Adipose Tissue Of Obese Animals Research Articles

Short-term strength exercise reduces the macrophage M1/M2 ratio in white adipose tissue of obese animals

Obesity can exacerbate the systemic inflammatory process, leading to increased infiltration of monocytes in white adipose tissue (WAT) and polarization of these cells into pro-inflammatory M1 macrophages, while reducing the population of anti-inflammatory M2 macrophages. Aerobic exercise has been shown to be effective in reducing the pro-inflammatory profile. However, the impact of strength training and the duration of training on macrophage polarization in the WAT of obese individuals have not been widely studied. Therefore, our aim was to investigate the effects of resistance exercise on macrophage infiltration and polarization in the epididymal and subcutaneous adipose tissue of obese mice. We compared the following groups: Control (CT), Obese (OB), Obese 7-day strength training (STO7d), and Obese 15-day strength training (STO15d). Macrophage populations were evaluated by flow cytometry: total macrophages (F4/80+), M1 (CD11c), and M2 (CD206) macrophages. Our results demonstrated that both training protocols improved peripheral insulin sensitivity by increasing AKT phosphorylation (Ser473). Specifically, the 7-day training regimen reduced total macrophage infiltration and M2 macrophage levels without altering M1 levels. In the STO15d group, significant differences were observed in total macrophage levels, M1 macrophages, and the M1/M2 ratio compared to the OB group. In the epididymal tissue, a reduction in the M1/M2 ratio was observed in the STO7d group. Overall, our data demonstrate that 15 days of strength exercise can reduce the M1/M2 ratio of macrophages in white adipose tissue.

Of mice and men: Considerations on adipose tissue physiology in animal models of obesity and human studies

The ever-increasing burden of obesity demands a better pathophysiological understanding, especially regarding adipose tissue pathophysiology. Animal models of obesity are of great importance in investigating potential mechanisms and implications of obesity. Many issues should be considered while interpreting the preclinical results as anatomical and pathophysiological differences exist among species. Importantly, the natural history of obesity development differs considerably. An important example of conflicting results among preclinical models and human physiological studies is that of adipose tissue oxygenation, where rodent models almost unanimously have shown the presence of hypoxia in the adipose tissue of obese animals while human studies have yielded conflicting results to date. Other issues which require further clarification before generalizing preclinical data in humans include adipose tissue browning, endocrine function and fibrosis. The aim of this mini-review is to synopsize similarities and differences between rodent models and humans, which should be taken into consideration in obesity studies.

HDAC6-mediated acetylation of lipid droplet-binding protein CIDEC regulates fat-induced lipid storage.

Obesity is characterized by aberrant fat accumulation. However, the intracellular signaling pathway that senses dietary fat and leads to fat storage remains elusive. Here, we have observed that the levels of histone deacetylase 6 (HDAC6) and the related family member HDAC10 are markedly reduced in adipose tissues of obese animals and humans. Mice with adipocyte-specific depletion of Hdac6 exhibited increased fat accumulation and reduced insulin sensitivity. In normal adipocytes, we found that reversal of P300/CBP-associated factor-induced (PCAF-induced) acetylation at K56 on cell death-inducing DFFA-like effector C (CIDEC, also known as FSP27) critically regulated lipid droplet fusion and lipid storage. Importantly, HDAC6 deacetylates CIDEC, leading to destabilization and reduced lipid droplet fusion. Accordingly, we observed elevated levels of CIDEC and its acetylated form in HDAC-deficient adipocytes as well as the adipose tissue of obese animals and humans. Fatty acids (FAs) prevented CIDEC deacetylation by promoting the dissociation of CIDEC from HDAC6, which resulted in increased association of CIDEC with PCAF on the endoplasmic reticulum. Control of CIDEC acetylation required the conversion of FAs to triacylglycerols. Thus, we have revealed a signaling axis that is involved in the coordination of nutrient availability, protein acetylation, and cellular lipid metabolic responses.

