Environmentally relevant levels of bisphenol A affect uterine decidualization and embryo implantation through the estrogen receptor/serum and glucocorticoid-regulated kinase 1/epithelial sodium ion channel α-subunit pathway in a mouse model

Abstract

Objective: To investigate whether bisphenol A (BPA) exposure is associated with uterine decidualization and embryo implantation failure in mice.

Design: Experimental animal study and in vitro study.

Setting: University-based infertility center.

Animal(s): ICR mice.

Intervention(s): Mice treated with different doses of BPA; Ishikawa cells cultured in medium of different concentrations of BPA.

Main outcome measure(s): Embryo implantation sites, uterine weight, quantitative real-time reverse transcriptase-polymerase chain reaction, Western blot analysis, hematoxylin and eosin staining, and immunohistochemical, cell proliferation, and statistical analyses.

Result(s): In the experiment of mouse model, administration of 1-100 μg/kg/day of BPA by gavage led to reduction of the number of embryo implantation sites in a dose-dependent manner; 100 μg/kg/day of BPA statistically significantly reduced the number of implantation sites compared with the control group. The uterine weight change (the wet weight of the decidualized uterine horn divided by the wet weight of the undecidualized uterine horn of the mouse) in groups exposed to BPA (100-10,000 μg/kg/day) were statistically significantly lower compared with the control group. Immunohistochemical analysis demonstrated that administration of 100, 1,000, or 10,000 μg/kg/day of BPA by gavage statistically significantly down-regulated the expression of epithelial Na⁺ channel α-subunit (ENaCα) in the luminal epithelial cells and desmin in decidual cells of the oil-induced decidualized uterine horns. Administration of 100 μg/kg/day BPA on embryo days 0.5-3.5 by gavage statistically significantly decreased the level of uterine serum and glucocorticoid-regulated kinase 1 (SGK1) protein expression on embryo days 4 and 6. After treatment with 0.001, 0.01, 0.1, or 1.0 μg/mL of BPA for 48 hours, the SGK1, ENaCα, and phospho-SGK1 protein expression of Ishikawa cells was down-regulated, and the effect of BPA on SGK1 could be abrogated by fulvestrant.

Conclusion(s): Our study provides the first indication that BPA exposure at levels as low as 100 μg/kg/day can impair embryo implantation in mice and BPA can affect decidualization of the uterus in mouse model. Our results suggest that BPA can down-regulate SGK1 and ENaCα protein expression through estrogen receptors in Ishikawa cells.

Keywords: Bisphenol A; endocrine disrupting chemicals; implantation failure; infertility.