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Haug M, Reischl B, Nübler S, Kiriaev L, Mázala DAG, Houweling PJ, North KN, Friedrich O, Head SI. Absence of the Z-disc protein α-actinin-3 impairs the mechanical stability of Actn3KO mouse fast-twitch muscle fibres without altering their contractile properties or twitch kinetics. Skelet Muscle 2022; 12:14. [PMID: 35733150 PMCID: PMC9219180 DOI: 10.1186/s13395-022-00295-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Accepted: 05/03/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND A common polymorphism (R577X) in the ACTN3 gene results in the complete absence of the Z-disc protein α-actinin-3 from fast-twitch muscle fibres in ~ 16% of the world's population. This single gene polymorphism has been subject to strong positive selection pressure during recent human evolution. Previously, using an Actn3KO mouse model, we have shown in fast-twitch muscles, eccentric contractions at L0 + 20% stretch did not cause eccentric damage. In contrast, L0 + 30% stretch produced a significant ~ 40% deficit in maximum force; here, we use isolated single fast-twitch skeletal muscle fibres from the Actn3KO mouse to investigate the mechanism underlying this. METHODS Single fast-twitch fibres are separated from the intact muscle by a collagenase digest procedure. We use label-free second harmonic generation (SHG) imaging, ultra-fast video microscopy and skinned fibre measurements from our MyoRobot automated biomechatronics system to study the morphology, visco-elasticity, force production and mechanical strength of single fibres from the Actn3KO mouse. Data are presented as means ± SD and tested for significance using ANOVA. RESULTS We show that the absence of α-actinin-3 does not affect the visco-elastic properties or myofibrillar force production. Eccentric contractions demonstrated that chemically skinned Actn3KO fibres are mechanically weaker being prone to breakage when eccentrically stretched. Furthermore, SHG images reveal disruptions in the myofibrillar alignment of Actn3KO fast-twitch fibres with an increase in Y-shaped myofibrillar branching. CONCLUSIONS The absence of α-actinin-3 from the Z-disc in fast-twitch fibres disrupts the organisation of the myofibrillar proteins, leading to structural weakness. This provides a mechanistic explanation for our earlier findings that in vitro intact Actn3KO fast-twitch muscles are significantly damaged by L0 + 30%, but not L0 + 20%, eccentric contraction strains. Our study also provides a possible mechanistic explanation as to why α-actinin-3-deficient humans have been reported to have a faster decline in muscle function with increasing age, that is, as sarcopenia reduces muscle mass and force output, the eccentric stress on the remaining functional α-actinin-3 deficient fibres will be increased, resulting in fibre breakages.
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Affiliation(s)
- Michael Haug
- Institute of Medical Biotechnology, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany
| | - Barbara Reischl
- Institute of Medical Biotechnology, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany
| | - Stefanie Nübler
- Institute of Medical Biotechnology, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany
| | - Leonit Kiriaev
- School of Medicine, Western Sydney University, Sydney, NSW, 2560, Australia.,School of Medical Science, University of New South Wales, Sydney, NSW, Australia
| | - Davi A G Mázala
- Department of Kinesiology, College of Health Professions, Towson University, Towson, MD, USA
| | - Peter J Houweling
- Murdoch Children's Research Institute, Melbourne, VIC, Australia.,Department of Paediatrics, University of Melbourne, Melbourne, VIC, Australia
| | - Kathryn N North
- Murdoch Children's Research Institute, Melbourne, VIC, Australia.,Department of Paediatrics, University of Melbourne, Melbourne, VIC, Australia
| | - Oliver Friedrich
- Institute of Medical Biotechnology, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany.,School of Medicine, Western Sydney University, Sydney, NSW, 2560, Australia.,School of Medical Science, University of New South Wales, Sydney, NSW, Australia
| | - Stewart I Head
- School of Medicine, Western Sydney University, Sydney, NSW, 2560, Australia. .,School of Medical Science, University of New South Wales, Sydney, NSW, Australia. .,Murdoch Children's Research Institute, Melbourne, VIC, Australia.
