Impaired macrophage autophagy increases the immune response in obese mice by promoting proinflammatory macrophage polarization

Recent evidence that excessive lipid accumulation can decrease cellular levels of autophagy and that autophagy regulates immune responsiveness suggested that impaired macrophage autophagy may promote the increased innate immune activation that underlies obesity. Primary bone marrow-derived macrophages (BMDM) and peritoneal macrophages from high-fat diet (HFD)-fed mice had decreased levels of autophagic flux indicating a generalized impairment of macrophage autophagy in obese mice. To assess the effects of decreased macrophage autophagy on inflammation, mice with a Lyz2-Cre-mediated knockout of Atg5 in macrophages were fed a HFD and treated with low-dose lipopolysaccharide (LPS). Knockout mice developed systemic and hepatic inflammation with HFD feeding and LPS. This effect was liver specific as knockout mice did not have increased adipose tissue inflammation. The mechanism by which the loss of autophagy promoted inflammation was through the regulation of macrophage polarization. BMDM and Kupffer cells from knockout mice exhibited abnormalities in polarization with both increased proinflammatory M1 and decreased anti-inflammatory M2 polarization as determined by measures of genes and proteins. The heightened hepatic inflammatory response in HFD-fed, LPS-treated knockout mice led to liver injury without affecting steatosis. These findings demonstrate that autophagy has a critical regulatory function in macrophage polarization that downregulates inflammation. Defects in macrophage autophagy may underlie inflammatory disease states such as the decrease in macrophage autophagy with obesity that leads to hepatic inflammation and the progression to liver injury.

The sexually dimorphic role of adipose and adipocyte estrogen receptors in modulating adipose tissue expansion, inflammation, and fibrosis

Our data demonstrate that estrogens, estrogen receptor-α (ERα), and estrogen receptor-β (ERβ) regulate adipose tissue distribution, inflammation, fibrosis, and glucose homeostasis, by determining that αERKO mice have increased adipose tissue inflammation and fibrosis prior to obesity onset. Selective deletion of adipose tissue ERα in adult mice using a novel viral vector technology recapitulated the findings in the total body ERα null mice. Generation of a novel mouse model, lacking ERα specifically from adipocytes (AdipoERα), demonstrated increased markers of fibrosis and inflammation, especially in the males. Additionally, we found that the beneficial effects of estrogens on adipose tissue require adipocyte ERα. Lastly, we determined the role of ERβ in regulating inflammation and fibrosis, by breeding the AdipoERα into the βERKO background and found that in the absence of adipocyte ERα, ERβ has a protective role. These data suggest that adipose tissue and adipocyte ERα protects against adiposity, inflammation, and fibrosis in both males and females.

Brown adipose tissue derived VEGF-A modulates cold tolerance and energy expenditure

We recently reported that local overexpression of VEGF-A in white adipose tissue (WAT) protects against diet-induced obesity and metabolic dysfunction. The observation that VEGF-A induces a “brown adipose tissue (BAT)-like” phenotype in WAT prompted us to further explore the direct function of VEGF-A in BAT. We utilized a doxycycline (Dox)-inducible, brown adipocyte-specific VEGF-A transgenic overexpression model to assess direct effects of VEGF-A in BAT in vivo. We observed that BAT-specific VEGF-A expression increases vascularization and up-regulates expression of both UCP1 and PGC-1α in BAT. As a result, the transgenic mice show increased thermogenesis during chronic cold exposure. In diet-induced obese mice, introducing VEGF-A locally in BAT rescues capillary rarefaction, ameliorates brown adipocyte dysfunction, and improves deleterious effects on glucose and lipid metabolism caused by a high-fat diet challenge. These results demonstrate a direct positive role of VEGF-A in the activation and expansion of BAT.

Small molecules for fat combustion: targeting obesity

Obesity is increasing in an alarming rate worldwide, which causes higher risks of some diseases, such as type 2 diabetes, cardiovascular diseases, and cancer. Current therapeutic approaches, either pancreatic lipase inhibitors or appetite suppressors, are generally of limited effectiveness. Brown adipose tissue (BAT) and beige cells dissipate fatty acids as heat to maintain body temperature, termed non-shivering thermogenesis; the activity and mass of BAT and beige cells are negatively correlated with overweight and obesity. The existence of BAT and beige cells in human adults provides an effective weight reduction therapy, a process likely to be amenable to pharmacological intervention. Herein, we combed through the physiology of thermogenesis and the role of BAT and beige cells in combating with obesity. We summarized the thermogenic regulators identified in the past decades, targeting G protein-coupled receptors, transient receptor potential channels, nuclear receptors and miscellaneous pathways. Advances in clinical trials were also presented. The main purpose of this review is to provide a comprehensive and up-to-date knowledge from the biological importance of thermogenesis in energy homeostasis to the representative thermogenic regulators for treating obesity. Thermogenic regulators might have a large potential for further investigations to be developed as lead compounds in fighting obesity.

EBF2 promotes the recruitment of beige adipocytes in white adipose tissue

Objective

The induction of beige/brite adipose cells in white adipose tissue (WAT) is associated with protection against high fat diet-induced obesity and insulin resistance in animals. The helix-loop-helix transcription factor Early B-Cell Factor-2 (EBF2) regulates brown adipose tissue development. Here, we asked if EBF2 regulates beige fat cell biogenesis and protects animals against obesity.

