Adipose Tissue Inflammation In Obesity Research Articles

Decreased Proteasomal Function Exacerbates Endoplasmic Reticulum Stress-Induced Chronic Inflammation in Obese Adipose Tissue

Low-grade chronic inflammation contributes to both aging and the pathogenesis of age-related diseases. White adipose tissue (WAT) in obese individuals exhibits chronic inflammation, which is associated with obesity-related disorders. Aging exacerbates obesity-related inflammation in WAT; however, the molecular mechanisms underlying chronic inflammation and its exacerbation by aging remain unclear. Age-related decline in activity of the proteasome, a multi-subunit proteolytic complex, has been implicated in age-related diseases. This study employed a mouse model with decreased proteasomal function that exhibits age-related phenotypes to investigate the impact of adipocyte senescence on WAT inflammation. Transgenic mice expressing proteasomal subunit β5t with weak chymotrypsin-like activity suffer from reduced lifespan and develop age-related phenotypes. Mice fed with a high-fat diet (HFD) and suffering proteasomal dysfunction exhibited increased WAT inflammation, increased infiltration of pro-inflammatory M1-like macrophages, and increased pro-inflammatory adipocytokines like monocyte chemoattractant protein-1, plasminogen activator inhibitor-1, and tumor necrosis factor αwhich are all associated with activation of endoplasmic reticulum (ER) stress-related pathways. Impaired proteasomal activity also activated ER stress-related molecules and induced expression of pro-inflammatory adipocytokines in adipocyte-like cells differentiated from 3T3-L1 cells. Collective evidence suggests that impaired proteasomal activity increases ER stress and that subsequent inflammatory pathways play pivotal roles in WAT inflammation. Since proteasomal function declines with age, age-related proteasome impairment may be involved in obesity-related inflammation among the elderly.

Serum levels of Vanin-2 increase with obesity in relation to inflammation of adipose tissue and may be a predictor of bariatric surgery outcomes.

Excessive obesity can lead to dysfunction in adipose tissue, which contributes to the development of comorbidities associated with obesity, such as type 2 diabetes (T2D), cardiovascular and cerebrovascular disease, among others. Previous research has mainly focused on the Vanin family in systemic inflammatory diseases or predicting its role in tumor prognosis, while neglecting its role as a secretory protein in adipose tissue inflammation and metabolism. The objective of this study was to compare the changes in Vanin-2 levels in the circulating blood of normal and obese individuals, and to assess its correlation with inflammatory factors in vivo. Furthermore, the study aimed to systematically evaluate its effectiveness in human weight loss surgery. Serum concentrations of Vanin-2 and inflammatory indicators were measured in 518 volunteers. Furthermore, the concentrations of Vanin-2 were measured both before and after weight loss through a dietetic program or laparoscopic sleeve gastrectomy (LSG). Additionally, we assessed the levels of insulin, adiponectin, and inflammation-related factors. The hormonal profile and changes in body weight were evaluated at baseline and 3 months after surgery. Serum levels of Vanin-2 were found to be significantly increased in individuals with overweight/obesity (OW/OB) group (controls 438.98 ± 72.44, OW/OB 530.89 ± 79.39 ug/L; p < 0.001). These increased levels were associated with IL-18, BMI, FAT%, and HOMA-IR. However, levels of Vanin-2 remained unchanged after conventional dietary treatment. On the other hand, weight loss induced by LSG resulted in a significant decrease in Vanin-2 concentrations from 586.44 ± 48.84 to 477.67 ± 30.27 ug/L (p < 0.001), and this decrease was associated with the Vanin-2 concentrations observed before the operation. Serum Vanin-2 is a highly effective biomarker for assessing adipose tissue inflammation in obesity and has the potential to serve as a predictor of bariatric surgery outcomes.

LRP1 is the cell-surface endocytosis receptor for vaspin in adipocytes.

