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Swindle N, Albury ANJ, Baroud B, Burney M, Tikunova SB. Molecular and functional consequences of mutations in the central helix of cardiac troponin C. Arch Biochem Biophys 2014; 548:46-53. [PMID: 24650606 DOI: 10.1016/j.abb.2014.03.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Revised: 03/04/2014] [Accepted: 03/05/2014] [Indexed: 01/28/2023]
Abstract
The objective of this work was to investigate the role of acidic residues within the exposed middle segment of the central helix of cTnC in (1) cTnC-cTnI interactions, (2) Ca(2+) binding and exchange with the regulatory N-domain of cTnC in increasingly complex biochemical systems, and (3) ability of the cTn complex to regulate actomyosin ATPase. In order to achieve this objective, we introduced the D87A/D88A and E94A/E95A/E96A mutations into the central helix of cTnC. The D87A/D88A and E94A/E95A/E96A mutations decreased affinity of cTnC for the regulatory region of cTnI. The Ca(2+) sensitivity of the regulatory N-domain of isolated cTnC was decreased by the D87A/D88A, but not E94A/E95A/E96A mutation. However, both the D87A/D88A and E94A/E95A/E96A mutations desensitized the cTn complex and reconstituted thin filaments to Ca(2+). Decreases in the Ca(2+) sensitivity of the cTn complex and reconstituted thin filaments were, at least in part, due to faster rates of Ca(2+) dissociation. In addition, the D87A/D88A and E94A/E95A/E96A mutations desensitized actomyosin ATPase to Ca(2+), and decreased maximal actomyosin ATPase activity. Thus, our results indicate that conserved acidic residues within the exposed middle segment of the central helix of cTnC are important for the proper regulatory function of the cTn complex.
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Affiliation(s)
- Nicholas Swindle
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States
| | - Acchia N J Albury
- Department of Biology, Wingate University, Wingate, NC 28174, United States
| | - Belal Baroud
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States
| | - Maryam Burney
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States
| | - Svetlana B Tikunova
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77004, United States.
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Chen C, Liu JB, Bian ZP, Xu JD, Wu HF, Gu CR, Shi Y, Zhang JN, Chen XJ, Yang D. Cardiac troponin I is abnormally expressed in non-small cell lung cancer tissues and human cancer cells. INTERNATIONAL JOURNAL OF CLINICAL AND EXPERIMENTAL PATHOLOGY 2014; 7:1314-1324. [PMID: 24817928 PMCID: PMC4014212] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Accepted: 02/07/2014] [Indexed: 06/03/2023]
Abstract
Cardiac troponin I (cTnI) is the only sarcomeric protein identified to date that is expressed exclusively in cardiac muscle. Its expression in cancer tissues has not been reported. Herein, we examined cTnI expression in non-small cell lung cancer (NSCLC) tissues, human adenocarcinoma cells SPCA-1 (lung) and BGC 823 (gastric) by immunohistochemistry, western blot analysis and real-time PCR. Immunopositivity for cTnI was demonstrated in 69.4% (34/49) NSCLC tissues evaluated, and was strong intensity in 35.3% (6/17) lung squamous cell carcinoma cases. The non-cancer-bearing lung tissues except tuberculosis (9/9, 100%) showed negative staining for cTnI. Seven monoclonal antibodies (mAbs) against human cTnI were applied in immunofluorescence. The result showed that the staining pattern within SPCA-1 and BGC 823 was dependent on the epitope of the cTnI mAbs. The membrane and nucleus of cancer cells were stained by mAbs against N-terminal peptides of cTnI, and cytoplasm was stained by mAbs against the middle and C-terminal peptides of cTnI. A ~25 kD band was identified by anti-cTnI mAb in SPCA-1 and BGC 823 extracts by western blot, as well as in cardiomyocyte extracts. The cTnI mRNA expressions in SPCA-1 and BGC 823 cells were about ten thousand times less than that in cardiomyocytes. Our study shows for the first time that cTnI protein and mRNA were abnormally expressed in NSCLC tissues, SPCA-1 and BGC 823 cells. These findings challenge the conventional view of cTnI as a cardiac-specific protein, enabling the potential use of cTnI as a diagnostic marker or targeted therapy for cancer.
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Affiliation(s)
- Chao Chen
- Research Institute of Cardiovascular Disease, The First Affiliated Hospital of Nanjing Medical University300 Guangzhou Road, Nanjing 210029, China
| | - Jia-Bao Liu
- Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University300 Guangzhou Road, Nanjing 210029, China
| | - Zhi-Ping Bian
- Research Institute of Cardiovascular Disease, The First Affiliated Hospital of Nanjing Medical University300 Guangzhou Road, Nanjing 210029, China
| | - Jin-Dan Xu
- Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University300 Guangzhou Road, Nanjing 210029, China
| | - Heng-Fang Wu
- Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University300 Guangzhou Road, Nanjing 210029, China
| | - Chun-Rong Gu
- Research Institute of Cardiovascular Disease, The First Affiliated Hospital of Nanjing Medical University300 Guangzhou Road, Nanjing 210029, China
| | - Yi Shi
- Department of Respiratory and Critical Care Medicine, Jinling Hospital, School of Medicine, Nanjing University305 Zhongshan East Road, Nanjing 210002, China
| | - Ji-Nan Zhang
- Research Institute of Cardiovascular Disease, The First Affiliated Hospital of Nanjing Medical University300 Guangzhou Road, Nanjing 210029, China
| | - Xiang-Jian Chen
- Research Institute of Cardiovascular Disease, The First Affiliated Hospital of Nanjing Medical University300 Guangzhou Road, Nanjing 210029, China
| | - Di Yang
- Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University300 Guangzhou Road, Nanjing 210029, China
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53
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Alves ML, Dias FAL, Gaffin RD, Simon JN, Montminy EM, Biesiadecki BJ, Hinken AC, Warren CM, Utter MS, Davis RT, Sakthivel S, Robbins J, Wieczorek DF, Solaro RJ, Wolska BM. Desensitization of myofilaments to Ca2+ as a therapeutic target for hypertrophic cardiomyopathy with mutations in thin filament proteins. ACTA ACUST UNITED AC 2014; 7:132-143. [PMID: 24585742 DOI: 10.1161/circgenetics.113.000324] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
BACKGROUND Hypertrophic cardiomyopathy (HCM) is a common genetic disorder caused mainly by mutations in sarcomeric proteins and is characterized by maladaptive myocardial hypertrophy, diastolic heart failure, increased myofilament Ca(2+) sensitivity, and high susceptibility to sudden death. We tested the following hypothesis: correction of the increased myofilament sensitivity can delay or prevent the development of the HCM phenotype. METHODS AND RESULTS We used an HCM mouse model with an E180G mutation in α-tropomyosin (Tm180) that demonstrates increased myofilament Ca(2+) sensitivity, severe hypertrophy, and diastolic dysfunction. To test our hypothesis, we reduced myofilament Ca(2+) sensitivity in Tm180 mice by generating a double transgenic mouse line. We crossed Tm180 mice with mice expressing a pseudophosphorylated cardiac troponin I (S23D and S24D; TnI-PP). TnI-PP mice demonstrated a reduced myofilament Ca(2+) sensitivity compared with wild-type mice. The development of pathological hypertrophy did not occur in mice expressing both Tm180 and TnI-PP. Left ventricle performance was improved in double transgenic compared with their Tm180 littermates, which express wild-type cardiac troponin I. Hearts of double transgenic mice demonstrated no changes in expression of phospholamban and sarcoplasmic reticulum Ca(2+) ATPase, increased levels of phospholamban and troponin T phosphorylation, and reduced phosphorylation of TnI compared with Tm180 mice. Moreover, expression of TnI-PP in Tm180 hearts inhibited modifications in the activity of extracellular signal-regulated kinase and zinc finger-containing transcription factor GATA in Tm180 hearts. CONCLUSIONS Our data strongly indicate that reduction of myofilament sensitivity to Ca(2+) and associated correction of abnormal relaxation can delay or prevent development of HCM and should be considered as a therapeutic target for HCM.
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Affiliation(s)
- Marco L Alves
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL.,Department of Physiology and Department of Cell Biology, Federal University of Parana, Curitiba, Brazil
| | - Fernando A L Dias
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL.,Department of Physiology and Department of Cell Biology, Federal University of Parana, Curitiba, Brazil
| | - Robert D Gaffin
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Jillian N Simon
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Eric M Montminy
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Brandon J Biesiadecki
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL.,Department of Physiology and Cell Biology, The Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH
| | - Aaron C Hinken
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Chad M Warren
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Megan S Utter
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Robert T Davis
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Sadayappan Sakthivel
- Division of Molecular Cardiovascular Biology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati
| | - Jeffrey Robbins
- Division of Molecular Cardiovascular Biology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati
| | - David F Wieczorek
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati, College of Medicine
| | - R John Solaro
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
| | - Beata M Wolska
- Department of Medicine, Section of Cardiology, University of Illinois, Chicago, IL.,Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois, Chicago, IL
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54
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Rungatscher A, Hallström S, Giacomazzi A, Linardi D, Milani E, Tessari M, Luciani GB, Scarabelli TM, Mazzucco A, Faggian G. Role of calcium desensitization in the treatment of myocardial dysfunction after deep hypothermic circulatory arrest. Crit Care 2013; 17:R245. [PMID: 24138817 PMCID: PMC4056352 DOI: 10.1186/cc13071] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2013] [Accepted: 09/17/2013] [Indexed: 11/10/2022] Open
Abstract
Introduction Rewarming from deep hypothermic circulatory arrest (DHCA) produces calcium desensitization by troponin I (cTnI) phosphorylation which results in myocardial dysfunction. This study investigated the acute overall hemodynamic and metabolic effects of epinephrine and levosimendan, a calcium sensitizer, on myocardial function after rewarming from DHCA. Methods Forty male Wistar rats (400 to 500 g) underwent cardiopulmonary bypass (CPB) through central cannulation and were cooled to a core temperature of 13°C to 15°C within 30 minutes. After DHCA (20 minutes) and CPB-assisted rewarming (60 minutes) rats were randomly assigned to 60 minute intravenous infusion with levosimendan (0.2 μg/kg/min; n = 15), epinephrine (0.1 μg/kg/min; n = 15) or saline (control; n = 10). Systolic and diastolic functions were evaluated at different preloads with a conductance catheter. Results The slope of left ventricular end-systolic pressure volume relationship (Ees) and preload recruitable stroke work (PRSW) recovered significantly better with levosimendan compared to epinephrine (Ees: 85 ± 9% vs 51 ± 11%, P<0.003 and PRSW: 78 ± 5% vs 48 ± 8%, P<0.005; baseline: 100%). Levosimendan but not epinephrine reduced left ventricular stiffness shown by the end-diastolic pressure-volume relationship and improved ventricular relaxation (Tau). Levosimendan preserved ATP myocardial content as well as energy charge and reduced plasma lactate concentrations. In normothermia experiments epinephrine in contrast to Levosimendan increased cTnI phosphorylation 3.5-fold. After rewarming from DHCA, cTnI phosphorylation increased 4.5-fold in the saline and epinephrine group compared to normothermia but remained unchanged with levosimendan. Conclusions Levosimendan due to prevention of calcium desensitization by cTnI phosphorylation is more effective than epinephrine for treatment of myocardial dysfunction after rewarming from DHCA.
