Sorbonne Université, Inserm, Research Unit on Cardiovascular and Metabolic Diseases, UMRS-1166, 75013 Paris, France.
Division of Neurology, Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA.
Front Biosci (Landmark Ed). 2022 Jun 30;27(7):209. doi: 10.31083/j.fbl2707209.
Pathogenic variants in , 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.
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.
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.
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 gating-deficient channel was able to rescue the slowed inactivation kinetics of the C-terminal truncated R1860X (ΔCter) variant, suggesting coupled gating.
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.
编码心脏钠离子通道 α 亚基 Nav1.5 的 基因中的致病变体可导致危及生命的心律失常，例如 Brugada 综合征、心脏传导缺陷和长 QT 综合征。每个 Nav1.5 突变对通道运输和门控能力产生独特的后果，这导致了多种表型。最近，我们发现钠离子通道 α 亚基 Nav1.5、Nav1.1 和 Nav1.2 可以二聚化，从而解释了一些 Nav1.5 致病变体通过运输缺陷或偶联门控对 WT 通道发挥显性负效应的能力。
本研究旨在探讨 Nav1.5 通道是否可以相互合作或互补，以挽救钠离子电流（INa）。这种机制可能有助于解释携带钠通道致病变体的家族成员中经常观察到的基因型-表型不一致。
使用膜片钳和免疫细胞化学分析，分别在转染 WT 和 3 种突变通道的 HEK293 细胞和大鼠新生心肌细胞中研究生物物理特性和细胞定位。这 3 种突变通道是根据其特定的运输和/或门控特性选择的。
正如先前报道的，单独在 HEK293 细胞中表达的突变通道 G1743R 和 R878C 均使 INa 完全失活，G1743R 通过运输缺陷，而 R878C 通过门控缺陷。在这里，我们表明，非功能的 G1743R 和 R878C 两种突变通道的共表达导致 INa 的部分恢复，表明 Nav1.5 α 亚基的运输具有协同作用。令人惊讶的是，我们还发现了一种协同作用机制，其中 R878C 门控缺陷通道能够挽救 C 端截断 R1860X（ΔCter）变体的缓慢失活动力学，表明偶联门控。
总之，我们的结果进一步证明了 Nav 通道能够相互作用并调节彼此的运输和门控，这一特性可能有助于解释携带钠通道致病变体的家族成员之间经常观察到的基因型-表型不一致。
