The Kisspeptin and Kisspeptin receptor in follicular microenvironment: is that really necessary for oocyte maturation and fertilisation?

Abstract

The aim of this study was to determine whether Kisspeptin and Kisspeptin receptor in the follicular microenvironment is necessary for human oocyte maturation and fertilisation. The cumulus cell (CC) and follicle fluids (FF) obtained from the first aspirated follicles (n = 52) from 32 patients were divided into three groups considering nuclear maturation and fertilisation results of oocytes: (1) Metaphase I or germinal vesicle stage oocytes (incomplete nuclear maturation, n = 10), (2) unfertilised metaphase II oocytes (incomplete cytoplasmic maturation, n = 16), and (3) fertilised metaphase II oocytes (completed nuclear-cytoplasmic maturation, n = 26). The gene expression levels were assessed by RT-PCR. The levels of Kisspeptin (KISS1) and Kisspeptin receptor (KISS1R) were measured by ELISA. There were no significant efficacy KISS1 and KISS1R gene expressions in cumulus cells in terms of oocyte nuclear maturation stage (Group 1, vs Group 2 + Group 3) (respectively p = .49; p = .45). In terms of the cytoplasmic maturation stage (Group 2, vs Group 3); KISS1 and KISS1R expressions in CCs were comparable (respectively p = .07; p = .08). In FFs, KISS1 and KISS1R concentrations were similar between all groups (respectively p = .86; p = .26). In conclusion, the relative KISS1 and KISS1R expressions in CC and also KISS1 and KISS1R level of FF were independent of oocytes nuclear and/or cytoplasmic maturation. Impact statementWhat is already known on this subject? It has been demonstrated that Kisspeptin is an essential regulator of reproductive function and plays a key role in the modulation of GnRH secretion and gonadotropin release. Still, no information is available about the link between gene expression or concentration in the follicular microenvironment and oocyte development.What do the results of this study add? The study has shown that the relative Kisspeptin (KISS1) and Kisspeptin receptor (KISS1R) and expressions in cumulus cell (CC) and also KISS1 and KISS1R levels of follicle fluids (FF) were independent of oocytes nuclear and/or cytoplasmic maturation.What are the implications of these findings for clinical practice and/or further research? Based on the findings, it is difficult to establish a concept that kisspeptin can directly induce oocyte maturation. Nevertheless, to confirm these findings, further studies with a larger sample size are needed.

Keywords: Kisspeptin; Kisspeptin receptor; fertilisation; final oocyte maturation; follicular micro-environment.