Markers of Muscle Protein Synthesis and Breakdown in Fast‐Twitch Skeletal Muscle of Rodents Aged 3 to 24 Months

Abstract

OBJECTIVEMuscle protein synthesis (MPS) and muscle protein degradation (MPD) are well known modulators for muscle mass maintenance. Given that fast‐twitch skeletal muscle atrophies with aging, we sought to examine the effects of aging on MPS and MPD markers in the plantaris muscle of rodents ranging from 3 to 24 months.MEHTODSMale Fischer 344 rats (300–600g) were successfully aged to 3, 6, 12, 18 and 24 months, were injected with puromycin (0.02 mg/g body mass), euthanized, plantaris muscle was extracted and wet skeletal muscle weights were obtained. Muscle tissue was then processed for biochemical processing. MPS was assessed via the SUNsET method, and MPD was assessed using whole lane densitometry via ubiquitin immunoblotting.RESULTSRelative plantaris masses revealed significant between‐group differences throughout the lifespan (p<0.001); specifically, masses were 18% greater in 3 versus 18 month old rats (p<0.001) and 23% greater in 3 versus 24 month old rats (p<0.001). Interestingly, MPS levels did not differ between 3 month old rats versus all other age groups. However, MPS levels were 2.42‐fold greater in 18 month old versus 24 month old rats (p<0.05). Poly‐ubiquinated protein levels were not different between any of the age groups.CONCLUSIONIt appears that plantaris muscle atrophy occurs with aging. However, this does not appear to be reflected via decrements in MPS or increases in protein polyubiquination. Mechanisms related to fast‐twitch skeletal muscle atrophy remain to be determined and should be further investigated.Support or Funding InformationThis study was supported in part by a contract from The University of Tampa (to M.D.R. from J.M.W.) as well as laboratory start‐up funds from M.D.R.