Role of epigenetic regulation of Igf2 and H19 in 2,3,7,8-Tetrachlorobenzo-p-dioxin (TCDD)-induced ovarian toxicity in offspring rats

Serum metabolism distribution in individuals exposed to dioxins: A case study of residents near the municipal solid waste incinerators in China

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) have attracted considerable attention owing to their environmental persistence, bioaccumulation, and high toxicity. This study aimed to investigate changes in serum metabolites following exposure to PCDD/Fs and to reveal a novel pathogenesis of PCDD/Fs. Serum samples were collected from 75 residents living near a municipal solid waste incinerator in China to analyse the relationship between PCDD/Fs and serum metabolic components. The serum level in the low-exposure group [19.07 (13.44-23.89) pg-TEQ/L] was significantly lower than that in the high-exposure group [115.60 (52.28-592.65) pg-TEQ/L]. Non-targeted metabolomic studies based on liquid chromatography-high resolution mass spectrometry have been applied to the metabolomic analysis of serum. Thirty-seven metabolites with significant differences among the different groups were identified as biomarkers. Pathway analysis revealed that high dioxin exposure perturbed various biological processes, including glycerol phospholipid metabolism and the interconversion of pentose and glucuronate. The results of a population health survey showed that the serum dioxin concentration in patients with diabetes was significantly higher than that in the control population. These findings suggest that dioxin exposure is associated with several potential adverse health risks, including inflammation, diabetes, and cardiovascular disease, through metabolic changes.

Human-relevant exposure to di-n-butyl phthalate tampers with the ovarian insulin-like growth factor 1 system and disrupts folliculogenesis in young adult mice

Phthalates are compounds used in consumer and medical products worldwide. Phthalate exposure in women has been demonstrated by detection of phthalate metabolites in their urine and ovarian follicular fluid. High urinary phthalate burden has been associated with reduced ovarian reserve and oocyte retrieval in women undergoing assisted reproduction. Unfortunately, no mechanistic explanation for these associations is available. In short term in vivo and in vitro animal studies modeling human-relevant exposures to di-n-butyl phthalate (DBP), we have identified ovarian folliculogenesis as a target for phthalate exposures. In the present study, we investigated whether DBP exposure negatively influences insulin-like growth factor 1 (IGF1) signaling in the ovary and disrupts ovarian folliculogenesis. CD-1 female mice were exposed to corn oil (vehicle) or DBP (10 µg/kg/day, 100 µg/kg/day, or 1000 mg/kg/day) for 20-32 days. Ovaries were collected as animals reached the proestrus stage to achieve estrous cycle synchronization. Levels of mRNAs encoding IGF1 and 2 (Igf1 and Igf2), IGF1 receptor (Igf1r), and IGF-binding proteins 1-6 (Ifgbp1-6) were measured in whole ovary homogenates. Ovarian follicle counts and immunostaining for phosphorylated IGF1R protein (pIGF1R) were used to evaluate folliculogenesis and IGF1R activation, respectively. DBP exposure, at a realistic dose that some women may experience (100 µg/kg/day for 20-32 days), reduced ovarian Igf1 and Igf1r mRNA expression and reduced small ovarian follicle numbers and primary follicle pIGF1R positivity in DBP-treated mice. These findings reveal that DBP tampers with the ovarian IGF1 system and provide molecular insight into how phthalates could influence the ovarian reserve in females.

