Project description:Mutations in RNA binding motif protein 20 (RBM20) are a common cause of dilated cardiomyopathy (DCM). Many RBM20 mutations cluster within an arginine/serine rich (RS-rich) domain, resulting in mis-localization of RBM20 to ribonucleoprotein granules within the cytoplasm, abnormal splicing of cardiac genes, and cardiomyocyte dysfunction. We used adenine base editing (ABE) and prime editing to correct pathogenic p.R634Q and p.R636S mutations in the RS-rich domain in human isogenic induced pluripotent stem cell-derived cardiomyocytes. We also created humanized Rbm20R636Q mutant mice, which succumbed to severe cardiac dysfunction, heart failure and premature death. Systemic delivery of ABE components by adeno-associated virus in these mice restored cardiac function and extended life span. These findings demonstrate the potential of precise correction of genetic mutations as a promising therapeutic approach for DCM.
Project description:Mutations in RNA binding motif protein 20 (RBM20) are a common cause of dilated cardiomyopathy (DCM). Many RBM20 mutations cluster within an arginine/serine rich (RS-rich) domain, resulting in mis-localization of RBM20 to ribonucleoprotein granules within the cytoplasm, abnormal splicing of cardiac genes, and cardiomyocyte dysfunction. We used adenine base editing (ABE) and prime editing to correct pathogenic p.R634Q and p.R636S mutations in the RS-rich domain in human isogenic induced pluripotent stem cell-derived cardiomyocytes. We also created humanized Rbm20R636Q mutant mice, which succumbed to severe cardiac dysfunction, heart failure and premature death. Systemic delivery of ABE components by adeno-associated virus in these mice restored cardiac function and extended life span. These findings demonstrate the potential of precise correction of genetic mutations as a promising therapeutic approach for DCM.
Project description:Dilated cardiomyopathy (DCM) is the second most common cause for heart failure with no cure except a high-risk heart transplantation. Approximately 30% of DCM patients harbor heritable mutations which are amenable to CRISPR-based gene therapy1. However, challenges related to delivery of the editing complex and off-target concerns hamper the broad applicability of CRISPR agents in the heart2. We employed a combination of the viral gene transfer vector AAVMYO with superior targeting specificity of heart muscle tissue3 and CRISPR base editors to repair patient mutations in the cardiac splice factor Rbm20, which cause aggressive and arrhythmogenic DCM4. Using optimized conditions, we could improve splice defects in human iPSC-derived cardiomyocytes (iPSC-CMs) and repair >70% of cardiomyocytes in two Rbm20 knock-in mouse models that we generated to serve as an in vivo platform of our editing strategy. Treatment of juvenile mice restored the localization defect of RBM20 in 75% of cells and splicing of RBM20 targets including TTN. Three months after injection, cardiac dilation and ejection fraction reached wildtype levels. Single-nuclei RNA sequencing (snRNA-seq) uncovered restoration of the transcriptional profile across all major cardiac cell types and whole-genome sequencing (WGS) revealed no evidence for aberrant off-target editing. Our study highlights the potential of base editors combined with AAVMYO to achieve gene repair for treatment of hereditary cardiac diseases.
Project description:Mutations in RBM20, a splicing factor that targets multiple pivotal cardiac genes including TTN and CAMK2D, cause a clinically aggressive form of dilated cardiomyopathy (DCM) with a high risk of malignant ventricular arrhythmias. We hypothesized that the RBM20 target CAMK2D contributes critically to RBM20 cardiomyopathy. Here, we sequenced the hearts of Rbm20/Camk2d double knockout mice, as well as the hearts of Rbm20-R636Q knock-in mice treated with the CAMK2 inhibitor Hesperadin.
Project description:The RNA-binding protein RBM20 has been implicated in dilated cardiomyopathy (DCM), a major cause of chronic heart failure. To determine how RBM20 regulates alternative splicing, we combined transcriptome-wide CLIP-seq, RNA-seq, and quantitative proteomics in cell culture, rat, and human hearts. Our analyses revealed a distinct RBM20 RNA-recognition element in predominantly intronic binding sites and linked repression of exon splicing with RBM20-binding near 3prime- and 5prime-splice sites. Our proteomic data show RBM20 interaction with U1- and U2-snRNPs and suggests splicing repression through spliceosome stalling at complex A. Among direct RBM20 targets are several genes involved in DCM as well as new genes not previously associated with the disease process. In human failing hearts, we demonstrate that reduced expression levels of RBM20 affect alternative splicing of several direct targets, indicating that differences in RBM20 gene expression may affect cardiac function. These findings reveal a new mechanism to understand the pathogenesis of human heart failure. The provided data files for RNA-seq contain information for reads that map to human RBM20 only.
