Phosphoproteomics Identifies CK2 as a Negative Regulator of Beige Adipocyte Thermogenesis and Energy Expenditure.
ABSTRACT: Catecholamines promote lipolysis both in brown and white adipocytes, whereas the same stimuli preferentially activate thermogenesis in brown adipocytes. Molecular mechanisms for the adipose-selective activation of thermogenesis remain poorly understood. Here, we employed quantitative phosphoproteomics to map global and temporal phosphorylation profiles in brown, beige, and white adipocytes under ?3-adrenenoceptor activation and identified kinases responsible for the adipose-selective phosphorylation profiles. We found that casein kinase2 (CK2) activity is preferentially higher in white adipocytes than brown/beige adipocytes. Genetic or pharmacological blockade of CK2 in white adipocytes activates the thermogenic program in response to cAMP stimuli. Such activation is largely through reduced CK2-mediated phosphorylation of class I HDACs. Notably, inhibition of CK2 promotes beige adipocyte biogenesis and leads to an increase in whole-body energy expenditure and ameliorates diet-induced obesity and insulin resistance. These results indicate that CK2 is a plausible target to rewire the ?3-adrenenoceptor signaling cascade that promotes thermogenesis in adipocytes.
Project description:?-Adrenergic receptor (?-AR) signaling is a pathway controlling adaptive thermogenesis in brown or beige adipocytes. Here we investigate the biological roles of the transcription factor Foxp1 in brown/beige adipocyte differentiation and thermogenesis. Adipose-specific deletion of Foxp1 leads to an increase of brown adipose activity and browning program of white adipose tissues. The Foxp1-deficient mice show an augmented energy expenditure and are protected from diet-induced obesity and insulin resistance. Consistently, overexpression of Foxp1 in adipocytes impairs adaptive thermogenesis and promotes diet-induced obesity. A robust change in abundance of the ?3-adrenergic receptor (?3-AR) is observed in brown/beige adipocytes from both lines of mice. Molecularly, Foxp1 directly represses ?3-AR transcription and regulates its desensitization behavior. Taken together, our findings reveal Foxp1 as a master transcriptional repressor of brown/beige adipocyte differentiation and thermogenesis, and provide an important clue for its targeting and treatment of obesity.
Project description:Obesity is an increasing health problem worldwide. Its related comorbidities imply a high cost for the National Health System and diminish a patient's life quality. Adipose tissue is composed of three types of cells. White adipocytes are involved in fat storage and secretion of hormones. Brown adipocytes are involved in thermogenesis and caloric expenditure. Beige adipocytes are transitional adipocytes that in response to various stimuli can turn from white to brown and could be protective against the obesity, enhancing energy expenditure. The conversion of white in beige adipose tissue is a potential new therapeutic target for obesity. Cannabinoid receptors (CB) regulate thermogenesis, food intake and inflammation. CB1 ablation or inhibition helps reducing body weight and food intake. Stimulation of CB2 limits inflammation and promotes anti-obesity effects by reducing food intake and weight gain. Its genetic ablation results in adiposity development. CB receptors are also responsible for transforming white adipose tissue towards beige or brown adipocytes, therefore their modulation can be considered potential anti-obesity target. CB1 principal localization in central nervous system represents an important limit. Stimulation of CB2, principally localized on peripheral cells instead, should facilitate the anti-obesity effects without exerting remarkable psychotropic activity.
Project description:Iron homeostasis is essential for maintaining cellular function in a wide range of cell types. However, whether iron affects the thermogenic properties of adipocytes is currently unknown. Using integrative analyses of multi-omics data, transferrin receptor 1 (Tfr1) is identified as a candidate for regulating thermogenesis in beige adipocytes. Furthermore, it is shown that mice lacking Tfr1 specifically in adipocytes have impaired thermogenesis, increased insulin resistance, and low-grade inflammation accompanied by iron deficiency and mitochondrial dysfunction. Mechanistically, the cold treatment in beige adipocytes selectively stabilizes hypoxia-inducible factor 1-alpha (HIF1?), upregulating the Tfr1 gene, and thermogenic adipocyte-specific Hif1? deletion reduces thermogenic gene expression in beige fat without altering core body temperature. Notably, Tfr1 deficiency in interscapular brown adipose tissue (iBAT) leads to the transdifferentiation of brown preadipocytes into white adipocytes and muscle cells; in contrast, long-term exposure to a low-iron diet fails to phenocopy the transdifferentiation effect found in Tfr1-deficient mice. Moreover, mice lacking transmembrane serine protease 6 (Tmprss6) develop iron deficiency in both inguinal white adipose tissue (iWAT) and iBAT, and have impaired cold-induced beige adipocyte formation and brown fat thermogenesis. Taken together, these findings indicate that Tfr1 plays an essential role in thermogenic adipocytes via both iron-dependent and iron-independent mechanisms.
