Adipocytokine Orosomucoid Integrates Inflammatory and Metabolic Signals to Preserve Energy Homeostasis by Resolving Immoderate Inflammation

Orosomucoid (ORM), also called α-1 acid glycoprotein, is an abundant plasma protein that is an immunomodulator induced by stressful conditions such as infections. In this study, we reveal that Orm is induced selectively in the adipose tissue of obese mice to suppress excess inflammation that otherwise disturbs energy homeostasis. Adipose Orm levels were elevated by metabolic signals, including insulin, high glucose, and free fatty acid, as well as by the proinflammatory cytokine tumor necrosis factor-α, which is found in increased levels in the adipose tissue of morbid obese subjects. In both adipocytes and macrophages, ORM suppressed proinflammatory gene expression and pathways such as NF-κB and mitogen-activated protein kinase signalings and reactive oxygen species generation. Concomitantly, ORM relieved hyperglycemia-induced insulin resistance as well as tumor necrosis factor-α-mediated lipolysis in adipocytes. Accordingly, ORM improved glucose and insulin tolerance in obese and diabetic db/db mice. Taken together, our results suggest that ORM integrates inflammatory and metabolic signals to modulate immune responses to protect adipose tissue from excessive inflammation and thereby from metabolic dysfunction.     

Hydroxytyrosol ameliorates insulin resistance by modulating endoplasmic reticulum stress and prevents hepatic steatosis in diet-induced obesity mice

Endoplasmic reticulum (ER) is a principal organelle responsible for energy and nutrient management. Its dysfunction has been viewed in the context of obesity and related glucolipid metabolic disorders. However, therapeutic approaches to improve ER adaptation and systemic energy balance in obesity are limited. Thus, we examined whether hydroxytyrosol (HT), an important polyphenolic compound found in virgin olive oil, could correct the metabolic impairments in diet-induced obesity (DIO) mice. Here, we found that HT gavage for 10 weeks significantly ameliorated glucose homeostasis and chronic inflammation and decreased hepatic steatosis in DIO mice. At the molecular level, ER stress indicators, inflammatory and insulin signaling markers demonstrated that high-fat diet (HFD)-induced ER stress and insulin resistance (IR) in insulin sensitive tissue were corrected by HT. In vitro studies confirmed that HT supplementation (100 μM) attenuated palmitate-evoked ER stress, thus rescuing the downstream JNK/IRS pathway. As a result from suppression of ER stress in the liver, HT further decreased hepatic sterol regulatory element-binding protein-1 expression (SREBP1). Additionally, aberrant expression of genes involved in hepatic lipogenesis (SREBP1, ACC, FAS, SCD1) caused by HFD was restored by HT. These findings suggested that HT ameliorated chronic inflammation and IR and decreased hepatic steatosis in obesity by beneficial modulation of ER stress.     

Role of ERO1-α–mediated stimulation of inositol 1,4,5-triphosphate receptor activity in endoplasmic reticulum stress–induced apoptosis

Endoplasmic reticulum (ER) stress–induced apoptosis is involved in many diseases, but the mechanisms linking ER stress to apoptosis are incompletely understood. Based on roles for C/EPB homologous protein (CHOP) and ER calcium release in apoptosis, we hypothesized that apoptosis involves the activation of inositol 1,4,5-triphosphate (IP3) receptor (IP3R) via CHOP-induced ERO1-α (ER oxidase 1 α). In ER-stressed cells, ERO1-α is induced by CHOP, and small interfering RNA (siRNA) knockdown of ERO1-α suppresses apoptosis. IP3-induced calcium release (IICR) is increased during ER stress, and this response is blocked by siRNA-mediated silencing of ERO1-α or IP3R1 and by loss-of-function mutations in Ero1a or Chop. Reconstitution of ERO1-α in Chop^−/− macrophages restores ER stress–induced IICR and apoptosis. In vivo, macrophages from wild-type mice but not Chop^−/− mice have elevated IICR when the animals are challenged with the ER stressor tunicamycin. Macrophages from insulin-resistant ob/ob mice, another model of ER stress, also have elevated IICR. These data shed new light on how the CHOP pathway of apoptosis triggers calcium-dependent apoptosis through an ERO1-α–IP3R pathway.     

