beta(3)-adrenergic stimulation differentially inhibits insulin signaling and decreases insulin-induced glucose uptake in brown adipocytes

Beneficial Metabolic Effects of Mirabegron In Vitro and in High-Fat Diet-Induced Obese Mice

Mirabegron, a β3-adrenergic receptor agonist, has been shown to stimulate the activity of brown fat and increase the resting metabolic rate in humans. However, it is unknown whether mirabegron can reduce body weight and improve metabolic health. We investigated the antiobesity effects of mirabegron using both in vitro and in vivo models. Mouse brown preadipocytes and 3T3-L1 cells were treated with different concentrations of mirabegron (0.03-3 µg/ml), and the expression of brown fat-related genes was measured by quantitative real-time polymerase chain reaction. Furthermore, male C57BL/6J mice were fed a high-fat diet for 10 weeks, and mirabegron (2 mg/kg body weight) or a vehicle control was delivered to the interscapular brown adipose tissue (iBAT) using ALZET osmotic pumps from week 7 to 10. The metabolic parameters and tissues were analyzed. In both mouse brown preadipocytes and 3T3-L1 cells, mirabegron stimulated uncoupling protein 1 (UCP1) expression. In animal studies, mirabegron-treated mice had a lower body weight and adiposity. Lipid droplets in the iBAT of mirabegron-treated mice were fewer and smaller in size compared with those from vehicle-treated mice. H&E staining and immunohistochemistry indicated that mirabegron increased the abundance of beige cells in inguinal white adipose tissue (iWAT). Compared with vehicle-treated mice, mirabegron-treated mice had a higher gene expression of UCP1 (14-fold) and cell death-inducing DNA fragmentation factor alpha-like effector A (CIDEA) (4-fold) in iWAT. Furthermore, mirabegron-treated mice had improved glucose tolerance and insulin sensitivity. Taken together, mirabegron enhances UCP1 expression and promotes browning of iWAT, which are accompanied by improved glucose tolerance and insulin sensitivity and prevention from high-fat diet-induced obesity.

Metabolic Consequences of Obstructive Sleep Apnea Especially Pertaining to Diabetes Mellitus and Insulin Sensitivity

Obstructive sleep apnea (OSA) and diabetes has been known to be closely related to each other and both diseases impact highly on the public health. There are many evidence of reports that OSA is associated with diabetes with a bidirectional correlation. A possible causal mechanism of OSA to diabetes is intermittent hypoxemia and diabetes to OSA is microvascular complication. However, OSA and diabetes have a high prevalence rate in public and shares the common overlap characteristic and risk factors such as age, obesity, and metabolic syndrome that make it difficult to establish the exact pathophysiologic mechanism between them. In addition, studies demonstrating that treatment of OSA may help prevent diabetes or improve glycemic control have not shown convincing result but have become a great field of interest research. This review outlines the bidirectional correlation between OSA and diabetes and explore the pathophysiologic mechanisms by approaching their basic etiologies.

Secretory Proteome of Brown Adipocytes in Response to cAMP-Mediated Thermogenic Activation

Background: The secretory properties of brown adipose tissue are thought to contribute to the association between active brown fat and a healthy metabolic status. Although a few brown adipokines have been identified, a comprehensive knowledge of the brown adipose tissue secretome is lacking.

Methods: Here, to examine the effects of thermogenic activation of brown adipocytes on protein secretion, we used isobaric tags for relative and absolute quantification (iTRAQ) analysis to determine how the secreted proteome of brown adipocytes (that detected in cell culture medium) differed in response to cAMP.

Results: Our results indicated that 56 secreted proteins were up-regulated in response to cAMP. Of them, nearly half (29) corresponded to extracellular matrix components and regulators. Several previously known adipokines, were also detected. Unexpectedly, we also found five components of the complement system. Only 15 secreted proteins were down-regulated by cAMP; of them three were ECM-related and none was related to the complement system. We observed a partial concordance between the cAMP-regulated release of proteins (both from proteomics and from antibody-based quantification of specific proteins) and the cAMP-mediated regulation of their encoding transcript for the up-regulated secreted proteins. However, a stronger concordance was seen for the down-regulated secreted proteins.

Conclusions: The present results highlight the need to investigate previously unrecognized processes such as the role of extracellular matrix in thermogenic activation-triggered brown fat remodeling, as well as the intriguing question of how brown adipocyte-secreted complement factors contribute to the signaling properties of active brown adipose tissue.

In Vitro Models for Study of Brown Adipocyte Biology

Brown adipocytes are the key cell type in brown adipose tissue (BAT) that express the genes required for heat production through the process of thermogenesis. Brown adipocyte cell culture models are important for researching the molecular pathways that control cell autonomous processes. In vitro tools for the study of brown adipocytes include BAT explant cultures and BAT primary cultures that are first proliferated and then differentiated. A number of stable brown preadipocyte cell lines have been generated by the expression transforming factors such as SV40 T antigen. The application of these cell lines reduces the requirement for animal tissue which is needed for primary culture and explants. Furthermore, brown adipocyte cell lines that effectively recapitulate the properties of brown adipocytes permit large-scale experimental procedures that are generally unfeasible with primary cultures that undergo a restricted number of cell divisions. Cell lines are valuable for applications such as large-scale endogenous protein expression, ChIP assay, and procedures requiring antibiotic selection over several cell divisions including stable exogenous gene expression and CRISR/Cas9 gene editing.

Ginsenoside Rb2 Alleviates Obesity by Activation of Brown Fat and Induction of Browning of White Fat

Ginsenoside Rb2 (Rb2), the most abundant saponin contained in Panax ginseng, has been used to treat variety of metabolic diseases. However, its effects in obesity and potential mechanisms are not well-understood. In the present study, we investigated metabolic performance with a Rb2 supplement in diet-induced obese (DIO) mice, focusing on the effects and mechanisms of Rb2 on brown and beige fat functions. Our results demonstrated that Rb2 effectively reduced body weight, improved insulin sensitivity, as well as induced energy expenditure in DIO mice. Histological and gene analysis revealed that Rb2 induced activation of brown fat and browning of white fat by reducing lipid droplets, stimulating uncoupling protein 1 (UCP1) staining, and increasing expression of thermogenic and mitochondrial genes, which could be recapitulated in 3T3-L1, C3H10T1/2, and primary adipocytes. In addition, Rb2 induced phosphorylation of AMP-activated protein kinase (AMPK) both in vitro and in vivo. These effects were shown to be dependent on AMPK since its inhibitor blocked Rb2 from inducing expressions of Pgc1α and Ucp1. Overall, the present study revealed that Rb2 activated brown fat and induced browning of white fat, which increased energy expenditure and thermogenesis, and consequently ameliorated obesity and metabolic disorders. These suggest that Rb2 holds promise in treating obesity.

Thyroid hormone (T3) stimulates brown adipose tissue activation via mitochondrial biogenesis and MTOR-mediated mitophagy

