Chronic Inflammation In Adipose Tissue Research Articles

Macrophage Polarization Mediated by Mitochondrial Dysfunction Induces Adipose Tissue Inflammation in Obesity.

Obesity is one of the prominent global health issues, contributing to the growing prevalence of insulin resistance and type 2 diabetes. Chronic inflammation in adipose tissue is considered as a key risk factor for the development of insulin resistance and type 2 diabetes in obese individuals. Macrophages are the most abundant immune cells in adipose tissue and play an important role in adipose tissue inflammation. Mitochondria are critical for regulating macrophage polarization, differentiation, and survival. Changes to mitochondrial metabolism and physiology induced by extracellular signals may underlie the corresponding state of macrophage activation. Macrophage mitochondrial dysfunction is a key mediator of obesity-induced macrophage inflammatory response and subsequent systemic insulin resistance. Mitochondrial dysfunction drives the activation of the NLRP3 inflammasome, which induces the release of IL-1β. IL-1β leads to decreased insulin sensitivity of insulin target cells via paracrine signaling or infiltration into the systemic circulation. In this review, we discuss the new findings on how obesity induces macrophage mitochondrial dysfunction and how mitochondrial dysfunction induces NLRP3 inflammasome activation. We also summarize therapeutic approaches targeting mitochondria for the treatment of diabetes.

Adipokines, Hepatokines and Myokines: Focus on Their Role and Molecular Mechanisms in Adipose Tissue Inflammation.

Chronic low-grade inflammation in adipose tissue (AT) is a hallmark of obesity and contributes to various metabolic disorders, such as type 2 diabetes and cardiovascular diseases. Inflammation in ATs is characterized by macrophage infiltration and the activation of inflammatory pathways mediated by NF-κB, JNK, and NLRP3 inflammasomes. Adipokines, hepatokines and myokines — proteins secreted from AT, the liver and skeletal muscle play regulatory roles in AT inflammation via endocrine, paracrine, and autocrine pathways. For example, obesity is associated with elevated levels of pro-inflammatory adipokines (e.g., leptin, resistin, chemerin, progranulin, RBP4, WISP1, FABP4, PAI-1, Follistatin-like1, MCP-1, SPARC, SPARCL1, and SAA) and reduced levels of anti-inflammatory adipokines such as adiponectin, omentin, ZAG, SFRP5, CTRP3, vaspin, and IL-10. Moreover, some hepatokines (Fetuin A, DPP4, FGF21, GDF15, and MANF) and myokines (irisin, IL-6, and DEL-1) also play pro- or anti-inflammatory roles in AT inflammation. This review aims to provide an updated understanding of these organokines and their role in AT inflammation and related metabolic abnormalities. It serves to highlight the molecular mechanisms underlying the effects of these organokines and their clinical significance. Insights into the roles and mechanisms of these organokines could provide novel and potential therapeutic targets for obesity-induced inflammation.

147-OR: Glucose Intolerance of Hereditary Progeria Werner Syndrome and Cellular Senescence in Their Adipose Tissue

Background: Werner syndrome (WS) is a hereditary premature aging disorder in which various signs of accelerated aging develop after puberty. These signs include gray hair, cataracts, diabetes, myocardial infarction, and malignant tumors. Patients with WS frequently show severe insulin resistance, visceral fat accumulation, and subcutaneous fat atrophy, leading to myocardial infarction due to atherosclerosis. However, the mechanism of accelerated aging and its effect on adipose tissue dysfunction and glucose intolerance remain unclear. Materials and Methods: We evaluated visceral fat area and insulin resistance using the glucose clamp method in four Japanese patients with WS. Stromal vascular fraction (SVF) was obtained from the subcutaneous adipose tissue of WS patients (WSVF) . Healthy individuals and phenotypes were examined. Results: The median glucose infusion rate (GIR) was 3.78 mg/kg/min (interquartile range 3.05, 4.25; insulin infusion rate=1.25 mU/kg/min; normal range >6 mg/kg/min) . All Japanese patients showed severe insulin resistance, sarcopenia, and visceral fat accumulation. The visceral fat area and GIR were inversely correlated (R2=0.72) . In vitro analysis of WSVF revealed early replicative senescence and an increase in SAβgal staining. A significant increase was observed in the expression of senescence-associated secretory phenotypes (SASP) , such as IL1B, IL6, and CXCL8 (p<0.01) , and the senescence marker CDKN2A (p=0.094) . RNA-seq analysis showed that genes related to cell adhesion and cell structure were upregulated in WSVF, whereas genes related to chromosomes, nuclear division, and cell cycle were downregulated. Adipose differentiation was suppressed in WSVF. Conclusions: SVF from the adipose tissue of WS patients exhibited cellular senescence and increased inflammatory cytokine production. Cellular senescence and chronic inflammation of adipose tissue induced by SASP may exacerbate insulin resistance in WS patients. Disclosure D.Sawada: None. T.Takatani: None. H.Hamada: None. K.Yokote: None. H.Kato: n/a. Y.Maezawa: None. D.Kinoshita: None. S.Funayama: None. H.Kaneko: None. T.Minamizuka: None. M.Koshizaka: None. T.Shiohama: None. Funding JSPS (20K17485) , AMED (21bm0804016h0005)

