101
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Mechanical and Energetic Consequences of HCM-Causing Mutations. J Cardiovasc Transl Res 2009; 2:441-51. [DOI: 10.1007/s12265-009-9131-8] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/17/2009] [Accepted: 09/15/2009] [Indexed: 10/20/2022]
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102
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Kontrogianni-Konstantopoulos A, Ackermann MA, Bowman AL, Yap SV, Bloch RJ. Muscle giants: molecular scaffolds in sarcomerogenesis. Physiol Rev 2009; 89:1217-67. [PMID: 19789381 PMCID: PMC3076733 DOI: 10.1152/physrev.00017.2009] [Citation(s) in RCA: 186] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Myofibrillogenesis in striated muscles is a highly complex process that depends on the coordinated assembly and integration of a large number of contractile, cytoskeletal, and signaling proteins into regular arrays, the sarcomeres. It is also associated with the stereotypical assembly of the sarcoplasmic reticulum and the transverse tubules around each sarcomere. Three giant, muscle-specific proteins, titin (3-4 MDa), nebulin (600-800 kDa), and obscurin (approximately 720-900 kDa), have been proposed to play important roles in the assembly and stabilization of sarcomeres. There is a large amount of data showing that each of these molecules interacts with several to many different protein ligands, regulating their activity and localizing them to particular sites within or surrounding sarcomeres. Consistent with this, mutations in each of these proteins have been linked to skeletal and cardiac myopathies or to muscular dystrophies. The evidence that any of them plays a role as a "molecular template," "molecular blueprint," or "molecular ruler" is less definitive, however. Here we review the structure and function of titin, nebulin, and obscurin, with the literature supporting a role for them as scaffolding molecules and the contradictory evidence regarding their roles as molecular guides in sarcomerogenesis.
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103
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Marston S, Copeland O, Jacques A, Livesey K, Tsang V, McKenna WJ, Jalilzadeh S, Carballo S, Redwood C, Watkins H. Evidence from human myectomy samples that MYBPC3 mutations cause hypertrophic cardiomyopathy through haploinsufficiency. Circ Res 2009; 105:219-22. [PMID: 19574547 DOI: 10.1161/circresaha.109.202440] [Citation(s) in RCA: 183] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Most sarcomere gene mutations that cause hypertrophic cardiomyopathy are missense alleles that encode dominant negative proteins. The potential exceptions are mutations in the MYBPC3 gene (encoding cardiac myosin-binding protein-C [MyBP-C]), which frequently encode truncated proteins. OBJECTIVE We sought to determine whether there was evidence of haploinsufficiency in hypertrophic cardiomyopathy caused by MYBPC3 mutations by comparing left ventricular muscle from patients undergoing surgical myectomy with samples from donor hearts. METHODS AND RESULTS MyBP-C protein and mRNA levels were quantitated using immunoblotting and RT-PCR. Nine of 37 myectomy samples had mutations in MYBPC3: 2 missense alleles (Glu258Lys, Arg502Trp) and 7 premature terminations. No specific truncated MyBP-C peptides were detected in whole muscle homogenates of hypertrophic cardiomyopathy tissue. However, the overall level of MyBP-C in myofibrils was significantly reduced (P<0.0005) in tissue containing either a truncation or missense MYBPC3 mutation: 0.76+/-0.03 compared with 1.00+/-0.05 in donor and 1.01+/-0.06 in non-MYBPC3 mutant myectomies. CONCLUSIONS The absence of any detectable truncated MyBP-C argues against its incorporation in the myofiber and any dominant negative effect. In contrast, the lowered relative level of full length protein in both truncation and missense MYBPC3 mutations argues strongly that haploinsufficiency is sufficient to cause the disease.
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Affiliation(s)
- Steven Marston
- Department of Cardiovascular Medicine, University of Oxford, Level 6 West Wing, John Radcliffe Hospital, Oxford OX39DU, United Kingdom
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104
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TOWBIN JEFFREYA. Hypertrophic Cardiomyopathy. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2009; 32 Suppl 2:S23-31. [DOI: 10.1111/j.1540-8159.2009.02381.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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105
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Friedrich FW, Bausero P, Sun Y, Treszl A, Kramer E, Juhr D, Richard P, Wegscheider K, Schwartz K, Brito D, Arbustini E, Waldenstrom A, Isnard R, Komajda M, Eschenhagen T, Carrier L. A new polymorphism in human calmodulin III gene promoter is a potential modifier gene for familial hypertrophic cardiomyopathy. Eur Heart J 2009; 30:1648-55. [DOI: 10.1093/eurheartj/ehp153] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
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106
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Bahrudin U, Morisaki H, Morisaki T, Ninomiya H, Higaki K, Nanba E, Igawa O, Takashima S, Mizuta E, Miake J, Yamamoto Y, Shirayoshi Y, Kitakaze M, Carrier L, Hisatome I. Ubiquitin-proteasome system impairment caused by a missense cardiac myosin-binding protein C mutation and associated with cardiac dysfunction in hypertrophic cardiomyopathy. J Mol Biol 2008; 384:896-907. [PMID: 18929575 DOI: 10.1016/j.jmb.2008.09.070] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2008] [Revised: 09/09/2008] [Accepted: 09/22/2008] [Indexed: 11/19/2022]
Abstract
The ubiquitin-proteasome system is responsible for the disappearance of truncated cardiac myosin-binding protein C, and the suppression of its activity contributes to cardiac dysfunction. This study investigated whether missense cardiac myosin-binding protein C gene (MYBPC3) mutation in hypertrophic cardiomyopathy (HCM) leads to destabilization of its protein, causes UPS impairment, and is associated with cardiac dysfunction. Mutations were identified in Japanese HCM patients using denaturing HPLC and sequencing. Heterologous expression was investigated in COS-7 cells as well as neonatal rat cardiac myocytes to examine protein stability and proteasome activity. The cardiac function was measured using echocardiography. Five novel MYBPC3 mutations -- E344K, DeltaK814, Delta2864-2865GC, Q998E, and T1046M -- were identified in this study. Compared with the wild type and other mutations, the E334K protein level was significantly lower, it was degraded faster, it had a higher level of polyubiquination, and increased in cells pretreated with the proteasome inhibitor MG132 (50 microM, 6 h). The electrical charge of its amino acid at position 334 influenced its stability, but E334K did not affect its phosphorylation. The E334K protein reduced cellular 20 S proteasome activity, increased the proapoptotic/antiapoptotic protein ratio, and enhanced apoptosis in transfected Cos-7 cells and neonatal rat cardiac myocytes. Patients carrying the E334K mutation presented significant left ventricular dysfunction and dilation. The conclusion is the missense MYBPC3 mutation E334K destabilizes its protein through UPS and may contribute to cardiac dysfunction in HCM through impairment of the ubiquitin-proteasome system.
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Affiliation(s)
- Udin Bahrudin
- Division of Regenerative Medicine and Therapeutics, Institute of Regenerative Medicine and Biofunction, Tottori University Graduate School of Medical Science, Yonago, Japan
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107
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Saber W, Begin KJ, Warshaw DM, VanBuren P. Cardiac myosin binding protein-C modulates actomyosin binding and kinetics in the in vitro motility assay. J Mol Cell Cardiol 2008; 44:1053-1061. [PMID: 18482734 PMCID: PMC2519167 DOI: 10.1016/j.yjmcc.2008.03.012] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Revised: 02/17/2008] [Accepted: 03/12/2008] [Indexed: 11/19/2022]
Abstract
The modulatory role of whole cardiac myosin binding protein-C (cMyBP-C) on myosin force and motion generation was assessed in an in vitro motility assay. The presence of cMyBP-C at an approximate molar ratio of cMyBP-C to whole myosin of 1:2, resulted in a 25% reduction in thin filament velocity (P<0.002) with no effect on relative isometric force under maximally activated conditions (pCa 5). Cardiac MyBP-C was capable of inhibiting actin filament velocity in a concentration-dependent manner using either whole myosin, HMM or S1, indicating that the cMyBP-C does not have to bind to myosin LMM or S2 subdomains to exert its effect. The reduction in velocity by cMyBP-C was independent of changes in ionic strength or excess inorganic phosphate. Co-sedimentation experiments demonstrated S1 binding to actin is reduced as a function of cMyBP-C concentration in the presence of ATP. In contrast, S1 avidly bound to actin in the absence of ATP and limited cMyBP-C binding, indicating that cMyBP-C and S1 compete for actin binding in an ATP-dependent fashion. However, based on the relationship between thin filament velocity and filament length, the cMyBP-C induced reduction in velocity was independent of the number of cross-bridges interacting with the thin filament. In conclusion, the effects of cMyBP-C on velocity and force at both maximal and submaximal activation demonstrate that cMyBP-C does not solely act as a tether between the myosin S2 and LMM subdomains but likely affects both the kinetics and recruitment of myosin cross-bridges through its direct interaction with actin and/or myosin head.
