Characterization of thorn-shaped astrocytes in white matter of temporal lobe in Alzheimer's disease brains.

Thorn-shaped astrocytes (TsA) are mainly localized in the periventricular white matter of the temporal lobe in a subgroup of aged individuals usually in the context of Alzheimer's disease (AD). Immunohistochemistry of TsA shows 4Rtau deposition, tau phosphorylation at different sites recognized with phosphospecific anti-tau antibodies Thr181, Ser202, Ser214, Thr231, Ser396, Ser422, and clones AT8 and PHF-1, and conformational changes revealed with Alz50 and MC-1 antibodies; TsA are also immunostained with antibodies to active tau kinases MAPK/ERK-P, SAPK/JNK-P, p38-P and GSK-3β. These findings are common to neurofibrillary tangles in AD. However, TsA are not stained with 3Rtau antibodies, and they are seldom stained or not at all with phosphospecific tauSer262 and with Tau-C3 antibody, which recognizes the latter tau truncation at aspartic acid 421. Previous studies have shown that tau phosphorylation at Ser262 reduces tau binding to microtubules and increases caspase-3 activity, whereas tau truncation at aspartic acid 421 is associated with tau ubiquitination, and toxic effects of tau. In this line, ubiquitin is not accumulated in TsA, and in situ end-labeling of nuclear DNA fragmentation shows absence of degeneration in TsA. These observations support the concept that tau lesions in neurons differ from those seen in TsA in AD.