Beige adipocytes mediate the neuroprotective and anti-inflammatory effects of subcutaneous fat in obese mice

Visceral obesity increases risk of cognitive decline in humans, but subcutaneous adiposity does not. Here, we report that beige adipocytes are indispensable for the neuroprotective and anti-inflammatory effects of subcutaneous fat. Mice lacking functional beige fat exhibit accelerated cognitive dysfunction and microglial activation with dietary obesity. Subcutaneous fat transplantation also protects against chronic obesity in wildtype mice via beige fat-dependent mechanisms. Beige adipocytes restore hippocampal synaptic plasticity following transplantation, and these effects require the anti-inflammatory cytokine interleukin-4 (IL4). After observing beige fat-mediated induction of IL4 in meningeal T-cells, we investigated the contributions of peripheral lymphocytes in donor fat. There was no sign of donor-derived lymphocyte trafficking between fat and brain, but recipient-derived lymphocytes were required for the effects of transplantation on cognition and microglial morphology. These findings indicate that beige adipocytes oppose obesity-induced cognitive impairment, with a potential role for IL4 in the relationship between beige fat and brain function.

Beiging Modulates Inflammatory Adipogenesis in Salt-Treated and MEK6-Transfected Adipocytes

To investigate whether the beiging process changes the interactive effects of salt and MEK6 gene on inflammatory adipogenesis, the salt treatment (NaCl 50 mM) and MEK6 transfection of Tg^(+/+) cells were performed with white adipocytes (WAT) and beige-like-adipocytes (BLA). BLA induced by T3 were confirmed by UCP-1 expression and the MEK6 protein was 3.5 times higher in MEK6 transfected WAT than the control. The adipogenic genes, PPAR-γ and C/EBP-α, were 1.5 times more highly expressed in the salt-treated groups than the non-salt-treated groups, and adipogenesis was greatly increased in Tg^(+/+) WAT compared to non-transfected Tg^(−/−). The adipogenesis induced by salt treatment and MEK6 transfection was significantly reduced in BLA. The inflammatory adipocytokines, TNF-α, IL-1β, and IL-6, were increased in the salt-treated Tg^(+/+) WAT, but an anti-inflammation biomarker, the adiponectin/leptin ratio, was reduced in Tg^(+/+), to tenth of that in Tg^(−/−). However, the production of adipocytokines in WAT was strongly weakened in BLA, although a combination of salt and MEK6 transfection had the most significant effects on inflammation in both WAT and BLA. Oxygen consumption in mitochondria was maximized in salt-treated and MEK6 transfected WAT, but it was decreased by 50% in BLA. In conclusion, beiging controls the synergistic effects of salt and MEK6 on adipogenesis, inflammation, and energy expenditure.

The natural compound rutaecarpine promotes white adipocyte browning through activation of the AMPK-PRDM16 axis

The prevalence of obesity is increasing globally and is associated with many metabolic disorders, such as type 2 diabetes and cardiovascular diseases. In recent years, a number of studies suggest that promotion of white adipose browning represents a promising strategy to combat obesity and its related metabolic disorders. The aim of this study was to identify compounds that induce adipocyte browning and elucidate their mechanism of action. Among the 500 natural compounds screened, a small molecule named Rutaecarpine, was identified as a positive regulator of adipocyte browning both in vitro and in vivo. KEGG pathway analysis from RNA-seq data suggested that the AMPK signaling pathway was regulated by Rutaecarpine, which was validated by Western blot analysis. Furthermore, inhibition of AMPK signaling mitigated the browning effect of Rutaecaripine. The effect of Rutaecaripine on adipocyte browning was also abolished upon deletion of Prdm16, a downstream target of AMPK pathway. In collusion, Rutaecarpine is a potent chemical agent to induce adipocyte browning and may serve as a potential drug candidate to treat obesity.