Project description:Dilated cardiomyopathy (DCM) is a common cause of heart failure and mutations in RNA-binding motif protein 20 (RBM20) are linked to hereditary DCM. However, the role of unmutated RBM20 in idiopathic DCM is still ambiguous. In this study, we found that RBM20 expression was upregulated by the transcription factor c-JUN in idiopathic DCM. Mice with cardiomyocyte-specific RBM20 overexpression (RBM20cKI) resulted in heart failure with ventricle dilation and lysosome accumulation. Using LysoTracker and a tandem fluorescence RFP-GFP-LC3 reporter system, we elucidated RBM20 blocks autophagic flux in DCM by alkalinizing lysosomal pH. RNA sequencing revealed RBM20 overexpression leads to vacuolar H+-ATPase proton translocation domain subunit a1 (Atp6v0a1) exon6 and exon7 exclusion, which was validated by sanger sequencing and serial amplification product electrophoresis. Transgenic expression of full-length Atp6v0a1 isotype attenuated cardiac dysfunction and restored lysosomal acidification in RBM20cKI mice. Our data suggest that RBM20 activity precisely regulates various cellular process in cardiomyocytes and any therapy targeting RBM20 requires extra cautious.
Project description:Tyrosine kinase inhibitors (TKIs), as a class of small-molecule drugs that exert anti-tumor effects by inhibiting tyrosine kinase-catalyzed phosphorylation, have been used in the treatment of various cancers. Sorafenib, as a multi-targeted TKI drug, is the first-line treatment for advanced renal cell carcinoma and unresectable hepatocellular carcinoma. However, sorafenib has repeatedly been reported to cause cardiac events in patients without a history of heart diseases during clinical use, indicating that it has cardiotoxicity. Alternative splicing of cardiac contraction-related genes happens during heart development and cardiac diseases, and is critical for heart function. However, whether alternative splicing plays a role in drug-induced cardiotoxicity remains unexplored. RBM20 is an important cardiac-specific splicing factor, mutations of which cause dilated cardiomyopathy or other cardiac dysfunctions. Rbm20 also mediates alternative splicing of genes essential for heart contraction, which is often negatively affected in drug-induced cardiotoxicity. Existing studies do not fully explain the mechanism of sorafenib cardiotoxicity, and none of the relationship between cardiotoxicity of sorafenib and alternative splicing mediated by tissue-specific splicing factors, such as Rbm20, have been reported. In order to explore whether cardiac-specific alternative splicing plays a role in sorafenib-induced cardiotoxicity, we establish both cell and animal models of cardiotoxicity, and obtain the following results: (1) By constructing a rat animal model administered with sorafenib, we find that sorafenib causes abnormal cardiac function in rats, and the genes that undergo alternative splicing in rat hearts are related to cytoskeleton of actin; (2) Alternatively spliced genes induced by sorafenib in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are enriched in sarcomere, actin filament, calcium transient regulation, mitochondria, all of which are critical for cardiac contraction. These genes are associated with dilated cardiomyopathy, hypertrophic cardiomyopathy and other cardiomyopathy; (3) Sorafenib induces a decrease in the expression of cardiac-specific splicing factor RBM20; (3) Many genes whose splicing are altered by sorafenib overlap with Rbm20 targets, indicating that sorafenib may affect alternative splicing through Rbm20; (4) Sorafenib induces pathogenic alternative splicing of FHOD3, which is a RBM20 target gene and participates in myocardial sarcomere formation. Sorafenib also affects alternative splicing of SLC25A3, which encodes a phosphate transporter on the mitochondrial inner membrane and regulates ATP synthesis; (5) Enhancing the expression of RBM20 rescues the cardiotoxicity of sorafenib by reducing apoptosis and increasing ATP levels, which is mediated by reversing the alternative splicing of FHOD3 and SLC25A3 induced by sorafenib. This paper uncovers that sorafenib reduces the expression of RBM20 to cause pathogenic alternative splicing of genes related to myocardial sarcomere and energy mechanism, resulting in abnormal myocardial function. Increasing the expression of RBM20 reverses the alternative splicing of FHOD3 and SLC25A3 associated with cardiac sarcomeres and mitochondria respectively, rescuing the cardiotoxicity of sorafenib.
Project description:RBM20 is a cardiac splicing factor responsible for splicing of several cardiac genes such as TTN, TRDN, RyR2, PDLIM1, and CAMK2D. Mutations in RBM20 are a major cause of familial dilated cardiomyopathy (DCM), and lead to missplicing of RBM20 target genes. Here, we describe a novel pathogenic truncating mutation, RBM20 c.1222dupC, identified in a patient with mitral valve prolapse and late onset familial DCM. This mutation introduces a premature termination codon and generates a truncated protein of ~55 kDa in vitro. Splicing assays demonstrated complete loss of activity and no dominant-negative effect on WT RBM20. Overexpression in NRCMs revealed that the truncated protein localized to both cytoplasm and nucleus, partially co-localizing with WT RBM20, despite lacking the RS and RRM domains. To model the patient’s condition, we generated heterozygous c.1222dupC iPSC-derived cardiomyocytes. Western blot analysis of endogenous RBM20 revealed a strong reduction in RBM20 protein level. RT-PCR revealed splicing defects in canonical RBM20 targets, and RNA-sequencing identified widespread splicing abnormalities, including in established RBM20 targets (TTN, RyR2, CAMK2D, and CACNA1G). Together, these findings establish RBM20 c.1222dupC as a pathogenic truncating variant that causes DCM primarily through haploinsufficiency.