Proteomic analysis of age-related changes in ovine cerebrospinal fluid

Cerebrospinal fluid (CSF) circulates through the brain and has a unique composition reflecting the biological processes of the brain. Identifying ageing CSF biomarkers can aid in understanding the ageing process and interpreting CSF protein changes in neurodegenerative diseases. In this study, ovine CSF proteins from young (1-2 year old), middle aged (3-6 year old) and old (7-10 year old) sheep were systemically studied. CSF proteins were labelled with iTRAQ tagging reagents and fractionated by 2-dimensional high performance, liquid chromatography. Tryptic peptides were identified using MS/MS fragmentation ions for sequencing and quantified from iTRAQ reporter ion intensities at m/z 114, 115, 116 and 117. Two hundred thirty one peptides were detected, from which 143 proteins were identified. There were 52 proteins with > 25% increase in concentrations in the old sheep compared to the young. 33 of them increased > 25% but < 50%, 13 increased > 50% but < 1 fold, 6 increased > 1 fold [i.e. haptoglobin (Hp), haemoglobin, neuroendocrine protein 7B2, IgM, fibrous sheath interacting protein 1, vimentin]. There were 18 proteins with > 25% decrease in concentrations in the old sheep compared to the young. 17 of them decreased > 25% but < 50%, and histone deacetylase 7 (HDAC7) was gradually decreased for over 80%. Glutathione S-transferase was decreased in middle aged CSF compared to both young and old CSF. The differential expressions of 3 proteins (Hp, neuroendocrine protein 7B2, IgM) were confirmed by immunoassays. These data expand our current knowledge regarding ovine CSF proteins, supply the necessary information to understand the ageing process in the brain and provide a basis for diagnosis of neurodegenerative diseases.