1
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Liu C, Ruppel KM, Spudich JA. Motility Assay to Probe the Calcium Sensitivity of Myosin and Regulated Thin Filaments. Methods Mol Biol 2024; 2735:169-189. [PMID: 38038849 PMCID: PMC10773985 DOI: 10.1007/978-1-0716-3527-8_10] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2023]
Abstract
Calcium-dependent activation of the thin filament mediated by the troponin-tropomyosin complex is key in the regulation of actin-myosin based muscle contraction. Perturbations to this system, either physiological (e.g., phosphorylation of myosin light chains) or pathological (e.g., mutations that cause familial cardiomyopathies), can alter calcium sensitivity and thus have important implications in human health and disease. The in vitro motility assay provides a quantitative and precise method to study the calcium sensitivity of the reconstituted myosin-thin filament motile system. Here we present a simple and robust protocol to perform calcium-dependent motility of β-cardiac myosin and regulated thin filaments. The experiment is done on a multichannel microfluidic slide requiring minimal amounts of proteins. A complete velocity vs. calcium concentration curve is produced from one experiment in under 1 h.
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Affiliation(s)
- Chao Liu
- Department of Biochemistry, Beckman Center B405, Stanford University School of Medicine, Stanford, CA, USA
- Cardiovascular Institute, Stanford University, Stanford, CA, USA
- Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA, USA
| | - Kathleen M Ruppel
- Department of Biochemistry, Beckman Center B405, Stanford University School of Medicine, Stanford, CA, USA.
- Cardiovascular Institute, Stanford University, Stanford, CA, USA.
- Department of Pediatrics (Cardiology), Stanford University, Stanford, CA, USA.
| | - James A Spudich
- Department of Biochemistry, Beckman Center B405, Stanford University School of Medicine, Stanford, CA, USA.
- Cardiovascular Institute, Stanford University, Stanford, CA, USA.
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2
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Dawson JE, Sellmann T, Porath K, Bader R, van Rienen U, Appali R, Köhling R. Cell-cell interactions and fluctuations in the direction of motility promote directed migration of osteoblasts in direct current electrotaxis. Front Bioeng Biotechnol 2022; 10:995326. [PMID: 36277406 PMCID: PMC9582662 DOI: 10.3389/fbioe.2022.995326] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Accepted: 09/20/2022] [Indexed: 11/13/2022] Open
Abstract
Under both physiological (development, regeneration) and pathological conditions (cancer metastasis), cells migrate while sensing environmental cues in the form of mechanical, chemical or electrical stimuli. In the case of bone tissue, osteoblast migration is essential in bone regeneration. Although it is known that osteoblasts respond to exogenous electric fields, the underlying mechanism of electrotactic collective movement of human osteoblasts is unclear. Here, we present a computational model that describes the osteoblast cell migration in a direct current electric field as the motion of a collection of active self-propelled particles and takes into account fluctuations in the direction of single-cell migration, finite-range cell-cell interactions, and the interaction of a cell with the external electric field. By comparing this model with in vitro experiments in which human primary osteoblasts are exposed to a direct current electric field of different field strengths, we show that cell-cell interactions and fluctuations in the migration direction promote anode-directed collective migration of osteoblasts.
