Stimulatory effect of insulin on 5alpha-reductase type 1 (SRD5A1) expression through an Akt-dependent pathway in ovarian granulosa cells

Endocrinology. 2010 Oct;151(10):5030-7. doi: 10.1210/en.2010-0444. Epub 2010 Sep 1.

Abstract

Elevated levels of 5α-reduced androgens have been shown to be associated with hyperandrogenism and hyperinsulinemia, the leading causes of ovulatory dysfunction in women. 5α-Dihydrotestosterone reduces ovarian granulosa cell proliferation by inhibiting FSH-mediated mitogenic signaling pathways. The present study examined the effect of insulin on 5α-reductase, the enzyme that catalyses the conversion of androgens to their 5α-derivatives. Granulosa cells isolated from immature rat ovaries were cultured in serum-free, phenol red-free DMEM-F12 media and treated with different doses of insulin (0, 0.1, 1.0, and 10.0 μg/ml) for different time intervals up to 12 h. The expression of 5α-reductase type 1 mRNA, the predominant isoform found in granulosa cells, showed a significant (P<0.05) increase in response to the insulin treatment up to 12 h compared with control. The catalytic activity of 5α-reductase enzyme was also stimulated in a dose-depended manner (P<0.05). Inhibiting the Akt-dependent signaling pathway abolished the insulin-mediated increase in 5α-reductase mRNA expression, whereas inhibition of the ERK-dependent pathway had no effect. The dose-dependent increase in 5α-reductase mRNA expression as well as catalytic activity seen in response to insulin treatment was also demonstrated in the human granulosa cell line (KGN). In addition to increased mRNA expression, a dose-dependent increase in 5α-reductase protein expression in response to insulin was also seen in KGN cells, which corroborated well with that of mRNA expression. These results suggest that elevated levels of 5α-reduced androgens seen in hyperinsulinemic conditions might be explained on the basis of a stimulatory effect of insulin on 5α-reductase in granulosa cells. The elevated levels of these metabolites, in turn, might adversely affect growth and proliferation of granulosa cells, thereby impairing follicle growth and ovulation.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • 3-Oxo-5-alpha-Steroid 4-Dehydrogenase / genetics*
  • 3-Oxo-5-alpha-Steroid 4-Dehydrogenase / metabolism
  • Animals
  • Cells, Cultured
  • Dose-Response Relationship, Drug
  • Enzyme Activation / drug effects
  • Female
  • Gene Expression Regulation, Enzymologic / drug effects
  • Granulosa Cells / drug effects*
  • Granulosa Cells / enzymology
  • Granulosa Cells / metabolism
  • Humans
  • Insulin / pharmacology*
  • Membrane Proteins / genetics*
  • Membrane Proteins / metabolism
  • Oncogene Protein v-akt / metabolism
  • Oncogene Protein v-akt / physiology*
  • Ovary / drug effects
  • Ovary / metabolism
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Signal Transduction / drug effects
  • Signal Transduction / genetics
  • Up-Regulation / drug effects

Substances

  • Insulin
  • Membrane Proteins
  • RNA, Messenger
  • 3-Oxo-5-alpha-Steroid 4-Dehydrogenase
  • Srd5a1 protein, rat
  • Oncogene Protein v-akt