FAM13A and POM121C are candidate genes for fasting insulin: functional follow-up analysis of a genome-wide association study

Aims/hypothesis: By genome-wide association meta-analysis, 17 genetic loci associated with fasting serum insulin (FSI), a marker of systemic insulin resistance, have been identified. To define potential culprit genes in these loci, in a cross-sectional study we analysed white adipose tissue (WAT) expression of 120 genes in these loci in relation to systemic and adipose tissue variables, and functionally evaluated genes demonstrating genotype-specific expression in WAT (eQTLs). Methods: Abdominal subcutaneous adipose tissue biopsies were obtained from 114 women. Basal lipolytic activity was measured as glycerol release from adipose tissue explants. Adipocytes were isolated and insulin-stimulated incorporation of radiolabelled glucose into lipids was used to quantify adipocyte insulin sensitivity. Small interfering RNA-mediated knockout in human mesenchymal stem cells was used for functional evaluation of genes. Results: Adipose expression of 48 of the studied candidate genes associated significantly with FSI, whereas expression of 24, 17 and 2 genes, respectively, associated with adipocyte insulin sensitivity, lipolysis and/or WAT morphology (i.e. fat cell size relative to total body fat mass). Four genetic loci contained eQTLs. In one chromosome 4 locus (rs3822072), the FSI-increasing allele associated with lower FAM13A expression and FAM13A expression associated with a beneficial metabolic profile including decreased WAT lipolysis (regression coefficient, R = −0.50, p = 5.6 × 10−7). Knockdown of FAM13A increased lipolysis by ~1.5- fold and the expression of LIPE (encoding hormone-sensitive lipase, a rate-limiting enzyme in lipolysis). At the chromosome 7 locus (rs1167800), the FSI-increasing allele associated with lower POM121C expression. Consistent with an insulin-sensitising function, POM121C expression associated with systemic insulin sensitivity (R = −0.22, p = 2.0 × 10−2), adipocyte insulin sensitivity (R = 0.28, p = 3.4 × 10−3) and adipose hyperplasia (R = −0.29, p = 2.6 × 10−2). POM121C knockdown decreased expression of all adipocyte-specific markers by 25–50%, suggesting that POM121C is necessary for adipogenesis. Conclusions/interpretation: Gene expression and adipocyte functional studies support the notion that FAM13A and POM121C control adipocyte lipolysis and adipogenesis, respectively, and might thereby be involved in genetic control of systemic insulin sensitivity

Differential Mitochondrial Gene Expression in Adipose Tissue Following Weight Loss Induced by Diet or Bariatric Surgery

Context: Mitochondria are essential for cellular energy homeostasis, yet their role in subcutaneous adipose tissue (SAT) during different types of weight-loss interventions remains unknown. Objective: To investigate how SAT mitochondria change following diet-induced and bariatric surgery-induced weight-loss interventions in 4 independent weight-loss studies. Methods: The DiOGenes study is a European multicenter dietary intervention with an 8-week low caloric diet (LCD; 800 kcal/d; n = 261) and 6-month weight-maintenance (n = 121) period. The Kuopio Obesity Surgery study (KOBS) is a Roux-en-Y gastric bypass (RYGB) surgery study (n = 172) with a 1-year follow-up. We associated weight-loss percentage with global and 2210 mitochondria-related RNA transcripts in linear regression analysis adjusted for age and sex. We repeated these analyses in 2 studies. The Finnish CRYO study has a 6-week LCD (800-1000 kcal/d; n = 19) and a 10.5-month follow-up. The Swedish DEOSH study is a RYGB surgery study with a 2-year (n = 49) and 5-year (n = 37) follow-up. Results: Diet-induced weight loss led to a significant transcriptional downregulation of oxidative phosphorylation (DiOGenes; ingenuity pathway analysis [IPA] z-scores: -8.7 following LCD, -4.4 following weight maintenance; CRYO: IPA z-score: -5.6, all P < 0.001), while upregulation followed surgery-induced weight loss (KOBS: IPA z-score: 1.8, P < 0.001; in DEOSH: IPA z-scores: 4.0 following 2 years, 0.0 following 5 years). We confirmed an upregulated oxidative phosphorylation at the proteomics level following surgery (IPA z-score: 3.2, P < 0.001). Conclusions: Differentially regulated SAT mitochondria-related gene expressions suggest qualitative alterations between weight-loss interventions, providing insights into the potential molecular mechanistic targets for weight-loss success.Peer reviewe

