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Donkervoort S, van de Locht M, Ronchi D, Reunert J, McLean CA, Zaki M, Orbach R, de Winter JM, Conijn S, Hoomoedt D, Neto OLA, Magri F, Viaene AN, Foley AR, Gorokhova S, Bolduc V, Hu Y, Acquaye N, Napoli L, Park JH, Immadisetty K, Miles LB, Essawi M, McModie S, Ferreira LF, Zanotti S, Neuhaus SB, Medne L, ElBagoury N, Johnson KR, Zhang Y, Laing NG, Davis MR, Bryson-Richardson RJ, Hwee DT, Hartman JJ, Malik FI, Kekenes-Huskey PM, Comi GP, Sharaf-Eldin W, Marquardt T, Ravenscroft G, Bönnemann CG, Ottenheijm CAC. Pathogenic TNNI1 variants disrupt sarcomere contractility resulting in hypo- and hypercontractile muscle disease. Sci Transl Med 2024; 16:eadg2841. [PMID: 38569017 DOI: 10.1126/scitranslmed.adg2841] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Accepted: 03/11/2024] [Indexed: 04/05/2024]
Abstract
Troponin I (TnI) regulates thin filament activation and muscle contraction. Two isoforms, TnI-fast (TNNI2) and TnI-slow (TNNI1), are predominantly expressed in fast- and slow-twitch myofibers, respectively. TNNI2 variants are a rare cause of arthrogryposis, whereas TNNI1 variants have not been conclusively established to cause skeletal myopathy. We identified recessive loss-of-function TNNI1 variants as well as dominant gain-of-function TNNI1 variants as a cause of muscle disease, each with distinct physiological consequences and disease mechanisms. We identified three families with biallelic TNNI1 variants (F1: p.R14H/c.190-9G>A, F2 and F3: homozygous p.R14C), resulting in loss of function, manifesting with early-onset progressive muscle weakness and rod formation on histology. We also identified two families with a dominantly acting heterozygous TNNI1 variant (F4: p.R174Q and F5: p.K176del), resulting in gain of function, manifesting with muscle cramping, myalgias, and rod formation in F5. In zebrafish, TnI proteins with either of the missense variants (p.R14H; p.R174Q) incorporated into thin filaments. Molecular dynamics simulations suggested that the loss-of-function p.R14H variant decouples TnI from TnC, which was supported by functional studies showing a reduced force response of sarcomeres to submaximal [Ca2+] in patient myofibers. This contractile deficit could be reversed by a slow skeletal muscle troponin activator. In contrast, patient myofibers with the gain-of-function p.R174Q variant showed an increased force to submaximal [Ca2+], which was reversed by the small-molecule drug mavacamten. Our findings demonstrated that TNNI1 variants can cause muscle disease with variant-specific pathomechanisms, manifesting as either a hypo- or a hypercontractile phenotype, suggesting rational therapeutic strategies for each mechanism.
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Affiliation(s)
- Sandra Donkervoort
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Martijn van de Locht
- Department of Physiology, Amsterdam UMC (location VUmc), Amsterdam, 1081 HV Netherlands
| | - Dario Ronchi
- Dino Ferrari Center, Department of Pathophysiology and Transplantation, University of Milan, Milan, 20135, Italy
| | - Janine Reunert
- Department of General Pediatrics, University of Münster, Münster, 48149, Germany
| | - Catriona A McLean
- Department of Anatomical Pathology, Alfred Hospital, Melbourne, Victoria, 3004, Australia
- Faculty of Medicine, Nursing, and Health Sciences, Monash University, Melbourne, Victoria, 3168, Australia
| | - Maha Zaki
- Clinical Genetics Department, Human Genetics and Genome Research Institute, National Research Centre, Cairo, 12622, Egypt
| | - Rotem Orbach
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Josine M de Winter
- Department of Physiology, Amsterdam UMC (location VUmc), Amsterdam, 1081 HV Netherlands
| | - Stefan Conijn
- Department of Physiology, Amsterdam UMC (location VUmc), Amsterdam, 1081 HV Netherlands
| | - Daan Hoomoedt
- Department of Physiology, Amsterdam UMC (location VUmc), Amsterdam, 1081 HV Netherlands
| | - Osorio Lopes Abath Neto
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Francesca Magri
- Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Neurology Unit, Milan, 20122, Italy
| | - Angela N Viaene
- Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, University of Pennsylvania Perelman School of Medicine, Philadelphia, 19104 PA, USA
| | - A Reghan Foley
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Svetlana Gorokhova
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
- Department of Medical Genetics, Timone Children's Hospital, APHM, Marseille, 13005, France
- INSERM, U1251-MMG, Aix-Marseille Université, Marseille, 13009, France
| | - Véronique Bolduc
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Ying Hu
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Nicole Acquaye
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Laura Napoli
- Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Neuromuscular and Rare Disease Unit, Milan, 20122, Italy
| | - Julien H Park
- Department of General Pediatrics, University Hospital Münster, Münster, 48149 Germany
| | - Kalyan Immadisetty
- Department of Cell and Molecular Physiology, Loyola University, Chicago, IL 60153, USA
| | - Lee B Miles
- School of Biological Sciences, Monash University, Melbourne, Victoria, 3800, Australia
| | - Mona Essawi
- Medical Molecular Genetics Department, Human Genetics and Genome Research Institute, National Research Centre, Cairo, 12622, Egypt
| | - Salar McModie
- Department of Neurology, Alfred Health, Melbourne, Victoria, 3004, Australia
| | - Leonardo F Ferreira
- Department of Physiology, Amsterdam UMC (location VUmc), Amsterdam, 1081 HV Netherlands
- Department of Orthopaedic Surgery, Duke University School of Medicine, Durham, NC 27710, USA
| | - Simona Zanotti
- Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Neuromuscular and Rare Disease Unit, Milan, 20122, Italy
| | - Sarah B Neuhaus
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Livija Medne
- Division of Human Genetics, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Nagham ElBagoury
- Medical Molecular Genetics Department, Human Genetics and Genome Research Institute, National Research Centre, Cairo, 12622, Egypt
| | - Kory R Johnson
- Bioinformatics Core, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Yong Zhang
- Bioinformatics Core, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Nigel G Laing
