Visceral Adipose Tissue Inflammation Research Articles

1702-P: Altered Gene Expression Signatures following COVID-19 Infections and/or mRNA Vaccination in Human Adipose Tissue

Obesity is associated with an increase in morbidity and mortality from Coronavirus disease- 2019 (COVID-19). Adipose tissue (AT) demonstrates high expression of angiotensin-converting enzyme 2 (ACE2), a host cell entry factor of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 has been shown to infect AT, where it continues to proliferate, thereby contributing to local inflammation. Since visceral AT inflammation may play a role in the pathogenesis of type 2 diabetes, we investigated the molecular and histological AT signatures after a Covid-19 infection and/or mRNA vaccination. We investigated 54 paired subcutaneous (SC) and visceral adipose tissue (VAT) biopsies from the Leipzig Obesity BioBank in subgroups based on positive versus negative SARS-CoV-2 infection as well as mRNA vaccination status in comparison to BMI and age matched controls obtained before appearance of Covid-19 (N=27). We compared gene expression signatures by RNA-Sequencing analyses, morphology changes in AT as well as circulating inflammation markers across the groups. In relation to a Covid-19 infection, we find a distinct gene expression signature and morphology in AT suggesting that SARS-CoV-2 affects AT and may mediate the disease course. In this context, inflammation of AT, but also an altered secretion profile from AT could link obesity to its metabolic complications, but also to long Covid-19 disease courses. Disclosure S.Krupka: None. M.Blüher: Advisory Panel; Boehringer Ingelheim Inc., Lilly, Novo Nordisk, Consultant; Novo Nordisk Foundation, Speaker's Bureau; Amgen Inc., AstraZeneca, Bayer Inc., Daiichi Sankyo, Novartis, Sanofi-Aventis Deutschland GmbH. N.Klöting: None.

ASSESSMENT OF MACROPHAGE INFLAMMATORY ACTIVITY ON VISCERAL ADIPOSE TISSUE IN HIGH-FAT DIET-INDUCED OBESE MICE BY 18F- FDG PET/CT

Objective: Obesity induced inflamed visceral adipose tissue (VAT) secretes pro-inflammatory cytokines thereby promoting systemic inflammation and insulin resistance which further exacerbate obesity-related cardiovascular disease (CVD). Macrophages are the key players in the development of obesity-associated VAT inflammation. Extensive clinical studies have reported that 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) can be used to evaluate the macrophage inflammatory activity on VAT in human beings. However, due to difficulty in human VAT biopsy, pathologic correlations were lacking and there was a few study on preclinical animal models. Here, we investigated whether 18F-FDG PET/CT could reflect the macrophage inflammatory activity on VAT in high-fat diet-induced obese mice. Design and method: Obese animal models were induced by a high-fat diet (60% fat) for 20 weeks using the male C57BL/6 mice. Insulin tolerance test was performed to evaluate the status of insulin resistance and C-reactive protein (CRP) was measured to assess the status of systemic inflammation. All animals underwent 18F-FDG PET/CT before sacrifice. Macrophage inflammatory activity was evaluated using the maximum standardized uptake value (SUVmax). Flow cytometry-, histological-, and molecular analyses were performed on harvested VAT. Results: All obese animals showed insulin resistance which resembled the human metabolic syndrome, a key pathophysiological process that contributes to increase CVD risk. VAT SUVmax was increased in obese mice and significantly correlated with the levels of CRP. Furthermore, VAT from obese mice showed increased macrophage infiltration, compared to normal mice. Conclusions: 18F-FDG PET/CT could visualize and evaluate the macrophage inflammatory activity on obesity-driven inflamed VAT in obese mice model. Our preclinical study strongly supports the clinical application of 18F-FDG PET/CT in the assessment of VAT inflammation to patients who are vulnerable to CVD.

