Alpha-synuclein accumulates in Lewy bodies in Parkinson's disease and dementia with Lewy bodies but not in Alzheimer's disease beta-amyloid plaque cores

Dysfunctional energy and future perspective of low dose H2O2 as protective agent in neurodegenerative disease

The number of people with neurodegenerative disease continues to increase every year. A new perspective is needed to overcome this disease. In this review, researchers collected information about dysfunctional energy in neurodegenerative diseases driven by mitochondria. Mitochondrial dysregulation can cause damage to the neuron system. The increase in the amount and interaction of α-synuclein with SAMM50 and GABARAPL1 in the mitochondria is one of the factors causing neurodegenerative disease. As an energy provider in the body, the existence of harmonization in the regulation of mitochondria, specifically the mitochondrial outer membrane, is important. Low-dose hydrogen peroxide (H₂O₂) has neuroprotective abilities to overcome the impairment function of mitochondria in neurodegenerative patients. Based on computational simulation of this case, it can be used as a basic concept for the development of the role of H₂O₂ in neurodegenerative diseases.

Disease mechanisms as subtypes: Lysosomal dysfunction in the endolysosomal Parkinson's disease subtype

Parkinson's disease (PD) remains one of the most prevalent neurodegenerative disorders. It has become increasingly recognized that PD is not one disease but a constellation of many, with distinct cellular mechanisms driving pathology and neuronal loss in each given subtype. Endolysosomal trafficking and lysosomal degradation are crucial to maintain neuronal homeostasis and vesicular trafficking. It is clear that deficits in endolysosomal signaling data support the existence of an endolysosomal PD subtype. This chapter describes how cellular pathways involved in endolysosomal vesicular trafficking and lysosomal degradation in neurons and immune cells can contribute to PD. Last, as inflammatory processes including phagocytosis and cytokine release are central in glia-neuron interactions, a spotlight on the role of neuroinflammation plays in the pathogenesis of this PD subtype is also explored.

G2019S LRRK2 Mutation Enhances MPP+-Induced Inflammation of Human Induced Pluripotent Stem Cells-Differentiated Dopaminergic Neurons

Induced pluripotent stem cells (iPSCs) offer an unprecedented opportunity to mimic human diseases of related cell types, but it is unclear whether they can successfully mimic age-related diseases such as Parkinson’s disease (PD). We generated iPSCs lines from three patients with familial PD associated with the G2019S mutation in the LRRK2 gene and one age-matched healthy individual (control). During long-term culture, dopaminergic (DA) neurons differentiated from iPSCs of G2019S LRRK2 PD patients exhibited morphological changes, including a reduced number of neurites and neurite arborization, which were not evident in DA neurons differentiated from control iPSCs. To mimic PD pathology in vitro, we used 1-methyl-4-phenylpyridium (MPP⁺) to damage DA neurons and found that DA neurons differentiated from patients with G2019S LRRK2 mutation significantly reduced the survival rate and increased apoptosis compared with the controls. We also found that the mRNA level of inflammatory factors [interleukin (IL)-1β, tumor necrosis factor-α, cyclooxygenase-2, IL-6, and inducible NO synthase] with G2019S LRRK2 mutation were higher than control group after exposure to MPP⁺. Our study provides an in vitro model based on iPSCs that captures the patients’ genetic complexity and investigates the pathogenesis of familial PD cases in a disease-associated cell type.

Opportunities and challenges of alpha-synuclein as a potential biomarker for Parkinson's disease and other synucleinopathies

Parkinson’s disease (PD), the second most common progressive neurodegenerative disease, develops and progresses for 10–15 years before the clinical diagnostic symptoms of the disease are manifested. Furthermore, several aspects of PD pathology overlap with other neurodegenerative diseases (NDDs) linked to alpha-synuclein (aSyn) aggregation, also called synucleinopathies. Therefore, there is an urgent need to discover and validate early diagnostic and prognostic markers that reflect disease pathophysiology, progression, severity, and potential differences in disease mechanisms between PD and other NDDs. The close association between aSyn and the development of pathology in synucleinopathies, along with the identification of aSyn species in biological fluids, has led to increasing interest in aSyn species as potential biomarkers for early diagnosis of PD and differentiate it from other synucleinopathies. In this review, we (1) provide an overview of the progress toward mapping the distribution of aSyn species in the brain, peripheral tissues, and biological fluids; (2) present comparative and critical analysis of previous studies that measured total aSyn as well as other species such as modified and aggregated forms of aSyn in different biological fluids; and (3) highlight conceptual and technical gaps and challenges that could hinder the development and validation of reliable aSyn biomarkers; and (4) outline a series of recommendations to address these challenges. Finally, we propose a combined biomarker approach based on integrating biochemical, aggregation and structure features of aSyn, in addition to other biomarkers of neurodegeneration. We believe that capturing the diversity of aSyn species is essential to develop robust assays and diagnostics for early detection, patient stratification, monitoring of disease progression, and differentiation between synucleinopathies. This could transform clinical trial design and implementation, accelerate the development of new therapies, and improve clinical decisions and treatment strategies.

Immunohistochemical Demonstration of the pGlu79 α-Synuclein Fragment in Alzheimer’s Disease and Its Tg2576 Mouse Model

The deposition of β-amyloid peptides and of α-synuclein proteins is a neuropathological hallmark in the brains of Alzheimer’s disease (AD) and Parkinson’s disease (PD) subjects, respectively. However, there is accumulative evidence that both proteins are not exclusive for their clinical entity but instead co-exist and interact with each other. Here, we investigated the presence of a newly identified, pyroglutamate79-modified α-synuclein variant (pGlu79-aSyn)—along with the enzyme matrix metalloproteinase-3 (MMP-3) and glutaminyl cyclase (QC) implicated in its formation—in AD and in the transgenic Tg2576 AD mouse model. In the human brain, pGlu79-aSyn was detected in cortical pyramidal neurons, with more distinct labeling in AD compared to control brain tissue. Using immunohistochemical double and triple labelings and confocal laser scanning microscopy, we demonstrate an association of pGlu79-aSyn, MMP-3 and QC with β-amyloid plaques. In addition, pGlu79-aSyn and QC were present in amyloid plaque-associated reactive astrocytes that were also immunoreactive for the chaperone heat shock protein 27 (HSP27). Our data are consistent for the transgenic mouse model and the human clinical condition. We conclude that pGlu79-aSyn can be generated extracellularly or within reactive astrocytes, accumulates in proximity to β-amyloid plaques and induces an astrocytic protein unfolding mechanism involving HSP27.

