Visceral Adipose Tissue Inflammation Research Articles

Alleviation of salt-induced exacerbation of cardiac, renal, and visceral fat pathology in rats with metabolic syndrome by surgical removal of subcutaneous fat

ObjectivesEvidence suggests that visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) should be considered as distinct types of white fat. Although VAT plays a key role in metabolic syndrome (MetS), the role of subcutaneous adipose tissue (SAT) has been unclear. DahlS.Z-Leprfa/Leprfa (DS/obese) rats, an animal model of MetS, develop adipocyte hypertrophy and inflammation to similar extents in SAT and VAT. We have now investigated the effects of salt loading and SAT removal on cardiac, renal, and VAT pathology in DS/obese rats.MethodsDS/obese rats were subjected to surgical removal of inguinal SAT or sham surgery at 8 weeks of age. They were provided with a 0.3% NaCl solution as drinking water or water alone for 4 weeks from 9 weeks of age.ResultsSalt loading exacerbated hypertension, insulin resistance, as well as left ventricular (LV) hypertrophy, inflammation, fibrosis, and diastolic dysfunction in DS/obese rats. It also reduced both SAT and VAT mass but aggravated inflammation only in VAT. Although SAT removal did not affect LV hypertrophy in salt-loaded DS/obese rats, it attenuated hypertension, insulin resistance, and LV injury as well as restored fat mass and alleviated inflammation and the downregulation of adiponectin gene expression in VAT. In addition, whereas salt loading worsened renal injury as well as upregulated the expression of renin–angiotensin-aldosterone system-related genes in the kidney, these effects were suppressed by removal of SAT.ConclusionsSAT removal attenuated salt-induced exacerbation of MetS and LV and renal pathology in DS/obese rats. These beneficial effects of SAT removal are likely attributable, at least in part, to inhibition of both VAT and systemic inflammation.

Adipose tissue remodelling in obese subjects is a determinant of presence and severity of fatty liver disease.

Experimental data suggest that visceral adipose tissue (VAT) dysfunction contributes to non-alcoholic fatty liver disease (NAFLD) development in obesity, however, data on humans are limited. Aims of this study were to investigate the relationship between NAFLD and VAT morphofunctional impairment and to determine whether the extent of VAT remodelling is associated with liver damage and metabolic alterations in obesity. We analysed data from 40 obese individuals candidate to bariatric surgery in whom paired intraoperative liver and omental biopsies were performed for diagnosing NAFLD and VAT inflammation by immunohistochemistry and mRNA expression studies. Within our study population, NAFLD was significantly associated with greater VAT CD68+ macrophages infiltration (P = .04), fibrosis (P = .04) and impaired microvascular density (P = .03) as well as increased expression of markers of local hypoxia, apoptosis and inflammation (UNC5B, CASP7, HIF1-α, IL-8, MIP2, WISP-1, all P < .01). The degree of VAT inflammation correlated with the severity of hepatic injury (steatosis, inflammation, fibrosis; all P < .01) and impaired gluco-metabolic profile. In obese patients, NAFLD is associated in a dose-dependent manner with signs of VAT remodelling, which reflect more severe clinical metabolic impairment. Our study depicts morphological alterations and novel mediators of VAT dysfunction, adding knowledge for future therapeutic approaches to NAFLD and its metabolic complications.

Caloric restriction-induced weight loss with a high-fat diet does not fully recover visceral adipose tissue inflammation in previously obese C57BL/6 mice.

