Neonatal diethylstilbestrol exposure induces persistent elevation of c-fos expression and hypomethylation in its exon-4 in mouse uterus

Child health, developmental plasticity, and epigenetic programming

Plasticity in developmental programming has evolved in order to provide the best chances of survival and reproductive success to the organism under changing environments. Environmental conditions that are experienced in early life can profoundly influence human biology and long-term health. Developmental origins of health and disease and life-history transitions are purported to use placental, nutritional, and endocrine cues for setting long-term biological, mental, and behavioral strategies in response to local ecological and/or social conditions. The window of developmental plasticity extends from preconception to early childhood and involves epigenetic responses to environmental changes, which exert their effects during life-history phase transitions. These epigenetic responses influence development, cell- and tissue-specific gene expression, and sexual dimorphism, and, in exceptional cases, could be transmitted transgenerationally. Translational epigenetic research in child health is a reiterative process that ranges from research in the basic sciences, preclinical research, and pediatric clinical research. Identifying the epigenetic consequences of fetal programming creates potential applications in clinical practice: the development of epigenetic biomarkers for early diagnosis of disease, the ability to identify susceptible individuals at risk for adult diseases, and the development of novel preventive and curative measures that are based on diet and/or novel epigenetic drugs.

DPP4 gene DNA methylation in the omentum is associated with its gene expression and plasma lipid profile in severe obesity

Severely obese subjects with the metabolic syndrome (MS) have higher dipeptidyl peptidase-4 (DPP4) expression in their visceral adipose tissue (VAT) compared to obese individuals without MS. We tested the hypothesis that methylation level of CpG sites in the DPP4 promoter CpG island in VAT was genotype-dependent and associated with DPP4 mRNA abundance and MS-related phenotypes. The VAT DNA was extracted in 92 severely obese premenopausal women undergoing biliopancreatic derivation for the treatment of obesity. Women were nondiabetic and none of them used medication to treat MS features. Cytosine methylation rates (%) of 102 CpG sites in the DPP4 CpG island were assessed by pyrosequencing of sodium bisulfite-treated DNA. Methylation rates were >10% for CpG sites 94-102. Their mean methylation rate (%Meth(94-102)) was different between genotypes for DPP4 polymorphisms rs13015258 (P = 0.001), rs17848915 (P = 0.0004), and c.1926 G>A (P = 0.001). The %Meth(94-102) correlated negatively with DPP4 mRNA abundance (r = -0.25, P < 0.05) and positively with plasma high-density lipoprotein (HDL) cholesterol concentrations (r = 0.22, P < 0.05), whereas DPP4 mRNA abundance correlated positively with plasma total-/HDL-cholesterol ratio (r = 0.25; P < 0.05). In the VAT of nondiabetic severely obese women, genotype-dependent methylation levels of specific CpG sites in the DPP4 promoter CpG island were associated with DPP4 gene expression and variability in the plasma lipid profile. Higher DPP4 gene expression in VAT and its relationship with the plasma lipid profile may be explained by actually unknown DPP4 biological effect or, to another extent, may also be a marker of VAT inflammation known to be associated with metabolic disturbances.

Epigenetic effects of endocrine-disrupting chemicals on female reproduction: an ovarian perspective

The link between in utero and neonatal exposure to environmental toxicants, such as endocrine-disrupting chemicals (EDCs) and adult female reproductive disorders is well established in both epidemiological and animal studies. Recent studies examining the epigenetic mechanisms involved in mediating the effects of EDCs on female reproduction are gathering momentum. In this review, we describe the developmental processes that are susceptible to EDC exposures in female reproductive system, with a special emphasis on the ovary. We discuss studies with select EDCs that have been shown to have physiological and correlated epigenetic effects in the ovary, neuroendocrine system, and uterus. Importantly, EDCs that can directly target the ovary can alter epigenetic mechanisms in the oocyte, leading to transgenerational epigenetic effects. The potential mechanisms involved in such effects are also discussed.

[Hormonal imprinting--the unforeseeable future]

Hormonal imprinting takes place at the first encounter between the developing receptor and the target hormone, perinatally, causing life-long changes in the binding capacity of the receptor and the indexes influenced by it. Perinatal hormonal imprinting is absolutely needed for the maturation of receptor, however, at the same time, molecules similar to the target hormone (related hormones, synthetic drugs acting at receptor level, chemicals, environmental pollutants etc.) can cause faulty imprinting, also with (morphological, biochemical, receptorial, behavioral) consequences for life. Although imprinting is characteristic and inevitable perinatally, it can be provoked in any period of life in developing cells, especially at the weanling and adolescent age (late imprinting). There is no gene mutation during imprinting, however, the methylation pattern of the genes changes and that inherits epigenetically the imprinting, which is manifested in disposition to diseases or in diseases (e.g. tumor formation, metabolic syndrome). Imprinting is inherited between generations that could cause--in the present chemical world--evolutionary consequences. Thus, medicaments or preventive drugs, e.g. pregnancy protecting drugs or oral contraceptive pills should be given cautiously, especially in the critical periods, considering that consequences are manifested always after a long period (sometimes decades) or in the next generations.