Vaspin is a serine protease inhibitor that protects against adipose tissue inflammation and insulin resistance, two key drivers of adipocyte dysfunction and metabolic disorders in obesity. Inhibition of target proteases such as KLK7 has been shown to reduce adipose tissue inflammation in obesity, while vaspin binding to cell surface GRP78 has been linked to reduced obesity-induced ER stress and insulin resistance in the liver. However, the molecular mechanisms by which vaspin directly affects cellular processes in adipocytes remain unknown. Using fluorescently labeled vaspin, we found that vaspin is rapidly internalized by mouse and human adipocytes, but less efficiently by endothelial, kidney, liver, and neuronal cells. Internalization occurs by active, clathrin-mediated endocytosis, which is dependent on vaspin binding to the LRP1 receptor, rather than GRP78 as previously thought. This was demonstrated by competition experiments and RNAi-mediated knock-down in adipocytes and by rescuing vaspin internalization in LRP1-deficient Pea13 cells after transfection with a functional LRP1 minireceptor. Vaspin internalization is further increased in mature adipocytes after insulin-stimulated translocation of LRP1. Although vaspin has nanomolar affinity for LRP1 clusters II-IV, binding to cell surface heparan sulfates is required for efficient LRP1-mediated internalization. Native, but not cleaved vaspin, and also vaspin polymers are efficiently endocytosed, and ultimately targeted for lysosomal degradation. Our study provides mechanistic insight into the uptake and degradation of vaspin in adipocytes, thereby broadening our understanding of its functional repertoire. We hypothesize the vaspin-LRP1 axis to be an important mediator of vaspin effects not only in adipose tissue but also in other LRP1-expressing cells.

Abstract 15626: Novel Function Annotation Tool Revealed Obesity-Induced Inflammation is Exacerbated by miR-150 Regulated B Cell Receptor Signaling

B cells exacerbate obesity-induced metabolic dysfunction and become the second most abundant immune lineage in obese adipose tissue. However, high-resolution strategies to interrogate cellular dynamics driving B cell responses under chronic obesity stress are lacking, stifling innovative B cell-targeted therapies against obesity-induced health&amp;nbsp;risk. Our previous work established the potent role of&amp;nbsp;miR-150 in adipose tissue&amp;nbsp;B cells’ (ATB) pro-inflammatory responses under obesity. This project aims to elucidate the mechanism of miR-150 regulated ATB actions that bolster obesity-induced inflammation. Method: We employed single-cell techniques to decipher obesity-perturbed signaling networks in B cell-specific miR-150 gain/loss of function mouse models&amp;nbsp; in vivo and&amp;nbsp; ex vivo . We utilized our novel B cell function annotation tool, B-RAY, to&amp;nbsp;quantify&amp;nbsp;B cell cytokine production, antibody secretion, and antigen presentation from single-cell RNA-Seq. These strengths permitted several key findings: Result: A) miR-150 overexpression in mature B cells alone improved systemic glucose tolerance in obesity, despite similar body adiposity. In line, miR-150 knock-out worsened glucose tolerance. B) In obese adipose tissue, B cells were skewed towards higher cytokine production and antigen presentation and away from antibody secretion compared to lean tissue. Importantly, ATBs in obesity displayed increased activity of miR-150 direct targets, Myb, Etf1, and Elk1, and reduced expression of miR-150. C) ATBs in obesity were enriched in B cell receptor (BCR) signaling and downstream cascades. miR-150 overexpression B cells exhibited reduced BCR-mediated Syk phosphorylation and calcium influx, while miR-150 knock-out yielded enhanced responses. Conclusion: These results support the hypothesis that miR-150 regulation of ATBs limits chronic inflammation in obese adipose tissue via modulating BCR signaling to prevent excessive B cell cytokine production and antigen presentation. Future work will investigate ATB actions and BCR activation in&amp;nbsp;miR-150 gain/loss of function mice&amp;nbsp;across time in diet-induced obesity. Collectively, this work will elucidate an important immunoregulatory network bolstering obesity-induced inflammation and health risk.

The Role of Adipocyte Endoplasmic Reticulum Stress in Obese Adipose Tissue Dysfunction: A Review.

