Peripheral nerve myelin contains a relatively high amount of glycoprotein compared to that of the central nervous system. The studies proposed are designed to test the hypothesis that the synthesis and metabolism, as well as the degradation of PNS myelin in health and disease are interrelated with the integrity of the carbohydrate chain. Thus, myelination, demyelination and remyelination, aging, and metabolic diseases affecting the peripheral nerve such as diabetes may affect carbohydrate synthesis, processing, and stability, which may, in turn, have an influence on the maintenance of the myelin sheath. Assays in the peripheral nerve representing steps in synthesis of the oligo- saccharide chain will be devised. These include the synthesis of dolichol phosphatedisaccharide, the synthesis of the high-mannose carbohydrate chain, and the linkage of the chain to newly- synthesized glycoprotein PO. These steps will be assessed in myelin development, in aged animals, in nerves undergoing demyelination and remyelination as a result of intraneural injection of lysolecithin and of cutting the sciatic nerve (Wallerian degeneration), and in experimental diabetes. The progression of normal processing of the carbohydrate chain in the Golgi membranes will also be assessed with the enzyme endoglycosidase H which cleaves the carbohydrate chain from incompletely-processed glycoproteins. Peripheral nerve degradation, in most cases, is mediated by macrophages. It is likely that myelin must be abnormal in some way in order to be preferentially phagocytized by macrophages. PNS myelin will be altered in various ways such as by opsonizing with specific antibodies, and by synthesizing myelin in the presence of various processing inhibitors so that the carbohydrate chain is abnormal. These myelin preparations will be cocultured with macrophages and the uptake, phagocytosis, and metabolism of the myelin will be measured by chemical means. The mechanism of lipid and protein destruction, and the relative time sequence of these processes will be measured. The effect of phagocytosis of myelin and of interferon-gamma on the elaboration of various degradative factors by the macrophages will also be explored. Since relatively little is known about glycoprotein metabolism in peripheral nerve, the results of these experiments should greatly increase our understanding of the relationships between glycoproteins and PNS myelin in health and disease.
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