Methods

In addition to primary cell culture studies, we used ​Ebf2 knockout mice and mice overexpressing EBF2 in the adipose tissue to study the necessity and sufficiency of EBF2 to induce beiging in vivo.

Results

We found that EBF2 is required for beige adipocyte development in mice. Subcutaneous WAT or primary adipose cell cultures from Ebf2 knockout mice did not induce Uncoupling Protein 1 (UCP1) or a thermogenic program following adrenergic stimulation. Conversely, over-expression of EBF2 in adipocyte cultures induced UCP1 expression and a brown-like/beige fat-selective differentiation program. Transgenic expression of Ebf2 in adipose tissues robustly stimulated beige adipocyte development in the WAT of mice, even while housed at thermoneutrality. EBF2 overexpression was sufficient to increase mitochondrial function in WAT and protect animals against high fat diet-induced weight gain.

Conclusions

Taken together, our results demonstrate that EBF2 controls the beiging process and suggest that activation of EBF2 in WAT could be used to reduce obesity.

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Loss of Ebf2 prevents induction of beige adipocytes in inguinal WAT.

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Ectopic expression of Ebf2 promotes beige fat induction in inguinal WAT.

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Ectopic Ebf2 expression protects against high fat diet-induced obesity.

Role of the circadian clock gene Per2 in adaptation to cold temperature

Adaptive thermogenesis allows mammals to resist to cold. For instance, in brown adipose tissue (BAT) the facultative uncoupling of the proton gradient from ATP synthesis in mitochondria is used to generate systemic heat. However, this system necessitates an increase of the Uncoupling protein 1 (Ucp1) and its activation by free fatty acids. Here we show that mice without functional Period2 (Per2) were cold sensitive because their adaptive thermogenesis system was less efficient. Upon cold-exposure, Heat shock factor 1 (HSF1) induced Per2 in the BAT. Subsequently, PER2 as a co-activator of PPARα increased expression of Ucp1. PER2 also increased Fatty acid binding protein 3 (Fabp3), a protein important to transport free fatty acids from the plasma to mitochondria to activate UCP1. Hence, in BAT PER2 is important for the coordination of the molecular response of mice exposed to cold by synchronizing UCP1 expression and its activation.

Mice lacking neutral amino acid transporter B(0)AT1 (Slc6a19) have elevated levels of FGF21 and GLP-1 and improved glycaemic control

OBJECTIVE

Type 2 diabetes arises from insulin resistance of peripheral tissues followed by dysfunction of β-cells in the pancreas due to metabolic stress. Both depletion and supplementation of neutral amino acids have been discussed as strategies to improve insulin sensitivity. Here we characterise mice lacking the intestinal and renal neutral amino acid transporter B(0)AT1 (Slc6a19) as a model to study the consequences of selective depletion of neutral amino acids.

METHODS

Metabolic tests, analysis of metabolite levels and signalling pathways were used to characterise mice lacking the intestinal and renal neutral amino acid transporter B(0)AT1 (Slc6a19).

RESULTS

Reduced uptake of neutral amino acids in the intestine and loss of neutral amino acids in the urine causes an overload of amino acids in the lumen of the intestine and reduced systemic amino acid availability. As a result, higher levels of glucagon-like peptide 1 (GLP-1) are produced by the intestine after a meal, while the liver releases the starvation hormone fibroblast growth factor 21 (FGF21). The combination of these hormones generates a metabolic phenotype that is characterised by efficient removal of glucose, particularly by the heart, reduced adipose tissue mass, browning of subcutaneous white adipose tissue, enhanced production of ketone bodies and reduced hepatic glucose output.

CONCLUSIONS

Reduced neutral amino acid availability improves glycaemic control. The epithelial neutral amino acid transporter B(0)AT1 could be a suitable target to treat type 2 diabetes.

Phenotypic comparison of common mouse strains developing high-fat diet-induced hepatosteatosis

Genetic predisposition and environmental factors contribute to an individual's susceptibility to develop hepatosteatosis. In a systematic, comparative survey we focused on genotype-dependent and -independent adaptations early in the pathogenesis of hepatosteatosis by characterizing C3HeB/FeJ, C57BL/6NTac, C57BL/6J, and 129P2/OlaHsd mice after 7, 14, or 21 days high-fat-diet exposure. Strain-specific metabolic responses during diet challenge and liver transcript signatures in mild hepatosteatosis outline the suitability of particular strains for investigating the relationship between hepatocellular lipid content and inflammation, glucose homeostasis, insulin action, or organelle physiology. Genetic background-independent transcriptional adaptations in liver paralleling hepatosteatosis suggest an early increase in the organ's vulnerability to oxidative stress damage what could advance hepatosteatosis to steatohepatitis. "Universal" adaptations in transcript signatures and transcription factor regulation in liver link insulin resistance, type 2 diabetes mellitus, cancer, and thyroid hormone metabolism with hepatosteatosis, hence, facilitating the search for novel molecular mechanisms potentially implicated in the pathogenesis of human non-alcoholic-fatty-liver-disease.

