Role of Dietary Leucine on Amino Acid Transporter mRNA Expression Following Resistance Exercise
Tyler A. Churchward-Venne Medicine & Science in Sports & Exercise. 2012 44(5S): p 444
Skeletal muscle amino acid transporters (AAT) may play a key role in the regulation of muscle protein metabolism via their ability to transport amino acids (AA) across the sarcolemma and
relay signals to downstream protein targets. The mRNA expression of some AAT is increased after essential amino acid (EAA) intake and resistance exercise (RE); however, the combined
effect of AA and RE on AAT mRNA expression and whether greater leucine intake alters the response is unknown.
PURPOSE: To examine the effect of AA/whey protein intake (with high and low leucine content) after RE on the mRNA expression of select AAT in human skeletal muscle.
METHODS: 24 adult men (22±1 y) completed unilateral knee-extensor RE before consuming one of the following: WHEY (25 g whey protein); LEU (6.25 g whey protein supplemented with
leucine to be iso-leucine with WHEY); and EAA-LEU (6.25 g whey protein supplemented with EAA except leucine to be iso-EAA with WHEY for each EAA except for leucine). Muscle
biopsies were obtained before RE and 1, 3, and 5h after from both rested-fed (FED) and exercise-fed legs (EX-FED). qRT-PCR was used to determine changes in mRNA expression of LAT-1,
CD-98, and PAT-1 AAT and members of the general AA control pathway GCN-2 and ATF-4.
RESULTS: mRNA expression of CD-98 and LAT-1 (fold-change from basal) increased in FED and EX-FED, however the response at 5h was greater in EX-FED (CD-98 FED = 2.17 vs. EXFED
= 3.52 (P=0.003); LAT-1 FED = 3.58 vs. EX-FED = 5.18 (P=0.025)). PAT-1 increased in FED and EX-FED, however EX-FED was greater in WHEY vs. EAA-LEU (WHEY = 3.26 vs.
EAA-LEU = 1.89 (P=0.031). ATF-4 showed time dependent changes in all treatments while the FED response of GCN-2 was greater in LEU vs. WHEY and EAA-LEU at 5h (LEU = 2.07 vs.
WHEY = 1.44 vs. EAA-LEU = 1.02 (P=0.004)).
CONCLUSION: RE prior to whey protein/AA intake increases the mRNA expression of select AAT above feeding alone at 5h post RE.
WHEY induced greater changes in PAT-1 vs. EAALEU suggesting unique benefits of whey protein that extend beyond total leucine content.
EAA-LEU resulted in robust increases in select AAT comparable to LEU despite containing ~75% less leucine, suggesting that a high leucine content is not critical in increasing AAT expression after AA intake. The functional physiological significance of these changes remains to be elucidated.