OBEDIS Core Variables Project : European Expert Guidelines on a Minimal Core Set of Variables to Include in Randomized, Controlled Clinical Trials of Obesity Interventions

Heterogeneity of interindividual and intraindividual responses to interventions is often observed in randomized, controlled trials for obesity. To address the global epidemic of obesity and move toward more personalized treatment regimens, the global research community must come together to identify factors that may drive these heterogeneous responses to interventions. This project, called OBEDIS (OBEsity Diverse Interventions Sharing - focusing on dietary and other interventions), provides a set of European guidelines for a minimal set of variables to include in future clinical trials on obesity, regardless of the specific endpoints. Broad adoption of these guidelines will enable researchers to harmonize and merge data from multiple intervention studies, allowing stratification of patients according to precise phenotyping criteria which are measured using standardized methods. In this way, studies across Europe may be pooled for better prediction of individuals' responses to an intervention for obesity - ultimately leading to better patient care and improved obesity outcomes.Peer reviewe

ApoB100-LDL Acts as a Metabolic Signal from Liver to Peripheral Fat Causing Inhibition of Lipolysis in Adipocytes

International audienceBACKGROUND: Free fatty acids released from adipose tissue affect the synthesis of apolipoprotein B-containing lipoproteins and glucose metabolism in the liver. Whether there also exists a reciprocal metabolic arm affecting energy metabolism in white adipose tissue is unknown. METHODS AND FINDINGS: We investigated the effects of apoB-containing lipoproteins on catecholamine-induced lipolysis in adipocytes from subcutaneous fat cells of obese but otherwise healthy men, fat pads from mice with plasma lipoproteins containing high or intermediate levels of apoB100 or no apoB100, primary cultured adipocytes, and 3T3-L1 cells. In subcutaneous fat cells, the rate of lipolysis was inversely related to plasma apoB levels. In human primary adipocytes, LDL inhibited lipolysis in a concentration-dependent fashion. In contrast, VLDL had no effect. Lipolysis was increased in fat pads from mice lacking plasma apoB100, reduced in apoB100-only mice, and intermediate in wild-type mice. Mice lacking apoB100 also had higher oxygen consumption and lipid oxidation. In 3T3-L1 cells, apoB100-containing lipoproteins inhibited lipolysis in a dose-dependent fashion, but lipoproteins containing apoB48 had no effect. ApoB100-LDL mediated inhibition of lipolysis was abolished in fat pads of mice deficient in the LDL receptor (Ldlr(-/-)Apob(100/100)). CONCLUSIONS: Our results show that the binding of apoB100-LDL to adipocytes via the LDL receptor inhibits intracellular noradrenaline-induced lipolysis in adipocytes. Thus, apoB100-LDL is a novel signaling molecule from the liver to peripheral fat deposits that may be an important link between atherogenic dyslipidemias and facets of the metabolic syndrome

Monomeric Tartrate Resistant Acid Phosphatase Induces Insulin Sensitive Obesity

Obesity is associated with macrophage infiltration of adipose tissue, which may link adipose inflammation to insulin resistance. However, the impact of inflammatory cells in the pathophysiology of obesity remains unclear

Neurotrophic factors and their receptors structure-function relationships and signalling mechanisms

