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Iorga B, Kraft T. Why make a strong muscle weaker? J Gen Physiol 2021; 153:212267. [PMID: 34106212 PMCID: PMC8193566 DOI: 10.1085/jgp.202112928] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Affiliation(s)
- Bogdan Iorga
- Department of Molecular and Cell Physiology, Hannover Medical School, Hannover, Germany.,Department of Physical Chemistry, Faculty of Chemistry, University of Bucharest, Bucharest, Romania
| | - Theresia Kraft
- Department of Molecular and Cell Physiology, Hannover Medical School, Hannover, Germany
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2
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Rayani K, Lin E, Craig C, Lamothe M, Shafaattalab S, Gunawan M, Li AY, Hove-Madsen L, Tibbits GF. Zebrafish as a model of mammalian cardiac function: Optically mapping the interplay of temperature and rate on voltage and calcium dynamics. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2018; 138:69-90. [DOI: 10.1016/j.pbiomolbio.2018.07.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Revised: 07/09/2018] [Accepted: 07/10/2018] [Indexed: 12/27/2022]
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3
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Philipson DJ, DePasquale EC, Yang EH, Baas AS. Emerging pharmacologic and structural therapies for hypertrophic cardiomyopathy. Heart Fail Rev 2018; 22:879-888. [PMID: 28856513 DOI: 10.1007/s10741-017-9648-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Hypertrophic cardiomyopathy is the most common inherited heart disease. Although it was first described over 50 years ago, there has been little in the way of novel disease-specific therapeutic development for these patients. Current treatment practice largely aims at symptomatic control using old drugs made for other diseases and does little to modify the disease course. Septal reduction by surgical myectomy or percutaneous alcohol septal ablation are well-established treatments for pharmacologic-refractory left ventricular outflow tract obstruction in hypertrophic cardiomyopathy patients. In recent years, there has been a relative surge in the development of innovative therapeutics, which aim to target the complex molecular pathophysiology and resulting hemodynamics that underlie hypertrophic cardiomyopathy. Herein, we review the new and emerging therapeutics for hypertrophic cardiomyopathy, which include pharmacologic attenuation of sarcomeric calcium sensitivity, allosteric inhibition of cardiac myosin, myocardial metabolic modulation, and renin-angiotensin-aldosterone system inhibition, as well as structural intervention by percutaneous mitral valve plication and endocardial radiofrequency ablation of septal hypertrophy. In conclusion, while further development of these therapeutic strategies is ongoing, they each mark a significant and promising advancement in treatment for hypertrophic cardiomyopathy patients.
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Affiliation(s)
- Daniel J Philipson
- Department of Medicine, UCLA, 200 UCLA Medical Plaza Suite 420, Los Angeles, CA, 90095, USA.
| | - Eugene C DePasquale
- Ahmanson-UCLA Cardiomyopathy Center, Division of Cardiology, Department of Medicine, UCLA, Los Angeles, CA, USA
| | - Eric H Yang
- Division of Cardiology, Department of Medicine, UCLA, Los Angeles, CA, USA
| | - Arnold S Baas
- Ahmanson-UCLA Cardiomyopathy Center, Division of Cardiology, Department of Medicine, UCLA, Los Angeles, CA, USA
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Friedrich FW, Flenner F, Nasib M, Eschenhagen T, Carrier L. Epigallocatechin-3-Gallate Accelerates Relaxation and Ca 2+ Transient Decay and Desensitizes Myofilaments in Healthy and Mybpc3-Targeted Knock-in Cardiomyopathic Mice. Front Physiol 2016; 7:607. [PMID: 27994558 PMCID: PMC5136558 DOI: 10.3389/fphys.2016.00607] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 11/22/2016] [Indexed: 11/13/2022] Open
Abstract
Background: Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac muscle disease with left ventricular hypertrophy, interstitial fibrosis and diastolic dysfunction. Increased myofilament Ca2+ sensitivity could be the underlying cause of diastolic dysfunction. Epigallocatechin-3-gallate (EGCg), a catechin found in green tea, has been reported to decrease myofilament Ca2+ sensitivity in HCM models with troponin mutations. However, whether this is also the case for HCM-associated thick filament mutations is not known. Therefore, we evaluated whether EGCg affects the behavior of cardiomyocytes and myofilaments of an HCM mouse model carrying a gene mutation in cardiac myosin-binding protein C and exhibiting both increased myofilament Ca2+ sensitivity and diastolic dysfunction. Methods and Results: Acute effects of EGCg were tested on fractional sarcomere shortening and Ca2+ transients in intact ventricular myocytes and on force-Ca2+ relationship of skinned ventricular muscle strips isolated from Mybpc3-targeted knock-in (KI) and wild-type (WT) mice. Fractional sarcomere shortening and Ca2+ transients were analyzed at 37°C under 1-Hz pacing in the absence or presence of EGCg (1.8 μM). At baseline and in the absence of Fura-2, KI cardiomyocytes displayed lower diastolic sarcomere length, higher fractional sarcomere shortening, longer time to peak shortening and time to 50% relengthening than WT cardiomyocytes. In WT and KI neither diastolic sarcomere length nor fractional sarcomere shortening were influenced by EGCg treatment, but relaxation time was reduced, to a greater extent in KI cells. EGCg shortened time to peak Ca2+ and Ca2+ transient decay in Fura-2-loaded WT and KI cardiomyocytes. EGCg did not influence phosphorylation of phospholamban. In skinned cardiac muscle strips, EGCg (30 μM) decreased Ca2+ sensitivity in both groups. Conclusion: EGCg hastened relaxation and Ca2+ transient decay to a larger extent in KI than in WT cardiomyocytes. This effect could be partially explained by myofilament Ca2+ desensitization.
