1
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Mead AF, Wood NB, Nelson SR, Palmer BM, Yang L, Previs SB, Ploysangngam A, Kennedy GG, McAdow JF, Tremble SM, Zimmermann MA, Cipolla MJ, Ebert AM, Johnson AN, Gurnett CA, Previs MJ, Warshaw DM. Functional role of myosin-binding protein H in thick filaments of developing vertebrate fast-twitch skeletal muscle. J Gen Physiol 2024; 156:e202413604. [PMID: 39373654 DOI: 10.1085/jgp.202413604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2024] [Revised: 08/01/2024] [Accepted: 09/20/2024] [Indexed: 10/08/2024] Open
Abstract
Myosin-binding protein H (MyBP-H) is a component of the vertebrate skeletal muscle sarcomere with sequence and domain homology to myosin-binding protein C (MyBP-C). Whereas skeletal muscle isoforms of MyBP-C (fMyBP-C, sMyBP-C) modulate muscle contractility via interactions with actin thin filaments and myosin motors within the muscle sarcomere "C-zone," MyBP-H has no known function. This is in part due to MyBP-H having limited expression in adult fast-twitch muscle and no known involvement in muscle disease. Quantitative proteomics reported here reveal that MyBP-H is highly expressed in prenatal rat fast-twitch muscles and larval zebrafish, suggesting a conserved role in muscle development and prompting studies to define its function. We take advantage of the genetic control of the zebrafish model and a combination of structural, functional, and biophysical techniques to interrogate the role of MyBP-H. Transgenic, FLAG-tagged MyBP-H or fMyBP-C both localize to the C-zones in larval myofibers, whereas genetic depletion of endogenous MyBP-H or fMyBP-C leads to increased accumulation of the other, suggesting competition for C-zone binding sites. Does MyBP-H modulate contractility in the C-zone? Globular domains critical to MyBP-C's modulatory functions are absent from MyBP-H, suggesting that MyBP-H may be functionally silent. However, our results suggest an active role. In vitro motility experiments indicate MyBP-H shares MyBP-C's capacity as a molecular "brake." These results provide new insights and raise questions about the role of the C-zone during muscle development.
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Affiliation(s)
- Andrew F Mead
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT, USA
- Cardiovascular Research Institute, University of Vermont , Burlington, VT, USA
| | - Neil B Wood
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT, USA
| | - Shane R Nelson
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT, USA
- Cardiovascular Research Institute, University of Vermont , Burlington, VT, USA
| | - Bradley M Palmer
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT, USA
- Cardiovascular Research Institute, University of Vermont , Burlington, VT, USA
| | - Lin Yang
- National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY, USA
| | - Samantha Beck Previs
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT, USA
- Cardiovascular Research Institute, University of Vermont , Burlington, VT, USA
| | - Angela Ploysangngam
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT, USA
| | - Guy G Kennedy
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT, USA
| | - Jennifer F McAdow
- Department of Neurlogical Sciences, Larner College of Medicine, University of Vermont, Burlington, VT, USA
| | - Sarah M Tremble
- Department of Electrical and Biomedical Engineering, College of Engineering and Mathematical Sciences, University of Vermont, Burlington, VT, USA
| | - Marcus A Zimmermann
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT, USA
- Cardiovascular Research Institute, University of Vermont , Burlington, VT, USA
| | - Marilyn J Cipolla
- Department of Electrical and Biomedical Engineering, College of Engineering and Mathematical Sciences, University of Vermont, Burlington, VT, USA
- Department of Neurology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Alicia M Ebert
- Department of Biology, College of Arts and Sciences, University of Vermont, Burlington, VT, USA
| | - Aaron N Johnson
- Department of Developmental Biology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Christina A Gurnett
- Department of Developmental Biology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Michael J Previs
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT, USA
- Cardiovascular Research Institute, University of Vermont , Burlington, VT, USA
| | - David M Warshaw
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT, USA
- Cardiovascular Research Institute, University of Vermont , Burlington, VT, USA
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2
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Kooiker K, Gan QF, Yu M, Sa N, Mohran S, Cheng Y, Flint G, Neys S, Gao C, Nissen D, McMillen T, Asencio A, Ma W, Irving TC, Moussavi-Harami F, Regnier M. Mechanisms of a novel regulatory light chain-dependent cardiac myosin inhibitor. J Gen Physiol 2024; 156:e202313503. [PMID: 39083045 PMCID: PMC11291911 DOI: 10.1085/jgp.202313503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Revised: 05/14/2024] [Accepted: 07/12/2024] [Indexed: 09/13/2024] Open
Abstract
Hypertrophic cardiomyopathy (HCM) is a genetic disease of the heart characterized by thickening of the left ventricle (LV), hypercontractility, and impaired relaxation. HCM is caused primarily by heritable mutations in sarcomeric proteins, such as β myosin heavy chain. Until recently, medications in clinical use for HCM did not directly target the underlying contractile changes in the sarcomere. Here, we investigate a novel small molecule, RLC-1, identified in a bovine cardiac myofibril high-throughput screen. RLC-1 is highly dependent on the presence of a regulatory light chain to bind to cardiac myosin and modulate its ATPase activity. In demembranated rat LV trabeculae, RLC-1 decreased maximal Ca2+-activated force and Ca2+ sensitivity of force, while it increased the submaximal rate constant for tension redevelopment. In myofibrils isolated from rat LV, both maximal and submaximal Ca2+-activated force are reduced by nearly 50%. Additionally, the fast and slow phases of relaxation were approximately twice as fast as DMSO controls, and the duration of the slow phase was shorter. Structurally, x-ray diffraction studies showed that RLC-1 moved myosin heads away from the thick filament backbone and decreased the order of myosin heads, which is different from other myosin inhibitors. In intact trabeculae and isolated cardiomyocytes, RLC-1 treatment resulted in decreased peak twitch magnitude and faster activation and relaxation kinetics. In conclusion, RLC-1 accelerated kinetics and decreased force production in the demembranated tissue, intact tissue, and intact whole cells, resulting in a smaller cardiac twitch, which could improve the underlying contractile changes associated with HCM.
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Affiliation(s)
- Kristina Kooiker
- Division of Cardiology, Medicine, University of Washington, Seattle, WA, USA
- Center of Translational Muscle Research, University of Washington , Seattle, WA, USA
- Center for Cardiovascular Biology, University of Washington , Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington , Seattle, WA, USA
| | - Qing-Fen Gan
- Bristol Myers Squibb Research , Brisbane, CA, USA
| | - Ming Yu
- Bristol Myers Squibb Research , Brisbane, CA, USA
| | - Na Sa
- Bristol Myers Squibb Research , Brisbane, CA, USA
| | - Saffie Mohran
- Division of Cardiology, Medicine, University of Washington, Seattle, WA, USA
- Center of Translational Muscle Research, University of Washington , Seattle, WA, USA
- Center for Cardiovascular Biology, University of Washington , Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington , Seattle, WA, USA
| | - Yuanhua Cheng
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Galina Flint
- Center of Translational Muscle Research, University of Washington , Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington , Seattle, WA, USA
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Stephanie Neys
- Division of Cardiology, Medicine, University of Washington, Seattle, WA, USA
- Center of Translational Muscle Research, University of Washington , Seattle, WA, USA
- Center for Cardiovascular Biology, University of Washington , Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington , Seattle, WA, USA
| | - Chengqian Gao
- College of Basic Medical Sciences, Dalian Medical University , Dalian, China
| | - Devin Nissen
- Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Tim McMillen
- Center of Translational Muscle Research, University of Washington , Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington , Seattle, WA, USA
- Department of Anesthesiology and Pain Medicine, University of Washington, Seattle, WA, USA
| | - Anthony Asencio
- Center of Translational Muscle Research, University of Washington , Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington , Seattle, WA, USA
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Weikang Ma
- Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Thomas C Irving
- Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Farid Moussavi-Harami
- Division of Cardiology, Medicine, University of Washington, Seattle, WA, USA
- Center of Translational Muscle Research, University of Washington , Seattle, WA, USA
- Center for Cardiovascular Biology, University of Washington , Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington , Seattle, WA, USA
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA
| | - Michael Regnier
- Center of Translational Muscle Research, University of Washington , Seattle, WA, USA
- Center for Cardiovascular Biology, University of Washington , Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington , Seattle, WA, USA
- Department of Bioengineering, University of Washington, Seattle, WA, USA
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3
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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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4
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Turner KL, Vander Top BJ, Kooiker KB, Mohran S, Mandrycky C, McMillen T, Regnier M, Irving TC, Ma W, Tanner BCW. The structural and functional effects of myosin regulatory light chain phosphorylation are amplified by increases in sarcomere length and [Ca 2+]. J Physiol 2024. [PMID: 39283968 DOI: 10.1113/jp286802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2024] [Accepted: 08/21/2024] [Indexed: 10/04/2024] Open
Abstract
Precise regulation of sarcomeric contraction is essential for normal cardiac function. The heart must generate sufficient force to pump blood throughout the body, but either inadequate or excessive force can lead to dysregulation and disease. Myosin regulatory light chain (RLC) is a thick-filament protein that binds to the neck of the myosin heavy chain. Post-translational phosphorylation of RLC (RLC-P) by myosin light chain kinase is known to influence acto-myosin interactions, thereby increasing force production and Ca2+-sensitivity of contraction. Here, we investigated the role of RLC-P on cardiac structure and function as sarcomere length and [Ca2+] were altered. We found that at low, non-activating levels of Ca2+, RLC-P contributed to myosin head disorder, though there were no effects on isometric stress production and viscoelastic stiffness. With increases in sarcomere length and Ca2+-activation, the structural changes due to RLC-P become greater, which translates into greater force production, greater viscoelastic stiffness, slowed myosin detachment rates and altered nucleotide handling. Altogether, these data suggest that RLC-P may alter thick-filament structure by releasing ordered, off-state myosin. These more disordered myosin heads are available to bind actin, which could result in greater force production as Ca2+ levels increase. However, prolonged cross-bridge attachment duration due to slower ADP release could delay relaxation long enough to enable cross-bridge rebinding. Together, this work further elucidates the effects of RLC-P in regulating muscle function, thereby promoting a better understanding of thick-filament regulatory contributions to cardiac function in health and disease. KEY POINTS: Myosin regulatory light chain (RLC) is a thick-filament protein in the cardiac sarcomere that can be phosphorylated (RLC-P), and changes in RLC-P are associated with cardiac dysfunction and disease. This study assesses how RLC-P alters cardiac muscle structure and function at different sarcomere lengths and calcium concentrations. At low, non-activating levels of Ca2+, RLC-P contributed to myofilament disorder, though there were no effects on isometric stress production and viscoelastic stiffness. With increases in sarcomere length and Ca2+-activation, the structural changes due to RLC-P become greater, which translates into greater force production, greater viscoelastic stiffness, slower myosin detachment rate and altered cross-bridge nucleotide handling rates. This work elucidates the role of RLC-P in regulating muscle function and facilitates understanding of thick-filament regulatory protein contributions to cardiac function in health and disease.
