Bisphenol A modulates germ cell differentiation and retinoic acid signaling in mouse ES cells

The impact of endocrine-disrupting chemicals on stem cells: Mechanisms and implications for human health

Endocrine-disrupting chemicals (EDCs) are compounds, either natural or man-made, that interfere with the normal functioning of the endocrine system. There is increasing evidence that exposure to EDCs can have profound adverse effects on reproduction, metabolic disorders, neurological alterations, and increased risk of hormone-dependent cancer. Stem cells (SCs) are integral to these pathological processes, and it is therefore crucial to understand how EDCs may influence SC functionality. This review examines the literature on different types of EDCs and their effects on various types of SCs, including embryonic, adult, and cancer SCs. Possible molecular mechanisms through which EDCs may influence the phenotype of SCs are also evaluated. Finally, the possible implications of these effects on human health are discussed. The available literature demonstrates that EDCs can influence the biology of SCs in a variety of ways, including by altering hormonal pathways, DNA damage, epigenetic changes, reactive oxygen species production and alterations in the gene expression patterns. These disruptions may lead to a variety of cell fates and diseases later in adulthood including increased risk of endocrine disorders, obesity, infertility, reproductive abnormalities, and cancer. Therefore, the review emphasizes the importance of raising broader awareness regarding the intricate impact of EDCs on human health.

BPA Exposure Affects Mouse Gastruloids Axial Elongation by Perturbing the Wnt/β-Catenin Pathway

Mammalian embryos are very vulnerable to environmental toxicants (ETs) exposure. Bisphenol A (BPA), one of the most diffused ETs, exerts endocrine-disrupting effects through estro-gen-mimicking and hormone-like properties, with detrimental health effects, including on reproduction. However, its impact during the peri-implantation stages is still unclear. This study, using gastruloids as a 3D stem cell-based in vitro model of embryonic development, showed that BPA exposure arrests their axial elongation when present during the Wnt/β-catenin pathway activation period by β-catenin protein reduction. Gastruloid reshaping might have been impeded by the downregulation of Snail, Slug and Twist, known to suppress E-cadherin expression and to activate the N-cadherin gene, and by the low expression of the N-cadherin protein. Also, the lack of gastruloids elongation might be related to altered exit of BPA-exposed cells from the pluripotency condition and their following differentiation. In conclusion, here we show that the inhibition of gastruloids' axial elongation by BPA might be the result of the concomitant Wnt/β-catenin perturbation, reduced N-cadherin expression and Oct4, T/Bra and Cdx2 altered patter expression, which all together concur in the impaired development of mouse gastruloids.

Bisphenol-A Abrogates Proliferation and Differentiation of C2C12 Mouse Myoblasts via Downregulation of Phospho-P65 NF-κB Signaling Pathway

Previous studies showed that bisphenol-A (BPA), a monomer of polycarbonate plastic, is leached out and contaminated in foods and beverages. This study aimed to investigate the effects of BPA on the myogenesis of adult muscle stem cells. C2C12 myoblasts were treated with BPA in both proliferation and differentiation conditions. Cytotoxicity, cell proliferation and differentiation, antioxidant activity, apoptosis, myogenic regulatory factors (MRFs) gene expression, and mechanism of BPA on myogenesis were examined. C2C12 myoblasts exposed to 25-50 µM BPA showed abnormal morphology, expressing numerous and long cytoplasmic extensions. Cell proliferation was inhibited and was accumulated in subG1 and S phases of the cell cycle, subsequently leading to apoptosis confirmed by nuclear condensation and the expression of apoptosis markers, cleaved caspase-9 and caspase-3. In addition, the activity of antioxidant enzymes, catalase, superoxide dismutase, and glutathione peroxidase was significantly decreased. Meanwhile, BPA suppressed myoblast differentiation by decreasing the number and size of multinucleated myotubes via the modulation of MRF gene expression. Moreover, BPA significantly inhibited the phosphorylation of P65 NF-κB in both proliferation and differentiation conditions. Altogether, the results revealed the adverse effects of BPA on myogenesis leading to abnormal growth and development via the inhibition of phospho-P65 NF-κB.

AOP Key Event Relationship report: Linking decreased retinoic acid levels with disrupted meiosis in developing oocytes

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The first case study to develop and publish an individual KER as a stand-alone unit of information under the AOP framework overseen by the OECD.

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Full description of a KER linking decreased all-trans retinoic acid (atRA) levels in developing ovaries with disrupted meiotic entry of oogonia.

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KER described is associated with an intended AOP linking inhibition of the atRA producing ALDH1A enzymes with reduced fertility in women.

The Adverse Outcome Pathway (AOP) concept is an emerging tool in regulatory toxicology that uses simplified descriptions to show cause-effect relationships between stressors and toxicity outcomes in intact organisms. The AOP structure is a modular framework, with Key Event Relationships (KERs) representing the unit of causal relationship based on existing knowledge, describing the connection between two Key Events. Because KERs are the only unit to support inference it has been argued recently that KERs should be recognized as the core building blocks of knowledge assembly within the AOP-Knowledge Base. Herein, we present a first case to support this proposal and provide a full description of a KER linking decreased all-trans retinoic acid (atRA) levels in developing ovaries with disrupted meiotic entry of oogonia. We outline the evidence to support a role for atRA in inducing meiosis in oogonia across mammals; this is important because elements of the RA synthesis/degradation pathway are recognized targets for numerous environmental chemicals. The KER we describe will be used to support an intended AOP linking inhibition of the atRA producing ALDH1A enzymes with reduced fertility in women.

Effects of 2,2',4,4'-tetrabromodiphenyl ether on the development of mouse embryonic stem cells

2,2',4,4'-Tetrabromodiphenyl ether (BDE47) poses potential risks to reproduction and development, but the mechanism of its toxicity has not yet been elucidated. To explore the developmental toxicity of BDE47, mouse embryonic stem cells (mESCs), which are ideal models for testing the developmental toxicity of environmental contaminants in vitro, were exposed to BDE47 (0.04 μM, 1 μM, 25 μM, or 100 μM) for 24 h or 48 h in this study. Our results indicated that BDE47 treatment changed the morphology of mESCs, inhibited cell viability and increased apoptosis. In addition, alkaline phosphatase (AP) staining in mESCs was significantly decreased after BDE47 treatment (25 μM and 100 μM), indicating that BDE47 treatment affected the pluripotency of mESCs. Through a cell immunofluorescence assay, we found that the fluorescence intensities of Oct4, Sox2 and Nanog were all significantly lower in the group treated with the highest BDE47 concentration (100 μM) than in the control group, consistent with the qRT-PCR and Western blot results. The levels of miR-145 and miR-34a, which regulate genes related to cell differentiation, were significantly increased in BDE47-treated mESCs, further clarifying the potential mechanism. Overall, our findings demonstrate that BDE47 exposure upregulates the expression of miR-145 and miR-34a and in turn downregulates the expression of Oct4, Sox2 and Nanog, thereby affecting apoptosis and pluripotency and causing toxicity during embryonic development.

Examining the Developmental Trajectory of an in Vitro Model of Mouse Primordial Germ Cells following Exposure to Environmentally Relevant Bisphenol A Levels

BACKGROUND

Animal-based studies indicate that bisphenol A (BPA) exposure is detrimental to reproductive health, but its impact on the earliest stages of germ cell development remains poorly defined.

OBJECTIVES

Using a murine in vitro model of early germ cell specification and differentiation, we sought to assess whether exposure to low levels of BPA prior to formation of primordial germ cells (PGCs) alters their differentiation trajectory and unique molecular program.

METHODS

We used an established method of in vitro differentiation of mouse embryonic stem cells (ESCs) into epiblast-like cells (EpiLCs) followed by PGC-like cells (PGCLCs), which together recapitulate defined stages of early germ cell development. Cellular consequences were determined using hemocytometer-based cell counting, fixation, and intracellular staining, followed by flow cytometry/fluorescence-activated cell sorting (FACS) of cells exposed to increasing concentrations (range: 1 nM-10 μM) of BPA. To interrogate and characterize gene expression differences resulting from BPA exposure, we also generated RNA-seq libraries from RNA extracted from FACS-purified PGCLCs and performed transcriptome analysis using bioinformatics-based approaches.

RESULTS

Exposure of EpiLCs to BPA resulted in higher numbers of cells that were associated with a higher proportion of cells in S-phase as well as a lower proportion undergoing apoptosis; this difference occurred in a concentration-dependent manner. Exposure also resulted in a greater fraction of EpiLCs showing signs of DNA damage. Remarkably, EpiLC exposure did not negatively affect PGC specification and resulted in a concentration-dependent effect on PGCLC proliferation in XX but not XY cells. PGCLC transcriptome analysis revealed an aberrant program with significant deregulation of X-linked genes and retrotransposon expression. Differential gene expression analysis also revealed the deregulation of genes associated with lipid metabolism as well as deregulated expression of genes associated with later stages of gametogenesis.

CONCLUSIONS

To the best of our knowledge our findings represent the first characterization of the consequences of early BPA exposure on a model of mammalian PGC development, highlighting altered cell behavior, altered underlying pathways, and altered molecular processes. https://doi.org/10.1289/EHP8196.

