Adipose Macrophage Research Articles

Concentrated Ambient PM2.5-Induced Inflammation and Endothelial Dysfunction in a Murine Model of Neural IKK2 Deficiency.

Background:Exposure to ambient fine particulate matter () is associated with cardiovascular mortality, but underlying pathophysiologic mechanisms are not fully understood. Hypothalamic inflammation, characterized by the activation of Inhibitor kappaB kinase 2/Nuclear factor kappaB () signaling pathway, may play an important role in the pathogenesis of cardiovascular diseases. We recently demonstrated that hypothalamic inflammation is increased in mice exposed to concentrated ambient (CAP).Objectives:In the present study, we used a neuron-specific IKK2 knockout mouse model to examine the role of neural IKK2 expression and hypothalamic inflammation in the pathophysiologic effects of .Methods: We assessed inflammatory and vascular responses in () and littermate (control) mice after 4 mo of exposure to filtered air (FA) or CAP.Results:CAP exposure was associated with significantly higher tumor necrosis factor- and interleukin (IL)-6 mRNA in the hypothalamus of control mice, but not mice. In addition, CAP exposure–induced increases in bronchoalveolar lavage fluid (BALF) leukocytes, pulmonary macrophage infiltration and IL-6 expression, plasma and levels, adipose macrophage infiltration and expression, and endothelial dysfunction were reduced or absent in mice compared with controls.Conclusions:Our findings support a role of neural IKK2 in CAP exposure–induced local and systemic pro-inflammatory cytokine expression, pulmonary and adipose inflammation, and endothelial dysfunction, thus providing insight into pathophysiologic mechanisms that may mediate effects of exposure. https://doi.org/10.1289/EHP2311

Circulating Monocyte Chemoattractant Protein-1 Levels and Lumbar Bone Mineral Density in Korean Women.

BackgroundMonocyte chemoattractant protein-1 (MCP-1) is expressed in adipose tissue, macrophages, endothelial cells, and osteoblasts by parathyroid hormone administration. Circulating MCP-1 levels are positively correlated with the degree of obesity. However, whether circulating MCP-1 affects bone metabolism is unclear. Therefore, in this study, the association between circulating MCP-1 levels and lumbar bone mineral density (BMD) based on menopausal status was assessed.MethodsWe recruited 109 premenopausal and 46 postmenopausal Korean women and examined the association between circulating MCP-1 concentrations and various parameters including lumbar BMD based on menopausal status.ResultsA significant increase in body weight, abdominal circumference, body mass index, and MCP-1 levels (from 245.9±73.5 to 336.5±101.7 pg/mL) and significant decrease (from 0.992±0.114 to 0.772±0.113 g/cm2) in lumbar BMD were observed after menopause. However, circulating MCP-1 levels were not correlated with any parameters including lumbar BMD in premenopausal or postmenopausal women.ConclusionCirculating MCP-1 levels were not correlated with lumbar BMD regardless of menopausal status.

Intermittent fasting promotes adipose thermogenesis and metabolic homeostasis via VEGF-mediated alternative activation of macrophage

Intermittent fasting (IF), a periodic energy restriction, has been shown to provide health benefits equivalent to prolonged fasting or caloric restriction. However, our understanding of the underlying mechanisms of IF-mediated metabolic benefits is limited. Here we show that isocaloric IF improves metabolic homeostasis against diet-induced obesity and metabolic dysfunction primarily through adipose thermogenesis in mice. IF-induced metabolic benefits require fasting-mediated increases of vascular endothelial growth factor (VEGF) expression in white adipose tissue (WAT). Furthermore, periodic adipose-VEGF overexpression could recapitulate the metabolic improvement of IF in non-fasted animals. Importantly, fasting and adipose-VEGF induce alternative activation of adipose macrophage, which is critical for thermogenesis. Human adipose gene analysis further revealed a positive correlation of adipose VEGF-M2 macrophage-WAT browning axis. The present study uncovers the molecular mechanism of IF-mediated metabolic benefit and suggests that isocaloric IF can be a preventive and therapeutic approach against obesity and metabolic disorders.

