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Arts T, Lyon A, Delhaas T, Kuster DWD, van der Velden J, Lumens J. Translating myosin-binding protein C and titin abnormalities to whole-heart function using a novel calcium-contraction coupling model. J Mol Cell Cardiol 2024; 190:13-23. [PMID: 38462126 DOI: 10.1016/j.yjmcc.2024.03.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Revised: 01/15/2024] [Accepted: 03/01/2024] [Indexed: 03/12/2024]
Abstract
Mutations in cardiac myosin-binding protein C (cMyBP-C) or titin may respectively lead to hypertrophic (HCM) or dilated (DCM) cardiomyopathies. The mechanisms leading to these phenotypes remain unclear because of the challenge of translating cellular abnormalities to whole-heart and system function. We developed and validated a novel computer model of calcium-contraction coupling incorporating the role of cMyBP-C and titin based on the key assumptions: 1) tension in the thick filament promotes cross-bridge attachment mechanochemically, 2) with increasing titin tension, more myosin heads are unlocked for attachment, and 3) cMyBP-C suppresses cross-bridge attachment. Simulated stationary calcium-tension curves, isotonic and isometric contractions, and quick release agreed with experimental data. The model predicted that a loss of cMyBP-C function decreases the steepness of the calcium-tension curve, and that more compliant titin decreases the level of passive and active tension and its dependency on sarcomere length. Integrating this cellular model in the CircAdapt model of the human heart and circulation showed that a loss of cMyBP-C function resulted in HCM-like hemodynamics with higher left ventricular end-diastolic pressures and smaller volumes. More compliant titin led to higher diastolic pressures and ventricular dilation, suggesting DCM-like hemodynamics. The novel model of calcium-contraction coupling incorporates the role of cMyBP-C and titin. Its coupling to whole-heart mechanics translates changes in cellular calcium-contraction coupling to changes in cardiac pump and circulatory function and identifies potential mechanisms by which cMyBP-C and titin abnormalities may develop into HCM and DCM phenotypes. This modeling platform may help identify distinct mechanisms underlying clinical phenotypes in cardiac diseases.
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Affiliation(s)
- Theo Arts
- Department of Biomedical Engineering, Cardiovascular Research Center Maastricht (CARIM), Maastricht University, 6200MD Maastricht, the Netherlands.
| | - Aurore Lyon
- Department of Biomedical Engineering, Cardiovascular Research Center Maastricht (CARIM), Maastricht University, 6200MD Maastricht, the Netherlands
| | - Tammo Delhaas
- Department of Biomedical Engineering, Cardiovascular Research Center Maastricht (CARIM), Maastricht University, 6200MD Maastricht, the Netherlands
| | - Diederik W D Kuster
- Department of Physiology, Amsterdam University Medical Center, 1081HZ Amsterdam, the Netherlands
| | - Jolanda van der Velden
- Department of Physiology, Amsterdam University Medical Center, 1081HZ Amsterdam, the Netherlands
| | - Joost Lumens
- Department of Biomedical Engineering, Cardiovascular Research Center Maastricht (CARIM), Maastricht University, 6200MD Maastricht, the Netherlands
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2
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Huang X, Torre I, Chiappi M, Yin Z, Vydyanath A, Cao S, Raschdorf O, Beeby M, Quigley B, de Tombe PP, Liu J, Morris EP, Luther PK. Cryo-electron tomography of intact cardiac muscle reveals myosin binding protein-C linking myosin and actin filaments. J Muscle Res Cell Motil 2023; 44:165-178. [PMID: 37115473 PMCID: PMC10542292 DOI: 10.1007/s10974-023-09647-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2022] [Accepted: 03/29/2023] [Indexed: 04/29/2023]
Abstract
Myosin binding protein C (MyBP-C) is an accessory protein of the thick filament in vertebrate cardiac muscle arranged over 9 stripes of intervals of 430 Å in each half of the A-band in the region called the C-zone. Mutations in cardiac MyBP-C are a leading cause of hypertrophic cardiomyopathy the mechanism of which is unknown. It is a rod-shaped protein composed of 10 or 11 immunoglobulin- or fibronectin-like domains labelled C0 to C10 which binds to the thick filament via its C-terminal region. MyBP-C regulates contraction in a phosphorylation dependent fashion that may be through binding of its N-terminal domains with myosin or actin. Understanding the 3D organisation of MyBP-C in the sarcomere environment may provide new light on its function. We report here the fine structure of MyBP-C in relaxed rat cardiac muscle by cryo-electron tomography and subtomogram averaging of refrozen Tokuyasu cryosections. We find that on average MyBP-C connects via its distal end to actin across a disc perpendicular to the thick filament. The path of MyBP-C suggests that the central domains may interact with myosin heads. Surprisingly MyBP-C at Stripe 4 is different; it has weaker density than the other stripes which could result from a mainly axial or wavy path. Given that the same feature at Stripe 4 can also be found in several mammalian cardiac muscles and in some skeletal muscles, our finding may have broader implication and significance. In the D-zone, we show the first demonstration of myosin crowns arranged on a uniform 143 Å repeat.
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Affiliation(s)
- Xinrui Huang
- Department of Biochemistry and Biophysics, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT, 06516, USA
| | - Iratxe Torre
- National Heart and Lung Institute, Imperial College London, London, SW7 2AZ, UK
| | - Michele Chiappi
- National Heart and Lung Institute, Imperial College London, London, SW7 2AZ, UK
| | - Zhan Yin
- National Heart and Lung Institute, Imperial College London, London, SW7 2AZ, UK
| | - Anupama Vydyanath
- National Heart and Lung Institute, Imperial College London, London, SW7 2AZ, UK
| | - Shuangyi Cao
- National Heart and Lung Institute, Imperial College London, London, SW7 2AZ, UK
| | | | - Morgan Beeby
- Department of Life Sciences, Imperial College London, London, SW7 2AZ, UK
| | - Bonnie Quigley
- Department of Life Sciences, Imperial College London, London, SW7 2AZ, UK
| | - Pieter P de Tombe
- National Heart and Lung Institute, Imperial College London, London, SW7 2AZ, UK
- Department of Physiology and Biophysics, University of Illinois at Chicago, 835 S. Wolcott Ave, Chicago, IL, 60612, USA
- Phymedexp, Université de Montpellier, Inserm, CNRS, Montpellier, France
| | - Jun Liu
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT, 06516, USA
| | - Edward P Morris
- Division of Structural Biology, Institute of Cancer Research, London, SW3 6JB, UK
- School of Molecular Biosciences, University of Glasgow, Garscube Campus, Jarrett Building, 351, Bearsden Road, Glasgow, G61 1QH, UK
| | - Pradeep K Luther
- National Heart and Lung Institute, Imperial College London, London, SW7 2AZ, UK.
- Cardiac Function Section, National Heart and Lung Institute, Imperial College London, London, SW7 2AZ, UK.
