Macrophage Accumulation In Adipose Tissue Research Articles

Kdm2a deficiency in macrophages enhances thermogenesis to protect mice against HFD-induced obesity by enhancing H3K36me2 at the Pparg locus

Kdm2a catalyzes H3K36me2 demethylation to play an intriguing epigenetic regulatory role in cell proliferation, differentiation, and apoptosis. Herein we found that myeloid-specific knockout of Kdm2a (LysM-Cre-Kdm2af/f, Kdm2a−/−) promoted macrophage M2 program by reprograming metabolic homeostasis through enhancing fatty acid uptake and lipolysis. Kdm2a−/− increased H3K36me2 levels at the Pparg locus along with augmented chromatin accessibility and Stat6 recruitment, which rendered macrophages with preferential M2 polarization. Therefore, the Kdm2a−/− mice were highly protected from high-fat diet (HFD)-induced obesity, insulin resistance, and hepatic steatosis, and featured by the reduced accumulation of adipose tissue macrophages and repressed chronic inflammation following HFD challenge. Particularly, Kdm2a−/− macrophages provided a microenvironment in favor of thermogenesis. Upon HFD or cold challenge, the Kdm2a−/− mice manifested higher capacity for inducing adipose browning and beiging to promote energy expenditure. Collectively, our findings demonstrate the importance of Kdm2a-mediated H3K36 demethylation in orchestrating macrophage polarization, providing novel insight that targeting Kdm2a in macrophages could be a viable therapeutic approach against obesity and insulin resistance.

C-C motif chemokine receptor 9 regulates obesity-induced insulin resistance via inflammation of the small intestine in mice.

Accumulation of adipose tissue macrophages is considered pivotal in the development of obesity-associated inflammation and insulin resistance. In addition, recent studies suggest an involvement of the intestine as the primary organ in inducing hyperglycaemia and insulin resistance. We have reported that the C-C motif chemokine receptor (CCR) CCR9 is associated with intestinal immunity and has a pathogenic role in various liver diseases. However, its contribution to type 2 diabetes is unknown. In the current study, we aimed to clarify the involvement of CCR9 in the pathology of type 2 diabetes and the potential underlying mechanisms. To elucidate how CCR9 affects the development of metabolic phenotypes, we examined the impact of CCR9 deficiency on the pathogenesis of type 2 diabetes using male C57BL/6J (wild-type [WT]) and CCR9-deficient (CCR9 knockout [KO]) mice fed a 60% high-fat diet (HFD) for 12weeks. WT and Ccr9KO mice fed an HFD exhibited a comparable weight gain; however, glucose tolerance and insulin resistance were significantly improved in Ccr9KO mice. Moreover, visceral adipose tissue (VAT) and the liver of Ccr9KO mice presented with less inflammation and increased expression of glucose metabolism-related genes than WT mice. Ccr9 and Ccl25 expression were specifically higher in the small intestine but was not altered by HFD feeding and type 2 diabetes development. Accumulation of IFN-γ-producing CD4+ T lymphocytes and increased intestinal permeability in the small intestine was observed in WT mice following HFD feeding, but these changes were suppressed in HFD-fed Ccr9KO mice. Adoptive transfer of gut-tropic CCR9-expressing T lymphocytes partially reversed the favourable glucose tolerance found in Ccr9KO mice via exacerbated inflammation in the small intestine and VAT. CCR9 plays a central role in the pathogenesis of type 2 diabetes by inducing an inflammatory shift in the small intestine. Our findings support CCR9 as a new therapeutic target for type 2 diabetes via the gut-VAT-liver axis.

Adipocytes and macrophages secretomes coregulate catecholamine-synthesizing enzymes.

