Abstract

Proteins experience a wide range of post-translational modifications (PTMs) that regulate their activity, cellular localisation and turnover. This is a highly dynamic state with considerable cross-talk and dysregulation of PTMs either at the enzyme or substrate level is a common feature of many diseases representing a rich source of pharmacodynamic and clinical biomarkers. We have developed different approaches to measure disease-relevant PTMs using state of the art mass spectrometry.

SysQuant is a comprehensive workflow for the analysis and interpretation of changes in phosphorylation across an entire proteome. We have applied SysQuant to the analysis of brains from an experimental model of Alzheimer’s disease and verified the mode of action of orally available inhibitors of brain CK1D which reduces tau phosphorylation, blocks CDK5 signalling and provides improved cognitive behaviour. This data set comprises >23,000 phosphorylation sites on >14,000 proteins providing potent pharmacodynamic markers which will be presented.

The differential proteolysis of amyloid precursor protein leads to multiple Abeta isoforms in CSF and the ratio of 1-40/1-42 peptides is a useful diagnostic aid. However it is now believed that disease modifying anti-amyloid therapies may affect a broader population of Abeta isoforms and we have developed a targeted mass spectrometry method to measure up to 12 different Abeta isoforms in CSF. The diagnostic value in a small cohort of AD patients will be presented.

Finally, we have explored the role of glycosylation of key plasma proteins previously reported as potential clinical biomarkers. For plasma clusterin we identified over 40 different isoforms, only a few of which have diagnostic utility. The implications of this for biomarker discovery and validation will be discussed.