Abstract Body (Do not enter title and authors here): Objective: Pathogenic variants in LMNA are associated with early-onset atrial fibrillation (EOAF) but the pathophysiological mechanisms by which atrial myopathy leads to AF are poorly understood. Here, we investigated electrophysiologic (EP) and epigenetic mechanisms by which a heterozygous pathogenic LMNA-S143P mutation causes EOAF utilizing mature human induced pluripotent stem cell-derived atrial cardiomyocytes (hiPSC-aCMs) generated from a large Caucasian kindred with a strong cardiac phenotype.
Hypothesis: Atrial myopathy due to the LMNA-S143P mutation, creates an arrhythmogenic substrate for AF by causing ion channel and chromatin remodeling.
Approach: We performed clinical phenotyping and genetic testing of the proband and family members. hiPSC-aCMs generated from family members and CRISPR-corrected isogenic control (CRISPR-GC) were characterized by optical voltage mapping, calcium transient measurements, and whole-cell patch clamp analysis. Transcriptomic and epigenetic analysis was performed by RNA-sequencing (seq) and assay for transposase-accessible chromatin followed by sequencing (ATAC-seq).
Results: The proband presented with EOAF at 35 years. Cardiac MRI and transthoracic echocardiogram revealed an atrial myopathy and low voltage electrograms but preserved left ventricular ejection fraction (56%). Cascade screening of the LMNA-S143P kindred confirmed co-segregation of the variant with AF, conduction disease, and dilated cardiomyopathy (Fig. A). EP analysis showed that the LMNA-S143P hiPSC-aCMs exhibited heterogeneity of action potential duration (APD)(Fig. B); decreased Na⁺ current (Fig. C) and delayed after-depolarizations (Fig. D). Integrated analysis of RNA and ATAC-seq revealed significant enrichment of genes associated with Wnt signaling pathway, cytoskeletal remodeling and activation of calcium signaling (Fig. E-I) Congruently, we found high enrichment of CAMK2 kinase as well as TCF and NFAT transcription factors associated with Wnt signaling (Fig. F-G) .
Conclusion: Our results suggest that cytoskeletal remodeling and triggered calcium release mediated by NFAT and CAMK2 respectively create an arrhythmogenic substrate for atrial myopathy and AF highlighting their therapeutic potential.