IGF-1 receptor signaling pathways and effects of AMPK activation on IGF-1-induced progesterone secretion in hen granulosa cells

IGF-1 plays a key role in the proliferation and differentiation of granulosa cells. However, the molecular mechanism of IGF-1 action in avian granulosa cells during follicle maturation is unclear. Here, we first studied IGF-1 receptor (IGF-IR) expression, IGF-1-induced progesterone production and some IGF-IR signaling pathways in granulosa cells from different follicles. IGF-IR (mRNA and protein) was higher in fresh or cultured granulosa cells from the largest follicles (171 or 172) than in those from smaller follicles (173 or 174). In vitro, IGF-1 treatment (110(-8) M, 36 h) increased progesterone secretion by four-fold in mixed F3 and F4 (F3/4) granulosa cells and by 1.5-fold in F1 granulosa cells. IGF- 1 (10(-8) M, 30 min)-induced increases in tyrosine phosphorylation of IGF-IR beta subunit and phosphorylation of ERK were higher in 171 than in F3/4 granulosa cells. Interestingly, IGF-1 stimulation (10-8 M, 10 min) decreased the level of AMPK Thr172 phosphorylation in F1 and 173/4 granulosa cells. We have recently showed that AMPK (AMP-activated protein kinase) is a protein kinase involved in the steroidogenesis in chicken granulosa cells. We then studied the effects of AMPK activation by AICAR (5-aminoimidazole-4-caiboxamide ribonucleoside), an activator of AMPK, on IGF-1-induced progesterone secretion by 173/4 and F1 granulosa cells. AICAR treatment (1 mM, 36 h) increased IGF-1-induced progesterone, secretion, StAR protein levels and decreased ERK phosphorylation in F1 granulosa cells. Opposite data were observed in 173/4 granulosa cells. Adenovirus-mediated expression of dominant negative AMPK totally reversed the effects of AICAR on IGF-1-induced progesterone secretion, StAR protein production and ERK phosphorylation in both 173/4 and F1 granulosa cells. Thus, a variation of energy metabolism through AMPK activation could modulate differently IGF-1-induced progesterone production in F1 and 173/4 granulosa cells. (c) 2007 Elsevier Inc. All rights reserved.