Paracrine Regulation of Adipose Tissue Macrophages by Their Neighbors in the Microenvironment of Obese Adipose Tissue.

Obesity has recently been defined as a chronic low-grade inflammatory disease. Obesity-induced inflammation of adipose tissue (AT) is an essential trigger for insulin resistance (IR) and related metabolic diseases. Although the underlying molecular basis of this inflammation has not been fully identified, there is consensus that the recruited and activated macrophages in AT are the most important culprits of AT chronic inflammation. Adipose tissue macrophages (ATMs) are highly plastic and could be polarized from an anti-inflammatory M2 to proinflammatory M1 phenotypes on stimulation by microenvironmental signals from obese AT. Many efforts have been made to elucidate the molecular signaling pathways of macrophage polarization; however, the upstream drivers governing and activating macrophage polarization have rarely been summarized, particularly regulatory messages from the AT microenvironment. In addition to adipocytes, the AT bed also contains a variety of immune cells, stem cells, as well as vascular, neural, and lymphatic tissues throughout, which together orchestrate the AT microenvironment. Here, we summarize how the aforesaid neighbors of ATMs in the AT microenvironment send messages to ATMs and thus regulate its phenotype during obesity. Deciphering the biology and polarization of ATMs in the obese environment is expected to provide a precise immunotherapy for adipose inflammation and obesity-related metabolic diseases.

Time Course of Fat Accumulation in Various Organs of Young OLETF Rats

PurposeExcessive fat accumulation induces chronic inflammation in the white adipose tissue (WAT), which leads and accelerates to obesity‐related health problems such as glucose intolerance, insulin resistance, and dyslipidemia. Determination of the time course of fat accumulation in obesity might allow identification of target tissues to treat the health problems in each stage. The purpose of the present study was to investigate the relationship between inflammatory changes and time course of fat accumulation in various organs.MethodsMale Otsuka Long‐Evans Tokushima fatty (OLETF) rats were used as spontaneous obesity animals. All rats were fed a standard diet containing 55.3% carbohydrate and water ad libitum. From 4‐ to 20‐week‐old, blood samples from vena cava and samples of the epididymal adipose tissue, retroperitoneal adipose tissue, mesenteric adipose tissue, and inguinal subcutaneous adipose tissue as WAT, brown adipose tissue (BAT) from interscapular region, liver, pancreas, and plantaris muscles were analyzed histologically every 2 weeks. Collected serum was used to detect triglyceride (TG) and free fatty acid (FFA) concentrations. Tissue samples were sliced and stained with hematoxylin and eosin or oil red O for histological observation.ResultsBody weight in OLETF rats increased linearly from 4‐ to 20‐week‐old. Although the wet weight and adipocyte diameter of the epididymal adipose tissue also increased throughout the experimental period, the values of inguinal subcutaneous adipose tissue increased by 10‐week‐old and were almost the same after 10‐week‐old. The liver TG levels increased from 4‐ to 8‐week‐old. However, hypertriglyceridemia, BAT whitening, and hepatic steatosis were not observed at this period. The serum TG levels increased after 10‐week‐old. Additionally, the number of whitened unilocular adipocytes with a diameter >10 μm in the BAT increased after 10‐week‐old and oil red O positive lipid droplets were usually observed in the liver at this period. Not only the serum TG levels but also the serum FFA levels increased after 18‐week‐old. Additionally, enlarged adipocytes with a diameter >130 μm and crown like structure indicating inflammatory change were often observed in the epididymal adipose tissue and retroperitoneal adipose tissue, not in mesenteric adipose tissue and inguinal subcutaneous adipose tissue, at this period. Fatty pancreas and intramuscular fat deposition were not observed throughout the experimental period.ConclusionAdipocyte hypertrophy in the visceral WAT and fatty liver could precede dyslipidemia in young OLETF rats and continuous obesity subsequently proceed to ectopic fat accumulation including BAT whitening and chronic inflammation in the epididymal adipose tissue and retroperitoneal adipose tissue with higher FFA levels. Hyperphagia mainly on carbohydrate could contribute to ectopic fat accumulation in the liver and BAT whitening, not to fatty pancreas and intramuscular fat deposition in young stage.

