correlates with adiposity, brown fat might play an important role in human obesity and energy homeostasis. New evidence suggests two types of thermogenic adipocytes with distinct developmental and anatomical features: classical brown adipocytes and beige adipocytes. Beige adipocyte has recently attracted special interest because of its ability to dissipate energy and the possible ability to differentiate themselves from white adipocytes. The presence of brown and beige adipocyte in human adults has acquired attention as a possible therapeutic intervention for metabolic diseases. Importantly, adult human brown appears to be mainly composed of beige-like adipocytes, making this cell type an attractive therapeutic target for obesity and obesity-related diseases, such as atherosclerosis, arterial hypertension and diabetes mellitus type 2. Because many epigenetics changes can affect beige adipocyte differentiation from adipose progenitor cells, the knowledge of the circumstances that affect the development of beige adipocyte cells may be important to new pathways in the treatment of metabolic diseases. New molecules have emerged as possible therapeutic targets, which through the impulse to develop beige adipocytes can be useful for clinical studies. In this review will discuss some recent observations arising from the unique physiological capacity of these cells and their possible role as ways to treat obesity and diabetes mellitus type 2.

Adipose PTEN regulates adult adipose tissue homeostasis and redistribution via a PTEN-leptin-sympathetic loop

OBJECTIVE

Despite the large body of work describing the tumor suppressor functions of Phosphatase and tensin homologue deleted on chromosome ten (PTEN), its roles in adipose homeostasis of adult animals are not yet fully understood. Here, we sought to determine the role of PTEN in whole-body adipose homeostasis.

METHODS

We genetically manipulated PTEN in specific fat depots through recombinant adeno-associated viral vector (rAAV)-based gene transfer of Cre recombinase to adult PTEN^flox mice. Additionally, we used a denervation agent, 6OHDA, to assess the role of sympathetic signaling in PTEN-related adipose remodeling. Furthermore, we chemically manipulated AKT signaling via a pan-AKT inhibitor, MK-2206, to assess the role of AKT in PTEN-related adipose remodeling. Finally, to understand the role of leptin and central signaling on peripheral tissues, we knocked down hypothalamic leptin receptor with a microRNA delivered by a rAAV vector.

RESULTS

Knockdown PTEN in individual fat depot resulted in massive expansion of the affected fat depot through activation of AKT signaling associated with suppression of lipolysis and induction of leptin. This hypertrophic expansion of the affected fat depot led to upregulation of PTEN level, higher lipolysis, and induction of white fat browning in other fat depots, and the compensatory reduced fat mass to maintain a set point of whole-body adiposity. Administration of AKT inhibitor MK-2206 prevented the adipose PTEN knockdown-associated effects. 6OHDA-mediated denervation demonstrated that sympathetic innervation was required for the PTEN knockdown-induced adipose redistribution. Knockdown hypothalamic leptin receptor attenuated the adipose redistribution induced by PTEN deficiency in individual fat depot.

CONCLUSIONS

Our results demonstrate the essential role of PTEN in adipose homeostasis, including mass and distribution in adulthood, and reveal an "adipose PTEN-leptin-sympathetic nervous system" feedback loop to maintain a set point of adipose PTEN and whole-body adiposity.

Genome-Wide Identification and Characterization of Long Noncoding RNAs of Brown to White Adipose Tissue Transformation in Goats

Long noncoding RNAs (lncRNAs) play an important role in the thermogenesis and energy storage of brown adipose tissue (BAT). However, knowledge of the cellular transition from BAT to white adipose tissue (WAT) and the potential role of lncRNAs in goat adipose tissue remains largely unknown. In this study, we analyzed the transformation from BAT to WAT using histological and uncoupling protein 1 (UCP1) gene analyses. Brown adipose tissue mainly existed within the goat perirenal fat at 1 day and there was obviously a transition from BAT to WAT from 1 day to 1 year. The RNA libraries constructed from the perirenal adipose tissues of 1 day, 30 days, and 1 year goats were sequenced. A total number of 21,232 lncRNAs from perirenal fat were identified, including 5393 intronic-lncRNAs and 3546 antisense-lncRNAs. Furthermore, a total of 548 differentially expressed lncRNAs were detected across three stages (fold change ≥ 2.0, false discovery rate (FDR) < 0.05), and six lncRNAs were validated by qPCR. Furthermore, trans analysis found lncRNAs that were transcribed close to 890 protein-coding genes. Additionally, a coexpression network suggested that 4519 lncRNAs and 5212 mRNAs were potentially in trans-regulatory relationships (r > 0.95 or r < -0.95). In addition, Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses showed that the targeted genes were involved in the biosynthesis of unsaturated fatty acids, fatty acid elongation and metabolism, the citrate cycle, oxidative phosphorylation, the mitochondrial respiratory chain complex, and AMP-activated protein kinase (AMPK) signaling pathways. The present study provides a comprehensive catalog of lncRNAs involved in the transformation from BAT to WAT and provides insight into understanding the role of lncRNAs in goat brown adipogenesis.

Beige Fat, Adaptive Thermogenesis, and Its Regulation by Exercise and Thyroid Hormone

While it is now understood that the proper expansion of adipose tissue is critically important for metabolic homeostasis, it is also appreciated that adipose tissues perform far more functions than simply maintaining energy balance. Adipose tissue performs endocrine functions, secreting hormones or adipokines that affect the regulation of extra-adipose tissues, and, under certain conditions, can also be major contributors to energy expenditure and the systemic metabolic rate via the activation of thermogenesis. Adipose thermogenesis takes place in brown and beige adipocytes. While brown adipocytes have been relatively well studied, the study of beige adipocytes has only recently become an area of considerable exploration. Numerous suggestions have been made that beige adipocytes can elicit beneficial metabolic effects on body weight, insulin sensitivity, and lipid levels. However, the potential impact of beige adipocyte thermogenesis on systemic metabolism is not yet clear and an understanding of beige adipocyte development and regulation is also limited. This review will highlight our current understanding of beige adipocytes and select factors that have been reported to elicit the development and activation of thermogenesis in beige cells, with a focus on factors that may represent a link between exercise and 'beiging', as well as the role that thyroid hormone signaling plays in beige adipocyte regulation.

Housing temperature affects the acute and chronic metabolic adaptations to exercise in mice

KEY POINTS

Mice are commonly housed at room temperatures below their thermoneutral zone meaning they are exposed to chronic thermal stress. Endurance exercise induces browning and mitochondrial biogenesis in white adipose tissue of rodents, but there are conflicting reports of this phenomenon in humans. We hypothesized that the ambient room temperature at which mice are housed could partially explain these discrepant reports between humans and rodents. We housed mice at room temperature or thermoneutrality and studied their physiological responses to acute and chronic exercise. We found that thermoneutral housing altered running behaviour and glucose homeostasis, and further, that exercise-induced markers of mitochondrial biogenesis and the browning of white adipose tissue were reduced in mice housed at thermoneutrality.

