Deciphering adipose tissue heterogeneity

Cell-Type Composition Affects Adipose Gene Expression Associations With Cardiometabolic Traits

Understanding differences in adipose gene expression between individuals with different levels of clinical traits may reveal the genes and mechanisms leading to cardiometabolic diseases. However, adipose is a heterogeneous tissue. To account for cell-type heterogeneity, we estimated cell-type proportions in 859 subcutaneous adipose tissue samples with bulk RNA sequencing (RNA-seq) using a reference single-nuclear RNA-seq data set. Cell-type proportions were associated with cardiometabolic traits; for example, higher macrophage and adipocyte proportions were associated with higher and lower BMI, respectively. We evaluated cell-type proportions and BMI as covariates in tests of association between >25,000 gene expression levels and 22 cardiometabolic traits. For >95% of genes, the optimal, or best-fit, models included BMI as a covariate, and for 79% of associations, the optimal models also included cell type. After adjusting for the optimal covariates, we identified 2,664 significant associations (P ≤ 2e-6) for 1,252 genes and 14 traits. Among genes proposed to affect cardiometabolic traits based on colocalized genome-wide association study and adipose expression quantitative trait locus signals, 25 showed a corresponding association between trait and gene expression levels. Overall, these results suggest the importance of modeling cell-type proportion when identifying gene expression associations with cardiometabolic traits.

ARTICLE HIGHLIGHTS

Higher Intra-Abdominal Visceral Adipose Tissue Mass Is Associated With Lower Rates of Clinical and Endoscopic Remission in Patients With Inflammatory Bowel Diseases Initiating Biologic Therapy: Results of the Constellation Study

BACKGROUND & AIMS

We sought to assess the association between intra-abdominal visceral adipose tissue (IA-VAT) and response to 3 different biologic drugs in patients with inflammatory bowel disease (IBD) and to investigate its effects on inflammatory cytokine expression, pharmacokinetics, and intestinal microbiota.

METHODS

We prospectively enrolled subjects with active IBD initiating infliximab, vedolizumab, or ustekinumab and a healthy control group. Baseline body composition (including IA-VAT as percent of total body mass [IA-VAT%]) was measured using GE iDXA scan. Primary outcome was corticosteroid- free deep remission at weeks 14-16, defined as Harvey Bradshaw Index <5 for Crohn's disease and partial Mayo score <2 for ulcerative colitis, with a normal C-reactive protein and fecal calprotectin. Secondary outcomes were corticosteroid-free deep remission and endoscopic remission (Endoscopic Mayo Score ≤1 in ulcerative colitis or Simple Endoscopic Score for Crohn's disease ≤2) at weeks 30-46.

RESULTS

A total of 141 patients with IBD and 51 healthy controls were included. No differences in body composition parameters were seen between the IBD and healthy control cohorts. Patients with higher IA-VAT% were less likely to achieve corticosteroid-free deep remission (P < .001) or endoscopic remission (P = .02) vs those with lower IA-VAT%. Furthermore, nonresponders with high IA-VAT% had significantly higher serum interleukin-6 and tumor necrosis factor at baseline compared with responders and patients with low IA-VAT%. Drug pharmacokinetic properties and microbiota diversity were similar when comparing high and low IA-VAT% groups.

CONCLUSIONS

Higher IA-VAT% was independently associated with worse outcomes. This association could be driven at least partially by discrete differences in inflammatory cytokine expression.

Identifying novel regulatory effects for clinically relevant genes through the study of the Greek population

BACKGROUND

Expression quantitative trait loci (eQTL) studies provide insights into regulatory mechanisms underlying disease risk. Expanding studies of gene regulation to underexplored populations and to medically relevant tissues offers potential to reveal yet unknown regulatory variants and to better understand disease mechanisms. Here, we performed eQTL mapping in subcutaneous (S) and visceral (V) adipose tissue from 106 Greek individuals (Greek Metabolic study, GM) and compared our findings to those from the Genotype-Tissue Expression (GTEx) resource.

RESULTS

We identified 1,930 and 1,515 eGenes in S and V respectively, over 13% of which are not observed in GTEx adipose tissue, and that do not arise due to different ancestry. We report additional context-specific regulatory effects in genes of clinical interest (e.g. oncogene ST7) and in genes regulating responses to environmental stimuli (e.g. MIR21, SNX33). We suggest that a fraction of the reported differences across populations is due to environmental effects on gene expression, driving context-specific eQTLs, and suggest that environmental effects can determine the penetrance of disease variants thus shaping disease risk. We report that over half of GM eQTLs colocalize with GWAS SNPs and of these colocalizations 41% are not detected in GTEx. We also highlight the clinical relevance of S adipose tissue by revealing that inflammatory processes are upregulated in individuals with obesity, not only in V, but also in S tissue.

CONCLUSIONS

By focusing on an understudied population, our results provide further candidate genes for investigation regarding their role in adipose tissue biology and their contribution to disease risk and pathogenesis.

Adipocyte- and Monocyte-Mediated Vicious Circle of Inflammation and Obesity (Review of Cellular and Molecular Mechanisms)

Monocytes play a key role in the development of metabolic syndrome, and especially obesity. Given the complex features of their development from progenitor cells, whose regulation is mediated by their interactions with bone marrow adipocytes, the importance of a detailed study of the heterogeneous composition of monocytes at the molecular and systemic levels becomes clear. Research argues for monocytes as indicators of changes in the body's metabolism and the possibility of developing therapeutic strategies to combat obesity and components of metabolic syndrome based on manipulations of the monocyte compound of the immune response. An in-depth study of the heterogeneity of bone-marrow-derived monocytes and adipocytes could provide answers to many questions about the pathogenesis of obesity and reveal their therapeutic potential.

Anti-Obesity Effect and Mechanism of Chitooligosaccharides Were Revealed Based on Lipidomics in Diet-Induced Obese Mice

Chitooligosaccharide (COS) is a natural product from the ocean, and while many studies have reported its important role in metabolic diseases, no study has systematically elaborated the anti-obesity effect and mechanism of COS. Herein, COSM (MW ≤ 3000 Da) was administered to diet-induced obese mice by oral gavage once daily for eight weeks. The results show that COSM administration reduced body weight; slowed weight gain; reduced serum Glu, insulin, NEFA, TC, TG, and LDL-C levels; increased serum HSL and HDL-C levels; improved inflammation; and reduced lipid droplet size in adipose tissue. Further lipidomic analysis of adipose tissue revealed that 31 lipid species are considered to be underlying lipid biomarkers in COS therapy. These lipids are mainly enriched in pathways involving insulin resistance, thermogenesis, cholesterol metabolism, glyceride metabolism and cyclic adenosine monophosphate (cAMP), which sheds light on the weight loss mechanism of COS. The Western blot assay demonstrated that COSM intervention can improve insulin resistance, inhibit de novo synthesis, and promote thermogenesis and β-oxidation in mitochondria by the AMPK pathway, thereby alleviating high-fat diet-induced obesity. In short, our study can provide a more comprehensive direction for the application of COS in obesity based on molecular markers.

The Function of MondoA and ChREBP Nutrient-Sensing Factors in Metabolic Disease

Obesity is a major global public health concern associated with an increased risk of many health problems, including type 2 diabetes, heart disease, stroke, and some types of cancer. Obesity is also a critical factor in the development of insulin resistance and type 2 diabetes. Insulin resistance is associated with metabolic inflexibility, which interferes with the body's ability to switch from free fatty acids to carbohydrate substrates, as well as with the ectopic accumulation of triglycerides in non-adipose tissue, such as that of skeletal muscle, the liver, heart, and pancreas. Recent studies have demonstrated that MondoA (MLX-interacting protein or MLXIP) and the carbohydrate response element-binding protein (ChREBP, also known as MLXIPL and MondoB) play crucial roles in the regulation of nutrient metabolism and energy homeostasis in the body. This review summarizes recent advances in elucidating the function of MondoA and ChREBP in insulin resistance and related pathological conditions. This review provides an overview of the mechanisms by which MondoA and ChREBP transcription factors regulate glucose and lipid metabolism in metabolically active organs. Understanding the underlying mechanism of MondoA and ChREBP in insulin resistance and obesity can foster the development of new therapeutic strategies for treating metabolic diseases.