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Affiliation(s)
- Felix W Friedrich
- Cardiovascular Research Center, Department of Experimental Pharmacology and Toxicology, University Medical Center Hamburg-EppendorfHamburg, Germany; German Centre for Cardiovascular Research (DZHK)Hamburg, Germany
| | - Frederik Flenner
- Cardiovascular Research Center, Department of Experimental Pharmacology and Toxicology, University Medical Center Hamburg-EppendorfHamburg, Germany; German Centre for Cardiovascular Research (DZHK)Hamburg, Germany
| | - Mahtab Nasib
- Cardiovascular Research Center, Department of Experimental Pharmacology and Toxicology, University Medical Center Hamburg-EppendorfHamburg, Germany; German Centre for Cardiovascular Research (DZHK)Hamburg, Germany
| | - Thomas Eschenhagen
- Cardiovascular Research Center, Department of Experimental Pharmacology and Toxicology, University Medical Center Hamburg-EppendorfHamburg, Germany; German Centre for Cardiovascular Research (DZHK)Hamburg, Germany
| | - Lucie Carrier
- Cardiovascular Research Center, Department of Experimental Pharmacology and Toxicology, University Medical Center Hamburg-EppendorfHamburg, Germany; German Centre for Cardiovascular Research (DZHK)Hamburg, Germany
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Elhamine F, Iorga B, Krüger M, Hunger M, Eckhardt J, Sreeram N, Bennink G, Brockmeier K, Pfitzer G, Stehle R. Postnatal Development of Right Ventricular Myofibrillar Biomechanics in Relation to the Sarcomeric Protein Phenotype in Pediatric Patients with Conotruncal Heart Defects. J Am Heart Assoc 2016; 5:JAHA.116.003699. [PMID: 27353610 PMCID: PMC4937289 DOI: 10.1161/jaha.116.003699] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Background The postnatal development of myofibrillar mechanics, a major determinant of heart function, is unknown in pediatric patients with tetralogy of Fallot and related structural heart defects. We therefore determined the mechanical properties of myofibrils isolated from right ventricular tissue samples from such patients in relation to the developmental changes of the isoforms expression pattern of key sarcomere proteins involved in the contractile process. Methods and Results Tissue samples from the infundibulum obtained during surgery from 25 patients (age range 15 days to 11 years, median 7 months) were split into half for mechanical investigations and expression analysis of titin, myosin heavy and light chain 1, troponin‐T, and troponin‐I. Of these proteins, fetal isoforms of only myosin light chain 1 (ALC‐1) and troponin‐I (ssTnI) were highly expressed in neonates, amounting to, respectively, 40% and 80%, while the other proteins had switched to the adult isoforms before or around birth. ALC‐1 and ssTnI expression subsequently declined monoexponentially with a halftime of 4.3 and 5.8 months, respectively. Coincident with the expression of ssTnI, Ca2+ sensitivity of contraction was high in neonates and subsequently declined in parallel with the decline in ssTnI expression. Passive tension positively correlated with Ca2+ sensitivity but not with titin expression. Contraction kinetics, maximal Ca2+‐activated force, and the fast phase of the biphasic relaxation positively correlated with the expression of ALC‐1. Conclusions The developmental changes in myofibrillar biomechanics can be ascribed to fetal‐to‐adult isoform transition of key sarcomeric proteins, which evolves regardless of the specific congenital cardiac malformations in our pediatric patients.
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Affiliation(s)
- Fatiha Elhamine
- Institute of Vegetative Physiology, University of Cologne, Köln, Germany
| | - Bogdan Iorga
- Institute of Vegetative Physiology, University of Cologne, Köln, Germany Department of Physical Chemistry, University of Bucharest, Romania
| | - Martina Krüger
- Institute of Vegetative Physiology, University of Cologne, Köln, Germany
| | - Mona Hunger
- Clinics for Anesthesiology and Surgical Intensive Care, University of Cologne, Köln, Germany
| | - Jan Eckhardt
- Institute of Vegetative Physiology, University of Cologne, Köln, Germany
| | | | | | | | - Gabriele Pfitzer
- Institute of Vegetative Physiology, University of Cologne, Köln, Germany
| | - Robert Stehle
- Institute of Vegetative Physiology, University of Cologne, Köln, Germany
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6
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Vikhorev PG, Ferenczi MA, Marston SB. Instrumentation to study myofibril mechanics from static to artificial simulations of cardiac cycle. MethodsX 2016; 3:156-70. [PMID: 27047763 PMCID: PMC4796715 DOI: 10.1016/j.mex.2016.02.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Accepted: 02/28/2016] [Indexed: 01/26/2023] Open
Abstract
Many causes of heart muscle diseases and skeletal muscle diseases are inherited and caused by mutations in genes of sarcomere proteins which play either a structural or contractile role in the muscle cell. Tissue samples from human hearts with mutations can be obtained but often samples are only a few milligrams and it is necessary to freeze them for storage and transportation. Myofibrils are the fundamental contractile components of the muscle cell and retain all structural elements and contractile proteins performing in contractile event; moreover viable myofibrils can be obtained from frozen tissue.We are describing a versatile technique for measuring the contractility and its Ca2+ regulation in single myofibrils. The control of myofibril length, incubation medium and data acquisition is carried out using a digital acquisition board via computer software. Using computer control it is possible not only to measure contractile and mechanical parameters but also simulate complex protocols such as a cardiac cycle to vary length and medium independently. This single myofibril force assay is well suited for physiological measurements. The system can be adapted to measure tension amplitude, rates of contraction and relaxation, Ca2+ dependence of these parameters in dose-response measurements, length-dependent activation, stretch response, myofibril elasticity and response to simulated cardiac cycle length changes. Our approach provides an all-round quantitative way to measure myofibrils performance and to observe the effect of mutations or posttranslational modifications. The technique has been demonstrated by the study of contraction in heart with hypertrophic or dilated cardiomyopathy mutations in sarcomere proteins.
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Affiliation(s)
- Petr G Vikhorev
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Michael A Ferenczi
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Singapore
| | - Steven B Marston
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
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7
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Genge CE, Lin E, Lee L, Sheng X, Rayani K, Gunawan M, Stevens CM, Li AY, Talab SS, Claydon TW, Hove-Madsen L, Tibbits GF. The Zebrafish Heart as a Model of Mammalian Cardiac Function. Rev Physiol Biochem Pharmacol 2016; 171:99-136. [PMID: 27538987 DOI: 10.1007/112_2016_5] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Zebrafish (Danio rerio) are widely used as vertebrate model in developmental genetics and functional genomics as well as in cardiac structure-function studies. The zebrafish heart has been increasingly used as a model of human cardiac function, in part, due to the similarities in heart rate and action potential duration and morphology with respect to humans. The teleostian zebrafish is in many ways a compelling model of human cardiac function due to the clarity afforded by its ease of genetic manipulation, the wealth of developmental biological information, and inherent suitability to a variety of experimental techniques. However, in addition to the numerous advantages of the zebrafish system are also caveats related to gene duplication (resulting in paralogs not present in human or other mammals) and fundamental differences in how zebrafish hearts function. In this review, we discuss the use of zebrafish as a cardiac function model through the use of techniques such as echocardiography, optical mapping, electrocardiography, molecular investigations of excitation-contraction coupling, and their physiological implications relative to that of the human heart. While some of these techniques (e.g., echocardiography) are particularly challenging in the zebrafish because of diminutive size of the heart (~1.5 mm in diameter) critical information can be derived from these approaches and are discussed in detail in this article.
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Affiliation(s)
- Christine E Genge
- Molecular Cardiac Physiology Group, Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6
| | - Eric Lin
- Molecular Cardiac Physiology Group, Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6
| | - Ling Lee
- BC Children's Hospital Research Institute, Vancouver, BC, Canada, V5Z 4H4
| | - XiaoYe Sheng
- BC Children's Hospital Research Institute, Vancouver, BC, Canada, V5Z 4H4
| | - Kaveh Rayani
- Molecular Cardiac Physiology Group, Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6
| | - Marvin Gunawan
- Molecular Cardiac Physiology Group, Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6
| | - Charles M Stevens
- Molecular Cardiac Physiology Group, Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6.,BC Children's Hospital Research Institute, Vancouver, BC, Canada, V5Z 4H4
| | - Alison Yueh Li
- Molecular Cardiac Physiology Group, Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6
| | - Sanam Shafaat Talab
- Molecular Cardiac Physiology Group, Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6
| | - Thomas W Claydon
- Molecular Cardiac Physiology Group, Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6
| | - Leif Hove-Madsen
- Molecular Cardiac Physiology Group, Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6.,Cardiovascular Research Centre CSIC-ICCC, Hospital de Sant Pau, Barcelona, Spain
| | - Glen F Tibbits
- Molecular Cardiac Physiology Group, Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6. .,BC Children's Hospital Research Institute, Vancouver, BC, Canada, V5Z 4H4.
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8
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Flenner F, Friedrich FW, Ungeheuer N, Christ T, Geertz B, Reischmann S, Wagner S, Stathopoulou K, Söhren KD, Weinberger F, Schwedhelm E, Cuello F, Maier LS, Eschenhagen T, Carrier L. Ranolazine antagonizes catecholamine-induced dysfunction in isolated cardiomyocytes, but lacks long-term therapeutic effects in vivo in a mouse model of hypertrophic cardiomyopathy. Cardiovasc Res 2015; 109:90-102. [PMID: 26531128 DOI: 10.1093/cvr/cvv247] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2015] [Accepted: 10/27/2015] [Indexed: 12/19/2022] Open
Abstract
AIMS Hypertrophic cardiomyopathy (HCM) is often accompanied by increased myofilament Ca(2+) sensitivity and diastolic dysfunction. Recent findings indicate increased late Na(+) current density in human HCM cardiomyocytes. Since ranolazine has the potential to decrease myofilament Ca(2+) sensitivity and late Na(+) current, we investigated its effects in an Mybpc3-targeted knock-in (KI) mouse model of HCM. METHODS AND RESULTS Unloaded sarcomere shortening and Ca(2+) transients were measured in KI and wild-type (WT) cardiomyocytes. Measurements were performed at baseline (1 Hz) and under increased workload (30 nM isoprenaline (ISO), 5 Hz) in the absence or presence of 10 µM ranolazine. KI myocytes showed shorter diastolic sarcomere length at baseline, stronger inotropic response to ISO, and drastic drop of diastolic sarcomere length under increased workload. Ranolazine attenuated ISO responses in WT and KI cells and prevented workload-induced diastolic failure in KI. Late Na(+) current density was diminished and insensitive to ranolazine in KI cardiomyocytes. Ca(2+) sensitivity of skinned KI trabeculae was slightly decreased by ranolazine. Phosphorylation analysis of cAMP-dependent protein kinase A-target proteins and ISO concentration-response measurements on muscle strips indicated antagonism at β-adrenoceptors with 10 µM ranolazine shifting the ISO response by 0.6 log units. Six-month treatment with ranolazine (plasma level >20 µM) demonstrated a β-blocking effect, but did not reverse cardiac hypertrophy or dysfunction in KI mice. CONCLUSION Ranolazine improved tolerance to high workload in mouse HCM cardiomyocytes, not by blocking late Na(+) current, but by antagonizing β-adrenergic stimulation and slightly desensitizing myofilaments to Ca(2+). This effect did not translate in therapeutic efficacy in vivo.
