Low-grade Inflammation In Adipose Tissue Research Articles

Sex differences during the course of diet-induced obesity in mice: adipose tissue expandability and glycemic control

Adverse effects of obesity on glucose homeostasis are linked to low-grade adipose tissue inflammation and accumulation of lipids in non-adipose tissues. The goal of this study was to evaluate the role of adipose tissue plasticity in a less severe deterioration of glucose homeostasis in females compared with males during the course of high-fat (HF) feeding in mice. Mice of the C57BL/6N strain were fed either a chow or obesogenic HF diet for up to 35 weeks after weaning. Metabolic markers and hormones in plasma, glucose homeostasis, adipocyte size and inflammatory status of gonadal (gWAT) and subcutaneous (scWAT) adipose depots and liver steatosis were evaluated at 15 and 35 weeks of HF feeding. HF-fed males were heavier than females until week ∼20, after which the body weights stabilized at a similar level (55-58 g) in both sexes. Greater weight gain and fat accumulation in females were associated with larger adipocytes in gWAT and scWAT at week 35. Although adipose tissue macrophage infiltration was in general less frequent in scWAT, it was reduced in both fat depots of female as compared with male mice; however, the expression of inflammatory markers in gWAT was similar in both sexes at week 35. In females, later onset of the impairment of glucose homeostasis and better insulin sensitivity were associated with higher plasma levels of adiponectin (weeks 0, 15 and 35) and reduced hepatosteatosis (weeks 15 and 35). Compared with males, female mice demonstrate increased capacity for adipocyte enlargement in response to a long-term HF feeding, which is associated with reduced adipose tissue macrophage infiltration and lower fat deposition in the liver, and with better insulin sensitivity. Our data suggest that adipose tissue expandability linked to adiponectin secretion might have a role in the sex differences observed in obesity-associated metabolic disorders.

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.

Molecular Therapy for Obesity and Diabetes Based on a Long-Term Increase in Hepatic Fatty-Acid Oxidation §Δ

Obesity-induced insulin resistance is associated with both ectopic lipid deposition and chronic, low-grade adipose tissue inflammation. Despite their excess fat, obese individuals show lower fatty-acid oxidation (FAO) rates. This has raised the question of whether burning off the excess fat could improve the obese metabolic phenotype. Here we used human-safe nonimmunoreactive adeno-associated viruses (AAV) to mediate long-term hepatic gene transfer of carnitine palmitoyltransferase 1A (CPT1A), the key enzyme in fatty-acid β-oxidation, or its permanently active mutant form CPT1AM, to high-fat diet-treated and genetically obese mice. High-fat diet CPT1A- and, to a greater extent, CPT1AM-expressing mice showed an enhanced hepatic FAO which resulted in increased production of CO(2) , adenosine triphosphate, and ketone bodies. Notably, the increase in hepatic FAO not only reduced liver triacylglyceride content, inflammation, and reactive oxygen species levels but also systemically affected a decrease in epididymal adipose tissue weight and inflammation and improved insulin signaling in liver, adipose tissue, and muscle. Obesity-induced weight gain, increase in fasting blood glucose and insulin levels, and augmented expression of gluconeogenic genes were restored to normal only 3 months after AAV treatment. Thus, CPT1A- and, to a greater extent, CPT1AM-expressing mice were protected against obesity-induced weight gain, hepatic steatosis, diabetes, and obesity-induced insulin resistance. In addition, genetically obese db/db mice that expressed CPT1AM showed reduced glucose and insulin levels and liver steatosis. A chronic increase in liver FAO improves the obese metabolic phenotype, which indicates that AAV-mediated CPT1A expression could be a potential molecular therapy for obesity and diabetes.

Adipose tissue macrophages inhibit adipogenesis of mesenchymal precursor cells via wnt-5a in humans

In patients with obesity and type 2 diabetes, adipose tissue is infiltrated by macrophages known to alter adipogenesis of mesenchymal precursor cells via secretion of proinflammatory cytokines. Recently, it has been shown that under certain conditions, immune cells can also express wnt-5a, a factor known to inhibit adipogenesis in humans. Therefore, in this study we aimed to investigate whether macrophages affect adipogenesis of mesenchymal precursor cells via wnt-5a. Wnt-5a was found to be expressed in adipose tissue macrophages in obese and type 2 diabetic human subjects in vivo by immunohistochemistry of adipose tissue biopsies. Furthermore, wnt-5a was detectable in circulating CD14(+) blood monocytes of human subjects with obesity and type 2 diabetes on RNA level by real-time PCR. Besides expression analysis in vivo, we also performed functional studies to explore the role of wnt-5a in low-grade inflammation of adipose tissue. In a cell culture experiment, macrophage-conditioned differentiation medium inhibited adipogenesis of 3T3-L1 cells. This inhibitory effect was restored by adding neutralising anti-wnt-5a antibodies. In conclusion, our data indicate that macrophages alter adipogenesis of 3T3-L1 cells not only via classical proinflammatory cytokines, but also via wnt signalling molecules.