Selective targeting of the TLR2/MyD88/NF-κB pathway reduces α-synuclein spreading in vitro and in vivo

Pathways to control the spreading of α-synuclein (α-syn) and associated neuropathology in Parkinson’s disease (PD), multiple system atrophy (MSA) and dementia with Lewy bodies (DLB) are unclear. Here, we show that preformed α-syn fibrils (PFF) increase the association between TLR2 and MyD88, resulting in microglial activation. The TLR2-interaction domain of MyD88 (wtTIDM) peptide-mediated selective inhibition of TLR2 reduces PFF-induced microglial inflammation in vitro. In PFF-seeded A53T mice, the nasal administration of the wtTIDM peptide, NEMO-binding domain (wtNBD) peptide, or genetic deletion of TLR2 reduces glial inflammation, decreases α-syn spreading, and protects dopaminergic neurons by inhibiting NF-κB. In summary, α-syn spreading depends on the TLR2/MyD88/NF-κB pathway and it can be reduced by nasal delivery of wtTIDM and wtNBD peptides.

The mechanisms underlying the spreading of α-synuclein in various α-synucleinopathies are unclear. Here, the authors show that targeting the TLR2/MyD88/NF-κB pathway can reduce α-synuclein spreading, reduce neuroinflammation, and protect dopaminergic neurons in vitro and in mouse models

Impact of Fatty Acid-Binding Proteins in α-Synuclein-Induced Mitochondrial Injury in Synucleinopathy

Synucleinopathies are diverse diseases with motor and cognitive dysfunction due to progressive neuronal loss or demyelination, due to oligodendrocyte loss in the brain. While the etiology of neurodegenerative disorders (NDDs) is likely multifactorial, mitochondrial injury is one of the most vital factors in neuronal loss and oligodendrocyte dysfunction, especially in Parkinson’s disease, dementia with Lewy body, multiple system atrophy, and Krabbe disease. In recent years, the abnormal accumulation of highly neurotoxic α-synuclein in the mitochondrial membrane, which leads to mitochondrial dysfunction, was well studied. Furthermore, fatty acid-binding proteins (FABPs), which are members of a superfamily and are essential in fatty acid trafficking, were reported to trigger α-synuclein oligomerization in neurons and glial cells and to target the mitochondrial outer membrane, thereby causing mitochondrial loss. Here, we provide an updated overview of recent findings on FABP and α-synuclein interactions and mitochondrial injury in NDDs.

Enhanced Susceptibility of PINK1 Knockout Rats to α-Synuclein Fibrils

The main neuropathological hallmarks of Parkinson's disease (PD) are loss of dopaminergic neurons in the substantia nigra and intraneuronal protein aggregates immunoreactive for α-synuclein phosphorylated at serine 129 (pS129). Most cases of PD are idiopathic; however, genetic mutations have been identified in several genes linked to familial PD. Mutations in the gene encoding α-synuclein are causally linked to dominantly inherited forms of PD and mutations in the PTEN-induced kinase-1 (PINK1) gene are linked to recessively inherited forms of PD. Because abnormal α-synuclein protein aggregates appear spontaneously in PINK1 knockout (KO) rats, we hypothesize that PINK1-deficiency causes endogenous α-synuclein to be more prone to aggregation. α-Synuclein aggregation does not normally occur in mice or rats, however, it can be induced by intracranial injection of α-synuclein pre-formed fibrils (PFFs), which also induces loss of dopaminergic nigral neurons 3-6 months post-injection. Because PINK1-deficiency is linked to early-onset PD, we further hypothesize that PINK1 KO rats will show earlier PFF-induced neurodegeneration compared to wild-type (WT) rats. Herein, we report that intracranial injection of α-synuclein PFFs into the dorsal striatum induced more abundant pS129 α-synuclein in PINK1 KO rat brains compared to WT littermate controls. Moreover, the synuclein extracted from the brains of PFF-injected PINK1 KO rats was more insoluble compared to PFF-injected WT littermates, suggesting greater progression of α-synuclein pathology in PINK1 KO rats. Four weeks post-injection, PFFs caused significant loss of dopaminergic neurons in the substantia nigra of PINK1 KO rats, but not WT controls. Together, our results indicate that PINK1 deficiency increases vulnerability to α-synuclein aggregation and dopaminergic neurodegeneration in vivo.

Do Lewy bodies contain alpha-synuclein fibrils? and Does it matter? A brief history and critical analysis of recent reports

Several lines of evidence from neuropathological studies, human genetics, in vitro aggregation studies and cellular and animal models support the hypothesis that aSyn plays a central role in the formation of Lewy pathologies. These are cytoplasmic proteinaceous and lipid-rich inclusions that represent key pathological hallmarks of Parkinson's disease (PD) and other neurodegenerative diseases, collectively referred to as synucleinopathies. For decades, light microscopy and electron microscopy studies of these inclusions have consistently shown that they are rich in filamentous structures that exhibit distinct distribution and organizational patterns depending on where they occur in the brain (e.g., classical brain-stem Lewy bodies (LBs) and cortical LBs) and the type of synucleinopathies. Although the identity of the protein that form these filaments was a subject of debate for decades, the discovery of PD-linked aSyn mutations, the demonstration that LBs are enriched in insoluble forms of aSyn, and the ability of aSyn to form fibrils of similar dimensions have led to convergence on the hypothesis that aSyn fibrils are key components of LBs. In a recent study, Shahmoradian et al used a combination of advanced electron microscopy and immunofluorescence based imaging techniques to investigate the structure, composition, and architecture of LBs from postmortem brain tissues of individuals with PD or other synucleinopathies (Shahmoradian et al., 2019). The paper's main conclusions suggest that "lipid membrane fragments and distorted organelles together with a non-fibrillar form of αSyn are the main structural building blocks for the formation of Lewy pathology". Their proposal that LBs are devoid of aSyn fibrils or that LB formation occurs independently of aSyn fibril formation casts doubts on a substantial body of work that forms the foundation of many of the current basic and translational research programs in academia and industry. In this article, I present a critical analysis of their data and claims in the context of the existing literature In addition, I examine the extent to which their findings and proposed models of the mechanisms of LB formation are consistent with existing data and are supported by other experimental evidence. The results from this analysis caution against overinterpretation of observations from a single report, especially given the limitations of the techniques and experimental approaches used by Shahmoradian et al and for more collaborative and systematic efforts to revisit and characterize LBs and other aSyn pathologies in the brain pathologies at the biochemical, morphological and structural level.

Beyond the synucleinopathies: alpha synuclein as a driving force in neurodegenerative comorbidities

The fundamental role that alpha-synuclein (aSyn) plays in the pathogenesis of neurodegenerative synucleinopathies, including Parkinson’s disease, dementia with Lewy bodies, and multiple system atrophy, is a well-accepted fact. A wealth of experimental evidence has linked this relatively small but ubiquitously expressed protein to a plethora of cytopathologic mechanisms and suggests that aSyn may be capable of seeding the progressive spread of synucleinopathy throughout the brain. Beyond the synucleinopathies, the abnormal deposition of aSyn is frequently seen in a variety of other neurodegenerative proteinopathies including Alzheimer’s disease. In spite of the fact that the frequency of concomitant aSyn pathology in these disorders is such that it can be considered the rule rather than the exception, the potential role that aSyn may have in these disorders has received relatively little attention.

