Downregulation of miR-133 and miR-590 contributes to nicotine-induced atrial remodelling in canines

The present study was designed to decipher molecular mechanisms underlying nicotine's promoting atrial fibrillation (AF) by inducing atrial structural remodelling. The canine model of AF was successfully established by nicotine administration and rapid pacing. The atrial fibroblasts isolated from healthy dogs were treated with nicotine. The role of microRNAs (miRNAs) on the expression and regulation of transforming growth factor-β1 (TGF-β1), TGF-β receptor type II (TGF-βRII), and collagen production was evaluated in vivo and in vitro. Administration of nicotine for 30 days increased AF vulnerability by ∼eight- to 15-fold in dogs. Nicotine stimulated remarkable collagen production and atrial fibrosis both in vitro in cultured canine atrial fibroblasts and in vivo in atrial tissues. Nicotine produced significant upregulation of expression of TGF-β1 and TGF-βRII at the protein level, and a 60–70% decrease in the levels of miRNAs miR-133 and miR-590. This downregulation of miR-133 and miR-590 partly accounts for the upregulation of TGF-β1 and TGF-βRII, because our data established TGF-β1 and TGF-βRII as targets for miR-133 and miR-590 repression. Transfection of miR-133 or miR-590 into cultured atrial fibroblasts decreased TGF-β1 and TGF-βRII levels and collagen content. These effects were abolished by the antisense oligonucleotides against miR-133 or miR-590. The effects of nicotine were prevented by an α7 nicotinic acetylcholine receptor antagonist. We conclude that the profibrotic response to nicotine in canine atrium is critically dependent upon downregulation of miR-133 and miR-590.