Macrophages block insulin action in adipocytes by altering expression of signaling and glucose transport proteins

Human immunodeficiency virus and type 2 diabetes

The prevalence of diabetes is higher amongst individuals infected with HIV. The major contributor to hyperglycaemia is thought to be iatrogenic, with protease inhibitors being most commonly associated to insulin resistance. This article is to update general practitioners on the diagnosis and management of diabetes in HIV-infected patients. Specific considerations are highlighted including interactions of particular diabetic drugs with antiretroviral therapy (ART). We articulate why the use of Hemoglobin A1c (HbA1c) testing is not recommended as a diagnostic tool.

Bone morphogenetic protein-7 (BMP-7) augments insulin sensitivity in mice with type II diabetes mellitus by potentiating PI3K/AKT pathway

A direct link between development of insulin resistance and the presence of chronic inflammation, in case of obesity exists, with cytokines playing an important role in glucose metabolism. Members of TGF-β superfamily, including bone morphogenetic proteins (BMPs), have been shown to be involved in islet morphogenesis, establishment of β-cell mass and adipose cell fate determination. Here, we demonstrate a novel and direct role of BMP-4 and -7 in the regulation of glucose homeostasis and insulin resistance. An age-dependent increase in serum BMP-4 and decrease in serum BMP-7 levels was observed in animal models of type II diabetes. In this study, BMP-7 and -4 have been demonstrated to have antagonistic effects on insulin signaling and thereby on glucose homeostasis. BMP-7 augmented glucose uptake in the insulin sensitive tissues such as the adipose and muscle by increasing Glut4 translocation to the plasma membrane through phosphorylation and activation of PDK1 and Akt, and phosphorylation and translocation of FoxO1 to the cytoplasm in liver/HepG2 cells. Restoration of BMP-7 levels in serum of diabetic animals resulted in decreased blood glucose levels in contrast to age matched untreated control groups, opening up a new therapeutic avenue for diabetes. On the contrary, BMP-4 inhibited insulin signaling through activation of PKC-θ isoform, and resulted in insulin resistance through the attenuation of insulin signaling. BMP-7 therefore is an attractive candidate for tackling a multifaceted disease such as diabetes, since it not only reduces body fat, but also strengthens insulin signaling, causing improved glucose uptake and ameliorating peripheral insulin resistance. © 2017 BioFactors, 43(2):195-209, 2017.

Adipose tissue macrophages impair preadipocyte differentiation in humans

AIM

The physiologic mechanisms underlying the relationship between obesity and insulin resistance are not fully understood. Impaired adipocyte differentiation and localized inflammation characterize adipose tissue from obese, insulin-resistant humans. The directionality of this relationship is not known, however. The aim of the current study was to investigate whether adipose tissue inflammation is causally-related to impaired adipocyte differentiation.

METHODS

Abdominal subcutaneous(SAT) and visceral(VAT) adipose tissue was obtained from 20 human participants undergoing bariatric surgery. Preadipocytes were isolated, and cultured in the presence or absence of CD14+ macrophages obtained from the same adipose tissue sample. Adipocyte differentiation was quantified after 14 days via immunofluorescence, Oil-Red O, and adipogenic gene expression. Cytokine secretion by mature adipocytes cultured with or without CD14+macrophages was quantified.

RESULTS

Adipocyte differentiation was significantly lower in VAT than SAT by all measures (p<0.001). With macrophage removal, SAT preadipocyte differentiation increased significantly as measured by immunofluorescence and gene expression, whereas VAT preadipocyte differentiation was unchanged. Adipocyte-secreted proinflammatory cytokines were higher and adiponectin lower in media from VAT vs SAT: macrophage removal reduced inflammatory cytokine and increased adiponectin secretion from both SAT and VAT adipocytes. Differentiation of preadipocytes from SAT but not VAT correlated inversely with systemic insulin resistance.

CONCLUSIONS

The current results reveal that proinflammatory immune cells in human SAT are causally-related to impaired preadipocyte differentiation, which in turn is associated with systemic insulin resistance. In VAT, preadipocyte differentiation is poor even in the absence of tissue macrophages, pointing to inherent differences in fat storage potential between the two depots.

Effects of prenatal low protein and postnatal high fat diets on visceral adipose tissue macrophage phenotypes and IL-6 expression in Sprague Dawley rat offspring

Adipose tissue macrophages (ATM) are implicated in adipose tissue inflammation and obesity-related insulin resistance. Maternal low protein models result in fetal programming of obesity. The study aims to answer whether maternal undernutrition by protein restriction affects the ATM M1 or M2 phenotype under postnatal high fat diet in F1 offspring. Using a rat model of prenatal low protein (LP, 8% protein) diet followed by a postnatal high fat energy diet (HE, 45% fat) or low fat normal energy diet (NE, 10% fat) for 12 weeks, we investigated the effects of these diets on adiposity, programming of the offspring ATM phenotype, and the associated inflammatory response in adipose tissue. Fat mass in newborn and 12-week old LP fed offspring was lower than that of normal protein (20%; NP) fed offspring; however, the adipose tissue growth rate was higher compared to the NP fed offspring. While LP did not affect the number of CD68⁺ or CD206⁺ cells in adipose tissue of NE offspring, it attenuated the number of these cells in offspring fed HE. In offspring fed HE, LP offspring had a lower percentage of CD11c⁺CD206⁺ ATMs, whose abundancy was correlated with the size of the adipocytes. Noteworthy, similar to HE treatment, LP increased gene expression of IL-6 within ATMs. Two-way ANOVA showed an interaction of prenatal LP and postnatal HE on IL-6 and IL-1β transcription. Overall, both LP and HE diets impact ATM phenotype by affecting the ratio of CD11c⁺CD206⁺ ATMs and the expression of IL-6.

Divergent effects of a designer natriuretic peptide CD-NP in the regulation of adipose tissue and metabolism

Objective

Obesity is defined as an abnormal increase in white adipose tissue (WAT) and is a major risk factor for type 2 diabetes and cardiovascular disease. Brown adipose tissue (BAT) dissipates energy and correlates with leanness. Natriuretic peptides have been shown to be beneficial for brown adipocyte differentiation and browning of WAT.

Methods

Here, we investigated the effects of an optimized designer natriuretic peptide (CD-NP) on murine adipose tissues in vitro and in vivo.

Results

In murine brown and white adipocytes, CD-NP activated cGMP production, promoted adipogenesis, and increased thermogenic markers. Consequently, mice treated for 10 days with CD-NP exhibited increased “browning” of WAT. To study CD-NP effects on diet-induced obesity (DIO), we delivered CD-NP for 12 weeks. Although CD-NP reduced inflammation in WAT, CD-NP treated DIO mice exhibited a significant increase in body mass, worsened glucose tolerance, and hepatic steatosis. Long-term CD-NP treatment resulted in an increased expression of the NP scavenging receptor (NPR-C) and decreased lipolytic activity.

Conclusions

NP effects differed depending on the duration of treatment raising questions about the rational of natriuretic peptide treatment in obese patients.

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The optimized designer natriuretic peptide CD-NP promotes adipogenesis.

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Duration of treatment is decisive: short-term promotes browning whereas long-term treatment exacerbates obesity and diabetes.

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Long-term CD-NP treatment reduces WAT inflammation and increases adiponectin expression.