Characterization of Human Subcutaneous Adipose Tissue and Validation of the Banking Procedure for Autologous Transplantation

Adipose tissue (AT) is composed of a heterogeneous population which comprises both progenitor and differentiated cells. This heterogeneity allows a variety of roles for the AT, including regenerative functions. In fact, autologous AT is commonly used to repair soft tissue defects, and its cryopreservation could be a useful strategy to reduce the patient discomfort caused by multiple harvesting procedures. Our work aimed to characterize the cryopreserved AT and to validate its storage for up to three years for clinical applications. AT components (stromal vascular fraction-SVF and mature adipocytes) were isolated in fresh and cryopreserved samples using enzymatic digestion, and cell viability was assessed by immunofluorescence (IF) staining. Live, apoptotic and necrotic cells were quantified using cytometry by evaluating phosphatidylserine binding to fluorescent-labeled Annexin V. A multiparametric cytometry was also used to measure adipogenic (CD34+CD90+CD31-CD45-) and endothelial (CD34+CD31+CD45-) precursors and endothelial mature cells (CD34-CD31+CD45-). The maintenance of adipogenic abilities was evaluated using in vitro differentiation of SVF cultures and fluorescent lipid staining. We demonstrated that AT that is cryopreserved for up to three years maintains its differentiation potential and cellular composition. Given our results, a clinical study was started, and two patients had successful transplants without any complications using autologous cryopreserved AT.

Droplet Digital PCR Quantification of Selected Intracellular and Extracellular microRNAs Reveals Changes in Their Expression Pattern during Porcine In Vitro Adipogenesis

Extracellular miRNAs have attracted considerable interest because of their role in intercellular communication, as well as because of their potential use as diagnostic and prognostic biomarkers for many diseases. It has been shown that miRNAs secreted by adipose tissue can contribute to the pathophysiology of obesity. Detailed knowledge of the expression of intracellular and extracellular microRNAs in adipocytes is thus urgently required. The system of in vitro differentiation of mesenchymal stem cells (MSCs) into adipocytes offers a good model for such an analysis. The aim of this study was to quantify eight intracellular and extracellular miRNAs (miR-21a, miR-26b, miR-30a, miR-92a, miR-146a, miR-148a, miR-199, and miR-383a) during porcine in vitro adipogenesis using droplet digital PCR (ddPCR), a highly sensitive method. It was found that only some miRNAs associated with the inflammatory process (miR-21a, miR-92a) were highly expressed in differentiated adipocytes and were also secreted by cells. All miRNAs associated with adipocyte differentiation were highly abundant in both the studied cells and in the cell culture medium. Those miRNAs showed a characteristic expression profile with upregulation during differentiation.

Comparing lipid remodeling of brown adipose tissue, white adipose tissue, and liver after one-week high fat diet intervention with quantitative Raman microscopy

Brown adipose tissue (BAT) consists of highly metabolically active adipocytes that catabolize nutrients to produce heat. Playing an active role in triacylglycerol (TAG) clearance, research has shown that dietary fatty acids can modulate the TAG chemistry deposition in BAT after weeks-long dietary intervention, similar to what has been shown in white adipose tissue (WAT). Our objective was to compare the influence of sustained, nonchronic dietary intervention (a 1-week interval) on WAT and interscapular BAT lipid metabolism and deposition in situ. We use quantitative, label-free chemical microscopy to show that 1 week of high fat diet (HFD) intervention results in dramatically larger lipid droplet (LD) growth in BAT (and liver) compared to LD growth in inguinal WAT (IWAT). Moreover, BAT showed lipid remodeling as increased unsaturated TAGs in LDs, resembling the dietary lipid composition, while WAT (and liver) did not show lipid remodeling on this time scale. Concurrently, expression of genes involved in lipid metabolism, particularly desaturases, was reduced in BAT and liver from HFD-fed mice after 1 week. Our data show that BAT lipid chemistry remodels exceptionally fast to dietary lipid intervention compared WAT, which further points towards a role in TAG clearance.

Interleukin-33 inhibits glucose uptake in human adipocytes and its expression in adipose tissue is elevated in insulin resistance and type 2 diabetes

OBJECTIVE

Interleukin-33 (IL-33) is associated with obesity-related inflammation. We aim to investigate IL-33 expression in subcutaneous adipose tissue (SAT) in type 2 diabetes (T2D) subjects and its effects on human adipocyte glucose uptake.

METHODS

Expression of IL-33 was analysed in SAT from cohort studies including subjects with and without obesity and T2D and correlated with insulin resistance and obesity markers. Magnetic resonance imaging (MRI) of tissue fat volumes was performed. We investigated the effects of IL-33 treatment on ex vivo adipocyte glucose uptake.

RESULTS

T2D subjects had higher IL-33 gene and protein expression in SAT than the control subjects. IL-33 mRNA expression was positively correlated with markers of dysglycemia (e.g. HbA1c), insulin resistance (e.g. HOMA-IR) and adiposity (BMI, visceral adipose tissue volume, liver and pancreas fat %). In multiple linear regression analyses, insulin resistance and T2D status were the strongest predictors of IL-33, independent of BMI. IL-33 mRNA expression was negatively correlated with expression of genes regulating adipocyte glucose uptake, lipid storage, and adipogenesis (e.g.glucose transporter 1 and 4 (GLUT1/4), fatty acid binding protein 4 (FABP4), and PPARG). Additionally, incubation of SAT with IL-33 reduced adipocyte glucose uptake and GLUT4 gene and protein expression.

CONCLUSIONS

Our findings suggest that T2D subjects have higher IL-33 gene and protein expressionin SATthan control subjects, which is associated with insulin resistance and reduced gene expression of lipid storage and adipogenesis markers. IL-33 may reduce adipocyte glucose uptake. This opens up a potential pharmacological route for reversing insulin resistance in T2D and prediabetes.

Single-cell sequencing unveils key contributions of immune cell populations in cancer-associated adipose wasting

Adipose tissue loss seen with cancer-associated cachexia (CAC) may functionally drive cachexia development. Using single-cell transcriptomics, we unveil a large-scale comprehensive cellular census of the stromal vascular fraction of white adipose tissues from patients with or without CAC. We report depot- and disease-specific clusters and developmental trajectories of adipose progenitors and immune cells. In adipose tissues with CAC, clear pro-inflammatory transitions were discovered in adipose progenitors, macrophages and CD8+ T cells, with dramatically remodeled cell interactome among these cells, implicating a synergistic effect in promoting tissue inflammation. Remarkably, activated CD8+ T cells contributed specifically to increased IFNG expression in adipose tissues from cachexia patients, and displayed a significant pro-catabolic effect on adipocytes in vitro; whereas macrophage depletion resulted in significantly rescued adipose catabolism and alleviated cachexia in a CAC animal model. Taken together, these results unveil causative mechanisms underlying the chronical inflammation and adipose wasting in CAC.

Dexamethasone-Induced Adipose Tissue Redistribution and Metabolic Changes: Is Gene Expression the Main Factor? An Animal Model of Chronic Hypercortisolism

Chronic hypercortisolism has been associated with the development of several metabolic alterations, mostly caused by the effects of chronic glucocorticoid (GC) exposure over gene expression. The metabolic changes can be partially explained by the GC actions on different adipose tissues (ATs), leading to central obesity. In this regard, we aimed to characterize an experimental model of iatrogenic hypercortisolism in rats with significant AT redistribution. Male Wistar rats were distributed into control (CT) and GC-treated, which received dexamethasone sodium phosphate (0.5 mg/kg/day) by an osmotic minipump, for 4 weeks. GC-treated rats reproduced several characteristics observed in human hypercortisolism/Cushing’s syndrome, such as HPA axis inhibition, glucose intolerance, insulin resistance, dyslipidemia, hepatic lipid accumulation, and AT redistribution. There was an increase in the mesenteric (meWAT), perirenal (prWAT), and interscapular brown (BAT) ATs mass, but a reduction of the retroperitoneal (rpWAT) mass compared to CT rats. Overexpressed lipolytic and lipogenic gene profiles were observed in white adipose tissue (WAT) of GC rats as BAT dysfunction and whitening. The AT remodeling in response to GC excess showed more importance than the increase of AT mass per se, and it cannot be explained just by GC regulation of gene transcription.