The thyroid hormone triiodothyronine (T₃) activates thermogenesis by uncoupling electron transport from ATP synthesis in brown adipose tissue (BAT) mitochondria. Although T₃ can induce thermogenesis by sympathetic innervation, little is known about its cell autonomous effects on BAT mitochondria. We thus examined effects of T₃ on mitochondrial activity, autophagy, and metabolism in primary brown adipocytes and BAT and found that T₃ increased fatty acid oxidation and mitochondrial respiration as well as autophagic flux, mitophagy, and mitochondrial biogenesis. Interestingly, there was no significant induction of intracellular reactive oxygen species (ROS) despite high mitochondrial respiration and UCP1 induction by T₃. However, when cells were treated with Atg5 siRNA to block autophagy, induction of mitochondrial respiration by T₃ decreased, and was accompanied by ROS accumulation, demonstrating a critical role for autophagic mitochondrial turnover. We next generated an Atg5 conditional knockout mouse model (Atg5 cKO) by injecting Ucp1 promoter-driven Cre-expressing adenovirus into Atg5^Flox/Flox mice to examine effects of BAT-specific autophagy on thermogenesis in vivo. Hyperthyroid Atg5 cKO mice exhibited lower body temperature than hyperthyroid or euthyroid control mice. Metabolomic analysis showed that T₃ increased short and long chain acylcarnitines in BAT, consistent with increased β-oxidation. T₃ also decreased amino acid levels, and in conjunction with SIRT1 activation, decreased MTOR activity to stimulate autophagy. In summary, T₃ has direct effects on mitochondrial autophagy, activity, and turnover in BAT that are essential for thermogenesis. Stimulation of BAT activity by thyroid hormone or its analogs may represent a potential therapeutic strategy for obesity and metabolic diseases. Abbreviations: ACACA: acetyl-Coenzyme A carboxylase alpha; AMPK: AMP-activated protein kinase; Acsl1: acyl-CoA synthetase long-chain family member 1; ATG5: autophagy related 5; ATG7: autophagy related 7; ATP: adenosine triphosphate; BAT: brown adipose tissue; cKO: conditional knockout; COX4I1: cytochrome c oxidase subunit 4I1; Cpt1b: carnitine palmitoyltransferase 1b, muscle; CQ: chloroquine; DAPI: 4',6-diamidino-2-phenylindole; DIO2: deiodinase, iodothyronine, type 2; DMEM: Dulbecco's modified Eagle's medium; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; Fabp4: fatty acid binding protein 4, adipocyte; FBS: fetal bovine serum; FCCP: carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone; FGF: fibroblast growth factor; FOXO1: forkhead box O1; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; Gpx1: glutathione peroxidase 1; Lipe: lipase, hormone sensitive; MAP1LC3B: microtubule-associated protein 1 light chain 3; mRNA: messenger RNA; MTORC1: mechanistic target of rapamycin kinase complex 1; NAD: nicotinamide adenine dinucleotide; Nrf1: nuclear respiratory factor 1; OCR: oxygen consumption rate; PBS: phosphate-buffered saline; PCR: polymerase chain reaction; PPARGC1A: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; Pnpla2: patatin-like phospholipase domain containing 2; Prdm16: PR domain containing 16; PRKA: protein kinase, AMP-activated; RPS6KB: ribosomal protein S6 kinase; RFP: red fluorescent protein; ROS: reactive oxygen species; SD: standard deviation; SEM: standard error of the mean; siRNA: small interfering RNA; SIRT1: sirtuin 1; Sod1: superoxide dismutase 1, soluble; Sod2: superoxide dismutase 2, mitochondrial; SQSTM1: sequestosome 1; T₃: 3,5,3'-triiodothyronine; TFEB: transcription factor EB; TOMM20: translocase of outer mitochondrial membrane 20; UCP1: uncoupling protein 1 (mitochondrial, proton carrier); ULK1: unc-51 like kinase 1; VDAC1: voltage-dependent anion channel 1; WAT: white adipose tissue.

LincRNA H19 protects from dietary obesity by constraining expression of monoallelic genes in brown fat

Increasing brown adipose tissue (BAT) thermogenesis in mice and humans improves metabolic health and understanding BAT function is of interest for novel approaches to counteract obesity. The role of long noncoding RNAs (lncRNAs) in these processes remains elusive. We observed maternally expressed, imprinted lncRNA H19 increased upon cold-activation and decreased in obesity in BAT. Inverse correlations of H19 with BMI were also observed in humans. H19 overexpression promoted, while silencing of H19 impaired adipogenesis, oxidative metabolism and mitochondrial respiration in brown but not white adipocytes. In vivo, H19 overexpression protected against DIO, improved insulin sensitivity and mitochondrial biogenesis, whereas fat H19 loss sensitized towards HFD weight gains. Strikingly, paternally expressed genes (PEG) were largely absent from BAT and we demonstrated that H19 recruits PEG-inactivating H19-MBD1 complexes and acts as BAT-selective PEG gatekeeper. This has implications for our understanding how monoallelic gene expression affects metabolism in rodents and, potentially, humans.

Brown adipose tissue (BAT) thermogenesis counteracts obesity and promotes metabolic health. The role of long non-coding RNAs (lncRNAs) in the regulation of this process is not well understood. Here the authors identify a maternally expressed lncRNA, H19, that increases BAT oxidative metabolism and energy expenditure.

Effects of Genistein on Differentiation and Viability of Human Visceral Adipocytes

Obesity can lead to pathological growth of adipocytes by inducing inflammation and oxidative stress. Genistein could be a potential candidate for the treatment of obesity due to its antioxidant properties. Specific kits were used to examine the effects of genistein vs adiponectin on human visceral pre-adipocytes differentiation, cell viability, mitochondrial membrane potential, and oxidative stress in pre-adipocytes and in white/brown adipocytes. Western Blot was performed to examine changes in protein activation/expression. Genistein increased human visceral pre-adipocytes differentiation and browning, and caused a dose-related improvement of cell viability and mitochondrial membrane potential. Similar effects were observed in brown adipocytes and in white adipocytes, although in white cells the increase of cell viability was inversely related to the dose. Moreover, genistein potentiated AMP-activated protein kinase (AMPK)/mitofusin2 activation/expression in pre-adipocytes and white/brown adipocytes and protected them from the effects of hydrogen peroxide. The effects caused by genistein were similar to those of adiponectin. The results obtained showed that genistein increases human visceral pre-adipocytes differentiation and browning, protected against oxidative stress in pre-adipocytes and white/brown adipocytes through mechanisms related to AMPK-signalling and the keeping of mitochondrial function.

Cyanidin-3-O-β-glucoside regulates the activation and the secretion of adipokines from brown adipose tissue and alleviates diet induced fatty liver

AIM

Cyanidin-3-O-β-glucoside (Cy-3-G) the most abundant monomer of anthocyanins has multiple protective effects on many diseases. To date, whether Cy-3-G could regulate the function of brown adipose tissue (BAT) is still unclear and whether this regulation could influence the secretion of adipokines from BAT to prevent non-alcoholic fatty liver disease (NAFLD) indirectly remains to be explored. In this study we investigated the effect of Cy-3-G on BAT and the potential role of Cy-3-G to prevent fatty liver through regulating the secretion of BAT.

METHODS

Male C57BL/6 J mice were fed with a high fat high cholesterol (HFC) diet with or without 200 mg/kg B.W Cy-3-G for 8 weeks. In in vitro experiments, the differentiated brown adipocytes (BAC) and C3H10T1/2 clone8 cells were treated with 0.2 mM palmitate with or without Cy-3-G for 72 or 96 h. Then the culture media of C3H10T1/2 clone8 cells were collected for measuring the adipokines secretion by immunoblot assay and were applied to culture HepG2 cells or LO2 cells for 24 h. Lipid accumulation in HepG2 cells or LO2 cells were evaluated by oil red O staining.

RESULTS

Here we found that Cy-3-G regulated the activation of BAT and the expression of adipokines in BAT which were disrupted by HFC diet and alleviated diet induced fatty liver in mice. In in vitro experiments, Cy-3-G inhibited the release of adipokines including extracellular nicotinamide phosphoribosyltransferase (eNAMPT) and fibroblast growth factor 21 (FGF21) from differentiated C3H10T1/2 clone8 cells induced by palmitate, which was accompanied by a reduction of lipid accumulation in HepG2 cells and LO2 cells cultured by the corresponding collected media of C3H10T1/2 clone8 cells.

CONCLUSIONS

These results indicate that Cy-3-G can regulate the thermogenic and secretory functions of BAT. Furthermore, our data suggest that the protective effect of Cy-3-G on hepatic lipid accumulation is probably via regulating the secretion of adipokines from BAT.

Increased Ifi202b/IFI16 expression stimulates adipogenesis in mice and humans

AIMS/HYPOTHESIS

Obesity results from a constant and complex interplay between environmental stimuli and predisposing genes. Recently, we identified the IFN-activated gene Ifi202b as the most likely gene responsible for the obesity quantitative trait locus Nob3 (New Zealand Obese [NZO] obesity 3). The aim of this study was to evaluate the effects of Ifi202b on body weight and adipose tissue biology, and to clarify the functional role of its human orthologue IFI16.

METHODS

The impact of Ifi202b and its human orthologue IFI16 on adipogenesis was investigated by modulating their respective expression in murine 3T3-L1 and human Simpson-Golabi-Behmel syndrome (SGBS) pre-adipocytes. Furthermore, transgenic mice overexpressing IFI202b were generated and characterised with respect to metabolic traits. In humans, expression levels of IFI16 in adipose tissue were correlated with several variables of adipocyte function.