ABSTRACT

Mice are often housed at temperatures below their thermoneutral zone resulting in compensatory increases in thermogenesis. Despite this, many studies report housing mice at room temperature (RT), likely for the convenience of the researchers studying them. As such, the conflicting reports between humans and rodents regarding the ability of exercise to increase mitochondrial and thermogenic markers in white adipose tissue may be explained by the often-overlooked variable, housing temperature. To test this hypothesis, we housed male C57BL/6 mice at RT (22°C) or thermoneutrality (TN) (29°C) with or without access to a voluntary running wheel for 6 weeks or subjected them to an acute exhaustive bout of treadmill running. We examined the gene expression and protein content of select mitochondrial and thermogenic markers in skeletal muscle, epididymal white adipose tissue (eWAT), inguinal white adipose tissue (iWAT) and brown adipose tissue (BAT). We also assessed adipocyte morphology and indices of glucose homeostasis. Housing temperature influenced glucose tolerance and insulin action in vivo, yet the beneficial effects of exercise, both acute and chronic, remained intact in eWAT, BAT and skeletal muscle irrespective of housing temperature. Housing mice at TN led to an attenuation of some of the effects of exercise on iWAT. Collectively, we present data characterizing the acute and chronic metabolic adaptations to exercise at different housing temperatures and demonstrate, for the first time, that temperature influences the ability of exercise to increase markers of mitochondrial biogenesis and the browning of white adipose tissue.

Nutritional and non-nutritional agents that stimulate white adipose tissue browning

Obesity is a public health problem present in both developed and developing countries. The white adipose tissue (WAT) is the main deposit of lipids when there is an excess of energy. Its pathological growth is directly linked to the development of obesity and to a wide number of comorbidities, such as insulin-resistance, cardiovascular disease, among others. In this scenario, it becomes imperative to develop new approaches to the treatment and prevention of obesity and its comorbidities. It has been documented that the browning of WAT could be a suitable strategy to tackle the obesity epidemic that is developing worldwide. Currently there is an intense search for bioactive compounds with anti-obesity properties, which present the particular ability to generate thermogenesis in the brown adipose tissue (BAT) or beige. The present study provide recent information of the bioactive nutritional compounds capable of inducing thermogenesis and therefore capable of generate positive effects on health.

Mitochondrial-Derived Peptide MOTS-c Increases Adipose Thermogenic Activation to Promote Cold Adaptation

Cold exposure stress causes hypothermia, cognitive impairment, liver injury, and cardiovascular diseases, thereby increasing morbidity and mortality. Paradoxically, cold acclimation is believed to confer metabolic improvement to allow individuals to adapt to cold, harsh conditions and to protect them from cold stress-induced diseases. However, the therapeutic strategy to enhance cold acclimation remains less studied. Here, we demonstrate that the mitochondrial-derived peptide MOTS-c efficiently promotes cold adaptation. Following cold exposure, the improvement of adipose non-shivering thermogenesis facilitated cold adaptation. MOTS-c, a newly identified peptide, is secreted by mitochondria. In this study, we observed that the level of MOTS-c in serum decreased after cold stress. MOTS-c treatment enhanced cold tolerance and reduced lipid trafficking to the liver. In addition, MOTS-c dramatically upregulated brown adipose tissue (BAT) thermogenic gene expression and increased white fat “browning”. This effect might have been mediated by MOTS-c-activated phosphorylation of the ERK signaling pathway. The inhibition of ERK signaling disturbed the up-regulatory effect of MOTS-c on thermogenesis. In summary, our results indicate that MOTS-c treatment is a potential therapeutic strategy for defending against cold stress by increasing the adipose thermogenesis via the ERK pathway.

Enriched environment inhibits breast cancer progression in obese models with intact leptin signaling

Obesity is becoming a global epidemic and is a risk factor for breast cancer. Environmental enrichment (EE), a model recapitulating an active lifestyle, leads to leanness, resistance to diet-induced obesity (DIO) and cancer. One mechanism is the activation of the hypothalamic-sympathoneural-adipocyte (HSA) axis. This results in the release of norepinephrine onto adipose tissue inducing a drop of leptin. This study aimed to test the effects of EE on breast cancer onset and progression while considering the effect of leptin by utilizing the transgenic MMTV-PyMT model as well as several models of varied leptin signaling. EE was highly effective at reducing weight gain, regardless of the presence of leptin. However, the effects of EE on tumor progression were dependent on leptin signaling. EE decreased leptin and reduced mammary tumor growth rate in MMTV-PyMT spontaneous and DIO transplantation models; in contrast, the absence of leptin in ob/ob mice resulted in increased tumor growth likely due to elevated norepinephrine levels. Our results suggest that the microenvironment is critical in breast tumorigenesis and that the drop in leptin is an important peripheral mediator of the EE anti-breast cancer effects, offsetting the potential pro-tumorigenic effects of norepinephrine responding to a complex environment.

Long-term environmental enrichment affects microglial morphology in middle age mice

Aging is associated with increased central nervous system inflammation, in large part due to dysfunctional microglia. Environmental enrichment (EE) provides a model for studying the dynamics of lifestyle factors in the development of age-related neuroinflammation and microglial dysfunction. EE results in improvements in learning and memory, metabolism, and mental health in a variety of animal models. We recently reported that implementing EE in middle age promotes healthy aging. In the present study, we investigated whether EE influences microglial morphology, and whether EE is associated with changes in expression of microglial and neuroinflammatory markers. Inflammatory cytokines and MHC-II were reduced following 12-month EE in 10-month-old mice. Long-term EE for 7.5 months resulted in broad increases in Iba1 expression in hippocampus, hypothalamus, and amygdala detected by immunohistochemistry. Quantification of microglial morphology reveal both hypertrophy and ramification in these three brain regions, without increases in microglial cell density. These data indicate that long-term EE implemented in middle age results in a microglial state distinct from that of normal aging in standard laboratory housing, in specific brain regions, associated with reduced neuroinflammatory markers and improvement of systemic metabolism.

Exercise Rescues Gene Pathways Involved in Vascular Expansion and Promotes Functional Angiogenesis in Subcutaneous White Adipose Tissue

Exercise mitigates chronic diseases such as diabetes, cardiovascular diseases, and obesity; however, the molecular mechanisms governing protection from these diseases are not completely understood. Here we demonstrate that exercise rescues metabolically compromised high fat diet (HFD) fed mice, and reprograms subcutaneous white adipose tissue (scWAT). Using transcriptomic profiling, scWAT was analyzed for HFD gene expression changes that were rescued by exercise. Gene networks involved in vascularization were identified as prominent targets of exercise, which led us to investigate the vasculature architecture and endothelial phenotype. Vascular density in scWAT was found to be compromised in HFD, and exercise rescued this defect. Similarly, angiogenic capacity as measured by ex vivo capillary sprouting was significantly promoted with exercise. Together, these data demonstrate that exercise enhances scWAT vascularization and functional capacity for angiogenesis, and can prevent the detrimental effects of HFD. The improvement in these indices correlates with improvement of whole-body metabolism, suggesting that scWAT vascularization may be a potential therapeutic target for metabolic disease.

