Accelerated alpha-synuclein aggregation after differentiation of SH-SY5Y neuroblastoma cells

Lipid levels correlate with neuronal and dopaminergic markers during the differentiation of SH-SY5Y cells

Parkinson's Disease (PD) is characterised by the loss of dopaminergic neurons and the deposition of protein inclusions called Lewy Bodies (LBs). LBs are heterogeneous structures composed of protein and lipid molecules and their main constituent is the presynaptic protein α-synuclein. SH-SY5Y cells are neuroblastoma cells commonly used to model PD because they express dopaminergic markers and α-synuclein and they can be differentiated into neuronal cells using established protocols. Despite increasing evidence pointing towards a role of lipids in PD, limited knowledge is available on the lipidome of undifferentiated and differentiated SH-SY5Y cells. Using a combination of lipidomics, proteomics, morphological and electrophysiological measurements, we identified specific lipids, including sphingolipids, whose levels are affected by the differentiation of SH-SY5Y neuroblastoma cells and found that the levels of these lipids correlate with those of neuronal and dopaminergic markers. These results provide a quantitative characterisation of the changes in lipidome associated with the differentiation of SH-SY5Y cells into more neuronal and dopaminergic-like phenotype and serve as a basis for further characterisation of lipid disruptions in association with PD and its risk factors in this dopaminergic-like neuronal cell model.

ErbB2pY -1248 as a predictive biomarker for Parkinson's disease based on research with RPPA technology and in vivo verification

AIMS

This study aims to reveal a promising biomarker for Parkinson's disease (PD) based on research with reverse phase protein array (RPPA) technology for the first time and in vivo verification, which gains time for early intervention in PD, thus increasing the effectiveness of treatment and reducing disease morbidity.

METHODS AND RESULTS

We employed RPPA technology which can assess both total and post-translationally modified proteins to identify biomarker candidates of PD in a cellular PD model. As a result, the phosphorylation (pY-1248) of the epidermal growth factor receptor (EGFR) ErbB2 is a promising biomarker candidate for PD. In addition, lapatinib, an ErbB2 tyrosine kinase inhibitor, was used to verify this PD biomarker candidate in vivo. We found that lapatinib-attenuated dopaminergic neuron loss and PD-like behavior in the zebrafish PD model. Accordingly, the expression of ErbB2pY-1248 significantly increased in the MPTP-induced mouse PD model. Our results suggest that ErbB2pY-1248 is a predictive biomarker for PD.

CONCLUSIONS

In this study, we found that ErbB2pY-1248 is a predictive biomarker of PD by using RPPA technology and in vivo verification. It offers a new perspective on PD diagnosing and treatment, which will be essential in identifying individuals at risk of PD. In addition, this study provides new ideas for digging into biomarkers of other neurodegenerative diseases.

Lewy Body-like Pathology and Loss of Dopaminergic Neurons in Midbrain Organoids Derived from Familial Parkinson's Disease Patient

Progressive accumulation of α-Synuclein (αSyn) in Lewy bodies (LBs) and loss of dopaminergic (DA) neurons are the hallmark pathological features of Parkinson's disease (PD). Although currently available in vitro and in vivo models have provided crucial information about PD pathogenesis, the mechanistic link between the progressive accumulation of αSyn into LBs and the loss of DA neurons is still unclear. To address this, it is critical to model LB formation and DA neuron loss, the two key neuropathological aspects of PD, in a relevant in vitro system. In this study, we developed a human midbrain-like organoid (hMBO) model of PD. We demonstrated that hMBOs generated from induced pluripotent stem cells (hiPSCs), derived from a familial PD (fPD) patient carrying αSyn gene (SNCA) triplication accumulate pathological αSyn over time. These cytoplasmic inclusions spatially and morphologically resembled diverse stages of LB formation and were composed of key markers of LBs. Importantly, the progressive accumulation of pathological αSyn was paralleled by the loss of DA neurons and elevated apoptosis. The model developed in this study will complement the existing in vitro models of PD and will provide a unique platform to study the spatiotemporal events governing LB formation and their relation with neurodegeneration. Furthermore, this model will also be beneficial for in vitro screening and the development of therapeutic compounds.

Deciphering the prion-like behavior of pathogenic protein aggregates in neurodegenerative diseases

Neurodegenerative diseases are hitherto classified based on their core clinical features, the anatomical distribution of neurodegeneration, and the cell populations mainly affected. On the other hand, the wealth of neuropathological, genetic, molecular and biochemical studies have identified the existence of distinct insoluble protein aggregates in the affected brain regions. These findings have spread the use of a collective term, proteinopathy, for neurodegenerative disorders with particular type of structurally altered protein accumulation. Particularly, a recent breakthrough in this field came with the discovery that these protein aggregates can transfer from one cell to another, thereby converting normal proteins to potentially toxic, misfolded species in a prion-like manner. In this review, we focus specifically on the molecular and cellular basis that underlies the seeding activity and transcellular spreading phenomenon of neurodegeneration-related protein aggregates, and discuss how these events contribute to the disease progression.

The antioxidant Rutin counteracts the pathological impact of α-synuclein on the enteric nervous system in vitro

Motoric disturbances in Parkinson's disease (PD) derive from the loss of dopaminergic neurons in the substantia nigra. Intestinal dysfunctions often appear long before manifestation of neuronal symptoms, suggesting a strong correlation between gut and brain in PD. Oxidative stress is a key player in neurodegeneration causing neuronal cell death. Using natural antioxidative flavonoids like Rutin, might provide intervening strategies to improve PD pathogenesis. To explore the potential effects of micro (mRutin) compared to nano Rutin (nRutin) upon the brain and the gut during PD, its neuroprotective effects were assessed using an in vitro PD model. Our results demonstrated that Rutin inhibited the neurotoxicity induced by A53T α-synuclein (Syn) administration by decreasing oxidized lipids and increasing cell viability in both, mesencephalic and enteric cells. For enteric cells, neurite outgrowth, number of synaptic vesicles, and tyrosine hydroxylase positive cells were significantly reduced when treated with Syn. This could be reversed by the addition of Rutin. nRutin revealed a more pronounced result in all experiments. In conclusion, our study shows that Rutin, especially the nanocrystals, are promising natural compounds to protect neurons from cell death and oxidative stress during PD. Early intake of Rutin may provide a realizable option to prevent or slow PD pathogenesis.

Biochemical characterization of proliferative and differentiated SH-SY5Y cell line as a model for Parkinson's disease

Parkinson's disease is a multifactorial neurodegenerative disease. The cellular pathology includes dopamine depletion, decrease in mitochondrial complex I enzyme activity, lysosomal glucocerebrosidase enzyme activity and glutathione levels. The SH-SY5Y human neuroblastoma cell line is one of the most widely used cell line models for Parkinson's disease. However, the consensus on its suitability as a model in its proliferative or differentiated state is lacking. In this study, we characterized and compared the biochemical processes most often studied in PD. This in proliferative and differentiated phenotypes of SH-SY5Y cells and several differences were found. Most notably, extracellular dopamine metabolism was significantly higher in differentiated SH-SY5Y. Furthermore, there was a greater variability in glutathione levels in proliferative phenotype (+/- 49%) compared to differentiated (+/- 16%). Finally, enzyme activity assay revealed significant increase in the lysosomal enzyme glucocerebrosidase activity in differentiated phenotype. In contrast, our study has found similarities between the two phenotypes in mitochondrial electron transport chain activity and tyrosine hydroxylase protein expression. The results of this study demonstrate that despite coming from the same cell line, these cells possess some key differences in their biochemistry. This highlights the importance of careful characterization of relevant disease pathways to assess the suitability of cell lines, such as SH-SY5Y cells, for modelling PD or other diseases, i.e. when using the same cell line but different differentiation states.

