Visfatin is expressed in human granulosa cells: regulation by metformin through AMPK/SIRT1 pathways and its role in steroidogenesis.

Visfatin is a cytokine hormone and an enzyme involved in metabolic (obesity, type II diabetes) and immune disorders. Some data suggest a role of visfatin in ovarian function. Here, we identified visfatin in human follicles and investigated the molecular mechanisms involved in the regulation of its expression in response to insulin sensitizers, metformin (MetF) and rosiglitazone, in primary human granulosa cells (hGCs) and in a human ovarian granulosa-like tumour cell line (KGN). We also studied the effects of human recombinant visfatin (RhVisf) on steroid production and on the activation of various signalling pathways. By RT-PCR, immunoblotting and immunohistochemistry, we showed that visfatin is expressed not only in hGCs and KGN cells, but also in human cumulus cells and oocytes. In hGCs and KGN cells, MetF increased visfatin mRNA in a dose-dependent manner (0.1, 1 and 10 mM), and rosiglitazone increased visfatin mRNA expression (only at 10 µM) after treatments for 24 h, whereas both reduced it after 48 h of incubation. This regulation was confirmed at the protein level for the MetF treatment only. Using the compound C and Aicar, inhibitor and activator of AMP-activated protein kinase (AMPK), respectively, and Sirtinol, an inhibitor of sirtuin-1 (SIRT1), we observed that these MetF effects on visfatin expression were mediated through the AMPK/SIRT1 signalling pathways. RhVisf (10 ng/ml) significantly increased insulin-like growth factor-1 (IGF-1) (10 nM)- but not FSH (10 nM)-induced secretion of progesterone and estradiol as determined by radioimmunoassay and IGF-1-induced thymidine incorporation in hGCs and KGN cells. Finally, rhVisf rapidly activates the mitogen-activated protein kinase pathway via ERK1/2, P38 and Akt phosphorylation under basal conditions in primary hGC cells. In conclusion, visfatin is present in ovarian human follicles, and in hGCs and KGN cells, visfatin increases IGF-1-induced steroidogenesis and cell proliferation and MetF regulates visfatin expression through the AMPK/SIRT1 signalling pathway.