Abstract 14212: Aortic Stenosis in Mice and Men; Myocardial Activation of Pro-Hypertrophic NFAT Transcription Factor Isoforms is Attenuated by Relief of Pressure Overload
Aortic stenosis (AS) is a major health problem causing hypertrophy and failure. Dephosphorylation of the four nuclear factor of activated T-cell (NFATc) transcription factors by Ca2+-dependent calcineurin is thought to be central, regulating pro-hypertrophic signaling and as much as 10% of human cardiac genes. NFATc1-c4 are believed to play specific roles, yet it is unknown whether all four are activated in human heart disease. Although calcineurin-NFAT is a promising therapeutic target, it remains uncertain whether NFAT signaling can be reversed, such as after aortic valve replacement (AVR) for aortic stenosis (AS). We investigated NFATc1-c4 isoform activation and reversibility in pressure-overloaded human and murine hearts. Using antibodies validated for NFATc1-c4 specificity, we investigated myocardial NFATc activation in biopsies sampled per-operatively from AS patients and controls (n=17), and in experimental AS/AVR, aortic banding (AB)/debanding (DB) and sham-operated controls, in wild-type (n=36) and NFAT-luciferase (n=51) reporter mice. NFATc1-c4 proteins were substantially up-regulated in AS/AB despite minor mRNA changes. Increased NFATc activation was confirmed by 1.5-/4.8-fold increase in a direct target gene of NFATc, the regulator of calcineurin 1-4 (RCAN1-4), in AS/AB, although considerable NFATc1-c4 fractions remained phosphorylated (inactive). mRNA of all four NFATc correlated positively to RCAN1-4 in the human heart. In mice, DB significantly reduced AB-induced hypertrophy (ventricular weight, wall thickness) and failure (lung weight, atrial diameter), and normalized fractional shortening and body weight. Importantly, DB caused complete reversal of RCAN1-4 (8.4- to 0.9-fold), reduced NFAT-luciferase activity (8.3- to 2.6-fold) and reduced NFATc1-c4 protein. NFATc-regulatory enzymes, i.e. calcineurin, GSK-3β, Akt and MAPKs (ERK/JNK/p38), and NFATc-activating transient receptor potential canonical (TRPC1/3/6) membrane channels, were elevated in AS/AB and reversed by DB. Our data suggest that all four NFATc isoforms participate in the early human hypertrophic response. Attenuated NFAT signaling by relief of pressure overload in mice indicates reversal of NFAT activation in AS patients after AVR.
- © 2012 by American Heart Association, Inc.