PARENT SESSION

(T521) POSSIBLE ROLE OF IGF BINDING PROTEIN-7 ON STEROIDOGENESIS IN GRANULOSA CELLS DERIVED FROM PREOVULATORY FOLLICLE IN RATS.

Tamura, Kazuhiro¹, Matsushita, Mayumi¹, Kutsukake, Masahiko¹, Kogo, Hiroshi¹, ¹ Tokyo University of Pharmacy and Life Science, Tokyo, Japan

ABSTRACT- IGF binding protein-7 (mac25/angiomodulin/IGFBP-rP1), which has a highly conserved region of follistatin (the activin-binding protein), has been shown to be present in granulosa cells of large antral follicles in porcine. Activins are implicated as autocrine and paracrine factors in follicular functions. Granulosa cell-derived follistatin is essential for the development of follicles and the induction of ovulation. This study was, therefore, designed to detect endogenous IGF binding protein-7 (IGFBP-7) in the follicle and examine the interaction between IGFBP-7 and activin in steroidogenesis of preovulatory follicles in rats. Endogenous IGFBP-7 protein was detected in follicular fluid by immunoblot analysis, and IGFBP-7 mRNA expression was found in cultured granulosa cells using RT-PCR analysis. Subconfluency ovarian granulosa cells harvested from immature rats 2 days after treatment with equine chorionic gonadotropin (eCG) were cultured for 24 h in chemically defined serum-free media in the presence of FSH and/or activin. Co-incubation of FSH and activin A increased the expression of CYP19 (aromatase) mRNA and 17beta-estradiol levels in the culture media, compared to those in the cells treated with FSH or activin A alone. Inclusion of recombinant murine IGFBP-7 in the culture medium caused a dose-dependent decrease in the levels of FSH and activin A-enhanced CYP19 mRNA as well as a decrease in 17beta-estradiol levels between 3 and 30 ng/mL. IGFBP-7 did not affect the mRNA expression of betaA/ alpha-subunits of activin, its receptor type I or II (Act RI/Act RII), or follistatin in granulosa cells. These results suggest that IGFBP-7 suppresses estrogen production in granulosa cells, and lead to the view that this secreted protein may be one of the intra-ovarian regulators that are associated with the terminal differentiation of granulosa cells. Thus, IGFBP-7 appears to behave similar to follistatin in inhibiting the actions of activin during follicular development.

KEY WORDS: IGFBP-7, granulosa cells, activin, IGFBP