Diet-induced Adipose Tissue Inflammation Research Articles

Gasdermin D Deficiency Does Not Protect Mice from High-Fat Diet-Induced Glucose Intolerance and Adipose Tissue Inflammation.

The adipose tissue NLRP3 inflammasome has recently emerged as a contributor to obesity-related metabolic inflammation. Recent studies have demonstrated that the activation of the NLRP3 inflammasome cleaves gasdermin D (GSDMD) and induces pyroptosis, a proinflammatory programmed cell death. However, whether GSDMD is involved in the regulation of adipose tissue function and the development of obesity-induced metabolic disease remains unknown. The aim of the present study was to investigate the role of GSDMD in adipose tissue inflammation as well as whole-body metabolism using GSDMD-deficient mice fed a high-fat diet (HFD) for 30 weeks. The effects of GSDMD deficiency on adipose tissue, liver, and isolated macrophages from wild-type (WT) and GSDMD knockout (KO) mice were examined. In addition, 3T3-L1 cells were used to examine the expression of GSDMD during adipogenesis. The results demonstrate that although HFD-induced inflammation was partly ameliorated in isolated macrophages and liver, adipose tissue remained unaffected by GSDMD deficiency. Compared with the WT HFD mice, GSDMD KO HFD mice exhibited a mild increase in HFD-induced glucose intolerance with increased systemic and adipose tissue IL-1β levels. Interestingly, GSDMD deficiency caused accumulation of fat mass when challenged with HFD, partly by suppressing the expression of peroxisome proliferator-activated receptor gamma (PPARγ). The expression of GSDMD mRNA and protein was dramatically suppressed during adipocyte differentiation and was inversely correlated with PPARγ expression. Together, these findings indicate that GSDMD is not a prerequisite for HFD-induced adipose tissue inflammation and suggest a noncanonical function of GSDMD in regulation of fat mass through PPARγ.

Oxy210, a Semi-Synthetic Oxysterol, Exerts Anti-Inflammatory Effects in Macrophages via Inhibition of Toll-like Receptor (TLR) 4 and TLR2 Signaling and Modulation of Macrophage Polarization.

Inflammatory responses by the innate and adaptive immune systems protect against infections and are essential to health and survival. Many diseases including atherosclerosis, osteoarthritis, rheumatoid arthritis, psoriasis, and obesity involve persistent chronic inflammation. Currently available anti-inflammatory agents, including non-steroidal anti-inflammatory drugs, steroids, and biologics, are often unsafe for chronic use due to adverse effects. The development of effective non-toxic anti-inflammatory agents for chronic use remains an important research arena. We previously reported that oral administration of Oxy210, a semi-synthetic oxysterol, ameliorates non-alcoholic steatohepatitis (NASH) induced by a high-fat diet in APOE*3-Leiden.CETP humanized mouse model of NASH and inhibits expression of hepatic and circulating levels of inflammatory cytokines. Here, we show that Oxy210 also inhibits diet-induced white adipose tissue inflammation in APOE*3-Leiden.CETP mice, evidenced by the inhibition of adipose tissue expression of IL-6, MCP-1, and CD68 macrophage marker. Oxy210 and related analogs exhibit anti-inflammatory effects in macrophages treated with lipopolysaccharide in vitro, mediated through inhibition of toll-like receptor 4 (TLR4), TLR2, and AP-1 signaling, independent of cyclooxygenase enzymes or steroid receptors. The anti-inflammatory effects of Oxy210 are correlated with the inhibition of macrophage polarization. We propose that Oxy210 and its structural analogs may be attractive candidates for future therapeutic development for targeting inflammatory diseases.

Serglycin Is Involved in Adipose Tissue Inflammation in Obesity

Abstract Chronic local inflammation of adipose tissue is an important feature of obesity. Serglycin is a proteoglycan highly expressed by various immune cell types known to infiltrate adipose tissue under obese conditions. To investigate if serglycin expression has an impact on diet-induced adipose tissue inflammation, we subjected Srgn+/+ and Srgn−/− mice (C57BL/6J genetic background) to an 8-wk high-fat and high-sucrose diet. The total body weight was the same in Srgn+/+ and Srgn−/− mice after diet treatment. Expression of white adipose tissue genes linked to inflammatory pathways were lower in Srgn−/− mice. We also noted reduced total macrophage abundance, a reduced proportion of proinflammatory M1 macrophages, and reduced formation of crown-like structures in adipose tissue of Srgn−/− compared with Srgn+/+ mice. Further, Srgn−/− mice had more medium-sized adipocytes and fewer large adipocytes. Differentiation of preadipocytes into adipocytes (3T3-L1) was accompanied by reduced Srgn mRNA expression. In line with this, analysis of single-cell RNA sequencing data from mouse and human adipose tissue supports that Srgn mRNA is predominantly expressed by various immune cells, with low expression in adipocytes. Srgn mRNA expression was higher in obese compared with lean humans and mice, accompanied by an increased expression of immune cell gene markers. SRGN and inflammatory marker mRNA expression was reduced upon substantial weight loss in patients after bariatric surgery. Taken together, this study introduces a role for serglycin in the regulation of obesity-induced adipose inflammation.