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Affiliation(s)
- Kyrah L Turner
- School of Molecular Biosciences, Washington State University, Pullman, WA, USA
| | - Blake J Vander Top
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA, USA
| | - Kristina B Kooiker
- Division of Cardiology, Department of Medicine, University of Washington, Seattle, WA, USA
- Center for Translational Muscle Research, University of Washington, Seattle, WA, USA
- Center for Cardiovascular Biology, University of Washington, Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA
| | - Saffie Mohran
- Division of Cardiology, Department of Medicine, University of Washington, Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Christian Mandrycky
- Division of Cardiology, Department of Medicine, University of Washington, Seattle, WA, USA
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Tim McMillen
- Division of Cardiology, Department of Medicine, University of Washington, Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Michael Regnier
- Division of Cardiology, Department of Medicine, University of Washington, Seattle, WA, USA
- Center for Translational Muscle Research, University of Washington, Seattle, WA, USA
- Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, USA
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Thomas C Irving
- Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
- Center for Synchrotron Radiation Research and Instrumentation, Illinois Institute of Technology, Chicago, IL, USA
| | - Weikang Ma
- Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
- Center for Synchrotron Radiation Research and Instrumentation, Illinois Institute of Technology, Chicago, IL, USA
| | - Bertrand C W Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA, USA
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5
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Jiratrakanvong J, Shao J, Li J, Menendez Alvarez M, Li X, Das P, Nikseresht G, Miskin N, Huo R, Nabon J, Leduc T, Zhang E, Ma W, Agam G, Irving TC. MuscleX: data analysis software for fiber diffraction patterns from muscle. JOURNAL OF SYNCHROTRON RADIATION 2024; 31:1401-1408. [PMID: 39078694 PMCID: PMC11371035 DOI: 10.1107/s1600577524006167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2024] [Accepted: 06/24/2024] [Indexed: 07/31/2024]
Abstract
MuscleX is an integrated, open-source computer software suite for data reduction of X-ray fiber diffraction patterns from striated muscle and other fibrous systems. It is written in Python and runs on Linux, Microsoft Windows or macOS. Most modules can be run either from a graphical user interface or in a `headless mode' from the command line, suitable for incorporation into beamline control systems. Here, we provide an overview of the general structure of the MuscleX software package and describe the specific features of the individual modules as well as examples of applications.
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Affiliation(s)
- Jiranun Jiratrakanvong
- BioCAT, CSRRI and Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Jinjian Shao
- Department of Computer Science, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Jiaqi Li
- Department of Computer Science, Illinois Institute of Technology, Chicago, IL 60616, USA
| | | | - Xintian Li
- Department of Computer Science, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Prajwal Das
- Department of Computer Science, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Grant Nikseresht
- Department of Computer Science, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Nikhil Miskin
- Department of Computer Science, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Ran Huo
- Department of Computer Science, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Jules Nabon
- BioCAT, CSRRI and Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Tristan Leduc
- BioCAT, CSRRI and Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Eric Zhang
- BioCAT, CSRRI and Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Weikang Ma
- BioCAT, CSRRI and Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Gady Agam
- Department of Computer Science, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Thomas C Irving
- BioCAT, CSRRI and Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
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6
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Nakada M, Kanda J, Uchiyama H, Matsumura K. Nanoscale intracellular ultrastructures affected by osmotic pressure using small-angle X-ray scattering. Biophys Chem 2024; 312:107287. [PMID: 38981174 DOI: 10.1016/j.bpc.2024.107287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2024] [Revised: 06/12/2024] [Accepted: 06/26/2024] [Indexed: 07/11/2024]
Abstract
Although intracellular ultrastructures have typically been studied using microscopic techniques, it is difficult to observe ultrastructures at the submicron scale of living cells due to spatial resolution (fluorescence microscopy) or high vacuum environment (electron microscopy). We investigate the nanometer scale intracellular ultrastructures of living CHO cells in various osmolality using small-angle X-ray scattering (SAXS), and especially the structures of ribosomes, DNA double helix, and plasma membranes in-cell environment are observed. Ribosomes expand and contract in response to osmotic pressure, and the inter-ribosomal correlation occurs under isotonic and hyperosmolality. The DNA double helix is not dependent on the osmotic pressure. Under high osmotic pressure, the plasma membrane folds into form a multilamellar structure with a periodic length of about 6 nm. We also study the ultrastructural changes caused by formaldehyde fixation, freezing and heating.
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Affiliation(s)
- Masaru Nakada
- Toray Research Center, Inc., 2-11 Sonoyama 3-chome, Otsu, Shiga 520-8567, Japan.
| | - Junko Kanda
- Toray Research Center, Inc., 2-11 Sonoyama 3-chome, Otsu, Shiga 520-8567, Japan
| | - Hironobu Uchiyama
- Toray Research Center, Inc., 2-11 Sonoyama 3-chome, Otsu, Shiga 520-8567, Japan
| | - Kazuaki Matsumura
- School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan
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7
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Zhao J, Qi L, Yuan S, Irving TC, Ma W. Differences in thick filament activation in fast rodent skeletal muscle and slow porcine cardiac muscle. J Physiol 2024; 602:2751-2762. [PMID: 38695322 PMCID: PMC11178443 DOI: 10.1113/jp286072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Accepted: 04/16/2024] [Indexed: 06/15/2024] Open
Abstract
There is a growing appreciation that regulation of muscle contraction requires both thin filament and thick filament activation in order to fully activate the sarcomere. The prevailing mechano-sensing model for thick filament activation was derived from experiments on fast-twitch muscle. We address the question whether, or to what extent, this mechanism can be extrapolated to the slow muscle in the hearts of large mammals, including humans. We investigated the similarities and differences in structural signatures of thick filament activation in porcine myocardium as compared to fast rat extensor digitorum longus (EDL) skeletal muscle under relaxed conditions and sub-maximal contraction using small angle X-ray diffraction. Thick and thin filaments were found to adopt different structural configurations under relaxing conditions, and myosin heads showed different changes in configuration upon sub-maximal activation, when comparing the two muscle types. Titin was found to have an X-ray diffraction signature distinct from those of the overall thick filament backbone, and its spacing change appeared to be positively correlated to the force exerted on the thick filament. Structural changes in fast EDL muscle were found to be consistent with the mechano-sensing model. In porcine myocardium, however, the structural basis of mechano-sensing is blunted suggesting the need for additional activation mechanism(s) in slow cardiac muscle. These differences in thick filament regulation can be related to their different physiological roles where fast muscle is optimized for rapid, burst-like, contractions, and the slow cardiac muscle in large mammalian hearts adopts a more finely tuned, graded response to allow for their substantial functional reserve. KEY POINTS: Both thin filament and thick filament activation are required to fully activate the sarcomere. Thick and thin filaments adopt different structural configurations under relaxing conditions, and myosin heads show different changes in configuration upon sub-maximal activation in fast extensor digitorum longus muscle and slow porcine cardiac muscle. Titin has an X-ray diffraction signature distinct from those of the overall thick filament backbone and this titin reflection spacing change appeared to be directly proportional to the force exerted on the thick filament. Mechano-sensing is blunted in porcine myocardium suggesting the need for additional activation mechanism(s) in slow cardiac muscle. Fast skeletal muscle is optimized for rapid, burst-like contractions, and the slow cardiac muscle in large mammalian hearts adopts a more finely tuned graded response to allow for their substantial functional reserve.
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Affiliation(s)
- Jing Zhao
- College of Basic Medical Sciences, Dalian Medical University, Dalian, Liaoning, China
| | - Lin Qi
- Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Shengyao Yuan
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Thomas C Irving
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
- Center for Synchrotron Radiation Research and Instrumentation, Illinois Institute of Technology, Chicago, IL, USA
| | - Weikang Ma
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
- Center for Synchrotron Radiation Research and Instrumentation, Illinois Institute of Technology, Chicago, IL, USA
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8
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Tune T, Sponberg S. Nanometer scale difference in myofilament lattice structure of muscle alter muscle function in a spatially explicit model. ARXIV 2024:arXiv:2405.19443v1. [PMID: 38855552 PMCID: PMC11160890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/11/2024]
Abstract
Crossbridge binding, state transitions, and force in active muscle is dependent on the radial spacing between the myosin-containing thick filament and the actin-containing thin filament in the filament lattice. This radial lattice spacing has been previously shown through spatially explicit modeling and experimental efforts to greatly affect quasi-static, isometric, force production in muscle. It has recently been suggested that this radial spacing might also be able to drive differences in mechanical function, or net work, under dynamic oscillations like those which occur in muscles in vivo. However, previous spatially explicit models either had no radial spacing dependence, meaning the lattice spacing could not be investigated, or did include radial spacing dependence but could not reproduce in vivo net work during dynamic oscillations and only investigated isometric contractions. Here we show the first spatially explicit model to include radial crossbridge dependence which can produce mechanical function similar to real muscle. Using this spatially explicit model of a half sarcomere, we show that when oscillated at strain amplitudes and frequencies like those in the hawk moth Manduca sexta, mechanical function (net work) does depend on the lattice spacing. In addition, since the trajectory of lattice spacing changes during dynamic oscillation can vary from organism to organism, we can prescribe a trajectory of lattice spacing changes in the spatially explicit half sarcomere model and investigate the extent to which the time course of lattice spacing changes can affect mechanical function. We simulated a half sarcomere undergoing dynamic oscillations and prescribed the Poisson's ratio of the lattice to be either 0 (constant lattice spacing) or 0.5 (isovolumetric lattice spacing changes). We also simulated net work using lattice spacing data taken from Manduca sexta which has a variable Poisson's ratio. Our simulation results indicate that the lattice spacing can change the mechanical function of muscle, and that in some cases a 1 nm difference can switch the net work of the half sarcomere model from positive (motor-like) to negative (brake-like).
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Affiliation(s)
- Travis Tune
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia, USA
| | - Simon Sponberg
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia, USA
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
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9
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Hessel AL, Kuehn MN, Han SW, Ma W, Irving TC, Momb BA, Song T, Sadayappan S, Linke WA, Palmer BM. Fast myosin binding protein C knockout in skeletal muscle alters length-dependent activation and myofilament structure. Commun Biol 2024; 7:648. [PMID: 38802450 PMCID: PMC11130249 DOI: 10.1038/s42003-024-06265-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2023] [Accepted: 04/29/2024] [Indexed: 05/29/2024] Open
Abstract
In striated muscle, the sarcomeric protein myosin-binding protein-C (MyBP-C) is bound to the myosin thick filament and is predicted to stabilize myosin heads in a docked position against the thick filament, which limits crossbridge formation. Here, we use the homozygous Mybpc2 knockout (C2-/-) mouse line to remove the fast-isoform MyBP-C from fast skeletal muscle and then conduct mechanical functional studies in parallel with small-angle X-ray diffraction to evaluate the myofilament structure. We report that C2-/- fibers present deficits in force production and calcium sensitivity. Structurally, passive C2-/- fibers present altered sarcomere length-independent and -dependent regulation of myosin head conformations, with a shift of myosin heads towards actin. At shorter sarcomere lengths, the thin filament is axially extended in C2-/-, which we hypothesize is due to increased numbers of low-level crossbridges. These findings provide testable mechanisms to explain the etiology of debilitating diseases associated with MyBP-C.
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Affiliation(s)
- Anthony L Hessel
- Institute of Physiology II, University of Muenster, Muenster, Germany.
| | - Michel N Kuehn
- Institute of Physiology II, University of Muenster, Muenster, Germany
| | - Seong-Won Han
- Institute of Physiology II, University of Muenster, Muenster, Germany
| | - Weikang Ma
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, USA
| | - Thomas C Irving
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, USA
| | - Brent A Momb
- Department of Kinesiology, University of Massachusetts-Amherst, Amherst, MA, USA
| | - Taejeong Song
- Center for Cardiovascular Research, Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH, USA
| | - Sakthivel Sadayappan
- Center for Cardiovascular Research, Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH, USA
| | - Wolfgang A Linke
- Institute of Physiology II, University of Muenster, Muenster, Germany
| | - Bradley M Palmer
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT, USA.
