NACP, the precursor protein of the non-amyloid beta/A4 protein (A beta) component of Alzheimer disease amyloid, binds A beta and stimulates A beta aggregation

Role of the Gut Microbiome and Bacterial Amyloids in the Development of Synucleinopathies

Less than ten years ago, evidence began to accumulate about association between the changes in the composition of gut microbiota and development of human synucleinopathies, in particular sporadic form of Parkinson's disease. We collected data from more than one hundred and thirty experimental studies that reported similar results and summarized the frequencies of detection of different groups of bacteria in these studies. It is important to note that it is extremely rare that a unidirectional change in the population of one or another group of microorganisms (only an elevation or only a reduction) was detected in the patients with Parkinson's disease. However, we were able to identify several groups of bacteria that were overrepresented in the patients with Parkinson's disease in the analyzed studies. There are various hypotheses about the molecular mechanisms that explain such relationships. Usually, α-synuclein aggregation is associated with the development of inflammatory processes that occur in response to the changes in the microbiome. However, experimental evidence is accumulating on the influence of bacterial proteins, including amyloids (curli), as well as various metabolites, on the α-synuclein aggregation. In the review, we provided up-to-date information about such examples.

Alpha Synuclein: Neurodegeneration and Inflammation

Alpha-Synuclein (α-Syn) is one of the most important molecules involved in the pathogenesis of Parkinson's disease and related disorders, synucleinopathies, but also in several other neurodegenerative disorders with a more elusive role. This review analyzes the activities of α-Syn, in different conformational states, monomeric, oligomeric and fibrils, in relation to neuronal dysfunction. The neuronal damage induced by α-Syn in various conformers will be analyzed in relation to its capacity to spread the intracellular aggregation seeds with a prion-like mechanism. In view of the prominent role of inflammation in virtually all neurodegenerative disorders, the activity of α-Syn will also be illustrated considering its influence on glial reactivity. We and others have described the interaction between general inflammation and cerebral dysfunctional activity of α-Syn. Differences in microglia and astrocyte activation have also been observed when in vivo the presence of α-Syn oligomers has been combined with a lasting peripheral inflammatory effect. The reactivity of microglia was amplified, while astrocytes were damaged by the double stimulus, opening new perspectives for the control of inflammation in synucleinopathies. Starting from our studies in experimental models, we extended the perspective to find useful pointers to orient future research and potential therapeutic strategies in neurodegenerative disorders.

α-Synuclein and Mechanisms of Epigenetic Regulation

Synucleinopathies are a group of neurodegenerative diseases with common pathological lesions associated with the excessive accumulation and abnormal intracellular deposition of toxic species of α-synuclein. The shared clinical features are chronic progressive decline of motor, cognitive, and behavioral functions. These disorders include Parkinson's disease, dementia with Lewy body, and multiple system atrophy. Vigorous research in the mechanisms of pathology of these illnesses is currently under way to find disease-modifying treatment and molecular markers for early diagnosis. α-Synuclein is a prone-to-aggregate, small amyloidogenic protein with multiple roles in synaptic vesicle trafficking, neurotransmitter release, and intracellular signaling events. Its expression is controlled by several mechanisms, one of which is epigenetic regulation. When transmitted to the nucleus, α-synuclein binds to DNA and histones and participates in epigenetic regulatory functions controlling specific gene transcription. Here, we discuss the various aspects of α-synuclein involvement in epigenetic regulation in health and diseases.

Insights into aggregation dynamics of NACore peptides from coarse-grained simulations

Alpha(α)-synuclein is closely related to the pathogenesis of Parkinson's disease (PD). The NACore, a fragment of α-synuclein, is considered to be the key region of α-synuclein that causes PD. The aggregation dynamics of NACores are studied via coarse-grained molecular dynamics simulations. We find that NACores can self-assemble into a large cluster at high concentrations. The aggregation dynamics can be divided into three stages. The growth kinetics for the first and second stages follows the power law, S_max  ~ t^γ , with the second stage faster than the first one. The characteristic lifetime for the high concentration is 40 times larger than that for the low concentration, implying the low fluidity. Understanding the aggregation dynamics of NACores is helpful to develop drugs for therapeutic prevention and intervention.

Alpha-synuclein: a pathological factor with Aβ and tau and biomarker in Alzheimer's disease

BACKGROUND

Alpha-synuclein (α-syn) is considered the main pathophysiological protein component of Lewy bodies in synucleinopathies. α-Syn is an intrinsically disordered protein (IDP), and several types of structural conformations have been reported, depending on environmental factors. Since IDPs may have distinctive functions depending on their structures, α-syn can play different roles and interact with several proteins, including amyloid-beta (Aβ) and tau, in Alzheimer's disease (AD) and other neurodegenerative disorders.

MAIN BODY

In previous studies, α-syn aggregates in AD brains suggested a close relationship between AD and α-syn. In addition, α-syn directly interacts with Aβ and tau, promoting mutual aggregation and exacerbating the cognitive decline. The interaction of α-syn with Aβ and tau presented different consequences depending on the structural forms of the proteins. In AD, α-syn and tau levels in CSF were both elevated and revealed a high positive correlation. Especially, the CSF α-syn concentration was significantly elevated in the early stages of AD. Therefore, it could be a diagnostic marker of AD and help distinguish AD from other neurodegenerative disorders by incorporating other biomarkers.

CONCLUSION

The overall physiological and pathophysiological functions, structures, and genetics of α-syn in AD are reviewed and summarized. The numerous associations of α-syn with Aβ and tau suggested the significance of α-syn, as a partner of the pathophysiological roles in AD. Understanding the involvements of α-syn in the pathology of Aβ and tau could help address the unresolved issues of AD. In particular, the current status of the CSF α-syn in AD recommends it as an additional biomarker in the panel for AD diagnosis.

Ultrastructural and biochemical classification of pathogenic tau, α-synuclein and TDP-43

Intracellular accumulation of abnormal proteins with conformational changes is the defining neuropathological feature of neurodegenerative diseases. The pathogenic proteins that accumulate in patients' brains adopt an amyloid-like fibrous structure and exhibit various ultrastructural features. The biochemical analysis of pathogenic proteins in sarkosyl-insoluble fractions extracted from patients' brains also shows disease-specific features. Intriguingly, these ultrastructural and biochemical features are common within the same disease group. These differences among the pathogenic proteins extracted from patients' brains have important implications for definitive diagnosis of the disease, and also suggest the existence of pathogenic protein strains that contribute to the heterogeneity of pathogenesis in neurodegenerative diseases. Recent experimental evidence has shown that prion-like propagation of these pathogenic proteins from host cells to recipient cells underlies the onset and progression of neurodegenerative diseases. The reproduction of the pathological features that characterize each disease in cellular and animal models of prion-like propagation also implies that the structural differences in the pathogenic proteins are inherited in a prion-like manner. In this review, we summarize the ultrastructural and biochemical features of pathogenic proteins extracted from the brains of patients with neurodegenerative diseases that accumulate abnormal forms of tau, α-synuclein, and TDP-43, and we discuss how these disease-specific properties are maintained in the brain, based on recent experimental insights.