Caloric restriction (CR) reduces body weight and systemic inflammation, but the effects on adipose tissue under dietary lipid overload are controversial. We evaluated the effects of CR-induced weight loss with a high-fat diet on adipose tissue inflammation of obese mice. Male mice were assigned into low-fat diet (LF) and high-fat diet (HF) groups. After 8 weeks, the mice in the HF group were reassigned for another 7 weeks into the following 3 conditions: (i) kept in the HF condition; (ii) changed to low-fat diet ad libitum (LFAL); and (iii) changed to high-fat calorie-restricted (RHF) diet to reach LFAL body weight. Serum markers, adipocytokines, morphology, and inflammatory infiltrates in retroperitoneal adipose tissue (RAT) were accessed. The body weights of the LFAL and RHF groups were reduced, equaling the body weights of the LF group. The LFAL mice had restored almost all inflammatory markers as the LF mice, except tumor necrosis factor-alpha (TNF-α), monocyte chemoattractant protein-1 (MCP-1), and adiponectin. Compared with the HF group, the RHF group had lowered visceral adiposity, retroperitoneal adipocyte sizes, and RAT inflammatory cell infiltration, as well as TNF-α, interleukin-6, and hepatic and serum C-reactive protein, which were higher than that of the LFAL group; adiponectin and MCP-1 did not change. CR with high-fat diet reduced body weight and attenuated visceral adiposity but did not fully recover visceral tissue inflammation. Novelty Caloric restriction in a high-fat diet ameliorated visceral adiposity. Caloric restriction in a high-fat diet did not recover visceral adipose tissue inflammation.

Research Highlights

Research Highlights

T reg-specific insulin receptor deletion prevents diet-induced and age-associated metabolic syndrome.

Adipose tissue (AT) regulatory T cells (T regs) control inflammation and metabolism. Diet-induced obesity causes hyperinsulinemia and diminishes visceral AT (VAT) T reg number and function, but whether these two phenomena were mechanistically linked was unknown. Using a T reg-specific insulin receptor (Insr) deletion model, we found that diet-induced T reg dysfunction is driven by T reg-intrinsic insulin signaling. Compared with Foxp3cre mice, after 13 wk of high-fat diet, Foxp3creInsrfl/fl mice exhibited improved glucose tolerance and insulin sensitivity, effects associated with lower AT inflammation and increased numbers of ST2+ T regs in brown AT, but not VAT. Similarly, Foxp3creInsrfl/fl mice were protected from the metabolic effects of aging, but surprisingly had reduced VAT T regs and increased VAT inflammation compared with Foxp3cre mice. Thus, in both diet- and aging-associated hyperinsulinemia, excessive Insr signaling in T regs leads to undesirable metabolic outcomes. Ablation of Insr signaling in T regs represents a novel approach to mitigate the detrimental effects of hyperinsulinemia on immunoregulation of metabolic syndrome.

Thermoneutrality Reduces the Beneficial Metabolic Effects of Eicosapentaenoic Acid on White Adipose Tissue in Diet-Induced Obese Mice

Abstract Objectives At ambient temperature (23°C), eicosapentaenoic acid (EPA), an omega-3 polyunsaturated fatty acid reduces visceral adipose tissue (VAT) inflammation, adipocyte size and improves overall metabolic profile in diet-induced obese (DIO) mice, potentially through upregulation of uncoupling protein 1 (UCP-1). The goal of this study is to determine whether effects of EPA are maintained at thermoneutrality, and/or mediated by UCP-1, and if so through which cellular mechanisms. Methods Wild type (WT) and UCP-1 knockout (KO) B6 male mice were housed at thermoneutral temperature (28–30°C) and fed high fat (HF, 45% kcal fat) supplemented with or without EPA (36 g/kg diet). Serum, VAT (epididymal fat) and cecal microbiome specimens were analyzed. Results EPA reduced adiposity and improved glucose tolerance in EPA-fed KO mice (P &amp;lt; 0.05), but not in EPA-fed WT mice. EPA supplementation lowered VAT mass in both genotypes (P &amp;lt; 0.05); however, there were no diet or genotype-related differences in adipocyte size or serum triglyceride levels. Both genotypes fed EPA had lower serum resistin levels compared to respective HF (P &amp;lt; 0.01). EPA showed trends towards increased serum adiponectin levels compared to HF fed mice in both genotypes, with KO-EPA group having the highest concentration. There was no significant difference in the expression of IL-6 in VAT among the groups, while MCP-1 mRNA was expressed more in KO groups compared to WT groups (P &amp;lt; 0.01). Diet had no effect on expression of anti-inflammatory markers in both WT and KO mice. There were no genotype or diet effects on expression of genes involved in lipid metabolism and mitochondrial energy metabolism. Cecal microbiome showed no differences in the species diversity (Shannon index) between genotypes or diet types. However, only in the KO group, the Bacteroidetes/Firmicutes ratio was increased by EPA. Conclusions Compared to previous work at ambient temperatures, VAT does not mediate protective effects of EPA in DIO mice at thermoneutral temperature. Moreover, EPA effects are independent of UCP-1 as it produced beneficial effects on glucose tolerance and adiposity in KO mice, which may be in part mediated by changes in microbiome. Further mechanistic studies are ongoing to understand the mechanisms mediating EPA and UCP-1 effects in VAT. Funding Sources Funded by NIH (NCCIH and NIA).

