Genome-wide survey reveals predisposing diabetes type 2-related DNA methylation variations in human peripheral blood

DNA methylation mediates development of HbA1c-associated complications in type 1 diabetes

Metabolic memory, the persistent benefits of early glycaemic control on preventing and/or delaying the development of diabetic complications, has been observed in the Diabetes Control and Complications Trial (DCCT) and in the Epidemiology of Diabetes Interventions and Complications (EDIC) follow-up study, but the underlying mechanisms remain unclear. Here, we show the involvement of epigenetic DNA methylation (DNAme) in metabolic memory by examining its associations with preceding glycaemic history, and with subsequent development of complications over an 18-yr period in the blood DNA of 499 randomly selected DCCT participants with type 1 diabetes who are also followed up in EDIC. We demonstrate the associations between DNAme near the closeout of DCCT and mean HbA1c during DCCT (mean-DCCT HbA1c) at 186 cytosine-guanine dinucleotides (CpGs) (FDR < 15%, including 43 at FDR < 5%), many of which were located in genes related to complications. Exploration studies into biological function reveal that these CpGs are enriched in binding sites for the C/EBP transcription factor, as well as enhancer/transcription regions in blood cells and haematopoietic stem cells, and open chromatin states in myeloid cells. Mediation analyses show that, remarkably, several CpGs in combination explain 68-97% of the association of mean-DCCT HbA1c with the risk of complications during EDIC. In summary, DNAme at key CpGs appears to mediate the association between hyperglycaemia and complications in metabolic memory, through modifying enhancer activity at myeloid and other cells.

The role of DNA methylation in the pathogenesis of type 2 diabetes mellitus

Diabetes mellitus (DM) is a chronic condition characterised by β cell dysfunction and persistent hyperglycaemia. The disorder can be due to the absence of adequate pancreatic insulin production or a weak cellular response to insulin signalling. Among the three types of DM, namely, type 1 DM (T1DM), type 2 DM (T2DM), and gestational DM (GDM); T2DM accounts for almost 90% of diabetes cases worldwide.

Epigenetic traits are stably heritable phenotypes that result from certain changes that affect gene function without altering the gene sequence. While epigenetic traits are considered reversible modifications, they can be inherited mitotically and meiotically. In addition, epigenetic traits can randomly arise in response to environmental factors or certain genetic mutations or lesions, such as those affecting the enzymes that catalyse the epigenetic modification. In this review, we focus on the role of DNA methylation, a type of epigenetic modification, in the pathogenesis of T2DM.

Disease Activity-Associated Alteration of mRNA m5 C Methylation in CD4+ T Cells of Systemic Lupus Erythematosus

Epigenetic processes including RNA methylation, post-translational modifications, and non-coding RNA expression have been associated with the heritable risks of systemic lupus erythematosus (SLE). In this study, we aimed to explore the dysregulated expression of 5-methylcytosine (m⁵C) in CD4⁺ T cells from patients with SLE and the potential function of affected mRNAs in SLE pathogenesis. mRNA methylation profiles were ascertained through chromatography-coupled triple quadrupole mass spectrometry in CD4⁺ T cells from two pools of patients with SLE exhibiting stable activity, two pools with moderate-to-major activity, and two pools of healthy controls (HCs). Simultaneously, mRNA methylation profiles and expression profiling were performed using RNA-Bis-Seq and RNA-Seq, respectively. Integrated mRNA methylation and mRNA expression bioinformatics analysis was comprehensively performed. mRNA methyltransferase NSUN2 expression was validated in CD4⁺ T cells from 27 patients with SLE and 28 HCs using real-time polymerase chain reaction and western blot analyses. Hypomethylated-mRNA profiles of NSUN2-knockdown HeLa cells and of CD4⁺ T cells of patients with SLE were jointly analyzed using bioinformatics. Eleven methylation modifications (including elevated Am, 3′OMeA, m¹A, and m⁶A and decreased Ψ, m³C, m¹G, m⁵U, and t⁶A levels) were detected in CD4⁺ T cells of patients with SLE. Additionally, decreased m⁵C levels, albeit increased number of m⁵C-containing mRNAs, were observed in CD4⁺ T cells of patients with SLE compared with that in CD4⁺ T cells of HCs. m⁵C site distribution in mRNA transcripts was highly conserved and enriched in mRNA translation initiation sites. In particular, hypermethylated m⁵C or/and significantly up-regulated genes in SLE were significantly involved in immune-related and inflammatory pathways, including immune system, cytokine signaling pathway, and interferon signaling. Compared to that in HCs, NSUN2 expression was significantly lower in SLE CD4⁺ T cells. Notably, hypomethylated m⁵C genes in SLE and in NSUN2-knockdown HeLa cells revealed linkage between eukaryotic translation elongation and termination, and mRNA metabolism. Our study identified novel aberrant m⁵C mRNAs relevant to critical immune pathways in CD4⁺ T cells from patients with SLE. These data provide valuable perspectives for future studies of the multifunctionality and post-transcriptional significance of mRNA m⁵C modification in SLE.

Dietary natural products as epigenetic modifiers in aging-associated inflammation and disease

Covering: up to 2020Chronic, low-grade inflammation is linked to aging and has been termed "inflammaging". Inflammaging is considered a key contributor to the development of metabolic dysfunction and a broad spectrum of diseases or disorders including declines in brain and heart function. Genome-wide association studies (GWAS) coupled with epigenome-wide association studies (EWAS) have shown the importance of diet in the development of chronic and age-related diseases. Moreover, dietary interventions e.g. caloric restriction can attenuate inflammation to delay and/or prevent these diseases. Common themes in these studies entail the use of phytochemicals (plant-derived compounds) or the production of short chain fatty acids (SCFAs) as epigenetic modifiers of DNA and histone proteins. Epigenetic modifications are dynamically regulated and as such, serve as potential therapeutic targets for the treatment or prevention of age-related disease. In this review, we will focus on the role for natural products that include phytochemicals and short chain fatty acids (SCFAs) as regulators of these epigenetic adaptations. Specifically, we discuss regulators of methylation, acetylation and acylation, in the protection from chronic inflammation driven metabolic dysfunction and deterioration of neurocognitive and cardiac function.

DNA Methylation Biomarkers in Aging and Age-Related Diseases

Recent research efforts provided compelling evidence of genome-wide DNA methylation alterations in aging and age-related disease. It is currently well established that DNA methylation biomarkers can determine biological age of any tissue across the entire human lifespan, even during development. There is growing evidence suggesting epigenetic age acceleration to be strongly linked to common diseases or occurring in response to various environmental factors. DNA methylation based clocks are proposed as biomarkers of early disease risk as well as predictors of life expectancy and mortality. In this review, we will summarize key advances in epigenetic clocks and their potential application in precision health. We will also provide an overview of progresses in epigenetic biomarker discovery in Alzheimer's, type 2 diabetes, and cardiovascular disease. Furthermore, we will highlight the importance of prospective study designs to identify and confirm epigenetic biomarkers of disease.

Epigenetic Profiling in Severe Sepsis: A Pilot Study of DNA Methylation Profiles in Critical Illness

OBJECTIVES

Epigenetic alterations are an important regulator of gene expression in health and disease; however, epigenetic data in sepsis are lacking. To demonstrate proof of concept and estimate effect size, we performed the first epigenome-wide methylation analysis of whole blood DNA samples from a cohort of septic and nonseptic critically ill patients.

DESIGN

A nested case-control study using genomic DNA isolated from whole blood from septic (n = 66) and nonseptic (n = 68) critically ill patients on "Day 1" of ICU admission. Methylation patterns were identified using Illumina 450K arrays with percent methylation expressed as β values. After quality control, 134 participants and 414,818 autosomal cytosine-phosphate-guanine sites were used for epigenome-wide methylation analyses.

SETTING

Tertiary care hospitals.

SUBJECTS

Critically ill septic and nonseptic patients.

INTERVENTIONS

Observational study.