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Matrigel 3D bioprinting of contractile human skeletal muscle models recapitulating exercise and pharmacological responses. Commun Biol 2021; 4:1183. [PMID: 34650188 PMCID: PMC8516940 DOI: 10.1038/s42003-021-02691-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2020] [Accepted: 09/16/2021] [Indexed: 12/25/2022] Open
Abstract
A key to enhance the low translatability of preclinical drug discovery are in vitro human three-dimensional (3D) microphysiological systems (MPS). Here, we show a new method for automated engineering of 3D human skeletal muscle models in microplates and functional compound screening to address the lack of muscle wasting disease medication. To this end, we adapted our recently described 24-well plate 3D bioprinting platform with a printhead cooling system to allow microvalve-based drop-on-demand printing of cell-laden Matrigel containing primary human muscle precursor cells. Mini skeletal muscle models develop within a week exhibiting contractile, striated myofibers aligned between two attachment posts. As an in vitro exercise model, repeated high impact stimulation of contractions for 3 h by a custom-made electrical pulse stimulation (EPS) system for 24-well plates induced interleukin-6 myokine expression and Akt hypertrophy pathway activation. Furthermore, the known muscle stimulators caffeine and Tirasemtiv acutely increase EPS-induced contractile force of the models. This validated new human muscle MPS will benefit development of drugs against muscle wasting diseases. Moreover, our Matrigel 3D bioprinting platform will allow engineering of non-self-organizing complex human 3D MPS. Alave-Furrer et al adapted their recently-developed 3D bioprinting platform to allow microvalve-based drop-on-demand printing of cell-laden Matrigel containing primary human muscle precursor cells. Their bioprinting platform recapitulated aspects of exercise and pharmacological responses and thus could aid the engineering of more complex 3D microphysiological systems.
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Mitochondria-localized AMPK responds to local energetics and contributes to exercise and energetic stress-induced mitophagy. Proc Natl Acad Sci U S A 2021; 118:2025932118. [PMID: 34493662 PMCID: PMC8449344 DOI: 10.1073/pnas.2025932118] [Citation(s) in RCA: 84] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Accepted: 08/05/2021] [Indexed: 12/25/2022] Open
Abstract
Mitochondria form a complex, interconnected reticulum that is maintained through coordination among biogenesis, dynamic fission, and fusion and mitophagy, which are initiated in response to various cues to maintain energetic homeostasis. These cellular events, which make up mitochondrial quality control, act with remarkable spatial precision, but what governs such spatial specificity is poorly understood. Herein, we demonstrate that specific isoforms of the cellular bioenergetic sensor, 5' AMP-activated protein kinase (AMPKα1/α2/β2/γ1), are localized on the outer mitochondrial membrane, referred to as mitoAMPK, in various tissues in mice and humans. Activation of mitoAMPK varies across the reticulum in response to energetic stress, and inhibition of mitoAMPK activity attenuates exercise-induced mitophagy in skeletal muscle in vivo. Discovery of a mitochondrial pool of AMPK and its local importance for mitochondrial quality control underscores the complexity of sensing cellular energetics in vivo that has implications for targeting mitochondrial energetics for disease treatment.
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Marcucci L, Canato M, Protasi F, Stienen GJM, Reggiani C. A 3D diffusional-compartmental model of the calcium dynamics in cytosol, sarcoplasmic reticulum and mitochondria of murine skeletal muscle fibers. PLoS One 2018; 13:e0201050. [PMID: 30048500 PMCID: PMC6062086 DOI: 10.1371/journal.pone.0201050] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2018] [Accepted: 07/06/2018] [Indexed: 11/19/2022] Open
Abstract
Variations of free calcium concentration ([Ca2+]) are powerful intracellular signals, controlling contraction as well as metabolism in muscle cells. To fully understand the role of calcium redistribution upon excitation and contraction in skeletal muscle cells, the local [Ca2+] in different compartments needs to be taken into consideration. Fluorescent probes allow the determination of [Ca2+] in the cytosol where myofibrils are embedded, the lumen of the sarcoplasmic reticulum (SR) and the mitochondrial matrix. Previously, models have been developed describing intracellular calcium handling in skeletal and cardiac muscle cells. However, a comprehensive model describing the kinetics of the changes in free calcium concentration in these three compartments is lacking. We designed a new 3D compartmental model of the half sarcomere with radial symmetry, which accounts for diffusion of Ca2+ into the three compartments and simulates its dynamics at rest and at various rates of stimulation in mice skeletal muscle fibers. This model satisfactorily reproduces both the amplitude and time course of the variations of [Ca2+] in the three compartments in mouse fast fibers. As an illustration of the applicability of the model, we investigated the effects of Calsequestrin (CSQ) ablation. CSQ is the main Ca2+ buffer in the SR, localized in close proximity of its calcium release sites and near to the mitochondria. CSQ knock-out mice muscles still preserve a near-normal contractile behavior, but it is unclear whether this is caused by additional SR calcium buffering or a significant contribution of calcium entry from extracellular space, via stored-operated calcium entry (SOCE). The model enabled quantitative assessment of these two scenarios by comparison to measurements of local calcium in the cytosol, the SR and the mitochondria. In conclusion, the model represents a useful tool to investigate the impact of protein ablation and of pharmacological interventions on intracellular calcium dynamics in mice skeletal muscle.