Microtubule-Associated Proteins with Regulatory Functions by Day and Pathological Potency at Night

The sensing, integrating, and coordinating features of the eukaryotic cells are achieved by the complex ultrastructural arrays and multifarious functions of the cytoskeleton, including the microtubule network. Microtubules play crucial roles achieved by their decoration with proteins/enzymes as well as by posttranslational modifications. This review focuses on the Tubulin Polymerization Promoting Protein (TPPP/p25), a new microtubule associated protein, on its "regulatory functions by day and pathological functions at night". Physiologically, the moonlighting TPPP/p25 modulates the dynamics and stability of the microtubule network by bundling microtubules and enhancing the tubulin acetylation due to the inhibition of tubulin deacetylases. The optimal endogenous TPPP/p25 level is crucial for its physiological functions, to the differentiation of oligodendrocytes, which are the major constituents of the myelin sheath. Pathologically, TPPP/p25 forms toxic oligomers/aggregates with α-synuclein in neurons and oligodendrocytes in Parkinson's disease and Multiple System Atrophy, respectively; and their complex is a potential therapeutic drug target. TPPP/p25-derived microtubule hyperacetylation counteracts uncontrolled cell division. All these issues reveal the anti-mitotic and α-synuclein aggregation-promoting potency of TPPP/p25, consistent with the finding that Parkinson's disease patients have reduced risk for certain cancers.

Advancement in the modelling and therapeutics of Parkinson's disease

Since the discovery of L-dopa in the middle of the 20th century (1960s), there is not any neuroprotective therapy available although significant development has been made in the treatment of symptomatic Parkinson's disease (PD). Neurological disorders like PD can be modelled in animals so as to recapitulates most of the symptoms seen in PD patients. In aging population, PD is the second most common neurodegenerative disease after Alzheimer's disease, even though significant outcomes have been achieved in PD research yet it still is a mystery to solve the treatments for PD. In the last two decades, PD models have provided enhanced precision into the understanding of the process of PD disease, its etiology, pathology, and molecular mechanisms behind it. Furthermore, at the same time as cellular models have helped to recognize specific events, animal models, both toxic and genetic, have replicated almost all of the hallmarks of PD and are very helpful for testing and finding new strategies for neuroprotection. Recently, in both classical and newer models, major advances have been done in the modelling of supplementary PD features have come into the light. In this review, we have try to provide an updated summary of the characteristics of these models related to in vitro and in vivo models, animal models for PD, stem cell model for PD, newer 3D model as well as the strengths and limitations of these most popular PD models.

Rapid Growth Cone Uptake and Dynein-Mediated Axonal Retrograde Transport of Negatively Charged Nanoparticles in Neurons Is Dependent on Size and Cell Type

Nanoparticles (NPs) are now used in numerous technologies and serve as carriers for several new classes of therapeutics. Studies of the distribution of NPs in vivo demonstrate that they can be transported through biological barriers and are concentrated in specific tissues. Here, transport behavior, and final destination of polystyrene NPs are reported in primary mouse cortical neurons and SH-SY5Y cells, cultured in two-compartmental microfluidic devices. In both cell types, negative polystyrene NPs (PS(-)) smaller than 100 nm are taken up by the axons, undergo axonal retrograde transport, and accumulate in the somata. Examination of NP transport reveals different transport mechanisms depending on the cell type, particle charge, and particle internalization by the lysosomes. In cortical neurons, PS(-) inside lysosomes and 40 nm positive polystyrene NPs undergo slow axonal transport, whereas PS(-) outside lysosomes undergo fast axonal transport. Inhibition of dynein in cortical neurons decreases the transport velocity and cause a dose-dependent reduction in the number of accumulated PS(-), suggesting that the fast axonal transport is dynein mediated. These results show that the axonal retrograde transport of NPs depends on the endosomal pathway taken and establishes a means for screening nanoparticle-based therapeutics for diseases that involve neurons.

A new hypothesis for Parkinson's disease pathogenesis: GTPase-p38 MAPK signaling and autophagy as convergence points of etiology and genomics

The combination of genetics and genomics in Parkinson´s disease has recently begun to unveil molecular mechanisms possibly underlying disease onset and progression. In particular, catabolic processes such as autophagy have been increasingly gaining relevance as post-mortem evidence and experimental models suggested a participation in neurodegeneration and alpha-synuclein Lewy body pathology. In addition, familial Parkinson´s disease linked to LRRK2 and alpha-synuclein provided stronger correlation between etiology and alterations in autophagy. More detailed cellular pathways are proposed and genetic risk factors that associate with idiopathic Parkinson´s disease provide further clues in dissecting contributions of single players. Nevertheless, the fine-tuning of these processes remains elusive, as the initial stages of the pathways are not yet clarified.In this review, we collect literature evidence pointing to autophagy as the common, downstream target of Parkinsonian dysfunctions and augment current knowledge on the factors that direct the subsequent steps. Cell and molecular biology evidence indicate that p38 signaling underlies neurodegeneration and autoptic observations suggest a participation in neuropathology. Moreover, alpha-synuclein and LRRK2 also appear involved in the p38 pathway with additional roles in the regulation of GTPase signaling. Small GTPases are critical modulators of p38 activation and thus, their functional interaction with aSyn and LRRK2 could explain much of the detailed mechanics of autophagy in Parkinson´s disease.We propose a novel hypothesis for a more comprehensive working model where autophagy is controlled by upstream pathways, such as GTPase-p38, that have been so far underexplored in this context. In addition, etiological factors (LRRK2, alpha-synuclein) and risk loci might also combine in this common mechanism, providing a powerful experimental setting to dissect the cause of both familial and idiopathic disease.

Transfer of disrupted-in-schizophrenia 1 aggregates between neuronal-like cells occurs in tunnelling nanotubes and is promoted by dopamine

The disrupted-in-schizophrenia 1 (DISC1) gene was identified as a genetic risk factor for chronic mental illnesses (CMI) such as schizophrenia, bipolar disorder and severe recurrent depression. Insoluble aggregated DISC1 variants were found in the cingular cortex of sporadic, i.e. non-genetic, CMI patients. This suggests protein pathology as a novel, additional pathogenic mechanism, further corroborated in a recent transgenic rat model presenting DISC1 aggregates. Since the potential role of aggregation of DISC1 in sporadic CMI is unknown, we investigated whether DISC1 undergoes aggregation in cell culture and could spread between neuronal cells in a prion-like manner, as shown for amyloid proteins in neurodegenerative diseases. Co-culture experiments between donor cells forming DISC1 aggregates and acceptor cells showed that 4.5% of acceptor cells contained donor-derived DISC1 aggregates, thus indicating an efficient transfer in vitro. DISC1 aggregates were found inside tunnelling nanotubes (TNTs) and transfer was enhanced by increasing TNT formation and notably by dopamine treatment, which also induces DISC1 aggregation. These data indicate that DISC1 aggregates can propagate between cells similarly to prions, thus providing some molecular basis for the role of protein pathology in CMI.

