Genome-wide peripheral blood leukocyte DNA methylation microarrays identified a single association with inflammatory bowel diseases

Epigenetic alterations in inflammatory bowel disease and cancer

Overwhelming evidences supports the idea that inflammatory bowel disease (IBD) is caused by a complex interplay between genetic alterations of multiple genes and an aberrant interaction with environmental factors. There is growing evidence that epigenetic factors can play a significant part in the pathogenesis of IBD. Significant effort has been invested in uncovering genetic and epigenetic factors, which may increase the risk of IBD, but progress has been slow, and few IBD-specific factors have been detected so far. It has been known for decades that DNA methylation is the most well studied epigenetic modification, and analysis of DNA methylation is leading to a new generation of cancer biomarkers. Therefore, in this review, we summarize the role of DNA methylation alteration in IBD pathogenesis, and discuss specific genes or genetic loci using recent molecular technology advances. Here, we suggest that DNA methylation should be studied in depth to understand the molecular pathways of IBD pathogenesis, and discuss epigenetic studies of IBD that may have a significant impact on the field of IBD research.

Two-stage genome-wide methylation profiling in childhood-onset Crohn's Disease implicates epigenetic alterations at the VMP1/MIR21 and HLA loci

BACKGROUND

As a result of technological and analytical advances, genome-wide characterization of key epigenetic alterations is now feasible in complex diseases. We hypothesized that this may provide important insights into gene-environmental interactions in Crohn's disease (CD) and is especially pertinent to early onset disease.

METHODS

The Illumina 450K platform was applied to assess epigenome-wide methylation profiles in circulating leukocyte DNA in discovery and replication pediatric CD cohorts and controls. Data were corrected for differential leukocyte proportions. Targeted replication was performed in adults using pyrosequencing. Methylation changes were correlated with gene expression in blood and intestinal mucosa.

RESULTS

We identified 65 individual CpG sites with methylation alterations achieving epigenome-wide significance after Bonferroni correction (P < 1.1 × 10(-7)), and 19 differently methylated regions displaying unidirectional methylation change. There was a highly significant enrichment of methylation changes around GWAS single nucleotide polymorphisms (P = 3.7 × 10(-7)), notably the HLA region and MIR21. Two-locus discriminant analysis in the discovery cohort predicted disease in the pediatric replication cohort with high accuracy (area under the curve, 0.98). The findings strongly implicate the transcriptional start site of MIR21 as a region of extended epigenetic alteration, containing the most significant individual probes (P = 1.97 × 10(-15)) within a GWAS risk locus. In extension studies, we confirmed hypomethylation of MIR21 in adults (P = 6.6 × 10(-5), n = 172) and show increased mRNA expression in leukocytes (P < 0.005, n = 66) and in the inflamed intestine (P = 1.4 × 10(-6), n = 99).

CONCLUSIONS

We demonstrate highly significant and replicable differences in DNA methylation in CD, defining the disease-associated epigenome. The data strongly implicate known GWAS loci, with compelling evidence implicating MIR21 and the HLA region.

DNA methylation age of human tissues and cell types

Background

It is not yet known whether DNA methylation levels can be used to accurately predict age across a broad spectrum of human tissues and cell types, nor whether the resulting age prediction is a biologically meaningful measure.

Results

I developed a multi-tissue predictor of age that allows one to estimate the DNA methylation age of most tissues and cell types. The predictor, which is freely available, was developed using 8,000 samples from 82 Illumina DNA methylation array datasets, encompassing 51 healthy tissues and cell types. I found that DNA methylation age has the following properties: first, it is close to zero for embryonic and induced pluripotent stem cells; second, it correlates with cell passage number; third, it gives rise to a highly heritable measure of age acceleration; and, fourth, it is applicable to chimpanzee tissues. Analysis of 6,000 cancer samples from 32 datasets showed that all of the considered 20 cancer types exhibit significant age acceleration, with an average of 36 years. Low age-acceleration of cancer tissue is associated with a high number of somatic mutations and TP53 mutations, while mutations in steroid receptors greatly accelerate DNA methylation age in breast cancer. Finally, I characterize the 353 CpG sites that together form an aging clock in terms of chromatin states and tissue variance.

Conclusions

I propose that DNA methylation age measures the cumulative effect of an epigenetic maintenance system. This novel epigenetic clock can be used to address a host of questions in developmental biology, cancer and aging research.

Who should receive biologic therapy for IBD?: The rationale for the application of a personalized approach

The therapeutic approach in inflammatory bowel disease has evolved to target end-organ inflammation to heal intestinal mucosa and avoid structural damage. Objective therapeutic monitoring is required to achieve this goal. Earlier intervention with biologic therapy has been shown, indirectly, to be associated with higher clinical response and remission rates. A personalized approach to risk stratification with consideration of key clinical factors and inflammatory biomarker concentrations is recommended when deciding whether or not to start a patient on biologic therapy.

