Genetics and Epigenetics in Obesity: What Do We Know so Far?

PURPOSE OF REVIEW: Enormous progress has been made in understanding the genetic architecture of obesity and the correlation of epigenetic marks with obesity and related traits. This review highlights current research and its challenges in genetics and epigenetics of obesity. RECENT FINDINGS: Recent progress in genetics of polygenic traits, particularly represented by genome-wide association studies, led to the discovery of hundreds of genetic variants associated with obesity, which allows constructing polygenic risk scores (PGS). In addition, epigenome-wide association studies helped identifying novel targets and methylation sites being important in the pathophysiology of obesity and which are essential for the generation of methylation risk scores (MRS). Despite their great potential for predicting the individual risk for obesity, the use of PGS and MRS remains challenging. Future research will likely discover more loci being involved in obesity, which will contribute to better understanding of the complex etiology of human obesity. The ultimate goal from a clinical perspective will be generating highly robust and accurate prediction scores allowing clinicians to predict obesity as well as individual responses to body weight loss-specific life-style interventions.

Obesity Is Associated with Distorted Proteoglycan Expression in Adipose Tissue.

Proteoglycans are central components of the extracellular matrix (ECM) and binding partners for inflammatory chemokines. Morphological differences in the ECM and increased inflammation are prominent features of the white adipose tissues in patients with obesity. The impact of obesity and weight loss on the expression of specific proteoglycans in adipose tissue is not well known. This study aimed to investigate the relationship between adiposity and proteoglycan expression. We analyzed transcriptomic data from two human bariatric surgery cohorts. In addition, RT-qPCR was performed on adipose tissues from female and male mice fed a high-fat diet. Both visceral and subcutaneous adipose tissue depots were analyzed. Adipose mRNA expression of specific proteoglycans, proteoglycan biosynthetic enzymes, proteoglycan partner molecules, and other ECM-related proteins were altered in both human cohorts. We consistently observed more profound alterations in gene expression of ECM targets in the visceral adipose tissues after surgery (among others VCAN (p = 0.000309), OGN (p = 0.000976), GPC4 (p = 0.00525), COL1A1 (p = 0.00221)). Further, gene analyses in mice revealed sex differences in these two tissue compartments in obese mice. We suggest that adipose tissue repair is still in progress long after surgery, which may reflect challenges in remodeling increased adipose tissues. This study can provide the basis for more mechanistic studies on the role of proteoglycans in adipose tissues in obesity.

The emergent role of mitochondrial RNA modifications in metabolic alterations.

Mitochondrial epitranscriptomics refers to the modifications occurring in all the different RNA types of mitochondria. Although the number of mitochondrial RNA modifications is less than those in cytoplasm, substantial evidence indicates that they play a critical role in accurate protein synthesis. Recent evidence supported those modifications in mitochondrial RNAs also have crucial implications in mitochondrial-related diseases. In the light of current knowledge about the involvement, the association between mitochondrial RNA modifications and diseases arises from studies focusing on mutations in both mitochondrial and nuclear DNA genes encoding enzymes involved in such modifications. Here, we review the current evidence available for mitochondrial RNA modifications and their role in metabolic disorders, and we also explore the possibility of using them as promising targets for prevention and early detection. Finally, we discuss future directions of mitochondrial epitranscriptomics in these metabolic alterations, and how these RNA modifications may offer a new diagnostic and theragnostic avenue for preventive purposes. This article is categorized under: RNA Processing > RNA Editing and Modification.

SMUG1 regulates fat homeostasis leading to a fatty liver phenotype in mice.

Fatty liver diseases are a major health threat across the western world, leading to cirrhosis and premature morbidity and mortality. Recently, a correlation between the base excision repair enzyme SMUG1 and metabolic homeostasis was identified. As the molecular mechanisms remain unknown, we exploited a SMUG1-knockout mouse model to gain insights into this association by characterizing the liver phenotype in young vs old SMUG1-null mice. We observed increased weight and fat content in one-year old animals, with altered activity of enzymes important for fatty acids influx and uptake. Consistently, lipidomic profiling showed accumulation of free fatty acids and triglycerides in SMUG1-null livers. Old SMUG1-knockout mice also displayed increased hepatocyte senescence and DNA damage at telomeres. Interestingly, RNA sequencing revealed widespread changes in the expression of lipid metabolic genes already in three months old animals. In summary, SMUG1 modulates fat metabolism favouring net lipogenesis and resulting in development of a fatty liver phenotype.