Invited review: Unearthing the mechanisms of age-related neurodegenerative disease using Caenorhabditis elegans

As human life expectancy increases, neurodegenerative diseases present a growing public health threat, for which there are currently few effective treatments. There is an urgent need to understand the molecular and genetic underpinnings of these disorders so new therapeutic targets can be identified. Here we present the argument that the simple nematode worm Caenorhabditis elegans is a powerful tool to rapidly study neurodegenerative disorders due to their short lifespan and vast array of genetic tools, which can be combined with characterization of conserved neuronal processes and behavior orthologous to those disrupted in human disease. We review how pre-existing C. elegans models provide insight into human neurological disease as well as an overview of current tools available to study neurodegenerative diseases in the worm, with an emphasis on genetics and behavior. We also discuss open questions that C. elegans may be particularly well suited for in future studies and how worms will be a valuable preclinical model to better understand these devastating neurological disorders.

α-synuclein-assisted oligomerization of β-amyloid (1-42)

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative disorders, characterized by aggregation of amyloid polypeptides, β-amyloid (Aβ) and α-synuclein (αS), respectively. Aβ and αS follow similar aggregation pathways, starting from monomers, to soluble toxic oligomeric assemblies, and to insoluble fibrils. Various studies have suggested overlaps in the pathologies of AD and PD, and have shown Aβ-αS interactions. Unfortunately, whether these protein-protein interactions lead to self- and co-assembly of Aβ and αS into oligomers - a potentially toxic synergistic mechanism - is poorly understood. Among the various Aβ isoforms, interactions of Aβ containing 42 amino acids (Aβ (1-42), referred to as Aβ42) with αS are of most direct relevance due to the high aggregation propensity and the strong toxic effect of this Aβ isoform. In this study, we carefully determined molecular consequences of interactions between Aβ42 and αS in their respective monomeric, oligomeric, and fibrillar forms using a comprehensive set of experimental tools. We show that the three αS conformers, namely, monomers, oligomers and fibrils interfered with fibrillization of Aβ42. Specifically, αS monomers and oligomers promoted oligomerization and stabilization of soluble Aβ42, possibly via direct binding or co-assembly, while αS fibrils hindered soluble Aβ42 species from converting into insoluble aggregates by the formation of large oligomers. We also provide evidence that the interactions with αS were mediated by various parts of Aβ42, depending on Aβ42 and αS conformers. Furthermore, we compared similarities and dissimilarities between Aβ42-αS and Aβ40-αS interactions. Overall, the present study provides a comprehensive depiction of the molecular interplay between Aβ42 and αS, providing insight into its synergistic toxic mechanism.

Examining the Toxicity of α-Synuclein in Neurodegenerative Disorders

Simple Summary

Neurodegenerative disorders are complex disorders that display a variety of clinical manifestations. The second-most common neurodegenerative disorder is Parkinson’s disease, and the leading pathological protein of the disorder is considered to be α-synuclein. Nonetheless, α-synuclein accumulation also seems to result in multiple system atrophy and dementia with Lewy bodies. In order to obtain a more proficient understanding in the pathological progression of these synucleinopathies, it is crucial to observe the post-translational modifications of α-synuclein and the conformations of α-synuclein, as well as its role in the dysfunction of cellular pathways.

Abstract

α-synuclein is considered the main pathological protein in a variety of neurodegenerative disorders, such as Parkinson’s disease, multiple system atrophy, and dementia with Lewy bodies. As of now, numerous studies have been aimed at examining the post-translational modifications of α-synuclein to determine their effects on α-synuclein aggregation, propagation, and oligomerization, as well as the potential cellular pathway dysfunctions caused by α-synuclein, to determine the role of the protein in disease progression. Furthermore, α-synuclein also appears to contribute to the fibrilization of tau and amyloid beta, which are crucial proteins in Alzheimer’s disease, advocating for α-synuclein’s preeminent role in neurodegeneration. Due to this, investigating the mechanisms of toxicity of α-synuclein in neurodegeneration may lead to a more proficient understanding of the timeline progression in neurodegenerative synucleinopathies and could thereby lead to the development of potent targeted therapies.

Inhibition of alpha-synuclein aggregation by AM17, a synthetic resveratrol derivative

Parkinson's disease (PD) is linked to the aberrant self-assembly of the amyloid protein, α-synuclein (αS), where αS monomers aggregate to form oligomers and fibrils. Out of the three conformers, αS oligomers are the major toxic agents in PD, while αS fibrils may work as a reservoir for toxic oligomeric conformers. Thus, compounds that inhibit aggregation of αS monomers and disaggregate αS oligomers and fibrils may serve as therapeutic agents against PD. In this regard, resveratrol and its synthetic derivatives (e.g., AM17, which contains a copper ion-selective ionophoric motif) have previously been examined for their inhibitory effects on aggregation of amyloid proteins, such as the β-amyloid peptide implicated in Alzheimer's disease. In the current study, we employed an array of experimental tools, such as Thioflavin T fluorescence, transmission electron microscopy, immuno-dot blot assays, SDS- and native-PAGE, and circular dichroism, to determine the impact of AM17 and resveratrol on αS aggregation. To the best of our knowledge, we show for the first time that AM17 not only inhibits aggregation of αS monomers but also disaggregates αS oligomers and fibrils, independent of the copper ions. Similar αS aggregation inhibitory effects were observed with resveratrol only in the presence of the copper ion. The present study supports the high promise of applicability of AM17 as an effective amyloid aggregation inhibitor for various conformers and protein sequences.

Collusion of α-Synuclein and Aβ aggravating co-morbidities in a novel prion-type mouse model

BACKGROUND

The misfolding of host-encoded proteins into pathological prion conformations is a defining characteristic of many neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and Lewy body dementia. A current area of intense study is the way in which the pathological deposition of these proteins might influence each other, as various combinations of co-pathology between prion-capable proteins are associated with exacerbation of disease. A spectrum of pathological, genetic and biochemical evidence provides credence to the notion that amyloid β (Aβ) accumulation can induce and promote α-synuclein pathology, driving neurodegeneration.

METHODS

To assess the interplay between α-synuclein and Aβ on protein aggregation kinetics, we crossed mice expressing human α-synuclein (M20) with APPswe/PS1dE9 transgenic mice (L85) to generate M20/L85 mice. We then injected α-synuclein preformed fibrils (PFFs) unilaterally into the hippocampus of 6-month-old mice, harvesting 2 or 4 months later.

RESULTS

Immunohistochemical analysis of M20/L85 mice revealed that pre-existing Aβ plaques exacerbate the spread and deposition of induced α-synuclein pathology. This process was associated with increased neuroinflammation. Unexpectedly, the injection of α-synuclein PFFs in L85 mice enhanced the deposition of Aβ; whereas the level of Aβ deposition in M20/L85 bigenic mice, injected with α-synuclein PFFs, did not differ from that of mice injected with PBS.

CONCLUSIONS

These studies reveal novel and unexpected interplays between α-synuclein pathology, Aβ and neuroinflammation in mice that recapitulate the pathology of Alzheimer's disease and Lewy body dementia.

Alpha-Synuclein Post-translational Modifications: Implications for Pathogenesis of Lewy Body Disorders

Lewy Body Disorders (LBDs) lie within the spectrum of age-related neurodegenerative diseases now frequently categorized as the synucleinopathies. LBDs are considered to be among the second most common form of neurodegenerative dementias after Alzheimer's disease. They are progressive conditions with variable clinical symptoms embodied within specific cognitive and behavioral disorders. There are currently no effective treatments for LBDs. LBDs are histopathologically characterized by the presence of abnormal neuronal inclusions commonly known as Lewy Bodies (LBs) and extracellular Lewy Neurites (LNs). The inclusions predominantly comprise aggregates of alpha-synuclein (aSyn). It has been proposed that post-translational modifications (PTMs) such as aSyn phosphorylation, ubiquitination SUMOylation, Nitration, o-GlcNacylation, and Truncation play important roles in the formation of toxic forms of the protein, which consequently facilitates the formation of these inclusions. This review focuses on the role of different PTMs in aSyn in the pathogenesis of LBDs. We highlight how these PTMs interact with aSyn to promote misfolding and aggregation and interplay with cell membranes leading to the potential functional and pathogenic consequences detected so far, and their involvement in the development of LBDs.