Kdm6a suppresses the alternative activation of macrophages and impairs energy expenditure in obesity

Histone lysine demethylase 6a (Kdm6a) mediates the removal of repressive trimethylation from histone H3 lysine 27 (H3K27me3) to activate target gene expression. Obesity is associated with metabolic inflammation, and adipose tissue macrophages (ATMs) are key players orchestrating metabolic inflammation. However, it is still unclear whether the Kdm6a pathway in ATMs regulates energy homeostasis. Here, we identified Kdm6a as a critical epigenetic switch that modulates macrophage polarisation and further disrupts energy balance. Myeloid-specific Kdm6a knockout in Kdm6a^F/Y;Lyz2-Cre mice significantly reversed the high-fat diet (HFD)-induced M1–M2 imbalance in white adipose tissue (WAT) and blocked HFD-induced obesity. The brown adipose tissue (BAT) activity, WAT browning and energy expenditure were significantly increased in Kdm6a^F/Y;Lyz2-Cre mice. Furthermore, Kdm6a regulated the Ire1α expression in a demethylase activity-dependent manner and augmented the M2 polarisation of macrophages. Macrophage with higher Kdm6a significantly promotes adipogenesis in white adipocyte and inhibits thermogenesis in beige adipocytes. These results suggest that the Kdm6a in macrophages drives obesity and metabolic syndrome by impairing BAT activity and WAT differentiation.Subject terms: Interleukins, Epigenetics     

The role of uncoupling protein 2 in macrophages and its impact on obesity-induced adipose tissue inflammation and insulin resistance

The development of a chronic, low-grade inflammation originating from adipose tissue in obese subjects is widely recognized to induce insulin resistance, leading to the development of type 2 diabetes. The adipose tissue microenvironment drives specific metabolic reprogramming of adipose tissue macrophages, contributing to the induction of tissue inflammation. Uncoupling protein 2 (UCP2), a mitochondrial anion carrier, is thought to separately modulate inflammatory and metabolic processes in macrophages and is up-regulated in macrophages in the context of obesity and diabetes. Here, we investigate the role of UCP2 in macrophage activation in the context of obesity-induced adipose tissue inflammation and insulin resistance. Using a myeloid-specific knockout of UCP2 (Ucp2^ΔLysM), we found that UCP2 deficiency significantly increases glycolysis and oxidative respiration, both unstimulated and after inflammatory conditions. Strikingly, fatty acid loading abolished the metabolic differences between Ucp2^ΔLysM macrophages and their floxed controls. Furthermore, Ucp2^ΔLysM macrophages show attenuated pro-inflammatory responses toward Toll-like receptor-2 and -4 stimulation. To test the relevance of macrophage-specific Ucp2 deletion in vivo, Ucp2^ΔLysM and Ucp2^fl/fl mice were rendered obese and insulin resistant through high-fat feeding. Although no differences in adipose tissue inflammation or insulin resistance was found between the two genotypes, adipose tissue macrophages isolated from diet-induced obese Ucp2^ΔLysM mice showed decreased TNFα secretion after ex vivo lipopolysaccharide stimulation compared with their Ucp2^fl/fl littermates. Together, these results demonstrate that although UCP2 regulates both metabolism and the inflammatory response of macrophages, its activity is not crucial in shaping macrophage activation in the adipose tissue during obesity-induced insulin resistance.     

Hepatic metabolic adaptation and adipose tissue expansion are altered in mice with steatohepatitis induced by high-fat high sucrose diet

Background: Obesity is a chronic progressive disease with several metabolic alterations. Nonalcoholic fatty liver disease (NAFLD) is an important comorbidity of obesity that can progress to nonalcoholic steatohepatitis (NASH), cirrhosis or hepatocarcinoma. This study aimed at clarifying the molecular mechanisms underlying the metabolic alterations in hepatic and adipose tissue during high-fat high-sucrose diet-induced NAFLD development in mice. Methods: Twenty-four male mice (C57BL/6J) were randomly allocated into 3 groups (n = 8 mice per group) to receive a chow diet, a high-fat diet (HFD), or a high-fat high-sucrose diet (HF-HSD) for 20 weeks. At sacrifice, liver and adipose tissue were obtained for histopathological, metabolomic, and protein expression analyses. Results: HF-HSD (but not HFD) was associated with NASH and increased oxidative stress. These animals presented an inhibition of hepatic autophagy and alterations in AMP-activated protein kinase/mammalian target of rapamycin activity. We also observed that the ability of metabolic adaptation was adversely affected by the increase of damaged mitochondria. NASH development was associated with changes in adipose tissue dynamics and increased amounts of saturated fatty acids, monounsaturated fatty acids and polyunsaturated fatty acids in visceral adipose tissue. Conclusion: HF-HSD led to a metabolic blockage and impaired hepatic mitochondria turnover. In addition, the continuous accumulation of fatty acids produced adipose tissue dysfunction and hepatic fat accumulation that favored the progression to NASH.     

