Adipose Tissue Macrophage Inflammation Research Articles

Myeloid SENP3 deficiency protects mice from diet and age-induced obesity via regulation of YAP1 SUMOylation

Obesity is characterized by chronic low-grade inflammation, which is driven by macrophage infiltration in adipose tissue and leads to elevated cytokines such as interleukin-1β (IL-1β) in the circulation and tissues. Previous studies demonstrate that SENP3, a redox-sensitive SUMO2/3-specific protease, is strongly implicated in the development and progression of cancer and cardiovascular diseases. However, the role of SENP3 in obesity-associated inflammation remains largely unknown. To better understand the effects of SENP3 on adipose tissue macrophage (ATM) activation and function within the context of obesity, we generated mice with myeloid-specific deletion of SENP3 (Senp3flox/flox;Lyz2-Cre mice). We found that the expression of SENP3 is dramatically increased in ATMs during high-fat diet (HFD)-induced obesity in mice. Senp3flox/flox;Lyz2-Cre mice show lower body weight gain and reduced adiposity and adipocyte size after challenged with HFD and during aging. Myeloid-specific SENP3 deletion attenuates macrophage infiltration in adipose tissue and reduces serum levels of inflammatory factors during diet and age-induced obesity. Furthermore, we found that SENP3 knockout markedly inhibits cytokine release from macrophage after lipopolysaccharide and palmitic acid treatment in vitro. Mechanistically, in cultured peritoneal macrophages, SENP3 protein level is enhanced by IL-1β, in parallel with the upregulation of Yes-associated protein 1 (YAP1). Moreover, we demonstrated that SENP3 modulates de-SUMO modification of YAP1 and SENP3 deletion abolishes the upregulation of YAP1 induced by IL-1β. Most importantly, SENP3 deficiency reduces YAP1 protein level in adipose tissue during obesity. Our results highlight the important role of SENP3 in ATM inflammation and diet and age-induced obesity.

Ponatinib modulates the metabolic profile of obese mice by inhibiting adipose tissue macrophage inflammation.

Obesity-induced metabolic syndrome is a rapidly growing conundrum, reaching epidemic proportions globally. Chronic inflammation in obese adipose tissue plays a key role in metabolic syndrome with a series of local and systemic effects such as inflammatory cell infiltration and inflammatory cytokine secretion. Adipose tissue macrophages (ATM), as one of the main regulators in this process, are particularly crucial for pharmacological studies on obesity-related metabolic syndrome. Ponatinib, a multi-targeted tyrosine kinase inhibitor originally used to treat leukemia, has recently been found to improve dyslipidemia and atherosclerosis, suggesting that it may have profound effect on metabolic syndrome, although the mechanisms underlying have not yet been revealed. Here we discovered that ponatinib significantly improved insulin sensitivity in leptin deficient obese mice. In addition to that, ponatinib treatment remarkably ameliorated high fat diet-induced hyperlipidemia and inhibited ectopic lipid deposition in the liver. Interestingly, although ponatinib did not reduce but increase the weight of white adipose tissue (WAT), it remarkably suppressed the inflammatory response in WAT and preserved its function. Mechanistically, we showed that ponatinib had no direct effect on hepatocyte or adipocyte but attenuated free fatty acid (FFA) induced macrophage transformation from pro-inflammatory to anti-inflammatory phenotype. Moreover, adipocytes co-cultured with FFA-treated macrophages exhibited insulin resistance, while pre-treat these macrophages with ponatinib can ameliorate this process. These results suggested that the beneficial effects of ponatinib on metabolic disorders are achieved by inhibiting the inflammatory phenotypic transformation of ATMs, thereby maintaining the physiological function of adipose tissue under excessive obesity. The data here not only revealed the novel therapeutic function of ponatinib, but also provided a theoretical basis for the application of multi-target tyrosine kinase inhibitors in metabolic diseases.

Visceral adipose tissue-directed FGF21 gene therapy improves metabolic and immune health in BTBR mice

Fibroblast growth factor 21 (FGF21) is a peptide hormone that serves as a potent effector of energy homeostasis. Increasingly, FGF21 is viewed as a promising therapeutic agent for type 2 diabetes, fatty liver disease, and other metabolic complications. Exogenous administration of native FGF21 peptide has proved difficult due to unfavorable pharmacokinetic properties. Here, we utilized an engineered serotype adeno-associated viral (AAV) vector coupled with a dual-cassette design to selectively overexpress FGF21 in visceral adipose tissue of insulin-resistant BTBR T+Itpr3tf/J (BTBR) mice. Under high-fat diet conditions, a single, low-dose intraperitoneal injection of AAV-FGF21 resulted in sustained benefits, including improved insulin sensitivity, glycemic processing, and systemic metabolic function and reduced whole-body adiposity, hepatic steatosis, inflammatory cytokines, and adipose tissue macrophage inflammation. Our study highlights the potential of adipose tissue as a FGF21 gene-therapy target and the promise of minimally invasive AAV vectors as therapeutic agents for metabolic diseases.

