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De Bortoli M, Meraviglia V, Mackova K, Frommelt LS, König E, Rainer J, Volani C, Benzoni P, Schlittler M, Cattelan G, Motta BM, Volpato C, Rauhe W, Barbuti A, Zacchigna S, Pramstaller PP, Rossini A. Modeling incomplete penetrance in arrhythmogenic cardiomyopathy by human induced pluripotent stem cell derived cardiomyocytes. Comput Struct Biotechnol J 2023; 21:1759-1773. [PMID: 36915380 PMCID: PMC10006475 DOI: 10.1016/j.csbj.2023.02.029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 02/16/2023] [Accepted: 02/16/2023] [Indexed: 02/19/2023] Open
Abstract
Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) are commonly used to model arrhythmogenic cardiomyopathy (ACM), a heritable cardiac disease characterized by severe ventricular arrhythmias, fibrofatty myocardial replacement and progressive ventricular dysfunction. Although ACM is inherited as an autosomal dominant disease, incomplete penetrance and variable expressivity are extremely common, resulting in different clinical manifestations. Here, we propose hiPSC-CMs as a powerful in vitro model to study incomplete penetrance in ACM. Six hiPSC lines were generated from blood samples of three ACM patients carrying a heterozygous deletion of exon 4 in the PKP2 gene, two asymptomatic (ASY) carriers of the same mutation and one healthy control (CTR), all belonging to the same family. Whole exome sequencing was performed in all family members and hiPSC-CMs were examined by ddPCR, western blot, Wes™ immunoassay system, patch clamp, immunofluorescence and RNASeq. Our results show molecular and functional differences between ACM and ASY hiPSC-CMs, including a higher amount of mutated PKP2 mRNA, a lower expression of the connexin-43 protein, a lower overall density of sodium current, a higher intracellular lipid accumulation and sarcomere disorganization in ACM compared to ASY hiPSC-CMs. Differentially expressed genes were also found, supporting a predisposition for a fatty phenotype in ACM hiPSC-CMs. These data indicate that hiPSC-CMs are a suitable model to study incomplete penetrance in ACM.
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Key Words
- ABC, active ß-catenin
- ACM, arrhythmogenic cardiomyopathy
- ASY, asymptomatic
- Arrhythmogenic cardiomyopathy
- BBB, bundle-branch block
- CMs, cardiomyocytes
- CTR, control
- Cx43, connexin-43
- DEGs, differentially expressed genes
- GATK, Genome Analysis Toolkit
- Human induced pluripotent stem cell derived cardiomyocytes
- ICD, implantable cardioverter-defibrillator
- ID, intercalated disk
- Incomplete penetrance
- LBB, left bundle-branch block
- MRI, magnetic resonance imagingmut, mutated
- NSVT, non-sustained ventricular tachycardia
- RV, right ventricle
- hiPSC, human induced pluripotent stem cell
- wt, wild type
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Affiliation(s)
- Marzia De Bortoli
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy
| | - Viviana Meraviglia
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy.,Department of Anatomy and Embryology, Leiden University Medical Center, 2316 Leiden, the Netherlands
| | - Katarina Mackova
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy
| | - Laura S Frommelt
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy
| | - Eva König
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy
| | - Johannes Rainer
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy
| | - Chiara Volani
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy.,Universita` degli Studi di Milano, The Cell Physiology MiLab, Department of Biosciences, Milano, Italy
| | - Patrizia Benzoni
- Universita` degli Studi di Milano, The Cell Physiology MiLab, Department of Biosciences, Milano, Italy
| | - Maja Schlittler
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy
| | - Giada Cattelan
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy
| | - Benedetta M Motta
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy
| | - Claudia Volpato
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy
| | - Werner Rauhe
- San Maurizio Hospital, Department of Cardiology, Bolzano, Italy
| | - Andrea Barbuti
- Universita` degli Studi di Milano, The Cell Physiology MiLab, Department of Biosciences, Milano, Italy
| | - Serena Zacchigna
- International Centre for Genetic Engineering and Biotechnology (ICGEB), Cardiovascular Biology Laboratory, Trieste, Italy
| | - Peter P Pramstaller
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy
| | - Alessandra Rossini