The ominous triad of adipose tissue dysfunction: inflammation, fibrosis, and impaired angiogenesis

There are three dominant contributors to the pathogenesis of dysfunctional adipose tissue (AT) in obesity: unresolved inflammation, inappropriate extracellular matrix (ECM) remodeling and insufficient angiogenic potential. The interactions of these processes during AT expansion reflect both a linear progression as well as feed-forward mechanisms. For example, both inflammation and inadequate angiogenic remodeling can drive fibrosis, which can in turn promote migration of immune cells into adipose depots and impede further angiogenesis. Therefore, the relationship between the members of this triad is complex but important for our understanding of the pathogenesis of obesity. Here we untangle some of these intricacies to highlight the contributions of inflammation, angiogenesis, and the ECM to both "healthy" and "unhealthy" AT expansion.

Latent Inflammation and Insulin Resistance in Adipose Tissue

Obesity is a growing problem in modern society and medicine. It closely associates with metabolic disorders such as type 2 diabetes mellitus (T2DM) and hepatic and cardiovascular diseases such as nonalcoholic fatty liver disease, atherosclerosis, myocarditis, and hypertension. Obesity is often associated with latent inflammation; however, the link between inflammation, obesity, T2DM, and cardiovascular diseases is still poorly understood. Insulin resistance is the earliest feature of metabolic disorders. It mostly develops as a result of dysregulated insulin signaling in insulin-sensitive cells, as compared to inactivating mutations in insulin receptor or signaling proteins that occur relatively rare. Here, we argue that inflammatory signaling provides a link between latent inflammation, obesity, insulin resistance, and metabolic disorders. We further hypothesize that insulin-activated PI3-kinase pathway and inflammatory signaling mediated by several IκB kinases may constitute negative feedback leading to insulin resistance at least in the fat tissue. Finally, we discuss perspectives for anti-inflammatory therapies in treating the metabolic diseases.

2-deoxyglucose inhibits induction of chemokine expression in 3T3-L1 adipocytes and adipose tissue explants

OBJECTIVE

To determine the influence of glycolytic inhibition on the adipocyte inflammatory response.

METHODS

To determine the effect of 2-deoxyglucose (2-DOG) on the inflammatory response, mature 3T3-L1 adipocytes were co-treated with 2-DOG and LPS or TNF. To determine the effect of endoplasmic reticulum stress on TNF-induced induction of chemokines, adipocytes were pretreated with thapsigargin or salubrinal. Chemokine mRNA levels were determined using quantitative real-time PCR, and secretion of CCL2 was determined by Western blot.

RESULTS

2-DOG treatment reduced the ability of LPS and TNF to induce CCL2 mRNA levels and reduced secreted CCL2 protein levels in a dose-dependent manner. A similar pattern of mRNA regulation was observed for other chemokines. The attenuation of TNF-induced CCL2 mRNA levels occurred regardless of whether glucose or pyruvate was present in the media, suggesting that mechanisms other than glycolysis might mediate the observed effects. Treatment with the endoplasmic reticulum stressor thapsigargin and the endoplasmic reticulum signaling activator salubrinal reduced chemokine mRNA levels similarly to 2-DOG.

CONCLUSIONS

Collectively, our data indicate that 2-DOG suppresses inflammatory chemokine induction in adipocytes. The effects of 2-DOG do not seem to be linked to glycolysis but correlate with endoplasmic reticulum stress activation.

Molecular Mechanisms of Latent Inflammation in Metabolic Syndrome. Possible Role of Sirtuins and Peroxisome Proliferator-Activated Receptor Type γ

The problem of metabolic syndrome is one of the most important in medicine today. The main hazard of metabolic syndrome is development of latent inflammation in adipose tissue, which promotes atherosclerosis, non-alcoholic fatty liver disease, myocarditis, and a number of other illnesses. Therefore, understanding of molecular mechanisms of latent inflammation in adipose tissue is very important for treatment of metabolic syndrome. Three main components that arise during hypertrophy and hyperplasia of adipocytes underlie such inflammation: endoplasmic reticulum stress, oxidative stress, and hypoxia. Each of these components mediates activation in different ways of the key factor of inflammation - NF-κB. For metabolic syndrome therapy, it is suggested to influence a number of inflammatory signaling components by activating other cell factors to suppress development of inflammation. Such potential factors are peroxisome proliferator-activated receptors type γ that suppress transcription factor NF-κB through direct contact or via kinase of a NF-κB inhibitor (IKK), and also the antiinflammatory transcription factor AP-1. Other possible targets are type 3 NAD+-dependent histone deacetylases (sirtuins). There are mutually antagonistic relationships between NF-κB and sirtuin type 1 that prevent development of inflammation in metabolic syndrome. Moreover, sirtuin type 1 inhibits the antiinflammatory transcription factor AP-1. Study of the influence of these factors on the relationship between macrophages and adipocytes, macrophages, and adipose tissue-derived stromal cells can help to understand mechanisms of signaling and development of latent inflammation in metabolic syndrome.

Clinical Update: Cardiovascular Disease in Diabetes Mellitus: Atherosclerotic Cardiovascular Disease and Heart Failure in Type 2 Diabetes Mellitus - Mechanisms, Management, and Clinical Considerations

Cardiovascular disease remains the principal cause of death and disability among patients with diabetes mellitus. Diabetes mellitus exacerbates mechanisms underlying atherosclerosis and heart failure. Unfortunately, these mechanisms are not adequately modulated by therapeutic strategies focusing solely on optimal glycemic control with currently available drugs or approaches. In the setting of multifactorial risk reduction with statins and other lipid-lowering agents, antihypertensive therapies, and antihyperglycemic treatment strategies, cardiovascular complication rates are falling, yet remain higher for patients with diabetes mellitus than for those without. This review considers the mechanisms, history, controversies, new pharmacological agents, and recent evidence for current guidelines for cardiovascular management in the patient with diabetes mellitus to support evidence-based care in the patient with diabetes mellitus and heart disease outside of the acute care setting.

The role of adipokines in chronic inflammation

Adipose tissue has traditionally been defined as connective tissue that stores excess calories in the form of triacylglycerol. However, the physiologic functions attributed to adipose tissue are expanding, and it is now well established that adipose tissue is an endocrine gland. Among the endocrine factors elaborated by adipose tissue are the adipokines; hormones, similar in structure to cytokines, produced by adipose tissue in response to changes in adipocyte triacylglycerol storage and local and systemic inflammation. They inform the host regarding long-term energy storage and have a profound influence on reproductive function, blood pressure regulation, energy homeostasis, the immune response, and many other physiologic processes. The adipokines possess pro- and anti-inflammatory properties and play a critical role in integrating systemic metabolism with immune function. In calorie restriction and starvation, proinflammatory adipokines decline and anti-inflammatory adipokines increase, which informs the host of energy deficits and contributes to the suppression of immune function. In individuals with normal metabolic status, there is a balance of pro- and anti-inflammatory adipokines. This balance shifts to favor proinflammatory mediators as adipose tissue expands during the development of obesity. As a consequence, the proinflammatory status of adipose tissue contributes to a chronic low-grade state of inflammation and metabolic disorders associated with obesity. These disturbances are associated with an increased risk of metabolic disease, type 2 diabetes, cardiovascular disease, and many other pathological conditions. This review focuses on the impact of energy homeostasis on the adipokines in immune function.

