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Research focusing on adipose immunometabolism has been expanded from inflammation in white fat during obesity development to immune cell function regulating thermogenic fat, energy expenditure, and systemic metabolism. This opinion discusses our current understanding of how resident immune cells within the thermogenic fat niche may regulate whole-body energy homeostasis. Furthermore, various types of immune cells can synthesize acetylcholine (ACh) and regulate important physiological functions. We highlight a unique subset of cholinergic macrophages within subcutaneous adipose tissue, termed cholinergic adipose macrophages (ChAMs); these macrophages interact with beige adipocytes through cholinergic receptor nicotinic alpha 2 subunit (CHRNA2) signaling to induce adaptive thermogenesis. We posit that these newly identified thermoregulatory macrophages may broaden our view of immune system functions for maintaining metabolic homeostasis and potentially treating obesity and metabolic disorders.

Brown and beige adipocytes dissipate energy in a nonshivering thermogenesis manner, exerting beneficial effects on metabolic homeostasis. CHCHD10 is a nuclear-encoded mitochondrial protein involved in cristae organization; however, its role in thermogenic adipocytes remains unknown. We identify CHCHD10 as a novel regulator for adipocyte thermogenesis. CHCHD10 is dramatically upregulated during thermogenic adipocyte activation by PPARγ-PGC1α and positively correlated with UCP1 expression in adipose tissues from humans and mice. We generated adipocyte-specific Chchd10 knockout mice (Chchd10-AKO) and found that depleting CHCHD10 leads to impaired UCP1-dependent thermogenesis and energy expenditure in the fasting state, with no effect in the fed state. Lipolysis in adipocytes is disrupted by CHCHD10 deficiency, while augmented lipolysis through ATGL overexpression recovers adipocyte thermogenesis in Chchd10-AKO mice. Consistently, overexpression of Chchd10 activates thermogenic adipocytes. Mechanistically, CHCHD10 deficiency results in the disorganization of mitochondrial cristae, leading to impairment of oxidative phosphorylation complex assembly in mitochondria, which in turn inhibits ATP generation. Decreased ATP results in downregulation of lipolysis by reducing nascent protein synthesis of ATGL, thereby suppressing adipocyte thermogenesis. As a result, Chchd10-AKO mice are prone to develop high-fat diet–induced metabolic disorders. Together, our findings reveal an essential role of CHCHD10 in regulating lipolysis and the thermogenic program in adipocytes.

Recent studies indicate existence of beige adipocytes in adults. Upon activation, beige adipocytes burn energy for thermogenesis and contribute to regulation of energy balance. In this study, we have analyzed whether Jinlida granules (JLD) could activate beige adipocytes. JLD suspended in 0.5% carboxymethyl cellulose (CMC) was gavage fed to db/db mice at a daily dose of 3.8 g/kg. After 10 weeks, body weight, biochemical, and histological analyses were performed. In situ hybridization, immunofluorescence, and western blotting were conducted to test beige adipocyte activation in mice. X9 cells were induced with induction medium and maintenance medium containing 400 μg/mL of JLD. After completion of induction, cells were analyzed by Nile red staining, time polymerase chain reaction (PCR), western blotting, and immunofluorescence to understand the effect of JLD on the activation of beige adipocytes. A molecular docking method was used to preliminarily identify compounds in JLD, which hold the potential activation effect on uncoupling protein 1 (UCP1). JLD treatment significantly improved obesity in db/db mice. Biochemical results showed that JLD reduced blood glucose (GLU), triglyceride (TG), and low-density lipoprotein cholesterol (LDL) levels as well as liver aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels in mice. Hematoxylin and eosin staining (H&E) showed that JLD reduced hepatocyte ballooning changes in the liver. Immunofluorescence showed that JLD increased the expression of the thermogenic protein, UCP1, in the beige adipose tissue of mice. JLD also increased the expression of UCP1 and inhibited the expression of miR-27a in X9 cells. Molecular docking results showed that epmedin B, epmedin C, icariin, puerarin, and salvianolic acid B had potential activation effects on UCP1. The results suggest that JLD may activate beige adipocytes by inhibiting miR-27a expression, thereby promoting thermogenesis in beige adipocytes. This study provides a new pharmacological basis for the clinical use of JLD.

Ear mesenchymal stem cells (EMSCs) have been investigated to differentiate into adipocytes, chondrocytes, and muscle cells in vitro. However, the factors controlling adipogenesis of this stem cell population in vitro, function, and type of adipocytes raised from them are still unclear. Here we found that genetics have a modest effect on adipogenic capacity of EMSCs. Adipocytes differentiated from EMSCs have a potential function in lipid metabolism as indicated by expression of lipogenic genes and this function of EMSC adipocytes is regulated by genetics. EMSCs failed to be differentiated into brite/brown adipocytes due to their lack of a thermogenic program, but adipocytes raised from EMSCs showed a fate of white adipocytes. Overall, our data suggest that EMSCs differentiate into functional white adipocytes in vitro and this is genetic-dependent.

