P65 inactivation in adipocytes and macrophages attenuates adipose inflammatory response in lean but not in obese mice

Puerarin suppresses macrophage M1 polarization to alleviate renal inflammatory injury through antagonizing TLR4/MyD88-mediated NF-κB p65 and JNK/FoxO1 activation

BACKGROUND

Acute kidney injury (AKI) is a clinically common and serious renal dysfunction, characterized by inflammation and damage to tubular epithelial cells. Puerarin, an isoflavone derivative isolated from Pueraria lobata, has been proven to possess exceptional effectiveness in reducing inflammation. However, the effects and underlying mechanisms of puerarin on AKI remain uncertain.

PURPOSE

This study investigated the possible therapeutic effects of puerarin on AKI and explored its underlying mechanism.

STUDY DESIGN AND METHODS

The effects of puerarin on AKI and macrophage polarization were investigated in lipopolysaccharide (LPS)-induced or unilateral ureteral obstruction (UUO)-induced mouse models in vivo and LPS-treated macrophages (Raw264.7) in vitro. Additionally, the effects of puerarin on inflammation-related signaling pathways were analyzed.

RESULTS

Administration of puerarin effectively alleviated kidney dysfunction and reduced inflammatory response in LPS-induced and UUO-induced AKI. In vitro, puerarin treatment inhibited the polarization of M1 macrophages and the release of inflammatory factors in Raw264.7 cells stimulated by LPS. Mechanistically, puerarin downregulated the activities of NF-κB p65 and JNK/FoxO1 signaling pathways. The application of SRT1460 to activate FoxO1 or anisomycin to activate JNK eliminated puerarin-mediated inhibition of JNK/FoxO1 signaling, leading to suppression of macrophage M1 polarization and reduction of inflammatory factors. Further studies showed that puerarin bound to Toll/interleukin-1 receptor (TIR) domain of MyD88 protein, hindering its binding with TLR4, ultimately resulting in downstream NF-κB p65 and JNK/FoxO1 signaling inactivation.

CONCLUSIONS

Puerarin antagonizes NF-κB p65 and JNK/FoxO1 activation via TLR4/MyD88 pathway, thereby suppressing macrophage polarization towards M1 phenotype and alleviating renal inflammatory damage.

Inflammation causes insulin resistance in mice via interferon regulatory factor 3 (IRF3)-mediated reduction in FAHFA levels

Obesity-induced inflammation causes metabolic dysfunction, but the mechanisms remain elusive. Here we show that the innate immune transcription factor interferon regulatory factor (IRF3) adversely affects glucose homeostasis through induction of the endogenous FAHFA hydrolase androgen induced gene 1 (AIG1) in adipocytes. Adipocyte-specific knockout of IRF3 protects male mice against high-fat diet-induced insulin resistance, whereas overexpression of IRF3 or AIG1 in adipocytes promotes insulin resistance on a high-fat diet. Furthermore, pharmacological inhibition of AIG1 reversed obesity-induced insulin resistance and restored glucose homeostasis in the setting of adipocyte IRF3 overexpression. We, therefore, identify the adipocyte IRF3/AIG1 axis as a crucial link between obesity-induced inflammation and insulin resistance and suggest an approach for limiting the metabolic dysfunction accompanying obesity.

Biological activities, Molecular mechanisms, and Clinical application of Naringin in Metabolic syndrome

Metabolic syndrome has become major health problems in recent decades, and natural compounds receive considerable attention in the management of metabolic syndrome. Among them, naringin is abundant in citrus fruits and tomatoes. Many studies have investigated the therapeutic effects of naringin in metabolic syndrome. This review discusses in vitro and in vivo studies on naringin and implications for clinical trials on metabolic syndrome such as diabetes mellitus, obesity, nonalcoholic fatty liver disease, dyslipidemia, and hypertension over the past decades, overviews the molecular mechanisms by which naringin targets metabolic syndrome, and analyzes possible correlations between the different mechanisms. This review provides a theoretical basis for the further application of naringin in the treatment of metabolic syndrome.

Production of a p65fl/fl/LysMCre mouse model with dysfunctional NF-κB signaling in bone marrow-derived macrophages

Here, we describe the production and characterization of a novel p65fl/fl/LysMCre mouse model, which lacks canonical nuclear factor-kappaB member RelA/p65 (indicated as p65 hereafter) in bone marrow-derived macrophages. Cultured bone marrow-derived macrophages that lack p65 protein reveal NF-κB signaling deficiencies, a reduction in phagocytic ability, and reduced ability to produce nitrites. Despite abnormal bone marrow-derived macrophage function, p65fl/fl/LysMCre mice do not exhibit differences in naïve systemic immune profiles or colony forming units and time to death following Salmonella infection as compared to controls. Additionally, p65fl/fl/LysMCre mice, especially females, display splenomegaly, but no other obvious physical or behavioral differences as compared to control animals. As bone marrow-derived macrophages from this transgenic model are almost completely devoid of canonical nuclear factor-kappaB pathway member p65, this model has the potential for being very useful in investigating bone marrow-derived macrophage NF-kappaB signaling in diverse biological and biomedical studies.

RELA governs a network of islet-specific metabolic genes necessary for beta cell function

AIMS/HYPOTHESIS

NF-κB activation unites metabolic and inflammatory responses in many diseases yet less is known about the role that NF-κB plays in normal metabolism. In this study we investigated how RELA impacts the beta cell transcriptional landscape and provides network control over glucoregulation.

METHODS

We generated novel mouse lines harbouring beta cell-specific deletion of either the Rela gene, encoding the canonical NF-κB transcription factor p65 (βp65KO mice), or the Ikbkg gene, encoding the NF-κB essential modulator NEMO (βNEMOKO mice), as well as βA20Tg mice that carry beta cell-specific and forced transgenic expression of the NF-κB-negative regulator gene Tnfaip3, which encodes the A20 protein. Mouse studies were complemented by bioinformatics analysis of human islet chromatin accessibility (assay for transposase-accessible chromatin with sequencing [ATAC-seq]), promoter capture Hi-C (pcHi-C) and p65 binding (chromatin immunoprecipitation-sequencing [ChIP-seq]) data to investigate genome-wide control of the human beta cell metabolic programme.

RESULTS

Rela deficiency resulted in complete loss of stimulus-dependent inflammatory gene upregulation, consistent with its known role in governing inflammation. However, Rela deletion also rendered mice glucose intolerant because of functional loss of insulin secretion. Glucose intolerance was intrinsic to beta cells as βp65KO islets failed to secrete insulin ex vivo in response to a glucose challenge and were unable to restore metabolic control when transplanted into secondary chemical-induced hyperglycaemic recipients. Maintenance of glucose tolerance required Rela but was independent of classical NF-κB inflammatory cascades, as blocking NF-κB signalling in vivo by beta cell knockout of Ikbkg (NEMO), or beta cell overexpression of Tnfaip3 (A20), did not cause severe glucose intolerance. Thus, basal p65 activity has an essential and islet-intrinsic role in maintaining normal glucose homeostasis. Genome-wide bioinformatic mapping revealed the presence of p65 binding sites in the promoter regions of specific metabolic genes and in the majority of islet enhancer hubs (~70% of ~1300 hubs), which are responsible for shaping beta cell type-specific gene expression programmes. Indeed, the islet-specific metabolic genes Slc2a2, Capn9 and Pfkm identified within the large network of islet enhancer hub genes showed dysregulated expression in βp65KO islets.

CONCLUSIONS/INTERPRETATION

These data demonstrate an unappreciated role for RELA as a regulator of islet-specific transcriptional programmes necessary for the maintenance of healthy glucose metabolism. These findings have clinical implications for the use of anti-inflammatories, which influence NF-κB activation and are associated with diabetes.

NF-κB in monocytes and macrophages - an inflammatory master regulator in multitalented immune cells

Nuclear factor κB (NF-κB) is a dimeric transcription factor constituted by two of five protein family members. It plays an essential role in inflammation and immunity by regulating the expression of numerous chemokines, cytokines, transcription factors, and regulatory proteins. Since NF-κB is expressed in almost all human cells, it is important to understand its cell type-, tissue-, and stimulus-specific roles as well as its temporal dynamics and disease-specific context. Although NF-κB was discovered more than 35 years ago, many questions are still unanswered, and with the availability of novel technologies such as single-cell sequencing and cell fate-mapping, new fascinating questions arose. In this review, we will summarize current findings on the role of NF-κB in monocytes and macrophages. These innate immune cells show high plasticity and dynamically adjust their effector functions against invading pathogens and environmental cues. Their versatile functions can range from antimicrobial defense and antitumor immune responses to foam cell formation and wound healing. NF-κB is crucial for their activation and balances their phenotypes by finely coordinating transcriptional and epigenomic programs. Thereby, NF-κB is critically involved in inflammasome activation, cytokine release, and cell survival. Macrophage-specific NF-κB activation has far-reaching implications in the development and progression of numerous inflammatory diseases. Moreover, recent findings highlighted the temporal dynamics of myeloid NF-κB activation and underlined the complexity of this inflammatory master regulator. This review will provide an overview of the complex roles of NF-κB in macrophage signal transduction, polarization, inflammasome activation, and cell survival.

