Epigenetics and the Exposome: DNA Methylation as a Proxy for Health Impacts of Prenatal Environmental Exposures.

The accumulation of every day exposures can impact health across the life course, but our understanding of such exposures is impeded by our ability to delineate the relationship between an individual's early life exposome and later life health effects. Measuring the exposome is challenging. Exposure assessed at a given time point captures a snapshot of the exposome but does not represent the full spectrum of exposures across the life course. In addition, the assessment of early life exposures and their effects is often further challenged by lack of relevant samples and the time gap between exposures and related health outcomes in later life. Epigenetics, specifically DNA methylation, has the potential to overcome these barriers as environmental epigenetic perturbances can be retained through time. In this review, we describe how DNA methylation can be framed in the world of the exposome. We offer three compelling examples of common environmental exposures, including cigarette smoke, the endocrine active compound bisphenol A (BPA), and the metal lead (Pb), to illustrate the application of DNA methylation as a proxy to measure the exposome. We discuss areas for future explorations and current limitations of this approach. Epigenetic profiling is a promising and rapidly developing tool and field of study, offering us a unique and powerful way to assess the early life exposome and its effects across different life stages.

Perinatal Lead Exposure Promotes Sex-Specific Epigenetic Programming of Disease-Relevant Pathways in Mouse Heart.

Environmental contaminants such as the metal lead (Pb) are associated with cardiovascular disease, but the underlying molecular mechanisms are poorly understood. In particular, little is known about how exposure to Pb during early development impacts the cardiac epigenome at any point across the life course and potential differences between sexes. In a mouse model of human-relevant perinatal exposures, we utilized RNA-seq and Enhanced Reduced Representation Bisulfite Sequencing (ERRBS) to investigate the effects of Pb exposure during gestation and lactation on gene expression and DNA methylation, respectively, in the hearts of male and female mice at weaning. For ERRBS, we identified differentially methylated CpGs (DMCs) or differentially methylated 1000 bp regions (DMRs) based on a minimum absolute change in methylation of 10% and an FDR < 0.05. For gene expression data, an FDR < 0.05 was considered significant. No individual genes met the FDR cutoff for gene expression; however, we found that Pb exposure leads to significant changes in the expression of gene pathways relevant to cardiovascular development and disease. We further found that Pb promotes sex-specific changes in DNA methylation at hundreds of gene loci (280 DMCs and 99 DMRs in males, 189 DMCs and 121 DMRs in females), and pathway analysis revealed that these CpGs and regions collectively function in embryonic development. In males, differential methylation also occurred at genes related to immune function and metabolism. We then investigated whether genes exhibiting differential methylation at weaning were also differentially methylated in hearts from a cohort of Pb-exposed mice at adulthood. We found that a single gene, Galnt2, showed differential methylation in both sexes and time points. In a human cohort investigating the influence of prenatal Pb exposure on the epigenome, we also observed an inverse association between first trimester Pb concentrations and adolescent blood leukocyte DNA methylation at a locus in GALNT2, suggesting that this gene may represent a biomarker of Pb exposure across species. Together, these data, across two time points in mice and in a human birth cohort study, collectively demonstrate that Pb exposure promotes sex-specific programming of the cardiac epigenome, and provide potential mechanistic insight into how Pb causes cardiovascular disease.

Environmental Epigenomes.