Naringenin is a kind of natural citrus flavonoid with various biological and pharmacological functions. Several studies have reported the anti-obesity effect of naringenin, but its potential mechanism of action (MoA) on beige adipose browning remains unclear. Here, we investigated whether naringenin induces gut microbe-host interactions to promote beige adipose thermogenesis and browning. Naringenin treatment alleviated obesity, increased body's energy expenditure and activated inguinal white adipose tissue thermogenesis and browning in high fat diet (HFD) fed mice. In addition, naringenin improved HFD-induced gut microbiota dysbiosis and increased short-chain fatty acid (SCFA) levels (especially acetic acid) in a host's cecum and serum. Furthermore, using antibiotic treatment and gut microbe transplantation, we found that gut microbes played an indispensable role in naringenin-induced beige fat browning and naringenin-exerted anti-obesity effects. Our study suggests that naringenin activated beige adipose thermogenesis and browning by gut microbe-SCFA-host interactions, which increase energy expenditure and prevent HFD-induced obesity.

Brown and beige fat protect against cold environments and obesity by catabolizing stored energy to generate heat. This process is achieved by controlling thermogenesis-related gene expression and the development of brown/beige fat through the induction of transcription factors, most notably PPARγ. However, the cofactors that induce the expression of thermogenic genes with PPARγ are still not well understood. In this study, we explored the role of SOX4 in adaptive thermogenesis and its relationship with PPARγ.

Beige adipocyte, the third and relatively new type of adipocyte, can emerge in white adipose tissue (WAT) under thermogenic stimulations that is termed as browning of WAT. Recent studies suggest that browning of WAT deserves more attention and therapies targeting browning of WAT can be helpful for reducing obesity. Beyond the major inducers of browning, namely cold and β 3-adrenergic stimulation, beige adipocytes are affected by several factors, and excess adiposity per se may also influence the browning process. The objective of the present review is to provide an overview of recent clinical and preclinical studies on the hormonal and nonhormonal factors that affect the browning of WAT. This review further focuses on the role of obesity per se on browning process.

Brown adipose tissue (BAT) is a specialized tissue for nonshivering thermogenesis to dissipate energy as heat. Although BAT research has long been limited mostly in small rodents, the rediscovery of metabolically active BAT in adult humans has dramatically promoted the translational studies on BAT in health and diseases. Moreover, several remarkable advancements have been made in brown fat biology over the past decade: The molecular and functional analyses of inducible thermogenic adipocytes (socalled beige adipocytes) arising from a developmentally different lineage from classical brown adipocytes have been accelerated. In addition to a well-established thermogenic activity of uncoupling protein 1 (UCP1), several alternative thermogenic mechanisms have been discovered, particularly in beige adipocytes. It has become clear that BAT influences other peripheral tissues and controls their functions and systemic homeostasis of energy and metabolic substrates, suggesting BAT as a metabolic regulator, other than for thermogenesis. This notion is supported by discovering that various paracrine and endocrine factors are secreted from BAT. We review the current understanding of BAT pathophysiology, particularly focusing on its role as a metabolic regulator in small rodents and also in humans.

There is growing interest in the health benefits of natural plant pigments such as anthocyanins and curcumin. In this review, we introduce how these pigments can contribute to the prevention of diabetes and obesity by stimulating glucagon-like peptide-1 (GLP-1) secretion or inducing beige adipocyte formation. Of the anthocyanins, delphinidin 3-rutinoside (D3R) was shown to increase GLP-1 secretion. Pre-administered D3R-rich blackcurrant extract (BCE) significantly ameliorated glucose tolerance after intraperitoneal glucose injection in rats by stimulating the secretion of GLP-1 and subsequently inducing insulin secretion. D3R did not break down significantly in the gastrointestinal tract for at least 45-60 min after BCE administration. An increase in endogenous GLP-1 secretion induced by food-derived factors may help to reduce the dosages of diabetic medicines and prevent diabetes. Curcumin has various biological functions, including anti-obesity and anti-diabetic properties. However, high doses of curcumin have been administered in most animal and human trials to date, due mainly to the poor solubility of native curcumin in water and its low oral bioavailability. We demonstrated that a highly dispersible and bioavailable curcumin formulation (HC), but not native curcumin, induces the formation of beige adipocytes. Furthermore, co-administration of HC and artepillin C (a characteristic constituent of Brazilian propolis) at lower doses significantly induces beige adipocyte formation in mice, but administration of the same dose of HC or artepillin C alone does not. Our studies demonstrate that curcumin formulations or the co-administration of curcumin with other food-derived factors provide effects that native curcumin alone does not.

The full array of cold-responsive cell types within white adipose tissue that drive thermogenic beige adipocyte biogenesis remains undefined. We demonstrate that acute cold challenge elicits striking transcriptomic changes specifically within DPP4+ PDGFRβ+ adipocyte precursor cells, including a β-adrenergic receptor CREB-mediated induction in the expression of the prothermogenic cytokine, Il33. Doxycycline-inducible deletion of Il33 in PDGFRβ+ cells at the onset of cold exposure attenuates ILC2 accumulation and beige adipocyte accrual. These studies highlight the multifaceted roles for adipocyte progenitors and the ability of select mesenchymal subpopulations to relay neuronal signals to tissue-resident immune cells in order to regulate tissue plasticity.

