ABSTRACT: OBJECTIVE:Cold and ?3-adrenergic receptor (AR) agonists activate beige adipocyte biogenesis in white adipose tissue (WAT). The two stimuli also induce expression of inflammatory cytokines in WAT. The low-grade inflammation may further promote WAT browning. However, the mechanisms to reconcile these two biological processes remain to be elucidated. In this study, we aim to investigate the roles of the rate-limiting polyamine catabolic enzyme spermidine/spermine N1-acetyltransferase (SAT1) in regulating beige adipocyte biogenesis and inflammation. METHODS:Adipose-specific SAT1 knockout mice (SAT1-aKO) were generated by crossing adiponectin-cre to SAT1-lox/lox mice. Metabolic phenotype was investigated. Primary pre-adipocytes were isolated from inguinal WAT (iWAT) and differentiated to adipocytes for studying beige adipocyte biogenesis. RESULT:The expression and enzymatic activity of SAT1 were up-regulated in iWAT upon cold and ?3-AR stimulation. SAT1-aKO mice developed late-onset obesity on a high-fat diet with impaired cold-induced beige adipocyte biogenesis and energy expenditure. RNA-seq analysis of iWAT from cold-challenged SAT1-aKO mice revealed that, in addition to beige adipocyte biogenesis signatures, the immune response markers were highly enriched among reduced genes. In cultured adipocytes, SAT1 overexpression or pharmacological activation with N1, N11-diethylnorspermine (DENSpm) elevated oxygen consumption and increased the expression of beige adipocyte marker UCP1 and PGC-1?. DENSpm treatment of adipocytes also increased the expression of inflammatory genes. SAT1 activation enhanced hydrogen peroxide production in adipocytes. Antioxidant N-acetylcysteine abrogated the elevated UCP1 expression and reversed some inflammatory genes induced by SAT1 activation. CONCLUSIONS:SAT1 activation plays a key role in cold and ?3-AR agonist-induced beige adipocyte biogenesis and low-grade inflammation.
Project description:Obesity occurs when excess energy accumulates in white adipose tissue (WAT), whereas brown adipose tissue (BAT), which is specialized in dissipating energy through thermogenesis, potently counteracts obesity. White adipocytes can be converted to thermogenic "brown-like" cells (beige cells; WAT browning) under various stimuli, such as cold exposure. AMP-activated protein kinase (AMPK) is a crucial energy sensor that regulates energy metabolism in multiple tissues. However, the role of AMPK in adipose tissue function, especially in the WAT browning process, is not fully understood. To illuminate the effect of adipocyte AMPK on energy metabolism, we generated Adiponectin-Cre-driven adipose tissue-specific AMPK ?1/?2 KO mice (AKO). These AKO mice were cold intolerant and their inguinal WAT displayed impaired mitochondrial integrity and biogenesis, and reduced expression of thermogenic markers upon cold exposure. High-fat-diet (HFD)-fed AKO mice exhibited increased adiposity and exacerbated hepatic steatosis and fibrosis and impaired glucose tolerance and insulin sensitivity. Meanwhile, energy expenditure and oxygen consumption were markedly decreased in the AKO mice both in basal conditions and after stimulation with a ?3-adrenergic receptor agonist, CL 316,243. In contrast, we found that in HFD-fed obese mouse model, chronic AMPK activation by A-769662 protected against obesity and related metabolic dysfunction. A-769662 alleviated HFD-induced glucose intolerance and reduced body weight gain and WAT expansion. Notably, A-769662 increased energy expenditure and cold tolerance in HFD-fed mice. A-769662 treatment also induced the browning process in the inguinal fat depot of HFD-fed mice. Likewise, A-769662 enhanced thermogenesis in differentiated inguinal stromal vascular fraction (SVF) cells via AMPK signaling pathway. In summary, a lack of adipocyte AMPK? induced thermogenic impairment and obesity in response to cold and nutrient-overload, respectively, whereas chronic AMPK activation by A-769662 promoted WAT browning in inguinal WAT and protected against HFD-induced obesity and related metabolic dysfunction. These findings reveal a vital role for adipocyte AMPK in regulating the browning process in inguinal WAT and in maintaining energy homeostasis, which suggests that the targeted activation of adipocyte AMPK may be a promising strategy for anti-obesity therapy.
Project description:Accumulating evidence from both animal and human studies suggests that activation of beige fat increases cellular energy expenditure, ultimately reducing adiposity. Here, we report the central role of adipocyte-derived lysyl oxidase (Lox) in the formation of thermogenic beige fat. Mice exposed to cold or a β3 agonist showed drastically lower Lox expression in thermogenically activated beige fat. Importantly, inhibition of Lox activity with BAPN stimulated biogenesis of beige fat in inguinal white adipose tissue (iWAT) under housing conditions and potentiated cold-induced adaptive thermogenesis and beiging in both iWAT and epididymal white adipose tissue (eWAT). Notably, white adipocytes with Lox repression undergo transdifferentiation into beige adipocytes which can be suppressed by tumor necrosis factor-α (TNFα) via ERK activation. This work provides new insight into the molecular control to expand beige fat by Lox inhibition and suggest the potential for utilizing inhibitor of Lox to treat the emerging epidemics of obesity and diabetes.