Single-Cell RNA-Seq Identifies Dynamic Cardiac Transition Program from Adipose Derived Cells Induced by Leukemia Inhibitory Factor

Adipose-derived cells (ADCs) from white adipose tissue (WAT) are promising stem cell candidates because of their large regenerative reserves and the potential for cardiac regeneration. However, given the heterogeneity of ADC and its unsolved mechanisms of cardiac acquisition, ADC-cardiac transition efficiency remains low. In this study, we explored the heterogeneity of ADCs and the cellular kinetics of 39,432 single-cell transcriptomes along the leukemia inhibitory factor (LIF) induced ADC-cardiac transition. We identified distinct ADC subpopulations that reacted differentially to LIF when entering the cardiomyogenic program, further demonstrating that ADC-myogenesis is time-dependent and initiates from transient changes in nuclear factor erythroid 2-related factor 2 (Nrf2) signaling. At later stages, pseudotime analysis of ADCs navigated a trajectory with two branches corresponding to activated myofibroblast or cardiomyocyte-like cells. Our findings offer a high-resolution dissection of ADC heterogeneity and cell fate during ADC-cardiac transition, thus providing new insights into potential cardiac stem cells.

RNA-seq Based Transcriptome Analysis Reveals The Cross-Talk of Macrophage and Adipocyte of Chicken Subcutaneous Adipose Tissue during The Embryonic and Post-Hatch Period

With high fecundity and short production cycle, poultry is one of the important sources of meat. During the embryonic and post-hatch period, the higher death rate caused huge economic losses in poultry production. Our previous study showed that chick subcutaneous adipose tissue is an important energy supply tissue besides yolk. Therefore, the metabolic mechanism of subcutaneous adipose tissue in chicks could provide a new perspective of brooding. The objectives of the current study were to evaluate the differences between chick subcutaneous adipose tissue and abdominal adipose tissue before and after hatching and reveal the cross-talk of different cells within the chick subcutaneous adipose tissue. The results of RNA-seq and weighted gene co-expression network analysis (WGCNA) of chick subcutaneous and abdominal adipose tissues showed that the function of chick subcutaneous tissue was related to immunoreaction, and macrophage could be the major immune infiltration cell type in chicken subcutaneous adipose tissue, which were also verified by qPCR, HE stain, and IHC. The results of free fatty acids (FFAs)-induced the cross-talk between macrophages and adipocytes showed that FFAs-Ccl2 (chicken CCL26) axis could have an important role in lipid transportation in adipose tissue. The results of Oil Red O and Nile red stain demonstrated that macrophages have the ability to absorb FFAs quickly. Interestingly, according to the genomic organization of CCL family with representative vertebrate species, we found that chicken CCL26 could be the major chemokine in chicken adipocyte as the status of CCL2 in mammal adipocyte. In conclusion, we demonstrate that FFA-induced Ccl2 (chicken CCL26) secretion is crucial in determining fat depot-selective adipose tissue macrophage (ATM) infiltration, which could be an important medium of lipid transportation in chicken subcutaneous adipose tissue. These findings may have multiple important implications for understanding macrophage biology with chick subcutaneous adipose tissue and provide theoretical basis for lipid metabolism in poultry brooding.

Obesity I: Overview and molecular and biochemical mechanisms

Obesity is a chronic, relapsing condition characterized by excess body fat. Its prevalence has increased globally since the 1970s, and the number of obese and overweight people is now greater than those underweight. Obesity is a multifactorial condition, and as such, many components contribute to its development and pathogenesis. This is the first of three companion reviews that consider obesity. This review focuses on the genetics, viruses, insulin resistance, inflammation, gut microbiome, and circadian rhythms that promote obesity, along with hormones, growth factors, and organs and tissues that control its development. It shows that the regulation of energy balance (intake vs. expenditure) relies on the interplay of a variety of hormones from adipose tissue, gastrointestinal tract, pancreas, liver, and brain. It details how integrating central neurotransmitters and peripheral metabolic signals (e.g., leptin, insulin, ghrelin, peptide YY_3-36) is essential for controlling energy homeostasis and feeding behavior. It describes the distinct types of adipocytes and how fat cell development is controlled by hormones and growth factors acting via a variety of receptors, including peroxisome proliferator-activated receptor-gamma, retinoid X, insulin, estrogen, androgen, glucocorticoid, thyroid hormone, liver X, constitutive androstane, pregnane X, farnesoid, and aryl hydrocarbon receptors. Finally, it demonstrates that obesity likely has origins in utero. Understanding these biochemical drivers of adiposity and metabolic dysfunction throughout the life cycle lends plausibility and credence to the "obesogen hypothesis" (i.e., the importance of environmental chemicals that disrupt these receptors to promote adiposity or alter metabolism), elucidated more fully in the two companion reviews.

Leptin as a key regulator of the adipose organ

Leptin is a hormone primarily produced by the adipose tissue in proportion to the size of fat stores, with a primary function in the control of lipid reserves. Besides adipose tissue, leptin is also produced by other tissues, such as the stomach, placenta, and mammary gland. Altogether, leptin exerts a broad spectrum of short, medium, and long-term regulatory actions at the central and peripheral levels, including metabolic programming effects that condition the proper development and function of the adipose organ, which are relevant for its main role in energy homeostasis. Comprehending how leptin regulates adipose tissue may provide important clues to understand the pathophysiology of obesity and related diseases, such as type 2 diabetes, as well as its prevention and treatment. This review focuses on the physiological and long-lasting regulatory effects of leptin on adipose tissue, the mechanisms and pathways involved, its main outcomes on whole-body physiological homeostasis, and its consequences on chronic diseases.

Effect of Hypertension, Waist-to-Height Ratio, and Their Transitions on the Risk of Type 2 Diabetes Mellitus: Analysis from the China Health and Retirement Longitudinal Study

BACKGROUND

Diabetes is a major reason of death and disability worldwide and frequently coexists with hypertension and central obesity. This study is aimed at investigating the effects of hypertension, waist-to-height ratio (WHtR), and their dynamic transitions on type 2 diabetes mellitus (T2DM) onset among middle-aged and elderly people in China.

METHODS

We analyzed 9843 participants free of T2DM (average age, 59.04 ± 9.26 years) at baseline from the China Health and Retirement Longitudinal Study. We classified the participants into the following four categories based on hypertension and WHtR statuses: nonhypertensive with a normal WHtR (NHNW); hypertensive with a normal WHtR (HTNW); nonhypertensive with an elevated WHtR (NHEW); and hypertensive with an elevated WHtR (HTEW). By using a Cox proportional hazards regression model, we assessed whether hypertension, WHtR, and their transitions over time correlated with T2DM risk.

RESULTS

During the follow-up of 8 years, 1263 participants developed incident T2DM. The hazard ratio (HR) for T2DM was 1.48 (95% CI: 1.12, 1.97), 1.56 (95% CI: 1.27, 1.92), and 2.15 (95% CI: 1.74, 2.67) in the HTNW, NHEW, and HTEW groups, respectively, compared with the NHNW group after controlling for confounding factors. When stratified by statuses of hypertension and WHtR transitions, the participants who transitioned from HTNW to HTEW (HR = 1.98, 95% CI: 1.24-3.17), or NHEW to NHNW/HTNW (HR = 1.74, 95% CI: 1.14-2.65), or remained NHEW (HR = 1.42, 95% CI: 1.04-1.93), or NHEW to HTEW (HR = 2.40, 95% CI: 1.66-3.49), or remained HTEW (HR = 2.51, 95% CI: 1.87-3.37) during the follow-up period showed a higher T2DM risk than the consistently NHNW participants.

CONCLUSIONS

Being HTNW, NHEW or HTEW or occurring adverse transitions between those states was strongly associated with T2DM onset. Effectively warding off hypertension and central obesity or preventing their further aggravation may substantially decrease the T2DM risk.

Selective targeting of angiopoietin-like 3 (ANGPTL3) with vupanorsen for the treatment of patients with familial partial lipodystrophy (FPLD): results of a proof-of-concept study

BACKGROUND

Familial partial lipodystrophy (FPLD) is a rare disease characterized by selective loss of peripheral subcutaneous fat, associated with dyslipidemia and diabetes mellitus. Reductions in circulating levels of ANGPTL3 are associated with lower triglyceride and other atherogenic lipids, making it an attractive target for treatment of FPLD patients. This proof-of-concept study was conducted to assess the efficacy and safety of targeting ANGPTL3 with vupanorsen in patients with FPLD.

