Expression of growth-related genes in young and older human skeletal muscle following an acute stimulation of protein synthesis

Abstract

Muscle growth is associated with an activation of the mTOR signaling pathway and satellite cell regulators. The purpose of this study was to determine whether 17 selected genes associated with mTOR/muscle protein synthesis and the satellite cells/myogenic program are differentially expressed in young and older human skeletal muscle at rest and in response to a potent anabolic stimulus [resistance exercise + essential amino acid ingestion (RE+EAA)]. Twelve male subjects (6 young, 6 old) completed a bout of heavy resistance exercise. Muscle biopsies were obtained before and at 3 and 6 h post RE+EAA. Subjects ingested leucine-enriched essential amino acids at 1 h postexercise. mRNA expression was determined using qRT-PCR. At rest, hVps34 mRNA was elevated in the older subjects (P < 0.05) while there was a tendency for levels of myoD, myogenin, and TSC2 mRNA to be higher than young. The anabolic stimulus (RE+EAA) altered mRNAs associated with mTOR regulation. Notably, REDD2 decreased in both age groups (P < 0.05) but the expression of Rheb mRNA increased only in the young. Finally, cMyc mRNA was elevated (P < 0.05) in both young and old at 6 h post RE+EAA. Furthermore, RE+EAA also increased expression of several mRNAs associated with satellite function in the young (P < 0.05), while expression of these mRNAs did not change in the old. We conclude that several anabolic genes in muscle are more responsive in young men post RE+EAA. Our data provide new insights into the regulation of genes important for transcription and translation in young and old human skeletal muscle post RE+EAA.

Figures

Fig. 1.

mRNAs associated with negative mTOR regulation. Data represent REDD1 (A), REDD2 (B), TSC1 (C), and TSC2 (D) mRNA expression between young and older subjects 3 and 6 h post resistance exercise + essential amino acid ingestion (RE+EAA). *Significantly different from basal (P < 0.05). #Significantly different from older subjects (P < 0.05).

Fig. 2.

mRNAs associated with positive mTOR regulation. Data represent Rheb (A) and cMyc (B) mRNA expression between young and older subjects 3 and 6 h post RE+EAA. *Significantly different from basal (P < 0.05). #Significantly different from older subjects (P < 0.05).

Fig. 3.

mRNAs associated with satellite cell regulation. Data represent mib2 (A) and myostatin (B) mRNA expression between young and older subjects 3 and 6 h post RE+EAA. *Significantly different from basal (P < 0.05). #Significantly different from older subjects (P < 0.05).

Fig. 4.

mRNAs associated with satellite cell regulation. Data represent IGF-1R (A), myoD (B), and myogenin (C) mRNA expression between young and older subjects 3 and 6 h post RE+EAA. *Significantly different from basal (P < 0.05). #Significantly different from older subjects (P < 0.05).