- Neurogenetics Unit, Department of Diagnostic Genomics, PathWest Laboratory Medicine, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia
- Centre for Medical Research University of Western Australia, Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia
| | - Mark R Davis
- Neurogenetics Unit, Department of Diagnostic Genomics, PathWest Laboratory Medicine, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia
| | | | - Darren T Hwee
- Research and Development, Cytokinetics Inc., South San Francisco, CA 94080, USA
| | - James J Hartman
- Research and Development, Cytokinetics Inc., South San Francisco, CA 94080, USA
| | - Fady I Malik
- Research and Development, Cytokinetics Inc., South San Francisco, CA 94080, USA
| | | | - Giacomo Pietro Comi
- Dino Ferrari Center, Department of Pathophysiology and Transplantation, University of Milan, Milan, 20135, Italy
- Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Neuromuscular and Rare Disease Unit, Milan, 20122, Italy
| | - Wessam Sharaf-Eldin
- Medical Molecular Genetics Department, Human Genetics and Genome Research Institute, National Research Centre, Cairo, 12622, Egypt
| | - Thorsten Marquardt
- Department of General Pediatrics, University of Münster, Münster, 48149, Germany
| | - Gianina Ravenscroft
- Centre for Medical Research University of Western Australia, Harry Perkins Institute of Medical Research, QEII Medical Centre, Nedlands, Western Australia, 6009, Australia
| | - Carsten G Bönnemann
- Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Coen A C Ottenheijm
- Department of Physiology, Amsterdam UMC (location VUmc), Amsterdam, 1081 HV Netherlands
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2
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Cao Y, Redd MA, Fang C, Mizikovsky D, Li X, Macdonald PS, King GF, Palpant NJ. New Drug Targets and Preclinical Modelling Recommendations for Treating Acute Myocardial Infarction. Heart Lung Circ 2023:S1443-9506(23)00139-7. [PMID: 37230806 DOI: 10.1016/j.hlc.2022.12.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 11/28/2022] [Accepted: 12/15/2022] [Indexed: 05/27/2023]
Abstract
Acute myocardial infarction (AMI) is the leading cause of morbidity and mortality worldwide and the primary underlying risk factor for heart failure. Despite decades of research and clinical trials, there are no drugs currently available to prevent organ damage from acute ischaemic injuries of the heart. In order to address the increasing global burden of heart failure, drug, gene, and cell-based regeneration technologies are advancing into clinical testing. In this review we highlight the burden of disease associated with AMI and the therapeutic landscape based on market analyses. New studies revealing the role of acid-sensitive cardiac ion channels and other proton-gated ion channels in cardiac ischaemia are providing renewed interest in pre- and post-conditioning agents with novel mechanisms of action that may also have implications for gene- and cell-based therapeutics. Furthermore, we present guidelines that couple new cell technologies and data resources with traditional animal modelling pipelines to help de-risk drug candidates aimed at treating AMI. We propose that improved preclinical pipelines and increased investment in drug target identification for AMI is critical to stem the increasing global health burden of heart failure.
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Affiliation(s)
- Yuanzhao Cao
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Meredith A Redd
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Chen Fang
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Dalia Mizikovsky
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Xichun Li
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Peter S Macdonald
- Cardiopulmonary Transplant Unit, St Vincent's Hospital, Sydney, NSW, Australia
| | - Glenn F King
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia; Australian Research Council Centre of Excellence for Innovations in Peptide and Protein Science, The University of Queensland, Brisbane, Qld, Australia
| | - Nathan J Palpant
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia.
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Wheelwright M, Mikkila J, Bedada FB, Mandegar MA, Thompson BR, Metzger JM. Advancing physiological maturation in human induced pluripotent stem cell-derived cardiac muscle by gene editing an inducible adult troponin isoform switch. Stem Cells 2020; 38:1254-1266. [PMID: 32497296 DOI: 10.1002/stem.3235] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Accepted: 05/11/2020] [Indexed: 01/11/2023]
Abstract
Advancing maturation of stem cell-derived cardiac muscle represents a major barrier to progress in cardiac regenerative medicine. Cardiac muscle maturation involves a myriad of gene, protein, and cell-based transitions, spanning across all aspects of cardiac muscle form and function. We focused here on a key developmentally controlled transition in the cardiac sarcomere, the functional unit of the heart. Using a gene-editing platform, human induced pluripotent stem cell (hiPSCs) were engineered with a drug-inducible expression cassette driving the adult cardiac troponin I (cTnI) regulatory isoform, a transition shown to be a rate-limiting step in advancing sarcomeric maturation of hiPSC cardiac muscle (hiPSC-CM) toward the adult state. Findings show that induction of the adult cTnI isoform resulted in the physiological acquisition of adult-like cardiac contractile function in hiPSC-CMs in vitro. Specifically, cTnI induction accelerated relaxation kinetics at baseline conditions, a result independent of alterations in the kinetics of the intracellular Ca2+ transient. In comparison, isogenic unedited hiPSC-CMs had no cTnI induction and no change in relaxation function. Temporal control of adult cTnI isoform induction did not alter other developmentally regulated sarcomere transitions, including myosin heavy chain isoform expression, nor did it affect expression of SERCA2a or phospholamban. Taken together, precision genetic targeting of sarcomere maturation via inducible TnI isoform switching enables physiologically relevant adult myocardium-like contractile adaptations that are essential for beat-to-beat modulation of adult human heart performance. These findings have relevance to hiPSC-CM structure-function and drug-discovery studies in vitro, as well as for potential future clinical applications of physiologically optimized hiPSC-CM in cardiac regeneration/repair.
