Base Editing Corrects Mutations for Cardiac Disease in Mice

Point mutations in the lamin A (LMNA) gene cause several human diseases, ranging from congenital muscular dystrophy to premature aging, collectively known as laminopathies, which affect skeletal muscles and the heart. While existing therapies can mitigate the symptoms of these conditions, there is no cure.

Base-editing methods have recently emerged as tools for correcting point mutations without creating double-stranded breaks in DNA unlike other gene editing methods, leading many to consider base editing a safer therapeutic strategy. However, base editing of LMNA-associated mutations that cause cardiac disease has remained unexplored. This motivated researchers, led by Eric Olson at the University of Texas Southwestern Medical Center, to develop a targeted base editing therapy for these pathologies.

In a recent study, published in Proceedings of the National Academy of Sciences, the team studied two mouse models carrying human mutations associated with either skeletal or cardiac muscle laminopathies.¹ Base editing prevented the pathological phenotypes associated with these conditions and extended the treated mice’s lifespan, highlighting the potential of base editing as a therapeutic tool.

First, the researchers gathered somatic cells from patients with mutations in LMNA associated with cardiac disease: R249Q, a guanine-to-adenine mutation linked to cardiomyopathy, and L35P, a thymine-to-cytosine mutation associated with congenital muscular dystrophy. They reprogrammed the somatic cells into induced pluripotent stem-cell-derived cardiomyocytes (iPSC-CMs), which they then used to optimize base editing strategies for the LMNA variants.

After screening single guide RNAs in their CRISPR/Cas system, the team identified two candidates to correct the LMNA mutations at their respective bases in the iPSC-CMs. Both approaches corrected abnormalities in contraction and calcium fluctuation in cells derived from patients, compared to wild type cells.

Next, the researchers aimed to test these approaches in an in vivo humanized mouse model, which carried the LMNA mutations associated with human disease. For instance, mice with homozygous R249Q mutations exhibited altered electrocardiogram (ECG) activity, arrhythmias, and died prematurely—reflecting pathologies seen in cardiomyopathy. Likewise, mice carrying the L35P mutation had reduced heart sizes and various skeletal muscle groups compared to healthy mice.

The team then injected the R249Q, L35P, and wild type groups of mice with genetic material encoding the respective base-editing tools carried on adeno-associated viruses four days after birth. They monitored cardiac function over the course of eight months and found that the treatment rescued the heart abnormalities, observed through histological staining and ECG analysis, and extended the animals’ lifespans.

While the researchers acknowledged some discrepancies between homo- and heterozygous phenotypes in mice and humans, they remarked that the mouse model represents a valuable tool in studying laminopathies and further aim to optimize their base editing methodology.