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

<jats:title>Abstract</jats:title> <jats:sec> <jats:title>Aims</jats:title> <jats:p>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.</jats:p> </jats:sec> <jats:sec> <jats:title>Methods and results</jats:title> <jats:p>Induced pluripotent stem cells (hiPSCs) from a patient carrying a LMNA point mutation (c.665A&amp;gt;C, p.His222Pro) and a CRISPR/Cas9 corrected isogenic control hiPSC clones were differentiated into cardiomyocytes (hiPSC-CMs), with no difference in the differentiation yield and in sarcomere organization 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 reuptake. 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.</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusion</jats:title> <jats:p>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.</jats:p> </jats:sec>