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Patel JR, Park KJ, Bradshaw AS, Phan T, Fitzsimons DP. Cooperative mechanisms underlie differences in myocardial contractile dynamics between large and small mammals. J Gen Physiol 2023; 155:e202213315. [PMID: 37725091 PMCID: PMC10509357 DOI: 10.1085/jgp.202213315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Revised: 06/08/2023] [Accepted: 08/29/2023] [Indexed: 09/21/2023] Open
Abstract
Ca2+ binding to troponin C (TnC) and myosin cross-bridge binding to actin act in a synergistic cooperative manner to modulate myocardial contraction and relaxation. The responsiveness of the myocardial thin filament to the activating effects of Ca2+ and myosin cross-bridge binding has been well-characterized in small mammals (e.g., mice). Given the nearly 10-fold difference in resting heart rates and twitch kinetics between small and large mammals, it is unlikely that the cooperative mechanisms underlying thin filament activation are identical in these two species. To test this idea, we measured the Ca2+ dependencies of steady-state force and the rate constant of force redevelopment (ktr) in murine and porcine permeabilized ventricular myocardium. While murine myocardium exhibited a steep activation-dependence of ktr, the activation-dependent profile of ktr was significantly reduced in porcine ventricular myocardium. Further insight was attained by examining force-pCa and ktr-pCa relationships. In the murine myocardium, the pCa50 for ktr was right-shifted compared with the pCa50 for force, meaning that increases in steady-state force occurred well before increases in the rate of force redevelopment were observed. In the porcine myocardium, we observed a tighter coupling of the force-pCa and ktr-pCa relationships, as evidenced by near-maximal rates of force redevelopment at low levels of Ca2+ activation. These results demonstrate that the molecular mechanisms underlying the cooperative activation of force are a dynamic property of the mammalian heart, involving, at least in part, the species- and tissue-specific expression of cardiac myosin heavy chain isoforms.
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Affiliation(s)
- Jitandrakumar R. Patel
- Department of Cell and Regenerative Biology, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
| | - Kayla J.V. Park
- Department of Animal, Veterinary, and Food Sciences, College of Agricultural and Life Sciences, University of Idaho, Moscow, ID, USA
| | - Aidan S. Bradshaw
- Department of Animal, Veterinary, and Food Sciences, College of Agricultural and Life Sciences, University of Idaho, Moscow, ID, USA
| | - Tuan Phan
- Institute for Modeling Collaboration and Innovation, University of Idaho, Moscow, ID, USA
| | - Daniel P. Fitzsimons
- Department of Animal, Veterinary, and Food Sciences, College of Agricultural and Life Sciences, University of Idaho, Moscow, ID, USA
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2
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Dowling P, Gargan S, Swandulla D, Ohlendieck K. Fiber-Type Shifting in Sarcopenia of Old Age: Proteomic Profiling of the Contractile Apparatus of Skeletal Muscles. Int J Mol Sci 2023; 24:ijms24032415. [PMID: 36768735 PMCID: PMC9916839 DOI: 10.3390/ijms24032415] [Citation(s) in RCA: 24] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 01/20/2023] [Accepted: 01/23/2023] [Indexed: 01/28/2023] Open
Abstract
The progressive loss of skeletal muscle mass and concomitant reduction in contractile strength plays a central role in frailty syndrome. Age-related neuronal impairments are closely associated with sarcopenia in the elderly, which is characterized by severe muscular atrophy that can considerably lessen the overall quality of life at old age. Mass-spectrometry-based proteomic surveys of senescent human skeletal muscles, as well as animal models of sarcopenia, have decisively improved our understanding of the molecular and cellular consequences of muscular atrophy and associated fiber-type shifting during aging. This review outlines the mass spectrometric identification of proteome-wide changes in atrophying skeletal muscles, with a focus on contractile proteins as potential markers of changes in fiber-type distribution patterns. The observed trend of fast-to-slow transitions in individual human skeletal muscles during the aging process is most likely linked to a preferential susceptibility of fast-twitching muscle fibers to muscular atrophy. Studies with senescent animal models, including mostly aged rodent skeletal muscles, have confirmed fiber-type shifting. The proteomic analysis of fast versus slow isoforms of key contractile proteins, such as myosin heavy chains, myosin light chains, actins, troponins and tropomyosins, suggests them as suitable bioanalytical tools of fiber-type transitions during aging.
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Affiliation(s)
- Paul Dowling
- Department of Biology, Maynooth University, National University of Ireland, W23 F2H6 Maynooth, Co. Kildare, Ireland
- Kathleen Lonsdale Institute for Human Health Research, Maynooth University, W23 F2H6 Maynooth, Co. Kildare, Ireland
| | - Stephen Gargan
- Department of Biology, Maynooth University, National University of Ireland, W23 F2H6 Maynooth, Co. Kildare, Ireland
- Kathleen Lonsdale Institute for Human Health Research, Maynooth University, W23 F2H6 Maynooth, Co. Kildare, Ireland
| | - Dieter Swandulla
- Institute of Physiology, University of Bonn, D53115 Bonn, Germany
| | - Kay Ohlendieck
- Department of Biology, Maynooth University, National University of Ireland, W23 F2H6 Maynooth, Co. Kildare, Ireland
- Kathleen Lonsdale Institute for Human Health Research, Maynooth University, W23 F2H6 Maynooth, Co. Kildare, Ireland
- Correspondence: ; Tel.: +353-1-7083842
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3
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Hassoun R, Budde H, Mügge A, Hamdani N. Cardiomyocyte Dysfunction in Inherited Cardiomyopathies. Int J Mol Sci 2021; 22:11154. [PMID: 34681814 PMCID: PMC8541428 DOI: 10.3390/ijms222011154] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 10/08/2021] [Accepted: 10/13/2021] [Indexed: 01/10/2023] Open
Abstract
Inherited cardiomyopathies form a heterogenous group of disorders that affect the structure and function of the heart. Defects in the genes encoding sarcomeric proteins are associated with various perturbations that induce contractile dysfunction and promote disease development. In this review we aimed to outline the functional consequences of the major inherited cardiomyopathies in terms of myocardial contraction and kinetics, and to highlight the structural and functional alterations in some sarcomeric variants that have been demonstrated to be involved in the pathogenesis of the inherited cardiomyopathies. A particular focus was made on mutation-induced alterations in cardiomyocyte mechanics. Since no disease-specific treatments for familial cardiomyopathies exist, several novel agents have been developed to modulate sarcomere contractility. Understanding the molecular basis of the disease opens new avenues for the development of new therapies. Furthermore, the earlier the awareness of the genetic defect, the better the clinical prognostication would be for patients and the better the prevention of development of the disease.