Genetic Deficiency of TRAF5 Promotes Adipose Tissue Inflammation and Aggravates Diet-Induced Obesity in Mice.

Objective: The accumulation of inflammatory leukocytes is a prerequisite of adipose tissue inflammation during cardiometabolic disease. We previously reported that a genetic deficiency of the intracellular signaling adaptor TRAF5 (TNF [tumor necrosis factor] receptor-associated factor 5) accelerates atherosclerosis in mice by increasing inflammatory cell recruitment. Here, we tested the hypothesis that an impairment of TRAF5 signaling modulates adipose tissue inflammation and its metabolic complications in a model of diet-induced obesity in mice. Approach and Results: To induce diet-induced obesity and adipose tissue inflammation, wild-type or Traf5-/- mice consumed a high-fat diet for 18 weeks. Traf5-/- mice showed an increased weight gain, impaired insulin tolerance, and increased fasting blood glucose. Weight of livers and peripheral fat pads was increased in Traf5-/- mice, whereas lean tissue weight and growth were not affected. Flow cytometry of the stromal vascular fraction of visceral adipose tissue from Traf5-/- mice revealed an increase in cytotoxic T cells, CD11c+ macrophages, and increased gene expression of proinflammatory cytokines and chemokines. At the level of cell types, expression of TNF[alpha], MIP (macrophage inflammatory protein)-1[alpha], MCP (monocyte chemoattractant protein)-1, and RANTES (regulated on activation, normal T-cell expressed and secreted) was significantly upregulated in Traf5-deficient adipocytes but not in Traf5-deficient leukocytes from visceral adipose tissue. Finally, Traf5 expression was lower in adipocytes from obese patients and mice and recovered in adipose tissue of obese patients one year after bariatric surgery. Conclusions: We show that a genetic deficiency of TRAF5 in mice aggravates diet-induced obesity and its metabolic derangements by a proinflammatory response in adipocytes. Our data indicate that TRAF5 may promote anti-inflammatory and obesity-preventing signaling events in adipose tissue.

Lipocalin 2 Deficiency Diminishes the Metabolic Effect of Ketogenic Diet in Female Mice

Obesity is a worldwide public health concern, and prevalence in the United States is continuously increasing. Treatment of obesity ranges from dietary approaches to gastric surgery; there is no one-size-fits-all approach. In recent years, the ketogenic diet (KD) has become a popular approach for weight loss and metabolic health promotion. The main mechanism of weight loss caused by this diet is to promote the body to use fat as its primary form of energy by drastically reducing carbohydrate intake. Understanding the molecular mechanisms that contribute to the metabolic effect of the KD is critical for determining the appropriateness of this dietary approach. At the cellular and molecular level, the KD has been known to activate mitochondrial function and thermogenesis in thermogenic adipose tissue to stimulate fat utilization. However, specific molecules and genes that are involved in this metabolic regulation remain largely unknown. Lipocalin-2 (LCN2) has been characterized as an adipokine by our group and others. In our previous studies, LCN2 has been suggested as a critical regulator of mitochondrial function and thermogenesis in energy metabolism. LCN2 knockout (KO) mice exhibit impaired thermogenesis as well as exacerbated diet-induced obesity and adipose tissue inflammation. It is of interest to know if LCN2 plays a role in KD-induced energy metabolism. In this study, wild type (WT) and LCN2 KO female mice at 10 months of age were fed either a ketogenic diet or regular chow diet (RCD) for 10 weeks, followed by metabolic assessments including food intake, body weight, fat mass, and histology of tissues. Our results showed that there was no significant difference in daily food intake between WT and LCN2 KO mice under either the RCD or KD. However, we did find thatafter 10 weeks of KD, WT mice had significant loss of body weight by ~15% as well as significantly decreased inguinal and gonadal fat mass when compared with control mice fed a RCD. Interestingly, this effect on body weight and fat mass was not observed in LCN2 KO mice; the body weight and inguinal and gonadal fat depots were not significantly different between RCD- and KD-fed LCN2 KO mice. From the histology of the liver and adipose tissue, the KD led to significantly increased small adipocytes in the inguinal adipose tissue of WT mice, suggesting a healthy remodeling of this tissue. Intriguingly, this remodeling effect was completely absent in LCN2 KO mice. Moreover, we found that in WT mice the KD caused increased lipid accumulation in the liver compared to RCD. This reflects increased utilization of fatty acids and production of ketones. More strikingly, the KD resulted in liver lipid accumulation more profoundly in LCN2 KO mice, which may be due to mitochondrial dysfunction and defective fatty acid oxidation in the absence of LCN2. Together, we demonstrate that LCN2 deficiency diminishes the metabolic effect of the KD. This suggests that the role of LCN2 in regulating mitochondrial metabolism, thermogenesis, and other unknown physiological activities may be an important mechanism by which the KD leads to weight loss and improved metabolic health.

