Role and regulation of X-linked inhibitor of apoptosis protein expression during development of the rat ovarian follicle in vitro

Follicle stimulating hormone (FSH) is an important survival factor in the ovarian follicular development. Inhibitor of apoptosis proteins (IAPs) is a family of intracellular anti-apoptosic proteins. X-linked IAP (XIAP) has been shown to be involved in multiple biological activities (e.g. inhibition of caspase activities, promotion of ubiquitin-proteasome-mediated protein degradation, regulation of cell signaling pathways). The present thesis research project examines: (1) the role and gonadotropic regulation of XIAP expression in rat granulosa cells during ovarian follicular development and atresia; (2) the possible involvement of intra-ovarian factors such as transforming growth factor alpha (TGFalpha) in the FSH-induced XIAP expression and follicular development; and (3) the signal pathways involved in the gonadotropic up-regulation of XIAP during follicular development in vitro. A follicle culture system coupled to an adenoviral gene manipulation procedure has been established. FSH significantly increased follicular growth as evident by increases in follicular size, cell number and DNA contents in vitro. While cultured pre-antral or early-antral follicles showed a low XIAP content and evidence of apoptosis in the absence of FSH, gonadotropin addition increased XIAP content and suppressed apoptosis. At low FSH concentration, adenoviral XIAP sense cDNA expression increased follicular cell XIAP and DNA contents, reduced apoptosis, and enhanced follicular growth, while XIAP antisense elicited opposite responses. FSH-induced XIAP up-regulation appeared mediated, in part, by the secretion and action of follicular TGFalpha. In cultured rat follicles, FSH-stimulated estradiol production, TGFalpha secretion, XIAP expression and follicular growth were suppressed by intra-follicular injection of a neutralizing anti-TGFalpha antibody or addition of the estradiol antagonist ICI 182780 to the culture media. These results support my hypothesis that the FSH induces follicular growth by stimulating granulosa cell proliferation via theca TGFalpha secretion and action in response to increased granulosa cell estradiol synthesis. Since the promoter region of XIAP gene has nuclear kappa B (NFkappaB) binding site, it is possible that the transcription of XIAP is mediated via NFkappaB activation. FSH increased rat granulosa cell XIAP mRNA abundance and protein content. While the gonadotropin induced granulosa cell NFkappaB translocation from cytoplasm to nucleus and increased NFkappaB-DNA binding activity, pretreatment with an NFkappaB translocation inhibitor suppressed FSH-stimulated XIAP expression. (Abstract shortened by UMI.