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Ruiz LP, Macpherson PC, Brooks SV. Maintenance of subsynaptic myonuclei number is not driven by neural input. Front Physiol 2023; 14:1266950. [PMID: 37822678 PMCID: PMC10562629 DOI: 10.3389/fphys.2023.1266950] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Accepted: 09/12/2023] [Indexed: 10/13/2023] Open
Abstract
The development and maintenance of neuromuscular junctions (NMJ) are supported by a specialized population of myonuclei that are referred to as the subsynaptic myonuclei (SSM). The relationship between the number of SSM and the integrity of the NMJ as well as the impact of a loss of innervation on SSM remain unclear. This study aimed to clarify these associations by simultaneously analyzing SSM counts and NMJ innervation status in three distinct mouse models of acute and chronic NMJ disruption. SSM were identified using fluorescent immunohistochemistry for Nesprin1 expression, which is highly enriched in SSM, along with anatomical location beneath the muscle fiber motor endplate. Acute denervation, induced by surgical nerve transection, did not affect SSM number after 7 days. Additionally, no significant changes in SSM number were observed during normal aging or in mice with chronic oxidative stress (Sod1 -/-). Both aging WT mice and Sod1 -/- mice accumulated degenerating and denervated NMJ in skeletal muscle, but there was no correlation between innervation status of a given NMJ and SSM number in aged or Sod1 -/- mice. These findings challenge the notion that a loss of SSM is a primary driver of NMJ degradation and leave open questions of the mechanisms that regulate SSM number as well as the physiological significance of the precise SSM number. Further investigations are required to define other properties of the SSM, such as transcriptional profiles and structural integrity, to better understand their role in NMJ maintenance.
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Affiliation(s)
- Lloyd P. Ruiz
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, United States
| | - Peter C. Macpherson
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, United States
| | - Susan V. Brooks
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, United States
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States
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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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Jones RG, Dimet-Wiley A, Haghani A, da Silva FM, Brightwell CR, Lim S, Khadgi S, Wen Y, Dungan CM, Brooke RT, Greene NP, Peterson CA, McCarthy JJ, Horvath S, Watowich SJ, Fry CS, Murach KA. A molecular signature defining exercise adaptation with ageing and in vivo partial reprogramming in skeletal muscle. J Physiol 2023; 601:763-782. [PMID: 36533424 PMCID: PMC9987218 DOI: 10.1113/jp283836] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Accepted: 12/12/2022] [Indexed: 12/23/2022] Open
Abstract
Exercise promotes functional improvements in aged tissues, but the extent to which it simulates partial molecular reprogramming is unknown. Using transcriptome profiling from (1) a skeletal muscle-specific in vivo Oct3/4, Klf4, Sox2 and Myc (OKSM) reprogramming-factor expression murine model; (2) an in vivo inducible muscle-specific Myc induction murine model; (3) a translatable high-volume hypertrophic exercise training approach in aged mice; and (4) human exercise muscle biopsies, we collectively defined exercise-induced genes that are common to partial reprogramming. Late-life exercise training lowered murine DNA methylation age according to several contemporary muscle-specific clocks. A comparison of the murine soleus transcriptome after late-life exercise training to the soleus transcriptome after OKSM induction revealed an overlapping signature that included higher JunB and Sun1. Also, within this signature, downregulation of specific mitochondrial and muscle-enriched genes was conserved in skeletal muscle of long-term exercise-trained humans; among these was muscle-specific Abra/Stars. Myc is the OKSM factor most induced by exercise in muscle and was elevated following exercise training in aged mice. A pulse of MYC rewired the global soleus muscle methylome, and the transcriptome after a MYC pulse partially recapitulated OKSM induction. A common signature also emerged in the murine MYC-controlled and exercise adaptation transcriptomes, including lower muscle-specific Melusin and reactive oxygen species-associated Romo1. With Myc, OKSM and exercise training in mice, as well habitual exercise in humans, the complex I accessory subunit Ndufb11 was lower; low Ndufb11 is linked to longevity in rodents. Collectively, exercise shares similarities with genetic in vivo partial reprogramming. KEY POINTS: Advances in the last decade related to cellular epigenetic reprogramming (e.g. DNA methylome remodelling) toward a pluripotent state via the Yamanaka transcription factors Oct3/4, Klf4, Sox2 and Myc (OKSM) provide a window into potential mechanisms for combatting the deleterious effects of cellular ageing. Using global gene expression analysis, we compared the effects of in vivo OKSM-mediated partial reprogramming in skeletal muscle fibres of mice to the effects of late-life murine exercise training in muscle. Myc is the Yamanaka factor most induced by exercise in skeletal muscle, and so we compared the MYC-controlled transcriptome in muscle to Yamanaka factor-mediated and exercise adaptation mRNA landscapes in mice and humans. A single pulse of MYC is sufficient to remodel the muscle methylome. We identify partial reprogramming-associated genes that are innately altered by exercise training and conserved in humans, and propose that MYC contributes to some of these responses.
