Potential Role Of MG53 In The Regulation Of Tranaforming-growthfactor-β1-induced Atrial Fibrosis And Vulnerability To Atrial Fibrillation

Background:Atrial fibrosis,the major characteristics of atrial structural remodeling,plays a critical role in promoting atrial fibrillation(AF)initiation and maintenance which via the transforming growth factor-β1(TGF-β1)/Smad pathway.The proliferation and migration of atrial fibroblasts are significant in the progress of atrial fibrosis.MG53,also known as,is most abundantly expressed in rat and mouse myocardium and has multiple biological functions.However,the biological and pathological roles of it in cardiac fibrosis remain elusive.Methods:Thirty right atrial specimens obtained from patients undergoing corrective heart surgery were divided into three groups:patients with congenital heart disease and sinus rhythm(CHD +SR)(n=10);patients with rheumatic heart disease and sinus rhythm(RHD+ SR)(n=10);patients with rheumatic heart disease and atrial fibrillation(RHD+AF)(n= 10).Fibrosis was assessed by histological examination,and expression of MG53 and TGF-β1 were evaluated by immunohistochemistry,quantitative real-time PCR and Western blotting.The expression of a-SMA and collagen I were measured by quantitative real-time PCR and Western blotting.The rat atrial fibroblasts isolated from 14-day-old neonatal Sprague-Dawley rats were treated with small interference RNA(siRNA)to silence MG53 and adenovirus to overexpression MG53.TGF-β1,α-SMA,phosphorylated Smad2(pSmad2)and collagen I was measured by Western blotting after transfection.A Boyden chamber assay and scratch-wound assay were used to evaluated the migration of atrial fibroblasts while a cell-counting assay was performed to determine the proliferation of cells.Besides,MG53 was measured by Quantitative Real-Time PCR and Western blotting after stimulating of TGF-β1.Results:The histology results showed a gradually increase of atrial fibrosis in patients of CHD + SR,RHD + SR and RHD + AF groups.The expression of mRNA and protein levels of MG53,TGF-β1,α-SMA and collagen I raised correspondingly among CHD + SR,RHD + SR and RHD + AF groups.The transfection of atrial fibroblasts indicate that depletion the MG53 can cause down-regulation of the transforming growth factor(TGF)-β1 signaling pathway,while the overexpression of MG53 can up-regulate of the pathway.Besides,MG53 can regulate the proliferation and migration of atrial fibroblasts.And exogenous TGF-β1 can hold in the expression of MG53.Conclusions:Our study has,for the first time,demonstrated that MG5 3 has expressed in human atrium,and increased with the extend of atrial fibrosis which can induce atrial fibrillation.We have concluded that MG53 is may be a potential upstream of TGF-β1/Smad pathway in human atrium and rat atrial fibroblasts which suggests that it may be implicated in TGF-β1/Smad pathway-induced atrial fibrosis in patients with AF.