Linking immunity, epigenetics, and cancer in inflammatory bowel disease

Most of what is known about the pathogenesis of inflammatory bowel disease (IBD) pertains to complex interplay between host genetics, immunity, and environmental factors. Epigenetic modifications play pivotal roles in intestinal immunity and mucosal homeostasis as well as mediating gene-environment interactions. In this article, we provide a historical account of epigenetic research either directly related or pertinent to the pathogenesis and management of IBD. We further collate emerging evidence supporting roles for epigenetic mechanisms in relevant aspects of IBD biology, including deregulated immunity, host-pathogen recognition and mucosal integrity. Finally, we highlight key epigenetic mechanisms that link chronic inflammation to specific IBD comorbidities, including colitis-associated cancer and discuss their potential utility as novel biomarkers or pharmacologic targets in IBD therapy.

Systems biology in inflammatory bowel diseases: ready for prime time

PURPOSE OF REVIEW

Ulcerative colitis and Crohn's disease are the two predominant types of inflammatory bowel disease (IBD), affecting over 1.4 million individuals in the United States. IBD results from complex interactions between pathogenic components, including genetic and epigenetic factors, the immune response, and the microbiome, through an unknown sequence of events. The purpose of this review is to describe a systems biology approach to IBD as a novel and exciting methodology aiming at developing novel IBD therapeutics based on the integration of molecular and cellular 'omics' data.

RECENT FINDINGS

Recent evidence suggested the presence of genetic, epigenetic, transcriptomic, proteomic, and metabolomic alterations in IBD patients. Furthermore, several studies have shown that different cell types including fibroblasts, epithelial, immune, and endothelial cells together with the intestinal microbiota are involved in IBD pathogenesis. Novel computational methodologies have been developed aiming to integrate high-throughput molecular data.

SUMMARY

A systems biology approach could potentially identify the central regulators (hubs) in the IBD interactome and improve our understanding of the molecular mechanisms involved in IBD pathogenesis. The future IBD therapeutics should be developed on the basis of targeting the central hubs in the IBD network.

DNA methylation-associated colonic mucosal immune and defense responses in treatment-naïve pediatric ulcerative colitis

Inflammatory bowel diseases (IBD) are emerging globally, indicating that environmental factors may be important in their pathogenesis. Colonic mucosal epigenetic changes, such as DNA methylation, can occur in response to the environment and have been implicated in IBD pathology. However, mucosal DNA methylation has not been examined in treatment-naïve patients. We studied DNA methylation in untreated, left sided colonic biopsy specimens using the Infinium HumanMethylation450 BeadChip array. We analyzed 22 control (C) patients, 15 untreated Crohn’s disease (CD) patients, and 9 untreated ulcerative colitis (UC) patients from two cohorts. Samples obtained at the time of clinical remission from two of the treatment-naïve UC patients were also included into the analysis. UC-specific gene expression was interrogated in a subset of adjacent samples (5 C and 5 UC) using the Affymetrix GeneChip PrimeView Human Gene Expression Arrays. Only treatment-naïve UC separated from control. One-hundred-and-twenty genes with significant expression change in UC (> 2-fold, P &lt; 0.05) were associated with differentially methylated regions (DMRs). Epigenetically associated gene expression changes (including gene expression changes in the IFITM1, ITGB2, S100A9, SLPI, SAA1, and STAT3 genes) were linked to colonic mucosal immune and defense responses. These findings underscore the relationship between epigenetic changes and inflammation in pediatric treatment-naïve UC and may have potential etiologic, diagnostic, and therapeutic relevance for IBD.

Accounting for cellular heterogeneity is critical in epigenome-wide association studies

Background

Epigenome-wide association studies of human disease and other quantitative traits are becoming increasingly common. A series of papers reporting age-related changes in DNA methylation profiles in peripheral blood have already been published. However, blood is a heterogeneous collection of different cell types, each with a very different DNA methylation profile.

Results

Using a statistical method that permits estimating the relative proportion of cell types from DNA methylation profiles, we examine data from five previously published studies, and find strong evidence of cell composition change across age in blood. We also demonstrate that, in these studies, cellular composition explains much of the observed variability in DNA methylation. Furthermore, we find high levels of confounding between age-related variability and cellular composition at the CpG level.

Conclusions

Our findings underscore the importance of considering cell composition variability in epigenetic studies based on whole blood and other heterogeneous tissue sources. We also provide software for estimating and exploring this composition confounding for the Illumina 450k microarray.

