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Genetic studies have recently highlighted the importance of fat distribution, as well as overall adiposity, in the pathogenesis of obesity-associated diseases. Using a large study (n = 1,288) from 4 independent cohorts, we aimed to investigate the relationship between mean adipocyte area and obesity-related traits, and identify genetic factors associated with adipocyte cell size. To perform the first large-scale study of automatic adipocyte phenotyping using both histological and genetic data, we developed a deep learning-based method, the Adipocyte U-Net, to rapidly derive mean adipocyte area estimates from histology images. We validate our method using three state-of-the-art approaches; CellProfiler, Adiposoft and floating adipocytes fractions, all run blindly on two external cohorts. We observe high concordance between our method and the state-of-the-art approaches (Adipocyte U-net vs. CellProfiler: R2visceral = 0.94, P < 2.2 × 10−16, R2subcutaneous = 0.91, P < 2.2 × 10−16), and faster run times (10,000 images: 6mins vs 3.5hrs). We applied the Adipocyte U-Net to 4 cohorts with histology, genetic, and phenotypic data (total N = 820). After meta-analysis, we found that mean adipocyte area positively correlated with body mass index (BMI) (Psubq = 8.13 × 10−69, βsubq = 0.45; Pvisc = 2.5 × 10−55, βvisc = 0.49; average R2 across cohorts = 0.49) and that adipocytes in subcutaneous depots are larger than their visceral counterparts (Pmeta = 9.8 × 10−7). Lastly, we performed the largest GWAS and subsequent meta-analysis of mean adipocyte area and intra-individual adipocyte variation (N = 820). Despite having twice the number of samples than any similar study, we found no genome-wide significant associations, suggesting that larger sample sizes and a homogenous collection of adipose tissue are likely needed to identify robust genetic associations., Author summary Fundamental aspects of biology such as how the size or number of adipocytes relates to obesity and cardiometabolic health are still unanswered. To answer such questions, fast, accurate and automated measurements need to be acquired, free from human biases. Glastonbury et al., 2020 describe a novel machine learning method to perform rapid acquisition of adipocyte area estimates from histological imaging data. Using these imaging derived phenotypes, Glastonbury et al., 2020 assess the relationship between adipocyte size and a range of cardio-metabolic comorbidities, demonstrating that adipocyte size can vary depending on where adipose is stored throughout the body. By tying genetics with imaging data, Glastonbury et al., 2020 were able to demonstrate that previous findings associating adipocyte size with Type 2 Diabetes variants, are likely to be false positives. This study provides a means of being able to scale up GWAS type analyses to imaging derived phenotypes.

Glucagon-like peptide-1 (GLP-1) analogues aid weight loss that improves obesity-associated adipose tissue (AT) dysfunction. GLP-1 treatment may however also directly influence AT that expresses the GLP-1 receptor (GLP-1R). The present study aimed to assess the impact of GLP-1 analogue treatment on subcutaneous AT (SCAT) inflammatory and fibrotic responses, compared with weight loss by calorie reduction (control). Among the 39 participants with Type 2 diabetes recruited, 30 age-matched participants were randomized to 4 months treatment with Liraglutide (n=22) or calorie restriction based on dietetic counselling (n=8). Assessments included clinical characteristics and repeated subcutaneous abdominal AT biopsies. Liraglutide resulted in weight loss in most participants (−3.12±1.72 kg, P=0.007) and significant reduction in visceral AT (VAT). It was more effective in lowering fasting glucose, in comparison with weight loss by dieting. However, tumour necrosis factor-α (TNFA) AT-expression (P=0.0005), macrophage chemoattractant protein-1 (MCP-1) expression (P=0.027) and its serum levels (P=0.048) increased with Liraglutide, suggestive of an inflammatory response unlike in the diet arm in which a trend of lower cluster of differentiation 14 (CD14) expression (P=0.09) was found. Liraglutide treatment also increased expression of factors involved in extracellular matrix (ECM) deposition, transforming growth factor-β (TGFB) and collagen type 1 alpha 1 chain (COL1A1) (TGFB1: before 0.73±0.09 arbitrary units (AU), after 1.00±0.13 AU, P=0.006; COL1A1: 0.84±0.09 AU compared with 1.49±0.26 AU, P=0.026). Liraglutide thus appears to induce an inflammatory response in AT and influences ECM remodelling. Despite its superior effect on glycaemia, Liraglutide does not improve obesity-associated AT dysfunction in subcutaneous tissue. It is yet unclear whether this limits AT storage capacity for lipids. This may be of importance in patients being re-exposed to positive energy balance such as post GLP-1 discontinuation.