Resistance to visceral obesity is associated with increased locomotion in mice expressing an endothelial cell-specific fibroblast growth factor 1 transgene

Overdevelopment of visceral adipose is positively correlated with the etiology of obesity-associated pathologies including cardiovascular disease and insulin resistance. However, identification of genetic, molecular, and physiological factors regulating adipose development and function in response to nutritional stress is incomplete. Fibroblast Growth Factor 1 (FGF1) is a cytokine expressed and released by both adipocytes and endothelial cells under hypoxia, thermal, and oxidative stress. Expression of Fibroblast Growth Factor 1 (FGF1) in adipose is required for normal depot development and remodeling. Loss of FGF1 leads to deleterious changes in adipose morphology, metabolism, and insulin resistance. Conversely, diabetic and obese mice injected with recombinant FGF1 display improvements in insulin sensitivity and a reduction in adiposity. We report in this novel, in vivo study that transgenic mice expressing an endothelial-specific FGF1 transgene (FGF1-Tek) are resistant to high-fat diet-induced abdominal adipose accretion and are more glucose-tolerant than wild-type control animals. Metabolic chamber analyses indicate that suppression of the development of visceral adiposity and insulin resistance was not associated with alterations in appetite or resting metabolic rate in the FGF1-Tek strain. Instead, FGF1-Tek mice display increased locomotor activity that likely promotes the utilization of dietary fatty acids before they can accumulate in adipose and liver. This study provides insight into the impact that genetic differences dictating the production of FGF1 has on the risk for developing obesity-related metabolic disease in response to nutritional stress.

Voluntary wheel running in the late dark phase ameliorates diet-induced obesity in mice without altering insulin action

Metabolic dysfunction and Type 2 diabetes are associated with perturbed circadian rhythms. However, exercise appears to ameliorate circadian disturbances, as it can phase-shift or reset the internal clock system. Evidence is emerging that exercise at a distinct time of day can correct misalignments of the circadian clock and influence energy metabolism. This suggests that timing of exercise training can be important for the prevention and management of metabolic dysfunction. In this study, obese, high-fat diet-fed mice were subjected to voluntary wheel running (VWR) at two different periods of the day to determine the effects of time-of-day-restricted VWR on basal and insulin-stimulated glucose disposal. VWR in the late dark phase reduced body weight gain compared with VWR in the beginning of the dark phase. Conversely, time-of-day-restricted VWR did not influence insulin action and glucose disposal, since skeletal muscle and adipose tissue glucose uptake and insulin signaling remained unaffected. Protein abundance of the core clock proteins, brain-muscle arnt-like 1 (BMAL1), and circadian locomotor output control kaput (CLOCK), were increased in skeletal muscle after VWR, independent of whether mice had access to running wheels in the early or late dark phase. Collectively, we provide evidence that VWR in the late dark phase ameliorates diet-induced obesity without altering insulin action or glucose homeostasis.

NEW & NOTEWORTHY Exercise appears to ameliorate circadian disturbances as it can entrain the internal clock system. We provide evidence that voluntary wheel running increases core clock protein abundance and influences diet-induced obesity in mice in a time-of-day-dependent manner. However, the effect of time-of-day-restricted voluntary wheel running on body weight gain is not associated with enhanced basal- and insulin-stimulated glucose disposal, suggesting that time-of-day-restricted voluntary wheel running affects energy homeostasis rather than glucose homeostasis.

Emerging Roles of Sympathetic Nerves and Inflammation in Perivascular Adipose Tissue

Perivascular adipose tissue (PVAT) is no longer recognised as simply a structural support for the vasculature, and we now know that PVAT releases vasoactive factors which modulate vascular function. Since the discovery of this function in 1991, PVAT research is rapidly growing and the importance of PVAT function in disease is becoming increasingly clear. Obesity is associated with a plethora of vascular conditions; therefore, the study of adipocytes and their effects on the vasculature is vital. PVAT contains an adrenergic system including nerves, adrenoceptors and transporters. In obesity, the autonomic nervous system is dysfunctional; therefore, sympathetic innervation of PVAT may be the key mechanistic link between increased adiposity and vascular disease. In addition, not all obese people develop vascular disease, but a common feature amongst those that do appears to be the inflammatory cell population in PVAT. This review will discuss what is known about sympathetic innervation of PVAT, and the links between nerve activation and inflammation in obesity. In addition, we will examine the therapeutic potential of exercise in sympathetic stimulation of adipose tissue.

Hypothalamic gene transfer of BDNF promotes healthy aging in mice

The aging process and age-related diseases all involve perturbed energy adaption and impaired ability to cope with adversity. Brain-derived neurotrophic factor (BDNF) in the hypothalamus plays important role in regulation of energy balance. Our previous studies show that recombinant adeno-associated virus (AAV)-mediated hypothalamic BDNF gene transfer alleviates obesity, diabetes, and metabolic syndromes in both diet-induced and genetic models. Here we examined the efficacy and safety of a built-in autoregulatory system to control transgene BDNF expression mimicking the body's natural feedback systems in middle-aged mice. Twelve-month-old mice were treated with either autoregulatory BDNF vector or yellow fluorescence protein (YFP) control, maintained on normal diet, and monitored for 28 weeks. BDNF gene transfer prevented the development of aging-associated metabolic declines characterized by: preventing aging-associated weight gain, reducing adiposity, reversing the decline of brown fat activity, increasing adiponectin while reducing leptin and insulin in circulation, improving glucose tolerance, increasing energy expenditure, alleviating hepatic steatosis, and suppressing inflammatory genes in the hypothalamus and adipose tissues. Moreover, BDNF treatment reduced anxiety-like and depression-like behaviors. These safety and efficacy data provide evidence that hypothalamic BDNF is a target for promoting healthy aging.

Cold and Exercise: Therapeutic Tools to Activate Brown Adipose Tissue and Combat Obesity

The rise in obesity over the last several decades has reached pandemic proportions. Brown adipose tissue (BAT) is a thermogenic organ that is involved in energy expenditure and represents an attractive target to combat both obesity and type 2 diabetes. Cold exposure and exercise training are two stimuli that have been investigated with respect to BAT activation, metabolism, and the contribution of BAT to metabolic health. These two stimuli are of great interest because they have both disparate and converging effects on BAT activation and metabolism. Cold exposure is an effective mechanism to stimulate BAT activity and increase glucose and lipid uptake through mitochondrial uncoupling, resulting in metabolic benefits including elevated energy expenditure and increased insulin sensitivity. Exercise is a therapeutic tool that has marked benefits on systemic metabolism and affects several tissues, including BAT. Compared to cold exposure, studies focused on BAT metabolism and exercise display conflicting results; the majority of studies in rodents and humans demonstrate a reduction in BAT activity and reduced glucose and lipid uptake and storage. In addition to investigations of energy uptake and utilization, recent studies have focused on the effects of cold exposure and exercise on the structural lipids in BAT and secreted factors released from BAT, termed batokines. Cold exposure and exercise induce opposite responses in terms of structural lipids, but an important overlap exists between the effects of cold and exercise on batokines. In this review, we will discuss the similarities and differences of cold exposure and exercise in relation to their effects on BAT activity and metabolism and its relevance for the prevention of obesity and the development of type 2 diabetes.

