Leukocyte Nuclear Morphology Alterations in Dilated Cardiomyopathy Caused by a Lamin AC Truncating Mutation (LMNA/Ser431*) Are Modified by the Presence of a LAP2 Missense Polymorphism (TMPO/Arg690Cys)

The clinical phenotype of LMNA-associated dilated cardiomyopathy (DCM) varies even among individuals who share the same mutation. LMNA encodes lamin AC, which interacts with the lamin-associated protein 2 alpha (LAP2α) encoded by the TMPO gene. The LAP2α/Arg690Cys polymorphism is frequent in Latin America and was previously found to disrupt LAP2α-Lamin AC interactions in vitro. We identified a DCM patient heterozygous for both a lamin AC truncating mutation (Ser431*) and the LAP2α/Arg690Cys polymorphism. We performed protein modeling and docking experiments, and used confocal microscopy to compare leukocyte nuclear morphology among family members with different genotype combinations (wild type, LAP2α Arg690Cys heterozygous, lamin AC/Ser431* heterozygous, and LAP2α Arg690Cys/lamin AC Ser431* double heterozygous). Protein modeling predicted that 690Cys destabilizes the LAP2α homodimer and impairs lamin AC-LAP2α docking. Lamin AC-deficient nuclei (Ser431* heterozygous) showed characteristic blebs and invaginations, significantly decreased nuclear area, and increased elongation, while LAP2α/Arg690Cys heterozygous nuclei showed a lower perimeter and higher circularity than wild-type nuclei. LAP2α Arg690Cys apparently attenuated the effect of LMNA Ser431* on the nuclear area and fully compensated for its effect on nuclear circularity. Altogether, the data suggest that LAP2α/Arg690Cys may be one of the many factors contributing to phenotype variation of LMNA-associated DCM.