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Gregorich ZR, Yanghai Z, Kamp TJ, Granzier H, Guo W. Mechanisms of RBM20 Cardiomyopathy: Insights From Model Systems. CIRCULATION. GENOMIC AND PRECISION MEDICINE 2024; 17:e004355. [PMID: 38288598 PMCID: PMC10923161 DOI: 10.1161/circgen.123.004355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2024]
Abstract
RBM20 (RNA-binding motif protein 20) is a vertebrate- and muscle-specific RNA-binding protein that belongs to the serine-arginine-rich family of splicing factors. The RBM20 gene was first identified as a dilated cardiomyopathy-linked gene over a decade ago. Early studies in Rbm20 knockout rodents implicated disrupted splicing of RBM20 target genes as a causative mechanism. Clinical studies show that pathogenic variants in RBM20 are linked to aggressive dilated cardiomyopathy with early onset heart failure and high mortality. Subsequent studies employing pathogenic variant knock-in animal models revealed that variants in a specific portion of the arginine-serine-rich domain in RBM20 not only disrupt splicing but also hinder nucleocytoplasmic transport and lead to the formation of RBM20 biomolecular condensates in the sarcoplasm. Conversely, mice harboring a disease-associated variant in the RRM (RNA recognition motif) do not show evidence of adverse remodeling or exhibit sudden death despite disrupted splicing of RBM20 target genes. Thus, whether disrupted splicing, biomolecular condensates, or both contribute to dilated cardiomyopathy is under debate. Beyond this, additional questions remain, such as whether there is sexual dimorphism in the presentation of RBM20 cardiomyopathy. What are the clinical features of RBM20 cardiomyopathy and why do some individuals develop more severe disease than others? In this review, we summarize the reported observations and discuss potential mechanisms of RBM20 cardiomyopathy derived from studies employing in vivo animal models and in vitro human-induced pluripotent stem cell-derived cardiomyocytes. Potential therapeutic strategies to treat RBM20 cardiomyopathy are also discussed.
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Affiliation(s)
- Zachery R. Gregorich
- Department of Animal and Dairy Sciences, University of Wisconsin-Madison, Madison, WI
| | - Zhang Yanghai
- Department of Animal and Dairy Sciences, University of Wisconsin-Madison, Madison, WI
| | - Timothy J. Kamp
- Cellular and Molecular Arrhythmia Research Program, University of Wisconsin-Madison, Madison, WI
- Department of Medicine, University of Wisconsin-Madison, Madison, WI
- Cardiovascular Research Center, University of Wisconsin-Madison, Madison, WI
| | - Henk Granzier
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ
| | - Wei Guo
- Department of Animal and Dairy Sciences, University of Wisconsin-Madison, Madison, WI
- Cardiovascular Research Center, University of Wisconsin-Madison, Madison, WI
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Ponzoni M, Coles JG, Maynes JT. Rodent Models of Dilated Cardiomyopathy and Heart Failure for Translational Investigations and Therapeutic Discovery. Int J Mol Sci 2023; 24:ijms24043162. [PMID: 36834573 PMCID: PMC9963155 DOI: 10.3390/ijms24043162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 01/22/2023] [Accepted: 02/01/2023] [Indexed: 02/09/2023] Open
Abstract
Even with modern therapy, patients with heart failure only have a 50% five-year survival rate. To improve the development of new therapeutic strategies, preclinical models of disease are needed to properly emulate the human condition. Determining the most appropriate model represents the first key step for reliable and translatable experimental research. Rodent models of heart failure provide a strategic compromise between human in vivo similarity and the ability to perform a larger number of experiments and explore many therapeutic candidates. We herein review the currently available rodent models of heart failure, summarizing their physiopathological basis, the timeline of the development of ventricular failure, and their specific clinical features. In order to facilitate the future planning of investigations in the field of heart failure, a detailed overview of the advantages and possible drawbacks of each model is provided.
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Affiliation(s)
- Matteo Ponzoni
- Division of Cardiovascular Surgery, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada
- Program in Translational Medicine, SickKids Research Institute, Toronto, ON M5G 0A4, Canada
| | - John G. Coles
- Division of Cardiovascular Surgery, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada
- Program in Translational Medicine, SickKids Research Institute, Toronto, ON M5G 0A4, Canada
- Correspondence: (J.G.C.); (J.T.M.)
| | - Jason T. Maynes
- Department of Anesthesia and Pain Medicine, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada
- Program in Molecular Medicine, SickKids Research Institute, Toronto, ON M5G 0A4, Canada
- Department of Anesthesiology and Pain Medicine, University of Toronto, Toronto, ON M5G 1E2, Canada
- Correspondence: (J.G.C.); (J.T.M.)
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Sun M, Jin Y, Zhang Y, Gregorich ZR, Ren J, Ge Y, Guo W. SR Protein Kinases Regulate the Splicing of Cardiomyopathy-Relevant Genes via Phosphorylation of the RSRSP Stretch in RBM20. Genes (Basel) 2022; 13:1526. [PMID: 36140694 PMCID: PMC9498672 DOI: 10.3390/genes13091526] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Revised: 08/22/2022] [Accepted: 08/23/2022] [Indexed: 11/16/2022] Open
Abstract
(1) Background: RNA binding motif 20 (RBM20) regulates mRNA splicing specifically in muscle tissues. Missense mutations in the arginine/serine (RS) domain of RBM20 lead to abnormal gene splicing and have been linked to severe dilated cardiomyopathy (DCM) in human patients and animal models. Interestingly, many of the reported DCM-linked missense mutations in RBM20 are in a highly conserved RSRSP stretch within the RS domain. Recently, it was found that the two Ser residues within this stretch are constitutively phosphorylated, yet the identity of the kinase(s) responsible for phosphorylating these residues, as well as the function of RSRSP phosphorylation, remains unknown. (2) Methods: The ability of three known SR protein kinases (SRPK1, CLK1, and AKT2) to phosphorylate the RBM20 RSRSP stretch and regulate target gene splicing was evaluated by using both in vitro and in vivo approaches. (3) Results: We found that all three kinases phosphorylated S638 and S640 in the RSRSP stretch and regulated RBM20 target gene splicing. While SRPK1 and CLK1 were both capable of directly phosphorylating the RS domain in RBM20, whether AKT2-mediated control of the RS domain phosphorylation is direct or indirect could not be determined. (4) Conclusions: Our results indicate that SR protein kinases regulate the splicing of a cardiomyopathy-relevant gene by modulating phosphorylation of the RSRSP stretch in RBM20. These findings suggest that SR protein kinases may be potential targets for the treatment of RBM20 cardiomyopathy.
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Affiliation(s)
- Mingming Sun
- Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA
| | - Yutong Jin
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Yanghai Zhang
- Department of Animal and Dairy Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Zachery R Gregorich
- Department of Animal and Dairy Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Jun Ren
- Department of Cardiology, Shanghai Institute of Cardiovascular Diseases, Zhongshan Hospital Fudan University, Shanghai 200032, China
| | - Ying Ge
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
- Department of Cell and Regenerative Biology, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53706, USA
- Human Proteomics Program, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Wei Guo
- Department of Animal and Dairy Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA
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The Mechanisms of Thin Filament Assembly and Length Regulation in Muscles. Int J Mol Sci 2022; 23:ijms23105306. [PMID: 35628117 PMCID: PMC9140763 DOI: 10.3390/ijms23105306] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 05/05/2022] [Accepted: 05/06/2022] [Indexed: 02/01/2023] Open
Abstract
The actin containing tropomyosin and troponin decorated thin filaments form one of the crucial components of the contractile apparatus in muscles. The thin filaments are organized into densely packed lattices interdigitated with myosin-based thick filaments. The crossbridge interactions between these myofilaments drive muscle contraction, and the degree of myofilament overlap is a key factor of contractile force determination. As such, the optimal length of the thin filaments is critical for efficient activity, therefore, this parameter is precisely controlled according to the workload of a given muscle. Thin filament length is thought to be regulated by two major, but only partially understood mechanisms: it is set by (i) factors that mediate the assembly of filaments from monomers and catalyze their elongation, and (ii) by factors that specify their length and uniformity. Mutations affecting these factors can alter the length of thin filaments, and in human cases, many of them are linked to debilitating diseases such as nemaline myopathy and dilated cardiomyopathy.
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Zhang Y, Wang C, Sun M, Jin Y, Braz CU, Khatib H, Hacker TA, Liss M, Gotthardt M, Granzier H, Ge Y, Guo W. RBM20 phosphorylation and its role in nucleocytoplasmic transport and cardiac pathogenesis. FASEB J 2022; 36:e22302. [PMID: 35394688 PMCID: PMC9233413 DOI: 10.1096/fj.202101811rr] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2021] [Revised: 03/21/2022] [Accepted: 03/24/2022] [Indexed: 12/13/2022]
Abstract
Arginine-serine (RS) domain(s) in splicing factors are critical for protein-protein interaction in pre-mRNA splicing. Phosphorylation of RS domain is important for splicing control and nucleocytoplasmic transport in the cell. RNA-binding motif 20 (RBM20) is a splicing factor primarily expressed in the heart. A previous study using phospho-antibody against RS domain showed that RS domain can be phosphorylated. However, its actual phosphorylation sites and function have not been characterized. Using middle-down mass spectrometry, we identified 16 phosphorylation sites, two of which (S638 and S640 in rats, or S637 and S639 in mice) were located in the RSRSP stretch in the RS domain. Mutations on S638 and S640 regulated splicing, promoted nucleocytoplasmic transport and protein-RNA condensates. Phosphomimetic mutations on S638 and S640 indicated that phosphorylation was not the major cause for RBM20 nucleocytoplasmic transport and condensation in vitro. We generated a S637A knock-in (KI) mouse model (Rbm20S637A ) and observed the reduced RBM20 phosphorylation. The KI mice exhibited aberrant gene splicing, protein condensates, and a dilated cardiomyopathy (DCM)-like phenotype. Transcriptomic profiling demonstrated that KI mice had altered expression and splicing of genes involving cardiac dysfunction, protein localization, and condensation. Our in vitro data showed that phosphorylation was not a direct cause for nucleocytoplasmic transport and protein condensation. Subsequently, the in vivo results reveal that RBM20 mutations led to cardiac pathogenesis. However, the role of phosphorylation in vivo needs further investigation.
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Affiliation(s)
- Yanghai Zhang
- Department of Animal and Dairy SciencesUniversity of Wisconsin‐MadisonWisconsinUSA
| | - Chunyan Wang
- Department of Animal and Dairy SciencesUniversity of Wisconsin‐MadisonWisconsinUSA
| | - Mingming Sun
- Department of Animal ScienceUniversity of WyomingLaramieWyomingUSA
| | - Yutong Jin
- Department of ChemistryUniversity of Wisconsin‐MadisonMadisonWisconsinUSA
| | - Camila Urbano Braz
- Department of Animal and Dairy SciencesUniversity of Wisconsin‐MadisonWisconsinUSA
| | - Hasan Khatib
- Department of Animal and Dairy SciencesUniversity of Wisconsin‐MadisonWisconsinUSA
| | - Timothy A. Hacker
- Division of Cardiovascular MedicineDepartment of MedicineUniversity of Wisconsin School of Medicine and Public HealthMadisonWisconsinUSA
| | - Martin Liss
- Neuromuscular and Cardiovascular Cell BiologyMax Delbrueck Center for Molecular Medicine in the Helmholtz AssociationBerlinGermany
| | - Michael Gotthardt
- Neuromuscular and Cardiovascular Cell BiologyMax Delbrueck Center for Molecular Medicine in the Helmholtz AssociationBerlinGermany
- Charité UniversitätsmedizinBerlinGermany
| | - Henk Granzier
- Department of Cellular and Molecular MedicineUniversity of ArizonaTucsonArizonaUSA
| | - Ying Ge
- Department of ChemistryUniversity of Wisconsin‐MadisonMadisonWisconsinUSA
- Department of Cell and Regenerative BiologySchool of Medicine and Public HealthUniversity of Wisconsin‐MadisonMadisonWisconsinUSA
- Human Proteomics ProgramSchool of Medicine and Public HealthUniversity of Wisconsin‐MadisonMadisonWisconsinUSA
| | - Wei Guo
- Department of Animal and Dairy SciencesUniversity of Wisconsin‐MadisonWisconsinUSA
- Department of Animal ScienceUniversity of WyomingLaramieWyomingUSA
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Rhoden A, Schulze T, Pietsch N, Christ T, Hansen A, Eschenhagen T. Comprehensive analyses of the inotropic compound omecamtiv mecarbil in rat and human cardiac preparations. Am J Physiol Heart Circ Physiol 2022; 322:H373-H385. [PMID: 35030072 DOI: 10.1152/ajpheart.00534.2021] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Omecamtiv mecarbil (OM), a myosin activator, was reported to induce complex concentration- and species-dependent effects on contractile function and clinical studies indicated a low therapeutic index with diastolic dysfunction at concentrations above 1 µM. To further characterize effects of OM in a human context and under different preload conditions, we constructed a setup that allows isometric contractility analyses of human induced pluripotent stem cell (hiPSC)-derived engineered heart tissues (EHTs). The results were compared to effects of OM on the very same EHTs measured under auxotonic conditions. OM induced a sustained, concentration-dependent increase in time-to-peak under all conditions (maximally 2-3 fold). Peak force, in contrast, was increased by OM only in human, but not rat EHTs and only under isometric conditions, varied between hiPSC lines and showed a biphasic concentration-dependency with maximal effects at 1 µM. Relaxation time tended to fall under auxotonic and strongly increase under isometric conditions, again with biphasic concentration-dependency. Diastolic tension concentration-dependently increased under all conditions. The latter was reduced by an inhibitor of the mitochondrial sodium calcium exchanger (CGP-37157). OM induced increases in mitochondrial oxidation in isolated cardiomyocytes, indicating that OM, an inotrope that does not increase intracellular and mitochondrial Ca2+, can induce mismatch between an increase in ATP and ROS production and unstimulated mitochondrial redox capacity. Taken together, we developed a novel setup well suitable for isometric measurements of EHTs. The effects of OM on contractility and diastolic tension are complex with concentration-, time-, species- and loading-dependent differences. Effects on mitochondrial function require further studies.