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Affiliation(s)
- Roua Hassoun
- Institut für Forschung und Lehre (IFL), Molecular and Experimental Cardiology, Ruhr University Bochum, 44801 Bochum, Germany
- Department of Cardiology, St. Josef-Hospital and Bergmannsheil, Ruhr University Bochum, 44801 Bochum, Germany
| | - Heidi Budde
- Institut für Forschung und Lehre (IFL), Molecular and Experimental Cardiology, Ruhr University Bochum, 44801 Bochum, Germany
- Department of Cardiology, St. Josef-Hospital and Bergmannsheil, Ruhr University Bochum, 44801 Bochum, Germany
| | - Andreas Mügge
- Institut für Forschung und Lehre (IFL), Molecular and Experimental Cardiology, Ruhr University Bochum, 44801 Bochum, Germany
- Department of Cardiology, St. Josef-Hospital and Bergmannsheil, Ruhr University Bochum, 44801 Bochum, Germany
| | - Nazha Hamdani
- Institut für Forschung und Lehre (IFL), Molecular and Experimental Cardiology, Ruhr University Bochum, 44801 Bochum, Germany
- Department of Cardiology, St. Josef-Hospital and Bergmannsheil, Ruhr University Bochum, 44801 Bochum, Germany
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4
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Barrick SK, Greenberg L, Greenberg MJ. A troponin T variant linked with pediatric dilated cardiomyopathy reduces the coupling of thin filament activation to myosin and calcium binding. Mol Biol Cell 2021; 32:1677-1689. [PMID: 34161147 PMCID: PMC8684737 DOI: 10.1091/mbc.e21-02-0082] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Dilated cardiomyopathy (DCM) is a significant cause of pediatric heart failure. Mutations in proteins that regulate cardiac muscle contraction can cause DCM; however, the mechanisms by which molecular-level mutations contribute to cellular dysfunction are not well understood. Better understanding of these mechanisms might enable the development of targeted therapeutics that benefit patient subpopulations with mutations that cause common biophysical defects. We examined the molecular- and cellular-level impacts of a troponin T variant associated with pediatric-onset DCM, R134G. The R134G variant decreased calcium sensitivity in an in vitro motility assay. Using stopped-flow and steady-state fluorescence measurements, we determined the molecular mechanism of the altered calcium sensitivity: R134G decouples calcium binding by troponin from the closed-to-open transition of the thin filament and decreases the cooperativity of myosin binding to regulated thin filaments. Consistent with the prediction that these effects would cause reduced force per sarcomere, cardiomyocytes carrying the R134G mutation are hypocontractile. They also show hallmarks of DCM that lie downstream of the initial insult, including disorganized sarcomeres and cellular hypertrophy. These results reinforce the importance of multiscale studies to fully understand mechanisms underlying human disease and highlight the value of mechanism-based precision medicine approaches for DCM.
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Affiliation(s)
- Samantha K Barrick
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Lina Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
| | - Michael J Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
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5
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Chen YJ, Chien CS, Chiang CE, Chen CH, Cheng HM. From Genetic Mutations to Molecular Basis of Heart Failure Treatment: An Overview of the Mechanism and Implication of the Novel Modulators for Cardiac Myosin. Int J Mol Sci 2021; 22:6617. [PMID: 34205587 PMCID: PMC8234187 DOI: 10.3390/ijms22126617] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2021] [Revised: 06/11/2021] [Accepted: 06/17/2021] [Indexed: 02/06/2023] Open
Abstract
Heart failure (HF) is a syndrome encompassing several important etiologies that lead to the imbalance between oxygen demand and supply. Despite the usage of guideline-directed medical therapy for HF has shown better outcomes, novel therapeutic strategies are desirable, especially for patients with preserved or mildly reduced left ventricular ejection fraction. In this regard, understanding the molecular basis for cardiomyopathies is expected to fill in the knowledge gap and generate new therapies to improve prognosis for HF. This review discusses an evolutionary mechanism designed to regulate cardiac contraction and relaxation through the most often genetically determined cardiomyopathies associated with HF. In addition, both the myosin inhibitor and myosin activator are promising new treatments for cardiomyopathies. A comprehensive review from genetic mutations to the molecular basis of direct sarcomere modulators will help shed light on future studies for a better characterization of HF etiologies and potential therapeutic targets.
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Affiliation(s)
- Yu-Jen Chen
- Department of Internal Medicine, Division of Cardiovascular Medicine, Wan Fang Hospital, Taipei Medical University, Taipei 116081, Taiwan;
- Department of Internal Medicine, Division of Cardiology, School of Medicine, College of Medicine, Taipei Medical University, Taipei 110301, Taiwan
- Institute of Public Health, National Yang Ming Chiao Tung University, Taipei 112304, Taiwan
| | - Chian-Shiu Chien
- Innovative Cellular Therapy Center, Department of Medical Research, Taipei Veterans General Hospital, Taipei 112201, Taiwan;
| | - Chern-En Chiang
- General Clinical Research Center, Taipei Veterans General Hospital, Taipei 112201, Taiwan;
- Department of Medicine, National Yang Ming Chiao Tung University College of Medicine, Taipei 112304, Taiwan
| | - Chen-Huan Chen
- Department of Medical Education, Taipei Veterans General Hospital, Taipei 112201, Taiwan;
- College of Medicine, National Yang Ming Chiao Tung University, Taipei 112201, Taiwan
| | - Hao-Min Cheng
- Institute of Public Health, National Yang Ming Chiao Tung University, Taipei 112304, Taiwan
- Department of Medicine, National Yang Ming Chiao Tung University College of Medicine, Taipei 112304, Taiwan
- Center for Evidence-Based Medicine, Taipei Veterans General Hospital, Taipei 112201, Taiwan
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6
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Pertici I, Taft MH, Greve JN, Fedorov R, Caremani M, Manstein DJ. Allosteric modulation of cardiac myosin mechanics and kinetics by the conjugated omega-7,9 trans-fat rumenic acid. J Physiol 2021; 599:3639-3661. [PMID: 33942907 DOI: 10.1113/jp281563] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Accepted: 04/28/2021] [Indexed: 01/23/2023] Open
Abstract
KEY POINTS Direct binding of rumenic acid to the cardiac myosin-2 motor domain increases the release rate for orthophosphate and increases the Ca2+ responsiveness of cardiac muscle at low load. Physiological cellular concentrations of rumenic acid affect the ATP turnover rates of the super-relaxed and disordered relaxed states of β-cardiac myosin, leading to a net increase in myocardial metabolic load. In Ca2+ -activated trabeculae, rumenic acid exerts a direct inhibitory effect on the force-generating mechanism without affecting the number of force-generating motors. In the presence of saturating actin concentrations rumenic acid binds to the β-cardiac myosin-2 motor domain with an EC50 of 200 nM. Molecular docking studies provide information about the binding site, the mode of binding, and associated allosteric communication pathways. Free rumenic acid may exceed thresholds in cardiomyocytes above which contractile efficiency is reduced and interference with small molecule therapeutics, targeting cardiac myosin, occurs. ABSTRACT Based on experiments using purified myosin motor domains, reconstituted actomyosin complexes and rat heart ventricular trabeculae, we demonstrate direct binding of rumenic acid, the cis-delta-9-trans-delta-11 isomer of conjugated linoleic acid, to an allosteric site located in motor domain of mammalian cardiac myosin-2 isoforms. In the case of porcine β-cardiac myosin, the EC50 for rumenic acid varies from 10.5 μM in the absence of actin to 200 nM in the presence of saturating concentrations of actin. Saturating concentrations of rumenic acid increase the maximum turnover of basal and actin-activated ATPase activity of β-cardiac myosin approximately 2-fold but decrease the force output per motor by 23% during isometric contraction. The increase in ATP turnover is linked to an acceleration of the release of the hydrolysis product orthophosphate. In the presence of 5 μM rumenic acid, the difference in the rate of ATP turnover by the super-relaxed and disordered relaxed states of cardiac myosin increases from 4-fold to 20-fold. The equilibrium between the two functional myosin states is not affected by rumenic acid. Calcium responsiveness is increased under zero-load conditions but unchanged under load. Molecular docking studies provide information about the rumenic acid binding site, the mode of binding, and associated allosteric communication pathways. They show how the isoform-specific replacement of residues in the binding cleft induces a different mode of rumenic acid binding in the case of non-muscle myosin-2C and blocks binding to skeletal muscle and smooth muscle myosin-2 isoforms.