Anthocyanin-Rich Aronia Berry Extract Mitigates High-Fat and High-Sucrose Diet-Induced Adipose Tissue Inflammation by Inhibiting Nuclear Factor-κB Activation.

Obesity-induced inflammation in adipose tissue (AT) promotes the development of metabolic dysregulations by increasing macrophage recruitment in the stromal vascular fraction (SVF). The activation of nuclear factor-κB (NF-κB) signaling in macrophages serves as a pivotal mediator of AT inflammatory responses by increasing the expression of proinflammatory genes in obesity. Given the purported anti-inflammatory effects of berry consumption in humans, we evaluated if anthocyanin-rich aronia berry extract (ARN) can prevent obesity-induced AT inflammation in vivo. We also examined whether ARN suppresses lipopolysaccharide (LPS)-induced NF-κB activation in RAW 264.7 macrophages and mouse bone marrow-derived macrophages (BMDMs). Male C57BL/6J mice were fed a low-fat diet, a high-fat (HF), and high-sucrose (HS) diet or HF/HS diet supplemented with 0.2% ARN (HF/HS + ARN) for 14 weeks. Compared to HF-/HS-fed mice, ARN supplementation tended to decrease fasting serum glucose (P = .07). Furthermore, ARN supplementation significantly inhibited the phosphorylation of NF-κB p65 in epididymal AT with a concomitant decrease in the expression of Cd11b and Tnfα mRNAs in epididymal SVF isolated, compared with those from HF-/HS-fed mice. Consistent with these in vivo findings, ARN treatment significantly decreased the phosphorylation of p65 in LPS-stimulated RAW 264.7 macrophages and BMDMs. Moreover, ARN suppressed LPS-induced mRNA expression of inflammation mediators (iNos, Cox-2, Tnfα, Mcp-1, and Il-6) and glycolysis markers (Glut1, G6pdh, and Hk1) in both cell types. Taken together, our in vivo and in vitro results suggest that ARN supplementation may attenuate obesity-induced AT inflammation by inhibiting NF-κB signaling and glycolytic pathway in macrophages.

Adipose tissue inflammation and systemic insulin resistance in mice with diet-induced obesity is possibly associated with disruption of PFKFB3 in hematopoietic cells

AbstractObesity-associated inflammation in white adipose tissue (WAT) is a causal factor of systemic insulin resistance; however, precisely how immune cells regulate WAT inflammation in relation to systemic insulin resistance remains to be elucidated. The present study examined a role for 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) in hematopoietic cells in regulating WAT inflammation and systemic insulin sensitivity. Male C57BL/6J mice were fed a high-fat diet (HFD) or low-fat diet (LFD) for 12 weeks and examined for WAT inducible 6-phosphofructo-2-kinase (iPFK2) content, while additional HFD-fed mice were treated with rosiglitazone and examined for PFKFB3 mRNAs in WAT stromal vascular cells (SVC). Also, chimeric mice in which PFKFB3 was disrupted only in hematopoietic cells and control chimeric mice were also fed an HFD and examined for HFD-induced WAT inflammation and systemic insulin resistance. In vitro, adipocytes were co-cultured with bone marrow-derived macrophages and examined for adipocyte proinflammatory responses and insulin signaling. Compared with their respective levels in controls, WAT iPFK2 amount in HFD-fed mice and WAT SVC PFKFB3 mRNAs in rosiglitazone-treated mice were significantly increased. When the inflammatory responses were analyzed, peritoneal macrophages from PFKFB3-disrputed mice revealed increased proinflammatory activation and decreased anti-inflammatory activation compared with control macrophages. At the whole animal level, hematopoietic cell-specific PFKFB3 disruption enhanced the effects of HFD feeding on promoting WAT inflammation, impairing WAT insulin signaling, and increasing systemic insulin resistance. In vitro, adipocytes co-cultured with PFKFB3-disrupted macrophages revealed increased proinflammatory responses and decreased insulin signaling compared with adipocytes co-cultured with control macrophages. These results suggest that PFKFB3 disruption in hematopoietic cells only exacerbates HFD-induced WAT inflammation and systemic insulin resistance.Using approaches involving chimeric mice and macrophage-adipocyte cocultures, the authors demonstrate that PFKFB3 disruption only in hematopoietic cells exacerbates the severity of diet-induced adipose tissue inflammation and systemic insulin resistance. Mechanistically, macrophage factors generated in response to PFKFB3 disruption act to enhance adipocyte proinflammatory responses and impair adipocyte insulin signaling.

