Immune Modulation of Brown(ing) Adipose Tissue in Obesity

Adipocyte Mitochondria: Deciphering Energetic Functions across Fat Depots in Obesity and Type 2 Diabetes

Adipose tissue, a central player in energy balance, exhibits significant metabolic flexibility that is often compromised in obesity and type 2 diabetes (T2D). Mitochondrial dysfunction within adipocytes leads to inefficient lipid handling and increased oxidative stress, which together promote systemic metabolic disruptions central to obesity and its complications. This review explores the pivotal role that mitochondria play in altering the metabolic functions of the primary adipocyte types, white, brown, and beige, within the context of obesity and T2D. Specifically, in white adipocytes, these dysfunctions contribute to impaired lipid processing and an increased burden of oxidative stress, worsening metabolic disturbances. Conversely, compromised mitochondrial function undermines their thermogenic capabilities, reducing the capacity for optimal energy expenditure in brown adipocytes. Beige adipocytes uniquely combine the functional properties of white and brown adipocytes, maintaining morphological similarities to white adipocytes while possessing the capability to transform into mitochondria-rich, energy-burning cells under appropriate stimuli. Each type of adipocyte displays unique metabolic characteristics, governed by the mitochondrial dynamics specific to each cell type. These distinct mitochondrial metabolic phenotypes are regulated by specialized networks comprising transcription factors, co-activators, and enzymes, which together ensure the precise control of cellular energy processes. Strong evidence has shown impaired adipocyte mitochondrial metabolism and faulty upstream regulators in a causal relationship with obesity-induced T2D. Targeted interventions aimed at improving mitochondrial function in adipocytes offer a promising therapeutic avenue for enhancing systemic macronutrient oxidation, thereby potentially mitigating obesity. Advances in understanding mitochondrial function within adipocytes underscore a pivotal shift in approach to combating obesity and associated comorbidities. Reigniting the burning of calories in adipose tissues, and other important metabolic organs such as the muscle and liver, is crucial given the extensive role of adipose tissue in energy storage and release.

NDUFA9 and its crotonylation modification promote browning of white adipocytes by activating mitochondrial function in mice

Protein crotonylation plays a role in regulating cellular metabolism, gene expression, and other biological processes. NDUFA9 (NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 9) is closely associated with the activity and function of mitochondrial respiratory chain complex I. Mitochondrial function and respiratory chain are closely related to browning of white adipocytes, it's speculated that NDUFA9 and its crotonylation are associated with browning of white adipocytes. Firstly, the effect of NDUFA9 on white adipose tissue was verified in white fat browning model mice, and it was found that NDUFA9 promoted mitochondrial respiration, thermogenesis, and browning of white adipose tissue. Secondly, in cellular studies, it was discovered that NDUFA9 facilitated browning of white adipocytes by enhancing mitochondrial function, mitochondrial complex I activity, ATP synthesis, and mitochondrial respiration. Again, the level of NDUFA9 crotonylation was increased by treating cells with vorinostat (SAHA)+sodium crotonate (NaCr) and overexpressing NDUFA9, it was found that NDUFA9 crotonylation promoted browning of white adipocytes. Meanwhile, the acetylation level of NDUFA9 was increased by treating cells with SAHA+sodium acetate (NaAc) and overexpressing NDUFA9, the assay revealed that NDUFA9 acetylation inhibited white adipocytes browning. Finally, combined with the competitive relationship between acetylation and crotonylation, it was also demonstrated that NDUFA9 crotonylation promoted browning of white adipocytes. Above results indicate that NDUFA9 and its crotonylation modification promote mitochondrial function, which in turn promotes browning of white adipocytes. This study establishes a theoretical foundation for the management and intervention of obesity, which is crucial in addressing obesity and related medical conditions in the future.

PPAR-γ regulates the polarization of M2 macrophages to improve the microenvironment for autologous fat grafting

The unpredictable survival rate of autologous fat grafting (AFG) seriously affects its clinical application. Improving the survival rate of AFG has become an unresolved issue in plastic surgery. Peroxisome proliferator-activated receptor-γ (PPAR-γ) regulates the adipogenic differentiation of adipocytes, but the functional mechanism in AFG remains unclear. In this study, we established an animal model of AFG and demonstrated the superior therapeutic effect of PPAR-γ regulation in the process of AFG. From day 3 after fat grafting, the PPAR-γ agonist rosiglitazone group consistently showed better adipose integrity, fewer oil cysts, and fibrosis. Massive macrophage infiltration was observed after 7 days. At the same time, M2 macrophages begin to appear. At day 14, M2 macrophages gradually became the dominant cell population, which suppressed inflammation and promoted revascularization and fat regeneration. In addition, transcriptome sequencing showed that the differentially expressed genes in the Rosiglitazone group were associated with the pathways of adipose regeneration, differentiation, and angiogenesis; these results provide new ideas for clinical treatment.

Intermittent vs. continuous swimming training on adipokines and pro-inflammatory cytokines in metabolic syndrome experimental model

OBJECTIVES

In this study, metabolic syndrome-affected rats were studied to examine how intermittent and continuous swimming training influenced adipokines and pro-inflammatory cytokines.

METHODS

Forty-eight male Wistar rats were randomized in this experimental study into four groups (n=8), including normal control (NC), metabolic syndrome (MS), continuous swimming training with metabolic syndrome (CT-MS: load 0-3% body mass, 5 d/wk, for 8 weeks), and intermittent swimming training with metabolic syndrome (IT-MS: load 5-16% body mass, 5 d/wk, for 8 weeks). The serum levels of metrnl, adipolin, irisin, leptin, TNF-α, and IL-6 were measured using the ELISA test.

RESULTS

The IT-MS and NC groups exhibited significantly lower leptin concentrations than the CT-MS group (p=0.001). The irisin, meteorin, and adipolin serum levels increased significantly in CT-MS and IT relative to the NC and CT-MS groups (p=0.001), with the changes being more pronounced in the IT group (p=0.05). TNF-α and IL-6 were inclined in the CT-MS group compared with the other three groups (p=0.001), while IL-6 was increased in the IT group (p=0.024).

CONCLUSIONS

Intermittent swimming is more effective than continuous swimming training in improving adipokines in rats with metabolic syndrome.