Fndc5 loss-of-function attenuates exercise-induced browning of white adipose tissue in mice

Fibronectin type III domain containing 5 (Fndc5) is a transmembrane protein highly expressed in the skeletal muscle. It was reported that exercise promotes the shedding of the extracellular domain of Fndc5, generating a circulating peptide (irisin) that cross-talks to adipose tissues to convert lipid-storing white adipocytes to energy-catabolizing beige adipocytes. However, the requirement of Fndc5 in mediating the beneficial effect of exercise remains to be determined. Here, we created a mouse model of Fndc5 mutation through transcription activator-like effector nuclease-mediated DNA targeting. The Fndc5 mutant mice have normal skeletal muscle development, growth, regeneration, as well as glucose and lipid metabolism at resting state, even when fed a high-fat diet. In response to running exercise, however, the Fndc5 mutant mice exhibit reduced glucose tolerance and insulin sensitivity and have lower maximal oxygen consumption compared with the exercised wild-type mice. Mechanistically, Fndc5 mutation attenuates exercise-induced browning of white adipose tissue that is crucial for the metabolic benefits of physical activities. These data provide genetic evidence that Fndc5 is dispensable for muscle development and basal metabolism but essential for exercise-induced browning of white adipose tissues in mice.-Xiong, Y., Wu, Z., Zhang, B., Wang, C., Mao, F., Liu, X., Hu, K., Sun, X., Jin, W., Kuang, S. Fndc5 loss-of-function attenuates exercise-induced browning of white adipose tissue in mice.

Exosomal circRNA derived from gastric tumor promotes white adipose browning by targeting the miR-133/PRDM16 pathway

Cancer-related cachexia is a metabolic syndrome characterized by a wasting disorder of adipose and skeletal muscle and is accompanied by body weight loss and systemic inflammation. The treatment options for cancer cachexia are limited, and the molecular mechanism remains poorly understood. Circular RNAs (circRNAs) are a novel family of endogenous noncoding RNAs that have been proposed to regulate gene expression in mammals. Exosomes are small vesicles derived from cells, and recent studies have shown that circRNAs are stable in exosomes. However, little is known about the biological role of circRNAs in exosomes. In our study, we showed that circRNAs in plasma exosomes have specific expression features in gastric cancer (GC), and ciRS-133 is linked with the browning of white adipose tissue (WAT) in GC patients. Exosomes derived from GC cells deliver ciRS-133 into preadipocytes, promoting the differentiation of preadipocytes into brown-like cells by activating PRDM16 and suppressing miR-133. Moreover, knockdown of ciRS-133 reduced cancer cachexia in tumor-implanted mice, decreasing oxygen consumption and heat production. Thus, exosome-delivered circRNAs are involved in WAT browning and play a key role in cancer-associated cachexia.

Exercise Training Induces Depot-Specific Adaptations to White and Brown Adipose Tissue

Exercise affects whole-body metabolism through adaptations to various tissues, including adipose tissue (AT). Recent studies investigated exercise-induced adaptations to AT, focusing on inguinal white adipose tissue (WAT), perigonadal WAT, and interscapular brown adipose tissue (iBAT). Although these AT depots play important roles in metabolism, they account for only ∼50% of the AT mass in a mouse. Here, we investigated the effects of 3 weeks of exercise training on all 14 AT depots. Exercise induced depot-specific effects in genes involved in mitochondrial activity, glucose metabolism, and fatty acid uptake and oxidation in each adipose tissue (AT) depot. These data demonstrate that exercise training results in unique responses in each AT depot; identifying the depot-specific adaptations to AT in response to exercise is essential to determine how AT contributes to the overall beneficial effect of exercise.

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This study investigates the effects of exercise on all adipose tissue (AT) depots

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Exercise training induces unique metabolic changes to BAT, scWAT, and vWAT

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Exercise training differentially affects each AT depot within BAT, scWAT, and vWAT

Enriched environment regulates thymocyte development and alleviates experimental autoimmune encephalomyelitis in mice

Environmental and social factors have profound impacts on immune homeostasis. Our work on environmental enrichment (EE) has revealed a novel anti-obesity and anticancer phenotype associated with enhanced activity of CD8+ cytotoxic T lymphocytes in secondary lymphoid tissues. Here we investigated how an EE modulated thymus and thymocyte development. EE decreased thymus mass and cellularity, decreased the double positive thymocyte population, increased the proportion of CD8+ T cells, reduced the CD4:CD8 ratio, and downregulated CD69 expression in T cells. In a model of multiple sclerosis: experimental autoimmune encephalomyelitis (EAE), EE alleviated symptoms, inhibited spinal cord inflammation through regulation of type 1 T-helper cells mediated by glucocorticoid receptor signaling, and prevented EAE-induced thymic disturbance. Our mechanistic studies demonstrated that hypothalamic BDNF activated a hypothalamic-pituitary-adrenal axis mediating the EE's thymic effects. Our results indicate that a lifestyle intervention links the nervous, endocrine, and adaptive immune system, allowing the body to adapt to internal and external environments.

Exercise Induces White Adipose Tissue Browning Across the Weight Spectrum in Humans

While the effect of exercise on white adipose tissue browning and metabolic improvement in rodents is clear, there are few studies in humans with inconclusive results. Thus, the aim of the study was to assess whether an exercise intervention promotes subcutaneous adipose tissue browning in humans, and whether this response is associated with metabolic improvement in three groups of individuals defined by body mass index (BMI) (kg/m²). Sedentary adult subjects with different BMI were enrolled in a 12-week bicycle-training program (3 times per week, intensity 70-80% HRmax). Brown and beige gene expression in subcutaneous adipose tissue (scWAT) biopsies, and serum glucose, insulin, lipid, adipokine, and myokine levels were compared before and after the exercise intervention. Thirty-three non-diabetic subjects (mean age 30.4 ± 4.6 years; 57.57% female; 13 normal weight, 10 overweight and 10 with obesity) completed the exercise intervention. Without any significant change in body composition, exercise improved several metabolic parameters, most notably insulin resistance and particularly in the overweight group. Circulating adiponectin, apelin, and irisin exercise-induced changes predicted 60% of the insulin sensitivity improvement. After exercise UCP1, TBX1, CPT1B scWAT expression significantly increased, along with P2RX5 significant positive staining. These changes are compatible with scWAT browning, however, they were not associated with glucose metabolism improvement. In conclusion, 12-weeks of exercise training produced brown/beige gene expression changes in abdominal scWAT of non-diabetic individuals with different BMI, which did not contribute to the metabolic improvement. However, this result should not be interpreted as a lack of effect of browning on metabolic parameters. These findings suggest that a bigger effect is needed and should not preclude the development of more effective strategies of browning. Furthermore, exercise-induced changes in adiponectin, apelin, and irisin predicted insulin sensitivity improvement, supporting the important role of adipokines and myokines in metabolism homeostasis.

