Developmental Exposure to Endocrine Disruptors: Fertility and Gene Expression ProfilesEPA Grant Number: R827402
Title: Developmental Exposure to Endocrine Disruptors: Fertility and Gene Expression Profiles
Investigators: Zacharewski, Timothy
Current Investigators: Zacharewski, Timothy , Chou, Karen , Saama, Peter
Institution: Michigan State University
EPA Project Officer: Louie, Nica
Project Period: September 1, 1999 through July 31, 2002
Project Amount: $738,712
RFA: Endocrine Disruptors (1999) RFA Text | Recipients Lists
Research Category: Economics and Decision Sciences , Endocrine Disruptors , Health , Safer Chemicals
Description:It has been hypothesized that exposure to weak estrogenic chemicals during critical periods of development may contribute to the manifestation of adverse effects at later stages of life. Although these chemicals do not necessarily share obvious structural similarity to the prototypical estrogen, 17b-estradiol (E2) (2), it is believed that these effects are mediated by the estrogen receptor (ER) and result from the inappropriate modulation of gene expression at critical times during development. However, other mechanisms of action that are independent of the ER can not be discounted. The long-term objective of this study is to elucidate how developmental exposure to estrogenic substances modulate gene expression profiles, leading to compromised male reproductive fitness at later stages of life.
There is concern that exposure to estrogenic substances during development results in compromised fertility in sexually mature adults as manifested by decreased sperm counts (11). Support for this hypothesis comes from selected epidemiological studies that report dramatic decreases in sperm counts over the last 50 years. Results from rodent studies indicate that potent estrogenic chemicals such as diethylstilbestrol (DES) can adversely affect sperm counts and quality. However, the ability of weak estrogenic chemicals to adversely affect sperm counts and quality in sexually mature adults as a result of exposure during development has been extensively debated. This project will further examine the physiological (i.e. sperm counts and quality) and molecular (i.e. testicular and epididymal gene expression profiles) effects of developmental exposure to DES and investigate the effects of genistein (GEN) and o,p'-dichlorodiphenyltrichlorothane (o,p'-DDT), two environmentally relevant, albeit weak estrogenic endocrine disruptors. Pregnant C57BL/6 mice will be gavaged throughout gestation and lactation until the pups are weaned. Developmental landmarks will be monitored as the male pups mature. Sperm will be assessed using motion analysis and in vitro fertilization assays at 15 and 45 weeks of age. Changes in testicular and epididymal gene expression levels will be examined at 15 and 45 weeks of age using a customized genome-scale expression array assay. The General Linear Model (GLM) will be used as a novel statistical approach to discern dose-dependent and temporal associations between effects on sperm quality and changes in gene expression profiles. Cluster analysis for each chemical will then be performed to sort genes into groups that have responded in a similar fashion. Results from these statistical analyses will be compared in order to reveal common gene expression patterns. These patterns will identify critical target genes, discern possible mechanisms involved in ER-mediated modulation of sperm parameters and discover roles for genes with unknown function. Results from this study will also identify novel biomarkers for testicular/epididymal toxicants that adversely affect sperm counts and quality. For the purposes of risk assessment, elucidating correlations between physiological effects and changes at the molecular level (i.e. modulation of gene expression profiles) is critically important in order to establish potential mechanisms of action and to confirm that changes in the expression of gene networks translate into the manifestation of a toxic response. Moreover, results from these studies may identify novel gene targets that are involved in the toxicity of endocrine disruptors that could lead to the development of biomarkers for reproductive toxicants.