Paternal genetic intergenerational and transgenerational effects of cadmium exposure on hormone synthesis disorders in progeny ovarian granulosa cells

To investigate the paternal genetic effects of cadmium (Cd) exposure on hormone synthesis disorders in the ovarian granulosa cells (GCs) of offspring. Here, male Sprague‒Dawley (SD) rats were gavaged with CdCl₂ (0, 0.5, 2, 8 mg/kg) from postnatal day (PND) 28-56, followed by mating with newly purchased healthy adult females to produce F1, and F1 adult males (PND 56) were mated with newly purchased healthy adult females to produce F2. The serum levels of estradiol (E₂) and progesterone (Pg) decreased in F1 but essentially returned to normal in F2. The levels of StAR, CYP11A1, CYP17A1, CYP19A1, and SF-1 showed different alterations in F1 and F2 ovarian GCs. The expression patterns of miRNAs and imprinted genes related to hormone synthesis in GCs of F1 and F2 differed, but methylation of hormone synthesis-related genes was not significantly altered (except for individual loci in F1). In addition, there were significant changes in the expression of imprinted genes and miRNAs in F0 and F1 sperm. We conclude that paternal Cd exposure causes intergenerational genetic effects (hormone synthesis disorders) and transgenerational effects (reparative changes in hormone synthesis function) in ovarian GCs. These genetic effects were related to the downregulation of StAR in F1 and the upregulation of CYP17A1, CYP19A1, StAR and SF-1 in F2. Important changes in miRNAs and imprinted genes were also observed, but not all alterations originated from paternal inheritance.

Human relevant exposure to di-n-butyl phthalate tampers with the ovarian insulin-like growth factor 1 system and disrupts folliculogenesis in young adult mice

Phthalates are compounds used in consumer and medical products worldwide. Phthalate exposure in women has been demonstrated by detection of phthalate metabolites in their urine and ovarian follicular fluid. High urinary phthalate burden has been associated with reduced ovarian reserve and oocyte retrieval in women undergoing assisted reproduction. Unfortunately, no mechanistic explanation for these associations is available. In short term in vivo and in vitro animal studies modeling human relevant exposures to di-n-butyl phthalate (DBP), we have identified ovarian folliculogenesis as a target for phthalate exposures. In the present study, we investigated whether DBP exposure negatively influences insulin-like growth factor 1 (IGF) signaling in the ovary and disrupts ovarian folliculogenesis. CD-1 female mice were exposed to corn oil (vehicle) or DBP (10 or 100 μg/kg/day) for 20-32 days. Ovaries were collected as animals reached the proestrus stage to achieve estrous cycle synchronization. Levels of mRNAs encoding IGF1 and 2 ( Igf1 and Igf2 ), IGF1 receptor ( Igf1r ), and IGF binding proteins 1-6 ( Ifgbp1-6 ) were measured in whole ovary homogenates. Ovarian follicle counts and immunostaining for phosphorylated IGF1R protein (pIGF1R) were used to evaluate folliculogenesis and IGF1R activation, respectively. DBP exposure, at a realistic dose that some women may experience (100 μg/kg/day for 20-32 days), reduced ovarian Igf1 and Igf1r mRNA expression and reduced small ovarian follicle numbers and primary follicle pIGF1R positivity in DBP-treated mice. These findings reveal that DBP tampers with the ovarian IGF1 system and provide molecular insight into how phthalates could influence the ovarian reserve in females.

Lipid metabolism disorders associated with dioxin exposure in a cohort of Chinese male workers revealed by a comprehensive lipidomics study

Dioxins, environmentally stable and ubiquitous, have been found to induce metabolic changes especially in lipids and be related to multiple diseases. However, limited study is available on lipid alternations related to human exposure to dioxins. This study aims to explore the serum lipidomic characterization and to understand the underlying mechanisms of adverse health risks associated with dioxin exposure. A lipidomic study integrating nontargeted lipidomics, and targeted free fatty acid (FFA) and acyl-coenzyme A (acyl-CoA) analyses were conducted to investigate the 94 serum samples from two groups of male workers with remarkably different dioxin concentrations. The obtained results exhibited distinct lipidomic signatures between the high and low exposed groups. A total of 37 lipids were identified with the significant changes. The results revealed that dioxin exposure caused accumulations of triglyceride (TG), ceramide (Cer) and sphingoid (So), remodeling of glycerophospholipid (GP), imbalanced FFA metabolism, as well as upregulation of platelet-activating factor (PAF). These findings implied the associations between dioxin exposure and potential adverse health risks including inflammation, apoptosis, cardiovascular diseases (CVDs), and liver diseases. This study is the first to explain the associations between dioxin exposure and health effects at the level of lipid metabolism.