Ado-Mediated Depletion of Taurine Impairs Mitochondrial Respiratory Capacity and Alters the Chromatin Landscape of Inguinal Adipose Tissue

Non-shivering thermogenesis (NST) has strong potential to combat obesity; however, a safe molecular approach to activate this process has not yet been identified. The sulfur amino acid taurine has the ability to safely activate NST and confer protection against obesity and metabolic disease in both mice and humans, but the mechanism of this action is unknown. In this study, we discover that a suite of taurine biosynthetic enzymes, especially that of cysteamine dioxygenase (ADO), significantly increases in response to β3 adrenergic signaling in inguinal adipose tissue (IWAT) in order to increase intracellular concentrations of taurine. We further show that ADO is critical for thermogenic mitochondrial respiratory function as its ablation in adipocytes significantly reduces taurine levels, which leads to declines in mitochondrial oxygen consumption rates. Finally, we demonstrate via assay for transposase-accessible chromatin with sequencing (ATAC-seq) that taurine supplementation in beige adipocytes has the ability to remodel the chromatin landscape to increase the chromatin accessibility and transcription of genes, such as glucose-6-phosphate isomerase 1 (Gpi1), which are critical for NST. Taken together, our studies highlight a potential mechanism for taurine in the activation of NST that can be leveraged toward the treatment of obesity and metabolic disease.

Inherited stress resiliency prevents the development of metabolic alterations in diet-induced obese mice

OBJECTIVE

Chronic stress promotes obesity and metabolic comorbidities. The ability of individuals to cope with stress may serve as an important parameter in the development of obesity-related metabolic outcomes. The aim of this study was to clarify whether differences in stress response affect metabolic health under obesity.

METHODS

The study was performed in a selectively bred mouse model of social dominance (Dom) and submissiveness (Sub), which exhibit stress resilience or vulnerability, respectively. Mice were given a high-fat diet (HFD) or standard diet, followed by physiological, histological, and molecular analyses.

RESULTS

The HFD caused hyperleptinemia, glucose intolerance, insulin resistance, steatosis of the liver and pancreas, and brown adipose tissue whitening in Sub mice, whereas Dom mice were protected from these consequences of the HFD. The HFD increased circulating levels of interleukin (IL)-1β and induced the expression of proinflammatory genes in the liver and in epididymal white adipose tissue of Sub mice, with no changes in Dom mice. The Cox2 inhibitor celecoxib (15 mg/kg/d) reduced serum IL-1β, improved glucose tolerance and insulin sensitivity, and prevented hepatic and brown adipose tissue whitening in HFD-fed Sub mice.

CONCLUSIONS

The extent of stress resiliency is associated with inflammation and contributes to population heterogeneity in the development of healthy or unhealthy obesity.

Knocking Down CDKN2A in 3D hiPSC-Derived Brown Adipose Progenitors Potentiates Differentiation, Oxidative Metabolism and Browning Process

Human induced pluripotent stem cells (hiPSCs) have the potential to be differentiated into any cell type, making them a relevant tool for therapeutic purposes such as cell-based therapies. In particular, they show great promise for obesity treatment as they represent an unlimited source of brown/beige adipose progenitors (hiPSC-BAPs). However, the low brown/beige adipocyte differentiation potential in 2D cultures represents a strong limitation for clinical use. In adipose tissue, besides its cell cycle regulator functions, the cyclin-dependent kinase inhibitor 2A (CDKN2A) locus modulates the commitment of stem cells to the brown-like type fate, mature adipocyte energy metabolism and the browning of adipose tissue. Here, using a new method of hiPSC-BAPs 3D culture, via the formation of an organoid-like structure, we silenced CDKN2A expression during hiPSC-BAP adipogenic differentiation and observed that knocking down CDKN2A potentiates adipogenesis, oxidative metabolism and the browning process, resulting in brown-like adipocytes by promoting UCP1 expression and beiging markers. Our results suggest that modulating CDKN2A levels could be relevant for hiPSC-BAPs cell-based therapies.

Renal AA amyloidosis: presentation, diagnosis, and current therapeutic options: a review

Amyloid A amyloidosis is thought to be the second most common form of systemic amyloidosis behind amyloidosis secondary to monoclonal Ig. It is the result of deposition of insoluble fibrils in the extracellular space of tissues and organs derived from the precursor protein serum amyloid A, an acute phase reactant synthesized excessively in the setting of chronic inflammation. The kidney is the most frequent organ involved. Most patients present with proteinuria and kidney failure. The diagnosis is made through tissue biopsy with involvement of the glomeruli in most cases, but also often of the vessels and the tubulointerstitial compartment. The treatment usually targets the underlying etiology and consists increasingly of blocking the inflammatory cascade of cytokines with interleukin-1 inhibitors, interleukin-6 inhibitors, and tumor necrosis factor-α inhibitors to reduce serum amyloid A protein formation. This strategy has also shown efficacy in cases where an underlying etiology cannot be readily identified and has significantly improved the prognosis of this entity. In addition, there has been increased interest at developing effective therapies able to clear amyloid deposits from tissues, albeit with mitigated results so far.

The impact of high intensity interval training on serum omentin-1 levels, lipid profile, and insulin resistance in obese men with type 2 diabetes mellitus

BACKGROUND: High-intensity interval training (HIIT) is an effective exercise method that could lead to favorable changes in obese and diabetic subjects. OBJECTIVE: To investigate the effects of HIIT on serum omentin-1 levels, lipid profile, and insulin resistance in diabetic obese men. METHODS: Fifty obese men suffering from T2DM with ages between 40 and 60 years were enrolled. Subjects were divided into two groups: the HIIT (n= 26) and control group (n= 24). The HIIT group subjects underwent 12 weeks (3 sessions per week) of HIIT program, while the control group subjects kept to their normal daily activities. Fasting blood glucose levels, serum omentin-1 levels, lipid profile, and insulin resistance were evaluated at baseline and after the experiment. RESULTS: HIIT resulted in significant improvements in the subjects’ body composition, serum omentin-1 levels, lipid profiles, fasting insulin, HOMA-IR (p< 0.05). Further, highly significant negative correlations were observed between serum omentin levels, on the one hand, and body mass index, body weight, and waist circumference, on the other. CONCLUSIONS: Twelve weeks of HIIT may be an effective training strategy to improve serum omentin-1 levels, body composition, lipid profile, and insulin sensitivity in diabetic obese men.

The benefits of adipocyte metabolism in bone health and regeneration

Patients suffering from musculoskeletal diseases must cope with a diminished quality of life and an increased burden on medical expenses. The interaction of immune cells and mesenchymal stromal cells during bone regeneration is one of the key requirements for the restoration of skeletal integrity. While stromal cells of the osteo-chondral lineage support bone regeneration, an excessive accumulation of cells of the adipogenic lineage is thought to promote low-grade inflammation and impair bone regeneration. Increasing evidence indicates that pro-inflammatory signaling from adipocytes is responsible for various chronic musculoskeletal diseases. This review aims to summarize the features of bone marrow adipocytes by phenotype, function, secretory features, metabolic properties and their impact on bone formation. In detail, the master regulator of adipogenesis and prominent diabetes drug target, peroxisome proliferator-activated receptor γ (PPARG), will be debated as a potential therapeutic approach to enhance bone regeneration. We will explore the possibilities of using clinically established PPARG agonists, the thiazolidinediones (TZDs), as a treatment strategy to guide the induction of a pro-regenerative, metabolically active bone marrow adipose tissue. The impact of this PPARG induced bone marrow adipose tissue type on providing the necessary metabolites to sustain osteogenic-as well as beneficial immune cells during bone fracture healing will be highlighted.