DNA methylation levels in the 5' flanking region of the vitellogenin I gene in liver and brain of adult zebrafish (Danio rerio)--sex and tissue differences and effects of 17alpha-ethinylestradiol exposure

Vitellogenin is produced in the liver of sexually mature female fish in response to endogenous estrogens. Exogenous estrogens also induce synthesis of vitellogenin in the liver of male and juvenile fish and vitellogenin is a frequently used biomarker for estrogen exposure. The epigenetic state, e.g. histone acetylation and DNA methylation, in the region of a gene or in its 5' flanking region influences the gene expression. DNA methylation positions in multicellular eukaryotes are mostly found on cytosine bases located 5' to guanine, i.e. in CpG sites. Here, we have for the first time analyzed the DNA methylation levels of three CpG sites located in the 5' flanking region of the vitellogenin I gene in liver and brain from adult zebrafish (Danio rerio) utilizing Pyrosequencing technology. This sequencing technique allows determination of methylation levels of multiple individual CpG sites. Our purpose was to assess any differences in methylation levels related to sex, tissue and exposure to estrogen. Out of the seven vitellogenin genes identified in the zebrafish, vitellogenin I is the most highly expressed during vitellogenesis. We found that the methylation levels of all three CpG sites were higher in male liver than in female liver. In brain, which does not express vitellogenin, females and males showed similar, high methylation levels in the analyzed CpG positions. Exposure of adult zebrafish to 17alpha-ethinylestradiol (100 ng/L) for 14 days decreased the methylation levels in the 5' flanking region of vitellogenin I in the liver in both females and males. These results suggest that induced expression of vitellogenin in fish following exposure to estrogens might involve alterations in DNA methylation.

Methylation of a single intronic CpG mediates expression silencing of the PMP24 gene in prostate cancer

BACKGROUND

We previously demonstrated that a putative anti-tumor gene, peroxisomal membrane protein 4, 24 kDa (PMP24 or PXMP4), is silenced via DNA methylation of a CpG island in its 5' flanking region (5'-CGI) in prostate cancer (PCa) cells.

METHODS

To identify demethylation hypersensitive site(s) in PMP24 5'-CGI, PC-3 cells with methylated 5'-CGI were treated with a low-dose of 5-aza-2'-deoxycytidine (5-aza-dC) just sufficient to reactivate gene expression, referred as the limited demethylation approach. Gel shift assays and promoter analyzes were performed to demonstrate the role of the hypersensitive site in PMP24 gene regulation. Transfection of a methylated oligonucleotide corresponding to the hypersensitive site was conducted to determine the effect of site-specific methylation on the gene expression. Bisulfite sequencing analysis was performed to reveal the methylation status of PMP24 promoter in cultured cells and microdissected samples. In situ hybridization was applied to determine expression positivity of PMP24 mRNA.

RESULTS

A 5-aza-dC hypersensitive site encompasses two CpG dinucleotides in intron 1 was identified. Methylation of the first, but not the second, CpG dinucleotide of this site disrupted DNA-protein interactions and suppressed the gene expression. Using archival specimens, we found the first CpG dinucleotide of the hypersensitive site is hypermethylated with a loss of PMP24 mRNA expression in microdissected PCa cells when compared to normal prostatic epithelial cells.

CONCLUSIONS

These findings support a critical role for a single intronic CpG dinucleotide in PMP24 gene regulation through DNA methylation. The data suggest that methylation-mediated silencing of PMP24 is a molecular event associated with prostate carcinogenesis.

Response of adult mouse uterus to early disruption of estrogen receptor-alpha signaling is influenced by Krüppel-like factor 9

Inappropriate early exposure of the hormone-responsive uterus to estrogenic compounds is associated with increased risk for adult reproductive diseases including endometrial cancers. While the dysregulation of estrogen receptor-alpha (ESR1) signaling is well acknowledged to mediate early events in tumor initiation, mechanisms contributing to sustained ESR1 activity later in life and leading to induction of oncogenic pathways remain poorly understood. We had shown previously that the transcription factor Krüppel-like factor 9 (KLF9) represses ESR1 expression and activity in Ishikawa endometrial glandular epithelial cells. We hypothesized that KLF9 functions as a tumor suppressor, and that loss of its expression enhances ESR1 signaling. Here, we evaluated the contribution of KLF9 to early perturbations in uterine ESR1 signaling pathways elicited by the administration of synthetic estrogen diethylstilbestrol (DES) to wild-type (WT) and Klf9 null (KO) mice on postnatal days (PNDs) 1-5. Uterine tissues collected at PND84 were subjected to histological, immunological, and molecular analyses. Compared with WT mice, KO mice demonstrated larger endometrial glands and lower endometrial gland numbers; DES exposure exacerbated these differences. Loss of KLF9 expression resulted in increased glandular ESR1 immunoreactivity with DES, without effects on serum estradiol levels. Quantitative RT-PCR analyses indicated altered expression of uterine genes commonly dysregulated in endometrial cancers (Akt1, Mmp9, Slpi, and Tgfbeta1) and of those involved in growth regulation (Fos, Myc, Tert, and Syk), with loss of Klf9, alone or in concert with DES. Our data support a molecular network between KLF9 and ESR1 in the uterus, and suggest that silencing of KLF9 may contribute to endometrial dysfunctions initiated by aberrant estrogen action.

Epigenetic transgenerational actions of environmental factors in disease etiology

The ability of environmental factors to promote a phenotype or disease state not only in the individual exposed but also in subsequent progeny for successive generations is termed transgenerational inheritance. The majority of environmental factors such as nutrition or toxicants such as endocrine disruptors do not promote genetic mutations or alterations in DNA sequence. However, these factors do have the capacity to alter the epigenome. Epimutations in the germline that become permanently programmed can allow transmission of epigenetic transgenerational phenotypes. This review provides an overview of the epigenetics and biology of how environmental factors can promote transgenerational phenotypes and disease.

Xenoestrogen-induced regulation of EZH2 and histone methylation via estrogen receptor signaling to PI3K/AKT

Although rapid, membrane-activated estrogen receptor (ER) signaling is no longer controversial, the biological function of this nongenomic signaling is not fully characterized. We found that rapid signaling from membrane-associated ER regulates the histone methyltransferase enhancer of Zeste homolog 2 (EZH2). In response to both 17beta-estradiol (E2) and the xenoestrogen diethylstilbestrol, ER signaling via phosphatidylinositol 3-kinase/protein kinase B phosphorylates EZH2 at S21, reducing levels of trimethylation of lysine 27 on histone H3 in hormone-responsive cells. During windows of uterine development that are susceptible to developmental reprogramming, activation of this ER signaling pathway by diethylstilbestrol resulted in phosphorylation of EZH2 and reduced levels of trimethylation of lysine 27 on histone H3 in chromatin of the developing uterus. Furthermore, activation of nongenomic signaling reprogrammed the expression profile of estrogen-responsive genes in uterine myometrial cells, suggesting this as a potential mechanism for developmental reprogramming caused by early-life exposure to xenoestrogens. These data demonstrate that rapid ER signaling provides a direct linkage between xenoestrogen-induced nuclear hormone receptor signaling and modulation of the epigenetic machinery during tissue development.

