Clinical and biochemical correlates of insoluble alpha-synuclein in dementia with Lewy bodies

Mutant mice with rod-specific VPS35 deletion exhibit retinal α-synuclein pathology-associated degeneration

Vacuolar protein sorting 35 (VPS35), the core component of the retromer complex which regulates endosomal trafficking, is genetically linked with Parkinson's disease (PD). Impaired vision is a common non-motor manifestation of PD. Here, we show mouse retinas with VPS35-deficient rods exhibit synapse loss and visual deficit, followed by progressive degeneration concomitant with the emergence of Lewy body-like inclusions and phospho-α-synuclein (P-αSyn) aggregation. Ultrastructural analyses reveal VPS35-deficient rods accumulate aggregates in late endosomes, deposited as lipofuscins bound to P-αSyn. Mechanistically, we uncover a protein network of VPS35 and its interaction with HSC70. VPS35 deficiency promotes sequestration of HSC70 and P-αSyn aggregation in late endosomes. Microglia which engulf lipofuscins and P-αSyn aggregates are activated, displaying autofluorescence, observed as bright dots in fundus imaging of live animals, coinciding with pathology onset and progression. The Rod∆Vps35 mouse line is a valuable tool for further mechanistic investigation of αSyn lesions and retinal degenerative diseases.

CRISPR-Cas9-Based Technology and Its Relevance to Gene Editing in Parkinson's Disease

Parkinson’s disease (PD) and other chronic and debilitating neurodegenerative diseases (NDs) impose a substantial medical, emotional, and financial burden on individuals and society. The origin of PD is unknown due to a complex combination of hereditary and environmental risk factors. However, over the last several decades, a significant amount of available data from clinical and experimental studies has implicated neuroinflammation, oxidative stress, dysregulated protein degradation, and mitochondrial dysfunction as the primary causes of PD neurodegeneration. The new gene-editing techniques hold great promise for research and therapy of NDs, such as PD, for which there are currently no effective disease-modifying treatments. As a result, gene therapy may offer new treatment options, transforming our ability to treat this disease. We present a detailed overview of novel gene-editing delivery vehicles, which is essential for their successful implementation in both cutting-edge research and prospective therapeutics. Moreover, we review the most recent advancements in CRISPR-based applications and gene therapies for a better understanding of treating PD. We explore the benefits and drawbacks of using them for a range of gene-editing applications in the brain, emphasizing some fascinating possibilities.

Multi-platform quantitation of alpha-synuclein human brain proteoforms suggests disease-specific biochemical profiles of synucleinopathies

Based on immunostainings and biochemical analyses, certain post-translationally modified alpha-synuclein (aSyn) variants, including C-terminally truncated (CTT) and Serine-129 phosphorylated (pSer129) aSyn, are proposed to be involved in the pathogenesis of synucleinopathies such as Parkinson’s disease with (PDD) and without dementia (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). However, quantitative information about aSyn proteoforms in the human brain in physiological and different pathological conditions is still limited. To address this, we generated sequential biochemical extracts of the substantia nigra, putamen and hippocampus from 28 donors diagnosed and neuropathologically-confirmed with different synucleinopathies (PD/PDD/DLB/MSA), as well as Alzheimer’s disease, progressive supranuclear palsy, and aged normal subjects. The tissue extracts were used to build a reverse phase array including 65 aSyn antibodies for detection. In this multiplex approach, we observed increased immunoreactivity in donors with synucleinopathies compared to controls in detergent-insoluble fractions, mainly for antibodies against CT aSyn and pSer129 aSyn. In addition, despite of the restricted sample size, clustering analysis suggested disease-specific immunoreactivity signatures in patient groups with different synucleinopathies. We aimed to validate and quantify these findings using newly developed immunoassays towards total, 119 and 122 CTT, and pSer129 aSyn. In line with previous studies, we found that synucleinopathies shared an enrichment of post-translationally modified aSyn in detergent-insoluble fractions compared to the other analyzed groups. Our measurements allowed for a quantitative separation of PDD/DLB patients from other synucleinopathies based on higher detergent-insoluble pSer129 aSyn concentrations in the hippocampus. In addition, we found that MSA stood out due to enrichment of CTT and pSer129 aSyn also in the detergent-soluble fraction of the SN and putamen. Together, our results achieved by multiplexed and quantitative immunoassay-based approaches in human brain extracts of a limited sample set point to disease-specific biochemical aSyn proteoform profiles in distinct neurodegenerative disorders.