DNA methylation changes in inflammatory bowel disease

The cause of inflammatory bowel disease, encompassing Crohn's disease and ulcerative colitis, remains a mystery but evidence is accumulating that complex interactions between the genetic background and the gut microbiota of the host and environmental factors associated with rapid industrialization and westernized life styles may underlie its pathogenesis. Recent epigenetic studies have suggested that interactions between environment and host DNA may play a leading role in the phenotypical expression of both diseases, explaining amongst others the differences in disease expression in monozygotic twins. DNA methylation is the most studied epigenetic modification and during the last decade its correlation to IBD pathogenesis has been well established. Genes from different molecular pathways have been studied but till now there is no standardized database of methylated genes in IBD. Thus, a thorough and in depth study of DNA methylation, its potential relation to IBD and its interaction with the available pharmaceutical armamentarium is of great interest.

DNA hypermethylation and DNA hypomethylation is present at different loci in chronic kidney disease

Genetic risk factors for chronic kidney disease (CKD) are being identified through international collaborations. By comparison, epigenetic risk factors for CKD have only recently been considered using population-based approaches. DNA methylation is a major epigenetic modification that is associated with complex diseases, so we investigated methylome-wide loci for association with CKD. A total of 485,577 unique features were evaluated in 255 individuals with CKD (cases) and 152 individuals without evidence of renal disease (controls). Following stringent quality control, raw data were quantile normalized and β values calculated to reflect the methylation status at each site. The difference in methylation status was evaluated between cases and controls with resultant P values adjusted for multiple testing. Genes with significantly increased and decreased levels of DNA methylation were considered for biological relevance by functional enrichment analysis using KEGG pathways in Partek Genomics Suite. Twenty-three genes, where more than one CpG per loci was identified with Padjusted<10(-8), demonstrated significant methylation changes associated with CKD and additional support for these associated loci was sought from published literature. Strong biological candidates for CKD that showed statistically significant differential methylation include CUX1, ELMO1, FKBP5, INHBA-AS1, PTPRN2, and PRKAG2 genes; several genes are differentially methylated in kidney tissue and RNA-seq supports a functional role for differential methylation in ELMO1 and PRKAG2 genes. This study reports the largest, most comprehensive, genome-wide quantitative evaluation of DNA methylation for association with CKD. Evidence confirming methylation sites influence development of CKD would stimulate research to identify epigenetic therapies that might be clinically useful for CKD.

DNA methylation data analysis and its application to cancer research

With the rapid development of genome-wide high-throughput technologies, including expression arrays, SNP arrays and next-generation sequencing platforms, enormous amounts of molecular data have been generated and deposited in the public domain. The application of computational approaches is required to yield biological insights from this enormous, ever-growing resource. A particularly interesting subset of these resources is related to epigenetic regulation, with DNA methylation being the most abundant data type. In this paper, we will focus on the analysis of DNA methylation data and its application to cancer studies. We first briefly review the molecular techniques that generate such data, much of which has been obtained with the use of the most recent version of Infinium HumanMethylation450 BeadChip(®) technology (Illumina, CA, USA). We describe the coverage of the methylome by this technique. Several examples of data mining are provided. However, it should be understood that reliance on a single aspect of epigenetics has its limitations. In the not too distant future, these defects may be rectified, providing scientists with previously unavailable opportunities to explore in detail the role of epigenetics in cancer and other disease states.

Beyond gene discovery in inflammatory bowel disease: the emerging role of epigenetics

In the past decade, there have been fundamental advances in our understanding of genetic factors that contribute to the inflammatory bowel diseases (IBDs) Crohn's disease and ulcerative colitis. The latest international collaborative studies have brought the number of IBD susceptibility gene loci to 163. However, genetic factors account for only a portion of overall disease variance, indicating a need to better explore gene-environment interactions in the development of IBD. Epigenetic factors can mediate interactions between the environment and the genome; their study could provide new insight into the pathogenesis of IBD. We review recent progress in identification of genetic factors associated with IBD and discuss epigenetic mechanisms that could affect development and progression of IBD.

Epigenetics and the developmental origins of inflammatory bowel diseases

The gut microbiota, the intestinal mucosa and the host immune system are among the large biological networks involved in the development of inflammatory bowel disease (IBD), which includes Crohn disease (CD) and ulcerative colitis (UC). Host genetics and environmental factors can significantly modulate the interactive relationships among these biological systems and influence predilection toward IBD. High monozygotic twin discordance rates and the rapid rise in the prevalence of IBD indicate that environmental influences may be as important or even more important in their pathogenesis than genetic susceptibility. However, the nature and timing of environmental factors critical for inducing IBD remain largely unknown. The molecular mechanisms and the key biological component(s) that may be affected by such factors are also in question. Epigenetic changes, such as DNA methylation (the methylation of cytosines followed by a guanine in CpG dinucleotides) can be modified by environmental influences during finite developmental periods and have been implicated in the pathogenesis of IBD. Mucosal DNA methylation can also react to changes in the commensal microbiota, underscoring the intercalating relationships among the large biological systems involved in gastrointestinal disorders. Therefore, transient environmental influences during specific periods of development may induce critical change(s) in an isolated or concomitant fashion within the intestinal biomic networks and lead to increased susceptibility to IBD. The present review focuses on the emerging paradigm shift considering IBD to originate from critical environmental effects during pre- and postnatal development.

