In humans and animals, exercise and other forms of increased contractile activity are known to inhibit the muscle wasting associated with diseases and experimental conditions resulting from glucocorticoid excess. Recent evidence also indicates that preserving muscle glutamine concentration has the potential to serve as another therapeutic deterrent to muscle atrophy. By examining hormone-responsive, up- regulated (glutamine synthetase, GS) and down-regulated (myosin heavy chains) genes as models for understanding protein regulation, the long- term objectives are to elucidate the molecular events by which exercise and glutamine therapy prevents atrophy from this state. The first overall goal (aims one and two) is: to determine whether maintaining muscle glutamine concentration by glutamine supplementation prevents muscle wasting from glucocorticoids; to evaluate whether glutamine regulates glutamine synthetase expression at a posttranslational level; To determine whether preserving muscle glutamine concentration interferes with the glucocorticoid-mediated depression of myosin heavy chain synthesis; and to examine whether the combination of exercise and glutamine therapy can produce additive effect in atrophy prevention. A second research goal (aims three and four) is directed at examining whether alpha-ketoglutarate supplementation prevents atrophy through maintenance of muscle glutamine levels; whether alpha-ketoglutarate can antagonize hormone-mediated changes in glutamine synthetase expression and in myosin heavy chain synthesis; and whether the combination of glutamine and alpha-ketoglutarate supplementation are essential for optimally preserving muscle glutamine and in protecting against-atrophy. Results from the present grant period have shown that increased contractile activity diminishes basal and glucorticoid-induced GS enzyme activity and mRNA content. Consequently, using transgenic animals, a third goal (aim five) will determine whether the endurance training effects on GS are: (a) indicative of a generalized glucocorticoid response in muscle; (b) director at promoter elements on the GS gene; and (c) directed at an activating transcription factor/cyclic AMP- response element enhancer region of the gene. This project will establish the extent of the individual and combined contributions of glutamine, alpha-ketoglutarate, and exercise in producing optimal therapeutic conditions against atrophy. These results will further establish the importance of GS in the regulation of muscle mass and the mechanism of its gene regulation by exercise. New basic knowledge can be obtained into the reported anabolic effects of glutamine on protein synthesis and the relationship of these alterations with preservation of muscle mass. An understanding of the mechanisms associated with this type of atrophy and atrophy prevention can provide the basis for therapy as well as in identifying the mechanisms underlying other types of muscle wasting conditions and diseases.
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