Histone H3 methyltransferase Ezh2 promotes white adipocytes but inhibits brown and beige adipocyte differentiation in mice

Obesity is a disease characterized by imbalance between energy intake and expenditure, excessive energy store in white adipocytes, but brown and beige adipocytes consume energy to relieve obesity. In this study, we want to explore the role of the histone H3 methyltransferase Ezh2 in the differentiation of white, brown and beige adipocytes with Ezh2 conditional knockout mice (Ezh2^flox/floxPrx1-cre) and mouse embryonic fibroblasts (MEFs). The results showed that Ezh2-deficient mice have a leaner phenotype and less white adipose tissues. The morphological changes in the adipose tissue included smaller white adipose tissue depots, white adipocytes with smaller diameter, smaller lipid droplets inside the brown adipocytes and more beige adipocytes in the Ezh2-deficient mice compared with the control. The differentiation markers of white adipocytes in Ezh2 knockout mice decreased; Ucp1 and other browning markers increased in brown and beige adipocytes. The Ezh2 knockout mice could better tolerate cold stimulation, and they can also resist obesity and insulin resistance induced by a high-fat diet. The Ezh2 inhibitor GSK126 could inhibit the differentiation of MEFs into white adipocytes but promote their differentiation into brown/beige adipocytes. The H3K27me3 demethylase Jmjd3/UTX inhibitor GSKJ4 inhibited MEFs' differentiation into brown/beige adipocytes. These results showed that Ezh2 promotes the differentiation of white adipocytes and inhibits the differentiation of brown and beige adipocytes in vivo and in vitro through its methylase activity and this may represent new knowledge for obesity therapeutic strategy.

Lactate fluxes mediated by the monocarboxylate transporter-1 are key determinants of the metabolic activity of beige adipocytes

Activation of energy-dissipating brown/beige adipocytes represents an attractive therapeutic strategy against metabolic disorders. While lactate is known to induce beiging through the regulation of Ucp1 gene expression, the role of lactate transporters on beige adipocytes' ongoing metabolic activity remains poorly understood. To explore the function of the lactate-transporting monocarboxylate transporters (MCTs), we used a combination of primary cell culture studies, 13C isotopic tracing, laser microdissection experiments, and in situ immunofluorescence of murine adipose fat pads. Dissecting white adipose tissue heterogeneity revealed that the MCT1 is expressed in inducible beige adipocytes as the emergence of uncoupling protein 1 after cold exposure was restricted to a subpopulation of MCT1-expressing adipocytes suggesting MCT1 as a marker of inducible beige adipocytes. We also observed that MCT1 mediates bidirectional and simultaneous inward and outward lactate fluxes, which were required for efficient utilization of glucose by beige adipocytes activated by the canonical β3-adrenergic signaling pathway. Finally, we demonstrated that significant lactate import through MCT1 occurs even when glucose is not limiting, which feeds the oxidative metabolism of beige adipocytes. These data highlight the key role of lactate fluxes in finely tuning the metabolic activity of beige adipocytes according to extracellular metabolic conditions and reinforce the emerging role of lactate metabolism in the control of energy homeostasis.

Recruitment of Thermogenic Fat: Trigger of Fat Burning

Brown and beige adipose tissues possess the remarkable capacity to convert energy into heat, which potentially opens novel therapeutic perspectives targeting the epidemic of metabolic syndromes such as obesity and type 2 diabetes. These thermogenic fats implement mitochondrial oxidative phosphorylation and uncouple respiration to catabolize fatty acids and glucose, which leads to an increase in energy expenditure. In particular, beige adipocytes that arise in white adipose tissue display their thermogenic capacity through various noncanonical mechanisms. This review aims to summarize the general overview of thermogenic fat, especially including the UCP1-independent adaptive thermogenesis and the emerging mechanisms of "beiging", which may provide more evidence of targeting thermogenic fat to counteract obesity and other metabolic disorders in humans.

