Downregulation of HDAC2 attenuates ventricular arrhythmias in a mouse model of cardiac hypertrophy through upregulation of KCHIP2 expression.

Decrease in repolarizing K+ currents, particularly the fast component of transient outward K+ current (Ito,f), prolongs action potential duration (APD) and predisposes the heart to ventricular arrhythmia during cardiac hypertrophy. Histone deacetylases (HDACs) have been suggested to participate in the development of cardiac hypertrophy, and class I HDAC inhibition has been found to attenuate pathological remodeling. This study investigated the potential therapeutic effects of HDAC2 on ventricular arrhythmia in pressure overload-induced cardiac hypertrophy. An in vivo cardiac hypertrophic model was produced by performing transverse aortic constriction (TAC) surgery, and an in vitro cardiomyocyte hypertrophy model by stimulating neonatal rat ventricular myocytes (NRVMs) with phenylephrine (PE). HDAC2 expression was upregulated in TAC mouse hearts and in PE-stimulated cardiomyocytes. Susceptibility to ventricular arrhythmia was increased in TAC mice, while Ito,f was decreased and APD was prolonged in TAC cardiomyocytes. Heart-specific knockdown of HDAC2 (HKD) by RNA interference increased Ito,f, shortened APD and decreased susceptibility to ventricular arrhythmia. Concomitantly, HKD increased the expression of the obligatory β subunit of Ito,f, KChIP2, which is downregulated in hypertrophic hearts. The effects of HKD on KChIP2 expression, Ito,f and APD were also observed in PE-stimulated cardiomyocytes. Mechanistically, HKD increased H3K4me3 abundance and H3K4me3 enrichment at the Kcnip2 promoter in cardiomyocytes. HKD also decreased the expression of KDM5, the H3K4me3 demethylase, which resulted in H3K4me3 upregulation. While investigating the regulatory mechanisms underlying the effect of HDAC2 on KDM5 stability, we identified CNOT4 as the active KDM5 ubiquitinase in cardiomyocytes. HKD increased CNOT4 expression and CNOT4-KDM5 interactions, and thus enhanced the polyubiquitinated degradation of KDM5. HDAC2 inhibition serves as a novel therapeutic strategy for preventing cardiac hypertrophy-associated electrophysiological remodeling. Furthermore, we identified a novel signaling pathway of CNOT4-mediated KDM5 degradation contributing to the upregulation of H3K4me3-mediated KChIP2 expression in response to HDAC2 inhibition.