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Bruns H, Czajka TS, Sztucki M, Brandenburg S, Salditt T. Sarcomere, troponin, and myosin X-ray diffraction signals can be resolved in single cardiomyocytes. Biophys J 2024; 123:3024-3037. [PMID: 38956875 PMCID: PMC11427778 DOI: 10.1016/j.bpj.2024.06.029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 04/18/2024] [Accepted: 06/28/2024] [Indexed: 07/04/2024] Open
Abstract
Cardiac function relies on the autonomous molecular contraction mechanisms in the ventricular wall. Contraction is driven by ordered motor proteins acting in parallel to generate a macroscopic force. The averaged structure can be investigated by diffraction from model tissues such as trabecular and papillary cardiac muscle using collimated synchrotron beams, offering high resolution in reciprocal space. In the ventricular wall, however, the muscle tissue is compartmentalized into smaller branched cardiomyocytes, with a higher degree of disorder. We show that X-ray diffraction is now also capable of resolving the structural organization of actomyosin in single isolated cardiomyocytes of the ventricular wall. In addition to the hexagonal arrangement of thick and thin filaments, the diffraction signal of the hydrated and fixated cardiomyocytes was sufficient to reveal the myosin motor repeat (M3), the troponin complex repeat (Tn), and the sarcomere length. The sarcomere length signal comprised up to 13 diffraction orders, which were used to compute the sarcomere density profile based on Fourier synthesis. The Tn and M3 spacings were found in the same range as previously reported for other muscle types. The approach opens up a pathway to record the structural dynamics of living cells during the contraction cycle, toward a more complete understanding of cardiac muscle function.
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Affiliation(s)
| | | | - Michael Sztucki
- ESRF - European Synchrotron Radiation Facility, Grenoble, France
| | - Sören Brandenburg
- Department of Cardiology and Pneumology, University Medical Center Göttingen, Göttingen, Germany
| | - Tim Salditt
- Institute for X-ray Physics, Göttingen, Germany.
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Abstract
Force generation in striated muscle is primarily controlled by structural changes in the actin-containing thin filaments triggered by an increase in intracellular calcium concentration. However, recent studies have elucidated a new class of regulatory mechanisms, based on the myosin-containing thick filament, that control the strength and speed of contraction by modulating the availability of myosin motors for the interaction with actin. This review summarizes the mechanisms of thin and thick filament activation that regulate the contractility of skeletal and cardiac muscle. A novel dual-filament paradigm of muscle regulation is emerging, in which the dynamics of force generation depends on the coordinated activation of thin and thick filaments. We highlight the interfilament signaling pathways based on titin and myosin-binding protein-C that couple thin and thick filament regulatory mechanisms. This dual-filament regulation mediates the length-dependent activation of cardiac muscle that underlies the control of the cardiac output in each heartbeat.
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Affiliation(s)
- Elisabetta Brunello
- Randall Centre for Cell and Molecular Biophysics, School of Basic and Medical Biosciences and British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom; ,
| | - Luca Fusi
- Randall Centre for Cell and Molecular Biophysics, School of Basic and Medical Biosciences and British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom; ,
- Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London, London, United Kingdom
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3
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Short B. Examining the calcium sensitivity of skeletal muscle thick filaments. J Gen Physiol 2023; 155:e202313501. [PMID: 37966794 PMCID: PMC10651394 DOI: 10.1085/jgp.202313501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2023] Open
Abstract
JGP study (this issue, Caremani et al. https://doi.org/10.1085/jgp.202313393) reveals that the calcium sensitivity of thick filament structure in skeletal muscle is greater than that of force, offering new insights into the mechanisms of thick filament activation.
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Affiliation(s)
- Ben Short
- Science Writer, Rockefeller University Press, New York, NY, USA
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Caremani M, Fusi L, Reconditi M, Piazzesi G, Narayanan T, Irving M, Lombardi V, Linari M, Brunello E. Dependence of myosin filament structure on intracellular calcium concentration in skeletal muscle. J Gen Physiol 2023; 155:e202313393. [PMID: 37756601 PMCID: PMC10533363 DOI: 10.1085/jgp.202313393] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Revised: 07/15/2023] [Accepted: 09/05/2023] [Indexed: 09/29/2023] Open
Abstract
Contraction of skeletal muscle is triggered by an increase in intracellular calcium concentration that relieves the structural block on actin-binding sites in resting muscle, potentially allowing myosin motors to bind and generate force. However, most myosin motors are not available for actin binding because they are stabilized in folded helical tracks on the surface of myosin-containing thick filaments. High-force contraction depends on the release of the folded motors, which can be triggered by stress in the thick filament backbone, but additional mechanisms may link the activation of the thick filaments to that of the thin filaments or to intracellular calcium concentration. Here, we used x-ray diffraction in combination with temperature-jump activation to determine the steady-state calcium dependence of thick filament structure and myosin motor conformation in near-physiological conditions. We found that x-ray signals associated with the perpendicular motors characteristic of isometric force generation had almost the same calcium sensitivity as force, but x-ray signals associated with perturbations in the folded myosin helix had a much higher calcium sensitivity. Moreover, a new population of myosin motors with a longer axial periodicity became prominent at low levels of calcium activation and may represent an intermediate regulatory state of the myosin motors in the physiological pathway of filament activation.
