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BOR - Papers in Press, published online ahead of print May 23, 2007.
Biol Reprod 2007, 10.1095/biolreprod.106.058867
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Submitted November 9, 2006
Returned for revision December 23, 2006
Accepted May 18, 2007

Ovary


Effect of Insulin-Like Growth Factor-Binding Protein 7 on Steroidogenesis in Granulosa Cells Derived from Equine Chorionic Gonadotropin-Primed Immature Rat Ovaries

Kazuhiro Tamura *, Mayumi Matsushita , Aiju Endo , Masahiko Kutsukake , and Hiroshi Kogo

* To whom correspondence should be addressed. E-mail: hiro{at}ps.toyaku.ac.jp.

Abstract
Insulin-like growth factor (IGF) binding protein 7 (IGFBP7) is a secreted protein that regulates cellular proliferation, adhesion, and angiogenesis and has low affinity for IGF compared to IGFBP16. We sought to determine whether IGFBP7 is present in follicular fluid and to elucidate whether IGFBP7 participates in the steroidogenesis of rat mature follicles. Follicular fluid and granulosa cells (GCs) were collected from immature rats 2 days after their treatment with equine chorionic gonadotropin (eCG). IGFBP7 protein was detected in the follicular fluid and the conditioned medium of cultured ovarian granulosa cells by immunoblot analysis. When subconfluent GCs were cultured and treated with FSH and activin, co-incubation with FSH and activin markedly increased GC expression of Cyp19a1 (aromatase) mRNA and 17{beta}-estradiol secretion. The addition of recombinant murine IGFBP7 to these cultures decreased in the activin-enhanced FSH-stimulated Cyp19a1 mRNA levels in the cells and suppressed the 17{beta}-estradiol levels in the culture medium. Treatment of GCs with Igfbp7-specific siRNA, which knocked down Igfbp7 expression, increased the FSH-stimulated levels of Cyp19a1 but not Cyp11a1 expression. Basal and FSH-stimulated 17{beta}-estradiol secretion into the culture medium was also enhanced by Igfbp7 siRNA. These results suggest that IGFBP7 suppresses estrogen production in GCs. These observations support the notion that this protein, which is secreted into the follicular fluid, may serve as an intra-ovarian factor that negatively regulates GC differentiation.

Key words: Ovary • Estradiol • Follicle • Granulosa cells • Insulin


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