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Age-related differences in lean mass, protein synthesis and skeletal muscle markers of proteolysis after bed rest and exercise rehabilitation.
- Source :
- Journal of Physiology; Sep2015, Vol. 593 Issue 18, p4259-4273, 15p
- Publication Year :
- 2015
-
Abstract
- Key points Five days of bed rest resulted in a reduction in leg lean mass and strength in older adults., After bed rest, older (but not younger) adults had reduced amino acid-induced anabolic sensitivity (blunted muscle protein synthesis; MPS) and enhanced markers associated with the ubiquitin proteasome and autophagy-lysosomal systems (increase in molecular markers related to muscle proteolysis)., Younger adults did not lose leg lean mass (via DXA) after 5 days of bed rest despite blunted amino acid-induced mTORC1 signalling and increased skeletal muscle REDD1, REDD2 and MURF1 mRNA expression., Exercise rehabilitation restored bed rest-induced deficits in lean mass, strength, nutrient-induced protein anabolism (protein synthesis and mTORC1 signalling) and select muscle proteolytic markers in older adults., Abstract Bed rest-induced muscle loss and impaired muscle recovery may contribute to age-related sarcopenia. It is unknown if there are age-related differences in muscle mass and muscle anabolic and catabolic responses to bed rest. A secondary objective was to determine if rehabilitation could reverse bed rest responses. Nine older and fourteen young adults participated in a 5-day bed rest challenge (BED REST). This was followed by 8 weeks of high intensity resistance exercise (REHAB). Leg lean mass (via dual-energy X-ray absorptiometry; DXA) and strength were determined. Muscle biopsies were collected during a constant stable isotope infusion in the postabsorptive state and after essential amino acid (EAA) ingestion on three occasions: before (PRE), after bed rest and after rehabilitation. Samples were assessed for protein synthesis, mTORC1 signalling, REDD1/2 expression and molecular markers related to muscle proteolysis (MURF1, MAFBX, AMPKα, LC3II/I, Beclin1). We found that leg lean mass and strength decreased in older but not younger adults after bedrest ( P < 0.05) and was restored after rehabilitation. EAA-induced mTORC1 signalling and protein synthesis increased before bed rest in both age groups ( P < 0.05). Although both groups had blunted mTORC1 signalling, increased REDD2 and MURF1 mRNA after bedrest, only older adults had reduced EAA-induced protein synthesis rates and increased MAFBX mRNA, p-AMPKα and the LC3II/I ratio ( P < 0.05). We conclude that older adults are more susceptible than young persons to muscle loss after short-term bed rest. This may be partially explained by a combined suppression of protein synthesis and a marginal increase in proteolytic markers. Finally, rehabilitation restored bed rest-induced deficits in lean mass and strength in older adults. [ABSTRACT FROM AUTHOR]
- Subjects :
- PROTEOLYSIS
PROTEIN synthesis
MUSCLE proteins
BED rest
EXERCISE physiology
PHYSIOLOGY
Subjects
Details
- Language :
- English
- ISSN :
- 00223751
- Volume :
- 593
- Issue :
- 18
- Database :
- Complementary Index
- Journal :
- Journal of Physiology
- Publication Type :
- Academic Journal
- Accession number :
- 109463546
- Full Text :
- https://doi.org/10.1113/JP270699