Obesity associates with macrophage accumulation in adipose tissue where these infiltrating cells interact with adipocytes and contribute to the systemic chronic metabolic inflammation present in immunometabolic diseases. Tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) are two of the main enzymes of catecholamines (CA) synthesis. Adipocytes and macrophages produce, secrete and respond to CA, but the regulation of their synthesis in the interplay between immune and metabolic systems remains unknown. A model of indirect cell coculture with conditioned medium (CM) from RAW 264.7 macrophages with or without LPS-activation and 3T3-L1 adipocytes and preadipocytes was established to study the effect of cellular secretomes on the expression of the above enzymes. During the adipocyte differentiation process, we found a decrease of TH and PNMT expression. The secretome from LPS-activated macrophages downregulated TH and PNMT expression in preadipocytes, but not in mature adipocytes. Mature adipocytes CM induced a decrease of PNMT levels in RAW 264.7 macrophages. Pre and mature adipocytes showed a similar pattern of TH, PNMT and peroxisome proliferator-activated receptor gamma expression after exposure to pro and anti-inflammatory cytokines. We evidenced macrophages and adipocytes coregulate the expression of CA synthesis enzymes through secretome, with non-inflammatory signaling networks possibly being involved. Mediators released by macrophages seem to equally affect CA production by adipocytes, while adipocytes secretome preferentially affect AD production by macrophages. CA synthesis seems to be more determinant in early stages of adipogenic differentiation. Our results suggest that CA are key signaling molecules in the regulation of immune-metabolic crosstalk within the adipose tissue.

Nanocarriers targeting adipose macrophages increase glucocorticoid anti-inflammatory potency to ameliorate metabolic dysfunction.

Obesity is associated with systemic inflammation due to macrophage accumulation in adipose tissue (AT). AT macrophages are, therefore, a target for therapeutics to modulate inflammation and prevent comorbidities. Because inflammatory processes have pleiotropic effects throughout the body and are intertwined with metabolic axes, systemic anti-inflammatory therapies are often harmful. We report that targeting AT macrophages using dextran nanocarriers radically alters the pharmacology of anti-inflammatory glucocorticoids, uncoupling the metabolic axis in obese mice. Following a single treatment, expression of inflammatory mediators and markers of inflammatory macrophages decreased with a nearly 20-fold higher potency compared with free drug. As a result, long-term treatment resulted in potent fat mobilization, AT reduction, weight loss, improved glucose tolerance, and altered AT gene expression profiles that led to elevated liver stress. Two weeks after treatment ceased, gene expression of inflammatory mediators in AT remained lower than obese controls, while gene expression related to metabolic function improved. These data demonstrate that nanocarriers show potential for amelioration of obesity-related AT inflammation and metabolic dysfunction, highlighting an important opportunity for nanomedicine to impact chronic metabolic disorders with complex and poorly understood etiology.

Remodeling of Macrophages in White Adipose Tissue under the Conditions of Obesity as well as Lipolysis.

Adipose tissue macrophages (ATM) are a major source of low-grade inflammation in obesity, and yet reasons driving ATM accumulation in white adipose tissue (WAT) are not fully understood. Emerging evidence suggested that ATM underwent extensive remodeling in obesity. In addition to abundance, ATM in obesity were lipid-laden and metabolically reprogrammed, which in turn was tightly related to their functional alterations and persistence in obesity. Herein, we aimed to discuss that activation of lipid sensing signaling associated with metabolic reprogramming in ATM was indispensible for their migration, retention, or proliferation in obesity. Likewise, lipolysis also induced similar but transient ATM remodeling. Therefore, we assumed that obesity might share overlapping mechanisms with lipolysis in remodeling ATM. Formation of crown-like structures (CLS) in WAT was presumably a common event initiating ATM remodeling, with a spectrum of lipid metabolites released from adipocytes being potential signaling molecules. Moreover, adipose interlerkin-6 (IL-6) exhibited homologous alterations by obesity and lipolysis. Thus, we postulated a positive feedback loop between ATM and adipocytes via IL-6 signaling backing ATM persistence by comparison of ATM remodeling under obesity and lipolysis. An elucidation of ATM persistence could help to provide novel therapeutic targets for obesity-associated inflammation.

Talabostat Alleviates Obesity and Associated Metabolic Dysfunction via Suppression of Macrophage-Driven Adipose Inflammation.

Adipose tissue macrophages (ATMs) play critical roles in obesity-associated inflammation that contributes to metabolic dysfunction. Talabostat (TB) exerts some therapeutic effects on tumors and obesity. However, it remains unknown whether the metabolic benefits of TB on obesity is dependent on ATM-mediated adipose inflammation. Male C57BL/6J mice were fed a normal chow diet (NCD) or a high-fat diet for 12 weeks, and mice were orally administered TB daily at a low dose (0.5 mg/kg). Administration of TB to mice fed a high-fat diet significantly improved adiposity and obesity-associated metabolic dysfunction, including glucose intolerance and insulin resistance, hyperlipidemia and hepatic steatosis, which were accompanied by increased whole-body energy expenditure. RNA sequencing analysis revealed extensive alterations in the transcriptome profiles associated with lipid metabolism and immune responses in adipose tissue of obese mice. Notably, TB treatment led to a significant reduction in ATM accumulation and a shift of the activation state of ATMs from the proinflammatory M1-like to the anti-inflammatory M2-like phenotype. Moreover, depletion of ATMs significantly abolished the TB-induced metabolic benefits. Our study demonstrates that TB at a low dose could increase energy expenditure and control ATM-mediated adipose inflammation in obese mice, thereby alleviating obesity and its associated metabolic dysfunction.

