电重构在心房颤动（房颤）的发生和发展过程中占有重要地位，Cav1.2钙通道是电重构的始动因素和最主要的分子基础。microRNA（miRNA）作为生命科学界研究的新焦点，在心血管系统中的关键调控作用不断得以阐明。本项目组前期通过miRNA芯片技术发现非瓣膜性房颤患者左心耳组织中miR-155的表达上调导致了预测的靶基因CACNA1C和相应Cav1.2蛋白表达下调，更重要的是体外构建报告载体实验发现miR-155可以结合到CACNA1C的3'-UTR区，提示miR-155有可能通过调控Cav1.2的表达，参与了房颤的电重构。本研究拟通过人心房肌细胞和小鼠的房颤模型，结合基因敲除和转基因小鼠，从细胞分子水平和动物实验探讨miR-155调控Cav1.2电重构的机制。本研究不仅对阐明miRNA调控电重构的机制有重要意义，而且为寻找可逆转电重构的新靶点奠定了理论基础，为房颤的上游治疗提供了新的思路。

Atrial fibrillation (AF) is the most common sustained cardiac rhythm disorder, and is associated with pronounced morbidity, mortality, and socio-economic burden. An important acknowledgement is that AF atrial electric remodeling in a way that promotes its occurrence and maintenance. Decreased L-type Ca2+ current (ICaL) is a consistent feature of atrial remodeling and is believed to contribute importantly to the action potential duration abbreviation that shortens refractoriness and promotes AF. Evidence has proved ICaL reduction is associated with transcriptional downregulation of the Cav1.2 (ICaL α-subunit). However, the mechanisms of Cav1.2 downregulation are poorly understood. MicroRNAs (miRNAs) are ~22-nucleotide single-stranded RNAs that inhibit the expression of specific mRNA targets through Watson-Crick base pairing between the miRNA 'seed region' and sequences commonly located in the 3'-untranslated regions. Although the cellular mechanisms and gene mutations responsible for numerous cardiovascular disorders have been extensively studied, it has become apparent only recently that miRNAs have key roles in cardiovascular development and disease. In our previous study which supported by NSFC, the miRNA transcriptome was analyzed by microarray and verified by real-time reverse-transcription polymerase chain reaction with left atrial samples from nonvalvular AF patients and healthy control. MiR-155, miR-142-3p, miR-19b, miR-223, miR-146b-5p, miR-486-5p, miR-301b, miR-193b, miR-519b were found to be upregulated by >2 fold, whereas miR-193a-5p were downregulated. In particular, miR-155 level was elevated by 5.7-fold in AF patients relative to healthy control. Furthermore, computational prediction identified CACNA1C, which encode Cav1.2, as direct targets of miR-155.In the meantime, construction of reporter plasmids and reporter assays showed that miR-155 represses the Luciferase activity of the 3' untranslated regions of CACNA1C. This work reveals a potential link between the regulation of Cav1.2 and miR-155. In this application, we are going to test this hypothesis. We plan to combine in vitro culture model of human atrial cardiomyocytes and AF mice to assess (1) whether miR-155 contributes ICaL reduction and Cav1.2 downregulation in vivo cellular electrophysiological remodeling by patch clamp and single-cell RT-PCR; (2) whether forced expression of miR-155 is able to recapitulate the phenotypes of AF and Cav1.2 remodeling with a miR-155 transgene mouse model; and (3) whether downregulation of endogenous miR-155 could reduces AF vulnerability and prevent Cav1.2 remodeling with a miR-155 knock down mouse model. The accomplishment of this application will provide a new understanding of underlying mechanisms of atrial remodeling to allow for the definition of novel molecular targets in AF. And it is tempting to pave the avenue for more specific novel drug targets and potential for developing that missing pharmacopeia for AF.