Low-Dose BPA Exposure Alters the Mesenchymal and Epithelial Transcriptomes of the Mouse Fetal Mammary Gland

Abstract

Exposure of rodent fetuses to low doses of the endocrine disruptor bisphenol A (BPA) causes subtle morphological changes in the prenatal mammary gland and results in pre-cancerous and cancerous lesions during adulthood. To examine whether the BPA-induced morphological alterations of the fetal mouse mammary glands are a) associated with changes in mRNA expression reflecting estrogenic actions and/or b) dependent on the estrogen receptor α (ERα), we compared the transcriptomal effects of BPA and the steroidal estrogen ethinylestradiol (EE2) on fetal mammary tissues of wild type and ERα knock-out mice. Mammary glands from fetuses of dams exposed to vehicle, 250 ng BPA/kg BW/d or 10 ng EE2/kg BW/d from embryonic day (E) 8 were harvested at E19. Transcriptomal analyses on the ductal epithelium and periductal stroma revealed altered expression of genes involved in the focal adhesion and adipogenesis pathways in the BPA-exposed stroma while genes regulating the apoptosis pathway changed their expression in the BPA-exposed epithelium. These changes in gene expression correlated with previously reported histological changes in matrix organization, adipogenesis, and lumen formation resulting in enhanced maturation of the fat-pad and delayed lumen formation in the epithelium of BPA-exposed fetal mammary glands. Overall similarities in the transcriptomal effects of BPA and EE2 were more pronounced in the epithelium, than in the stroma. In addition, the effects of BPA and EE2 on the expression of various genes involved in mammary stromal-epithelial interactions were suppressed in the absence of ERα. These observations support a model whereby BPA and EE2 act directly on the stroma, which expresses ERα, ERβ and GPR30 in fetal mammary glands, and that the stroma, in turn, affects gene expression in the epithelium, where ERα and ERβ are below the level of detection at this stage of development.

Effects of oral exposure to bisphenol A on gene expression and global genomic DNA methylation in the prostate, female mammary gland, and uterus of NCTR Sprague-Dawley rats

“…These include the above mentioned Ho et al (2006) and Tang et al (2012) studies that report gene expression modulation in the prostate of Sprague-Dawley rats treated subcutaneously with 10 μg BPA/kg bw/day on PND 1, 3, and 5. The modulation of female mammary gland gene expression in rodent models was reported by Moral et al (2008; Sprague-Dawley rats, 25 and 250 μg BPA/kg bw/day, daily gavage, from GD 10 to 21), Wadia et al (2013; ERα (+/+) and ERα (−/−) C57BL/6 mice, 250 ng BPA/kg BW/day, subcutaneous osmotic pump, from GD 8 to 19), and Dhimolea et al (2014; Wistar-Furth rats, 250 μg BPA/kg bw/day, subcutaneous osmotic pump, from GD 9 to PND 1). Similarly, in our study, several genes were found to be modulated both in PND 4 prostate and female mammary glands in the “low BPA” dose range versus the vehicle control.…”

Impact of diethylhexyl phthalate on gene expression and development of mammary glands of pregnant mouse

“…Our in vitro data also showed similar biological effects, which further supported our in vivo data. Previous data have indicated that BPA affects the expressions of genes related to apoptosis signaling pathways, rather than the ERα and ERβ signaling pathways in epithelium cells (Wadia et al 2013). The density of mammary buds significantly increases when rhesus monkeys are exposed to BPA, and acceleration of mammogenesis is observed, but the changes in ER expression are not significant (Tharp et al 2012).…”

“…The results are presented as mean ± SD. Asterisk (* or **) indicates significant difference (P < 0.05 or P < 0.01) discussed (Kim et al 2004;Venkata et al 2006;Wadia et al 2007Wadia et al , 2013Dairkee et al 2013;Paulose et al 2015;Bhan et al 2014;Dhimolea et al 2014). According to the epidemiological investigations carried out in Europe and America in the past 50 years, exposure to EEs during pregnancy causes enhanced morbidity of breast carcinoma in the next generations.…”

“…Bhan et al have demonstrated that BPA and DES induce gene expressions in both cultured human breast cancer cells (MCF7) and the mammary glands of rats, and alter the epigenetic programming of the HOTAIR promoter, leading to endocrine disruption in vitro and in vivo (Bhan et al 2014). Soto's group has also demonstrated that BPA affects the transcriptomes of fetal mammary gland and may act directly on stromal cells, which in turn affect gene expression in epithelial cells (Wadia et al 2013). Furthermore, they have found that BPA exposure impacts the epigenome of postnatal and adult mammary gland and alters gene expression in rat fetus (Dhimolea et al 2014).…”

Endocrine disrupting chemicals as the potential risk factor for estrogen-dependent cancers

“…59 The positive correlation between exposure to different BPA concentrations and changes in these structures was confirmed in animal studies. 60 Oral exposure to higher doses of BPA (5 μg -5 mg/l of drinking water corresponding to 0.6 μg to 1.2 mg/kg body weight) resulted in alterations in the number of terminal endbuds. Likewise, after exposure to DES, perinatal exposure to BPA increases epithelial cell numbers in the mammary gland in adulthood.…”