Thermoneutrality-Induced Macrophage Accumulation in Brown Adipose Tissue Does Not Impair the Tissue's Competence for Cold-Induced Thermogenic Recruitment.

Brown adipose tissue from mice living under conditions approaching human thermal and nutritional conditions (prolonged exposure to thermoneutral temperature and to an energy-rich (high-fat, high-sugar) diet) — referred to as “physiologically humanized” mice, displays morphological and molecular characteristics significantly different from those observed in young, chow-fed mice maintained at room temperature — referred to as “standard” mice. Here, we further examined brown fat from physiologically humanized and standard mice, as well as from mice exposed to thermoneutrality for a long time but not to an energy-rich diet - referred to here as “long-term thermoneutral” mice. Global transcriptome analysis of brown fat revealed that genes that were the most upregulated in brown fat of thermoneutral mice (both physiologically humanized and long-term thermoneutral) were those related to inflammatory processes, including genes expressed selectively in macrophages. Cellular and molecular analyses confirmed that brown fat from thermoneutral mice was heavily infiltrated by macrophages, predominantly organized into crown-like structures. However, despite this, the brown fat of thermoneutral mice retained full competence to attain the greatest possible recruitment state and became macrophage-depleted during the process of cold acclimation. Thus, profound macrophage accumulation does not influence the thermogenic recruitment competence of brown fat.

Macrophage Accumulation and Angiogenesis in Epicardial Adipose Tissue in Cardiac Patients with or without Chronic Heart Failure

Routinely measuring epicardial fat had become a novel tool for cardiovascular risk stratification. Structural changes in epicardial adipose tissue (EAT), including fat thickness, inflammation, and angiogenesis, have been described in coronary artery disease (CAD) patients. We proposed to measure EAT thickness and characterize inflammatory infiltrate and angiogenesis in epicardial adipose tissue in CAD patients with and without chronic heart failure (CHF), established by cardiac dysfunction on echocardiography (left ventricular ejection fraction, LVEF ≤ 50%) and symptoms of heart failure (New York Heart Association (NYHA) functional class II or III).The study included 15 patients with CAD (demonstrated by coronary angiography),, who underwent right atrial appendages (RAA) excision during coronary artery bypass graft (CABG). The study was performed by histopathological, immunohistochemical (IHC), and morphometrical analysis. EAT thickness was assessed by using morphometry applied on routine histological stains. Inflammatory cell infiltration and angiogenesis were investigated immunohistochemically by using antibodies against CD68 and CD34 markers. Diminished EAT thickness in the CAD patients with CHF was associated with increased macrophage infiltration and reduced angiogenesis of the EAT as compared to CAD patients without CHF. In conclusion, the present study on epicardial fat samples of the RAA suggested that high expression of CD68 appeared to be associated with severe deterioration of heart function in CAD patients who underwent myocardial revascularization consisting of CABG.

Estrogen enhances browning in adipose tissue by M2 macrophage polarization via heme oxygenase-1.

Loss of ovarian function results in increased fat mass, leading to the accumulation of adipose tissue macrophages that participate in chronic inflammation. We hypothesized that ovariectomy (OVX)-induced increases in body weight and fat mass are associated with decreased adipose tissue (AT) browning due to estrogen (E2 ) deficiency. In mice, OVX decreased AT browning along with increased body weight, fat mass, and size of lipid droplets 12 weeks after surgery. Exogenous E2 recovered the OVX-induced changes. AT browning was enhanced by M2 macrophages induced by exogenous E2. E2 -induced M2 polarization occurred due to the increased expression of heme oxygenase-1 (HO-1) in macrophages, leading to decreased reactive oxygen species levels. Collectively, we demonstrated that E2 enhances AT browning via M2 polarization mediated by HO-1.