MEASUREMENTS AND MAIN RESULTS

A total of 668 differentially methylated regions corresponding to 443 genes were identified. Known sepsis-associated genes included complement component 3; angiopoietin 2; myeloperoxidase; lactoperoxidase; major histocompatibility complex, class I, A; major histocompatibility complex, class II, isotype DR β I; major histocompatibility complex, class I, C; and major histocompatibility complex, class II, isotype DQ β I. When compared with whole blood gene expression data from seven external datasets containing septic and nonseptic patients, 81% of the differentially methylated region-associated genes were differentially expressed in one or more datasets and 31% in three or more datasets. Functional analysis showed enrichment for antigen processing and presentation, methyltransferase activity, cell adhesion, and cell junctions. Analysis by weighted gene coexpression network analysis revealed DNA comethylation modules that were associated with clinical traits including severity of illness, need for vasopressors, and length of stay.

CONCLUSIONS

DNA methylation marks may provide important causal and potentially biomarker information in critically ill patients with sepsis.

Insulin-resistance and depression cohort data mining to identify nutraceutical related DNA methylation biomarker for type 2 diabetes

Insulin-resistance (IR) is one of the most important precursors of type 2 diabetes (T2D). Recent evidence suggests an association of depression with the onset of T2D. Accumulating evidence shows that depression and T2D share common biological origins, and DNA methylation examination might reveal the link between lifestyle, disease risk, and potential therapeutic targets for T2D. Here we hypothesize that integrative mining of IR and depression cohort data will facilitate predictive biomarkers identification for T2D. We utilized a newly proposed method to extract gene-level information from probe level data on genome-wide DNA methylation array. We identified a set of genes associated with IR and depression in clinical cohorts. By overlapping the IR-related nutraceutical-gene network with depression networks, we identified a common subnetwork centered with Vitamin D Receptor (VDR) gene. Preliminary clinical validation of gene methylation set in a small cohort of T2D patients and controls was established using the Sequenome matrix-assisted laser desorption ionization-time flight mass spectrometry. A set of sites in the promoter regions of VDR showed a significant difference between T2D patients and controls. Using a logistic regression model, the optimal prediction performance of these sites was AUC = 0.902，and an odds ratio = 19.76. Thus, monitoring the methylation status of specific VDR promoter region might help stratify the high-risk individuals who could potentially benefit from vitamin D dietary supplementation. Our results highlight the link between IR and depression, and the DNA methylation analysis might facilitate the search for their shared mechanisms in the etiology of T2D.

The effects of bariatric surgery on clinical profile, DNA methylation, and ageing in severely obese patients

BACKGROUND

Severe obesity is a growing, worldwide burden and conventional therapies including radical change of diet and/or increased physical activity have limited results. Bariatric surgery has been proposed as an alternative therapy showing promising results. It leads to substantial weight loss and improvement of comorbidities such as type 2 diabetes. Increased adiposity is associated with changes in epigenetic profile, including DNA methylation. We investigated the effect of bariatric surgery on clinical profile, DNA methylation, and biological age estimated using Horvath's epigenetic clock.

RESULTS

To determine the impact of bariatric surgery and subsequent weight loss on clinical traits, a cohort of 40 severely obese individuals (BMI = 30-73 kg/m²) was examined at the time of surgery and at three follow-up visits, i.e., 3, 6, and 12 months after surgery. The majority of the individuals were women (65%) and the mean age at surgery was 45.1 ± 8.1 years. We observed a significant decrease over time in BMI, fasting glucose, HbA1c, HOMA-IR, insulin, total cholesterol, triglycerides, LDL and free fatty acids levels, and a significant small increase in HDL levels (all p values < 0.05). Epigenome-wide association analysis revealed 4857 differentially methylated CpG sites 12 months after surgery (at Bonferroni-corrected p value < 1.09 × 10^-7). Including BMI change in the model decreased the number of significantly differentially methylated CpG sites by 51%. Gene set enrichment analysis identified overrepresentation of multiple processes including regulation of transcription, RNA metabolic, and biosynthetic processes in the cell. Bariatric surgery in severely obese patients resulted in a decrease in both biological age and epigenetic age acceleration (EAA) (mean = - 0.92, p value = 0.039).

CONCLUSIONS

Our study shows that bariatric surgery leads to substantial BMI decrease and improvement of clinical outcomes observed 12 months after surgery. These changes explained part of the association between bariatric surgery and DNA methylation. We also observed a small, but significant improvement of biological age. These epigenetic changes may be modifiable by environmental lifestyle factors and could be used as potential biomarkers for obesity and in the future for obesity related comorbidities.

Changes in Body Composition and FTO Whole Blood DNA Methylation Among Japanese Women: A Randomized Clinical Trial of Weight-Loss Program

OBJECTIVE

DNA methylation is an epigenetic mechanism that regulates gene expression. The obesity-related (FTO) gene is the first gene found to be associated with fat mass and obesity. However, no studies have examined the relationship between weight-loss intervention effect and FTO methylation in obese individuals with whole blood DNA. The purpose of this study was to quantify FTO whole blood DNA methylation and investigate the relationship between body composition, exercise capacity, and blood parameters with a 6-month weight-loss program intervention.

PARTICIPANTS AND METHODS

Eighteen female participants (mean age, 50.6 ±12.1 years, body mass index (BMI), 33.5 ± 6.2 kg/m²) who completed a 6-month weight-loss program at the obesity outpatient department at the Health Science Center of Kansai Medical University Hospital from March 2017 to October 2018 were included in the analysis. Participants were randomized into a normal treatment group (NTG) and a group with additional resistance training (RTG). Body composition, exercise tolerance and metabolic index were measured in each participant. DNA methylation status in whole blood samples was determined using pyrosequencing. All measurements were taken during the first visit and at the 6-month post-intervention visit.

RESULTS

The methylation rate was significantly decreased in the NTG in CpG1 (p=0.011) and total value of CpG (p=0.011), whereas in the treatment group containing resistance training (RTG), CpG3 (p=0.038) was increased significantly. Furthermore, the independent factors that determine %CpG3 of RTG were visceral fat area change rate (%VFA) (β = -0.568, P = 0.007, R2 = 0.527) and resistance training (β = 0.517, P = 0.012, R2 = 0.527), which have been extracted.

CONCLUSION

A 6-month weight-loss program, including resistance training, may be associated with decreased visceral fat area changes and increased RTG CpG3 methylation changes. However, further replication studies with larger sample sizes are warranted to verify the findings of this study.

DNA methylation at LRP1 gene locus mediates the association between maternal total cholesterol changes in pregnancy and cord blood leptin levels

Placental lipids transfer is essential for optimal fetal development, and alterations of these mechanisms could lead to a higher risk of adverse birth outcomes. Low-density lipoprotein receptor (LDLR), LDL receptor-related protein 1 (LRP1), and scavenger receptor class B type 1 (SCARB1) genes are encoding lipoprotein receptors expressed in the placenta where they participate in cholesterol exchange from maternal to fetal circulation. The aim of this study was thus to investigate the association between maternal lipid changes occurring in pregnancy, placental DNA methylation (DNAm) variations at LDLR, LRP1, and SCARB1 gene loci, and newborn's anthropometric profile at birth. Sixty-nine normoglycemic women were followed from the first trimester of pregnancy until delivery. Placental DNAm was quantified at 43 Cytosine-phosphate-Guanines (CpGs) at LDLR, LRP1, and SCARB1 gene loci using pyrosequencing: 4 CpGs were retained for further analysis. Maternal clinical data were collected at each trimester of pregnancy. Newborns' data were collected from medical records. Statistical models included minimally newborn sex and gestational and maternal age. Maternal total cholesterol changes during pregnancy (ΔT3-T1) were correlated with DNAm variations at LDLR (r = -0.32, p = 0.01) and LRP1 (r = 0.34, p = 0.007). DNAm at these loci was also correlated with newborns' cord blood triglyceride and leptin levels. Mediation analysis supports a causal relationship between maternal cholesterol changes, DNAm levels at LRP1 locus, and cord blood leptin concentration (pmediation = 0.02). These results suggest that LRP1 DNAm link maternal blood cholesterol changes in pregnancy and offspring adiposity at birth, which provide support for a better follow-up of blood lipids in pregnancy.

DNA Methylation and Type 2 Diabetes: the Use of Mendelian Randomization to Assess Causality

Purpose of Review

This review summarises recent advances in the field of epigenetics in order to understand the aetiology of type 2 diabetes (T2D).

