CD8+ effector T cells contribute to macrophage recruitment and adipose tissue inflammation in obesity

Transcriptional profiling reveals a role for RORalpha in regulating gene expression in obesity-associated inflammation and hepatic steatosis

Retinoid-related orphan receptor (ROR)α4 is the major RORα isoform expressed in adipose tissues and liver. In this study we demonstrate that RORα-deficient staggerer mice (RORα(sg/sg)) fed with a high-fat diet (HFD) exhibited reduced adiposity and hepatic triglyceride levels compared with wild-type (WT) littermates and were resistant to the development of hepatic steatosis, adipose-associated inflammation, and insulin resistance. Gene expression profiling showed that many genes involved in triglyceride synthesis and storage, including Cidec, Cidea, and Mogat1, were expressed at much lower levels in liver of RORα(sg/sg) mice. In contrast, overexpression of RORα in mouse hepatoma Hepa1-6 cells significantly increased the expression of genes that were repressed in RORα(sg/sg) liver, including Sult1b1, Adfp, Cidea, and ApoA4. ChIP and promoter analysis suggested that several of these genes were regulated directly by RORα. In addition to reduced lipid accumulation, inflammation was greatly diminished in white adipose tissue (WAT) of RORα(sg/sg) mice fed with an HFD. The infiltration of macrophages and the expression of many immune response and proinflammatory genes, including those encoding various chemo/cytokines, Toll-like receptors, and TNF signaling proteins, were significantly reduced in RORα(sg/sg) WAT. Moreover, RORα(sg/sg) mice fed with an HFD were protected from the development of insulin resistance. RORα(sg/sg) mice consumed more oxygen and produced more carbon dioxide, suggesting increased energy expenditure in this genotype. Our study indicates that RORα plays a critical role in the regulation of several aspects of metabolic syndrome. Therefore, RORα may provide a novel therapeutic target in the management of obesity and associated metabolic diseases.

Stromal Vascular Fraction From Adipose Tissue Forms Profound Vascular Network Through the Dynamic Reassembly of Blood Endothelial Cells

Objective—

Tremendous efforts have been made to establish effective therapeutic neovascularization using adipose tissue-derived stromal vascular fraction (SVF), but the efficiency is low, and underlying mechanisms and their interaction with the host in a new microenvironment are poorly understood.

Methods and Results—

Here we demonstrate that direct implantation of SVF derived from donor adipose tissue can create a profound vascular network through the disassembly and reassembly of blood endothelial cells at the site of implantation. This neovasculature successfully established connection with recipient blood vessels to form a functionally perfused circuit. Addition of vascular growth factors to the SVF implant improved the efficiency of functional neovasculature formation. In contrast, spheroid culture of SVF before implantation reduced the capacity of vasculature formation, possibly because of cellular alteration. Implanting SVF into the mouse ischemic hindlimb induced the robust formation of a local neovascular network and salvaged the limb. Moreover, the coimplantation of SVF prevented fat absorption in the subcutaneous adipose tissue graft model.

Conclusion—

Freshly isolated SVF can effectively induce new vessel formation through the dynamic reassembly of blood endothelial cells and could be applied to achieve therapeutic neovascularization for relieving ischemia and preventing fat absorption in an autologous manner.

Alternative macrophage activation and metabolism

Obesity and its attendant metabolic disorders represent the great public health challenge of our time. Recent evidence suggests that onset of inflammation in metabolic tissues pathogenically links obesity to insulin resistance and type 2 diabetes. In this review, we briefly summarize the extant literature, paying special attention to the central role of the tissue-associated macrophage in the initiation of metabolic inflammation. We argue that rather than representing simple inflammatory disease, obesity and metabolic syndrome represent derangements in macrophage activation with concomitant loss of metabolic coordination. As such, the sequelae of obesity are as much products of the loss of positive macrophage influences as they are of the presence of deleterious inflammation. The therapeutic implications of this conclusion are profound because they suggest that pharmacologic targeting of macrophage activation, rather than simply inflammation, might be efficacious in treating this global epidemic.

T lymphocyte activation in visceral adipose tissue of patients with oesophageal adenocarcinoma

Background

Visceral adipose tissue may fuel obesity-associated chronic inflammation and tumorigenesis. T cells may be important in visceral adipose tissue in driving inflammation, but they have not yet been characterized in patients with cancer. This study aimed to characterize T lymphocytes in visceral adipose tissue and peripheral blood from patients with oesophageal adenocarcinoma.

Methods

Omental fat was taken from 35 patients with oesophageal adenocarcinoma at the start of surgery. Flow cytometry was performed to assess T cell activation status and cytokine production in omentum and peripheral blood.

Results

A large population of lymphocytes was present in the omentum. Omental CD4+ and CD8+ T cells displayed significantly enhanced expression of the T cell activation markers CD69 (P < 0·001) and CD107a (CD8+ T cells: P < 0·01), and significantly decreased CD62L expression (P < 0·05), compared with blood. Significantly higher proportions of CD45RO+ T cells compared with CD45RA+ T cells were present in omentum (P < 0·001 and P = 0·012 for CD4+ and CD8+ cells respectively). Interferon γ was the most abundant cytokine expressed by omental T cells, with a significantly higher level than in blood and subcutaneous adipose tissue (P < 0·01).

Conclusion

Visceral adipose tissue is a rich source of activated proinflammatory CD4+ and CD8+ T cells. It may fuel chronic inflammation via T cell-mediated pathways.

Immune cells in adipose tissue: key players in metabolic disorders

Obesity, defined as the excess development of adipose tissue, is an important risk factor for metabolic and cardiovascular diseases such as type 2 diabetes, hypertension and atherosclerosis. Over the past few years, metabolic inflammation has emerged as a major process underlying the link between obesity and its associated pathologies. Adipose tissue appears to play a primary and crucial role as a source and site of inflammation. Accumulation of immune cells within adipose tissue occurs in obese conditions. The present review focuses on the relationship between adipose tissue and immune cells, including macrophages, dendritic cells, T and B lymphocytes, and natural killer cells, in both the physiological state and under obese conditions. The factors involved in the accumulation of both myeloid and lymphoid cells in adipose tissue are also described. In addition, the role of adipose-tissue immune cells on adipocyte metabolism and cells of the adipose tissue stromal-vascular fraction are discussed, with particular emphasis on the cross-talk between macrophages and adipocytes, together with recent reports of T lymphocytes in adipose tissue.

RNAi-based therapeutic strategies for metabolic disease

RNA interference (RNAi) is a robust gene silencing mechanism that degrades mRNAs complementary to the antisense strands of double-stranded, short interfering RNAs (siRNAs). As a therapeutic strategy, RNAi has an advantage over small-molecule drugs, as virtually all genes are susceptible to targeting by siRNA molecules. This advantage is, however, counterbalanced by the daunting challenge of achieving safe, effective delivery of oligonucleotides to specific tissues in vivo. Lipid-based carriers of siRNA therapeutics can now target the liver in metabolic diseases and are being assessed in clinical trials for the treatment of hypercholesterolemia. For this indication, a chemically modified oligonucleotide that targets endogenous small RNA modulators of gene expression (microRNAs) is also under investigation in clinical trials. Emerging 'self-delivery' siRNAs that are covalently linked to lipophilic moieties show promise for the future development of therapies. Besides the liver, inflammation of the adipose tissue in patients with obesity and type 2 diabetes mellitus may be an attractive target for siRNA therapeutics. Administration of siRNAs encapsulated within glucan microspheres can silence genes in inflammatory phagocytic cells, as can certain lipid-based carriers of siRNA. New technologies that combine siRNA molecules with antibodies or other targeting molecules also appear encouraging. Although still at an early stage, the emergence of RNAi-based therapeutics has the potential to markedly influence our clinical future.