DnaJ/Hsp40 Family and Parkinson's Disease

Parkinson's disease (PD) is the second most common devastating neurodegenerative disorder after Alzheimer's disease. The precise molecular and cellular basis underlying PD still remains uncertain; however, accumulating evidence suggests that neuronal cell death is caused by a combination of environmental and genetic factors. Over the previous two decades, more than 20 genes have been identified as the cause of and/or risk for PD. Because sporadic and familial forms of PD have many similarities in clinical and neuropathological features, common molecular pathways, such as aberrant mitochondrial and protein homeostasis, are likely to exist in both conditions. Of the various genes and proteins involved in PD, the versatile DnaJ/Hsp40 co-chaperones have attracted particular attention since several genes encoding this protein family have been successively identified as the cause of the familial forms of PD/Parkinsonism. In this review, we will introduce the current knowledge regarding the integratory and modulatory effect of DnaJ/Hsp40 in various cellular functions and argue how the failure of these proteins may initiate and/or facilitate of the disease.

A Protein Aggregation Inhibitor, Leuco-Methylthioninium Bis(Hydromethanesulfonate), Decreases α-Synuclein Inclusions in a Transgenic Mouse Model of Synucleinopathy

α-Synuclein (α-Syn) aggregation is a pathological feature of synucleinopathies, neurodegenerative disorders that include Parkinson's disease (PD). We have tested whether N,N,N',N'-tetramethyl-10H-phenothiazine-3,7-diaminium bis(hydromethanesulfonate) (leuco-methylthioninium bis(hydromethanesulfonate); LMTM), a tau aggregation inhibitor, affects α-Syn aggregation in vitro and in vivo. Both cellular and transgenic models in which the expression of full-length human α-Syn (h-α-Syn) fused with a signal sequence peptide to promote α-Syn aggregation were used. Aggregated α-Syn was observed following differentiation of N1E-115 neuroblastoma cells transfected with h-α-Syn. The appearance of aggregated α-Syn was inhibited by LMTM, with an EC50 of 1.1 μM, with minimal effect on h-α-Syn mRNA levels being observed. Two independent lines of mice (L58 and L62) transgenic for the same fusion protein accumulated neuronal h-α-Syn that, with aging, developed into fibrillary inclusions characterized by both resistance to proteinase K (PK)-cleavage and their ability to bind thiazin red. There was a significant decrease in α-Syn-positive neurons in multiple brain regions following oral treatment of male and female mice with LMTM administered daily for 6 weeks at 5 and 15 mg MT/kg. The early aggregates of α-Syn and the late-stage fibrillar inclusions were both susceptible to inhibition by LMTM, a treatment that also resulted in the rescue of movement and anxiety-related traits in these mice. The results suggest that LMTM may provide a potential disease modification therapy in PD and other synucleinopathies through the inhibition of α-Syn aggregation.

Endogenous Alpha-Synuclein Protein Analysis from Human Brain Tissues Using Single-Molecule Pull-Down Assay

Alpha-synuclein (α-SYN) is a central molecule in Parkinson's disease pathogenesis. Despite several studies, the molecular nature of endogenous α-SYN especially in human brain samples is still not well understood due to the lack of reliable methods and the limited amount of biospecimens. Here, we introduce α-SYN single-molecule pull-down (α-SYN SiMPull) assay combined with in vivo protein crosslinking to count individual α-SYN protein and assess its native oligomerization states from biological samples including human postmortem brains. This powerful single-molecule assay can be highly useful in diagnostic applications using various specimens for neurodegenerative diseases including Alzheimer's disease and Parkinson's disease.

Glucose-6-phosphatase-α participates in dopaminergic differentiation

OBJECTIVE

 Induction of dopaminergic (DA) differentiation is a cell-based therapy for Parkinson's disease (PD). Here, we explore the key factors of DA differentiation with a focus on glucose-6-phosphatase (G6Pase), a marker enzyme for the endoplasmic reticulum (ER) associated with cell differentiation.

METHODS

 We cultured SH-SY5Y human neuroblastoma cells, a model system for PD research, and added glial cell-derived neurotrophic factor (GDNF; 25, 50, or 100 ng/ml) to stimulate differentiation. Subsequently, several methods, such as microRNA/mRNA microarrays, quantitative real-time polymerase chain reaction (qRT-PCR) and western blot were used to detect target genes and proteins respectively.

RESULTS

 Light microscopy revealed that 50 ng/ml GDNF most effectively induced DA differentiation. MicroRNA/mRNA microarrays identified that G6PC mRNA was significantly upregulated, which might be influenced by three downregulated microRNAs. Follow-up qRT-PCR results were consistent with the microarray findings, and western blots also supported the results.

DISCUSSION

Taken together, our results demonstrate that G6PC, a subunit of G6Pase, participates in DA differentiation. Our findings may contribute to provide a foundation for the research on the mechanism of DA differentiation as well as cell-based therapy for PD.

Alpha-synuclein prevents the formation of spherical mitochondria and apoptosis under oxidative stress

Oxidative stress (OS), mitochondrial dysfunction, and dysregulation of alpha-synuclein (aSyn) homeostasis are key pathogenic factors in Parkinson's disease. Nevertheless, the role of aSyn in mitochondrial physiology remains elusive. Thus, we addressed the impact of aSyn specifically on mitochondrial response to OS in neural cells. We characterize a distinct type of mitochondrial fragmentation, following H₂O₂ or 6-OHDA-induced OS, defined by spherically-shaped and hyperpolarized mitochondria, termed "mitospheres". Mitosphere formation mechanistically depended on the fission factor Drp1, and was paralleled by reduced mitochondrial fusion. Furthermore, mitospheres were linked to a decrease in mitochondrial activity, and preceded Caspase3 activation. Even though fragmentation of dysfunctional mitochondria is considered to be a prerequisite for mitochondrial degradation, mitospheres were not degraded via Parkin-mediated mitophagy. Importantly, we provide compelling evidence that aSyn prevents mitosphere formation and reduces apoptosis under OS. In contrast, aSyn did not protect against Rotenone, which led to a different, previously described donut-shaped mitochondrial morphology. Our findings reveal a dichotomic role of aSyn in mitochondrial biology, which is linked to distinct types of stress-induced mitochondrial fragmentation. Specifically, aSyn may be part of a cellular defense mechanism preserving neural mitochondrial homeostasis in the presence of increased OS levels, while not protecting against stressors directly affecting mitochondrial function.