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55
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Posttranslational modifications of cardiac troponin T: An overview. J Mol Cell Cardiol 2013; 63:47-56. [DOI: 10.1016/j.yjmcc.2013.07.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Revised: 06/18/2013] [Accepted: 07/08/2013] [Indexed: 12/22/2022]
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Lu QW, Wu XY, Morimoto S. Inherited cardiomyopathies caused by troponin mutations. JOURNAL OF GERIATRIC CARDIOLOGY : JGC 2013; 10:91-101. [PMID: 23610579 PMCID: PMC3627712 DOI: 10.3969/j.issn.1671-5411.2013.01.014] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Revised: 11/13/2012] [Accepted: 01/30/2013] [Indexed: 01/25/2023]
Abstract
Genetic investigations of cardiomyopathy in the recent two decades have revealed a large number of mutations in the genes encoding sarcomeric proteins as a cause of inherited hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), or restrictive cardiomyopathy (RCM). Most functional analyses of the effects of mutations on cardiac muscle contraction have revealed significant changes in the Ca(2+)-regulatory mechanism, in which cardiac troponin (cTn) plays important structural and functional roles as a key regulatory protein. Over a hundred mutations have been identified in all three subunits of cTn, i.e., cardiac troponins T, I, and C. Recent studies on cTn mutations have provided plenty of evidence that HCM- and RCM-linked mutations increase cardiac myofilament Ca(2+) sensitivity, while DCM-linked mutations decrease it. This review focuses on the functional consequences of mutations found in cTn in terms of cardiac myofilament Ca(2+) sensitivity, ATPase activity, force generation, and cardiac troponin I phosphorylation, to understand potential molecular and cellular pathogenic mechanisms of the three types of inherited cardiomyopathy.
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Affiliation(s)
- Qun-Wei Lu
- Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Center for Human Genome Research, Huazhong University of Science and Technology, Wuhan 430074, China
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57
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Henze M, Patrick SE, Hinken A, Scruggs SB, Goldspink P, de Tombe PP, Kobayashi M, Ping P, Kobayashi T, Solaro RJ. New insights into the functional significance of the acidic region of the unique N-terminal extension of cardiac troponin I. BIOCHIMICA ET BIOPHYSICA ACTA 2013; 1833:823-32. [PMID: 22940544 PMCID: PMC3548050 DOI: 10.1016/j.bbamcr.2012.08.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 08/10/2012] [Accepted: 08/18/2012] [Indexed: 11/29/2022]
Abstract
Previous structural studies indicated a special functional role for an acidic region composed of residues 1-10 in the unique N-terminal peptide of cardiac troponin I (cTnI). Employing LC-MS/MS, we determined the presence of phosphorylation sites at S5/S6 in cTnI from wild type mouse hearts as well as in hearts of mice chronically expressing active protein kinase C-ε (PKCε) and exhibiting severe dilated cardiomyopathy (DCM). To determine the functional significance of these phosphorylations, we cloned and expressed wild-type cTnI, (Wt), and cTnI variants expressing pseudo-phosphorylation cTnI-(S5D), cTnI(S6D), as well as cTnI(S5A) and cTnI(S6A). We exchanged native Tn of detergent-extracted (skinned) fiber bundles with Tn reconstituted with the variant cTnIs and measured tension and cross-bridge dynamics. Compared to controls, myofilaments controlled by cTnI with pseudo-phosphorylation (S6D) or Ala substitution (S6A) demonstrated a significant depression in maximum tension, ATPase rate, and ktr, but no change in half-maximally activating Ca(2+). In contrast, pseudo-phosphorylation at position 5 (S5D) had no effects, although S5A induced an increase in Ca(2+)-sensitivity with no change in maximum tension or ktr. We further tested the impact of acidic domain modifications on myofilament function in studies examining the effects of cTnI(A2V), a mutation linked to DCM. This mutation significantly altered the inhibitory activity of cTnI as well as cooperativity of activation of myofilament tension, but not when S23/S24 were pseudo-phosphorylated. Our data indicate a new functional and pathological role of amino acid modifications in the N-terminal acidic domain of cTnI that is modified by phosphorylations at cTnI(S23/S24). This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.
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Affiliation(s)
- Marcus Henze
- Department of Physiology and Biophysics, Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, IL 60612
| | - Stacey E. Patrick
- Department of Physiology and Biophysics, Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, IL 60612
| | - Aaron Hinken
- Department of Physiology and Biophysics, Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, IL 60612
| | - Sarah B. Scruggs
- Departments of Physiology and Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095
| | - Paul Goldspink
- Department of Physiology Medical College of Wisconsin, Milwaukee, WI, 53226
| | - Pieter P. de Tombe
- Department of Cellular and Molecular Physiology, Loyola University, Maywood, IL 60153
| | - Minae Kobayashi
- Department of Physiology and Biophysics, Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, IL 60612
| | - Peipei Ping
- Departments of Physiology and Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095
| | - Tomoyoshi Kobayashi
- Department of Physiology and Biophysics, Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, IL 60612
| | - R. John Solaro
- Department of Physiology and Biophysics, Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, Chicago, IL 60612
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Memo M, Leung MC, Ward DG, dos Remedios C, Morimoto S, Zhang L, Ravenscroft G, McNamara E, Nowak KJ, Marston SB, Messer AE. Familial dilated cardiomyopathy mutations uncouple troponin I phosphorylation from changes in myofibrillar Ca²⁺ sensitivity. Cardiovasc Res 2013; 99:65-73. [PMID: 23539503 DOI: 10.1093/cvr/cvt071] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AIMS The pure form of familial dilated cardiomyopathy (DCM) is mainly caused by mutations in genes encoding sarcomeric proteins. Previous measurements using recombinant proteins suggested that DCM mutations in thin filament proteins decreased myofibrillar Ca(2+) sensitivity, but exceptions were reported. We re-investigated the molecular mechanism of familial DCM using native proteins. METHODS AND RESULTS We used the quantitative in vitro motility assay and native troponin and tropomyosin to study DCM mutations in troponin I, troponin T, and α-tropomyosin. Four mutations reduced myofilament Ca(2+) sensitivity, but one mutation (TPM1 E54K) did not alter Ca(2+) sensitivity and another (TPM1 D230N) increased Ca(2+) sensitivity. In thin filaments from normal human and mouse heart, protein kinase A (PKA) phosphorylation of troponin I caused a two- to three-fold decrease in myofibrillar Ca(2+) sensitivity. However, Ca(2+) sensitivity did not change with the level of troponin I phosphorylation in any of the DCM-mutant containing thin filaments (E40K, E54K, and D230N in α-tropomyosin; R141W and ΔK210 in cardiac troponin T; K36Q in cardiac troponin I; G159D in cardiac troponin C, and E361G in cardiac α-actin). This 'uncoupling' was observed with native mutant protein from human and mouse heart and with recombinant mutant protein expressed in baculovirus/Sf9 systems. Uncoupling was independent of the fraction of mutated protein present above 0.55. CONCLUSION We conclude that DCM-causing mutations in thin filament proteins abolish the relationship between myofilament Ca(2+) sensitivity and troponin I phosphorylation by PKA. We propose that this blunts the response to β-adrenergic stimulation and could be the cause of DCM in the long term.
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Affiliation(s)
- Massimiliano Memo
- Myocardial Function, NHLI, Imperial College London, London, W12 0NN, UK
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Wang H, Chalovich JM, Marriott G. Structural dynamics of troponin I during Ca2+-activation of cardiac thin filaments: a multi-site Förster resonance energy transfer study. PLoS One 2012; 7:e50420. [PMID: 23227172 PMCID: PMC3515578 DOI: 10.1371/journal.pone.0050420] [Citation(s) in RCA: 10] [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: 08/08/2012] [Accepted: 10/23/2012] [Indexed: 12/20/2022] Open
Abstract
A multi-site, steady-state Förster resonance energy transfer (FRET) approach was used to quantify Ca2+-induced changes in proximity between donor loci on human cardiac troponin I (cTnI), and acceptor loci on human cardiac tropomyosin (cTm) and F-actin within functional thin filaments. A fluorescent donor probe was introduced to unique and key cysteine residues on the C- and N-termini of cTnI. A FRET acceptor probe was introduced to one of three sites located on the inner or outer domain of F-actin, namely Cys-374 and the phalloidin-binding site on F-actin, and Cys-190 of cTm. Unlike earlier FRET analyses of protein dynamics within the thin filament, this study considered the effects of non-random distribution of dipoles for the donor and acceptor probes. The major conclusion drawn from this study is that Ca2+ and myosin S1-binding to the thin filament results in movement of the C-terminal domain of cTnI from the outer domain of F-actin towards the inner domain, which is associated with the myosin-binding. A hinge-linkage model is used to best-describe the finding of a Ca2+-induced movement of the C-terminus of cTnI with a stationary N-terminus. This dynamic model of the activation of the thin filament is discussed in the context of other structural and biochemical studies on normal and mutant cTnI found in hypertrophic cardiomyopathies.
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Affiliation(s)
- Hui Wang
- Department of Pharmacology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina, United States of America
| | - Joseph M. Chalovich
- Department of Biochemistry and Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States of America
| | - Gerard Marriott
- Department of Bioengineering, University of California, Berkeley, California, United States of America
- * E-mail:
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Bayliss CR, Jacques AM, Leung MC, Ward DG, Redwood CS, Gallon CE, Copeland O, McKenna WJ, Dos Remedios C, Marston SB, Messer AE. Myofibrillar Ca(2+) sensitivity is uncoupled from troponin I phosphorylation in hypertrophic obstructive cardiomyopathy due to abnormal troponin T. Cardiovasc Res 2012; 97:500-8. [PMID: 23097574 DOI: 10.1093/cvr/cvs322] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AIMS We studied the relationship between myofilament Ca(2+) sensitivity and troponin I (TnI) phosphorylation by protein kinase A at serines 22/23 in human heart troponin isolated from donor hearts and from myectomy samples from patients with hypertrophic obstructive cardiomyopathy (HOCM). METHODS AND RESULTS We used a quantitative in vitro motility assay. With donor heart troponin, Ca(2+) sensitivity is two- to three-fold higher when TnI is unphosphorylated. In the myectomy samples from patients with HOCM, the mean level of TnI phosphorylation was low: 0.38 ± 0.19 mol Pi/mol TnI compared with 1.60 ± 0.19 mol Pi/mol TnI in donor hearts, but no difference in myofilament Ca(2+) sensitivity was observed. Thus, troponin regulation of thin filament Ca(2+) sensitivity is abnormal in HOCM hearts. HOCM troponin (0.29 mol Pi/mol TnI) was treated with protein kinase A to increase the level of phosphorylation to 1.56 mol Pi/mol TnI. No difference in EC(50) was found in thin filaments containing high and low TnI phosphorylation levels. This indicates that Ca(2+) sensitivity is uncoupled from TnI phosphorylation in HOCM heart troponin. Coupling could be restored by replacing endogenous troponin T (TnT) with the recombinant TnT T3 isoform. No difference in Ca(2+) sensitivity was observed if TnI was exchanged into HOCM heart troponin or if TnT was exchanged into the highly phosphorylated donor heart troponin. Comparison of donor and HOCM heart troponin by mass spectrometry and with adduct-specific antibodies did not show any differences in TnT isoform expression, phosphorylation or any post-translational modifications. CONCLUSION An abnormality in TnT is responsible for uncoupling myofibrillar Ca(2+) sensitivity from TnI phosphorylation in the septum of HOCM patients.