Colchicine to decrease NLRP3-activated inflammation and improve obesity-related metabolic dysregulation

Obesity is a major risk-factor for the development of insulin resistance, type 2 diabetes, and cardiovascular disease. Circulating molecules associated with obesity, such as saturated fatty acids and cholesterol crystals, stimulate the innate immune system to incite a chronic inflammatory state. Studies in mouse models suggest that suppressing the obesity-induced chronic inflammatory state may prevent or reverse obesity-associated metabolic dysregulation. Human studies, however, have been far less positive, possibly because targeted interventions were too far downstream of the inciting inflammatory events. Recently, it has been shown that, within adipose tissue macrophages, assembly of a multi-protein member of the innate immune system, the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, is essential for the induction of this inflammatory state. Microtubules enable the necessary spatial arrangement of the components of the NLRP3 inflammasome in the cell, leading to its activation and propagation of the inflammatory cascade. Colchicine, a medication classically used for gout, mediates its anti-inflammatory effect by inhibiting tubulin polymerization, and has been shown to attenuate macrophage NLRP3 inflammasome arrangement and activation in vitro and in vivo. Given these findings, we hypothesize that, in at-risk individuals (those with obesity-induced inflammation and metabolic dysregulation), long-term colchicine use will lead to suppression of inflammation and thus cause improvements in insulin sensitivity and other obesity-related metabolic impairments.

Increased T cell immunoglobulin and mucin domain containing 4 (TIM-4) is negatively correlated with serum concentrations of interleukin-1β in type 2 diabetes

BACKGROUND

T cell immunoglobulin and mucin domain containing 4 (TIM-4), a novel immune regulator, is selectively expressed on antigen-presenting cells, especially macrophages and mature dendritic cells. Although TIM-4 plays key roles in mutiple immune diseases, whether it is involved in type 2 diabetes mellitus (T2D) remains unknown. The aim of the present study was to investigate the expression of TIM-4 in T2D and determine its significance in disease progression.

METHODS

Peripheral blood mononuclear cells (PBMC) were isolated from T2D patients and healthy controls to measure TIM-4 mRNA expression by real-time polymerase chain reaction (PCR), and sera were collected to determine interleukin (IL)-1β concentrations and other clinical indicators (high-sensitivity C-reactive protein [hsCRP], total cholesterol, low-density lipoprotein cholesterol [LDL-C], high-density lipoprotein cholesterol, triglyceride, fasting glucose, HbA1c, aspartate aminotransferase, and alanine aminotransferase).

RESULTS

Expression of TIM-4 mRNA was increased significantly in PBMCs from T2D patients compared with healthy controls. There was a positive correlation between TIM-4 mRNA expression and serum concentrations of hsCRP. However, there was a negative correlation between TIM-4 mRNA expression and IL-1β concentrations, indicating the potential role for TIM-4 to negatively regulate IL-1β production. In addition, TIM-4 mRNA expression was negatively correlated with lowLDL-C, and there was a tendency for a negative relationship between TIM-4 mRNA expression and HbA1c.

CONCLUSIONS

The results of the present study indicate that TIM-4 contributes, at least in part, to the pathogenesis of T2D, possibly by regulating IL-1β.

Time-dependent behavioral, neurochemical, and metabolic dysregulation in female C57BL/6 mice caused by chronic high-fat diet intake

High-fat diet (HFD) induced obesity is associated not only with metabolic dysregulation, e.g., impaired glucose homeostasis and insulin sensitivity, but also with neurological dysfunction manifested with aberrant behavior and/or neurotransmitter imbalance. Most studies have examined HFD's effects predominantly in male subjects, either in the periphery or on the brain, in isolation and after a finite feeding period. In this study, we evaluated the time-course of selected metabolic, behavioral, and neurochemical effects of HFD intake in parallel and at multiple time points in female (C57BL/6) mice. Peripheral effects were evaluated at three feeding intervals (short: 5-6 weeks, long: 20-22 weeks, and prolonged: 33-36 weeks). Central effects were evaluated only after long and prolonged feeding durations; we have previously reported those effects after the short (5-6 weeks) feeding duration. Ongoing HFD feeding resulted in an obese phenotype characterized by increased visceral adiposity and, after prolonged HFD intake, an increase in liver and kidney weights. Peripherally, 5 weeks of HFD intake was sufficient to impair glucose tolerance significantly, with the deleterious effects of HFD being greater with prolonged intake. Similarly, 5 weeks of HFD consumption was sufficient to impair insulin sensitivity. However, sensitivity to insulin after prolonged HFD intake was not different between control, low-fat diet (LFD) and HFD-fed mice, most likely due to age-dependent decrease in insulin sensitivity in the LFD-fed mice. HFD intake also induced bi-phasic hepatic inflammation and it increased gut permeability. Behaviorally, prolonged intake of HFD caused mice to be hypoactive and bury fewer marbles in a marble burying task; the latter was associated with significantly impaired hippocampal serotonin homeostasis. Cognitive (short-term recognition memory) function of mice was unaffected by chronic HFD feeding. Considering our prior findings of short-term (5-6 weeks) HFD-induced central (hyperactivity/anxiety and altered ventral hippocampal neurochemistry) effects and our current results, it seems that in female mice some metabolic/inflammatory dysregulations caused by HFD, such as gut permeability, appear early and persist, whereas others, such as glucose intolerance, are exaggerated with continuous HFD feeding; behaviorally, prolonged HFD consumption mainly affects locomotor activity and anxiety-like responses, likely due to the advanced obesity phenotype; neurochemically, the serotonergic system appears to be most sensitive to continued HFD feeding.

The relation of saturated fatty acids with low-grade inflammation and cardiovascular disease

The mantra that dietary (saturated) fat must be minimized to reduce cardiovascular disease (CVD) risk has dominated nutritional guidelines for decades. Parallel to decreasing intakes of fat and saturated fatty acids (SFA), there have been increases in carbohydrate and sugar intakes, overweight, obesity and type 2 diabetes mellitus. The "lipid hypothesis" coined the concept that fat, especially SFA, raises blood low-density lipoprotein-cholesterol and thereby CVD risk. In view of current controversies regarding their adequate intakes and effects, this review aims to summarize research regarding this heterogenic group of fatty acids and the mechanisms relating them to (chronic) systemic low-grade inflammation, insulin resistance, metabolic syndrome and notably CVD. The intimate relationship between inflammation and metabolism, including glucose, fat and cholesterol metabolism, revealed that the dyslipidemia in Western societies, notably increased triglycerides, "small dense" low-density lipoprotein and "dysfunctional" high-density lipoprotein, is influenced by many unfavorable lifestyle factors. Dietary SFA is only one of these, not necessarily the most important, in healthy, insulin-sensitive people. The environment provides us not only with many other proinflammatory stimuli than SFA but also with many antiinflammatory counterparts. Resolution of the conflict between our self-designed environment and ancient genome may rather rely on returning to the proinflammatory/antiinflammatory balance of the Paleolithic era in consonance with the 21st century culture. Accordingly, dietary guidelines might reconsider recommendations for SFA replacement and investigate diet in a broader context, together with nondietary lifestyle factors. This should be a clear priority, opposed to the reductionist approach of studying the effects of single nutrients, such as SFA.

Regulation of metabolism by the innate immune system

Low-grade tissue inflammation induced by obesity can result in insulin resistance, which in turn is a key cause of type 2 diabetes mellitus. Cells of the innate immune system produce cytokines and other factors that impair insulin signalling, which contributes to the connection between obesity and the onset of type 2 diabetes mellitus. Here, we review the innate immune cells involved in secreting inflammatory factors in the obese state. In the adipose tissue, these cells include proinflammatory adipose tissue macrophages and natural killer cells. We also discuss the role of innate immune cells, such as anti-inflammatory adipose tissue macrophages, eosinophils, group 2 innate lymphoid cells and invariant natural killer T cells, in maintaining an anti-inflammatory and insulin-sensitive environment in the lean state. In the liver, both Kupffer cells and recruited hepatic macrophages can contribute to decreased hepatic insulin sensitivity. Proinflammatory macrophages might also adversely affect insulin sensitivity in the skeletal muscle and pancreatic β-cell function. Finally, this Review provides an overview of the mechanisms for regulating proinflammatory immune responses that could lead to future therapeutic opportunities to improve insulin sensitivity.