Inflammasome-driven catecholamine catabolism in macrophages blunts lipolysis during ageing.

Catecholamine-induced lipolysis, the first step in generation of energy substrates through hydrolysis of triglycerides (TGs) 1, declines with age 2,3. The defect in mobilization of free fatty acids (FFA) in elderly is accompanied with increased visceral adiposity, lower exercise capacity, failure to maintain core body temperature during cold stress, and reduced ability to survive starvation. While catecholamine signaling in adipocytes is normal in elderly, how lipolysis is impaired in aging remains unknown 2,4. Here we uncover that the adipose tissue macrophages (ATMs) regulate age-related reduction in adipocyte lipolysis by lowering the bioavailability of norepinephrine (NE). Unexpectedly, unbiased whole transcriptome analyses of adipose macrophages revealed that aging upregulates genes controlling catecholamine degradation in an NLRP3 inflammasome-dependent manner. Deletion of NLRP3 in aging restored catecholamine-induced lipolysis through downregulation of growth differentiation factor-3 (GDF3) and monoamine oxidase-a (MAOA) that is known to degrade NE. Consistent with this, deletion of GDF3 in inflammasome-activated macrophages improved lipolysis by decreasing MAOA and caspase-1. Furthermore, inhibition of MAOA reversed age-related reduction in adipose tissue NE concentration and restored lipolysis with increased levels of key lipolytic enzymes, adipose triglyceride lipase (ATGL) and hormone sensitive lipase (HSL). Our study reveals that targeting neuro-innate signaling between sympathetic nervous system and macrophages may offer new approaches to mitigate chronic inflammation-induced metabolic impairment and functional decline.

N-acetylcysteine Counteracts Adipose Tissue Macrophage Infiltration and Insulin Resistance Elicited by Advanced Glycated Albumin in Healthy Rats.

Background: Advanced glycation endproducts elicit inflammation. However, their role in adipocyte macrophage infiltration and in the development of insulin resistance, especially in the absence of the deleterious biochemical pathways that coexist in diabetes mellitus, remains unknown. We investigated the effect of chronic administration of advanced glycated albumin (AGE-albumin) in healthy rats, associated or not with N-acetylcysteine (NAC) treatment, on insulin sensitivity, adipose tissue transcriptome and macrophage infiltration and polarization.Methods: Male Wistar rats were intraperitoneally injected with control (C) or AGE-albumin alone, or, together with NAC in the drinking water. Biochemical parameters, lipid peroxidation, gene expression and protein contents were, respectively, determined by enzymatic techniques, reactive thiobarbituric acid substances, RT-qPCR and immunohistochemistry or immunoblot. Carboxymethyllysine (CML) and pyrraline (PYR) were determined by LC/mass spectrometry (LC-MS/MS) and ELISA.Results: CML and PYR were higher in AGE-albumin as compared to C. Food consumption, body weight, systolic blood pressure, plasma lipids, glucose, hepatic and renal function, adipose tissue relative weight and adipocyte number were similar among groups. In AGE-treated animals, insulin resistance, adipose macrophage infiltration and Col12a1 mRNA were increased with no changes in M1 and M2 phenotypes as compared to C-albumin-treated rats. Total GLUT4 content was reduced by AGE-albumin as compared to C-albumin. NAC improved insulin sensitivity, reduced urine TBARS, adipose macrophage number and Itgam and Mrc mRNA and increased Slc2a4 and Ppara. CD11b, CD206, Ager, Ddost, Cd36, Nfkb1, Il6, Tnf, Adipoq, Retn, Arg, and Il12 expressions were similar among groups.Conclusions: AGE-albumin sensitizes adipose tissue to inflammation due to macrophage infiltration and reduces GLUT4, contributing to insulin resistance in healthy rats. NAC antagonizes AGE-albumin and prevents insulin resistance. Therefore, it may be a useful tool in the prevention of AGE action on insulin resistance and long-term complications of DM.