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Affiliation(s)
- Alexandra Rhoden
- Institute of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.,DZHK (German Center for Cardiovascular Research), partner site Hamburg/Kiel/Lübeck, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Thomas Schulze
- Institute of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Niels Pietsch
- Institute of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.,DZHK (German Center for Cardiovascular Research), partner site Hamburg/Kiel/Lübeck, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Torsten Christ
- Institute of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.,DZHK (German Center for Cardiovascular Research), partner site Hamburg/Kiel/Lübeck, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Arne Hansen
- Institute of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.,DZHK (German Center for Cardiovascular Research), partner site Hamburg/Kiel/Lübeck, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Thomas Eschenhagen
- Institute of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.,DZHK (German Center for Cardiovascular Research), partner site Hamburg/Kiel/Lübeck, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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Crocini C, Gotthardt M. Cardiac sarcomere mechanics in health and disease. Biophys Rev 2021; 13:637-652. [PMID: 34745372 PMCID: PMC8553709 DOI: 10.1007/s12551-021-00840-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 08/27/2021] [Indexed: 12/23/2022] Open
Abstract
The sarcomere is the fundamental structural and functional unit of striated muscle and is directly responsible for most of its mechanical properties. The sarcomere generates active or contractile forces and determines the passive or elastic properties of striated muscle. In the heart, mutations in sarcomeric proteins are responsible for the majority of genetically inherited cardiomyopathies. Here, we review the major determinants of cardiac sarcomere mechanics including the key structural components that contribute to active and passive tension. We dissect the molecular and structural basis of active force generation, including sarcomere composition, structure, activation, and relaxation. We then explore the giant sarcomere-resident protein titin, the major contributor to cardiac passive tension. We discuss sarcomere dynamics exemplified by the regulation of titin-based stiffness and the titin life cycle. Finally, we provide an overview of therapeutic strategies that target the sarcomere to improve cardiac contraction and filling.
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Affiliation(s)
- Claudia Crocini
- Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC), Neuromuscular and Cardiovascular Cell Biology, Berlin, Germany
- German Center for Cardiovascular Research (DZHK) Partner Site Berlin, Berlin, Germany
- BioFrontiers Institute & Department of Molecular and Cellular Development, University of Colorado Boulder, Boulder, USA
| | - Michael Gotthardt
- Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC), Neuromuscular and Cardiovascular Cell Biology, Berlin, Germany
- German Center for Cardiovascular Research (DZHK) Partner Site Berlin, Berlin, Germany
- Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany
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RBM20-Related Cardiomyopathy: Current Understanding and Future Options. J Clin Med 2021; 10:jcm10184101. [PMID: 34575212 PMCID: PMC8468976 DOI: 10.3390/jcm10184101] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2021] [Revised: 09/07/2021] [Accepted: 09/08/2021] [Indexed: 12/13/2022] Open
Abstract
Splice regulators play an essential role in the transcriptomic diversity of all eukaryotic cell types and organ systems. Recent evidence suggests a contribution of splice-regulatory networks in many diseases, such as cardiomyopathies. Adaptive splice regulators, such as RNA-binding motif protein 20 (RBM20) determine the physiological mRNA landscape formation, and rare variants in the RBM20 gene explain up to 6% of genetic dilated cardiomyopathy (DCM) cases. With ample knowledge from RBM20-deficient mice, rats, swine and induced pluripotent stem cells (iPSCs), the downstream targets and quantitative effects on splicing are now well-defined and the prerequisites for corrective therapeutic approaches are set. This review article highlights some of the recent advances in the field, ranging from aspects of granule formation to 3D genome architectures underlying RBM20-related cardiomyopathy. Promising therapeutic strategies are presented and put into context with the pathophysiological characteristics of RBM20-related diseases.
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Guo W, Zhu C, Yin Z, Zhang Y, Wang C, Walk AS, Lin Y, McKinsey TA, Woulfe KC, Ren J, Chew HG. The ryanodine receptor stabilizer S107 ameliorates contractility of adult Rbm20 knockout rat cardiomyocytes. Physiol Rep 2021; 9:e15011. [PMID: 34523260 PMCID: PMC8440945 DOI: 10.14814/phy2.15011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2021] [Revised: 07/27/2021] [Accepted: 07/31/2021] [Indexed: 02/07/2023] Open
Abstract
RNA binding motif 20 (RBM20) cardiomyopathy has been detected in approximately 3% of populations afflicted with dilated cardiomyopathy (DCM). It is well conceived that RBM20 cardiomyopathy is provoked by titin isoform switching in combination with resting Ca2+ leaking. In this study, we characterized the cardiac function in Rbm20 knockout (KO) rats at 3-, 6-, 9-, and 12-months of age and examined the effect of the ryanodine receptor stabilizer S107 on resting intracellular levels and cardiomyocyte contractile properties. Our results revealed that even though Rbm20 depletion promoted expression of larger titin isoform and reduced myocardial stiffness in young rats (3 months of age), the established DCM phenotype required more time to embellish. S107 restored elevated intracellular Ca2+ to normal levels and ameliorated cardiomyocyte contractile properties in isolated cardiomyocytes from 6-month-old Rbm20 KO rats. However, S107 failed to preserve cardiac homeostasis in Rbm20 KO rats at 12 months of age, unexpectedly, likely due to the existence of multiple pathogenic mechanisms. Taken together, our data suggest the therapeutic promises of S107 in the management of RBM20 cardiomyopathy.
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Affiliation(s)
- Wei Guo
- Department of Animal and Dairy SciencesUniversity of Wisconsin‐MadisonMadisonWisconsinUSA
| | - Chaoqun Zhu
- Department of Animal ScienceUniversity of WyomingLaramieWyomingUSA
- Department of PharmacologyUniversity of CaliforniaDavisCalifornia95616USA
| | - Zhiyong Yin
- Department of Animal ScienceUniversity of WyomingLaramieWyomingUSA
- Department of Cardiovascular MedicineXijing HospitalFourth Military Medical University15 Changle West RoadXi'anShanxiChina
| | - Yanghai Zhang
- Department of Animal and Dairy SciencesUniversity of Wisconsin‐MadisonMadisonWisconsinUSA
| | - Chunyan Wang
- Department of Animal and Dairy SciencesUniversity of Wisconsin‐MadisonMadisonWisconsinUSA
| | | | - Ying‐Hsi Lin
- Division of Cardiology, and Consortium for Fibrosis Research & TranslationDepartment of MedicineUniversity of Colorado Anschutz Medical CampusAuroraColoradoUSA
| | - Timothy A. McKinsey
- Division of Cardiology, and Consortium for Fibrosis Research & TranslationDepartment of MedicineUniversity of Colorado Anschutz Medical CampusAuroraColoradoUSA
| | - Kathleen C. Woulfe
- Division of Cardiology, and Consortium for Fibrosis Research & TranslationDepartment of MedicineUniversity of Colorado Anschutz Medical CampusAuroraColoradoUSA
| | - Jun Ren
- School of PharmacyUniversity of WyomingLaramieWyomingUSA
| | - Herbert G. Chew
- Department of BiologyWestern Wyoming CollegeRock SpringsWyomingUSA
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Abstract
PURPOSE OF REVIEW This review aims to give an update on recent findings related to the cardiac splicing factor RNA-binding motif protein 20 (RBM20) and RBM20 cardiomyopathy, a form of dilated cardiomyopathy caused by mutations in RBM20. RECENT FINDINGS While most research on RBM20 splicing targets has focused on titin (TTN), multiple studies over the last years have shown that other splicing targets of RBM20 including Ca2+/calmodulin-dependent kinase IIδ (CAMK2D) might be critically involved in the development of RBM20 cardiomyopathy. In this regard, loss of RBM20 causes an abnormal intracellular calcium handling, which may relate to the arrhythmogenic presentation of RBM20 cardiomyopathy. In addition, RBM20 presents clinically in a highly gender-specific manner, with male patients suffering from an earlier disease onset and a more severe disease progression. Further research on RBM20, and treatment of RBM20 cardiomyopathy, will need to consider both the multitude and relative contribution of the different splicing targets and related pathways, as well as gender differences.
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Maimaiti R, Zhu C, Zhang Y, Ding Q, Guo W. RBM20-Mediated Pre-mRNA Splicing Has Muscle-Specificity and Differential Hormonal Responses between Muscles and in Muscle Cell Cultures. Int J Mol Sci 2021; 22:2928. [PMID: 33805770 PMCID: PMC7999644 DOI: 10.3390/ijms22062928] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 03/10/2021] [Accepted: 03/11/2021] [Indexed: 11/16/2022] Open
Abstract
Pre-mRNA splicing plays an important role in muscle function and diseases. The RNA binding motif 20 (RBM20) is a splicing factor that is predominantly expressed in muscle tissues and primarily regulates pre-mRNA splicing of Ttn, encoding a giant muscle protein titin that is responsible for muscle function and diseases. RBM20-mediated Ttn splicing has been mostly studied in heart muscle, but not in skeletal muscle. In this study, we investigated splicing specificity in different muscle types in Rbm20 knockout rats and hormonal effects on RBM20-mediated splicing both in cellulo and in vivo studies. The results revealed that RBM20 is differentially expressed across muscles and RBM20-mediated splicing is muscle-type specific. In the presence of RBM20, Ttn splicing responds to hormones in a muscle-type dependent manner, while in the absence of RBM20, Ttn splicing is not affected by hormones. In differentiated and undifferentiated C2C12 cells, RBM20-mediated splicing in response to hormonal effects is mainly through genomic signaling pathway. The knowledge gained from this study may help further understand muscle-specific gene splicing in response to hormone stimuli in different muscle types.
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Affiliation(s)
- Rexiati Maimaiti
- Animal Science Department, University of Wyoming, Laramie, WY 82071, USA; (R.M.); (C.Z.)
| | - Chaoqun Zhu
- Animal Science Department, University of Wyoming, Laramie, WY 82071, USA; (R.M.); (C.Z.)
| | - Yanghai Zhang
- Animal and Dairy Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA; (Y.Z.); (Q.D.)
| | - Qiyue Ding
- Animal and Dairy Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA; (Y.Z.); (Q.D.)
| | - Wei Guo
- Animal and Dairy Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA; (Y.Z.); (Q.D.)
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Angiotensin II Influences Pre-mRNA Splicing Regulation by Enhancing RBM20 Transcription Through Activation of the MAPK/ELK1 Signaling Pathway. Int J Mol Sci 2019; 20:ijms20205059. [PMID: 31614708 PMCID: PMC6829565 DOI: 10.3390/ijms20205059] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2019] [Revised: 10/05/2019] [Accepted: 10/07/2019] [Indexed: 12/31/2022] Open
Abstract
RNA binding motif 20 (RBM20) is a key regulator of pre-mRNA splicing of titin and other genes that are associated with cardiac diseases. Hormones, like insulin, triiodothyronine (T3), and angiotensin II (Ang II), can regulate gene-splicing through RBM20, but the detailed mechanism remains unclear. This study was aimed at investigating the signaling mechanism by which hormones regulate pre-mRNA splicing through RBM20. We first examined the role of RBM20 in Z-, I-, and M-band titin splicing at different ages in wild type (WT) and RBM20 knockout (KO) rats using RT-PCR; we found that RBM20 is the predominant regulator of I-band titin splicing at all ages. Then we treated rats with propylthiouracil (PTU), T3, streptozotocin (STZ), and Ang II and evaluated the impact of these hormones on the splicing of titin, LIM domain binding 3 (Ldb3), calcium/calmodulin-dependent protein kinase II gamma (Camk2g), and triadin (Trdn). We determined the activation of mitogen-activated protein kinase (MAPK) signaling in primary cardiomyocytes treated with insulin, T3, and Ang II using western blotting; MAPK signaling was activated and RBM20 expression increased after treatment. Two downstream transcriptional factors c-jun and ETS Transcription Factor (ELK1) can bind the promoter of RBM20. A dual-luciferase activity assay revealed that Ang II, but not insulin and T3, can trigger ELK1 and thus promote transcription of RBM20. This study revealed that Ang II can trigger ELK1 through activation of MAPK signaling by enhancing RBM20 expression which regulates pre-mRNA splicing. Our study provides a potential therapeutic target for the treatment of cardiac diseases in RBM20-mediated pre-mRNA splicing.