Induction of epigenetic alterations by dietary and other environmental factors

Dietary and other environmental factors induce epigenetic alterations which may have important consequences for cancer development. This chapter summarizes current knowledge of the impact of dietary, lifestyle, and environmental determinants of cancer risk and proposes that effects of these exposures might be mediated, at least in part, via epigenetic mechanisms. Evidence is presented to support the hypothesis that all recognized epigenetic marks (including DNA methylation, histone modification, and microRNA (miRNA) expression) are influenced by environmental exposures, including diet, tobacco, alcohol, physical activity, stress, environmental carcinogens, genetic factors, and infectious agents which play important roles in the etiology of cancer. Some of these epigenetic modifications change the expression of tumor suppressor genes and oncogenes and, therefore, may be causal for tumorigenesis. Further work is required to understand the mechanisms through which specific environmental factors produce epigenetic changes and to identify those changes which are likely to be causal in the pathogenesis of cancer and those which are secondary, or bystander, effects. Given the plasticity of epigenetic marks in response to cancer-related exposures, such epigenetic marks are attractive candidates for the development of surrogate endpoints which could be used in dietary or lifestyle intervention studies for cancer prevention. Future research should focus on identifying epigenetic marks which are (i) validated as biomarkers for the cancer under study; (ii) readily measured in easily accessible tissues, for example, blood, buccal cells, or stool; and (iii) altered in response to dietary or lifestyle interventions for which there is convincing evidence for a relationship with cancer risk.

Epigenetic inheritance in mammals: evidence for the impact of adverse environmental effects

The epigenome is the overall epigenetic state of a cell and represents the ensemble of chromatin modifications. It is an essential mechanism for the regulation of the genome that depends on modifications of DNA and histones but does not involve any change of the DNA sequence. It was previously assumed that in order for appropriate cellular development and differentiation to occur in mammals, the epigenome was fully erased and reestablished between generations. However, several examples of incomplete erasure at specific genes have been reported, and this is suggested to be associated with the epigenetic inheritance of gene profiles. Although the existence of such a mode of inheritance has been controversial, there is increasing evidence that it does occur in rodents and humans. In this review, we discuss the evidence that adverse environmental factors can affect not only the individuals directly exposed to these factors but also their offspring. Because the epigenome is sensitive to environmental influence and, in some cases, can, in part, be transmitted across generations, it provides a potential mechanism for the transgenerational transmission of the impact of environmental factors. Environmental factors examined include exposure to toxicants, diet, and postnatal care, and DNA methylation is the main mechanism discussed in this review.

Epigenetic transgenerational effects of endocrine disruptors on male reproduction

Endocrine-disrupting chemicals generally function as steroid receptor signaling antagonists or agonists that influence development to promote adult-onset disease. Exposure to the endocrine disruptors during the initiation of male reproductive tract development interferes with the normal hormonal signaling and formation of male reproductive organs. In particular, exposure to the endocrine disruptor vinclozolin promotes transgenerational transmission of adult-onset disease states such as male infertility, increased frequencies of tumors, prostate disease, kidney diseases, and immune abnormalities that develop as males age. An epigenetic change in the germ line would be involved in the transgenerational transmission of these induced phenotypes. Nevertheless, other studies have also reported transgenerational transmission of induced epigenetic changes, without altering the germ line. Here we propose a nomenclature to help clarify both cases of transgenerational epigenetic transmission. An intrinsic epigenetic transgenerational process would require a germ-line involvement, a permanent alteration in the germ cell epigenome, and only one exposure to the environmental factor. An extrinsic epigenetic transgenerational process would involve an epigenetic alteration in a somatic tissue and require exposure at each generation to maintain the transgenerational phenotype.

Long-term effects of environmental endocrine disruptors on reproductive physiology and behavior

It is well established that, over the course of development, hormones shape the vertebrate brain such that sex specific physiology and behaviors emerge. Much of this occurs in discrete developmental windows that span gestation through the prenatal period, although it is now becoming clear that at least some of this process continues through puberty. Perturbation of this developmental progression can permanently alter the capacity for reproductive success. Wildlife studies have revealed that exposure to endocrine disrupting compounds (EDCs), either naturally occurring or man made, can profoundly alter reproductive physiology and ultimately impact entire populations. Laboratory studies in rodents and other species have elucidated some of the mechanisms by which this occurs and strongly indicate that humans are also vulnerable to disruption. Use of hormonally active compounds in human medicine has also unfortunately revealed that the developing fetus can be exposed to and affected by endocrine disruptors, and that it might take decades for adverse effects to manifest. Research within the field of environmental endocrine disruption has also contributed to the general understanding of how early life experiences can alter reproductive physiology and behavior through non-genomic, epigenetic mechanisms such as DNA methylation and histone acetylation. These types of effects have the potential to impact future generations if the germ line is affected. This review provides an overview of how exposure to EDCs, particularly those that interfere with estrogen action, impacts reproductive physiology and behaviors in vertebrates.