Bile Acids, FXR, and Metabolic Effects of Bariatric Surgery

Overweight and obesity represent major risk factors for diabetes and related metabolic diseases. Obesity is associated with a chronic and progressive inflammatory response leading to the development of insulin resistance and type 2 diabetes (T2D) mellitus, although the precise mechanism mediating this inflammatory process remains poorly understood. The most effective intervention for the treatment of obesity, bariatric surgery, leads to glucose normalization and remission of T2D. Recent work in both clinical studies and animal models supports bile acids (BAs) as key mediators of these effects. BAs are involved in lipid and glucose homeostasis primarily via the farnesoid X receptor (FXR) transcription factor. BAs are also involved in regulating genes involved in inflammation, obesity, and lipid metabolism. Here, we review the novel role of BAs in bariatric surgery and the intersection between BAs and immune, obesity, weight loss, and lipid metabolism genes.

The Bone Marrow-Derived Stromal Cells: Commitment and Regulation of Adipogenesis

Bone marrow (BM) microenvironment represents an important compartment of bone that regulates bone homeostasis and the balance between bone formation and bone resorption depending on the physiological needs of the organism. Abnormalities of BM microenvironmental dynamics can lead to metabolic bone diseases. BM stromal cells (also known as skeletal or mesenchymal stem cells) [bone marrow stromal stem cell (BMSC)] are multipotent stem cells located within BM stroma and give rise to osteoblasts and adipocytes. However, cellular and molecular mechanisms of BMSC lineage commitment to adipocytic lineage and regulation of BM adipocyte formation are not fully understood. In this review, we will discuss recent findings pertaining to identification and characterization of adipocyte progenitor cells in BM and the regulation of differentiation into mature adipocytes. We have also emphasized the clinical relevance of these findings.

Autocrine selection of a GLP-1R G-protein biased agonist with potent antidiabetic effects

Glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) agonists have emerged as treatment options for type 2 diabetes mellitus (T2DM). GLP-1R signals through G-protein-dependent, and G-protein-independent pathways by engaging the scaffold protein β-arrestin; preferential signalling of ligands through one or the other of these branches is known as ‘ligand bias'. Here we report the discovery of the potent and selective GLP-1R G-protein-biased agonist, P5. We identified P5 in a high-throughput autocrine-based screening of large combinatorial peptide libraries, and show that P5 promotes G-protein signalling comparable to GLP-1 and Exendin-4, but exhibited a significantly reduced β-arrestin response. Preclinical studies using different mouse models of T2DM demonstrate that P5 is a weak insulin secretagogue. Nevertheless, chronic treatment of diabetic mice with P5 increased adipogenesis, reduced adipose tissue inflammation as well as hepatic steatosis and was more effective at correcting hyperglycaemia and lowering haemoglobin A_1c levels than Exendin-4, suggesting that GLP-1R G-protein-biased agonists may provide a novel therapeutic approach to T2DM.

GLP-1 is a gut hormone with glucose-lowering activity. Here the authors report the peptide, P5, a variant of the GLP-1 receptor agonist exendin-4, with 'biased' signalling activity, and show that P5 improves glucose homeostasis in diabetic mice by increasing adipose tissue hyperplasia.

TNF-alpha modulates adipose macrophage polarization to M1 phenotype in response to scorpion venom

OBJECTIVE

We previously reported that Androctonus australis hector (Aah) venom and its toxic fraction affect adipose tissue metabolism. However, the contribution of immune system and the role of adipose tissue macrophages (ATMs) in the progression of inflammation induced by scorpion venom remain largely unknown.

METHODS

Here we evaluate the capacity of the toxic fraction of Aah venom (FTox-G50) to induce the expression of M1 and M2 markers genes on adipose tissue and isolated stromal vascular cells (SVC). Quantitative real-time PCR was performed on the SVC 24 h after FTox-G50 venom injection to assess the gene expressions of IL12p40, IL23, and other macrophages-associated markers.

RESULTS

We found that ATM from FTox-G50-venom-injected mice markedly increased the expressions of IL-12p40 and IL-23. Furthermore, the expression of nitric oxide synthase 2 (an M1 marker) was up-regulated, but the expression of Arginase1 (an M2 marker) was not. Systemic injection of a chemical inhibitor directed against TNF-α binding reduced the expression of inflammatory M1 macrophage markers and the MAPKpk2 gene, a key mediator of inflammatory signaling.

CONCLUSION

These results indicate that TNF-α is a physiological regulator of inflammation and macrophage activation induced by scorpion venom.

Fat in flames: influence of cytokines and pattern recognition receptors on adipocyte lipolysis

Adipose tissue has the largest capacity to store energy in the body and provides energy through the release of free fatty acids during times of energy need. Different types of immune cells are recruited to adipose tissue under various physiological conditions, indicating that these cells contribute to the regulation of adipose tissue. One major pathway influenced by a number of immune cells is the release of free fatty acids through lipolysis during both physiological (e.g., cold stress) and pathophysiological processes (e.g., obesity, type 2 diabetes). Adipose tissue expansion during obesity leads to immune cell infiltration and adipose tissue remodeling, a homeostatic process that promotes inflammation in adipose tissue. The release of proinflammatory cytokines stimulates lipolysis and causes insulin resistance, leading to adipose tissue dysfunction and systemic disruptions of metabolism. This review focuses on the interactions of cytokines and other inflammatory molecules that regulate adipose tissue lipolysis during physiological and pathophysiological states.

Long-Lasting Metabolic Imbalance Related to Obesity Alters Olfactory Tissue Homeostasis and Impairs Olfactory-Driven Behaviors

Obesity is associated with chronic food intake disorders and binge eating. Food intake relies on the interaction between homeostatic regulation and hedonic signals among which, olfaction is a major sensory determinant. However, its potential modulation at the peripheral level by a chronic energy imbalance associated to obese status remains a matter of debate. We further investigated the olfactory function in a rodent model relevant to the situation encountered in obese humans, where genetic susceptibility is juxtaposed on chronic eating disorders. Using several olfactory-driven tests, we compared the behaviors of obesity-prone Sprague-Dawley rats (OP) fed with a high-fat/high-sugar diet with those of obese-resistant ones fed with normal chow. In OP rats, we reported 1) decreased odor threshold, but 2) poor olfactory performances, associated with learning/memory deficits, 3) decreased influence of fasting, and 4) impaired insulin control on food seeking behavior. Associated with these behavioral modifications, we found a modulation of metabolism-related factors implicated in 1) electrical olfactory signal regulation (insulin receptor), 2) cellular dynamics (glucorticoids receptors, pro- and antiapoptotic factors), and 3) homeostasis of the olfactory mucosa and bulb (monocarboxylate and glucose transporters). Such impairments might participate to the perturbed daily food intake pattern that we observed in obese animals.

Inflamed macrophage microvesicles induce insulin resistance in human adipocytes

BACKGROUND

Cytokines secreted by adipose tissue macrophages (ATMs) significantly alter adipocyte function, inducing inflammatory responses and decreasing insulin sensitivity. However, little relevant information is available regarding the role of microvesicles (MVs) derived from ATMs in macrophage-adipocyte crosstalk.

METHODS

MVs were generated by stimulation of M1 or M2 phenotype THP-1 macrophages and incubated with human primary mature adipocytes and differentiated adipocytes. Subsequently, insulin-stimulated phosphorylation of Akt (pAkt) and glucose uptake were determined. Glucose transporter 4 (GLUT4) translocation and nuclear translocation of nuclear factor (NF)-kappa B were also analyzed in treated adipocytes.