Brevibacillus laterosporus BL1, a promising probiotic, prevents obesity and modulates gut microbiota in mice fed a high-fat diet

Scope

Probiotics are a potential preventive strategy for obesity. However, with discrete efficacy and limited species of probiotics, there is a demand for novel strains with excellent anti-obesity properties. This study aimed to investigate the effects of Brevibacillus laterosporus BL1 on preventing obesity in high-fat diet (HFD)-fed mice.

Methods and results

C57BL/6 male mice were randomly assigned to four groups (n = 10) and fed a control diet, HFD, HFD plus B. laterosporus BL1, and HFD plus supernatant of B. laterosporus BL1, respectively for 8 weeks. The results showed that prophylactic B. laterosporus BL1 treatment reduced body weight gain by 41.26% in comparison to the HFD group, and this difference was accompanied by a reduction in body fat mass and the weight of inguinal white adipose tissues and epididymal white adipose tissue (-33.39%, -39.07%, and -43.75%, respectively). Moreover, the B. laterosporus BL1-mediated improvements in lipid profile, insulin resistance, and chronic inflammation were associated with the regulation of gene expression related to lipid metabolism and enhancement of brown adipose tissue thermogenesis. Particularly, B. laterosporus BL1 intervention significantly improved HFD-induced gut flora dysbiosis, as evidenced by a reverse in the relative abundance of Bacillota and Bacteroidota, as well as an increase in the relative abundance of bacteria that produce short-chain fatty acids (SCFAs), which in turn increased SCFAs levels.

Conclusion

Our findings found for the first time that B. laterosporus BL1 may be a promising probiotic for prevention of obesity associated with the regulation of gut microbiota.

The evolving view of thermogenic fat and its implications in cancer and metabolic diseases

The incidence of metabolism-related diseases like obesity and type 2 diabetes mellitus has reached pandemic levels worldwide and increased gradually. Most of them are listed on the table of high-risk factors for malignancy, and metabolic disorders systematically or locally contribute to cancer progression and poor prognosis of patients. Importantly, adipose tissue is fundamental to the occurrence and development of these metabolic disorders. White adipose tissue stores excessive energy, while thermogenic fat including brown and beige adipose tissue dissipates energy to generate heat. In addition to thermogenesis, beige and brown adipocytes also function as dynamic secretory cells and a metabolic sink of nutrients, like glucose, fatty acids, and amino acids. Accordingly, strategies that activate and expand thermogenic adipose tissue offer therapeutic promise to combat overweight, diabetes, and other metabolic disorders through increasing energy expenditure and enhancing glucose tolerance. With a better understanding of its origins and biological functions and the advances in imaging techniques detecting thermogenesis, the roles of thermogenic adipose tissue in tumors have been revealed gradually. On the one hand, enhanced browning of subcutaneous fatty tissue results in weight loss and cancer-associated cachexia. On the other hand, locally activated thermogenic adipocytes in the tumor microenvironment accelerate cancer progression by offering fuel sources and is likely to develop resistance to chemotherapy. Here, we enumerate current knowledge about the significant advances made in the origin and physiological functions of thermogenic fat. In addition, we discuss the multiple roles of thermogenic adipocytes in different tumors. Ultimately, we summarize imaging technologies for identifying thermogenic adipose tissue and pharmacologic agents via modulating thermogenesis in preclinical experiments and clinical trials.

Tolerance to Glucose and Lipid High Metabolic Reactions After Burns in an Obese Rat Model

The goal of this study was to determine what effect obese body weight and a burn injury can have on the metabolism of glucose and lipids in rats. We used a 3 * 3 factorial model design to provide basic glucose and lipid metabolic data characterizing the interaction between different weight and burn injury groups. Two hundred Sprague Dawley rats were categorized into three weight groups (normal, overweight, obese) and then further divided into control, second-degree, and third-degree burn groups. Our model compared interactions between weight and burn injury factors according to the above groups. Blood glucose and lipid metabolism indicators were monitored on the 1st, 3rd, 7th, and 14th days after burn injury occurred, and burned skin and blood samples were collected for testing. Compared with the normal weight group, the overweight group's fast blood glucose, fast insulin, and homeostasis model assessment of insulin resistance were higher (P < .05), and FBG in the obese group was higher than the normal weight group (P < .05). Burn injuries combined with obese body weight had an interactive effect on fast blood glucose, fast insulin, and homeostasis model assessment of insulin resistance after burn injury (P < .05). Burn injury combined with obese body weight had an interaction on low-density lipoprotein cholesterol on the 3rd day after burn injury (P < .05). Burn injury combined with obese weight had no interaction on triglyceride, total cholesterol, and high-density lipoprotein cholesterol (P > .05). Rats in the overweight and obese weight groups were observed to develop an adaptation and tolerance to a higher metabolic rate after burn injuries occurred.

Immune Cells in Thermogenic Adipose Depots: The Essential but Complex Relationship

Brown adipose tissue (BAT) is a unique organ in mammals capable of dissipating energy in form of heat. Additionally, white adipose tissue (WAT) can undergo browning and perform thermogenesis. In recent years, the research community has aimed to harness thermogenic depot functions for new therapeutic strategies against obesity and the metabolic syndrome; hence a comprehensive understanding of the thermogenic fat microenvironment is essential. Akin to WAT, immune cells also infiltrate and reside within the thermogenic adipose tissues and perform vital functions. As highly plastic organs, adipose depots rely on crucial interplay with these tissue resident cells to conserve their healthy state. Evidence has accumulated to show that different immune cell populations contribute to thermogenic adipose tissue homeostasis and activation through complex communicative networks. Furthermore, new studies have identified -but still not fully characterized further- numerous immune cell populations present in these depots. Here, we review the current knowledge of this emerging field by describing the immune cells that sway the thermogenic adipose depots, and the complex array of communications that influence tissue performance.

ADH5-mediated NO bioactivity maintains metabolic homeostasis in brown adipose tissue

Brown adipose tissue (BAT) thermogenic activity is tightly regulated by cellular redox status, but the underlying molecular mechanisms are incompletely understood. Protein S-nitrosylation, the nitric-oxide-mediated cysteine thiol protein modification, plays important roles in cellular redox regulation. Here we show that diet-induced obesity (DIO) and acute cold exposure elevate BAT protein S-nitrosylation, including UCP1. This thermogenic-induced nitric oxide bioactivity is regulated by S-nitrosoglutathione reductase (GSNOR; alcohol dehydrogenase 5 [ADH5]), a denitrosylase that balances the intracellular nitroso-redox status. Loss of ADH5 in BAT impairs cold-induced UCP1-dependent thermogenesis and worsens obesity-associated metabolic dysfunction. Mechanistically, we demonstrate that Adh5 expression is induced by the transcription factor heat shock factor 1 (HSF1), and administration of an HSF1 activator to BAT of DIO mice increases Adh5 expression and significantly improves UCP1-mediated respiration. Together, these data indicate that ADH5 controls BAT nitroso-redox homeostasis to regulate adipose thermogenesis, which may be therapeutically targeted to improve metabolic health.