TNP [N2-(m-Trifluorobenzyl), N6-(p-nitrobenzyl)purine] ameliorates diet induced obesity and insulin resistance via inhibition of the IP6K1 pathway

Objective

Obesity and type 2 diabetes (T2D) lead to various life-threatening diseases such as coronary heart disease, stroke, osteoarthritis, asthma, and neurodegeneration. Therefore, extensive research is ongoing to identify novel pathways that can be targeted in obesity/T2D. Deletion of the inositol pyrophosphate (5-IP7) biosynthetic enzyme, inositol hexakisphosphate kinase-1 (IP6K1), protects mice from high fat diet (HFD) induced obesity (DIO) and insulin resistance. Yet, whether this pathway is a valid pharmacologic target in obesity/T2D is not known. Here, we demonstrate that TNP [N2-(m-Trifluorobenzyl), N6-(p-nitrobenzyl)purine], a pan-IP6K inhibitor, has strong anti-obesity and anti-diabetic effects in DIO mice.

Methods

Q-NMR, GTT, ITT, food intake, energy expenditure, QRT-PCR, ELISA, histology, and immunoblot studies were conducted in short (2.5-week)- and long (10-week)-term TNP treated DIO C57/BL6 WT and IP6K1-KO mice, under various diet and temperature conditions.

Results

TNP, when injected at the onset of HFD-feeding, decelerates initiation of DIO and insulin resistance. Moreover, TNP facilitates weight loss and restores metabolic parameters, when given to DIO mice. However, TNP does not reduce weight gain in HFD-fed IP6K1-KO mice. TNP specifically enhances insulin sensitivity in DIO mice via Akt activation. TNP decelerates weight gain primarily by enhancing thermogenic energy expenditure in the adipose tissue. Accordingly, TNP's effect on body weight is partly abolished whereas its impact on glucose homeostasis is preserved at thermoneutral temperature.

Conclusion

Pharmacologic inhibition of the inositol pyrophosphate pathway has strong therapeutic potential in obesity, T2D, and other metabolic diseases.

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Pharmacologic inhibition of IP6K by TNP, at the onset of high fat feeding, decelerates initiation of DIO and insulin resistance in mice.

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TNP, when treated to DIO mice, promotes weight loss and restores metabolic homeostasis.

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TNP does not reduce high fat diet induced weight gain in IP6K1-KO mice.

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TNP promotes insulin sensitivity by stimulating Akt activity, whereas it reduces body weight primarily by enhancing thermogenic energy expenditure.

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Long-term TNP treatment does not display deleterious side effects.

An overview on medicinal perspective of thiazolidine-2,4-dione: A remarkable scaffold in the treatment of type 2 diabetes

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TZDs, an important pharmacophore in the treatment of diabetes.

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Various analog-based synthetic strategies and biological significance are discussed.

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Clinical studies using TZDs along with other antidiabetic agents are also highlighted.

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SAR has been discussed to suggest the interactions between derivatives and receptor sites.

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Pyrazole, chromone, and acid-based TZDs can be considered as potential lead molecules.

Diabetes or diabetes mellitus is a complex or polygenic disorder, which is characterized by increased levels of glucose (hyperglycemia) and deficiency in insulin secretion or resistance to insulin over an elongated period in the liver and peripheral tissues. Thiazolidine-2,4-dione (TZD) is a privileged scaffold and an outstanding heterocyclic moiety in the field of drug discovery, which provides various opportunities in exploring this moiety as an antidiabetic agent. In the past few years, various novel synthetic approaches had been undertaken to synthesize different derivatives to explore them as more potent antidiabetic agents with devoid of side effects (i.e., edema, weight gain, and bladder cancer) of clinically used TZD (pioglitazone and rosiglitazone). In this review, an effort has been made to summarize the up to date research work of various synthetic strategies for TZD derivatives as well as their biological significance and clinical studies of TZDs in combination with other category as antidiabetic agents. This review also highlights the structure-activity relationships and the molecular docking studies to convey the interaction of various synthesized novel derivatives with its receptor site.

Inhibition of citrate cotransporter Slc13a5/mINDY by RNAi improves hepatic insulin sensitivity and prevents diet-induced non-alcoholic fatty liver disease in mice

Objective

Non-alcoholic fatty liver disease is a world-wide health concern and risk factor for cardio-metabolic diseases. Citrate uptake modifies intracellular hepatic energy metabolism and is controlled by the conserved sodium-dicarboxylate cotransporter solute carrier family 13 member 5 (SLC13A5, mammalian homolog of INDY: mINDY). In Drosophila melanogaster and Caenorhabditis elegans INDY reduction decreased whole-body lipid accumulation. Genetic deletion of Slc13a5 in mice protected from diet-induced adiposity and insulin resistance. We hypothesized that inducible hepatic mINDY inhibition should prevent the development of fatty liver and hepatic insulin resistance.

