Potential epigenetic biomarkers of obesity-related insulin resistance in human whole-blood

DNA Methylation Is a Potential Biomarker for Cardiometabolic Health in Mexican Children and Adolescents

DNA methylation (DNAm) is a plausible mechanism underlying cardiometabolic abnormalities, but evidence is limited among youth. This analysis included 410 offspring of the Early Life Exposure in Mexico to Environmental Toxicants (ELEMENT) birth cohort followed up to two time points in late childhood/adolescence. At Time 1, DNAm was quantified in blood leukocytes at long interspersed nuclear elements (LINE-1), H19, and 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD-2), and at Time 2 in peroxisome proliferator-activated receptor alpha (PPAR-α). At each time point, cardiometabolic risk factors were assessed including lipid profiles, glucose, blood pressure, and anthropometry. Linear mixed effects models were used for LINE-1, H19, and 11β-HSD-2 to account for the repeated-measure outcomes. Linear regression models were conducted for the cross-sectional association between PPAR-α with the outcomes. DNAm at LINE-1 was associated with log glucose at site 1 [β = -0.029, p = 0.0006] and with log high-density lipoprotein cholesterol at site 3 [β = 0.063, p = 0.0072]. 11β-HSD-2 DNAm at site 4 was associated with log glucose (β = -0.018, p = 0.0018). DNAm at LINE-1 and 11β-HSD-2 was associated with few cardiometabolic risk factors among youth in a locus-specific manner. These findings underscore the potential for epigenetic biomarkers to increase our understanding of cardiometabolic risk earlier in life.

Modulation of the Inflammatory Response in Polycystic Ovary Syndrome (PCOS)-Searching for Epigenetic Factors

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age. Despite its incidence, the syndrome is poorly understood and remains underdiagnosed, and female patients are diagnosed with a delay. The heterogenous nature of this complex disorder results from the combined occurrence of genetic, environmental, endocrine, and behavioral factors. Primary clinical manifestations of PCOS are derived from the excess of androgens (anovulation, polycystic ovary morphology, lack of or scanty, irregular menstrual periods, acne and hirsutism), whereas the secondary manifestations include multiple metabolic, cardiovascular, and psychological disorders. Dietary and lifestyle factors play important roles in the development and course of PCOS, which suggests strong epigenetic and environmental influences. Many studies have shown a strong association between PCOS and chronic, low-grade inflammation both in the ovarian tissue and throughout the body. In the vast majority of PCOS patients, elevated values of inflammatory markers or their gene markers have been reported. Development of the vicious cycle of the chronic inflammatory state in PCOS is additionally stimulated by hyperinsulinemia and obesity. Changes in DNA methylation, histone acetylation and noncoding RNA levels are presented in this review in the context of oxidative stress, reactive oxygen species, and inflammatory signaling in PCOS. Epigenetic modulation of androgenic activity in response to inflammatory signaling is also discussed.

The potential of DNA methylation as a biomarker for obesity and smoking

DNA methylation is an epigenetic modification that has consistently been shown to be linked with a variety of human traits and diseases. Because DNA methylation is dynamic and potentially reversible in nature and can reflect environmental exposures and predict the onset of diseases, it has piqued interest as a potential disease biomarker. DNA methylation patterns are more stable than transcriptomic or proteomic patterns, and they are relatively easy to measure to track exposure to different environments and risk factors. Importantly, technologies for DNA methylation quantification have become increasingly cost effective-accelerating new research in the field-and have enabled the development of novel DNA methylation biomarkers. Quite a few DNA methylation-based predictors for a number of traits and diseases already exist. Such predictors show potential for being more accurate than self-reported or measured phenotypes (such as smoking behavior and body mass index) and may even hold potential for applications in clinics. In this review, we will first discuss the advantages and challenges of DNA methylation biomarkers in general. We will then review the current state and future potential of DNA methylation biomarkers in two human traits that show rather consistent alterations in methylome-obesity and smoking. Lastly, we will briefly speculate about the future prospects of DNA methylation biomarkers, and possible ways to achieve them.