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Affiliation(s)
- Matthew Wheelwright
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Jennifer Mikkila
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Fikru B Bedada
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Mohammad A Mandegar
- Gladstone Institute of Cardiovascular Disease, San Francisco, California, USA
| | - Brian R Thompson
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Joseph M Metzger
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
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4
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Effects of Long-Term High-Altitude Hypoxia on Myocardial Protein Kinase A Activity and Troponin I Isoforms in Fetal and Nonpregnant Sheep. ACTA ACUST UNITED AC 2016. [DOI: 10.1016/s1071-55760300042-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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5
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Thompson BR, Houang EM, Sham YY, Metzger JM. Molecular determinants of cardiac myocyte performance as conferred by isoform-specific TnI residues. Biophys J 2014; 106:2105-14. [PMID: 24853739 DOI: 10.1016/j.bpj.2014.04.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Revised: 03/14/2014] [Accepted: 04/04/2014] [Indexed: 11/27/2022] Open
Abstract
Troponin I (TnI) is the molecular switch of the sarcomere. Cardiac myocytes express two isoforms of TnI during development. The fetal heart expresses the slow skeletal TnI (ssTnI) isoform and shortly after birth ssTnI is completely and irreversibly replaced by the adult cardiac TnI (cTnI) isoform. These two isoforms have important functional differences; broadly, ssTnI is a positive inotrope, especially under acidic/hypoxic conditions, whereas cTnI facilitates faster relaxation performance. Evolutionary directed changes in cTnI sequence suggest cTnI evolved to favor relaxation performance in the mammalian heart. To investigate the mechanism, we focused on several notable TnI isoform and trans-species-specific residues located in TnI's helix 4 using structure/function and molecular dynamics analyses. Gene transduction of adult cardiac myocytes by cTnIs with specific helix 4 ssTnI substitutions, Q157R/A164H/E166V/H173N (QAEH), and A164H/H173N (AH), were investigated. cTnI QAEH is similar in these four residues to ssTnI and nonmammalian chordate cTnIs, whereas cTnI AH is similar to fish cTnI in these four residues. In comparison to mammalian cTnI, cTnI QAEH and cTnI AH showed increased contractility and slowed relaxation, which functionally mimicked ssTnI expressing myocytes. cTnI QAEH molecular dynamics simulations demonstrated altered intermolecular interactions between TnI helix 4 and cTnC helix A, specifically revealing a new, to our knowledge, electrostatic interaction between R171of cTnI and E15 of cTnC, which structurally phenocopied the ssTnI conformation. Free energy perturbation calculation of cTnC Ca(2+) binding for these conformations showed relative increased calcium binding for cTnI QAEH compared to cTnI. Taken together, to our knowledge, these new findings provide evidence that the evolutionary-directed coordinated acquisition of residues Q157, A164, E166, H173 facilitate enhanced relaxation performance in mammalian adult cardiac myocytes.
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Affiliation(s)
- Brian R Thompson
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota
| | - Evelyne M Houang
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota; Center for Drug Design, University of Minnesota Academic Health Center, Minneapolis, Minnesota
| | - Yuk Y Sham
- Center for Drug Design, University of Minnesota Academic Health Center, Minneapolis, Minnesota
| | - Joseph M Metzger
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota.
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6
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Harmelink C, Peng Y, DeBenedittis P, Chen H, Shou W, Jiao K. Myocardial Mycn is essential for mouse ventricular wall morphogenesis. Dev Biol 2013; 373:53-63. [PMID: 23063798 PMCID: PMC3508168 DOI: 10.1016/j.ydbio.2012.10.005] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Revised: 09/11/2012] [Accepted: 10/04/2012] [Indexed: 01/27/2023]
Abstract
MYCN is a highly conserved transcription factor with multifaceted roles in development and disease. Mutations in MYCN are associated with Feingold syndrome, a developmental disorder characterized in part by congenital heart defects. Mouse models have helped elucidate MYCN functions; however its cardiac-specific roles during development remain unclear. We employed a Cre/loxp strategy to uncover the specific activities of MYCN in the developing mouse myocardium. Myocardial deletion of Mycn resulted in a thin-myocardial wall defect with dramatically reduced trabeculation. The mutant heart defects strongly resemble the phenotype caused by disruption of BMP10 and Neuregulin-1 (NRG1) signaling pathways, two central mediators of myocardial wall development. Our further examination showed that expression of MYCN is regulated by both BMP and NRG1 signaling. The thin-wall defect in mutant hearts is caused by a reduction in both cell proliferation and cell size. MYCN promotes cardiomyocyte proliferation through regulating expression of cell cycle regulators (including CCND1, CCND2, and ID2) and promotes cardiomyocyte growth through regulating expression of p70S6K. In addition, expression of multiple sarcomere proteins is altered in Mycn myocardial-inactivation embryos, indicating its essential role for proper cardiomyocyte differentiation. In summary, Mycn acts downstream of BMP and NRG1 cardiogenic signaling pathways to promote normal myocardial wall morphogenesis.
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Affiliation(s)
- Cristina Harmelink
- Department of Genetics, The University of Alabama at Birmingham, Birmingham, AL 35294
| | - Yin Peng
- Department of Genetics, The University of Alabama at Birmingham, Birmingham, AL 35294
| | - Paige DeBenedittis
- Department of Genetics, The University of Alabama at Birmingham, Birmingham, AL 35294
| | - Hanying Chen
- Herman B Wells Center for Pediatric Research, Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN 46202
| | - Weinian Shou
- Herman B Wells Center for Pediatric Research, Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN 46202
| | - Kai Jiao
- Department of Genetics, The University of Alabama at Birmingham, Birmingham, AL 35294
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Nichols R, Bass C, Demers L, Larsen B, Li E, Blewett N, Converso-Baran K, Russell MW, Westfall MV. Structure-activity studies of RFamide-related peptide-1 identify a functional receptor antagonist and novel cardiac myocyte signaling pathway involved in contractile performance. J Med Chem 2012; 55:7736-45. [PMID: 22909119 DOI: 10.1021/jm300760m] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Human RFamide-related peptide-1 (hRFRP-1, MPHSFANLPLRF-NH(2)) binds to neuropeptide FF receptor 2 (NPFF(2)R) to dramatically diminish cardiovascular performance. hRFRP-1 and its signaling pathway may provide targets to address cardiac dysfunction. Here, structure-activity relationship, transcript, Ca(2+) transient, and phospholabeling data indicate the presence of a hRFRP-1 pathway in cardiomyocytes. Alanyl-substituted and N-terminal truncated analogues identified that R(11) was essential for activity, hRFRP-1((8-12)) mimicked hRFRP-1, and [A(11)]hRFRP-1((8-12)) antagonized the effect of hRFRP-1 in cellular and integrated cardiac performance. RFRP and NPFF(2)R transcripts were amplified from cardiomyocytes and heart. Maintenance of the Ca(2+) transient when hRFRP-1 impaired myocyte shortening indicated the myofilament was its primary downstream target. Enhanced myofilament protein phosphorylation detected after hRFRP-1 treatment but absent in [A(11)]hRFRP-1((8-12))-treated cells was consistent with this result. Protein kinase C (PKC) but not PKA inhibitor diminished the influence of hRFRP-1 on the Ca(2+) transient. Molecules targeting this pathway may help address cardiovascular disease.
