Generation and characterization of SCN5A loss-of-function mutant mice modeling human brugada syndrome

Purpose: Loss-of-function mutations of the cardiac sodium channel are associated with arrhythmic disorders including Brugada syndrome and isolated cardiac conduction disease (ICCD). Brugada syndrome is characterized by a strong male predominance, while female mutant carriers often show isolated signs of ICCD. In this study we analyzed the effect of the human SCN5A-G1408R mutation in vivo using a mouse knock-in model. Methods: Mice carrying the human SCN5A mutation G1408R were generated by homologous recombination. Ten to twelve month old heterozygous mutant and WT mice were analyzed using surface ECG, telemetric recordings of conscious mice, electrophysiological studies of Langendorff-perfused hearts and patch-clamp electrophysiology of isolated cardiomyocytes. Histological analysis included hematoxylin/eosin and Masson trichrome staining. Results: Homozygous animals die before birth, while heterozygous are viable. Mutant mice exhibit sinus node and conduction disease with prolongation of sinus node recovery time, PR-interval, P wave duration and QRS interval. Administration of flecainide (10mg/kg BW i.p.) aggravated conduction disturbances (high grade SA and AV block) of mutant mice, indicating a reduced conduction reserve in mutant animals. Remarkably, 80% (12/15) of male G1408R animals developed ventricular tachycardias (VT) after injection of flecainide, while only 14% (2/14) of their female littermates and 0% (0/14) of WT animals showed VT, indicating male predominance in the susceptibility towards VT. Electrophysiological analysis of Langendorff-perfused hearts showed a significant prolongation of activation times and longer ventricular effective refractory periods while monophasic action potentials were shortened in hearts from mutant vs. WT animals. Patch-clamp electrophysiology revealed significantly decreased sodium current densities in cardiomyocytes from mutant animal hearts. Histological analysis indicated no apparent structural abnormalities among mutant animals of both genders except for mild age dependent interstitial fibrosis similar to WT controls. Conclusions: We report the generation of SCN5A-G1408R knock-in mice, characterized by male predominance for ventricular tachyarrhythmias and female association with conduction disorders. The model closely resembles the human disease and offers a valuable tool for the investigation of disease triggers and modifying mechanisms.