Abstract Body (Do not enter title and authors here): Background: Pathogenic variants in LMNA-encoded lamin A/C cause a genetic cardiomyopathy marked by conduction disease, atrial and ventricular arrhythmias, and systolic dysfunction. The mechanisms underlying phenotypic differences between Ig-like and coiled-coil domain missense variants remains unclear. Here, we developed a novel suppression-and-replacement disease modeling (SupRep-DM) platform to screen LMNA missense variant function and prioritize mechanistically informative phenotypes.

Methods: LMNA-SupRep-DM is a dual-component lentiviral system that enables simultaneous knockdown of endogenous LMNA via an LMNA-targeted shRNA and replacement with an shRNA-immune mutant lamin A cDNA encoding the pathogenic variant of interest with HA-tag. HEK293T cells and iPSC-derived cardiomyocytes (iPSC-CMs) were transduced with 9 unique SupRep-DM constructs harboring variants in either the coiled-coil (E82K, K97E, R216C, H222P, T224I, R335W) or Ig-like (R471H, R541C, R541H) domains. Cells were stained using HA-specific antibodies, imaged by confocal microscopy, and analyzed for nuclear morphology, aggregate burden, and fluorescence intensity. Statistics: Dunnett’s test and one-way ANOVA.

Results: In HEK293T cells, 8/9 LMNA variants significantly reduced nuclear circularity (p< 0.05), most notably in K97E (-11%, n=89), R471H (-12%, n=62), and R541C (-9%, n=104). Additionally, K97E increased nuclear area (+24%) and R541C decreased it (−29%) vs wild-type (WT, p<0.0001). Lamin A intensity was significantly reduced in K97E, R471H, and R541C, but increased in T224I and R335W vs WT. In iPSC-CMs, Ig-fold variants R541C and R541H significantly reduced nuclear circularity (−28%, –34%), increased elongation (+42%, +49%), and elevated lamin A aggregates ~4–5-fold vs WT (p≤0.0005). R471H and the coiled-coil variant E82K also increased aggregate burden, while the remaining variants (K97E, R216C, H222P, T224I, R335W) showed no significant effects in iPSC-CMs.

Conclusions: LMNA missense variants cause domain-specific nuclear disruptions, with variants localizing to the Ig-like domain inducing nuclear deformities and consistent aggregation across both cellular models. Coiled-coil variants showed more variable, context-dependent effects. The more pronounced phenotypes in iPSC-CMs may reflect contraction-mediated stress absent in HEK293T cells. The SupRep-DM platform sensitively detects these structural changes, demonstrating its utility for mechanistic prioritization of LMNA variants.