The Influence of Environmental Factors on Ovarian Function, Follicular Genesis, and Oocyte Quality

Endocrine-disrupting chemicals (EDCs) exist ubiquitously in the environment. Epidemiological data suggest that the increasing prevalence of infertility may be related to the numerous chemicals. Exposure to EDCs may have significant adverse impacts on the reproductive system including fertility, ovarian reserve, and sex steroid hormone levels. This chapter covers the common exposure ways, the origins of EDCs, and their effects on ovarian function, follicular genesis, and oocyte quality. Furthermore, we will review the origin and the physiology of ovarian development, as well as explore the mechanisms in which EDCs act on the ovary from human and animal data. And then, we will focus on the bisphenol A (BPA), which has been shown to reduce fertility and ovarian reserve, as well as disrupt steroidogenesis in animal and human models. Finally, we will discuss the future direction of prevention and solution methods.

Perinatal exposure to Bisphenol A disturbs the early differentiation of male germ cells

Understanding the effects of Bisphenol A (BPA) on early germ cell differentiation and their consequences in adult life is an area of growing interest in the field of endocrine disruption. Herein, we investigate whether perinatal exposure to BPA affects the differentiation of male germ cells in early life using a transgenic mouse expressing the GFP reporter protein under the Oct4 promoter. In this model, the expression of GFP reflects the expression of the Oct4 gene. This pluripotency gene is required to maintain the spermatogonial stem cells in an undifferentiated stage. Thus, GFP expression was used as a parameter to evaluate the effect of BPA on early germ cell development. Female pregnant transgenic mice were exposed to BPA by oral gavage, from embryonic day 5.5 to postnatal day 7 (PND7). The effects of BPA on male germ cell differentiation were evaluated at PND7, while sperm quality, testicular morphology, and protein expression of androgen receptor and proliferating cell nuclear antigen were studied at PND130. We found that perinatal/lactational exposure to BPA up-regulates the expression of Oct4-driven GFP in testicular cells at PND7. This finding suggests a higher proportion of undifferentiated spermatogonia in BPA-treated animals compared with non-exposed mice. Moreover, in adulthood, the number of spermatozoa per epididymis was reduced in those animals perinatally exposed to BPA. This work shows that developmental exposure to BPA disturbed the normal differentiation of male germ cells early in life, mainly by altering the expression of Oct4 and exerted long-lasting sequelae at the adult stage, affecting sperm count and testis.

Effects of Bisphenol A on Foxl2 gene expression and DNA damage in adult viviparous fish Goodeaatripinnis

Bisphenol A (BPA) is an emerging pollutant of global concern. Viviparous fish Goodea atripinnis is endemic to the Central Mexican Plateau where BPA was detected; however, few studies examined the influence of this chemical on native viviparous fish. The effects of BPA (sublethal dose) were determined on DNA integrity and Foxl2 expression in G. atripinnis gonads, and interactions of BPA with FOXL2 protein. Genotoxicity analysis revealed that % comets, at 14 and 28 days and comet tail length (at 14 days) were significantly higher in exposed compared to controls. In general, the % DNA tail was not markedly higher in BPA-treated fish; however, tail moment related to tail length exhibited significant increases in DNA damage. RT-qPCR assays showed Foxl2 overexpression after 14 and 28 days of exposure in females; while in males, Foxl2 was overexpressed after 28 days. In silico analysis demonstrated that BPA interacted with seven residues located in FOXL2 homeodomain. In summary, sublethal BPA doses induced DNA damage and changes in Foxl2 expression in gonadal cells of G. atripinnis, which may adversely affect reproduction in BPA-exposed wild populations. Foxl2 overexpression and BPA-FOXL2 interaction suggested alterations in processes involving Foxl2. Viviparous fish may thus serve as potential non-conventional models for assessing pollutants effects.

A suggested bisphenol A metabolite (MBP) interfered with reproductive organ development in the chicken embryo while a human-relevant mixture of phthalate monoesters had no such effects

Bisphenol A (BPA) and phthalate diesters are ubiquitous environmental contaminants. While these compounds have been reported as reproductive toxicants, their effects may partially be attributed to metabolites. The aim of this study was to examine reproductive organ development in chicken embryos exposed to the BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP; 100 µg/g egg) or a human-relevant mixture of 4 phthalate monoesters (85 µg/g egg). The mixture was designed within the EU project EDC-MixRisk based upon a negative association with anogenital distance in boys at 21 months of age in a Swedish pregnancy cohort. Chicken embryos were exposed in ovo from an initial stage of gonad differentiation (embryonic day 4) and dissected two days prior to anticipated hatching (embryonic day 19). No discernible effects were noted on reproductive organs in embryos exposed to the mixture. MBP-treated males exhibited retention of Müllerian ducts and feminization of the left testicle, while MBP-administered females displayed a diminished the left ovary. In the left testicle of MBP-treated males, mRNA expression of female-associated genes was upregulated while the testicular marker gene SOX9 was downregulated, corroborating a feminizing effect by MBP. Our results demonstrate that MBP, but not the phthalate monoester mixture, disrupts both male and female reproductive organ development in an avian embryo model.