Hepatic IRF3 fuels dysglycemia in obesity through direct regulation of Ppp2r1b

Inflammation has profound but poorly understood effects on metabolism, especially in the context of obesity and nonalcoholic fatty liver disease (NAFLD). Here, we report that hepatic interferon regulatory factor 3 (IRF3) is a direct transcriptional regulator of glucose homeostasis through induction of Ppp2r1b, a component of serine/threonine phosphatase PP2A, and subsequent suppression of glucose production. Global ablation of IRF3 in mice on a high-fat diet protected against both steatosis and dysglycemia, whereas hepatocyte-specific loss of IRF3 affects only dysglycemia. Integration of the IRF3-dependent transcriptome and cistrome in mouse hepatocytes identifies Ppp2r1b as a direct IRF3 target responsible for mediating its metabolic actions on glucose homeostasis. IRF3-mediated induction of Ppp2r1b amplified PP2A activity, with subsequent dephosphorylation of AMPKα and AKT. Furthermore, suppression of hepatic Irf3 expression with antisense oligonucleotides reversed obesity-induced insulin resistance and restored glucose homeostasis in obese mice. Obese humans with NAFLD displayed enhanced activation of liver IRF3, with reversion after bariatric surgery. Hepatic PPP2R1B expression correlated with HgbA1C and was elevated in obese humans with impaired fasting glucose. We therefore identify the hepatic IRF3-PPP2R1B axis as a causal link between obesity-induced inflammation and dysglycemia and suggest an approach for limiting the metabolic dysfunction accompanying obesity-associated NAFLD.

NF-κB regulates brown adipocyte function through suppression of ANT2

The transcription factor nuclear factor of kappa-light-chain-enhancer of activated B cells (NF-κB) is expressed in brown adipocytes, but its role remains largely unknown in the cells. This issue was addressed in current study by examining NF-κB in brown adipocytes in vitro and in vivo. NF-κB activity was increased by differentiation of brown adipocytes through elevation of p65 (RelA) expression. The transcriptional activity of NF-κB was induced by the cold stimulation with an elevation in S276 phosphorylation of p65 protein. Inactivation of NF-κB in brown adipocytes made the knockout mice [uncoupling protein 1 (Ucp1)–CreER–p65^f/f, U-p65-KO] intolerant to the cold environment. The brown adipocytes exhibited an increase in apoptosis, a decrease in cristae density and uncoupling activity in the interscapular brown adipose tissue (iBAT) of p65-KO mice. The alterations became severer after cold exposure of the KO mice. The brown adipocytes of mice with NF-κB activation (p65 overexpression, p65-OE) exhibited a set of opposite alterations with a reduction in apoptosis, an increase in cristae density and uncoupling activity. In mechanism, NF-κB inhibited expression of the adenine nucleotide translocase 2 (ANT2) in the control of apoptosis. Data suggest that NF-κB activity is increased in brown adipocytes by differentiation and cold stimulation to protect the cells from apoptosis through down-regulation of ANT2 expression.

Effects of Chronic Intermittent Hypoxia and Chronic Sleep Fragmentation on Gut Microbiome, Serum Metabolome, Liver and Adipose Tissue Morphology

Chronic intermittent hypoxia (CIH) and chronic sleep fragmentation (CSF) are two cardinal pathological features of obstructive sleep apnea (OSA). Dietary obesity is a crucial risk intermediator for OSA and metabolic disorders. Gut microbiota affect hepatic and adipose tissue morphology under conditions of CIH or CSF through downstream metabolites. However, the exact relationship is unclear. Herein, chow and high-fat diet (HFD)-fed mice were subjected to CIH or CSF for 10 weeks each and compared to normoxia (NM) or normal sleep (NS) controls. 16S rRNA amplicon sequencing, untargeted liquid chromatography-tandem mass spectrometry, and histological assessment of liver and adipose tissues were used to investigate the correlations between the microbiome, metabolome, and lipid metabolism under CIH or CSF condition. Our results demonstrated that CIH and CSF regulate the abundance of intestinal microbes (such as Akkermansia mucinphila, Clostridium spp., Lactococcus spp., and Bifidobacterium spp.) and functional metabolites, such as tryptophan, free fatty acids, branched amino acids, and bile acids, which influence adipose tissue and hepatic lipid metabolism, and the level of lipid deposition in tissues and peripheral blood. In conclusion, CIH and CSF adversely affect fecal microbiota composition and function, and host metabolism; these findings provide new insight into the independent and synergistic effects of CIH, CSF, and HFD on lipid disorders.

