Unlock the Thermogenic Potential of Adipose Tissue: Pharmacological Modulation and Implications for Treatment of Diabetes and Obesity

Hepatic protein kinase Cbeta deficiency mitigates late-onset obesity

Although aging is associated with progressive adiposity and a decline in liver function, the underlying molecular mechanisms and metabolic interplay are incompletely understood. Here, we demonstrate that aging induces hepatic protein kinase Cbeta (PKCβ) expression, while hepatocyte PKCβ deficiency (PKCβHep-/-) in mice significantly attenuates obesity in aged mice fed a high-fat diet. Compared with control PKCβfl/fl mice, PKCβHep-/- mice showed elevated energy expenditure with augmentation of oxygen consumption and carbon dioxide production which was dependent on β3-adrenergic receptor signaling, thereby favoring negative energy balance. This effect was accompanied by induction of thermogenic genes in brown adipose tissue (BAT) and increased BAT respiratory capacity, as well as a shift to oxidative muscle fiber type with an improved mitochondrial function, thereby enhancing oxidative capacity of thermogenic tissues. Furthermore, in PKCβHep-/- mice, we determined that PKCβ overexpression in the liver mitigated elevated expression of thermogenic genes in BAT. In conclusion, our study thus establishes hepatocyte PKCβ induction as a critical component of pathophysiological energy metabolism by promoting progressive hepatic and extrahepatic metabolic derangements in energy homeostasis, contributing to late-onset obesity. These findings have potential implications for augmenting thermogenesis as a means of combating aging-induced obesity.

Loss of Brain Angiogenesis Inhibitor-3 (BAI3) G-Protein Coupled Receptor in Mice Regulates Adaptive Thermogenesis by Enhancing Energy Expenditure

Effective energy expenditure is critical for maintaining body weight (BW). However, underlying mechanisms contributing to increased BW remain unknown. We characterized the role of brain angiogenesis inhibitor-3 (BAI3/ADGRB3), an adhesion G-protein coupled receptor (aGPCR), in regulating BW. A CRISPR/Cas9 gene editing approach was utilized to generate a whole-body deletion of the BAI3 gene (BAI3-/-). In both BAI3-/- male and female mice, a significant reduction in BW was observed compared to BAI3+/+ control mice. Quantitative magnetic imaging analysis showed that lean and fat masses were reduced in male and female mice with BAI3 deficiency. Total activity, food intake, energy expenditure (EE), and respiratory exchange ratio (RER) were assessed in mice housed at room temperature using a Comprehensive Lab Animal Monitoring System (CLAMS). While no differences were observed in the activity between the two genotypes in male or female mice, energy expenditure was increased in both sexes with BAI3 deficiency. However, at thermoneutrality (30 °C), no differences in energy expenditure were observed between the two genotypes for either sex, suggesting a role for BAI3 in adaptive thermogenesis. Notably, in male BAI3-/- mice, food intake was reduced, and RER was increased, but these attributes remained unchanged in the female mice upon BAI3 loss. Gene expression analysis showed increased mRNA abundance of thermogenic genes Ucp1, Pgc1α, Prdm16, and Elov3 in brown adipose tissue (BAT). These outcomes suggest that adaptive thermogenesis due to enhanced BAT activity contributes to increased energy expenditure and reduced BW with BAI3 deficiency. Additionally, sex-dependent differences were observed in food intake and RER. These studies identify BAI3 as a novel regulator of BW that can be potentially targeted to improve whole-body energy expenditure.

Progress and obstacles in transplantation of brown adipose tissue or engineered cells with thermogenic potential for metabolic benefits

Transplantation of brown adipose tissue (BAT), engineered thermogenic progenitor cells, and adipocytes have received much attention for the improvement of obesity and metabolic disorders. However, even though the thermogenic and metabolic potential exists early after transplantation, the whitening of the brown fat graft occurs with metabolic function significantly impaired. In this review, specific experiment designs, graft outcomes, and metabolic benefits for the transplantation of BAT or engineered cells will be discussed. The current advancements will offer guidance to further investigation, and the obstacles appearing in previous studies will require innovation of BAT transplantation methods.

FTO gene expression in diet-induced obesity is downregulated by Solanum fruit supplementation

The Fat Mass and Obesity-associated (FTO) gene has been shown to play an important role in developing obesity, manifesting in traits such as increased body mass index, increased waist-to-hip ratio, and the distribution of adipose tissues, which increases the susceptibility to various metabolic syndromes. In this study, we evaluated the impact of fruit-based diets of Solanum melongena (SMF) and Solanum aethiopicum fruits (SAF) on the FTO gene expression levels in a high-fat diet (HFD)-induced obese animals. Our results showed that the mRNA level of the FTO gene was downregulated in the hypothalamus, and white and brown adipose tissue following three and six weeks of treatment with SMF- and SAF-based diets in the HFD-induced obese animals. Additionally, the Solanum fruit supplementation exhibited a curative effect on obesity-associated abrasions on the white adipose tissue (WAT), hypothalamus, and liver. Our findings collectively suggest the anti-obesity potential of SMF and SAF via the downregulation of the FTO gene.

The involvement of the adrenergic nervous system in activating human brown adipose tissue and browning

Obesity is a chronic condition of multifactorial etiology characterized by excessive body fat due to a calorie intake higher than energy expenditure. Given the intrinsic limitations of surgical interventions and the difficulties associated with lifestyle changes, pharmacological manipulation is currently one of the main therapies for metabolic diseases. Approaches aiming to promote energy expenditure through induction of thermogenesis have been explored and, in this context, brown adipose tissue (BAT) activation and browning have been shown to be promising strategies. Although such processes are physiologically stimulated by the sympathetic nervous system, not all situations that are known to increase adrenergic signaling promote a concomitant increase in BAT activation or browning in humans. Thus, a better understanding of factors involved in the thermogenesis attributed to these tissues is needed to enable the development of future therapies against obesity. Herein we carry out a critical review of original articles in humans under conditions previously known to trigger adrenergic responses-namely, cold, catecholamine-secreting tumor (pheochromocytoma and paraganglioma), burn injury, and adrenergic agonists-and discuss which of them are associated with increased BAT activation and browning. BAT is clearly stimulated in individuals exposed to cold or treated with high doses of the β3-adrenergic agonist mirabegron, whereas browning is certainly induced in patients after burn injury or with pheochromocytoma, as well as in individuals treated with β3-adrenergic agonist mirabegron for at least 10 weeks. Given the potential effect of increasing energy expenditure, adrenergic stimuli are promising strategies in the treatment of metabolic diseases.