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Affiliation(s)
- Irene Pertici
- PhysioLab, University of Florence, Florence, 50019, Italy.,Institute for Biophysical Chemistry, OE4350, Medizinische Hochschule Hannover, Hannover, 30625, Germany
| | - Manuel H Taft
- Institute for Biophysical Chemistry, OE4350, Medizinische Hochschule Hannover, Hannover, 30625, Germany
| | - Johannes N Greve
- Institute for Biophysical Chemistry, OE4350, Medizinische Hochschule Hannover, Hannover, 30625, Germany
| | - Roman Fedorov
- Division of Structural Biochemistry, OE8830, Medizinische Hochschule Hannover, Hannover, 30625, Germany.,RESiST, Cluster of Excellence 2155, Medizinische Hochschule Hannover, Hannover, 30625, Germany
| | - Marco Caremani
- PhysioLab, University of Florence, Florence, 50019, Italy
| | - Dietmar J Manstein
- Institute for Biophysical Chemistry, OE4350, Medizinische Hochschule Hannover, Hannover, 30625, Germany.,Division of Structural Biochemistry, OE8830, Medizinische Hochschule Hannover, Hannover, 30625, Germany.,RESiST, Cluster of Excellence 2155, Medizinische Hochschule Hannover, Hannover, 30625, Germany
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7
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Racca AW, Rynkiewicz MJ, LaFave N, Ghosh A, Lehman W, Moore JR. M8R tropomyosin mutation disrupts actin binding and filament regulation: The beginning affects the middle and end. J Biol Chem 2020; 295:17128-17137. [PMID: 33020181 PMCID: PMC7863880 DOI: 10.1074/jbc.ra120.014713] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Revised: 09/28/2020] [Indexed: 11/06/2022] Open
Abstract
Dilated cardiomyopathy (DCM) is associated with mutations in cardiomyocyte sarcomeric proteins, including α-tropomyosin. In conjunction with troponin, tropomyosin shifts to regulate actomyosin interactions. Tropomyosin molecules overlap via tropomyosin-tropomyosin head-to-tail associations, forming a continuous strand along the thin filament. These associations are critical for propagation of tropomyosin's reconfiguration along the thin filament and key for the cooperative switching between heart muscle contraction and relaxation. Here, we tested perturbations in tropomyosin structure, biochemistry, and function caused by the DCM-linked mutation, M8R, which is located at the overlap junction. Localized and nonlocalized structural effects of the mutation were found in tropomyosin that ultimately perturb its thin filament regulatory function. Comparison of mutant and WT α-tropomyosin was carried out using in vitro motility assays, CD, actin co-sedimentation, and molecular dynamics simulations. Regulated thin filament velocity measurements showed that the presence of M8R tropomyosin decreased calcium sensitivity and thin filament cooperativity. The co-sedimentation of actin and tropomyosin showed weakening of actin-mutant tropomyosin binding. The binding of troponin T's N terminus to the actin-mutant tropomyosin complex was also weakened. CD and molecular dynamics indicate that the M8R mutation disrupts the four-helix bundle at the head-to-tail junction, leading to weaker tropomyosin-tropomyosin binding and weaker tropomyosin-actin binding. Molecular dynamics revealed that altered end-to-end bond formation has effects extending toward the central region of the tropomyosin molecule, which alter the azimuthal position of tropomyosin, likely disrupting the mutant thin filament response to calcium. These results demonstrate that mutation-induced alterations in tropomyosin-thin filament interactions underlie the altered regulatory phenotype and ultimately the pathogenesis of DCM.
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Affiliation(s)
- Alice Ward Racca
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts, USA
| | - Michael J Rynkiewicz
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA
| | - Nicholas LaFave
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts, USA
| | - Anita Ghosh
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA
| | - William Lehman
- Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts, USA
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts, USA.
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8
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Kalda M, Vendelin M. Cardiac muscle regulatory units are predicted to interact stronger than neighboring cross-bridges. Sci Rep 2020; 10:5530. [PMID: 32218497 PMCID: PMC7099078 DOI: 10.1038/s41598-020-62452-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Accepted: 03/14/2020] [Indexed: 11/09/2022] Open
Abstract
Strong interactions between cross-bridges (XB) and regulatory units (RU) lead to a steep response of cardiac muscle to an increase in intracellular calcium. We developed a model to quantitatively assess the influence of different types of interactions within the sarcomere on the properties of cardiac muscle. In the model, the ensembles consisting of cross-bridge groups connected by elastic tropomyosin are introduced, and their dynamics is described by a set of partial differential equations. Through large scans in the free energy landscape, we demonstrate the different influence of RU-RU, XB-XB, and XB-RU interactions on the cooperativity coefficient of calcium binding, developed maximal force, and calcium sensitivity. The model solution was fitted to reproduce experimental data on force development during isometric contraction, shortening in physiological contraction, and ATP consumption by acto-myosin. On the basis of the fits, we quantified the free energy change introduced through RU-RU and XB-XB interactions and showed that RU-RU interaction leads to ~ 5 times larger change in the free energy profile of the reaction than XB-XB interaction. Due to the deterministic description of muscle contraction and its thermodynamic consistency, we envision that the developed model can be used to study heart muscle biophysics on tissue and organ levels.
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Affiliation(s)
- Mari Kalda
- Laboratory of Systems Biology, Department of Cybernetics, School of Science, Tallinn University of Technology, 12618, Tallinn, Estonia
| | - Marko Vendelin
- Laboratory of Systems Biology, Department of Cybernetics, School of Science, Tallinn University of Technology, 12618, Tallinn, Estonia.
