2012 Progress Report: Mechanisms of In Utero BPA Exposure on Fetal Gonad Development

EPA Grant Number: R834593C003
Subproject: this is subproject number 003 , established and managed by the Center Director under grant R834593
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Novel Methods to Assess Effects of Bisphenol A & Phthalates on Child Development
Center Director: Schantz, Susan L.
Title: Mechanisms of In Utero BPA Exposure on Fetal Gonad Development
Investigators: Flaws, Jodi
Institution: University of Illinois at Urbana-Champaign
EPA Project Officer: Hahn, Intaek
Project Period: February 15, 2010 through February 14, 2014
Project Period Covered by this Report: February 15, 2012 through February 14,2013
RFA: Children's Environmental Health and Disease Prevention Research Centers: Formative Centers (with NIEHS) (2009) RFA Text |  Recipients Lists
Research Category: Children's Health , Health

Objective:

Project 3 was designed to test the hypothesis that in utero exposure to BPA causes gonadal defects via estrogen receptor alpha (ERα). To test this hypothesis, we proposed to investigate whether: 1) loss of ERα renders developing gonads insensitive to deleterious effects of BPA and 2) overexpression of ERα increases the susceptibility of embryos to BPA.

Progress Summary:

Before we could properly design experiments to determine if maternal BPA exposure exerts its toxicity through ER pathways in gonads of offspring, we needed to determine whether maternal exposure to BPA affects testis or ovarian development in mice. Pregnant CD-1 dams were orally dosed with tocopherol-stripped corn oil (vehicle) or BPA from E10.5-E17.5. This time period covers sex determination, testis cord organization/expansion and ovarian formation. Pups were collected via Caesarean section at E19.0, shortly before birth. All pups were counted, weighed, and subjected to measurements of anogenital distance (AGD). The gonads were subjected to histological evaluations.

In utero exposure to BPA did not alter litter size or AGD compared to controls. Histological analysis revealed abnormal testis morphology in 80% of testes exposed to 0.5 µg/kg/day of BPA and 50% of testes in the 50 g/kg/day BPA treatment groups. Dysgenic BPA-exposed testes contained fewer testis cord cross-sections and increased interstitial area compared to vehicle controls. Underdevelopment of the testis cords was particularly evident near the rete testes, where uncoiled lengths of testis cord appeared as finger-like projections. Collectively, these data indicate that maternal BPA exposure alters testis development in the offspring, and that the effects of BPA are likely non-monotonic because the low dose of BPA exerts a more dramatic effect than the high dose of BPA.

Ovaries from BPA exposed mice were less cellular with more dense and congested vascularization than ovaries from vehicle exposed mice. The percentage of abnormal primordial follicles in the BPA exposed ovaries was significantly increased compared to the vehicle control (vehicle control = 16.19 ± 1.99 %; BPA 0.5 µg/kg/day = 36 ± 3.36%; BPA 50 µg/kg/day = 27.55 ± 1.65%, n = 3, p < 0.05). Collectively, these data indicate that prenatal BPA exposure reduces healthy primordial follicle numbers.

Next, we examined whether neonatal BPA exposure alters the developing ovary. This was important to do because the mouse ovary continues to form primordial follicles during the early neonatal period (PND1-8). Neonatal ovaries were collected, individually cultured in media ± dimethylsulfoxide (DMSO; vehicle) or BPA at 0.01-10 µg/ml for 8 days, and morphologically examined. This system best allows us to test the direct effects of BPA on two critical processes in ovarian development: germ cell nest breakdown and primordial follicle formation. Ovaries treated with BPA (1-10 µg/ml) had more germ cells in nests, and fewer primordial and primary follicles compared to control. This suggests that neonatal BPA exposure interferes with germ cell nest breakdown and inhibits primordial follicle assembly.

We also used a validated follicle culture system to test whether BPA exposure directly causes toxicity to adolescent ovarian follicles. Antral follicles (10-15 follicles/ovary) from adolescent ovaries were cultured in media containing DMSO or BPA for 96-120 hours. Every 24 hours, we measured follicular growth. After 96-120 hours, follicles were processed for histological evaluation of atresia and media were collected for measurements of sex steroid hormones. Antral follicles treated with vehicle remained viable and grew for the entire culture period. Antral follicles treated with BPA (100 µg/ml) did not grow, and instead had an increased incidence of atresia, suggesting that BPA inhibits growth and induces atresia of adolescent antral follicles. BPA (10-100 µg/ml) inhibited progesterone, dehydroepiandrosterone, androstenedione, estrone, testosterone, and estradiol production. Pregnenolone co-treatment was able to increase production of pregnenolone, progesterone, and dehydroepiandrosterone and maintain androstenedione and estrone levels in BPA treated follicles compared to DMSO controls, but was unable to protect testosterone or estradiol levels. Further, pregnenolone was unable to protect follicles from BPA induced inhibition of steroidogenic enzymes compared to the DMSO control. Collectively, these data show that BPA targets the estradiol biosynthesis pathway in the ovary.

To determine whether loss of ERα renders gonads insensitive to BPA during adolescence, we co-treated adolescent antral follicles with BPA and estradiol (E2) to examine if E2 binding to ERs blocks BPA-induced growth inhibition. Exposure to BPA (100 µg/ml) decreased follicle growth compared to DMSO and E2 controls. E2 co-treatment did not protect antral follicles from BPA-induced inhibition of growth. Further, we pre-treated antral follicles with the ER antagonist ICI to examine if ICI blocks BPA-induced growth inhibition. Exposure to BPA (100 µg/ml) decreased follicle growth compared to DMSO and ICI controls. Pre-treatment with ICI did not protect antral follicles from BPA-induced inhibition of growth. These data suggest that BPA may not exert toxicity in ovaries through ER pathways.