Role of WNT pathway in the determination of human mesenchymal stem cells into preadipocytes

The development of obesity is characterised not only by increased storage of lipids in existing fat cells but also by the generation of new adipocytes from progenitor cells. This process, called adipogenesis, can be divided into two related steps. First, during determination, multipotent mesenchymal stem cells commit to preadipocytes. These cells exhibit similar morphology compared with stem cells; however, they are committed to the adipogenic lineage and are not longer able to transform into osteoblasts, myocytes or chondrocytes. Secondly, during differentiation, preadipocytes become mature fat cells. As in other developmental processes, adipogenesis is tightly regulated at a molecular level by several transcription factors. Within the last decade, it has also become clear how the activity of these transcription factors is coordinated by extracellular signals. In this respect, secreted WNT signalling molecules are particularly important. Several members of the WNT family have been shown to inhibit early steps of adipogenesis. Conversely, endogenous inhibitors of WNT signalling were found to promote generation of adipocytes, indicating a fundamental role of these bioactive peptides in adipogenesis. From a pathophysiological point of view, it is of interest that polymorphisms in genes of the WNT signalling system have been associated with the development of obesity and type 2 diabetes in humans. Moreover, recent findings indicate that certain WNT molecules are involved in the so-called low-grade inflammation of adipose tissue, which is crucial in the development of obesity-associated insulin resistance. These important findings in nutritional and metabolic medicine will be summarised in the present review.

Adipose tissue inflammation and insulin resistance: all obese humans are not created equal

In recent years, it has become widely accepted that obesity is characterized by a chronic low-grade inflammation of adipose tissue that predisposes affected individuals to insulin resistance, Type 2 diabetes and other disorders associated with the metabolic syndrome. On the other hand, a subset of obese individuals appears to be protected against insulin resistance and the disorders to which it predisposes. The comparison between such insulin-sensitive and insulin-resistant obese individuals offers a unique opportunity to identify key factors that either contribute to or prevent the development of insulin resistance in humans, without the confounding effect of a major difference in fat mass. In the previous issue of the Biochemical Journal, Barbarroja et al. reported that insulin-sensitive obese individuals show less inflammation in their visceral adipose tissue than a group of insulin-resistant subjects matched for BMI (body mass index). This finding reinforces the concept that inflammation in adipose tissue may be a cause of insulin resistance in most obese individuals, although it does not prove it. Further studies will be required for this purpose, as well as to identify the pathogenetic factors that determine whether or not adipose tissue of an obese individual becomes inflamed.

Regulation of adipokine secretion byn-3 fatty acids

Obesity leads to several chronic morbidities including type 2 diabetes, dyslipidaemia, atherosclerosis and hypertension, which are major components of the metabolic syndrome. White adipose tissue (WAT) metabolism and WAT-derived factors (fatty acids and adipokines) play an important role in the development of these metabolic disturbances. In fact, dysregulated adipokine secretion from the expanded WAT of obese individuals contributes to the development of systemic low-grade inflammation, insulin resistance and metabolic syndrome. The n-3 PUFA EPA and DHA have been widely reported to have protective effects in a range of chronic inflammatory conditions including obesity. In fact, n-3 PUFA have been shown to ameliorate low-grade inflammation in adipose tissue associated with obesity and up-regulate mitochondrial biogenesis and induce beta-oxidation in WAT in mice. Moreover, the ability of n-3 PUFA to regulate adipokine gene expression and secretion has been observed both in vitro and in vivo in rodents and human subjects. The present article reviews: (1) the physiological role of adiponectin, leptin and pre-B cell colony-enhancer factor/visfatin, three adipokines with immune-modulatory properties involved in the regulation of metabolism and insulin sensitivity and (2) the actions of n-3 PUFA on these adipokines focusing on the underlying mechanisms and the potential relationship with the beneficial effects of these fatty acids on obesity-associated metabolic disorders. It can be concluded that the ability of n-3 PUFA to improve obesity and insulin resistance conditions partially results from the modulation of WAT metabolism and the secretion of bioactive adipokines including leptin, adiponectin and visfatin.