Epigenetic effects of glucocorticoids

The early nurturing environment has persistent influences on developmental programming of inter-individual differences in metabolic and endocrine function that contribute to emotional and cognitive performance through life. These effects are mediated, in part, through neonatal programming of hypothalamic-pituitary-adrenal (HPA) axis function. Animal models support this hypothesis. For example, in the rat natural variations in maternal care influence HPA axis stress reactivity in the offspring via long-term changes in tissue-specific gene expression. Studies in vivo and in vitro show that maternal licking and grooming increases glucocorticoid receptor expression in the offspring via increased hippocampal serotonergic tone accompanied by increased histone acetylase transferase activity, histone acetylation and DNA demethylation mediated by the transcription factor nerve growth factor-inducible protein-A. These effects are reversed by early postnatal cross-fostering and by pharmacological manipulations, including trichostatin A (TSA) and l-methionine administration in adulthood. These studies demonstrate that an epigenetic state of a gene can be established through early in life experience, and is potentially reversible in adult life. Accordingly, epigenetic modifications in target gene promoters in response to environmental demand may ensure stable yet dynamic regulation that mediates persistent changes in biological and behavioral phenotype over the lifespan.

Prospects for epigenetic epidemiology

Epigenetic modification can mediate environmental influences on gene expression and can modulate the disease risk associated with genetic variation. Epigenetic analysis therefore holds substantial promise for identifying mechanisms through which genetic and environmental factors jointly contribute to disease risk. The spatial and temporal variance in epigenetic profile is of particular relevance for developmental epidemiology and the study of aging, including the variable age at onset for many common diseases. This review serves as a general introduction to the topic by describing epigenetic mechanisms, with a focus on DNA methylation; genetic and environmental factors that influence DNA methylation; epigenetic influences on development, aging, and disease; and current methodology for measuring epigenetic profile. Methodological considerations for epidemiologic studies that seek to include epigenetic analysis are also discussed.

The dynamic and static modification of the epigenome by hormones: a role in the developmental origin of hormone related cancers

There are numerous diseases associated with abnormal hormonal regulation and these include cancers of the breast and prostate. There is substantial evidence that early hormonal perturbations (in utero or during early development) are associated with increased disease susceptibility later in life. These perturbations may arise from exposure to environmental agents or endocrine disruptors which mimic hormones and disrupt normal hormonal signaling. Epigenetic alterations have often been proposed as the underlying mechanism by which early hormonal perturbations may give rise to disease in adulthood. Currently, there is minimal evidence to support a direct link between early hormonal perturbations and epigenetic modifications; or between epigenetic alterations and subsequent onset of cancer. Given that epigenetic modifications may play an important role in hormone-dependent cancers, it is essential to better understand the relationship between the hormonal environment and epigenetic modifications in both normal and disease states. In this review, we highlight several important studies which support the hypothesis that: hormonal perturbations early in life may result in epigenetic changes that may modify hormone receptor function, thereby contributing to an increased risk of developing hormone-related cancers.

Toxicogenomics: transcription profiling for toxicology assessment

Toxicogenomics, the application of transcription profiling to toxicology, has been widely used for elucidating the molecular and cellular actions of chemicals and other environmental stressors on biological systems, predicting toxicity before any functional damages, and classification of known or new toxicants based on signatures of gene expression. The success of a toxicogenomics study depends upon close collaboration among experts in different fields, including a toxicologist or biologist, a bioinformatician, statistician, physician and, sometimes, mathematician. This review is focused on toxicogenomics studies, including transcription profiling technology, experimental design, significant gene extraction, toxicological results interpretation, potential pathway identification, database input and the applications of toxicogenomics in various fields of toxicological study.

Neonatal exposure to diethylstilbestrol alters expression of DNA methyltransferases and methylation of genomic DNA in the mouse uterus

Perinatal exposure to diethylstilbestrol (DES) can have numerous adverse effects on the reproductive organs later in life, such as vaginal clear-cell adenocarcinoma. Epigenetic processes including DNA methylation may be involved in the mechanisms. We subcutaneously injected DES to neonatal C57BL/6 mice. At days 5, 14, and 30, expressions of DNA methyltransferases (Dnmts) Dnmt1, Dnmt3a, and Dnmt3b, and transcription factors Sp1 and Sp3 were examined. We also performed restriction landmark genomic scanning (RLGS) to detect aberrant DNA methylation. Real-time RT-PCR revealed that expressions of Dnmt1, Dnmt3b, and Sp3 were decreased at day 5 in DES-treated mice, and that those of Dnmt1, Dnmt3a, and Sp1 were also decreased at day 14. RLGS analysis revealed that 5 genomic loci were demethylated, and 5 other loci were methylated by DES treatment. Two loci were cloned, and differential DNA methylation was quantified. Our results indicated that DES altered the expression levels of Dnmts and DNA methylation.

The role of parental and grandparental epigenetic alterations in familial cancer risk

Epigenetic alterations of the genome such as DNA promoter methylation and chromatin remodeling play an important role in tumorigenesis. These modifications take place throughout development with subsequent events occurring later in adulthood. Recent studies, however, suggest that some epigenetic alterations that influence cancer risk are inherited through the germline from parent to child and are observed in multiple generations. Epigenetic changes may be inherited as Mendelian, non-Mendelian, or environmentally induced traits. Here, we will discuss Mendelian, non-Mendelian, and environmentally induced patterns of multigenerational epigenetic alterations as well as some possible mechanisms for how these events may be occurring.