The SH-SY5Y cell line in Parkinson's disease research: a systematic review

Parkinson’s disease (PD) is a devastating and highly prevalent neurodegenerative disease for which only symptomatic treatment is available. In order to develop a truly effective disease-modifying therapy, improvement of our current understanding of the molecular and cellular mechanisms underlying PD pathogenesis and progression is crucial. For this purpose, standardization of research protocols and disease models is necessary. As human dopaminergic neurons, the cells mainly affected in PD, are difficult to obtain and maintain as primary cells, current PD research is mostly performed with permanently established neuronal cell models, in particular the neuroblastoma SH-SY5Y lineage. This cell line is frequently chosen because of its human origin, catecholaminergic (though not strictly dopaminergic) neuronal properties, and ease of maintenance. However, there is no consensus on many fundamental aspects that are associated with its use, such as the effects of culture media composition and of variations in differentiation protocols. Here we present the outcome of a systematic review of scientific articles that have used SH-SY5Y cells to explore PD. We describe the cell source, culture conditions, differentiation protocols, methods/approaches used to mimic PD and the preclinical validation of the SH-SY5Y findings by employing alternative cellular and animal models. Thus, this overview may help to standardize the use of the SH-SY5Y cell line in PD research and serve as a future user’s guide.

Cellular models for Parkinson's disease

Developing new therapeutic strategies for Parkinson's disease requires cellular models. Current models reproduce the two most salient changes found in the brains of patients with Parkinson's disease: The degeneration of dopaminergic neurons and the existence of protein aggregates consisting mainly of α-synuclein. Cultured cells offer many advantages over studying Parkinson's disease directly in patients or in animal models. At the same time, the choice of a specific cellular model entails the requirement to focus on one aspect of the disease while ignoring others. This article is intended for researchers planning to use cellular models for their studies. It describes for commonly used cell types the aspects of Parkinson's disease they model along with technical advantages and disadvantages. It might also be helpful for researchers from other fields consulting literature on cellular models of Parkinson's disease. Important models for the study of dopaminergic neuron degeneration include Lund human mesencephalic cells and primary neurons, and a case is made for the use of non-dopaminergic cells to model pathogenesis of non-motor symptoms of Parkinson's disease. With regard to α-synuclein aggregates, this article describes strategies to induce and measure aggregates with a focus on fluorescent techniques. Cellular models reproduce the two most salient changes of Parkinson's disease, the degeneration of dopaminergic neurons and the existence of α-synuclein aggregates. This article is intended for researchers planning to use cellular models for their studies. It describes for commonly used cell types and treatments the aspects of Parkinson's disease they model along with technical advantages and disadvantages. Furthermore, this article describes strategies to induce and measure aggregates with a focus on fluorescent techniques. This article is part of a special issue on Parkinson disease.

Glia and alpha-synuclein in neurodegeneration: A complex interaction

α-Synucleinopathies (ASP) comprise adult-onset, progressive neurodegenerative disorders such as Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA) that are characterized by α-synuclein (AS) aggregates in neurons or glia. PD and DLB feature neuronal AS-positive inclusions termed Lewy bodies (LB) whereas glial cytoplasmic inclusions (GCIs, Papp-Lantos bodies) are recognized as the defining hallmark of MSA. Furthermore, AS-positive cytoplasmic aggregates may also be seen in astroglial cells of PD/DLB and MSA brains. The glial AS-inclusions appear to trigger reduced trophic support resulting in neuronal loss. Moreover, microgliosis and astrogliosis can be found throughout the neurodegenerative brain and both are key players in the initiation and progression of ASP. In this review, we will highlight AS-dependent alterations of glial function and their impact on neuronal vulnerability thereby providing a detailed summary on the multifaceted role of glia in ASP.

VPS35 dysfunction impairs lysosomal degradation of α-synuclein and exacerbates neurotoxicity in a Drosophila model of Parkinson's disease

Mutations in vacuolar protein sorting 35 (VPS35) have been linked to familial Parkinson's disease (PD). VPS35, a component of the retromer, mediates the retrograde transport of cargo from the endosome to the trans-Golgi network. Here we showed that retromer depletion increases the lysosomal turnover of the mannose 6-phosphate receptor, thereby affecting the trafficking of cathepsin D (CTSD), a lysosome protease involved in α-synuclein (αSYN) degradation. VPS35 knockdown perturbed the maturation step of CTSD in parallel with the accumulation of αSYN in the lysosomes. Furthermore, we found that the knockdown of Drosophila VPS35 not only induced the accumulation of the detergent-insoluble αSYN species in the brain but also exacerbated both locomotor impairments and mild compound eye disorganization and interommatidial bristle loss in flies expressing human αSYN. These findings indicate that the retromer may play a crucial role in αSYN degradation by modulating the maturation of CTSD and might thereby contribute to the pathogenesis of the disease.

Drug targets from genetics: α-synuclein

One of the critical issues in Parkinson disease (PD) research is the identity of the specific toxic, pathogenic moiety. In PD, mutations in α-synuclein (αsyn) or multiplication of the SNCA gene encoding αsyn, result in a phenotype of cellular inclusions, cell death, and brain dysfunction. While the historical point of view has been that the macroscopic aggregates containing αsyn are the toxic species, in the last several years evidence has emerged that suggests instead that smaller soluble species--likely oligomers containing misfolded αsyn--are actually the toxic moiety and that the fibrillar inclusions may even be a cellular detoxification pathway and less harmful. If soluble misfolded species of αsyn are the toxic moieties, then cellular mechanisms that degrade misfolded αsyn would be neuroprotective and a rational target for drug development. In this review we will discuss the fundamental mechanisms underlying αsyn toxicity including oligomer formation, oxidative stress, and degradation pathways and consider rational therapeutic strategies that may have the potential to prevent or halt αsyn induced pathogenesis in PD.

Suppression of dynamin GTPase decreases α-synuclein uptake by neuronal and oligodendroglial cells: a potent therapeutic target for synucleinopathy

Background

The intracellular deposition of misfolded proteins is a common neuropathological hallmark of most neurodegenerative disorders. Increasing evidence suggests that these pathogenic proteins may spread to neighboring cells and induce the propagation of neurodegeneration.

Results

In this study, we have demonstrated that α-synuclein (αSYN), a major constituent of intracellular inclusions in synucleinopathies, was taken up by neuronal and oligodendroglial cells in both a time- and concentration-dependent manner. Once incorporated, the extracellular αSYN was immediately assembled into high-molecular-weight oligomers and subsequently formed cytoplasmic inclusion bodies. Furthermore, αSYN uptake by neurons and cells of the oligodendroglial lineage was markedly decreased by the genetic suppression and pharmacological inhibition of the dynamin GTPases, suggesting the involvement of the endocytic pathway in this process.

Conclusions

Our findings shed light on the mode of αSYN uptake by neuronal and oligodendroglial cells and identify therapeutic strategies aimed at reducing the propagation of protein misfolding.

["Pathophysiology and clinical presentation of Parkinson's disease-up to date" pathomechanisms of Parkinson's disease]

The tetrad of Parkinson's disease (PD) including tremor, rigidity, akinesia and postural instability are attributed to the loss of dopaminergic neurons in the substantia nigra. Both environmental factors and genetic predisposition are supposed to be implicated in the initiation and progression of the disease. Particularly, much attention has been focused on α-synuclein (αSYN) since αSYN is not only found in Lewy bodies characteristic of PD, but also mutations in the gene for αSYN can cause inherited forms of PD. Recent studies have shown that αSYN can be secreted into the extracellular milieu, thereby propagate Lewy pathology to neighboring cells in a prion-like manner. This concept sounds attractive as an acceptable explanation for the stereotypic distribution of Lewy pathology in PD. In addition to the classic motor symptoms, a variety of non-motor manifestations may affect on the patient's quality of life. Of all, hyposmia is prevalent in PD and may precede the onset of motor symptoms. We found that odor identification test scores correlated positively with the impairment of short-term memory and visuospatial functions. Furthermore, our data from fear-conditioning experiment indicated that the key player in the processing of emotional memories appears to be the amygdala, which has tight connections to primary olfactory areas.