Luteolin reduces adipose tissue macrophage inflammation and insulin resistance in postmenopausal obese mice

Previously, we showed that loss of ovarian function in mice fed high-fat diet exacerbated insulin resistance and adipose tissue inflammation. In the current study, we tested whether consumption of luteolin, an anti-inflammatory flavonoid, could mitigate adipose tissue inflammation and insulin resistance in obese ovariectomized mice. Nine-week-old ovariectomized C57BL/6 mice were fed a low-fat diet, high-fat diet (HFD) or HFD supplemented with 0.005% luteolin (HFD+L) for 16 weeks. Results showed no difference in body weight or fat mass between mice fed HFD+L and those fed HFD. However, luteolin supplementation resulted in lower CD11c+ macrophages in gonadal adipose tissue, as well as a trend toward lower macrophage infiltration. Luteolin supplementation also significantly lowered mRNA expression of inflammatory and M1 markers MCP-1, CD11c, TNF-α and IL-6, while maintaining expression of M2 marker MGL1. Consistent with this, the in vitro luteolin treatment, with or without the presence of estrogen, inhibited lipopolysaccharide-induced polarization of RAW 264.7 cells toward M1 phenotype. We further found that luteolin supplementation protected mice from insulin resistance induced by HFD consumption; this improved insulin resistance was correlated with reductions in CD11c+ adipose tissue macrophages. Taken together, these findings indicate that dietary luteolin supplementation attenuates adipose tissue inflammation and insulin resistance found in mice with loss of ovarian function coupled with an HFD intake, and this effect may be partly mediated through suppressing M1-like polarization of macrophages in adipose tissue. These results have clinical implication in implementing dietary intervention for prevention of metabolic syndrome associated with postmenopause and obesity.

Clcn3 deficiency ameliorates high-fat diet-induced obesity and adipose tissue macrophage inflammation in mice.

Obesity induces accumulation of adipose tissue macrophages (ATMs) and ATM-driven inflammatory responses that promote the development of glucose and lipid metabolism disorders. ClC-3 chloride channel/antiporter, encoded by the Clcn3, is critical for some basic cellular functions. Our previous work has shown significant alleviation of type 2 diabetes in Clcn3 knockout (Clcn3−/−) mice. In the present study we investigated the role of Clcn3 in high-fat diet (HFD)-induced obesity and ATM inflammation. To establish the mouse obesity model, both Clcn3−/− mice and wild-type mice were fed a HFD for 4 or 16 weeks. The metabolic parameters were assessed and the abdominal total adipose tissue was scanned using computed tomography. Their epididymal fat pad tissue and adipose tissue stromal vascular fraction (SVF) cells were isolated for analyses. We found that the HFD-fed Clcn3−/− mice displayed a significant decrease in obesity-induced body weight gain and abdominal visceral fat accumulation as well as an improvement of glucose and lipid metabolism as compared with HFD-fed wild-type mice. Furthermore, the Clcn3 deficiency significantly attenuated HFD-induced ATM accumulation, HFD-increased F4/80+ CD11c+ CD206− SVF cells as well as HFD-activated TLR-4/NF-κB signaling in epididymal fat tissue. In cultured human THP-1 macrophages, adenovirus-mediated transfer of Clcn3 specific shRNA inhibited, whereas adenovirus-mediated cDNA overexpression of Clcn3 enhanced lipopolysaccharide-induced activation of NF-κB and TLR-4. These results demonstrate a novel role for Clcn3 in HFD-induced obesity and ATM inflammation.

Macrophage Lamin A/C Regulates Inflammation and the Development of Obesity-Induced Insulin Resistance.

