Abstract 3: Interaction Between NFκB and NFAT Coordinates Cardiac Hypertrophy and Pathological Remodeling

Abstract

Both NFAT and NFkB are Rel homology domain-containing family members of transcription factors whose independent activities are critically involved in regulating cardiac hypertrophy and failure. Here we identified a novel transcriptional regulatory mechanism whereby NFkB and NFAT directly interact and synergistically promote transcriptional activation of one another in cardiomyoctes. We showed that NFkB-p65 co-immunoprecipitates with NFAT isoforms in cardiomyocytes, and this interaction is mapped to the Rel homology domain (RHD) within p65. Intriguingly, overexpression of p65-RHD disrupts the association between endogenous p65 and NFATc1, leading to reduced NFAT luciferase activity. Overexpression of p65-RHD or IKKβ leads to significant nuclear translocation of NFATc1, and expression of a constitutively nuclear NFATc1-SA similarly facilitated p65 nuclear translocation, further suggesting a physical interaction between p65 and NFATc1. Indeed, we observed that combined overexpression of p65 and NFAT leads to synergistic activation of NFAT transcriptional activity in cardiomyocytes. Conversely, NFAT transcriptional activity in cardiomyocytes is significantly reduced by inhibition of NFkB with IkBαM or dominant negative IKKβ. Importantly, hypertrophic agonist-induced NFAT activity is also significantly reduced in NFkB-p65 null MEFs compared to wild-type MEFs, while adenoviral-mediated expression of p65 restored NFAT luciferase activity in p65 null MEFs. In vivo, cardiac-specific deletion of NFkB-p65 using a Cre-LoxP system caused a ∼ 50% reduction in NFAT activity in NFAT-luciferase reporter mice. Moreover, ablation of p65 in the mouse heart decreased the hypertrophic response following pressure overload stimulation, reduced the degree of pathological remodeling, and preserved contractile function. Taken together, our results suggest a direct interaction between NFAT and NFkB pathways that may serve as a novel signaling mechanism in cardiac hypertrophy and failure.