On the Immunometabolic Role of NF-κB in Adipocytes

Two decades of research have established that Nuclear Factor-κB (NF-κB) signaling plays a critical role in reprogramming the fat cell transcriptome towards inflammation in response to overnutrition and metabolic stress. Several groups have suggested that inhibition of NF-κB signaling could have metabolic benefits for obesity-associated adipose tissue inflammation. However, two significant problems arise with this approach. The first is how to deliver general NF-κB inhibitors into adipocytes without allowing these compounds to disrupt normal functioning in cells of the immune system. The second issue is that general inhibition of canonical NF-κB signaling in adipocytes will likely lead to a massive increase in adipocyte apoptosis under conditions of metabolic stress, leading full circle into a secondary inflammation (However, this problem may not be true for non-canonical NF-κB signaling.). This review will focus on the research that has examined canonical and non-canonical NF-κB signaling in adipocytes, focusing on genetic studies that examine loss-of-function of NF-κB specifically in fat cells. Although the development of general inhibitors of canonical NF-κB signaling seems unlikely to succeed in alleviating adipose tissue inflammation in humans, the door remains open for more targeted therapeutics. In principle, these would include compounds that interrogate NF-κB DNA binding, protein-protein interactions, or post-translational modifications that partition NF-κB activity towards some genes and away from others in adipocytes. I also discuss the possibility for inhibitors of non-canonical NF-κB signaling to realize success in mitigating fat cell dysfunction in obesity. To plant the seeds for such approaches, much biochemical “digging” in adipocytes remains; this includes identifying—in an unbiased manner–NF-κB direct and indirect targets, genomic DNA binding sites for all five NF-κB subunits, NF-κB protein-protein interactions, and post-translational modifications of NF-κB in fat cells.

IRF3 reduces adipose thermogenesis via ISG15-mediated reprogramming of glycolysis

Adipose thermogenesis is repressed in obesity, reducing the homeostatic capacity to compensate for chronic overnutrition. Inflammation inhibits adipose thermogenesis, but little is known about how this occurs. Here we showed that the innate immune transcription factor IRF3 is a strong repressor of thermogenic gene expression and oxygen consumption in adipocytes. IRF3 achieved this by driving expression of the ubiquitin-like modifier ISG15, which became covalently attached to glycolytic enzymes, thus reducing their function and decreasing lactate production. Lactate repletion was able to restore thermogenic gene expression, even when the IRF3/ISG15 axis was activated. Mice lacking ISG15 phenocopied mice lacking IRF3 in adipocytes, as both had elevated energy expenditure and were resistant to diet-induced obesity. These studies provide a deep mechanistic understanding of how the chronic inflammatory milieu of adipose tissue in obesity prevents thermogenic compensation for overnutrition.

PS-341 alleviates chronic low-grade inflammation and improves insulin sensitivity through the inhibition of TM4 (UBAC2) degradation

Background

The TM4 (UBAC2) protein, which contains 4 transmembrane domains and one ubiquitin binding domain, is mainly expressed in cell and nuclear membranes. The current research aimed to explore the role of TM4 in metabolic inflammation and to examine whether the ubiquitin–proteasome inhibitor PS-341 could regulate the function of TM4.

Methods

The metabolic phenotypes of TM4 knockout (KO) mice were studied. We next explored the association between the polymorphisms of TM4 and obesity in a Chinese Han population. TM4 expression in the visceral fat of obese patients who underwent laparoscopic cholecystectomy was also analysed. Finally, the effect of PS-341 on the degradation and function of the TM4 protein was investigated in vivo and in vitro.