Long-term hypercortisolism induces lipogenesis promoting palmitic acid accumulation and inflammation in visceral adipose tissue compared with HFD-induced obesity.

Glucocorticoids (GCs) play critical roles in adipose tissue metabolism. Here, we compare in a mouse model the effects of chronic glucocorticoid excess and diet-induced obesity on white adipose tissue mass and distribution, by focusing on visceral adipose tissue (VAT) fatty acid composition changes, the role of de novo lipogenesis (DNL) and the inflammatory state. We used a noninvasive mouse model of hypercortisolism to compare GC-induced effects on adipose tissue with diet-induced obesity [high-fat diet (HFD) 45%] and control mice after 10 wk of treatment. Subcutaneous adipose tissue (SAT) and VAT mass and distribution were measured by nuclear magnetic resonance imaging (NMRI). Fatty acid composition in VAT was analyzed by NMR spectroscopy and gas chromatography. Gene expression of key enzymes involved in DNL was analyzed in liver and VAT. Macrophage infiltration markers and proinflammatory cytokines were measured by gene expression in VAT. HFD or GC treatment induced similar fat mass expansion with comparable distribution between SAT and VAT depots. However, in VAT, GCs induce DNL, higher palmitic acid (PA), macrophage infiltration, and proinflammatory cytokine levels, accompanied by systemic nonesterified fatty acid (NEFA) elevation, hyperinsulinemia, and higher homeostatic model assessment for insulin resistance (HOMA-IR) levels compared with diet-induced obesity. Thus, chronic hypercortisolism induces DNL and fatty acid composition changes toward increased SFA and reduced polyunsaturated fatty acid (PUFA) levels in VAT, promoting macrophage recruitment and proinflammatory cytokines, suggesting a worse cardiometabolic profile even compared with HFD mice.

Role of immunological disorders, endothelial dysfunction and hemostatic disorders in the genesis of arterial hypertension in the metabolic syndrome

Mortality from diseases of the circulatory system is a challenge for the modern health care. Arterial hypertension (AH) mostly contributes to development of cardiovascular complications. It often proceeds against the background of metabolic disorders. Pathogenesis of hypertension is currently being considered a multifactorial disease. Pathogenesis of hypertension certainly has distinct features in presence of metabolic disorders,. Therefore, it is relevant to summarize current literature on the role of immunological disorders, endothelial dysfunction and hemostatic disorders in AH genesis during metabolic syndrome (MS). Most authors agree with existence of several mechanisms that determine relationships between AH and insulin resistance. Development of hypertension in MS patients with is a consequence of immunometabolic processes. Abdominal obesity is an important component of MS. It is associated with chronic inflammation of visceral adipose tissue, its excessive infiltration by immune cells, and increased production of adipokines and cytokines (TNFα, IL-6) with hypertension. AH is associated with a significant increase in T cells, that mediate endothelial dysfunction (ED) and provide a link between hypertension and subsequent atherosclerosis. T lymphocytes trigger a cascade of reactions. IL-17 is the end product of these events It is involved not only in increasing blood pressure, but also contributes to the development of vascular wall stiffness in АН patients. Thus, the relationship between several types of immune cells leads to inflammatory reactions, including those of vascular wall, initiating endothelial dysfunction. Chronic non-specific inflammation in MS, supported by the cytokine system, is a triggering mechanism for ED progression. Excessive production of endothelin-1 and inhibition of nitric oxide production are the classic markers of ED. Immune damage leads to imbalance in the production of vasoconstrictor and vasodilating substances, proliferative and antiproliferative factors in endothelium. It was shown that ED is an integral aspect of the insulin resistance syndrome in pathogenesis of arterial hypertension associated with metabolic disorders, and contributes to its worsening, increased vascular reactivity and further AH development. According to modern studies, it has been shown that excessive synthesis of pro-inflammatory cytokines introduces disturbances in the system of vascular hemostasis. When studying the effects of metabolic disorders upon hemostatic system, we may conclude that activation of fibrinolytic and plasma chains occurs in the same way for both men and women, with small gender characteristics of individual components. The rheological properties of the blood are also changed with developing MS. Systematization of the available literature data on the issue under study can serve as a basis for determining prognostic criteria of hypertension progression and risk of thrombotic complications.

