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Kaushik G, Engler AJ. From stem cells to cardiomyocytes: the role of forces in cardiac maturation, aging, and disease. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 126:219-42. [PMID: 25081620 DOI: 10.1016/b978-0-12-394624-9.00009-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Stem cell differentiation into a variety of lineages is known to involve signaling from the extracellular niche, including from the physical properties of that environment. What regulates stem cell responses to these cues is there ability to activate different mechanotransductive pathways. Here, we will review the structures and pathways that regulate stem cell commitment to a cardiomyocyte lineage, specifically examining proteins within muscle sarcomeres, costameres, and intercalated discs. Proteins within these structures stretch, inducing a change in their phosphorylated state or in their localization to initiate different signals. We will also put these changes in the context of stem cell differentiation into cardiomyocytes, their subsequent formation of the chambered heart, and explore negative signaling that occurs during disease.
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Affiliation(s)
- Gaurav Kaushik
- Department of Bioengineering, University of California, San Diego, La Jolla, California, USA
| | - Adam J Engler
- Department of Bioengineering, University of California, San Diego, La Jolla, California, USA
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52
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Confocal microscopy of cardiac myocytes. Methods Mol Biol 2013. [PMID: 24052352 DOI: 10.1007/978-1-60761-847-8_8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/01/2023]
Abstract
Detailed methods are provided for the preparation and confocal imaging of cardiac myocyte development and differentiation. Examples include protocols for the analysis of cultured myocytes as well as vibratome sections of hearts from embryonic and adult tissue. Techniques include routine labeling of F-actin with phalloidin as well as multiple labeling protocols for colocalization studies and cell volume analysis.
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53
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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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Clark KA, Kadrmas JL. Drosophila melanogaster muscle LIM protein and alpha-actinin function together to stabilize muscle cytoarchitecture: a potential role for Mlp84B in actin-crosslinking. Cytoskeleton (Hoboken) 2013; 70:304-16. [PMID: 23606669 PMCID: PMC3716849 DOI: 10.1002/cm.21106] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Revised: 03/04/2013] [Accepted: 03/06/2013] [Indexed: 02/06/2023]
Abstract
Stabilization of tissue architecture during development and growth is essential to maintain structural integrity. Because of its contractile nature, muscle is especially susceptible to physiological stresses, and has multiple mechanisms to maintain structural integrity. The Drosophila melanogaster Muscle LIM Protein (MLP), Mlp84B, participates in muscle maintenance, yet its precise mechanism of action is still controversial. Through a candidate approach, we identified α-actinin as a protein that functions with Mlp84B to ensure muscle integrity. α-actinin RNAi animals die primarily as pupae, and Mlp84B RNAi animals are adult viable. RNAi knockdown of Mlp84B and α-actinin together produces synergistic early larval lethality and destabilization of Z-line structures. We recapitulated these phenotypes using combinations of traditional loss-of-function alleles and single-gene RNAi. We observe that Mlp84B induces the formation of actin loops in muscle cell nuclei in the absence of nuclear α-actinin, suggesting Mlp84B has intrinsic actin cross-linking activity, which may complement α-actinin cross-linking activity at sites of actin filament anchorage. These results reveal a molecular mechanism for MLP stabilization of muscle and implicate reduced actin crosslinking as the primary destabilizing defect in MLP-associated cardiomyopathies. Our data support a model in which α-actinin and Mlp84B have important and overlapping functions at sites of actin filament anchorage to preserve muscle structure and function.
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Affiliation(s)
- Kathleen A. Clark
- Huntsman Cancer Institute, University of Utah, Salt Lake City, UT 84112
- Department of Biology, University of Utah, Salt Lake City, UT 84112
- Department of Oncological Sciences, University of Utah, Salt Lake City, UT 84112
| | - Julie L. Kadrmas
- Huntsman Cancer Institute, University of Utah, Salt Lake City, UT 84112
- Department of Oncological Sciences, University of Utah, Salt Lake City, UT 84112
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55
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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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56
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Catterson JH, Heck MMS, Hartley PS. Fermitins, the orthologs of mammalian Kindlins, regulate the development of a functional cardiac syncytium in Drosophila melanogaster. PLoS One 2013; 8:e62958. [PMID: 23690969 PMCID: PMC3655056 DOI: 10.1371/journal.pone.0062958] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Accepted: 03/26/2013] [Indexed: 11/18/2022] Open
Abstract
The vertebrate Kindlins are an evolutionarily conserved family of proteins critical for integrin signalling and cell adhesion. Kindlin-2 (KIND2) is associated with intercalated discs in mice, suggesting a role in cardiac syncytium development; however, deficiency of Kind2 leads to embryonic lethality. Morpholino knock-down of Kind2 in zebrafish has a pleiotropic effect on development that includes the heart. It therefore remains unclear whether cardiomyocyte Kind2 expression is required for cardiomyocyte junction formation and the development of normal cardiac function. To address this question, the expression of Fermitin 1 and Fermitin 2 (Fit1, Fit2), the two Drosophila orthologs of Kind2, was silenced in Drosophila cardiomyocytes. Heart development was assessed in adult flies by immunological methods and videomicroscopy. Silencing both Fit1 and Fit2 led to a severe cardiomyopathy characterised by the failure of cardiomyocytes to develop as a functional syncytium and loss of synchrony between cardiomyocytes. A null allele of Fit1 was generated but this had no impact on the heart. Similarly, the silencing of Fit2 failed to affect heart function. In contrast, the silencing of Fit2 in the cardiomyocytes of Fit1 null flies disrupted syncytium development, leading to severe cardiomyopathy. The data definitively demonstrate a role for Fermitins in the development of a functional cardiac syncytium in Drosophila. The findings also show that the Fermitins can functionally compensate for each other in order to control syncytium development. These findings support the concept that abnormalities in cardiomyocyte KIND2 expression or function may contribute to cardiomyopathies in humans.
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Affiliation(s)
- James H. Catterson
- The University of Edinburgh/British Heart Foundation Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, Midlothian, United Kingdom
| | - Margarete M. S. Heck
- The University of Edinburgh/British Heart Foundation Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, Midlothian, United Kingdom
| | - Paul S. Hartley
- The University of Edinburgh/British Heart Foundation Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, Midlothian, United Kingdom
- * E-mail:
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57
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Touvron M, Escoubet B, Mericskay M, Angelini A, Lamotte L, Santini MP, Rosenthal N, Daegelen D, Tuil D, Decaux JF. Locally expressed IGF1 propeptide improves mouse heart function in induced dilated cardiomyopathy by blocking myocardial fibrosis and SRF-dependent CTGF induction. Dis Model Mech 2012; 5:481-91. [PMID: 22563064 PMCID: PMC3380711 DOI: 10.1242/dmm.009456] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Cardiac fibrosis is critically involved in the adverse remodeling accompanying dilated cardiomyopathies (DCMs), which leads to cardiac dysfunction and heart failure (HF). Connective tissue growth factor (CTGF), a profibrotic cytokine, plays a key role in this deleterious process. Some beneficial effects of IGF1 on cardiomyopathy have been described, but its potential role in improving DCM is less well characterized. We investigated the consequences of expressing a cardiac-specific transgene encoding locally acting IGF1 propeptide (muscle-produced IGF1; mIGF1) on disease progression in a mouse model of DCM [cardiac-specific and inducible serum response factor (SRF) gene disruption] that mimics some forms of human DCM. Cardiac-specific mIGF1 expression substantially extended the lifespan of SRF mutant mice, markedly improved cardiac functions, and delayed both DCM and HF. These protective effects were accompanied by an overall improvement in cardiomyocyte architecture and a massive reduction of myocardial fibrosis with a concomitant amelioration of inflammation. At least some of the beneficial effects of mIGF1 transgene expression were due to mIGF1 counteracting the strong increase in CTGF expression within cardiomyocytes caused by SRF deficiency, resulting in the blockade of fibroblast proliferation and related myocardial fibrosis. These findings demonstrate that SRF plays a key role in the modulation of cardiac fibrosis through repression of cardiomyocyte CTGF expression in a paracrine fashion. They also explain how impaired SRF function observed in human HF promotes fibrosis and adverse cardiac remodeling. Locally acting mIGF1 efficiently protects the myocardium from these adverse processes, and might thus represent a therapeutic avenue to counter DCM.
