Abstract 236: HDAC5 is Required for Recruitment of an HDAC1/Sin3a Repressor Complex to the Ncx1 Promoter During Cardiac Hypertrophy

Abstract

Background: Pressure overload can lead to aberrant gene expression and subsequent adverse hypertrophic changes in cardiac tissue. Histone deacetylases (HDACs) play an important role in alteration of gene expression during cardiac hypertrophy. We observed that class I/IIb HDAC inhibitors, TSA and Vorinostat prevent upregulation of the sodium calcium exchanger gene, Ncx1 , in response to cardiac hypertrophy. Chromatin immunoprecipitation (ChIP) demonstrates the class I HDAC, HDAC1, class IIa HDAC, HDAC5 and co-repressor, Sin3a are recruited to the Ncx1 promoter via Nkx2.5. Class IIa HDACs have very poor catalytic activity and can interact with many specific transcription factors. Thus, we hypothesized , that the class IIa, HDAC5 acts as a scaffold to recruit the class I HDAC/Sin3a complex to the Ncx1 promoter. Methods and Results: To test our hypothesis adult cardiomyocytes were treated with either vehicle (control) or class specific HDAC inhibitors: class I (Entinostat), or class IIa (dPAHA). We found that class I HDAC inhibitor, Entinostat, abrogates adrenergic stimulated upregulation of Ncx1 expression in adult cardiomyocytes to almost control levels (p<0.05 Student’s t; n=4), while class IIa HDAC inhibitor, dPAHA has no effect on adrenergic stimulated upregulation of Ncx1 expression (p>0.05 Student’s t; n=4). Also, Entinostat inhibits Ncx1 upregulation in a transaortic constriction (TAC) model of hypertrophy. We assessed the role class IIa HDAC5 in Ncx1 regulation, by subjecting HDAC5-Knockout mice (HDAC5-KO) to TAC. We saw no induction of Ncx1 expression post-TAC (n=5). Furthermore, Co-IP and ChIP analyses show that interactions between the Sin3a/HDAC1 complex and Nkx2.5 are lost in the absence of HDAC5 expression and fail to be recruited to the Ncx1 promoter. To conclude , our data suggests the catalytic activity of HDAC5 is not essential but rather HDAC5 is a scaffold that recruits the class I HDAC1–Sin3a complex to the Ncx1 promoter. Our novel findings provide insight into possible roles of class IIa HDACs in regulation of gene expression and efficacy of HDAC inhibitors to treat cardiac pathologies.