Levels of normal and abnormally phosphorylated tau in different cellular and regional compartments of Alzheimer disease and control brains

Abstract

Microtubule associated protein tau is abnormally phosphorylated in Alzheimer disease (AD) brain. In the present study we investigated (i) whether tau is axonal or both axonal and somatodendritic, (ii) whether tau is a marker of Alzheimer neurofibrillary pathology, and (iii) whether the levels of tau in the cytosol (100,000 x g supernate) from AD brain are altered. Frozen autopsied tissue from 20 AD, 17 normal aged and 15 neurological control cases obtained 3-8 h postmortem were analyzed. Levels of normal, total, and abnormally phosphorylated tau were determined by a radioimmunoslot-blot assay using mAb Tau-1 as the primary antibody. Both frontal gray matter homogenate and cytosol from normal brains had 3&45% higher levels of normal tau than the corresponding fractions from the white matter. In AD frontal and temporal cortices, the total tau levels were 6-to 7-fold higher than in cerebellar cortex (P < 0.01 and P < 0.02). Furthermore, tau levels of cerebellar cortex, an area of the brain unaffected with Alzheimer neurofibrillary changes, were indistinguishable between AD and control groups. The levels of normal tau in cytosol from both frontal gray and white matters in AD were reduced by approximately 40% (P < 0.05). The levels of total tau in AD frontal and temporal cortex were 4-to 5-fold higher than in the corresponding tissue from control cases (P < 0.01) and this increase was in the form of abnormally phosphorylated tau. These studies suggest (i) that there is probably at least as much tau in the somatodendritic compartment as in the axonal compartment, (ii) that the abnormally phosphorylated tau is a biochemical marker of the neurofibrillary pathology in AD, and (iii) that the levels of normal tau are significantly reduced in the 100,000 x g brain supernate from AD cases.

Biometals and Their Therapeutic Implications in Alzheimer's Disease

“…Iron treatment to cultured neurons increases tau phosphorylation [153][154][155][156], so upstream iron elevation might increase pathological tau in AD. Total tau levels are also decreased in AD cortex [157][158][159][160], and we showed that loss of tau expression causes iron-and agedependent cognitive loss and cortical atrophy in mice [64]. Tau is required for APP trafficking to the neuronal membrane [64].…”

Normalizing the gene dosage of Dyrk1A in a mouse model of Down syndrome rescues several Alzheimer's disease phenotypes

“…Abnormal tau expression and hyperphosphorylation are common features in AD and DS (Khatoon et al, 1994;Oyama et al, 1994), causing abnormalities in the cytoskeleton. In addition, increases in tau expression have been reported in other mouse models of AD and aging (Manich et al, 2011;Doehner et al, 2010;Madhusudan et al, 2009).…”

Lithium suppression of tau induces brain iron accumulation and neurodegeneration

“…43,44,45 In tauopathies (such as AD and PD), insoluble tau aggregates are accompanied by a fall in soluble tau levels in affected tissue. 43,46,47,48,49,50,51 We have argued that this will lead to a loss of tau function that could cause neurodegeneration, as tau functions to lower neuronal iron levels by promoting the presentation of the amyloid protein precursor (APP) to the neuronal surface, 43 where it promotes the efflux of iron. 52,53,54 Without soluble tau, neurons accumulate iron to toxic levels, and hence tau-knockout mice develop a parkinsonism with impaired-cognition phenotype that is rescued by iron chelation.…”