The GnRH Metabolite, GnRH-(1-5), Functions via an orphan receptor, GPR173

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Program Director/Principal Investigator (Last, First, Middle): Wu, T. John Project Summary Disorders of puberty in both boys and girls are increasingly recognized for its impact on mental, social and physical health. There are significant negative correlations between precocious puberty with metabolic disorders such as obesity, anorexia and polycystic ovarian syndrome. Likewise, there is also a correlation with mental health consequence including depression and anxiety disorders. Gonadotropin-releasing hormone (GnRH) was first isolated in the mammal and shown to be the primary regulator of the reproductive system through its initiation of pituitary gonadotropin release. During development, an increase in GnRH release occurs that is critical for the initiation of puberty. This increase is attributable, at least in part, to activation of the GnRH neurosecretory system. Discerning the underlying cause of central disorder of puberty remains an important research effort. In addition to the complex regulation of GnRH synthesis, release, and function, further evidence suggests that the processing of GnRH produces yet another layer of complexity in its activity. GnRH is processed by a zinc metalloendopeptidase EC 3.4.24.15 (EP24.15) that cleaves the hormone at the covalent bond between the 5th and 6th residue of the decapeptide (Tyr5-Gly6) to form GnRH-(1-5). We have shown that GnRH-(1-5) is not merely a degradation product but regulates a number of functions related to reproduction. These include facilitation of lordosis behavior, autoregulation of its gene expression and secretion as well as regulate GnRH neuronal migration. Interestingly, there is little evidence to suggest that GnRH-(1-5) may bind to its cognate receptor, the GnRH receptor. Our laboratory recently identified the orphan G-protein coupled receptor (GPR)-173 to bind to GnRH-(1-5) with high affinity. Not much is known about GPR173. Our preliminary results show that GPR173 expression is increased during puberty. Thus, we wish to determine if GnRH-(1-5) may be involved in regulating puberty via GPR173. To that end, we propose 2 specific aims to test the hypothesis that the increase in GnRH neuronal activity during puberty is mediated by GnRH-(1-5) via GPR173. We will approach these studies by describing the anatomical localization of GPR173 (Aim 1) and by determining whether the timing of puberty is altered when GPR173 expression is down- regulated. These studies will use the well characterized Sprague Dawley rat model of puberty. Specific Aim 1 will determine the neuroanatomical expression of GPR173 in male and female rats before and after the onset of puberty. These studies will include immunocytochemical studies examining its expression in a rostro-caudal manner as well as its potential co-localization with the GnRH neuron. We will determine the GPR173 protein and mRNA expression levels. Specific Aim 2 will determine the role of GPR173 in mediating puberty. Antisense oligonucleotides to GPR173 will be administered to pre-pubertal female rats to determine whether its down-regulation may alter the timing of puberty. Inhibitors to EP24.15 will also be administered to prevent GnRH-(1-5) production. PHS 398/2590 (Rev. 06/09) Page 2 Continuation Format Page