Phoenixin Activates Immortalized GnRH and Kisspeptin Neurons Through the Novel Receptor GPR173.
Mol Endocrinol 2016;
30:872-88. [PMID:
27268078 DOI:
10.1210/me.2016-1039]
[Citation(s) in RCA: 80] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Reproductive function is coordinated by kisspeptin (Kiss) and GnRH neurons. Phoenixin-20 amide (PNX) is a recently described peptide found to increase GnRH-stimulated LH secretion in the pituitary. However, the effects of PNX in the hypothalamus, the putative signaling pathways, and PNX receptor have yet to be identified. The mHypoA-GnRH/GFP and mHypoA-Kiss/GFP-3 cell lines represent populations of GnRH and Kiss neurons, respectively. PNX increased GnRH and GnRH receptor (GnRH-R) mRNA expression, as well as GnRH secretion, in the mHypoA-GnRH/GFP cell model. In the mHypoA-Kiss/GFP-3 cell line, PNX increased Kiss1 mRNA expression. CCAAT/enhancer-binding protein (C/EBP)-β, octamer transcription factor-1 (Oct-1), and cAMP response element binding protein (CREB) binding sites are localized to the 5' flanking regions of the GnRH, GnRH-R, and Kiss1 genes. PNX decreased C/EBP-β mRNA expression in both cell models and increased Oct-1 mRNA expression in the mHypoA-GnRH/GFP neurons. PNX increased CREB phosphorylation in both cell models and phospho-ERK1/2 in the mHypoA-GnRH/GFP cell model, whereas inhibiting the cAMP/protein kinase A pathway prevented PNX induction of GnRH and Kiss1 mRNA expression. Importantly, we determined that the G protein-coupled receptor, GPR173, was strongly expressed in both GnRH and kisspeptin cell models and small interfering RNA knockdown of GPR173 prevented the PNX-mediated up-regulation of GnRH, GnRH-R, and Kiss1 mRNA expression and the down-regulation of C/EBP-β mRNA expression. PNX also increased GPR173 mRNA expression in the mHypoA-GnRH/GFP cells. Taken together, these studies are the first to implicate that PNX acts through GPR173 to activate the cAMP/protein kinase A pathway through CREB, and potentially C/EBP-β and/or Oct-1 to increase GnRH, GnRH-R, and Kiss1 gene expression, ultimately having a stimulatory effect on reproductive function.
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