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10
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Lewis CTA, Melhedegaard EG, Ognjanovic MM, Olsen MS, Laitila J, Seaborne RAE, Gronset M, Zhang C, Iwamoto H, Hessel AL, Kuehn MN, Merino C, Amigo N, Frobert O, Giroud S, Staples JF, Goropashnaya AV, Fedorov VB, Barnes B, Toien O, Drew K, Sprenger RJ, Ochala J. Remodeling of skeletal muscle myosin metabolic states in hibernating mammals. eLife 2024; 13:RP94616. [PMID: 38752835 PMCID: PMC11098559 DOI: 10.7554/elife.94616] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/18/2024] Open
Abstract
Hibernation is a period of metabolic suppression utilized by many small and large mammal species to survive during winter periods. As the underlying cellular and molecular mechanisms remain incompletely understood, our study aimed to determine whether skeletal muscle myosin and its metabolic efficiency undergo alterations during hibernation to optimize energy utilization. We isolated muscle fibers from small hibernators, Ictidomys tridecemlineatus and Eliomys quercinus and larger hibernators, Ursus arctos and Ursus americanus. We then conducted loaded Mant-ATP chase experiments alongside X-ray diffraction to measure resting myosin dynamics and its ATP demand. In parallel, we performed multiple proteomics analyses. Our results showed a preservation of myosin structure in U. arctos and U. americanus during hibernation, whilst in I. tridecemlineatus and E. quercinus, changes in myosin metabolic states during torpor unexpectedly led to higher levels in energy expenditure of type II, fast-twitch muscle fibers at ambient lab temperatures (20 °C). Upon repeating loaded Mant-ATP chase experiments at 8 °C (near the body temperature of torpid animals), we found that myosin ATP consumption in type II muscle fibers was reduced by 77-107% during torpor compared to active periods. Additionally, we observed Myh2 hyper-phosphorylation during torpor in I. tridecemilineatus, which was predicted to stabilize the myosin molecule. This may act as a potential molecular mechanism mitigating myosin-associated increases in skeletal muscle energy expenditure during periods of torpor in response to cold exposure. Altogether, we demonstrate that resting myosin is altered in hibernating mammals, contributing to significant changes to the ATP consumption of skeletal muscle. Additionally, we observe that it is further altered in response to cold exposure and highlight myosin as a potentially contributor to skeletal muscle non-shivering thermogenesis.
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Affiliation(s)
| | | | - Marija M Ognjanovic
- Department of Biomedical Sciences, University of CopenhagenCopenhagenDenmark
| | - Mathilde S Olsen
- Department of Biomedical Sciences, University of CopenhagenCopenhagenDenmark
| | - Jenni Laitila
- Department of Biomedical Sciences, University of CopenhagenCopenhagenDenmark
| | - Robert AE Seaborne
- Department of Biomedical Sciences, University of CopenhagenCopenhagenDenmark
- Centre for Human and Applied Physiological Sciences, Faculty of Life Sciences & Medicine, King’s College LondonLondonUnited Kingdom
| | - Magnus Gronset
- Department of Cellular and Molecular Medicine, University of CopenhagenCopenhagenDenmark
| | - Changxin Zhang
- Department of Computational Medicine and Bioinformatics, University of MichiganAnn ArborUnited States
| | - Hiroyuki Iwamoto
- Spring-8, Japan Synchrotron Radiation Research InstituteHyogoJapan
| | - Anthony L Hessel
- Institute of Physiology II, University of MuensterMuensterGermany
- Accelerated Muscle Biotechnologies ConsultantsBostonUnited States
| | - Michel N Kuehn
- Institute of Physiology II, University of MuensterMuensterGermany
- Accelerated Muscle Biotechnologies ConsultantsBostonUnited States
| | | | | | - Ole Frobert
- Department of Clinical Medicine, Faculty of Health, Aarhus UniversityAarhusDenmark
- Faculty of Health, Department of Cardiology, Örebro UniversityÖrebroSweden
| | - Sylvain Giroud
- Energetics Lab, Department of Biology, Northern Michigan UniversityMarquetteUnited States
- Research Institute of Wildlife Ecology, Department of Interdisciplinary Life Sciences, University of Veterinary Medicine ViennaViennaAustria
| | - James F Staples
- Department of Biology, University of Western OntarioLondonCanada
| | - Anna V Goropashnaya
- Center for Transformative Research in Metabolism, Institute of Arctic Biology, University of Alaska FairbanksFairbanksUnited States
| | - Vadim B Fedorov
- Center for Transformative Research in Metabolism, Institute of Arctic Biology, University of Alaska FairbanksFairbanksUnited States
| | - Brian Barnes
- Center for Transformative Research in Metabolism, Institute of Arctic Biology, University of Alaska FairbanksFairbanksUnited States
| | - Oivind Toien
- Center for Transformative Research in Metabolism, Institute of Arctic Biology, University of Alaska FairbanksFairbanksUnited States
| | - Kelly Drew
- Center for Transformative Research in Metabolism, Institute of Arctic Biology, University of Alaska FairbanksFairbanksUnited States
| | - Ryan J Sprenger
- Department of Zoology, University of British ColumbiaVancouverCanada
| | - Julien Ochala
- Department of Biomedical Sciences, University of CopenhagenCopenhagenDenmark
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11
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Mead AF, Wood NB, Nelson SR, Palmer BM, Yang L, Previs SB, Ploysangngam A, Kennedy GG, McAdow JF, Tremble SM, Cipolla MJ, Ebert AM, Johnson AN, Gurnett CA, Previs MJ, Warshaw DM. Functional role of myosin-binding protein H in thick filaments of developing vertebrate fast-twitch skeletal muscle. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.10.593199. [PMID: 38798399 PMCID: PMC11118323 DOI: 10.1101/2024.05.10.593199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2024]
Abstract
Myosin-binding protein H (MyBP-H) is a component of the vertebrate skeletal muscle sarcomere with sequence and domain homology to myosin-binding protein C (MyBP-C). Whereas skeletal muscle isoforms of MyBP-C (fMyBP-C, sMyBP-C) modulate muscle contractility via interactions with actin thin filaments and myosin motors within the muscle sarcomere "C-zone," MyBP-H has no known function. This is in part due to MyBP-H having limited expression in adult fast-twitch muscle and no known involvement in muscle disease. Quantitative proteomics reported here reveal MyBP-H is highly expressed in prenatal rat fast-twitch muscles and larval zebrafish, suggesting a conserved role in muscle development, and promoting studies to define its function. We take advantage of the genetic control of the zebrafish model and a combination of structural, functional, and biophysical techniques to interrogate the role of MyBP-H. Transgenic, FLAG-tagged MyBP-H or fMyBP-C both localize to the C-zones in larval myofibers, whereas genetic depletion of endogenous MyBP-H or fMyBP-C leads to increased accumulation of the other, suggesting competition for C-zone binding sites. Does MyBP-H modulate contractility from the C-zone? Globular domains critical to MyBP-C's modulatory functions are absent from MyBP-H, suggesting MyBP-H may be functionally silent. However, our results suggest an active role. Small angle x-ray diffraction of intact larval tails revealed MyBP-H contributes to the compression of the myofilament lattice accompanying stretch or contraction, while in vitro motility experiments indicate MyBP-H shares MyBP-C's capacity as a molecular "brake". These results provide new insights and raise questions about the role of the C-zone during muscle development.
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Affiliation(s)
- Andrew F. Mead
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT 05405
- Cardiovascular Research Institute, University of Vermont, Burlington, VT 05405
| | - Neil B. Wood
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT 05405
| | - Shane R. Nelson
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT 05405
- Cardiovascular Research Institute, University of Vermont, Burlington, VT 05405
| | - Bradley M. Palmer
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT 05405
- Cardiovascular Research Institute, University of Vermont, Burlington, VT 05405
| | - Lin Yang
- National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY 11973
| | - Samantha Beck Previs
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT 05405
- Cardiovascular Research Institute, University of Vermont, Burlington, VT 05405
| | - Angela Ploysangngam
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT 05405
| | - Guy G. Kennedy
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT 05405
| | - Jennifer F. McAdow
- Department of Neurlogical Sciences, Larner College of Medicine, University of Vermont, Burlington, VT 05405
| | - Sarah M. Tremble
- Department of Electrical and Biomedical Engineering, College of Engineering and Mathematical Sciences, University of Vermont, Burlington, VT 05405
| | - Marilyn J. Cipolla
- Department of Electrical and Biomedical Engineering, College of Engineering and Mathematical Sciences, University of Vermont, Burlington, VT 05405
- Department of Neurology, Washington University School of Medicine in St. Louis, St. Louis, MO 63110
| | - Alicia M. Ebert
- Department of Biology, College of Arts and Sciences, University of Vermont, Burlington, VT 05405
| | - Aaron N. Johnson
- Department of Developmental Biology, Washington University School of Medicine in St. Louis, St. Louis, MO 63110
| | - Christina A. Gurnett
- Department of Developmental Biology, Washington University School of Medicine in St. Louis, St. Louis, MO 63110
| | - Michael J. Previs
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT 05405
- Cardiovascular Research Institute, University of Vermont, Burlington, VT 05405
| | - David M. Warshaw
- Department of Molecular Physiology and Biophysics, Larner College of Medicine, University of Vermont, Burlington, VT 05405
- Cardiovascular Research Institute, University of Vermont, Burlington, VT 05405
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12
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Hessel AL, Kuehn MN, Engels NM, Nissen DL, Freundt JK, Ma W, Irving TC, Linke WA. Titin-Based Force Modulates Cardiac Thick and Thin Filaments. Circ Res 2024; 134:1026-1028. [PMID: 38482667 PMCID: PMC11046451 DOI: 10.1161/circresaha.123.323988] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 04/13/2024]
Affiliation(s)
- Anthony L. Hessel
- Institute of Physiology II, University of Muenster; Muenster, Germany
| | - Michel N. Kuehn
- Institute of Physiology II, University of Muenster; Muenster, Germany
| | - Nichlas M. Engels
- Department of Cellular and Molecular Medicine, University of Arizona; Tucson, AZ, USA
| | - Devin L. Nissen
- BioCAT, Department of Biology, Illinois Institute of Technology; Chicago, USA
| | | | - Weikang Ma
- BioCAT, Department of Biology, Illinois Institute of Technology; Chicago, USA
| | - Thomas C. Irving
- BioCAT, Department of Biology, Illinois Institute of Technology; Chicago, USA
| | - Wolfgang A Linke
- Institute of Physiology II, University of Muenster; Muenster, Germany
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13
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Hessel AL, Engels NM, Kuehn MN, Nissen D, Sadler RL, Ma W, Irving TC, Linke WA, Harris SP. Myosin-binding protein C regulates the sarcomere lattice and stabilizes the OFF states of myosin heads. Nat Commun 2024; 15:2628. [PMID: 38521794 PMCID: PMC10960836 DOI: 10.1038/s41467-024-46957-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Accepted: 03/15/2024] [Indexed: 03/25/2024] Open
Abstract
Muscle contraction is produced via the interaction of myofilaments and is regulated so that muscle performance matches demand. Myosin-binding protein C (MyBP-C) is a long and flexible protein that is tightly bound to the thick filament at its C-terminal end (MyBP-CC8C10), but may be loosely bound at its middle- and N-terminal end (MyBP-CC1C7) to myosin heads and/or the thin filament. MyBP-C is thought to control muscle contraction via the regulation of myosin motors, as mutations lead to debilitating disease. We use a combination of mechanics and small-angle X-ray diffraction to study the immediate and selective removal of the MyBP-CC1C7 domains of fast MyBP-C in permeabilized skeletal muscle. We show that cleavage leads to alterations in crossbridge kinetics and passive structural signatures of myofilaments that are indicative of a shift of myosin heads towards the ON state, highlighting the importance of MyBP-CC1C7 to myofilament force production and regulation.
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Affiliation(s)
- Anthony L Hessel
- Institute of Physiology II, University of Muenster, Muenster, Germany.