Results

TM4 KO mice developed obesity, hepatosteatosis, hypertension, and glucose intolerance under a high-fat diet. TM4 counterregulated Nur77, IKKβ, and NF-kB both in vivo and in vitro. The TM4 SNP rs147851454 is significantly associated with obesity after adjusting for age and sex (OR 1.606, 95% CI 1.065–2.422 P = 0.023) in 3394 non-diabetic and 1862 type 2 diabetic adults of Han Chinese. TM4 was significantly downregulated in the visceral fat of obese patients. PS-341 induced TM4 expression through inhibition of TM4 degradation in vitro. In db/db mice, PS-341 administration led to downregulation of Nur77/IKKβ/NF-κB expression in visceral fat and liver, and alleviation of hyperglycaemia, hypertension, and glucose intolerance. The hyperinsulinaemic-euglycaemic clamp demonstrated that PS-341 improved the glucose infusion rate and alleviated insulin resistance in db/db mice.

Conclusions

PS-341 alleviates chronic low-grade inflammation and improves insulin sensitivity through inhibition of TM4 degradation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12986-021-00579-8.

Adipocytes fail to maintain cellular identity during obesity due to reduced PPARγ activity and elevated TGFβ-SMAD signaling

Objective

Obesity due to overnutrition causes adipose tissue dysfunction, which is a critical pathological step on the road to type 2 diabetes (T2D) and other metabolic disorders. In this study, we conducted an unbiased investigation into the fundamental molecular mechanisms by which adipocytes transition to an unhealthy state during obesity.

Methods

We used nuclear tagging and translating ribosome affinity purification (NuTRAP) reporter mice crossed with Adipoq-Cre mice to determine adipocyte-specific 1) transcriptional profiles (RNA-seq), 2) promoter and enhancer activity (H3K27ac ChIP-seq), 3) and PPARγ cistrome (ChIP-seq) profiles in mice fed chow or a high-fat diet (HFD) for 10 weeks. We also assessed the impact of the PPARγ agonist rosiglitazone (Rosi) on gene expression and cellular state of adipocytes from the HFD-fed mice. We integrated these data to determine the transcription factors underlying adipocyte responses to HFD and conducted functional studies using shRNA-mediated loss-of-function approaches in 3T3-L1 adipocytes.

Results

Adipocytes from the HFD-fed mice exhibited reduced expression of adipocyte markers and metabolic genes and enhanced expression of myofibroblast marker genes involved in cytoskeletal organization, accompanied by the formation of actin filament structures within the cell. PPARγ binding was globally reduced in adipocytes after HFD feeding, and Rosi restored the molecular and cellular phenotypes of adipocytes associated with HFD feeding. We identified the TGFβ1 effector protein SMAD to be enriched at HFD-induced promoters and enhancers and associated with myofibroblast signature genes. TGFβ1 treatment of mature 3T3-L1 adipocytes induced gene expression and cellular changes similar to those seen after HFD in vivo, and knockdown of Smad3 blunted the effects of TGFβ1.

Conclusions

Our data demonstrate that adipocytes fail to maintain cellular identity after HFD feeding, acquiring characteristics of a myofibroblast-like cell type through reduced PPARγ activity and elevated TGFβ-SMAD signaling. This cellular identity crisis may be a fundamental mechanism that drives functional decline of adipose tissues during obesity.

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Adipocytes after HFD intake exhibit defects in cellular identity maintenance.

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Adipocytes develop actin filament networks in obesity.

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Altered PPARγ activity mediates defective adipocyte identity phenotypes.

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TGFβ-SMAD pathways promote HFD-induced aberrant phenotype of adipocytes.

Lymphatic vessels in human adipose tissue

Despite being considered present in most vascularised tissues, lymphatic vessels have not been properly shown in human adipose tissue (AT). Our goal in this study is to investigate an unanswered question in AT biology, regarding lymphatic network presence in tissue parenchyma. Using human subcutaneous (S-) and visceral (V-) AT samples with whole mount staining for lymphatic specific markers and three-dimensional imaging, we showed lymphatic capillaries and larger lymphatic vessels in the human VAT. Conversely, in the human SAT, microcirculatory lymphatic vascular structures were rarely detected and no initial lymphatics were found.

