Kir2.1 dysfunction at the sarcolemma and the sarcoplasmic reticulum causes arrhythmias in a mouse model of Andersen–Tawil syndrome type 1

Abstract

Andersen–Tawil syndrome type 1 (ATS1) is associated with life-threatening arrhythmias of unknown mechanism. In this study, we generated and characterized a mouse model of ATS1 carrying the trafficking-deficient mutant Kir2.1Δ314-315 channel. The mutant mouse recapitulates the electrophysiological phenotype of ATS1, with QT prolongation exacerbated by flecainide or isoproterenol, drug-induced QRS prolongation, increased vulnerability to reentrant arrhythmias and multifocal discharges resembling catecholaminergic polymorphic ventricular tachycardia (CPVT). Kir2.1Δ314-315 cardiomyocytes display significantly reduced inward rectifier K+ and Na+ currents, depolarized resting membrane potential and prolonged action potentials. We show that, in wild-type mouse cardiomyocytes and skeletal muscle cells, Kir2.1 channels localize to sarcoplasmic reticulum (SR) microdomains, contributing to intracellular Ca2+ homeostasis. Kir2.1Δ314-315 cardiomyocytes exhibit defective SR Kir2.1 localization and function, as intact and permeabilized Kir2.1Δ314-315 cardiomyocytes display abnormal spontaneous Ca2+ release events. Overall, defective Kir2.1 channel function at the sarcolemma and the SR explain the life-threatening arrhythmias in ATS1 and its overlap with CPVT.

Extracellular Kir2.1 C122Y Mutant Upsets Kir2.1-PIP 2 Bonds and Is Arrhythmogenic in Andersen-Tawil Syndrome

“…24 Disruption of 1 or both microdomains leads to malfunction of Kir2.1 and Na V 1.5 channels that might trigger arrhythmias. However, unlike the defective distribution pattern that was demonstrated for the trafficking deficient mutation Kir2.1 Δ314-315,24 immunolocalization and confocal image analysis of isolated ventricular cardiomyocytes from Kir2.1 C122Y animals revealed an unaltered distribution pattern for both Kir2.1 and Na V 1.5 channels (Figure 3A and 3B). When we determined the percentage of membrane expression using an anti-Na + /K + ATPase immunostaining, the results again showed a similar distribution of Kir2.1 and Na V 1.5 channels in Kir2.1 WT and Kir2.1 C122Y cells, with a small but significant reduction in Na V 1.5 accumulation level in mutant cardiomyocytes (Figure 3C).…”

“…The other is at the sarcoplasmic reticulum (SR) where Kir2.1 functions to control calcium homeostasis (Figure 3A and 3B). 24 Disruption of 1 or both microdomains leads to malfunction of Kir2.1 and Na V 1.5 channels that might trigger arrhythmias. However, unlike the defective distribution pattern that was demonstrated for the trafficking deficient mutation Kir2.1 Δ314-315,24 immunolocalization and confocal image analysis of isolated ventricular cardiomyocytes from Kir2.1 C122Y animals revealed an unaltered distribution pattern for both Kir2.1 and Na V 1.5 channels (Figure 3A and 3B).…”

“…Interestingly, Macías et al 24 have recently shown an SR microdomain of functional Kir2.1 channels contributing to intracellular Ca 2+ homeostasis that could explain the phenotypic overlapping between ATS1 and catecholaminergic PVT in some patients. 44,45 Ca 2+ fluxes across the SR membrane are bidirectional and need a charge-compensating countercurrent, ensuring that the SR membrane potential remains near 0 mV during the e-c coupling process.…”

“…Nonetheless, the precise mechanism either by breaking the disulfide bond between Cys 122 -to-Cys 154 or the incorporation of a tyrosine residue by which the C122Y mutation interferes with Kir2.1 binding to PIP 2 molecules is beyond the scope of this study and remains to be fully elucidated. Interestingly, Macías et al 24 have recently shown an SR microdomain of functional Kir2.1 channels contributing to intracellular Ca 2+ homeostasis that could explain the phenotypic overlapping between ATS1 and catecholaminergic PVT in some patients. 44,45 Ca 2+ fluxes across the SR membrane are bidirectional and need a charge-compensating countercurrent, ensuring that the SR membrane potential remains near 0 mV during the e-c coupling process.…”

“…The gene therapy approach using AAVs has been used successfully to generate various arrhythmogenic disease models, such as Brugada syndrome, 30 catecholaminergic polymorphic ventricular tachycardia, 31 and ATS1. 24 We used intravenous AAV-mediated cardiac-specific gene transfer 22 to generate male and female mice expressing human Kir2.1 WT or Kir2.1 C122Y proteins. We confirmed AAV infection throughout the heart with cardiomyocytes stably expressing the specific targeted transgenes (Figure S1).…”