Dermatopontin, A Novel Adipokine Promoting Adipose Tissue Extracellular Matrix Remodelling and Inflammation in Obesity.

Compelling evidence suggests that dermatopontin (DPT) regulates collagen and fibronectin fibril formation, the induction of cell adhesion and the prompting of wound healing. We aimed to evaluate the role of DPT on obesity and its associated metabolic alterations as well as its impact in visceral adipose tissue (VAT) inflammation and extracellular matrix (ECM) remodelling. Samples obtained from 54 subjects were used in a case-control study. Circulating and VAT expression levels of DPT as well as key ECM remodelling- and inflammation-related genes were analysed. The effect of pro- and anti-inflammatory mediators on the transcript levels of DPT in visceral adipocytes was explored. The impact of DPT on ECM remodelling and inflammation pathways was also evaluated in cultured adipocytes. We show that obesity and obesity-associated type 2 diabetes (T2D) increased (p < 0.05) circulating levels of DPT. In this line, DPT mRNA in VAT was increased (p < 0.05) in obese patients with and without T2D. Gene expression levels of DPT were enhanced (p < 0.05) in human visceral adipocytes after the treatment with lipopolysaccharide, tumour growth factor (TGF)-β and palmitic acid, whereas a downregulation (p < 0.05) was detected after the stimulation with interleukin (IL)-4 and IL-13, critical cytokines mediating anti-inflammatory pathways. Additionally, we revealed that DPT increased (p < 0.05) the expression of ECM- (COL6A3, ELN, MMP9, TNMD) and inflammation-related factors (IL6, IL8, TNF) in human visceral adipocytes. These findings provide, for the first time, evidence of a novel role of DPT in obesity and its associated comorbidities by influencing AT remodelling and inflammation.

Drug Targeting of Plasminogen Activator Inhibitor-1 Inhibits Metabolic Dysfunction and Atherosclerosis in a Murine Model of Metabolic Syndrome.