Metabolic syndrome and obesity are the cornerstones of liver fibrosis in HIV-monoinfected patients.

Metabolic syndrome (MetS) and nonalcoholic fatty liver disease have become a common finding in HIV-infected patients. However, the severity, risk factors and pathogenesis of liver fibrosis in this population have been poorly documented. To assess the impact of MetS on liver fibrosis and analyze the association between MetS, liver fibrosis and markers of adipose tissue and macrophage activation. In a matched cohort of HIV-1-monoinfected patients with and without MetS, after exclusion of other causes of liver disease, we assessed liver stiffness measurement and measured levels of serum adipokines, homeostasis model assessment index and soluble CD163 (sCD163) and CD14 as markers of fat, insulin resistance and macrophage/monocyte activation, respectively. A total of 468 HIV-monoinfected individuals were enrolled; 405 (203 with MetS/202 without MetS) were analyzed. Patients with MetS were older and 49% had insulin resistance. The prevalence of significant liver fibrosis (≥F2) was higher in patients with MetS [25.1%, 95% confidence interval (19.3-31.2)] compared with those without MetS [7.9%, (4.6-12.5), P < 0.0001]. In multivariate analysis with adjustment on MetS, obesity [odds ratio: 3.0 (1.1-8.4)] and homeostasis model assessment [1.1 (1.007-1.2)] were independent factors of advanced fibrosis (>= F3).. Serum levels of adipokines and sCD163 were significantly associated with the degree of liver fibrosis. When adjusted on MetS, leptin and sCD163 remained strongly associated with fibrosis/cirrhosis, whereas HIV parameters and antiretroviral therapy were not. In HIV-monoinfected patients, MetS is an important risk factor of liver fibrosis. Adipose tissue and macrophage activation might be key players in the development of liver fibrosis but the exact mechanisms need to be elucidated.

LB.02.01] ATHEROSCLEROTIC PLAQUE INFLAMMATION SYNCHRONIZE WITH INFLAMMATORY ACTIVITY OF VISCERAL FAT

Objective: Visceral adipose tissue is thought to confer increased cardiovascular risk through leukocyte infiltration and increased adipose macrophage activity. Previous positron emission tomography (PET) studies using fluorodeoxyglucose (FDG) demonstrated that increased FDG uptake could reflect the severity of inflammation in atherosclerotic plaque. We hypothesized that active atherosclerotic change in the major arteries would accompany increased inflammation within visceral fat and it could be detected in humans using combined FDG PET/computed tomography (CT). Design and method: We observed 44 consecutive subjects with cardiovascular disease. For all of them, an one-hour PET/CT (from brain to foot) was performed after injection of FDG (370–555 MBq). FDG uptake in the aorta or its major branches was evaluated visually and semiquantitatively. Maximal standard uptake values (SUV) of the highest regions of interest were calculated in the subcutaneous fat and visceral fat area, separately. Results: Significant FDG uptake in the arterial wall was noted in 21 patients (plaque positive; PP group), all of whom have experienced acute cardiovascular events (acute coronary syndrome or ischemic stroke) within a week. The other 23 patients (plaque negative; PN group) had chronic stable angina or asymptomatic carotid stenosis. Visceral fat SUV was significantly higher as compared to subcutaneous fat SUV (0.49 ± 0.15 vs. 0.15 ± 0.05, p < 0.001) in PP group, whereas there was no significant difference in PN group (0.18 ± 0.07 vs. 0.16 ± 0.03, p = 0.622). When we compared two groups, PP group showed higher visceral fat SUV than PN group (p < 0.001). In terms of subcutaneous fat SUV, the results were similar in two groups (p = 0.773). Conclusions: We demonstrated that atherosclerotic plaque inflammation was associated with increased inflammation within visceral fat. Our results need to be confirmed by comparison with histologic or other imaging findings. Further evaluation to determine whether metabolic activity of visceral adipose tissue is a marker or mediator of vascular inflammation is also needed.

