Estrogen Receptor β Mediates Rapid Estrogen Actions on Gonadotropin-Releasing Hormone NeuronsIn Vivo

Abstract

The gonadal steroid estrogen exerts an important modulatory influence on the activity of multiple neuronal networks. In addition to classical genomic mechanisms of action, estrogen also exerts poorly understood rapid, nongenomic effects on neurons. To examine whether estrogen may exert rapid actions on intracellular signaling within gonadotropin-releasing hormone (GnRH) neurons in vivo, we examined the phosphorylation status of cAMP response element-binding protein (CREB) in these cells after the administration of 17-␤-estradiol to ovariectomized (OVX) mice. The percentage of GnRH neurons expressing phosphorylated CREB was increased more than sixfold ( p Ͻ 0.05) in a time-and dose-dependent manner by estrogen, with the increase first observed 15 min after estrogen administration. A series of in vitro studies demonstrated that estrogen acted directly on native GnRH neurons to phosphorylate CREB, but that estrogen conjugated to bovine serum albumin was without effect. The role of classical estrogen receptors (ERs) was evaluated using ER knock-out mice in vivo. The effect of estrogen on CREB phosphorylation in GnRH neurons was normal in ER␣ knock-out mice but completely absent in ER␤ knock-out mice. Finally, studies in intact female mice revealed levels of CREB phosphorylation within GnRH neurons that were equivalent to those of estrogen-treated OVX mice. These observations demonstrate that ER␤ mediates the rapid, direct effects of estrogen on the GnRH neuronal phenotype, and that these actions persist under physiological conditions. They also provide the first evidence for a role of ER␤ in nongenomic estrogen signaling within the brain in vivo.

Membrane-initiated estrogen signaling in hypothalamic neurons

“…The actions of E2-BSA in mouse GnRH neurons are abrogated by pertussis toxin treatment and not by inhibition of gene transcription, supporting a role for a G proteincoupled membrane receptor (Temple et al, 2004, Temple andWray, 2005). However, in vivo studies have provided evidence for ERβ in the E2-induced rapid (15 min) induction of pCREB in mouse GnRH neurons (Abraham et al, 2003). Collectively, these findings indicate that there are multiple acute actions of E2 in GnRH neurons, some of which involve ERβ.…”

“…One view is that both nuclear and plasma membrane-associated ERs might be products of the same genes (Razandi et al, 1999, Boulware et al, 2005, Pedram et al, 2006, Szegõ et al, 2006, Dewing et al, 2007. This belief stems primarily from the fact that many of the rapid effects of E2 can be induced by selective ERα or ERβ ligands, antagonized by the ER antagonist, ICI 182,780, or are lost in animals bearing mutations in ERα and/or ERβ genes (Couse and Korach, 1999, Singer et al, 1999, Dubal et al, 2001, Wade et al, 2001, Abraham et al, 2003, Boulware et al, 2005. Another view is that estrogen activates a unique membrane ER (mER) (Gu et al, 1999, Toran-Allerand, 2004, Toran-Allerand, 2005, Qiu et al, 2006b).…”

“…These actions of estrogen via pCREB result in activation of genes encoding neurotransmitters such as dopamine, enkephalin, dynorphin and neurotensin, which are all critical for hypothalamic function (Gu et al, 1996, Watters andDorsa, 1998). Moreover, in hypothalamic (mouse) GnRH neurons the rapid phosphorylation of CREB following E2 treatment is observed in ERα but not in ERβ knockout mice indicating a role for ERβ in the acute activation by pCREB in GnRH neurons (Abraham et al, 2003).…”

“…The latter findings combined with recent technological advances, such as the development of ER mutants and transgenic animals expressing green fluorescent protein (GFP) in GnRH neurons, have greatly facilitated studies to understand the cellular mechanisms by which GnRH neurons are regulated by estrogen (Spergel et al, 1999, Suter et al, 2000, Kato et al, 2003, Han et al, 2005, Abraham et al, 2003, Smith et al, 2006, Wintermantel et al, 2006. A series of recent publications show that in mouse hypothalamic neuronal explants and in primate nasal placode cultures, E2 augments synchronous intracellular Ca 2+ oscillations in GnRH neurons (Temple et al, 2004, Temple and Wray, 2005, Abe et al, 2007.…”

Modulation of hypothalamic neuronal activity through a novel G-protein-coupled estrogen membrane receptor

“…This belief stems primarily from the fact that many of the rapid effects of E 2 can be induced by selective ERα or ERβ ligands, antagonized by the ER antagonist, ICI 182,780 or are lost in animals bearing mutations in ERα and/or ERβ genes [15,46,[49][50][51][52]. In ERα-deficient mice, rapid estrogen responses in certain regions of the mouse brain are lost [53], whereas the rapid action of estradiol in mouse hippocampal and arcuate neurons is not [18,54].…”