Adipose Tissue Is a Neglected Viral Reservoir and an Inflammatory Site during Chronic HIV and SIV Infection

Two of the crucial aspects of human immunodeficiency virus (HIV) infection are (i) viral persistence in reservoirs (precluding viral eradication) and (ii) chronic inflammation (directly associated with all-cause morbidities in antiretroviral therapy (ART)-controlled HIV-infected patients). The objective of the present study was to assess the potential involvement of adipose tissue in these two aspects. Adipose tissue is composed of adipocytes and the stromal vascular fraction (SVF); the latter comprises immune cells such as CD4⁺ T cells and macrophages (both of which are important target cells for HIV). The inflammatory potential of adipose tissue has been extensively described in the context of obesity. During HIV infection, the inflammatory profile of adipose tissue has been revealed by the occurrence of lipodystrophies (primarily related to ART). Data on the impact of HIV on the SVF (especially in individuals not receiving ART) are scarce. We first analyzed the impact of simian immunodeficiency virus (SIV) infection on abdominal subcutaneous and visceral adipose tissues in SIVmac251 infected macaques and found that both adipocytes and adipose tissue immune cells were affected. The adipocyte density was elevated, and adipose tissue immune cells presented enhanced immune activation and/or inflammatory profiles. We detected cell-associated SIV DNA and RNA in the SVF and in sorted CD4⁺ T cells and macrophages from adipose tissue. We demonstrated that SVF cells (including CD4⁺ T cells) are infected in ART-controlled HIV-infected patients. Importantly, the production of HIV RNA was detected by in situ hybridization, and after the in vitro reactivation of sorted CD4⁺ T cells from adipose tissue. We thus identified adipose tissue as a crucial cofactor in both viral persistence and chronic immune activation/inflammation during HIV infection. These observations open up new therapeutic strategies for limiting the size of the viral reservoir and decreasing low-grade chronic inflammation via the modulation of adipose tissue-related pathways.     

Adipose tissue macrophage in immune regulation of metabolism

The prevalence of obesity and type 2 diabetes is escalating to an epidemic proportion worldwide.Obesity is known to be associated with a state of chronic,low-grade inflammation.Emerging lines of evidence have shown that both innate and adaptive immune responses play crucial roles in the control of metabolic homeostasis.Macrophages in adipose tissues are the essential effector cells in orchestrating metabolic inflammation,which is thought to promote the pathogenic progression of obesity and obesity-related disorders.Here we discuss our current understanding of the distinct modes of activation of adipose tissue macrophages,which can sense the metabolic cues and exert profound effects upon adipose homeostasis.Targeting macrophages in adipose tissues may provide new avenues for developing immunomodulation-based therapeutics against obesity and obesity-associated metabolic diseases.     

Obesity and weight loss result in increased adipose tissue ABCG1 expression in db/db mice

The prevalence of obesity has reached epidemic proportions and is associated with several co-morbid conditions including diabetes, dyslipidemia, cancer, atherosclerosis and gallstones. Obesity is associated with low systemic inflammation and an accumulation of adipose tissue macrophages (ATMs) that are thought to modulate insulin resistance. ATMs may also modulate adipocyte metabolism and take up lipids released during adipocyte lipolysis and cell death. We suggest that high levels of free cholesterol residing in adipocytes are released during these processes and contribute to ATM activation and accumulation during obesity and caloric restriction. Db/db mice were studied for extent of adipose tissue inflammation under feeding conditions of ad libitum (AL) and caloric restriction (CR). The major finding was a marked elevation in epididymal adipose ABCG1 mRNA levels with obesity and CR (6-fold and 16-fold, respectively) over that seen for lean wild-type mice. ABCG1 protein was also elevated for CR as compared to AL adipose tissue. ABCG1 is likely produced by cholesterol loaded ATMs since this gene is not highly expressed in adipocytes and ABCG1 expression is sterol mediated. Our data supports the concept that metabolic changes in adipocytes due to demand lipolysis and cell death lead to cholesterol loading of ATMs. Based on finding cholesterol-loaded peritoneal leukocytes with elevated levels of ABCG1 in CR as compared to AL mice, we suggest that pathways for cholesterol trafficking out of adipose tissue involve ATM egress as well as ABCG1 mediated cholesterol efflux. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).     