Persistent hypomethylation in the promoter of nucleosomal binding protein 1 (Nsbp1) correlates with overexpression of Nsbp1 in mouse uteri neonatally exposed to diethylstilbestrol or genistein

Neonatal exposure of CD-1 mice to diethylstilbestrol (DES) or genistein (GEN) induces uterine adenocarcinoma in aging animals. Uterine carcinogenesis in this model is ovarian dependent because its evolution is blocked by prepubertal ovariectomy. This study seeks to discover novel uterine genes whose expression is altered by such early endocrine disruption via an epigenetic mechanism. Neonatal mice were treated with 1 or 1000 microg/kg DES, 50 mg/kg GEN, or oil (control) on d 1-5. One group of treated mice was killed before puberty on d 19. Others were ovariectomized or left intact, and killed at 6 and 18 months of age. Methylation-sensitive restriction fingerprinting was performed to identify differentially methylated sequences associated with neonatal exposure to DES/GEN. Among 14 candidates, nucleosomal binding protein 1 (Nsbp1), the gene for a nucleosome-core-particle binding protein, was selected for further study because of its central role in chromatin remodeling. In uteri of immature control mice, Nsbp1 promoter CpG island (CGI) was minimally methylated. Once control mice reached puberty, the Nsbp1 CGI became hypermethylated, and gene expression declined further. In contrast, in neonatal DES/GEN-treated mice, the Nsbp1 CGI stayed anomalously hypomethylated, and the gene exhibited persistent overexpression throughout life. However, if neonatal DES/GEN-treated mice were ovariectomized before puberty, the CGI remained minimally to moderately methylated, and gene expression was subdued except in the group treated with 1000 microg/kg DES. Thus, the life reprogramming of uterine Nsbp1 expression by neonatal DES/GEN exposure appears to be mediated by an epigenetic mechanism that interacts with ovarian hormones in adulthood.

Developmental exposure to Bisphenol a impairs the uterine response to ovarian steroids in the adult

Morphoregulator genes like members of the Hox gene family regulate uterine development and are associated with endocrine-related processes such as endometrial proliferation and differentiation in the adult uterus. Exposure to neonatal endocrine disruptors could affect signaling events governed by Hox genes, altering the developmental trajectory of the uterus with lasting consequences. We investigated whether neonatal exposure to bisphenol A (BPA) alters Hoxa10 and Hoxa11 mRNA uterine expression shortly after treatment as well as in the adult. Moreover, we studied whether xenoestrogen exposure may affect the adult uterine response to hormonal stimuli. Newborn females received vehicle, 0.05 mg/kg.d BPA, 20 mg/kg*d BPA, or diethylstilbestrol (0.2 microg/kg*d) on postnatal d 1, 3, 5, and 7). At postnatal d 8, real time RT-PCR assays showed a decrease in Hoxa10 and Hoxa11 expression in all xenoestrogen-treated groups. To evaluate the long-term effects, we used adult ovariectomized rats with hormonal replacement. The subepithelial stroma in BPA- and diethylstilbestrol-treated animals showed an impaired proliferative response to steroid treatment associated with a silencing of Hoxa10 but not associated with changes in the methylation pattern of the Hoxa10 promoter. BPA animals showed that the Hoxa10 reduction was accompanied by an increased stromal expression of the silencing mediator for retinoic acid and thyroid hormone receptor. The spatial coexpression of steroid receptors Hoxa10 and silencing mediator for retinoic acid and thyroid hormone receptor was established using immunofluorescence. Our data indicate that postnatal BPA exposure affects the steroid hormone-responsiveness of uterine stroma in adulthood. Whether this impaired hormonal response is associated with effects on uterine receptivity and decidualization is currently under investigation.

Effect of tamoxifen treatment on global and insulin-like growth factor 2-H19 locus-specific DNA methylation in rat spermatozoa and its association with embryo loss

OBJECTIVE

To determine the effect of tamoxifen treatment on global and insulin-like growth factor 2-H19 imprinting control region (Igf2-H19 ICR)-specific DNA methylation in rat spermatozoa and analyze its association with postimplantation loss.

DESIGN

Experimental prospective study.

SETTING

Animal research and academic research facility.

SUBJECT(S)

Male and female 75-day-old Holtzman rats.

INTERVENTION(S)

Global and Igf2-H19 ICR-specific DNA methylation was analyzed in an epididymal sperm sample in control and tamoxifen-treated rats at a dose of 0.4 mg tamoxifen/kg/day. DNA methylation status was correlated to postimplantation loss in females mated with tamoxifen-treated males.

MAIN OUTCOME MEASURE(S)

Global sperm DNA methylation level, methylation status of Igf2-H19 ICR in sperm, postimplantation loss.

RESULT(S)

Tamoxifen treatment significantly reduced methylation at Igf2-H19 ICR in epididymal sperm. However, the global methylation level was not altered. A mating experiment confirmed a significant increase in postimplantation loss upon tamoxifen treatment and showed significant correlation with methylation at Igf2-H19 ICR.

CONCLUSION(S)

Reduced DNA methylation at Igf2-H19 ICR in rat spermatozoa upon tamoxifen treatment indicated a role of estrogen-associated signaling in the acquisition of paternal-specific imprints during spermatogenesis. In addition, association between DNA methylation and postimplantation loss suggests that errors in paternal imprints at Igf2-H19 ICR could affect embryo development.

Developmental reprogramming of IGF signaling and susceptibility to endometrial hyperplasia in the rat

In rodents, a brief neonatal exposure of the developing reproductive tract to the xenoestrogen, diethylstilbestrol (DES) reprograms developing tissues to increase susceptibility to tumorigenesis in adult animals, including uterine adenocarcinoma. Progression from a normal endometrium to carcinoma occurs via the intermediate stage of endometrial hyperplasia. We previously reported that endometrial hyperplasia in postmenopausal women is linked to abnormal insulin-like growth factor-I (IGF-I) signaling. To identify early events involved in the development of hyperplasia in the endometrium, we examined expression and activation of IGF-I pathway components in endometrium of rats exposed to DES. By 5 months of age, 36/60 (60%) of rats exposed to DES on days 3-5 after birth developed endometrial hyperplasia compared to 0% of vehicle-treated controls. Consistent with activation of a mitogenic signaling pathway, Ki67-positive cells increased in DES-exposed endometrium despite compromised ovarian function and hypoestrogenic milieu characteristic of DES-exposed animals. The endometrium of DES-exposed rats overexpressed IGF-II and insulin receptor substrate-1 (IRS-1) and exhibited elevated Akt expression and activation (as judged by phosphorylation) and mTOR signaling (phosphorylation of S6) compared to vehicle-treated endometrium. In contrast to vehicle-treated endometrium, in which negative feedback to IRS-1 was observed (phosphorylation of S636/639), negative feedback to IRS-1 was absent in DES-exposed endometrium. These data support a central role for IGF-I signaling in the development of both human and rodent endometrial hyperplasia. Furthermore, both global activation of IGF-IR signaling and abrogation of negative feedback to IRS-1 appear to be reprogrammed by DES in endometrial hyperplasia, implicating for the first time loss of negative feedback to IRS-1 in development of a preneoplastic lesion.