Spermidine ameliorates high-fat diet-induced hepatic steatosis and adipose tissue inflammation in preexisting obese mice

AimsThe therapeutic effects of spermidine on preexisting obese mice have been not fully elucidated. In this study, we assessed the anti-obesity impact of spermidine on high-fat diet (HFD)-induced obese mice. Main methodsC57BL/6J mice were fed a HFD for 16 weeks to induce obesity, and then treated with or without spermidine via drinking water for additional 8 weeks. The contributions of spermidine in regulating obesity phenotypes and metabolic syndrome were further evaluated. Key findingsSpermidine administration lowered fat mass and plasma lipid profile in HFD-induced obese mice without affecting body weight. In addition, spermidine attenuated hepatic steatosis by regulating lipid metabolism and enhancing antioxidant capacity. Moreover, spermidine reduced adipose tissue inflammation by decreasing inflammatory cytokine and chemokines expression, and these results might contributed to the enhanced thermogenic gene expression in brown adipose tissue. Furthermore, spermidine treatment enhanced gut barrier function by up-regulating tight junction- and mucin-related gene expression. SignificanceSpermidine-mediated protective impacts involve the regulation of lipid metabolism, inflammation response, gut barrier function and thermogenesis. These findings demonstrate that spermidine has potentials in treating obesity.

CB2R agonist JWH-133 attenuates chronic inflammation by restraining M1 macrophage polarization via Nrf2/HO-1 pathway in diet-induced obese mice

AimsCannabinoid receptor 2 (CB2R) is an important regulator of immunoinflammatory responses. Interestingly, studies have demonstrated that CB2R was expressed in metabolically active tissue, so we speculated that CB2R might have a crucial impact on energy balance. We thus examined the anti-inflammatory activities of CB2R and a CB2R agonist, JWH-133, in diet-induced obese in mice as well as in cultured macrophages. Materials and methodsWe evaluated the in vivo effect of JWH-133 on diet-induced adipose tissue inflammation. We also assessed the in vitro effects of JWH-133 on lipopolysaccharide (LPS)-induced inflammation in RAW264.7 macrophages, with a focus on the nuclear factor E2-related factor 2/heme oxygenase 1 (Nrf2/HO-1) signaling pathway. Key findingsWe found that JWH-133 reduced body weight gain, relieved glucose tolerance, and enhanced insulin sensitivity in a mouse model. It also down-regulated the expression of M1 macrophage biomarkers (tumor necrosis factor-α, interleukin (IL)-6, inducible nitric oxide synthase (iNOS), IL-1β, CC motif chemokine ligand 2, and C-X-C motif chemokine 10) in vivo and in vitro, but up-regulated levels of M2 macrophage biomarkers (IL-10 and arginase-1) in both mice and cultured macrophages. Furthermore, the underlying mechanisms were studied in an LPS-treated RAW264.7 cell line. We found a role for JWH-133 in controlling M1 macrophage polarization by activating the Nrf2/HO-1 pathway, while the effect of JWH-133 was diminished by a HO-1 inhibitor, Sn(IV) protoporphyrin IX dichloride. SignificanceJWH-133 showed anti-obesity effects that ameliorated pro-inflammatory M1 macrophage polarization through the Nrf2/HO-1 pathway. Therefore, our results provide a new proof for the potential use of the CB2R agonist, JWH-133, in the treatment of obesity.

CD81 Controls Beige Fat Progenitor Cell Growth and Energy Balance via FAK Signaling

Adipose tissues dynamically remodel their cellular composition in response to external cues by stimulating beige adipocyte biogenesis; however, the developmental origin and pathways regulating this process remain insufficiently understood owing to adipose tissue heterogeneity. Here, we employed single-cell RNA-seq and identified a unique subset of adipocyte progenitor cells (APCs) that possessed the cell-intrinsic plasticity to give rise to beige fat. This beige APC population is proliferative and marked by cell-surface proteins, including PDGFRα, Sca1, and CD81. Notably, CD81 is not only a beige APC marker but also required for de novo beige fat biogenesis following cold exposure. CD81 forms a complex with αV/β1 and αV/β5 integrins and mediates the activation of integrin-FAK signaling in response to irisin. Importantly, CD81 loss causes diet-induced obesity, insulin resistance, and adipose tissue inflammation. These results suggest that CD81 functions as a key sensor of external inputs and controls beige APC proliferation and whole-body energy homeostasis.

