Inhibition of glyceroneogenesis by histone deacetylase 3 contributes to lipodystrophy in mice with adipose tissue inflammation

Transcriptomics analyses combined with intestinal microorganism survey suggest Resveratrol (RSV) anti-aging and anti-oxidant effects in silkworm (Bombyx mori)

The growing elderly population presents a significant concern, with the prolongation of life expectancy, aging diseases are becoming increasingly common. Resveratrol (RSV) has emerged as a promising compound for disease prevention. However, the effect of RSV on lifespan extension in different organisms, particularly the model organism silkworm, remains inconsistent. We conducted aging experiments using silkworm (B. mori) and employed transcriptomics to investigate the therapeutic effects of RSV on lifespan extension and healthy lifespan in silkworms. RSV increased the survival rate by 8.57 %-12.12 % and enhanced the antioxidant capacity of silkworms. Transcriptomic analysis demonstrated that genes in signaling pathways such as AMPK and FoxO were significantly upregulated. 16SrRNA sequencing of gut contents showed an increase in beneficial bacterial strains under the action of RSV. This study aims to enhance our understanding of lifespan regulation mechanisms using the silkworm model and provide new targets for anti-aging antioxidants research to delay the onset of age-related diseases.

Dissecting Histone Deacetylase 3 in Multiple Disease Conditions: Selective Inhibition as a Promising Therapeutic Strategy

The acetylation of histone and non-histone proteins has been implicated in several disease states. Modulation of such epigenetic modifications has therefore made histone deacetylases (HDACs) important drug targets. HDAC3, among various class I HDACs, has been signified as a potentially validated target in multiple diseases, namely, cancer, neurodegenerative diseases, diabetes, obesity, cardiovascular disorders, autoimmune diseases, inflammatory diseases, parasitic infections, and HIV. However, only a handful of HDAC3-selective inhibitors have been reported in spite of continuous efforts in design and development of HDAC3-selective inhibitors. In this Perspective, the roles of HDAC3 in various diseases as well as numerous potent and HDAC3-selective inhibitors have been discussed in detail. It will surely open up a new vista in the discovery of newer, more effective, and more selective HDAC3 inhibitors.

The mechanisms of vascular aging

Vascular senescence is one of the hotspots in current research. With global average life expectancy increasing, delaying or reducing aging and age-related diseases has become a pressing issue for improving quality of life. Vascular senescence is an independent risk factor for age-related cardiovascular diseases (CVD) and results in the deterioration of CVD. Nevertheless, the underlying mechanisms of the vascular senescence have not been expressly illustrated. In this review, we attempt to summarize the recent literature in the field and discuss the major mechanisms involved in vascular senescence. We also underline key molecular aspects of aging-associated vascular dysfunction in the attempt to highlight potential innovative therapeutic targets to delay the onset of age-related diseases.

Whole transcriptome RNA-seq reveals key regulatory factors involved in type 2 diabetes pathology in peripheral fat of Asian Indians

The prevalence of Type 2 Diabetes has reached an epidemic proportion particularly in south Asian countries. We have earlier shown that the anatomical fat distribution, termed 'thin fat phenotype' in this population indeed plays a major role for their T2D-predisposition it is indeed the sick fat or adiposopathy, which is the root cause of metabolic syndrome and diabetes and affects both-peripheral, as well as visceral adipose tissue compartments. In present study, we have attempted to unravel the altered regulatory mechanisms at the level of transcription factors, and miRNAs those may likely accounts to T2D pathophysiology in femoral subcutaneous adipose tissue. We prioritized transcription factors and protein kinases as likely upstream regulators of obtained differentially expressed genes in this RNA-seq study. An inferred network of these upstream regulators was then derived and the role of TFs and miRNAs in T2D pathophysiology was explored. In conclusions, this RNS-Seq study finds that peripheral subcutaneous adipose tissue among Asian Indians show pathology characterized by altered lipid, glucose and protein metabolism, adipogenesis defect and inflammation. A network of regulatory transcription factors, protein kinases and microRNAs have been imputed which converge on the process of adipogenesis. As the majority of these genes also showed altered expression in diabetics and some of them are also circulatory, therefore they deserve further investigation for potential clinical diagnostic and therapeutic applications.