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Affiliation(s)
- Jonathan Edward Dawson
- Institute of General Electrical Engineering, University of Rostock, Rostock, Germany
- Department of Chemistry and Physics, Augusta University, Augusta, GA, United States
- *Correspondence: Jonathan Edward Dawson, ; Rüdiger Köhling,
| | - Tina Sellmann
- Oscar-Langendorff-Institute of Physiology, Rostock University Medical Center, Rostock, Germany
| | - Katrin Porath
- Oscar-Langendorff-Institute of Physiology, Rostock University Medical Center, Rostock, Germany
| | - Rainer Bader
- Department of Life, Light and Matter, Interdisciplinary Faculty, University of Rostock, Rostock, Germany
- Biomechanics and Implant Research Lab, Department of Orthopedics, Rostock University Medical Center, Rostock, Germany
| | - Ursula van Rienen
- Institute of General Electrical Engineering, University of Rostock, Rostock, Germany
- Department of Life, Light and Matter, Interdisciplinary Faculty, University of Rostock, Rostock, Germany
- Department of Ageing of Individuals and Society, Interdisciplinary Faculty, University of Rostock, Rostock, Germany
| | - Revathi Appali
- Institute of General Electrical Engineering, University of Rostock, Rostock, Germany
- Department of Ageing of Individuals and Society, Interdisciplinary Faculty, University of Rostock, Rostock, Germany
| | - Rüdiger Köhling
- Oscar-Langendorff-Institute of Physiology, Rostock University Medical Center, Rostock, Germany
- Department of Ageing of Individuals and Society, Interdisciplinary Faculty, University of Rostock, Rostock, Germany
- Center for Translational Neuroscience Research, Rostock University Medical Center, Rostock, Germany
- *Correspondence: Jonathan Edward Dawson, ; Rüdiger Köhling,
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3
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Stewart TJ, Murthy V, Dugan SP, Baker JE. Velocity of myosin-based actin sliding depends on attachment and detachment kinetics and reaches a maximum when myosin-binding sites on actin saturate. J Biol Chem 2021; 297:101178. [PMID: 34508779 PMCID: PMC8560993 DOI: 10.1016/j.jbc.2021.101178] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 09/02/2021] [Accepted: 09/07/2021] [Indexed: 11/22/2022] Open
Abstract
Molecular motors such as kinesin and myosin often work in groups to generate the directed movements and forces critical for many biological processes. Although much is known about how individual motors generate force and movement, surprisingly, little is known about the mechanisms underlying the macroscopic mechanics generated by multiple motors. For example, the observation that a saturating number, N, of myosin heads move an actin filament at a rate that is influenced by actin–myosin attachment and detachment kinetics is accounted for neither experimentally nor theoretically. To better understand the emergent mechanics of actin–myosin mechanochemistry, we use an in vitro motility assay to measure and correlate the N-dependence of actin sliding velocities, actin-activated ATPase activity, force generation against a mechanical load, and the calcium sensitivity of thin filament velocities. Our results show that both velocity and ATPase activity are strain dependent and that velocity becomes maximized with the saturation of myosin-binding sites on actin at a value that is 40% dependent on attachment kinetics and 60% dependent on detachment kinetics. These results support a chemical thermodynamic model for ensemble motor mechanochemistry and imply molecularly explicit mechanisms within this framework, challenging the assumption of independent force generation.
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Affiliation(s)
- Travis J Stewart
- Department of Pharmacology, University of Nevada, Reno School of Medicine, Reno, Nevada, USA
| | - Vidya Murthy
- Department of Biomedical Engineering, University of Nevada, Reno, Nevada, USA
| | - Sam P Dugan
- Department of Pharmacology, University of Nevada, Reno School of Medicine, Reno, Nevada, USA
| | - Josh E Baker
- Department of Pharmacology, University of Nevada, Reno School of Medicine, Reno, Nevada, USA.
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4
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Rohde M, Ziebart J, Kirschstein T, Sellmann T, Porath K, Kühl F, Delenda B, Bahls C, van Rienen U, Bader R, Köhling R. Human Osteoblast Migration in DC Electrical Fields Depends on Store Operated Ca 2+-Release and Is Correlated to Upregulation of Stretch-Activated TRPM7 Channels. Front Bioeng Biotechnol 2019; 7:422. [PMID: 31921825 PMCID: PMC6920109 DOI: 10.3389/fbioe.2019.00422] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Accepted: 11/29/2019] [Indexed: 12/04/2022] Open
Abstract
Fracture healing and bone regeneration, particularly in the elderly, remains a challenge. There is an ongoing search for methods to activate osteoblasts, and the application of electrical fields is an attractive approach in this context. Although it is known that such electromagnetic fields lead to osteoblast migration and foster mesenchymal osteogenic differentiation, so far the mechanisms of osteoblast activation remain unclear. Possible mechanisms could rely on changes in Ca2+-influx via ion channels, as these are known to modulate osteoblast activity, e.g., via voltage-sensitive, stretch-sensitive, transient-receptor-potential (TRP) channels, or store-operated release. In the present in vitro study, we explored whether electrical fields are able to modulate the expression of voltage-sensitive calcium channels as well as TRP channels in primary human osteoblast cell lines. We show migration speed is significantly increased in stimulated osteoblasts (6.4 ± 2.1 μm/h stimulated, 3.6 ± 1.1 μm/h control), and directed toward the anode. However, within a range of 154–445 V/m, field strength did not correlate with migration velocity. Neither was there a correlation between electric field and voltage-gated calcium channel (Cav3.2 and Cav1.4) expression. However, the expression of TRPM7 significantly correlated positively to electric field strength. TRPM7 channel blockade using NS8593, in turn, did not significantly alter migration speed, nor did blockade of Cav3.2 and Cav1.4 channels using Ni+ or verapamil, respectively, while a general Ca2+-influx block using Mg2+ accelerated migration. Stimulating store-operated Ca2+-release significantly reduced migration speed, while blocking IP3 had only a minor effect (at low and high concentrations of 2-APB, respectively). We conclude that (i) store operated channels negatively modulate migration speed and that (ii) the upregulation of TRPM7 might constitute a compensatory mechanism-which might explain how increasing expression levels at increasing field strengths result in constant migration speeds.