- Accelerated Muscle Biotechnologies Consultants, Boston, MA, USA.
| | - Nichlas M Engels
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ, USA
| | - Michel N Kuehn
- Institute of Physiology II, University of Muenster, Muenster, Germany
- Accelerated Muscle Biotechnologies Consultants, Boston, MA, USA
| | - Devin Nissen
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Rachel L Sadler
- Department of Physiology, University of Arizona, Tucson, AZ, USA
| | - Weikang Ma
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Thomas C Irving
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Wolfgang A Linke
- Institute of Physiology II, University of Muenster, Muenster, Germany
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14
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Lewis CTA, Melhedegaard EG, Ognjanovic MM, Olsen MS, Laitila J, Seaborne RAE, Gronset MN, Zhang C, Iwamoto H, Hessel AL, Kuehn MN, Merino C, Amigo N, Frobert O, Giroud S, Staples JF, Goropashnaya AV, Fedorov VB, Barnes BM, Toien O, Drew KL, Sprenger RJ, Ochala J. Remodelling of Skeletal Muscle Myosin Metabolic States in Hibernating Mammals. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.11.14.566992. [PMID: 38014200 PMCID: PMC10680686 DOI: 10.1101/2023.11.14.566992] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
Hibernation is a period of metabolic suppression utilized by many small and large mammal species to survive during winter periods. As the underlying cellular and molecular mechanisms remain incompletely understood, our study aimed to determine whether skeletal muscle myosin and its metabolic efficiency undergo alterations during hibernation to optimize energy utilization. We isolated muscle fibers from small hibernators, Ictidomys tridecemlineatus and Eliomys quercinus and larger hibernators, Ursus arctos and Ursus americanus. We then conducted loaded Mant-ATP chase experiments alongside X-ray diffraction to measure resting myosin dynamics and its ATP demand. In parallel, we performed multiple proteomics analyses. Our results showed a preservation of myosin structure in U. arctos and U. americanus during hibernation, whilst in I. tridecemlineatus and E. quercinus, changes in myosin metabolic states during torpor unexpectedly led to higher levels in energy expenditure of type II, fast-twitch muscle fibers at ambient lab temperatures (20°C). Upon repeating loaded Mant-ATP chase experiments at 8°C (near the body temperature of torpid animals), we found that myosin ATP consumption in type II muscle fibers was reduced by 77-107% during torpor compared to active periods. Additionally, we observed Myh2 hyper-phosphorylation during torpor in I. tridecemilineatus, which was predicted to stabilize the myosin molecule. This may act as a potential molecular mechanism mitigating myosin-associated increases in skeletal muscle energy expenditure during periods of torpor in response to cold exposure. Altogether, we demonstrate that resting myosin is altered in hibernating mammals, contributing to significant changes to the ATP consumption of skeletal muscle. Additionally, we observe that it is further altered in response to cold exposure and highlight myosin as a potentially contributor to skeletal muscle non-shivering thermogenesis.
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15
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Ma W, del Rio CL, Qi L, Prodanovic M, Mijailovich S, Zambataro C, Gong H, Shimkunas R, Gollapudi S, Nag S, Irving TC. Myosin in autoinhibited off state(s), stabilized by mavacamten, can be recruited in response to inotropic interventions. Proc Natl Acad Sci U S A 2024; 121:e2314914121. [PMID: 38346202 PMCID: PMC10895252 DOI: 10.1073/pnas.2314914121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2023] [Accepted: 01/08/2024] [Indexed: 02/15/2024] Open
Abstract
Mavacamten is a FDA-approved small-molecule therapeutic designed to regulate cardiac function at the sarcomere level by selectively but reversibly inhibiting the enzymatic activity of myosin. It shifts myosin toward ordered off states close to the thick filament backbone. It remains elusive whether these myosin heads in the off state(s) can be recruited in response to physiological stimuli when required to boost cardiac output. We show that cardiac myosins stabilized in these off state(s) by mavacamten are recruitable by 1) Ca2+, 2) increased chronotropy [heart rate (HR)], 3) stretch, and 4) β-adrenergic (β-AR) stimulation, all known physiological inotropic interventions. At the molecular level, we show that Ca2+ increases myosin ATPase activity by shifting mavacamten-stabilized myosin heads from the inactive super-relaxed state to the active disordered relaxed state. At the myofilament level, both Ca2+ and passive lengthening can shift mavacamten-ordered off myosin heads from positions close to the thick filament backbone to disordered on states closer to the thin filaments. In isolated rat cardiomyocytes, increased stimulation rates enhanced shortening fraction in mavacamten-treated cells. This observation was confirmed in vivo in telemetered rats, where left-ventricular dP/dtmax, an index of inotropy, increased with HR in mavacamten-treated animals. Finally, we show that β-AR stimulation in vivo increases left-ventricular function and stroke volume in the setting of mavacamten. Our data demonstrate that the mavacamten-promoted off states of myosin in the thick filament are at least partially activable, thus preserving cardiac reserve mechanisms.
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Affiliation(s)
- Weikang Ma
- Biophysics Collaborative Access Team, Department of Biology, Illinois Institute of Technology, Chicago, IL60616
- Center for Synchrotron Radiation Research and Instrumentation, Illinois Institute of Technology, Chicago, IL60616
| | - Carlos L. del Rio
- Cardiovascular Drug Discovery, Bristol Myers Squibb, Brisbane, CA94005
- Cardiac Consulting, San Mateo, CA94010
| | - Lin Qi
- Department of Biology, Illinois Institute of Technology, Chicago, IL60616
| | - Momcilo Prodanovic
- Institute for Information Technologies, University of Kragujevac, Kragujevac34000, Serbia
- FilamenTech, Inc., Newtown, MA02458
| | | | | | - Henry Gong
- Department of Biology, Illinois Institute of Technology, Chicago, IL60616
| | - Rafael Shimkunas
- Cardiovascular Drug Discovery, Bristol Myers Squibb, Brisbane, CA94005
| | - Sampath Gollapudi
- Cardiovascular Drug Discovery, Bristol Myers Squibb, Brisbane, CA94005
| | - Suman Nag
- Cardiovascular Drug Discovery, Bristol Myers Squibb, Brisbane, CA94005
| | - Thomas C. Irving
- Biophysics Collaborative Access Team, Department of Biology, Illinois Institute of Technology, Chicago, IL60616
- Center for Synchrotron Radiation Research and Instrumentation, Illinois Institute of Technology, Chicago, IL60616
- Department of Biology, Illinois Institute of Technology, Chicago, IL60616
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16
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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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17
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Jani VP, Song T, Gao C, Gong H, Sadayappan S, Kass DA, Irving TC, Ma W. The structural OFF and ON states of myosin can be decoupled from the biochemical super- and disordered-relaxed states. PNAS NEXUS 2024; 3:pgae039. [PMID: 38328779 PMCID: PMC10849796 DOI: 10.1093/pnasnexus/pgae039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Accepted: 01/19/2024] [Indexed: 02/09/2024]
Abstract
There is a growing awareness that both thick-filament and classical thin-filament regulations play central roles in modulating muscle contraction. Myosin ATPase assays have demonstrated that under relaxed conditions, myosin may reside either in a high-energy-consuming disordered-relaxed (DRX) state available for binding actin to generate force or in an energy-sparing super-relaxed (SRX) state unavailable for actin binding. X-ray diffraction studies have shown that the majority of myosin heads are in a quasi-helically ordered OFF state in a resting muscle and that this helical ordering is lost when myosin heads are turned ON for contraction. It has been assumed that myosin heads in SRX and DRX states are equivalent to the OFF and ON states, respectively, and the terms have been used interchangeably. In this study, we use X-ray diffraction and ATP turnover assays to track the structural and biochemical transitions of myosin heads, respectively, induced with either omecamtiv mecarbil (OM) or piperine in relaxed porcine myocardium. We find that while OM and piperine induce dramatic shifts of myosin heads from the OFF to the ON state, there are no appreciable changes in the population of myosin heads in the SRX and DRX states in both unloaded and loaded preparations. Our results show that biochemically defined SRX and DRX can be decoupled from structurally defined OFF and ON states. In summary, while SRX/DRX and OFF/ON transitions can be correlated in some cases, these two phenomena are measured using different approaches, reflect different properties of the thick filament, and should be investigated and interpreted separately.
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Affiliation(s)
- Vivek P Jani
- Department of Biomedical Engineering, The Johns Hopkins School of Medicine, Baltimore, MD 21205, USA
- Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Taejeong Song
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45229, USA
| | - Chengqian Gao
- College of Basic Medical Sciences, Dalian Medical University, Dalian, Liaoning 116044, China
| | - Henry Gong
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Sakthivel Sadayappan
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45229, USA
| | - David A Kass
- Department of Biomedical Engineering, The Johns Hopkins School of Medicine, Baltimore, MD 21205, USA
- Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Thomas C Irving
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
- Center for Synchrotron Radiation Research and Instrumentation, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Weikang Ma
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
- Center for Synchrotron Radiation Research and Instrumentation, Illinois Institute of Technology, Chicago, IL 60616, USA
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18
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Mohran S, Kooiker K, Mahoney-Schaefer M, Mandrycky C, Kao K, Tu AY, Freeman J, Moussavi-Harami F, Geeves M, Regnier M. The biochemically defined super relaxed state of myosin-A paradox. J Biol Chem 2024; 300:105565. [PMID: 38103642 PMCID: PMC10819765 DOI: 10.1016/j.jbc.2023.105565] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2023] [Revised: 11/06/2023] [Accepted: 12/06/2023] [Indexed: 12/19/2023] Open
Abstract
The biochemical SRX (super-relaxed) state of myosin has been defined as a low ATPase activity state. This state can conserve energy when the myosin is not recruited for muscle contraction. The SRX state has been correlated with a structurally defined ordered (versus disordered) state of muscle thick filaments. The two states may be linked via a common interacting head motif (IHM) where the two heads of heavy meromyosin (HMM), or myosin, fold back onto each other and form additional contacts with S2 and the thick filament. Experimental observations of the SRX, IHM, and the ordered form of thick filaments, however, do not always agree, and result in a series of unresolved paradoxes. To address these paradoxes, we have reexamined the biochemical measurements of the SRX state for porcine cardiac HMM. In our hands, the commonly employed mantATP displacement assay was unable to quantify the population of the SRX state with all data fitting very well by a single exponential. We further show that mavacamten inhibits the basal ATPases of both porcine ventricle HMM and S1 (Ki, 0.32 and 1.76 μM respectively) while dATP activates HMM cooperatively without any evidence of an SRX state. A combination of our experimental observations and theories suggests that the displacement of mantATP in purified proteins is not a reliable assay to quantify the SRX population. This means that while the structurally defined IHM and ordered thick filaments clearly exist, great care must be employed when using the mantATP displacement assay.
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Affiliation(s)
- Saffie Mohran
- Department of Bioengineering, University of Washington, Seattle, Washington, USA; Center for Translational Muscle Research, University of Washington, Seattle, Washington, USA
| | - Kristina Kooiker
- Center for Translational Muscle Research, University of Washington, Seattle, Washington, USA; Division of Cardiology, University of Washington, Seattle, Washington, USA
| | | | - Christian Mandrycky
- Department of Bioengineering, University of Washington, Seattle, Washington, USA; Center for Translational Muscle Research, University of Washington, Seattle, Washington, USA
| | - Kerry Kao
- Department of Bioengineering, University of Washington, Seattle, Washington, USA
| | - An-Yue Tu
- Department of Bioengineering, University of Washington, Seattle, Washington, USA; Center for Translational Muscle Research, University of Washington, Seattle, Washington, USA
| | - Jeremy Freeman
- Division of Cardiology, University of Washington, Seattle, Washington, USA
| | - Farid Moussavi-Harami
- Department of Bioengineering, University of Washington, Seattle, Washington, USA; Center for Translational Muscle Research, University of Washington, Seattle, Washington, USA; Division of Cardiology, University of Washington, Seattle, Washington, USA
| | - Michael Geeves
- School of Biosciences, University of Kent, Canterbury, UK.
| | - Michael Regnier
- Department of Bioengineering, University of Washington, Seattle, Washington, USA; Center for Translational Muscle Research, University of Washington, Seattle, Washington, USA.