Clinical Manifestations and Molecular Backgrounds of Parkinson's Disease Regarding Genes Identified From Familial and Population Studies

Over the past 20 years, numerous robust analyses have identified over 20 genes related to familial Parkinson's disease (PD), thereby uncovering its molecular underpinnings and giving rise to more sophisticated approaches to investigate its pathogenesis. α-Synuclein is a major component of Lewy bodies (LBs) and behaves in a prion-like manner. The discovery of α-Synuclein enables an in-depth understanding of the pathology behind the generation of LBs and dopaminergic neuronal loss. Understanding the pathophysiological roles of genes identified from PD families is uncovering the molecular mechanisms, such as defects in dopamine biosynthesis and metabolism, excessive oxidative stress, dysfunction of mitochondrial maintenance, and abnormalities in the autophagy–lysosome pathway, involved in PD pathogenesis. This review summarizes the current knowledge on familial PD genes detected by both single-gene analyses obeying the Mendelian inheritance and meta-analyses of genome-wide association studies (GWAS) from genome libraries of PD. Studying the functional role of these genes might potentially elucidate the pathological mechanisms underlying familial PD and sporadic PD and stimulate future investigations to decipher the common pathways between the diseases.

α-Synuclein-mediated neurodegeneration in Dementia with Lewy bodies: the pathobiology of a paradox

Dementia with Lewy bodies (DLB) is epitomized by the pathognomonic manifestation of α-synuclein-laden Lewy bodies within selectively vulnerable neurons in the brain. By virtue of prion-like inheritance, the α-synuclein protein inexorably undergoes extensive conformational metamorphoses and culminate in the form of fibrillar polymorphs, instigating calamitous damage to the brain's neuropsychological networks. This epiphenomenon is nebulous, however, by lingering uncertainty over the quasi "pathogenic" behavior of α-synuclein conformers in DLB pathobiology. Despite numerous attempts, a monolithic "α-synuclein" paradigm that is able to untangle the enigma enshrouding the clinicopathological spectrum of DLB has failed to emanate. In this article, we review conceptual frameworks of α-synuclein dependent cell-autonomous and non-autonomous mechanisms that are likely to facilitate the transneuronal spread of degeneration through the neuraxis. In particular, we describe how the progressive demise of susceptible neurons may evolve from cellular derangements perpetrated by α-synuclein misfolding and aggregation. Where pertinent, we show how these bona fide mechanisms may mutually accentuate α-synuclein-mediated neurodegeneration in the DLB brain.

CK1BP Reduces α-Synuclein Oligomerization and Aggregation Independent of Serine 129 Phosphorylation

The pathological accumulation of α-Synuclein (α-Syn) is the hallmark of neurodegenerative α-synucleinopathies, including Parkinsons's disease (PD). In contrast to the mostly non-phosphorylated soluble α-Syn, aggregated α-Syn is usually phosphorylated at serine 129 (S129). Therefore, S129-phosphorylation is suspected to interfere with α-Syn aggregation. Among other kinases, protein kinase CK1 (CK1) is known to phosphorylate α-Syn at S129. We overexpressed CK1 binding protein (CK1BP) to inhibit CK1 kinase activity. Using Bimolecular Fluorescence Complementation (BiFC) in combination with biochemical methods, we monitored the S129 phosphorylation and oligomerization of α-Syn in HEK293T cells. We found that CK1BP reduced the overall protein levels of α-Syn. Moreover, CK1BP concomitantly reduced S129 phosphorylation, oligomerization and the amount of insoluble α-Syn. Analyzing different α-Syn variants including S129 mutations, we show that the effects of CK1BP on α-Syn accumulation were independent of S129 phosphorylation. Further analysis of an aggregating polyglutamine (polyQ) protein confirmed a phosphorylation-independent decrease in aggregation. Our results imply that the inhibition of CK1 activity by CK1BP might exert beneficial effects on NDDs in general. Accordingly, CK1BP represents a promising target for the rational design of therapeutic approaches to cease or at least delay the progression of α-synucleinopathies.

