Estrogen regulation of gene expression in GnRH neurons

Estrogen plays an essential role in the regulation of the female reproductive hormone axis, and specifically is a major regulator of GnRH neuronal function in the female brain. GnRH neuronal cell lines were used to explore the direct effects of estradiol on gene expression in GnRH neurons. The presence of estrogen receptor (ER) binding sites was established by a receptor-binding assay, and estrogen receptor alpha and beta mRNA were identified in GN11 cells and ER beta in GT1-7 cells using RT-PCR analysis of mRNA. MY was more abundantly expressed in GN11 cells than ERR as assessed by real-time PCR. Additionally, GN11 cells expressed significantly more of both ER alpha and beta than GT1-7 cells. Functional studies in GN11 and GT1-7 demonstrated estrogen down regulation of endogenous mouse GnRH mRNA levels using quantitative real-time PCR (qRT-PCR). Correspondingly, estradiol also reduced secretion of GnRH from both the GN11 and GT1-7 cell lines. Since estradiol has been shown to regulate progesterone receptor (PR) expression; similar studies were performed demonstrating an estradiol mediated increase in PR in both cell lines. Estrachol regulation of ER expression was also explored and these studies indicated that estradiol decreased ER alpha and ER beta mRNA levels in a dose-dependent manner in GN11 and GT1-7 cells. These effects were blocked by the addition of the estrogen receptor antagonist ICI 182,780. Both PPT, a specific ERa agonist, and DPN, a specific ER beta agonist, inhibited GnRH gene expression in GN11 cells, but only DPN inhibited GnRH gene expression in GT1-7 cells, consistent with their undetectable levels of ER alpha expression. These studies characterize a direct inhibitory effect of estrachol on GnRH in GnRH neurons, and a direct stimulatory effect of estradiol on PR gene expression. In addition, the agonist studies indicate that there is a functional overlap of ER alpha and ER beta regulation in GnRH neurons. These studies may give insight into the molecular regulation of estrogen negative feedback in the central reproductive axis. (C) 2009 Elsevier Ireland Ltd. All rights reserved.