1
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Korb A, Tajbakhsh S, Comai GE. Functional specialisation and coordination of myonuclei. Biol Rev Camb Philos Soc 2024; 99:1164-1195. [PMID: 38477382 DOI: 10.1111/brv.13063] [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: 04/10/2023] [Revised: 01/30/2024] [Accepted: 02/02/2024] [Indexed: 03/14/2024]
Abstract
Myofibres serve as the functional unit for locomotion, with the sarcomere as fundamental subunit. Running the entire length of this structure are hundreds of myonuclei, located at the periphery of the myofibre, juxtaposed to the plasma membrane. Myonuclear specialisation and clustering at the centre and ends of the fibre are known to be essential for muscle contraction, yet the molecular basis of this regionalisation has remained unclear. While the 'myonuclear domain hypothesis' helped explain how myonuclei can independently govern large cytoplasmic territories, novel technologies have provided granularity on the diverse transcriptional programs running simultaneously within the syncytia and added a new perspective on how myonuclei communicate. Building upon this, we explore the critical cellular and molecular sources of transcriptional and functional heterogeneity within myofibres, discussing the impact of intrinsic and extrinsic factors on myonuclear programs. This knowledge provides new insights for understanding muscle development, repair, and disease, but also opens avenues for the development of novel and precise therapeutic approaches.
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Affiliation(s)
- Amaury Korb
- Institut Pasteur, Université Paris Cité, CNRS UMR 3738, Stem Cells & Development Unit, 25 rue du Dr. Roux, Institut Pasteur, Paris, F-75015, France
| | - Shahragim Tajbakhsh
- Institut Pasteur, Université Paris Cité, CNRS UMR 3738, Stem Cells & Development Unit, 25 rue du Dr. Roux, Institut Pasteur, Paris, F-75015, France
| | - Glenda E Comai
- Institut Pasteur, Université Paris Cité, CNRS UMR 3738, Stem Cells & Development Unit, 25 rue du Dr. Roux, Institut Pasteur, Paris, F-75015, France
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2
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Sun C, Swoboda CO, Petrany MJ, Parameswaran S, VonHandorf A, Weirauch MT, Lepper C, Millay DP. Lineage tracing of newly accrued nuclei in skeletal myofibers uncovers distinct transcripts and interplay between nuclear populations. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.24.554609. [PMID: 37662191 PMCID: PMC10473681 DOI: 10.1101/2023.08.24.554609] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/05/2023]
Abstract
Multinucleated skeletal muscle cells have an obligatory need to acquire additional nuclei through fusion with activated skeletal muscle stem cells when responding to both developmental and adaptive growth stimuli. A fundamental question in skeletal muscle biology has been the reason underlying this need for new nuclei in syncytial cells that already harbor hundreds of nuclei. To begin to answer this long-standing question, we utilized nuclear RNA-sequencing approaches and developed a lineage tracing strategy capable of defining the transcriptional state of recently fused nuclei and distinguishing this state from that of pre-existing nuclei. Our findings reveal the presence of conserved markers of newly fused nuclei both during development and after a hypertrophic stimulus in the adult. However, newly fused nuclei also exhibit divergent gene expression that is determined by the myogenic environment to which they fuse. Moreover, accrual of new nuclei through fusion is required for nuclei already resident in adult myofibers to mount a normal transcriptional response to a load-inducing stimulus. We propose a model of mutual regulation in the control of skeletal muscle development and adaptations, where newly fused and pre-existing myonuclear populations influence each other to maintain optimal functional growth.
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Affiliation(s)
- Chengyi Sun
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
| | - Casey O. Swoboda
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
- Division of Biomedical Informatics, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
| | - Michael J. Petrany
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
| | - Sreeja Parameswaran
- Division of Human Genetics, Center for Autoimmune Genetics and Etiology (CAGE), Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
| | - Andrew VonHandorf
- Division of Human Genetics, Center for Autoimmune Genetics and Etiology (CAGE), Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
| | - Matthew T. Weirauch
- Division of Biomedical Informatics, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
- Division of Human Genetics, Center for Autoimmune Genetics and Etiology (CAGE), Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA
| | - Christoph Lepper
- Department of Physiology & Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, USA
| | - Douglas P. Millay
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA
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3
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Hansson KA, Eftestøl E. Scaling of nuclear numbers and their spatial arrangement in skeletal muscle cell size regulation. Mol Biol Cell 2023; 34:pe3. [PMID: 37339435 PMCID: PMC10398882 DOI: 10.1091/mbc.e22-09-0424] [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: 09/19/2022] [Revised: 03/29/2023] [Accepted: 04/28/2023] [Indexed: 06/22/2023] Open
Abstract
Many cells display considerable functional plasticity and depend on the regulation of numerous organelles and macromolecules for their maintenance. In large cells, organelles also need to be carefully distributed to supply the cell with essential resources and regulate intracellular activities. Having multiple copies of the largest eukaryotic organelle, the nucleus, epitomizes the importance of scaling gene products to large cytoplasmic volumes in skeletal muscle fibers. Scaling of intracellular constituents within mammalian muscle fibers is, however, poorly understood, but according to the myonuclear domain hypothesis, a single nucleus supports a finite amount of cytoplasm and is thus postulated to act autonomously, causing the nuclear number to be commensurate with fiber volume. In addition, the orderly peripheral distribution of myonuclei is a hallmark of normal cell physiology, as nuclear mispositioning is associated with impaired muscle function. Because underlying structures of complex cell behaviors are commonly formalized by scaling laws and thus emphasize emerging principles of size regulation, the work presented herein offers more of a unified conceptual platform based on principles from physics, chemistry, geometry, and biology to explore cell size-dependent correlations of the largest mammalian cell by means of scaling.
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Affiliation(s)
- Kenth-Arne Hansson
- Section for Health and Exercise Physiology, Inland Norway University of Applied Sciences, 2624 Lillehammer, Norway
| | - Einar Eftestøl
- Department of Biosciences, University of Oslo, 0371 Oslo, Norway
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4
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Bagley JR, Denes LT, McCarthy JJ, Wang ET, Murach KA. The myonuclear domain in adult skeletal muscle fibres: past, present and future. J Physiol 2023; 601:723-741. [PMID: 36629254 PMCID: PMC9931674 DOI: 10.1113/jp283658] [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] [Received: 08/12/2022] [Accepted: 01/06/2023] [Indexed: 01/12/2023] Open
Abstract
Most cells in the body are mononuclear whereas skeletal muscle fibres are uniquely multinuclear. The nuclei of muscle fibres (myonuclei) are usually situated peripherally which complicates the equitable distribution of gene products. Myonuclear abundance can also change under conditions such as hypertrophy and atrophy. Specialised zones in muscle fibres have different functions and thus distinct synthetic demands from myonuclei. The complex structure and regulatory requirements of multinuclear muscle cells understandably led to the hypothesis that myonuclei govern defined 'domains' to maintain homeostasis and facilitate adaptation. The purpose of this review is to provide historical context for the myonuclear domain and evaluate its veracity with respect to mRNA and protein distribution resulting from myonuclear transcription. We synthesise insights from past and current in vitro and in vivo genetically modified models for studying the myonuclear domain under dynamic conditions. We also cover the most contemporary knowledge on mRNA and protein transport in muscle cells. Insights from emerging technologies such as single myonuclear RNA-sequencing further inform our discussion of the myonuclear domain. We broadly conclude: (1) the myonuclear domain can be flexible during muscle fibre growth and atrophy, (2) the mechanisms and role of myonuclear loss and motility deserve further consideration, (3) mRNA in muscle is actively transported via microtubules and locally restricted, but proteins may travel far from a myonucleus of origin and (4) myonuclear transcriptional specialisation extends beyond the classic neuromuscular and myotendinous populations. A deeper understanding of the myonuclear domain in muscle may promote effective therapies for ageing and disease.
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Affiliation(s)
- James R. Bagley
- Muscle Physiology Laboratory, Department of Kinesiology, San Francisco State University, San Francisco, California
| | | | - John J. McCarthy
- The Center for Muscle Biology, University of Kentucky, Lexington, Kentucky
- Department of Physiology, College of Medicine, University of Kentucky
| | - Eric T. Wang
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics, University of Florida, Gainesville, Florida
- Myology Institute, University of Florida
- Genetics Institute, University of Florida
| | - Kevin A. Murach
- Exercise Science Research Center, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas
- Cell and Molecular Biology Graduate Program, University of Arkansas
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5
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Nadkarni AV, Heald R. Reconstitution of muscle cell microtubule organization in vitro. Cytoskeleton (Hoboken) 2022; 78:492-502. [PMID: 35666041 DOI: 10.1002/cm.21710] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 05/31/2022] [Accepted: 06/01/2022] [Indexed: 11/06/2022]
Abstract
Skeletal muscle differentiation occurs as muscle precursor cells (myoblasts) elongate and fuse to form multinucleated syncytial myotubes in which the highly-organized actomyosin sarcomeres of muscle fibers assemble. Although less well characterized, the microtubule cytoskeleton also undergoes dramatic rearrangement during myogenesis. The centrosome-nucleated microtubule array found in myoblasts is lost as the nuclear membrane acquires microtubule nucleating activity and microtubules emerge from multiple sites in the cell, eventually rearranging into a grid-like pattern in myotubes. In order to characterize perinuclear microtubule organization using a biochemically tractable system, we isolated nuclei from mouse C2C12 skeletal muscle cells during the course of differentiation and incubated them in cytoplasmic extracts prepared from eggs of the frog Xenopus laevis. Whereas centrosomes associated with myoblast nuclei gave rise to radial microtubule arrays in extracts, myotube nuclei produced a sun-like pattern with microtubules transiently nucleating from the entire nuclear envelope. Perinuclear microtubule growth was suppressed by inhibition of Aurora A kinase or by degradation of RNA, treatments that also inhibited microtubule growth from sperm centrosomes. Myotube nuclei displayed microtubule motor-based movements leading to their separation, as occurs in myotubes. This in vitro assay therefore recapitulates key features of microtubule organization and nuclear movement observed during muscle cell differentiation. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Ambika V Nadkarni
- Department of Molecular & Cell Biology, University of California, Berkeley, CA, USA
| | - Rebecca Heald
- Department of Molecular & Cell Biology, University of California, Berkeley, CA, USA
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6
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Buckley KH, Nestor-Kalinoski AL, Pizza FX. Positional Context of Myonuclear Transcription During Injury-Induced Muscle Regeneration. Front Physiol 2022; 13:845504. [PMID: 35492593 PMCID: PMC9040890 DOI: 10.3389/fphys.2022.845504] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Accepted: 03/02/2022] [Indexed: 01/31/2023] Open
Abstract
Fundamental aspects underlying downstream processes of skeletal muscle regeneration, such as myonuclear positioning and transcription are poorly understood. This investigation begins to address deficiencies in knowledge by examining the kinetics of myonuclear accretion, positioning, and global transcription during injury-induced muscle regeneration in mice. We demonstrate that myonuclear accretion plateaus within 7 days of an injury and that the majority (∼70%) of myonuclei are centrally aligned in linear arrays (nuclear chains) throughout the course of regeneration. Relatively few myonuclei were found in a peripheral position (∼20%) or clustered (∼10%) together during regeneration. Importantly, transcriptional activity of individual myonuclei in nuclear chains was high, and greater than that of peripheral or clustered myonuclei. Transcription occurring primarily in nuclear chains elevated the collective transcriptional activity of regenerating myofibers during the later stage of regeneration. Importantly, the number of myonuclei in chains and their transcriptional activity were statistically correlated with an increase in myofiber size during regeneration. Our findings demonstrate the positional context of transcription during regeneration and highlight the importance of centralized nuclear chains in facilitating hypertrophy of regenerating myofibers after injury.