Research in epigenetics has dramatically risen during the last decade to include aspects of environmental biology. However, many questions remain regarding the effects of environmental stressors on the epigenome, incorporating the particular role of epigenetic mechanisms in the adaptation and evolution of organisms in changing environments. Epigenetics is commonly defined as mitotically and/or meiotically heritable changes in gene function that occur without altering the underlying DNA sequence. It encompasses DNA (hydroxy)methylation, histone modifications, chromatin structure, and non-coding RNAs that may be inherited across generations under certain circumstances. Epigenetic mechanisms are perfect candidates to extend our understanding of the impact of environmental stressors on organisms and to explain the rapid phenomenon of adaptive evolution. Existing evidence shows that environmental cues can affect the epigenome and modify gene expression accordingly. These changes can then induce phenotypic modifications that are morphological, physiological, or behavioral at the organismal level. In this Special Issue focusing on environmental epigenetics, we provide an overview of influences to the epigenome that are driven by various environmental and evolutionary factors, with a particular focus on DNA methylation (DNAm). Five research groups have contributed insightful studies or reviews on (1) DNAm and demethylation events affected by the exposome; (2) DNAm as a potential biomarker to determine cardiometabolic risk early in life; (3) consequences of DNAm across multiple generations; (4) DNAm variation within natural animal populations; and (5) epigenetic mechanisms in genetically uniform organisms. Collectively, the articles from this Special Issue consistently support that environmental changes can induce long-lasting epigenetic effects within a given organism pertaining to individual risk for disease, or multi-generational impacts that ultimately impact evolution.

Developmental exposures to common environmental contaminants, DEHP and lead, alter adult brain and blood hydroxymethylation in mice.

Introduction: The developing epigenome changes rapidly, potentially making it more sensitive to toxicant exposures. DNA modifications, including methylation and hydroxymethylation, are important parts of the epigenome that may be affected by environmental exposures. However, most studies do not differentiate between these two DNA modifications, possibly masking significant effects. Methods: To investigate the relationship between DNA hydroxymethylation and developmental exposure to common contaminants, a collaborative, NIEHS-sponsored consortium, TaRGET II, initiated longitudinal mouse studies of developmental exposure to human-relevant levels of the phthalate plasticizer di(2-ethylhexyl) phthalate (DEHP), and the metal lead (Pb). Exposures to 25 mg DEHP/kg of food (approximately 5 mg DEHP/kg body weight) or 32 ppm Pb-acetate in drinking water were administered to nulliparous adult female mice. Exposure began 2 weeks before breeding and continued throughout pregnancy and lactation, until offspring were 21 days old. At 5 months, perinatally exposed offspring blood and cortex tissue were collected, for a total of 25 male mice and 17 female mice (n = 5-7 per tissue and exposure). DNA was extracted and hydroxymethylation was measured using hydroxymethylated DNA immunoprecipitation sequencing (hMeDIP-seq). Differential peak and pathway analysis was conducted comparing across exposure groups, tissue types, and animal sex, using an FDR cutoff of 0.15. Results: DEHP-exposed females had two genomic regions with lower hydroxymethylation in blood and no differences in cortex hydroxymethylation. For DEHP-exposed males, ten regions in blood (six higher and four lower) and 246 regions (242 higher and four lower) and four pathways in cortex were identified. Pb-exposed females had no statistically significant differences in blood or cortex hydroxymethylation compared to controls. Pb-exposed males, however, had 385 regions (all higher) and six pathways altered in cortex, but no differential hydroxymethylation was identified in blood. Discussion: Overall, perinatal exposure to human-relevant levels of two common toxicants showed differences in adult DNA hydroxymethylation that was specific to sex, exposure type, and tissue, but male cortex was most susceptible to hydroxymethylation differences by exposure. Future assessments should focus on understanding if these findings indicate potential biomarkers of exposure or are related to functional long-term health effects.

Toxicoepigenetics for Risk Assessment: Bridging the Gap Between Basic and Regulatory Science.

Toxicoepigenetics examines the health effects of environmental exposure associated with, or mediated by, changes in the epigenome. Despite high expectations, toxicoepigenomic data and methods have yet to become significantly utilized in chemical risk assessment. This article draws on a social science framework to highlight hitherto overlooked structural barriers to the incorporation of toxicoepigenetics in risk assessment and to propose ways forward. The present barriers stem not only from the lack of maturity of the field but also from differences in constraints and standards between the data produced by toxicoepigenetics and the regulatory science data that risk assessment processes require. Criteria and strategies that frame the validation of knowledge used for regulatory purposes limit the application of basic research in toxicoepigenetics toward risk assessment. First, the need in regulatory toxicology for standardized methods that form a consensus between regulatory agencies, basic research, and the industry conflicts with the wealth of heterogeneous data in toxicoepigenetics. Second, molecular epigenetic data do not readily translate into typical toxicological endpoints. Third, toxicoepigenetics investigates new forms of toxicity, in particular low-dose and long-term effects, that do not align well with the traditional framework of regulatory toxicology. We propose that increasing the usefulness of epigenetic data for risk assessment will require deliberate efforts on the part of the toxicoepigenetics community in 4 areas: fostering the understanding of epigenetics among risk assessors, developing knowledge infrastructure to demonstrate applicability, facilitating the normalization and exchange of data, and opening the field to other stakeholders.

