<i>LMNA</i> Haploinsufficiency in Human iPSC-Derived Cardiac Organoids Reveals Early Fibrotic Signaling as a Therapeutically Targetable Process

ABSTRACT Mutations in LMNA are a major cause of dilated cardiomyopathy (DCM), however, the earliest pathogenic events that precede clinical disease remain poorly understood. Here, we identify a novel intronic LMNA splice-site variant (c.937-1G&gt;A) that disrupts pre-mRNA processing, induces nonsense-mediated decay, and results in LMNA haploinsufficiency. Using patient-derived induced pluripotent stem cells differentiated into self-patterning human cardiac organoids, we model the earliest consequences of LMNA deficiency in a multicellular human cardiac context. Single-nucleus transcriptomics revealed coordinated remodeling across cardiomyocytes, fibroblasts, epicardial cells, vascular smooth muscle cells, and pacemaker cells, indicating that LMNA haploinsufficiency initiates a multicellular disease program. Functionally, LMNA -mutant organoids exhibit impaired contractile dynamics and calcium handling, along with a tendency toward increased arrhythmic activity. These changes are accompanied by the activation of pro-fibrotic transcriptional programs and increased periostin secretion, identifying early fibroblast activation as a prominent feature of LMNA -associated disease initiation in this model. Together, our findings demonstrate that LMNA haploinsufficiency is sufficient to trigger early multicellular remodeling and profibrotic signaling prior to overt cardiomyopathy. More broadly, this study highlights human cardiac organoids as a platform for defining the earliest mechanisms of inherited cardiomyopathy and identifying therapeutic opportunities at stages when the disease may still be reversible.