Experimental Evidence of 2,3,7,8-Tetrachlordibenzo-p-Dioxin (TCDD) Transgenerational Effects on Reproductive Health

Previous studies have demonstrated that endocrine disruptors (EDs) can promote the transgenerational inheritance of disease susceptibility. Among the many existing EDs, 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) affects reproductive health, including in humans, following direct occupational exposure or environmental disasters, for instance the Agent Orange sprayed during the Vietnam War. Conversely, few studies have focused on TCDD multigenerational and transgenerational effects on human reproductive health, despite the high amount of evidence in animal models of such effects on male and female reproductive health that mimic human reproductive system disorders. Importantly, these studies show that paternal ancestral TCDD exposure substantially contributes to pregnancy outcome and fetal health, although pregnancy outcome is considered tightly related to the woman’s health. In this work, we conducted a systematic review of the literature and a knowledge synthesis in order (i) to describe the findings obtained in rodent models concerning TCDD transgenerational effects on reproductive health and (ii) to discuss the epigenetic molecular alterations that might be involved in this process. As ancestral toxicant exposure cannot be changed in humans, identifying the crucial reproductive functions that are negatively affected by such exposure may help clinicians to preserve male and female fertility and to avoid adverse pregnancy outcomes.

The insulin-like growth factor system: A target for endocrine disruptors?

The insulin-like growth factor (IGF) system is a critical regulator of growth, especially during fetal development, while also playing a central role in metabolic homeostasis. Endocrine disruptors (EDs) are ubiquitous compounds able to interfere with hormone action and impact human health. For example, exposure to EDs is associated with decreased birthweight and increased incidence of metabolic disorders. Therefore, the IGF system is a potential target for endocrine disruption. This review summarises the state of the science regarding effects of exposure to major classes of endocrine disruptors (dioxins and dioxin-like compounds, polycyclic aromatic hydrocarbons, polybrominated diphenyl ethers, phthalates, perfluoroalkyl substances and bisphenol A) on the IGF system. Evidence from both experimental models (in vitro and in vivo) and epidemiological studies is presented. In addition, possible molecular mechanisms of action and effects on methylation are discussed. There is a large body of evidence supporting the link between dioxins and dioxin-like compounds and IGF disruption, but mixed findings have been reported in human studies. On the other hand, although only a few animal studies have investigated the effects of phthalates on the IGF system, their negative association with IGF levels and methylation status has been more consistently reported in humans. For polybrominated diphenyl ethers, perfluoroalkyl substances and bisphenol A the evidence is still limited. Despite a lack of studies for some ED classes linking ED exposure to changes in IGF levels, and the need for further research to improve reproducibility and determine the degree of risk posed by EDs to the IGF system, this is clearly an area of concern.

Ameliorative effect of recombinant human lactoferrin on the premature ovarian failure in rats after cyclophosphamide treatments

