Humanin and MOTS-c Attenuate Atrial Fibrillation by Suppressing Fibrosis and Mitochondrial Dysfunction

Background: Atrial fibrillation (AF) is a common clinical arrhythmia associated with mitochondrial dysfunction, oxidative stress, and atrial fibrosis. Mitochondrial-derived peptides (MDPs), including humanin (HN) and MOTS-c, exhibit cytoprotective properties, but their role in AF remains largely unknown. Objective: This study aimed to investigate the expression of HN and MOTS-c in AF patients and to evaluate their therapeutic potential and underlying mechanisms in an AngII-induced mouse model and primary cardiac cells. Methods: HN and MOTS-c expression in human atrial tissues was analyzed using public GEO data, immunohistochemistry, and immunofluorescence. Plasma levels were measured in a matched cohort (39 AF patients, 39 sinus rhythm controls). Murine AF models (male C57BL/6J mice, n = 36) and primary rat cardiomyocytes and fibroblasts were exposed to angiotensin II (AngII) with or without treatment with HNG (an HN analogue) or MOTS-c. Results: HN and MOTS-c were significantly downregulated in human AF atrial tissue, and their levels inversely correlated with fibrosis extent. Plasma MOTS-c was decreased in AF patients and inversely correlated with NT-proBNP. In vivo, HNG or MOTS-c treatment reduced AF inducibility and attenuated AngII-induced atrial fibrosis and hypertrophy. Peptide treatment was associated with improved mitochondrial ultrastructure, reduced mitochondrial fission proteins (Drp1, Fis1), and lower pro-inflammatory cytokines (IL-1β, IL-6) in mouse atria. In primary cardiomyocytes, both peptides mitigated AngII-induced oxidative stress. In fibroblasts, they directly inhibited AngII-induced activation, proliferation, and migration. Exploratory RNA-seq suggested that HNG predominantly affects cell adhesion pathways, while MOTS-c acts on metabolic processes. Conclusions: Downregulation of HN and MOTS-c in human AF is associated with disease severity. In murine models, HNG or MOTS-c administration attenuates atrial fibrosis and mitochondrial dysfunction and reduces AF inducibility. These findings suggest that MDPs may represent a novel therapeutic avenue for AF, although further validation with larger cohorts and mechanistic studies are required.