Human metastable epiallele candidates link to common disorders

Metastable epialleles (MEs) are mammalian genomic loci where epigenetic patterning occurs before gastrulation in a stochastic fashion leading to systematic interindividual variation within one species. Importantly, periconceptual nutritional influences may modulate the establishment of epigenetic changes, such as DNA methylation at MEs. Based on these characteristics, we exploited Infinium HumanMethylation450 BeadChip kits in a 2-tissue parallel screen on peripheral blood leukocyte and colonic mucosal DNA from 10 children without identifiable large intestinal disease. This approach led to the delineation of 1776 CpG sites meeting our criteria for MEs, which associated with 1013 genes. The list of ME candidates exhibited overlaps with recently identified human genes (including CYP2E1 and MGMT, where methylation has been associated with Parkinson disease and glioblastoma, respectively) in which perinatal DNA methylation levels where linked to maternal periconceptual nutrition. One hundred 18 (11.6%) of the ME candidates overlapped with genes where DNA methylation correlated (r > 0.871; p < 0.055) with expression in the colon mucosa of 5 independent control children. Genes involved in homophilic cell adhesion (including cadherin-associated genes) and developmental processes were significantly overrepresented in association with MEs. Additional filtering of gene expression-correlated MEs defined 35 genes, associated with 2 or more CpG sites within a 10 kb genomic region, fulfilling the ME criteria. DNA methylation changes at a number of these genes have been linked to various forms of human disease, including cancers, such as asthma and acute myeloid leukemia (ALOX12), gastric cancer (EBF3), breast cancer (NAV1), colon cancer and acute lymphoid leukemia (KCNK15), Wilms tumor (protocadherin gene cluster; PCDHAs) and colorectal cancer (TCERG1L), suggesting a potential etiologic role for MEs in tumorigenesis and underscoring the possible developmental origins of these malignancies. The presented compendium of ME candidates may accelerate our understanding of the epigenetic origins of common human disorders.

Environmental epigenetics: prospects for studying epigenetic mediation of exposure-response relationships

Changes in epigenetic marks such as DNA methylation and histone acetylation are associated with a broad range of disease traits, including cancer, asthma, metabolic disorders, and various reproductive conditions. It seems plausible that changes in epigenetic state may be induced by environmental exposures such as malnutrition, tobacco smoke, air pollutants, metals, organic chemicals, other sources of oxidative stress, and the microbiome, particularly if the exposure occurs during key periods of development. Thus, epigenetic changes could represent an important pathway by which environmental factors influence disease risks, both within individuals and across generations. We discuss some of the challenges in studying epigenetic mediation of pathogenesis and describe some unique opportunities for exploring these phenomena.

SMAD4 haploinsufficiency associates with augmented colonic inflammation in select humans and mice

SMAD4 is a common mediator of the TGF-beta signaling pathway. One of the members of this pathway, TGF-beta 1, has an important role in controlling gut inflammation in relation to the continuous stimulation of the intestinal microbiota. SMAD4 haploinsufficiency in humans has been linked to juvenile polyposis hereditary hemorrhagic telangiectasia syndrome (JP/HHT; OMIM#17505). Hematochezia and colonic mucosal inflammation suggestive of inflammatory bowel diseases (IBD) have been reported in JP/HHT. Stimulated by recent experience with two affected pediatric patients presented here, we explored the potential role of Smad4 haploinsufficiency in a murine model of colonic inflammation. Smad4(+/-) mice were maintained on a mixed C57/129SvEv background. Chronic colitis was induced with repeated administration of dextran sulfate sodium (DSS) in drinking water. The colonic mucosal microbiota was interrogated by massively parallel pyrosequencing of the bacterial 16S rRNA gene. 66.7% of Smad4(+/-) mice were sensitive to DSS colitis compared to 14.3% of wild type (Chi-Square p=0.036). The augmented colitis was associated with microbiota separation in the Smad4(+/-) mice. Enterococcus and Enterococcus faecalis specifically was increased in abundance in the colitis-prone animals. Smad4 haploinsufficiency can associate with increased susceptibility to large bowel inflammation in mammals with variable penetrance in association with the colonic mucosal microbiota. These findings may reveal implications not only towards colonic inflammation in the setting of SMAD4 haploinsufficiency, but for colorectal cancer as well.