1
|
Rode C, Tomalka A, Blickhan R, Siebert T. Structurally motivated models to explain the muscle's force-length relationship. Biophys J 2023; 122:3541-3543. [PMID: 37279747 PMCID: PMC10502428 DOI: 10.1016/j.bpj.2023.05.026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2023] [Revised: 05/10/2023] [Accepted: 05/19/2023] [Indexed: 06/08/2023] Open
Affiliation(s)
- Christian Rode
- Institute of Sport Science, Department of Biomechanics, University of Rostock, Rostock, Germany.
| | - André Tomalka
- Motion and Exercise Science, University of Stuttgart, Stuttgart, Germany
| | - Reinhard Blickhan
- Institute of Sport Science, Friedrich-Schiller-University Jena, Jena, Germany
| | - Tobias Siebert
- Motion and Exercise Science, University of Stuttgart, Stuttgart, Germany; Stuttgart Center of Simulation Science, University of Stuttgart, Stuttgart, Germany
| |
Collapse
|
2
|
Rockenfeller R, Günther M, Hooper SL. Sarcomere mechanics in the double-actin-overlap zone. Biophys J 2023; 122:3544-3548. [PMID: 37582376 PMCID: PMC10502458 DOI: 10.1016/j.bpj.2023.08.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Revised: 08/01/2023] [Accepted: 08/02/2023] [Indexed: 08/17/2023] Open
Affiliation(s)
| | - Michael Günther
- Biomechanics and Biorobotics, Stuttgart Center for Simulation Sciences (SC SimTech), Universität Stuttgart, Stuttgart, Germany; Friedrich-Schiller-Universität, Jena, Germany
| | - Scott L Hooper
- Neuroscience Program, Department of Biological Sciences, Ohio University, Athens, Ohio
| |
Collapse
|
3
|
Tomalka A, Heim M, Klotz A, Rode C, Siebert T. Ultrastructural and kinetic evidence support that thick filaments slide through the Z-disc. J R Soc Interface 2022; 19:20220642. [PMID: 36475390 PMCID: PMC9727675 DOI: 10.1098/rsif.2022.0642] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
How myofilaments operate at short mammalian skeletal muscle lengths is unknown. A common assumption is that thick (myosin-containing) filaments get compressed at the Z-disc. We provide ultrastructural evidence of sarcomeres contracting down to 0.44 µm-approximately a quarter of thick filament resting length-in long-lasting contractions while apparently keeping a regular, parallel thick filament arrangement. Sarcomeres produced force at such extremely short lengths. Furthermore, sarcomeres adopted a bimodal length distribution with both modes below lengths where sarcomeres are expected to generate force in classic force-length measurements. Mammalian fibres did not restore resting length but remained short after deactivation, as previously reported for amphibian fibres, and showed increased forces during passive re-elongation. These findings are incompatible with viscoelastic thick filament compression but agree with predictions of a model incorporating thick filament sliding through the Z-disc. This more coherent picture of mechanical mammalian skeletal fibre functioning opens new perspectives on muscle physiology.
Collapse
Affiliation(s)
- André Tomalka
- Motion and Exercise Science, University of Stuttgart, Stuttgart, Germany
| | - Maximilian Heim
- Motion and Exercise Science, University of Stuttgart, Stuttgart, Germany
| | - Annika Klotz
- Motion and Exercise Science, University of Stuttgart, Stuttgart, Germany
| | - Christian Rode
- Institute of Sport Science, Department of Biomechanics, University of Rostock, Rostock, Germany
| | - Tobias Siebert
- Motion and Exercise Science, University of Stuttgart, Stuttgart, Germany,Stuttgart Center for Simulation Science, University of Stuttgart, Stuttgart, Germany
| |
Collapse
|
4
|
Rockenfeller R, Günther M, Hooper SL. Muscle active force-length curve explained by an electrophysical model of interfilament spacing. Biophys J 2022; 121:1823-1855. [PMID: 35450825 PMCID: PMC9199101 DOI: 10.1016/j.bpj.2022.04.019] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 11/02/2021] [Accepted: 04/14/2022] [Indexed: 11/20/2022] Open
Abstract
The active isometric force-length relation (FLR) of striated muscle sarcomeres is central to understanding and modeling muscle function. The mechanistic basis of the descending arm of the FLR is well explained by the decreasing thin:thick filament overlap that occurs at long sarcomere lengths. The mechanistic basis of the ascending arm of the FLR (the decrease in force that occurs at short sarcomere lengths), alternatively, has never been well explained. Because muscle is a constant-volume system, interfilament lattice distances must increase as sarcomere length shortens. This increase would decrease thin and thick-filament electrostatic interactions independently of thin:thick filament overlap. To examine this effect, we present here a fundamental, physics-based model of the sarcomere that includes filament molecular properties, calcium binding, sarcomere geometry including both thin:thick filament overlap and interfilament radial distance, and electrostatics. The model gives extremely good fits to existing FLR data from a large number of different muscles across their entire range of measured activity levels, with the optimized parameter values in all cases lying within anatomically and physically reasonable ranges. A local first-order sensitivity analysis (varying individual parameters while holding the values of all others constant) shows that model output is most sensitive to a subset of model parameters, most of which are related to sarcomere geometry, with model output being most sensitive to interfilament radial distance. This conclusion is supported by re-running the fits with only this parameter subset being allowed to vary, which increases fit errors only moderately. These results show that the model well reproduces existing experimental data, and indicate that changes in interfilament spacing play as central a role as changes in filament overlap in determining the FLR, particularly on its ascending arm.