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Affiliation(s)
| | - Luca Fusi
- Randall Centre for Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King’s College London, London, UK
- Centre for Human and Applied Physiological Sciences, King’s College London, London, UK
| | - Massimo Reconditi
- PhysioLab, University of Florence, Florence, Italy
- Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, Florence, Italy
| | | | | | - Malcolm Irving
- Randall Centre for Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King’s College London, London, UK
| | | | - Marco Linari
- PhysioLab, University of Florence, Florence, Italy
- Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, Florence, Italy
| | - Elisabetta Brunello
- Randall Centre for Cell and Molecular Biophysics and British Heart Foundation Centre of Research Excellence, King’s College London, London, UK
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Ochala J, Lewis CTA, Beck T, Iwamoto H, Hessel AL, Campbell KS, Pyle WG. Predominant myosin superrelaxed state in canine myocardium with naturally occurring dilated cardiomyopathy. Am J Physiol Heart Circ Physiol 2023; 325:H585-H591. [PMID: 37505469 DOI: 10.1152/ajpheart.00369.2023] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Revised: 07/12/2023] [Accepted: 07/24/2023] [Indexed: 07/29/2023]
Abstract
Dilated cardiomyopathy (DCM) is a naturally occurring heart failure condition in humans and dogs, notably characterized by a reduced contractility and ejection fraction. As the identification of its underlying cellular and molecular mechanisms remain incomplete, the aim of the present study was to assess whether the molecular motor myosin and its known relaxed conformational states are altered in DCM. For that, we dissected and skinned thin cardiac strips from left ventricle obtained from six DCM Doberman Pinschers and six nonfailing (NF) controls. We then used a combination of Mant-ATP chase experiments and X-ray diffraction to assess both energetic and structural changes of myosin. Using the Mant-ATP chase protocol, we observed that in DCM dogs, the amount of myosin molecules in the ATP-conserving conformational state, also known as superrelaxed (SRX), is significantly increased when compared with NF dogs. This alteration can be rescued by applying EMD-57033, a small molecule activating myosin. Conversely, with X-ray diffraction, we found that in DCM dogs, there is a higher proportion of myosin heads in the vicinity of actin when compared with NF dogs (1,0 to 1,1 intensity ratio). Hence, we observed an uncoupling between energetic (Mant-ATP chase) and structural (X-ray diffraction) data. Taken together, these results may indicate that in the heart of Doberman Pinschers with DCM, myosin molecules are potentially stuck in a nonsequestered but ATP-conserving SRX state, that can be counterbalanced by EMD-57033 demonstrating the potential for a myosin-centered pharmacological treatment of DCM.NEW & NOTEWORTHY The key finding of the present study is that, in left ventricles of dogs with a naturally occurring dilated cardiomyopathy, relaxed myosin molecules favor a nonsequestered superrelaxed state potentially impairing sarcomeric contractility. This alteration is rescuable by applying a small molecule activating myosin known as EMD-57033.
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Affiliation(s)
- Julien Ochala
- Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
| | | | - Thomas Beck
- Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Hiroyuki Iwamoto
- SPring-8, Japan Synchrotron Radiation Research Institute, Hyogo, Japan
| | - Anthony L Hessel
- Institute of Physiology II, University of Muenster, Muenster, Germany
- Accelerated Muscle Biotechnologies, Boston, Massachusetts, United States
| | - Kenneth S Campbell
- Department of Physiology, University of Kentucky, Lexington, Kentucky, United States
- Division of Cardiovascular Medicine, University of Kentucky, Lexington, Kentucky, United States
| | - W Glen Pyle
- IMPART Investigator Team, Dalhousie Medicine, Saint John, New Brunswick, Canada
- Department of Biomedical Sciences, University of Guelph, Guelph, Ontario, Canada
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Kim H, Heckman CJ. A dynamic calcium-force relationship model for sag behavior in fast skeletal muscle. PLoS Comput Biol 2023; 19:e1011178. [PMID: 37289805 DOI: 10.1371/journal.pcbi.1011178] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Accepted: 05/12/2023] [Indexed: 06/10/2023] Open
Abstract
In vitro studies using isolated or skinned muscle fibers suggest that the sigmoidal relationship between the intracellular calcium concentration and force production may depend upon muscle type and activity. The goal of this study was to investigate whether and how the calcium-force relationship changes during force production under physiological conditions of muscle excitation and length in fast skeletal muscles. A computational framework was developed to identify the dynamic variation in the calcium-force relationship during force generation over a full physiological range of stimulation frequencies and muscle lengths in cat gastrocnemius muscles. In contrast to the situation in slow muscles such as the soleus, the calcium concentration for the half-maximal force needed to drift rightward to reproduce the progressive force decline, or sag behavior, observed during unfused isometric contractions at the intermediate length under low-frequency stimulation (i.e., 20 Hz). The slope at the calcium concentration for the half-maximal force was required to drift upward for force enhancement during unfused isometric contractions at the intermediate length under high-frequency stimulation (i.e., 40 Hz). The slope variation in the calcium-force relationship played a crucial role in shaping sag behavior across different muscle lengths. The muscle model with dynamic variations in the calcium-force relationship also accounted for the length-force and velocity-force properties measured under full excitation. These results imply that the calcium sensitivity and cooperativity of force-inducing crossbridge formation between actin and myosin filaments may be operationally altered in accordance with the mode of neural excitation and muscle movement in intact fast muscles.
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Affiliation(s)
- Hojeong Kim
- Division of Biotechnology, Institute of Convergence Research, DGIST, Daegu, Republic of Korea
- Department of Interdisciplinary Studies, DGIST, Daegu, Republic of Korea
| | - Charles J Heckman
- Department of Neuroscience, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States of America
- Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States of America
- Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States of America
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