P1939Tumor necrosis factor receptor-associated factor 5 (TRAF-5) deficiency exacerbates diet-induced adipose tissue inflammation and aggravates metabolic syndrome in mice

Abstract Introduction Many clinical and experimental observations have established an association between visceral obesity and chronic adipose tissue inflammation. Potent pro-inflammatory mediators such as TNFα, CD40 and IL-1β are regulated by Tumor necrosis factor (TNF) receptor-associated factors (TRAFs). TRAF5 deficiency accelerates atherogenesis in mice by increasing inflammatory leukocyte recruitment. Since inflammatory cell invasion is also a prerequisite of adipose tissue inflammation, we tested the hypothesis that deficient TRAF5 signaling aggravates adipose tissue inflammation and its metabolic complications in a murine diet-induced obesity (DIO) model. Purpose We aimed to clarify the role of TRAF5 in adipose tissue inflammation and metabolic syndrome. Methods TRAF5−/− mice and gender- and age-matched wild-type (WT) mice consumed a high fat diet (HFD, 45%kcal from fat) or a matched low-fat diet (LFD, 10%kcal from fat) for 18 weeks to induce DIO and adipose tissue inflammation. All mice were then subjected to subsequent analysis, including glucose and insulin tolerance testing, body composition assessment by MRI imaging, flow cytometry, gene expression of different tissues, plasma analysis and histology. Finally, we studied if TRAF5 expression was associated with metabolic syndrome in humans by analyzing plasma and adipocytes samples from 62 patients of the Tumor-Necrosis-Factor Receptor Associated in Cardiovascular Risk Study (TRAFICS). Results TRAF5 expression was significantly attenuated in isolated WT-adipocytes and WT-macrophages after 18 weeks of HFD compared to LFD-fed controls. TRAF5−/− mice on HFD gained significantly more weight compared to TRAF5-competent mice and showed an aggravated metabolic phenotype, including impaired insulin tolerance, hyperinsulinemia and increased fasting glucose plasma levels. The weight gain in TRAF5−/− mice was attributable to a significant increase in adipose tissue and liver weight. Further analysis of the visceral adipose tissue revealed enhanced macrophage accumulation and increased pro-inflammatory CD11c+ subset polarization in HFD-fed TRAF5−/− mice. In line with an increased migratory capacity of inflammatory cells, we observed enhanced peritoneal invasion of leukocytes and subsets in TRAF5−/− mice. Accordingly, TRAF5 deficiency increased inflammatory cytokine expression and ameliorated parameters of insulin sensitivity in adipose tissue. Finally, patients with metabolic syndrome displayed decreased TRAF5 expression in blood and adipocytes compared to humans without metabolic syndrome. Conclusion We show that genetic deficiency of TRAF5 aggravates metabolic syndrome in murine diet-induced obesity. Enhanced accumulation of leukocytes subsets in adipose tissue serves as the likely mechanism. We conclude that TRAF5 signaling properties may favorably affect metabolic disease. Acknowledgement/Funding Forschungskommission Medizinische Fakultät Universität Freiburg, MOTI-VATE Promotionskolleg der Medizinischen Fakultät Freiburg (EKFS)

Kruppel-like factor 6 and miR-223 signaling axis regulates macrophage-mediated inflammation.

Macrophage-mediated inflammation is an explicitly robust biologic response that plays a critical role in maintaining tissue homeostasis by eliminating deleterious agents. These tissue macrophages tailor appropriate responses to external cues by altering inflammatory gene expression. Therefore, transcription factors and regulators that modulate inflammatory gene expression play an essential role in shaping the macrophage inflammatory response. Here, we identify that Kruppel-like factor (KLF)6 promotes inflammation by restraining microRNA-223 (miR-223) expression in macrophages. We uncovered that pro- and anti-inflammatory agents oppositely regulate KLF6 and miR-223 expression in macrophages. Using complementary gain- and loss-of-function studies, we observed that overexpression of KLF6 attenuates and deficiency of KLF6 elevates miR-223 expression in macrophages. Furthermore, heightened miR-223 expression in KLF6-deficient macrophages significantly attenuates inducible proinflammatory gene expression. Concordantly, myeloid-Klf6 deficiency significantly curbs diet-induced adipose tissue inflammation, obesity, glucose intolerance, and insulin resistance. At the molecular level, KLF6 directly represses miR-223 expression by occupying its promoter region. More importantly, genetic inhibition of miR-223-3P in KLF6-deficient macrophages completely reversed attenuated proinflammatory gene expression in macrophages. Collectively, our studies reveal that KLF6 promotes proinflammatory gene expression and functions by repressing miR-223 expression in macrophages.-Kim, G.-D., Ng, H. P., Patel, N., Mahabeleshwar, G. H. Kruppel-like factor 6 and miR-223 signaling axis regulates macrophage-mediated inflammation.

Spred2 Regulates High Fat Diet-Induced Adipose Tissue Inflammation, and Metabolic Abnormalities in Mice.

