GnRH(1-5), a metabolite of gonadotropin-releasing hormone, enhances luteinizing hormone release <i>via</i> activation of kisspeptin neurons in female rats

Abstract

Accumulating evidence suggests that kisspeptin neurons in the arcuate nucleus (ARC), which coexpress neurokinin B and dynorphin, are involved in gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) pulse generation, while the anteroventral periventricular nucleus (AVPV) kisspeptin neurons are responsible for GnRH/LH surge generation. The present study aims to examine whether GnRH(1-5), a GnRH metabolite, regulates LH release via kisspeptin neurons. GnRH(1-5) was intracerebroventricularly injected to ovariectomized and estrogen-treated Wistar-Imamichi female rats. Immediately after the central GnRH(1-5) administration at 2 nmol, plasma LH concentration increased, resulting in significantly higher levels of the area under the curve and baseline of plasma LH concentrations compared to vehicle-injected controls. On the other hand, in Kiss1 knockout rats, GnRH(1-5) administration failed to affect LH secretion, suggesting that the facilitatory effect of GnRH(1-5) on LH release is mediated by kisspeptin neurons. Double in situ hybridization (ISH) for Kiss1 and Gpr101, a GnRH(1-5) receptor gene, revealed that few Kiss1-expressing cells coexpress Gpr101 in both ARC and AVPV. On the other hand, double ISH for Gpr101 and Slc17a6, a glutamatergic marker gene, revealed that 29.2% of ARC Gpr101-expressing cells coexpress Slc17a6. Further, most of the AVPV and ARC Kiss1-expressing cells coexpress Grin1, a gene encoding a subunit of NMDA receptor. Taken together, these results suggest that the GnRH(1-5)-GPR101 signaling facilitates LH release via indirect activation of kisspeptin neurons and that glutamatergic neurons may mediate the signaling. This provides a new aspect of kisspeptin-and GnRH-neuronal communication with the presence of stimulation from GnRH to kisspeptin neurons in female rats.

Conditional kisspeptin neuron-specific <i>Kiss1</i> knockout with newly generated <i>Kiss1</i>-floxed and <i>Kiss1</i>-Cre mice replicates a hypogonadal phenotype of global <i>Kiss1</i> knockout mice

“…Animals then immediately received subcutaneous Silastic implants (internal diameter: 1.57 mm; outer diameter: 3.18 mm; 3 mm in length; Dow Corning, Midland, MI, USA) that were filled with estradiol-17β (E 2 ; Sigma-Aldrich, St Louis, MO, USA) dissolved in peanut oil at 10 µg/ml. The E 2 implant was chosen based on our previous studies [42][43][44] to visualize Kiss1 gene expression in both the AVPV and ARC: the size and dose were adjusted according to the animal body weight. Ovaries were weighed and stored at -80 o C until analysis for Kiss1 and Cre mRNA expression.…”

HEREDITARY ENDOCRINE TUMOURS: CURRENT STATE-OF-THE-ART AND RESEARCH OPPORTUNITIES: GPR101, an orphan GPCR with roles in growth and pituitary tumorigenesis

“…Several studies revealed a strong expression in the CNS in different species (zebrafish, rodents and humans), suggesting its function has been conserved during evolution. In particular, GPR101 is highly expressed in the amygdala and hypothalamus, especially the ARC, and in the nucleus accumbens (NAc) (Bates et al 2006, Nilaweera et al 2007, Regard et al 2008, GTEx Consortium 2013, Ronnekleiv et al 2014, Trivellin et al 2014, Ehrlich et al 2018, LaRese et al 2019, Ieda et al 2020. Other human tissues showing moderate mRNA expression are fat, optic nerve and lymphocytes (Trivellin et al 2016a).…”

“…Starvation was also found to increase Gpr101 expression in the posterior hypothalamus, while ob/ob obese mice showed decreased expression. Within the ARC, Gpr101 is expressed in about 50% of the neurons expressing the anorexigenic peptide proopiomelanocortin (POMC) (Nilaweera et al 2007) and in glutamatergic neurons (Ieda et al 2020), while thyrotropin-releasing hormone (TRH) positive neurons expressed Gpr101 in the lateral hypothalamus (Mickelsen et al 2019). All these brain regions are implicated in various aspects of feeding and reward (Uribe-Cerda et al 2018).…”

“…Very few kisspeptin neurons express Gpr101, while Gpr101 is found in the glutamatergic neurons (Ieda et al 2020). Since glutamate stimulates luteinizing hormone (LH) release from the pituitary by affecting kisspeptin neurons (Uenoyama et al 2015), these findings raise the possibility that GPR101 signaling may facilitate LH release via indirect activation of kisspeptin neurons (Ieda et al 2020). Further studies are therefore necessary to shed light on the precise role played by GPR101 in reproduction.…”

“…In 2014, the same year we described X-LAG, GnRH-(1-5), a processed pentapeptide cleaved from GnRH, was reported as a putative GPR101 ligand (Cho-Clark et al 2014). GnRH-(1-5) is involved in reproduction by regulating GnRH and LH levels (Wu et al 2005, Ieda et al 2020. In Ishikawa cells (endometrial cancer), following GPR101 binding, GnRH-(1-5) induced EGF release, followed by EGF receptor (EGFR) phosphorylation and activation of downstream signaling pathways; this ultimately led to increased proliferation, migration and invasion (Cho-Clark et al 2014.…”