Enhanced expression of PAI-1 (plasminogen activator inhibitor-1) has been implicated in atherosclerosis formation in humans with obesity and metabolic syndrome. However, little is known about the effects of pharmacological targeting of PAI-1 on atherogenesis. This study examined the effects of pharmacological PAI-1 inhibition on atherosclerosis formation in a murine model of obesity and metabolic syndrome. Approach and Results: LDL receptor-deficient (ldlr-/-) mice were fed a Western diet high in cholesterol, fat, and sucrose to induce obesity, metabolic dysfunction, and atherosclerosis. Western diet triggered significant upregulation of PAI-1 expression compared with normal diet controls. Addition of a pharmacological PAI-1 inhibitor (either PAI-039 or MDI-2268) to Western diet significantly inhibited obesity and atherosclerosis formation for up to 24 weeks without attenuating food consumption. Pharmacological PAI-1 inhibition significantly decreased macrophage accumulation and cell senescence in atherosclerotic plaques. Recombinant PAI-1 stimulated smooth muscle cell senescence, whereas a PAI-1 mutant defective in LRP1 (LDL receptor-related protein 1) binding did not. The prosenescent effect of PAI-1 was blocked by PAI-039 and R2629, a specific anti-LRP1 antibody. PAI-039 significantly decreased visceral adipose tissue inflammation, hyperglycemia, and hepatic triglyceride content without altering plasma lipid profiles. Pharmacological targeting of PAI-1 inhibits atherosclerosis in mice with obesity and metabolic syndrome, while inhibiting macrophage accumulation and cell senescence in atherosclerotic plaques, as well as obesity-associated metabolic dysfunction. PAI-1 induces senescence of smooth muscle cells in an LRP1-dependent manner. These results help to define the role of PAI-1 in atherosclerosis formation and suggest a new plasma-lipid-independent strategy for inhibiting atherogenesis.

Sex drives Tregs into fat.

Androgens promote inflammation in visceral adipose tissue (VAT), leading to the expansion of a distinct IL-33 producing stromal population and recruitment of Tregs.

Critical role of arginase 2 in obesity‐induced metabolic dysregulation in female mice: Implication of macrophage inflammatory response

We have previously shown that deletion of the mitochondrial isoform of the ureahydrolase enzyme (A2) protected against obesity‐induced metabolic dysregulation in “male” mice fed high fat high sucrose diet (HFHS) for 16 weeks. Additionally, A2 expression was upregulated 1.5‐fold in visceral adipose tissue (VAT) of WT "male" mice fed HFHS vs WT fed normal chow diet (ND). Interestingly, A2 expression was elevated 3‐fold in VAT of WT HFHS "female" mice vs WT ND. In the current study, we determined the consequences of global A2 deletion in “female” mice on the same diet protocol. Body weight was measured weekly, adiposity was measured using nuclear magnetic resonance and metabolic activity was assessed using indirect calorimetry. Increases in body weight in WT HFHS female mice, VAT weight and total adiposity were abrogated in A2−/− HFHS mice by 24, 84 and 54%, respectively (p&lt;0.05). Glucose tolerance tests showed a significantly reduced area under the curve in A2−/− HFHS mice vs WT (p&lt;0.05). The leaner phenotype observed in A2−/− mice was in line with the improved metabolic activity as evidenced by increased energy expenditure, volume of O2 consumed and CO2 produced in A2−/− mice fed HFHS vs WT HFHS. Obesity‐induced VAT inflammation and vascular rarefaction contribute to unhealthy expansion of adipose tissue resulting in disrupted metabolic and endocrine functions. VAT sections from WT HFHS stained with isolectin B4 revealed reduced vascular density which was preserved in A2−/− HFHS. Flowcytometry analysis of stromal vascular fraction isolated from VAT of WT HFHS mice showed an increase in proinflammatory M1 macrophages (F4/80+CD11c+) (p=0.06) and a significant decrease in antiinflammatory M2 macrophages (F4/80+CD206+) (p&lt;0.05), the latter was not affected in male mice. These effects were blunted in A2−/− HFHS female mice, reducing the M1/M2 ratio towards a favorable, less inflammatory state. Given the role of A2 in polarizing macrophages to an inflammatory state in vivo, we wished to determine the specific effect of macrophage A2 on inflammatory responses. Peritoneal macrophages from WT and A2−/− female mice were isolated, cultured in vitro and treated with 100 ng/ml lipopolysaccharide (LPS) or vehicle for 24 hr. WT macrophages exposed to LPS showed an activated inflammasome pathway (increased expressions of NLRP3 and pro‐IL‐1β) compared to control group (p&lt;0.05). These effects of LPS were blunted in isolated A2−/− macrophages, indicating that A2 promotes inflammatory macrophage responses in female mice. Collectively, our data show that A2 is a critical mediator of obesity‐induced metabolic dysregulation, VAT vascular rarefaction and increased macrophage inflammatory responses in female mice.Support or Funding InformationR01 HL070215, R01 EY01176 &amp; AHA17PRE33660321

