Excessive follicle-stimulating hormone during ovarian stimulation of cattle may induce premature luteinization of most ovulatory-size follicles

Abstract

High FSH doses during ovarian stimulation are detrimental to ovulatory follicle function and decrease live birth rate in cattle and women. However, the mechanism whereby excessive FSH causes ovarian dysfunction is unknown. This study tested the hypothesis that excessive FSH during ovarian stimulation induce premature luteinization of ovulatory-size follicles. Small ovarian reserve heifers were injected twice daily for four days with 70 IU (N = 7 heifers) or 210 IU (N = 6 heifers) Folltropin-V (commercial FSH-enriched preparation of porcine pituitary glands with minor (<1%) LH contamination, cpFSH). Ovulatory-size (≥10 mm) follicles were excised from ovaries after the last cpFSH injection and hormone concentrations in follicular fluid (FF) were determined using ELISA. Luteinization was monitored by assessing cumulus cell-oocyte complex (COC) morphology and measuring concentrations of estradiol (E), progesterone (P) and oxytocin (O) in FF. COC were classified as having compact (cCOC) or expanded (eCOC) cumulus cell layers, and as estrogen-active (EA, E:P in FF ≥1), estrogen-inactive (EI, E:P in FF ≤1 > 0.1) or extreme-estrogen-inactive (EEI, E:P in FF ≤0.1). A high proportion (72%) of ovulatory-size follicles in 210 IU, but not 70 IU, dose heifers displayed eCOC. The high dose also produced higher proportions of EI or EEI follicles which had lower E:P ratio and/or E but higher P and/or O concentrations compared with the 70 IU dose heifers. In conclusion, excessive cpFSH doses during ovarian stimulation may induce premature luteinization of most ovulatory-size follicles in heifers with small ovarian reserves.

Ovarian stimulation with excessive FSH doses causes cumulus cell and oocyte dysfunction in small ovarian reserve heifers

“…Severe abnormalities in multiple cell-signaling pathways in granulosa and cumulus cells and oocytes critical for folliculogenesis, steroidogenesis, luteinization, cell survival, ovulation, and oocyte maturation and quality characterize this disorder. Consequently, although the precise mechanisms remain unclear, FHD likely causes or contributes to the inhibition of ovulatory-size follicle growth, reduction in estradiol production, promotion of premature cumulus expansion and luteinization, and diminution of ovulation rate in response to hCG, as we observed during ovarian stimulation of the SORH model with Ex-cpFSH ( Karl et al , 2021 ; Clark et al , 2022a , b ). Our observations support the hypothesis that Ex-cpFSH doses during ovarian stimulation dysregulate cumulus function and oocyte maturation.…”

“…This was accomplished by manually interrogating our published whole transcriptome data set to determine whether any of the previously identified Ex-cpFSH-induced cumulus cell differentially expressed genes (DEGs) ( Clark et al , 2022b ) are altered in all ovulatory-size follicles independent of individual follicular phenotypic differences, and whether these DEGs have known roles in cumulus cell function and oocyte maturation. We reasoned that cpFSH-induced overexpression of cumulus genes in all ovulatory-size follicles could explain the premature cumulus expansion observed in nearly all ovulatory-size follicles developing in response to Ex-cpFSH doses in our studies ( Clark et al , 2022a , b ). Second, we tested whether the Ex-cpFSH-induced premature cumulus expansion observed in our studies ( Clark et al , 2022a , b ) is accompanied by altered oocyte nuclear maturation before (premature) or after an ovulatory hCG stimulus, or during IVM.…”

“…We reasoned that cpFSH-induced overexpression of cumulus genes in all ovulatory-size follicles could explain the premature cumulus expansion observed in nearly all ovulatory-size follicles developing in response to Ex-cpFSH doses in our studies ( Clark et al , 2022a , b ). Second, we tested whether the Ex-cpFSH-induced premature cumulus expansion observed in our studies ( Clark et al , 2022a , b ) is accompanied by altered oocyte nuclear maturation before (premature) or after an ovulatory hCG stimulus, or during IVM.…”

“…Using the SORH model, we also established that ovarian stimulation with the Ex-cpFSH doses results in premature cumulus cell expansion and luteinization (as measured by low intrafollicular estradiol but high progesterone and oxytocin concentrations) prior to an ovulatory hCG stimulus in a large proportion of the ovulatory-size follicles ( Clark et al , 2022a ). Furthermore, based on whole transcriptome analysis data, we concluded that Ex-cpFSH doses during ovarian stimulation cause follicular hyperstimulation dysgenesis (FHD) in all ovulatory-size follicles ( Clark et al , 2022b ).…”

Dose-response functional and transcriptomic effects of follicle-stimulating hormone onex vivomouse folliculogenesis

“…Gonadotropin-dependent folliculogenesis, a crucial step for supporting the eventual follicle maturation, ovulation, luteinization, and reproductive cycles and fertility, is well conserved across many mammalian species. Both insufficient and excessive FSH have been linked to poor female reproductive outcomes (1,2,(21)(22)(23)(24)(25)29,30). Here we performed a dose-response functional and transcriptomic analysis of FSH using an ex vivo folliculogenesis and oogenesis system.…”