title: Proteasome inhibition stabilizes tau inclusions in oligodendroglial cells that occur after treatment with okadaic acid.
abstract: Tau-positive inclusions in oligodendrocytes are consistent neuropathological features of corticobasal degeneration, progressive supranuclear palsy, and frontotemporal dementias with Parkinsonism linked to chromosome 17. Here we show by immunohistochemistry that tau-positive oligodendroglial inclusion bodies also contain the small heat-shock protein (HSP) alphaB-crystallin but not HSP70. To study the molecular mechanisms underlying inclusion body formation, we engineered an oligodendroglia cell line (OLN-t40) to overexpress the longest human tau isoform. Treatment of OLN-t40 cells with okadaic acid (OA), an inhibitor of protein phosphatase 2A, caused tau hyperphosphorylation and a decrease in the binding of tau to microtubules. Simultaneously, tau-positive aggregates that also stained with the amyloid-binding dye thioflavin-S as well as with antibodies to tau and alphaB-crystallin were detected. However, they were only transiently expressed and were degraded within 24 hr. When the proteasomal apparatus was inhibited by carbobenzoxy-l-leucyl-l-leucyl-l-leucinal (MG-132) after OA treatment, the aggregates were stabilized and were still detectable after 18 hr in the absence of OA. Incubation with MG-132 alone inhibited tau proteolysis and led to the induction of HSPs, including alphaB-crystallin and to its translocation to the perinuclear region, but did not induce the formation of thioflavin-S-positive aggregates. Hence, although tau hyperphosphorylation induced by protein phosphatase inhibition contributes to pathological aggregate formation, only hyperphosporylation of tau followed by proteasome inhibition leads to stable fibrillary deposits of tau similar to those observed in neurodegenerative diseases.
authors.affiliation: University of Oldenburg, Department of Biology, Molecular Neurobiology, D-26111 Oldenburg, Germany.
authors.forename: Olaf
authors.initials: O
authors.lastname: Goldbaum
authors.forename: Malte
authors.initials: M
authors.lastname: Oppermann
authors.forename: Melanie
authors.initials: M
authors.lastname: Handschuh
authors.forename: Deepa
authors.initials: D
authors.lastname: Dabir
authors.forename: Bin
authors.initials: B
authors.lastname: Zhang
authors.forename: Mark S
authors.initials: MS
authors.lastname: Forman
authors.forename: John Q
authors.initials: JQ
authors.lastname: Trojanowski
authors.forename: Virginia M-Y
authors.initials: VM
authors.lastname: Lee
authors.forename: Christiane
authors.initials: C
authors.lastname: Richter-Landsberg
mesh_terms: D052160:Benzothiazoles; D001921:Brain / Q000378:metabolism / Q000473:pathology; D002460:Cell Line; D003546:Cysteine Endopeptidases; D003599:Cytoskeleton / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D006801:Humans; D007150:Immunohistochemistry; D002479:Inclusion Bodies / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D007976:Leupeptins / Q000494:pharmacology; D008870:Microtubules / Q000378:metabolism; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D019319:Okadaic Acid / Q000494:pharmacology*; D009836:Oligodendroglia / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex; D054648:Protein Phosphatase 2; D024801:Tauopathies / Q000378:metabolism / Q000473:pathology; D013844:Thiazoles; D038203:alpha-Crystallin B Chain / Q000378:metabolism; D016875:tau Proteins / Q000378:metabolism*
chemical_list: D052160:Benzothiazoles; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D007976:Leupeptins; D009097:Multienzyme Complexes; D013844:Thiazoles; D038203:alpha-Crystallin B Chain; D016875:tau Proteins; D019319:Okadaic Acid; C009462:thioflavin T; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde