Fibroblast Inward-Rectifier Potassium Current Upregulation in Profibrillatory Atrial Remodeling

Abstract

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 ( I K1 ) 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 I K1 . RMP was significantly increased by CHF (from −43.2±0.8 mV, control, to −55.5±0.9 mV). CHF upregulated I K1 (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 2+ (300 μmol/L) decreased the RMP and suppressed the RMP difference between controls and dogs with CHF. Store-operated Ca 2+ entry (Fura-2-acetoxymethyl ester) and fibroblast proliferation (flow cytometry) were enhanced by CHF. Lentivirus-mediated overexpression of KCNJ2 enhanced I K1 and hyperpolarized fibroblasts. Functional KCNJ2 suppression by lentivirus-mediated expression of a dominant negative KCNJ2 construct suppressed I K1 and depolarized RMP. Overexpression of KCNJ2 increased Ca 2+ entry and fibroblast proliferation, whereas the dominant negative KCNJ2 construct had opposite effects. Fibroblast hyperpolarization to mimic CHF effects on RMP enhanced the Ca 2+ entry. MicroRNA-26a, which targets KCNJ2, was downregulated in CHF fibroblasts. Knockdown of endogenous microRNA-26 to mimic CHF effects unregulated I K1 . Conclusions: CHF upregulates fibroblast KCNJ2 expression and currents, thereby hyperpolarizing RMP, increasing Ca 2+ 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.

Calcium‐dependent potassium channels control proliferation of cardiac progenitor cells and bone marrow‐derived mesenchymal stem cells

“…) and fibroblasts (Qi et al . ), the membrane potential of freshly isolated eCPCs is not set by Kir channels. We found that the resting membrane potential of c‐Kit + eCPCs depends predominantly on the intermediate‐conductance Ca 2+ ‐activated channel KCa3.1.…”

Novel role of the clustered miR‐23b‐3p and miR‐27b‐3p in enhanced expression of fibrosis‐associated genes by targeting TGFBR3 in atrial fibroblasts

“…6 Non-coding RNAs (ncRNAs) comprise over 95% of the total RNA transcripts in eukaryotic cells. 17 MiR-23b-3p and miR-27b-3p are located within a single transcription unit from a microRNA cluster on human chromosome 9 (www.mirdb.org). 8 MicroRNA (miRNA) is an endogenous non-coding RNA with about 22 nucleotides and is involved in a variety of biological processes and diseases by inhibiting the protein translation process of the target gene.…”

Electro-mechanical dynamics of spiral waves in a discrete 2D model of human atrial tissue

“…Due to the microscopic size of myocytes, further investigation is needed on whether this has any effect when progressing to organ scale. Another limitation of the tissue simulations is that only myocytes are considered: the fibroblast may play a role in modulating the excitation wave propagation in AF [49] and thus warrants future investigations incorporating fibroblasts into the model. A third limitation is that the present paper focuses only on idealised tissue with aligned fibres, uniform cell types and contact bond strength, as the main focus was the comparison of spiral wave properties amongst the three cases.…”