- Institute for Biomedicine (Affiliated to the University of Lübeck), Eurac Research, Bolzano, Italy
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Pinali C, Bennett HJ, Davenport JB, Caldwell JL, Starborg T, Trafford AW, Kitmitto A. Three-dimensional structure of the intercalated disc reveals plicate domain and gap junction remodeling in heart failure. Biophys J 2015; 108:498-507. [PMID: 25650918 DOI: 10.1016/j.bpj.2014.12.001] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 11/20/2014] [Accepted: 12/01/2014] [Indexed: 10/24/2022] Open
Abstract
The intercalated disc (ICD) orchestrates electrochemical and mechanical communication between neighboring cardiac myocytes, properties that are perturbed in heart failure (HF). Although structural data from transmission electron microscopy two-dimensional images have provided valuable insights into the domains forming the ICD, there are currently no three-dimensional (3D) reconstructions for an entire ICD in healthy or diseased hearts. Here, we aimed to understand the link between changes in protein expression in an ovine tachypacing-induced HF model and ultrastructural remodeling of the ICD by determining the 3D intercalated disc architecture using serial block face scanning electron microscopy. In the failing myocardium there is no change to the number of ICDs within the left ventricle, but there is an almost doubling of the number of discs with a surface area of <1.0 × 10(8)μm(2) in comparison to control. The 3D reconstructions further revealed that there is remodeling of the plicate domains and gap junctions with vacuole formation around and between the contributing membranes that form the ICDs in HF. Biochemical analysis revealed upregulation of proteins involved in stabilizing the adhesive and mechanical properties consistent with the morphological changes. Our studies here have shown that in tachypacing-induced HF mechanical stresses are associated with both structural and molecular alterations. To our knowledge, these data together provide novel, to our knowledge, insights as to how remodeling at the molecular and structural levels leads to impaired intercellular communication.
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Affiliation(s)
- Christian Pinali
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, Manchester, United Kingdom
| | - Hayley J Bennett
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, Manchester, United Kingdom
| | - J Bernard Davenport
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, Manchester, United Kingdom
| | - Jessica L Caldwell
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, Manchester, United Kingdom
| | - Tobias Starborg
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Andrew W Trafford
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, Manchester, United Kingdom
| | - Ashraf Kitmitto
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, Manchester, United Kingdom.
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3
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Abstract
The members of the nebulin protein family, including nebulin, nebulette, LASP-1, LASP-2, and N-RAP, contain various numbers of nebulin repeats and bind to actin, but are otherwise heterogeneous with regard to size, expression pattern, and function. This review focuses on the roles of nebulin family members in the heart. Nebulin is the largest member predominantly expressed in skeletal muscle, where it stretches along the thin filament. In heart, nebulin is detectable only at low levels and its absence has no apparent effects. Nebulette is similar in structure to the nebulin C-terminal Z-line region and specifically expressed in heart. Nebulette gene mutations have been identified in dilated cardiomyopathy patients and transgenic mice overexpressing nebulette mutants partially recapitulate the human pathology. In contrast, nebulette knockout mice show no functional phenotype, but exhibit Z-line widening. LASP-2 is an isoform of nebulette expressed in multiple tissues, including the heart. It is present in the Z-line and intercalated disc and able to bind and cross-link filamentous actin. LASP-1 is similar in structure to LASP-2, but expressed only in non-muscle tissue. N-RAP is present in myofibril precursors during myofibrillogenesis and thought to be involved in myofibril assembly, while it is localized at the intercalated disc in adult heart. Additional in vivo models are required to provide further insights into the functions of nebulin family members in the heart.
