Abstract 9687: Aldosterone Enhances MR/NADPH Oxidase Physical Association, and Induces Cardiomyocyte Hypertrophy and Cardiac Fibroblast Proliferation via Amplification of IL-18 Signaling

Abstract

Hyperaldosteronism is associated with inflammation, progressive myocardial hypertrophy, fibrosis and adverse remodeling. Since interleukin (IL)-18 is a hypertrophic and mitogenic inflammatory cytokine, we investigated whether Aldosterone (Aldo)-induced cardiomyocyte (CaM) hypertrophy and cardiac fibroblast (CF) proliferation and migration are IL-18 dependent. Aldo-induced hypertrophy of primary rat CaM was inhibited by the mineralocorticoid receptor (MR) antagonists spiranolactone, and eplerenone. Interestingly, knockdown of IL-18, or its neutralization with IL-18BP or polyclonal anti-rat IgG blunted Aldo’s growth effects. In CaM, Aldo induced IL-18 expression via DPI-inhibitable, Nox2- and Nox4-dependent ROS generation, and NF-κB and AP-1 activation. Knockdown of Nox2, Nox4, p65 or c-Jun inhibited IL-18 and IL-18Rα expression and CaM growth. Further, using GST pull-down assays and co-immunoprecipitation/immunoblotting, we demonstrate for the first time that MR physically associates with Nox2 and Nox4 both in vitro and in vivo under basal conditions, and Aldo enhances their interactions in vivo. In CF, Aldo stimulated DPI-inhibitable, Nox4-dependent ROS generation, IL-18, IL-18Rα, and MMP-9 induction, and IL-18-dependent migration and proliferation. In these cells, MR was found bound to Nox4. Continuous infusion of Aldo into rats resulted in myocardial hypertrophy and fibrosis, DPI-inhibitable ROS generation, MR binding to Nox2 and Nox4, and IL-18, IL-18Rα, and MMP-9 expression in the heart. Co-treatment with spironolactone blunted these effects. Notably, Aldo-induced myocardial hypertrophy and fibrosis were markedly attenuated in IL-18-null mice. These results demonstrate that Aldo amplifies IL-18 signaling in both cell types by inducing IL-18 and its receptor expression. Importantly, Aldo-induced cardiomyocyte hypertrophy and fibroblast proliferation are IL-18 dependent, and may involve the direct interaction of MR with NADPH oxidases. IL-18 is a potential therapeutic target in Aldo-induced myocardial hypertrophy, fibrosis and adverse remodeling.