RESULTS

In mice, IFI202b overexpression caused obesity (Δ body weight at the age of 30 weeks: 10.2 ± 1.9 g vs wild-type mice) marked by hypertrophic fat mass expansion, increased expression of Zfp423 (encoding the transcription factor zinc finger protein [ZFP] 423) and white-selective genes (Tcf21, Tle3), and decreased expression of thermogenic genes (e.g. Cidea, Ucp1). Compared with their wild-type littermates, Ifi202b transgenic mice displayed lower body temperature, hepatosteatosis and systemic insulin resistance. Suppression of IFI202b/IFI16 in pre-adipocytes impaired adipocyte differentiation and triacylglycerol storage. Humans with high levels of IFI16 exhibited larger adipocytes, an enhanced inflammatory state and impaired insulin-stimulated glucose uptake in white adipose tissue.

CONCLUSIONS/INTERPRETATION

Our findings reveal novel functions of Ifi202b and IFI16, demonstrating their role as obesity genes. These genes promote white adipogenesis and fat storage, thereby facilitating the development of obesity-associated insulin resistance.

Distinct signalling properties of insulin receptor substrate (IRS)-1 and IRS-2 in mediating insulin/IGF-1 action

Insulin/IGF-1 action is driven by a complex and highly integrated signalling network. Loss-of-function studies indicate that the major insulin/IGF-1 receptor substrate (IRS) proteins, IRS-1 and IRS-2, mediate different biological functions in vitro and in vivo, suggesting specific signalling properties despite their high degree of homology. To identify mechanisms contributing to the differential signalling properties of IRS-1 and IRS-2 in the mediation of insulin/IGF-1 action, we performed comprehensive mass spectrometry (MS)-based phosphoproteomic profiling of brown preadipocytes from wild type, IRS-1^-/- and IRS-2^-/- mice in the basal and IGF-1-stimulated states. We applied stable isotope labeling by amino acids in cell culture (SILAC) for the accurate quantitation of changes in protein phosphorylation. We found ~10% of the 6262 unique phosphorylation sites detected to be regulated by IGF-1. These regulated sites included previously reported substrates of the insulin/IGF-1 signalling pathway, as well as novel substrates including Nuclear Factor I X and Semaphorin-4B. In silico prediction suggests the protein kinase B (PKB), protein kinase C (PKC), and cyclin-dependent kinase (CDK) as the main mediators of these phosphorylation events. Importantly, we found preferential phosphorylation patterns depending on the presence of either IRS-1 or IRS-2, which was associated with specific sets of kinases involved in signal transduction downstream of these substrates such as PDHK1, MAPK3, and PKD1 for IRS-1, and PIN1 and PKC beta for IRS-2. Overall, by generating a comprehensive phosphoproteomic profile from brown preadipocyte cells in response to IGF-1 stimulation, we reveal both common and distinct insulin/IGF-1 signalling events mediated by specific IRS proteins.

Inflammation and Fibrosis in Perirenal Adipose Tissue of Patients With Aldosterone-Producing Adenoma

The prevalence of primary aldosteronism is much higher than previously thought. Recent studies have shown that primary aldosteronism is related to a higher risk of cardiovascular events. However, the underlying mechanism is not yet clear. Here we investigate the characteristics, including inflammation, fibrosis, and adipokine expression, of adipose tissues from different deposits in patients with aldosterone-producing adenoma (APA). Inflammation and fibrosis changes were evaluated in perirenal and subcutaneous adipose tissues obtained from patients with APA (n = 16), normotension (NT; n = 10), and essential hypertension (EH; n = 5) undergoing laparoscopic surgery. We also evaluated the effect of aldosterone in isolated human perirenal adipose tissue stromal vascular fraction (SVF) cells and investigated the effect of aldosterone in mouse 3T3-L1 and brown preadipocytes. Compared with the EH group, significantly higher levels of interleukin-6 (IL-6) and tumor necrosis factor-α messenger RNA (mRNA) and protein were observed in perirenal adipose tissue of patients with APA. Expression of genes related to fibrosis and adipogenesis in perirenal adipose tissue was notably higher in patients with APA than in patients with NT and EH. Aldosterone significantly induced IL-6 and fibrosis gene mRNA expression in differentiated SVF cells. Aldosterone treatment enhanced mRNA expression of genes associated with inflammation and fibrosis and stimulated differentiation of 3T3-L1 and brown preadipocytes. In conclusion, these data indicate that high aldosterone in patients with APA may induce perirenal adipose tissue dysfunction and lead to inflammation and fibrosis, which may be involved in the high risk of cardiovascular events observed in patients with primary aldosteronism.

Male Brown Fat-Specific Double Knockout of IGFIR/IR: Atrophy, Mitochondrial Fission Failure, Impaired Thermogenesis, and Obesity

It is unknown how the lack of insulin receptor (IR)/insulinlike growth factor I receptor (IGFIR) in a tissue-specific manner affects brown fat development and mitochondrial integrity and function, as well as its effect on the redistribution of the adipose organ and the metabolic status. To address this important issue, we developed IR/IGFIR double-knockout (DKO) in a brown adipose tissue-specific manner. Lack of those receptors caused severe brown fat atrophy, enhanced beige cell clusters in inguinal fat; loss of mitochondrial mass; mitochondrial damage related to cristae disruption; and the loss of proteins involved in autophagosome formation, mitophagy, mitochondrial quality control, and dynamics and thermogenesis. More important, DKO mice showed an impaired thermogenesis upon cold exposure, based on a failure in the mitochondrial fission mechanisms and a much lower uncoupling protein 1 transcription rate and content. As a result, DKO mice under normal conditions showed an obesity susceptibility, revealed by increased body fat mass and insulin resistance. Upon consumption of a high-fat diet, DKO mice displayed frank obesity, as shown by increased body weight, increased adiposity, insulin resistance, hyperinsulinemia, and hypertriglyceridemia, all consistent with a metabolic syndrome. Collectively, our data suggest a cause-and-effect relationship between failure in brown fat thermogenesis and increased adiposity and obesity.

Novel Pharmacological Probes Reveal ABHD5 as a Locus of Lipolysis Control in White and Brown Adipocytes

Current knowledge regarding acute regulation of adipocyte lipolysis is largely based on receptor-mediated activation or inhibition of pathways that influence intracellular levels of cAMP, thereby affecting protein kinase A (PKA) activity. We recently identified synthetic ligands of α-β-hydrolase domain containing 5 (ABHD5) that directly activate adipose triglyceride lipase (ATGL) by dissociating ABHD5 from its inhibitory regulator, perilipin-1 (PLIN1). In the current study, we used these novel ligands to determine the direct contribution of ABHD5 to various aspects of lipolysis control in white (3T3-L1) and brown adipocytes. ABHD5 ligands stimulated adipocyte lipolysis without affecting PKA-dependent phosphorylation on consensus sites of PLIN1 or hormone-sensitive lipase (HSL). Cotreatment of adipocytes with synthetic ABHD5 ligands did not alter the potency or maximal lipolysis efficacy of the β-adrenergic receptor (ADRB) agonist isoproterenol (ISO), indicating that both target a common pool of ABHD5. Reducing ADRB/PKA signaling with insulin or desensitizing ADRB suppressed lipolysis responses to a subsequent challenge with ISO, but not to ABHD5 ligands. Lastly, despite strong treatment differences in PKA-dependent phosphorylation of HSL, we found that ligand-mediated activation of ABHD5 led to complete triglyceride hydrolysis, which predominantly involved ATGL, but also HSL. These results indicate that the overall pattern of lipolysis controlled by ABHD5 ligands is similar to that of isoproterenol, and that ABHD5 plays a central role in the regulation of adipocyte lipolysis. As lipolysis is critical for adaptive thermogenesis and in catabolic tissue remodeling, ABHD5 ligands may provide a means of activating these processes under conditions where receptor signaling is compromised.

