Abstract 238: Class I HDAC inhibition prevents Ncx1 upregulation by stabilizing an HDAC5-HDAC1/Sin3a Repressor Complex during cardiac hypertrophy.

Abstract

Cardiac hypertrophy is often associated with the activation of signaling pathways that perpetuate altered calcium efflux and influx. One gene that is upregulated and contributes to altered intracellular calcium concentrations and worsening contractility during cardiac hypertrophy is the Sodium Calcium Exchanger ( Ncx1 ). Molecular studies implicate histone deacetylases (HDACs) in possibly regulating the expression of this gene. Our recent work reveals that HDAC1, HDAC5 and Sin3a interact and are recruited to the Ncx1 promoter through the Nkx2.5 transcription factor. Interestingly, we observed greater associated/interaction of the HDAC1-HDAC5/Sin3a repressor complex upon broad HDAC inhibition. Taken together, we hypothesized that HDAC inhibition, stabilizes an HDAC1-HDAC5/Sin3a repressor complex during cardiac hypertrophy. We addressed this hypothesis by treating isolated adult cardiomyocytes with class specific HDAC inhibitors since HDAC1 is a Class I HDAC and HDAC5 is a Class IIa HDAC. Co-Immunoprecipitation (Co-IP) revealed a greater association of repressor complex molecules in the presence of Entinostat, a Class I HDAC inhibitor compared to both non-treated control and TSA, a broad HDAC inhibitor (n=3). These works show enhanced recruitment Sin3a (co-repressor) at the proximal promoter of NCX1 as demonstrated by Chromatin-Immunoprecipitation (ChIP) (n=3). To test whether these observations translated into in vivo models, we subjected mice to transaortic constriction (TAC) to induce hypertrophy. In this model, Co-IP revealed results that similar to our in vitro studies with greater immuno- detection of repressor complex component, Sin3a after immune-precipitation with HDAC1. Furthermore, our ChIP data showed a greater PCR product amplification of proximal Ncx1 promoter, from experimental groups that were subjected to Entinostat (n=3). Our cumulative data suggests that Class I HDAC inhibition stabilizes a repressor complex on the Ncx1 promoter that hinders hypertrophy- mediated Ncx1 upregulation. Class specific HDAC inhibition may be useful in the stabilization and repression of aberrantly expressed genes that contribute to poor clinical outcomes in cardiac hypertrophy.