Background

Heart failure (HF) leads to ventricular electrical remodeling, QT-Prolongation, ventricular arrhythmia, and sudden cardiac death, greatly contributing to the high mortality and morbidity of HF. Alterations of ion channel remodeling, resulting in action potential (AP) prolongation, represent one responsible pathophysiologic mechanism. Proarrhythmic remodeling in early stages of HF is not well characterized. We hypothesized that histone deacetylases (HDAC) 1 and 2 regulate ion channel expression and affect heart failure-associated electrical remodeling of the left ventricle (LV).

Methods

Heart failure was induced in domestic pigs by atrial burst pacing for 14 days via an implanted right atrial pacing lead. Electro-, echocardiographic, and electrophysiological measurements were performed prior pacemaker implantation and after the follow-up period. LV tissue was analyzed by Western blot, immunofluorescence staining (IF), and real-time qPCR. AP duration (APD) at 90% repolarization (APD₉₀) measurements were carried out in neonatal murine cardiomyocytes (NMCM) after transfection of siRNA targeting Hdac1 and Hdac2. Ion channel expression after Hdac knockdown in NMCM was analyzed using real-time qPCR.

Results

Porcine early HF was characterized by mild reduction of left ventricular ejection fraction (51%), increased QRS duration (+25%), prolonged QTc intervals (+10%), and increased ventricular effective refractory periods. HDAC2 protein expression was reduced in immunofluorescence (-42%) and Western Blot (-24%), whereas HDAC1 expression was increased significantly in immunofluorescence analysis (+21%) and numerically in western blot (+20%). Consistent with prolonged ventricular repolarization, KCNJ2 was numerically downregulated (-41%). Transcriptional upregulation was observed in KCNQ1 (+139%), KCNJ3 (+74%), and CACNA1C (+43%), while HCN4 transcript levels were numerically increased (+87%).

In siRNA-mediated knockdown of Hdac1 (-78%) in NMCM, upregulation of Hcn4 (+120%) and compensatory upregulation of Hdac2 (+57%) were observed. In contrast, knockdown of Hdac2 (-90%) lead to reduced mRNA-levels of Hcn4 (-33%) without compensatory Hdac1 upregulation. Knockdown of Hdac2 furthermore induced numerical downregulation of Kcnj2 (-27%) and Kcnj5 (-20%), while Kcnd3 transcript levels were increased (+75%).

The prolongated ventricular repolarization in the animal model was recapitulated in NMCM, where knockdown of Hdac2 increased APD₉₀ (+51%). Hdac1 knockdown did not significantly affect APD₉₀.

Conclusion

This study underlines the mechanistic relevance of HDAC2 on electrical remodeling and a novel pathophysiological mechanism of ventricular arrhythmogenesis in early heart failure. Altered ion channel expression is linked to reduced HDAC2 levels and causes action potential prolongation, that contributes to the induction of ventricular arrhythmia in HF.

The observation of these changes in an early stage of heart failure emphasizes the importance of HDAC2 in HF-associated ventricular electrical remodeling and the possible use of HDAC-modulating therapeutical approaches for prevention of ventricular arrhythmia and sudden cardiac death related to HF.