Adipose tissue dysfunction plays an important role in metabolic diseases associated with chronic inflammation, insulin resistance and lipid ectopic deposition in obese patients. In recent years, it has been found that under the stimulation of adipocyte endoplasmic reticulum stress (ERS), the over-activated ER unfolded protein response (UPR) exacerbates the inflammatory response of adipose tissue by interfering with the normal metabolism of adipose tissue, promotes the secretion of adipokines, and affects the browning and thermogenic pathways of adipose tissue, ultimately leading to the manifestation of metabolic syndrome such as ectopic lipid deposition and disorders of glucolipid metabolism in obese patients. This paper mainly summarizes the relationship between adipocyte ERS and obese adipose tissue dysfunction and provides an overview of the mechanisms by which ERS induces metabolic disorders such as catabolism, thermogenesis and inflammation in obese adipose tissue through the regulation of molecules and pathways such as NF-κB, ADPN, STAMP2, LPIN1, TRIP-Br2, NF-Y and SIRT2 and briefly describes the current mechanisms targeting adipocyte endoplasmic reticulum stress to improve obesity and provide ideas for intervention and treatment of obese adipose tissue dysfunction.

IRF3 in adipose tissue inflammation and metabolism

Abstract Dysfunction of adipocytes and adipose tissue is a primary defect in obesity and obesity-associated metabolic diseases. Interferon regulatory factor 3 (IRF3) has been implicated in adipogenesis. However, the role of IRF3 in obesity and obesity associated disorders still remains unclear. Here we show that IRF3 expression in human adipose tissue was positively associated with insulin sensitivity and negatively associated with type 2 diabetes. In mouse preadipocytes, IRF3 not only acts as a brake negatively regulating the adipogenic transcriptional network centered on the PPARg pathway, but also is important for the functionality of adipocytes. In macrophages, IRF3 inhibits inflammatory cytokine expression through IFNb/IL-10 axis, thereby restraining adipose tissue inflammation in obesity. Mice deficient in IRF3 developed obesity and type 2 diabetes spontaneously associated with increased adipose tissue inflammation. This study demonstrates that IRF3 regulates the biology of multiple cell types including adipocytes and macrophages to prevent the development of obesity and obesity-related complications, hence, could be a target for therapeutic interventions for prevention and treatment of obesity-associated metabolic disorders. National Medical Research Council of Singapore

Secretory Factors from Calcium-Sensing Receptor-Activated SW872 Pre-Adipocytes Induce Cellular Senescence and A Mitochondrial Fragmentation-Mediated Inflammatory Response in HepG2 Cells

Adipose tissue inflammation in obesity has a deleterious impact on organs such as the liver, ultimately leading to their dysfunction. We have previously shown that activation of the calcium-sensing receptor (CaSR) in pre-adipocytes induces TNF-α and IL-1β expression and secretion; however, it is unknown whether these factors promote hepatocyte alterations, particularly promoting cell senescence and/or mitochondrial dysfunction. We generated conditioned medium (CM) from the pre-adipocyte cell line SW872 treated with either vehicle (CMveh) or the CaSR activator cinacalcet 2 µM (CMcin), in the absence or presence of the CaSR inhibitor calhex 231 10 µM (CMcin+cal). HepG2 cells were cultured with these CM for 120 h and then assessed for cell senescence and mitochondrial dysfunction. CMcin-treated cells showed increased SA-β-GAL staining, which was absent in TNF-α- and IL-1β-depleted CM. Compared to CMveh, CMcin arrested cell cycle, increased IL-1β and CCL2 mRNA, and induced p16 and p53 senescence markers, which was prevented by CMcin+cal. Crucial proteins for mitochondrial function, PGC-1α and OPA1, were decreased with CMcin treatment, concomitant with fragmentation of the mitochondrial network and decreased mitochondrial transmembrane potential. We conclude that pro-inflammatory cytokines TNF-α and IL-1β secreted by SW872 cells after CaSR activation promote cell senescence and mitochondrial dysfunction, which is mediated by mitochondrial fragmentation in HepG2 cells and whose effects were reversed with Mdivi-1. This investigation provides new evidence about the deleterious CaSR-induced communication between pre-adipocytes and liver cells, incorporating the mechanisms involved in cellular senescence.

