Regulating human oocyte maturation in vitro: a hypothesis based on oocytes retrieved from small antral follicles during ovarian tissue cryopreservation.

Objective: To characterize the hormonal environment in spent medium and cumulus cell gene expression during human IVM using oocytes from small antral follicles (SAFs) retrieved from surplus medulla tissue after ovarian tissue cryopreservation.

Methods: Immature oocytes from surplus medulla tissue underwent 42-h IVM in media with varying FSH and LH concentrations (0, 10, 100 IU/L FSH, and 100 IU/L FSH + 100 IU/L LH). Oocyte maturation was assessed by germinal vesicle (GV), metaphase I (MI), or metaphase II (MII) stages. Gene expression of FSHR, LHCGR, AMH, CYP19 A1, and INHA in cumulus cells was analyzed by RT-qPCR, and GDF9, AMH, inhibin-B, inhibin-A, and total inhibin were measured in the spent media by ELISA.

Results: Increased FSH concentrations downregulated FSHR expression and upregulated LHCGR, which correlated with MII transition. GDF9 concentrations in the spent medium significantly decreased with higher FSH, as did GDF9, AMH, and inhibin-B in MII oocytes. Inhibin-A levels tended to be higher in the media of MII oocytes. FSHR expression was positively associated with inhibin-B and negatively with inhibin-A, while LHCGR showed the opposite pattern and was also negatively linked to GDF9 concentration.

Conclusions: FSH-induced LHCGR expression, along with FSHR downregulation, is closely linked to oocyte maturation. Reduced GDF9 secretion from oocytes facilitates LHCGR expression on cumulus cells, while FSH and LH collectively induced hormones like inhibin-A, which likely support oocyte maturation.