miR-140-5p Ameliorates Atrial Fibrillation in Cardiomyocytes by Targeting the Water Channel Protein Aquaporin 4

Background and Objectives: MicroRNAs (miRNAs) are small, non-coding RNAs that control gene expression patterns by inducing the degradation of messenger RNAs (mRNAs). Furthermore, miRNAs are known to play an important role in the pathogenesis of atrial fibrillation (AF). AF is typically diagnosed using an electrocardiogram. However, this study investigated whether specific miRNAs could be involved in alleviating AF by regulating aquaporin 4 (AQP4). Methods: HL-1 cells were transfected with either miRNA negative control (NC) or miR-140-5p, followed by incubation with or without tachypacing (TP) condition. We investigated the protein expression of calcium-handling and inflammation-related proteins in control, control + miR-NC, control + miR-140-5p, TP, and TP + miR-140-5p groups by Western blotting. Also, the relative mRNA expression of AQP4 was determined through real-time polymerase chain reaction. Results: Compared to the control, miR-140-3p was increased in the TP-induced AF group. Additionally, AQP4 protein expression and mRNA level were increased in the AF group along with inflammation-related proteins toll-like receptor 4, nucleotide-binding domain-like receptor protein 3, ERK, AKT, and interleukin-1β. The increase in such proteins was mitigated through miR-140-5p treatment. In accordance with these results, calcium-handling protein markers CaMKII, phospholamban, and ryanodine receptor 2 gene were also increased in the AF group and alleviated with miR-140-5p treatment. Conclusions: miR-140-5p is engaged in suppressing the expression of AQP4 in TP-induced AF HL-1 cells. In doing so, miR-140-5p reduced the risk of AF by suppressing inflammation and phosphorylation of Ca-handling proteins.