Phosphorylation of Lamin A/C at serine 22 modulates Na v 1.5 function

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 Na v 1.5. 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 Na v 1.5 activity. To test this hypothesis, we assessed Na v 1.5 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 Na v 1.5 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 Na v 1.5. 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 Na v 1.5 function and contributes to the mechanism by which R545H‐LMNA alters Na v 1.5 function. The differential impact of complete versus partial loss of Ser 22 phosphorylation suggests a threshold of phosphorylation that is required for full Na v 1.5 modulation. This is the first study to link Lamin A/C phosphorylation to Na v 1.5 function.