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Affiliation(s)
- Ruthann Nichols
- Department of Biological Chemistry, The University of Michigan Medical School , Ann Arbor, Michigan 48109, USA.
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8
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Shaffer JF, Gillis TE. Evolution of the regulatory control of vertebrate striated muscle: the roles of troponin I and myosin binding protein-C. Physiol Genomics 2010; 42:406-19. [PMID: 20484158 DOI: 10.1152/physiolgenomics.00055.2010] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Troponin I (TnI) and myosin binding protein-C (MyBP-C) are key regulatory proteins of contractile function in vertebrate muscle. TnI modulates the Ca2+ activation signal, while MyBP-C regulates cross-bridge cycling kinetics. In vertebrates, each protein is distributed as tissue-specific paralogs in fast skeletal (fs), slow skeletal (ss), and cardiac (c) muscles. The purpose of this study is to characterize how TnI and MyBP-C have changed during the evolution of vertebrate striated muscle and how tissue-specific paralogs have adapted to different physiological conditions. To accomplish this we have completed phylogenetic analyses using the amino acid sequences of all known TnI and MyBP-C isoforms. This includes 99 TnI sequences (fs, ss, and c) from 51 different species and 62 MyBP-C sequences from 26 species, with representatives from each vertebrate group. Results indicate that the role of protein kinase A (PKA) and protein kinase C (PKC) in regulating contractile function has changed during the evolution of vertebrate striated muscle. This is reflected in an increased number of phosphorylatable sites in cTnI and cMyBP-C in endothermic vertebrates and the loss of two PKC sites in fsTnI in a common ancestor of mammals, birds, and reptiles. In addition, we find that His132, Val134, and Asn141 in human ssTnI, previously identified as enabling contractile function during cellular acidosis, are present in all vertebrate cTnI isoforms except those from monotremes, marsupials, and eutherian mammals. This suggests that the replacement of these residues with alternative residues coincides with the evolution of endothermy in the mammalian lineage.
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Affiliation(s)
- Justin F. Shaffer
- Department of Bioengineering, University of Washington, Seattle, Washington; and
| | - Todd E. Gillis
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
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9
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Davis J, Westfall MV, Townsend D, Blankinship M, Herron TJ, Guerrero-Serna G, Wang W, Devaney E, Metzger JM. Designing heart performance by gene transfer. Physiol Rev 2008; 88:1567-651. [PMID: 18923190 DOI: 10.1152/physrev.00039.2007] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The birth of molecular cardiology can be traced to the development and implementation of high-fidelity genetic approaches for manipulating the heart. Recombinant viral vector-based technology offers a highly effective approach to genetically engineer cardiac muscle in vitro and in vivo. This review highlights discoveries made in cardiac muscle physiology through the use of targeted viral-mediated genetic modification. Here the history of cardiac gene transfer technology and the strengths and limitations of viral and nonviral vectors for gene delivery are reviewed. A comprehensive account is given of the application of gene transfer technology for studying key cardiac muscle targets including Ca(2+) handling, the sarcomere, the cytoskeleton, and signaling molecules and their posttranslational modifications. The primary objective of this review is to provide a thorough analysis of gene transfer studies for understanding cardiac physiology in health and disease. By comparing results obtained from gene transfer with those obtained from transgenesis and biophysical and biochemical methodologies, this review provides a global view of cardiac structure-function with an eye towards future areas of research. The data presented here serve as a basis for discovery of new therapeutic targets for remediation of acquired and inherited cardiac diseases.
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Affiliation(s)
- Jennifer Davis
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA
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10
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Davis J, Wen H, Edwards T, Metzger JM. Allele and species dependent contractile defects by restrictive and hypertrophic cardiomyopathy-linked troponin I mutants. J Mol Cell Cardiol 2008; 44:891-904. [PMID: 18423659 PMCID: PMC2443058 DOI: 10.1016/j.yjmcc.2008.02.274] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/12/2007] [Revised: 02/13/2008] [Accepted: 02/16/2008] [Indexed: 11/15/2022]
Abstract
Restrictive cardiomyopathy (RCM) is a debilitating disease characterized by impaired ventricular filling, reduced ventricular volumes, and severe diastolic dysfunction. Hypertrophic cardiomyopathy (HCM) is characterized by ventricular hypertrophy and heightened risk of premature sudden cardiac death. These cardiomyopathies can result from mutations in the same gene that encodes for cardiac troponin I (cTnI). Acute genetic engineering of adult rat cardiac myocytes was used to ascertain whether primary physiologic outcomes could distinguish between RCM and HCM alleles at the cellular level. Co-transduction of cardiac myocytes with wild-type (WT) cTnI and RCM/HCM linked mutants in cTnI's inhibitory region (IR) demonstrated that WT cTnI preferentially incorporated into the sarcomere over IR mutants. The cTnI IR mutants exhibited minor effects in single myocyte Ca(2+)-activated tension assays yet prolonged relaxation and Ca(2+) decay. In comparison RCM cTnI mutants in the helix-4/C-terminal region demonstrated a) hyper-sensitivity to Ca(2+) under loaded conditions, b) slowed myocyte mechanical relaxation and Ca(2+) transient decay, c) frequency-dependent Ca(2+)-independent diastolic tone, d) heightened myofilament incorporation and e) irreversible cellular contractile defects with acute diltiazem administration. For species comparison, a subset of cTnI mutants were tested in isolated adult rabbit cardiac myocytes. Here, RCM and HCM mutant cTnIs exerted similar effects of slowed myocyte relaxation and Ca(2+) transient decay but did not show variable phenotypes by cTnI region. This study highlights cellular contractile defects by cardiomyopathy mutant cTnIs that are allele and species dependent. The species dependent results in particular raise important issues toward elucidating a unifying mechanistic pathway underlying the inherited cardiomyopathies.
