Sex steroids and odorants modulate gonadotropin-releasing hormone secretion in primary cultures of human olfactory cells

Olfactory neurons and GnRH neurons share a common origin during development . In the nasal epithelia, GnRH neurons persist throughout fetal life and ad ulthood. The fate and function of these neurons in vivo have remained unkno wn. In a previous in vitro study, we isolated, cloned, and propagated prima ry long term cell cultures from the olfactory neuroepithelium of 8- to 12-w eek-old human fetuses. These cells expressed both neural proteins as well a s olfactory genes and were responsive to odorant stimuli. We now report tha t these human olfactory cells also express the GnRH gene and protein. Combi ned HPLC and RIA studies have indicated that these cells release authentic GnRH in spent media The release of GnRH was time dependent and was positive ly affected by sex steroids and odorants. Immunohistochemical data demonstr ated the presence of sex steroid receptors in these cells. The presence of the alpha- and beta-subtypes of the estrogen receptor was also demonstrated by RT-PCR and Western blot analysis. When the cells were stimulated with i ncreasing concentrations of 17 beta-estradiol in the presence of a fixed co ncentration of progesterone (10(-7) mol/L), the combination of the two ster oids induced a 3- to 4-fold increase in GnRH secretion. This stimulatory ef fect was completely blunted by tamoxifen. Neither 17 beta-estradiol nor pro gesterone was effective when tested separately. Treatment with increasing c oncentrations of the odorant, l-carvone, induced a time- and dose-dependent dramatic increase in GnRH protein release (1000-fold increase) and gene ex pression. Repeated application of the stimulus resulted in a progressive lo wer responsiveness of the cells. To our knowledge, this is the first time t hat primary cell cultures from human fetal olfactory neuroepithelium have b een shown to express and release GnRH. Our results also demonstrate that th ese cultures, which are sensitive to sex steroids and odorants, can be usef ul models in the study of the complex array of regulatory factors that fine ly tune GnRH secretion in humans.