Investigating 5-hydroxymethylcytosine (5hmC): the state of the art

Analysen epigenetischer Marker aus Liquid Biopsies: Informationen von jenseits des Genoms

Die Analyse epigenetischer Marker aus Liquid Biopsies erlaubt Einblicke in physiologische und pathologische Prozesse im Körper einer Person, die über die reine Sequenzinformation hinausgehen. Insbesondere das DNA-Methylierungsmuster sowie die Expressionsmuster von mRNA und ncRNA sind aus Liquid Biopsies erfassbar. Damit werden ganze Gruppen neuer potenzieller Biomarker einer nicht invasiven und ökonomischen Diagnostik zugänglich. Darüber hinaus und im Gegensatz zur reinen DNA-Sequenzanalyse von Liquid Biopsies erlaubt die hohe Gewebespezifität epigenetischer Marker auch die Bestimmung der Herkunft der analysierten Nukleinsäuren z. B. in Bezug auf ein betroffenes Organ. Angesichts der fallenden Kosten für Sequenzierungen und des technologischen Fortschritts, der die Nachweisgrenzen immer weiter zu immer sensitiveren Anwendungen verschiebt, könnten epigenetische Untersuchungen aus Liquid Biopsies den Trend zu einer Individualisierung in der Medizin weiter forcieren.

Epigenetic mechanisms involved in the effects of stress exposure: focus on 5-hydroxymethylcytosine

5-hydroxymethylcytosine (5hmC) is a recently re-discovered transient intermediate in the active demethylation pathway that also appears to play an independent role in modulating gene function. Epigenetic marks, particularly 5-methylcytosine, have been widely studied in relation to stress-related disorders given the long-lasting effect that stress has on these marks. 5hmC is a good candidate for involvement in the etiology of these disorders given its elevated concentration in mammalian neurons, its dynamic regulation during development of the central nervous system, and its high variability among individuals. Although we are unaware of any studies published to date examining 5 hmC profiles in human subjects who have developed a psychiatric disorder after a life stressor, there is emerging evidence from the animal literature that 5hmC profiles are altered in the context of fear-conditioning paradigms and stress exposure, suggesting a possible role for 5hmC in the biological underpinnings of stress-related disorders. In this review, the authors examine the available approaches for profiling 5hmC and describe their advantages and disadvantages as well as discuss the studies published thus far investigating 5hmC in the context of fear-related learning and stress exposure in animals. The authors also highlight the global versus locus-specific regulation of 5hmC in these studies. Finally, the limitations of the current studies and their implications are discussed.

5-Hydroxymethylcytosine Remodeling Precedes Lineage Specification during Differentiation of Human CD4(+) T Cells

5-methylcytosine (5mC) is converted to 5-hydroxymethylcytosine (5hmC) by the TET family of enzymes as part of a recently discovered active DNA de-methylation pathway. 5hmC plays important roles in regulation of gene expression and differentiation and has been implicated in T cell malignancies and autoimmunity. Here, we report early and widespread 5mC/5hmC remodeling during human CD4(+) T cell differentiation ex vivo at genes and cell-specific enhancers with known T cell function. We observe similar DNA de-methylation in CD4(+) memory T cells in vivo, indicating that early remodeling events persist long term in differentiated cells. Underscoring their important function, 5hmC loci were highly enriched for genetic variants associated with T cell diseases and T-cell-specific chromosomal interactions. Extensive functional validation of 22 risk variants revealed potentially pathogenic mechanisms in diabetes and multiple sclerosis. Our results support 5hmC-mediated DNA de-methylation as a key component of CD4(+) T cell biology in humans, with important implications for gene regulation and lineage commitment.

Water-bridged hydrogen bond formation between 5-hydroxylmethylcytosine (5-hmC) and its 3'-neighbouring bases in A- and B-form DNA duplexes

5-Hydroxylmethylcytosine (5hmC) has been recognized as the sixth base with important biological functions in many tissues and cell types. We present here the high-resolution crystal structures and molecular simulation studies of both A-form and B-form DNA duplexes containing 5hmC. We observed that 5hmC interacts with its 3'-neighboring bases through water-bridged hydrogen bonds and these interactions may affect the further oxidation of 5hmC.

Next-Generation Sequencing Approaches in Cancer: Where Have They Brought Us and Where Will They Take Us?

Next-generation sequencing (NGS) technologies and data have revolutionized cancer research and are increasingly being deployed to guide clinicians in treatment decision-making. NGS technologies have allowed us to take an “omics” approach to cancer in order to reveal genomic, transcriptomic, and epigenomic landscapes of individual malignancies. Integrative multi-platform analyses are increasingly used in large-scale projects that aim to fully characterize individual tumours as well as general cancer types and subtypes. In this review, we examine how NGS technologies in particular have contributed to “omics” approaches in cancer research, allowing for large-scale integrative analyses that consider hundreds of tumour samples. These types of studies have provided us with an unprecedented wealth of information, providing the background knowledge needed to make small-scale (including “N of 1”) studies informative and relevant. We also take a look at emerging opportunities provided by NGS and state-of-the-art third-generation sequencing technologies, particularly in the context of translational research. Cancer research and care are currently poised to experience significant progress catalyzed by accessible sequencing technologies that will benefit both clinical- and research-based efforts.