Cholesterol 25-hydroxylase (CH25H) as a promoter of adipose tissue inflammation in obesity and diabetes

ObjectiveExpansion of visceral adipose tissue (VAT) and metabolic inflammation are consequences of obesity and associated with type 2 diabetes (T2DM). Metabolically activated adipose tissue macrophages (ATMs) undergo qualitative and quantitative changes that influence their inflammatory responses. How these cells contribute to insulin resistance (IR) in humans is not well understood. Cholesterol 25-Hydroxylase (CH25H) converts cholesterol into 25-Hydroxycholesterol (25-HC), an oxysterol that modulates immune responses. Using human and murine models, we investigated the role of CH25H in metabolic inflammation. MethodsWe performed transcriptomic (RNASeq) analysis on the human whole AT biopsies and sorted ATMs from obese non-diabetic (NDM) and obese diabetic (DM) subjects to inquire if CH25H was increased in DM. We challenged mice lacking Ch25h with a high-fat diet (HFD) to characterize their metabolic and immunologic profiling. Ch25h KO mice and human adipose tissue biopsies from NDM and DM subjects were analyzed. LC-MS was conducted to measure 25-HC level in AT. In vitro analysis permitted us to investigate the effect of 25-HC on cytokine expression. ResultsIn our RNASeq analysis of human visceral and subcutaneous biopsies, gene pathways related to inflammation were increased in obese DM vs. non-DM subjects that included CH25H. CH25H was enriched in the stromal vascular fraction of human adipose tissue and highly expressed in CD206+ human ATMs by flow cytometry analysis. We measured the levels of the oxysterols, 25-HC and 7α25diHC, in human visceral adipose tissue samples and showed a correlation between BMI and 25-HC. Using mouse models of diet-induced obesity (DIO), we found that HFD-induced Ch25h expression in eWAT and increased levels of 25-HC in AT. On HFD, Ch25h KO mice became obese but exhibited reduced plasma insulin levels, improved insulin action, and decreased ectopic lipid deposit. Improved insulin sensitivity in Ch25h KO mice was due to attenuation of CD11c+ adipose tissue macrophage infiltration in eWAT. Finally, by testing AT explants, bone marrow-derived macrophages (BMDMs) and SVF cells from Ch25h deficient mice, we observed that 25-HC is required for the expression of pro-inflammatory genes. 25-HC was also able to induce inflammatory genes in preadipocytes. ConclusionsOur data suggest a critical role for CH25H/25-HC in the progression of meta-inflammation and insulin resistance in obese humans and mouse models of obesity. In response to obesogenic stimuli, CH25H/25-HC could exert a pro-inflammatory role.

Obesity Reshapes Visceral Fat-Derived MHC I Associated-Immunopeptidomes and Generates Antigenic Peptides to Drive CD8+ T Cell Responses.

SummaryAdaptive CD8+ T cells were observed to contribute to the initiation and progression of obesity-induced visceral adipose tissue (VAT) chronic inflammation that is critically linked to metabolic disorders. Numerous peptides presented by the major histocompatibility complex (MHC) class I molecules at the cell surface are collectively termed as MHC I-associated immunopeptidome (MIP) for the interaction with CD8+ T cells. We conducted the in-depth mapping of MIP of VAT from lean and obese mice using large-scale high-resolution mass spectrometry and observed that obesity significantly alters the landscape of VAT MIPs. Additionally, the obese VAT-exclusive MIP source proteome reflected a distinct obesity-associated signature. A peptide derived from lactate dehydrogenase A (LDHA) or B chain, named LDHA237-244, was identified as an obese VAT-exclusive immunogenic peptide that was capable of eliciting pro-inflammatory CD8+ T cells responses. Our findings suggest that certain immunogenic peptides generated by obesity may trigger CD8+ T cell-mediated VAT inflammation.