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Wang Z, Grange M, Pospich S, Wagner T, Kho AL, Gautel M, Raunser S. Structures from intact myofibrils reveal mechanism of thin filament regulation through nebulin. Science 2022; 375:eabn1934. [PMID: 35175800 DOI: 10.1126/science.abn1934] [Citation(s) in RCA: 54] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
In skeletal muscle, nebulin stabilizes and regulates the length of thin filaments, but the underlying mechanism remains nebulous. In this work, we used cryo-electron tomography and subtomogram averaging to reveal structures of native nebulin bound to thin filaments within intact sarcomeres. This in situ reconstruction provided high-resolution details of the interaction between nebulin and actin, demonstrating the stabilizing role of nebulin. Myosin bound to the thin filaments exhibited different conformations of the neck domain, highlighting its inherent structural variability in muscle. Unexpectedly, nebulin did not interact with myosin or tropomyosin, but it did interact with a troponin T linker through two potential binding motifs on nebulin, explaining its regulatory role. Our structures support the role of nebulin as a thin filament "molecular ruler" and provide a molecular basis for studying nemaline myopathies.
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Affiliation(s)
- Zhexin Wang
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | - Michael Grange
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | - Sabrina Pospich
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | - Thorsten Wagner
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | - Ay Lin Kho
- Randall Centre for Cell and Molecular Biophysics, School of Basic and Medical Biosciences, Kings College London BHF Centre of Research Excellence, Guy's Campus, London SE1 1UL, UK
| | - Mathias Gautel
- Randall Centre for Cell and Molecular Biophysics, School of Basic and Medical Biosciences, Kings College London BHF Centre of Research Excellence, Guy's Campus, London SE1 1UL, UK
| | - Stefan Raunser
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
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4
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Pezhouman A, Nguyen NB, Sercel AJ, Nguyen TL, Daraei A, Sabri S, Chapski DJ, Zheng M, Patananan AN, Ernst J, Plath K, Vondriska TM, Teitell MA, Ardehali R. Transcriptional, Electrophysiological, and Metabolic Characterizations of hESC-Derived First and Second Heart Fields Demonstrate a Potential Role of TBX5 in Cardiomyocyte Maturation. Front Cell Dev Biol 2021; 9:787684. [PMID: 34988079 PMCID: PMC8722677 DOI: 10.3389/fcell.2021.787684] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Accepted: 11/25/2021] [Indexed: 12/03/2022] Open
Abstract
Background: Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) can be used as a source for cell delivery to remuscularize the heart after myocardial infarction. Despite their therapeutic potential, the emergence of ventricular arrhythmias has limited their application. We previously developed a double reporter hESC line to isolate first heart field (FHF: TBX5+NKX2-5+) and second heart field (SHF: TBX5-NKX2-5+) CMs. Herein, we explore the role of TBX5 and its effects on underlying gene regulatory networks driving phenotypical and functional differences between these two populations. Methods: We used a combination of tools and techniques for rapid and unsupervised profiling of FHF and SHF populations at the transcriptional, translational, and functional level including single cell RNA (scRNA) and bulk RNA sequencing, atomic force and quantitative phase microscopy, respirometry, and electrophysiology. Results: Gene ontology analysis revealed three biological processes attributed to TBX5 expression: sarcomeric structure, oxidative phosphorylation, and calcium ion handling. Interestingly, migratory pathways were enriched in SHF population. SHF-like CMs display less sarcomeric organization compared to FHF-like CMs, despite prolonged in vitro culture. Atomic force and quantitative phase microscopy showed increased cellular stiffness and decreased mass distribution over time in FHF compared to SHF populations, respectively. Electrophysiological studies showed longer plateau in action potentials recorded from FHF-like CMs, consistent with their increased expression of calcium handling genes. Interestingly, both populations showed nearly identical respiratory profiles with the only significant functional difference being higher ATP generation-linked oxygen consumption rate in FHF-like CMs. Our findings suggest that FHF-like CMs display more mature features given their enhanced sarcomeric alignment, calcium handling, and decreased migratory characteristics. Finally, pseudotime analyses revealed a closer association of the FHF population to human fetal CMs along the developmental trajectory. Conclusion: Our studies reveal that distinguishing FHF and SHF populations based on TBX5 expression leads to a significant impact on their downstream functional properties. FHF CMs display more mature characteristics such as enhanced sarcomeric organization and improved calcium handling, with closer positioning along the differentiation trajectory to human fetal hearts. These data suggest that the FHF CMs may be a more suitable candidate for cardiac regeneration.
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Affiliation(s)
- Arash Pezhouman
- Division of Cardiology, Department of Internal Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Eli and Edythe Broad Stem Cell Research Center, University of California, Los Angeles, Los Angeles, CA, United States
| | - Ngoc B. Nguyen
- Division of Cardiology, Department of Internal Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Eli and Edythe Broad Stem Cell Research Center, University of California, Los Angeles, Los Angeles, CA, United States
- Molecular, Cellular and Integrative Physiology Graduate Program, University of California, Los Angeles, Los Angeles, CA, United States
| | - Alexander J. Sercel
- Molecular Biology Interdepartmental Doctoral Program, University of California, Los Angeles, Los Angeles, CA, United States
| | - Thang L. Nguyen
- Department of Bioengineering, University of California, Los Angeles, Los Angeles, CA, United States
| | - Ali Daraei
- Division of Cardiology, Department of Internal Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Shan Sabri
- Department of Biological Chemistry, University of California, Los Angeles, Los Angeles, CA, United States
| | - Douglas J. Chapski
- Department of Anesthesiology and Perioperative Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Melton Zheng
- Division of Cardiology, Department of Internal Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Alexander N. Patananan
- Department of Bioengineering, University of California, Los Angeles, Los Angeles, CA, United States
| | - Jason Ernst
- Eli and Edythe Broad Stem Cell Research Center, University of California, Los Angeles, Los Angeles, CA, United States
- Department of Biological Chemistry, University of California, Los Angeles, Los Angeles, CA, United States
- Molecular Biology Institute, University of California, Los Angeles, Los Angeles, CA, United States
- Jonsson Comprehensive Cancer Center, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Kathrin Plath
- Eli and Edythe Broad Stem Cell Research Center, University of California, Los Angeles, Los Angeles, CA, United States
- Department of Biological Chemistry, University of California, Los Angeles, Los Angeles, CA, United States
- Jonsson Comprehensive Cancer Center, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Thomas M. Vondriska
- Department of Anesthesiology and Perioperative Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Department of Physiology, University of California, Los Angeles, Los Angeles, CA, United States
- Department of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Michael A. Teitell
- Department of Bioengineering, University of California, Los Angeles, Los Angeles, CA, United States
- Molecular Biology Institute, University of California, Los Angeles, Los Angeles, CA, United States
- Jonsson Comprehensive Cancer Center, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Department of Pediatrics, University of California, Los Angeles, Los Angeles, CA, United States
| | - Reza Ardehali
- Division of Cardiology, Department of Internal Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Eli and Edythe Broad Stem Cell Research Center, University of California, Los Angeles, Los Angeles, CA, United States
- Molecular, Cellular and Integrative Physiology Graduate Program, University of California, Los Angeles, Los Angeles, CA, United States
- Molecular Biology Institute, University of California, Los Angeles, Los Angeles, CA, United States
- *Correspondence: Reza Ardehali,
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5
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Wang Z, Grange M, Wagner T, Kho AL, Gautel M, Raunser S. The molecular basis for sarcomere organization in vertebrate skeletal muscle. Cell 2021; 184:2135-2150.e13. [PMID: 33765442 PMCID: PMC8054911 DOI: 10.1016/j.cell.2021.02.047] [Citation(s) in RCA: 80] [Impact Index Per Article: 26.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Revised: 01/27/2021] [Accepted: 02/22/2021] [Indexed: 12/20/2022]
Abstract
Sarcomeres are force-generating and load-bearing devices of muscles. A precise molecular picture of how sarcomeres are built underpins understanding their role in health and disease. Here, we determine the molecular architecture of native vertebrate skeletal sarcomeres by electron cryo-tomography. Our reconstruction reveals molecular details of the three-dimensional organization and interaction of actin and myosin in the A-band, I-band, and Z-disc and demonstrates that α-actinin cross-links antiparallel actin filaments by forming doublets with 6-nm spacing. Structures of myosin, tropomyosin, and actin at ~10 Å further reveal two conformations of the "double-head" myosin, where the flexible orientation of the lever arm and light chains enable myosin not only to interact with the same actin filament, but also to split between two actin filaments. Our results provide unexpected insights into the fundamental organization of vertebrate skeletal muscle and serve as a strong foundation for future investigations of muscle diseases.