Developmental programming and endocrine disruptor effects on reproductive neuroendocrine systems

The ability of a species to reproduce successfully requires the careful orchestration of developmental processes during critical time points, particularly the late embryonic and early postnatal periods. This article begins with a brief presentation of the evidence for how gonadal steroid hormones exert these imprinting effects upon the morphology of sexually differentiated hypothalamic brain regions, the mechanisms underlying these effects, and their implications in adulthood. Then, I review the evidence that aberrant exposure to hormonally-active substances such as exogenous endocrine-disrupting chemicals (EDCs), may result in improper hypothalamic programming, thereby decreasing reproductive success in adulthood. The field of endocrine disruption has shed new light on the discipline of basic reproductive neuroendocrinology through studies on how early life exposures to EDCs may alter gene expression via non-genomic, epigenetic mechanisms, including DNA methylation and histone acetylation. Importantly, these effects may be transmitted to future generations if the germline is affected via transgenerational, epigenetic actions. By understanding the mechanisms by which natural hormones and xenobiotics affect reproductive neuroendocrine systems, we will gain a better understanding of normal developmental processes, as well as develop the potential ability to intervene when development is disrupted.

Proceedings of the Summit on Environmental Challenges to Reproductive Health and Fertility: executive summary

The 2007 Summit on Environmental Challenges to Reproductive Health and Fertility convened scientists, health care professionals, community groups, political representatives, and the media to hear presentations on the impact of environmental contaminants on reproductive health and fertility, and to discuss opportunities to improve health through research, education, communication, and policy. Environmental reproductive health focuses on exposures to environmental contaminants, particularly during critical periods of development, and their potential effects on future reproductive health, including conception, fertility, pregnancy, adolescent development, and adult health. Approximately 87,000 chemical substances are registered for commercial use in the United States, with ubiquitous human exposures to environmental contaminants in air, water, food, and consumer products. Exposures during critical windows of susceptibility may result in adverse effects with lifelong and even intergenerational health impacts. Effects can include impaired development and function of the reproductive tract and permanently altered gene expression, leading to metabolic and hormonal disorders, reduced fertility and fecundity, and illnesses such as testicular, prostate, uterine, and cervical cancers later in life. This executive summary reviews effects of pre- and postnatal exposures on male and female reproductive health, and provides a series of recommendations for advancing the field in the areas of research, policy, health care, and community action.

Key developments in endocrine disrupter research and human health

Environmental etiologies involving exposures to chemicals that mimic endogenous hormones are proposed for a number of adverse human health effects, including infertility, abnormal prenatal and childhood development, and reproductive cancers (National Research Council, 1999; World Health Organization, 2002). Endocrine disrupters represent a significant area of environmental research with important implications for human health. This article provides an overview of some of the key developments in this field that may enhance our ability to assess the human health risks posed by exposure to endocrine disrupters. Advances in methodologies of hazard identification (toxicogenomics, transcriptomics, proteomics, metabolomics, bioinformatics) are discussed, as well as epigenetics and emerging biological endpoints.

Proceedings of the Summit on Environmental Challenges to Reproductive Health and Fertility: executive summary

The 2007 Summit on Environmental Challenges to Reproductive Health and Fertility convened scientists, health care professionals, community groups, political representatives, and the media to hear presentations on the impact of environmental contaminants on reproductive health and fertility, and to discuss opportunities to improve health through research, education, communication, and policy. Environmental reproductive health focuses on exposures to environmental contaminants, particularly during critical periods of development, and their potential effects on future reproductive health, including conception, fertility, pregnancy, adolescent development, and adult health. Approximately 87,000 chemical substances are registered for commercial use in the United States, with ubiquitous human exposures to environmental contaminants in air, water, food, and consumer products. Exposures during critical windows of susceptibility may result in adverse effects with lifelong and even intergenerational health impacts. Effects can include impaired development and function of the reproductive tract and permanently altered gene expression, leading to metabolic and hormonal disorders, reduced fertility and fecundity, and illnesses such as testicular, prostate, uterine, and cervical cancers later in life. This executive summary reviews effects of pre- and postnatal exposures on male and female reproductive health, and provides a series of recommendations for advancing the field in the areas of research, policy, health care, and community action.

Fetal and early postnatal environmental exposures and reproductive health effects in the female

This short review presents current research into the role of the environment in normal female reproductive function and pathogenesis, specifically focusing on the ovary and uterus.

Maternal nutrient supplementation counteracts bisphenol A-induced DNA hypomethylation in early development

The hypothesis of fetal origins of adult disease posits that early developmental exposures involve epigenetic modifications, such as DNA methylation, that influence adult disease susceptibility. In utero or neonatal exposure to bisphenol A (BPA), a high-production-volume chemical used in the manufacture of polycarbonate plastic, is associated with higher body weight, increased breast and prostate cancer, and altered reproductive function. This study shows that maternal exposure to this endocrine-active compound shifted the coat color distribution of viable yellow agouti (Avy) mouse offspring toward yellow by decreasing CpG (cytosine-guanine dinucleotide) methylation in an intracisternal A particle retrotransposon upstream of the Agouti gene. CpG methylation also was decreased at another metastable locus, the CDK5 activator-binding protein (CabpIAP). DNA methylation at the Avy locus was similar in tissues from the three germ layers, providing evidence that epigenetic patterning during early stem cell development is sensitive to BPA exposure. Moreover, maternal dietary supplementation, with either methyl donors like folic acid or the phytoestrogen genistein, negated the DNA hypomethylating effect of BPA. Thus, we present compelling evidence that early developmental exposure to BPA can change offspring phenotype by stably altering the epigenome, an effect that can be counteracted by maternal dietary supplements.