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Affiliation(s)
- Kole H. Buckley
- School of Exercise and Rehabilitation Sciences, University of Toledo, Toledo, OH, United States
| | | | - Francis X. Pizza
- School of Exercise and Rehabilitation Sciences, University of Toledo, Toledo, OH, United States
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7
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Microtubule-based transport is essential to distribute RNA and nascent protein in skeletal muscle. Nat Commun 2021; 12:6079. [PMID: 34707124 PMCID: PMC8551216 DOI: 10.1038/s41467-021-26383-9] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2021] [Accepted: 10/04/2021] [Indexed: 12/18/2022] Open
Abstract
While the importance of RNA localization in highly differentiated cells is well appreciated, basic principles of RNA localization in skeletal muscle remain poorly characterized. Here, we develop a method to detect and quantify single molecule RNA localization patterns in skeletal myofibers, and uncover a critical role for directed transport of RNPs in muscle. We find that RNAs localize and are translated along sarcomere Z-disks, dispersing tens of microns from progenitor nuclei, regardless of encoded protein function. We find that directed transport along the lattice-like microtubule network of myofibers becomes essential to achieve this localization pattern as muscle development progresses; disruption of this network leads to extreme accumulation of RNPs and nascent protein around myonuclei. Our observations suggest that global active RNP transport may be required to distribute RNAs in highly differentiated cells and reveal fundamental mechanisms of gene regulation, with consequences for myopathies caused by perturbations to RNPs or microtubules.
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8
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Murach KA, Fry CS, Dupont-Versteegden EE, McCarthy JJ, Peterson CA. Fusion and beyond: Satellite cell contributions to loading-induced skeletal muscle adaptation. FASEB J 2021; 35:e21893. [PMID: 34480776 PMCID: PMC9293230 DOI: 10.1096/fj.202101096r] [Citation(s) in RCA: 46] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2021] [Revised: 08/13/2021] [Accepted: 08/17/2021] [Indexed: 12/14/2022]
Abstract
Satellite cells support adult skeletal muscle fiber adaptations to loading in numerous ways. The fusion of satellite cells, driven by cell-autonomous and/or extrinsic factors, contributes new myonuclei to muscle fibers, associates with load-induced hypertrophy, and may support focal membrane damage repair and long-term myonuclear transcriptional output. Recent studies have also revealed that satellite cells communicate within their niche to mediate muscle remodeling in response to resistance exercise, regulating the activity of numerous cell types through various mechanisms such as secretory signaling and cell-cell contact. Muscular adaptation to resistance and endurance activity can be initiated and sustained for a period of time in the absence of satellite cells, but satellite cell participation is ultimately required to achieve full adaptive potential, be it growth, function, or proprioceptive coordination. While significant progress has been made in understanding the roles of satellite cells in adult muscle over the last few decades, many conclusions have been extrapolated from regeneration studies. This review highlights our current understanding of satellite cell behavior and contributions to adaptation outside of regeneration in adult muscle, as well as the roles of satellite cells beyond fusion and myonuclear accretion, which are gaining broader recognition.
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Affiliation(s)
- Kevin A Murach
- The Center for Muscle Biology, University of Kentucky, Lexington, Kentucky, USA.,Molecular Muscle Mass Regulation Laboratory, Exercise Science Research Center, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas, USA.,Cell and Molecular Biology Program, University of Arkansas, Fayetteville, Arkansas, USA
| | - Christopher S Fry
- The Center for Muscle Biology, University of Kentucky, Lexington, Kentucky, USA.,Department of Athletic Training and Clinical Nutrition, College of Health Sciences, University of Kentucky, Lexington, Kentucky, USA
| | - Esther E Dupont-Versteegden
- The Center for Muscle Biology, University of Kentucky, Lexington, Kentucky, USA.,Department of Physical Therapy, College of Health Sciences, University of Kentucky, Lexington, Kentucky, USA
| | - John J McCarthy
- The Center for Muscle Biology, University of Kentucky, Lexington, Kentucky, USA.,Department of Physiology, College of Medicine, University of Kentucky, Lexington, Kentucky, USA
| | - Charlotte A Peterson
- The Center for Muscle Biology, University of Kentucky, Lexington, Kentucky, USA.,Department of Physical Therapy, College of Health Sciences, University of Kentucky, Lexington, Kentucky, USA.,Department of Physiology, College of Medicine, University of Kentucky, Lexington, Kentucky, USA
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9
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Morgan J, Muntoni F. Changes in Myonuclear Number During Postnatal Growth -Implications for AAV Gene Therapy for Muscular Dystrophy. J Neuromuscul Dis 2021; 8:S317-S324. [PMID: 34334413 PMCID: PMC8673494 DOI: 10.3233/jnd-210683] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Adult skeletal muscle is a relatively stable tissue, as the multinucleated muscle fibres contain post-mitotic myonuclei. During early postnatal life, muscle growth occurs by the addition of skeletal muscle stem cells (satellite cells) or their progeny to growing muscle fibres. In Duchenne muscular dystrophy, which we shall use as an example of muscular dystrophies, the muscle fibres lack dystrophin and undergo necrosis. Satellite-cell mediated regeneration occurs, to repair and replace the necrotic muscle fibres, but as the regenerated muscle fibres still lack dystrophin, they undergo further cycles of degeneration and regeneration.AAV gene therapy is a promising approach for treating Duchenne muscular dystrophy. But for a single dose of, for example, AAV coding for dystrophin, to be effective, the treated myonuclei must persist, produce sufficient dystrophin and a sufficient number of nuclei must be targeted. This latter point is crucial as AAV vector remains episomal and does not replicate in dividing cells. Here, we describe and compare the growth of skeletal muscle in rodents and in humans and discuss the evidence that myofibre necrosis and regeneration leads to the loss of viral genomes within skeletal muscle. In addition, muscle growth is expected to lead to the dilution of the transduced nuclei especially in case of very early intervention, but it is not clear if growth could result in insufficient dystrophin to prevent muscle fibre breakdown. This should be the focus of future studies.
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Affiliation(s)
- Jennifer Morgan
- The Dubowitz Neuromuscular Centre, UCL Great Ormond Street Institute of Child Health, London, UK.,National Institute for Health Research, Great Ormond Street Institute of Child Health Biomedical Research Centre, University College London, London, UK
| | - Francesco Muntoni
- The Dubowitz Neuromuscular Centre, UCL Great Ormond Street Institute of Child Health, London, UK.,National Institute for Health Research, Great Ormond Street Institute of Child Health Biomedical Research Centre, University College London, London, UK
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10
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Prasad V, Millay DP. Skeletal muscle fibers count on nuclear numbers for growth. Semin Cell Dev Biol 2021; 119:3-10. [PMID: 33972174 DOI: 10.1016/j.semcdb.2021.04.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 03/30/2021] [Accepted: 04/19/2021] [Indexed: 02/06/2023]
Abstract
Skeletal muscle cells are noteworthy for their syncytial nature, with each myofiber accumulating hundreds or thousands of nuclei derived from resident muscle stem cells (MuSCs). These nuclei are accrued through cell fusion, which is controlled by the two essential fusogens Myomaker and Myomerger that are transiently expressed within the myogenic lineage. While the absolute requirement of fusion for muscle development has been known for decades, the underlying need for the magnitude of multinucleation in muscle remains mysterious. Possible advantages of multinucleation include the potential it affords for transcriptional diversity within these massive cells, and as a means of increasing DNA content to support optimal cell size and function. In this article, we review recent advances that elucidate the relationship between myonuclear numbers and establishment of myofiber size, and discuss how this new information refines our understanding of the concept of myonuclear domains (MND), the cytoplasmic volumes that each resident myonucleus can support. Finally, we explore the potential consequences and costs of multinucleation and its impacts on myonuclear transcriptional reserve capacity, growth potential, myofiber size regulation, and muscle adaptability. We anticipate this report will not only serve to highlight the latest advances in the basic biology of syncytial muscle cells but also provide information to help design the next generation of therapeutic strategies to maintain muscle mass and function.
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Affiliation(s)
- Vikram Prasad
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA
| | - Douglas P Millay
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA; Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH 45229, USA.
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11
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Hansson KA, Eftestøl E, Bruusgaard JC, Juvkam I, Cramer AW, Malthe-Sørenssen A, Millay DP, Gundersen K. Myonuclear content regulates cell size with similar scaling properties in mice and humans. Nat Commun 2020; 11:6288. [PMID: 33293572 PMCID: PMC7722898 DOI: 10.1038/s41467-020-20057-8] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Accepted: 10/30/2020] [Indexed: 12/12/2022] Open
Abstract
Muscle fibers are the largest cells in the body, and one of its few syncytia. Individual cell sizes are variable and adaptable, but what governs cell size has been unclear. We find that muscle fibers are DNA scarce compared to other cells, and that the nuclear number (N) adheres to the relationship N = aVb where V is the cytoplasmic volume. N invariably scales sublinearly to V (b < 1), making larger cells even more DNA scarce. N scales linearly to cell surface in adult humans, in adult and developing mice, and in mice with genetically reduced N, but in the latter the relationship eventually fails when they reach adulthood with extremely large myonuclear domains. Another exception is denervation-atrophy where nuclei are not eliminated. In conclusion, scaling exponents are remarkably similar across species, developmental stages and experimental conditions, suggesting an underlying scaling law where DNA-content functions as a limiter of muscle cell size.