Activation of brown fat thermogenesis increases energy expenditure and alleviates obesity. Sympathetic nervous system (SNS) is important in brown/beige adipocyte thermogenesis. Here we discover a fat-derived “adipokine” neurotrophic factor neurotrophin 3 (NT-3) and its receptor Tropomyosin receptor kinase C (TRKC) as key regulators of SNS growth and innervation in adipose tissue. NT-3 is highly expressed in brown/beige adipocytes, and potently stimulates sympathetic neuron neurite growth. NT-3/TRKC regulates a plethora of pathways in neuronal axonal growth and elongation. Adipose tissue sympathetic innervation is significantly increased in mice with adipocyte-specific NT-3 overexpression, but profoundly reduced in mice with TRKC haploinsufficiency (TRKC +/−). Increasing NT-3 via pharmacological or genetic approach promotes beige adipocyte development, enhances cold-induced thermogenesis and protects against diet-induced obesity (DIO); whereas TRKC + /− or SNS TRKC deficient mice are cold intolerant and prone to DIO. Thus, NT-3 is a fat-derived neurotrophic factor that regulates SNS innervation, energy metabolism and obesity. Activation of brown adipose tissue thermogenesis increases energy expenditure and promotes weight loss in mice. Here the authors identify neurotrophic factor neurotrophin 3 (NT-3) as an adipokine that regulates sympathetic nervous system growth and innervation in adipose tissue and increases white adipose beiging.

We recently showed that NOTUM, a liver-secreted Wnt inhibitor, can acutely promote browning of white adipose. We now report studies of chronic overexpression of NOTUM in liver indicating that it protects against diet-induced obesity and improves glucose homeostasis in mice. Adeno-associated virus (AAV) vectors were used to overexpress GFP or mouse Notum in the livers of male C57BL/6J mice and the mice were fed an obesifying diet. After 14 weeks of high fat, high sucrose diet feeding, the AAV-Notum mice exhibited decreased obesity and improved glucose tolerance compared to the AAV-GFP mice. Gene expression and immunoblotting analysis of the inguinal fat and brown fat revealed increased expression of beige/brown adipocyte markers in the AAV-Notum group, suggesting enhanced thermogenic capacity by NOTUM. A β3 adrenergic receptor agonist-stimulated lipolysis test suggested increased lipolysis capacity by NOTUM. The levels of collagen and C–C motif chemokine ligand 2 (CCL2) in the epididymal white adipose tissue of the AAV-Notum mice were significantly reduced, suggesting decreased fibrosis and inflammation, respectively. RNA sequencing analysis of inguinal white adipose of 4-week chow diet-fed mice revealed a highly significant enrichment of extracellular matrix (ECM) functional cluster among the down-regulated genes in the AAV-Notum group, suggesting a potential mechanism contributing to improved glucose homeostasis. Our in vitro studies demonstrated that recombinant human NOTUM protein blocked the inhibitory effects of WNT3A on brown adipocyte differentiation. Furthermore, NOTUM attenuated WNT3A’s effects on upregulation of TGF-β signaling and its downstream targets. Overall, our data suggest that NOTUM modulates adipose tissue function by promoting thermogenic capacity and inhibiting fibrosis through inhibition of Wnt signaling.

Background Dietary bioactive compounds have been demonstrated to produce several health benefits. Genistein, an isoflavone of soy protein, and resveratrol, a polyphenol from grapes, have been shown to improve insulin sensitivity and to stimulate white adipose tissue (WAT) browning, leading to increased energy expenditure. However, it has not been demonstrated in humans whether genistein or resveratrol have the capacity to stimulate the differentiation of stromal vascular fraction (SVF) cells from white fat into beige adipocytes. Subjects/methods With this aim, we assessed whether stromal vascular fraction cells obtained from biopsies of the subdermal fat depots of subjects with normal body weight (NW) or from subjects with overweight/obesity with (OIR) or without (OIS) insulin resistance were able to differentiate into the beige adipose tissue lineage in vitro, by exposing the cells to genistein, resveratrol, or the combination of both. Results The results showed that SVF cells obtained from NW or OIS subjects were able to differentiate into beige adipocytes according to an increased expression of beige biomarkers including UCP1, PDRM-16, PGC1α, CIDEA, and SHOX2 upon exposure to genistein. However, SVF cells from OIR subjects were unable to differentiate into beige adipocytes with any of the inducers. Exposure to resveratrol or the combination of resveratrol/genistein did not significantly stimulate the expression of browning markers in any of the groups studied. We found that the non-responsiveness of the SVF from subjects with obesity and insulin resistance to any of the inducers was associated with an increase in the expression of endoplasmic reticulum stress markers. Conclusion Consumption of genistein may stimulate WAT browning mainly in NW or OIS subjects. Thus, obesity associated with insulin resistance may be considered as a condition that prevents some beneficial effects of some dietary bioactive compounds.