Signaling Targets Related to Antiobesity Effects of Capsaicin: A Scoping Review

The search for new antiobesogenic agents is increasing because of the current obesity pandemic. Capsaicin (Caps), an exogenous agonist of the vanilloid receptor of transient potential type 1 (TRPV1), has shown promising results in the treatment of obesity. This scoping review aims to verify the pathways mediating the effects of Caps in obesity and the different methods adopted to identify these pathways. The search was carried out using data from the EMBASE, MEDLINE (PubMed), Web of Science, and SCOPUS databases. Studies considered eligible evaluated the mechanisms of action of Caps in obesity models or cell types involved in obesity. Nine studies were included and 100% (n = 6) of the in vivo studies showed a high risk of bias. Of the 9 studies, 66.6% (n = 6) administered Caps orally in the diet and 55.5% (n = 5) used a concentration of Caps of 0.01% in the diet. In vitro, the most tested concentration was 1 μM (88.9%; n = 8). Capsazepine was the antagonist chosen by 66.6% (n = 6) of the studies. Seven studies (77.8%) linked the antiobesogenic effects of Caps to TRPV1 activation and 3 (33.3%) indicated peroxisome proliferator-activated receptor (PPAR) involvement as an upstream connection to TRPV1, rather than a direct metabolic target of Caps. The main secondary effects of Caps were lower weight gain (33.3%; n = 3) or loss (22.2%; n = 2), greater improvement in lipid profile (33.3%; n = 3), lower white adipocyte adipogenesis (33.3%; n = 3), browning process activation (44.4%; n = 4), and higher brown adipocyte activity (33.3%; n = 3) compared with those of the control treatment. Some studies have shown that PPAR agonists modulate TRPV1 activity, and no study has evaluated the simultaneous antagonism of these 2 receptors. Consequently, further studies are necessary to elucidate the role of each of these signaling molecules in the antiobesogenic effects of Caps.

Obesity protects against sepsis-induced and norepinephrine-induced white adipose tissue browning

Sepsis is a dysregulated systemic response to infection and can lead to organ damage and death. Obesity is a significant problem worldwide and affects outcomes from sepsis. Our laboratory demonstrated that white adipose tissue (WAT) undergoes browning during sepsis, a process whereby WAT adopts a brown adipose tissue phenotype. However, this browning process was not observed in obese mice during sepsis. White adipose tissue browning is detrimental in patients with burn injury and cancer. We hypothesize that norepinephrine (NE) induces WAT browning in nonobese mice but not in obese mice similarly to sepsis-induced WAT browning. Six-week-old C57BL/6 male mice were randomized to a high-fat diet or normal diet. After 6-7 wk of feeding, polymicrobial sepsis was induced by cecal ligation and puncture (CLP). Norepinephrine was administered intraperitoneally via osmotic minipumps for 18 h or 72 h (no CLP) at which time tissue and plasma were harvested. Controls were mice that underwent CLP (no NE) with 18-h harvest. A separate group of mice underwent pretreatment with NE or vehicle infusion for 72 h, CLP was performed, and at 18 h had tissue and plasma harvested. Sepsis resulted in significant weight loss in both nonobese and obese mice. NE treatment alone caused weight loss in obese mice. Septic nonobese mice had higher uncoupling protein-1 (UCP1) expression compared with control and obese septic mice. NE treatment increased UCP1 expression in nonobese, but not obese mice. NE-treated obese septic mice had lower lung myeloperoxidase (MPO) activity, alanine aminotransferase (ALT), aspartate aminotransferase (AST), TNFα, and IL-6 levels compared with NE-treated nonobese septic mice. Obesity protects mice from septic-induced and NE-induced WAT browning.NEW & NOTEWORTHY White adipose tissue browning is detrimental in patients with burn injury and cancer. WAT browning occurs in nonobese mice and can be induced by β receptor norepinephrine infusion, but obese mice are resistant to sepsis-induced and norepinephrine-induced WAT browning. We propose that the lack of WAT browning and unchanged inflammatory cytokine response may contribute to the protection of obese mice from sepsis.

Towards an understanding of the mechanoreciprocity process in adipocytes and its perturbation with aging

Adipose tissue (AT) is a complex organ, with multiple functions that are essential for maintaining metabolic health. A feature of AT is its capability to expand in response to physiological challenges, such as pregnancy and aging, and during chronic states of positive energy balance occurring throughout life. AT grows through adipogenesis and/or an increase in the size of existing adipocytes. One process that is required for healthy AT growth is the remodeling of the extracellular matrix (ECM), which is a necessary step to restore mechanical homeostasis and maintain tissue integrity and functionality. While the relationship between mechanobiology and adipogenesis is now well recognized, less is known about the role of adipocyte mechanosignaling pathways in AT growth. In this review article, we first summarize evidence linking ECM remodelling to AT expansion and how its perturbation is associated to a metabolically unhealthy phenotype. Subsequently, we highlight findings suggesting that molecules involved in the dynamic, bidirectional process (mechanoreciprocity) enabling adipocytes to sense changes in the mechanical properties of the ECM are interconnected to pathways regulating lipid metabolism. Finally, we discuss processes through which aging may influence the ability of adipocytes to appropriately respond to alterations in ECM composition.

FGF21 promotes thermogenic gene expression as an autocrine factor in adipocytes

The contribution of adipose-derived FGF21 to energy homeostasis is unclear. Here we show that browning of inguinal white adipose tissue (iWAT) by β-adrenergic agonists requires autocrine FGF21 signaling. Adipose-specific deletion of the FGF21 co-receptor β-Klotho renders mice unresponsive to β-adrenergic stimulation. In contrast, mice with liver-specific ablation of FGF21, which eliminates circulating FGF21, remain sensitive to β-adrenergic browning of iWAT. Concordantly, transgenic overexpression of FGF21 in adipocytes promotes browning in a β-Klotho-dependent manner without increasing circulating FGF21. Mechanistically, we show that β-adrenergic stimulation of thermogenic gene expression requires FGF21 in adipocytes to promote phosphorylation of phospholipase C-γ and mobilization of intracellular calcium. Moreover, we find that the β-adrenergic-dependent increase in circulating FGF21 occurs through an indirect mechanism in which fatty acids released by adipocyte lipolysis subsequently activate hepatic PPARα to increase FGF21 expression. These studies identify FGF21 as a cell-autonomous autocrine regulator of adipose tissue function.

Abu-Odeh et al. demonstrate that autocrine action of FGF21 is a required second signal promoting thermogenic gene expression in catecholamine-stimulated adipocytes. Hepatic FGF21 secretions, secondary to catecholamine-stimulated adipocyte lipolysis, are dispensable for adipose tissue browning. These studies identify FGF21 as a cell-autonomous autocrine regulator of adipose tissue function.

Regulatory roles of G-protein coupled receptors in adipose tissue metabolism and their therapeutic potential

The high incidence of obesity has increased the need to discover new therapeutic targets to combat obesity and obesity-related metabolic diseases. Obesity is defined as an abnormal accumulation of adipose tissue, which is one of the major metabolic organs that regulate energy homeostasis. However, there are currently no approved anti-obesity therapeutics that directly target adipose tissue metabolism. With recent advances in the understanding of adipose tissue biology, molecular mechanisms involved in brown adipose tissue expansion and metabolic activation have been investigated as potential therapeutic targets to increase energy expenditure. This review focuses on G-protein coupled receptors (GPCRs) as they are the most successful class of druggable targets in human diseases and have an important role in regulating adipose tissue metabolism. We summarize recent findings on the major GPCR classes that regulate thermogenesis and mitochondrial metabolism in adipose tissue. Improved understanding of GPCR signaling pathways that regulate these processes could facilitate the development of novel pharmacological approaches to treat obesity and related metabolic disorders.