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Affiliation(s)
- Christopher R Bayliss
- Myocardial Function, NHLI, Imperial Centre for Translational and Experimental Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
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Zhang L, Song Z, Chang H, Wang YY, Yu ZB. Enhanced N-terminal degradation of troponin I blunts cardiac function responsiveness to isoproterenol in 4-week tail-suspended rats. Mol Med Rep 2012; 7:271-9. [PMID: 23042367 DOI: 10.3892/mmr.2012.1119] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2012] [Accepted: 10/01/2012] [Indexed: 11/05/2022] Open
Abstract
The N-terminal extension of cardiac troponin I (cTnI) is important in regulating cardiac function. Although the normal rat myocardium shows some cTnI N-terminal degradation (cTnI-ND), exposure to 4 weeks of tail-suspension markedly increased cTnI-ND. We hypothesized that the increased cTnI-ND in tail-suspended rats may affect cardiac function, particularly during β-adrenergic (β-A) stimulation. The increase in cardiac output with isoproterenol (ISO) treatment was smaller in tail-suspended rats compared with controls. Left ventricular end-diastolic pressure was elevated and increases in maximal rates of left ventricular pressure development and relaxation were lower during ISO treatment in tail-suspended rats. Response to ISO, forskolin, DB-cAMP and IBMX was also lower in cardiomyocytes from tail-suspended rats. The increase in shortening and re-lengthening the rates of cardiomyocytes at a maximal dose of ISO, forskolin, DB-cAMP and IBMX treatment was limited in tail-suspended rats. There was no difference in Ca2+ sensitivity of the isometric force between tail-suspended and control rats, although Ca2+ sensitivity was decreased less in tail-suspended rats versus control rats during PKA phosphorylation. There was no difference in PKA protein expression and activation during ISO stimulation between the two groups. Due to the increase in cTnI-ND, ISO-induced phosphorylation of cTnI was reduced in tail-suspended rats. The total phospholamban expression and phosphorylation by ISO was unaltered in tail-suspended rat hearts. These data suggest that enhanced cTnI-ND following 4-week tail-suspension is a major component of the β-A receptor signaling pathway, depressing cardiac function under ISO stimulation.
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Affiliation(s)
- Lin Zhang
- Department of Aerospace Physiology, Fourth Military Medical University, Xi'an 710032, PR China
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Donaldson C, Palmer BM, Zile M, Maughan DW, Ikonomidis JS, Granzier H, Meyer M, VanBuren P, LeWinter MM. Myosin cross-bridge dynamics in patients with hypertension and concentric left ventricular remodeling. Circ Heart Fail 2012; 5:803-11. [PMID: 23014131 DOI: 10.1161/circheartfailure.112.968925] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Hypertension (HTN) causes concentric left ventricular remodeling, defined as an increased relative wall thickness or overt left ventricular hypertrophy, and associated diastolic dysfunction. HTN and concentric remodeling are also common precursors to heart failure with a preserved ejection fraction. It is not known whether the myofilament contributes to diastolic dysfunction in patients with concentric remodeling. METHODS AND RESULTS Intraoperative myocardial biopsies were obtained in 15 male patients undergoing coronary bypass grafting, all with normal left ventricular ejection fraction and wall motion. Eight patients had a history of HTN and concentric remodeling. Seven without HTN or remodeling served as controls. Myocardial strips were dissected and demembranated with detergent. Isometric tension was measured and sinusoidal length perturbation analysis performed at sarcomere length 2.2 μm and pCa 8 to 4.5. Sinusoidal analysis provides estimates of cross-bridge dynamics, including rate constants of attachment and detachment and cross-bridge attachment time. The normalized isometric tension-pCa relation was similar in HTN and controls. However, cross-bridge attachment time was significantly prolonged at submaximal [Ca(2+)] (pCa ≥6.5) in HTN patients. Analysis of protein phosphorylation revealed ≈25% reduction in phosphorylation of troponin I in HTN patients (P<0.05). CONCLUSIONS Compared with controls, patients with HTN and concentric remodeling display prolonged cross-bridge attachment time at submaximal [Ca(2+)] without a change in the tension-pCa relation. Prolonged cross-bridge attachment time implicates altered cross-bridge dynamics as a cause of slowed relaxation in these patients. This finding was associated with reduced phosphorylation of troponin I, suggesting decreased phosphorylation of protein kinase A/G sites as a mechanism.
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63
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A PagP fusion protein system for the expression of intrinsically disordered proteins in Escherichia coli. Protein Expr Purif 2012; 85:148-51. [PMID: 22841980 DOI: 10.1016/j.pep.2012.07.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Revised: 07/13/2012] [Accepted: 07/16/2012] [Indexed: 11/21/2022]
Abstract
PagP, a beta-barrel membrane protein found in Gram-negative bacteria, expresses robustly in inclusion bodies when its signal sequence is removed. We have developed a new fusion protein expression system based on PagP and demonstrated its utility in the expression of the unstructured N-terminal region of human cardiac troponin I (residues 1-71). A yield of 100mg fusion protein per liter M9 minimal media was obtained. The troponin I fragment was removed from PagP using cyanogen bromide cleavage at methionine residues followed by nickel affinity chromatography. We further demonstrate that optimal cleavage requires complete reduction of methionine residues prior to cyanogen bromide treatment, and this is effectively accomplished using potassium iodide under acidic conditions. The PagP-based fusion protein system is more effective at targeting proteins into inclusion bodies than a commercially available system that uses ketosteroid isomerase; it thus represents an important advance for producing large quantities of unfolded peptides or proteins in Escherichia coli.
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64
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Clause KC, Tchao J, Powell MC, Liu LJ, Huard J, Keller BB, Tobita K. Developing cardiac and skeletal muscle share fast-skeletal myosin heavy chain and cardiac troponin-I expression. PLoS One 2012; 7:e40725. [PMID: 22808244 PMCID: PMC3393685 DOI: 10.1371/journal.pone.0040725] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2011] [Accepted: 06/14/2012] [Indexed: 01/26/2023] Open
Abstract
Skeletal muscle derived stem cells (MDSCs) transplanted into injured myocardium can differentiate into fast skeletal muscle specific myosin heavy chain (sk-fMHC) and cardiac specific troponin-I (cTn-I) positive cells sustaining recipient myocardial function. We have recently found that MDSCs differentiate into a cardiomyocyte phenotype within a three-dimensional gel bioreactor. It is generally accepted that terminally differentiated myocardium or skeletal muscle only express cTn-I or sk-fMHC, respectively. Studies have shown the presence of non-cardiac muscle proteins in the developing myocardium or cardiac proteins in pathological skeletal muscle. In the current study, we tested the hypothesis that normal developing myocardium and skeletal muscle transiently share both sk-fMHC and cTn-I proteins. Immunohistochemistry, western blot, and RT-PCR analyses were carried out in embryonic day 13 (ED13) and 20 (ED20), neonatal day 0 (ND0) and 4 (ND4), postnatal day 10 (PND10), and 8 week-old adult female Lewis rat ventricular myocardium and gastrocnemius muscle. Confocal laser microscopy revealed that sk-fMHC was expressed as a typical striated muscle pattern within ED13 ventricular myocardium, and the striated sk-fMHC expression was lost by ND4 and became negative in adult myocardium. cTn-I was not expressed as a typical striated muscle pattern throughout the myocardium until PND10. Western blot and RT-PCR analyses revealed that gene and protein expression patterns of cardiac and skeletal muscle transcription factors and sk-fMHC within ventricular myocardium and skeletal muscle were similar at ED20, and the expression patterns became cardiac or skeletal muscle specific during postnatal development. These findings provide new insight into cardiac muscle development and highlight previously unknown common developmental features of cardiac and skeletal muscle.
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Affiliation(s)
- Kelly C. Clause
- Cardiovascular Development Research Program, Children’s Hospital of Pittsburgh of University of Pittsburgh Medical Center, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Jason Tchao
- Cardiovascular Development Research Program, Children’s Hospital of Pittsburgh of University of Pittsburgh Medical Center, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Mary C. Powell
- Cardiovascular Development Research Program, Children’s Hospital of Pittsburgh of University of Pittsburgh Medical Center, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Li J. Liu
- Cardiovascular Development Research Program, Children’s Hospital of Pittsburgh of University of Pittsburgh Medical Center, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Department of Developmental Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Johnny Huard
- Department of Orthopedic Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- McGowan Institutes for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Bradley B. Keller
- Department of Pediatrics, University of Louisville, Louisville, Kentucky, United States of America
| | - Kimimasa Tobita
- Cardiovascular Development Research Program, Children’s Hospital of Pittsburgh of University of Pittsburgh Medical Center, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Department of Developmental Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- McGowan Institutes for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- * E-mail:
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65
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Albury ANJ, Swindle N, Swartz DR, Tikunova SB. Effect of hypertrophic cardiomyopathy-linked troponin C mutations on the response of reconstituted thin filaments to calcium upon troponin I phosphorylation. Biochemistry 2012; 51:3614-21. [PMID: 22489623 DOI: 10.1021/bi300187k] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The objective of this work was to investigate the effect of hypertrophic cardiomyopathy-linked A8V and E134D mutations in cardiac troponin C (cTnC) on the response of reconstituted thin filaments to calcium upon phosphorylation of cardiac troponin I (cTnI) by protein kinase A. The phosphorylation of cTnI at protein kinase A sites was mimicked by the S22D/S23D double mutation in cTnI. Our results demonstrate that the A8V and E134D mutations had no effect on the extent of calcium desensitization of reconstituted thin filaments induced by cTnI pseudophosphorylation. However, the A8V mutation enhanced the effect of cTnI pseudophosphorylation on the rate of dissociation of calcium from reconstituted thin filaments and on the calcium dependence of actomyosin ATPase. Consequently, while the A8V mutation still led to a slower rate of dissociation of calcium from reconstituted thin filaments upon pseudophosphorylation of cTnI, the ability of the A8V mutation to decrease the rate of calcium dissociation was weakened. In addition, the ability of the A8V mutation to sensitize actomyosin ATPase to calcium was weakened after cTnI was replaced by the phosphorylation mimetic of cTnI. Consistent with the hypothesis that the E134D mutation is benign, it exerted a minor to no effect on the rate of dissociation of calcium from reconstituted thin filaments or on the calcium sensitivity of actomyosin ATPase, regardless of the cTnI phosphorylation status. In conclusion, our study enhances our understanding of how cardiomyopathy-linked cTnC mutations affect the response of reconstituted thin filaments to calcium upon cTnI phosphorylation.