B cells promote insulin resistance through modulation of T cells and production of pathogenic IgG antibodies

Chronic inflammation characterized by T cell and macrophage infiltration of visceral adipose tissue (VAT) is a hallmark of obesity-associated insulin resistance and glucose intolerance. Here we show a fundamental pathogenic role for B cells in the development of these metabolic abnormalities. B cells accumulate in VAT in diet-induced obese (DIO) mice, and DIO mice lacking B cells are protected from disease despite weight gain. B cell effects on glucose metabolism are mechanistically linked to the activation of proinflammatory macrophages and T cells and to the production of pathogenic IgG antibodies. Treatment with a B cell-depleting CD20 antibody attenuates disease, whereas transfer of IgG from DIO mice rapidly induces insulin resistance and glucose intolerance. Moreover, insulin resistance in obese humans is associated with a unique profile of IgG autoantibodies. These results establish the importance of B cells and adaptive immunity in insulin resistance and suggest new diagnostic and therapeutic modalities for managing the disease.

Novel C-C chemokine receptor 2 antagonists in metabolic disease: a review of recent developments

INTRODUCTION

C-C chemokine ligand 2 (CCL2), also known as monocyte chemoattractant protein-1, and its receptor, C-C chemokine receptor 2 (CCR2), play important roles in various inflammatory diseases. Recently, it has been reported that the CCL2/CCR2 pathway also has an important role in the pathogenesis of metabolic syndrome through its association with obesity and related systemic complications.

AREAS COVERED

This review focuses on the roles of CCR2 in the pathogenesis of adipose tissue inflammation and other organ damage associated with metabolic syndrome, which is still a matter of debate in many studies. It also covers the use of novel CCR2 antagonists as therapies in such conditions.

EXPERT OPINION

There is abundant experimental evidence that the CCL2/CCR2 pathway may be involved in chronic low-grade inflammation of adipose tissue in obesity and related metabolic diseases. Although animal models of diabetes and obesity, as well as human trials, have produced controversial results, there is continued interest in the roles of CCR2 inhibition in metabolic disease. Further identification of the mechanisms for recruitment and activation of phagocytes and determination of the roles of other chemokines are needed. Future study of these fundamental questions will provide a clearer understanding of adipose tissue biology and potential therapeutic targets for treatment of obesity-related metabolic disease, including diabetic nephropathy.

Inflammation correlates with markers of T-cell subsets including regulatory T cells in adipose tissue from obese patients

Accumulation of cytotoxic and T-helper (T(h))1 cells together with a loss of regulatory T cells in gonadal adipose tissue was recently shown to contribute to obesity-induced adipose tissue inflammation and insulin resistance in mice. Human data on T-cell populations in obese adipose tissue and their potential functional relevance are very limited. We aimed to investigate abundance and proportion of T-lymphocyte sub-populations in human adipose tissue in obesity and potential correlations with anthropometric data, insulin resistance, and systemic and adipose tissue inflammation. Therefore, we analyzed expression of marker genes specific for pan-T cells and T-cell subsets in visceral and subcutaneous adipose tissue from highly obese patients (BMI >40 kg/m(2), n = 20) and lean to overweight control subjects matched for age and sex (BMI <30 kg/m(2); n = 20). All T-cell markers were significantly upregulated in obese adipose tissue and correlated with adipose tissue inflammation. Proportions of cytotoxic T cells and T(h)1 cells were unchanged, whereas those of regulatory T cells and T(h)2 were increased in visceral adipose tissue from obese compared to control subjects. Systemic and adipose tissue inflammation positively correlated with the visceral adipose abundance of cytotoxic T cells and T(h)1 cells but also regulatory T cells within the obese group. Therefore, this study confirms a potential role of T cells in human obesity-driven inflammation but does not support a loss of protective regulatory T cells to contribute to adipose tissue inflammation in obese patients as suggested by recent animal studies.

Diet-induced adipose tissue inflammation and liver steatosis are prevented by DPP-4 inhibition in diabetic mice

OBJECTIVE

Diet composition alters the metabolic states of adipocytes and hepatocytes in diabetes. The effects of dipeptidyl peptidase-4 (DPP-4) inhibition on adipose tissue inflammation and fatty liver have been obscure. We investigated the extrapancreatic effects of DPP-4 inhibition on visceral fat and the liver.

RESEARCH DESIGN AND METHODS

We investigated diet-induced metabolic changes in β-cell-specific glucokinase haploinsufficient (Gck(+/-)) diabetic mice. We challenged animals with a diet containing a combination of sucrose and oleic acid (SO) or sucrose and linoleic acid (SL). Next, we assessed the effects of a DPP-4 inhibitor, des-fluoro-sitagliptin, on adipose tissue inflammation and hepatic steatosis.

RESULTS

The epididymal fat weight and serum leptin level were significantly higher in Gck(+/-) mice fed SL than in mice fed SO, although no significant differences in body weight or adipocyte size were noted. Compared with SO, SL increased the numbers of CD11c(+) M1 macrophages and CD8(+) T-cells in visceral adipose tissue and the expression of E-selectin, P-selectin, and plasminogen activator inhibitor-1 (PAI-1). DPP-4 inhibition significantly prevented adipose tissue infiltration by CD8(+) T-cells and M1 macrophages and decreased the expression of PAI-1. The production of cytokines by activated T-cells was not affected by DPP-4 inhibition. Furthermore, DPP-4 inhibition prevented fatty liver in both wild-type and Gck(+/-) mice. DPP-4 inhibition also decreased the expressions of sterol regulatory element-binding protein-1c, stearoyl-CoA desaturase-1, and fatty acid synthase, and increased the expression of peroxisome proliferator-activated receptor-α in the liver.

CONCLUSIONS

Our findings indicated that DPP-4 inhibition has extrapancreatic protective effects against diet-induced adipose tissue inflammation and hepatic steatosis.

Proteome of human subcutaneous adipose tissue stromal vascular fraction cells versus mature adipocytes based on DIGE

Adipose tissue contains a heterogeneous population of mature adipocytes, endothelial cells, immune cells, pericytes, and preadipocytic stromal/stem cells. To date, a majority of proteomic analyses have focused on intact adipose tissue or isolated adipose stromal/stem cells in vitro. In this study, human subcutaneous adipose tissue from multiple depots (arm and abdomen) obtained from female donors was separated into populations of stromal vascular fraction cells and mature adipocytes. Out of 960 features detected by 2-D gel electrophoresis, a total of 200 features displayed a 2-fold up- or down-regulation relative to each cell population. The protein identity of 136 features was determined. Immunoblot analyses comparing SVF relative to adipocytes confirmed that carbonic anhydrase II was up-regulated in both adipose depots while catalase was up-regulated in the arm only. Bioinformatic analyses of the data set determined that cytoskeletal, glycogenic, glycolytic, lipid metabolic, and oxidative stress related pathways were highly represented as differentially regulated between the mature adipocytes and stromal vascular fraction cells. These findings extend previous reports in the literature with respect to the adipose tissue proteome and the consequences of adipogenesis. The proteins identified may have value as biomarkers for monitoring the physiology and pathology of cell populations within subcutaneous adipose depots.