A β-Wrapin Targeting the N-Terminus of α-Synuclein Monomers Reduces Fibril-Induced Aggregation in Neurons

Reducing α-synuclein pathology constitutes a plausible strategy against Parkinson’s disease. As we recently demonstrated, the β-wrapin protein AS69 binds an N-terminal region in monomeric α-synuclein, interferes with fibril nucleation, and reduces α-synuclein aggregation in vitro and in a fruit fly model of α-synuclein toxicity. The aim of this study was to investigate whether AS69 also reduces α-synuclein pathology in mammalian neurons. To induce α-synuclein pathology, primary mouse neurons were exposed to pre-formed fibrils (PFF) of human α-synuclein. PFF were also injected into the striatum of A30P-α-synuclein transgenic mice. The extent of α-synuclein pathology was determined by phospho-α-synuclein staining and by Triton X-100 solubility. The degeneration of neuronal somata, dendrites, and axon terminals was determined by immunohistochemistry. AS69 and PFF were taken up by primary neurons. AS69 did not alter PFF uptake, but AS69 did reduce PFF-induced α-synuclein pathology. PFF injection into mouse striatum led to α-synuclein pathology and dystrophic neurites. Co-injection of AS69 abrogated PFF-induced pathology. AS69 also reduced the PFF-induced degeneration of dopaminergic axon terminals in the striatum and the degeneration of dopaminergic dendrites in the substantia nigra pars reticulata. AS69 reduced the activation of astroglia but not microglia in response to PFF injection. Collectively, AS69 reduced PFF-induced α-synuclein pathology and the associated neurodegeneration in primary neurons and in mouse brain. Our data therefore suggest that small proteins binding the N-terminus of α-synuclein monomers are promising strategies to modify disease progression in Parkinson’s disease.

Isoform-specific upregulation of FynT kinase expression is associated with tauopathy and glial activation in Alzheimer's disease and Lewy body dementias

Cumulative data suggest the involvement of Fyn tyrosine kinase in Alzheimer's disease (AD). Previously, our group has shown increased immunoreactivities of the FynT isoform in AD neocortex (with no change in the alternatively spliced FynB isoform) which associated with neurofibrillary degeneration and reactive astrogliosis. Since both the aforementioned neuropathological features are also variably found in Lewy Body dementias (LBD), we investigated potential perturbations of Fyn expression in the post-mortem neocortex of patients with AD, as well as those diagnosed as having one of the two main subgroups of LBD: Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB). We found selective upregulation of FynT expression in AD, PDD, and DLB which also correlated with cognitive impairment. Furthermore, increased FynT expression correlated with hallmark neuropathological lesions, soluble β-amyloid, and phosphorylated tau, as well as markers of microglia and astrocyte activation. In line with the human post-mortem studies, cortical FynT expression in aged mice transgenic for human P301S tau was upregulated and further correlated with accumulation of aggregated phosphorylated tau as well as with microglial and astrocytic markers. Our findings provide further evidence for the involvement of FynT in neurodegenerative dementias, likely via effects on tauopathy and neuroinflammation.

Analysis of α-synuclein species enriched from cerebral cortex of humans with sporadic dementia with Lewy bodies

Since researchers identified α-synuclein as the principal component of Lewy bodies and Lewy neurites, studies have suggested that it plays a causative role in the pathogenesis of dementia with Lewy bodies and other ‘synucleinopathies’. While α-synuclein dyshomeostasis likely contributes to the neurodegeneration associated with the synucleinopathies, few direct biochemical analyses of α-synuclein from diseased human brain tissue currently exist. In this study, we analysed sequential protein extracts from a substantial number of patients with neuropathological diagnoses of dementia with Lewy bodies and corresponding controls, detecting a shift of cytosolic and membrane-bound physiological α-synuclein to highly aggregated forms. We then fractionated aqueous extracts (cytosol) from cerebral cortex using non-denaturing methods to search for soluble, disease-associated high molecular weight species potentially associated with toxicity. We applied these fractions and corresponding insoluble fractions containing Lewy-type aggregates to several reporter assays to determine their bioactivity and cytotoxicity. Ultimately, high molecular weight cytosolic fractions enhances phospholipid membrane permeability, while insoluble, Lewy-associated fractions induced morphological changes in the neurites of human stem cell-derived neurons. While the concentrations of soluble, high molecular weight α-synuclein were only slightly elevated in brains of dementia with Lewy bodies patients compared to healthy, age-matched controls, these observations suggest that a small subset of soluble α-synuclein aggregates in the brain may drive early pathogenic effects, while Lewy body-associated α-synuclein can drive neurotoxicity.