A Mixture of Endocrine Disrupting Chemicals Associated with Lower Birth Weight in Children Induces Adipogenesis and DNA Methylation Changes in Human Mesenchymal Stem Cells

Endocrine Disrupting Chemicals (EDCs) are man-made compounds that alter functions of the endocrine system. Environmental mixtures of EDCs might have adverse effects on human health, even though their individual concentrations are below regulatory levels of concerns. However, studies identifying and experimentally testing adverse effects of real-life mixtures are scarce. In this study, we aimed at evaluating an epidemiologically identified EDC mixture in an experimental setting to delineate its cellular and epigenetic effects. The mixture was established using data from the Swedish Environmental Longitudinal Mother and child Asthma and allergy (SELMA) study where it was associated with lower birth weight, an early marker for prenatal metabolic programming. This mixture was then tested for its ability to change metabolic programming of human mesenchymal stem cells. In these cells, we assessed if the mixture induced adipogenesis and genome-wide DNA methylation changes. The mixture increased lipid droplet accumulation already at concentrations corresponding to levels measured in the pregnant women of the SELMA study. Furthermore, we identified differentially methylated regions in genes important for adipogenesis and thermogenesis. This study shows that a mixture reflecting human real-life exposure can induce molecular and cellular changes during development that could underlie adverse outcomes.

Examining the association between adiposity and DNA methylation: A systematic review and meta-analysis

Obesity is associated with widespread differential DNA methylation (DNAm) patterns, though there have been limited overlap in the obesity-associated cytosine-guanine nucleotide pair (CpG) sites that have been identified in the literature. We systematically searched four databases for studies published until January 2020. Eligible studies included cross-sectional, longitudinal, or intervention studies examining adiposity and genome-wide DNAm in non-pregnant adults aged 18-75 in all tissue types. Study design and results were extracted in the descriptive review. Blood-based DNAm results in body mass index (BMI) and waist circumference (WC) were meta-analyzed using weighted sum of Z-score meta-analysis. Of the 10,548 studies identified, 46 studies were included in the systematic review with 18 and nine studies included in the meta-analysis of BMI and WC, respectively. In the blood, 77 and four CpG sites were significant in three or more studies of BMI and WC, respectively. Using a genome-wide threshold for significance, 52 blood-based CpG sites were significantly associated with BMI. These sites have previously been associated with many obesity-related diseases including type 2 diabetes, cardiovascular disease, Crohn's disease, and depression. Our study shows that DNAm at 52 CpG sites represent potential mediators of obesity-associated chronic diseases and may be novel intervention or therapeutic targets to protect against obesity-associated chronic diseases.

Exosomes and Obesity-Related Insulin Resistance

Exosomes are extracellular vesicles, delivering signal molecules from donor cells to recipient cells. The cargo of exosomes, including proteins, DNA and RNA, can target the recipient tissues and organs, which have an important role in disease development. Insulin resistance is a kind of pathological state, which is important in the pathogeneses of type 2 diabetes mellitus (T2DM), gestational diabetes mellitus and Alzheimer's disease. Furthermore, obesity is a kind of inducement of insulin resistance. In this review, we summarized recent research advances on exosomes and insulin resistance, especially focusing on obesity-related insulin resistance. These studies suggest that exosomes have great importance in the development of insulin resistance in obesity and have great potential for use in the diagnosis and therapy of insulin resistance.

Methylation status of vault RNA 2-1 promoter is a predictor of glycemic response to glucagon-like peptide-1 analog therapy in type 2 diabetes mellitus

INTRODUCTION

Therapeutic efficiency of glucagon-like peptide-1 (GLP-1) analog is about 50%-70% in type 2 diabetes mellitus (T2DM). Discovery of potential genetic biomarkers for prediction of treatment efficiency of GLP-1 analog before therapy is still necessary. We assess whether DNA methylation was associated with glycemic response to GLP-1 analog therapy in patients with poorly controlled T2DM.

RESEARCH DESIGN AND METHODS

Genomic DNA was extracted from the peripheral blood of training (n=10) and validation (n=128) groups of patients with T2DM receiving GLP-1 analogs. DNA methylome was analyzed using Infinium Human Methylation EPIC Bead Chip in the training group. The candidate genes were examined using a pyrosequencing platform in the validation group. The association between DNA methylation status and glycemic response to GLP-1 was analyzed in these patients.

