Proteolytic clearance of extracellular α-synuclein as a new therapeutic approach against Parkinson disease

Abnormal Expression of Proteolytic Stress-Related Proteins and Protective Effect of Fibrinolytic Enzymes in Prion Diseases

Prion diseases are fatal, irreversible, and infectious neurodegenerative diseases caused by proteinase K-resistant prion protein (PrPSc). Against PrPSc, several endogenous proteases involved in cellular degradation mechanisms can be activated to remove PrPSc. However, since PrPSc shows proteinase K resistance, we presumed that undegradable PrPSc induces positive feedback on the overactivation of the cellular degradation mechanisms and is correlated with proteolytic stress and exacerbation of the progression of prion diseases. We investigated the expression pattern of proteolytic stress-related proteins in the brains of ME7 scrapie-infected mice at 7 months postinfection and sporadic Creutzfeldt-Jakob disease (CJD) patients using western blotting and immunohistochemistry (IHC). In addition, we analyzed the 3D structure and binding complexes of prion protein (PrP) with nattokinase and lumbrokinase using in silico programs, including SWISS-MODEL and HawkDock. To fundamentally reduce proteolytic stress by the degradation of PrPSc, we performed an in vitro evaluation of the PrPSc degradation abilities of fibrinolytic enzymes, including nattokinase and lumbrokinase. Furthermore, we assessed the protective effects of nattokinase and lumbrokinase in ME7 scrapie-infected mice. We observed an abnormal accumulation of proteolytic stress-related proteins, including CD10, cathepsin B, cathepsin D, and matrix metalloproteinase 9 (MMP9), in the brains of ME7 scrapie-infected mice and sporadic CJD patients. In addition, we identified that nattokinase and lumbrokinase can stably bind to PrP. Furthermore, we identified significant in vitro degradation of PrPSc derived from ME7 scrapie-infected mice and sporadic CJD patients by nattokinase and lumbrokinase. Last, we found in vivo protective effects of nattokinase and lumbrokinase against prion disease in ME7 scrapie-infected mice. To the best of our knowledge, this is the first report on the identification of proteolytic stress-related novel potential biomarkers and the therapeutic potential of nattokinase and lumbrokinase for prion diseases.

CNS/PNS proteoglycans functionalize neuronal and astrocyte niche microenvironments optimizing cellular activity by preserving membrane polarization dynamics, ionic microenvironments, ion fluxes, neuronal activation, and network neurotransductive capacity

Central and peripheral nervous system (CNS/PNS) proteoglycans (PGs) have diverse functional roles, this study examined how these control cellular behavior and tissue function. The CNS/PNS extracellular matrix (ECM) is a dynamic, responsive, highly interactive, space-filling, cell supportive, stabilizing structure maintaining tissue compartments, ionic microenvironments, and microgradients that regulate neuronal activity and maintain the neuron in an optimal ionic microenvironment. The CNS/PNS contains a high glycosaminoglycan content (60% hyaluronan, HA) and a diverse range of stabilizing PGs. Immobilization of HA in brain tissues by HA interactive hyalectan PGs preserves tissue hydration and neuronal activity, a paucity of HA in brain tissues results in a pro-convulsant epileptic phenotype. Diverse CS, KS, and HSPGs stabilize the blood-brain barrier and neurovascular unit, provide smart gel neurotransmitter neuron vesicle storage and delivery, organize the neuromuscular junction basement membrane, and provide motor neuron synaptic plasticity, and photoreceptor and neuron synaptic functions. PG-HA networks maintain ionic fluxes and microgradients and tissue compartments that contribute to membrane polarization dynamics essential to neuronal activation and neurotransduction. Hyalectans form neuroprotective perineuronal nets contributing to synaptic plasticity, memory, and cognitive learning. Sialoglycoprotein associated with cones and rods (SPACRCAN), an HA binding CSPG, stabilizes the inter-photoreceptor ECM. HSPGs pikachurin and eyes shut stabilize the photoreceptor synapse aiding in phototransduction and neurotransduction with retinal bipolar neurons crucial to visual acuity. This is achieved through Laminin G motifs in pikachurin, eyes shut, and neurexins that interact with the dystroglycan-cytoskeleton-ECM-stabilizing synaptic interconnections, neuronal interactive specificity, and co-ordination of regulatory action potentials in neural networks.