C/EBP Homologous Protein-induced Macrophage Apoptosis Protects Mice from Steatohepatitis

Nonalcoholic fatty liver disease is a heterogeneous disorder characterized by liver steatosis; inflammation and fibrosis are features of the progressive form nonalcoholic steatohepatitis. The endoplasmic reticulum stress response is postulated to play a role in the pathogenesis of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis. In particular, C/EBP homologous protein (CHOP) is undetectable under normal conditions but is induced by cellular stress, including endoplasmic reticulum stress. Chop wild type (Chop^+/+) and knock-out (Chop^−/−) mice were used in these studies to elucidate the role of CHOP in the pathogenesis of fatty liver disease. Paradoxically, Chop^−/− mice developed greater liver injury, inflammation, and fibrosis than Chop^+/+ mice, with greater macrophage activation. Primary, bone marrow-derived, and peritoneal macrophages from Chop^+/+ and Chop^−/− were challenged with palmitic acid, an abundant saturated free fatty acid in plasma and liver lipids. Where palmitic acid treatment activated Chop^+/+ and Chop^−/− macrophages, Chop^−/− macrophages were resistant to its lipotoxicity. Chop^−/− mice were sensitized to liver injury in a second model of dietary steatohepatitis using the methionine-choline-deficient diet. Analysis of bone marrow chimeras between Chop^−/− and Chop^+/+ mice demonstrated that Chop in macrophages protects from liver injury and inflammation when fed the methionine-choline-deficient diet. We conclude that Chop deletion has a proinflammatory effect in fatty liver injury apparently due to decreased cell death of activated macrophages, resulting in their net accumulation in the liver. Thus, macrophage CHOP plays a key role in protecting the liver from steatohepatitis likely by limiting macrophage survival during lipotoxicity.     

ABCG1 regulates mouse adipose tissue macrophage cholesterol levels and ratio of M1 to M2 cells in obesity and caloric restriction

In addition to triacylglycerols, adipocytes contain a large reserve of unesterified cholesterol. During adipocyte lipolysis and cell death seen during severe obesity and weight loss, free fatty acids and cholesterol become available for uptake and processing by adipose tissue macrophages (ATMs). We hypothesize that ATMs become cholesterol enriched and participate in cholesterol clearance from adipose tissue. We previously showed that ABCG1 is robustly upregulated in ATMs taken from obese mice and further enhanced by caloric restriction. Here, we found that ATMs taken from obese and calorie-restricted mice derived from transplantation of WT or Abcg1-deficient bone marrow are cholesterol enriched. ABCG1 levels regulate the ratio of classically activated (M1) to alternatively activated (M2) ATMs and their cellular cholesterol content. Using WT and Abcg1^−/− cultured macrophages, we found that Abcg1 is most highly expressed by M2 macrophages and that ABCG1 deficiency is sufficient to retard macrophage chemotaxis. However, changes in myeloid expression of Abcg1 did not protect mice from obesity or impaired glucose homeostasis. Overall, ABCG1 modulates ATM cholesterol content in obesity and weight loss regimes leading to an alteration in M1 to M2 ratio that we suggest is due to the extent of macrophage egress from adipose tissue.     

High-Fat Diet-Induced Adiposity,Adipose Inflammation,Hepatic Steatosis and Hyperinsulinemia in Outbred CD-1 Mice

High-fat diet (HFD) has been applied to a variety of inbred mouse strains to induce obesity and obesity related metabolic complications. In this study, we determined HFD induced development of metabolic disorders on outbred female CD-1 mice in a time dependent manner. Compared to mice on regular chow, HFD-fed CD-1 mice gradually gained more fat mass and consequently exhibited accelerated body weight gain, which was associated with adipocyte hypertrophy and up-regulated expression of adipose inflammatory chemokines and cytokines such as Mcp-1 and Tnf-α. Increased fat accumulation in white adipose tissue subsequently led to ectopic fat deposition in brown adipose tissue, giving rise to whitening of brown adipose tissue without altering plasma level of triglyceride. Ectopic fat deposition was also observed in the liver, which was associated with elevated expression of key genes involved in hepatic lipid sequestration, including Ppar-γ2, Cd36 and Mgat1. Notably, adipose chronic inflammation and ectopic lipid deposition in the liver and brown fat were accompanied by glucose intolerance and insulin resistance, which was correlated with hyperinsulinemia and pancreatic islet hypertrophy. Collectively, these results demonstrate sequentially the events that HFD induces physiological changes leading to metabolic disorders in an outbred mouse model more closely resembling heterogeneity of the human population.     