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Affiliation(s)
- Zhexin Wang
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
| | - Michael Grange
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
| | - Thorsten Wagner
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
| | - Ay Lin Kho
- The Randall Centre for Cell and Molecular Biophysics, School of Basic and Medical Biosciences, Kings College London BHF Excellence Centre, New Hunt's House, Guy's Campus, London SE1 1UL, UK
| | - Mathias Gautel
- The Randall Centre for Cell and Molecular Biophysics, School of Basic and Medical Biosciences, Kings College London BHF Excellence Centre, New Hunt's House, Guy's Campus, London SE1 1UL, UK
| | - Stefan Raunser
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany.
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6
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Virot E, Spandan V, Niu L, van Rees WM, Mahadevan L. Elastohydrodynamic Scaling Law for Heart Rates. PHYSICAL REVIEW LETTERS 2020; 125:058102. [PMID: 32794888 DOI: 10.1103/physrevlett.125.058102] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Accepted: 06/04/2020] [Indexed: 06/11/2023]
Abstract
Animal hearts are soft shells that actively pump blood to oxygenate tissues. Here, we propose an allometric scaling law for the heart rate based on the idea of elastohydrodynamic resonance of a fluid-loaded soft active elastic shell that buckles and contracts axially when twisted periodically. We show that this picture is consistent with numerical simulations of soft cylindrical shells that twist-buckle while pumping a viscous fluid, yielding optimum ejection fractions of 35%-40% when driven resonantly. Our scaling law is consistent with experimental measurements of heart rates over 2 orders of magnitude, and provides a mechanistic basis for how metabolism scales with organism size. In addition to providing a physical rationale for the heart rate and metabolism of an organism, our results suggest a simple design principle for soft fluidic pumps.
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Affiliation(s)
- E Virot
- John A. Paulson School of Engineering and Applied Sciences, Harvard University
| | - V Spandan
- John A. Paulson School of Engineering and Applied Sciences, Harvard University
| | - L Niu
- Department of Physics, Harvard University, Cambridge, Massachusetts 02139, USA
| | - W M van Rees
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02138, USA
| | - L Mahadevan
- John A. Paulson School of Engineering and Applied Sciences, Harvard University
- Department of Physics, Harvard University, Cambridge, Massachusetts 02139, USA
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA
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7
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Powers JD, Bianco P, Pertici I, Reconditi M, Lombardi V, Piazzesi G. Contracting striated muscle has a dynamic I-band spring with an undamped stiffness 100 times larger than the passive stiffness. J Physiol 2020; 598:331-345. [PMID: 31786814 DOI: 10.1113/jp278713] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2019] [Accepted: 11/21/2019] [Indexed: 12/20/2022] Open
Abstract
KEY POINTS Fast sarcomere-level mechanics in contracting intact fibres from frog skeletal muscle reveal an I-band spring with an undamped stiffness 100 times larger than the known static stiffness. This undamped stiffness remains constant in the range of sarcomere length 2.7-3.1 µm, showing the ability of the I-band spring to adapt its length to the width of the I-band. The stiffness and tunability of the I-band spring implicate titin as a force contributor that, during contraction, allows weaker half-sarcomeres to equilibrate with in-series stronger half-sarcomeres, preventing the development of sarcomere length inhomogeneity. This work opens new possibilities for the detailed in situ description of the structural-functional basis of muscle dysfunctions related to mutations or site-directed mutagenesis in titin that alter the I-band stiffness. ABSTRACT Force and shortening in the muscle sarcomere are due to myosin motors from thick filaments pulling nearby actin filaments toward the sarcomere centre. Thousands of serially linked sarcomeres in muscle make the shortening (and the shortening speed) macroscopic, while the intrinsic instability of in-series force generators is likely prevented by the cytoskeletal protein titin that connects the thick filament with the sarcomere end, working as an I-band spring that accounts for the rise of passive force with sarcomere length (SL). However, current estimates of titin stiffness, deduced from the passive force-SL relation and single molecule mechanics, are much smaller than what is required to avoid the development of large inhomogeneities among sarcomeres. In this work, using 4 kHz stiffness measurements on a population of sarcomeres selected along an intact fibre isolated from frog skeletal muscle contracting at different SLs (temperature 4°C), we measure the undamped stiffness of an I-band spring that at SL > 2.7 µm attains a maximum constant value of ∼6 pN nm-1 per half-thick filament, two orders of magnitude larger than expected from titin-related passive force. We conclude that a titin-like dynamic spring in the I-band, made by an undamped elastic element in-series with damped elastic elements, adapts its length to the SL with kinetics that provide force balancing among serially linked sarcomeres during contraction. In this way, the I-band spring plays a fundamental role in preventing the development of SL inhomogeneity.
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Affiliation(s)
- Joseph D Powers
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
- Bioengineering, University of Washington, 3720 15th Ave NE, Seattle, WA, 98105, USA
| | - Pasquale Bianco
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
| | - Irene Pertici
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
| | - Massimo Reconditi
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
| | - Vincenzo Lombardi
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
| | - Gabriella Piazzesi
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
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8
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Estimation of Forces on Actin Filaments in Living Muscle from X-ray Diffraction Patterns and Mechanical Data. Int J Mol Sci 2019; 20:ijms20236044. [PMID: 31801239 PMCID: PMC6928692 DOI: 10.3390/ijms20236044] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2019] [Revised: 11/12/2019] [Accepted: 11/26/2019] [Indexed: 11/17/2022] Open
Abstract
Many biological processes are triggered or driven by mechanical forces in the cytoskeletal network, but these transducing forces have rarely been assessed. Striated muscle, with its well-organized structure provides an opportunity to assess intracellular forces using small-angle X-ray fiber diffraction. We present a new methodology using Monte Carlo simulations of muscle contraction in an explicit 3D sarcomere lattice to predict the fiber deformations and length changes along thin filaments during contraction. Comparison of predicted diffraction patterns to experimental meridional X-ray reflection profiles allows assessment of the stepwise changes in intermonomer spacings and forces in the myofilaments within living muscle cells. These changes along the filament length reflect the effect of forces from randomly attached crossbridges. This approach enables correlation of the molecular events, such as the current number of attached crossbridges and the distributions of crossbridge forces to macroscopic measurements of force and length changes during muscle contraction. In addition, assessments of fluctuations in local forces in the myofilaments may reveal how variations in the filament forces acting on signaling proteins in the sarcomere M-bands and Z-discs modulate gene expression, protein synthesis and degradation, and as well to mechanisms of adaptation of muscle in response to changes in mechanical loading.