RESULTS

The most differential methylation region between those with a good (responsive) and poor (unresponsive) glycemic response to GLP-1 analog therapy was located on chromosome 5q31.1 (135415693 to 135416613), the promoter of VTRNA2-1 in the training group. The methylation status of the VTRNA2-1 promoter was examined in the validation group via pyrosequencing reaction, and the hypomethylation of VTRNA2-1 (<40% methylation) was significantly associated with poor glycemic response to GLP-1 treatment (OR 2.757, 95% CI 1.240 to 6.130, p=0.011). Since the VTRNA2-1 promoter region was previously reported maternal imprinting extended to the adjacent centromeric CCCTC-binding factor site that contained an A/C polymorphism (rs2346018), which was associated with methylation density of VTRNA2-1, this A/C polymorphism was also integrated to analyze association with glycemic response to GLP-1 analog therapy. In patients with the A allele of rs2346018 and hypomethylation (<40%) on the VTRNA2-1 promoter, the OR increased to 4.048 (95% CI 1.438 to 11.389, p=0.007).

CONCLUSIONS

The glycemic response to GLP-1 analog treatment is associated with the methylation status of the VTRNA2-1 promoter and polymorphism of rs2346018.

Epigenetics of Hepatic Insulin Resistance

Insulin resistance (IR) is largely recognized as a unifying feature that underlies metabolic dysfunction. Both lifestyle and genetic factors contribute to IR. Work from recent years has demonstrated that the epigenome may constitute an interface where different signals may converge to promote IR gene expression programs. Here, we review the current knowledge of the role of epigenetics in hepatic IR, focusing on the roles of DNA methylation and histone post-translational modifications. We discuss the broad epigenetic changes observed in the insulin resistant liver and its associated pathophysiological states and leverage on the wealth of 'omics' studies performed to discuss efforts in pinpointing specific loci that are disrupted by these changes. We envision that future studies, with increased genomic resolution and larger cohorts, will further the identification of biomarkers of early onset hepatic IR and assist the development of targeted interventions. Furthermore, there is growing evidence to suggest that persistent epigenetic marks may be acquired over prolonged exposure to disease or deleterious exposures, highlighting the need for preventative medicine and long-term lifestyle adjustments to avoid irreversible or long-term alterations in gene expression.

The many lives of Myc in the pancreatic β-cell

Diabetes results from insufficient numbers of functional pancreatic β-cells. Thus, increasing the number of available functional β-cells ex vivo for transplantation, or regenerating them in situ in diabetic patients, is a major focus of diabetes research. The transcription factor, Myc, discovered decades ago lies at the nexus of most, if not all, known proliferative pathways. Based on this, many studies in the 1990s and early 2000s explored the potential of harnessing Myc expression to expand β-cells for diabetes treatment. Nearly all these studies in β-cells used pathophysiological or supraphysiological levels of Myc and reported enhanced β-cell death, dedifferentiation, or the formation of insulinomas if cooverexpressed with Bcl-xL, an inhibitor of apoptosis. This obviously reduced the enthusiasm for Myc as a therapeutic target for β-cell regeneration. However, recent studies indicate that "gentle" induction of Myc expression enhances β-cell replication without induction of cell death or loss of insulin secretion, suggesting that appropriate levels of Myc could have therapeutic potential for β-cell regeneration. Furthermore, although it has been known for decades that Myc is induced by glucose in β-cells, very little is known about how this essential anabolic transcription factor perceives and responds to nutrients and increased insulin demand in vivo. Here we summarize the previous and recent knowledge of Myc in the β-cell, its potential for β-cell regeneration, and its physiological importance for neonatal and adaptive β-cell expansion.

Mitochondria and T2D: Role of Autophagy, ER Stress, and Inflammasome

Type 2 diabetes (T2D) is one of the main current threats to human health. Both T2D and its numerous clinical complications are related to mitochondrial dysfunction and oxidative stress. Over the past decade, great progress has been made in extending our knowledge about the signaling events regulated by mitochondria. However, the links among mitochondrial impairment, oxidative stress, autophagy, endoplasmic reticulum (ER) stress, and activation of the inflammasome still need to be clarified. In light of this deficit, we aim to provide a review of the existing literature concerning the complicated crosstalk between mitochondrial impairment, autophagy, ER stress, and the inflammasome in the molecular pathogenesis of T2D.