α-Synuclein aggregation and modulating factors

Aggregated a-synuclein is the major component of inclusions in Parkinson's disease and other synucleinopathy brains indicating that a-syn aggregation is associated with the pathogenesis of neurodegenerative disorders. Although the mechanisms underlying a-syn aggregation and toxicity are not fully elucidated, it is clear that a-syn undergoes post-translational modifications and interacts with numerous proteins and other macromolecules, metals, hormones, neurotransmitters, drugs and poisons that can all modulate its aggregation propensity. The current and most recent findings regarding the factors modulating a-syn aggregation process are discussed in detail.

The AAA-ATPase VPS4 regulates extracellular secretion and lysosomal targeting of α-synuclein

Many neurodegenerative diseases share a common pathological feature: the deposition of amyloid-like fibrils composed of misfolded proteins. Emerging evidence suggests that these proteins may spread from cell-to-cell and encourage the propagation of neurodegeneration in a prion-like manner. Here, we demonstrated that α-synuclein (αSYN), a principal culprit for Lewy pathology in Parkinson's disease (PD), was present in endosomal compartments and detectably secreted into the extracellular milieu. Unlike prion protein, extracellular αSYN was mainly recovered in the supernatant fraction rather than in exosome-containing pellets from the neuronal culture medium and cerebrospinal fluid. Surprisingly, impaired biogenesis of multivesicular body (MVB), an organelle from which exosomes are derived, by dominant-negative mutant vacuolar protein sorting 4 (VPS4) not only interfered with lysosomal targeting of αSYN but facilitated αSYN secretion. The hypersecretion of αSYN in VPS4-defective cells was efficiently restored by the functional disruption of recycling endosome regulator Rab11a. Furthermore, both brainstem and cortical Lewy bodies in PD were found to be immunoreactive for VPS4. Thus, VPS4, a master regulator of MVB sorting, may serve as a determinant of lysosomal targeting or extracellular secretion of αSYN and thereby contribute to the intercellular propagation of Lewy pathology in PD.

Gelsolin co-occurs with Lewy bodies in vivo and accelerates α-synuclein aggregation in vitro

Deposition of fibrillar α-synuclein as Lewy bodies is the neuropathological hallmark of Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Apart from α-synuclein, these intraneuronal inclusions contain over 250 different proteins. The actin binding protein gelsolin, has previously been suggested to be part of the Lewy body, but its potential role in α-synuclein aggregation remains unknown. Here, we studied the association between gelsolin and α-synuclein in brain tissue from PD and DLB patients as well as in a cell model for α-synuclein aggregation. Moreover, the potential effect of gelsolin on α-synuclein fibrillization was also investigated. Our data demonstrate that gelsolin co-occured with α-synuclein in Lewy bodies from affected human brain as well as with Lewy body-like inclusions in α-synuclein over expressing cells. Furthermore, in the presence of calcium chloride, gelsolin was found to enhance the aggregation rate of α-synuclein in vitro. Moreover, no apparent structural differences could be observed between fibrils formed in the presence or absence of gelsolin. Further studies on gelsolin and other Lewy body associated proteins are warranted to learn more about their potential role in the α-synuclein aggregation process.

L-DOPA: a scapegoat for accelerated neurodegeneration in Parkinson's disease?

There is consensus that amelioration of the motor symptoms of Parkinson's disease is most effective with L-DOPA (levodopa). However, this necessary therapeutic step is biased by an enduring belief that L-DOPA is toxic to the remaining substantia nigra dopaminergic neurons by itself, or by specific metabolites such as dopamine. The concept of L-DOPA toxicity originated from pre-clinical studies conducted mainly in cell culture, demonstrating that L-DOPA or its derivatives damage dopaminergic neurons due to oxidative stress and other mechanisms. However, the in vitro data remain controversial as some studies showed neuroprotective, rather than toxic action of the drug. The relevance of this debate needs to be considered in the context of the studies conducted on animals and in clinical trials that do not provide convincing evidence for L-DOPA toxicity in vivo. This review presents the current views on the pathophysiology of Parkinson's disease, focusing on mitochondrial dysfunction and oxidative/proteolytic stress, the factors that can be affected by L-DOPA or its metabolites. We then critically discuss the evidence supporting the two opposing views on the effects of L-DOPA in vitro, as well as the animal and human data. We also address the problem of inadequate experimental models used in these studies. L-DOPA remains the symptomatic 'hero' of Parkinson's disease. Whether it contributes to degeneration of nigral dopaminergic neurons, or is a 'scapegoat' for explaining undesirable or unexpected effects of the treatment, remains a hotly debated topic.

Phytic Acid Protects against 6-Hydroxydopamine-Induced Dopaminergic Neuron Apoptosis in Normal and Iron Excess Conditions in a Cell Culture Model

Iron may play an important role in Parkinson's disease (PD) since it can induce oxidative stress-dependent neurodegeneration. The objective of this study was to determine whether the iron chelator, phytic acid (IP6) can protect against 6-hydroxydopamine- (6-OHDA-) induced apoptosis in immortalized rat mesencephalic dopaminergic cells under normal and iron-excess conditions. Caspase-3 activity was increased about 6-fold after 6-OHDA treatment (compared to control; P < .001) and 30 μmol/L IP6 pretreatment decreased it by 38% (P < .05). Similarly, a 63% protection (P < .001) against 6-OHDA induced DNA fragmentation was observed with IP6 pretreatment. Under iron-excess condition, a 6-fold increase in caspase-3 activity (P < .001) and a 42% increase in DNA fragmentation (P < .05) with 6-OHDA treatment were decreased by 41% (P < .01) and 27% (P < .05), respectively, with 30 μmol/L IP6. Together, our data suggest that IP6 protects against 6-OHDA-induced cell apoptosis in both normal and iron-excess conditions, and IP6 may offer neuroprotection in PD.

Role of TPPP/p25 on α-synuclein-mediated oligodendroglial degeneration and the protective effect of SIRT2 inhibition in a cellular model of multiple system atrophy

Multiple system atrophy (MSA) is a progressive neurodegenerative disorder presenting variable combinations of parkinsonism, cerebellar ataxia, corticospinal and autonomic dysfunction. Alpha-synuclein (α-SYN)-immunopositive glial cytoplasmic inclusions (GCIs) represent the neuropathological hallmark of MSA, and tubulin polymerization promoting protein (TPPP)/p25 in oligodendroglia has been known as a potent stimulator of α-SYN aggregation. To gain insight into the molecular pathomechanisms of GCI formation and subsequent oligodendroglial degeneration, we ectopically expressed α-SYN and TPPP in HEK293T and oligodendroglial KG1C cell lines. Here we showed that TPPP specifically accelerated α-SYN oligomer formation and co-immunoprecipitation analysis revealed the specific interaction of TPPP and α-SYN. Moreover, phosphorylation of α-SYN at Ser-129 facilitated the TPPP-mediated α-SYN oligomerization. TPPP facilitated α-SYN-positive cytoplasmic perinuclear inclusions mimicking GCI in both cell lines; however, apoptotic cell death was only observed in KG1C cells. This apoptotic cell death was partly rescued by sirtuin 2 (SIRT2) inhibition. Together, our results provide further insight into the molecular pathogenesis of MSA and potential therapeutic approaches.