Diphyllin Improves High-Fat Diet-Induced Obesity in Mice Through Brown and Beige Adipocytes

Brown adipose tissue (BAT) and beige adipose tissue dissipate metabolic energy and mediate nonshivering thermogenesis, thereby boosting energy expenditure. Increasing the browning of BAT and beige adipose tissue is expected to be a promising strategy for combatting obesity. Through phenotype screening of C3H10-T1/2 mesenchymal stem cells, diphyllin was identified as a promising molecule in promoting brown adipocyte differentiation. In vitro studies revealed that diphyllin promoted C3H10-T1/2 cell and primary brown/beige preadipocyte differentiation and thermogenesis, which resulted increased energy consumption. We synthesized the compound and evaluated its effect on metabolism in vivo. Chronic experiments revealed that mice fed a high-fat diet (HFD) with 100 mg/kg diphyllin had ameliorated oral glucose tolerance and insulin sensitivity and decreased body weight and fat content ratio. Adaptive thermogenesis in HFD-fed mice under cold stimulation and whole-body energy expenditure were augmented after chronic diphyllin treatment. Diphyllin may be involved in regulating the development of brown and beige adipocytes by inhibiting V-ATPase and reducing intracellular autophagy. This study provides new clues for the discovery of anti-obesity molecules from natural products.

Cold-induced beigeing of stem cell-derived adipocytes is not fully reversible after return to normothermia

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.

NFIA differentially controls adipogenic and myogenic gene program through distinct pathways to ensure brown and beige adipocyte differentiation

The transcription factor nuclear factor I-A (NFIA) is a regulator of brown adipocyte differentiation. Here we show that the C-terminal 17 amino acid residues of NFIA (which we call pro#3 domain) are required for the transcriptional activity of NFIA. Full-length NFIA—but not deletion mutant lacking pro#3 domain—rescued impaired expression of PPARγ, the master transcriptional regulator of adipogenesis and impaired adipocyte differentiation in NFIA-knockout cells. Mechanistically, the ability of NFIA to penetrate chromatin and bind to the crucial Pparg enhancer is mediated through pro#3 domain. However, the deletion mutant still binds to Myod1 enhancer to repress expression of MyoD, the master transcriptional regulator of myogenesis as well as proximally transcribed non-coding RNA called ^DRReRNA, via competition with KLF5 in terms of enhancer binding, leading to suppression of myogenic gene program. Therefore, the negative effect of NFIA on the myogenic gene program is, at least partly, independent of the positive effect on PPARγ expression and its downstream adipogenic gene program. These results uncover multiple ways of action of NFIA to ensure optimal regulation of brown and beige adipocyte differentiation.

Obesity and its complications including type 2 diabetes are growing concerns worldwide. While white adipocytes generally store energy in the form of lipid, classical brown and cold- or β-adrenergic stimulation-induced beige adipocytes dissipate chemical energy in the form of heat through uncoupling protein-1 (Ucp1). Since the re-discovery of human brown and beige adipocytes, it has been considered a promising target for the treatment of obesity. During mesenchymal development, not only activation of brown/beige adipocyte gene program but also repression of muscle gene program is required to achieve thermogenic adipocyte differentiation. Previously, we identified the transcription factor nuclear factor I-A (NFIA) as a regulator of brown adipocyte differentiation. Here we show that the C-terminal 17 amino acid residues of NFIA, which we call pro#3 domain, is required for activation of adipocyte differentiation. However, the deletion mutant which lacks this domain is still able to suppress muscle gene program by repressing the expression of Myod1, which encode the master transcriptional regulator of myogenesis, MyoD. We demonstrate that NFIA activates adipogenesis and also “actively” suppresses myogenesis through distinct molecular pathways to ensure brown and beige adipocyte differentiation.

Systems-Genetics-Based Inference of a Core Regulatory Network Underlying White Fat Browning

Recruitment of brite/beige cells, known as browning of white adipose tissue (WAT), is an efficient way to turn an energy-storing organ into an energy-dissipating one and may therefore be of therapeutic value in combating obesity. However, a comprehensive understanding of the regulatory mechanisms mediating WAT browning is still lacking. Here, we exploit the large natural variation in WAT browning propensity between inbred mouse strains to gain an inclusive view of the core regulatory network coordinating this cellular process. Combining comparative transcriptomics, perturbation-based validations, and gene network analyses, we present a comprehensive gene regulatory network of inguinal WAT browning, revealing up to four distinct regulatory modules with key roles for uncovered transcriptional factors, while also providing deep insights into the genetic architecture of brite adipogenesis. The presented findings therefore greatly increase our understanding of the molecular drivers mediating the intriguing cellular heterogeneity and plasticity of adipose tissue.