Maternal diabetes and obesity influence the fetal epigenome in a largely Hispanic population

Background

Obesity and diabetes mellitus are directly implicated in many adverse health consequences in adults as well as in the offspring of obese and diabetic mothers. Hispanic Americans are particularly at risk for obesity, diabetes, and end-stage renal disease. Maternal obesity and/or diabetes through prenatal programming may alter the fetal epigenome increasing the risk of metabolic disease in their offspring. The aims of this study were to determine if maternal obesity or diabetes mellitus during pregnancy results in a change in infant methylation of CpG islands adjacent to targeted genes specific for obesity or diabetes disease pathways in a largely Hispanic population.

Methods

Methylation levels in the cord blood of 69 newborns were determined using the Illumina Infinium MethylationEPIC BeadChip. Over 850,000 different probe sites were analyzed to determine whether maternal obesity and/or diabetes mellitus directly attributed to differential methylation; epigenome-wide and regional analyses were performed for significant CpG sites.

Results

Following quality control, agranular leukocyte samples from 69 newborns (23 normal term (NT), 14 diabetes (DM), 23 obese (OB), 9 DM/OB) were analyzed for over 850,000 different probe sites. Contrasts between the NT, DM, OB, and DM/OB were considered. After correction for multiple testing, 15 CpGs showed differential methylation from the NT, associated with 10 differentially methylated genes between the diabetic and non-diabetic subgroups, CCDC110, KALRN, PAG1, GNRH1, SLC2A9, CSRP2BP, HIVEP1, RALGDS, DHX37, and SCNN1D. The effects of diabetes were partly mediated by the altered methylation of HOOK2, LCE3C, and TMEM63B. The effects of obesity were partly mediated by the differential methylation of LTF and DUSP22.

Conclusions

The presented data highlights the associated altered methylation patterns potentially mediated by maternal diabetes and/or obesity. Larger studies are warranted to investigate the role of both the identified differentially methylated loci and the effects on newborn body composition and future health risk factors for metabolic disease. Additional future consideration should be targeted to the role of Hispanic inheritance. Potential future targeting of transgenerational propagation and developmental programming may reduce population obesity and diabetes risk.

Epigenetic Programming and Fetal Metabolic Programming

Fetal metabolic programming caused by the adverse intrauterine environment can induce metabolic syndrome in adult offspring. Adverse intrauterine environment introduces fetal long-term relatively irreversible changes in organs and metabolism, and thus causes fetal metabolic programming leading metabolic syndrome in adult offspring. Fetal metabolic programming of obesity and insulin resistance plays a key role in this process. The mechanism of fetal metabolic programming is still not very clear. It is suggested that epigenetic programming, also induced by the adverse intrauterine environment, is a critical underlying mechanism of fetal metabolic programming. Fetal epigenetic programming affects gene expression changes and cellular function through epigenetic modifications without DNA nucleotide sequence changes. Epigenetic modifications can be relatively stably retained and transmitted through mitosis and generations, and thereby induce the development of metabolic syndrome in adult offspring. This manuscript provides an overview of the critical role of epigenetic programming in fetal metabolic programming.

Effects of bariatric surgery on DNA methylation in adults: a systematic review and meta-analysis

BACKGROUND

DNA methylation is an epigenetic mechanism through which environmental factors, including obesity, influence health. Obesity is a major modifiable risk factor for many common diseases, including cardiovascular diseases and cancer. Obesity-induced metabolic stress and inflammation are key mechanisms that affect disease risk and that may result from changes in methylation of metabolic and inflammatory genes.

OBJECTIVES

This review aims to report the effects of weight loss induced by bariatric surgery (BS) on DNA methylation in adults with obesity focusing on changes in metabolic and inflammatory genes.

METHODS

A systematic review was performed using MEDLINE, EMBASE, and Scopus, to identify studies in adult humans that reported DNA methylation after BS.

