Analysis of human tau in cerebrospinal fluid

Alzheimer's disease (AD) is the most common form of dementia. Neuropathologically, it is characterized by two major hallmarks: neurofibrillary tangles (NFT) formed from hyperphosphorylated versions of the tau-protein, and neuritic plaques (NP) containing mostly beta-amyloid peptides (A beta) that are formed from the amyloid precursor protein (APP) by enzymatic cleavage. Despite much progress in recent years, the causes of sporadic (i.e., nonfamiliar) AD are still unclear and its valid diagnosis still relies on autopsy. Clinically used biomarkers present in cerebrospinal fluid (CSF), that is, unphosphorylated or phosphorylated tau and A beta-peptides of different lengths, lack the necessary specificity and sensitivity. Here, we describe a novel strategy to characterize tau versions present in CSF with respect to their molecular mass and isoelectric point. Aliquots of 1 mL CSF (i.e., 700 to 1300 pg tau) from nondemented persons and histopathologically confirmed AD cases were depleted for six dominant proteins, separated by two-dimensional gel electrophoresis, and then electro-transferred onto PVDF-membranes. Tau was detected with monoclonal antibody (mAb) HT7 conjugated with horseradish peroxidase (HRP). In this way, a complex tau pattern was identified in CSF that was very similar to the tau preparations from autopsy brain samples. The presented strategy enables the analysis of the phosphorylation and processing status of tau in CSF samples from healthy people and patients diagnosed with different neurological disorders. This more-detailed information on circulating tau versions and their clearance rates may facilitate the development of new diagnostic tools.