Over 60% of the PNS myelin proteins are glycoproteins, therefore their metabolic properties, synthesis, and degradation may largely determine the behavior of this membrane. We intend to investigate the levels of enzymes involved in glycosylation of myelin proteins in the peripheral nerve of rats during myelination, in mature and aged animals, and also in various stages of demyelination-remyelination resulting from intraneural injection of lysophosphatidyl choline. Enzymes to be investigated include UDP-N-acetylglucosamine-dolichol phosphate transferase, dolichol pyrophosphate-glucose oligosaccharide formation, dolichol pyrophosphate oligosaccharide protein oligosaccharide transferase, and Alpha-D mannosidase. The effects of addition of exogenous dolichol phosphate and oligosaccharide acceptor protein will be examined. We hope to determine which glycosylation steps might be limiting for myelin glycoproteins synthesis in the aging animals, and whether certain ones are limiting or increased during the surge of remyelination after demyelination. The relationships between P0, 23K, and 19K proteins will be investigated to determine whether these are synthesized in parallel or derived in sequence. We will use in vitro biosynthesis systems interrupted with cycloheximide to determine changes in ratio of these proteins after cessation of synthesis, autoclysis experiments, and in vitro translation. High molecular weight glycoproteins are excellent candidates for """"""""recognition"""""""" factors between Schwann cells, axons, and myelin. We will search for such proteins which might be activated during demyelination-remyelination episodes using uptake of labeled amino acids into proteins and glycoproteins as indicators of activation. We will identify such """"""""recognition"""""""" factors and characterize them using specific extracting substances and lectins. The manner of destruction of myelin glycoproteins by inflammatory cells including lymphocytes and macrophages will be explored by incubating cultured activated cells with PNS myelin or enriched preparations of P0, then characterizing their breakdown products. These experiments should yield new findings about PNS myelin, the mechanisms of synthesis of its glycoproteins, the limitations of glycoprotein synthesis in aging and demyelination, and the mechanism of its destruction. These findings will be applicable to a number of kinds of peripheral neuropathies.
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