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Affiliation(s)
- Frederik Flenner
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Martinistraße 52, D-20246 Hamburg, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Hamburg, Germany
| | - Felix W Friedrich
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Martinistraße 52, D-20246 Hamburg, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Hamburg, Germany
| | - Nele Ungeheuer
- Clinic for Cardiology and Pneumology, Georg-August-University Göttingen, Göttingen, Germany
| | - Torsten Christ
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Martinistraße 52, D-20246 Hamburg, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Hamburg, Germany
| | - Birgit Geertz
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Martinistraße 52, D-20246 Hamburg, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Hamburg, Germany
| | - Silke Reischmann
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Martinistraße 52, D-20246 Hamburg, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Hamburg, Germany
| | - Stefan Wagner
- Clinic for Cardiology and Pneumology, Georg-August-University Göttingen, Göttingen, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Göttingen, Göttingen, Germany Department for Internal Medicine II, University Hospital Regensburg, Regensburg, Germany
| | - Konstantina Stathopoulou
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Martinistraße 52, D-20246 Hamburg, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Hamburg, Germany
| | - Klaus-Dieter Söhren
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Martinistraße 52, D-20246 Hamburg, Germany
| | - Florian Weinberger
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Martinistraße 52, D-20246 Hamburg, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Hamburg, Germany
| | - Edzard Schwedhelm
- DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Hamburg, Germany Department of Clinical Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Friederike Cuello
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Martinistraße 52, D-20246 Hamburg, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Hamburg, Germany
| | - Lars S Maier
- Clinic for Cardiology and Pneumology, Georg-August-University Göttingen, Göttingen, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Göttingen, Göttingen, Germany Department for Internal Medicine II, University Hospital Regensburg, Regensburg, Germany
| | - Thomas Eschenhagen
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Martinistraße 52, D-20246 Hamburg, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Hamburg, Germany
| | - Lucie Carrier
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Martinistraße 52, D-20246 Hamburg, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Hamburg, Germany
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9
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Sheng JJ, Jin JP. TNNI1, TNNI2 and TNNI3: Evolution, regulation, and protein structure-function relationships. Gene 2015; 576:385-94. [PMID: 26526134 DOI: 10.1016/j.gene.2015.10.052] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Revised: 09/21/2015] [Accepted: 10/20/2015] [Indexed: 12/11/2022]
Abstract
Troponin I (TnI) is the inhibitory subunit of the troponin complex in the sarcomeric thin filament of striated muscle and plays a central role in the calcium regulation of contraction and relaxation. Vertebrate TnI has evolved into three isoforms encoded by three homologous genes: TNNI1 for slow skeletal muscle TnI, TNNI2 for fast skeletal muscle TnI and TNNI3 for cardiac TnI, which are expressed under muscle type-specific and developmental regulations. To summarize the current knowledge on the TnI isoform genes and products, this review focuses on the evolution, gene regulation, posttranslational modifications, and structure-function relationship of TnI isoform proteins. Their physiological and medical significances are also discussed.
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Affiliation(s)
- Juan-Juan Sheng
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, USA
| | - Jian-Ping Jin
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, USA.
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10
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Vikhorev PG, Song W, Wilkinson R, Copeland O, Messer AE, Ferenczi MA, Marston SB. The dilated cardiomyopathy-causing mutation ACTC E361G in cardiac muscle myofibrils specifically abolishes modulation of Ca(2+) regulation by phosphorylation of troponin I. Biophys J 2015; 107:2369-80. [PMID: 25418306 PMCID: PMC4241448 DOI: 10.1016/j.bpj.2014.10.024] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Revised: 09/25/2014] [Accepted: 10/16/2014] [Indexed: 01/30/2023] Open
Abstract
Phosphorylation of troponin I by protein kinase A (PKA) reduces Ca2+ sensitivity and increases the rate of Ca2+ release from troponin C and the rate of relaxation in cardiac muscle. In vitro experiments indicate that mutations that cause dilated cardiomyopathy (DCM) uncouple this modulation, but this has not been demonstrated in an intact contractile system. Using a Ca2+-jump protocol, we measured the effect of the DCM-causing mutation ACTC E361G on the equilibrium and kinetic parameters of Ca2+ regulation of contractility in single transgenic mouse heart myofibrils. We used propranolol treatment of mice to reduce the level of troponin I and myosin binding protein C (MyBP-C) phosphorylation in their hearts before isolating the myofibrils. In nontransgenic mouse myofibrils, the Ca2+ sensitivity of force was increased, the fast relaxation phase rate constant, kREL, was reduced, and the length of the slow linear phase, tLIN, was increased when the troponin I phosphorylation level was reduced from 1.02 to 0.3 molPi/TnI (EC50 P/unP = 1.8 ± 0.2, p < 0.001). Native myofibrils from ACTC E361G transgenic mice had a 2.4-fold higher Ca2+ sensitivity than nontransgenic mouse myofibrils. Strikingly, the Ca2+ sensitivity and relaxation parameters of ACTC E361G myofibrils did not depend on the troponin I phosphorylation level (EC50 P/unP = 0.88 ± 0.17, p = 0.39). Nevertheless, modulation of the Ca2+ sensitivity of ACTC E361G myofibrils by sarcomere length or EMD57033 was indistinguishable from that of nontransgenic myofibrils. Overall, EC50 measured in different conditions varied over a 7-fold range. The time course of relaxation, as defined by tLIN and kREL, was correlated with EC50 but varied by just 2.7- and 3.3-fold, respectively. Our results confirm that troponin I phosphorylation specifically alters the Ca2+ sensitivity of isometric tension and the time course of relaxation in cardiac muscle myofibrils. Moreover, the DCM-causing mutation ACTC E361G blunts this phosphorylation-dependent response without affecting other parameters of contraction, including length-dependent activation and the response to EMD57033.