This study investigated the effect of recombinant human lactoferrin (rhLF) on the premature ovarian failure (POF) of rats. After cyclophosphamide treatments, the POF rats were divided into the following groups: normal control group (NC), low-dose group (LD), medium-dose group (MD) and high-dose group (HD) of rhLF. After drug administrations, the ovarian indexes and hormonal levels were detected. After follicle number count, the proliferation and apoptosis were analyzed with the expressions of genes related with oogenesis, reactive oxygen species (ROS) production and apoptosis detected, followed by the calculation of oxidative stress and protein expressions. After 4-hydroperoxy cyclophosphamide (4-HC) treatments, the effect of rhLF on the proliferation, ROS production and gene expressions of primary rat granulosa cells (GCs) cultured in vitro were detected. After mating, the fertilities of POF rats were recorded. The result showed that the rhLF administrations up-regulated the ovarian index with the number of developing follicles increased and the decreases of hormonal levels conferred. The Ki-67 intensities of the MD and HD groups were up-regulated with the Tunnel intensities decreased. The rhLF treatments significantly promoted the expression of oogenesis, antioxidant and anti-apoptosis related genes. The expression of Bax and Caspase 3 were decreased with the expression of Bcl-2 up-regulated after rhLF administrations. The in vitro treatments of rhLF effectively conferred the toxicity of 4-HC on primary rat GCs. The fertility assessment showed the rhLF treatments up-regulated the offspring’s’ folliculogenesis, which confirmed the ameliorative role of rhLF on the POF damages via the inhibition of ROS production in GCs.

The role of epigenetics in the reproductive toxicity of environmental endocrine disruptors

Environmental endocrine disruptors (EEDs) seriously endanger human health by interfering with the normal function of reproductive systems. In males, EEDs can affect sperm formation and semen quality as well spermatogenesis, ultimately reducing fertility. In females, EEDs can affect uterine development and the expression levels of reproduction-related genes, ultimately reducing female fertility and the normal development of the fetus. There are a large number of putative mechanisms by which EEDs can induce reproductive toxicity, and many studies have shown the involvement of epigenetics. In this review, we summarize the role of DNA methylation, noncoding RNAs, genomic imprinting, chromatin remodeling and histone modification in the reproductive toxicity of EEDs.

DNA Methylation Patterns in CD4+ T Cells of Naïve and Influenza A Virus-Infected Mice Developmentally Exposed to an Aryl Hydrocarbon Receptor Ligand

BACKGROUND

Early life environmental exposures can have lasting effects on the function of the immune system and contribute to disease later in life. Epidemiological studies have linked early life exposure to xenobiotics that bind the aryl hydrocarbon receptor (AhR) with dysregulated immune responses later in life. Among the immune cells influenced by developmental activation of the AhR are CD 4 + T cells. Yet, the underlying affected cellular pathways via which activating the AhR early in life causes the responses of CD 4 + T cells to remain affected into adulthood remain unclear.

OBJECTIVE

Our goal was to identify cellular mechanisms that drive impaired CD 4 + T-cell responses later in life following maternal exposure to an exogenous AhR ligand.

METHODS

C57BL/6 mice were vertically exposed to the prototype AhR ligand, 2,3,7,8-tetrachlorodibenzo-p -dioxin (TCDD), throughout gestation and early postnatal life. The transcriptome and DNA methylation patterns were evaluated in CD 4 + T cells isolated from naïve and influenza A virus (IAV)-infected adult mice that were developmentally exposed to TCDD or vehicle control. We then assessed the influence of DNA methylation-altering drug therapies on the response of CD 4 + T cells from developmentally exposed mice to infection.

RESULTS

Gene and protein expression showed that developmental AhR activation reduced CD 4 + T-cell expansion and effector functions during IAV infection later in life. Furthermore, whole-genome bisulfite sequencing analyses revealed that developmental AhR activation durably programed DNA methylation patterns across the CD 4 + T-cell genome. Treatment of developmentally exposed offspring with DNA methylation-altering drugs alleviated some, but not all, of the impaired CD 4 + T-cell responses.

DISCUSSION

Taken together, these results indicate that skewed DNA methylation is one of the mechanisms by which early life exposures can durably change the function of T cells in mice. Furthermore, treatment with DNA methylation-altering drugs after the exposure restored some aspects of CD 4 + T-cell functional responsiveness. https://doi.org/10.1289/EHP7699.

