Metformin decreases IGF1-induced cell proliferation and protein synthesis through AMP-activated protein kinase in cultured bovine granulosa cells

Abstract

Although its mechanism of action is still unclear, metformin is an anti-diabetic drug effective to restore cyclicity and spontaneous ovulation in women with polycystic ovary syndrome. It may also reduce the risk of cancer. We have recently shown that metformin treatment decreases steroidogenesis through AMP-activated kinase (AMPK) in granulosa cells of various species. Here, we investigated the effects and the molecular mechanisms of metformin in IGF1-induced proliferation and protein synthesis in cultured bovine granulosa cells. Treatment with metformin (10 mM) for 24 h reduced cell proliferation and the levels of cyclin D2 and E, and increased the associations cyclin D2/p21 and cyclin D2/p27 without affecting cell viability in response to IGF1 (10 K8 M). It also decreased IGF1-induced protein synthesis and phosphorylation of P70S6 kinase and ribosomal S6 protein. Interestingly, metformin treatment for 1 h decreased MAPK3/1 (ERK1/2) and P90RSK phosphorylation without affecting AKT phosphorylation in response to IGF1. Adenovirusmediated expression of dominant-negative AMPK totally abolished the effects of metformin on cell proliferation and phosphorylation of P70S6K in response to IGF1. It also eliminated the inhibitory effects of metformin on MAPK3/1 and P90RSK phosphorylation. Taken together, our results strongly suggest that metformin reduces cell growth, protein synthesis, MAPK3/1, and P90RSK phosphorylation in response to IGF1 through an AMPK-dependent mechanism in cultured bovine granulosa cells.

Involvement of adipokines, AMPK, PI3K and the PPAR signaling pathways in ovarian follicle development and cancer

“…In cultured bovine granulosa cells, metformin inhibits proliferation and protein synthesis in response to IGF-1 through an AMPK-dependent mechanism as indicated in the Fig. 2A (Tosca et al, 2010). Furthermore, in primary rat granulosa cells, FSH promotes granulosa cell proliferation by increasing cyclin D2 mRNA expression and by reducing p27 kip expression by inhibiting AMPK activation through an Akt-dependent pathway (Kayampilly and Menon, 2009).…”

Metformin in Cancer Therapy: A New Perspective for an Old Antidiabetic Drug?

“…Metformin decreases insulinemia and could, therefore, indirectly inhibit insulin-promoting effects. By contrast, metformin does not seem to affect the serum concentrations of insulin-like growth factor (IGF-1), a growth promoting tumor, and prevents the proliferative effect of IGF-1 through AMPK in bovine granulosa cells (16). In addition, hyperinsulinemia decreases the amount of IGF binding protein available (IGFBP), resulting in the increase of active (free) IGF1.…”

The impact of adipose tissue-derived factors on the hypothalamic-pituitary-gonadal (HPG) axis

“…Indeed, metformin, a potent insulin sensitizer, suppresses IGF1-induced cell proliferation and protein synthesis through AMP-activated protein kinase in cultured bovine granulosa cells. 65 It should be borne in mind that metformin is now the first-line treatment for obesity-induced polycystic ovaries. High levels of saturated free fatty acids, such as palmitic acid and stearic acid, suppress granulosa cell survival due to increased apoptosis, as evidenced by DNA ladder formation and annexin V-EGFP/propidium iodide staining.…”