Synergistic Modulation of Inflammatory but not Metabolic Effects of High-Fat Feeding by CCR2 and CX3CR1.

ObjectiveTo explore the impact of dual targeting of C-C motif chemokine receptor-2 (CCR2) and fractalkine receptor (CX3CR1) on the metabolic and inflammatory consequences of high fat diet (HFD)-induced obesity.MethodsC57BL/6J wild type (WT), Cx3cr1−/−, Ccr2−/− and Cx3cr1−/−Ccr2−/− double knockout male and female mice were fed a 45% HFD for up to 25 weeks starting at 12-weeks of age.ResultsAll groups gained weight at a similar rate and developed similar degree of adiposity, hyperglycemia, glucose intolerance and impairment of insulin sensitivity in response to HFD. As expected, the circulating monocyte count was decreased in Ccr2−/− and Cx3cr1−/−Ccr2−/−, but not in Cx3cr1−/− Mice. Flow cytometric analysis of perigonadal adipose of male, but not female, mice revealed trends to lower CD11c+MGL1− M1- like macrophages and higher CD11c−MGL1+ M2- like macrophages as a percentage of CD45+F4/80+CD11b+ macrophages in Cx3cr1−/−Ccr2−/− mice vs. WT mice, suggesting reduced adipose tissue macrophage activation. In contrast, single knockout of Ccr2 or Cx3cr1 did not differ in their adipose macrophage phenotypes.ConclusionAlthough CCR2 and CX3CR1 may synergistically impact inflammatory phenotypes, their joint deficiency did not influence metabolic effects of 45% HFD-induced obesity in these model conditions.

Very-long-chain ω-3 fatty acid supplements and adipose tissue functions: a randomized controlled trial

Background: Increased omega-3 (n-3) fatty acid consumption is reported to benefit patients with metabolic syndrome, possibly due to improved adipose tissue function.Objective: We tested the effects of high-dose, very-long-chain ω-3 fatty acids on adipose tissue inflammation and insulin regulation of lipolysis.Design: A double-blind, placebo-controlled study compared 6 mo of 3.9 g eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)/d (4.2 g total ω-3/d; n = 12) with a placebo (4.2 g oleate/d; n = 9) in insulin-resistant adults. Before and after treatment, the volunteers underwent adipose tissue biopsies to measure the total (CD68+), pro- (CD14+ = M1), and anti- (CD206+ = M2) inflammatory macrophages, crown-like structures, and senescent cells, as well as a 2-step pancreatic clamping with a [U-13C]palmitate infusion to determine the insulin concentration needed to suppress palmitate flux by 50% (IC50(palmitate)f).Results: In the ω-3 group, the EPA and DHA contributions to plasma free fatty acids increased (P = 0.0003 and P = 0.003, respectively), as did the EPA and DHA content in adipose tissue (P < 0.0001 and P < 0.0001, respectively). Despite increases in adipose and plasma EPA and DHA in the ω-3 group, there were no significant changes in the IC50(palmitate)f (19 ± 2 compared with 24 ± 3 μIU/mL), adipose macrophages (total: 31 ± 2/100 adipocytes compared with 33 ± 2/100 adipocytes; CD14+: 13 ± 2/100 adipocytes compared with 14 ± 2/100 adipocytes; CD206+: 28 ± 2/100 adipocytes compared with 29 ± 3/100 adipocytes), crown-like structures (1 ± 0/10 images compared with 1 ± 0/10 images), or senescent cells (4% ± 1% compared with 4% ± 1%). There were no changes in these outcomes in the placebo group.Conclusions: Six months of high-dose ω-3 supplementation raised plasma and adipose ω-3 fatty acid concentrations but had no beneficial effects on adipose tissue lipolysis or inflammation in insulin-resistant adults. This trial was registered at clinicaltrials.gov as NCT01686568.

