ObjectiveParkinson’s disease is characterised neuropathologically by α-synuclein aggregation. Currently, there is no blood test to predict the underlying pathology or distinguish Parkinson’s from atypical parkinsonian syndromes. We assessed the clinical utility of serum neuronal exosomes as biomarkers across the spectrum of Parkinson’s disease, multiple system atrophy and other proteinopathies.MethodsWe performed a cross-sectional study of 664 serum samples from the Oxford, Kiel and Brescia cohorts consisting of individuals with rapid eye movement sleep behavioural disorder, Parkinson’s disease, dementia with Lewy bodies, multiple system atrophy, frontotemporal dementia, progressive supranuclear palsy, corticobasal syndrome and controls. Longitudinal samples were analysed from Parkinson’s and control individuals. We developed poly(carboxybetaine-methacrylate) coated beads to isolate L1 cell adhesion molecule (L1CAM)-positive extracellular vesicles with characteristics of exosomes and used mass spectrometry or multiplexed electrochemiluminescence to measure exosomal proteins.ResultsMean neuron-derived exosomal α-synuclein was increased by twofold in prodromal and clinical Parkinson’s disease when compared with multiple system atrophy, controls or other neurodegenerative diseases. With 314 subjects in the training group and 105 in the validation group, exosomal α-synuclein exhibited a consistent performance (AUC=0.86) in separating clinical Parkinson’s disease from controls across populations. Exosomal clusterin was elevated in subjects with non-α-synuclein proteinopathies. Combined neuron-derived exosomal α-synuclein and clusterin measurement predicted Parkinson’s disease from other proteinopathies with AUC=0.98 and from multiple system atrophy with AUC=0.94. Longitudinal sample analysis showed that exosomal α-synuclein remains stably elevated with Parkinson’s disease progression.ConclusionsIncreased α-synuclein egress in serum neuronal exosomes precedes the diagnosis of Parkinson’s disease, persists with disease progression and in combination with clusterin predicts and differentiates Parkinson’s disease from atypical parkinsonism.

A subset of nonsteroidal anti-inflammatory drugs (NSAIDs) has been shown to preferentially reduce the secretion of the highly amyloidogenic, 42-residue amyloid-beta peptide Abeta42. We found that Rho and its effector, Rho-associated kinase, preferentially regulated the amount of Abeta42 produced in vitro and that only those NSAIDs effective as Rho inhibitors lowered Abeta42. Administration of Y-27632, a selective Rock inhibitor, also preferentially lowered brain levels of Abeta42 in a transgenic mouse model of Alzheimer's disease. Thus, the Rho-Rock pathway may regulate amyloid precursor protein processing, and a subset of NSAIDs can reduce Abeta42 through inhibition of Rho activity.

Lithium is one of the most widely used mood-stabilizing agents for the treatment of bipolar disorder. Although the underlying mechanism(s) of this mood stabilizer remains controversial, recent evidence linking lithium to neurotrophic/neuroprotective effects (Choi and Sung (2000) 1475, 225-230; Davies et al. (2000) 351, 95-105) suggests novel benefits of this drug in addition to mood stabilization. Here, we report that both lithium as well as valproic acid (VPA) inhibit beta-amyloid peptide (Abeta) production in HEK293 cells stably transfected with Swedish amyloid precursor protein (APP)(751) and in the brains of the PDAPP (APP(V717F)) Alzheimer's disease transgenic mouse model at clinically relevant plasma concentrations. Both lithium and VPA are known to be glycogen synthase kinase-3 (GSK3) inhibitors. Our studies reveal that GSK3beta is a potential downstream kinase, which modulates APP processing because inhibition of GSK3 activity by either a dominant negative GSK3beta kinase-deficient construct or GSK3beta antisense oligonucleotide mimics lithium and VPA effects. Moreover, lithium treatment abolished GSK3beta-mediated Abeta increase in the brains of GSK3beta transgenics and reduced plaque burden in the brains of the PDAPP (APP(V717F)) transgenic mice.

A robust top down proteomics method is presented for profiling alpha-synuclein species from autopsied human frontal cortex brain tissue from Parkinson's cases and controls. The method was used to test the hypothesis that pathology associated brain tissue will have a different profile of post-translationally modified alpha-synuclein than the control samples. Validation of the sample processing steps, mass spectrometry based measurements, and data processing steps were performed. The intact protein quantitation method features extraction and integration of m/z data from each charge state of a detected alpha-synuclein species and fitting of the data to a simple linear model which accounts for concentration and charge state variability. The quantitation method was validated with serial dilutions of intact protein standards. Using the method on the human brain samples, several previously unreported modifications in alpha-synuclein were identified. Low levels of phosphorylated alpha synuclein were detected in brain tissue fractions enriched for Lewy body pathology and were marginally significant between PD cases and controls (p = 0.03).

Mutations in Leucine-rich repeat kinase 2 (LRRK2) are a common cause of inherited Parkinson's disease (PD). The protein is large and complex, but pathogenic mutations cluster in a region containing GTPase and kinase domains. LRRK2 can autophosphorylate in vitro within a dimer pair, although the significance of this reaction is unclear. Here, we mapped the sites of autophosphorylation within LRRK2 and found several potential phosphorylation sites within the GTPase domain. Using mass spectrometry, we found that Thr1343 is phosphorylated and, using kinase dead versions of LRRK2, show that this is an autophosphorylation site. However, we also find evidence for additional sites in the GTPase domain and in other regions of the protein suggesting that there may be multiple autophosphorylation sites within LRRK2. These data suggest that the kinase and GTPase activities of LRRK2 may exhibit complex autoregulatory interdependence.