Adipose Tissue Of Obese Humans Research Articles

Adipocyte-derived extracellular vesicles regulate survival and function of pancreatic β cells.

Extracellular vesicles (EVs) are implicated in the crosstalk between adipocytes and other metabolic organs, and an altered biological cargo has been observed in EVs from human obese adipose tissue (AT). Yet, the role of adipocyte-derived EVs in pancreatic β cells remains to be determined. Here, we explored the effects of EVs released from adipocytes isolated from both rodents and humans and human AT explants on survival and function of pancreatic β cells and human pancreatic islets. EVs from healthy 3T3-L1 adipocytes increased survival and proliferation and promoted insulin secretion in INS-1E β cells and human pancreatic islets, both those untreated or exposed to cytokines or glucolipotoxicity, whereas EVs from inflamed adipocytes caused β cell death and dysfunction. Human lean adipocyte-derived EVs produced similar beneficial effects, whereas EVs from obese AT explants were harmful for human EndoC-βH3 β cells. We observed differential expression of miRNAs in EVs from healthy and inflamed adipocytes, as well as alteration in signaling pathways and expression of β cell genes, adipokines, and cytokines in recipient β cells. These in vitro results suggest that, depending on the physiopathological state of AT, adipocyte-derived EVs may influence β cell fate and function.

Signal Transducer and Activator of Transcription 3 (STAT3) Suppresses STAT1/Interferon Signaling Pathway and Inflammation in Senescent Preadipocytes.

Obesity promotes premature aging and dysfunction of white adipose tissue (WAT) through the accumulation of cellular senescence. The senescent cells burden in WAT has been linked to inflammation, insulin-resistance (IR), and type 2 diabetes (T2D). There is limited knowledge about molecular mechanisms that sustain inflammation in obese states. Here, we describe a robust and physiologically relevant in vitro system to trigger senescence in mouse 3T3-L1 preadipocytes. By employing transcriptomics analyses, we discovered up-regulation of key pro-inflammatory molecules and activation of interferon/signal transducer and activator of transcription (STAT)1/3 signaling in senescent preadipocytes, and expression of downstream targets was induced in epididymal WAT of obese mice, and obese human adipose tissue. To test the relevance of STAT1/3 signaling to preadipocyte senescence, we used Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR associated protein 9 (CRISPR/Cas9) technology to delete STAT1/3 and discovered that STAT1 promoted growth arrest and cooperated with cyclic Guanosine Monophosphate-Adenosine Monophosphate (GMP-AMP) synthase-stimulator of interferon genes (cGAS-STING) to drive the expression of interferon β (IFNβ), C-X-C motif chemokine ligand 10 (CXCL10), and interferon signaling-related genes. In contrast, we discovered that STAT3 was a negative regulator of STAT1/cGAS-STING signaling—it suppressed senescence and inflammation. These data provide insights into how STAT1/STAT3 signaling coordinates senescence and inflammation through functional interactions with the cGAS/STING pathway.

Changes in VGF and C3aR1 gene expression in human adipose tissue in obesity.

The VGF gene, which has been shown to be metabolically associated with energy balance, glucose homeostasis, insulin secretion process, and biological processes related to overeating, is prominent in relation to obesity. TLQP-21 neuropeptide, derived from the VGF, is considered to promote lipolysis by the beta-adrenergic pathway through targeting the C3aR1 receptor located in the adipocyte membrane. In this study, we aimed to measure the expression levels of the VGF and C3aR1 genes in the adipose tissue of obese subjects and individuals with normal weight determined based on body mass index (BMI), and to reveal the correlation of these levels with obesity. VGF and C3aR1 gene expression levels were measured using Real Time Polymerase Chain Reaction (RT PCR) in the visceral adipose tissue (VAT) samples of 52 obese patients (BMI ≥ 35kg/m2) and 21 non-obese controls (BMI = 18.5-24.9kg/m2). The results were statistically analyzed. The VGF expression was lower and the C3aR1 gene expression was higher in obese patients compared to the non-obese control group (p < 0.05). In obese patients, there was a statistically significant positive correlation of 85.6% between VGF and C3aR1, in which when one level increased, the other also increased (p < 0.05, r = 0.856). The findings show that the VGF may be significantly associated with obesity and is very important since it is the first to measure the level of VGF gene expression in human adipose tissue. This research provides new evidence of a link between obesity and VGF/C3aR1 and in the future may help design strategies to combat obesity.