High-Fat Diet-Induced Dysregulation of Immune Cells Correlates with Macrophage Phenotypes and Chronic Inflammation in Adipose Tissue.

Obesity is a complex disease associated with various metabolic abnormalities, cardiovascular diseases, and low-grade chronic inflammation. Inflammation associated with T helper 1 (Th1) immune cells is dominant in adipose tissue (AT) and exerts metabolically deleterious impacts. The precise mechanism of alteration in AT immune system and its effect on metabolic homeostasis remains unclear. In this study, we investigated how a high-fat diet (HFD) alters the AT immune response and influences inflammation during obesity. HFD consumption amends the metabolic parameters, including body weight, glucose, and insulin levels. We observed increased infiltration of Th17 cells, a subset of dendritic cells (CD103+), and M1 macrophages in AT of mice fed HFD compared to those fed a normal diet (ND). In mice that were fed HFD, we also observed a reduction in regulatory T cells (Tregs) relative to the numbers of these cells in mice fed ND. Corresponding with this, mice in the HFD group exhibited higher levels of proinflammatory cytokines and chemokines than those in the ND group. We also observed alterations in signaling pathways, including increased protein expression of IRF3, TGFβ1, and mRNA expression of IL-6, KLF4, and STAT3 in the AT of the mice fed HFD as compared to those fed ND. Further, HFD-fed mice exhibited decreased protein expression of peroxisome proliferator-activated receptor-gamma (PPAR-γ) compared to mice fed ND, suggesting that PPAR-γ functions as a negative regulator of Th17 cell differentiation. These results suggest that HFD induces increased levels of inflammatory cytokines and key immune cells, including Th17, M1 macrophages, and CD103+ dendritic cells, and reduces levels of PPAR-γ and Tregs to sustain AT inflammation. This study supports the notion that dysregulation of Th17/Tregs, which polarizes macrophages towards M1 phenotypes in part through TGFβ1-IRF3-STAT3 and negatively regulates PPAR-γ mediated pathways, results in AT inflammation during obesity.

RANKL Impairs the TLR4 Pathway by Increasing TRAF6 and RANK Interaction in Macrophages.

High serum levels of osteoprotegerin (OPG) are found in patients with obesity, type 2 diabetes, sepsis, or septic shock and are associated with a high mortality rate in stroke. The primary known function of OPG is to bind to the receptor activator of NF-κB ligand (RANKL), and by doing so, it inhibits the binding between RANKL and its receptor (RANK). TLR4 signaling in macrophages involves TRAF6 recruitment and contributes to low-grade chronic inflammation in adipose tissue. LPS is a classical activator of the TLR4 pathway and induces the expression of inflammatory cytokines in macrophages. We have previously observed that in the presence of RANKL, there is no LPS-induced activation of TLR4 in macrophages. In this study, we investigated the crosstalk between RANK and TLR4 pathways in macrophages stimulated with both RANKL and LPS to unveil the role of OPG in inflammatory processes. We found that RANKL inhibits TLR4 activation by binding to RANK, promoting the binding between TRAF6 and RANK, lowering TLR4 activation and the expression of proinflammatory mediators. Furthermore, high OPG levels aggravate inflammation by inhibiting RANKL. Our findings elect RANKL as a candidate for drug development as a way to mitigate the impact of obesity-induced inflammation in patients.

Adipose invariant NKT cells interact with CD1d-expressing macrophages to regulate obesity-related inflammation.

