Abstract 138: Inhibition of Stress-inducible Genes That Distinguish Pathological Cardiac Hypertrophy via Targeting Acidic Nuclear Protein 32e

Abstract

Cardiac hypertrophy is a manifestation of an increase in the workload imposed on the heart. The cause, duration, and extent of the workload dictate the physiological vs. pathological nature of the hypertrophy and its likelihood to transition into cardiac failure. Our goal is to identify differences between these 2 forms of hypertrophy by examining the binding patterns of key basic transcription factors and regulators in a genome-wide fashion. Our data show that a pause-release mechanism of RNA polymerase II (pol II) bound to the transcriptional start site (TSS) induces housekeeping/essential genes (~ 63% of expressed genes), in a synchronous and incremental fashion that is proportional to the increase in myocyte size and does not require de novo pol II binding. This mechanism is responsible for the increase in cell size and mass that constitute hypertrophy in both physiological and pathological forms. Superimposed on this is a second and critical group of genes (~3.5%) that are stress-induced in the pathological form of hypertrophy but are minimally, if at all, expressed in the postnatal and adult heart (e.g. Acta1, Ankrd1, Xirp2, Nppa, Col1a1 ..etc). In contrast to the housekeeping genes, these genes require de novo pol II recruitment and exhibit a robust increase in expression. To further identify the transcriptional mechanisms that distinguish these sets of genes, we performed chromatin immunoprecipitation-deep sequencing (ChIP-Seq) analysis for cyclin-dependent kinase 9 (Cdk9) and histone H2A.z. The results reveal an increase in Cdk9 at the TSS of paused genes vs. an increase at TSS and throughout the gene body of inducible genes. In contrast, H2A.z levels remained constant. However, we found that Acidic Nuclear Protein 32e (Anp32e), a nuclear protein phosphatase 2A (PP2A) inhibitor, interacted with H2A.z and regulated phosphorylation of Cdk9. Interestingly, knockdown of Anp32e during pressure overload hypertrophy resulted in 70-90% inhibition of stress-inducible genes, but only an incremental inhibition of the increase in cardiac size. Thus, we propose that targeting Anp32e may partially revert pathological hypertrophy to a more physiological form via specifically inhibiting the stress-induced genes while preserving the increase in cardiac mass.