Abstract 2812: A Possible Mechanism of Reduced Sodium Current in Human Heart Failure
Background: Voltage-gated Na+ channels (SCN5a) are responsible for generating the main current for excitation propagation in heart. SCN5a current is reduced in heart failure, and this may contribute to the associated sudden death risk. The mechanism for current reduction is unknown. Recently, we have identified three truncated mRNA splice variants, designated as E28B, E28C, and E28D. E28C and E28D have been shown upregulated in heart failure. We investigated the mechanism whereby these variants are upregulated and have a dominant negative effect on SCN5a current.
Methods: Human Jurkat cells express SCN5a and were treated with hypoxia (0% O2) or Angiotensin II (AngII; 200nM). The total RNA was extracted at 4 time points (30 min, 24h, 48 h, and 72h). The expression of SCN5a and variants, signaling molecule HIF-α, downstream splicing factors hLuc7A and RBM25, and the unfolded protein response protein PERK were measured by RT-PCR. β-actin was used as an internal control. Cells were exposed to siRNA specific to HIF-α, hLuc7A, RBM25, and PERK for 48h prior to treatment with AngII or hypoxia and then examined by RT-PCR. 05), associated with 50±6% (p<0.05) and 40±5% (p<0.05) increases in SCN5a variant C; 40±6% (p<0.05) and 45±6% (p<0.05) increases in variant D mRNA abundances, respectively. This upregulation could be blocked by siRNA for HIF-α, hLuc7A, or RBM25. PERK, a key signaling molecule in the unfolded protein response (UPR), is also induced 250±13 % (p<0.05) by hypoxia or 150±16% (p<0.05) by AngII. siRNA to PERK partial reversed the SCN5a downregulation caused by hypoxia or AngII.
Conclusion: Splicing pathway HIF-1 α/hLuc7A/RBM25 may responsible for SCN5a variant upregulation in human heart failure. SCN5a variants likely have their dominant negative effect on the full length channel by activation PERK-mediated UPR. These molecules may provide new targets for arrhythmia risk mitigation in human heart failure.
This research has received full or partial funding support from the American Heart Association, National Center.