Acute exposure to triphenyl phosphate inhibits the proliferation and cardiac differentiation of mouse embryonic stem cells and zebrafish embryos

Attention has recently paid to the interaction of triphenyl phosphate (TPHP) and body tissues, particularly within the reproductive and development systems, due to its endocrine-disrupting properties. However, the acute effects of TPHP on early embryonic development remain unclear. Here, we used mouse embryonic stem cells (mESC) and zebrafish embryos to investigate whether TPHP is an embryo toxicant. First, we found that continuous exposure of TPHP decreased the proliferation and increased the apoptotic populations of mESCs in a concentration-dependent manner. Results of mass spectrometry showed that the intracellular concentration of TPHP reached 39.45 ± 7.72 µg/g w/w after 3 hr of acute exposure with TPHP (38.35 μM) but gradually decreased from 3 hr to 48 hr. Additionally, DNA damage was detected in mESCs after a short-term treatment with TPHP, which in turn, activated DNA damage responses, leading to cell cycle arrest by changing the expression levels of p53, proliferating cell nuclear antigen, and Y15-phosphorylated Cdk I. Furthermore, our results revealed that short-term treatment with TPHP disturbed cardiac differentiation by decreasing the expression levels of Oct4, Sox2, and Nanog and transiently reduced the glycolysis capacity in mESCs. In zebrafish embryos, exposure to TPHP resulted in broad, concentration-dependent developmental defects and coupled with heart malformation and reduced heart rate. In conclusion, the two models demonstrate that acute exposure to TPHP affects early embryonic development and disturbs the cardiomyogenic differentiation.

Effects of exposure to BPF on development and sexual differentiation during early life stages of zebrafish (Danio rerio)

Bisphenol F (BPF) has become a predominant bisphenol contaminant in recent years. It has significant estrogenic properties in both in vivo and in vitro studies. We have previously studied the disrupting mechanisms of BPF on the hypothalamic-pituitary-gonadal axis of adult zebrafish. However, the effects of BPF exposure on development and sexual differentiation of zebrafish embryos/larvae remain unclear. To determine the effects of BPF on the critical stage of sex differentiation in zebrafish, zebrafish embryos/larvae were exposed to 1, 10, 100, and 1000 μg/L BPF from fertilization to 60 days post-fertilization (dpf). Developmental malformations were induced by exposure to BPF from 2 h post-fertilization (hpf), with a LC₅₀ of 10,030 μg/L at 96 hpf and 9391 μg/L at 120 hpf. Long-term exposure during sex differentiation tended to result in a female sex ratio bias. Histological analyses at 60 dpf indicated that the development of ovo-testes and immature ovaries was induced by 100 and 1000 μg/L BPF. Homogenate testosterone levels decreased and 17β-estradiol levels increased in zebrafish in a concentration-dependent manner. BPF exposure suppressed gene expression of double sex, Mab3-related transcription factor 1(dmrt1), fushi tarazu factor 1d (ff1d), sry-box containing gene 9a (sox9a) and anti-Mullerian hormone (amh); induced expression of the forkhead box L2 transcription factor (foxl2), leading to increased expression of aromatase (cyp19a1a), which promoted production of estrogens, and further caused phenotypic feminization of zebrafish. These results suggest that developmental exposure to BPF has adverse effects on sexual differentiation, and the results were useful for a BPF risk assessment.

Effects of environmental Bisphenol A exposures on germ cell development and Leydig cell function in the human fetal testis

BACKGROUND

Using an organotypic culture system termed human Fetal Testis Assay (hFeTA) we previously showed that 0.01 μM BPA decreases basal, but not LH-stimulated, testosterone secreted by the first trimester human fetal testis. The present study was conducted to determine the potential for a long-term antiandrogenic effect of BPA using a xenograft model, and also to study the effect of BPA on germ cell development using both the hFETA and xenograft models.

METHODS

Using the hFeTA system, first trimester testes were cultured for 3 days with 0.01 to 10 μM BPA. For xenografts, adult castrate male nude mice were injected with hCG and grafted with first trimester testes. Host mice received 10 μM BPA (~ 500 μg/kg/day) in their drinking water for 5 weeks. Plasma levels of total and unconjugated BPA were 0.10 μM and 0.038 μM respectively. Mice grafted with second trimester testes received 0.5 and 50 μg/kg/day BPA by oral gavage for 5 weeks.