DNA methylation patterns reflect individual's lifestyle independent of obesity.

OBJECTIVE: Obesity is driven by modifiable lifestyle factors whose effects may be mediated by epigenetics. Therefore, we investigated lifestyle effects on blood DNA methylation in participants of the LIFE-Adult study, a well-characterised population-based cohort from Germany. RESEARCH DESIGN AND METHODS: Lifestyle scores (LS) based on diet, physical activity, smoking and alcohol intake were calculated in 4107 participants of the LIFE-Adult study. Fifty subjects with an extremely healthy lifestyle and 50 with an extremely unhealthy lifestyle (5th and 95th percentiles LS) were selected for genome-wide DNA methylation analysis in blood samples employing Illumina Infinium® Methylation EPIC BeadChip system technology. RESULTS: Differences in DNA methylation patterns between body mass index groups (<25 vs. >30 kg/m2 ) were rather marginal compared to inter-lifestyle differences (0 vs. 145 differentially methylated positions [DMPs]), which identified 4682 differentially methylated regions (DMRs; false discovery rate [FDR <5%) annotated to 4426 unique genes. A DMR annotated to the glutamine-fructose-6-phosphate transaminase 2 (GFPT2) locus showed the strongest hypomethylation (∼6.9%), and one annotated to glutamate rich 1 (ERICH1) showed the strongest hypermethylation (∼5.4%) in healthy compared to unhealthy lifestyle individuals. Intersection analysis showed that diet, physical activity, smoking and alcohol intake equally contributed to the observed differences, which affected, among others, pathways related to glutamatergic synapses (adj. p < .01) and axon guidance (adj. p < .05). We showed that methylation age correlates with chronological age and waist-to-hip ratio with lower DNA methylation age (DNAmAge) acceleration distances in participants with healthy lifestyles. Finally, two identified top DMPs for the alanyl aminopeptidase (ANPEP) locus also showed the strongest expression quantitative trait methylation in blood. CONCLUSIONS: DNA methylation patterns help discriminate individuals with a healthy versus unhealthy lifestyle, which may mask subtle methylation differences derived from obesity.

Serglycin Is Involved in Adipose Tissue Inflammation in Obesity.

Chronic local inflammation of adipose tissue is an important feature of obesity. Serglycin is a proteoglycan highly expressed by various immune cell types known to infiltrate adipose tissue under obese conditions. To investigate if serglycin expression has an impact on diet-induced adipose tissue inflammation, we subjected Srgn +/+ and Srgn -/- mice (C57BL/6J genetic background) to an 8-wk high-fat and high-sucrose diet. The total body weight was the same in Srgn +/+ and Srgn -/- mice after diet treatment. Expression of white adipose tissue genes linked to inflammatory pathways were lower in Srgn -/- mice. We also noted reduced total macrophage abundance, a reduced proportion of proinflammatory M1 macrophages, and reduced formation of crown-like structures in adipose tissue of Srgn -/- compared with Srgn +/+ mice. Further, Srgn -/- mice had more medium-sized adipocytes and fewer large adipocytes. Differentiation of preadipocytes into adipocytes (3T3-L1) was accompanied by reduced Srgn mRNA expression. In line with this, analysis of single-cell RNA sequencing data from mouse and human adipose tissue supports that Srgn mRNA is predominantly expressed by various immune cells, with low expression in adipocytes. Srgn mRNA expression was higher in obese compared with lean humans and mice, accompanied by an increased expression of immune cell gene markers. SRGN and inflammatory marker mRNA expression was reduced upon substantial weight loss in patients after bariatric surgery. Taken together, this study introduces a role for serglycin in the regulation of obesity-induced adipose inflammation.

m6A Regulators in Human Adipose Tissue - Depot-Specificity and Correlation With Obesity.

