Pituitary-derived FSH has greater follicle-stimulating bioactivity than recombinant FSH possibly due to glycoform variants†

Abstract

Follicular stimulating hormone (FSH) is the primary gonadotropin regulating ovarian follicular development and is widely utilized in assisted reproduction. Our previous research indicated that different glycoforms of the FSH Beta-subunit influence follicular development in vivo, but their specific roles across various folliculogenesis stages remained unclear. In this study, we compared 2 commercial FSH preparations: pituitary-derived FSH (pFSH), which contains both hypo- and fully glycosylated Beta-subunit forms, and recombination FSH (rFSH), predominantly consisting of fully glycosylated forms. Using an in vitro follicular culture model, we observed that pFSH was more effective than rFSH in stimulating follicular growth and promoting antrum formation in preantral follicles. pFSH also rescued insufficient preantral follicle growth and antrum formation caused by rFSH. Besides, pFSH more efficiently drove small antral follicle growth than rFSH. Additionally, pFSH significantly increased the granulosa cells (GCs) proliferation and effectively inhibited apoptosis, thereby protecting growing follicles from atresia. pFSH also induced higher steroidogenesis than rFSH. Mechanistically, pFSH activated key downstream signaling including PKA/CREB, MAPK/ERK and PI3K/AKT more efficiently than rFSH. Importantly, pre-treating antral follicles with pFSH significantly improved ovulation rate following hCG administration. This was linked to a rapid upregulation of LHCGR expression and enhanced MAPK/ERK signaling activity. Collectively, our data support that pFSH, with its mixture of hypo- and fully glycosylated forms, has greater bioactivity in promoting preantral-antral transition, antral follicle growth and ovulation compared to rFSH, which mainly consists fully glycosylated FSH. Application of mixed glycoforms or hypo-glycosylated FSH may improve the outcomes in assisted reproduction.

Keywords: Antral follicles; Follicular development; Fsh; Glycoform; Ovulation; Pre-antral follicles.