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19
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Shi R, Reichardt M, Fiegle DJ, Küpfer LK, Czajka T, Sun Z, Salditt T, Dendorfer A, Seidel T, Bruegmann T. Contractility measurements for cardiotoxicity screening with ventricular myocardial slices of pigs. Cardiovasc Res 2023; 119:2469-2481. [PMID: 37934066 PMCID: PMC10651213 DOI: 10.1093/cvr/cvad141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Revised: 05/22/2023] [Accepted: 07/10/2023] [Indexed: 11/08/2023] Open
Abstract
AIMS Cardiotoxicity is one major reason why drugs do not enter or are withdrawn from the market. Thus, approaches are required to predict cardiotoxicity with high specificity and sensitivity. Ideally, such methods should be performed within intact cardiac tissue with high relevance for humans and detect acute and chronic side effects on electrophysiological behaviour, contractility, and tissue structure in an unbiased manner. Herein, we evaluate healthy pig myocardial slices and biomimetic cultivation setups (BMCS) as a new cardiotoxicity screening approach. METHODS AND RESULTS Pig left ventricular samples were cut into slices and spanned into BMCS with continuous electrical pacing and online force recording. Automated stimulation protocols were established to determine the force-frequency relationship (FFR), frequency dependence of contraction duration, effective refractory period (ERP), and pacing threshold. Slices generated 1.3 ± 0.14 mN/mm2 force at 0.5 Hz electrical pacing and showed a positive FFR and a shortening of contraction duration with increasing pacing rates. Approximately 62% of slices were able to contract for at least 6 days while showing stable ERP, contraction duration-frequency relationship, and preserved cardiac structure confirmed by confocal imaging and X-ray diffraction analysis. We used specific blockers of the most important cardiac ion channels to determine which analysis parameters are influenced. To validate our approach, we tested five drug candidates selected from the Comprehensive in vitro Proarrhythmia Assay list as well as acetylsalicylic acid and DMSO as controls in a blinded manner in three independent laboratories. We were able to detect all arrhythmic drugs and their respective mode of action on cardiac tissue including inhibition of Na+, Ca2+, and hERG channels as well as Na+/Ca2+ exchanger. CONCLUSION We systematically evaluate this approach for cardiotoxicity screening, which is of high relevance for humans and can be upscaled to medium-throughput screening. Thus, our approach will improve the predictive value and efficiency of preclinical cardiotoxicity screening.
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Affiliation(s)
- Runzhu Shi
- Institute for Cardiovascular Physiology, University Medical Center Göttingen, Humboldtallee 23, 37073 Göttingen, Göttingen, Germany
- International Research Training Group 1816, University Medical Center Göttingen, Göttingen, Germany
| | - Marius Reichardt
- Institute for Cardiovascular Physiology, University Medical Center Göttingen, Humboldtallee 23, 37073 Göttingen, Göttingen, Germany
- Institute for X-ray Physics, University of Göttingen, Göttingen, Germany
| | - Dominik J Fiegle
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany
| | - Linda K Küpfer
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany
| | - Titus Czajka
- Institute for X-ray Physics, University of Göttingen, Göttingen, Germany
| | - Zhengwu Sun
- Walter-Brendel-Centre of Experimental Medicine, Hospital of the University Munich, Munich, Germany
| | - Tim Salditt
- Institute for X-ray Physics, University of Göttingen, Göttingen, Germany
- Cluster of Excellence ‘Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells’ (MBExC), University of Göttingen, Göttingen, Germany
| | - Andreas Dendorfer
- Walter-Brendel-Centre of Experimental Medicine, Hospital of the University Munich, Munich, Germany
- German Centre of Cardiovascular Research (DZHK), Munich Heart Alliance, Munich, Germany
| | - Thomas Seidel
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany
| | - Tobias Bruegmann
- Institute for Cardiovascular Physiology, University Medical Center Göttingen, Humboldtallee 23, 37073 Göttingen, Göttingen, Germany
- Cluster of Excellence ‘Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells’ (MBExC), University of Göttingen, Göttingen, Germany
- German Center for Cardiovascular Research (DZHK), Partner site Göttingen, Göttingen, Germany
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20
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Hessel AL, Kuehn MN, Engels NM, Nissen DL, Freundt JK, Ma W, Irving TC, Linke WA. Titin-based force regulates cardiac myofilament structures mediating length-dependent activation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.09.566413. [PMID: 38014235 PMCID: PMC10680614 DOI: 10.1101/2023.11.09.566413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
The Frank-Starling law states that the heart's stroke volume increases with greater preload due to increased venous return, allowing the heart to adapt to varying circulatory demands. Molecularly, increasing preload increases sarcomere length (SL), which alters sarcomere structures that are correlated to increased calcium sensitivity upon activation. The titin protein, spanning the half-sarcomere, acts as a spring in the I-band, applying a SL-dependent force suggested to pull against and alter myofilaments in a way that supports the Frank-Starling effect. To evaluate this, we employed the titin cleavage (TC) model, where a tobacco-etch virus protease recognition site is inserted into distal I-band titin and allows for rapid, specific cleavage of titin in an otherwise-healthy sarcomere. Here, we evaluated the atomic-level structures of amyopathic cardiac myofilaments following 50% titin cleavage under passive stretch conditions using small-angle X-ray diffraction, which measures these structures under near-physiological (functional) conditions. We report that titin-based forces in permeabilized papillary muscle regulate both thick and thin myofilament structures clearly supporting titin's role in the Frank-Starling mechanism.
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21
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Hessel AL, Kuehn M, Han SW, Ma W, Irving TC, Momb BA, Song T, Sadayappan S, Linke WA, Palmer BM. Fast myosin binding protein C knockout in skeletal muscle alters length-dependent activation and myofilament structure. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.19.563160. [PMID: 37961718 PMCID: PMC10634671 DOI: 10.1101/2023.10.19.563160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
In striated muscle, some sarcomere proteins regulate crossbridge cycling by varying the propensity of myosin heads to interact with actin. Myosin-binding protein C (MyBP-C) is bound to the myosin thick filament and is predicted to interact and stabilize myosin heads in a docked position against the thick filament and limit crossbridge formation, the so-called OFF state. Via an unknown mechanism, MyBP-C is thought to release heads into the so-called ON state, where they are more likely to form crossbridges. To study this proposed mechanism, we used the C2-/- mouse line to knock down fast-isoform MyBP-C completely and total MyBP-C by ~24%, and conducted mechanical functional studies in parallel with small-angle X-ray diffraction to evaluate the myofilament structure. We report that C2-/- fibers presented deficits in force production and reduced calcium sensitivity. Structurally, passive C2-/- fibers presented altered SL-independent and SL-dependent regulation of myosin head ON/OFF states, with a shift of myosin heads towards the ON state. Unexpectedly, at shorter sarcomere lengths, the thin filament was axially extended in C2-/- vs. non-transgenic controls, which we postulate is due to increased low-level crossbridge formation arising from relatively more ON myosins in the passive muscle that elongates the thin filament. The downstream effect of increasing crossbridge formation in a passive muscle on contraction performance is not known. Such widespread structural changes to sarcomere proteins provide testable mechanisms to explain the etiology of debilitating MyBP-C-associated diseases.
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Affiliation(s)
- Anthony L. Hessel
- Institute of Physiology II, University of Muenster; Muenster, Germany
| | - Michel Kuehn
- Institute of Physiology II, University of Muenster; Muenster, Germany
| | - Seong-Won Han
- Institute of Physiology II, University of Muenster; Muenster, Germany
| | - Weikang Ma
- BioCAT, Department of Biology, Illinois Institute of Technology; Chicago, USA
| | - Thomas C. Irving
- BioCAT, Department of Biology, Illinois Institute of Technology; Chicago, USA
| | - Brent A. Momb
- Department of Kinesiology, University of Massachusetts – Amherst; Amherst, MA, USA
| | - Taejeong Song
- Center for Cardiovascular Research, Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH, USA
| | - Sakthivel Sadayappan
- Center for Cardiovascular Research, Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati, Cincinnati, OH, USA
| | - Wolfgang A. Linke
- Institute of Physiology II, University of Muenster; Muenster, Germany
| | - Bradley M. Palmer
- Department of Molecular Physiology and Biophysics, University of Vermont; Burlington, VT, USA
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22
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Ma W, Jani VP, Song T, Gao C, Gong H, Sadayappan S, Kass DA, Irving TC. The structural OFF and ON states of myosin can be decoupled from the biochemical super-relaxed and disordered-relaxed states. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.18.562891. [PMID: 37904972 PMCID: PMC10614925 DOI: 10.1101/2023.10.18.562891] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/01/2023]
Abstract
There is a growing awareness that both thick filament and classical thin filament regulation play central roles in modulating muscle contraction. Myosin ATPase assays have demonstrated that under relaxed conditions, myosin may reside in either a high energy-consuming disordered-relaxed (DRX) state available for binding actin to generate force, or in an energy-sparing super-relaxed (SRX) state unavailable for actin binding. X-ray diffraction studies have shown the majority of myosin heads are in a quasi-helically ordered OFF state in a resting muscle and that this helical ordering is lost when myosin heads are turned ON for contraction. It has been assumed that myosin heads in SRX and DRX states are equivalent to the OFF and ON state respectively and the terms have been used interchangeably. Here, we use X-ray diffraction and ATP turnover assays to track the structural and biochemical transitions of myosin heads respectively induced with either omecamtiv mecarbil (OM) or piperine in relaxed porcine myocardium. We find that while OM and piperine induce dramatic shifts of myosin heads from the OFF to ON states, there are no appreciable changes in the population of myosin heads in the SRX and DRX states in both unloaded and loaded preparations. Our results show that biochemically defined SRX and DRX can be decoupled from structurally-defined OFF and ON states. In summary, while SRX/DRX and OFF/ON transitions can be correlated in some cases, these two phenomena are measured using different approaches, do not necessarily reflect the same properties of the thick filament and should be investigated and interpreted separately.
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Affiliation(s)
- Weikang Ma
- Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Vivek P. Jani
- Department of Biomedical Engineering, The Johns Hopkins School of Medicine, Baltimore, MD
- Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD
| | - Taejeong Song
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati, OH, USA
| | - Chengqian Gao
- College of Basic Medical Sciences, Dalian Medical University, Dalian, Liaoning, China
| | - Henry Gong
- Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Sakthivel Sadayappan
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, University of Cincinnati, OH, USA
| | - David A. Kass
- Department of Biomedical Engineering, The Johns Hopkins School of Medicine, Baltimore, MD
- Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD
| | - Thomas C. Irving
- Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
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23
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Ma W, Lee KH, Delligatti CE, Davis MT, Zheng Y, Gong H, Kirk JA, Craig R, Irving T. The structural and functional integrities of porcine myocardium are mostly preserved by cryopreservation. J Gen Physiol 2023; 155:e202313345. [PMID: 37398997 PMCID: PMC10318404 DOI: 10.1085/jgp.202313345] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Revised: 05/05/2023] [Accepted: 06/21/2023] [Indexed: 07/04/2023] Open
Abstract
Structural and functional studies of heart muscle are important to gain insights into the physiological bases of cardiac muscle contraction and the pathological bases of heart disease. While fresh muscle tissue works best for these kinds of studies, this is not always practical to obtain, especially for heart tissue from large animal models and humans. Conversely, tissue banks of frozen human hearts are available and could be a tremendous resource for translational research. It is not well understood, however, how liquid nitrogen freezing and cryostorage may impact the structural integrity of myocardium from large mammals. In this study, we directly compared the structural and functional integrity of never-frozen to previously frozen porcine myocardium to investigate the consequences of freezing and cryostorage. X-ray diffraction measurements from hydrated tissue under near-physiological conditions and electron microscope images from chemically fixed porcine myocardium showed that prior freezing has only minor effects on structural integrity of the muscle. Furthermore, mechanical studies similarly showed no significant differences in contractile capabilities of porcine myocardium with and without freezing and cryostorage. These results demonstrate that liquid nitrogen preservation is a practical approach for structural and functional studies of myocardium.
