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

Abstract

Background: Pathogenic variants in SCN5A, the gene encoding the cardiac Na + channel α-subunit Nav1.5, result in life-threatening arrhythmias, e.g., Brugada syndrome, cardiac conduction defects and long QT syndrome. This variety of phenotypes is underlied by the fact that each Nav1.5 mutation has unique consequences on the channel trafficking and gating capabilities. Recently, we established that sodium channel α-subunits Nav1.5, Nav1.1 and Nav1.2 could dimerize, thus, explaining the potency of some Nav1.5 pathogenic variants to exert dominant-negative effect on WT channels, either by trafficking deficiency or coupled gating. Objective: The present study sought to examine whether Nav1.5 channels can cooperate, or transcomplement each other, to rescue the Na + current (INa). Such a mechanism could contribute to explain the genotype-phenotype discordance often observed in family members carrying Na + -channel pathogenic variants. Methods: Patch-clamp and immunocytochemistry analysis were used to investigate biophysical properties and cellular localization in HEK293 cells and rat neonatal cardiomyocytes transfected respectively with WT and 3 mutant channels chosen for their particular trafficking and/or gating properties. Results: As previously reported, the mutant channels G1743R and R878C expressed alone in HEK293 cells both abolished INa, G1743R through a trafficking deficiency and R878C through a gating deficiency. Here, we showed that coexpression of both G1743R and R878C nonfunctioning channels resulted in a partial rescue of INa, demonstrating a cooperative trafficking of Nav1.5 α-subunits. Surprisingly, we also showed a cooperation mechanism whereby the R878C gatingdeficient channel was able to rescue the slowed inactivation kinetics of the C-terminal truncated R1860X (∆Cter) variant, suggesting coupled gating. Conclusions: Altogether, our results add to the evidence that Nav channels are able to interact and regulate each other's trafficking and gating, a feature that likely contributes to explain the genotype-phenotype discordance often observed between members of a kindred carrying a Na + -channel pathogenic variant.

Cortical Neurons Adjust the Action Potential Onset Features as a Function of Stimulus Type

“…Another explanation for the observed AP initiation properties was associated with the expression of multiple voltage-gated channels or their gating mechanism. Cooperative gating between sodium channels was suggested to reproduce the sharp AP onset and variability in modeling studies [16,33], which was supported by recent evidence in cardiac Na_v1.5 [34][35][36][37]. On the other hand, changes in resting potential could influence neuronal excitability and hence the AP shape.…”

Ion channel trafficking implications in heart failure

“…Variants in the Na + channel were discovered to be linked with a trafficking defect, leading to HF ( 212 ). A recent study demonstrated that two different variants of Nav1.5 can interact with each other to rescue the I Na ( 181 ). Specifically, this study showed that one variant of Na + channel, trafficking-deficient but gating-competent, was able to restore a fraction of the I Na by interacting with another Na + channel variant that was trafficking-competent but gating-deficient.…”

Exploring the Oligomerization of Nav1.5 and Its Implication for the Dominant-Negative Effect

“…12 For instance, some loss-offunction mutants exerting dominant-negative effect were shown to impact biosynthesis, degradation, cell surface addressment, and functional output of the wildtype Na v 1.5 presumably due to oligomerization between the channels. 13,14 Therefore, identification of the sites or domains of Na v 1.5 responsible for its oligomerization could provide new insights into the molecular mechanisms underlying cardiac arrhythmias. This review discusses the current literature describing several proposed mechanisms of Na v 1.5 oligomerization: 1) direct cis-interactions of α-subunits; 2) indirect cis-interactions mediated by 14-3-3 proteins; and 3) indirect cis-and trans-interactions mediated by auxiliary subunits.…”