Abstract 10468: Clinical and Experimental Aortic Stenosis; Attenuation of Activated Pro-Hypertrophic NFAT Transcription Factor Isoforms During Reverse Remodeling
Aortic stenosis (AS) is a common valvular lesion causing hypertrophy and failure. Activation of nuclear factor of activated T-cell (NFAT) transcription factors by Ca2+-calcineurin is a central pro-hypertrophic pathway, yet it is unknown if all four NFATc1-c4 isoforms are activated. Moreover, it is uncertain whether NFAT signaling is reversible such as in aortic valve replacement (AVR) for AS. We investigated NFATc1-c4 activation and reversibility in clinical and experimental AS.
Using antibodies validated for NFATc1-c4 specificity, myocardial NFATc activation was studied in biopsies sampled per-operatively from AS patients (n=34), and in experimental aortic banding (AB)/debanding (DB), in wild-type (n=105) and NFAT-luciferase (n=51) mice. NFATc1-c4 proteins were substantially up-regulated in AS despite minor mRNA changes. Increased NFAT activation was confirmed by 1.5-/2.6-fold increase mRNA/protein of a direct target gene of NFATc, RCAN1-4, despite considerable phosphorylation (inactive NFAT). Positive correlations to RCAN1-4 suggested all isoforms to contribute to NFAT activation. Increased protein levels of Ca2+-regulatory channels (LTCC 4.8-fold, TTCC 6.5-fold, RyR2 6.8-fold, NCX1 2.1-fold, PMCA 2.8-fold, PLN 1.4-fold and serca2 2.1-fold) indicated elevated Ca2+ to activate NFAT. In mice, AB for 24 hrs, 1-3 weeks (hypertrophy) and 16-18 weeks (end-stage failure) increased RCAN1-4 mRNA/protein 2-12-fold. 1week of DB after 1week of AB reduced hypertrophy (ventricular weight, wall thickness) and failure (lung weight, atrial diameter), normalized body weight and improved fractional shortening. Importantly, DB caused complete reversal of RCAN1-4 (8.4- to 0.9-fold) and reduced NFAT-luciferase activity (8.3- to 2.6-fold). In contrast to AS, in human end-stage failure, NFATc4 was dephosphorylated, and after left ventricular assist device (LVAD), RCAN1-4 protein was reversed in two out five patients, suggesting lower potential for reversibility.
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.
- © 2013 by American Heart Association, Inc.