Proton leak regulates mitochondrial reactive oxygen species generation in endothelial cell activation and inflammation - A novel concept

Mitochondria are capable of detecting cellular insults and orchestrating inflammatory responses. Mitochondrial reactive oxygen species (mtROS) are intermediates that trigger inflammatory signaling cascades in response to our newly proposed conditional damage associated molecular patterns (DAMP). We recently reported that increased proton leak regulates mtROS generation and thereby exert physiological and pathological activation of endothelial cells. Herein, we report the recent progress in determining the roles of proton leak in regulating mtROS, and highlight several important findings: 1) The majority of mtROS are generated in the complexes I and III of electron transport chain (ETC); 2) Inducible proton leak and mtROS production are mutually regulated; 3) ATP synthase-uncoupled ETC activity and mtROS regulate both physiological and pathological endothelial cell activation and inflammation initiation; 4) Mitochondrial Ca²⁺ uniporter and exchanger proteins have an impact on proton leak and mtROS generation; 5) MtROS connect signaling pathways between conditional DAMP-regulated immunometabolism and histone post-translational modifications (PTM) and gene expression. Continuous improvement of our understanding in this aspect of mitochondrial function would provide novel insights and generate novel therapeutic targets for the treatment of sterile inflammatory disorders such as metabolic diseases, cardiovascular diseases and cancers.

Dynamic of lipid droplets and gene expression in response to β-aminoisobutyric acid treatment on 3T3-L1 cells

Research on adipobiology has recognized the browning process of white adipocytes as a potential therapeutic strategy for the treatment of obesity and related morbidities. Physical exercise stimulates the secretion of myokines, such as b-aminoisobutyric acid (BAIBA), which in turn promotes adaptive thermogenesis. White adipocyte conversion to brown cells involves dynamic changes in lipid droplet (LD) dimension and in the transcription of brown-specific marker genes. This study analyzes the effect of different doses of BAIBA and at different days of development on 3T3-L1 cells by evaluating morphological changes in LDs and the expression of browning gene markers. Results suggested that the highest concentration of BAIBA after 4 days of differentiation produced the most significant effects. The number of LDs per cell increased in comparison to control cells, whereas the surface area significantly decreased. Brown adipocyte markers were up-regulated, but the effect of treatment was lost at 10 days of differentiation. The thermogenic program induced by BAIBA may reflect a rapid adaptation of adipose tissue to physical exercise. This connection stresses the beneficial impact of physical exercise on metabolic health. The thermogenic program induced by BAIBA may reflect a rapid adaptation of adipose tissue to physical exercise. This connection stresses the beneficial impact of physical exercise on metabolic health.

Exercise training-induced effects on the abdominal subcutaneous adipose tissue phenotype in humans with obesity

Rodent studies have indicated that physical exercise may improve adipose tissue function. We investigated the effects of a 12-wk supervised, progressive exercise training program on adipocyte morphology and abdominal subcutaneous adipose tissue function in metabolically well-phenotyped subjects with obesity. Men with obesity ( n = 21) participated in a 12-wk supervised, progressive, combined exercise training program consisting of aerobic exercise (30 min at 70% of maximal power output 2 times/wk) and resistance exercise (3 × 10 repetitions at 60% of 1 repeated maximum 1 time/wk), with adjustment of exercise intensity every 4 wk. At baseline and after intervention, abdominal subcutaneous adipose tissue biopsies were collected to determine 1) adipocyte morphology, 2) gene expression of markers for lipolysis, inflammation, browning, adipokines, and mitochondrial biogenesis/function, 3) protein expression of mitochondrial oxidative phosphorylation (OXPHOS) complexes, and 4) ex vivo basal and β2-adrenergic stimulated lipolysis. The exercise training program, which increased maximal aerobic capacity ( P < 0.001) and muscle strength ( P < 0.001), slightly reduced adipose tissue mass (~0.7 kg, P = 0.021) but did not affect abdominal subcutaneous adipocyte size ( P = 0.744), adipose tissue gene expression of markers for mitochondrial biogenesis and function, browning, lipolysis, inflammation and adipokines, total OXPHOS protein content ( P = 0.789), or β2-adrenergic sensitivity of lipolysis ( P = 0.555). A 12-wk supervised, progressive exercise training program did not alter abdominal subcutaneous adipocyte morphology and adipose tissue gene/protein expression of markers related to adipose tissue function or β2-adrenergic sensitivity of lipolysis in male subjects with obesity.

NEW & NOTEWORTHY Studies that investigated the effects of exercise training on adipose tissue function in well-phenotyped humans are scarce. We demonstrate that 12 wk of supervised exercise training improved physical fitness and peripheral insulin sensitivity but did not alter abdominal subcutaneous adipocyte morphology, adipose tissue gene and protein expression of markers related to adipose tissue function, or β2-adrenergic receptor-mediated lipolysis in men with obesity. A prolonged and/or more intense training program may be required to improve human adipose tissue function.

Changes in the function and phenotype of resident peritoneal macrophages after housing in an enriched environment

Exposure to an enriched environment (EE) affects not only brain functions but also immune responses upon viral or bacterial infections. In this study, we examined changes in the phagocytic response and chemokine production of resident peritoneal macrophages after mice had been housed under EE conditions for 6 or 8 weeks, and then explored the possibility that EE could cause a change in the macrophage phenotype by means of flow cytometry as well as quantitative RT-PCR. The percentages of EE macrophages phagocytosing S. aureus and apoptotic neutrophils were significantly larger than those of standard environment (SE) macrophages. After coculturing with S. aureus, EE macrophages tended to produce greater amounts of chemokines such as MIP-2, KC and MCP-1 than SE ones, although the increases for MIP-2 and KC were not statistically significant. As compared with SE macrophages, EE macrophages included more CD40-positive cells (M1 marker), and expressed more mRNAs of IL-6 (M1 marker) and IRF4 (M2 marker), and less mRNA of CD38 (M1 marker), suggesting either the possibility that EE macrophages are a mixed population of M1 and M2 macrophages or the possibility that they are a unique population with a mixed M1 and M2 macrophage phenotype.

