Cardiac Arrhythmia

The general focus of Dr. Jalife's laboratory is the understanding of the cellular and molecular mechanisms of arrhythmias and sudden cardiac death (SCD).

The objective is to understand the emerging role of macromolecular ion channel complexes in the mechanisms of SCD in inherited diseases. Our recent identification of the interaction of the main sodium channel in the ventricles (NaV1.5) with the rectifying potassium channel (Kir2.1) in the control of cardiac excitability offers an exceptional opportunity to define the molecular basis of SCD. Evidence indicates that NaV1.5 and Kir2.1 form "channelosomes" and that they physically interact with partner proteins (adapters, scaffolds, and enzymes that regulate the function of electrical currents). Both channels have direct links to inherited diseases known as “channelopathies”. The Andersen-Tawil Syndrome type 1 (ATS1), also known as Long QT Syndrome type 7, is mediated by loss-of-function mutations in the gene KCNJ2 that encodes the inward rectifier potassium channel Kir2.1. Gain-of-function mutations in the same gene cause Short QT Syndrome type 3 (SQTS3). Loss-of-function defects in SCN5A, the gene that encodes the main cardiac sodium channel NaV1.5, give rise to Brugada Syndrome (BrS). On the other hand, defects in the dystrophin gene that result in Duchenne Muscular Dystrophy (DMD) lead to dysfunction of both Kir2.1 and NaV1.5, leading to arrhythmias and SCD, which further highlights the relevance of the interaction of ion channels with other multiple proteins in the mechanisms of heart diseases.

Cardiac Arrhythmia

Our approach is multidisciplinary, and includes the use of transgenic mouse models generated by adeno-associated virus (AAV) mediated gene transfer, as well as human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) made from somatic cells (epithelial fibroblasts) of patients carrying a given mutation or normal hiPSC-CMs modified by CRISPR/Cas9 genomic editing. We can implement this technology thanks to established collaborations with three different hospitals in Spain, Virgen de las Nieves Hospital in Granada, La Fe Hospital in Valencia and Central University Hospital of Asturias in Oviedo.

We use a wide variety of mutually complementary technologies to understand the electrophysiological mechanisms underlying the inheritable disease under study, including electrocardiogram (ECG), intracardiac stimulation, patch-clamping, optical mapping, RNAseq, Western blotting, proteomics, and immunocytochemistry.

Our most recent findings include the exciting discovery that iPSC-CM from patients with DMD have a dysfunctional NaV1.5-Kir2.1 channalosome that can be rescued by scaffolding protein α1- syntrophin (SNTA1 gene), restoring ion channels in the membrane (published in the journal eLife). Consequently, cell excitability is increased, and arrhythmias are prevented in cardiomyocytes derived from DMD patients. In addition to this, we have generated an AAV-mediated cardiac-specific mouse model of ATS1 expressing a trafficking-deficient mutant protein (Kir2.1∆314-315), which reproduces the cardiac electrical defects observed in patients with ATS1. These defects are due to a dual dysfunction produced by the KCNJ2 mutation: one in the sarcolemma, which results in reduced excitability and abnormal conduction, and the other in the sarcoplasmic reticulum, where the SR Kir2.1 mutant channels directly alter calcium dynamics across the sarcoplasmic reticulum (published in the journal Nature Cardiovascular Research). 

Our studies are complemented by computational modeling of ion channel structure, channel-ligand interactions, and more recently antiarrhythmic drug design in parallel with experimentation in human and animal models. Altogether, our studies are expected to yield essential information that should improve antiarrhythmic therapy toward prevention of SCD in patients suffering from inheritable cardiac diseases.