Recent Findings

DNA methylation at a number of loci has been shown to be robustly associated with T2D, including TXNIP, ABCG1, CPT1A, and SREBF1. However, due to the cross-sectional nature of many epidemiological studies and predominant analysis in samples derived from blood rather than disease relevant tissues, inferring causality is difficult. We therefore outline the use of Mendelian randomisation (MR) as one method able to assess causality in epigenetic studies of T2D.

Summary

Epidemiological studies have been fruitful in identifying epigenetic markers of T2D. Triangulation of evidence including utilisation of MR is essential to delineate causal from non-causal biomarkers of disease. Understanding the causality of epigenetic markers in T2D more fully will aid prioritisation of CpG sites as early biomarkers to detect disease or in drug development to target epigenetic mechanisms in order to treat patients.

A pilot study of peripheral blood DNA methylation models as predictors of knee osteoarthritis radiographic progression: data from the Osteoarthritis Initiative (OAI)

Knee osteoarthritis (OA) is a leading cause of chronic disability worldwide, but no diagnostic or prognostic biomarkers are available. Increasing evidence supports epigenetic dysregulation as a contributor to OA pathogenesis. In this pilot study, we investigated epigenetic patterns in peripheral blood mononuclear cells (PBMCs) as models to predict future radiographic progression in OA patients enrolled in the longitudinal Osteoarthritis Initiative (OAI) study. PBMC DNA was analyzed from baseline OAI visits in 58 future radiographic progressors (joint space narrowing at 24 months, sustained at 48 months) compared to 58 non-progressors. DNA methylation was quantified via Illumina microarrays and beta- and M-values were used to generate linear classification models. Data were randomly split into a 60% development and 40% validation subsets, models developed and tested, and cross-validated in a total of 40 cycles. M-value based models outperformed beta-value based models (ROC-AUC 0.81 ± 0.01 vs. 0.73 ± 0.02, mean ± SEM, comparison p = 0.002), with a mean classification accuracy of 73 ± 1% (mean ± SEM) for M- and 69 ± 1% for beta-based models. Adjusting for covariates did not significantly alter model performance. Our findings suggest that PBMC DNA methylation-based models may be useful as biomarkers of OA progression and warrant additional evaluation in larger patient cohorts.

Diabetes in pregnancy and epigenetic mechanisms-how the first 9 months from conception might affect the child's epigenome and later risk of disease

Diabetes in pregnancy is not only associated with increased risk of pregnancy complications and subsequent maternal metabolic disease, but also increases the risk of long-term metabolic disease in the offspring. At the interface between genetic and environmental factors, epigenetic variation established in utero represents a plausible link between the in utero environment and later disease susceptibility. The identification of an epigenetic fingerprint of diabetes in pregnancy linked to the metabolic health of the offspring might provide novel biomarkers for the identification of offspring most at risk, before the onset of metabolic dysfunction, for targeted monitoring and intervention. In this Personal View, we (1) highlight the scale of the problem of diabetes in pregnancy, (2) summarise evidence for the variation in offspring epigenetic profiles following exposure to diabetes in utero, and (3) outline potential future approaches to further understand the mechanisms by which exposure to maternal metabolic dysfunction in pregnancy is transmitted through generations.

The effect of age on DNA methylation in whole blood among Bangladeshi men and women

BACKGROUND

It is well-known that methylation changes occur as humans age, however, understanding how age-related changes in DNA methylation vary by sex is lacking. In this study, we characterize the effect of age on DNA methylation in a sex-specific manner and determine if these effects vary by genomic context. We used the Illumina HumanMethylation 450 K array and DNA derived from whole blood for 400 adult participants (189 males and 211 females) from Bangladesh to identify age-associated CpG sites and regions and characterize the location of these age-associated sites with respect to CpG islands (vs. shore, shelf, or open sea) and gene regions (vs. intergenic). We conducted a genome-wide search for age-associated CpG sites (among 423,604 sites) using a reference-free approach to adjust for cell type composition (the R package RefFreeEWAS) and performed an independent replication analysis of age-associated CpGs.

RESULTS

The number of age-associated CpGs (p < 5 x 10- 8) were 986 among men and 3479 among women of which 2027(63.8%) and 572 (64.1%) replicated (using Bonferroni adjusted p < 1.2 × 10- 5). For both sexes, age-associated CpG sites were more likely to be hyper-methylated with increasing age (compared to hypo-methylated) and were enriched in CpG islands and promoter regions compared with other locations and all CpGs on the array. Although we observed strong correlation between chronological age and previously-developed epigenetic age models (r ≈ 0.8), among our top (based on lowest p-value) age-associated CpG sites only 12 for males and 44 for females are included in these prediction models, and the median chronological age compared to predicted age was 44 vs. 51.7 in males and 45 vs. 52.1 in females.

CONCLUSIONS

Our results describe genome-wide features of age-related changes in DNA methylation. The observed associations between age and methylation were generally consistent for both sexes, although the associations tended to be stronger among women. Our population may have unique age-related methylation changes that are not captured in the established methylation-based age prediction model we used, which was developed to be non-tissue-specific.

Insights into the Role of DNA Methylation and Protein Misfolding in Diabetes Mellitus

Background:

Diabetes mellitus is a metabolic disorder that is characterized by impaired glucose tolerance resulting from defects in insulin secretion, insulin action, or both. Epigenetic modifications, which are defined as inherited changes in gene expression that occur without changes in gene sequence, are involved in the etiology of diabetes.

Methods:

In this review, we focused on the role of DNA methylation and protein misfolding and their contribution to the development of both type 1 and type 2 diabetes mellitus.

Results:

Changes in DNA methylation in particular are highly associated with the development of diabetes. Protein function is dependent on their proper folding in the endoplasmic reticulum. Defective protein folding and consequently their functions have also been reported to play a role. Early treatment of diabetes has proven to be of great benefit, as even transient hyperglycemia may lead to pathological effects and complications later on. This has been explained by the theory of the development of a metabolic memory in diabetes. The basis for this metabolic memory was attributed to oxidative stress, chronic inflammation, non-enzymatic glycation of proteins and importantly, epigenetic changes. This highlights the importance of linking new therapeutics targeting epigenetic mechanisms with traditional antidiabetic drugs.

Conclusion:

Although new data is evolving on the relation between DNA methylation, protein misfolding, and the etiology of diabetes, more studies are required for developing new relevant diagnostics and therapeutics.

Epigenetic disturbances in obesity and diabetes: Epidemiological and functional insights

BACKGROUND

Obesity and type 2 diabetes (T2D) are major public health issues worldwide, and put a significant burden on the healthcare system. Genetic variants, along with traditional risk factors such as diet and physical activity, could account for up to approximately a quarter of disease risk. Epigenetic factors have demonstrated potential in accounting for additional phenotypic variation, along with providing insights into the causal relationship linking genetic variants to phenotypes.

SCOPE OF REVIEW

In this review article, we discuss the epidemiological and functional insights into epigenetic disturbances in obesity and diabetes, along with future research directions and approaches, with a focus on DNA methylation.

MAJOR CONCLUSIONS

Epigenetic mechanisms have been shown to contribute to obesity and T2D disease development, as well as potential differences in disease risks between ethnic populations. Technology to investigate epigenetic profiles in diseased individuals and tissues has advanced significantly in the last years, and suggests potential in application of epigenetic factors in clinical monitoring and as therapeutic options.

Nutritional Factors, DNA Methylation, and Risk of Type 2 Diabetes and Obesity: Perspectives and Challenges

A healthy diet improves life expectancy and helps to prevent common chronic diseases such as type 2 diabetes (T2D) and obesity. The mechanisms driving these effects are not fully understood, but are likely to involve epigenetics. Epigenetic mechanisms control gene expression, maintaining the DNA sequence, and therefore the full genomic information inherited from our parents, unchanged. An interesting feature of epigenetic changes lies in their dynamic nature and reversibility. Accordingly, they are susceptible to correction through targeted interventions. Here we will review the evidence supporting a role for nutritional factors in mediating metabolic disease risk through DNA methylation changes. Special emphasis will be placed on the potential of using DNA methylation traits as biomarkers to predict risk of obesity and T2D as well as on their response to dietary and pharmacological (epi-drug) interventions.

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.