Endoproteolysis of cellular prion protein by plasmin hinders propagation of prions

Many questions surround the underlying mechanism for the differential metabolic processing observed for the prion protein (PrP) in healthy and prion-infected mammals. Foremost, the physiological α-cleavage of PrP interrupts a region critical for both toxicity and conversion of cellular PrP (PrP ^C ) into its misfolded pathogenic isoform (PrP ^Sc ) by generating a glycosylphosphatidylinositol (GPI)-anchored C1 fragment. During prion diseases, alternative β-cleavage of PrP becomes prominent, producing a GPI-anchored C2 fragment with this particular region intact. It remains unexplored whether physical up-regulation of α-cleavage can inhibit disease progression. Furthermore, several pieces of evidence indicate that a disintegrin and metalloproteinase (ADAM) 10 and ADAM17 play a much smaller role in the α-cleavage of PrP ^C than originally believed, thus presenting the need to identify the primary protease(s) responsible. For this purpose, we characterized the ability of plasmin to perform PrP α-cleavage. Then, we conducted functional assays using protein misfolding cyclic amplification (PMCA) and prion-infected cell lines to clarify the role of plasmin-mediated α-cleavage during prion propagation. Here, we demonstrated an inhibitory role of plasmin for PrP ^Sc formation through PrP α-cleavage that increased C1 fragments resulting in reduced prion conversion compared with non-treated PMCA and cell cultures. The reduction of prion infectious titer in the bioassay of plasmin-treated PMCA material also supported the inhibitory role of plasmin on PrP ^Sc replication. Our results suggest that plasmin-mediated endoproteolytic cleavage of PrP may be an important event to prevent prion propagation.

Therapeutic functions of astrocytes to treat α-synuclein pathology in Parkinson’s disease

Intraneuronal inclusions of misfolded α-synuclein (α-syn) and prion-like spread of the pathologic α-syn contribute to progressive neuronal death in Parkinson’s disease (PD). Despite the pathologic significance, no efficient therapeutic intervention targeting α-synucleinopathy has been developed. In this study, we provide evidence that astrocytes, especially those cultured from the ventral midbrain (VM), show therapeutic potential to alleviate α-syn pathology in multiple in vitro and in vivo α-synucleinopathic models. Regulation of neuronal α-syn proteostasis underlies the therapeutic function of astrocytes. Specifically, VM-derived astrocytes inhibited neuronal α-syn aggregation and transmission in a paracrine manner by correcting not only intraneuronal oxidative and mitochondrial stresses but also extracellular inflammatory environments, in which α-syn proteins are prone to pathologic misfolding. The astrocyte-derived paracrine factors also promoted disassembly of extracellular α-syn aggregates. In addition to the aggregated form of α-syn, VM astrocytes reduced total α-syn protein loads both by actively scavenging extracellular α-syn fibrils and by a paracrine stimulation of neuronal autophagic clearance of α-syn. Transplantation of VM astrocytes into the midbrain of PD model mice alleviated α-syn pathology and protected the midbrain dopamine neurons from neurodegeneration. We further showed that cografting of VM astrocytes could be exploited in stem cell–based therapy for PD, in which host-to-graft transmission of α-syn pathology remains a critical concern for long-term cell therapeutic effects.

Association between plasminogen activator inhibitor-1 gene polymorphisms and susceptibility to Parkinson's disease in Chinese patients

PURPOSE

Parkinson's disease (PD) is a neurodegenerative disease that usually leads to memory impairment, cognitive decline and dementia. Previous studies have reported that plasminogen activator inhibitor-1 (PAI-1) gene polymorphisms play important roles in cardiovascular diseases, obesity, inflammation and other diseases. However, the role of PAI-1 in the diagnosis of Parkinson's disease has not been reported so far.

METHODS

This study was a case-control study. This study included 131 PD patients and 97 healthy volunteers. polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to analyze the polymorphic loci of five different regions in PAI-1 gene (rs2227631, rs1799889, rs6092, rs2227694 and rs7242). 60 PD patients and 60 healthy volunteers were selected to detect the plasma PAI-1 concentration. The allele and genotype frequencies of SNPs were assessed using the SHEsis program.

