A Heart Failure-Associated SCN5A Splice Variant Leads to a Reduction in Sodium Current Through Coupled-Gating With the Wild-Type Channel

Abstract

Nav1.5, encoded by the gene SCN5A, is the predominant voltage-gated sodium channel expressed in the heart. It initiates the cardiac action potential and thus is crucial for normal heart rhythm and function. Dysfunctions in Nav1.5 have been involved in multiple congenital or acquired cardiac pathological conditions such as Brugada syndrome (BrS), Long QT Syndrome Type 3, and heart failure (HF), all of which can lead to sudden cardiac death (SCD) – one of the leading causes of death worldwide. Our lab has previously reported that Nav1.5 forms dimer channels with coupled gating. We also found that Nav1.5 BrS mutants can exert a dominant-negative (DN) effect and impair the function of wildtype (WT) channels through coupled-gating with the WT. It was previously reported that reduction in cardiac sodium currents (INa), observed in HF, could be due to the increased expression of an SCN5A splice variant – E28D, which results in a truncated sodium channel (Nav1.5-G1642X). In this study, we hypothesized that this SCN5A splice variant leads to INa reduction in HF through biophysical coupling with the WT. We showed that Nav1.5-G1642X is a non-functional channel but can interact with the WT, resulting in a DN effect on the WT channel. We found that both WT and the truncated channel Nav1.5-G1642X traffic at the cell surface, suggesting biophysical coupling. Indeed, we found that the DN effect can be abolished by difopein, an inhibitor of the biophysical coupling. Interestingly, the sodium channel polymorphism H558R, which has beneficial effect in HF patients, could also block the DN effect. In summary, the HF-associated splice variant Nav1.5-G1642X suppresses sodium currents in heart failure patients through a mechanism involving coupled-gating with the wildtype sodium channel.

Trafficking and Gating Cooperation Between Deficient Nav1.5-mutant Channels to Rescue INa

“…We have also evidenced that Na v 1.5 α-subunits form dimers through an interaction site located in the domain I-II linker, and that Na v 1.5 channels not only interact but also gate as dimers [10]. More recently, we and others reported that dominant negative suppression exerted by Na v 1.5 mutants could also be caused by impairing the WT gating probability, a mechanism resulting from the coupled gating of Na v channel α-subunits [6,8,11]. Altogether, these observations led us to examine the capacity of Na + channels to transcomplement trafficking or gating-deficient mutant channels to rescue I Na .…”

“…Unlike potassium channel genes, which encode one fourth of tetramers constituting functional channels, Na v 1.5 channels were thought to be structured as monomers, since the gene encodes the entire 4domain channel α-subunit. It was thus unexpected to report Na v 1.5 mutants with a dominant-negative effect on wildtype (WT) channels, i.e., a decrease of I Na exceeding the 50% of current density expected in case of haploinsufficiency observed when coexpressing some mutants with WT channels in a 1:1 ratio to mimic patient heterozygosity, as we and others did [2][3][4][5][6][7][8][9]. Furthermore, we demonstrated that Na v 1.5 α-subunits could interact with each other and that a trafficking-efficient mutant channel was able to drive a trafficking-deficient one to the surface membrane [3].…”

“…However, we recently established that Na + channels were able to interact and form functional dimers [3,10,11]. We also demonstrated that voltage-gated Na + channels display coupled gating properties [6,10,11], a central mechanism for proper propagation of the action potential in cardiac cells. So far, such a gating cooperation has been described to explain a dominant-negative effect of mutant non-functional Na v 1.5 channels on WT channels [6,10,11].…”

“…In recent studies [6,11], we reported that dominant negative effect of mutant Na v 1.5 channels was not only exerted through trafficking but that coupled gating could also be involved. This led us to hypothesize that such gating transcomplementation could, conversely, rescue I Na .…”

Dominant negative effects ofSCN5Amissense variants

“…The multifunctional regulatory protein 14-3-3 has been reported to be critical for mediating Na V 1.5 dimerization, and an operative mechanism in select cases of the dominant negative effect (8). Indeed, difopein, an inhibitor of 14-3-3, (37) was shown to restore WT activity when co-expressed with dominant negative variants (8, 38). While targeting 14-3-3 may not be an appropriate therapeutic strategy given its role in myriad cellular processes, alternative mechanisms to promote selective degradation of aberrant channels and preserve WT function remain highly desirable.…”