Epigenome-wide association study in whole blood on type 2 diabetes among sub-Saharan African individuals: findings from the RODAM study

BACKGROUND

Type 2 diabetes (T2D) results from a complex interplay between genetics and the environment. Several epigenome-wide association studies (EWAS) have found DNA methylation loci associated with T2D in European populations. However, data from African populations are lacking. We undertook the first EWAS for T2D among sub-Saharan Africans, aiming at identifying ubiquitous and novel DNA methylation loci associated with T2D.

METHODS

The Illumina 450k DNA-methylation array was used on whole blood samples of 713 Ghanaian participants (256 with T2D, 457 controls) from the cross-sectional Research on Obesity and Diabetes among African Migrants (RODAM) study. Differentially methylated positions (DMPs) for T2D and HbA1c were identified through linear regression analysis adjusted for age, sex, estimated cell counts, hybridization batch, array position and body mass index (BMI). We also did a candidate analysis of previously reported EWAS loci for T2D in non-African populations, identified through a systematic literature search.

RESULTS

Four DMPs [cg19693031 (TXNIP), cg04816311 (C7orf50), cg00574958 (CPT1A), cg07988171 (TPM4)] were associated with T2D after correction for inflation by possible systematic biases. The most strongly associated DMP-cg19693031, TXNIP (P = 2.6E-19) -showed hypomethylation in T2D cases compared with controls. Two out of the four DMPs [cg19693031 (TXNIP), cg04816311 (C7orf50)] remained associated with T2D after adjustment for BMI, and one locus [cg07988171 (TPM4)] that has not been reported previously.

CONCLUSIONS

In this first EWAS for T2D in sub-Saharan Africans, we have identified four DMPs at epigenome-wide level, one of which is novel. These findings provide insight into the epigenetic loci that underlie the burden of T2D in sub-Saharan Africans.

A Perception on Genome-Wide Genetic Analysis of Metabolic Traits in Arab Populations

Despite dedicated nation-wide efforts to raise awareness against the harmful effects of fast-food consumption and sedentary lifestyle, the Arab population continues to struggle with an increased risk for metabolic disorders. Unlike the European population, the Arab population lacks well-established genetic risk determinants for metabolic disorders, and the transferability of established risk loci to this population has not been satisfactorily demonstrated. The most recent findings have identified over 240 genetic risk loci (with ~400 independent association signals) for type 2 diabetes, but thus far only 25 risk loci (ADAMTS9, ALX4, BCL11A, CDKAL1, CDKN2A/B, COL8A1, DUSP9, FTO, GCK, GNPDA2, HMG20A, HNF1A, HNF1B, HNF4A, IGF2BP2, JAZF1, KCNJ11, KCNQ1, MC4R, PPARγ, SLC30A8, TCF7L2, TFAP2B, TP53INP1, and WFS1) have been replicated in Arab populations. To our knowledge, large-scale population- or family-based association studies are non-existent in this region. Recently, we conducted genome-wide association studies on Arab individuals from Kuwait to delineate the genetic determinants for quantitative traits associated with anthropometry, lipid profile, insulin resistance, and blood pressure levels. Although these studies led to the identification of novel recessive variants, they failed to reproduce the established loci. However, they provided insights into the genetic architecture of the population, the applicability of genetic models based on recessive mode of inheritance, the presence of genetic signatures of inbreeding due to the practice of consanguinity, and the pleiotropic effects of rare disorders on complex metabolic disorders. This perspective presents analysis strategies and study designs for identifying genetic risk variants associated with diabetes and related traits in Arab populations.

Novel positioning from obesity to cancer: FTO, an m6A RNA demethylase, regulates tumour progression

PURPOSE

The fat mass- and obesity-associated (FTO) gene on chromosome 16q12.2 shows an intimate association with obesity and body mass index. Recently, research into the FTO gene and its expression product has attracted widespread interest due to the identification of FTO as an N6-methyladenosine (m6A) demethylase. FTO primarily regulates the m6A levels of downstream targets via their 3' untranslated regions. FTO not only plays a critical role in obesity-related diseases but also is involved in the occurrence, development and prognosis of many types of cancer, such as acute myeloid leukaemia, glioblastoma and breast cancer. Currently, studies indicate that FTO is a crucial component of m6A modification, it regulates cancer stem cell function, and promotes the growth, self-renewal and metastasis of cancer cells. In this review, we summarized and analysed the data regarding the structural features and biological functions of FTO as well as its association with different cancers and possible molecular mechanisms.

METHODS

We systematically reviewed the related literatures regarding FTO and its demethylation activity in many pathologic and physiological processes, especially in cancer-related diseases based on PubMed databases in this article.

RESULTS

Mounting evidence indicated that FTO plays a critical role in occurrence, progression and treatment of various cancers, even acting as a cancer oncogene in acute myeloid leukaemia, research on which is no longer restricted to metabolic diseases such as obesity and diabetes.

CONCLUSION

Considering FTO's critical role in many diseases, FTO may become a new promising target for the diagnosis and treatment of various diseases in the near future, especially for specific types of cancers, such as acute myeloid leukaemia, glioblastoma and breast cancer.

Analysis of repeated leukocyte DNA methylation assessments reveals persistent epigenetic alterations after an incident myocardial infarction

Background

Most research into myocardial infarctions (MIs) have focused on preventative efforts. For survivors, the occurrence of an MI represents a major clinical event that can have long-lasting consequences. There has been little to no research into the molecular changes that can occur as a result of an incident MI. Here, we use three cohorts to identify epigenetic changes that are indicative of an incident MI and their association with gene expression and metabolomics.

Results

Using paired samples from the KORA cohort, we screened for DNA methylation loci (CpGs) whose change in methylation is potentially indicative of the occurrence of an incident MI between the baseline and follow-up exams. We used paired samples from the NAS cohort to identify 11 CpGs which were predictive in an independent cohort. After removing two CpGs associated with medication usage, we were left with an “epigenetic fingerprint” of MI composed of nine CpGs. We tested this fingerprint in the InCHIANTI cohort where it moderately discriminated incident MI occurrence (AUC = 0.61, P = 6.5 × 10⁻³). Returning to KORA, we associated the epigenetic fingerprint loci with cis-gene expression and integrated it into a gene expression-metabolomic network, which revealed links between the epigenetic fingerprint CpGs and branched chain amino acid (BCAA) metabolism.

Conclusions

There are significant changes in DNA methylation after an incident MI. Nine of these CpGs show consistent changes in multiple cohorts, significantly discriminate MI in independent cohorts, and were independent of medication usage. Integration with gene expression and metabolomics data indicates a link between MI-associated epigenetic changes and BCAA metabolism.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0588-7) contains supplementary material, which is available to authorized users.

Critical evaluation of linear regression models for cell-subtype specific methylation signal from mixed blood cell DNA

Epigenome-wide association studies seek to identify DNA methylation sites associated with clinical outcomes. Difference in observed methylation between specific cell-subtypes is often of interest; however, available samples often comprise a mixture of cells. To date, cell-subtype estimates have been obtained from mixed-cell DNA data using linear regression models, but the accuracy of such estimates has not been critically assessed. We evaluated linear regression performance for cell-subtype specific methylation estimation using a 450K methylation array dataset of both mixed-cell and cell-subtype sorted samples from six healthy males. CpGs associated with each cell-subtype were first identified using t-tests between groups of cell-subtype sorted samples. Subsequent reduced panels of reliably accurate CpGs were identified from mixed-cell samples using an accuracy heuristic (D). Performance was assessed by comparing cell-subtype specific estimates from mixed-cells with corresponding cell-sorted mean using the mean absolute error (MAE) and the Coefficient of Determination (R²). At the cell-subtype level, methylation levels at 3272 CpGs could be estimated to within a MAE of 5% of the expected value. The cell-subtypes with the highest accuracy were CD56⁺ NK (R² = 0.56) and CD8⁺T (R² = 0.48), where 23% of sites were accurately estimated. Hierarchical clustering and pathways enrichment analysis confirmed the biological relevance of the panels. Our results suggest that linear regression for cell-subtype specific methylation estimation is accurate only for some cell-subtypes at a small fraction of cell-associated sites but may be applicable to EWASs of disease traits with a blood-based pathology. Although sample size was a limitation in this study, we suggest that alternative statistical methods will provide the greatest performance improvements.