Intricate Regulation of Phosphoenolpyruvate Carboxykinase (PEPCK) Isoforms in Normal Physiology and Disease

BACKGROUND

The phosphoenolpyruvate carboxykinase (PEPCK) isoforms are considered as rate-limiting enzymes for gluconeogenesis and glyceroneogenesis pathways. PEPCK exhibits several interesting features such as a) organelle-specific isoforms (cytosolic and a mitochondrial) in vertebrate clade, b) tissue-specific expression of isoforms and c) organism-specific requirement of ATP or GTP as a cofactor. In higher organisms, PEPCK isoforms are intricately regulated and activated through several physiological and pathological stimuli such as corticoids, hormones, nutrient starvation and hypoxia. Isoform-specific transcriptional/translational regulation and their interplay in maintaining glucose homeostasis remain to be fully understood. Mounting evidence indicates the significant involvement of PEPCK isoforms in physiological processes (development and longevity) and in the progression of a variety of diseases (metabolic disorders, cancer, Smith-Magenis syndrome).

OBJECTIVE

The present systematic review aimed to assimilate existing knowledge of transcriptional and translational regulation of PEPCK isoforms derived from cell, animal and clinical models.

CONCLUSION

Based on current knowledge and extensive bioinformatics analysis, in this review we have provided a comparative (epi)genetic understanding of PCK1 and PCK2 genes encompassing regulatory elements, disease-associated polymorphisms, copy number variations, regulatory miRNAs and CpG densities. We have also discussed various exogenous and endogenous modulators of PEPCK isoforms and their signaling mechanisms. A comprehensive review of existing knowledge of PEPCK regulation and function may enable identification of the underlying gaps to design new pharmacological strategies and interventions for the diseases associated with gluconeogenesis.

Adipose tissue mRNA expression of HDAC1, HDAC3 and HDAC9 in obese women in relation to obesity indices and insulin resistance

It is well-established that an impaired adipose tissue function and morphology caused by a dysregulated gene expression contribute substantially to obesity. Nowadays, animal model studies and in vitro surveys provide evidence for possible roles of HDACs as emerging epigenetic players in the pathogenesis of obesity. However, the clinical pertinence of HDACs in the field of obesity research in humans is not yet obvious. Here, we investigated mRNA expression of HDAC1, 3 and 9 in visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) of obese female participants (n = 20) and normal-weight women (n = 19). We also evaluated the association of the afore-mentioned HDACs gene expression with obesity indices, insulin resistance parameters, and other obesity-related characteristics. Our data revealed the mRNA level of HDAC1 was significantly decreased in both VAT and SAT of obese women, compared to controls. Moreover, the SAT mRNA expression of HDAC3 and VAT mRNA levels of HDAC9 were significantly lower in obese subjects than those found in controls. We observed that HDAC1 and HDAC3 expression in adipose tissue from the whole population is inversely correlated with obesity indices; BMI, waist, hip and waist-to-height ratio (WHtR). Moreover, we found that HDAC3 expression in adipose tissue had an inverse correlation with HOMA-IR, insulin levels, and serum concentration of hs-CRP. Moreover, VAT HDAC9 mRNA level is inversely correlated with obesity indices; BMI, waist, hip and WHtR and with HOMA-IR, insulin levels, and serum concentration of hs-CRP. Hence, it seems that decreased HDAC1,3 and 9 mRNA expression in adipose tissue might be associated with obesity and related abnormalities. However, more studies are needed to establish this concept.

Histone deacetylases in cardiovascular and metabolic diseases

Histone deacetylases (HDACs) regulate gene transcription by catalyzing the removal of acetyl groups from key lysine residues in nucleosomal histones and via the recruitment of other epigenetic regulators to DNA promoter/enhancer regions. Over the past two decades, HDACs have been implicated in multiple processes pertinent to cardiovascular and metabolic diseases, including cardiac hypertrophy and remodeling, fibrosis, calcium handling, inflammation and energy metabolism. The development of small molecule HDAC inhibitors and genetically modified loss- and gain-of-function mouse models has allowed interrogation of the roles of specific HDAC isoforms in these processes. Isoform-selective HDAC inhibitors may prove to be powerful therapeutic agents for the treatment of cardiovascular diseases, obesity and diabetes.