Methods

Adult C57BL/6J mice were fed a Western diet (60% kcal from fat, 21% kcal from carbohydrate) ad libitum. Knockdown of mINDY was induced by weekly injection of a chemically modified, liver-selective siRNA for 8 weeks. Mice were metabolically characterized and the effect of mINDY suppression on glucose tolerance as well as insulin sensitivity was assessed with an ipGTT and a hyperinsulinemic-euglycemic clamp. Hepatic lipid accumulation was determined by biochemical measurements and histochemistry.

Results

Within the 8 week intervention, hepatic mINDY expression was suppressed by a liver-selective siRNA by over 60%. mINDY knockdown improved hepatic insulin sensitivity (i.e. insulin-induced suppression of endogenous glucose production) of C57BL/6J mice in the hyperinsulinemic-euglycemic clamp. Moreover, the siRNA-mediated mINDY inhibition prevented neutral lipid storage and triglyceride accumulation in the liver, while we found no effect on body weight.

Conclusions

We show that inducible mINDY inhibition improved hepatic insulin sensitivity and prevented diet-induced non-alcoholic fatty liver disease in adult C57BL6/J mice. These effects did not depend on changes of body weight or body composition.

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mINDY/Slc13a5 knockdown was induced by liver-selective siRNA in mice.

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Liver-selective knockdown of mINDY improved hepatic insulin sensitivity.

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Liver-selective knockdown of mINDY prevented steatosis hepatis.

FGF21 does not require adipocyte AMP-activated protein kinase (AMPK) or the phosphorylation of acetyl-CoA carboxylase (ACC) to mediate improvements in whole-body glucose homeostasis

Objective

Fibroblast growth factor 21 (FGF21) shows great potential for the treatment of obesity and type 2 diabetes, as its long-acting analogue reduces body weight and improves lipid profiles of participants in clinical studies; however, the intracellular mechanisms mediating these effects are poorly understood. AMP-activated protein kinase (AMPK) is an important energy sensor of the cell and a molecular target for anti-diabetic medications. This work examined the role of AMPK in mediating the glucose and lipid-lowering effects of FGF21.

Methods

Inducible adipocyte AMPK β1β2 knockout mice (iβ1β2AKO) and littermate controls were fed a high fat diet (HFD) and treated with native FGF21 or saline for two weeks. Additionally, HFD-fed mice with knock-in mutations on the AMPK phosphorylation sites of acetyl-CoA carboxylase (ACC)1 and ACC2 (DKI mice) along with wild-type (WT) controls received long-acting FGF21 for two weeks.

Results

Consistent with previous studies, FGF21 treatment significantly reduced body weight, adiposity, and liver lipids in HFD fed mice. To add, FGF21 improved circulating lipids, glycemic control, and insulin sensitivity. These effects were independent of adipocyte AMPK and were not associated with changes in browning of white (WAT) and brown adipose tissue (BAT). Lastly, we assessed whether FGF21 exerted its effects through the AMPK/ACC axis, which is critical in the therapeutic benefits of the anti-diabetic medication metformin. ACC DKI mice had improved glucose and insulin tolerance and a reduction in body weight, body fat and hepatic steatosis similar to WT mice in response to FGF21 administration.

Conclusions

These data illustrate that the metabolic improvements upon FGF21 administration are independent of adipocyte AMPK, and do not require the inhibitory action of AMPK on ACC. This is in contrast to the anti-diabetic medication metformin and suggests that the treatment of obesity and diabetes with the combination of FGF21 and AMPK activators merits consideration.

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FGF21 reduces adiposity and improves insulin resistance in mice fed a high-fat diet.

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FGF21 improves insulin sensitivity and hepatic steatosis independent of adipocyte AMPK.

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FGF21 treatment does not elicit an increase in browning of BAT or WAT.

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In contrast to metformin, FGF21's intracellular mechanism is not through AMPK/ACC.

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Findings suggest that combination of FGF21 and AMPK activators could be of benefit.

Leptin action via LepR-b Tyr1077 contributes to the control of energy balance and female reproduction

Leptin action in the brain signals the repletion of adipose energy stores, suppressing feeding and permitting energy expenditure on a variety of processes, including reproduction. Leptin binding to its receptor (LepR-b) promotes the tyrosine phosphorylation of three sites on LepR-b, each of which mediates distinct downstream signals. While the signals mediated by LepR-b Tyr1138 and Tyr985 control important aspects of energy homeostasis and LepR-b signal attenuation, respectively, the role of the remaining LepR-b phosphorylation site (Tyr1077) in leptin action has not been studied. To examine the function of Tyr1077, we generated a "knock-in" mouse model expressing LepR-b (F1077), which is mutant for LepR-b Tyr1077. Mice expressing LepR-b (F1077) demonstrate modestly increased body weight and adiposity. Furthermore, females display impairments in estrous cycling. Our results suggest that signaling by LepR-b Tyr1077 plays a modest role in the control of metabolism by leptin, and is an important link between body adiposity and the reproductive axis.

Skeletal muscle salt inducible kinase 1 promotes insulin resistance in obesity

OBJECTIVE

Insulin resistance causes type 2 diabetes mellitus and hyperglycemia due to excessive hepatic glucose production and inadequate peripheral glucose uptake. Our objectives were to test the hypothesis that the proposed CREB/CRTC2 inhibitor salt inducible kinase 1 (SIK1) contributes to whole body glucose homeostasis in vivo by regulating hepatic transcription of gluconeogenic genes and also to identify novel SIK1 actions on glucose metabolism.

