Targeting the I_Ks Channel PKA Phosphorylation Axis to Restore Its Function in High-Risk LQT1 Variants

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Ion Channel Function

Background:

• The KCNQ1+KCNE1 (I_Ks) potassium channel regulates cardiac adaptation to stress via cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway phosphorylation.
• Variants in KCNQ1 cause long-QT syndrome type 1 (LQT1), with defective cAMP effects increasing cardiac arrest risk.
• The precise molecular link between I_Ks phosphorylation and function, and loss of cAMP sensitivity in high-risk mutations, remains unclear.

Purpose of the Study:

• To elucidate the molecular determinants of I_Ks channel regulation by PKA phosphorylation.
• To investigate the clinical relevance of identified phosphorylation sites in LQT1 variants.
• To identify potential therapeutic strategies for high-risk LQT1 mutations.

Main Methods:

• Utilized patch clamp and voltage clamp fluorometry to study wild-type and mutant KCNQ1/I_Ks channels.
• Analyzed clinical phenotypic penetrance of LQT1 mutations to assess risk.
• Employed patient-specific induced pluripotent stem-cell models to validate mechanistic findings.

Main Results:

• Identified key residues forming the I_Ks channel PKA phosphorylation axis, spanning the N-terminus to the central pore.
• Found that high-penetrance LQT1 variants cluster along this phosphorylation axis, confirming clinical relevance.
• Demonstrated that ML277, a small molecule targeting the axis center, rescues cAMP defects in high-risk LQT1 variants and alleviates abnormalities in patient-derived cardiomyocytes.

Conclusions:

• Elucidated the molecular mechanism of PKA-dependent I_Ks channel phosphorylation.
• Established the I_Ks channel PKA phosphorylation axis as a critical determinant of channel function and LQT1 risk.
• Provided evidence for ML277 as a potential antiarrhythmic therapeutic strategy for high-risk LQT1 patients.