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58
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Cardiac remodeling is not modulated by overexpression of muscle LIM protein (MLP). Basic Res Cardiol 2012; 107:262. [DOI: 10.1007/s00395-012-0262-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2010] [Revised: 02/14/2012] [Accepted: 03/07/2012] [Indexed: 12/17/2022]
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59
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Li A, Ponten F, dos Remedios CG. The interactome of LIM domain proteins: The contributions of LIM domain proteins to heart failure and heart development. Proteomics 2012; 12:203-25. [DOI: 10.1002/pmic.201100492] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2011] [Revised: 11/07/2011] [Accepted: 11/08/2011] [Indexed: 12/22/2022]
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60
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The sarcomeric Z-disc and Z-discopathies. J Biomed Biotechnol 2011; 2011:569628. [PMID: 22028589 PMCID: PMC3199094 DOI: 10.1155/2011/569628] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Accepted: 08/12/2011] [Indexed: 02/06/2023] Open
Abstract
The sarcomeric Z-disc defines the lateral borders of the sarcomere and has primarily been seen as a structure important for mechanical stability. This view has changed dramatically within the last one or two decades. A multitude of novel Z-disc proteins and their interacting partners have been identified, which has led to the identification of additional functions and which have now been assigned to this structure. This includes its importance for intracellular signalling, for mechanosensation and mechanotransduction in particular, an emerging importance for protein turnover and autophagy, as well as its molecular links to the t-tubular system and the sarcoplasmic reticulum. Moreover, the discovery of mutations in a wide variety of Z-disc proteins, which lead to perturbations of several of the above-mentioned systems, gives rise to a diverse group of diseases which can be termed Z-discopathies. This paper provides a brief overview of these novel aspects as well as points to future research directions.
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61
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Tropomodulin capping of actin filaments in striated muscle development and physiology. J Biomed Biotechnol 2011; 2011:103069. [PMID: 22013379 PMCID: PMC3196151 DOI: 10.1155/2011/103069] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Accepted: 08/18/2011] [Indexed: 11/17/2022] Open
Abstract
Efficient striated muscle contraction requires precise assembly and regulation of diverse actin filament systems, most notably the sarcomeric thin filaments of the contractile apparatus. By capping the pointed ends of actin filaments, tropomodulins (Tmods) regulate actin filament assembly, lengths, and stability. Here, we explore the current understanding of the expression patterns, localizations, and functions of Tmods in both cardiac and skeletal muscle. We first describe the mechanisms by which Tmods regulate myofibril assembly and thin filament lengths, as well as the roles of closely related Tmod family variants, the leiomodins (Lmods), in these processes. We also discuss emerging functions for Tmods in the sarcoplasmic reticulum. This paper provides abundant evidence that Tmods are key structural regulators of striated muscle cytoarchitecture and physiology.
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62
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Buyandelger B, Ng KE, Miocic S, Piotrowska I, Gunkel S, Ku CH, Knöll R. MLP (muscle LIM protein) as a stress sensor in the heart. Pflugers Arch 2011; 462:135-42. [PMID: 21484537 PMCID: PMC3114083 DOI: 10.1007/s00424-011-0961-2] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2010] [Revised: 03/11/2011] [Accepted: 03/24/2011] [Indexed: 01/22/2023]
Abstract
Muscle LIM protein (MLP, also known as cysteine rich protein 3 (CSRP3, CRP3)) is a muscle-specific-expressed LIM-only protein. It consists of 194 amino-acids and has been described initially as a factor involved in myogenesis (Arber et al. Cell 79:221-231, 1994). MLP soon became an important model for experimental cardiology when it was first demonstrated that MLP deficiency leads to myocardial hypertrophy followed by a dilated cardiomyopathy and heart failure phenotype (Arber et al. Cell 88:393-403, 1997). At this time, this was the first genetically altered animal model to develop this devastating disease. Interestingly, MLP was also found to be down-regulated in humans with heart failure (Zolk et al. Circulation 101:2674-2677, 2000) and MLP mutations are able to cause hypertrophic and dilated forms of cardiomyopathy in humans (Bos et al. Mol Genet Metab 88:78-85, 2006; Geier et al. Circulation 107:1390-1395, 2003; Hershberger et al. Clin Transl Sci 1:21-26, 2008; Knöll et al. Cell 111:943-955, 2002; Knöll et al. Circ Res 106:695-704, 2010; Mohapatra et al. Mol Genet Metab 80:207-215, 2003). Although considerable efforts have been undertaken to unravel the underlying molecular mechanisms-how MLP mutations, either in model organisms or in the human setting cause these diseases are still unclear. In contrast, only precise knowledge of the underlying molecular mechanisms will allow the development of novel and innovative therapeutic strategies to combat this otherwise lethal condition. The focus of this review will be on the function of MLP in cardiac mechanosensation and we shall point to possible future directions in MLP research.
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Affiliation(s)
- Byambajav Buyandelger
- Myocardial Genetics, British Heart Foundation-Centre for Research Excellence, National Heart & Lung Institute, Imperial College, South Kensington Campus, Flowers Building, 4th floor, London, SW7 2AZ, UK
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63
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Van Sligtenhorst I, Ding ZM, Shi ZZ, Read RW, Hansen G, Vogel P. Cardiomyopathy in α-Kinase 3 (ALPK3)–Deficient Mice. Vet Pathol 2011; 49:131-41. [DOI: 10.1177/0300985811402841] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Cardiomyopathy developed in mice deficient for α-kinase 3 (ALPK3), a nuclear kinase previously implicated in the differentiation of cardiomyocytes. Alpk3–/– mice were produced according to normal Mendelian ratios and appeared normal except for a nonprogressive cardiomyopathy that had features of both hypertrophic and dilated forms of cardiomyopathy. Cardiac hypertrophy in Alpk3–/– mice was characterized by increased thickness of both left and right ventricular (LV and RV) walls and by markedly increased heart weight and increased heart weight/body weight and heart weight/tibia length ratios. Magnetic resonance imaging studies confirmed the increased thickness in both septal and LV free walls at end-diastole, although there was no significant change in LV wall thickness at end-systole. Myocardial hypertrophy was the predominant feature in Alpk3–/– mice, but several changes more typically associated with dilated cardiomyopathy included a marked increase in end-diastolic and end-systolic LV volume, as well as reduced cardiac output, stroke volume, and ejection fractions, suggesting LV chamber dilation. Magnetic resonance imaging showed a 50% reduction in both septal and free wall LV contractility in Alpk3–/– mice. Interstitial fibrosis and inflammation were notably absent in Alpk3–/– mice; however, light and electron microscopy revealed altered cardiomyocyte architecture, characterized by reduced numbers of abnormal intercalated discs being associated with mild disarray of myofibrils. These lesions could account for the impaired contractility of the myofibrillar apparatus and contribute to the pathogenesis of cardiomyopathy in Alpk3–/– mice.