Obese adipose tissue extracellular vesicles raise breast cancer cell malignancy.

Obesity is a chronic low-grade inflammatory condition that strongly impacts breast cancer. Aside from inflammatory mediators, obese adipose tissue (AT) secretes high amounts of extracellular vesicles (EVs), which are capable of transferring molecules to target cells and promoting cell-to-cell communication. Here, we investigated how soluble mediators and EVs secreted by human obese AT influence MCF-7 and MDA-MB-231 mammary adenocarcinoma cell lines by modulating cell proliferation, migration, invasion, and signaling pathways. Both cell lineages were stimulated with conditioned media (CM) or EVs obtained from cultures of AT explants collected from lean or obese individuals who underwent plastic or bariatric surgeries, respectively. EVs derived from obese AT increased the proliferative potential of both cell lines and further potentiated the migratory and invasive properties of MDA-MB-231 cells. The proliferative effects of CM and EVs on MCF-7 cells were dependent on ERK/MAPK pathway activation, while the migration and invasiveness of MDA-MB-231 cells were dependent on PI3K/AKT pathway activation. Furthermore, CM derived from obese AT potentiated the pro-angiogenic effect of MDA-MB-231 on endothelial cells. We also detected that EVs derived from obese AT were enriched in leptin and bioactive matrix metallopeptidase 9 (MMP9), and stimulation of MDA-MD-231 cells with those EVs or CM derived from obese AT potentiated the release of MMP9 by those cells. Our data indicate that obese AT secretes molecules and EVs with pro-tumoral activities capable of increasing breast cancer cell malignancy and provide strong evidence of the key role of AT-derived EV signaling in the tumor microenvironment.

Loss of G protein pathway suppressor 2 in human adipocytes triggers lipid remodeling by upregulating ATP binding cassette subfamily G member 1

ObjectiveAdipogenesis is critical for adipose tissue remodeling during the development of obesity. While the role of transcription factors in the orchestration of adipogenic pathways is already established, the involvement of coregulators that transduce regulatory signals into epigenome alterations and transcriptional responses remains poorly understood. The aim of our study was to investigate which pathways are controlled by G protein pathway suppressor 2 (GPS2) during the differentiation of human adipocytes. MethodsWe generated a unique loss-of-function model by RNAi depletion of GPS2 in human multipotent adipose-derived stem (hMADS) cells. We thoroughly characterized the coregulator depletion-dependent pathway alterations during adipocyte differentiation at the level of transcriptome (RNA-seq), epigenome (ChIP-seq H3K27ac), cistrome (ChIP-seq GPS2), and lipidome. We validated the in vivo relevance of the identified pathways in non-diabetic and diabetic obese patients. ResultsThe loss of GPS2 triggers the reprogramming of cellular processes related to adipocyte differentiation by increasing the responses to the adipogenic cocktail. In particular, GPS2 depletion increases the expression of BMP4, an important trigger for the commitment of fibroblast-like progenitors toward the adipogenic lineage and increases the expression of inflammatory and metabolic genes. GPS2-depleted human adipocytes are characterized by hypertrophy, triglyceride and phospholipid accumulation, and sphingomyelin depletion. These changes are likely a consequence of the increased expression of ATP-binding cassette subfamily G member 1 (ABCG1) that mediates sphingomyelin efflux from adipocytes and modulates lipoprotein lipase (LPL) activity. We identify ABCG1 as a direct transcriptional target, as GPS2 depletion leads to coordinated changes of transcription and H3K27 acetylation at promoters and enhancers that are occupied by GPS2 in wild-type adipocytes. We find that in omental adipose tissue of obese humans, GPS2 levels correlate with ABCG1 levels, type 2 diabetic status, and lipid metabolic status, supporting the in vivo relevance of the hMADS cell-derived in vitro data. ConclusionOur study reveals a dual regulatory role of GPS2 in epigenetically modulating the chromatin landscape and gene expression during human adipocyte differentiation and identifies a hitherto unknown GPS2-ABCG1 pathway potentially linked to adipocyte hypertrophy in humans.

