Inhibitory effect of cadmium on estrogen signaling in zebrafish brain and protection by zinc

The present study was conducted to assess the effects of Cd exposure on estrogen signaling in the zebrafish brain, as well as the potential protective role of Zn against Cd-induced toxicity. For this purpose, the effects on transcriptional activation of the estrogen receptors (ERs), aromatase B (Aro-B) protein expression and molecular expression of related genes were examined in vivo using wild-type and transgenic zebrafish embryos. For in vitro studies, an ER-negative glial cell line (U251MG) transfected with different zebrafish ER subtypes (ER, ER1 and ER2) was also used. Embryos were exposed either to estradiol (E-2), Cd, E-2+Cd or E-2+Cd+Zn for 72 h and cells were exposed to the same treatments for 30 h. Our results show that E-2 treatment promoted the transcriptional activation of ERs and increased Aro-B expression, at both the protein and mRNA levels. Although exposure to Cd, does not affect the studied parameters when administered alone, it significantly abolished the E-2-stimulated transcriptional response of the reporter gene for the three ER subtypes in U251-MG cells, and clearly inhibited the E-2 induction of Aro-B in radial glial cells of zebrafish embryos. These inhibitory effects were accompanied by a significant downregulation of the expression of esr1, esr2a, esr2b and cyp19a1b genes compared to the E-2-treated group used as a positive control. Zn administration during simultaneous exposure to E-2 and Cd strongly stimulated zebrafish ERs transactivation and increased Aro-B protein expression, whereas mRNA levels of the three ERs as well as the cyp19a1b remained unchanged in comparison with Cd-treated embryos. In conclusion, our results clearly demonstrate that Cd acts as a potent anti-estrogen in vivo and in vitro, and that Cd-induced E-2 antagonism can be reversed, at the protein level, by Zn supplement. Copyright (c) 2016 John Wiley & Sons, Ltd. This study was conducted to assess the effects of Cd exposure on estrogen signaling in the zebrafish brain, and the potential protective role of Zn against Cd-induced toxicity. Effects on the transcriptional activation of estrogen receptors, aromatase B protein expression and molecular expression of related genes were examined. Our results demonstrate that Cd acts as a potent anti-estrogen in vivo and in vitro, and that Cd-induced estradiol antagonism can be reversed, at the protein level, by Zn supplement.