Role of tau in Alzheimer's dementia and other neurodegenerative diseases

Alzheimer's disease (AD) is defined histopathologically by beta-amyloid (Aβ) senile plaques and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. The question as to which of these lesions takes precedence in AD pathology has long been an issue of debate. The amyloid cascade hypothesis, currently the predominant hypothesis, considers Aβ peptide to be responsible for the major neurodegeneration observed in AD while the cytoskeleton hypothesis states that tau hyperphosphorylation and subsequent aggregation may be central to the neurodegeneration observed in AD. This review focuses on tau mutations, phosphorylation sites, tau isoforms and the neurohistopathology of AD, and three other tauopathies to demonstrate that disease progression and neuronal loss in AD correlate also with pathological tau and not just amyloid deposition. Although tau is at the center of all these neurodegenerative diseases, there exist differences in morphology, isoforms, phosphorylation sites and mutations in each of these tauopathies. The tauopathies discussed in this review are AD, progressive supranuclear palsy, Pick's disease, and frontotemporal dementia and Parkinsonism linked to chromosome 17.