EXPERIMENTAL STUDY Human GnRH-secreting cultured neurons express activin bA subunit mRNA and secrete dimeric activin A

Objective: To evaluate the expression of activin bA-subunit mRNA and the secretion of activin A in/from cultured GnRH-secreting neuronal cells cloned from human olfactory epithelium (FNC-B4), which showed biochemical and antigenic properties of GnRH-secreting neurons. Design: FNC-B4 cells were cultured in basal and conditioned media. Methods: Reverse transcription-polymerase chain reaction (RTR±PCR) evaluated the expression of activin bA-subunit mRNA. By using a speci®c ELISA, dimeric activin A concentrations were measured in culture media, in the absence or presence of carvone or forskolin and with different doses of progesterone, GnRH, and estradiol. Results: RT±PCR experiments performed on total RNA isolated from FNC-B4 cells, using speci®c primers for the activin bA gene, showed a 787 bp DNA band corresponding to the bA gene. FNC-B4 cells secreted activin A, and the highest accumulation in conditioned medium was achieved after 3 h culture: the addition of forskolin, but not of carvone, was able to stimulate the release of activin A from cultured neuronal cells (P < 0.01). When progesterone or GnRH was added, a signi®cant accumulation of activin A was observed (P < 0.01), while estradiol administration did not signi®cantly affect activin A secretion. Conclusion: To date, this is the only study, in an in vitro human model reporting, that GnRH-secreting neuronal cells expressed activin bA-subunit mRNA, and released dimeric activin A in culture medium. The expression and secretion of activin suggests that in these cells activin A might exert its action by autocrine/paracrine mechanisms. European Journal of Clinical Endocrinology 143 133±138