11β-Hydroxysteroid dehydrogenase type 1 is an important regulator at the interface of obesity and inflammation

Systemic glucocorticoid excess, as exemplified by the Cushing syndrome, leads to obesity and all further symptoms of the metabolic syndrome. The current obesity epidemic, however, is not characterized by increased plasma cortisol concentrations, but instead comes along with chronic low-grade inflammation in adipose tissue and concomitant increased levels of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1, gene HSD11B1), a parameter known to cause obesity in a mouse model. 11β-HSD1 represents an intracellular amplifier of active glucocorticoid, thus enhances the associated effects on the inflammatory response as well as on nutrient and energy metabolism, and may therefore cause and exacerbate obesity by local increase of glucocorticoid concentrations. Obtained by extensive literature and database searching, the present review includes comprehensive lists of primary glucocorticoid-sensitive genes and gene products as well as of the thus far known regulators of HSD11B1 expression with implication in inflammation and metabolic disease. Collectively, the data clearly show that, in addition to amplifying active glucocorticoid and thus profoundly modulating inflammation and nutrient metabolism, 11β-HSD1 is subject to tight control of multiple additional immunomodulatory and metabolic regulators. Hence, 11β-HSD1 acts at the interface of inflammation and obesity and represents an efficient integrator and effector of local inflammatory and metabolic state.

In vivo imaging of obesity-induced inflammation in adipose tissue

Obesity is associated with low-grade inflammation in adipose tissue, which contributes to the development of obesity-related diseases such as insulin resistance, hypertension and arteriosclerosis. Here we developed an animal model that non-invasively monitors inflammation in adipose tissue using in vivo bioluminescent imaging (BLI) technique. In vitro, stimulation with TNFα or co-culture with RAW264 macrophages increased bioluminescence in 3T3-L1 adipocytes expressing NF-κB-mediated luciferase gene (3T3-L1/NF-κB-re-luc2P). In vivo, lipopolysaccharide increased bioluminescence in mice transplanted with 3T3-L1/NF-κB-re-luc2P cells. Moreover, light emission derived from implanted cells was significantly higher in diet-induced obese mice transplanted with 3T3-L1/NF-κB-re-luc2P than in lean mice. Our results showed that BLI technique and 3T3-L1/NF-κB-re-luc2P cells provide a useful approach to non-invasively monitor obesity-induced inflammation in adipose tissue in in vivo.

Where is the SPARC in adipose-tissue inflammation?

Although low-grade inflammation of adipose tissue is thought to be central to the development of insulin resistance in individuals with obesity, the underlying cause of this inflammatory state remains elusive. A new study by Kos and colleagues suggests that the glycoprotein SPARC limits adipose-tissue expansion and promotes inflammation and insulin resistance.

N-3 PUFA: bioavailability and modulation of adipose tissue function

Adipose tissue has a key role in the development of metabolic syndrome (MS), which includes obesity, type 2 diabetes, dyslipidaemia, hypertension and other disorders. Systemic insulin resistance represents a major factor contributing to the development of MS in obesity. The resistance is precipitated by impaired adipose tissue glucose and lipid metabolism, linked to a low-grade inflammation of adipose tissue and secretion of pro-inflammatory adipokines. Development of MS could be delayed by lifestyle modifications, while both dietary and pharmacological interventions are required for the successful therapy of MS. The n-3 long-chain (LC) PUFA, EPA and DHA, which are abundant in marine fish, act as hypolipidaemic factors, reduce cardiac events and decrease the progression of atherosclerosis. Thus, n-3 LC PUFA represent healthy constituents of diets for patients with MS. In rodents n-3 LC PUFA prevent the development of obesity and impaired glucose tolerance. The effects of n-3 LC PUFA are mediated transcriptionally by AMP-activated protein kinase and by other mechanisms. n-3 LC PUFA activate a metabolic switch toward lipid catabolism and suppression of lipogenesis, i.e. in the liver, adipose tissue and small intestine. This metabolic switch improves dyslipidaemia and reduces ectopic deposition of lipids, resulting in improved insulin signalling. Despite a relatively low accumulation of n-3 LC PUFA in adipose tissue lipids, adipose tissue is specifically linked to the beneficial effects of n-3 LC PUFA, as indicated by (1) the prevention of adipose tissue hyperplasia and hypertrophy, (2) the induction of mitochondrial biogenesis in adipocytes, (3) the induction of adiponectin and (4) the amelioration of adipose tissue inflammation by n-3 LC PUFA.

