The long-range objective of this research program is to define chemical properties of nerve and other tissues which exert a trophic influence on the development of muscle. Our recent studies have demonstrated that transferrin (Tf) is present in adult avian sciatic nerves and has profound myotrophic effects in vitro. While Tf is required by virtually all types of cells in tissue culture, its precise biological role has not been defined. In particular, little is known about the effects of Tf on cellular metabolism and gene expression in developing and adult muscles. Thus, the immediate goals of this proposal are to clarify the roles of Tf and the Tf/receptor interaction in muscle metabolism and to investigate the mechanism by which Tf influences muscle development.
Three specific aims are proposed. 1) To study the role of Tf and its receptors in developing muscle in vitro and in vivo. Our studies demonstrate that Tf receptors are present on developing muscle and that labeled Tf is specifically accumulated by this tissue. Experiments will now be conducted to determine the specific binding and uptake of Tf, to purify Tf receptors and to produce specific antibodies to them and to demonstrate the number and distribution of Tf receptors in developing and adult muscle. Antibodies to Tf receptors will also be used to determine the conseqences of receptor blockade. 2) To examine the role of Tf in the gene expression of the glycolytic enzyme, aldolase. Recent data show that Tf induces a 2-5-fold increase in the muscle-specific form of adolase, A4. The neuronal (C4) and myogenic forms of aldolase will be purified and antibodies to these isoenzymes will be produced. The role of Tf in the expression of aldolase isoenzymes will be determined by blocking the Tf receptors with specific antibodies during muscle development. 3) To investigate the regulation of Tf receptor expression by such influences as neural tissue, innervation and muscle activity. These studies will involve: (i) co-cultures of nerve and muscle; (ii) electrical stimulation of cultured muscle; and (iii) denervation of wing muscles in ovo. The results of these studies will yield fundamental information regarding the physiological action of Tf in muscle development. Such information can contribute to an understanding of factors underlying degenerative diseases of muscle such as muscular atrophy and muscular dystrophy.
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