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The effects of insulin on 3 beta-hydroxysteroid dehydrogenase expression in human luteinized granulosa cells
1Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center at Dallas 75235, USA.
Objective:
We determined the relative effects of insulin and FSH on progesterone accumulation as well as activity, protein content, and mRNA expression of 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) in human luteinized granulosa cells.
Methods:
Luteinized granulosa cells obtained from women undergoing in vitro fertilization were plated and grown to near confluence and treated with FSH, insulin, or a combination of insulin and FSH. Progesterone production as well as enzyme activity, protein content, and mRNA expression for 3 beta HSD were evaluated.
Results:
Progesterone production was not affected by insulin alone but increased threefold in the presence of FSH (50 ng/microL) alone. The presence of FSH plus insulin (100 nmol/L) caused a significant increase in progesterone accumulation greater than that of FSH alone. The already high basal levels of 3 beta HSD activity were unaffected by insulin alone but increased 1.7-fold in the presence of FSH. The combination of FSH (50 ng/mL) and insulin (100 nmol/L) increased activity 1.3-fold over FSH alone (P < .02). Insulin (greater than 100 nmol/L) alone increased 3 beta HSD protein content as measured by Western analysis 1.8-2-fold over basal levels, whereas FSH alone increased protein content 2.8-fold, and was further augmented by the addition of insulin in a dose-related fashion up to 3.5-fold over basal levels. Insulin increased 3 beta HSD mRNA twofold over basal levels; FSH alone increased mRNA expression of 3 beta HSD 3.2-fold. In the presence of insulin plus FSH, 3 beta HSD mRNA expression increased 7.6-fold over basal levels. For comparison, insulin also stimulated cytochrome P450 aromatase activity, P450 aromatase protein, and mRNA but to a greater degree than that seen for 3 beta HSD.
Conclusion:
Insulin is a regulator of both 3 beta HSD and aromatase expression in human granulosa cells. Elevated insulin levels could therefore affect steroid production in human granulosa cells and presumably alter the menstrual cycle and fertility.