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

Abstract

Background: Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice and the pulmonary vein (PV) is the most important AF trigger. Neuregulin 1β (NRG1β), 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 NRG1β on the PVs and explore the underlying mechanisms.

Methods: A 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 NRG1β (10 nM) incubation for 4 h.

Results: NRG1β-treated PVs had faster beating rates and a higher incidence of triggered activity than control PVs. The increased PV spontaneous beating rate induced by NRG1β could be mitigated by ranolazine (a late Na⁺ current inhibitor, 10 μM), KN93 (1 μM) and AIP (1 μΜ) (CaMKII inhibitors) and AKTi (AKT-1/2 inhibitor, 10 μM). NRG1β-treated PV cardiomyocytes demonstrated larger late Na⁺ and Na⁺-Ca²⁺ exchanger current than control PV cardiomyocytes. AIP decreased late Na⁺ current in NRG1β-treated PV cardiomyocytes. Furthermore, NRG1β-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 NRG1β could be alleviated by KN93. Additionally, NRG1β-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 NRG1β-treated PV cardiomyocytes.

Conclusion: By modulating electrophysiological characteristics, Ca²⁺ homeostasis, and enhancing oxidative stress through AKT/CaMKII signalling, NRG1β increased PV arrhythmogenesis with increasing RyR-dependent SR Ca²⁺ leak of PV cardiomyocytes.