Distinct Luteinization Profiles of Cultured Human Granulosa Cells from Small Antral and Preovulatory Follicles.

Context: The transformation of follicular granulosa cells into luteal cells of the corpus luteum remains poorly understood in the human ovary.

Objective: To investigate the luteinization process and steroidogenic differences between granulosa cells from small antral and preovulatory follicles in vitro.

Design: Granulosa-lutein cells were obtained from 12 women undergoing IVF treatment, while follicular granulosa cells from unstimulated small antral follicles and corpus luteum were collected from 18 women undergoing ovarian tissue cryopreservation. Cells were cultured for up to 96 hours or 12 days with or without androstenedione or testosterone supplementation and analyzed using RT-qPCR and steroid hormone assays.Setting: University Hospital of Copenhagen, Denmark, and Wake Forest Institute for Regenerative Medicine, USA.

Results: In follicular granulosa cells, luteinization markers (CYP11A1, p<0.05; STAR, p<0.001) increased within 24-48 hours, while granulosa markers (HSD17β1, p<0.001; CYP19A1, p<0.05) decreased within 6-12 hours. LHCGR remained unchanged. By 48 hours, gene expression resembled that of the corpus luteum. In contrast, granulosa-lutein cells exhibited highly luteinized profiles from day 0, with significantly higher progesterone/(17)estradiol ratios. Androgen supplementation and long-term FSH exposure did not alter luteinization.

Conclusions: This study uniquely demonstrates that unstimulated follicular granulosa cells undergo a gradual, intrinsic luteinization process, independent of external hormonal triggers. In contrast, granulosa-lutein cells are already highly luteinized upon aspiration. These findings challenge conventional views on luteinization and highlight intrinsic cellular programming as a key driver, offering new insights into ovarian physiology and potential therapeutic targets for reproductive disorders.