Identification and characterization of adipose tissue-derived human antibodies with “anti-self” specificity

Abstract We have previously shown that the human obese adipose tissue (AT) contributes to increased secretion of adipocyte-specific IgG antibodies in individuals with obesity. We have also shown that this occurs without any exogenous stimulation, because the ongoing process of cell death in the obese AT leads to the release of “self” antigens able to induce chronic stimulation of B cells. Here, we confirm and extend our initial observation on a different cohort of individuals, and we show that also the plasma of obese individuals is enriched in IgG antibodies with specificities for adipocyte-derived antigens. Adipocyte-specific IgG secreted in the obese AT are significantly correlated with those present in plasma. Using immunoprecipitation and mass spectrometry, we have identified these antigenic specificities. The antigens are almost exclusively intracellular or cell-associated, usually not “self” antigens, but they are released by cells dying in the AT. These antigens will be used in protein arrays to screen plasma from individuals with obesity and also with autoimmune diseases. We have indeed preliminary evidence that the plasma of Rheumatoid Arthritis patients is enriched in adipocyte-specific IgG antibodies, suggesting that obesity may contribute to pathogenicity in autoimmune patients. Finally, we show for the first time that not only macrophages but also adipocytes in the obese AT are efficient antigen-presenting cells and stimulate the secretion of IgG autoimmune antibodies. They do so because they express the antigen-presenting molecules CD1d and, to a lesser extent, MHC class II, as well as the co-stimulatory molecule CD86. These results may lead to the development of novel therapeutic strategies to controlautoimmunity.

Identification and Characterization of Adipose Tissue-Derived Human Antibodies With "Anti-self" Specificity.

We have previously shown that the human obese adipose tissue (AT) contributes to increased secretion of adipocyte-specific IgG antibodies in individuals with obesity. This occurs without any exogenous stimulation, because the ongoing process of cell death in the obese AT leads to the release of “self” antigens able to induce chronic stimulation of B cells. We have identified several mechanisms responsible for the release of “self” antigens, such as hypoxia, cell cytotoxicity, and DNA damage. In this paper, we confirm and extend our initial observation on a different cohort of individuals, and we show that also the plasma of these individuals is enriched in IgG antibodies with specificities for adipocyte-derived antigens. Adipocyte-specific IgG secreted in the obese AT are significantly correlated with those present in plasma. Using immunoprecipitation and mass spectrometry, we have identified these antigenic specificities. The antigens are almost exclusively intracellular or cell-associated, usually not recognized as “self” antigens, but they are released by cells dying in the AT. We also show for the first time that the adipocytes in the obese AT contribute to the secretion of IgG autoimmune antibodies and this seems to be due to their expression of the antigen-presenting molecules CD1d and, to a much lesser extent, MHC class II, as our mechanistic experiments performed in mice have shown. These results may lead to the development of novel therapeutic strategies to control autoimmunity.

The Rho GTPase RND3 regulates adipocyte lipolysis

BackgroundAdipose tissue plays a crucial role in diet- and obesity-related insulin resistance, with implications for several metabolic diseases. Identification of novel target genes and mechanisms that regulate adipocyte function could lead to improved treatment strategies. RND3 (RhoE/Rho8), a Rho-related GTP-binding protein that inhibits Rho kinase (ROCK) signaling, has been linked to diverse diseases such as apoptotic cardiomyopathy, heart failure, cancer and type 2 diabetes, in part by regulating cytoskeleton dynamics and insulin-mediated glucose uptake. ResultsWe here investigated the expression of RND3 in adipose tissue in human obesity, and discovered a role for RND3 in regulating adipocyte metabolism. In cross-sectional and prospective studies, we observed 5-fold increased adipocyte levels of RND3 mRNA in obesity, reduced levels after surgery-induced weight loss, and positive correlations of RND3 mRNA with adipocyte size and surrogate measures of insulin resistance (HOMA2-IR and circulating triglyceride/high-density lipoprotein cholesterol (TAG/HDL-C) ratio). By screening for RND3-dependent gene expression following siRNA-mediated RND3 knockdown in differentiating human adipocytes, we found downregulation of inflammatory genes and upregulation of genes related to adipocyte ipolysis and insulin signaling. Treatment of adipocytes with tumor necrosis factor alpha (TNFα), lipopolysaccharide (LPS), hypoxia or cAMP analogs increased RND3 mRNA levels 1.5–2-fold. Functional assays in primary human adipocytes confirmed that RND3 knockdown reduces cAMP- and isoproterenol-induced lipolysis, which were mimicked by treating cells with ROCK inhibitor. This effect could partly be explained by reduced protein expression of adipose triglyceride lipase (ATGL) and phosphorylated hormone-sensitive lipase (HSL). ConclusionWe here uncovered a novel differential expression of adipose RND3 in obesity and insulin resistance, which may at least partly depend on a causal effect of RND3 on adipocyte lipolysis.