BACKGROUND/OBJECTIVES: Lysyl oxidase (LOX) is an enzyme crucial for collagen fibre crosslinking and thus for fibrosis development. Fibrosis is characterised by a surplus of collagen fibre accumulation and is amongst others also a feature of obesity-associated dysfunctional adipose tissue (AT) which has been linked with type 2 diabetes. We hypothesised that in type 2 diabetes and obesity LOX expression and activity will be increased as a consequence of worsening AT dysfunction. This study aimed to provide a comprehensive characterisation of LOX in human AT.METHODS: LOX mRNA expression was analysed in omental and abdominal subcutaneous AT obtained during elective surgery from subjects with a wide range of BMI, with and without diabetes. In addition, LOX expression was studied in subcutaneous AT before and 9.5 months after bariatric surgery. To study the mechanism of LOX changes, its expression and activity were assessed after either hypoxia, recombinant human leptin or glucose treatment of AT explants. In addition, LOX response to acute inflammation was tested after stimulation by a single injection of lipopolysaccharide versus saline solution (control) in healthy men, in vivo. Quantity of mRNA was measured by RT-qPCR.RESULTS: LOX expression was higher in obesity and correlated with BMI while, in vitro, leptin at high concentrations, as a potential feedback mechanism, suppressed its expression. Neither diabetes status, nor hyperglycaemia affected LOX. Hypoxia and lipopolysaccharide-induced acute inflammation increased LOX AT expression, latter was independent of macrophage infiltration.CONCLUSIONS: Whilst LOX may not be affected by obesity-associated complications such as diabetes, our results confirm that LOX is increased by hypoxia and inflammation as underlying mechanism for its upregulation in adipose tissue with obesity.

Aims Obstructive sleep apnea syndrome (OSAS) is associated with increased cardiovascular risk and diabetes independent of obesity. We investigated whether adipose tissue dysfunction is exacerbated due to increased tissue hypoxia. Methods Adipose tissue (AT) oxygenation was measured with a Clarke-type electrode (p AT O 2 ) in 16 men with OSAS before and after 4 months of continuous positive airway pressure therapy (CPAP) and in BMI-matched controls. Oxygenation was simultaneously monitored in arterial blood by pulse oximetry (SaO 2 ); mixed blood in AT microcirculation by reflectance spectroscopy (S AT O 2 ) along with blood flow. Markers of hypoxia, adipo- and angiogenesis, inflammation and fibrosis were analysed in AT and serum. Results OSAS subjects were more insulin resistant. Despite lower arterial SaO 2 (95.4±1.3% vs. 97.1±1.6%, P =0.013) in subjects with OSAS, there was no difference in the oxygen content of AT microcirculation (61.6±18.4 vs. 72.2±7.0%, P =0.07) or p AT O 2 (49.2±7.5 vs. 50.4±14.7mmHg, P =0.83) between groups. Resting AT blood flow was higher in OSAS compared to controls (108.5±22.7 vs. 78.9±24.9au, P P =0.049) and fibrosis (COL3A1 P =0.02), a trend of higher HIF1A expression ( P =0.06) and reduced adipogenesis (PPARG P =0.006). After CPAP, only expression of the lipid deposition marker LPL increased (30%, P =0.047). Conclusions Adipose tissue of awake OSAS subjects appears no more hypoxic than adipose tissue of BMI-matched controls despite daytime hypoxaemia. Increased adipose tissue blood flow may be explained by an increased inflammatory response. We observe features of adipose dysfunction in subjects with OSAS, which attribute to increased cardiometabolic risk associated with this condition.