In this article we postulate that aSyn may in fact be a key protein in driving the pathogenic processes in neurodegenerative comorbidities. In addition to reviewing the frequency of concomitant deposition of aSyn in the neurodegenerative proteinopathies, we also consider our current understanding of the interaction of aSyn with other neurodegenerative disease-associated proteins, including tau, TDP-43, amyloid-β and prion protein, in the context of neuropathologic studies describing the anatomical sites of potential concomitant pathology. We conclude that a growing body of evidence, encompassing neuropathology studies in human brain, animal models of concomitant proteinopathies and studies employing sophisticated methods of probing protein-protein interaction, cumulatively suggest that aSyn is well positioned to exert a strong influence on the pathogenesis of the neurodegenerative comorbidities.

We hope to stimulate research in this emerging field and consider that future studies exploring the contribution of aSyn to the pathogenic processes in neurodegenerative comorbidities may provide critical information pertaining to diagnosis and the development of vital disease modifying treatments for these devastating diseases.

Spreading of α-Synuclein and Tau: A Systematic Comparison of the Mechanisms Involved

Alzheimer's disease (AD) and Parkinson's disease (PD) are age-associated neurodegenerative disorders characterized by the misfolding and aggregation of alpha-synuclein (aSyn) and tau, respectively. The coexistence of aSyn and tau aggregates suggests a strong overlap between tauopathies and synucleinopathies. Interestingly, misfolded forms of aSyn and tau can propagate from cell to cell, and throughout the brain, thereby templating the misfolding of native forms of the proteins. The exact mechanisms involved in the propagation of the two proteins show similarities, and are reminiscent of the spreading characteristic of prion diseases. Recently, several models were developed to study the spreading of aSyn and tau. Here, we discuss the mechanisms involved, the similarities and differences between the spreading of the two proteins and that of the prion protein, and the different cell and animal models used for studying these processes. Ultimately, a deeper understanding of the molecular mechanisms involved may lead to the identification of novel targets for therapeutic intervention in a variety of devastating neurodegenerative diseases.

Living in Promiscuity: The Multiple Partners of Alpha-Synuclein at the Synapse in Physiology and Pathology

Alpha-synuclein (α-syn) is a small protein that, in neurons, localizes predominantly to presynaptic terminals. Due to elevated conformational plasticity, which can be affected by environmental factors, in addition to undergoing disorder-to-order transition upon interaction with different interactants, α-syn is counted among the intrinsically disordered proteins (IDPs) family. As with many other IDPs, α-syn is considered a hub protein. This function is particularly relevant at synaptic sites, where α-syn is abundant and interacts with many partners, such as monoamine transporters, cytoskeletal components, lipid membranes, chaperones and synaptic vesicles (SV)-associated proteins. These protein–protein and protein–lipid membrane interactions are crucial for synaptic functional homeostasis, and alterations in α-syn can cause disruption of this complex network, and thus a failure of the synaptic machinery. Alterations of the synaptic environment or post-translational modification of α-syn can induce its misfolding, resulting in the formation of oligomers or fibrillary aggregates. These α-syn species are thought to play a pathological role in neurodegenerative disorders with α-syn deposits such as Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), which are referred to as synucleinopathies. Here, we aim at revising the complex and promiscuous role of α-syn at synaptic terminals in order to decipher whether α-syn molecular interactants may influence its conformational state, contributing to its aggregation, or whether they are just affected by it.

The Synucleinopathies: Twenty Years On

In 2017, it is two hundred years since James Parkinson provided the first complete clinical description of the disease named after him, fifty years since the introduction of high-dose D,L-DOPA treatment and twenty years since α-synuclein aggregation came to the fore. In 1998, multiple system atrophy joined Parkinson's disease and dementia with Lewy bodies as the third major synucleinopathy. Here we review our work, which led to the identification of α-synuclein in Lewy bodies, Lewy neurites and Papp-Lantos bodies, as well as what has happened since. Some of the experiments described were carried out in collaboration with ML Schmidt, JQ Trojanowski and VMY Lee.

Role of neurotoxicants and traumatic brain injury in α-synuclein protein misfolding and aggregation

Protein misfolding and aggregation are key pathological features of many neurodegenerative diseases including Parkinson's disease (PD) and other forms of human Parkinsonism. PD is a complex and multifaceted disorder whose etiology is not fully understood. However, several lines of evidence support the multiple hit hypothesis that genetic vulnerability and environmental toxicants converge to trigger PD pathology. Alpha-synuclein (α-Syn) aggregation in the brain is an important pathophysiological characteristic of synucleinopathies including PD. Epidemiological and experimental studies have shown that metals and pesticides play a crucial role in α-Syn aggregation leading to the onset of various neurodegenerative diseases including PD. In this review, we will emphasize key findings of several epidemiological as well as experimental studies of metal- and pesticide-induced α-Syn aggregation and neurodegeneration. We will also discuss other factors such as traumatic brain injury and oxidative insult in the context of α-Syn-related neurodegenerative processes.

Curcumin Pyrazole and its derivative (N-(3-Nitrophenylpyrazole) Curcumin inhibit aggregation, disrupt fibrils and modulate toxicity of Wild type and Mutant α-Synuclein

Accumulating evidence suggests that deposition of neurotoxic α-synuclein aggregates in the brain during the development of neurodegenerative diseases like Parkinson’s disease can be curbed by anti-aggregation strategies that either disrupt or eliminate toxic aggregates. Curcumin, a dietary polyphenol exhibits anti-amyloid activity but the use of this polyphenol is limited owing to its instability. As chemical modifications in curcumin confiscate this limitation, such efforts are intensively performed to discover molecules with similar but enhanced stability and superior properties. This study focuses on the inhibitory effect of two stable analogs of curcumin viz. curcumin pyrazole and curcumin isoxazole and their derivatives against α-synuclein aggregation, fibrillization and toxicity. Employing biochemical, biophysical and cell based assays we discovered that curcumin pyrazole (3) and its derivative N-(3-Nitrophenylpyrazole) curcumin (15) exhibit remarkable potency in not only arresting fibrillization and disrupting preformed fibrils but also preventing formation of A11 conformation in the protein that imparts toxic effects. Compounds 3 and 15 also decreased neurotoxicity associated with fast aggregating A53T mutant form of α-synuclein. These two analogues of curcumin described here may therefore be useful therapeutic inhibitors for the treatment of α-synuclein amyloidosis and toxicity in Parkinson’s disease and other synucleinopathies.

