Neuronal kinase stimulation leads to aberrant tau phosphorylation and neurotoxicity

Neurofibrillary tangles in Alzheimer's disease brain consist mainly of abnormally phosphorylated tau proteins organised in paired helical filaments. Induction of tau phosphorylation in living neurons by hyperstimulation is monitored by specific monoclonal antibodies, such as AT-8 and PHF-1. By quantitative immunocytochemistry, we show that aberrant phosphorylation at the Ser199/Ser202 epitope (AT-8) and at the Ser 396 epitope (PHF-1) are moderately induced, proportionally to the degree of kinase stimulation. Whereas AT8 expression is prominent after 48 h, cell death becomes significant at 72 h and is related to the degree of stimulation and the expression level of aberrant tau phosphorylation. Time-lapse videomicroscopy of individual neuroblastoma cells suggest that hyperstimulation leads to a form of morphological over-differentiation. Immediately before cell death, some cells tend to display some features of mitosis. The data suggest a strong correlation between the expression of specific PHF-epitopes and subsequent cell death. The extended time scale of toxicity in this model may be appropriate to study in more detail the steps leading to aberrant phosphorylation associated neurotoxicity.