Regulation of microbiota-GLP1 axis by sennoside A in diet-induced obese mice

Sennoside A (SA) is a bioactive component of Chinese herbal medicines with an activity of irritant laxative, which is often used in the treatment of constipation and obesity. However, its activity remains unknown in the regulation of insulin sensitivity. In this study, the impact of SA on insulin sensitivity was tested in high fat diet (HFD)-induced obese mice through dietary supplementation. At a dosage of 30 mg/kg/day, SA improved insulin sensitivity in the mice after 8-week treatment as indicated by HOMA-IR (homeostatic model assessment for insulin resistance) and glucose tolerance test (GTT). SA restored plasma level of glucagon-like peptide 1 (GLP1) by 90% and mRNA expression of Glp1 by 80% in the large intestine of HFD mice. In the mechanism, SA restored the gut microbiota profile, short chain fatty acids (SCFAs), and mucosal structure in the colon. A mitochondrial stress was observed in the enterocytes of HFD mice with ATP elevation, structural damage, and complex dysfunction. The mitochondrial response was induced in enterocytes by the dietary fat as the same responses were induced by palmitic acid in the cell culture. The mitochondrial response was inhibited in HFD mice by SA treatment. These data suggest that SA may restore the function of microbiota–GLP1 axis to improve glucose metabolism in the obese mice.

Restoration of GLP-1 secretion by Berberine is associated with protection of colon enterocytes from mitochondrial overheating in diet-induced obese mice

Objective

L-cell dysfunction is reported for GLP-1 reduction in type 2 diabetes. However, the mechanism of dysfunction remains unknown. In this study, we examined mitochondrial function in the mechanistic study in diet-induced obese (DIO) mice.

Subjects

C57BL/6 mice were fed a high-fat diet (HFD) for 16 weeks to establish the DIO model for GLP-1 reduction. The mice were then treated with berberine (BBR) (100 mg/kg/day) for 8 weeks to test the impact on GLP-1 expression. Mitochondrial activities of the colon enterocytes were compared among three groups of mice (lean, DIO, and DIO + BBR) at the end of treatment. Gut microbiota and short-chain fatty acids (SCFAs) were examined to understand the mitochondrial responses. A cellular model treated with palmitic acid (PA) was used in the mechanism study.

Results

A reduction in GLP-1 expression was observed in DIO mice with mitochondrial stress responses in the colon enterocytes. The mitochondria exhibited cristae loss, membrane rupture, and mitochondrial swelling, which was observed with an increase in ATP abundance, complex I activity, and deficiency in the activities of complexes II and IV. Those changes were associated with dysbiosis and a reduction in SCFAs in the colon of DIO mice. In the cellular model, an increase in ATP abundance, loss of mitochondrial potential, and elevation of apoptosis were induced by PA. All of the alterations in DIO mice and the cellular model were attenuated by BBR.

Conclusion

The mitochondrial stress responses were observed in the colon enterocytes of DIO mice for GLP-1 reduction. The stress was prevented by BBR in the restoration of GLP-1 expression, in which BBR may act through direct and indirect mechanisms.

Atorvastatin reduces cardiac and adipose tissue inflammation in rats with metabolic syndrome

BACKGROUND

Statins are strong inhibitors of cholesterol biosynthesis and help to prevent cardiovascular disease. They also exert additional pleiotropic effects that include an anti-inflammatory action and are independent of cholesterol, but the molecular mechanisms underlying these additional effects have remained unclear. We have now examined the effects of atorvastatin on cardiac and adipose tissue inflammation in DahlS.Z-Lepr^fa/Lepr^fa (DS/obese) rats, which we previously established as a model of metabolic syndrome (MetS).

METHODS AND RESULTS

DS/obese rats were treated with atorvastatin (6 or 20mgkg^-1day^-1) from 9 to 13weeks of age. Atorvastatin ameliorated cardiac fibrosis, diastolic dysfunction, oxidative stress, and inflammation as well as adipose tissue inflammation in these animals at both doses. The high dose of atorvastatin reduced adipocyte hypertrophy to a greater extent than did the low dose. Atorvastatin inhibited the up-regulation of peroxisome proliferator-activated receptor γ gene expression in adipose tissue as well as decreased the serum adiponectin concentration in DS/obese rats. It also activated AMP-activated protein kinase (AMPK) as well as inactivated nuclear factor-κB (NF-κB) in the heart of these animals. The down-regulation of AMPK and NF-κB activities in adipose tissue of DS/obese rats was attenuated and further enhanced, respectively, by atorvastatin treatment.

CONCLUSIONS

The present results suggest that the anti-inflammatory effects of atorvastatin on the heart and adipose tissue are attributable at least partly to increased AMPK activity and decreased NF-κB activity in this rat model of MetS.

