title: Hypothalamic action of phoenixin to control reproductive hormone secretion in females: importance of the orphan G protein-coupled receptor Gpr173.
abstract: Sexual maturation and maintenance of reproductive function are regulated by neurohormonal communication between the hypothalamus, pituitary, and gonads (referred to as the HPG axis). Phoenixin (PNX) is a newly identified, endogenous peptide abundantly produced in the hypothalamus and shown to be an important mediator of ovarian cyclicity. However, the underlying mechanisms by which phoenixin functions within the HPG axis are unknown. Previous in vitro studies demonstrated a direct action of PNX on gonadotrophs to potentiate gonadotrophin-releasing hormone (GnRH) induced luteinizing hormone (LH) secretion. Therefore, we hypothesized that centrally derived phoenixin regulates the preovulatory LH surge required for ovarian cyclicity. We observed a significant dose-related increase in the level of plasma LH in diestrous, female rats that were given an intracerebroventricular injection of PNX compared with vehicle-treated controls. While this suggests that even under low-estrogen conditions, PNX acts centrally to stimulate the HPG axis, further characterization is contingent on the elucidation of its cognate receptor. Using the "deductive ligand receptor matching strategy," we identified the orphan G protein-coupled receptor, Gpr173, as our top candidate. In cultured pituitary cells, siRNA-targeted compromise of Gpr173 abrogated PNX's action to potentiate GnRH-stimulated LH secretion. In addition, siRNA-mediated knockdown of endogenous Gpr173, which localized to several hypothalamic sites related to reproductive function, not only significantly extended the estrous cycle but also prevented the PNX-induced LH secretion in diestrous, female rats. These studies are the first to demonstrate a functional relationship between PNX and Gpr173 in reproductive physiology and identify a potential therapeutic target for ovulatory dysfunction.
authors.affiliation: Department of Pharmacology and Physiology, Saint Louis University School of Medicine, St. Louis, Missouri; and.
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Stein
authors.affiliation: Department of Pharmacology and Physiology, Saint Louis University School of Medicine, St. Louis, Missouri; and.
authors.forename: Chloe W
authors.initials: CW
authors.lastname: Tullock
authors.affiliation: Department of Pharmacology and Physiology, Saint Louis University School of Medicine, St. Louis, Missouri; and.
authors.forename: Stacy K
authors.initials: SK
authors.lastname: Mathews
authors.affiliation: Department of Molecular and Integrative Physiology, University of Michigan School of Medicine, Ann Arbor, Michigan.
authors.forename: David
authors.initials: D
authors.lastname: Garcia-Galiano
authors.affiliation: Department of Molecular and Integrative Physiology, University of Michigan School of Medicine, Ann Arbor, Michigan.
authors.forename: Carol F
authors.initials: CF
authors.lastname: Elias
authors.affiliation: Department of Pharmacology and Physiology, Saint Louis University School of Medicine, St. Louis, Missouri; and.
authors.forename: Willis K
authors.initials: WK
authors.lastname: Samson
authors.affiliation: Department of Pharmacology and Physiology, Saint Louis University School of Medicine, St. Louis, Missouri; and gyosten@slu.edu.
authors.forename: Gina L C
authors.initials: GL
authors.lastname: Yosten
mesh_terms: D000818:Animals; D030762:Estrous Cycle / Q000502:physiology*; D005260:Female; D007028:Hypothalamic Hormones / Q000378:metabolism*; D007031:Hypothalamus / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000378:metabolism*; D036361:Peptide Hormones / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D012098:Reproduction / Q000502:physiology*
chemical_list: D007028:Hypothalamic Hormones; D007986:Luteinizing Hormone; D036361:Peptide Hormones; D043562:Receptors, G-Protein-Coupled; C000620933:gpr173 protein, rat; C000705635:phoenixin
keywords: Gpr173; estrous cyclicity; luteinizing hormone; phoenixin