RANKL induces beige adipocyte differentiation in preadipocytes

The receptor activator of nuclear factor-κB (NF-κB) (RANK), its ligand (RANKL), and the decoy receptor osteoprotegerin (OPG) are a triad of proteins that regulate bone metabolism, and serum OPG is considered a biomarker for cardiovascular diseases and Type 2 diabetes; however, the implications of OPG in adipose tissue metabolism remains elusive. In this study, we investigate RANK-RANKL-OPG signaling in white adipose tissue browning. Histological analysis of osteoprotegerin knockout (OPG-/-) mice showed subcutaneous white adipose tissue (sWAT) browning, resistance for high-fat diet-induced weight gain, and preserved glucose metabolism compared with wild-type (WT) mice. Stromal vascular fraction (SVF) cells from sWAT of OPG-/- mice showed multilocular morphology and higher expression of brown adipocyte marker genes compared with those from the WT group. Infusion of RANKL induced browning and elevated respiratory rates in sWAT, along with increased whole body oxygen consumption in mice measured by indirect calorimetry. Subcutaneous WAT-derived SVF and 3T3-L1 cells, but not mature white adipocytes, differentiated into beige adipose tissue in the presence of RANKL. Moreover, SVF cells, even under white adipocyte differentiation, showed multilocular lipid droplet, lower lipid content, and increased expression of beige adipocyte markers with RANKL stimulation. In this study, we show for the first time the contribution of RANKL to increase energy expenditure by inducing beige adipocyte differentiation in preadipocytes.

Role of small proliferative adipocytes: possible beige cell progenitors

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 < SPA < mature white adipocytes. In addition, proliferin was detected only in SPA. SPA differentiated more effectively into lipid-laden cells than SVC. Moreover, differentiated SPA expressed uncoupling protein 1 and mitochondria-related genes more than differentiated SVC. Treatment of SPA with pioglitazone and CL316243, a specific β3-adrenergic receptor agonist, differentiated SPA into beige-like cells. Therefore, SPA are able to differentiate into beige cells. SPA isolated from epididymal fat (epididymal SPA), but not SPA from inguinal fat (inguinal SPA), expressed a marker of visceral adipocyte precursor, WT1. However, no significant differences were detected in the expression levels of adipocyte-specific genes or neuronal genes between epididymal and inguinal SPA. The ability to differentiate into lipid-laden cells in epididymal SPA was a little superior to that in inguinal SPA, whereas the ability to differentiate into beige-like cells was greater in inguinal SPA than epididymal SPA. In conclusion, SPA may be progenitors of beige cells.

Betatrophin knockdown induces beiging and mitochondria biogenesis of white adipocytes

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.

Cell reprogramming using extracellular vesicles from differentiating stem cells into white/beige adipocytes

Stem cell-derived extracellular vesicles (EVs) offer alternative approaches to stem cell-based therapy for regenerative medicine. In this study, stem cell EVs derived during differentiation are developed to use as cell-free therapeutic systems by inducing tissue-specific differentiation. EVs are isolated from human adipose-derived stem cells (HASCs) during white and beige adipogenic differentiation (D-EV and BD-EV, respectively) via tangential flow filtration. D-EV and BD-EV can successfully differentiate HASCs into white and beige adipocytes, respectively. D-EV are transplanted with collagen/methylcellulose hydrogels on the backs of BALB/c mice, and they produce numerous lipid droplets in injected sites. Treatments of BD-EV attenuate diet-induced obesity through browning of adipose tissue in mice. Furthermore, high-fat diet-induced hepatic steatosis and glucose tolerance are improved by BD-EV treatment. miRNAs are responsible for the observed effects of BD-EV. These results reveal that secreted EVs during stem cell differentiation into white adipocytes or beige adipocytes can promote cell reprogramming.