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Affiliation(s)
- Acchia N J Albury
- Department of Biology, Wingate University, Wingate, North Carolina 28174, United States
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66
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Zhang H, Ge Y. Comprehensive analysis of protein modifications by top-down mass spectrometry. ACTA ACUST UNITED AC 2012; 4:711. [PMID: 22187450 DOI: 10.1161/circgenetics.110.957829] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Mass spectrometry (MS)-based proteomics is playing an increasingly important role in cardiovascular research. Proteomics includes identification and quantification of proteins and the characterization of protein modifications, such as posttranslational modifications and sequence variants. The conventional bottom-up approach, involving proteolytic digestion of proteins into small peptides before MS analysis, is routinely used for protein identification and quantification with high throughput and automation. Nevertheless, it has limitations in the analysis of protein modifications, mainly because of the partial sequence coverage and loss of connections among modifications on disparate portions of a protein. An alternative approach, top-down MS, has emerged as a powerful tool for the analysis of protein modifications. The top-down approach analyzes whole proteins directly, providing a "bird's-eye" view of all existing modifications. Subsequently, each modified protein form can be isolated and fragmented in the mass spectrometer to locate the modification site. The incorporation of the nonergodic dissociation methods, such as electron-capture dissociation (ECD), greatly enhances the top-down capabilities. ECD is especially useful for mapping labile posttranslational modifications that are well preserved during the ECD fragmentation process. Top-down MS with ECD has been successfully applied to cardiovascular research, with the unique advantages in unraveling the molecular complexity, quantifying modified protein forms, complete mapping of modifications with full-sequence coverage, discovering unexpected modifications, identifying and quantifying positional isomers, and determining the order of multiple modifications. Nevertheless, top-down MS still needs to overcome some technical challenges to realize its full potential. Herein, we reviewed the advantages and challenges of the top-down method, with a focus on its application in cardiovascular research.
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Affiliation(s)
- Han Zhang
- Department of Physiology, School of Medicine and Public Health, University of Wisconsin-Madison, USA
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67
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Maharaj R. Diastolic dysfunction and heart failure with a preserved ejection fraction: Relevance in critical illness and anaesthesia. J Saudi Heart Assoc 2012; 24:99-121. [PMID: 23960679 DOI: 10.1016/j.jsha.2012.01.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2011] [Revised: 01/22/2012] [Accepted: 01/23/2012] [Indexed: 01/19/2023] Open
Abstract
Epidemiological and clinical studies suggest that HF with a preserved ejection fraction will become the more common form of HF which clinicians will encounter. The spectrum of diastolic disease extends from the asymptomatic phase to fulminant cardiac failure. These patients are commonly encountered in operating rooms and critical care units. A clearer understanding of the underlying pathophysiology and clinical implications of HF with a preserved ejection fraction is fundamental to directing further research and to evaluate interventions. This review highlights the impact of diastolic dysfunction and HF with a preserved ejection fraction during the perioperative period and during critical illness.
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Affiliation(s)
- R Maharaj
- Department of Intensive Care Medicine, Kings College Hospital, London SE5 9RS, UK
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van den Wijngaard A, Volders P, Van Tintelen JP, Jongbloed JDH, van den Berg MP, Lekanne Deprez RH, Mannens MMAM, Hofmann N, Slegtenhorst M, Dooijes D, Michels M, Arens Y, Jongbloed R, Smeets BJM. Recurrent and founder mutations in the Netherlands: cardiac Troponin I (TNNI3) gene mutations as a cause of severe forms of hypertrophic and restrictive cardiomyopathy. Neth Heart J 2011; 19:344-51. [PMID: 21533915 PMCID: PMC3144325 DOI: 10.1007/s12471-011-0135-z] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
BACKGROUND About 2-7% of familial cardiomyopathy cases are caused by a mutation in the gene encoding cardiac troponin I (TNNI3). The related clinical phenotype is usually severe with early onset. Here we report on all currently known mutations in the Dutch population and compared these with those described in literature. METHODS TheTNNI3 gene was screened for mutations in all coding exons and flanking intronic sequences in a large cohort of cardiomyopathy patients. All Dutch index cases carrying a TNNI3 mutation that are described in this study underwent extensive cardiological evaluation and were listed by their postal codes. RESULTS In 30 families, 14 different mutations were identified. Three TNNI3 mutations were found relatively frequently in both familial and non-familial cases of hypertrophic cardiomyopathy (HCM) or restrictive cardiomyopathy (RCM). Haplotype analysis showed that p.Arg145Trp and p.Ser166Phe are founder mutations in the Netherlands, while p.Glu209Ala is not. The majority of Dutch TNNI3 mutations were associated with a HCM phenotype. Mean age at diagnosis was 36.5 years. Mutations causing RCM occurred less frequently, but were identified in very young children with a poor prognosis. CONCLUSION In line with previously published data, we found TNNI3 mutations to be rare and associated with early onset and severe clinical presentation.
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Affiliation(s)
- A van den Wijngaard
- Department of Clinical Genetics, Maastricht University Medical Center, Maastricht, the Netherlands,
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Dong X, Sumandea CA, Chen YC, Garcia-Cazarin ML, Zhang J, Balke CW, Sumandea MP, Ge Y. Augmented phosphorylation of cardiac troponin I in hypertensive heart failure. J Biol Chem 2011; 287:848-57. [PMID: 22052912 DOI: 10.1074/jbc.m111.293258] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
An altered cardiac myofilament response to activating Ca(2+) is a hallmark of human heart failure. Phosphorylation of cardiac troponin I (cTnI) is critical in modulating contractility and Ca(2+) sensitivity of cardiac muscle. cTnI can be phosphorylated by protein kinase A (PKA) at Ser(22/23) and protein kinase C (PKC) at Ser(22/23), Ser(42/44), and Thr(143). Whereas the functional significance of Ser(22/23) phosphorylation is well understood, the role of other cTnI phosphorylation sites in the regulation of cardiac contractility remains a topic of intense debate, in part, due to the lack of evidence of in vivo phosphorylation. In this study, we utilized top-down high resolution mass spectrometry (MS) combined with immunoaffinity chromatography to determine quantitatively the cTnI phosphorylation changes in spontaneously hypertensive rat (SHR) model of hypertensive heart disease and failure. Our data indicate that cTnI is hyperphosphorylated in the failing SHR myocardium compared with age-matched normotensive Wistar-Kyoto rats. The top-down electron capture dissociation MS unambiguously localized augmented phosphorylation sites to Ser(22/23) and Ser(42/44) in SHR. Enhanced Ser(22/23) phosphorylation was verified by immunoblotting with phospho-specific antibodies. Immunoblot analysis also revealed up-regulation of PKC-α and -δ, decreased PKCε, but no changes in PKA or PKC-β levels in the SHR myocardium. This provides direct evidence of in vivo phosphorylation of cTnI-Ser(42/44) (PKC-specific) sites in an animal model of hypertensive heart failure, supporting the hypothesis that PKC phosphorylation of cTnI may be maladaptive and potentially associated with cardiac dysfunction.
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Affiliation(s)
- Xintong Dong
- Human Proteomics Program, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706, USA
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71
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Kirkpatrick KP, Robertson AS, Klaiman JM, Gillis TE. The influence of trout cardiac troponin I and PKA phosphorylation on the Ca2+ affinity of the cardiac troponin complex. ACTA ACUST UNITED AC 2011; 214:1981-8. [PMID: 21613513 DOI: 10.1242/jeb.052860] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The trout heart is 10-fold more sensitive to Ca(2+) than the mammalian heart. This difference is due, in part, to cardiac troponin C (cTnC) from trout having a greater Ca(2+) affinity than human cTnC. To determine what other proteins are involved, we cloned cardiac troponin I (cTnI) from the trout heart and determined how it alters the Ca(2+) affinity of a cTn complex containing all mammalian components (mammalian cTn). Ca(2+) activation of the complex was characterized using a human cTnC mutant that contains anilinonapthalenesulfote iodoacetamide attached to Cys53. When the cTn complex containing labeled human cTnC was titrated with Ca(2+), its fluorescence changed, reaching an asymptote upon saturation. Our results reveal that trout cTnI lacks the N-terminal extension found in cTnI from all other vertebrate groups. This protein domain contains two targets (Ser23 and Ser24) for protein kinase A (PKA) and protein kinase C. When these are phosphorylated, the rate of cardiomyocyte relaxation increases. When rat cTnI in the mammalian cTn complex was replaced with trout cTnI, the Ca(2+) affinity was increased ∼1.8-fold. This suggests that trout cTnI contributes to the high Ca(2+) sensitivity of the trout heart. Treatment of the two cTn complexes with PKA decreased the Ca(2+) affinity of both complexes. However, the change for the complex containing rat cTnI was 2.2-fold that of the complex containing trout cTnI. This suggests that the phosphorylation of trout cTnI does not play as significant a role in regulating cTn function in trout.
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Affiliation(s)
- Kelly P Kirkpatrick
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1
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Zhang Z, Akhter S, Mottl S, Jin JP. Calcium-regulated conformational change in the C-terminal end segment of troponin I and its binding to tropomyosin. FEBS J 2011; 278:3348-59. [PMID: 21777381 DOI: 10.1111/j.1742-4658.2011.08250.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The troponin complex plays an essential role in the thin filament regulation of striated muscle contraction. Of the three subunits of troponin, troponin I (TnI) is the actomyosin ATPase inhibitory subunit and its effect is released upon Ca(2+) binding to troponin C. The exon-8-encoded C-terminal end segment represented by the last 24 amino acids of cardiac TnI is highly conserved and is critical to the inhibitory function of troponin. Here, we investigated the function and calcium regulation of the C-terminal end segment of TnI. A TnI model molecule was labeled with Alexa Fluor 532 at a Cys engineered at the C-terminal end and used to reconstitute the tertiary troponin complex. A Ca(2+) -regulated conformational change in the C-terminus of TnI was shown by a sigmoid-shape fluorescence intensity titration curve similar to that of the CD calcium titration curve of troponin C. Such corresponding Ca(2+) responses are consistent with the function of troponin as a coordinated molecular switch. Reconstituted troponin complex containing a mini-troponin T lacking its two tropomyosin-binding sites showed a saturable binding to tropomyosin at pCa 9 but not at pCa 4. This Ca(2+) -regulated binding was diminished when the C-terminal 19 amino acids of cardiac TnI were removed. These results provided novel evidence for suggesting that the C-terminal end segment of TnI participates in the Ca(2+) regulation of muscle thin filament through interaction with tropomyosin.
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Affiliation(s)
- Zhiling Zhang
- Evanston Northwestern Healthcare and Northwestern University, Evanston, IL, USA
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73
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Zhang J, Guy MJ, Norman HS, Chen YC, Xu Q, Dong X, Guner H, Wang S, Kohmoto T, Young KH, Moss RL, Ge Y. Top-down quantitative proteomics identified phosphorylation of cardiac troponin I as a candidate biomarker for chronic heart failure. J Proteome Res 2011; 10:4054-65. [PMID: 21751783 DOI: 10.1021/pr200258m] [Citation(s) in RCA: 146] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The rapid increase in the prevalence of chronic heart failure (CHF) worldwide underscores an urgent need to identify biomarkers for the early detection of CHF. Post-translational modifications (PTMs) are associated with many critical signaling events during disease progression and thus offer a plethora of candidate biomarkers. We have employed a top-down quantitative proteomics methodology for comprehensive assessment of PTMs in whole proteins extracted from normal and diseased tissues. We systematically analyzed 36 clinical human heart tissue samples and identified phosphorylation of cardiac troponin I (cTnI) as a candidate biomarker for CHF. The relative percentages of the total phosphorylated cTnI forms over the entire cTnI populations (%P(total)) were 56.4 ± 3.5%, 36.9 ± 1.6%, 6.1 ± 2.4%, and 1.0 ± 0.6% for postmortem hearts with normal cardiac function (n = 7), early stage of mild hypertrophy (n = 5), severe hypertrophy/dilation (n = 4), and end-stage CHF (n = 6), respectively. In fresh transplant samples, the %P(total) of cTnI from nonfailing donor (n = 4), and end-stage failing hearts (n = 10) were 49.5 ± 5.9% and 18.8 ± 2.9%, respectively. Top-down MS with electron capture dissociation unequivocally localized the altered phosphorylation sites to Ser22/23 and determined the order of phosphorylation/dephosphorylation. This study represents the first clinical application of top-down MS-based quantitative proteomics for biomarker discovery from tissues, highlighting the potential of PTMs as disease biomarkers.
