The Research Of SCN5A Mutations Participate In The Molecular Disease Mechanism Of Left Ventricular Noncompaction Cardiomyopathy Occurring Arrhythmia

Background:Voltage gated sodium channel is one of the most important depolarization cation channels in myocardial cell membrane.It determines the formation and amplitude of phase 0 action potential.SCN5A sodium channel(Nav1.5 protein channel)is the main sodium channel subtype in the heart,which is composed of sodium channel a Subunits and β Subunits.The SCN5A gene encodes the Nav1.5 channel a Subunits,and determine the biophysical function of the channel,β Subunits play an auxiliary role in regulating channel function.SCN5A sodium channel widely exists in atrial,ventricular and Purkinje fibers.It is the target protein of class I antiarrhythmic drugs.Mutations in cardiac sodium channel SCN5A can induce gain or loss of channel function.Gain-of-function mutations can induce long QT syndrome type 3(LQT3)and possibly atrial fibrillation(AF),but loss-of-function mutations are related to a variety of phenotypes,such as Brugada syndrome(BrS),sick sinus syndrome,cardiac conduction disease and possibly dilated cardiomyopathy.The phenotypes caused by SCN5A mutations vary due to the direct effect of the mutation on channel biophysical characteristics,but also with age,body temperature,sex and between regions of the heart.This variability of clinical phenotype makes genotype-phenotype correlations difficult.Previous studies focused on SCN5A gene mutation directly affecting the biophysical function of channel,leading to LQT3,AF,dilated cardiomyopathy,sick sinus syndrome and other cardiomyopathy.However,in recent years,studies have shown that SCN5A mutation is also found in some patients with structural cardiomyopathy,such as left ventricular noncompaction cardiomyopathy(LVNC),and the proportion of patients carrying the mutation is not low.Because the main clinical manifestations of LVNC are malignant arrhythmia,sudden death and acute heart failure,we speculate that ion channel mutation plays a pathogenic role.Therefore,we conducted study deeply on whether SCN5A mutation is a pathogenic factor of arrhythmia in patients with LVNC.Objective:To investigate the contribution of SCN5A variants to Left Ventricular Noncompaction Cardiomyopathy with ventricular tachycardia or arrhythmia.Methods:We recruited 27 cases with LVNC who underwent heart transplant in our hospital.We showed seven heterozygous single-nucleotide SCN5A variants by Exome-sequencing,and functionally analyzed these variant channels by patch clamping.SCN5 A wild-type plasmids and these SCN5A mutant plasmids were constructed by molecular cloning and point mutation techniques in vitro.The wild-type SCN5A channel and the mutant SCN5A channel were expressed on the membrane of CHO-K1 model cells and human induced pluripotent stem cells(iPS-CM)cells by liposome transfection and adenovirus vector,respectively.The electrophysiological differences between mutant and wild-type SCN5A ion channels were detected by patch clamp technique and CardioExcyte 96 system.Results:We found that nearly half(44.4%)of the 27 sporadic patients with Left ventricular noncompaction carry the sodium channel alpha-subunit gene(SCN5A)variants(H558R、G292S、P1090L、V1951L、R1193Q、R1195H、A1180V).These patients accompany with ventricular tachycardia and arrhythmia.The biophysical characteristics of variant channels expressed in CHO-K1 cell are different from human iPS-derived cardiomyocytes(Ips-CM).These variants are almost gain of function through enhancing the activation of channels(R1195H、V1951L)or undermine the fast inactivation of the channel(P1090L).Moreover,whether the six variant channels are expressed on CHO-K1 or iPS-derived cardiomyocytes,the slow inactivation are all weakened.When expressed in iPS-derived cardiomyocytes,the recovery from inactivation of variants is much slower.The field potential firing frequency increased,and the filed potential durations became shorter.The beat rate and pulse width(90%)were changed.Arrhythmia like fibrillation was observed in cardiomyocytes.It implies that changes of electrophysiological characteristics of the variant SCN5A channels may be one of the causes of arrhythmia in LVNC patients.in addition,The SCN5A protein level in the left ventricular myocardial tissues of patients with LVNC is decreased but increased in HCM heart tissues.It implies that decrease of SCN5A protein in LVNC heart tissues may be also involved in the pathophysiology of LVNC.Conclusions:Mutations in the SCN5A are involved in the pathophysiology of LVNC and responsible for a large fraction of Left Ventricular Noncompaction Cardiomyopathy with ventricular tachycardia or arrhythmia.