Disruption of Epithelial HDAC3 in Intestine Prevents Diet-Induced Obesity in Mice

BACKGROUND & AIMS

Intestinal microbiota modulate metabolism and associate closely with epithelial cells in the intestine. In intestinal epithelial cells (IECs), histone deacetylase 3 (HDAC3) integrates microbiota-derived signals to control intestinal homeostasis. We investigated whether HDAC3 in IECs regulates metabolism and the development of obesity in mice.

METHODS

Adult C57BL/6 (control) mice and mice with constitutive or inducible IEC-specific disruption of Hdac3 (HDAC3ΔIEC mice) were placed on a standard chow or high-fat diet (HFD, 60% kcal from fat). We measured body composition, weight, glucose tolerance, and energy expenditure. IECs were isolated from small intestine and gene expression, and lipid levels were analyzed. HDAC3 levels were determined in 43 pediatric patient ileal biopsy samples and compared with body weight.

RESULTS

Control mice fed an HFD gained weight, became obese, and had reduced glucose tolerance with increased serum insulin, whereas HFD-fed HDAC3ΔIEC mice did not develop obesity. Serum levels of triglycerides were reduced in HDAC3ΔIEC mice, and these mice had less liver fat and smaller adipocytes, compared with HFD-fed control mice. HDAC3ΔIEC mice had similar food intake and activity as control mice, but higher energy expenditure because of increased catabolism. IECs from HDAC3ΔIEC mice had altered expression levels of genes that regulate metabolism in response to the microbiota (such as Chka, Mttp, Apoa1, and Pck1) and accumulated triglycerides compared with IECs from control mice. The microbiota-derived short-chain fatty acid butyrate was decreased in obese mice. Butyrate significantly reduced the activity of HDAC3 and increased Pck1 expression in only control IECs. Administration of butyrate to control mice with diet-induced obesity, but not HDAC3ΔIEC mice, led to significant weight loss. Disruption of HDAC3 in IECs of mice after they became obese led to weight loss and improved metabolic profile. Levels of HDAC3 in intestinal biopsy samples correlated with patient weight.

CONCLUSIONS

We found that epithelial HDAC3 promotes development of diet-induced obesity in studies of mice and that butyrate reduces activity of HDAC3 in IECs to prevent diet-induced obesity. This pathway might be manipulated to prevent or reduce obesity-associated disease.

Ablation of systemic SIRT1 activity promotes nonalcoholic fatty liver disease by affecting liver-mesenteric adipose tissue fatty acid mobilization

Sirtuin 1 (SIRT1) has been reported to protect against nonalcoholic fatty liver disease (NAFLD) development. The mechanism of how SIRT1 deacetylase activity affects NAFLD has not been well investigated. The current investigation addressed the causal effect of systemic SIRT1 activity on NAFLD development and the underlying mechanism involved in both liver and mesenteric adipose tissue (MAT). Both SIRT1 homozygous mice ablated the catalytic activity (sirt1^Y/Y) and their corresponding wild type littermates (WT) were fed a high fat diet (HFD, 60% calories from fat) for 34weeks. Sirt1^Y/Y mice showed significantly higher level of hepatic triglyceride which was accompanied with higher levels of SREBP-1 and SCD1and decreased phosphorylation of LKB1 and AMPK in the liver. Compared with WT mice, mRNA expression of lipogenic genes (lxrα, srebp-1c, scd1 and fas) in the MAT increased significantly in sirt1^Y/Y mice. Fatty acid oxidation biomarkers (acox1, acox3, cpt, ucp1, sirt3) in both liver and MAT were comparable between groups. Interestingly, we observed that in sirt1^Y/Y mice, the mRNA level of hormone sensitive lipase (hsl), adipose triglyceride lipase (atgl) and perilipin-2 (plin-2), all involved in lipolysis, significantly increased in MAT, but not in epididymal adipose tissue. These changes positively correlated with circulating free fatty acid (FFA) concentrations and higher hepatic mRNA expression of cd36 for FFA uptake. The present study has provided novel evidence to suggest that under HFD-induced metabolic surplus, the lack of SIRT1 catalytic activity promotes release of FFA from MAT and escalate NAFLD by interfering with lipid homeostasis in both liver and MAT.