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Affiliation(s)
- Weikang Ma
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Kyoung Hwan Lee
- Electron Microscopy Facility, UMass Chan Medical School, Worcester, MA, USA
| | | | - M. Therese Davis
- Department of Cell and Molecular Physiology, Loyola University Chicago, Chicago, IL, USA
| | - Yahan Zheng
- College of Basic Medical Sciences, Dalian Medical University, Dalian, China
| | - Henry Gong
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Jonathan A. Kirk
- Department of Cell and Molecular Physiology, Loyola University Chicago, Chicago, IL, USA
| | - Roger Craig
- Division of Cell Biology and Imaging, Department of Radiology, University of Massachusetts Medical School, Worcester, MA, USA
| | - Thomas Irving
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
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24
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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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25
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Ma W, del Rio CL, Qi L, Prodanovic M, Mijailovich S, Zambataro C, Gong H, Shimkunas R, Gollapudi S, Nag S, Irving TC. Myosin in autoinhibited off state(s), stabilized by mavacamten, can be recruited via inotropic effectors. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.10.536292. [PMID: 37090664 PMCID: PMC10120679 DOI: 10.1101/2023.04.10.536292] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/25/2023]
Abstract
Mavacamten is a novel, FDA-approved, small molecule therapeutic designed to regulate cardiac function by selectively but reversibly inhibiting the enzymatic activity of myosin. It shifts myosin towards ordered off states close to the thick filament backbone. It remains unresolved whether mavacamten permanently sequesters these myosin heads in the off state(s) or whether these heads can be recruited in response to physiological stimuli when required to boost cardiac output. We show that cardiac myosins stabilized in these off state(s) by mavacamten are recruitable by Ca2+, increased heart rate, stretch, and β-adrenergic (β-AR) stimulation, all known physiological inotropic effectors. At the molecular level, we show that, in presence of mavacamten, Ca2+ increases myosin ATPase activity by shifting myosin heads from the reserve super-relaxed (SRX) state to the active disordered relaxed (DRX) state. At the myofilament level, both Ca2+ and passive lengthening can shift ordered off myosin heads from positions close to the thick filament backbone to disordered on states closer to the thin filaments in the presence of mavacamten. In isolated rat cardiomyocytes, increased stimulation rates enhanced shortening fraction in mavacamten-treated cells. This observation was confirmed in vivo in telemetered rats, where left-ventricular dP/dtmax, an index of inotropy, increased with heart rate in mavacamten treated animals. Finally, we show that β-AR stimulation in vivo increases left-ventricular function and stroke volume in the setting of mavacamten. Our data demonstrate that the mavacamten-promoted off states of myosin in the thick filament are activable, at least partially, thus leading to preservation of cardiac reserve mechanisms.
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Affiliation(s)
- Weikang Ma
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Carlos L. del Rio
- Cardiovascular Drug Discovery, Bristol Myers Squibb, Brisbane, CA 94005
| | - Lin Qi
- Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Momcilo Prodanovic
- Institute for Information Technologies, University of Kragujevac, Kragujevac, Serbia
- FilamenTech, Inc., Newtown, MA 02458, USA
| | | | | | - Henry Gong
- Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
| | - Rafael Shimkunas
- Cardiovascular Drug Discovery, Bristol Myers Squibb, Brisbane, CA 94005
| | - Sampath Gollapudi
- Cardiovascular Drug Discovery, Bristol Myers Squibb, Brisbane, CA 94005
| | - Suman Nag
- Cardiovascular Drug Discovery, Bristol Myers Squibb, Brisbane, CA 94005
| | - Thomas C. Irving
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL, USA
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26
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Kooiker KB, Mohran S, Turner KL, Ma W, Martinson A, Flint G, Qi L, Gao C, Zheng Y, McMillen TS, Mandrycky C, Mahoney-Schaefer M, Freeman JC, Costales Arenas EG, Tu AY, Irving TC, Geeves MA, Tanner BC, Regnier M, Davis J, Moussavi-Harami F. Danicamtiv Increases Myosin Recruitment and Alters Cross-Bridge Cycling in Cardiac Muscle. Circ Res 2023; 133:430-443. [PMID: 37470183 PMCID: PMC10434831 DOI: 10.1161/circresaha.123.322629] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/04/2023] [Revised: 07/10/2023] [Accepted: 07/13/2023] [Indexed: 07/21/2023]
Abstract
BACKGROUND Modulating myosin function is a novel therapeutic approach in patients with cardiomyopathy. Danicamtiv is a novel myosin activator with promising preclinical data that is currently in clinical trials. While it is known that danicamtiv increases force and cardiomyocyte contractility without affecting calcium levels, detailed mechanistic studies regarding its mode of action are lacking. METHODS Permeabilized porcine cardiac tissue and myofibrils were used for X-ray diffraction and mechanical measurements. A mouse model of genetic dilated cardiomyopathy was used to evaluate the ability of danicamtiv to correct the contractile deficit. RESULTS Danicamtiv increased force and calcium sensitivity via increasing the number of myosins in the ON state and slowing cross-bridge turnover. Our detailed analysis showed that inhibition of ADP release results in decreased cross-bridge turnover with cross bridges staying attached longer and prolonging myofibril relaxation. Danicamtiv corrected decreased calcium sensitivity in demembranated tissue, abnormal twitch magnitude and kinetics in intact cardiac tissue, and reduced ejection fraction in the whole organ. CONCLUSIONS As demonstrated by the detailed studies of Danicamtiv, increasing myosin recruitment and altering cross-bridge cycling are 2 mechanisms to increase force and calcium sensitivity in cardiac muscle. Myosin activators such as Danicamtiv can treat the causative hypocontractile phenotype in genetic dilated cardiomyopathy.
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Affiliation(s)
- Kristina B. Kooiker
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
| | - Saffie Mohran
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Kyrah L. Turner
- School of Molecular Biosciences, Washington State University (K.L.T.)
| | - Weikang Ma
- Department of Biology, Illinois Institute of Technology, Chicago (W.M., L.Q., T.C.I.)
| | - Amy Martinson
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Department of Laboratory Medicine and Pathology (A.M., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Galina Flint
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Lin Qi
- Department of Biology, Illinois Institute of Technology, Chicago (W.M., L.Q., T.C.I.)
| | - Chengqian Gao
- College of Basic Medical Sciences, Dalian Medical University, Liaoning, China (C.G., Y.Z.)
| | - Yahan Zheng
- College of Basic Medical Sciences, Dalian Medical University, Liaoning, China (C.G., Y.Z.)
| | - Timothy S. McMillen
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Anesthesiology and Pain Medicine (T.S.M.), University of Washington
| | - Christian Mandrycky
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Max Mahoney-Schaefer
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
| | - Jeremy C. Freeman
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
| | | | - An-Yu Tu
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Thomas C. Irving
- Department of Biology, Illinois Institute of Technology, Chicago (W.M., L.Q., T.C.I.)
| | - Michael A. Geeves
- School of Biosciences, Division of Natural Sciences, University of Kent, Canterbury, United Kingdom (M.A.G.)
| | - Bertrand C.W. Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University (B.C.W.T.)
| | - Michael Regnier
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Jennifer Davis
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Department of Laboratory Medicine and Pathology (A.M., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Farid Moussavi-Harami
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Department of Laboratory Medicine and Pathology (A.M., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
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Narayanan T, Chèvremont W, Zinn T. Small-angle X-ray scattering in the era of fourth-generation light sources. J Appl Crystallogr 2023; 56:939-946. [PMID: 37555224 PMCID: PMC10405582 DOI: 10.1107/s1600576723004971] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Accepted: 06/05/2023] [Indexed: 08/10/2023] Open
Abstract
Recently, fourth-generation synchrotron sources with several orders of magnitude higher brightness and higher degree of coherence compared with third-generation sources have come into operation. These new X-ray sources offer exciting opportunities for the investigation of soft matter and biological specimens by small-angle X-ray scattering (SAXS) and related scattering methods. The improved beam properties together with the advanced pixel array detectors readily enhance the angular resolution of SAXS and ultra-small-angle X-ray scattering in the pinhole collimation. The high degree of coherence is a major boost for the X-ray photon correlation spectroscopy (XPCS) technique, enabling the equilibrium dynamics to be probed over broader time and length scales. This article presents some representative examples illustrating the performance of SAXS and XPCS with the Extremely Brilliant Source at the European Synchrotron Radiation Facility. The rapid onset of radiation damage is a significant challenge with the vast majority of samples, and appropriate protocols need to be adopted for circumventing this problem.
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Affiliation(s)
| | | | - Thomas Zinn
- ESRF – The European Synchrotron, 38043 Grenoble, France
- Diamond Light Source, Didcot OX11 0DE, United Kingdom
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28
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Jani V, Aslam MI, Fenwick AJ, Ma W, Gong H, Milburn G, Nissen D, Cubero Salazar IM, Hanselman O, Mukherjee M, Halushka MK, Margulies KB, Campbell KS, Irving TC, Kass DA, Hsu S. Right Ventricular Sarcomere Contractile Depression and the Role of Thick Filament Activation in Human Heart Failure With Pulmonary Hypertension. Circulation 2023; 147:1919-1932. [PMID: 37194598 PMCID: PMC10270283 DOI: 10.1161/circulationaha.123.064717] [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: 03/16/2023] [Accepted: 04/17/2023] [Indexed: 05/18/2023]
Abstract
BACKGROUND Right ventricular (RV) contractile dysfunction commonly occurs and worsens outcomes in patients with heart failure with reduced ejection fraction and pulmonary hypertension (HFrEF-PH). However, such dysfunction often goes undetected by standard clinical RV indices, raising concerns that they may not reflect aspects of underlying myocyte dysfunction. We thus sought to characterize RV myocyte contractile depression in HFrEF-PH, identify those components reflected by clinical RV indices, and uncover underlying biophysical mechanisms. METHODS Resting, calcium-, and load-dependent mechanics were prospectively studied in permeabilized RV cardiomyocytes isolated from explanted hearts from 23 patients with HFrEF-PH undergoing cardiac transplantation and 9 organ donor controls. RESULTS Unsupervised machine learning using myocyte mechanical data with the highest variance yielded 2 HFrEF-PH subgroups that in turn mapped to patients with decompensated or compensated clinical RV function. This correspondence was driven by reduced calcium-activated isometric tension in decompensated clinical RV function, whereas surprisingly, many other major myocyte contractile measures including peak power and myocyte active stiffness were similarly depressed in both groups. Similar results were obtained when subgroups were first defined by clinical indices, and then myocyte mechanical properties in each group compared. To test the role of thick filament defects, myofibrillar structure was assessed by x-ray diffraction of muscle fibers. This revealed more myosin heads associated with the thick filament backbone in decompensated clinical RV function, but not compensated clinical RV function, as compared with controls. This corresponded to reduced myosin ATP turnover in decompensated clinical RV function myocytes, indicating less myosin in a crossbridge-ready disordered-relaxed (DRX) state. Altering DRX proportion (%DRX) affected peak calcium-activated tension in the patient groups differently, depending on their basal %DRX, highlighting potential roles for precision-guided therapeutics. Last, increasing myocyte preload (sarcomere length) increased %DRX 1.5-fold in controls but only 1.2-fold in both HFrEF-PH groups, revealing a novel mechanism for reduced myocyte active stiffness and by extension Frank-Starling reserve in human heart failure. CONCLUSIONS Although there are many RV myocyte contractile deficits in HFrEF-PH, commonly used clinical indices only detect reduced isometric calcium-stimulated force, which is related to deficits in basal and recruitable %DRX myosin. Our results support use of therapies to increase %DRX and enhance length-dependent recruitment of DRX myosin heads in such patients.