Background Fat grafting is commonly used in treating soft-tissue defects. However, the basic biology behind fat grafting is still not fully understood. Evidence of adipose browning into beige adipose tissue after fat grafting was revealed, but its role in fat grafting remains unclear. Methods Induced beige adipocytes and adipose-derived stem cells were obtained from human lipoaspirates and labeled with green fluorescent protein. Nude mice were each injected with 300 mg of human lipoaspirate containing green fluorescent protein-labeled adipose-derived stem cells, green fluorescent protein-labeled induced beige adipocytes, or phosphate-buffered saline. Grafted fat was harvested after 1, 4, 8, and 12 weeks for immunohistochemistry and histologic examination. Graft retention, vascularization, and adipogenic gene expression were compared. Results After 7 days' induction, adipocytes achieved browning with multilocular lipid droplets, increased mitochondria, and up-regulated browning gene expression. Fat graft retention rates at week 12 were significantly higher after injection of induced beige adipocytes than after injection of phosphate-buffered saline (46.0 ± 4.9 percent versus 31.0 ± 3.6 percent; p = 0.01), but were similar after injection of induced beige adipocytes and adipose-derived stem cells (p > 0.05). Induced beige adipocytes underwent rewhitening into white adipocytes and showed up-regulation of peroxisome proliferator-activated receptor-γ expression. Induced beige adipocytes enhanced angiogenesis, but were not active in forming vessel structures. Conclusions Induced beige adipocytes and adipose-derived stem cells were comparable in improving fat graft retention rates. Induced beige adipocytes promote angiogenesis in a paracrine manner and are prone to rewhitening after fat grafting.

Thermogenic brown or beige adipocytes dissipate energy in the form of heat and thereby counteract obesity and related metabolic complications. The microRNA cluster, miR-130b/301b, is highly expressed in adipose tissues and has been implicated in metabolic diseases as a post-transcriptional regulator of mitochondrial biogenesis and lipid metabolism. We investigated the roles of miR-130b/301b in regulating beige adipogenesis in vivo and in vitro. miR-130b/301b declined in adipose progenitor cells during beige adipogenesis, while forced overexpression of miR-130b-3p or miR-301b-3p suppressed uncoupling protein 1 (UCP1) and mitochondrial respiration, suggesting a decline in miR-130b-3p or miR-301b-3p is required for adipocyte precursors to develop the beige phenotype. Mechanistically, miR-130b/301b directly targeted AMP-activated protein kinase (AMPKα1) and suppressed peroxisome proliferator-activated receptor gamma coactivator 1-alpha (Pgc-1α), key regulators of brown adipogenesis and mitochondrial biogenesis. Mice lacking the miR-130b/301b microRNA cluster showed reduced visceral adiposity and less weight gain. miR-130b/301b null mice exhibited improved glucose tolerance, increased UCP1 and AMPK activation in subcutaneous fat (iWAT), and increased response to cold-induced energy expenditure. Together, these data identify the miR-130b/301b cluster as a new regulator that suppresses beige adipogenesis involving PGC-1α and AMPK signaling in iWAT and is therefore a potential therapeutic target against obesity and related metabolic disorders.

Adipose tissue (AT) is highly plastic and heterogeneous in response to environmental and nutritional changes. The development of heat-dissipating beige adipocytes in white AT (WAT) through a process known as browning (or beiging) has garnered much attention as a promising therapeutic strategy for obesity and its related metabolic complications. This is due to its inducibility in response to thermogenic stimulation and its association with improved metabolic health. WAT consists of adipocytes, nerves, vascular endothelial cells, various types of immune cells, adipocyte progenitor cells, and fibroblasts. These cells contribute to the formation of beige adipocytes through the release of protein factors that significantly influence browning capacity. In addition, inter-organ crosstalk is also important for beige adipocyte biogenesis. Here, we summarize recent findings on fat depot-specific differences, secretory factors participating in intercellular and inter-organ communications that regulate the recruitment of thermogenic beige adipocytes, as well as challenges in targeting beige adipocytes as a potential anti-obese therapy.

Objective:Recent studies have identified key transcriptional regulators of brown adipose tissue (BAT) differentiation and function, but posttranscriptional control of this network by microRNAs remains incompletely understood. MiR-33 critically regulates genes involved in metabolic pathways, including cholesterol efflux, reverse cholesterol transport, fatty acid oxidation, and autophagy. Given its role in metabolic homeostasis, we investigated whether miR-33 participates in the regulation of BAT activity, white adipose beiging, and adaptive thermogenesis.Approach and Results:Using primary immortalized brown adipocytes and 10T1/2 cells, we show that miR-33 levels are reduced in brown fat differentiated cells compared with preadipocytes and in response to thermogenic activators. Furthermore, in mice exposed to cold, levels of miR-33 in BAT are rapidly downregulated consistent with a role for miR-33 in repressing adaptive thermogenesis. Using in silico prediction, we identified numerous putative miR-33 target genes in the thermogenic pathway conserved in mice and humans, including regulators of brown adipocyte differentiation and function and mitochondrial activity. We focused our investigation on transcriptional regulators of UCP1 (uncoupling protein 1) and of BAT-enriched genes and demonstrate that miR-33 repressesZfp516,Dio2, andPpargc1ain vitro and in vivo. Treatment of mice with inhibitors of miR-33 increased expression of these miR-33 target genes in brown and subcutaneous white adipose tissue, upregulating expression of UCP1, and rendering mice resistant to cold challenge.Conclusions:Collectively, our findings demonstrate that miR-33 targets key genes involved in BAT activation and white adipose beiging and expand our understanding of how miR-33 coordinately regulates pathways involved in metabolic homeostasis.