Inhibition of mitochondrial fusion by α-synuclein is rescued by PINK1, Parkin and DJ-1

Aggregation of α-synuclein (αS) is involved in the pathogenesis of Parkinson's disease (PD) and a variety of related neurodegenerative disorders. The physiological function of αS is largely unknown. We demonstrate with in vitro vesicle fusion experiments that αS has an inhibitory function on membrane fusion. Upon increased expression in cultured cells and in Caenorhabditis elegans, αS binds to mitochondria and leads to mitochondrial fragmentation. In C. elegans age-dependent fragmentation of mitochondria is enhanced and shifted to an earlier time point upon expression of exogenous αS. In contrast, siRNA-mediated downregulation of αS results in elongated mitochondria in cell culture. αS can act independently of mitochondrial fusion and fission proteins in shifting the dynamic morphologic equilibrium of mitochondria towards reduced fusion. Upon cellular fusion, αS prevents fusion of differently labelled mitochondrial populations. Thus, αS inhibits fusion due to its unique membrane interaction. Finally, mitochondrial fragmentation induced by expression of αS is rescued by coexpression of PINK1, parkin or DJ-1 but not the PD-associated mutations PINK1 G309D and parkin Δ1-79 or by DJ-1 C106A.

Mechanisms of neuronal death in synucleinopathy

α-synuclein is a key molecule in the pathogenesis of synucleinopathy including Parkinson's disease and multiple system atrophy. In this mini-review, we mainly focus on recent data obtained from cellular models of synucleinopathy and discuss the possible mechanisms of neurodegeneration. Recent progress suggests that the aggregate formation of α-synuclein is cytoprotective and that its precursor oligomer (protofibril) may be cytotoxic. The catechol-derived quinones are the candidate molecules that facilitate the oligomer formation of α-synuclein. Furthermore, the cellular membranes are shown to be the primary targets injured by mutant α-synucleins, and the mitochondrial dysfunction seems to be an initial step in the neuronal death.

Low-dose bafilomycin attenuates neuronal cell death associated with autophagy-lysosome pathway dysfunction

We have shown previously that the plecomacrolide antibiotics bafilomycin A1 and B1 significantly attenuate cerebellar granule neuron death resulting from agents that disrupt lysosome function. To further characterize bafilomycin-mediated cytoprotection, we examined its ability to attenuate the death of naïve and differentiated neuronal SH-SY5Y human neuroblastoma cells from agents that induce lysosome dysfunction in vitro, and from in vivo dopaminergic neuron death in C. elegans. Low-dose bafilomycin significantly attenuated SH-SY5Y cell death resulting from treatment with chloroquine, hydroxychloroquine amodiaquine and staurosporine. Bafilomycin also attenuated the chloroquine-induced reduction in processing of cathepsin D, the principal lysosomal aspartic acid protease, to its mature 'active' form. Chloroquine induced autophagic vacuole accumulation and inhibited autophagic flux, effects that were attenuated upon treatment with bafilomycin and were associated with a significant decrease in chloroquine-induced accumulation of detergent-insoluble alpha-synuclein oligomers. In addition, bafilomycin significantly and dose-dependently attenuated dopaminergic neuron death in C. elegans resulting from in vivo over-expression of human wild-type alpha-synuclein. Together, our findings suggest that low-dose bafilomycin is cytoprotective in part through its maintenance of the autophagy-lysosome pathway, and underscores its therapeutic potential for treating Parkinson's disease and other neurodegenerative diseases that exhibit disruption of protein degradation pathways and accumulation of toxic protein species.

A novel, high-efficiency cellular model of fibrillar alpha-synuclein inclusions and the examination of mutations that inhibit amyloid formation

Intracytoplasmic alpha-synuclein (alpha-syn) amyloidogenic inclusions are a major pathological feature of Parkinson's disease, dementia with Lewy body disease and multiple systems atrophy. The mechanisms involved in the formation and inhibition of these aggregates are areas of intense investigation. The present study characterizes a novel cellular model for the study of alpha-syn aggregation, incorporating nucleation-dependent aggregation and a new function for calcium phosphate precipitation. Cultured cells were readily induced to develop large, cytoplasmic alpha-syn filamentous aggregates that were hyperphosphorylated, often ubiquitinated and thioflavin positive. These cellular aggregates formed in the majority of transfected cells and recruited approximately half of endogenously expressed alpha-syn. Using this system, we examined single-point mutations that inhibit alpha-syn amyloid formation in vitro. Three mutations (V66P, T72P and T75P) significantly hindered alpha-syn aggregation in this cell model. The T75P mutant, which could abrogate amyloid formation of wild-type alpha-syn in vitro, did not prevent wild-type alpha-syn cellular aggregates. These studies suggest that the propensity of alpha-syn to form cellular aggregates may be more pronounced than in isolated in vitro studies. This novel high-efficiency cellular model of alpha-syn aggregation is a valuable system that may be used to further understand alpha-syn aggregation and allow for the generation of future therapeutics.

Autophagy protects the rotenone-induced cell death in alpha-synuclein overexpressing SH-SY5Y cells

Loss of dopaminergic cells induced by alpha-synuclein accumulation in substantia nigra causes the development of Parkinson's disease (PD). To date, although autophagy has been implicated in the pathology of PD, the molecular mechanism is still unclear. To study the role of autophagy in PD pathogenesis, we established stable SH-SY5Y cell lines overexpressing wild-type or mutant alpha-synuclein proteins (A30P or A53T). Overexpression of mutant alpha-synuclein induced some protein aggregates and cell death in the absence of drug. LC3-II protein, a critical marker for autophagy, was produced in an autophagy-dependent manner. The rotenone-induced cell death was interrupted by autophagy stimulation. Autophagy activation also restored the mitochondrial membrane potential (MMP) impaired by rotenone in mutant alpha-synuclein expressing cells. Additionally, autophagy activation significantly relieved rotenone-induced ROS accumulation and HIF-1alpha expression in neuronal cells expressing mutant alpha-synuclein proteins. These findings indicate that autophagy plays an important scavenger role against harmful influence of toxic protein aggregates produced in rotenone-treated cells.