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Affiliation(s)
| | - Z-M. Ding
- Department of Cardiology, Lexicon Pharmaceuticals Inc, The Woodlands, TX
| | - Z-Z. Shi
- Department of Cardiology, Lexicon Pharmaceuticals Inc, The Woodlands, TX
| | - R. W. Read
- Department of Pathology, Lexicon Pharmaceuticals Inc, The Woodlands, TX
| | - G. Hansen
- Department of Molecular Genetics, Lexicon Pharmaceuticals Inc, The Woodlands, TX
| | - P. Vogel
- Department of Pathology, Lexicon Pharmaceuticals Inc, The Woodlands, TX
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Micromechanical regulation in cardiac myocytes and fibroblasts: implications for tissue remodeling. Pflugers Arch 2011; 462:105-17. [PMID: 21308471 DOI: 10.1007/s00424-011-0931-8] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Revised: 01/25/2011] [Accepted: 01/25/2011] [Indexed: 10/18/2022]
Abstract
Cells of the myocardium are at home in one of the most mechanically dynamic environments in the body. At the cellular level, pulsatile stimuli of chamber filling and emptying are experienced as cyclic strains (relative deformation) and stresses (force per unit area). The intrinsic characteristics of tension-generating myocytes and fibroblasts thus have a continuous mechanical interplay with their extrinsic surroundings. This review explores the ways that the micromechanics at the scale of single cardiac myocytes and fibroblasts have been measured, modeled, and recapitulated in vitro in the context of adaptation. Both types of cardiac cells respond to externally applied strain, and many of the intracellular mechanosensing pathways have been identified with the careful manipulation of experimental variables. In addition to strain, the extent of loading in myocytes and fibroblasts is also regulated by cues from the microenvironment such as substrate surface chemistry, stiffness, and topography. Combinations of these structural cues in three dimensions are needed to mimic the micromechanical complexity derived from the extracellular matrix of the developing, healthy, or pathophysiologic heart. An understanding of cardiac cell micromechanics can therefore inform the design and composition of tissue engineering scaffolds or stem cell niches for future applications in regenerative medicine.
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65
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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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66
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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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67
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Iskratsch T, Lange S, Dwyer J, Kho AL, dos Remedios C, Ehler E. Formin follows function: a muscle-specific isoform of FHOD3 is regulated by CK2 phosphorylation and promotes myofibril maintenance. ACTA ACUST UNITED AC 2011; 191:1159-72. [PMID: 21149568 PMCID: PMC3002041 DOI: 10.1083/jcb.201005060] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Phosphorylation of the muscle-specific formin splice variant FHOD3 by CK2 regulates its stability, myofibril targeting, and myofibril integrity. Members of the formin family are important for actin filament nucleation and elongation. We have identified a novel striated muscle–specific splice variant of the formin FHOD3 that introduces a casein kinase 2 (CK2) phosphorylation site. The specific targeting of muscle FHOD3 to the myofibrils in cardiomyocytes is abolished in phosphomutants or by the inhibition of CK2. Phosphorylation of muscle FHOD3 also prevents its interaction with p62/sequestosome 1 and its recruitment to autophagosomes. Furthermore, we show that muscle FHOD3 efficiently promotes the polymerization of actin filaments in cardiomyocytes and that the down-regulation of its expression severely affects myofibril integrity. In murine and human cardiomyopathy, we observe reduced FHOD3 expression with a concomitant isoform switch and change of subcellular targeting. Collectively, our data suggest that a muscle-specific isoform of FHOD3 is required for the maintenance of the contractile structures in heart muscle and that its function is regulated by posttranslational modification.
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Affiliation(s)
- Thomas Iskratsch
- The Muscle Cell Biology Section, Randall Division of Cell and Molecular Biophysics, British Heart Foundation Research Excellence Centre, King's College London, London SE1 1UL, England, UK
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68
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Schoenauer R, Emmert MY, Felley A, Ehler E, Brokopp C, Weber B, Nemir M, Faggian GG, Pedrazzini T, Falk V, Hoerstrup SP, Agarkova I. EH-myomesin splice isoform is a novel marker for dilated cardiomyopathy. Basic Res Cardiol 2010; 106:233-47. [PMID: 21069531 PMCID: PMC3032906 DOI: 10.1007/s00395-010-0131-2] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2010] [Revised: 09/29/2010] [Accepted: 10/25/2010] [Indexed: 11/05/2022]
Abstract
The M-band is the prominent cytoskeletal structure that cross-links the myosin and titin filaments in the middle of the sarcomere. To investigate M-band alterations in heart disease, we analyzed the expression of its main components, proteins of the myomesin family, in mouse and human cardiomyopathy. Cardiac function was assessed by echocardiography and compared to the expression pattern of myomesins evaluated with RT-PCR, Western blot, and immunofluorescent analysis. Disease progression in transgenic mouse models for dilated cardiomyopathy (DCM) was accompanied by specific M-band alterations. The dominant splice isoform in the embryonic heart, EH-myomesin, was strongly up-regulated in the failing heart and correlated with a decrease in cardiac function (R = −0.86). In addition, we have analyzed the expressions of myomesins in human myocardial biopsies (N = 40) obtained from DCM patients, DCM patients supported by a left ventricular assist device (LVAD), hypertrophic cardiomyopathy (HCM) patients and controls. Quantitative RT-PCR revealed that the EH-myomesin isoform was up-regulated 41-fold (P < 0.001) in the DCM patients compared to control patients. In DCM hearts supported by a LVAD and HCM hearts, the EH-myomesin expression was comparable to controls. Immunofluorescent analyses indicate that EH-myomesin was enhanced in a cell-specific manner, leading to a higher heterogeneity of the myocytes’ cytoskeleton through the myocardial wall. We suggest that the up-regulation of EH-myomesin denotes an adaptive remodeling of the sarcomere cytoskeleton in the dilated heart and might serve as a marker for DCM in mouse and human myocardium.
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Affiliation(s)
- Roman Schoenauer
- Swiss Center for Regenerative Medicine, University of Zurich, Zurich, Switzerland
- Department of Surgical Research, University Hospital Zurich, Rämistrasse 100, 8091 Zurich, Switzerland
| | - Maximilian Y. Emmert
- Swiss Center for Regenerative Medicine, University of Zurich, Zurich, Switzerland
- Department of Surgical Research, University Hospital Zurich, Rämistrasse 100, 8091 Zurich, Switzerland
- Clinic for Cardiovascular Surgery, University Hospital Zurich, Zurich, Switzerland
| | - Allison Felley
- Department of Medicine, University of Lausanne Medical School, Lausanne, Switzerland
| | - Elisabeth Ehler
- The Randall Division of Cell and Molecular Biophysics and the Cardiovascular Division, King’s College London, London, UK
| | - Chad Brokopp
- Swiss Center for Regenerative Medicine, University of Zurich, Zurich, Switzerland
- Department of Surgical Research, University Hospital Zurich, Rämistrasse 100, 8091 Zurich, Switzerland
| | - Benedikt Weber
- Swiss Center for Regenerative Medicine, University of Zurich, Zurich, Switzerland
- Department of Surgical Research, University Hospital Zurich, Rämistrasse 100, 8091 Zurich, Switzerland
- Clinic for Cardiovascular Surgery, University Hospital Zurich, Zurich, Switzerland
| | - Mohamed Nemir
- Department of Medicine, University of Lausanne Medical School, Lausanne, Switzerland
| | - Giuseppe G. Faggian
- Division of Cardiac Surgery and Cardiology, University of Verona, Verona, Italy
| | - Thierry Pedrazzini
- Department of Medicine, University of Lausanne Medical School, Lausanne, Switzerland
| | - Volkmar Falk
- Clinic for Cardiovascular Surgery, University Hospital Zurich, Zurich, Switzerland
| | - Simon P. Hoerstrup
- Swiss Center for Regenerative Medicine, University of Zurich, Zurich, Switzerland
- Department of Surgical Research, University Hospital Zurich, Rämistrasse 100, 8091 Zurich, Switzerland
- Clinic for Cardiovascular Surgery, University Hospital Zurich, Zurich, Switzerland
| | - Irina Agarkova
- Swiss Center for Regenerative Medicine, University of Zurich, Zurich, Switzerland
- Department of Surgical Research, University Hospital Zurich, Rämistrasse 100, 8091 Zurich, Switzerland
- Clinic for Cardiovascular Surgery, University Hospital Zurich, Zurich, Switzerland
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69
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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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70
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Abstract
Intercalated disks (ICDs) are highly organized cell-cell adhesion structures, which connect cardiomyocytes to one another. They are composed of three major complexes: desmosomes, fascia adherens, and gap junctions. Desmosomes and fascia adherens junction are necessary for mechanically coupling and reinforcing cardiomyocytes, whereas gap junctions are essential for rapid electrical transmission between cells. Because human genetics and mouse models have revealed that mutations and/or deficiencies in various ICD components can lead to cardiomyopathies and arrhythmias, considerable attention has focused on the biologic function of the ICD. This review will discuss recent scientific developments related to the ICD and focus on its role in regulating cardiac muscle structure, signaling, and disease.