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9
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Mijailovich SM, Stojanovic B, Nedic D, Svicevic M, Geeves MA, Irving TC, Granzier HL. Nebulin and titin modulate cross-bridge cycling and length-dependent calcium sensitivity. J Gen Physiol 2019; 151:680-704. [PMID: 30948421 PMCID: PMC6504291 DOI: 10.1085/jgp.201812165] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Revised: 01/15/2019] [Accepted: 03/03/2019] [Indexed: 12/13/2022] Open
Abstract
Various mutations in the structural proteins nebulin and titin that are present in human disease are known to affect the contractility of striated muscle. Loss of nebulin is associated with reduced actin filament length and impairment of myosin binding to actin, whereas titin is thought to regulate muscle passive elasticity and is likely involved in length-dependent activation. Here, we sought to assess the modulation of muscle function by these sarcomeric proteins by using the computational platform muscle simulation code (MUSICO) to quantitatively separate the effects of structural changes, kinetics of cross-bridge cycling, and calcium sensitivity of the thin filaments. The simulations show that variation in thin filament length cannot by itself account for experimental observations of the contractility in nebulin-deficient muscle, but instead must be accompanied by a decreased myosin binding rate. Additionally, to match the observed calcium sensitivity, the rate of TnI detachment from actin needed to be increased. Simulations for cardiac muscle provided quantitative estimates of the effects of different titin-based passive elasticities on muscle force and activation in response to changes in sarcomere length and interfilament lattice spacing. Predicted force-pCa relations showed a decrease in both active tension and sensitivity to calcium with a decrease in passive tension and sarcomere length. We conclude that this behavior is caused by partial redistribution of the muscle load between active muscle force and titin-dependent passive force, and also by redistribution of stretch along the thin filament, which together modulate the release of TnI from actin. These data help advance understanding of how nebulin and titin mutations affect muscle function.
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Affiliation(s)
- Srboljub M Mijailovich
- Department of Chemistry and Chemical Biology, Northeastern University, Boston, MA .,Department of Biological Sciences, Illinois Institute of Technology, Chicago, IL
| | - Boban Stojanovic
- University of Kragujevac, Faculty of Science, Kragujevac, Serbia
| | - Djordje Nedic
- University of Kragujevac, Faculty of Science, Kragujevac, Serbia
| | - Marina Svicevic
- University of Kragujevac, Faculty of Science, Kragujevac, Serbia
| | - Michael A Geeves
- Department of Biosciences, University of Kent, Canterbury, Kent, UK
| | - Thomas C Irving
- Department of Biological Sciences, Illinois Institute of Technology, Chicago, IL
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10
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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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11
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Proposed mechanism for the length dependence of the force developed in maximally activated muscles. Sci Rep 2019; 9:1317. [PMID: 30718530 PMCID: PMC6362285 DOI: 10.1038/s41598-018-36706-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2018] [Accepted: 11/20/2018] [Indexed: 11/08/2022] Open
Abstract
The molecular bases of the Frank-Starling law of the heart and of its cellular counterpart, the length dependent activation (LDA), are largely unknown. However, the recent discovery of the thick filament activation, a second pathway beside the well-known calcium mediated thin filament activation, is promising for elucidating these mechanisms. The thick filament activation is mediated by the tension acting on it through the mechano-sensing (MS) mechanism and can be related to the LDA via the titin passive tension. Here, we propose a mechanism to explain the higher maximum tension at longer sarcomere lengths generated by a maximally activated muscle and test it in-silico with a single fiber and a ventricle model. The active tension distribution along the thick filament generates a reservoir of inactive motors at its free-end that can be activated by passive tension on a beat-to-beat timescale. The proposed mechanism is able to quantitatively account for the observed increment in tension at the fiber level, however, the ventricle model suggests that this component of the LDA is not crucial in physiological conditions.
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12
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Caremani M, Pinzauti F, Powers JD, Governali S, Narayanan T, Stienen GJM, Reconditi M, Linari M, Lombardi V, Piazzesi G. Inotropic interventions do not change the resting state of myosin motors during cardiac diastole. J Gen Physiol 2018; 151:53-65. [PMID: 30510036 PMCID: PMC6314382 DOI: 10.1085/jgp.201812196] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 10/26/2018] [Indexed: 11/20/2022] Open
Abstract
When striated (skeletal and cardiac) muscle is in its relaxed state, myosin motors are packed in helical tracks on the surface of the thick filament, folded toward the center of the sarcomere, and unable to bind actin or hydrolyze ATP (OFF state). This raises the question of whatthe mechanism is that integrates the Ca2+-dependent thin filament activation, making myosin heads available for interaction with actin. Here we test the interdependency of the thin and thick filament regulatory mechanisms in intact trabeculae from the rat heart. We record the x-ray diffraction signals that mark the state of the thick filament during inotropic interventions (increase in sarcomere length from 1.95 to 2.25 µm and addition of 10-7 M isoprenaline), which potentiate the twitch force developed by an electrically paced trabecula by up to twofold. During diastole, none of the signals related to the OFF state of the thick filament are significantly affected by these interventions, except the intensity of both myosin-binding protein C- and troponin-related meridional reflections, which reduce by 20% in the presence of isoprenaline. These results indicate that recruitment of myosin motors from their OFF state occurs independently and downstream from thin filament activation. This is in agreement with the recently discovered mechanism based on thick filament mechanosensing in which the number of motors available for interaction with actin rapidly adapts to the stress on the thick filament and thus to the loading conditions of the contraction. The gain of this positive feedback may be modulated by both sarcomere length and the degree of phosphorylation of myosin-binding protein C.
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Affiliation(s)
| | | | | | | | | | - Ger J M Stienen
- Department of Physiology, VU University Medical Center, Amsterdam, The Netherlands
| | | | - Marco Linari
- PhysioLab, University of Florence, Firenze, Italy
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13
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Pinzauti F, Pertici I, Reconditi M, Narayanan T, Stienen GJM, Piazzesi G, Lombardi V, Linari M, Caremani M. The force and stiffness of myosin motors in the isometric twitch of a cardiac trabecula and the effect of the extracellular calcium concentration. J Physiol 2018; 596:2581-2596. [PMID: 29714038 PMCID: PMC6023834 DOI: 10.1113/jp275579] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Accepted: 04/13/2018] [Indexed: 01/22/2023] Open
Abstract
KEY POINTS Fast sarcomere-level mechanics in intact trabeculae, which allows the definition of the mechano-kinetic properties of cardiac myosin in situ, is a fundamental tool not only for understanding the molecular mechanisms of heart performance and regulation, but also for investigating the mechanisms of the cardiomyopathy-causing mutations in the myosin and testing small molecules for therapeutic interventions. The approach has been applied to measure the stiffness and force of the myosin motor and the fraction of motors attached during isometric twitches of electrically paced trabeculae under different extracellular Ca2+ concentrations. Although the average force of the cardiac myosin motor (∼6 pN) is similar to that of the fast myosin isoform of skeletal muscle, the stiffness (1.07 pN nm-1 ) is 2- to 3-fold smaller. The increase in the twitch force developed in the presence of larger extracellular Ca2+ concentrations is fully accounted for by a proportional increase in the number of attached motors. ABSTRACT The mechano-kinetic properties of the cardiac myosin were studied in situ, in trabeculae dissected from the right ventricle of the rat heart, by measuring the stiffness of the half-sarcomere both at the twitch force peak (Tp ) of an electrically paced intact trabecula at different extracellular Ca2+ concentrations ([Ca2+ ]o ), and in the same trabecula after skinning and induction of rigor. Taking into account the contribution of filament compliance to half-sarcomere compliance and the lattice geometry, we found that the stiffness of the cardiac myosin motor is 1.07 ± 0.09 pN nm-1 , which is slightly larger than that of the slow myosin isoform of skeletal muscle (0.6-0.8 pN nm-1 ) and 2- to 3-fold smaller than that of the fast skeletal muscle isoform. The increase in Tp from 61 ± 4 kPa to 93 ± 9 kPa, induced by raising [Ca2+ ]o from 1 to 2.5 mm at sarcomere length ∼2.2 μm, is accompanied by an increase of the half-sarcomere stiffness that is explained by an increase of the fraction of actin-attached motors from 0.08 ± 0.01 to 0.12 ± 0.02, proportional to Tp . Consequently, each myosin motor bears an average force of 6.14 ± 0.52 pN independently of Tp and [Ca2+ ]o . The application of fast sarcomere-level mechanics to intact trabeculae to define the mechano-kinetic properties of the cardiac myosin in situ represents a powerful tool for investigating cardiomyopathy-causing mutations in the myosin motor and testing specific therapeutic interventions.