Obesity-induced chronic low-grade inflammation, in particular in adipose tissue, contributes to the development of insulin resistance and type 2 diabetes. However, the mechanism by which obesity induces adipose tissue inflammation has not been completely elucidated. Recent studies suggest that alteration of the nuclear lamina is associated with age-associated chronic inflammation in humans and fly. These findings led us to investigate whether the nuclear lamina regulates obesity-mediated chronic inflammation. In this study, we show that lamin A/C mediates inflammation in macrophages. The gene and protein expression levels of lamin A/C are significantly increased in epididymal adipose tissues from obese rodent models and omental fat from obese human subjects compared to their lean controls. Flow cytometry and gene expression analyses reveal that the protein and gene expression levels of lamin A/C are increased in adipose tissue macrophages (ATMs) by obesity. We further show that ectopic overexpression of lamin A/C in macrophages spontaneously activates NF-κB, and increases the gene expression levels of proinflammatory genes, such as Il6, Tnf, Ccl2, and Nos2. Conversely, deletion of lamin A/C in macrophages reduces LPS-induced expression of these proinflammatory genes. Importantly, we find that myeloid cell-specific lamin A/C deficiency ameliorates obesity-induced insulin resistance and adipose tissue inflammation. Thus, our data suggest that lamin A/C mediates the activation of ATM inflammation by regulating NF-κB, thereby contributing to the development of obesity-induced insulin resistance.

Hepatocyte-secreted DPP4 in obesity promotes adipose inflammation and insulin resistance.

Obesity-induced metabolic disease involves functional integration among several organs via circulating factors, but little is known about crosstalk between liver and visceral adipose tissue (VAT). In obesity, VAT becomes populated with inflammatory adipose tissue macrophages (ATMs). In obese humans, there is a close correlation between adipose tissue inflammation and insulin resistance, and in obese mice, blocking systemic or ATM inflammation improves insulin sensitivity. However, processes that promote pathological adipose tissue inflammation in obesity are incompletely understood. Here we show that obesity in mice stimulates hepatocytes to synthesize and secrete dipeptidyl peptidase 4 (DPP4), which acts with plasma factor Xa to inflame ATMs. Silencing expression of DPP4 in hepatocytes suppresses inflammation of VAT and insulin resistance; however, a similar effect is not seen with the orally administered DPP4 inhibitor sitagliptin. Inflammation and insulin resistance are also suppressed by silencing expression of caveolin-1 or PAR2 in ATMs; these proteins mediate the actions of DPP4 and factor Xa, respectively. Thus, hepatocyte DPP4 promotes VAT inflammation and insulin resistance in obesity, and targeting this pathway may have metabolic benefits that are distinct from those observed with oral DPP4 inhibitors.

Metabolically Activated Adipose Tissue Macrophages Perform Detrimental and Beneficial Functions during Diet-Induced Obesity

During obesity, adipose tissue macrophages (ATMs) adopt a metabolically activated (MMe) phenotype. However, the functions of MMe macrophages are poorly understood. Here, we combine proteomic and functional methods to demonstrate that, in addition to potentiating inflammation, MMe macrophages promote dead adipocyte clearance through lysosomal exocytosis. We identify NADPH oxidase2 (NOX2) as a driver of the inflammatory and adipocyte-clearing properties of MMe macrophages and show that, compared to wild-type, Nox2-/- mice exhibit a time-dependent metabolic phenotype during diet-induced obesity. After 8weeks of high-fat feeding, Nox2-/- mice exhibit attenuated ATM inflammation and mildly improved glucose tolerance. After 16weeks of high-fat feeding, Nox2-/- mice develop severe insulin resistance, hepatosteatosis, and visceral lipoatrophy characterized by dead adipocyte accumulation and defective ATM lysosomal exocytosis, a phenotype reproduced in myeloid cell-specific Nox2-/- mice. Collectively, our findings suggest that MMe macrophages perform detrimental and beneficial functions whose contribution to metabolic phenotypes during obesity is determined by disease progression.

Prenatal methyl-donor supplemented diet increases endoplasmic reticulum stress and inflammation in adipose tissue CD11b+ cells in F1 mice

Abstract The risk for development of metabolic and cardiovascular diseases in later life is increasing, as the population is becoming overweight and obese at earlier ages. Early-life nutritional programming influences late-life disease susceptibility across generations, in part through epigenetic mechanisms including DNA methylation. Using mouse models, it has been shown that prenatal diet rich in methyl donors (L-methionine, vitamin B-12, folic acid, choline, betaine, zinc) can increase airway reactivity but improves cardiovascular disease outcomes in F1 mice. Here, we used a prenatal diet enriched with methyl-donors to study the impact of the prenatal diet in the context of diet-induced obese F1 C57Bl/6 mice fed a 40% high-fat diet (HFD) for 16 weeks. F1 mice exposed to the prenatal methyl donor supplemented diet have increased number of adipose tissue ‘crown-like structures’ consisting of primarily CD11b+ cells. The prenatal diet was found to increase the expression of adipose tissue endoplasmic reticulum (ER) stress response genes Chop, Bip, and Atf4 in HFD F1 mice. Obesity-induced ER stress has been linked to adipose tissue chronic inflammation. We have previously established that ER stress contributes to aging adipose tissue macrophage inflammation. Interestingly, Mcp-1 and Tnfα gene expression were found to be increased in the CD11b+ cells of F1 mice adipose tissue. The results strongly support an important role of prenatal methyl-donors exposure in modulating diet-induced obesity ER stress response and inflammation in offspring.

