Changes in gene expression following long-term in vitro exposure of Macaca mulatta trophoblast stem cells to biologically relevant levels of endocrine disruptors

Mono(2-ethylhexyl) phthalate induces transcriptomic changes in placental cells based on concentration, fetal sex, and trophoblast cell type

Phthalates are ubiquitous plasticizer chemicals found in consumer products. Exposure to phthalates during pregnancy has been associated with adverse pregnancy and birth outcomes and differences in placental gene expression in human studies. The objective of this research was to evaluate global changes in placental gene expression via RNA sequencing in two placental cell models following exposure to the phthalate metabolite mono(2-ethylhexyl) phthalate (MEHP). HTR-8/SVneo and primary syncytiotrophoblast cells were exposed to three concentrations (1, 90, 180 µM) of MEHP for 24 h with DMSO (0.1%) as a vehicle control. mRNA and lncRNAs were quantified using paired-end RNA sequencing, followed by identification of differentially expressed genes (DEGs), significant KEGG pathways, and enriched transcription factors (TFs). MEHP caused gene expression changes across all concentrations for HTR-8/SVneo and primary syncytiotrophoblast cells. Sex-stratified analysis of primary cells identified different patterns of sensitivity in response to MEHP dose by sex, with male placentas being more responsive to MEHP exposure. Pathway analysis identified 11 KEGG pathways significantly associated with at least one concentration in both cell types. Four ligand-inducible nuclear hormone TFs (PPARG, PPARD, ESR1, AR) were enriched in at least three treatment groups. Overall, we demonstrated that MEHP differentially affects placental gene expression based on concentration, fetal sex, and trophoblast cell type. This study confirms prior studies, as enrichment of nuclear hormone receptor TFs were concordant with previously published mechanisms of phthalate disruption, and generates new hypotheses, as we identified many pathways and genes not previously linked to phthalate exposure.

Dose-response mapping of MEHP exposure with metabolic changes of trophoblast cell and determination of sensitive markers

Mono(2-ethylhexyl) phthalate (MEHP) is a metabolite of DEHP which is one of phthalic acid esters (PAEs) widely used in daily necessities. Moreover, MEHP has been proven to have stronger biological toxicity comparing to DEHP. In particular, several recent population-based studies have reported that intrauterine exposure to MEHP results in adverse pregnancy outcomes. To explore the mechanisms and metabolic biomarkers of MEHP exposure, we examined the metabolic status of HTR-8/Svneo cell lines exposed to different doses of MEHP (0, 1.25, 5.0, 20 μM). Global and dose-response metabolomics tools were used to identify metabolic perturbations and sensitive markers associated with MEHP. Only 22 metabolic features (accounted for <1 %) were significantly changed when exposed to 1.25 μM. However, when the exposure dose was increased to 5 or 20 μM, the number of significantly changed metabolic features exceeded 300 (approximately 10 %). In particular, amino acid metabolism, pyrimidine metabolism and glutathione metabolism were widely affected according to the enrich analysis of those significant altered metabolites, which has and have previously been reported to be closely related to fetal development. Moreover, 5'-UMP and N-acetylputrescine with the lowest effective concentrations (EC_-10 = 0.1 μM and EC₊₁₀ = 0.11 μM, respectively) were identified as sensitive endogenous biomarkers of MEHP exposure.

The effect of endocrine-disrupting chemicals on placental development

Endocrine-disrupting chemicals (EDCs) or endocrine disruptors are substances that are either naturally occurring or artificial and are released into the natural environment. Humans are exposed to EDCs through ingestion, inhalation, and skin contact. Many everyday household items, such as plastic bottles and containers, the liners of metal food cans, detergents, flame retardants, food, gadgets, cosmetics, and pesticides, contain endocrine disruptors. Each hormone has a unique chemical makeup and structural attributes. The way that endocrine hormones connect to receptors is described as a "lock and key" mechanism, with each hormone serving as the key (lock). This mechanism is enabled by the complementary shape of receptors to their hormone, which allows the hormone to activate the receptors. EDCs are described as exogenous chemicals or compounds that have a negative impact on organisms' health by interacting with the functioning of the endocrine system. EDCs are associated with cancer, cardiovascular risk, behavioural disorders, autoimmune abnormalities, and reproductive disorders. EDCs exposure in humans is highly harmful during critical life stages. Nonetheless, the effect of EDCs on the placenta is often underestimated. The placenta is especially sensitive to EDCs due to its abundance of hormone receptors. In this review, we evaluated the most recent data on the effects of EDCs on placental development and function, including heavy metals, plasticizers, pesticides, flame retardants, UV filters and preservatives. The EDCs under evaluation have evidence from human biomonitoring and are found in nature. Additionally, this study indicates important knowledge gaps that will direct future research on the topic.