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Affiliation(s)
- Petr G Vikhorev
- National Heart and Lung Institute, Imperial College London, London, UK
| | - Weihua Song
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore
| | - Ross Wilkinson
- National Heart and Lung Institute, Imperial College London, London, UK
| | - O'Neal Copeland
- National Heart and Lung Institute, Imperial College London, London, UK
| | - Andrew E Messer
- National Heart and Lung Institute, Imperial College London, London, UK
| | - Michael A Ferenczi
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore
| | - Steven B Marston
- National Heart and Lung Institute, Imperial College London, London, UK.
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11
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Elhamine F, Radke MH, Pfitzer G, Granzier H, Gotthardt M, Stehle R. Deletion of the titin N2B region accelerates myofibrillar force development but does not alter relaxation kinetics. J Cell Sci 2014; 127:3666-74. [PMID: 24982444 DOI: 10.1242/jcs.141796] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Cardiac titin is the main determinant of sarcomere stiffness during diastolic relaxation. To explore whether titin stiffness affects the kinetics of cardiac myofibrillar contraction and relaxation, we used subcellular myofibrils from the left ventricles of homozygous and heterozygous N2B-knockout mice which express truncated cardiac titins lacking the unique elastic N2B region. Compared with myofibrils from wild-type mice, myofibrils from knockout and heterozygous mice exhibit increased passive myofibrillar stiffness. To determine the kinetics of Ca(2+)-induced force development (rate constant kACT), myofibrils from knockout, heterozygous and wild-type mice were stretched to the same sarcomere length (2.3 µm) and rapidly activated with Ca(2+). Additionally, mechanically induced force-redevelopment kinetics (rate constant kTR) were determined by slackening and re-stretching myofibrils during Ca(2+)-mediated activation. Myofibrils from knockout mice exhibited significantly higher kACT, kTR and maximum Ca(2+)-activated tension than myofibrils from wild-type mice. By contrast, the kinetic parameters of biphasic force relaxation induced by rapidly reducing [Ca(2+)] were not significantly different among the three genotypes. These results indicate that increased titin stiffness promotes myocardial contraction by accelerating the formation of force-generating cross-bridges without decelerating relaxation.
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Affiliation(s)
- Fatiha Elhamine
- Institute of Vegetative Physiology, University of Cologne, Robert Koch Str. 39, D-50931 Köln, Germany
| | - Michael H Radke
- Neuromuscular and Cardiovascular Cell Biology, Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Str. 10, D-13125 Berlin, Germany
| | - Gabriele Pfitzer
- Institute of Vegetative Physiology, University of Cologne, Robert Koch Str. 39, D-50931 Köln, Germany
| | - Henk Granzier
- Sarver Molecular Cardiovascular Research and Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85724, USA
| | - Michael Gotthardt
- Neuromuscular and Cardiovascular Cell Biology, Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Str. 10, D-13125 Berlin, Germany
| | - Robert Stehle
- Institute of Vegetative Physiology, University of Cologne, Robert Koch Str. 39, D-50931 Köln, Germany
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12
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Sheng JJ, Jin JP. Gene regulation, alternative splicing, and posttranslational modification of troponin subunits in cardiac development and adaptation: a focused review. Front Physiol 2014; 5:165. [PMID: 24817852 PMCID: PMC4012202 DOI: 10.3389/fphys.2014.00165] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Accepted: 04/10/2014] [Indexed: 12/19/2022] Open
Abstract
Troponin plays a central role in regulating the contraction and relaxation of vertebrate striated muscles. This review focuses on the isoform gene regulation, alternative RNA splicing, and posttranslational modifications of troponin subunits in cardiac development and adaptation. Transcriptional and posttranscriptional regulations such as phosphorylation and proteolysis modifications, and structure-function relationships of troponin subunit proteins are summarized. The physiological and pathophysiological significances are discussed for impacts on cardiac muscle contractility, heart function, and adaptations in health and diseases.