Dihydromyricetin and Salvianolic acid B inhibit alpha-synuclein aggregation and enhance chaperone-mediated autophagy

BACKGROUND

Progressive accumulation of α-synuclein is a key step in the pathological development of Parkinson's disease. Impaired protein degradation and increased levels of α-synuclein may trigger a pathological aggregation in vitro and in vivo. The chaperone-mediated autophagy (CMA) pathway is involved in the intracellular degradation processes of α-synuclein. Dysfunction of the CMA pathway impairs α-synuclein degradation and causes cytotoxicity.

RESULTS

In the present study, we investigated the effects on the CMA pathway and α-synuclein aggregation using bioactive ingredients (Dihydromyricetin (DHM) and Salvianolic acid B (Sal B)) extracted from natural medicinal plants. In both cell-free and cellular models of α-synuclein aggregation, after administration of DHM and Sal B, we observed significant inhibition of α-synuclein accumulation and aggregation. Cells were co-transfected with a C-terminal modified α-synuclein (SynT) and synphilin-1, and then treated with DHM (10 μM) and Sal B (50 μM) 16 hours after transfection; levels of α-synuclein aggregation decreased significantly (68% for DHM and 75% for Sal B). Concomitantly, we detected increased levels of LAMP-1 (a marker of lysosomal homeostasis) and LAMP-2A (a key marker of CMA). Immunofluorescence analyses showed increased colocalization between LAMP-1 and LAMP-2A with α-synuclein inclusions after treatment with DHM and Sal B. We also found increased levels of LAMP-1 and LAMP-2A both in vitro and in vivo, along with decreased levels of α-synuclein. Moreover, DHM and Sal B treatments exhibited anti-inflammatory activities, preventing astroglia- and microglia-mediated neuroinflammation in BAC-α-syn-GFP transgenic mice.

CONCLUSIONS

Our data indicate that DHM and Sal B are effective in modulating α-synuclein accumulation and aggregate formation and augmenting activation of CMA, holding potential for the treatment of Parkinson's disease.

Heterogeneity in α-synuclein subtypes and their expression in cortical brain tissue lysates from Lewy body diseases and Alzheimer's disease

AIMS

Lewy body diseases are neuropathologically characterized by the abnormal accumulation of α-synuclein (α-syn) protein within vulnerable neurons. Although studies have evaluated α-syn in post mortem brain tissue, previous findings have been limited by typically employing pan-α-syn antibodies that may not recognize disease-relevant forms of protein. We investigated the presence of α-syn species present in post mortem brain tissues from Lewy body disease and Alzheimer's disease.

METHODS

Soluble and insoluble/aggregated α-syn from frontal cortex of post mortem brain tissues form Parkinson's disease (PD), dementia with Lewy bodies (DLB), Alzheimer's disease (AD) and aged control cases were sequentially extracted using buffers with increasing detergent concentrations. Enzyme-linked immunosorbent assay (ELISA) was used to quantify the levels of total-, oligomeric- and phosphorylated-Ser129-α-syn (t-, o- and pS129-α-syn). ELISA data were validated by western blot and compared to histological data from the same region of the contralateral hemisphere.

RESULTS

There was no difference in t-α-syn levels between groups in the aqueous-soluble, detergent-soluble or urea-soluble tissue fractions. However, aqueous-soluble non-phosphorylated o-α-syn was increased not only in PD and DLB but also in AD without neocortical Lewy bodies. In PD and AD, pS129-α-syn was increased in the detergent-soluble tissue fragment and, in AD, this was positively correlated with the burden of tau pathology. Increased levels of urea-soluble pS129-α-syn were demonstrated only in DLB tissue lysates but this did not correlate with Lewy body pathological burden.

