Muscle fibre size and myonuclear positioning in trained and aged humans

Author:

Battey Edmund123ORCID,Levy Yotam1ORCID,Pollock Ross D.1ORCID,Pugh Jamie N.4ORCID,Close Graeme L.4ORCID,Kalakoutis Michaeljohn15ORCID,Lazarus Norman R.1,Harridge Stephen D. R.1ORCID,Ochala Julien13ORCID,Stroud Matthew J.2ORCID

Affiliation:

1. Centre for Human & Applied Physiological Sciences, Faculty of Life Sciences & Medicine King's College London London UK

2. British Heart Foundation Centre of Research Excellence, School of Cardiovascular Medicine and Sciences King's College London London UK

3. Department of Biomedical Sciences, Faculty of Medical and Health Sciences University of Copenhagen Copenhagen Denmark

4. School of Sport and Exercise Sciences, Tom Reilly Building, Byrom Street Liverpool John Moores University Liverpool UK

5. Randall Centre for Cell and Molecular Biophysics, Faculty of Life Sciences & Medicine King's College London London UK

Abstract

AbstractChanges in myonuclear architecture and positioning are associated with exercise adaptations and ageing. However, data on the positioning and number of myonuclei following exercise are inconsistent. Additionally, whether myonuclear domains (MNDs; i.e., the theoretical volume of cytoplasm within which a myonucleus is responsible for transcribing DNA) and myonuclear positioning are altered with age remains unclear. The aim of this investigation was to investigate relationships between age and activity status and myonuclear domains and positioning. Vastus lateralis muscle biopsies from younger endurance‐trained (YT) and older endurance‐trained (OT) individuals were compared with age‐matched untrained counterparts (YU and OU; OU samples were acquired during surgical operation). Serial, optical z‐slices were acquired throughout isolated muscle fibres and analysed to give three‐dimensional coordinates for myonuclei and muscle fibre dimensions. The mean cross‐sectional area (CSA) of muscle fibres from OU individuals was 33%–53% smaller compared with the other groups. The number of nuclei relative to fibre CSA was 90% greater in OU compared with YU muscle fibres. Additionally, scaling of MND volume with fibre size was altered in older untrained individuals. The myonuclear arrangement, in contrast, was similar across groups. Fibre CSA and most myonuclear parameters were significantly associated with age in untrained individuals, but not in trained individuals. These data indicate that regular endurance exercise throughout the lifespan might better preserve the size of muscle fibres in older age and maintain the relationship between fibre size and MND volumes. Inactivity, however, might result in reduced muscle fibre size and altered myonuclear parameters.

Funder

Medical Research Council

Bupa Foundation

King's College London

Publisher

Wiley

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