RESULTS

M1 macrophage-derived MVs (M1 MVs) significantly reduced protein abundance of insulin-induced Akt phosphorylation in human primary mature adipocytes and differentiated adipocytes, when compared with the same concentration of M2 macrophage-derived MVs (M2 MVs). In contrast to M2 MVs, which enhanced the insulin-induced glucose uptake measured by 2-NBDG, M1 MVs decreased this effect in treated adipocytes. M1 MVs treatment also brought about a significant increase in the nuclear translocation of nuclear factor (NF)-kappa B, coupled with a decrease in pAkt level and GLUT4 translocation compared with M2 MVs-treated adipocytes. These effects were reversed by BAY 11-7085, a NF- kappa B specific inhibitor.

CONCLUSIONS

MVs derived from proinflammatory (M1) macrophages may, at least in part, contribute to the pathogenesis of obesity-induced insulin resistance, reducing insulin signal transduction and decreasing glucose uptake in human adipocytes, through NF-kappa B activation. Therefore, these MVs may be potential therapy candidates for the management of type 2 diabetes mellitus.

Minireview: Emerging Concepts in Islet Macrophage Biology in Type 2 Diabetes

Chronic systemic inflammation is a hallmark feature of obesity and type 2 diabetes. Both resident and recruited islet macrophages contribute to the proinflammatory milieu of the diabetic islet. However, macrophages also appear to be critical for β-cell formation during development and support β-cell replication in experimental models of pancreas regeneration. In light of these findings, perhaps macrophages in the islet need to be viewed more as a fulcrum where deleterious inflammatory activation is balanced with beneficial tissue repair processes. Undoubtedly, defining the factors that contribute to the ontogeny, heterogeneity, and functionality of macrophages in normal, diseased, and regenerating islets will be necessary to determine whether that fulcrum can be moved to preserve functional β-cell mass in persons with diabetes. The intent of this review is to introduce the reader to emerging concepts of islet macrophage biology that may challenge the perception that macrophage accumulation in islets is merely a pathological feature of type 2 diabetes.

Is interleukin-1β a culprit in macrophage-adipocyte crosstalk in obesity?

Adipose tissue remodeling occurs in obesity, characterized by adipocyte hypertrophy and increased infiltration of macrophages which also shift to a proinflammatory phenotype. Factors derived from these macrophages significantly alter adipocyte function, such as repressing adipogenesis, inducing inflammatory response and desensitizing insulin action. As macrophages produce a cocktail of inflammatory signals, identifying the key factors that mediate the detrimental effects may offer effective therapeutic targets. IL-1β, a major cytokine produced largely by macrophages, is implicated in the development of obesity-associated insulin resistance. In this article, we discuss recent advances in our understanding of the role of IL-1β in macrophage-adipocyte crosstalk in obesity. IL-1β impairs insulin sensitivity in adipose tissue by inhibition of insulin signal transduction. Blocking the activity of IL-1β, its receptor binding or production improves insulin signaling and action in human adipocytes. This is in parallel with a reduction in macrophage-stimulated proinflammatory profile and lipolysis. Targeting IL-1β may be beneficial for protecting against obesity-related insulin resistance at the tissue and systemic levels.

Noncanonical Wnt signaling promotes obesity-induced adipose tissue inflammation and metabolic dysfunction independent of adipose tissue expansion

Adipose tissue dysfunction plays a pivotal role in the development of insulin resistance in obese individuals. Cell culture studies and gain-of-function mouse models suggest that canonical Wnt proteins modulate adipose tissue expansion. However, no genetic evidence supports a role for endogenous Wnt proteins in adipose tissue dysfunction, and the role of noncanonical Wnt signaling remains largely unexplored. Here we provide evidence from human, mouse, and cell culture studies showing that Wnt5a-mediated, noncanonical Wnt signaling contributes to obesity-associated metabolic dysfunction by increasing adipose tissue inflammation. Wnt5a expression is significantly upregulated in human visceral fat compared with subcutaneous fat in obese individuals. In obese mice, Wnt5a ablation ameliorates insulin resistance, in parallel with reductions in adipose tissue inflammation. Conversely, Wnt5a overexpression in myeloid cells augments adipose tissue inflammation and leads to greater impairments in glucose homeostasis. Wnt5a ablation or overexpression did not affect fat mass or adipocyte size. Mechanistically, Wnt5a promotes the expression of proinflammatory cytokines by macrophages in a Jun NH2-terminal kinase-dependent manner, leading to defective insulin signaling in adipocytes. Exogenous interleukin-6 administration restores insulin resistance in obese Wnt5a-deficient mice, suggesting a central role for this cytokine in Wnt5a-mediated metabolic dysfunction. Taken together, these results demonstrate that noncanonical Wnt signaling contributes to obesity-induced insulin resistance independent of adipose tissue expansion.

Macrophage elastase suppresses white adipose tissue expansion with cigarette smoking

Macrophage elastase (MMP12) is a key mediator of cigarette smoke (CS)-induced emphysema, yet its role in other smoking related pathologies remains unclear. The weight suppressing effects of smoking are a major hindrance to cessation efforts, and MMP12 is known to suppress the vascularization on which adipose tissue growth depends by catalyzing the formation of antiangiogenic peptides endostatin and angiostatin. The goal of this study was to determine the role of MMP12 in adipose tissue growth and smoking-related suppression of weight gain. Whole body weights and white adipose depots from wild-type and Mmp12-deficient mice were collected during early postnatal development and after chronic CS exposure. Adipose tissue specimens were analyzed for angiogenic and adipocytic markers and for content of the antiangiogenic peptides endostatin and angiostatin. Cultured 3T3-L1 adipocytes were treated with adipose tissue homogenate to examine its effects on vascular endothelial growth factor (VEGF) expression and secretion. MMP12 content and activity were increased in the adipose tissue of wild-type mice at 2 weeks of age, leading to elevated endostatin production, inhibition of VEGF secretion, and decreased adipose tissue vascularity. By 8 weeks of age, adipose MMP12 levels subsided, and the protein was no longer detectable. However, chronic CS exposure led to macrophage accumulation and restored adipose MMP12 activity, thereby suppressing adipose tissue mass and vascularity. Our results reveal a novel systemic role for MMP12 in postnatal adipose tissue expansion and smoking-associated weight loss by suppressing vascularity within the white adipose tissue depots.

Epicardial fat thickness as cardiovascular risk factor and therapeutic target in patients with rheumatoid arthritis treated with biological and nonbiological therapies

Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with high cardiovascular morbidity and mortality. Epicardial adipose tissue (EAT) thickness may act as a therapeutic target during treatments with drugs modulating the adipose tissue. We evaluate EAT thickness in RA patients treated with biological and nonbiological disease-modifying antirheumatic drugs (DMARDs). A cross-sectional study was conducted with a cohort of 34 female RA patients and 16 controls matched for age and body mass index (BMI). Plasma glucose, basal insulin, plasma lipids, and high-sensitivity C-reactive protein (hs-CRP) were assessed. EAT thickness and left ventricular mass (LVM) were measured by echocardiography. No significant differences in waist circumference (WC), blood pressure, fasting blood glucose, basal insulin, and lipid parameters were found between the groups. The control group showed lower concentrations (P = 0.033) of hs-CRP and LVM (P = 0.0001) than those of the two RA groups. Patients treated with TNF-α inhibitors showed significantly lower EAT thickness than those treated with nonbiological DMARDs (8.56 ± 1.90 mm versus 9.71 ± 1.45 mm; P = 0.04). Women with no RA revealed reduced EAT thickness (5.39 ± 1.52 mm) as compared to all RA patients (P = 0.001). Results suggest that RA patients have greater EAT thickness than controls regardless of BMI and WC.