Deoxyhypusine synthase haploinsufficiency attenuates acute cytokine signaling

Deoxyhypusine synthase (DHS) catalyzes the post-translational formation of the amino acid hypusine. Hypusine is unique to the eukaryotic translational initiation factor 5A (eIF5A), and is required for its functions in mRNA shuttling, translational elongation, and stress granule formation. In recent studies, we showed that DHS promotes cytokine and ER stress signaling in the islet β cell and thereby contributes to its dysfunction in the setting of diabetes mellitus. Here, we review the evidence supporting a role for DHS (and hypusinated eIF5A) in cellular stress responses, and provide new data on the phenotype of DHS knockout mice. We show that homozygous knockout mice are embryonic lethal, but heterozygous knockout mice appear normal with no evidence of growth or metabolic deficiencies. Mouse embryonic fibroblasts from heterozygous knockout mice attenuate acute cytokine signaling, as evidenced by reduced production of inducible nitric oxide synthase, but show no statistically significant defects in proliferation or cell cycle progression. Our data are discussed with respect to the utility of sub-maximal inhibition of DHS in the setting of inflammatory states, such as diabetes mellitus.

Deficiency of haematopoietic-cell-derived IL-10 does not exacerbate high-fat-diet-induced inflammation or insulin resistance in mice

AIMS/HYPOTHESIS

Recent work has identified the important roles of M1 pro-inflammatory and M2 anti-inflammatory macrophages in the regulation of insulin sensitivity. Specifically, increased numbers of M2 macrophages and a decrease in M1 macrophages within the adipose tissue are associated with a state of enhanced insulin sensitivity. IL-10 is an anti-inflammatory cytokine and is a critical effector molecule of M2 macrophages.

METHODS

In the present study, we examined the contribution of haematopoietic-cell-derived IL-10 to the development of obesity-induced inflammation and insulin resistance. We hypothesised that haematopoietic-cell-restricted deletion of IL-10 would exacerbate obesity-induced inflammation and insulin resistance. Lethally irradiated wild-type recipient mice receiving bone marrow from either wild-type or Il10-knockout mice were placed on either a chow or a high-fat diet for a period of 12 weeks and assessed for alterations in body composition, tissue inflammation and glucose and insulin tolerance.

RESULTS

Contrary to our hypothesis, neither inflammation, as measured by the activation of pro-inflammatory stress kinases and gene expression of several pro-inflammatory cytokines in the adipose tissue and liver, nor diet-induced obesity and insulin resistance were exacerbated by the deletion of haematopoietic-cell-derived IL-10. Interestingly, however, Il10 mRNA expression and IL-10 protein production in liver and/or adipose tissue were markedly elevated in Il10-knockout bone-marrow-transplanted mice relative to wild-type bone marrow-transplanted mice.

CONCLUSIONS/INTERPRETATION

These data show that deletion of IL-10 from the haematopoietic system does not potentiate high-fat diet-induced inflammation or insulin resistance.

Excess body weight and obesity--the link with gastrointestinal and hepatobiliary cancer

Excess body weight (EBW) is an independent risk factor for many human malignancies, including cancers throughout the gastrointestinal and hepatobiliary tract from the esophagus to the colorectum. The relative risk of gastrointestinal cancer in obese individuals is approximately 1.5-2.0 times that for normal weight individuals, with organ-specific and gender-specific differences for specific cancers. The association between EBW and risk of premalignant stages of gastrointestinal carcinogenesis, such as colorectal adenoma and Barrett esophagus, is similar, implying a role for EBW during the early stages of carcinogenesis that could be relevant to preventative strategies. EBW also impacts negatively on gastrointestinal cancer outcomes. The mechanistic basis of the association between EBW and carcinogenesis remains incompletely understood. Postulated mechanisms include increased insulin and insulin-like growth factor signaling and chronic inflammation (both linked to the metabolic syndrome), as well as signaling via adipokines, such as leptin. The role of obesity-related changes in the intestinal microbiome in gastrointestinal carcinogenesis deserves further attention. Whether weight loss leads to reduced future gastrointestinal and liver cancer risk has yet to be fully explored. There is some support for the idea that weight loss negatively regulates colorectal carcinogenesis. In addition, data suggest a reduction in risk of several cancers in the first 10 years after bariatric surgery.

Novel pathway of adipogenesis through cross-talk between adipose tissue macrophages, adipose stem cells and adipocytes: evidence of cell plasticity

Introduction

Previous studies highlight a complex relationship between lineage and phenotype for adipose tissue macrophages (ATMs), adipose stem cells (ASCs), and adipocytes, suggesting a high degree of plasticity of these cells. In the present study, using a novel co-culture system, we further characterized the interaction between ATMs, ASCs and adipocytes.

Research Design and Methods

Human adipocytes and the stromal vascular fraction containing ATMs and ASCs were isolated from human adipose tissue and co-cultured for 24 hours. FACS was used to characterize ATMs and ASCs before and after co-culture. Preadipocytes generated after co-culture were characterized by immunostaining for DLK (preadipocytes), CD14 and CD68 (ATMs), CD34 (ASCs), and Nile Red staining for lipid drops. qRT-PCR was used to quantify adipogenic markers such as C/EBPα and PPARγ. A novel fluorescent nanobead lineage tracing method was utilized before co-culture where fluorescent nanobeads were internalized by CD68 (+) ATMs.

Results

Co-culture of adipocytes with ATMs and ASCs increased the formation of new preadipocytes, thereby increasing lipid accumulation and C/EBPα and PPARγ gene expression. Preadipocytes originating after co-culture were positive for markers of preadipocytes, ATMs and ASCs. Moreover, fluorescent nanobeads were internalized by ATMs before co-culture and the new preadipocytes formed after co-culture also contained fluorescent nanobeads, suggesting that new preadipocytes originated in part from ATMs. The formation of CD34(+)/CD68(+)/DLK (+) cell spheres supported the interaction of ATMs, ASCs and preadipocytes.

Conclusions

Cross-talk between adipocytes, ATMs and ASCs promotes preadipocyte formation. The regulation of this novel adipogenic pathway involves differentiation of ATMs to preadipocytes. The presence of CD34(+)/CD68(+)/DLK(+) cells grouped in spheres suggest that paracrine interactions between these cell types plays an important role in the generation and proliferation of new preadipocytes. This phenomenon may reflect the in vivo plasticity of adipose tissue in which ATMs play an additional role during inflammation and other disease states. Understanding this novel pathway could influence adipogenesis, leading to new treatments for obesity, inflammation, and type 2 diabetes.

Eosinophils sustain adipose alternatively activated macrophages associated with glucose homeostasis

Eosinophils are associated with helminth immunity and allergy, often in conjunction with alternatively activated macrophages (AAMs). Adipose tissue AAMs are necessary to maintain glucose homeostasis and are induced by the cytokine interleukin-4 (IL-4). Here, we show that eosinophils are the major IL-4-expressing cells in white adipose tissues of mice, and, in their absence, AAMs are greatly attenuated. Eosinophils migrate into adipose tissue by an integrin-dependent process and reconstitute AAMs through an IL-4- or IL-13-dependent process. Mice fed a high-fat diet develop increased body fat, impaired glucose tolerance, and insulin resistance in the absence of eosinophils, and helminth-induced adipose tissue eosinophilia enhances glucose tolerance. Our results suggest that eosinophils play an unexpected role in metabolic homeostasis through maintenance of adipose AAMs.