Inducible beige adipocytes improve impaired glucose metabolism in interscapular BAT-removal mice

Inducible beige adipocytes are emerging as an interesting issue in obesity and metabolism research. There is a neglected possibility that brown adipocytes are equally activated when external stimuli induce the formation of beige adipocytes. Thus, the question is whether beige adipocytes have the same functions as brown adipocytes when brown adipose tissue (BAT) is lacking. This question has not been well studied. Therefore we determine the beneficial effects of beige adipocytes upon cold challenge or CL316243 treatments in animal models of interscapular BAT (iBAT) ablation by surgical denervation. We found that denervated iBAT were activated by cold exposure and CL316243 treatments. The data show that beige adipocytes partly contribute to the improvement of impaired glucose metabolism resulting from denervated iBAT. Thus, we further used iBAT-removal animal models to abolish iBAT functions completely. We found that beige adipocytes upon cold exposure or CL316243 treatments improved impaired glucose metabolism and enhanced glucose uptake in iBAT-removal mice. The insulin signaling was activated in iBAT-removal mice upon cold exposure. Both the activation of insulin signaling and up-regulation of glucose transporter expression were observed in iBAT-removal mice with CL316243 treatments. The data show that inducible beige adipocytes may have different mechanisms to improve impaired glucose metabolism. Inducible beige adipocytes can also enhance energy expenditure and lipolytic activity of white adipose tissues when iBAT is lacking. We provide direct evidences for the beneficial effect of inducible beige adipocytes in glucose metabolism and energy expenditure in the absence of iBAT in vivo.

Control of Adipose Cell Browning and Its Therapeutic Potential

Adipose tissue is the largest endocrine organ in humans and has an important influence on many physiological processes throughout life. An increasing number of studies have described the different phenotypic characteristics of fat cells in adults. Perhaps one of the most important properties of fat cells is their ability to adapt to different environmental and nutritional conditions. Hypothalamic neural circuits receive peripheral signals from temperature, physical activity or nutrients and stimulate the metabolism of white fat cells. During this process, changes in lipid inclusion occur, and the number of mitochondria increases, giving these cells functional properties similar to those of brown fat cells. Recently, beige fat cells have been studied for their potential role in the regulation of obesity and insulin resistance. In this context, it is important to understand the embryonic origin of beige adipocytes, the response of adipocyte to environmental changes or modifications within the body and their ability to transdifferentiate to elucidate the roles of these cells for their potential use in therapeutic strategies for obesity and metabolic diseases. In this review, we discuss the origins of the different fat cells and the possible therapeutic properties of beige fat cells.

Decreased UCP-1 expression in beige adipocytes from adipose-derived stem cells of type 2 diabetes patients associates with mitochondrial ROS accumulation during obesity

OBJECTIVE

Adipose derived stem cells (ADSC) are defective in metabolic disorders in various functionalities and properties including differentiation, multipotent state, metabolism and immunomodulation. However, the role of ADSC beiging potential in promoting of type 2 diabetes mellitus (T2DM) development remains unclear. Here we uncover association between potential of subcutaneous ADSC to beige differentiation and T2DM in patients with obesity.

METHODS

ADSC were isolated from subcutaneous adipose tissue of patients with long morbid obesity (BMI > 35 kg/m2) and normal glucose tolerance (NGT) or T2DM. ADSC were differentiated into white or beige adipocytes and levels of thermogenic markers, lipid metabolism and electron transport chain (ETC) genes was analyzed by Western blotting and RT-PCR. ROS production was estimated by fluorescent microscopy.

RESULTS

We have shown decreased UCP-1 expression in beige adipocytes from T2DM patients. Nevertheless, signal and expression activities of lipolysis were equal in NGT and T2DM beige adipocytes. Expression analysis of ETC genes also has not shown any statistically significant differences. Interestingly, we revealed increased mitochondrial ROS production in T2DM beige adipocytes during beige differentiation.

CONCLUSIONS

In summary, compromised UCP1 expression in beige adipocytes of T2DM patients may cause increase of mitochondrial ROS. Elevated oxidative level is liable to act as damaging mechanism leading to insulin resistance or, alternatively, serve as compensatory mechanism for thermogenesis activation.

Organic Cation Transporters in Health and Disease

The organic cation transporters (OCTs) OCT1, OCT2, OCT3, novel OCT (OCTN)1, OCTN2, multidrug and toxin exclusion (MATE)1, and MATE kidney-specific 2 are polyspecific transporters exhibiting broadly overlapping substrate selectivities. They transport organic cations, zwitterions, and some uncharged compounds and operate as facilitated diffusion systems and/or antiporters. OCTs are critically involved in intestinal absorption, hepatic uptake, and renal excretion of hydrophilic drugs. They modulate the distribution of endogenous compounds such as thiamine, L-carnitine, and neurotransmitters. Sites of expression and functions of OCTs have important impact on energy metabolism, pharmacokinetics, and toxicity of drugs, and on drug-drug interactions. In this work, an overview about the human OCTs is presented. Functional properties of human OCTs, including identified substrates and inhibitors of the individual transporters, are described. Sites of expression are compiled, and data on regulation of OCTs are presented. In addition, genetic variations of OCTs are listed, and data on their impact on transport, drug treatment, and diseases are reported. Moreover, recent data are summarized that indicate complex drug-drug interaction at OCTs, such as allosteric high-affinity inhibition of transport and substrate dependence of inhibitor efficacies. A hypothesis about the molecular mechanism of polyspecific substrate recognition by OCTs is presented that is based on functional studies and mutagenesis experiments in OCT1 and OCT2. This hypothesis provides a framework to imagine how observed complex drug-drug interactions at OCTs arise. Finally, preclinical in vitro tests that are performed by pharmaceutical companies to identify interaction of novel drugs with OCTs are discussed. Optimized experimental procedures are proposed that allow a gapless detection of inhibitory and transported drugs.

Chronic arsenic exposure impairs adaptive thermogenesis in male C57BL/6J mice

The global prevalence of type 2 diabetes (T2D) has doubled since 1980. Human epidemiological studies support arsenic exposure as a risk factor for T2D, although the precise mechanism is unclear. We hypothesized that chronic arsenic ingestion alters glucose homeostasis by impairing adaptive thermogenesis, i.e., body heat production in cold environments. Arsenic is a pervasive environmental contaminant, with more than 200 million people worldwide currently exposed to arsenic-contaminated drinking water. Male C57BL/6J mice exposed to sodium arsenite in drinking water at 300 μg/L for 9 wk experienced significantly decreased metabolic heat production when acclimated to chronic cold tolerance testing, as evidenced by indirect calorimetry, despite no change in physical activity. Arsenic exposure increased total fat mass and subcutaneous inguinal white adipose tissue (iWAT) mass. RNA sequencing analysis of iWAT indicated that arsenic dysregulated mitochondrial processes, including fatty acid metabolism. Western blotting in WAT confirmed that arsenic significantly decreased TOMM20, a correlate of mitochondrial abundance; PGC1A, a master regulator of mitochondrial biogenesis; and, CPT1B, the rate-limiting step of fatty acid oxidation (FAO). Our findings show that chronic arsenic exposure impacts the mitochondrial proteins of thermogenic tissues involved in energy expenditure and substrate regulation, providing novel mechanistic evidence for arsenic's role in T2D development.