Homology modeling and molecular docking studies on Type II diabetes complications reduced PPARγ receptor with various ligand molecules

Peroxisome proliferator-activated receptor gamma (PPARγ), a type II nuclear receptor present in adipose tissue, colon and macrophages. It reduces the hyperglycemia associated metabolic syndromes. Particularly, type II diabetes-related cardiovascular system risk in human beings. The fatty acid storage and glucose metabolism are regulated by PPARγ activation in human body. According to recent reports commercially available PPARγ activating drugs have been causing severe side effects. At the same time, natural products have been proved to be a promising area of drug discovery. Recently, many studies have been attempted to screen and identify a potential drug candidate to activate PPARγ. Hence, in this study we have selected some of the bio-active molecules from traditional medicinal plants. Molecular docking studies have been carried out against the target, PPARγ. We Results suggested that Punigluconin has a efficient docking score and it is found to have good binding affinities than other ligands. Hence, we concluded that Punigluconin is a better drug candidate for activation of PPARγ gene expression. Further studies are necessary to confirm their efficacy and possibly it can develop as a potential drug in future.

IGF1 Shapes Macrophage Activation in Response to Immunometabolic Challenge

In concert with their phagocytic activity, macrophages are thought to regulate the host immunometabolic responses primarily via their ability to produce specific cytokines and metabolites. Here, we show that IL-4-differentiated, M2-like macrophages secrete IGF1, a hormone previously thought to be exclusively produced from liver. Ablation of IGF1 receptors from myeloid cells reduced phagocytosis, increased macrophages in adipose tissue, elevated adiposity, lowered energy expenditure, and led to insulin resistance in mice fed a high-fat diet. The investigation of adipose macrophage phenotype in obese myeloid IGF1R knockout (MIKO) mice revealed a reduction in transcripts associated with M2-like macrophage activation. Furthermore, the MIKO mice infected with helminth Nippostrongylus brasiliensis displayed delayed resolution from infection with normal insulin sensitivity. Surprisingly, cold challenge did not trigger an overt M2-like state and failed to induce tyrosine hydroxylase expression in adipose tissue macrophages of control or MIKO mice. These results show that IGF1 signaling shapes the macrophage-activation phenotype.

Particulate Air pollution mediated effects on insulin resistance in mice are independent of CCR2

BackgroundChronic exposure to fine ambient particulate matter (PM2.5) induces insulin resistance. CC-chemokine receptor 2 (CCR2) appears to be essential in diet-induced insulin resistance implicating an important role for systemic cellular inflammation in the process. We have previously suggested that CCR2 is important in PM2.5 exposure-mediated inflammation leading to insulin resistance under high fat diet situation. The present study assessed the importance of CCR2 in PM2.5 exposure-induced insulin resistance in the context of normal diet.Methods and ResultsC57BL/6 and CCR2-/- mice were subjected to exposure to concentrated ambient PM2.5 or filtered air for 6 months. In C57BL/6 mice, concentrated ambient PM2.5 exposure induced whole-body insulin resistance, macrophage infiltration into the adipose tissue, and upregulation of phosphoenolpyruvate carboxykinase (PEPCK) in the liver. While CCR2 deficiency reduced adipose macrophage content in the PM2.5-exposed animals, it did not improve systemic insulin resistance. This lack of improvement in insulin resistance was paralleled by increased hepatic expression of genes in PEPCK and inflammation.ConclusionCCR2 deletion failed to attenuate PM2.5 exposure-induced insulin resistance in mice fed on normal diet. The present study indicates that PM2.5 may dysregulate glucose metabolism directly without exerting proinflammatory effects.

Adipocyte-Specific Enhancement of Angiotensin II Type 1 Receptor-Associated Protein Ameliorates Diet-Induced Visceral Obesity and Insulin Resistance.