RESULTS

Of 15,996 screened titles, 15 intervention studies were identified, all of which reported significantly lower body mass index postsurgery. DNA methylation was assessed in 5 different tissues (blood = 7 studies, adipose tissues = 4, skeletal muscle = 2, liver, and spermatozoa). Twelve studies reported significant changes in DNA methylation after BS. Meta-analysis showed that BS increased methylation of PDK4 loci in skeletal muscle and blood in 2 studies, while the effects of BS on IL6 methylation levels in blood were inconsistent. BS had no overall effect on LINE1 or PPARGC1 methylation.

CONCLUSION

The current evidence supports the reversibility of DNA methylation at specific loci in response to BS-induced weight loss. These changes are consistent with improved metabolic and inflammatory profiles of patients after BS. However, the evidence regarding the effects of BS on DNA methylation in humans is limited and inconsistent, which makes it difficult to combine and compare data across studies.

DNA methylome profiling in identical twin pairs discordant for body mass index

OBJECTIVE

Body mass index (BMI) serves as an important measurement of obesity and adiposity, which are highly correlated with cardiometabolic diseases. Although high heritability has been estimated, the identified genetic variants by genetic association studies only explain a small proportion of BMI variation. As an active effort for further exploring the molecular basis of BMI variation, large-scale epigenome-wide association studies have been conducted but with limited number of loci reported, perhaps due to poorly controlled confounding factors, including genetic factors. Being genetically identical, monozygotic twins discordant for BMI are ideal subjects for analyzing the epigenetic association between DNA methylation and BMI, providing perfect control on their genetic makeups largely responsible for BMI variation.

SUBJECTS

We performed an epigenome-wide association study on BMI using 30 identical twin pairs (15 male and 15 female pairs) with age ranging from 39 to 72 years and degree of BMI discordance ranging from 3-7.5 kg/m². Methylation data from whole blood samples were collected using the reduced representation bisulfite sequencing technique.

RESULTS

After adjusting for blood cell composition and clinical variables, we identified 136 CpGs with p-value < 1e-4, 30 CpGs with p < 1e-05 but no CpGs reached genome-wide significance. Genomic region-based analysis found 11 differentially methylated regions harboring coding and non-coding genes some of which were validated by gene expression analysis on independent samples.

CONCLUSIONS

Our DNA methylation sequencing analysis on identical twins provides new references for the epigenetic regulation on BMI and obesity.

LINE-1 in Obesity and Cardiometabolic Diseases: A Systematic Review

Epigenetic mechanisms may play an important role in the etiology of obesity and cardiometabolic diseases, by activating or silencing the related-genes. Scientific evidence has suggested that LINE-1 methylation is associated with body composition and obesity-related diseases, including insulin resistance, type 2 diabetes mellitus, and cardiovascular disease (CVD). It also has been evaluated as predictor of weight loss. The studies' results are still conflicting, and positive and negative associations have been found to LINE-1 methylation regarding adiposity and cardiometabolic markers. Overall, this review presents observational (cross-sectional and longitudinal) studies and interventions (diet, exercises, and bariatric surgery) that evaluated the relationship of the LINE-1 methylation with obesity, weight loss, dyslipidemias, hypertension, insulin resistance, CVD, and metabolic syndrome. TEACHING POINTS Epigenetic mechanisms may play an important role in the etiology of obesity and cardiometabolic diseases. Many studies have related methylation of LINE-1 with cardiometabolic diseases; however, the results are still controversial. The relationship between the etiology of chronic diseases and the methylation of LINE-1 is not fully elucidated. With advances in epigenetic studies, related mechanisms may be early biomarkers in weight change and cardiometabolic risk.

Role of epigenomic mechanisms in the onset and management of insulin resistance

The prevalence of insulin resistance (IR) is increasing rapidly worldwide and it is a relevant health problem because it is associated with several diseases, such as type 2 diabetes, cardiovascular disorders and cancer. Understanding the mechanisms involved in IR onset and progression will open new avenues for identifying biomarkers for preventing and treating IR and its co-diseases. Epigenetic mechanisms such as DNA methylation are important factors that mediate the environmental effect in the genome by regulating gene expression and consequently its effect on the phenotype and the development of disease. Taking into account that IR results from a complex interplay between genes and the environment and that epigenetic marks are reversible, disentangling the relationship between IR and epigenetics will provide new tools to improve the management and prevention of IR. Here, we review the current scientific evidence regarding the association between IR and epigenetic markers as mechanisms involved in IR development and potential management.

