Glycogen Synthase Kinase 3-β (GSK3-β) is a negative regulator for cardiac hypertrophy. This kinase controls protein synthesis mainly via activation of both the translation initiation factor eIF2Be and the transcription factor NFAT. Testosterone induces cardiomyocyte hypertrophy, but if GSK3-β participates in this event is unknown. Here we have studied whether the inhibition of GSK3-β is involved in testosterone-induced cardiac hypertrophy.Testosterone (100 nM) inhibited GSK3-β (phosphorylation increase at Ser9) and activated the factor eIF2Be (phosphorylation decrease at Ser539). Moreover, pharmacological inhibition of GSK3-β by 1-azakenpaullone (10 μM) increases the hormone-induced eIF2Be activation.GSK3-β inhibition can be mediated by PI3K/Akt or MEK/ERK1/2 pathways. PI3K/Akt inhibitors LY-292002 (1 μM) and Akt-inhibitor-VIII (10 μM) blocked the testosterone-induced GSK3-β phophorylation, whereas ERK1/2 inhibitor (PD98059 50 μM) had not effect. NFAT is well characterized downstream target for GSK3-β. Testosterone increased the NFAT-luc activity and this was blocked by NFAT inhibitors CsA (1 μM) and FK506 (1 μM). Moreover, GSK3-β inhibition increased NFAT activity.In order to investigate the GSK3-β/NFAT contribution to testosterone-induced hypertrophy, we evaluate the expression of skeletal α-actin (SKA). Testosterone and 1-azakenpaullone increased SKA expression while NFAT inhibition blocked the testosterone-induced SKA increases.These results suggest that testosterone-induced cardiomyocyte hypertrophy involves inhibition of GSK3-β through PI3K/Akt pathway and activation of both NFAT and eIF2Be.Fondecyt: 1090276