Collapse
Affiliation(s)
| | - Michael Günther
- Biomechanics and Biorobotics, Stuttgart Center for Simulation Sciences (SC SimTech), Universität Stuttgart, Stuttgart, Germany; Friedrich-Schiller-Universität, Jena, Germany
| | - Scott L Hooper
- Neuroscience Program, Department of Biological Sciences, Ohio University, Athens, Ohio
| |
Collapse
|
5
|
Rode C, Siebert T, Tomalka A, Blickhan R. Myosin filament sliding through the Z-disc relates striated muscle fibre structure to function. Proc Biol Sci 2016; 283:20153030. [PMID: 26936248 DOI: 10.1098/rspb.2015.3030] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Striated muscle contraction requires intricate interactions of microstructures. The classic textbook assumption that myosin filaments are compressed at the meshed Z-disc during striated muscle fibre contraction conflicts with experimental evidence. For example, myosin filaments are too stiff to be compressed sufficiently by the muscular force, and, unlike compressed springs, the muscle fibres do not restore their resting length after contractions to short lengths. Further, the dependence of a fibre's maximum contraction velocity on sarcomere length is unexplained to date. In this paper, we present a structurally consistent model of sarcomere contraction that reconciles these findings with the well-accepted sliding filament and crossbridge theories. The few required model parameters are taken from the literature or obtained from reasoning based on structural arguments. In our model, the transition from hexagonal to tetragonal actin filament arrangement near the Z-disc together with a thoughtful titin arrangement enables myosin filament sliding through the Z-disc. This sliding leads to swivelled crossbridges in the adjacent half-sarcomere that dampen contraction. With no fitting of parameters required, the model predicts straightforwardly the fibre's entire force-length behaviour and the dependence of the maximum contraction velocity on sarcomere length. Our model enables a structurally and functionally consistent view of the contractile machinery of the striated fibre with possible implications for muscle diseases and evolution.
Collapse
Affiliation(s)
- Christian Rode
- Department of Motion Science, Friedrich-Schiller-University Jena, Jena 07749, Thuringia, Germany
| | - Tobias Siebert
- Institute of Sport- and Movement Science, University of Stuttgart, Stuttgart 70174, Baden-Wuerttemberg, Germany
| | - Andre Tomalka
- Institute of Sport- and Movement Science, University of Stuttgart, Stuttgart 70174, Baden-Wuerttemberg, Germany
| | - Reinhard Blickhan
- Department of Motion Science, Friedrich-Schiller-University Jena, Jena 07749, Thuringia, Germany
| |
Collapse
|
6
|
Shabarchin AA, Tsaturyan AK. Proposed role of the M-band in sarcomere mechanics and mechano-sensing: a model study. Biomech Model Mechanobiol 2009; 9:163-75. [DOI: 10.1007/s10237-009-0167-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2008] [Accepted: 07/22/2009] [Indexed: 01/18/2023]
|
7
|
Gokhin DS, Bang ML, Zhang J, Chen J, Lieber RL. Reduced thin filament length in nebulin-knockout skeletal muscle alters isometric contractile properties. Am J Physiol Cell Physiol 2009; 296:C1123-32. [PMID: 19295172 DOI: 10.1152/ajpcell.00503.2008] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Nebulin (NEB) is a large, rod-like protein believed to dictate actin thin filament length in skeletal muscle. NEB gene defects are associated with congenital nemaline myopathy. The functional role of NEB was investigated in gastrocnemius muscles from neonatal wild-type (WT) and NEB knockout (NEB-KO) mice, whose thin filaments have uniformly shorter lengths compared with WT mice. Isometric stress production in NEB-KO skeletal muscle was reduced by 27% compared with WT skeletal muscle on postnatal day 1 and by 92% on postnatal day 7, consistent with functionally severe myopathy. NEB-KO muscle was also more susceptible to a decline in stress production during a bout of 10 cyclic isometric tetani. Length-tension properties in NEB-KO muscle were altered in a manner consistent with reduced thin filament length, with length-tension curves from NEB-KO muscle demonstrating a 7.4% narrower functional range and an optimal length reduced