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Affiliation(s)
- Farah Sheikh
- Department of Medicine, University of California-San Diego, CA 92093, USA
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71
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Zhao H, Lv D, Zhang W, Dong W, Feng J, Xiang Z, Huang L, Qin C, Zhang L. Ginsenoside-Rb1 attenuates dilated cardiomyopathy in cTnT(R141W) transgenic mouse. J Pharmacol Sci 2010; 112:214-22. [PMID: 20168043 DOI: 10.1254/jphs.09314fp] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
Abstract
Familial dilated cardiomyopathy (FDCM) is caused by defective genes and specific medicines are not currently available to treat this. Ginsenoside-Rb1 provides cardioprotection in the experimental models of myocardial ischemia-reperfusion injury. Here we investigate Rb1's effect on DCM in cTnT(R141W) transgenic mouse. The transgene-positive mice aged 2 months were randomized into the model group and Rb1 [70 mg/(kg.day)] group; transgene-negative mice were used as a control. After 4-month treatment, cardiac function was assessed by echocardiography; cardiac tissues were prepared for histology and electron microscopy. Expression levels of molecular markers of cardiac hypertrophy, fibrosis, and intercalated disc proteins were detected by RT-PCR. Rb1 significantly decreased mortality, chamber dilation, and contractile dysfunction in cTnT(R141W) mice. Rb1 attenuated cardiac hypertrophy, interstitial fibrosis, ultrastructural degeneration, and intercalated disc remodeling in DCM hearts. Western blotting showed that Rb1 significantly decreased heparin-binding epidermal growth factor-like growth factor (HB-EGF) expression and signal transduction and activators of transcription 3 (STAT3) activation, which were gradually increased in DCM hearts. Our results showed that Rb1 clearly alleviated cardiac dysfunction and remodeling in the cTnT(R141W) transgenic mouse, indicating its potential utility in the treatment of FDCM.
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Affiliation(s)
- Haiping Zhao
- Key Laboratory of Human Disease Comparative Medicine, Ministry of Health, Institute of Laboratory Animal Science, Chinese Academy of Medical Science & Comparative Medicine Center, Peking Union Medical College, China
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72
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Ordered assembly of the adhesive and electrochemical connections within newly formed intercalated disks in primary cultures of adult rat cardiomyocytes. J Biomed Biotechnol 2010; 2010:624719. [PMID: 20467587 PMCID: PMC2868981 DOI: 10.1155/2010/624719] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2009] [Accepted: 02/17/2010] [Indexed: 02/06/2023] Open
Abstract
The intercalated disk (ID) is a complex structure that electromechanically couples adjoining cardiac myocytes into a functional syncitium. The integrity of the disk is essential for normal cardiac function, but how the diverse elements are assembled into a fully integrated structure is not well understood. In this study, we examined the assembly of new IDs in primary cultures of adult rat cardiac myocytes. From 2 to 5 days after dissociation, the cells flatten and spread, establishing new cell-cell contacts in a manner that recapitulates the in vivo processes that occur during heart development and myocardial remodeling. As cells make contact with their neighbors, transmembrane adhesion proteins localize along the line of apposition, concentrating at the sites of membrane attachment of the terminal sarcomeres. Cx43 gap junctions and ankyrin-G, an essential cytoskeletal component of voltage gated sodium channel complexes, were secondarily recruited to membrane domains involved in cell-cell contacts. The consistent order of the assembly process suggests that there are specific scaffolding requirements for integration of the mechanical and electrochemical elements of the disk. Defining the relationships that are the foundation of disk assembly has important implications for understanding the mechanical dysfunction and cardiac arrhythmias that accompany alterations of ID architecture.
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73
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Hirschy A, Croquelois A, Perriard E, Schoenauer R, Agarkova I, Hoerstrup SP, Taketo MM, Pedrazzini T, Perriard JC, Ehler E. Stabilised beta-catenin in postnatal ventricular myocardium leads to dilated cardiomyopathy and premature death. Basic Res Cardiol 2010; 105:597-608. [PMID: 20376467 DOI: 10.1007/s00395-010-0101-8] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/22/2010] [Revised: 03/24/2010] [Accepted: 03/25/2010] [Indexed: 12/22/2022]
Abstract
Beta-catenin is a component of the intercalated disc in cardiomyocytes, but can also be involved in signalling and activation of gene transcription. We wanted to determine how long-term changes in beta-catenin expression levels would affect mature cardiomyocytes. Conditional transgenic mice that either lacked beta-catenin or that expressed a non-degradable form of beta-catenin in the adult ventricle were created. While mice lacking beta-catenin in the ventricle do not have an overt phenotype, mice expressing a non-degradable form develop dilated cardiomyopathy and do not survive beyond 5 months. A detailed analysis could reveal that this phenotype is correlated with a distinct localisation of beta-catenin in adult cardiomyocytes, which cannot be detected in the nucleus, no matter how much protein is present. Our report is the first study that addresses long-term effects of either the absence of beta-catenin or its stabilisation on ventricular cardiomyocytes and it suggests that beta-catenin's role in the nucleus may be of little significance in the healthy adult heart.
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Affiliation(s)
- Alain Hirschy
- Institute of Cell Biology, ETH Zurich-Hönggerberg, Switzerland
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74
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Wheeler MA, Warley A, Roberts RG, Ehler E, Ellis JA. Identification of an emerin-beta-catenin complex in the heart important for intercalated disc architecture and beta-catenin localisation. Cell Mol Life Sci 2010; 67:781-96. [PMID: 19997769 PMCID: PMC11115513 DOI: 10.1007/s00018-009-0219-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2009] [Revised: 10/29/2009] [Accepted: 11/16/2009] [Indexed: 10/20/2022]
Abstract
How mutations in the protein emerin lead to the cardiomyopathy associated with X-linked Emery-Dreifuss muscular dystrophy (X-EDMD) is unclear. We identified emerin at the adherens junction of the intercalated disc, where it co-localised with the catenin family of proteins. Emerin bound to wild type beta-catenin both in vivo and in vitro. Mutating the GSK3beta phosphorylation sites on beta-catenin abolished this binding. Wild type but not mutant forms of emerin associated with X-EDMD were able to reduce beta-catenin protein levels. Cardiomyocytes from emerin-null mice hearts exhibited erroneous beta-catenin distribution and intercalated disc architecture. Treatment of wild type cardiomyocytes with phenylephrine, which inactivates GSK3beta, redistributed emerin and beta-catenin. Emerin was identified as a direct target of GSK3beta activity since exogenous expression of GSK3beta reduced emerin levels at the nuclear envelope. We propose that perturbation to or total loss of the emerin-beta-catenin complex compromises both intercalated disc function and beta-catenin signalling in cardiomyocytes.
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Affiliation(s)
- Matthew A Wheeler
- The Randall Division of Cell and Molecular Biophysics, King's College London, New Hunts House, Guy's Campus, London, SE1 1UL, UK.
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75
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Zhao HP, Lü D, Zhang W, Zhang L, Wang SM, Ma CM, Qin C, Zhang LF. Protective action of tetramethylpyrazine phosphate against dilated cardiomyopathy in cTnT(R141W) transgenic mice. Acta Pharmacol Sin 2010; 31:281-8. [PMID: 20154713 DOI: 10.1038/aps.2010.6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
AIM Dilated cardiomyopathy (DCM) is the most common cause of heart failure, and pharmacological intervention is not currently available. Here we investigate the effect of tetramethylpyrazine phosphate (TMPP) on the progression of DCM in the cTnT(R141W) transgenic mouse model. METHODS The cTnT(R141W) transgenic mice aged 2 months were divided into model group and TMPP group, whereas age-matched nontransgenic mice were used as wild-type control. TMPP 45 mg.kg(-1).d(-1) was administered for 7 months. Following assessment of cardiac function by echocardiography, cardiac tissues were prepared for histology and electron microscopy. Levels of molecular markers for cardiomyocyte hypertrophy and fibrosis were detected by RT-PCR. Expression of structural proteins of the sarcomere and intercalated disc was determined by Western blot. RESULTS TMPP significantly prevented cardiac dilatation and dysfunction with the development of DCM, and decreased mortality by 54%. TMPP decreased HW/BW ratios and expression of hypertrophic markers BNP and ACTA1, as well as reduced interstitial collagen deposition and expression of profibrotic markers Col1a1 and Col3a1. TMPP attenuated ultrastructural disruption caused by cTnT(R141W) expression and decreased expression of structural proteins myotilin and E-cadherin which were up-regulated in the cTnT(R141W) heart. Moreover, TMPP reduced the mRNA expression of Calm1 and Camk2b in the cTnT(R141W) heart. CONCLUSION Our results suggest that TMPP could be a promising drug for prevention and treatment of DCM.