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Affiliation(s)
- Jennifer Davis
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan, USA
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Soeding PE, Royse CF, Wright CE, Royse AG, Angus JA. Inoprotection: the perioperative role of levosimendan. Anaesth Intensive Care 2008; 35:845-62. [PMID: 18084975 DOI: 10.1177/0310057x0703500602] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Levosimendan is emerging as a novel cardioprotective inotrope. Levosimendan augments myocardial contractility by sensitising contractile myofilaments to calcium without increasing myosin adenosine triphosphatase activity or oxygen consumption. Levosimendan activates cellular adenosine triphosphate-dependent potassium channels, a mechanism which is postulated to protect cells from ischaemia in a manner similar to ischaemic preconditioning. Levosimendan may therefore protect the ischaemic myocardium during ischaemia-reperfusion as well as improve the contractile function of the heart. Adenosine triphosphate-dependent potassium channel activation by levosimendan may also be protective in other tissues, such as coronary vascular endothelium, kidney and brain. Clinical trials in patients with decompensated heart failure and myocardial ischaemia show levosimendan to improve haemodynamic performance and potentially improve survival. This paper reviews the known pharmacology of levosimendan, the clinical experience with the drug to date and the potential use of levosimendan as a cardioprotective agent during surgery.
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Affiliation(s)
- P E Soeding
- Cardiovascular Therapeutics Unit, Department of Pharmacology, University of Melbourne, Melbourne, Victoria, Australia
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12
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Day S, Davis J, Westfall M, Metzger J. Genetic engineering and therapy for inherited and acquired cardiomyopathies. Ann N Y Acad Sci 2007; 1080:437-50. [PMID: 17132800 DOI: 10.1196/annals.1380.033] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The cardiac myofilaments consist of a highly ordered assembly of proteins that collectively generate force in a calcium-dependent manner. Defects in myofilament function and its regulation have been implicated in various forms of acquired and inherited human heart disease. For example, during cardiac ischemia, cardiac myocyte contractile performance is dramatically downregulated due in part to a reduced sensitivity of the myofilaments to calcium under acidic pH conditions. Over the last several years, the thin filament regulatory protein, troponin I, has been identified as an important mediator of this response. Mutations in troponin I and other sarcomere genes are also linked to several distinct inherited cardiomyopathic phenotypes, including hypertrophic, dilated, and restrictive cardiomyopathies. With the cardiac sarcomere emerging as a central player for such a diverse array of human heart diseases, genetic-based strategies that target the myofilament will likely have broad therapeutic potential. The development of safe vector systems for efficient gene delivery will be a critical hurdle to overcome before these types of therapies can be successfully applied. Nonetheless, studies focusing on the principles of acute genetic engineering of the sarcomere hold value as they lay the essential foundation on which to build potential gene-based therapies for heart disease.
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Affiliation(s)
- Sharlene Day
- Department of Internal Medicine, University of Michigan, 1301 E. Catherine Street, Ann Arbor MI 48109-0622, USA
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13
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Day SM, Westfall MV, Metzger JM. Tuning cardiac performance in ischemic heart disease and failure by modulating myofilament function. J Mol Med (Berl) 2007; 85:911-21. [PMID: 17396243 DOI: 10.1007/s00109-007-0181-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2007] [Revised: 02/20/2007] [Accepted: 03/01/2007] [Indexed: 12/31/2022]
Abstract
The cardiac myofilaments are composed of highly ordered arrays of proteins that coordinate cardiac contraction and relaxation in response to the rhythmic waves of [Ca(2+)] during the cardiac cycle. Several cardiac disease states are associated with altered myofilament protein interactions that contribute to cardiac dysfunction. During acute myocardial ischemia, the sensitivity of the myofilaments to activating Ca(2+) is drastically reduced, largely due to the effects of intracellular acidosis on the contractile machinery. Myofilament Ca(2+) sensitivity remains compromised in post-ischemic or "stunned" myocardium even after complete restoration of blood flow and intracellular pH, likely because of covalent modifications of or proteolytic injury to contractile proteins. In contrast, myofilament Ca(2+) sensitivity can be increased in chronic heart failure, owing in part to decreased phosphorylation of troponin I, the inhibitory subunit of the troponin regulatory complex. We highlight, in this paper, the central role of the myofilaments in the pathophysiology of each of these distinct disease entities, with a particular focus on the molecular switch protein troponin I. We also discuss the beneficial effects of a genetically engineered cardiac troponin I, with a histidine button substitution at C-terminal residue 164, for a variety of pathophysiologic conditions, including hypoxia, ischemia, ischemia-reperfusion and chronic heart failure.
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Affiliation(s)
- Sharlene M Day
- Department of Internal Medicine, University of Michigan, 1150 W. Medical Center Drive, 7301 MSRB III, Ann Arbor, MI 48109-0644, USA.
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14
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Abstract
Inotropic agents are indispensable for the improvement of cardiac contractile dysfunction in acute or decompensated heart failure. Clinically available agents, including sympathomimetic amines (dopamine, dobutamine, noradrenaline) and selective phosphodiesterase-3 inhibitors (amrinone, milrinone, olprinone and enoximone) act via cAMP/protein kinase A (PKA)-mediated facilitation of intracellular Ca2+ mobilisation. Phosphodiesterase-3 inhibitors also have a vasodilatory action, which plays a role in improving haemodynamic parameters in certain patients, and are termed inodilators. The available inotropic agents suffer from risks of Ca2+ overload leading to arrhythmias, myocardial cell injury and ultimately, cell death. In addition, they are energetically disadvantageous because of an increase in activation energy and cellular metabolism. Furthermore, they lose their effectiveness under pathophysiological conditions, such as acidosis, stunned myocardium and heart failure. Pimobendan and levosimendan (that act by a combination of an increase in Ca2+ sensitivity and phosphodiesterase-3 inhibition) appear to be more beneficial among existing agents. Novel Ca2+ sensitisers that are under basic research warrant clinical trials to replace available inotropic agents.