Serum metabolic changes associated with dioxin exposure in a Chinese male cohort

Dioxins, a group of persistent organic pollutants, have been proved to correlate with ranges of diseases by activating the aryl hydrocarbon receptor (AhR). However, previous dioxin toxicity studies primarily focused on the activation of AhR with signaling pathways at gene and protein levels. The investigation of underlying mechanisms at the metabolic level is still necessary. In this study, serum samples of 48 and 47 healthy participants with the highest and lowest dioxin levels based on quartile distribution of the serum dioxin concentrations of 215 male adults were selected for metabolomics analysis by using liquid chromatography coupled with orbitrap high-resolution mass spectrometry to investigate dioxin-related metabolic responses. The identified potential biomarkers included acylcarnitines, fatty acids and derivatives, glycerophospholipids, etc. suggested that metabolic pathways such as fatty acid β-oxidation, essential fatty acid metabolism, arachidonic acid metabolism, glycerophospholipid and sphingolipid metabolism and purine metabolism were disturbed by dioxin exposure. The results indicated that people with high dioxin exposure levels were at the potential health risks of inflammation, liver and cardiovascular diseases. The metabolic findings may help understand the link between dioxin exposure and the diseases.

Epigenetic Regulation of Cancer Stem Cells by the Aryl Hydrocarbon Receptor Pathway

Compelling evidence has demonstrated that tumor bulk comprises distinctive subset of cells generally referred as cancer stem cells (CSCs) that have been proposed as a strong sustainer and promoter of tumorigenesis and therapeutic resistance. These distinguished properties of CSCs have raised interest in understanding the molecular mechanisms that govern the maintenance of these cells. Numerous experimental and epidemiological studies have demonstrated that exposure to environmental toxins such as the polycyclic aromatic hydrocarbons (PAHs) is strongly involved in cancer initiation and progression. The PAH-induced carcinogenesis is shown to be mediated through the activation of a cytosolic receptor, aryl hydrocarbon receptor (AhR)/Cytochrome P4501A pathway, suggesting a possible direct link between AhR and CSCs. Several recent studies have investigated the role of AhR in CSCs self-renewal and maintenance, however the molecular mechanisms and particularly the epigenetic regulations of CSCs by the AhR/CYP1A pathway have not been reviewed before. In this review, we first summarize the crosstalk between AhR and cancer genetics, with a particular emphasis on the mechanisms relevant to CSCs such as Wnt/β-catenin, Notch, NF-κB, and PTEN-PI3K/Akt signaling pathways. The second part of this review discusses the recent advances and studies highlighting the epigenetic mechanisms mediated by the AhR/CYP1A pathway that control CSC gene expression, self-renewal, and chemoresistance in various human cancers. Furthermore, the review also sheds light on the importance of targeting the epigenetic pathways as a novel therapeutic approach against CSCs.

Multigenerational and transgenerational effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure on ovarian reserve and follicular development through AMH/AMHR2 pathway in adult female rats

2,3,7,8-Tetrachlorobenzo-p-dioxin (TCDD), one of the key endocrine disruptors, has been shown to cause reproductive and developmental disorders. Our previous studies have primarily focused on TCDD induced impairment of ovarian follicular development in female F1 rats. It is unknown whether TCDD exposure will interfere with follicular development by altering mRNA expression of anti-Müllerian hormone (AMH) and AMH receptor type II (AMHR2) in the ovary. In the present study, pregnant Sprague Dawley rats were treated with TCDD (100 or 500 ng/kg body weight) dissolved in a corn oil vehicle by gavage from gavage from gestational days (GD) 8-14, while the control group received solely corn oil. The F1 rats were mated with unexposed males for the F2 generation, while another portion of the female offspring (F2) were mated for the F3 generation. Serum AMH levels and ovarian AMH/AMHR2 mRNA expression in the adult female offspring (F1, F2 and F3 generations) were measured. Follicle count and granulosa cell apoptosis were evaluated in the F2 and F3 generations. The results showed that in the F2 generation, TCDD exposure affected the number of primordial follicles, secondary follicles, and corpora lutea. It also increased serum AMH concentration and the apoptosis rate of granulosa cells. These results might be associated with the upregulation of AMH/AMHR2 mRNA expression in the ovary. In conclusion, TCDD exposure reduced the ovarian reserve in rats and inhibited follicular development in adult female offspring, an effect that persisted for multiple generations. The altered AMH and AMHR2 mRNA expression may contribute to the observed adverse effects.

