Kisspeptin and the HPG axis

Kisspeptin is the master regulator of the hypothalamic-pituitary-gonadal (HPG) axis — the chain of signals that controls puberty, the menstrual cycle, and reproductive function in adults. Discovered as the product of the KISS1 gene in 1996 and originally studied as a metastasis suppressor, its reproductive role was not recognized until 2003, when researchers found that humans with inactivating mutations in its receptor (KISS1R, also called GPR54) failed to enter puberty.

Kisspeptin neurons in the hypothalamus stimulate GnRH (gonadotropin-releasing hormone) neurons. GnRH then drives the pituitary to release LH and FSH, which act on the ovaries to produce estradiol and progesterone, support follicle development, and trigger ovulation. Without kisspeptin signaling, the rest of the cascade goes silent — which is why loss-of-function mutations cause hypogonadotropic hypogonadism.

Two populations of kisspeptin neurons matter most. Neurons in the arcuate nucleus generate the pulsatile GnRH rhythm that sustains baseline reproductive function. Neurons in the anteroventral periventricular nucleus generate the preovulatory LH surge in response to rising estrogen — the positive feedback loop unique to female physiology.

Investigators at Imperial College London and elsewhere have studied kisspeptin administration in women with hypothalamic amenorrhea, where stress, low body weight, or excessive exercise have suppressed normal GnRH pulsatility. Kisspeptin infusion can restore LH pulses in these women, demonstrating that the downstream pituitary-ovarian machinery is intact and the lesion is upstream.

Kisspeptin has also been investigated as a trigger for oocyte maturation in IVF cycles, with the rationale that it produces a more physiological LH surge than the standard hCG trigger and may carry a lower risk of ovarian hyperstimulation syndrome. Multiple Phase II studies have been published; broader Phase III work is ongoing.

Before kisspeptin, GnRH was the highest known node in the reproductive cascade. The discovery that an upstream peptide regulates GnRH itself reorganized the textbook diagram of the HPG axis and opened a new pharmacological target for conditions ranging from delayed puberty to infertility. Most of the research base in women was built in the last fifteen years, which is unusually recent for a hormone of this importance.