Developmental toxicant exposures and sex-specific effects on epigenetic programming and cardiovascular health across generations.

Despite substantial strides in diagnosis and treatment, cardiovascular diseases (CVDs) continue to represent the leading cause of death in the USA and around the world, resulting in significant morbidity and loss of productive years of life. It is increasingly evident that environmental exposures during early development can influence CVD risk across the life course. CVDs exhibit marked sexual dimorphism, but how sex interacts with environmental exposures to affect cardiovascular health is a critical and understudied area of environmental health. Emerging evidence suggests that developmental exposures may have multi- and transgenerational effects on cardiovascular health, with potential sex differences; however, further research in this important area is urgently needed. Lead (Pb), phthalate plasticizers, and perfluoroalkyl substances (PFAS) are ubiquitous environmental contaminants with numerous adverse human health effects. Notably, recent evidence suggests that developmental exposure to each of these toxicants has sex-specific effects on cardiovascular outcomes, but the underlying mechanisms, and their effects on future generations, require further investigation. This review article will highlight the role for the developmental environment in influencing cardiovascular health across generations, with a particular emphasis on sex differences and epigenetic mechanisms. In particular, we will focus on the current evidence for adverse multi and transgenerational effects of developmental exposures to Pb, phthalates, and PFAS and highlight areas where further research is needed.

PIWI-Interacting RNA (piRNA) and Epigenetic Editing in Environmental Health Sciences.

PURPOSE OF REVIEW: The epigenome modulates gene expression in response to environmental stimuli. Modifications to the epigenome are potentially reversible, making them a promising therapeutic approach to mitigate environmental exposure effects on human health. This review details currently available genome and epigenome editing technologies and highlights ncRNA, including piRNA, as potential tools for targeted epigenome editing. RECENT FINDINGS: Zinc finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), and clustered regularly interspaced short palindromic repeats (CRISPR) associated nuclease (CRISPR/Cas) research has significantly advanced genome editing technology, with broad promise in genetic research and targeted therapies. Initial epigenome-directed therapies relied on global modification and suffered from limited specificity. Adapted from current genome editing tools, zinc finger protein (ZFP), TALE, and CRISPR/nuclease-deactivated Cas (dCas) systems now confer locus-specific epigenome editing, with promising applicability in the field of environmental health sciences. However, high incidence of off-target effects and time taken for screening limit their use. FUTURE DEVELOPMENT: ncRNA serve as a versatile biomarker with well-characterized regulatory mechanisms that can easily be adapted to edit the epigenome. For instance, the transposon silencing mechanism of germline PIWI-interacting RNAs (piRNA) could be engineered to specifically methylate a given gene, overcoming pitfalls of current global modifiers. Future developments in epigenome editing technologies will inform risk assessment through mechanistic investigation and serve as potential modes of intervention to mitigate environmentally induced adverse health outcomes later in life.

Sex-Specific Alterations in Cardiac DNA Methylation in Adult Mice by Perinatal Lead Exposure.