CONCLUSIONS

Taken together, these findings suggest that DLB have elevated levels of insoluble pS129-α-syn, but that increased levels of aqueous-soluble o-α-syn and detergent-soluble pS129-α-syn are also observed in PD and AD, suggesting different changes to α-syn across the spectrum of neurodegenerative proteopathies.

Exogenous α-synuclein hinders synaptic communication in cultured cortical primary rat neurons

Amyloid aggregates of the protein α-synuclein (αS) called Lewy Bodies (LB) and Lewy Neurites (LN) are the pathological hallmark of Parkinson's disease (PD) and other synucleinopathies. We have previously shown that high extracellular αS concentrations can be toxic to cells and that neurons take up αS. Here we aimed to get more insight into the toxicity mechanism associated with high extracellular αS concentrations (50-100 μM). High extracellular αS concentrations resulted in a reduction of the firing rate of the neuronal network by disrupting synaptic transmission, while the neuronal ability to fire action potentials was still intact. Furthermore, many cells developed αS deposits larger than 500 nm within five days, but otherwise appeared healthy. Synaptic dysfunction clearly occurred before the establishment of large intracellular deposits and neuronal death, suggesting that an excessive extracellular αS concentration caused synaptic failure and which later possibly contributed to neuronal death.

Aptamers Selected for Recognizing Amyloid β-Protein-A Case for Cautious Optimism

Aptamers are versatile oligonucleotide ligands used for molecular recognition of diverse targets. However, application of aptamers to the field of amyloid β-protein (Aβ) has been limited so far. Aβ is an intrinsically disordered protein that exists in a dynamic conformational equilibrium, presenting time-dependent ensembles of short-lived, metastable structures and assemblies that have been generally difficult to isolate and characterize. Moreover, despite understanding of potential physiological roles of Aβ, this peptide has been linked to the pathogenesis of Alzheimer disease, and its pathogenic roles remain controversial. Accumulated scientific evidence thus far highlights undesirable or nonspecific interactions between selected aptamers and different Aβ assemblies likely due to the metastable nature of Aβ or inherent affinity of RNA oligonucleotides to β-sheet-rich fibrillar structures of amyloidogenic proteins. Accordingly, lessons drawn from Aβ–aptamer studies emphasize that purity and uniformity of the protein target and rigorous characterization of aptamers’ specificity are important for realizing and garnering the full potential of aptamers selected for recognizing Aβ or other intrinsically disordered proteins. This review summarizes studies of aptamers selected for recognizing different Aβ assemblies and highlights controversies, difficulties, and limitations of such studies.

Increased Transforming Growth Factor β2 in the Neocortex of Alzheimer's Disease and Dementia with Lewy Bodies is Correlated with Disease Severity and Soluble Aβ42 Load

BACKGROUND

Of the three transforming growth factor (TGF)-β isoforms known, TGFβ1 deficits have been widely reported in Alzheimer's disease (AD) and studied as a potential therapeutic target. In contrast, the status of TGFβ2, which has been shown to mediate amyloid-β (Aβ)-mediated neuronal death, are unclear both in AD and in Lewy body dementias (LBD) with differential neuritic plaque and neurofibrillary tangle burden.

OBJECTIVE

To measure neocortical TGFβ2 levels and their correlations with neuropathological and clinical markers of disease severity in a well-characterized cohort of AD as well as two clinical subtypes of LBD, dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD), known to manifest relatively high and low Aβ plaque burden, respectively.

METHODS

Postmortem samples from temporal cortex (BA21) were measured for TGFβ2 using a Luminex-based platform, and correlated with scores for neuritic plaques, neurofibrillary tangles, α-synuclein pathology, dementia severity (as measured by annual decline of Mini-Mental State Examination scores) as well as soluble and total fractions of brain Aβ42.

RESULTS

TGFβ2 was significantly increased in AD and DLB, but not in PDD. TGFβ2 also correlated with scores for neurofibrillary tangles, Lewy bodies (within the LBD group), dementia severity, and soluble Aβ42 concentration, but not with neuritic plaque scores, total Aβ42, or monomeric α-synuclein immunoreactivity.