New insights on the effects of ionic liquid structural changes at the gene expression level: Molecular mechanisms of toxicity in Daphnia magna

Knowledge on the molecular basis of ionic liquids' (ILs) ecotoxicity is critical for the development of these designer solvents as their structure can be engineered to simultaneously meet functionality performance and environmental safety. The molecular effects of ILs were investigated by using RNA-sequencing following Daphnia magna exposure to imidazolium- and cholinium-based ILs: 1-ethyl-3-methylimidazolium chloride ([C₂mim]Cl), 1-dodecyl-3-methylimidazolium chloride ([C₁₂mim]Cl) and cholinium chloride ([Chol]Cl)-; the selection allowing to compare different families and cation alkyl chains. ILs shared mechanisms of toxicity focusing e.g. cellular membrane and cytoskeleton, oxidative stress, energy production, protein biosynthesis, DNA damage, disease initiation. [C₂mim]Cl and [C₁₂mim]Cl were the least and the most toxic ILs at the transcriptional level, denoting the role of the alkyl chain as a driver of ILs toxicity. Also, it was reinforced that [Chol]Cl is not devoid of environmental hazardous potential regardless of its argued biological compatibility. Unique gene expression signatures could also be identified for each IL, enlightening specific mechanisms of toxicity.

Disorders of synaptic vesicle fusion machinery

The revolution in genetic technology has ushered in a new age for our understanding of the underlying causes of neurodevelopmental, neuromuscular and neurodegenerative disorders, revealing that the presynaptic machinery governing synaptic vesicle fusion is compromised in many of these neurological disorders. This builds upon decades of research showing that disturbance to neurotransmitter release via toxins can cause acute neurological dysfunction. In this review, we focus on disorders of synaptic vesicle fusion caused either by toxic insult to the presynapse or alterations to genes encoding the key proteins that control and regulate fusion: the SNARE proteins (synaptobrevin, syntaxin-1 and SNAP-25), Munc18, Munc13, synaptotagmin, complexin, CSPα, α-synuclein, PRRT2 and tomosyn. We discuss the roles of these proteins and the cellular and molecular mechanisms underpinning neurological deficits in these disorders.

Possible Role of Amyloid Cross-Seeding in Evolvability and Neurodegenerative Disease

Aging-related neurodegenerative disorders are frequently associated with the aggregation of multiple amyloidogenic proteins (APs), although the reason why such detrimental phenomena have emerged in the post-reproductive human brain across evolution is unclear. Speculatively, APs might provide physiological benefits for the human brain during developmental/reproductive stages. Of relevance, it is noteworthy that cross-seeding (CS) of APs has recently been characterized in cellular and animal models of neurodegenerative disease, and that normal physiological CS of multiple APs has also been observed in lower organisms, including yeast and bacteria. In this context, our main objective is to discuss a possible involvement of the CS of APs in promoting evolvability, a hypothetical view regarding the function of APs as an inheritance of acquired characteristics against human brain stressors, which are transgenerationally transmitted to offspring via germ cells. Mechanistically, the protofibrils formed by the CS of multiple APs might confer hormesis more potently than individual APs. By virtue of greater encoded stress information in parental brains being available, the brains of offspring can cope more efficiently with forth-coming stressors. On the other hand, subsequent neurodegeneration caused by APs in parental brain through the antagonistic pleiotropy mechanism in aging, may suggest that synergistically, multiple APs might be more detrimental compared to singular AP in neurodegeneration. Taken together, we suggest that the CS of multiple APs might be involved in both evolvability and neurodegenerative disease in human brain, which may be mechanistically and therapeutically important.

Amyloid-Beta Peptides Trigger Aggregation of Alpha-Synuclein In Vitro

Alzheimer's disease (AD) and Parkinson's disease (PD), including dementia with Lewy bodies (DLB), account for the majority of dementia cases worldwide. Interestingly, a significant number of patients have clinical and neuropathological features of both AD and PD, i.e., the presence of amyloid deposits and Lewy bodies in the neocortex. The identification of α-synuclein peptides in amyloid plaques in DLB brain led to the hypothesis that both peptides mutually interact with each other to facilitate neurodegeneration. In this article, we report the influence of Aβ(1-42) and pGlu-Aβ(3-42) on the aggregation of α-synuclein in vitro. The aggregation of human recombinant α-synuclein was investigated using thioflavin-T fluorescence assay. Fibrils were investigated by means of antibody conjugated immunogold followed by transmission electron microscopy (TEM). Our data demonstrate a significantly increased aggregation propensity of α-synuclein in the presence of minor concentrations of Aβ(1-42) and pGlu-Aβ(3-42) for the first time, but without effect on toxicity on mouse primary neurons. The analysis of the composition of the fibrils by TEM combined with immunogold labeling of the peptides revealed an interaction of α-synuclein and Aβ in vitro, leading to an accelerated fibril formation. The analysis of kinetic data suggests that significantly enhanced nucleus formation accounts for this effect. Additionally, co-occurrence of α-synuclein and Aβ and pGlu-Aβ, respectively, under pathological conditions was confirmed in vivo by double immunofluorescent labelings in brains of aged transgenic mice with amyloid pathology. These observations imply a cross-talk of the amyloid peptides α-synuclein and Aβ species in neurodegeneration. Such effects might be responsible for the co-occurrence of Lewy bodies and plaques in many dementia cases.

Interactions between Soluble Species of β-Amyloid and α-Synuclein Promote Oligomerization while Inhibiting Fibrillization

Aggregations of β-amyloid (Aβ) and α-synuclein (αS) into oligomeric and fibrillar assemblies are the pathological hallmarks of Alzheimer's and Parkinson's diseases, respectively. Although Aβ and αS affect different regions of the brain and are separated at the cellular level, there is evidence of their eventual interaction in the pathology of both disorders. Characterization of interactions of Aβ and αS at various stages of their aggregation pathways could reveal mechanisms and therapeutic targets for the prevention and cure of these neurodegenerative diseases. In this study, we comprehensively examined the interactions and their molecular manifestations using an array of characterization tools. We show for the first time that αS monomers and oligomers, but not αS fibrils, inhibit Aβ fibrillization while promoting oligomerization of Aβ monomers and stabilizing preformed Aβ oligomers via coassembly, as judged by Thioflavin T fluorescence, transmission electron microscopy, and SDS- and native-PAGE with fluorescently labeled peptides/proteins. In contrast, soluble Aβ species, such as monomers and oligomers, aggregate into fibrils, when incubated alone under the otherwise same condition. Our study provides evidence that the interactions with αS soluble species, responsible for the effects, are mediated primarily by the C-terminus of Aβ, when judged by competitive immunoassays using antibodies recognizing various fragments of Aβ. We also show that the C-terminus of Aβ is a primary site for its interaction with αS fibrils. Collectively, these data demonstrate aggregation state-specific interactions between αS and Aβ and offer insight into a molecular basis of synergistic biological effects between the two polypeptides.

