T. Barni et al., Sex steroids and odorants modulate gonadotropin-releasing hormone secretion in primary cultures of human olfactory cells, J CLIN END, 84(11), 1999, pp. 4266-4273
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.