Neuregulin 1β enhances pulmonary vein arrhythmogenesis by modulating electrophysiological characteristics, calcium and sodium homeostasis via the AKT/CaMKII pathway

BackgroundAtrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice and the pulmonary vein (PV) is the most important AF trigger. Neuregulin 1 beta (NRG1 beta), which is elevated in patients with paroxysmal AF, may activate signalling pathways that mediate cellular adaptations and subsequent stress in the myocardium. The objectives of this study were to study the effects of NRG1 beta on the PVs and explore the underlying mechanisms.MethodsA conventional microelectrode, a whole-cell patch clamp, Western blotting and immunofluorescent confocal microscopy were used to investigate electrical activity, calcium (Ca2+) regulation, protein expression, ionic currents, reactive oxygen species and cytosolic sodium ([Na+]i) in isolated rabbit PV tissue and single cardiomyocytes with or without NRG1 beta (10 nM) incubation for 4 h.ResultsNRG1 beta-treated PVs had faster beating rates and a higher incidence of triggered activity than control PVs. The increased PV spontaneous beating rate induced by NRG1 beta could be mitigated by ranolazine (a late Na+ current inhibitor, 10 mu M), KN93 (1 mu M) and AIP (1 mu Mu) (CaMKII inhibitors) and AKTi (AKT-1/2 inhibitor, 10 mu M). NRG1 beta-treated PV cardiomyocytes demonstrated larger late Na+ and Na+-Ca2+ exchanger current than control PV cardiomyocytes. AIP decreased late Na+ current in NRG1 beta-treated PV cardiomyocytes. Furthermore, NRG1 beta-treated PV cardiomyocytes had smaller intracellular Ca2+ transients and reduced sarcoplasmic reticulum Ca2+ contents, but higher levels of [Na+]i, oxidative stress and RyR-dependent SR Ca2+ leak than control PV cardiomyocytes. The increased RyR-dependent SR Ca2+ leak by NRG1 beta could be alleviated by KN93. Additionally, NRG1 beta-treated PV cardiomyocytes exhibited upregulated AKT, pAKT, ERK, pERK, CaMKII and pCaMKII, while SERCA2a and PLB were downregulated. AKTi can downregulate oxi-CaMKII and CaMKII in NRG1 beta-treated PV cardiomyocytes.ConclusionBy modulating electrophysiological characteristics, Ca2+ homeostasis, and enhancing oxidative stress through AKT/CaMKII signalling, NRG1 beta increased PV arrhythmogenesis with increasing RyR-dependent SR Ca2+ leak of PV cardiomyocytes.