RFamide-Related Peptide-3 Receptor Gene Expression in GnRH and Kisspeptin Neurons and GnRH-Dependent Mechanism of Action

Abstract

RFamide-related peptide-3 (RFRP-3) is known to inhibit the activity of GnRH neurons. It is not yet clear whether its G protein-coupled receptors, GPR147 and GPR74, are present on GnRH neurons or on afferent inputs of the GnRH neuronal network or whether RFRP-3 can inhibit gonadotropin secretion independently of GnRH. We tested the following: 1) whether GnRH is essential for the effects of RFRP-3 on LH secretion; 2) whether RFRP-3 neurons project to GnRH and rostral periventricular kisspeptin neurons in mice, and 3) whether Gpr147 and Gpr74 are expressed by these neurons. Intravenous treatment with the GPR147 antagonist RF9 increased plasma LH concentration in castrated male rats but was unable to do so in the presence of the GnRH antagonist cetrorelix. Dual-label immunohistochemistry revealed that approximately 26% of GnRH neurons from male and diestrous female mice were apposed by RFRP-3 fibers, and 19% of kisspeptin neurons from proestrous female mice were apposed by RFRP-3 fibers. Using immunomagnetic purification of GnRH and kisspeptin cells, single-cell nested RT-PCR, and in situ hybridization, we showed that 33% of GnRH neurons and 9-16% of rostral periventricular kisspeptin neurons expressed Gpr147, whereas Gpr74 was not expressed in either population. These data reveal that RFRP-3 can act at two levels of the GnRH neuronal network (i.e. the GnRH neurons and the rostral periventricular kisspeptin neurons) to modulate reproduction but is unable to inhibit gonadotropin secretion independently of GnRH.

The involvement of gonadotropin inhibitory hormone and kisspeptin in the metabolic regulation of reproduction

“…Importantly, the activities of these neurons, as will be discussed below, are altered during negative energy balance conditions (Castellano & Tena-Sempere 2013, Wahab et al 2013a, Roa & Tena-Sempere 2014. Also, these neurons have been documented to directly cross-talk with GnRH-containing neurons (Irwig et al 2004, Parhar et al 2004, Han et al 2005, Messager et al 2005, Clarkson & Herbison 2006, Decourt et al 2008, Smith et al 2008, 2009b, 2012, Rizwan et al 2012. Moreover, expression of KP and GnIHRs has been noted on GnRH neurons (Irwig et al 2004, Parhar et al 2004, Han et al 2005, Messager et al 2005, Ubuka et al 2009b.…”

“…GnIHR is expressed in several brain areas including GnRH-containing neurons ( Fig. 1; Ubuka et al 2008, 2009b, 2012, Rizwan et al 2012. In addition to its hypothalamic expression, GnIHR expression has been reported in the pituitary (Ubuka et al 2009b) and the gonads (McGuire & Bentley 2010).…”

Molecular, cellular, morphological, physiological and behavioral aspects of gonadotropin-inhibitory hormone

“…On the other hand, no direct effect of RF9 in terms of gonadotropin secretion was detected at the pituitary in vitro (Pineda et al, 2010b). Rizwan et al (2012) have investigated (1) whether RFRP-3 can directly inhibit LH secretion without inhibiting GnRH neurons; (2) whether RFRP-3 neurons project to GnRH neurons and rostral periventricular kisspeptin neurons, and (3) whether GPR147 is expressed by these neurons in rodents. Intravenous treatment with RF9 increased plasma LH concentrations in castrated male rats but was unable to do so in the presence of the GnRH antagonist cetrorelix.…”

Developmental changes in the role of gonadotropin-inhibitory hormone (GnIH) and its receptors in the reproductive axis of male Xiaomeishan pigs

“…The highest levels of GPR74 expression were found on postnatal day 3 followed by a gradual decrease from postnatal day 3 to postnatal day 120. GPR74, to which GnIH binds with lower affinity (Bonini et al, 2000), is not expressed in GnRH neurons (Rizwan et al, 2012). The fact that GPR147 and GPR74 bind differentially to various G protein subtypes (Gouarderes et al, 2007) implies the potential for both, stimulatory and inhibitory biological functions of these two receptors, through changes in adenylate cyclase and cAMP response element mediated transcriptional regulation depending on the cellular context (Zhao et al, 2010).…”