Exosomal MicroRNA-1 Regulate Cx43 Expression via Tbx18 in Culture Atrial Fibroblasts under Rapid Electrical Stimulation.

Background: MicroRNAs (miRs) are involved in cardiac remodeling, and tachyarrhythmia can regulate miR expression. While microRNA-1 (miR-1) is essential for genes involved in atrial tachyarrhythmia, the effect of rapid electrical stimulation (RES) on fibroblast-derived exosomal miR-1 is unknown. This study investigated the molecular regulation of exosomal miR-1 and its therapeutic potential in human atrial fibroblasts (HCF-aa) using RES. Methods: HCF-aa were cultured in a pacer dish and exposed to RES (0.5 V/cm and 10 Hz). We then investigated whether miR-1 expression could be regulated in HCF-aa under RES, and examined the effects on T-box transcription factor 18 (Tbx18) and connexin 43 (Cx43) protein levels. Results: RES initially upregulated and subsequently downregulated exosomal miR-1 expression. Overexpression of miR-1 reduced Tbx18 levels but increased Cx43 expression in HCF-aa after 64 hours of RES. Conversely, mutant miR-1 and miR-1 antagomir significantly reduced Cx43 expression. Luciferase reporter assays indicated that miR-1 antagomir pretreatment suppressed the transcriptional activity of Tbx18 on the Cx43 promoter, an effect reversed by mutating the Tbx18 binding site. RES for 24 hours increased exosomal miR-1 and led to a reduction in Tbx18 3'-UTR luciferase activity; this effect was mitigated by mutating the hsa-miR-1-3p binding site. Immunohistochemical staining confirmed that miR-1 antagomir downregulated Cx43, while Tbx18 siRNA upregulated Cx43 in RES-exposed HCF-aa. Conclusions: In HCF-aa under RES, miR-1 and Tbx18 regulated Cx43 expression, with miR-1 modulating Cx43 through Tbx18. These findings provide insights into the molecular mechanisms of cardiac remodeling and offer potential therapeutic targets for treating tachyarrhythmia.