Expression Defects of SCN5A Common Polymorphisms S524Y and H558R in the Q1077 Splice Variant Can Be Rescued by...

Area of Science:

• Cardiovascular genetics
• Molecular cardiology
• Pharmacology

Background:

• The cardiac sodium channel Na_V1.5, encoded by SCN5A, is crucial for heart electrical activity.
• Loss-of-function mutations in SCN5A are linked to inherited arrhythmia syndromes.
• Common SCN5A polymorphisms, like H558R and S524Y, and splice variants (Q1077del, Q1077) influence Na_V1.5 function.

Purpose of the Study:

• To investigate the functional impact of SCN5A polymorphisms H558R and S524Y in the context of the Q1077 splice variant.
• To determine if the antiarrhythmic drug mexiletine can rescue expression deficiencies caused by these polymorphisms in the Q1077 background.

Main Methods:

• Engineered SCN5A polymorphisms (H558R, S524Y) into Q1077del and Q1077 splice backgrounds.
• Assessed Na_V1.5 current densities using electrophysiology.
• Treated cells with mexiletine and evaluated rescue effects on current density and cell-surface expression via flow cytometry.

Main Results:

• Na_V1.5 current densities were normal in the Q1077del variant with polymorphisms but significantly reduced in the Q1077 variant.
• Mexiletine treatment (500 μM) significantly increased current density for both S524Y/Q1077 and H558R/Q1077 variants.
• Mexiletine rescue was associated with increased cell-surface expression of Na_V1.5.

Conclusions:

• The SCN5A Q1077 splice variant exacerbates functional defects of common polymorphisms H558R and S524Y.
• Mexiletine effectively rescues Na_V1.5 expression and function defects caused by these polymorphisms in the Q1077 background.
• These findings suggest potential therapeutic implications for mexiletine in patients with SCN5A loss-of-function phenotypes influenced by these polymorphisms.