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Affiliation(s)
- Ronald G. Jones
- University of Arkansas, Exercise Science Research Center, Department of Health, Human Performance, and Recreation, Fayetteville, AR, USA
| | | | - Amin Haghani
- University of California Los Angeles, Department of Human Genetics, Los Angeles, CA, USA
- Altos Labs, San Diego, CA, USA
| | - Francielly Morena da Silva
- University of Arkansas, Exercise Science Research Center, Department of Health, Human Performance, and Recreation, Fayetteville, AR, USA
- University of Arkansas, Cachexia Research Laboratory, Department of Health, Human Performance, and Recreation, Fayetteville, AR, USA
| | - Camille R. Brightwell
- University of Kentucky Center for Muscle Biology, Lexington, KY, USA
- University of Kentucky, Department of Athletic Training and Clinical Nutrition, Lexington, KY, USA
| | - Seongkyun Lim
- University of Arkansas, Exercise Science Research Center, Department of Health, Human Performance, and Recreation, Fayetteville, AR, USA
- University of Arkansas, Cachexia Research Laboratory, Department of Health, Human Performance, and Recreation, Fayetteville, AR, USA
| | - Sabin Khadgi
- University of Arkansas, Exercise Science Research Center, Department of Health, Human Performance, and Recreation, Fayetteville, AR, USA
| | - Yuan Wen
- University of Kentucky Center for Muscle Biology, Lexington, KY, USA
- University of Kentucky, Department of Physical Therapy, Lexington, KY, USA
| | - Cory M. Dungan
- University of Kentucky Center for Muscle Biology, Lexington, KY, USA
- University of Kentucky, Department of Physical Therapy, Lexington, KY, USA
| | | | - Nicholas P. Greene
- University of Arkansas, Exercise Science Research Center, Department of Health, Human Performance, and Recreation, Fayetteville, AR, USA
- University of Arkansas, Cachexia Research Laboratory, Department of Health, Human Performance, and Recreation, Fayetteville, AR, USA
- University of Arkansas, Cell and Molecular Biology Graduate Program, Fayetteville, AR, USA
| | - Charlotte A. Peterson
- University of Kentucky Center for Muscle Biology, Lexington, KY, USA
- University of Kentucky, Department of Physical Therapy, Lexington, KY, USA
- University of Kentucky, Department of Physiology, Lexington, KY, USA
| | - John J. McCarthy
- Altos Labs, San Diego, CA, USA
- University of Kentucky, Department of Physiology, Lexington, KY, USA
| | - Steve Horvath
- University of California Los Angeles, Department of Human Genetics, Los Angeles, CA, USA
- Altos Labs, San Diego, CA, USA
| | - Stanley J. Watowich
- Ridgeline Therapeutics, Houston, TX, USA
- University of Texas Medical Branch, Department of Biochemistry and Molecular Biology, Galveston, TX, USA
| | - Christopher S. Fry
- University of Kentucky Center for Muscle Biology, Lexington, KY, USA
- University of Kentucky, Department of Athletic Training and Clinical Nutrition, Lexington, KY, USA
| | - Kevin A. Murach
- University of Arkansas, Exercise Science Research Center, Department of Health, Human Performance, and Recreation, Fayetteville, AR, USA
- University of Arkansas, Cell and Molecular Biology Graduate Program, Fayetteville, AR, USA
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Battey E, Ross JA, Hoang A, Wilson DGS, Han Y, Levy Y, Pollock RD, Kalakoutis M, Pugh JN, Close GL, Ellison-Hughes GM, Lazarus NR, Iskratsch T, Harridge SDR, Ochala J, Stroud MJ. Myonuclear alterations associated with exercise are independent of age in humans. J Physiol 2023. [PMID: 36597809 DOI: 10.1113/jp284128] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Accepted: 12/19/2022] [Indexed: 01/05/2023] Open
Abstract