Histone Deacetylases and Cardiometabolic Diseases

Cardiometabolic disease, emerging as a worldwide epidemic, is a combination of metabolic derangements leading to type 2 diabetes mellitus and cardiovascular disease. Genetic and environmental factors are linked through epigenetic mechanisms to the pathogenesis of cardiometabolic disease. Post-translational modifications of histone tails, including acetylation and deacetylation, epigenetically alter chromatin structure and dictate cell-specific gene expression patterns. The histone deacetylase family comprises 18 members that regulate gene expression by altering the acetylation status of nucleosomal histones and by functioning as nuclear transcriptional corepressors. Histone deacetylases regulate key aspects of metabolism, inflammation, and vascular function pertinent to cardiometabolic disease in a cell- and tissue-specific manner. Histone deacetylases also likely play a role in the metabolic memory of diabetes mellitus, an important clinical aspect of the disease. Understanding the molecular, cellular, and physiological functions of histone deacetylases in cardiometabolic disease is expected to provide insight into disease pathogenesis, risk factor control, and therapeutic development.

Epigenetic regulation of the NR4A orphan nuclear receptor NOR1 by histone acetylation

The nuclear receptor NOR1 is an immediate-early response gene implicated in the transcriptional control of proliferation. Since the expression level of NOR1 is rapidly induced through cAMP response element binding (CREB) protein-dependent promoter activation, we investigated the contribution of histone acetylation to this transient induction. We demonstrate that NOR1 transcription is induced by histone deacetylase (HDAC) inhibition and by depletion of HDAC1 and HDAC3. HDAC inhibition activated the NOR1 promoter, increased histone acetylation and augmented the recruitment of phosphorylated CREB to the promoter. Furthermore, HDAC inhibition increased Ser133 phosphorylation of CREB and augmented NOR1 protein stability. These data outline previously unrecognized mechanisms of NOR1 regulation and illustrate a key role for histone acetylation in the rapid induction of NOR1.

New insights into insulin: The anti-inflammatory effect and its clinical relevance

Hyperglycemia, a commonly exhibited metabolic disorder in critically ill patients, activates the body’s inflammatory defense mechanism, causing the waterfall release of numerous inflammatory mediators and cytokines, and eventually leads to organ damage. As the only glucose-lowering hormone in the body, insulin not only alleviates the detrimental effects of hyperglycemia through its metabolic regulation, but also directly modulates inflammatory mediators and acts upon immune cells to enhance immunocompetence. In this sense, hyperglycemia is pro-inflammatory whereas insulin is anti-inflammatory. Therefore, during the past 50 years, insulin has not only been used in the treatment of diabetes, but has also been put into practical use in dealing with cardiovascular diseases and critical illnesses. This review summarizes the recent advances regarding the anti-inflammatory effects of insulin in both basic research and clinical trials, with the hope of aiding in the design of further experimental research and promoting effective insulin administration in clinical practice.

Interplay of pro- and anti-inflammatory cytokines to determine lipid accretion in adipocytes

OBJECTIVE

Obesity is associated with an increase in various pro-inflammatory and anti-inflammatory cytokines, but the interplay of these cytokines is incompletely understood. We conducted experiments to test a broader hypothesis that a dynamic interplay of pro-inflammatory and anti-inflammatory cytokines controls lipid storage in adipocytes.

DESIGN

Three experiments were designed to test the overall hypothesis that proinflammatory cytokine (for example, tumor necrosis factor-α (TNF-α) inhibits anti-inflammatory cytokine (for example, adiponectin) activity in an attempt to limit excess lipid accumulation in adipocytes.

RESULTS

Experiment one showed that in pro-inflammatory animal models (ap2-P65, ob/ob and high-fat diet-induced obese mice), the increase in TNF-α expression was associated with a decrease in adiponectin expression. Experiment two showed that in 3T3-L1 adipocytes, TNF-α significantly reduced lipid accumulation and glucose uptake induced by adiponectin, and increased lipolysis. Experiment three showed that in 3T3-L1 adipocytes, TNF-α reduced mRNA and protein expression of adiponectin. Adiponectin gene transcription and mRNA stability were both reduced by TNF-α. The expression of peroxisome proliferator-activated receptor gamma, an activator of adiponectin gene promoter, was reduced by TNF-α. The inhibitory activity of TNF-α was blocked by the chemical inhibitors of NF-κB and super suppressor IκBα.

CONCLUSIONS

TNF-α opposes the action of adiponectin in the regulation of lipid metabolism, and inhibits adiponectin expression at transcriptional and post-transcriptional levels. The results suggest that pro-inflammatory cytokine inhibit anti-inflammatory cytokine in adipocytes to reduce lipid storage. This suggests a potential role of anti-inflammatory cytokines in the control of adipose tissue expansion.