Obesity is accompanied by and accelerated with chronic inflammation in adipose tissue, especially visceral adipose tissue (VAT). This low-level inflammation predisposes the host to the development of metabolic disease, most notably type 2 diabetes. We have focused on the capacity of glycolipid-reactive, CD1d-restricted natural killer T (NKT) cells to modulate obesity and its associated metabolic sequelae. We previously reported that CD1d knockout (KO) mice are partially protected against the development of obesity-associated insulin resistance, and these findings were recapitulated in mice with an adipocyte-specific CD1d deficiency, suggesting that NKT cell-adipocyte interactions play a critical role in exacerbating disease. However, many other CD1d-expressing cells contribute to the in vivo responses of NKT cells to lipid antigens. In the present study, we examined the role of CD1d expression by macrophages (Mϕ) in the development of obesity-associated metabolic inflammation using LysMcre-cd1d1f/f mice where the CD1d1gene is disrupted in a Mϕ-specific manner. Unexpectedly, these animals contained a higher frequency of T-bet+ CD4+ T cells in VAT with increased production of Th1 cytokines that aggravated VAT inflammation. Mϕ from mutant mice displayed increased production of IL-12p40, suggesting M1 polarization. These findings indicate that interactions of CD1d on Mϕ with NKT cells play a beneficial role in obesity-associated VAT inflammation and insulin resistance with a sharp contrast to an aggravating role of CD1d in another type of antigen-presenting cell, dendritic cells.

Impact of metabolic syndrome on the risk of endometrial cancer and the role of lifestyle in prevention.

Endometrial cancer (EC) is the second gynecological cancer with the highest global incidence. Among many associated risk factors, metabolic syndrome (MetS) is an important and preventable one. It comprises a group of conditions that often occur together: central adiposity, hyperglycemia, arterial hypertension, and atherogenic dyslipidemia. This review aimed to describe the epidemiological and biological relationship between MetS and EC, focusing on the role of lifestyle in prevention. A literature search was carried out in the PubMed database. 4824 publications were screened, and 123 were included for this review. The association between MetS and EC has been described. Chronic adipose tissue inflammation and insulin resistance are involved in the development of obesity, particularly visceral adiposity. These changes promote the ideal environment for the development of EC. Strategies based on lifestyle modifications may be effective for the prevention of MetS and consequently EC. Some of these modifications include adopting a diet rich in fruits, vegetables, whole grains, and legumes, depending to the accessibility of these foods for each region. Avoiding ultra-processed foods and increasing daily physical activity were also some suggested modifications. We propose that women be screened for MetS to establish early treatment and to possibly prevent EC. Clinical trials designed to prove the effect of lifestyle modifications on the prevention of EC are needed.

CD40L-expressing CD4+ T cells prime adipose-derived stromal cells to produce inflammatory chemokines

The therapeutic potential of culture-adapted adipose-derived stromal cells (ASCs) is largely related to their production of immunosuppressive factors that are inducible in vitro by priming with inflammatory stimuli, in particular tumor necrosis factor-α (TNFα) and interferon-γ (IFNγ). In vivo, obesity is associated with chronic inflammation of white adipose tissue, including accumulation of neutrophils, infiltration by IFNγ/TNFα-producing immune cells, and ASC dysfunction. In the current study, we identified in obese patients a simultaneous upregulation of CD40Lin the adipose tissue stroma vascular fraction (AT-SVF), correlated with the Th1 gene signature, and an overexpression of CD40 by native ASCs. Moreover, activated CD4+ T cells upregulated CD40 on culture-expanded ASCs and triggered their production of IL-8 in a CD40L-dependent manner, leading to an increased capacity to recruit neutrophils. Finally, activation of ASCs by sCD40L or CD40L-expressing CD4+ T cells relies on both canonical and non-canonical NF-κB pathways, and IL-8 was found to be coregulated with NF-κB family members in AT-SVF. These data identify the CD40-CD40L axis as a priming mechanism of ASCs, able to modulate their cross talk with neutrophils in an inflammatory context, and their functional capacity for therapeutic applications.

Electroacupuncture Stimulation Regulates Adipose Lipolysis via Catecholamine Signaling Mediated by NLRP3 Suppression in Obese Rats.