International audience; Aldose reductases (AKR1B) are widely expressed oxidoreductases whose physiological function remains elusive. Some isoforms are genuine prostaglandin F2α (PGF2α) synthases, suggesting they might influence adipose homeostasis because PGF2α inhibits adipogenesis. This was shown by Akr1b7 gene ablation in the mouse, which resulted in increased adiposity related to a lower PGF2α content in fat. Yet humans have no ortholog gene for Akr1b7, so the role of aldose reductases in human adipose homeostasis remains to be explored. We analyzed expression of genes encoding human and mouse aldose reductase isoforms in adipose tissues and differentiating adipocytes to assess conserved mechanisms regulating PGF2α synthesis and adipogenesis. The Akr1b3 gene encoded the most abundant isoform in mouse adipose tissue, whereas Akr1b7 encoded the only isoform enriched in the stromal vascular fraction. Most mouse aldose reductase gene expression peaked in early adipogenesis of 3T3-L1 cells and diminished with differentiation. In contrast with its mouse ortholog Akr1b3, AKR1B1 expression increased throughout differentiation of human multipotent adipose-derived stem cells, paralleling PGF2α release, whereas PGF2α receptor (FP) levels collapsed in early differentiation. Pharmacological inhibition of aldose reductase using Statil altered PGF2α production and enhanced human multipotent adipose-derived stem adipocyte differentiation. As expected, the adipogenic effects of Statil were counteracted by an FP agonist (cloprostenol). Thus, in both species aldose reductase-dependent PGF2α production could be important in early differentiation to restrict adipogenesis. PGF2α antiadipogenic signaling could then be toned down through the FP receptor or aldose reductases down-regulation in human and mouse cells, respectively. Our data suggest that aldose reductase inhibitors could have obesogenic potential.

BACKGROUND/OBJECTIVES: Subjects with type-2 diabetes are typically obese with dysfunctional adipose tissue (AT). Glucagon-like peptide-1 (GLP-1) analogues are routinely used to improve glycaemia. Although, they also aid weight loss that improves AT function, their direct effect on AT function is unclear. To explore GLP-1 analogues’ influence on human AT’s cytokine and extracellular matrix (ECM) regulation, we therefore obtained and treated omental (OMAT) and subcutaneous (SCAT) AT samples with Exendin-4, an agonist of the GLP-1 receptor (GLP-1R). SUBJECTS/METHODS: OMAT and abdominal SCAT samples obtained from women during elective surgery at the Royal Devon & Exeter Hospital (UK) were treated with increasing doses of Exendin-4. Changes in RNA expression of adipokines, inflammatory cytokines, ECM components and their regulators were assessed and protein secretion analysed by ELISA. GLP-1R protein accumulation was compared in paired AT depot samples. RESULTS: Exendin-4 induced an increase in OMAT adiponectin (P=0.02) and decrease in elastin expression (P=0.03) in parallel with reduced elastin secretion (P=0.04). In contrast to OMAT, we did not observe an effect on SCAT. There was no change in the expression of inflammatory markers (CD14, TNFA, MCP-1), collagens, TGFB1 or CTGF. GLP-1R accumulation was higher in SCAT. CONCLUSIONS: Independently of weight loss, which may bias findings of in vivo studies, GLP-1 analogues modify human OMAT physiology favourably by increasing the insulin-sensitising cytokine adiponectin. However, the reduction of elastin and no apparent effect on AT’s inflammatory cytokines suggest that GLP-1 analogues may be less beneficial to AT function, especially if there is no associated weight loss.

The aldose reductase (human AKR1B1/mouse Akr1b3) has been the focus of many research because of its role in diabetic complications. The starting point of these alterations is the massive entry of glucose in polyol pathway where it is converted into sorbitol by this enzyme. However, the issue of aldose reductase function in non-diabetic condition remains unresolved. Aldose reductase-like enzymes (AKR1B10, Akr1b7 and Akr1b8) are highly related isoforms often co-expressed with bona fide aldose reductase, making functional analysis of one or the other isoform a challenging task. AKR1B/Akr1b members share at least 65% protein identity and the general ability to reduce many redundant substrates such as aldehydes provided from lipid peroxidation, steroids and their by-products and xenobiotics in vitro. Based on these properties, AKR1B/Akr1b are generally considered as detoxifying enzymes. Considering that divergences should be more informative than similarities to help understanding their physiological functions, we chose to review specific hallmarks of each human/mouse isoforms by focusing on tissue distribution and specific mechanisms of gene regulation. Indeed, although the aldose reductase shows ubiquitous expression, aldose reductase-like proteins exhibit tissue-specific patterns of expression. We focused on 3 organs where certain isoforms are enriched, the adrenal gland, enterohepatic and adipose tissues and tried to connect recent enzymatic and regulation data with endocrine and metabolic functions of these organs. We presented recent mouse models showing unsuspected physiological functions in the regulation of glucido-lipidic metabolism and adipose tissue homeostasis. Beyond the widely accepted idea that AKR1B/Akr1b are detoxification enzymes, these recent reports provide growing evidences that they are able to modify or generate signal molecules. This conceptually shifts this class of enzymes from unenviable status of scavenger to upper class of messengers.