Prion-like propagation of α-synuclein in neurodegenerative diseases

Prions are defined as proteinaceous infectious particles that do not contain nucleic acids. Neuropathological investigations of post-mortem brains and recent studies of experimental transmission have suggested that amyloid-like abnormal protein aggregates, which are the defining feature of many neurodegenerative diseases, behave like prions and propagate throughout the brain. This prion-like propagation may be the underlying mechanism of onset and progression of neurodegenerative diseases, although the precise molecular mechanisms involved remain unclear. However, in vitro and in vivo experimental models of prion-like propagation using pathogenic protein seeds are well established and are extremely valuable for the exploration and evaluation of novel drugs and therapies for neurodegenerative diseases for which there is no effective treatment. In this chapter, we introduce the experimental models of prion-like propagation of α-synuclein, which is accumulated in Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy, and we describe their applications for the development of new diagnostic and therapeutic modalities. We also introduce the concept of "α-syn strains," which may underlie the pathological and clinical diversity of α-synucleinopathies.

Quantifying Co-Oligomer Formation by α-Synuclein

Small oligomers of the protein α-synuclein (αS) are highly cytotoxic species associated with Parkinson's disease (PD). In addition, αS can form co-aggregates with its mutational variants and with other proteins such as amyloid-β (Aβ) and tau, which are implicated in Alzheimer's disease. The processes of self-oligomerization and co-oligomerization of αS are, however, challenging to study quantitatively. Here, we have utilized single-molecule techniques to measure the equilibrium populations of oligomers formed in vitro by mixtures of wild-type αS with its mutational variants and with Aβ40, Aβ42, and a fragment of tau. Using a statistical mechanical model, we find that co-oligomer formation is generally more favorable than self-oligomer formation at equilibrium. Furthermore, self-oligomers more potently disrupt lipid membranes than do co-oligomers. However, this difference is sometimes outweighed by the greater formation propensity of co-oligomers when multiple proteins coexist. Our results suggest that co-oligomer formation may be important in PD and related neurodegenerative diseases.

Cause and consequence of Aβ - Lipid interactions in Alzheimer disease pathogenesis

Self-templating propagation of protein aggregate conformations is increasingly becoming a significant factor in many neurological diseases. In Alzheimer disease (AD), intrinsically disordered amyloid-β (Aβ) peptides undergo aggregation that is sensitive to environmental conditions. High-molecular weight aggregates of Aβ that form insoluble fibrils are deposited as senile plaques in AD brains. However, low-molecular weight aggregates called soluble oligomers are known to be the primary toxic agents responsible for neuronal dysfunction. The aggregation process is highly stochastic involving both homotypic (Aβ-Aβ) and heterotypic (Aβ with interacting partners) interactions. Two of the important members of interacting partners are membrane lipids and surfactants, to which Aβ shows a perpetual association. Aβ-membrane interactions have been widely investigated for more than two decades, and this research has provided a wealth of information. Although this has greatly enriched our understanding, the objective of this review is to consolidate the information from the literature that collectively showcases the unique phenomenon of lipid-mediated Aβ oligomer generation, which has largely remained inconspicuous. This is especially important because Aβ aggregate "strains" are increasingly becoming relevant in light of the correlations between the structure of aggregates and AD phenotypes. Here, we will focus on aspects of Aβ-lipid interactions specifically from the context of how lipid modulation generates a wide variety of biophysically and biochemically distinct oligomer sub-types. This, we believe, will refocus our thinking on the influence of lipids and open new approaches in delineating the mechanisms of AD pathogenesis. This article is part of a Special Issue entitled: Protein Aggregation and Misfolding at the Cell Membrane Interface edited by Ayyalusamy Ramamoorthy.

A Genome-Wide Association Study of α-Synuclein Levels in Cerebrospinal Fluid

α-Synuclein is a 140-amino acid protein produced predominantly by neurons in the brain which plays a role in the regulation of neurotransmitter release, synaptic function, and plasticity, thus making it the focus in understanding the etiology of a group of neurodegenerative diseases. We conducted genome-wide association studies (GWAS) of α-synuclein levels in cerebrospinal fluid (CSF) with 209 non-Hispanic white participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI-1) cohort using a linear regression model to identify novel variants associated with α-synuclein concentration. The minor allele (T) of rs7072338 in the long intergenic non-protein coding RNA 1515 (LINC01515) and the minor allele (T) of rs17794023 in clusterin-associated protein 1 (CLUAP1) were associated with higher CSF α-synuclein levels at genome-wide significance (P = 4.167 × 10^-9 and 9.56 × 10^-9, respectively). In addition, single nucleotide polymorphisms (SNPs) near amyloid beta precursor protein (APP) (rs1394839) (P = 2.31 × 10^-7), Rap guanine nucleotide exchange factor 1 (RAPGEF1) (rs10901091) (P = 8.07 × 10^-7), and two intergenic loci on chromosome 2 and 14 (rs11687064 P = 2.50 × 10^-7and rs7147386 P = 4.05 × 10^-7) were identified as suggestive loci associated with CSF α-synuclein levels. We have identified significantly associated SNPs for CSF α-synuclein. These associations have important implications for a better understanding of α-synuclein regulation and allow researchers to further explore the relationships between these SNPs and α-synuclein-related neurodegenerative disorders.

Genetics of Synucleinopathies

Parkinson's disease (PD), diffuse Lewy body disease (DLBD), and multiple system atrophy (MSA) constitute the three major neurodegenerative disorders referred to as synucleinopathies because both genetic and pathological results implicate the α-synuclein protein in their pathogenesis. PD and DLBD are recognized as closely related diseases with substantial clinical and pathological overlap. MSA, on the other hand, has a distinctive clinical presentation and neuropathological profile. In this review, we will summarize the evidence linking α-synuclein to these three disorders. Hundreds of patients with point or copy number mutations in the gene encoding α-synuclein, SNCA, have been reported in the literature in association with hereditary, autosomal dominant forms of PD, DLBD, or neurodegenerative disease with parkinsonism. The copy number mutations show a dosage effect with age at onset and severity correlating with the number of extra copies of SNCA a patient carries. Common variation in and around the SNCA gene has also been found by genome-wide association studies to be associated with increased risk for apparently sporadic PD, with some evidence that these variants exert their effect through modest increases in α-synuclein expression. Complementing the genetic evidence linking α-synuclein to PD and DLBD is the pathological finding that α-synuclein is a major constituent of Lewy bodies and Lewy neurites in the brains of patients with the common sporadic form of PD. On the other hand, there is little genetic evidence linking SNCA to MSA despite strong neuropathological evidence of α-synuclein aggregation in oligodendroglial cells in MSA patients. Evidence is now emerging that α-synuclein aggregates can have different protein conformations, referred to as strains, similar to what has been shown in prion disease. The different phenotypes in hereditary PD/DLBD versus MSA are likely, therefore, to be the result not only of how specific mutations affect protein expression and turnover, but also a more complex interaction between intrinsic and extrinsic factors governing aggregation and strain formation.