Visceral adipose tissue Tregs and the cells that nurture them

Visceral adipose tissue (VAT) is a primary site for storage of excess energy, but it also serves as an important endocrine organ that impacts organismal metabolism. Chronic, low-grade inflammation of VAT, and eventually systemically, is one of the major drivers of obesity-associated insulin resistance and metabolic abnormalities. A unique population of regulatory T cells (Tregs), with a distinct transcriptional profile and antigen receptor repertoire resides in VAT, keeps inflammation in check and regulates organismal metabolism. Accumulation of these cells depends on interactions with other local immunocytes and, importantly, subtypes of VAT mesenchymal stromal cells (VmSCs) that are either immunomodulators or adipogenic. We summarize our current understanding of the phenotype, function, dependencies, derivation, and modulations of VAT Tregs, and review the heterogeneity and regulation of VmSCs as well as their cross talk with VAT Tregs. Lastly, we discuss imperative questions remaining to be answered.

Sex-specific adipose tissue imprinting of regulatory T cells.

Adipose tissue is an energy store and a dynamic endocrine organ1,2. In particular, visceral adipose tissue (VAT) is critical for the regulation of systemic metabolism3,4. Impaired VAT function-for example, in obesity-is associated with insulin resistance and type 2 diabetes5,6. Regulatory T (Treg) cells that express the transcription factor FOXP3 are critical for limiting immune responses and suppressing tissue inflammation, including in the VAT7-9. Here we uncover pronounced sexual dimorphism in Treg cells in the VAT. Male VAT was enriched for Treg cells compared with female VAT, and Treg cells from male VAT were markedly different from their female counterparts in phenotype, transcriptional landscape and chromatin accessibility. Heightened inflammation in the male VAT facilitated the recruitment of Treg cells via the CCL2-CCR2 axis. Androgen regulated the differentiation of a unique IL-33-producing stromal cell population specific to the male VAT, which paralleled the local expansion of Treg cells. Sex hormones also regulated VAT inflammation, which shaped the transcriptional landscape of VAT-resident Treg cells in a BLIMP1 transcription factor-dependent manner. Overall, we find that sex-specific differences in Treg cells from VAT are determined by the tissue niche in a sex-hormone-dependent manner to limit adipose tissue inflammation.

Obesogenic Memory Maintains Adipose Tissue Inflammation and Insulin Resistance.

Background:Obesity is characterized by visceral adipose tissue (AT) inflammation. Immunosuppressive regulatory T cells (Tregs), phagocytic M2-like macrophages, and innate lymphoid cells type 2 (ILC2) control lean AT inflammation to maintain systemic insulin sensitivity, while the loss of these cells in obesity leads to AT inflammation and insulin resistance (IR).Objective:The objective of this study was to determine if weight loss following obesity would correct AT inflammation and systemic metabolism.Results:After six months of high fat diet (HFD) in male C57/Bl6 mice, flow analyses of epidydimal AT stromal vascular fraction (SVF) revealed depleted Tregs by 50%, doubling of CD8+ T cells, tripling of pro-inflammatory M1-like macrophages, and an 80% drop in ILC2 cells associated with changes in pro-inflammatory adipocyte and macrophage gene expression. Despite normalization of body weight, fat, and adipocyte size, mice ingesting 3 months of high-fat diet (HFD) followed by 3 months of chow-diet remained more insulin resistant and glucose intolerant than chow-fed animals. Adipocytes, AT Tregs, CD8+ T cells, ILC2 cells, and M1-like macrophages all failed to normalize with weight loss.Conclusions:Persistent AT inflammation contributes to the maintenance of IR despite body weight and fat normalization in previously obese mice. These findings highlight the importance of obesity prevention to avoid the consequences of “obesogenic memory.”