Biophysical characterization of α-synuclein and its controversial structure

α-synuclein, a presynaptic protein of poorly defined function, constitutes the main component of Parkinson disease-associated Lewy bodies. Extensive biophysical investigations have provided evidence that isolated α-synuclein is an intrinsically disordered protein (IDP) in vitro. Subsequently serving as a model IDP in numerous studies, α-synuclein has aided in the development of many technologies used to characterize IDPs and arguably represents the most thoroughly analyzed IDP to date. Recent reports, however, have challenged the disordered nature of α-synuclein inside cells and have instead proposed a physiologically relevant helical tetramer. Despite α-synuclein's rich biophysical history, a single coherent picture has not yet emerged concerning its in vivo structure, dynamics, and physiological role(s). We present herein a review of the biophysical discoveries, developments, and models pertinent to the characterization of α-synuclein's structure and analysis of the native tetramer controversy.

LRRK2 mutant iPSC-derived DA neurons demonstrate increased susceptibility to oxidative stress

Studies of Parkinson's disease (PD) have been hindered by lack of access to affected human dopaminergic (DA) neurons. Here, we report generation of induced pluripotent stem cells that carry the p.G2019S mutation (G2019S-iPSCs) in the Leucine-Rich Repeat Kinase-2 (LRRK2) gene, the most common PD-related mutation, and their differentiation into DA neurons. The high penetrance of the LRRK2 mutation and its clinical resemblance to sporadic PD suggest that these cells could provide a valuable platform for disease analysis and drug development. We found that DA neurons derived from G2019S-iPSCs showed increased expression of key oxidative stress-response genes and α-synuclein protein. The mutant neurons were also more sensitive to caspase-3 activation and cell death caused by exposure to stress agents, such as hydrogen peroxide, MG-132, and 6-hydroxydopamine, than control DA neurons. This enhanced stress sensitivity is consistent with existing understanding of early PD phenotypes and represents a potential therapeutic target.

Genetic variability in SNCA and Parkinson's disease

Over the last decades, increasing knowledge about the genetic architecture of Parkinson's disease has provided novel insights into the pathogenesis of the disorder, generating hypotheses for further research. Characterizing the role of SNCA, encoding the α-synuclein protein, has been a particularly important aspect of this development. The identification of SNCA as the first gene implicated in monogenic parkinsonism led to the recognition of α-synuclein as a key protein in the pathogenesis and a major component of pathological hallmark lesions. An association between common variants in SNCA and risk of sporadic Parkinson's disease has been established through numerous studies. We review our current understanding of SNCA variability contributing to Parkinson's disease, highlighting the characterization of functionally relevant susceptibility alleles as a major future challenge. We argue that new strategies will be needed to pinpoint the variants that are ultimately responsible for the signals detected in association studies, where targeted resequencing may represent an attractive initial approach.

Specific antibodies to soluble alpha-synuclein conformations in intravenous immunoglobulin preparations

Alpha-synuclein is the major protein in Lewy bodies, the hallmark pathological finding in Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Although normally intracellular, it also can be secreted, so extracellular alpha-synuclein may contribute to neuronal injury. Serum antibodies to alpha-synuclein could exert protective effects by increasing alpha-synuclein's movement out of the brain and, if they cross the blood-brain barrier, by inhibiting its neurotoxic effects. The objective of this study was to measure antibody concentrations to alpha-synuclein monomer and soluble oligomers in three intravenous immunoglobulin (IVIG) preparations, Gamunex (Talecris Biotherapeutics), Gammagard (Baxter Healthcare) and Flebogamma (Grifols Biologicals). Antibodies were measured in native IVIG preparations and after antibody-antigen complex dissociation. IVIG's non-specific binding was subtracted from its total binding to alpha-synuclein to calculate specific anti-alpha-synuclein antibody concentrations. Specific antibodies to alpha-synuclein monomer and/or soluble oligomers were detected in all IVIG products. In native IVIG preparations, the highest anti-monomer concentrations were in Gammagard and the highest anti-oligomer concentrations were in Gamunex; the extent to which lot-to-lot variation may have contributed to these differences was not determined. Antibody-antigen complex dissociation had variable effects on these antibody levels. The IVIG preparations did not inhibit alpha-synuclein oligomer formation, although they changed the distribution and intensity of some oligomer bands on Western blots. The presence of antibodies to soluble alpha-synuclein conformations in IVIG preparations suggests that their effects should be studied in animal models of synucleinopathies, as a first step to determine their feasibility as a possible treatment for PD and other synucleinopathies.

Accumulation of cellular prion protein within dystrophic neurites of amyloid plaques in the Alzheimer's disease brain

Amyloid plaques, a well-known hallmark of Alzheimer's disease (AD), are formed by aggregated β-amyloid (Aβ). The cellular prion protein (PrPc) accumulates concomitantly with Aβ in amyloid plaques. One type of amyloid plaque, classified as a neuritic plaque, is composed of an amyloid core and surrounding dystrophic neurites. PrPc immunoreactivity reminiscent of dystrophic neurites is observed in neuritic plaques. Proteinase K treatment prior to immunohistochemistry removes PrPc immunoreactivity from amyloid plaques, whereas Aβ immunoreactivity is enhanced by this treatment. In the present study, we used a chemical pretreatment by a sarkosyl solution (0.1% sarkosyl, 75 mM NaOH, 2% NaCl), instead of proteinase K treatment, to evaluate PrPc accumulation within amyloid plaques. Since PrPc within amyloid plaques is removed by this chemical pretreatment, we can recognize that the PrP species deposits within amyloid plaques were PrPc. We could observe that PrPc accumulation in dystrophic neurites occurred differently compared with Aβ or hyperphosphorylated tau aggregation in the AD brain. These results could support the hypothesis that PrPc accumulation in dystrophic neurites reflects a response to impairments in cellular degradation, endocytosis, or transport mechanisms associated with AD rather than a non-specific cross-reactivity between PrPc and aggregated Aβ or tau.

The morbid anatomy of dementia in Parkinson's disease

Dementia in Parkinson's disease (PD/PDD) is a common complication with a prevalence of up to 50%, but the specific changes underlying the cognitive decline remain undefined. Neuronal degeneration resulting in the dysfunction of multiple subcortical neurochemical projection systems has been described along with Lewy body-type pathology in cortical and limbic regions. Advanced alpha-synuclein (alphaSyn) pathology is not necessarily sufficient for producing dementia and concomitant Alzheimer's disease (AD) change has also been proposed as a possible substrate of PDD. A lack of consensus in the extant literature likely stems from clinical heterogeneity and variable reliability in clinical characterisation as well as other historical and methodological issues. The concurrent presence of abnormally deposited alphaSyn, amyloid-beta and tau proteins in the PDD brain and the interaction of these molecules in a linked pathological cascade of AD and PD-related mechanisms may prove important in determining the underlying pathological process for the development of dementia in PD and this concept of combined pathologies awaits further investigation.