Serum dioxin and DNA methylation in the sperm of operation ranch hand veterans exposed to Agent Orange

BACKGROUND

Exposure to the herbicide Agent Orange during the Vietnam War was widespread and is associated with numerous adverse health outcomes. A continuing concern of veterans is the possibility that exposure to the dioxin-containing herbicide might induce adverse reproductive outcomes. We sought to assess whether exposure to Agent Orange in Vietnam was associated with changes in DNA methylation in sperm in a subset of Vietnam veterans who participated in the Air Force Health Study (AFHS).

METHODS

We studied 37 members of the AFHS chosen to have no, low, medium or high exposure to Agent Orange, based upon serum dioxin levels obtained during a series of examinations. DNA from stored semen was extracted and DNA methylation assessed on the Illumina 450 K platform.

RESULTS

Initial epigenome-wide analysis returned no loci that survived control for false discovery. However, the TEAD3 gene had four different CpG sites that showed loss of DNA methylation associated with dioxin exposure. Analysis assessing regional DNA methylation changes revealed 36 gene regions, including the region of the imprinted gene H19 to have altered DNA methylation associated with high exposure compared to the low exposure group. Additional comparison of our data with sperm DNA methylation data from Russian boys exposed to dioxin found an additional 5 loci that were altered in both studies and exhibited a consistent direction of association.

CONCLUSIONS

Studying a small number of sperm samples from veterans enrolled in the AFHS, we did not find evidence of significant epigenome-wide alterations associated with exposure to Agent Orange. However, additional analysis showed that the H19 gene region is altered in the sperm of Agent Orange-exposed Ranch Hand veterans. Our study also replicated several findings of a prior study of dioxin-exposed Russian boys. These results provide additional candidate loci for further investigation and may have implications for the reproductive health of dioxin-exposed individuals.

Transgenerational impairment of ovarian induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) associated with Igf2 and H19 in adult female rat

2,3,7,8-Tetrachlorobenze-p-dioxin (TCDD), one of representive Endocrine Disrupting Chemicals (EDCs), has potential adverse effects on human health. Direct exposure to TCDD has been implicated in ovarian follicles development and functions deficits in adulthood. However, it is rarely reported whether indirect exposure to TCDD can cause similar negative impact on F3. The aim of our study was to evaluate the effect of ancestral TCDD exposure on ovarian toxicity in offspring rats (F3), focusing on the Igf2/H19 pathway which was important for follicular development. Pregnant Sprague-Dawley female rats (F0) were given with either vehicle or TCDD (100 or 500 ng/kg BW/day) by gavages during days 8-14 of gestation. Ovarian development and functions of F3 generation was assessed using the ovary coefficient, the vaginal opening time, and regularity of estrous cycle, ovarian pathology, follicles counts and apoptosis of granular cells. The level of E2, FSH and LH in the serum was also detected. Results showed that in the F3 generation 500 ng/kg BW/day TCDD group, ovarian coefficient, LH concentration in serum and number of primary follicles were decreased, and the apoptosis of granular cells was significantly increased. The abnormal rate of estrous cycle and advance rate of vaginal opening time displayed a significantly increase in TCDD-treated groups. RT-PCR analysis showed that the expression level of H19 mRNA in ovary of TCDD treated F3 female rats was increased, compared to the control. Our data showed that ancestral TCDD exposure may impair transgenerational adult ovary development and functions, which may be related to an inhibition of the Igf2/H19 pathway in the ovarian.