Cellular cholesterol homeostasis supports visceral adipose tissue (VAT) regulatory T cell (Treg) accumulation and promotes metabolic health

Abstract A unique population of regulatory T cells (Tregs), characterized by a clonally expanded TCR repertoire and distinct transcriptional profile, is highly enriched in the visceral adipose tissue (VAT) at steady state but is lost during obesity, which exacerbates VAT inflammation and promotes metabolic disease. Therefore, understanding the factors that control the accumulation of VAT Tregs, which might be dysregulated during obesity, is important for developing novel therapies for obesity-associated metabolic diseases. Here we show that cellular cholesterol homeostasis is particularly important for VAT Treg accumulation and function. First, bulk RNA sequencing analysis of VAT Tregs from mice fed long-term high fat diet (HFD) showed a reduction in gene expression involved in cholesterol homeostasis (CH), corresponding to loss of VAT Tregs in vivo. Second, we found that VAT Tregs showed increased cholesterol-associated gene expression, cholesterol levels, and cholesterol uptake compared to lymphoid Tregs at steady state, suggesting this pathway is particularly important for VAT Tregs. Third, CRISPR-Cas9-mediated ablation of Srebf2, the master regulator of cholesterol homeostasis, followed by adoptive Treg transfer or Treg-specific germline deletion of Srebf2(Foxp3cre Srebf2-flox) reduced Tregs in the VAT, but not those in other tissues. Deletion of Srebf2in Tregs also increased VAT inflammatory cytokine expression, inflammatory cell infiltration, and insulin resistance in mice following short-term HFD feeding. These data highlight an importance of cellular CH for VAT Treg accumulation and function and implicate this pathway as a potential therapeutic target for treatment of obesity-associated metabolic diseases. NIH R01 (5R01DK128061-02)

Ascorbic acid reduces insulin resistance and pancreatic steatosis by regulating adipocyte hypertrophy in obese ovariectomized mice.

Ascorbic acid has been suggested to regulate obesity in obese male rodents.Moreover, increased adipocyte size has been associated with metabolic disease. Thus, we investigated the effects of ascorbic acid on adipocyte hypertrophy and insulin resistance in high-fat diet (HFD)-induced obese ovariectomized (OVX) C57BL/6J mice, an animal model of obese postmenopausal women. Administration of ascorbic acid (5%w/w in diet for 18 weeks) reduced the size of visceral adipocytes without changes in body weight and adipose tissue mass in HFD-fed obese OVX mice compared with obese OVX mice that did not receive ascorbic acid. Ascorbic acid inhibited adipose tissue inflammation, as shown by the decreased number of crown-like structures and CD68-positive macrophages in visceral adipose tissues. Ascorbic acid-treated mice exhibited improved hyperglycemia, hyperinsulinemia, and glucose and insulin tolerance compared with nontreated obese mice. Pancreatic islet size and insulin-positive β-cell area in ascorbic acid-treated obese OVX mice decreased to the levels observed in low-fat diet-fed lean mice. Ascorbic acid also suppressed pancreatic triglyceride accumulation in obese mice. These results suggest that ascorbic acid may reduce insulin resistance and pancreatic steatosis partly by suppressing visceral adipocyte hypertrophy and adipose tissue inflammation in obese OVX mice.

Estrogen contributes to the sex difference in the occurrence of senescence-related T cells during the development of visceral adipose tissue inflammation.