内质网应激响应在脂肪组织中的代谢调节作用

在真核细胞中,内质网是蛋白合成、加工及质量监控的关键细胞器,也是Ca2+储存及脂质合成的重要场所.细胞通过未折叠蛋白响应(unfolded protein response,UPR)感应外界不同刺激引发的内质网应激,在维持细胞功能稳态中发挥至关重要的作用.在哺乳动物中,三个位于内质网的跨膜蛋白——肌醇依赖酶la(ino...     

Increasing Adipocyte Lipoprotein Lipase Improves Glucose Metabolism in High Fat Diet-induced Obesity

Lipid accumulation in liver and skeletal muscle contributes to co-morbidities associated with diabetes and obesity. We made a transgenic mouse in which the adiponectin (Adipoq) promoter drives expression of lipoprotein lipase (LPL) in adipocytes to potentially increase adipose tissue lipid storage. These mice (Adipoq-LPL) have improved glucose and insulin tolerance as well as increased energy expenditure when challenged with a high fat diet (HFD). To identify the mechanism(s) involved, we determined whether the Adipoq-LPL mice diverted dietary lipid to adipose tissue to reduce peripheral lipotoxicity, but we found no evidence for this. Instead, characterization of the adipose tissue of the male mice after HFD challenge revealed that the mRNA levels of peroxisome proliferator-activated receptor-γ (PPARγ) and a number of PPARγ-regulated genes were higher in the epididymal fat pads of Adipoq-LPL mice than control mice. This included adiponectin, whose mRNA levels were increased, leading to increased adiponectin serum levels in the Adipoq-LPL mice. In many respects, the adipose phenotype of these animals resembles thiazolidinedione treatment except for one important difference, the Adipoq-LPL mice did not gain more fat mass on HFD than control mice and did not have increased expression of genes in adipose such as glycerol kinase, which are induced by high affinity PPAR agonists. Rather, there was selective induction of PPARγ-regulated genes such as adiponectin in the adipose of the Adipoq-LPL mice, suggesting that increasing adipose tissue LPL improves glucose metabolism in diet-induced obesity by improving the adipose tissue phenotype. Adipoq-LPL mice also have increased energy expenditure.     

Impact of caloric restriction on AMPK and endoplasmic reticulum stress in peripheral tissues and circulating peripheral blood mononuclear cells from Zucker rats

The activation of endoplasmic reticulum (ER) stress and a reduction of AMP-dependent protein kinase (AMPK) phosphorylation have been described in obesity. We hypothesize that a moderate caloric restriction (CR) might contribute to reducing ER stress and increasing AMPK phosphorylation in peripheral tissues from genetically obese Zucker fa/fa rats and in peripheral blood mononuclear cells (PBMCs).Zucker Lean and Zucker fa/fa rats were fed with chow diet either ad libitum (AL) (C, as controls) or 80% of AL (CR) for 2 weeks, giving rise to four experimental groups: Lean C, Lean CR, fa/fa C and fa/fa CR.CR significantly increased AMPK phosphorylation in the liver, perirenal adipose tissue (PRAT) and PBMCs from fa/fa rats but not in the subcutaneous AT (SCAT), suggesting a reduced response of SCAT to CR. Liver samples of fa/fa rats exhibited an increased mRNA expression of PERK, EIF-2α, XBP-1(s), Chop and caspase 3, which was significantly reduced by CR. PRAT exhibited an overexpression of Edem and PDIA-4 in fa/fa rats, but only PDIA-4 expression was reduced by CR. eIF-2α phosphorylation was significantly increased in all studied tissues from fa/fa rats and reduced by CR. A negative correlation was detected between p-AMPK and p-eIF-2α in the liver, PRAT and PBMCs from fa/fa rats but not in SCAT.This study shows that a moderate CR reduces ER stress and improves AMPK phosphorylation in several peripheral tissues and in circulating PBMCs, suggesting that alterations observed in PBMCs could reflect metabolic alterations associated with obesity.