Abstract 19435: Critical Role of microRNAs miR-26 and miR-101 in Atrial Electrical Remodeling in Experimental Atrial Fibrillation
A prominent finding in electrical remodeling in atrial fibrillation (AF) is a shortening of refractory period favoring reentry, which is primarily due to a shortening of atrial action potential as a result of two critical changes: reduction of L-type Ca2+ current ICaL and increases in inward rectifier K+ current IK1. We have previously identified miR-328 as a critical determinant for depressed ICaL in AF. We report here that miR-26 and miR-101 play a significant role in upregulating IK1 in AF. Deregulated miRNAs in a canine model of AF induced by atrial tachypacing were first identified by microarray and subsequently verified by real-time RT -PCR. We found miR-26 and miR-101 being significantly downregulated in AF. We then verified KCNJ2 encoding Kir2.1 protein for IK1 as a cognate target for miR-26 and miR-101. Transfection of miR-26 or miR-101 reduced Kir2.1 protein level whereas application of the miR-26 antisense oligomers (AMO-26) to knockdown endogenous miR-26 caused a robust increase in Kir2.1 level, indicating a relief of tonic repression of Kir2.1 by endogenous miR-26. By comparison, transfection of AMO-101 alone only slightly up-regulated Kir2.1, which can be explained by the higher abundance of miR-26 than miR-101 in cardiac cells. Accordingly, miR-26 or miR-101 depressed whilst AMO-26 or AMO-101 enhanced, IK1 current density, with whole-cell patch-clamp recordings. We then characterized the core promoter regions of miR-26 and miR-101 genes and identified NFAT, a transcription factor which has been shown to be enhanced in its activity in AF, as a transcriptional repressor of these two miRNA genes. Further, application of in vivo knockdown oligo against miR-26 or miR-101 to mice enhanced the AF vulnerability as indicated by the reduced number of animals with successful induction of AF and shortened duration of AF once induced. Our study therefore revealed that miRNAs are critically involved in AF and the associated atrial electrical remodeling. It is likely that enhanced NFAT activity in AF downregulates miR-26 and miR-101 transcription, which results in relief of repression of KCNJ2/Kir2.1 thereby an increase in IK1, leading to shortening of atrial action potential and creating the substrate for AF and AF remodeling.
- © 2010 by American Heart Association, Inc.