IGF1 induces up-regulation of steroidogenic and apoptotic regulatory genes via activation of phosphatidylinositol-dependent kinase/AKT in bovine granulosa cells
2010
IGF1, a potent stimulator of cellular proliferation, differentiation and development, regulates granulosa cell steroidogenesis and apoptosis during follicular development. Depending upon species and stage of follicular growth, IGF1 acts on granulosa cell steroidogenesis either alone or together with FSH. We examined the mechanism of action of IGF1 in bovine granulosa cells in serum-free culture without insulin to determine its potential role in the regulation of steroidogenic and apoptotic regulatory gene expression and to investigate the interaction of FSH with IGF1 on this mechanism. Bovine granulosa cells treated with IGF1 demonstrated a significant increase in 17β-oestradiol (OE₂) production, cell number and in mRNA expression of CYP11A1, HSD3B1, CYP19A1, BAX, type 1 IGF receptor (IGF1R) and FSHR, while FSH alone had no significant effects. IGF1 or FSH alone or both together had no effect on BCL2 expression. IGF1 with FSH resulted in a synergistic increase in granulosa cell number and in mRNA expression of CYP19A1 and IGF1R without altering OE₂ production. IGF1 stimulated the phosphoinositide 3'-OH kinase (PI3K) but not the MAPK pathway in granulosa cells, as evidenced by increased phosphorylation of AKT but not extracellular-regulated kinase 1/2. Addition of the PI3K pathway inhibitor LY294002 (but not the MAPK pathway inhibitor PD98059) abrogated the increased expression of genes induced by IGF1. IGF1 therefore up-regulates the steroidogenic and apoptotic regulatory genes via activation of PI3K/AKT in bovine granulosa cells. The synergistic action of IGF1 with FSH is of likely key importance for the development of small antral follicles before selection; subsequently, other factors such as LH may also become necessary for continued cell survival.
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