title: Binding and internalization of lysosomal enzymes by primary cultures of rat glia.
abstract: Highly purified cultures of rat astrocytes and oligodendrocytes were examined for their ability to bind and internalize lysosomal enzymes. Astrocytes displayed a saturable uptake of beta-glucosidase and beta-galactosidase. The uptake was specifically inhibited by mannose-6-phosphate but not by several other sugars or sugar phosphates, indicating that the process was mediated by mannose-6-phosphate receptors. When cells were allowed to take up 125I-beta-glucosidase for 1 hr at 37 degrees C and subcellular organelles were isolated, the enzyme was shown to comigrate with a lysosomal organelle marker enzyme, suggesting that the enzyme was targeted to lysosomes. Astrocyte receptors were probed directly by binding of 125I labeled beta-glucosidase to astrocyte membranes at 4 degrees C. Binding was saturable and competitively inhibited by mannose-6-phosphate. In contrast to the astrocytes, cultured oligodendrocytes showed no specific binding or uptake of the lysosomal enzymes. Immunocytochemical staining of mixed glial cultures supported the biochemical data; only the astrocytes stained positive with anti-mannose-6-phosphate receptor antibodies.
authors.forename: D F
authors.initials: DF
authors.lastname: Hill
authors.forename: P N
authors.initials: PN
authors.lastname: Bullock
authors.forename: F
authors.initials: F
authors.lastname: Chiappelli
authors.forename: L H
authors.initials: LH
authors.lastname: Rome
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000201:enzymology*; D002352:Carrier Proteins / Q000502:physiology; D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D002540:Cerebral Cortex; D005696:Galactosidases / Q000378:metabolism*; D005959:Glucosidases / Q000378:metabolism*; D008247:Lysosomes / Q000201:enzymology*; D009457:Neuroglia / Q000201:enzymology*; D009836:Oligodendroglia / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D017527:Receptor, IGF Type 2; D001616:beta-Galactosidase / Q000378:metabolism*; D001617:beta-Glucosidase / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D017527:Receptor, IGF Type 2; D005696:Galactosidases; D005959:Glucosidases; D001617:beta-Glucosidase; D001616:beta-Galactosidase