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Najafi A, van de Locht M, Schuldt M, Schönleitner P, van Willigenburg M, Bollen I, Goebel M, Ottenheijm CAC, van der Velden J, Helmes M, Kuster DWD. End-diastolic force pre-activates cardiomyocytes and determines contractile force: role of titin and calcium. J Physiol 2019; 597:4521-4531. [PMID: 31314138 PMCID: PMC6852589 DOI: 10.1113/jp277985] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Accepted: 07/10/2019] [Indexed: 12/22/2022] Open
Abstract
Titin functions as a molecular spring, and cardiomyocytes are able, through splicing, to control the length of titin. We hypothesized that together with diastolic [Ca2+], titin‐based stretch pre‐activates cardiomyocytes during diastole and is a major determinant of force production in the subsequent contraction. Through this mechanism titin would play an important role in active force development and length‐dependent activation. Mutations in the splicing factor RNA binding motif protein 20 (RBM20) result in expression of large, highly compliant titin isoforms. We measured single cardiomyocyte work loops that mimic the cardiac cycle in wild‐type (WT) and heterozygous (HET) RBM20‐deficient rats. In addition, we studied the role of diastolic [Ca2+] in membrane‐permeabilized WT and HET cardiomyocytes. Intact cardiomyocytes isolated from HET left ventricles were unable to produce normal levels of work (55% of WT) at low pacing frequencies, but this difference disappeared at high pacing frequencies. Length‐dependent activation (force–sarcomere length relationship) was blunted in HET cardiomyocytes, but the force–end‐diastolic force relationship was not different between HET and WT cardiomyocytes. To delineate the effects of diastolic [Ca2+] and titin pre‐activation on force generation, measurements were performed in detergent‐permeabilized cardiomyocytes. Cardiac twitches were simulated by transiently exposing permeabilized cardiomyocytes to 2 µm Ca2+. Increasing diastolic [Ca2+] from 1 to 80 nm increased force development twofold in WT. Higher diastolic [Ca2+] was needed in HET. These findings are consistent with our hypothesis that pre‐activation increases active force development. Highly compliant titin allows cells to function at higher diastolic [Ca2+].
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Affiliation(s)
- Aref Najafi
- Amsterdam UMC, Vrije Universiteit Amsterdam, Physiology, Amsterdam Cardiovascular Sciences, de Boelelaan 1117, 1081 HZ, Amsterdam, the Netherlands.,Netherlands Heart Institute, PO box 19258, 3501 DG, Utrecht, the Netherlands
| | - Martijn van de Locht
- Amsterdam UMC, Vrije Universiteit Amsterdam, Physiology, Amsterdam Cardiovascular Sciences, de Boelelaan 1117, 1081 HZ, Amsterdam, the Netherlands
| | - Maike Schuldt
- Amsterdam UMC, Vrije Universiteit Amsterdam, Physiology, Amsterdam Cardiovascular Sciences, de Boelelaan 1117, 1081 HZ, Amsterdam, the Netherlands
| | | | | | - Ilse Bollen
- Amsterdam UMC, Vrije Universiteit Amsterdam, Physiology, Amsterdam Cardiovascular Sciences, de Boelelaan 1117, 1081 HZ, Amsterdam, the Netherlands
| | - Max Goebel
- Amsterdam UMC, Vrije Universiteit Amsterdam, Physiology, Amsterdam Cardiovascular Sciences, de Boelelaan 1117, 1081 HZ, Amsterdam, the Netherlands
| | - Coen A C Ottenheijm
- Amsterdam UMC, Vrije Universiteit Amsterdam, Physiology, Amsterdam Cardiovascular Sciences, de Boelelaan 1117, 1081 HZ, Amsterdam, the Netherlands
| | - Jolanda van der Velden
- Amsterdam UMC, Vrije Universiteit Amsterdam, Physiology, Amsterdam Cardiovascular Sciences, de Boelelaan 1117, 1081 HZ, Amsterdam, the Netherlands.,Netherlands Heart Institute, PO box 19258, 3501 DG, Utrecht, the Netherlands
| | - Michiel Helmes
- Amsterdam UMC, Vrije Universiteit Amsterdam, Physiology, Amsterdam Cardiovascular Sciences, de Boelelaan 1117, 1081 HZ, Amsterdam, the Netherlands.,Ionoptix, de Boelelaan 1108, 1081 HV, Amsterdam, the Netherlands.,CytoCypher, de Boelelaan 1108, 1081 HV, Amsterdam, the Netherlands
| | - Diederik W D Kuster
- Amsterdam UMC, Vrije Universiteit Amsterdam, Physiology, Amsterdam Cardiovascular Sciences, de Boelelaan 1117, 1081 HZ, Amsterdam, the Netherlands
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14
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Schwahn DJ, Pleitner JM, Greaser ML. Megaesophagus Is a Major Pathological Condition in Rats With a Large Deletion in the Rbm20 Gene. Vet Pathol 2019; 57:151-159. [PMID: 31221019 PMCID: PMC7221460 DOI: 10.1177/0300985819854224] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
A spontaneously arising, loss-of-function mutation in the RNA binding motif protein 20
(Rbm20) gene, which encodes a nuclear splicing protein,
was previously identified as the underlying reason for expression of an abnormally large
TITIN (TTN) protein in a rat model of cardiomyopathy. An outbreak of Pseudomonas aeruginosa led to submission of rats with dyspnea, sneezing,
lethargy, nasal discharge, and/or unexpected death for diagnostic evaluation. Necropsy
revealed underlying megaesophagus in Rbm20–/–
rats. Further phenotyping of this rat strain and determination of the size of esophageal
TTN was undertaken. The Rbm20-defective rats developed
megaesophagus at an early age (26 weeks) with high frequency (13/32, 41%). They also often
exhibited secondary rhinitis (9/32, 28%), aspiration pneumonia (8/32, 25%), and otitis
media/interna (6/32, 19%). In addition, these rats had a high prevalence of hydronephrosis
(13/32, 41%). RBM20 is involved in splicing multiple RNA transcripts, one of which is the
muscle-specific protein TTN. Rbm20 mutations are a
significant cause of dilated cardiomyopathy in humans. In Rbm20-defective rats, TTN size was significantly increased in the skeletal
muscle of the esophagus. Megaesophagus in this rat strain (maintained on a mixed genetic
background) is hypothesized to result from altered TTN stretch signaling in esophageal
skeletal muscle. This study describes a novel mechanism for the development of
megaesophagus, which may be useful for understanding the pathogenesis of megaesophagus in
humans and offers insights into potential myogenic causes of this condition. This is the
first report of megaesophagus and other noncardiac pathogenic changes associated with
mutation of Rbm20 in any species.
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Affiliation(s)
- Denise J Schwahn
- Research Animal Resources Center and Muscle Biology Laboratory, University of Wisconsin, Madison, WI, USA
| | | | - Marion L Greaser
- Muscle Biology Laboratory, University of Wisconsin, Madison, WI, USA
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15
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Chen Z, Maimaiti R, Zhu C, Cai H, Stern A, Mozdziak P, Ge Y, Ford SP, Nathanielsz PW, Guo W. Z-band and M-band titin splicing and regulation by RNA binding motif 20 in striated muscles. J Cell Biochem 2018; 119:9986-9996. [PMID: 30133019 PMCID: PMC6218289 DOI: 10.1002/jcb.27328] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Accepted: 06/28/2018] [Indexed: 12/12/2022]
Abstract
Titin (TTN) has multifunctional roles in sarcomere assembly, mechanosignaling transduction, and muscle stiffness. TTN splicing generates variable protein sizes with different functions. Therefore, understanding TTN splicing is important to develop a novel treatment for TTN-based diseases. The I-band TTN splicing regulated by RNA binding motif 20 (RBM20) has been extensively studied. However, the Z- and M-band splicing and regulation remain poorly understood. Herein, we aimed to define the Z- and M-band splicing in striated muscles and determined whether RBM20 regulates the Z- and M-band splicing. We discovered four new Z-band TTN splicing variants, and one of them dominates in mouse, rat, sheep, and human hearts. But only one form can be detected in frog and chicken hearts. In skeletal muscles, three new Z repeats (Zr) were detected, and Zr4 to 6 exclusion dominates in the fast muscles, whereas Zr4 skipping dominates in the slow muscle. No developmental changes were detected in the Z-band. In the M-band, two new variants were discovered with alternative 3' splice site in exon363 (Mex5) and alternative 5' splice site in intron 362. However, only the sheep heart expresses two new variants rather than other species. Skeletal muscles express three M-band variants with altered ratios of Mex5 inclusion to Mex5 exclusion. Finally, we revealed that RBM20 does not regulate the Z- and M-band splicing in the heart, but does in skeletal muscles. Taken together, we characterized the Z- and M-band splicing and provided the first evidence of the role of RBM20 in the Z- and M-band TTN splicing.
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Affiliation(s)
- Zhilong Chen
- Department of Animal Science, College of Animal Science and Technology, Northwest A&F University, Yangling, Shanxi, China
- Department of Animal Science, University of Wyoming, Laramie, Wyoming
| | - Rexiati Maimaiti
- Department of Animal Science, University of Wyoming, Laramie, Wyoming
| | - Chaoqun Zhu
- Department of Animal Science, University of Wyoming, Laramie, Wyoming
| | - Hanfang Cai
- Department of Animal Science, College of Animal Science and Technology, Northwest A&F University, Yangling, Shanxi, China
- Department of Animal Science, University of Wyoming, Laramie, Wyoming
| | - Allysa Stern
- Prestage Department of Poultry Science, North Carolina State University, Raleigh, North Carolina
| | - Paul Mozdziak
- Prestage Department of Poultry Science, North Carolina State University, Raleigh, North Carolina
| | - Ying Ge
- Department of Cell and Regenerative Biology, Human Proteomics Program, University of Wisconsin, Madison, Wisconsin
- Department of Chemistry, Human Proteomics Program, University of Wisconsin, Madison, Wisconsin
| | - Stephen P Ford
- Department of Animal Science, University of Wyoming, Laramie, Wyoming
| | | | - Wei Guo
- Department of Animal Science, University of Wyoming, Laramie, Wyoming
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16
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Lindqvist J, van den Berg M, van der Pijl R, Hooijman PE, Beishuizen A, Elshof J, de Waard M, Girbes A, Spoelstra-de Man A, Shi ZH, van den Brom C, Bogaards S, Shen S, Strom J, Granzier H, Kole J, Musters RJP, Paul MA, Heunks LMA, Ottenheijm CAC. Positive End-Expiratory Pressure Ventilation Induces Longitudinal Atrophy in Diaphragm Fibers. Am J Respir Crit Care Med 2018; 198:472-485. [PMID: 29578749 PMCID: PMC6118031 DOI: 10.1164/rccm.201709-1917oc] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2017] [Accepted: 03/26/2018] [Indexed: 01/11/2023] Open
Abstract
RATIONALE Diaphragm weakness in critically ill patients prolongs ventilator dependency and duration of hospital stay and increases mortality and healthcare costs. The mechanisms underlying diaphragm weakness include cross-sectional fiber atrophy and contractile protein dysfunction, but whether additional mechanisms are at play is unknown. OBJECTIVES To test the hypothesis that mechanical ventilation with positive end-expiratory pressure (PEEP) induces longitudinal atrophy by displacing the diaphragm in the caudal direction and reducing the length of fibers. METHODS We studied structure and function of diaphragm fibers of mechanically ventilated critically ill patients and mechanically ventilated rats with normal and increased titin compliance. MEASUREMENTS AND MAIN RESULTS PEEP causes a caudal movement of the diaphragm, both in critically ill patients and in rats, and this caudal movement reduces fiber length. Diaphragm fibers of 18-hour mechanically ventilated rats (PEEP of 2.5 cm H2O) adapt to the reduced length by absorbing serially linked sarcomeres, the smallest contractile units in muscle (i.e., longitudinal atrophy). Increasing the compliance of titin molecules reduces longitudinal atrophy. CONCLUSIONS Mechanical ventilation with PEEP results in longitudinal atrophy of diaphragm fibers, a response that is modulated by the elasticity of the giant sarcomeric protein titin. We postulate that longitudinal atrophy, in concert with the aforementioned cross-sectional atrophy, hampers spontaneous breathing trials in critically ill patients: during these efforts, end-expiratory lung volume is reduced, and the shortened diaphragm fibers are stretched to excessive sarcomere lengths. At these lengths, muscle fibers generate less force, and diaphragm weakness ensues.