Vascular Adhesion Protein 1 Mediates Gut Microbial Flagellin-Induced Inflammation, Leukocyte Infiltration, and Hepatic Steatosis

Toll-like receptor 5 ligand, flagellin, and Vascular Adhesion Protein-1 (VAP-1) are involved in non-alcoholic fatty liver disease (NAFLD). This study aimed to determine whether VAP-1 mediates flagellin-induced hepatic fat accumulation. The effects of flagellin on adipocyte VAP-1 expression were first studied in vitro. Then, flagellin (100 ng/mouse) or saline was intraperitoneally injected to C57BL/6J WT and C57BL/6-Aoc3-/- (VAP-1 KO) mice on high-fat diet twice a week every two weeks for 10-weeks. After that, the effects on inflammation, insulin signaling, and metabolism were studied in liver and adipose tissues. Hepatic fat was quantified histologically and biochemically. Because flagellin challenge increased VAP-1 expression in human adipocytes, we used VAP-1 KO mice to determine whether VAP-1 regulates the inflammatory and metabolic effects of flagellin in vivo. In mice, VAP-1 mediated flagellin-induced inflammation, leukocyte infiltration and lipolysis in visceral adipose tissue. Consequently, increased release of glycerol led to hepatic steatosis in WT but not KO mice. Flagellin-induced hepatic fibrosis was not mediated by VAP-1. VAP-1 KO mice harbored more inflammation-related microbes than WT, while flagellin did not affect the gut microbiota. Our results suggest that by acting on visceral adipose tissue, flagellin increased leukocyte infiltration that induced lipolysis. Further, the released glycerol participated in hepatic fat accumulation. In conclusion, the results describe that gut microbial flagellin through VAP-1 induced hepatic steatosis.

α-Mangostin remodels visceral adipose tissue inflammation to ameliorate age-related metabolic disorders in mice.

Low-grade chronic adipose tissue inflammation contributes to the onset and development of aging-related insulin resistance and type 2 diabetes. In the current study, α-mangostin, a xanthone isolated from mangosteen (Garcinia mangostana), was identified to ameliorate lipopolysaccharides-induced acute adipose tissue inflammation in mice, by reducing the expression of pro-inflammatory cytokines and chemokines. In a cohort of young (3 months) and old (18–20 months) mice, α-mangostin mitigated aging-associated adiposity, hyperlipidemia, and insulin resistance. Further study showed that α-mangostin alleviated aging-related adipose tissue inflammation by reducing macrophage content and shifting pro-inflammatory macrophage polarization. Moreover, α-mangostin protected the old mice against liver injury through suppressing the secretion of microRNA-155-5p from macrophages. The above results demonstrated that α-mangostin represents a new scaffold to alleviate adipose tissue inflammation, which might be a novel candidate to treat aging-related metabolic disorders.

Pharmacological myeloperoxidase (MPO) inhibition in an obese/hypertensive mouse model attenuates obesity and liver damage, but not cardiac remodeling

Lifestyle factors are important drivers of chronic diseases, including cardiovascular syndromes, with low grade inflammation as a central player. Attenuating myeloperoxidase (MPO) activity, an inflammatory enzyme associated with obesity, hypertension and heart failure, could have protective effects on multiple organs. Herein, the effects of the novel oral available MPO inhibitor AZM198 were studied in an obese/hypertensive mouse model which displays a cardiac phenotype. Eight week old male C57BL6/J mice received 16 weeks of high fat diet (HFD) combined with angiotensin II (AngII) infusion during the last 4 weeks, with low fat diet and saline infusion as control. Treated animals showed therapeutic AZM198 levels (2.1 µM), corresponding to 95% MPO inhibition. AZM198 reduced elevated circulating MPO levels in HFD/AngII mice to normal values. Independent of food intake, bodyweight increase and fat accumulation were attenuated by AZM198, alongside with reduced visceral adipose tissue (VAT) inflammation and attenuated severity of nonalcoholic steatohepatitis. The HFD/AngII perturbation caused impaired cardiac relaxation and contraction, and increased cardiac hypertrophy and fibrosis. AZM198 treatment did, however, not improve these cardiac parameters. Thus, AZM198 had positive effects on the main lipid controlling tissues in the body, namely adipose tissue and liver. This did, however, not directly result in improved cardiac function.