RESULTS

We found that GG genotype frequency and G allele frequency of rs2227631 was significantly higher in the PD patients. Statistically significant difference for rs1799889 could be observed in overdominant model. In subgroup analysis, a significant difference in genotype frequency distribution and allele frequency was found for rs2227631 and rs1799889 between early-onset PD group and the control group. For cognitive dysfunction, the subcomponent showed that GG genotype frequency and G allele frequency of rs2227631 was significantly higher in normal cognition group. The codominant model of rs1799889 was significantly different between the cognitive impairment group and the control group. In addition, the expression of PAI-1 in plasma of PD patients was significantly higher than that of controls, and further analysis showed that the expression of PAI-1 in patients with cognitive impairment was significantly higher than that in patients with cognitive normal.

CONCLUSION

Our results indicate that the PAI-1 gene rs2227631 and rs1799889 polymorphisms were significantly associated with PD susceptibility in the Chinese Han population. PAI-1 has the potential to become a new therapeutic target and diagnostic marker.

Alpha-synuclein research: defining strategic moves in the battle against Parkinson's disease

With the advent of the genetic era in Parkinson's disease (PD) research in 1997, α-synuclein was identified as an important player in a complex neurodegenerative disease that affects >10 million people worldwide. PD has been estimated to have an economic impact of $51.9 billion in the US alone. Since the initial association with PD, hundreds of researchers have contributed to elucidating the functions of α-synuclein in normal and pathological states, and these remain critical areas for continued research. With this position paper the authors strive to achieve two goals: first, to succinctly summarize the critical features that define α-synuclein's varied roles, as they are known today; and second, to identify the most pressing knowledge gaps and delineate a multipronged strategy for future research with the goal of enabling therapies to stop or slow disease progression in PD.

Effect of aquaporin 4 protein overexpression in nigrostriatal system on development of Parkinson's disease

OBJECTS

Recent studies indicated that aquaporin 4 (AQP4), as the main water channel in the central nervous system (CNS), participated in the onset and progression of Parkinson's disease (PD). But how the AQP4 influenced the exacerbation of PD has not been described in detail. In this study, the effect of the AQP4 protein overexpression in nigrostriatal system that include substantia nigra (SN) and striatum (CPu) on the development of PD was investigated.

METHODS

Forty male Sprague Dawley rats were equally divided into two groups at random: PD group and control group, PD group undergoing surgery and receiving 6-hydroxydopamine (6-OHDA). Using MRI tracer-based method, extracellular space (ECS) diffusion parameters of nigrostriatal system for all rats were measured, including the clearance coefficient (k') and the half-life (t_1/2). Immunohistochemistry of AQP4 was performed for 20 rats.

RESULTS

The area of dark-stained AQP4 immunoreactivity increased markedly in SN of PD rats, there were significant differences between two groups (SN: t = 5.809, p < 0.0001; CPu: t = 5.943, p < 0.0001). And the diffusion parameters were significantly greater in PD group than that of control group, including k' (SN: t = 5.519, p < 0.0001; CPu: t = 2.149, p = 0.045) and t_1/2 (SN: t = 6.131, p < 0.0001; CPu: t = 6.708, p < 0.0001). There was a significant positive correlation between the AQP4 expression level and the k' values (SN: r = 0.827, p = 0.0031; CPu: r = 0.641, p = 0.0046), and a significant negative correlation between AQP4 and the t_1/2 values (SN: r=-0.654, p = 0.0403; CPu: r=-0.664, p = 0.0362).

CONCLUSIONS

The results indicated that AQP4 expression was increased in nigrostriatal system of PD rats, therefore, the overexpression of AQP4 led to acceleration of the diffusion and drainage process of drugs in ECS, reduced the effect of drugs for the treatment of PD, inhibited the development of PD.

Synergy between plasminogen activator inhibitor-1, α-synuclein, and neuroinflammation in Parkinson's disease