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Affiliation(s)
- Juan-Juan Sheng
- Department of Physiology, Wayne State University School of Medicine Detroit, MI, USA
| | - Jian-Ping Jin
- Department of Physiology, Wayne State University School of Medicine Detroit, MI, USA
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13
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Song W, Vikhorev PG, Kashyap MN, Rowlands C, Ferenczi MA, Woledge RC, MacLeod K, Marston S, Curtin NA. Mechanical and energetic properties of papillary muscle from ACTC E99K transgenic mouse models of hypertrophic cardiomyopathy. Am J Physiol Heart Circ Physiol 2013; 304:H1513-24. [PMID: 23604709 DOI: 10.1152/ajpheart.00951.2012] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We compared the contractile performance of papillary muscle from a mouse model of hypertrophic cardiomyopathy [α-cardiac actin (ACTC) E99K mutation] with nontransgenic (non-TG) littermates. In isometric twitches, ACTC E99K papillary muscle produced three to four times greater force than non-TG muscle under the same conditions independent of stimulation frequency and temperature, whereas maximum isometric force in myofibrils from these muscles was not significantly different. ACTC E99K muscle relaxed slower than non-TG muscle in both papillary muscle (1.4×) and myofibrils (1.7×), whereas the rate of force development after stimulation was the same as non-TG muscle for both electrical stimulation in intact muscle and after a Ca²⁺ jump in myofibrils. The EC₅₀ for Ca²⁺ activation of force in myofibrils was 0.39 ± 0.33 μmol/l in ACTC E99K myofibrils and 0.80 ± 0.11 μmol/l in non-TG myofibrils. There were no significant differences in the amplitude and time course of the Ca²⁺ transient in myocytes from ACTC E99K and non-TG mice. We conclude that hypercontractility is caused by higher myofibrillar Ca²⁺ sensitivity in ACTC E99K muscles. Measurement of the energy (work + heat) released in actively cycling heart muscle showed that for both genotypes, the amount of energy turnover increased with work done but with decreasing efficiency as energy turnover increased. Thus, ACTC E99K mouse heart muscle produced on average 3.3-fold more work than non-TG muscle, and the cost in terms of energy turnover was disproportionately higher than in non-TG muscles. Efficiency for ACTC E99K muscle was in the range of 11-16% and for non-TG muscle was 15-18%.
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Affiliation(s)
- Weihua Song
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
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14
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Disease-related cardiac troponins alter thin filament Ca2+ association and dissociation rates. PLoS One 2012; 7:e38259. [PMID: 22675533 PMCID: PMC3366952 DOI: 10.1371/journal.pone.0038259] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2012] [Accepted: 05/04/2012] [Indexed: 11/19/2022] Open
Abstract
The contractile response of the heart can be altered by disease-related protein modifications to numerous contractile proteins. By utilizing an IAANS labeled fluorescent troponin C, [Formula: see text], we examined the effects of ten disease-related troponin modifications on the Ca(2+) binding properties of the troponin complex and the reconstituted thin filament. The selected modifications are associated with a broad range of cardiac diseases: three subtypes of familial cardiomyopathies (dilated, hypertrophic and restrictive) and ischemia-reperfusion injury. Consistent with previous studies, the majority of the protein modifications had no effect on the Ca(2+) binding properties of the isolated troponin complex. However, when incorporated into the thin filament, dilated cardiomyopathy mutations desensitized (up to 3.3-fold), while hypertrophic and restrictive cardiomyopathy mutations, and ischemia-induced truncation of troponin I, sensitized the thin filament to Ca(2+) (up to 6.3-fold). Kinetically, the dilated cardiomyopathy mutations increased the rate of Ca(2+) dissociation from the thin filament (up to 2.5-fold), while the hypertrophic and restrictive cardiomyopathy mutations, and the ischemia-induced truncation of troponin I decreased the rate (up to 2-fold). The protein modifications also increased (up to 5.4-fold) or decreased (up to 2.5-fold) the apparent rate of Ca(2+) association to the thin filament. Thus, the disease-related protein modifications alter Ca(2+) binding by influencing both the association and dissociation rates of thin filament Ca(2+) exchange. These alterations in Ca(2+) exchange kinetics influenced the response of the thin filament to artificial Ca(2+) transients generated in a stopped-flow apparatus. Troponin C may act as a hub, sensing physiological and pathological stimuli to modulate the Ca(2+)-binding properties of the thin filament and influence the contractile performance of the heart.
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15
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Kurosaka S, Leu NA, Pavlov I, Han X, Ribeiro PAB, Xu T, Bunte R, Saha S, Wang J, Cornachione A, Mai W, Yates JR, Rassier DE, Kashina A. Arginylation regulates myofibrils to maintain heart function and prevent dilated cardiomyopathy. J Mol Cell Cardiol 2012; 53:333-41. [PMID: 22626847 DOI: 10.1016/j.yjmcc.2012.05.007] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/18/2012] [Revised: 04/25/2012] [Accepted: 05/12/2012] [Indexed: 01/25/2023]
Abstract
Protein arginylation mediated by arginyltransferase (ATE1) is essential for heart formation during embryogenesis, however its cell-autonomous role in cardiomyocytes and the differentiated heart muscle has never been investigated. To address this question, we generated cardiac muscle-specific Ate1 knockout mice, in which Ate1 deletion was driven by α-myosin heavy chain promoter (αMHC-Ate1 mouse). These mice were initially viable, but developed severe cardiac contractility defects, dilated cardiomyopathy, and thrombosis over time, resulting in high rates of lethality after 6months of age. These symptoms were accompanied by severe ultrastructural defects in cardiac myofibrils, seen in the newborns and far preceding the onset of cardiomyopathy, suggesting that these defects were primary and likely underlay the development of the future heart defects. Several major sarcomeric proteins were arginylated in vivo. Moreover, Ate1 deletion in the hearts resulted in a significant reduction of active and passive myofibril forces, suggesting that arginylation is critical for both myofibril structural integrity and contractility. Thus, arginylation is essential for maintaining the heart function by regulation of the major myofibril proteins and myofibril forces, and its absence in the heart muscle leads to progressive heart failure through cardiomyocyte-specific defects.