CONCLUSIONS

TGFβ2 is increased in the temporal cortex of AD and DLB, and its correlations with neuropathological and clinical markers of disease severity as well as with soluble Aβ42 load suggest a potential pathogenic role in mediating the neurotoxicity of non-fibrillar Aβ. Our study also indicates the potential utility of targeting TGFβ2 in pharmacotherapeutic approaches to AD and DLB.

Autophagy inhibition promotes SNCA/alpha-synuclein release and transfer via extracellular vesicles with a hybrid autophagosome-exosome-like phenotype

The autophagy-lysosome pathway (ALP) regulates intracellular homeostasis of the cytosolic protein SNCA/alpha-synuclein and is impaired in synucleinopathies, including Parkinson disease and dementia with Lewy bodies (DLB). Emerging evidence suggests that ALP influences SNCA release, but the underlying cellular mechanisms are not well understood. Several studies identified SNCA in exosome/extracellular vesicle (EV) fractions. EVs are generated in the multivesicular body compartment and either released upon its fusion with the plasma membrane, or cleared via the ALP. We therefore hypothesized that inhibiting ALP clearance 1) enhances SNCA release via EVs by increasing extracellular shuttling of multivesicular body contents, 2) alters EV biochemical profile, and 3) promotes SNCA cell-to-cell transfer. Indeed, ALP inhibition increased the ratio of extra- to intracellular SNCA and upregulated SNCA association with EVs in neuronal cells. Ultrastructural analysis revealed a widespread, fused multivesicular body-autophagosome compartment. Biochemical characterization revealed the presence of autophagosome-related proteins, such as LC3-II and SQSTM1. This distinct "autophagosome-exosome-like" profile was also identified in human cerebrospinal fluid (CSF) EVs. After a single intracortical injection of SNCA-containing EVs derived from CSF into mice, human SNCA colocalized with endosome and neuronal markers. Prominent SNCA immunoreactivity and a higher number of neuronal SNCA inclusions were observed after DLB patient CSF EV injections. In summary, this study provides compelling evidence that a) ALP inhibition increases SNCA in neuronal EVs, b) distinct ALP components are present in EVs, and c) CSF EVs transfer SNCA from cell to cell in vivo. Thus, macroautophagy/autophagy may regulate EV protein composition and consequently progression in synucleinopathies.

Expanding role of molecular chaperones in regulating α-synuclein misfolding; implications in Parkinson's disease

Protein misfolding under stressful environmental conditions cause several cellular problems owing to the disturbed cellular protein homeostasis, which may further lead to neurological disorders like Parkinson's disease (PD), Alzheimer's disease (AD), Amyloid lateral sclerosis and Huntington disease (HD). The presence of cellular defense mechanisms like molecular chaperones and proteasomal degradation systems prevent protein misfolding and aggregation. Molecular chaperones plays primary role in preventing protein misfolding by mediating proper native folding, unfolding and refolding of the polypeptides along with vast number of cellular functions. In past few years, the understanding of molecular chaperone mechanisms has been expanded enormously although implementation to prevent protein aggregation diseases is still deficient. We in this review evaluated major classes of molecular chaperones and their mechanisms relevant for preventing protein aggregation, specific case of α-synuclein aggregation. We also evaluate the molecular chaperone function as a novel therapeutic approach and the chaperone inhibitors or activators as small molecular drug targets.

Gut Microbiota Regulate Motor Deficits and Neuroinflammation in a Model of Parkinson's Disease

The intestinal microbiota influence neurodevelopment, modulate behavior, and contribute to neurological disorders. However, a functional link between gut bacteria and neurodegenerative diseases remains unexplored. Synucleinopathies are characterized by aggregation of the protein α-synuclein (αSyn), often resulting in motor dysfunction as exemplified by Parkinson's disease (PD). Using mice that overexpress αSyn, we report herein that gut microbiota are required for motor deficits, microglia activation, and αSyn pathology. Antibiotic treatment ameliorates, while microbial re-colonization promotes, pathophysiology in adult animals, suggesting that postnatal signaling between the gut and the brain modulates disease. Indeed, oral administration of specific microbial metabolites to germ-free mice promotes neuroinflammation and motor symptoms. Remarkably, colonization of αSyn-overexpressing mice with microbiota from PD-affected patients enhances physical impairments compared to microbiota transplants from healthy human donors. These findings reveal that gut bacteria regulate movement disorders in mice and suggest that alterations in the human microbiome represent a risk factor for PD.

