Arrhythmogenic Biophysical Phenotype for SCN5A Mutation S1787N Depends upon Splice Variant Background and Intracellular Acidosis.
BACKGROUND
SCN5A is a susceptibility gene for type 3 long QT syndrome, Brugada syndrome, and sudden infant death syndrome. INa dysfunction from mutated SCN5A can depend upon the splice variant background in which it is expressed and also upon environmental factors such as acidosis. S1787N was reported previously as a LQT3-associated mutation and has also been observed in 1 of 295 healthy white controls. Here, we determined the in vitro biophysical phenotype of SCN5A-S1787N in an effort to further assess its possible pathogenicity.


RESULTS
We engineered S1787N in the two most common alternatively spliced SCN5A isoforms, the major isoform lacking a glutamine at position 1077 (Q1077del) and the minor isoform containing Q1077, and expressed these two engineered constructs in HEK293 cells for electrophysiological study. Macroscopic voltage-gated INa was measured 24 hours after transfection with standard whole-cell patch clamp techniques. We applied intracellular solutions with pH7.4 or pH6.7. S1787N in the Q1077 background had WT-like INa including peak INa density, activation and inactivation parameters, and late INa amplitude in both pH 7.4 and pH 6.7. However, with S1787N in the Q1077del background, the percentages of INa late/peak were increased by 2.1 fold in pH 7.4 and by 2.9 fold in pH 6.7 when compared to WT.


CONCLUSIONS
The LQT3-like biophysical phenotype for S1787N depends on both the SCN5A splice variant and on the intracellular pH. These findings provide further evidence that the splice variant and environmental factors affect the molecular phenotype of cardiac SCN5A-encoded sodium channel (Nav1.5), has implications for the clinical phenotype, and may provide insight into acidosis-induced arrhythmia mechanisms.
Department of Cardiology, China Meitan General Hospital, Beijing, China; Department of Medicine, Division of Cardiovascular Medicine, University of Wisconsin, Madison, WI, United States of America.
Rou-Mu
RM
Hu
Department of Medicine, Division of Cardiovascular Medicine, University of Wisconsin, Madison, WI, United States of America; Departments of Pediatrics, and Cellular & Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, PA, United States of America.
Bi-Hua
BH
Tan
Departments of Medicine, Pediatrics, and Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, MN, United States of America.
David J
DJ
Tester
Departments of Pediatrics, and Cellular & Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, PA, United States of America.
Chunhua
C
Song
Department of Medicine, Division of Cardiovascular Medicine, University of Wisconsin, Madison, WI, United States of America.
Yang
Y
He
Departments of Pediatrics, and Cellular & Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, PA, United States of America.
Sinisa
S
Dovat
Departments of Pediatrics, and Cellular & Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, PA, United States of America.
Blaise Z
BZ
Peterson
Departments of Medicine, Pediatrics, and Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, MN, United States of America.
Michael J
MJ
Ackerman
Department of Medicine, Division of Cardiovascular Medicine, University of Wisconsin, Madison, WI, United States of America.
Jonathan C
JC
Makielski
D000138:Acidosis / Q000150:complications / Q000235:genetics* / Q000473:pathology; D001145:Arrhythmias, Cardiac / Q000209:etiology; D001483:Base Sequence; D000075224:Cardiac Conduction System Disease; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008133:Long QT Syndrome / Q000235:genetics / Q000473:pathology; D008564:Membrane Potentials; D016297:Mutagenesis, Site-Directed; D062554:NAV1.5 Voltage-Gated Sodium Channel / Q000235:genetics* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012326:RNA Splicing
D062554:NAV1.5 Voltage-Gated Sodium Channel; D020033:Protein Isoforms; C568320:SCN5A protein, human