METHODS

We created conditional (floxed) SIK1-knockout mice and studied glucose metabolism in animals with global, liver, adipose or skeletal muscle Sik1 deletion. We examined cAMP-dependent regulation of SIK1 and the consequences of SIK1 depletion on primary mouse hepatocytes. We probed metabolic phenotypes in tissue-specific SIK1 knockout mice fed high fat diet through hyperinsulinemic-euglycemic clamps and biochemical analysis of insulin signaling.

RESULTS

SIK1 knockout mice are viable and largely normoglycemic on chow diet. On high fat diet, global SIK1 knockout animals are strikingly protected from glucose intolerance, with both increased plasma insulin and enhanced peripheral insulin sensitivity. Surprisingly, liver SIK1 is not required for regulation of CRTC2 and gluconeogenesis, despite contributions of SIK1 to hepatocyte CRTC2 and gluconeogenesis regulation ex vivo. Sik1 mRNA accumulates in skeletal muscle of obese high fat diet-fed mice, and knockout of SIK1 in skeletal muscle, but not liver or adipose tissue, improves insulin sensitivity and muscle glucose uptake on high fat diet.

CONCLUSIONS

SIK1 is dispensable for glycemic control on chow diet. SIK1 promotes insulin resistance on high fat diet by a cell-autonomous mechanism in skeletal muscle. Our study establishes SIK1 as a promising therapeutic target to improve skeletal muscle insulin sensitivity in obese individuals without deleterious effects on hepatic glucose production.

Thioesterase superfamily member 1 suppresses cold thermogenesis by limiting the oxidation of lipid droplet-derived fatty acids in brown adipose tissue

OBJECTIVE

Non-shivering thermogenesis in brown adipose tissue (BAT) plays a central role in energy homeostasis. Thioesterase superfamily member 1 (Them1), a BAT-enriched long chain fatty acyl-CoA thioesterase, is upregulated by cold and downregulated by warm ambient temperatures. Them1 (-/-) mice exhibit increased energy expenditure and resistance to diet-induced obesity and diabetes, but the mechanistic contribution of Them1 to the regulation of cold thermogenesis remains unknown.

METHODS

Them1 (-/-) and Them1 (+/+) mice were subjected to continuous metabolic monitoring to quantify the effects of ambient temperatures ranging from thermoneutrality (30 °C) to cold (4 °C) on energy expenditure, core body temperature, physical activity and food intake. The effects of Them1 expression on O2 consumption rates, thermogenic gene expression and lipolytic protein activation were determined ex vivo in BAT and in primary brown adipocytes.

RESULTS

Them1 suppressed thermogenesis in mice even in the setting of ongoing cold exposure. Without affecting thermogenic gene transcription, Them1 reduced O2 consumption rates in both isolated BAT and primary brown adipocytes. This was attributable to decreased mitochondrial oxidation of endogenous but not exogenous fatty acids.

CONCLUSIONS

These results show that Them1 may act as a break on uncontrolled heat production and limit the extent of energy expenditure. Pharmacologic inhibition of Them1 could provide a targeted strategy for the management of metabolic disorders via activation of brown fat.

High fat diet-induced modifications in membrane lipid and mitochondrial-membrane protein signatures precede the development of hepatic insulin resistance in mice

Objective

Excess lipid intake has been implicated in the pathophysiology of hepatosteatosis and hepatic insulin resistance. Lipids constitute approximately 50% of the cell membrane mass, define membrane properties, and create microenvironments for membrane-proteins. In this study we aimed to resolve temporal alterations in membrane metabolite and protein signatures during high-fat diet (HF)-mediated development of hepatic insulin resistance.

Methods

We induced hepatosteatosis by feeding C3HeB/FeJ male mice an HF enriched with long-chain polyunsaturated C18:2n6 fatty acids for 7, 14, or 21 days. Longitudinal changes in hepatic insulin sensitivity were assessed via the euglycemic-hyperinsulinemic clamp, in membrane lipids via t-metabolomics- and membrane proteins via quantitative proteomics-analyses, and in hepatocyte morphology via electron microscopy. Data were compared to those of age- and litter-matched controls maintained on a low-fat diet.

Results

Excess long-chain polyunsaturated C18:2n6 intake for 7 days did not compromise hepatic insulin sensitivity, however, induced hepatosteatosis and modified major membrane lipid constituent signatures in liver, e.g. increased total unsaturated, long-chain fatty acid-containing acyl-carnitine or membrane-associated diacylglycerol moieties and decreased total short-chain acyl-carnitines, glycerophosphocholines, lysophosphatidylcholines, or sphingolipids. Hepatic insulin sensitivity tended to decrease within 14 days HF-exposure. Overt hepatic insulin resistance developed until day 21 of HF-intervention and was accompanied by morphological mitochondrial abnormalities and indications for oxidative stress in liver. HF-feeding progressively decreased the abundance of protein-components of all mitochondrial respiratory chain complexes, inner and outer mitochondrial membrane substrate transporters independent from the hepatocellular mitochondrial volume in liver.