Sphingosine kinase 1 regulates adipose proinflammatory responses and insulin resistance

Adipose dysfunction resulting from chronic inflammation and impaired adipogenesis has increasingly been recognized as a major contributor to obesity-mediated insulin resistance, but the molecular mechanisms that maintain healthy adipocytes and limit adipose inflammation remain unclear. Here, we used genetic and pharmacological approaches to delineate a novel role for sphingosine kinase 1 (SK1) in metabolic disorders associated with obesity. SK1 phosphorylates sphingosine to form sphingosine 1 phosphate (S1P), a bioactive sphingolipid with numerous roles in inflammation. SK1 mRNA expression was increased in adipose tissue of diet-induced obese (DIO) mice and obese type 2 diabetic humans. In DIO mice, SK1 deficiency increased markers of adipogenesis and adipose gene expression of the anti-inflammatory molecules IL-10 and adiponectin and reduced adipose tissue macrophage (ATM) recruitment and proinflammatory molecules TNFα and IL-6. These changes were associated with enhanced insulin signaling in adipose and muscle and improved systemic insulin sensitivity and glucose tolerance in SK1(-/-) mice. Specific pharmacological inhibition of SK1 in WT DIO mice also reduced adipocyte and ATM inflammation and improved overall glucose homeostasis. These data suggest that the SK1-S1P axis could be an attractive target for the development of treatments to ameliorate adipose inflammation and insulin resistance associated with obesity and type 2 diabetes.

Regulation of Diet-Induced Adipose Tissue and Systemic Inflammation by Salicylates and Pioglitazone

It is increasingly accepted that chronic inflammation participates in obesity-induced insulin resistance and type 2 diabetes (T2D). Salicylates and thiazolidinediones (TZDs) both have anti-inflammatory and anti-hyperglycemic properties. The present study compared the effects of these drugs on obesity-induced inflammation in adipose tissue (AT) and AT macrophages (ATMs), as well as the metabolic and immunological phenotypes of the animal models. Both drugs improved high fat diet (HFD)-induced insulin resistance. However, salicylates did not affect AT and ATM inflammation, whereas Pioglitazone improved these parameters. Interestingly, HFD and the drug treatments all modulated systemic inflammation as assessed by changes in circulating immune cell numbers and activation states. HFD increased the numbers of circulating white blood cells, neutrophils, and a pro-inflammatory monocyte subpopulation (Ly6Chi), whereas salicylates and Pioglitazone normalized these cell numbers. The drug treatments also decreased circulating lymphocyte numbers. These data suggest that obesity induces systemic inflammation by regulating circulating immune cell phenotypes and that anti-diabetic interventions suppress systemic inflammation by normalizing circulating immune phenotypes.