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76
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Mechanical stress-induced sarcomere assembly for cardiac muscle growth in length and width. J Mol Cell Cardiol 2010; 48:817-23. [PMID: 20188736 DOI: 10.1016/j.yjmcc.2010.02.016] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/30/2009] [Revised: 02/15/2010] [Accepted: 02/17/2010] [Indexed: 12/27/2022]
Abstract
A ventricular myocyte experiences changes in length and load during every beat of the heart and has the ability to remodel cell shape to maintain cardiac performance. Specifically, myocytes elongate in response to increased diastolic strain by adding sarcomeres in series, and they thicken in response to continued systolic stress by adding filaments in parallel. Myocytes do this while still keeping the resting sarcomere length close to its optimal value at the peak of the length-tension curve. This review focuses on the little understood mechanisms by which direction of growth is matched in a physiologically appropriate direction. We propose that the direction of strain is detected by differential phosphorylation of proteins in the costamere, which then transmit signaling to the Z-disc for parallel or series addition of thin filaments regulated via the actin capping processes. In this review, we link mechanotransduction to the molecular mechanisms for regulation of myocyte length and width.
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77
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Seeger TS, Frank D, Rohr C, Will R, Just S, Grund C, Lyon R, Luedde M, Koegl M, Sheikh F, Rottbauer W, Franke WW, Katus HA, Olson EN, Frey N. Myozap, a novel intercalated disc protein, activates serum response factor-dependent signaling and is required to maintain cardiac function in vivo. Circ Res 2010; 106:880-90. [PMID: 20093627 DOI: 10.1161/circresaha.109.213256] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
RATIONALE The intercalated disc (ID) is a highly specialized cell-cell contact structure that ensures mechanical and electric coupling of contracting cardiomyocytes. Recently, the ID has been recognized to be a hot spot of cardiac disease, in particular inherited cardiomyopathy. OBJECTIVE Given its complex structure and function we hypothesized that important molecular constituents of the ID still remain unknown. METHODS AND RESULTS Using a bioinformatics screen, we discovered and cloned a previously uncharacterized 54 kDa cardiac protein which we termed Myozap (Myocardium-enriched zonula occludens-1-associated protein). Myozap is strongly expressed in the heart and lung. In cardiac tissue it localized to the ID and directly binds to desmoplakin and zonula occludens-1. In a yeast 2-hybrid screen for additional binding partners of Myozap we identified myosin phosphatase-RhoA interacting protein (MRIP), a negative regulator of Rho activity. Myozap, in turn, strongly activates SRF-dependent transcription through its ERM (Ezrin/radixin/moesin)-like domain in a Rho-dependent fashion. Finally, in vivo knockdown of the Myozap ortholog in zebrafish led to severe contractile dysfunction and cardiomyopathy. CONCLUSIONS Taken together, these findings reveal Myozap as a previously unrecognized component of a Rho-dependent signaling pathway that links the intercalated disc to cardiac gene regulation. Moreover, its subcellular localization and the observation of a severe cardiac phenotype in zebrafish, implicate Myozap in the pathogenesis of cardiomyopathy.
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Affiliation(s)
- Thalia S Seeger
- Professor of Internal Medicine and Cardiology, Department of Cardiology and Angiology, University Hospital Schleswig-Holstein, Campus Kiel, Schittenhelmstr. 12, 24105 Kiel, Germany
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Ottenheijm CAC, Granzier H. Role of titin in skeletal muscle function and disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 682:105-22. [PMID: 20824522 DOI: 10.1007/978-1-4419-6366-6_6] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
This review covers recent developments in the titin field. Most recent reviews have discussed titin's role in cardiac function: here we will mainly focus on skeletal muscle, and discuss recent advances in the understanding of titin's role in skeletal muscle function and disease.
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79
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Knöll R, Kostin S, Klede S, Savvatis K, Klinge L, Stehle I, Gunkel S, Kötter S, Babicz K, Sohns M, Miocic S, Didié M, Knöll G, Zimmermann WH, Thelen P, Bickeböller H, Maier LS, Schaper W, Schaper J, Kraft T, Tschöpe C, Linke WA, Chien KR. A common MLP (muscle LIM protein) variant is associated with cardiomyopathy. Circ Res 2009; 106:695-704. [PMID: 20044516 DOI: 10.1161/circresaha.109.206243] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
RATIONALE We previously discovered the human 10T-->C (Trp4Arg) missense mutation in exon 2 of the muscle LIM protein (MLP, CSRP3) gene. OBJECTIVE We sought to study the effects of this single-nucleotide polymorphism in the in vivo situation. METHODS AND RESULTS We now report the generation and detailed analysis of the corresponding Mlp(W4R/+) and Mlp(W4R/W4R) knock-in animals, which develop an age- and gene dosage-dependent hypertrophic cardiomyopathy and heart failure phenotype, characterized by almost complete loss of contractile reserve under catecholamine induced stress. In addition, evidence for skeletal muscle pathology, which might have implications for human mutation carriers, was observed. Importantly, we found significantly reduced MLP mRNA and MLP protein expression levels in hearts of heterozygous and homozygous W4R-MLP knock-in animals. We also detected a weaker in vitro interaction of telethonin with W4R-MLP than with wild-type MLP. These alterations may contribute to an increased nuclear localization of W4R-MLP, which was observed by immunohistochemistry. CONCLUSIONS Given the well-known high frequency of this mutation in Caucasians of up to 1%, our data suggest that (W4R-MLP) might contribute significantly to human cardiovascular disease.
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Affiliation(s)
- Ralph Knöll
- Heart Centre, Georg August University, Götingen, Germany.
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80
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Vogel B, Meder B, Just S, Laufer C, Berger I, Weber S, Katus HA, Rottbauer W. In-vivo characterization of human dilated cardiomyopathy genes in zebrafish. Biochem Biophys Res Commun 2009; 390:516-22. [DOI: 10.1016/j.bbrc.2009.09.129] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2009] [Accepted: 09/30/2009] [Indexed: 11/30/2022]
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81
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Gunkel S, Heineke J, Hilfiker-Kleiner D, Knöll R. MLP: A stress sensor goes nuclear. J Mol Cell Cardiol 2009; 47:423-5. [DOI: 10.1016/j.yjmcc.2009.07.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/22/2009] [Revised: 06/18/2009] [Accepted: 07/09/2009] [Indexed: 01/01/2023]
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82
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Mohapatra B, Vick GW, Fraser CD, Clunie SK, Towbin JA, Sinagra G, Vatta M. Short-term mechanical unloading and reverse remodeling of failing hearts in children. J Heart Lung Transplant 2009; 29:98-104. [PMID: 19783184 DOI: 10.1016/j.healun.2009.06.030] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2009] [Revised: 06/13/2009] [Accepted: 06/20/2009] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND Mechanical support using a left ventricular assist device (LVAD) can lead to functional recovery of the myocardium in patients with end-stage heart failure (HF). Molecular remodeling, cytoskeletal disruption, and apoptosis activation are associated with abnormal gene expression in the failing ventricular myocardium of HF subjects and can normalize in response to medium- and long-term mechanical unloading in adults. However, there is little knowledge of the changes in gene expression after short-term mechanical support in children with HF. METHODS We evaluated left ventricular biopsies from 4 children with HF. The children had implantation of a continuous- or a pulsatile-flow LVAD for 8 to 16 days before undergoing heart transplantation. At the time of LVAD insertion and removal, we performed quantitative real-time polymerase chain reaction (QPCR) to study the expression of 326 genes encoding for structural, transcriptional, and signaling pathways proteins, and immunoblot analysis on dystrophin and apoptotic factors. RESULTS Short-term LVAD therapy significantly decreased brain natriuretic peptide (BNP) levels from pre-LVAD (3,584.5 +/- 378.3 pg/ml [95% CI]) to post-LVAD (447.5 +/- 52.7 pg/ml [95% CI]) in 2 patients in whom comparative BNP measurements were available. In addition, short-term LVAD therapy reduced HF and apoptosis markers, whereas it upregulated structural proteins, including dystrophin, as well as pro-hypertrophic and pro-inotropic markers. Furthermore, LVAD therapy normalized expression of genes involved in calcium homeostasis, cell growth, and differentiation. CONCLUSIONS Our pilot study suggests that even short-term LVAD therapy in children with severe HF can reverse molecular remodeling. This favorable effect should be taken into consideration in eligible children with significant ventricular dysfunction.
