Tau Protein Quantification in Human Cerebrospinal Fluid by Targeted Mass Spectrometry at High Sequence Coverage Provides Insights into Its Primary Structure Heterogeneity

• DOI: 10.1021/acs.jproteome.5b01001
• Publication Date: 2016-01-08T01:17:08Z
• Authors: Nicolas R Barthélemy; François Fenaille; Christophe Hirtz; Nicolas Sergeant; Susanna Schraen-M...; Jérôme Vialaret; Luc Buée; Audrey Gabelle; Christophe Junot; Sylvain Lehmann; François Becher
• Keywords: 0301 basic medicine; [SDV]Life Sciences [q-bio]; Molecular Sequence Data; 610; Reproducibility of Results; tau Proteins; Mass Spectrometry; 3. Good health; 03 medical and health sciences; Humans; Amino Acid Sequence; Peptides; Biomarkers; Chromatography, Liquid

Tau protein plays a major role in neurodegenerative disorders, appears to be a central biomarker of neuronal injury in cerebrospinal fluid (CSF), and is a promising target for Alzheimer's disease immunotherapies. To quantify tau at high sensitivity and gain insights into its naturally occurring structural variations in human CSF, we coupled absolute quantification using protein standard with the multiplex detection capability of targeted high-resolution mass spectrometry (MS) on a Quadrupole-Orbitrap instrument. Using recombinant tau we developed a step-by-step workflow optimization including an extraction protocol that avoided affinity reagents and achieved the monitoring of 22 tau peptides uniformly distributed along the tau sequence. The lower limits of quantification ranged (LLOQ) from 150 to 1500 pg/mL depending on the peptide. Applied to endogenous CSF tau, up to 19 peptides were detected. Interestingly, there were significant differences in the abundance of peptides depending on their position in the sequence, with peptides from the tau mid-domain appearing significantly more abundant than peptides from the N- and C-terminus domains. This MS-based strategy provided results complementary to those of previous ELISA or Western Blot studies of CSF tau and could be applied to tau monitoring in human CSF cohorts.