Changes in the Brain-Derived Neurotrophic Factor Are Associated with Improvements in Diabetes Risk Factors after Exercise Training in Adolescents with Obesity: The HEARTY Randomized Controlled Trial

Obesity in youth increases the risk of type 2 diabetes (T2D), and both are risk factors for neurocognitive deficits. Exercise attenuates the risk of obesity and T2D while improving cognitive function. In adults, these benefits are associated with the actions of the brain-derived neurotrophic factor (BDNF), a protein critical in modulating neuroplasticity, glucose regulation, fat oxidation, and appetite regulation in adults. However, little research exists in youth. This study examined the associations between changes in diabetes risk factors and changes in BDNF levels after 6 months of exercise training in adolescents with obesity. The sample consisted of 202 postpubertal adolescents with obesity (70% females) aged 14-18 years who were randomized to 6 months of aerobic and/or resistance training or nonexercise control. All participants received a healthy eating plan designed to induce a 250/kcal deficit per day. Resting serum BDNF levels and diabetes risk factors, such as fasting glucose, insulin, homeostasis model assessment (HOMA-B-beta cell insulin secretory capacity) and (HOMA-IS-insulin sensitivity), and hemoglobin A1c (HbA1c), were measured after an overnight fast at baseline and 6 months. There were no significant intergroup differences on changes in BDNF or diabetes risk factors. In the exercise group, increases in BDNF were associated with reductions in fasting glucose (β = -6.57, SE = 3.37, p = 0.05) and increases in HOMA-B (β = 0.093, SE = 0.03, p = 0.004) after controlling for confounders. No associations were found between changes in diabetes risk factors and BDNF in controls. In conclusion, exercise-induced reductions in some diabetes risk factors were associated with increases in BDNF in adolescents with obesity, suggesting that exercise training may be an effective strategy to promote metabolic health and increases in BDNF, a protein favoring neuroplasticity. This trial is registered with ClinicalTrials.gov NCT00195858, September 12, 2005 (funded by the Canadian Institutes of Health Research).

Adipose Organ Development and Remodeling

During the last decades, research on adipose tissues has spread in parallel with the extension of obesity. Several observations converged on the idea that adipose tissues are organized in a large organ with endocrine and plastic properties. Two parenchymal components: white (WATs) and brown adipose tissues (BATs) are contained in subcutaneous and visceral compartments. Although both have endocrine properties, their function differs: WAT store lipids to allow intervals between meals, BAT burns lipids for thermogenesis. In spite of these opposite functions, they share the ability for reciprocal reversible transdifferentiation to tackle special physiologic needs. Thus, chronic need for thermogenesis induces browning and chronic positive energy balance induce whitening. Lineage tracing and data from explant studies strongly suggest other remodeling properties of this organ. During pregnancy and lactation breast WAT transdifferentiates into milk-secreting glands, composed by cells with abundant cytoplasmic lipids (pink adipocytes) and in the postlactation period pink adipocytes transdifferentiate back into WAT and BAT. The plastic properties of mature adipocytes are supported also by a liposecretion process in vitro where adult cell in culture transdifferentiate to differentiated fibroblast-like elements able to give rise to different phenotypes (rainbow adipocytes). In addition, the inflammasome system is activated in stressed adipocytes from obese adipose tissue. These adipocytes die and debris are reabsorbed by macrophages inducing a chronic low-grade inflammation, potentially contributing to insulin resistance and T2 diabetes. Thus, the plastic properties of this organ could open new therapeutic perspectives in the obesity-related metabolic disease and in breast pathologies. © 2018 American Physiological Society. Compr Physiol 8:1357-1431, 2018.

Muscle-Adipose Tissue Cross Talk

Exercise training results in adaptations to both skeletal muscle and white adipose tissue (WAT) and protects against metabolic disorders including obesity and type 2 diabetes. Exercise-induced adaptations include an altered profile of secreted proteins, both myokines (from skeletal muscle) and adipokines (from adipose tissue). These secreted proteins may act in an endocrine manner to facilitate tissue-to-tissue communication and "cross talk," likely working together to improve overall metabolic health. Some studies suggest that contracting skeletal muscles release myokines that may function to alter the phenotype of WAT, including WAT "beiging," in which there is increased expression of beige marker genes and increased presence of multilocular cells within the WAT.

Implementation of environmental enrichment after middle age promotes healthy aging

With increases in life expectancy, it is vital to understand the dynamics of aging, their interaction with lifestyle factors, and the connections to age-related disease processes. Our work on environmental enrichment (EE), a housing environment boosting mental health, has revealed a novel anticancer and anti-obesity phenotype mediated by a brain-fat axis: the hypothalamic-sympathoneural-adipocyte (HSA) axis in young animals. Here we investigated EE effects on healthspan and lifespan when initiated after middle age. Short-term EE for six weeks activated the HSA axis in 10-month-old mice. Long-term EE for twelve months reduced adiposity, improved glucose tolerance, decreased leptin levels, enhanced motor abilities, and inhibited anxiety. In addition to adipose remodeling, EE decreased age-related liver steatosis, reduced hepatic glucose production, and increased glucose uptake by liver and adipose tissue contributing to the improved glycemic control. The EE-induced liver modulation was associated with a suppression of protein kinase Cε. Moreover, EE down-regulated the expression of inflammatory genes in the brain, adipose, and liver. EE initiated at 18-month of age significantly improved glycemic control and showed a trend of positive impact on mean lifespan. These data suggest that EE induces metabolic and behavioral adaptations that are shared by factors known to increase healthspan and lifespan.

Common traits between the beige fat-inducing stimuli

Adipose tissues play an essential role in regulating the metabolic homeostasis and can be found in almost all parts of the body. Excessive adiposity leads to obesity and can contribute to metabolic and other disorders. Adipocytes show remarkable plasticity in their function, which can be pushed toward energy storage, or energy expenditure-a `browning' of fat. Browning is controlled by the cellular milieu of the adipose tissue, with sympathetic innervation and by immune responses as key integrators of the signals that promote browning. Here, we describe the latest contributions to our understanding of how different metabolic stimuli can shape the adipocyte function. We especially focus on the role of the gut microbiota and the negative energy balance in regulating the browning.

Role of Human Brown Fat in Obesity, Metabolism and Cardiovascular Disease: Strategies to Turn Up the Heat

Human brown adipose tissue (BAT) was re-discovered in 2009 by several independent groups, who showed that it is present and active in adults, as judged from the profound uptake of the glucose analogue radiotracer ¹⁸F-fluorodeoxyglucose in positron-emission tomography and computed tomography scan analysis after cold exposure. A potential clinical implication of activating BAT relates to its high metabolic activity and its potential role in stimulating energy expenditure (i.e. resting energy expenditure, meal-induced thermogenesis, and cold-induced thermogenesis), which makes it an attractive target to reduce adiposity. Moreover, due to its ability to oxidise glucose and lipids, BAT activation may also potentially exert beneficial metabolic and cardiovascular effects through reducing glucose and lipid levels, respectively. This review describes the potential role of human BAT in the prevention and treatment of obesity, metabolism, and cardiovascular disease focusing on its impact on energy expenditure and management of body fat accumulation as well as on glucose and lipid metabolism. This article also summarises the strategies that are currently being studied to activate human BAT.

Fatty acid activation in thermogenic adipose tissue

Channeling carbohydrates and fatty acids to thermogenic tissues, including brown and beige adipocytes, have garnered interest as an approach for the management of obesity-related metabolic disorders. Mitochondrial fatty acid oxidation (β-oxidation) is crucial for the maintenance of thermogenesis. Upon cellular fatty acid uptake or following lipolysis from triglycerides (TG), fatty acids are esterified to coenzyme A (CoA) to form active acyl-CoA molecules. This enzymatic reaction is essential for their utilization in β-oxidation and thermogenesis. The activation and deactivation of fatty acids are regulated by two sets of enzymes called acyl-CoA synthetases (ACS) and acyl-CoA thioesterases (ACOT), respectively. The expression levels of ACS and ACOT family members in thermogenic tissues will determine the substrate availability for β-oxidation, and consequently the thermogenic capacity. Although the role of the majority of ACS and ACOT family members in thermogenesis remains unclear, recent proceedings link the enzymatic activities of ACS and ACOT family members to metabolic disorders and thermogenesis. Elucidating the contributions of specific ACS and ACOT family members to trafficking of fatty acids towards thermogenesis may reveal novel targets for modulating thermogenic capacity and treating metabolic disorders.

