Adipose tissue contribution to plasma fibroblast growth factor 21 and fibroblast activation protein in obesity.

Fibroblast growth factor 21 (FGF21) is an important regulator of energy metabolism. FGF21 is inactivated by fibroblast activation protein (FAP). We investigated whether FGF21 and/or FAP are secreted from human white adipose tissue of individuals with obesity by measuring total FGF21, active FGF21, and FAP concentrations in arterialized blood and venous blood draining the subcutaneous abdominal adipose tissue (scAT). Measurements were performed under fasting conditions and after a high fat meal before and after diet-induced weight loss in 16 adults with BMI 27-35 kg/m2. FGF21 was not released from scAT, neither before nor after weight loss in agreement with an undetectable gene expression of FGF21 in this tissue. Although scAT showed significant gene expression of FAP, no release of FAP from the tissue could be detected. The high fat meal increased postprandial circulating FGF21 but not FAP. Circulating levels of FAP but not FGF21 were significantly reduced after weight loss. On the other hand, FAP expression in scAT was increased. In conclusion, release from scAT does not appear to contribute to circulating concentrations of FGF21 and FAP and their responses to ingestion of a high fat meal or weight loss, respectively, in individuals with obesity.

A computational model of postprandial adipose tissue lipid metabolism derived using human arteriovenous stable isotope tracer data.

Given the association of disturbances in non-esterified fatty acid (NEFA) metabolism with the development of Type 2 Diabetes and Non-Alcoholic Fatty Liver Disease, computational models of glucose-insulin dynamics have been extended to account for the interplay with NEFA. In this study, we use arteriovenous measurement across the subcutaneous adipose tissue during a mixed meal challenge test to evaluate the performance and underlying assumptions of three existing models of adipose tissue metabolism and construct a new, refined model of adipose tissue metabolism. Our model introduces new terms, explicitly accounting for the conversion of glucose to glyceraldehye-3-phosphate, the postprandial influx of glycerol into the adipose tissue, and several physiologically relevant delays in insulin signalling in order to better describe the measured adipose tissues fluxes. We then applied our refined model to human adipose tissue flux data collected before and after a diet intervention as part of the Yoyo study, to quantify the effects of caloric restriction on postprandial adipose tissue metabolism. Significant increases were observed in the model parameters describing the rate of uptake and release of both glycerol and NEFA. Additionally, decreases in the model's delay in insulin signalling parameters indicates there is an improvement in adipose tissue insulin sensitivity following caloric restriction.

Estimating real cell size distribution from cross-section microscopy imaging.

MOTIVATION: Microscopy imaging is an essential tool for medical diagnosis and molecular biology. It is particularly useful for extracting information about disease states, tissue heterogeneity and cell specific parameters such as cell type or cell size from biological specimens. However, the information obtained from the images is likely to be subjected to sampling and observational bias with respect to the underlying cell size/type distributions. RESULTS: We present an algorithm, Estimate Tissue Cell Size/Type Distribution (EstiTiCS), for the adjustment of the underestimation of the number of small cells and the size of measured cells while accounting for the section thickness independent of the tissue type. We introduce the sources of bias under different tissue distributions and their effect on the measured values with simulation experiments. Furthermore, we demonstrate our method on histological sections of paraffin-embedded adipose tissue sample images from 57 people from a dietary intervention study. This data consists of measured cell size and its distribution over the dietary intervention period at four time points. Adjusting for the bias with EstiTiCS results in a closer fit to the true/expected adipocyte size distribution with earlier studies. Therefore, we conclude that our method is suitable as the final step in estimating the tissue wide cell type/size distribution from microscopy imaging pipeline. AVAILABILITY AND IMPLEMENTATION: Source code and its documentation are available at https://github.com/michaelLenz/EstiTiCS The whole pipeline of our method is implemented in R and makes use of the 'nloptr' package. Adipose tissue data used for this study are available on request. CONTACT: Michael.Lenz@Maastrichtuniversity.nl, Gokhan.Ertaylan@Maastrichtuniversity.nl.

Weight loss-induced stress in subcutaneous adipose tissue is related to weight regain.