Project description:Adipocytes deficient in fatty acid synthase (iAdFASNKO) emit signals that mimic cold exposure to enhance the appearance of thermogenic beige adipocytes in mouse inguinal white adipose tissues (iWATs). Both cold exposure and iAdFASNKO upregulate the sympathetic nerve fiber (SNF) modulator Neuregulin 4 (Nrg4), activate SNFs, and require adipocyte cyclic AMP/protein kinase A (cAMP/PKA) signaling for beige adipocyte appearance, as it is blocked by adipocyte Gs? deficiency. Surprisingly, however, in contrast to cold-exposed mice, neither iWAT denervation nor Nrg4 loss attenuated adipocyte browning in iAdFASNKO mice. Single-cell transcriptomic analysis of iWAT stromal cells revealed increased macrophages displaying gene expression signatures of the alternately activated type in iAdFASNKO mice, and their depletion abrogated iWAT beiging. Altogether, these findings reveal that divergent cellular pathways are sufficient to cause adipocyte browning. Importantly, adipocyte signaling to enhance alternatively activated macrophages in iAdFASNKO mice is associated with enhanced adipose thermogenesis independent of the sympathetic neuron involvement this process requires in the cold.
Project description:OBJECTIVE:Development of brown-like/beige adipocytes in white adipose tissue (WAT) helps to reduce obesity. Thus we investigated the effects of resveratrol, a dietary polyphenol capable of preventing obesity and related complications in humans and animal models, on brown-like adipocyte formation in inguinal WAT (iWAT). METHODS:CD1 female mice (5-month old) were fed a high-fat diet with/without 0.1% resveratrol. In addition, primary stromal vascular cells separated from iWAT were subjected to resveratrol treatment. Markers of brown-like (beige) adipogenesis were measured and the involvement of AMP-activated protein kinase (AMPK) ?1 was assessed using conditional knockout. RESULTS:Resveratrol significantly increased mRNA and/or protein expression of brown adipocyte markers, including uncoupling protein 1 (UCP1), PR domain-containing 16, cell death-inducing DFFA-like effector A, elongation of very long-chain fatty acids protein 3, peroxisome proliferator-activated receptor-? coactivator 1?, cytochrome c and pyruvate dehydrogenase, in differentiated iWAT stromal vascular cells (SVCs), suggesting that resveratrol induced brown-like adipocyte formation in vitro. Concomitantly, resveratrol markedly enhanced AMPK?1 phosphorylation and differentiated SVC oxygen consumption. Such changes were absent in cells lacking AMPK?1, showing that AMPK?1 is a critical mediator of resveratrol action. Resveratrol also induced beige adipogenesis in vivo along with the appearance of multiocular adipocytes, increased UCP1 expression and enhanced fatty acid oxidation. CONCLUSIONS:Resveratrol induces brown-like adipocyte formation in iWAT via AMPK?1 activation and suggest that its beneficial antiobesity effects may be partly due to the browning of WAT and, as a consequence, increased oxygen consumption.
Project description:Beige adipocytes can dissipate energy as heat. Elaborate communication between metabolism and gene expression is important in the regulation of beige adipocytes. Although lipid droplet (LD) binding proteins play important roles in adipose tissue biology, it remains unknown whether perilipin 3 (Plin3) is involved in the regulation of beige adipocyte formation and thermogenic activities. In this study, we demonstrate that Plin3 ablation stimulates beige adipocytes and thermogenic gene expression in inguinal white adipose tissue (iWAT). Compared with wild-type mice, Plin3 knockout mice were cold tolerant and displayed enhanced basal and stimulated lipolysis in iWAT, inducing peroxisome proliferator-activated receptor α (PPARα) activation. In adipocytes, Plin3 deficiency promoted PPARα target gene and uncoupling protein 1 expression and multilocular LD formation upon cold stimulus. Moreover, fibroblast growth factor 21 expression and secretion were upregulated, which was attributable to activated PPARα in Plin3-deficient adipocytes. These data suggest that Plin3 acts as an intrinsic protective factor preventing futile beige adipocyte formation by limiting lipid metabolism and thermogenic gene expression.
Project description:Beige fat is a potential therapeutic target for obesity and other metabolic diseases due to its inducible brown fat-like functions. Inguinal white adipose tissue (iWAT) can undergo robust brown remodeling with appropriate stimuli and is therefore widely considered as a representative beige fat depot. However, adipose tissues residing in different anatomic depots exhibit a broad range of plasticity, raising the possibility that better beige fat depots with greater plasticity may exist. Here we identified and characterized a novel, naturally-existing beige fat depot, thigh adipose tissue (tAT). Unlike classic WATs, tAT maintains beige fat morphology at room temperature, whereas high-fat diet (HFD) feeding or aging promotes the development of typical WAT features, namely unilocular adipocytes. The brown adipocyte gene expression in tAT is consistently higher than in iWAT under cold exposure, HFD feeding, and rosiglitazone treatment conditions. Our molecular profiling by RNA-Seq revealed up-regulation of energy expenditure pathways and repressed inflammation in tAT relative to eWAT and iWAT. Furthermore, we demonstrated that the master fatty acid oxidation regulator peroxisome proliferator-activated receptor ? is dispensable for maintaining and activating the beige character of tAT. Therefore, we have identified tAT as a natural beige adipose depot in mice with a unique molecular profile that does not require peroxisome proliferator-activated receptor ?.