Home alone: a systematic review and meta-analysis on the effects of individual housing on body weight, food intake and visceral fat mass in rodents

Rats and mice are widely used to study environmental effects on psychological and metabolic health. Study designs differ widely and are often characterized by varying (social) housing conditions. In itself, housing has a profound influence on physiology and behaviour of rodents, affecting energy balance and sustainable metabolic health. However, evidence for potential long-term consequences of individual versus social housing on body weight and metabolic phenotype is inconsistent. We conducted a systematic literature review and meta-analyses assessing effects of individual versus social housing of rats and mice, living under well-accepted laboratory conditions, on measures of metabolic health, including body weight, food intake and visceral adipose tissue mass. Seventy-one studies were included in this review; 59 were included in the meta-analysis. Whilst housing did not affect body weight, both food intake and visceral adipose tissue mass were significantly higher in individually compared with socially housed animals. A combination of emotional stress and lack of social thermoregulation likely contributed to these effects. Increased awareness of consequences and improved specifications of housing conditions are necessary to accurately evaluate efficacy of drugs, diets or other interventions on metabolic and other health outcomes because housing conditions are rarely considered as possible moderators of reported outcomes.

Effects of exercise on brown and beige adipocytes

Physical exercise leads to beneficial effects in numerous tissues and organ systems and offers protection against obesity and type 2 diabetes. Recent studies have investigated the role of exercise on brown adipose tissue (BAT) and white adipose tissue (WAT), and have indicated marked adaptations to each tissue with exercise. Studies investigating the effects of exercise on BAT have produced conflicting results, with some showing an increase in the thermogenic activity of BAT and some demonstrating a decrease in the thermogenic activity of BAT. Human studies have observed a down-regulation of BAT activity (measured by a reduction in glucose uptake) in response to exercise. In WAT, exercise decreases adipocyte size, alters gene expression, and increases mitochondrial activity. Transplantation of exercise-trained subcutaneous WAT (scWAT) improves whole-body metabolic health. In rodents, exercise also results in a beiging of scWAT. Thus, exercise-induced changes to adipose tissue may be part of the mechanism by which exercise improves metabolic health.

Developmental origins of adult health and disease: The metabolic role of BDNF from early life to adulthood

Accumulating evidence suggests that the origins of adult disease may occur during fetal life. Thus, the concept of "developmental programming" has been introduced and supported by epidemiological and experimental data. This concept supports the idea that the nutritional and hormonal status during pregnancy could interfere in metabolism control. The mechanisms responsible for this "developmental programming" remain poorly documented. Current research indicates that neurotrophins and particularly brain-derived neurotrophic factor (BDNF) may play a crucial role in this process. Although mainly expressed in the nervous system, BDNF and its receptor, tropomyosin-related kinase B (TrkB), are immunolocalized in several regions of the human placenta and have important functions during pregnancy. BDNF serves widespread roles in regulating energy homeostasis in both fetuses and adults, by controlling patterns of fetal growth, adult feeding and physical activity, and by regulating glucose metabolism in peripheral tissues. Impaired BDNF signaling may be implicated in the etiopathogenesis of the metabolic syndrome. Novel BDNF-focused interventions are being developed for obesity, diabetes and neurological disorders. The aim of this article is to provide a brief comprehensive literary review regarding the potential implications of BDNF in "developmental programming", through regulation of metabolism and energy balance from early life to adulthood.

Obesity, Inflammation, Toll-Like Receptor 4 and Fatty Acids

Obesity leads to an inflammatory condition that is directly involved in the etiology of cardiovascular diseases, type 2 diabetes mellitus, and certain types of cancer. The classic inflammatory response is an acute reaction to infections or to tissue injuries, and it tends to move towards resolution and homeostasis. However, the inflammatory process that was observed in individuals affected by obesity and metabolic syndrome differs from the classical inflammatory response in certain respects. This inflammatory process manifests itself systemically and it is characterized by a chronic low-intensity reaction. The toll-like receptor 4 (TLR4) signaling pathway is acknowledged as one of the main triggers of the obesity-induced inflammatory response. The aim of the present review is to describe the role that is played by the TLR4 signaling pathway in the inflammatory response and its modulation by saturated and omega-3 polyunsaturated fatty acids. Studies indicate that saturated fatty acids can induce inflammation by activating the TLR4 signaling pathway. Conversely, omega-3 polyunsaturated fatty acids, such as eicosapentaenoic acid and docosahexaenoic acid, exert anti-inflammatory actions through the attenuation of the activation of the TLR4 signaling pathway by either lipopolysaccharides or saturated fatty acids.

The tumor secretory factor ZAG promotes white adipose tissue browning and energy wasting

Cachexia is a complex tissue-wasting syndrome characterized by inflammation, hypermetabolism, increased energy expenditure, and anorexia. Browning of white adipose tissue (WAT) is one of the significant factors that contribute to energy wasting in cachexia. By utilizing a cell implantation model, we demonstrate here that the lipid mobilizing factor zinc-α₂-glycoprotein (ZAG) induces WAT browning in mice. Increased circulating levels of ZAG not only induced lipolysis in adipose tissues but also caused robust browning in WAT. Stimulating WAT progenitors with ZAG recombinant protein or expression of ZAG in mouse embryonic fibroblasts (MEFs) strongly enhanced brown-like differentiation. At the molecular level, ZAG stimulated peroxisome proliferator-activated receptor γ (PPARγ) and early B cell factor 2 expression and promoted their recruitment to the PR/SET domain 16 (Prdm16) promoter, leading to enhanced expression of Prdm16, which determines brown cell fate. In brown adipose tissue, ZAG stimulated the expression of PPARγ and PPARγ coactivator 1α and promoted recruitment of PPARγ to the uncoupling protein 1 (Ucp1) promoter, leading to increased expression of Ucp1. Overall, our results reveal a novel function of ZAG in WAT browning and highlight the targeting of ZAG as a potential therapeutic application in humans with cachexia.-Elattar, S., Dimri, M., Satyanarayana, A. The tumor secretory factor ZAG promotes white adipose tissue browning and energy wasting.