PPARγ and PPARα synergize to induce robust browning of white fat in vivo

OBJECTIVE

Peroxisome proliferator-activated receptors (PPARs) are key transcription factors that regulate adipose development and function, and the conversion of white into brown-like adipocytes. Here we investigated whether PPARα and PPARγ activation synergize to induce the browning of white fat.

METHODS

A selection of PPAR activators was tested for their ability to induce the browning of both mouse and human white adipocytes in vitro, and in vivo in lean and obese mice.

RESULTS

All dual PPARα/γ activators tested robustly increased uncoupling protein 1 (Ucp1) expression in both mouse and human adipocytes in vitro, with tesaglitazar leading to the largest Ucp1 induction. Importantly, dual PPARα/γ activator tesaglitazar strongly induced browning of white fat in vivo in both lean and obese male mice at thermoneutrality, greatly exceeding the increase in Ucp1 observed with the selective PPARγ activator rosiglitazone. While selective PPARγ activation was sufficient for the conversion of white into brown-like adipocytes in vitro, dual PPARα/γ activation was superior to selective PPARγ activation at inducing white fat browning in vivo. Mechanistically, the superiority of dual PPARα/γ activators is mediated at least in part via a PPARα-driven increase in fibroblast growth factor 21 (FGF21). Combined treatment with rosiglitazone and FGF21 resulted in a synergistic increase in Ucp1 mRNA levels both in vitro and in vivo. Tesaglitazar-induced browning was associated with increased energy expenditure, enhanced insulin sensitivity, reduced liver steatosis, and an overall improved metabolic profile compared to rosiglitazone and vehicle control groups.

CONCLUSIONS

PPARγ and PPARα synergize to induce robust browning of white fat in vivo, via PPARγ activation in adipose, and PPARα-mediated increase in FGF21.

Nanotechnology advances towards development of targeted-treatment for obesity

Obesity through its association with type 2 diabetes (T2D), cancer and cardiovascular diseases (CVDs), poses a serious health threat, as these diseases contribute to high mortality rates. Pharmacotherapy alone or in combination with either lifestyle modification or surgery, is reliable in maintaining a healthy body weight, and preventing progression to obesity-induced diseases. However, the anti-obesity drugs are limited by non-specificity and unsustainable weight loss effects. As such, novel and improved approaches for treatment of obesity are urgently needed. Nanotechnology-based therapies are investigated as an alternative strategy that can treat obesity and be able to overcome the drawbacks associated with conventional therapies. The review presents three nanotechnology-based anti-obesity strategies that target the white adipose tissues (WATs) and its vasculature for the reversal of obesity. These include inhibition of angiogenesis in the WATs, transformation of WATs to brown adipose tissues (BATs), and photothermal lipolysis of WATs. Compared to conventional therapy, the targeted-nanosystems have high tolerability, reduced side effects, and enhanced efficacy. These effects are reproducible using various nanocarriers (liposomes, polymeric and gold nanoparticles), thus providing a proof of concept that targeted nanotherapy can be a feasible strategy that can combat obesity and prevent its comorbidities.

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.

Sepsis Induces Adipose Tissue Browning in Nonobese Mice But Not in Obese Mice

Severe sepsis and septic shock are the biggest cause of mortality in critically ill patients. Obesity today is one of the world's greatest health challenges. Little is known about the extent of involvement of the white adipose tissue (WAT) in sepsis and how it is being modified by obesity. We sought to explore the involvement of the WAT in sepsis. We hypothesize that sepsis induces browning of the WAT and that obesity alters the response of WAT to sepsis. Six-week-old C57BL/6 mice were randomized to a high-fat diet to induce obesity (obese group) or control diet (nonobese group). After 6 to 11 weeks of feeding, polymicrobial sepsis was induced by cecal ligation and puncture (CLP). Mice were sacrificed at 0, 18, and 72 h after CLP and epididymal WAT (eWAT), inguinal WAT, and brown adipose tissue (BAT) harvested. Both types of WAT were processed for light microscopy and transmission electron microscopy to assess for morphological changes in both obese and nonobese mice. Tissues were processed for immunohistochemistry, image analyses, and molecular analyses. BATs were used as a positive control. Nonobese mice have an extensive breakdown of the unilocular lipid droplet and smaller adipocytes in WAT compared with obese mice after sepsis. Neutrophil infiltration increases in eWAT in nonobese mice after sepsis but not in obese mice. Nonobese septic mice have an increase in mitochondrial density compared with obese septic mice. Furthermore, nonobese septic mice have an increase in uncoupling protein-1 expression. Although the WAT of nonobese mice have multiple changes characteristic of browning during sepsis, these changes are markedly blunted in obesity.

The Impact of the Adipose Organ Plasticity on Inflammation and Cancer Progression

Obesity is characterized by chronic and low-grade systemic inflammation, an increase of adipose tissue, hypertrophy, and hyperplasia of adipocytes. Adipose tissues can be classified into white, brown, beige and pink adipose tissues, which display different regulatory, morphological and functional characteristics of their adipocyte and immune cells. Brown and white adipocytes can play a key role not only in the control of energy homeostasis, or through the balance between energy storage and expenditure, but also by the modulation of immune and inflammatory responses. Therefore, brown and white adipocytes can orchestrate important immunological crosstalk that may deeply impact the tumor microenvironment and be crucial for cancer establishment and progression. Recent works have indicated that white adipose tissues can undergo a process called browning, in which an inducible brown adipocyte develops. In this review, we depict the mechanisms involved in the differential role of brown, white and pink adipocytes, highlighting their structural, morphological, regulatory and functional characteristics and correlation with cancer predisposition, establishment, and progression. We also discuss the impact of the increased adiposity in the inflammatory and immunological modulation. Moreover, we focused on the plasticity of adipocytes, describing the molecules produced and secreted by those cells, the modulation of the signaling pathways involved in the browning phenomena of white adipose tissue and its impact on inflammation and cancer.

Enhanced β-adrenergic signalling underlies an age-dependent beneficial metabolic effect of PI3K p110α inactivation in adipose tissue

The insulin/IGF-1 signalling pathway is a key regulator of metabolism and the rate of ageing. We previously documented that systemic inactivation of phosphoinositide 3-kinase (PI3K) p110α, the principal PI3K isoform that positively regulates insulin signalling, results in a beneficial metabolic effect in aged mice. Here we demonstrate that deletion of p110α specifically in the adipose tissue leads to less fat accumulation over a significant part of adult life and allows the maintenance of normal glucose tolerance despite insulin resistance. This effect of p110α inactivation is due to a potentiating effect on β-adrenergic signalling, which leads to increased catecholamine-induced energy expenditure in the adipose tissue. Our findings provide a paradigm of how partial inactivation of an essential component of the insulin signalling pathway can have an overall beneficial metabolic effect and suggest that PI3K inhibition could potentiate the effect of β-adrenergic agonists in the treatment of obesity and its associated comorbidities.