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Affiliation(s)
- Lorenzo Marcucci
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Marta Canato
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Feliciano Protasi
- CeSI-Met - Center for Research on Ageing and Translational Medicine, Chieti, Italy
- Department of Medicine and Aging Science; University G. d’Annunzio, Chieti, Italy
| | - Ger J. M. Stienen
- Department of Physiology, VU University Medical Centre, Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands
| | - Carlo Reggiani
- Department of Biomedical Sciences, University of Padova, Padova, Italy
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Li R, Steyn FJ, Stout MB, Lee K, Cully TR, Calderón JC, Ngo ST. Development of a high-throughput method for real-time assessment of cellular metabolism in intact long skeletal muscle fibre bundles. J Physiol 2016; 594:7197-7213. [PMID: 27619319 DOI: 10.1113/jp272988] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Accepted: 09/07/2016] [Indexed: 12/28/2022] Open
Abstract
KEY POINTS We developed a method that allows for real-time assessment of cellular metabolism in isolated, intact long skeletal muscle fibre bundles from adult mice. This method can be used to study changes in mitochondrial function and fuel utilisation in live skeletal muscle fibre bundles. Our method enables flexibility in experimental design and high-throughput assessment of mitochondrial parameters in isolated skeletal muscle fibre bundles. Extensor digitorum longus (EDL) fibre bundles obtained from chronic high-fat diet fed mice had lower basal oxygen consumption under FCCP-induced maximal respiration, when compared to control chow-fed mice. EDL fibre bundles obtained from chronic high-fat diet fed mice had enhanced mitochondrial oxidation capacity under FCCP-induced maximal respiration, when compared to control chow-fed mice. ABSTRACT Metabolic dysfunction in skeletal muscle contributes to the aetiology and development of muscle diseases and metabolic diseases. As such, assessment of skeletal muscle cellular bioenergetics provides a powerful means to understand the role of skeletal muscle metabolism in disease and to identify possible therapeutic targets. Here, we developed a method that allows for the real-time assessment of cellular respiration in intact skeletal muscle fibre bundles obtained from the extensor digitorum longus (EDL) muscle of adult mice. Using this method, we assessed the contribution of ATP turnover and proton leak to basal mitochondrial oxygen consumption rate (OCR). Our data demonstrate that the mitochondria in EDL fibres are loosely coupled. Moreover, in the presence of carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), we show that palmitate exposure induced comparable peak OCR and higher total OCR in EDL fibre bundles when compared to pyruvate exposure, suggesting that fatty acids might be a more sustainable fuel source for skeletal muscle when mitochondria are driven to maximal respiration. Application of this method to EDL fibre bundles obtained from chronic high-fat diet fed mice revealed lower basal OCR and enhanced mitochondrial oxidation capacity in the presence of FCCP when compared to the chow-diet fed control mice. By using a 96-well microplate format, our method provides a flexible and efficient platform to investigate mitochondrial parameters of intact skeletal muscle fibres obtained from adult mice.
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Affiliation(s)
- Rui Li
- School of Biomedical Sciences, University of Queensland, Brisbane, Australia
| | - Frederik J Steyn
- School of Biomedical Sciences, University of Queensland, Brisbane, Australia.,University of Queensland Centre for Clinical Research, Brisbane, Australia
| | - Michael B Stout
- Robert and Arlene Kogod Center on Aging, Mayo Clinic, Rochester, MN, USA
| | - Kevin Lee
- School of Biomedical Sciences, University of Queensland, Brisbane, Australia
| | - Tanya R Cully
- School of Biomedical Sciences, University of Queensland, Brisbane, Australia
| | - Juan C Calderón
- Department of Physiology and Biochemistry, Physiology and Biochemistry Research Group-PHYSIS, Faculty of Medicine, University of Antioquia, Medellín, Colombia
| | - Shyuan T Ngo
- School of Biomedical Sciences, University of Queensland, Brisbane, Australia.,University of Queensland Centre for Clinical Research, Brisbane, Australia.,Queensland Brain Institute, University of Queensland, Brisbane, Australia.,Department of Neurology, Royal Brisbane and Women's Hospital, Brisbane, Australia
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Hernández-Ochoa EO, Vanegas C, Iyer SR, Lovering RM, Schneider MF. Alternating bipolar field stimulation identifies muscle fibers with defective excitability but maintained local Ca(2+) signals and contraction. Skelet Muscle 2016; 6:6. [PMID: 26855765 PMCID: PMC4743112 DOI: 10.1186/s13395-016-0076-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Accepted: 01/05/2016] [Indexed: 11/25/2022] Open
Abstract