Blockade of class IB phosphoinositide-3 kinase ameliorates obesity-induced inflammation and insulin resistance

Obesity and insulin resistance, the key features of metabolic syndrome, are closely associated with a state of chronic, low-grade inflammation characterized by abnormal macrophage infiltration into adipose tissues. Although it has been reported that chemokines promote leukocyte migration by activating class IB phosphoinositide-3 kinase (PI3Kγ) in inflammatory states, little is known about the role of PI3Kγ in obesity-induced macrophage infiltration into tissues, systemic inflammation, and the development of insulin resistance. In the present study, we used murine models of both diet-induced and genetically induced obesity to examine the role of PI3Kγ in the accumulation of tissue macrophages and the development of obesity-induced insulin resistance. Mice lacking p110γ (Pik3cg(-/-)), the catalytic subunit of PI3Kγ, exhibited improved systemic insulin sensitivity with enhanced insulin signaling in the tissues of obese animals. In adipose tissues and livers of obese Pik3cg(-/-) mice, the numbers of infiltrated proinflammatory macrophages were markedly reduced, leading to suppression of inflammatory reactions in these tissues. Furthermore, bone marrow-specific deletion and pharmacological blockade of PI3Kγ also ameliorated obesity-induced macrophage infiltration and insulin resistance. These data suggest that PI3Kγ plays a crucial role in the development of both obesity-induced inflammation and systemic insulin resistance and that PI3Kγ can be a therapeutic target for type 2 diabetes.

Acute and chronic saturated fatty acid treatment as a key instigator of the TLR-mediated inflammatory response in human adipose tissue, in vitro

A post-prandial increase in saturated fatty acids (SFAs) and glucose (Glc) activates an inflammatory response, which may be prolonged following restoration of physiological SFAs and Glc levels--a finding referred to as 'metabolic memory'. This study examined chronic and oscillating SFAs and Glc on the inflammatory signalling pathway in human adipose tissue (AT) and adipocytes (Ads) and determined whether Ads are subject to "metabolic memory." Abdominal (Abd) subcutaneous (Sc) explants and Ads were treated with chronic low glucose (L-Glc): 5.6 mM and high glucose (H-Glc): 17.5 mM, with low (0.2 mM) and high (2 mM) SFA for 48 h. Abd Sc explants and Ads were also exposed to the aforementioned treatment regimen for 12-h periods, with alternating rest periods of 12 h in L-Glc. Chronic treatment with L-Glc and high SFAs, H-Glc and high SFAs up-regulated key factors of the nuclear factor-κB (NFκB) pathway in Abd Sc AT and Ads (TLR4, NFκB; P<.05), whilst down-regulating MyD88. Oscillating Glc and SFA concentrations increased TLR4, NFκB, IKKβ (P<.05) in explants and Ads and up-regulated MyD88 expression (P<.05). Both tumor necrosis factor α and interleukin 6 (P<.05) secretion were markedly increased in chronically treated Abd Sc explants and Ads whilst, with oscillating treatments, a sustained inflammatory effect was noted in absence of treatment. Therefore, SFAs may act as key instigators of the inflammatory response in human AT via NFκB activation, which suggests that short-term exposure of cells to uncontrolled levels of SFAs and Glc leads to a longer-term inflammatory insult within the Ad, which may have important implications for patients with obesity and Type 2 diabetes.

Adipose tissue as a dedicated reservoir of functional mast cell progenitors

White adipose tissue (WAT) is a heterogeneous tissue, found in various locations throughout the body, containing mature adipocytes and the stroma-vascular fraction (SVF). The SVF includes a large proportion of immune hematopoietic cells, among which, mast cells that contribute to diet-induced obesity. In this study, we asked whether mast cells present in mice adipose tissue could derive from hematopoietic stem/progenitor cells (HSPC) identified in the tissue. We therefore performed both in vitro and in vivo experiments dedicated to monitoring the progeny of WAT-derived HSPC. The entire study was conducted in parallel with bone marrow-derived cells, considered the gold standard for hematopoietic-lineage studies. Here, we demonstrate that adipose-derived HSPC contain a precursor-cell population committed to the mast cell lineage, and able to efficiently home to peripheral organs such as intestine and skin, where it acquires properties of functional tissue mast cells. Additionally, WAT contains a significant mast cell progenitor population, suggesting that the entire mast cell lineage process take place in WAT. Considering the quantitative importance of WAT in the adult organism and the increasing roles recently assigned to mast cells in physiopathology, WAT may represent an important source of mast cells in physiological and pathological situations.

State of the union between metabolism and the immune system in type 2 diabetes

Lymphocytes and myeloid cells (monocyte/macrophages) have important roles in multiple types of diseases characterized by unresolved inflammation. The relatively recent appreciation of obesity, insulin resistance and type 2 diabetes (T2D) as chronic inflammatory diseases has stimulated interest in understanding the role of immune cells in metabolic imbalance. Myeloid cells regulate inflammation through cytokine production and the adipose tissue remodeling that accompanies hyper-nutrition, thus are critical players in metabolic homeostasis. More recently, multiple studies have indicated a role for T cells in obesity-associated inflammation and insulin resistance in model organisms, with parallel work indicating that pro-inflammatory changes in T cells also associate with human T2D. Furthermore, the expansion of T cells with similar antigen-binding sites in obesity and T2D indicates these diseases share characteristics previously attributed to inflammatory autoimmune disorders. Parallel pro-inflammatory changes in the B-cell compartment of T2D patients have also been identified. Taken together, these studies indicate that in addition to accepted pro-inflammatory roles of myeloid cells in T2D, pro-inflammatory skewing of both major lymphocyte subsets has an important role in T2D disease pathogenesis. Basic immunological principles suggest that alterations in lymphocyte function in obesity and T2D patients are an integral part of a feed-forward pro-inflammatory loop involving additional cell types. Importantly, the pro-inflammatory loop almost inevitably includes adipocytes, known to respond to pro-inflammatory, pro-diabetogenic cytokines originating from the myeloid and lymphoid compartments. We propose a model for inflammation in T2D that functionally links lymphocyte, myeloid and adipocyte contributions, and importantly proposes that tools for B-cell ablation or regulation of T-cell subset balance may have a place in the endocrinologist's limited arsenal.

Peripheral blood gene expression profiles in metabolic syndrome, coronary artery disease and type 2 diabetes

To determine if individuals with metabolic disorders possess unique gene expression profiles, we compared transcript levels in peripheral blood from patients with coronary artery disease, type 2 diabetes and their precursor state, metabolic syndrome to those of control subjects and subjects with rheumatoid arthritis. The gene expression profile of each metabolic state was distinguishable from controls and correlated with other metabolic states more than with rheumatoid arthritis. Of note, subjects in the metabolic cohorts over-expressed gene sets that participate in the innate immune response. Genes involved in activation of the pro-inflammatory transcription factor, NF-κB, were over-expressed in coronary artery disease while genes differentially expressed in type 2 diabetes play key roles in T cell activation and signaling. RT-PCR validation confirmed microarray results. Furthermore, several genes differentially expressed in human metabolic disorders have been previously shown to participate in inflammatory responses in murine models of obesity and Type 2 diabetes. Taken together, these data demonstrate that peripheral blood from individuals with metabolic disorders display overlapping and non-overlapping patterns of gene expression indicative of unique, underlying immune processes.