Lean, but not obese, fat is enriched for a unique population of regulatory T cells that affect metabolic parameters.

Obesity is accompanied by chronic, low-grade inflammation of adipose tissue, which promotes insulin resistance and type-2 diabetes. These findings raise the question of how fat inflammation can escape the powerful armamentarium of cells and molecules normally responsible for guarding against a runaway immune response. CD4(+) Foxp3(+) T regulatory (T(reg)) cells with a unique phenotype were highly enriched in the abdominal fat of normal mice, but their numbers were strikingly and specifically reduced at this site in insulin-resistant models of obesity. Loss-of-function and gain-of-function experiments revealed that these T(reg) cells influenced the inflammatory state of adipose tissue and, thus, insulin resistance. Cytokines differentially synthesized by fat-resident regulatory and conventional T cells directly affected the synthesis of inflammatory mediators and glucose uptake by cultured adipocytes. These observations suggest that harnessing the anti-inflammatory properties of T(reg) cells to inhibit elements of the metabolic syndrome may have therapeutic potential.

N-3 Fatty acids and rosiglitazone improve insulin sensitivity through additive stimulatory effects on muscle glycogen synthesis in mice fed a high-fat diet

Fatty acids of marine origin, i.e. docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) act as hypolipidaemics, but they do not improve glycaemic control in obese and diabetic patients. Thiazolidinediones like rosiglitazone are specific activators of peroxisome proliferator-activated receptor gamma, which improve whole-body insulin sensitivity. We hypothesised that a combined treatment with a DHA and EPA concentrate (DHA/EPA) and rosiglitazone would correct, by complementary additive mechanisms, impairments of lipid and glucose homeostasis in obesity. Male C57BL/6 mice were fed a corn oil-based high-fat diet. The effects of DHA/EPA (replacing 15% dietary lipids), rosiglitazone (10 mg/kg diet) or a combination of both on body weight, adiposity, metabolic markers and adiponectin in plasma, as well as on liver and muscle gene expression and metabolism were analysed. Euglycaemic-hyperinsulinaemic clamps were used to characterise the changes in insulin sensitivity. The effects of the treatments were also analysed in dietary obese mice with impaired glucose tolerance (IGT). DHA/EPA and rosiglitazone exerted additive effects in prevention of obesity, adipocyte hypertrophy, low-grade adipose tissue inflammation, dyslipidaemia and insulin resistance, while inducing adiponectin, suppressing hepatic lipogenesis and decreasing muscle ceramide concentration. The improvement in glucose tolerance reflected a synergistic stimulatory effect of the combined treatment on muscle glycogen synthesis and its sensitivity to insulin. The combination treatment also reversed dietary obesity, dyslipidaemia and IGT. DHA/EPA and rosiglitazone can be used as complementary therapies to counteract dyslipidaemia and insulin resistance. The combination treatment may reduce dose requirements and hence the incidence of adverse side effects of thiazolidinedione therapy.

Adipose proteome analysis: focus on mediators of insulin resistance

As is well known, adipose tissue is an important site for lipid metabolism and insulin-responsive glucose uptake. The recent discovery of the endocrine function of adipose tissue and the association of obesity with chronic low-grade inflammation in adipose tissue has reinforced the concept of the central role of adipose tissue in mediating obesity-linked insulin resistance and metabolic dysregulation. The study of adipose cells has provided new insights into the mechanism underlying insulin resistance as well as the therapeutic strategies for diabetes. Numerous efforts have been made in identifying key molecular regulators of insulin action and metabolism, including the utilization of advanced proteomics technology. Various proteomic approaches have been applied to identify the adipose secretome, protein-expression profiling and post-translational modifications in adipose cells in the pathological state. In this review, we summarize the recent advances in the proteomics of adipose tissue, and discuss the identified proteins that potentially play important roles in insulin resistance and diabetes.