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Affiliation(s)
- Marie-Louise Bang
- Institute of Genetic and Biomedical Research, UOS Milan, National Research Council
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4
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Wilsbacher LD, Coughlin SR. Analysis of cardiomyocyte development using immunofluorescence in embryonic mouse heart. J Vis Exp 2015:52644. [PMID: 25866997 PMCID: PMC4401388 DOI: 10.3791/52644] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
During heart development, the generation of myocardial-specific structural and functional units including sarcomeres, contractile myofibrils, intercalated discs, and costameres requires the coordinated assembly of multiple components in time and space. Disruption in assembly of these components leads to developmental heart defects. Immunofluorescent staining techniques are used commonly in cultured cardiomyocytes to probe myofibril maturation, but this ex vivo approach is limited by the extent to which myocytes will fully differentiate in culture, lack of normal in vivo mechanical inputs, and absence of endocardial cues. Application of immunofluorescence techniques to the study of developing mouse heart is desirable but more technically challenging, and methods often lack sufficient sensitivity and resolution to visualize sarcomeres in the early stages of heart development. Here, we describe a robust and reproducible method to co-immunostain multiple proteins or to co-visualize a fluorescent protein with immunofluorescent staining in the embryonic mouse heart and use this method to analyze developing myofibrils, intercalated discs, and costameres. This method can be further applied to assess cardiomyocyte structural changes caused by mutations that lead to developmental heart defects.
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Affiliation(s)
- Lisa D Wilsbacher
- Feinberg Cardiovascular Research Institute, Northwestern University; Cardiovascular Research Institute, University of California, San Francisco;
| | - Shaun R Coughlin
- Cardiovascular Research Institute, University of California, San Francisco
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Wilson AJ, Schoenauer R, Ehler E, Agarkova I, Bennett PM. Cardiomyocyte growth and sarcomerogenesis at the intercalated disc. Cell Mol Life Sci 2013; 71:165-81. [PMID: 23708682 PMCID: PMC3889684 DOI: 10.1007/s00018-013-1374-5] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2013] [Revised: 04/27/2013] [Accepted: 05/13/2013] [Indexed: 12/02/2022]
Abstract
Cardiomyocytes grow during heart maturation or disease-related cardiac remodeling. We present evidence that the intercalated disc (ID) is integral to both longitudinal and lateral growth: increases in width are accommodated by lateral extension of the plicate tread regions and increases in length by sarcomere insertion within the ID. At the margin between myofibril and the folded membrane of the ID lies a transitional junction through which the thin filaments from the last sarcomere run to the ID membrane and it has been suggested that this junction acts as a proto Z-disc for sarcomere addition. In support of this hypothesis, we have investigated the ultrastructure of the ID in mouse hearts from control and dilated cardiomyopathy (DCM) models, the MLP-null and a cardiac-specific β-catenin mutant, cΔex3, as well as in human left ventricle from normal and DCM samples. We find that the ID amplitude can vary tenfold from 0.2 μm up to a maximum of ~2 μm allowing gradual expansion during heart growth. At the greatest amplitude, equivalent to a sarcomere length, A-bands and thick filaments are found within the ID membrane loops together with a Z-disc, which develops at the transitional junction position. Here, also, the tops of the membrane folds, which are rich in αII spectrin, become enlarged and associated with junctional sarcoplasmic reticulum. Systematically larger ID amplitudes are found in DCM samples. Other morphological differences between mouse DCM and normal hearts suggest that sarcomere inclusion is compromised in the diseased hearts.