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Affiliation(s)
- Jiang Zhang
- School of Medicine and Public Health and School of Pharmacy, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
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74
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Zhang J, Zhang H, Ayaz-Guner S, Chen YC, Dong X, Xu Q, Ge Y. Phosphorylation, but not alternative splicing or proteolytic degradation, is conserved in human and mouse cardiac troponin T. Biochemistry 2011; 50:6081-92. [PMID: 21639091 DOI: 10.1021/bi2006256] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Cardiac troponin T (cTnT), the tropomyosin binding subunit of the troponin complex, plays a pivotal regulatory role in the Ca(2+)-mediated interaction between actin thin filament and myosin thick filament. The post-translational modifications (PTMs) and alternative splicing of cTnT may represent important regulatory mechanisms of cardiac contractility. However, a complete characterization of PTMs and alternatively spliced isoforms in cTnT present in vivo is lacking. Top-down protein mass spectrometry (MS) analyzes whole proteins, thus providing a global view of all types of modifications, including PTMs and sequence variants, simultaneously in one spectrum without a priori knowledge. In this study, we applied an integrated immunoaffinity chromatography and top-down MS approach to comprehensively characterize PTMs and alternatively spliced isoforms of cTnT purified from healthy human and wild-type mouse heart tissue. High-resolution Fourier transform MS revealed that human cTnT (hcTnT) and mouse cTnT (mcTnT) have similar phosphorylation patterns, whereas higher molecular heterogeneity was observed for mcTnT than hcTnT. Further MS/MS fragmentation of monophosphorylated hcTnT and mcTnT by electron capture dissociation and collisionally activated dissociation unambiguously identified Ser1 as the conserved in vivo phosphorylation site. In contrast, we identified a single spliced isoform for hcTnT but three alternatively spliced isoforms for mcTnT. Moreover, we observed distinct proteolytic degradation products for hcTnT and mcTnT. This study also demonstrates the advantage of top-down MS/MS with complementary fragmentation techniques for the identification of modification sites in the highly acidic N-terminal region of cTnT.
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Affiliation(s)
- Jiang Zhang
- Human Proteomics Program, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706, USA
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75
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Gillis TE, Klaiman JM. The influence of PKA treatment on the Ca2+ activation of force generation by trout cardiac muscle. J Exp Biol 2011; 214:1989-96. [DOI: 10.1242/jeb.052084] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
β-Adrenergic stimulation of the mammalian heart increases heart rate, the strength of contraction as well as the kinetics of force generation and relaxation. These effects are due to the phosphorylation of select membrane and thin filament proteins by cAMP-activated protein kinase (PKA). At the level of the sarcomere, it is typically the phosphorylation of cardiac myosin binding protein C (cMyBP-C) and cardiac troponin I (cTnI) that is responsible for the change in the kinetics of contraction and relaxation. Trout cTnI (ScTnI) lacks two critical PKA targets within the N-terminus of the protein that, when phosphorylated in mammalian cTnI, cause a reduction in myofilament Ca2+ affinity. To determine what role the contractile element plays in the response of the trout heart to β-adrenergic stimulation, we characterized the influence of PKA treatment on the Ca2+ activation of skinned preparations dissected from ventricular trabeculae. In these experiments, isometric force generation and the rate of force development were measured over a range of Ca2+ concentrations. The results demonstrate that PKA treatment does not influence the Ca2+ sensitivity of force generation but it decreases maximum force generation by 25% and the rate of force re-development at maximal activation by 46%. Analysis of the trabeculae preparations for phosphoproteins revealed that PKA treatment phosphorylated myosin light chain 2 but not cTnI or cMyBP-C. These results indicate that the function of the trout cardiac contractile element is altered by PKA phosphorylation but in a manner different from that in mammalian heart.
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Affiliation(s)
- Todd E. Gillis
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1
| | - Jordan M. Klaiman
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1
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76
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Sancho Solis R, Ge Y, Walker JW. A preferred AMPK phosphorylation site adjacent to the inhibitory loop of cardiac and skeletal troponin I. Protein Sci 2011; 20:894-907. [PMID: 21416543 PMCID: PMC3125873 DOI: 10.1002/pro.623] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2010] [Revised: 03/01/2011] [Accepted: 03/07/2011] [Indexed: 12/15/2022]
Abstract
5'-AMP-activated protein kinase (AMPK) is a serine/threonine protein kinase that is activated when cellular AMP to ATP ratios rise, potentially serving as a key regulator of cellular energetics. Among the known targets of AMPK are catabolic and anabolic enzymes, but little is known about the ability of this kinase to phosphorylate myofilament proteins and thereby regulating the contractile apparatus of striated muscles. Here, we demonstrate that troponin I isoforms of cardiac (cTnI) and fast skeletal (fsTnI) muscles are readily phosphorylated by AMPK. For cTnI, two highly conserved serine residues were identified as AMPK sites using a combination of high-resolution top-down electron capture dissociation mass spectrometry, (32) P-incorporation, synthetic peptides, phospho-specific antibodies, and site-directed mutagenesis. These AMPK sites in cTnI were Ser149 adjacent to the inhibitory loop and Ser22 in the cardiac-specific N-terminal extension, at the level of cTnI peptides, the intact cTnI subunit, whole cardiac troponin complexes and skinned cardiomyocytes. Phosphorylation time-course experiments revealed that Ser149 was the preferred site, because it was phosphorylated 12-16-fold faster than Ser22 in cTnI. Ser117 in fsTnI, analogous to Ser149 in cTnI, was phosphorylated with similar kinetics as cTnI Ser149. Hence, the master energy-sensing protein AMPK emerges as a possibly important regulator of cardiac and skeletal contractility via phosphorylation of a preferred site adjacent to the inhibitory loop of the thin filament protein TnI.
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Affiliation(s)
- Raquel Sancho Solis
- Department of Physiology, School of Medicine and Public Health, University of Wisconsin-MadisonWI 53706
| | - Ying Ge
- Department of Physiology, School of Medicine and Public Health, University of Wisconsin-MadisonWI 53706
- Human Proteomics Program, School of Medicine and Public Health, University of Wisconsin-MadisonWI 53706
| | - Jeffery W Walker
- Department of Physiology, University of ArizonaTucson, Arizona 85724
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Christian F, Szaszák M, Friedl S, Drewianka S, Lorenz D, Goncalves A, Furkert J, Vargas C, Schmieder P, Götz F, Zühlke K, Moutty M, Göttert H, Joshi M, Reif B, Haase H, Morano I, Grossmann S, Klukovits A, Verli J, Gáspár R, Noack C, Bergmann M, Kass R, Hampel K, Kashin D, Genieser HG, Herberg FW, Willoughby D, Cooper DMF, Baillie GS, Houslay MD, von Kries JP, Zimmermann B, Rosenthal W, Klussmann E. Small molecule AKAP-protein kinase A (PKA) interaction disruptors that activate PKA interfere with compartmentalized cAMP signaling in cardiac myocytes. J Biol Chem 2011; 286:9079-96. [PMID: 21177871 PMCID: PMC3058960 DOI: 10.1074/jbc.m110.160614] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2010] [Revised: 12/12/2010] [Indexed: 12/22/2022] Open
Abstract
A-kinase anchoring proteins (AKAPs) tether protein kinase A (PKA) and other signaling proteins to defined intracellular sites, thereby establishing compartmentalized cAMP signaling. AKAP-PKA interactions play key roles in various cellular processes, including the regulation of cardiac myocyte contractility. We discovered small molecules, 3,3'-diamino-4,4'-dihydroxydiphenylmethane (FMP-API-1) and its derivatives, which inhibit AKAP-PKA interactions in vitro and in cultured cardiac myocytes. The molecules bind to an allosteric site of regulatory subunits of PKA identifying a hitherto unrecognized region that controls AKAP-PKA interactions. FMP-API-1 also activates PKA. The net effect of FMP-API-1 is a selective interference with compartmentalized cAMP signaling. In cardiac myocytes, FMP-API-1 reveals a novel mechanism involved in terminating β-adrenoreceptor-induced cAMP synthesis. In addition, FMP-API-1 leads to an increase in contractility of cultured rat cardiac myocytes and intact hearts. Thus, FMP-API-1 represents not only a novel means to study compartmentalized cAMP/PKA signaling but, due to its effects on cardiac myocytes and intact hearts, provides the basis for a new concept in the treatment of chronic heart failure.
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Affiliation(s)
- Frank Christian
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Márta Szaszák
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Sabine Friedl
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Stephan Drewianka
- Biaffin GmbH & Co. KG, AVZ 2, Heinrich-Plett-Strasse 40, 34132 Kassel, Germany
| | - Dorothea Lorenz
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Andrey Goncalves
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Jens Furkert
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Carolyn Vargas
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Peter Schmieder
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Frank Götz
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Kerstin Zühlke
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Marie Moutty
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Hendrikje Göttert
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Mangesh Joshi
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Bernd Reif
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Hannelore Haase
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Ingo Morano
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Solveig Grossmann
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Anna Klukovits
- the Department of Pharmacodynamics and Biopharmacy, University of Szeged, H-6720 Szeged, Eötvös u. 6., Hungary
| | - Judit Verli
- the Department of Pharmacodynamics and Biopharmacy, University of Szeged, H-6720 Szeged, Eötvös u. 6., Hungary
| | - Róbert Gáspár
- the Department of Pharmacodynamics and Biopharmacy, University of Szeged, H-6720 Szeged, Eötvös u. 6., Hungary
| | - Claudia Noack
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Martin Bergmann
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Robert Kass
- Columbia University Medical Center, New York, New York 10032
| | - Kornelia Hampel
- Biaffin GmbH & Co. KG, AVZ 2, Heinrich-Plett-Strasse 40, 34132 Kassel, Germany
| | - Dmitry Kashin
- Biolog Life Science Institute, Flughafendamm 9A, 28199 Bremen, Germany
| | | | - Friedrich W. Herberg
- the Department of Biochemistry, University of Kassel, Heinrich-Plett-Strasse 40, 34109 Kassel, Germany
| | - Debbie Willoughby
- the Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1 PD, United Kingdom
| | - Dermot M. F. Cooper
- the Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1 PD, United Kingdom
| | - George S. Baillie
- Neuroscience and Molecular Pharmacology, Wolfson Link and Davidson Buildings, University of Glasgow, University Avenue, Glasgow G12 8QQ, United Kingdom, and
| | - Miles D. Houslay
- Neuroscience and Molecular Pharmacology, Wolfson Link and Davidson Buildings, University of Glasgow, University Avenue, Glasgow G12 8QQ, United Kingdom, and
| | - Jens Peter von Kries
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
| | - Bastian Zimmermann
- Biaffin GmbH & Co. KG, AVZ 2, Heinrich-Plett-Strasse 40, 34132 Kassel, Germany
| | - Walter Rosenthal
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
- Molecular Pharmacology and Cell Biology, Charité-University Medicine Berlin, Thielallee 73, 14195 Berlin, Germany
| | - Enno Klussmann
- From the Leibniz Institute for Molecular Pharmacology, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13125 Berlin, Germany
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78
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Moss RL, Fitzsimons DP. Regulation of contraction in mammalian striated muscles--the plot thick-ens. ACTA ACUST UNITED AC 2011; 136:21-7. [PMID: 20584889 PMCID: PMC2894544 DOI: 10.1085/jgp.201010471] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Richard L Moss
- Department of Physiology and Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, USA.
