Basic/Translational Science -> Intact Heart Electrophysiology (includes Pharmacology and Optical Mapping) D-BT01 - Cardiac Electrophysiology Society (CES): Lunch and Young Investigator Award Poster Session (ID 41) Special Session

D-BT01-02 - The Role Of Novel Brugada Syndrome Gene MAPRE2 In Cardiac Electrophysiology (ID 11)

Abstract

Background: Brugada syndrome (BrS) is a significant cause of sudden cardiac death in young men with structurally normal hearts. Despite recent advances, only ~30% of BrS has a known genetic cause. A recent GWAS found 9 novel loci associated with BrS, including one near MAPRE2, which encodes microtubule end-binding protein 2.
Objective: To understand the role of MAPRE2 in cardiac electrophysiology and BrS pathogenesis.
Methods: Using CRISPR/Cas9, a loss-of-function mutant of the highly homologous mapre2 was generated in zebrafish. Cardiac function of 3 day-post-fertilization (dpf) embryos was measured using high-speed videos while isolated hearts were optically mapped using a voltage-sensitive dye. Adult fish were studied using surface ECG while isolated ventricular myocytes were studied using patch clamp.
Results: No increased mortality, structural abnormalities, or cardiac dysfunction were observed at 3dpf in the mapre2 KOs compared to WT siblings. However, voltage mapping of isolated hearts at 3dpf (WT, n=7 vs. KO, n=12) showed a significant decrease in ventricular conduction velocity (31.4±3.7 vs. 21.1±3.0 mm/s; P<0.05) and action potential (AP) upstroke velocity (Vmax; 98.6±2.5 vs. 81.2±7.6 1/s; P<0.05), as well as a significant increase in ventricular AP duration (APD) at 80% repolarization (260±16 vs. 346±29 ms; P<0.05). ECG of adult fish (WT, n=5 vs. KO, n=6) showed a decrease in HR under the same level of tricaine anesthesia (123±8 vs. 93±4 bpm; P<0.05), and an increase in QRS duration (33.3±2.1 vs. 42.9±1.6 ms; P<0.01) and QTc (352±18 vs. 437±17; P<0.05). Patch clamp of isolated ventricular myocytes (WT, n=13 vs. KO, n=11) showed a significant decrease in Vmax (165±12 vs. 91±10 1/s; P<0.0001) and ≈45% reduction in Na+ current density (P<0.05) without changes in the (in)activation curves. Furthermore, there was a significant increase in APD at 90% repolarization in the KOs (170±9 vs. 219±11 ms; P<0.01).
Conclusion: Genetic ablation of mapre2 led to a decrease in Na+ current function, a hallmark of BrS. Furthermore, mapre2 ablation led to significant APD prolongation which may be related to an increase in late Na+ current and/or dysfunction in Ca2+ or K+ currents. Taken together, MAPRE2 may be a novel causative gene in a subset of BrS patients.
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