Scd1 controls de novo beige fat biogenesis through succinate-dependent regulation of mitochondrial complex II

Preadipocytes can give rise to either white adipocytes or beige adipocytes. Owing to their distinct abilities in nutrient storage and energy expenditure, strategies that specifically promote "beiging" of adipocytes hold great promise for counterbalancing obesity and metabolic diseases. Yet, factors dictating the differentiation fate of adipocyte progenitors remain to be elucidated. We found that stearoyl-coenzyme A desaturase 1 (Scd1)-deficient mice, which resist metabolic stress, possess augmentation in beige adipocytes under basal conditions. Deletion of Scd1 in mature adipocytes expressing Fabp4 or Ucp1 did not affect thermogenesis in mice. Rather, Scd1 deficiency shifted the differentiation fate of preadipocytes from white adipogenesis to beige adipogenesis. Such effects are dependent on succinate accumulation in adipocyte progenitors, which fuels mitochondrial complex II activity. Suppression of mitochondrial complex II by Atpenin A5 or oxaloacetic acid reverted the differentiation potential of Scd1-deficient preadipocytes to white adipocytes. Furthermore, supplementation of succinate was found to increase beige adipocyte differentiation both in vitro and in vivo. Our data reveal an unappreciated role of Scd1 in determining the cell fate of adipocyte progenitors through succinate-dependent regulation of mitochondrial complex II.

Bola3 Regulates Beige Adipocyte Thermogenesis via Maintaining Mitochondrial Homeostasis and Lipolysis

Mitochondrial iron-sulfur (Fe-S) cluster is an important cofactor for the maturation of Fe-S proteins, which are ubiquitously involved in energy metabolism; however, factors facilitating this process in beige fat have not been established. Here, we identified BolA family member 3 (Bola3), as one of 17 mitochondrial Fe-S cluster assembly genes, was the most significant induced gene in the browning program of white adipose tissue. Using lentiviral-delivered shRNA in vitro, we determined that Bola3 deficiency inhibited thermogenesis activity without affecting lipogenesis in differentiated beige adipocytes. The inhibition effect of Bola3 knockdown might be through impairing mitochondrial homeostasis and lipolysis. This was evidenced by the decreased expression of mitochondria related genes and respiratory chain complexes, attenuated mitochondrial formation, reduced mitochondrial maximal respiration and inhibited isoproterenol-stimulated lipolysis. Furthermore, BOLA3 mRNA levels were higher in human deep neck brown fat than in the paired subcutaneous white fat, and were positively correlated with thermogenesis related genes (UCP1, CIDEA, PRDM16, PPARG, COX7A1, and LIPE) expression in human omental adipose depots. This study demonstrates that Bola3 is associated with adipose tissue oxidative capacity both in mice and human, and it plays an indispensable role in beige adipocyte thermogenesis via maintaining mitochondrial homeostasis and adrenergic signaling-induced lipolysis.

Expression and Secretion of an Atrial Natriuretic Peptide in Beige-Like 3T3-L1 Adipocytes

The browning of white adipose tissue (beige adipocytes) stimulates energy expenditure. Omega-3 fatty acids have been shown to induce thermogenic action in adipocytes via G-protein coupled receptor 120 (GPR120). Atrial natriuretic peptide (ANP) is a peptide hormone that plays the role of maintaining normal blood pressure in kidneys to inhibit Na⁺ reuptake. Recently, ANP was found to induce adipocyte browning by binding to NPR1, an ANP receptor. However, the expression of ANP in adipocytes has not yet been studied. Therefore, in this study, we investigate the expression of ANP in beige-like adipocytes induced by docosahexaenoic acids (DHA), T3, or a PPAR agonist, rosiglitazone. First, we found that brown adipocyte-specific genes were upregulated in beige-like adipocytes. DHA promoted ANP expression in beige-like cells, whereas DHA-induced ANP expression was abolished by GPR120 knockout. ANP secretion of beige-like adipocytes was increased via PKC/ERK1/2 signaling in the GPR120 pathway. Furthermore, ANP secreted from beige-like adipocytes acted on HEK-293 cells, the recipient cells, leading to increased cGMP activity. After the NPR1 knockdown of HEK-293 cells, cGMP activity was not changed. Taken together, our findings indicate that beige-like adipocytes induce ANP secretion, which may contribute to improving obesity-associated metabolic disease.