A Sex‐Specific Role for Egr1 in Mediating Norepinephrine‐Induced Contraction in Mesenteric Arteries

The immediate early transcription factor early growth response 1 (Egr1) is upregulated in smooth muscle cells of atherosclerotic plaques and in adipose tissue of obese animals and humans. In a heterologous endothelial cell expression system, Egr1 overexpression upregulated the α2δ accessory subunit of the L‐type voltage gated Ca2+ channel (Fu et al, Gene; 2003). Moreover, Ca2+ influx via voltage‐gated Ca2+ channels increased Egr1 expression, suggesting that Egr1 regulates ion channel flux and vascular tone. In light of these findings, we tested the hypothesis that mesenteric arteries (MA; 2nd order) from Egr1 knockout (KO) mice would exhibit reduced contractility compared to MA from their wild‐type (WT) litter mates. Isolated vessel contractility was assessed using wire myography (DMT 620M). A small rightward shift in cumulative concentration response curves to norepinephrine (NE, 10−9 – 10−5M) in MA from male KO mice compared to WT littermates (−log EC50 = 5.96±0.11 vs −5.68±0.03 M NE, respectively; p=0.08) was observed, while there was no difference in NE‐induced contraction in female KO and WT mice. Neither maximal NE‐induced constriction nor maximal acetylcholine‐induced relaxation in NE‐preconstricted MA was different between male KO and WT mice or female KO and WT mice. Current studies are leveraging RNAseq to assess global transcriptome profiles of aorta from male and female WT and KO mice, to determine which pathways are impacted by Egr1. Our preliminary arterial contractility data suggest that smooth muscle Egr1 plays a role in modulating vascular tone.Support or Funding InformationThis work was funded by USDA‐ARS Project 6026‐51000‐010‐05S.

Green tea extract activates AMPK and ameliorates white adipose tissue metabolic dysfunction induced by obesity.

Beneficial effects of green tea (GT) polyphenols against obesity have been reported. However, until this moment the molecular mechanisms of how green tea can modulate obesity and regulates fat metabolism, particularly in adipose tissue, remain poorly understood. The aim of this study was to evaluate the role of GT extract in the adipose tissue of obese animals and its effect on weight gain, metabolism and function (de novo lipogenesis and lipolysis), and the involvement of AMP-activated protein kinase (AMPK). Male Wistar rats were treated with GT by gavage (12weeks/5days/week; 500mg/kg of body weight), and obesity was induced by cafeteria diet (8weeks). Here, we show that obese rats treated with GT showed a significant reduction in indicators of obesity such as hyperlipidemia, fat synthesis, body weight, and fat depots as compared to those treated with standard control diet. AMPK was induced in adipose tissue in rats that were treated with GT and likely restored insulin sensitivity, increased mRNA expression of GLUT4, reducing the concentrations of plasma and liver lipid content, also stimulating fatty acid oxidation in the same tissue. Importantly, repression of de novo lipogenesis in the adipose tissue, reduced lipid droplets in the liver, and the development of insulin resistance in diet-induced obese rats were accompanied by AMPK activation. Our study identified that metabolic changes caused by GT intake induced AMPK activation and modulate the expression of genes involved in metabolism, particularly in adipose tissue, thus offering a therapeutic strategy to combat insulin resistance, dyslipidemia, and obesity in rats.

HIF-2α Blows Out the Flames of Adipose Tissue Macrophages to Keep Obesity in a Safe Zone

In 1993, Hotamisligil et al. (1) broke new ground by linking immune response and metabolism. A striking observation in this early study was the upregulation of the inflammatory cytokine tumor necrosis factor-α in adipose tissue (AT) of obese and insulin-resistant animals. Although adipocytes were thought to be the major source of inflammatory cytokines in fat, Weisberg et al. (2) later showed that macrophages accumulate in the AT of obese animals, creating a state of low-grade inflammation that could trigger insulin resistance. Since then, the concept of “immunometabolism” has gradually evolved, and many types of immune cells have been shown to contribute to AT inflammation and insulin resistance (3). For instance, macrophages secrete proinflammatory cytokines and other factors, which could impair insulin sensitivity. In light of this evidence, it has been suggested that decreasing inflammation in AT could attenuate the diabetic state. In support of this idea is the fact that anti-inflammatory drugs appear to have provided proof-of-concept that inflammation is linked to the deleterious effects of insulin resistance in animals (4,5). Paradoxically, recent studies suggest that inflammation is also required for maintaining AT homeostasis (6–8). These complex findings emphasize the need for a more nuanced understanding of the role immune cells play in the development of insulin resistance. Adipose tissue macrophages (ATMs) have been categorized into two distinct populations: proinflammatory (M1) and anti-inflammatory (M2). While ATM subpopulations have overlapping inflammatory …

