Highlight
- LMNA L204P mutation leads to aberrant WNT5a/RhoA signaling causing actin filament depolymerization in cardiomyocytes from EDMD patients.
- Disrupted actin dynamics result in malformed nuclear envelopes, impaired connexin 43 trafficking, arrhythmias, and contractile dysfunction in iPSC-derived and engineered heart tissues.
- Pharmacological activation of WNT5a/RhoA pathway and stabilization of actin filaments rescue functional deficits and arrhythmic phenotypes.
- A knock-in mouse model replicates human cardiac abnormalities, supporting translational relevance and therapeutic exploration.
Background: Disease Burden and Clinical Context
Emery-Dreifuss muscular dystrophy (EDMD) is a rare hereditary disorder characterized by early onset joint contractures, progressive skeletal muscle wasting, and serious cardiac manifestations. Cardiac involvement, primarily seen in patients with mutations in the LMNA gene encoding nuclear lamins A/C, includes conduction defects such as atrioventricular block and life-threatening ventricular arrhythmias. These cardiac complications often necessitate implantable devices or ultimately heart transplantation, with approximately 20% of cases progressing to this advanced stage. Despite advances in understanding LMNA mutations’ effects on nuclear structure, the detailed molecular pathways linking these genetic alterations to cardiac pathogenic phenotypes have remained poorly defined, limiting therapy development.
Study Design and Methodology
This study investigated the pathogenic mechanisms of LMNA sequence variations through a multipronged approach involving patient-derived induced pluripotent stem cells (iPSCs), gene editing, engineered heart tissue models, and an animal model. Five EDMD patients harboring LMNA mutations, predominantly the L204P variant, were recruited. Patient skin or blood cells were reprogrammed into iPSCs using a non-integrating Sendai virus system. Two healthy donor-derived iPSC lines were used as controls.
Using genome editing techniques, the L204P mutation was corrected in patient iPSCs to generate isogenic controls, thereby isolating mutation-specific phenotypes. Cardiomyocytes were differentiated via monolayer protocols from these cells, producing iPSC-derived cardiomyocytes (iPSC-CMs). To recreate tissue-level function, three-dimensional engineered heart tissues capable of force generation were fabricated from iPSC-CMs. Additionally, an Lmna L204P heterozygous knock-in mouse model was developed to recapitulate the human cardiac phenotype in vivo.
Key Findings
Cellular and Structural Abnormalities:
EDMD patient-derived iPSC-CMs showed disorganization of sarcomeres—the fundamental contractile units of the heart muscle—and malformations of the nuclear envelope, consistent with laminopathy pathology. These cells also displayed arrhythmic electrical activity and diminished contractile performance compared to healthy and gene-corrected controls.
Multi-Omics and Chromatin Analysis:
Comprehensive transcriptomic and epigenetic profiling revealed that LMNA directly regulates the WNT5A gene promoter, a key regulator of non-canonical WNT signaling. The Leu204Pro mutation resulted in reduced chromatin accessibility and suppressed WNT5A transcription in affected cardiomyocytes, linking LMNA mutation to downregulation of WNT5A expression.
Mechanistic Insights into Actin Dynamics:
The decrease of WNT5a led to diminished signaling through RhoA, a small GTPase critical to actin cytoskeleton organization. This signaling inactivation caused actin depolymerization and inhibited actin polymerization in EDMD iPSC-CMs. Disrupted actin filaments compromised nuclear envelope integrity and impaired trafficking of connexin 43 (Cx43), a gap junction protein essential for electrical coupling between cardiomyocytes. The reduced cell-cell border localization of Cx43 contributed to arrhythmogenesis.
Therapeutic Interventions:
Exogenous supplementation of WNT5a protein, pharmacological activation of RhoA, or treatment with actin polymerization stabilizers rescued these pathogenic defects in EDMD iPSC-CMs. Engineered heart tissues constructed from EDMD iPSC-CMs showed severely impaired contractile force, which improved significantly upon RhoA activation.
Animal Model Validation:
Lmna L204P knock-in mice developed cardiac dysfunction and stress-induced arrhythmias, supporting the translational significance of the findings and providing an in vivo platform for further therapeutic testing.
Expert Commentary
This study elucidates a previously undefined mechanistic link between LMNA mutations and cardiac dysfunction via WNT5a-mediated regulation of actin cytoskeletal dynamics. Prior research has established LMNA’s role in nuclear structure and gene regulation, but this work extends the pathophysiological framework to include defective cytoskeletal remodeling influencing membrane protein trafficking and electrophysiological stability.
The combined use of human iPSC technology, genome editing, engineered tissues, and a knock-in mouse model represents a robust translational paradigm, reinforcing the potential of targeting the WNT5a/RhoA/actin axis for therapeutic development. Nevertheless, the findings require validation in broader patient cohorts and exploration of long-term efficacy and safety of proposed pharmacologic agents.
Conclusion
Aberrant WNT5a-mediated actin filament dynamics constitute a central mechanism driving cardiac abnormalities in LMNA-related Emery-Dreifuss muscular dystrophy. The identification of WNT5a/RhoA signaling and actin assembly as modifiable elements offers promising avenues for therapeutic intervention aimed at ameliorating conduction defects, arrhythmias, and contractile failure in this severe cardiac-laminopathy syndrome. Future clinical translation depends on refining these strategies and confirming their effects in vivo.