MicroRNA-27a, downregulated in human obesity, exerts an antiapoptotic function in adipocytes.

Adipocyte apoptosis is a key initial event that contributes to macrophage infiltration into adipose tissue (AT) and thus triggers AT inflammation in obesity. MicroRNA-27a (miR-27a) was shown to mediate the pathological processes of many metabolic disorders; however, whether miR-27a is involved in adipocyte apoptosis of obese AT remains unknown. The present study aimed to investigate the alteration of miR-27a in obese individuals and its antiapoptotic function in adipocytes. In vivo, serum samples and omental adipose tissue from humans as well as epididymal fat pads from mice were collected to detect miR-27a expression. In vitro, 3T3-L1 preadipocytes and mature adipocytes were treated with TNF-α to induce apoptosis and transfected with a mimic for overexpressing miR-27a-3p. The results showed that miR-27a was markedly decreased in the serum and AT of obese human patients and in the AT of high-fat diet-fed mice. Regression analyses revealed that the serum level of miR-27a was correlated with metabolic parameters in human obesity. Notably, TNF-α induced cell apoptosis in both preadipocytes and mature adipocytes, as evidenced by the upregulation of cleaved caspase 3 and cleaved caspase 8 and the ratio of Bax to Bcl-2, while these effects were partly diminished by miR-27a overexpression. In addition, TUNEL and Hoechst 33258 staining verified that miR-27a overexpression markedly inhibited the apoptosis of adipocytes under TNF-α stimulation. Thus, miR-27a was downregulated in the AT of obese subjects with proapoptotic status, and overexpression of miR-27a exerted an antiapoptotic effect on preadipocytes, providing a novel potential target for preventing AT dysfunction.

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

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

Netrin-1 Promotes Visceral Adipose Tissue Inflammation in Obesity and Is Associated with Insulin Resistance.

Netrin (NTN)-1 exhibits pro- and anti-inflammatory roles in different settings, playing important roles in the obesity-associated low-grade chronic inflammation. We aimed to determine the impact of NTN-1 on obesity and obesity-associated type 2 diabetes, as well as its role in visceral adipose tissue (VAT) inflammation. A total of 91 subjects were enrolled in this case-control study. Circulating levels of NTN-1 and its receptor neogenin (NEO)-1 were determined before and after weight loss achieved by caloric restriction and bariatric surgery. mRNA levels of NTN1 and NEO1 were assessed in human VAT, liver, and peripheral blood mononuclear cells. In vitro studies in human visceral adipocytes and human monocytic leukemia cells (THP-1)-derived macrophages were performed to analyze the impact of inflammation-related mediators on the gene expression levels of NTN1 and its receptor NEO1 as well as the effect of NTN-1 on inflammation. Increased (p < 0.001) circulating concentrations of NTN-1 in obesity decreased (p < 0.05) after diet-induced weight loss being also associated with a reduction in glucose (p < 0.01) and insulin levels (p < 0.05). Gene expression levels of NTN1 and NEO1 were upregulated (p < 0.05) in the VAT from patients with obesity with the highest expression in the stromovascular fraction cells compared with mature adipocytes (p < 0.01). NTN1 expression levels were enhanced (p < 0.01) under hypoxia and by inflammatory factors in both adipocytes and macrophages. Adipocyte-conditioned media strongly upregulated (p < 0.001) the mRNA levels of NTN1 in macrophages. The treatment of adipocytes with NTN-1 promoted the upregulation (p < 0.05) of pro-inflammatory and chemotactic molecules as well as its receptor NEO1. Collectively, these findings suggest that NTN-1 regulates VAT chronic inflammation and insulin resistance in obesity.

Macrophage Polarization Mediated by Mitochondrial Dysfunction Induces Adipose Tissue Inflammation in Obesity.