RESULTS

With first trimester human testes, using the hFeTA model, 10 μM BPA increased germ cell apoptosis. In xenografts, germ cell density was also reduced by BPA exposure. Importantly, BPA exposure significantly decreased the percentage of germ cells expressing the pluripotency marker AP-2γ, whilst the percentage of those expressing the pre-spermatogonial marker MAGE-A4 significantly increased. BPA exposure did not affect hCG-stimulated androgen production in first and second trimester xenografts as evaluated by both plasma testosterone level and seminal vesicle weight in host mice.

CONCLUSIONS

Exposure to BPA at environmentally relevant concentrations impairs germ cell development in first trimester human fetal testis, whilst gonadotrophin-stimulated testosterone production was unaffected in both first and second trimester testis. Studies using first trimester human fetal testis demonstrate the complementarity of the FeTA and xenograft models for determining the respective short-term and long term effects of environmental exposures.

Environmental influences on ovarian dysgenesis - developmental windows sensitive to chemical exposures

A woman's reproductive health and ability to have children directly affect numerous aspects of her life, from personal well-being and socioeconomic standing, to morbidity and lifespan. In turn, reproductive health depends on the development of correctly functioning ovaries, a process that starts early during fetal life. Early disruption to ovarian programming can have long-lasting consequences, potentially manifesting as disease much later in adulthood. A growing body of evidence suggests that exposure to chemicals early in life, including endocrine-disrupting chemicals, can cause a range of disorders later in life, such as those described in the ovarian dysgenesis syndrome hypothesis. In this Review, we discuss four specific time windows during which the ovary is particularly sensitive to disruption by exogenous insults: gonadal sex determination, meiotic division, follicle assembly and the first wave of follicle recruitment. To date, most evidence points towards the germ cell lineage being the most vulnerable to chemical exposure, particularly meiotic division and follicle assembly. Environmental chemicals and pharmaceuticals, such as bisphenols or mild analgesics (including paracetamol), can also affect the somatic cell lineages. This Review summarizes our current knowledge pertaining to environmental chemicals and pharmaceuticals, and their potential contributions to the development of ovarian dysgenesis syndrome. We also highlight knowledge gaps that need addressing to safeguard female reproductive health.

Effect of bisphenol A on reproductive processes: A review of in vitro, in vivo and epidemiological studies

As bisphenol A (BPA) is characterized by a pronounced influence on human hormonal regulation, particular attention has been aimed at understanding its role in reproductive processes in males and females, as well as on fetal development. Owing to the increasing number of alarming reports on the negative consequences of the presence of BPA in human surroundings, more and more studies are being undertaken to clarify the negative effects of BPA on human reproductive processes. The aim of this work was to collect and summarize data on the influence of BPA exposure on reproductive health. Based on an analysis of selected publications it was stated that there is strong proof confirming that BPA is an ovarian, uterine and prostate toxicant at a level below the lowest observed adverse effect level (50 mg kg^-1 bodyweight) as well as a level below the proposed safe level (4 μg kg^-1 bodyweight). It seems there is also reliable evidence in relation to the negative effect of BPA on sperm quality and motility. Limited evidence also pertains to the case of the potential of BPA to affect polycystic ovary syndrome occurrence. Although in epidemiological studies this disease was common, in studies on animal models such results were still not confirmed. No unambiguous results of epidemiological studies and with animal models were obtained in relation to the evaluation of associations between BPA and implantation failure in women, evaluation of associations between BPA and sexual dysfunction in men, and impact of BPA on birth rate, birth weight and length of gestation. Copyright © 2017 John Wiley & Sons, Ltd.

Stem cell toxicology: a powerful tool to assess pollution effects on human health

Environmental pollution is a global problem; the lack of comprehensive toxicological assessments may lead to increased health risks. To fully understand the health effects of pollution, it is paramount to implement fast, efficient and specific toxicity screening that relies on human models rather than on time-consuming, expensive and often inaccurate tests involving live animals. Human stem cell toxicology represents a valid alternative to traditional toxicity assays because it takes advantage of the ability of stem cells to differentiate into multiple cell types and tissues of the human body. Thus, this branch of toxicology provides a possibility to assess cellular, embryonic, developmental, reproductive and functional toxicity in vitro within a single system highly relevant to human physiology. In this review, we describe the development, performance and future perspectives of stem cell toxicology, with an emphasis on how it can meet the increasing challenges posed by environmental pollution in the modern world.

