Expression of functional ciliary neurotrophic factor receptors in immortalized gonadotrophin-releasing hormone-secreting neurones

Ciliary neurotrophic factor (CNTF), a cytokine of the interleukin-6 superfamily, is known to exert pleiotropic actions, including regulation of food intake and permissive effects on reproduction, by facilitating the release of gonadotrophin-releasing hormone (GnRH) and gonadotrophins. CNTF activates membrane receptors (CNTF-Rs) composed of one ligand-specific binding subunit, defined CNTFR alpha, and two signal transducing subunits, termed leukaemia inhibitory factor receptor (LIFR) and gp130. However, it is not clear whether the effects of CNTF on GnRH release result from either a direct or an indirect action on GnRH-secreting hypothalamic neurones, or from a combination of these events. The hypothesis of a direct effect of CNTF was thus tested using the GT1-7 GnRH-secreting cell line. CNTF-R expression and CNTF-induced modulation of the Janus kinase (JAK2)-signal transducer and activator of transcription 3 (STAT3) pathway and of GnRH release were evaluated. GT1-7 cells were found to express CNTFR alpha, LIFR and gp130 genes, as shown by reverse transcription-polymerase chain reaction analysis, and the corresponding proteins, analysed by immunofluorescence and western blot. CNTFR alpha, LIFR and gp130 immunoreactive bands had an approximate size of 50, 190 and 130 kDa, respectively. Treatment of GT1-7 cells with 10(-12) M CNTF for 15-60 min resulted in a marked and transient increase of STAT3 phosphorylation via activation of JAK2. A 30-min exposure of GT1-7 cells to different CNTF concentrations increased the accumulation of GnRH into the culture medium, with a maximal effect at 10(-11) M. In conclusion, the present results provide new information about the regulation of the reproductive axis by CNTF, and suggest that it might operate at the hypothalamic level by directly influencing the activity of GnRH-secreting neurones, in addition to the possible indirect effects via interneurones proposed by previous studies.