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Affiliation(s)
- Kenth-Arne Hansson
- Department of Biosciences, University of Oslo, Oslo, Norway
- Center for Integrative Neuroplasticity, Department of Biosciences, University of Oslo, Oslo, Norway
| | - Einar Eftestøl
- Department of Biosciences, University of Oslo, Oslo, Norway
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, USA
| | - Jo C Bruusgaard
- Department of Biosciences, University of Oslo, Oslo, Norway
- Center for Integrative Neuroplasticity, Department of Biosciences, University of Oslo, Oslo, Norway
- Department of Health Sciences, Kristiania University College, Oslo, Norway
| | - Inga Juvkam
- Department of Biosciences, University of Oslo, Oslo, Norway
| | - Alyssa W Cramer
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, USA
| | - Anders Malthe-Sørenssen
- Center for Integrative Neuroplasticity, Department of Biosciences, University of Oslo, Oslo, Norway
- Department of Physics, University of Oslo, Oslo, Norway
| | - Douglas P Millay
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, USA
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, USA
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12
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Cramer AAW, Prasad V, Eftestøl E, Song T, Hansson KA, Dugdale HF, Sadayappan S, Ochala J, Gundersen K, Millay DP. Nuclear numbers in syncytial muscle fibers promote size but limit the development of larger myonuclear domains. Nat Commun 2020; 11:6287. [PMID: 33293533 PMCID: PMC7722938 DOI: 10.1038/s41467-020-20058-7] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Accepted: 10/30/2020] [Indexed: 12/11/2022] Open
Abstract
Mammalian cells exhibit remarkable diversity in cell size, but the factors that regulate establishment and maintenance of these sizes remain poorly understood. This is especially true for skeletal muscle, comprised of syncytial myofibers that each accrue hundreds of nuclei during development. Here, we directly explore the assumed causal relationship between multinucleation and establishment of normal size through titration of myonuclear numbers during mouse neonatal development. Three independent mouse models, where myonuclear numbers were reduced by 75, 55, or 25%, led to the discovery that myonuclei possess a reserve capacity to support larger functional cytoplasmic volumes in developing myofibers. Surprisingly, the results revealed an inverse relationship between nuclei numbers and reserve capacity. We propose that as myonuclear numbers increase, the range of transcriptional return on a per nuclear basis in myofibers diminishes, which accounts for both the absolute reliance developing myofibers have on nuclear accrual to establish size, and the limits of adaptability in adult skeletal muscle.
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Affiliation(s)
- Alyssa A W Cramer
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA
| | - Vikram Prasad
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA
| | - Einar Eftestøl
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA
- Department of Biosciences, University of Oslo, Oslo, Norway
| | - Taejeong Song
- Department of Internal Medicine, Division of Cardiovascular Health and Disease, University of Cincinnati College of Medicine, Cincinnati, OH, 45229, USA
| | - Kenth-Arne Hansson
- Department of Biosciences, University of Oslo, Oslo, Norway
- Center for Integrative Neuroplasticity (CINPLA), Department of Biosciences, University of Oslo, Oslo, Norway
| | - Hannah F Dugdale
- Center of Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | - Sakthivel Sadayappan
- Department of Internal Medicine, Division of Cardiovascular Health and Disease, University of Cincinnati College of Medicine, Cincinnati, OH, 45229, USA
| | - Julien Ochala
- Center of Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
- Randall Center for Cell and Molecular Biophysics, School of Basic & Medical Biosciences, Faculty of Life Sciences & Medicine, Guy's Campus, King's College London, London, UK
- Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
| | | | - Douglas P Millay
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA.
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, 45229, USA.
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13
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Computational Assessment of Transport Distances in Living Skeletal Muscle Fibers Studied In Situ. Biophys J 2020; 119:2166-2178. [PMID: 33121941 DOI: 10.1016/j.bpj.2020.10.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 09/10/2020] [Accepted: 10/07/2020] [Indexed: 11/22/2022] Open
Abstract
Transport distances in skeletal muscle fibers are mitigated by these cells having multiple nuclei. We have studied mouse living slow (soleus) and fast (extensor digitorum longus) muscle fibers in situ and determined cellular dimensions and the positions of all the nuclei within fiber segments. We modeled the effect of placing nuclei optimally and randomly using the nuclei as the origin of a transportation network. It appeared that an equidistant positioning of nuclei minimizes transport distances along the surface for both muscles. In the soleus muscle, however, which were richer in nuclei, positioning of nuclei to reduce transport distances to the cytoplasm were of less importance, and these fibers exhibit a pattern not statistically different from a random positioning of nuclei. We also simulated transport times for myoglobin and found that they were remarkably similar between the two muscles despite differences in nuclear patterning and distances. Together, these results highlight the importance of spatially distributed nuclei to minimize transport distances to the surface when nuclear density is low, whereas it appears that the distribution are of less importance at higher nuclear densities.
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14
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Beedour R, Ross JA, Levy Y, Ochala J. Effect of PGC1-beta ablation on myonuclear organisation. J Muscle Res Cell Motil 2019; 40:335-341. [PMID: 31485877 PMCID: PMC6831542 DOI: 10.1007/s10974-019-09549-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Skeletal muscle fibres are large, elongated multinucleated cells. Each nucleus within a myofibre is responsible for generating gene products for a finite volume of cytoplasm-the myonuclear domain (MND). Variation in MND sizes during atrophy, hypertrophy and disease states, are common. The factors that contribute to definitive MND sizes are not yet fully understood. Previous work has shown that peroxisome proliferator-activated receptor gamma coactivator 1α (PGC1-α) modulates MND volume, presumably to support increased biogenesis of mitochondria. The transcriptional co-regulator peroxisome proliferator-activated receptor gamma coactivator 1β (PGC1-β) is a homologue of PGC1-α with overlapping functions. To investigate the role of this protein in MND size regulation, we studied a mouse skeletal muscle specific knockout (cKO). Myofibres were isolated from the fast twitch extensor digitorum longus (EDL) muscle, membrane-permeabilised and analysed in 3 dimensions using confocal microscopy. PGC1-β ablation resulted in no significant difference in MND size between cKO and wild type (WT) mice, however, subtle differences in nuclear morphology were observed. To determine whether these nuclear shape changes were associated with alterations in global transcriptional activity, acetyl histone H3 immunostaining was carried out. We found there was no significant difference in nuclear fluorescence intensity between the two genotypes. Overall, the results suggest that PGC-1α and PGC-1β play different roles in regulating nuclear organisation in skeletal muscle; however, further work is required to pinpoint their exact functions.
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Affiliation(s)
- Ryan Beedour
- Faculty of Life Sciences & Medicine, School of Basic and Medical Biosciences, Centre of Human and Applied Physiological Sciences, King's College London, London, UK
| | - Jacob A Ross
- Faculty of Life Sciences & Medicine, School of Basic and Medical Biosciences, Centre of Human and Applied Physiological Sciences, King's College London, London, UK
| | - Yotam Levy
- Faculty of Life Sciences & Medicine, School of Basic and Medical Biosciences, Centre of Human and Applied Physiological Sciences, King's College London, London, UK
| | - Julien Ochala
- Faculty of Life Sciences & Medicine, School of Basic and Medical Biosciences, Centre of Human and Applied Physiological Sciences, King's College London, London, UK.
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15
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Vieira S, Moran E. Effects of egg of origin and chick post-hatch nutrition on broiler live performance and meat yields. WORLD POULTRY SCI J 2019. [DOI: 10.1079/wps19990009] [Citation(s) in RCA: 97] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- S.L. Vieira
- Departamento de Zootecnia, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 7712, C.P. 776, Porto Alegre 91501–970, Brazil
| | - E.T. Moran
- Department of Poultry Science, Auburn University, Auburn, Alabama 36849–5416, USA
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16
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Moffatt CB, Cohen-Fix O. The Multiple Ways Nuclei Scale on a Multinucleated Muscle Cell Scale. Dev Cell 2019; 49:3-5. [PMID: 30965034 PMCID: PMC6720106 DOI: 10.1016/j.devcel.2019.03.018] [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] [Indexed: 11/30/2022]
Abstract
In mononucleated cells, nuclear size scales with cell size, but does this relationship extend to multinucleated cells? In this issue of Developmental Cell,Windner et al. (2019) examine scaling of nuclei in multinucleated Drosophila muscle fibers and identify global and local cellular inputs that contribute to nuclear size regulation.
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Affiliation(s)
- Caitlin B Moffatt
- The Laboratory of Biochemistry and Genetics, The National Institute of Diabetes and Digestive and Kidney Diseases, The National Institutes of Health, Bethesda, MD 20892, USA
| | - Orna Cohen-Fix
- The Laboratory of Biochemistry and Genetics, The National Institute of Diabetes and Digestive and Kidney Diseases, The National Institutes of Health, Bethesda, MD 20892, USA.
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17
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Lee H, Kim K, Kim B, Shin J, Rajan S, Wu J, Chen X, Brown MD, Lee S, Park JY. A cellular mechanism of muscle memory facilitates mitochondrial remodelling following resistance training. J Physiol 2018; 596:4413-4426. [PMID: 30099751 DOI: 10.1113/jp275308] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2018] [Accepted: 04/23/2018] [Indexed: 12/18/2022] Open
Abstract
KEY POINTS Referring to the muscle memory theory, previously trained muscles acquire strength and volume much faster than naive muscles. Using extreme experimental models such as synergist ablation or steroid administration, previous studies have demonstrated that the number of nuclei increases when a muscle becomes enlarged, which serves as a cellular muscle memory mechanism for the muscle. In the present study, we found that, when rats were subjected to physiologically relevant resistance training, the number of myonuclei increased and was retained during a long-term detraining period. The acquired myonuclei were related to a greater degree of muscle hypertrophic and mitochondrial biogenesis processes following subsequent hypertrophic conditions. Our data suggest a cellular mechanism supporting the notion that exposing young muscles to resistance training would help to restore age-related muscle loss coupled with mitochondrial dysfunction in later life. ABSTRACT Muscle hypertrophy induced by resistance training is accompanied by an increase in the number of myonuclei. The acquired myonuclei are viewed as a cellular component of muscle memory by which muscle enlargement is promoted during a re-training period. In the present study, we investigated the effect of exercise preconditioning on mitochondrial remodelling induced by resistance training. Sprague-Dawley rats were divided into four groups: untrained control, training, pre-training or re-training. The training groups were subjected to weight loaded-ladder climbing exercise training. Myonuclear numbers were significantly greater (up to 20%) in all trained muscles compared to untrained controls. Muscle mass was significantly higher in the re-training group compared to the training group (∼2-fold increase). Mitochondrial content, mitochondrial biogenesis gene expression levels and mitochondrial DNA copy numbers were significantly higher in re-trained muscles compared to the others. Oxidative myofibres (type I) were significantly increased only in the re-trained muscles. Furthermore, in vitro studies using insulin-like growth factor-1-treated L6 rat myotubes demonstrated that myotubes with a higher myonuclear number confer greater expression levels of both mitochondrial and nuclear genes encoding for constitutive and regulatory mitochondrial proteins, which also showed a greater mitochondrial respiratory function. These data suggest that myonuclei acquired from previous training facilitate mitochondrial biogenesis in response to subsequent retraining by (at least in part) enhancing cross-talk between mitochondria and myonuclei in the pre-conditioned myofibres.
