title: Skeletal muscle autophagy and protein breakdown following resistance exercise are similar in younger and older adults.
abstract: BACKGROUND
  The loss of skeletal muscle mass and strength during aging, sarcopenia, increases the risk for falls and dependency. Resistance exercise (RE) training is effective at improving muscle mass and strength in older adults; however, aging is associated with reduced training-induced hypertrophy. Recent research has illustrated an impaired muscle protein synthetic response following an acute bout of RE in older adults but much less is known regarding the effect of acute RE on muscle protein breakdown (MPB). We hypothesize that the ubiquitin proteasome system and the autophagosomal-lysosomal system may regulate the overall rate of MPB during postexercise recovery.
  
  
  METHODS
  Muscle biopsies of the vastus lateralis were sampled from 16 older (age = 70±2 years) and 16 younger (age = 27±2 years) participants at baseline and at 3, 6, and 24 hours following an acute bout of RE. In conjunction with stable isotopic techniques to measure MPB, we utilized immunoblotting and RT-PCR to examine protein and mRNA expression for key signaling molecules in both the ubiquitin proteasome system and the autophagosomal-lysosomal system.
  
  
  RESULTS
  MuRF1 mRNA expression increased, whereas GABARAP mRNA decreased after RE in both younger and older adults (p < .05). The LC3B-II/LC3B-I protein ratio decreased in both groups after RE (p < .05), but MPB was not different 24 hour post-RE in either group (p > .05).
  
  
  CONCLUSIONS
  Aging does not influence skeletal MPB, autophagy, or the ubiquitin proteasome system following an acute bout of RE. Therefore, targeting the muscle protein synthesis response to exercise may hold more promise in the prevention of sarcopenia.
authors.affiliation: Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas 77555-1144, USA.
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Fry
authors.forename: Micah J
authors.initials: MJ
authors.lastname: Drummond
authors.forename: Erin L
authors.initials: EL
authors.lastname: Glynn
authors.forename: Jared M
authors.initials: JM
authors.lastname: Dickinson
authors.forename: David M
authors.initials: DM
authors.lastname: Gundermann
authors.forename: Kyle L
authors.initials: KL
authors.lastname: Timmerman
authors.forename: Dillon K
authors.initials: DK
authors.lastname: Walker
authors.forename: Elena
authors.initials: E
authors.lastname: Volpi
authors.forename: Blake B
authors.initials: BB
authors.lastname: Rasmussen
mesh_terms: D000367:Age Factors; D000368:Aged; D001343:Autophagy; D005260:Female; D006801:Humans; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D055070:Resistance Training
chemical_list: D009124:Muscle Proteins