Chronic low-grade inflammation of visceral adipose tissue can cause obesity-associated insulin resistance, leading to metabolic syndrome. However, anti-inflammatory drugs and those for obesity management can lead to serious side effects such as abnormal heart rate and blood pressure. Consequently, this study aimed to explore the therapeutic potential of electroacupuncture stimulation (ES) for obesity and associated chronic inflammation. Sprague-Dawley male rats were fed a high-fat diet (HFD) for ten weeks to build an obesity model, and half of the diet-induced obesity (DIO) rats were received ES. The levels of inflammatory factors were detected by ELISA and qPCR analysis. The nerve-associated macrophages were marked with immunofluorescence staining. The molecular mechanism of NLRP3 inflammasome in ES was determined by the NLRP3 inflammasome activation model. Compared to HDF rats, ES showed decreased body weight and chronic inflammatory damage. Specifically, this occurred via a decrease in monoamine oxidase-A (MAOA) expression, which suppressed noradrenaline degradation. MAOA is expressed in nerve-associated macrophages (NAMs), and ES attenuated NAMs by suppressing the NLRP3 inflammasome. The NLRP3 agonist blocked the noradrenaline degradation-reducing effect of ES, and an increase in lipolysis via the inhibition of the NLRP3 inflammasome attenuated NAMs. Thus, our findings suggest that ES induced lipolysis via activation of the NLRP3 inflammasome in nerve-associated macrophages (NAMs), independently of sympathetic nervous system activity.

Astaxanthin, a Marine Carotenoid, Maintains the Tolerance and Integrity of Adipose Tissue and Contributes to Its Healthy Functions.

Recently, obesity-induced insulin resistance, type 2 diabetes, and cardiovascular disease have become major social problems. We have previously shown that Astaxanthin (AX), which is a natural antioxidant, significantly ameliorates obesity-induced glucose intolerance and insulin resistance. It is well known that AX is a strong lipophilic antioxidant and has been shown to be beneficial for acute inflammation. However, the actual effects of AX on chronic inflammation in adipose tissue (AT) remain unclear. To observe the effects of AX on AT functions in obese mice, we fed six-week-old male C57BL/6J on high-fat-diet (HFD) supplemented with or without 0.02% of AX for 24 weeks. We determined the effect of AX at 10 and 24 weeks of HFD with or without AX on various parameters including insulin sensitivity, glucose tolerance, inflammation, and mitochondrial function in AT. We found that AX significantly reduced oxidative stress and macrophage infiltration into AT, as well as maintaining healthy AT function. Furthermore, AX prevented pathological AT remodeling probably caused by hypoxia in AT. Collectively, AX treatment exerted anti-inflammatory effects via its antioxidant activity in AT, maintained the vascular structure of AT and preserved the stem cells and progenitor’s niche, and enhanced anti-inflammatory hypoxia induction factor-2α-dominant hypoxic response. Through these mechanisms of action, it prevented the pathological remodeling of AT and maintained its integrity.

꾸지뽕 열매 발효식초의 3T3-L1 세포에서 항염증 및 인슐린 저항성 개선 효과

Obesity is associated with chronic low-grade adipose tissue inflammation, leading to insulin resistance. Inflammation associated with insulin resistance is an interesting area of biomedical research and is expected to affect insulin signaling pathways via the downregulation of glucose transporters. In the present study, we investigated the inhibitory effects of Maclura tricuspidata fruit vinegar (MFV) against TNF-α-induced inflammation and insulin resistance in 3T3-L1 adipocytes. Differentiated 3T3-L1 adipocytes were pretreated with MFV at various concentrations and then cultured with TNF-α to induce insulin resistance. Then, lipid droplets, inflammatory cytokine and glucose uptake, PPARγ and GLUT4 expression, and IRS-1 phosphorylation were analyzed. MFV attenuated the TNF-α-induced decrease in lipid droplets and glucose uptake and inhibited TNF-α-induced inflammatory cytokine, IL-6, and MCP-1 production. MFV reversed the decrease in adiponectin produced by TNF-α. Furthermore, MFV upregulated the TNF-α-induced suppression of PPARγ and GLUT4 protein expression and reduced the TNF-α-induced phosphorylation of IRS-1. These findings suggest that MFV effectively ameliorates TNF-α-induced insulin resistance; accordingly, we recommend the use of MFV for the control and management of insulin resistance and its associated complications.

Inflammatory mechanisms linking obesity and tendinopathy.

