Dihydrotestosterone and Leptin Regulate Gonadotropin-Releasing Hormone (GnRH) Expression and Secretion in Human GnRH-Secreting Neuroblasts

Abstract

The reversal of hypogonadotropic hypogonadism (HH), occurring after discontinuation of testosterone therapy in adolescents with delayed puberty and in a small percentage of adults with congenital HH, suggests a role for androgens in favoring a spontaneous recovery of reproductive function. We investigated the effect of androgens and leptin on gonadotropin-releasing hormone (GnRH) expression and secretion in human GnRH-secreting neuroblasts (FNC-B4). Quantitative real-time polymerase chain reaction RT-PCR for mRNA expression and radioimmunoassay for GnRH secretion were used. Immunohistochemical studies assessed GnRH protein expression. FNC-B4 migration was analyzed with multiwell Boyden chamber technique. Effects of the non-aromatizable androgen dihydrotestosterone (DHT) and leptin in FNC-B4 were tested after 24 and 48 hours. Exposure to increasing concentrations of DHT after 24 hours significantly stimulated GnRH mRNA in FNC-B4. This effect was still present after prolonged exposure (48 hours). Similarly, treatment with leptin significantly induced GnRH mRNA after 24 hours, but not at 48 hours. Interestingly, mRNA for leptin receptors (LEPR) was significantly reduced after 48 hours of leptin, while, at this time point, it was stimulated by DHT. Coincubation for 48 hours with leptin and DHT maintained the stimulatory effect on both GnRH and LEPR mRNA, suggesting that DHT could stabilize the leptin effect by preventing downregulation of LEPR. Similar results were obtained for GnRH protein expression analysis. Moreover, both DHT and leptin increased GnRH release into the culture medium. We also found that DHT or leptin treatment significantly increased FNC-B4 basal migration. As we previously found that GnRH stimulates FNC-B4 migration, we hypothesized that this effect could be mediated by DHT- and leptin-induced GnRH release. Accordingly, the GnRH antagonist cetrorelix inhibited DHT- and leptin-induced migration. Our results suggest that androgens (adequate hormonal status) could have a positive effect on GnRH neuronal activity by synergizing with leptin (adequate energy status) in the regulatory mechanisms required for reproductive and sexual fitness.