Parkinson's disease (PD) is a progressive degenerative nervous system disorder and is the second most common neurodegenerative disorder in the elderly population. The disease originates from the loss of dopamine-producing neurons in the substantia nigra in the brain, resulting in unregulated activity of the basal ganglia. Αlpha-synuclein (α-syn) is a protein found to aggregate in the substantia nigra region of patients with PD, forming Lewy Body inclusions; its aggregation may contribute to neuronal cell death in PD. This work hypothesizes about the synergistic relationship between α-syn aggregation and neuroinflammation to up-regulate expression of the serine protease inhibitor (serpin) plasminogen activator inhibitor-1 (PAI-1). The protease, plasmin, has been shown to cleave extracellular α-syn (including its monomeric, oligomeric, and fibrillary forms), resulting in less aggregation and Lewy Body formation. The zymogen plasminogen is converted to its active serine protease form, plasmin, either by tissue plasminogen activator (tPA) or by urokinase plasminogen activator (uPA) bound to urokinase receptor (uPAR). Both tPA and uPA/uPAR are inhibited by PAI-1. Thus, when PAI-1 levels increase, less plasmin is generated, which would lead to reduced proteolysis of α-syn. Expression of PAI-1 is increased both in inflammatory environments and in the presence of extracellular α-syn aggregates. This scenario suggests a pathological amplification loop: increased extracellular α-syn aggregation activates an inflammatory response from microglia and astrocytes, increasing PAI-1 levels, and decreasing the generation of plasmin. With reduced plasmin, less α-syn can be cleaved, and aggregation continues, sustaining the pathological process. Understanding this putative pathogenic loop could provide insight into the means by which neurodegeneration progresses in PD, and it may offer possible novel therapeutic strategies.

Autophagy Modulation as a Treatment of Amyloid Diseases

Amyloids are fibrous proteins aggregated into toxic forms that are implicated in several chronic disorders. More than 30 diseases show deposition of fibrous amyloid proteins associated with cell loss and degeneration in the affected tissues. Evidence demonstrates that amyloid diseases result from protein aggregation or impaired amyloid clearance, but the connection between amyloid accumulation and tissue degeneration is not clear. Common examples of amyloid diseases are Alzheimer's disease (AD), Parkinson's disease (PD) and tauopathies, which are the most common forms of neurodegenerative diseases, as well as polyglutamine disorders and certain peripheral metabolic diseases. In these diseases, increased accumulation of toxic amyloid proteins is suspected to be one of the main causative factors in the disease pathogenesis. It is therefore important to more clearly understand how these toxic amyloid proteins accumulate as this will aide in the development of more effective preventive and therapeutic strategies. Protein homeostasis, or proteostasis, is maintained by multiple cellular pathways-including protein synthesis, quality control, and clearance-which are collectively responsible for preventing protein misfolding or aggregation. Modulating protein degradation is a very complex but attractive treatment strategy used to remove amyloid and improve cell survival. This review will focus on autophagy, an important clearance pathway of amyloid proteins, and strategies for using it as a potential therapeutic target for amyloid diseases. The physiological role of autophagy in cells, pathways for its modulation, its connection with apoptosis, cell models and caveats in developing autophagy as a treatment and as a biomarker is discussed.

New Perspectives on Roles of Alpha-Synuclein in Parkinson's Disease

Parkinson’s disease (PD) is one of the synucleinopathies spectrum of disorders typified by the presence of intraneuronal protein inclusions. It is primarily composed of misfolded and aggregated forms of alpha-synuclein (α-syn), the toxicity of which has been attributed to the transition from an α-helical conformation to a β-sheetrich structure that polymerizes to form toxic oligomers. This could spread and initiate the formation of “LB-like aggregates,” by transcellular mechanisms with seeding and subsequent permissive templating. This hypothesis postulates that α-syn is a prion-like pathological agent and responsible for the progression of Parkinson’s pathology. Moreover, the involvement of the inflammatory response in PD pathogenesis has been reported on the excessive microglial activation and production of pro-inflammatory cytokines. At last, we describe several treatment approaches that target the pathogenic α-syn protein, especially the oligomers, which are currently being tested in advanced animal experiments or are already in clinical trials. However, there are current challenges with therapies that target α-syn, for example, difficulties in identifying varying α-syn conformations within different individuals as well as both the cost and need of long-duration large trials.

FYCO1 mediates clearance of α-synuclein aggregates through a Rab7-dependent mechanism

