The W101C KCNJ5 Mutation Induces Slower Pacing by Constitutively Active GIRK Channels in hiPSC-Derived Cardiomyocytes

Mutations in the KCNJ5 gene, encoding one of the major subunits of cardiac G-protein-gated inwardly rectifying K+ (GIRK) channels, have been recently linked to inherited forms of sinus node dysfunction. Here, the pathogenic mechanism of the W101C KCNJ5 mutation underlying sinus bradycardia in a patient-derived cellular disease model of sinus node dysfunction (SND) was investigated. A human-induced pluripotent stem cell (hiPSCs) line of a mutation carrier was generated, and CRISPR/Cas9-based gene targeting was used to correct the familial mutation as a control line. Both cell lines were further differentiated into cardiomyocytes (hiPSC-CMs) that robustly expressed GIRK channels which underly the acetylcholine-regulated K+ current (I-K,I-ACh). hiPSC-CMs with the W101C KCNJ5 mutation (hiPSC(W101C)-CM) had a constitutively active I-K,I-ACh under baseline conditions; the application of carbachol was able to increase I-K,I-ACh, further indicating that not all available cardiac GIRK channels were open at baseline. Additionally, hiPSC(W101C)-CM had a more negative maximal diastolic potential (MDP) and a slower pacing frequency confirming the bradycardic phenotype. Of note, the blockade of the constitutively active GIRK channel with XAF-1407 rescued the phenotype. These results provide further mechanistic insights and may pave the way for the treatment of SND patients with GIRK channel dysfunction.

Automated summary

This study investigates the pathogenic mechanism of the W101C KCNJ5 mutation in sinus bradycardia, a type of sinus node dysfunction. By generating patient-derived induced pluripotent stem cells (hiPSCs) and correcting the mutation, the researchers were able to differentiate these cells into cardiomyocytes and study their characteristics. The study found that the mutated cardiomyocytes had a constitutively active potassium current and exhibited a slower pacing frequency, indicating the presence of bradycardia. Interestingly, the blockade of the mutated GIRK channel rescued the phenotype. These findings provide insights into the mechanisms underlying sinus node dysfunction and suggest potential treatment options for patients with GIRK channel dysfunction.