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Affiliation(s)
- Walid Saber
- Department of Medicine, University of Vermont, College of Medicine, Burlington, VT, USA
| | - Kelly J Begin
- Department of Medicine, University of Vermont, College of Medicine, Burlington, VT, USA
| | - David M Warshaw
- Department of Molecular Physiology and Biophysics, University of Vermont, College of Medicine, Burlington, VT, USA
| | - Peter VanBuren
- Department of Medicine, University of Vermont, College of Medicine, Burlington, VT, USA; Department of Molecular Physiology and Biophysics, University of Vermont, College of Medicine, Burlington, VT, USA.
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108
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Tanjore RR, Rangaraju A, Kerkar PG, Calambur N, Nallari P. MYBPC3 gene variations in hypertrophic cardiomyopathy patients in India. Can J Cardiol 2008; 24:127-30. [PMID: 18273486 DOI: 10.1016/s0828-282x(08)70568-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
Abstract
BACKGROUND Hypertrophic cardiomyopathy (HCM) is a complex cardiac muscular disorder, inherited as an autosomal dominant disease with variable penetrance. Cardiac myosin-binding protein C (MyBPC) is the predominant myosin-binding protein isoform in the heart muscle. One hundred forty-seven mutations have been detected in MYBPC3, accounting for 15% of all HCM cases. OBJECTIVE To screen exons 16, 18, 19, 22, 24, 28, 30, 31 and 34 in the MYBPC3 gene in Indian HCM patients. METHODS Sixty control and 95 HCM samples were collected from cardiology units of the CARE Hospital (Nampally, Banjara Hills, Secunderabad, India) for genomic DNA isolation followed by polymerase chain reaction and single-stranded conformational polymorphism analysis. RESULTS Screening of the exons revealed two variations - one novel frame shift mutation in exon 19 at the nucleotide position 11577-11578 and one novel single nucleotide polymorphism (SNP) in codon 1093 of exon 31, coding for glycine with a C>T transition (GGC/GGT), in addition to the seven known SNPs mainly in the intronic region and one known missense mutation D770N in this population. CONCLUSION The novel frame shift mutation identified in exon 19, D570fs, with the insertion of an adenine residue in codon 570 coding for aspartate, results in a premature termination codon that produces a truncated protein lacking myosin- and titin-binding sites, explaining the role of the nonsense-mediated decay pathway. A novel SNP identified in codon 1093 of exon 31 was found to be a synonymous codon, which may have a regulatory effect at the translational level, attributing to affinity differences between codon-anticodon interactions. The screening of this gene may be relevant in the Indian context.
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Affiliation(s)
- Reena R Tanjore
- Department of Genetics, Osmania University, Jamai Osmania PO, Hyderabad, Andhra Pradesh, India
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109
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110
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Micro-exons of the cardiac myosin binding protein C gene: flanking introns contain a disproportionately large number of hypertrophic cardiomyopathy mutations. Eur J Hum Genet 2008; 16:1062-9. [PMID: 18337725 DOI: 10.1038/ejhg.2008.52] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Hypertrophic cardiomyopathy is primarily caused by mutations in genes encoding cardiac sarcomere proteins. Large screening studies identify mutations in 35-65% of the diagnosed patients and 15-30% of these are discovered within the MYBPC3 gene encoding the cardiac myosin binding protein C. The aim of this study is to determine whether intronic variation flanking the three micro-exons in MYBPC3 is disease-causing. Two hundred and fifty unrelated patients with hypertrophic cardiomyopathy were genotyped in MYBPC3, using automated single-strand conformation polymorphism, and sequenced for confirmation. Mutations located in the flanking introns of the MYBPC3 micro-exons were examined using in silico methods. Ectopic expression of mRNA in blood leukocytes in the respective patients was examined using reverse transcription-PCR. A total of seven mutations were discovered in the introns flanking the two micro-exons 10 and 14, but none were found in introns flanking exon 11. Functional studies together with co-segregation analysis indicate that four mutations are associated with HCM, in the respective patients. All four mutations result in premature termination codons, which suggests that haploinsufficiency is a pathogenic mechanism of this type of mutation. It is demonstrated that the use of in silico methods together with RNA studies on peripheral blood leukocytes is a useful tool to evaluate the potential effects of mutations on pre-mRNA splicing.
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111
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Govada L, Carpenter L, da Fonseca PCA, Helliwell JR, Rizkallah P, Flashman E, Chayen NE, Redwood C, Squire JM. Crystal structure of the C1 domain of cardiac myosin binding protein-C: implications for hypertrophic cardiomyopathy. J Mol Biol 2008; 378:387-97. [PMID: 18374358 DOI: 10.1016/j.jmb.2008.02.044] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2008] [Revised: 02/17/2008] [Accepted: 02/19/2008] [Indexed: 11/24/2022]
Abstract
C-protein is a major component of skeletal and cardiac muscle thick filaments. Mutations in the gene encoding cardiac C-protein [cardiac myosin binding protein-C (cMyBP-C)] are one of the principal causes of hypertrophic cardiomyopathy. cMyBP-C is a string of globular domains including eight immunoglobulin-like and three fibronectin-like domains termed C0-C10. It binds to myosin and titin, and probably to actin, and may have both a structural and a regulatory role in muscle function. To help to understand the pathology of the known mutations, we have solved the structure of the immunoglobulin-like C1 domain of MyBP-C by X-ray crystallography to a resolution of 1.55 A. Mutations associated with hypertrophic cardiomyopathy are clustered at one end towards the C-terminus, close to the important C1C2 linker, where they alter the structural integrity of this region and its interactions.
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Affiliation(s)
- Lata Govada
- Biomolecular Medicine Department, SORA Division, Imperial College London, London SW7 2AZ, UK
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112
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Xin B, Puffenberger E, Tumbush J, Bockoven JR, Wang H. Homozygosity for a novel splice site mutation in the cardiac myosin-binding protein C gene causes severe neonatal hypertrophic cardiomyopathy. Am J Med Genet A 2008; 143A:2662-7. [PMID: 17937428 DOI: 10.1002/ajmg.a.31981] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Hypertrophic cardiomyopathy is typically inherited in an autosomal dominant pattern and has a variable age of onset and prognosis. Mutations in the myosin-binding protein C (MYBPC3) gene are one of the most frequent genetic causes of the disease. Patients with MYBPC3 mutations generally have a late onset and a relatively good prognosis. We report here more than 20 Old Order Amish children with severe neonatal hypertrophic cardiomyopathy caused by a novel homozygous splice site mutation in the MYBPC3 gene. The affected children typically presented with signs and symptoms of congestive heart failure during the first 3 weeks of life. Echocardiography revealed hypertrophic non-obstructive cardiomyopathy. These children had a life span averaging 3-4 months. All patients died from heart failure before 1 year of age unless they received a heart transplant. A genome-wide mapping study was performed in three patients. The disease related gene was localized to a 4.6 Mb region on chromosome 11p11.2-p11.12. This homozygous block contained MYBPC3, a previously identified cardiomyopathy related gene. We identified a novel homozygous mutation, c.3330 + 2T > G, in the splice-donor site of MYBPC3 intron 30. The mutation resulted in skipping of the 140-bp exon 30, which led to a frame shift and premature stop codon in exon 31 (p.Asp1064GlyfsX38). We have found a substantial incidence of this phenotype in Old Order Amish communities. It is also concerning that many unidentified heterozygous individuals who are at risk for development of hypertrophic cardiomyopathy do not receive proper medical attention in the communities.
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Affiliation(s)
- Baozhong Xin
- Das Deutsch Center Clinic for Special Needs Children, Middlefield, Ohio 44062, USA
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113
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Pohlmann L, Kröger I, Vignier N, Schlossarek S, Krämer E, Coirault C, Sultan KR, El-Armouche A, Winegrad S, Eschenhagen T, Carrier L. Cardiac myosin-binding protein C is required for complete relaxation in intact myocytes. Circ Res 2007; 101:928-38. [PMID: 17823372 DOI: 10.1161/circresaha.107.158774] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The role of cardiac myosin-binding protein C (cMyBP-C) in cardiac contraction is still not fully resolved. Experimental ablation of cMyBP-C by various means resulted in inconsistent changes in Ca2+ sensitivity and increased velocity of force of skinned preparations. To evaluate how these effects are integrated in an intact, living myocyte context, we investigated consequences of cMyBP-C ablation in ventricular myocytes and left atria from cMyBP-C knock-out (KO) mice compared with wild-type (WT). At 6 weeks, KO myocytes exhibited mild hypertrophy that became more pronounced by 30 weeks. Isolated cells from KO exhibited markedly lower diastolic sarcomere length (SL) without change in diastolic Ca2+. The lower SL in KO was partly abolished by the actin-myosin ATPase inhibitors 2,3-butanedione monoxime or blebbistatin, indicating residual actin-myosin interaction in diastole. The relationship between cytosolic Ca2+ and SL showed that KO cells started to contract at lower Ca2+ without reaching a higher maximum, yielding a smaller area of the phase-plane diagram. Both sarcomere shortening and Ca2+ transient were prolonged in KO. Isolated KO left atria exhibited a marked increase in sensitivity to external Ca2+ and, in contrast to WT, continued to develop twitch force at low micromolar Ca2+. Taken together, the main consequence of cMyBP-C ablation was a defect in diastolic relaxation and a smaller dynamic range of cell shortening, both of which likely result from the increased myofilament Ca2+ sensitivity. Our findings indicate that cMyBP-C functions as a restraint on myosin-actin interaction at low Ca2+ and short SL to allow complete relaxation during diastole.