The stromal-vascular fraction of adipose tissue contributes to major differences between subcutaneous and visceral fat depots

Adipose tissue represents a complex tissue both in terms of its cellular composition, as it includes mature adipocytes and the various cell types comprising the stromal-vascular fraction (SVF), and in relation to the distinct biochemical, morphological and functional characteristics according to its anatomical location. Herein, we have characterized the proteomic profile of both mature adipocyte and SVF from human visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) fat depots in order to unveil differences in the expression of proteins which may underlie the distinct association of VAT and SAT to several pathologies. Specifically, 24 proteins were observed to be differentially expressed between SAT SVF versus VAT SVF from lean individuals. Immunoblotting and RT-PCR analysis confirmed the differential regulation of the nuclear envelope proteins lamin A/C, the membrane-cytoskeletal linker ezrin and the enzyme involved in retinoic acid production, aldehyde dehydrogenase 1A2, in the two fat depots. In sum, the observation that proteins with important cell functions are differentially distributed between VAT and SAT and their characterization as components of SVF or mature adipocytes pave the way for future research on the molecular basis underlying diverse adipose tissue-related pathologies such as metabolic syndrome or lipodystrophy.

DPP4 gene DNA methylation in the omentum is associated with its gene expression and plasma lipid profile in severe obesity

Severely obese subjects with the metabolic syndrome (MS) have higher dipeptidyl peptidase-4 (DPP4) expression in their visceral adipose tissue (VAT) compared to obese individuals without MS. We tested the hypothesis that methylation level of CpG sites in the DPP4 promoter CpG island in VAT was genotype-dependent and associated with DPP4 mRNA abundance and MS-related phenotypes. The VAT DNA was extracted in 92 severely obese premenopausal women undergoing biliopancreatic derivation for the treatment of obesity. Women were nondiabetic and none of them used medication to treat MS features. Cytosine methylation rates (%) of 102 CpG sites in the DPP4 CpG island were assessed by pyrosequencing of sodium bisulfite-treated DNA. Methylation rates were >10% for CpG sites 94-102. Their mean methylation rate (%Meth(94-102)) was different between genotypes for DPP4 polymorphisms rs13015258 (P = 0.001), rs17848915 (P = 0.0004), and c.1926 G>A (P = 0.001). The %Meth(94-102) correlated negatively with DPP4 mRNA abundance (r = -0.25, P < 0.05) and positively with plasma high-density lipoprotein (HDL) cholesterol concentrations (r = 0.22, P < 0.05), whereas DPP4 mRNA abundance correlated positively with plasma total-/HDL-cholesterol ratio (r = 0.25; P < 0.05). In the VAT of nondiabetic severely obese women, genotype-dependent methylation levels of specific CpG sites in the DPP4 promoter CpG island were associated with DPP4 gene expression and variability in the plasma lipid profile. Higher DPP4 gene expression in VAT and its relationship with the plasma lipid profile may be explained by actually unknown DPP4 biological effect or, to another extent, may also be a marker of VAT inflammation known to be associated with metabolic disturbances.

Dipeptidyl peptidase IV inhibitor sitagliptin reduces local inflammation in adipose tissue and in pancreatic islets of obese mice

Adipose tissue inflammation and reduced pancreatic β-cell function are key issues in the development of cardiovascular disease and progressive metabolic dysfunction in type 2 diabetes mellitus. The aim of this study was to determine the effect of the DPP IV inhibitor sitagliptin on adipose tissue and pancreatic islet inflammation in a diet-induced obesity model. C57Bl/6J mice were placed on a high-fat (60% kcal fat) diet for 12 wk, with or without sitagliptin (4 g/kg) as a food admix. Sitagliptin significantly reduced fasting blood glucose by 21% as well as insulin by ∼25%. Sitagliptin treatment reduced body weight without changes in overall body mass index or in the epididymal and retroperitoneal fat mass. However, sitagliptin treatment led to triple the number of small adipocytes despite reducing the number of the very large adipocytes. Sitagliptin significantly reduced inflammation in the adipose tissue and pancreatic islet. Macrophage infiltration in adipose tissue evaluated by immunostaining for Mac2 was reduced by sitagliptin (P < 0.01), as was the percentage of CD11b+/F4/80+ cells in the stromal vascular fraction (P < 0.02). Sitagliptin also reduced adipocyte mRNA expression of inflammatory genes, including IL-6, TNFα, IL-12(p35), and IL-12(p40), 2.5- to fivefold as well as 12-lipoxygenase protein expression. Pancreatic islets were isolated from animals after treatments. Sitagliptin significantly reduced mRNA expression of the following inflammatory cytokines: MCP-1 (3.3-fold), IL-6 (2-fold), IL-12(p40) (2.2-fold), IL-12(p35) (5-fold, P < 0.01), and IP-10 (2-fold). Collectively, the results indicate that sitagliptin has anti-inflammatory effects in adipose tissue and in pancreatic islets that accompany the insulinotropic effect.

Energy-restricted high-fat diets only partially improve markers of systemic and adipose tissue inflammation

This study aimed at investigating whether the weight loss due to energy-restricted high-fat diets is accompanied with parallel improvements in metabolic markers and adipose tissue inflammation. Eight-week-old C57BL/6J mice were given free access to a low-fat (LF) or a high-fat (45% of energy from fat-HF) diet for 6 months. Restricting intake of the HF diet by 30% (HFR) during the last 2 months of the HF feeding trial decreased fasting plasma insulin, homeostasis model assessment of insulin resistance (HOMA(IR)), and plasma triglyceride levels and improved hepatic steatosis compared to ad libitum HF feeding, indicating an improved metabolic profile. Further, analysis of gonadal white adipose tissue (GWAT) gene expression by microarray and quantitative PCR analyses demonstrated that HFR downregulated expression of genes linked to cell and focal adhesion, cytokine-cytokine receptor interaction, and endoplasmic reticulum (ER)-associated degradation pathway. However, HFR had no effect on circulating plasminogen activator inhibitor-1 (PAI-1) and nonesterified fatty acid levels, which were persistently higher in both HF and HFR groups compared to the LF group. Furthermore, HFR had a negative effect on plasma total adiponectin level. Finally, while HFR decreased GWAT monocyte chemotactic protein-1 (MCP-1), interleukin-2 (IL-2), and PAI-1 levels, it did not affect several other cytokines including granulocyte-macrophage colony-stimulating factor, interferon-γ, IL-1β, IL-6, and IL-10. In summary, energy-restricted high-fat diets improve insulin sensitivity, while only partially improving markers of systemic and adipose tissue inflammation. In conclusion, our study supports the recommended low-fat intake for overall cardiovascular health.

Role of the adipocyte-specific NF-κB activity in the regulation of IP-10 and T cell migration

Infiltration of immune cells into adipose tissue plays a central role in the pathophysiology of obesity-associated low-grade inflammation. The aim of this study was to analyze the role of adipocyte NF-κB signaling in the regulation of the chemokine/adipokine interferon-γ-induced protein 10 kDa (IP-10) and adipocyte-mediated T cell migration. Therefore, the regulation of IP-10 was investigated in adipose tissue of male C57BL/6J mice, primary human and 3T3-L1 preadipocytes/adipocytes. To specifically block the NF-κB pathway, 3T3-L1 cells stably overexpressing a transdominant mutant of IκBα were generated, and the chemical NF-κB inhibitor Bay117082 was used. Adipocyte-mediated T cell migration was assessed by a migration assay. It could be shown that IP-10 expression was higher in mature adipocytes compared with preadipocytes. Induced IP-10 expression and secretion were completely blocked by an NF-κB inhibitor in 3T3-L1 and primary human adipocytes. Stable overexpression of a transdominant mutant of IκBα in 3T3-L1 adipocytes led to an inhibition of basal and stimulated IP-10 expression and secretion. T cell migration was induced by 3T3-L1 adipocyte-conditioned medium, and both basal and induced T cell migration was strongly inhibited by stable overexpression of a transdominant IκBα mutant. In addition, with the use of an anti-IP-10 antibody, a significant decrease of adipocyte-induced T cell migration was shown. In conclusion, in this study, we could demonstrate that the NF-κB pathway is essential for the regulation of IP-10 in 3T3-L1 and primary human adipocytes. Adipocytes rather than preadipocytes contribute to NF-κB-dependent IP-10 expression and secretion. Furthermore, NF-κB-dependent factors and especially IP-10 represent novel signals from adipocytes to induce T cell migration.

