Bisphenol A (BPA) and 17α-ethinyl estradiol (EE) are estrogenic endocrine disrupting chemicals (EDCs) that adversely affect the structure and function of the uterus. Humans are ubiquitously exposed to BPA via consumption of contaminated food and beverage from polycarbonate packaging or food cans. Humans are exposed to EE through the use of oral contraceptives. While human exposure to these EDCs is widespread, little is known how these compounds alter physiological responses that lead to increased incidence of uterine pathology.
The purpose of this dissertation was to investigate and characterize uterine pathologies and associated alterations in immune responsiveness and fibrosis. Two mouse strains were used, the CD1 and the C57Bl/6N strains. Exposure during adulthood included mating, parturition, and offspring rearing and mice were exposed for 12-15 weeks. Whole life exposure included placental transfer, as well as direct oral consumption, exposing mice until postnatal day (PND) 90. In order to closely mimic human exposure, mice were orally exposed through diet to known concentrations of control (0 ppm), BPA (0.03, 0.3, 3, 30, or 300 ppm), or EE (0.0001, 0.001, 0.01, 0.1, or 1.3 ppm), which resulted in calculated BPA doses of 0.04, 0.4, 4, 40, and 400 mg/kg/day and EE doses of 0.00002, 0.0002, and 0.001 mg/kg/day. Other exogenous estrogenic compounds from housing, bedding, and water were eliminated.
Two distinct immune-related and fibrotic uterine pathologies were identified. Pyometra developed in C57Bl/6N mice exposed to BPA or EE during adulthood. An equine endometrosis-like phenotype, characterized by increased gland nests and stromal and periglandular fibrosis, naturally occurred in control C57Bl/6N mice. In CD1 mice, this fibrotic phenotype was present in the 30 ppm BPA group. Exposure to BPA significantly increased Col1a1 and Col3a1 expression and decreased Mmp2 and Timp2 expression. Expression and activity of matrix metalloproteinases, MMP2 and MMP14, were significantly decreased in both the control C57Bl/6N and 30 ppm BPA-exposed CD1 mice compared to control CD1 mice. However, both strains presented with an increased immune response, quantified as the percentage of F4/80-positive cells. The C57Bl/6N strain had a significant increase in endometrial macrophages at a lower dose of BPA (0.03 ppm) than the CD1 strain (30 ppm) exposed during adulthood. In both exposure models, CD1 mice had increased macrophages in the 30 ppm BPA group.
This dissertation research was the first report of BPA altering the immune response or collagen accumulation in the uterus, leading to the induction of pyometra or an equine endometrosis-like phenotype. It was also the first report of strain-specific differences in sensitivity to the actions of BPA on these endpoints of interest. Finally, this research highlighted the potential for exposure to estrogenic compounds such as BPA and EE to impact the development and progression of fibrotic and immune-related uterine diseases. However, based on the differences observed between the two generations, physiological changes that occur during mating, pregnancy, and parturition may be necessary for estrogenic compounds to elicit fibrotic effects. These studies also emphasized the importance of understanding differences in sensitivity to estrogenic compounds between mouse strains.