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Affiliation(s)
- Lutz Pohlmann
- Institute of Experimental and Clinical Pharmacology and Toxicology, University Medical Center Hamburg-Eppendorf, D-20246 Hamburg, Germany
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114
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Arimura T, Matsumoto Y, Okazaki O, Hayashi T, Takahashi M, Inagaki N, Hinohara K, Ashizawa N, Yano K, Kimura A. Structural analysis of obscurin gene in hypertrophic cardiomyopathy. Biochem Biophys Res Commun 2007; 362:281-7. [PMID: 17716621 DOI: 10.1016/j.bbrc.2007.07.183] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2007] [Accepted: 07/20/2007] [Indexed: 11/26/2022]
Abstract
Hypertrophic cardiomyopathy (HCM) is a cardiac disease characterized by left ventricular hypertrophy with diastolic dysfunction. Molecular genetic studies have revealed that HCM is caused by mutations in genes for sarcomere/Z-band components including titin/connectin and its associate proteins. However, disease-causing mutations can be found in about half of the patients, suggesting that other disease-causing genes remain to be identified. To explore a novel disease gene, we searched for obscurin gene (OBSCN) mutations in HCM patients, because obscurin interacts with titin/connectin. Two linked variants, Arg4344Gln and Ala4484Thr, were identified in a patient and functional analyses demonstrated that Arg4344Gln affected binding of obscurin to Z9-Z10 domains of titin/connectin, whereas Ala4484Thr did not. Myc-tagged obscurin showed that Arg4344Gln impaired obscurin localization to Z-band. These observations suggest that the obscurin abnormality may be involved in the pathogenesis of HCM.
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MESH Headings
- Adult
- Amino Acid Sequence
- Animals
- Animals, Newborn
- Cardiomyopathy, Hypertrophic/genetics
- Cardiomyopathy, Hypertrophic/pathology
- Cells, Cultured
- DNA Mutational Analysis
- Guanine Nucleotide Exchange Factors/chemistry
- Guanine Nucleotide Exchange Factors/genetics
- Guanine Nucleotide Exchange Factors/metabolism
- Humans
- Immunoprecipitation
- Models, Molecular
- Molecular Sequence Data
- Muscle Proteins/chemistry
- Muscle Proteins/genetics
- Muscle Proteins/metabolism
- Mutation
- Myocytes, Cardiac/cytology
- Myocytes, Cardiac/metabolism
- Protein Binding
- Protein Serine-Threonine Kinases
- Protein Structure, Tertiary
- Rats
- Rats, Sprague-Dawley
- Rho Guanine Nucleotide Exchange Factors
- Sarcomeres/metabolism
- Sequence Homology, Amino Acid
- Transfection
- Two-Hybrid System Techniques
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Affiliation(s)
- Takuro Arimura
- Department of Molecular Pathogenesis, Medical Research Institute and Laboratory of Genome Diversity, School of Biomedical Science, Tokyo Medical and Dental University, 2-3-10 Kandasurugadai, Chiyoda-ku, Tokyo 101-0062, Japan
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115
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Kulikovskaya I, McClellan GB, Levine R, Winegrad S. Multiple forms of cardiac myosin-binding protein C exist and can regulate thick filament stability. ACTA ACUST UNITED AC 2007; 129:419-28. [PMID: 17470661 PMCID: PMC2154376 DOI: 10.1085/jgp.200609714] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Although absence or abnormality of cardiac myosin binding protein C (cMyBP-C) produces serious structural and functional abnormalities of the heart, function of the protein itself is not clearly understood, and the cause of the abnormalities, unidentified. Here we report that a major function of cMyBP-C may be regulating the stability of the myosin-containing contractile filaments through phosphorylation of cMyBP-C. Antibodies were raised against three different regions of cMyBP-C to detect changes in structure within the molecule, and loss of myosin heavy chain was used to monitor degradation of the thick filament. Results from Western blotting and polyacrylamide gel electrophoresis indicate that cMyBP-C can exist in two different forms that produce, respectively, stable and unstable thick filaments. The stable form has well-ordered myosin heads and requires phosphorylation of the cMyBP-C. The unstable form has disordered myosin heads. In tissue with intact cardiac cells, the unstable unphosphorylated cMyBP-C is more easily proteolyzed, causing thick filaments first to release cMyBP-C and/or its proteolytic peptides and then myosin. Filaments deficient in cMyBP-C are fragmented by shear force well tolerated by the stable form. We hypothesize that modulation of filament stability can be coupled at the molecular level with the strength of contraction by the sensitivity of each to the concentration of calcium ions.
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Affiliation(s)
- Irina Kulikovskaya
- Department of Physiology, University of Philadelphia School of Medicine, Philadelphia, PA 19104, USA.
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116
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Hinken AC, Solaro RJ. A dominant role of cardiac molecular motors in the intrinsic regulation of ventricular ejection and relaxation. Physiology (Bethesda) 2007; 22:73-80. [PMID: 17420299 DOI: 10.1152/physiol.00043.2006] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Molecular motors housed in myosins of the thick filament react with thin-filament actins and promote force and shortening in the sarcomeres. However, other actions of these motors sustain sarcomeric activation by cooperative feedback mechanisms in which the actin-myosin interaction promotes thin-filament activation. Mechanical feedback also affects the actin-myosin interaction. We discuss current concepts of how these relatively under-appreciated actions of molecular motors are responsible for modulation of the ejection time and isovolumic relaxation in the beating heart.
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Affiliation(s)
- Aaron C Hinken
- Department of Physiology and Biophysics and Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, IL, USA
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117
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Mogensen J. Troponin mutations in cardiomyopathies. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 592:201-26. [PMID: 17278367 DOI: 10.1007/978-4-431-38453-3_18] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Jens Mogensen
- Department of Cardiology, Skejby University Hospital Aarhus, Denmark
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118
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Haim TE, Dowell C, Diamanti T, Scheuer J, Tardiff JC. Independent FHC-related cardiac troponin T mutations exhibit specific alterations in myocellular contractility and calcium kinetics. J Mol Cell Cardiol 2007; 42:1098-110. [PMID: 17490679 DOI: 10.1016/j.yjmcc.2007.03.906] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2006] [Revised: 03/19/2007] [Accepted: 03/26/2007] [Indexed: 10/23/2022]
Abstract
Mutations in cardiac troponin T (cTnT) are linked to a severe form of Familial Hypertrophic Cardiomyopathy. Patients carrying mutations flanking the tropomyosin-binding domain of cTnT (R92L and Delta160E) develop distinct clinical syndromes. In order to better understand the cellular pathophysiology underlying these clinically relevant differences, we studied isolated adult left ventricular myocytes from independent transgenic cTnT mouse lines carrying either a 35% (Delta160E) or 50% (R92L) replacement of the endogenous cTnT with the mutant forms. Measurement of baseline myocellular contraction revealed that the Delta160E cells had significant decreases in the peak rate of contraction and percent shortening as compared to either R92L or Non-TG myocytes. In addition, while both Delta160E and R92L myocytes demonstrated a decrease in the peak rate of relaxation as compared to Non-TG, the magnitude of the difference was significantly greater in Delta160E cells. Concurrent myocyte [Ca2+](i) transient measurements revealed that while the alterations in the peak rates and times of the rise and decline of the [Ca2+](i) transient were similar to the changes in the respective measures of sarcomeric mechanics, R92L cells also exhibited reduced rates of the rise and decline of the [Ca2+](i) transient but did not exhibit these reductions in terms of sarcomeric mechanics. Of note, only Delta160E, and not R92L myocytes, demonstrated significant reductions in SR Ca2+ load and uptake, corresponding to the impairments seen in the [Ca2+](i) and mechanical transients. Finally, Western analysis revealed a significant Delta160E-specific reduction in the SERCA2a/PLB ratio, which may well underlie the observed alterations in Ca2+ homeostasis. Therefore, independent cTnT mutations result in significant mutation-specific effects in Ca2+ handling that may, in part, contribute to the observed clinical variability in cTnT-related FHC.
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Affiliation(s)
- Todd E Haim
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
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119
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120
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Abstract
Despite the fact that the heart requires huge amounts of energy to sustain contractile function, it has limited energy reserves and must therefore continually produce large amounts of adenosine triphosphate (ATP) to sustain function. Fatty acids are the primary energy substrate of the adult heart, with more than 60% of the energy normally obtained from the oxidation of fatty acids, the remainder coming from the metabolism of carbohydrates. Alterations in both the rates of ATP production and the type of energy substrate used by the heart can have consequences on contractile function, as well as on its ability to respond to energetic stresses. Switches in myocardial substrate utilization and energy production rates have been shown to occur in various cardiomyopathies, as well as in any subsequent heart failure. Heart failure is characterized by an inefficient pumping of the heart, which fails to meet the energy requirements of the body. A number of cardiomyopathies can lead to heart failure. This paper will review the alterations in energy metabolism that occur in a number cardiomyopathies, including ischemic and diabetic cardiomyopathies, as well as hypertrophic cardiomyopathies resulting from mutations in enzymes involved in energy metabolism, such as 5' adenosine monophosphate-activated protein kinase (AMPK).