by 0.13 muscle lengths. Expression patterns of myosin heavy chain isoforms and total myosin content did not account for the functional differences between WT and NEB-KO muscle. These data indicate that NEB is essential for active stress production, maintenance of functional integrity during cyclic activation, and length-tension properties consistent with a role in specifying normal thin filament length. Continued analysis of NEB's functional properties will strengthen the understanding of force transmission and thin filament length regulation in skeletal muscle and may provide insights into the molecular processes that give rise to nemaline myopathy.
Collapse
Affiliation(s)
- David S Gokhin
- Dept. of Orthopaedic Surgery, University of California-San Diego and Veterans Affairs Medical Center, San Diego, CA 92161, USA
| | | | | | | | | |
Collapse
|
8
|
Trombitás K. Connecting filaments: a historical prospective. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2001; 481:1-23. [PMID: 10987063 DOI: 10.1007/978-1-4615-4267-4_1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
This short review covers the development of the extensible filament research from the very beginning until the most recent results. This work emphasizes the milestones of discovery, which led us from initial observations that were solely ultrastructural to the molecular understanding of the extensible process of these filaments.
Collapse
Affiliation(s)
- K Trombitás
- Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, USA
| |
Collapse
|
9
|
Bullard B, Goulding D, Ferguson C, Leonard K. Links in the chain: the contribution of kettin to the elasticity of insect muscles. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2001; 481:207-18; discussion 219-20. [PMID: 10987074 DOI: 10.1007/978-1-4615-4267-4_12] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Asynchronous flight muscle fibers are activated by periodic stretches and need to be stiff for strain to be transmitted to the contractile system. Kettin associated with thin filaments and projectin with thick filaments contribute to fiber stiffness. Kettin extends along thin filaments with the N-terminus in the Z-disc and the C-terminus outside. C filaments connecting thick filaments to the Z-disc contain projectin but not kettin. Insect flight myofibrils have a titin PEVK epitope which is only exposed on stretch, suggesting it is short and inaccessible. It is concluded that kettin stiffens thin filaments near the Z-disc and projectin and titin provide elasticity to C filaments.
Collapse
Affiliation(s)
- B Bullard
- European Molecular Biology Laboratory, Heidelberg, Germany
| | | | | | | |
Collapse
|
10
|
Trombitás K, Freiburg A, Greaser M, Labeit S, Granzier H. From connecting filaments to co-expression of titin isoforms. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2001; 481:405-18. [PMID: 10987086 DOI: 10.1007/978-1-4615-4267-4_24] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Abstract
The molecular basis of elasticity in insect flight muscle has been analyzed using both the mechanism of extensibility of titin filaments (Trombitás et al., J. Cell Biol. 1998;140:853-859), and the sequence of projectin (Daley et al., J. Mol. Biol. 1998;279:201-210). Since a PEVK-like domain is not found in the projectin sequence, it is suggested that the sarcomere elongation causes the slightly "contracted" projectin extensible region to straighten without requiring Ig/Fn domain unfolding. Thus, the extensible region of the projectin may be viewed as a single entropic spring. The serially linked entropic spring model developed for skeletal muscle titin was applied to titin in the heart. The discovery of unique N2B sequence extension in physiological sarcomere length range (Helmes et al., Circ. Res. 1999;84:1339-1352) suggests that cardiac titin can be characterized as a serially linked three-spring system. Two different cardiac titin isoform (N2BA and N2B) co-exist in the heart. These isoforms can be differentiated by immunoelectron microscopy using antibody against sequences C-terminal of the unique N2B sequence, which is present in both isoforms. Immunolabeling experiments show that the two different isoform are co-expressed within the same sarcomere.