Combining DNA methylation and RNA sequencing data of cancer for supervised knowledge extraction

Background

In the Next Generation Sequencing (NGS) era a large amount of biological data is being sequenced, analyzed, and stored in many public databases, whose interoperability is often required to allow an enhanced accessibility. The combination of heterogeneous NGS genomic data is an open challenge: the analysis of data from different experiments is a fundamental practice for the study of diseases. In this work, we propose to combine DNA methylation and RNA sequencing NGS experiments at gene level for supervised knowledge extraction in cancer.

Methods

We retrieve DNA methylation and RNA sequencing datasets from The Cancer Genome Atlas (TCGA), focusing on the Breast Invasive Carcinoma (BRCA), the Thyroid Carcinoma (THCA), and the Kidney Renal Papillary Cell Carcinoma (KIRP). We combine the RNA sequencing gene expression values with the gene methylation quantity, as a new measure that we define for representing the methylation quantity associated to a gene. Additionally, we propose to analyze the combined data through tree- and rule-based classification algorithms (C4.5, Random Forest, RIPPER, and CAMUR).

Results

We extract more than 15,000 classification models (composed of gene sets), which allow to distinguish the tumoral samples from the normal ones with an average accuracy of 95%. From the integrated experiments we obtain about 5000 classification models that consider both the gene measures related to the RNA sequencing and the DNA methylation experiments.

Conclusions

We compare the sets of genes obtained from the classifications on RNA sequencing and DNA methylation data with the genes obtained from the integration of the two experiments. The comparison results in several genes that are in common among the single experiments and the integrated ones (733 for BRCA, 35 for KIRP, and 861 for THCA) and 509 genes that are in common among the different experiments. Finally, we investigate the possible relationships among the different analyzed tumors by extracting a core set of 13 genes that appear in all tumors. A preliminary functional analysis confirms the relation of part of those genes (5 out of 13 and 279 out of 509) with cancer, suggesting to focus further studies on the new individuated ones.

Electronic supplementary material

The online version of this article (10.1186/s13040-018-0184-6) contains supplementary material, which is available to authorized users.

Genome-wide methylation analysis identifies ELOVL5 as an epigenetic biomarker for the risk of type 2 diabetes mellitus

Genome-wide DNA methylation has been implicated in complex human diseases. Here, we identified epigenetic biomarkers for type 2 diabetes (T2D) underlying obesogenic environments. In a blood-based DNA methylation analysis of 11 monozygotic twins (MZTW) discordant for T2D, we discovered genetically independent candidate methylation sites. In a follow-up replication study (17 MZTW pairs) for external validation, we replicated the T2D-association at a novel CpG signal in the ELOVL fatty acid elongase 5 (ELOVL5) gene specific to T2D-discordant MZTW. For concordant DNA methylation signatures in tissues, we further confirmed that a CpG site (cg18681426) was associated with adipogenic differentiation between human preadipocytes and adipocytes isolated from the same biopsy sample. In addition, the ELOVL5 gene was significantly differentially expressed in adipose tissues from unrelated T2D patients and in human pancreatic islets. Our results demonstrate that blood-derived DNA methylation is associated with T2D risk as a proxy for cumulative epigenetic status in human adipose and pancreatic tissues. Moreover, ELOVL5 expression was increased in cellular and mouse models of induced obesity-related diabetes. These findings may provide new insights into epigenetic architecture by uncovering methylation-based biomarkers.

Molecular Biomarkers for Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is a growing public health problem worldwide. The condition is associated with perinatal complications and an increased risk for future metabolic disease in both mothers and their offspring. In recent years, molecular biomarkers received considerable interest as screening tools for GDM. The purpose of this review is to provide an overview of the current status of single-nucleotide polymorphisms (SNPs), DNA methylation, and microRNAs as biomarkers for GDM. PubMed, Scopus, and Web of Science were searched for articles published between January 1990 and August 2018. The search terms included “gestational diabetes mellitus”, “blood”, “single-nucleotide polymorphism (SNP)”, “DNA methylation”, and “microRNAs”, including corresponding synonyms and associated terms for each word. This review updates current knowledge of the candidacy of these molecular biomarkers for GDM with recommendations for future research avenues.

BayesCCE: a Bayesian framework for estimating cell-type composition from DNA methylation without the need for methylation reference

We introduce a Bayesian semi-supervised method for estimating cell counts from DNA methylation by leveraging an easily obtainable prior knowledge on the cell-type composition distribution of the studied tissue. We show mathematically and empirically that alternative methods which attempt to infer cell counts without methylation reference only capture linear combinations of cell counts rather than provide one component per cell type. Our approach allows the construction of components such that each component corresponds to a single cell type, and provides a new opportunity to investigate cell compositions in genomic studies of tissues for which it was not possible before.

Genome-wide DNA methylation analysis of human peripheral blood reveals susceptibility loci of diabetes-related hearing loss

Diabetes-related hearing loss (DRHL) is a complication of diabetes mellitus that is drawing more attention currently. DNA methylation has a critical role in the pathogenesis of type 2 diabetes mellitus (T2DM) and its complications. Therefore, we investigated the genome-wide DNA methylation of peripheral blood of T2DM patients with/without hearing loss in order to explore the susceptibility loci of DRHL. Between DRHL group and control group, 113 gene sites were identified to be differentially methylated regions (DMRs). Among 38 DMRs with whole samples, the classification accuracy is up to 90%. With alignment to T2DM susceptibility genes and deafness genes published, KCNJ11 was found to be the only overlapped gene. The DNA methylation level of KCNJ11 was associated with stroke (t = 2.595, p < 0.05), but not with diabetic nephropathy and diabetic retinopathy. The detective rate of distortion product otoacoustic emissions (DPOAE) from low to high frequencies (0.7-6 kHz) on the right ear was significantly correlated with the methylation level of KCNJ11. The auditory brainstem response (ABR) threshold on the right ear was also correlated (r = 0.678, p < 0.05). This DNA methylation profile indicates the susceptibility loci of DRHL. The potassium metabolism may have a critical role in the hearing loss caused by hyperglycemia.

Genome-wide analysis of DNA methylation in human peripheral leukocytes identifies potential biomarkers of nonalcoholic fatty liver disease

The aim of the present study was to uncover the role of leukocytic DNA methylation in the evaluation of nonalcoholic fatty liver disease (NAFLD). Patients with biopsy-proven NAFLD (n=35) and normal controls (n=30) were recruited from Chinese Han population. Their DNA methylation in peripheral leukocytes was subjected to genome-wide profiling. The association between differential methylation of CpG sites and NAFLD was further investigated on the basis of histopathological classification, bioinformatics, and pyrosequencing. A panel of 863 differentially methylated CpG sites dominated by global hypomethylation, characterized the NAFLD patients. Hypomethylated CpG sites of Acyl-CoA synthetase long-chain family member 4 (ACSL4) (cg15536552) and carnitine palmitoyltransferase 1C (CPT1C) (cg21604803) associated with the increased risk of NAFLD [cg15536552, odds ratio (OR): 11.44, 95% confidence interval (CI): 1.04‑125.37, P=0.046; cg21604803, OR: 6.57, 95% CI: 1.02-42.15, P=0.047] at cut-off β-values of <3.36 (ACSL4 cg15536552) and <3.54 (CPT1C cg21604803), respectively, after the adjustment of age, sex, body mass index (BMI) and homeostasis model assessment of insulin resistant (HOMA-IR). Their methylation levels also served as biomarkers of NAFLD (ACSL4 cg15536552, AUC: 0.80, 95% CI: 0.62-0.98, P=0.009; CPT1C cg21604803, AUC: 0.78, 95% CI: 0.65-0.91, P=0.001). Pathologically, lowered methylation level (β-values <3.26) of ACSL4 (cg15536552) conferred susceptibility to nonalcoholic steatohepatitis (NASH). Taken together, genome-wide hypomethylation of peripheral leukocytes may differentiate NAFLD patients from normal controls. The leukocytic hypomethylated ACSL4 (cg15536552) was suggested to be a biomarker for the pathological characteristics of NAFLD.