A systematic review on the role of environmental toxicants in stem cells aging

Stem cells are an important target for environmental toxicants. As they are the main source for replenishing of organs in the body, any changes in their normal function could affect the regenerative potential of organs, leading to the appearance of age-related disease and acceleration of the aging process. Environmental toxicants could exert their adverse effect on stem cell function via multiple cellular and molecular mechanisms, resulting in changes in the stem cell differentiation fate and cell transformation, and reduced self-renewal capacity, as well as induction of stress-induced cellular senescence. The present review focuses on the effect of environmental toxicants on stem cell function associated with the aging process. We categorized environmental toxicants according to their preferred molecular mechanism of action on stem cells, including changes in genomic, epigenomic, and proteomic levels and enhancing oxidative stress. Pesticides, tobacco smoke, radiation and heavy metals are well-studied toxicants that cause stem cell dysfunction via induction of oxidative stress. Transgenerational epigenetic changes are the most important effects of a variety of toxicants on germ cells and embryos that are heritable and could affect health in the next several generations. A better understanding of the underlying mechanisms of toxicant-induced stem cell aging will help us to develop therapeutic intervention strategies against environmental aging. Meanwhile, more efforts are required to find the direct in vivo relationship between adverse effect of environmental toxicants and stem cell aging, leading to organismal aging.

Retinoid-xenobiotic interactions: the Ying and the Yang

The literature provides compelling evidence pointing to tight metabolic interactions between retinoids and xenobiotics. These are extensive and important for understanding xenobiotic actions in the body. Within the body, retinoids affect xenobiotic metabolism and actions and conversely, xenobiotics affect retinoid metabolism and actions. This article summarizes data that establish the importance of retinoid-dependent metabolic pathways for sustaining the body's responses to xenobiotic exposure, including the roles of all-trans- and 9-cis-retinoic acid for protecting mammals from harmful xenobiotic effects and for ensuring xenobiotic elimination from the body. This review will also consider molecular mechanisms underlying xenobiotic toxicity focusing on how this may contribute to retinoid deficiency and disruption of normal retinoid homeostasis. Special attention is paid to xenobiotic molecular targets (nuclear receptors, regulatory proteins, enzymes, and transporters) which affect retinoid metabolism and signaling.

Effects of the environmental estrogenic contaminants bisphenol A and 17α-ethinyl estradiol on sexual development and adult behaviors in aquatic wildlife species

Endocrine disrupting chemicals (EDCs), including the mass-produced component of plastics, bisphenol A (BPA) are widely prevalent in aquatic and terrestrial habitats. Many aquatic species, such as fish, amphibians, aquatic reptiles and mammals, are exposed daily to high concentrations of BPA and ethinyl estradiol (EE2), estrogen in birth control pills. In this review, we will predominantly focus on BPA and EE2, well-described estrogenic EDCs. First, the evidence that BPA and EE2 are detectable in almost all bodies of water will be discussed. We will consider how BPA affects sexual and neural development in these species, as these effects have been the best characterized across taxa. For instance, such chemicals have been in many cases reported to cause sex-reversal of males to females. Even if these chemicals do not overtly alter the gonadal sex, there are indications that several EDCs might demasculinize male-specific behaviors that are essential for attracting a mate. In so doing, these chemicals may reduce the likelihood that these males reproduce. If exposed males do reproduce, the concern is that they will then be passing on compromised genetic fitness to their offspring and transmitting potential transgenerational effects through their sperm epigenome. We will thus consider how diverse epigenetic changes might be a unifying mechanism of how BPA and EE2 disrupt several processes across species. Such changes might also serve as universal species diagnostic biomarkers of BPA and other EDCs exposure. Lastly, the evidence that estrogenic EDCs-induced effects in aquatic species might translate to humans will be considered.

Emerging methods to generate artificial germ cells from stem cells

Germ cells are responsible for the transmission of genetic and epigenetic information across generations. At present, the number of infertile couples is increasing worldwide; these infertility problems can be traced to environmental pollutions, infectious diseases, cancer, psychological or work-related stress, and other factors, such as lifestyle and genetics. Notably, lack of germ cells and germ cell loss present real obstacles in infertility treatment. Recent research aimed at producing gametes through artificial germ cell generation from stem cells may offer great hope for affected couples to treat infertility in the future. Therefore, this rapidly emerging area of artificial germ cell generation from nongermline cells has gained considerable attention from basic and clinical research in the fields of stem cell biology, developmental biology, and reproductive biology. Here, we review the state of the art in artificial germ cell generation.