Nutri-epigenomics: lifelong remodelling of our epigenomes by nutritional and metabolic factors and beyond

The phenotype of an individual is the result of complex interactions between genotype, epigenome and current, past and ancestral environment, leading to lifelong remodelling of our epigenomes. Various replication-dependent and -independent epigenetic mechanisms are involved in developmental programming, lifelong stochastic and environmental deteriorations, circadian deteriorations, and transgenerational effects. Several types of sequences can be targets of a host of environmental factors and can be associated with specific epigenetic signatures and patterns of gene expression. Depending on the nature and intensity of the insult, the critical spatiotemporal windows and developmental or lifelong processes involved, these epigenetic alterations can lead to permanent changes in tissue and organ structure and function, or to reversible changes using appropriate epigenetic tools. Given several encouraging trials, prevention and therapy of age- and lifestyle-related diseases by individualised tailoring of optimal epigenetic diets or drugs are conceivable. However, these interventions will require intense efforts to unravel the complexity of these epigenetic, genetic and environment interactions and to evaluate their potential reversibility with minimal side effects.

Disruption of the developing female reproductive system by phytoestrogens: Genistein as an example

Studies in our laboratory have shown that exposure to genistein causes deleterious effects on the developing female reproductive system. Mice treated neonatally on days 1-5 by subcutaneous injection of genistein (0.5-50 mg/kg) exhibited altered ovarian differentiation leading to multioocyte follicles (MOFs) at 2 months of age. Ovarian function and estrous cyclicity were also disrupted by neonatal exposure to genistein with increasing severity observed over time. Reduced fertility was observed in mice treated with genistein (0.5, 5, or 25 mg/kg) and infertility was observed at 50 mg/kg. Mammary gland and behavioral endpoints were also affected by neonatal genistein treatment. Further, transgenerational effects were observed; female offspring obtained from breeding genistein treated females (25 mg/kg) to control males had increased MOFs. Thus, neonatal treatment with genistein at environmentally relevant doses caused adverse consequences on female development which is manifested in adulthood. Whether adverse effects occur in human infants exposed to soy-based products such as soy infant formulas is unknown but the neonatal murine model may help address some of the current uncertainties since we have shown that many effects obtained from feeding genistin, the glycosolated form of genistein found in soy formula, are similar to those obtained from injecting genistein.

Epigenetic reprogramming and imprinting in origins of disease

The traditional view that gene and environment interactions control disease susceptibility can now be expanded to include epigenetic reprogramming as a key determinant of origins of human disease. Currently, epigenetics is defined as heritable changes in gene expression that do not alter DNA sequence but are mitotically and transgenerationally inheritable. Epigenetic reprogramming is the process by which an organism's genotype interacts with the environment to produce its phenotype and provides a framework for explaining individual variations and the uniqueness of cells, tissues, or organs despite identical genetic information. The main epigenetic mediators are histone modification, DNA methylation, and non-coding RNAs. They regulate crucial cellular functions such as genome stability, X-chromosome inactivation, gene imprinting, and reprogramming of non-imprinting genes, and work on developmental plasticity such that exposures to endogenous or exogenous factors during critical periods permanently alter the structure or function of specific organ systems. Developmental epigenetics is believed to establish "adaptive" phenotypes to meet the demands of the later-life environment. Resulting phenotypes that match predicted later-life demands will promote health, while a high degree of mismatch will impede adaptability to later-life challenges and elevate disease risk. The rapid introduction of synthetic chemicals, medical interventions, environmental pollutants, and lifestyle choices, may result in conflict with the programmed adaptive changes made during early development, and explain the alarming increases in some diseases. The recent identification of a significant number of epigenetically regulated genes in various model systems has prepared the field to take on the challenge of characterizing distinct epigenomes related to various diseases. Improvements in human health could then be redirected from curative care to personalized, preventive medicine based, in part, on epigenetic markings etched in the "margins" of one's genetic make-up.

In utero-initiated cancer: the role of reactive oxygen species

It is becoming more evident that not only can drugs and environmental chemicals interfere with normal fetal development by causing structural malformations, such as limb defects, but that xenobiotic exposure during development can also cause biochemical and functional abnormalities that may ultimately lead to cancer later on in life. Fetal toxicity may be partly mediated by the embryonic bioactivation of xenobiotics to free radical intermediates that can lead to oxidative stress and potentially lead, in some cases, to carcinogenesis. Using a number of examples, this review will focus on the role of reactive oxygen species (ROS) in the mechanisms pertaining to in utero initiated cancers.

Techniques used in studies of epigenome dysregulation due to aberrant DNA methylation: an emphasis on fetal-based adult diseases

Epigenetic changes are heritable modifications that do not involve alterations in the primary DNA sequence. They regulate crucial cellular functions such as genome stability, X-chromosome inactivation, and gene imprinting. Epidemiological and experimental observations now suggest that such changes may also explain the fetal basis of adult diseases such as cancer, obesity, diabetes, cardiovascular disorders, neurological diseases, and behavioral modifications. The main molecular events known to initiate and sustain epigenetic modifications are histone modification and DNA methylation. This review specifically focuses on existing and emerging technologies used in studying DNA methylation, which occurs primarily at CpG dinucleotides in the genome. These include standard exploratory tools used for global profiling of DNA methylation and targeted gene investigation: methylation sensitive restriction fingerprinting (MSRF), restriction landmark genomic scanning (RLGS), methylation CpG island amplification-representational difference analysis (MCA-RDA), differential methylation hybridization (DMH), and cDNA microarrays combined with treatment with demethylating agents and inhibitors of histone deacetylase. The basic operating principals, resource requirements, applications, and benefits and limitations of each methodology are discussed. Validation methodologies and functional assays needed to establish the role of a CpG-rich sequence in regulating the expression of a target or candidate gene are outlined. These include in silico database searches, methylation status studies (bisulfite genomic sequencing, COBRA, MS-PCR, MS-SSCP), gene expression studies, and promoter activity analyses. Our intention is to give readers a starting point for choosing methodologies and to suggest a workflow to follow during their investigations. We believe studies of epigenetic changes such as DNA methylation hold great promise in understanding the early origins of adult diseases and in advancing their diagnosis, prevention, and treatment.