Background: N6-methyladenosine (m6A) is one of the most abundant post-transcriptional modifications on mRNA influencing mRNA metabolism. There is emerging evidence for its implication in metabolic disease. No comprehensive analyses on gene expression of m6A regulators in human adipose tissue, especially in paired adipose tissue depots, and its correlation with clinical variables were reported so far. We hypothesized that inter-depot specific gene expression of m6A regulators may differentially correlate with clinical variables related to obesity and fat distribution. Methods: We extracted intra-individually paired gene expression data (omental visceral adipose tissue (OVAT) N=48; subcutaneous adipose tissue (SAT) N=56) of m6A regulators from an existing microarray dataset. We also measured gene expression in another sample set of paired OVAT and SAT (N=46) using RT-qPCR. Finally, we extracted existing gene expression data from peripheral mononuclear blood cells (PBMCs) and single nucleotide polymorphisms (SNPs) in METTL3 and YTHDF3 from genome wide data from the Sorbs population (N=1049). The data were analysed for differential gene expression between OVAT and SAT; and for association with obesity and clinical variables. We further tested for association of SNP markers with gene expression and clinical traits. Results: In adipose tissue we observed that several m6A regulators (WTAP, VIRMA, YTHDC1 and ALKBH5) correlate with obesity and clinical variables. Moreover, we found adipose tissue depot specific gene expression for METTL3, WTAP, VIRMA, FTO and YTHDC1. In PBMCs, we identified ALKBH5 and YTHDF3 correlated with obesity. Genetic markers in METTL3 associate with BMI whilst SNPs in YTHDF3 are associated with its gene expression. Conclusions: Our data show that expression of m6A regulators correlates with obesity, is adipose tissue depot-specific and related to clinical traits. Genetic variation in m6A regulators adds an additional layer of variability to the functional consequences.

Up-to-date on the evidence linking miRNA-related epitranscriptomic modifications and disease settings. Can these modifications affect cross-kingdom regulation?

The field of epitranscriptomics is rapidly developing. Several modifications (e.g. methylations) have been identified for different RNA types. Current evidence shows that chemical RNA modifications can influence the whole molecule's secondary structure, translatability, functionality, stability, and degradation, and some are dynamically and reversibly modulated. miRNAs, in particular, are not only post-transcriptional modulators of gene expression but are themselves submitted to regulatory mechanisms. Understanding how these modifications are regulated and the resulting pathological consequences when dysregulation occurs is essential for the development of new therapeutic targets. In humans and other mammals, dietary components have been shown to affect miRNA expression and may also induce chemical modifications in miRNAs. The identification of chemical modifications in miRNAs (endogenous and exogenous) that can impact host gene expression opens up an alternative way to select new specific therapeutic targets.Hence, the aim of this review is to briefly address how RNA epitranscriptomic modifications can affect miRNA biogenesis and to summarize the existing evidence showing the connection between the (de)regulation of these processes and disease settings. In addition, we hypothesize on the potential effect certain chemical modifications could have on the potential cross-kingdom journey of dietary plant miRNAs.

Cohort profile: Epigenetics in Pregnancy (EPIPREG) - population-based sample of European and South Asian pregnant women with epigenome-wide DNA methylation (850k) in peripheral blood leukocytes.

Pregnancy is a valuable model to study the association between DNA methylation and several cardiometabolic traits, due to its direct potential to influence mother's and child's health. Epigenetics in Pregnancy (EPIPREG) is a population-based sample with the aim to study associations between DNA-methylation in pregnancy and cardiometabolic traits in South Asian and European pregnant women and their offspring. This cohort profile paper aims to present our sample with genetic and epigenetic data and invite researchers with similar cohorts to collaborative projects, such as replication of ours or their results and meta-analysis. In EPIPREG we have quantified epigenome-wide DNA methylation in maternal peripheral blood leukocytes in gestational week 28±1 in Europeans (n = 312) and South Asians (n = 168) that participated in the population-based cohort STORK Groruddalen, in Norway. DNA methylation was measured with Infinium MethylationEPIC BeadChip (850k sites), with technical validation of four CpG sites using bisulphite pyrosequencing in a subset (n = 30). The sample is well characterized with few missing data on e.g. genotype, universal screening for gestational diabetes, objectively measured physical activity, bioelectrical impedance, anthropometrics, biochemical measurements, and a biobank with maternal serum and plasma, urine, placenta tissue. In the offspring, we have repeated ultrasounds during pregnancy, cord blood, and anthropometrics up to 4 years of age. We have quantified DNA methylation in peripheral blood leukocytes in nearly all eligible women from the STORK Groruddalen study, to minimize the risk of selection bias. Genetic principal components distinctly separated Europeans and South Asian women, which fully corresponded with the self-reported ethnicity. Technical validation of 4 CpG sites from the methylation bead chip showed good agreement with bisulfite pyrosequencing. We plan to study associations between DNA methylation and cardiometabolic traits and outcomes.