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Affiliation(s)
- Bhagyalaxmi Mohapatra
- Department of Pediatric Cardiology, Baylor College of Medicine and Texas Children's Hospital, Houston, Texas 77030, USA
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83
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Muscle LIM protein interacts with cofilin 2 and regulates F-actin dynamics in cardiac and skeletal muscle. Mol Cell Biol 2009; 29:6046-58. [PMID: 19752190 DOI: 10.1128/mcb.00654-09] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The muscle LIM protein (MLP) and cofilin 2 (CFL2) are important regulators of striated myocyte function. Mutations in the corresponding genes have been directly associated with severe human cardiac and skeletal myopathies, and aberrant expression patterns have often been observed in affected muscles. Herein, we have investigated whether MLP and CFL2 are involved in common molecular mechanisms, which would promote our understanding of disease pathogenesis. We have shown for the first time, using a range of biochemical and immunohistochemical methods, that MLP binds directly to CFL2 in human cardiac and skeletal muscles. The interaction involves the inter-LIM domain, amino acids 94 to 105, of MLP and the amino-terminal domain, amino acids 1 to 105, of CFL2, which includes part of the actin depolymerization domain. The MLP/CFL2 complex is stronger in moderately acidic (pH 6.8) environments and upon CFL2 phosphorylation, while it is independent of Ca(2+) levels. This interaction has direct implications in actin cytoskeleton dynamics in regulating CFL2-dependent F-actin depolymerization, with maximal depolymerization enhancement at an MLP/CFL2 molecular ratio of 2:1. Deregulation of this interaction by intracellular pH variations, CFL2 phosphorylation, MLP or CFL2 gene mutations, or expression changes, as observed in a range of cardiac and skeletal myopathies, could impair F-actin depolymerization, leading to sarcomere dysfunction and disease.
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84
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Satomi-Kobayashi S, Ueyama T, Mueller S, Toh R, Masano T, Sakoda T, Rikitake Y, Miyoshi J, Matsubara H, Oh H, Kawashima S, Hirata KI, Takai Y. Deficiency of nectin-2 leads to cardiac fibrosis and dysfunction under chronic pressure overload. Hypertension 2009; 54:825-31. [PMID: 19667252 DOI: 10.1161/hypertensionaha.109.130443] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The intercalated disc, a cell-cell contact site between neighboring cardiac myocytes, plays an important role in maintaining the homeostasis of the heart by transmitting electric and mechanical signals. Changes in the architecture of the intercalated disc have been observed in dilated cardiomyopathy. Among cell-cell junctions in the intercalated disc, adherens junctions are involved in anchoring myofibrils and transmitting force. Nectins are Ca(2+)-independent, immunoglobulin-like cell-cell adhesion molecules that exist in adherens junctions. However, the role of nectins in cardiac homeostasis and integrity of the intercalated disc are unknown. Among the isoforms of nectins, nectin-2 and -4 were expressed at the intercalated disc in the heart. Nectin-2-knockout mice showed normal cardiac structure and function under physiological conditions. Four weeks after banding of the ascending aorta, cardiac function was significantly impaired in nectin-2-knockout mice compared with wild-type mice, although both nectin-2-knockout and wild-type mice developed similar degrees of cardiac hypertrophy. Banded nectin-2-knockout mice displayed cardiac fibrosis more evidently than banded wild-type mice. The disruption of the intercalated discs and disorganized myofibrils were observed in banded nectin-2-knockout mice. Furthermore, the number of apoptotic cardiac myocytes was increased in banded nectin-2-knockout mice. In the hearts of banded nectin-2-knockout mice, Akt remained at lower phosphorylation levels until 2 weeks after banding, whereas c-Jun N-terminal kinase and p38 mitogen-activated protein kinase were highly phosphorylated compared with those of wild-type mice. These results indicate that nectin-2 is required to maintain structure and function of the intercalated disc and protects the heart from pressure-overload-induced cardiac dysfunction.
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Affiliation(s)
- Seimi Satomi-Kobayashi
- Department of Cardiovascular Medicine, Kyoto Prefectural University of Medicine, 465 Kajii-cho Kawaramachi-Hirokoji, Kamigyo-ku, Kyoto, Japan
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85
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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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86
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Noorman M, van der Heyden MA, van Veen TA, Cox MG, Hauer RN, de Bakker JM, van Rijen HV. Cardiac cell–cell junctions in health and disease: Electrical versus mechanical coupling. J Mol Cell Cardiol 2009; 47:23-31. [DOI: 10.1016/j.yjmcc.2009.03.016] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/21/2009] [Revised: 03/12/2009] [Accepted: 03/19/2009] [Indexed: 10/21/2022]
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87
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Chronic treatment with clenbuterol modulates endothelial progenitor cells and circulating factors in a murine model of cardiomyopathy. J Cardiovasc Transl Res 2009; 2:182-90. [PMID: 20559986 DOI: 10.1007/s12265-009-9089-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Accepted: 01/27/2009] [Indexed: 10/21/2022]
Abstract
The purpose of this study was to determine the effects of chronic treatment with the beta 2 adrenergic receptor agonist clenbuterol on endothelial progenitor cells (EPC) in a well-characterized model of heart failure, the muscle LIM protein knockout (MLP(-/-)) mouse. MLP(-/-) mice were treated daily with clenbuterol (2 mg/kg) or saline subcutaneously for 6 weeks. Clenbuterol led to a 30% increase in CD31(+) cells in the bone marrow of MLP(-/-) heart failure mice (p < 0.004). Clenbuterol did not improve ejection fraction. Clenbuterol treatment in MLP(-/-) mice was associated with significant changes in the following circulating factors: tissue inhibitor of metalloproteinase-type 1, leukemia inhibitory factor 1, C-reactive protein, apolipoprotein A1, fibroblast growth factor 2, serum glutamic oxaloacetic transaminase, macrophage-derived chemokine, and monocyte chemoattractant protein-3. Clenbuterol treatment in the MLP(-/-) model of heart failure did not rescue heart function, yet did increase CD31(+) cells in the bone marrow. This is the first evidence that a beta 2 agonist increases EPC proliferation in the bone marrow in a preclinical model of heart failure.
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88
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Gehmlich K, Geier C, Milting H, Fürst D, Ehler E. Back to square one: what do we know about the functions of Muscle LIM Protein in the heart? J Muscle Res Cell Motil 2008; 29:155-8. [DOI: 10.1007/s10974-008-9159-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2008] [Accepted: 12/03/2008] [Indexed: 11/28/2022]
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89
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Abstract
Mutations in genes encoding the nuclear envelope proteins emerin and lamin A/C lead to a range of tissue-specific degenerative diseases. These include dilated cardiomyopathy, limb-girdle muscular dystrophy and X-linked and autosomal dominant EDMD (Emery–Dreifuss muscular dystrophy). The molecular mechanisms underlying these disorders are poorly understood; however, recent work using animal models has identified a number of signalling pathways that are altered in response to the deletion of either emerin or lamin A/C or expression of Lmna mutants found in patients with laminopathies. A distinguishing feature of patients with EDMD is the association of a dilated cardiomyopathy with conduction defects. In the present article, we describe several of the pathways altered in response to an EDMD phenotype, which are known to be key mediators of hypertrophic growth, and focus on a possible role of an emerin–β-catenin interaction in the pathogenesis of this disease.