Chronic low-grade inflammation in visceral adipose tissues triggers the development of obesity-related insulin resistance, leading to the metabolic syndrome, a serious health condition with higher risk of cardiovascular disease, diabetes, and stroke. In the present study, we investigated whether Sprouty-related EVH1-domain-containing protein 2 (Spred2), a negative regulator of the Ras/Raf/ERK/MAPK pathway, plays a role in the development of high fat diet (HFD)-induced obesity, adipose tissue inflammation, metabolic abnormalities, and insulin resistance. Spred2 knockout (KO) mice, fed with HFD, exhibited an augmented body weight gain, which was associated with enhanced adipocyte hypertrophy in mesenteric white adipose tissue (mWAT) and deteriorated dyslipidemia, compared with wild-type (WT) controls. The number of infiltrating macrophages with a M1 phenotype, and the crown-like structures, composed of macrophages surrounding dead or dying adipocytes, were more abundant in Spred2 KO-mWAT compared to in WT-mWAT. Exacerbated adipose tissue inflammation in Spred2 KO mice led to aggravated insulin resistance and fatty liver disease. To analyze the mechanism(s) that caused adipose tissue inflammation, cytokine response in mWAT was investigated. Stromal vascular fraction that contained macrophages from Spred2 KO-mWAT showed elevated levels of tumor necrosis factor α (TNFα) and monocyte chemoattractant protein-1 (MCP-1/CCL2) compared with those from WT-mWAT. Upon stimulation with palmitate acid (PA), bone marrow-derived macrophages (BMDMs) derived from Spred2 KO mice secreted higher levels of TNFα and MCP-1 than those from WT mice with enhanced ERK activation. U0126, a MEK inhibitor, reduced the PA-induced cytokine response. Taken together, these results suggested that Spred2, in macrophages, negatively regulates high fat diet-induced obesity, adipose tissue inflammation, metabolic abnormalities, and insulin resistance by inhibiting the ERK/MAPK pathway. Thus, Spred2 represents a potential therapeutic tool for the prevention of insulin resistance and resultant metabolic syndrome.

The DNA Repair Protein OGG1 Protects Against Obesity by Altering Mitochondrial Energetics in White Adipose Tissue

Obesity and related metabolic pathologies represent a significant public health concern. Obesity is associated with increased oxidative stress that damages genomic and mitochondrial DNA. Oxidatively-induced lesions in both DNA pools are repaired via the base-excision repair pathway, initiated by DNA glycosylases such as 8-oxoguanine DNA glycosylase (OGG1). Global deletion of OGG1 and common OGG1 polymorphisms render mice and humans susceptible to metabolic disease. However, the relative contribution of mitochondrial OGG1 to this metabolic phenotype is unknown. Here, we demonstrate that transgenic targeting of OGG1 to mitochondria confers significant protection from diet-induced obesity, insulin resistance, and adipose tissue inflammation. These favorable metabolic phenotypes are mediated by an increase in whole body energy expenditure driven by specific metabolic adaptations, including increased mitochondrial respiration in white adipose tissue of OGG1 transgenic (Ogg1Tg) animals. These data demonstrate a critical role for a DNA repair protein in modulating mitochondrial energetics and whole-body energy balance.

Diet-Induced Adipose Tissue Inflammation and Hypoxia Are Reversed by GLP-1 Potentially via Improved Microcirculation

Obesity is considered as an inflammatory disease. A proposed trigger of the inflammation is hypoxia, which occurs when the enlargement of vascular network is not sufficient to support the expanding adipocytes. Exenatide, a GLP-1 receptor agonist, plays an anti-inflammatory role in obesity, but the mechanisms are poorly understood. The current study investigated the effects of exenatide on inflammation, hypoxia and microcirculation in epididymal fat of high-fat diet induced obese mice. Here, 8-week-old male C57BL/6 mice were randomly divided into 2 groups: NC group (normal control) and HF group (high-fat diet). After 12 weeks diet induction, HF group was further divided into 2 groups: HF group (HF+saline) and HF+EX group (HF+exenatide, 24nmol/kg/day). Compared with NC group, HF group showed significant increases in weight gain and impaired glucose tolerance; serum inflammatory cytokine levels (IL-6, TNF-α, MCP-1) were elevated. Immunohistochemistry staining of F4/80 showed that macrophage infiltration increased in adipose tissue. The mRNA expressions of hypoxia-induced gene (HIF-1a, eNOS) were significantly upregulated. However, laser confocal microscopy showed that capillary density was reduced in HF group. After 4 weeks exenatide treatment, all the obese induced immune disorder (e.g., inflammatory cytokine levels, macrophage infiltration) and hypoxia were significantly ameliorated, leading to an improved energy homeostasis in HF mice when compared with those receiving saline treatment. Proteins levels of PECAM-1 and VEGF-R2 which are indicators of angiogenesis were obviously elevated and capillary density measured by confocal was dramatically increased by exenatide in epididymal fat tissues. As insufficient vasculature may trigger hypoxia and inflammation in obesity, our results indicated that inflammation and hypoxia in obesity could be reversed by GLP-1 potentially via improved angiogenesis and microcirculation in adipose tissue. Disclosure F. Xu: None. Z. Chen: None. Y. Xian: None. H.R. Deng: None. W. Xu: None. H. Liang: None. J. Weng: None.

