Amino acid transporters in the regulation of human skeletal muscle protein metabolism

Abstract

Purpose of review: To highlight recent research on amino acid sensing and signaling and the role of amino acid transporters in the regulation of human skeletal muscle protein metabolism.

Recent findings: The mechanisms that sense amino acid availability and activate mechanistic target of rapamycin complex 1 signaling and protein synthesis are emerging, with multiple new proteins and intracellular amino acid sensors recently identified. Amino acid transporters have a role in the delivery of amino acids to these intracellular sensors and new findings provide further support for amino acid transporters as possible extracellular amino acid sensors. There is growing evidence in human skeletal muscle that amino acid transporter expression is dynamic and responsive to various stimuli, indicating amino acid transporters may have a unique role in the regulation of human skeletal muscle adaptation.

Summary: There is a clear need to further examine the role of amino acid transporters in human skeletal muscle and their link to cellular amino acid sensing and signaling in the control of protein metabolism. A better understanding of amino acid transport and transporters will allow us to optimize nutritional strategies to accelerate muscle health and improve outcomes for clinical populations.

Figure 1

Schematic of the mechanisms regulating protein metabolism in response to increased amino acid availability and the role of amino acid transporters. GATOR, GTPase activating protein [GAP] activity toward Rags; Gln, glutamine; LAT1, system L amino acid transporter; MLCK II, myosin light-chain kinase II; mTORC1, mechanistic target of rapamycin complex 1; PAT1, proton-assisted amino acid transporter 1; RAGs, Ras-related GTPases; SNAT2, system A amino acid transporter.