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Affiliation(s)
- Amanda J Wilson
- Randall Division of Cell and Molecular Biophysics, King's College London, New Hunt's House, Guy's Campus, London, SE1 1UL, UK,
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6
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Scaffolds and chaperones in myofibril assembly: putting the striations in striated muscle. Biophys Rev 2011; 3:25-32. [PMID: 21666840 DOI: 10.1007/s12551-011-0043-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Sarcomere assembly in striated muscles has long been described as a series of steps leading to assembly of individual proteins into thick filaments, thin filaments and Z-lines. Decades of previous work focused on the order in which various structural proteins adopted the striated organization typical of mature myofibrils. These studies led to the view that actin and α-actinin assemble into premyofibril structures separately from myosin filaments, and that these structures are then assembled into myofibrils with centered myosin filaments and actin filaments anchored at the Z-lines. More recent studies have shown that particular scaffolding proteins and chaperone proteins are required for individual steps in assembly. Here, we review the evidence that N-RAP, a LIM domain and nebulin repeat protein, scaffolds assembly of actin and α-actinin into I-Z-I structures in the first steps of assembly; that the heat shock chaperone proteins Hsp90 & Hsc70 cooperate with UNC-45 to direct the folding of muscle myosin and its assembly into thick filaments; and that the kelch repeat protein Krp1 promotes lateral fusion of premyofibril structures to form mature striated myofibrils. The evidence shows that myofibril assembly is a complex process that requires the action of particular catalysts and scaffolds at individual steps. The scaffolds and chaperones required for assembly are potential regulators of myofibrillogenesis, and abnormal function of these proteins caused by mutation or pathological processes could in principle contribute to diseases of cardiac and skeletal muscles.
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7
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Lu S, Crawford GL, Dore J, Anderson SA, Despres D, Horowits R. Cardiac-specific NRAP overexpression causes right ventricular dysfunction in mice. Exp Cell Res 2011; 317:1226-37. [PMID: 21276443 DOI: 10.1016/j.yexcr.2011.01.020] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2010] [Revised: 01/14/2011] [Accepted: 01/19/2011] [Indexed: 01/08/2023]
Abstract
The muscle-specific protein NRAP is concentrated at cardiac intercalated disks, plays a role in myofibril assembly, and is upregulated early in mouse models of dilated cardiomyopathy. Using a tet-off system, we developed novel transgenic lines exhibiting cardiac-specific NRAP overexpression ~2.5 times greater than normal. At 40-50 weeks, NRAP overexpression resulted in dilation and decreased ejection fraction in the right ventricle, with little effect on the left ventricle. Expression of transcripts encoding brain natriuretic peptide and skeletal α-actin was increased by cardiac-specific NRAP overexpression, indicative of a cardiomyopathic response. NRAP overexpression did not alter the levels or organization of N-cadherin and connexin-43. The results show that chronic NRAP overexpression in the mouse leads to right ventricular cardiomyopathy by 10 months, but that the early NRAP upregulation previously observed in some mouse models of dilated cardiomyopathy is unlikely to account for the remodeling of intercalated disks and left ventricular dysfunction observed in those cases.
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Affiliation(s)
- Shajia Lu
- National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA
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8
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Pappas CT, Bliss KT, Zieseniss A, Gregorio CC. The Nebulin family: an actin support group. Trends Cell Biol 2010; 21:29-37. [PMID: 20951588 DOI: 10.1016/j.tcb.2010.09.005] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Revised: 09/08/2010] [Accepted: 09/09/2010] [Indexed: 11/25/2022]
Abstract
Nebulin, a giant, actin-binding protein, is the largest member of a family of proteins (including N-RAP, nebulette, lasp-1 and lasp-2) that are assembled in a variety of cytoskeletal structures, and expressed in different tissues. For decades, nebulin has been thought to act as a molecular ruler, specifying the precise length of actin filaments in skeletal muscle. However, emerging evidence suggests that nebulin should not be viewed as a ruler but as an actin filament stabilizer required for length maintenance. Nebulin has also been implicated recently in an array of regulatory functions independent of its role in actin filament length regulation. In this review, we discuss the current evolutionary, biochemical, and functional data for the nebulin family of proteins - a family whose members, both large and small, function as cytoskeletal scaffolds and stabilizers.