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79
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Agnetti G, Husberg C, Van Eyk JE. Divide and conquer: the application of organelle proteomics to heart failure. Circ Res 2011; 108:512-26. [PMID: 21335433 PMCID: PMC3936251 DOI: 10.1161/circresaha.110.226910] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2010] [Accepted: 11/19/2010] [Indexed: 01/16/2023]
Abstract
Chronic heart failure is a worldwide cause of mortality and morbidity and is the final outcome of a number of different etiologies. This reflects both the complexity of the disease and our incomplete understanding of its underlying molecular mechanisms. One experimental approach to address this is to study subcellular organelles and how their functions are activated and synchronized under physiological and pathological conditions. In this review, we discuss the application of proteomic technologies to organelles and how this has deepened our perception of the cellular proteome and its alterations with heart failure. The use of proteomics to monitor protein quantity and posttranslational modifications has revealed a highly intricate and sophisticated level of protein regulation. Posttranslational modifications have the potential to regulate organelle function and interplay most likely by targeting both structural and signaling proteins throughout the cell, ultimately coordinating their responses. The potentials and limitations of existing proteomic technologies are also discussed emphasizing that the development of novel methods will enhance our ability to further investigate organelles and decode intracellular communication.
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Affiliation(s)
- Giulio Agnetti
- The Johns Hopkins Bayview Proteomics Center, Johns Hopkins University, Baltimore, US
- INRC, Dept. of Biochemistry, University of Bologna, Italy
| | - Cathrine Husberg
- The Johns Hopkins Bayview Proteomics Center, Johns Hopkins University, Baltimore, US
- Institute for Experimental Medical Research, Oslo University Hospital - Ullevaal, Norway
| | - Jennifer E. Van Eyk
- The Johns Hopkins Bayview Proteomics Center, Johns Hopkins University, Baltimore, US
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80
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Houmeida A, Heeley DH, Belknap B, White HD. Mechanism of regulation of native cardiac muscle thin filaments by rigor cardiac myosin-S1 and calcium. J Biol Chem 2010; 285:32760-32769. [PMID: 20696756 DOI: 10.1074/jbc.m109.098228] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have studied the mechanism of activation of native cardiac thin filaments by calcium and rigor myosin. The acceleration of the rate of 2'-deoxy-3'-O-(N-methylanthraniloyl)ADP (mdADP) dissociation from cardiac myosin-S1-mdADP-P(i) and cardiac myosin-S1-mdADP by native cardiac muscle thin filaments was measured using double mixing stopped-flow fluorescence. Relative to inhibited thin filaments (no bound calcium or rigor S1), fully activated thin filaments (with both calcium and rigor-S1 bound) increase the rate of product dissociation from the physiologically important pre-power stroke myosin-mdADP-P(i) by a factor of ∼75. This can be compared with only an ∼6-fold increase in the rate of nucleotide diphosphate dissociation from nonphysiological myosin-mdADP by the fully activated thin filaments relative to the fully inhibited thin filaments. These results show that physiological levels of regulation are not only dependent on the state of the thin filament but also on the conformation of the myosin. Less than 2-fold regulation is due to a change in affinity of myosin-ADP-P(i) for thin filaments such as would be expected by a simple "steric blocking" of the myosin-binding site of the thin filament by tropomyosin. Although maximal activation requires both calcium and rigor myosin-S1 bound to the cardiac filament, association with a single ligand produces ∼70% maximal activation. This can be contrasted with skeletal thin filaments in which calcium alone only activated the rate of product dissociation ∼20% of maximum, and rigor myosin produces ∼30% maximal activation.
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Affiliation(s)
- Ahmed Houmeida
- From the Department of Biochemistry, University of Nouakchott, Nouakchott 5026, Mauritania
| | - David H Heeley
- Department of Biochemistry, Memorial University, St. Johns, Newfoundland A1B 3X9, Canada
| | - Betty Belknap
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia 23507
| | - Howard D White
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia 23507.
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81
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Lin Y, Fu Q, Zhu J, Miller JM, Van Eyk JE. Development of a Qualitative Sequential Immunoassay for Characterizing the Intrinsic Properties of Circulating Cardiac Troponin I. Clin Chem 2010; 56:1307-19. [DOI: 10.1373/clinchem.2009.135186] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
BACKGROUND
With myocardial infarction (MI), cardiac troponin is released from the heart into circulation, where it can be detected with immunoassays independently quantifying cardiac troponin I (cTnI) or cTnT. There is, however, no single immunoassay that sequentially probes the posttranslational modification status of cTnI or directly characterizes whether circulating cTnI is bound to cTnC and/or cTnT. Here we describe the development of a qualitative immunoassay to directly probe the primary and ternary structure of circulating cTnI through diffractive optics technology (dotLab® System, Axela).
METHODS
Anti-cTnI antibody 8I-7 was immobilized on a patterned sensor to capture cTnI. One or more detector antibodies were sequentially introduced to probe for amino acid sequence integrity or phosphorylation status of cTnI, or its association with cTnC and/or cTnT. Respective immunocaptures were recorded as real-time diffractive intensities (DIs), and the DI differences were analyzed. Each immunodetection was independent of the others but was done in a single sequential assay.
RESULTS
This diffraction-based immunoassay successfully characterized cTnI. The unamplified assay determined whether cTnI was degraded at N-terminus and/or C-terminus or phosphorylated. Sequential application of multiple detector antibodies without an antibody-stripping step enables real-time interrogation of 5 different epitopes of cTnI, or direct detection of the cTn complex (cTnI–cTnC–cTnT) in a single sequential assay. Finally, this assay was optimized with amplification to directly detect circulating cTnI bound to cTnC and cTnT in serum from an MI patient.
CONCLUSIONS
The dot® Immunoassay is the first qualitative sequential immunoassay to address the direct interactions of the troponin subunits and various modified forms of cTnI.
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Affiliation(s)
- Yixin Lin
- Axela Inc., Toronto, Ontario, Canada
| | - Qin Fu
- Department of Medicine and
| | | | | | - Jennifer E Van Eyk
- Department of Medicine and
- Departments of Biological Chemistry and Biomedical Engineering and Johns Hopkins Bayview Proteomics Center, Johns Hopkins University, Baltimore, MD
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82
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Avner BS, Hinken AC, Yuan C, Solaro RJ. H2O2 alters rat cardiac sarcomere function and protein phosphorylation through redox signaling. Am J Physiol Heart Circ Physiol 2010; 299:H723-30. [PMID: 20562337 DOI: 10.1152/ajpheart.00050.2010] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
ROS, such as H(2)O(2), are a component of pathological conditions in many organ systems and have been reported to be elevated in cardiac pathophysiology. The experiments presented here test the hypothesis that H(2)O(2) induces alterations in cardiac myofilament function by the posttranslational modification of sarcomeric proteins indirectly through PKC signaling. In vitro assessment of actomyosin Mg(2+)-ATPase activity of myofibrillar fractions showed blunted relative ATP consumption in the relaxed state (pCa 8.0) in response to treatment with 0.5 mM H(2)O(2) before myofilament isolation. The effect was attributable to downstream "redox signaling," inasmuch as the direct application of H(2)O(2) to isolated myofibrils did not alter Mg(2+)-ATPase activity. Ca(2+)-ATPase activity, which was used as a measure of myofibrillar myosin function, was unaffected by H(2)O(2). Functional experiments using rat cardiac trabeculae treated with 0.5 or 5 mM H(2)O(2) followed by detergent extraction of membranes demonstrated increased Ca(2+) sensitivity of force production, a faster rate of force redevelopment, and (for 5 mM) decreased maximum tension. Biochemical analysis of myocardial samples treated with 0.5 mM H(2)O(2) demonstrated increased phosphorylation of two sarcomeric proteins: cardiac troponin I and myosin-binding protein-C. These changes were eliminated by a general PKC inhibitor. However, H(2)O(2) and the general PKC activator PMA induced different phosphorylation patterns in cardiomyocytes in which PKC-delta was elevated by viral infection. These data provide evidence that PKC-dependent redox signaling affects the function of cardiac myofilaments and indicate modification of specific proteins through this signaling mechanism.
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Affiliation(s)
- Benjamin S Avner
- Department of Physiology and Biophysics and Center for Cardiovascular Research, College of Medicine, University of Illinois, Chicago, Illinois 60612-7342, USA
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83
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Zhang J, Dong X, Hacker TA, Ge Y. Deciphering modifications in swine cardiac troponin I by top-down high-resolution tandem mass spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2010; 21:940-8. [PMID: 20223681 PMCID: PMC3056346 DOI: 10.1016/j.jasms.2010.02.005] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2009] [Revised: 01/30/2010] [Accepted: 02/04/2010] [Indexed: 05/12/2023]
Abstract
Cardiac troponin I (cTnI) is an important regulatory protein in cardiac muscle, and its modification represents a key mechanism in the regulation of cardiac muscle contraction and relaxation. cTnI is often referred to as the "gold-standard" serum biomarker for diagnosing patients with acute cardiac injury since it is unique to the heart and released into the circulation following necrotic death of cardiac tissue. The swine (Sus scrofa) heart model is extremely valuable for cardiovascular research since the heart anatomy and coronary artery distribution of swine are almost identical to those of humans. Herein, we report a comprehensive characterization of the modifications in swine cTnI using top-down high-resolution tandem mass spectrometry in conjugation with immunoaffinity chromatography purification. High-resolution high accuracy mass spectrometry revealed that swine cTnI affinity purified from domestic pig hearts was N-terminally acetylated and phosphorylated. Electron capture disassociation is uniquely suited for localization of labile phosphorylations, which unambiguously identified Ser22/Ser23 as the only basally phosphorylated sites that are well-known to be regulated by protein kinase A and protein kinase C. Moreover, a combination of tandem mass spectrometry with sequence homology alignment effectively localized a single amino acid polymorphism, V116A, representing a novel genetic variant of swine cTnI. Overall, our studies demonstrated the unique power of top-down high-resolution tandem mass spectrometry in the characterization of protein modifications, including labile phosphorylation and unexpected sequence variants.