Initial successful weight loss is often followed by weight regain after the dietary intervention. Compared with lean people, cellular stress in adipose tissue is increased in obese subjects. However, the relation between cellular stress and the risk for weight regain after weight loss is unclear. Therefore, we determined the expression levels of stress proteins during weight loss and weight maintenance in relation to weight regain. In vivo findings were compared with results from in vitro cultured human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes. In total, eighteen healthy subjects underwent an 8-week diet programme with a 10-month follow-up. Participants were categorised as weight maintainers or weight regainers (WR) depending on their weight changes during the intervention. Abdominal subcutaneous adipose tissue biopsies were obtained before and after the diet and after the follow-up. In vitro differentiated SGBS adipocytes were starved for 96 h with low (0·55 mm) glucose. Levels of stress proteins were determined by Western blotting. WR showed increased expressions of ß-actin, calnexin, heat shock protein (HSP) 27, HSP60 and HSP70. Changes of ß-actin, HSP27 and HSP70 are linked to HSP60, a proposed key factor in weight regain after weight loss. SGBS adipocytes showed increased levels of ß-actin and HSP60 after 96 h of glucose restriction. The increased level of cellular stress proteins in the adipose tissue of WR probably resides in the adipocytes as shown by in vitro experiments. Cellular stress accumulated in adipose tissue during weight loss may be a risk factor for weight regain.

The cilium: a cellular antenna with an influence on obesity risk.

Primary cilia are organelles that are present on many different cell types, either transiently or permanently. They play a crucial role in receiving signals from the environment and passing these signals to other parts of the cell. In that way, they are involved in diverse processes such as adipocyte differentiation and olfactory sensation. Mutations in genes coding for ciliary proteins often have pleiotropic effects and lead to clinical conditions, ciliopathies, with multiple symptoms. In this study, we reviewed observations from ciliopathies with obesity as one of the symptoms. It shows that variation in cilia-related genes is itself not a major cause of obesity in the population but may be a part of the multifactorial aetiology of this complex condition. Both common polymorphisms and rare deleterious variants may contribute to the obesity risk. Genotype-phenotype relationships have been noticed. Among the ciliary genes, obesity differs with regard to severity and age of onset, which may relate to the influence of each gene on the balance between pro- and anti-adipogenic processes. Analysis of the function and location of the proteins encoded by these ciliary genes suggests that obesity is more linked to activities at the basal area of the cilium, including initiation of the intraflagellar transport, but less to the intraflagellar transport itself. Regarding the role of cilia, three possible mechanistic processes underlying obesity are described: adipogenesis, neuronal food intake regulation and food odour perception.

Plasma Levels of Triglycerides and IL-6 Are Associated With Weight Regain and Fat Mass Expansion.

CONTEXT: Long-term weight loss (WL) maintenance is the biggest challenge for overweight and obesity because of the almost unavoidable phenomenon of partial or even total weight regain (WR) after WL. OBJECTIVE: In the present study we investigated the relations of (the changes of) adipocyte size and other risk biomarkers with WR during the follow-up of the Yoyo dietary intervention. METHODS: In this randomized controlled study, 48 overweight/obese participants underwent a very-low-calorie diet to lose weight, followed by a weight-stable period of 4 weeks and a follow-up period of 9 months. Anthropometric measurements, adipocyte volume of abdominal subcutaneous adipose tissue, and plasma metabolic parameters (free fatty acids [FFAs], triglycerides [TGs], total cholesterol, glucose, insulin, homeostasis model assessment of insulin resistance [HOMA-IR], interleukin 6 [IL-6], angiotensin-converting enzyme [ACE] activity, retinol binding protein 4 [RBP4]) at the beginning and the end of follow-up were analyzed. RESULTS: Our results show that changes of TGs, IL-6, HOMA-IR, and ACE are significantly positively correlated with WR. Multiple linear regression analysis shows that only TG and IL-6 changes remained significantly correlated with WR and increased body fat mass. Moreover, the change in HOMA-IR was tightly correlated with the change in TGs. Surprisingly, change in adipocyte volume during follow-up was not correlated with WR nor with other factors, but positive correlations between adipocyte volume and HOMA-IR were found at the beginning and end of the follow-up. CONCLUSION: These results suggest that TGs and IL-6 are independently linked to WR via separate mechanisms, and that HOMA-IR and adipocyte volume may indirectly link to WR through the change of plasma TGs.

Diet Composition, Glucose Homeostasis, and Weight Regain in the YoYo Study.