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Affiliation(s)
- Johan Lindqvist
- Cellular and Molecular Medicine, University of Arizona, Tucson, Arizona
| | | | - Robbert van der Pijl
- Cellular and Molecular Medicine, University of Arizona, Tucson, Arizona
- Department of Physiology
| | | | - Albertus Beishuizen
- Department of Intensive Care, Medisch Spectrum Twente, Enschede, the Netherlands; and
| | | | | | | | | | - Zhong-Hua Shi
- Department of Critical Care Medicine, Beijing Tiantan Hospital, Capital Medical University, Beijing, PR China
| | | | | | - Shengyi Shen
- Cellular and Molecular Medicine, University of Arizona, Tucson, Arizona
| | - Joshua Strom
- Cellular and Molecular Medicine, University of Arizona, Tucson, Arizona
| | - Henk Granzier
- Cellular and Molecular Medicine, University of Arizona, Tucson, Arizona
| | | | | | - Marinus A. Paul
- Department of Cardiothoracic Surgery, Vrije Universiteit Medical Center, Amsterdam, the Netherlands
| | | | - Coen A. C. Ottenheijm
- Cellular and Molecular Medicine, University of Arizona, Tucson, Arizona
- Department of Physiology
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17
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Phosphorylation of the RSRSP stretch is critical for splicing regulation by RNA-Binding Motif Protein 20 (RBM20) through nuclear localization. Sci Rep 2018; 8:8970. [PMID: 29895960 PMCID: PMC5997748 DOI: 10.1038/s41598-018-26624-w] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Accepted: 05/14/2018] [Indexed: 11/08/2022] Open
Abstract
RBM20 is a major regulator of heart-specific alternative pre-mRNA splicing of TTN encoding a giant sarcomeric protein titin. Mutation in RBM20 is linked to autosomal-dominant familial dilated cardiomyopathy (DCM), yet most of the RBM20 missense mutations in familial and sporadic cases were mapped to an RSRSP stretch in an arginine/serine-rich region of which function remains unknown. In the present study, we identified an R634W missense mutation within the stretch and a G1031X nonsense mutation in cohorts of DCM patients. We demonstrate that the two serine residues in the RSRSP stretch are constitutively phosphorylated and mutations in the stretch disturb nuclear localization of RBM20. Rbm20S637A knock-in mouse mimicking an S635A mutation reported in a familial case showed a remarkable effect on titin isoform expression like in a patient carrying the mutation. These results revealed the function of the RSRSP stretch as a critical part of a nuclear localization signal and offer the Rbm20S637A mouse as a good model for in vivo study.
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18
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Guo W, Sun M. RBM20, a potential target for treatment of cardiomyopathy via titin isoform switching. Biophys Rev 2018; 10:15-25. [PMID: 28577155 PMCID: PMC5803173 DOI: 10.1007/s12551-017-0267-5] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Accepted: 05/16/2017] [Indexed: 12/18/2022] Open
Abstract
Cardiomyopathy, also known as heart muscle disease, is an unfavorable condition leading to alterations in myocardial contraction and/or impaired ability of ventricular filling. The onset and development of cardiomyopathy have not currently been well defined. Titin is a giant multifunctional sarcomeric filament protein that provides passive stiffness to cardiomyocytes and has been implicated to play an important role in the origin and development of cardiomyopathy and heart failure. Titin-based passive stiffness can be mainly adjusted by isoform switching and post-translational modifications in the spring regions. Recently, genetic mutations of TTN have been identified that can also contribute to variable passive stiffness, though the detailed mechanisms remain unclear. In this review, we will discuss titin isoform switching as it relates to alternative splicing during development stages and differences between species and muscle types. We provide an update on the regulatory mechanisms of TTN splicing controlled by RBM20 and cover the roles of TTN splicing in adjusting the diastolic stiffness and systolic compliance of the healthy and the failing heart. Finally, this review attempts to provide future directions for RBM20 as a potential target for pharmacological intervention in cardiomyopathy and heart failure.
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Affiliation(s)
- Wei Guo
- Animal Science, University of Wyoming, Laramie, WY, 82071, USA.
- Center for Cardiovascular Research and Integrative Medicine, University of Wyoming, Laramie, WY, 82071, USA.
| | - Mingming Sun
- Animal Science, University of Wyoming, Laramie, WY, 82071, USA
- Center for Cardiovascular Research and Integrative Medicine, University of Wyoming, Laramie, WY, 82071, USA
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19
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Muscle-Specific Mis-Splicing and Heart Disease Exemplified by RBM20. Genes (Basel) 2018; 9:genes9010018. [PMID: 29304022 PMCID: PMC5793171 DOI: 10.3390/genes9010018] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Revised: 12/23/2017] [Accepted: 12/27/2017] [Indexed: 11/17/2022] Open
Abstract
Alternative splicing is an essential post-transcriptional process to generate multiple functional RNAs or proteins from a single transcript. Progress in RNA biology has led to a better understanding of muscle-specific RNA splicing in heart disease. The recent discovery of the muscle-specific splicing factor RNA-binding motif 20 (RBM20) not only provided great insights into the general alternative splicing mechanism but also demonstrated molecular mechanism of how this splicing factor is associated with dilated cardiomyopathy. Here, we review our current knowledge of muscle-specific splicing factors and heart disease, with an emphasis on RBM20 and its targets, RBM20-dependent alternative splicing mechanism, RBM20 disease origin in induced Pluripotent Stem Cells (iPSCs), and RBM20 mutations in dilated cardiomyopathy. In the end, we will discuss the multifunctional role of RBM20 and manipulation of RBM20 as a potential therapeutic target for heart disease.
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20
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Hiemstra JA, Veteto AB, Lambert MD, Olver TD, Ferguson BS, McDonald KS, Emter CA, Domeier TL. Chronic low-intensity exercise attenuates cardiomyocyte contractile dysfunction and impaired adrenergic responsiveness in aortic-banded mini-swine. J Appl Physiol (1985) 2018; 124:1034-1044. [PMID: 29357490 DOI: 10.1152/japplphysiol.00840.2017] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Exercise improves clinical outcomes in patients diagnosed with heart failure with reduced ejection fraction (HFrEF), in part via beneficial effects on cardiomyocyte Ca2+ cycling during excitation-contraction coupling (ECC). However, limited data exist regarding the effects of exercise training on cardiomyocyte function in patients diagnosed with heart failure with preserved ejection fraction (HFpEF). The purpose of this study was to investigate cardiomyocyte Ca2+ handling and contractile function following chronic low-intensity exercise training in aortic-banded miniature swine and test the hypothesis that low-intensity exercise improves cardiomyocyte function in a large animal model of pressure overload. Animals were divided into control (CON), aortic-banded sedentary (AB), and aortic-banded low-intensity trained (AB-LIT) groups. Left ventricular cardiomyocytes were electrically stimulated (0.5 Hz) to assess Ca2+ homeostasis (fura-2-AM) and unloaded shortening during ECC under conditions of baseline pacing and pacing with adrenergic stimulation using dobutamine (1 μM). Cardiomyocytes in AB animals exhibited depressed Ca2+ transient amplitude and cardiomyocyte shortening vs. CON under both conditions. Exercise training attenuated AB-induced decreases in cardiomyocyte Ca2+ transient amplitude but did not prevent impaired shortening vs. CON. With dobutamine, AB-LIT exhibited both Ca2+ transient and shortening amplitude similar to CON. Adrenergic sensitivity, assessed as the time to maximum inotropic response following dobutamine treatment, was depressed in the AB group but normal in AB-LIT animals. Taken together, our data suggest exercise training is beneficial for cardiomyocyte function via the effects on Ca2+ homeostasis and adrenergic sensitivity in a large animal model of pressure overload-induced heart failure. NEW & NOTEWORTHY Conventional treatments have failed to improve the prognosis of heart failure with preserved ejection fraction (HFpEF) patients. Our findings show chronic low-intensity exercise training can prevent cardiomyocyte dysfunction and impaired adrenergic responsiveness in a translational large animal model of chronic pressure overload-induced heart failure with relevance to human HFpEF.
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Affiliation(s)
- Jessica A Hiemstra
- Department of Biomedical Sciences, School of Veterinary Medicine, University of Missouri , Columbia, Missouri
| | - Adam B Veteto
- Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri , Columbia, Missouri
| | - Michelle D Lambert
- Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri , Columbia, Missouri
| | - T Dylan Olver
- Department of Biomedical Sciences, School of Veterinary Medicine, University of Missouri , Columbia, Missouri
| | - Brian S Ferguson
- Department of Biomedical Sciences, School of Veterinary Medicine, University of Missouri , Columbia, Missouri
| | - Kerry S McDonald
- Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri , Columbia, Missouri
| | - Craig A Emter
- Department of Biomedical Sciences, School of Veterinary Medicine, University of Missouri , Columbia, Missouri
| | - Timothy L Domeier
- Department of Medical Pharmacology and Physiology, School of Medicine, University of Missouri , Columbia, Missouri
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21
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Streckfuss-Bömeke K, Tiburcy M, Fomin A, Luo X, Li W, Fischer C, Özcelik C, Perrot A, Sossalla S, Haas J, Vidal RO, Rebs S, Khadjeh S, Meder B, Bonn S, Linke WA, Zimmermann WH, Hasenfuss G, Guan K. Severe DCM phenotype of patient harboring RBM20 mutation S635A can be modeled by patient-specific induced pluripotent stem cell-derived cardiomyocytes. J Mol Cell Cardiol 2017; 113:9-21. [PMID: 28941705 DOI: 10.1016/j.yjmcc.2017.09.008] [Citation(s) in RCA: 63] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2017] [Revised: 09/01/2017] [Accepted: 09/19/2017] [Indexed: 10/18/2022]
Abstract
The ability to generate patient-specific induced pluripotent stem cells (iPSCs) provides a unique opportunity for modeling heart disease in vitro. In this study, we generated iPSCs from a patient with dilated cardiomyopathy (DCM) caused by a missense mutation S635A in RNA-binding motif protein 20 (RBM20) and investigated the functionality and cell biology of cardiomyocytes (CMs) derived from patient-specific iPSCs (RBM20-iPSCs). The RBM20-iPSC-CMs showed abnormal distribution of sarcomeric α-actinin and defective calcium handling compared to control-iPSC-CMs, suggesting disorganized myofilament structure and altered calcium machinery in CMs of the RBM20 patient. Engineered heart muscles (EHMs) from RBM20-iPSC-CMs showed that not only active force generation was impaired in RBM20-EHMs but also passive stress of the tissue was decreased, suggesting a higher visco-elasticity of RBM20-EHMs. Furthermore, we observed a reduced titin (TTN) N2B-isoform expression in RBM20-iPSC-CMs by demonstrating a reduction of exon skipping in the PEVK region of TTN and an inhibition of TTN isoform switch. In contrast, in control-iPSC-CMs both TTN isoforms N2B and N2BA were expressed, indicating that the TTN isoform switch occurs already during early cardiogenesis. Using next generation RNA sequencing, we mapped transcriptome and splicing target profiles of RBM20-iPSC-CMs and identified different cardiac gene networks in response to the analyzed RBM20 mutation in cardiac-specific processes. These findings shed the first light on molecular mechanisms of RBM20-dependent pathological cardiac remodeling leading to DCM. Our data demonstrate that iPSC-CMs coupled with EHMs provide a powerful tool for evaluating disease-relevant functional defects and for a deeper mechanistic understanding of alternative splicing-related cardiac diseases.
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Affiliation(s)
- Katrin Streckfuss-Bömeke
- Department of Cardiology and Pneumology, Universitätsmedizin Göttingen, Germany; DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Germany
| | - Malte Tiburcy
- DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Germany; Institute of Pharmacology and Toxicology, Universitätsmedizin Göttingen, Germany
| | - Andrey Fomin
- DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Germany; Department of Cardiovascular Physiology, Ruhr University Bochum, Germany
| | - Xiaojing Luo
- Institute of Pharmacology and Toxicology, Technische Universität Dresden, Germany
| | - Wener Li
- Institute of Pharmacology and Toxicology, Technische Universität Dresden, Germany
| | - Claudia Fischer
- Department of Cardiology and Pneumology, Universitätsmedizin Göttingen, Germany; DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Germany
| | - Cemil Özcelik
- Cardiovascular Genetics, Experimental and Clinical Research Center, Charité-Universitätsmedizin Berlin, Germany; Medizinischen Klinik I Kardiologie, Gastroenterologie und Diabetologie, Knappschaftskrankenhaus Recklingshausen, Germany
| | - Andreas Perrot
- Cardiovascular Genetics, Experimental and Clinical Research Center, Charité-Universitätsmedizin Berlin, Germany
| | - Samuel Sossalla
- Department of Cardiology and Pneumology, Universitätsmedizin Göttingen, Germany; DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Germany; Department of Internal Medicine 2 - Cardiology, University Medical Center Regensburg, Germany
| | - Jan Haas
- Department of Cardiology, University of Heidelberg, Germany; DZHK, Partner Site Heidelberg, Germany
| | | | - Sabine Rebs
- Department of Cardiology and Pneumology, Universitätsmedizin Göttingen, Germany
| | - Sara Khadjeh
- Department of Cardiology and Pneumology, Universitätsmedizin Göttingen, Germany; DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Germany
| | - Benjamin Meder
- Department of Cardiology, University of Heidelberg, Germany; DZHK, Partner Site Heidelberg, Germany
| | - Stefan Bonn
- German Center for Neurodegenerative Diseases, Göttingen and Tübingen, Germany; Institute of Medical Systems Biology, Center for Molecular Neurobiology, University Clinic Hamburg-Eppendorf, Hamburg, Germany
| | - Wolfgang A Linke
- DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Germany; Department of Cardiovascular Physiology, Ruhr University Bochum, Germany
| | - Wolfram-Hubertus Zimmermann
- DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Germany; Institute of Pharmacology and Toxicology, Universitätsmedizin Göttingen, Germany
| | - Gerd Hasenfuss
- Department of Cardiology and Pneumology, Universitätsmedizin Göttingen, Germany; DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Germany
| | - Kaomei Guan
- Department of Cardiology and Pneumology, Universitätsmedizin Göttingen, Germany; Institute of Pharmacology and Toxicology, Technische Universität Dresden, Germany.