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Affiliation(s)
- Satoshi Kurosaka
- Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104, USA
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16
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Liu B, Lee RS, Biesiadecki BJ, Tikunova SB, Davis JP. Engineered troponin C constructs correct disease-related cardiac myofilament calcium sensitivity. J Biol Chem 2012; 287:20027-36. [PMID: 22511780 DOI: 10.1074/jbc.m111.334953] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Aberrant myofilament Ca(2+) sensitivity is commonly observed with multiple cardiac diseases, especially familial cardiomyopathies. Although the etiology of the cardiomyopathies remains unclear, improving cardiac muscle Ca(2+) sensitivity through either pharmacological or genetic approaches shows promise of alleviating the disease-related symptoms. Due to its central role as the Ca(2+) sensor for cardiac muscle contraction, troponin C (TnC) stands out as an obvious and versatile target to reset disease-associated myofilament Ca(2+) sensitivity back to normal. To test the hypothesis that aberrant myofilament Ca(2+) sensitivity and its related function can be corrected through rationally engineered TnC constructs, three thin filament protein modifications representing different proteins (troponin I or troponin T), modifications (missense mutation, deletion, or truncation), and disease subtypes (familial or acquired) were studied. A fluorescent TnC was utilized to measure Ca(2+) binding to TnC in the physiologically relevant biochemical model system of reconstituted thin filaments. Consistent with the pathophysiology, the restrictive cardiomyopathy mutation, troponin I R192H, and ischemia-induced truncation of troponin I (residues 1-192) increased the Ca(2+) sensitivity of TnC on the thin filament, whereas the dilated cardiomyopathy mutation, troponin T ΔK210, decreased the Ca(2+) sensitivity of TnC on the thin filament. Rationally engineered TnC constructs corrected the abnormal Ca(2+) sensitivities of the thin filament, reconstituted actomyosin ATPase activity, and force generation in skinned trabeculae. Thus, the present study provides a novel and versatile therapeutic strategy to restore diseased cardiac muscle Ca(2+) sensitivity.
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Affiliation(s)
- Bin Liu
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio 43210, USA
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17
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Iorga B, Neacsu CD, Neiss WF, Wagener R, Paulsson M, Stehle R, Pfitzer G. Micromechanical function of myofibrils isolated from skeletal and cardiac muscles of the zebrafish. ACTA ACUST UNITED AC 2011; 137:255-70. [PMID: 21357732 PMCID: PMC3047611 DOI: 10.1085/jgp.201010568] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The zebrafish is a potentially important and cost-effective model for studies of development, motility, regeneration, and inherited human diseases. The object of our work was to show whether myofibrils isolated from zebrafish striated muscle represent a valid subcellular contractile model. These organelles, which determine contractile function in muscle, were used in a fast kinetic mechanical technique based on an atomic force probe and video microscopy. Mechanical variables measured included rate constants of force development (kACT) after Ca2+ activation and of force decay (τREL−1) during relaxation upon Ca2+ removal, isometric force at maximal (Fmax) or partial Ca2+ activations, and force response to an external stretch applied to the relaxed myofibril (Fpass). Myotomal myofibrils from larvae developed greater active and passive forces, and contracted and relaxed faster than skeletal myofibrils from adult zebrafish, indicating developmental changes in the contractile organelles of the myotomal muscles. Compared with murine cardiac myofibrils, measurements of adult zebrafish ventricular myofibrils show that kACT, Fmax, Ca2+ sensitivity of the force, and Fpass were comparable and τREL−1 was smaller. These results suggest that cardiac myofibrils from zebrafish, like those from mice, are suitable contractile models to study cardiac function at the sarcomeric level. The results prove the practicability and usefulness of mechanical and kinetic investigations on myofibrils isolated from larval and adult zebrafish muscles. This novel approach for investigating myotomal and myocardial function in zebrafish at the subcellular level, combined with the powerful genetic manipulations that are possible in the zebrafish, will allow the investigation of the functional primary consequences of human disease–related mutations in sarcomeric proteins in the zebrafish model.
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Affiliation(s)
- Bogdan Iorga
- Institute of Vegetative Physiology, University of Cologne, Cologne 50931, Germany.
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18
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Solaro RJ, Sheehan KA, Lei M, Ke Y. The curious role of sarcomeric proteins in control of diverse processes in cardiac myocytes. ACTA ACUST UNITED AC 2011; 136:13-9. [PMID: 20584888 PMCID: PMC2894547 DOI: 10.1085/jgp.201010462] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- R John Solaro
- Department of Physiology and Biophysics and Center for Cardiovascular Research, University of Illinois at Chicago College of Medicine, Chicago, IL 60611, USA.
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19
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Pinto JR, Reynaldo DP, Parvatiyar MS, Dweck D, Liang J, Jones MA, Sorenson MM, Potter JD. Strong cross-bridges potentiate the Ca(2+) affinity changes produced by hypertrophic cardiomyopathy cardiac troponin C mutants in myofilaments: a fast kinetic approach. J Biol Chem 2010; 286:1005-13. [PMID: 21056975 DOI: 10.1074/jbc.m110.168583] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
This spectroscopic study examined the steady-state and kinetic parameters governing the cross-bridge effect on the increased Ca(2+) affinity of hypertrophic cardiomyopathy-cardiac troponin C (HCM-cTnC) mutants. Previously, we found that incorporation of the A8V and D145E HCM-cTnC mutants, but not E134D into thin filaments (TFs), increased the apparent Ca(2+) affinity relative to TFs containing the WT protein. Here, we show that the addition of myosin subfragment 1 (S1) to TFs reconstituted with these mutants in the absence of MgATP(2-), the condition conducive to rigor cross-bridge formation, further increased the apparent Ca(2+) affinity. Stopped-flow fluorescence techniques were used to determine the kinetics of Ca(2+) dissociation (k(off)) from the cTnC mutants in the presence of TFs and S1. At a high level of complexity (i.e. TF + S1), an increase in the Ca(2+) affinity and decrease in k(off) was achieved for the A8V and D145E mutants when compared with WT. Therefore, it appears that the cTnC Ca(2+) off-rate is most likely to be affected rather than the Ca(2+) on rate. At all levels of TF complexity, the results obtained with the E134D mutant reproduced those seen with the WT protein. We conclude that strong cross-bridges potentiate the Ca(2+)-sensitizing effect of HCM-cTnC mutants on the myofilament. Finally, the slower k(off) from the A8V and D145E mutants can be directly correlated with the diastolic dysfunction seen in these patients.