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Affiliation(s)
- Christopher T Pappas
- Department of Cell Biology, and Molecular Cardiovascular Research Program, The University of Arizona, Tucson, AZ, USA
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9
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Lu S, Borst DE, Horowits R. Expression and alternative splicing of N-RAP during mouse skeletal muscle development. ACTA ACUST UNITED AC 2009; 65:945-54. [PMID: 18792955 DOI: 10.1002/cm.20317] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
N-RAP alternative splicing and protein localization were studied in developing skeletal muscle tissue from pre- and postnatal mice and in fusing primary myotubes in culture. Messages encoding N-RAP-s and N-RAP-c, the predominant isoforms of N-RAP detected in adult skeletal muscle and heart, respectively, were present in a 5:1 ratio in skeletal muscle isolated from E16.5 embryos. N-RAP-s mRNA levels increased three-fold over the first 3 weeks of postnatal development, while N-RAP-c mRNA levels remained low. N-RAP alternative splicing during myotube differentiation in culture was similar to the pattern observed in embryonic and neonatal muscle, with N-RAP-s expression increasing and N-RAP-c mRNA levels remaining low. In both developing skeletal muscle and cultured myotubes, N-RAP protein was primarily associated with developing myofibrillar structures containing alpha-actinin, but was not present in mature myofibrils. The results establish that N-RAP-s is the predominant spliced form of N-RAP present throughout skeletal muscle development.
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Affiliation(s)
- Shajia Lu
- Laboratory of Muscle Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892-8024, USA
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Manisastry SM, Zaal KJM, Horowits R. Myofibril assembly visualized by imaging N-RAP, alpha-actinin, and actin in living cardiomyocytes. Exp Cell Res 2009; 315:2126-39. [PMID: 19233165 DOI: 10.1016/j.yexcr.2009.02.006] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2009] [Revised: 02/03/2009] [Accepted: 02/03/2009] [Indexed: 11/15/2022]
Abstract
N-RAP is a striated muscle-specific scaffolding protein that organizes alpha-actinin and actin into symmetrical I-Z-I structures in developing myofibrils. Here we determined the order of events during myofibril assembly through time-lapse confocal microscopy of cultured embryonic chick cardiomyocytes coexpressing fluorescently tagged N-RAP and either alpha-actinin or actin. During de novo myofibril assembly, N-RAP assembled in fibrillar structures within the cell, with dots of alpha-actinin subsequently organizing along these structures. The initial fibrillar structures were reminiscent of actin fibrils, and coassembly of N-RAP and actin into newly formed fibrils supported this. The alpha-actinin dots subsequently broadened to Z-lines that were wider than the underlying N-RAP fibril, and N-RAP fluorescence intensity decreased. FRAP experiments showed that most of the alpha-actinin dynamically exchanged during all stages of myofibril assembly. In contrast, less than 20% of the N-RAP in premyofibrils was exchanged during 10-20 min after photobleaching, but this value increased to 70% during myofibril maturation. The results show that N-RAP assembles into an actin containing scaffold before alpha-actinin recruitment; that the N-RAP scaffold is much more stable than the assembling structural components; that N-RAP dynamics increase as assembly progresses; and that N-RAP leaves the structure after assembly is complete.
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Affiliation(s)
- Shyam M Manisastry
- National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA
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11
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Risebro CA, Searles RG, Melville AAD, Ehler E, Jina N, Shah S, Pallas J, Hubank M, Dillard M, Harvey NL, Schwartz RJ, Chien KR, Oliver G, Riley PR. Prox1 maintains muscle structure and growth in the developing heart. Development 2008; 136:495-505. [PMID: 19091769 DOI: 10.1242/dev.030007] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Impaired cardiac muscle growth and aberrant myocyte arrangement underlie congenital heart disease and cardiomyopathy. We show that cardiac-specific inactivation of the murine homeobox transcription factor Prox1 results in the disruption of expression and localisation of sarcomeric proteins, gross myofibril disarray and growth-retarded hearts. Furthermore, we demonstrate that Prox1 is required for direct transcriptional regulation of the genes encoding the structural proteins alpha-actinin, N-RAP and zyxin, which collectively function to maintain an actin-alpha-actinin interaction as the fundamental association of the sarcomere. Aspects of abnormal heart development and the manifestation of a subset of muscular-based disease have previously been attributed to mutations in key structural proteins. Our study reveals an essential requirement for direct transcriptional regulation of sarcomere integrity, in the context of enabling foetal cardiomyocyte hypertrophy, maintenance of contractile function and progression towards inherited or acquired myopathic disease.