Impaired adipogenesis and insulin resistance in epicardial fat-mesenchymal cells from patients with cardiovascular disease

The thickness of epicardial adipose tissue (EAT), which is an inflammatory source for coronary artery disease (CAD), correlates with insulin resistance. One trigger factor is impaired adipogenesis. Here, our aim was to clarify the underlying mechanisms of insulin resistance on EAT-mesenchymal cells (MC). EAT and subcutaneous adipose tissue (SAT) were collected from 19 patients who were undergoing heart surgery. Their dedifferentiated adipocytes (DAs) and/or MCs were cultured. After the induction of adipogenesis or stimulation with insulin, the expression of adipokines was analyzed using real-time polymerase chain reaction (PCR). Colorimetric assays were performed to measure glucose levels and proliferation rate. Proteins modifications were detected via the proteomic approach and Western blot. Our results showed lower adipogenic ability in EAT-MCs than in SAT-MCs. Maximum adiponectin levels were reached within 28-35 days of exposure to adipogenic inducers. Moreover, the adipogenesis profile in EAT-MCs was dependent on the patients' clinical characteristics. The low adipogenic ability of EAT-MCs might be associated with an insulin-resistant state because chronic insulin treatment reduced the inflammatory cytokine expression levels, improved the glucose consumption, and increased the post-translational modifications (PTMs) of the glycolytic enzyme phosphoglycerate mutase 1 (PGAM1). We found lower adipogenic ability in EAT-MCs than in SAT-MCs. This lower ability level was dependent on gender and the presence of diabetes, obesity, and CAD. Low adipogenesis ability and insulin resistance in EAT-MCs might shed light on the association between EAT dysfunction and cardiovascular disease.

CCR2 antagonism in patients with type 2 diabetes mellitus: a randomized, placebo-controlled study

AIMS

Macrophage recruitment through C-C motif chemokine receptor-2 (CCR2) into adipose tissue is believed to play a role in the development of insulin resistance and type 2 diabetes mellitus (T2DM). The objective of this Phase 2 proof-of-concept study was to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of JNJ-41443532, an orally bioavailable CCR2 antagonist, in patients with T2DM.

METHODS

This was a 4-week, double-blind, placebo-controlled, randomized, multicenter study. A total of 89 patients were randomized to receive either 250- or 1000-mg of JNJ-41443532 twice daily, 30-mg of pioglitazone once daily (reference arm), or placebo. The primary endpoint was change from baseline in 23-h weighted mean glucose (WMG); secondary endpoints included change from baseline in fasting plasma glucose (FPG), insulin resistance (Homeostatic Model Assessment [HOMA-IR]), insulin secretion (HOMA-%B) and body weight.

RESULTS

Absorption of JNJ-41443532 into the systemic circulation occurred at a median tmax of 2 h, and the mean t½ was approximately 8 h for both doses; plasma systemic exposures increased slightly more than dose-proportionally. After 4 weeks, reductions in 23-h WMG and FPG were observed in all treatment groups compared with placebo and were significantly lower for 250-mg JNJ-41443532 and pioglitazone. HOMA-IR was lower for all treatment groups, but significantly lower only for pioglitazone. Conversely, HOMA-%B was increased for all groups, but significantly increased only for 250-mg JNJ-41443532. All groups, including placebo, had decreased body weight over time. There were no clinically significant findings during routine safety assessments and the incidence of treatment-emergent adverse events was similar across all groups.

CONCLUSIONS

Administration of JNJ-41443532 resulted in modest improvement in glycaemic parameters compared with placebo, and was generally well tolerated in patients with T2DM.

α-Naphthoflavone modulates inflammatory response in adipocytes-macrophages interaction through NFκB signaling

OBJECTIVE

Our previous study demonstrated that α-naphthoflavone (α-NF) inhibits mouse 3T3-L1 pre-adipocytes differentiation via PPARγ, a key transcription factor in adipogenesis. Due to the critical role of inflammation in adipogenesis, we speculated that the suppression role of α-NF in adipogenesis might involve in modulation of cytokines secretion raised by adipocyte differentiation cocktail. Therefore, the present study aims to investigate the role of α-NF in modulating of inflammatory response during adipocytes differentiation and adipocyte-macrophage interaction.

METHODS

Conditioned medium from different doses of α-NF treated 10-day differentiated 3T3-L1 adipocytes were collected to culture RAW264.7 macrophages. Conditioned medium from activated macrophages and α-NF pre-treated macrophage were used to investigate the effects of α-NF in adipocytes differentiation. Cultured cells and medium were harvested for RT-PCR, Western blot and ELISA.

RESULTS

α-NF dose-dependently decreased TNF-α and IL-6 and increased IL-10 expression induced by IDM (Insulin, dexamethasone, isobutylmethylxanthine) in 3T3-L1 pre-adipocytes. Conditioned medium from α-NF treated 3T3-L1 differentiated cells inhibited inflammatory response in mouse macrophage cell line RAW264.7 in contrast to IDM control medium. NFĸB activation elicited by IDM was suppressed by α-NF in a dose-response manner. Consequently, decreased TNF-α and increased IL-10 secretion, downstream targets of NFĸB signaling pathway, were observed with α-NF in macrophages. Finally, Conditioned medium from α-NF pre-treated, LPS-activated macrophages ameliorated the suppression of 3T3-L1 adipogenesis by LPS activated macrophages.

CONCLUSION

Our results suggest that α-NF regulates inflammation response in both adipocytes and macrophages and adipocyte-macrophage interaction which contributes to pre-adipocyte differentiation.

A macrophage NBR1-MEKK3 complex triggers JNK-mediated adipose tissue inflammation in obesity

The c-Jun NH(2)-terminal kinase (JNK) is a critical determinant of obesity-associated inflammation and glucose intolerance. The upstream mechanisms controlling this pathway are still unknown. Here we report that the levels of the PB1 domain-containing adaptor NBR1 correlated with the expression of proinflammatory molecules in adipose tissue from human patients with metabolic syndrome, suggesting that NBR1 plays a key role in adipose-tissue inflammation. We also show that NBR1 inactivation in the myeloid compartment impairs the function, M1 polarization, and chemotactic activity of macrophages; prevents inflammation of adipose tissue; and improves glucose tolerance in obese mice. Furthermore, we demonstrate that an interaction between the PB1 domains of NBR1 and the mitogen-activated kinase kinase 3 (MEKK3) enables the formation of a signaling complex required for the activation of JNK. Together, these discoveries identify an NBR1-MEKK3 complex as a key regulator of JNK signaling and adipose tissue inflammation in obesity.

The role of adipose tissue immune cells in obesity and low-grade inflammation

Adipose tissue (AT) lies at the crossroad of nutrition, metabolism, and immunity; AT inflammation was proposed as a central mechanism connecting obesity with its metabolic and vascular complications. Resident immune cells constitute the second largest AT cellular component after adipocytes and as such play important roles in the maintenance of AT homeostasis. Obesity-induced changes in their number and activity result in the activation of local and later systemic inflammatory response, marking the transition from simple adiposity to diseases such as type 2 diabetes mellitus, arterial hypertension, and ischemic heart disease. This review has focused on the various subsets of immune cells in AT and their role in the development of AT inflammation and obesity-induced insulin resistance.

