LMNA p.H222P mutation causes contractile dysfunction via impaired mitochondrial calcium uptake in human cardiac laminopathy

AIMS: Mutations in the LMNA gene, which encodes lamin A/C, cause a variety of diseases known as laminopathies. Some mutations are particularly associated with the occurrence of dilated cardiomyopathy and heart failure, but the genotype-phenotype relationship and underlying mechanisms are unclear. METHODS AND RESULTS: Induced pluripotent stem cells (hiPSCs) from a patient carrying a LMNA point mutation (c.665A>C, p.His222Pro) and a CRISPR/Cas9 corrected isogenic control hiPSCs clones were differentiated into cardiomyocytes (hiPSC-CMs), with no difference in the differentiation yield and in sarcomere organisation between the two cell lines. However, 3D cardiac organoids generated with LMNA p.H222P hiPSC-CMs showed an impaired contractility compared to control organoids. Calcium transient recordings in LMNA p.H222P mutant cardiomyocytes showed a significantly higher calcium transient amplitude with a significantly slower calcium re-uptake. Transcriptomic analyses suggested a global mitochondrial dysfunction and in particular an impaired mitochondrial calcium uptake with a significantly decreased expression of the mitochondrial calcium uniporter (MCU). This decrease in MCU expression was confirmed by western blot and was accompanied by an increased MICU1:MCU ratio, as well as an increased PDH Ser232 and PDH Ser300 phosphorylation, indicating an altered mitochondrial calcium uptake in the LMNA mutant hiPSC-CMs. Consistently, lower mitochondrial respiration and ATP levels were found in LMNA p.H222P hiPSC-CMs as compared to isogenic controls. Strikingly, treatment with the MCU activator amorolfine restored mitochondrial calcium uptake and improved contractility in LMNA mutant hiPSC-CMs. CONCLUSIONS: Our results establish a direct mechanistic link between nuclear envelope dysfunction and impaired mitochondrial function, and highlight the MCU complex as a potential therapeutic target in LMNA-related cardiomyopathy. More broadly, this work provides a paradigm for connecting gene-specific nuclear defects to mitochondrial dysfunction in inherited cardiomyopathies.