Impact of In Vitro Long-Term Low-Level DEHP Exposure on Gene Expression Profile in Human Granulosa Cells

Here, we applied a model of long-term exposure of human granulosa cells to low environmentally relevant levels of di(2-ethylhexyl) phthalate (DEHP). This approach provides more relevant data regarding the impact of DEHP on the function of human granulosa cells. The immortalized human granulosa cells HGrC1 were exposed to 50 nM and 250 nM DEHP for four weeks. The cells were collected every week to analyze the basal granulosa cells’ functions. A portion of the DEHP-exposed cells was stimulated with forskolin (FOR) for 48 h. Steroidogenesis was investigated using ELISA, whereas DNBQ sequencing and RT-qPCR were used to analyze gene expression. The results show that steroidogenesis was not affected by DEHP exposure. RNAsequencing shows that DEHP caused week- and concentration-specific changes in various genes and functions in HGrC1. Sulfotransferase family 1A member 3 (SULT1A3) and 4 (SULT1A4), which are involved in catecholamine metabolism, were the most prominent genes affected by DEHP under both the basal and FOR-stimulated conditions in all four weeks of exposure. This study showed, for the first time, that SULT1A3 and SULT1A4 are expressed in human granulosa cells, are regulated by FOR, and are affected by low-level DEHP exposure. These data provide new insight into the relationship between DEHP, SULT1A3, and SULT1A4 in human granulosa cells.

Tributyltin chloride exposure to post-ejaculatory sperm reduces motility, mitochondrial function and subsequent embryo development

CONTEXT

Male exposure to environmental toxicants can disrupt spermatogenesis and sperm function. However, consequences of environmentally relevant organotin exposure to post-ejaculatory mammalian spermatozoa on fertility are poorly understood.

AIMS

Determine the consequences of tributyltin chloride (TBT) exposure on post-ejaculatory sperm function and subsequent embryo development.

METHODS

Frozen-thawed bovine sperm were exposed to TBT (0.1-100nM) for 90min (acute) and 6h (short-term) followed by quantification of multiple sperm kinematics via computer aided sperm analysis. JC-1 dye was used to measure mitochondrial membrane potential. Sperm were then exposed to TBT for 90min in non-capacitating conditions, washed several times by centrifugation and applied to gamete co-incubation for in vitro embryo production to the blastocyst stage.

KEY RESULTS

100nM TBT decreased total motility (88 vs 79%), progressive motility (80 vs 70%) curvilinear velocity and beat-cross frequency for 90min with similar phenotypes at 6h (P<0.05). Sperm mitochondrial membrane potential was lower in 10 and 100nM groups after 6h (P≤0.05). Embryos fertilised from TBT-exposed sperm had reduced cleavage rate (80 vs 62%) and 8-16 cell morula development (55 vs 24%) compared to development from unexposed sperm.

CONCLUSIONS

Exposure of post-ejaculatory mammalian sperm to TBT alters sperm function through lowered motility and mitochondrial membrane potential. Fertilisation of oocytes with TBT-exposed sperm reduces embryo development through mechanisms of paternal origin.

IMPLICATIONS

Acute and short-term environmental exposure of post-ejaculatory sperm to organotins and endocrine disrupting chemicals such as TBT contribute to idiopathic subfertility and early embryo loss.