Association of blood leukocyte DNA methylation at LINE-1 and growth-related candidate genes with pubertal onset and progression

Puberty is a developmentally plastic phase. Variations in pubertal tempo have implications for the risk of later adult diseases. Influences on pubertal tempo have been widely discussed, but the underlying biological mechanisms remain unclear. Epigenetic modifications are known to regulate development processes; they could play an important role in affecting pubertal outcomes. We conducted a population-based analysis to investigate the association of peripubertal blood DNA methylation at LINE-1 and growth-related candidate genes with pubertal onset and progression in healthy adolescents. The analytic sample included 114 males and 129 females aged 10 to 18 years. DNA methylation at growth-related candidate loci IGF2, H19, HSD11B2, as well as LINE-1 repetitive elements were quantified. Cox survival and ordinal regression models were used to examine sex- and locus-specific associations of epigenetic markers with pubertal development using physician-assessed Tanner stages and self-reported menarche, adjusted for covariates. Among boys, DNA methylation at H19 was associated with later pubarche. HSD11B2 methylation was associated with earlier onset of pubic hair and genitalia development and slower pubertal progression. IGF2 was associated with later onset of genital development. Among girls, LINE-1 methylation was associated with later onset of breast development. For each percent increase of methylation at H19, there was 5% increased odds in the earlier onset of breast development. DNA methylation of IGF2 was associated with earlier onset of pubic hair. DNA methylation at genes known to influence early-life growth may also influence pubertal outcomes.

Decreased blood pressure is related to changes in NF-kB promoter methylation levels after bariatric surgery

BACKGROUND

Obesity is characterized by a chronic, low-grade inflammation, and bariatric surgery is proposed as an effective treatment for reducing the obesity-related co-morbidities. Epigenetic modifications could be involved in the metabolic improvement after surgery.

OBJECTIVE

The main aim of this study was to evaluate whether DNA methylation pattern from genes related to inflammation and insulin response is associated with the metabolic improvement after bariatric surgery in morbidly obese patients and if these changes depend on the surgical procedure.

SETTING

University hospital, Spain.

METHODS

We studied 60 severely obese patients; 31 underwent Roux-en-Y gastric bypass and 29 underwent laparoscopic sleeve gastrectomy. All patients were examined before and at 6 months after bariatric surgery. DNA methylation profile of genes related to the inflammatory response and insulin sensitivity was measured by pyrosequencing.

RESULTS

The promoter methylation levels of the NFKB1 gene were increased significantly after surgery (2.16 ± .9 versus 2.8 ± 1.03). The decrease in blood pressure, both systolic and diastolic, after surgery was significantly associated with the changes in the promoter methylation levels of the NFKB1 gene (β = -.513, P = .003 and β = -.543, P = .004, respectively). A decrease in inflammation status, measured by high sensitivity C-reactive protein values, was associated with changes in SLC19A1 methylation levels.

CONCLUSION

Our study shows for the first time an association between NFKB1 methylation levels and blood pressure after bariatric surgery, highlighting the possible function of this gene in the regulation of arterial pressure. Regarding SLC19A1, this gene could position as a potential target linking inflammation and insulin resistance.

Aberrant DNA Methylation Involved in Obese Women with Systemic Insulin Resistance

Background

Epigenetics has been recognized as a significant regulator in many diseases. White adipose tissue (WAT) epigenetic dysregulation is associated with systemic insulin resistance (IR). The aim of this study was to survey the differential methylation of genes in obese women with systemic insulin resistance by DNA methylation microarray.

Methods

The genome-wide methylation profile of systemic insulin resistant obese women was obtained from Gene Expression Omnibus database. After data preprocessing, differing methylation patterns between insulin resistant and sensitive obese women were identified by Student's t-test and methylation value differences. Network analysis was then performed to reveal co-regulated genes of differentially methylated genes. Functional analysis was also implemented to reveal the underlying biological processes related to systemic insulin resistance in obese women.

Results

Relative to insulin sensitive obese women, we initially screened 10,874 differentially methylated CpGs, including 7402 hyper-methylated sites and 6073 hypo-methylated CpGs. Our analysis identified 4 significantly differentially methylated genes, including SMYD3, UST, BCL11A, and BAI3. Network and functional analyses found that these differentially methylated genes were mainly involved in chondroitin and dermatan sulfate biosynthetic processes.

