IdentIFICatIon oF noVel BIoMarKer CandIdates In tHe CereBrosPInal FluId ProteoMe oF druG-naïVe ParKInson’s dIsease PatIents

Background: Cerebrospinal fluid (CSF) is in close contact with the extracellular fluid surrounding brain cells and therefore holds great promise as a source of biomarkers for Parkinson’s disease (PD). PD biomarkers could improve the early diagnostic accuracy of PD, may be used to identify patients at risk of developing PD, stratify patients into subtypes and monitor disease progression. The current proteomics study was performed to identify novel CSF biomarker candidates for PD using two independent patient cohorts. Methods: We first analysed the CSF proteome in a discovery cohort of 10 drug-naïve PD patients and 10 neurologically healthy controls using a workflow involving immuno-depletion of highabundant proteins, mono-dimensional SDS-PAGE in conjunction with nanoLC-MS/MS-based proteomics and label-free protein quantification. Identified differentially expressed proteins were subsequently compared to a second proteomics dataset of an independent cohort of 12 medicated PD patients and 13 controls. Functional annotation as well as pathway and network analysis were performed to gain insight into the molecular processes associated with deregulated proteins. results: Ninety out of 1284 identified proteins in the discovery dataset were differentially expressed in PD patients compared to controls. Some proteins have previously been related to PD, such as chromogranin A (CHGA; down-regulated in PD). Ninety-seven percent of proteins of the discovery dataset overlapped with the 2115 proteins identified in the verification cohort. Three overlapping candidate biomarkers were found: myelin protein P0 (MPZ; up-regulated in PD), plastin-2 (LCP1; down-regulated in PD) and acid sphingomyelinase-like phosphodiesterase 3b (SMPDL3B; down-regulated in PD). Network analysis of proteins showing co-regulation between the two datasets showed subnetworks involved in complement activation, inflammation-related processes and axon guidance. Conclusion: Our proteomics analysis of CSF in PD patients and controls yielded several novel candidate biomarkers and suggests a central role for complement activation, inflammation and axon guidance in the pathogenesis of PD. Further technical and clinical validation of prioritized candidates in larger cohorts should delineate their potential as early diagnostic, prognostic and/or progression biomarkers for PD. Karin d. van dijk1,2, davide Chiasserini3, Thang V. Pham3, sander r. Piersma3, Jaco C. Knol3, Kathrin Brockmann4, Mathias toft5, Thomas Gasser4, Henk W. Berendse2, Connie r. Jimenez3*, Wilma d.J. van de Berg1* 1Department of Anatomy and Neurosciences, Neuroscience Campus Amsterdam, VU University Medical Center, Amsterdam, The Netherlands, 2Department of Neurology, Neuroscience Campus Amsterdam, VU University Medical Center, Amsterdam, The Netherlands, 3OncoProteomics Laboratory of the Department of Medical Oncology, VU University Medical Center, Amsterdam, The Netherlands, 4Department of Neurogedegenerative Diseases, University of Tübingen, Germany, 5Department of Neurology, Oslo University Hospital, Norway. *Shared senior authorship