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Affiliation(s)
- Maysa Taha
- Cardiovascular Research Group, University of Alberta, Edmonton, Alberta, Canada
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121
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Mora R, Merino JL, Peinado R, Olias F, García-Guereta L, del Cerro MJ, Tarín MN, Molano J. Miocardiopatía hipertrófica: Baja frecuencia de mutaciones en el gen de la cadena pesada de la betamiosina cardiaca. Rev Esp Cardiol 2006. [DOI: 10.1157/13091891] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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122
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Hyun C, Filippich LJ. Molecular genetics of sudden cardiac death in small animals - a review. Vet J 2006; 171:39-50. [PMID: 16427581 DOI: 10.1016/j.tvjl.2004.10.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/08/2004] [Indexed: 10/25/2022]
Abstract
Sudden cardiac death in small animals is uncommon but often occurs due to cardiac conduction defects or myocardial diseases. Primary cardiac conduction defects are mainly caused by mutations in genes involved in impulse conduction processes (e.g., gap-junction genes and transcription factors) or repolarisation processes (e.g., ion-channel genes), whereas primary cardiomyopathies are mainly caused by defective force generation or force transmission due to gene mutations in either sarcomeric or cytoskeleton proteins. Although over 50 genes have been identified in humans directly or indirectly related to sudden cardiac death, no genetic aetiologies have been identified in small animals. Sudden cardiac deaths have been also reported in German Shepherds and Boxers. A better understanding of molecular genetic aetiologies for sudden cardiac death will be required for future study toward unveiling aetiology in sudden cardiac death in small animals.
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Affiliation(s)
- Changbaig Hyun
- Victor Chang Cardiac Research Institute, 384 Victoria Street, Darlinghurst, NSW 2010, Australia
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123
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Tardiff JC. Sarcomeric proteins and familial hypertrophic cardiomyopathy: linking mutations in structural proteins to complex cardiovascular phenotypes. Heart Fail Rev 2006; 10:237-48. [PMID: 16416046 DOI: 10.1007/s10741-005-5253-5] [Citation(s) in RCA: 146] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Hypertrophic Cardiomyopathy (HCM) is a relatively common primary cardiac disorder defined as the presence of a hypertrophied left ventricle in the absence of any other diagnosed etiology. HCM is the most common cause of sudden cardiac death in young people which often occurs without precedent symptoms. The overall clinical phenotype of patients with HCM is broad, ranging from a complete lack of cardiovascular symptoms to exertional dyspnea, chest pain, and sudden death, often due to arrhythmias. To date, 270 independent mutations in nine sarcomeric protein genes have been linked to Familial Hypertrophic Cardiomyopathy (FHC), thus the clinical variability is matched by significant genetic heterogeneity. While the final clinical phenotype in patients with FHC is a result of multiple factors including modifier genes, environmental influences and genotype, initial screening studies had suggested that individual gene mutations could be linked to specific prognoses. Given that the sarcomeric genes linked to FHC encode proteins with known functions, a vast array of biochemical, biophysical and physiologic experimental approaches have been applied to elucidate the molecular mechanisms that underlie the pathogenesis of this complex cardiovascular disorder. In this review, to illustrate the basic relationship between protein dysfunction and disease pathogenesis we focus on representative gene mutations from each of the major structural components of the cardiac sarcomere: the thick filament (beta MyHC), the thin filament (cTnT and Tm) and associated proteins (MyBP-C). The results of these studies will lead to a better understanding of FHC and eventually identify targets for therapeutic intervention.
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Affiliation(s)
- Jil C Tardiff
- Department of Physiology and Biophysics and the Department of Medicine (Cardiology), Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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124
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Binder J, Ommen SR, Gersh BJ, Van Driest SL, Tajik AJ, Nishimura RA, Ackerman MJ. Echocardiography-guided genetic testing in hypertrophic cardiomyopathy: septal morphological features predict the presence of myofilament mutations. Mayo Clin Proc 2006; 81:459-67. [PMID: 16610565 DOI: 10.4065/81.4.459] [Citation(s) in RCA: 150] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
OBJECTIVE To examine the relationship among age, septal morphological subtype, and presence of hypertrophic cardiomyopathy (HCM)-associated myofilament mutations. PATIENTS AND METHODS Comprehensive mutation analysis of the 8 HCM susceptibility genes that encode the myofilaments of the cardiac sarcomere was performed previously in 382 unrelated patients with HCM. Blinded to genotype status, we used echocardiography to characterize the left ventricular morphological features. Multivariate regression was used to assess the relationship among morphological subtypes, clinical data, and genetic variables. RESULTS The mean +/- SD age of the patients was 41.6+/-19.0 years, with 126 patients 50 years or older at initial diagnosis. The septal morphological subtype was sigmold in 181 (47%), reverse in 132 (35%), apical variant in 37 (10%), and neutral in 32 (8%). The HCM-associated myofilament mutations were Identified in 143 patients (37%). Multivariate analysis showed that the reverse curvature septal morphological subtype was a strong predictor of genotype-positive status (odds ratio, 21; P<.001). Overall, the yield of HCM genetic testing was 79% in the setting of reverse curvature HCM but only 8% in sigmold septal HCM. CONCLUSION In stark contrast to HCM in young patients, elderly patients with HCM display a predominantly sigmoid septal morphological subtype and uncommonly have perturbations of known HCM susceptibility genes. Independent of age, septal morphological subtype strongly predicts the presence or absence of HCM-associated myofilament mutations and may enable echocardiography-guided genetic testing for HCM.
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Affiliation(s)
- Josepha Binder
- Division of Cardiovascular Diseases, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
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125
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Winegrad S. Cardiac myosin binding protein C: modulator of contractility. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2006; 565:269-81; discussion 281-2, 405-15. [PMID: 16106981 DOI: 10.1007/0-387-24990-7_20] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Affiliation(s)
- Saul Winegrad
- Department of Physiology, University of Pennsylvania, Philadelphia, Pa, USA
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126
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Kubo T, Kitaoka H, Okawa M, Matsumura Y, Hitomi N, Yamasaki N, Furuno T, Takata J, Nishinaga M, Kimura A, Doi YL. Lifelong Left Ventricular Remodeling of Hypertrophic Cardiomyopathy Caused by a Founder Frameshift Deletion Mutation in the Cardiac Myosin-Binding Protein C Gene Among Japanese. J Am Coll Cardiol 2005; 46:1737-43. [PMID: 16256878 DOI: 10.1016/j.jacc.2005.05.087] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/17/2005] [Revised: 04/25/2005] [Accepted: 05/25/2005] [Indexed: 11/30/2022]
Abstract
OBJECTIVES We studied the longitudinal evolution of hypertrophic cardiomyopathy (HCM) caused by a founder frameshift mutation in the cardiac myosin-binding protein C (MyBPC) gene. BACKGROUND Mutations in the MyBPC gene have been associated with delayed expression of HCM and a good prognosis. Few studies, however, demonstrated the phenotype-genotype correlations in the longitudinal study. METHODS We studied long-term evolution of clinical features of 15 unrelated families who were found to have an identical frameshift mutation in the MyBPC gene: a one-base deletion of a thymidine at nucleotide 11645 (V592fs/8). RESULTS Thirty-nine individuals in 15 families were genotype-positive. Thirty of the 39 individuals with the mutation were phenotype-positive. The disease penetrance was 100% in subjects > or =50 years and 65% in those <50 years. "End-stage" HCM (ejection fraction <50%) was observed in 7 (18%) of the 39 genotype-positive individuals (7 [23%] of the 30 phenotype-positive patients); 6 of them were 60 years or older. Seven patients were hospitalized for treatment of repeated congestive heart failure, and four patients died or had implantable cardioverter-defibrillator discharge (13%; incidence, 1.4%/year) during a mean follow-up period of 9.2 +/- 5.5 years. CONCLUSIONS Elderly patients with a V592fs/8 mutation in the MyBPC gene may evolve into the "end-stage" HCM, characterized by left ventricular systolic dysfunction, cavity dilation, and irreversible heart failure. The clinical course in patients with this mutation is not benign in the long run, with progressive left ventricular remodeling with advancing age.