Molecular docking of Glyceroneogenesis pathway intermediates with Peroxisome Proliferator- Activated Receptor-Alpha (PPAR-α)

Peroxisome proliferator-activated receptor alpha (PPAR-α) belongs to the nuclear receptor superfamily of proteins. It is one of the principle regulators of metabolism and lipid homeostasis whose malfunction leads to complications including obesity and type 2 diabetes. In the adipose tissue, glyceroneogenesis is a unique pathway through which pyruvate is converted into glycerol-3- phosphate (G3P) in a multistep process. Previous findings demonstrated that glyceroneogenesis regulates triacylglycerol synthesis and adipogenesis. This led us to hypothesize that one of the pathway intermediate is physiologically relevant PPAR-α ligand. In the present study using in silico docking, we proved that glycerate, dihydroxy acetone phosphate, glyceraldehyde-3-phosphate, and G3P are key glyceroneogenesis pathway intermediates which bind to PPAR-α. They bind PPAR-α with comparable binding energy and docking score to that of (2s)-2-ethoxy-3-[4-(2-{4-[(methylsulfonyl)oxy]phenyl}ethoxy)phenyl]propanoic acid(AZ-2), a synthetic high affinity ligand of PPAR-α. These intermediates could be studied further as potential physiologically relevant activators of PPAR-α in vitro and in vivo.

Regulation of 11β-HSD1 expression during adipose tissue expansion by hypoxia through different activities of NF-κB and HIF-1α

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) is involved in the pathogenesis of type 2 diabetes by generating active glucocorticoids (cortisol and corticosterone) that are strong inhibitors of angiogenesis. However, the mechanism of 11β-HSD1 gene expression and its relationship to adipose angiogenesis are largely unknown. To address this issue, we examined 11β-HSD1 expression in visceral and subcutaneous adipose tissue (AT) of diet-induced obese (DIO) mice during weight gain and investigated the gene regulation by hypoxia in vitro. 11β-HSD1 mRNA was reduced in the adipose tissues during weight gain in DIO mice, and the reduction was associated with an elevated expression of angiogenic factors. In vitro, 11β-HSD1 expression was induced in mRNA and protein by hypoxia. Of the two transcription factors activated by hypoxia, the nuclear factor-κB (NF-κB) enhanced but the hypoxia inducible factor-1α (HIF-1α) reduced 11β-HSD1 expression. 11β-HSD1 expression was elevated by NF-κB in epididymal fat of aP2-p65 mice. The hypoxia-induced 11β-HSD1 expression was attenuated by NF-κB inactivation in p65-deficient cells but enhanced by HIF-1 inactivation in HIF-1α-null cells. These data suggest that 11β-HSD1 expression is upregulated by NF-κB and downregulated by HIF-1α. During AT expansion in DIO mice, the reduction of 11β-HSD1 expression may reflect a dominant HIF-1α activity in the adipose tissue. This study suggests that NF-κB may mediate the inflammatory cytokine signal to upregulate 11β-HSD1 expression.

Histone deacetylases as targets for treatment of multiple diseases

HDACs (histone deacetylases) are a group of enzymes that deacetylate histones as well as non-histone proteins. They are known as modulators of gene transcription and are associated with proliferation and differentiation of a variety of cell types and the pathogenesis of some diseases. Recently, HDACs have come to be considered crucial targets in various diseases, including cancer, interstitial fibrosis, autoimmune and inflammatory diseases, and metabolic disorders. Pharmacological inhibitors of HDACs have been used or tested to treat those diseases. In the present review, we will examine the application of HDAC inhibitors in a variety of diseases with the focus on their effects of anti-cancer, fibrosis, anti-inflammatory, immunomodulatory activity and regulating metabolic disorders.