Differential Effects of Niacin on High-Fat Diet–Induced Adipose Tissue Inflammation and Nonalcoholic Fatty Liver Disease in C57BL6/J and B6129SF2/J Mice

Pharmacological doses of niacin improve adipose tissue (AT) inflammation and nonalcoholic fatty liver disease (NAFLD) in rodents chronically fed a high-fat diet (HFD). However, recent mouse studies have demonstrated significant metabolic changes in different strains of mice fed a HFD. Therefore, the aim of this study was to assess the effect of niacin on both AT inflammation and liver steatosis in two mouse strains, C57BL6/J (B6) and B6129SF2/J (B6129), under HFD feeding. Thirty-two male B6 and 32 male B6129 mice were randomized into four groups: Chow/Vehicle (CV), Chow/Niacin (CN), HFD/Vehicle (HV), and HFD/Niacin (HN). They were fed either a chow (10% fat) or HFD (60% fat) for 20 weeks. Niacin (360 mg/kg/day) or vehicle was added to the drinking water from week 5 until the end of the study. As expected, HFD-fed mice gained more weight than chow-fed mice in both strains, with no difference in weight gain between strains. Crown-like structure (CLS) number, a hallmark of AT inflammation, was increased in HV mice of both strains compared to CV mice. In addition, HV B6 mice had higher CLS number than HV B6129 mice. In B6129 mice, niacin decreased CLS number in HN compared to HV mice, while this decrease was not observed in B6 mice. Liver weight to body weight (L/B) ratio, liver triglyceride (TG) content and NASH score was increased in HV compared to CV B6 mice. In contrast, in B6129 mice, only NASH score was increased in HV compared to CV controls. Niacin had no impact on L/B ratio, TG content, or NASH score in B6 mice. However, in B6129 mice, niacin increased all three parameters in HN compared to HV mice. In conclusion, there are strain differential effects on AT inflammation and NAFLD induced by HFD feeding. Interestingly, liver steatosis is significantly increased in HFD-fed B6129 mice treated with niacin. This increase is potentially due to methyl deficiency, as niacin is a potent hepatic methyl consumer and 129 mice are more sensitive to methyl deficiency. Disclosure H. Fang: None. E. Graff: None. Z. Li: None. R.L. Judd: None.

Endoplasmic reticulum chaperone GRP78 regulates macrophage function and insulin resistance in diet-induced obesity.

Obesity-mediated inflammation is a major cause of insulin resistance, and macrophages play an important role in this process. The 78-kDa glucose-regulated protein (GRP78) is a major endoplasmic reticulum chaperone that modulates unfolded protein response (UPR), and mice with GRP78 heterozygosity were resistant to diet-induced obesity. Here, we show that mice with macrophage-selective ablation of GRP78 (Lyz- GRP78-/-) are protected from skeletal muscle insulin resistance without changes in obesity compared with wild-type mice after 9 wk of high-fat diet. GRP78-deficient macrophages demonstrated adapted UPR with up-regulation of activating transcription factor (ATF)-4 and M2-polarization markers. Diet-induced adipose tissue inflammation was reduced, and bone marrow-derived macrophages from Lyz- GRP78-/- mice demonstrated a selective increase in IL-6 expression. Serum IL-13 levels were elevated by >4-fold in Lyz- GRP78-/- mice, and IL-6 stimulated the myocyte expression of IL-13 and IL-13 receptor. Lastly, recombinant IL-13 acutely increased glucose metabolism in Lyz- GRP78-/- mice. Taken together, our data indicate that GRP78 deficiency activates UPR by increasing ATF-4, and promotes M2-polarization of macrophages with a selective increase in IL-6 secretion. Macrophage-derived IL-6 stimulates the myocyte expression of IL-13 and regulates muscle glucose metabolism in a paracrine manner. Thus, our findings identify a novel crosstalk between macrophages and skeletal muscle in the modulation of obesity-mediated insulin resistance.-Kim, J. H., Lee, E., Friedline, R. H., Suk, S., Jung, D. Y., Dagdeviren, S., Hu, X., Inashima, K., Noh, H. L., Kwon, J. Y., Nambu, A., Huh, J. R., Han, M. S., Davis, R. J., Lee, A. S., Lee, K. W., Kim, J. K. Endoplasmic reticulum chaperone GRP78 regulates macrophage function and insulin resistance in diet-induced obesity.