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Affiliation(s)
- Toru Kubo
- Department of Medicine and Geriatrics, Kochi Medical School, Kochi, Japan
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127
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Meurs KM, Sanchez X, David RM, Bowles NE, Towbin JA, Reiser PJ, Kittleson JA, Munro MJ, Dryburgh K, Macdonald KA, Kittleson MD. A cardiac myosin binding protein C mutation in the Maine Coon cat with familial hypertrophic cardiomyopathy. Hum Mol Genet 2005; 14:3587-93. [PMID: 16236761 DOI: 10.1093/hmg/ddi386] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Hypertrophic cardiomyopathy (HCM) is one of the most common causes of sudden cardiac death in young adults and is a familial disease in at least 60% of cases. Causative mutations have been identified in several sarcomeric genes, including the myosin binding protein C (MYBPC3) gene. Although numerous causative mutations have been identified, the pathogenetic process is still poorly understood. A large animal model of familial HCM in the cat has been identified and may be used for additional study. As the first spontaneous large animal model of this familial disease, feline familial HCM provides a valuable model for investigators to evaluate pathophysiologic processes and therapeutic (pharmacologic or genetic) manipulations. The MYBPC3 gene was chosen as a candidate gene in this model after identifying a reduction in the protein in myocardium from affected cats in comparison to control cats (P<0.001). DNA sequencing was performed and sequence alterations were evaluated for evidence that they changed the amino acid produced, that the amino acid was conserved and that the protein structure was altered. We identified a single base pair change (G to C) in the feline MYBPC3 gene in affected cats that computationally alters the protein conformation of this gene and results in sarcomeric disorganization. We have identified a causative mutation in the feline MYBPC3 gene that results in the development of familial HCM. This is the first report of a spontaneous mutation causing HCM in a non-human species. It should provide a valuable model for evaluating pathophysiologic processes and therapeutic manipulations.
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Affiliation(s)
- Kathryn M Meurs
- Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210, USA.
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128
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Oakley CE, Hambly BD, Curmi PMG, Brown LJ. Myosin binding protein C: structural abnormalities in familial hypertrophic cardiomyopathy. Cell Res 2004; 14:95-110. [PMID: 15115610 DOI: 10.1038/sj.cr.7290208] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The muscle protein myosin binding protein C (MyBPC) is a large multi-domain protein whose role in the sarcomere is complex and not yet fully understood. Mutations in MyBPC are strongly associated with the heart disease familial hypertrophic cardiomyopathy (FHC) and these experiments of nature have provided some insight into the intricate workings of this protein in the heart. While some regions of the MyBPC molecule have been assigned a function in the regulation of muscle contraction, the interaction of other regions with various parts of the myosin molecule and the sarcomeric proteins, actin and titin, remain obscure. In addition, several intra-domain interactions between adjacent MyBPC molecules have been identified. Although the basic structure of the molecule (a series of immunoglobulin and fibronectin domains) has been elucidated, the assembly of MyBPC in the sarcomere is a topic for debate. By analysing the MyBPC sequence with respect to FHC-causing mutations it is possible to identify individual residues or regions of each domain that may be important either for binding or regulation. This review looks at the current literature, in concert with alignments and the structural models of MyBPC, in an attempt to understand how FHC mutations may lead to the disease state.
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Affiliation(s)
- Cecily E Oakley
- Department of Pathology, University of Sydney, NSW 2006, Australia.
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129
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Abstract
Sudden cardiac death (SCD) is devastating at any age, but even more so when the individual affected is young and asymptomatic, and the death is entirely unexpected. SCD is a catastrophic complication of hypertrophic cardiomyopathy (HCM) and may be the first manifestation of this disease. HCM is an inherited intrinsic disease of the myocardium characterized by left ventricular hypertrophy without chamber dilatation, in the absence of either a systemic or other cardiac disease, which may cause a similar magnitude of hypertrophy. HCM may be a clinically silent disease. Indeed, the pathologist may be the first to encounter a case of HCM at autopsy. HCM has wide-ranging implications for affected families, who will require cardiac screening and genetic counselling even if mutations are not known. Therefore, prompt and accurate diagnosis of HCM is vital. This review article will focus on the pathological diagnosis of HCM, recent advances in the genetics of this disease, and common pitfalls which may arise, leading to diagnostic uncertainty.
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MESH Headings
- Autopsy/standards
- Cardiomyopathy, Hypertrophic/complications
- Cardiomyopathy, Hypertrophic/diagnosis
- Cardiomyopathy, Hypertrophic/genetics
- Cardiomyopathy, Hypertrophic/pathology
- Coronary Vessels/pathology
- Death, Sudden, Cardiac/etiology
- Death, Sudden, Cardiac/prevention & control
- Female
- Fibrosis
- Genetic Testing
- Humans
- Hypertrophy, Left Ventricular/pathology
- Male
- Mutation
- Myocytes, Cardiac/pathology
- Myocytes, Cardiac/ultrastructure
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Affiliation(s)
- S E Hughes
- Department of Histopathology, Royal Free and University College Medical School, University College London and UCL Hospitals NHS Trust, London, UK.
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130
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Mogensen J, Murphy RT, Kubo T, Bahl A, Moon JC, Klausen IC, Elliott PM, McKenna WJ. Frequency and clinical expression of cardiac troponin I mutations in 748 consecutive families with hypertrophic cardiomyopathy. J Am Coll Cardiol 2004; 44:2315-25. [PMID: 15607392 DOI: 10.1016/j.jacc.2004.05.088] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2004] [Accepted: 05/04/2004] [Indexed: 11/19/2022]
Abstract
OBJECTIVES The aim of this study was to evaluate the potential utility of genetic diagnosis in clinical management of families with hypertrophic cardiomyopathy (HCM) caused by mutations in the gene for cardiac troponin I (TNNI3). BACKGROUND Knowledge about the clinical disease expression of sarcomeric gene mutations in HCM has predominantly been obtained by investigations of single individuals (probands) or selected families. To establish the role of genetic diagnosis in HCM families, systematic investigations of probands and their relatives are needed. METHODS Cardiac troponin I was investigated by direct sequencing and fluorescent (F)-SSCP analysis in 748 consecutive HCM families. Relatives of HCM probands with TNNI3 mutations were invited for cardiovascular and genetic assessment. RESULTS The prevalence of TNNI3 mutations was 3.1%. Mutations appeared to cluster in exons 7 and 8. A total of 100 mutation carriers were identified in 23 families with 13 different mutations (6 novel). Disease penetrance was 48%. Patients were diagnosed from the second to eighth decade of life. The morphologic spectrum observed represented a wide range of HCM. Two offspring of clinically unaffected mutation carriers were resuscitated from cardiac arrest, and an additional four individuals died suddenly as their initial presentation. Six individuals experienced other disease-related deaths. CONCLUSIONS The clinical expression of TNNI3 mutations was very heterogeneous and varied both within and between families with no apparent mutation- or gene-specific disease pattern. The data suggest that disease development may be monitored by regular assessment of cardiac symptoms and electrocardiographic abnormalities. Genetic diagnosis of TNNI3 is valuable in identifying clinically unaffected mutation carriers at risk of disease development and facilitates accurate management and counseling.
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Affiliation(s)
- Jens Mogensen
- Department of Cardiological Sciences, St. George's Hospital Medical School, London, United Kingdom.
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131
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Katsuragi N, Morishita R, Nakamura N, Ochiai T, Taniyama Y, Hasegawa Y, Kawashima K, Kaneda Y, Ogihara T, Sugimura K. Periostin as a novel factor responsible for ventricular dilation. Circulation 2004; 110:1806-13. [PMID: 15381649 DOI: 10.1161/01.cir.0000142607.33398.54] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Periostin is highly expressed in the myocardium in patients with heart failure. However, no report has documented the function of periostin. To identify the function of periostin in the pathophysiology of heart failure, overexpression or loss of function of the periostin gene was examined by direct transfection into the rat heart. METHODS AND RESULTS Rats transfected with the periostin gene by the HVJ-liposome method showed left ventricular (LV) dilation as assessed by echocardiography, accompanied by an increase in periostin expression. Consistently significant differences were observed in LV pressure, LV end-diastolic pressure, LV dP/dt(max), and LV dP/dt(min) at 6 and 12 weeks after transfection in rats transfected with the periostin gene, accompanied by a decrease in cardiac myocytes and an increase in collagen deposition. Importantly, periostin has the ability to inhibit the spreading of myocytes and the adhesion of cardiac fibroblasts with or without fibronectin. Markers of cardiac dysfunction such as brain natriuretic peptide and endothelin-1 gene expression were significantly increased after transfection in the LV of rats transfected with the periostin gene. These data demonstrate that overexpression of the periostin gene led to cardiac dysfunction. Thus, we examined the inhibition of periostin in Dahl salt-sensitive rats by an antisense strategy because periostin is highly expressed in heart failure. Importantly, inhibition of periostin gene expression resulted in a significant increase in survival rate, accompanied by an improvement of LV function. CONCLUSIONS The present study demonstrates the contribution of the periostin gene to cardiac dilation in animal models. Inhibition of periostin might become a new therapeutic target for the treatment of heart failure.