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Lu S, Horowits R. Role of nonmuscle myosin IIB and N-RAP in cell spreading and myofibril assembly in primary mouse cardiomyocytes. ACTA ACUST UNITED AC 2008; 65:747-61. [PMID: 18615632 DOI: 10.1002/cm.20299] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
We investigated the role of nonmuscle myosin heavy chain (NMHC) IIB in cultured embryonic mouse cardiomyocytes by specific knockdown using RNA interference. NMHC IIB protein levels decreased 90% compared with mock-transfected cells by 3 days post transfection. NMHC IIB knockdown resulted in a slow decrease in N-RAP protein levels over 6 days with no change in N-RAP transcript levels. N-RAP is a scaffold for alpha-actinin and actin assembly during myofibrillogenesis, and we quantitated myofibril accumulation by morphometric analysis of alpha-actinin organization. Between 3 and 6 days, NMHC IIB knockdown was accompanied by the abolishment of cardiomyocyte spreading. During this period the rate of myofibril accumulation steadily decreased, correlating with the slowly decreasing levels of N-RAP. Between 6 and 8 days NMHC IIB and N-RAP protein levels recovered, and cardiomyocyte spreading and myofibril accumulation resumed. Inhibition of proteasome function using MG132 led to accumulation of excess N-RAP, and the secondary decrease in N-RAP that otherwise accompanied NMHC IIB knockdown was abolished. The results show that NMHC IIB knockdown led to decreased N-RAP levels through proteasome-mediated degradation. Furthermore, these proteins have distinct functional roles, with NMHC IIB playing a role in cardiomyocyte spreading and N-RAP functioning in myofibril assembly.
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Affiliation(s)
- Shajia Lu
- Department of Health and Human Services, Laboratory of Muscle Biology, National Institute of Arthritis, Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda 20892-8024, Maryland, USA
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13
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Krp1 (Sarcosin) promotes lateral fusion of myofibril assembly intermediates in cultured mouse cardiomyocytes. Exp Cell Res 2008; 314:1177-91. [PMID: 18178185 DOI: 10.1016/j.yexcr.2007.12.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2007] [Revised: 12/07/2007] [Accepted: 12/07/2007] [Indexed: 11/23/2022]
Abstract
Krp1, also called sarcosin, is a cardiac and skeletal muscle kelch repeat protein hypothesized to promote the assembly of myofibrils, the contractile organelles of striated muscles, through interaction with N-RAP and actin. To elucidate its role, endogenous Krp1 was studied in primary embryonic mouse cardiomyocytes. While immunofluorescence showed punctate Krp1 distribution throughout the cell, detergent extraction revealed a significant pool of Krp1 associated with cytoskeletal elements. Reduction of Krp1 expression with siRNA resulted in specific inhibition of myofibril accumulation with no effect on cell spreading. Immunostaining analysis and electron microscopy revealed that cardiomyocytes lacking Krp1 contained sarcomeric proteins with longitudinal periodicities similar to mature myofibrils, but fibrils remained thin and separated. These thin myofibrils were degraded by a scission mechanism distinct from the myofibril disassembly pathway observed during cell division in the developing heart. The data are consistent with a model in which Krp1 promotes lateral fusion of adjacent thin fibrils into mature, wide myofibrils and contribute insight into mechanisms of myofibrillogenesis and disassembly.