IL-21 Is a Major Negative Regulator of IRF4-Dependent Lipolysis Affecting Tregs in Adipose Tissue and Systemic Insulin Sensitivity

Obesity elicits immune cell infiltration of adipose tissue provoking chronic low-grade inflammation. Regulatory T cells (Tregs) are specifically reduced in adipose tissue of obese animals. Since interleukin (IL)-21 plays an important role in inducing and maintaining immune-mediated chronic inflammatory processes and negatively regulates Treg differentiation/activity, we hypothesized that it could play a role in obesity-induced insulin resistance. We found IL-21 and IL-21R mRNA expression upregulated in adipose tissue of high-fat diet (HFD) wild-type (WT) mice and in stromal vascular fraction from human obese subjects in parallel to macrophage and inflammatory markers. Interestingly, a larger infiltration of Treg cells was seen in the adipose tissue of IL-21 knockout (KO) mice compared with WT animals fed both normal diet and HFD. In a context of diet-induced obesity, IL-21 KO mice, compared with WT animals, exhibited lower body weight, improved insulin sensitivity, and decreased adipose and hepatic inflammation. This metabolic phenotype is accompanied by a higher induction of interferon regulatory factor 4 (IRF4), a transcriptional regulator of fasting lipolysis in adipose tissue. Our data suggest that IL-21 exerts negative regulation on IRF4 and Treg activity, developing and maintaining adipose tissue inflammation in the obesity state.

Hypooxytocinaemia in obese Zucker rats relates to oxytocin degradation in liver and adipose tissue

The metabolic action of oxytocin has recently been intensively studied to assess the ability of the peptide to regulate energy homeostasis. Despite the obvious weight-reducing effect of oxytocin observed in experimental studies, plasma oxytocin levels were found to be unchanged or even elevated in human obesity. The aim of our study was to evaluate the changes in the oxytocin system in Zucker rats, an animal model closely mirroring morbid obesity in humans. Plasma oxytocin levels were measured in obese Zucker rats and lean controls by enzyme immunoassay after plasma extraction. The expression of oxytocin and oxytocin receptor (OXTR) was assessed at the mRNA and protein levels by quantitative real-time PCR and immunoblotting respectively. Plasma and tissue activity of oxytocinase, the main enzyme involved in oxytocin degradation, were measured by fluorometric assay using an arylamide derivate as the substrate. Obese Zucker rats displayed a marked reduction in plasma oxytocin levels. Elevated liver and adipose tissue oxytocinase activity was noticed in obese Zucker rats. Hypothalamic oxytocin gene expression was not altered by the obese phenotype. OXTR mRNA and protein levels were upregulated in the adipose tissue of obese animals in contrast to the reduced OXTR protein levels in skeletal muscle. Our results show that obesity is associated with reduced plasma oxytocin due to increased peptide degradation by liver and adipose tissue rather than changes in hormone synthesis. This study highlights the importance of the oxytocin system in the pathogenesis of obesity and suggests oxytocinase inhibition as a candidate approach in the therapy of obesity.

Low sodium diet and adipokine secretion: Implications for the cardiovascular system?

The influence of dietary sodium intake on cardiovascular risk factors has been a matter of decade-long discussions. Needed is a clear-cut elucidation of the beneficial mechanisms of action of reduced salt intake. In a recent study, lean and obese mice were subjected to a high or low salt diet for 16 weeks. The low salt diet tremendously reduced fasting insulin in obese animals, and HOMA-IR was improved. Reduced adiponectin expression in the heart and in peritoneal adipose tissue in obese animals was restored or even increased compared to normal levels with the low salt diet. Corresponding with the beneficial effect on adiponectin, inflammatory markers were reduced to lean levels by the low salt diet. Whether the increase in adiponectin would have been larger if the rise in aldosterone had been prevented is one of the questions raised by this study. The data obtained in this animal study are based on a robust methodological basis for two reasons: first, the long-term intervention of 16 weeks clearly represents a strength of the study; second, dietary sodium restriction was modest, as judged by only 2-fold increased plasma renin activity. Overall, the data presented by Baudrand et al. in the current issue of NMCD may path the way to a better understanding of the mode of action of modest sodium restriction. However, a replication of the results in a more human-like diet-induced obesity mouse model is warranted.

Macrophage Glucose-6-Phosphate Dehydrogenase Stimulates Proinflammatory Responses with Oxidative Stress

Glucose-6-phosphate dehydrogenase (G6PD) is a key enzyme that regulates cellular redox potential. In this study, we demonstrate that macrophage G6PD plays an important role in the modulation of proinflammatory responses and oxidative stress. The G6PD levels in macrophages in the adipose tissue of obese animals were elevated, and G6PD mRNA levels positively correlated with those of proinflammatory genes. Lipopolysaccharide (LPS) and free fatty acids, which initiate proinflammatory signals, stimulated macrophage G6PD. Overexpression of macrophage G6PD potentiated the expression of proinflammatory and pro-oxidative genes responsible for the aggravation of insulin sensitivity in adipocytes. In contrast, when macrophage G6PD was inhibited or suppressed via chemical inhibitors or small interfering RNA (siRNA), respectively, basal and LPS-induced proinflammatory gene expression was attenuated. Furthermore, macrophage G6PD increased activation of the p38 mitogen-activated protein kinase (MAPK) and NF-κB pathways, which may lead to a vicious cycle of oxidative stress and proinflammatory cascade. Together, these data suggest that an abnormal increase of G6PD in macrophages promotes oxidative stress and inflammatory responses in the adipose tissue of obese animals.

Combined B- and T-cell deficiency does not protect against obesity-induced glucose intolerance and inflammation

Obesity-induced inflammation is associated with insulin resistance and morphologically characterized by macrophage influx into the adipose tissue. Recently, various other immune cells, including B- and T-cells, have been shown to participate in modulating adipose tissue inflammation during the development of obesity. We show that HFD-feeding modulates the influx of B and T-cells into adipose tissue of obese animals, suggestive of a role of the adaptive immune system in the development of adipose tissue inflammation. Despite a lower bodyweight after HFD-feeding, gene expression levels of CD68, F4/80 and MCP-1 in white adipose tissue were enhanced in SCID animals that lack B- and T-cells. Moreover, conditioned medium from adipose tissue explants of HFD-fed SCID mice revealed increased release of IL-6 and CXCL1 compared to WT animals. Compared to WT mice, glucose tolerance was impaired in B- and T-cell deficient mice after HFD-feeding. Thus, complete B- and T-cell deficiency does not protect against HFD-induced adipose tissue inflammation and glucose intolerance. In contrast, SCID mice showed an increased pro-inflammatory status at the level of the adipose tissue in some cytokines. Our findings suggest that a delicate balance between various B- and T-cell populations controls adipose tissue inflammation.

Clodronate Liposomes Improve Metabolic Profile and Reduce Visceral Adipose Macrophage Content in Diet-Induced Obese Mice

BackgroundObesity-related adipose inflammation has been thought to be a causal factor for the development of insulin resistance and type 2 diabetes. Infiltrated macrophages in adipose tissue of obese animals and humans are an important source for inflammatory cytokines. Clodronate liposomes can ablate macrophages by inducing apoptosis. In this study, we aim to determine whether peritoneal injection of clodronate liposomes has any beneficial effect on systemic glucose homeostasis/insulin sensitivity and whether macrophage content in visceral adipose tissue will be reduced in diet-induced obese (DIO) mice.Methodology/Principal FindingsClodronate liposomes were used to deplete macrophages in lean and DIO mice. Macrophage content in visceral adipose tissue, metabolic parameters, glucose and insulin tolerance, adipose and liver histology, adipokine and cytokine production were examined. Hyperinsulinemic-euglycemic clamp study was also performed to assess systemic insulin sensitivity. Peritoneal injection of clodronate liposomes significantly reduced blood glucose and insulin levels in DIO mice. Systemic glucose tolerance and insulin sensitivity were mildly improved in both lean and DIO mice treated with clodronate liposomes by intraperitoneal (ip) injection. Hepatosteatosis was dramatically alleviated and suppression of hepatic glucose output was markedly increased in DIO mice treated with clodronate liposomes. Macrophage content in visceral adipose tissue of DIO mice was effectively decreased without affecting subcutaneous adipose tissue. Interestingly, levels of insulin sensitizing hormone adiponectin, including the high molecular weight form, were significantly elevated in circulation.Conclusions/SignificanceIntraperitoneal injection of clodronate liposomes reduces visceral adipose tissue macrophages, improves systemic glucose homeostasis and insulin sensitivity in DIO mice, which can be partially attributable to increased adiponectin levels.