The effects of triclosan on pluripotency factors and development of mouse embryonic stem cells and zebrafish

Triclosan (TCS) poses potential risks to reproduction and development due to its endocrine-disrupting properties. However, the mechanism of TCS's effects on early embryonic development is little known. Embryonic stem cells (ESC) and zebrafish embryos provide valuable models for testing the toxic effects of environmental chemicals on early embryogenesis. In this study, mouse embryonic stem cells (mESC) were acutely exposed to TCS for 24 h, and general cytotoxicity and the effect of TCS on pluripotency were then evaluated. In addition, zebrafish embryos were exposed to TCS from 2- to 24-h post-fertilization (hpf), and their morphology was evaluated. In mESC, alkaline phosphatase staining was significantly decreased after treatment with the highest concentration of TCS (50 μM). Although the expression levels of Sox2 mRNA were not changed, the mRNA levels of Oct4 and Nanog in TCS-treated groups were significantly decreased compared to controls. In addition, the protein levels of Oct4, Sox2 and Nanog were significantly reduced in response to TCS treatment. MicroRNA (miR)-134, an expression inhibitor of pluripotency markers, was significantly increased in TCS-treated mESC. In zebrafish experiments, after 24 hpf of treatment, the controls had developed to the late stage of somitogenesis, while embryos exposed to 300 μg/L of TCS were still at the early stage of somitogenesis, and three genes (Oct4, Sox2 and Nanog) were upregulated in treated groups when compared with the controls. The two models demonstrated that TCS may affect early embryonic development by disturbing the expression of the pluripotency markers (Oct4, Sox2 and Nanog).

Long-term effects of chromatin remodeling and DNA damage in stem cells induced by environmental and dietary agents

The presence of histones acts as a barrier to protein access; thus chromatin remodeling must occur for essential processes such as transcription and replication. In conjunction with histone modifications, DNA methylation plays critical roles in gene silencing through chromatin remodeling. Chromatin remodeling is also interconnected with the DNA damage response, maintenance of stem cell properties, and cell differentiation programs. Chromatin modifications have increasingly been shown to produce long-lasting alterations in chromatin structure and transcription. Recent studies have shown environmental exposures in utero have the potential to alter normal developmental signaling networks, physiologic responses, and disease susceptibility later in life during a process known as developmental reprogramming. In this review we discuss the long-term impact of exposure to environmental compounds, the chromatin modifications that they induce, and the differentiation and developmental programs of multiple stem and progenitor cell types altered by exposure. The main focus is to highlight agents present in the human lifestyle that have the potential to promote epigenetic changes that impact developmental programs of specific cell types, may promote tumorigenesis through altering epigenetic marks, and may be transgenerational, for example, those able to be transmitted through multiple cell divisions.

Actions of endocrine-disrupting chemicals on stem/progenitor cells during development and disease

Development and fate of the stem cell are regulated by extrinsic signals from the environment. Endocrine-disrupting chemicals which perturb hormonal signaling in utero and during early childhood may cause deregulation of multiple developmental processes, ranging from breakdown of stem cell niche architecture, developmental reprograming and altered stem cell fate to impaired organ and gonad development and sexual differentiation. Therefore, study of the environmental effects on stem cell integrity and normal development is a new and emerging focus for developmental biologists and cell toxicologists. When combined with new human and mouse stem cell-based models, stem cell differentiation dynamics can be studied in more biologically relevant ways. In this study, we review the current status of our understanding of the molecular mechanisms by which endocrine disruptors alter embryonic stem cell and adult stem/progenitor cell fate, organ development, cancer stem cell activity, and tumorigenesis.

Adverse effects of bisphenol A on male reproductive function

BPA is a ubiquitous environmental contaminant, resulting mainly from manufacturing,use or disposal of plastics of which it is a component, and the degradation of industrial plastic-related wastes. Growing evidence from research on laboratory animals, wildlife, and humans supports the view that BPA produces an endocrine disrupting effect and adversely affects male reproductive function. To better understand the adverse effects caused by exposure to BPA, we performed an up-to-date literature review on the topic, with particular emphasis on in utero exposure, and associated effects on spermatogenesis, steroidogenesis, and accessory organs.BPA studies on experimental animals show that effects are generally more detrimental during in utero exposure, a critical developmental stage for the embryo. BPA has been found to produce several defects in the embryo, such as feminization of male fetuses, atrophy of the testes and epididymides, increased prostate size, shortening of AGD, disruption of BTB, and alteration of adult sperm parameters (e.g.,sperm count, motility, and density). BPA also affects embryo thyroid development.During the postnatal and pubertal periods and adulthood, BPA affects the hypothalamic-pituitary-testicular axis by modulating hormone (e.g., LH and FSH,androgen and estrogen) synthesis, expression and function of respective receptors(ER, AR). These effects alter sperm parameters. BPA also induces oxidative stress in the testis and epididymis, by inhibiting antioxidant enzymes and stimulating lipid peroxidation. This suggests that employing antioxidants may be a promising strategy to relieve BPA-induced disturbances.Epidemiological studies have also provided data indicating that BPA alters male reproductive function in humans. These investigations revealed that men occupationally exposed to BPA had high blood/urinary BPA levels, and abnormal semen parameters. BPA-exposed men also showed reduced libido and erectile ejaculatory difficulties; moreover, the overall BPA effects on male reproduction appear to be more harmful if exposure occurs in utero. The regulation of BPA and BPA-related products should be reinforced, particularly where exposure during the fetal period can occur. The current TDI for BPA is proposed as 25 and 50 1-1g/kg bwt/day (European Food Safety Authority and Health Canada, respectively). Based on the evidence available, we believe that a TDI value of 5 1-1g/kg bwt/day is more appropriate (the endpoint is modulation of rat testicular function). Certain BPA derivatives are being considered as alternatives to BPA. However, certain of these related products display adverse effects that are similar to those of BPA. These effects should be carefully considered before using them as final alternatives to BPA in plastic production.