Brown adipose tissue (BAT) and beige fat function in energy expenditure in part due to their role in thermoregulation, making these tissues attractive targets for treating obesity and metabolic disorders. While prolonged cold exposure promotes de novo recruitment of brown adipocytes, the exact sources of cold-induced thermogenic adipocytes are not completely understood. Here, we identify transient receptor potential cation channel subfamily V member 1 (Trpv1)+ vascular smooth muscle (VSM) cells as previously unidentified thermogenic adipocyte progenitors. Single-cell RNA sequencing analysis of interscapular brown adipose depots reveals, in addition to the previously known platelet-derived growth factor receptor (Pdgfr)α-expressing mesenchymal progenitors, a population of VSM-derived adipocyte progenitor cells (VSM-APC) expressing the temperature-sensitive cation channel Trpv1. We demonstrate that cold exposure induces the proliferation of Trpv1+ VSM-APCs and enahnces their differentiation to highly thermogenic adipocytes. Together, these findings illustrate the landscape of the thermogenic adipose niche at single-cell resolution and identify a new cellular origin for the development of brown and beige adipocytes.

Adipose tissue is a complex organ consisting of a mixture of mature adipocytes and stromal vascular cells. It displays a remarkable ability to adapt to environmental and dietary cues by changing its morphology and metabolic capacity. This plasticity is demonstrated by the emergence of interspersed thermogenic beige adipocytes within white depots in response to catecholamines secretion. Coordinated cellular interaction between different cell types within the tissue and a fine-tuned transcriptional program synergistically take place to promote beige remodeling. However, both cell–cell interactions and molecular mechanisms governing beige adipocyte appearance and maintenance are poorly understood. In this and the previous issue of Genes & Development, Shao and colleagues (pp. 1461–1474) and Shan and colleagues (pp. 1333–1338) advance our understanding of these issues and, in doing so, highlight potential therapeutic strategies to combat obesity-associated diseases.

Brown/beige adipocyte thermogenesis is a process that is important for energy balance. The thermogenesis of brown/beige adipocytes occurs in the mitochondria, which is modulated by the dynamic balance between mitochondrial fusion and fission. Mitophagy is also involved in mitochondrial dynamics. The sorting and assembly machinery (SAM) complex protein, SAMM50, plays a key role in mitochondrial dynamics and quality control through regulating mitophagy. However, the roles of SAMM50 in the thermogenesis of beige adipocytes remain unknown. Thus, the objective of this study was to conduct functional analyses of SAMM50. The expression of mitochondrial fusion genes was repressed by SAMM50 knockdown but was not altered by SAMM50 overexpression. These results agreed with the distribution of the fluorescence-stained mitochondria and an mtDNA copy number. In contrast, the expression of mitochondrial fission genes showed an opposite outcome. As a result, suppression by the SAMM50 shRNA inhibited the expression of thermogenic genes (UCP1, PPARGC1A, DIO2, ELOVL3, CIDEA, and CIDEC) and mitochondrial-related genes (CYCS, COX7A1, TFAM, CPT1B, and CPT2). Conversely, SAMM50 overexpression promoted the expression of the thermogenic genes and mitochondrial genes. Thus, SAMM50 links the balance between the mitochondrial dynamics and thermogenesis of beige adipocytes.

Obesity, which is associated with type 2 diabetes, is a threat to human health. There are studies, which suggest that some compounds can induce browning of white adipocytes to combat obesity. In this study, we selected nonivamide, an analog of capsaicin, to detect whether it influenced the browning of porcine white adipocytes. First, we found 25 μM nonivamide promoted apoptosis of porcine subcutaneous pre-adipocytes. After pre-adipocytes differentiation, nonivamide inhibited adipogenesis by reducing the expressions of Pparγ, Cebpα, while it promoted lipolysis by up-regulating Hsl, Atgl. Nonivamide also induced browning of porcine subcutaneous adipocytes by up-regulating the expression of brown and beige adipocyte gene markers, such as Prdm16, Cidea, and Slc27a1. Additionally, thermogenesis gene markers Cpt1a and Cpt1b were significantly up-regulated by nonivamide. Furthermore, nonivamide promoted mitochondrial biogenesis by up-regulating the expression of Tfam, Nrf1, Nrf2, and Tomm20. In conclusion, nonivamide is a potent compound to induce porcine adipocyte browning for treating obesity.

