Increased tau phosphorylation at the Ser396 epitope after amyloid beta-exposure in organotypic cultures.

The hallmarks of Alzheimer's disease include extracellular plaques primarily consisting of amyloid-beta peptide and intracellular neurofibrillary tangles composed of highly phosphorylated tau protein. We report that exposure of organotypic hippocampal cultures to synthetic amyloid-beta peptide(25-35) (50 microM, 96 h) causes neurodegeneration concomitant with a significant increase in tau phosphorylation at the Ser epitope (+60%). Furthermore, the level of active glycogen synthase kinase-3beta (GSK-3beta [pTyr]) was increased (+55%) after amyloid-beta peptide(25-35) exposure. These findings support the role of amyloid-beta peptide as a mediator of tau phosphorylation and demonstrate the usefulness of organotypic cultures for investigating the link between amyloid-beta peptide-induced neurotoxicity and tau phosphorylation. Our results also confirm that amyloid-beta peptide induces activation of glycogen synthase kinase-3beta.