Environmental factors play an important role in the etiology of cardiovascular diseases. Cardiovascular diseases exhibit marked sexual dimorphism; however, the sex-specific effects of environmental exposures on cardiac health are incompletely understood. Perinatal and adult exposures to the metal lead (Pb) are linked to several adverse cardiovascular outcomes, but the sex-specific effects of this toxicant on the heart have received little attention. Perinatal environmental exposures can lead to disease through disruption of the normal epigenetic programming that occurs during early development. Using a mouse model of human-relevant perinatal environmental exposure, we investigated the effects of exposure to Pb during gestation and lactation on DNA methylation in the hearts of adult offspring mice (n = 6 per sex). Two weeks prior to mating, dams were assigned to control or Pb acetate (32 ppm) water, and exposure continued until offspring were weaned at three weeks of age. Enhanced reduced-representation bisulfite sequencing was used to measure DNA methylation in the hearts of offspring at five months of age. Although Pb exposure stopped at three weeks of age, we discovered hundreds of differentially methylated cytosines (DMCs) and regions (DMRs) in males and females at five months of age. DMCs/DMRs and their associated genes were sex-specific, with a small, but statistically significant subset overlapping between sexes. Pathway analysis revealed altered methylation of genes important for cardiac and other tissue development in males, and histone demethylation in females. Together, these data demonstrate that perinatal exposure to Pb induces sex-specific changes in cardiac DNA methylation that are present long after cessation of exposure, and highlight the importance of considering sex in environmental epigenetics and mechanistic toxicology studies.

Tissue and sex-specific programming of DNA methylation by perinatal lead exposure: implications for environmental epigenetics studies.

Early developmental environment can influence long-term health through reprogramming of the epigenome. Human environmental epigenetics studies rely on surrogate tissues, such as blood, to assess the effects of environment on disease-relevant but inaccessible target tissues. However, the extent to which environment-induced epigenetic changes are conserved between these tissues is unclear. A better understanding of this conservation is imperative for effective design and interpretation of human environmental epigenetics studies. The Toxicant Exposures and Responses by Genomic and Epigenomic Regulators of Transcription (TaRGET II) consortium was established by the National Institute of Environmental Health Sciences to address the utility of surrogate tissues as proxies for toxicant-induced epigenetic changes in target tissues. We and others have recently reported that perinatal exposure to lead (Pb) is associated with adverse metabolic outcomes. Here, we investigated the sex-specific effects of perinatal exposure to a human environmentally relevant level of Pb on DNA methylation in paired liver and blood samples from adult mice using enhanced reduced-representation bisulphite sequencing. Although Pb exposure ceased at 3 weeks of age, we observed thousands of sex-specific differentially methylated cytosines in the blood and liver of Pb-exposed animals at 5 months of age, including 44 genomically imprinted loci. We observed significant tissue overlap in the genes mapping to differentially methylated cytosines. A small but significant subset of Pb-altered genes exhibit basal sex differences in gene expression in the mouse liver. Collectively, these data identify potential molecular targets for Pb-induced metabolic diseases, and inform the design of more robust human environmental epigenomics studies.

LncRNA NR_030777 Alleviates Paraquat-Induced Neurotoxicity by Regulating Zfp326 and Cpne5.

Paraquat (PQ) is herbicide widely used in agricultural production. It is identified as an environmental toxicant that could lead to neurodegeneration damage. Parkinson's disease (PD) is a central nervous system degenerative disease that occurs in the elderly. Main risk factors for PD include genetic and environmental variables, but its specific mechanism is still not well understood. Emerging evidence suggests that long noncoding RNAs (lncRNAs) play an important role in PD. LncRNA NR_030777 has a full length of 2208 bp and is highly conserved among species. RNA profiling showed a significant alteration in lncRNA NR_030777 expression upon PQ-induced neurotoxicity. However, little is known on the functional relevance of lncRNA NR_030777 in the development of PQ. In this study, we discovered a vital protective role of lncRNA NR_030777 in PQ-induced neurotoxicity. The expression of NR_030777 correlates with elevated level of reactive oxygen species induced by PQ. In addition, activated expression of NR_030777 alleviates neurotoxicity by regulating the expression of Zfp326 and Copine 5. We report that lncRNA NR_030777 has a vital protective role in neurotoxicity induced by environmental toxicants such as PQ. This study could serve as an exemplary case for lncRNAs to be considered as a potential target for the prevention and treatment of PQ-induced neurodegenerative disorders such as PD.