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Affiliation(s)
- Marco Rohde
- Rostock University Medical Center, Oscar-Langendorff-Institute of Physiology, Rostock, Germany
| | - Josefin Ziebart
- Biomechanics and Implant Research Lab, Department of Orthopedics, Rostock University Medical Center, Rostock, Germany
| | - Timo Kirschstein
- Rostock University Medical Center, Oscar-Langendorff-Institute of Physiology, Rostock, Germany
| | - Tina Sellmann
- Rostock University Medical Center, Oscar-Langendorff-Institute of Physiology, Rostock, Germany
| | - Katrin Porath
- Rostock University Medical Center, Oscar-Langendorff-Institute of Physiology, Rostock, Germany
| | - Friederike Kühl
- Rostock University Medical Center, Oscar-Langendorff-Institute of Physiology, Rostock, Germany
| | - Bachir Delenda
- Faculty of Computer Science and Electrical Engineering, Institute of General Electrical Engineering, University of Rostock, Rostock, Germany
| | - Christian Bahls
- Faculty of Computer Science and Electrical Engineering, Institute of General Electrical Engineering, University of Rostock, Rostock, Germany
| | - Ursula van Rienen
- Faculty of Computer Science and Electrical Engineering, Institute of General Electrical Engineering, University of Rostock, Rostock, Germany.,Interdisciplinary Faculty, University of Rostock, Rostock, Germany
| | - Rainer Bader
- Biomechanics and Implant Research Lab, Department of Orthopedics, Rostock University Medical Center, Rostock, Germany.,Interdisciplinary Faculty, University of Rostock, Rostock, Germany
| | - Rüdiger Köhling
- Rostock University Medical Center, Oscar-Langendorff-Institute of Physiology, Rostock, Germany.,Interdisciplinary Faculty, University of Rostock, Rostock, Germany
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5
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Reddy GR, West TM, Jian Z, Jaradeh M, Shi Q, Wang Y, Chen-Izu Y, Xiang YK. Illuminating cell signaling with genetically encoded FRET biosensors in adult mouse cardiomyocytes. J Gen Physiol 2018; 150:1567-1582. [PMID: 30242036 PMCID: PMC6219686 DOI: 10.1085/jgp.201812119] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 08/04/2018] [Accepted: 09/04/2018] [Indexed: 12/15/2022] Open
Abstract
FRET-based biosensors are powerful tools to study intracellular signaling that require long culture times for adenoviral infection. Reddy et al. have developed a method for culturing adult mouse cardiomyocytes involving blebbistatin, which preserves cell morphology for up to 50 h after adenoviral infection. FRET-based biosensor experiments in adult cardiomyocytes are a powerful way of dissecting the spatiotemporal dynamics of the complicated signaling networks that regulate cardiac health and disease. However, although much information has been gleaned from FRET studies on cardiomyocytes from larger species, experiments on adult cardiomyocytes from mice have been difficult at best. Thus the large variety of genetic mouse models cannot be easily used for this type of study. Here we develop cell culture conditions for adult mouse cardiomyocytes that permit robust expression of adenoviral FRET biosensors and reproducible FRET experimentation. We find that addition of 6.25 µM blebbistatin or 20 µM (S)-nitro-blebbistatin to a minimal essential medium containing 10 mM HEPES and 0.2% BSA maintains morphology of cardiomyocytes from physiological, pathological, and transgenic mouse models for up to 50 h after adenoviral infection. This provides a 10–15-h time window to perform reproducible FRET readings using a variety of CFP/YFP sensors between 30 and 50 h postinfection. The culture is applicable to cardiomyocytes isolated from transgenic mouse models as well as models with cardiac diseases. Therefore, this study helps scientists to disentangle complicated signaling networks important in health and disease of cardiomyocytes.