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Affiliation(s)
- Jiang Zhang
- Human Proteomics Program, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
- The School of Pharmacy, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Xintong Dong
- Human Proteomics Program, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Timothy A. Hacker
- Department of Medicine, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Ying Ge
- Human Proteomics Program, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
- Department of Physiology, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
- Corresponding author: Dr. Ying Ge, Human Proteomics Program and Department of Physiology, School of Medicine and Public Health, University of Wisconsin-Madison, 1300 University Ave., SMI 130, Madison, Wisconsin, USA. Tel: 608-263-9212, Fax: 608-265-5512,
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84
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Li Y, Charles PYJ, Nan C, Pinto JR, Wang Y, Liang J, Wu G, Tian J, Feng HZ, Potter JD, Jin JP, Huang X. Correcting diastolic dysfunction by Ca2+ desensitizing troponin in a transgenic mouse model of restrictive cardiomyopathy. J Mol Cell Cardiol 2010; 49:402-11. [PMID: 20580639 DOI: 10.1016/j.yjmcc.2010.04.017] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2009] [Revised: 04/19/2010] [Accepted: 04/29/2010] [Indexed: 10/19/2022]
Abstract
Several cardiac troponin I (cTnI) mutations are associated with restrictive cardiomyopathy (RCM) in humans. We have created transgenic mice (cTnI(193His) mice) that express the corresponding human RCM R192H mutation. Phenotype of this RCM animal model includes restrictive ventricles, biatrial enlargement and sudden cardiac death, which are similar to those observed in RCM patients carrying the same cTnI mutation. In the present study, we modified the overall cTnI in cardiac muscle by crossing cTnI(193His) mice with transgenic mice expressing an N-terminal truncated cTnI (cTnI-ND) that enhances relaxation. Protein analyses determined that wild type cTnI was replaced by cTnI-ND in the heart of double transgenic mice (Double TG), which express only cTnI-ND and cTnI R193H in cardiac myocytes. The presence of cTnI-ND effectively rescued the lethal phenotype of RCM mice by reducing the mortality rate. Cardiac function was significantly improved in Double TG mice when measured by echocardiography. The hypersensitivity to Ca(2+) and the prolonged relaxation of RCM cTnI(193His) cardiac myocytes were completely reversed by the presence of cTnI-ND in RCM hearts. The results demonstrate that myofibril hypersensitivity to Ca(2+) is a key mechanism that causes impaired relaxation in RCM cTnI mutant hearts and Ca(2+) desensitization by cTnI-ND can correct diastolic dysfunction and rescue the RCM phenotypes, suggesting that Ca(2+) desensitization in myofibrils is a therapeutic option for treatment of diastolic dysfunction without interventions directed at the systemic beta-adrenergic-PKA pathways.
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Affiliation(s)
- Yuejin Li
- Department of Basic Science, College of Biomedical Science, Florida Atlantic University, Boca Raton, FL 33431, USA
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85
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Han YS, Tveita T, Prakash YS, Sieck GC. Mechanisms underlying hypothermia-induced cardiac contractile dysfunction. Am J Physiol Heart Circ Physiol 2010; 298:H890-7. [PMID: 20023122 PMCID: PMC7938765 DOI: 10.1152/ajpheart.00805.2009] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2009] [Accepted: 12/14/2009] [Indexed: 11/22/2022]
Abstract
Rewarming patients after profound hypothermia may result in acute heart failure and high mortality (50-80%). However, the underlying pathophysiological mechanisms are largely unknown. We characterized cardiac contractile function in the temperature range of 15-30 degrees C by measuring the intracellular Ca(2+) concentration ([Ca(2+)](i)) and twitch force in intact left ventricular rat papillary muscles. Muscle preparations were loaded with fura-2 AM and electrically stimulated during cooling at 15 degrees C for 1.5 h before being rewarmed to the baseline temperature of 30 degrees C. After hypothermia/rewarming, peak twitch force decreased by 30-40%, but [Ca(2+)](i) was not significantly altered. In addition, we assessed the maximal Ca(2+)-activated force (F(max)) and Ca(2+) sensitivity of force in skinned papillary muscle fibers. F(max) was decreased by approximately 30%, whereas the pCa required for 50% of F(max) was reduced by approximately 0.14. In rewarmed papillary muscle, both total cardiac troponin I (cTnI) phosphorylation and PKA-mediated cTnI phosphorylation at Ser23/24 were significantly increased compared with controls. We conclude that after hypothermia/rewarming, myocardial contractility is significantly reduced, as evidenced by reduced twitch force and F(max). The reduced myocardial contractility is attributed to decreased Ca(2+) sensitivity of force rather than [Ca(2+)](i) itself, resulting from increased cTnI phosphorylation.
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Affiliation(s)
- Young-Soo Han
- Dept. of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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86
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Rescue of familial cardiomyopathies by modifications at the level of sarcomere and Ca2+ fluxes. J Mol Cell Cardiol 2010; 48:834-42. [PMID: 20079744 DOI: 10.1016/j.yjmcc.2010.01.003] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/02/2009] [Revised: 12/30/2009] [Accepted: 01/06/2010] [Indexed: 12/21/2022]
Abstract
Cardiomyopathies are a heterogeneous group of diseases of the myocardium associated with mechanical and/or electrical dysfunction that frequently show inappropriate ventricular hypertrophy or dilation. Current data suggest that numerous mutations in several genes can cause cardiomyopathies, and the severity of their phenotypes is also influenced by modifier genes. Two major types of inherited cardiomyopathies include familial hypertrophic cardiomyopathy (FHC) and dilated cardiomyopathy (DCM). FHC typically involves increased myofilament Ca(2+) sensitivity associated with diastolic dysfunction, whereas DCM often results in decreased myofilament Ca(2+) sensitivity and systolic dysfunction. Besides alterations in myofilament Ca(2+) sensitivity, alterations in the levels of Ca(2+)-handling proteins have also been described in both diseases. Recent work in animal models has attempted to rescue FHC and DCM via modifications at the myofilament level, altering Ca(2+) homeostasis by targeting Ca(2+)-handling proteins, such as the sarcoplasmic reticulum ATPase and phospholamban, or by interfering with the products of different modifiers genes. Although attempts to rescue cardiomyopathies in animal models have shown great promise, further studies are needed to validate these strategies in order to provide more effective and specific treatments.
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87
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Galińska A, Hatch V, Craig R, Murphy AM, Van Eyk JE, Wang CLA, Lehman W, Foster DB. The C terminus of cardiac troponin I stabilizes the Ca2+-activated state of tropomyosin on actin filaments. Circ Res 2009; 106:705-11. [PMID: 20035081 DOI: 10.1161/circresaha.109.210047] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
RATIONALE Ca(2+) control of troponin-tropomyosin position on actin regulates cardiac muscle contraction. The inhibitory subunit of troponin, cardiac troponin (cTn)I is primarily responsible for maintaining a tropomyosin conformation that prevents crossbridge cycling. Despite extensive characterization of cTnI, the precise role of its C-terminal domain (residues 193 to 210) is unclear. Mutations within this region are associated with restrictive cardiomyopathy, and C-terminal deletion of cTnI, in some species, has been associated with myocardial stunning. OBJECTIVE We sought to investigate the effect of a cTnI deletion-removal of 17 amino acids from the C terminus- on the structure of troponin-regulated tropomyosin bound to actin. METHODS AND RESULTS A truncated form of human cTnI (cTnI(1-192)) was expressed and reconstituted with troponin C and troponin T to form a mutant troponin. Using electron microscopy and 3D image reconstruction, we show that the mutant troponin perturbs the positional equilibrium dynamics of tropomyosin in the presence of Ca(2+). Specifically, it biases tropomyosin position toward an "enhanced C-state" that exposes more of the myosin-binding site on actin than found with wild-type troponin. CONCLUSIONS In addition to its well-established role of promoting the so-called "blocked-state" or "B-state," cTnI participates in proper stabilization of tropomyosin in the "Ca(2+)-activated state" or "C-state." The last 17 amino acids perform this stabilizing role. The data are consistent with a "fly-casting" model in which the mobile C terminus of cTnI ensures proper conformational switching of troponin-tropomyosin. Loss of actin-sensing function within this domain, by pathological proteolysis or cardiomyopathic mutation, may be sufficient to perturb tropomyosin conformation.
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Affiliation(s)
- Agnieszka Galińska
- Department of Physiology & Biophysics, Boston University School of Medicine, 72 E Concord St., Boston, MA 02118, USA
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88
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Fonfara S, Loureiro J, Swift S, James R, Cripps P, Dukes-McEwan J. Cardiac troponin I as a marker for severity and prognosis of cardiac disease in dogs. Vet J 2009; 184:334-9. [PMID: 19703781 DOI: 10.1016/j.tvjl.2009.04.004] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2008] [Revised: 03/31/2009] [Accepted: 04/02/2009] [Indexed: 11/20/2022]
Abstract
The use of cardiac troponin I (cTnI) to assess the severity of disease and prognosis in 120 dogs presented for cardiac evaluation was analysed. cTnI concentrations were measured using a commercially available assay. Dogs were placed into three groups: group 1, cTnI0.15ng/mL; group 2, cTnI 0.151-1.0ng/mL; group 3, cTnI>1.01ng/mL. Dogs in group 1 were significantly younger (P<0.0001) and had no or stable cardiac diseases and longest survival times, whereas those in groups 2 and 3 had severe cardiac diseases and significantly reduced survival times (P<0.0001). Thirty dogs with initially increased cTnI concentrations had a repeat assay less than 2months later with significant reductions in cTnI concentrations (P=0.005). Initial cTnI concentrations could not differentiate dogs that survived in group 3 from those that did not. However, dogs that survived showed significant cTnI reductions (P=0.015) in the repeated assay in contrast to the dogs that died (P=0.22). It was concluded that cTnI is useful in assessing the prognosis and severity of cardiac diseases in dogs, and progression and response to treatment can be assessed by repeat sampling. cTnI concentrations >1.0ng/mL and persistent increases in cTnI concentrations are indicators of a poor prognosis in dogs with cardiac disease.
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Affiliation(s)
- S Fonfara
- Small Animal Teaching Hospital, University of Liverpool, Neston, School of Veterinary Science, Leahurst, Neston CH64 7TE, UK.
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89
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Kooij V, Boontje N, Zaremba R, Jaquet K, dos Remedios C, Stienen GJM, van der Velden J. Protein kinase C alpha and epsilon phosphorylation of troponin and myosin binding protein C reduce Ca2+ sensitivity in human myocardium. Basic Res Cardiol 2009; 105:289-300. [PMID: 19655190 PMCID: PMC2807945 DOI: 10.1007/s00395-009-0053-z] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/27/2009] [Revised: 07/20/2009] [Accepted: 07/22/2009] [Indexed: 12/01/2022]
Abstract
Previous studies indicated that the increase in protein kinase C (PKC)-mediated myofilament protein phosphorylation observed in failing myocardium might be detrimental for contractile function. This study was designed to reveal and compare the effects of PKCα- and PKCε-mediated phosphorylation on myofilament function in human myocardium. Isometric force was measured at different [Ca2+] in single permeabilized cardiomyocytes from failing human left ventricular tissue. Activated PKCα and PKCε equally reduced Ca2+ sensitivity in failing cardiomyocytes (ΔpCa50 = 0.08 ± 0.01). Both PKC isoforms increased phosphorylation of troponin I- (cTnI) and myosin binding protein C (cMyBP-C) in failing cardiomyocytes. Subsequent incubation of failing cardiomyocytes with the catalytic subunit of protein kinase A (PKA) resulted in a further reduction in Ca2+ sensitivity, indicating that the effects of both PKC isoforms were not caused by cross-phosphorylation of PKA sites. Both isozymes showed no effects on maximal force and only PKCα resulted in a modest significant reduction in passive force. Effects of PKCα were only minor in donor cardiomyocytes, presumably because of already saturated cTnI and cMyBP-C phosphorylation levels. Donor tissue could therefore be used as a tool to reveal the functional effects of troponin T (cTnT) phosphorylation by PKCα. Massive dephosphorylation of cTnT with alkaline phosphatase increased Ca2+ sensitivity. Subsequently, PKCα treatment of donor cardiomyocytes reduced Ca2+ sensitivity (ΔpCa50 = 0.08 ± 0.02) and solely increased phosphorylation of cTnT, but did not affect maximal and passive force. PKCα- and PKCε-mediated phosphorylation of cMyBP-C and cTnI as well as cTnT decrease myofilament Ca2+ sensitivity and may thereby reduce contractility and enhance relaxation of human myocardium.