Cellular and molecular effects ofn−3 polyunsaturated fatty acids on adipose tissue biology and metabolism

Adipose tissue and its secreted products, adipokines, have a major role in the development of obesity-associated metabolic derangements including Type 2 diabetes. Conversely, obesity and its metabolic sequelae may be counteracted by modulating metabolism and secretory functions of adipose tissue. LC-PUFAs (long-chain polyunsaturated fatty acids) of the n-3 series, namely DHA (docosahexaenoic acid; C(22:6n-3)) and EPA (eicosapentaenoic acid; C(20:5n-3)), exert numerous beneficial effects, such as improvements in lipid metabolism and prevention of obesity and diabetes, which partially result from the metabolic action of n-3 LC-PUFAs in adipose tissue. Recent studies highlight the importance of mitochondria in adipose tissue for the maintenance of systemic insulin sensitivity. For instance, both n-3 LC-PUFAs and the antidiabetic drugs TZDs (thiazolidinediones) induce mitochondrial biogenesis and beta-oxidation. The activation of this 'metabolic switch' in adipocytes leads to a decrease in adiposity. Both n-3 LC-PUFAs and TZDs ameliorate a low-grade inflammation of adipose tissue associated with obesity and induce changes in the pattern of secreted adipokines, resulting in improved systemic insulin sensitivity. In contrast with TZDs, which act as agonists of PPARgamma (peroxisome-proliferator-activated receptor-gamma) and promote differentiation of adipocytes and adipose tissue growth, n-3 LC-PUFAs affect fat cells by different mechanisms, including the transcription factors PPARalpha and PPARdelta. Some of the effects of n-3 LC-PUFAs on adipose tissue depend on their active metabolites, especially eicosanoids. Thus treatments affecting adipose tissue by multiple mechanisms, such as combining n-3 LC-PUFAs with either caloric restriction or antidiabetic/anti-obesity drugs, should be explored.

Foxo1 increases pro-inflammatory gene expression by inducing C/EBPβ in TNF-α-treated adipocytes

Obesity is associated with a low-grade inflammation in adipose tissue resulting from increased production of pro-inflammatory cytokines and which can subsequently contribute to the development of insulin resistance. However, the mechanisms underlying the transcriptional regulation of pro-inflammatory genes are still unclear. Here we show that tumor necrosis factor (TNF)-α treatment attenuated Akt-dependent phosphorylation of Foxo1 and enhanced transcriptional activity of Foxo1. We found that Foxo1 increased the expression of CCAAT/enhancer binding protein (C/EBPβ, a positive regulator of monocyte chemoattractant protein (MCP)-1 and interleukin (IL)-6 genes, through directly binding to its promoter. Furthermore, knockdown of Foxo1 as well as C/EBPβ inhibits TNF-α-induced expression of MCP-1 and IL-6 in 3T3-L1 adipocytes. These findings suggest that activation of Foxo1 triggered by TNF-α up-regulates the expression of C/EBPβ in 3T3-L1 adipocytes, thereby leading to an increased production of pro-inflammatory cytokines, MCP-1 and IL-6.

Aging Up-Regulates Expression of Inflammatory Mediators in Mouse Adipose Tissue

Obesity is a leading risk factor for type 2 diabetes (T2D). Aging is associated with an increase in T2D incidence, which is not totally explained by the much lower prevalence of obesity in the elderly. Low-grade inflammation in adipose tissue (AT) contributes to insulin resistance and T2D. Thus, we determined whether inflammatory responses are up-regulated with age in AT. The results showed that visceral AT from old C57BL mice had significantly higher mRNA expression of the proinflammatory cytokines IL-1beta, IL-6, TNF-alpha, and COX-2 and lower expression of anti-inflammatory PPAR-gamma than those of young mice. We further showed that adipocytes (AD) and not stromal vascular cells including macrophages (Mphi) were the cells responsible for this higher inflammatory state of the aged AT, suggesting that the age-associated increase in AT inflammation is distinguished from that seen in obesity, in which Mphi are the main contributors. However, peritoneal Mphi of either age (young or old) produced more TNF-alpha and IL-6 after incubation in old AD-conditioned medium compared with young AD-conditioned medium. This suggests that in addition to producing more inflammatory cytokines, AD from old mice induce a higher inflammatory response in other cells. Sphingolipid ceramide was higher in old compared with young AD. Reducing ceramide levels or inhibiting NF-kappaB activation decreased cytokine production, whereas the addition of ceramide increased cytokine production in young AD to a level comparable to that seen in old AD, suggesting that ceramide-induced activation of NF-kappaB plays a key role in AT inflammation.