Endothelial-to-Mesenchymal Transition in Human Adipose Tissue Vasculature Alters the Particulate Secretome and Induces Endothelial Dysfunction.

Endothelial cells (EC) in obese adipose tissue (AT) are exposed to a chronic proinflammatory environment that may induce a mesenchymal-like phenotype and altered function. The objective of this study was to establish whether endothelial-to-mesenchymal transition (EndoMT) is present in human AT in obesity and to investigate the effect of such transition on endothelial function and the endothelial particulate secretome represented by extracellular vesicles (EV). Approach and Results: We identified EndoMT in obese human AT depots by immunohistochemical co-localization of CD31 or vWF and α-SMA (alpha-smooth muscle actin). We showed that AT EC exposed in vitro to TGF-β (tumor growth factor-β), TNF-α (tumor necrosis factor-α), and IFN-γ (interferon-γ) undergo EndoMT with progressive loss of endothelial markers. The phenotypic change results in failure to maintain a tight barrier in culture, increased migration, and reduced angiogenesis. EndoMT also reduced mitochondrial oxidative phosphorylation and glycolytic capacity of EC. EVs produced by EC that underwent EndoMT dramatically reduced angiogenic capacity of the recipient naïve ECs without affecting their migration or proliferation. Proteomic analysis of EV produced by EC in the proinflammatory conditions showed presence of several pro-inflammatory and immune proteins along with an enrichment in angiogenic receptors. We demonstrated the presence of EndoMT in human AT in obesity. EndoMT in vitro resulted in production of EV that transferred some of the functional and metabolic features to recipient naïve EC. This result suggests that functional and molecular features of EC that underwent EndoMT in vivo can be disseminated in a paracrine or endocrine fashion and may induce endothelial dysfunction in distant vascular beds.

Metabolically activated adipose tissue macrophages link obesity to triple-negative breast cancer.

Obesity is associated with increased incidence and severity of triple-negative breast cancer (TNBC); however, mechanisms underlying this relationship are incompletely understood. Here, we show that obesity reprograms mammary adipose tissue macrophages to a pro-inflammatory metabolically activated phenotype (MMe) that alters the niche to support tumor formation. Unlike pro-inflammatory M1 macrophages that antagonize tumorigenesis, MMe macrophages are pro-tumorigenic and represent the dominant macrophage phenotype in mammary adipose tissue of obese humans and mice. MMe macrophages release IL-6 in an NADPH oxidase 2 (NOX2)-dependent manner, which signals through glycoprotein 130 (GP130) on TNBC cells to promote stem-like properties including tumor formation. Deleting Nox2 in myeloid cells or depleting GP130 in TNBC cells attenuates obesity-augmented TNBC stemness. Moreover, weight loss reverses the effects of obesity on MMe macrophage inflammation and TNBC tumor formation. Our studies implicate MMe macrophage accumulation in mammary adipose tissue as a mechanism for promoting TNBC stemness and tumorigenesis during obesity.

Mechanisms for secretion of antibodies with “anti-self” reactivity by the human obese adipose tissue

Abstract We have shown that the human obese subcutaneous adipose tissue(SAT)contributes to systemic and B cell intrinsic inflammation and increased secretion of autoimmune antibodies. Immune cells are recruited to the SAT by chemokines released by both adipocytes and infiltrating immune cells. We have identified several mechanisms responsible for the release of “self” antigens in the human obese SAT, induction of class switch and production of autoimmune antibodies, such as hypoxia, NK cell cytotoxicity and DNA damage, which induce cell death and further release of pro-inflammatory cytokines. All these processes, in the context of an inflammatory environment like the obese SAT, stimulate the production of autoimmune IgG antibodies which have been described to be pathogenic. We have identified “self” antigens that stimulate the secretion of autoimmune antibodies in cultures of SAT-derived immune cells, using a Protein G immunoprecipitation protocol to purify the autoantibodies, combined with mass spectrometry. Results show that around 25% of these “self” antigens are found at high frequency in all the individuals evaluated so far in independent experiments. Moreover, &amp;gt;90% of these “self” antigens (lipid and protein antigens, DNA, RNA) are cytoplasmic, nuclear or membrane-associated. These results allow the identification of novel pathways to manipulate in order to decrease pathogenic immune responses during aging.

