Highlighted Topic Regulation of Protein Metabolism in Exercise and Recovery Nutritional and Contractile Regulation of Human Skeletal Muscle Protein Synthesis and Mtorc1 Signaling Translational Control of Muscle Protein Synthesis

and contractile regulation of human skeletal muscle protein synthesis and mTORC1 signaling. this review we discuss current findings in the human skeletal muscle literature describing the acute influence of nutrients (leucine-enriched essential amino acids in particular) and resistance exercise on muscle protein synthesis and mammalian target of rapamycin complex 1 (mTORC1) signaling. We show that essential amino acids and an acute bout of resistance exercise independently stimulate human skeletal muscle protein synthesis. It also appears that ingestion of essential amino acids following resistance exercise leads to an even larger increase in the rate of muscle protein synthesis compared with the independent effects of nutrients or muscle contraction. Until recently the cellular mechanisms responsible for controlling the rate of muscle protein synthesis in humans were unknown. In this review, we highlight new studies in humans that have clearly shown the mTORC1 signaling pathway is playing an important regulatory role in controlling muscle protein synthesis in response to nutrients and/or muscle contraction. We propose that essential amino acid ingestion shortly following a bout of resistance exercise is beneficial in promoting skeletal muscle growth and may be useful in counteracting muscle wasting in a variety of conditions such as aging, cancer cachexia, physical inactivity, and perhaps during rehabilitation following trauma or surgery. HUMAN SKELETAL MUSCLE PROTEIN metabolism has received significant attention over the past few decades because of its relevance to aging, disease processes, and physical inactivity. The importance of skeletal muscle is obvious since it comprises nearly 40% of body weight, constitutes between 50 and 75% of all proteins (73), and is imperative for locomotion. However, it is also important as an amino acid reservoir, for energy consumption and for fuels for other tissues (e.g., brain, immune cells). Skeletal muscle proteins turnover regularly such that 1–2% of proteins are synthesized and broken down daily (111). The turnover of proteins involves the ongoing processes of protein synthesis and breakdown. A positive net protein balance occurs when proteins accumulate in excess of their removal (e.g., following nutrient ingestion), whereas a negative net protein balance occurs when the breakdown of proteins exceeds that of their synthesis (e.g., fasting). The initial work of Professors Michael J. Rennie and Robert R. Wolfe contributed significantly to the understanding of the muscle protein metabolism field in humans by incorporating stable isotope techniques concurrently with skeletal muscle biopsies in the 1980s and 1990s. Because of these breakthroughs, researchers can now …