Based on several randomized clinical trials, it has been suggested that baseline glucose homeostasis interacts with the influence of diet composition on weight loss and weight loss maintenance. In this secondary analysis of the YoYo study, a study investigating predictors of weight loss maintenance, we tested the hypothesis that (self-selected) dietary carbohydrate and/or fibre intake interact with the glucose homeostasis parameters for weight loss maintenance. Sixty-one overweight or obese individuals lost around 10 kg of body weight on an energy-restricted diet and were then followed for 9 months. During this period, participants were advised to maintain their body weight and eat a healthy diet without further recommendations on calorie intake or diet composition. Contrary to our hypothesis, carbohydrate intake showed no positive association with weight regain after weight loss, and no interaction with baseline fasting glucose concentration was found. There was a non-significant negative association between fibre intake and weight regain (B = -0.274, standard error (SE) 0.158, p = 0.090), but again, no interaction with fasting plasma glucose was found. In conclusion, the data from the YoYo study do not support a role for baseline glucose homeostasis in determining the association between self-reported carbohydrate and/or fibre intake and weight regain after weight loss.

Adipocyte abundances of CES1, CRYAB, ENO1 and GANAB are modified in-vitro by glucose restriction and are associated with cellular remodelling during weight regain.

Long-term weight loss maintenance is a problem of overweight and obesity. Changes of gene expression during weight loss (WL) by calorie restriction (CR) are linked to the risk of weight regain (WR). However, detailed information on genes/proteins involved in the mechanism is still lacking. Therefore, we developed an in-vitro model system for glucose restriction (GR) and refeeding (RF) to uncover proteome differences between GR with RF vs normal feeding, of which we explored the relation with WR after WL. Human Simpson-Golabi-Behmel Syndrome cells were subjected to changing levels of glucose to mimic the condition of CR and RF. Proteome profiling was performed by liquid chromatography tandem mass spectrometry. This in-vitro model revealed 44 proteins differentially expressed after GR and RF versus feeding including proteins of the focal adhesions. Four proteins showed a persistent up- or down-regulation: liver carboxylesterase (CES1), mitochondrial superoxide dismutase [Mn] (SOD2), alpha-crystallin B-chain (CRYAB), alpha-enolase (ENO1). In-vivo weight loss-induced RNA expression changes linked CES1, CRYAB and ENO1 to WR. Moreover, of these 44 proteins, CES1 and glucosidase II alpha subunit (GANAB) during follow up correlated with WR. Correlation clustering of in-vivo protein expression data indicated an interaction of these proteins with structural components of the focal adhesions and cytoplasmic filaments in the adipocytes.

Combined Analysis of Stress- and ECM-Related Genes in Their Effect on Weight Regain.

OBJECTIVE: During weight loss, the volume of adipocytes decreases, leading to stress because of the misfit between the cell contents and the surrounding extracellular matrix (ECM). This stress can be resolved by remodeling the ECM or the restorage of triglycerides within the adipocytes. The objective of this study was to investigate the existence of a connection between stress-related and ECM-related genes that is associated with weight regain. METHODS: Thirty-one participants with overweight or obesity followed a 5-week very-low-calorie diet (500 kcal/d) with a subsequent 4-week weight-stable diet (WS), and then an uncontrolled 9-month follow-up. Adipose tissue biopsies were collected for microarray analysis. A correlation and interaction analysis was performed with the weight regain percentage (WR%) ([weight after follow-up - weight after WS] ÷ weight after WS × 100%) by using two gene sets that were previously defined as "stress-related" (n = 107) and "ECM-related" genes (n = 277). RESULTS: During WS, a coexpression network of 8 stress-related genes and 15 ECM-related genes correlating with WR% could be constructed, with links to multiple biological processes. Interaction analysis between stress- and ECM-related genes revealed that several gene combinations were highly related to weight regain. CONCLUSIONS: Our findings underscore the importance of the connection between stress- and ECM-related genes in the risk for weight regain.

Effect of diet-induced weight loss on angiopoietin-like protein 4 and adipose tissue lipid metabolism in overweight and obese humans.