Chronic tendinopathy is a debilitating tendon disorder with disappointing treatment outcomes. This review focuses on the potential roles of chronic low-grade inflammation in promoting tendinopathy in obesity. A systematic literature search was performed to identify all clinical studies supporting the actions of obesity-associated inflammatory mediators in the development of tendinopathy. The mechanisms of obesity-induced chronic inflammation in adipose tissue are firstly reviewed. Common inflammatory mediators potentially linking obesity and the development of tendinopathy, and their association with mechanical overuse, are discussed, along with pre-clinical evidences and a systematic literature search on clinical studies. The potential contribution of local adipose tissues in the promotion of inflammation, pain and tendon degeneration is then discussed. The future research directions are proposed.Translational potential statementBetter understanding of the roles of obesity-associated inflammatory mediators on tendons will clarify the pathophysiological drivers of tendinopathy in patients with obesity and identify possible treatment targets. Further studies on the mechanisms of obesity-induced chronic inflammation on tendon are a promising direction for the treatment of tendinopathy.

GPNMB protects against obesity-related metabolic disorders by attenuating macrophage-derived inflammation in white adipose tissue through CD44 receptor-dependent mechanism

Abstract Introduction Obesity is a worldwide health issue frequently linked to cardiovascular disease. Obesity is closely associated with chronic low-grade inflammation in adipose tissue caused by macrophage infiltration and activation, which leads to metabolic disorders. We discovered glycoprotein non-metastatic melanoma protein B (GPNMB) as a gene that is robustly expressed in white adipose tissue of obese mice. Purpose We aim to elucidate the role of GPNMB in obesity and its related metabolic disorders. Methods We generated GPNMB-knockout (KO) mice and assessed body weight, insulin sensitivity, and inflammation-related phenotypes after 12 weeks of high fat-diet (HFD) feeding. For in vitro experiment, we isolated peritoneal macrophages from wild-type (WT) and GPNMB-KO mice to explore their inflammatory phenotypes. Results After HFD feeding, obesity-related metabolic disorders were markedly worsened in GPNMB-KO mice, assessed by insulin and glucose tolerance test, although the weight gain and adiposity were similar between WT and GPNMB-KO mice. Expression of inflammatory cytokines was significantly increased in WAT of GPNMB-KO mice, in addition to a remarkable increase in crown-like structures. Peritoneal macrophages isolated from GPNMB-KO mice exhibited higher inflammatory cytokine levels, and significantly impaired the adipocytes insulin sensitivity in an endocrine manner. Recombinant soluble GPNMB attenuated the inflammatory capabilities in peritoneal macrophages isolated from GPNMB-KO mice. We identified that GPNMB inhibits the NF-κB signaling through binding to the CD44 receptor, and therefore negatively regulates inflammatory responses in macrophages. Conclusion Our study demonstrates GPNMB as an adipokine that protects against obesity-related metabolic disorders by reducing macrophage-derived inflammation, which in turn improves adipocytes functions and consequently preserves systemic metabolic health. Therefore, GPNMB is an attractive therapeutic target for the treatment of obesity-related metabolic disorders. Funding Acknowledgement Type of funding sources: None.

GPNMB plays a protective role against obesity-related metabolic disorders by reducing macrophage inflammatory capacity

Obesity is a global health problem that is often related to cardiovascular and metabolic diseases. Chronic low-grade inflammation in white adipose tissue (WAT) is a hallmark of obesity. Previously, during a search for differentially expressed genes in WAT of obese mice, we identified glycoprotein nonmetastatic melanoma protein B (GPNMB), of which expression was robustly induced in pathologically expanded WAT. Here, we investigated the role of GPNMB in obesity-related metabolic disorders utilizing GPNMB-deficient mice. When fed a high-fat diet (HFD), GPNMB-deficient mice showed body weight and adiposity similar to those of wild-type (WT) mice. Nonetheless, insulin and glucose tolerance tests revealed significant obesity-related metabolic disorders in GPNMB-KO mice compared with WT mice fed with HFD. Chronic WAT inflammation was remarkably worsened in HFD-fed GPNMB-KO mice, accompanied by a striking increase in crown-like structures, typical hallmarks for diseased WAT. Macrophages isolated from GPNMB-KO mice were observed to produce more inflammatory cytokines than those of WT mice, a difference abolished by supplementation with recombinant soluble GPNMB extracellular domain. We demonstrated that GPNMB reduced the inflammatory capacity of macrophages by inhibiting NF-κB signaling largely through binding to CD44. Finally, we showed that macrophage depletion by addition of clodronate liposomes abolished the worsened WAT inflammation and abrogated the exacerbation of metabolic disorders in GPNMB-deficient mice fed on HFD. Our data reveal that GPNMB negatively regulates macrophage inflammatory capacities and ameliorates the WAT inflammation in obesity; therefore we conclude that GPNMB is a promising therapeutic target for the treatment of metabolic disorders associated with obesity.

