The precise molecular mechanism of how misfolded α-synuclein (α-Syn) accumulates and spreads in synucleinopathies is still unknown. Here, we show the role of the cellular prion protein (PrPC) in mediating the uptake and the spread of recombinant α-Syn amyloids. The in vitro data revealed that the presence of PrPC fosters the higher uptake of α-Syn amyloid fibrils, which was also confirmed in vivo in wild type (Prnp +/+) compared to PrP knock-out (Prnp −/−) mice. Additionally, the presence of α-Syn amyloids blocked the replication of scrapie prions (PrPSc) in vitro and ex vivo, indicating a link between the two proteins. Indeed, whilst PrPC is mediating the internalization of α-Syn amyloids, PrPSc is not able to replicate in their presence. This observation has pathological relevance, since several reported case studies show that the accumulation of α-Syn amyloid deposits in Creutzfeldt-Jakob disease patients is accompanied by a longer disease course.

Background Parkinson’s disease (PD) is a neurodegenerative disorder whose diagnosis is often challenging because symptoms may overlap with neurodegenerative parkinsonisms. PD is characterized by intraneuronal accumulation of abnormal α-synuclein in brainstem while neurodegenerative parkinsonisms might be associated with accumulation of either α-synuclein, as in the case of Multiple System Atrophy (MSA) or tau, as in the case of Corticobasal Degeneration (CBD) and Progressive Supranuclear Palsy (PSP), in other disease-specific brain regions. Definite diagnosis of all these diseases can be formulated only neuropathologically by detection and localization of α-synuclein or tau aggregates in the brain. Compelling evidence suggests that trace-amount of these proteins can appear in peripheral tissues, including receptor neurons of the olfactory mucosa (OM). Methods We have set and standardized the experimental conditions to extend the ultrasensitive Real Time Quaking Induced Conversion (RT-QuIC) assay for OM analysis. In particular, by using human recombinant α-synuclein as substrate of reaction, we have assessed the ability of OM collected from patients with clinical diagnoses of PD and MSA to induce α-synuclein aggregation, and compared their seeding ability to that of OM samples collected from patients with clinical diagnoses of CBD and PSP. Results Our results showed that a significant percentage of MSA and PD samples induced α-synuclein aggregation with high efficiency, but also few samples of patients with the clinical diagnosis of CBD and PSP caused the same effect. Notably, the final RT-QuIC aggregates obtained from MSA and PD samples owned peculiar biochemical and morphological features potentially enabling their discrimination. Conclusions Our study provide the proof-of-concept that olfactory mucosa samples collected from patients with PD and MSA possess important seeding activities for α-synuclein. Additional studies are required for (i) estimating sensitivity and specificity of the technique and for (ii) evaluating its application for the diagnosis of PD and neurodegenerative parkinsonisms. RT-QuIC analyses of OM and cerebrospinal fluid (CSF) can be combined with the aim of increasing the overall diagnostic accuracy of these diseases, especially in the early stages. Electronic supplementary material The online version of this article (10.1186/s40035-019-0164-x) contains supplementary material, which is available to authorized users.

The intrinsically disordered and amyloidogenic protein -synuclein (AS) has been linked to several neurodegenerative states, including Parkinson's disease. Here, nano-electrospray-ionization mass spectrometry (nano-ESI-MS), ion mobility (IM), and native top-down electron transfer dissociation (ETD) techniques are employed to study AS interaction with small molecules known to modulate its aggregation, such as epigallocatechin-3-gallate (EGCG) and dopamine (DA). The complexes formed by the two ligands under identical conditions reveal peculiar differences. While EGCG engages AS in compact conformations, DA preferentially binds to the protein in partially extended conformations. The two ligands also have different effects on AS structure as assessed by IM, with EGCG leading to protein compaction and DA to its extension. Native top-down ETD on the protein-ligand complexes shows how the different observed modes of binding of the two ligands could be related to their known opposite effects on AS aggregation. The results also show that the protein can bind either ligand in the absence of any covalent modifications, such as e.g. oxidation.

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Aggregation of α-synuclein plays a crucial role in the pathogenesis of synucleinopathies, a group of neurodegenerative diseases including Parkinson disease (PD), dementia with Lewy bodies (DLB), diffuse Lewy body disease (DLBD) and multiple system atrophy (MSA). The common feature of these diseases is a pathological deposition of protein aggregates, known as Lewy bodies (LBs) in the central nervous system. The major component of these aggregates is α-synuclein, a natively unfolded protein, which may undergo dramatic structural changes resulting in the formation of β-sheet rich assemblies. In vitro studies have shown that recombinant α-synuclein protein may polymerize into amyloidogenic fibrils resembling those found in LBs. These aggregates may be uptaken and propagated between cells in a prion-like manner. Here we present the mechanisms and kinetics of α-synuclein aggregation in vitro, as well as crucial factors affecting this process. We also describe how PD-linked α-synuclein mutations and some exogenous factors modulate in vitro aggregation. Furthermore, we present a current knowledge on the mechanisms by which extracellular aggregates may be internalized and propagated between cells, as well as the mechanisms of their toxicity.