Adenosine 5'-monophosphate-activated protein kinase regulates progesterone secretion in rat granulosa cells

The AMP-activated protein kinase (AMPK) is a major regulator of energy metabolism involved in fatty acid and cholesterol synthesis. In the ovary, cholesterol plays a key role in steroid production. We report the presence of AMPK in rat ovaries, and we have investigated its role in granulosa cells. We show using RT-PCR and Western blot that the mRNAs for the alpha1/2 and beta1/2 subunits and the proteins are found in the ovaries. Immunohistochemistry localized the alpha1 AMPK subunit in granulosa cells, corpus luteum, and oocyte and less abundantly in theca cells. Treatment with 1 mm 5-amino-imidazole-4-carboxyamide-1-beta-D-ribofuranoside (AICAR), an activator of AMPK, increased dose-dependent and time-dependent phosphorylation of AMPKalpha1 on Thr172 in primary granulosa cells. Simultaneously, phosphorylation of acetyl-coenzyme A carboxylase at Ser79 was also increased. AICAR treatment for 48 h halved progesterone secretion, 3beta-HSD protein and mRNA levels, and phosphorylation of both basal MAPK ERK1/2 and p38 and in response to IGF-I and/or FSH in granulosa cells. AICAR treatment (1 mM) had no detectable effect on basal and FSH- and/or IGF-I-induced estradiol production and on granulosa cell proliferation or viability. Adenovirus-mediated expression of dominant negative AMPK totally abolished the effects of AICAR on progesterone secretion, 3beta-HSD protein production, and MAPK ERK1/2 and p38 phosphorylation. Moreover, we showed using specific in- hibitors of ERK1/2 and p38 MAPK that the MAPK ERK1/2 and not p38 is involved in progesterone secretion and 3beta-HSD expression, strongly suggesting that the activation of AMPK in response to AICAR reduces progesterone production through the MAPK ERK1/2 signaling pathway in rat granulosa cells.