Abstract 16184: Lamin A Deficiency Leads to Electrophysiological and Nuclear Abnormalities Reminiscent of Atrial Cardiomyopathy in Zebrafish

Abstract

Introduction: Mutations in the lamin A/C ( LMNA ) gene have been causally linked to atrial arrhythmias and cardiac conduction disease (CCD) in young adults. However, the mechanism by which the laminopathy leads to perturbed cardiac electrophysiology has not been fully elucidated. Hypothesis: We hypothesize that protein-truncating variants in LMNA will impair the mechano-protection force in the nuclear envelope and will lead to early-onset cardiomyocyte degeneration and CCD. Methods: In a multi-regional registry of early-onset CCD and atrial fibrillation in Japan, we performed whole-exome DNA sequencing of 23 probands. Using CRISPR/Cas9, we generated indels of candidate gene homologues in zebrafish and characterized cardiac physiology using optical mapping technology and immunohistochemistry. Results: Among all probands, our study revealed four rare nonsense variants in the nuclear protein-coding genes. We focused on a LMNA protein-truncating variant, c.339dupT (p.K114X fsX1), and created a variant in the zebrafish lmna that produced a similar truncation. Lmna -/- zebrafish larvae showed shortened atrial action potential duration (APD) (msec.) compared to wild-type controls (162 ± 19 vs 227 ± 79, p<0.05), while conduction velocities (CV) did not vary between the genotypes. In contrast, the atrioventricular canal of lmna -/- embryos exhibited prolonged APD (399 ± 51 vs 322 ± 47, p<0.05) and slower CV (mm/sec.) (0.37 ± 0.12 vs 0.57 ± 0.12, p<0.05) than controls. Immunohistochemistry demonstrated that atrial cardiomyocytes of embryonic lmna -/- zebrafish displayed significantly decreased cell numbers and smaller cell size compared to those of controls, which in turn developed into abnormal nuclear structures in adult. Conclusions: These findings suggest that lamin A is a prerequisite for proper atrial cardiomyocyte morphology in embryonic zebrafish, and is indispensable for correct cardiac electrophysiology and -conduction.