Adipokines in inflammation and metabolic disease

The worldwide epidemic of obesity has brought considerable attention to research aimed at understanding the biology of adipocytes (fat cells) and the events occurring in adipose tissue (fat) and in the bodies of obese individuals. Accumulating evidence indicates that obesity causes chronic low-grade inflammation and that this contributes to systemic metabolic dysfunction that is associated with obesity-linked disorders. Adipose tissue functions as a key endocrine organ by releasing multiple bioactive substances, known as adipose-derived secreted factors or adipokines, that have pro-inflammatory or anti-inflammatory activities. Dysregulated production or secretion of these adipokines owing to adipose tissue dysfunction can contribute to the pathogenesis of obesity-linked complications. In this Review, we focus on the role of adipokines in inflammatory responses and discuss their potential as regulators of metabolic function.

Visceral adipose inflammation in obesity is associated with critical alterations in tregulatory cell numbers

Background

The development of insulin resistance (IR) in mouse models of obesity and type 2 diabetes mellitus (DM) is characterized by progressive accumulation of inflammatory macrophages and subpopulations of T cells in the visceral adipose. Regulatory T cells (Tregs) may play a critical role in modulating tissue inflammation via their interactions with both adaptive and innate immune mechanisms. We hypothesized that an imbalance in Tregs is a critical determinant of adipose inflammation and investigated the role of Tregs in IR/obesity through coordinated studies in mice and humans.

Methods and Findings

Foxp3-green fluorescent protein (GFP) “knock-in” mice were randomized to a high-fat diet intervention for a duration of 12 weeks to induce DIO/IR. Morbidly obese humans without overt type 2 DM (n = 13) and lean controls (n = 7) were recruited prospectively for assessment of visceral adipose inflammation. DIO resulted in increased CD3⁺CD4⁺, and CD3⁺CD8⁺ cells in visceral adipose with a striking decrease in visceral adipose Tregs. Treg numbers in visceral adipose inversely correlated with CD11b⁺CD11c⁺ adipose tissue macrophages (ATMs). Splenic Treg numbers were increased with up-regulation of homing receptors CXCR3 and CCR7 and marker of activation CD44. In-vitro differentiation assays showed an inhibition of Treg differentiation in response to conditioned media from inflammatory macrophages. Human visceral adipose in morbid obesity was characterized by an increase in CD11c⁺ ATMs and a decrease in foxp3 expression.

Conclusions

Our experiments indicate that obesity in mice and humans results in adipose Treg depletion. These changes appear to occur via reduced local differentiation rather than impaired homing. Our findings implicate a role for Tregs as determinants of adipose inflammation.

Adipocyte-macrophage interaction may mediate LPS-induced low-grade inflammation: Potential link with metabolic complications

Chronic low-grade infection has been suggested to be associated with metabolic disorder such as diabetes. However, the molecular mechanism underlying this important association is largely unknown. The only clue established so far is that many subjects exhibit elevated levels of C-reactive protein as measured by highly sensitive assay. Here, we hypothesized that adipocyte–macrophage interaction plays a key role in amplifying such low grade infection to the level of influencing metabolic disorders. The presence of macrophages in abdominal adipose tissues was investigated by immunohistochemistry. To see whether molecules associated with acute phase protein, LPS signaling, and persistent recruitment of monocytes, are produced at higher amounts in adipocytes co-cultured with macrophages stimulated with low concentration of LPS (1 ng/ml), we measured serum amyloid A (SAA), LPS binding protein (LBP), soluble CD14 (sCD14), and RANTES levels in culture supernatant of co-cultures. Lastly, we investigated in vivo effect of low-grade LPS infusion on the production of these molecules using obese model mice. The macrophages were certainly identified in abdominal adipose tissues. Investigated molecules, especially LBP, SAA, and RANTES were produced at higher amounts in co-cultures stimulated with LPS compared with the cells without LPS. The ob/ob, and high-fat diet-induced obesity mice produced higher amounts of LBP, SAA, and RANTES one day after LPS infusion (1 ng/ml/g body weight) compared with ob/– and normal-fat fed control mice. Thus, adipocytes and infiltrated macrophages, and their interaction with low endotoxin stimulation appear to play an important role in amplifying and maintaining LPS-induced low-grade inflammation.

The NLRP3 inflammasome instigates obesity-induced inflammation and insulin resistance

Emergence of chronic ‘sterile’ inflammation during obesity in absence of overt infection or autoimmune process is a puzzling phenomenon. The Nod Like Receptor (NLR) family of innate immune cell sensors like the Nlrp3 inflammasome are implicated in recognizing certain non-microbial origin ‘danger–signals’ leading to caspase-1 activation and subsequent IL-1β and IL-18 secretion. We show that reduction in adipose tissue expression of Nlrp3 is coupled with decreased inflammation and improved insulin–sensitivity in obese type-2 diabetic patients. The Nlrp3 inflammasome senses the lipotoxicity–associated ceramide to induce caspase-1 cleavage in macrophages and adipose tissue. Ablation of Nlrp3 prevented the obesity–induced inflammasome activation in fat depots and liver together with enhanced insulin–signalling. Furthermore, elimination of Nlrp3 in obesity reduced IL-18 and adipose tissue IFNγ along with an increase in naïve and reduction in effector adipose tissue T cells. Collectively, these data establish that Nlrp3 inflammasome senses obesity–associated ‘danger–signals’ and contributes to obesity–induced inflammation and insulin–resistance.

NF-κB, inflammation, and metabolic disease

Metabolic disorders including obesity, type 2 diabetes, and atherosclerosis have been viewed historically as lipid storage disorders brought about by overnutrition. It is now widely appreciated that chronic low-grade inflammation plays a key role in the initiation, propagation, and development of metabolic diseases. Consistent with its central role in coordinating inflammatory responses, numerous recent studies have implicated the transcription factor NF-κB in the development of such diseases, thereby further establishing inflammation as a critical factor in their etiology and offering hope for the development of new therapeutic approaches for their treatment.

Nuclear orphan receptor TAK1/TR4-deficient mice are protected against obesity-linked inflammation, hepatic steatosis, and insulin resistance

OBJECTIVE

The nuclear receptor TAK1/TR4/NR2C2 is expressed in several tissues that are important in the control of energy homeostasis. In this study, we investigate whether TAK1 functions as a regulator of lipid and energy homeostasis and has a role in metabolic syndrome.

RESEARCH DESIGN AND METHODS

We generated TAK1-deficient (TAK1⁻(/)⁻) mice to study the function of TAK1 in the development of metabolic syndrome in aged mice and mice fed a high-fat diet (HFD). (Immuno)histochemical, biochemical, and gene expression profile analyses were performed to determine the effect of the loss of TAK1 expression on lipid homeostasis in liver and adipose tissues. In addition, insulin sensitivity, energy expenditure, and adipose-associated inflammation were compared in wild-type (WT) and TAK1⁻(/)⁻ mice fed a HFD.

