Phosphorylation of Lamin A/C at serine 22 modulates Nav 1.5 function.

Abstract

Variants in the LMNA gene, which encodes for Lamin A/C, are associated with cardiac conduction disease (CCD). We previously reported that Lamin A/C variants p.R545H and p.A287Lfs*193, which were identified in CCD patients, decreased peak I Na in HEK‐293 cells expressing Nav1.5. Decreased peak I Na in the cardiac conduction system could account for patients’ atrioventricular block. We found that serine 22 (Ser 22) phosphorylation of Lamin A/C was decreased in the p.R545H variant and hypothesized that lamin phosphorylation modulated Nav1.5 activity. To test this hypothesis, we assessed Nav1.5 function in HEK‐293 cells co‐transfected with LMNA variants or treated with the small molecule LBL1 (lamin‐binding ligand 1). LBL1 decreased Ser 22 phosphorylation by 65% but did not affect Nav1.5 function. To test the complete loss of phosphorylation, we generated a version of LMNA with serine 22 converted to alanine 22 (S22A‐LMNA); and a version of mutant R545H‐LMNA that mimics phosphorylation via serine 22 to aspartic acid 22 substitution (S22D‐R545H‐LMNA). We found that S22A‐LMNA inhibited Lamin‐mediated activation of peak I Na by 63% and shifted voltage‐dependency of steady‐state inactivation of Nav1.5. Conversely, S22D‐R545H‐LMNA abolished the effects of mutant R545H‐LMNA on voltage‐dependency but not peak I Na. We conclude that Lamin A/C Ser 22 phosphorylation can modulate Nav1.5 function and contributes to the mechanism by which R545H‐LMNA alters Nav1.5 function. The differential impact of complete versus partial loss of Ser 22 phosphorylation suggests a threshold of phosphorylation that is required for full Nav1.5 modulation. This is the first study to link Lamin A/C phosphorylation to Nav1.5 function.