Study of the cardiac sodium channel in a mouse model of Scn5a haploinsufficiency towards a novel approach of therapy

Abstract

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Sorbonne Université doctoral scolarship INSERM Introduction Brugada syndrome (BrS) is an inherited cardiac arrhythmia that greatly increases the risk of sudden death as a result of ventricular fibrillation. Approximately 20% of BrS cases can be attributed to a mutation in SCN5A, the gene encoding the alpha-subunit Nav1.5 of the cardiac sodium-channel, which carries the sodium current INa. These mutations typically lead to loss-of-function of Nav1.5, resulting in a decrease in INa and most of them (»70 %) are responsible for haploinsufficiency. In the Scn5a+/- mouse model, a sodium-channel dysfunction phenotype is observed, characterized by conduction abnormalities (PR and QRS interval prolongation), a 50% reduction in INa, and an increased susceptibility to arrhythmias. Aim The aim of this study was to assess the impact of the overexpression of a Nav1.5-peptide, which has been found to enhance INa, in Scn5a+/- mice, as a novel approach of therapy. Methods We used AAV9-systemic injection to overexpress the Nav1.5-peptide into the heart of Scn5a+/- mice to gauge their susceptibility to arrhythmias induced by intracardiac pacing. We also examined the Nav1.5-peptide effects on endogenous Nav1.5 expression through molecular biology and biochemistry analyses. Results The duration of PR and QRS intervals in the hearts of Scn5a+/- mice was restored to normal by overexpression of the Nav1.5-peptide (PR interval = 46.3 ± 0.9 ms, n=22 in Scn5a+/- mice vs 40.4 ± 0.8 ms, n= 23 in WT mice, P<0.0001 and 42.6 ± 0.9 ms, n=11 in Scn5a+/- +Nav1.5-peptide, P<0.05; QRS interval = 15.2 ± 0.4, n=22 ms in Scn5a+/- mice vs 13.2 ± 0.4 ms, n=23 in WT mice, P<0.01 and 13.6 ± 0.4 ms, n=14 in Scn5a+/- +Nav1.5-peptide, P<0.05). Additionally, overexpression of the Nav1.5-peptide seemed to protect Scn5a+/- mice from induced arrhythmic events caused by programmed-ventricular stimulation (total premature beats = 1.3 ± 0.4 in Scn5a+/- mice, n = 13 vs 0.2 ± 0.2, n = 6 in injected Scn5a+/- mice, NS and 0.2 ± 0.2, n = 12 in WT mice, P< 0.05). There were no significant differences in total Nav1.5 expression between injected and non-injected mice as shown by RT-qPCR and Western-blots, but the expression of Nav1.5 at the plasma membrane appeared to be restored by overexpression of the Nav1.5-peptide (Nav1.5/N-cadherin ratio = 0.50 ± 0.08, n = 11 in Scn5a+/- mice vs 1 ± 0.15, n= 11 in WT mice, P< 0.05 and 0.94 ± 0.13, n = 11 in injected Scn5a+/- mice, P< 0.05). Conclusion Gene therapy with Nav1.5-peptide can attenuate both conduction defects and increased arrhythmia inducibility observed in Scn5a+/- mice. Although additional studies will be needed to confirm and explore further our results, this could be promising to treat patients with « sodium-channel dysfunction » such as BrS.