β-Amyloid and Corticosterone-induced Changes to tau Protein in Primary Cultures of Hippocampal Neurons

Abstract

Objectives: Alzheimer's disease (AD) and depression are neuropsychiatric disorders that bear a complex interplay within individuals suffering concomitantly from both illnesses. Under physiological settings, tau protein binds to microtubules to maintain the structural stability and dynamics of the neuronal cytoskeleton. Pathological modifications to tau have been implicated in neurodegenerative diseases such as AD, where aberrant hyperphosphorylation of tau has been shown to compromise the integrity of the microtubule network. In contrast, tau has not been well studied in models of depression. We aim to compare the role of tau in vitro following ß-amyloid (Aß)-induced AD and corticosterone-induced depression. In addition, we also aim to investigate tau modifications under co-treatment of both Aß and corticosterone. Methods: Immunoreactivity for a-tubulin, tau and phospho-tau (pS396, pS404) was examined in primary cultures of hippocampal neurons prepared from embryonic day 18 Sprague Dawley rats. Phosphorylation of tau protein was examined by both Western-blot and immunofluorescent staining. Results: Similar intense immunofluorescence of pS396 and pS404 tau neurons was observed following exposure to Aß and corticosterone. Also, both treatments of Aß and corticosterone demonstrated a decrease in colocalization between tau and a-tubulin. In addition, co-treatments of both Aß and corticosterone also induced aberrant modifications of tau. Conclusions: The results suggest that tau undergoes similar pathological changes in Aß and corticosterone-treated hippocampal neurons, providing insight into the common role of tau abnormalities in propagating pathophysiology of disease. Future studies should investigate how abnormally phosphorylated tau contributes to dendritic regression.