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14
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Zieseniss A, Terasaki AG, Gregorio CC. Lasp-2 expression, localization, and ligand interactions: A new Z-disc scaffolding protein. ACTA ACUST UNITED AC 2007; 65:59-72. [DOI: 10.1002/cm.20244] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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15
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Dhume A, Lu S, Horowits R. Targeted disruption of N-RAP gene function by RNA interference: a role for N-RAP in myofibril organization. ACTA ACUST UNITED AC 2006; 63:493-511. [PMID: 16767749 DOI: 10.1002/cm.20141] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
N-RAP is a muscle-specific protein concentrated in myofibril precursors during sarcomere assembly and at intercalated disks in adult heart. We used RNA interference to achieve a targeted decrease in N-RAP transcript and protein levels in primary cultures of embryonic mouse cardiomyocytes. N-RAP transcript levels were decreased by approximately 70% within 2 days following transfection with N-RAP specific siRNA. N-RAP protein levels steadily decreased over several days, reaching approximately 50% of control levels within 6 days. N-RAP protein knockdown was associated with decreased myofibril assembly, as assessed by alpha-actinin organization into mature striations. Transcripts encoding N-RAP binding proteins associated with assembling or mature myofibrils, such as alpha-actinin, Krp1, and muscle LIM protein, were expressed at normal levels during N-RAP protein knockdown, and alpha-actinin and Krp-1 protein levels were also unchanged. Transcripts encoding muscle myosin heavy chain and nonmuscle myosin heavy chain IIB were also expressed at relatively normal levels. However, decreased N-RAP protein levels were associated with dramatic changes in the encoded myosin proteins, with muscle myosin heavy chain levels increasing and nonmuscle myosin heavy chain IIB decreasing. N-RAP transcript and protein levels recovered to normal by days 6 and 7, respectively, and the changes in myofibril organization and myosin heavy chain isoform levels were reversed. Our data indicate that we can achieve transient N-RAP protein knockdown using the RNA interference technique and that alpha-actinin organization into myofibrils in cardiomyocytes is closely linked to N-RAP protein levels. Finally, N-RAP protein levels regulate the balance between nonmuscle myosin IIB and muscle myosin by post-trancriptional mechanisms.
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Affiliation(s)
- Ashwini Dhume
- Laboratory of Muscle Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health (Department of Health and Human Services), Bethesda, MD 20892, USA
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van der Ven PFM, Ehler E, Vakeel P, Eulitz S, Schenk JA, Milting H, Micheel B, Fürst DO. Unusual splicing events result in distinct Xin isoforms that associate differentially with filamin c and Mena/VASP. Exp Cell Res 2006; 312:2154-67. [PMID: 16631741 DOI: 10.1016/j.yexcr.2006.03.015] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2006] [Revised: 03/14/2006] [Accepted: 03/15/2006] [Indexed: 11/19/2022]
Abstract
Filamin c is the predominantly expressed filamin isoform in striated muscles. It is localized in myofibrillar Z-discs, where it binds FATZ and myotilin, and in myotendinous junctions and intercalated discs. Here, we identify Xin, the protein encoded by the human gene 'cardiomyopathy associated 1' (CMYA1) as filamin c binding partner at these specialized structures where the ends of myofibrils are attached to the sarcolemma. Xin directly binds the EVH1 domain proteins Mena and VASP. In the adult heart, Xin and Mena/VASP colocalize with filamin c in intercalated discs. In cultured cardiomyocytes, the proteins also localize in the nonstriated part of myofibrils, where sarcomeres are assembled and an extensive reorganization of the actin cytoskeleton occurs. Unusual intraexonic splicing events result in the existence of three Xin isoforms that associate differentially with its ligands. The identification of the complex filamin c-Xin-Mena/VASP provides a first glance on the role of Xin in the molecular mechanisms involved in developmental and adaptive remodeling of the actin cytoskeleton during cardiac morphogenesis and sarcomere assembly.
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Affiliation(s)
- Peter F M van der Ven
- Department of Molecular Cell Biology, University of Bonn, Ulrich-Haberland-Str. 61a, D-53121 Bonn, Germany.
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