BackgroundThe renin–angiotensin system has a pivotal role in the pathophysiology of visceral obesity. Angiotensin II type 1 receptor (AT1R) is a major player in the signal transduction of the renin–angiotensin system, and the overactivation of this signaling contributes to the progression of visceral obesity. We have shown that the AT1R‐associated protein (ATRAP) promotes AT1R internalization from the cell surface into cytoplasm along with the suppression of overactivation of tissue AT1R signaling. In this study, we examined whether the enhancement of adipose ATRAP expression could efficiently prevent diet‐induced visceral obesity and insulin resistance.Methods and ResultsWe generated adipocyte‐specific ATRAP transgenic mice using a 5.4‐kb adiponectin promoter, and transgenic mice and littermate control mice were fed either a low‐ or high‐fat diet for 10 weeks. Although the physiological phenotypes of the transgenic and control mice fed a low‐fat diet were comparable, the transgenic mice exhibited significant protection against high‐fat diet–induced adiposity, adipocyte hypertrophy, and insulin resistance concomitant with an attenuation of adipose inflammation, macrophage infiltration, and adipokine dysregulation. In addition, when mice were fed a high‐fat diet, the adipose expression of glucose transporter type 4 was significantly elevated and the level of adipose phospho‐p38 mitogen‐activated protein kinase was significantly attenuated in the transgenic mice compared with control mice.ConclusionsResults presented in this study suggested that the enhancement in adipose ATRAP plays a protective role against the development of diet‐induced visceral obesity and insulin resistance through improvement of adipose inflammation and function via the suppression of overactivation of adipose AT1R signaling. Consequently, adipose tissue ATRAP is suggested to be an effective therapeutic target for the treatment of visceral obesity.

Inflammation, but not recruitment, of adipose tissue macrophages requires signalling through Mac-1 (CD11b/CD18) in diet-induced obesity (DIO).

Cell accumulation is a prerequisite for adipose tissue inflammation. The leukocyte integrin Mac-1 (CD11b/CD18, αMβ2) is a classic adhesion receptor critically regulating inflammatory cell recruitment. Here, we tested the hypothesis that a genetic deficiency and a therapeutic modulation of Mac-1 regulate adipose tissue inflammation in a mouse model of diet-induced obesity (DIO). C57Bl6/J mice genetically deficient (Mac-1-/-) or competent for Mac-1 (WT) consumed a high fat diet for 20 weeks. Surprisingly, Mac-1-/- mice presented with increased diet-induced weight gain, decreased insulin sensitivity in skeletal muscle and in the liver in insulin-clamps, insulin secretion deficiency and elevated glucose levels in fasting animals, and dyslipidaemia. Unexpectedly, accumulation of adipose tissue macrophages (ATMs) was unaffected, while gene expression indicated less inflamed adipose tissue and macrophages in Mac-1-/- mice. In contrast, inflammatory gene expression at distant locations, such as in skeletal muscle, was not changed. Treatment of ATMs with an agonistic anti-Mac-1 antibody, M1/70, induced pro-inflammatory genes in cell culture. In vivo, treatment with M1/70 induced a hyper-inflammatory phenotype with increased expression of IL-6 and MCP-1, whereas accumulation of ATMs did not change. Finally, inhibition of Mac-1's adhesive interaction to CD40L by the peptide inhibitor cM7 did not affect myeloid cell accumulation in adipose tissue. We present the surprising finding that adhesive properties of the leukocyte integrin Mac-1 are not required for macrophage accumulation in adipose tissue. Instead, Mac-1 modulates inflammatory gene expression in macrophages. These findings question the net effect of integrin blockade in cardio-metabolic disease.

Impact of Pioglitazone on Macrophage Dynamics in Adipose Tissues of Cecal Ligation and Puncture-Treated Mice.