Background The development, survival and maintenance of the vertebrate nervous system requires the continous supply of a set of polypeptides termed neurotrophic factors. Among these, the neurotrophins (NTs) and members of the transforming growth factor-B (TGF-B) superfamily have raised substantial hopes for future clinical applications. Mammalian NTs comprise four members to date, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4). NTs interact with two distinct classes of cell-surface receptors: members of the receotor tyrosine kinase family Trk, and p75NTR a smaller receptor that lacks intrisic catalytic activity. While p75NTR binds all neurotrophins with equal affinity, activation of Trks is specific in that NGF activates TrkA, BDNF and NT-4 interact with TrkB and NT-3 activates TrkC. In addition, NT-3 can signal, albeit to a lesser extent, through TrkA and TrkB. While the function of Trks as signalling receptors is well established, the role of p75NTR is less clear. In contrast to the restricted number of neurotrophins, members of the TGF-B superfamily comprise a heterogenous collection of pleiotropic proteins grouped into several subfamilies. These include the prototypic TGF-Bs, activins and bone morphogenetic proteins (BMP). Most members have been shown to signal through a unique heteromeric complex comprised of two classes of serine threonine kinase receptors termed type I and II. Type II receptors are constitutively active kinases with the ability to bind ligand on their own, while type I receptors require type II receptors in order to interact with ligand efficiently. Aims In the first part of the present thesis we focused our attention on the enigmatic p75NTR, We set out to determine residues in neurotrophins responsible for interaction with p75NTR and to define functional roles for p75NTR in vertebrate neurons. In the second part, we studied receptors expressed in different neuronal tissues. We sought to investigate the expression levels of neurotrophin receptors in neuronal tumours and embarked on a project aimed at isolating and characterizing novel receptors for the TGF-B superfamily expressed in the nervous system. Results By site-directed mutagenesis we generated recombinant neurotrophin molecules where specific residues were replaced by alanine. Using a range of in vitro assays we compared the activity of mutant molecules with native protein. This allowed us to assess the importance of each individual residue in receptor binding and activation. In the first study we mapped a major functional epitope in BDNF, NT-3 and NT-4 involved in binding to p75NTR, This is located in two spatially close loop regions in one end of the molecules and is formed by only 2-3 positively charged residues. Albeit similar, this epitope is clearly different in its precise conformation between the different neurotrophins. Furthermore it appears to be dispensable for binding and activation of Trks. Interestingly, on cells coexpressing p75NTR and cognate Trks, NT-4, but not BDNF or NT-3 seems to require p75NTR binding in order to activate TrkB efficiently, indicating that p75NTR may modulate neuronal responsiveness to NT-4. In the second study we were able to determine that the major determinant in NT-3 responsible for its interaction with the non-cognate receptors TrkA and TrkB proved to be the same epitope used for p75NTR binding, demonstrating that the interaction between NT-3 and non-cognate Trks is very localized. In the third report we assessed the functional role of p75NTR in NGF responsive vertebrate neurons with the use of a mutant NGF selectively deficient in p75NTR binding. We conclude that binding to p75NTR modulates TrkA function, by enhancing TrkA mediated neuronal survival in response to NGF when the factor is present in limiting amounts or when cell-surface receptor expression is altered. In the last mutagenesis study we assessed the role of a conserved loop region situated in one end of the NGF-molecule. Positively charged residues were shown to be important for p75NTR binding, in line with the previously shown involvement of basic residues in binding to p75NTR, In the last two reports we focused our attention on receptors for neurotrophic factors. Neurotrophins and their receptors are believed to play a role in childhood neuroblastoma tumours (NB). We analyzed the expression pattern of mRNA coding for TrkC and found that high levels of expression correlated with favourable tumour stage and clinical outcome. This indicates that determination of TrkC mRNA may be of clinical significance in the evaluation of patients with NB. In our final work, we isolated a novel type I receptor (ALK-7) for the TGF-B superfamily expressed in the nervous system. ALK-7 is predominantly expressed in adult neurons of the central nervous system and can interact with type ll receptors for activin and TGF-B in a ligand dependent manner, althoughwe were unable to demonstrate physical interactions between ALK-7 and the ligands. These results suggest that ALK 7 may be the receptor for a novel member of the TGF-B superfamily with neurotrophic activites. Keywords: neurotrophins, nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, neurotrophin-4, p75 neurotrophin receptor, neuroblastoma, serine/threonine kinase receptors ISBN 91-628-2458-

