Regulation of muscle protein synthesis in humans | …
T1 - Amino acid transporters in the regulation of human skeletal muscle protein metabolism
in the regulation of human muscle protein synthesis ..
Studies in which IGF-I has been perfused locally indicate that IGF-I preferentially stimulates protein synthesis in muscle (Fryburg, 1994), whereas systemically administered IGF-I only stimulates muscle protein synthesis when additional amino acids are supplied (Fryburg et al., 1995). The roles of circulating versus local IGF-I and of free versus bound fractions, as well as the importance of each individual binding protein, remain to be determined.
It has been reported that in elderly in comparison with young subjects, there is a decline in the synthesis rate of mixed muscle protein—both total and myofibrillar proteins (Welle et al., 1993; Yarasheski et al., 1993). Interestingly, a recent study demonstrated that not only did synthesis of muscle mitochondrial proteins (pivotal to oxidative phosphorylation and ATP generation) decrease in the elderly, but also that this 40-percent decrease in mitochondrial protein synthesis occurred as early as middle age (average age 52 years) (Rooyackers et al., 1996) (). The decline in mitochondrial protein synthesis was markedly more pronounced than the concomitant 10- to 15-percent decline in synthesis rates of mixed muscle proteins (Rooyackers et al., 1996). These changes were also associated with a decline in cytochrome-c-oxidase activity and endurance capacity (Rooyackers et al., 1996) (). It is possible that the decline in mitochondrial protein synthesis may cause the impairment of endurance capacity and the more pronounced muscle fatigability in the aging population. In addition, robust ATP production is crucial for synthesis of other muscle proteins. A general decline in synthesis rates of several muscle proteins
Regulation of muscle protein synthesis and the ..
AB - 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.
But add in an intense training session with the right nutrient intake at the right time and things change; protein synthesis is activated and degradation is suppressed. The result is an accumulation of muscle protein over time, as shown in the figure below.
Regulation of protein synthesis by insulin
Comprising close to 50 percent of total body weight in lean individuals, skeletal (or striated) muscle constitutes the largest single component of the body and serves as the major repository of protein (close to 50 percent of total body protein) and free amino acids in the body. Besides its locomotive functions, skeletal muscle is also an important metabolic organ. Metabolic functions are crucial not only for locomotion but also for maintaining homeostasis of substrates in the circulation and providing amino acids for various body functions. Mitochondria in skeletal muscle convert energy from nutrients into adenosine triphosphate (ATP) by oxidative phosphorylation. For mechanical functions involving mainly locomotion, this chemical energy (ATP) is further
converted into mechanical energy by the enzymatic (ATPase) action of myosin and actin in the sarcomere (). In this process, a major proportion of the energy loss inevitably appears as heat. Under resting conditions, muscle accounts for 20 to 30 percent of total resting energy expenditure, the variability of which to a large extent is determined by differences in muscle metabolism (Zurlo et al., 1990). Under conditions of cold exposure and shivering thermogenesis, the function of muscle as a "heater" for the body and the resultant energy loss become still more conspicuous. In addition, skeletal muscle supplies amine acids for synthesis of proteins in other tissues (crucial during wound healing), for the immune functions, and for gluconeogenesis (alanine and glutamine) under catabolic conditions. Skeletal muscle also oxidizes glucose and fatty acids and stores large amounts of glycogen postprandially.
Protein Synthesis -Translation and Regulation
Cholesterol: Synthesis, Metabolism, Regulation
Skeletal muscle is a plastic organ that is maintained by multiple pathways regulating cell and protein turnover
Building Muscle: Molecular Regulation of Myogenesis
Nutrient signalling in the regulation of human muscle protein synthesis.
You Don't Need Large Amounts Of Protein To Build Muscle
Nutritional and contractile regulation of human skeletal muscle protein synthesis and mTORC1 ..
Glycogenolysis in muscle and liver - Tuscany Diet
That doesn't mean we should discount carbs as far as protein synthesis goes; they increase insulin levels, which may still be important. Muscles are primed for increased protein synthesis for 24+ hours after training, but the acute burst in protein synthesis that occurs as a result of training or amino acid intake only lasts for a few hours.
Dietary Protein and Exercise: A Review at …
synthesis. The tissue concentration of a specific protein is determined by the balance between protein breakdown and protein synthesis. Nutrient supply to the muscle tissue (for ATP production) and the removal of metabolic by-products (e.g., carbon dioxide) are dependent on uninterrupted and dynamic circulatory systems. All of these individual processes are controlled by regulatory mechanisms, which include circulating and local levels of hormones and substrates, which in turn are influenced by the physiological state of the individual in terms of age, gender, nutritional status, exercise, and chronic or acute illness. Using aging as an example, this brief review outlines some of the control mechanisms and other biological factors involved in the regulation of muscle mass and function.
Enhanced Protein Translation Underlies ..
AB - The mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) are important nutrient- and energy-sensing and signalling proteins in skeletal muscle. AMPK activation decreases muscle protein synthesis by inhibiting mTOR signalling to regulatory proteins associated with translation initiation and elongation. On the other hand, essential amino acids (leucine in particular) and insulin stimulate mTOR signalling and protein synthesis. We hypothesized that anabolic nutrients would be sensed by both AMPK and mTOR, resulting in an acute and potent stimulation of human skeletal muscle protein synthesis via enhanced translation initiation and elongation. We measured muscle protein synthesis and mTOR-associated upstream and downstream signalling proteins in young male subjects (n = 14) using stable isotopic and immunoblotting techniques. Following a first muscle biopsy, subjects in the 'Nutrition' group ingested a leucine-enriched essential amino acid-carbohydrate mixture (EAC). Subjects in the Control group did not consume nutrients. A second biopsy was obtained 1 h later. Ingestion of EAC significantly increased muscle protein synthesis, modestly reduced AMPK phosphorylation, and increased Akt/PKB (protein kinase B) and mTOR phosphorylation (P 0.05). We conclude that anabolic nutrients alter the phosphorylation status of both AMPK- and mTOR-associated signalling proteins in human muscle, in association with an increase in protein synthesis not only via enhanced translation initiation but also through signalling promoting translation elongation.
Creatine Supplement - Unbiased Review on Usage, …
(such as myosin heavy chain and mitochondrial proteins) occurs with age (Balagopal et al., 1997; Rooyackers et al., 1996; Welle et al., 1993; Yarasheski et al., 1993), perhaps reflecting the inability of mitochondria to produce sufficient ATP. Furthermore, recent studies have demonstrated that synthesis rates of myosin heavy chain, a major myofibrillar protein involved in hydrolysis of ATP and conversion of chemical energy from ATP to mechanical energy, also decline by middle age (Balagopal et al., 1997). These results suggest that the aging process selectively affects the ATP-generating machinery of muscle and imply that any intervention should seek to restrict this loss of mitochondrial capacity. In addition, the reduced synthesis rate of myosin heavy chain is compatible with the notion that the ability to maintain adequate muscle protein quality declines with age, thereby potentially compromising the efficiency of the locomotive apparatus to extract mechanical energy from fuel stores. As discussed below, it is likely that age associated decrements in circulating levels of anabolic hormones, such as growth hormone (GH), insulin-like growth factor I (IGF-I), sex steroids, and fading effectiveness of insulin are all involved in the involution of muscle that occurs with aging.
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