The intrafollicular IGF-l system amplifies gonadotropin hormone action in granulosa cells. IGF-I alone or in combination with FSH can induce gonadotropin receptors, steroidogenic enzymes and promote follicular survival. The important interptay among IGF-I and FSH is underscored by the striking similarity of ovaries in IGF-I knockout, FSH knockout and FSH receptor knockout mice. The follicles in these mice are arrested in the early antral stage ol development. Whereas the mechanism of action of FSH is well known to involve the cAMP/protein kinase A signaling pathway, almost nothing is known about the intracellular actions of IGF-I in the ovary. Furthermore, recent studies by others and our preliminary data suggest that some of the signaling pathways utilized by IGF-I and FSH converge. The proposed studies are designed to test the overall hypothesis that IGF-I induced P1-3-kinase signaling pathway is required for granulosa cell survival and amplification of FSH-induced granulosa cell differentiation. The specific questions to be answered in this proposal are:
Aim 1) Are the signaling events initiated by IGF-I amplified in response to FSH? Hypothesis: The IGF-I dependent P1-3-kinase signaling pathway in granulosa cells is augmented by FSH.
Aim 2) Are the survival effects of IGF-I and FSH mediated by parallel or converging intracellular signaling pathways? Hypothesis I: The survival effects of IGF-I and FSH are mediated by P1-3-kinase/Akt mediated phosphorylation of Bad. Hypothesis II: IGF-I and FSH elevate the cellular ratio of antiapoptotic (e.g., Bc12, Bcl-Xlong, Mci-I) to pro -apoptotic proteins (e.g., Bad, Bax, Bok) and inhibit caspase activity.
Aim 3) Is FSH directed granulosa cell differentiation mediated via IGF-I dependent signaling systems? Hypothesis: IGF-I stimulated P1-3-kinase signaling events amplifies FSH directed expression of differentiation, whereas ERK signaling represses djfferentiation. We will employ specific chemical inhibitors and adenovirus vectors that express dominant negative or active signaling molecules to dissect the IGF-I and FSH directed signaling pathways that are responsible for granulosa cell survival or granulosa cell differentiation. Further characterization of the IGF-I and FSH signaling events and their interactions are likely to provide new insights into how multiple genes are coordinately regulated by trophic factors during follicle development. Our studies are expected to translate into more effective treatments for controlling follicle selection and development, ovulation and fertility. This new insight may uncover mechanistic defects that underlay disorders of folliculogenesis, premature ovarian failure and disorders such as polycystic ovarian syndrome.
