The integrity of blood–brain‐barrier (BBB) is essential for normal brain functions, synaptic remodeling, and angiogenesis. BBB disruption is a common pathology during Parkinson's disease (PD), and has been hypothesized to contribute to the progression of PD. However, the molecular mechanism of BBB disruption in PD needs further investigation. Here, A53T PD mouse and a 3‐cell type in vitro BBB model were used to study the roles of α‐synuclein (α‐syn) in BBB disruption with the key results confirmed in the brains of PD patients obtained at autopsy. The A53T PD mouse studies showed that the expression of tight junction‐related proteins decreased, along with increased vascular permeability and accumulation of oligomeric α‐syn in activated astrocytes in the brain. The in vitro BBB model studies demonstrated that treatment with oligomeric α‐syn, but not monomeric or fibrillar α‐syn, resulted in significant disruption of BBB integrity. This process involved the expression and release of vascular endothelial growth factor A (VEGFA) and nitric oxide (NO) from oligomeric α‐syn treated astrocytes. Increased levels of VEGFA and iNOS were also observed in the brain of PD patients. Blocking the VEGFA signaling pathway in the in vitro BBB model effectively protected the barrier against the harmful effects of oligomeric α‐syn. Finally, the protective effects on BBB integrity associated with inhibition of VEGFA signaling pathway was also confirmed in PD mice. Taken together, our study concluded that oligomeric α‐syn is critically involved in PD‐associated BBB disruption, in a process that is mediated by astrocyte‐derived VEGFA.

Parkinson's disease is a neurodegenerative disorder characterized by the transmission and accumulation of toxic species of α-synuclein (α-syn). Extracellular vesicles (EVs) are believed to play a vital role in the spread of toxic α-syn species. Recently, peripheral α-syn pathology has been investigated, but little attention has been devoted to erythrocytes, which contain abundant α-syn. In this study, we first demonstrated that erythrocyte-derived EVs isolated from Parkinson's disease patients carried elevated levels of oligomeric α-syn, compared to those from healthy controls. Moreover, human erythrocyte-derived EVs, when injected into peripheral blood in a mouse model of Parkinson's disease, were found to readily cross the blood-brain barrier (BBB). These EVs accumulated in astrocyte endfeet, a component of the BBB, where they impaired glutamate uptake, likely via interaction between excitatory amino acid transporter 2 (EAAT2) and oligomeric α-syn. These data suggest that erythrocyte-derived EVs and the oligomeric α-syn carried in them may play critical roles in the progression or even initiation of Parkinson's disease. Additionally, the mechanisms involved are attributable at least in part to dysfunction of astrocytes induced by these EVs. These observations provide new insight into the understanding of the mechanisms involved in Parkinson's disease.

No abstract

Objective: Accumulation of α-synuclein (α-syn) in neurons is a prominent feature of Parkinson's disease (PD). Recently, researchers have considered that extracellular vesicles (EVs) may play an important role in protein exportation and propagation, and α-syn-containing EVs derived from the central nervous system (CNS) have been detected in peripheral blood. However, mechanistic insights into CNS-derived EVs have not been well-described. Methods: Likely neurogenic EVs were purified from the plasma of PD patients and healthy controls using a wellestablished immunoprecipitation assay with anti-L1CAM-coated beads. A Prnp-SNCA A53T transgenic PD mouse model was used to evaluate the neuronal pathology induced by PD-derived L1CAM-purified EVs. EV-associated microRNA (miRNA) profiling was used to screen for altered miRNAs in PD-derived L1CAM-purified EVs. Results: PD patient-derived L1CAM-purified (likely neurogenic) EVs facilitated α-syn pathology and neuron loss in Prnp-SNCA A53T transgenic PD mice. The miRNA, novel_miR_44438, was significantly increased in the PD group, which promoted α-syn accumulation and neuronal degeneration in a dose-dependent manner. Novel _miR_44438 directly targets NDST1 mRNA and inhibits the function of heparan sulfate, thus preventing exosome biogenesis and α-syn release from exosomes. Interpretation: Novel_miR_44438 in PD-derived L1CAM-purified EVs inhibits the α-syn efflux from neurons thereby promoting the pathological accumulation and aggregation of α-syn.

Background Immune system dysfunction, including higher levels of peripheral monocytes and inflammatory cytokines, is an important feature of Parkinson’s disease (PD) pathogenesis, although the mechanism underlying the process remains to be investigated. In the central nervous system, it is well-known that α-synuclein (α-syn), a key protein involved in PD, activates microglia potently, and it is also reported that α-syn exists in the peripheral system, especially in erythrocytes or red blood cells (RBC) at exceedingly high concentration. The current study focused on the possibility that RBC-derived α-syn mediates the sensitization of peripheral monocytes in PD patients. Methods The hyperactivation of monocytes was assessed quantitatively by measuring mRNA levels of typical inflammatory cytokines (including IL-1β, IL-6 and TNF-α) and protein levels of secreted inflammatory cytokines (including pro-inflammatory cytokines: IL-1β, IL-6, TNF-α, IL-8, IFN-γ, IL-2, and IL-12p70 and anti-inflammatory cytokines: IL-4, IL-10, and IL-13). Western blot, nanoparticle tracking analysis and electron microscopy were used to characterize RBC-derived extracellular vesicles (RBC-EVs). Inhibitors of endocytosis and leucine-rich repeat kinase 2 (LRRK2), another key protein involved in PD, were used to investigate how these two factors mediated the process of monocyte sensitization by RBC-EVs. Results Increased inflammatory sensitization of monocytes was observed in PD patients and PD model mice. We found that α-syn-containing RBC-EVs isolated from PD model mice or free form oligomeric α-syn induced the inflammatory sensitization of THP-1 cells, and demonstrated that endocytosis was a requirement for this pathophysiological pathway. Furthermore, the hyperactivation of THP-1 cells induced by RBC-EVs was associated with increased LRRK2 production and kinase activity. The phenomenon of inflammatory sensitization of human monocytes and increased LRRK2 were also observed by the treatment of RBC-EVs isolated from PD patients. Conclusions Our data provided new insight into how hyperactivation of monocytes occurs in PD patients, and identified the central role played by α-syn-containing RBC-EVs in this process.