Effect of BPA on the germination, root development, seedling growth and leaf differentiation under different light conditions in Arabidopsis thaliana

Bisphenol A (BPA) is a well-known environmental toxic substance, which exerts unfavorable effects through endocrine disruptor (ER)-dependent and ER-independent mechanisms to threaten ecological systems seriously. BPA may also interact with other environmental factors, such as light and heavy metals, to have a synergetic effect in plants. However, there is little data concerning the toxic effect of BPA on the primary producers-plants and its possible interaction with light-dependent response. Here, the effects of BPA on germination, fresh weight, tap root length, and leaf differentiation were studied in Arabidopsis thaliana under different parts of light spectrum (dark, red, yellow, green, blue, and white light). Our results showed that low-dose BPA (1.0, 5.0 µM) caused an increase in the fresh weight, the tap root length and the lateral root formation of A. thaliana seedlings, while high-dose BPA (10.0, 25.0 µM) show an inhibition effect in a dose-dependent manner. Unlike karrikins, the effects of BPA on germination fresh weight and tap roots length under various light conditions are similar, which imply that BPA has no notable role in priming light response in germination and early seedling growth in A. thaliana. Meanwhile, BPA exposure influences the differentiation of A. thaliana leaf blade significantly in a light-dependent manner with little to no effect in dark and clear effect under red illumination.

Generation of germ cells in vitro in the era of induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are stem cells that can be artificially generated via "cellular reprogramming" using gene transduction in somatic cells. iPSCs have enormous potential in stem-cell biology as they can give rise to numerous cell lineages, including the three germ layers. An evaluation of germ-line competency by blastocyst injection or tetraploid complementation, however, is critical for determining the developmental potential of mouse iPSCs towards germ cells. Recent studies have demonstrated that primordial germ cells obtained by the in vitro differentiation of iPSCs produce functional gametes as well as healthy offspring. These findings illustrate not only that iPSCs are developmentally similar to embryonic stem cells (ESCs), but also that somatic cells from adult tissues can produce gametes in vitro, that is, if they are reprogrammed into iPSCs. In this review, we discuss past and recent advances in the in vitro differentiation of germ cells using pluripotent stem cells, with an emphasis on ESCs and iPSCs. While this field of research is still at a stage of infancy, it holds great promises for investigating the mechanisms of germ-cell development, especially in humans, and for advancing reproductive and developmental engineering technologies in the future.

Effect of bisphenol A on pluripotency of mouse embryonic stem cells and differentiation capacity in mouse embryoid bodies

Bisphenol A (BPA) poses potential risks to reproduction and development. However, the mechanism of BPA's effects on early embryonic development is still unknown. Embryonic stem cells (ESC) and embryoid bodies (EB) provide valuable in vitro models for testing the toxic effects of environmental chemicals in early embryogenesis. In this study, mouse embryonic stem cells (mESC) were acutely exposed to BPA for 24h, and general cytotoxicity and the effect of BPA on pluripotency were then evaluated. Meanwhile, mouse embryoid bodies (mEB) were exposed to BPA up to 6 days and their differentiation capacity was evaluated. In mESC and mEB, we found that BPA up-regulated pluripotency markers (Oct4, Sox2 and Nanog) at mRNA and/or protein levels. Moreover, BPA increased the mRNA levels of endodermal markers (Gata4,Sox17) and mesodermal markers (Sma,Desmin), and reduced the mRNA levels of ectodermal markers (Nestin,Fgf5) in mEB. Furthermore, microRNA(miR)-134, an expression inhibitor of pluripotency markers including Oct4, Sox2 and Nanog, was decreased both in BPA-treated mESC and mEB. These results firstly indicate that BPA may disturb pluripotency in mESC and differentiation of mEB, and may inhibit ectodermal lineage differentiation of mEB while miR-134 may play a key role underlying this effect.