Resveratrol exerts anti-obesity effects via mechanisms involving down-regulation of adipogenic and inflammatory processes in mice

Resveratrol is a natural polyphenolic stilbene derivative found in a variety of edible fruits, including nuts, berries, and grape skin. Although resveratrol has been suggested to improve thermogenesis in the brown adipose tissues of obese animals, there have been no reports on the anti-adipogenic and anti-inflammatory effects of resveratrol in the white adipose tissues of obese animals. The primary aim of this study was to investigate whether resveratrol attenuates high-fat diet (HFD)-induced adipogenesis and inflammation in the epididymal fat tissues of mice and to explore the underlying mechanisms involved in this attenuation. In comparison with HFD-fed mice, mice fed with a 0.4% resveratrol-supplemented diet (RSD) showed significantly lower body weight gain (−48%), visceral fat-pad weights (−58%), and plasma levels of triglyceride, FFA, total cholesterol, glucose, tumor necrosis factor (TNF) α, and monocyte chemoattractant protein-1 (MCP1). Resveratrol significantly reversed the HFD-induced up-regulation of galanin-mediated signaling molecules (GalR1/2, PKCδ, Cyc-D, E2F1, and p-ERK) and key adipogenic genes (PPARγ2, C/EBPα, SREBP-1c, FAS, LPL, aP2, and leptin) in the epididymal adipose tissues of mice. Furthermore, resveratrol significantly attenuated the HFD-induced up-regulation of pro-inflammatory cytokines (TNFα, IFNα, IFNβ, and IL-6) and their upstream signaling molecules (TLR2/4, MyD88, Tirap, TRIF, TRAF6, IRF5, p-IRF3, and NF-κB) in the adipose tissues of mice. The results of this study suggest that resveratrol inhibits visceral adipogenesis by suppressing the galanin-mediated adipogenesis signaling cascade. It may also attenuate cytokine production in the adipose tissue by repressing the TLR2- and TLR4-mediated pro-inflammatory signaling cascades in HFD-fed mice.

Adipocyte Apoptosis, a Link between Obesity, Insulin Resistance, and Hepatic Steatosis

Adipocyte death has been reported in both obese humans and rodents. However, its role in metabolic disorders, including insulin resistance, hepatic steatosis, and inflammation associated with obesity has not been studied. We now show using real-time reverse transcription-PCR arrays that adipose tissue of obese mice display a pro-apoptotic phenotype. Moreover, caspase activation and adipocyte apoptosis were markedly increased in adipose tissue from both mice with diet-induced obesity and obese humans. These changes were associated with activation of both the extrinsic, death receptor-mediated, and intrinsic, mitochondrial-mediated pathways of apoptosis. Genetic inactivation of Bid, a key pro-apoptotic molecule that serves as a link between these two cell death pathways, significantly reduced caspase activation, adipocyte apoptosis, prevented adipose tissue macrophage infiltration, and protected against the development of systemic insulin resistance and hepatic steatosis independent of body weight. These data strongly suggest that adipocyte apoptosis is a key initial event that contributes to macrophage infiltration into adipose tissue, insulin resistance, and hepatic steatosis associated with obesity in both mice and humans. Inhibition of adipocyte apoptosis may be a new therapeutic strategy for the treatment of obesity-associated metabolic complications.

Anti-inflammatory effect of atorvastatin ameliorates insulin resistance in monosodium glutamate–treated obese mice