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9
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Small Molecule Effectors of Myosin Function. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1239:61-84. [DOI: 10.1007/978-3-030-38062-5_5] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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10
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Sundar S, Rynkiewicz MJ, Ghosh A, Lehman W, Moore JR. Cardiomyopathy Mutation Alters End-to-End Junction of Tropomyosin and Reduces Calcium Sensitivity. Biophys J 2019; 118:303-312. [PMID: 31882250 DOI: 10.1016/j.bpj.2019.11.3396] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 10/30/2019] [Accepted: 11/18/2019] [Indexed: 12/24/2022] Open
Abstract
Muscle contraction is governed by tropomyosin (Tpm) shifting azimuthally between three states on F-actin (B-, C-, and M-states) in response to calcium binding to troponin and actomyosin cross-bridge formation. The Tpm coiled coil polymerizes head to tail along the long-pitch helix of F-actin to form continuous superhelical cables that wrap around the actin filaments. The end-to-end bonds formed between the N- and C-terminus of adjacent Tpm molecules define Tpm continuity and play a critical role in the ability of Tpm to cooperatively bind to actin, thus facilitating Tpm conformational switching to cooperatively propagate along F-actin. We expect that a missense mutation in this critical overlap region associated with dilated cardiomyopathy, A277V, will alter Tpm binding and thin filament activation by altering the overlap structure. Here, we used cosedimentation assays and in vitro motility assays to determine how the mutation alters Tpm binding to actin and its ability to regulate actomyosin interactions. Analytical viscometry coupled with molecular dynamics simulations showed that the A277V mutation results in enhanced Tpm end-to-end bond strength and a reduced curvature of the Tpm overlap domain. The mutant Tpm exhibited enhanced actin-Tpm binding affinity, consistent with overlap stabilization. The observed A277V-induced decrease in cooperative activation observed with regulated thin filament motility indicates that increased overlap stabilization is not correlated with Tpm-Tpm overlap binding strength or mechanical rigidity as is often assumed. Instead, A277V-induced structural changes result in local and delocalized increases in Tpm flexibility and prominent coiled-coil twisting in pseudorepeat 4. An A277V-induced decrease in Ca2+ sensitivity, consistent with a mutation-induced bolstering of the B-state Tpm-actin electrostatic contacts and an increased Tpm troponin T1 binding affinity, was also observed.
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Affiliation(s)
- SaiLavanyaa Sundar
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts
| | - Michael J Rynkiewicz
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts
| | - Anita Ghosh
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts
| | - William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts.
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11
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Multiscale Hill-type modeling of the mechanical muscle behavior driven by the neural drive in isometric conditions. Comput Biol Med 2019; 115:103480. [PMID: 31629271 DOI: 10.1016/j.compbiomed.2019.103480] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 10/01/2019] [Accepted: 10/01/2019] [Indexed: 11/20/2022]
Abstract
In this study, we present a new model describing the mechanical behavior of the skeletal muscle during isometric contraction. This model is based on a former Hill-inspired model detailing the electromechanical behavior of the muscle based on the Huxley formulation. However, in this new multiscale model the muscle is represented at the Motor Unit (MU) scale. The proposed model is driven by a physiological input describing the firing moments of the activated MUs. Definition of both voluntary and evoked MU recruitment schemes are described, enabling the study of both contractions in isometric conditions. During this type of contraction, there is no movement of the joints and the tendon-muscle complex remains at the same length. Moreover, some well-established macroscopic relationships such as force-length or force-velocity properties are considered. A comparison with a twitch model using the same input definition is provided with both recruitment schemes exhibiting limitations of twitch type models. Finally, the proposed model is validated with a comparison between simulated and recorded force profiles following eight electrical stimulations pulses in isometric conditions. The simulated muscle force was generated to mimic the one recorded from the quadriceps of a patient implanted with a functional electrical stimulation neuroprosthesis. This validation demonstrates the ability of the proposed model to reproduce realistically the skeletal muscle contractions and to take into account subject-specific parameters.
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12
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Aboelkassem Y, Powers JD, McCabe KJ, McCulloch AD. Multiscale Models of Cardiac Muscle Biophysics and Tissue Remodeling in Hypertrophic Cardiomyopathies. CURRENT OPINION IN BIOMEDICAL ENGINEERING 2019; 11:35-44. [PMID: 31886450 DOI: 10.1016/j.cobme.2019.09.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Myocardial hypertrophy is the result of sustained perturbations to the mechanical and/or neurohormonal homeostasis of cardiac cells and is driven by integrated, multiscale biophysical and biochemical processes that are currently not well defined. In this brief review, we highlight recent computational and experimental models of cardiac hypertrophy that span mechanisms from the molecular level to the tissue level. Specifically, we focus on: (i) molecular-level models of the structural dynamics of sarcomere proteins in hypertrophic hearts, (ii) cellular-level models of excitation-contraction coupling and mechanosensitive signaling in disease-state myocytes, and (iii) organ-level models of myocardial growth kinematics and predictors thereof. Finally, we discuss how spanning these scales and combining multiple experimental/computational models will provide new information about the processes governing hypertrophy and potential methods to prevent or reverse them.
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Affiliation(s)
- Yasser Aboelkassem
- Department of Bioengineering, University of California San Diego, La Jolla, CA 92093, USA
| | - Joseph D Powers
- Department of Bioengineering, University of California San Diego, La Jolla, CA 92093, USA
| | - Kimberly J McCabe
- Department of Computational Physiology, Simula Research Laboratory, Lysaker, Norway
| | - Andrew D McCulloch
- Department of Bioengineering, University of California San Diego, La Jolla, CA 92093, USA
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13
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Lehman W, Moore JR, Campbell SG, Rynkiewicz MJ. The Effect of Tropomyosin Mutations on Actin-Tropomyosin Binding: In Search of Lost Time. Biophys J 2019; 116:2275-2284. [PMID: 31130236 PMCID: PMC6588729 DOI: 10.1016/j.bpj.2019.05.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Revised: 05/06/2019] [Accepted: 05/09/2019] [Indexed: 12/14/2022] Open
Abstract
The initial binding of tropomyosin onto actin filaments and then its polymerization into continuous cables on the filament surface must be precisely tuned to overall thin-filament structure, function, and performance. Low-affinity interaction of tropomyosin with actin has to be sufficiently strong to localize the tropomyosin on actin, yet not so tight that regulatory movement on filaments is curtailed. Likewise, head-to-tail association of tropomyosin molecules must be favorable enough to promote tropomyosin cable formation but not so tenacious that polymerization precedes filament binding. Arguably, little molecular detail on early tropomyosin binding steps has been revealed since Wegner's seminal studies on filament assembly almost 40 years ago. Thus, interpretation of mutation-based actin-tropomyosin binding anomalies leading to cardiomyopathies cannot be described fully. In vitro, tropomyosin binding is masked by explosive tropomyosin polymerization once cable formation is initiated on actin filaments. In contrast, in silico analysis, characterizing molecular dynamics simulations of single wild-type and mutant tropomyosin molecules on F-actin, is not complicated by tropomyosin polymerization at all. In fact, molecular dynamics performed here demonstrates that a midpiece tropomyosin domain is essential for normal actin-tropomyosin interaction and that this interaction is strictly conserved in a number of tropomyosin mutant species. Elsewhere along these mutant molecules, twisting and bending corrupts the tropomyosin superhelices as they "lose their grip" on F-actin. We propose that residual interactions displayed by these mutant tropomyosin structures with actin mimic ones that occur in early stages of thin-filament generation, as if the mutants are recapitulating the assembly process but in reverse. We conclude therefore that an initial binding step in tropomyosin assembly onto actin involves interaction of the essential centrally located domain.
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Affiliation(s)
- William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts.
