beta-Amyloid-Induced Tau Phosphorylation does not Correlate with Degeneration in Cultured Neurons

Treatment of cultured neurons with beta-amyloid (Abeta) evokes multiple consequences, including calcium influx, production of reactive oxygen species (ROS), hyperphosphorylation of tau. Which of these events is the major cause of Abeta-induced neurodegeneration has been the subject of controversy. We undertook to determine whether or not the accumulation of hyperphosphorylated tau mediated neurodegeneration. Murine cortical neurons demonstrated increased phospho-tau immunoreactivity between 2-8 hr after treatment of murine cortical neurons with Abeta_25-35. Cultures underwent overall neurodegeneration between 8-16 hr as ascertained by phase-contrast microscopy, a commercial "live/dead" assay and externalization of phosphatidyl serine. Unexpectedly, however, the healthiest-appearing neurons in Abeta-treated cultures contained relatively more phospho-tau immunoreactivity, while obviously degenerating neurons contained less; degenerating neurons often contained less phospho-tau immunoreactivity than did non-Abeta-treated control neurons. By contrast, accumulation of reactive oxygen species, previously demonstrated to mediate Abeta-induced neurodegeneration, was most prominent within visibly-degenerating neurons. These studies do not address the long-term consequences of PHF formation; however, they indicate that tau hyperphosphorylation, although a consequence of Abeta treatment, does not directly contribute to acute degeneration of cultured neurons.