Base editing effectively prevents the early-onset hypertrophic cardiomyopathy in Mybpc3 mutant mice

Pathogenic variants in MYBPC3 (myosin-binding protein C3) are the leading cause of genetic hypertrophic cardiomyopathy (HCM). Currently, there is no specific and effective treatment for this disease. Base editing is an emerging modality for treating monogenic diseases; however, its effect on MYBPC3 cardiomyopathy remains unexplored. Mybpc3-R946X/R946X mice developed early-onset left ventricular hypertrophy, systolic dysfunction, ventricular dilatation, and arrythmias. SpRY-ABEmax inefficiently corrected the Mybpc3-R946X mutation. In contrast, SpRY-ABE8e increased the efficiency by 3.6-fold and retained low level off-target editing. In vivo administration of SpRY-ABE8e efficiently corrected Mybpc3-R946X mutation in cardiomyocytes and prevented heart function decline, hypertrophic cardiomyopathy, and ventricular dysfunction. The therapeutic efficacy of SpRY-ABE8e-mediated gene correction surmounted AAV-mediated Mybpc3 gene replacement.Our study unveiled the immense potential of base editing to treat fatal inherited cardiomyopathies and opened a new avenue for the therapeutic managements of inherited cardiac diseases. Overall design: We generated an HCM mouse model bearing an Mybpc3 premature termination codon (p.R946X) analogous to a common human MYBPC3 pathogenic variant. We developed two base editors, SpRY-ABEmax and SpRY-ABE8e, with broad sgRNA recognition sites for genome correction. We used lentivirus to transduce the base editors to mouse embryonic fibroblasts with Mybpc3 mutation for in vitro assessment. For in vivo therapy, we used adenovirus-associated virus serotype 9 (AAV9) to specifically express the editors in the cardiomyocytes. We measured on- and off-target editing efficiency by high throughput DNA and RNA sequencing.