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, Massachusetts
| | - Stuart G Campbell
- Departments of Biomedical Engineering and Cellular and Molecular Physiology, Yale University, New Haven, Connecticut
| | - Michael J Rynkiewicz
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts
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14
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Dasbiswas K, Hu S, Schnorrer F, Safran SA, Bershadsky AD. Ordering of myosin II filaments driven by mechanical forces: experiments and theory. Philos Trans R Soc Lond B Biol Sci 2019; 373:rstb.2017.0114. [PMID: 29632266 DOI: 10.1098/rstb.2017.0114] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/30/2017] [Indexed: 12/27/2022] Open
Abstract
Myosin II filaments form ordered superstructures in both cross-striated muscle and non-muscle cells. In cross-striated muscle, myosin II (thick) filaments, actin (thin) filaments and elastic titin filaments comprise the stereotypical contractile units of muscles called sarcomeres. Linear chains of sarcomeres, called myofibrils, are aligned laterally in registry to form cross-striated muscle cells. The experimentally observed dependence of the registered organization of myofibrils on extracellular matrix elasticity has been proposed to arise from the interactions of sarcomeric contractile elements (considered as force dipoles) through the matrix. Non-muscle cells form small bipolar filaments built of less than 30 myosin II molecules. These filaments are associated in registry forming superstructures ('stacks') orthogonal to actin filament bundles. Formation of myosin II filament stacks requires the myosin II ATPase activity and function of the actin filament crosslinking, polymerizing and depolymerizing proteins. We propose that the myosin II filaments embedded into elastic, intervening actin network (IVN) function as force dipoles that interact attractively through the IVN. This is in analogy with the theoretical picture developed for myofibrils where the elastic medium is now the actin cytoskeleton itself. Myosin stack formation in non-muscle cells provides a novel mechanism for the self-organization of the actin cytoskeleton at the level of the entire cell.This article is part of the theme issue 'Self-organization in cell biology'.
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Affiliation(s)
- Kinjal Dasbiswas
- James Franck Institute, University of Chicago, Chicago, IL 60637, USA
| | - Shiqiong Hu
- Mechanobiology Institute, National University of Singapore, Singapore 117411, Republic of Singapore.,Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Frank Schnorrer
- Aix Marseille University, CNRS, IBDM, 13288 Marseille, France
| | - Samuel A Safran
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Alexander D Bershadsky
- Mechanobiology Institute, National University of Singapore, Singapore 117411, Republic of Singapore .,Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
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15
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Moving beyond simple answers to complex disorders in sarcomeric cardiomyopathies: the role of integrated systems. Pflugers Arch 2019; 471:661-671. [PMID: 30848350 DOI: 10.1007/s00424-019-02269-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Accepted: 03/01/2019] [Indexed: 12/26/2022]
Abstract
The classic clinical definition of hypertrophic cardiomyopathy (HCM) as originally described by Teare is deceptively simple, "left ventricular hypertrophy in the absence of any identifiable cause." Longitudinal studies, however, including a seminal study performed by Frank and Braunwald in 1968, clearly described the disorder much as we know it today, a complex, progressive, and highly variable cardiomyopathy affecting ~ 1/500 individuals worldwide. Subsequent genetic linkage studies in the early 1990s identified mutations in virtually all of the protein components of the cardiac sarcomere as the primary molecular cause of HCM. In addition, a substantial proportion of inherited dilated cardiomyopathy (DCM) has also been linked to sarcomeric protein mutations. Despite our deep understanding of the overall function of the sarcomere as the primary driver of cardiac contractility, the ability to use genotype in patient management remains elusive. A persistent challenge in the field from both the biophysical and clinical standpoints is how to rigorously link high-resolution protein dynamics and mechanics to the long-term cardiovascular remodeling process that characterizes these complex disorders. In this review, we will explore the depth of the problem from both the standpoint of a multi-subunit, highly conserved and dynamic "machine" to the resultant clinical and structural human phenotype with an emphasis on new, integrative approaches that can be widely applied to identify both novel disease mechanisms and new therapeutic targets for these primary biophysical disorders of the cardiac sarcomere.
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16
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Lehman W, Rynkiewicz MJ, Moore JR. A new twist on tropomyosin binding to actin filaments: perspectives on thin filament function, assembly and biomechanics. J Muscle Res Cell Motil 2019; 41:23-38. [PMID: 30771202 DOI: 10.1007/s10974-019-09501-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2018] [Accepted: 02/07/2019] [Indexed: 02/07/2023]
Abstract
Tropomyosin, best known for its role in the steric regulation of muscle contraction, polymerizes head-to-tail to form cables localized along the length of both muscle and non-muscle actin-based thin filaments. In skeletal and cardiac muscles, tropomyosin, under the control of troponin and myosin, moves in a cooperative manner between blocked, closed and open positions on filaments, thereby masking and exposing actin-binding sites necessary for myosin crossbridge head interactions. While the coiled-coil signature of tropomyosin appears to be simple, closer inspection reveals surprising structural complexity required to perform its role in steric regulation. For example, component α-helices of coiled coils are typically zippered together along a continuous core hydrophobic stripe. Tropomyosin, however, contains a number of anomalous, functionally controversial, core amino acid residues. We argue that the atypical residues at this interface, including clusters of alanines and a charged aspartate, are required for preshaping tropomyosin to readily fit to the surface of the actin filament, but do so without compromising tropomyosin rigidity once the filament is assembled. Indeed, persistence length measurements of tropomyosin are characteristic of a semi-rigid cable, in this case conducive to cooperative movement on thin filaments. In addition, we also maintain that tropomyosin displays largely unrecognized and residue-specific torsional variance, which is involved in optimizing contacts between actin and tropomyosin on the assembled thin filament. Corresponding twist-induced stiffness may also enhance cooperative translocation of tropomyosin across actin filaments. We conclude that anomalous core residues of tropomyosin facilitate thin filament regulatory behavior in a multifaceted way.
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Affiliation(s)
- William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA, USA.
| | - Michael J Rynkiewicz
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA, USA
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts-Lowell, Lowell, MA, USA
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17
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van der Velden J, Stienen GJM. Cardiac Disorders and Pathophysiology of Sarcomeric Proteins. Physiol Rev 2019; 99:381-426. [PMID: 30379622 DOI: 10.1152/physrev.00040.2017] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The sarcomeric proteins represent the structural building blocks of heart muscle, which are essential for contraction and relaxation. During recent years, it has become evident that posttranslational modifications of sarcomeric proteins, in particular phosphorylation, tune cardiac pump function at rest and during exercise. This delicate, orchestrated interaction is also influenced by mutations, predominantly in sarcomeric proteins, which cause hypertrophic or dilated cardiomyopathy. In this review, we follow a bottom-up approach starting from a description of the basic components of cardiac muscle at the molecular level up to the various forms of cardiac disorders at the organ level. An overview is given of sarcomere changes in acquired and inherited forms of cardiac disease and the underlying disease mechanisms with particular reference to human tissue. A distinction will be made between the primary defect and maladaptive/adaptive secondary changes. Techniques used to unravel functional consequences of disease-induced protein changes are described, and an overview of current and future treatments targeted at sarcomeric proteins is given. The current evidence presented suggests that sarcomeres not only form the basis of cardiac muscle function but also represent a therapeutic target to combat cardiac disease.