Background Most cultured enzymatically dissociated adult myofibers exhibit spatially uniform (UNI) contractile responses and Ca2+ transients over the entire myofiber in response to electric field stimuli of either polarity applied via bipolar electrodes. However, some myofibers only exhibit contraction and Ca2+ transients at alternating (ALT) ends in response to alternating polarity field stimulation. Here, we present for the first time the methodology for identification of ALT myofibers in primary cultures and isolated muscles, as well as a study of their electrophysiological properties. Results We used high-speed confocal microscopic Ca2+ imaging, electric field stimulation, microelectrode recordings, immunostaining, and confocal microscopy to characterize the properties of action potential-induced Ca2+ transients, contractility, resting membrane potential, and staining of T-tubule voltage-gated Na+ channel distribution applied to cultured adult myofibers. Here, we show for the first time, with high temporal and spatial resolution, that normal control myofibers with UNI responses can be converted to ALT response myofibers by TTX addition or by removal of Na+ from the bathing medium, with reappearance of the UNI response on return of Na+. Our results suggest disrupted excitability as the cause of ALT behavior and indicate that the ALT response is due to local depolarization-induced Ca2+ release, whereas the UNI response is triggered by action potential propagation over the entire myofiber. Consistent with this interpretation, local depolarizing monopolar stimuli give uniform (propagated) responses in UNI myofibers, but only local responses at the electrode in ALT myofibers. The ALT responses in electrically inexcitable myofibers are consistent with expectations of current spread between bipolar stimulating electrodes, entering (hyperpolarizing) one end of a myofiber and leaving (depolarizing) the other end of the myofiber. ALT responses were also detected in some myofibers within intact isolated whole muscles from wild-type and MDX mice, demonstrating that ALT responses can be present before enzymatic dissociation. Conclusions We suggest that checking for ALT myofiber responsiveness by looking at the end of a myofiber during alternating polarity stimuli provides a test for compromised excitability of myofibers, and could be used to identify inexcitable, damaged or diseased myofibers by ALT behavior in healthy and diseased muscle. Electronic supplementary material The online version of this article (doi:10.1186/s13395-016-0076-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Erick O Hernández-Ochoa
- Department of Biochemistry and Molecular Biology, School of Medicine, University of Maryland, Baltimore, 108 N. Greene Street, Baltimore, MD 21201 USA
| | - Camilo Vanegas
- Department of Biochemistry and Molecular Biology, School of Medicine, University of Maryland, Baltimore, 108 N. Greene Street, Baltimore, MD 21201 USA
| | - Shama R Iyer
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, MD 21201 USA
| | - Richard M Lovering
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, MD 21201 USA
| | - Martin F Schneider
- Department of Biochemistry and Molecular Biology, School of Medicine, University of Maryland, Baltimore, 108 N. Greene Street, Baltimore, MD 21201 USA
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Selvin D, Renaud JM. Changes in myoplasmic Ca2+ during fatigue differ between FDB fibers, between glibenclamide-exposed and Kir6.2-/- fibers and are further modulated by verapamil. Physiol Rep 2015; 3:3/3/e12303. [PMID: 25742954 PMCID: PMC4393149 DOI: 10.14814/phy2.12303] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
One objective of this study was to document how individual FDB muscle fibers depend on the myoprotection of KATP channels during fatigue. Verapamil, a CaV1.1 channel blocker, prevents large increases in unstimulated force during fatigue in KATP-channel-deficient muscles. A second objective was to determine if verapamil reduces unstimulated [Ca(2+)]i in KATP-channel-deficient fibers. We measured changes in myoplasmic [Ca(2+)] ([Ca(2+)]i) using two KATP-channel-deficient models: (1) a pharmacological approach exposing fibers to glibenclamide, a channel blocker, and (2) a genetic approach using fibers from null mice for the Kir6.2 gene. Fatigue was elicited with one tetanic contraction every sec for 3 min. For all conditions, large differences in fatigue kinetics were observed from fibers which had greater tetanic [Ca(2+)]i at the end than at the beginning of fatigue to fibers which eventually completely failed to release Ca(2+) upon stimulation. Compared to control conditions, KATP-channel-deficient fibers had a greater proportion of fiber with large decreases in tetanic [Ca(2+)]i, fade and complete failure to release Ca(2+) upon stimulation. There was, however, a group of KATP-channel-deficient fibers that had similar fatigue kinetics to those of the most fatigue-resistant control fibers. For the first time, differences in fatigue kinetics were observed between Kir6.2(-/-) and glibenclamide-exposed muscle fibers. Verapamil significantly reduced unstimulated and tetanic [Ca(2+)]i. It is concluded that not all fibers are dependent on the myoprotection of KATP channels and that the decrease in unstimulated force by verapamil reported in a previous studies in glibenclamide-exposed fibers is due to a reduction in Ca(2+) load by reducing Ca(2+) influx through CaV1.1 channels between and during contractions.
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Affiliation(s)
- David Selvin
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Jean-Marc Renaud
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
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