Beneficial impacts of fermented celery (Apium graveolens L.) juice on obesity prevention and gut microbiota modulation in high-fat diet fed mice

Metabolic syndrome caused obesity has long been recognized as a risk of health. Celery and celery extracts have various medicinal properties, such as anti-diabetes and anti-inflammatory properties and blood glucose and serum lipid reduction. However, the effect of probiotic fermentation on celery juice and the association between fermented celery juice (FCJ) and obesity were unclear. This study aimed to evaluate the beneficial effects of FCJ on high-fat diet (HFD) induced obesity and related metabolic syndromes. C57BL/6 mice were randomly divided into six groups (n = 15 per group) fed either a normal diet (ND) or HFD with or without CJ/FCJ (10 g kg^-1 day^-1) by oral gavage for 12 weeks. Here we demonstrated that the probiotic fermentation of celery juice (CJ) could enhance the active ingredients in celery, such as total polyphenols, flavonoids, vitamin C and SOD. Compared to the slight improvement induced by CJ ingestion, FCJ intake significantly inhibited body weight gain, prevented dyslipidemia and hyperglycemia, and suppressed visceral fat accumulation. Furthermore, 16S rRNA sequencing analysis revealed that FCJ intake altered the composition of gut microbiota, increasing the ratio of Firmicutes/Bacteroidetes and the relative abundance of beneficial bacteria (Lactobacillus, Ruminococcaceae_UCG-014, Faecalibaculum and Blautia), and decreasing the relative abundance of harmful bacteria (Alloprevotella and Helicobacter). These findings suggest that FCJ can prevent HFD-induced obesity and become a novel gut microbiota modulator to prevent HFD-induced gut dysbiosis and obesity-related metabolic disorders.

Differential Effects of 17,18-EEQ and 19,20-EDP Combined with Soluble Epoxide Hydrolase Inhibitor t-TUCB on Diet-Induced Obesity in Mice

17,18-Epoxyeicosatetraenoic acid (17,18-EEQ) and 19,20-epoxydocosapentaenoic acid (19,20-EDP) are bioactive epoxides produced from n-3 polyunsaturated fatty acid eicosapentaenoic acid and docosahexaenoic acid, respectively. However, these epoxides are quickly metabolized into less active diols by soluble epoxide hydrolase (sEH). We have previously demonstrated that an sEH inhibitor, t-TUCB, decreased serum triglycerides (TG) and increased lipid metabolic protein expression in the brown adipose tissue (BAT) of diet-induced obese mice. This study investigates the preventive effects of t-TUCB (T) alone or combined with 19,20-EDP (T + EDP) or 17,18-EEQ (T + EEQ) on BAT activation in the development of diet-induced obesity and metabolic disorders via osmotic minipump delivery in mice. Both T + EDP and T + EEQ groups showed significant improvement in fasting glucose, serum triglycerides, and higher core body temperature, whereas heat production was only significantly increased in the T + EEQ group. Moreover, both the T + EDP and T + EEQ groups showed less lipid accumulation in the BAT. Although UCP1 expression was not changed, PGC1α expression was increased in all three treated groups. In contrast, the expression of CPT1A and CPT1B, which are responsible for the rate-limiting step for fatty acid oxidation, was only increased in the T + EDP and T + EEQ groups. Interestingly, as a fatty acid transporter, CD36 expression was only increased in the T + EEQ group. Furthermore, both the T + EDP and T + EEQ groups showed decreased inflammatory NFκB signaling in the BAT. Our results suggest that 17,18-EEQ or 19,20-EDP combined with t-TUCB may prevent high-fat diet-induced metabolic disorders, in part through increased thermogenesis, upregulating lipid metabolic protein expression, and decreasing inflammation in the BAT.

The effects of physical activity on adipokines in individuals with overweight/obesity across the lifespan: A narrative review

This narrative review summarizes current knowledge on the effects of physical activity (PA) on adipokine levels in individuals with overweight and obesity. Approximately 90 investigations including randomized control, cross-sectional and longitudinal studies that reported on the effects of a single session of PA (acute) or long-term PA (chronic) on adipokine levels in individuals with overweight/obesity were reviewed. The findings support the notion that there is consensus on the benefits of chronic exercise training-regardless of the mode (resistance vs. aerobic), intensity and cohort (healthy vs. diabetes)-on adipokine levels (such as tumour necrosis factor-alpha, interleukin-6, adiponectin, visfatin, omentin-1 and leptin). However, several confounding factors (frequency, intensity, time and type of exercise) can alter the magnitude of the effects of an acute exercise session. Available evidence suggests that PA, as a part of routine lifestyle behaviour, improves obesity complications by modulating adipokine levels. However, additional research is needed to help identify the most effective interventions to elicit the most beneficial changes in adipokine levels in individuals with overweight/obesity.

Adipose Tissue Immunomodulation: A Novel Therapeutic Approach in Cardiovascular and Metabolic Diseases

Adipose tissue is a critical regulator of systemic metabolism and bodily homeostasis as it secretes a myriad of adipokines, including inflammatory and anti-inflammatory cytokines. As the main storage pool of lipids, subcutaneous and visceral adipose tissues undergo marked hypertrophy and hyperplasia in response to nutritional excess leading to hypoxia, adipokine dysregulation, and subsequent low-grade inflammation that is characterized by increased infiltration and activation of innate and adaptive immune cells. The specific localization, physiology, susceptibility to inflammation and the heterogeneity of the inflammatory cell population of each adipose depot are unique and thus dictate the possible complications of adipose tissue chronic inflammation. Several lines of evidence link visceral and particularly perivascular, pericardial, and perirenal adipose tissue inflammation to the development of metabolic syndrome, insulin resistance, type 2 diabetes and cardiovascular diseases. In addition to the implication of the immune system in the regulation of adipose tissue function, adipose tissue immune components are pivotal in detrimental or otherwise favorable adipose tissue remodeling and thermogenesis. Adipose tissue resident and infiltrating immune cells undergo metabolic and morphological adaptation based on the systemic energy status and thus a better comprehension of the metabolic regulation of immune cells in adipose tissues is pivotal to address complications of chronic adipose tissue inflammation. In this review, we discuss the role of adipose innate and adaptive immune cells across various physiological and pathophysiological states that pertain to the development or progression of cardiovascular diseases associated with metabolic disorders. Understanding such mechanisms allows for the exploitation of the adipose tissue-immune system crosstalk, exploring how the adipose immune system might be targeted as a strategy to treat cardiovascular derangements associated with metabolic dysfunctions.