Considering that inflammation contributes to obesity-induced insulin resistance and that statins have been reported to have other effects beyond cholesterol lowering, the present study aimed to investigate whether atorvastatin treatment has anti-inflammatory action in white adipose tissue of obese mice, consequently improving insulin sensitivity. Insulin sensitivity in vivo (by insulin tolerance test); metabolic-hormonal profile; plasma tumor necrosis factor (TNF)– α, interleukin (IL)-6, and adiponectin; adipose tissue immunohistochemistry; glucose transporter (GLUT) 4; adiponectin; TNF- α; IL-1 β; and IL-6 gene expression; and I κB kinase (IKK)– α/ β activity were assessed in 23-week-old monosodium glutamate–induced obese mice untreated or treated with atorvastatin for 4 weeks. Insulin-resistant obese mice had increased plasma triglyceride, insulin, TNF- α, and IL-6 plasma levels. Adipose tissue of obese animals showed increased macrophage infiltration, IKK- α (42%, P < .05) and IKK- β (73%, P < .05) phosphorylation, and TNF- α and IL-6 messenger RNA (mRNA) (∼15%, P < .05) levels, and decreased GLUT4 mRNA and protein (30%, P < .05) levels. Atorvastatin treatment lowered cholesterol, triglyceride, insulin, TNF- α, and IL-6 plasma levels, and restored whole-body insulin sensitivity. In adipose tissue, atorvastatin decreased macrophage infiltration and normalized IKK- α/ β phosphorylation; TNF- α, IL-6, and GLUT4 mRNA; and GLUT4 protein to control levels. The present findings demonstrate that atorvastatin has anti-inflammatory effects on adipose tissue of obese mice, which may be important to its local and whole-body insulin-sensitization effects.

MCP-1 (Monocyte Chemotactic Protein-1)-induced Protein, a Recently Identified Zinc Finger Protein, Induces Adipogenesis in 3T3-L1 Pre-adipocytes without Peroxisome Proliferator-activated Receptor γ

Adipogenesis is a key differentiation process relevant to obesity and associated diseases such as type 2 diabetes. This process involves temporally regulated genes controlled by a set of transcription factors, CCAAT/enhancer-binding proteins (C/EBP) beta, C/EBPdelta, and C/EBPalpha and peroxisome proliferator-activated receptor gamma (PPARgamma). Currently, PPARgamma is universally accepted as the master regulator that is necessary and sufficient to induce adipogenesis as no known factor can induce adipogenesis without PPARgamma. We present evidence that a novel zinc finger protein, MCP-1-induced protein (MCPIP), can induce adipogenesis without PPARgamma. Classical adipogenesis-inducing medium induces MCP-1 production and expression of MCPIP in 3T3-L1 cells before the induction of the C/EBP family of transcription factors and PPARgamma. Knockdown of MCPIP prevents their expression and adipogenesis as measured by expression of adipocyte markers and lipid droplet accumulation. Treatment of 3T3-L1 cells with MCP-1 or forced expression of MCPIP induces expression of C/EBPbeta, C/EBPdelta, C/EBPalpha, and PPARgamma and adipogenesis without any other inducer. Forced expression of MCPIP induces expression of the C/EBP family of transcription factors and adipogenesis in PPARgamma(-/-) mouse embryonic fibroblasts. Thus, MCPIP is a newly identified protein that can induce adipogenesis without PPARgamma.

Reducing glycosphingolipid content in adipose tissue of obese mice restores insulin sensitivity, adipogenesis and reduces inflammation

Adipose tissue is a critical mediator in obesity-induced insulin resistance. Previously we have demonstrated that pharmacological lowering of glycosphingolipids and subsequently GM3 by using the iminosugar AMP-DNM, strikingly improves glycemic control. Here we studied the effects of AMP-DNM on adipose tissue function and inflammation in detail to provide an explanation for the observed improved glucose homeostasis. Leptin-deficient obese (LepOb) mice were fed AMP-DNM and its effects on insulin signalling, adipogenesis and inflammation were monitored in fat tissue. We show that reduction of glycosphingolipid biosynthesis in adipose tissue of LepOb mice restores insulin signalling in isolated ex vivo insulin-stimulated adipocytes. We observed improved adipogenesis as the number of larger adipocytes was reduced and expression of genes like peroxisome proliferator-activated receptor (PPAR) γ, insulin responsive glucose transporter (GLUT)-4 and adipsin increased. In addition, we found that adiponectin gene expression and protein were increased by AMP-DNM. As a consequence of this improved function of fat tissue we observed less inflammation, which was characterized by reduced numbers of adipose tissue macrophages (crown-like structures) and reduced levels of the macrophage chemo attractants monocyte-chemoattractant protein-1 (Mcp-1/Ccl2) and osteopontin (OPN). In conclusion, pharmacological lowering of glycosphingolipids by inhibition of glucosylceramide biosynthesis improves adipocyte function and as a consequence reduces inflammation in adipose tissue of obese animals.

