Altered expression of hyperpolarization-activated cyclic nucleotide-gated channels and microRNA-1 and -133 in patients with age-associated atrial fibrillation

Hyperpolarization-activated cyclic nucleotide-gated (HCN) cation channels mediate pacemaker currents in the atrium. The microRNA (miR) families miR-1 and miR-133 regulate the expression of multiple genes involved in myocardial function, including HCN channels. It was hypothesized that agedependent changes in HCN2, HCN4, miR1 and miR133 expression may contribute to ageassociated atrial fibrillation, and therefore the correlation between expression levels, among adult (≤65 years) and aged patients (≥65 years), and sinus rhythm was determined. Right atrial appendage samples were collected from 60 patients undergoing coronary artery bypass grafting. Reverse transcription-quantitative polymerase chain reaction (PCR) and western blot analyses were performed in order to determine target RNA and protein expression levels. Compared with aged patients with sinus rhythm, aged patients with atrial fibrillation exhibited significantly higher HCN2 and HCN4 channel mRNA and protein expression levels (P<0.05), but significantly lower expression levels of miR1 and miR133 (P<0.05). In addition, aged patients with sinus rhythm exhibited significantly higher expression levels of HCN2 and HCN4 channel mRNA and protein (P<0.05), but significantly lower expression levels of miR1 and 133 (P<0.05), compared with those of adult patients with sinus rhythm. Expression levels of HCN2 and HCN4 increased with age, and a greater increase was identified in patients with ageassociated atrial fibrillation compared with that in those with aged sinus rhythm. These electrophysiological changes may contribute to the induction of ectopic premature beats that trigger atrial fibrillation.