Chronic stress, epigenetics, and adipose tissue metabolism in the obese state

In obesity, endocrine and metabolic perturbations, including those induced by chronic activation of the hypothalamus-pituitary-adrenal axis, are associated with the accumulation of adipose tissue and inflammation. Such changes are attributable to a combination of genetic and epigenetic factors that are influenced by the environment and exacerbated by chronic activation of the hypothalamus-pituitary-adrenal axis. Stress exposure at different life stages can alter adipose tissue metabolism directly through epigenetic modification or indirectly through the manipulation of hypothalamic appetite regulation, and thereby contribute to endocrine changes that further disrupt whole-body energy balance. This review synthesizes current knowledge, with an emphasis on human clinical trials, to describe metabolic changes in adipose tissue and associated endocrine, genetic and epigenetic changes in the obese state. In particular, we discuss epigenetic changes induced by stress exposure and their contribution to appetite and adipocyte dysfunction, which collectively promote the pathogenesis of obesity. Such knowledge is critical for providing future directions of metabolism research and targets for treating metabolic disorders.

Ghrelin ameliorates tumor-induced adipose tissue atrophy and inflammation via Ghrelin receptor-dependent and -independent pathways

Adipose tissue (AT) atrophy is a hallmark of cancer cachexia contributing to increased morbidity/mortality. Ghrelin has been proposed as a treatment for cancer cachexia partly by preventing AT atrophy. However, the mechanisms mediating ghrelin's effects are incompletely understood, including the extent to which its only known receptor, GHSR-1a, is required for these effects. This study characterizes the pathways involved in AT atrophy in the Lewis Lung Carcinoma (LLC)-induced cachexia model and those mediating the effects of ghrelin in Ghsr ^+/+ and Ghsr ^-/- mice. We show that LLC causes AT atrophy by inducing anorexia, and increasing lipolysis, AT inflammation, thermogenesis and energy expenditure. These changes were greater in Ghsr ^-/-. Ghrelin administration prevented LLC-induced anorexia only in Ghsr ^+/+, but prevented WAT lipolysis, inflammation and atrophy in both genotypes, although its effects were greater in Ghsr ^+/+. LLC-induced increases in BAT inflammation, WAT and BAT thermogenesis, and energy expenditure were not affected by ghrelin. In conclusion, ghrelin ameliorates WAT inflammation, fat atrophy and anorexia in LLC-induced cachexia. GHSR-1a is required for ghrelin's orexigenic effect but not for its anti-inflammatory or fat-sparing effects.

The essential function of IL-33 in metabolic regulation

Interleukin-33 (IL-33) is produced by various types of cells under physical or pathological conditions. As a multifunctional partner in health and disease, current evidence reveals that IL-33 also participates in several metabolic processes. IL-33 has been proven to contribute to regulating the activity of ST2+ group 2 innate lymphoid cells and regulatory T cells in adipose, which leads to the shift of insulin sensitivity and glucose clearance in glucose metabolism, thermogenesis, and adipocyte beiging in adipose metabolism. In this review, we briefly summarize the biological characteristics of Il-33 and discuss its regulatory function in glucose and adipose metabolism. By clarifying the underlying mechanism of IL-33, we highlight the crosstalk between immune response and metabolic processes mediated by IL-33.

BMP4 facilitates beige fat biogenesis via regulating adipose tissue macrophages

Thermogenic beige fat improves metabolism and prevents obesity. Emerging evidence shows that the activation of M2 macrophages stimulates beige adipogenesis, whereas the activation of M1 macrophages, which play a major role in inflammation, impedes beige adipogenesis. Thus, the identification of factors that regulate adipose tissue macrophages (ATMs) will help clarify the mechanism involved in beiging. Here, we found that one of the secreted proteins in adipose tissue, namely, BMP4, alters the ATM profile in subcutaneous adipose tissue by activating M2 and inhibiting M1 macrophages. Mechanistically, the BMP4-stimulated p38/MAPK/STAT6/PI3K-AKT signalling pathway is involved. Meanwhile, BMP4 improved the potency of M2 macrophages to induce beige fat biogenesis. Considering that the overexpression of BMP4 in adipose tissue promotes the beiging of subcutaneous adipose tissue and improves insulin sensitivity, these findings provide evidence that BMP4 acts as an activator of beige fat by targeting immuno-metabolic pathways.

Inflammatory Signaling and Brown Fat Activity

Obesity is characterized by a state of chronic inflammation in adipose tissue mediated by the secretion of a range of inflammatory cytokines. In comparison to WAT, relatively little is known about the inflammatory status of brown adipose tissue (BAT) in physiology and pathophysiology. Because BAT and brown/beige adipocytes are specialized in energy expenditure they have protective roles against obesity and associated metabolic diseases. BAT appears to be is less susceptible to developing inflammation than WAT. However, there is increasing evidence that inflammation directly alters the thermogenic activity of brown fat by impairing its capacity for energy expenditure and glucose uptake. The inflammatory microenvironment can be affected by cytokines secreted by immune cells as well as by the brown adipocytes themselves. Therefore, pro-inflammatory signals represent an important component of the thermogenic potential of brown and beige adipocytes and may contribute their dysfunction in obesity.

Novel imaging biomarkers: epicardial adipose tissue evaluation

Epicardial adipose tissue (EAT) is a metabolically activated beige adipose tissue, non-homogeneously surrounding the myocardium. Physiologically, EAT regulates toxic fatty acids, protects the coronary arteries against mechanical strain, regulates proinflammatory cytokines, stimulates the production of nitric oxide, reduces oxidative stress, and works as a thermogenic source against hypothermia. Conversely, EAT has pathologic paracrine interactions with the surrounded vessels, and might favour the onset of atrial fibrillation. In addition, initial atherosclerotic lesions can promote inflammation and trigger the EAT production of cytokines increasing vascular inflammation, which, in turn, may help the development of collateral vessels but also of self-stimulating, dysregulated inflammatory process, increasing coronary artery disease severity. Variations in EAT were also linked to metabolic syndrome. Echocardiography first estimated EAT measuring its thickness on the free wall of the right ventricle but does not allow accurate volumetric EAT estimates. Cardiac CT (CCT) and cardiac MR (CMR) allow for three-dimensional EAT estimates, the former showing higher spatial resolution and reproducibility but being limited by radiation exposure and long segmentation times, the latter being radiation-free but limited by lower spatial resolution and reproducibility, higher cost, and difficulties for obese patients. EAT radiodensity at CCT could to be related to underlying metabolic processes. The correlation between EAT and response to certain pharmacological therapies has also been investigated, showing promising results. In the future, semi-automatic or fully automatic techniques, machine/deep-learning methods, if validated, will facilitate research for various EAT measures and may find a place in CCT/CMR reporting.

