Channel HCN4 mutation R666Q associated with sporadic arrhythmia decreases channel electrophysiological function and...

Area of Science:

• Cardiovascular Genetics
• Molecular Cardiology
• Ion Channel Physiology

Background:

• Mutations in HCN4 are linked to arrhythmias, but QT prolongation is uncommon.
• HCN4 mutations can cause sinus bradycardia and other cardiac rhythm disturbances.

Purpose of the Study:

• To investigate the functional impact of a newly identified HCN4 mutation, HCN4-R666Q, found in arrhythmia patients.
• To elucidate the molecular mechanisms underlying the HCN4-R666Q mutation's contribution to cardiac arrhythmias.

Main Methods:

• Clinical and genetic analysis of patients with the HCN4-R666Q mutation.
• Functional characterization using whole-cell voltage-clamp electrophysiology.
• Assessment of protein expression, localization, and degradation via qPCR, Western blot, confocal microscopy, and co-immunoprecipitation.
• Investigation of proteasome-mediated degradation pathways.

Main Results:

• The HCN4-R666Q mutation significantly decreased HCN4 channel current density over time compared to wildtype.
• HCN4-R666Q exhibited increased susceptibility to ubiquitin-proteasome system degradation.
• Proteasome inhibitor treatment partially rescued the reduced current density of HCN4-R666Q.
• The mutation was identified in patients presenting with sinus bradycardia, QT prolongation, and ventricular tachycardia.

Conclusions:

• The HCN4-R666Q mutation impairs HCN4 channel function through both reduced current density and decreased protein stability.
• This dual mechanism provides novel insights into the pathogenesis of HCN4-related cardiac arrhythmias.
• Understanding HCN4-R666Q's effects is crucial for diagnosing and potentially treating associated cardiac rhythm disorders.