Inhibition of p38mapk Reduces Adipose Tissue Inflammation in Aging Mediated by Arginase-II

Background: Adipose tissue inflammation occurs not only in obesity but also in aging and is mechanistically linked with age-associated diseases. Studies show that ablation of the l-arginine-metabolizing enzyme arginase-II (Arg-II) reduces adipose tissue inflammation and improves glucose tolerance in obesity. However, the role of Arg-II in aging adipose tissue inflammation is not clear. Objective: This study investigated the role of Arg-II in age-associated adipose tissue inflammation. Methods: Visceral adipose tissues of young (3–6 months) and old (20–24 months) wild-type (WT) and Arg-II^−/− mice were investigated. Immunofluorescence confocal microscopy was performed for analysis of macrophage accumulation and cellular localization of arginase and cytokines; expression of arginase and cytokines was analyzed by qRT-PCR or immunoblotting or ELISA; activation of mitogen-activated protein kinases in adipose tissues was analyzed by immunoblotting; and arginase activity was measured by colorimetric determination of urea production. Results: In the old WT mice, there is more macrophage accumulation in the visceral adipose tissues than in Arg-II knockout animals. An age-associated increase in arginase activity and Arg-II expression in adipose tissues of WT mice is observed. Arg-II knockout enhances Arg-I expression and activity, but inhibits interleukin (IL)-6 expression and secretion and reduces active p38mapk in aging adipose tissue macrophages and stromal cells. Treatment of aging adipose tissues of WT mice with a specific p38mapk inhibitor SB203580 reduces IL-6 secretion. Conclusions: Arg-II promotes IL-6 production in aging adipose tissues through p38mapk. The results suggest that targeting Arg-II or inhibiting p38mapk could be beneficial in reducing age-associated adipose tissue inflammation.

SUN-LB101 NRF2 Represses Obesity-Associated Adipose Tissue Inflammation in Mice

Obesity is associated with type 2 diabetes, cardiovascular disease and increased incidence of cancer. Chronic inflammation, mainly emanating from adipose tissue, has been proposed to be one of the links between obesity and these pathologies. Thus, identification of new targets against obesity and especially obesity-induced inflammation is needed urgently. Transcription factor Nrf2 (NF-E2-related-factor-2) plays a central role in cytoprotective responses to oxidative and electrophilic stresses and also exerts anti-inflammatory effects in rodent models of inflammation. However, whether activation of Nrf2 signaling pathway influences obesity-associated inflammation in adipose tissue is not well established. To this end, we generated mice with systemic activation of the Nrf2 pathway (Keap1flox/–), as well as mouse models with tissue-specific Nrf2 pathway activation: adipocyte-specific (Fabp4Cre::Keap1flox/ flox) and myeloid cell-specific (LymCre::Keap1flox/ flox). These mice were exposed to a high-fat diet (HFD) 60% kcal fat regimen for 6-weeks or crossed into the db/db background. Keap1flox/– mice showed a dramatic decrease of the numbers of F4/80-positive macrophages in white adipose tissue (WAT). Interestingly, both Fabp4Cre::Keap1flox/ flox and LymCre::Keap1flox/ flox mice showed suppression of F4/80-positive macrophages in WAT as well, suggesting enhanced Nrf2 signaling in either adipocytes or myeloid cells might contribute to anti-inflammatory effects in WAT under the stress of HFD. Transcript levels of inflammatory markers, especially macrophage F4/80 and Cd68 and the chemokine Ccl2 were decreased in the WAT from Keap1flox/– mice on the standard diet and also in the WAT of Keap1flox/– mice in the db/db background. Pharmacological activation of the Nrf2 pathway by treatment with CDDO-Im also suppressed Ccl2 expression in WAT of HFD fed mice and db/db mice. As CCL2 is a key mediator of macrophage accumulation in adipose tissue, we further studied the potential effect of Nrf2 on the transcriptional regulation of Ccl2 using 3T3-L1 preadipocyte and RAW264.7 macrophage cell lines. Treatment of both lines with the small molecule inducer of Nrf2, diethyl maleate significantly suppressed LPS-induced expression of Ccl2. Analysis using luciferase reporter assay revealed that a Nrf2 binding site in the Ccl2 5’ flanking region from -235 to +85 contributed to gene silencing of Ccl2 by activation of Nrf2. Our findings suggest that the druggable Nrf2 pathway may be an effective target to combat obesity-associated inflammation in adipose tissue and its’ concomitant metabolic disorders. Supported by AMED BINDS JP19am0101001 (MY), 19H05649 (MY), 16KK0195 (AU), NIH R35 CA197222 (TWK), JSPS OT 290125 (YY).