Conclusions

We assume HF-induced modifications in membrane lipid- and protein-signatures prior to and during changes in hepatic insulin action in liver alter membrane properties – in particular those of mitochondria which are highly abundant in hepatocytes. In turn, a progressive decrease in the abundance of mitochondrial membrane proteins throughout HF-exposure likely impacts on mitochondrial energy metabolism, substrate exchange across mitochondrial membranes, contributes to oxidative stress, mitochondrial damage, and the development of insulin resistance in liver.

Emerging Roles of Adipose Tissue in the Pathogenesis of Psoriasis and Atopic Dermatitis in Obesity

Obesity is a growing epidemic worldwide, and it is also considered a major environmental factor contributing to the pathogenesis of inflammatory skin diseases, including psoriasis (PSO) and atopic dermatitis (AD). Moreover, obesity worsens the course and impairs the treatment response of these inflammatory skin diseases. Emerging evidence highlights that hypertrophied adipocytes and infiltrated immune cells secrete a variety of molecules, including fatty acids and adipokines, such as leptin, adiponectin, and a panel of cytokines/chemokines that modulate our immune system. In this review, we describe how adipose hypertrophy leads to a chronic low-grade inflammatory state in obesity and how obesity-related inflammatory factors are involved in the pathogenesis of PSO and/or AD. Finally, we discuss the potential role of antimicrobial peptides, mechanical stress and impairment of epidermal barrier function mediated by fast expansion, and dermal fat in modulating skin inflammation. Together, this review summarizes the current literature on how obesity is associated with the pathogenesis of PSO and AD, highlighting the potentially important but overlooked immunomodulatory role of adipose tissue in the skin.

Asperuloside stimulates metabolic function in rats across several organs under high-fat diet conditions, acting like the major ingredient of Eucommia leaves with anti-obesity activity

Eucommia leaves (Eucommia ulmoides Oliver) contain chlorogenic acid (a caffeic acid derivative) and geniposidic acid and asperuloside (ASP), iridoid glucosides used in beverages. We used a metabolic syndrome rat model, produced by feeding a 35 % high-fat diet (HFD), to examine potential anti-obesity and anti-metabolic syndrome effects and mechanisms of chronic administration of ASP. These effects were compared with Eucommia leaf extract (ELE), the positive control, which exhibits anti-obesity effects. A total of six rats were studied for 3 months in five groups. ASP suppressed body weight, visceral fat weight, food intake and circulating levels of glucose, insulin and lipids, and increased the plasma adiponectin level in rats on a HFD. These effects are similar to those of ELE, except for the influence on the plasma glucose level. RT-PCR studies showed that ASP (like ELE with known anti-obesity effects) diminished isocitrate dehydrogenase 3α, NADH dehydrogenase flavoprotein 1 (Comp I) mRNA and fatty acid synthase levels (white adipose tissue), increased carnitine palmitoyltransferase 1α and acyl-CoA dehydrogenase, very-long-chain mRNA levels (liver), and increased Glut4, citrate synthase, isocitrate dehydrogenase 3α, succinyl CoA synthase, peroxisomal 3-ketoacyl-CoA thiolase, dihydrolipoamide succinyl transferase and succinate dehydrogenase mRNA levels (skeletal muscle) under HFD conditions. Interestingly, ASP administration resulted in significantly increased mRNA levels of uncoupling protein 1 (UCP1) in the brown adipose tissue of HFD-fed rats; ELE did not affect the expression of UCP1. The increased expression of UCP1 may be negated by many ingredients other than ASP in the ELE. These findings suggest that chronic administration of ASP stimulates anti-obesity and anti-metabolic syndrome activity in HFD-fed rats across several organs, similar to ELE administration; thus, ASP may be an important ingredient of ELE.

Adipocyte-specific Hypoxia-inducible gene 2 promotes fat deposition and diet-induced insulin resistance

Objective

Adipose tissue relies on lipid droplet (LD) proteins in its role as a lipid-storing endocrine organ that controls whole body metabolism. Hypoxia-inducible Gene 2 (Hig2) is a recently identified LD-associated protein in hepatocytes that promotes hepatic lipid storage, but its role in the adipocyte had not been investigated. Here we tested the hypothesis that Hig2 localization to LDs in adipocytes promotes adipose tissue lipid deposition and systemic glucose homeostasis.

Method

White and brown adipocyte-deficient (Hig2^fl/fl × Adiponection cre+) and selective brown/beige adipocyte-deficient (Hig2^fl/fl × Ucp1 cre+) mice were generated to investigate the role of Hig2 in adipose depots. Additionally, we used multiple housing temperatures to investigate the role of active brown/beige adipocytes in this process.

Results

Hig2 localized to LDs in SGBS cells, a human adipocyte cell strain. Mice with adipocyte-specific Hig2 deficiency in all adipose depots demonstrated reduced visceral adipose tissue weight and increased glucose tolerance. This metabolic effect could be attributed to brown/beige adipocyte-specific Hig2 deficiency since Hig2^fl/fl × Ucp1 cre+ mice displayed the same phenotype. Furthermore, when adipocyte-deficient Hig2 mice were moved to thermoneutral conditions in which non-shivering thermogenesis is deactivated, these improvements were abrogated and glucose intolerance ensued. Adipocyte-specific Hig2 deficient animals displayed no detectable changes in adipocyte lipolysis or energy expenditure, suggesting that Hig2 may not mediate these metabolic effects by restraining lipolysis in adipocytes.