Maternal Glucose and LDL-Cholesterol Levels Are Related to Placental Leptin Gene Methylation, and, Together With Nutritional Factors, Largely Explain a Higher Methylation Level Among Ethnic South Asians.

Background: Leptin, mainly secreted by fat cells, plays a core role in the regulation of appetite and body weight, and has been proposed as a mediator of metabolic programming. During pregnancy leptin is also secreted by the placenta, as well as being a key regulatory cytokine for the development, homeostatic regulation and nutrient transport within the placenta. South Asians have a high burden of type 2 diabetes, partly attributed to a "thin-fat-phenotype". Objective: Our aim was to investigate how maternal ethnicity, adiposity and glucose- and lipid/cholesterol levels in pregnancy are related to placental leptin gene (LEP) DNA methylation. Methods: We performed DNA methylation analyses of 13 placental LEP CpG sites in 40 ethnic Europeans and 40 ethnic South Asians participating in the STORK-Groruddalen cohort. Results: South Asian ethnicity and gestational diabetes (GDM) were associated with higher placental LEP methylation. The largest ethnic difference was found for CpG11 [5.8% (95% CI: 2.4, 9.2), p<0.001], and the strongest associations with GDM was seen for CpG5 [5.2% (1.4, 9.0), p=0.008]. Higher maternal LDL-cholesterol was associated with lower placental LEP methylation, in particular for CpG11 [-3.6% (-5.5, -1.4) per one mmol/L increase in LDL, p<0.001]. After adjustments, including for nutritional factors involved in the one-carbon-metabolism cycle (vitamin D, B12 and folate levels), ethnic differences in placental LEP methylation were strongly attenuated, while associations with glucose and LDL-cholesterol persisted. Conclusions: Maternal glucose and lipid metabolism is related to placental LEP methylation, whilst metabolic and nutritional factors largely explain a higher methylation level among ethnic South Asians.

Epigenetic signatures associated with maternal body mass index or gestational weight gain: a systematic review.

Maternal body mass index (BMI) and gestational weight gain (GWG) impacts both the mother's and the child's health, and epigenetic modifications have been suggested to mediate some of these effects in offspring. This systematic review aimed to summarize the current literature on associations between maternal BMI and GWG and epigenetic marks. We performed systematic searches in PubMed and EMBASE and manual searches of reference lists. We included 49 studies exploring the association between maternal BMI and/or GWG and DNA methylation or miRNA; 7 performed in maternal tissues, 13 in placental tissue and 38 in different offspring tissues. The most consistent findings were reported for the relationship between maternal BMI, in particular pre-pregnant BMI, and expression of miRNA Let-7d in both maternal blood and placental tissue, methylation of the gene HIF3A in umbilical cord blood and umbilical tissue, and with expression in the miR-210 target gene, BDNF in placental tissue and cord blood. Correspondingly, methylation of BDNF was also found in placental tissue and cord blood. The current evidence suggests that maternal BMI is associated with some epigenetic signatures in the mother, the placenta and her offspring, which could indicate that some of the effects proposed by the Developmental Origins of Health and Disease-hypothesis may be mediated by epigenetic marks. In conclusion, there is a need for large, well-designed studies and meta-analyses that can clarify the relationship between BMI, GWG and epigenetic changes.

DNA methylation signature in blood mirrors successful weight-loss during lifestyle interventions: the CENTRAL trial.

BACKGROUND: One of the major challenges in obesity treatment is to explain the high variability in the individual's response to specific dietary and physical activity interventions. With this study, we tested the hypothesis that specific DNA methylation changes reflect individual responsiveness to lifestyle intervention and may serve as epigenetic predictors for a successful weight-loss. METHODS: We conducted an explorative genome-wide DNA methylation analysis in blood samples from 120 subjects (90% men, mean ± SD age = 49 ± 9 years, body mass-index (BMI) = 30.2 ± 3.3 kg/m2) from the 18-month CENTRAL randomized controlled trial who underwent either Mediterranean/low-carbohydrate or low-fat diet with or without physical activity. RESULTS: Analyses comparing male subjects with the most prominent body weight-loss (responders, mean weight change - 16%) vs. non-responders (+ 2.4%) (N = 10 each) revealed significant variation in DNA methylation of several genes including LRRC27, CRISP2, and SLFN12 (all adj. P < 1 × 10-5). Gene ontology analysis indicated that biological processes such as cell adhesion and molecular functions such as calcium ion binding could have an important role in determining the success of interventional therapies in obesity. Epigenome-wide association for relative weight-loss (%) identified 15 CpGs being negatively correlated with weight change after intervention (all combined P < 1 × 10- 4) including new and also known obesity candidates such as NUDT3 and NCOR2. A baseline DNA methylation score better predicted successful weight-loss [area under the curve (AUC) receiver operating characteristic (ROC) = 0.95-1.0] than predictors such as age and BMI (AUC ROC = 0.56). CONCLUSIONS: Body weight-loss following 18-month lifestyle intervention is associated with specific methylation signatures. Moreover, methylation differences in the identified genes could serve as prognostic biomarkers to predict a successful weight-loss therapy and thus contribute to advances in patient-tailored obesity treatment.

