Developmental toxicity of environmental chemicals

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DESCRIPTION (provided by applicant): The goal of the proposed research is to investigate mechanisms mediating disruption by bisphenol A (BPA) of cellular signalling systems during prostate and seminal vesicle development. BPA leaches from plastic resulting in significant fetal exposure in humans. Exposure of fetal mice to low doses of BPA results in a permanent increase in prostate gland number, overall size and androgen receptors (AR), while a permanent decrease in seminal vesicle size occurs; preliminary evidence suggests this is due to a decrease in the enzyme 5a-reductase, required for dihydrotestosterone (DHT) formation. Our first hypothesis is that the effects of low, environmentally relevant doses of BPA (and low doses of diethylstilbestrol, DES, as a positive control) in the fetal mouse prostate occur via binding to estrogen receptor alpha (ERa), induction of EGF and, subsequently, also IGF-1 gene activity (and synthesis of these growth factors), leading to a permanent increase in AR gene expression and AR protein. Our second hypothesis is that much higher doses of DES, but not BPA, will result in the opposite outcome and interfere with prostate development via competing with DHT for binding to AR. In the seminal vesicles, we predict that there will be a dose-dependent inhibition of EGF and IGF-1, resulting in a permanent dose-related down-regulation of 5a-reductase activity. To test these hypotheses our first specific aim is to conduct in vivo studies in which pregnant CD-1 mice are administered environmentally relevant doses of BPA (and also DES). Our second specific aim is to conduct in vivo studies with high doses of BPA and DES, up to the maximum tolerated dose. Our third specific aim involves removing the fetal urogenital sinus and Wolffian ducts for studies in primary culture to answer specific mechanistic questions by administering very low through sub-lethal doses of DES and BPA. We will also determine whether EGF and IGF-l mimic effects of DES and BPA, and if administering antibodies to these proteins inhibits effects. The fourth specific aim is to determine whether high doses of DES, but not BPA, compete with DHT for binding to AR, thus producing an antiandrogenic effect. In these studies the prostate and seminal vesicles will be examined on gestation day 18, postnatal day 3 and in adult offspring. We will initially focus on AR, ERa, ERB, 5a-reductase, EGF and IGF-1, and measure both mRNA levels by RT-PCR and protein levels by western blot analysis. Organ morphology will be determined by 3-D computer reconstruction from histological sections, coupled with in situ hybridization and immunocytochemistry for the above mRNAs and corresponding proteins, including markers for cell types, proliferation and apoptosis. 5a-reductase activity will be determined by radiometric assay.