DNA methylation landscapes in the pathogenesis of type 2 diabetes mellitus

Although genetic variations and environmental factors are vital to the development and progression of type 2 diabetes mellitus (T2DM), emerging literature suggest that epigenetics, especially DNA methylation, play a key role in the pathogenesis of T2DM by affecting insulin secretion of pancreatic β cells and the body’s resistance to insulin. Previous studies have elucidated how DNA methylation interacted with various factors in T2DM pathogenesis. This review summarized the role of related methylation genes in insulin-sensitive organs, such as pancreatic islets, skeletal muscle, liver, brain and adipose tissue, as well as peripheral blood cells, comparing the tissue similarity and specificity of methylated genes, aiming at a better understanding of the pathogenesis of T2DM and providing new ideas for the personalized treatment of this metabolism-associated disease.

DNA methylation and the potential role of demethylating agents in prevention of progressive chronic kidney disease

Chronic kidney disease (CKD) is a global epidemic, and its major risk factors include obesity and type 2 diabetes. Obesity not only promotes metabolic dysregulation and the development of diabetic kidney disease but also may independently lead to CKD by a variety of mechanisms, including endocrine and metabolic dysfunction, inflammation, oxidative stress, altered renal hemodynamics, and lipotoxicity. Deleterious renal effects of obesity can also be transmitted from one generation to the next, and it is increasingly recognized that offspring of obese mothers are predisposed to CKD. Epigenetic modifications are changes that regulate gene expression without altering the DNA sequence. Of these, DNA methylation is the most studied. Epigenetic imprints, particularly DNA methylation, are laid down during critical periods of fetal development, and they may provide a mechanism by which maternal-fetal transmission of chronic disease occurs. Our current review explores the evidence for the role of DNA methylation in the development of CKD, diabetic kidney disease, diabetes, and obesity. DNA methylation has been implicated in renal fibrosis-the final pathophysiologic pathway in the development of end-stage kidney disease-which supports the notion that demethylating agents may play a potential therapeutic role in preventing development and progression of CKD.-Larkin, B. P., Glastras, S. J., Chen, H., Pollock, C. A., Saad, S. DNA methylation and the potential role of demethylating agents in prevention of progressive chronic kidney disease.

Profiling DNA methylation differences between inbred mouse strains on the Illumina Human Infinium MethylationEPIC microarray

The Illumina Infinium MethylationEPIC provides an efficient platform for profiling DNA methylation in humans at over 850,000 CpGs. Model organisms such as mice do not currently benefit from an equivalent array. Here we used this array to measure DNA methylation in mice. We defined probes targeting conserved regions and performed differential methylation analysis and compared between the array-based assay and affinity-based DNA sequencing of methyl-CpGs (MBD-seq) and reduced representation bisulfite sequencing. Mouse samples consisted of 11 liver DNA from two strains, C57BL/6J (B6) and DBA/2J (D2), that varied widely in age. Linear regression was applied to detect differential methylation. In total, 13,665 probes (1.6% of total probes) aligned to conserved CpGs. Beta-values (β-value) for these probes showed a distribution similar to that in humans. Overall, there was high concordance in methylation signal between the EPIC array and MBD-seq (Pearson correlation r = 0.70, p-value < 0.0001). However, the EPIC probes had higher quantitative sensitivity at CpGs that are hypo- (β-value < 0.3) or hypermethylated (β-value > 0.7). In terms of differential methylation, no EPIC probe detected a significant difference between age groups at a Benjamini-Hochberg threshold of 10%, and the MBD-seq performed better at detecting age-dependent change in methylation. However, the top most significant probe for age (cg13269407; uncorrected p-value = 1.8 x 10-5) is part of the clock CpGs used to estimate the human epigenetic age. For strain, 219 EPIC probes detected significant differential methylation (FDR cutoff 10%) with ~80% CpGs associated with higher methylation in D2. This higher methylation profile in D2 compared to B6 was also replicated by the MBD-seq data. To summarize, we found only a small subset of EPIC probes that target conserved sites. However, for this small subset the array provides a reliable assay of DNA methylation and can be effectively used to measure differential methylation in mice.

Dual Effect of IL-6 -174 G/C Polymorphism and Promoter Methylation in the Risk of Coronary Artery Disease Among South Indians

Inflammation plays an important role in the pathogenesis of atherosclerosis and coronary syndromes; moreover, various lines of evidence suggest that genetic factors do contribute to the risk of coronary artery disease (CAD). The proinflammatory cytokine IL-6 is a central mediator of inflammation associated with CAD. The present study is aimed to investigate the association of single nucleotide polymorphism in the promoter region of the IL-6 gene (-174 G > C) and methylation with the susceptibility of CAD. Genotyping of IL-6 -174 G/C polymorphism was performed by PCR-RFLP. Methylation-specific PCR method was used to study the IL-6 gene promoter methylation. Analysis of 470 subjects (265 CAD patients and 205 controls) showed association of the -174 G/C variant with the CAD risk in dominant model (OR 1.58, 95% CI, 1.024-2.23, P = 0.04). Further, the analysis of the distribution of genotypes and alleles of -174 G > C polymorphism according to clinical features of CAD, revealed significant association of genotype and allele (OR 1.86, 95% CI 1.18-2.84 P = 0.01, and OR 1.71, 95% CI 1.09-2.23 P = 0.02 respectively) with diabetes, and we found no association with hypertension (OR 0.95, 95% CI 0.57-1.59, P = 0.8). We also analyzed the methylation status of IL-6 promoter region between cases and controls showed significant hypo methylation in CAD subjects (OR 2.36, 95% CI 1.51-4.259, P = 0.006). Additionally, GC, CC genotypes and C allele carriers show hypomethylation in CAD cases compared to controls (54.58 vs. 76.85%, 29.83 vs. 40% respectively). In conclusion, the promoter polymorphism -174 G/C is associated with CAD risk and further carriers of 'C' allele at -174 locus showed significant hypo methylation which could contribute to increased risk of CAD. The present study highlights the association of allele and genotypes with differential DNA methylation of CpG islands in the IL-6 promoter region which may affect IL-6 gene regulation.

DNA methylation markers associated with type 2 diabetes, fasting glucose and HbA1c levels: a systematic review and replication in a case-control sample of the Lifelines study

AIMS/HYPOTHESIS

Epigenetic mechanisms may play an important role in the aetiology of type 2 diabetes. Recent epigenome-wide association studies (EWASs) identified several DNA methylation markers associated with type 2 diabetes, fasting glucose and HbA_1c levels. Here we present a systematic review of these studies and attempt to replicate the CpG sites (CpGs) with the most significant associations from these EWASs in a case-control sample of the Lifelines study.

METHODS

We performed a systematic literature search in PubMed and EMBASE for EWASs to test the association between DNA methylation and type 2 diabetes and/or glycaemic traits and reviewed the search results. For replication purposes we selected 100 unique CpGs identified in peripheral blood, pancreas, adipose tissue and liver from 15 EWASs, using study-specific Bonferroni-corrected significance thresholds. Methylation data (Illumina 450K array) in whole blood from 100 type 2 diabetic individuals and 100 control individuals from the Lifelines study were available. Multivariate linear models were used to examine the associations of the specific CpGs with type 2 diabetes and glycaemic traits.

RESULTS

From the 52 CpGs identified in blood and selected for replication, 15 CpGs showed nominally significant associations with type 2 diabetes in the Lifelines sample (p < 0.05). The results for five CpGs (in ABCG1, LOXL2, TXNIP, SLC1A5 and SREBF1) remained significant after a stringent multiple-testing correction (changes in methylation from -3% up to 3.6%, p < 0.0009). All associations were directionally consistent with the original EWAS results. None of the selected CpGs from the tissue-specific EWASs were replicated in our methylation data from whole blood. We were also unable to replicate any of the CpGs associated with HbA_1c levels in the healthy control individuals of our sample, while two CpGs (in ABCG1 and CCDC57) for fasting glucose were replicated at a nominal significance level (p < 0.05).

CONCLUSIONS/INTERPRETATION

A number of differentially methylated CpGs reported to be associated with type 2 diabetes in the EWAS literature were replicated in blood and show promise for clinical use as disease biomarkers. However, more prospective studies are needed to support the robustness of these findings.

Epigenetic Signature of Impaired Fasting Glucose in the Old Order Amish

Introduction

Type 2 Diabetes (T2D) is a common chronic disease with substantial disease burden and economic impact. Lifestyle changes can significantly alter the course of the disease, if detected at an early stage. DNA methylation signature may serve as a biomarker for early detection of increased T2D risk.