Obesity is one of the prominent global health issues, contributing to the growing prevalence of insulin resistance and type 2 diabetes. Chronic inflammation in adipose tissue is considered as a key risk factor for the development of insulin resistance and type 2 diabetes in obese individuals. Macrophages are the most abundant immune cells in adipose tissue and play an important role in adipose tissue inflammation. Mitochondria are critical for regulating macrophage polarization, differentiation, and survival. Changes to mitochondrial metabolism and physiology induced by extracellular signals may underlie the corresponding state of macrophage activation. Macrophage mitochondrial dysfunction is a key mediator of obesity-induced macrophage inflammatory response and subsequent systemic insulin resistance. Mitochondrial dysfunction drives the activation of the NLRP3 inflammasome, which induces the release of IL-1β. IL-1β leads to decreased insulin sensitivity of insulin target cells via paracrine signaling or infiltration into the systemic circulation. In this review, we discuss the new findings on how obesity induces macrophage mitochondrial dysfunction and how mitochondrial dysfunction induces NLRP3 inflammasome activation. We also summarize therapeutic approaches targeting mitochondria for the treatment of diabetes.

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.

The Role of Short-Chain Fatty Acids in Mediating Very Low-Calorie Ketogenic Diet-Infant Gut Microbiota Relationships and Its Therapeutic Potential in Obesity.

As the very low-calorie ketogenic diet (VLCKD) gains increased interest as a therapeutic approach for many diseases, little is known about its therapeutic use in childhood obesity. Indeed, the role of VLCKD during pregnancy and lactation in influencing short chain fatty acid (SCFA)-producing bacteria and the potential mechanisms involved in the protective effects on obesity are still unclear. Infants are characterized by a diverse gut microbiota composition with higher abundance of SCFA-producing bacteria. Maternal VLCKD during pregnancy and lactation stimulates the growth of diverse species of SCFA-producing bacteria, which may induce epigenetic changes in infant obese gene expression and modulate adipose tissue inflammation in obesity. Therefore, this review aims to determine the mechanistic role of SCFAs in mediating VLCKD-infant gut microbiota relationships and its protective effects on obesity.

Tumor Necrosis Receptor Superfamily Interact with Fusion and Fission of Mitochondria of Adipose Tissue in Obese Patients without Type 2 Diabetes.

Interactions between receptors and ligands of the tumor necrosis factor superfamily (TNFSF) provide costimulatory signals that control the survival, proliferation, differentiation, and effector function of immune cells. All components of the TNF superfamily are associated with NF-kB functions that are not limited to cell death and may promote survival in the face of adipose tissue inflammation in obesity. Inflammation dysfunction of mitochondria is a key factor associated with insulin resistance in obesity. The aim of the study was to analyze the relationship of soluble forms of receptors and ligands of the TNF superfamily in blood plasma with mitochondrial dynamics in adipose tissue (greater omentum (GO) and subcutaneous adipose tissue (Sat)) of obese patients with and without type 2 diabetes mellitus (T2DM). Increased plasma sTNF-R1, sTNF-R2, sTNFRSF8 receptors, and ligands TNFSF12, TNFSF13, TNFSF13B are characteristic of obese patients without T2DM. The TNF-a levels in blood plasma were associated with a decrease in MFN2 gene expression in GO and IL-10 in blood plasma. The TNFSF12 levels contributed to a decrease in glucose levels, a decrease in BMI, and an increase in IL-10 levels by influencing the MFN2 gene expression in GO, which supports mitochondrial fusion.

Fecal microbiota transplantation does not alter bacterial translocation and visceral adipose tissue inflammation in individuals with obesity.