Chaperones in Neurodegeneration

Cellular protein homeostasis (proteostasis) maintains the integrity of the proteome and includes protein synthesis, folding, oligomerization, and turnover; chaperone proteins assist with all of these processes. Neurons appear to be especially susceptible to failures in proteostasis, and this is now increasingly recognized as a major origin of neurodegenerative disease. This review, based on a mini-symposium presented at the 2015 Society for Neuroscience meeting, describes new work in the area of neuronal proteostasis, with a specific focus on the roles and therapeutic uses of protein chaperones. We first present a brief review of protein misfolding and aggregation in neurodegenerative disease. We then discuss different aspects of chaperone control of neuronal proteostasis on topics ranging from chaperone engineering, to chaperone-mediated blockade of protein oligomerization and cytotoxicity, to the potential rescue of neurodegenerative processes using modified chaperone proteins.

SIGNIFICANCE STATEMENT

Aberrant protein homeostasis within neurons results in protein misfolding and aggregation. In this review, we discuss specific roles for protein chaperones in the oligomerization, assembly, and disaggregation of proteins known to be abnormally folded in neurodegenerative disease. Collectively, our goal is to identify therapeutic mechanisms to reduce the cellular toxicity of abnormal aggregates.

Autophagy modulates SNCA/α-synuclein release, thereby generating a hostile microenvironment

SNCA/α-synuclein aggregation plays a crucial role in synucleinopathies such as Parkinson disease and dementia with Lewy bodies. Aggregating and nonaggregating SNCA species are degraded by the autophagy-lysosomal pathway (ALP). Previously, we have shown that the ALP is not only responsible for SNCA degradation but is also involved in the intracellular aggregation process of SNCA. An additional role of extracellular SNCA in the pathology of synucleinopathies substantiating a prion-like propagation hypothesis has been suggested since released SNCA species and spreading of SNCA pathology throughout neural cells have been observed. However, the molecular interplay between intracellular pathways, SNCA aggregation, release, and response of the local microenvironment remains unknown. Here, we attributed SNCA-induced toxicity mainly to secreted species in a cell culture model of SNCA aggregation and in SNCA transgenic mice: We showed that ALP inhibition by bafilomycinA1 reduced intracellular SNCA aggregation but increased secretion of smaller oligomers that exacerbated microenvironmental response including uptake, inflammation, and cellular damage. Low-aggregated SNCA was predominantly released by exosomes and RAB11A-associated pathways whereas high-aggregated SNCA was secreted by membrane shedding. In summary, our study revealed a novel role of the ALP by linking protein degradation to nonclassical secretion for toxic SNCA species. Thus, impaired ALP in the diseased brain not only limits intracellular degradation of misfolded proteins, but also leads to a detrimental microenvironmental response due to enhanced SNCA secretion. These findings suggest that the major toxic role of SNCA is related to its extracellular species and further supports a protective role of intracellular SNCA aggregation.

Drosophila as an In Vivo Model for Human Neurodegenerative Disease

With the increase in the ageing population, neurodegenerative disease is devastating to families and poses a huge burden on society. The brain and spinal cord are extraordinarily complex: they consist of a highly organized network of neuronal and support cells that communicate in a highly specialized manner. One approach to tackling problems of such complexity is to address the scientific questions in simpler, yet analogous, systems. The fruit fly, Drosophila melanogaster, has been proven tremendously valuable as a model organism, enabling many major discoveries in neuroscientific disease research. The plethora of genetic tools available in Drosophila allows for exquisite targeted manipulation of the genome. Due to its relatively short lifespan, complex questions of brain function can be addressed more rapidly than in other model organisms, such as the mouse. Here we discuss features of the fly as a model for human neurodegenerative disease. There are many distinct fly models for a range of neurodegenerative diseases; we focus on select studies from models of polyglutamine disease and amyotrophic lateral sclerosis that illustrate the type and range of insights that can be gleaned. In discussion of these models, we underscore strengths of the fly in providing understanding into mechanisms and pathways, as a foundation for translational and therapeutic research.

