Evidence that dehydroepiandrosterone, DHEA, directly inhibits GnRH gene expression in GT1-7 hypothalamic neurons

Dehydroepiandrosterone (DHEA) has been reported to have diverse effects on overall physiology, although its mechanism of action and specific receptor are not yet known. We have used the immortalized, clonal GT1-7 hypothalamic neurons to study DHEA effects on gonadotropin-releasing hormone (GnRH) gene expression. DHEA (10(-4) M) downregulates GnRH transcription by 39, 70 and 83% at 24, 36, and 48 h, respectively, while DHEA-sulphate had no effect. Hydroxyflutamide a specific androgen receptor (AR) antagonist, and cyproterone acetate or trilostane, both inhibitors of 3 beta-hydroxysteroid dehydrogenase/delta 4,5 isomerase, the rate-limiting enzyme for the conversion of DHEA to sex steroids, did not affect the ability of DHEA to downregulate GnRH gene expression. We found that GT1-7 cells did not express aromatase, thereby precluding conversion to estrogen. Analysis of [(14)C] DHEA metabolism by thin layer chromatography indicates that the main metabolites produced are 7 alpha- and 7 beta-hydroxy DHEA, and 7-oxo DHEA, although these steroids were not able to repress GnRH gene expression alone. Cell viability studies indicated that the transcriptional repression observed is not due to GT1-7 cell death. Interestingly, SV40 T-antigen mRNA levels, under the control of 2.3 kb of the rat GnRH gene 5' regulatory region, are also repressed by DHEA. Our studies indicate that DHEA has direct effects on GnRH transcription that appear to be unique from those observed after conversion to other steroidogenic compounds.