Targeting post-infarct inflammation by PET imaging: comparison of (68)Ga-citrate and (68)Ga-DOTATATE with (18)F-FDG in a mouse model

Imaging of inflammation early after myocardial infarction (MI) is a promising approach to the guidance of novel molecular interventions that support endogenous healing processes. (18)F-FDG PET has been used, but may be complicated by physiological myocyte uptake. We evaluated the potential of two alternative imaging targets: lactoferrin binding by (68)Ga-citrate and somatostatin receptor binding by (68)Ga-DOTATATE.

METHODS

C57Bl/6 mice underwent permanent coronary artery ligation. Serial PET imaging was performed 3 - 7 days after MI using (68)Ga-citrate, (68)Ga-DOTATATE, or (18)F-FDG with ketamine/xylazine suppression of myocyte glucose uptake. Myocardial perfusion was evaluated by (13)N-ammonia PET and cardiac geometry by contrast-enhanced ECG-gated CT.

RESULTS

Mice exhibited a perfusion defect of 30 - 40% (of the total left ventricle) with apical anterolateral wall akinesia and thinning on day 7 after MI. (18)F-FDG with ketamine/xylazine suppression demonstrated distinct uptake in the infarct region, as well as in the border zone and remote myocardium. The myocardial standardized uptake value in MI mice was significantly higher than in healthy mice under ketamine/xylazine anaesthesia (1.9 ± 0.4 vs. 1.0 ± 0.1). (68)Ga images exhibited high blood pool activity with no specific myocardial uptake up to 90 min after injection (tissue-to-blood contrast 0.9). (68)Ga-DOTATATE was rapidly cleared from the blood, but myocardial SUV was very low (0.10 ± 0.03).

CONCLUSION

Neither (68)Ga nor (68)Ga-DOTATATE is a useful alternative to (18)F-FDG for PET imaging of myocardial inflammation after MI in mice. Among the three tested approaches, (18)F-FDG with ketamine/xylazine suppression of cardiomyocyte uptake remains the most practical imaging marker of post-infarct inflammation.

Interleukin-1β mediates macrophage-induced impairment of insulin signaling in human primary adipocytes

Adipose tissue expansion during obesity is associated with increased macrophage infiltration. Macrophage-derived factors significantly alter adipocyte function, inducing inflammatory responses and decreasing insulin sensitivity. Identification of the major factors that mediate detrimental effects of macrophages on adipocytes may offer potential therapeutic targets. IL-1β, a proinflammatory cytokine, is suggested to be involved in the development of insulin resistance. This study investigated the role of IL-1β in macrophage-adipocyte cross-talk, which affects insulin signaling in human adipocytes. Using macrophage-conditioned (MC) medium and human primary adipocytes, we examined the effect of IL-1β antagonism on the insulin signaling pathway. Gene expression profile and protein abundance of insulin signaling molecules were determined, as was the production of proinflammatory cytokine/chemokines. We also examined whether IL-1β mediates MC medium-induced alteration in adipocyte lipid storage. MC medium and IL-1β significantly reduced gene expression and protein abundance of insulin signaling molecules, including insulin receptor substrate-1, phosphoinositide 3-kinase p85α, and glucose transporter 4 and phosphorylation of Akt. In contrast, the expression and release of the proinflammatory markers, including IL-6, IL-8, monocyte chemotactic protein-1, and chemokine (C-C motif) ligand 5 by adipocytes were markedly increased. These changes were significantly reduced by blocking IL-1β activity, its receptor binding, or its production by macrophages. MC medium-inhibited expression of the adipogenic factors and -stimulated lipolysis was also blunted with IL-1β neutralization. We conclude that IL-1β mediates, at least in part, the effect of macrophages on insulin signaling and proinflammatory response in human adipocytes. Blocking IL-1β could be beneficial for preventing obesity-associated insulin resistance and inflammation in human adipose tissue.

Artemisia dracunculus L. extract ameliorates insulin sensitivity by attenuating inflammatory signalling in human skeletal muscle culture

AIMS

Bioactives of Artemisia dracunculus L. (termed PMI 5011) have been shown to improve insulin action by increasing insulin signalling in skeletal muscle. However, it was not known if PMI 5011's effects are retained during an inflammatory condition. We examined the attenuation of insulin action and whether PMI 5011 enhances insulin signalling in the inflammatory environment with elevated cytokines.

METHODS

Muscle cell cultures derived from lean, overweight and diabetic-obese subjects were used. Expression of pro-inflammatory genes and inflammatory response of human myotubes were evaluated by real-time polymerase chain reaction (RT-PCR). Insulin signalling and activation of inflammatory pathways in human myotubes were evaluated by multiplex protein assays.

RESULTS

We found increased gene expression of monocyte chemoattractant protein 1 (MCP1) and TNFα (tumour necrosis factor alpha), and basal activity of the NFkB (nuclear factor kappa-light-chain-enhancer of activated B cells) pathway in myotubes derived from diabetic-obese subjects as compared with myotubes derived from normal-lean subjects. In line with this, basal Akt phosphorylation (Ser473) was significantly higher, while insulin-stimulated phosphorylation of Akt (Ser473) was lower in myotubes from normal-overweight and diabetic-obese subjects compared with normal-lean subjects. PMI 5011 treatment reduced basal phosphorylation of Akt and enhanced insulin-stimulated phosphorylation of Akt in the presence of cytokines in human myotubes. PMI 5011 treatment led to an inhibition of cytokine-induced activation of inflammatory signalling pathways such as Erk1/2 and IkBα (nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha)-NFkB and moreover, NFkB target gene expression, possibly by preventing further propagation of the inflammatory response within muscle tissue.

CONCLUSIONS

PMI 5011 improved insulin sensitivity in diabetic-obese myotubes to the level of normal-lean myotubes despite the presence of pro-inflammatory cytokines.

Diet-induced obesity promotes myelopoiesis in hematopoietic stem cells

Obesity is associated with an activated macrophage phenotype in multiple tissues that contributes to tissue inflammation and metabolic disease. To evaluate the mechanisms by which obesity potentiates myeloid activation, we evaluated the hypothesis that obesity activates myeloid cell production from bone marrow progenitors to potentiate inflammatory responses in metabolic tissues. High fat diet-induced obesity generated both quantitative increases in myeloid progenitors as well as a potentiation of inflammation in macrophages derived from these progenitors. In vivo, hematopoietic stem cells from obese mice demonstrated the sustained capacity to preferentially generate inflammatory CD11c⁺ adipose tissue macrophages after serial bone marrow transplantation. We identified that hematopoietic MyD88 was important for the accumulation of CD11c⁺ adipose tissue macrophage accumulation by regulating the generation of myeloid progenitors from HSCs. These findings demonstrate that obesity and metabolic signals potentiate leukocyte production and that dietary priming of hematopoietic progenitors contributes to adipose tissue inflammation.

IL-10 cytokine released from M2 macrophages is crucial for analgesic and anti-inflammatory effects of acupuncture in a model of inflammatory muscle pain

Muscle pain is a common medical problem that is difficult to treat. One nonpharmacological treatment used is acupuncture, a procedure in which fine needles are inserted into body points with the intent of relieving pain and other symptoms. Here we investigated the effects of manual acupuncture (MA) on modulating macrophage phenotype and interleukin-10 (IL-10) concentrations in animals with muscle inflammation. Carrageenan, injected in the gastrocnemius muscle of mice, induces an inflammatory response characterized by mechanical hyperalgesia and edema. The inflammation is initially a neutrophilic infiltration that converts to a macrophage-dominated inflammation by 48 h. MA of the Sanyinjiao or Spleen 6 (SP6) acupoint reduces nociceptive behaviors, heat, and mechanical hyperalgesia and enhanced escape/avoidance and the accompanying edema. SP6 MA increased muscle IL-10 levels and was ineffective in reducing pain behaviors and edema in IL-10 knockout (IL-10(-/-)) mice. Repeated daily treatments with SP6 MA induced a phenotypic switch of muscle macrophages with reduced M1 macrophages (pro-inflammatory cells) and an increase of M2 macrophages (anti-inflammatory cells and important IL-10 source). These findings provide new evidence that MA produces a phenotypic switch in macrophages and increases IL-10 concentrations in muscle to reduce pain and inflammation.