Interaction with synphilin-1 promotes inclusion formation of alpha-synuclein: mechanistic insights and pathological implication

alpha-Synuclein (alpha-Syn) is the major component of Lewy bodies (LBs) deposited in the brains of patients with Parkinson's disease. Synphilin-1 (Sph1) is a novel alpha-Syn-interacting protein also present in the LBs. However, the roles of alpha-Syn-Sph1 interaction in LB formation and in the related pathogenesis are still unclear. We have studied the interaction between alpha-Syn and Sph1 by biochemical and structural approaches and found that the central coiled-coil domain of Sph1 specifically interacts with the N-terminal stretch of alpha-Syn. When overexpressed in HEK 293T cells, Sph1 forms inclusions together with alpha-Syn, but the Sph1-positive inclusions cannot recruit the N-terminally truncated alpha-Syn. The central portion of Sph1 can also recruit alpha-Syn and induce inclusion formation through its coiled-coil domain. These observations demonstrate that the alpha-Syn-Sph1 interaction significantly promotes the formation of cytoplasmic alpha-Syn inclusions, which may have implications for LB formation in neural cells. We have also elucidated solution structure of the coiled-coil domain of Sph1 and its interaction with the N-terminal peptide of alpha-Syn. The specific interaction between alpha-Syn and Sph1 provides mechanistic insights into the inclusion-body formation in cells and pathological implication in Parkinson's disease.

Ectopic localization of FOXO3a protein in Lewy bodies in Lewy body dementia and Parkinson's disease

Lewy bodies and Lewy neurites constitute the cardinal neuropathological features of both Parkinson's disease (PD) and Lewy body dementia (LBD). Whereas α-synuclein has been found to be the major component of the Lewy body, the mechanisms by which neurons degenerate, as well as basic mechanisms involved in the formation of α-synuclein-related inclusions, remain obscure. We have suggested previously that potential mechanisms are likely to leave a "molecular signature" or protein adduct within the Lewy body, and have found examples of such signatures in previous studies. In this study, we demonstrate increased FOXO3 in association with Lewy bodies and Lewy neurites in LBD and PD brain tissue. Since FOXO proteins are involved in several pathways responsible for the regulation of cell death, cell proliferation, and cell metabolism, the ectopic localization of FOXO3 to Lewy bodies provides evidence that aberrations in basic cellular biochemistry may contribute to inclusion formation, which is likely more complex than a simple "gain of function" toxicity as is commonly opined. In light of the known interaction of FOXO3 and 14-3-3, basic protein-protein interaction between these proteins and α-synuclein may be key.

Parkin protects mitochondrial genome integrity and supports mitochondrial DNA repair

Mutations in the parkin gene are the most common cause of recessive familial Parkinson disease (PD). Parkin has been initially characterized as an ubiquitin E3 ligase, but the pathological relevance of this activity remains uncertain. Recently, an impressive amount of evidence has accumulated that parkin is involved in the maintenance of mitochondrial function and biogenesis. We used a human neuroblastoma cell line as a model to study the influence of endogenous parkin on mitochondrial genomic integrity. Using an unbiased chromatin immunoprecipitation approach, we found that parkin is associated physically with mitochondrial DNA (mtDNA) in proliferating as well as in differentiated SH-SY5Y cells. In vivo, the association of parkin with mtDNA could be confirmed in brain tissue of mouse and human origin. Replication and transcription of mtDNA were enhanced in SH-SY5Y cells over-expressing the parkin gene. The ability of parkin to support mtDNA-metabolism was impaired by pathogenic parkin point mutations. Most importantly, we show that parkin protects mtDNA from oxidative damage and stimulates mtDNA repair. Moreover, higher susceptibility of mtDNA to reactive oxygen species and reduced mtDNA repair capacity was observed in parkin-deleted fibroblasts of a PD patient. Our data indicate a novel role for parkin in directly supporting mitochondrial function and protecting mitochondrial genomic integrity from oxidative stress.

Aggregate formation and toxicity by wild-type and R621C synphilin-1 in the nigrostriatal system of mice using adenoviral vectors

Synphilin-1 was described as a protein interacting with alpha-synuclein and is commonly found in Lewy bodies, the pathological hallmark of Parkinson's disease (PD). Our group has previously described and characterized in vitro a mutation in the synphilin-1 gene (R621C) in PD patients. Providing the first characterization of synphilin-1 expression in an animal model, we here used adenoviral gene transfer to study the effects of wild-type (WT) and R621C synphilin-1 in dopaminergic neurons in mouse brain. As synphilin-1 is commonly used to trigger aggregation of alpha-synuclein in cell culture, we investigated not only non-transgenic C57Bl/6 mice but also A30P-alpha-synuclein transgenic animals. Both WT synphilin-1 and R621C synphilin-1 led to the formation of Thioflavine-S positive inclusions in C57Bl/6 mice and degeneration of dopaminergic neurons in the substantia nigra. R621C synphilin-1 induced more aggregate formation than WT synphilin-1 in A30P-alpha-synuclein transgenic mice, consistent with the role of the R621C mutation as a susceptibility factor for PD. Synphilin-1 expression may be used to improve current mouse models of PD, as it induced both the formation of aggregates and degeneration of dopaminergic neurons, two core characteristics of PD that have not been well reproduced with expression of alpha-synuclein.

Curcumin inhibits aggregation of alpha-synuclein

Aggregation of amyloid-beta protein (Abeta) is a key pathogenic event in Alzheimer's disease (AD). Curcumin, a constituent of the Indian spice Turmeric is structurally similar to Congo Red and has been demonstrated to bind Abeta amyloid and prevent further oligomerization of Abeta monomers onto growing amyloid beta-sheets. Reasoning that oligomerization kinetics and mechanism of amyloid formation are similar in Parkinson's disease (PD) and AD, we investigated the effect of curcumin on alpha-synuclein (AS) protein aggregation. In vitro model of AS aggregation was developed by treatment of purified AS protein (wild-type) with 1 mM Fe3+ (Fenton reaction). It was observed that the addition of curcumin inhibited aggregation in a dose-dependent manner and increased AS solubility. The aggregation-inhibiting effect of curcumin was next investigated in cell culture utilizing catecholaminergic SH-SY5Y cell line. A model system was developed in which the red fluorescent protein (DsRed2) was fused with A53T mutant of AS and its aggregation examined under different concentrations of curcumin. To estimate aggregation in an unbiased manner, a protocol was developed in which the images were captured automatically through a high-throughput cell-based screening microscope. The obtained images were processed automatically for aggregates within a defined dimension of 1-6 microm. Greater than 32% decrease in mutant alpha-synuclein aggregation was observed within 48 h subsequent to curcumin addition. Our data suggest that curcumin inhibits AS oligomerization into higher molecular weight aggregates and therefore should be further explored as a potential therapeutic compound for PD and related disorders.

Single particle characterization of iron-induced pore-forming alpha-synuclein oligomers

Aggregation of alpha-synuclein is a key event in several neurodegenerative diseases, including Parkinson disease. Recent findings suggest that oligomers represent the principal toxic aggregate species. Using confocal single-molecule fluorescence techniques, such as scanning for intensely fluorescent targets (SIFT) and atomic force microscopy, we monitored alpha-synuclein oligomer formation at the single particle level. Organic solvents were used to trigger aggregation, which resulted in small oligomers ("intermediate I"). Under these conditions, Fe(3+) at low micromolar concentrations dramatically increased aggregation and induced formation of larger oligomers ("intermediate II"). Both oligomer species were on-pathway to amyloid fibrils and could seed amyloid formation. Notably, only Fe(3+)-induced oligomers were SDS-resistant and could form ion-permeable pores in a planar lipid bilayer, which were inhibited by the oligomer-specific A11 antibody. Moreover, baicalein and N'-benzylidene-benzohydrazide derivatives inhibited oligomer formation. Baicalein also inhibited alpha-synuclein-dependent toxicity in neuronal cells. Our results may provide a potential disease mechanism regarding the role of ferric iron and of toxic oligomer species in Parkinson diseases. Moreover, scanning for intensely fluorescent targets allows high throughput screening for aggregation inhibitors and may provide new approaches for drug development and therapy.