AimsVisceral adipose tissue inflammation is a fundamental mechanism of insulin resistance in obesity and type 2 diabetes. Translocation of intestinal bacteria has been suggested as a driving factor for the inflammation. However, although bacterial DNA was detected in visceral adipose tissue of humans with obesity, it is unclear to what extent this is contamination or whether the gut microbiota is causally involved. Effects of fecal microbiota transplantation (FMT) on bacterial translocation and visceral adipose tissue inflammation in individuals with obesity and insulin resistance were assessed.Material and MethodsEight individuals with clinically severe obesity (body mass index [BMI] >35 kg/m2) and metabolic syndrome received lean donor FMT 4 weeks prior to elective bariatric surgery. The participants were age‐, sex‐, and BMI‐matched to 16 controls that underwent no fecal transplantation. Visceral adipose tissue was collected during surgery. Bacterial translocation was assessed by 16S rRNA gene sequencing of adipose tissue and feces. Pro‐inflammatory cytokine expression and histopathological analyses of visceral adipose tissue were performed to assess inflammation.ResultsFecal microbiota transplantation significantly altered gut microbiota composition. Visceral adipose tissue contained a very low quantity of bacterial DNA in both groups. No difference in visceral bacterial DNA content between groups was observed. Also, visceral expression of pro‐inflammatory cytokines and macrophage infiltration did not differ between groups. No correlation between inflammatory tone and bacterial translocation was observed.ConclusionsVisceral bacterial DNA content and level of inflammation were not altered upon FMT. Thus, bacterial translocation may not be the main driver of visceral adipose tissue inflammation in obesity.

Nutrient regulation of inflammatory signalling in obesity and vascular disease.

Despite obesity and diabetes markedly increasing the risk of developing cardiovascular diseases, the molecular and cellular mechanisms that underlie this association remain poorly characterised. In the last 20 years it has become apparent that chronic, low-grade inflammation in obese adipose tissue may contribute to the risk of developing insulin resistance and type 2 diabetes. Furthermore, increased vascular pro-inflammatory signalling is a key event in the development of cardiovascular diseases. Overnutrition exacerbates pro-inflammatory signalling in vascular and adipose tissues, with several mechanisms proposed to mediate this. In this article, we review the molecular and cellular mechanisms by which nutrients are proposed to regulate pro-inflammatory signalling in adipose and vascular tissues. In addition, we examine the potential therapeutic opportunities that these mechanisms provide for suppression of inappropriate inflammation in obesity and vascular disease.

Adipocytes, Innate Immunity and Obesity: A Mini-Review.

The role of adipose tissue (AT) inflammation in obesity and its multiple related-complications is a rapidly expanding area of scientific interest. Within the last 30 years, the role of the adipocyte as an endocrine and immunologic cell has been progressively established. Like the macrophage, the adipocyte is capable of linking the innate and adaptive immune system through the secretion of adipokines and cytokines; exosome release of lipids, hormones, and microRNAs; and contact interaction with other immune cells. Key innate immune cells in AT include adipocytes, macrophages, neutrophils, and innate lymphoid cells type 2 (ILC2s). The role of the innate immune system in promoting adipose tissue inflammation in obesity will be highlighted in this review. T cells and B cells also play important roles in contributing to AT inflammation and are discussed in this series in the chapter on adaptive immunity.

1199-P: The Oncogene MDM2 Induces M1 Macrophage Polarization and Adipose Tissue Inflammation in Obesity

Obesity is characterized by chronic low-grade inflammation that contributes to the pathogenesis of type 2 diabetes. Adipose tissue macrophages predominantly switch to a pro-inflammatory phenotype known as M1 during obesity. The accumulation of pro-inflammatory M macrophages in obese adipose tissue results in the secretion of a cluster of pro-inflammatory cytokines that instigate adipose tissue inflammation and insulin resistance. Here we discovered that expression of oncoprotein murine double minute 2 (MDM2) was elevated in obese white adipose tissues. Also, MDM2 protein expression was drastically induced in macrophages activated with lipopolysaccharide (LPS) and interferon-γ (IFNγ). Mice with myeloid cells-specific MDM2 haploinsufficiency (Mye-MDM2 KO mice) were generated and subjected to high-fat-diet (HFD) feeding. After 16 weeks of HFD feeding, obesity-induced glucose intolerance and insulin resistance were alleviated in Mye-MDM2 KO mice with reference to their wild type (WT) controls. Systemic inflammation induced by LPS injection was also reduced in Mye-MDM2 KO mice. In vitro, expression of M1 genes induced by LPS and IFNγ were inhibited in bone marrow-derived macrophages with haplodeficiency of MDM2. Similarly, pharmacological inhibition of MDM2 with the small molecule inhibitor Nutlin-3a attenuates pro-inflammatory cytokines secretion by macrophages. Mechanistically, haplodeletion of MDM2 led to decreased expression of glycolytic genes in BMDM during M1 activation. Taken together, we demonstrated a novel role of MDM2 in regulating glycolysis and M1 macrophage activation in addition to its role as a negative regulator of p53 tumour suppressor protein, suggesting it as a potential therapeutic target for treating type 2 diabetes. Disclosure K. Cheng: None. Funding Hong Kong General Research Fund (17100717)

