Insulin-like growth factor I enhancement of steroidogenesis by bovine granulosa cells and thecal cells: dependence on de novo cholesterol synthesis.
Studies were conducted to determine the importance of de novo cholesterol synthesis and cholesterol side-chain cleavage enzyme in the action of IGF-I in bovine granulosa and thecal cells. Granulosa and thecal cells from bovine follicles were cultured for 2 days in 10% fetal calf serum and then treated with luteinizing hormone (100 ng/ml) and IGF-I (0 or 100 ng/ml) for an additional 2 days in serum-free medium. During the last 24 h of treatment, cells were concomitantly treated with simvastatin (0, 0.5 or 5 micrograms/ml) or 25-hydroxycholesterol (0 or 10 micrograms/ml). Simvastatin, a potent inhibitor of the key enzyme controlling de novo cholesterol synthesis, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, completely inhibited (P < 0.05) progesterone production by granulosa cells and progesterone and androstenedione production by thecal cells. Simvastatin also inhibited (P < 0.05) granulosa cell and thecal cell proliferation. Concomitant treatment with mevalonate, an immediate product of HMG-CoA reductase, attenuated the inhibitory effect of simvastatin on progesterone and androstenedione production by thecal cells and blocked the inhibitory effect of simvastatin on cell proliferation. The addition of 25-hydroxycholesterol, a substrate for cholesterol side-chain cleavage enzyme, had no effect (P > 0.10) on IGF-I-stimulated progesterone or androstenedione production by thecal cells and actually inhibited (P < 0.05) IGF-I-stimulated progesterone production by granulosa cells. These results provide indirect evidence indicating that stimulation of HMG-CoA reductase is an important locus of IGF-I action in bovine granulosa and thecal cells, whereas IGF-I has little or no effect on side-chain cleavage enzyme activity in these same cell types under the culture conditions employed.
Spicer
L J
LJ
Department of Animal Science, Oklahoma State University, Stillwater 74078, USA.
Hamilton
T D
TD
Keefer
B E
BE
D000735:Androstenedione / Q000096:biosynthesis*; D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D002784:Cholesterol / Q000096:biosynthesis*; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000378:metabolism; D005260:Female; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism; D006888:Hydroxycholesterols / Q000494:pharmacology; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008148:Lovastatin / Q000031:analogs & derivatives / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000494:pharmacology; D008798:Mevalonic Acid / Q000494:pharmacology; D010053:Ovary / Q000187:drug effects / Q000378:metabolism*; D011374:Progesterone / Q000096:biosynthesis*; D019821:Simvastatin; D013268:Stimulation, Chemical; D013799:Theca Cells / Q000187:drug effects / Q000378:metabolism
D000924:Anticholesteremic Agents; D006888:Hydroxycholesterols; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D000735:Androstenedione; D011374:Progesterone; D007334:Insulin-Like Growth Factor I; C007997:25-hydroxycholesterol; D007986:Luteinizing Hormone; D002784:Cholesterol; D008148:Lovastatin; D019821:Simvastatin; D002786:Cholesterol Side-Chain Cleavage Enzyme; D008798:Mevalonic Acid