Oxidative stress-induced phosphorylation, degradation and aggregation of alpha-synuclein are linked to upregulated CK2 and cathepsin D

Intracellular accumulation of alpha-synuclein (alpha-Syn) as filamentous aggregates is a pathological feature shared by Parkinson's disease, dementia with Lewy bodies and multiple system atrophy, referred to as synucleinopathies. To understand the mechanisms underlying alpha-Syn aggregation, we established a tetracycline-off inducible transfectant (3D5) of neuronal lineage overexpressing human wild-type alpha-Syn. Alpha-Syn aggregation was initiated by exposure of 3D5 cells to FeCl2. The exposure led to formation of alpha-Syn inclusions and oligomers of 34, 54, 68 kDa and higher molecular weights. The oligomers displayed immunoreactivity with antibodies to the amino-, but not to the carboxyl (C)-, terminus of alpha-Syn, indicating that C-terminally truncated alpha-Syn is a major component of oligomers. FeCl2 exposure also promoted accumulation of S129 phosphorylated monomeric alpha-Syn (P alpha-Syn) and casein kinase 2 (CK2); however, G-protein-coupled receptor kinase 2 was reduced. Treatment of FeCl2-exposed cells with CK2 inhibitors (DRB or TBB) led to decreased formation of alpha-Syn inclusions, oligomers and P alpha-Syn. FeCl2 exposure also enhanced the activity/level of cathepsin D. Treatment of the FeCl2-exposed cells with pepstatin A or NH4Cl led to reduced formation of oligomers/inclusions as well as of approximately 10 and 12 kDa truncated alpha-Syn. Our results indicate that alpha-Syn phosphorylation caused by FeCl2 is due to CK2 upregulation, and that lysosomal proteases may have a role in producing truncated alpha-Syn for oligomer assembly.

Overexpression of DSCR1 blocks zinc-induced neuronal cell death through the formation of nuclear aggregates

The Down syndrome (DS) candidate region gene 1 (DSCR1) is localized near DS critical region on chromosome 21 and is overexpressed in the brains of DS patients. Although DSCR1 was known for a modulator of calcineurin, the overexpression of DSCR1 is thought to play a role in neuronal cell death. Zinc, one of the most abundant transition metals in the brain, may also contribute to selective neuronal cell death when present in excessive amounts. In the present study, we investigated the effect of DSCR1 overexpression on zinc-induced cell death in hippocampal neuroprogenitor cells. The overexpression of DSCR1 caused apoptotic cell death without an apparent formation of intracellular protein inclusions. Upon exposure to zinc, soluble DSCR1 levels were significantly decreased and insoluble levels were enhanced to a similar extent, which were partially caused by the zinc-induced inhibition of proteasomal activity and a consequently diminished degradation of DSCR1. Furthermore, zinc treatment induced the formation of nuclear DSCR1 aggregates, which blocked zinc-induced cell death. These findings indicate that, although the up-regulation of DSCR1 levels exerts a cytotoxic effect, the addition of zinc leads to the formation of cytoprotective nuclear aggregates in neuronal cells.

Role of Neu4L sialidase and its substrate ganglioside GD3 in neuronal apoptosis induced by catechol metabolites

Mammalian sialidases are key enzymes in the degradation of glycoconjugates. Neu4L sialidase is localized to mitochondria and specifically expressed in brain. To elucidate the pathophysiological roles of Neu4L in the nervous system, we investigated the possible involvement of Neu4L in the apoptotic neurodegeneration under the existence of catechol metabolites generated by tyrosinase. We demonstrated that: (i) the expression level of Neu4L was dramatically decreased prior to apoptosis; (ii) the apoptotic phenotype was characterized by cytochrome c release into cytosol concomitant with the trafficking of ganglioside GD3 to mitochondria; and (iii) the inhibitor of glucosylceramide synthase partially recovered cell viability. Neu4L and its substrate GD3 may act as key molecules in the mitochondrial apoptotic pathway in neuronal cells.

Limitations of cellular models in Parkinson's disease research

Cell cultures for Parkinson's disease research have the advantage of virtually unlimited access, they allow rapid screening for disease pathogenesis and drug candidates, and they restrict the necessary number of animal experiments. Limitations of cell cultures, include that the survival of neurons is dependent upon the culture conditions; that the cells do not develop their natural neuronal networks. In most cases, neurons are deprived from the physiological afferent and efferent connections. In Parkinson's disease research, mesencephalic slice cultures, primary immature dopaminergic neurons and immortalized cell lines--either in a proliferating state or in a differentiated state--are used. Neuronal cultures may be plated in the presence or absence of glial cells and serum. These different culture conditions as well as the selection of outcome parameters (morphological evaluation, viability assays, biochemical assays, metabolic assays) have a strong influence on the results of the experiments and the conclusions drawn from them. A primary example is the question of whether L-Dopa is toxic to dopaminergic neurons or whether it provides neurotrophic effects: In pure, neuronal-like cultures, L-Dopa provides toxicity, whereas in the presence of glial cells, it provides trophic effects when applied. The multitude of factors that influence the data generated from cell culture experiments indicates that in order to obtain clear-cut and unambiguous results, investigators need to choose their model carefully and are encouraged to verify their main results with different models.

Relationship Among α-Synuclein Accumulation, Dopamine Synthesis, and Neurodegeneration in Parkinson Disease Substantia Nigra

The histologic hallmark of Parkinson disease (PD) is loss of pigmented neurons in the substantia nigra (SN) and locus ceruleus (LC) with accumulation of alpha-synuclein (alphaS). It has been reported that tyrosine hydroxylase (TH)-negative pigmented neurons are present in these nuclei of patients with PD. However, the relationship between TH immunoreactivity and alphaS accumulation remains uncertain. We immunohistochemically examined the SN and LC from patients with PD (n = 10) and control subjects (n = 7). A correlation study indicated a close relationship among decreased TH immunoreactivity, alphaS accumulation, and neuronal loss. In addition, 10% of pigmented neurons in the SN and 54.9% of those in the LC contained abnormal alphaS aggregates. Moreover, 82.3% of pigmented neurons bearing alphaS aggregates in the SN and 39.2% of those in the LC lacked TH immunoreactivity, suggesting that pigmented neurons in the SN have a greater tendency to lack TH activity than those in the LC. Recent studies have shown that this decrease of TH activity leads to a decrease of cytotoxic substances and that decreased dopamine synthesis leads to a reduction of cytotoxic alphaS oligomers. Therefore, the decrease of TH immunoreactivity in pigmented neurons demonstrated here can be considered to represent a cytoprotective mechanism in PD.