Pioglitazone improves sepsis-induced organ injury accompanied with anti-inflammatory effects on visceral adipose tissue. However, its action in adipose immune cells remains to be ascertained. We investigated the effects of pioglitazone on visceral adipose macrophage population and polarisation in cecal ligation and puncture (CLP)-induced sepsis mice. Eight-week-old male mice were assigned to 3 groups: 1) sham-operated group, 2) CLP group, or 3) pioglitazone-treated CLP group. Pioglitazone (10 mg/kg) was injected intraperitonally for 7 d and CLP surgery was performed. Visceral adipose tissues were collected 24 h after the surgery. mRNA expression of several macrophage markers (inducible nitric oxide synthase (iNOS) for M1, arginase1 (Arg1) and interleukin (IL)-10 for M2, CD163 and F4/80 for mature macrophages) and inflammatory adipokines (IL-6, monocyte chemoattractant protein-1: MCP-1) was quantified by real-time RT-PCR. Tissue sections were subjected to the immunohistochemical analysis and the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) assay. CLP significantly enhanced Arg1, IL-10 and iNOS mRNA expressions as compared with the sham group, and pioglitazone significantly increased the mRNA level of CD163 and F4/80 in CLP mice. Expression of IL-6 and MCP-1 stimulated by CLP was reduced by pioglitazone treatment. Increased CD11b/c- and CD163-positive cells as well as apoptotic cells were observed in the CLP group and the pioglitazone-treated group. The data indicate that M1/M2 macrophage activation of visceral adipose tissues is induced in CLP-induced mice, and the function of macrophages recruited from surrounding organs may be modulated by pioglitazone treatment.

My D88-Dependent Interplay Between Myeloid and Endothelial Cells in the Initiation and Progression of Obesity-Associated Inflammatory Diseases

Low-grade systemic inflammation is often associated with metabolic syndrome, which plays a critical role in the development of the obesity-associated inflammatory diseases, including insulin resistance and atherosclerosis. Here, we investigate how Toll-like receptor-MyD88 signaling in myeloid and endothelial cells coordinately participates in the initiation and progression of high fat diet-induced systemic inflammation and metabolic inflammatory diseases. MyD88 deficiency in myeloid cells inhibits macrophage recruitment to adipose tissue and their switch to an M1-like phenotype. This is accompanied by substantially reduced diet-induced systemic inflammation, insulin resistance, and atherosclerosis. MyD88 deficiency in endothelial cells results in a moderate reduction in diet-induced adipose macrophage infiltration and M1 polarization, selective insulin sensitivity in adipose tissue, and amelioration of spontaneous atherosclerosis. Both in vivo and ex vivo studies suggest that MyD88-dependent GM-CSF production from the endothelial cells might play a critical role in the initiation of obesity-associated inflammation and development of atherosclerosis by priming the monocytes in the adipose and arterial tissues to differentiate into M1-like inflammatory macrophages. Collectively, these results implicate a critical MyD88-dependent interplay between myeloid and endothelial cells in the initiation and progression of obesity-associated inflammatory diseases. DisclosuresNo relevant conflicts of interest to declare.

Efficient Targeting of Adipose Tissue Macrophages in Obesity with Polysaccharide Nanocarriers.

Obesity leads to an increased risk for type 2 diabetes, heart disease, stroke, and cancer. The causal link between obesity and these pathologies has recently been identified as chronic low-grade systemic inflammation initiated by pro-inflammatory macrophages in visceral adipose tissue. Current medications based on small-molecule drugs yield significant off-target side effects with long-term use, and therefore there is a major need for targeted therapies. Here we report that nanoscale polysaccharides based on biocompatible glucose polymers can efficiently target adipose macrophages in obese mice. We synthesized a series of dextran conjugates with tunable size linked to contrast agents for positron emission tomography, fluorophores for optical microscopy, and anti-inflammatory drugs for therapeutic modulation of macrophage phenotype. We observed that larger conjugates efficiently distribute to visceral adipose tissue and selectively associate with macrophages after regional peritoneal administration. Up to 63% of the injected dose remained in visceral adipose tissue 24 h after administration, resulting in >2-fold higher local concentration compared to liver, the dominant site of uptake for most nanomedicines. Furthermore, a single-dose treatment of anti-inflammatory conjugates significantly reduced pro-inflammatory markers in adipose tissue of obese mice. Importantly, all components of these therapeutic agents are approved for clinical use. This work provides a promising nanomaterials-based delivery strategy to inhibit critical factors leading to obesity comorbidities and demonstrates a unique transport mechanism for drug delivery to visceral tissues. This approach may be further applied for high-efficiency targeting of other inflammatory diseases of visceral organs.

