Protein and Amino Acid Supplementation Does Not Alter Proteolytic Gene Expression following Immobilization

Abstract

Objective. To determine if supplementation of protein and amino acids (PAA) decreases skeletal muscle expression of atrophy-related genes, muscle mass, and strength during immobilization in humans. Methods. Twenty males wore a lower-limb immobilization boot for 28 days and consumed either a PAA supplement (28 g protein) or carbohydrate placebo (28 g maltodextrose), while consuming their normal daily diet. Testing sessions included dietary analysis, lower-leg girth and body composition measurements, strength testing, and gastrocnemius muscle biopsies. Muscle was analyzed for mRNA expression of markers in the ubiquitin and calpain systems, myostatin, TNF-α, and NF-κB. Results. All genes of interest increased over time (P < .05), but there was no difference between groups. Lower-leg girth decreased over time (P = 0.02); however, there were no significant changes in body composition or strength. Conclusion. Short-term lower-limb disuse, despite the absence of significant muscle atrophy, is associated with increases in skeletal muscle gene expression of several proteolysis-related genes. These changes do not appear to be altered by oral PAA supplementation.

Substantial skeletal muscle loss occurs during only 5 days of disuse

“…Myostatin, a proposed 'master' negative regulator of skeletal muscle mass in animals (McPherron & Lee 1997, Mosher et al 2007) and humans (Schuelke et al 2004), acts via the inhibition of mammalian target of rapamycin (mTOR) muscle protein synthesis signalling (Rodriguez et al 2011) and by initiating muscle protein breakdown through the ubiquitin-proteasome system (McFarlane et al 2006). Consistent with previous animal (Murphy et al 2011) and human , Gustafsson et al 2010, Bunn et al 2011) disuse studies, we report a clear up-regulation of myostatin gene expression in response to 5 and 14 days of limb immobilization (Fig. 3).…”

“…, Bunn et al . ) disuse studies, we report a clear up‐regulation of myostatin gene expression in response to 5 and 14 days of limb immobilization (Fig. ).…”

TNFa is Involved in the Development of Disuse Muscle Atrophy Through the Acid Sphingomyelinase/ Ceramide Up-Regulation and Pro-Oxidant Signaling

“…A group of authors [7] using a model of 14-day hindlimb immobilization in Wistar rats have demonstrated the elevated plasma and muscle TNF-α levels along with oxidative stress and NF-kB signaling activation. The other authors [8] obtained the similar results in human: TNF-α, NF-κB, myostatin, ubiquitin and calpain mRNA were over-expressed after 28-day lower-limb immobilization.…”

“…The data indicating the roles of cytokines including TNFa in disuse muscle atrophy are very few, despite the growing interest to this problem emerging in the recent years. TNFa contribution to disuse muscle atrophy was described in a number of works [3][4][5][6][7][8].…”

Prevention of Skeletal Muscle Wasting: Disuse Atrophy and Sarcopenia

“…However, 28 days of immobilization with protein and amino acid supplementation [28g protein) did not prevent increases in myostatin, MuRF1 or MAFbx over time [101].…”