METHODS

This was an open-label study. Four patients with FPLD (two with pathogenic variants in LMNA gene, and two with no causative genetic variant), diabetes (HbA1c ≥ 7.0 % and ≤ 12 %), hypertriglyceridemia (≥ 500 mg/dL), and hepatic steatosis (hepatic fat fraction, HFF ≥ 6.4 %) were included. Patients received vupanorsen subcutaneously at a dose of 20 mg weekly for 26 weeks. The primary endpoint was the percent change from baseline in fasting triglycerides at Week 27. Other endpoints analyzed at the same time point included changes in ANGPTL3, fasting lipids and lipoproteins, insulin secretion/sensitivity, postprandial lipids, and glycemic changes in response to a mixed meal test, HFF measured by MRI, and body composition measured by dual-energy absorptiometry (DEXA).

RESULTS

Baseline mean ± SD fasting triglyceride level was 9.24 ± 4.9 mmol/L (817.8 ± 431.9 mg/dL). Treatment resulted in reduction in fasting levels of triglycerides by 59.9 %, ANGPTL3 by 54.7 %, and in several other lipoproteins/lipids, including very low-density lipoprotein cholesterol by 53.5 %, non-high-density lipoprotein cholesterol by 20.9 %, and free fatty acids (FFA) by 41.7 %. The area under the curve for postprandial triglycerides, FFA, and glucose was reduced by 60 %, 32 %, and 14 %, respectively. Treatment with vupanorsen also resulted in 55 % reduction in adipose tissue insulin resistance index, while other insulin sensitivity indices and HbA1c levels were not changed. Additional investigations into HFF and DEXA parameters suggested dynamic changes in fat partitioning during treatment. Adverse events observed were related to common serious complications associated with diabetes and FPLD. Vupanorsen was well tolerated, and there was no effect on platelet count.

CONCLUSIONS

Although limited, these results suggest that targeting ANGPTL3 with vupanorsen could address several metabolic abnormalities in patients with FPLD.

Chromatin accessibility and gene expression during adipocyte differentiation identify context-dependent effects at cardiometabolic GWAS loci

Chromatin accessibility and gene expression in relevant cell contexts can guide identification of regulatory elements and mechanisms at genome-wide association study (GWAS) loci. To identify regulatory elements that display differential activity across adipocyte differentiation, we performed ATAC-seq and RNA-seq in a human cell model of preadipocytes and adipocytes at days 4 and 14 of differentiation. For comparison, we created a consensus map of ATAC-seq peaks in 11 human subcutaneous adipose tissue samples. We identified 58,387 context-dependent chromatin accessibility peaks and 3,090 context-dependent genes between all timepoint comparisons (log2 fold change>1, FDR<5%) with 15,919 adipocyte- and 18,244 preadipocyte-dependent peaks. Adipocyte-dependent peaks showed increased overlap (60.1%) with Roadmap Epigenomics adipocyte nuclei enhancers compared to preadipocyte-dependent peaks (11.5%). We linked context-dependent peaks to genes based on adipocyte promoter capture Hi-C data, overlap with adipose eQTL variants, and context-dependent gene expression. Of 16,167 context-dependent peaks linked to a gene, 5,145 were linked by two or more strategies to 1,670 genes. Among GWAS loci for cardiometabolic traits, adipocyte-dependent peaks, but not preadipocyte-dependent peaks, showed significant enrichment (LD score regression P<0.005) for waist-to-hip ratio and modest enrichment (P < 0.05) for HDL-cholesterol. We identified 659 peaks linked to 503 genes by two or more approaches and overlapping a GWAS signal, suggesting a regulatory mechanism at these loci. To identify variants that may alter chromatin accessibility between timepoints, we identified 582 variants in 454 context-dependent peaks that demonstrated allelic imbalance in accessibility (FDR<5%), of which 55 peaks also overlapped GWAS variants. At one GWAS locus for palmitoleic acid, rs603424 was located in an adipocyte-dependent peak linked to SCD and exhibited allelic differences in transcriptional activity in adipocytes (P = 0.003) but not preadipocytes (P = 0.09). These results demonstrate that context-dependent peaks and genes can guide discovery of regulatory variants at GWAS loci and aid identification of regulatory mechanisms.

Cardiovascular and metabolic diseases are widespread, and an increased understanding of genetic mechanisms behind these diseases could improve treatment. Chromatin accessibility and gene expression in relevant cell contexts can guide identification of regulatory elements and genetic mechanisms for disease traits. A relevant context for cardiovascular and metabolic disease traits is adipocyte differentiation. To identify regulatory elements and genes that display differences in activity during adipocyte differentiation, we profiled chromatin accessibility and gene expression in a human cell model of preadipocytes and adipocytes. We identified chromatin regions that change accessibility during differentiation and predicted genes they may affect. We also linked these chromatin regions to genetic variants associated with risk of disease. At one genomic region linked to fatty acids, a chromatin region more accessible in adipocytes linked to a fatty acid synthesis gene and exhibited allelic differences in transcriptional activity in adipocytes but not preadipocytes. These results demonstrate that chromatin regions and genes that change during cell context can guide discovery of regulatory variants and aid identification of disease mechanisms.

Understanding the heterogeneity and functions of metabolic tissue macrophages

Growing evidence places tissue-resident macrophages as essential gatekeepers of metabolic organ homeostasis, including the adipose tissue and the pancreatic islets. Therein, macrophages may adopt specific phenotypes and ensure local functions. Recent advances in single cell genomic analyses provide a comprehensive map of adipose tissue macrophage subsets and their potential roles are now better apprehended. Whether they are beneficial or detrimental, macrophages overall contribute to the proper adipose tissue expansion under steady state and during obesity. By contrast, macrophages residing inside pancreatic islets, which may exert fundamental functions to fine tune insulin secretion, have only started to attract attention and their cellular heterogeneity remains to be established. The present review will focus on the latest findings exploring the phenotype and the properties of macrophages in adipose tissue and pancreatic islets, questioning early beliefs and future perspectives in the field of immunometabolism.

Effects of maternal undernutrition during late pregnancy on the regulatory factors involved in growth and development in ovine fetal perirenal brown adipose tissue

Objective

The experiment was conducted to evaluate the effects of maternal undernutrition during late pregnancy on the expressions of genes involved in growth and development in ovine fetal perirenal brown adipose tissue (BAT).

Methods

Eighteen ewes with singleton fetuses were allocated to three groups at day 90 of pregnancy: restricted group 1 (RG1, 0.33 MJ metabolisable energy [ME]/kg body weight [BW]^0.75/d, n = 6), restricted group 2 (RG2, 0.18 MJ ME/kg BW^0.75/d, n = 6), and a control group (CG, ad libitum, 0.67 MJ ME/kg BW^0.75/d, n = 6). The fetuses were removed at day 140 of pregnancy. All data were analyzed by using the analysis of variance procedure.

Results

The perirenal fat weight (p = 0.0077) and perirenal fat growth rate (p = 0.0074) were reduced in RG2 compared to CG. In fetal perirenal BAT, the protein level of uncoupling protein 1 (UCP1) (p = 0.0001) was lower in RG1 and RG2 compared with CG and UCP1 mRNA expression (p = 0.0265) was decreased in RG2. The protein level of myogenic factor 5 (Myf5) was also decreased in RG2 (p = 0.0001). In addition, mRNA expressions of CyclinA (p = 0.0109), CyclinB (p = 0.0019), CyclinD (p = 0.0015), cyclin-dependent kinase 1 (CDK1) (p = 0.0001), E2F transcription factor 1 (E2F1) (p = 0.0323), E2F4 (p = 0.0101), and E2F5 (p = 0.0018) were lower in RG1 and RG2. There were decreased protein expression of peroxisome proliferator-activated receptor-γ (PPARγ) (p = 0.0043) and mRNA expression of CCAAT/enhancer-binding protein-α (C/EBPα) (p = 0.0307) in RG2 and decreased PPARγ mRNA expression (p = 0.0008) and C/EBPα protein expression (p = 0.0015) in both RG2 and RG1. Furthermore, mRNA expression of bone morphogenetic protein 4 (BMP4) (p = 0.0083) and BMP7 (p = 0.0330) decreased in RG2 and peroxisome proliferator-activated receptor co-activator-1α (PGC-1α) reduced in RG2 and RG1.

Conclusion

Our observations support that repression of regulatory factors promoting differentiation and development results in the inhibition of BAT maturation in fetal perirenal fat during late pregnancy with maternal undernutrition.