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Affiliation(s)
- Viola Kooij
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands.
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90
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Matsuba D, Terui T, O-Uchi J, Tanaka H, Ojima T, Ohtsuki I, Ishiwata S, Kurihara S, Fukuda N. Protein kinase A-dependent modulation of Ca2+ sensitivity in cardiac and fast skeletal muscles after reconstitution with cardiac troponin. ACTA ACUST UNITED AC 2009; 133:571-81. [PMID: 19433622 PMCID: PMC2713144 DOI: 10.1085/jgp.200910206] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Protein kinase A (PKA)-dependent phosphorylation of troponin (Tn)I represents a major physiological mechanism during β-adrenergic stimulation in myocardium for the reduction of myofibrillar Ca2+ sensitivity via weakening of the interaction with TnC. By taking advantage of thin filament reconstitution, we directly investigated whether or not PKA-dependent phosphorylation of cardiac TnI (cTnI) decreases Ca2+ sensitivity in different types of muscle: cardiac (porcine ventricular) and fast skeletal (rabbit psoas) muscles. PKA enhanced phosphorylation of cTnI at Ser23/24 in skinned cardiac muscle and decreased Ca2+ sensitivity, of which the effects were confirmed after reconstitution with the cardiac Tn complex (cTn) or the hybrid Tn complex (designated as PCRF; fast skeletal TnT with cTnI and cTnC). Reconstitution of cardiac muscle with the fast skeletal Tn complex (sTn) not only increased Ca2+ sensitivity, but also abolished the Ca2+-desensitizing effect of PKA, supporting the view that the phosphorylation of cTnI, but not that of other myofibrillar proteins, such as myosin-binding protein C, primarily underlies the PKA-induced Ca2+ desensitization in cardiac muscle. Reconstitution of fast skeletal muscle with cTn decreased Ca2+ sensitivity, and PKA further decreased Ca2+ sensitivity, which was almost completely restored to the original level upon subsequent reconstitution with sTn. The essentially same result was obtained when fast skeletal muscle was reconstituted with PCRF. It is therefore suggested that the PKA-dependent phosphorylation or dephosphorylation of cTnI universally modulates Ca2+ sensitivity associated with cTnC in the striated muscle sarcomere, independent of the TnT isoform.
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Affiliation(s)
- Douchi Matsuba
- Department of Cell Physiology, Jikei University School of Medicine, Tokyo 105-8461, Japan
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91
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Warren CM, Kobayashi T, Solaro RJ. Sites of intra- and intermolecular cross-linking of the N-terminal extension of troponin I in human cardiac whole troponin complex. J Biol Chem 2009; 284:14258-66. [PMID: 19321456 DOI: 10.1074/jbc.m807621200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Our previous studies (Howarth, J. W., Meller, J., Solaro, R. J., Trewhella, J., and Rosevear, P. R. (2007) J. Mol. Biol. 373, 706-722) of the unique N-terminal region of human cardiac troponin I (hcTnI), predicted a possible intramolecular interaction near the basic inhibitory peptide. To explore this possibility, we generated single cysteine mutants (hcTnI-S5C and hcTnI-I19C), which were labeled with the hetero-bifunctional cross-linker benzophenone-4-maleimide. The labeled hcTnI was reconstituted to whole troponin and exposed to UV light to form cross-linked proteins. Reversed-phase high-performance liquid chromatography and SDS-PAGE indicated intra- and intermolecular cross-linking with hcTnC and hcTnT. Moreover, using tandem mass spectrometry and Edman sequencing, specific intramolecular sites of interaction were determined at position Met-154 (I19C mutant) and Met-155 (S5C mutant) of hcTnI and intermolecular interactions at positions Met-47 and Met-80 of hcTnC in all conditions. Even though specific intermolecular cross-linked sites did not differ, the relative abundance of cross-linking was altered. We also measured the Ca(2+)-dependent ATPase rate of reconstituted thin filament-myosin-S1 preparation regulated by either cross-linked or non-labeled troponin. Ca(2+) regulation of the ATPase rate was lost when the Cys-5 hcTnI mutant was cross-linked in the absence of Ca(2+), but only partially inhibited with Cys-19 cross-linking in either the presence or absence of Ca(2+). This result indicates different functional effects of cross-linking to Met-154 and Met-155, which are located on different sides of the hcTnI switch peptide. Our data provide novel evidence identifying interactions of the hcTnI-N terminus with specific intra- and intermolecular sites.
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Affiliation(s)
- Chad M Warren
- Department of Physiology and Biophysics and the Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
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92
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Hamdani N, de Waard M, Messer AE, Boontje NM, Kooij V, van Dijk S, Versteilen A, Lamberts R, Merkus D, Dos Remedios C, Duncker DJ, Borbely A, Papp Z, Paulus W, Stienen GJM, Marston SB, van der Velden J. Myofilament dysfunction in cardiac disease from mice to men. J Muscle Res Cell Motil 2009; 29:189-201. [PMID: 19140019 DOI: 10.1007/s10974-008-9160-y] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2008] [Accepted: 12/07/2008] [Indexed: 01/08/2023]
Abstract
In healthy human myocardium a tight balance exists between receptor-mediated kinases and phosphatases coordinating phosphorylation of regulatory proteins involved in cardiomyocyte contractility. During heart failure, when neurohumoral stimulation increases to compensate for reduced cardiac pump function, this balance is perturbed. The imbalance between kinases and phosphatases upon chronic neurohumoral stimulation is detrimental and initiates cardiac remodelling, and phosphorylation changes of regulatory proteins, which impair cardiomyocyte function. The main signalling pathway involved in enhanced cardiomyocyte contractility during increased cardiac load is the beta-adrenergic signalling route, which becomes desensitized upon chronic stimulation. At the myofilament level, activation of protein kinase A (PKA), the down-stream kinase of the beta-adrenergic receptors (beta-AR), phosphorylates troponin I, myosin binding protein C and titin, which all exert differential effects on myofilament function. As a consequence of beta-AR down-regulation and desensitization, phosphorylation of the PKA-target proteins within the cardiomyocyte may be decreased and alter myofilament function. Here we discuss involvement of altered PKA-mediated myofilament protein phosphorylation in different animal and human studies, and discuss the roles of troponin I, myosin binding protein C and titin in regulating myofilament dysfunction in cardiac disease. Data from the different animal and human studies emphasize the importance of careful biopsy procurement, and the need to investigate localization of kinases and phosphatases within the cardiomyocyte, in particular their co-localization with cardiac myofilaments upon receptor stimulation.
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Affiliation(s)
- Nazha Hamdani
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands
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93
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Giannoni A, Giovannini S, Clerico A. Measurement of circulating concentrations of cardiac troponin I and T in healthy subjects: a tool for monitoring myocardial tissue renewal? Clin Chem Lab Med 2009; 47:1167-77. [DOI: 10.1515/cclm.2009.320] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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94
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Kobayashi T, Jin L, de Tombe PP. Cardiac thin filament regulation. Pflugers Arch 2008; 457:37-46. [PMID: 18421471 DOI: 10.1007/s00424-008-0511-8] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Revised: 03/19/2008] [Accepted: 03/25/2008] [Indexed: 12/17/2022]
Abstract
Myocardial contraction is initiated upon the release of calcium into the cytosol from the sarcoplasmic reticulum following membrane depolarization. The fundamental physiological role of the heart is to pump an amount blood that is determined by the prevailing requirements of the body. The physiological control systems employed to accomplish this task include regulation of heart rate, the amount of calcium release, and the response of the cardiac myofilaments to activator calcium ions. Thin filament activation and relaxation dynamics has emerged as a pivotal regulatory system tuning myofilament function to the beat-to-beat regulation of cardiac output. Maladaptation of thin filament dynamics, in addition to dysfunctional calcium cycling, is now recognized as an important cellular mechanism causing reduced cardiac pump function in a variety of cardiac diseases. Here, we review current knowledge regarding protein-protein interactions involved in the dynamics of thin filament activation and relaxation and the regulation of these processes by protein kinase-mediated phosphorylation.
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Affiliation(s)
- Tomoyoshi Kobayashi
- Department of Physiology & Biophysics, University of Illinois at Chicago, Chicago, IL 60612, USA
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95
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Ryall JG, Schertzer JD, Murphy KT, Allen AM, Lynch GS. Chronic beta2-adrenoceptor stimulation impairs cardiac relaxation via reduced SR Ca2+-ATPase protein and activity. Am J Physiol Heart Circ Physiol 2008; 294:H2587-95. [PMID: 18408128 DOI: 10.1152/ajpheart.00985.2007] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We determined the cardiovascular effects of chronic beta2-adrenoceptor (beta2-AR) stimulation in vivo and examined the mechanism for the previously observed prolonged diastolic relaxation. Rats (3 mo old; n = 6), instrumented with implantable radiotelemeters, received the selective beta2-AR agonist formoterol (25 microg.kg(-1).day(-1) ip) for 4 wk, with selected cardiovascular parameters measured daily throughout this period, and for a further 7 days after cessation of treatment. Chronic beta2-AR stimulation was associated with an increase in heart rate (HR) of 17% (days 1-14) and 5% (days 15-28); a 11% (days 1-14) and 6% (days 15-28) decrease in mean arterial blood pressure; and a 24% (days 1-14) increase in the rate of cardiac relaxation (-dP/dt) compared with initial values (P < 0.05). Cessation of beta2-AR stimulation resulted in an 8% decrease in HR and a 7% decrease in -dP/dt, compared with initial values (P < 0.05). The prolonged cardiac relaxation with chronic beta2-AR stimulation was associated with a 30% decrease in the maximal rate (Vmax) of sarco(endo)plasmic reticulum Ca2+ -ATPase (SERCA) activity, likely attributed to a 50% decrease in SERCA2a protein (P < 0.05). glycogen synthase kinase-3beta (GSK-3beta) has been implicated as a negative regulator of SERCA2 gene transcription, and we observed a approximately 60% decrease (P < 0.05) in phosphorylated GSK-3beta protein after chronic beta2-AR stimulation. Finally, we found a 40% decrease (P < 0.05) in the mRNA expression of the novel A kinase anchoring protein AKAP18, also implicated in beta2-AR-mediated cardiac relaxation. These findings highlight some detrimental cardiovascular effects of chronic beta2-AR agonist administration and identify concerns for their current and future use for treating asthma or for conditions where muscle wasting and weakness are indicated.
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Affiliation(s)
- James G Ryall
- Basic and Clinical Myology Laboratory, Department of Physiology, University of Melbourne, Victoria, Australia
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