Identification of cerebrospinal fluid biomarkers for parkinsonism using a proteomics approach

Abstract

The aim of our study was to investigate cerebrospinal fluid (CSF) tryptic peptide profiles as potential diagnostic biomarkers for the discrimination of parkinsonian disorders. CSF samples were collected from individuals with parkinsonism, who had an uncertain diagnosis at the time of inclusion and who were followed for up to 12 years in a longitudinal study. We performed shotgun proteomics to identify tryptic peptides in CSF of Parkinson’s disease (PD, n = 10), multiple system atrophy patients (MSA, n = 5) and non-neurological controls (n = 10). We validated tryptic peptides with differential levels between PD and MSA using a newly developed selected reaction monitoring (SRM) assay in CSF of PD (n = 46), atypical parkinsonism patients (AP; MSA, n = 17; Progressive supranuclear palsy; n = 8) and non-neurological controls (n = 39). We identified 191 tryptic peptides that differed significantly between PD and MSA, of which 34 met our criteria for SRM development. For 14/34 peptides we confirmed differences between PD and AP. These tryptic peptides discriminated PD from AP with moderate-to-high accuracy. Random forest modelling including tryptic peptides plus either clinical assessments or other CSF parameters (neurofilament light chain, phosphorylated tau protein) and age improved the discrimination of PD vs. AP. Our results show that the discovery of tryptic peptides by untargeted and subsequent validation by targeted proteomics is a suitable strategy to identify potential CSF biomarkers for PD versus AP. Furthermore, the tryptic peptides, and corresponding proteins, that we identified as differential biomarkers may increase our current knowledge about the disease-specific pathophysiological mechanisms of parkinsonism.

Cerebrospinal Fluid Metabolome in Parkinson’s Disease and Multiple System Atrophy

“…In addition, the levels of 28 proteins were increased and levels of 20 proteins were decreased in a total of 73 proteins detected in MSA [16,20,73,95]. Of the differentially expressed proteins, the expression of seven proteins was increased and expression of nine proteins was decreased in PD and MSA compared to healthy controls [16,20,73,95]. Of the proteins increased in both PD and MSA, the increment of insulin-like growth factor 2 (IGF2), glial fibrillary acidic protein (GFAP), eotaxin, and interleukin 10 (IL10) was more pronounced in MSA and that of seizure 6-like protein 2 (SEZ6L2), 45 kDa calcium-binding protein (SDF4), and granulocyte colony-stimulating factor (G-CSF) was more pronounced in PD.…”

“…In the proteome profile of PD, levels of 30 proteins were increased and levels of 40 proteins were decreased in a total of 110 proteins [16,[19][20][21]73,94,95]. In addition, the levels of 28 proteins were increased and levels of 20 proteins were decreased in a total of 73 proteins detected in MSA [16,20,73,95]. Of the differentially expressed proteins, the expression of seven proteins was increased and expression of nine proteins was decreased in PD and MSA compared to healthy controls [16,20,73,95].…”

“…Changes in the protein levels have been analyzed in the CSF of PD and MSA patients against healthy individuals. In the proteome profile of PD, levels of 30 proteins were increased and levels of 40 proteins were decreased in a total of 110 proteins [16,[19][20][21]73,94,95]. In addition, the levels of 28 proteins were increased and levels of 20 proteins were decreased in a total of 73 proteins detected in MSA [16,20,73,95].…”

“…Several proteins have been reported to be more abundant and uniquely identified in CSF than in serum [12]. Thus, CSF has been the target biological fluid as a biomarker for metabolites, microRNAs, and proteins in PD and MSA [8,[13][14][15][16].…”

“…For example, metabolomics alone failed to detect delicate nanotoxicity using traditional assay methods [17], while assessment using integrated omics with metabolomics and transcriptomics has been shown to provide a more sensitive and detailed toxicological evaluation of cellular responses to identify novel nanotoxicological biomarkers [18]. Moreover, several studies have suggested the analysis of the proteome [16,[19][20][21] and microRNA [13,22] in the CSF of patients with PD and/or MSA. Therefore, integrated omics with metabolomics and proteomics and/or microRNA analysis may contribute to more precise evaluations based on symptoms between PD and MSA in the future.…”