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Affiliation(s)
- Vivek Jani
- Department of Biomedical Engineering (V.J., O.H., D.A.K.), Johns Hopkins School of Medicine, Baltimore, MD
- Division of Cardiology, Department of Medicine (V.J., A.J.F., I.M.C.S., M.M., D.A.K., S.H.), Johns Hopkins School of Medicine, Baltimore, MD
| | - M. Imran Aslam
- Division of Cardiology, Department of Medicine, University of Texas San Antonio School of Medicine (M.I.A.)
| | - Axel J. Fenwick
- Division of Cardiology, Department of Medicine (V.J., A.J.F., I.M.C.S., M.M., D.A.K., S.H.), Johns Hopkins School of Medicine, Baltimore, MD
| | - Weikang Ma
- Biophysics Collaborative Access Team (BioCAT), Department of Biology, Illinois Institute of Technology, Chicago (W.M., H.G., D.N., T.C.I.)
| | - Henry Gong
- Biophysics Collaborative Access Team (BioCAT), Department of Biology, Illinois Institute of Technology, Chicago (W.M., H.G., D.N., T.C.I.)
| | - Gregory Milburn
- Division of Cardiovascular Medicine, Department of Medicine, University of Kentucky, Lexington (G.M., K.S.C.)
| | - Devin Nissen
- Biophysics Collaborative Access Team (BioCAT), Department of Biology, Illinois Institute of Technology, Chicago (W.M., H.G., D.N., T.C.I.)
| | - Ilton M. Cubero Salazar
- Division of Cardiology, Department of Medicine (V.J., A.J.F., I.M.C.S., M.M., D.A.K., S.H.), Johns Hopkins School of Medicine, Baltimore, MD
| | - Olivia Hanselman
- Department of Biomedical Engineering (V.J., O.H., D.A.K.), Johns Hopkins School of Medicine, Baltimore, MD
| | - Monica Mukherjee
- Division of Cardiology, Department of Medicine (V.J., A.J.F., I.M.C.S., M.M., D.A.K., S.H.), Johns Hopkins School of Medicine, Baltimore, MD
| | - Marc K. Halushka
- Division of Cardiovascular Pathology, Department of Pathology (M.K.H.), Johns Hopkins School of Medicine, Baltimore, MD
| | - Kenneth B. Margulies
- Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia (K.B.M.)
| | - Kenneth S. Campbell
- Division of Cardiovascular Medicine, Department of Medicine, University of Kentucky, Lexington (G.M., K.S.C.)
| | - Thomas C. Irving
- Biophysics Collaborative Access Team (BioCAT), Department of Biology, Illinois Institute of Technology, Chicago (W.M., H.G., D.N., T.C.I.)
| | - David A. Kass
- Department of Biomedical Engineering (V.J., O.H., D.A.K.), Johns Hopkins School of Medicine, Baltimore, MD
- Division of Cardiology, Department of Medicine (V.J., A.J.F., I.M.C.S., M.M., D.A.K., S.H.), Johns Hopkins School of Medicine, Baltimore, MD
| | - Steven Hsu
- Division of Cardiology, Department of Medicine (V.J., A.J.F., I.M.C.S., M.M., D.A.K., S.H.), Johns Hopkins School of Medicine, Baltimore, MD
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Prodanovic M, Wang Y, Mijailovich SM, Irving T. Using Multiscale Simulations as a Tool to Interpret Equatorial X-ray Fiber Diffraction Patterns from Skeletal Muscle. Int J Mol Sci 2023; 24:8474. [PMID: 37239821 PMCID: PMC10218096 DOI: 10.3390/ijms24108474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 05/04/2023] [Accepted: 05/05/2023] [Indexed: 05/28/2023] Open
Abstract
Synchrotron small-angle X-ray diffraction is the method of choice for nm-scale structural studies of striated muscle under physiological conditions and on millisecond time scales. The lack of generally applicable computational tools for modeling X-ray diffraction patterns from intact muscles has been a significant barrier to exploiting the full potential of this technique. Here, we report a novel "forward problem" approach using the spatially explicit computational simulation platform MUSICO to predict equatorial small-angle X-ray diffraction patterns and the force output simultaneously from resting and isometrically contracting rat skeletal muscle that can be compared to experimental data. The simulation generates families of thick-thin filament repeating units, each with their individually predicted occupancies of different populations of active and inactive myosin heads that can be used to generate 2D-projected electron density models based on known Protein Data Bank structures. We show how, by adjusting only a few selected parameters, we can achieve a good correspondence between experimental and predicted X-ray intensities. The developments presented here demonstrate the feasibility of combining X-ray diffraction and spatially explicit modeling to form a powerful hypothesis-generating tool that can be used to motivate experiments that can reveal emergent properties of muscle.
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Affiliation(s)
- Momcilo Prodanovic
- Institute for Information Technologies, University of Kragujevac, 34000 Kragujevac, Serbia;
- FilamenTech, Inc., Newton, MA 02458, USA;
| | - Yiwei Wang
- Department of Applied Mathematics, Illinois Institute of Technology, Chicago, IL 60616, USA;
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
- Department of Mathematics, University of California, Riverside, CA 92521, USA
| | | | - Thomas Irving
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
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30
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Jani V, Aslam MI, Fenwick AJ, Ma W, Gong H, Milburn G, Nissen D, Salazar IC, Hanselman O, Mukherjee M, Halushka MK, Margulies KB, Campbell K, Irving TC, Kass DA, Hsu S. Right Ventricular Sarcomere Contractile Depression and the Role of Thick Filament Activation in Human Heart Failure with Pulmonary Hypertension. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.09.531988. [PMID: 36945606 PMCID: PMC10029011 DOI: 10.1101/2023.03.09.531988] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/14/2023]
Abstract
Rationale Right ventricular (RV) contractile dysfunction commonly occurs and worsens outcomes in heart failure patients with reduced ejection fraction and pulmonary hypertension (HFrEF-PH). However, such dysfunction often goes undetected by standard clinical RV indices, raising concerns that they may not reflect aspects of underlying myocyte dysfunction. Objective To determine components of myocyte contractile depression in HFrEF-PH, identify those reflected by clinical RV indices, and elucidate their underlying biophysical mechanisms. Methods and Results Resting, calcium- and load-dependent mechanics were measured in permeabilized RV cardiomyocytes isolated from explanted hearts from 23 HFrEF-PH patients undergoing cardiac transplantation and 9 organ-donor controls. Unsupervised machine learning using myocyte mechanical data with the highest variance yielded two HFrEF-PH subgroups that in turn mapped to patients with depressed (RVd) or compensated (RVc) clinical RV function. This correspondence was driven by reduced calcium-activated isometric tension in RVd, while surprisingly, many other major myocyte contractile measures including peak power, maximum unloaded shortening velocity, and myocyte active stiffness were similarly depressed in both groups. Similar results were obtained when subgroups were first defined by clinical indices, and then myocyte mechanical properties in each group compared. To test the role of thick-filament defects, myofibrillar structure was assessed by X-ray diffraction of muscle fibers. This revealed more myosin heads associated with the thick filament backbone in RVd but not RVc, as compared to controls. This corresponded to reduced myosin ATP turnover in RVd myocytes, indicating less myosin in a cross-bridge ready disordered-relaxed (DRX) state. Altering DRX proportion (%DRX) affected peak calcium-activated tension in the patient groups differently, depending on their basal %DRX, highlighting potential roles for precision-guided therapeutics. Lastly, increasing myocyte preload (sarcomere length) increased %DRX 1.5-fold in controls but only 1.2-fold in both HFrEF-PH groups, revealing a novel mechanism for reduced myocyte active stiffness and by extension Frank-Starling reserve in human HF. Conclusions While there are multiple RV myocyte contractile deficits In HFrEF-PH, clinical indices primarily detect reduced isometric calcium-stimulated force related to deficits in basal and recruitable %DRX myosin. Our results support use of therapies to increase %DRX and enhance length-dependent recruitment of DRX myosin heads in such patients.
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31
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Hessel AL, Kuehn M, Palmer BM, Nissen D, Mishra D, Joumaa V, Freundt J, Ma W, Nishikawa KC, Irving T, Linke WA. The distinctive mechanical and structural signatures of residual force enhancement in myofibers. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.19.529125. [PMID: 36865266 PMCID: PMC9980001 DOI: 10.1101/2023.02.19.529125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
Abstract
In muscle, titin proteins connect myofilaments together and are thought to be critical for contraction, especially during residual force enhancement (RFE) when force is elevated after an active stretch. We investigated titin's function during contraction using small-angle X-ray diffraction to track structural changes before and after 50% titin cleavage and in the RFE-deficient, mdm titin mutant. We report that the RFE state is structurally distinct from pure isometric contractions, with increased thick filament strain and decreased lattice spacing, most likely caused by elevated titin-based forces. Furthermore, no RFE structural state was detected in mdm muscle. We posit that decreased lattice spacing, increased thick filament stiffness, and increased non-crossbridge forces are the major contributors to RFE. We conclude that titin directly contributes to RFE.
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Affiliation(s)
- Anthony L. Hessel
- Institute of Physiology II, University of Muenster; Muenster, Germany
| | - Michel Kuehn
- Institute of Physiology II, University of Muenster; Muenster, Germany
| | - Bradley M. Palmer
- Department of Molecular Physiology and Biophysics, University of Vermont; Burlington, VT, 05405-1705, USA
| | - Devin Nissen
- BioCAT, Department of Biology, Illinois Institute of Technology; Chicago, IL, USA
| | - Dhruv Mishra
- Department of Biological Sciences, University of Northern Arizona; Flagstaff AZ, USA
| | - Venus Joumaa
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, AB T2N1N4, Canada
| | - Johanna Freundt
- Institute of Physiology II, University of Muenster; Muenster, Germany
| | - Weikang Ma
- BioCAT, Department of Biology, Illinois Institute of Technology; Chicago, IL, USA
| | - Kiisa C. Nishikawa
- Department of Biological Sciences, University of Northern Arizona; Flagstaff AZ, USA
| | - Thomas Irving
- BioCAT, Department of Biology, Illinois Institute of Technology; Chicago, IL, USA
| | - Wolfgang A. Linke
- Institute of Physiology II, University of Muenster; Muenster, Germany
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32
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Kooiker KB, Mohran S, Turner KL, Ma W, Flint G, Qi L, Gao C, Zheng Y, McMillen TS, Mandrycky C, Martinson A, Mahoney-Schaefer M, Freeman JC, Costales Arenas EG, Tu AY, Irving TC, Geeves MA, Tanner BCW, Regnier M, Davis J, Moussavi-Harami F. Danicamtiv increases myosin recruitment and alters the chemomechanical cross bridge cycle in cardiac muscle. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.31.526380. [PMID: 36778318 PMCID: PMC9915609 DOI: 10.1101/2023.01.31.526380] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Modulating myosin function is a novel therapeutic approach in patients with cardiomyopathy. Detailed mechanism of action of these agents can help predict potential unwanted affects and identify patient populations that can benefit most from them. Danicamtiv is a novel myosin activator with promising preclinical data that is currently in clinical trials. While it is known danicamtiv increases force and cardiomyocyte contractility without affecting calcium levels, detailed mechanistic studies regarding its mode of action are lacking. Using porcine cardiac tissue and myofibrils we demonstrate that Danicamtiv increases force and calcium sensitivity via increasing the number of myosin in the "on" state and slowing cross bridge turnover. Our detailed analysis shows that inhibition of ADP release results in decreased cross bridge turnover with cross bridges staying on longer and prolonging myofibril relaxation. Using a mouse model of genetic dilated cardiomyopathy, we demonstrated that Danicamtiv corrected calcium sensitivity in demembranated and abnormal twitch magnitude and kinetics in intact cardiac tissue. Significance Statement Directly augmenting sarcomere function has potential to overcome limitations of currently used inotropic agents to improve cardiac contractility. Myosin modulation is a novel mechanism for increased contraction in cardiomyopathies. Danicamtiv is a myosin activator that is currently under investigation for use in cardiomyopathy patients. Our study is the first detailed mechanism of how Danicamtiv increases force and alters kinetics of cardiac activation and relaxation. This new understanding of the mechanism of action of Danicamtiv can be used to help identify patients that could benefit most from this treatment.
