Epigenetic regulation of cardiac electrophysiology in atrial fibrillation: HDAC2 determines action potential duration and suppresses NRSF in cardiomyocytes.

Atrial fibrillation (AF) is associated with electrical remodeling, leading to cellular electrophysiological dysfunction and arrhythmia perpetuation. Emerging evidence suggests a key role for epigenetic mechanisms in the regulation of ion channel expression. Histone deacetylases (HDACs) control gene expression through deacetylation of histone proteins. We hypothesized that class I HDACs in complex with neuron-restrictive silencer factor (NRSF) determine atrial K+ channel expression. AF was characterized by reduced atrial HDAC2 mRNA levels and upregulation of NRSF in humans and in a pig model, with regional differences between right and left atrium. In vitro studies revealed inverse regulation of Hdac2 and Nrsf in HL-1 atrial myocytes. A direct association of HDAC2 with active regulatory elements of cardiac K+ channels was revealed by chromatin immunoprecipitation. Specific knock-down of Hdac2 and Nrsf induced alterations of K+ channel expression. Hdac2 knock-down resulted in prolongation of action potential duration (APD) in neonatal rat cardiomyocytes, whereas inactivation of Nrsf induced APD shortening. Potential AF-related triggers were recapitulated by experimental tachypacing and mechanical stretch, respectively, and exerted differential effects on the expression of class I HDACs and K+ channels in cardiomyocytes. In conclusion, HDAC2 and NRSF contribute to AF-associated remodeling of APD and K+ channel expression in cardiomyocytes via direct interaction with regulatory chromatin regions. Specific modulation of these factors may provide a starting point for the development of more individualized treatment options for atrial fibrillation.

Inhibition of Histone Deacetylases Induces K+ Channel Remodeling and Action Potential Prolongation in HL-1 Atrial Cardiomyocytes.

BACKGROUND/AIMS: Cardiac arrhythmias are triggered by environmental stimuli that may modulate expression of cardiac ion channels. Underlying epigenetic regulation of cardiac electrophysiology remains incompletely understood. Histone deacetylases (HDACs) control gene expression and cardiac integrity. We hypothesized that class I/II HDACs transcriptionally regulate ion channel expression and determine action potential duration (APD) in cardiac myocytes. METHODS: Global class I/II HDAC inhibition was achieved by administration of trichostatin A (TSA). HDAC-mediated effects on K+ channel expression and electrophysiological function were evaluated in murine atrial cardiomyocytes (HL-1 cells) using real-time PCR, Western blot, and patch clamp analyses. Electrical tachypacing was employed to recapitulate arrhythmia-related effects on ion channel remodeling in the absence and presence of HDAC inhibition. RESULTS: Global HDAC inhibition increased histone acetylation and prolonged APD90 in atrial cardiomyocytes compared to untreated control cells. Transcript levels of voltage-gated or inwardly rectifying K+ channels Kcnq1, Kcnj3 and Kcnj5 were significantly reduced, whereas Kcnk2, Kcnj2 and Kcnd3 mRNAs were upregulated. Ion channel remodeling was similarly observed at protein level. Short-term tachypacing did not induce significant transcriptional K+ channel remodeling. CONCLUSION: The present findings link class I/II HDAC activity to regulation of ion channel expression and action potential duration in atrial cardiomyocytes. Clinical implications for HDAC-based antiarrhythmic therapy and cardiac safety of HDAC inhibitors require further investigation.

TREK-1 (K2P2.1) K+ channels are suppressed in patients with atrial fibrillation and heart failure and provide therapeutic targets for rhythm control.

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Concomitant heart failure (HF) poses a particular therapeutic challenge and is associated with prolonged atrial electrical refractoriness compared with non-failing hearts. We hypothesized that downregulation of atrial repolarizing TREK-1 (K2P2.1) K+ channels contributes to electrical remodeling during AF with HF, and that TREK-1 gene transfer would provide rhythm control via normalization of atrial effective refractory periods in this AF subset. In patients with chronic AF and HF, atrial TREK-1 mRNA levels were reduced by 82% (left atrium) and 81% (right atrium) compared with sinus rhythm (SR) subjects. Human findings were recapitulated in a porcine model of atrial tachypacing-induced AF and reduced left ventricular function. TREK-1 mRNA (-66%) and protein (-61%) was suppressed in AF animals at 14-day follow-up compared with SR controls. Downregulation of repolarizing TREK-1 channels was associated with prolongation of atrial effective refractory periods versus baseline conditions, consistent with prior observations in humans with HF. In a preclinical therapeutic approach, pigs were randomized to either atrial Ad-TREK-1 gene therapy or sham treatment. Gene transfer effectively increased TREK-1 protein levels and attenuated atrial effective refractory period prolongation in the porcine AF model. Ad-TREK-1 increased the SR prevalence to 62% during follow-up in AF animals, compared to 35% in the untreated AF group. In conclusion, TREK-1 downregulation and rhythm control by Ad-TREK-1 transfer suggest mechanistic and potential therapeutic significance of TREK-1 channels in a subgroup of AF patients with HF and prolonged atrial effective refractory periods. Functional correction of ionic remodeling through TREK-1 gene therapy represents a novel paradigm to optimize and specify AF management.