It remains unclear whether sex differences exist during the development of visceral adipose tissue (VAT) inflammation associated with obesity. The purpose of this study was to clarify sex differences in the occurrence of senescence-related T cells (CD44high PD-1+ CD4+), which play a key role in the progression of VAT inflammation associated with high-fat diet (HFD)-induced obesity. Phase 1: C57BL/6N mice were fed either a control diet (HFC) or HFD for 5 wk. The area under the curve of the oral glucose-tolerance test (oGTT) was maximal at 15 wk in HFD-fed males and at 21 wk in females. At 17 wk, VAT weights were similar, but an increase in the number of macrophages in the VAT was observed only in HFD-fed males. In addition, the numbers of regulatory and senescence-related T cells were consistently higher in males than in females. Phases 2 and 3: 6-wk-old female mice were randomly divided into sham operation and bilateral ovariectomy (OVX) groups and fed either an HFC or HFD from 7 wk. OVX mice were subjected to 17β-estradiol releasing or placebo pellet implantation and fed an HFC. Body and VAT weights were higher in the OVX group than in the sham. The number of macrophages did not change in the OVX group with either diet. HFC-fed OVX mice exhibited high senescence-related T cells in the VAT, resembling HFC-fed male mice. This change was abolished by 17β-estradiol replacement. Thus, we demonstrated different accumulation patterns of VAT immune cells between the sexes, revealing a role for estrogen in the appearance of senescence-related T cells.NEW & NOTEWORTHY The accumulation pattern of adipose tissue differs between the sexes; however, it is unclear whether sex differences exist during the development of adipose tissue inflammation and whether estrogen plays a role. We demonstrated sex differences in immune cells' subpopulation of visceral adipose tissue. The proinflammatory environment appeared earlier in males than in females. In addition, our results suggest that estrogen plays a role in visceral adipose tissue inflammation, particularly by regulating the appearance of senescence-related T cells.

Regulatory T cells differentiation in visceral adipose tissues contributes to insulin resistance by regulating JAZF-1/PPAR-γ pathway.

Regulatory T cell (Treg) activity and differentiation in visceral adipose tissue (VAT) play an important role in inhibiting chronic inflammation and insulin resistance. Whether JAZF-1 and PPAR-γ mediate VAT Treg differentiation to promote the inhibition of chronic inflammation and insulin resistance remains unclear. Here, we investigated the roles of JAZF-1 and PPAR-γ in VAT Treg differentiation, inflammation and insulin resistance using a transgenic mouse model. First, we determined that the levels of glucose and insulin biochemical markers in the JAZF-1 transgenic general feeding or high-fat groups were lower than those in the wild-type general feeding or high-fat groups. Second, the levels of CD4+ , CD25+ , and FOXP3+ differentiation markers in the JAZF-1 transgenic general feeding or high-fat groups were significantly higher than those in the wild-type groups. PPAR-γ inhibition was associated with low levels of CD4+ , CD25+ and FOXP3+ differentiation markers. Third, the levels of TNF-α, IL-1β and IL-6 in the JAZF-1 transgenic groups were lower than those in the wild-type groups, whereas IL-10 and TGF-β levels were higher in the JAZF-1 transgenic groups than in the wild-type groups. After using the PPAR-γ inhibitor, we observed that TNF-α, IL-1β and IL-6 increased, while IL-10 and TGF-β decreased. We found that JAZF-1 and PPAR-γ could promote Tregs differentiation and regulate insulin resistance by synergistically decreasing the expression levels of TNF-α, IL-1β and IL-6 and increasing those of IL-10 and TGF-β.

Identification of major hub genes involved in high-fat diet-induced obese visceral adipose tissue based on bioinformatics approach

ABSTRACT High-fat diet (HFD) can cause obesity, inducing dysregulation of the visceral adipose tissue (VAT). This study aimed to explore potential biological pathways and hub genes involved in obese VAT, and for that, bioinformatic analysis of multiple datasets was performed. The expression profiles (GSE30247, GSE167311 and GSE79434) were downloaded from Gene Expression Omnibus. Overlapping differentially expressed genes (ODEGs) between normal diet and HFD groups in GSE30247 and GSE167311 were selected to run protein–protein interaction network, GO and KEGG analysis. The hub genes in ODEGs were screened by Cytoscape software and further verified in GSE79434 and obese mouse model. A total of 747 ODEGs (599 up-regulated and 148 down-regulated) were screened, and the GO and KEGG analysis showed that the up-regulated ODEGs were significantly enriched in inflammatory response and extracellular matrix receptor interaction pathways. On the other hand, the down-regulated ODEGs were involved in metabolic pathways; however, there were no significant KEGG pathways. Furthermore, six hub genes, Mki67, Rac2, Itgb2, Emr1, Tyrobp and Csf1r were acquired. These pathways and genes were verified in GSE79434 and VAT of obese mice. This study revealed that HFD induced VAT expansion, inflammation and fibrosis, and the hub genes could be used as therapeutic biomarkers in obesity.