Autophagy and Alzheimer's Disease: From Molecular Mechanisms to Therapeutic Implications

Alzheimer’s disease (AD) is the most common cause of progressive dementia in the elderly. It is characterized by a progressive and irreversible loss of cognitive abilities and formation of senile plaques, composed mainly of amyloid β (Aβ), and neurofibrillary tangles (NFTs), composed of tau protein, in the hippocampus and cortex of afflicted humans. In brains of AD patients the metabolism of Aβ is dysregulated, which leads to the accumulation and aggregation of Aβ. Metabolism of Aβ and tau proteins is crucially influenced by autophagy. Autophagy is a lysosome-dependent, homeostatic process, in which organelles and proteins are degraded and recycled into energy. Thus, dysfunction of autophagy is suggested to lead to the accretion of noxious proteins in the AD brain. In the present review, we describe the process of autophagy and its importance in AD. Additionally, we discuss mechanisms and genes linking autophagy and AD, i.e., the mTOR pathway, neuroinflammation, endocannabinoid system, ATG7, BCL2, BECN1, CDK5, CLU, CTSD, FOXO1, GFAP, ITPR1, MAPT, PSEN1, SNCA, UBQLN1, and UCHL1. We also present pharmacological agents acting via modulation of autophagy that may show promise in AD therapy. This review updates our knowledge on autophagy mechanisms proposing novel therapeutic targets for the treatment of AD.

Monomeric and fibrillar α-synuclein exert opposite effects on the catalytic cycle that promotes the proliferation of Aβ42 aggregates

The coaggregation of the amyloid-β peptide (Aβ) and α-synuclein is commonly observed in a range of neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. The complex interplay between Aβ and α-synuclein has led to seemingly contradictory results on whether α-synuclein promotes or inhibits Aβ aggregation. Here, we show how these conflicts can be rationalized and resolved by demonstrating that different structural forms of α-synuclein exert different effects on Aβ aggregation. Our results demonstrate that whereas monomeric α-synuclein blocks the autocatalytic proliferation of Aβ42 (the 42-residue form of Aβ) fibrils, fibrillar α-synuclein catalyses the heterogeneous nucleation of Aβ42 aggregates. It is thus the specific balance between the concentrations of monomeric and fibrillar α-synuclein that determines the outcome of the Aβ42 aggregation reaction.

α-synuclein toxicity in neurodegeneration: mechanism and therapeutic strategies

Alterations in α-synuclein dosage lead to familial Parkinson's disease (PD), and its accumulation results in synucleinopathies that include PD, dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Furthermore, α-synuclein contributes to the fibrilization of amyloid-b and tau, two key proteins in Alzheimer's disease, which suggests a central role for α-synuclein toxicity in neurodegeneration. Recent studies of factors contributing to α-synuclein toxicity and its disruption of downstream cellular pathways have expanded our understanding of disease pathogenesis in synucleinopathies. In this Review, we discuss these emerging themes, including the contributions of aging, selective vulnerability and non-cell-autonomous factors such as α-synuclein cell-to-cell propagation and neuroinflammation. Finally, we summarize recent efforts toward the development of targeted therapies for PD and related synucleinopathies.

Effects of in vitro and in vivo avermectin exposure on alpha synuclein expression and proteasomal activity in pigeons

Avermectins (AVMs) are used worldwide in agriculture and veterinary medicine. Residues of avermectin drugs, causing toxicological effects on non-target organisms, have raised great concern. The aim of this study was to investigate the effects of AVM on the expression levels of alpha synuclein (α-Syn) and proteasomal activity in pigeon (Columba livia) neurons both in vivo and in vitro. The results showed that, the mRNA and protein levels of α-Syn increased in AVM treated groups relative to control groups in the cerebrum, cerebellum and optic lobe in vivo. Dose-dependent decreases in the proteasomal activity (i.e., chymotrypsin-like, trypsin-like and peptidylglutamyl peptidehydrolase) were observed both in vivo and in vitro. The results suggested that AVM could induce the expression levels of α-Syn and inhibit the normal physiological function of proteasome in brain tissues and neurons. The information presented in this study is helpful to understand the mechanism of AVM-induced neurotoxicology in birds.

Generation of Rabbit Monoclonal Antibody to Amyloid-β38 (Aβ38): Increased Plasma Aβ38 Levels in Down Syndrome

Secreted soluble amyloid-β (Aβ)38 is the second most prominent Aβ form next to Aβ40, and is found in cerebrospinal fluid (CSF) and blood. Recent studies have shown the importance of quantitation of CSF Aβ38 levels in combination with those of Aβ40 and Aβ42 to support the diagnosis of Alzheimer's disease (AD), and other neurodegenerative diseases, and to facilitate drug discovery studies. However, the availability of reliable and specific Aβ38 monoclonal antibody is limited. Our first aim was to generate and partially characterize rabbit monoclonal antibody (RabmAb) to Aβ38. The antibody was specific to Aβ38, since it did not react with Aβ37, Aβ39, Aβ40, or Aβ42 in ELISA or immunoblotting. The antibody was sensitive enough to measure Aβ38 levels in plasma. Our second aim was to quantitate Aβ38 levels in plasma from older Down syndrome (DS) persons and age-matched controls. Persons with DS (35 years and older) have neuropathological changes characteristic of AD. Studies have shown that plasma Aβ40 and Aβ42 levels are higher in older persons with DS than in controls. However, none examined Aβ38 levels in DS. Our quantitation data showed that, like Aβ40 and Aβ42 plasma levels, Aβ38 plasma levels were higher in DS than in controls. Longitudinal studies will determine whether plasma Aβ38 levels in combination with levels of Aβ40 and Aβ42 are useful to predict early signs of AD in DS.

Understanding Aspects of Aluminum Exposure in Alzheimer's Disease Development

Aluminum is a ubiquitously abundant nonessential element. Aluminum has been associated with neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis, and dialysis encephalopathy. Many continue to regard aluminum as controversial although increasing evidence supports the implications of aluminum in the pathogenesis of AD. Aluminum causes the accumulation of tau protein and Aβ protein in the brain of experimental animals. Aluminum induces neuronal apoptosis in vivo and in vitro, either by endoplasmic stress from the unfolded protein response, by mitochondrial dysfunction, or a combination of them. Some, people who are exposed chronically to aluminum, either from through water and/or food, have not shown any AD pathology, apparently because their gastrointestinal barrier is more effective. This article is written keeping in mind mechanisms of action of aluminum neurotoxicity with respect to AD.

Intracellular Dynamics of Synucleins: "Here, There and Everywhere"

Synucleins are small, soluble proteins expressed primarily in neural tissue and in certain tumors. The synuclein family consists of three members: α-, β-, and γ-synucleins present only in vertebrates. Members of the synuclein family have high sequence identity, especially in the N-terminal regions. The synuclein gene family came into the spotlight, when one of its members, α-synuclein, was found to be associated with Parkinson's disease and other neurodegenerative disorders, whereas γ-synuclein was linked to several forms of cancer. There are a lot of controversy and exciting debates concerning members of the synuclein family, including their normal functions, toxicity, role in pathology, transmission between cells and intracellular localization. Important findings which remain undisputable for many years are synuclein localization in synapses and their role in the regulation of synaptic vesicle trafficking, whereas their presence and function in mitochondria and nucleus is a debated topic. In this review, we present the data on the localization of synucleins in two intracellular organelles: the nucleus and mitochondria.