We then tested the hypothesis that ERα overexpression increases the susceptibility of pups to BPA. Pregnant control and ER overexpressing dams were orally dosed with tocopherol-stripped corn oil (vehicle) or BPA from E10.5 to birth. On PND0, pup weight was decreased in the pups from BPA 0.5 µg/kg/day treated ER overexpressing dams compared to BPA 0.5 µg/kg/day treated control dams. AGDs of males from BPA 50 µg/kg/day treated ERα overexpressing dams were smaller than pups from BPA 50 µg/kg/day treated control dams. In female pups from control mice, BPA 50 µg/kg/day significantly increased the numbers of dying germ cells compared to vehicle controls. In female pups from ERα overexpressing dams, BPA did not affect germ cells and primordial follicles compared to vehicle. BPA did not alter testes cord formation in pups from ERα overexpressing dams. These data suggest that ERα overexpressors may be more sensitive than control mice to BPA-induced changes in pup weight and AGD, but not in gonadal parameters.

To further determine if ERα overexpression makes the ovary more sensitive to BPA, we treated ERα overexpressing and control antral follicles from adolescent mice with vehicle or BPA. BPA (100 µg/ml) decreased follicle growth compared to DMSO in control and ERα overexpressing follicles from 72-120 hrs. BPA (1-10 µg/ml) did not affect growth in either control or ERα overexpressing follicles. Collectively, these data suggest that overexpression of ERα does not render antral follicles more sensitive to BPA than controls.

Future Activities:

During the next funding period, we plan to follow-up on studies conducted during this funding period. Specifically, we plan to conduct experiments designed to help determine why BPA exerts different effects on the ovaries from ERα overexpressing and control mice. Such experiments will include comparing the effects of BPA on the expression of key genes involved in ovarian development and function in ERα overexpressing and control mice. Further, we plan to examine the effects of BPA on the gonads at additional time points. During the current funding period, we only examined gonads at birth so we plan to conduct dosing experiments in which we collect and examine gonads at embryonic time points as well as additional post-natal time points. In addition, we plan to further analyze the testes and diethylstilbestrol (DES)-treated tissues collected during the experiment conducted during this funding period. Specifically, we will determine if BPA affects testes development in both control and ERα overexpressing mice. We also will examine the effects of DES on the developing gonads. Further, we plan to follow-up on our findings that BPA inhibits steroidogenesis in the ovary. Such experiments will be designed to determine how BPA inhibits steroidogenesis in vitro and to determine whether it has similar effects in vivo.


Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other subproject views: All 3 publications 3 publications in selected types All 3 journal articles
Other center views: All 35 publications 7 publications in selected types All 7 journal articles
Type Citation Sub Project Document Sources
Journal Article Brannick KE, Craig ZR, Himes AD, Peretz JR, Wang W, Flaws JA, Raetzman LT. Prenatal exposure to low doses of bisphenol A increases pituitary proliferation and gonadotroph number in female mice offspring at birth. Biology of Reproduction 2012;87(4):82 (10 pp.). R834593 (2012)
R834593 (Final)
R834593C001 (Final)
R834593C003 (2012)
  • Full-text from PubMed
  • Abstract from PubMed
  • Associated PubMed link
  • Full-text: Biology of Reproduction-Full Text HTML
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  • Abstract: Biology of Reproduction-Abstract
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  • Other: Biology of Reproduction-Full Text PDF
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  • Journal Article Peretz J, Gupta RK, Singh J, Hernandez-Ochoa I, Flaws JA. Bisphenol A impairs follicle growth, inhibits steroidogenesis, and downregulates rate-limiting enzymes in the estradiol biosynthesis pathway. Toxicological Sciences 2011;119(1):209-217. R834593 (2012)
    R834593 (Final)
    R834593C001 (Final)
    R834593C003 (2012)
  • Full-text from PubMed
  • Abstract from PubMed
  • Associated PubMed link
  • Full-text: Oxford Journals-Full Text HTML
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  • Abstract: Oxford Journals-Abstract
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  • Other: Oxford Journals-Full Text PDF
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  • Journal Article Peretz J, Craig ZR, Flaws JA. Bisphenol A inhibits follicle growth and induces atresia in cultured mouse antral follicles independently of the genomic estrogenic pathway. Biology of Reproduction 2012;87(3):63 (11 pp.). R834593 (2012)
    R834593 (Final)
    R834593C001 (Final)
    R834593C003 (2012)
  • Full-text from PubMed
  • Abstract from PubMed
  • Associated PubMed link
  • Full-text: Biology of Reproduction-Full Text HTML
    Exit
  • Abstract: Biology of Reproduction-Abstract
    Exit
  • Other: Biology of Reproduction-Full Text PDF
    Exit
  • Supplemental Keywords:

    BPA, ovary, testis, gonads, estrogen receptors, RFA, Health, Scientific Discipline, Environmental Chemistry, Health Risk Assessment, Risk Assessments, Biochemistry, Children's Health, children's vulnerablity, biological markers, developmental disorders

    Relevant Websites:

    Children's Environmental Health Research Center at Illinois Exit /

    Progress and Final Reports:

    Original Abstract
  • 2010
  • 2011
  • Final Report

  • Main Center Abstract and Reports:

    R834593    Novel Methods to Assess Effects of Bisphenol A & Phthalates on Child Development

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R834593C001 Prenatal Exposure to BPA/Phthalates: Infant Physical and Behavioral Development
    R834593C002 Adolescent Exposure to BPA/Phthalates Cognitive and Behavioral Development
    R834593C003 Mechanisms of In Utero BPA Exposure on Fetal Gonad Development
    R834593C004 Effects of Bisphenol A on the Developing Cortex