Drastic transformation of visceral adipose tissue and peripheral CD4 T cells in obesity.

Obesity has a pronounced effect on the immune response in systemic organs that results in not only insulin resistance but also altered immune responses to infectious diseases and malignant tumors. Obesity-associated microenvironmental changes alter transcriptional expression and metabolism in T cells, leading to alterations in T-cell differentiation, proliferation, function, and survival. Adipokines, cytokines, and lipids derived from obese visceral adipose tissue (VAT) may also contribute to the systemic T-cell phenotype, resulting in obesity-specific pathogenesis. VAT T cells, which have multiple roles in regulating homeostasis and energy utilization and defending against pathogens, are most susceptible to obesity. In particular, many studies have shown that CD4 T cells are deeply involved in the homeostasis of VAT endocrine and metabolic functions and in obesity-related chronic inflammation. In obesity, macrophages and adipocytes in VAT function as antigen-presenting cells and contribute to the obesity-specific CD4 T-cell response by inducing CD4 T-cell proliferation and differentiation into inflammatory effectors via interactions between major histocompatibility complex class II and T-cell receptors. When obesity persists, prolonged stimulation by leptin and circulating free fatty acids, repetitive antigen stimulation, activating stress responses, and hypoxia induce exhaustion of CD4 T cells in VAT. T-cell exhaustion is characterized by restricted effector function, persistent expression of inhibitory receptors, and a transcriptional state distinct from functional effector and memory T cells. Moreover, obesity causes thymic regression, which may result in homeostatic proliferation of obesity-specific T-cell subsets due to changes in T-cell metabolism and gene expression in VAT. In addition to causing T-cell exhaustion, obesity also accelerates cellular senescence of CD4 T cells. Senescent CD4 T cells secrete osteopontin, which causes further VAT inflammation. The obesity-associated transformation of CD4 T cells remains a negative legacy even after weight loss, causing treatment resistance of obesity-related conditions. This review discusses the marked transformation of CD4 T cells in VAT and systemic organs as a consequence of obesity-related microenvironmental changes.

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.

Insulin resistance and adipose tissue inflammation induced by a high-fat diet are attenuated in the absence of hepcidin

Increased body iron stores and inflammation in adipose tissue have been implicated in the pathogenesis of insulin resistance (IR) and type 2 diabetes mellitus. However, the underlying basis of these associations is unclear. To attempt to investigate this, we studied the development of IR and associated inflammation in adipose tissue in the presence of increased body iron stores. Male hepcidin knock-out (Hamp1−/−) mice, which have increased body iron stores, and wild-type (WT) mice were fed a high-fat diet (HFD) for 12 and 24 weeks. Development of IR and metabolic parameters linked to this, insulin signaling in various tissues, and inflammation and iron-related parameters in visceral adipose tissue were studied in these animals. HFD-feeding resulted in impaired glucose tolerance in both genotypes of mice. In response to the HFD for 24 weeks, Hamp1−/− mice gained less body weight and developed less systemic IR than corresponding WT mice. This was associated with less lipid accumulation in the liver and decreased inflammation and lipolysis in the adipose tissue in the knock-out mice, than in the WT animals. Fewer macrophages infiltrated the adipose tissue in the knockout mice than in wild-type mice, with these macrophages exhibiting a predominantly anti-inflammatory (M2-like) phenotype and indirect evidence of a possible lowered intracellular iron content. The absence of hepcidin was thus associated with attenuated inflammation in the adipose tissue and increased whole-body insulin sensitivity, suggesting a role for it in these processes.