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MESH Headings
- Animals
- Cell Adhesion Molecules/genetics
- Cell Adhesion Molecules/physiology
- Cell Line
- Cell Size/drug effects
- Cells, Cultured/drug effects
- DNA, Complementary/genetics
- Fibroblasts/cytology
- Fibroblasts/drug effects
- Fibronectins/antagonists & inhibitors
- Fibronectins/pharmacology
- Gene Expression Regulation
- Hemodynamics
- Hypertrophy, Left Ventricular/diagnostic imaging
- Hypertrophy, Left Ventricular/genetics
- Hypertrophy, Left Ventricular/metabolism
- Male
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/ultrastructure
- Oligodeoxyribonucleotides, Antisense/pharmacology
- RNA, Messenger/biosynthesis
- Rats
- Rats, Inbred Dahl
- Rats, Sprague-Dawley
- Recombinant Fusion Proteins/biosynthesis
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/physiology
- Reverse Transcriptase Polymerase Chain Reaction
- Spodoptera
- Transfection
- Ultrasonography
- Ventricular Dysfunction, Left/diagnostic imaging
- Ventricular Dysfunction, Left/genetics
- Ventricular Dysfunction, Left/metabolism
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Affiliation(s)
- Naruto Katsuragi
- Daiichi Suntory Biomedical Research Ltd, 1-1-1 Wakayamadai Shimamoto-cho, Mishima-gun, Osaka, Japan
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132
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Kulikovskaya I, McClellan G, Flavigny J, Carrier L, Winegrad S. Effect of MyBP-C binding to actin on contractility in heart muscle. ACTA ACUST UNITED AC 2004; 122:761-74. [PMID: 14638934 PMCID: PMC2229591 DOI: 10.1085/jgp.200308941] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In contrast to skeletal muscle isoforms of myosin binding protein C (MyBP-C), the cardiac isoform has 11 rather than 10 fibronectin or Ig modules (modules are identified as C0 to C10, NH2 to COOH terminus), 3 phosphorylation sites between modules C1 and C2, and 28 additional amino acids rich in proline in C5. Phosphorylation between C1 and C2 increases maximum Ca-activated force (Fmax), alters thick filament structure, and increases the probability of myosin heads on the thick filament binding to actin on the thin filament. Unphosphorylated C1C2 fragment binds to myosin, but phosphorylation inhibits the binding. MyBP-C also binds to actin. Using two types of immunoprecipitation and cosedimentation, we show that fragments of MyBP-C containing C0 bind to actin. In low concentrations C0-containing fragments bind to skinned fibers when the NH2 terminus of endogenous MyBP-C is bound to myosin, but not when MyBP-C is bound to actin. C1C2 fragments bind to skinned fibers when endogenous MyBP-C is bound to actin but not to myosin. Disruption of interactions of endogenous C0 with a high concentration of added C0C2 fragments produces the same effect on contractility as extraction of MyBP-C, namely decrease in Fmax and increase in Ca sensitivity. These results suggest that cardiac contractility can be regulated by shifting the binding of the NH2 terminus of MyBP-C between actin and myosin. This mechanism may have an effect on diastolic filling of the heart.
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Affiliation(s)
- Irina Kulikovskaya
- Department of Physiology, School of Medicine, University of Pennsylvania Philadelphia, PA 19104, USA
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133
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Palmer BM, Noguchi T, Wang Y, Heim JR, Alpert NR, Burgon PG, Seidman CE, Seidman JG, Maughan DW, LeWinter MM. Effect of Cardiac Myosin Binding Protein-C on Mechanoenergetics in Mouse Myocardium. Circ Res 2004; 94:1615-22. [PMID: 15155526 DOI: 10.1161/01.res.0000132744.08754.f2] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We examined the effect of cardiac myosin binding protein-C (cMyBP-C) on contractile efficiency in isovolumically contracting left ventricle (LV) and on internal viscosity and oscillatory work production in skinned myocardial strips. A 6-week diet of 0.15% 6-n-propyl-2-thiouracil (PTU) was fed to wild-type (+/+(PTU)) and homozygous-truncated cMyBP-C (t/t(PTU)) mice starting at age approximately 8 weeks and leading to a myosin heavy chain (MHC) isoform profile of 10% alpha-MHC and 90% beta-MHC in both groups. Western blot analysis confirmed that cMyBP-C was present in the +/+(PTU) and effectively absent in the t/t(PTU). Total LV mechanical energy per beat was quantified as pressure-volume area (PVA). O2 consumption (Vo2) per beat was plotted against PVA at varying LV volumes. The reciprocal of the slope of the linear Vo2-PVA relation represents the contractile efficiency of converting O2 to mechanical energy. Contractile efficiency was significantly enhanced in t/t(PTU) (26.1+/-2.6%) compared with +/+(PTU) (17.1+/-1.6%). In skinned myocardial strips, maximum isometric tension was similar in t/t(PTU) (18.7+/-2.1 mN x mm(-2)) and +/+(PTU) (21.9+/-4.0 mN x mm(-2)), but maximum oscillatory work induced by sinusoidal length perturbations occurred at higher frequencies in t/t(PTU) (7.31+/-1.17 Hz) compared with +/+(PTU) (4.48+/-0.60 Hz) and was significantly more sensitive to phosphate concentration in the t/t(PTU). Under rigor conditions, the internal viscous load was significantly lower in the t/t(PTU) compared with +/+(PTU), ie, approximately 40% lower at 1 Hz. These results collectively suggest that contractile efficiency is enhanced in the t/t(PTU), probably through a reduced loss of mechanical energy by a viscous load normally provided by cMyBP-C and through a gain of phosphate-dependent oscillatory work normally inhibited by cMyBP-C.
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Affiliation(s)
- Bradley M Palmer
- Department of Molecular Physiology and Biophysics, University of Vermont College of Medicine, University of Vermont, Burlington, Vt 05405, USA.
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134
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Abstract
Myosin binding protein-C (MyBP-C) is a thick filament–associated protein localized to the crossbridge-containing C zones of striated muscle sarcomeres. The cardiac isoform is composed of eight immunoglobulin I–like domains and three fibronectin 3–like domains and is known to be a physiological substrate of cAMP-dependent protein kinase. MyBP-C contributes to thick filament structure via interactions at its C-terminus with the light meromyosin section of the myosin rod and with titin. The protein also has a role in the regulation of contraction, due to the binding of its N-terminus to the subfragment-2 portion of myosin, which reduces actomyosin ATPase activity; phosphorylation abolishes this interaction, resulting in release of the “brake” on crossbridge cycling. Several structural models of the interaction of MyBP-C with myosin have been proposed, although its precise arrangement on the thick filament remains to be elucidated. Mutations in the gene encoding cardiac MyBP-C are a common cause of hypertrophic cardiomyopathy, and this has led to increased interest in the protein’s function. Investigation of disease-causing mutations in domains with unknown function has led to further insights into the mechanism of cMyBP-C action. This Review aims to collate the published data on those aspects of MyBP-C that are well characterized and to consider new and emerging data that further define its structural and regulatory roles and its arrangement in the sarcomere. We also speculate on the mechanisms by which hypertrophic cardiomyopathy–causing truncation and missense mutations affect the normal functioning of the sarcomere.
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Affiliation(s)
- Emily Flashman
- Department of Cardiovascular Medicine, University of Oxford, UK
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135
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Winegrad S. Myosin-binding protein C (MyBP-C) in cardiac muscle and contractility. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2004; 538:31-40; discussion 40-1. [PMID: 15098652 DOI: 10.1007/978-1-4419-9029-7_3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
Abstract
Both the MyBP-C motif between C1 and C2 and the C5 module are important regions for implementing the effect of MyBP-C on myosin and on contractility but in different ways. C5 may determine the folding of MyBP-C and the manner in which MyBP-C interacts with myosin. In spite of its apparent importance this interaction does not appear to be physiologically regulated. Its alteration by mutation however can have a major effect on contractility. On the other hand, the effect of the motif is regulated by phosphorylation and appears to be an important part of a physiological mechanism(s) for modulating contractility. Thick filaments isolated from cardiac muscle exist in one of three different structures (Levine et al 2001). Different degrees of phosphorylation of MyBP-C can produce transitions among the three structures. The combination of the binding results of Flashman et al (2002) with the data of McClellan et al (2001) suggests that the C5 interaction with C8 is critical in maintaining the normal structure of thick filaments and the normal function of the force generators in the filaments. The cardiac-specific sequence in C5 and its normal interaction with another part of the same or a different MyBP-C may be required for the correct 3 dimensional shape of the three MyBP-C molecules at each locus in the C zone and the normal structure of the thick filament. The normal interactions may be necessary to allow transitions in binding and filament structure that are associated with phosphorylation of the MyBP-C motif.
