Aims: Atrial fibrillation (AF), a common tachyarrhythmia in clinical practice, is associated with increased oxidative stress. Structural remodelling in atrial myocytes, including myofibril degradation, is an important characteristic of AF. However, the mechanism underlying AF-induced cellular structural remodelling remains unclear. The aim of this study was to investigate the role of oxidative stress and related factors in tachycardia-induced atrial structural remodelling.
Methods and results: Cultured atrial-derived myocytes (HL-1 cell line) were subjected to electrical stimulation. Immunofluorescence and immunoblotting were used to evaluate oxidative stress, myofibril degradation, and transforming growth factor-β (TGF-β) expression. Tachypacing in HL-1 cells induced TGF-β expression, pronounced oxidative stress including up-regulation of NADPH oxidases (Nox2/4), and myofibril degradation. Oxidative stress scavenger, NADPH oxidase inhibitors, and small-interfering RNAs for Nox2/4 blocked tachypacing-induced myofibril degradation, suggesting that Nox-derived oxidative stress may lead to tachycardia-induced myofibril degradation. Blockade of TGF-β signalling by neutralizing TGF-β antibodies attenuated myofibril loss in response to tachypacing, implicating autocrine and/or paracrine roles for TGF-β in such effects. Tachypacing also induced the activation of p-Smad3 (an effective mediator of TGF-β) and small-interfering RNAs for Nox2/4 attenuated its activation, supporting a crosstalk between both signalling pathways. Furthermore, TGF-β expression, oxidative stress, and myofibril loss were greater in the atria of patients with AF than those with sinus rhythm.
Conclusions: Rapid activation in atrial myocytes promotes myofibril degradation through autocrine/paracrine TGF-β signalling and increased oxidative stress. These findings provide an important mechanistic insight into AF-related structural remodelling.