Design

DNA methylation profiling was performed using the Illumina Infinium Human Methylation 450K Bead chip array in 24 normoglycemic Old Order Amish (OOA) individuals who later developed Impaired Fasting Glucose (IFG) (cases), and 24 OOA individuals who remained normoglycemic after an average follow up of 10 years (controls). Cases and controls were matched on age, sex, BMI, baseline fasting glucose, and glucose level after 2 h from 75 g Oral Glucose Tolerance Test (OGTT).

Results

Association analysis found no significant difference in either global methylation or individual probe methylation between cases and controls, however, the top 34 suggestive significant sites were located in genes with interesting biological links to T2D and glycemic traits. These genes include BTC that plays a role in pancreatic cell proliferation and insulin secretion, ITGA1 a known bone mineral density gene that was recently found to be associated also with T2D and glycemic traits, and may explain the link between T2D and BMD, and RPTOR and TSC2 both of which are part of insulin signaling pathway.

Conclusions

These results may shed light on the initiation and development of hyperglycemia and T2D and help to identify high risk individuals for early intervention; however, further studies are required for validation.

Blood-Based DNA Methylation Biomarkers for Type 2 Diabetes: Potential for Clinical Applications

Type 2 diabetes (T2D) is a leading cause of death and disability worldwide. It is a chronic metabolic disorder that develops due to an interplay of genetic, lifestyle, and environmental factors. The biological onset of the disease occurs long before clinical symptoms develop, thus the search for early diagnostic and prognostic biomarkers, which could facilitate intervention strategies to prevent or delay disease progression, has increased considerably in recent years. Epigenetic modifications represent important links between genetic, environmental and lifestyle cues and increasing evidence implicate altered epigenetic marks such as DNA methylation, the most characterized and widely studied epigenetic mechanism, in the pathogenesis of T2D. This review provides an update of the current status of DNA methylation as a biomarker for T2D. Four databases, Scopus, Pubmed, Cochrane Central, and Google Scholar were searched for studies investigating DNA methylation in blood. Thirty-seven studies were identified, and are summarized with respect to population characteristics, biological source, and method of DNA methylation quantification (global, candidate gene or genome-wide). We highlight that differential methylation of the TCF7L2, KCNQ1, ABCG1, TXNIP, PHOSPHO1, SREBF1, SLC30A8, and FTO genes in blood are reproducibly associated with T2D in different population groups. These genes should be prioritized and replicated in longitudinal studies across more populations in future studies. Finally, we discuss the limitations faced by DNA methylation studies, which include including interpatient variability, cellular heterogeneity, and lack of accounting for study confounders. These limitations and challenges must be overcome before the implementation of blood-based DNA methylation biomarkers into a clinical setting. We emphasize the need for longitudinal prospective studies to support the robustness of the current findings of this review.

C.7van MeursJoyce8IsaacsAaron9JansenRick10FrankeLude11BoomsmaDorret I.12PoolRené12van DongenJenny12HottengaJouke J.12van GreevenbroekMarleen MJ13StehouwerCoen D. A.13van der KallenCarla J. H.13SchalkwijkCasper G.13WijmengaCisca11FrankeLude11ZhernakovaSasha11TigchelaarEttje F.11SlagboomP. Eline6BeekmanMarian6DeelenJoris6van HeemstDiana14VeldinkJan H.15van den BergLeonard H.15van DuijnCornelia M.9HofmanBert A.16IsaacsAaron9UitterlindenAndré G.8van MeursJoyce8JhamaiP. Mila8VerbiestMichael8SuchimanH. Eka D.6VerkerkMarijn8van der BreggenRuud6van RooijJeroen8LakenbergNico6MeiHailiang17van ItersonMaarten6van GalenMichiel7BotJan18ZhernakovaDasha V.11JansenRick10van’t HofPeter17DeelenPatrick11NoorenIrene18’t HoenPeter A. C.7HeijmansBastiaan T.6MoedMatthijs6FrankeLude11VermaatMartijn7ZhernakovaDasha V.11LuijkRené6BonderMarc Jan11van ItersonMaarten6DeelenPatrick11van DijkFreerk19van GalenMichiel7ArindrartoWibowo17KielbasaSzymon M.20SwertzMorris A.19van ZwetErik W.20JansenRick10HoenPeter-Bram’t7HeijmansBastiaan T.6. DNA methylation signatures of educational attainment

Educational attainment is a key behavioural measure in studies of cognitive and physical health, and socioeconomic status. We measured DNA methylation at 410,746 CpGs (N = 4152) and identified 58 CpGs associated with educational attainment at loci characterized by pleiotropic functions shared with neuronal, immune and developmental processes. Associations overlapped with those for smoking behaviour, but remained after accounting for smoking at many CpGs: Effect sizes were on average 28% smaller and genome-wide significant at 11 CpGs after adjusting for smoking and were 62% smaller in never smokers. We examined sources and biological implications of education-related methylation differences, demonstrating correlations with maternal prenatal folate, smoking and air pollution signatures, and associations with gene expression in cis, dynamic methylation in foetal brain, and correlations between blood and brain. Our findings show that the methylome of lower-educated people resembles that of smokers beyond effects of their own smoking behaviour and shows traces of various other exposures.

The effects of DNA methylation on human psychology

DNA methylation is a fundamental epigenetic modification in the human genome; pivotal in development, genomic imprinting, X inactivation, chromosome stability, gene expression and methylation aberrations are involved in an array of human diseases. Methylation at promoters is associated with transcriptional repression, whereas gene body methylation is generally associated with gene expression. Extrinsic factors such as age, diets and lifestyle affect DNA methylation which consequently alters gene expression. Stress, anxiety, depression, life satisfaction, emotion among numerous other psychological factors also modify DNA methylation patterns. This correlation is frequently investigated in four candidate genes; NR3C1, SLC6A4, BDNF and OXTR, since regulation of these genes directly impact responses to social situations, stress, threats, behaviour and neural functions. Such studies underpin the hypothesis that DNA methylation is involved in deviant human behaviour, psychological and psychiatric conditions. These candidate genes may be targeted in future to assess the correlation between methylation, social experiences and long-term behavioural phenotypes in humans; and may potentially serve as biomarkers for therapeutic intervention.

Personalized epigenetic management of diabetes

The novel genome-wide assays of epigenetic marks have resulted in a greater understanding of how genetics and the environment interact in the development and inheritance of diabetes. Chronic hyperglycemia induces epigenetic changes in multiple organs, contributing to diabetic complications. Specific epigenetic-modifying compounds have been developed to erase these modifications, possibly slowing down the onset of diabetes-related complications. The current review is an update of the previously published paper, describing the most recent advances in the epigenetics of diabetes.

Connecting the Dots Between Fatty Acids, Mitochondrial Function, and DNA Methylation in Atherosclerosis

PURPOSE OF REVIEW

The quest for factors and mechanisms responsible for aberrant DNA methylation in human disease-including atherosclerosis-is a promising area of research. This review focuses on the role of fatty acids (FAs) as modulators of DNA methylation-in particular the role of mitochondrial beta-oxidation in FA-induced changes in DNA methylation during the progression of atherosclerosis.

RECENT FINDINGS

Recent publications have advanced the knowledge in all areas touched by this review: the causal role of lipids in shaping the DNA methylome, the associations between chronic degenerative disease and mitochondrial function, the lipid composition of the atheroma, and the relevance of DNA hypermethylation in atherosclerosis. Evidence is beginning to emerge, linking the dynamics of FA type abundance, mitochondrial function, and DNA methylation in the atheroma and systemically. In particular, this review highlights mitochondrial beta-oxidation as an important regulator of DNA methylation in metabolic disease. Despite the many questions still unanswered, this area of research promises to identify mechanisms and molecular factors that establish a pathological gene expression pattern in atherosclerosis.

DNA methylation of candidate genes in peripheral blood from patients with type 2 diabetes or the metabolic syndrome

INTRODUCTION

The prevalence of type 2 diabetes (T2D) and the metabolic syndrome (MetS) is increasing and several studies suggested an involvement of DNA methylation in the development of these metabolic diseases. This study was designed to investigate if differential DNA methylation in blood can function as a biomarker for T2D and/or MetS.

