Regulation of Gonadotropin-Releasing Hormone (GnRH) Gene Expression by 5α-Dihydrotestosterone in GnRH-Secreting GT1–7 Hypothalamic Neurons¹

Abstract

Hypothalamic GnRH secretory neurons are precisely regulated by circulating gonadal steroids. However, the question of whether these cells are directly responsive to steroid hormones remains a central and controversial issue in reproductive science. In the present study, we demonstrate the expression of androgen receptor (AR) in a mouse hypothalamic GnRH-secreting cell line, GT1-7. AR messenger RNA was detected by Northern blot analysis of 10 microg total cellular RNA. Western blot analysis revealed a 110K AR immunoreactive band, and saturation binding analysis confirmed the presence of a high affinity low capacity androgen binding entity (Kd = 0.06 nM; Bmax = 12.4 fmol/mg protein). In addition, GT1-7 cells were found to express ARA70, an AR-specific coactivator that has been reported to enhance transactivational activity of the AR. GT1-7 cells transiently transfected with an androgen responsive MMTV-luciferase reporter construct displayed a 4.2-fold induction of luciferase reporter gene activity by 1 nM 5alpha-dihydrotestosterone (DHT), further demonstrating the presence of a functional AR. Treatment of GT1-7 cells with 1 or 10 nM DHT resulted in approximately 55% reduction in GnRH messenger RNA measured at 24 and 36 h after treatment. This repression was completely blocked by hydroxyflutamide, an AR antagonist. These results provide the first demonstration that androgen acts directly through an AR-mediated pathway to repress GnRH gene expression in hypothalamic GnRH-secreting neurons.