Dietary conjugated linoleic acid preserves pancreatic function and reduces inflammatory markers in obese, insulin-resistant rats

Pancreatic preservation is an important part of diabetes management that may occur with improved peripheral insulin sensitivity and attenuated low-grade adipose tissue inflammation. The objective of the current study was to determine the response of obese, insulin-resistant fa/fa Zucker rats vs lean controls to dietary conjugated linoleic acid (CLA) supplementation with respect to pancreatic islet size, insulin resistance, and markers of inflammation and adipose glucose uptake. Six-week-old fa/fa and lean Zucker rats (n = 20 per genotype) were fed either a 1.5% CLA mixture or control diet for 8 weeks. Oral glucose tolerance testing was conducted at 7.5 weeks. Fasting serum haptoglobin, insulin, and C-peptide were assayed, and select messenger RNA (mRNA) and protein markers of inflammation and glucose metabolism were measured in adipose and liver tissues. CLA-fed fa/fa Zucker rats had smaller islet cell size, improved oral glucose tolerance and insulinemia, and attenuated serum haptoglobin levels compared with control-fed fa/fa Zucker rats, despite no differences in body weight and a slightly higher visceral adipose mass. CLA did not alter insulin sensitivity or islet size in lean Zucker rats. The CLA-fed fa/fa rats also had greater adipose glucose transporter-4 mRNA and less adipose tumor necrosis factor α mRNA and protein compared with control-fed fa/fa rats. In contrast, other markers of inflammation and glucose metabolism including adipose macrophage inflammatory factor, macrophage inflammatory protein-2, and liver pyruvate carboxylase and pyruvate dehydrogenase kinase 4 were not significantly changed. These results suggest that CLA supplementation preserved pancreatic function in conjunction with improved peripheral glucose use and reduced inflammation in fa/fa Zucker rats.

Aging increases expression of inflammatory mediators in mouse adipose tissue (AT)

The incidence of type 2 diabetes (T2D) increases with age. Low-grade inflammation in AT is implicated in development of insulin resistance and T2D. We conducted a study to determine if inflammatory responses are upregulated with age in AT. Results show that visceral AT from old mice had significantly higher expression of mRNA levels of IL-1β, IL-6, TNF-α, and COX-2 than those of young mice (263, 208, 165, and 73%, higher respectively). In determining the relative contribution of different components of AT to these age-related changes, we found that adipocytes (AD) from old mice produced significantly more (2 to 3 folds) IL-6 and PGE2 than those from young mice while no significant age difference was observed in their production by stromal vascular cells. There was no significant effect of age on number of Mϕ/g AT and Mϕ of either age group produced significantly more IL-6 when incubated in conditioned medium from old AD compared to that of young. Blocking NF-κB activation reduced IL-6 production while addition of ceramide or sphingomyelinase increased IL-6 production in young AD to a level comparable to that of old AD. Inhibiting de novo ceramide synthesis reduced IL-6 production by AD. NF-κB regulates expression of inflammatory products including COX-2 and IL-6. Ceramide was shown to increase COX-2 expression in aged Mϕ through NF-κB activation. Thus, these data suggest a potential role for ceramide and NF-κB in the age-related increase of AT inflammation. Further research is needed to fully determine the underlying mechanisms of the observed effects and their contribution to T2D in the aged. Supported by USDA #58-1950-9-001 and NIA #R01 AG009140-10A1.

A Unique Role of Monocyte Chemoattractant Protein 1 among Chemokines in Adipose Tissue of Obese Subjects

Low-grade inflammation in adipose tissue may contribute to insulin resistance in obesity. However, the roles of individual inflammatory mediators in adipose tissue are poorly understood. The objective of this study was to determine which inflammation markers are most overexpressed at the gene level in adipose tissue in human obesity and how this relates to corresponding protein secretion. We examined gene expression profiles in 17 lean and 20 obese subjects. The secretory pattern of relevant corresponding proteins was examined in human s.c. adipose tissue or isolated fat cells in vitro and in vivo in several obese or lean cohorts. In ranking gene expression, defined pathways associated with obesity and immune and defense responses scored high. Among seven markedly overexpressed chemokines, only monocyte chemoattractant protein 1 (MCP1) was released from adipose tissue and isolated fat cells in vitro. In obesity, the secretion and expression of MCP1 in adipose tissue pieces were more than 6- and 2-fold increased, respectively, but there was no change in circulating MCP1 levels. There was no net release of MCP1, but there was a net release of leptin, in vivo from adipose tissue into the circulation. Obesity is associated with the increased expression of several chemokine genes in adipose tissue. However, only MCP1 is secreted into the extracellular space, where it primarily acts as a local factor, because little or no spillover into the circulation occurs. MCP1 influences the function of adipocytes, is a recruitment factor for macrophages, and may be a crucial link among chemokines between adipose tissue inflammation and insulin resistance.