Background Effective stem cell therapy is dependent on the stem cell quality that is determined by their differentiation potential, impairment of which leads to poor engraftment and survival into the target cells. However, limitations in our understanding and the lack of reliable markers that can predict their maturation efficacies have hindered the development of stem cells as an effective therapeutic strategy. Our previous study identified CD10, a pro-adipogenic, depot-specific prospective cell surface marker of human adipose-derived stem cells (ASCs). Here, we aim to determine if CD10 can be used as a prospective marker to predict mature adipocyte quality and play a direct role in adipocyte maturation. Methods We first generated 14 primary human subject-derived ASCs and stable immortalized CD10 knockdown and overexpression lines for 4 subjects by the lentiviral transduction system. To evaluate the role of CD10 in adipogenesis, the adipogenic potential of the human subject samples were scored against their respective CD10 transcript levels. Assessment of UCP1 expression levels was performed to correlate CD10 levels to the browning potential of mature ASCs. Quantitative polymerase chain reaction (qPCR) and Western blot analysis were performed to determine CD10-dependent regulation of various targets. Seahorse analysis of oxidative metabolism and lipolysis assay were studied. Lastly, as a proof-of-concept study, we used CD10 as a prospective marker for screening nuclear receptor ligands library. Results We identified intrinsic CD10 levels as a positive determinant of adipocyte maturation as well as browning potential of ASCs. Interestingly, CD10 regulates ASC’s adipogenic maturation non-canonically by modulating endogenous lipolysis without affecting the classical peroxisome proliferator-activated receptor gamma (PPARγ)-dependent adipogenic pathways. Furthermore, our CD10-mediated screening analysis identified dexamethasone and retinoic acid as stimulator and inhibitor of adipogenesis, respectively, indicating CD10 as a useful biomarker for pro-adipogenic drug screening. Conclusion Overall, we establish CD10 as a functionally relevant ASC biomarker, which may be a prerequisite to identify high-quality cell populations for improving metabolic diseases.

Mammalian adipose tissue can be divided into two major types, namely, white adipose tissue (WAT) and brown adipose tissue (BAT). According to classical view, the main function of WAT is to store excess energy in the form of triglycerides, while BAT is a thermogenic tissue that acts a pivotal part in maintaining the core body temperature. White adipocytes display high plasticity and can transdifferentiate into beige adipocytes which have many similar morphological and functional properties with brown adipocytes under the stimulations of exercise, cold exposure and other factors. This phenomenon is also known as ‘browning of WAT’. In addition to transdifferentiation, beige adipocytes can also come from de novo differentiation from tissue-resident progenitors. Activating BAT and inducing browning of WAT can accelerate the intake of glycolipids and reduce the insulin secretion requirement, which may be a new strategy to improve glycolipids metabolism and insulin resistance of obese and type 2 diabetes mellitus (T2DM) patients. This review mainly discusses the significance of brown and beige adipose tissues in the treatment of obesity and T2DM, and focuses on the effect of the browning agent on obesity and T2DM, which provides a brand-new theoretical reference for the prevention and treatment of obesity and T2DM.

Beige/brite adipocytes, which express high levels of uncoupling protein 1 (UCP1) to generate heat using stored triglycerides, are induced under specific stimuli such as cold exposure in inguinal white adipose tissue (iWAT). Although extracellular microenvironments such as extracellular matrix (ECM) stiffness are known to regulate cell behaviors, including cell differentiation into adipocytes, the effect on iWAT cells is unknown. In this study, we show that rigid ECM promotes the cell spreading of iWAT-derived preadipocytes. Furthermore, the expression of UCP1 and other thermogenic genes in iWAT cells is promoted when the cells are cultured on rigid ECM. The expression of mTOR, a kinase known to regulate the differentiation to beige adipocytes, is decreased on rigid substrates. These results suggest that ECM stiffness plays an important role in the differentiation to beige adipocytes.

White adipose tissue (WAT) browning may have beneficial effects for treating metabolic syndrome. miRNA are important regulators of the differentiation, development, and function of brown and beige adipocytes. Here, we found that the cold-inducible miRNA17-92 cluster is enriched in brown adipose tissue (BAT) compared with WAT. Overexpression of the miR17-92 cluster in C3H10T1/2 cells, a mouse mesenchymal stem cell line, enhanced the thermogenic capacity of adipocytes. Furthermore, we observed a significant reduction in adiposity in adipose tissue-specific miR17-92 cluster transgenic (TG) mice. This finding is partly explained by dramatic increases in white fat browning and energy expenditure. Interestingly, the miR17-92 cluster stimulated WAT browning without altering BAT activity in mice. In addition, when we removed the intrascapular BAT (iBAT), the TG mice could maintain their body temperature well under cold exposure. At the molecular level, we found that the miR17-92 cluster targets Rb1, a beige cell repressor in WAT. The present study reveals a critical role for the miR17-92 cluster in regulating WAT browning. These results may be helpful for better understanding the function of beige fat, which could compensate for the lack of BAT in humans, and may open new avenues for combatting metabolic syndrome.

Adipose thermogenesis is the energy lost as heat through metabolism of macronutrients in specialized fat cells, or adipocytes (1). This program is activated by neuronal, hormonal, and metabolic cues in response to cold temperature, dietary excess, and time of day. The capacity of thermogenic adipocytes to dissipate macronutrient calories as heat is vital to body temperature defense in rodents and, likely, human infants. In adult humans, this tissue serves as a catabolic "sink" to burn off excess blood macronutrients, and its activity is linked to improved body weight regulation, glucose and lipid control, and cardiometabolic health (2). Stimulating adipose thermogenesis is an appealing strategy to counteract metabolic disruptions, such as obesity and type 2 diabetes, but has yet to yield a pharmacotherapy that is both safe and efficacious. However, deeper interrogation of heat-producing macronutrient pathways and the emerging roles of macronutrients in shaping thermogenic capacity offer the possibility of finally unlocking this distinct biology.