Parkinson-linked genes and toxins that affect neuronal cell death through the Bcl-2 family

Parkinson's disease (PD) results from the death of specific neuronal populations in the CNS. Potential causative factors include environmental toxins and gene mutations that can combine to dysregulate the processing and degradation of alpha-synuclein. Oxidative stress induced by the neurotoxins MPTP, paraquat, maneb, and rotenone causes lipid peroxidation and protein misfolding that affects cell death through members of the Bcl-2 family. Sufficient activation of Bax and Bak facilitates mitochondrial outer-membrane permeabilization, which releases death-inducing factors that cause apoptotic and nonapoptotic programmed cell death. The formation of alpha-synuclein aggregates is a defining pathologic feature of PD and is induced by these neurotoxins as well as several Parkinson-linked familial mutations. Of the familial mutations identified thus far, two of the loci encode proteins associated with ubiquitin-proteasome degradation of misfolded proteins (Parkin and Uch-L1), and two encode proteins associated with mitochondria and oxidative stress (DJ-1 and PINK1). Both gene and toxin findings indicate that dopaminergic neuron losses in PD are the result of oxidative stress affecting mitochondria function and ubiquitin-proteasome activity. Here we describe how related cell death mechanisms are involved in the pathophysiology of Parkinson's disease.

What determines the molecular composition of abnormal protein aggregates in neurodegenerative disease?

Abnormal protein aggregates, in the form of either extracellular plaques or intracellular inclusions, are an important pathological feature of the majority of neurodegenerative disorders. The major molecular constituents of these lesions, viz., beta-amyloid (Abeta), tau, and alpha-synuclein, have played a defining role in the diagnosis and classification of disease and in studies of pathogenesis. The molecular composition of a protein aggregate, however, is often complex and could be the direct or indirect consequence of a pathogenic gene mutation, be the result of cell degeneration, or reflect the acquisition of new substances by diffusion and molecular binding to existing proteins. This review examines the molecular composition of the major protein aggregates found in the neurodegenerative diseases including the Abeta and prion protein (PrP) plaques found in Alzheimer's disease (AD) and prion disease, respectively, and the cellular inclusions found in the tauopathies and synucleinopathies. The data suggest that the molecular constituents of a protein aggregate do not directly cause cell death but are largely the consequence of cell degeneration or are acquired during the disease process. These findings are discussed in relation to diagnosis and to studies of to disease pathogenesis.

Applications of electron paramagnetic resonance to studies of neurological disease

Electron paramagnetic resonance spectroscopy (EPR) has the potential to give much detail on the structure of the paramagnetic transition ion coordination sites, principally of Cu2+, in a number of proteins associated with central nervous system diseases. Since these sites have been implicated in misfolding/mis-oligomerisation events associated with neurotoxic molecular species and/or the catalysis of damaging redox reactions in neurodegeneration, an understanding of their structure is important to the development of therapeutic agents. Nevertheless EPR, by its nature an in vitro technique, has its limitations in the study of such complex biochemical systems involving self-associating proteins that are sensitive to their chemical environment. These limitations are at the instrumental and theoretical level, which must be understood and the EPR data interpreted in the light of other biophysical and biochemical studies if useful conclusions are to be drawn.

Disease-modifying drugs and Parkinson's disease

Symptomatic medications, l-Dopa and dopaminergic agents, remain the only clinically pertinent pharmacological treatment proven effective and available for the large population of patients with Parkinson's disease. The challenge for the pharmaceutical industry is to develop disease-modifying drugs which could arrest, delay or at least oppose the progression of the specific pathogenic processes underlying Parkinson's disease. The purpose of this review, based on recent biological and genetic data to be validated with appropriate animal models, was to re-examine the putative neuroprotective agents in Parkinson's disease and discuss the development of new strategies with the ultimate goal of demonstrating neurocytoprotective activity in this neurodegenerative disease. Since guidelines for research on neurocytoprotective drugs remain to be written, innovation will be the key to success of future clinical trials. It is reasonable to expect that future advances in our understanding of the pathogenic processes of Parkinson's disease will open the way to new perspectives for the treatment of other neurodegenerative diseases.

Neuropathology, biochemistry, and biophysics of alpha-synuclein aggregation

Aggregation of alpha-synuclein, an abundant and conserved pre-synaptic brain protein, is implicated as a critical factor in several neurodegenerative diseases. These diseases, known as synucleinopathies, include Parkinson's disease, dementia with Lewy bodies (LBs), diffuse LB disease, the LB variant of Alzheimer's disease, multiple system atrophy, and neurodegeneration with brain iron accumulation type I. Although the precise nature of in vivoalpha-synuclein function remains elusive, considerable knowledge has been accumulated about its structural properties and conformational behavior. alpha-Synuclein is a typical natively unfolded protein. It is characterized by the lack of rigid, well-defined, 3-D structure and possesses remarkable conformational plasticity. The structure of this protein depends dramatically on its environment and it accommodates a number of unrelated conformations. This paper provides an overview of the biochemistry, biophysics, and neuropathology of alpha-synuclein aggregation.

Locomotor activity and evoked dopamine release are reduced in mice overexpressing A30P-mutated human alpha-synuclein

We have generated a transgenic mouse line overexpressing mutated human A30P alpha-synuclein under the control of the prion-related protein promoter. Immunohistology revealed mutated human A30P alpha-synuclein protein in numerous brain areas, but no gross morphological changes, Lewy bodies, or loss of dopaminergic cell bodies. The transgenic mice displayed decreased locomotion, impaired motor coordination, and balance. In vivo voltammetry showed that A30P mice responded to longer stimulation of the ascending dopaminergic pathways with less dopamine release in striatum and had a slower rate of dopamine decline after repeated stimulations or after alpha-methyl-p-tyrosine-HCl treatment. However, dopamine re-uptake or transporter levels were similar in transgenic and control mice. Our data provide evidence that overexpression of mutated human A30P alpha-synuclein in mice leads to a reduced size of the dopamine storage pool. This is in agreement with the previously postulated involvement of alpha-synuclein in the turnover of transmitter vesicles and may explain the observed motor deficits in A30P mice.