Treatment of growth hormone attenuates hepatic steatosis in hyperlipidemic mice via downregulation of hepatic CD36 expression

ABSTRACT The recombinant human growth hormone (GH) has been used for the treatment of growth hormone deficiency (GHD) and diverse short stature state, and its physiological and therapeutic effects are well documented. However, since the effect of GH treatment on metabolic disorders has not been well characterized, we injected GH to Western diet-fed low-density lipoprotein receptor-deficient (Ldlr −/−) mice to understand the exact effect of GH on metabolic diseases including atherosclerosis, hepatic steatosis, and obesity. Exogenous GH treatment increased plasma IGF-1 concentration and decreased body weight without affecting serum lipid profiles. GH treatment changed neither atherosclerotic lesion size nor collagen and smooth muscle cells accumulation in the lesion. GH treatment reduced macrophage accumulation in adipose tissue. Importantly, GH treatment attenuated hepatic steatosis and inflammation. The hepatic expression IL-1β mRNA were decreased by GH treatment. The mRNA and protein levels of CD36 were markedly decreased in GH treated mice without significant changes in other molecules related to lipid metabolism. Therefore, the treatment of GH treatment could attenuate hepatic steatosis and inflammation with downregulation of CD36 expression in hyperlipidemic condition.

2-Methoxyestradiol inhibits high fat diet-induced obesity in rats through modulation of adipose tissue macrophage infiltration and immunophenotype

Recently, experimental studies demonstrated that 2-methoxyestradiol (2ME2) ameliorates high fat diet (HFD)-induced obesity and restores insulin sensitivity. However, the mechanisms underlying these effects are unveiled yet. The current study was undertaken to test the hypothesis that 2ME2 exerts its effects by modulating adipose tissue macrophages (ATMs) accumulation, polarization and immunophenotypes. The experiment was carried out in males Wistar rats (n = 28) for 13 consecutive weeks. In HFD-fed group; body weight, glucose intolerance, serum insulin, HOMA-IR, lipid profile and adipose tissue (AT) weight were significantly higher compared to normal standard diet (NSD)- fed rats. However, treatment of HFD-fed rats with 2ME2 (200 μg/kg/day; i.p. from the beginning of the 9th week) resulted in significant enhancements in all these parameters as compared to HFD-fed rats. Treatment with 2ME2 was associated with a significant reduction in macrophage infiltration in the AT, shifting macrophage polarization towards M2 phenotype as indicated by significant decrease in the expression of pro-inflammatory M1 macrophages markers (IL-6, IL-1β, CD11c and iNOS) and concurrent significant increase in the M2 anti-inflammatory macrophage markers (Arginase 1 and IL-10). 2ME2 ameliorates HFD-induced obesity and glucose intolerance through inhibition of ATM infiltration in AT and shifting macrophage polarization from pro-inflammatory M1 to M2 anti-inflammatory phenotypes.

Adipose tissue macrophages: Unique polarization and bioenergetics in obesity.

Macrophages comprise a majority of the resident immune cells in adipose tissue (AT) and regulate both tissue homeostasis in the lean state and metabolic dysregulation in obesity. Since the AT environment rapidly changes based upon systemic energy status, AT macrophages (ATMs) must adapt phenotypically and metabolically. There is a distinct dichotomy in the polarization and bioenergetics of in vitro models, with M2 macrophages utilizing oxidative phosphorylation (OX PHOS) and M1 macrophages utilizing glycolysis. Early studies suggested differential polarization of ATMs, with M2-like macrophages predominant in lean AT and M1-like macrophages in obese AT. However, recent studies show that the phenotypic plasticity of ATMs is far more complicated, which is also reflected in their bioenergetics. Multiple ATM populations exist along the M2 to M1 continuum and appear to utilize both glycolysis and OX PHOS in obesity. The significance of the dual fuel bioenergetics is unclear and may be related to an intermediate polarization, their buffering capacity, or the result of a mixed population of distinct polarized ATMs. Recent evidence also suggests that ATMs of lean mice serve as a substrate buffer or reservoir to modulate lipid, catecholamine, and iron availability. Furthermore, recent models of weight loss and weight cycling reveal additional roles for ATMs in systemic metabolism. Evaluating ATM phenotype and intracellular metabolism together may more accurately illuminate the consequences of ATM accumulation in obese AT, lending further insight into obesity-related comorbidities in humans.