Parkinson's disease can be caused by mutations in the α-synuclein gene and is characterized by aggregates of α-synuclein protein. We have previously shown that over-expression of the small GTPase Rab7 can induce clearance of α-synuclein aggregates. In this study, we investigate which Rab7 effectors mediate this effect. To model Parkinson's disease, we expressed the pathogenic A53T mutant of α-synuclein in HEK293T cells and Drosophila melanogaster. We tested the Rab7 effectors FYVE and coiled-coil domain-containing protein 1 (FYCO1) and Rab-interacting lysosomal protein (RILP). FYCO1-EGFP-decorated vesicles containing α-synuclein. RILP-EGFP also decorated vesicular structures, but they did not contain α-synuclein. FYCO1 over-expression reduced the number of cells with α-synuclein aggregates, defined as visible particles of EGFP-tagged α-synuclein, whereas RILP did not. FYCO1 but not RILP reduced the amount of α-synuclein protein as assayed by western blot, increased the disappearance of α-synuclein aggregates in time-lapse microscopy and decreased α-synuclein-induced toxicity assayed by the Trypan blue assay. siRNA-mediated knockdown of FYCO1 but not RILP reduced Rab7-induced aggregate clearance. Collectively, these findings indicate that FYCO1 and not RILP mediates Rab7-induced aggregate clearance. The effect of FYCO1 on aggregate clearance was blocked by dominant negative Rab7 indicating that FYCO1 requires active Rab7 to function. Electron microscopic analysis and insertion of lysosomal membranes into the plasma membrane indicate that FYCO1 could lead to secretion of α-synuclein aggregates. Extracellular α-synuclein as assayed by ELISA was, however, not increased with FYCO1. Coexpression of FYCO1 in the fly model decreased α-synuclein aggregates as shown by the filter trap assay and rescued the locomotor deficit resulting from neuronal A53T-α-synuclein expression. This latter finding confirms that a pathway involving Rab7 and FYCO1 stimulates degradation of α-synuclein and could be beneficial in patients with Parkinson's disease. Open Data: Materials are available on https://cos.io/our-services/open-science-badges/ https://osf.io/93n6m/.

Lipopolysaccharide-binding protein (LBP) can reverse the amyloid state of fibrin seen or induced in Parkinson's disease

The thrombin-induced polymerisation of fibrinogen to form fibrin is well established as a late stage of blood clotting. It is known that Parkinson's Disease (PD) is accompanied by dysregulation in blood clotting, but it is less widely known as a coagulopathy. In recent work, we showed that the presence of tiny amounts of bacterial lipopolysaccharide (LPS) in healthy individuals could cause clots to adopt an amyloid form, and this could be observed via scanning electron microscopy (SEM) or via the fluorescence of thioflavin-T. This could be prevented by the prior addition of lipopolysaccharide-binding protein (LBP). We had also observed by SEM this unusual clotting in the blood of patients with Parkinson's Disease. We hypothesised, and here show, that this too can be prevented by LBP in the context of PD. This adds further evidence implicating inflammatory microbial cell wall products as an accompaniment to the disease, and may be part of its aetiology. This may lead to novel treatment strategies in PD designed to target microbes and their products.

Protein Partners of α-Synuclein in Health and Disease

α-synuclein is normally situated in the nerve terminal but it accumulates and aggregates in axons and cell bodies in synucleinopathies such as Parkinson's disease. The conformational changes occurring during α-synucleins aggregation process affects its interactions with other proteins and its subcellular localization. This review focuses on interaction partners of α-synuclein within different compartments of the cell with a focus on those preferentially binding aggregated α-synuclein. The aggregation state of α-synuclein also affects its catabolism and we hypothesize impaired macroautophagy is involved neuronal excretion of α-synuclein species responsible for the prion-like spreading of α-synuclein pathology.

Review: Novel treatment strategies targeting alpha-synuclein in multiple system atrophy as a model of synucleinopathy

Neurodegenerative disorders with alpha-synuclein (α-syn) accumulation (synucleinopathies) include Parkinson's disease (PD), PD dementia, dementia with Lewy bodies and multiple system atrophy (MSA). Due to the involvement of toxic α-syn aggregates in the molecular origin of these disorders, developing effective therapies targeting α-syn is a priority as a disease-modifying alternative to current symptomatic treatments. Importantly, the clinical and pathological attributes of MSA make this disorder an excellent candidate as a synucleinopathy model for accelerated drug development. Recent therapeutic strategies targeting α-syn in in vivo and in vitro models of MSA, as well as in clinical trials, have been focused on the pathological mechanisms of α-syn synthesis, aggregation, clearance, and/or cell-to-cell propagation of its neurotoxic conformers. Here we summarize the most relevant approaches in this direction, with emphasis on their potential as general synucleinopathy modifiers, and enumerate research areas for potential improvement in MSA drug discovery.