Cellular and functional actions of tofacitinib related to the pathophysiology of hibernoma development

Tofacitinib is an oral JAK inhibitor for the treatment of rheumatoid arthritis. In the 2-year carcinogenicity study with tofacitinib, increased incidence of hibernoma (a neoplasm of brown adipose tissue [BAT]) was noted in female rats at ≥30 mg/kg/day (≥41x human exposure multiples). Thus, signaling pathways within BAT were investigated by measuring BAT: weight, cell proliferation biomarkers, content of basal and prolactin-induced phosphorylated Signal Transducer and Activator of Transcription (STAT), and uncoupling protein 1 (UCP-1). The relationship between cardiovascular hemodynamics and plasma norepinephrine (NE) levels was also investigated. Tofacitinib administered to female rats at doses of 10, 30, or 75 mg/kg/day for 14 days increased BAT weight at 75 mg/kg/day and cell proliferation at ≥30 mg/kg/day. JAK inhibition, observed as lower pSTAT3 and pSTAT5 in BAT, was noted at ≥10 mg/kg/day, while lower activity of BAT was observed as lower UCP-1 protein at ≥30 mg/kg/day. In cultured brown adipocytes, prolactin-induced increase in pSTAT5 and pSTAT3 were inhibited by tofacitinib in a concentration-dependent manner. Tofacitinib lowered blood pressure, increased heart rate, and resulted in dose-dependent increases in circulating NE. Thus, JAK/STAT inhibition in BAT and sympathetic stimulation are two factors which might contribute to the genesis of hibernomas by tofacitinib in rats.

Locally Induced Adipose Tissue Browning by Microneedle Patch for Obesity Treatment

Obesity is one of the most serious public health problems in the 21st century that may lead to many comorbidities such as type-2 diabetes, cardiovascular diseases, and cancer. Current treatments toward obesity including diet, physical exercise, pharmacological therapy, as well as surgeries are always associated with low effectiveness or undesired systematical side effects. In order to enhance treatment efficiency with minimized side effects, we developed a transcutaneous browning agent patch to locally induce adipose tissue transformation. This microneedle-based patch can effectively deliver browning agents to the subcutaneous adipocytes in a sustained manner and switch on the "browning" at the targeted region. It is demonstrated that this patch reduces treated fat pad size, increases whole body energy expenditure, and improves type-2 diabetes in vivo in a diet-induced obesity mouse model.

Albiflorin ameliorates obesity by inducing thermogenic genes via AMPK and PI3K/AKT in vivo and in vitro

OBJECTIVE

Brown adipose tissue (BAT) activation has been identified as a possible target to treat obesity and to protect against metabolic diseases by increasing energy consumption. We explored whether albiflorin (AF), a natural compound, could contribute to lowering the high risk of obesity with BAT and primary brown preadipocytes in vivo and in vitro.

MATERIALS/METHODS

Human adipose tissue-derived mesenchymal stem cells (hAMSCs) were cultured with adipogenic differentiation media with or without AF. Male C57BL/6J mice (n=5 per group) were fed a high-fat diet (HFD) for six weeks with or without AF. Brown preadipocytes from the interscapular BAT of mice were cultured with or without AF.

RESULTS

In white adipogenic differentiation of hAMSCs, AF treatment significantly reduced the formation of lipid droplets and the expression of adipogenesis-related genes. In HFD-induced obese C57BL/6J mice, AF treatment significantly reduced body weight gain as well as the weights of the white adipose tissue, liver and spleen. Furthermore, AF induced the expression of genes involved in thermogenic function in BAT. In primary brown adipocytes, AF effectively stimulated the expressions of thermogenic genes and markedly up-regulated the AMP-activated protein kinase (AMPK) signaling pathway. Pretreatment with phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 nullified the induction of the thermogenic genes by AF in primary brown adipocytes. Moreover, AF activated beige cell marker genes induced by the pharmacological activation of peroxisome proliferator-activated receptor γ in hAMSCs.

CONCLUSION

This study shows that AF prevents the development of obesity in hAMSCs and mice fed an HFD and that it is also capable of stimulating the differentiation of brown adipocytes through the modulation of thermogenic genes by AMPK and PI3K/AKT.

miRNA-32 Drives Brown Fat Thermogenesis and Trans-activates Subcutaneous White Fat Browning in Mice

Brown adipose tissue (BAT) activation and subcutaneous white fat browning are essential components of the thermogenic response to cold stimulus in mammals. microRNAs have been shown to regulate both processes in cis. Here, we identify miR-32 as a BAT-specific super-enhancer-associated miRNA in mice that is selectively expressed in BAT and further upregulated during cold exposure. Inhibiting miR-32 in vivo led to impaired cold tolerance, decreased BAT thermogenesis, and compromised white fat browning as a result of reduced serum FGF21 levels. Further examination showed that miR-32 directly represses its target gene Tob1, thereby activating p38 MAP kinase signaling to drive FGF21 expression and secretion from BAT. BAT-specific miR-32 overexpression led to increased BAT thermogenesis and serum FGF21 levels, which further promotes white fat browning in trans. Our results suggested miR-32 and Tob1 as modulators of FGF21 signaling that can be manipulated for therapeutic benefit against obesity and metabolic syndrome.

Epistatic interaction between the lipase-encoding genes Pnpla2 and Lipe causes liposarcoma in mice

Liposarcoma is an often fatal cancer of fat cells. Mechanisms of liposarcoma development are incompletely understood. The cleavage of fatty acids from acylglycerols (lipolysis) has been implicated in cancer. We generated mice with adipose tissue deficiency of two major enzymes of lipolysis, adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL), encoded respectively by Pnpla2 and Lipe. Adipocytes from double adipose knockout (DAKO) mice, deficient in both ATGL and HSL, showed near-complete deficiency of lipolysis. All DAKO mice developed liposarcoma between 11 and 14 months of age. No tumors occurred in single knockout or control mice. The transcriptome of DAKO adipose tissue showed marked differences from single knockout and normal controls as early as 3 months. Gpnmb and G0s2 were among the most highly dysregulated genes in premalignant and malignant DAKO adipose tissue, suggesting a potential utility as early markers of the disease. Similar changes of GPNMB and G0S2 expression were present in a human liposarcoma database. These results show that a previously-unknown, fully penetrant epistatic interaction between Pnpla2 and Lipe can cause liposarcoma in mice. DAKO mice provide a promising model for studying early premalignant changes that lead to late-onset malignant disease.

Liposarcoma is an often fatal adult-onset tumor of fat tissue. Lipolysis, the central pathway of fat tissue metabolism, has been implicated in cancer. We generated mice that were deficient in two key enzymes of lipolysis, adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL). Strikingly, all mice with combined ATGL and HSL deficiency developed liposarcoma by 11–14 months of age. No liposarcoma occurred in single knockout or normal controls. Transcriptome analysis revealed that a subset of genes is dysregulated by 3 months of age. Our study reveals a novel epistatic interaction in fat cells between these two lipase genes and that causes a unique form of liposarcoma in mice. The double knockout mice provide a novel tool to study the early stages of liposarcoma development, prognostic markers and preventive treatments.

Rheb Inhibits Beiging of White Adipose Tissue via PDE4D5-Dependent Downregulation of the cAMP-PKA Signaling Pathway

Beiging of white adipose tissue has potential antiobesity and antidiabetes effects, yet the underlying signaling mechanisms remain to be fully elucidated. Here we show that adipose-specific knockout of Rheb, an upstream activator of mechanistic target of rapamycin complex 1 (mTORC1), protects mice from high-fat diet-induced obesity and insulin resistance. On the one hand, Rheb deficiency in adipose tissue reduced mTORC1 signaling, increased lipolysis, and promoted beiging and energy expenditure. On the other hand, overexpression of Rheb in primary adipocytes significantly inhibited CREB phosphorylation and uncoupling protein 1 (UCP1) expression. Mechanistically, fat-specific knockout of Rheb increased cAMP levels, cAMP-dependent protein kinase (PKA) activity, and UCP1 expression in subcutaneous white adipose tissue. Interestingly, treating primary adipocytes with rapamycin only partially alleviated the suppressing effect of Rheb on UCP1 expression, suggesting the presence of a novel mechanism underlying the inhibitory effect of Rheb on thermogenic gene expression. Consistent with this notion, overexpression of Rheb stabilizes the expression of cAMP-specific phosphodiesterase 4D5 (PDE4D5) in adipocytes, whereas knockout of Rheb greatly reduced cellular levels of PDE4D5 concurrently with increased cAMP levels, PKA activation, and UCP1 expression. Taken together, our findings reveal Rheb as an important negative regulator of beige fat development and thermogenesis. In addition, Rheb is able to suppress the beiging effect through an mTORC1-independent mechanism.