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Affiliation(s)
- Hojun Lee
- Department of Kinesiology, College of Public Health, Temple University, Philadelphia, PA, USA.,Cardiovascular Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA.,School of Sports and Health Science, Kyungsung University, Busan, South Korea.,Mechanical & Molecular Myology Lab, Department of Rehabilitation Medicine and College of Medicine, Seoul National University, Bundang Hospital, Seongnam, South Korea
| | - Kijeong Kim
- School of Exercise and Sport Science, University of Ulsan, Ulsan, South Korea
| | - Boa Kim
- Department of Kinesiology, College of Public Health, Temple University, Philadelphia, PA, USA.,Cardiovascular Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA
| | - Junchul Shin
- Department of Kinesiology, College of Public Health, Temple University, Philadelphia, PA, USA.,Cardiovascular Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA
| | - Sudarsan Rajan
- Center for Translational Medicine, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA
| | - Jingwei Wu
- Department of Epidemiology and Biostatistics, College of Public Health, Temple University, Philadelphia, PA, USA
| | - Xiongwen Chen
- Cardiovascular Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA
| | | | - Sukho Lee
- Department of Counseling, Health and Kinesiology, Texas A&M University-San Antonio, San Antonio, TX, USA
| | - Joon-Young Park
- Department of Kinesiology, College of Public Health, Temple University, Philadelphia, PA, USA.,Cardiovascular Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, USA
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18
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Ross JA, Levy Y, Svensson K, Philp A, Schenk S, Ochala J. SIRT1 regulates nuclear number and domain size in skeletal muscle fibers. J Cell Physiol 2018; 233:7157-7163. [PMID: 29574748 PMCID: PMC5993587 DOI: 10.1002/jcp.26542] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 02/12/2018] [Indexed: 12/16/2022]
Abstract
Skeletal muscle fibers are giant multinucleated cells wherein individual nuclei govern the protein synthesis in a finite volume of cytoplasm; this is termed the myonuclear domain (MND). The factors that control MND size remain to be defined. In the present study, we studied the contribution of the NAD+‐dependent deacetylase, sirtuin 1 (SIRT1), to the regulation of nuclear number and MND size. For this, we isolated myofibers from mice with tissue‐specific inactivation (mKO) or inducible overexpression (imOX) of SIRT1 and analyzed the 3D organisation of myonuclei. In imOX mice, the number of nuclei was increased whilst the average MND size was decreased as compared to littermate controls. Our findings were the opposite in mKO mice. Muscle stem cell (satellite cell) numbers were reduced in mKO muscles, a possible explanation for the lower density of myonuclei in these mice; however, no change was observed in imOX mice, suggesting that other factors might also be involved, such as the functional regulation of stem cells/muscle precursors. Interestingly, however, the changes in the MND volume did not impact the force‐generating capacity of muscle fibers. Taken together, our results demonstrate that SIRT1 is a key regulator of MND sizes, although the underlying molecular mechanisms and the cause‐effect relationship between MND and muscle function remain to be fully defined.
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Affiliation(s)
- Jacob A Ross
- School of Basic and Medical Biosciences, Faculty of Life Sciences and Medicine, King's College London, London, UK
| | - Yotam Levy
- School of Basic and Medical Biosciences, Faculty of Life Sciences and Medicine, King's College London, London, UK
| | - Kristoffer Svensson
- Department of Orthopaedic Surgery, University of California San Diego, La Jolla, California.,Biomedical Sciences Graduate Program, University of California San Diego, La Jolla, California
| | - Andrew Philp
- School of Sport and Exercise Sciences, University of Birmingham, Birmingham, UK
| | - Simon Schenk
- Department of Orthopaedic Surgery, University of California San Diego, La Jolla, California.,Biomedical Sciences Graduate Program, University of California San Diego, La Jolla, California
| | - Julien Ochala
- School of Basic and Medical Biosciences, Faculty of Life Sciences and Medicine, King's College London, London, UK
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19
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Cheng MA, Farmer E, Huang C, Lin J, Hung CF, Wu TC. Therapeutic DNA Vaccines for Human Papillomavirus and Associated Diseases. Hum Gene Ther 2018; 29:971-996. [PMID: 29316817 DOI: 10.1089/hum.2017.197] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Human papillomavirus (HPV) has long been recognized as the causative agent of cervical cancer. High-risk HPV types 16 and 18 alone are responsible for over 70% of all cases of cervical cancers. More recently, HPV has been identified as an etiological factor for several other forms of cancers, including oropharyngeal, anogenital, and skin. Thus, the association of HPV with these malignancies creates an opportunity to control these HPV lesions and HPV-associated malignancies through immunization. Strategies to prevent or to therapeutically treat HPV infections have been developed and are still pushing innovative boundaries. Currently, commercial prophylactic HPV vaccines are widely available, but they are not able to control established infections or lesions. As a result, there is an urgent need for the development of therapeutic HPV vaccines, to treat existing infections, and to prevent the development of HPV-associated cancers. In particular, DNA vaccination has emerged as a promising form of therapeutic HPV vaccine. DNA vaccines have great potential for the treatment of HPV infections and HPV-associated cancers due to their safety, stability, simplicity of manufacturability, and ability to induce antigen-specific immunity. This review focuses on the current state of therapeutic HPV DNA vaccines, including results from recent and ongoing clinical trials, and outlines different strategies that have been employed to improve their potencies. The continued progress and improvements made in therapeutic HPV DNA vaccine development holds great potential for innovative ways to effectively treat HPV infections and HPV-associated diseases.
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Affiliation(s)
- Max A Cheng
- 1 Department of Pathology, Johns Hopkins Medical Institutions , Baltimore, Maryland
| | - Emily Farmer
- 1 Department of Pathology, Johns Hopkins Medical Institutions , Baltimore, Maryland
| | - Claire Huang
- 1 Department of Pathology, Johns Hopkins Medical Institutions , Baltimore, Maryland
| | - John Lin
- 1 Department of Pathology, Johns Hopkins Medical Institutions , Baltimore, Maryland
| | - Chien-Fu Hung
- 1 Department of Pathology, Johns Hopkins Medical Institutions , Baltimore, Maryland.,2 Department of Oncology, Johns Hopkins Medical Institutions , Baltimore, Maryland
| | - T-C Wu
- 1 Department of Pathology, Johns Hopkins Medical Institutions , Baltimore, Maryland.,2 Department of Oncology, Johns Hopkins Medical Institutions , Baltimore, Maryland.,3 Department of Obstetrics and Gynecology, Johns Hopkins Medical Institutions , Baltimore, Maryland.,4 Department of Molecular Microbiology and Immunology, Johns Hopkins Medical Institutions , Baltimore, Maryland
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20
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Egner IM, Bruusgaard JC, Gundersen K. Satellite cell depletion prevents fiber hypertrophy in skeletal muscle. Development 2017; 143:2898-906. [PMID: 27531949 DOI: 10.1242/dev.134411] [Citation(s) in RCA: 142] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 06/28/2016] [Indexed: 12/18/2022]
Abstract
The largest mammalian cells are the muscle fibers, and they have multiple nuclei to support their large cytoplasmic volumes. During hypertrophic growth, new myonuclei are recruited from satellite stem cells into the fiber syncytia, but it was recently suggested that such recruitment is not obligatory: overload hypertrophy after synergist ablation of the plantaris muscle appeared normal in transgenic mice in which most of the satellite cells were abolished. When we essentially repeated these experiments analyzing the muscles by immunohistochemistry and in vivo and ex vivo imaging, we found that overload hypertrophy was prevented in the satellite cell-deficient mice, in both the plantaris and the extensor digitorum longus muscles. We attribute the previous findings to a reliance on muscle mass as a proxy for fiber hypertrophy, and to the inclusion of a significant number of regenerating fibers in the analysis. We discuss that there is currently no model in which functional, sustainable hypertrophy has been unequivocally demonstrated in the absence of satellite cells; an exception is re-growth, which can occur using previously recruited myonuclei without addition of new myonuclei.
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Affiliation(s)
- Ingrid M Egner
- Department of Biosciences, University of Oslo, Blindern, Oslo N-0316, Norway
| | - Jo C Bruusgaard
- Department of Biosciences, University of Oslo, Blindern, Oslo N-0316, Norway Department of Health Sciences, Kristiania University College, P.O. Box 1190, Sentrum, Oslo N-0107, Norway
| | - Kristian Gundersen
- Department of Biosciences, University of Oslo, Blindern, Oslo N-0316, Norway
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21
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Zhang M, Gould M. Segmental Distribution of Myosin Heavy Chain Isoforms Within Single Muscle Fibers. Anat Rec (Hoboken) 2017; 300:1636-1642. [DOI: 10.1002/ar.23578] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2016] [Accepted: 10/06/2016] [Indexed: 11/08/2022]
Affiliation(s)
- Ming Zhang
- Anatomy Department; University of Otago; Dunedin 9054 New Zealand
| | - Maree Gould
- Anatomy Department; University of Otago; Dunedin 9054 New Zealand
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22
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Ross JA, Pearson A, Levy Y, Cardel B, Handschin C, Ochala J. Exploring the Role of PGC-1α in Defining Nuclear Organisation in Skeletal Muscle Fibres. J Cell Physiol 2016; 232:1270-1274. [PMID: 27861863 DOI: 10.1002/jcp.25678] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Accepted: 11/03/2016] [Indexed: 12/16/2022]
Abstract
Muscle fibres are multinucleated cells, with each nucleus controlling the protein synthesis in a finite volume of cytoplasm termed the myonuclear domain (MND). What determines MND size remains unclear. In the present study, we aimed to test the hypothesis that the level of expression of the transcriptional coactivator PGC-1α and subsequent activation of the mitochondrial biogenesis are major contributors. Hence, we used two transgenic mouse models with varying expression of PGC-1α in skeletal muscles. We isolated myofibres from the fast twitch extensor digitorum longus (EDL) and slow twitch diaphragm muscles. We then membrane-permeabilised them and analysed the 3D spatial arrangements of myonuclei. In EDL muscles, when PGC-1α is over-expressed, MND volume decreases; whereas, when PGC-1α is lacking, no change occurs. In the diaphragm, no clear difference was noted. This indicates that PGC-1α and the related mitochondrial biogenesis programme are determinants of MND size. PGC-1α may facilitate the addition of new myonuclei in order to reach MND volumes that can support an increased mitochondrial density. J. Cell. Physiol. 232: 1270-1274, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Jacob A Ross
- Centre of Human and Aerospace Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | - Adam Pearson
- Centre of Human and Aerospace Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | - Yotam Levy
- Centre of Human and Aerospace Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | | | | | - Julien Ochala
- Centre of Human and Aerospace Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
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23
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Gundersen K. Muscle memory and a new cellular model for muscle atrophy and hypertrophy. ACTA ACUST UNITED AC 2016; 219:235-42. [PMID: 26792335 DOI: 10.1242/jeb.124495] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Memory is a process in which information is encoded, stored, and retrieved. For vertebrates, the modern view has been that it occurs only in the brain. This review describes a cellular memory in skeletal muscle in which hypertrophy is 'remembered' such that a fibre that has previously been large, but subsequently lost its mass, can regain mass faster than naive fibres. A new cell biological model based on the literature, with the most reliable methods for identifying myonuclei, can explain this phenomenon. According to this model, previously untrained fibres recruit myonuclei from activated satellite cells before hypertrophic growth. Even if subsequently subjected to grave atrophy, the higher number of myonuclei is retained, and the myonuclei seem to be protected against the elevated apoptotic activity observed in atrophying muscle tissue. Fibres that have acquired a higher number of myonuclei grow faster when subjected to overload exercise, thus the nuclei represent a functionally important 'memory' of previous strength. This memory might be very long lasting in humans, as myonuclei are stable for at least 15 years and might even be permanent. However, myonuclei are harder to recruit in the elderly, and if the long-lasting muscle memory also exists in humans, one should consider early strength training as a public health advice. In addition, myonuclei are recruited during steroid use and encode a muscle memory, at least in rodents. Thus, extending the exclusion time for doping offenders should be considered.
