KISS1R

KISS1R is the class A GPCR that sits immediately upstream of GnRH neurons and controls the master switch for pubertal onset and reproductive cyclicity. Kisspeptin signaling through KISS1R is the proximate trigger for pulsatile GnRH release, and loss-of-function KISS1R mutations cause normosmic hypogonadotropic hypogonadism (nHH) - establishing it as the key node linking metabolic state, circadian rhythm, and sex steroid feedback to the HPG axis. KISS1R is also a metastasis suppressor receptor in multiple cancers. Kisspeptin-54 (Kp-54, Kp-10 active fragment) and synthetic analogs are in clinical trials for fertility, hypogonadism, and as diagnostic probes for GnRH neuron reserve.

KISS1R (chromosome 19p13.3, 398 aa) is a Gq/11-coupled class A GPCR. The endogenous ligands - kisspeptin-54, kisspeptin-14, kisspeptin-13, and kisspeptin-10 - all derive from the KISS1 gene product (145 aa precursor) by proteolytic processing and share a C-terminal RF-amide motif (Arg-Phe-NH₂) essential for receptor activation. Kisspeptin-10 (the 10 C-terminal residues) is the minimal sequence for full KISS1R activation (EC₅₀ ~1 nM); the N-terminal extension in Kp-54 mainly extends plasma half-life. Signaling: Gq/11 → PLC-β → IP3/DAG → intracellular Ca²⁺ transient and PKC → ERK1/2 → GnRH neuron membrane depolarization via TRPC channel activation. KISS1R also activates Gs/cAMP in some cell types. Hypothalamic KNDy neurons (arcuate nucleus) co-express kisspeptin, neurokinin B, and dynorphin - NKB and dynorphin provide autocrine regulation of kisspeptin pulse generation. The AVPV nucleus expresses kisspeptin neurons that mediate the estrogen-positive feedback LH surge. Inactivating KISS1R mutations (Gln58Leu, Arg331X among others) abolish GnRH pulsatility and prevent puberty. Activating mutations cause central precocious puberty. KISS1R is also expressed in placenta, breast cancer, and melanoma, where kisspeptin signaling suppresses invasion and metastasis through FAK/Rho/MAPK cytoskeletal effects.

No KISS1R agonist or antagonist is currently approved, but clinical development is active. Intravenous Kp-54 infusion restores LH pulsatility in women with hypothalamic amenorrhea and triggers the LH surge in IVF protocols. MVT-602 (Kp-10 analog) is in Phase 2 for IVF ovulation triggering and has demonstrated efficacy with lower ovarian hyperstimulation syndrome risk than hCG. Kp-10 analogs are also being studied for male hypogonadotropic hypogonadism. For peptide research, the tractable recipes are: C-terminal RF-amide-anchored Kp-10 analogs with N-terminal Aib or D-amino acid substitutions for DPP-4 and metalloprotease resistance; cyclic kisspeptin-10 analogs constrained by lactam bridges at positions 1–5 for improved receptor selectivity and half-life; fatty acid–conjugated Kp-54 fragments for once-weekly SC dosing; and KISS1R antagonist peptidomimetics (e.g., peptide 234, p234) as research tools for dissecting KNDy pulse generation mechanisms.