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90
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Sagave JF, Moser M, Ehler E, Weiskirchen S, Stoll D, Günther K, Büttner R, Weiskirchen R. Targeted disruption of the mouse Csrp2 gene encoding the cysteine- and glycine-rich LIM domain protein CRP2 result in subtle alteration of cardiac ultrastructure. BMC DEVELOPMENTAL BIOLOGY 2008; 8:80. [PMID: 18713466 PMCID: PMC2529283 DOI: 10.1186/1471-213x-8-80] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/19/2008] [Accepted: 08/19/2008] [Indexed: 11/23/2022]
Abstract
Background The cysteine and glycine rich protein 2 (CRP2) encoded by the Csrp2 gene is a LIM domain protein expressed in the vascular system, particularly in smooth muscle cells. It exhibits a bimodal subcellular distribution, accumulating at actin-based filaments in the cytosol and in the nucleus. In order to analyze the function of CRP2 in vivo, we disrupted the Csrp2 gene in mice and analysed the resulting phenotype. Results A ~17.3 kbp fragment of the murine Csrp2 gene containing exon 3 through 6 was isolated. Using this construct we confirmed the recently determined chromosomal localization (Chromosome 10, best fit location between markers D10Mit203 proximal and D10Mit150 central). A gene disruption cassette was cloned into exon 4 and a mouse strain lacking functional Csrp2 was generated. Mice lacking CRP2 are viable and fertile and have no obvious deficits in reproduction and survival. However, detailed histological and electron microscopic studies reveal that CRP2-deficient mice have subtle alterations in their cardiac ultrastructure. In these mice, the cardiomyocytes display a slight increase in their thickness, indicating moderate hypertrophy at the cellular level. Although the expression of several intercalated disc-associated proteins such as β-catenin, N-RAP and connexin-43 were not affected in these mice, the distribution of respective proteins was changed within heart tissue. Conclusion We conclude that the lack of CRP2 is associated with alterations in cardiomyocyte thickness and hypertrophy.
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Affiliation(s)
- Julia F Sagave
- Institute of Clinical Chemistry and Pathobiochemistry, RWTH- University Hospital Aachen, Germany.
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91
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Mays TA, Binkley PF, Lesinski A, Doshi AA, Quaile MP, Margulies KB, Janssen PM, Rafael-Fortney JA. Claudin-5 levels are reduced in human end-stage cardiomyopathy. J Mol Cell Cardiol 2008; 45:81-7. [DOI: 10.1016/j.yjmcc.2008.04.005] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/31/2008] [Revised: 04/15/2008] [Accepted: 04/16/2008] [Indexed: 11/27/2022]
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92
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Geier C, Gehmlich K, Ehler E, Hassfeld S, Perrot A, Hayess K, Cardim N, Wenzel K, Erdmann B, Krackhardt F, Posch MG, Bublak A, Nägele H, Scheffold T, Dietz R, Chien KR, Spuler S, Fürst DO, Nürnberg P, Özcelik C. Beyond the sarcomere: CSRP3 mutations cause hypertrophic cardiomyopathy. Hum Mol Genet 2008; 17:2753-65. [DOI: 10.1093/hmg/ddn160] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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93
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Förster C. Tight junctions and the modulation of barrier function in disease. Histochem Cell Biol 2008; 130:55-70. [PMID: 18415116 PMCID: PMC2413111 DOI: 10.1007/s00418-008-0424-9] [Citation(s) in RCA: 424] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/18/2008] [Indexed: 12/22/2022]
Abstract
Tight junctions create a paracellular barrier in epithelial and endothelial cells protecting them from the external environment. Two different classes of integral membrane proteins constitute the tight junction strands in epithelial cells and endothelial cells, occludin and members of the claudin protein family. In addition, cytoplasmic scaffolding molecules associated with these junctions regulate diverse physiological processes like proliferation, cell polarity and regulated diffusion. In many diseases, disruption of this regulated barrier occurs. This review will briefly describe the molecular composition of the tight junctions and then present evidence of the link between tight junction dysfunction and disease.
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Affiliation(s)
- Carola Förster
- Institute of Anatomy and Cell Biology, University of Würzburg, Koellikerstrasse 6, 97070, Würzburg, Germany.
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94
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Pieperhoff S, Franke WW. The area composita of adhering junctions connecting heart muscle cells of vertebrates. VI. Different precursor structures in non-mammalian species. Eur J Cell Biol 2008; 87:413-30. [PMID: 18420304 DOI: 10.1016/j.ejcb.2008.02.005] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Revised: 02/06/2008] [Accepted: 02/08/2008] [Indexed: 12/29/2022] Open
Abstract
Recent studies on the formation and molecular organization of the mammalian heart have emphasized the architectural and functional importance of the adhering junctions (AJs), which are densely clustered in the bipolar end regions (intercalated disks, IDs) connecting the elongated cardiomyocytes of the adult heart. Moreover, we learned from genetic studies of mutated AJ proteins that desmosomal proteins, which for the most part are integral components of ID-specific composite AJs (areae compositae, AC), are essential in heart development and function. Developmental studies have shown that the bipolar concentration of cardiomyocyte AJs in IDs is a rather late process and only completed postnatally. Here we report that in the adult hearts of diverse lower vertebrates (fishes, amphibia, birds) most AJs remain separate and distinct in molecular character, representing either fasciae adhaerentes, maculae adhaerentes (desmosomes) or--less frequently--some form of AC. In the mature hearts of the amphibian and fish species examined a large proportion of the AJs connecting cardiomyocytes is not clustered in the IDs but remains located on the lateral surfaces where they appear either as puncta adhaerentia or as desmosomes. In many places, these puncta connect parallel cardiomyocytes in spectacular ladder-like regular arrays (scalae adhaerentes) correlated with--and connected by--electron-dense plaque-like material to sarcomeric Z-bands. In the avian hearts, on the other hand, most AJs are clustered in the IDs but only a small proportion of the desmosomes appears as AC, compared to the dominance of distinct fasciae adhaerentes. We conclude that the fusion and amalgamation of AJs and desmosomes to ACs is a late process both in ontogenesis and in evolution. The significance and possible functional implications of the specific junctional structures in vertebrate evolution and the class-specific requirements of architectural and molecular assembly adaptation during regeneration processes are discussed.
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Affiliation(s)
- Sebastian Pieperhoff
- Division of Cell Biology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany
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95
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unc-94 encodes a tropomodulin in Caenorhabditis elegans. J Mol Biol 2007; 374:936-50. [PMID: 17976644 DOI: 10.1016/j.jmb.2007.10.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2007] [Revised: 09/29/2007] [Accepted: 10/01/2007] [Indexed: 11/21/2022]
Abstract
unc-94 is one of about 40 genes in Caenorhabditis elegans that, when mutant, displays an abnormal muscle phenotype. Two mutant alleles of unc-94, su177 and sf20, show reduced motility and brood size and disorganization of muscle structure. In unc-94 mutants, immunofluorescence microscopy shows that a number of known sarcomeric proteins are abnormal, but the most dramatic effect is in the localization of F-actin, with some abnormally accumulated near muscle cell-to-cell boundaries. Electron microscopy shows that unc-94(sf20) mutants have large accumulations of thin filaments near the boundaries of adjacent muscle cells. Multiple lines of evidence prove that unc-94 encodes a tropomodulin, a conserved protein known from other systems to bind to both actin and tropomyosin at the pointed ends of actin thin filaments. su177 is a splice site mutation in intron 1, which is specific to one of the two unc-94 isoforms, isoform a; sf20 has a stop codon in exon 5, which is shared by both isoform a and isoform b. The use of promoter-green fluorescent protein constructs in transgenic animals revealed that unc-94a is expressed in body wall, vulval and uterine muscles, whereas unc-94b is expressed in pharyngeal, anal depressor, vulval and uterine muscles and in spermatheca and intestinal epithelial cells. By Western blot, anti-UNC-94 antibodies detect polypeptides of expected size from wild type, wild-type-sized proteins of reduced abundance from unc-94(su177), and no detectable unc-94 products from unc-94(sf20). Using these same antibodies, UNC-94 localizes as two closely spaced parallel lines flanking the M-lines, consistent with localization to the pointed ends of thin filaments. In addition, UNC-94 is localized near muscle cell-to-cell boundaries.