Dieldrin-induced neurotoxicity: relevance to Parkinson's disease pathogenesis

Parkinson's disease (PD) is increasingly recognized as a neurodegenerative disorder strongly associated with environmental chemical exposures. Recent epidemiological data demonstrate that environmental risk factors may play a dominant role as compared to genetic factors in the etiopathogenesis of idiopathic Parkinson's disease. Identification of key genetic defects such as alpha-synuclein and parkin mutations in PD also underscores the important role of genetic factors in the disease. Thus, understanding the interplay between genes and environment in PD may be critical to unlocking the mysteries of this 200-year-old neurodegenerative disease. Pesticides and metals are the most common classes of environmental chemicals that promote dopaminergic degeneration. The organochlorine pesticide dieldrin has been found in human PD postmortem brain tissues, suggesting that this pesticide has potential to promote nigral cell death. Though dieldrin has been banned, humans continue to be exposed to the pesticide through contaminated dairy products and meats due to the persistent accumulation of the pesticide in the environment. This review summarizes various neurotoxic studies conducted in both cell culture and animals models following dieldrin exposure and discusses their relevance to key pathological mechanisms associated with nigral dopaminergic degeneration including oxidative stress, mitochondrial dysfunction, protein aggregation, and apoptosis.

Agrin binds alpha-synuclein and modulates alpha-synuclein fibrillation

Recent studies have begun to investigate the role of agrin in brain and suggest that agrin's function likely extends beyond that of a synaptogenic protein. Particularly, it has been shown that agrin is associated with the pathological lesions of Alzheimer's disease (AD) and may contribute to the formation of beta-amyloid (Abeta) plaques in AD. We have extended the analysis of agrin's function in neurodegenerative diseases to investigate its role in Parkinson's disease (PD). Alpha-synuclein is a critical molecular determinant in familial and sporadic PD, with the formation of alpha-synuclein fibrils being enhanced by sulfated macromolecules. In the studies reported here, we show that agrin binds to alpha-synuclein in a heparan sulfate-dependent (HS-dependent) manner, induces conformational changes in this protein characterized by beta-sheet structure, and enhances insolubility of alpha-synuclein. We also show that agrin accelerates the formation of protofibrils by alpha-synuclein and decreases the half-time of fibril formation. The association of agrin with PD lesions was also explored in PD human brain, and these studies shown that agrin colocalizes with alpha-synuclein in neuronal Lewy bodies in the substantia nigra of PD brain. These studies indicate that agrin is capable of accelerating the formation of insoluble protein fibrils in a second common neurodegenerative disease. These findings may indicate shared molecular mechanisms leading to the pathophysiology in these two neurodegenerative disorders.

Overlap between neurodegenerative disorders

Neurodegenerative disorders are characterized by the formation of distinct pathological changes in the brain, including extracellular protein deposits, cellular inclusions, and changes in cell morphology. Since the earliest published descriptions of these disorders, diagnosis has been based on clinicopathological features, namely, the coexistence of a specific clinical profile together with the presence or absence of particular types of lesion. In addition, the molecular profile of lesions has become an increasingly important feature both in the diagnosis of existing disorders and in the description of new disease entities. Recent studies, however, have reported considerable overlap between the clinicopathological features of many disorders leading to difficulties in the diagnosis of individual cases and to calls for a new classification of neurodegenerative disease. This article discusses: (i) the nature and degree of the overlap between different neurodegenerative disorders and includes a discussion of Alzheimer's disease, dementia with Lewy bodies, the fronto-temporal dementias, and prion disease; (ii) the factors that contribute to disease overlap, including historical factors, the presence of disease heterogeneity, age-related changes, the problem of apolipoprotein genotype, and the co-occurrence of common diseases; and (iii) whether the current nosological status of disorders should be reconsidered.

The role of α-synuclein in neurodegenerative diseases

Alpha-synuclein is a 140 amino acid neuronal protein that has been associated with several neurodegenerative diseases. A point mutation in the gene coding for the alpha-synuclein protein was the first discovery linking this protein to a rare familial form of Parkinson's disease (PD). Subsequently, other mutations in the alpha-synuclein gene have been identified in familial PD. The aggregated proteinaceous inclusions called Lewy bodies found in PD and cortical Lewy body dementia (LBD) were discovered to be predominantly alpha-synuclein. Aberrant aggregation of alpha-synuclein has been detected in an increasing number of neurodegenerative diseases, collectively known as synucleopathies. Alpha-synuclein exists physiologically in both soluble and membrane-bound states, in unstructured and alpha-helical conformations, respectively. The physiological function of alpha-synuclein appears to require its translocation between these subcellular compartments and interconversion between the 2 conformations. Abnormal processing of alpha-synuclein is predicted to lead to pathological changes in its binding properties and function. In this review, genetic and environmental risk factors for alpha-synuclein pathology are described. Various mechanisms for in vitro and in vivo alpha-synuclein aggregation and neurotoxicity are summarized, and their relevance to neuropathology is explored.

Aggregation promoting C-terminal truncation of alpha-synuclein is a normal cellular process and is enhanced by the familial Parkinson's disease-linked mutations

Abnormal biology of alpha-synuclein (alpha-Syn) is directly implicated in the pathogenesis of Parkinson's disease and other alpha-synucleinopathies. Herein, we demonstrate that C-terminally truncated alpha-Syn (alpha-SynDeltaC), enriched in the pathological alpha-Syn aggregates, is normally generated from full-length alpha-Syn independent of alpha-Syn aggregation in brains and in cultured cells. The accumulation of alpha-SynDeltaC is enhanced in neuronal cells as compared with nonneuronal cells. Significantly, the expression of familial Parkinson's disease-linked mutant alpha-Syn is associated with the enhanced cellular accumulation of alpha-SynDeltaC. Moreover, substoichiometric amounts of alpha-SynDeltaC enhance the in vitro aggregation of the more abundant full-length alpha-Syn. Finally, cases of alpha-synucleinopathy exhibit increases in the total soluble alpha-Syn and a higher proportion of soluble alpha-SynDeltaC, a condition favoring the aggregation of alpha-Syn. Collectively, our results indicate that the biology behind the generation and accumulation of alpha-SynDeltaC is likely to have relevance for the initiation and the progression of alpha-Syn aggregation in vivo.

Insoluble alpha-synuclein in Alzheimer's disease without Lewy body formation

Insoluble alpha-synuclein plays a central role in Lewy body diseases, with considerable controversy as to whether it plays a similar role in Alzheimer's disease (AD). We assessed the tissue location and solubility of cortical alpha-synuclein in AD (without Lewy body formation) compared with controls, using sequential extraction procedures and Western immunoblotting to quantify different alpha-synuclein species in their different solubility states. Controls had no insoluble cortical alpha-synuclein and a ratio of soluble:lipid-associated alpha-synuclein of 1.2-/+0.1. Total alpha-synuclein protein was significantly increased in AD and concentrated within the lipid-associated fraction (soluble:lipid ratio 0.9-/+0.05, soluble:insoluble 1.5-/+0.1, lipid:insoluble 1.7-/+0.1) which proved difficult to localize in paraffin-embedded tissue. Tissues prepared without lipid extraction revealed alpha-synuclein-immunoreactivity in the amorphous components of mature cored AD plaques. This lipid-association of alpha-synuclein in mature AD plaques links this protein with other lipid changes thought to be important in disease pathogenesis.