Inflammation during obesity is not all bad: evidence from animal and human studies

Chronic inflammation is a characteristic of obesity and is associated with accompanying insulin resistance, a hallmark of type 2 diabetes mellitus (T2DM). Although proinflammatory cytokines are known for their detrimental effects on adipose tissue function and insulin sensitivity, their beneficial effects in the regulation of metabolism have not drawn sufficient attention. In obesity, inflammation is initiated by a local hypoxia to augment angiogenesis and improve adipose tissue blood supply. A growing body of evidence suggests that macrophages and proinflammatory cytokines are essential for adipose remodeling and adipocyte differentiation. Phenotypes of multiple lines of transgenic mice consistently suggest that proinflammatory cytokines increase energy expenditure and act to prevent obesity. Removal of proinflammatory cytokines by gene knockout decreases energy expenditure and induces adult-onset obesity. In contrast, elevation of proinflammatory cytokines augments energy expenditure and decreases the risk for obesity. Anti-inflammatory therapies have been tested in more than a dozen clinical trials to improve insulin sensitivity and glucose homeostasis in patients with T2DM, and the results are not encouraging. One possible explanation is that anti-inflammatory therapies also attenuate the beneficial effects of inflammation in stimulating energy expenditure, which may have limited the efficacy of the treatment by promoting energy accumulation. Thus, the positive effects of proinflammatory events should be considered in evaluating the impact of inflammation in obesity and type 2 diabetes.

Systems biology of adipose tissue metabolism: regulation of growth, signaling and inflammation

Adipose tissue (AT) depots actively regulate whole body energy homeostasis by orchestrating complex communications with other physiological systems as well as within the tissue. Adipocytes readily respond to hormonal and nutritional inputs to store excess nutrients as intracellular lipids or mobilize the stored fat for utilization. Co-ordinated regulation of metabolic pathways balancing uptake, esterification, and hydrolysis of lipids is accomplished through positive and negative feedback interactions of regulatory hubs comprising several pleiotropic protein kinases and nuclear receptors. Metabolic regulation in adipocytes encompasses biogenesis and remodeling of uniquely large lipid droplets (LDs). The regulatory hubs also function as energy and nutrient sensors, and integrate metabolic regulation with intercellular signaling. Over-nutrition causes hypertrophic expansion of adipocytes, which, through incompletely understood mechanisms, initiates a cascade of metabolic and signaling events leading to tissue remodeling and immune cell recruitment. Macrophage activation and polarization toward a pro-inflammatory phenotype drives a self-reinforcing cycle of pro-inflammatory signals in the AT, establishing an inflammatory state. Sustained inflammation accelerates lipolysis and elevates free fatty acids in circulation, which robustly correlates with development of obesity-related diseases. The adipose regulatory network coupling metabolism, growth, and signaling of multiple cell types is exceedingly complex. While components of the regulatory network have been individually studied in exquisite detail, systems approaches have rarely been utilized to comprehensively assess the relative engagements of the components. Thus, need and opportunity exist to develop quantitative models of metabolic and signaling networks to achieve a more complete understanding of AT biology in both health and disease.

Visceral and subcutaneous adipose tissue from lean women respond differently to lipopolysaccharide-induced alteration of inflammation and glyceroneogenesis

OBJECTIVE

Experimental endotoxaemia induces subcutaneous adipose tissue inflammation and systemic insulin resistance in lean subjects. Glyceroneogenesis, by limiting free fatty acids (FFA) release from adipocytes, controls FFA homoeostasis and systemic insulin sensitivity. The roles of subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) in metabolic deregulation are intrinsically different. We compared the effect of lipopolysaccharide (LPS) on the inflammation profiles of SAT and VAT explants from lean women, as well as on glyceroneogenesis, to test whether these two fat depots have intrinsically different responses to this metabolic endotoxin.

DESIGN

Abdominal SAT and VAT explants from eight lean women were treated in vitro with LPS. Their inflammatory status was evaluated by cytokine gene expression and secretion; glyceroneogenesis was evaluated by cytosolic phosphoenolpyruvate carboxykinase activity and FFA vs glycerol release.

RESULTS

In the basal state, the cytokine status and expression of macrophage markers were lower in SAT than VAT. In the presence of 100 ng ml(-1) LPS, SAT exhibited a strong inflammatory response (increased interleukin-6 and tumor necrosis factor-α expression) and increased release of FFA due to inhibition of glyceroneogenesis, whereas VAT was only mildly affected. The effects of LPS on both tissues were blocked by the nuclear factor-κB (NF-κB) inhibitor, parthenolide. A significant effect of LPS on VAT occurred only at 1 μg ml(-1) LPS.

CONCLUSION

SAT explants from lean women are more sensitive to LPS-induced NF-κB activation than are VAT explants, leading to a depot-specific dysfunction of FFA storage. As SAT is the major player in FFA homoeostasis, this SAT dysfunction could be associated with visceral fat hypertrophy and systemic lipid disorders.