Conclusions

We conclude that Hig2 localizes to LDs in adipocytes, promoting adipose tissue lipid deposition and that its selective deficiency in active brown/beige adipose tissue mediates improved glucose tolerance at 23 °C. Reversal of this phenotype at thermoneutrality in the absence of detectable changes in energy expenditure, adipose mass, or liver triglyceride suggests that Hig2 deficiency triggers a deleterious endocrine or neuroendocrine pathway emanating from brown/beige fat cells.

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Hig2 localizes to lipid droplets in adipocytes and promotes adipose tissue lipid deposition.

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Its selective deficiency in active brown/beige adipose tissue mediates improved glucose tolerance at 23 °C.

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Metabolic improvements are independent of changes in lipolysis.

Loss of ADAMTS5 enhances brown adipose tissue mass and promotes browning of white adipose tissue via CREB signaling

Objective

A potential strategy to treat obesity – and the associated metabolic consequences – is to increase energy expenditure. This could be achieved by stimulating thermogenesis through activation of brown adipose tissue (BAT) and/or the induction of browning of white adipose tissue (WAT). Over the last years, it has become clear that several metalloproteinases play an important role in adipocyte biology. Here, we investigated the potential role of ADAMTS5.

Methods

Mice deficient in ADAMTS5 (Adamts5^−/−) and wild-type (Adamts5^+/+) littermates were kept on a standard of Western-type diet for 15 weeks. Energy expenditure and heat production was followed by indirect calorimetry. To activate thermogenesis, mice were treated with the β3-adrenergic receptor (β₃-AR) agonist CL-316,243 or alternatively, exposed to cold for 2 weeks.

Results

Compared to Adamts5^+/+ mice, Adamts5^−/− mice have significantly more interscapular BAT and marked browning of their subcutaneous (SC) WAT. Thermogenic pathway analysis indicated, in the absence of ADAMTS5, enhanced β₃-AR signaling via activation of the cAMP response element-binding protein (CREB). Additional β₃-AR stimulation with CL-316,243 promoted browning of WAT in Adamts5^+/+ mice but had no additive effect in Adamts5^−/− mice. However, cold exposure induced more pronounced browning of WAT in Adamts5^−/− mice.

Conclusions

These data indicate that ADAMTS5 plays a functional role in development of BAT and browning of WAT. Hence, selective targeting of ADAMTS5 could provide a novel therapeutic strategy for treatment/prevention of obesity and metabolic diseases.

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Mice deficient in ADAMTS5 have elevated interscapular brown adipose tissue mass.

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ADAMTS5 deficient mice show increased browning of their white adipose tissue.

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The thermogenic profile is enhanced via adrenergic signaling and CREB activation.

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ADAMTS5 seems an attractive therapeutic target for metabolic diseases.

Dynamic upregulation of CD24 in pre-adipocytes promotes adipogenesis

The development of mature adipocytes from pre-adipocytes is a highly regulated process. CD24 is a glycophosphatidylinositol-linked cell surface receptor that has been identified as a critical cell surface marker for identifying pre-adipocytes that are able to reconstitute white adipose tissue (WAT) in vivo. Here, we examined the role and regulation of CD24 during adipogenesis in vitro. We found that CD24 mRNA and protein expression is upregulated early during adipogenesis in the 3T3-L1 pre-adipocytes and in murine primary pre-adipocytes isolated from subcutaneous and visceral WAT, followed by downregulation in mature adipocytes. CD24 mRNA expression was found to be dependent on increased transcription due to increased promoter activity in response to activation of a pre-existing transcriptional regulator. Furthermore, either intracellular cAMP or dexamethasone were sufficient to increase expression in pre-adipocytes, while both additively increased CD24 expression. Preventing the increase in CD24 expression, by siRNA-mediated knock-down, resulted in fewer mature lipid-laden adipocytes and decreased expression of mature adipogenic genes. Therefore, conditions experienced during adipogenesis in vitro are sufficient to increase CD24 expression, which is necessary for differentiation. Overall, we conclude that the dynamic upregulation of CD24 actively promotes adipogenesis in vitro.

FTO is necessary for the induction of leptin resistance by high-fat feeding

OBJECTIVE

Loss of function FTO mutations significantly impact body composition in humans and mice, with Fto-deficient mice reported to resist the development of obesity in response to a high-fat diet (HFD). We aimed to further explore the interactions between FTO and HFD and determine if FTO can influence the adverse metabolic consequence of HFD.

METHODS

We studied mice deficient in FTO in two well validated models of leptin resistance (HFD feeding and central palmitate injection) to determine how Fto genotype may influence the action of leptin. Using transcriptomic analysis of hypothalamic tissue to identify relevant pathways affected by the loss of Fto, we combined data from co-immunoprecipitation, yeast 2-hybrid and luciferase reporter assays to identify mechanisms through which FTO can influence the development of leptin resistant states.