Insulin-degrading enzyme prevents α-synuclein fibril formation in a nonproteolytical manner

The insulin-degrading enzyme (IDE) degrades amyloidogenic proteins such as Amyloid β (Αβ) and Islet Amyloid Polypeptide (IAPP), i.e. peptides associated with Alzheimer’s disease and type 2 diabetes, respectively. In addition to the protease activity normally associated with IDE function an additional activity involving the formation of stable, irreversible complexes with both Αβ and α-synuclein, an amyloidogenic protein involved in Parkinson’s disease, was recently proposed. Here, we have investigated the functional consequences of IDE-α-synuclein interactions in vitro. We demonstrate that IDE in a nonproteolytic manner and at sub-stoichiometric ratios efficiently inhibits α-synuclein fibril formation by binding to α-synuclein oligomers making them inert to amyloid formation. Moreover, we show that, within a defined range of α-synuclein concentrations, interaction with α-synuclein oligomers increases IDE’s proteolytic activity on a fluorogenic substrate. We propose that the outcomes of IDE-α-synuclein interactions, i.e. protection against α-synuclein amyloid formation and stimulated IDE protease activity, may be protective in vivo.

α-Synuclein modifies mutant huntingtin aggregation and neurotoxicity in Drosophila

Protein misfolding and aggregation is a major hallmark of neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). Until recently, the consensus was that each aggregation-prone protein was characteristic of each disorder [α-synuclein (α-syn)/PD, mutant huntingtin (Htt)/HD, Tau and amyloid beta peptide/AD]. However, growing evidence indicates that aggregation-prone proteins can actually co-aggregate and modify each other's behavior and toxicity, suggesting that this process may also contribute to the overlap in clinical symptoms across different diseases. Here, we show that α-syn and mutant Htt co-aggregate in vivo when co-expressed in Drosophila and produce a synergistic age-dependent increase in neurotoxicity associated to a decline in motor function and life span. Altogether, our results suggest that the co-existence of α-syn and Htt in the same neuronal cells worsens aggregation-related neuropathologies and accelerates disease progression.

Cerebrospinal fluid levels of phosphorylated tau and Aβ1-38/Aβ1-40/Aβ1-42 in Alzheimer's disease with PS1 mutations

We studied seven cases of Alzheimer's disease (AD). Six of the patients had presenilin 1 (PS1) mutations (PS1AD). Three novel PS1 mutations (T99A, H131R and L219R) and three other missense mutations (M233L, H163R and V272A) were found in the PS1AD group. We measured the levels of phosphorylated tau (ptau-181, ptau-199) and Aβ (Aβ1-42, Aβ1-40 and Aβ1-38) in the cerebrospinal fluid (CSF) of PS1AD patients, early-onset sporadic AD (EOSAD), late-onset sporadic AD (LOSAD) and non-demented subjects (ND). The CSF levels of Aβ1-42 in the three AD groups were significantly lower than those of the ND group (p < 0.0001). CSF levels of Aβ1-42 in the PS1AD group were significantly lower than those in the two sporadic AD groups. The Aβ1-40 and Aβ1-38 levels in the CSF of the PS1AD group were significantly lower than those of the three other groups (p < 0.0001, respectively). The levels of Aβ1-40, Aβ1-38 and Aβ1-42 in the CSF of the PS1AD group remained lower than those of the ND group for 4 years. Not only CSF Aβ1-42, but also Aβ1-40 and Aβ1-38 decreased in the advanced stages of PS1AD.

Enteric alpha-synuclein expression is increased in Parkinson's disease but not Alzheimer's disease

BACKGROUND AND OBJECTIVE

Alpha-synuclein (α-Syn) is immunohistochemically detectable in enteric neurons in some subjects. We determined its age distribution in the general autopsy population and in an age-matched subset investigated differences with Parkinson's (PD) and Alzheimer's diseases (AD).

METHODS

Archival autopsy samples of colon from 95 cases (77 general population, 10 PD, and 8 AD) were immunostained with monoclonal antibody KM51. α-Syn detectability was semiquantitatively graded 1 to 3.

RESULTS

α-Syn was detectable in 52% of the general population, and its level of expression did not change between ages 40 and 91. All PD subjects were α-Syn positive, with higher prevalence (P = 0.001) and grade (P = 0.003) than age-matched controls. AD subjects were no more likely to be α-Syn positive or have a higher grade than controls.

CONCLUSIONS

Either PD develops selectively in the enterically α-Syn-positive population subset or PD induces this expression. Absence of increased α-Syn expression in AD points to differences in pathogenesis.

An in vitro perspective on the molecular mechanisms underlying mutant huntingtin protein toxicity

Huntington's disease (HD) is a devastating neurodegenerative disorder whose main hallmark is brain atrophy. However, several peripheral organs are considerably affected and their symptoms may, in fact, manifest before those resulting from brain pathology. HD is of genetic origin and caused by a mutation in the huntingtin gene. The mutated protein has detrimental effects on cell survival, but whether the mutation leads to a gain of toxic function or a loss of function of the altered protein is still highly controversial. Most currently used in vitro models have been designed, to a large extent, to investigate the effects of the aggregation process in neuronal-like cells. However, as the pathology involves several other organs, new in vitro models are critically needed to take into account the deleterious effects of mutant huntingtin in peripheral tissues, and thus to identify new targets that could lead to more effective clinical interventions in the early course of the disease. This review aims to present current in vitro models of HD pathology and to discuss the knowledge that has been gained from these studies as well as the new in vitro tools that have been developed, which should reflect the more global view that we now have of the disease.

Cross-seeding effects of amyloid β-protein and α-synuclein

Amyloid β-protein (Aβ) and α-synuclein (αS) are the primary components of amyloid plaques and Lewy bodies (LBs), respectively. Previous in vitro and in vivo studies have suggested that interactions between Aβ and αS are involved in the pathogenesis of Alzheimer's disease and LB diseases. However, the seeding effects of their aggregates on their aggregation pathways are not completely clear. To investigate the cross-seeding effects of Aβ and αS, we examined how sonicated fibrils or cross-linked oligomers of Aβ40, Aβ42, and αS affected their aggregation pathways using thioflavin T(S) assay and electron microscopy. Fibrils and oligomers of Aβ40, Aβ42, and αS acted as seeds, and affected the aggregation pathways within and among species. The seeding effects of αS fibrils were higher than those of Aβ40 and Aβ42 fibrils in the Aβ40 and Aβ42 aggregation pathways, respectively. We showed that Aβ and αS acted as seeds and affected each other's aggregation pathways in vitro, which may contribute to our understanding of the molecular mechanisms of interactions between Alzheimer's disease and LB diseases pathologies.

α-Synuclein modifies huntingtin aggregation in living cells

Several neurodegenerative disorders are characterized by the accumulation of proteinaceous inclusions in the central nervous system. These inclusions are frequently composed of a mixture of aggregation-prone proteins. Here, we used a bimolecular fluorescence complementation assay to study the initial steps of the co-aggregation of huntingtin (Htt) and α-synuclein (α-syn), two aggregation-prone proteins involved in Huntington's disease (HD) and Parkinson's disease (PD), respectively. We found that Htt (exon 1) oligomerized with α-syn and sequestered it in the cytosol. In turn, α-syn increased the number of cells displaying aggregates, decreased the number of aggregates per cell and increased the average size of the aggregates. Our results support the idea that co-aggregation of aggregation-prone proteins can contribute to the histopathology of neurodegenerative disorders.

Α-synuclein misfolding and Parkinson's disease

Substantial evidence links α-synuclein, a small highly conserved presynaptic protein with unknown function, to both familial and sporadic Parkinson's disease (PD). α-Synuclein has been identified as the major component of Lewy bodies and Lewy neurites, the characteristic proteinaceous deposits that are the hallmarks of PD. α-Synuclein is a typical intrinsically disordered protein, but can adopt a number of different conformational states depending on conditions and cofactors. These include the helical membrane-bound form, a partially-folded state that is a key intermediate in aggregation and fibrillation, various oligomeric species, and fibrillar and amorphous aggregates. The molecular basis of PD appears to be tightly coupled to the aggregation of α-synuclein and the factors that affect its conformation. This review examines the different aggregation states of α-synuclein, the molecular mechanism of its aggregation, and the influence of environmental and genetic factors on this process.