RESULTS

TAK1-deficient (TAK1⁻(/)⁻) mice are resistant to the development of age- and HFD-induced metabolic syndrome. Histo- and biochemical analyses showed significantly lower hepatic triglyceride levels and reduced lipid accumulation in adipose tissue in TAK1⁻(/)⁻ mice compared with WT mice. Gene expression profiling analysis revealed that the expression of several genes encoding proteins involved in lipid uptake and triglyceride synthesis and storage, including Cidea, Cidec, Mogat1, and CD36, was greatly decreased in the liver and primary hepatocytes of TAK1⁻(/)⁻ mice. Restoration of TAK1 expression in TAK1⁻(/)⁻ hepatocytes induced expression of several lipogenic genes. Moreover, TAK1⁻(/)⁻ mice exhibited reduced infiltration of inflammatory cells and expression of inflammatory genes in white adipose tissue, and were resistant to the development of glucose intolerance and insulin resistance. TAK1⁻(/)⁻ mice consume more oxygen and produce more carbon dioxide than WT mice, suggesting increased energy expenditure.

CONCLUSIONS

Our data reveal that TAK1 plays a critical role in the regulation of energy and lipid homeostasis, and promotes the development of metabolic syndrome. TAK1 may provide a new therapeutic target in the management of obesity, diabetes, and liver steatosis.

Inflammation, oxidative stress, and obesity

Obesity is a chronic disease of multifactorial origin and can be defined as an increase in the accumulation of body fat. Adipose tissue is not only a triglyceride storage organ, but studies have shown the role of white adipose tissue as a producer of certain bioactive substances called adipokines. Among adipokines, we find some inflammatory functions, such as Interleukin-6 (IL-6); other adipokines entail the functions of regulating food intake, therefore exerting a direct effect on weight control. This is the case of leptin, which acts on the limbic system by stimulating dopamine uptake, creating a feeling of fullness. However, these adipokines induce the production of reactive oxygen species (ROS), generating a process known as oxidative stress (OS). Because adipose tissue is the organ that secretes adipokines and these in turn generate ROS, adipose tissue is considered an independent factor for the generation of systemic OS. There are several mechanisms by which obesity produces OS. The first of these is the mitochondrial and peroxisomal oxidation of fatty acids, which can produce ROS in oxidation reactions, while another mechanism is over-consumption of oxygen, which generates free radicals in the mitochondrial respiratory chain that is found coupled with oxidative phosphorylation in mitochondria. Lipid-rich diets are also capable of generating ROS because they can alter oxygen metabolism. Upon the increase of adipose tissue, the activity of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), was found to be significantly diminished. Finally, high ROS production and the decrease in antioxidant capacity leads to various abnormalities, among which we find endothelial dysfunction, which is characterized by a reduction in the bioavailability of vasodilators, particularly nitric oxide (NO), and an increase in endothelium-derived contractile factors, favoring atherosclerotic disease.

THP-1 Macrophages and SGBS Adipocytes - A New Human in vitro Model System of Inflamed Adipose Tissue

Obesity is associated with an accumulation of macrophages in adipose tissue. This inflammation of adipose tissue is a key event in the pathogenesis of several obesity-related disorders, particularly insulin resistance. Here, we summarized existing model systems that mimic the situation of inflamed adipose tissue in vitro, most of them being murine. Importantly, we introduce our newly established human model system which combines the THP-1 monocytic cell line and the preadipocyte cell strain Simpson-Golabi-Behmel syndrome (SGBS). THP-1 cells, which originate from an acute monocytic leukemia, differentiate easily into macrophages in vitro. The human preadipocyte cell strain SGBS was recently introduced as a unique tool to study human fat cell functions. SGBS cells are characterized by a high capacity for adipogenic differentiation. SGBS adipocytes are capable of fat cell-specific metabolic functions such as insulin-stimulated glucose uptake, insulin-stimulated de novo lipogenesis and β-adrenergic-stimulated lipolysis and they secrete typical adipokines including leptin, adiponectin, and RBP4. Applying either macrophage-conditioned medium or a direct co-culture of macrophages and fat cells, our model system can be used to distinguish between paracrine and cell-contact dependent effects. In conclusion, we propose this model as a useful tool to study adipose inflammation in vitro. It represents an inexpensive, highly reproducible human system. The methods described here can be easily extended for usage of primary human macrophages and fat cells.

Animal models of nonalcoholic fatty liver disease

In 1980, Ludwig and colleagues described a series of patients with liver histology characterized by the accumulation of fat and the presence of hepatic necroinflammation in the absence of a history of excessive alcohol consumption. They coined the term nonalcoholic steatohepatitis (NASH), which today is regarded as one of the most common causes of liver disease in affluent countries. NASH is a subset of a larger spectrum of diseases termed fatty liver disease (including alcoholic and nonalcoholic fatty liver disease; AFLD and NAFLD, respectively). NAFLD and NASH are linked to visceral adiposity, insulin resistance, dyslipidemia and type 2 diabetes, and are increasing due to the prevalence of the metabolic syndrome. In this context, research has been undertaken using animals to model human steatosis and NAFLD to NASH disease progression. This Review discusses the prevalent dietary and inflammation-based genetic animal models described in recent years.

Deficiency in the extracellular signal-regulated kinase 1 (ERK1) protects leptin-deficient mice from insulin resistance without affecting obesity

AIMS/HYPOTHESIS

Extracellular signal-regulated kinase (ERK) activity is increased in adipose tissue in obesity and type 2 diabetes mellitus and strong evidences suggests that it is implicated in the downregulation of insulin signalling and action in the insulin-resistant state. To determine the role of ERK1 in obesity-associated insulin resistance in vivo, we inactivated Erk1 (also known as Mapk3) in obese leptin-deficient mice (ob/ob).

METHODS

Mice of genotype ob/ob-Erk1⁻(/)⁻ were obtained by crossing Erk1⁻(/)⁻ mice with ob/ob mice. Glucose tolerance and insulin sensitivity were studied in 12-week-old mice. Tissue-specific insulin sensitivity, insulin signalling, liver steatosis and adipose tissue inflammation were determined.

RESULTS

While ob/ob-Erk1⁻(/)⁻ and ob/ob mice exhibited comparable body weight and adiposity, ob/ob-Erk1⁻(/)⁻ mice did not develop hyperglycaemia and their glucose tolerance was improved. Hyperinsulinaemic-euglycaemic clamp studies demonstrated an increase in whole-body insulin sensitivity in the ob/ob-Erk1⁻(/)⁻ mice associated with an increase in both insulin-stimulated glucose disposal in skeletal muscles and adipose tissue insulin sensitivity. This occurred in parallel with improved insulin signalling in both tissues. The ob/ob-Erk1⁻(/)⁻ mice were also partially protected against hepatic steatosis with a strong reduction in acetyl-CoA carboxylase level. These metabolic improvements were associated with reduced expression of mRNA encoding inflammatory cytokine and T lymphocyte markers in the adipose tissue.

CONCLUSIONS/INTERPRETATION

Our results demonstrate that the targeting of ERK1 could partially protect obese mice against insulin resistance and liver steatosis by decreasing adipose tissue inflammation and by increasing muscle glucose uptake. Our results indicate that deregulation of the ERK1 pathway could be an important component in obesity-associated metabolic disorders.