Quercus infectoria inhibits Set7/NF-κB inflammatory pathway in macrophages exposed to a diabetic environment

Chronic inflammation plays a key role in the pathogenesis of myriad complications associated with diabetes and thus anti-inflammatory therapies may ameliorate these complications. Quercus infectoria (Qi) extract has been shown to downregulate inflammatory processes; however, the molecular mechanisms of this anti-inflammatory activity remain unclear. The hypothesis of our study was that Qi extract exerts its anti-inflammatory effect by downregulating the Set7/NF-κB pathway. Bone marrow-derived macrophages (BMM) were treated with high glucose plus palmitate medium (HG/Pa) to simulate the diabetic environment. Compared with control conditions, HG/Pa elevated expression Set7, expression and activity of NF-κB along with expression of several inflammatory cytokines. These changes were associated with increased levels of intracellular reactive oxygen species (ROS). Moreover, similar alterations were demonstrated in BMM derived from mice fed a high fat diet (HFD) compared to those from lean mice, suggesting that HFD-induced changes in BM progenitors persist throughout differentiation and culture. Importantly, Qi extract dose-dependently reduced Set7, p65 and inflammatory cytokine expression relative to vehicle controls in both HG/Pa-and HFD-treated BMM. Finally, macrophages/monocytes isolated from wounds of diabetic mice that were treated with Qi solution exhibited lower expression of the inflammatory cytokines, IL-1β and TNF-α, compared with vehicle treated wounds, demonstrating translation to the in vivo diabetic environment. Taken together, data from this study suggests that Qi downregulates diabetes-induced activity of the Set7/NF-kB pathway.

Divergent functions of endotrophin on different cell populations in adipose tissue

Endotrophin is a cleavage product of collagen 6 (Col6) in adipose tissue (AT). Previously, we demonstrated that endotrophin serves as a costimulator to trigger fibrosis and inflammation within the unhealthy AT milieu. However, how endotrophin affects lipid storage and breakdown in AT and how different cell types in AT respond to endotrophin stimulation remain unknown. In the current study, by using a doxycycline-inducible mouse model, we observed significant upregulation of adipogenic genes in the white AT (WAT) of endotrophin transgenic mice. We further showed that the mice exhibited inhibited lipolysis and accelerated hypertrophy and hyperplasia in WAT. To investigate the effects of endotrophin in vitro, we incubated different cell types from AT with conditioned medium from endotrophin-overexpressing 293T cells. We found that endotrophin activated multiple pathological pathways in different cell types. Particularly in 3T3-L1 adipocytes, endotrophin triggered a fibrotic program by upregulating collagen genes and promoted abnormal lipid accumulation by downregulating hormone-sensitive lipolysis gene and decreasing HSL phosphorylation levels. In macrophages isolated from WAT, endotrophin stimulated higher expression of the collagen-linking enzyme lysyl oxidase and M1 proinflammatory marker genes. In the stromal vascular fraction isolated from WAT, endotrophin induced upregulation of both profibrotic and proinflammatory genes. In conclusion, our study provides a new perspective on the effect of endotrophin in abnormal lipid accumulation and a mechanistic insight into the roles played by adipocytes and a variety of other cell types in AT in shaping the unhealthy microenvironment upon endotrophin treatment.

IRF3 promotes adipose inflammation and insulin resistance and represses browning

The chronic inflammatory state that accompanies obesity is a major contributor to insulin resistance and other dysfunctional adaptations in adipose tissue. Cellular and secreted factors promote the inflammatory milieu of obesity, but the transcriptional pathways that drive these processes are not well described. Although the canonical inflammatory transcription factor NF-κB is considered to be the major driver of adipocyte inflammation, members of the interferon regulatory factor (IRF) family may also play a role in this process. Here, we determined that IRF3 expression is upregulated in the adipocytes of obese mice and humans. Signaling through TLR3 and TLR4, which lie upstream of IRF3, induced insulin resistance in murine adipocytes, while IRF3 knockdown prevented insulin resistance. Furthermore, improved insulin sensitivity in IRF3-deficient mice was associated with reductions in intra-adipose and systemic inflammation in the high fat-fed state, enhanced browning of subcutaneous fat, and increased adipose expression of GLUT4. Taken together, the data indicate that IRF3 is a major transcriptional regulator of adipose inflammation and is involved in maintaining systemic glucose and energy homeostasis.