Adult Hippocampal Neurogenesis Can Be Enhanced by Cold Challenge Independently From Beigeing Effects

In this study, we investigated the effects of cold challenge on adult hippocampal neurogenesis (AHN) and hippocampal gene expression and whether these are mediated by beigeing of peripheral fat tissues. Cold challenge (6 ± 2°C) for 1 and 4 weeks was found to induce beigeing effects in inguinal white adipose tissue based on hematoxylin and eosin staining as well as uncoupled protein-1 immunohistochemical staining. In the hippocampus, cold challenge for 1 or 4 weeks increased dentate gyrus neurogenesis and expression of genes related to AHN, including notch signaling, G protein-coupled receptor signaling, and adrenergic beta receptor-1. However, this enhancement of neurogenesis and gene expression by cold challenge was not shown by administration of CL 316,243, which induces peripheral beigeing similar to cold challenge but does not cross the blood–brain barrier. These results suggest that cold challenge promotes AHN and central expression of AHN-related, signaling, and β1-adrenergic receptors genes, and that peripheral beigeing by itself is not sufficient to mediate these effects. Considering the increase in AHN and gene expression changes, cold challenge may offer a novel approach to hippocampal modulation.

Strength training and aerobic exercise alter mitochondrial parameters in brown adipose tissue and equally reduce body adiposity in aged rats

With aging, there is a reduction in mitochondrial activity, and several changes occur in the body composition, including increased adiposity. The dysfunction of mitochondrial activity causes changes and adaptations in tissue catabolic characteristics. Among them, we can mention brown adipose tissue (BAT). BAT's main function is lipid oxidation for heat production, hence playing a role in adaptive thermogenesis induced by environmental factors such as exercise. It is known that exercise causes a series of metabolic changes, including loss body fat; however, there is still no consensus in the academic community about whether both strength and aerobic exercise equally reduces adiposity. Therefore, this study aimed to evaluate the effects of strength training and aerobic exercise regimes on adiposity, proteins regulating mitochondrial activity, and respiratory complexes in BAT of old rats. The rats were divided in two control groups: young control (YC; N = 5), and old control (OC; N = 5), and two exercise groups: strength training (OST; N = 5), and aerobic treadmill training (OAT; N = 5). Rats were subjected to an 8-week exercise regime, and their body composition parameters were evaluated (total body weight, adiposity index, and BAT weight). In addition, mitochondrial biogenesis proteins (PGC-1α, SIRT1, and pAMPK) and respiratory chain activity (complexes I, II/III, III, and IV) were evaluated. Results showed that OST and OAT exercise protocols significantly increased the mitochondrial regulatory molecules and respiratory chain activity, while body fat percentage and adiposity index significantly decreased. Taken together, both OST and OAT exercise increased BAT weight, activity of respiratory complexes, and regulatory proteins in BAT and equally reduced body adiposity.

Organic cation transporter 3 (Oct3) is a distinct catecholamines clearance route in adipocytes mediating the beiging of white adipose tissue

Beiging of white adipose tissue (WAT) is a particularly appealing target for therapeutics in the treatment of metabolic diseases through norepinephrine (NE)-mediated signaling pathways. Although previous studies report NE clearance mechanisms via SLC6A2 on sympathetic neurons or proinflammatory macrophages in adipose tissues (ATs), the low catecholamine clearance capacity of SLC6A2 may limit the cleaning efficiency. Here, we report that mouse organic cation transporter 3 (Oct3; Slc22a3) is highly expressed in WAT and displays the greatest uptake rate of NE as a selective non-neural route of NE clearance in white adipocytes, which differs from other known routes such as adjacent neurons or macrophages. We further show that adipocytes express high levels of NE degradation enzymes Maoa, Maob, and Comt, providing the molecular basis on NE clearance by adipocytes together with its reuptake transporter Oct3. Under NE administration, ablation of Oct3 induces higher body temperature, thermogenesis, and lipolysis compared with littermate controls. After prolonged cold challenge, inguinal WAT (ingWAT) in adipose-specific Oct3-deficient mice shows much stronger browning characteristics and significantly elevated expression of thermogenic and mitochondrial biogenesis genes than in littermate controls, and this response involves enhanced β-adrenergic receptor (β-AR)/protein kinase A (PKA)/cyclic adenosine monophosphate (cAMP)-responsive element binding protein (Creb) pathway activation. Glycolytic genes are reprogrammed to significantly higher levels to compensate for the loss of ATP production in adipose-specific Oct3 knockout (KO) mice, indicating the fundamental role of glucose metabolism during beiging. Inhibition of β-AR largely abolishes the higher lipolytic and thermogenic activities in Oct3-deficient ingWAT, indicating the NE overload in the vicinity of adipocytes in Oct3 KO adipocytes. Of note, reduced functional alleles in human OCT3 are also identified to be associated with increased basal metabolic rate (BMR). Collectively, our results demonstrate that Oct3 governs β-AR activity as a NE recycling transporter in white adipocytes, offering potential therapeutic applications for metabolic disorders.

Effect of ambient temperature on the proliferation of brown adipocyte progenitors and endothelial cells during postnatal BAT development in Syrian hamsters

In Syrian hamsters, brown adipose tissue (BAT) develops postnatally through the proliferation and differentiation of brown adipocyte progenitors. In the study reported here, we investigated how ambient temperature influenced BAT formation in neonatal hamsters. In both hamsters raised at 23 or 30 °C, the interscapular fat changed from white to brown coloration in an age-dependent manner and acquired the typical morphological features of BAT by day 16. However, the expression of uncoupling protein 1, a brown adipocyte marker, and of vascular endothelial growth factor α were lower in the group raised at 30 °C than in that raised at 23 °C. Immunofluorescent staining revealed that the proportion of Ki67-expressing progenitors and endothelial cells was lower in the 30 °C group than in the 23 °C group. These results indicate that warm ambient temperature suppresses the proliferation of brown adipocyte progenitors and endothelial cells and negatively affects the postnatal development of BAT in Syrian hamsters.

Berberine is a potential therapeutic agent for metabolic syndrome via brown adipose tissue activation and metabolism regulation

Berberine (BBR), an isoquinoline alkaloid that derived from the Chinese medicinal plant Coptis chinensis, has been identified with multiple pharmacological activities, including regulating glucose and cholesterol levels, anti-obesity effects and anti-diabetic effects. Due to its multiple activities, BBR and its metabolites have drawn great attention in biomedical research and clinical practices. After the recent re-discovery of brown adipose tissue (BAT) in adult humans, stimulating energy-dissipating via BAT activation and white-to-brown adipose tissue conversion have been regarded as potential therapeutic strategies for obesity and diabetes. Recent studies have demonstrated the activities of BBR in the activation of BAT and white-to-brown adipose tissue conversion, showing significant effectiveness in the treatment of diabetes. This review has summarized current studies that focused on the effect of BBR in the treatment of metabolic syndrome, especially in regulating BAT activities. Besides, the potential and molecular mechanisms of BBR in treating other risk factors of metabolic syndrome, including insulin resistance and dyslipidemia, are also reviewed, showing the great potential of BBR in treating the metabolic syndrome systematically.

Effect of sitagliptin on energy metabolism and brown adipose tissue in overweight individuals with prediabetes: a randomised placebo-controlled trial

AIMS/HYPOTHESIS

The aim of this study was to evaluate the effect of sitagliptin on glucose tolerance, plasma lipids, energy expenditure and metabolism of brown adipose tissue (BAT), white adipose tissue (WAT) and skeletal muscle in overweight individuals with prediabetes (impaired glucose tolerance and/or impaired fasting glucose).

