Location: Arkansas Children's Nutrition CenterTitle: Mammary gland morphology and gene expression signature of prepubertal male and female rats following exposure to exogenous estradiol Author
Submitted to: Experimental Biology and Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2013
Publication Date: 9/15/2013
Citation: Racine-Miousee, I., Gomez-Acevedo, H., Sharma, N., Vantrease, J., Hennings, L., Shankar, K., Cleves, M.A., Badger, T.M., Ronis, M.J. 2013. Mammary gland morphology and gene expression signature of prepubertal male and female rats following exposure to exogenous estradiol. Experimental Biology and Medicine. 238(9):1033-1046. Interpretive Summary: In order to properly screen chemicals for health effects resulting from actions similar to those of female estrogen hormones, it is essential to understand the effects of treatment with estrogens themselves. Because gene expression is one of the main markers of estrogen actions, we have assessed effects of three doses of estradiol (low, medium, and high) on the structure of the breast and breast gene expression in young male and female rats before puberty. The breast was more responsive to estradiol treatment in males than in females. There was a significant change in breast structures and an increase in the expression of amphiregulin, a protein known to drive breast development. In females, the highest dose of estradiol tested increased the expression of genes for breast milk proteins, as well as muscle proteins involved in milk release. Therefore, the young male rat breast is a very sensitive tissue for use in screening estrogen-like actions of environmental chemicals, using breast structure changes coupled to an examination of changes in gene expression. In contrast, young females were poorly responsive to estradiol treatment.
Technical Abstract: In order to characterize the actions of xenoestrogens, it is essential to possess a solid portrait of the physiological effects of exogenous estradiol. We assessed effects of three doses of exogenous estradiol (E2) (0.1, 1.0 and 10 micrograms/kg/day) on the mammary gland morphology and gene expression profiles of prepubertal male and female rats compared to vehicle-treated controls. The male mammary gland was more responsive to E2 treatment than in females, with 509 genes regulated >2-fold in a dose-dependent manner in males and only 174 in females. In males, E2 treatment increased the number of terminal end buds (TEBs) and the expression of proliferating cell nuclear antigen (PCNA) protein (P<0.05), both of which are indicators of proliferation. This change was linked to a significant increase in the expression of the gene encoding amphiregulin, which is known to induce TEB formation. There was also a dose-dependent increase in the estrogen-regulated gene encoding the progesterone receptor (P<0.05). In intact females, despite lack of changes in mammary morphology, we observed a dose-dependent increase in the expression of genes encoding three milk proteins; whey acidic protein, casein beta, and casein kappa (P<0.05). There was a significant downregulation of both estrogen receptors in response to E2 treatment. These results suggest that the male rat mammary gland is very sensitive to exogenous E2 just prior to puberty. The dose-dependent increase observed in amphiregulin and progesterone receptor gene expression was linked to morphological changes and represents a reliable and sensitive tool to evaluate estrogenicity. In contrast intact prepubertal females were comparatively poorly responsive.