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Affiliation(s)
- Saul Winegrad
- Department of Physiology, School of Medicine, University of Pennsylvania, Philadelphia, PA 19072, USA
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136
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Harada K, Potter JD. Familial Hypertrophic Cardiomyopathy Mutations from Different Functional Regions of Troponin T Result in Different Effects on the pH and Ca2+ Sensitivity of Cardiac Muscle Contraction. J Biol Chem 2004; 279:14488-95. [PMID: 14722098 DOI: 10.1074/jbc.m309355200] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To understand the molecular function of troponin T (TnT) in the Ca(2+) regulation of muscle contraction as well as the molecular pathogenesis of familial hypertrophic cardiomyopathy (FHC), eight FHC-linked TnT mutations, which are located in different functional regions of human cardiac TnT (HCTnT), were produced, and their structural and functional properties were examined. Circular dichroism spectroscopy demonstrated different secondary structures of these TnT mutants. Each of the recombinant HCTnTs was incorporated into porcine skinned fibers along with human cardiac troponin I (HCTnI) and troponin C (HCTnC), and the Ca(2+) dependent isometric force development of these troponin-replaced fibers was determined at pH 7.0 and 6.5. All eight mutants altered the contractile properties of skinned cardiac fibers. E244D potentiated the maximum force development without changing Ca(2+) sensitivity. In contrast, the other seven mutants increased the Ca(2+) sensitivity of force development but not the maximal force. R92L, R92W, and R94L also decreased the change in Ca(2+) sensitivity of force development observed on lowering the pH from 7 to 6.5, when compared with wild type TnT. The examination of additional mutants, H91Q and a double mutant H91Q/R92W, suggests that mutations in a region including residues 91-94 in HCTnT can perturb the proper response of cardiac contraction to changes in pH. These results suggest that different regions of TnT may contribute to the pathogenesis of TnT-linked FHC through different mechanisms.
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Affiliation(s)
- Keita Harada
- Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, Miami, Florida 33101, USA
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137
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Wuyts W, Waeber G, Meinecke P, Schüler H, Goecke TO, Van Hul W, Bartsch O. Proximal 11p deletion syndrome (P11pDS): additional evaluation of the clinical and molecular aspects. Eur J Hum Genet 2004; 12:400-6. [PMID: 14872200 DOI: 10.1038/sj.ejhg.5201163] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The combination of multiple exostoses (EXT) and enlarged parietal foramina (foramina parietalia permagna, FPP) represent the main features of the proximal 11p deletion syndrome (P11pDS), a contiguous gene syndrome (MIM 601224) caused by an interstitial deletion on the short arm of chromosome 11. Here we present clinical aspects of two new P11pDS patients and the clinical follow-up of one patient reported in the original paper describing this syndrome. Recognised clinical signs include EXT, FPP, mental retardation, facial asymmetry, asymmetric calcification of coronary sutures, defective vision (severe myopia, nystagmus, strabismus), skeletal anomalies (small hands and feet, tapering fingers), heart defect, and anal stenosis. In addition fluorescence in situ hybridisation and molecular analysis were performed to gain further insight in potential candidate genes involved in P11pDS.
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Affiliation(s)
- Wim Wuyts
- Department of Medical Genetics, University of Antwerp, Belgium.
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138
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Jääskeläinen P, Miettinen R, Kärkkäinen P, Toivonen L, Laakso M, Kuusisto J. Genetics of hypertrophic cardiomyopathy in eastern Finland: few founder mutations with benign or intermediary phenotypes. Ann Med 2004; 36:23-32. [PMID: 15000344 DOI: 10.1080/07853890310017161] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
Hypertrophic cardiomyopathy (HCM) is a genetically and clinically heterogeneous myocardial disease caused by mutations in genes encoding sarcomeric proteins. To assess the genetic background and phenotypic expression of HCM in eastern Finland, we screened 35 unrelated patients with HCM from the Kuopio University Hospital area for variants in 9 genes encoding sarcomeric proteins with the PCR-SSCP method. We herewith describe our previous findings in five sarcomeric genes and also report hitherto unpublished data on four additional sarcomeric genes. Mutations in the cardiac myosin-binding protein C gene (MYBPC3) were most frequent, accounting for 26% of cases. A novel mutation (Gln1061X) in this gene was the most common mutation, found in 6 of 35 families and accounting for 17% of all cases. Other novel mutations in MYBPC3 (IVS5-2A --> C, IVS14-13G --> A, and Ex25deltaLys) were found in one family each. A previously described alpha-tropomyosin (TPM1) mutation (Asp175Asn) was found in 11% of cases. Haplotype analysis suggested that the two most common variants (MYBPC3-Gln1061X and TPM1-Asp175Asn) were founder mutations. Only one mutation (Arg719Trp) in the beta-myosin heavy chain gene (MYH7) was found in one family, and no disease-causing mutations were found in the genes encoding alpha-actin, cardiac troponin I, T, C, or myosin essential and regulatory light chains. Altogether, the aforementioned 6 mutations found in MYBPC3, TPM1, and MYH7 accounted for 61% of familial and 40% of all HCM cases. The mutations were associated mostly with benign or intermediary phenotypes with only few HCM-related deaths. We conclude that the genetic profile of HCM in eastern Finland is unique, characterized by few founder mutations with benign or intermediary phenotypes.
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139
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140
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Wang Q, Moncman CL, Winkelmann DA. Mutations in the motor domain modulate myosin activity and myofibril organization. J Cell Sci 2003; 116:4227-38. [PMID: 12953063 DOI: 10.1242/jcs.00709] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
We have investigated the functional impact on cardiac myofibril organization and myosin motor activity of point mutations associated with familial hypertrophic cardiomyopathies (FHC). Embryonic chicken cardiomyocytes were transfected with vectors encoding green fluorescent protein (GFP) fused to a striated muscle myosin heavy chain (GFP-myosin). Within 24 hours of transfection, the GFP-myosin is found co-assembled with the endogenous myosin in striated myofibrils. The wild-type GFP-myosin had no effect on the organization of the contractile cytoskeleton of the cardiomyocytes. However, expression of myosin with the R403Q FHC mutation resulted in a small but significant decrease in myofibril organization, and the R453C and G584R mutations caused a more dramatic increase in myofibril disarray. The embryonic cardiomyocytes beat spontaneously in culture and this was not affected by expression of the wild-type or mutant GFP-myosin. For the biochemical analysis of myosin motor activity, replication defective adenovirus was used to express the wild-type and mutant GFP-myosin in C2C12 myotubes. The R403Q mutation enhanced actin filament velocity but had no effect on the myosin duty ratio. The R453C and G584R mutations impaired actin filament movement and both increased the duty ratio. The effects of these mutations on myosin motor activity correlate with changes in myofibril organization of live cardiomyocytes. Thus, mutations associated with hypertrophic cardiomyopathies that alter myosin motor activity can also impair myofibril organization.
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Affiliation(s)
- Qun Wang
- Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
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141
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Erdmann J, Daehmlow S, Wischke S, Senyuva M, Werner U, Raible J, Tanis N, Dyachenko S, Hummel M, Hetzer R, Regitz-Zagrosek V. Mutation spectrum in a large cohort of unrelated consecutive patients with hypertrophic cardiomyopathy. Clin Genet 2003; 64:339-49. [PMID: 12974739 DOI: 10.1034/j.1399-0004.2003.00151.x] [Citation(s) in RCA: 156] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Defects in nine sarcomeric protein genes are known to cause hypertrophic cardiomyopathy (HCM). Mutation types and frequencies in large cohorts of consecutive and unrelated patients have not yet been determined. We, therefore, screened HCM patients for mutations in six sarcomeric genes: myosin-binding protein C3 (MYBPC3), MYH7, cardiac troponin T (TNNT2), alpha-tropomyosin (TPM1), cardiac troponin I (TNNI3), and cardiac troponin C (TNNC1). HCM was diagnosed in 108 consecutive patients by echocardiography (septum >15 mm, septal/posterior wall >1.3 mm), angiography, or based on a state after myectomy. Single-strand conformation polymorphism analysis was used for mutation screening, followed by DNA-sequencing. A total of 34 different mutations were identified in 108 patients: 18 mutations in MYBPC3 in 20 patients [intervening sequence (intron) 7 + 1G > A and Q1233X were found twice], 13 missense mutations in MYH7 in 14 patients (R807H was found twice), and one amino acid change in TPM1, TNNT2, and TNNI3, respectively. No disease-causing mutation was found in TNNC1. Cosegregation with the HCM phenotype could be demonstrated for 13 mutations (eight mutations in MYBPC3 and five mutations in MYH7). Twenty-eight of the 37 mutation carriers (76%) reported a positive family history with at least one affected first-grade relative; only eight mutations occurred sporadically (22%). MYBPC3 was the gene that most frequently caused HCM in our population. Systematic mutation screening in large samples of HCM patients leads to a genetic diagnosis in about 30% of unrelated index patients and in about 57% of patients with a positive family history.
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Affiliation(s)
- J Erdmann
- Department of Internal Medicine II/Cardiology, University of Regensburg, Regensburg, Germany.