Conclusion

Based on our study, we propose several epigenetic biomarkers that may be related to obesity-associated insulin resistance. Our results provide new insights into the epigenetic regulation of disease etiology and also identify novel targets for insulin resistance treatment in obese women.

Adipocyte Expression of SLC19A1 Links DNA Hypermethylation to Adipose Tissue Inflammation and Insulin Resistance

CONTEXT

Insulin resistance (IR) is promoted by a chronic low-grade inflammation in white adipose tissue (WAT). The latter might be regulated through epigenetic mechanisms such as DNA methylation. The one carbon cycle (1CC) is a central metabolic process governing DNA methylation.

OBJECTIVE

To identify adipocyte-expressed 1CC genes linked to WAT inflammation, IR, and their causal role.

DESIGN

Cohort study.

SETTING

Outpatient academic clinic.

PARTICIPANTS

Obese and nonobese subjects.

METHODS

Gene expression and DNA methylation arrays were performed in subcutaneous WAT and isolated adipocytes. In in vitro differentiated human adipocytes, gene knockdown was achieved by small interfering RNA, and analyses included microarray, quantitative polymerase chain reaction, DNA methylation by enzyme-linked immunosorbent assay and pyrosequencing, protein secretion by enzyme-linked immunosorbent assay, targeted metabolomics, and luciferase reporter and thermal shift assays.

MAIN OUTCOME MEASURES

Effects on adipocyte inflammation.

RESULTS

In adipocytes from obese individuals, global DNA hypermethylation was associated positively with gene expression of proinflammatory pathways. Among the 1CC genes, IR in vivo and proinflammatory gene expression in WAT were most strongly and inversely associated with SLC19A1, a gene encoding a membrane folate carrier. SLC19A1 knockdown in human adipocytes perturbed intracellular 1CC metabolism, induced global DNA hypermethylation, and increased expression of proinflammatory genes. Several CpG loci linked SLC19A1 to inflammation; validation studies were focused on the chemokine C-C motif chemokine ligand 2 (CCL2) in which methylation in the promoter (cg12698626) regulated CCL2 expression and CCL2 secretion through altered transcriptional activity.

CONCLUSIONS

Reduced SLC19A1 expression in human adipocytes induces DNA hypermethylation, resulting in increased expression of specific proinflammatory genes, including CCL2. This constitutes an epigenetic mechanism that might link dysfunctional adipocytes to WAT inflammation and IR.

INSIG2 rs7566605 single nucleotide variant and global DNA methylation index levels are associated with weight loss in a personalized weight reduction program

Single nucleotide polymorphisms associated with lipid metabolism and energy balance are implicated in the weight loss response caused by nutritional interventions. Diet-induced weight loss is also associated with differential global DNA methylation. DNA methylation has been proposed as a predictive biomarker for weight loss response. Personalized biomarkers for successful weight loss may inform clinical decisions when deciding between behavioral and surgical weight loss interventions. The aim of the present study was to investigate the association between global DNA methylation, genetic variants associated with energy balance and lipid metabolism, and weight loss following a non-surgical weight loss regimen. The present study included 105 obese participants that were enrolled in a personalized weight loss program based on their allelic composition of the following five energy balance and lipid metabolism-associated loci: Near insulin-induced gene 2 (INSIG2); melanocortin 4 receptor; adrenoceptor β2; apolipoprotein A5; and G-protein subunit β3. The present study investigated the association between a global DNA methylation index (GDMI), the allelic composition of the five energy balance and lipid metabolism-associated loci, and weight loss during a 12 month program, after controlling for age, sex and body mass index (BMI). The results demonstrated a significant association between the GDMI and near INSIG2 locus, after adjusting for BMI and weight loss, and significant trends were observed when stratifying by gender. In conclusion, a combination of genetic and epigenetic biomarkers may be used to design personalized weight loss interventions, enabling adherence and ensuring improved outcomes for obesity treatment programs. Precision weight loss programs designed based on molecular information may enable the creation of personalized interventions for patients, that use genomic biomarkers for treatment design and for treatment adherence monitoring, thus improving response to treatment.