OR19-04 Hypoglycosylated FSH Enhances Ovarian Follicle Development and Gamete Quality

Abstract Disclosure: A. Converse: None. T. Kumar: None. F.E. Duncan: None. Gamete quality depends on the proper growth and maturation of the ovarian follicle, which consists of the oocyte and its supporting somatic cells. FSH is essential for follicle growth as female Fshb and Fshr null mice are infertile due to arrested follicle development. Macroheterogeneity in N-glycosylation on the FSHß-subunit confers differential bioactivities with hypoglycosylated FSH21 exhibiting higher FSHR binding affinity and bioactivity compared to fully glycosylated FSH24. In females, there is a shift from the highly bioactive FSH21 to FSH24 with increasing age which occurs coordinately with the age-dependent decline in female fertility. In this study, we used an encapsulated in vitro follicle growth assay to test the hypothesis that FSH glycoforms have differential abilities to promote follicle development and gamete quality. Early-stage (preantral) ovarian follicles were isolated from CD-1 mice, cultured in media containing 10 ng/ml of either FSH21 or FSH24 for up to 12 days, and then ex vivo ovulation was induced. While both glycoforms maintained >75% follicle survival through day 12, follicles treated with FSH21 were significantly larger than FSH24-treated follicles between days 4 and 12 of culture. Over the 12 day culture, FSH21-treated follicles grew from 110.9 ± 9.2 µm to 251.3 ± 24.4 µm, while FSH24-treated follicles grew from 109.3 ± 7.1 µm to 229.7 ± 15.4 µm. This difference in growth correlated with a 13.4 and 4.5-fold increase in estradiol secretion by FSH21-treated follicles compared to FSH24 treatment on days 8 and 12, respectively. After ex vivo maturation, FSH21-treated follicles produced a higher proportion (76.9%) of meiotically competent gametes that reached the metaphase II (MII)-arrested state compared to FSH24-treated follicles (62.5%). Furthermore, normal meiotic spindle configuration was observed in 76% of MII eggs from the FSH21 cohort but only 50% of the FSH24 cohort. These results indicate that FSH21 is more bioactive than FSH24 in promoting follicle development and high-quality oocytes. Mechanistically, this is likely due in part to the differential effects of FSH21 and FSH24 on the formation of transzonal projections (TZPs), which are cytoplasmic filaments essential for granulosa-oocyte communication. By 24 hrs, FSH21-treated follicles had more TZPs than FSH24-treated follicles, as demonstrated by increased actin staining (1.6x) and Myo10 foci (5.1x) in the zona pellucida region. Thus, the early establishment of TZPs and increased somatic-oocyte communication in FSH21-treated follicles ultimately results in a more developmentally competent gamete. In addition, we anticipate that ongoing transcriptomic analysis of 24 hr FSH glycoform-treated follicles will highlight other processes involved in early follicle development that contribute to the observed differential effects on oocyte quality. Presentation Date: Saturday, June 17, 2023