Adipose-PAS interactions in the context of its localised bio-engineering potential (Review)

Adipocytes are a known source of stem cells. They are easy to harvest, and are a suitable candidate for autogenous grafts. Adipose derived stem cells (ADSCs) have multiple target tissues which they can differentiate into, including bone and cartilage. In adipose tissue, ADSCs are able to differentiate, as well as providing energy and a supply of cytokines/hormones to manage the hypoxic and lipid/hormone saturated adipose environment. The plasminogen activation system (PAS) controls the majority of proteolytic activities in both adipose and wound healing environments, allowing for rapid cellular migration and tissue remodelling. While the primary activation pathway for PAS occurs through the urokinase plasminogen activator (uPA), which is highly expressed by endothelial cells, its function is not limited to enabling revascularisation. Proteolytic activity is dependent on protease activation, localisation, recycling mechanisms and substrate availability. uPA and uPA activated plasminogen allows pluripotent cells to arrive to new local environments and fulfil the niche demands. However, overstimulation, the acquisition of a migratory phenotype and constant protein turnover can be unconducive to the formation of structured hard and soft tissues. To maintain a suitable healing pattern, the proteolytic activity stimulated by uPA is modulated by plasminogen activator inhibitor 1. Depending on the physiological settings, different parts of the remodelling mechanism are activated with varying results. Utilising the differences within each microenvironment to recreate a desired niche is a valid therapeutic bio-engineering approach. By controlling the rate of protein turnover combined with a receptive stem cell lineage, such as ADSC, a novel avenue on the therapeutic opportunities may be identified, which can overcome limitations, such as scarcity of stem cells, low angiogenic potential or poor host tissue adaptation.

Diabetes Mellitus and Its Metabolic Complications: The Role of Adipose Tissues

Many approaches have been used in the effective management of type 2 diabetes mellitus. A recent paradigm shift has focused on the role of adipose tissues in the development and treatment of the disease. Brown adipose tissues (BAT) and white adipose tissues (WAT) are the two main types of adipose tissues with beige subsets more recently identified. They play key roles in communication and insulin sensitivity. However, WAT has been shown to contribute significantly to endocrine function. WAT produces hormones and cytokines, collectively called adipocytokines, such as leptin and adiponectin. These adipocytokines have been proven to vary in conditions, such as metabolic dysfunction, type 2 diabetes, or inflammation. The regulation of fat storage, energy metabolism, satiety, and insulin release are all features of adipose tissues. As such, they are indicators that may provide insights on the development of metabolic dysfunction or type 2 diabetes and can be considered routes for therapeutic considerations. The essential roles of adipocytokines vis-a-vis satiety, appetite, regulation of fat storage and energy, glucose tolerance, and insulin release, solidifies adipose tissue role in the development and pathogenesis of diabetes mellitus and the complications associated with the disease.

Narrating the story ARC of adipose tissue aging

In this issue of Developmental Cell, Nguyen et al. use scRNA-seq to explore the changing cellular landscape of subcutaneous adipose tissue during aging. In the process, they discover a new population of cells called age-dependent regulatory cells (ARC), which contributes to age-related adipose tissue dysfunction that drives metabolic disease.

Lipid and glucose metabolism in white adipocytes: pathways, dysfunction and therapeutics

In mammals, the white adipocyte is a cell type that is specialized for storage of energy (in the form of triacylglycerols) and for energy mobilization (as fatty acids). White adipocyte metabolism confers an essential role to adipose tissue in whole-body homeostasis. Dysfunction in white adipocyte metabolism is a cardinal event in the development of insulin resistance and associated disorders. This Review focuses on our current understanding of lipid and glucose metabolic pathways in the white adipocyte. We survey recent advances in humans on the importance of adipocyte hypertrophy and on the in vivo turnover of adipocytes and stored lipids. At the molecular level, the identification of novel regulators and of the interplay between metabolic pathways explains the fine-tuning between the anabolic and catabolic fates of fatty acids and glucose in different physiological states. We also examine the metabolic alterations involved in the genesis of obesity-associated metabolic disorders, lipodystrophic states, cancers and cancer-associated cachexia. New challenges include defining the heterogeneity of white adipocytes in different anatomical locations throughout the lifespan and investigating the importance of rhythmic processes. Targeting white fat metabolism offers opportunities for improved patient stratification and a wide, yet unexploited, range of therapeutic opportunities.

Perirenal Adipose Tissue-Current Knowledge and Future Opportunities

The perirenal adipose tissue (PRAT), a component of visceral adipose tissue, has been recently recognized as an important factor that contributes to the maintenance of the cardiovascular system and kidney homeostasis. PRAT is a complex microenvironment consisting of a mixture of white adipocytes and dormant and active brown adipocytes, associated with predipocytes, sympathetic nerve endings, vascular structures, and different types of inflammatory cells. In this review, we summarize the current knowledge about PRAT and discuss its role as a major contributing factor in the pathogenesis of hypertension, obesity, chronic renal diseases, and involvement in tumor progression. The new perspectives of PRAT as an endocrine organ and recent knowledge regarding the possible activation of dormant brown adipocytes are nowadays considered as new areas of research in obesity, in close correlation with renal and cardiovascular pathology. Supplementary PRAT complex intervention in tumor progression may reveal new pathways involved in carcinogenesis and, implicitly, may identify additional targets for tailored cancer therapy.

Isolation and Differentiation of Primary White and Brown Preadipocytes from Newborn Mice

The understanding of the mechanisms underlying adipocyte differentiation and function has greatly benefited from the use of immortalized white preadipocyte cell lines. These cultured cell lines, however, have limitations. They do not fully capture the diverse functional spectrum of the heterogenous adipocyte populations that are now known to exist within white adipose depots. To provide a more physiologically relevant model to study the complexity of white adipose tissue, a protocol has been developed and optimized to enable simultaneous isolation of primary white and brown adipocyte progenitors from newborn mice, their rapid expansion in culture, and their differentiation in vitro into mature, fully functional adipocytes. The primary advantage of isolating primary cells from newborn, rather than adult mice, is that the adipose depots are actively developing and are, therefore, a rich source of proliferating preadipocytes. Primary preadipocytes isolated using this protocol differentiate rapidly upon reaching confluence and become fully mature in 4-5 days, a temporal window that accurately reflects the appearance of developed fat pads in newborn mice. Primary cultures prepared using this strategy can be expanded and studied with high reproducibility, making them suitable for genetic and phenotypic screens and enabling the study of the cell-autonomous adipocyte phenotypes of genetic mouse models. This protocol offers a simple, rapid, and inexpensive approach to study the complexity of adipose tissue in vitro.

The Role of Mondo Family Transcription Factors in Nutrient-Sensing and Obesity

In the past several decades obesity has become one of the greatest health burdens worldwide. Diet high in fats and fructose is one of the main causes for the prevalence of metabolic disorders including obesity. Promoting brown or beige adipocyte development and activity is regarded as a potential treatment of obesity. Mondo family transcription factors including MondoA and carbohydrate response element binding protein (ChREBP) are critical for nutrient-sensing in multiple metabolic organs including the skeletal muscle, liver, adipose tissue and pancreas. Under normal nutrient conditions, MondoA and ChREBP contribute to maintaining metabolic homeostasis. When nutrient is overloaded, Mondo family transcription factors directly regulate glucose and lipid metabolism in brown and beige adipocytes or modulate the crosstalk between metabolic organs. In this review, we aim to provide an overview of recent advances in the understanding of MondoA and ChREBP in sensing nutrients and regulating obesity or related pathological conditions.

Toward a Consensus View of Mammalian Adipocyte Stem and Progenitor Cell Heterogeneity

White adipose tissue (WAT) is a cellularly heterogeneous endocrine organ that not only serves as an energy reservoir, but also actively participates in metabolic homeostasis. Among the main constituents of adipose tissue are adipocytes, which arise from adipose stem and progenitor cells (ASPCs). While it is well known that these ASPCs reside in the stromal vascular fraction (SVF) of adipose tissue, their molecular heterogeneity and functional diversity is still poorly understood. Driven by the resolving power of single-cell transcriptomics, several recent studies provided new insights into the cellular complexity of ASPCs among different mammalian fat depots. In this review, we present current knowledge on ASPCs, their population structure, hierarchy, fat depot-specific nature, function, and regulatory mechanisms, and discuss not only the similarities, but also the differences between mouse and human ASPC biology.