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Affiliation(s)
- Kristian Gundersen
- Department of Biosciences, University of Oslo, Blindernveien 31, Oslo N0316, Norway
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24
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Adams GR, Bamman MM. Characterization and regulation of mechanical loading-induced compensatory muscle hypertrophy. Compr Physiol 2013; 2:2829-70. [PMID: 23720267 DOI: 10.1002/cphy.c110066] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
In mammalian systems, skeletal muscle exists in a dynamic state that monitors and regulates the physiological investment in muscle size to meet the current level of functional demand. This review attempts to consolidate current knowledge concerning development of the compensatory hypertrophy that occurs in response to a sustained increase in the mechanical loading of skeletal muscle. Topics covered include: defining and measuring compensatory hypertrophy, experimental models, loading stimulus parameters, acute responses to increased loading, hyperplasia, myofiber-type adaptations, the involvement of satellite cells, mRNA translational control, mechanotransduction, and endocrinology. The authors conclude with their impressions of current knowledge gaps in the field that are ripe for future study.
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Affiliation(s)
- Gregory R Adams
- Department of Physiology and Biophysics, University of California Irvine, Irvine, California, USA.
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25
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Nevalainen M, Kaakinen M, Metsikkö K. Distribution of mRNA transcripts and translation activity in skeletal myofibers. Cell Tissue Res 2013; 353:539-48. [PMID: 23736382 DOI: 10.1007/s00441-013-1659-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Accepted: 05/06/2013] [Indexed: 01/26/2023]
Abstract
We examine the distribution of gene products in skeletal myofibers, which are highly differentiated multinucleated cells exhibiting a specific cellular architecture. In situ hybridization studies of adult rat myofibers with a single nucleus infected with influenza virus suggested that the viral mRNA products were distributed beneath the sarcolemma around the nucleus of origin. In situ hybridization studies with a poly-T oligonucleotide probe to detect endogenous mRNAs indicated their concentration around the nuclei and distribution beneath the sarcolemma in a cross-striated fashion at the A-I junctions (costamers). Labeling with bromouridine resulted in a similar distribution pattern. The ribosomal distribution pattern indicated concentration around the myonuclei but an intracellular component was also seen. Localization of the translating ribosomes by puromycylation revealed prominent spots perinuclearly and in the core regions of the myofibers. These spots flanked Golgi elements. Our results thus suggest that the total mRNA pool is heavily concentrated within the perinuclear and subsarcolemmal regions. However, the ribosomes and the translational activity did not follow this distribution pattern, so the mRNA transcripts were not restricted to a region beneath the sarcolemma. Furthermore, experiments utilizing green fluorescent protein showed the rapid movement of proteins within the endomembrane system, which thus facilitated proteins to reach their site of function irrespective of the site of synthesis.
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Affiliation(s)
- Mika Nevalainen
- Department of Anatomy and Cell Biology, Institute of Biomedicine, University of Oulu, P.O. Box 5000, Aapistie 7, FI-90014, Oulu, Finland.
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26
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Kocha KM, Genge CE, Moyes CD. Origins of interspecies variation in mammalian muscle metabolic enzymes. Physiol Genomics 2011; 43:873-83. [PMID: 21586671 DOI: 10.1152/physiolgenomics.00025.2011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Do the transcriptional mechanisms that control an individual's mitochondrial content, PGC1α (peroxisome proliferator-activated receptor γ coactivator-1α) and NRF1 (nuclear respiratory factor-1), also cause differences between species? We explored the determinants of cytochrome c oxidase (COX) activities in muscles from 12 rodents differing 1,000-fold in mass. Hindlimb muscles differed in scaling patterns from isometric (soleus, gastrocnemius) to allometric (tibialis anterior, scaling coefficient = -0.16). Consideration of myonuclear domain reduced the differences within species, but interspecies differences remained. For tibialis anterior, there was no significant scaling relationship in mRNA/g for COX4-1, PGC1α, or NRF1, yet COX4-1 mRNA/g was a good predictor of COX activity (r(2) = 0.55), PGC1α and NRF1 mRNA correlated with each other (r(2) = 0.42), and both could predict COX4-1 mRNA (r(2) = 0.48 and 0.52) and COX activity (r(2) = 0.55 and 0.49). This paradox was resolved by multivariate analysis, which explained 90% of interspecies variation, about equally partitioned between mass effects and PGC1α (or NRF1) mRNA levels, independent of mass. To explore the determinants of PGC1α mRNA, we analyzed 52 mammalian PGC1α proximal promoters and found no size dependence in regulatory element distribution. Likewise, the activity of PGC1α promoter reporter genes from 30 mammals showed no significant relationship with body mass. Collectively, these studies suggest that not all muscles scale equivalently, but for those that show allometric scaling, transcriptional regulation of the master regulators, PGC1α and NRF1, does not account for scaling patterns, though it does contribute to interspecies differences in COX activities independent of mass.
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Affiliation(s)
- K M Kocha
- Department of Biology, Queen's University, Kingston, Ontario, Canada
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27
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Skuk D, Tremblay JP. Intramuscular cell transplantation as a potential treatment of myopathies: clinical and preclinical relevant data. Expert Opin Biol Ther 2011; 11:359-74. [PMID: 21204740 DOI: 10.1517/14712598.2011.548800] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
INTRODUCTION Myopathies produce deficits in skeletal muscle function and, in some cases, literally progressive loss of skeletal muscles. The transplantation of cells able to differentiate into myofibers is an experimental strategy for the potential treatment of some of these diseases. AREAS COVERED Among the two routes used to deliver cells to skeletal muscles, that is intramuscular and intravascular, this paper focuses on the intramuscular route due to our expertise and because it is the most used in animal experiments and the only tested so far in humans. Given the absence of recent reviews about clinical observations and the profusion based on mouse results, this review prioritizes observations made in humans and non-human primates. The review provides a vision of cell transplantation in myology centered on what can be learned from clinical trials and from preclinical studies in non-human primates and leading mouse studies. EXPERT OPINION Experiments on myogenic cell transplantation in mice are essential to quickly identify potential treatments, but studies showing the possibility to scale up the methods in large mammals are indispensable to determine their applicability in humans and to design clinical protocols.
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Affiliation(s)
- Daniel Skuk
- CHUQ Research Center - CHUL, Neurosciences Division - Human Genetics, 2705 Boulevard Laurier, Quebec, Quebec G1V 4G2, Canada.
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28
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Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining. Proc Natl Acad Sci U S A 2010; 107:15111-6. [PMID: 20713720 DOI: 10.1073/pnas.0913935107] [Citation(s) in RCA: 206] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Effects of previous strength training can be long-lived, even after prolonged subsequent inactivity, and retraining is facilitated by a previous training episode. Traditionally, such "muscle memory" has been attributed to neural factors in the absence of any identified local memory mechanism in the muscle tissue. We have used in vivo imaging techniques to study live myonuclei belonging to distinct muscle fibers and observe that new myonuclei are added before any major increase in size during overload. The old and newly acquired nuclei are retained during severe atrophy caused by subsequent denervation lasting for a considerable period of the animal's lifespan. The myonuclei seem to be protected from the high apoptotic activity found in inactive muscle tissue. A hypertrophy episode leading to a lasting elevated number of myonuclei retarded disuse atrophy, and the nuclei could serve as a cell biological substrate for such memory. Because the ability to create myonuclei is impaired in the elderly, individuals may benefit from strength training at an early age, and because anabolic steroids facilitate more myonuclei, nuclear permanency may also have implications for exclusion periods after a doping offense.
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29
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van Gemert AMC, van der Laan AMA, Pilgram GSK, Fradkin LG, Noordermeer JN, Tanke HJ, Jost CR. In vivo monitoring of mRNA movement in Drosophila body wall muscle cells reveals the presence of myofiber domains. PLoS One 2009; 4:e6663. [PMID: 19684860 PMCID: PMC2722729 DOI: 10.1371/journal.pone.0006663] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2009] [Accepted: 07/06/2009] [Indexed: 01/31/2023] Open
Abstract
BACKGROUND In skeletal muscle each muscle cell, commonly called myofiber, is actually a large syncytium containing numerous nuclei. Experiments in fixed myofibers show that mRNAs remain localized around the nuclei in which they are produced. METHODOLOGY/PRINCIPAL FINDINGS In this study we generated transgenic flies that allowed us to investigate the movement of mRNAs in body wall myofibers of living Drosophila embryos. We determined the dynamic properties of GFP-tagged mRNAs using in vivo confocal imaging and photobleaching techniques and found that the GFP-tagged mRNAs are not free to move throughout myofibers. The restricted movement indicated that body wall myofibers consist of three domains. The exchange of mRNAs between the domains is relatively slow, but the GFP-tagged mRNAs move rapidly within these domains. One domain is located at the centre of the cell and is surrounded by nuclei while the other two domains are located at either end of the fiber. To move between these domains mRNAs have to travel past centrally located nuclei. CONCLUSIONS/SIGNIFICANCE These data suggest that the domains made visible in our experiments result from prolonged interactions with as yet undefined structures close to the nuclei that prevent GFP-tagged mRNAs from rapidly moving between the domains. This could be of significant importance for the treatment of myopathies using regenerative cell-based therapies.
