Small-Molecule Integrated Stress Response Inhibitor Reduces Susceptibility to Postinfarct Atrial Fibrillation in Rats via the Inhibition of Integrated Stress Responses

Phosphorylation of the eukaryotic translation initiation factor 2 α-subunit (eIF2ɑ)，which subsequently upregulates activating transcription factor 4 (ATF4), is the core event in the integrated stress response (ISR) pathway. Previous studies indicate phosphorylation of eIF2ɑ 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/day, 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 connexin43 expression. Results showed a significant increase in the AF vulnerability and the activation of ISR in LA as evidenced by enhanced eIF2α 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 iNOS/CD68-positive macrophage) and autophagy as determined by expression of LC3. Further, ISRIB treatment reversed the expression of relevant ion channel (i.e., Nav1.5, Cav1.2, and Kv4.3) and Cx43 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 Activation of integrated stress response (ISR) pathway as evidenced by enhanced eIF2α phosphorylation in left atrium plays a key role in atrial fibrillation (AF). A small-molecule ISR inhibitor (ISRIB) reduces AF and atrial arrhythmogenic substrate. The mechanism of ISRIB may be mediated by suppressing ISR pathway-related cardiac fibrosis, inflammatory macrophage infiltration, autophagy, and restoring the expression of ion channel and Cx43. This study suggests a key dysfunctional role for ISR in pathogenesis of AF with implications for novel treatment.