Molecular Mechanism Of Familiar Atrioventricular Block And Dilated Cardiomyopathy Induced By A Novo Complex Mutation Of LMNA

Background: Atrioventricular Block(AVB)is a kind of arrhythmia caused by abnormal electrical conduction between the atria and ventricles during the electrical stimulation of the heart.AVB can be divided into three degrees: the first degree,the second degree and the third degree according to the different severity of block.In recent years,association between AVB and familial heredity are reported and a series of pathogenic genes have been identified.In earlier clinic study,we found a family which have been diagnosed with the third degree atrioventricular block and dilated cardiomyopathy,and the present study focused on the disease pathogenic genomic mechanism.Methods and Results: Sanger sequencing was used to analyze the pathogenicity of the reported pathogenic genes,including TRPM4,SCN5 A,SCN1B,NKX2.5,CLCA2 and LMNA,related to the atrioventricular block and dilated cardiomyopathy.We construct the plasmid of wild type and mutant of pathogenic gene(LMNA),then transfect into Hela cell lines.The subcellular localization of the wild type and mutant was detected through Laser confocal microscopy(FV1000,Olympus).The expression of protein level was analyzed by Western-blot.Genetic analysis and the sequencing results showed that there was a complex mutation in LMNA gene.The results of Western-blot showed that the expression of mutant was abnormal and the results of subcellular localization indicated that the wild-type was located in the nuclear membrane of the nucleus,but the mutant was located in both nuclear membrane and nuclear.When the function of LMNA is abnormal,it can lead to the death and fibrosis of the atrioventricular node cells,and the decrease of the atrioventricular conduction rate and the occurrence of atrioventricular block.Autophagy and apoptosis are important forms of cell death,LC3-Ⅱ is one of the most important protein in the process of autophagy and always been used as a molecular marker of autophagy.Western-blot was used to make sure if the autophagy have occurred,but the result showed that the expression of LC3-Ⅱprotein did not changed in cells transfected with the LMNA mutational plasmid.Discussion and Conclusion: In the present study,we identified a novo mutation,the mutation of this kind can make the protein encoded by the gene can not be correctly located in the cell nuclear membrane,which leads to the abnormal structure of the nuclear lamina.The nuclear lamina showed a cyclical changes in cell division,so the abnormal nuclear layer will have an important effect on the normal cell morphology,cell signal transduction and normal cell cycle,which leads to the abnormal cell death.Abnormal death of cells may be the cause of AVB in the family members.LMNA gene has previously been reported to associated with Alzheimer disease,familial partial lipodystrophy,limb girdle muscular dystrophy and other laminopathy,but the relationship between hereditary atrioventricular block and LMNA gene is not reported domestically.This is the first time in our study found that atrioventricular block and lamin gene LMNA has a direct correlation.By the way,this kind of new complicate mutation have not yet been reported.So our discovery not only enriches the LMNA gene mutation type library,but also provide a new pathway for the prevention of atrioventricular block and the further study of the pathogenesis of the disease.