Introduction:
Skeletal muscle mass is regulated by the net balance between muscle protein synthesis and breakdown. Essential amino acids are the substrates of muscle protein and activate muscle anabolism strongly (1). Leucine, one of the essential amino acids, has the strongest anabolic capacity and is known to exert this after being transported into muscle cells through L-type amino acid transporter 1 (LAT1) (1-3). However, the role of LAT1 in skeletal muscle protein synthesis and hypertrophy is not fully understood.
Aims:
Here, we made murine C2C12 myoblasts overexpressing the LAT1 and investigated the role of LAT1 in muscle growth and muscle protein synthesis response after leucine administration.
Methods:
LAT1 overexpressing cells (LAT1-OE) and control cells were made by transferring the LAT1 gene or vehicle into C2C12 myoblasts using in vitro electroporation (n = 6 for each group). One day after the electroporation, the cells were cultured in DMEM containing 2% horse serum and induced differentiation into myotubes for 6 days. After the differentiation, the myotubes were administered with 5 mM leucine. Data were analyzed using t-test or two-way ANOVA (LAT1-OE × Leucine). If an interaction was observed, Sidak multiple-comparison test was performed.
Results:
The LAT1-OE myotubes showed a lower fusion index and embryotic myosin heavy chain expression compared to the control myotubes (P < 0.05). The LAT1-OE myotubes showed lower mTORC1 activity (indicated by the expression of phosphorylated p70S6KThr389) compared to the control myotubes (main effect of LAT1-OE, P < 0.05), but mTORC1 activation induced by leucine administration was not influenced (main effect of leucine, P < 0.05).
Conclusion:
These results suggest that the expression of LAT1 negatively regulates muscle growth but does not have a negative effect on the response to leucine administration.