METHODS

Pyrosequencing analyses were performed for the candidate genes KCNJ11, PPARγ, PDK4, KCNQ1, SCD1, PDX1, FTO and PEG3 in peripheral blood leukocytes (PBLs) from 25 patients diagnosed with only T2D, 9 patients diagnosed with T2D and MetS and 11 control subjects without any metabolic disorders.

RESULTS

No significant differences in gene-specific methylation between patients and controls were observed, although a trend towards significance was observed for PEG3. Differential methylation was observed between the groups in 4 out of the 42 single CpG loci located in the promoters regions of the genes FTO, KCNJ11, PPARγ and PDK4. A trend towards a positive correlation was observed for PEG3 methylation with HDL cholesterol levels.

DISCUSSION

Altered levels of DNA methylation in PBLs of specific loci might serve as a biomarker for T2D or MetS, although further investigation is required.

rs9939609 FTO genotype associations with FTO methylation level influences body mass and telomere length in an Australian rural population

BACKGROUND

The fat mass- and obesity-associated (FTO) gene influences energy homeostasis in humans. Although the obesity-related variant, rs9939609 has been replicated across a number of cohort studies, there remains significant variance and a low to modest association. Telomere length is another commonly reported obesity risk factor. We hypothesize understanding the associations between FTO rs9939609 with FTO methylation and telomere length will provide a more accurate assessment of obesity risk.

METHODS

Overall, 942 participants free of diabetes or pre-diabetes were included in the retrospective study. Leukocyte genomic DNA was analyzed for rs9939609 genotyping, FTO gene methylation and leukocyte telomere length (LTL) measurement.

RESULTS

In general linear models, rs9939609 AA genotypes were associated with increased fat percentage (3.15%, P=0.001), fat mass (4.16 kg, P=0.001), body mass index (BMI) (1.38, P=0.006) and waist circumference (3.35 cm, P=0.006), but not with FTO methylation or LTL in this overall population. However, when participants were stratified into higher and lower FTO methylation groups, the AA genotype possesses a 2.04-fold increased obesity risk in comparison to TT genotype (95%CI, 1.07-3.89, P=0.031) in participants with a higher FTO methylation level, but this association was absent in the lower FTO methylation sub-group. Moreover, AT and AA genotype carriers were associated with shorter LTL compared to TT carriers (P=0.020 and P=0.111, respectively) in the higher FTO methylation level group. However, this association was absent in the lower methylation group. Furthermore, FTO gene methylation level was significantly associated with LTL in the 942 samples (P=0.017).

CONCLUSIONS

FTO rs9939609 is associated with obesity risk and LTL in this study, where this association is only observed at higher, but not lower, FTO methylation levels of participants. Our data suggest association of multiple factors, including FTO methylation level, may be involved in one of several mechanisms underlying the commonly reported obesity risk of this FTO polymorphism.

Genome-Wide Methylation Analysis Identifies Specific Epigenetic Marks In Severely Obese Children

Obesity is a heterogeneous disease with many different subtypes. Epigenetics could contribute to these differences. The aim of this study was to investigate genome-wide DNA methylation searching for methylation marks associated with obesity in children and adolescents. We studied DNA methylation profiles in whole blood cells from 40 obese children and controls using Illumina Infinium HumanMethylation450 BeadChips. After correction for cell heterogeneity and multiple tests, we found that compared to lean controls, 31 CpGs are differentially methylated in obese patients. A greatest proportion of these CpGs is hypermethylated in obesity and located in CpG shores regions. We next focused on severely obese children and identified 151 differentially methylated CpGs among which 10 with a difference in methylation greater than 10%. The top pathways enriched among the identified CpGs included the "IRS1 target genes" and several pathways in cancer diseases. This study represents the first effort to search for differences in methylation in obesity and severe obesity, which may help understanding these different forms of obesity and their complications.

Genome-wide physical activity interactions in adiposity - A meta-analysis of 200,452 adults

Physical activity (PA) may modify the genetic effects that give rise to increased risk of obesity. To identify adiposity loci whose effects are modified by PA, we performed genome-wide interaction meta-analyses of BMI and BMI-adjusted waist circumference and waist-hip ratio from up to 200,452 adults of European (n = 180,423) or other ancestry (n = 20,029). We standardized PA by categorizing it into a dichotomous variable where, on average, 23% of participants were categorized as inactive and 77% as physically active. While we replicate the interaction with PA for the strongest known obesity-risk locus in the FTO gene, of which the effect is attenuated by ~30% in physically active individuals compared to inactive individuals, we do not identify additional loci that are sensitive to PA. In additional genome-wide meta-analyses adjusting for PA and interaction with PA, we identify 11 novel adiposity loci, suggesting that accounting for PA or other environmental factors that contribute to variation in adiposity may facilitate gene discovery.

Specific CpG hyper-methylation leads to Ankrd26 gene down-regulation in white adipose tissue of a mouse model of diet-induced obesity

Epigenetic modifications alter transcriptional activity and contribute to the effects of environment on the individual risk of obesity and Type 2 Diabetes (T2D). Here, we have estimated the in vivo effect of a fat-enriched diet (HFD) on the expression and the epigenetic regulation of the Ankyrin repeat domain 26 (Ankrd26) gene, which is associated with the onset of these disorders. In visceral adipose tissue (VAT), HFD exposure determined a specific hyper-methylation of Ankrd26 promoter at the −436 and −431 bp CpG sites (CpGs) and impaired its expression. Methylation of these 2 CpGs impaired binding of the histone acetyltransferase/transcriptional coactivator p300 to this same region, causing hypo-acetylation of histone H4 at the Ankrd26 promoter and loss of binding of RNA Pol II at the Ankrd26 Transcription Start Site (TSS). In addition, HFD increased binding of DNA methyl-transferases (DNMTs) 3a and 3b and methyl-CpG-binding domain protein 2 (MBD2) to the Ankrd26 promoter. More importantly, Ankrd26 down-regulation enhanced secretion of pro-inflammatory mediators by 3T3-L1 adipocytes as well as in human sera. Thus, in mice, the exposure to HFD induces epigenetic silencing of the Ankrd26 gene, which contributes to the adipose tissue inflammatory secretion profile induced by high-fat regimens.

DNA methylation at modifier genes of lung disease severity is altered in cystic fibrosis

Background

Lung disease progression is variable among cystic fibrosis (CF) patients and depends on DNA mutations in the CFTR gene, polymorphic variations in disease modifier genes, and environmental exposure. The contribution of genetic factors has been extensively investigated, whereas the mechanism whereby environmental factors modulate the lung disease is unknown. In this project, we hypothesized that (i) reiterative stress alters the epigenome in CF-affected tissues and (ii) DNA methylation variations at disease modifier genes modulate the lung function in CF patients.

Results

We profiled DNA methylation at CFTR, the disease-causing gene, and at 13 lung modifier genes in nasal epithelial cells and whole blood samples from 48 CF patients and 24 healthy controls. CF patients homozygous for the p.Phe508del mutation and ≥18-year-old were stratified according to the lung disease severity. DNA methylation was measured by bisulfite and next-generation sequencing. The DNA methylation profile allowed us to correctly classify 75% of the subjects, thus providing a CF-specific molecular signature. Moreover, in CF patients, DNA methylation at specific genes was highly correlated in the same tissue sample. We suggest that gene methylation in CF cells may be co-regulated by disease-specific trans-factors. Three genes were differentially methylated in CF patients compared with controls and/or in groups of pulmonary severity: HMOX1 and GSTM3 in nasal epithelial samples; HMOX1 and EDNRA in blood samples. The association between pulmonary severity and DNA methylation at EDNRA was confirmed in blood samples from an independent set of CF patients. Also, lower DNA methylation levels at GSTM3 were associated with the GSTM3*B allele, a polymorphic 3-bp deletion that has a protective effect in cystic fibrosis.

Conclusions

DNA methylation levels are altered in nasal epithelial and blood cell samples from CF patients. Analysis of CFTR and 13 lung disease modifier genes shows DNA methylation changes of small magnitude: some of them are a consequence of the disease; other changes may result in small expression variations that collectively modulate the lung disease severity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0300-8) contains supplementary material, which is available to authorized users.