GSK-3 beta/NFAT Signaling Is Involved in Testosterone-Induced Cardiac Myocyte Hypertrophy

Abstract

Testosterone induces cardiac hypertrophy through a mechanism that involves a concerted crosstalk between cytosolic and nuclear signaling pathways. Nuclear factor of activated T-cells (NFAT) is associated with the promotion of cardiac hypertrophy, glycogen synthase kinase-3 beta (GSK-3 beta) is considered to function as a negative regulator, mainly by modulating NFAT activity. However, the role played by calcineurin-NFAT and GSK-3 beta signaling in testosterone-induced cardiac hypertrophy has remained unknown. Here, we determined that testosterone stimulates cardiac myocyte hypertrophy through NFAT activation and GSK-3 beta inhibition. Testosterone increased the activity of NFAT-luciferase (NFAT-Luc) in a time-and dose-dependent manner, with the activity peaking after 24 h of stimulation with 100 nM testosterone. NFAT-Luc activity induced by testosterone was blocked by the calcineurin inhibitors FK506 and cyclosporine A and by 11R-VIVIT, a specific peptide inhibitor of NFAT. Conversely, testosterone inhibited GSK-3 beta activity as determined by increased GSK-3 beta phosphorylation at Ser9 and beta-catenin protein accumulation, and also by reduction in beta-catenin phosphorylation at residues Ser33, Ser37, and Thr41. GSK-3 beta inhibition with 1-azakenpaullone or a GSK-3 beta-targeting siRNA increased NFAT-Luc activity, whereas overexpression of a constitutively active GSK-3 beta mutant (GSK-3 beta S9A) inhibited NFAT-Luc activation mediated by testosterone. Testosterone-induced cardiac myocyte hypertrophy was established by increased cardiac myocyte size and [H-3]-leucine incorporation (as a measurement of cellular protein synthesis). Calcineurin-NFAT inhibition abolished and GSK-3 beta inhibition promoted the hypertrophy stimulated by testosterone. GSK-3 beta activation by GSK-3 beta S9A blocked the increase of hypertrophic markers induced by testosterone. Moreover, inhibition of intracellular androgen receptor prevented testosterone-induced NFAT-Luc activation. Collectively, these results suggest that cardiac myocyte hypertrophy induced by testosterone involves a cooperative mechanism that links androgen signaling with the recruitment of NFAT through calcineurin activation and GSK-3 beta inhibition.