Regulation of muscle growth and lipid metabolism | Régulation de la croissance musculaire et du métabolisme lipidique
2002
Grizard, J. ((Institut National de la Recherche Agronomique, St-Genès-Champanelle (France). Centre de Clermont-Ferrand Theix Lyon, Laboratoire d'Etude du Métabolisme Azoté)) | Orzechowski, A.
Many attempts have been made to improve meat quality and muscle growth, and to reduce muscle wasting. Central to these strategies is a comprehensive knowledge of the regulation of muscle development and metabolism in various species. Muscle growth results from hypertrophying myofibers, which increase their myonuclear number by recruitment of satellite cells. Determined myoblasts, under conditions that favour differentiation, align and fuse to form multinucleated myotubes, however, the mechanisms underlying the recruitment of satellite cells to hyperplastic or hypertrophic growth have not been established. Ontogenesis of skeletal muscle includes many steps regulated by cytokines and hormones acting through transcription of muscle regulatory factors (MRFs). Recently discovered MRF called myostatin focuses special attention since it represses muscle growth. The glucocorticoid action and the oxidative stress has also to be considered especially face to muscle cell death. Other hormonal factors such as leptin also need special concern due to their impact on body gains and tissue repartitioning. Muscle, as a proportion of total protein, increases from approximately 30 to 45 per cent for most species during the postnatal life. Due to its slow rate of protein turnover, muscle accounts for only 20-35 per cent of whole body protein synthesis. The increase in protein synthesis and the decrease in proteolysis both accounted for postprandial muscle anabolism. Insulin, p70S6 kinase and amino acids appear as the main mediators of these pathways. Substrate availability is therefore major in the control of muscle protein disposition. It has been suggested that longitudinal bone growth may be the primary target for overall somatic growth regulation since skeletal muscle growth could be dependant on a potentiating stimulus of bone growth possibly exerted by passive stretch. The intact nervous system seems to be indispensable for normal growth of the bones. Specific micronutrients (e.g. minerals and flavonoids) are potential tools to improve bone mineralisation and prevent osteoporosis. Finally, crucial metabolic link between muscle and adipose tissue concerns free fatty acids. The relation between muscle function and lipid metabolism focuses special attention. Adipocytes are decisive for the deposition of body fat. Studies on lipid metabolism were essentially performed in an attempt to meet the requirements of consumers (conjugated linoleic acid effects, supplementation with polyunsaturated fatty acids). Summaries of 19 communications
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