Comprehensive Quantitative Profiling of Tau and Phosphorylated Tau Peptides in Cerebrospinal Fluid by Mass Spectrometry Provides New Biomarker Candidates

Article type: Research Article

Authors: Russell, Claire L.^{a; *} | Mitra, Vikram^a | Hansson, Karl^b | Blennow, Kaj^{b; c} | Gobom, Johan^{b; c} | Zetterberg, Henrik^{b; c; d} | Hiltunen, Mikko^{e; f} | Ward, Malcolm^a | Pike, Ian^a

Affiliations: [a] Proteome Sciences plc, South Wing Laboratory, Institute of Psychiatry, De Crespigny Park, London, UK | [b] Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry, The Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden | [c] Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, Mölndal, Sweden | [d] Department of Molecular Neuroscience, University College London, Institute of Neurology, Queen Square, London, UK | [e] Institute of Biomedicine, University of Eastern Finland, Kuopio, Finland | [f] Department of Neurology, Kuopio University Hospital, Kuopio, Finland

Correspondence: [*] Correspondence to: Claire Russell, Proteome Sciences plc, South Wing Laboratory, Institute of Psychiatry, De Crespigny Park, London, SE5 8AF, UK. Tel.: +44 207 848 5113; E-mail: Claire.Russell@Proteomics.com.

Abstract: Aberrant tau phosphorylation is a hallmark in Alzheimer’s disease (AD), believed to promote formation of paired helical filaments, the main constituent of neurofibrillary tangles in the brain. While cerebrospinal fluid (CSF) levels of total tau and tau phosphorylated at threonine residue 181 (pThr181) are established core biomarkers for AD, the value of alternative phosphorylation sites, which may have more direct relevance to pathology, for early diagnosis is not yet known, largely due to their low levels in CSF and lack of standardized detection methods. To overcome sensitivity limitations for analysis of phosphorylated tau in CSF, we have applied an innovative mass spectrometry (MS) workflow, TMTcalibratortrademark, to enrich and enhance the detection of phosphoproteome components of AD brain tissue in CSF, and enable the quantitation of these analytes. We aimed to identify which tau species present in the AD brain are also detectable in CSF and which, if any, are differentially regulated with disease. Over 75% coverage of full-length (2N4R) tau was detected in the CSF with 47 phosphopeptides covering 31 different phosphorylation sites. Of these, 11 phosphopeptides were upregulated by at least 40%, along with an overall increase in tau levels in the CSF of AD patients relative to controls. Use of the TMTcalibratortrademark workflow dramatically improved our ability to detect tau-derived peptides that are directly related to human AD pathology. Further validation of regulated tau peptides as early biomarkers of AD is warranted and is currently being undertaken.

Keywords: Alzheimer’s disease, biomarkers, cerebrospinal fluid, mass spectrometry, neurodegenerative disease, phosphorylation, post translational modifications, tau

DOI: 10.3233/JAD-160633

Journal: Journal of Alzheimer's Disease, vol. 55, no. 1, pp. 303-313, 2017