Deoxyhypusine Synthase Promotes a Pro-Inflammatory Macrophage Phenotype

Obesity is characterized by adipose tissue expansion, macrophage infiltration, and the development of chronic low-grade meta-inflammation that drives insulin resistance and metabolic dysfunction. Eukaryotic translation initiation factor 5A (eIF5A) is the only protein known to be uniquely post-translationally modified and activated by deoxyhypusine synthase (DHPS) to generate a hypusine (Hyp) residue. Activated eIF5A controls the translation of a subset of mRNAs that play a role in inflammation, but a role for the DHPS/eIF5AHyp axis in obesity-associated adipose tissue inflammation has not been tested. We found DHPS/eIF5AHyp levels to be increased in the stromal vascular fraction of adipose tissue from mice fed a high fat diet and in murine macrophages activated to a proinflammatory M1 phenotype. DHPS deficiency in M1 macrophages decreased global mRNA translation and protein synthesis of key inflammatory mediators, IL-1β and MIP-1α. Transcriptomes of LPS+IFN-γ-stimulated DHPS-deficient macrophages revealed reduced characteristics of an M1 signature and a phenotypic switch consistent with characteristics of an anti-inflammatory M2 signature. In support of these observations, macrophage migration in a zebrafish tailfin injury model was reduced with chemical inhibition of DHPS, and DHPS deficiency in myeloid cells of HFD-fed mice inhibited M1 macrophage accumulation in adipose tissue and improved glucose tolerance. Together, these findings indicate that DHPS is required for the translation of a subset of mRNAs required for inflammation and chemotaxis in macrophages and may contribute to a proinflammatory M1-like phenotype.

Enhanced glycolysis and HIF-1\u03b1 activation in adipose tissue macrophages sustains local and systemic interleukin-1\u03b2 production in obesity

During obesity, macrophages infiltrate the visceral adipose tissue and promote inflammation that contributes to type II diabetes. Evidence suggests that the rewiring of cellular metabolism can regulate macrophage function. However, the metabolic programs that characterize adipose tissue macrophages (ATM) in obesity are poorly defined. Here, we demonstrate that ATM from obese mice exhibit metabolic profiles characterized by elevated glycolysis and oxidative phosphorylation, distinct from ATM from lean mice. Increased activation of HIF-1α in ATM of obese visceral adipose tissue resulted in induction of IL-1β and genes in the glycolytic pathway. Using a hypoxia-tracer, we show that HIF-1α nuclear translocation occurred both in hypoxic and non-hypoxic ATM suggesting that both hypoxic and pseudohypoxic stimuli activate HIF-1α and its target genes in ATM during diet-induced obesity. Exposure of macrophages to the saturated fatty acid palmitate increased glycolysis and HIF-1α expression, which culminated in IL-1β induction thereby simulating pseudohypoxia. Using mice with macrophage-specific targeted deletion of HIF-1α, we demonstrate the critical role of HIF-1α-derived from macrophages in regulating ATM accumulation, and local and systemic IL-1β production, but not in modulating systemic metabolic responses. Collectively, our data identify enhanced glycolysis and HIF-1α activation as drivers of low-grade inflammation in obesity.

CD11c-MHC2low Macrophages Are a New Inflammatory and Dynamic Subset in Murine Adipose Tissue.

BackgroundThe prevalence of obesity is rising and leads to increased morbidity and mortality. Adipose tissue inflammation, due to accumulation and activation of adipose tissue macrophages (ATMs), is a key driver of this phenomenon. Macrophages are heterogeneous cells, adapting quickly to the microenvironment, resulting in so-called M1 or M2 macrophages. In this study, we describe the dynamics and inflammatory properties of a newly identified ATM subset in obese mice.MethodsLDLR-/- mice received a high fat diet (HFD) for 5 weeks or 16 weeks to induce obesity. Adipose tissues were isolated and immune cell subsets were analyzed with flow cytometry or microarray analysis. Bone marrow transplantation (BMT) using CD45.1 and CD45.2 LDLR-/- mice was performed to determine ATM origin.ResultsUpon HFD, there is a massive increase of ATM subsets in the adipose tissue. CD11c−M2 ATMs could be subdivided based on their MHC2 expression into CD11c−MHC2high ATMs and previously unidentified CD11c−MHC2low ATMs. CD11c−MHC2low ATMs accumulated very rapidly after 10 days of HFD, after which they increased even further with prolonged HFD. Microarray data showed that CD11c−MHC2low ATMs resembled CD11c−MHC2high ATMs in the steady state, but became more inflammatory during development of obesity. In vitro stimulation of bone marrow-derived macrophages with palmitate, abundantly present in HFD, resulted in the induction of the CD11c−MHC2low phenotype.ConclusionsAmong M2 macrophages, a novel pro-inflammatory subset of macrophages was found based on their low level of MHC2 expression. This subset may play a role in the development of adipose tissue inflammation.

High-fat diet triggers obesity-related early infiltration of macrophages into adipose tissue and transient reduction of blood monocyte count

Infiltration of adipose tissue macrophages (ATMs) is a typical feature of obesity, and circulating immune cells may indicate immune cell accumulation. However, it remains unclear whether this is true in the early stages of obesity. This study aimed to define the role of blood monocytes in obesity and the relationship between blood monocytes and ATMs in early-stage obesity. Two groups of male C57BL/6 J mice were fed on a 60 % high-fat diet (HFD) or a 10 % fat normal diet (ND), respectively, and monitored at 1, 2, 3, 7, and 12 weeks. Populations of circulating blood monocytes (CD11b + CD115+), ATMs (F4/80+CD11b+), and their subtypes were collected and analyzed using flow cytometry and immunofluorescence. Some cytokines (TNF-a, IL-1β) and chemokines (CCL2, CCL7) were also analyzed by real-time PCR. HFD induced obesity, dramatic fat expansion, and accumulation of ATMs in mice after 12 weeks. However, an acute and transient reduction of circulating monocyte count, elevated expression of CD11c in ly6clow monocytes, and concurrent infiltration of ATMs into visceral adipose tissues (VAT) were observed as early as 1 week after initiating HFD. Further, HFD-induced changes in VAT, but not blood monocyte count, were partially reversed upon reverting to ND for 6 weeks. An acute but transient reduction of blood monocyte count was observed at the early stages of HFD feeding, which might be related to early infiltration of macrophages into adipose tissues. We believe that blood monocytes could be targeted as a new obesity treatment following additional studies.

A350 Macrophage of adipose tissue inhibited adipocyte differentiation via Fas signaling reducing Akt in obesity

The obesity epidemic has forced efforts to understand the mechanisms controlling adipocytes differentiation and adiposetissue development. Adipose tissue, primarily composed of mature adipocytes and stromal vascular fraction (SVF)cells, goes through a series of changes in its quantity and composition during the onset and development of obesity and plays a key role in maintaining both whole body energy homeostasis and endocrine function. Adipose tissue macrophages (ATMs)accumulation has been reported to participate in inflammatory pathways that are activated in adipose tissues of obese individual. This study were designed to understand the roles that SVF cells and ATMs play in adipogenic differentiation and explore its detailed signal transduction mechanisms.

MiR-146a Deficiency Accelerates Hepatic Inflammation Without Influencing Diet-induced Obesity in Mice

miR-146a, an anti-inflammatory microRNA, is shown to be a negative regulator of adipocyte inflammation. However, the functional contribution of miR-146a in the development of obesity is not defined. In order to determine whether miR-146a influences diet-induced obesity, mice that were either wild type (WT) or miR-146a deficient (KO) were fed with high (60% kcal) fat diet (HFD) for 16 weeks. Deficiency of miR-146a did not influence obesity measured as HFD-induced body weight and fat mass gain, or metabolism of glucose and insulin tolerance. In addition, adipocyte apoptosis, adipose tissue collagen and macrophage accumulation as detected by TUNEL, Picro Sirius and F4/80 immunostaining, respectively, were comparable between the two groups of mice. Although, miR-146a deficiency had no influence on HFD-induced hepatic lipid accumulation, interestingly, it significantly increased obesity-induced inflammatory responses in liver tissue. The present study demonstrates that miR-146a deficiency had no influence on the development of HFD-induced obesity and adipose tissue remodeling, whereas it significantly increased hepatic inflammation in obese mice. This result suggests that miR-146a regulates hepatic inflammation during development of obesity.