Mechanisms underlying dysfunctional CaV1.2 and NaV1.5 function during Brugada syndrome.in the heart

In heart, cardiac action potential is regulated by regulated ion influx through many ion channels including voltage-gated Na+, Ca2+, and K+. Inherited and acquired mutations in these ion channels underlie life-threatening cardiac arrhythmias and diseases. Brugada syndrome (BrS) is a genetically inherited cardiac disease characterized by ST segment elevation, ventricular tachycardia and ventricular fibrillation. Patients with this disease are at increased risk of sudden cardiac death and sudden unexplained death syndrome. Currently more than 300 mutations in 10 genes have been known to be associated with BrS predominantly the NaV1.5 and CaV1.2 channels. The mechanisms and molecular determinants controlling NaV1.5 and CaV1.2 mutant channels have not been rigorously tested in heart cells owing to the large size of the pore forming subunits of these channels. This deficit is a critical barrier to fundamental understanding of how BrS mutations in these channels lead to cardiac disease. Our long-term objective is to understand the precise molecular mechanisms underlying suppressed NaV1.5 and CaV1.2 channel function in heart across a spectrum of BrS NaV1.5 and CaV1.2 mutations and to bridge the insights to advance personalized therapy for BrS and cardiac arrhythmias. We propose two specific aims: 1. Elucidate the impact of distinct BrS mutations in CaV1.2 on cardiac action potential and trafficking of mutant channels in heart cells and determine underlying mechanisms. We hypothesize that the two mutations in CaV1.2 A39V and G490R known to be a causal factor in BrS type 3, disrupt channel function by a combination of biophysical and trafficking defects and that elucidating the functional impact of these mutations directly in cardiomyocytes will be more predictive of the underlying mechanisms. 2. Determine the mechanisms by which 4 BrS mutations in NaV1.5 - R965C, A997S, E1784K and D1816VfsX7 suppress channel function using mutant channels expressed in adult cardiomyocytes. We hypothesize that unique BrS mutations in SCN5A cause disease due to a combination of unique biophysical and trafficking abnormalities, and that identifying the underlying molecular mechanisms governing SCN5A dysfunction directly in cardiomyocytes will be more indicative of disease penetrance. (AHA Program: Scientist Development Grant)