AMPK regulates macrophage polarization in adipose tissue inflammation and NASH

Molecular and Translational Medicine, Dept. of Medicine I, University Medical Center, Johannes Gutenberg University Mainz, Langenbeckstrase 1,55116 Mainz, GermanyCOMMENTARY ON:Hematopoietic AMPK beta1 reduces mouse adipose tissue mac-rophage inflammation and insulin resistance in obesity. Galic S,Fullerton MD, Schertzer JD, Sikkema S, Marcinko K, Walkley CR,Izon D, Honeyman J, Chen ZP, van Denderen BJ, Kemp BE, Stein-berg GR. J Clin Invest 2011;121(12):4903–15. Copyright 2011.Reprinted with permission of American Society for ClinicalInvestigation.http://www.ncbi.nlm.nih.gov/pubmed/22080866Abstract: Individuals who are obese are frequently insulin resistant,putting them at increased risk of developing type 2 diabetes and itsassociated adverse health conditions. The accumulation in adiposetissue of macrophages in an inflammatory state is a hallmark ofobesity-induced insulin resistance. Here, we reveal a role for AMPKb1 in protecting macrophages from inflammation under high lipidexposure. Genetic deletion of the AMPK b1 subunit in mice (referredto herein as b1( / ) mice) reduced macrophage AMPK activity,acetyl-CoA carboxylase phosphorylation, and mitochondrial content,resulting in reduced rates of fatty acid oxidation. b1( / ) macro-phages displayed increased levels of diacylglycerol and markers ofinflammation, effects that were reproduced in WT macrophages byinhibiting fatty acid oxidation and, conversely, prevented by phar-macological activation of AMPK b1-containing complexes. The effectof AMPK b1 loss in macrophages was tested in vivo by transplanta-tion of bone marrow from WT or b1( / ) mice into WT recipients.When challenged with a high-fat diet, mice that received b1( / )bone marrowdisplayedenhancedadiposetissue macrophage inflam-mation and liver insulin resistance compared with animals thatreceived WT bone marrow. Thus, activation of AMPK b1 and increas-ing fatty acid oxidation in macrophages may represent a new thera-peutic approach for the treatment of insulin resistance. 2011 European Association for the Study of the Liver. Publishedby Elsevier B.V. All rights reserved.Obesity has long been linked to type 2 diabetes (T2D), but theinvolved metabolic dysregulation is incompletely understood.Galic et al. [1] recently reported that adenosine monophosphatekinase (AMPK) b1 plays a hitherto unknown role in modulatingobesity-induced insulin resistance. AMPK is a central regulatorof energy balance. Decreased cellular energy status, as reflectedby accumulation of AMP, activates AMPK which turns on expres-sion of catabolic enzymes that permit ATP production and shutsdown energy consuming biosynthetic pathways. Thus, AMPK isa central regulator of fatty acid, cholesterol, and glucose homeo-stasis through phosphorylation of metabolism-regulatingenzymes including acetyl-CoA carboxylase (ACC), glycogen syn-thase (GS), glucose transporter 4 (GLUT4), HMG-CoA reductase,hormone-sensitive lipase (HSL), and mammalian target of rapa-mycin (mTOR). AMPK is a heterotrimer of a catalytic

Hematopoietic AMPK β1 reduces mouse adipose tissue macrophage inflammation and insulin resistance in obesity

Individuals who are obese are frequently insulin resistant, putting them at increased risk of developing type 2 diabetes and its associated adverse health conditions. The accumulation in adipose tissue of macrophages in an inflammatory state is a hallmark of obesity-induced insulin resistance. Here, we reveal a role for AMPK β1 in protecting macrophages from inflammation under high lipid exposure. Genetic deletion of the AMPK β1 subunit in mice (referred to herein as β1(-/-) mice) reduced macrophage AMPK activity, acetyl-CoA carboxylase phosphorylation, and mitochondrial content, resulting in reduced rates of fatty acid oxidation. β1(-/-) macrophages displayed increased levels of diacylglycerol and markers of inflammation, effects that were reproduced in WT macrophages by inhibiting fatty acid oxidation and, conversely, prevented by pharmacological activation of AMPK β1-containing complexes. The effect of AMPK β1 loss in macrophages was tested in vivo by transplantation of bone marrow from WT or β1(-/-) mice into WT recipients. When challenged with a high-fat diet, mice that received β1(-/-) bone marrow displayed enhanced adipose tissue macrophage inflammation and liver insulin resistance compared with animals that received WT bone marrow. Thus, activation of AMPK β1 and increasing fatty acid oxidation in macrophages may represent a new therapeutic approach for the treatment of insulin resistance.

Tissue factor–protease-activated receptor 2 signaling promotes diet-induced obesity and adipose inflammation

Tissue factor (TF), the initiator of the coagulation cascade, mediates coagulation factor VIIa-dependent activation of protease activated receptor-2 (PAR2). Here we delineate an unexpected role for coagulation signaling in obesity and its complications. Mice lacking PAR2 (F2rl1) or the cytoplasmic domain of TF (F3) are protected from high fat diet (HFD) induced weight gain and insulin resistance. In hematopoietic cells, genetic deletion of TF-PAR2 signaling reduces adipose tissue macrophage inflammation and specific pharmacological inhibition of macrophage TF signaling rapidly ameliorates insulin resistance. In contrast, non-hematopoietic cell TF-VIIa-PAR2 signaling specifically promotes obesity. Mechanistically, adipocyte TF cytoplasmic domain dependent VIIa signaling suppresses Akt phosphorylation with concordant adverse transcriptional changes of key regulators of obesity and metabolism. Pharmacological blockade of adipocyte TF in vivo reverses these effects of TF-VIIa signaling and rapidly improves energy expenditure. Thus, TF signaling is a potential therapeutic target to improve impaired metabolism and insulin resistance in obesity.