Collapse
Affiliation(s)
- K Trombitás
- Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, USA
| | | | | | | | | |
Collapse
|
11
|
Trombitás K, Pollack GH. Actin filaments in honeybee-flight muscle move collectively. CELL MOTILITY AND THE CYTOSKELETON 1995; 32:145-50. [PMID: 8681397 DOI: 10.1002/cm.970320215] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
To investigate the pattern of actin-filament translation in the intact myofibrillar matrix, we carried out electron micrographic experiments on the "rigor-stretch" model of insect-flight muscle. In this model, thin filaments are mechanically severed from their connections to the Z-line and may then slide freely over the myosin filaments when activated. The model is similar to the in vitro motility assay in that untethered actin filaments slide over myosin, but here the natural filament lattice is retained: sliding takes place through the lattice of thick filaments. We find, in this model, that while the extent of thin filament translation is variable from sarcomere to sarcomere, filaments never translate far enough to enter the opposite I-band. Unlike the in vitro motility assay, where the actin filament translates over the entire thick filament even with "incorrectly" polarized cross-bridges as the sole driver, in this intact filament-lattice model, cross-bridges are apparently unable to move filaments in both directions. We also find that the pattern of filament translation is collective. Although the extent of translation may vary among sarcomeres, in any given half-sarcomere all actin filaments translate by the same degree. Further, the extent of translation is the same in both halves of a given sarcomere. In rare instances where the extent of translation exhibited a transverse gradient across the myofibrillar half-sarcomere, the gradient was similar on both sides of the sarcomere. Filament translation within the sarcomere is thus collective. Some mechanism ensures that nearby but distinctly separated actin filaments move together and that cooperative-like behavior therefore extends to the supramolecular level.
Collapse
Affiliation(s)
- K Trombitás
- Center for Bioengineering, University of Washington, Seattle 98195, USA
| | | |
Collapse
|
12
|
Abstract
The uniform angle and conformation of myosin subfragment 1 (S1) bound to actin filaments (F-actin) attest to the precise alignment and stereospecificity of the binding of these two contractile proteins. Because actin filaments are polar, myosin heads must swing or rotate about the head-tail junction in order to bind. Electron microscopy of isolated thick filaments and of myosin molecules suggests that the molecules are flexible, but myosin fragments and crossbridges have been reported not to interact with inappropriately oriented actin filaments. Here we describe myofibrillar defects engendered by a site-directed mutation within the flight-muscle-specific actin gene of the fruitfly Drosophila. The mutation apparently retards sarcomere assembly: peripheral thick and thin filaments are misregistered and not incorporated into the Z-line. Therefore, a myosin filament encounters thin filaments with the 'wrong' polarity. We show that myosin heads tethered in a single thick filament can bind with opposite rigor crossbridge angles to flanking thin filaments, which are apparently of opposite polarities. Preservation of identical actomyosin interfaces requires that sets of heads originating from opposite sides of the thick filament swivel 180 degrees relative to each other, implying that myosin crossbridges are as flexible as isolated molecules.
Collapse
Affiliation(s)
- M C Reedy
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710
| | | | | |
Collapse
|
13
|
Trombitás K, Tigyi-Sebes A. How actin filament polarity affects crossbridge force in doubly-overlapped insect muscle. J Muscle Res Cell Motil 1985; 6:447-59. [PMID: 4066928 DOI: 10.1007/bf00712582] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
We wished to find out why the internal resistance to shortening, which is negligible above rest length, becomes progressively more important with shortening below rest length. For this reason the movement of detached actin filaments in isometric sarcomeres treated with activating solution has been studied in insect flight muscle after breaking the filaments from the Z lines by stretching fibres in rigor. Evidence of sliding motion of such filaments has been produced by experimentally inducing double overlap zones in activating solution. It was deduced that the forces generated by individual crossbridges are comparable to the internal resistance to relative filament motion. Furthermore the final position of broken actin filaments indicated that wrongly polarized actin slides freely past activated crossbridges, but prevents these same bridges from exerting force on adjacent correctly polarized actin. Apparently only those bridges which are located in the normal overlap zones can generate effective force. It is therefore probable that the isometric tension is directly proportional to the number of bridges overlapped in the normal overlap zones for any sarcomere length equal to or greater than the thick filament length.
Collapse
|