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Affiliation(s)
- Jolanda van der Velden
- Amsterdam UMC, Vrije Universiteit Amsterdam, Physiology, Amsterdam Cardiovascular Sciences, Amsterdam , The Netherlands ; and Department of Physiology, Kilimanjaro Christian Medical University College, Moshi, Tanzania
| | - Ger J M Stienen
- Amsterdam UMC, Vrije Universiteit Amsterdam, Physiology, Amsterdam Cardiovascular Sciences, Amsterdam , The Netherlands ; and Department of Physiology, Kilimanjaro Christian Medical University College, Moshi, Tanzania
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18
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Campbell KS, Yengo CM, Lee LC, Kotter J, Sorrell VL, Guglin M, Wenk JF. Closing the therapeutic loop. Arch Biochem Biophys 2019; 663:129-131. [PMID: 30639169 DOI: 10.1016/j.abb.2019.01.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 12/12/2018] [Accepted: 01/08/2019] [Indexed: 11/28/2022]
Affiliation(s)
- Kenneth S Campbell
- Department of Physiology, University of Kentucky, United States; Division of Cardiovascular Medicine, University of Kentucky, United States.
| | - Christopher M Yengo
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, United States
| | - Lik-Chuan Lee
- Department of Mechanical Engineering, Michigan State University, United States
| | - John Kotter
- Division of Cardiovascular Medicine, University of Kentucky, United States
| | - Vincent L Sorrell
- Division of Cardiovascular Medicine, University of Kentucky, United States
| | - Maya Guglin
- Division of Cardiovascular Medicine, University of Kentucky, United States
| | - Jonathan F Wenk
- Department of Mechanical Engineering and Department of Surgery, University of Kentucky, United States
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19
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Vikhorev PG, Vikhoreva NN. Cardiomyopathies and Related Changes in Contractility of Human Heart Muscle. Int J Mol Sci 2018; 19:ijms19082234. [PMID: 30065175 PMCID: PMC6121228 DOI: 10.3390/ijms19082234] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2018] [Revised: 07/22/2018] [Accepted: 07/27/2018] [Indexed: 02/07/2023] Open
Abstract
About half of hypertrophic and dilated cardiomyopathies cases have been recognized as genetic diseases with mutations in sarcomeric proteins. The sarcomeric proteins are involved in cardiomyocyte contractility and its regulation, and play a structural role. Mutations in non-sarcomeric proteins may induce changes in cell signaling pathways that modify contractile response of heart muscle. These facts strongly suggest that contractile dysfunction plays a central role in initiation and progression of cardiomyopathies. In fact, abnormalities in contractile mechanics of myofibrils have been discovered. However, it has not been revealed how these mutations increase risk for cardiomyopathy and cause the disease. Much research has been done and still much is being done to understand how the mechanism works. Here, we review the facts of cardiac myofilament contractility in patients with cardiomyopathy and heart failure.
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Affiliation(s)
- Petr G Vikhorev
- National Heart and Lung Institute, Imperial College London, London W12 0NN, UK.
| | - Natalia N Vikhoreva
- Heart Science Centre, Magdi Yacoub Institute, Harefield Hospital, London UB9 6JH, UK.
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20
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The Molecular Mechanisms of Mutations in Actin and Myosin that Cause Inherited Myopathy. Int J Mol Sci 2018; 19:ijms19072020. [PMID: 29997361 PMCID: PMC6073311 DOI: 10.3390/ijms19072020] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2018] [Revised: 07/06/2018] [Accepted: 07/08/2018] [Indexed: 12/23/2022] Open
Abstract
The discovery that mutations in myosin and actin genes, together with mutations in the other components of the muscle sarcomere, are responsible for a range of inherited muscle diseases (myopathies) has revolutionized the study of muscle, converting it from a subject of basic science to a relevant subject for clinical study and has been responsible for a great increase of interest in muscle studies. Myopathies are linked to mutations in five of the myosin heavy chain genes, three of the myosin light chain genes, and three of the actin genes. This review aims to determine to what extent we can explain disease phenotype from the mutant genotype. To optimise our chances of finding the right mechanism we must study a myopathy where there are a large number of different mutations that cause a common phenotype and so are likely to have a common mechanism: a corollary to this criterion is that if any mutation causes the disease phenotype but does not correspond to the proposed mechanism, then the whole mechanism is suspect. Using these criteria, we consider two cases where plausible genotype-phenotype mechanisms have been proposed: the actin “A-triad” and the myosin “mesa/IHD” models.
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21
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Force-Dependent Recruitment from the Myosin Off State Contributes to Length-Dependent Activation. Biophys J 2018; 115:543-553. [PMID: 30054031 DOI: 10.1016/j.bpj.2018.07.006] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Accepted: 07/02/2018] [Indexed: 11/21/2022] Open
Abstract
Cardiac muscle develops more force when it is activated at longer lengths. The concentration of Ca2+ required to develop half-maximal force also decreases. These effects are known as length-dependent activation and are thought to play critical roles in the Frank-Starling relationship and cardiovascular homeostasis. The molecular mechanisms underpinning length-dependent activation remain unclear, but recent experiments suggest that they may include recruitment of myosin heads from the off (sometimes called super-relaxed) state. This manuscript presents a mathematical model of muscle contraction that was developed to investigate this hypothesis. Myosin heads in the model transitioned between an off state (that could not interact with actin), an on state (that could bind to actin), and a single attached state. Simulations were fitted to experimental data using multidimensional parameter optimization. Statistical analysis showed that a model in which the rate of the off-to-on transition increased linearly with force reproduced the length-dependent behavior of chemically permeabilized myocardium better than a model with a constant off-to-on transition rate (F-test, p < 0.001). This result suggests that the thick-filament transitions are modulated by force. Additional calculations showed that the model incorporating a mechanosensitive thick filament could also reproduce twitch responses measured in a trabecula stretched to different lengths. A final set of simulations was then used to test the model. These calculations predicted how reducing passive stiffness would impact the length dependence of the calcium sensitivity of contractile force. The prediction (a 60% reduction in ΔpCa50) mimicked the 58% reduction in ΔpCa50 in myocardium from rats that expressed a giant isoform of titin and had low resting tension. Together, these computational results suggest that force-dependent recruitment of myosin heads from the thick-filament off state contributes to length-dependent activation and the Frank-Starling relationship.
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22
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Trivedi DV, Adhikari AS, Sarkar SS, Ruppel KM, Spudich JA. Hypertrophic cardiomyopathy and the myosin mesa: viewing an old disease in a new light. Biophys Rev 2017; 10:27-48. [PMID: 28717924 PMCID: PMC5803174 DOI: 10.1007/s12551-017-0274-6] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Accepted: 06/12/2017] [Indexed: 12/15/2022] Open
Abstract
The sarcomere is an exquisitely designed apparatus that is capable of generating force, which in the case of the heart results in the pumping of blood throughout the body. At the molecular level, an ATP-dependent interaction of myosin with actin drives the contraction and force generation of the sarcomere. Over the past six decades, work on muscle has yielded tremendous insights into the workings of the sarcomeric system. We now stand on the cusp where the acquired knowledge of how the sarcomere contracts and how that contraction is regulated can be extended to an understanding of the molecular mechanisms of sarcomeric diseases, such as hypertrophic cardiomyopathy (HCM). In this review we present a picture that combines current knowledge of the myosin mesa, the sequestered state of myosin heads on the thick filament, known as the interacting-heads motif (IHM), their possible interaction with myosin binding protein C (MyBP-C) and how these interactions can be abrogated leading to hyper-contractility, a key clinical manifestation of HCM. We discuss the structural and functional basis of the IHM state of the myosin heads and identify HCM-causing mutations that can directly impact the equilibrium between the 'on state' of the myosin heads (the open state) and the IHM 'off state'. We also hypothesize a role of MyBP-C in helping to maintain myosin heads in the IHM state on the thick filament, allowing release in a graded manner upon adrenergic stimulation. By viewing clinical hyper-contractility as the result of the destabilization of the IHM state, our aim is to view an old disease in a new light.