Project description:White adipocytes store excess energy in the form of triglycerides, whereas brown and beige adipocytes dissipate energy in the form of heat. This thermogenic function relies on the activation of brown and beige adipocyte-specific gene programmes that are coordinately regulated by adipose-selective chromatin architectures and by a set of unique transcriptional and epigenetic regulators. A number of transcriptional and epigenetic regulators are also required for promoting beige adipocyte biogenesis in response to various environmental stimuli. A better understanding of the molecular mechanisms governing the generation and function of brown and beige adipocytes is necessary to allow us to control adipose cell fate and stimulate thermogenesis. This may provide a therapeutic approach for the treatment of obesity and obesity-associated diseases, such as type 2 diabetes.
Project description:BACKGROUND:Recent studies suggest human neck brown adipose tissue (BAT) to consist of 'brown adipocyte (BA)-like' or beige adipocytes. However, little is known about their thermogenic function. Within the beige adipocyte transcriptome, fibroblast growth factor-21 (FGF21) is a gene whose protein product acts as an adipokine, regulating cold-induced thermogenesis in animals. Here, we explored (i) the adipogenic potential, thermogenic function and FGF21 secretory capacity of beige adipocytes derived from human neck fat and (ii) the role of FGF21 in modulating adipose bioenergetics. METHODS:Progenitors isolated from human cervical fat were differentiated into adipocytes with either a BA-like or white adipocyte (WA) phenotype. FGF21 secretion was measured by enzyme-linked immuosorbent assay. Real-time PCR/western blotting was used to determine cellular mRNA/protein levels. Extracellular flux bioanalyzer was used to quantify adipocyte oxygen consumption and fatty acid oxidation. Adipocyte heat production was measured by infrared thermography. RESULTS:Under hormonal manipulation, primary human neck pre-adipocytes differentiated into adipocytes with either BA-like or WA phenotypes, on gene/protein and functional levels. BA-like cells expressed beige but not classic BA markers. During BA differentiation, FGF21 gene expression and secretion were increased, and were augmented following norepinephrine exposure (a cold mimic in vitro). Differentiated WA expressed ?-klotho, a critical co-factor mediating FGF21 action. Treatment of WA with FGF21-induced UCP1 expression and increased oxygen consumption, respiratory uncoupling, norepinephrine-mediated thermogenesis, fatty acid oxidation and heat production, thus recapitulating the association between cold-induced FGF21 secretion and cold-induced thermogenesis in vivo. CONCLUSION:Beige adipocytes are thermogenic in humans. FGF21 is a beige adipokine capable of promoting a brown fat-like thermogenic program in WAs. SIGNIFICANCE:This study provides first evidence of inducible functional thermogenic beige adipogenesis in human neck fat. FGF21 holds promise as a cold-induced beige adipokine with metabolic benefits of therapeutic relevance through browning of white adipose tissue.
Project description:Brown and beige fat share a remarkably similar transcriptional program that supports fuel oxidation and thermogenesis. The chromatin-remodeling machinery that governs genome accessibility and renders adipocytes poised for thermogenic activation remains elusive. Here we show that BAF60a, a subunit of the SWI/SNF chromatin-remodeling complexes, serves an indispensable role in cold-induced thermogenesis in brown fat. BAF60a maintains chromatin accessibility at PPAR? and EBF2 binding sites for key thermogenic genes. Surprisingly, fat-specific BAF60a inactivation triggers more pronounced cold-induced browning of inguinal white adipose tissue that is linked to induction of MC2R, a receptor for the pituitary hormone ACTH. Elevated MC2R expression sensitizes adipocytes and BAF60a-deficient adipose tissue to thermogenic activation in response to ACTH stimulation. These observations reveal an unexpected dichotomous role of BAF60a-mediated chromatin remodeling in transcriptional control of brown and beige gene programs and illustrate a pituitary-adipose signaling axis in the control of thermogenesis.