RELATIONSHIP BETWEEN A SEDENTARY LIFESTYLE AND ADIPOSE INSULIN RESISTANCE

Sedentary people have insulin resistance in skeletal muscle but whether this also occurs in fat cells is unknown and was examined. Insulin inhibition of hydrolysis of triglycerides (antilipolysis) and stimulation of triglyceride formation (lipogenesis) was investigated in subcutaneous fat cells from 204 sedentary and 336 physically active subjects. Insulin responsiveness (maximum hormone effect) and sensitivity (half maximum effective concentration) were determined. In 69 women hyperinsulinemia-induced circulating fatty acid levels were measured. In 128 women adipose gene expression was analyzed. Responsiveness of insulin for antilipolysis (60% inhibition) and lipogenesis (2-fold stimulation) were similar between sedentary and active subjects. Sensitivity for both measures was about 10-fold decreased in sedentary subjects (p<0.01). However, only the association between antilipolysis sensitivity and physical activity remained significant when adjusting for body mass index, age, sex, waist-to-hip ratio, fat cell size and cardiometabolic disorders in multiple regression. Fatty acid levels decreased following hyperinsulinemia but remained higher in sedentary compared to active women (p=0.01). mRNA expression of insulin receptor and its substrates 1 and 2 was decreased in sedentary subjects. In conclusion, while the maximum effect is preserved, the sensitivity to insulin’s antilipolytic effect in subcutaneous fat cells is selectively lower in sedentary subjects. </p

Saturated fatty acids in human visceral adipose tissue are associated with increased 11-beta-hydroxysteroid-dehydrogenase type 1 expression

Background: Visceral fat accumulation is associated with metabolic disease. It is therefore relevant to study factors that regulate adipose tissue distribution. Recent data shows that overeating saturated fatty acids promotes greater visceral fat storage than overeating unsaturated fatty acids. Visceral adiposity is observed in states of hypercortisolism, and the enzyme 11-beta-hydroxysteroid-dehydrogenase type 1 (11 beta-hsd1) is a major regulator of cortisol activity by converting inactive cortisone to cortisol in adipose tissue. We hypothesized that tissue fatty acid composition regulates body fat distribution through local effects on the expression of 11 beta-hsd1 and its corresponding gene (HSD11B1) resulting in altered cortisol activity. Findings: Visceral- and subcutaneous adipose tissue biopsies were collected during Roux-en-Y gastric bypass surgery from 45 obese women (BMI; 41 +/- 4 kg/m(2)). The fatty acid composition of each biopsy was measured and correlated to the mRNA levels of HSD11B1. 11 beta-hsd1 protein levels were determined in a subgroup (n = 12) by western blot analysis. Our main finding was that tissue saturated fatty acids (e.g. palmitate) were associated with increased 11 beta-hsd1 gene- and protein-expression in visceral but not subcutaneous adipose tissue. Conclusions: The present study proposes a link between HSD11B1 and saturated fatty acids in visceral, but not subcutaneous adipose tissue. Nutritional regulation of visceral fat mass through HSD11B1 is of interest for the modulation of metabolic risk and warrants further investigation

Saturated fatty acids in human visceral adipose tissue are associated with increased 11-beta-hydroxysteroid-dehydrogenase type 1 expression

Background: Visceral fat accumulation is associated with metabolic disease. It is therefore relevant to study factors that regulate adipose tissue distribution. Recent data shows that overeating saturated fatty acids promotes greater visceral fat storage than overeating unsaturated fatty acids. Visceral adiposity is observed in states of hypercortisolism, and the enzyme 11-beta-hydroxysteroid-dehydrogenase type 1 (11 beta-hsd1) is a major regulator of cortisol activity by converting inactive cortisone to cortisol in adipose tissue. We hypothesized that tissue fatty acid composition regulates body fat distribution through local effects on the expression of 11 beta-hsd1 and its corresponding gene (HSD11B1) resulting in altered cortisol activity. Findings: Visceral- and subcutaneous adipose tissue biopsies were collected during Roux-en-Y gastric bypass surgery from 45 obese women (BMI; 41 +/- 4 kg/m(2)). The fatty acid composition of each biopsy was measured and correlated to the mRNA levels of HSD11B1. 11 beta-hsd1 protein levels were determined in a subgroup (n = 12) by western blot analysis. Our main finding was that tissue saturated fatty acids (e.g. palmitate) were associated with increased 11 beta-hsd1 gene- and protein-expression in visceral but not subcutaneous adipose tissue. Conclusions: The present study proposes a link between HSD11B1 and saturated fatty acids in visceral, but not subcutaneous adipose tissue. Nutritional regulation of visceral fat mass through HSD11B1 is of interest for the modulation of metabolic risk and warrants further investigation