Genetically programmed changes in transcription of the novel progranulin regulator.

Progranulin is a glycoprotein marking chronic inflammation in obesity and type 2 diabetes. Previous studies suggested PSRC1 (proline and serine rich coiled-coil 1) to be a target of genetic variants associated with serum progranulin levels. We aimed to identify potentially functional variants and characterize their role in regulation of PSRC1. Phylogenetic module complexity analysis (PMCA) prioritized four polymorphisms (rs12740374, rs629301, rs660240, rs7528419) altering transcription factor binding sites with an overall score for potential regulatory function of Sall > 7.0. The effects of these variants on transcriptional activity and binding of transcription factors were tested by luciferase reporter and electrophoretic mobility shift assays (EMSA). In parallel, blood DNA promoter methylation of two regions was tested in subjects with a very high (N = 100) or a very low (N = 100) serum progranulin. Luciferase assays revealed lower activities in vectors carrying the rs629301-A compared with the C allele. Moreover, EMSA indicated a different binding pattern for the two rs629301 alleles, with an additional prominent band for the A allele, which was finally confirmed with the supershift for the Yin Yang 1 transcription factor (YY1). Subjects with high progranulin levels manifested a significantly higher mean DNA methylation (P < 1 × 10-7) in one promoter region, which was in line with a significantly lower PSRC1 mRNA expression levels in blood (P = 1 × 10-3). Consistently, rs629301-A allele was associated with lower PSRC1 mRNA expression (P < 1 × 10-7). Our data suggest that the progranulin-associated variant rs629301 modifies the transcription of PSRC1 through alteration of YY1 binding capacity. DNA methylation studies further support the role of PSRC1 in regulation of progranulin serum levels. KEY MESSAGES: PSRC1 (proline and serine rich coiled-coil 1) SNPs are associated with serum progranulin levels. rs629301 regulates PSRC1 expression by affecting Yin Yang 1 transcription factor (YY1) binding. PSRC1 is also epigenetically regulated in subjects with high progranulin levels.

Developmentally Driven Changes in Adipogenesis in Different Fat Depots Are Related to Obesity.

Subcutaneous (sc) and visceral (vis) adipose tissue (AT) contribute to the variability in pathophysiological consequences of obesity and adverse fat distribution. To gain insights into the molecular mechanisms distinguishing vis and sc fat, we compared the transcriptome during differentiation of immortalized adipocytes from murine epididymal (epi) and inguinal (ing) AT. RNA was extracted on different days of adipogenesis (-2, 0, 2, 4, 6, 8) and analyzed using Clariom™ D mouse assays (Affymetrix) covering >214,900 transcripts in >66,100 genes. Transcript Time Course Analysis revealed 137 differentially expressed genes. The top genes with most divergent expression dynamics included developmental genes like Alx1, Lhx8, Irx1/2, Hoxc10, Hoxa5/10, and Tbx5/15. According to pathway analysis the majority of the genes were enriched in pathways related to AT development. Finally, in paired samples of human vis and sc AT (N = 63), several of these genes exhibited depot-specific variability in expression which correlated closely with body mass index and/or waist-to-hip ratio. In conclusion, intrinsically programmed differences in gene expression patterns during adipogenesis suggest that fat depot specific regulation of adipogenesis contributes to individual risk of obesity.

FGF6 and FGF9 regulate UCP1 expression independent of brown adipogenesis.

