The Electrophysiological Mechanisms Of Short QT Syndrome Induced By Sodium Channel Gene SCN5A Mutation

Background:Short QT syndrome(SQTS)is a highly malignant hereditary arrhythmia with a shortened QT interval on the electrocardiogram and prone to ventricular tachyarrhythmias(ventricular tachycardia and ventricular fibrillation),leading to syncope and sudden cardiac death.The cardiac sodium channel alpha subunit(Nav1.5)encoded by the SCN5 A gene is a key protein that maintains the normal excitability of cardiomyocytes.It has been found that SCN5 A gene mutation is closely related to a variety of hereditary arrhythmias(such as long QT syndrome,Brugada syndrome,hereditary cardiac conduction diseases),the abnormal expression and regulation of Nav1.5 caused by mutation is an important molecular biological basis for the occurrence of arrhythmias.In addition,Nav1.5 binds to a variety of interacting proteins to form a multiprotein complex that is involved in the regulation of sodium channel function.MOG1 protein is a novel sodium channel regulatory protein.Preliminary studies have found that MOG1 can act on sodium channels and promote the transport of Nav1.5 from the intracellular to the cell membrane,but its specific regulatory mechanism remains unclear.Our team’s previous study screened the sodium channel SCN5 A mutation E428 G in a patient with SQTS,but its role in SQTS and the specific pathogenesis are still unclear.pathogenesis of SQTS,but the specific mechanism is still unclear.Objective:The purpose of this study was to investigate the effect of SCN5 A gene mutation(E428G)on the electrophysiological function of sodium channels and the role of MOG1 protein in this process.Methods:The wild-type(WT)plasmid of Nav1.5 and MOG1 were constructed,.At the same time,the mutant(E428G)plasmid was constructed by gene-directed mutagenesis technique using wild-type Nav1.5 as a template.The above plasmidswere transfected into human embryonic kidney 293 T cells(HEK293T),and the experiment was divided into four groups: WT,E428 G,WT+MOG1,E428G+MOG1.Whole cell patch clamp,cell membrane protein separation and immunoblotting technique were used to analyze the electrophysiological properties of sodium ion channels and their expression on cell membranes.Results:(1)Cell electrophysiological studies showed that the E428 G mutation resulted in a 70% increase in peak sodium current,and a 30% reduction in late sodium current,steady state activation(SSA)and steady-state inactivation curve(SSA)revealed a hyperpolarization shift compared to the WT group.In the WT group,the peak sodium current was significantly increased 1.5 times after the expression of MOG1,the SSA curve shifted to the negative polarization direction,and the SSI curve did not shift significantly.However,the E428 G mutant group overexpressed MOG1 revealed that the peak sodium current decreased by 30% significantly,the SSA curve shifted to the negative polarization direction and the SSI curve has no significant offset.In addition,compared with the WT+MOG1 group,the peak sodium current and the late sodium current of the E428G+MOG1 group were reduced by 50% and 30%,respectively,the SSA curve shifted toward the negative polarization direction,and the SSI curve did not shift significantly.(2)Western blots showed that E4258 G increased the sodium channel membrane protein by 1.8-fold compared with the WT group.When overexpressing MOG1,MOG1 increased the sodium channel membrane protein of the WT group by 70%,while MOG1 reduced the expression of sodium channel membrane protein by about37% in the E428 G group.In addition,there was no significant change in cell membrane protein expression of E428G+MOG1 sodium channel compared to WT+MOG1.Conclusion:(1)The E428 G mutation resulted in a significant loss of sodium channel function(late sodium current decreases),which may be the electrophysiological mechanism by which this mutation causes SQTS.(2)MOG1 showed different effects on wild-type and mutant(E428G)Nav1.5:Promoted transport of wild-type Nav1.5 to the membrane and inhibited transport of mutant(E428G)Nav1.5 to the membrane.