ESPE Abstracts

The synthesis of many peptides involves several post-translational steps which converts precursors into bioactive peptide. One of these steps results in the α-amidation of the C-terminal from a glycine through a bifunctional enzyme called the peptidylglycine α-amidating monooxygenase (PAM). Although the physiological role of Kisspeptin (KP) in the control of GnRH secretion is well known, the exact molecular form of the bioactive hypothalamic KP remains elusive. By analogy with mature Kisspeptin synthesized by the placenta, the hypothalamic KP is suspected to be a peptide of 54 residues with an α-amidated C-terminal end (KP54). Here, we report a new variant of KISS1 identified in patients with defects of the gonadotropic axis which was supposed to alter the α-amidation of KP54. The index case was seen for bilateral cryptorchidism and micropenis at the age of 1 year. Gonadotropins and testosterone were prepubertal and AMH and inhibin B levels low (29.5 ng/ml, N>53, 64 pg/ml, N>94). One of his sisters was referred at the age of 13 years for absence of pubertal development, persisting at the age of 15. She was S1P1, with a bone age of 10 years. Estradiol was undetectable, LH (0.3 IU/L) and FSH (2.4 IU/L) increased to 5.2 IU/L and 11.9 IU/L. Brain MRI and pituitary evaluation were normal and other causes of delayed puberty were ruled out. Exome analysis revealed an homozygous variant in KISS1 (c.364G>T) substituting a serine for glycine¹²² in the proband and his sister and both parents were heterozygous for the variant. The 138 amino-acids hypothalamic precursor of KP54 is supposed to be cleaved by proconvertase at the dibasic motif ⁶⁷RR⁶⁸ and ¹²³KR¹²⁴ to form KP54-G¹²² which is then transformed to KP54 by the PAM. To demonstrate that KP54-S¹²² was unable to be converted into KP54, an original mass spectrometry method was developed. KP54 was detected in the supernatant of WT- KISS1 expressing HEK293 cells. In c.364G>T- KISS1 transfected cells, KP54 was not detected in cell supernatant whereas trypsin digestion of the protein intracellular extract detected the KP54-S¹²² precursor. Our analysis demonstrates that the substitution of Gly¹²² by a serine impairs the synthesis of KP54. The description of this new molecular mechanism of KISS1 associated gonadotropic deficiency brings new knowledge on the synthesis of the bioactive hypothalamic Kisspeptin.