Tau-inclusion body formation in oligodendroglia: the role of stress proteins and proteasome inhibition.

Filamentous tau-positive inclusions in neurons and glia are a unifying mechanism underlying a variety of late onset neurodegenerative disorders termed "tauopathies". Oligodendroglial lesions and white matter pathology have long been underestimated and are specifically prominent in frontotemporal dementias (FTDs), such as Pick's disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17). Oligodendrocytes contain an extensive microtubule network and express the microtubule-associated protein tau. Tau-positive inclusion bodies in oligodendrocytes are positively stained with antibodies against ubiquitin and heat shock proteins (HSPs). Specifically the small HSP alphaB-crystallin has been identified in oligodendroglial lesions. HSPs act as molecular chaperones and prevent the accumulation of abnormal proteins, and support proteolytic degradation by targeting non-reparable proteins to the ubiquitin proteasomal pathway. HSPs and the proteasomal system closely work together. The present report summarizes recent data on HSP induction and aggregate formation in oligodendroglia cell culture systems, indicating that posttranslational modification of tau, HSP induction and alterations of the proteasomal system, which might occur during aging and disease processes, are involved in the neuropathological events leading to aggregate formation and degeneration.