Insulin-like growth factor-I-mediated amplification of follicle-stimulating hormone-supported progesterone accumulation by cultured rat granulosa cells: enhancement of steroidogenic enzyme activity and expression

• Published in: Biology of reproduction 1997-04, Vol.56 (4), p.946-953
• Main Authors: DEMOURA, M. D, CHOI, D, ADASHI, E. Y, PAYNE, D. W
• Format: Article
• Language: English
• Subjects: 3-Hydroxysteroid Dehydrogenases - biosynthesis; 3-Hydroxysteroid Dehydrogenases - metabolism; Animals; Biological and medical sciences; Biotransformation; Cells, Cultured; Cholesterol Side-Chain Cleavage Enzyme - biosynthesis; Cholesterol Side-Chain Cleavage Enzyme - metabolism; Dose-Response Relationship, Drug; Drug Synergism; Female; Follicle Stimulating Hormone - pharmacology; Fundamental and applied biological sciences. Psychology; Granulosa Cells - drug effects; Granulosa Cells - metabolism; Hormone metabolism and regulation; Insulin-Like Growth Factor I - pharmacology; Kinetics; Mammalian female genital system; Pregnenolone - metabolism; Progesterone - metabolism; Rats; Rats, Sprague-Dawley; Transcription, Genetic - drug effects; Vertebrates: reproduction
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1095/biolreprod56.4.946

A body of information now supports the existence of an ovarian intrafollicular insulin-like growth factor (IGF)-I system concerned with the amplification of FSH action at the level of the rat granulosa cell. In this study we examined the ability of IGF-I to modulate the basal and FSH-supported activity and expression of key steroidogenic enzymes concerned with progesterone generation and metabolism in cultured granulosa cells from immature rats. The provision of IGF-I stimulated FSH-supported (20 ng/ml) accumulation of progesterone in a dose-dependent manner, reaching a plateau at an IGF-I dose of 50 ng/ml. This dose of IGF-I substantially enhanced FSH action over a broad range of FSH concentrations, reaching a maximum at an FSH dose of 20 ng/ml. Pulse labeling of FSH-pretreated cells with [3H]pregnenolone revealed relatively rapid (< 5 h) transformation to [3H]progesterone and other distal products that was accelerated by the concurrent addition of IGF-I. These changes in progesterone metabolism were associated with IGF-I-mediated enhancement of the activities and expression of key steroidogenic enzymes. Specifically, treatment with IGF-I produced significant augmentation of the FSH-stimulated activities of cholesterol side-chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase/ isomerase (3 beta-HSD) enzymes (2.4- and 1.8-fold, respectively). Similarly, P450scc and type I 3 beta-HSD transcripts were elevated by FSH in a dose-dependent manner, the concurrent addition of IGF-I further increasing expression (up to an additional 3-fold) in the range of 1-5 ng/ml (but not at the maximally stimulating dose of 20 ng/ml FSH). The addition of IGF-I also increased basal levels of type I 3 beta-HSD transcripts (3.8-fold). IGF-I enhanced FSH-stimulated 20 alpha-HSD activity and transcripts (2.3-fold and 1.8-fold, respectively) and increased the basal levels of 20 alpha-HSD transcripts (3-fold). Basal levels of 5 alpha-reductase were slightly elevated (1.3-fold) by IGF-I, but the FSH-attenuated activity was unchanged. Taken together, these findings suggest that IGF-I enhances the FSH-supported accumulation of progesterone in cultured granulosa cells through up-regulation of the expression and activity of key enzymes in the steroidogenic pathway. The acceleration of progesterone accumulation reflects a newly established steady state, favoring the activities of progesterone-forming over progesterone-metabolizing enzymes.