Adipocytes play an essential role in the maintenance of whole-body energy homeostasis. White adipocytes regulate energy storage, whereas brown and beige adipocytes regulate energy expenditure and heat production. De novo production of adipocytes (i.e. adipogenesis) and their functions are dynamically controlled by environmental cues. Environmental changes (e.g. temperature, nutrients, hormones, cytokines) are transmitted via intracellular signaling to facilitate short-term responses and long-term adaptation in adipocytes; however, the molecular mechanisms that link the environment and epigenome are poorly understood. Our recent studies have demonstrated that environmental cues dynamically regulate interactions between transcription factors and epigenomic chromatin regulators, which together trigger combinatorial changes in chromatin structure to influence gene expression in adipocytes. Thus, environmental sensing by the concerted action of multiple chromatin-associated protein complexes is a key determinant of the epigenetic regulation of adipocyte functions.

Although the optimal therapy for myocardial infarction includes reperfusion to restore blood flow to the ischemic area, myocardial injury after ischemia/reperfusion usually leads to an inflammatory response, oxidative stress, and cardiomyocyte apoptosis. In this study, rat adipose-derived stem cells were differentiated into low-thermogenic beige adipocytes (LBACs) and high-thermogenic beige adipocytes (HBACs) to study the different cardioprotective effects of heterogeneous expression of brown adipocytes. We found that antioxidant and antiapoptotic factors in H9c2 cardiomyocytes were upregulated by high levels of secreted FGF21 in HBAC conditioned medium (HBAC-CM), whereas FGF21 in HBAC-CM did not affect antioxidative or antiapoptotic cell death in H9c2 cardiomyocytes with Nrf2 knockdown. These results show that NRF2 mediates antioxidative and antiapoptotic effects through the HBAC-secreted factor FGF21. Consistent with this finding, the expression of antioxidant and antiapoptotic genes was upregulated by highly secreted FGF21 after HBAC-CM treatment compared to LBAC-CM treatment in H9c2 cardiomyocytes via NRF2 activation. Furthermore, HBAC-CM significantly attenuated ischemic rat heart tissue injury via NRF2 activation. Based on these findings, we propose that HBAC-CM exerts beneficial effects in rat cardiac ischemia/reperfusion injury by modulating NRF2 and has potential as a promising therapeutic agent for myocardial infarction.

Background Antiretroviral therapy (ART) containing integrase strand transfer inhibitors (INSTIs) has been associated with weight gain in both ART initiation and switch studies, especially in women, but the underlying mechanisms are unclear. Methods The effects of dolutegravir (DTG) on food intake, energy expenditure, oxygen consumption in female mice, and gene expression from adipose tissues were assessed. Human and murine preadipocytes were treated with DTG either during differentiation into mature brown/beige adipocytes or postdifferentiation. Lipid accumulation, lipolysis, β-adrenergic response, adipogenic markers, mitochondrial respiration, and insulin response were analyzed. Results Two-week administration of DTG to female mice reduced energy expenditure, which was accompanied by decreased uncoupling protein 1 (UCP1) expression in brown/beige adipose tissues. In vitro studies showed that DTG significantly reduced brown adipogenic markers, especially UCP1 in brown and beige adipocytes, whereas drugs from other classes did not. Furthermore, a loss of UCP1 by DTG led to a decrease in mitochondrial complex IV component, followed by a reduction in mitochondrial respiratory capacity and reduced insulin-stimulated glucose uptake. Conclusions Our findings show that DTG targets UCP1 and mitochondrial functions in brown and beige adipocytes and disrupts thermogenic functions in preclinical models, providing the potential mechanisms by which DTG suppresses energy expenditure leading to weight gain.

During the first month of postnatal life, adipose tissue depots of mice go through a drastic, but transient, remodeling process. Between postnatal days 10 and 20, several white fat depots display a strong and sudden surge in beige adipocyte emergence that reverts until day 30. At the same time, brown fat depots appear to undergo an opposite phenomenon. We comprehensively describe these events, their depot specificity and known environmental and genetic interactions, such as maternal diet, housing temperature and mouse strain. We further discuss potential mechanisms and plausible purposes, including the tempting hypothesis that postnatal transient remodeling creates a lasting adaptive capacity still detectable in adult animals. Finally, we propose postnatal adipose tissue remodeling as a model process to investigate mechanisms of beige adipocyte recruitment advantageous to cold exposure or adrenergic stimulation in its entirely endogenous sequence of events without external manipulation.

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

Non-alcoholic steatohepatitis (NASH) is linked to adipose tissue dysfunction, with weight loss being the only treatment shown to reverse it. Due to this correlation with obesity, the study of adipose tissue and adipocytes is an important step in understanding the pathogenesis of this disease. Here, we describe the isolation process of the stromal vascular fraction (SVF) of adipose tissue. The SVF contains the foundational cells that will differentiate into adipocytes. These cells can be isolated and subsequently differentiated in vitro into white and beige adipocytes. We outline the in vitro differentiation of pre-adipocytes into cultured white and beige adipocytes using both human and mouse adipose tissue.