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Affiliation(s)
- Darshan V Trivedi
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Arjun S Adhikari
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Saswata S Sarkar
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Kathleen M Ruppel
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA. .,Department of Pediatrics (Cardiology), Stanford University School of Medicine, Stanford, CA, 94305, USA.
| | - James A Spudich
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA.
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23
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The Relaxation Properties of Myofibrils Are Compromised by Amino Acids that Stabilize α-Tropomyosin. Biophys J 2017; 112:376-387. [PMID: 28122223 DOI: 10.1016/j.bpj.2016.12.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Revised: 12/06/2016] [Accepted: 12/08/2016] [Indexed: 12/20/2022] Open
Abstract
We investigated the functional impact of α-tropomyosin (Tm) substituted with one (D137L) or two (D137L/G126R) stabilizing amino acid substitutions on the mechanical behavior of rabbit psoas skeletal myofibrils by replacing endogenous Tm and troponin (Tn) with recombinant Tm mutants and purified skeletal Tn. Force recordings from myofibrils (15°C) at saturating [Ca2+] showed that Tm-stabilizing substitutions did not significantly affect the maximal isometric tension and the rates of force activation (kACT) and redevelopment (kTR). However, a clear effect was observed on force relaxation: myofibrils with D137L/G126R or D137L Tm showed prolonged durations of the slow phase of relaxation and decreased rates of the fast phase. Both Tm-stabilizing substitutions strongly decreased the slack sarcomere length (SL) at submaximal activating [Ca2+] and increased the steepness of the SL-passive tension relation. These effects were reversed by addition of 10 mM 2,3-butanedione 2-monoxime. Myofibrils also showed an apparent increase in Ca2+ sensitivity. Measurements of myofibrillar ATPase activity in the absence of Ca2+ showed a significant increase in the presence of these Tms, indicating that single and double stabilizing substitutions compromise the full inhibition of contraction in the relaxed state. These data can be understood with the three-state (blocked-closed-open) theory of muscle regulation, according to which the mutations increase the contribution of the active open state in the absence of Ca2+ (M-). Force measurements on myofibrils substituted with C-terminal truncated TnI showed similar compromised relaxation effects, indicating the importance of TnI-Tm interactions in maintaining the blocked state. It appears that reducing the flexibility of native Tm coiled-coil structure decreases the optimum interactions of the central part of Tm with the C-terminal region of TnI. This results in a shift away from the blocked state, allowing myosin binding and activity in the absence of Ca2+. This work provides a basis for understanding the effects of disease-producing mutations in muscle proteins.
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24
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Lehman W. Switching Muscles On and Off in Steps: The McKillop-Geeves Three-State Model of Muscle Regulation. Biophys J 2017; 112:2459-2466. [PMID: 28552313 DOI: 10.1016/j.bpj.2017.04.053] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Revised: 04/14/2017] [Accepted: 04/21/2017] [Indexed: 01/12/2023] Open
Abstract
BJ Classic highlighting the article "Regulation of the interaction between actin and myosin subfragment 1: evidence for three states of the thin filament."
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Affiliation(s)
- William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts.
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25
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Abstract
Tropomyosin is the archetypal-coiled coil, yet studies of its structure and function have proven it to be a dynamic regulator of actin filament function in muscle and non-muscle cells. Here we review aspects of its structure that deviate from canonical leucine zipper coiled coils that allow tropomyosin to bind to actin, regulate myosin, and interact directly and indirectly with actin-binding proteins. Four genes encode tropomyosins in vertebrates, with additional diversity that results from alternate promoters and alternatively spliced exons. At the same time that periodic motifs for binding actin and regulating myosin are conserved, isoform-specific domains allow for specific interaction with myosins and actin filament regulatory proteins, including troponin. Tropomyosin can be viewed as a universal regulator of the actin cytoskeleton that specifies actin filaments for cellular and intracellular functions.
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26
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Månsson A. Actomyosin based contraction: one mechanokinetic model from single molecules to muscle? J Muscle Res Cell Motil 2016; 37:181-194. [PMID: 27864648 PMCID: PMC5383694 DOI: 10.1007/s10974-016-9458-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Accepted: 11/09/2016] [Indexed: 12/26/2022]
Abstract
Bridging the gaps between experimental systems on different hierarchical scales is needed to overcome remaining challenges in the understanding of muscle contraction. Here, a mathematical model with well-characterized structural and biochemical actomyosin states is developed to that end. We hypothesize that this model accounts for generation of force and motion from single motor molecules to the large ensembles of muscle. In partial support of this idea, a wide range of contractile phenomena are reproduced without the need to invoke cooperative interactions or ad hoc states/transitions. However, remaining limitations exist, associated with ambiguities in available data for model definition e.g.: (1) the affinity of weakly bound cross-bridges, (2) the characteristics of the cross-bridge elasticity and (3) the exact mechanistic relationship between the force-generating transition and phosphate release in the actomyosin ATPase. Further, the simulated number of attached myosin heads in the in vitro motility assay differs several-fold from duty ratios, (fraction of strongly attached ATPase cycle times) derived in standard analysis. After addressing the mentioned issues the model should be useful in fundamental studies, for engineering of myosin motors as well as for studies of muscle disease and drug development.
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Affiliation(s)
- Alf Månsson
- Department of Chemistry and Biomedical Sciences, Faculty of Health and Life Sciences, Linnaeus University, 39182, Kalmar, Sweden.
