Abstract
Phosphorylation of the eukaryotic translation initiation factor 2 α-subunit, which subsequently upregulates activating transcription factor 4 (ATF4), is the core event in the integrated stress response (ISR) pathway. Previous studies indicate phosphorylation of eukaryotic translation initiation factor 2 ɑ-subunit in atrial tissue in response to atrial fibrillation (AF). This study investigated the role of ISR pathway in experimental AF by using a small-molecule ISR inhibitor (ISRIB). Accordingly, rats were subjected to coronary artery occlusion to induce myocardial infarction (MI), or sham operation, and received either trans-ISRIB (2 mg/kg/d, i.p.) or vehicle for seven days. Thereafter, animals were subjected to the AF inducibility test by transesophageal rapid burst pacing followed by procurement of left atrium (LA) for assessment of atrial fibrosis, inflammatory indices, autophagy-related proteins, ISR activation, ion channel, and connexin 43 expression. Results showed a significant increase in the AF vulnerability and the activation of ISR in LA as evidenced by enhanced eukaryotic translation initiation factor 2 ɑ-subunit phosphorylation. ISRIB treatment suppressed upregulation of ATF4, fibrosis as indexed by determination of α-smooth muscle actin and collagen levels, inflammatory macrophage infiltration (i.e., CD68 and inducible nitric oxide synthase/CD68-positive macrophage), and autophagy as determined by expression of light chain 3. Further, ISRIB treatment reversed the expression of relevant ion channel (i.e., the voltage-gated sodium channel 1.5 , L-type voltage-dependent calcium channel 1.2, and voltage-activated A-type potassium ion channel 4.3) and connexin 43 remodeling. Collectively, the results suggest that the ISR is a key pathway in pathogenesis of AF, post-MI, and represents a novel target for treatment of AF. SIGNIFICANCE STATEMENT: The activation of integrated stress response (ISR) pathway as evidenced by enhanced eukaryotic translation initiation factor 2 ɑ-subunit phosphorylation in left atrium plays a key role in atrial fibrillation (AF). ISR inhibitor (ISRIB) reduces AF occurrence and atrial proarrhythmogenic substrate. The beneficial action of ISRIB may be mediated by suppressing ISR pathway-related cardiac fibrosis, inflammatory macrophage infiltration, autophagy, and restoring the expression of ion channel and connexin 43. This study suggests a key dysfunctional role for ISR in pathogenesis of AF with implications for novel treatment.
Highlights
Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice, and associated with stroke, congestive heart failure, and mortality (Guo et al, 2015; Lippi et al, 2020)
To assess whether ISR inhibitor (ISRIB) administration affects cardiac function post-myocardial infarction (MI), we investigated the echocardiographic parameters after ISRIB treatment in post-MI rats (Table 1)
ISRIB treatment significantly ameliorated the decline of ejection fraction (EF), fractional shortening (FS), and ventricular enlargement in MI rats, but the treatment did not affect the aforementioned parameters in sham-operated animals
Summary
Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice, and associated with stroke, congestive heart failure, and mortality (Guo et al, 2015; Lippi et al, 2020). S This article has supplemental material available at jpet.aspetjournals.org. Public health problem (Krijthe et al, 2013) associated with high costs of medical care of affected individuals (Stewart et al, 2002). Available therapies for AF include antiarrhythmic drug, catheter ablation, and surgical ablation, each with limitations like adverse effects, inconsistent efficacy, and high recurrence rates (Heijman et al, 2016). Recent studies identified new pathophysiological mechanisms of AF, including cardiac fibrosis (Nattel, 2017), oxidative stress (Antonopoulos et al, 2019), apoptosis, autophagy (Chen et al, 2011; Wiersma et al, 2017), inflammation (Zhou and Dudley, 2020), atrial ion-channel dysfunction, Ca21-handling abnormalities, autonomic neural dysregulation, and atrial remodeling (Andrade et al, 2014)
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