Mast cells and metabolic syndrome

Mast cells are critical effectors in the development of allergic diseases and in many immunoglobulin E-mediated immune responses. These cells exert their physiological and pathological activities by releasing granules containing histamine, cytokines, chemokines, and proteases, including mast cell-specific chymase and tryptase. Like macrophages and T lymphocytes, mast cells are inflammatory cells, and they participate in the pathogenesis of inflammatory diseases such as cardiovascular complications and metabolic disorders. Recent observations suggested that mast cells are involved in insulin resistance and type 2 diabetes. Data from animal models proved the direct participation of mast cells in diet-induced obesity and diabetes. Although the mechanisms by which mast cells participate in these metabolic diseases are not fully understood, established mast cell pathobiology in cardiovascular diseases and effective mast cell inhibitor medications used in pre-formed obesity and diabetes in experimental models offer hope to patients with these common chronic inflammatory diseases. This article is part of a Special Issue entitled: Mast cells in inflammation.

Oxidized LDL and lysophosphatidylcholine stimulate plasminogen activator inhibitor-1 expression through reactive oxygen species generation and ERK1/2 activation in 3T3-L1 adipocytes

Plasminogen activator inhibitor-1 (PAI-1) is secreted from adipose tissue and is considered to be a risk factor for both atherosclerosis and insulin resistance. Here we report for the first time that PAI-1 expression is enhanced by oxidized low-density lipoprotein (OxLDL) and its lipid component lysophosphatidylcholine (LPC) in mouse 3T3-L1 adipocytes. In fully differentiated 3T3-L1 cells, OxLDL treatment increased the mRNA expression and protein secretion of PAI-1 in a dose- and time-dependent manner, whereas native LDL had no effect. The addition of an anti-CD36 antibody suppressed OxLDL-stimulated PAI-1 expression by 50%, suggesting that adipose-derived CD36 contributes to roughly half of the PAI-1 expression stimulated by OxLDL. In addition, pharmacological experiments showed that the OxLDL-stimulated enhancement in PAI-1 expression was mediated through the generation of reactive oxygen species (ROS) and phosphorylation of extracellular signal-regulated kinase 1/2. Furthermore, LPC, a major lipid component of OxLDL, was responsible for the enhanced expression of PAI-1 as phospholipase A(2)-treated acetyl LDL, which generates LPC, strongly stimulated PAI-1 expression, whereas acetyl LDL itself had no such activity. These data demonstrate that the uptake of OxLDL and, in particular, its lipid component LPC into adipocytes triggers aberrant ROS-mediated PAI-1 expression, which may be involved in the pathogenesis of metabolic syndrome.

Mast cells, macrophages, and crown-like structures distinguish subcutaneous from visceral fat in mice

Obesity is accompanied by adipocyte death and accumulation of macrophages and mast cells in expanding adipose tissues. Considering the differences in biological behavior of fat found in different anatomical locations, we explored the distribution of mast cells, solitary macrophages, and crown-like structures (CLS), the surrogates for dead adipocytes, in subcutaneous and abdominal visceral fat of lean and diet-induced obese C57BL/6 mice. In fat depots of lean mice, mast cells were far less prevalent than solitary macrophages. Subcutaneous fat contained more mast cells, but fewer solitary macrophages and CLS, than visceral fat. Whereas no significant change in mast cell density of subcutaneous fat was observed, obesity was accompanied by a substantial increase in mast cells in visceral fat. CLS became prevalent in visceral fat of obese mice, and the distribution paralleled mast cells. Adipose tissue mast cells contained and released preformed TNF-α, the cytokine implicated in the pathogenesis of obesity-linked insulin resistance. In summary, subcutaneous fat differed from visceral fat by immune cell composition and a lower prevalence of CLS both in lean and obese mice. The increase in mast cells in visceral fat of obese mice suggests their role in the pathogenesis of obesity and insulin resistance.

Dietary deoxynucleic acid induces type 2 T-helper immune response through toll-like receptor 9 in mice

BACKGROUND

It has been shown that dietary nucleotides modulate immune response. Due to their unique properties in immune responses, nucleotides are used as immunonutrition in the field of clinical nutrition.

AIM OF THE STUDY

In this study, we examined the effect of dietary deoxynucleic acid (DNA) on antigen (Ag)-specific immune response in ovalbumin (OVA)-immunized BALB/c mice and determined the mechanism using toll-like receptor 9 (TLR9) knock-out (KO) mice.

METHODS

BALB/c or TLR9 KO mice were fed control and 1% DNA diets and immunized with OVA. Spleen cells from OVA-immunized mice were stimulated with OVA in vitro, and the contents of IFN-γ and IL-4 in supernatants were measured by an ex vivo system. CD11c(+) dendritic cells were purified, and ability of cytokine induction to CD4(+) cells was examined.

RESULTS

The level of OVA-specific IL-4 production in the DNA group was significantly higher than that in the control group. In contrast, the level of OVA-specific IFN-γ production in the DNA group was lower than that in the control group. The DNA diet decreased Ag-specific IL-4 production and enhanced Ag-specific IFN-γ production in TLR9 KO mice. CD11c(+) DCs from mice fed the DNA diet had a greater ability than CD11c(+) DCs from mice fed the control diet to induce the production of IL-4 from DO11.10 CD4(+) T cells.

CONCLUSIONS

Dietary DNA increases Ag-specific IL-4 production and decreases IFN-γ production through a TLR9-dependent pathway. CD11c(+) dendritic cells are target cells in dietary DNA-induced immune regulation.

T-lymphocyte responses to intestinally absorbed antigens can contribute to adipose tissue inflammation and glucose intolerance during high fat feeding

BACKGROUND

Obesity is associated with inflammation of visceral adipose tissues, which increases the risk for insulin resistance. Animal models suggest that T-lymphocyte infiltration is an important early step, although it is unclear why these cells are attracted. We have recently demonstrated that dietary triglycerides, major components of high fat diets, promote intestinal absorption of a protein antigen (ovalbumin, "OVA"). The antigen was partly transported on chylomicrons, which are prominently cleared in adipose tissues. We hypothesized that intestinally absorbed gut antigens may cause T-lymphocyte associated inflammation in adipose tissue.

METHODOLOGY/PRINCIPAL FINDINGS

Triglyceride absorption promoted intestinal absorption of OVA into adipose tissue, in a chylomicron-dependent manner. Absorption tended to be higher in mesenteric than subcutaneous adipose tissue, and was lowest in gonadal tissue. OVA immunoreactivity was detected in stromal vascular cells, including endothelial cells. In OVA-sensitized mice, OVA feeding caused marked accumulation of CD3+ and osteopontin+ cells in mesenteric adipose tissue. The accumulating T-lymphocytes were mainly CD4+. As expected, high-fat (60% kCal) diets promoted mesenteric adipose tissue inflammation compared to low-fat diets (10% Kcal), as reflected by increased expression of osteopontin and interferon-gamma. Immune responses to dietary OVA further increased diet-induced osteopontin and interferon-gamma expression in mesenteric adipose. Inflammatory gene expression in subcutaneous tissue did not respond significantly to OVA or dietary fat content. Lastly, whereas OVA responses did not significantly affect bodyweight or adiposity, they significantly impaired glucose tolerance.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that loss or lack of immunological tolerance to intestinally absorbed T-lymphocyte antigens can contribute to mesenteric adipose tissue inflammation and defective glucose metabolism during high-fat dieting.