Visualization of macrophage inflammatory activity on visceral obesity in high-fat diet-induced obese mice by 18F-FDG PET/CT

Abstract Background Obesity induced inflamed visceral adipose tissue (VAT) secretes pro-inflammatory cytokines thereby promoting systemic inflammation and insulin resistance which further exacerbate obesity-related cardiovascular disease (CVD). Macrophages are the key players in the development of obesity-associated VAT inflammation. Extensive clinical studies have reported that 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) can be used to evaluate the macrophage inflammatory activity on VAT in human beings. However, due to difficulty in human VAT biopsy, pathologic correlations were lacking and there was a few study on preclinical animal models. Purpose Here, we investigated whether 18F-FDG PET/CT could reflect the macrophage inflammatory activity on VAT in high-fat diet-induced obese mice. Methods Obese animal models were induced by a high-fat diet (60% fat) for 20 weeks using the male C57BL/6 mice. Insulin tolerance test was performed to evaluate the status of insulin resistance and C-reactive protein (CRP) was measured to assess the status of systemic inflammation. All animals underwent 18F-FDG PET/CT before sacrifice. Macrophage inflammatory activity was evaluated using the maximum standardized uptake value (SUVmax). Flow cytometry-, histological-, and molecular analyses were performed on harvested VAT. Results All obese animals showed insulin resistance which resembled the human metabolic syndrome, a key pathophysiological process that contributes to increase CVD risk. VAT SUVmax was increased in obese mice and significantly correlated with the levels of CRP. Furthermore, VAT from obese mice showed increased macrophage infiltration, compared to normal mice. Conclusions 18F-FDG PET/CT could visualize and evaluate the macrophage inflammatory activity on obesity-driven inflamed VAT in obese mice model. Our preclinical study strongly supports the clinical application of 18F-FDG PET/CT in the assessment of VAT inflammation to patients who are vulnerable to CVD. Funding Acknowledgement Type of funding sources: None.

Cytokine and metabolic regulation of adipose tissue Tregs.

Since their discovery over a decade ago, much has been learned regarding the importance and function of visceral adipose tissue (VAT)-resident regulatory T cells (Tregs). VAT Tregs play a critical role in controlling VAT inflammation and alleviating metabolic disease. However, this population is disrupted in obesity which exacerbates VAT inflammation and metabolic abnormalities. Therefore, understanding the factors governing the accumulation and maintenance of VAT Tregs, both at steady state and under disease conditions, is crucial for identifying the mechanisms underlying obesity-associated metabolic disease and developing novel therapies. Expansion and maintenance of the VAT Treg compartment is strongly influenced by factors in the local tissue microenvironment, including cytokines, T-cell receptor ligands, hormones, and various metabolites. This mini-review will primarily focus on recent advances in our understandings regarding the regulation of mouse epididymal VAT (eVAT) Tregs, which are the most thoroughly characterized VAT Treg population, by tissue microenvironmental factors and cellular metabolic processes. We will also briefly discuss the limited knowledge available regarding the regulation of mouse ovarian VAT (oVAT) Tregs and human omental VAT Tregs, highlight some lingering questions, and provide a prospective view on where the field is heading.

Tregs in visceral adipose tissue up-regulate circadian-clock expression to promote fitness and enforce a diurnal rhythm of lipolysis.

Regulatory T cells (Tregs) in nonlymphoid organs provide critical brakes on inflammation and regulate tissue homeostasis. Although so-called "tissue Tregs" are phenotypically and functionally diverse, serving to optimize their performance and survival, up-regulation of pathways related to circadian rhythms is a feature they share. Yet the diurnal regulation of Tregs and its consequences are controversial and poorly understood. Here, we profiled diurnal variations in visceral adipose tissue (VAT) and splenic Tregs in the presence and absence of core-clock genes. VAT, but not splenic, Tregs up-regulated their cell-intrinsic circadian program and exhibited diurnal variations in their activation and metabolic state. BMAL1 deficiency specifically in Tregs led to constitutive activation and poor oxidative metabolism in VAT, but not splenic, Tregs. Disruption of core-clock components resulted in loss of fitness: BMAL1-deficient VAT Tregs were preferentially lost during competitive transfers and in heterozygous TregBmal1Δ females. After 16 weeks of high-fat diet feeding, VAT inflammation was increased in mice harboring BMAL1-deficient Tregs, and the remaining cells lost the transcriptomic signature of bona fide VAT Tregs. Unexpectedly, VAT Tregs suppressed adipocyte lipolysis, and BMAL1 deficiency specifically in Tregs abrogated the characteristic diurnal variation in adipose tissue lipolysis, resulting in enhanced suppression of lipolysis throughout the day. These findings argue for the importance of the cell-intrinsic clock program in optimizing VAT Treg function and fitness.