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27
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Papadaki M, Marston SB. The Importance of Intrinsically Disordered Segments of Cardiac Troponin in Modulating Function by Phosphorylation and Disease-Causing Mutations. Front Physiol 2016; 7:508. [PMID: 27853436 PMCID: PMC5089987 DOI: 10.3389/fphys.2016.00508] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Accepted: 10/17/2016] [Indexed: 11/18/2022] Open
Abstract
Troponin plays a central role in regulation of muscle contraction. It is the Ca2+ switch of striated muscles including the heart and in the cardiac muscle it is physiologically modulated by PKA-dependent phosphorylation at Ser22 and 23. Many cardiomyopathy-related mutations affect Ca2+ regulation and/or disrupt the relationship between Ca2+ binding and phosphorylation. Unlike the mechanism of heart activation, the modulation of Ca2+-sensitivity by phosphorylation of the cardiac specific N-terminal segment of TnI (1–30) is structurally subtle and has proven hard to investigate. The crystal structure of cardiac troponin describes only the relatively stable core of the molecule and the crucial mobile parts of the molecule are missing including TnI C-terminal region, TnI (1–30), TnI (134–149) (“inhibitory” peptide) and the C-terminal 28 amino acids of TnT that are intrinsically disordered. Recent studies have been performed to answer this matter by building structural models of cardiac troponin in phosphorylated and dephosphorylated states based on peptide NMR studies. Now these have been updated by more recent concepts derived from molecular dynamic simulations treating troponin as a dynamic structure. The emerging model confirms the stable core structure of troponin and the mobile structure of the intrinsically disordered segments. We will discuss how we can describe these segments in terms of dynamic transitions between a small number of states, with the probability distributions being altered by phosphorylation and by HCM or DCM-related mutations that can explain how Ca2+-sensitivity is modulated by phosphorylation and the effects of mutations.
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Affiliation(s)
- Maria Papadaki
- Department of Cell and Molecular Physiology, Loyola University of Chicago Maywood, IL, USA
| | - Steven B Marston
- Myocardial Function, National Heart and Lung Institute, Imperial College London London, UK
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28
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Sewanan LR, Moore JR, Lehman W, Campbell SG. Predicting Effects of Tropomyosin Mutations on Cardiac Muscle Contraction through Myofilament Modeling. Front Physiol 2016; 7:473. [PMID: 27833562 PMCID: PMC5081029 DOI: 10.3389/fphys.2016.00473] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2016] [Accepted: 10/03/2016] [Indexed: 12/23/2022] Open
Abstract
Point mutations to the human gene TPM1 have been implicated in the development of both hypertrophic and dilated cardiomyopathies. Such observations have led to studies investigating the link between single residue changes and the biophysical behavior of the tropomyosin molecule. However, the degree to which these molecular perturbations explain the performance of intact sarcomeres containing mutant tropomyosin remains uncertain. Here, we present a modeling approach that integrates various aspects of tropomyosin's molecular properties into a cohesive paradigm representing their impact on muscle function. In particular, we considered the effects of tropomyosin mutations on (1) persistence length, (2) equilibrium between thin filament blocked and closed regulatory states, and (3) the crossbridge duty cycle. After demonstrating the ability of the new model to capture Ca-dependent myofilament responses during both dynamic and steady-state activation, we used it to capture the effects of hypertrophic cardiomyopathy (HCM) related E180G and D175N mutations on skinned myofiber mechanics. Our analysis indicates that the fiber-level effects of the two mutations can be accurately described by a combination of changes to the three tropomyosin properties represented in the model. Subsequently, we used the model to predict mutation effects on muscle twitch. Both mutations led to increased twitch contractility as a consequence of diminished cooperative inhibition between thin filament regulatory units. Overall, simulations suggest that a common twitch phenotype for HCM-linked tropomyosin mutations includes both increased contractility and elevated diastolic tension.
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Affiliation(s)
- Lorenzo R Sewanan
- Department of Biomedical Engineering, Yale UniversityNew Haven, CT, USA; Yale School of Medicine, Yale UniversityNew Haven, CT, USA
| | - Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts Lowell Lowell, MA, USA
| | - William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine Boston, MA, USA
| | - Stuart G Campbell
- Department of Biomedical Engineering, Yale UniversityNew Haven, CT, USA; Department of Cellular and Molecular Physiology, Yale School of MedicineNew Haven, CT, USA
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Mechano-chemical Interactions in Cardiac Sarcomere Contraction: A Computational Modeling Study. PLoS Comput Biol 2016; 12:e1005126. [PMID: 27716775 PMCID: PMC5055322 DOI: 10.1371/journal.pcbi.1005126] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Accepted: 09/01/2016] [Indexed: 11/19/2022] Open
Abstract
We developed a model of cardiac sarcomere contraction to study the calcium-tension relationship in cardiac muscle. Calcium mediates cardiac contraction through its interactions with troponin (Tn) and subsequently tropomyosin molecules. Experimental studies have shown that a slight increase in intracellular calcium concentration leads to a rapid increase in sarcomeric tension. Though it is widely accepted that the rapid increase is not possible without the concept of cooperativity, the mechanism is debated. We use the hypothesis that there exists a base level of cooperativity intrinsic to the thin filament that is boosted by mechanical tension, i.e. a high level of mechanical tension in the thin filament impedes the unbinding of calcium from Tn. To test these hypotheses, we developed a computational model in which a set of three parameters and inputs of calcium concentration and sarcomere length result in output tension. Tension as simulated appeared in good agreement with experimentally measured tension. Our results support the hypothesis that high tension in the thin filament impedes Tn deactivation by increasing the energy required to detach calcium from the Tn. Given this hypothesis, the model predicted that the areas with highest tension, i.e. closest to the Z-disk end of the single overlap region, show the largest concentration of active Tn's.
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Koubassova NA, Bershitsky SY, Ferenczi MA, Narayanan T, Tsaturyan AK. Tropomyosin movement is described by a quantitative high-resolution model of X-ray diffraction of contracting muscle. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2016; 46:335-342. [PMID: 27640143 DOI: 10.1007/s00249-016-1174-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 09/01/2016] [Accepted: 09/02/2016] [Indexed: 10/21/2022]
Abstract
Contraction of skeletal and cardiac muscle is controlled by Ca2+ ions via regulatory proteins, troponin (Tn) and tropomyosin (Tpm) associated with the thin actin filaments in sarcomeres. In the absence of Ca2+, Tn-C binds actin and shifts the Tpm strand to a position where it blocks myosin binding to actin, keeping muscle relaxed. According to the three-state model (McKillop and Geeves Biophys J 65:693-701, 1993), upon Ca2+ binding to Tn, Tpm rotates about the filament axis to a 'closed state' where some myosin heads can bind actin. Upon strong binding of myosin heads to actin, Tpm rotates further to an 'open' position where neighboring actin monomers also become available for myosin binding. Azimuthal Tpm movement in contracting muscle is detected by low-angle X-ray diffraction. Here we used high-resolution models of actin-Tpm filaments based on recent cryo-EM data for calculating changes in the intensities of X-ray diffraction reflections of muscle upon transitions between different states of the regulatory system. Calculated intensities of actin layer lines provide a much-improved fit to the experimental data obtained from rabbit muscle fibers in relaxed and rigor states than previous lower-resolution models. We show that the intensity of the second actin layer line at reciprocal radii from 0.15 to 0.3 nm-1 quantitatively reports the transition between different states of the regulatory system independently of the number of myosin heads bound to actin.
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Affiliation(s)
- Natalia A Koubassova
- Institute of Mechanics, M.V. Lomonosov Moscow University, 1 Michurinsky prosp., Moscow, 119192, Russia.
| | - Sergey Y Bershitsky
- Institute of Immunology and Physiology, Ural Branch of the Russian Academy of Sciences, Yekaterinburg, Russia
| | - Michael A Ferenczi
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Singapore
| | | | - Andrey K Tsaturyan
- Institute of Mechanics, M.V. Lomonosov Moscow University, 1 Michurinsky prosp., Moscow, 119192, Russia
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