Human wild-type alpha-synuclein impairs neurogenesis

Neurodegenerative diseases classified as synucleinopathies are characterized by alpha-synuclein inclusions. In these disorders, alpha-synuclein accumulates within glial or neuronal cells in the brain including regions of adult neurogenesis. We hypothesized a pathophysiological role for alpha-synuclein in newly generated cells of the adult brain and in this study examined regions of neurogenesis in adult mice overexpressing human wild-type alpha-synuclein under the control of the platelet-derived growth factor promoter. The number of proliferating cells and the fate of newly generated cells were analyzed in the olfactory bulb system and in the hippocampal dentate gyrus. There were no effects on proliferation detectable; however, significantly less neurogenesis and fewer neurons were observed in the olfactory bulb as well as in the hippocampus of adult human alpha-synuclein mice compared to control littermates. This effect was almost exclusively due to diminished survival of neuronal precursors in the target regions of neurogenesis. Our data imply that the finely tuned equilibrium of neuronal cell birth and death in neurogenic regions may be altered in human alpha-synuclein-overexpressing mice. We hypothesize that reduced adult neurogenesis in the olfactory bulb may contribute to olfactory deficits in neurodegenerative disorders associated with alpha-synuclein inclusions.

Alteration in α-synuclein mRNA expression in Parkinson's disease

The presynaptic protein alpha-synuclein is considered to play an important role in the pathophysiology of Parkinson's disease (PD). Point mutations in the alpha-synuclein gene have been demonstrated in familial PD and alpha-synuclein is a major component of Lewy bodies, the pathological hallmark of the sporadic disease. It is not clear whether abnormal accumulation of alpha-synuclein is the result of abnormal levels of expression of the gene in neurodegenerative conditions. Expression of alpha-synuclein mRNA was therefore studied in control and PD brain using semiquantitative in situ hybridization. alpha-synuclein was expressed widely and hybridization signal was seen in most cortical regions, hippocampus, cerebellum, and brain stem. There was little mRNA in the striatum and no hybridization signal was detected in glia. High levels of alpha-synuclein mRNA expression in neurons did not seem to be a marker for Lewy body formation. Abundant signal was seen both in regions in which Lewy body deposition occurs commonly in idiopathic PD (PD), such as substantia nigra and frontal and temporal cortex, as well as in less susceptible regions, e.g. visual cortex. Quantitative comparison of mRNA expression in regions of predilection for Lewy body formation showed that mRNA expression was reduced significantly in melanized substantia nigra neurons and frontal cortex neurons in Parkinson's disease. In substantia nigra neurons there seemed to be a negative correlation between cellular mRNA expression and disease duration. These findings are in broad agreement with other studies of the expression of alpha-synuclein mRNA in human brain and suggest that Lewy body formation is unlikely to be the result of overexpression of alpha-synuclein.

α-Synuclein: Normal Function and Role in Neurodegenerative Diseases

Synucleins are a family of small, highly charged proteins expressed predominantly in neurons. Since their discovery and characterization during the last decade, much has been learned about their structure, potential functions, interactions with other proteins, and roles in disease. One of these proteins, alpha-synuclein (alpha-syn), is the major building block of pathological inclusions that characterize many neurodegenerative disorders, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and neurodegeneration with brain iron accumulation type 1 (NBIA-1), which collectively are termed synucleinopathies. Furthermore, genetic and biological studies support a role for alpha-syn in the pathophysiology of these diseases. Therefore, research must be continued in order to better understand the functions of the synuclein proteins under normal physiological conditions as well as their role in diseases.

Parkinson's disease: the thalamic components of the limbic loop are severely impaired by alpha-synuclein immunopositive inclusion body pathology

The Parkinson's disease (PD)-related inclusion body pathology comprises Lewy bodies (LBs) as well as Lewy neurites (LNs). The distribution and severity of this pathology were investigated in the thalamus of 12 autopsy cases with clinically diagnosed and neuropathologically confirmed PD. The LBs and LNs were visualized by immunoreactions against the protein alpha-synuclein. In the human thalamus during PD, a specific and highly stereotypical distribution pattern of LBs and LNs evolves. As in cortical and other subcortical regions, the components of human thalamus assigned to the limbic loop bear the brunt of the PD-related pathology. In contrast, the thalamic components integrated into the striatal and cerebellar loops as well as the primary sensory nuclei of the thalamus show at best a mildly developed pathology. Damage to the thalamic components of the limbic loop nuclei may contribute not only to the cognitive, emotional, and autonomic symptoms of PD but to the somatomotor and oculomotor dysfunctions as well.

Is methamphetamine abuse a risk factor in parkinsonism?

Parkinsons disease (PD) is a neurodegenerative disorder with increased incidence in individuals beyond 50 years of age. The etiology of PD is currently not known, but it appears that environmental factors may play an important role. The molecular basis of PD is the nearly complete loss of the neurotransmitter dopamine (DA) in the basal ganglia (caudate/putamen). The decrease in dopamine levels is the result of degeneration of dopamine-containing neurons in the substantia nigra. This biochemical deficit in the nigrostriatal pathway leads to the emergence of motor impairments typical of PD. Methamphetamine (METH) is a psychostimulant drug with increasing use in certain segments of the population in the United States and worldwide. In experimental animal models and human studies, METH administration has been shown to decrease markers of dopaminergic neuron terminal integrity in the basal ganglia. A long-standing question has been whether the reductions in dopaminergic markers induced by METH constitute degenerative changes or reflect drug-induced modulation. Resolving this question is important because the irreversible loss of dopaminergic function may increase the likelihood of Parkinsonism with advancing age.

Selective insolubility of alpha-synuclein in human Lewy body diseases is recapitulated in a transgenic mouse model

alpha-Synuclein (alpha-SYN) is deposited in intraneuronal cytoplasmic inclusions (Lewy bodies, LBs) characteristic for Parkinson's disease (PD) and LB dementias. alpha-SYN forms LB-like fibrils in vitro, in contrast to its homologue beta-SYN. Here we have investigated the solubility of SYNs in human LB diseases and in transgenic mice expressing human wild-type and PD-associated mutant [A30P]alpha-SYN driven by the brain neuron-specific promoter, Thy1. Distinct alpha-SYN species were detected in the detergent-insoluble fractions from brains of patients with PD, dementia with LBs, and neurodegeneration with brain iron accumulation type 1 (formerly known as Hallervorden-Spatz disease). Using the same extraction method, detergent-insolubility of human alpha-SYN was observed in brains of transgenic mice. In contrast, neither endogenous mouse alpha-SYN nor beta-SYN were detected in detergent-insoluble fractions from transgenic mouse brains. The nonamyloidogenic beta-SYN was incapable of forming insoluble fibrils because amino acids 73 to 83 in the central region of alpha-SYN are absent in beta-SYN. In conclusion, the specific accumulation of detergent-insoluble alpha-SYN in transgenic mice recapitulates a pivotal feature of human LB diseases.