Regulation of white and brown adipocyte differentiation by RhoGAP DLC1

Adipose tissues constitute an important component of metabolism, the dysfunction of which can cause obesity and type II diabetes. Here we show that differentiation of white and brown adipocytes requires Deleted in Liver Cancer 1 (DLC1), a Rho GTPase Activating Protein (RhoGAP) previously studied for its function in liver cancer. We identified Dlc1 as a super-enhancer associated gene in both white and brown adipocytes through analyzing the genome-wide binding profiles of PPARγ, the master regulator of adipogenesis. We further observed that Dlc1 expression increases during differentiation, and knockdown of Dlc1 by siRNA in white adipocytes reduces the formation of lipid droplets and the expression of fat marker genes. Moreover, knockdown of Dlc1 in brown adipocytes reduces expression of brown fat-specific genes and diminishes mitochondrial respiration. Dlc1-/- knockout mouse embryonic fibroblasts show a complete inability to differentiate into adipocytes, but this phenotype can be rescued by inhibitors of Rho-associated kinase (ROCK) and filamentous actin (F-actin), suggesting the involvement of Rho pathway in DLC1-regulated adipocyte differentiation. Furthermore, PPARγ binds to the promoter of Dlc1 gene to regulate its expression during both white and brown adipocyte differentiation. These results identify DLC1 as an activator of white and brown adipocyte differentiation, and provide a molecular link between PPARγ and Rho pathways.

Cyclin C regulates adipogenesis by stimulating transcriptional activity of CCAAT/enhancer-binding protein α

Brown adipose tissue is important for maintaining energy homeostasis and adaptive thermogenesis in rodents and humans. As disorders arising from dysregulated energy metabolism, such as obesity and metabolic diseases, have increased, so has interest in the molecular mechanisms of adipocyte biology. Using a functional screen, we identified cyclin C (CycC), a conserved subunit of the Mediator complex, as a novel regulator for brown adipocyte formation. siRNA-mediated CycC knockdown (KD) in brown preadipocytes impaired the early transcriptional program of differentiation, and genetic KO of CycC completely blocked the differentiation process. RNA sequencing analyses of CycC-KD revealed a critical role of CycC in activating genes co-regulated by peroxisome proliferator activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα). Overexpression of PPARγ2 or addition of the PPARγ ligand rosiglitazone rescued the defects in CycC-KO brown preadipocytes and efficiently activated the PPARγ-responsive promoters in both WT and CycC-KO cells, suggesting that CycC is not essential for PPARγ transcriptional activity. In contrast, CycC-KO significantly reduced C/EBPα-dependent gene expression. Unlike for PPARγ, overexpression of C/EBPα could not induce C/EBPα target gene expression in CycC-KO cells or rescue the CycC-KO defects in brown adipogenesis, suggesting that CycC is essential for C/EBPα-mediated gene activation. CycC physically interacted with C/EBPα, and this interaction was required for C/EBPα transactivation domain activity. Consistent with the role of C/EBPα in white adipogenesis, CycC-KD also inhibited differentiation of 3T3-L1 cells into white adipocytes. Together, these data indicate that CycC activates adipogenesis in part by stimulating the transcriptional activity of C/EBPα.

Dopamine directly increases mitochondrial mass and thermogenesis in brown adipocytes

Brown adipose tissue (BAT) is key to energy homeostasis. By virtue of its thermogenic potential, it may dissipate excessive energy, regulate body weight and increase insulin sensitivity. Catecholamines are critically involved in the regulation of BAT thermogenesis, yet research has focussed on the effects of noradrenaline and adrenaline. Some evidence suggests a role of dopamine (DA) in BAT thermogenesis, but the cellular mechanisms involved have not been addressed. We employed our extensively characterised murine brown adipocyte cells. D1-like and D2-like receptors were detectable at the protein level. Stimulation with DA caused an increase in cAMP concentrations. Oxygen consumption rates (OCR), mitochondrial membrane potential (Δψ_m) and uncoupling protein 1 (UCP1) levels increased after 24 h of treatment with either DA or a D1-like specific receptor agonist. A D1-like receptor antagonist abolished the DA-mediated effect on OCR, Δψ_m and UCP1. DA induced the release of fatty acids, which did not additionally alter DA-mediated increases of OCR. Mitochondrial mass (as determined by (i) CCCP- and oligomycin-mediated effects on OCR and (ii) immunoblot analysis of mitochondrial proteins) also increased within 24 h. This was accompanied by an increase in peroxisome proliferator-activated receptor gamma co-activator 1 alpha protein levels. Also, DA caused an increase in p38 MAPK phosphorylation and pharmacological inhibition of p38 MAPK abolished the DA-mediated effect on Δψ_m In summary, our study is the first to reveal direct D1-like receptor and p38 MAPK-mediated increases of thermogenesis and mitochondrial mass in brown adipocytes. These results expand our understanding of catecholaminergic effects on BAT thermogenesis.

Glucocorticoid Receptor Accelerates, but Is Dispensable for, Adipogenesis

Dexamethasone (DEX), a synthetic ligand for glucocorticoid receptor (GR), is routinely used to stimulate adipogenesis in culture. GR-depleted preadipocytes show adipogenesis defects 1 week after induction of differentiation. However, it has remained unclear whether GR is required for adipogenesis in vivo By deleting GR in precursors of brown adipocytes, we found unexpectedly that GR is dispensable for brown adipose tissue development in mice. In culture, GR-deficient primary or immortalized white and brown preadipocytes showed severely delayed adipogenesis 1 week after induction of differentiation. However, when differentiation was extended to 3 weeks, GR-deficient preadipocytes showed levels of adipogenesis marker expression and lipid accumulation similar to those of the wild-type cells, indicating that DEX-bound GR accelerates, but is dispensable for, adipogenesis. Consistently, DEX accelerates, but is dispensable for, adipogenesis in culture. We show that DEX-bound GR accelerates adipogenesis by directly promoting the expression of adipogenic transcription factors CCAAT/enhancer-binding protein alpha (C/EBPα), C/EBPβ, C/EBPδ, KLF5, KLF9, and peroxisome proliferator-activated receptor γ (PPARγ) in the early phase of differentiation. Mechanistically, DEX-bound GR recruits histone H3K27 acetyltransferase CBP to promote activation of C/EBPβ-primed enhancers of adipogenic genes. These results clarify the role of GR in adipogenesis in vivo and demonstrate that DEX-mediated activation of GR accelerates, but is dispensable for, adipogenesis.

Distinct Roles of Transcription Factors KLF4, Krox20, and Peroxisome Proliferator-Activated Receptor γ in Adipogenesis

Much of our knowledge on adipogenesis comes from cell culture models of preadipocyte differentiation. Adipogenesis is induced by treating confluent preadipocytes with the adipogenic cocktail, which activates transcription factors (TFs) glucocorticoid receptor (GR) and CREB within minutes and increases expression of TFs C/EBPβ, C/EBPδ, KLF4, and Krox20 within hours. All of these TFs have been shown to be capable of promoting adipogenesis in culture when they are overexpressed. However, it has remained unclear whether endogenous KLF4 and Krox20 are required for adipogenesis in culture and in vivo Using conditional knockout mice and derived white and brown preadipocytes, we show that endogenous KLF4 and Krox20 are dispensable for adipogenesis in culture and for brown adipose tissue development in mice. In contrast, the master adipogenic TF peroxisome proliferator-activated receptor γ (PPARγ) is essential. These results challenge the existing model on transcriptional regulation in the early phase of adipogenesis and highlight the need of studying adipogenesis in vivo.

