Grantee Research Project Results
2008 Progress Report: Low Dose Effects of In Utero Exposure to Cadmium on Puberty
EPA Grant Number: R832136Title: Low Dose Effects of In Utero Exposure to Cadmium on Puberty
Investigators: Martin, Mary Beth , Hilakivi-Clarke, Leena , Lumpkin, Michael
Institution: Georgetown University
EPA Project Officer: Hahn, Intaek
Project Period: December 1, 2004 through November 30, 2007 (Extended to November 30, 2009)
Project Period Covered by this Report: December 1, 2007 through November 30,2008
Project Amount: $738,798
RFA: Development and Characterization of Biological Systems for Studying Low Dose Effects of Endocrine Disrupting Chemicals (2004) RFA Text | Recipients Lists
Research Category: Endocrine Disruptors , Environmental Justice , Safer Chemicals
Objective:
During the last century, the onset of puberty and menarche in girls has occurred at significantly younger ages. Studies from our laboratory show that the heavy metal cadmium has potent estrogen-like activity in vitro and in vivo and that in utero exposure to environmentally relevant amounts of cadmium advances the onset of puberty, increases weight gain, and alters the development of the mammary gland in female rat offspring. This project is designed to test the hypothesis that in utero exposure to low doses of cadmium alters the hypothalamic-pituitary-gonadal axis and consequently alters the onset of puberty, predisposes to obesity, and accelerates the development of the mammary gland.
This project has 4 objectives:
Objective 1 will determine the dose-response effects of in utero exposure to cadmium on the onset of puberty, weight gain, and mammary gland development. Objective 2 is designed to determine the mechanism by which in utero exposure to cadmium alters the onset of puberty. Two hypotheses have been proposed for the regulation of the onset of puberty and will be tested. Objective 3 will determine the mechanism by which in utero exposure to cadmium alters weight gain. Objective 4 will determine the mechanism by which in utero exposure to cadmium accelerates the development of the mammary gland.
Progress Summary:
To determine whether the effects on mammary gland development were a consequence of altered gene expression, the expression of genes that are regulated by estradiol (i.e., ERα, PgR, and TGFα) or genes that have an altered methylation pattern in breast cancer (i.e., BRCA1 and ID4) were measured in the mammary gland and liver (negative control). Among the genes analyzed, only the expression of ERα mRNA in the mammary gland was altered. In control animals, the expression of ERα mRNA increased from postnatal day 0 to day 20. With the onset of puberty (postnatal day 20 to day 30), expression of ERα mRNA decreased due possibly to the negative feedback control by estradiol. In the in utero exposed animals, the expression of ERα mRNA increased from postnatal day 0 to day 20 but remained elevated following the onset of puberty.
To determine whether ERα mRNA remained elevated in adult animals, animals were again exposed in utero to cadmium or EE. Because estradiol regulates ERα expression, the in utero exposed animals were then ovariectomized on postnatal day 45 and the basal expression of ERα mRNA was measured on postnatal day 59. There was a 3.1-fold increase in ERα mRNA in animals treated in utero with cadmium and a 2.8-fold increase in animals treated in utero with estradiol, suggesting that the effects of in utero exposure on ERα expression in the mammary gland are sustained through development into adult life.
The rat ERα gene has five promoters (OS, ON, O, OT, and E1) that appear to confer tissue-specific expression. To determine whether in utero exposure to cadmium altered promoter usage, the 5’ untranslated region (5’UTR) of ERα mRNA was measured using primers specific for exons OS, ON, O, OT, and E1. The 5’UTRs of ERα were measured on postnatal day 1 to day 30 (young animals) and in the ovariectomized adult animals. In the mammary glands of both young and adult control animals, the 5’UTR of the ERα transcript is derived from exon O. In contrast to the control animals, the 5’UTR of the ERα transcript in animals (young and adult) exposed in utero to cadmium is derived from exons O and OT suggesting that in utero exposure to the metal alters promoter usage of the ERα gene. In addition to altering the 5’UTR of the ERα transcript, in utero exposure to cadmium resulted in a 3.4- and 2.8-fold increase in the transcripts derived from exons O and OT, respectively. Overexpression of ERα is believed to be the first event in the development of ER positive breast cancer suggesting that early life exposure to cadmium predisposes the gland to tumorigenesis in adult life.
To determine whether the increase in ERα mRNA was due to an increase in basal transcription of the ERα gene, a nuclear run on assay was performed. There was no difference in transcription of the ERα gene between control animals and animals exposed in utero to cadmium or EE, suggesting that the overexpression of ERα mRNA is due to a post-transcriptional mechanism.
Summary - Taken together, these data suggest that in utero exposure to environmentally relevant doses of cadmium alters mammary gland development by expanding the mammary stem and/or progenitor cell population and increases the basal expression of ERα mRNA as a result of two epigenetic modifications.
Future Activities:
We are currently defining the mechanism by which in utero exposure to the metal cadmium alters gene expression in the mammary gland.Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
endocrine disruptors, puberty, obesity, mammary gland development, RFA, Scientific Discipline, Health, PHYSICAL ASPECTS, Toxicology, Genetics, Environmental Chemistry, Health Risk Assessment, Endocrine Disruptors - Environmental Exposure & Risk, endocrine disruptors, Risk Assessments, Biochemistry, Physical Processes, Biology, Endocrine Disruptors - Human Health, altered gene expression, puberty, altered sexual development, EDCs, endocrine disrupting chemicals, exposure, developmental biology, animal models, gene expression, biological effects, cadmium, in utero exposure, HPG axisProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.