Prominent perikaryal expression of alpha- and beta-synuclein in neurons of dorsal root ganglion and in medullary neurons

Synucleins (syns) are a family of small, highly conserved proteins expressed predominantly in neurons. Although the normal function of syns is unknown, alpha-syn plays a pivotal role in several neurodegenerative diseases. The expression patterns of syns have been described in several studies, but much of this information was obtained before the cloning of all four members of this family of proteins and previous studies were limited to the analysis of single species. Here, we used antibodies specific for alpha-, beta-, and gamma-syn to study the patterns of expression in human, mouse, and rat nervous systems. Significant species-specific differences were detected in the expression of all three syns throughout the neuraxis. For example, gamma-syn is highly expressed in human cortex, while it is present only at low levels in mouse and rat cortex. Moreover, in contrast to previous reports that alpha- and beta-syns are normally localized predominantly at presynaptic terminals, we demonstrate that these proteins also are abundant in the perikarya of some neurons, such as in dorsal root ganglion. Intense alpha-syn immunoreactivity also was detected in the perikarya of human neurons in raphe, hypoglossal, and arcuate nuclei. These data underscore the need for additional studies to better understand the fundamental biological mechanism(s) targeting specific proteins to axonal terminals, as disruption of this process may be involved in the formation of pathological lesions.

Lewy body pathology in Alzheimer's disease

Lewy bodies, the characteristic pathological lesion of substantia nigra neurons in Parkinson's disease (PD), are frequently observed to accompany the amyloid plaque and neurofibrillary tangle pathology of Alzheimer's disease (AD). However the typical anatomic distribution of Lewy bodies in AD is distinct from PD. The most common site of occurrence is the amygdala, where Lewy bodies are observed in approximately 60% of both sporadic and familial AD. Other common sites of occurrence include the periamygdaloid and entorhinal cortex, while neocortical and brainstem areas develop Lewy bodies in a lower percentage of cases. In contrast, dementia with Lewy bodies (DLB), defined by widespread neocortical and brainstem Lewy bodies but frequently accompanied by variable levels of AD-type pathology, represents the other end of a spectrum of pathology associated with dementia. The observation of Lewy bodies in familial AD cases suggests that like neurofibrillary tangles, the formation of Lewy bodies can be induced by the pathological state caused by Abeta-amyloid overproduction. The role of Lewy body formation in the dysfunction and degeneration of neurons remains unclear. The protein alpha-synuclein appears to be an important structural component of Lewy bodies, an observation spurred by the discovery of point mutations in the alpha-synuclein gene linked to rare cases of autosomal dominant PD. Further investigation of alpha-synuclein and its relationship to pathological conditions promoting Lewy body formation in AD, PD, and DLB may yield further insight into pathogenesis of these diseases.

Parkin ubiquitinates the alpha-synuclein-interacting protein, synphilin-1: implications for Lewy-body formation in Parkinson disease

Parkinson disease is a common neurodegenerative disorder characterized by the loss of dopaminergic neurons and the presence of intracytoplasmic-ubiquitinated inclusions (Lewy bodies). Mutations in alpha-synuclein (A53T, A30P) and parkin cause familial Parkinson disease. Both these proteins are found in Lewy bodies. The absence of Lewy bodies in patients with parkin mutations suggests that parkin might be required for the formation of Lewy bodies. Here we show that parkin interacts with and ubiquitinates the alpha-synuclein-interacting protein, synphilin-1. Co-expression of alpha-synuclein, synphilin-1 and parkin result in the formation of Lewy-body-like ubiquitin-positive cytosolic inclusions. We further show that familial-linked mutations in parkin disrupt the ubiquitination of synphilin-1 and the formation of the ubiquitin-positive inclusions. These results provide a molecular basis for the ubiquitination of Lewy-body-associated proteins and link parkin and alpha-synuclein in a common pathogenic mechanism through their interaction with synphilin-1.

Alpha synuclein aggregation: is it the toxic gain of function responsible for neurodegeneration in Parkinson's disease?

Protein aggregation appears to be the common denominator in a series of distinct neurodegenerative diseases yet its role in the associated neuronal pathology in these various conditions remains elusive. In Parkinson's disease, localization of alpha synuclein aggregates within intracellular Lewy body occlusions represent a major hallmark of this disorder and suggest that such aggregation may play a causative role in the resulting dopaminergic cell loss. In this Viewpoint article, recent data is reviewed related to how alpha synuclein aggregation may occur, what cellular events might be responsible, and how this may interfere with normal cellular function(s). It appears likely that while aggregation of alpha synuclein may interfere with its normal function in the cell, this is not the primary cause of the related neurodegeneration.

Identification of the region of non-Abeta component (NAC) of Alzheimer's disease amyloid responsible for its aggregation and toxicity

The non-beta-amyloid (Abeta) component of Alzheimer's disease amyloid (NAC) and its precursor alpha-synuclein have been linked to amyloidogenesis in several neurodegenerative diseases. NAC and alpha-synuclein both form beta-sheet structures upon ageing, aggregate to form fibrils, and are neurotoxic. We recently established that a peptide comprising residues 3-18 of NAC retains these properties. To pinpoint the exact region responsible we have carried out assays of toxicity and physicochemical properties on smaller fragments of NAC. Toxicity was measured by the ability of fresh and aged peptides to inhibit the reduction of the redox dye 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) by rat pheochromocytoma PC12 cells and human neuroblastoma SHSY-5Y cells. On immediate dissolution, or after ageing, the fragments NAC(8-18) and NAC(8-16) are toxic, whereas NAC(12-18), NAC(9-16) and NAC(8-15) are not. Circular dichroism indicates that none of the peptides displays beta-sheet structure; rather all remain random coil throughout 24 h. However, in acetonitrile, an organic solvent known to induce beta sheet, fragments NAC(8-18) and NAC(8-16) both form beta-sheet structure. Only NAC(8-18) aggregates, as indicated by concentration of peptide remaining in solution after 3 days, and forms fibrils, as determined by electron microscopy. These findings indicate that residues 8-16 of NAC, equivalent to residues 68-76 in alpha-synuclein, comprise the region crucial for toxicity.