Kinase Inactive Tyrosine Kinase (Tyk2) Supports Differentiation of Brown Fat Cells

It has been known for decades that brown adipose tissue (BAT) plays a central role in maintaining body temperature in hibernating animals and human infants. Recently, it has become evident that there are also depots of brown fat in adult humans, and the mass of brown fat is inversely correlated with body weight. There are a variety of transcription factors implicated in the differentiation of classical Myf5+ brown preadipocytes, one of the most important of which is PRDM16. We have recently identified that in addition to PRDM16, the tyrosine kinase Tyk2 and the STAT3 transcription factor are required for the differentiation of Myf5 positive brown preadipocytes both in cell culture and in mice. Tyk2 is a member of the Jak family of tyrosine kinases, which are activated by exposure of cells to different cytokines and growth factors. In this study we report the surprising observation that a mutated form of Tyk2, which lacks tyrosine kinase activity (Tyk2KD) restores differentiation of brown preadipocytes in vitro as well as in Tyk2-/- mice. Furthermore, expression of the Tyk2KD transgene in brown fat reverses the obese phenotype of Tyk2-/- animals. Treatment of cells with Jak-selective inhibitors suggests that the mechanism by which Tyk2KD functions to restore BAT differentiation is by dimerizing with kinase active Jak1 or Jak2. These results indicate that there are redundant mechanisms by which members of the Jak family can contribute to differentiation of BAT.

β-Adrenergic Receptor and Insulin Resistance in the Heart

Insulin resistance is characterized by the reduced ability of insulin to stimulate tissue uptake and disposal of glucose including cardiac muscle. These conditions accelerate the progression of heart failure and increase cardiovascular morbidity and mortality in patients with cardiovascular diseases. It is noteworthy that some conditions of insulin resistance are characterized by up-regulation of the sympathetic nervous system, resulting in enhanced stimulation of β-adrenergic receptor (βAR). Overstimulation of βARs leads to the development of heart failure and is associated with the pathogenesis of insulin resistance in the heart. However, pathological consequences of the cross-talk between the βAR and the insulin sensitivity and the mechanism by which βAR overstimulation promotes insulin resistance remain unclear. This review article examines the hypothesis that βARs overstimulation leads to induction of insulin resistance in the heart.

mTORC1 is Required for Brown Adipose Tissue Recruitment and Metabolic Adaptation to Cold

In response to cold, brown adipose tissue (BAT) increases its metabolic rate and expands its mass to produce heat required for survival, a process known as BAT recruitment. The mechanistic target of rapamycin complex 1 (mTORC1) controls metabolism, cell growth and proliferation, but its role in regulating BAT recruitment in response to chronic cold stimulation is unknown. Here, we show that cold activates mTORC1 in BAT, an effect that depends on the sympathetic nervous system. Adipocyte-specific mTORC1 loss in mice completely blocks cold-induced BAT expansion and severely impairs mitochondrial biogenesis. Accordingly, mTORC1 loss reduces oxygen consumption and causes a severe defect in BAT oxidative metabolism upon cold exposure. Using in vivo metabolic imaging, metabolomics and transcriptomics, we show that mTORC1 deletion impairs glucose and lipid oxidation, an effect linked to a defect in tricarboxylic acid (TCA) cycle activity. These analyses also reveal a severe defect in nucleotide synthesis in the absence of mTORC1. Overall, these findings demonstrate an essential role for mTORC1 in the regulation of BAT recruitment and metabolism in response to cold.

The Effects of High Fat Diet and Resveratrol on Mitochondrial Activity of Brown Adipocytes

BACKGROUND

Resveratrol (RSV) is a polyphenolic phytoalexin that has many effects on metabolic diseases such as diabetes and obesity. Given the importance of brown adipose tissue (BAT) for energy expenditure, we investigated the effects of RSV on brown adipocytes.

METHODS

For the in vitro study, interscapular BAT was isolated from 7-week-old male Sprague Dawley rats. For the in vivo study, 7-week-old male Otsuka Long Evans Tokushima Fatty (OLETF) rats were divided into four groups and treated for 27 weeks with: standard diet (SD); SD+RSV (10 mg/kg body weight, daily); high fat diet (HFD); HFD+RSV. RSV was provided via oral gavage once daily during the in vivo experiments.

RESULTS

RSV treatment of primary cultured brown preadipocytes promoted mitochondrial activity, along with over-expression of estrogen receptor α (ER-α). In OLETF rats, both HFD and RSV treatment increased the weight of BAT and the differentiation of BAT. However, only RSV increased the mitochondrial activity and ER-α expression of BAT in the HFD-fed group. Finally, RSV improved the insulin sensitivity of OLETF rats by increasing the mitochondrial activity of BAT, despite having no effects on white adipocytes and muscles in either diet group.

CONCLUSION

RSV could improve insulin resistance, which might be associated with mitochondrial activity of brown adipocyte. Further studies evaluating the activity of RSV for both the differentiation and mitochondrial activity of BAT could be helpful in investigating the effects of RSV on metabolic parameters.

Fat accumulation in differentiated brown adipocytes is linked with expression of Hox genes

Homeobox (Hox) genes are involved in body plan of embryo along the anterior-posterior axis. Presence of several Hox genes in white adipose tissue (WAT) and brown adipose tissue (BAT) is indicative of involvement of Hox genes in adipogenesis. We propose that differentiation inducing agents viz. isobutyl-methyl-xanthine (IBMX), indomethacin, dexamethasone (DEX), triiodothyronine (T3) and insulin may regulate differentiation in brown adipose tissue through Hox genes. In vitro culture of brown fat stromalvascular fraction (SVF) in presence or absence of differentiation inducing agents was used for establishing relationship between fat accumulation in differentiated adipocytes and expression of Hox genes. Relative expression of Pref1, UCP1 and Hox genes was determined in different stages of adipogenesis. Presence or absence of IBMX, indomethacin and DEX during differentiation of proliferated pre-adipocytes resulted in marked differences in expression of Hox genes and lipid accumulation. In presence of these inducing agents, lipid accumulation as well as expression of HoxA1, HoxA5, HoxC4 &HoxC8 markedly enhanced. Irrespective of presence or absence of T3, insulin down regulates HoxA10. T3 results in over expression of HoxA5, HoxC4 and HoxC8 genes, whereas insulin up regulates expression of only HoxC8. Findings suggest that accumulation of fat in differentiated adipocytes is linked with expression of Hox genes.

Anti-obesity effects of Arctii Fructus (Arctium lappa) in white/brown adipocytes and high-fat diet-induced obese mice

Arctii Fructus prevents the development of obesity through the regulation of white/brown adipocytes.

Sustained βAR Stimulation Mediates Cardiac Insulin Resistance in a PKA-Dependent Manner

Insulin resistance is a condition in which cells are defective in response to the actions of insulin in tissue glucose uptake. Overstimulation of β-adrenergic receptors (βARs) leads to the development of heart failure and is associated with the pathogenesis of insulin resistance in the heart. However, the mechanisms by which sustained βAR stimulation affects insulin resistance in the heart are incompletely understood. In this study, we demonstrate that sustained βAR stimulation resulted in the inhibition of insulin-induced glucose uptake, and a reduction of insulin induced glucose transporter (GLUT)4 expression that were mediated by the β2AR subtype in cardiomyocytes and heart tissue. Overstimulation of β2AR inhibited the insulin-induced translocation of GLUT4 to the plasma membrane of cardiomyocytes. Additionally, βAR mediated cardiac insulin resistance by reducing glucose uptake and GLUT4 expression via the cAMP-dependent and protein kinase A-dependent pathways. Treatment with β-blockers, including propranolol and metoprolol antagonized isoproterenol-mediated insulin resistance in the heart. The data in this present study confirm a critical role for protein kinase A in βAR-mediated insulin resistance.