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142
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Nanni L, Pieroni M, Chimenti C, Simionati B, Zimbello R, Maseri A, Frustaci A, Lanfranchi G. Hypertrophic cardiomyopathy: two homozygous cases with "typical" hypertrophic cardiomyopathy and three new mutations in cases with progression to dilated cardiomyopathy. Biochem Biophys Res Commun 2003; 309:391-8. [PMID: 12951062 DOI: 10.1016/j.bbrc.2003.08.014] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
About 10% of cases of hypertrophic cardiomyopathy (HCM) evolve into dilated cardiomyopathy (DCM) with unknown causes. We studied 11 unrelated patients (pts) with HCM who progressed to DCM (group A) and 11 who showed "typical" HCM (group B). Mutational analysis of the beta-myosin heavy chain (MYH7), myosin-binding protein C (MYBPC3), and cardiac troponin T (TNNT2) genes demonstrated eight mutations affecting MYH7 or MYBPC3 gene, five of which were new mutations. In group A-pts, the first new mutation occurred in the myosin head-rod junction and the second occurred in the light chain-binding site. The third new mutation leads to a MYBPC3 lacking titin and myosin binding sites. In group B, two pts with severe HCM carried two homozygous MYBPC3 mutations and one with moderate hypertrophy was a compound heterozygous for MYBPC3 gene. We identified five unreported mutations, potentially "malignant" defects as for the associated phenotypes, but no specific mutations of HCM/DCM.
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MESH Headings
- Adult
- Aged
- Amino Acid Sequence
- Cardiomyopathy, Dilated/classification
- Cardiomyopathy, Dilated/diagnosis
- Cardiomyopathy, Dilated/genetics
- Cardiomyopathy, Hypertrophic, Familial/classification
- Cardiomyopathy, Hypertrophic, Familial/diagnosis
- Cardiomyopathy, Hypertrophic, Familial/genetics
- Carrier Proteins/blood
- Carrier Proteins/genetics
- Carrier Proteins/metabolism
- DNA Mutational Analysis/methods
- Female
- Genetic Predisposition to Disease/genetics
- Homozygote
- Humans
- Male
- Middle Aged
- Molecular Sequence Data
- Muscle Proteins/genetics
- Muscle Proteins/metabolism
- Mutation
- Sequence Alignment
- Sequence Analysis, Protein
- Troponin T/blood
- Troponin T/genetics
- Troponin T/metabolism
- Ventricular Myosins/blood
- Ventricular Myosins/genetics
- Ventricular Myosins/metabolism
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Affiliation(s)
- Luisa Nanni
- CRIBI Biotechnology Center, Università degli Studi di Padova, Padua, Italy
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143
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Sato N, Kawakami T, Nakayama A, Suzuki H, Kasahara H, Obinata T. A novel variant of cardiac myosin-binding protein-C that is unable to assemble into sarcomeres is expressed in the aged mouse atrium. Mol Biol Cell 2003; 14:3180-91. [PMID: 12925755 PMCID: PMC181559 DOI: 10.1091/mbc.e02-10-0685] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Cardiac myosin-binding protein-C (MyBP-C), also known as C-protein, is one of the major myosin-binding proteins localizing at A-bands. MyBP-C has three isoforms encoded by three distinct genes: fast-skeletal, slow-skeletal, and cardiac type. Herein, we are reporting a novel alternative spliced form of cardiac MyBP-C, MyBP-C(+), which includes an extra 30 nucleotides, encoding 10 amino acids in the carboxyl-terminal connectin/titin binding region. This alternative spliced form of MyBP-C(+) has a markedly decreased binding affinity to myosin filaments and connectin/titin in vitro and does not localize to A-bands in cardiac myocytes. When MyBP-C(+) was expressed in chicken cardiac myocytes, sarcomere structure was markedly disorganized, suggesting it has possible dominant negative effects on sarcomere organization. Expression of MyBP-C(+) is hardly detected in ventricles through cardiac development, but its expression gradually increases in atria and becomes the dominant form after 6 mo of age. The present study demonstrates an age-induced new isoform of cardiac MyBP-C harboring possible dominant negative effects on sarcomere assembly.
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Affiliation(s)
- Naruki Sato
- Department of Biology, Faculty of Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
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144
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145
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Chien KR. Genotype, phenotype: upstairs, downstairs in the family of cardiomyopathies. J Clin Invest 2003; 111:175-8. [PMID: 12531871 PMCID: PMC151886 DOI: 10.1172/jci17612] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Affiliation(s)
- Kenneth R Chien
- University of California, San Diego Institute of Molecular Medicine, University of California, San Diego School of Medicine, La Jolla, California 92093, USA.
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146
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Chien KR. Genotype, phenotype: upstairs, downstairs in the family of cardiomyopathies. J Clin Invest 2003. [DOI: 10.1172/jci200317612] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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147
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Hinkle A, Tobacman LS. Folding and function of the troponin tail domain. Effects of cardiomyopathic troponin T mutations. J Biol Chem 2003; 278:506-13. [PMID: 12409295 DOI: 10.1074/jbc.m209194200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Troponin contains a globular Ca(2+)-binding domain and an elongated tail domain composed of the N terminus of subunit troponin T (TnT). The tail domain anchors troponin to tropomyosin and actin, modulates myosin function, and is a site of cardiomyopathy-inducing mutations. Critical interactions between tropomyosin and troponin are proposed to depend on tail domain residues 112-136, which are highly conserved across phyla. Most cardiomyopathy mutations in TnT flank this region. Three such mutations were examined and had contrasting effects on peptide TnT-(1-156), promoting folding and thermal stability assessed by circular dichroism (F110I) or weakening folding and stability (T104V and to a small extent R92Q). Folding of both TnT-(1-156) and whole troponin was promoted by replacing bovine TnT Thr-104 with human TnT Ala-104, further indicating the importance of this cardiomyopathy site residue for protein folding. Mutation F110I markedly stabilized the troponin tail but weakened binding of holo-troponin to actin-tropomyosin 8-fold, suggesting that loss of flexibility impairs troponin tail function. The effect of the F110I mutation on troponin-tropomyosin binding to actin was much less, indicating this flexibility is particularly important for the interactions of troponin with tropomyosin. We suggest that most cardiomyopathic mutations in the troponin tail alter muscle function indirectly, by perturbing interactions between troponin and tropomyosin requisite for the complex effects of these proteins on myosin.
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Affiliation(s)
- Ashley Hinkle
- Department of Internal Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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148
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Mutational Profiles and Molecular Etiologies of Hypertrophic Cardiomyopathy and Dilated Cardiomyopathy in Asian Populations. ACTA ACUST UNITED AC 2003. [DOI: 10.1007/978-1-4615-0455-9_15] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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149
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Abstract
Myocardial disorders are major causes of morbidity and mortality, including heart failure, sudden death and the need for heart transplantation. The two most common forms of myocardial disorders, dilated cardiomyopathy and hypertrophic cardiomyopathy are paradigms of left ventricular systolic dysfunction and diastolic dysfunction. The genetics of these disorders are increasingly understood with the sarcomere playing a central role in the development of HCM and the link between sarcomere and sarcolemma being key to the development of DCM. In this review, the genetics of the myocardial diseases will be described.
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Affiliation(s)
- Jeffrey A Towbin
- Department of Pediatrics Cardiology, Baylor College of Medicine, One Baylor Plaza, Room 333E, Houston, TX 77030, USA.
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150
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Moolman-Smook J, Flashman E, de Lange W, Li Z, Corfield V, Redwood C, Watkins H. Identification of novel interactions between domains of Myosin binding protein-C that are modulated by hypertrophic cardiomyopathy missense mutations. Circ Res 2002; 91:704-11. [PMID: 12386147 DOI: 10.1161/01.res.0000036750.81083.83] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Cardiac myosin binding protein-C (cMyBPC) is a modular protein consisting of 11 domains whose precise function and sarcomeric arrangement are incompletely understood. Identification of hypertrophic cardiomyopathy (HCM)--causing missense mutations in cMyBPC has highlighted the significance of certain domains. Of particular interest is domain C5, an immunoglobulin-like domain with a cardiac-specific insert, which is of unknown function yet is the site of two HCM-causing missense mutations. To identify interactors with this region, a human cardiac cDNA library was screened in a yeast two-hybrid (Y2H) assay using the C5 sequence as bait. Screening >7x10(6) clones surprisingly revealed that domain C5 preferentially bound to clones encoding C-terminal fragments of cMyBPC; the interacting region was narrowed to domain C8 by deletion mapping. A surface plasmon resonance assay using purified recombinant cMyBPC domains was used to measure the affinity of C5 and C8 in vitro (K(a)=1x10(5) mol/L(-1)). This affinity was decreased about 2-fold by the HCM mutation R654H, and by at least 10-fold by the mutation N755K. Further Y2H assays also demonstrated specific binding between domains C7 and C10 of cMyBPC. Based on these novel interactions, and previous biochemical and structural data, we propose that cMyBPC molecules trimerize into a collar around the thick filament, with overlaps of domains C5-C7 of one cMyBPC with C8-C10 of another. We speculate that this interaction may be dynamically formed and released, thereby restricting or favoring cross-bridge formation, respectively. We suggest that the HCM mutations act by altering the cMyBPC collar, indicating its importance in thick filament structure and regulation.
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Affiliation(s)
- Johanna Moolman-Smook
- US/MRC Centre for Molecular and Cellular Biology, University of Stellenbosch, Tygerberg, South Africa
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