Cellular and Molecular Mechanisms with Epigenetic Regulation by Histone Deacetylation on Postopratetive Atrial and Pulmonary Vein Arrhythmogenesis

Background :Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. Postoperative AF is the leading tachyarrhythmias occurring in patients undergoing cardiac surgical procedures, and increases the operative complications, and early or late mortality. However, the pathophysiology of postoperative AF is unclear and the treatment for postoperative AF remains unsatisfied. Left atrium (LA) and pulmonary veins (PVs) are the most important AF substrate and trigger. AF is associated with electrical remodeling with high arrhythmogenesis in PVs and atrial substrates. In addition, sinoatrial node (SAN) dysfunction plays an important role in the pathophysiology of AF. Abnormal calcium regulations with calcium overload or calcium leaks can induce the occurrence of AF due to enhanced triggered activity. PVs and LA have more dysregulated calcium homeostasis and triggered activity. Therefore, postoperative responses may enhance arrhythmogenesis in AF triggers and substrates through modulation on calcium homeostasis. Histone deacetylases (HDACs), which are epigenetic regulators, play critical roles in altering gene expressions during the progression of remodeling processes of cardiovascular diseases. AF is associated with enhanced HDAC activity and HDAC inhibitor can suppress AF in animal model. Moreover, HDAC inhibition can modulate calcium homeostasis and suppress PV arrhythmogenesis or induced-AF. HDACs contain different classes, whereas different HDAC inhibition may differently regulate cardiac calcium homeostasis and electrical activity. The present study is to establish the postoperative AF models and study the cellar and molecular mechanisms with HDAC regulations underlying the genesis of postoperative AF. In the first year study, we will evaluate postoperative arrhythmogenesis, HDAC activity, histopathology in AF trigger and substrates, and study different HDAC inhibition on postoperative arrhythmogenesis and electrophysiological characteristics, and conduction properties on PV, SAN, RA and LA. In the 2nd year, we will study the ionic currents, and molecular changes underlying the postoperative arrhythmogenesis in AF substrates and triggers. In the 3rd year, we will evaluate the calcium hemostasis through image, molecular ways and single current recordings in postoperative AF triggers and substrates, and investigate whether different HDAC inhibition may differentially regulate calcium homeostasis. Methods: In the first year experiments, biochemical, electrocardiographic, and echocardiographic studies will be conducted in rabbits with and without (control) pericardiotomy, and in postoperative rabbits with different HDAC inhibitors (QD for 7 days, MPT0E014 of 10 mg/kg for pan HDAC inhibition, MS-275 of 10 mg/kg for selective HDAC1 and 3 inhibition, or MC-1568 of 10 mg/kg for selective HDAC4 and 6 inhibition). Conventional microelectrode techniques, Multi-electrode array analysis, and histological examinations were performed using the tissue preparations of the isolated rabbit PV, left atrium (LA), right atrium (RA) and sinoatrial node (SAN). Western blotting and enzyme assay will be used to study the expressions of HDAC proteins and activity in control and postoperative rabbits with and without HDAC inhibitors. In vivo atrial electrical activity and induced-AF (rapid atrial pacing and acetylcholine infusion) were measured by ECG and intracardiac electrograms in control and postoperative rabbits with and without HDAC inhibitors. In the 2nd year experiments, western blotting will be used to study the expressions of channel proteins, and connexin, and patch clamp will be used to study the ionic currents (sodium, calcium and potassium currents) in isolated tissue preparations or single PV, SAN, RA and RV cardiomyocytes in in control and postoperative rabbits with and without HDAC inhibitors. In the 3rd year experiments, we will conduct confocal microscopy with fluorescence to study the calcium homeostasis, calcium leak, and calcium spark and evaluate the SERCA2a activity and ryanodine receptor opening probability from single channel recordings in isolated single PV, SAN, RA and RV cardiomyocytes in control and postoperative rabbits with and without HDAC inhibitors. Western blotting will be used to study the expressions of calcium regulation proteins. Preliminary results: We found that postoperative rabbits had a high incidence of atria tachyarrhythmia and increased PV beating rates and triggered activity. These findings suggest that postoperative PVs had a high arrhythmogenesis, which can result in their high AF occurrence.