FSH Glycoforms and Ovarian Signaling Pathways

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PROJECT SUMMARY The long-term goal of this project is to study age-dependent mechanisms of follicle-stimulating hormone (FSH) actions in the ovary. FSH is a pituitary glycoprotein consisting of an α-and a β-subunit. Both the subunits are glycosylated with two N-linked sugar chains on each subunit. Glycosylation of FSH is estrous/menstrual cycle- and age-specific. Macro-heterogeneity results in FSH variants consisting of 2 sugar chains on the α subunit but either one or none on the β. These variants are known as hypo-glycosylated FSH glycoforms, FSH21, and FSH18, in contrast to the fully glycosylated FSH24. Interestingly, the abundance of hypo- and fully glycosylated FSH is age-dependent, with high levels of FSH21/18 glycoforms predominant in young women and FSH24 predominant in peri/post-menopausal women. This shift suggests a role of FSH24 in ovarian aging. In vitro studies and pharmacological rescue of Fshb null mice with recombinant hypo- and fully glycosylated FSH glycoforms indicate differences in regulation of known FSH-responsive ovarian genes and proteins downstream of FSH receptor (FSHR) signaling. However, the mechanisms by which these FSH glycoforms regulate ovarian signaling pathways in vivo are unknown. The central hypothesis is that age-specific FSH glycoforms act via FSHRs but regulate distinct downstream signaling cascades to elicit different gene/protein expression signatures in the ovary. This hypothesis will be tested using genetically engineered novel mouse models. In Aim 1, we will perform a trans-omics analysis by overlaying the gene, protein and phosphoprotein expression signatures in ovaries of Fshb null mice expressing individual FSH glycoforms to identify signaling networks regulated by each FSH glycoform. In Aim 2, we will test the hypothesis that the FSH glycoform specificity in FSHR-mediated signaling is achieved by recruitment of distinct protein complexes to activate different downstream gene/protein networks. Fshb null mice expressing individual FSH glycoform and His - tagged FSHRs in granulosa cells will be used. Pull-down experiments with an His tag-specific antibody followed by mass spectrometry analysis of ovarian proteins will allow us to identify the FSH glycoform-specific FSH receptor and receptor co-factor protein complexes in each case. In Aim 3, we will evaluate the direct effects of recombinant FSH glycoforms in secondary follicles obtained from reproductively young and old mice. Gene and protein expression profiling will be performed and how FSH glycoforms impact follicle growth and gamete quality in vitro will be determined. Successful completion of the proposed studies will advance our understanding of the mechanisms by which FSH glycoforms regulate selective recruitment of distinct FSHR - co-factor partner complexes to achieve FSHR-mediated signal transduction pathways in vivo in ovaries and provide a direct read out of FSH glycoform actions during in vitro folliculogenesis and oogenesis. Our mechanistic studies serve as the foundation for novel therapeutic opportunities to preserve ovarian function and will enable improved design of ovarian induction protocols, in alignment with the NICHD mission.