Estrogen regulation of gene expression in GnRH neurons

Abstract

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 α and β mRNA were identified in GN11 cells and ERβ in GT1-7 cells using RT-PCR analysis of mRNA. ERα was more abundantly expressed in GN11 cells than ERβ as assessed by real time PCR. Additionally, GN11 cells expressed significantly more of both ERα and β 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. Estradiol regulation of ER expression was also explored and these studies indicated that estradiol decreased ERα and ERβ 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 ERα agonist, and DPN, a specific ERβ 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 ERα expression. These studies characterize a direct inhibitory effect of estradiol on GnRH in GnRH neurons, and a direct stimulatory effect of estradiol on PR gene expression. In addition, the agonist studies indicate there is a functional overlap of ERα and ERβ regulation in GnRH neurons. These studies may give insight into the molecular regulation of estrogen negative feedback in the central reproductive axis.

Cell Models for the Study of Sex Steroid Hormone Neurobiology

“…Some studies report the presence of mRNA and protein for this receptor and binding of estrogen in GT1-7 cells [87–90,96], consistent with in vivo expression of ERα and ERβ receptors in GnRH neurons [97]. However, others have shown the absence of the ER receptor [94]. These differences in steroid hormone receptor profile may be partially mediated by the widely varied culturing conditions.…”

“…Further, GT1-7 has been shown to bind androgens [93]. Other steroid receptors present in GT1-7 cells are the progesterone receptor (PR) and the glucocorticoid receptor (GR) [94,95]. However, the presence of ERα is unclear.…”

“…These differences in steroid hormone receptor profile may be partially mediated by the widely varied culturing conditions. Generally, DMEM or DMEM/Ham's F-12 (1:1) media is used with 10% fetal bovine serum (FBS) [87–90,94] (Table 1), although one laboratory did use 5% horse serum and 5% fetal calf serum (FCS) instead of FBS [96]. Wide variations in supplements were also observed, consisting of sodium pyruvate, sodium bicarbonate, glucose, Glutamax, or L-glutamine added to the culture media [87–89,94,96].…”

“…Our laboratory has found GPR30, ERα, and ERβ mRNA in both cell lines (Table 1). Other laboratories have also shown ERα and ERβ mRNA and binding of radiolabeled estrogen to GN11 cells [87,94]. Additionally, the GN11 cell line contains PR mRNA, including membrane-associated PR (mPR) [94].…”

The G-Protein Coupled Estrogen Receptor (GPER/GPR30) is a Gonadotropin Receptor Dependent Positive Prognosticator in Ovarian Carcinoma Patients

“…Gonadotropin releasing hormone, being the physiological trigger for LH/FSH secretion, has been highlighted to be down-regulated by estrogen on mRNA level [13]. Since we recently discovered that gonadotropins might regulate the G protein-coupled estrogen receptor (GPER/GPR30) [14] a complex interaction of gonadotropin and estrogen mediated regulation is hypothesized.…”