Abstract 927: Heart Failure is Associated with Abnormal C-Terminal Splicing Variants of the Cardiac Sodium Channel
Background: Heart failure and loss of function of the cardiac Na+ channel (SCN5A) increase arrhythmic risk. We hypothesized that abnormal transcriptional regulation of this important ion channel during heart failure could contribute to arrhythmic risk.
Methods: SYBR quantitative RT-PCR was used to detect and characterize SCN5A mRNA splicing variants. Physiological significance was assessed by a gene-targeting strategy.
Results: We identified three novel C-terminal SCN5A mRNA splicing isoforms predicted to result in nonfunctional channels. In the ventricles of 13 heart failure patients, two of the isoforms were upregulated by 88.8% (p<0.01) and 70.4% (p<0.01), whereas the normal isoform was downregulated by 50.6% (p<0.01) when compared to patients with normal cardiac function. A gene-targeted mouse with a premature stop codon designed to mimic the effects of the abnormally spliced mRNA resulted in embryonic lethality. Whole-cell patch clamp analyses of ESC-derived cardiomyocytes expressing the truncation at one allele showed profound slowing of the action potential (AP) dV/dt and a shortening of AP duration. ESC-derived syncytial cardiomyocytes showed reductions in Na+ channel-dependent parameters, the extracellular field potential (FP) minimum and the FP rate of rise by 70.5% (p<0.05) and 45.5% (p<0.05), respectively. We identified all three splice variants in human lymphocytes, raising the possibility of future predictive testing.
Conclusion: We identified three novel mRNA splicing variants predicted to result in nonfunctional Na+ channels. These mRNA variants were increased in heart failure. A model of these variants suggested they were likely to have physiological relevance.