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Affiliation(s)
| | - Toni M West
- Department of Pharmacology, University of California at Davis, Davis, CA
| | - Zhong Jian
- Department of Pharmacology, University of California at Davis, Davis, CA
| | - Mark Jaradeh
- Department of Pharmacology, University of California at Davis, Davis, CA
| | - Qian Shi
- Department of Pharmacology, University of California at Davis, Davis, CA
| | - Ying Wang
- Department of Pharmacology, University of California at Davis, Davis, CA
| | - Ye Chen-Izu
- Department of Pharmacology, University of California at Davis, Davis, CA.,Department of Bioengineering, University of California at Davis, Davis, CA.,Department of Internal Medicine/Cardiology, University of California at Davis, Davis, CA
| | - Yang K Xiang
- Department of Pharmacology, University of California at Davis, Davis, CA .,Veterans Affairs Northern California Health Care System, Mather, CA
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6
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Solís C, Kim GH, Moutsoglou ME, Robinson JM. Ca 2+ and Myosin Cycle States Work as Allosteric Effectors of Troponin Activation. Biophys J 2018; 115:1762-1769. [PMID: 30249400 DOI: 10.1016/j.bpj.2018.08.033] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2017] [Revised: 08/22/2018] [Accepted: 08/24/2018] [Indexed: 10/28/2022] Open
Abstract
In cardiac muscle, troponin (Tn) and tropomyosin inhibit actin and myosin interactions through the steric blocking of myosin binding to F-actin. Ca2+ binding to Tn C modulates this inhibition. Thin filaments become activated upon Ca2+ binding, which enables strong binding of myosin with a concomitant release of ATP hydrolysis products and level arm swinging responsible for force generation. Despite this level of description, the current cross-bridge cycle model does not fully define the structural events that take place within Tn during combinatorial myosin and Ca2+ interventions. Here, we studied conformational changes within Tn bound to F-actin and tropomyosin by fluorescence lifetime imaging combined with Förster resonance energy transfer. Fluorescent dye molecules covalently bound to the Tn C C-lobe and Tn I C-terminal domain report Ca2+- and myosin-induced activation of Tn. Reconstituted thin filaments were deposited on a myosin-coated surface similar to an in vitro motility assay setup without filament sliding involved. Under all the tested conditions, Ca2+ was responsible for the most significant changes in Tn activation. Rigor myosin activated Tn at subsaturated Ca2+ conditions but not to the degree seen in thin filaments with Ca2+. ATP-γ-S did not affect Tn activation significantly; however, blebbistatin induced significant activation at subsaturating Ca2+ levels. The relation between the extent of Tn activation and its conformational flexibility suggests that active/inactive Tn states coexist in different proportions that depend on the combination of effectors. These results satisfy an allosteric activation model of the thin filament as a function of Ca2+ and the myosin catalytic cycle state.
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Affiliation(s)
- Christopher Solís
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota.
| | - Giho H Kim
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota
| | - Maria E Moutsoglou
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota
| | - John M Robinson
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota
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7
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Walcott S. Muscle activation described with a differential equation model for large ensembles of locally coupled molecular motors. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 90:042717. [PMID: 25375533 DOI: 10.1103/physreve.90.042717] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Indexed: 06/04/2023]
Abstract
Molecular motors, by turning chemical energy into mechanical work, are responsible for active cellular processes. Often groups of these motors work together to perform their biological role. Motors in an ensemble are coupled and exhibit complex emergent behavior. Although large motor ensembles can be modeled with partial differential equations (PDEs) by assuming that molecules function independently of their neighbors, this assumption is violated when motors are coupled locally. It is therefore unclear how to describe the ensemble behavior of the locally coupled motors responsible for biological processes such as calcium-dependent skeletal muscle activation. Here we develop a theory to describe locally coupled motor ensembles and apply the theory to skeletal muscle activation. The central idea is that a muscle filament can be divided into two phases: an active and an inactive phase. Dynamic changes in the relative size of these phases are described by a set of linear ordinary differential equations (ODEs). As the dynamics of the active phase are described by PDEs, muscle activation is governed by a set of coupled ODEs and PDEs, building on previous PDE models. With comparison to Monte Carlo simulations, we demonstrate that the theory captures the behavior of locally coupled ensembles. The theory also plausibly describes and predicts muscle experiments from molecular to whole muscle scales, suggesting that a micro- to macroscale muscle model is within reach.