Beige adipocytes possess the morphological and biochemical characteristics of brown adipocytes, including the mitochondrial uncoupling protein (UCP)1. Mesenchymal stem cells (MSCs) are somatic multipotent progenitors which differentiate into lipid‐laden adipocytes. Induction of MSC adipogenesis under hypothermic culture conditions (ie 32°C) promotes the appearance of a beige adipogenic phenotype, but the stability of this phenotypic switch after cells are returned to normothermic conditions of 37°C has not been fully examined. Here, cells transferred from 32°C to 37°C retained their multilocular beige‐like morphology and exhibited an intermediate gene expression profile, with both beige‐like and white adipocyte characteristics while maintaining UCP1 protein expression. Metabolic profile analysis indicated that the bioenergetic status of cells initially differentiated at 32°C adapted post‐transfer to 37°C, showing an increase in mitochondrial respiration and glycolysis. The ability of the transferred cells to respond under stress conditions (eg carbonyl cyanide‐4‐phenylhydrazone (FCCP) treatment) demonstrated higher functional capacity of enzymes involved in the electron transport chain and capability to supply substrate to the mitochondria. Overall, MSC‐derived adipocytes incubated at 32°C were able to remain metabolically active and retain brown‐like features after 3 weeks of acclimatization at 37°C, indicating these phenotypic characteristics acquired in response to environmental conditions are not fully reversible.

Human beige adipocytes (BAs) have potential utility for the development of therapeutics to treat diabetes and obesity-associated diseases. Although several reports have described the generation of beige adipocytes in vitro, their potential utility in cell therapy and drug discovery has not been reported. Here, we describe the generation of BAs from human adipose-derived stem/stromal cells (ADSCs) in serum-free medium with efficiencies >90%. Molecular profiling of beige adipocytes shows them to be similar to primary BAs isolated from human tissue. In vitro, beige adipocytes exhibit uncoupled mitochondrial respiration and cAMP-induced lipolytic activity. Following transplantation, BAs increase whole-body energy expenditure and oxygen consumption, while reducing body-weight in recipient mice. Finally, we show the therapeutic utility of BAs in a platform for high-throughput drug screening (HTS). These findings demonstrate the potential utility of BAs as a cell therapeutic and as a tool for the identification of drugs to treat metabolic diseases., Methods to generate beige adipocytes from a human cell source are inefficient. Here, the authors present a protocol that efficiently generates beige adipocytes from human adipose-derived stem cells (ADSCs), which have potential utility in therapeutic development relating to metabolic diseases such as type 2 diabetes.

Remodeling of energy-storing white fat into energy-consuming beige fat has led to a promising new approach to alleviate adiposity. Several studies have shown adipokines can induce white adipose tissue (WAT) beiging through autocrine or paracrine actions. Betatrophin, a novel adipokine, has been linked to energy expenditure and lipolysis but not clearly clarified. Here, we using high-fat diet-induced obesity to determine how betatrophin modulate beiging and adiposity. We found that betatrophin-knockdown mice displayed less white fat mass and decreased plasma TG and NEFA levels. Consistently, inhibition of betatrophin leads to the phenotype change of adipocytes characterized by increased mitochondria contents, beige adipocytes and mitochondria biogenesis-specific markers both in vivo and in vitro. Of note, blocking AMP-activated protein kinase (AMPK) signaling pathway is able to abolish enhanced beige-like characteristics in betatrophin-knockdown adipocytes. Collectively, downregulation of betatrophin induces beiging in white adipocytes through activation of AMPK signaling pathway. These processes suggest betatrophin as a latent therapeutic target for obesity.

Despite extensive investigation, the mechanisms underlying adipogenesis are not fully understood. We previously identified proliferative cells in adipose tissue expressing adipocyte-specific genes, which were named small proliferative adipocytes (SPA). In this study, we investigated the characteristics and roles of SPA in adipose tissue. Epididymal and inguinal fat was digested by collagenase, and then SPA were separated by centrifugation from stromal vascular cells (SVC) and mature white adipocytes. To clarify the feature of gene expression in SPA, microarray and real-time PCR were performed. The expression of adipocyte-specific genes and several neuronal genes was increased in the order of SVC

Beige adipocytes have become a promising therapeutic target to combat obesity. Our senior author Dr. B. Xue previously discovered a transient but significant induction of beige adipocytes in mice during early postnatal development, which peaked at postnatal day (P) 20 and then disappeared thereafter. However, the physiological mechanism underlying the transient induction of the developmental beige cells remains mystery. Interestingly, there exists a postnatal surge of leptin in mice at P10 before the appearance of the developmental beige adipocytes. Given the neurotropic effect of leptin during neuronal development and its role in activating the sympathetic nervous system (SNS), we tested the hypothesis that postnatal leptin surge is required for the transient induction of developmental beige adipocytes through sympathetic innervation. Unlike wild-type (WT) mice that were able to acquire the developmentally induced beige adipocytes at P20, ob/ob mice had much less uncoupling protein 1 (UCP1)-positive multilocular cells in inguinal white adipose tissue at the same age. This was consistent with reduced expression of UCP1 mRNA and protein levels in white fat of ob/ob mice. In contrast, daily injection of ob/ob mice with leptin between P8 and P16, mimicking the postnatal leptin surge, largely rescued the ability of these mice to acquire the developmentally induced beige adipocytes at P20, which was associated with enhanced sympathetic nerve innervation assessed by whole mount adipose tissue immunostaining of tyrosine hydroxylase. Our data demonstrate that the postnatal leptin surge is essential for the developmentally induced beige adipocyte formation in mice, possibly through increasing sympathetic nerve innervation.