Project description:Alternative mRNA splicing is an important mechanism for regulation of gene expression. Changes in gene expression contribute to the pathogenesis of heart failure. However, changes in mRNA splicing have not been systematically examined in heart disease. We hypothesized that mRNA splicing is changed in diseased hearts. We used the Affymetrix exon array, which separately measures expression of each known and computationally predicted exon, to globally evaluate changes in mRNA splicing in left ventricular myocardial RNA from control and ischemic cardiomyopathy (ICM) patients. We found that mRNA splicing is systematically changed in heart failure. RTPCR validated 9 previously unreported alternative splicing events. Furthermore, we demonstrated that the splicing of four key sarcomere genes, cardiac troponin T (TNNT2), cardiac troponin I (TNNI3), myosin heavy chain 7 (MYH7), and filamin C (FLNC), was significantly altered in ICM. Altered splicing of these genes in heart disease was confirmed in independent ICM samples, and in dilated cardiomyopathy and aortic stenosis. The minor variant fraction of these five genes was sufficient to classify samples into control or disease groups with 95% accuracy. Our data indicate that alternative splicing is systematically altered in human heart disease, suggesting that disease-associated perturbation of RNA splicing may contribute to the pathogenesis and development of heart failure. Disease-related changes in splicing of sarcomere genes may directly impact cardiomyocyte function.
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:Heart failure is associated with atrioventricular (AV) node dysfunction, and AV node dysfunction in the setting of heart failure is associated with an increased risk of mortality and heart failure hospitalisation. This study aims to understand the causes of AV node dysfunction in heart failure by studying changes in the whole nodal transcriptome. The mouse transverse aortic constriction model of heart failure was studied; functional changes were assessed using electrocardiography and echocardiography and the transcriptome of the AV node was quantified using RNA-seq. Heart failure was associated with a significant increase in the PR interval, indicating a slowing of AV node conduction and AV node dysfunction, and significant changes in 3,077 transcripts (5.6% of the transcriptome). Many systems were affected: transcripts supporting AV node conduction were downregulated and there were changes in transcripts identified by GWAS as determinants of the PR interval. In addition, there was evidence of remodelling of the sarcomere, a shift from fatty acid to glucose metabolism, and remodelling of the extracellular matrix. There was evidence of the causes of this widespread remodelling of the AV node: evidence of dysregulation of multiple intracellular signalling pathways, dysregulation of 109 protein kinases and 148 transcription factors, and an immune response with a proliferation of neutrophils, monocytes, macrophages and B lymphocytes and a dysregulation of 40 cytokines. In conclusion, inflammation and a widespread transcriptional remodelling of the AV node underlies AV node dysfunction in heart failure.
Project description:Background: Modulation of mRNA splicing acts as an important layer of gene regulation, in addition to transcriptional regulation and epigenetic modifications. RNA binding proteins (RBPs) play essential roles in mediating RNA splicing and are key regulators of heart development and function. Our previous studies demonstrated that RBPMS (RNA-binding protein with multiple splicing) regulates cardiac development through modulating mRNA splicing during embryogenesis. Here we explored the postnatal function of RBPMS in the heart. Methods: We ablated Rbpms in the heart by generating a cardiac-specific knockout mouse line (Myh6-Cre, Rbpmsfl/fl), and evaluated its cardiac functions by histology, echocardiography, and gene expression. Paired-end RNA sequencing and RT-PCR were performed to identify and validate splicing targets of RBPMS in adult mouse hearts. Proximity-dependent Biotin Identification (BioID) assay and mass spectrometry analysis were performed to identify RBPMS binding partners. We also measured contractility and calcium fluxes in isolated mouse cardiomyocytes, and contractile forces of cardiac papillary muscle. Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) were also used as a model to explore the influence of RBPMS on contractility of human cardiomyocytes. Results: he absence of Rbpms in the heart led to dilated cardiomyopathy (DCM) and heart failure, causing early death in mice. Mice with cardiac-specific knockout of Rbpms showed myocardium noncompaction with reduced cardiomyocyte number at the neonatal stage and developed DCM with pervasive myocardial fibrosis in adulthood. We found that RBPMS mediates a largely distinct RNA splicing profile in adult mouse hearts compared to neonatal hearts, indicating a stage-specific modulation of alternative RNA splicing by RBPMS. In adult hearts, RBPMS mainly influenced alternative splicing of genes associated with sarcomere structures and cardiomyocyte contraction, such as Ttn, Pdlim5 and Nexn, to generate new protein isoforms. In neonatal hearts, RBPMS influenced the splicing of cytoskeletal genes. RBMPS was associated with spliceosome factors and other RNA binding proteins that play important roles in the heart, such as RBM20 and GATA4. Importantly, we found that the absence of Rbpms caused severe cardiomyocyte contractile defects and reduced calcium sensitivity in both mouse and hiPSC-CMs. Our results demonstrated that Rbpms is crucial for postnatal cardiac function and cardiomyocyte contractility by regulating RNA alternative splicing. Conclusions: Loss of Rbpms in the heart causes reduced cardiomyocyte number and impaired cardiomyocyte contraction, leading to DCM and heart failure.