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Affiliation(s)
- Masao Endoh
- Department of Cardiovascular Pharmacology, Yamagata University School of Medicine, Yamagata, 2-2-2 Iida-nishi, 990-9585, Japan.
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15
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Murphy AM. Heart failure, myocardial stunning, and troponin: a key regulator of the cardiac myofilament. ACTA ACUST UNITED AC 2006; 12:32-8; quiz 39-40. [PMID: 16470090 DOI: 10.1111/j.1527-5299.2006.04320.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This review discusses post-translational modifications of myofilament regulatory proteins, particularly troponin, associated with heart failure and myocardial stunning--two common disease processes. Altered phosphorylation, partial proteolysis and, possibly, oxidative damage to myofilament proteins may result in abnormalities in both systolic and diastolic function. At a molecular level, these changes may lead to abnormalities in crossbridge cycling and tension development and result in inefficiencies in utilization of energy. Understanding these alterations may lead to new targeted therapies.
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Affiliation(s)
- Anne M Murphy
- Cardiology Division, Department of Pediatrics, Johns Hopkins University School of Medicine, Ross Building 1144, 720 Rutland Avenue, Baltimore, MD 21205, USA.
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16
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Day SM, Westfall MV, Fomicheva EV, Hoyer K, Yasuda S, La Cross NC, D'Alecy LG, Ingwall JS, Metzger JM. Histidine button engineered into cardiac troponin I protects the ischemic and failing heart. Nat Med 2006; 12:181-9. [PMID: 16429145 DOI: 10.1038/nm1346] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2005] [Accepted: 11/21/2005] [Indexed: 11/08/2022]
Abstract
The myofilament protein troponin I (TnI) has a key isoform-dependent role in the development of contractile failure during acidosis and ischemia. Here we show that cardiac performance in vitro and in vivo is enhanced when a single histidine residue present in the fetal cardiac TnI isoform is substituted into the adult cardiac TnI isoform at codon 164. The most marked effects are observed under the acute challenges of acidosis, hypoxia, ischemia and ischemia-reperfusion, in chronic heart failure in transgenic mice and in myocytes from failing human hearts. In the isolated heart, histidine-modified TnI improves systolic and diastolic function and mitigates reperfusion-associated ventricular arrhythmias. Cardiac performance is markedly enhanced in transgenic hearts during reperfusion despite a high-energy phosphate content similar to that in nontransgenic hearts, providing evidence for greater energetic economy. This pH-sensitive 'histidine button' engineered in TnI produces a titratable molecular switch that 'senses' changes in the intracellular milieu of the cardiac myocyte and responds by preferentially augmenting acute and long-term function under pathophysiological conditions. Myofilament-based inotropy may represent a therapeutic avenue to improve myocardial performance in the ischemic and failing heart.
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Affiliation(s)
- Sharlene M Day
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA
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17
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Westfall MV, Lee AM, Robinson DA. Differential contribution of troponin I phosphorylation sites to the endothelin-modulated contractile response. J Biol Chem 2005; 280:41324-31. [PMID: 16236710 DOI: 10.1074/jbc.m506043200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cardiac troponin I is a phosphorylation target for endothelin-activated protein kinase C. Earlier work in cardiac myocytes expressing nonphosphorylatable slow skeletal troponin I provided evidence that protein kinase C-mediated cardiac troponin I phosphorylation accelerates relaxation. However, replacement with the slow skeletal isoform also alters the myofilament pH response and the Ca2+ transient, which could influence endothelin-mediated relaxation. Here, differences in the Ca2+ transient could not explain the divergent relaxation response to endothelin in myocytes expressing cardiac versus slow skeletal troponin I nor could activation of Na+/H+ exchange. Three separate clusters within cardiac troponin I are phosphorylated by protein kinase C, and we set out to determine the contribution of the Thr144 and Ser23/Ser24 clusters to the endothelin-mediated contractile response. Myocyte replacement with a cardiac troponin I containing a Thr144 substituted with the Pro residue found in slow skeletal troponin I resulted in prolonged relaxation in response to acute endothelin compared with control myocytes. Ser23/Ser24 also is a target for protein kinase C phosphorylation of purified cardiac troponin I, and although this cluster was not acutely phosphorylated in intact myocytes, significant phosphorylation developed within 1 h after adding endothelin. Replacement of Ser23/Ser24 with Ala indicated that this cluster contributes significantly to relaxation during more prolonged endothelin stimulation. Overall, results with these mutants provide evidence that Thr144 plays an important role in the acute acceleration of relaxation, whereas Ser23/Ser24 contributes to relaxation during more prolonged activation of protein kinase C by endothelin.
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Affiliation(s)
- Margaret V Westfall
- Department of Surgery, University of Michigan, Ann Arbor, Michigan 48109, USA.
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18
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Harris SP, Rostkova E, Gautel M, Moss RL. Binding of myosin binding protein-C to myosin subfragment S2 affects contractility independent of a tether mechanism. Circ Res 2004; 95:930-6. [PMID: 15472117 DOI: 10.1161/01.res.0000147312.02673.56] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Mutations in the cardiac myosin binding protein-C gene (cMyBP-C) are among the most prevalent causes of inherited hypertrophic cardiomyopathy. Although most cMyBP-C mutations cause reading frameshifts that are predicted to encode truncated peptides, it is not known if or how expression of these peptides causes disease. One possibility is that because the N-terminus contains a unique binding site for the S2 subfragment of myosin, shortened cMyBP-C peptides could directly affect myosin contraction by binding to S2. To test this hypothesis, we compared the effects of a C1C2 protein containing the myosin S2 binding site on contractile properties in permeabilized myocytes from wild-type and cMyBP-C knockout mice. In wild-type myocytes, the C1C2 protein reversibly increased myofilament Ca2+ sensitivity of tension, but had no effect on resting tension. Identical results were observed in cMyBP-C knockout myocytes where C1C2 increased Ca2+ sensitivity of tension with the half-maximal response elicited at approximately 5 micromol/L C1C2. Maximum force was not affected by C1C2. However, phosphorylation of C1C2 by cAMP-dependent protein kinase reduced its ability to increase Ca2+ sensitivity. These results demonstrate that binding of the C1C2 peptide to S2 alone is sufficient to affect myosin contractile function and suggest that regulated binding of cMyBP-C to myosin S2 by phosphorylation directly influences myofilament Ca2+ sensitivity.