Toll-like receptor 4 (TLR4) deficient mice are protected from adipose tissue inflammation in aging.

Adipose tissue (AT) inflammation is a central mechanism for metabolic dysfunction in both diet-induced obesity and age-associated obesity. Studies in diet-induced obesity have characterized the role of Fetuin A (Fet A) in Free Fatty Acids (FFA)-mediated TLR4 activation and adipose tissue inflammation. However, the role of Fet A & TLR4 in aging-related adipose tissue inflammation is unknown. In the current study, analysis of epidymymal fat pads of C57/Bl6 male mice, we found that, in contrast to data from diet-induced obesity models, adipose tissue from aged mice have normal Fet A and TLR4 expression. Interestingly, aged TLR4-deficient mice have diminished adipose tissue inflammation compared to normal controls. We further demonstrated that reduced AT inflammation in old TLR4-deficient mice is linked to impaired ER stress, augmented autophagy activity, and diminished senescence phenomenon. Importantly, old TLR4-deficient mice have improved glucose tolerance compared to age-matched wild type mice, suggesting that the observed reduced AT inflammation in aged TLR4-deficient mice has important physiological consequences. Taken together, our present study establishes novel aspect of aging-associated AT inflammation that is distinct from diet-induced AT inflammation. Our results also provide strong evidence that TLR4 plays a significant role in promoting aging adipose tissue inflammation.

TRAIL deletion prevents liver inflammation but not adipose tissue inflammation during murine diet‐induced obesity

Tumor necrosis factor‐related apoptosis‐inducing ligand (TRAIL) and its cognate receptor(s) are up‐regulated in human and murine nonalcoholic steatohepatitis (NASH); however, the consequence of this enhanced expression on NASH pathogenesis remains unclear. TRAIL may either accentuate liver injury by promoting hepatic steatosis and inflammation or it may mitigate the disease process by improving systemic insulin resistance and averting hepatic fibrosis. Herein, we investigated the role of TRAIL in an obesity‐induced murine model of NASH. C57BL/6 wild‐type mice and Trail –/– mice were placed on a 20‐week standard chow or a high‐fat, high‐fructose, and high‐cholesterol (FFC) diet, which induces obesity, insulin resistance, and NASH. Metabolic phenotype, liver injury, inflammation and fibrosis, and adipose tissue homeostasis were examined. FFC diet‐fed Trail –/– mice displayed no difference in weight gain and metabolic profile when compared to wild‐type mice on the same diet. All FFC‐fed mice developed significant hepatic steatosis, which was attenuated in Trail –/– mice. TRAIL deficiency also significantly decreased FFC diet‐induced liver injury as manifested by reduced serum alanine aminotransferase values, hepatic terminal deoxynucleotidyl transferase‐mediated deoxyuridine triphosphate nick‐end labeling‐positive cells, and macrophage‐associated inflammation. FFC diet‐associated hepatic stellate cell activation and hepatic collagen deposition were also abrogated in Trail –/– mice. In contrast to the liver, TRAIL deletion did not improve FFC diet‐induced adipose tissue injury and inflammation and actually aggravated insulin resistance. Conclusion: NASH pathogenesis may be dissociated from other features of the metabolic syndrome, and liver‐targeted inhibition of TRAIL signaling may be salutary. (Hepatology Communications 2017;1:648–662)

NLRP3 Inflammasome controls adipose tissue macrophage activation during aging

Abstract Aging is associated with chronic inflammation and increased risk for degenerative disorders and diseases. In the elderly there is a development of insulin resistance, increased visceral adiposity and dysfunctional adipose tissue (AT) homeostasis; however the mechanisms of age-induced immune defects in AT is unclear. AT contains numerous immune populations, which play well-known roles in regulating both inflammatory responses and metabolic homeostasis. Our prior studies have identified that the canonical inflammasome, NLRP3, is required for diet-induced AT inflammation and age-related inflammation in multiple organs. We hypothesized that NLRP3 is required for age-induced changes in AT immune cells and that deficiency in Nlrp3 will improve AT function during aging. Here we show that unlike obesity, aging is associated with reduction in specific AT macrophages subsets. Whole transcriptome sequencing of AT macrophages from aged mice revealed increased caspase-1 activation and distinct signatures that were regulated in part by Nlrp3. Linear support vector regression and bioinformatics analyses revealed that AT macrophages do not display classical M1–M2 like transcriptome and display AT-specific signatures that are distinct from other tissue macrophages in gut, brain, liver and spleen. We identified that as compared to 24-month old WT, the aged Nlrp3−/− animals were protected from alterations in AT macrophage activation. Furthermore, Nlrp3-mediated reduction in AT inflammation and macrophage activation led to protection from age-related defects in AT function. Overall our findings suggest that NLRP3-dependent immune-metabolic interactions within AT contribute to age-related inflammation and metabolic dysfunction.