Obesity-associated Inflammation Induces microRNA-155 Expression in Adipocytes and Adipose Tissue: Outcome on Adipocyte Function

CONTEXT

Obesity alters adipose tissue's metabolic and endocrine functions and causes a chronic local and systemic low-grade inflammatory state to develop, generating obesity-associated complications. In the last decade, many entities contributing to and regulating this inflammatory state have been identified, among which are microRNAs.

OBJECTIVE

This study aimed to identify microRNA regulated in inflamed adipocytes and adipose tissue, and its effect on adipocyte biology.

DESIGN AND RESULTS

We screened the expression profile of TNFα-treated adipocytes (a major pro-inflammatory protein expressed in obese adipose tissue), and identified miR-155 as the most responsive microRNA. The involvement of TNFα on the basal miR-155 expression was confirmed in the adipose tissue of Tnfa−/− mice where miR-155 was significantly reduced. Also, mice overexpressing p65 or invalidated for p65 in adipose tissue respectively increased and decreased miR-155 expression, in line with the involvement of the nuclear factor κB (NF-κB) pathway in miR-155 induction. miR-155 expression was higher in obese subjects' adipose tissue than in that of normal-weight subjects, and correlated with TNFα expression and body mass index. Gain and loss of function of miR-155 showed its effect on adipocyte function, probably via its ability to target PPARγ mRNA 3′UTR. Interestingly, miR-155 overexpression also resulted in an increased inflammatory state in adipocytes.

CONCLUSION

Altogether, these data are evidence of a proinflammatory loop mediated by NF-κB and miR-155 that could participate in the amplification of inflammatory status in adipocytes.

Inactivation of NF-κB p65 (RelA) in Liver Improves Insulin Sensitivity and Inhibits cAMP/PKA Pathway

The transcription factor nuclear factor-κB (NF-κB) mediates inflammation and stress signals in cells. To test NF-κB in the control of hepatic insulin sensitivity, we inactivated NF-κB in the livers of C57BL/6 mice through deletion of the p65 gene, which was achieved by crossing floxed-p65 and Alb-cre mice to generate L-p65-knockout (KO) mice. KO mice did not exhibit any alterations in growth, reproduction, and body weight while on a chow diet. However, the mice on a high-fat diet (HFD) exhibited an improvement in systemic insulin sensitivity. Hepatic insulin sensitivity was enhanced as indicated by increased pyruvate tolerance, Akt phosphorylation, and decreased gene expression in hepatic gluconeogenesis. In the liver, a decrease in intracellular cAMP was observed with decreased CREB phosphorylation. Cyclic nucleotide phosphodiesterase-3B (PDE3B), a cAMP-degrading enzyme, was increased in mRNA and protein as a result of the absence of NF-κB activity. NF-κB was found to inhibit PDE3B transcription through three DNA-binding sites in the gene promoter in response to tumor necrosis factor-α. Body composition, food intake, energy expenditure, and systemic and hepatic inflammation were not significantly altered in KO mice on HFD. These data suggest that NF-κB inhibits hepatic insulin sensitivity by upregulating cAMP through suppression of PDE3B gene transcription.

Activation of NF-κB drives the enhanced survival of adipose tissue macrophages in an obesogenic environment

Objective

Macrophage accumulation in adipose tissue (AT) during obesity contributes to inflammation and insulin resistance. Recruitment of monocytes to obese AT has been the most studied mechanism explaining this accumulation. However, recent evidence suggests that recruitment-independent mechanisms may also regulate pro-inflammatory AT macrophage (ATM) numbers. The role of increased ATM survival during obesity has yet to be explored.

Results

We demonstrate that activation of apoptotic pathways is significantly reduced in ATMs from diet-induced and genetically obese mice. Concurrently, pro-survival Bcl-2 family member protein levels and localization to the mitochondria is elevated in ATMs from obese mice. This increased pro-survival signaling was associated with elevated activation of the transcription factor, NF-κB, and increased expression of its pro-survival target genes. Finally, an obesogenic milieu increased ATM viability only when NF-κB signaling pathways were functional.

Conclusions

Our data demonstrate that obesity promotes survival of inflammatory ATMs, possibly through an NF-κB-regulated mechanism.

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Macrophage apoptosis is decreased in obese adipose tissue.

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ATMs from obese mice display increased mitochondrial localization of Bcl-2.

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The pro-survival targets of NF-κB are increased in ATMs from obese mice.

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NF-κB activation in ATMs during metabolic stimulation increases their survival.

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Decreased ATM apoptosis contributes to macrophage accumulation in obesity.