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Affiliation(s)
- Sam Walcott
- Department of Mathematics, University of California, Davis, Davis, California 95616, USA
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8
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Sommese RF, Nag S, Sutton S, Miller SM, Spudich JA, Ruppel KM. Effects of troponin T cardiomyopathy mutations on the calcium sensitivity of the regulated thin filament and the actomyosin cross-bridge kinetics of human β-cardiac myosin. PLoS One 2013; 8:e83403. [PMID: 24367593 PMCID: PMC3867432 DOI: 10.1371/journal.pone.0083403] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Accepted: 11/13/2013] [Indexed: 11/20/2022] Open
Abstract
Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) lead to significant cardiovascular morbidity and mortality worldwide. Mutations in the genes encoding the sarcomere, the force-generating unit in the cardiomyocyte, cause familial forms of both HCM and DCM. This study examines two HCM-causing (I79N, E163K) and two DCM-causing (R141W, R173W) mutations in the troponin T subunit of the troponin complex using human β-cardiac myosin. Unlike earlier reports using various myosin constructs, we found that none of these mutations affect the maximal sliding velocities or maximal Ca2+-activated ADP release rates involving the thin filament human β-cardiac myosin complex. Changes in Ca2+ sensitivity using the human myosin isoform do, however, mimic changes seen previously with non-human myosin isoforms. Transient kinetic measurements show that these mutations alter the kinetics of Ca2+ induced conformational changes in the regulatory thin filament proteins. These changes in calcium sensitivity are independent of active, cycling human β-cardiac myosin.
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Affiliation(s)
- Ruth F. Sommese
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
| | - Suman Nag
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
| | - Shirley Sutton
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
| | - Susan M. Miller
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California, United States of America
| | - James A. Spudich
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
- * E-mail: (KR); (JS)
| | - Kathleen M. Ruppel
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
- Department of Pediatrics (Cardiology), Stanford University School of Medicine, Stanford, California, United States of America
- * E-mail: (KR); (JS)
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9
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Webb M, Jackson DR, Stewart TJ, Dugan SP, Carter MS, Cremo CR, Baker JE. The myosin duty ratio tunes the calcium sensitivity and cooperative activation of the thin filament. Biochemistry 2013; 52:6437-44. [PMID: 23947752 DOI: 10.1021/bi400262h] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In striated muscle, calcium binding to the thin filament (TF) regulatory complex activates actin-myosin ATPase activity, and actin-myosin kinetics in turn regulates TF activation. However, a quantitative description of the effects of actin-myosin kinetics on the calcium sensitivity (pCa50) and cooperativity (nH) of TF activation is lacking. With the assumption that TF structural transitions and TF-myosin binding transitions are inextricably coupled, we advanced the principles established by Kad et al. [Kad, N., et al. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 16990-16995] and Sich et al. [Sich, N. M., et al. (2011) J. Biol. Chem. 285, 39150-39159] to develop a simple model of TF regulation, which predicts that pCa50 varies linearly with duty ratio and that nH is maximal near physiological duty ratios. Using in vitro motility to determine the calcium sensitivity of TF sliding velocities, we measured pCa50 and nH at different myosin densities and in the presence of ATPase inhibitors. The observed effects of myosin density and actin-myosin duty ratio on pCa50 and nH are consistent with our model predictions. In striated muscle, pCa50 must match cytosolic calcium concentrations and a maximal nH optimizes calcium responsiveness. Our results indicate that pCa50 and nH can be predictably tuned through TF-myosin ATPase kinetics and that drugs and disease states that alter ATPase kinetics can, through their effects on calcium sensitivity, alter the efficiency of muscle contraction.
