National Heart, Lung, and Blood Institute 5R01HL163979-04

A Versatile Chemical-Genetic Approach to Determine Bases for Arrhythmogenesis and Sodium Channelopathies

This NIH-funded project at University of Iowa develops a chemical-genetic mouse model to study cardiac sodium channel NaV1.5's role in arrhythmias and cardiomyopathies by enabling acute, reversible channel silencing, aiming to elucidate mechanisms of SCN5A mutations and their effects on cardiac function.

Description

The voltage-gated sodium channel NaV1.5 controls cardiac excitability and is an established therapeutic target. Mutations in the SCN5A gene, which encodes NaV1.5, are associated with inherited arrhythmia syndromes (long QT syndrome, Brugada syndrome, congenital heart block) and dilated cardiomyopathy. While gain of function mutations that disrupt NaV1.5 inactivation explain action potential duration (APD) and QTc prolongation, the mechanisms by which loss of function NaV1.5 mutations cause the other diverse pathogenic outcomes are unresolved. The physiological significance of other Na+ channel genes expressed in the heart are also uncertain. Rodent models with gene-targeted Scn5a mutations can recapitulate some clinical features of disease, but their use is complicated by compensatory mechanisms that may occur early in development. In addition, the available pharmacological blockers of NaV1.5 block brain Na+ channels and other potential cardiac Na+ channels with equal or greater potency, limiting their utility. To advance understanding, a chemical-genetic model has been developed to achieve acute and reversible silencing of NaV1.5 in situ. This involves engineering a NaV1.5 channel with a high-affinity, isoform-specific binding site for GX drugs, enabling pharmacological control. CRISPR gene-editing replaced the endogenous Scn5a locus with this site in mice, creating a NaV1.5GX strain. Homozygous NaV1.5GX/GX mice have normal cardiac phenotypes, but application of GX compounds ablates Na+ current, allowing study of NaV1.5 function and SCN5A-mediated disease. The project will examine effects of acute NaV1.5 blockade on gene expression, calcium handling, ROS production, fibrosis, cardiac function, and arrhythmias, and compare to chronic blockade. It will also study structural and electrophysiological remodeling and develop platforms to study SCN5A mutations.

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