Project description:While it is now understood that the proper expansion of adipose tissue is critically important for metabolic homeostasis, it is also appreciated that adipose tissues perform far more functions than simply maintaining energy balance. Adipose tissue performs endocrine functions, secreting hormones or adipokines that affect the regulation of extra-adipose tissues, and, under certain conditions, can also be major contributors to energy expenditure and the systemic metabolic rate via the activation of thermogenesis. Adipose thermogenesis takes place in brown and beige adipocytes. While brown adipocytes have been relatively well studied, the study of beige adipocytes has only recently become an area of considerable exploration. Numerous suggestions have been made that beige adipocytes can elicit beneficial metabolic effects on body weight, insulin sensitivity, and lipid levels. However, the potential impact of beige adipocyte thermogenesis on systemic metabolism is not yet clear and an understanding of beige adipocyte development and regulation is also limited. This review will highlight our current understanding of beige adipocytes and select factors that have been reported to elicit the development and activation of thermogenesis in beige cells, with a focus on factors that may represent a link between exercise and 'beiging', as well as the role that thyroid hormone signaling plays in beige adipocyte regulation.
Project description:Lipocalin-2 (LCN2) has been previously characterized as an adipokine regulating thermogenic activation of brown adipose tissue and retinoic acid (RA)-induced thermogenesis in mice. The objective of this study was to explore the role and mechanism for LCN2 in the recruitment and retinoic acid-induced activation of brown-like or ‘beige’ adipocytes. We found LCN2 deficiency reduces key markers of thermogenesis including uncoupling protein-1 (UCP1) and peroxisome proliferator-activated receptor gamma coactivator 1? (PGC-1?) in inguinal white adipose tissue (iWAT) and inguinal adipocytes derived from Lcn2 ?/? mice. Lcn2 ?/? inguinal adipocytes have attenuated insulin-induced upregulation of thermogenic gene expression and p38 mitogen-activated protein kinase (p38MAPK) signaling pathway activation. This is accompanied by a lower basal and maximal oxidative capacity in Lcn2 ?/? inguinal adipocytes, indicating mitochondrial dysfunction. Recombinant Lcn2 was able to restore insulin-induced p38MAPK phosphorylation in both WT and Lcn2 ?/? inguinal adipocytes. Rosiglitazone treatment during differentiation of Lcn2 ?/? adipocytes is able to recruit beige adipocytes at a normal level, however, further activation of beige adipocytes by insulin and RA is impaired in the absence of LCN2. Further, the synergistic effect of insulin and RA on UCP1 and PGC-1? expression is markedly reduced in Lcn2 ?/? inguinal adipocytes. Most intriguingly, LCN2 and the retinoic acid receptor-alpha (RAR-?) are concurrently translocated to the plasma membrane of adipocytes in response to insulin, and this insulin-induced RAR-? translocation is absent in adipocytes deficient in LCN2. Our data suggest a novel LCN2-mediated pathway by which RA and insulin synergistically regulates activation of beige adipocytes via a non-genomic pathway of RA action.
Project description:We previously reported brown adipocytes can proliferate even after differentiation. To test the involvement of mature adipocyte proliferation in cell number control in fat tissue, we generated transgenic (Tg) mice over-expressing cell-cycle inhibitory protein p27 specifically in adipocytes, using the aP2 promoter. While there was no apparent difference in white adipose tissue (WAT) between wild-type (WT) and Tg mice, the amount of brown adipose tissue (BAT) was much smaller in Tg mice. Although BAT showed a normal cellular morphology, Tg mice had lower content of uncoupling protein 1 (UCP1) as a whole, and attenuated cold exposure- or ?3-adrenergic receptor (AR) agonist-induced thermogenesis, with a decrease in the number of mature brown adipocytes expressing proliferation markers. An agonist for the ?3-AR failed to increase the number of proliferating brown adipocytes, UCP1 content in BAT, and oxygen consumption in Tg mice, although the induction and the function of beige adipocytes in inguinal WAT from Tg mice were similar to WT mice. These results show that brown adipocyte proliferation significantly contributes to BAT development and adaptive thermogenesis in mice, but not to induction of beige adipocytes.
Project description:Thermogenesis in brown adipocytes, conferred by mitochondrial uncoupling protein 1 (UCP1), is receiving great attention because metabolically active brown adipose tissue may protect humans from metabolic diseases. In particular, the thermogenic function of brown-like adipocytes in white adipose tissue, known as brite (or beige) adipocytes, is currently of prime interest. A valid procedure to quantify the specific contribution of UCP1 to thermogenesis is thus of vital importance. Adrenergic stimulation of lipolysis is a common way to activate UCP1. We here report, however, that in this frequently applied setup, taking control over intracellular fatty acid levels is essential for the analysis of thermogenic function in cultured brown and brite adipocytes. By the application of these findings, we demonstrate that UCP1 is functionally thermogenic in intact brite adipocytes and adrenergic UCP1 activation is largely dependent on adipose triglyceride lipase (ATGL) rather than hormone sensitive lipase (HSL).