A study of abnormaly phosphorylated tau in glidl cells

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Tau-positive inclusions that occur in glial cells are called glial fibrillary tangles or, more simply, glial tangles. These include tuft-shaped astrocytes, thorn-shaped astrocytes, coiled bodies and argyrophilic threads. The latter two sltructures occur in oligodendroglia. The tau protein in glial tangles is hyperphosphorylated and has similar immunohistochemical profiles to that in neurofibrillary tangles (NFTs) except that there are no epitopes derived from alternatively spliced exon 2 and 3. In contrast to NFTs, glial tangles rarely show solid filaments. Such NFTs-associated molecules as ubiquitin, apolipoprotein E,alpha1-antichymotrypsin and heparan sulfate are all absent from glial tangles. These characteristics suggest that glial tangles resemble the pretangles which occur in neurons adn are thought to represent an early stage of NFTs. Tau pathology in neurodegenerative diseases takes heterogenous forms.Manifestation of partially phosphorylated tau in rat primary culture astrocytes was shown immunohistochemically by phosphorylated as well as non-phosphorylated tau antibodies and by immunoblots. Immunogenicity for tau gradually diminished during further culture、however, continuous and recurrent exposure to calcium ionophore maintained immunoreactivity for tau in culture astrocytes and moreover occurred phosphorylation at Ser 396. Electron microscopy showed tau distributed diffusely in the experimental astrocytes except for in the nucleus and mitochondria but no filamentous assembly was observed.