Transcriptomics and Other Omics Approaches to Investigate Effects of Xenobiotics on the Placenta

The conceptus is most vulnerable to developmental perturbation during its early stages when the events that create functional organ systems are being launched. As the placenta is in direct contact with maternal tissues, it readily encounters any xenobiotics in her bloodstream. Besides serving as a conduit for solutes and waste, the placenta possesses a tightly regulated endocrine system that is, of itself, vulnerable to pharmaceutical agents, endocrine disrupting chemicals (EDCs), and other environmental toxicants. To determine whether extrinsic factors affect placental function, transcriptomics and other omics approaches have become more widely used. In casting a wide net with such approaches, they have provided mechanistic insights into placental physiological and pathological responses and how placental responses may impact the fetus, especially the developing brain through the placenta-brain axis. This review will discuss how such omics technologies have been utilized to understand effects of EDCs, including the widely prevalent plasticizers bisphenol A (BPA), bisphenol S (BPS), and phthalates, other environmental toxicants, pharmaceutical agents, maternal smoking, and air pollution on placental gene expression, DNA methylation, and metabolomic profiles. It is also increasingly becoming clear that miRNA (miR) are important epigenetic regulators of placental function. Thus, the evidence to date that xenobiotics affect placental miR expression patterns will also be explored. Such omics approaches with mouse and human placenta will assuredly provide key biomarkers that may be used as barometers of exposure and can be targeted by early mitigation approaches to prevent later diseases, in particular neurobehavioral disorders, originating due to placental dysfunction.

A Comprehensive Assessment of Associations between Prenatal Phthalate Exposure and the Placental Transcriptomic Landscape

BACKGROUND

Phthalates are commonly used endocrine-disrupting chemicals that are ubiquitous in the general population. Prenatal phthalate exposure may alter placental physiology and fetal development, leading to adverse perinatal and childhood health outcomes.

OBJECTIVE

We examined associations between prenatal phthalate exposure in the second and third trimesters and the placental transcriptome at birth, including genes and long noncoding RNAs (lncRNAs), to gain insight into potential mechanisms of action during fetal development.

METHODS

The ECHO PATHWAYs consortium quantified 21 urinary phthalate metabolites from 760 women enrolled in the CANDLE study (Shelby County, TN) using high-performance liquid chromatography-tandem mass spectrometry. Placental transcriptomic data were obtained using paired-end RNA sequencing. Linear models were fitted to estimate separate associations between maternal urinary phthalate metabolite concentration during the second and third trimester and placental gene expression at birth, adjusted for confounding variables. Genes were considered differentially expressed at a Benjamini-Hochberg false discovery rate (FDR) p<0.05. Associations between phthalate metabolites and biological pathways were identified using self-contained gene set testing and considered significantly altered with an FDR-adjusted p<0.2.

RESULTS

We observed significant associations between second-trimester phthalate metabolites mono (carboxyisooctyl) phthalate (MCIOP), mono-2-ethyl-5-carboxypentyl phthalate, and mono-2-ethyl-5-oxohexyl phthalate and 18 genes in total, including four lncRNAs. Specifically, placental expression of NEAT1 was associated with multiple phthalate metabolites. Third-trimester MCIOP and mono-isobutyl phthalate concentrations were significantly associated with placental expression of 18 genes and two genes, respectively. Expression of genes within 27 biological pathways was associated with mono-methyl phthalate, MCIOP, and monoethyl phthalate concentrations.

DISCUSSION

To our knowledge, this is the first genome-wide assessment of the relationship between the placental transcriptome at birth and prenatal phthalate exposure in a large and diverse birth cohort. We identified numerous genes and lncRNAs associated with prenatal phthalate exposure. These associations mirror findings from other epidemiological and in vitro analyses and may provide insight into biological pathways affected in utero by phthalate exposure. https://doi.org/10.1289/EHP8973.