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22
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Insulin regulates titin pre-mRNA splicing through the PI3K-Akt-mTOR kinase axis in a RBM20-dependent manner. Biochim Biophys Acta Mol Basis Dis 2017; 1863:2363-2371. [PMID: 28676430 DOI: 10.1016/j.bbadis.2017.06.023] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Revised: 06/25/2017] [Accepted: 06/29/2017] [Indexed: 12/13/2022]
Abstract
Titin, a giant sarcomeric protein, is largely responsible for the diastolic properties of the heart. It has two major isoforms, N2B and N2BA due to pre-mRNA splicing regulated mainly by a splicing factor RNA binding motif 20 (RBM20). Mis-splicing of titin pre-mRNA in response to external stimuli may lead to altered ratio of N2B to N2BA, and thus, impaired cardiac contractile function. However, little is known about titin alternative splicing in response to external stimuli. Here, we reported the detailed mechanisms of titin alternative splicing in response to insulin. Insulin treatment in cultured neonatal rat cardiomyocytes (NRCMs) activated the PI3K-Akt-mTOR kinase axis, leading to increased N2B expression in the presence of RBM20, but not in NRCMs in the absence of RBM20. By inhibiting this kinase axis with inhibitors, decreased N2B isoform was observed in NRCMs and also in diabetic rat model treated with streptozotocin, but not in NRCMs and diabetic rats in the absence of RBM20. In addition to the alteration of titin isoform ratios in response to insulin, we found that RBM20 expression was increased in NRCMs with insulin treatment, suggesting that RBM20 levels were also regulated by insulin-induced kinase axis. Further, knockdown of p70S6K1 with siRNA reduced both RBM20 and N2B levels, while knockdown of 4E-BP1 elevated expression levels of RBM20 and N2B. These findings reveal a major signal transduction pathway for insulin-induced titin alternative splicing, and place RBM20 in a central position in the pathway, which is consistent with the reputed role of RBM20 in titin alternative splicing. Findings from this study shed light on gene therapeutic strategies at the molecular level by correction of pre-mRNA mis-splicing.
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23
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Stebbings GK, Williams AG, Herbert AJ, Lockey SJ, Heffernan SM, Erskine RM, Morse CI, Day SH. TTN
genotype is associated with fascicle length and marathon running performance. Scand J Med Sci Sports 2017; 28:400-406. [DOI: 10.1111/sms.12927] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/30/2017] [Indexed: 01/10/2023]
Affiliation(s)
- G. K. Stebbings
- MMU Sports Genomics Laboratory; Department of Exercise and Sport Science; Manchester Metropolitan University; Crewe UK
| | - A. G. Williams
- MMU Sports Genomics Laboratory; Department of Exercise and Sport Science; Manchester Metropolitan University; Crewe UK
- Institute of Sport, Exercise and Health; University College London; London UK
| | - A. J. Herbert
- MMU Sports Genomics Laboratory; Department of Exercise and Sport Science; Manchester Metropolitan University; Crewe UK
| | - S. J. Lockey
- MMU Sports Genomics Laboratory; Department of Exercise and Sport Science; Manchester Metropolitan University; Crewe UK
- School of Medical Education; Newcastle University; Newcastle upon Tyne UK
| | - S. M. Heffernan
- MMU Sports Genomics Laboratory; Department of Exercise and Sport Science; Manchester Metropolitan University; Crewe UK
| | - R. M. Erskine
- Institute of Sport, Exercise and Health; University College London; London UK
- School of Sport and Exercise Sciences; Liverpool John Moores University; Liverpool UK
| | - C. I. Morse
- MMU Sports Genomics Laboratory; Department of Exercise and Sport Science; Manchester Metropolitan University; Crewe UK
| | - S. H. Day
- MMU Sports Genomics Laboratory; Department of Exercise and Sport Science; Manchester Metropolitan University; Crewe UK
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Ait-Mou Y, Zhang M, Martin JL, Greaser ML, de Tombe PP. Impact of titin strain on the cardiac slow force response. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2017. [PMID: 28648628 DOI: 10.1016/j.pbiomolbio.2017.06.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Stretch of myocardium, such as occurs upon increased filling of the cardiac chamber, induces two distinct responses: an immediate increase in twitch force followed by a slower increase in twitch force that develops over the course of several minutes. The immediate response is due, in part, to modulation of myofilament Ca2+ sensitivity by sarcomere length (SL). The slowly developing force response, termed the Slow Force Response (SFR), is caused by a slowly developing increase in intracellular Ca2+ upon sustained stretch. A blunted immediate force response was recently reported for myocardium isolated from homozygous giant titin mutant rats (HM) compared to muscle from wild-type littermates (WT). Here, we examined the impact of titin isoform on the SFR. Right ventricular trabeculae were isolated and mounted in an experimental chamber. SL was measured by laser diffraction. The SFR was recorded in response to a 0.2 μm SL stretch in the presence of [Ca2+]o = 0.4 mM, a bathing concentration reflecting ∼50% of maximum twitch force development at 25 °C. Presence of the giant titin isoform (HM) was associated with a significant reduction in diastolic passive force upon stretch, and ∼50% reduction of the magnitude of the SFR; the rate of SFR development was unaffected. The sustained SL stretch was identical in both muscle groups. Therefore, our data suggest that cytoskeletal strain may underlie directly the cellular mechanisms that lead to the increased intracellular [Ca2+]i that causes the SFR, possibly by involving cardiac myocyte integrin signaling pathways.
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Affiliation(s)
- Younss Ait-Mou
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Ave, Maywood, IL 60153, United States
| | - Mengjie Zhang
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Ave, Maywood, IL 60153, United States
| | - Jody L Martin
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Ave, Maywood, IL 60153, United States
| | - Marion L Greaser
- Department of Animal Sciences, Muscle Biology Laboratory, University of Wisconsin - Madison, 1450 Linden Drive, Madison, WI 53706, United States
| | - Pieter P de Tombe
- Department of Cell and Molecular Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Ave, Maywood, IL 60153, United States.
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25
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Vikhlyantsev IM, Podlubnaya ZA. Nuances of electrophoresis study of titin/connectin. Biophys Rev 2017; 9:189-199. [PMID: 28555301 PMCID: PMC5498330 DOI: 10.1007/s12551-017-0266-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Accepted: 04/28/2017] [Indexed: 01/03/2023] Open
Abstract
Almost 40 years has passed since the discovery of giant elastic protein titin (also known as connectin) of striated and smooth muscles using gel electrophoresis. Sodium dodecyl sulfate polyacrylamide gel electrophoresis is a major technique for studying the isoform composition and content of titin. This review provides historical insights into the technical aspects of the electrophoresis methods used to identify titin and its isoforms. We particularly focus on the nuances of the technique that improve the preservation of its primary structure so that its high molecular weight isoforms can be visualized.
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Affiliation(s)
- Ivan M Vikhlyantsev
- Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Institutskaya Street 3, Pushchino, 142290, Russia.
- Pushchino State Institute of Natural Science, Nauki Street 3, Pushchino, 142290, Russia.
| | - Zoya A Podlubnaya
- Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Institutskaya Street 3, Pushchino, 142290, Russia
- Pushchino State Institute of Natural Science, Nauki Street 3, Pushchino, 142290, Russia
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26
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Zhu C, Chen Z, Guo W. Pre-mRNA mis-splicing of sarcomeric genes in heart failure. Biochim Biophys Acta Mol Basis Dis 2016; 1863:2056-2063. [PMID: 27825848 DOI: 10.1016/j.bbadis.2016.11.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2016] [Revised: 10/11/2016] [Accepted: 11/01/2016] [Indexed: 12/01/2022]
Abstract
Pre-mRNA splicing is an important biological process that allows production of multiple proteins from a single gene in the genome, and mainly contributes to protein diversity in eukaryotic organisms. Alternative splicing is commonly governed by RNA binding proteins to meet the ever-changing demands of the cell. However, the mis-splicing may lead to human diseases. In the heart of human, mis-regulation of alternative splicing has been associated with heart failure. In this short review, we focus on alternative splicing of sarcomeric genes and review mis-splicing related heart failure with relatively well studied Sarcomeric genes and splicing mechanisms with identified regulatory factors. The perspective of alternative splicing based therapeutic strategies in heart failure has also been discussed.
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Affiliation(s)
- Chaoqun Zhu
- Animal Science, College of Agriculture and Natural Resources, University of Wyoming, Laramie, WY 82071, USA
| | - Zhilong Chen
- Animal Science, College of Agriculture and Natural Resources, University of Wyoming, Laramie, WY 82071, USA; College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Wei Guo
- Animal Science, College of Agriculture and Natural Resources, University of Wyoming, Laramie, WY 82071, USA
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27
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Methawasin M, Strom JG, Slater RE, Fernandez V, Saripalli C, Granzier H. Experimentally Increasing the Compliance of Titin Through RNA Binding Motif-20 (RBM20) Inhibition Improves Diastolic Function In a Mouse Model of Heart Failure With Preserved Ejection Fraction. Circulation 2016; 134:1085-1099. [PMID: 27630136 DOI: 10.1161/circulationaha.116.023003] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 08/05/2016] [Indexed: 01/05/2023]
Abstract
BACKGROUND Left ventricular (LV) stiffening contributes to heart failure with preserved ejection fraction (HFpEF), a syndrome with no effective treatment options. Increasing the compliance of titin in the heart has become possible recently through inhibition of the splicing factor RNA binding motif-20. Here, we investigated the effects of increasing the compliance of titin in mice with diastolic dysfunction. METHODS Mice in which the RNA recognition motif (RRM) of one of the RNA binding motif-20 alleles was floxed and that expressed the MerCreMer transgene under control of the αMHC promoter (referred to as cRbm20ΔRRM mice) were used. Mice underwent transverse aortic constriction (TAC) surgery and deoxycorticosterone acetate (DOCA) pellet implantation. RRM deletion in adult mice was triggered by injecting raloxifene (cRbm20ΔRRM-raloxifene), with dimethyl sulfoxide (DMSO)-injected mice (cRbm20ΔRRM-DMSO) as the control. Diastolic function was investigated with echocardiography and pressure-volume analysis; passive stiffness was studied in LV muscle strips and isolated cardiac myocytes before and after elimination of titin-based stiffness. Treadmill exercise performance was also studied. Titin isoform expression was evaluated with agarose gels. RESULTS cRbm20ΔRRM-raloxifene mice expressed large titins in the hearts, called supercompliant titin (N2BAsc), which, within 3 weeks after raloxifene injection, made up ≈45% of total titin. TAC/DOCA cRbm20ΔRRM-DMSO mice developed LV hypertrophy and a marked increase in LV chamber stiffness as shown by both pressure-volume analysis and echocardiography. LV chamber stiffness was normalized in TAC/DOCA cRbm20ΔRRM-raloxifene mice that expressed N2BAsc. Passive stiffness measurements on muscle strips isolated from the LV free wall revealed that extracellular matrix stiffness was equally increased in both groups of TAC/DOCA mice (cRbm20ΔRRM-DMSO and cRbm20ΔRRM-raloxifene). However, titin-based muscle stiffness was reduced in the mice that expressed N2BAsc (TAC/DOCAcRbm20ΔRRM-raloxifene). Exercise testing demonstrated significant improvement in exercise tolerance in TAC/DOCA mice that expressed N2BAsc. CONCLUSIONS Inhibition of the RNA binding motif-20-based titin splicing system upregulates compliant titins, which improves diastolic function and exercise tolerance in the TAC/DOCA model. Titin holds promise as a therapeutic target for heart failure with preserved ejection fraction.
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Affiliation(s)
- Mei Methawasin
- From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson
| | - Joshua G Strom
- From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson
| | - Rebecca E Slater
- From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson
| | - Vanessa Fernandez
- From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson
| | - Chandra Saripalli
- From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson
| | - Henk Granzier
- From Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson.
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28
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Beqqali A, Bollen IAE, Rasmussen TB, van den Hoogenhof MM, van Deutekom HWM, Schafer S, Haas J, Meder B, Sørensen KE, van Oort RJ, Mogensen J, Hubner N, Creemers EE, van der Velden J, Pinto YM. A mutation in the glutamate-rich region of RNA-binding motif protein 20 causes dilated cardiomyopathy through missplicing of titin and impaired Frank-Starling mechanism. Cardiovasc Res 2016; 112:452-63. [PMID: 27496873 DOI: 10.1093/cvr/cvw192] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Accepted: 07/21/2016] [Indexed: 12/16/2022] Open
Abstract
AIM Mutations in the RS-domain of RNA-binding motif protein 20 (RBM20) have recently been identified to segregate with aggressive forms of familial dilated cardiomyopathy (DCM). Loss of RBM20 in rats results in missplicing of the sarcomeric gene titin (TTN). The functional and physiological consequences of RBM20 mutations outside the mutational hotspot of RBM20 have not been explored to date. In this study, we investigated the pathomechanism of DCM caused by a novel RBM20 mutation in human cardiomyocytes. METHODS AND RESULTS We identified a family with DCM carrying a mutation (RBM20(E913K/+)) in a glutamate-rich region of RBM20. Western blot analysis of endogenous RBM20 protein revealed strongly reduced protein levels in the heart of an RBM20(E913K/+ )carrier. RNA deep-sequencing demonstrated massive inclusion of exons coding for the spring region of titin in the RBM20(E913K/+ )carrier. Titin isoform analysis revealed a dramatic shift from the less compliant N2B towards the highly compliant N2BA isoforms in RBM20(E913K/+ )heart. Moreover, an increased sarcomere resting-length was observed in single cardiomyocytes and isometric force measurements revealed an attenuated Frank-Starling mechanism (FSM), which was rescued by protein kinase A treatment. CONCLUSION A mutation outside the mutational hotspot of RBM20 results in haploinsufficiency of RBM20. This leads to disturbed alternative splicing of TTN, resulting in a dramatic shift to highly compliant titin isoforms and an impaired FSM. These effects may contribute to the early onset, and malignant course of DCM caused by RBM20 mutations. Altogether, our results demonstrate that heterozygous loss of RBM20 suffices to profoundly impair myocyte biomechanics by its disturbance of TTN splicing.