Sex-Specific Programming of Cardiac DNA Methylation by Developmental Phthalate Exposure.

Phthalate plasticizers are ubiquitous chemicals linked to several cardiovascular diseases in animal models and humans. Despite this, the mechanisms by which phthalate exposures cause adverse cardiac health outcomes are unclear. In particular, whether phthalate exposures during pregnancy interfere with normal developmental programming of the cardiovascular system, and the resulting implications this may have for long-term disease risk, are unknown. Recent studies suggest that the effects of phthalates on metabolic and neurobehavioral outcomes are sex-specific. However, the influence of sex on cardiac susceptibility to phthalate exposures has not been investigated. One mechanism by which developmental exposures may influence long-term health is through altered programming of DNA methylation. In this work, we utilized an established mouse model of human-relevant perinatal exposure and enhanced reduced representation bisulfite sequencing to investigate the long-term effects of diethylhexyl phthalate (DEHP) exposure on DNA methylation in the hearts of adult male and female offspring at 5 months of age (n = 5-7 mice per sex and exposure). Perinatal DEHP exposure led to hundreds of sex-specific, differentially methylated cytosines (DMCs) and differentially methylated regions (DMRs) in the heart. Pathway analysis of DMCs revealed enrichment for several pathways in females, including insulin signaling, regulation of histone methylation, and tyrosine phosphatase activity. In males, DMCs were enriched for glucose transport, energy generation, and developmental programs. Notably, many sex-specific genes differentially methylated with DEHP exposure in our mouse model were also differentially methylated in published data of heart tissues collected from human heart failure patients. Together, these data highlight the potential role for DNA methylation in DEHP-induced cardiac effects and emphasize the importance of sex as a biological variable in environmental health studies.

Comprehensive histone epigenetics: A mass spectrometry based screening assay to measure epigenetic toxicity.

Evidence of the involvement of epigenetics in pathologies such as cancer, diabetes, and neurodegeneration has increased global interest in epigenetic modifications. For nearly thirty years, it has been known that cancer cells exhibit abnormal DNA methylation patterns. In contrast, the large-scale analysis of histone post-translational modifications (hPTMs) has lagged behind because classically, histone modification analysis has relied on site specific antibody-based techniques. Mass spectrometry (MS) is a technique that holds the promise to picture the histone code comprehensively in a single experiment. Therefore, we developed an MS-based method that is capable of tracking all possible hPTMs in an untargeted approach. In this way, trends in single and combinatorial hPTMs can be reported and enable prediction of the epigenetic toxicity of compounds. Moreover, this method is based on the use of human cells to provide preliminary data, thereby omitting the need to sacrifice laboratory animals. Improving the workflow and the user-friendliness in order to become a high throughput, easily applicable, toxicological screening assay is an ongoing effort. Still, this novel toxicoepigenetic assay and the data it generates holds great potential for, among others, pharmaceutical industry, food science, clinical diagnostics and, environmental toxicity screening. •There is a growing interest in epigenetic modifications, and more specifically in histone post-translational modifications (hPTMs).•We describe an MS-based workflow that is capable of tracking all possible hPTMs in an untargeted approach that makes use of human cells.•Improving the workflow and the user-friendliness in order to become a high throughput, easily applicable, toxicological screening assay is an ongoing effort.

Genomic Tools for Environmental Epigenetics and Implications for Public Health.

Epigenetics refers to the study of mitotically heritable and potentially reversible changes in gene expression unrelated to the DNA sequence itself, influenced by epigenetic marks including chromatin modifications, non-coding RNA and alterations to DNA itself via methylation and hydroxymethylation. Epigenetics has taken center stage in the study of diseases such as cancer, diabetes, and neurodegeneration; however, its integration into the field of environmental health sciences and toxicology (e.g. Toxicoepigenetics) is in its infancy. This review highlights the need to evaluate surrogate and target tissues in the field of toxicoepigenetics as the National Institute of Environmental Health Sciences (NIEHS) multi-phased Toxicant Exposure and Response by Genomic and Epigenomic Regulators of Transcription (TaRGET) consortia make headway, and the emergence of non-coding RNA biomarkers. The review also discusses lead (Pb) as a potential toxicoepigenetic exposure, where pre- and post-natal Pb exposure is associated with reprogramming of DNA methylation, histone modifications, and microRNA expression, representing potential biomarkers or predictors for Pb-induced health outcomes. Finally, new advances in epigenome editing, highlighting the potential of small ncRNA, will be explored for environmental health sciences research.