Epigenetic alterations as biomarkers in pancreatic ductal adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) prognosis remains very poor and has only marginally improved during the last decades. Epigenetic alterations have been the focus of many recent studies and offer valuable options for PDAC detection, prognosis and treatment. DNA methylation, histone modifications and microRNA (miR) level changes can be used as biomarkers. These alterations occur early in carcinogenesis and may be specific for PDAC. Additionally, epigenetic alterations can be analyzed from cell-free DNA, free-circulating nucleosomes or shed tumor cells in blood. High-throughput methods are available for miR and DNA methylation level detection. In particular, multiple promising miR level changes have been discovered. No single epigenetic biomarker that offers a sufficient specificity has been discovered yet, but patterns containing multiple independent biomarkers exist.

Electrical Ventricular Remodeling in Dilated Cardiomyopathy.

Ventricular arrhythmias contribute significantly to morbidity and mortality in patients with heart failure (HF). Pathomechanisms underlying arrhythmogenicity in patients with structural heart disease and impaired cardiac function include myocardial fibrosis and the remodeling of ion channels, affecting electrophysiologic properties of ventricular cardiomyocytes. The dysregulation of ion channel expression has been associated with cardiomyopathy and with the development of arrhythmias. However, the underlying molecular signaling pathways are increasingly recognized. This review summarizes clinical and cellular electrophysiologic characteristics observed in dilated cardiomyopathy (DCM) with ionic and structural alterations at the ventricular level. Furthermore, potential translational strategies and therapeutic options are highlighted.

Histone deacetylase 2-dependent ventricular electrical remodeling in a porcine model of early heart failure.

AIMS: Heart failure (HF) is linked to electrical remodeling that promotes ventricular arrhythmias. Underlying molecular signaling is insufficiently understood, in particular concerning patients with early disease stages. Previous observations suggest a key role for epigenetic mechanisms in cardiac remodeling processes. We hypothesized that histone deacetylases (HDACs) 1 and 2 contribute to cellular electrophysiological dysregulation in ventricular cardiomyocytes during HF development. MATERIALS AND METHODS: HDAC and ion channel expression was quantified in a porcine model of early HF induced by short-term atrial tachypacing, resulting in atrial fibrillation with rapid ventricular rate response. Anti-Hdac1 and anti-Hdac2 siRNA treatment was employed in neonatal murine cardiomyocytes (NMCM) to study effects of HDACs on ion channel mRNA expression and action potential duration (APD). KEY FINDINGS: Early HF was characterized by mild reduction of left ventricular ejection fraction, prolonged QTc intervals, and increased ventricular effective refractory periods. Delayed repolarization was linked to significant downregulation of HDAC2 in left ventricular (LV) tissue. In addition, there was a tendency towards reduced transcript expression of KCNJ2/Kir2.1 K+ channels. In NMCM, knock-down of Hdac2 recapitulated AP prolongation. Finally, siRNA-mediated suppression of Hdac2 reduced Kcnh2/Kv11.1 K+ channel expression. SIGNIFICANCE: Suppression of HDAC2 is linked to ventricular electrical remodeling of APD and ion channel expression in early stages of heart failure. This previously unrecognized mechanism may serve as basis for future approaches to prevention and treatment of ventricular arrhythmias.

Atrial myofibroblast activation and connective tissue formation in a porcine model of atrial fibrillation and reduced left ventricular function.

AIMS: Atrial fibrillation (AF) is associated with fibrosis that slows electrical conduction and causes perpetuation of the arrhythmia. The molecular characterization of AF pathophysiology may provide novel therapeutic options. This study was designed to elucidate profibrotic signaling and myofibroblast activation in a porcine model of atrial tachypacing-induced AF and reduced left ventricular function. MATERIALS AND METHODS: Ten domestic pigs were randomized to sinus rhythm (SR) or AF groups. Prior to AF induction and on day 14 the animals underwent echocardiographic examinations. Profibrotic pathways were analyzed in right atrial tissue obtained from AF animals compared to SR controls using histology, immunofluorescence microscopy, Western blot, and real-time PCR. KEY FINDINGS: AF was associated with atrial dilation, increased atrial fibrosis, and enhanced expression of collagens I and V in right atrial tissue after 14days follow-up. The fraction of α-smooth muscle actin (SMA)-producing activated myofibroblasts was elevated in AF, whereas the abundance of vimentin-expressing inactive fibroblasts was not affected. Profibrotic signaling involved upregulation of TGF-ß1, Smad2/3, and CTGF. SIGNIFICANCE: The transformation of atrial fibroblasts into myofibroblasts through activation of TGF-ß1 and CTGF emerged as potential cellular trigger of fibrogenesis. Prevention of fibroblast-to-myofibroblast switching may serve as target for remodeling-based antiarrhythmic AF therapy.