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Affiliation(s)
- Abdelaziz Beqqali
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
| | - Ilse A E Bollen
- Department of Physiology, VU University Medical Center, Institute for Cardiovascular Research (ICaR-VU), van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands
| | - Torsten B Rasmussen
- Department of Cardiology, Aarhus University Hospital, Norrebrogade 44, DK-8000, Aarhus, Denmark
| | - Maarten M van den Hoogenhof
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
| | - Hanneke W M van Deutekom
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
| | - Sebastian Schafer
- National Heart Research Institute Singapore, National Heart Centre Singapore, 5 Hospital Drive, Singapore 169609, Singapore Division of Cardiovascular & Metabolic Disorders, Duke-National University of Singapore, 8 College Road, Singapore 169857, Singapore
| | - Jan Haas
- Department of Internal Medicine III, Cardiology, University Hospital of Heidelberg, 69120 Heidelberg, Germany DZHK (German Centre for Cardiovascular Research), Oudenarder Straße 16, 13347 Berlin, Germany
| | - Benjamin Meder
- Department of Internal Medicine III, Cardiology, University Hospital of Heidelberg, 69120 Heidelberg, Germany DZHK (German Centre for Cardiovascular Research), Oudenarder Straße 16, 13347 Berlin, Germany
| | - Keld E Sørensen
- Department of Cardiology, Aarhus University Hospital, Norrebrogade 44, DK-8000, Aarhus, Denmark
| | - Ralph J van Oort
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
| | - Jens Mogensen
- Department of Cardiology, Odense University Hospital, Sdr. Boulevard 29, 5000 Odense, Denmark
| | - Norbert Hubner
- DZHK (German Centre for Cardiovascular Research), Oudenarder Straße 16, 13347 Berlin, Germany Charité-Universitätsmedizin, Charitéplatz 1, 10117 Berlin, Germany Cardiovascular and Metabolic Sciences, Max-Delbrück-Center for Molecular Medicine (MDC), Robert-Rössle-Str. 10, 13125 Berlin, Germany
| | - Esther E Creemers
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
| | - Jolanda van der Velden
- Department of Physiology, VU University Medical Center, Institute for Cardiovascular Research (ICaR-VU), van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands
| | - Yigal M Pinto
- Department of Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ, Amsterdam, The Netherlands
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29
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Ito J, Iijima M, Yoshimoto N, Niimi T, Kuroda S, Maturana AD. RBM20 and RBM24 cooperatively promote the expression of short enh splice variants. FEBS Lett 2016; 590:2262-74. [PMID: 27289039 DOI: 10.1002/1873-3468.12251] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2016] [Revised: 04/29/2016] [Accepted: 05/19/2016] [Indexed: 12/31/2022]
Abstract
PDZ-LIM protein ENH1 is a scaffold protein for protein kinases and transcriptional regulators. While ENH1 promotes the hypertrophic growth of cardiomyocytes, its short splice variant (ENH3) prevents the hypertrophic growth. The mechanism underlying the alternative splicing of enh mRNA between ENH short and long isoforms has remained unknown. Here, we found that two splicing factors, RNA-binding motif 20 (RBM20) and RNA-binding motif 24 (RBM24) together promoted the expression of short enh splice variants and bound the 5' intronic region of exon 11 containing an in-phase stop codon. In addition, expression of both RBMs is repressed by hypertrophic stimulations. Collectively, our results suggest that, in healthy conditions, RBM20 and RBM24 cooperate to promote the expression of short ENH isoforms.
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Affiliation(s)
- Jumpei Ito
- Graduate School of Bioagricultural Sciences, Nagoya University, Japan.,Japan Society for the Promotion of Science, Tokyo, Japan
| | - Masumi Iijima
- The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka, Japan
| | - Nobuo Yoshimoto
- The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka, Japan
| | - Tomoaki Niimi
- Graduate School of Bioagricultural Sciences, Nagoya University, Japan
| | - Shun'ichi Kuroda
- Graduate School of Bioagricultural Sciences, Nagoya University, Japan.,The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka, Japan
| | - Andrés D Maturana
- Graduate School of Bioagricultural Sciences, Nagoya University, Japan
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30
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Sequeira V, van der Velden J. Historical perspective on heart function: the Frank-Starling Law. Biophys Rev 2015; 7:421-447. [PMID: 28510104 DOI: 10.1007/s12551-015-0184-4] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Accepted: 09/21/2015] [Indexed: 12/18/2022] Open
Abstract
More than a century of research on the Frank-Starling Law has significantly advanced our knowledge about the working heart. The Frank-Starling Law mandates that the heart is able to match cardiac ejection to the dynamic changes occurring in ventricular filling and thereby regulates ventricular contraction and ejection. Significant efforts have been attempted to identify a common fundamental basis for the Frank-Starling heart and, although a unifying idea has still to come forth, there is mounting evidence of a direct relationship between length changes in individual constituents (cardiomyocytes) and their sensitivity to Ca2+ ions. As the Frank-Starling Law is a vital event for the healthy heart, it is of utmost importance to understand its mechanical basis in order to optimize and organize therapeutic strategies to rescue the failing human heart. The present review is a historic perspective on cardiac muscle function. We "revive" a century of scientific research on the heart's fundamental protein constituents (contractile proteins), to their assemblies in the muscle (the sarcomeres), culminating in a thorough overview of the several synergistically events that compose the Frank-Starling mechanism. It is the authors' personal beliefs that much can be gained by understanding the Frank-Starling relationship at the cellular and whole organ level, so that we can finally, in this century, tackle the pathophysiologic mechanisms underlying heart failure.
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Affiliation(s)
- Vasco Sequeira
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands.
| | - Jolanda van der Velden
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands.,ICIN- Netherlands Heart Institute, Utrecht, The Netherlands
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31
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Banerjee I, Carrion K, Serrano R, Dyo J, Sasik R, Lund S, Willems E, Aceves S, Meili R, Mercola M, Chen J, Zambon A, Hardiman G, Doherty TA, Lange S, del Álamo JC, Nigam V. Cyclic stretch of embryonic cardiomyocytes increases proliferation, growth, and expression while repressing Tgf-β signaling. J Mol Cell Cardiol 2015; 79:133-44. [PMID: 25446186 PMCID: PMC4302020 DOI: 10.1016/j.yjmcc.2014.11.003] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/22/2014] [Revised: 10/14/2014] [Accepted: 11/04/2014] [Indexed: 11/17/2022]
Abstract
Perturbed biomechanical stimuli are thought to be critical for the pathogenesis of a number of congenital heart defects, including Hypoplastic Left Heart Syndrome (HLHS). While embryonic cardiomyocytes experience biomechanical stretch every heart beat, their molecular responses to biomechanical stimuli during heart development are poorly understood. We hypothesized that biomechanical stimuli activate specific signaling pathways that impact proliferation, gene expression and myocyte contraction. The objective of this study was to expose embryonic mouse cardiomyocytes (EMCM) to cyclic stretch and examine key molecular and phenotypic responses. Analysis of RNA-Sequencing data demonstrated that gene ontology groups associated with myofibril and cardiac development were significantly modulated. Stretch increased EMCM proliferation, size, cardiac gene expression, and myofibril protein levels. Stretch also repressed several components belonging to the Transforming Growth Factor-β (Tgf-β) signaling pathway. EMCMs undergoing cyclic stretch had decreased Tgf-β expression, protein levels, and signaling. Furthermore, treatment of EMCMs with a Tgf-β inhibitor resulted in increased EMCM size. Functionally, Tgf-β signaling repressed EMCM proliferation and contractile function, as assayed via dynamic monolayer force microscopy (DMFM). Taken together, these data support the hypothesis that biomechanical stimuli play a vital role in normal cardiac development and for cardiac pathology, including HLHS.
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Affiliation(s)
- Indroneal Banerjee
- Department of Cardiology, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
| | - Katrina Carrion
- Department of Pediatrics (Cardiology), University of California San Diego, United States
| | - Ricardo Serrano
- Department of Mechanical and Aerospace Engineering, University of California San Diego, United States
| | - Jeffrey Dyo
- Department of Pediatrics (Cardiology), University of California San Diego, United States
| | - Roman Sasik
- Biomedical Genomics Microarray Core Facility, University of California San Diego, United States
| | - Sean Lund
- Department of Medicine, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
| | - Erik Willems
- Muscle Development and Regeneration Program, Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, United States
| | - Seema Aceves
- Department of Medicine, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States; Department of Pediatrics (Allergy), University of California San Diego, United States; Rady Children's Hospital San Diego, United States
| | - Rudolph Meili
- Department of Mechanical and Aerospace Engineering, University of California San Diego, United States; Cell and Developmental Biology, University of California San Diego, United States
| | - Mark Mercola
- Muscle Development and Regeneration Program, Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, United States
| | - Ju Chen
- Department of Cardiology, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
| | - Alexander Zambon
- School of Pharmacology Keck Graduate Institute, 9500 Gilman Drive, La Jolla, CA 92093, United States
| | - Gary Hardiman
- Department of Medicine, Medical University of South Carolina, 135 Cannon Street, Suite 303 MSC 835, Charleston, SC 29425, United States
| | - Taylor A Doherty
- Department of Medicine, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
| | - Stephan Lange
- Department of Cardiology, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
| | - Juan C del Álamo
- Department of Mechanical and Aerospace Engineering, University of California San Diego, United States; Institute for Engineering in Medicine, University of California San Diego, United States
| | - Vishal Nigam
- Department of Pediatrics (Cardiology), University of California San Diego, United States; Rady Children's Hospital San Diego, United States; Institute for Engineering in Medicine, University of California San Diego, United States.
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32
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Cieply B, Carstens RP. Functional roles of alternative splicing factors in human disease. WILEY INTERDISCIPLINARY REVIEWS-RNA 2015; 6:311-26. [PMID: 25630614 PMCID: PMC4671264 DOI: 10.1002/wrna.1276] [Citation(s) in RCA: 97] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Revised: 12/17/2014] [Accepted: 12/18/2014] [Indexed: 12/13/2022]
Abstract
Alternative splicing (AS) is an important mechanism used to generate greater transcriptomic and proteomic diversity from a finite genome. Nearly all human gene transcripts are alternatively spliced and can produce protein isoforms with divergent and even antagonistic properties that impact cell functions. Many AS events are tightly regulated in a cell-type or tissue-specific manner, and at different developmental stages. AS is regulated by RNA-binding proteins, including cell- or tissue-specific splicing factors. In the past few years, technological advances have defined genome-wide programs of AS regulated by increasing numbers of splicing factors. These splicing regulatory networks (SRNs) consist of transcripts that encode proteins that function in coordinated and related processes that impact the development and phenotypes of different cell types. As such, it is increasingly recognized that disruption of normal programs of splicing regulated by different splicing factors can lead to human diseases. We will summarize examples of diseases in which altered expression or function of splicing regulatory proteins has been implicated in human disease pathophysiology. As the role of AS continues to be unveiled in human disease and disease risk, it is hoped that further investigations into the functions of numerous splicing factors and their regulated targets will enable the development of novel therapies that are directed at specific AS events as well as the biological pathways they impact. WIREs RNA 2015, 6:311–326. doi: 10.1002/wrna.1276 For further resources related to this article, please visit the http://wires.wiley.com/remdoi.cgi?doi=10.1002/wrna.1276WIREs website. Conflict of interest: The authors have declared no conflicts of interest for this article.