Maternal levels of endocrine disrupting chemicals in the first trimester of pregnancy are associated with infant cord blood DNA methylation.

Endocrine disrupting chemicals (EDCs) pose a public health risk through disruption of normal biological processes. Identifying toxicoepigenetic mechanisms of developmental exposure-induced effects for EDCs, such as phthalates or bisphenol A (BPA), is essential. Here, we investigate whether maternal exposure to EDCs is predictive of infant DNA methylation at candidate gene regions. In the Michigan Mother-Infant Pairs (MMIP) cohort, DNA was extracted from cord blood leukocytes for methylation analysis by pyrosequencing (n = 116) and methylation changes related to first trimester levels of 9 phthalate metabolites and BPA. Growth and metabolism-related genes selected for methylation analysis included imprinted (IGF2, H19) and non-imprinted (PPARA, ESR1) genes along with LINE-1 repetitive elements. Findings revealed decreases in methylation of LINE-1, IGF2, and PPARA with increasing phthalate concentrations. For example, a log unit increase in ΣDEHP corresponded to a 1.03 [95% confidence interval (CI): -1.83, -0.22] percentage point decrease in PPARA methylation. Changes in DNA methylation were also inversely correlated with PPARA gene expression determined by RT-qPCR (r = -0.34, P = 0.02), thereby providing evidence in support of functional relevance. A sex-stratified analysis of EDCs and DNA methylation showed that some relationships were female-specific. For example, urinary BPA exposure was associated with a 1.35 (95%CI: -2.69, -0.01) percentage point decrease in IGF2 methylation and a 1.22 (95%CI: -2.27, -0.16) percentage point decrease in PPARA methylation in females only. These findings add to a body of evidence suggesting epigenetically labile regions may provide a conduit linking early exposures with disease risk later in life and that toxicoepigenetic susceptibility may be sex specific.

Paraquat and MPTP induce alteration in the expression profile of long noncoding RNAs in the substantia nigra of mice: Role of the transcription factor Nrf2.

Parkinson's disease (PD) is a common age-related degenerative disease of the central nervous system caused mainly by hereditary, pesticides, metals, and polychlorinated biphenyls. Paraquat (PQ), a widely used herbicide, causes PD. Long noncoding RNAs (lncRNAs) are nonprotein-coding transcripts, expressed in the brain and play irreplaceable roles in neurodegenerative diseases. NF-E2-related factor-2 (Nrf2) is an important genetic transcription regulator in oxidative stress. We aimed to discover novel PQ or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-Nrf2-related lncRNAs and explore their association with PD. 17157 lncRNAs and 13707 mRNAs (fold change ≥2, P < 0.05) were identified by Microarray. And the expressions of six lncRNAs were confirmed by using qRT-PCR and two by FISH. Coding-noncoding analysis and qRT-PCR were applied to discover the functions of lncRNAs and predict the targeted genes. In mice, PQ and MPTP exposure caused alteration of the lncRNA expression profile, suggesting lncRNAs may be involved in PQ- and MPTP-induced neurotoxicity. The changes in their lncRNA expression were distinct but related. PQ caused lncRNA expression profiling alteration in the substantia nigra (SN) through an interaction with Nrf2, thus changing the NR_027648/Zc3h14/Cybb and NR_030777/Zfp326/Cpne5 mRNA pathways. Similarly, MPTP caused lncRNA expression profiling alteration in SN through an interaction with Nrf2. Nrf2 may be involved in the development of neurodegeneration induced by PQ and MPTP via interaction with lncRNAs as the molecular mechanism. Our findings indicate the potential roles of lncRNAs in the development of PD by PQ or MPTP and provide positive insights into future mechanism studies.