Targeting senescent cells alleviates obesity-induced metabolic dysfunction.

Adipose tissue inflammation and dysfunction are associated with obesity‐related insulin resistance and diabetes, but mechanisms underlying this relationship are unclear. Although senescent cells accumulate in adipose tissue of obese humans and rodents, a direct pathogenic role for these cells in the development of diabetes remains to be demonstrated. Here, we show that reducing senescent cell burden in obese mice, either by activating drug‐inducible “suicide” genes driven by the p16Ink4a promoter or by treatment with senolytic agents, alleviates metabolic and adipose tissue dysfunction. These senolytic interventions improved glucose tolerance, enhanced insulin sensitivity, lowered circulating inflammatory mediators, and promoted adipogenesis in obese mice. Elimination of senescent cells also prevented the migration of transplanted monocytes into intra‐abdominal adipose tissue and reduced the number of macrophages in this tissue. In addition, microalbuminuria, renal podocyte function, and cardiac diastolic function improved with senolytic therapy. Our results implicate cellular senescence as a causal factor in obesity‐related inflammation and metabolic derangements and show that emerging senolytic agents hold promise for treating obesity‐related metabolic dysfunction and its complications.

GLP-1 Improves Adipocyte Insulin Sensitivity Following Induction of Endoplasmic Reticulum Stress.

Glucagon-like peptide 1 (GLP-1) improves insulin resistance of adipose tissue in obese humans. However, the mechanism of this effect is unclear. Perturbation of endoplasmic reticulum (ER) homeostasis impairs insulin signaling. We hypothesized that GLP-1 could directly improve insulin signaling in ER-stressed adipocytes. Here, we examined the effects of GLP-1 on ER stress response in fat cells in an obese and insulin-resistant murine model. We found that GLP-1 analog liraglutide reduced ER stress related gene expression in visceral fat cells accompanied by improved systemic insulin tolerance. Consistently, GLP-1 decreased CHOP expression and increased insulin stimulated AKT phosphorylation (p-AKT) in thapsigargin, a ER stress inducer, treated white fat cells differentiated from visceral stromal vascular fraction. We further found blocking CHOP expression increased insulin stimulated p-AKT in ER-stressed fat cells. Of note, we found mTOR signaling pathway contributed to the expression of ATF4 and subsequently the CHOP expression in ER stress response, while GLP-1 inhibited mTOR activity as exemplified by elevated autophagosome formation and increased LC3II/LC3I ratio. These findings suggest that GLP-1 directly modulates the ER stress response partially via inhibiting mTOR signaling pathway, leading to increased insulin sensitivity in adipocytes.

Obesity-induced insulin resistance and macrophage infiltration of the adipose tissue: A vicious cycle.

Obesity-induced insulin resistance and macrophage infiltration of the adipose tissue: A vicious cycle.

OP-27 - Cellular Senescence: At the Nexus of Mechanisms of Age- and Obesity-Related Metabolic Dysfunction

Obesity is a leading risk factor for diabetes and its co-morbidities. Adipose dysfunction occurs in obesity-related diabetes, but mechanisms responsible have been unclear. Although senescent cells accumulate in adipose tissue in obese humans and rodents, a causal role for senescent cells remains to be proven. Cellular senescence results in replicative arrest, resistance to apoptosis, and a pro-inflammatory senescence-associated secretory phenotype (SASP). We found that inhibiting the SASP or reducing senescent cell burden alleviates metabolic and adipose tissue dysfunction in obese mice. We reduced senescent cell abundance either by intermittent activation of drug-inducible “suicide” genes driven by the p16Ink4a promoter in transgenic mice or by treatment with senolytic drugs – drugs that selectively induce apoptosis in senescent cells. Reducing senescent cell burden improved enhanced insulin sensitivity without affecting body weight or food intake. Mediators of insulin resistance, including inflammatory cytokines and immune cell chemokines, were decreased by targeting senescent cells, while insulin-sensitizing adipogenic transcription factors were increased. Our findings implicate senescence in obesity-related inflammation and metabolic dysfunction. Intermittent treatment with senolytic agents is a potential strategy for treating obesity-related diabetes.