Adipose-Derived Stromal Cells Attenuate Adipose Inflammation in Obesity through Adipocyte Browning and Polarization of M2 Macrophages

Obesity is a metabolic condition associated with multiple health problems such as endocrine and metabolic dysfunction and chronic inflammation in adipose tissues. In this study, the ADSCs could be stimulated to differentiate into brown adipocyte with rosiglitazone treatment based on the Oil-Red-O staining trial. Furthermore, the multilocular lipid droplets located in the center was increased in differentiated brown adipocytes, and brown fat-associated proteins, UCP1, PPAR-γ, and LPL were highly expressed in brown adipocytes differentiated from ADSCs. Additionally, the results of animal experiments showed that both weight and amount of VLDL and LDL were decreased in the serum of obese mice after transplantation of rosiglitazone-induced brown adipocytes, while the level of HDL increased. Moreover, the proteins associated with lipid metabolism, LPA and UCP1, were downregulated, and the inflammatory response was suppressed through inhibition of the ITGAM/NF-κB-mediated proinflammatory responses and polarization of M2 macrophages. Similarly, the amounts of proinflammatory cytokines, TNF-α, IL-6, and IL-1β were decreased after rosiglitazone-induced brown adipocyte transplantation. On the contrary, anti-inflammatory cytokine IL-10 was significantly increased in both groups of obese mice, with or without brown adipocyte transplantation. Therefore, the adipose-derived stromal cells with induced browning could promote lipid consumption and alternative polarization of M2 macrophages to attenuate adipose inflammation in obesity mouse models, which thus provides a potential therapy for obesity.

A Renewable Source of Human Beige Adipocytes for Development of Therapies to Treat Metabolic Syndrome

Molecular- and cellular-based therapies have the potential to reduce obesity-associated disease. In response to cold, beige adipocytes form in subcutaneous white adipose tissue and convert energy stored in metabolic substrates to heat, making them an attractive therapeutic target. We developed a robust method to generate a renewable source of human beige adipocytes from induced pluripotent stem cells (iPSCs). Developmentally, these cells are derived from FOXF1⁺ mesoderm and progress through an expandable mural-like mesenchymal stem cell (MSC) to form mature beige adipocytes that display a thermogenically active profile. This includes expression of uncoupling protein 1 (UCP1) concomitant with increased uncoupled respiration. With this method, dysfunctional adipogenic precursors can be reprogrammed and differentiated into beige adipocytes with increased thermogenic function and anti-diabetic secretion potential. This resource can be used to (1) elucidate mechanisms that underlie the control of beige adipogenesis and (2) generate material for cellular-based therapies that target metabolic syndrome in humans.

Su et al. demonstrate a method for producing beige adipocytes from human induced pluripotent stem cells in a stepwise manner through defined precursor lineages. This renewable resource provides a developmental framework to study human beige adipogenesis and can be used to develop treatments for obesity-related disorders.

Mechanisms of weight regain after weight loss - the role of adipose tissue

One of the biggest challenges in the management of obesity is the prevention of weight regain after successful weight loss. Weight regain after weight loss has large interindividual variation. Although many factors probably contribute to this variation, we hypothesize that variability in biological responses associated with weight loss-induced shrinking of subcutaneous adipocytes has an important role. In this Review, we show that weight loss-induced variations in cellular stress, extracellular matrix remodelling, inflammatory responses, adipokine secretion and lipolysis seem to be associated with the amount of weight that is regained after successful weight loss. Weight regain could therefore, at least in part, depend on a combination of these factors. Further research on the causality of these associations could aid the development of effective strategies to prevent weight regain after successful weight loss.

Siah2 modulates sex-dependent metabolic and inflammatory responses in adipose tissue to a high-fat diet challenge

Background

The obesity-related risk of developing metabolic syndrome is higher in males than in females of reproductive age, likely due to estrogen-mediated reduced adipose tissue inflammation and fibrosis with hypertrophied adipocytes. Depletion of the ubiquitin ligase Siah2 reduced white adipose tissue inflammation and improved glucose metabolism in obese male mice. Siah2 is a transcriptional target of estrogen, but data is lacking about the effect of Siah2 on adipose tissue of females. We therefore evaluated the impact of Siah2 deficiency on white and brown adipose tissue in females of reproductive age.

Methods

Body composition, adipose tissue morphology, brown adipose tissue gene, and protein expression and adipocyte sizing were evaluated in wild-type and Siah2KO female and male mice fed a low-fat or high-fat diet. Glucose and insulin tolerance, fasting glucose, insulin, fatty acids and triglycerides, and gene expression of inflammation markers in perigonadal fat were evaluated in wild-type and Siah2KO female mice. Microarray analysis of brown fat gene expression was carried out in both sexes. Statistical analysis was assessed by unpaired two-tailed t test and repeated measures ANOVA.

Results

Siah2 deficiency improves glucose and insulin tolerance in the presence of hypertrophied white adipocytes in high-fat-fed female mice with percent fat comparable to male mice. While previous studies showed Siah2KO reduces the white adipose tissue inflammatory response in male mice, the response in females is biased toward the upregulation of M2-like markers in white adipose tissue. In contrast, loss of Siah2 leads to increased whitening of brown fat in males, but not in females. This corresponded to increased expression of markers of inflammation (F4/80, Ccl2) and thermogenic genes (Pgc1alpha, Dio2, Ucp-1) and proteins (PGC-1α, UCP-1) in females. Contrary to expectations, increased expression of thermogenic markers in females was coupled with a downregulation of ERalpha and ERRgamma protein levels.

Conclusions

The most striking sex-related effect of Siah2 deficiency is reduced whitening of brown fat in high-fat-fed females. Protection from accumulating unilocular adipocytes in the brown fat corresponds to increased expression of thermogenic genes and proteins in female, but not in male mice. These results raise the possibility that Siah2 contributes to the estrogen-related effects on brown fat function in males and females.

Electronic supplementary material

The online version of this article (10.1186/s13293-019-0233-y) contains supplementary material, which is available to authorized users.

Mechanisms of Impaired Brown Adipose Tissue Recruitment in Obesity

Brown adipose tissue (BAT) dissipates energy to produce heat. Thus, it has the potential to regulate body temperature by thermogenesis. For the last decade, BAT has been in the spotlight due to its rediscovery in adult humans. This is evidenced by over a hundred clinical trials that are currently registered to target BAT as a therapeutic tool in the treatment of metabolic diseases, such as obesity or diabetes. The goal of most of these trials is to activate the BAT thermogenic program via several approaches such as adrenergic stimulation, natriuretic peptides, retinoids, capsinoids, thyroid hormones, or glucocorticoids. However, the impact of BAT activation on total body energy consumption and the potential effect on weight loss is still limited. Other studies have focused on increasing the mass of thermogenic BAT. This can be relevant in obesity, where the activity and abundance of BAT have been shown to be drastically reduced. The aim of this review is to describe pathological processes associated with obesity that may influence the correct differentiation of BAT, such as catecholamine resistance, inflammation, oxidative stress, and endoplasmic reticulum stress. This will shed light on the thermogenic potential of BAT as a therapeutic approach to target obesity-induced metabolic diseases.