Uncoupling protein-1 (UCP1) plays a central role in energy dissipation in brown adipose tissue (BAT). Using high-throughput library screening of secreted peptides, we identify two fibroblast growth factors (FGF), FGF6 and FGF9, as potent inducers of UCP1 expression in adipocytes and preadipocytes. Surprisingly, this occurs through a mechanism independent of adipogenesis and involves FGF receptor-3 (FGFR3), prostaglandin-E2 and interaction between estrogen receptor-related alpha, flightless-1 (FLII) and leucine-rich-repeat-(in FLII)-interacting-protein-1 as a regulatory complex for UCP1 transcription. Physiologically, FGF6/9 expression in adipose is upregulated by exercise and cold in mice, and FGF9/FGFR3 expression in human neck fat is significantly associated with UCP1 expression. Loss of FGF9 impairs BAT thermogenesis. In vivo administration of FGF9 increases UCP1 expression and thermogenic capacity. Thus, FGF6 and FGF9 are adipokines that can regulate UCP1 through a transcriptional network that is dissociated from brown adipogenesis, and act to modulate systemic energy metabolism.

Role of the DNA repair genes H2AX and HMGB1 in human fat distribution and lipid profiles.

INTRODUCTION: Regional fat distribution strongly relates to metabolic comorbidities. We identified the DNA repair genes H2AX and HMGB1 to be differentially expressed between human subcutaneous (SAT) and omental visceral adipose tissue (OVAT) depots. As increased DNA damage is linked to metabolic disease, we here sought to analyze whether depot-specific H2AX and HMGB1 expression is related to anthropometric and metabolic profiles of obesity. We further tested for different H2AX mRNA regulatory mechanisms by analyzing promoter DNA methylation and genotyped rs7350 in the H2AX locus. RESEARCH DESIGN AND METHODS: Gene expression (OVAT n=48; SAT n=55) and DNA promoter methylation data (OVAT and SAT n=77) were extracted from an existing dataset as described elsewhere. Genotype data for the 3'untranslated region (3'UTR) H2AX variant rs7350 were generated by using the TaqMan genotyping system in 243 subjects of the same cohort. Statistical analyses were done using SPSS statistics software 24 and GraphPad Prism 6. RESULTS: We identified H2AX being higher (p=0.002) and HMGB1 being less expressed (p=0.0001) in OVAT compared with SAT. Further, we observed positive interdepot correlations of OVAT and SAT for both HMGB1 (p=1×10-6) and H2AX mRNA levels (p=0.024). Depot-specific associations were observed for both genes' methylation levels with either high density lipoprotein cholesterol, low density lipoprotein cholesterol, triglycerides and/or with OVAT/SAT-ratio (all p<0.05). A significantly lower level of total cholesterol in minor A-Allele carriers of rs7350 compared with AG and GG carriers (p=0.001) was observed. Additionally, subjects carrying the A-allele showed lower SAT HMGB1 expression level (p=0.030). CONCLUSION: Our results suggest a fat depot-specific regulation of H2AX and HMGB1 potentially mediated by both DNA methylation and genetic variation. Rs7350, DNA methylation and/or mRNA levels of H2AX and HMGB1 are related to lipid parameters. Further studies are warranted to evaluate the functional role of the DNA repair genes H2AX and HMGB1 in obesity and fat distribution.

(Epi)genetic regulation of CRTC1 in human eating behaviour and fat distribution.

BACKGROUND: In brain, CREB-regulated transcription co-activator 1 (CRTC1) is involved in metabolic dysregulation. In humans a SNP in CRTC1 was associated to body fat percentage and two SNPs affected RNA Pol II binding and chromatin structure, implying epigenetic regulation of CRTC1. We sought to understand the relevance of CRTC1 SNPs, DNA methylation and expression in human eating behaviour and its relationship to clinical variables of obesity in blood and adipose tissue. METHODS: 13 CRTC1 SNPs were included to analyze eating behaviour. For rs7256986, follow up association analyses were applied on DNA methylation, CRTC1 expression and clinical parameters. Linear regression was used throughout the study adjusted for age, sex and BMI. Besides data extraction from previous work, rs7256986 was de-novo genotyped and DNA methylation was evaluated by using pyrosequencing. FINDINGS: We found several SNPs in the CRTC1 locus nominally associated with human eating behaviour or 2hr postprandial insulin levels and observed a correlation with alcohol and coffee intake (all P < 0.05). G-allele carriers of rs7256986 showed slightly increased hip circumference. We showed that rs7256986 represents a methylation quantitative trait locus (meQTL) in whole blood and adipose tissue. The presence of the SNP and/or DNA methylation correlated with CRTC1 gene expression which in turn, related to BMI and fat distribution. INTERPRETATION: Our data support the known role of CRCT1 regulating energy metabolism in brain. Here, we highlight relevance of CRTC1 regulation in blood and adipose tissue. FUND: IFB AdiposityDiseases (BMBF); n609020-Scientia Fellows; Helse-SørØst; DFG: CRC 1052/1 and/2; Kompetenznetz Adipositas, German Diabetes Association.