METHODS

We performed a randomised, double-blinded, placebo-controlled trial in 30 overweight, Europid men (age 45.9 ± 6.2 years; BMI 28.8 ± 2.3 kg/m²) with prediabetes in the Leiden University Medical Center and the Alrijne Hospital between March 2015 and September 2016. Participants were initially randomly allocated to receive sitagliptin (100 mg/day) (n = 15) or placebo (n = 15) for 12 weeks, using a randomisation list that was set up by an unblinded pharmacist. All people involved in the study as well as participants were blinded to group assignment. Two participants withdrew from the study prior to completion (both in the sitagliptin group) and were subsequently replaced with two new participants that were allocated to the same treatment. Before and after treatment, fasting venous blood samples and skeletal muscle biopsies were obtained, OGTT was performed and body composition, resting energy expenditure and [¹⁸F] fluorodeoxyglucose ([¹⁸F]FDG) uptake by metabolic tissues were assessed. The primary study endpoint was the effect of sitagliptin on BAT volume and activity.

RESULTS

One participant from the sitagliptin group was excluded from analysis, due to a distribution error, leaving 29 participants for further analysis. Sitagliptin, but not placebo, lowered glucose excursion (-40%; p < 0.003) during OGTT, accompanied by an improved insulinogenic index (+38%; p < 0.003) and oral disposition index (+44%; p < 0.003). In addition, sitagliptin lowered serum concentrations of triacylglycerol (-29%) and very large (-46%), large (-35%) and medium-sized (-24%) VLDL particles (all p < 0.05). Body weight, body composition and energy expenditure did not change. In skeletal muscle, sitagliptin increased mRNA expression of PGC1β (also known as PPARGC1B) (+117%; p < 0.05), a main controller of mitochondrial oxidative energy metabolism. Although the primary endpoint of change in BAT volume and activity was not met, sitagliptin increased [¹⁸F] FDG uptake in subcutaneous WAT (sWAT; +53%; p < 0.05). Reported side effects were mild and transient and not necessarily related to the treatment.

CONCLUSIONS/INTERPRETATION

Twelve weeks of sitagliptin in overweight, Europid men with prediabetes improves glucose tolerance and lipid metabolism, as related to increased [¹⁸F] FDG uptake by sWAT, rather than BAT, and upregulation of the mitochondrial gene PGC1β in skeletal muscle. Studies on the effect of sitagliptin on preventing or delaying the progression of prediabetes into type 2 diabetes are warranted.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02294084.

FUNDING

This study was funded by Merck Sharp & Dohme Corp, Dutch Heart Foundation, Dutch Diabetes Research Foundation, Ministry of Economic Affairs and the University of Granada.

β-adrenergic Receptor Stimulation Revealed a Novel Regulatory Pathway via Suppressing Histone Deacetylase 3 to Induce Uncoupling Protein 1 Expression in Mice Beige Adipocyte

Browning of adipose tissue has been prescribed as a potential way to treat obesity, marked by the upregulation of uncoupling protein 1 (Ucp1). Several reports have suggested that histone deacetylase (HDAC) might regulate Ucp1 by remodelling chromatin structure, although the mechanism remains unclear. Herein, we investigate the effect of β-adrenergic receptor (β-AR) activation on the chromatin state of beige adipocyte. β-AR-stimulated Ucp1 expression via cold (in vivo) and isoproterenol (in vitro) resulted in acetylation of histone activation mark H3K27. H3K27 acetylation was also seen within Ucp1 promoter upon isoproterenol addition, favouring open chromatin for Ucp1 transcriptional activation. This result was found to be associated with the downregulation of class I HDAC mRNA, particularly Hdac3 and Hdac8. Further investigation showed that although HDAC8 activity decreased, Ucp1 expression was not altered when HDAC8 was activated or inhibited. In contrast, HDAC3 mRNA and protein levels were simultaneously downregulated upon isoproterenol addition, resulting in reduced recruitment of HDAC3 to the Ucp1 enhancer region, causing an increased H3K27 acetylation for Ucp1 upregulation. The importance of HDAC3 inhibition was confirmed through the enhanced Ucp1 expression when the cells were treated with HDAC3 inhibitor. This study highlights the novel mechanism of HDAC3-regulated Ucp1 expression during β-AR stimulation.

Luteolin-Enriched Artichoke Leaf Extract Alleviates the Metabolic Syndrome in Mice with High-Fat Diet-Induced Obesity

This current study aimed to elucidate the effects and possible underlying mechanisms of long-term supplementation with dietary luteolin (LU)-enriched artichoke leaf (AR) in high-fat diet (HFD)-induced obesity and its complications (e.g., dyslipidemia, insulin resistance, and non-alcoholic fatty liver disease) in C57BL/6N mice. The mice were fed a normal diet, an HFD, or an HFD plus AR or LU for 16 weeks. In the HFD-fed mice, AR decreased the adiposity and dyslipidemia by decreasing lipogenesis while increasing fatty acid oxidation, which contributed to better hepatic steatosis. LU also prevented adiposity and hepatic steatosis by suppressing lipogenesis while increasing biliary sterol excretion. Moreover, AR and LU prevented insulin sensitivity by decreasing the level of plasma gastric inhibitory polypeptide and activity of hepatic glucogenic enzymes, which may be linked to the lowering of inflammation as evidenced by the reduced plasma interleukin (IL)-6, IL-1β, and plasminogen activator inhibitor-1 levels. Although the anti-metabolic syndrome effects of AR and LU were similar, the anti-adiposity and anti-dyslipidemic effects of AR were more pronounced. These results in mice with diet-induced obesity suggest that long-term supplementation with AR can prevent adiposity and related metabolic disorders such as dyslipidemia, hepatic steatosis, insulin resistance, and inflammation.

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.

Cooperative role of the glucagon-like peptide-1 receptor and β3-adrenergic-mediated signalling on fat mass reduction through the downregulation of PKA/AKT/AMPK signalling in the adipose tissue and muscle of rats

AIM

To explore the cooperation of GLP-1 receptor and β3-adrenergic receptor (β3-AR)-mediated signalling in the control of fat mass/feeding behaviour by studying the effects of a combined therapy composed of the GLP-1R agonist liraglutide and the β3-AR agonist CL316243.

METHODS

The study included the analysis of key mechanisms regulating lipid/cholesterol metabolism, and thermogenesis in brown (BAT) and epididymal white (eWAT) adipose tissues, abdominal muscle and liver of male rats.

RESULTS

CL316243 (1 mg kg^-1 ) and liraglutide (100 μg kg^-1 ) co-administration over 6 days potentiated an overall negative energy balance (reduction in food intake, body weight gain, fat/non-fat mass ratio, liver fat content, and circulating levels of non-essential fatty acids, triglycerides, very low-density lipoprotein-cholesterol and leptin). These effects were accompanied by increased plasma levels of insulin and IL6. We also observed increased gene expression of uncoupling proteins regulating thermogenesis in BAT/eWAT (Ucp1) and muscle (Ucp2/3). Expression of transcription factor and enzymes involved either in de novo lipogenesis (Chrebp, Acaca, Fasn, Scd1, Insig1, Srebp1) or in fatty acid β-oxidation (Cpt1b) was enhanced in eWAT and/or muscle but decreased in BAT. Pparα and Pparγ, essentials in lipid flux/storage, were decreased in BAT/eWAT but increased in the muscle and liver. Cholesterol synthesis regulators (Insig2, Srebp2, Hmgcr) were particularly over-expressed in muscle. These GLP-1R/β3-AR-induced metabolic effects were associated with the downregulation of cAMP-dependent signalling pathways (PKA/AKT/AMPK).

