Cardiomyocyte vulnerability to lamin polymer disruption revealed by saturation mutagenesis

Abstract

Hundreds of mutations to the broadly expressed LMNA gene cause disease primarily within cardiac, muscular, and adipose tissues (1). Tissue-specific pathogenesis arises when mutant protein dysfunction collides with the unique demands of a specific cell type. Here, we decipher the cell-type-specific consequences of ~15,000 LMNA mutations by completing the first saturation mutagenesis screens in human induced pluripotent cells (hiPSCs) and hiPSC-derived cardiomyocytes using our newly developed single large serine integrase cassette exchange (SLICE) platform. We find that destabilization is a predominant consequence of pathogenic LMNA mutations, is selected against in human populations, and is associated with cardiomyopathy. Mutation sensitivity maps reveal Lamin A quality control at both the subunit and multimer level, resolve lateral and head-to-tail polymerization interfaces, and uncover a convergence between disruption of lamin polymer assembly and pathogenesis. Uniquely in cardiomyocytes, lamin A polymer assembly defects drive profound protein loss, nuclear abnormalities, and cellular toxicity, explaining the origins of cardiac specificity in laminopathy syndromes.