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:Hypoplastic left heart syndrome (HLHS) is characterized by underdevelopment of left sided structures including the ventricle, valves, and aorta1. Although the mechanisms of disease pathogenesis remain elusive due to a paucity of candidate genes and animal models, prevailing paradigm suggests that HLHS is a multigenic disease of co-occurring phenotypes2,3. Here, we report that zebrafish lacking two orthologs of the RNA binding protein RBFOX2, a gene previously linked to HLHS in humans4,5, display cardiovascular defects overlapping those in HLHS patients. In contrast to current models, we demonstrate that co-existing ventricular, valve, and aortic deficiencies in rbfox mutant zebrafish arise secondary to impaired myocardial function as all three phenotypes are rescued when Rbfox is expressed specifically in the myocardium. On a molecular and cellular level, we find diminished expression and alternative splicing of sarcomere and mitochondrial components in rbfox-deficient hearts that compromise sarcomere assembly and mitochondrial respiration, respectively. Injection of human RBFOX2 mRNA restores ventricular structure and function in rbfox mutant zebrafish, while HLHS-linked RBFOX2 variants fail to rescue. Taken together, our data suggest that mutations in RBFOX2 are causal for HLHS pathogenesis and provide a complimentary paradigm for HLHS emergence where co-existing ventricular, valve, and aortic deficiencies have a monogenic etiology caused by myocardial dysfunction.
Project description:The identification of novel cardiomyocyte-intrinsic factors that support ventricular function will expand the number of candidate genes and therapeutic options for heart failure, a leading cause of death worldwide. Here, we demonstrate that a conserved RNA-binding protein RBPMS2 is required for ventricular function in zebrafish and for myofibril organization and the regulation of intracellular calcium dynamics in zebrafish and human cardiomyocytes. A differential expression screen uncovered co-expression of rbpms2a and rbpms2b in zebrafish cardiomyocytes. Double knockout embryos suffer from compromised ventricular filling during the relaxation phase of the cardiac cycle, which significantly reduces cardiac output. Evaluating rbpms2-null embryos with splicing-sensitive differential expression analysis, quantitative PCR, and in situ hybridization revealed differential alternative splicing of cardiomyopathy genes including myosin binding protein C3 (mybpc3) and phospholamban (pln). Cardiomyocytes in double mutant ventricles and those derived from RBPMS2-null human induced pluripotent stem cells exhibit myofibril disarray and calcium handling abnormalities. Taken together, our data suggest that RBPMS2 performs a conserved role in regulating alternative splicing in cardiomyocytes, which is required for sarcomere organization, optimal calcium handling, and cardiac function.
Project description:The identification of novel cardiomyocyte-intrinsic factors that support ventricular function will expand the number of candidate genes and therapeutic options for heart failure, a leading cause of death worldwide. Here, we demonstrate that a conserved RNA-binding protein RBPMS2 is required for ventricular function in zebrafish and for myofibril organization and the regulation of intracellular calcium dynamics in zebrafish and human cardiomyocytes. A differential expression screen uncovered co-expression of rbpms2a and rbpms2b in zebrafish cardiomyocytes. Double knockout embryos suffer from compromised ventricular filling during the relaxation phase of the cardiac cycle, which significantly reduces cardiac output. Evaluating rbpms2-null embryos with splicing-sensitive differential expression analysis, quantitative PCR, and in situ hybridization revealed differential alternative splicing of cardiomyopathy genes including myosin binding protein C3 (mybpc3) and phospholamban (pln). Cardiomyocytes in double mutant ventricles and those derived from RBPMS2-null human induced pluripotent stem cells exhibit myofibril disarray and calcium handling abnormalities. Taken together, our data suggest that RBPMS2 performs a conserved role in regulating alternative splicing in cardiomyocytes, which is required for sarcomere organization, optimal calcium handling, and cardiac function.