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Affiliation(s)
- Benjamin Cieply
- Departments of Medicine (Renal) and Genetics, University of Pennsylvania, Perelman School of Medicine, Philadelphia, PA, USA
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33
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Hanft LM, Greaser ML, McDonald KS. Titin-mediated control of cardiac myofibrillar function. Arch Biochem Biophys 2014; 552-553:83-91. [PMID: 24269766 PMCID: PMC4028433 DOI: 10.1016/j.abb.2013.11.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Revised: 10/18/2013] [Accepted: 11/12/2013] [Indexed: 01/06/2023]
Abstract
According to the Frank-Starling relationship, ventricular pressure or stroke volume increases with end-diastolic volume. This is regulated, in large part, by the sarcomere length (SL) dependent changes in cardiac myofibrillar force, loaded shortening, and power. Consistent with this, both cardiac myofibrillar force and absolute power fall at shorter SL. However, when Ca(2+) activated force levels are matched between short and long SL (by increasing the activator [Ca(2+)]), short SL actually yields faster loaded shortening and greater peak normalized power output (PNPO). A potential mechanism for faster loaded shortening at short SL is that, at short SL, titin becomes less taut, which increases the flexibility of the cross-bridges, a process that may be mediated by titin's interactions with thick filament proteins. We propose a more slackened titin yields greater myosin head radial and azimuthal mobility and these flexible cross-bridges are more likely to maintain thin filament activation, which would allow more force-generating cross-bridges to work against a fixed load resulting in faster loaded shortening. We tested this idea by measuring SL-dependence of power at matched forces in rat skinned cardiac myocytes containing either N2B titin or a longer, more compliant N2BA titin. We predicted that, in N2BA titin containing cardiac myocytes, power-load curves would not be shifted upward at short SL compared to long SL (when force is matched). Consistent with this, peak normalized power was actually less at short SL versus long SL (at matched force) in N2BA-containing myocytes (N2BA titin: ΔPNPO (Short SL peak power minus long SL peak power)=-0.057±0.049 (n=5) versus N2B titin: ΔPNPO=+0.012±0.012 (n=5). These findings support a model whereby SL per se controls mechanical properties of cross-bridges and this process is mediated by titin. This myofibrillar mechanism may help sustain ventricular power during periods of low preloads, and perhaps a breakdown of this mechanism is involved in impaired function of failing hearts.
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Affiliation(s)
- Laurin M Hanft
- Department of Medical Pharmacology & Physiology, School of Medicine, University of Missouri, Columbia, MO 65212, United States
| | - Marion L Greaser
- Muscle Biology Laboratory, University of Wisconsin, Madison, WI 53706, United States
| | - Kerry S McDonald
- Department of Medical Pharmacology & Physiology, School of Medicine, University of Missouri, Columbia, MO 65212, United States.
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Herzog W. Mechanisms of enhanced force production in lengthening (eccentric) muscle contractions. J Appl Physiol (1985) 2014; 116:1407-17. [DOI: 10.1152/japplphysiol.00069.2013] [Citation(s) in RCA: 104] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In contrast to isometric and shortening contractions, many observations made on actively lengthening muscles cannot be readily explained with the sliding filament and cross-bridge theory. Specifically, residual force enhancement, the persistent increase in force following active muscle lengthening, beyond what one would expect based on muscle length, has not been explained satisfactorily. Here, we summarize the experimental evidence on residual force enhancement, critically evaluate proposed mechanisms for the residual force enhancement, and propose a mechanism for residual force enhancement that explains all currently agreed upon experimental observations. The proposed mechanism is based on the engagement of the structural protein titin upon muscle activation and an increase in titin's resistance to active compared with passive stretching. This change in resistance from the passive to the active state is suggested to be based on 1) calcium binding by titin upon activation, 2) binding of titin to actin upon activation, and 3) as a consequence of titin-actin binding—a shift toward stiffer titin segments that are used in active compared with passive muscle elongation. Although there is some experimental evidence for the proposed mechanism, it must be stressed that much of the details proposed here remain unclear and should provide ample research opportunities for scientists in the future. Nevertheless, the proposed mechanism for residual force enhancement explains all basic findings in this area of research.
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Affiliation(s)
- Walter Herzog
- Faculty of Kinesiology, University of Calgary, Alberta, Canada
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Beraldi R, Li X, Martinez Fernandez A, Reyes S, Secreto F, Terzic A, Olson TM, Nelson TJ. Rbm20-deficient cardiogenesis reveals early disruption of RNA processing and sarcomere remodeling establishing a developmental etiology for dilated cardiomyopathy. Hum Mol Genet 2014; 23:3779-91. [PMID: 24584570 DOI: 10.1093/hmg/ddu091] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Dilated cardiomyopathy (DCM) due to mutations in RBM20, a gene encoding an RNA-binding protein, is associated with high familial penetrance, risk of progressive heart failure and sudden death. Although genetic investigations and physiological models have established the linkage of RBM20 with early-onset DCM, the underlying basis of cellular and molecular dysfunction is undetermined. Modeling human genetics using a high-throughput pluripotent stem cell platform was herein designed to pinpoint the initial transcriptome dysfunction and mechanistic corruption in disease pathogenesis. Tnnt2-pGreenZeo pluripotent stem cells were engineered to knockdown Rbm20 (shRbm20) to determine the cardiac-pathogenic phenotype during cardiac differentiation. Intracellular Ca(2+) transients revealed Rbm20-dependent alteration in Ca(2+) handling, coinciding with known pathological splice variants of Titin and Camk2d genes by Day 24 of cardiogenesis. Ultrastructural analysis demonstrated elongated and thinner sarcomeres in the absence of Rbm20 that is consistent with human cardiac biopsy samples. Furthermore, Rbm20-depleted transcriptional profiling at Day 12 identified Rbm20-dependent dysregulation with 76% of differentially expressed genes linked to known cardiac pathology ranging from primordial Nkx2.5 to mature cardiac Tnnt2 as the initial molecular aberrations. Notably, downstream consequences of Rbm20-depletion at Day 24 of differentiation demonstrated significant dysregulation of extracellular matrix components such as the anomalous overexpression of the Vtn gene. By using the pluripotent stem cell platform to model human cardiac disease according to a stage-specific cardiogenic roadmap, we established a new paradigm of familial DCM pathogenesis as a developmental disorder that is patterned during early cardiogenesis and propagated with cellular mechanisms of pathological cardiac remodeling.
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Affiliation(s)
| | - Xing Li
- Division of Biomedical Statistics and Informatics, Department of Health Sciences Research
| | | | | | | | - Andre Terzic
- Division of Cardiovascular Diseases, Center of Regenerative Medicine, Division of Pediatric Cardiology, Molecular Pharmacology and Experimental Therapeutics
| | - Timothy M Olson
- Division of Cardiovascular Diseases, Division of Pediatric Cardiology, Molecular Pharmacology and Experimental Therapeutics
| | - Timothy J Nelson
- Center of Regenerative Medicine, Molecular Pharmacology and Experimental Therapeutics, General Internal Medicine and Transplant Center, Mayo Clinic, Rochester, MN 55905, USA
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Greaser ML, Pleitner JM. Titin isoform size is not correlated with thin filament length in rat skeletal muscle. Front Physiol 2014; 5:35. [PMID: 24550844 PMCID: PMC3910082 DOI: 10.3389/fphys.2014.00035] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Accepted: 01/16/2014] [Indexed: 01/17/2023] Open
Abstract
The mechanisms controlling thin filament length (TFL) in muscle remain controversial. It was recently reported that TFL was related to titin size, and that the latter might be involved in TFL determination. Titin plays several crucial roles in the sarcomere, but its function as it pertains to the thin filament has not been explored. We tested this relationship using several muscles from wild type rats and from a mutant rat model (Greaser et al., 2008) which results in increased titin size. Myofibrils were isolated from skeletal muscles [extensor digitorum longus (EDL), external oblique (EO), gastrocnemius (GAS), longissimus dorsi (LD), psoas major (PM), and tibialis anterior(TA)] using both adult wild type (WT) and homozygous mutant (HM) rats (n = 6 each). Phalloidin and antibodies against tropomodulin-4 (Tmod-4) and nebulin's N-terminus were used to determine TFL. The WT rats studied express skeletal muscle titin sizes ranging from 3.2 to 3.7 MDa, while the HM rats express a giant titin isoform sized at 3.8 MDa. No differences in phalloidin based TFL, nebulin distance, or Tmod distance were observed across genotypes. However, the HM rats demonstrated a significantly increased (p < 0.01) rest sarcomere length relative to the WT phenotype. It appears that the increased titin size, predominantly observed in HM rats' middle Ig domain, allows for increased extensibility. The data indicates that, although titin performs many sarcomeric functions, its correlation with TFL and structure could not be demonstrated in the rat.
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Affiliation(s)
- Marion L Greaser
- Muscle Biology Laboratory, Animal Sciences, University of Wisconsin-Madison Madison, WI, USA
| | - Jonathan M Pleitner
- Muscle Biology Laboratory, Animal Sciences, University of Wisconsin-Madison Madison, WI, USA
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37
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Giudice J, Cooper TA. RNA-binding proteins in heart development. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 825:389-429. [PMID: 25201112 DOI: 10.1007/978-1-4939-1221-6_11] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
RNA-binding proteins (RBPs) are key players of posttranscriptional regulation occurring during normal tissue development. All tissues examined thus far have revealed the importance of RBPs in the regulation of complex networks involved in organ morphogenesis, maturation, and function. They are responsible for controlling tissue-specific gene expression by regulating alternative splicing, mRNA stability, translation, and poly-adenylation. The heart is the first organ form during embryonic development and is also the first to acquire functionality. Numerous remodeling processes take place during late cardiac development since fetal heart first adapts to birth and then undergoes a transition to adult functionality. This physiological remodeling involves transcriptional and posttranscriptional networks that are regulated by RBPs. Disruption of the normal regulatory networks has been shown to cause cardiomyopathy in humans and animal models. Here we review the complexity of late heart development and the current information regarding how RBPs control aspects of postnatal heart development. We also review how activities of RBPs are modulated adding complexity to the regulation of developmental networks.
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Affiliation(s)
- Jimena Giudice
- Department of Pathology and Immunology, Baylor College of Medicine, Houston, TX, 77030, USA,
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38
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Pathophysiological defects and transcriptional profiling in the RBM20-/- rat model. PLoS One 2013; 8:e84281. [PMID: 24367651 PMCID: PMC3868568 DOI: 10.1371/journal.pone.0084281] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Accepted: 11/21/2013] [Indexed: 12/20/2022] Open
Abstract
Our recent study indicated that RNA binding motif 20 (Rbm20) alters splicing of titin and other genes. The current goals were to understand how the Rbm20(-/-) rat is related to physiological, structural, and molecular changes leading to heart failure. We quantitatively and qualitatively compared the expression of titin isoforms between Rbm20(-/-) and wild type rats by real time RT-PCR and SDS agarose electrophoresis. Isoform changes were linked to alterations in transcription as opposed to translation of titin messages. Reduced time to exhaustion with running in knockout rats also suggested a lower maximal cardiac output or decreased skeletal muscle performance. Electron microscopic observations of the left ventricle from knockout animals showed abnormal myofibril arrangement, Z line streaming, and lipofuscin deposits. Mutant skeletal muscle ultrastructure appeared normal. The results suggest that splicing alterations in Rbm20(-/-) rats resulted in pathogenic changes in physiology and cardiac ultrastructure. Secondary changes were observed in message levels for many genes whose splicing was not directly affected. Gene and protein expression data indicated the activation of pathophysiological and muscle stress-activated pathways. These data provide new insights on Rbm20 function and how its malfunction leads to cardiomyopathy.
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Vikhlyantsev IM, Okuneva AD, Shumilina UV, Salmov NN, Bobylev AG, Molochkov NV, Podlubnaya ZA. Method for isolation of intact titin (connectin) molecules from mammalian cardiac muscle. BIOCHEMISTRY (MOSCOW) 2013; 78:455-62. [PMID: 23848147 DOI: 10.1134/s0006297913050039] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Cardiac titin was isolated from rabbit and ground squirrel ventricular muscles by a method that was used earlier to obtain myofibrils with intact minor proteins located in A-bands of sarcomeres (Podlubnaya, Z. A., et al. (1989) J. Mol. Biol., 210, 655-658). Small pieces of cardiac muscle were incubated for 2-3 weeks at 4°C in Ca²⁺-depleting solution before their homogenization to decrease activity of Ca²⁺-dependent proteases. Then the muscle was homogenized, and titin was isolated by the method of Soteriou, A., et al. (1993) J. Cell Sci., 14, 119-123. In control experiments, titin was isolated from cardiac muscle without its preincubation in Ca²⁺-depleting solution. Sometimes control titin preparations contained only T2-fragment, but generally they contained ~5-20% N2B-isoform of titin along with its T2-fragment. Preparations of titin obtained from rabbit cardiac muscle by our method contained ~30-50% of N2BA- and N2B-titin isoforms along with its T2-fragment. The content of α-structures in titin isolated by our method was increased. Actomyosin ATPase activity in vitro increased in the presence of titin preparations containing more intact molecules. This result confirms the significant role of titin in the regulation of actin-myosin interaction in muscles. The method used by us to preserve titin might be used for isolation of other proteins that are substrates of Ca²⁺-dependent proteases.
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Affiliation(s)
- I M Vikhlyantsev
- Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia.
