Abstract 12627: I Na Remodeling and Conduction Deficits in a Murine Model of Human LMNA -R545H Mutation

Abstract

Introduction: We have identified a de novo mutation of LMNA ( LMNA -R545H) in a 34-year-old man with high-grade atrioventricular block. Studies in HEK-293 cells showed that LMNA -R545H reduced the amplitude and resulted in a shift in gating kinetics of the voltage-gated sodium current ( I Na ). These results have not been confirmed in cardiomyocytes. Hypothesis: (1) LMNA -R545H mutation replicates the electrocardiogram (ECG) phenotypes in vivo and (2) there is downregulation of I Na in cardiomyocytes. Methods: We used CRISPR/Cas9 to generate a knock-in mouse model with LMNA -R545H mutation. Isolated cardiomyocytes were used for whole-cell voltage-clamp studies of I Na . Results: Panel (A) shows P, PR, QTc intervals were significantly prolonged and the standard deviation (SD) of the RR intervals was increased during anesthesia in Lmna (R545H+/+) but not in Lmna (R545H+) mice compared with the wild-type control littermates (WT, N=5-8). In Langendorff perfused hearts, the sinus node recovery time (SNRT) and effective refractory period (ERP) were significantly prolonged in the Lmna (R545H+/+) compared with both WT and Lmna (R545H+) . Lmna (R545H+/+) cardiomyocytes showed decreased I Na current density (-20.1±2.3 pA/pF vs. -30.3±3.9 pA/pF, -40 mV, n=7-8, p<.05, Panel B) and prolonged the recovery time constant from I Na inactivation (τ, 36.3±2.2 ms vs. 22.9±1.6 ms, each n=5, p<.05, Panel C). There were no difference in Nav1.5 protein and mRNA levels between the Lmna (R545H+/+) and WT hearts. Conclusions: Homozygous LMNA -R545H mutation leads to reduced I Na , prolonged PR and QTc intervals, and increased sinus arrhythmias.