Activin-A Modulates Gonadotropin-Releasing Hormone Secretion from a Gonadotropin-Releasing Hormone-Secreting Neuronal Cell Line

Abstract

The recent development of GnRH-secreting neuronal cell lines (GT1-1, GT1-3 and GT1-7 clones) has provided a model system for the study of the neural regulation of GnRH expression and secretion. We report here that activin-A stimulates GnRH secretion by GT1-7 cells in a dose-dependent manner, with an EC50 of ∼2.5 ng/ml. The maximal response (50% stimulation) was achieved after 2 days of incubation with 20 ng/ml activin-A. Activin-A treatment increased total GnRH (secreted + cellular) in GT1-7 cells, possibly reflecting a stimulation of GnRH biosynthetic rates. The secretory effect of activin-A was also accompanied by a change in the cellular morphology to a more neuronal phenotype. The addition of TGF-β (10 ng/ml), which is structurally related to activins, did not significantly increase secretion of GnRH by GT1-7 cells illustrating the specificity of the activin effect on this cell line. Although inhibin (20 ng/ml) alone did not directly affect the spontaneous secretion of GnRH, it was able to partially block the stimulatory effect of activin. The present study with the GT1-7 clonal cell line suggests that activin, and perhaps inhibin, might act at hypothalamic sites to regulate reproduction through the control of GnRH production and/or secretion.

Activin-A stimulates hypothalamic gonadotropin-releasing hormone release by the explanted male rat hypothalamus: interaction with inhibin and androgens

“…Our findings, obtained from an experimental model employing a tissue with a preserved structure, confirmed that activin-A is able to stimulate GnRH release. However, in contrast to the study employing the GT1-7 cell line (Gonzalez-Manchion et al 1991), the maximal effect attained was stronger, it was obtained at a lower concentration (i.e. 10 vs 20 ng/ml), and it required only 6 h of incubation to became evident.…”

“…In addition, activin potentiates the effects of GnRH on FSH, but not LH, release (Ling et al 1986, Vale et al 1986. A monoclonal antibody against activin-B, added to a primary culture of anteropituitary cells, decreases FSH release and FSH -subunit mRNA expression, suggesting that activin may play an autocrine role in the regulation of FSH release (Corrigan et al 1991). Activin is also able to increase FSH serum levels in the whole animal with a maximal serum FSH increment observed after 4 h (Carroll et al 1991, Doi et al 1991, Rivier & Vale 1991.…”

“…This effect is completely overridden by inhibin and takes at least 4 h to become evident. No effect is detected on luteinizing hormone (LH) release and on LH -and -subunit mRNA expression (Carroll et al 1989, Corrigan et al 1991. In addition, activin potentiates the effects of GnRH on FSH, but not LH, release (Ling et al 1986, Vale et al 1986.…”

Human GnRH-secreting cultured neurons express activin betaA subunit mRNA and secrete dimeric activin A

“…The present data and the fact that these cells secrete both GnRH (16,25) and activin A in culture medium, suggest a reciprocal autocrine regulation. Although no data are to date available on activin action on FNC-B4 cells, reports that activin increases GnRH secretion from a GnRH-secreting cultured neuronal cell lines (11) and that activin A can stimulate the expression of GnRH receptor gene at transcriptional level (10), suggest that activin could also act in this way. On the basis of these ®ndings an interaction between activin and GnRH neuronal system in the human hypothalamus could be hypothesized.…”

The POU Homeodomain Transcription Factor Oct-1 Is Essential for Activity of the Gonadotropin-Releasing Hormone Neuron-Specific Enhancer

“…GnRH is a decapeptide hormone released in a pulsatile manner from a small number of specialized neurons scattered throughout the hypothalamus, which mediates CNS control of the neuroendocrine cascade that regulates reproductive function. The GT1 cells are uniquely suited as a model system for the study of the neuron-specific expression of the GnRH gene because they have retained many characteristics of GnRH neurons in vivo, including distinct neuronal morphology (24), expression of differentiated neuronal markers (11), secretion of GnRH in response to appropriate signals (7,8,26,36), and even pulsatile release of GnRH in cell culture (25,64). Using the GT1 cells as a model system, we have recently identified a neuron-specific enhancer between bases Ϫ1571 and Ϫ1863 upstream of the rat GnRH gene transcriptional start site that confers an approximately 50-fold increase in expression of the GnRH gene over that of the minimal 173-bp promoter (65).…”