Linking the Epigenome with Exposure Effects and Susceptibility: The Epigenetic Seed and Soil Model.

The epigenome is a dynamic mediator of gene expression that shapes the way that cells, tissues, and organisms respond to their environment. Initial studies in the emerging field of "toxicoepigenetics" have described either the impact of an environmental exposure on the epigenome or the association of epigenetic signatures with the onset or progression of disease; however, the majority of these pioneering studies examined the relationship between discrete epigenetic modifications and the effects of a single environmental factor. Although these data provide critical blocks with which we construct our understanding of the role of the epigenome in susceptibility and disease, they are akin to individual letters in a complex alphabet that is used to compose the language of the epigenome. Advancing the use of epigenetic data to gain a more comprehensive understanding of the mechanisms underlying exposure effects, identify susceptible populations, and inform the next generation risk assessment depends on our ability to integrate these data in a way that accounts for their cumulative impact on gene regulation. Here we will review current examples demonstrating associations between the epigenetic impacts of intrinsic factors, such as such as age, genetics, and sex, and environmental exposures shape the epigenome and susceptibility to exposure effects and disease. We will also demonstrate how the "epigenetic seed and soil" model can be used as a conceptual framework to explain how epigenetic states are shaped by the cumulative impacts of intrinsic and extrinsic factors and how these in turn determine how an individual responds to subsequent exposure to environmental stressors.

Perinatal lead (Pb) exposure results in sex and tissue-dependent adult DNA methylation alterations in murine IAP transposons.

Epidemiological and animal data suggest that adult chronic disease is influenced by early-life exposure-induced changes to the epigenome. Previously, we observed that perinatal lead (Pb) exposure results in persistent murine metabolic- and activity-related effects. Using phylogenetic and DNA methylation analysis, we have also identified novel intracisternal A particle (IAP) retrotransposons exhibiting regions of variable methylation as candidate loci for environmental effects on the epigenome. Here, we now evaluate brain and kidney DNA methylation profiles of four representative IAPs in adult mice exposed to human physiologically relevant levels of Pb two weeks prior to mating through lactation. When IAPs across the genome were evaluated globally, average (sd) methylation levels were 92.84% (3.74) differing by tissue (P < 0.001), but not sex or dose. By contrast, the four individual IAPs displayed tissue-specific Pb and sex effects. Medium Pb-exposed mice had 3.86% less brain methylation at IAP 110 (P < 0.01), while high Pb-exposed mice had 2.83% less brain methylation at IAP 236 (P = 0.01) and 1.77% less at IAP 506 (P = 0.05). Individual IAP DNA methylation differed by sex for IAP 110 in the brain and kidney, IAP 236 in the kidney, and IAP 1259 in the kidney. Using Tomtom, we identified three binding motifs that matched to each of our novel IAPs impacted by Pb, one of which (HMGA2) has been linked to metabolic-related conditions in both mice and humans. Thus, these recently identified IAPs display tissue-specific environmental lability as well as sex-specific differences supporting an epigenetic link between early exposure to Pb and later-in-life health outcomes. Environ. Mol. Mutagen. 58:540-550, 2017. © 2017 Wiley Periodicals, Inc.

The pharmacoepigenetics of drug metabolism and transport in breast cancer: review of the literature and in silico analysis.

The focus of this manuscript is on DNA methylation and miRNA regulation of drug-metabolizing enzymes and drug transporters involved in the disposition of drugs commonly used in breast cancer. We start with a review of the available scant literature and follow with an in silico analysis of the CpG islands and miRNA binding sites of genes of interest. We make the case that there is room for further research to include more genes and miRNAs despite the extensive sharing of miRNA targets by candidate genes of interest. We also stress on the role of peripheral blood as a source of pharmacoepigenetic biomarkers, and point out the lack of toxicoepigenetic studies in breast cancer.