IL-6 indirectly modulates the induction of glyceroneogenic enzymes in adipose tissue during exercise

BACKGROUND

Glyceroneogenesis is an important step in the control of fatty acid re-esterification with PEPCK and PDK4 being identified as key enzymes in this process. We have previously shown that glyceroneogenic enzymes such as PDK4 are rapidly induced in white adipose tissue during exercise. Recent studies have suggested that IL-6 regulates adipose tissue metabolism and gene expression during exercise. Interestingly, IL-6 has been reported to directly decrease PEPCK expression. The purpose of this investigation was to determine the role of IL-6 in modulating the effects of exercise on the expression of glyceroneogenic enzymes in mouse adipose tissue. We hypothesized that the exercise-mediated induction of PDK4 and PEPCK would be greater in adipose tissue from IL-6 deficient mice compared to wild type controls.

METHODOLOGY AND PRINCIPLE FINDINGS

Treatment of cultured epididymal adipose tissue (eWAT) with IL-6 (150 ng/ml) increased the phosphorylation of AMPK, ACC and STAT3 and induced SOCS3 mRNA levels while decreasing PEPCK and PDK4 mRNA. AICAR decreased the expression of PDK4 and PEPCK. The activation of AMPK by IL-6 was independent of increases in lipolysis. An acute bout of treadmill running (15 meters/minute, 5% incline, 90 minutes) did not induce SOCS3 or increase phosphorylation of STAT3 in eWAT, indicating that IL-6 signalling was not activated. Exercise-induced increases in PEPCK and PDK4 mRNA expression were attenuated in eWAT from IL-6(-/-) mice in parallel with a greater relative increase in AMPK phosphorylation compared to exercised WT mice. These changes occurred independent of alterations in beta-adrenergic signalling in adipose tissue from IL-6(-/-) mice.

CONCLUSIONS AND SIGNIFICANCE

Our findings question the role of IL-6 signalling in adipose tissue during exercise and suggest an indirect effect of this cytokine in the regulation of adipose tissue gene expression during exercise.

Epigenetic regulation of adipogenesis

PURPOSE OF REVIEW

Epigenetic regulation plays an essential role in cell differentiation, by allowing the establishment and maintenance of the gene-expression pattern of the mature cell type. Because of its importance in chronic diseases, adipogenesis is one of the best-studied differentiation processes. The hormonal and transcriptional cascades governing the differentiation of the adipocytes are well known, but the role of epigenetic mechanisms is only starting to emerge. In this review, we intend to summarize the recently described epigenetic events that participate in adipogenesis and their connections with the main factors that constitute the classical transcriptional cascade.

RECENT FINDINGS

The advent of high-throughput technologies has made possible the exhaustive analysis of the epigenetic phenomenons taking place during adipogenesis. The cooperative recruitment of CCAAT/enhancer-binding protein (C/EBPβ) and other early proadipogenic transcription factors to transcription factor hotspots shortly after induction of adipogenesis is required to establish a transient epigenomic state that then informs the recruitment of the later adipogenic transcription factors peroxisome proliferator-activated receptor (PPARγ) and C/EBPα to their target genes.

SUMMARY

Epigenetic marks and chromatin-modifying proteins contribute to adipogenesis and, through regulation of the phenotypic maintenance of the mature adipocytes, to the control of metabolism.

Histone deacetylase 3 mediates allergic skin inflammation by regulating expression of MCP1 protein

We have shown the induction of histone deacetylase 3 (HDAC3) in antigen-stimulated rat basophilic leukemia cells via NF-κB. We investigated the role of HDAC3 in allergic skin inflammation. We used a BALB/c mouse model of triphasic cutaneous anaphylaxis (triphasic cutaneous reaction; TpCR) and passive cutaneous anaphylaxis (PCA) to examine the role of HDAC3 in allergic skin inflammation. Triphasic cutaneous reaction involved induction of HDAC3 and was mediated by HDAC3. HDAC3 showed an interaction with FcεRIβ. Trichostatin A (TSA), an inhibitor of HDAC(s), disrupted this interaction. Cytokine array analysis showed that the down-regulation of HDAC3 led to the decreased secretion of monocyte chemoattractant protein 1 (MCP1). FcεRI was necessary for induction of HDAC3 and MCP1. ChIP assays showed that HDAC3, in association with Sp1 and c-Jun, was responsible for induction of MCP1 expression. TSA exerted a negative effect on induction of MCP1. HDAC3 exerted a negative regulation on expression of HDAC2 via interaction with Rac1. The down-regulation of HDAC3 or inactivation of Rac1 induced binding of HDAC2 to MCP1 promoter sequences. TSA exerted a negative effect on HDAC3-mediated TpCR. The BALB/c mouse model of PCA involved induction of HDAC3 and MCP1. HDAC3 and MCP1 were necessary for PCA that involved ear swelling, enhanced vascular permeability, and angiogenesis. Recombinant MCP1 enhanced β-hexosaminidase activity and histamine release and also showed angiogenic potential. TSA exerted a negative effect on PCA. Our data show HDAC3 as a valuable target for the development of allergic skin inflammation therapeutics.