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40
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Sequeira V, Nijenkamp LLAM, Regan JA, van der Velden J. The physiological role of cardiac cytoskeleton and its alterations in heart failure. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:700-22. [PMID: 23860255 DOI: 10.1016/j.bbamem.2013.07.011] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Revised: 07/01/2013] [Accepted: 07/08/2013] [Indexed: 12/11/2022]
Abstract
Cardiac muscle cells are equipped with specialized biochemical machineries for the rapid generation of force and movement central to the work generated by the heart. During each heart beat cardiac muscle cells perceive and experience changes in length and load, which reflect one of the fundamental principles of physiology known as the Frank-Starling law of the heart. Cardiac muscle cells are unique mechanical stretch sensors that allow the heart to increase cardiac output, and adjust it to new physiological and pathological situations. In the present review we discuss the mechano-sensory role of the cytoskeletal proteins with respect to their tight interaction with the sarcolemma and extracellular matrix. The role of contractile thick and thin filament proteins, the elastic protein titin, and their anchorage at the Z-disc and M-band, with associated proteins are reviewed in physiologic and pathologic conditions leading to heart failure. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé
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Affiliation(s)
- Vasco Sequeira
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
| | - Louise L A M Nijenkamp
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
| | - Jessica A Regan
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands; Department of Physiology, Molecular Cardiovascular Research Program, Sarver Heart Center, University of Arizona, Tucson, AZ 85724, USA
| | - Jolanda van der Velden
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands; ICIN-Netherlands Heart Institute, The Netherlands.
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41
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Vikhlyantsev IM, Podlubnaya ZA. New titin (connectin) isoforms and their functional role in striated muscles of mammals: facts and suppositions. BIOCHEMISTRY (MOSCOW) 2013; 77:1515-35. [PMID: 23379526 DOI: 10.1134/s0006297912130093] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
This review summarizes results of our studies on titin isoform composition in vertebrate striated muscles under normal conditions, during hibernation, real and simulated microgravity, and under pathological conditions (stiff-person syndrome, post-apoplectic spasticity, dilated cardiomyopathy, cardiac hypertrophy). Experimental evidence for the existence in mammalian striated muscles of higher molecular weight isoforms of titin (NT-isoforms) in addition to the known N2A-, N2BA-, and N2B-titin isoforms was obtained. Comparative studies of changes in titin isoform composition and structure-functional properties of human and animal striated muscles during adaptive and pathological processes led to a conclusion about the key role of NT-isoforms of titin in maintenance of sarcomere structure and contractile function of these muscles.
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Affiliation(s)
- I M Vikhlyantsev
- Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia.
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42
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Chung CS, Hutchinson KR, Methawasin M, Saripalli C, Smith JE, Hidalgo CG, Luo X, Labeit S, Guo C, Granzier HL. Shortening of the elastic tandem immunoglobulin segment of titin leads to diastolic dysfunction. Circulation 2013; 128:19-28. [PMID: 23709671 DOI: 10.1161/circulationaha.112.001268] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Diastolic dysfunction is a poorly understood but clinically pervasive syndrome that is characterized by increased diastolic stiffness. Titin is the main determinant of cellular passive stiffness. However, the physiological role that the tandem immunoglobulin (Ig) segment of titin plays in stiffness generation and whether shortening this segment is sufficient to cause diastolic dysfunction need to be established. METHODS AND RESULTS We generated a mouse model in which 9 Ig-like domains (Ig3-Ig11) were deleted from the proximal tandem Ig segment of the spring region of titin (IG KO). Exon microarray analysis revealed no adaptations in titin splicing, whereas novel phospho-specific antibodies did not detect changes in titin phosphorylation. Passive myocyte stiffness was increased in the IG KO, and immunoelectron microscopy revealed increased extension of the remaining titin spring segments as the sole likely underlying mechanism. Diastolic stiffness was increased at the tissue and organ levels, with no consistent changes in extracellular matrix composition or extracellular matrix-based passive stiffness, supporting a titin-based mechanism for in vivo diastolic dysfunction. Additionally, IG KO mice have a reduced exercise tolerance, a phenotype often associated with diastolic dysfunction. CONCLUSIONS Increased titin-based passive stiffness is sufficient to cause diastolic dysfunction with exercise intolerance.
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Affiliation(s)
- Charles S Chung
- Department of Physiology, University of Arizona, PO Box245051, Tucson AZ 85724, USA
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43
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Li S, Guo W, Dewey CN, Greaser ML. Rbm20 regulates titin alternative splicing as a splicing repressor. Nucleic Acids Res 2013; 41:2659-72. [PMID: 23307558 PMCID: PMC3575840 DOI: 10.1093/nar/gks1362] [Citation(s) in RCA: 103] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Titin, a sarcomeric protein expressed primarily in striated muscles, is responsible for maintaining the structure and biomechanical properties of muscle cells. Cardiac titin undergoes developmental size reduction from 3.7 megadaltons in neonates to primarily 2.97 megadaltons in the adult. This size reduction results from gradually increased exon skipping between exons 50 and 219 of titin mRNA. Our previous study reported that Rbm20 is the splicing factor responsible for this process. In this work, we investigated its molecular mechanism. We demonstrate that Rbm20 mediates exon skipping by binding to titin pre-mRNA to repress the splicing of some regions; the exons/introns in these Rbm20-repressed regions are ultimately skipped. Rbm20 was also found to mediate intron retention and exon shuffling. The two Rbm20 speckles found in nuclei from muscle tissues were identified as aggregates of Rbm20 protein on the partially processed titin pre-mRNAs. Cooperative repression and alternative 3' splice site selection were found to be used by Rbm20 to skip different subsets of titin exons, and the splicing pathway selected depended on the ratio of Rbm20 to other splicing factors that vary with tissue type and developmental age.
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Affiliation(s)
- Shijun Li
- Muscle Biology Laboratory, Department of Animal Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA
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44
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Li S, Guo W, Schmitt BM, Greaser ML. Comprehensive analysis of titin protein isoform and alternative splicing in normal and mutant rats. J Cell Biochem 2012; 113:1265-73. [PMID: 22105831 DOI: 10.1002/jcb.23459] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Titin is a giant protein with multiple functions in cardiac and skeletal muscles. Rat cardiac titin undergoes developmental isoform transition from the neonatal 3.7 MDa N2BA isoform to primarily the adult 2.97 MDa N2B isoform. An autosomal dominant mutation dramatically altered this transformation. Titins from eight skeletal muscles: Tibialis Anterior (TA), Longissimus Dorsi (LD) and Gastrocnemius (GA), Extensor Digitorum Longus (ED), Soleus (SO), Psoas (PS), Extensor Oblique (EO), and Diaphram (DI) were characterized in wild type and in homozygous mutant (Hm) rats with a titin splicing defect. Results showed that the developmental reduction in titin size is eliminated in the mutant rat so that the titins in all investigated skeletal muscles remain large in the adult. The alternative splicing of titin mRNA was found repressed by this mutation, a result consistent with the large titin isoform in the mutant. The developmental pattern of titin mRNA alternative splicing differs between heart and skeletal muscles. The retention of intron 49 reveals a possible mechanism for the absence of the N2B unique region in the expressed titin protein of skeletal muscle.
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Affiliation(s)
- Shijun Li
- Muscle Biology Laboratory, Department of Animal Sciences, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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45
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Mateja RD, Greaser ML, de Tombe PP. Impact of titin isoform on length dependent activation and cross-bridge cycling kinetics in rat skeletal muscle. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1833:804-11. [PMID: 22951219 DOI: 10.1016/j.bbamcr.2012.08.011] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Revised: 08/09/2012] [Accepted: 08/10/2012] [Indexed: 01/19/2023]
Abstract
The magnitude of length dependent activation in striated muscle has been shown to vary with titin isoform. Recently, a rat that harbors a homozygous autosomal mutation (HM) causing preferential expression of a longer, giant titin isoform was discovered (Greaser et al. 2005). Here, we investigated the impact of titin isoform on myofilament force development and cross-bridge cycling kinetics as function of sarcomere length (SL) in tibialis anterior skeletal muscle isolated from wild type (WT) and HM. Skeletal muscle bundles from HM rats exhibited reductions in passive tension, maximal force development, myofilament calcium sensitivity, maximal ATP consumption, and tension cost at both short and long sarcomere length (SL=2.8μm and SL=3.2μm, respectively). Moreover, the SL-dependent changes in these parameters were attenuated in HM muscles. Additionally, myofilament Ca(2+) activation-relaxation properties were assessed in single isolated myofibrils. Both the rate of tension generation upon Ca(2+) activation (kACT) as well as the rate of tension redevelopment following a length perturbation (kTR) were reduced in HM myofibrils compared to WT, while relaxation kinetics were not affected. We conclude that presence of a long isoform of titin in the striated muscle sarcomere is associated with reduced myofilament force development and cross-bridge cycling kinetics, and a blunting of myofilament length dependent activation. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.
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Affiliation(s)
- Ryan D Mateja
- Department of Cell and Molecular Physiology, Loyola University Medical Center, Maywood, IL 60153, USA
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46
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RBM20, a gene for hereditary cardiomyopathy, regulates titin splicing. Nat Med 2012; 18:766-73. [PMID: 22466703 DOI: 10.1038/nm.2693] [Citation(s) in RCA: 396] [Impact Index Per Article: 33.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Accepted: 01/31/2012] [Indexed: 01/15/2023]
Abstract
Alternative splicing has a major role in cardiac adaptive responses, as exemplified by the isoform switch of the sarcomeric protein titin, which adjusts ventricular filling. By positional cloning using a previously characterized rat strain with altered titin mRNA splicing, we identified a loss-of-function mutation in the gene encoding RNA binding motif protein 20 (Rbm20) as the underlying cause of pathological titin isoform expression. The phenotype of Rbm20-deficient rats resembled the pathology seen in individuals with dilated cardiomyopathy caused by RBM20 mutations. Deep sequencing of the human and rat cardiac transcriptome revealed an RBM20-dependent regulation of alternative splicing. In addition to titin (TTN), we identified a set of 30 genes with conserved splicing regulation between humans and rats. This network is enriched for genes that have previously been linked to cardiomyopathy, ion homeostasis and sarcomere biology. Our studies emphasize the key role of post-transcriptional regulation in cardiac function and provide mechanistic insights into the pathogenesis of human heart failure.
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47
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Patel JR, Pleitner JM, Moss RL, Greaser ML. Magnitude of length-dependent changes in contractile properties varies with titin isoform in rat ventricles. Am J Physiol Heart Circ Physiol 2011; 302:H697-708. [PMID: 22140043 DOI: 10.1152/ajpheart.00800.2011] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effects of differential expression of titin isoforms on sarcomere length (SL)-dependent changes in passive force, maximum Ca(2+)-activated force, apparent cooperativity in activation of force (n(H)), Ca(2+) sensitivity of force (pCa(50)), and rate of force redevelopment (k(tr)) were investigated in rat cardiac muscle. Skinned right ventricular trabeculae were isolated from wild-type (WT) and mutant homozygote (Ho) hearts expressing predominantly a smaller N2B isoform (2,970 kDa) and a giant N2BA-G isoform (3,830 kDa), respectively. Stretching WT and Ho trabeculae from SL 2.0 to 2.35 μm increased passive force, maximum Ca(2+)-activated force, and pCa(50), and it decreased n(H) and k(tr). Compared with WT trabeculae, the magnitude of SL-dependent changes in passive force, maximum Ca(2+)-activated force, pCa(50), and n(H) was significantly smaller in Ho trabeculae. These results suggests that, at least in rat ventricle, the magnitude of SL-dependent changes in passive force, maximum Ca(2+)-activated force, pCa(50), n(H), and k(tr) is defined by the titin isoform.
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49
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Voelkel T, Linke WA. Conformation-regulated mechanosensory control via titin domains in cardiac muscle. Pflugers Arch 2011; 462:143-54. [PMID: 21347754 PMCID: PMC3114084 DOI: 10.1007/s00424-011-0938-1] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2011] [Revised: 02/08/2011] [Accepted: 02/09/2011] [Indexed: 12/19/2022]
Abstract
The giant filamentous protein titin is ideally positioned in the muscle sarcomere to sense mechanical stimuli and transform them into biochemical signals, such as those triggering cardiac hypertrophy. In this review, we ponder the evidence for signaling hotspots along the titin filament involved in mechanosensory control mechanisms. On the way, we distinguish between stress and strain as triggers of mechanical signaling events at the cardiac sarcomere. Whereas the Z-disk and M-band regions of titin may be prominently involved in sensing mechanical stress, signaling hotspots within the elastic I-band titin segment may respond primarily to mechanical strain. Common to both stress and strain sensor elements is their regulation by conformational changes in protein domains.
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Affiliation(s)
- Tobias Voelkel
- Department of Cardiovascular Physiology, Institute of Physiology, Ruhr University Bochum, MA 3/56, 44780 Bochum, Germany
| | - Wolfgang A. Linke
- Department of Cardiovascular Physiology, Institute of Physiology, Ruhr University Bochum, MA 3/56, 44780 Bochum, Germany
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50
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Krüger M, Linke WA. The giant protein titin: a regulatory node that integrates myocyte signaling pathways. J Biol Chem 2011; 286:9905-12. [PMID: 21257761 DOI: 10.1074/jbc.r110.173260] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Titin, the largest protein in the human body, is well known as a molecular spring in muscle cells and scaffold protein aiding myofibrillar assembly. However, recent evidence has established another important role for titin: that of a regulatory node integrating, and perhaps coordinating, diverse signaling pathways, particularly in cardiomyocytes. We review key findings within this emerging field, including those related to phosphorylation of the titin springs, and also discuss how titin participates in hypertrophic gene regulation and protein quality control.
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Affiliation(s)
- Martina Krüger
- Department of Cardiovascular Physiology, Ruhr University Bochum, D-44780 Bochum, Germany.
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