CONCLUSION

Combined activation of GLP-1 and β3-ARs potentiate changes in peripheral pathways regulating lipid/cholesterol metabolism in a tissue-specific manner that favours a switch in energy availability/expenditure and may be useful for obesity treatment.

Factors involved in white-to-brown adipose tissue conversion and in thermogenesis: a review

Obesity is the result of energy intake chronically exceeding energy expenditure. Classical treatments against obesity do not provide a satisfactory long-term outcome for the majority of patients. After the demonstration of functional brown adipose tissue in human adults, great effort is being devoted to develop therapies based on the adipose tissue itself, through the conversion of fat-accumulating white adipose tissue into energy-dissipating brown adipose tissue. Anti-obesity treatments that exploit endogenous, pharmacological and nutritional factors to drive such conversion are especially in demand. In the present review, we summarize the current knowledge about the various molecules that can be applied in promoting white-to-brown adipose tissue conversion and energy expenditure and the cellular mechanisms involved.

GM13133 is a negative regulator in mouse white adipocytes differentiation and drives the characteristics of brown adipocytes

Obesity is tightly associated with the disturbance of white adipose tissue storing excess energy. Thermogenic adipocytes (brown and beige) exert a critical role of oxidizing nutrients at the high rates through non-shivering thermogenesis. The recruitment of brown characteristics in white adipocytes, termed browning, has been considered as a promising strategy for treating obesity and associated metabolic complications. Recently, long noncoding RNAs play a crucial role in regulating tissue development and participating in disease pathogenesis, yet their effects on the conversion of white into brown-like adipocytes and thermogenic function were not totally understood. Here, we identified a mouse brown adipose specific expressed lncRNA, termed GM13133. Moreover, a considerable amount of GM13133 is expressed in adipocytes and actively modulated by cold, β₃ -adrenergic agonist and cAMP stimuli, implying a potential role in the conversion from white to brown adipocytes. Overexpression of GM13133 did not affect the proliferation of mouse white pre-adipocytes, but inhibited white adipocyte differentiation by decreasing lipid accumulation. The forced expression of GM13133 also significantly drove the conversion of white into brown-like adipocytes with the enhanced mitochondrial biogenesis and the induced expression of brown adipocytes specific markers. A global mRNA analysis further indicated the possible regulatory role of cAMP signaling pathway in GM13133 mediated white-to-brown adipocytes conversion. Our results identified a lncRNA-mediated modulation in primary mouse white adipocyte differentiation and indicate the functional significance of GM13133 in promoting browning of white adipocytes and maintenance of thermogenesis, further providing a potential strategy to treating obesity.

Molecular implications of adenosine in obesity

Adenosine has broad activities in organisms due to the existence of multiple receptors, the differential adenosine concentrations necessary to activate these receptors and the presence of proteins able to synthetize, degrade or transport this nucleoside. All adenosine receptors have been reported to be involved in glucose homeostasis, inflammation, adipogenesis, insulin resistance, and thermogenesis, indicating that adenosine could participate in the process of obesity. Since adenosine seems to be associated with several effects, it is plausible that adenosine participates in the initiation and development of obesity or may function to prevent it. Thus, the purpose of this review was to explore the involvement of adenosine in adipogenesis, insulin resistance and thermogenesis, with the aim of understanding how adenosine could be used to avoid, treat or improve the metabolic state of obesity. Treatment with specific agonists and/or antagonists of adenosine receptors could reverse the obesity state, since adenosine receptors normalizes several mechanisms involved in obesity, such as lipolysis, insulin sensitivity and thermogenesis. Furthermore, obesity is a preventable state, and the specific activation of adenosine receptors could aid in the prevention of obesity. Nevertheless, for the treatment of obesity and its consequences, more studies and therapeutic strategies in addition to adenosine are necessary.

The role of adipose tissue in cancer-associated cachexia

Adipose tissue (fat) is a heterogeneous organ, both in function and histology, distributed throughout the body. White adipose tissue, responsible for energy storage and more recently found to have endocrine and inflammation-modulatory activities, was historically thought to be the only type of fat present in adult humans. The recent demonstration of functional brown adipose tissue in adults, which is highly metabolic, shifted this paradigm. Additionally, recent studies demonstrate the ability of white adipose tissue to be induced toward the brown adipose phenotype - "beige" or "brite" adipose tissue - in a process referred to as "browning." While these adipose tissue depots are under investigation in the context of obesity, new evidence suggests a maladaptive role in other metabolic disturbances including cancer-associated cachexia, which is the topic of this review. This syndrome is multifactorial in nature and is an independent factor associated with poor prognosis. Here, we review the contributions of all three adipose depots - white, brown, and beige - to the development and progression of cancer-associated cachexia. Specifically, we focus on the local and systemic processes involving these adipose tissues that lead to increased energy expenditure and sustained negative energy balance. We highlight key findings from both animal and human studies and discuss areas within the field that need further exploration. Impact statement Cancer-associated cachexia (CAC) is a complex, multifactorial syndrome that negatively impacts patient quality of live and prognosis. This work reviews a component of CAC that lacks prior discussion: adipose tissue contributions. Uniquely, it discusses all three types of adipose tissue, white, beige, and brown, their interactions, and their contributions to the development and progression of CAC. Summarizing key bench and clinical studies, it provides information that will be useful to both basic and clinical researchers in designing experiments, studies, and clinical trials.

Pharmacologic activation of estrogen receptor β increases mitochondrial function, energy expenditure, and brown adipose tissue

Most satiety-inducing obesity therapeutics, despite modest efficacy, have safety concerns that underscore the need for effective peripherally acting drugs. An attractive therapeutic approach for obesity is to optimize/maximize energy expenditure by increasing energy-utilizing thermogenic brown adipose tissue. We used in vivo and in vitro models to determine the role of estrogen receptor β (ER-β) and its ligands on adipose biology. RNA sequencing and metabolomics were used to determine the mechanism of action of ER-β and its ligands. Estrogen receptor β (ER-β) and its selective ligand reprogrammed preadipocytes and precursor stem cells into brown adipose tissue and increased mitochondrial respiration. An ER-β-selective ligand increased markers of tricarboxylic acid-dependent and -independent energy biogenesis and oxygen consumption in mice without a concomitant increase in physical activity or food consumption, all culminating in significantly reduced weight gain and adiposity. The antiobesity effects of ER-β ligand were not observed in ER-β-knockout mice. Serum metabolite profiles of adult lean and juvenile mice were comparable, while that of adult obese mice was distinct, indicating a possible impact of obesity on age-dependent metabolism. This phenotype was partially reversed by ER-β-selective ligand. These data highlight a new role for ER-β in adipose biology and its potential to be a safer alternative peripheral therapeutic target for obesity.-Ponnusamy, S., Tran, Q. T., Harvey, I., Smallwood, H. S., Thiyagarajan, T., Banerjee, S., Johnson, D. L., Dalton, J. T., Sullivan, R. D., Miller, D. D., Bridges, D., Narayanan, R. Pharmacologic activation of estrogen receptor β increases mitochondrial function, energy expenditure, and brown adipose tissue.