Placental outcomes of phthalate exposure

Proper placental development and function relies on hormone receptors and signaling pathways that make the placenta susceptible to disruption by endocrine disrupting chemicals, such as phthalates. Here, we review relevant research on the associations between phthalate exposures and dysfunctions of the development and function of the placenta, including morphology, physiology, and genetic and epigenetic effects. This review covers in vitro studies, in vivo studies in mammals, and studies in humans. We also discuss important gaps in the literature. Overall, the evidence indicates that toxicity to the placental and maternal-fetal interface is associated with exposure to phthalates. Further studies are needed to better elucidate the mechanisms through which phthalates act in the placenta as well as additional human studies that assess placental disruption through pregnancy with larger sample sizes.

Maternal exposure to tributyltin during early gestation increases adverse pregnancy outcomes by impairing placental development

Tributyltin (TBT) is a persistent organotin pollutant widely used as agricultural and wood biocides, exhibiting well-documented toxicity to reproductive functions in aquatic organisms. However, the effect of TBT on early pregnancy and placental development has been rarely studied in mice. Pregnant mice were fed with 0, 0.2, and 2 mg/kg/day TBT from gravid day 1 to day 8 or 13. TBT exposure led to an increase in the number of resorbed embryo and a reduction in the weight of fetus at gestational days 13. Further study showed that TBT significantly decreased placental weight and area, lowered laminin immunoreactivity and the expressions of placental development-related molecules including Fra1, Eomes, Hand1, and Ascl2. Moreover, TBT treatment markedly inhibited the placental proliferation and induced up-regulation of p53 and cleaved caspase-3 proteins, and down-regulation of Bcl-2 protein. In addition, TBT administration increased levels of malondialdehyde and H₂ O₂ and decreased activities of catalase and superoxide dismutase. Collectively, these results suggested TBT-induced adverse pregnancy outcomes during early pregnancy might be involved in developmental disorders of the placenta via dysregulation of key molecules, proliferation, apoptosis, and oxidative stress.

Gene expression in rat placenta after exposure to di(2-ethylhexyl) phthalate

The organic compound di(2-ethylhexyl) phthalate (DEHP) is widely used as a plasticizer in many products. Exposure to DEHP has been reported to lead to adverse pregnancy outcomes by suppressing placenta growth and development. The aim of this study was to determine the gene expression profiles of rat placenta exposed to (DEHP) and identify genes crucial for the DEHP response. Three groups of Wistar rats were administered an intragastric dose of 1,000 mg/kg DEHP, 500 mg/kg DEHP, or corn oil, RNA was isolated from placenta tissue, and hybridization was performed. Gene expression profiles were analyzed by identifying functional enrichment, differentially expressed genes (DEGs), protein-protein interaction (PPI) networks and modules, and transcription factor (TF)-miRNA-target regulatory networks. We obtained 2,032 DEGs, including cytochrome P450, family 2, subfamily R, polypeptide 1 (CYP2R1), sterol O-acyltransferase 2 (SOAT2), and 24-dehydrocholesterol reductase (DHCR24) from the steroid biosynthesis pathway and somatostatin receptor 4 (SSTR4) and somatostatin receptor 2 (SSTR2) in the neuroactive ligand-receptor interaction pathway. The PPI network included 476 nodes, 2,682 interaction pairs, and three sub-network modules. Moreover, eight miRNAs, three TFs, and 176 regulatory pairs were obtained from the TF-miRNA-target regulatory network. CYP2R1, SOAT2, DHCR24, SSTR4, and SSTR2 may affect DEHP influence on rat placenta development.

The impact of Di-(2-ethylhexyl) Phthalate and Mono(2-ethylhexyl) Phthalate in placental development, function, and pathophysiology