The impact of protein quantity during energy restriction on genome-wide gene expression in adipose tissue of obese humans.

Overweight and obesity is a growing health problem worldwide. The most effective strategy to reduce weight is energy restriction (ER). ER has been shown to be beneficial in disease prevention and it reduces chronic inflammation. Recent studies suggest that reducing the protein quantity of a diet contributes to the beneficial effects by ER. The organ most extensively affected during ER is white adipose tissue (WAT). The first objective was to assess changes in gene expression between a high-protein diet and a normal protein diet during ER. Second, the total effect of ER on changes in gene expression in WAT was assessed. In a parallel double-blinded controlled study, overweight older participants adhered to a 25% ER diet, either combined with high-protein intake (HP-ER, 1.7 g kg-1 per day), or with normal protein intake (NP-ER, 0.9 g kg-1 per day) for 12 weeks. From 10 HP-ER participants and 12 NP-ER participants subcutaneous WAT biopsies were collected before and after the diet intervention. Adipose tissue was used to isolate total RNA and to evaluate whole-genome gene expression changes upon a HP-ER and NP-ER diet. A different gene expression response between HP-ER and NP-ER was observed for 530 genes. After NP-ER, a downregulation in expression of genes linked to immune cell infiltration, adaptive immune response and inflammasome was found, whereas no such effect was found after HP-ER. HP-ER resulted in upregulation in expression of genes linked to cell cycle, GPCR signalling, olfactory signalling and nitrogen metabolism. Upon 25% ER, gene sets related to energy metabolism and immune response were decreased. Based on gene expression changes, we concluded that consumption of normal protein quantity compared with high-protein quantity during ER has a more beneficial effect on inflammation-related gene expression in WAT.

Physiologic and genetic evidence links hemopexin to triglycerides in mice and humans.

Elevated triglycerides predict insulin resistance and vascular disease in obesity, but how the inert triglyceride molecule is related to development of metabolic disease is unknown. To pursue novel potential mediators of triglyceride-associated metabolic disease, we used a forward genetics approach involving inbred mice and translated our findings to human subjects. Hemopexin (HPX) was identified as a differentially expressed gene within a quantitative trait locus associated with serum triglycerides in an F16 advanced intercross between the LG/J and SM/J strains of mice. Hpx expression was evaluated in both the reproductive fat pads and livers of mice representing three strains, LG/J (n=25), SM/J (n=27) and C57Bl/6J (n=19), on high- and low-fat diets. The effect of altered Hpx expression on adipogenesis was studied in 3T3-L1 cells. Circulating HPX protein along with HPX expression were characterized in subcutaneous white adipose tissue samples obtained from a cohort of metabolically abnormal (n=18) and of metabolically normal (n=24) obese human subjects. We further examined the relationship between HPX and triglycerides in human atherosclerotic plaques (n=18). HPX expression in mouse adipose tissue, but not in liver, was regulated by dietary fat regardless of genetic background. HPX increased in concert with adipogenesis in 3T3-L1 cells, and disruption of its expression impaired adipocyte differentiation. RNAseq data from the adipose tissue of obese humans showed differential expression of HPX based on metabolic disease status (P<0.05), and circulating HPX levels were correlated with serum triglycerides in these subjects (r=0.33; P=0.03). HPX was also found in an unbiased proteomic screen of human atherosclerotic plaques and shown to display differential abundance based on the extent of disease and triglyceride content (P<0.05). Our findings suggest that HPX is associated with triglycerides and provide a framework for understanding mechanisms underlying lipid metabolism and metabolic disease.

Adipose Tissue Dendritic Cells Are Independent Contributors to Obesity-Induced Inflammation and Insulin Resistance.