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

Objective

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

Methods

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

Results

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

Conclusions

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

•

Adipocytes after HFD intake exhibit defects in cellular identity maintenance.

•

Adipocytes develop actin filament networks in obesity.

•

Altered PPARγ activity mediates defective adipocyte identity phenotypes.

•

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

The causal effect of obesity on prediabetes and insulin resistance reveals the important role of adipose tissue in insulin resistance

Reverse causality has made it difficult to establish the causal directions between obesity and prediabetes and obesity and insulin resistance. To disentangle whether obesity causally drives prediabetes and insulin resistance already in non-diabetic individuals, we utilized the UK Biobank and METSIM cohort to perform a Mendelian randomization (MR) analyses in the non-diabetic individuals. Our results suggest that both prediabetes and systemic insulin resistance are caused by obesity (p = 1.2×10-3 and p = 3.1×10-24). As obesity reflects the amount of body fat, we next studied how adipose tissue affects insulin resistance. We performed both bulk RNA-sequencing and single nucleus RNA sequencing on frozen human subcutaneous adipose biopsies to assess adipose cell-type heterogeneity and mitochondrial (MT) gene expression in insulin resistance. We discovered that the adipose MT gene expression and body fat percent are both independently associated with insulin resistance (p≤0.05 for each) when adjusting for the decomposed adipose cell-type proportions. Next, we showed that these 3 factors, adipose MT gene expression, body fat percent, and adipose cell types, explain a substantial amount (44.39%) of variance in insulin resistance and can be used to predict it (p≤2.64×10-5 in 3 independent human cohorts). In summary, we demonstrated that obesity is a strong determinant of both prediabetes and insulin resistance, and discovered that individuals' adipose cell-type composition, adipose MT gene expression, and body fat percent predict their insulin resistance, emphasizing the critical role of adipose tissue in systemic insulin resistance.

[The immune system of adipose tissue: obesity-associated inflammation]

Adipose tissue is an important endocrine organ. Via its secretion products, it cross-talks with other organs of the body and communicates the filling state of its triglyceride stores. Obesity is characterized by the excessive accumulation of body fat and leads to the infiltration and accumulation of immune cells in white adipose tissue. In this review article we introduce the various immune cell populations of adipose tissue and discuss their local and systemic influence.

Comprehensive Analysis of mRNA and lncRNA Transcriptomes Reveals the Differentially Hypoxic Response of Preadipocytes During Adipogenesis

Local hypoxia has recently been reported to occur in the white adipose tissue (WAT) microenvironment during obesity. Adipocytes have a unique life cycle that reflects the different stages of adipogenesis in the WAT niche. Long non-coding RNAs (lncRNAs) play an important role in the cellular response to hypoxia. However, the differentially hypoxic responses of preadipocytes during adipogenesis and the potential role of lncRNAs in this process remain to be elucidated. Here, we evaluated the differentially hypoxic responses of primary hamster preadipocytes during adipogenesis and analyzed mRNA and lncRNA expression in same Ribo-Zero RNA-seq libraries. Hypoxia induced HIF-1α protein during adipogenesis and caused divergent changes of cell phenotypes. A total of 10,318 mRNAs were identified to be expressed in twenty libraries (five timepoints), and 3,198 differentially expressed mRNAs (DE mRNAs) were detected at five timepoints (hypoxia vs. normoxia). Functional enrichment analysis revealed the shared and specific hypoxia response pathways in the different stages of adipogenesis. Hypoxia differentially modulated the expression profile of adipose-associated genes, including adipokines, lipogenesis, lipolysis, hyperplasia, hypertrophy, inflammatory, and extracellular matrix. We also identified 4,296 lncRNAs that were expressed substantially and detected 1,431 DE lncRNAs at five timepoints. Two, 3, 5, 13, and 50 DE mRNAs at D0, D1, D3, D7, and D11, respectively, were highly correlated and locus-nearby DE lncRNAs and mainly involved in the cell cycle, vesicle-mediated transport, and mitochondrion organization. We identified 28 one-to-one lncRNA-mRNA pairs that might be closely related to adipocyte functions, such as ENSCGRT00015041780-Hilpda, TU2105-Cdsn, and TU17588-Ltbp3. These lncRNAs may represent the crucial regulation axis in the cellular response to hypoxia during adipogenesis. This study dissected the effects of hypoxia in the cell during adipogenesis, uncovered novel regulators potentially associated with WAT function, and may provide a new viewpoint for interpretation and treatment of obesity.

Lipidomics of brown and white adipose tissue: Implications for energy metabolism

Adipose tissue exerts multiple vital functions that critically maintain energy balance, including storing and expending energy, as well as secreting factors that systemically modulate nutrient metabolism. Since lipids are the major constituents of the adipocytes, it is unsurprising that the lipid composition of these cells plays a critical role in maintaining their functions and communicating with other organs and cells. In both positive and negative energy balance conditions, lipids and free fatty acids secreted from adipocytes exert either beneficial or detrimental effects in other tissues, such as the liver, pancreas and muscle. The way the adipocytes communicate with other organs tightly depends on the nature of their lipidome composition. Notwithstanding, the lipidome composition of the adipocytes is affected by physiological factors such as adipocyte type, gender and age, but also by environmental cues such as diet composition, thermal stress and physical activity. Here we provide an updated overview on how the adipose tissue lipidome profile is shaped by different physiological and environmental factors and how these changes impact the way the adipocytes regulate whole-body energy metabolism.

Perivascular adipose tissue: An immune cell metropolis

NEW FINDINGS

What is the topic of this review? The review discusses how eosinophils can contribute to the function of perivascular adipose tissue and explores the mechanisms involved. What advances does it highlight? Understanding the communication between the cell populations that constitute perivascular adipose tissue function is important for exploring therapeutic options in the treatment of obesity-related cardiovascular complications. This article highlights that eosinophils are able to contribute directly to healthy perivascular adipose tissue function. These immune cells contribute to adrenergic signalling and nitric oxide- and adiponectin-dependent mechanisms in perivascular adipose tissue.

ABSTRACT

Perivascular adipose tissue is a heterogeneous tissue that surrounds most blood vessels in the body. This review focuses on the contribution of eosinophils located within the adipose tissue to vascular contractility. A high-fat diet reduces the number of these immune cells within perivascular adipose tissue, and this loss is linked to an increase in vascular contractility and hypertension. We explored the mechanisms by which eosinophils contribute to this function using genetically modified mice, ex vivo assessment of contractility and pharmacological tools. We found that eosinophils contribute to adrenergic signalling and nitric oxide- and adiponectin-dependent mechanisms in perivascular adipose tissue. It is now important to explore whether manipulation of these pathways in obesity can alleviate cardiovascular complications, in order to determine whether eosinophils are a valid target for obesity-related disease.

The Heating Microenvironment: Intercellular Cross Talk Within Thermogenic Adipose Tissue

Adipose tissue serves as the body's primary energy storage site; however, findings in recent decades have transformed our understanding of the multifaceted roles of this adaptable organ. The ability of adipose tissue to undergo energy expenditure through heat generation is termed adaptive thermogenesis, a process carried out by thermogenic adipocytes. Adipocytes are the primary parenchymal cell type in adipose tissue, yet these cells are sustained within a rich stromal vascular microenvironment comprised of adipose stem cells and progenitors, immune cells, neuronal cells, fibroblasts, and endothelial cells. Intricate cross talk between these diverse cell types is essential in regulating the activation of thermogenic fat, and the past decade has shed significant light on how this intercellular communication functions. This review will draw upon recent findings and current perspectives on the sophisticated repertoire of cellular and molecular features that comprise the adipose thermogenic milieu.