Genetics and epigenetics in obesity.

Obesity is among the most threatening health burdens worldwide and its prevalence has markedly increased over the last decades. Obesity maybe considered a heritable trait. Identifications of rare cases of monogenic obesity unveiled that hypothalamic circuits and the brain-adipose axis play an important role in the regulation of energy homeostasis, appetite, hunger and satiety. For example, mutations in the leptin gene cause obesity through almost unsuppressed overeating. Common (multifactorial) obesity, most likely resulting from a concerted interplay of genetic, epigenetic and environmental factors, is clearly linked to genetic predisposition by multiple risk variants, which, however only account for a minor part of the general BMI variability. Although GWAS opened new avenues in elucidating the complex genetics behind common obesity, understanding the biological mechanisms relative to the specific risk contributing to obesity remains poorly understood. Non-genetic factors such as eating behavior or physical activity strongly modulate the individual risk for developing obesity. These factors may interact with genetic predisposition for obesity through epigenetic mechanisms. Thus, here, we review the current knowledge about monogenic and common (multifactorial) obesity highlighting the important recent advances in our knowledge on how epigenetic regulation is involved in the etiology of obesity.

DNA methylation of SSPN is linked to adipose tissue distribution and glucose metabolism.

DNA methylation is a crucial epigenetic mechanism in obesity and fat distribution. We explored the Sarcospan ( SSPN) gene locus by using genome-wide data sets comprising methylation and expression data, pyrosequencing analysis in the promoter region, and genetic analysis of an SNP variant rs718314, which was previously reported to associate with waist-to-hip ratio. We found that DNA methylation influences several clinical variables related to fat distribution and glucose metabolism, while SSPN mRNA levels showed directionally opposite effects on these traits. Complete DNA methylation of the SSPN promoter construct suppressed the gene expression of firefly luciferase in MCF7 cells. Moreover, rs718314 was associated with waist and with DNA methylation at CpG sites. Our data strongly support the role of the SSPN locus in body fat composition and glucose homeostasis, and suggest that this is most likely the result of changes in DNA methylation of SSPN in adipose tissue.-Keller, M., Klös, M., Rohde, K., Krüger, J., Kurze, T., Dietrich, A., Schön, M. R., Gärtner, D., Lohmann, T., Dreßler, M., Stumvoll, M., Blüher, M., Kovacs, P., Böttcher, Y. DNA methylation of SSPN is linked to adipose tissue distribution and glucose metabolism.

IRS1 DNA promoter methylation and expression in human adipose tissue are related to fat distribution and metabolic traits.

The SNP variant rs2943650 near IRS1 gene locus was previously associated with decreased body fat and IRS1 gene expression as well as an adverse metabolic profile in humans. Here, we hypothesize that these effects may be mediated by an interplay with epigenetic alterations. We measured IRS1 promoter DNA methylation and mRNA expression in paired human subcutaneous and omental visceral adipose tissue samples (SAT and OVAT) from 146 and 41 individuals, respectively. Genotyping of rs2943650 was performed in all individuals (N = 146). We observed a significantly higher IRS1 promoter DNA methylation in OVAT compared to SAT (N = 146, P = 8.0 × 10-6), while expression levels show the opposite effect direction (N = 41, P = 0.011). OVAT and SAT methylation correlated negatively with IRS1 gene expression in obese subjects (N = 16, P = 0.007 and P = 0.010). The major T-allele is related to increased DNA methylation in OVAT (N = 146, P = 0.019). Finally, DNA methylation and gene expression in OVAT correlated with anthropometric traits (waist- circumference waist-to-hip ratio) and parameters of glucose metabolism in obese individuals. Our data suggest that the association between rs2943650 near the IRS1 gene locus with clinically relevant variables may at least be modulated by changes in DNA methylation that translates into altered IRS1 gene expression.