The Role of PPARγ in the Transcriptional Control by Agonists and Antagonists

In recent years, peroxisome proliferator-activated receptor gamma (PPARγ) has been reported to be a target for the treatment of type II diabetes. Furthermore, it has received attention for its therapeutic potential in many other human diseases, including atherosclerosis, obesity, and cancers. Recent studies have provided evidence that the endogenously produced PPARγ antagonist, 2,3-cyclic phosphatidic acid (cPA), which is similar in structure to lysophosphatidic acid (LPA), inhibits cancer cell invasion and metastasis in vitro and in vivo. We recently observed that cPA negatively regulates PPARγ function by stabilizing the binding of the corepressor protein, silencing mediator of retinoic acid and thyroid hormone receptor. We also showed that cPA prevents neointima formation, adipocyte differentiation, lipid accumulation, and upregulation of PPARγ target gene transcription. We then analyzed the molecular mechanism of cPA's action on PPARγ. In this paper, we summarize the current knowledge on the mechanism of PPARγ-mediated transcriptional activity and transcriptional repression in response to novel lipid-derived ligands, such as cPA.

Why do anti-inflammatory therapies fail to improve insulin sensitivity?

Chronic inflammation occurs in obese conditions in both humans and animals. It also contributes to the pathogenesis of type 2 diabetes (T2D) through insulin resistance, a status in which the body loses its ability to respond to insulin. Inflammation impairs insulin signaling through the functional inhibition of IRS-1 and PPARγ. Insulin sensitizers (such as rosiglitazone and pioglitazone) inhibit inflammation while improving insulin sensitivity. Therefore, anti-inflammatory agents have been suggested as a treatment strategy for insulin resistance. This strategy has been tested in laboratory studies and clinical trials for more than 10 years; however, no significant progress has been made in any of the model systems. This status has led us to re-evaluate the biological significance of chronic inflammation in obesity. Recent studies have consistently asserted that obesity-associated inflammation helps to maintain insulin sensitivity. Inflammation stimulates local adipose tissue remodeling and promotes systemic energy expenditure. We propose that these beneficial activities of inflammation provide an underlying mechanism for the failure of anti-inflammatory therapy in the treatment of insulin resistance. Current literature will be reviewed in this article to present evidence that supports this viewpoint.

Stevioside ameliorates high-fat diet-induced insulin resistance and adipose tissue inflammation by downregulating the NF-κB pathway

Accumulating evidence suggests that adipose tissue is the main source of pro-inflammatory molecules that predispose individuals to insulin resistance. Stevioside (SVS) is a widely used sweetener with multiple beneficial effects for diabetic patients. In this study, we investigated the effect of SVS on insulin resistance and the pro-inflammatory state of adipose tissue in mice fed with a high-fat diet (HFD). Oral administration of SVS for 1month had no effect on body weight, but it significantly improved fasting glucose, basal insulin levels, glucose tolerance and whole body insulin sensitivity. Interestingly, these changes were accompanied with decreased expression levels of several inflammatory cytokines in adipose tissue, including TNF-α, IL6, IL10, IL1β, KC, MIP-1α, CD11b and CD14. Moreover, macrophage infiltration in adipose tissue was remarkably reduced by SVS. Finally, SVS significantly suppressed the nuclear factor-kappa b (NF-κB) signaling pathway in adipose tissue. Collectively, these results suggested that SVS may ameliorate insulin resistance in HFD-fed mice by attenuating adipose tissue inflammation and inhibiting the NF-κB pathway.