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Affiliation(s)
- Jose Renato Pinto
- Department of Molecular and Cellular Pharmacology, Miller School of Medicine, University of Miami, Miami, Florida 33136, USA
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20
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Gasanov AG, Bershova TV, Basargina EN, Bakanov MI. [Molecular mechanisms of genetic damages of the myocardium in cardiomyopathy]. BIOMEDIT︠S︡INSKAI︠A︡ KHIMII︠A︡ 2010; 56:319-28. [PMID: 20695211 DOI: 10.18097/pbmc20105603319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The review highlighted problems of reorganization of myocardical contractile and cytoskeletal proteins in cardiomyopathy (CM). The role of the genetic factors coding contractile proteins, proteins of thin and thick filaments, and also extracellular matrix proteins in processes of formation and development of hypertrophic (HCM) and dilated (DCM) cardiomyopathy are analyzed. The mechanisms responsible for the changes in cardiac proteins on regulation involved into force generation, its transfer, recycling ATP, impairments in transmembranal signals, that finally lead to cardiac cell dysfunction determining various manifestations of CM are considered.
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21
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Palpant NJ, Houang EM, Delport W, Hastings KEM, Onufriev AV, Sham YY, Metzger JM. Pathogenic peptide deviations support a model of adaptive evolution of chordate cardiac performance by troponin mutations. Physiol Genomics 2010; 42:287-99. [PMID: 20423961 DOI: 10.1152/physiolgenomics.00033.2010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In cardiac muscle, the troponin (cTn) complex is a key regulator of myofilament calcium sensitivity because it serves as a molecular switch required for translating myocyte calcium fluxes into sarcomeric contraction and relaxation. Studies of several species suggest that ectotherm chordates have myofilaments with heightened calcium responsiveness. However, genetic polymorphisms in cTn that cause increased myofilament sensitivity to activating calcium in mammals result in cardiac disease including arrhythmias, diastolic dysfunction, and increased susceptibility to sudden cardiac death. We hypothesized that specific residue modifications in the regulatory arm of troponin I (TnI) were critical in mediating the observed decrease in myofilament calcium sensitivity within the mammalian taxa. We performed large-scale phylogenetic analysis, atomic resolution molecular dynamics simulations and modeling, and computational alanine scanning. This study provides evidence that a His to Ala substitution within mammalian cardiac TnI (cTnI) reduced the thermodynamic potential at the interface between cTnI and cardiac TnC (cTnC) in the calcium-saturated state by disrupting a strong intermolecular electrostatic interaction. This key residue modification reduced myofilament calcium sensitivity by making cTnI molecularly untethered from cTnC. To meet the requirements for refined mammalian adult cardiac performance, we propose that compensatory evolutionary pressures favored mutations that enhanced the relaxation properties of cTn by decreasing its sensitivity to activating calcium.
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Affiliation(s)
- Nathan J Palpant
- Department of Integrative Biology and Physiology, University of Minnesota Academic Health Center, 321 Church Street SE, Minneapolis, MN 55455, USA
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Insights into the kinetics of Ca2+-regulated contraction and relaxation from myofibril studies. Pflugers Arch 2009; 458:337-57. [PMID: 19165498 DOI: 10.1007/s00424-008-0630-2] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2008] [Accepted: 12/24/2008] [Indexed: 01/06/2023]
Abstract
Muscle contraction results from force-generating interactions between myosin cross-bridges on the thick filament and actin on the thin filament. The force-generating interactions are regulated by Ca(2+) via specialised proteins of the thin filament. It is controversial how the contractile and regulatory systems dynamically interact to determine the time course of muscle contraction and relaxation. Whereas kinetics of Ca(2+)-induced thin-filament regulation is often investigated with isolated proteins, force kinetics is usually studied in muscle fibres. The gap between studies on isolated proteins and structured fibres is now bridged by recent techniques that analyse the chemical and mechanical kinetics of small components of a muscle fibre, subcellular myofibrils isolated from skeletal and cardiac muscle. Formed of serially arranged repeating units called sarcomeres, myofibrils have a complete fully structured ensemble of contractile and Ca(2+) regulatory proteins. The small diameter of myofibrils (few micrometres) facilitates analysis of the kinetics of sarcomere contraction and relaxation induced by rapid changes of [ATP] or [Ca(2+)]. Among the processes studied on myofibrils are: (1) the Ca(2+)-regulated switch on/off of the troponin complex, (2) the chemical steps in the cross-bridge adenosine triphosphatase cycle, (3) the mechanics of force generation and (4) the length dynamics of individual sarcomeres. These studies give new insights into the kinetics of thin-filament regulation and of cross-bridge turnover, how cross-bridges transform chemical energy into mechanical work, and suggest that the cross-bridge ensembles of each half-sarcomere cooperate with each other across the half-sarcomere borders. Additionally, we now have a better understanding of muscle relaxation and its impairment in certain muscle diseases.
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Solaro RJ, de Tombe PP. Review focus series: sarcomeric proteins as key elements in integrated control of cardiac function. Cardiovasc Res 2007; 77:616-8. [DOI: 10.1093/cvr/cvn004] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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