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Affiliation(s)
| | | | | | | | - Ger J. M. Stienen
- Department of PhysiologyVU University Medical CenterAmsterdamThe Netherlands
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14
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Abstract
Cell division in many eukaryotes is driven by a ring containing actin and myosin. While much is known about the main proteins involved, the precise arrangement of actin filaments within the contractile machinery, and how force is transmitted to the membrane, remains unclear. Here we use cryosectioning and cryofocused ion beam milling to gain access to cryopreserved actomyosin rings in Schizosaccharomyces pombe for direct 3D imaging by electron cryotomography. Our results show that straight, overlapping actin filaments, running nearly parallel to each other and to the membrane, form a loose bundle of ∼150 nm in diameter that "saddles" the inward-bending membrane at the leading edge of the division septum. The filaments do not make direct contact with the membrane. Our analysis of the actin filaments reveals the variability in filament number, nearest-neighbor distances between filaments within the bundle, their distance from the membrane, and angular distribution with respect to the membrane.
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15
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Titin-mediated thick filament activation, through a mechanosensing mechanism, introduces sarcomere-length dependencies in mathematical models of rat trabecula and whole ventricle. Sci Rep 2017; 7:5546. [PMID: 28717163 PMCID: PMC5514028 DOI: 10.1038/s41598-017-05999-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Accepted: 06/08/2017] [Indexed: 11/08/2022] Open
Abstract
Recent experimental evidence in skeletal muscle demonstrated the existence of a thick-filament mechanosensing mechanism, acting as a second regulatory system for muscle contraction, in addition to calcium-mediated thin filament regulation. These two systems cooperate to generate force, but the extent to which their interaction is relevant in physiologically contracting muscle was not yet assessed experimentally. Therefore, we included both regulatory mechanisms in a mathematical model of rat trabecula and whole ventricle. No additional regulatory mechanisms were considered in our model. Our simulations suggested that mechanosensing regulation is not limited to the initial phases of contraction but, instead, is crucial during physiological contraction. An important consequence of this finding is that titin mediated thick filament activation can account for several sarcomere length dependencies observed in contracting muscle. Under the hypothesis that a similar mechanism is acting on cardiac muscle, and within the limits of a finite element left ventricle model, we predict that these two regulatory mechanisms are crucial for the molecular basis of the Frank-Starling law of the heart.
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16
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Abstract
In this review we discuss the history and the current state of ideas related to the mechanism of size regulation of the thick (myosin) and thin (actin) filaments in vertebrate striated muscles. Various hypotheses have been considered during of more than half century of research, recently mostly involving titin and nebulin acting as templates or 'molecular rulers', terminating exact assembly. These two giant, single-polypeptide, filamentous proteins are bound in situ along the thick and thin filaments, respectively, with an almost perfect match in the respective lengths and structural periodicities. However, evidence still questions the possibility that the proteins function as templates, or scaffolds, on which the thin and thick filaments could be assembled. In addition, the progress in muscle research during the last decades highlighted a number of other factors that could potentially be involved in the mechanism of length regulation: molecular chaperones that may guide folding and assembly of actin and myosin; capping proteins that can influence the rates of assembly-disassembly of the myofilaments; Ca2+ transients that can activate or deactivate protein interactions, etc. The entire mechanism of sarcomere assembly appears complex and highly dynamic. This mechanism is also capable of producing filaments of about the correct size without titin and nebulin. What then is the role of these proteins? Evidence points to titin and nebulin stabilizing structures of the respective filaments. This stabilizing effect, based on linear proteins of a fixed size, implies that titin and nebulin are indeed molecular rulers of the filaments. Although the proteins may not function as templates in the assembly of the filaments, they measure and stabilize exactly the same size of the functionally important for the muscles segments in each of the respective filaments.
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17
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Mijailovich SM, Kayser-Herold O, Stojanovic B, Nedic D, Irving TC, Geeves MA. Three-dimensional stochastic model of actin-myosin binding in the sarcomere lattice. J Gen Physiol 2016; 148:459-488. [PMID: 27864330 PMCID: PMC5129740 DOI: 10.1085/jgp.201611608] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2016] [Revised: 09/01/2016] [Accepted: 11/04/2016] [Indexed: 11/29/2022] Open
Abstract
The effect of molecule tethering in three-dimensional (3-D) space on bimolecular binding kinetics is rarely addressed and only occasionally incorporated into models of cell motility. The simplest system that can quantitatively determine this effect is the 3-D sarcomere lattice of the striated muscle, where tethered myosin in thick filaments can only bind to a relatively small number of available sites on the actin filament, positioned within a limited range of thermal movement of the myosin head. Here we implement spatially explicit actomyosin interactions into the multiscale Monte Carlo platform MUSICO, specifically defining how geometrical constraints on tethered myosins can modulate state transition rates in the actomyosin cycle. The simulations provide the distribution of myosin bound to sites on actin, ensure conservation of the number of interacting myosins and actin monomers, and most importantly, the departure in behavior of tethered myosin molecules from unconstrained myosin interactions with actin. In addition, MUSICO determines the number of cross-bridges in each actomyosin cycle state, the force and number of attached cross-bridges per myosin filament, the range of cross-bridge forces and accounts for energy consumption. At the macroscopic scale, MUSICO simulations show large differences in predicted force-velocity curves and in the response during early force recovery phase after a step change in length comparing to the two simplest mass action kinetic models. The origin of these differences is rooted in the different fluxes of myosin binding and corresponding instantaneous cross-bridge distributions and quantitatively reflects a major flaw of the mathematical description in all mass action kinetic models. Consequently, this new approach shows that accurate recapitulation of experimental data requires significantly different binding rates, number of actomyosin states, and cross-bridge elasticity than typically used in mass action kinetic models to correctly describe the biochemical reactions of tethered molecules and their interaction energetics.
