Validation of α-Synuclein in L1CAM-Immunocaptured Exosomes as a Biomarker for the Stratification of Parkinsonian Syndromes

Abstract

Background: Parkinson's disease is characterized by intraneuronal α-synuclein aggregation. Currently there is no α-synuclein-based blood test in clinical practice.

Objectives: Our aim was to assess by means of further testing and analysis whether α-synuclein measurements in serum L1CAM-immunocaptured exosomes can differentiate Parkinson's disease from related movement disorders.

Methods: We used poly(carboxybetaine-methacrylate)-coated magnetic beads to isolate L1CAM-positive exosomes and triplexed electrochemiluminescence to measure exosomal α-synuclein, clusterin, and syntenin-1 from 267 serum samples. Combined analysis of our current and previously published data from the Oxford, Kiel, Brescia, and PROSPECT cohorts consisting of individuals (total n = 735) with Parkinson's disease (n = 290), multiple system atrophy (MSA, n = 50), progressive supranuclear palsy (n = 116), corticobasal syndrome (n = 88), and healthy controls (n = 191) was done using 2-stage (training vs validation) receiver operating characteristic analysis.

Results: We established that α-synuclein level in L1CAM-immunocaptured exosomes above 14 pg/mL is a robust biomarker across cohorts that distinguishes Parkinson's disease from MSA (AUC, 0.90 vs 0.98) or 4-repeat tauopathies (AUC, 0.93 vs 0.94). We confirmed that exosomal clusterin is elevated in subjects with 4-repeat tauopathy, and when combined with α-synuclein, it improved the performance of the assay in differentiating Parkinson's disease from 4-repeat tauopathies to AUC, 0.98 versus 0.99. Correction for the generic exosomal protein syntenin-1 did not consistently improve the performance of the assay.

Conclusions: α-Synuclein and clusterin in L1CAM-immunocaptured serum exosomes is a validated blood test for the molecular stratification of neuronal α-synucleinopathy (ie, Lewy body pathology) versus phenotypically related neurodegenerative movement disorders. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Keywords: L1CAM; biomarker; extracellular vesicles; neurodegeneration; synuclein.

FIG. 1

(A) Receiver operating characteristic (ROC) analysis was performed to evaluate the biomarker in distinguishing between PD and HC, between PD and MSA, and between PD and PSP + CBS using α‐Syn, Clu, and α‐Syn/Clu. We used a 2‐stage design model with discovery (Kiel + PROSPECT) and validation (Oxford + Brescia) cohorts to assess consistency across patient populations. (B) Summary of assay performance following ROC analysis across 2 groups training (blue) and validation (light brown) for each biomarker. Only the most significant (AUC > 0.80) are displayed. AUC, area under curve; Sens, sensitivity; Spec, specificity.