Putative positive role of inflammatory genes in fat deposition supported by altered gene expression in purified human adipocytes and preadipocytes from lean and obese adipose tissues

BackgroundObesity is a chronic low-grade inflammatory disease that is generally characterized by enhanced inflammation in obese adipose tissue (AT). Here, we investigated alterations in gene expression between lean and obese conditions using mRNA-Seq data derived from human purified adipocytes (ACs) and preadipocytes (preACs).ResultsTotal mRNA-seq data were generated with 27 AC and 21 preAC samples purified from human visceral AT collected during resection surgery in cancer patients, where the samples were classified into lean and obese categories by BMI > 25 kg/m2. We defined four classes of differentially expressed genes (DEGs) by comparing gene expression between (1) lean and obese ACs, (2) lean and obese preACs, (3) lean ACs and lean preACs, and 4) obese ACs and obese preACs. Based on an analysis of comparison 1, numerous canonical obesity-related genes, particularly inflammatory genes including IL-6, TNF-α and IL-1β, i.e., the genes that are expected to be upregulated in obesity conditions, were found to be expressed at significantly lower levels in obese ACs than in lean ACs. In contrast, some inflammatory genes were found to be expressed at higher levels in obese preACs than lean preACs in the analysis of comparison 2. The analysis of comparisons 3 and 4 showed that inflammatory gene classes were expressed at higher levels in differentiated ACs than undifferentiated preACs under both lean and obese conditions; however, the degree of upregulation was significantly greater for lean than for obese conditions. We validated our observations using previously published microarray transcriptome data deposited in the GEO database (GSE80654).ConclusionsTaken together, our analyses suggest that inflammatory genes are expressed at lower levels in obese ACs than in lean ACs because lean adipogenesis involves even greater enhancement of inflammatory responses than does obese adipogenesis.

Perivascular mesenchymal cells control adipose-tissue macrophage accrual in obesity.

Chronic low-grade white adipose tissue (WAT) inflammation is a hallmark of metabolic syndrome in obesity. Here, we demonstrate that a subpopulation of murine WAT perivascular (PDGFRβ+) cells, termed “fibro-inflammatory progenitors” (FIPs), activate pro-inflammatory signaling cascades shortly after the onset of high-fat diet feeding and regulate pro-inflammatory macrophage accumulation in WAT in a TLR4-dependent manner. FIPs activation in obesity is mediated by the downregulation of ZFP423, identified here as a transcriptional co-repressor of NFκB. ZFP423 suppresses the DNA-binding capacity of the p65 subunit of NFκB by inducing a p300 to NuRD co-regulator switch. Doxycycline-inducible expression of Zfp423 in PDGFRβ+ cells suppresses inflammatory signaling in FIPs and attenuates metabolic inflammation of visceral WAT in obesity. Inducible inactivation of Zfp423 in PDGFRβ+ cells increases FIP activity, exacerbates adipose macrophage accrual, and promotes WAT dysfunction. These studies implicate perivascular mesenchymal cells as important regulators of chronic adipose tissue inflammation in obesity and identify ZFP423 as a transcriptional break on NFκB signaling.