How kisspeptin entered reproductive research
The opening chapter takes place among melanoma cells. Reproductive hormones enter the story later.
The melanoma experiment
In 1996, KISS1 was identified as a metastasis-suppressor gene in human malignant melanoma. Introducing it into metastatic melanoma cells suppressed their spread in nude mice without abolishing tumour formation. The work involved a human cell line and a mouse model; its result was about metastatic behaviour in that setting.
This scientific change of rooms suits my curiosity. The familiar reproductive story can make the original experiment seem like a preface written for a later discovery. It had a substantial question of its own. I prefer to give it that space.
The gene was later found to encode kisspeptin neuropeptides. That connection is enough to make the transition to reproductive biology interesting. There is no need to recruit the melanoma result as an argument for a hormonal intervention.
Puberty and the receptor
The reproductive connection became much harder to dismiss when loss-of-function mutations in GPR54 were linked to failure of puberty in humans in 2003. Mice lacking the receptor reproduced the phenotype. GPR54, also called KISS1R, is the receptor through which kisspeptin signals.
The peptide itself also entered the genetic evidence: an inactivating KISS1 mutation caused hypogonadotropic hypogonadism with pubertal failure in a family. In that condition the reproductive hormone signals are insufficient. The receptor and the peptide therefore appear in different genetic findings pointing toward the same biological system.
The genetic turn is where this history becomes most convincing to me. The evidence has moved from putting a gene into cancer cells to observing what happens when a signalling system fails in people. Those are very different experiments. Their meeting makes the subject richer, while leaving each result attached to its own question.
From a biological role to human experiments
An early human infusion study found that kisspeptin-54 stimulated reproductive hormones in healthy men. Later, a trial in men with hypoactive sexual desire disorder examined sexual brain processing and penile tumescence. The latter word means swelling; in this experiment it described a measured physical response.
There were other branches. In a trial involving women at high risk of ovarian hyperstimulation syndrome during IVF, kisspeptin-54 triggered egg maturation. That is a fertility experiment in women, with a distinct purpose and population. Its place in this history is to show the breadth of the research questions, without borrowing its outcome for men.
I like the history best when it retains those changes of direction. A molecule associated with reproductive signalling can lead into hormonal timing, fertility and the processing of attraction. The next essay narrows the focus to testosterone and the timing of the response.