Bisphenol a affects endometrial stromal cells decidualization, involvement of epigenetic regulation
Introduction
BPA is widely used as a monomer or additive in the polycarbonate plastics and epoxy resin and other polymeric materials, to manufacture food and beverage containers, water piping, coatings, adhesives, high-performance composites and automotive and aircraft parts. The global consumption of BPA in different application areas was persistently increasing. It was assumed to reach to 10.6 million metric tons in 2022 [1]. BPA can leach from these plastics under normal conditions of use or be liberated from polymers exposed to heating, brushing, or specific pH ranges. Although many countries have prohibited the use of BPA in baby feeding bottles, 95 % of human urine samples contain BPA [2]. BPA is associated with female reproductive system diseases, such as endometriosis, recurrent miscarriages, and decreased pregnancy rate in women who seek assisted reproductive technologies [1,3,4]. These reproductive effects are likely due to the weak estrogenic activity of BPA. BPA exhibits affinity to both nuclear estrogen receptor (ER)-α and ER-β, although the activity of BPA is equivalent to 10−4 of estrogen [5]. Membrane-initiated signaling by ERs shows equimolar activation by BPA and estradiol [6]. BPA interacts with hormone receptors even at very low concentrations and interferes with hormone signaling, involved in hormonally-regulated processes such as reproduction and cells development [7,8]. BPA exposure lower than 1 nmol increase the production of reactive oxygen species (ROS), and the expression of inflammatory factors and genes in endometrium [9].
Once absorbed, BPA is conjugated in the liver by glucuronidation and excreted mainly through bile, but also through urine. This nonconjugated form of this compound in the blood is biologically active. Being lipophilic, it can accumulate in adipose tissue [10]. Although the life-span of BPA in vivo after ingestion is short, endometrial cells can retain BPA, as after exposure to BPA (1 nM and 1 μM) for 24 h, the medium obtained from endometrial cells first washed and then incubated with medium devoid of BPA still contains BPA, as well as the cell lysates, obtained in RIPA buffer [11].
The endometrium is highly controlled by ovarian steroidal hormones, and adequate endometrial decidualization is a prerequisite for successful implantation. The dynamic morphological and functional changes during the menstrual cycle are thought to be epigenetically regulated [12]. Trimethylated histone H3 lysine 4 (H3K4me3) is a conserved hallmark of promoters and transcriptional initiation. H3K27me3 is a repressive histone marker preferentially occupying the promoters of developmental genes [13]. Genome-wide histone modification studies have characterised the considerable changes in H3K27me3 and H3K4me3 patterns associated with endometrial decidualization [14,15]. Decidualization marker genes, PRL, IGFBP-1, and WNT4, are reported to be associated with epigenetics changes at their promoter regions, increased levels of H3K27ac (an active chromatin marker), and decreased levels of H3K27me3 [12,16,17].
Since environmental factors are believed to be involved in epigenetic modification [[18], [19], [20]], we hypothesize that BPA may alter histone modification during endometrial decidualization, leading to dysregulation of several key decidualization marker gene expression and impaired decidualization, consequent embryo implantation failure and infertility. In the present work, we studied the effect of BPA exposure on two pivotal histone methylation transferases, MLL1 and EZH2, in human endometrial stromal cells during in vitro decidualization. The two enzymes are responsible for histone H3K4me3 modification and H3K27me3 modification respectively.
Section snippets
Ethical approval
The use of human endometrium tissues was approved by Medical Ethics Committee, Zhongnan Hospital of Wuhan University Approval No. 2,017,061. The endometrium tissues were collected only after written informed consent from patients.
Cell culture
Human endometrial tissues were obtained at hysterectomy from patients (aged 40–47 years) with regular menstrual cycle, who underwent surgery for early stage of cervical cancer. Proliferative phase samples were timed based on the patients’ cycle day. All subjects were
BPA impairs decidualization of ESCs cells
The purity of primary endometrial stromal cells was assessed morphologically by immunofluorescence staining. Most cells were positive for mesenchymal marker vimentin (Supplementary Fig. 1A). The stromal cells population was over 99 % pure.
The endometrial stromal cells shape changed from an elongated typically fibroblastic appearance, to a more epithelial-type shape upon combination treatment of MPA and cAMP for 6 days (Fig. 1A, B). However, when 10 nM BPA or 10 μM BPA was added to the above
Discussion
Adequate decidualized endometrium behaves as a gatekeeper of embryo implantation in humans. Embryo factors are responsible for only one-third of implantation failures, whereas abnormal endometrial receptivity is responsible for approximately two-thirds of implantation failures [25]. Although we usually select high-quality embryos for transplantation in assisted reproductive technology, how to adjust the endometrium to the best state of receptivity has always been a thorny problem in clinical
Funding
This work was supported by the National Nature Science Foundation of China (no. 81771543).
CRediT authorship contribution statement
Yao Xiong: Methodology, Writing - original draft, Investigation, Visualization. Xue Wen: Investigation, Data Curation, Validation. Huimin Liu: Formal analysis, Investigation. Ming Zhang: Conceptualization, Writing - review & editing, Supervision. Yuanzhen Zhang: Conceptualization, Supervision, Funding acquisition.
Declaration of Competing Interest
The authors declare that there are no conflicts of interest.
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