Characterization of Tau in Cerebrospinal Fluid Using Mass Spectrometry

Abstract

The neurodegenerative disorder Alzheimer's disease (AD) is the most common cause of dementia in the elderly. The presence of neurofibrillary tangles, consisting of hyperphosphorylated tau protein, is one of the major neuropathologic characteristics of the disease, making this protein an attractive biomarker for AD and a possible target for therapy. Here, we describe an optimized immunoprecipitation mass spectrometry method that enables, for the first time, detailed characterization of tau in human cerebrospinal fluid. The identities of putative tau fragments were confirmed using nanoflow liquid chromatography and tandem mass spectrometry. Nineteen tryptic fragments of tau were detected, of which 16 are found in all tau isoforms while 3 represented unique tau isoforms. These results pave the way for clinical CSF studies on the tauopathies.

Differential Mass Spectrometry Profiles of Tau Protein in the Cerebrospinal Fluid of Patients with Alzheimer’s Disease, Progressive Supranuclear Palsy, and Dementia with Lewy Bodies

“…However, our results are coherent with the study of Meredith et al [30] which described N-and C-terminal fragments associated with a 17 kDa central core fragment. Differences in output observed between the present study and those by Portelius et al [28] and McAvoy et al [27] can be accounted for in various ways different origins. First, the MS methods used were different, and the fact that different preanalytical methods were used in particular (precipitation versus immunocapture) may have yielded different results.…”

“…Here, thanks to an adaptation of the "protein standard for absolute quantification" (PSAQ) approach [16], an original purification protocol not relying on immunocapture, and the latest generation of MS analyzers, we could monitor in parallel 18 peptides encompassing the entire Tau protein sequence and isoform diversity. Previous MS attempts to monitor Tau in the CSF of patients were in fact limited to a few peptides and/or relied on immunoprecipitation procedures [27,28]. Importantly, preanalytical procedures are a major issue in the field of proteomics research, as Greco et al have pointed out in connection with the CSF in particular [29].…”

The Human Tau Interactome: Binding to the Ribonucleoproteome, and Impaired Binding of the Proline-to-Leucine Mutant at Position 301 (P301L) to Chaperones and the Proteasome

“…Most frequently, these studies served to characterize post-translational modifications within tau (50 -53) and/or explored the merits of tau as a biomarker for neurodegenerative disease (54,55). Conceptually more similar to the current study were prior investigations that identified proteins that copurify with microtubules (56), explored the composition of neurofibrillar tangles (57), or investigated how the presence or absence of methylene blue alters the tau-associated proteome (58).…”

Fluid Biomarkers in Alzheimer Disease

“…There are several isoforms of the tau protein in CSF, and the molecule has numerous phosphorylation sites (Portelius et al 2008). The most commonly used ELISA method for T-tau is based on monoclonal antibodies that detect all isoforms of tau independently of phosphorylation state (Blennow et al 1995).…”