Environmental epigenomics and disease susceptibility

Epidemiological evidence increasingly suggests that environmental exposures early in development have a role in susceptibility to disease in later life. In addition, some of these environmental effects seem to be passed on through subsequent generations. Epigenetic modifications provide a plausible link between the environment and alterations in gene expression that might lead to disease phenotypes. An increasing body of evidence from animal studies supports the role of environmental epigenetics in disease susceptibility. Furthermore, recent studies have demonstrated for the first time that heritable environmentally induced epigenetic modifications underlie reversible transgenerational alterations in phenotype. Methods are now becoming available to investigate the relevance of these phenomena to human disease.

Developmental exposure to endocrine disruptors and the obesity epidemic

Xenobiotic and dietary compounds with hormone-like activity can disrupt endocrine signaling pathways that play important roles during perinatal differentiation and result in alterations that are not apparent until later in life. Evidence implicates developmental exposure to environmental hormone-mimics with a growing list of health problems. Obesity is currently receiving needed attention since it has potential to overwhelm health systems worldwide with associated illnesses such as diabetes and cardiovascular disease. Here, we review the literature that proposes an association of exposure to environmental endocrine disrupting chemicals with the development of obesity. We describe an animal model of developmental exposure to diethylstilbestrol (DES), a potent perinatal endocrine disruptor with estrogenic activity, to study mechanisms involved in programming an organism for obesity. This experimental animal model provides an example of the growing scientific field termed "the developmental origins of adult disease" and suggests new targets of abnormal programming by endocrine disrupting chemicals.

Cancer Susceptibility: Epigenetic Manifestation of Environmental Exposures

Cancer is a disease that results from both genetic and epigenetic changes. Discordant phenotypes and varying incidences of complex diseases such as cancer in monozygotic twins as well as genetically identical laboratory animals have long been attributed to differences in environmental exposures. Accumulating evidence indicates, however, that disparities in gene expression resulting from variable modifications in DNA methylation and chromatin structure in response to the environment also play a role in differential susceptibility to disease. Despite a growing consensus on the importance of epigenetics in the etiology of chronic human diseases, the genes most prone to epigenetic dysregulation are incompletely defined. Moreover, neither the environmental agents most strongly affecting the epigenome nor the critical windows of vulnerability to environmentally induced epigenetic alterations are adequately characterized. These major deficits in knowledge markedly impair our ability to understand fully the etiology of cancer and the importance of the epigenome in diagnosing and preventing this devastating disease.

Timing of Dietary Estrogenic Exposures and Breast Cancer Risk

The same dietary component, such as fat or phytochemicals in plant foods, can have an opposite effect on breast cancer risk if exposed in utero through a pregnant mother or at puberty. Dietary exposures during pregnancy often have similar effects on breast cancer risk among mothers and their female offspring. High fat intake and obesity are illustrative examples: excessive pregnancy weight gain that increases high birth weight is associated with increased breast cancer risk among mothers and daughters. High body weight during childhood is inversely linked to later breast cancer risk. The main reason why the age when dietary exposures occur determines their effect on breast cancer risk likely reflects the extensive programming of the mammary gland during fetal life and subsequent reprogramming at puberty and pregnancy. Programming is a series of epigenetic/transcriptional modifications in gene expression that can be influenced by changes in the hormonal environment induced, for example, by diet. Because epigenetic modifications are inherited by daughter cells, they can persist throughout life if they occur in mammary stem cells or uncommitted mammary myoepithelial or luminal progenitor cells. Our results indicate that the estrogen receptor (ER), mitogen-activated protein kinase (MAPK), and the tumor suppressors BRCA1, p53, and caveolin-1 are among the genes affected by diet-induced alterations in programming/reprogramming. Consequently, mammary gland morphology may be altered in a manner that increases or reduces susceptibility to malignant transformation, including an increase/reduction in cell proliferation, differentiation, and survival, or in the number of terminal end buds (TEBs) or pregnancy-induced mammary epithelial cells (PI-MECs) that are the sites where breast cancer is initiated. Thus, dietary exposures during pregnancy and puberty may play an important role in determining later risk by inducing epigenetic changes that modify vulnerability to breast cancer.

Fetal origins of breast cancer

Susceptibility to breast cancer might be pre-determined in utero. Alterations in the fetal hormonal environment, caused by either maternal diet or exposure to environmental factors with endocrine activities, can modify the epigenome, and these modifications are inherited in somatic daughter cells and maintained throughout life. These epigenetic modifications might lead to changes in mammary gland development, such as increased vulnerability of epithelial targets for malignant transformation. According to this hypothesis, on post-pubertal exposure to an initiating factor, such as a carcinogen, high levels of hormones and radiation, the mammary epithelial targets, perhaps stem cells, in terminal end buds/terminal ductal lobular units would be at an increased risk of malignant transformation. The increased susceptibility for cancer initiation might result from high levels of cell proliferation, reduced apoptosis and/or altered stromal regulation. Thus, maternal diet and environmental exposure might increase the risk of breast cancer by inducing permanent epigenetic changes in the fetus that alter the susceptibility to factors that can initiate breast cancer. Identifying the epigenetically altered target genes and their ligands might lead to strategies to prevent this disease in some women.