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Affiliation(s)
- Alice M. C. van Gemert
- Laboratory of Gene Expression and Imaging, Department of Molecular Cell Biology, Leiden University Medical C, Leiden, The Netherlands
| | - Annelies M. A. van der Laan
- Laboratory of Gene Expression and Imaging, Department of Molecular Cell Biology, Leiden University Medical C, Leiden, The Netherlands
| | - Gonneke S. K. Pilgram
- Laboratory of Developmental Neurobiology, Department of Molecular Cell Biology, Leiden University Medical C, Leiden, The Netherlands
| | - Lee G. Fradkin
- Laboratory of Developmental Neurobiology, Department of Molecular Cell Biology, Leiden University Medical C, Leiden, The Netherlands
| | - Jasprina N. Noordermeer
- Laboratory of Developmental Neurobiology, Department of Molecular Cell Biology, Leiden University Medical C, Leiden, The Netherlands
| | - Hans J. Tanke
- Laboratory of Gene Expression and Imaging, Department of Molecular Cell Biology, Leiden University Medical C, Leiden, The Netherlands
| | - Carolina R. Jost
- Laboratory of Gene Expression and Imaging, Department of Molecular Cell Biology, Leiden University Medical C, Leiden, The Netherlands
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Liu JX, Höglund AS, Karlsson P, Lindblad J, Qaisar R, Aare S, Bengtsson E, Larsson L. Myonuclear domain size and myosin isoform expression in muscle fibres from mammals representing a 100 000-fold difference in body size. Exp Physiol 2008; 94:117-29. [DOI: 10.1113/expphysiol.2008.043877] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Abstract
Satellite cells are small, mononuclear cells found in close association with striated skeletal muscles cells (myofibers). These cells appear to function as reserve myoblasts. A critical role for these cells in the process of muscle regeneration following injury has been clearly established. In that role, satellite cells have been shown to proliferate extensively. Some of the progeny of these cells then fuse with each other to form replacement myofibers, whereas others return to quiescence, thereby maintaining this reserve population. In response to injury, activated satellite cells can also fuse with damaged but viable myofibers to promote repair and regeneration. It has also been observed that satellite cells are activated during periods of significantly increased muscle loading and that some of these cells fuse with apparently undamaged myofibers as part of the hypertrophy process. The observation that the inactivation of satellite cell proliferation prevents most of the hypertrophy response to chronic increases in loading has lead to the hypothesis that a limitation to the expansion of myofiber size is imposed by the number of myonuclei present. Recent evidence suggests that a potential limitation to muscle hypertrophy, in the absence of a reserve supply of myonuclei, may be the inability to sustain increases in ribosomes, thereby limiting translational capacity.
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Affiliation(s)
- Gregory R Adams
- Department of Physiology and Biophysics, Medical Science I D335, University of California, Irvine, CA 92697, USA.
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Abstract
Myoblast transplantation (MT) is an experimental strategy for the potential treatment of myopathies. MT has two properties that make it potentially beneficial: genetic complementation and myogenic potential. Preclinical experiments on monkeys have shown that promising results can be obtained with MT in large muscles of primates depending on two conditions: appropriate immunosuppression and cell delivery by a method of high-density injections. Preclinical work on MT is being, or may be, addressed to: develop efficient methods of donor cell delivery applicable to clinics; control or avoid acute rejection by methods with the fewest secondary effects; understand the factors that condition the early survival of donor cells following transplantation; increase the success of each individual injection; re-engineer a functional structure in muscles that degenerates to fibrosis and fat substitution; and search for precursor cells with potential advantages over myoblasts.
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Affiliation(s)
- Daniel Skuk
- Centre de recherche du Centre hospitalier de l'Université Laval, Unité de recherche en Génétique humaine, CHUL du CHUQ, 2705, Boulevard Laurier, Québec, Canada.
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Baluska F, Volkmann D, Barlow PW. Eukaryotic cells and their cell bodies: Cell Theory revised. ANNALS OF BOTANY 2004; 94:9-32. [PMID: 15155376 PMCID: PMC4242365 DOI: 10.1093/aob/mch109] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
BACKGROUND Cell Theory, also known as cell doctrine, states that all eukaryotic organisms are composed of cells, and that cells are the smallest independent units of life. This Cell Theory has been influential in shaping the biological sciences ever since, in 1838/1839, the botanist Matthias Schleiden and the zoologist Theodore Schwann stated the principle that cells represent the elements from which all plant and animal tissues are constructed. Some 20 years later, in a famous aphorism Omnis cellula e cellula, Rudolf Virchow annunciated that all cells arise only from pre-existing cells. General acceptance of Cell Theory was finally possible only when the cellular nature of brain tissues was confirmed at the end of the 20th century. Cell Theory then rapidly turned into a more dogmatic cell doctrine, and in this form survives up to the present day. In its current version, however, the generalized Cell Theory developed for both animals and plants is unable to accommodate the supracellular nature of higher plants, which is founded upon a super-symplasm of interconnected cells into which is woven apoplasm, symplasm and super-apoplasm. Furthermore, there are numerous examples of multinucleate coenocytes and syncytia found throughout the eukaryote superkingdom posing serious problems for the current version of Cell Theory. SCOPE To cope with these problems, we here review data which conform to the original proposal of Daniel Mazia that the eukaryotic cell is composed of an elemental Cell Body whose structure is smaller than the cell and which is endowed with all the basic attributes of a living entity. A complement to the Cell Body is the Cell Periphery Apparatus, which consists of the plasma membrane associated with other periphery structures. Importantly, boundary structures of the Cell Periphery Apparatus, although capable of some self-assembly, are largely produced and maintained by Cell Body activities and can be produced from it de novo. These boundary structures serve not only as mechanical support for the Cell Bodies but they also protect them from the hostile external environment and from inappropriate interactions with adjacent Cell Bodies within the organism. CONCLUSIONS From the evolutionary perspective, Cell Bodies of eukaryotes are proposed to represent vestiges of hypothetical, tubulin-based 'guest' proto-cells. After penetrating the equally hypothetical actin-based 'host' proto-cells, tubulin-based 'guests' became specialized for transcribing, storing and partitioning DNA molecules via the organization of microtubules. The Cell Periphery Apparatus, on the other hand, represents vestiges of the actin-based 'host' proto-cells which have become specialized for Cell Body protection, shape control, motility and for actin-mediated signalling across the plasma membrane.
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Affiliation(s)
- Frantisek Baluska
- Institute of Cellular and Molecular Botany, University of Bonn, Kirschallee 1, 53175 Bonn, Germany.
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Bruusgaard JC, Liestøl K, Ekmark M, Kollstad K, Gundersen K. Number and spatial distribution of nuclei in the muscle fibres of normal mice studied in vivo. J Physiol 2003; 551:467-78. [PMID: 12813146 PMCID: PMC2343230 DOI: 10.1113/jphysiol.2003.045328] [Citation(s) in RCA: 173] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
We present here a new technique with which to visualize nuclei in living muscle fibres in the intact animal, involving injection of labelled DNA into single cells. This approach allowed us to determine the position of all of nuclei within a sarcolemma without labelling satellite cells. In contrast to what has been reported in tissue culture, we found that the nuclei were immobile, even when observed over several days. Nucleic density was uniform along the fibre except for the endplate and some myotendinous junctions, where the density was higher. The perijunctional region had the same number of nuclei as the rest of the fibre. In the extensor digitorum longus (EDL) muscle, the extrajunctional nuclei were elongated and precisely aligned to the long axis of the fibre. In the soleus, the nuclei were rounder and not well aligned. When comparing small and large fibres in the soleus, the number of nuclei varied approximately in proportion to cytoplasmic volume, while in the EDL the number was proportional to surface area. Statistical analysis revealed that the nuclei were not randomly distributed in either the EDL or the soleus. For each fibre, actual distributions were compared with computer simulations in which nuclei were assumed to repel each other, which optimizes the distribution of nuclei with respect to minimizing transport distances. The simulated patterns were regular, with clear row-like structures when the density of nuclei was low. The non-random and often row-like distribution of nuclei observed in muscle fibres may thus reflect regulatory mechanisms whereby nuclei repel each other in order to minimize transport distances.
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Affiliation(s)
- J C Bruusgaard
- Department of Biology, University of Oslo, Blindern, Norway
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35
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Adams GR, Caiozzo VJ, Haddad F, Baldwin KM. Cellular and molecular responses to increased skeletal muscle loading after irradiation. Am J Physiol Cell Physiol 2002; 283:C1182-95. [PMID: 12225982 DOI: 10.1152/ajpcell.00173.2002] [Citation(s) in RCA: 150] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Irradiation of rat skeletal muscles before increased loading has been shown to prevent compensatory hypertrophy for periods of up to 4 wk, possibly by preventing satellite cells from proliferating and providing new myonuclei. Recent work suggested that stem cell populations exist that might allow irradiated muscles to eventually hypertrophy over time. We report that irradiation essentially prevented hypertrophy in rat muscles subjected to 3 mo of functional overload (OL-Ir). The time course and magnitude of changes in cellular and molecular markers of anabolic and myogenic responses were similar in the OL-Ir and the contralateral nonirradiated, overloaded (OL) muscles for the first 3-7 days. These markers then returned to control levels in OL-Ir muscles while remaining elevated in OL muscles. The number of myonuclei and amount of DNA were increased markedly in OL but not OL-Ir muscles. Thus it appears that stem cells were not added to the irradiated muscles in this time period. These data are consistent with the theory that the addition of new myonuclei may be required for compensatory hypertrophy in the rat.
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Affiliation(s)
- Gregory R Adams
- Department of Physiology and Biophysics, Medical Sciences IC308, College of Medicine, University of California, Irvine, CA 92697, USA.
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36
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Schulze PC, Gielen S, Schuler G, Hambrecht R. Chronic heart failure and skeletal muscle catabolism: effects of exercise training. Int J Cardiol 2002; 85:141-9. [PMID: 12163219 DOI: 10.1016/s0167-5273(02)00243-7] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Although the clinical picture of cardiac cachexia is well-known in patients with advanced chronic heart failure (CHF) the factors that determine who is at risk for this progressive catabolic syndrome and who is not remain unclear. Different endocrine systems have been accused of being involved in this process: an imbalance between catabolic and anabolic steroids with an elevated cortisol/dihydroepiandrosterone ratio, an increased resting metabolic rate due to high levels of circulating catecholamines, various cytokines are activated in CHF (i.e. TNF-alpha, IL-6, IL-1beta and others), and elevated levels of growth hormone (GH) with inappropriately normal or low serum levels of insulin-like growth factor-I (IGF-I) have been described in cardiac cachexia. These catabolic factors contribute to peripheral muscle atrophy, augment the expression of the inducible nitric oxide synthase (iNOS), which in turn inhibits the aerobic cellular metabolism. The present review examines whether the catabolic factors can be influenced by a classical anabolic intervention: regular physical exercise training. Long-term training programs increase skeletal muscle cytochrome c oxidase activity and are associated with reduced local expression of pro-inflammatory cytokines as well as iNOS, and augment local IGF-I production. In concert, these beneficial effects of exercise training may help to retard the catabolic process in CHF finally leading to cardiac cachexia and death.
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Affiliation(s)
- Paul Christian Schulze
- Universität Leipzig, Herzzentrum GmbH, Klinik für Innere Medizin/Kardiologie, Russenstr. 19, 04289 Leipzig, Germany
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37
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Wilkins JT, Krivickas LS, Goldstein R, Suh D, Frontera WR. Contractile properties of adjacent segments of single human muscle fibers. Muscle Nerve 2001; 24:1319-26. [PMID: 11562911 DOI: 10.1002/mus.1150] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
A comparison of the contractile properties of adjacent segments of single human muscle fibers may help to explain the interaction among nuclear domains within the myofiber. Biopsy samples were obtained from the vastus lateralis muscle of 20 healthy untrained women (age 18-79 years). Single fibers (n = 38) were dissected and cut into halves (segments A and B). Segment diameter and depth were measured using an image analysis system. Maximal force (Po) was recorded during activation with calcium (pCa 4.5). Maximal unloaded shortening velocity (Vo) was calculated using the slack test. Myosin heavy chain (MyHC) expression was determined using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). A significant difference ( approximately 7%) in Po was seen between adjacent segments expressing type I MyHC that could not be attributed to differences in fiber size. Significant differences were observed in Vo even after adjusting for fiber type. A positive correlation was seen in Po (concordance coefficient Rho_C = 0.803) and Vo (Rho_C = 0.690) between segments, but concordance was less than perfect in both cases. Possible explanations for nonuniformity of contractile properties include random variations in physiological systems or variability of protein expression among nuclear domains.