Di(2-ethylhexyl) phthalate (DEHP) is a chemical widely distributed in the environment as is extensively used in the plastic industry. DEHP is considered an endocrine disruptor chemical (EDC) and humans are inevitably and unintentionally exposed to this EDC through several sources including food, beverages, cosmetics, medical devices, among others. DEHP exposure has been associated and may be involved in the development of various pathologies; importantly, pregnant women are a particular risk group considering that endocrine alterations during gestation may impact fetal programming leading to the development of several chronic diseases in adulthood. Recent studies have indicated that exposure to DEHP and its metabolite Mono(2-ethylhexyl) phthalate (MEHP) may impair placental development and function, which in turn would have a negative impact on fetal growth. Studies performed in several trophoblastic and placental models have shown the negative impact of DEHP and MEHP in key processes related to placental development such as implantation, differentiation, invasion and angiogenesis. In addition, many alterations in placental functions like hormone signaling, metabolism, transfer of nutrients, immunomodulation and oxidative stress response have been reported. Moreover, clinical-epidemiological evidence supports the association between DEHP exposure and adverse pregnancy outcomes and pathologies. In this review, we aim to summarize for the first time current knowledge about the impact of DEHP and MEHP exposure on placental development and pathophysiology, as well as the mechanisms involved. We also remark the importance of exploring DEHP and MEHP effects in different trophoblast cell populations and discuss new perspectives regarding this topic.

CLDN3 expression and function in pregnancy-induced hypertension

This aim of the present study was to investigate the expression and function of claudin 3 (CLDN3) in pregnancy-induced hypertension. The mRNA expression levels of CLDN3 in the placental tissue and peripheral blood of patients with pregnancy-induced hypertension were measured using reverse transcription-quantitative PCR. Human trophoblast HTR8/SVneo cells overexpressing CLDN3 were generated using a lentiviral vector. Cell Counting kit-8 (CCK-8) assay, flow cytometry, Transwell chamber assays, confocal laser scanning microscopy and western blot analysis were performed to detect cell proliferation, invasion, migration and apoptosis, in addition to matrix metalloproteinase (MMP) expression and ERK1/2 phosphorylation. The mRNA expression levels of CLDN3 were significantly reduced in the placental tissues and peripheral blood samples of patients with pregnancy-induced hypertension compared with healthy pregnant controls. CLDN3 overexpression significantly increased HTR8/SVneo cell proliferation, invasion and migration whilst reducing apoptosis. HTR8/SVneo cells overexpressing CLDN3 also exhibited increased myofiber levels, increased MMP-2 and MMP-9 expression and increased ERK1/2 signaling activity. CLDN3 downregulation may be associated with the pathogenesis of pregnancy-induced hypertension. In conclusion, CLDN3 promotes the proliferative and invasive capabilities of human trophoblast cells, with the underlying mechanisms possibly involving upregulation of MMP expression via the ERK1/2 signaling pathway.

Placenta Disrupted: Endocrine Disrupting Chemicals and Pregnancy

Endocrine disrupting chemicals (EDCs) are chemicals that can interfere with normal endocrine signals. Human exposure to EDCs is particularly concerning during vulnerable periods of life, such as pregnancy. However, often overlooked is the effect that EDCs may pose to the placenta. The abundance of hormone receptors makes the placenta highly sensitive to EDCs. We have reviewed the most recent advances in our understanding of EDC exposures on the development and function of the placenta such as steroidogenesis, spiral artery remodeling, drug-transporter expression, implantation and cellular invasion, fusion, and proliferation. EDCs reviewed include those ubiquitous in the environment with available human biomonitoring data. This review also identifies critical gaps in knowledge to drive future research in the field.

Acute in vitro exposure to environmentally relevant atrazine levels perturbs bovine preimplantation embryo metabolism and cell number

Atrazine is a widely used herbicide known to negatively alter endocrine systems and perturb metabolism. Preimplantation exposure to pesticides may adversely affect long-term health, however few studies examine the effect of environmental levels and whether specific periods of development are particularly sensitive. In this study, the effect of acute, preimplantation atrazine exposure (days 3.5-7.5 post-fertilization) at levels detected and deemed safe in drinking water (0.02 and 20 μg/L respectively) on in vitro bovine embryo development, quality, metabolism, and gene expression was investigated. Atrazine exposure had no effect on development or quality, but significantly reduced blastocyst total cell numbers, attributable to a decrease in trophectoderm cells. Notably, atrazine (20 μg/L) markedly increased carbohydrate metabolism. Therefore, short-term exposure to environmentally relevant atrazine concentrations perturbs bovine preimplantation embryo metabolism and cell number, highlighting a potential mechanism by which atrazine can mediate embryo viability and health.