Sex Differences in Long-term Metabolic Effects of Maternal Resveratrol Intake in Adult Rat Offspring

Maternal nutrition can affect the susceptibility of the offspring to metabolic disease later in life, suggesting that this period is a window of opportunity for intervention to reduce the risk of metabolic disease. Resveratrol, a natural polyphenol, has a wide range of beneficial properties including anti-obesogenic, anti-atherosclerotic, and anti-diabetic effects. We previously reported that maternal resveratrol intake during pregnancy and lactation has early metabolic effects in the offspring with these effects at weaning depending on the type of diet ingested by the mother and the offspring's sex. Here we analyzed whether these metabolic changes are maintained in the adult offspring and if they remain sex and maternal diet dependent. Wistar rats received a low-fat diet (LFD; 10.2% Kcal from fat) or high fat diet (HFD; 61.6% Kcal from fat) during pregnancy and lactation. Half of each group received resveratrol in their drinking water (50 mg/L). Offspring were weaned onto standard chow on postnatal day 21. Maternal resveratrol reduced serum cholesterol levels in all adult offspring from HFD mothers and increased it in adult female offspring from LFD mothers. Resveratrol increased visceral adipose tissue (VAT) in LFD offspring in both sexes but decreased it in male HFD offspring. Resveratrol shifted the distribution of VAT adipocyte size to a significantly higher incidence of large adipocytes, regardless of sex or maternal diet. These results clearly demonstrate that maternal resveratrol intake has long-lasting effects on metabolic health of offspring in a sex specific manner with these effects being highly dependent on the maternal diet.

Integrated metabolomics reveals altered lipid metabolism in adipose tissue in a model of extreme longevity

Adipose tissue plays an essential role in metabolic health. Ames dwarf mice are exceptionally long-lived and display metabolically beneficial phenotypes in their adipose tissue, providing an ideal model for studying the intersection between adipose tissue and longevity. To this end, we assessed the metabolome and lipidome of adipose tissue in Ames dwarf mice. We observed distinct lipid profiles in brown versus white adipose tissue of Ames dwarf mice that are consistent with increased thermogenesis and insulin sensitivity, such as increased cardiolipin and decreased ceramide concentrations. Moreover, we identified 5-hydroxyeicosapentaenoic acid (5-HEPE), an ω-3 fatty acid metabolite, to be increased in Ames dwarf brown adipose tissue (BAT), as well as in circulation. Importantly, 5-HEPE is increased in other models of BAT activation and is negatively correlated with body weight, insulin resistance, and circulating triglyceride concentrations in humans. Together, these data represent a novel lipid signature of adipose tissue in a mouse model of extreme longevity.

Adipose TBX1 regulates β-adrenergic sensitivity in subcutaneous adipose tissue and thermogenic capacity in vivo

OBJECTIVE

T-box 1 (TBX1) has been identified as a genetic marker of beige adipose tissue. TBX1 is a mesodermal development transcription factor essential for tissue patterning and cell fate determination. However, whether it plays a role in the process of adipose beiging or how it functions in adipose tissue has not been reported. Here, we examined the function of TBX1 in adipose tissue as well as adipose-derived stem cells from mice and humans.

METHODS

Adipose-specific TBX1 transgenic (TBX1 AdipoTG) and adipose-specific TBX1 knockout (TBX1 AdipoKO) mice were generated to explore the function of TBX1 in the process of adipose beiging, metabolism and energy homeostasis in vivo. In vitro, we utilized a siRNA mediated approach to determine the function of TBX1 during adipogenesis in mouse and human stem cells.

RESULTS

Adipose-specific overexpression of TBX1 was not sufficient to fully induce beiging and prevent diet-induced obesity. However, adipose TBX1 expression was necessary to defend body temperature during cold through regulation of UCP1 and for maintaining β3-adrenergic sensitivity and glucose homeostasis in vivo. Loss of adipose TBX1 expression enhanced basal lipolysis and reduced the size of subcutaneous iWAT adipocytes. Reduction of TBX1 expression via siRNA significantly impaired adipogenesis of mouse stromal vascular cells but significantly enhanced adipogenesis in human adipose derived stem cells.

CONCLUSIONS

Adipose expression of TBX1 is necessary, but not sufficient, to defend body temperature during cold via proper UCP1 expression. Adipose TBX1 expression was also required for proper insulin signaling in subcutaneous adipose as well as for maintaining β-adrenergic sensitivity, but overexpression of TBX1 was not sufficient to induce adipocyte beiging or to prevent diet-induced obesity. TBX1 expression is enriched in adipose stem cells in which it has contrasting effects on adipogenesis in mouse versus human cells. Collectively, these data demonstrate the importance of adipose TBX1 in the regulation of beige adipocyte function, energy homeostasis, and adipocyte development.

Mechanisms linking adipose tissue inflammation to cardiac hypertrophy and fibrosis

Adipose tissue is classically recognized as the primary site of lipid storage, but in recent years has garnered appreciation for its broad role as an endocrine organ comprising multiple cell types whose collective secretome, termed as adipokines, is highly interdependent on metabolic homeostasis and inflammatory state. Anatomical location (e.g. visceral, subcutaneous, epicardial etc) and cellular composition of adipose tissue (e.g. white, beige, and brown adipocytes, macrophages etc.) also plays a critical role in determining its response to metabolic state, the resulting secretome, and its potential impact on remote tissues. Compared with other tissues, the heart has an extremely high and constant demand for energy generation, of which most is derived from oxidation of fatty acids. Availability of this fatty acid fuel source is dependent on adipose tissue, but evidence is mounting that adipose tissue plays a much broader role in cardiovascular physiology. In this review, we discuss the impact of the brown, subcutaneous, and visceral white, perivascular (PVAT), and epicardial adipose tissue (EAT) secretome on the development and progression of cardiovascular disease (CVD), with a particular focus on cardiac hypertrophy and fibrosis.

Alterations in Serum Adropin, Adiponectin, and Proinflammatory Cytokine Levels in OSAS

Objective

The present study was planned to examine the relationships between obstructive sleep apnea syndrome (OSAS) and the newly revealed adipokines adropin and adiponectin concentrations that display significant metabolic and cardiovascular functions and the levels of proinflammatory cytokine levels.

Method

A total of 166 overweight and obese male patients with a body mass index (BMI) >27 kg/m² were included in the study. Among study participants, 84 were recently diagnosed with OSAS by polysomnography with an apnea-hypopnea index (AHI) ≥5, and 82 were nonapneic with normal polysomnography (AHI<5) findings. The serum adropin and adiponectin levels of all cases were analyzed via the enzyme-linked immunosorbent assay method. Serum interleukin-1 (IL-1) beta and tumor necrotizing factor-alpha (TNF-alpha) levels were determined using Luminex cytokine multiplex analyses.

Results

The mean age of the OSAS patients was 50.9 ± 5.7 years and BMI was 32.4 ± 6.0 kg/m², and there was no statistically significant difference determined with the control group (49.3 ± 5.8 years and 30.6 ± 5, 6 kg/m²) (p > 0.05). There were no statistically significant differences between the OSAS and control groups concerning total cholesterol, triglyceride, low-density lipoprotein (LDL), high-density lipoprotein (HDL), and glucose levels. Adiponectin was lower in the OSAS group at a statistically significant level in comparison with the control group and was related at a statistically significant level to OSAS intensity. Adropin concentration was determined to be higher in the OSAS group at a statistically significant level in comparison with the control group.

Conclusion

The results of our study suggest that increased adropin concentration may be an indicator of endothelium dysfunction in OSAS patients. Serum adropin and adiponectin levels may be new bioindicators used for diagnosis and risk assessment in OSAS patients.

Single-cell transcriptional networks in differentiating preadipocytes suggest drivers associated with tissue heterogeneity

White adipose tissue plays an important role in physiological homeostasis and metabolic disease. Different fat depots have distinct metabolic and inflammatory profiles and are differentially associated with disease risk. It is unclear whether these differences are intrinsic to the pre-differentiated stage. Using single-cell RNA sequencing, a unique network methodology and a data integration technique, we predict metabolic phenotypes in differentiating cells. Single-cell RNA-seq profiles of human preadipocytes during adipogenesis in vitro identifies at least two distinct classes of subcutaneous white adipocytes. These differences in gene expression are separate from the process of browning and beiging. Using a systems biology approach, we identify a new network of zinc-finger proteins that are expressed in one class of preadipocytes and is potentially involved in regulating adipogenesis. Our findings gain a deeper understanding of both the heterogeneity of white adipocytes and their link to normal metabolism and disease.

The origin of the heterogeneity of metabolic and inflammatory profiles exhibited by white adipocytes is little understood. Here, using scRNA-seq and computational methods, the authors show that differentiating preadipocytes exhibit gene expression differences and suggest underlying regulators.

