Hypoglycosylated FSH enhances oocyte quality via increased cell-to-cell interaction during mouse follicle development

Differences in follicle-stimulating hormone (FSH) ß-subunit N-glycosylation results in distinct FSH glycoforms. Hypoglycosylated FSH21 is more bioactive and abundant in reproductively young women, whereas fully glycosylated FSH24 shows lower bioactivity and a relative increase with age. To investigate if the coinciding shift in FSH glycoform abundance contributes to the age-dependent decline in oocyte quality, an encapsulated in vitro follicle growth system was utilized to examine the direct effects of FSH glycoforms on folliculogenesis and resulting oocyte quality. Long-term culture (10-12 days) with FSH21 (10 ng/ml) enhanced follicle growth, estradiol secretion, and oocyte quality compared to equivalent FSH24 treatment. FSH21 exhibited enhanced capacity to establish transzonal projections, gap junctions, and cell-to-cell communication within 24 hrs in culture. Transient inhibition of FSH21-mediated bidirectional communication abrogated the positive effects of FSH21 on follicle growth, estradiol secretion and oocyte quality. These findings indicate FSH21 promotes folliculogenesis and oocyte quality in vitro through increasing cell-to-cell communication early in folliculogenesis and that the shift in abundance from FSH21 to FSH24 with reproductive aging could contribute to the age-dependent decline in oocyte quality. To determine how FSH glycoforms modulate the transciptome of early secondary follicles, follicles were treated with 0, 1, or 10 ng/ml FSH21 or FSH24 for 24 hrs. Three biological replicates of each treatment were conducted.