Dynamic changes of adipose tissue leukocytes, including adipose tissue macrophage (ATM) and adipose tissue dendritic cells (ATDCs), contribute to obesity-induced inflammation and metabolic disease. However, clear discrimination between ATDC and ATM in adipose tissue has limited progress in the field of immunometabolism. In this study, we use CD64 to distinguish ATM and ATDC, and investigated the temporal and functional changes in these myeloid populations during obesity. Flow cytometry and immunostaining demonstrated that the definition of ATM as F4/80+CD11b+ cells overlaps with other leukocytes and that CD45+CD64+ is specific for ATM. The expression of core dendritic cell genes was enriched in CD11c+CD64- cells (ATDC), whereas core macrophage genes were enriched in CD45+CD64+ cells (ATM). CD11c+CD64- ATDCs expressed MHC class II and costimulatory receptors, and had similar capacity to stimulate CD4+ T cell proliferation as ATMs. ATDCs were predominantly CD11b+ conventional dendritic cells and made up the bulk of CD11c+ cells in adipose tissue with moderate high-fat diet exposure. Mixed chimeric experiments with Ccr2-/- mice demonstrated that high-fat diet-induced ATM accumulation from monocytes was dependent on CCR2, whereas ATDC accumulation was less CCR2 dependent. ATDC accumulation during obesity was attenuated in Ccr7-/- mice and was associated with decreased adipose tissue inflammation and insulin resistance. CD45+CD64+ ATM and CD45+CD64-CD11c+ ATDCs were identified in human obese adipose tissue and ATDCs were increased in s.c. adipose tissue compared with omental adipose tissue. These results support a revised strategy for unambiguous delineation of ATM and ATDC, and suggest that ATDCs are independent contributors to adipose tissue inflammation during obesity.

Histone macroH2A1.2 promotes metabolic health and leanness by inhibiting adipogenesis.

BackgroundObesity has tremendous impact on the health systems. Its epigenetic bases are unclear. MacroH2A1 is a variant of histone H2A, present in two alternatively exon-spliced isoforms macroH2A1.1 and macroH2A1.2, regulating cell plasticity and proliferation, during pluripotency and tumorigenesis. Their role in adipose tissue plasticity is unknown.ResultsHere, we show evidence that macroH2A1.1 protein levels in the visceral adipose tissue of obese humans positively correlate with BMI, while macroH2A1.2 is nearly absent. We thus introduced a constitutive GFP-tagged transgene for macroH2A1.2 in mice, and we characterized their metabolic health upon being fed a standard chow diet or a high fat diet. Despite unchanged food intake, these mice exhibit lower adipose mass and improved glucose metabolism both under a chow and an obesogenic diet. In the latter regimen, transgenic mice display smaller pancreatic islets and significantly less inflammation. MacroH2A1.2 overexpression in the mouse adipose tissue induced dramatic changes in the transcript levels of key adipogenic genes; genomic analyses comparing pre-adipocytes to mature adipocytes uncovered only minor changes in macroH2A1.2 genomic distribution upon adipogenic differentiation and suggested differential cooperation with transcription factors. MacroH2A1.2 overexpression markedly inhibited adipogenesis, while overexpression of macroH2A1.1 had opposite effects.ConclusionsMacroH2A1.2 is an unprecedented chromatin component powerfully promoting metabolic health by modulating anti-adipogenic transcriptional networks in the differentiating adipose tissue. Strategies aiming at enhancing macroH2A1.2 expression might counteract excessive adiposity in humans.Electronic supplementary materialThe online version of this article (doi:10.1186/s13072-016-0098-9) contains supplementary material, which is available to authorized users.

MARCH1 regulates insulin sensitivity by controlling cell surface insulin receptor levels.

Insulin resistance is a key driver of type 2 diabetes (T2D) and is characterized by defective insulin receptor (INSR) signalling. Although surface INSR downregulation is a well-established contributor to insulin resistance, the underlying molecular mechanisms remain obscure. Here we show that the E3 ubiquitin ligase MARCH1 impairs cellular insulin action by degrading cell surface INSR. Using a large-scale RNA interference screen, we identify MARCH1 as a negative regulator of INSR signalling. March1 loss-of-function enhances, and March1 overexpression impairs, hepatic insulin sensitivity in mice. MARCH1 ubiquitinates INSR to decrease cell surface INSR levels, but unlike other INSR ubiquitin ligases, MARCH1 acts in the basal state rather than after insulin stimulation. Thus, MARCH1 may help set the basal gain of insulin signalling. MARCH1 expression is increased in white adipose tissue of obese humans, suggesting that MARCH1 contributes to the pathophysiology of T2D and could be a new therapeutic target.