High Fat Diet-Induced CD8+ T Cells in Adipose Tissue Mediate Macrophages to Sustain Low-Grade Chronic Inflammation.

Obesity in the United States and worldwide reached epidemic proportions within the last 20 years. Obesity is a very powerful health determinant or indicator that facilitates the development and progression of several metabolic diseases, insulin resistance, and low-grade chronic inflammation. Low-grade chronic inflammation in adipose tissue (AT) is marked by the accumulation of T cells, macrophages, and other immune cells and increased production of proinflammatory cytokines. During the onset of obesity but before the influx of macrophages, the AT is infiltrated by T cells that are strongly implicated in the initiation of obesity-associated inflammation. In comparing mice fed a high-fat diet (HFD) with those fed a normal diet (ND), we observed in HFD epididymal AT induction and infiltration of activated T cells, an accumulation and polarization of macrophages, and an increase in populations of activated CD4+ T cells and CD8+ T cells that express CXCR3 or killer cell lectin-like receptor subfamily G member 1 (KLRG1). Levels of inflammatory cytokines and leptin and the results of in vitro co-culture experiments revealed interactions among HFD- and ND-induced CD8+ T cells, macrophages, and adipocytes. Our findings suggest that obese tissues activate and induce both CD4+ and CD8+ CD69+ T cells and augment the expression of CXCR3 receptors, which promotes the recruitment and numbers of pro-inflammatory M1 macrophages to maintain low-grade chronic inflammation. The results support the hypothesis that CXCR3-expressing CD8+T cells play an essential role in the initiation and maintenance of adipose tissue inflammation.

Effects of Des-acyl Ghrelin on Insulin Sensitivity and Macrophage Polarization in Adipose Tissue.

Background and ObjectivesObesity is the accumulation of adipose tissue caused by excess energy in the body, accompanied by long-term chronic low-grade inflammation of adipose tissue. More than 50% of interstitial cells in adipose tissue are macrophages, which produce cytokines closely related to insulin resistance. Macrophage biology is driven by two polarization phenotypes, M1 (proinflammatory) and M2 (anti-inflammatory). This study aimed to investigate the effect of gastric hormone des-acyl ghrelin (DAG) on the polarization phenotype of macrophages and elucidate the role of macrophages in adipose tissue inflammation and insulin sensitivity and its molecular mechanism.MethodsMice were subcutaneously administrated with DAG in osmotic minipumps. The mice were fed a normal diet or a high-fat diet (HFD). Different macrophage markers were detected by real-time revere transcription polymerase chain reaction.ResultsExogenous administration of DAG significantly inhibited the increase of adipocyte volume caused by HFD and reduced the number of rosette-like structures in adipose tissue. HFD in the control group significantly increased M1 macrophage markers, tumor necrosis factor α (TNFα), and inducible NO synthase (iNOS). However, these increases were reduced or even reversed after DAG administration in vitro. The M2 markers, macrophage galactose type C-type Lectin-1 (MGL1), arginase 1 (Arg1), and macrophage mannose receptor 1 (MRC1) were decreased by HFD, and the downward trend was inhibited or reversed after DAG administration. Although Arg1 was elevated after HFD, the fold increase after DAG administration in vitro was much greater than that in the control group.ConclusionDAG inhibits adipose tissue inflammation caused by HFD, reduces infiltration of macrophages in adipose tissue, and promotes polarization of macrophages to M2, thus alleviating obesity and improving insulin sensitivity.

