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Catabolic Regulation of the Expression of the Major Myelin Glycoprotein by Schwann Cells in Culture
Author(s) -
Brunden Kurt R.,
Windebank Anthony J.,
Poduslo Joseph F.
Publication year - 1990
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1990.tb01894.x
Subject(s) - myelin , swainsonine , catabolism , schwann cell , biology , glycoprotein , galactocerebroside , myelin associated glycoprotein , biochemistry , explant culture , cell culture , neuroglia , mannose , microbiology and biotechnology , metabolism , endocrinology , central nervous system , in vitro , oligodendrocyte , genetics
Previous studies have suggested that neonatal Schwann cell cultures deprived of axonal contact do not express components of the myelin membrane, including the major myelin glycoprotein, P 0 . In contrast, Schwann cells from permanently transected, adult nerve exhibit continued biosynthesis of P 0 after culture, suggesting that the ability to express the myelin glycoprotein may depend on the degree of cellular differentiation. To examine further the ability of Schwann cell cultures to express P 0 as a function of age, we have performed precursor incorporation studies on endoneurial explants from 4‐ to 12‐day‐old rat sciatic nerves after 5 days in culture. The data reveal that explants from 12‐day‐old animals synthesize detectable levels of this integral myelin protein when assayed by [ 3 H]mannose incorporation, even though there is no apparent myelin assembly in the cultures. Pulse–chase analysis of cultures from 12‐day‐old rats demonstrates that [ 3 H]mannose‐labeled P 0 is substantially degraded within 3 h. This catabolism largely can be prevented by the addition of swainsonine, ammonium chloride, or L‐methionine methyl ester to the pulse‐chase media. The former agent alters oligosaccharide processing whereas the latter two compounds inhibit lysosomal function. The P 0 synthesized by the 12‐day explant cultures following the addition of swainsonine is readily fucosylated, implying that the protein has progressed at least as far as the medial Golgi before its exit and subsequent catabolism. If cultures from 4‐, 6‐, and 8‐day‐old animals are analyzed for P 0 biosynthesis by [ 3 H]mannose incorporation in the presence of swainsonine, detectable levels of the glyoprotein are seen. The inability to demonstrate the presence of P 0 in earlier studies of neonatal cultures was presumably due in part to the rapid lysosomal catabolism of the protein after translation.