LAUSR

Mutations in RNA binding motif protein 20 (RBM20) are a common cause of familial dilated cardiomyopathy (DCM). Many RBM20 mutations cluster within an arginine/serine-rich (RS-rich) domain, which mediates nuclear localization. These mutations induce RBM20 mis-localization to form aberrant ribonucleoprotein (RNP) granules in the cytoplasm of cardiomyocytes and abnormal alternative splicing of cardiac genes, contributing to DCM. We used adenine base editing (ABE) and prime editing (PE) to correct pathogenic p.R634Q and p.R636S mutations in the RS-rich domain in human isogenic induced pluripotent stem cell (iPSC)–derived cardiomyocytes. Using ABE to correct RBM20R634Q human iPSCs, we achieved 92% efficiency of A-to-G editing, which normalized alternative splicing of cardiac genes, restored nuclear localization of RBM20, and eliminated RNP granule formation. In addition, we developed a PE strategy to correct the RBM20R636S mutation in iPSCs and observed A-to-C editing at 40% efficiency. To evaluate the potential of ABE for DCM treatment, we also created Rbm20R636Q mutant mice. Homozygous (R636Q/R636Q) mice developed severe cardiac dysfunction, heart failure, and premature death. Systemic delivery of ABE components containing ABEmax-VRQR-SpCas9 and single-guide RNA by adeno-associated virus serotype 9 in these mice restored cardiac function as assessed by echocardiography and extended life span. As seen by RNA sequencing analysis, ABE correction rescued the cardiac transcriptional profile of treated R636Q/R636Q mice, compared to the abnormal gene expression seen in untreated mice. These findings demonstrate the potential of precise correction of genetic mutations as a promising therapeutic approach for DCM. Description Adenine base editing and prime editing can correct RBM20 mutations in human cells and mice, resulting in correction of dilated cardiomyopathy. Editing RBM20 mutations Gene therapies could potentially cure familial cardiomyopathies, but improvements in editing efficiency and avoidance of off-target gene editing are needed. Here Nishiyama and colleagues used more precise adenine base editing (ABE) and prime editing (PE) approaches to correct pathogenic mutations in RNA binding motif protein 20 (RBM20), which commonly cause familial dilated cardiomyopathy. In human induced pluripotent stem cells, ABE corrected the p.R634Q mutation with 92% efficiency of A-to-G editing, whereas PE corrected p.R636S mutations with 40% efficiency of A-to-C editing. Cardiomyocytes derived from corrected iPS cells showed normal sarcomere structure and nuclear localization of RBM20. The authors then generated Rbm20R636Q mice that experienced cardiac dysfunction and life span. These findings suggest that precise gene editing approaches might be beneficial to treat familial dilated cardiomyopathies.—MN