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Affiliation(s)
- Samantha P Harris
- Department of Bioengineering, Box 357962, University of Washington, Seattle, WA 98195, USA.
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19
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Westfall MV, Metzger JM. Gene transfer of troponin I isoforms, mutants, and chimeras. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2004; 538:169-74; discussion 174. [PMID: 15098664 DOI: 10.1007/978-1-4419-9029-7_15] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Abstract
Thin filament proteins play an essential role in the regulation of myocardial pressure development. Within the thin filament of the sarcomere, troponin I (TnI) plays a key role in regulating the Ca(2+) sensitivity of force. During myocardial development, there is a transition in TnI isoform expression from the slow skeletal isoform (ssTnI) in embryonic/fetal myocardium to the cardiac isoform (cTnI) expressed in adult hearts. Over a similar developmental time window, the calcium sensitivity of force development also decreases. Gene transfer of ssTnI, and chimeras derived from ssTnI and cTnI, into adult ventricular myocytes have provided insights into the isoform-specific domains of TnI responsible for differentially influencing myofilament Ca(2+) sensitivity. Two separate isoform-specific regions, located in the carboxyl- and amino-portions of the protein, have been identified by comparing Ca(2+)-activated isometric tension in myocytes expressing the TnI isoforms or chimeras. The carboxyl-portion of TnI also contributes to isoform-dependent differences in myofilament sensitivity to acidic pH, which ensues during several myocardial disease states. In contrast, the diminished Ca(2+) sensitivity observed in response to beta-adrenergic-mediated phosphorylation of cardiac TnI requires the amino-portion of the cardiac TnI isoform yet, does not depend on the presence of a specific isoform in the carboxyl-region of TnI. Recent studies with a mutation linked to hypertrophic cardiomyopathy have demonstrated that changes in protein charge also influence the ability of TnI isoforms to regulate myofilament Ca(2+) sensitivity. Information gained from these, and future studies on more localized and specific changes in the amino acid sequence, may one day lead to the use of genetically engineered TnI for therapeutic manipulation of contractile function.
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Affiliation(s)
- Margaret V Westfall
- Department of Physiology, University of Michigan, 1301 E. Catherine St., Ann Arbor, MI 48109, USA.
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20
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Metzger JM, Westfall MV. Covalent and noncovalent modification of thin filament action: the essential role of troponin in cardiac muscle regulation. Circ Res 2004; 94:146-58. [PMID: 14764650 DOI: 10.1161/01.res.0000110083.17024.60] [Citation(s) in RCA: 136] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Troponin is essential for the regulation of cardiac contraction. Troponin is a sarcomeric molecular switch, directly regulating the contractile event in concert with intracellular calcium signals. Troponin isoform switching, missense mutations, proteolytic cleavage, and posttranslational modifications are known to directly affect sarcomeric regulation. This review focuses on physiologically relevant covalent and noncovalent modifications in troponin as part of a thematic series on cardiac thin filament function in health and disease.
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Affiliation(s)
- Joseph M Metzger
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Mich 48109, USA.
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21
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Westfall MV, Borton AR. Role of troponin I phosphorylation in protein kinase C-mediated enhanced contractile performance of rat myocytes. J Biol Chem 2003; 278:33694-700. [PMID: 12815045 DOI: 10.1074/jbc.m305404200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Our goal was to define the role of phosphorylated cardiac troponin-I in the adult myocyte contractile performance response to activated protein kinase C. In agreement with earlier work, endothelin enhanced both adult rat myocyte contractile performance and cardiac troponin-I phosphorylation. Protein kinase C participated in both responses. The role of cardiac troponin-I phosphorylation in the contractile function response to protein kinase C was further investigated using gene transfer into myocytes of troponin-I isoforms/mutants lacking one or more phosphorylation sites previously identified in purified cardiac troponin-I. Sarcomeric replacement with slow skeletal troponin-I-abrogated protein kinase C-mediated troponin-I phosphorylation. In functional studies, endothelin slowed relaxation in myocytes expressing slow skeletal troponin-I, while the relaxation rate increased in myocytes expressing cardiac troponin-I. Based on these results, acceleration of myocyte relaxation during protein kinase C activation largely depended on cardiac troponin-I phosphorylation. Experiments with troponin-I isoform chimeras provided evidence that phosphorylation sites in the amino portion of cardiac troponin I-mediated the protein kinase C acceleration of relaxation. The cardiac troponin-I Thr-144 phosphorylation site identified in earlier biochemical studies was not significantly phosphorylated during the acute contractile response. Thus, amino-terminal protein kinase C-dependent phosphorylation sites in cardiac troponin-I are likely responsible for the accelerated relaxation observed in adult myocytes.
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Affiliation(s)
- Margaret V Westfall
- Department of Surgery, University of Michigan, Ann Arbor, Michigan 48109-0686, USA.
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22
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Metzger JM, Michele DE, Rust EM, Borton AR, Westfall MV. Sarcomere thin filament regulatory isoforms. Evidence of a dominant effect of slow skeletal troponin I on cardiac contraction. J Biol Chem 2003; 278:13118-23. [PMID: 12551900 DOI: 10.1074/jbc.m212601200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Thin filament proteins tropomyosin (Tm), troponin T (TnT), and troponin I (TnI) form an allosteric regulatory complex that is required for normal cardiac contraction. Multiple isoforms of TnT, Tm, and TnI are differentially expressed in both cardiac development and disease, but concurrent TnI, Tm, and TnT isoform switching has hindered assignment of cellular function to these transitions. We systematically incorporated into the adult sarcomere the embryonic/fetal isoforms of Tm, TnT, and TnI by using gene transfer. In separate experiments, greater than 90% of native TnI and 40-50% of native Tm or TnT were specifically replaced. The Ca(2+) sensitivity of tension development was markedly enhanced by TnI replacement but not by TnT or Tm isoform replacement. Titration of TnI replacement from >90% to <30% revealed a dominant functional effect of slow skeletal TnI to modulate regulation. Over this range of isoform replacement, TnI, but not Tm or TnT embryonic isoforms, influenced calcium regulation of contraction, and this identifies TnI as a potential target to modify contractile performance in normal and diseased myocardium.