Cellular Origins of Beige Fat Cells Revisited

Activated beige adipocytes have therapeutic potential due to their ability to improve glucose and lipid homeostasis. To date, the origin of beige adipocytes remains enigmatic. Whether beige cells arise through de novo differentiation from resident precursors or through reprogramming of mature white adipocytes has been a topic of intense discussion. Here, we offer our perspective on the natural origin of beige adipocytes in mice. In particular, we revisit recent lineage-tracing studies that shed light on this issue and offer new insight into how environmental housing temperatures early in life influence the mode of beige adipocyte biogenesis upon cold exposure later in life. We suggest a unified model in which beige adipocytes (UCP1⁺ multilocular cells) in rodents initially arise predominantly from progenitors (i.e., de novo beige adipogenesis) upon the first exposure to cold temperatures and then interconvert between "dormant beige" and "active beige" phenotypes (i.e., beige cell activation) upon subsequent changes in environmental temperature. Importantly, we highlight experimental considerations needed to visualize de novo adipogenesis versus beige cell activation in mice. A precise understanding of the cellular origins of beige adipocytes emanating in response to physiological and pharmacological stimuli may better inform therapeutic strategies to recruit beige adipocytes in vivo.

Endoplasmic Reticulum Stress Impaired Uncoupling Protein 1 Expression via the Suppression of Peroxisome Proliferator-Activated Receptor γ Binding Activity in Mice Beige Adipocytes

Endoplasmic reticulum (ER) homeostasis is critical in maintaining metabolic regulation. Once it is disrupted due to accumulated unfolded proteins, ER homeostasis is restored via activation of the unfolded protein response (UPR); hence, the UPR affects diverse physiological processes. However, how ER stress influences adipocyte functions is not well known. In this study, we investigated the effect of ER stress in thermogenic capacity of mice beige adipocytes. Here, we show that the expression of uncoupling protein 1 (Ucp1) involved in thermoregulation is severely suppressed under ER stress conditions (afflicted by tunicamycin) in inguinal white adipose tissue (IWAT) both in vitro and in vivo. Further investigation showed that extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) were both activated after ER stress stimulation and regulated the mRNA levels of Ucp1 and peroxisome proliferator-activated receptor γ (Pparγ), which is known as a Ucp1 transcriptional activator, in vitro and ex vivo. We also found that Pparγ protein was significantly degraded, reducing its recruitment to the Ucp1 enhancer, thereby downregulating Ucp1 expression. Additionally, only JNK inhibition, but not ERK, rescued the Pparγ protein. These findings provide novel insights into the regulatory effect of ER stress on Ucp1 expression via Pparγ suppression in beige adipocytes.

CD105 maintains the thermogenic program of beige adipocytes by regulating Smad2 signaling

Beige adipocytes are thermogenic adipocytes with developmental and anatomical properties distinct from those of classical brown adipocytes. Recent studies have revealed several key molecular regulators of beige adipocyte development. CD105, also called endoglin, is a membrane protein composed of TGF-β receptor complex. It regulates TGF-β-family signal transduction and vascular formation in vivo. We report here that CD105 maintains the thermogenic gene program of beige adipocytes by regulating Smad2 signaling. Cd105^-/- adipocyte precursors showed augmented Smad2 activation and decreased expression of thermogenic genes such as Ucp1 and Prdm16-which encodes a transcriptional regulatory protein for thermogenesis-after adipogenic differentiation. Smad2 signaling augmentation by the constitutively active form of Smad2 decreased the expression of thermogenic genes in beige adipocytes. Loss of thermogenic activity in Cd105^-/- beige adipocytes was rescued by Prdm16 expression. These data reveal a novel function of CD105 in beige adipocytes: maintaining their thermogenic program by regulating Smad2 signaling.

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.