Angiopoietin-like protein 4 (ANGPTL4) plays a role in lipid partitioning by inhibiting lipoprotein lipase (LPL)-dependent plasma clearance of triacylglycerol in adipose tissue. We investigated the effects of diet-induced weight loss on plasma ANGPTL4 concentrations in relation to in vivo adipose tissue LPL activity and lipolysis and adipose tissue ANGPTL4 release in overweight/obese participants. Sixteen individuals (BMI: 28-35 kg/m2 ; 10 women) were randomized to a dietary intervention composed of either a low-calorie diet (1250 kcal/day) for 12 weeks (n = 9) or a very low-calorie diet (500 kcal/day) for 5 weeks, followed by a 4-week weight stable period. Before and after the intervention, we measured arteriovenous concentration differences in combination with adipose tissue blood flow before and after intake of a high-fat mixed meal with [U-13 C]-palmitate to assess in vivo adipose tissue LPL activity and lipolysis. The intervention significantly reduced body weight (-8.6 ± 0.6 kg, P < 0.001). Plasma ANGPTL4 concentrations were unaffected. Significant postprandial adipose tissue ANGPTL4 release into the circulation was observed (P < 0.01). No association was observed between plasma ANGPTL4 and in vivo LPL activity. After intervention, fasting and postprandial plasma ANGPTL4 concentrations were positively associated with adipose tissue nonesterified FA (NEFA) and glycerol release, reflecting in vivo adipose tissue lipolysis (fasting NEFA: P = 0.039 and postprandial NEFA: P = 0.003). In conclusion, plasma ANGPTL4 is unaffected by weight loss and is secreted from human adipose tissue after a high-fat meal in overweight/obese participants. Plasma ANGPTL4 concentrations were not related to in vivo adipose tissue LPL activity, but were positively associated with in vivo adipose tissue lipolysis after weight loss.

Adipose tissue autophagy related gene expression is associated with glucometabolic status in human obesity.

Adipose tissue autophagy (AT) is associated with human obesity and increased metabolic risk. Recent findings establish a role for autophagy in lipid metabolism. Here, we compared the expression of autophagy-related and lipolysis genes in human abdominal subcutaneous AT (SCAT) in overweight/obese subjects (n = 17) with or without impaired glucose tolerance in comparison with lean normal glucose tolerant individuals (n = 9), and investigated the association between AT autophagy and lipolysis. Human multipotent adipose-derived stem cells (hMADS) were used to investigate the effect of pharmacological HSL inhibition on changes in the autophagic flux. The expression of autophagy-related genes (ATG) 5, 7 and 12 in SCAT was significantly higher (p = 0.043, p = 0.015, p = 0.004, respectively) in overweight/obese compared to lean men, while expression of the classical lipases HSL (p = 0.092) and ATGL (p = 0.084) tended to be lower. ATG12 mRNA was positively correlated with BMI (r = 0.407, p = 0.039). ATG7 mRNA correlated positively with waist/hip ratio (WHR) (r = 0.420, p = 0.041), 2 h glucose concentration (r = 0.488, p = 0.011) and insulin (r = 0.419, p = 0.033). Multiple linear regressions revealed that ATG7 gene expression was positively related to 2 h glucose, independent of BMI, WHR and insulin. Gene expression interaction analysis showed that ATG7 mRNA negatively correlated with HSL (p<0.01) and ATGL mRNA expression (p<0.01). In line, treatment of differentiated hMADS with an HSL inhibitor increased LC3 accumulation, a marker of increased autophagic flux. Collectively, the present study demonstrated that a low expression of classical lipases in abdominal SCAT is accompanied by an increased expression of ATGs in overweight/obese subjects, which seems to be mainly related to glucose tolerance.

Profiling Cellular Processes in Adipose Tissue during Weight Loss Using Time Series Gene Expression.

Obesity is a global epidemic identified as a major risk factor for multiple chronic diseases and, consequently, diet-induced weight loss is used to counter obesity. The adipose tissue is the primary tissue affected in diet-induced weight loss, yet the underlying molecular mechanisms and changes are not completely deciphered. In this study, we present a network biology analysis workflow which enables the profiling of the cellular processes affected by weight loss in the subcutaneous adipose tissue. Time series gene expression data from a dietary intervention dataset with two diets was analysed. Differentially expressed genes were used to generate co-expression networks using a method that capitalises on the repeat measurements in the data and finds correlations between gene expression changes over time. Using the network analysis tool Cytoscape, an overlap network of conserved components in the co-expression networks was constructed, clustered on topology to find densely correlated genes, and analysed using Gene Ontology enrichment analysis. We found five clusters involved in key metabolic processes, but also adipose tissue development and tissue remodelling processes were enriched. In conclusion, we present a flexible network biology workflow for finding important processes and relevant genes associated with weight loss, using a time series co-expression network approach that is robust towards the high inter-individual variation in humans.