IRE1α-XBP1 is a novel branch in the transcriptional regulation of Ucp1 in brown adipocytes

The unfolded protein response (UPR) not only resolves endoplasmic reticulum (ER) stress, but also regulates cellular physiological functions. In this study, we first linked the UPR to the physiological roles of brown adipose tissue (BAT). BAT is one of the tissues that control energy homeostasis in the body. Brown adipocytes are able to dissipate energy in the form of heat owing to their mitochondrial protein, uncoupling protein 1 (UCP1). We found that one of the UPR branches, the IRE1α-XBP1 pathway, was activated during the transcriptional induction of Ucp1. Inhibiting the IRE1α-XBP1 pathway reduced the induction of Ucp1 expression. However, the activation of the IRE1α-XBP1 pathway by ER stress never upregulated Ucp1. On the other hand, the activation of protein kinase A (PKA) induced Ucp1 transcription through the activation of IRE1α-XBP1. The inhibition of PKA abrogated the activation of IRE1α-XBP1 pathway, while the inhibition of a p38 mitogen activated protein kinase (p38 MAPK), which is one of the downstream molecules of PKA, never suppressed the activation of IRE1α-XBP1 pathway. These data indicate that PKA-dependent IRE1α-XBP1 activation is crucial for the transcriptional induction of Ucp1 in brown adipocytes, and they demonstrate a novel, ER stress -independent role of the UPR during thermogenesis.

MAP kinase phosphatase 3 inhibits brown adipocyte differentiation via regulation of Erk phosphorylation

Brown fat has been highlight as a new therapeutic target for treatment of obesity and diabetes. However, molecular mechanism underlying brown adipogenesis are not fully understood. Here, we identified that MAP kinase phosphatase 3 (MKP3) has a novel role as regulator of brown adipocyte differentiation. The expression of MKP3 was significantly decreased during the early stage(s) of brown adipocyte differentiation in HIB-1B cells and primary cells. Ectopic expression of MKP3 led to reduced brown adipocyte differentiation, whereas depletion of MKP3 significantly enhanced the differentiation of primary brown preadipocytes. Consistently, we found an increased brown adipocyte differentiation in MKP3-null MEF cells. These inhibitory effects of MKP3 could be resulted via the temporal regulation of Erk activation. In recent, it was reported that MKP3 deficient mice are resistant to diet-induced obesity, and display enhanced energy expenditure. Taken together, we suggest that MKP3 could be an important factor in the regulation of brown adipocyte differentiation.

In vitro differentiation of mouse brown preadipocytes is enhanced by IGFBP-3 expression and reduced by IGFBP-3 silencing

OBJECTIVE

White adipocyte metabolism is regulated by insulin-like growth factor-binding protein (IGFBP)-3, but its effect on brown adipocytes is not known. This study investigated whether IGFBP-3 influences the proliferation and differentiation of brown preadipocytes in primary culture.

METHODS

In vitro growth and differentiation of brown preadipocytes from wild-type mice, transgenic mice overexpressing human IGFBP-3 (PGKBP3), or its non-IGF-binding Gly56/Gly80/Gly81-mutant (PGKmutBP3), and wild-type brown preadipocytes transfected with IGFBP-3 siRNA were studied by us. In addition to IGF-I and IGFBP-3 expression, brown preadipocyte growth and differentiation were assessed by antiproliferating cell nuclear antigen, oil red O, brown fat gene expression, and phosphorylation states of Akt and ERK.

RESULTS

Akt phosphorylation and IGF-I expression were paralleled by initial growth and differentiation and were slower for PGKBP3 brown preadipocytes than PGKmutBP3 and wild-type preadipocytes. Terminal adipocyte differentiation as assessed by lipid accumulation coincided with ERK inhibition and was greatest in PGKmutBP3 cells, followed by PGKBP3 cells and then wild-type cells, whereas adipocyte differentiation was poor after IGFBP-3 siRNA treatment. Thermogenic genes were increased by IGFBP-3 overexpression, but lower in differentiated PGKmutBP3 than PGKBP3 cells.

CONCLUSIONS

Brown adipocyte growth and differentiation in vitro were affected by the manipulation of IGFBP-3 expression, suggesting that IGFBP-3 is a factor regulating brown adipocyte fate.

STAT6-Dependent Collagen Synthesis in Human Fibroblasts Is Induced by Bovine Milk

Since the domestication of the urus, 10.000 years ago, mankind utilizes bovine milk for different purposes. Besides usage as a nutrient also the external application of milk on skin has a long tradition going back to at least the ancient Aegypt with Cleopatra VII as a great exponent. In order to test whether milk has impact on skin physiology, cultures of human skin fibroblasts were exposed to commercial bovine milk. Our data show significant induction of proliferation by milk (max. 2,3-fold, EC50: 2,5% milk) without toxic effects. Surprisingly, bovine milk was identified as strong inducer of collagen 1A1 synthesis at both, the protein (4-fold, EC50: 0,09% milk) and promoter level. Regarding the underlying molecular pathways, we show functional activation of STAT6 in a p44/42 and p38-dependent manner. More upstream, we identified IGF-1 and insulin as key factors responsible for milk-induced collagen synthesis. These findings show that bovine milk contains bioactive molecules that act on human skin cells. Therefore, it is tempting to test the herein introduced concept in treatment of atrophic skin conditions induced e.g. by UV light or corticosteroids.

The Role of PDE3B Phosphorylation in the Inhibition of Lipolysis by Insulin

Inhibition of adipocyte lipolysis by insulin is important for whole-body energy homeostasis; its disruption has been implicated as contributing to the development of insulin resistance and type 2 diabetes mellitus. The main target of the antilipolytic action of insulin is believed to be phosphodiesterase 3B (PDE3B), whose phosphorylation by Akt leads to accelerated degradation of the prolipolytic second messenger cyclic AMP (cAMP). To test this hypothesis genetically, brown adipocytes lacking PDE3B were examined for their regulation of lipolysis. In Pde3b knockout (KO) adipocytes, insulin was unable to suppress β-adrenergic receptor-stimulated glycerol release. Reexpressing wild-type PDE3B in KO adipocytes fully rescued the action of insulin against lipolysis. Surprisingly, a mutant form of PDE3B that ablates the major Akt phosphorylation site, murine S273, also restored the ability of insulin to suppress lipolysis. Taken together, these data suggest that phosphorylation of PDE3B by Akt is not required for insulin to suppress adipocyte lipolysis.

The role of mouse Akt2 in insulin-dependent suppression of adipocyte lipolysis in vivo

AIM/HYPOTHESIS

The release of fatty acids from adipocytes, i.e. lipolysis, is maintained under tight control, primarily by the opposing actions of catecholamines and insulin. A widely accepted model is that insulin antagonises catecholamine-dependent lipolysis through phosphorylation and activation of cAMP phosphodiesterase 3B (PDE3B) by the serine-threonine protein kinase Akt (protein kinase B). Recently, this hypothesis has been challenged, as in cultured adipocytes insulin appears, under some conditions, to suppress lipolysis independently of Akt.

METHODS

To address the requirement for Akt2, the predominant isoform expressed in classic insulin target tissues, in the suppression of fatty acid release in vivo, we assessed lipolysis in mice lacking Akt2.

RESULTS

In the fed state and following an oral glucose challenge, Akt2 null mice were glucose intolerant and hyperinsulinaemic, but nonetheless exhibited normal serum NEFA and glycerol levels, suggestive of normal suppression of lipolysis. Furthermore, insulin partially inhibited lipolysis in Akt2 null mice during an insulin tolerance test (ITT) and hyperinsulinaemic-euglycaemic clamp, respectively. In support of these in vivo observations, insulin antagonised catecholamine-induced lipolysis in primary brown fat adipocytes from Akt2-deficient mice.

CONCLUSIONS/INTERPRETATION

These data suggest that suppression of lipolysis by insulin in hyperinsulinaemic states can take place in the absence of Akt2.

Regulation of systemic energy homeostasis by serotonin in adipose tissues

Central serotonin (5-HT) is an anorexigenic neurotransmitter in the brain. However, accumulating evidence suggests peripheral 5-HT may affect organismal energy homeostasis. Here we show 5-HT regulates white and brown adipose tissue function. Pharmacological inhibition of 5-HT synthesis leads to inhibition of lipogenesis in epididymal white adipose tissue (WAT), induction of browning in inguinal WAT and activation of adaptive thermogenesis in brown adipose tissue (BAT). Mice with inducible Tph1 KO in adipose tissues exhibit a similar phenotype as mice in which 5-HT synthesis is inhibited pharmacologically, suggesting 5-HT has localized effects on adipose tissues. In addition, Htr3a KO mice exhibit increased energy expenditure and reduced weight gain when fed a high-fat diet. Treatment with an Htr2a antagonist reduces lipid accumulation in 3T3-L1 adipocytes. These data suggest important roles for adipocyte-derived 5-HT in controlling energy homeostasis.