Molecular signatures and functional analysis of beige adipocytes induced from in vivo intra-abdominal adipocytes

Beige adipocytes can be induced from white adipocytes and precursors upon stimulation by cold temperatures and act like brown adipocytes to increase energy expenditure. Most in vivo studies examining the mechanisms for the induction of beige adipocytes have focused on subcutaneous white adipose tissue (sWAT; benign fat) in the mouse. How intra-abdominal WAT (aWAT; malignant fat) develops into beige adipocytes remains obscure, largely because there is a lack of a good animal model for the induction of beige adipocytes from aWAT. To better understand the development of beige adipocytes from mammalian WATs, especially aWAT, we induced beige adipocytes from bat aWAT and mouse sWAT by exposure to cold temperatures and analyzed their molecular signatures. RNA sequencing followed by whole genome-wide expression analysis shows that beige adipocytes induced from bat aWAT, rather than sWAT, have molecular signatures resembling those of mouse sWAT-induced beige adipocytes and exhibit dynamic profiles similar to those of classical brown adipocytes. In addition, we identified molecular markers that were highly enriched in beige adipocytes and conserved between bat aWAT and mouse sWAT, a set that included the genes Uqcrc1 and Letm1. Furthermore, knockdown of Uqcrc1 and Letm1 expression shows that they are required not only for beige adipocyte differentiation but also for preadipocyte maturation. This study presents a new model for research into the induction of beige adipocytes from aWAT in vivo, which, when combined with models where beige adipocytes are induced from sWAT, provides insight into therapeutic approaches for combating obesity-related diseases in humans.

Actomyosin-Mediated Tension Orchestrates Uncoupled Respiration in Adipose Tissues

The activation of brown/beige adipose tissue (BAT) metabolism and the induction of uncoupling protein 1 (UCP1) expression are essential for BAT-based strategies to improve metabolic homeostasis. Here, we demonstrate that BAT utilizes actomyosin machinery to generate tensional responses following adrenergic stimulation, similar to muscle tissues. The activation of actomyosin mechanics is critical for the acute induction of oxidative metabolism and uncoupled respiration in UCP1+ adipocytes. Moreover, we show that actomyosin-mediated elasticity regulates the thermogenic capacity of adipocytes via the mechanosensitive transcriptional co-activators YAP and TAZ, which are indispensable for normal BAT function. These biomechanical signaling mechanisms may inform future strategies to promote the expansion and activation of brown/beige adipocytes.

A pivotal role of AMPK signaling in medicarpin-mediated formation of brown and beige

Obesity poses a substantial threat of a worldwide epidemic and requires better understanding of adipose-tissue biology as well as necessitates research into the etiology and therapeutic interventions. In this study, Medicarpin (Med), a natural pterocarpan, was selected (by screening) as a small-molecule inducer of adipocyte differentiation among 854 candidates by using C3H10T1/2 mesenchymal stem cell; a cellular model of adipogenesis. Med induced the expression of brown-adipocyte commitment marker Bmp7 as well as the early regulators of brown fat fate Pparγ, Prdm16, and Pgc-1α during differentiation of C3H10T1/2 mesenchymal stem cells. Med also induced the expression of a key thermogenic marker-uncoupling protein 1 (UCP1)-along with expression of other brown-fat-specific markers and beige-fat-specific markers. Of note, Med significantly reduced the expression of white fat markers too. Furthermore, Med treatment promoted formation of multilocular lipid droplets (LDs), expression of mitochondrial-biogenesis-related genes, and increased oxygen consumption. Gene silencing study revealed that Med promotes the development of brown- and beige-adipocyte characteristics in C3H10T1/2 mesenchymal stem cells through activation of the AMPK pathway, and our data allow us to propose Med as a candidate for therapeutics against obesity or related metabolic disorders. © 2017 BioFactors, 44(2):168-179, 2018.

Functional Human Beige Adipocytes From Induced Pluripotent Stem Cells

Activation of thermogenic beige adipocytes has recently emerged as a promising therapeutic target in obesity and diabetes. Relevant human models for beige adipocyte differentiation are essential to implement such therapeutic strategies. We report a straightforward and efficient protocol to generate functional human beige adipocytes from human induced pluripotent stem cells (hiPSCs). Without overexpression of exogenous adipogenic genes, our method recapitulates an adipogenic developmental pathway through successive mesodermal and adipogenic progenitor stages. hiPSC-derived adipocytes are insulin sensitive and display beige-specific markers and functional properties, including upregulation of thermogenic genes, increased mitochondrial content, and increased oxygen consumption upon activation with cAMP analogs. Engraftment of hiPSC-derived adipocytes in mice produces well-organized and vascularized adipose tissue, capable of β-adrenergic-responsive glucose uptake. Our model of human beige adipocyte development provides a new and scalable tool for disease modeling and therapeutic screening.