Reducing Glycosphingolipid Content in Adipose Tissue of Obese Mice Restores Insulin Sensitivity, Adipogenesis and Reduces Inflammation

Adipose tissue is a critical mediator in obesity-induced insulin resistance. Previously we have demonstrated that pharmacological lowering of glycosphingolipids and subsequently GM3 by using the iminosugar AMP-DNM, strikingly improves glycemic control. Here we studied the effects of AMP-DNM on adipose tissue function and inflammation in detail to provide an explanation for the observed improved glucose homeostasis. Leptin-deficient obese (LepOb) mice were fed AMP-DNM and its effects on insulin signalling, adipogenesis and inflammation were monitored in fat tissue. We show that reduction of glycosphingolipid biosynthesis in adipose tissue of LepOb mice restores insulin signalling in isolated ex vivo insulin-stimulated adipocytes. We observed improved adipogenesis as the number of larger adipocytes was reduced and expression of genes like peroxisome proliferator-activated receptor (PPAR) γ, insulin responsive glucose transporter (GLUT)-4 and adipsin increased. In addition, we found that adiponectin gene expression and protein were increased by AMP-DNM. As a consequence of this improved function of fat tissue we observed less inflammation, which was characterized by reduced numbers of adipose tissue macrophages (crown-like structures) and reduced levels of the macrophage chemo attractants monocyte-chemoattractant protein-1 (Mcp-1/Ccl2) and osteopontin (OPN). In conclusion, pharmacological lowering of glycosphingolipids by inhibition of glucosylceramide biosynthesis improves adipocyte function and as a consequence reduces inflammation in adipose tissue of obese animals.

Adiponectin is required to mediate rimonabant-induced improvement of insulin sensitivity but not body weight loss in diet-induced obese mice

The increase in adiponectin levels in obese patients with untreated dyslipidemia and its mRNA expression in adipose tissue of obese animals are one of the most interesting consequences of rimonabant treatment. Thus, part of rimonabant's metabolic effects could be related to an enhancement of adiponectin secretion and its consequence on the modulation of insulin action, as well as energy homeostasis. The present study investigated the effects of rimonabant in adiponectin knockout mice (Ad(-/-)) exposed to diet-induced obesity conditions. Six-week-old Ad(-/-) male mice and their wild-type littermate controls (Ad(+/+)) were fed a high-fat diet for 7 mo. During the last month, animals were administered daily either with vehicle or rimonabant by mouth (10 mg/kg). High-fat feeding induced weight gain by about 130% in both wild-type and Ad(-/-) mice. Obesity was associated with hyperinsulinemia and insulin resistance. Treatment with rimonabant led to a significant and similar decrease in body weight in both Ad(+/+) and Ad(-/-) mice compared with vehicle-treated animals. In addition, rimonabant significantly improved insulin sensitivity in Ad(+/+) mice compared with Ad(+/+) vehicle-treated mice by decreasing hepatic glucose production and increasing glucose utilization index in both visceral and subcutaneous adipose tissue. In contrast, rimonabant failed to improve insulin sensitivity in Ad(-/-) mice, despite the loss in body weight. Rimonabant's effect on body weight appeared independent of the adiponectin pathway, whereas adiponectin seems required to mediate rimonabant-induced improvement of insulin sensitivity in rodents.

Obesity causes a shift in metabolic flow of gangliosides in adipose tissues

Obesity is associated with insulin resistance and a mild chronic inflammation in adipose tissues. Recent studies suggested that GM3 ganglioside mediates dysfunction in insulin signaling. However, it has not been determined the ganglioside profiling in adipose tissues of obese animals. Here, we for the first time examined semi-quantitative ganglioside profiles in the adipose tissues of high fat- and high sucrose-induced obese, diabetic C57BL/6J mice by TLC and HPLC/mass spectrometry. In control adipose tissues GM3 dominated with traces of GM1 and GD1a; obesity led to a dramatic increase in GM2, GM1, and GD1a with the GM3 content unchanged. Similar results were obtained in KK and KKAy mice. Adipocytes separated from stromal vascular cells including macrophages contained more of those gangliosides in KKAy mice than in KK mice. These results underscore those gangliosides in the pathophysiology of obesity-related diseases.