Profiling of hypothalamic and hippocampal gene expression in chronically stressed rats treated with St. John's wort extract (STW 3-VI) and fluoxetine

RATIONALE

Hypericum perforatum L., known as St. John's wort (SJW), is used as a phytotherapeutic agent for the treatment of mild to moderate forms of depression.

OBJECTIVES

The aim of the present study was to evaluate the effect of SJW extract (STW 3-VI; 250 and 500 mg/kg; p.o.) and fluoxetine (10 mg/kg, p.o.) on genes involved in the pathogenesis of depression using a chronic restraint stress (CRS) model in rats. Of particular interest was the assessment of similarities and differences between SJW extract and fluoxetine on the gene expression level in two different brain regions.

RESULTS

Hypothalamic and hippocampal tissues were analyzed using the Affymetrix gene chip Rat Genome 230 2.0 Array, which comprises more than 30,000 rat transcripts. Limma program and PANTHER database were used to evaluate the microarray data. Genes involved in the pathways of inflammatory processes (Mapk8), oxidative stress (Gpx3, Gstm3, Sod3) or Alzheimer's disease (Sncb, Apbb1ip) were altered by both fluoxetine and SJW extract. For all groups, several signaling pathways were identified which could provide a link between the various hypotheses of depression.

CONCLUSION

In conclusion, microarray analysis proved to be a valuable tool to identify a large number of genes and resulting pathways that may serve as novel drug targets or predict drug responsiveness for SJW or fluoxetine. Based on our comprehensive analysis, it was possible to identify similarities and differences between SJW and fluoxetine which may help to better understand their molecular action and, in addition, help to find novel treatment strategies for stress-related depression.

A novel mechanism of non-Aβ component of Alzheimer's disease amyloid (NAC) neurotoxicity. Interplay between p53 protein and cyclin-dependent kinase 5 (Cdk5)

The non-Aβ component of Alzheimer's disease (AD) amyloid (NAC) is produced from the precursor protein NACP/α-synuclein (ASN) by till now unknown mechanism. Previous study showed that like ASN, NAC peptide induced oxidative/nitrosative stress and apoptosis. Our present study focused on the mechanisms of PC12 cells death evoked by NAC peptide, with particular consideration on the role of p53 protein. On the basis of molecular and transmission electron microscopic (TEM) analysis it was found that exogenous NAC peptide (10 μM) caused mitochondria dysfunction, enhanced free radical generation, and induced both apoptotic and autophagic cell death. Morphological and immunocytochemical evidence from TEM showed marked changes in expression and in translocation of proapoptotic protein Bax. We also observed time-dependent enhancement of Tp53 gene expression after NAC treatment. Free radicals scavenger N-tert-butyl-alpha-phenylnitrone (PBN, 1 mM) and p53 inhibitor (α-Pifithrin, 20 μM) significantly protected PC12 cells against NAC peptide-evoked cell death. In addition, exposure to NAC peptide resulted in higher expression of cyclin-dependent kinase 5 (Cdk5), one of the enzymes responsible for p53 phosphorylation and activation. Concomitantly, we observed the increase of expression of Cdk5r1 and Cdk5r2 genes, coding p35 and p39 peptides that are essential regulators of Cdk5 activity. Moreover, the specific Cdk5 inhibitor (BML-259, 10 μM) protected large population of cells against NAC-evoked cell death. Our findings indicate that NAC peptide exerts its toxic effect by activation of p53/Cdk5 and Bax-dependent apoptotic signaling pathway.

Familial associations of Alzheimer disease and essential tremor with Parkinson disease

BACKGROUND

We constructed a cohort of first-degree relatives of participants in a population-based case-control study of Parkinson disease (PD) and compared the occurrence of Alzheimer disease (AD) and essential tremor (ET) in relatives of PD cases and controls.

METHODS

We relied on proband interviews to assess family history in 372 probands with incident PD confirmed by a movement disorder specialist and 404 controls from three rural California counties.

RESULTS

Overall, for the 2980 first-degree relatives of PD cases, the risk of AD was not increased compared with the 2981 relatives of controls. But relatives of younger onset PD cases (<or=60 years of age) were three times more likely to have received an AD diagnosis [hazard ratios (HR): 2.86; 95%CI: 1.44, 5.71]. Our data also suggest that some relatives of PD probands might be at a slightly increased risk of receiving an ET diagnosis, especially relatives of tremor dominant cases (HR: 1.69; 95%CI 0.99, 2.88), younger onset cases (HR: 2.03; 95%CI 0.93, 4.44), and male relatives (HR: 2.31; 95%CI 1.13, 4.73). In addition, fathers of cases were almost 15 years younger than fathers of controls when diagnosed with ET. Results were stable in sensitivity analyses.

CONCLUSION

Our study suggests a familial susceptibility to AD amongst first-degree relatives of younger onset PD cases.

Oxidants induce alternative splicing of alpha-synuclein: Implications for Parkinson's disease

alpha-Synuclein (alpha-syn) is a presynaptic protein that is widely implicated in the pathophysiology of Parkinson's disease (PD). Emerging evidence indicates a strong correlation between alpha-syn aggregation and proteasomal dysfunction as one of the major pathways responsible for destruction of the dopamine neurons. Using parkinsonism mimetics (MPP(+), rotenone) and related oxidants, we have identified an oxidant-induced alternative splicing of alpha-syn mRNA, generating a shorter isoform of alpha-syn with deleted exon-5 (112-syn). This spliced isoform has an altered localization and profoundly inhibits proteasomal function. The generation of 112-syn was suppressed by constitutively active MEK-1 and enhanced by inhibition of the Erk-MAP kinase pathway. Overexpression of 112-syn exacerbated cell death in a human dopaminergic cell line compared to full-length protein. Expression of 112-syn and proteasomal dysfunction were also evident in the substantia nigra and to a lesser extent in striatum, but not in the cortex of MPTP-treated mice. We conclude that oxidant-induced alternative splicing of alpha-syn plays a crucial role in the mechanism of dopamine neuron cell death and thus contributes to PD.

Role of synucleins in Alzheimer's disease

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common causes of dementia and movement disorders in the elderly. While progressive accumulation of oligomeric amyloid-beta protein (Abeta) has been identified as one of the central toxic events in AD leading to synaptic dysfunction, accumulation of alpha-synuclein (alpha-syn) resulting in the formation of oligomers has been linked to PD. Most of the studies in AD have been focused on investigating the role of Abeta and Tau; however, recent studies suggest that alpha-syn might also play a role in the pathogenesis of AD. For example, fragments of alpha-syn can associate with amyloid plaques and Abeta promotes the aggregation of alpha-syn in vivo and worsens the deficits in alpha-syn tg mice. Moreover, alpha-syn has also been shown to accumulate in limbic regions in AD, Down's syndrome, and familial AD cases. Abeta and alpha-syn might directly interact under pathological conditions leading to the formation of toxic oligomers and nanopores that increase intracellular calcium. The interactions between Abeta and alpha-syn might also result in oxidative stress, lysosomal leakage, and mitochondrial dysfunction. Thus, better understanding the steps involved in the process of Abeta and alpha-syn aggregation is important in order to develop intervention strategies that might prevent or reverse the accumulation of toxic proteins in AD.

