Fibroblast Inward-Rectifier Potassium Current Upregulation in Profibrillatory Atrial Remodeling

• Published in: Circulation research 2015-02, Vol.116 (5), p.836-845
• Main Authors: Qi, Xiao-Yan, Huang, Hai, Ordog, Balazs, Luo, Xiaobin, Naud, Patrice, Sun, Yiguo, Wu, Chia-Tung, Dawson, Kristin, Tadevosyan, Artavazd, Chen, Yu, Harada, Masahide, Dobrev, Dobromir, Nattel, Stanley
• Format: Article
• Language: English
• Subjects: Animals; Atrial Fibrillation - etiology; Atrial Fibrillation - metabolism; Atrial Fibrillation - pathology; Atrial Remodeling - physiology; Calcium - metabolism; Cardiac Pacing, Artificial; Cell Cycle; Cell Division; Dogs; Female; Fibroblasts - metabolism; Fibroblasts - pathology; Fibrosis; Gene Expression Regulation; Genes, Reporter; Heart Failure - complications; Heart Failure - physiopathology; Ion Transport; Male; Membrane Potentials - physiology; MicroRNAs - antagonists & inhibitors; MicroRNAs - genetics; MicroRNAs - physiology; Patch-Clamp Techniques; Potassium - metabolism; Potassium Channels, Inwardly Rectifying - physiology; Recombinant Fusion Proteins - metabolism; Transduction, Genetic; Up-Regulation
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/CIRCRESAHA.116.305326

RATIONALE:Fibroblasts are involved in cardiac arrhythmogenesis and contribute to the atrial fibrillation substrate in congestive heart failure (CHF) by generating tissue fibrosis. Fibroblasts display robust ion currents, but their functional importance is poorly understood. OBJECTIVE:To characterize atrial fibroblast inward-rectifier K current (IK1) remodeling in CHF and its effects on fibroblast properties. METHODS AND RESULTS:Freshly isolated left atrial fibroblasts were obtained from controls and dogs with CHF (ventricular tachypacing). Patch clamp was used to record resting membrane potential (RMP) and IK1. RMP was significantly increased by CHF (from −43.2±0.8 mV, control, to −55.5±0.9 mV). CHF upregulated IK1 (eg, at −90 mV from −1.1±0.2 to −2.7±0.5 pA/pF) and increased the expression of KCNJ2 mRNA (by 52%) and protein (by 80%). Ba (300 μmol/L) decreased the RMP and suppressed the RMP difference between controls and dogs with CHF. Store-operated Ca entry (Fura-2-acetoxymethyl ester) and fibroblast proliferation (flow cytometry) were enhanced by CHF. Lentivirus-mediated overexpression of KCNJ2 enhanced IK1 and hyperpolarized fibroblasts. Functional KCNJ2 suppression by lentivirus-mediated expression of a dominant negative KCNJ2 construct suppressed IK1 and depolarized RMP. Overexpression of KCNJ2 increased Ca entry and fibroblast proliferation, whereas the dominant negative KCNJ2 construct had opposite effects. Fibroblast hyperpolarization to mimic CHF effects on RMP enhanced the Ca entry. MicroRNA-26a, which targets KCNJ2, was downregulated in CHF fibroblasts. Knockdown of endogenous microRNA-26 to mimic CHF effects unregulated IK1. CONCLUSIONS:CHF upregulates fibroblast KCNJ2 expression and currents, thereby hyperpolarizing RMP, increasing Ca entry, and enhancing atrial fibroblast proliferation. These effects are likely mediated by microRNA-26a downregulation. Remodeling-induced fibroblast KCNJ2 expression changes may play a role in atrial fibrillation promoting fibroblast remodeling and structural/arrhythmic consequences.