The Cleavage Effect of Mesenchymal Stem Cell and Its Derived Matrix Metalloproteinase-2 on Extracellular α-Synuclein Aggregates in Parkinsonian Models

Ample evidence has suggested that extracellular α‐synuclein aggregates would play key roles in the pathogenesis and progression of Parkinsonian disorders (PDs). In the present study, we investigated whether mesenchymal stem cells (MSCs) and their derived soluble factors could exert neuroprotective effects via proteolysis of extracellular α‐synuclein. When preformed α‐synuclein aggregates were incubated with MSC‐conditioned medium, α‐synuclein aggregates were disassembled, and insoluble and oligomeric forms of α‐synuclein were markedly decreased, thus leading to a significant increase in neuronal viability. In an animal study, MSC or MSC‐conditioned medium treatment decreased the expression of α‐synuclein oligomers and the induction of pathogenic α‐synuclein with an attenuation of apoptotic cell death signaling. Furthermore, we identified that matrix metalloproteinase‐2 (MMP‐2), a soluble factor derived from MSCs, played an important role in the degradation of extracellular α‐synuclein. Our data demonstrated that MSCs and their derived MMP‐2 exert neuroprotective properties through proteolysis of aggregated α‐synuclein in PD‐related microenvironments. Stem Cells Translational Medicine2017;6:949–961

The Interplay between Alpha-Synuclein Clearance and Spreading

Parkinson's Disease (PD) is a complex neurodegenerative disorder classically characterized by movement impairment. Pathologically, the most striking features of PD are the loss of dopaminergic neurons and the presence of intraneuronal protein inclusions primarily composed of alpha-synuclein (α-syn) that are known as Lewy bodies and Lewy neurites in surviving neurons. Though the mechanisms underlying the progression of PD pathology are unclear, accumulating evidence suggests a prion-like spreading of α-syn pathology. The intracellular homeostasis of α-syn requires the proper degradation of the protein by three mechanisms: chaperone-mediated autophagy, macroautophagy and ubiquitin-proteasome. Impairment of these pathways might drive the system towards an alternative clearance mechanism that could involve its release from the cell. This increased release to the extracellular space could be the basis for α-syn propagation to different brain areas and, ultimately, for the spreading of pathology and disease progression. Here, we review the interplay between α-syn degradation pathways and its intercellular spreading. The understanding of this interplay is indispensable for obtaining a better knowledge of the molecular basis of PD and, consequently, for the design of novel avenues for therapeutic intervention.

Protein Transmission, Seeding and Degradation: Key Steps for α-Synuclein Prion-Like Propagation

Converging lines of evidence suggest that cell-to-cell transmission and the self-propagation of pathogenic amyloidogenic proteins play a central role in the initiation and the progression of several neurodegenerative disorders. This "prion-like" hypothesis has been recently reported for α-synuclein, a presynaptic protein implicated in the pathogenesis of Parkinson's disease (PD) and related disorders. This review summarizes recent findings on α-synuclein prion-like propagation, focusing on its transmission, seeding and degradation and discusses some key questions that remain to be explored. Understanding how α-synuclein exits cells and propagates from one brain region to another will lead to the development of new therapeutic strategies for the treatment of PD, aiming at slowing or stopping the disease progression.

Nanomolar concentration of alpha-synuclein enhances dopaminergic neuronal survival via Akt pathway

Although alpha-synuclein is generally thought to have a pathological role in Parkinson's disease, accumulative evidence exists that alpha-synuclein has a neuroprotective effect. The aim of this study was to evaluate the effect of extracellular alpha-synuclein on dopaminergic cell survival. We assessed cell viability using the 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltertazolium bromide (MTT) assay both in undifferentiated SH-SY5Y (SHSY) cells and neuronally-differentiated SH-SY5Y (ndSHSY) cells after 24 hour treatment with monomeric alpha-synuclein at various concentrations (0 [control], 50, 100 nmol/L, 1 μmol/L). To determine whether cell viability assessed by MTT assay was affected by cell proliferation, 5-bromo-2’-deoxyuridine (BrdU) incorporation assay was performed. Level of both Akt and phosphorylated Akt was measured using western blot method in ndSHSY cells with or without 24 hour alpha-synuclein treatment. Cell viability was increased in ndSHSY cells at the nanomolar concentration of alpha-synuclein, but not in SHSY cells. Proportion of BrdU-positive ndSHSY cells was decreased in alpha-synuclein-treated group compared with control group. Level of phosphorylated Akt in alpha-synuclein-treated group was higher compared with the control group. Our study shows that extracellular alpha-synuclein at nanomolar concentration benefits dopaminergic cell survival via Akt pathway.