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.

Aberrant expression and demethylation of gamma-synuclein in colorectal cancer, correlated with progression of the disease

Recent evidence suggests that gamma-synuclein is abnormally expressed in a high percentage of tumor tissues of diversified cancer types, but rarely expressed in tumor-matched non-neoplastic adjacent tissues (NNAT). The molecular mechanism of CpG island demethylation may underlie aberrant gamma-synuclein expression. To fully understand the roles of aberrant gamma-synuclein expression and demethylation in the development of colorectal cancer (CRC), we examined the expression and methylation status of gamma-synuclein in 67 CRC samples, 30 NNAT samples, and five CRC cell lines as well. By using reverse transcription-polymerase chain reaction (RT-PCR), western blot, and immunohistochemistry analyses, gamma-synuclein expression was detected in both HT-29 and HCT116 cells, and was much higher in CRC samples than in NNAT samples (P < 0.05). The demethylating agent, 5-aza-2 cent-deoxycytidine, can induce re-expression of gamma-synuclein in COLO205, LoVo, and SW480 cells. Unmethylated gamma-synuclein alleles were detected in HT-29, HCT116, and LoVo cells by nested methylation-specific PCR, and the demethylated status of gamma-synuclein was much higher in CRC samples than in NNAT samples by real-time quantitative methylation-specific PCR (P < 0.05). The results of genomic bisulfite DNA sequencing further confirmed that the aberrant gamma-synuclein expression in CRC was primarily attributed to the demethylation of CpG island. The protein expression and demethylation status of gamma-synuclein in 67 CRC samples correlated with clinical stage, lymph node involvement, and distant metastasis. These findings suggest an involvement of aberrant gamma-synuclein expression and demethylation in progression of CRC, especially in advanced stages.

Mechanisms of hybrid oligomer formation in the pathogenesis of combined Alzheimer's and Parkinson's diseases

Background

Misfolding and pathological aggregation of neuronal proteins has been proposed to play a critical role in the pathogenesis of neurodegenerative disorders. Alzheimer's disease (AD) and Parkinson's disease (PD) are frequent neurodegenerative diseases of the aging population. While progressive accumulation of amyloid β protein (Aβ) oligomers has been identified as one of the central toxic events in AD, accumulation of α-synuclein (α-syn) resulting in the formation of oligomers and protofibrils has been linked to PD and Lewy body Disease (LBD). We have recently shown that Aβ promotes α-syn aggregation and toxic conversion in vivo, suggesting that abnormal interactions between misfolded proteins might contribute to disease pathogenesis. However the molecular characteristics and consequences of these interactions are not completely clear.

Methodology/Principal Findings

In order to understand the molecular mechanisms involved in potential Aβ/α-syn interactions, immunoblot, molecular modeling, and in vitro studies with α-syn and Aβ were performed. We showed in vivo in the brains of patients with AD/PD and in transgenic mice, Aβ and α-synuclein co-immunoprecipitate and form complexes. Molecular modeling and simulations showed that Aβ binds α-syn monomers, homodimers, and trimers, forming hybrid ring-like pentamers. Interactions occurred between the N-terminus of Aβ and the N-terminus and C-terminus of α-syn. Interacting α-syn and Aβ dimers that dock on the membrane incorporated additional α-syn molecules, leading to the formation of more stable pentamers and hexamers that adopt a ring-like structure. Consistent with the simulations, under in vitro cell-free conditions, Aβ interacted with α-syn, forming hybrid pore-like oligomers. Moreover, cells expressing α-syn and treated with Aβ displayed increased current amplitudes and calcium influx consistent with the formation of cation channels.

Conclusion/Significance

These results support the contention that Aβ directly interacts with α-syn and stabilized the formation of hybrid nanopores that alter neuronal activity and might contribute to the mechanisms of neurodegeneration in AD and PD. The broader implications of such hybrid interactions might be important to the pathogenesis of other disorders of protein misfolding.

alpha-Synuclein enhances secretion and toxicity of amyloid beta peptides in PC12 cells

alpha-Synuclein is the fundamental component of Lewy bodies which occur in the brain of 60% of sporadic and familial Alzheimer's disease patients. Moreover, a proteolytic fragment of alpha-synuclein, the so-called non-amyloid component of Alzheimer's disease amyloid, was found to be an integral part of Alzheimer's dementia related plaques. However, the role of alpha-synuclein in pathomechanism of Alzheimer's disease remains elusive. In particular, the relationship between alpha-synuclein and amyloid beta is unknown. In the present study we showed the involvement of alpha-synuclein in amyloid beta secretion and in the mechanism of amyloid beta evoked mitochondria dysfunction and cell death. Rat pheochromocytoma PC12 cells transfected with amyloid beta precursor protein bearing Swedish double mutation (APPsw) and control PC12 cells transfected with empty vector were used in this study. alpha-Synuclein (10microM) was found to increase by twofold amyloid beta secretion from control and APPsw PC12 cells. Moreover, alpha-synuclein decreased the viability of PC12 cells by about 50% and potentiated amyloid beta toxicity leading to mitochondrial dysfunction and caspase-dependent programmed cell death. Inhibitor of caspase-3 (Z-DEVD-FMK, 100microM), and a mitochondrial permeability transition pore blocker, cyclosporine A (2microM) protected PC12 cells against alpha-synuclein or amyloid beta evoked cell death. In contrast Z-DEVD-FMK and cyclosporine A were ineffective in APPsw cells containing elevated amount of amyloid beta treated with alpha-synuclein. It was found that the inhibition of neuronal and inducible nitric oxide synthase reversed the toxic effect of alpha-synuclein in control but not in APPsw cells. Our results indicate that alpha-synuclein enhances the release and toxicity of amyloid beta leading to nitric oxide mediated irreversible mitochondria dysfunction and caspase-dependent programmed cell death.

RNA interference mediated silencing of alpha-synuclein in MN9D cells and its effects on cell viability

OBJECTIVE

To silence the expression of alpha-synuclein in MN9D dopaminergic cells using vector mediated RNA interference (RNAi) and examined its effects on cell proliferation and viability.

METHODS

We identified two 19-nucleotide stretches within the coding region of the alpha-synuclein gene and designed three sets of oligonucleotides to generate double-stranded (ds) oligos. The ds oligos were inserted into the pENTR/H1/TO vector and transfected into MN9D dopaminergic cells. alpha-Synuclein expression was detected by RT-PCR, real-time PCR, immunocytochemistry staining and Western blot. In addition, we measured cell proliferation using growth curves and cell viability by 3-(4, 5)-dimethylthiahiazo (-z-y1)-3, 5-di- phenytetrazoliumromide (MTT).

RESULTS

The mRNA and protein levels of alpha-synuclein gene were significantly down-regulated in pSH2/alpha-SYN-transfected cells compared with control MN9D and pSH/CON-transfected MN9D cells, while pSH1/alpha-SYN-transfected cells showed no significant difference. Silencing alpha-synuclein expression does not affect cell proliferation but may decrease cell viability.

CONCLUSION

Our results demonstrated pSH2/alpha-SYN is an effective small interfering RNA (siRNA) sequence and potent silencing of mouse alpha-synuclein expression in MN9D cells by vector-based RNAi, which provides the tools for studying the normal function of alpha-synuclein and examining its role in Parkinson's disease (PD) pathogenesis. alpha-Synuclein may be important for the viability of MN9D cells, and loss of alpha-synuclein may induce cell injury directly or indirectly.