Abnormal brown adipose tissue mitochondrial structure and function in IL10 deficiency

Background

Inflammation is the most relevant mechanism linking obesity with insulin-resistance and metabolic disease. It impacts the structure and function of tissues and organs involved in metabolism, such as the liver, pancreatic islets and the hypothalamus. Brown adipose tissue has emerged as an important component of whole body energy homeostasis, controlling caloric expenditure through the regulation of non-shivering thermogenesis. However, little is known about the impact of systemic inflammation on the structure and function of brown adipose tissue.

Methods

The relations between IL10 and mitochondria structure/function and also with thermogenesis were evaluated by bioinformatics using human and rodent data. Real-time PCR, immunoblot, fluorescence and transmission electron microscopy were employed to determine the effect of IL10 in the brown adipose tissue of wild type and IL10 knockout mice.

Findings

IL10 knockout mice, a model of systemic inflammation, present severe structural abnormalities of brown adipose tissue mitochondria, which are round-shaped with loss of cristae structure and increased fragmentation. IL10 deficiency leads to newborn cold intolerance and impaired UCP1-dependent brown adipose tissue mitochondrial respiration. The reduction of systemic inflammation with an anti-TNFα monoclonal antibody partially rescued the structural but not the functional abnormalities of brown adipose tissue mitochondria. Using bioinformatics analyses we show that in both humans and mice, IL10 transcripts correlate with mitochondrial lipid metabolism and caspase gene expression.

Interpretation

IL10 and systemic inflammation play a central role in the regulation of brown adipose tissue by controlling mitochondrial structure and function.

Fund

Sao Paulo Research Foundation grant 2013/07607-8.

Modulation of Energy Expenditure by Estrogens and Exercise in Women

Reducing estrogen in women results in decreases in energy expenditure, but the mechanism(s) remain largely unknown. We postulate that the loss of estrogens in women is associated with increased accumulation of bone marrow-derived adipocytes in white adipose tissue, decreased activity of brown adipose tissue, and reduced levels of physical activity. Regular exercise may counteract the effects of estrogen deficiency.

Regulation of Energy Expenditure and Brown/Beige Thermogenic Activity by Interleukins: New Roles for Old Actors

Obesity rates and the burden of metabolic associated diseases are escalating worldwide Energy burning brown and inducible beige adipocytes in human adipose tissues (ATs) have attracted considerable attention due to their therapeutic potential to counteract the deleterious metabolic effects of nutritional overload and overweight. Recent research has highlighted the relevance of resident and recruited ATs immune cell populations and their signalling mediators, cytokines, as modulators of the thermogenic activity of brown and beige ATs. In this review, we first provide an overview of the developmental, cellular and functional heterogeneity of the AT organ, as well as reported molecular switches of its heat-producing machinery. We also discuss the key contribution of various interleukins signalling pathways to energy and metabolic homeostasis and their roles in the biogenesis and function of brown and beige adipocytes. Besides local actions, attention is also drawn to their influence in the central nervous system (CNS) networks governing energy expenditure.

Obesity is a significant susceptibility factor for idiopathic AA amyloidosis

BACKGROUND

To investigate obesity as susceptibility factor in patients with idiopathic AA amyloidosis.

METHODS

Clinical, biochemical and genetic data were obtained from 146 patients with AA amyloidosis. Control groups comprised 40 patients with long-standing inflammatory diseases without AA amyloidosis and 56 controls without any inflammatory disease.

FINDINGS

Patients with AA amyloidosis had either familial Mediterranean fever (FMF) or long-standing rheumatic diseases as underlying inflammatory disease (n = 111, median age 46 years). However, in a significant proportion of patients with AA amyloidosis no primary disease was identified (idiopathic AA; n = 37, median age 60 years). Patients with idiopathic AA amyloidosis were more obese and older than patients with AA amyloidosis secondary to FMF or rheumatic diseases. Serum leptin levels correlated with the body mass index (BMI) in all types of AA amyloidosis. Elevated leptin levels of more than 30 µg/l were detected in 18% of FMF/rheumatic + AA amyloidosis and in 40% of patients with idiopathic AA amyloidosis (p = .018). Finally, the SAA1 polymorphism was confirmed as a susceptibility factor for AA amyloidosis irrespective of the type of the disease.

CONCLUSIONS

Obesity, age and the SAA1 polymorphism are susceptibility factors for idiopathic AA amyloidosis. Recent advances in treatment of FMF and rheumatic disorders will decrease the incidence of AA amyloidosis due to these diseases. Idiopathic AA, however, might be an emerging problem in the ageing and increasingly obese population.

Food-derived regulatory factors against obesity and metabolic syndrome

Obesity is a key factor in metabolic syndrome. The study of metabolic syndrome focuses on the anti-weight gain properties of physiological mechanisms and food components. Abnormal energy metabolism is a major risk factor of metabolic syndrome. Chronic inflammation is a feature of obesity; cytokines from hypertrophied adipocytes cause inflammation in both adipose tissue and blood vessels, resulting in symptoms of metabolic syndrome. Tumor necrosis factor-α causes insulin resistance in adipocytes and regression of brown adipocytes, resulting in abnormal energy metabolism. Functional foods can serve as a strategy for prevention and treatment of obesity linked with metabolic processes in white and brown adipose tissues. Diet-induced thermogenesis caused by certain food components stimulates burning of stored fat within adipose tissues. A mechanistic understanding of dietary thermogenesis via the sympathetic nerve system will prove valuable for the development of precise strategies for the practical prevention of metabolic syndrome.

Supra-pharmacological concentration of capsaicin stimulates brown adipogenesis through induction of endoplasmic reticulum stress

We previously showed that brown (pre)adipocytes express Trpv1, a capsaicin receptor, and that capsaicin stimulates differentiation of brown preadipocytes in the late stages of brown adipogenesis. The present study revealed that treatment with 100 μM capsaicin stimulates brown adipogenesis by inducing endoplasmic reticulum (ER) stress. Treatment with capsaicin (100 μM) during brown adipogenesis enhanced lipid accumulation and the expression of Ucp1, a gene selectively expressed in brown adipocytes. Capsaicin treatment also caused an increase in the cytosolic calcium concentration even when extracellular calcium was removed. I-RTX, a Trpv1 inhibitor, did not modulate the increase in cytosolic calcium concentration, lipid accumulation or Ucp1 expression. Previous studies revealed that the release of calcium from the ER induces ER stress, leading to the conversion of X-box binding protein 1 (Xbp1) pre-mRNA to spliced Xbp1 (sXbp1) as well as the up-regulation of Chop expression. Capsaicin treatment increased the expression of sXbp1 and Chop in brown preadipocytes and did not enhance lipid accumulation or Ucp1 expression in Xbp1 knockdown cells. The present results describe a novel mechanism of brown adipogenesis regulation via ER stress that is induced by a supra-pharmacological concentration of capsaicin.