Project description:Beige/brite adipocytes are induced within white adipose tissues (WAT) and, when activated, consume glucose and fatty acids to produce heat. Classically, two stimuli have been used to trigger a beiging response: cold temperatures and β3-adrenergic receptor (<i>Adrb3</i>) agonists. These two beiging triggers have been used interchangeably but whether these two stimuli may induce beiging differently at cellular and molecular levels remains unclear. Here, we found that cold-induced beige adipocyte formation requires <i>Adrb</i>1, not <i>Adrb3</i>, activation. <i>Adrb</i>1 activation stimulates WAT resident perivascular (<i>Acta2</i>+) cells to form cold-induced beige adipocytes. In contrast, <i>Adrb3</i> activation stimulates mature white adipocytes to convert into beige adipocytes. Necessity tests, using mature adipocyte-specific <i>Prdm16</i> deletion strategies, demonstrated that adipocytes are required and are predominant source to generate <i>Adrb3</i>-induced, but not cold-induced, beige adipocytes. Collectively, we identify that cold temperatures and <i>Adrb3</i> agonists activate distinct cellular populations that express different β-adrenergic receptors to induce beige adipogenesis.
Project description:White adipose tissue (WAT) and brown adipose tissue (BAT) are innervated and regulated by the sympathetic nervous system (SNS). It is not clear, however, whether there are shared or separate central SNS outflows to WAT and BAT that regulate their function. We injected two isogenic strains of pseudorabies virus, a retrograde transneuronal viral tract tracer, with unique fluorescent reporters into interscapular BAT (IBAT) and inguinal WAT (IWAT) of the same Siberian hamsters to define SNS pathways to both. To test the functional importance of SNS coordinated control of BAT and WAT, we exposed hamsters with denervated SNS nerves to IBAT to 4°C for 16-24 h and measured core and fat temperatures and norepinephrine turnover (NETO) and uncoupling protein 1 (UCP1) expression in fat tissues. Overall, there were more SNS neurons innervating IBAT than IWAT across the neuroaxis. However, there was a greater percentage of singly labeled IWAT neurons in midbrain reticular nuclei than singly labeled IBAT neurons. The hindbrain had ~30-40% of doubly labeled neurons while the forebrain had ~25% suggesting shared SNS circuitry to BAT and WAT across the brain. The raphe nucleus, a key region in thermoregulation, had ~40% doubly labeled neurons. Hamsters with IBAT SNS denervation maintained core body temperature during acute cold challenge and had increased beige adipocyte formation in IWAT. They also had increased IWAT NETO, temperature, and UCP1 expression compared with intact hamsters. These data provide strong neuroanatomical and functional evidence of WAT and BAT SNS cross talk for thermoregulation and beige adipocyte formation.
Project description:Classical brown adipocytes such as those found in interscapular brown adipose tissue (iBAT) represent energy-burning cells, which have been postulated to play a pivotal role in energy metabolism. Brown adipocytes can also be found in white adipose tissue (WAT) depots [e.g., inguinal WAT (iWAT)] following adrenergic stimulation, and they have been referred to as "beige" adipocytes. Whether the presence of these adipocytes, which gives iWAT a beige appearance, can confer a white depot with some thermogenic activity remains to be seen. In consequence, we designed the present study to investigate the metabolic activity of iBAT, iWAT, and epididymal white depots in mice. Mice were either 1) kept at thermoneutrality (30°C), 2) kept at 30°C and treated daily for 14 days with an adrenergic agonist [CL-316,243 (CL)], or 3) housed at 10°C for 14 days. Metabolic activity was assessed using positron emission tomography imaging with fluoro-[(18)F]deoxyglucose (glucose uptake), fluoro-[(18)F]thiaheptadecanoic acid (fatty acid uptake), and [(11)C]acetate (oxidative activity). In each group, substrate uptakes and oxidative activity were measured in anesthetized mice in response to acute CL. Our results revealed iBAT as a major site of metabolic activity, which exhibited enhanced glucose and nonesterified fatty acid uptakes and oxidative activity in response to chronic cold and CL. On the other hand, beige adipose tissue failed to exhibit appreciable increase in oxidative activity in response to chronic cold and CL. Altogether, our results suggest that the contribution of beige fat to acute-CL-induced metabolic activity is low compared with that of iBAT, even after sustained adrenergic stimulation.
Project description: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 ?2-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.