Early-life dietary exposures mediate persistent shifts in the gut microbiome and visceral fat metabolism.

In utero dietary exposures are linked to the development of metabolic syndrome in adult offspring. These dietary exposures can potentially impact gut microbial composition and offspring metabolic health. Female BALB/c mice were administered a lard, lard + flaxseed oil, high sugar, or control diet 4 wk before mating, throughout mating, pregnancy, and lactation. Female offspring were offered low-fat control diet at weaning. Fecal 16S sequencing was performed. Untargeted metabolomics was performed on visceral adipose tissue (VAT) of adult female offspring. Immunohistochemistry was used to determine adipocyte size, VAT collagen deposition, and macrophage content. Hippurate was administered via weekly intraperitoneal injections to low-fat and high-fat diet-fed female mice and VAT fibrosis and collagen 1A (COL1A) were assessed by immunohistochemistry. Lard diet exposure was associated with elevated body and VAT weight and dysregulated glucose metabolism. Lard + flaxseed oil attenuated these effects. Lard diet exposures were associated with increased adipocyte diameter and VAT macrophage count. Lard + flaxseed oil reduced adipocyte diameter and fibrosis compared with the lard diet. Hippurate-associated bacteria were influenced by lard versus lard + flax exposures that persisted to adulthood. VAT hippurate was increased in lard + flaxseed oil compared with lard diet. Hippurate supplementation mitigated VAT fibrosis pathology. Maternal high-fat lard diet consumption resulted in long-term metabolic and gut microbiome programming in offspring, impacting VAT inflammation and fibrosis, and was associated with reduced VAT hippurate content. These traits were not observed in maternal high-fat lard + flaxseed oil diet-exposed offspring. Hippurate supplementation reduced VAT fibrosis. These data suggest that detrimental effects of early-life high-fat lard diet exposure can be attenuated by dietary omega-3 polyunsaturated fatty acid supplementation.

Reducing obesity and inflammation in mice with organically-derivatized polyoxovanadate clusters

Obesity, characterized by the dysregulation of energy balance in adipose tissue and other metabolic organs, is frequently accompanied by chronic low-grade inflammation. As long-acting insulin sensitizers, the organically-derivatized polyoxovanadates (POVs), can extend the dosing interval of antidiabetic drugs from hourly to almost daily. In this work, the protective activity of POVs is investigated by an eight-week in vivo experiment, in which a small amount of POVs was administrated orally to a mouse model of diet-induced obesity every day. The present study shows that administration of POVs significantly decreases the body weight of mice, reduces adipose tissue accumulation, and simultaneously reduces adipose tissue inflammation. In addition, the anti-obesogenic population of iNKT cells is protected potentially by POVs, which subsequently alleviates visceral adipose tissue inflammation in high-fat-diet (HFD)-fed mice against diet-induced obesity. By contrast, the change in body weight after POV treatment is the result of a substantial reduction in fat mass, with no obvious effects on lean body mass. These findings demonstrate that supplementary of POVs would be an effective way to combat obesity and metabolic disorders while lowering metabolic inflammation.

1417-P: Gut Microbiome Translocation to Visceral Adipose Tissue Promotes Recruitment of Adipose-Specific Neutrophils in Human Obesity

