Gonadal Cycle-Dependent Expression of Genes Encoding Peptide-, Growth Factor-, and Orphan G-Protein-Coupled Receptors in Gonadotropin- Releasing Hormone Neurons of Mice.

Csaba Vastagh,Norbert Solymosi,Imre Farkas,Veronika Csillag,Zsolt Liposits

doi:10.3389/fnmol.2020.594119

Abstract

Rising serum estradiol triggers the surge release of gonadotropin-releasing hormone (GnRH) at late proestrus leading to ovulation. We hypothesized that proestrus evokes alterations in peptidergic signaling onto GnRH neurons inducing a differential expression of neuropeptide-, growth factor-, and orphan G-protein-coupled receptor (GPCR) genes. Thus, we analyzed the transcriptome of GnRH neurons collected from intact, proestrous and metestrous GnRH-green fluorescent protein (GnRH-GFP) transgenic mice using Affymetrix microarray technique. Proestrus resulted in a differential expression of genes coding for peptide/neuropeptide receptors including Adipor1, Prokr1, Ednrb, Rtn4r, Nmbr, Acvr2b, Sctr, Npr3, Nmur1, Mc3r, Cckbr, and Amhr2. In this gene cluster, Adipor1 mRNA expression was upregulated and the others were downregulated. Expression of growth factor receptors and their related proteins was also altered showing upregulation of Fgfr1, Igf1r, Grb2, Grb10, and Ngfrap1 and downregulation of Egfr and Tgfbr2 genes. Gpr107, an orphan GPCR, was upregulated during proestrus, while others were significantly downregulated (Gpr1, Gpr87, Gpr18, Gpr62, Gpr125, Gpr183, Gpr4, and Gpr88). Further affected receptors included vomeronasal receptors (Vmn1r172, Vmn2r-ps54, and Vmn1r148) and platelet-activating factor receptor (Ptafr), all with marked downregulation. Patch-clamp recordings from mouse GnRH-GFP neurons carried out at metestrus confirmed that the differentially expressed IGF-1, secretin, and GPR107 receptors were operational, as their activation by specific ligands evoked an increase in the frequency of miniature postsynaptic currents (mPSCs). These findings show the contribution of certain novel peptides, growth factors, and ligands of orphan GPCRs to regulation of GnRH neurons and their preparation for the surge release.

Highlights

Gonadotropin-releasing hormone (GnRH) plays a key role in the regulation of reproduction (Merchenthaler et al, 1980; Knobil, 1988)
The physiological activity, hormone production, and neurohormone release of GnRH neurons are regulated by diverse neuronal circuits of the brain (Spergel, 2019a,b) and by various endocrine hormones and metabolic signals arriving from the periphery (Finn et al, 1998; Smith and Jennes, 2001; Campbell, 2007; Christian and Moenter, 2010; Farkas et al, 2013, 2016; Csillag et al, 2019)
GnRH neurons are regulated by ERβ (Hrabovszky et al, 2000, 2001), while their neuronal afferent systems are regulated by ERα (Christian et al, 2008; Yeo and Herbison, 2014; Dubois et al, 2015) or both ER subtypes

Summary

Introduction

Gonadotropin-releasing hormone (GnRH) plays a key role in the regulation of reproduction (Merchenthaler et al, 1980; Knobil, 1988). The proestrous phase is a functionally important exception when the rising level of E2 restructures the GnRH system together with its coupled regulatory neuronal circuits and prepares them for execution of the forthcoming GnRH surge release (Sarkar et al, 1976; Christian and Moenter, 2010) This positive regulatory feedback mechanism is propelled by E2 acting on estrogen receptors (ERα, ERβ, and GPR30) (Chu et al, 2009; Noel et al, 2009; Terasawa et al, 2009; Moenter and Chu, 2012) expressed in neuronal systems known to regulate reproduction centrally. GnRH neurons undergo activation in the preovulatory GnRH surge period, characterized by expression of the immediate early gene, c-Fos (Lee et al, 1990), enlarged transcriptional activity (Wang et al, 1995), induction of hormone synthesis (Gore and Roberts, 1997; Finn et al, 1998), and altered firing pattern (Christian et al, 2005; Farkas et al, 2013)

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Conclusion