Base Editing Corrects Fatal Heart Mutations in Mice and Human Stem Cells
Scientists used precise base editing to fix two deadly LMNA gene mutations, rescuing cardiac disease in humanized mice and patient-derived heart cells.
Summary
Mutations in the LMNA gene cause laminopathies—devastating heart and muscle diseases with no cure. Researchers at UT Southwestern developed two base editing strategies targeting the R249Q and L35P LMNA variants, which cause dilated cardiomyopathy with conduction defects and congenital muscular dystrophy, respectively. Using patient-derived iPSC-cardiomyocytes, they confirmed both mutations cause nuclear damage, DNA breaks, and abnormal calcium signaling. Humanized mice carrying these mutations developed arrhythmias, muscle wasting, and died prematurely. AAV9-delivered base editors administered at postnatal day 4 prevented cardiac pathology and extended lifespan in both mouse models. This work establishes base editing as a viable therapeutic platform for genetic cardiomyopathies.
Detailed Summary
Laminopathies are a family of genetic diseases caused by mutations in the LMNA gene, which encodes the structural nuclear envelope proteins Lamin A and C. Over 400 variants have been identified, most of them missense point mutations, and they produce a spectrum of devastating phenotypes including dilated cardiomyopathy, conduction defects, and muscular dystrophy. No curative therapies currently exist, and management is limited to symptom control.
This study targeted two specific LMNA point mutations: R249Q (c.G746>A), linked to dilated cardiomyopathy with conduction defects (DCM-CD), and L35P (c.T104>C), associated with congenital muscular dystrophy (CMD). Patient-derived peripheral blood mononuclear cells were reprogrammed into iPSCs and differentiated into cardiomyocytes (iPSC-CMs). R249Q iPSC-CMs showed nuclear aberrations, increased DNA damage markers, and abnormal calcium transients. L35P iPSC-CMs displayed abnormal contraction, elevated DNA damage, and reduced Lamin A/C protein expression, confirming that both variants disrupt fundamental cardiomyocyte biology.
To model disease in vivo, the team generated 'humanized' knock-in mice carrying the human pathogenic mutations via CRISPR-mediated homology-directed repair. Homozygous R249Q mice developed cardiac arrhythmias, conduction defects, and premature death. Homozygous L35P mice showed severe muscle wasting and shortened lifespan, while heterozygous L35P mice developed DCM—mirroring the human disease spectrum with high fidelity.
For therapeutic correction, the researchers designed an adenine base editor (ABE8e) strategy for R249Q and a cytosine base editor (CBE/SpRY) approach for L35P, each paired with optimized sgRNAs. In iPSC-CMs, precise correction fully rescued nuclear morphology, DNA damage, calcium handling, and contractile function. For in vivo delivery, split-intein AAV9 constructs encoding the N- and C-terminal halves of the base editors were injected intraperitoneally into neonatal mice (postnatal day 4) at 3×10¹⁴ vg/kg. AAV-mediated base editing prevented cardiac conduction defects and arrhythmias in R249Q mice and reduced muscular dystrophy and cardiac dysfunction in L35P mice, with measurable extension of lifespan in both models.
These results are significant because they demonstrate that both ABE and CBE platforms can achieve therapeutically meaningful correction of distinct LMNA mutations in clinically relevant models—without introducing double-strand DNA breaks. The work establishes a proof-of-concept framework for precision base editing therapy in laminopathies and potentially other genetic cardiomyopathies, though translation will require optimization of editing efficiency in adult cardiac tissue and rigorous off-target safety evaluation.
Key Findings
- ABE8e corrected LMNA R249Q in iPSC-CMs, rescuing nuclear damage, arrhythmias, and abnormal calcium transients.
- CBE/SpRY corrected LMNA L35P, restoring normal contraction and Lamin A/C protein levels in patient-derived cardiomyocytes.
- Humanized R249Q mice developed cardiac arrhythmias and premature death; L35P homozygotes showed severe muscle wasting.
- AAV9-delivered split-intein base editors administered at postnatal day 4 prevented cardiac pathology and extended lifespan in both mouse models.
- Heterozygous L35P mice developed dilated cardiomyopathy, closely modeling the human dominant disease presentation.
Methodology
Patient-derived iPSCs carrying heterozygous LMNA R249Q or L35P mutations were differentiated into cardiomyocytes for in vitro phenotyping and editing optimization. Humanized knock-in mouse models were generated via CRISPR-HDR. Therapeutic delivery used split-intein AAV9 vectors injected intraperitoneally at postnatal day 4 into neonatal mice.
Study Limitations
Editing was performed in neonatal mice, and efficacy in adult cardiac tissue—where cardiomyocytes are largely post-mitotic—remains to be established. Off-target base editing events were not comprehensively characterized in vivo. The humanized mouse models are homozygous for mutations that are typically heterozygous in human patients, potentially overstating disease severity relative to clinical presentations.
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