Skeletal muscle morphology and regulatory signalling in endurance-trained and sedentary individuals: The influence of ageing

• Published in: Experimental gerontology 2017-07, Vol.93, p.54-67
• Main Authors: Mikkelsen, U.R., Agergaard, J., Couppé, C., Grosset, J.F., Karlsen, A., Magnusson, S.P., Schjerling, P., Kjaer, M., Mackey, A.L.
• Format: Article
• Language: English
• Subjects: Ectopic adipose tissue; Inflammation; Intramuscular connective tissue; Master athletes; Perimysium; Sarcopenia
• ISSN: 0531-5565; 1873-6815
• DOI: 10.1016/j.exger.2017.04.001

Muscle mass in humans is inversely associated with circulating levels of inflammatory cytokines, but the interaction between ageing and training on muscle composition and the intra-muscular signalling behind inflammation and contractile protein synthesis and degradation is unknown. We studied 15 healthy life-long endurance runners, 12 age-matched untrained controls, 10 young trained and 12 young untrained individuals. Thigh muscle composition was investigated by magnetic resonance imaging (MRI), where non-contractile intramuscular tissue (NCIT) area (fat and connective tissue) was found to be greater in older but lower in trained individuals. Subcutaneous adipose tissue was also lower in trained individuals but was not affected by age. In vastus lateralis biopsies, no influence of age or training was found on levels of endomysial collagen, determined by Sirius Red and Collagen III staining, whereas perimysial organisation tended to be more complex in older individuals. No clear difference with training was seen on intramuscular inflammatory signalling, whereas lower protein levels of NFkB subunits p105, p50 and p65 were observed with ageing. Gene expression of IL6 and TNFα was not different between groups, while IL1-receptor and TNFα-receptor1 levels were lower with age. Myostatin mRNA was lower in older and trained groups, while expression of MuRF1 was lower in trained individuals and FoxO3 expression was greater in aged groups. The association of increased muscle NCIT with age-associated muscle loss in humans is not accompanied by any major alterations in intramuscular signalling for inflammation, but rather by direct regulatory factors for protein synthesis and proteolysis in skeletal muscle. •We analysed thigh muscle quality and inflammatory signalling in young and old men.•Older muscle had a greater content of non-contractile intramuscular tissue (NCIT).•The skeletal muscle of endurance trained vs. untrained men contained less NCIT.•Muscle perimysium tended to be more ramified in older individuals.•Differences were observed in signalling for protein turnover but not inflammation.