Hyperphosphorylated tau is elevated in Alzheimer's disease with psychosis

Psychosis occurs in 40-60% of Alzheimer's disease (AD) subjects, is heritable, and indicates a more rapidly progressive disease phenotype. Neuroimaging and postmortem evidence support an exaggerated prefrontal cortical synaptic deficit in AD with psychosis. Microtubule-associated protein tau is a key mediator of amyloid-β-induced synaptotoxicity in AD, and differential mechanisms of progressive intraneuronal phospho-tau accumulation and interneuronal spread of tau aggregates have recently been described. We hypothesized that psychosis in AD would be associated with greater intraneuronal concentration of phospho-tau and greater spread of tau aggregates in prefrontal cortex. We therefore evaluated prefrontal cortex phospho-tau in a cohort of 45 AD cases with and without psychosis. Intraneuronal phospho-tau concentration was higher in subjects with psychosis, while a measure of phospho-tau spread, volume fraction, was not. Across groups both measures were associated with lower scores on the Mini-Mental State Examination and Digit Span Backwards test. These novel findings indicate that tau phosphorylation may be accelerated in AD with psychosis, indicating a more dynamic, exaggerated pathology in AD with psychosis.