Kisspeptin directly stimulates gonadotropin-releasing hormone release via G protein-coupled receptor 54

Abstract

We have recently described a molecular gatekeeper of the hypothalamic-pituitary-gonadal axis with the observation that G protein-coupled receptor 54 (GPR54) is required in mice and men for the pubertal onset of pulsatile luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion to occur. In the present study, we investigate the possible central mode of action of GPR54 and kisspeptin ligand. First, we show that GPR54 transcripts are colocalized with gonadotropin-releasing hormone (GnRH) neurons in the mouse hypothalamus, suggesting that kisspeptin, the GPR54 ligand, may act directly on these neurons. Next, we show that GnRH neurons seem anatomically normal in gpr54-/- mice, and that they show projections to the median eminence, which demonstrates that the hypogonadism in gpr54-/- mice is not due to an abnormal migration of GnRH neurons (as occurs with KAL1 mutations), but that it is more likely due to a lack of GnRH release or absence of GnRH neuron stimulation. We also show that levels of kisspeptin injected i.p., which stimulate robust LH and FSH release in wild-type mice, have no effect in gpr54-/- mice, and therefore that kisspeptin acts directly and uniquely by means of GPR54 signaling for this function. Finally, we demonstrate by direct measurement, that the central administration of kisspeptin intracerebroventricularly in sheep produces a dramatic release of GnRH into the cerebrospinal fluid, with a parallel rise in serum LH, demonstrating that a key action of kisspeptin on the hypothalamo-pituitary-gonadal axis occurs directly at the level of GnRH release. The localization and GnRH release effects of kisspeptin thus define GPR54 as a major control point in the reproductive axis and suggest kisspeptin to be a neurohormonal effector.

Fig. 1.

Localization of GPR54 to GnRH neurons. (A and B) Coronal sections from gpr54^–/– mice preoptic hypothalami, showing neurons and dendrites double stained for β-galactosidase (blue) and GnRH (brown). (C) Representative medium-power field of preoptic areas. [Scale bars: 35 μm(A), 80 μm(B), and 45 μm(C).]

Fig. 2.

GnRH neuron morphology and localization in gpr54^–/– mice. Illustrated are coronal sections showing immunostained GnRH neurons in the preoptic area (A and B) (cell bodies and processes) and the median eminence (C and D) (nerve endings) of wild-type and mutant mice. [Scale bars: 45 μm(A and B) and 75 μm(C and D).]

Fig. 3.

Effect of i.p. kisspeptin injection on LH (A) and FSH (B) release in male wild-type (+/+) and mutant (–/–) mice.

Fig. 4.

Effect of kisspeptin on LH release in sheep. Representative profiles of serum LH secretion for two experimental sheep receiving 50 nmol of kisspeptin (intracerebroventricularly) over a 4-h infusion period (Right) or control animal receiving the vehicle (Left). The arrow indicates the time of the i.v. injection of 250 ng of GnRH.

Fig. 5.

Effect of kisspeptin on GnRH and LH secretion in sheep. Shown are CSF GnRH (filled squares) and serum LH (open circles) secretory profiles for three representative sheep before and after central administration of kisspeptin (50 nmol given over a 4-h period).