RESULTS

Mice deficient in Fto significantly increased their fat mass in response to HFD. Fto (+/-) and Fto (-/-) mice remained sensitive to the anorexigenic effects of leptin, both after exposure to a HFD or after acute central application of palmitate. Genes encoding components of the NFкB signalling pathway were down-regulated in the hypothalami of Fto-deficient mice following a HFD. When this pathway was reactivated in Fto-deficient mice with a single low central dose of TNFα, the mice became less sensitive to the effect of leptin. We identified a transcriptional coactivator of NFкB, TRIP4, as a binding partner of FTO and a molecule that is required for TRIP4 dependent transactivation of NFкB.

CONCLUSIONS

Our study demonstrates that, independent of body weight, Fto influences the metabolic outcomes of a HFD through alteration of hypothalamic NFкB signalling. This supports the notion that pharmacological modulation of FTO activity might have the potential for therapeutic benefit in improving leptin sensitivity, in a manner that is influenced by the nutritional environment.

Acute induction of uncoupling protein 1 by citrulline in cultured explants of white adipose tissue from lean and high-fat-diet-fed rats

A diet enriched with citrulline (CIT) reduces white adipose tissue (WAT) mass. We recently showed that CIT stimulated β-oxidation in rat WAT explants from young (2-4 months) but not old (25 months) rats. Here we show that both in old rats and high-fat-diet-fed young rats, uncoupling protein one (UCP1) mRNA and protein expressions were weaker than those in young control rats. Selectively in WAT from young rats, a 24h CIT treatment up-regulated expressions of UCP1, peroxisome proliferator-activated receptor-α (PPARα), PPARγ-coactivator-1-α and mitochondrial-transcription-factor-A whereas it down-regulated PPARγ2 gene expression, whatever the diet. These results suggest that CIT induces a new metabolic status in WAT, with increased β-oxidation and uncoupling of respiratory chain, resulting in energy expenditure that favors fat mass reduction.

Chronic high-fat feeding impairs adaptive induction of mitochondrial fatty acid combustion-associated proteins in brown adipose tissue of mice

Since brown adipose tissue (BAT) is involved in thermogenesis using fatty acids as a fuel, BAT activation is a potential strategy for treating obesity and diabetes. However, whether BAT fatty acid combusting capacity is preserved in these conditions has remained unclear. We therefore evaluated expression levels of fatty acid oxidation-associated enzymes and uncoupling protein 1 (Ucp1) in BAT by western blot using a diet-induced obesity C57BL/6J mouse model. In C57BL/6J mice fed a high-fat diet (HFD) over 2–4 weeks, carnitine palmitoyltransferase 2 (Cpt2), acyl-CoA thioesterase (Acot) 2, Acot11 and Ucp1 levels were significantly increased compared with baseline and control low-fat diet (LFD)-fed mice. Similar results were obtained in other mouse strains, including ddY, ICR and KK-Ay, but the magnitudes of the increase in Ucp1 level were much smaller than in C57BL/6J mice, with decreased Acot11 levels after HFD-feeding. In C57BL/6J mice, increased levels of these mitochondrial proteins declined to near baseline levels after a longer-term HFD-feeding (20 weeks), concurrent with the accumulation of unilocular, large lipid droplets in brown adipocytes. Extramitochondrial Acot11 and acyl-CoA oxidase remained elevated. Treatment of mice with Wy-14,643 also increased these proteins, but was less effective than 4 week-HFD, suggesting that mechanisms other than peroxisome proliferator-activated receptor α were also involved in the upregulation. These results suggest that BAT enhances its fatty acid combusting capacity in response to fat overload, however profound obesity deprives BAT of the responsiveness to fat, possibly via mitochondrial alteration.

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BAT activation is a potential strategy for treating obesity and diabetes.

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BAT enhances its fatty acid combusting capacity in response to high-fat feeding.

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Profound obesity deprives BAT of the responsiveness to fat overload.

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Susceptibility to BAT activation could depend on the degree of obesity.

Mast cell deficiency results in the accumulation of preadipocytes in adipose tissue in both obese and non-obese mice

Mast cells have been suggested to play key roles in adipogenesis. We herein show that the expression of preadipocyte, but not adipocyte, marker genes increases in the white adipose tissue of mast cell-deficient (Kit^W-sh/W-sh) mice under both obese and non-obese conditions. In vitro culturing with adipogenic factors revealed increased adipocytes differentiated from the Kit^W-sh/W-sh stromal vascular fraction, suggesting the accumulation of preadipocytes. Moreover, the increased expression of preadipocyte genes was restored by mast cell reconstitution in the Kit^W-sh/W-sh mice. These results suggest positive effects of mast cells on the preadipocyte to adipocyte transition under both physiological and pathological conditions.

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Mast cell-deficient mice are resistant to diet-induced obesity.

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The expression of preadipocyte genes is increased in their white adipose tissue.

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The content of preadipocytes is increased in the adipose stromal vascular fraction.

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Mast cell reconstitution restores the enhanced expression of preadipocyte genes.

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Mast cells may facilitate the preadipocyte–adipocyte transition in white adipose tissue.