Age-related decline in skeletal muscle structure and function can be mitigated by regular exercise. However, the precise mechanisms that govern this are not fully understood. The nucleus plays an active role in translating forces into biochemical signals (mechanotransduction), with the nuclear lamina protein lamin A regulating nuclear shape, nuclear mechanics and ultimately gene expression. Defective lamin A expression causes muscle pathologies and premature ageing syndromes, but the roles of nuclear structure and function in physiological ageing and in exercise adaptations remain obscure. Here, we isolated single muscle fibres and carried out detailed morphological and functional analyses on myonuclei from young and older exercise-trained individuals. Strikingly, myonuclei from trained individuals were more spherical, less deformable, and contained a thicker nuclear lamina than those from untrained individuals. Complementary to this, exercise resulted in increased levels of lamin A and increased myonuclear stiffness in mice. We conclude that exercise is associated with myonuclear remodelling, independently of age, which may contribute to the preservative effects of exercise on muscle function throughout the lifespan. KEY POINTS: The nucleus plays an active role in translating forces into biochemical signals. Myonuclear aberrations in a group of muscular dystrophies called laminopathies suggest that the shape and mechanical properties of myonuclei are important for maintaining muscle function. Here, striking differences are presented in myonuclear shape and mechanics associated with exercise, in both young and old humans. Myonuclei from trained individuals were more spherical, less deformable and contained a thicker nuclear lamina than untrained individuals. It is concluded that exercise is associated with age-independent myonuclear remodelling, which may help to maintain muscle function throughout the lifespan.
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Affiliation(s)
- E Battey
- Centre for Human & Applied Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
- British Heart Foundation Centre of Research Excellence, School of Cardiovascular Medicine and Sciences, King's College London, London, UK
- Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
| | - J A Ross
- British Heart Foundation Centre of Research Excellence, School of Cardiovascular Medicine and Sciences, King's College London, London, UK
| | - A Hoang
- British Heart Foundation Centre of Research Excellence, School of Cardiovascular Medicine and Sciences, King's College London, London, UK
| | - D G S Wilson
- School of Engineering and Materials Science, Queen Mary University of London, London, UK
| | - Y Han
- Centre for Human & Applied Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | - Y Levy
- Centre for Human & Applied Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | - R D Pollock
- Centre for Human & Applied Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | - M Kalakoutis
- Centre for Human & Applied Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
- Randall Centre for Cell and Molecular Biophysics, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | - J N Pugh
- School of Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK
| | - G L Close
- School of Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK
| | - G M Ellison-Hughes
- Centre for Human & Applied Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | - N R Lazarus
- Centre for Human & Applied Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | - T Iskratsch
- School of Engineering and Materials Science, Queen Mary University of London, London, UK
- Randall Centre for Cell and Molecular Biophysics, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | - S D R Harridge
- Centre for Human & Applied Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
| | - J Ochala
- Centre for Human & Applied Physiological Sciences, Faculty of Life Sciences & Medicine, King's College London, London, UK
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - M J Stroud
- British Heart Foundation Centre of Research Excellence, School of Cardiovascular Medicine and Sciences, King's College London, London, UK
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