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Affiliation(s)
- Joseph M Metzger
- Department of Physiology, School of Medicine, University of Michigan, Ann Arbor, Michigan 48109-0622, USA.
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23
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Abstract
Regulation of myocardial contractility by cardiotonic agents is achieved by an increase in intracellular Ca2+ mobilization (upstream mechanism), an increase in Ca2+ binding affinity to troponin C (central mechanism), or facilitation of the process subsequent to Ca2+ binding to troponin C (downstream mechanism). cAMP mediates the regulation induced by Ca2+ mobilizers such as beta-adrenoceptor agonists and selective phosphodiesterase III inhibitors acting through the upstream mechanism. These agents act likewise on the central mechanism to decrease Ca2+ sensitivity of troponin C in association with the cAMP-mediated phosphorylation of troponin I. In addition to such a well-known action of cAMP, recent experimental findings have revealed that Ca2+ sensitizers, such as levosimendan, OR-1896, and UD-CG 212 Cl, require the cAMP-mediated signaling for induction of Ca2+ sensitizing effect. These agents shift the [Ca2+] -force relationship to the left, but their positive inotropic effect (PIE) is inhibited by carbachol, which suppresses selectively the cAMP-mediated PIE. These findings imply that cAMP may play a crucial role in increasing the myofilament Ca2+ sensitivity by cross-talk with the action of individual cardiotonic agents. No clinically available cardiotonic agents act primarily via Ca2+ sensitization, but the PIE of pimobendan and levosimendan is partly mediated by an increase in myofilament Ca2+ sensitivity. Evidence is accumulating that cardiotonic agents with Ca2+ sensitizing action are more effective than agents that act purely via the upstream mechanism in clinical settings. Further clinical trials are required to establish the effectiveness of Ca2+ sensitizers in long-term therapy for congestive heart failure patients.
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Affiliation(s)
- Masao Endoh
- Department of Pharmacology, Yamagata University School of Medicine, Japan.
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24
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Podlowski S, Bramlage P, Baumann G, Morano I, Luther HP. Cardiac troponin I sense-antisense RNA duplexes in the myocardium. J Cell Biochem 2002. [DOI: 10.1002/jcb.10116] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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25
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Westfall MV, Metzger JM. Troponin I isoforms and chimeras: tuning the molecular switch of cardiac contraction. NEWS IN PHYSIOLOGICAL SCIENCES : AN INTERNATIONAL JOURNAL OF PHYSIOLOGY PRODUCED JOINTLY BY THE INTERNATIONAL UNION OF PHYSIOLOGICAL SCIENCES AND THE AMERICAN PHYSIOLOGICAL SOCIETY 2001; 16:278-81. [PMID: 11719605 DOI: 10.1152/physiologyonline.2001.16.6.278] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Troponin I, a key myofilament protein, plays a critical role in regulating force generation in striated muscle by acting as a Ca2+-dependent molecular switch. Domains contributing to the functional properties of troponin I have recently been defined in intact myofilaments of adult cardiac myocytes. This has been attained using gene transfer of chimeras derived from two troponin I isoforms expressed during cardiac development.
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Affiliation(s)
- M V Westfall
- Department of Physiology, University of Michigan, Ann Arbor, Michigan 48109-0686, USA
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26
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Wolska BM, Vijayan K, Arteaga GM, Konhilas JP, Phillips RM, Kim R, Naya T, Leiden JM, Martin AF, de Tombe PP, Solaro RJ. Expression of slow skeletal troponin I in adult transgenic mouse heart muscle reduces the force decline observed during acidic conditions. J Physiol 2001; 536:863-70. [PMID: 11691878 PMCID: PMC2278915 DOI: 10.1111/j.1469-7793.2001.00863.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. Acidosis in cardiac muscle is associated with a decrease in developed force. We hypothesized that slow skeletal troponin I (ssTnI), which is expressed in neonatal hearts, is responsible for the observed decreased response to acidic conditions. To test this hypothesis directly, we used adult transgenic (TG) mice that express ssTnI in the heart. Cardiac TnI (cTnI) was completely replaced by ssTnI either with a FLAG epitope introduced into the N-terminus (TG-ssTnI) or without the epitope (TG-ssTnI) in these mice. TG mice that express cTnI were also generated as a control TG line (TG-cTnI). Non-transgenic (NTG) littermates were used as controls. 2. We measured the force-calcium relationship in all four groups at pH 7.0 and pH 6.5 in detergent-extracted fibre bundles prepared from left ventricular papillary muscles. The force-calcium relationship was identical in fibre bundles from NTG and TG-cTnI mouse hearts, therefore NTG mice served as controls for TG-ssTnIand TG-ssTnI mice. Compared to NTG controls, the force generated by fibre bundles from TG mice expressing ssTnI was more sensitive to Ca(2+). The shift in EC(50) (the concentration of Ca(2+) at which half-maximal force is generated) caused by acidic pH was significantly smaller in fibre bundles isolated from TG hearts compared to those from NTG hearts. However, there was no difference in the force-calcium relationship between hearts from the TG-ssTnIand TG-ssTnI groups. 3. We also isolated papillary muscles from the right ventricle of NTG and TG mouse hearts expressing ssTnI and measured isometric force at extracellular pH 7.33 and pH 6.75. At acidic pH, after an initial decline, twitch force recovered to 60 +/- 3 % (n = 7) in NTG papillary muscles, 98 +/- 2 % (n = 5) in muscles from TG-ssTnIand 96 +/- 3 % (n = 7) in muscles from TG-ssTnI hearts. Our results indicate that TnI isoform composition plays a crucial role in the determination of myocardial force sensitivity to acidosis.
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Affiliation(s)
- B M Wolska
- Department of Medicine, Section of Cardiology, Department of Physiology and Biophysics, Program in Cardiovascular Sciences, University of Illinois at Chicago, Chicago, IL 60612, USA.
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