Prior Repeated Stress Attenuates Cold-Induced Immunomodulation Associated with "Browning" in Mesenteric Fat of Rats

Continuous exposure to cold leads to activation of adaptive thermogenesis in brown adipose tissue but also to induction of brown/beige cell phenotype in white adipose tissue. The aim of this work was to investigate whether prior exposure to immobilization (IMO) stress may affect immune response associated with adipocyte "browning" in mesenteric adipose tissue (mWAT). In the first experiment, Sprague-Dawley rats were exposed to acute (3 h) or prolonged (7 days) cold exposure (4 ± 1 °C). 7-day cold stimulated gene expression of uncoupling protein 1 and other "browning"-associated factors. In the second experiment, rats were immobilized for 7 days (2 h daily) followed by exposure to continuous cold for 1 or 7 days. Prior IMO exaggerated cold-induced sympathetic response manifested by elevated tyrosine hydroxylase (TH) protein and norepinephrine in mWAT. Induction of non-sympathetic catecholamine production demonstrated by elevated TH and PNMT (phenylethanolamine N-methyltransferase) mRNAs was observed after 7-day cold; however, prior IMO attenuated this response. 7-day cold-induced gene expression of anti-inflammatory mediators (IL-4, IL-13, IL-10, adiponectin), markers of M2 macrophages (Arg1, Retnlα), and eosinophil-associated molecules (eotaxin, IL-5), while inhibited expression of pro-inflammatory cytokines (IFNγ, IL-1b, IL-6, IL-17) and monocytes (MCP-1, Ly6C). This immune response was accompanied by elevated expression of uncoupling protein-1 and other thermogenic factors. Rats exposed to prior IMO exhibited inhibition of cold-induced immune and "browning"-related expression pattern. Overall, we demonstrated that 7-day cold-induced browning"-associated changes in rat mWAT, while prior history of repeated stress prevented this response.

Taming the Flames: Targeting White Adipose Tissue Browning in Hypermetabolic Conditions

In this era of increased obesity and diabetes prevalence, the browning of white adipose tissue (WAT) has emerged as a promising therapeutic target to induce weight loss and improve insulin sensitivity in this population. The browning process entails a shift in the WAT from primarily storing excess energy to the dissipation of energy as heat. However, this idealistic view of WAT browning being the savior of the metabolic syndrome has been criticized by studies in burn and cancer patients that have shown browning to be detrimental rather than beneficial. In fact, in the context of hypermetabolic states, the browning of WAT has presented with substantial clinical adverse outcomes related to cachexia, hepatic steatosis, and muscle catabolism. Therefore, the previous thought construct of understanding browning as an all-beneficial physiologic event has now been met with skepticism. In this review, we focus on current knowledge of browning of WAT and its adverse metabolic alterations during hypermetabolic states. We also discuss the regulators and signaling pathways involved in the browning process and their potential for being targeted by new or existing drugs to inhibit or alleviate browning, potentially leading to decreased hypermetabolism and improved clinical outcomes. Lastly, the imminent clinical applications of pharmacological agents are explored in the perspective of attenuating WAT browning and its associated adverse side effects reported in burn patients.

Adapting to obesity with adipose tissue inflammation

Adipose tissue not only has an important role in the storage of excess nutrients but also senses nutrient status and regulates energy mobilization. An overall positive energy balance is associated with overnutrition and leads to excessive accumulation of fat in adipocytes. These cells respond by initiating an inflammatory response that, although maladaptive in the long run, might initially be a physiological response to the stresses obesity places on adipose tissue. In this Review, we characterize adipose tissue inflammation and review the current knowledge of what triggers obesity-associated inflammation in adipose tissue. We examine the connection between adipose tissue inflammation and the development of insulin resistance and catecholamine resistance and discuss the ensuing state of metabolic inflexibility. Finally, we review the current and potential new anti-inflammatory treatments for obesity-associated metabolic disease.

Helminth antigens counteract a rapid high-fat diet-induced decrease in adipose tissue eosinophils

Brown adipose tissue (BAT) activation and white adipose tissue (WAT) beiging can increase energy expenditure and have the potential to reduce obesity and associated diseases. The immune system is a potential target in mediating brown and beige adipocyte activation. Type 2 and anti-inflammatory immune cells contribute to metabolic homeostasis within lean WAT, with a prominent role for eosinophils and interleukin (IL)-4-induced anti-inflammatory macrophages. We determined eosinophil numbers in epididymal WAT (EpAT), subcutaneous WAT (ScAT) and BAT after 1 day, 3 days or 1 week of high-fat diet (HFD) feeding in C57Bl/6 mice. One day of HFD resulted in a rapid drop in eosinophil numbers in EpAT and BAT, and after 3 days, in ScAT. In an attempt to restore this HFD-induced drop in adipose tissue eosinophils, we treated 1-week HFD-fed mice with helminth antigens from Schistosoma mansoni or Trichuris suis and evaluated whether the well-known protective metabolic effects of helminth antigens involves BAT activation or beiging. Indeed, antigens of both helminth species induced high numbers of eosinophils in EpAT, but failed to induce beiging. In ScAT, Schistosoma mansoni antigens induced mild eosinophilia, which was accompanied by slightly more beiging. No effects were observed in BAT. To study type 2 responses on brown adipocytes directly, T37i cells were stimulated with IL-4. This increased Ucp1 expression and strongly induced the production of eosinophil chemoattractant CCL11 (+26-fold), revealing that brown adipocytes themselves can attract eosinophils. Our findings indicate that helminth antigen-induced eosinophilia fails to induce profound beiging of white adipocytes.

Macrophage functions in lean and obese adipose tissue

Interactions between macrophages and adipocytes influence both metabolism and inflammation. Obesity-induced changes to macrophages and adipocytes lead to chronic inflammation and insulin resistance. This paper reviews the various functions of macrophages in lean and obese adipose tissue and how obesity alters adipose tissue macrophage phenotypes. Metabolic disease and insulin resistance shift the balance between numerous pro- and anti-inflammatory regulators of macrophages and create a feed-forward loop of increasing inflammatory macrophage activation and worsening adipocyte dysfunction. This ultimately leads to adipose tissue fibrosis and diabetes. The molecular mechanisms underlying these processes have therapeutic implications for obesity, metabolic syndrome, and diabetes.