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33
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Hammert WB, Kataoka R, Yamada Y, Seffrin A, Kang A, Seob Song J, Wong V, Spitz RW, Loenneke JP. The Potential Role of the Myosin Head for Strength Gain in Hypertrophied Muscle. Med Hypotheses 2023. [DOI: 10.1016/j.mehy.2023.111023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
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Structural OFF/ON transitions of myosin in relaxed porcine myocardium predict calcium-activated force. Proc Natl Acad Sci U S A 2023; 120:e2207615120. [PMID: 36696446 PMCID: PMC9945958 DOI: 10.1073/pnas.2207615120] [Citation(s) in RCA: 20] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Contraction in striated muscle is initiated by calcium binding to troponin complexes, but it is now understood that dynamic transition of myosin between resting, ordered OFF states on thick filaments and active, disordered ON states that can bind to thin filaments is critical in regulating muscle contractility. These structural OFF to ON transitions of myosin are widely assumed to correspond to transitions from the biochemically defined, energy-sparing, super-relaxed (SRX) state to the higher ATPase disordered-relaxed (DRX) state. Here we examined the effect of 2'-deoxy-ATP (dATP), a naturally occurring energy substrate for myosin, on the structural OFF to ON transitions of myosin motors in porcine cardiac muscle thick filaments. Small-angle X-ray diffraction revealed that titrating dATP in relaxation solutions progressively moves the myosin heads from ordered OFF states on the thick filament backbone to disordered ON states closer to thin filaments. Importantly, we found that the structural OFF to ON transitions are not equivalent to the biochemically defined SRX to DRX transitions and that the dATP-induced structural OFF to ON transitions of myosin motors in relaxed muscle are strongly correlated with submaximal force augmentation by dATP. These results indicate that structural OFF to ON transitions of myosin in relaxed muscle can predict the level of force attained in calcium-activated cardiac muscle. Computational modeling and stiffness measurements suggest a final step in the OFF to ON transition may involve a subset of DRX myosins that form weakly bound cross-bridges prior to becoming active force-producing cross-bridges.
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35
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Ma W, Nag S, Gong H, Qi L, Irving TC. Cardiac myosin filaments are directly regulated by calcium. J Gen Physiol 2022; 154:e202213213. [PMID: 36327149 PMCID: PMC9629851 DOI: 10.1085/jgp.202213213] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Revised: 07/25/2022] [Accepted: 10/03/2022] [Indexed: 11/06/2022] Open
Abstract
Classically, striated muscle contraction is initiated by calcium (Ca2+)-dependent structural changes in regulatory proteins on actin-containing thin filaments, which allow the binding of myosin motors to generate force. Additionally, dynamic switching between resting off and active on myosin states has been shown to regulate muscle contractility, a recently validated mechanism by novel myosin-targeted therapeutics. The molecular nature of this switching, however, is not understood. Here, using a combination of small-angle x-ray fiber diffraction and biochemical assays with reconstituted systems, we show that cardiac thick filaments are directly Ca2+-regulated. We find that Ca2+ induces a structural transition of myosin heads from ordered off states close to the thick filament to disordered on states closer to the thin filaments. Biochemical assays show a Ca2+-induced transition from an inactive super-relaxed (SRX) state(s) to an active disordered-relaxed (DRX) state(s) in synthetic thick filaments. We show that these transitions are an intrinsic property of cardiac myosin only when assembled into thick filaments and provide a fresh perspective on nature's two orthogonal mechanisms to regulate muscle contraction through the thin and the thick filaments.
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Affiliation(s)
- Weikang Ma
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL
| | - Suman Nag
- Department of Biochemistry, Bristol Myers Squibb, Brisbane, CA
| | - Henry Gong
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL
| | - Lin Qi
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL
| | - Thomas C. Irving
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL
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36
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Gong HM, Ma W, Regnier M, Irving TC. Thick filament activation is different in fast- and slow-twitch skeletal muscle. J Physiol 2022; 600:5247-5266. [PMID: 36342015 PMCID: PMC9772099 DOI: 10.1113/jp283574] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2022] [Accepted: 10/31/2022] [Indexed: 11/09/2022] Open
Abstract
The contractile properties of fast-twitch and slow-twitch skeletal muscles are primarily determined by the myosin isoform content and modulated by a variety of sarcomere proteins. X-ray diffraction studies of regulatory mechanisms in muscle contraction have focused predominately on fast- or mixed-fibre muscle with slow muscle being much less studied. Here, we used time-resolved X-ray diffraction to investigate the dynamic behaviour of the myofilament proteins in relatively pure slow-twitch-fibre rat soleus (SOL) and pure fast-twitch-fibre rat extensor digitorum longus (EDL) muscle during twitch and tetanic contractions at optimal length. During twitch contractions the diffraction signatures indicating a transition in the myosin heads from ordered OFF states, where heads are held close to the thick filament backbone, to disordered ON states, where heads are free to bind to thin filaments, were found in EDL and not in SOL muscle. During tetanic contraction, changes in the disposition of myosin heads as active tension develops is a quasi-stepwise process in EDL muscle whereas in SOL muscle this relationship appears to be linear. The observed reduced extensibility of the thick filaments in SOL muscle as compared to EDL muscles indicates a molecular basis for this behaviour. These data indicate that for the EDL, thick filament activation is a cooperative strain-induced mechano-sensing mechanism, whereas for the SOL, thick filament activation has a more graded response. These different approaches to thick filament regulation in fast- and slow-twitch muscles may be adaptations for short-duration, strong contractions versus sustained, finely controlled contractions, respectively. KEY POINTS: Fast-twitch muscle and slow-twitch muscle are optimized for strong, short-duration contractions and for tonic postural activity, respectively. Structural events (OFF to ON transitions) in the myosin-containing thick filaments in fast muscle help determine the timing and strength of contractions, but these have not been studied in slow-twitch muscle. The X-ray diffraction signatures of structural OFF to ON transitions are different in fast extensor digitorum longus (EDL) and slow soleus (SOL) muscle, being completely absent during twitches in soleus muscle and blunted during tetanic contractions SOL as compared to EDL Quasi-stepwise thick filament structural OFF to ON transitions in fast twitch muscle may be an adaptation for rapid, ballistic movements, whereas more graded OFF to ON structural transitions in slow-twitch muscle may be an adaptation for slower, finer motions.
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Affiliation(s)
- Henry M. Gong
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL
| | - Weikang Ma
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL
| | - Michael Regnier
- Department of Bioengineering, University of Washington, Seattle, WA
| | - Thomas C. Irving
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL
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37
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Awinda PO, Ma W, Turner KL, Zhao J, Gong H, Thompson MS, Campbell KS, Irving TC, Tanner BCW. MgADP Promotes Myosin Head Movement toward Actin at Low [Ca 2+] to Increase Force Production and Ca 2+-Sensitivity of Contraction in Permeabilized Porcine Myocardial Strips. Int J Mol Sci 2022; 23:ijms232315084. [PMID: 36499408 PMCID: PMC9737397 DOI: 10.3390/ijms232315084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 11/19/2022] [Accepted: 11/23/2022] [Indexed: 12/04/2022] Open
Abstract
Myosin cross-bridges dissociate from actin following Mg2+-adenosine triphosphate (MgATP) binding. Myosin hydrolyses MgATP into inorganic phosphate (Pi) and Mg2+-adenosine diphosphate (ADP), and release of these hydrolysis products drives chemo-mechanical energy transitions within the cross-bridge cycle to power muscle contraction. Some forms of heart disease are associated with metabolic or enzymatic dysregulation of the MgATP-MgADP nucleotide pool, resulting in elevated cytosolic [MgADP] and impaired muscle relaxation. We investigated the mechanical and structural effects of increasing [MgADP] in permeabilized myocardial strips from porcine left ventricle samples. Sarcomere length was set to 2.0 µm at 28 °C, and all solutions contained 3% dextran T-500 to compress myofilament lattice spacing to near-physiological values. Under relaxing low [Ca2+] conditions (pCa 8.0, where pCa = -log10[Ca2+]), tension increased as [MgADP] increased from 0-5 mM. Complementary small-angle X-ray diffraction measurements show that the equatorial intensity ratio, I1,1/I1,0, also increased as [MgADP] increased from 0 to 5 mM, indicating myosin head movement away from the thick-filament backbone towards the thin-filament. Ca2+-activated force-pCa measurements show that Ca2+-sensitivity of contraction increased with 5 mM MgADP, compared to 0 mM MgADP. These data show that MgADP augments tension at low [Ca2+] and Ca2+-sensitivity of contraction, suggesting that MgADP destabilizes the quasi-helically ordered myosin OFF state, thereby shifting the cross-bridge population towards the disordered myosin ON state. Together, these results indicate that MgADP enhances the probability of cross-bridge binding to actin due to enhancement of both thick and thin filament-based activation mechanisms.
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Affiliation(s)
- Peter O. Awinda
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164, USA
| | - Weikang Ma
- The Biophysics Collaborative Access Team (BioCAT), Illinois Institute of Technology, Chicago, IL 60616, USA
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Kyrah L. Turner
- School of Molecular Biosciences, Washington State University, Pullman, WA 99164, USA
| | - Jing Zhao
- College of Basic Medical Sciences, Dalian Medical University, Dalian 116044, China
| | - Henry Gong
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Mindy S. Thompson
- Division of Cardiovascular Medicine, University of Kentucky, Lexington, KY 40536, USA
- Department of Physiology, University of Kentucky, Lexington, KY 40536, USA
| | - Kenneth S. Campbell
- Division of Cardiovascular Medicine, University of Kentucky, Lexington, KY 40536, USA
- Department of Physiology, University of Kentucky, Lexington, KY 40536, USA
| | - Thomas C. Irving
- The Biophysics Collaborative Access Team (BioCAT), Illinois Institute of Technology, Chicago, IL 60616, USA
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Bertrand C. W. Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164, USA
- Correspondence: ; Tel.: +1-(509)-335-7785; Fax: +1-(509)-335-4650
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Jani V, Qian W, Yuan S, Irving T, Ma W. EMD-57033 Augments the Contractility in Porcine Myocardium by Promoting the Activation of Myosin in Thick Filaments. Int J Mol Sci 2022; 23:14517. [PMID: 36498844 PMCID: PMC9737153 DOI: 10.3390/ijms232314517] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Revised: 11/20/2022] [Accepted: 11/21/2022] [Indexed: 11/23/2022] Open
Abstract
Sufficient cardiac contractility is necessary to ensure the sufficient cardiac output to provide an adequate end-organ perfusion. Inadequate cardiac output and the diminished perfusion of vital organs from depressed myocardium contractility is a hallmark end-stage of heart failure. There are no available therapeutics that directly target contractile proteins to improve the myocardium contractility and reduce mortality. The purpose of this study is to present a proof of concept to aid in the development of muscle activators (myotropes) for augmenting the contractility in clinical heart failure. Here we use a combination of cardiomyocyte mechanics, the biochemical quantification of the ATP turnover, and small angle X-ray diffraction on a permeabilized porcine myocardium to study the mechanisms of EMD-57033 (EMD) for activating myosin. We show that EMD increases the contractility in a porcine myocardium at submaximal and systolic calcium concentrations. Biochemical assays show that EMD decreases the proportion of myosin heads in the energy sparing super-relaxed (SRX) state under relaxing conditions, which are less likely to interact with actin during contraction. Structural assays show that EMD moves the myosin heads in relaxed muscles from a structurally ordered state close to the thick filament backbone, to a disordered state closer to the actin filament, while simultaneously inducing structural changes in the troponin complex on the actin filament. The dual effects of EMD on activating myosin heads and the troponin complex provides a proof of concept for the use of small molecule muscle activators for augmenting the contractility in heart failure.
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Affiliation(s)
- Vivek Jani
- Department of Biomedical Engineering, The Johns Hopkins School of Medicine, The Johns Hopkins University, Baltimore, MD 20205, USA
- Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Wenjing Qian
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Shengyao Yuan
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Thomas Irving
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Weikang Ma
- BioCAT, Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA
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