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Affiliation(s)
- Srboljub M Mijailovich
- Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA 02115
- Department of Medicine, Tufts University School of Medicine, Boston, MA 021115
- Department of Chemistry and Chemical Biology, Northeastern University, Boston, MA 02115
| | - Oliver Kayser-Herold
- Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA 02115
| | - Boban Stojanovic
- Faculty of Science, University of Kragujevac, 34000 Kragujevac, Serbia
| | - Djordje Nedic
- Faculty of Science, University of Kragujevac, 34000 Kragujevac, Serbia
| | - Thomas C Irving
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616
| | - Michael A Geeves
- School of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ, England, UK
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18
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Thin filament length in the cardiac sarcomere varies with sarcomere length but is independent of titin and nebulin. J Mol Cell Cardiol 2016; 97:286-94. [PMID: 27139341 DOI: 10.1016/j.yjmcc.2016.04.013] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/24/2015] [Revised: 04/11/2016] [Accepted: 04/22/2016] [Indexed: 01/08/2023]
Abstract
Thin filament length (TFL) is an important determinant of the force-sarcomere length (SL) relation of cardiac muscle. However, the various mechanisms that control TFL are not well understood. Here we tested the previously proposed hypothesis that the actin-binding protein nebulin contributes to TFL regulation in the heart by using a cardiac-specific nebulin cKO mouse model (αMHC Cre Neb cKO). Atrial myocytes were studied because nebulin expression has been reported to be most prominent in this cell type. TFL was measured in right and left atrial myocytes using deconvolution optical microscopy and staining for filamentous actin with phalloidin and for the thin filament pointed-end with an antibody to the capping protein Tropomodulin-1 (Tmod1). Results showed that TFLs in Neb cKO and littermate control mice were not different. Thus, deletion of nebulin in the heart does not alter TFL. However, TFL was found to be ~0.05μm longer in the right than in the left atrium and Tmod1 expression was increased in the right atrium. We also tested the hypothesis that the length of titin's spring region is a factor controlling TFL by studying the Rbm20(ΔRRM) mouse which expresses titins that are ~500kDa (heterozygous mice) and ~1000kDa (homozygous mice) longer than in control mice. Results revealed that TFL was not different in Rbm20(ΔRRM) mice. An unexpected finding in all genotypes studied was that TFL increased as sarcomeres were stretched (~0.1μm per 0.35μm of SL increase). This apparent increase in TFL reached a maximum at a SL of ~3.0μm where TFL was ~1.05μm. The SL dependence of TFL was independent of chemical fixation or the presence of cardiac myosin-binding protein C (cMyBP-C). In summary, we found that in cardiac myocytes TFL varies with SL in a manner that is independent of the size of titin or the presence of nebulin.
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19
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Kumar M, Govindan S, Zhang M, Khairallah RJ, Martin JL, Sadayappan S, de Tombe PP. Cardiac Myosin-binding Protein C and Troponin-I Phosphorylation Independently Modulate Myofilament Length-dependent Activation. J Biol Chem 2015; 290:29241-9. [PMID: 26453301 DOI: 10.1074/jbc.m115.686790] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Indexed: 11/06/2022] Open
Abstract
β-Adrenergic stimulation in heart leads to increased contractility and lusitropy via activation of protein kinase A (PKA). In the cardiac sarcomere, both cardiac myosin binding protein C (cMyBP-C) and troponin-I (cTnI) are prominent myofilament targets of PKA. Treatment of permeabilized myocardium with PKA induces enhanced myofilament length-dependent activation (LDA), the cellular basis of the Frank-Starling cardiac regulatory mechanism. It is not known, however, which of these targets mediates the altered LDA and to what extent. Here, we employed two genetic mouse models in which the three PKA sites in cMyBP-C were replaced with either phospho-mimic (DDD) or phospho-null (AAA) residues. AAA- or DDD-permeabilized myocytes (n = 12-17) were exchanged (~93%) for recombinant cTnI in which the two PKA sites were mutated to either phospho-mimic (DD) or phospho-null (AA) residues. Force-[Ca(2+)] relationships were determined at two sarcomere lengths (SL = 1.9 μm and SL = 2.3 μm). Data were fit to a modified Hill equation for each individual cell preparation at each SL. LDA was indexed as ΔEC50, the difference in [Ca(2+)] required to achieve 50% force activation at the two SLs. We found that PKA-mediated phosphorylation of cMyBP-C and cTnI each independently contribute to enhance myofilament length-dependent activation properties of the cardiac sarcomere, with relative contributions of ~67 and ~33% for cMyBP-C for cTnI, respectively. We conclude that β-adrenergic stimulation enhances the Frank-Starling regulatory mechanism predominantly via cMyBP-C PKA-mediated phosphorylation. We speculate that this molecular mechanism enhances cross-bridge formation at long SL while accelerating cross-bridge detachment and relaxation at short SLs.
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Affiliation(s)
- Mohit Kumar
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Suresh Govindan
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Mengjie Zhang
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Ramzi J Khairallah
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Jody L Martin
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Sakthivel Sadayappan
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
| | - Pieter P de Tombe
- From the Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Ilinois 60153
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20
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Li F, Buck D, De Winter J, Kolb J, Meng H, Birch C, Slater R, Escobar YN, Smith JE, Yang L, Konhilas J, Lawlor MW, Ottenheijm C, Granzier HL. Nebulin deficiency in adult muscle causes sarcomere defects and muscle-type-dependent changes in trophicity: novel insights in nemaline myopathy. Hum Mol Genet 2015; 24:5219-33. [PMID: 26123491 DOI: 10.1093/hmg/ddv243] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Accepted: 06/22/2015] [Indexed: 01/07/2023] Open
Abstract
Nebulin is a giant filamentous protein that is coextensive with the actin filaments of the skeletal muscle sarcomere. Nebulin mutations are the main cause of nemaline myopathy (NEM), with typical adult patients having low expression of nebulin, yet the roles of nebulin in adult muscle remain poorly understood. To establish nebulin's functional roles in adult muscle, we studied a novel conditional nebulin KO (Neb cKO) mouse model in which nebulin deletion was driven by the muscle creatine kinase (MCK) promotor. Neb cKO mice are born with high nebulin levels in their skeletal muscles, but within weeks after birth nebulin expression rapidly falls to barely detectable levels Surprisingly, a large fraction of the mice survive to adulthood with low nebulin levels (<5% of control), contain nemaline rods and undergo fiber-type switching toward oxidative types. Nebulin deficiency causes a large deficit in specific force, and mechanistic studies provide evidence that a reduced fraction of force-generating cross-bridges and shortened thin filaments contribute to the force deficit. Muscles rich in glycolytic fibers upregulate proteolysis pathways (MuRF-1, Fbxo30/MUSA1, Gadd45a) and undergo hypotrophy with smaller cross-sectional areas (CSAs), worsening their force deficit. Muscles rich in oxidative fibers do not have smaller weights and can even have hypertrophy, offsetting their specific-force deficit. These studies reveal nebulin as critically important for force development and trophicity in adult muscle. The Neb cKO phenocopies important aspects of NEM (muscle weakness, oxidative fiber-type predominance, variable trophicity effects, nemaline rods) and will be highly useful to test therapeutic approaches to ameliorate muscle weakness.