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Affiliation(s)
- J T Wilkins
- Department of Physical Medicine and Rehabilitation, Harvard Medical School and Spaulding Rehabilitation Hospital, 125 Nashua Street, Boston, Massachusetts 02114, USA
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38
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Mozdziak PE, Pulvermacher PM, Schultz E. Muscle regeneration during hindlimb unloading results in a reduction in muscle size after reloading. J Appl Physiol (1985) 2001; 91:183-90. [PMID: 11408429 DOI: 10.1152/jappl.2001.91.1.183] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The hindlimb-unloading model was used to study the ability of muscle injured in a weightless environment to recover after reloading. Satellite cell mitotic activity and DNA unit size were determined in injured and intact soleus muscles from hindlimb-unloaded and age-matched weight-bearing rats at the conclusion of 28 days of hindlimb unloading, 2 wk after reloading, and 9 wk after reloading. The body weights of hindlimb-unloaded rats were significantly (P < 0.05) less than those of weight-bearing rats at the conclusion of hindlimb unloading, but they were the same (P > 0.05) as those of weight-bearing rats 2 and 9 wk after reloading. The soleus muscle weight, soleus muscle weight-to-body weight ratio, myofiber diameter, number of nuclei per millimeter, and DNA unit size were significantly (P < 0.05) smaller for the injured soleus muscles from hindlimb-unloaded rats than for the soleus muscles from weight-bearing rats at each recovery time. Satellite cell mitotic activity was significantly (P < 0.05) higher in the injured soleus muscles from hindlimb-unloaded rats than from weight-bearing rats 2 wk after reloading, but it was the same (P > 0.05) as in the injured soleus muscles from weight-bearing rats 9 wk after reloading. The injured soleus muscles from hindlimb-unloaded rats failed to achieve weight-bearing muscle size 9 wk after reloading, because incomplete compensation for the decrease in myonuclear accretion and DNA unit size expansion occurred during the unloading period.
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Affiliation(s)
- P E Mozdziak
- Department of Poultry Science, North Carolina State University, Raleigh, North Carolina 27695, USA.
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39
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Lu Z, Joseph D, Bugnard E, Zaal KJ, Ralston E. Golgi complex reorganization during muscle differentiation: visualization in living cells and mechanism. Mol Biol Cell 2001; 12:795-808. [PMID: 11294887 PMCID: PMC32267 DOI: 10.1091/mbc.12.4.795] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
During skeletal muscle differentiation, the Golgi complex (GC) undergoes a dramatic reorganization. We have now visualized the differentiation and fusion of living myoblasts of the mouse muscle cell line C2, permanently expressing a mannosidase-green fluorescent protein (GFP) construct. These experiments reveal that the reorganization of the GC is progressive (1-2 h) and is completed before the cells start fusing. Fluorescence recovery after photobleaching (FRAP), immunofluorescence, and immunogold electron microscopy demonstrate that the GC is fragmented into elements localized near the endoplasmic reticulum (ER) exit sites. FRAP analysis and the ER relocation of endogenous GC proteins by phospholipase A2 inhibitors demonstrate that Golgi-ER cycling of resident GC proteins takes place in both myoblasts and myotubes. All results support a model in which the GC reorganization in muscle reflects changes in the Golgi-ER cycling. The mechanism is similar to that leading to the dispersal of the GC caused, in all mammalian cells, by microtubule-disrupting drugs. We propose that the trigger for the dispersal results, in muscle, from combined changes in microtubule nucleation and ER exit site localization, which place the ER exit sites near microtubule minus ends. Thus, changes in GC organization that initially appear specific to muscle cells, in fact use pathways common to all mammalian cells.
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Affiliation(s)
- Z Lu
- Laboratory of Neurobiology, National Institute of Neurological Disorders and Stroke, Bethesda, Maryland 20892-4062, USA
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40
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Abstract
This article reviews the complexity, expression, genetics, regulation, function, and evolution of the avian myosin heavy chain (MyHC). The majority of pertinent studies thus far published have focussed on domestic chicken and, to a much lesser extent, Japanese quail. Where possible, information available about wild species has also been incorporated into this review. While studies of additional species might modify current interpretations, existing data suggest that some fundamental properties of myosin proteins and genes in birds are unique among higher vertebrates. We compare the characteristics of myosins in birds to those of mammals, and discuss potential molecular mechanisms and evolutionary forces that may explain how avian MyHCs acquired these properties.
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Affiliation(s)
- E Bandman
- Department of Food Science and Technology, University of California, Davis, California 95616, USA.
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41
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Abstract
A emergência da casca marca o final do período de incubação das aves. Esse período pode ter extremos que vão de 480 a 510 horas em galinhas domésticas. As aves precociais nascem com reservas nutricionais provenientes do albúmen e gema residuais contidos no saco vitelino, que são importantes nas primeiras horas de vida enquanto ocorre a adaptação à alimentação independente, com recursos obtidos no meio ambiente. Aparentemente, os pintainhos de corte não apresentam restrições significativas com relação à utilização dos nutrientes obtidos externamente. Uma exceção, de importância questionável, pode ser a possível redução na capacidade de emulsificação das gorduras devido a uma menor concentração de sais biliares momentaneamente disponíveis. Entretanto, o imediato alojamento com disponibilização de alimento e água acelera a adaptação das aves à vida independente e tem reflexos positivos no desempenho posterior. Atrasos no alojamento, seja ainda na câmara de eclosão, transporte ou manejo dos pintinhos, reduzem o potencial de síntese protéica muscular, especialmente na musculatura do peito. Por muitos anos, os produtores de frangos de corte têm usado programas nutricionais que incluem uma mesma dieta da eclosão até as 3 semanas de idade. Recentemente, tem havido um aumento no interesse comercial por uma dieta especializada que contemple as diferenças de adaptação dos primeiros dias de vida das aves. A existência de diferenças entre exigências nutricionais das aves nessa situação com relação a animais mais maduros é ainda uma incógnita, tendo em vista o volume pequeno de informações disponíveis.
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42
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Rosser BW, Farrar CM, Crellin NK, Andersen LB, Bandman E. Repression of myosin isoforms in developing and denervated skeletal muscle fibers originates near motor endplates. Dev Dyn 2000; 217:50-61. [PMID: 10679929 DOI: 10.1002/(sici)1097-0177(200001)217:1<50::aid-dvdy5>3.0.co;2-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
During development of chicken pectoralis muscle, a neonatal myosin heavy-chain isoform is supplanted progressively by an adult isoform. This expression is under neuronal control. In this study we test the hypothesis that developmental myosin transformations are initiated near the motor endplate of each muscle fiber, thereafter progressing toward the fiber ends. By using immunocytochemical methods, pectoralis muscle from chickens aged 1-115 days after hatching were labeled by antibody against neonatal isoform. Ellipse minor axis and mean optical density of labeled and/or unlabeled fiber profiles from each bird were measured by computer image analysis. Acetylcholinesterase (AChE) activity was demonstrated histochemically. Using serial cross sections, we show that smaller fiber profiles are the tapered ends of larger fiber profiles. The largest fiber profiles (central regions of the fibers) were the first to lose their neonatal myosin during development. Motor endplates were localized by AChE activity to the central regions of the fibers. The pectoralis of mature chickens was denervated for 3, 7, 15, or 21 days. After 2 weeks' denervation, neonatal myosin is first reexpressed in the fiber ends. Dev Dyn 2000;217:50-61.
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Affiliation(s)
- B W Rosser
- Department of Anatomy and Cell Biology, University of Saskatchewan, College of Medicine, Saskatoon, Saskatchewan, Canada.
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43
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Mozdziak PE, Pulvermacher PM, Schultz E. Unloading of juvenile muscle results in a reduced muscle size 9 wk after reloading. J Appl Physiol (1985) 2000; 88:158-64. [PMID: 10642376 DOI: 10.1152/jappl.2000.88.1.158] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The role of satellite cells and DNA unit size in determining muscle size was examined by inhibiting postnatal skeletal muscle development by using hindlimb suspension. Satellite cell mitotic activity and DNA unit size were determined in the soleus muscles from hindlimb-suspended and age-matched weight-bearing rats before the initiation of hindlimb suspension, at the conclusion of a 28-day hindlimb-suspension period, 2 wk after reloading, and 9 wk after reloading. The body weights of hindlimb-suspended rats were significantly (P < 0.05) less than those of weight-bearing rats at the conclusion of hindlimb suspension, but they were the same (P > 0. 05) as those of weight-bearing rats 9 wk after reloading. The soleus muscle weight, soleus muscle weight-to-body weight ratio, myofiber diameter, nuclei per millimeter, and DNA unit size for the hindlimb-suspended rats were significantly (P < 0.05) smaller than for the weight-bearing rats at all recovery times. Satellite cell mitotic activity was significantly (P < 0.05) higher in the soleus muscles from hindlimb-suspended rats 2 wk after reloading, but it was the same (P > 0.05) as in weight-bearing rats 9 wk after reloading. Juvenile soleus muscles failed to achieve normal muscle size 9 wk after reloading because there was incomplete compensation for the hindlimb-suspension-induced interruptions in myonuclear accretion and DNA unit size expansion.
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Affiliation(s)
- P E Mozdziak
- Department of Anatomy, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
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44
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Kessler PD, Byrne BJ. Myoblast cell grafting into heart muscle: cellular biology and potential applications. Annu Rev Physiol 1999; 61:219-42. [PMID: 10099688 DOI: 10.1146/annurev.physiol.61.1.219] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
This review surveys a wide range of cellular and molecular approaches to strengthening the injured or weakened heart, focusing on strategies to replace dysfunctional, necrotic, or apoptotic cardiomyocytes with new cells of mesodermal origin. A variety of cell types, including myogenic cell lines, adult skeletal myoblasts, immoratalized atrial cells, embryonic and adult cardiomyocytes, embryonic stem cells, tetratoma cells, genetically altered fibroblasts, smooth muscle cells, and bone marrow-derived cells have all been proposed as useful cells in cardiac repair and may have the capacity to perform cardiac work. We focus on the implantation of mesodermally derived cells, the best developed of the options. We review the developmental and cell biology that have stimulated these studies, examine the limitations of current knowledge, and identify challenges for the future, which we believe are considerable.
