Oestrogen Induces Rhythmic Expression of the Kisspeptin-1 Receptor 1 GPR54 in Hypothalamic Gonadotrophin-Releasing Hormone (GnRH)-Secreting GT1-7 Cells

• Published in: Journal of neuroendocrinology 2011-09, Vol.23 (9), p.823-830
• Main Authors: Tonsfeldt, Karen J., Goodall, Cheri P., Latham, Kristin L., Chappell, Patrick E.
• Format: Article
• Language: English
• ISSN: 0953-8194; 1365-2826
• DOI: 10.1111/j.1365-2826.2011.02188.x

Oestrogen-stimulated preovulatory gonadotrophin surges are temporally regulated in a way which remains not fully understood. Mammalian ovulation requires surges of gonadotrophin-releasing hormone (GnRH), released from specialized neurones in the hypothalamus. Surge regulation is mediated by ovarian oestrogen (E2) feedback- acting as a negative signal until the early afternoon of the pro-oestrus phase, at which point it stimulates robust increases in GnRH release. Multiple lines of evidence suggest a role for the circadian clock in surge generation, but the presence of endogenous oscillators in several neuronal populations throughout the mediobasal hypothalamus complicates elucidating the underlying mechanisms of circadian regulation. In this study, we propose that endogenous oscillators within GnRH neurones are modulated by oestrogen to elicit GnRH surge secretion. One mechanism by which this may occur is through the upregulation of receptors of known stimulators of GnRH, such as kisspeptin’s cognate receptor, GPR54. Through analysis of mRNA and protein abundance patterns, we found that high levels of E2 elicit circadian expression profiles of GPR54 in vitro , and that disruption of endogenous GnRH oscillators of the clock dampens this effect. Additionally, while kisspeptin administration to GT1-7 cells does not result in surge-level secretion, we observed increased GnRH secretion from GT1-7 cells treated with positive feedback levels of E2. These results in this in vitro neuronal model system suggest a possible mechanism whereby receptor expression levels, and thus GnRH sensitivity to kisspeptin, may change dramatically over the pro-oestrus day. In this way, elevated ovarian E2 may increase kisspeptidergic tone while simultaneously increasing GnRH neuronal sensitivity to this neuropeptide for maximal surge release.