2002 Progress Report: Endocrine Disruptors and Testis DevelopmentEPA Grant Number: R827405
Title: Endocrine Disruptors and Testis Development
Investigators: Skinner, Michael K.
Institution: Washington State University
EPA Project Officer: Louie, Nica
Project Period: August 1, 1999 through July 31, 2002
Project Period Covered by this Report: August 1, 2001 through July 31, 2002
Project Amount: $534,583
RFA: Endocrine Disruptors (1999) RFA Text | Recipients Lists
Research Category: Economics and Decision Sciences , Endocrine Disruptors , Health , Safer Chemicals
This research project is designed to develop a better understanding of how endocrine disruptors influence testis development and function. Of particular interest are the cell-cell interactions that regulate testis growth, size, and morphogenesis, which directly influence male fertility and sperm production. Sertoli cells are the epithelial cells responsible for the onset of embryonic testis development and maintenance of spermatogenesis in the adult testis. Preliminary research has demonstrated that two families of paracrine growth factors directly influence testis development and function. The hypothesis tested is that endocrine disruptors effect locally produced paracrine growth factors that are essential for testicular cell growth and differentiation during embryonic and postnatal testis development, and this directly influences male fertility and sperm production in the adult.
Abnormal testis development and male infertility caused by endocrine disruptors may, in part, be an effect of inappropriate control of testicular cell growth and differentiation during development. Preliminary studies indicate that the transforming growth factor families are critical for the embryonic testis growth. Preliminary studies also indicate that the neurotropin family of factors (i.e., NT3) has a critical role in the morphogenesis of testis development (i.e., sex cord or seminiferous tubule formation). The specific objectives of this research project are to: (1) investigate the effects of endocrine disruptors on the transforming growth factor families during testis development; (2) investigate the effects of endocrine disruptors on the neurotropin growth factor family during testis development; and (3) investigate the physiological effects of these endocrine disruptors during testis development on male fertility.
The completion of these studies will provide insight into the mechanisms that endocrine disruptors influence testis growth and function. Testicular cell growth and differentiation are essential for embryonic, prepubertal, pubertal, and adult testis function. Abnormal control of critical cell-cell interactions after treatment with endocrine disruptors is anticipated to result in male infertility. Inappropriate expression of the growth factors or receptors will result in subfertile males. Therefore, observations from the current research project will provide an understanding of the actions of endocrine disruptors on testis development and function. We intend to determine how environmental toxins with estrogenic (e.g., methoxychlor [MXC]) and anti-androgenic (e.g., vinclozoline) activities may impair male fertility by adversely affecting gonadal neurotropins and transforming growth factors.
The methods developed to assess the transforming growth factor (TGF) gene expression and protein expression have been utilized, along with the embryonic testis organ culture system developed to examine the effects of methoxychlor on mRNA levels. MXC at 0.2 µM suppresses TGF and epidermal growth factor (EGF) receptor mRNA levels. Currently, the TGF isoforms also are being investigated. The actions of methoxychlor and its metabolite hydroxyphenyl-1,1,1-trichloroethane (HPTE) on testis development have been established as shown in the publications below. The actions of vinclozoline also are being examined.
The methods developed to assess neurotropin gene expression have been utilized to examine the actions of methoxychlor. MXC suppressed NT3 and trkC mRNA levels. This correlated with methoxychlor’s ability to block cord formation in the developing testis and influence cell migrations. This now is being investigated more thoroughly and the actions of vinclozoline are being examined.
In vivo experiments with exposure of gestating mothers to methoxychlor demonstrated effects on the F1 generation. We noted a reduction in sperm function and increased spermatogenic cell apoptosis. Preliminary observations that this effect may be transgenerational have been obtained for F2 and F3 generations. Studies show this may be an effect of methylation status of the germ-line.
The future activities of this research project are to: (1) complete analysis of the effects on TGF, TGF1, TGF 2, and TGF 3 expression and relevant receptors with methoxychlor and vinclozoline. Correlate with morphologic and functional changes in embryonic testis development; (2) complete analysis of effects on all neurotropins and receptors with vinclozoline; and (3) extend analysis to F1, F2, and F3 generations to assess epigenetic effects on germ-line population through methylation studies.