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Affiliation(s)
- P D Kessler
- Peter Belfer Cardiac Laboratory, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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45
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Lin Z, Hijikata T, Zhang Z, Choi J, Holtzer S, Sweeney HL, Holtzer H. Dispensability of the actin-binding site and spectrin repeats for targeting sarcomeric alpha-actinin into maturing Z bands in vivo: implications for in vitro binding studies. Dev Biol 1998; 199:291-308. [PMID: 9698448 DOI: 10.1006/dbio.1998.8920] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
To explore the roles of specific domains of sarcomeric alpha-actinin (s-alpha-actinin) in the assembly and maintenance of striated myofibrils, myogenic cultures were transfected with four MYC-tagged s-alpha-actinin peptides. They were: (1) full-length sarcomeric alpha-actinin, (2) an N-terminal deletion that removed the actin-binding site only (MYC/A-), (3) a peptide that consisted of the actin-binding site only (MYC/A+), and (4) an N-terminal deletion that removed the EF-hands and titin-binding domains (MYC/EFT-). While cytotoxic in replicating myogenic cells, as they were in PtK2 cells, the four MYC peptides were not cytotoxic in postmitotic myotubes. In myotubes each of the four different MYC peptides were promptly and selectively incorporated into normal Z bands. The incorporation of MYC/A-, MYC/A+, and MYC/EFT- into Z bands suggests that (a) the actin-binding site, (b) the spectrin-repeats believed to be responsible for anti-parallel dimerization, and (c) the C-terminal EF-hands and titin-binding domains are each dispensable for targeting s-alpha-actinin/MYC peptides into Z bands. These findings could not have been predicted from the behavior of alpha-actinin (a) in binding assays in cell-free systems or (b) when expressed in transfected nonmuscle cells.
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Affiliation(s)
- Z Lin
- Department of Cell Biology, Beijing Institute for Cancer Research, Beijing Medical University, China
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46
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Rotundo RL, Rossi SG, Peng HB. Targeting acetylcholinesterase molecules to the neuromuscular synapse. JOURNAL OF PHYSIOLOGY, PARIS 1998; 92:195-8. [PMID: 9789807 DOI: 10.1016/s0928-4257(98)80009-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The functional integrity of the neuromuscular synapse requires that sufficient numbers of acetylcholinesterase (AChE) molecules be localized on the specialized extracellular matrix between the nerve terminal and the post-synaptic membrane. Multiple interrelated levels of regulation are necessary to accomplish this complex task including the spatial and temporal restriction of AChE mRNA expression within the muscle fiber, local translation and assembly of AChE polypeptides, and focused accumulation of AChE molecules on the extracellular matrix. This is accomplished in part through the organization of other extracellular matrix molecules into a complex which further associates with acetylcholine receptors and their accompanying molecules. Finally, the mature neuromuscular junction contains molecules which can act as receptors for the attachment of AChE which in turn may allow for the turnover of this enzyme at the synapse. This brief review will focus mainly on contributions from our laboratory towards understanding the mechanisms involved in organizing AChE molecules at the neuromuscular synapse.
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Affiliation(s)
- R L Rotundo
- Department of Cell Biology, University of Miami School of Medicine, Florida 33136, USA
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Duca KA, Chiu KP, Sullivan T, Berman SA, Bursztajn S. Nuclear clustering in myotubes: a proposed role in acetylcholine receptor mRNA expression. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1401:1-20. [PMID: 9459482 DOI: 10.1016/s0167-4889(97)00118-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
We investigated the functional relationship between nuclear topology, as expressed by degree and type of nuclear aggregation, and appearance of acetylcholine receptor (AChR) subunit mRNAs. Embryonic chick muscle cell cultures treated with the muscle activity blocking agents decamethonium (DCM), d-tubocurare (TBC), and tetrodotoxin (TTX) or co-cultured with cholinergic neurons were examined for the influence of muscle activity on nuclear aggregation and its effects on AChR alpha-, gamma-, and delta-subunit message expression. mRNA was measured by in situ hybridization and nuclei were visualized by bis-benzimide DNA staining. DCM and TBC treatments, as well as neuronal co-culture, resulted in increased nuclear clustering within myotubes and a per nucleus upregulation in mRNA expression relative to control for each subunit. The pattern of nuclear aggregation was treatment dependent, with more and larger aggregates found when myotubes were co-cultured with neurons. Moreover, as nuclear aggregates became larger: (1) nearly all nuclei within active aggregates expressed mRNA and (2) local accumulation (mRNA per unit area) was elevated relative to single nuclei, while per nucleus mRNA production decreased. To determine whether mRNA expression was transient and did not result in steady-state upregulation of AChR receptor protein, we performed a double labeling of surface AChRs with 125I-alpha-bungarotoxin (125I-alpha-BTX) concomitant to the in situ hybridization for mRNA quantification on TTX treated muscle cells. Surface receptor expression tracked mRNA expression forall types of nuclear topology observed, indicating that message levels are in fact reliable indicators of receptor population on the plasma membrane surface in myotubes. We propose that nuclear clustering is an organelle-level, accessory mechanism whereby cells concentrate relatively large amounts of AChR mRNA/protein in specific myotube regions.
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MESH Headings
- Animals
- Cell Nucleus/chemistry
- Cell Nucleus/metabolism
- Cells, Cultured
- Chick Embryo
- Coculture Techniques
- Decamethonium Compounds/pharmacology
- Gene Expression Regulation/physiology
- Muscle Fibers, Skeletal/chemistry
- Muscle Fibers, Skeletal/cytology
- Muscle Fibers, Skeletal/metabolism
- Muscle, Skeletal/cytology
- Muscle, Skeletal/innervation
- Neuromuscular Depolarizing Agents/pharmacology
- Neuromuscular Nondepolarizing Agents/pharmacology
- Neurons/cytology
- RNA, Messenger/analysis
- RNA, Messenger/genetics
- Receptors, Cholinergic/analysis
- Receptors, Cholinergic/genetics
- Sodium Channel Blockers
- Tetrodotoxin/pharmacology
- Tubocurarine/pharmacology
- Up-Regulation
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Affiliation(s)
- K A Duca
- Brandeis University, Department of Chemistry, Program in Biophysics, Waltham, MA 02254, USA.
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Ralston E, McLaren RS, Horowitz JA. Nuclear domains in skeletal myotubes: the localization of transferrin receptor mRNA is independent of its half-life and restricted by binding to ribosomes. Exp Cell Res 1997; 236:453-62. [PMID: 9367630 DOI: 10.1006/excr.1997.3753] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The retention of mRNAs near the nuclei that synthesize them may be an important feature of the organization of multinucleated skeletal myotubes. Here, we assess the possible role of two factors in this localization. First, we examine the role of mRNA half-life, by studying the distribution of the mRNA for the transferrin receptor (TfR), whose half-life can be manipulated in culture by changing the availability of iron. In situ hybridization of myotubes of the mouse muscle cell line C2 shows that TfR mRNA is concentrated in the core of the myotubes. Its distribution around the nuclei is often asymmetric and its concentration changes abruptly. Stable transcripts display the same asymmetric localization as unstable ones, suggesting that half-life does not determine subcellular localization of TfR mRNA. Differential effects of the protein synthesis inhibitors puromycin and cycloheximide suggest that the mRNA is retained in position by its association with ribosomes. We then examine the distribution of the rough endoplasmic reticulum (RER) and find it to be broader than the distribution of TfR mRNA. In contrast to TfR mRNA, the mRNA for a secreted immunoglobulin kappa light chain has a more uniform distribution. Taken together, the results suggest that TfR mRNA may associate with RER subdomains by specific targeting.
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Affiliation(s)
- E Ralston
- Laboratory of Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4062, USA.
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Abstract
BACKGROUND A skeletal muscle fiber consists of many successive "territories," each controlled by the nucleus residing in that territory. Because nuclei appear to control a specific amount of territory (nuclear domain), nuclei must be added to accommodate an increase in fiber size. Because growth and hypertrophy require the addition of nuclei to fibers, it is of interest to determine whether atrophy causes a decrease in myonuclear number. This study compared the myonuclear population in the soleus muscles of rats that had undergone atrophy due to 10 days of spaceflight in the space shuttle, Endeavour, with muscles of ground-based control animals (10 rats each). METHODS Myofibrillar ATPase activity was used to determine the major skeletal muscle fiber types in control rats and those having spent 10 days in space, and dystrophin antibodies were used to label the sarcolemma to identify underlying myonuclei. RESULTS Type I and II fibers were atrophied after the flight, but type I fibers were atrophied twice as much as type II. Myonuclei were counted in identified and measured fibers, and the distribution normalized to number per millimeter of fiber circumference; this was significantly greater in type II than in type I fibers in both groups of rats. However, although the muscle fibers from flight animals were significantly atrophied, the normalized number of nuclei were identical between control and flight animals, indicating that nuclei decreased in numbers as the fibers atrophied. CONCLUSION The nuclear domain is under strict control, and a decrease in the domain, as induced by atrophy, will cause nuclear degeneration and loss, which maintains a relatively constant size of the nuclear domain.
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Affiliation(s)
- R S Hikida
- Department of Biological Sciences, Ohio University, Athens 45701, USA
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Takahashi M, Hood DA. Protein import into subsarcolemmal and intermyofibrillar skeletal muscle mitochondria. Differential import regulation in distinct subcellular regions. J Biol Chem 1996; 271:27285-91. [PMID: 8910303 DOI: 10.1074/jbc.271.44.27285] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
To date, no studies have described the import of proteins in mitochondria obtained from skeletal muscle. In this tissue, mitochondria consist of the functionally and biochemically distinct intermyofibrillar (IMF) and subsarcolemmal (SS) subfractions, which are localized in specialized cellular compartments. This mitochondrial heterogeneity in muscle could be due, in part, to differential rates of protein import. To evaluate this possibility, the import of precursor malate dehydrogenase and ornithine carbamyltransferase proteins was investigated in isolated IMF and SS mitochondria in vitro. Import of these was 3-4-fold greater in IMF compared with SS mitochondria as a function of time. This could account for the higher malate dehydrogenase enzyme activity in IMF mitochondria. Divergent import rates in IMF and SS mitochondria likely result from a differential reliance on various components of the import pathway. SS mitochondria possess a greater content of the molecular chaperones hsp60 and Grp75, yet import is lower than in IMF mitochondria. On the other hand, adriamycin inhibition studies illustrated a greater reliance on acidic phospholipids (i.e. cardiolipin) for the import process in SS mitochondria. Matrix ATP levels were 3-fold higher in IMF mitochondria, but experiments in which ATP depletion was performed with atractyloside and oligomycin illustrated a dissociation between import rates and levels of ATP. In contrast, a close relationship was found between the rate of ATP production (i.e. mitochondrial respiration) and protein import. When respiratory rates in IMF and SS mitochondria were equalized, import rates in both subfractions were similar. These data indicate that 1) import rates are more closely related to the rate of ATP production than the steady state ATP level, 2) import into IMF and SS mitochondrial subfractions is regulated differently, and 3) mitochondrial heterogeneity within a cell type can be due to differences in the rates of protein import, suggesting that this step is a potentially regulatable event in determining the final mitochondrial phenotype.
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Affiliation(s)
- M Takahashi
- Departments of Biology and Kinesiology, York University, North York, Ontario M3J 1P3, Canada.
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