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96
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Gustafson-Wagner EA, Sinn HW, Chen YL, Wang DZ, Reiter RS, Lin JLC, Yang B, Williamson RA, Chen J, Lin CI, Lin JJC. Loss of mXinalpha, an intercalated disk protein, results in cardiac hypertrophy and cardiomyopathy with conduction defects. Am J Physiol Heart Circ Physiol 2007; 293:H2680-92. [PMID: 17766470 PMCID: PMC2394510 DOI: 10.1152/ajpheart.00806.2007] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The intercalated disk protein Xin was originally discovered in chicken striated muscle and implicated in cardiac morphogenesis. In the mouse, there are two homologous genes, mXinalpha and mXinbeta. The human homolog of mXinalpha, Cmya1, maps to chromosomal region 3p21.2-21.3, near a dilated cardiomyopathy with conduction defect-2 locus. Here we report that mXinalpha-null mouse hearts are hypertrophied and exhibit fibrosis, indicative of cardiomyopathy. A significant upregulation of mXinbeta likely provides partial compensation and accounts for the viability of the mXinalpha-null mice. Ultrastructural studies of mXinalpha-null mouse hearts reveal intercalated disk disruption and myofilament disarray. In mXinalpha-null mice, there is a significant decrease in the expression level of p120-catenin, beta-catenin, N-cadherin, and desmoplakin, which could compromise the integrity of the intercalated disks and functionally weaken adhesion, leading to cardiac defects. Additionally, altered localization and decreased expression of connexin 43 are observed in the mXinalpha-null mouse heart, which, together with previously observed abnormal electrophysiological properties of mXinalpha-deficient mouse ventricular myocytes, could potentially lead to conduction defects. Indeed, ECG recordings on isolated, perfused hearts (Langendorff preparations) show a significantly prolonged QT interval in mXinalpha-deficient hearts. Thus mXinalpha functions in regulating the hypertrophic response and maintaining the structural integrity of the intercalated disk in normal mice, likely through its association with adherens junctional components and actin cytoskeleton. The mXinalpha-knockout mouse line provides a novel model of cardiac hypertrophy and cardiomyopathy with conduction defects.
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97
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Clark KA, Bland JM, Beckerle MC. The Drosophila muscle LIM protein, Mlp84B, cooperates with D-titin to maintain muscle structural integrity. J Cell Sci 2007; 120:2066-77. [PMID: 17535853 DOI: 10.1242/jcs.000695] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Muscle LIM protein (MLP) is a cytoskeletal LIM-only protein expressed in striated muscle. Mutations in human MLP are associated with cardiomyopathy; however, the molecular mechanism by which MLP functions is not established. A Drosophila MLP homolog, mlp84B, displays many of the same features as the vertebrate protein, illustrating the utility of the fly for the study of MLP function. Animals lacking Mlp84B develop into larvae with a morphologically intact musculature, but the mutants arrest during pupation with impaired muscle function. Mlp84B displays muscle-specific expression and is a component of the Z-disc and nucleus. Preventing nuclear retention of Mlp84B does not affect its function, indicating that Mlp84B site of action is likely to be at the Z-disc. Within the Z-disc, Mlp84B is colocalized with the N-terminus of D-titin, a protein crucial for sarcomere organization and stretch mechanics. The mlp84B mutants phenotypically resemble weak D-titin mutants. Furthermore, reducing D-titin activity in the mlp84B background leads to pronounced enhancement of the mlp84B muscle defects and loss of muscle structural integrity. The genetic interactions between mlp84B and D-titin reveal a role for Mlp84B in maintaining muscle structural integrity that was not obvious from analysis of the mlp84B mutants themselves, and suggest Mlp84B and D-titin cooperate to stabilize muscle sarcomeres.
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Affiliation(s)
- Kathleen A Clark
- Huntsman Cancer Institute, Department of Biology, University of Utah, Salt Lake City, UT 84112, USA.
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98
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Franke WW, Schumacher H, Borrmann CM, Grund C, Winter-Simanowski S, Schlechter T, Pieperhoff S, Hofmann I. The area composita of adhering junctions connecting heart muscle cells of vertebrates – III: Assembly and disintegration of intercalated disks in rat cardiomyocytes growing in culture. Eur J Cell Biol 2007; 86:127-42. [PMID: 17275137 DOI: 10.1016/j.ejcb.2006.11.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2006] [Revised: 11/23/2006] [Accepted: 11/24/2006] [Indexed: 12/31/2022] Open
Abstract
For cell and molecular biological studies of heart formation and function cell cultures of embryonal, neonatal or adult hearts of various vertebrates, notably rat and chicken, have been widely used. As the myocardium-specific cell-cell junctions, the intercalated disks (ID), have recently been found to be particularly sensitive to losses of - or mutations in - certain cytoskeletal proteins, resulting in cardiac damages, we have examined the ID organization in primary cultures of cardiomyocytes obtained from neonatal rats. Using immunofluorescence and immunoelectron microscopy, we have studied the major ID components for up to 2 weeks in culture, paying special attention to spontaneously beating, individual cardiomyocytes and myocardial cell colonies. While our results demonstrate the formation of some ID-like cardiomyocyte-connecting junction arrays, they also reveal a variety of structural disorders such as rather extended, junction-free ID regions, sac-like invaginations and endocytotic blebs as well as accumulations of intracytoplasmic structures suggestive of endocytosed forms of junction-derived vesicles or of junction fragments resembling fascia adhaerens elements. Moreover, we have noticed a novel type of small, obviously plaque-free cytoplasmic vesicles containing one or both of the desmosomal cadherins, desmocollin Dsc2 and desmoglein Dsg2. We conclude that cardiomyocyte cultures are useful model systems for studies of certain aspects of myocardiac differentiation and functions but, on the other hand, show progressive disintegration and deterioration. The potential value of molecular markers and reagents in studies of myocardial pathology as well as in the monitoring of myocardial differentiation of so-called stem cells is discussed.
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Affiliation(s)
- Werner W Franke
- Division of Cell Biology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.
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99
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Panaviene Z, Moncman CL. Linker region of nebulin family members plays an important role in targeting these molecules to cellular structures. Cell Tissue Res 2006; 327:353-69. [PMID: 17177073 DOI: 10.1007/s00441-006-0305-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2006] [Accepted: 07/13/2006] [Indexed: 10/24/2022]
Abstract
The nebulin family of actin-binding proteins plays an essential role in cytoskeletal dynamics and actin filament stability. All of the family members are modular proteins with their key defining structural feature being the presence of the 35-residue nebulin modules. The family members now include nebulin, nebulette, N-RAP, LASP-1, and LIM-nebulette. Nebulin and nebulette are associated with the thin filament/Z-line junction of striated muscle. LASP-1 and LIM-nebulette are found within focal adhesions, and N-RAP is associated with muscle cellular junctions. Although much investigation has focused on the role of the interactions between nebulin modules and actin, each of these proteins contains other domains that are essential for their cellular targeting and functions. The serine-rich linker region of nebulette has previously been shown to serve just such a purpose by targeting the association of the nebulin modules to the cardiac Z-line in cultured cardiomyocytes. In this report, we analyze the targeting functions of the homologous regions of LASP-1 and LIM-nebulette in their incorporation into focal adhesions. We have found that the linker region of LASP-1 is indeed important for its cellular localization and that the shortened linker region of LIM-nebulette drives the association of nebulin modules to focal adhesions.
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Affiliation(s)
- Zivile Panaviene
- Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington, KY 40536, USA
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100
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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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