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Affiliation(s)
- Frank Li
- Department of Cellular and Molecular Medicine
| | | | - Josine De Winter
- Department of Physiology, VU University Medical Center, Amsterdam, The Netherlands
| | - Justin Kolb
- Department of Cellular and Molecular Medicine
| | - Hui Meng
- Department of Pathology and Laboratory Medicine, Medical College of Wisconsin, Milwaukee, WI, USA and
| | - Camille Birch
- Department of Physiology, University of Arizona, Tucson, AZ, USA
| | | | | | | | - Lin Yang
- Department of Biomedical Engineering, University of Florida, Gainesville, FL, USA
| | - John Konhilas
- Department of Physiology, University of Arizona, Tucson, AZ, USA
| | - Michael W Lawlor
- Department of Pathology and Laboratory Medicine, Medical College of Wisconsin, Milwaukee, WI, USA and
| | - Coen Ottenheijm
- Department of Cellular and Molecular Medicine, Department of Physiology, VU University Medical Center, Amsterdam, The Netherlands
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21
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Spudich JA. Hypertrophic and dilated cardiomyopathy: four decades of basic research on muscle lead to potential therapeutic approaches to these devastating genetic diseases. Biophys J 2014; 106:1236-49. [PMID: 24655499 PMCID: PMC3985504 DOI: 10.1016/j.bpj.2014.02.011] [Citation(s) in RCA: 198] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 01/30/2014] [Accepted: 02/04/2014] [Indexed: 01/10/2023] Open
Abstract
With the advent of technologies to obtain the complete sequence of the human genome in a cost-effective manner, this decade and those to come will see an exponential increase in our understanding of the underlying genetics that lead to human disease. And where we have a deep understanding of the biochemical and biophysical basis of the machineries and pathways involved in those genetic changes, there are great hopes for the development of modern therapeutics that specifically target the actual machinery and pathways altered by individual mutations. Prime examples of such a genetic disease are those classes of hypertrophic and dilated cardiomyopathy that result from single amino-acid substitutions in one of several of the proteins that make up the cardiac sarcomere or from the truncation of myosin binding protein C. Hypertrophic cardiomyopathy alone affects ∼1 in 500 individuals, and it is the leading cause of sudden cardiac death in young adults. Here I describe approaches to understand the molecular basis of the alterations in power output that result from these mutations. Small molecules binding to the mutant sarcomeric protein complex should be able to mitigate the effects of hypertrophic and dilated cardiomyopathy mutations at their sources, leading to possible new therapeutic approaches for these genetic diseases.
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Affiliation(s)
- James A Spudich
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California.
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22
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Stienen GJM. Pathomechanisms in heart failure: the contractile connection. J Muscle Res Cell Motil 2014; 36:47-60. [PMID: 25376563 DOI: 10.1007/s10974-014-9395-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2014] [Accepted: 10/20/2014] [Indexed: 01/07/2023]
Abstract
Heart failure is a multi-factorial progressive disease in which eventually the contractile performance of the heart is insufficient to meet the demands of the body, even at rest. A distinction can be made on the basis of the cause of the disease in genetic and acquired heart failure and at the functional level between systolic and diastolic heart failure. Here the basic determinants of contractile function of myocardial cells will be reviewed and an attempt will be made to elucidate their role in the development of heart failure. The following topics are addressed: the tension generating capacity, passive tension, the rate of tension development, the rate of ATP utilisation, calcium sensitivity of tension development, phosphorylation of contractile proteins, length dependent activation and stretch activation. The reduction in contractile performance during systole can be attributed predominantly to a loss of cardiomyocytes (necrosis), myocyte disarray and a decrease in myofibrillar density all resulting in a reduction in the tension generating capacity and likely also to a mismatch between energy supply and demand of the myocardium. This leads to a decline in the ejection fraction of the heart. Diastolic dysfunction can be attributed to fibrosis and an increase in titin stiffness which result in an increase in stiffness of the ventricular wall and hampers the filling of the heart with blood during diastole. A large number of post translation modifications of regulatory sarcomeric proteins influence myocardial function by altering calcium sensitivity of tension development. It is still unclear whether in concert these influences are adaptive or maladaptive during the disease process.
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Affiliation(s)
- G J M Stienen
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands,
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23
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Tanner BCW, Wang Y, Robbins J, Palmer BM. Kinetics of cardiac myosin isoforms in mouse myocardium are affected differently by presence of myosin binding protein-C. J Muscle Res Cell Motil 2014; 35:267-78. [PMID: 25287107 DOI: 10.1007/s10974-014-9390-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Accepted: 09/22/2014] [Indexed: 10/24/2022]
Abstract
We tested whether cardiac myosin binding protein-C (cMyBP-C) affects myosin cross-bridge kinetics in the two cardiac myosin heavy chain (MyHC) isoforms. Mice lacking cMyBP-C (t/t) and transgenic controls (WT(t/t)) were fed L-thyroxine (T4) to induce 90/10% expression of α/β-MyHC. Non-transgenic (NTG) and t/t mice were fed 6-n-propyl-2-thiouracil (PTU) to induce 100% expression of β-MyHC. Ca(2+)-activated, chemically-skinned myocardium underwent length perturbation analysis with varying [MgATP] to estimate the MgADP release rate (k(-ADP)) and MgATP binding rate (k(+ATP)). Values for (k(-ADP)) were not significantly different between t/t(T4) (102.2 ± 7.0 s(-1)) and WT(t/t)(T4) (91.3 ± 8.9 s(-1)), but k(+ATP)) was lower in t/t(T4) (165.9 ± 12.5 mM(-1) s(-1)) compared to WT(t/t)(T4) (298.6 ± 15.7 mM(-1) s(-1), P < 0.01). In myocardium expressing β-MyHC, values for k(-ADP) were higher in t/t(PTU) (24.8 ± 1.0 s(-1)) compared to NTG(PTU) (15.6 ± 1.3 s(-1), P < 0.01), and k(+ATP) was not different. At saturating [MgATP], myosin detachment rate approximates k(-ADP), and detachment rate decreased as sarcomere length (SL) was increased in both t/t(T4) and WT(t/t)(T4) with similar sensitivities to SL. In myocardium expressing β-MyHC, detachment rate decreased more as SL increased in t/t(PTU) (21.5 ± 1.3 s(-1) at 2.2 μm and 13.3 ± 0.9 s(-1) at 3.3 μm) compared to NTGPTU (15.8 ± 0.3 s(-1) at 2.2 μm and 10.9 ± 0.3 s(-1) at 3.3 μm) as detected by repeated-measures ANOVA (P < 0.01). These findings suggest that cMyBP-C reduces MgADP release rate for β-MyHC, but not for α-MyHC, even as the number of cMyBP-C that overlap with the thin filament is reduced to zero. Therefore, cMyBP-C appears to affect β-MyHC kinetics independent of its interaction with the thin filament.
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Affiliation(s)
- Bertrand C W Tanner
- Department of Molecular Physiology and Biophysics, University of Vermont, 122 HSRF, 149 Beaumont Ave., Burlington, VT, 05405, USA
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24
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Gokhin DS, Fowler VM. A two-segment model for thin filament architecture in skeletal muscle. Nat Rev Mol Cell Biol 2013; 14:113-9. [PMID: 23299957 DOI: 10.1038/nrm3510] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Correct specification of myofilament length is essential for efficient skeletal muscle contraction. The length of thin actin filaments can be explained by a novel 'two-segment' model, wherein the thin filaments consist of two concatenated segments, which are of either constant or variable length. This is in contrast to the classic 'nebulin ruler' model, which postulates that thin filaments are uniform structures, the lengths of which are dictated by nebulin. The two-segment model implicates position-specific microregulation of actin dynamics as a general principle underlying actin filament length and stability.