Alternating Diet as a Preventive and Therapeutic Intervention for High Fat Diet-induced Metabolic Disorder.

This study presents the alternating diet as a new strategy in combating obesity and metabolic diseases. Lean or obese mice were fed a high-fat diet (HFD) for five days and switched to a regular diet for one (5 + 1), two (5 + 2), or five (5 + 5) days before switching back to HFD to start the second cycle, for a total of eight weeks (for prevention) or five weeks (for treatment) without limiting animals’ access to food. Our results showed that animals with 5 + 2 and 5 + 5 diet alternations significantly inhibited body weight and fat mass gain compared to animals fed an HFD continuously. The dietary switch changed the pattern of daily caloric intake and suppressed HFD-induced adipose macrophage infiltration and chronic inflammation, resulting in improved insulin sensitivity and alleviated fatty liver. Alternating diet inhibited HFD-induced hepatic Pparγ-mediated lipid accumulation and activated the expression of Pparα and its target genes. Alternating diet in the 5 + 5 schedule induced weight loss in obese mice and reversed the progression of metabolic disorders, including hepatic steatosis, glucose intolerance, and inflammation. The results provide direct evidence to support that alternating diet represents a new intervention in dealing with the prevalence of diet-induced obesity.

Persistence of inflammatory adipose tissue immune cells despite weight loss in obese mice

Abstract Obesity causes dramatic changes to the adipose tissue immune environment including the recruitment and activation of macrophages. The inflammatory polarization of these cells is thought to play a critical role in the severity of insulin resistance associated with obesity. Weight loss can improve insulin resistance, but little is known concerning the effects of weight loss on immune activity in adipose. Diet switch from a 60% high-fat diet to 13% normal-fat diet was used to induce weight loss in diet-induced obese C57Bl/6 mice. Adipose tissue structural changes were evaluated by histology. Leukocyte populations were analyzed by flow cytometry, including sorting and comparing cytokine expression of adipose tissue macrophages before and after weight loss. Weight loss improved glucose tolerance and reduced serum insulin. However, extensive adipose fibrosis developed during weight loss and was associated with macrophage accumulation. Analysis of adipose macrophages after weight loss showed they retained an inflammatory gene expression profile similar to those found during obesity. These macrophages were derived primarily from older cells present during obesity. These macrophages were maintained though high proliferation and low apoptosis. The data indicate that inflammatory activation of adipose macrophages is not sufficient for whole body metabolic dysfunction, but the retained macrophages may promote adipose tissue fibrosis while impacting adipocyte health and function.

IEX-1 deficiency induces browning of white adipose tissue and resists diet-induced obesity.

Chronic inflammation plays a crucial role in the pathogenesis of obesity and insulin resistance. However, the primary mediators that affect energy homeostasis remain ill defined. Here, we report an unexpected role for immediate early response gene X-1 (IEX-1), a downstream target of NF-κB, in energy metabolism. We found that IEX-1 expression was highly induced in white adipose tissue (WAT) in both epidydmal and subcutaneous depots but not in interscapular brown adipose tissue (BAT) in mice fed a high fat diet (HFD). Null mutation of IEX-1 protected mice against HFD-induced adipose and hepatic inflammation, hepatic steatosis, and insulin resistance. Unexpectedly, IEX-1 knockout (IEX-1−/−) mice gained markedly less weight on HFD for 20 weeks as compared to wild-type (WT) littermates (37 ± 3 versus 48 ± 2 gm) due to increased energy expenditure. Mechanistically, we showed that IEX-1 deficiency induced browning and activated thermogenic genes program in WAT but not in BAT by promoting alternative activation of adipose macrophages. Consequently, IEX-1−/− mice exhibited enhanced thermogenesis (24 ± 0.1 versus 22 ± 0.1 kcal/hour/kg in WT mice) explaining increased energy expenditure and lean phenotype in these mice. In conclusion, the present study suggests that IEX-1 is a novel physiological regulator of energy homeostasis via its action in WAT.