VEGF-A-Expressing Adipose Tissue Shows Rapid Beiging and Enhanced Survival After Transplantation and Confers IL-4-Independent Metabolic Improvements

Adipocyte-derived vascular endothelial growth factor-A (VEGF-A) plays a crucial role in angiogenesis and contributes to adipocyte function and systemic metabolism, such as insulin resistance, chronic inflammation, and beiging of subcutaneous adipose tissue. Using a doxycycline-inducible adipocyte-specific VEGF-A-overexpressing mouse model, we investigated the dynamics of local VEGF-A effects on tissue beiging of adipose tissue transplants. VEGF-A overexpression in adipocytes triggers angiogenesis. We also observed a rapid appearance of beige fat cells in subcutaneous white adipose tissue as early as 2 days postinduction of VEGF-A. In contrast to conventional cold-induced beiging, VEGF-A-induced beiging is independent of interleukin-4. We subjected metabolically healthy VEGF-A-overexpressing adipose tissue to autologous transplantation. Transfer of subcutaneous adipose tissues taken from VEGF-A-overexpressing mice into diet-induced obese mice resulted in systemic metabolic benefits, associated with improved survival of adipocytes and a concomitant reduced inflammatory response. These effects of VEGF-A are tissue autonomous, inducing white adipose tissue beiging and angiogenesis within the transplanted tissue. Our findings indicate that manipulation of adipocyte functions with a bona fide angiogenic factor, such as VEGF-A, significantly improves the survival and volume retention of fat grafts and can convey metabolically favorable properties on the recipient on the basis of beiging.

The expanding problem of adipose depot remodeling and postnatal adipocyte progenitor recruitment

The rising incidence of obesity and associated metabolic diseases has increased the urgency in understanding all aspects of adipose tissue biology. This includes the function of adipocytes, how adipose tissue expands in obesity, and how expanded adipose tissues in adults can impact physiology. Here, we highlight the growing appreciation for the importance of de novo adipocyte differentiation to adipose tissue expansion in adult humans and animals. We detail recent efforts to identify adipose precursor populations that contribute to the physiological postnatal recruitment of white, brown, and beige adipocytes in mice, and summarize new data that reveal the complexity of adipose tissue development in vivo.

A Synergistic Antiobesity Effect by a Combination of Capsinoids and Cold Temperature Through Promoting Beige Adipocyte Biogenesis

Beige adipocytes emerge postnatally within the white adipose tissue in response to certain environmental cues, such as chronic cold exposure. Because of its highly recruitable nature and relevance to adult humans, beige adipocytes have gained much attention as an attractive cellular target for antiobesity therapy. However, molecular circuits that preferentially promote beige adipocyte biogenesis remain poorly understood. We report that a combination of mild cold exposure at 17°C and capsinoids, a nonpungent analog of capsaicin, synergistically and preferentially promotes beige adipocyte biogenesis and ameliorates diet-induced obesity. Gain- and loss-of-function studies show that the combination of capsinoids and cold exposure synergistically promotes beige adipocyte development through the β2-adrenoceptor signaling pathway. This synergistic effect on beige adipocyte biogenesis occurs through an increased half-life of PRDM16, a dominant transcriptional regulator of brown/beige adipocyte development. We document a previously unappreciated molecular circuit that controls beige adipocyte biogenesis and suggest a plausible approach to increase whole-body energy expenditure by combining dietary components and environmental cues.

Human Beige Adipocytes: Epiphenomenon or Drivers of Metabolic Improvements?

There is a lack of direct evidence that human brown or beige adipocytes improve whole-body energy homeostasis. In a recent study, Min et al. implanted proliferated human adipocyte progenitors from a 3D culture system in mice. Implants responded to adipogenic stimuli and had a beige-like phenotype upon induction that significantly improved systemic metabolic parameters.