Dietary Intake after Weight Loss and the Risk of Weight Regain: Macronutrient Composition and Inflammatory Properties of the Diet.

Weight regain after successful weight loss is a big problem in obesity management. This study aimed to investigate whether weight regain after a weight loss period is correlated with the macronutrient composition and/or the inflammatory index of the diet during that period. Sixty one overweight and obese adults participated in this experimental study. Subjects lost approximately 10% of their initial weight by means of very low-calorie diet for five weeks, or a low calorie diet for 12 weeks. After that, subjects in both groups followed a strict weight maintenance diet based on individual needs for four weeks, which was followed by a nine-month weight maintenance period without dietary counseling. Anthropometrics and dietary intake data were recorded before weight loss (baseline) and during the weight maintenance period. On average, participants regained approximately half of their lost weight. We found no evidence that macronutrient composition during the weight maintenance period was associated with weight regain. The dietary inflammatory index (r = 0.304, p = 0.032) was positively correlated with weight regain and remained significant after correction for physical activity (r = 0.287, p = 0.045). Our data suggest that the inflammatory properties of diet play a role in weight regain after weight loss in overweight and obese adults.

The effect of rate of weight loss on long-term weight regain in adults with overweight and obesity.

OBJECTIVE: To investigate the effect of rate of weight loss, with similar total weight loss, on weight regain in individuals with overweight and obesity. METHODS: Fifty-seven participants (BMI: 28-35 kg/m(2) ) underwent a dietary intervention (DI). They were randomized to a low-calorie diet (LCD; 1250 kcal/day) for 12 weeks (slow weight loss) or a very-low-calorie diet (VLCD; 500 kcal/day) for 5 weeks (rapid weight loss) (weight loss (WL) period) followed by a 4-week weight-stable (WS) period and 9 months follow-up. Body weight and body composition (BodPod) were determined at study start and after each period. RESULTS: Weight change was similar in both groups after WL (LCD: -8.2 kg and VLCD: -9.0 kg, P = 0.24). Weight regain after follow-up was not significantly different between groups (LCD: 4.2 kg and VLCD: 4.5 kg, P = 0.73). Percentage fat-free mass loss (%FFML) was higher in the VLCD-group compared to the LCD-group after DI (8.8% and 1.3%, respectively, P = 0.034) and was associated with weight regain during follow-up in the whole group (r = 0.325, P = 0.018). CONCLUSIONS: The present study showed that, with similar total weight loss, rate of weight loss did not affect weight regain. However, %FFML after DI was associated with weight regain.

Variation in extracellular matrix genes is associated with weight regain after weight loss in a sex-specific manner.

The extracellular matrix (ECM) of adipocytes is important for body weight regulation. Here, we investigated whether genetic variation in ECM-related genes is associated with weight regain among participants of the European DiOGenes study. Overweight and obese subjects (n = 469, 310 females, 159 males) were on an 8-week low-calorie diet with a 6-month follow-up. Body weight was measured before and after the diet, and after follow-up. Weight maintenance scores (WMS, regained weight as percentage of lost weight) were calculated based on the weight data. Genotype data were retrieved for 2903 SNPs corresponding to 124 ECM-related genes. Regression analyses provided us with six significant SNPs associated with the WMS in males: 3 SNPs in the POSTN gene and a SNP in the LAMB1, COL23A1, and FBLN5 genes. For females, 1 SNP was found in the FN1 gene. The risk of weight regain was increased by: the C/C genotype for POSTN in a co-dominant model (OR 8.25, 95 % CI 2.85-23.88) and the T/C-C/C genotype in a dominant model (OR 4.88, 95 % CI 2.35-10.16); the A/A genotype for LAMB1 both in a co-dominant model (OR 18.43, 95 % CI 2.35-144.63) and in a recessive model (OR 16.36, 95 % CI 2.14-124.9); the G/A genotype for COL23A1 in a co-dominant model (OR 3.94, 95 % CI 1.28-12.10), or the A-allele in a dominant model (OR 2.86, 95 % CI 1.10-7.49); the A/A genotype for FBLN5 in a co-dominant model (OR 13.00, 95 % CI 1.61-104.81); and the A/A genotype for FN1 in a recessive model (OR 2.81, 95 % CI 1.40-5.63). Concluding, variants of ECM genes are associated with weight regain after weight loss in a sex-specific manner.