Cell-autonomous activation of Hedgehog signaling inhibits brown adipose tissue development

Although recent studies have shown that brown adipose tissue (BAT) arises from progenitor cells that also give rise to skeletal muscle, the developmental signals that control the formation of BAT remain largely unknown. Here, we show that brown preadipocytes possess primary cilia and can respond to Hedgehog (Hh) signaling. Furthermore, cell-autonomous activation of Hh signaling blocks early brown-preadipocyte differentiation, inhibits BAT formation in vivo, and results in replacement of neck BAT with poorly differentiated skeletal muscle. Finally, we show that Hh signaling inhibits BAT formation partially through up-regulation of chicken ovalbumin upstream promoter transcription factor II (COUP-TFII). Taken together, our studies uncover a previously unidentified role for Hh as an inhibitor of BAT development.

Biocompatible flavone-based fluorogenic probes for quick wash-free mitochondrial imaging in living cells

Mitochondria, vital organelles existing in almost all eukaryotic cells, play a crucial role in energy metabolism and apoptosis of aerobic organisms. In this work, we report two new flavone-based fluorescent probes, MC-Mito1 and MC-Mito2, for monitoring mitochondria in living cells. These two probes exhibit remarkably low toxicity, good cell permeability, and high specificity; these probes complement the existing library of mitochondrial imaging agents. The new dyes give nearly no background fluorescence, and their application does not require tedious postwashing after cell staining. The appreciable tolerance of MC-Mito2 encourages a broader range of biological applications for understanding the cell degeneration and apoptosis mechanism.

Anti-obesity effects of granulocyte-colony stimulating factor in Otsuka-Long-Evans-Tokushima fatty rats

Granulocyte-colony stimulating factor (G-CSF) has molecular structures and intracellular signaling pathways that are similar to those of leptin and ciliary neurotropic factor (CNTF). It also has immune-modulatory properties. Given that leptin and CNTF play important roles in energy homeostasis and that obesity is an inflammatory condition in adipose tissue, we hypothesized that G-CSF could also play a role in energy homeostasis. We treated 12 38-week-old male Otsuka-Long-Evans-Tokushima fatty rats (OLETF, diabetic) and 12 age-matched male Long-Evans-Tokushima rats (LETO, healthy) with 200 µg/day G-CSF or saline for 5 consecutive days. Body weight reduction was greater in G-CSF-treated OLETF (G-CSF/OLETF) than saline-treated OLETF (saline/OLETF) following 8 weeks of treatment (−6.9±1.6% vs. −3.1±2.2%, p<0.05). G-CSF treatment had no effect on body weight in LETO or on food intake in either OLETF or LETO. Body fat in G-CSF/OLETF was more reduced than in saline/OLETF (−32.2±3.1% vs. −20.8±6.2%, p<0.05). Energy expenditure was higher in G-CSF/OLETF from 4 weeks after the treatments than in saline/OLETF. Serum levels of cholesterol, triglyceride, interleukin-6 and tumor necrosis factor-α were lower in G-CSF/OLETF than in saline/OLETF. Uncoupling protein-1 (UCP-1) expression in brown adipose tissue (BAT) was higher in G-CSF/OLETF than in saline/OLETF, but was unaffected in LETO. Immunofluorescence staining and PCR results revealed that G-CSF receptors were expressed in BAT. In vitro experiments using brown adipocyte primary culture revealed that G-CSF enhanced UCP-1 expression from mature brown adipocytes via p38 mitogen-activated protein kinase pathway. In conclusion, G-CSF treatment reduced body weight and increased energy expenditure in a diabetic model, and enhanced UCP-1 expression and decreased inflammatory cytokine levels may be associated with the effects of G-CSF treatment.

Rubi Fructus (Rubus coreanus) activates the expression of thermogenic genes in vivo and in vitro

OBJECTIVE

To investigate the anti-obesity effect of Rubi Fructus (RF) extract using brown adipose tissue (BAT) and primary brown preadipocytes in vivo and in vitro.

METHODS

Male C57BL/6 J mice (n=5 per group) were fed a high-fat diet (HFD) for 10 weeks with or without RF. Brown preadipocytes from the interscapular BAT of mice (age, post-natal days 1-3) were cultured with differentiation media (DM) including isobutylmethylxanthine, dexamethasone, T3, indomethacin and insulin with or without RF.

RESULTS

In HFD-induced obese C57BL/6 J mice, long-term RF treatment significantly reduced weight gain as well as the weights of the white adipose tissue, liver and spleen. Serum levels of total cholesterol and low-density lipoprotein cholesterol were also reduced in the HFD group which received RF treatment. Furthermore, RF induced thermogenic-, adipogenic- and mitochondria-related gene expressions in BAT. In primary brown adipocytes, RF effectively stimulated the expressions of thermogenic- and mitochondria-related genes. In addition, to examine whether LIPIN1, a regulator of adipocyte differentiation, is regulated by RF, Lipin1 small interfering RNA (siRNA) and RF were pretreated in primary brown adipocytes. Pretreatment with Lipin1 siRNA and RF downregulated the DM-induced expression levels of thermogenic- and mitochondria-related genes. Moreover, RF markedly upregulated AMP-activated protein kinase. Our study shows that RF is capable of stimulating the differentiation of brown adipocytes through the modulation of thermogenic genes.

CONCLUSIONS

This study demonstrates that RF prevents the development of obesity in mice fed with a HFD and that it is also capable of stimulating the differentiation of brown adipocytes through the modulation of thermogenic genes, which suggests that RF has potential as a therapeutic application for the treatment or prevention of obesity.

GADD45γ regulates the thermogenic capacity of brown adipose tissue

The coactivator peroxisome proliferator-activated receptor-gamma coactivator 1 α (PGC-1α) is widely considered a central transcriptional regulator of adaptive thermogenesis in brown adipose tissue (BAT). However, mice lacking PGC-1α specifically in adipose tissue have only mild thermogenic defects, suggesting the presence of additional regulators. Using the activity of estrogen-related receptors (ERRs), downstream effectors of PGC-1α, as read-out in a high-throughput genome-wide cDNA screen, we identify here growth arrest and DNA-damage-inducible protein 45 γ (GADD45γ) as a cold-induced activator of uncoupling protein 1 (UCP1) and oxidative capacity in BAT. Mice lacking Gadd45γ have defects in Ucp1 induction and the thermogenic response to cold. GADD45γ works by activating MAPK p38, which is a potent activator of ERRβ and ERRγ transcriptional function. GADD45γ activates ERRγ independently of PGC-1 coactivators, yet synergizes with PGC-1α to induce the thermogenic program. Our findings elucidate a previously unidentified GADD45γ/p38/ERRγ pathway that regulates BAT thermogenesis and may enable new approaches for the stimulation of energy expenditure. Our study also implicates GADD45 proteins as general metabolic regulators.

Vascular rarefaction mediates whitening of brown fat in obesity

Brown adipose tissue (BAT) is a highly vascularized organ with abundant mitochondria that produce heat through uncoupled respiration. Obesity is associated with a reduction of BAT function; however, it is unknown how obesity promotes dysfunctional BAT. Here, using a murine model of diet-induced obesity, we determined that obesity causes capillary rarefaction and functional hypoxia in BAT, leading to a BAT "whitening" phenotype that is characterized by mitochondrial dysfunction, lipid droplet accumulation, and decreased expression of Vegfa. Targeted deletion of Vegfa in adipose tissue of nonobese mice resulted in BAT whitening, supporting a role for decreased vascularity in obesity-associated BAT. Conversely, introduction of VEGF-A specifically into BAT of obese mice restored vascularity, ameliorated brown adipocyte dysfunction, and improved insulin sensitivity. The capillary rarefaction in BAT that was brought about by obesity or Vegfa ablation diminished β-adrenergic signaling, increased mitochondrial ROS production, and promoted mitophagy. These data indicate that overnutrition leads to the development of a hypoxic state in BAT, causing it to whiten through mitochondrial dysfunction and loss. Furthermore, these results link obesity-associated BAT whitening to impaired systemic glucose metabolism.