Analyzing Mitochondrial Function in Brown Adipocytes with a Bioenergetic Analyzer

Brown adipocytes are a cell type with high mitochondrial content and bioenergetic capacity. A critical means to measure mitochondrial function, macromolecule fuel usage, and other important phenotypes is with a bioenergetic analyzer. Here, we describe how to isolate, culture, and differentiate brown preadipocytes into mature adipocytes. We also explain how to perform a mitochondrial (mito) stress test, using the bioenergetic analyzer. The mito stress test is able to give researchers a plethora of insights into mitochondrial function, including basal respiration, proton leak, ATP production, maximal respiration, and reserve capacity, making it a powerful tool for analyzing brown adipocytes.

Increased Expression of the Leptin Gene in Adipose Tissue of Patients with Chronic Kidney Disease-The Possible Role of an Abnormal Serum Fatty Acid Profile

Chronic kidney disease (CKD) is associated with an increased level of leptin and an abnormal fatty acid (FA) profile in the serum. However, there are no data on the associations between them, and the reason for increased serum levels in patients with CKD is not well elucidated. Recently, we found that a CKD-related abnormal FA profile caused significant changes in the expression of genes involved in lipid metabolism in hepatocytes. The aim of this study was to examine whether leptin gene expression in subcutaneous adipose tissue (SAT) of patients with CKD may contribute to increased serum levels of this adipokine and whether the abnormal serum FA profile observed in CKD patients has an impact on leptin gene expression in adipocytes. The FA profile was measured in serum samples from patients with CKD and controls by GC–MS. The relative mRNA levels of leptin were measured in SAT by Real-Time PCR. Moreover, the effect of the CKD-related abnormal FA profile on leptin gene expression was studied in in vitro cultured 3T3-L1 adipocytes. Patients with CKD had higher concentrations of serum leptin than controls and higher expression level of the leptin gene in SAT. They also had increased serum monounsaturated FAs and decreased polyunsaturated FAs. The incubation of adipocytes with FAs isolated from CKD patients resulted in an increase of the levels of leptin mRNA. Increased leptin gene expression in SAT may contribute to elevated concentrations of these adipokine in patients with CKD. CKD-related alterations of the FA profile may contribute to elevated serum leptin concentrations in patients with CKD by increasing the gene expression of this adipokine in SAT.

Osteoporosis- and obesity-risk interrelationships: an epigenetic analysis of GWAS-derived SNPs at the developmental gene TBX15

A major challenge in translating findings from genome-wide association studies (GWAS) to biological mechanisms is pinpointing functional variants because only a very small percentage of variants associated with a given trait actually impact the trait. We used an extensive epigenetics, transcriptomics, and genetics analysis of the TBX15/WARS2 neighbourhood to prioritize this region's best-candidate causal variants for the genetic risk of osteoporosis (estimated bone density, eBMD) and obesity (waist-hip ratio or waist circumference adjusted for body mass index). TBX15 encodes a transcription factor that is important in bone development and adipose biology. Manual curation of 692 GWAS-derived variants gave eight strong candidates for causal SNPs that modulate TBX15 transcription in subcutaneous adipose tissue (SAT) or osteoblasts, which highly and specifically express this gene. None of these SNPs were prioritized by Bayesian fine-mapping. The eight regulatory causal SNPs were in enhancer or promoter chromatin seen preferentially in SAT or osteoblasts at TBX15 intron-1 or upstream. They overlap strongly predicted, allele-specific transcription factor binding sites. Our analysis suggests that these SNPs act independently of two missense SNPs in TBX15. Remarkably, five of the regulatory SNPs were associated with eBMD and obesity and had the same trait-increasing allele for both. We found that WARS2 obesity-related SNPs can be ascribed to high linkage disequilibrium with TBX15 intron-1 SNPs. Our findings from GWAS index, proxy, and imputed SNPs suggest that a few SNPs, including three in a 0.7-kb cluster, act as causal regulatory variants to fine-tune TBX15 expression and, thereby, affect both obesity and osteoporosis risk.

Cold-Activated Lipid Dynamics in Adipose Tissue Highlights a Role for Cardiolipin in Thermogenic Metabolism

Thermogenic fat expends energy during cold for temperature homeostasis, and its activity regulates nutrient metabolism and insulin sensitivity. We measured cold-activated lipid landscapes in circulation and in adipose tissue by MS/MS^ALL shotgun lipidomics. We created an interactive online viewer to visualize the changes of specific lipid species in response to cold. In adipose tissue, among the approximately 1,600 lipid species profiled, we identified the biosynthetic pathway of the mitochondrial phospholipid cardiolipin as coordinately activated in brown and beige fat by cold in wild-type and transgenic mice with enhanced browning of white fat. Together, these data provide a comprehensive lipid bio-signature of thermogenic fat activation in circulation and tissue and suggest pathways regulated by cold exposure.

Marrow Adipocytes: Origin, Structure, and Function

The skeleton harbors an array of lineage cells that have an essential role in whole body homeostasis. Adipocytes start the colonization of marrow space early in postnatal life, expanding progressively and influencing other components of the bone marrow through paracrine signaling. In this unique, closed, and hypoxic environment close to the endosteal surface and adjacent to the microvascular space the marrow adipocyte can store or provide energy, secrete adipokines, and target neighboring bone cells. Adipocyte progenitors can also migrate from the bone marrow to populate white adipose tissue, a process that accelerates during weight gain. The marrow adipocyte also has an endocrine role in whole body homeostasis through its varied secretome that targets distant adipose depots, skeletal muscle, and the nervous system. Further insights into the biology of this unique and versatile cell will undoubtedly lead to novel therapeutic approaches to metabolic and age-related disorders such as osteoporosis and diabetes mellitus.

Isolation, Characterization, Differentiation and Immunomodulatory Capacity of Mesenchymal Stromal/Stem Cells from Human Perirenal Adipose Tissue

Mesenchymal stromal/stem cells (MSCs) are immature multipotent cells, which represent a rare population in the perivascular niche within nearly all tissues. The most abundant source to isolate MSCs is adipose tissue. Currently, perirenal adipose tissue is rarely described as the source of MSCs. MSCs were isolated from perirenal adipose tissue (prASCs) from patients undergoing tumor nephrectomies, cultured and characterized by flow cytometry and their differentiation potential into adipocytes, chondrocytes, osteoblasts and epithelial cells. Furthermore, prASCs were stimulated with lipopolysaccharide (LPS), lipoteichoic acid (LTA) or a mixture of cytokines (cytomix). In addition, prASC susceptibility to human cytomegalovirus (HCMV) was investigated. The expression of inflammatory readouts was estimated by qPCR and immunoassay. HCMV infection was analyzed by qPCR and immunostaining. Characterization of cultured prASCs shows the cells meet the criteria of MSCs and prASCs can undergo trilineage differentiation. Cultured prASCs can be induced to differentiate into epithelial cells, shown by cytokeratin 18 expression. Stimulation of prASCs with LPS or cytomix suggests the cells are capable of initiating an inflammation-like response upon stimulation with LPS or cytokines, whereas, LTA did not induce a significant effect on the readouts (ICAM-1, IL-6, TNFα, MCP-1 mRNA and IL-6 protein). HCMV broadly infects prASCs, showing a viral load dependent cytopathological effect (CPE). Our current study summarizes the isolation and culture of prASCs, clearly characterizes the cells, and demonstrates their immunomodulatory potential and high permissiveness for HCMV.

The Regulation of Lipokines by Environmental Factors

Adipose tissue is a highly metabolically-active tissue that senses and secretes hormonal and lipid mediators that facilitate adaptations to metabolic tissues. In recent years, the role of lipokines, which are lipid species predominantly secreted from adipose tissue that act as hormonal regulators in many metabolic tissues, has been an important area of research for obesity and diabetes. Previous studies have identified that these secreted lipids, including palmitoleate, 12,13-diHOME, and fatty acid-hydroxy-fatty acids (FAHFA) species, are important regulators of metabolism. Moreover, environmental factors that directly affect the secretion of lipokines such as diet, exercise, and exposure to cold temperatures constitute attractive therapeutic strategies, but the mechanisms that regulate lipokine stimulation have not been thoroughly reviewed. In this study, we will discuss the chemical characteristics of lipokines that position them as attractive targets for chronic disease treatment and prevention and the emerging roles of lipokines as regulators of inter-tissue communication. We will define the target tissues of lipokines, and explore the ability of lipokines to prevent or delay the onset and development of chronic diseases. Comprehensive understanding of the lipokine synthesis and lipokine-driven regulation of metabolic outcomes is instrumental for developing novel preventative and therapeutic strategies that harness adipose tissue-derived lipokines.