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Affiliation(s)
- David S Gokhin
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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26
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Structural basis for myopathic defects engendered by alterations in the myosin rod. J Mol Biol 2011; 414:477-84. [PMID: 22037585 DOI: 10.1016/j.jmb.2011.10.019] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2011] [Revised: 10/03/2011] [Accepted: 10/12/2011] [Indexed: 12/12/2022]
Abstract
While mutations in the myosin subfragment 1 motor domain can directly disrupt the generation and transmission of force along myofibrils and lead to myopathy, the mechanism whereby mutations in the myosin rod influences mechanical function is less clear. Here, we used a combination of various imaging techniques and molecular dynamics simulations to test the hypothesis that perturbations in the myosin rod can disturb normal sarcomeric uniformity and, like motor domain lesions, would influence force production and propagation. We show that disrupting the rod can alter its nanomechanical properties and, in vivo, can drive asymmetric myofilament and sarcomere formation. Our imaging results indicate that myosin rod mutations likely disturb production and/or propagation of contractile force. This provides a unifying theory where common pathological cascades accompany both myosin motor and specific rod domain mutations. Finally, we suggest that sarcomeric inhomogeneity, caused by asymmetric thick filaments, could be a useful index of myopathic dysfunction.
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27
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Rakhilin S, Turner G, Katz M, Warden R, Irelan J, Abassi YA, Glass DJ. Electrical Impedance as a Novel Biomarker of Myotube Atrophy and Hypertrophy. ACTA ACUST UNITED AC 2011; 16:565-74. [DOI: 10.1177/1087057111401392] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Measuring myotube thickness is a physiological and unbiased approach for screening therapeutic compounds that prevent skeletal muscle atrophy or induce hypertrophy. However, an accurate cell thickness estimate is often quite challenging because of the extreme heterogeneity of the myotube cellular population and therefore the lack of a regular distribution of perturbed myotubes. Here the authors present a novel method to evaluate changes in myotube thickness via measuring cellular electrical impedance. They demonstrate that both qualitative and quantitative changes in electrical impedance as a function of cellular adhesion in real time correlate well with variation in myotube thickness caused by atrophy or hypertrophy agents. Conversely, pharmacologically blocking myotube hypertrophy prevents changes in electrical impedance. Thus, impedance can be used as a reliable and sensitive biomarker for myotube atrophy or hypertrophy. Application of this technique to drug screening might be beneficial in finding novel treatments preventing muscle atrophy and other diseases associated with any morphological change in cell shape.
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Affiliation(s)
- Sergey Rakhilin
- Novartis Institute for Biomedical Research, Cambridge, MA, USA
| | - Gordon Turner
- Novartis Institute for Biomedical Research, Cambridge, MA, USA
| | - Mark Katz
- Novartis Institute for Biomedical Research, Cambridge, MA, USA
| | - Robert Warden
- University of Pennsylvania, Bioengineering Department, Philadelphia, PA, USA
| | | | | | - David J. Glass
- Novartis Institute for Biomedical Research, Cambridge, MA, USA
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28
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Labeit S, Ottenheijm CAC, Granzier H. Nebulin, a major player in muscle health and disease. FASEB J 2010; 25:822-9. [PMID: 21115852 DOI: 10.1096/fj.10-157412] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Nebulin is a giant 600- to 900-kDa filamentous protein that is an integral component of the skeletal muscle thin filament. Its functions have remained largely nebulous because of its large size and the difficulty in extracting nebulin in a native state from muscle. Recent improvements in the field, especially the development of knockout mouse models deficient in nebulin (NEB-KO mice), indicate now that nebulin performs a surprisingly wide range of functions. In addition to a major role in thin-filament length specification, nebulin also functions in the regulation of muscle contraction, as indicated by the findings that muscle fibers deficient in nebulin have a higher tension cost, and develop less force due to reduced myofilament calcium sensitivity and altered crossbridge cycling kinetics. In addition, the function of nebulin extends to a role in calcium homeostasis. These novel functions indicate that nebulin might have evolved in vertebrate skeletal muscles to develop high levels of muscle force efficiently. Finally, the NEB-KO mouse models also highlight the role of nebulin in the assembly and alignment of the Z disks. Notably, rapid progress in understanding the roles of nebulin in vivo provides clinically important insights into how nebulin deficiency in patients with nemaline myopathy contributes to debilitating muscle weakness.
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Affiliation(s)
- Siegfried Labeit
- Department of Integrative Pathophysiology, Universitätsmedizin Mannheim, University of Heidelberg, Mannheim, Germany.
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29
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Luther PK. The vertebrate muscle Z-disc: sarcomere anchor for structure and signalling. J Muscle Res Cell Motil 2009; 30:171-85. [PMID: 19830582 PMCID: PMC2799012 DOI: 10.1007/s10974-009-9189-6] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2009] [Accepted: 09/23/2009] [Indexed: 02/04/2023]
Abstract
The Z-disc, appearing as a fine dense line forming sarcomere boundaries in striated muscles, when studied in detail reveals crosslinked filament arrays that transmit tension and house myriads of proteins with diverse functions. At the Z-disc the barbed ends of the antiparallel actin filaments from adjoining sarcomeres interdigitate and are crosslinked primarily by layers of α-actinin. The Z-disc is therefore the site of polarity reversal of the actin filaments, as needed to interact with the bipolar myosin filaments in successive sarcomeres. The layers of α-actinin determine the Z-disc width: fast fibres have narrow (~30–50 nm) Z-discs and slow and cardiac fibres have wide (~100 nm) Z-discs. Comprehensive reviews on the roles of the numerous proteins located at the Z-disc in signalling and disease have been published; the aim here is different, namely to review the advances in structural aspects of the Z-disc.
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Affiliation(s)
- Pradeep K Luther
- Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London, UK.
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30
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Littlefield RS, Fowler VM. Thin filament length regulation in striated muscle sarcomeres: pointed-end dynamics go beyond a nebulin ruler. Semin Cell Dev Biol 2008; 19:511-9. [PMID: 18793739 DOI: 10.1016/j.semcdb.2008.08.009] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2008] [Accepted: 08/19/2008] [Indexed: 01/18/2023]
Abstract
The actin (thin) filaments in striated muscle are highly regulated and precisely specified in length to optimally overlap with the myosin (thick) filaments for efficient myofibril contraction. Here, we review and critically discuss recent evidence for how thin filament lengths are controlled in vertebrate skeletal, vertebrate cardiac, and invertebrate (arthropod) sarcomeres. Regulation of actin polymerization dynamics at the slow-growing (pointed) ends by the capping protein tropomodulin provides a unified explanation for how thin filament lengths are physiologically optimized in all three muscle types. Nebulin, a large protein thought to specify thin filament lengths in vertebrate skeletal muscle through a ruler mechanism, may not control pointed-end actin dynamics directly, but instead may stabilize a large core region of the thin filament. We suggest that this stabilizing function for nebulin modifies the lengths primarily specified by pointed-end actin dynamics to generate uniform filament lengths in vertebrate skeletal muscle. We suggest that nebulette, a small homolog of nebulin, may stabilize a correspondingly shorter core region and allow individual thin filament lengths to vary according to working sarcomere lengths in vertebrate cardiac muscle. We present a unified model for thin filament length regulation where these two mechanisms cooperate to tailor thin filament lengths for specific contractile environments in diverse muscles.
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Affiliation(s)
- Ryan S Littlefield
- Center for Cell Dynamics, University of Washington, Friday Harbor Laboratories, Friday Harbor, WA 98250, USA
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31
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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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