Effect of ''Biao-Ben points association'' electro-acupuncture combined with dietary restriction on SIRT1 and UCP1 expression in brown adipose tissue of obese rats

AIM: To observe the effect of "Biao-Ben points association" electro-acupuncture combined with dietary control on SIRT1 and UCP1 expression in brown adipose tissue of obese rats.

METHODS: Forty rats with obesity induced with a high-fat diet were randomly divided into four groups, with 10 rats in each group. Rats in the model control group (C) were continued to be given a high-fat diet. Rats in the electro-acupuncture group (E) were treated with "Biao-Ben points association" electro-acupuncture. The dietary restriction group (R) was fed only 70% of high-fat diet to the control group. The electro-acupuncture combined with dietary restriction group (E + R) was treated with both acupuncture and dietary restriction. After 8 wk of treatment, changes of body weight, fasting glucose, insulin, triglycerides, and total cholesterol were recorded. The expression of silent information regulator 1 (SIRT1) and uncoupling protein 1 (UCP1) mRNA was detected in brown adipose tissue.

RESULTS: Compared with the C group, body weight, FPG, FINS, TG, and TC in the other three intervention groups were significantly lower (P < 0.01); these indexes were also significantly lower in the E + R group than in the other two intervention groups (P < 0.05). Compared with the C group, the expression of SIRT1 in the other three intervention groups was significantly higher (P < 0.01). Compared with the C group, the expression of UPC1 mRNA in the other three intervention groups was significantly higher (P < 0.01); UPC1 mRNA expression in the E + R group was also significantly higher than that in the other two intervention groups (P < 0.05).

CONCLUSION: "Biao-Ben points association" electro-acupuncture and dietary restriction might increase the heat production and result in weight loss by promoting the expression of SIRT1 and UCP1 in brown adipose tissue. The anti-obesity effect of "Biao-Ben points association" electro-acupuncture is comparable to that of dietary restriction, and there exist some synergistic effects between them.

'Adipaging': ageing and obesity share biological hallmarks related to a dysfunctional adipose tissue

The increasing ageing of our societies is accompanied by a pandemic of obesity and related cardiometabolic disorders. Progressive dysfunction of the white adipose tissue is increasingly recognized as an important hallmark of the ageing process, which in turn contributes to metabolic alterations, multi-organ damage and a systemic pro-inflammatory state ('inflammageing'). On the other hand, obesity, the paradigm of adipose tissue dysfunction, shares numerous biological similarities with the normal ageing process such as chronic inflammation and multi-system alterations. Accordingly, understanding the interplay between accelerated ageing related to obesity and adipose tissue dysfunction is critical to gain insight into the ageing process in general as well as into the pathophysiology of obesity and other related conditions. Here we postulate the concept of 'adipaging' to illustrate the common links between ageing and obesity and the fact that, to a great extent, obese adults are prematurely aged individuals.

Classification of Therapeutic and Experimental Drugs for Brown Adipose Tissue Activation: Potential Treatment Strategies for Diabetes and Obesity

OBJECTIVE

Increasing efforts are being made towards pharmacologic activation of brown adipose tissue (BAT) in animals and humans for potential use in the treatment of obesity and diabetes. We and others have reported a number of animal studies using either experimental or therapeutic drugs. There are now efforts to translate these findings to human studies. The goal of this review is to evaluate the various drugs currently being used that have the potential for BAT activation.

METHODS

Drugs were classified into 4 classes based on their mechanism of action. Class 1 drugs include the use of β3 adrenoceptor agonists for BAT activation. Class 2 drugs include drugs that affect norepinephrine levels and activate BAT with the potential of reducing obesity. Class 3 includes activators of peroxisome proliferator-activated receptor-γ in pursuit of lowering blood sugar, weight loss and diabetes and finally Class 4 includes natural products and other emerging drugs with limited information on BAT activation and their effects on diabetes and weight loss.

RESULTS

Class 1 drugs are high BAT activators followed by Class 2 and 3. Some of these drugs have now been extended to diabetes and obesity animal models and human BAT studies. Drugs in Class 3 are used clinically for Type 2 diabetes, but the extent of BAT involvement is unclear.

CONCLUSION

Further studies on the efficacy of these drugs in diabetes and measuring their effects on BAT activation using noninvasive imaging will help in establishing a clinical role of BAT.

Biology of Beige Adipocyte and Possible Therapy for Type 2 Diabetes and Obesity

All mammals own two main forms of fat. 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 instead of inducing fat accumulation can produce energy as heat. Since adult humans possess significant amounts of active brown fat depots and their 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 itself from white adipocytes. Importantly, adult human brown adipocyte appears to be mainly composed of beige-like adipocytes, making this cell type an attractive therapeutic target for obesity and obesity-related diseases. Because many epigenetic changes can affect beige adipocyte differentiation, the knowledge of the circumstances that affect the development of beige adipocyte cells may be important for therapeutic strategies. In this review we discuss some recent observations arising from the great physiological capacity of these cells and their possible role as ways to treat obesity and diabetes mellitus type 2.

Bone Marrow Adipose Tissue: To Be or Not To Be a Typical Adipose Tissue?

Bone marrow adipose tissue (BMAT) emerges as a distinct fat depot whose importance has been proved in the bone-fat interaction. Indeed, it is well recognized that adipokines and free fatty acids released by adipocytes can directly or indirectly interfere with cells of bone remodeling or hematopoiesis. In pathological states, such as osteoporosis, each of adipose tissues - subcutaneous white adipose tissue (WAT), visceral WAT, brown adipose tissue (BAT), and BMAT - is differently associated with bone mineral density (BMD) variations. However, compared with the other fat depots, BMAT displays striking features that makes it a substantial actor in bone alterations. BMAT quantity is well associated with BMD loss in aging, menopause, and other metabolic conditions, such as anorexia nervosa. Consequently, BMAT is sensed as a relevant marker of a compromised bone integrity. However, analyses of BMAT development in metabolic diseases (obesity and diabetes) are scarce and should be, thus, more systematically addressed to better apprehend the bone modifications in that pathophysiological contexts. Moreover, bone marrow (BM) adipogenesis occurs throughout the whole life at different rates. Following an ordered spatiotemporal expansion, BMAT has turned to be a heterogeneous fat depot whose adipocytes diverge in their phenotype and their response to stimuli according to their location in bone and BM. In vitro, in vivo, and clinical studies point to a detrimental role of BM adipocytes (BMAs) throughout the release of paracrine factors that modulate osteoblast and/or osteoclast formation and function. However, the anatomical dissemination and the difficulties to access BMAs still hamper our understanding of the relative contribution of BMAT secretions compared with those of peripheral adipose tissues. A further characterization of the phenotype and the functional regulation of BMAs are ever more required. Based on currently available data and comparison with other fat tissues, this review addresses the originality of the BMAT with regard to its development, anatomy, metabolic properties, and response to physiological cues.