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Affiliation(s)
- Milad Webb
- Department of Electrical and Biomedical Engineering, University of Nevada, Reno , Reno, Nevada 89557, United States
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10
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Lindqvist J, Iwamoto H, Blanco G, Ochala J. The fraction of strongly bound cross-bridges is increased in mice that carry the myopathy-linked myosin heavy chain mutation MYH4L342Q. Dis Model Mech 2013; 6:834-40. [PMID: 23335206 PMCID: PMC3634666 DOI: 10.1242/dmm.011155] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Accepted: 01/10/2013] [Indexed: 12/23/2022] Open
Abstract
Myosinopathies have emerged as a new group of diseases and are caused by mutations in genes encoding myosin heavy chain (MyHC) isoforms. One major hallmark of these diseases is skeletal muscle weakness or paralysis, but the underlying molecular mechanisms remain unclear. Here, we have undertaken a detailed functional study of muscle fibers from Myh4(arl) mice, which carry a mutation that provokes an L342Q change within the catalytic domain of the type IIb skeletal muscle myosin protein MYH4. Because homozygous animals develop rapid muscle-structure disruption and lower-limb paralysis, they must be killed by postnatal day 13, so all experiments were performed using skeletal muscles from adult heterozygous animals (Myh4(arl)/+). Myh4(arl)/+ mice contain MYH4(L342Q) expressed at 7% of the levels of the wild-type (WT) protein, and are overtly and histologically normal. However, mechanical and X-ray diffraction pattern analyses of single membrane-permeabilized fibers revealed, upon maximal Ca(2+) activation, higher stiffness as well as altered meridional and equatorial reflections in Myh4(arl)/+ mice when compared with age-matched WT animals. Under rigor conditions, by contrast, no difference was observed between Myh4(arl)/+ and WT mice. Altogether, these findings prove that, in adult MYH4(L342Q) heterozygous mice, the transition from weak to strong myosin cross-bridge binding is facilitated, increasing the number of strongly attached myosin heads, thus enhancing force production. These changes are predictably exacerbated in the type IIb fibers of homozygous mice, in which the embryonic myosin isoform is fully replaced by MYH4(L342Q), leading to a hypercontraction, muscle-structure disruption and lower-limb paralysis. Overall, these findings provide important insights into the molecular pathogenesis of skeletal myosinopathies.
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Affiliation(s)
- Johan Lindqvist
- Department of Neuroscience, Uppsala University, Uppsala 751 85, Sweden.
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11
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A Differential Equation Model for Tropomyosin-induced Myosin Cooperativity Describes Myosin–Myosin Interactions at Low Calcium. Cell Mol Bioeng 2012. [DOI: 10.1007/s12195-012-0259-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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12
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How do mutations in contractile proteins cause the primary familial cardiomyopathies? J Cardiovasc Transl Res 2011; 4:245-55. [PMID: 21424860 DOI: 10.1007/s12265-011-9266-2] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/19/2010] [Accepted: 02/17/2011] [Indexed: 01/11/2023]
Abstract
In this article, the available evidence about the functional effects of the contractile protein mutations that cause hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) is assessed. The molecular mechanism of the contractile apparatus of cardiac muscle and its regulation by Ca(2+) and PKA phosphorylation have been extensively studied. Therefore, when a number of point mutations in the contractile protein genes were found to cause the well-defined phenotypes of HCM and DCM, it was expected that the diseases could be explained at the molecular level. However, the search for a distinctive molecular phenotype did not yield rapid results. Now that a substantial number of mutations that cause HCM or DCM have been investigated in physiologically relevant systems and with a range of experimental techniques, a pattern is emerging. In the case of HCM, the hypothesis that the major effect of mutations is to increase myofibrillar Ca(2+)-sensitivity seems to be well established, but the mechanisms by which an increase in myofibrillar Ca(2+)-sensitivity induces hypertrophy remain obscure. In contrast, DCM mutations are not correlated with a specific effect on Ca(2+)-sensitivity. It has recently been proposed that DCM mutations uncouple troponin I phosphorylation from Ca(2+)-sensitivity changes, albeit based on only a few mutations so far. A plausible link between uncoupling and DCM has been proposed via blunting of the response to α-adrenergic stimulation.
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