Neutrophils protect against invading bacteria, and their unique role in adipose tissue inflammation and insulin resistance (IR) in obesity is increasingly recognized. We found that visceral adipose tissue (VAT) of obese (n=83) compared to lean (n=13) individuals had higher neutrophil abundance, correlating with IR. The obese subjects had elevated circulating plasma zonulin, a marker of intestinal permeability, and lipopolysaccharide-binding protein (LPSBP) , a marker of bacterial presence, consistent with evidence suggesting that changes in the microbiome and gut permeability in obesity permits the entry of gut bacteria and bacterial products into the circulation. Therefore, we tested for bacterial presence in VAT under sterile conditions. 16s rRNA analyses revealed that the family Streptococcaceae and an unnamed genus in the family Ruminococaceae were enriched in obese VAT contrary to order Bacilliales and genus Marvinobryantia in lean VAT, majorly originating from the GI tract. To confirm whether higher bacterial load is causal for VAT neutrophil abundance in obesity, we gavaged high-fat diet fed mice with fecal material from an obese human, which increased neutrophil, but not macrophage recruitment to VAT. As VAT is highly vascularized, we used RNA-seq to compare the gene expression signature of VAT neutrophils to peripheral blood neutrophils to eliminate the possibility that VAT neutrophils were circulating cells. Evidently, VAT neutrophils had a differential activation state compared to the circulating neutrophils, with a distinct gene expression pattern representing upregulated inflammatory, chemotactic, extracellular matrix, and ROS generation pathways. Overall, we find that that increased gut bacterial translocation enhances the recruitment of VAT specific neutrophils in obesity offering novel targets for managing VAT inflammation and comorbidities of obesity. Disclosure D.Shantaram: None. N.F.Williams: None. D.Spakowicz: None. W.Hsueh: None. A.M.Blaszczak: None. R.Hoyd: None. A.Smith: None. L.Antwi: None. J.Z.Liu: None. V.P.Wright: None. D.Bradley: None. Y.Liu: None.

Role of Biliverdin Reductase A in the Regulation of Insulin Signaling in Metabolic and Neurodegenerative Diseases: An Update.

Insulin signaling is a conserved pathway that orchestrates glucose and lipid metabolism, energy balance, and inflammation, and its dysregulation compromises the homeostasis of multiple systems. Insulin resistance is a shared hallmark of several metabolic diseases, including obesity, metabolic syndrome, and type 2 diabetes, and has been associated with cognitive decline during aging and dementia. Numerous mechanisms promoting the development of peripheral and central insulin resistance have been described, although most of them were not completely clarified. In the last decades, several studies have highlighted that biliverdin reductase-A (BVR-A), over its canonical role in the degradation of heme, acts as a regulator of insulin signaling. Evidence from human and animal studies show that BVR-A alterations are associated with the aberrant activation of insulin signaling, metabolic syndrome, liver steatosis, and visceral adipose tissue inflammation in obese and diabetic individuals. In addition, recent findings demonstrated that reduced BVR-A levels or impaired BVR-A activation contribute to the development of brain insulin resistance and metabolic alterations in Alzheimer’s disease. In this narrative review, we will provide an overview on the literature by focusing on the role of BVR-A in the regulation of insulin signaling and how BVR-A alterations impact on cell dysfunctions in both metabolic and neurodegenerative disorders.

Senescence and DNA Damage in Adipocytes and Fat Tissues and Its Potential Amelioration through Nutritional Interventions

Accumulating evidence demonstrates that senescence and the associated inflammatory phenotype (SASP) also occur in post-mitotic cells such as mature adipocytes. Visceral adipose tissue in humans is susceptible to inflammation due to nutritional imbalance and ageing. However, while adipose tissue has been well researched in the context of obesity, senescence of differentiated adipocytes has not been investigated thoroughly. Our group recently demonstrated that ageing and normal ad libitum (AL) nutrition in mice resulted in increased adipocyte size, DNA damage, p16INK4a expression and inflammation in visceral adipose tissue while some of these senescence markers could be alleviated by dietary restriction (DR). Moreover, another dietary restriction study described a “metabolic memory” as protection against AL-induced senescence after shifting mice from DR back to AL nutrition. Other recent DR studies on mice of different ages analysed the transcriptional profile of adipose tissue and described a metabolic memory for AL at high age. Finally, our group modelled nutritional imbalance in vitro through treatment of primary human subcutaneous and omental adipocytes with the saturated fatty acid (FA) palmitic acid (PA). This resulted in a significant increase in DNA damage as well as p16INK4a levels correlating with enhanced intracellular lipid accumulation. In contrast, DNA damage could be prevented with the unsaturated FA oleic acid (OA). With olive oil being an important part of the Mediterranean diet another study found also other oils such as argan oil to have similar effects of preventing DNA damage in vivo and in vitro. This review is focused on senescence, DNA damage and inflammation in WAT and adipocytes including nutritional interventions in vivo and in vitro. It also gives some basic background on these topics. However, it is not a systematic review but aims to highlight recent developments and nutritional interventions in the areas of senescence and DNA damage related to adipocyte tissues and cells.

