Phosphorylation of Lamin-A/C Modulates Peak Sodium Current in a Patient With Cardiac Conduction Disease

Introduction: Deleterious variants in the LMNA gene, which encodes for Lamin-A/C, have been shown to be associated with cardiac conduction diseases (CCDs) and cardiomyopathy. We previously reported that two LMNA variants found in patients presenting with CCDs can prevent the LMNA -mediated activation of peak sodium current (I Na ). In addition, western blot analyses showed phosphorylation of Lamin at serine 22 (S22) was reduced in HEK293 cells expressing either variant. Thus, we sought to investigate what potential role S22 plays on modulating Nav1.5 function. In this study, we focused our analyses on one of the two variants, which is c.1634Gu003eA (p.R545H) in LMNA . We tested the hypothesis that S22 affects peak I Na . Methods and Results: We generated two plasmids that mimic unphosphorylated wild type LMNA ( p.S22A ) and constitutively phosphorylated mutant LMNA ( p.S22D-p.R545H ). We measured and compared peak I Na using patch clamp techniques in HEK293 cells transfected with each LMNA and SCN5A plasmids. Our study showed that p.S22A significantly prevented the LMNA -mediated activation of peak I Na by 63% compared to wild type ( p.S22A : -121 ±11 pA/pF, N =10 vs. wild type LMNA : -340 ±45 pA/pF, N=10, Mann-Whitney U =2, p p.S22D-p.R545H partially restored the reduced peak I Na by 44% ( p.S22D-p.R545H : -137 ±43 pA/pF, N=7 vs. p.R545H : -95 ±15 pA/pF, N=10, Mann-Whitney U =27, p Conclusions: Our data indicate the loss of phosphorylation at S22 significantly reduces the LMNA -mediated activation of peak I Na . In the disease state, constitutive phosphorylation partially restores, yet fails to normalize peak I Na . Our observation suggests that S22 could represent a potential therapeutic target in patients with LMNA -mediated CCD. To our knowledge, this is the first study to functionally link phosphorylation of Lamin-A/C at S22 to peak I Na levels and Nav1.5 function.