Global DNA methylation and hydroxymethylation differ in hepatocellular carcinoma and cholangiocarcinoma and relate to survival rate

In addition to DNA methylation, hydroxymethylation of DNA is recognized as a novel epigenetic mark. Primary liver cancers, i.e., hepatocellular carcinoma (HCC) and cholangiocarcinoma (CC), are highly prevalent but epigenetically poorly characterized, so far. In the present study we measured global methylcytosine (mCyt) and hydroxymethylcytosine (hmCyt) in HCC and CC tissues and in peripheral blood mononuclear cell (PBMC) DNA to define mCyt and hmCyt status and, accordingly, the survival rate. Both mCyt and hmCyt were measured by a liquid chromatography/tandem mass spectrometry method in neoplastic and homologous nonneoplastic tissues, i.e., liver and gallbladder, and in PBMCs of 31 HCC and 16 CC patients. Content of mCyt was notably lower in HCC than in CC tissues (3.97% versus 5.26%, respectively; P < 0.0001). Significantly reduced mCyt was also detected in HCC compared to nonneoplastic tissue (3.97% versus 4.82% mCyt, respectively; P < 0.0001), but no such difference was found for CC versus homologous nonneoplastic tissue. Hydroxymethylation was significantly decreased in HCC versus nonneoplastic liver tissue (0.044 versus 0.128, respectively; P < 0.0001) and in CC versus both liver and gallbladder nonneoplastic tissue (0.030 versus 0.124, P = 0.026, and 0.030 versus 0.123, P = 0.006, respectively). When the survival rate was evaluated according to mCyt PBMC content by Kaplan-Meier analysis, patients with mCyt ≥5.59% had a significantly higher life expectancy than those with mCyt <5.59% (P = 0.034) at a follow-up period up to 48 months.

CONCLUSION

A significant DNA hypomethylation distinguishes HCC from CC, while DNA hypo-hydroxymethylation characterizes both HCC and CC, and a PBMC DNA mCyt content ≥5.59% relates to a favorable outcome in primary liver cancers.

DNA immunoprecipitation semiconductor sequencing (DIP-SC-seq) as a rapid method to generate genome wide epigenetic signatures

Modification of DNA resulting in 5-methylcytosine (5 mC) or 5-hydroxymethylcytosine (5hmC) has been shown to influence the local chromatin environment and affect transcription. Although recent advances in next generation sequencing technology allow researchers to map epigenetic modifications across the genome, such experiments are often time-consuming and cost prohibitive. Here we present a rapid and cost effective method of generating genome wide DNA modification maps utilising commercially available semiconductor based technology (DNA immunoprecipitation semiconductor sequencing; "DIP-SC-seq") on the Ion Proton sequencer. Focussing on the 5hmC mark we demonstrate, by directly comparing with alternative sequencing strategies, that this platform can successfully generate genome wide 5hmC patterns from as little as 500 ng of genomic DNA in less than 4 days. Such a method can therefore facilitate the rapid generation of multiple genome wide epigenetic datasets.

Genome-wide assays that identify and quantify modified cytosines in human disease studies

The number of different assays that has been published to study DNA methylation is extensive, complemented by recently described assays that test modifications of cytosine other than the most abundant 5-methylcytosine (5mC) variant. In this review, we describe the considerations involved in choosing how to study 5mC throughout the genome, with an emphasis on the common application of testing for epigenetic dysregulation in human disease. While microarray studies of 5mC continue to be commonly used, these lack the additional qualitative information from sequencing-based approaches that is increasingly recognized to be valuable. When we test the representation of functional elements in the human genome by several current assay types, we find that no survey approach interrogates anything more than a small minority of the nonpromoter cis-regulatory sites where DNA methylation variability is now appreciated to influence gene expression and to be associated with human disease. However, whole-genome bisulphite sequencing (WGBS) adds a substantial representation of loci at which DNA methylation changes are unlikely to be occurring with transcriptional consequences. Our assessment is that the most effective approach to DNA methylation studies in human diseases is to use targeted bisulphite sequencing of the cis-regulatory loci in a cell type of interest, using a capture-based or comparable system, and that no single design of a survey approach will be suitable for all cell types.

Effects of negative stressors on DNA methylation in the brain: implications for mood and anxiety disorders

Stress is a major contributor to anxiety and mood disorders. The recent discovery of epigenetic changes in the brain resulting from stress has enhanced our understanding of the mechanism by which stress is able to promote these disorders. Although epigenetics encompasses chemical modifications that occur at both DNA and histones, much attention has been focused on stress-induced DNA methylation changes on behavior. Here, we review the effect of stress-induced DNA methylation changes on physiological mechanisms that govern behavior and cognition, dysregulation of which can be harmful to mental health. A literature review was performed in the areas of DNA methylation, stress, and their impact on the brain and psychiatric illness. Key findings center on genes involved in the hypothalamic-pituitary-adrenal axis, neurotransmission and neuroplasticity. Using animal models of different stress paradigms and clinical studies, we detail how DNA methylation changes to these genes can alter physiological mechanisms that influence behavior. Appropriate levels of gene expression in the brain play an important role in mental health. This dynamic control can be disrupted by stress-induced changes to DNA methylation patterns. Advancement in other areas of epigenetics, such as histone modifications and the discovery of the novel DNA epigenetic mark, 5-hydroxymethylcytosine, could provide additional avenues to consider when determining the epigenetic effects of stress on the brain.