Adipose invariant NKT cells interact with CD1d-expressing macrophages to regulate obesity-related inflammation.

Obesity is accompanied by and accelerated with chronic inflammation in adipose tissue, especially visceral adipose tissue (VAT). This low-level inflammation predisposes the host to the development of metabolic disease, most notably type 2 diabetes. We have focused on the capacity of glycolipid-reactive, CD1d-restricted natural killer T (NKT) cells to modulate obesity and its associated metabolic sequelae. We previously reported that CD1d knockout (KO) mice are partially protected against the development of obesity-associated insulin resistance, and these findings were recapitulated in mice with an adipocyte-specific CD1d deficiency, suggesting that NKT cell-adipocyte interactions play a critical role in exacerbating disease. However, many other CD1d-expressing cells contribute to the in vivo responses of NKT cells to lipid antigens. In the present study, we examined the role of CD1d expression by macrophages (Mϕ) in the development of obesity-associated metabolic inflammation using LysMcre-cd1d1f/f mice where the CD1d1gene is disrupted in a Mϕ-specific manner. Unexpectedly, these animals contained a higher frequency of T-bet+ CD4+ T cells in VAT with increased production of Th1 cytokines that aggravated VAT inflammation. Mϕ from mutant mice displayed increased production of IL-12p40, suggesting M1 polarization. These findings indicate that interactions of CD1d on Mϕ with NKT cells play a beneficial role in obesity-associated VAT inflammation and insulin resistance with a sharp contrast to an aggravating role of CD1d in another type of antigen-presenting cell, dendritic cells.

Visceral fat inflammation and fat embolism are associated with lung's lipidic hyaline membranes in subjects with COVID-19.

BackgroundPreliminary data suggested that fat embolism could explain the importance of visceral obesity as a critical determinant of coronavirus disease-2019 (COVID-19).MethodsWe performed a comprehensive histomorphologic analysis of autoptic visceral adipose tissue (VAT), lungs and livers of 19 subjects with COVID-19 (COVID-19+), and 23 people without COVID-19 (controls). Human adipocytes (hMADS) infected with SARS-CoV-2 were also studied.ResultsAlthough there were no between-group differences in body-mass-index and adipocytes size, a higher prevalence of CD68+ macrophages among COVID-19+ VAT was detected (p = 0.005) and accompanied by crown-like structures presence, signs of adipocytes stress and death. Consistently, human adipocytes were successfully infected by SARS-CoV-2 in vitro and displayed lower cell viability. Being VAT inflammation associated with lipids spill-over from dead adipocytes, we studied lipids distribution by ORO. Lipids were observed within lungs and livers interstitial spaces, macrophages, endothelial cells, and vessels lumen, features suggestive of fat embolism syndrome, more prevalent among COVID-19+ (p < 0.001). Notably, signs of fat embolism were more prevalent among people with obesity (p = 0.03) independently of COVID-19 diagnosis, suggesting that such condition may be an obesity complication exacerbated by SARS-CoV-2 infection. Importantly, all infected subjects’ lungs presented lipids-rich (ORO+) hyaline membranes, formations associated with COVID-19-related pneumonia, present only in one control patient with non-COVID-19-related pneumonia. Importantly, transition aspects between embolic fat and hyaline membranes were also observed.ConclusionsThis study confirms the lung fat embolism in COVID-19+ patients and describes for the first time novel COVID-19-related features possibly underlying the unfavorable prognosis in people with COVID-19 and obesity.