A dangerous duo in adipose tissue: high-mobility group box 1 protein and macrophages

High-mobility group box 1 (HMGB1) protein first made headlines 40 years ago as a non-histone nuclear protein that regulates gene expression. Not so long ago, it was also shown that HMGB1 has an additional surprising function. When released into the extracellular milieu, HMGB1 triggers an inflammatory response by serving as an endogenous danger signal. The pro-inflammatory role of HMGB1 is now well-established and has been associated with several diseases, including sepsis, rheumatoid arthritis, and atherosclerosis. Yet very little is known about its role in obesity, wherein adipose tissue is typified by a persistent, smoldering inflammatory response instigated by high macrophage infiltrate that potentiates the risk of obesity-associated comorbidities. This mini-review focuses on the putative causal relationship between HMGB1 and macrophage pro-inflammatory activation in pathologically altered adipose tissue associated with obesity.

PPARγ and the global map of adipogenesis and beyond

Peroxisome proliferator-activated receptor γ (PPARγ) is a member of the nuclear receptor (NR) superfamily of ligand-dependent transcription factors (TFs) and function as a master regulator of adipocyte differentiation and metabolism. We review recent breakthroughs in the understanding of PPARγ gene regulation and function in the chromatin context. It is now clear that multiple TFs team up to induce PPARγ during adipogenesis, and that other TFs cooperate with PPARγ to ensure adipocyte-specific genomic binding and function. We discuss how this differs in other PPARγ-expressing cells such as macrophages and how these genome-wide mechanisms are preserved across species despite modest conservation of specific binding sites. These emerging considerations inform our understanding of PPARγ function as well as of adipocyte development and physiology.

Exaggerated effects of particulate matter air pollution in genetic type II diabetes mellitus

Background

Prior experimental and epidemiologic data support a link between exposure to fine ambient particulate matter (<2.5 μm in aerodynamic diameter, PM_2.5) and development of insulin resistance/Type II diabetes mellitus. This study was designed to investigate whether inhalational exposure of concentrated PM_2.5 in a genetically susceptible animal model would result in abnormalities in energy metabolism and exacerbation of peripheral glycemic control.

Methods

KKay mice, which are susceptible to Type II DM, were assigned to either concentrated ambient PM_2.5 or filtered air (FA) for 5–8 weeks via a whole body exposure system. Glucose tolerance, insulin sensitivity, oxygen consumption and heat production were evaluated. At euthanasia, blood, spleen and visceral adipose tissue were collected to measure inflammatory cells using flow cytometry. Standard immnunohistochemical methods, western blotting and quantitative PCR were used to assess targets of interest.

Results

PM_2.5 exposure influenced energy metabolism including O₂ consumption, CO₂ production, respiratory exchange ratio and thermogenesis. These changes were accompanied by worsened insulin resistance, visceral adiposity and inflammation in spleen and visceral adipose depots. Plasma adiponectin were decreased in response to PM_2.5 exposure while leptin levels increased. PM_2.5 exposure resulted in a significant increase in expression of inflammatory genes and decreased UCP1 expression in brown adipose tissue and activated p38 and ERK pathways in the liver of the KKay mice.

Conclusions

Concentrated ambient PM_2.5 exposure impairs energy metabolism, concomitant with abnormalities in glucose homeostasis, increased inflammation in insulin responsive organs, brown adipose inflammation and results in imbalance in circulating leptin/adiponectin levels in a genetically susceptible diabetic model. These results provide additional insights into the mechanisms surrounding air pollution mediated susceptibility to Type II DM.

Macrophages in homeostatic immune function

Macrophages are not only involved in inflammatory and anti-infective processes, but also play an important role in maintaining tissue homeostasis. In this review, we summarize recent evidence investigating the role of macrophages in controlling angiogenesis, metabolism as well as salt and water balance. Particularly, we summarize the importance of macrophage tonicity enhancer binding protein (TonEBP, also termed nuclear factor of activated T-cells 5 [NFAT5]) expression in the regulation of salt and water homeostasis. Further understanding of homeostatic macrophage function may lead to new therapeutic approaches to treat ischemia, hypertension and metabolic disorders.

Implication of the Tpl2 kinase in inflammatory changes and insulin resistance induced by the interaction between adipocytes and macrophages

Adipose tissue inflammation is associated with the development of insulin resistance. In obese adipose tissue, lipopolysaccharides (LPSs) and saturated fatty acids trigger inflammatory factors that mediate a paracrine loop between adipocytes and macrophages. However, the inflammatory signaling proteins underlying this cross talk remain to be identified. The mitogen-activated protein kinase kinase kinase tumor progression locus 2 (Tpl2) is activated by inflammatory stimuli, including LPS, and its expression is up-regulated in obese adipose tissue, but its role in the interaction between adipocytes and macrophages remains ill-defined. To assess the implication of Tpl2 in the cross talk between these 2 cell types, we used coculture system and conditioned medium (CM) from macrophages. Pharmacological inhibition of Tpl2 in the coculture markedly reduced lipolysis and cytokine production and prevented the decrease in adipocyte insulin signaling. Tpl2 knockdown in cocultured adipocytes reduced lipolysis but had a weak effect on cytokine production and did not prevent the alteration of insulin signaling. By contrast, Tpl2 silencing in cocultured macrophages resulted in a marked inhibition of cytokine production and prevented the alteration of adipocyte insulin signaling. Further, when Tpl2 was inhibited in LPS-activated macrophages, the produced CM did not alter adipocyte insulin signaling and did not induce an inflammatory response in adipocytes. By contrast, Tpl2 silencing in adipocytes did not prevent the deleterious effects of a CM from LPS-activated macrophages. Together, these data establish that Tpl2, mainly in macrophages, is involved in the cross talk between adipocytes and macrophages that promotes inflammatory changes and alteration of insulin signaling in adipocytes.

Role of macrophages in the altered epithelial function during a type 2 immune response induced by enteric nematode infection

Parasitic enteric nematodes induce a type 2 immune response characterized by increased production of Th2 cytokines, IL-4 and IL-13, and recruitment of alternatively activated macrophages (M2) to the site of infection. Nematode infection is associated with changes in epithelial permeability and inhibition of sodium-linked glucose absorption, but the role of M2 in these effects is unknown. Clodronate-containing liposomes were administered prior to and during nematode infection to deplete macrophages and prevent the development of M2 in response to infection with Nippostrongylus brasiliensis. The inhibition of epithelial glucose absorption that is associated with nematode infection involved a macrophage-dependent reduction in SGLT1 activity, with no change in receptor expression, and a macrophage-independent down-regulation of GLUT2 expression. The reduced transport of glucose into the enterocyte is compensated partially by an up-regulation of the constitutive GLUT1 transporter consistent with stress-induced activation of HIF-1α. Thus, nematode infection results in a “lean” epithelial phenotype that features decreased SGLT1 activity, decreased expression of GLUT2 and an emergent dependence on GLUT1 for glucose uptake into the enterocyte. Macrophages do not play a role in enteric nematode infection-induced changes in epithelial barrier function. There is a greater contribution, however, of paracellular absorption of glucose to supply the energy demands of host resistance. These data provide further evidence of the ability of macrophages to alter glucose metabolism of neighboring cells.