The Contribution of Arachidonic Acid Metabolites EETs to Inflammation in Obesity

Background: Obesity is associated with increased prevalence of type 2 diabetes and cardiovascular disease (CVD). Adipose tissue (AT) contains a complex immune environment and is a central contributor to heightened systemic inflammation in obese persons. Increased chronic inflammation in obesity contributes to metabolic disease by increasing insulin resistance, and to CVD by causing an atherogenic dyslipidemia and increasing endothelial cell dysfunction and activation. Despite these links between inflammation and cardiometabolic disease in obesity, there are no current targeted therapies to prevent or reverse chronic inflammation in AT.Epoxyeicosatrienoic acids (EETs) are lipid signaling molecules that act as potent vasodilators and promote sodium excretion in the kidney. Increasing EETs in rodents protects against hypertension and endothelial dysfunction. In humans, circulating EETs correlate with insulin sensitivity and are decreased in individuals with insulin resistance. EETs also decrease the inflammatory response to obesity in animal models, but the effect of EETs on inflammation in humans is currently unknown. EETs are hydrolyzed to less active forms by the enzyme soluble epoxide hydrolase (sEH), and we hypothesized that pharmacologic sEH inhibition with a specific inhibitor GSK2256294 (GSK) in obese patients would decrease AT inflammation.Methods: Thirty-four obese prediabetic individuals were treated with placebo and GSK in a crossover design (NCT03486223). Participants had a seven-week washout in between drugs, and the order of drug was randomized and blinded. In a subgroup of patients, we collected subcutaneous AT by liposuction and characterized T cell phenotypes by flow cytometry (N=7 paired samples).Results: GSK decreased sEH activity in plasma (47.3% vs placebo; P=0.008) and in AT (58.8% vs placebo; P=0.002). GSK also decreased serum F2-isoprostanes (P=0.03), which are markers of oxidative damage and inflammation. In seven paired AT samples, T helper (Th) 1 cells producing the pro-inflammatory cytokine IFNγ were reduced by treatment with GSK as compared with placebo (% of total lymphocytes: Placebo 13.6% ± 6.9, GSK 11.0% ± 5.6, P=0.03 Wilcoxon Signed Rank). In this small sample, we did not detect significant differences in the percentage of other IFNγ-producing cells (natural killer: Placebo 19.0% ± 9.0, GSK 13.3% ± 4.9, P=0.18; CD8: Placebo 12.0 ± 11.0, GSK 6.1 ± 4.6, P=0.61). In addition, we did not detect any change in Th17, Th2, or regulatory T cells.Conclusions: In a pilot study of seven individuals treated with placebo or an sEH inhibitor, we found that the sEH inhibitor decreased pro-inflammatory Th1 cells as compared with placebo in matched AT samples. Understanding the contribution of the EET/sEH pathway to inflammation in obesity could lead to new strategies to modulate AT and systemic inflammation and reduce the risk of CVD.

Inhibition of CXCR2 by Glucocorticoids in Adipose Tissue

Obesity-induced chronic adipose tissue inflammation is a significant risk factor for metabolic and cardiovascular disease (CVD), which affects 30.3 million adults in the United States. Interaction of adipocytes with hormonal, metabolic and immune systems play an integral role in the underlying pathophysiological mechanisms that leads to development of obesity-related complications. Despite this association, the mechanisms that coordinate the inflammatory mediators in causing adipose tissue inflammation are not well understood. Glucocorticoids (GC) are well known for their potent anti-inflammatory actions; however, the mechanism by which GC coordinate the inflammatory response of adipocytes are unknown. From our genome-wide microarray data derived from adipocyte-specific glucocorticoid receptor (GR) knockout (AdipoGRKO) mice, we found that GR inactivation leads to a significant increase in pro-inflammatory gene in white adipose tissue (WAT). Additionally, WAT isolated from AdipoGRKO mice showed significant increase in immune cell infiltration, which correlates with our gene expression data. Among the top up-regulated genes, we found the C-X-C Motif Chemokine Receptor 2 (Cxcr2), which is a powerful mediator of chemotaxis to the sites of inflammation. Although studies have shown the presence of Cxcr2 in adipocytes and suggested the contribution of Cxcr2 signaling in adipocyte development, its role in integrating adipose tissue inflammatory response is unknown. This led us to hypothesize that GR is critical to repress Cxcr2 gene expression and its pro inflammatory effects in adipocytes. Our in vitro studies using 3T3-L1 cells derived adipocytes showed that treatment with the synthetic glucocorticoid, Dexamethasone (Dex) led to a significant repression of Cxcr2 mRNA and protein levels. Furthermore, these effects are mediated by GR acting directly to repress Cxcr2 gene expression. Systemic administration of corticosterone significantly altered Cxcr2 expression in adipose tissue compared to untreated mice further supporting our results. Together our findings suggest that administration of glucocorticoids could inhibit adipose tissue inflammation and alleviate the comorbidities that arise from inflamed adipose tissue.