Exercise-induced adaptations to white and brown adipose tissue

The beneficial effects of exercise on skeletal muscle and the cardiovascular system have long been known. Recent studies have focused on investigating the effects of exercise on adipose tissue and the effects that these exercise-induced adaptations have on overall metabolic health. Examination of exercise-induced adaptations in both white adipose tissue (WAT) and brown adipose tissue (BAT) has revealed marked differences in each tissue with exercise. In WAT, there are changes to both subcutaneous WAT (scWAT) and visceral WAT (vWAT), including decreased adipocyte size and lipid content, increased expression of metabolic genes, altered secretion of adipokines and increased mitochondrial activity. Adaptations specific to scWAT include lipidomic remodeling of phospholipids and, in rodents, the beiging of scWAT. The changes to BAT are less clear: studies evaluating the effect of exercise on the BAT of humans and rodents have revealed contradictory data, making this an important area of current investigation. In this Review, we discuss the exercise-induced changes to WAT and BAT that have been reported by different studies and highlight the current questions in this field.

Animal models of obesity and diabetes mellitus

More than one-third of the worldwide population is overweight or obese and therefore at risk of developing type 2 diabetes mellitus. In order to mitigate this pandemic, safer and more potent therapeutics are urgently required. This necessitates the continued use of animal models to discover, validate and optimize novel therapeutics for their safe use in humans. In order to improve the transition from bench to bedside, researchers must not only carefully select the appropriate model but also draw the right conclusions. In this Review, we consolidate the key information on the currently available animal models of obesity and diabetes and highlight the advantages, limitations and important caveats of each of these models.

Oxygen-sensing neurons reciprocally regulate peripheral lipid metabolism via neuropeptide signaling in Caenorhabditis elegans

The mechanisms by which the sensory environment influences metabolic homeostasis remains poorly understood. In this report, we show that oxygen, a potent environmental signal, is an important regulator of whole body lipid metabolism. C. elegans oxygen-sensing neurons reciprocally regulate peripheral lipid metabolism under normoxia in the following way: under high oxygen and food absence, URX sensory neurons are activated, and stimulate fat loss in the intestine, the major metabolic organ for C. elegans. Under lower oxygen conditions or when food is present, the BAG sensory neurons respond by repressing the resting properties of the URX neurons. A genetic screen to identify modulators of this effect led to the identification of a BAG-neuron-specific neuropeptide called FLP-17, whose cognate receptor EGL-6 functions in URX neurons. Thus, BAG sensory neurons counterbalance the metabolic effect of tonically active URX neurons via neuropeptide communication. The combined regulatory actions of these neurons serve to precisely tune the rate and extent of fat loss to the availability of food and oxygen, and provides an interesting example of the myriad mechanisms underlying homeostatic control.

Circulating molecules that control brown/beige adipocyte differentiation and thermogenic capacity

Obesity may be counteracted by increased energy expenditure. Circulating molecules act in the adipose tissue to influence brown and beige adipocyte function, differentiation, and thermogenic capacity, which in turn affects substrate utilization and impacts energy balance at the organismal level. These molecules have been envisioned as biomarkers and potential candidates for pharmacological interventions to treat obesity. Here we summarize studies that demonstrate the roles of endogenous circulating molecules of a wide variety in regulating the thermogenic potential of brown and beige fat cells. This review describes the state-of-the-art in the field and helps researchers to prioritize their targets in future studies.

The antidepressant fluoxetine acts on energy balance and leptin sensitivity via BDNF

Leptin and Brain Derived Neurotrophic Factor (BDNF) pathways are critical players in body weight homeostasis. Noninvasive treatments like environmental stimulation are able to increase response to leptin and induce BDNF expression in the brain. Emerging evidences point to the antidepressant selective serotonin reuptake inhibitor Fluoxetine (FLX) as a drug with effects similar to environmental stimulation. FLX is known to impact on body weight, with mechanisms yet to be elucidated. We herein asked whether FLX affects energy balance, the leptin system and BDNF function. Adult lean male mice chronically treated with FLX showed reduced weight gain, higher energy expenditure, increased sensitivity to acute leptin, increased hypothalamic BDNF expression, associated to changes in white adipose tissue expression typical of “brownization”. In the Ntrk2^tm1Ddg/J model, carrying a mutation in the BDNF receptor Tyrosine kinase B (TrkB), these effects are partially or totally reversed. Wild type obese mice treated with FLX showed reduced weight gain, increased energy output, and differently from untreated obese mice, a preserved acute response to leptin in terms of activation of the intracellular leptin transducer STAT3. In conclusion, FLX impacts on energy balance and induces leptin sensitivity and an intact TrkB function is required for these effects to take place.

Subcutaneous inguinal white adipose tissue is responsive to, but dispensable for, the metabolic health benefits of exercise

Exercise training has robust effects on subcutaneous inguinal white adipose tissue (iWAT), characterized by a shift to a brown adipose tissue (BAT)-like phenotype. Consistent with this, transplantation of exercise-trained iWAT into sedentary rodents activates thermogenesis and improves glucose homeostasis, suggesting that iWAT metabolism may contribute to the beneficial effects of exercise. However, it is yet to be determined if adaptations in iWAT are necessary for the beneficial systemic effects of exercise. To test this, male C57BL/6 mice were provided access to voluntary wheel running (VWR) or remained as a cage control (SED) for 11 nights after iWAT removal via lipectomy (LIPX) or SHAM surgery. We found that SHAM and LIPX mice with access to VWR ran similar distances and had comparable reductions in body mass, increased food intake, and increased respiratory exchange ratio (RER). Further, VWR improved indexes of glucose homeostasis and insulin tolerance in both SHAM and LIPX mice. The lack of effect of LIPX in the response to VWR was not explained by compensatory increases in markers of mitochondrial biogenesis and thermogenesis in skeletal muscle, epididymal white adipose tissue, or interscapular brown adipose tissue. Together, these data demonstrate that mice with and without iWAT have comparable adaptations to VWR, suggesting that iWAT may be dispensable for the metabolic health benefits of exercise.

Molecular Therapy of Melanocortin-4-Receptor Obesity by an Autoregulatory BDNF Vector

Mutations in the melanocortin-4-receptor (MC4R) comprise the most common monogenic form of severe early-onset obesity, and conventional treatments are either ineffective long-term or contraindicated. Immediately downstream of MC4R-in the pathway for regulating energy balance-is brain-derived neurotrophic factor (BDNF). Our previous studies show that adeno-associated virus (AAV)-mediated hypothalamic BDNF gene transfer alleviates obesity and diabetes in both diet-induced and genetic models. To facilitate clinical translation, we developed a built-in autoregulatory system to control therapeutic gene expression mimicking the body's natural feedback systems. This autoregulatory approach leads to a sustainable plateau of body weight after substantial weight loss is achieved. Here, we examined the efficacy and safety of autoregulatory BDNF gene therapy in Mc4r heterozygous mice, which best resemble MC4R obese patients. Mc4r heterozygous mice were treated with either autoregulatory BDNF vector or YFP control and monitored for 30 weeks. BDNF gene therapy prevented the development of obesity and metabolic syndromes characterized by decreasing body weight and adiposity, suppressing food intake, alleviating hyperleptinemia and hyperinsulinemia, improving glucose and insulin tolerance, and increasing energy expenditure, without adverse cardiovascular function or behavioral disturbances. These safety and efficacy data provide preclinical evidence that BDNF gene therapy is a compelling treatment option for MC4R-deficient obese patients.