Cyclosporine A and MnTMPyP Alleviate α-Synuclein Expression and Aggregation in Cypermethrin-Induced Parkinsonism

Cypermethrin induces the mitochondrial dysfunction and oxidative damage to the nigrostriatal dopaminergic neurons leading to Parkinsonism in rats. Despite α-synuclein aggregation is reported to be critical in Parkinson's disease, its role and alliance with the mitochondrial dysfunction and oxidative damage leading to cypermethrin-induced Parkinsonism have not yet been deciphered. The present study aimed to examine the effect of cypermethrin on the expression and aggregation of α-synuclein and its subsequent connection with oxidative damage and mitochondrial dysfunction leading to the nigrostriatal dopaminergic neurodegeneration in the presence or absence of a mitochondrial membrane transition pore opening inhibitor, cyclosporine A and a superoxide dismutase/catalase mimetic, manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin pentachloride (MnTMPyP). The expression of α-synuclein, 3-nitrotyrosine (3-NT), 4-hydroxynonenal (4-HNE)-modified proteins, mitochondrial dysfunction-dependent apoptotic proteins, nitrite content, lipid peroxidation (LPO) and number of tyrosine hydroxylase (TH)-positive neurons were estimated in the substantia nigra and dopamine content in the striatum of control and treated rats employing standard procedures. Cypermethrin augmented the expression of α-synuclein, 3-NT, 4-HNE-modified proteins, caspase-3, mitochondrial Bax and cytosolic cytochrome-c along with nitrite and LPO and reduced the expression of cytosolic Bax, mitochondrial cytochrome-c, dopamine and number of TH-positive neurons. Cyclosporine A or MnTMPyP alleviated the expression and aggregation of α-synuclein along with indicators of the mitochondrial dysfunction, oxidative damage and dopaminergic neurodegeneration. The results demonstrate that cypermethrin induces α-synuclein expression and aggregation while cyclosporine A or MnTMPyP rescues from α-synuclein over-expression and aggregation along with the mitochondrial dysfunction and oxidative damage leading to Parkinsonism in rats.

Molecular chaperones and protein folding as therapeutic targets in Parkinson's disease and other synucleinopathies

Changes in protein metabolism are key to disease onset and progression in many neurodegenerative diseases. As a prime example, in Parkinson's disease, folding, post-translational modification and recycling of the synaptic protein α-synuclein are clearly altered, leading to a progressive accumulation of pathogenic protein species and the formation of intracellular inclusion bodies. Altered protein folding is one of the first steps of an increasingly understood cascade in which α-synuclein forms complex oligomers and finally distinct protein aggregates, termed Lewy bodies and Lewy neurites. In neurons, an elaborated network of chaperone and co-chaperone proteins is instrumental in mediating protein folding and re-folding. In addition to their direct influence on client proteins, chaperones interact with protein degradation pathways such as the ubiquitin-proteasome-system or autophagy in order to ensure the effective removal of irreversibly misfolded and potentially pathogenic proteins. Because of the vital role of proper protein folding for protein homeostasis, a growing number of studies have evaluated the contribution of chaperone proteins to neurodegeneration. We herein review our current understanding of the involvement of chaperones, co-chaperones and chaperone-mediated autophagy in synucleinopathies with a focus on the Hsp90 and Hsp70 chaperone system. We discuss genetic and pathological studies in Parkinson's disease as well as experimental studies in models of synucleinopathies that explore molecular chaperones and protein degradation pathways as a novel therapeutic target. To this end, we examine the capacity of chaperones to prevent or modulate neurodegeneration and summarize the current progress in models of Parkinson's disease and related neurodegenerative disorders.

Monoclonal antibodies selective for α-synuclein oligomers/protofibrils recognize brain pathology in Lewy body disorders and α-synuclein transgenic mice with the disease-causing A30P mutation

Inclusions of intraneuronal alpha-synuclein (α-synuclein) can be detected in brains of patients with Parkinson's disease and dementia with Lewy bodies. The aggregation of α-synuclein is a central feature of the disease pathogenesis. Among the different α-synuclein species, large oligomers/protofibrils have particular neurotoxic properties and should therefore be suitable as both therapeutic and diagnostic targets. Two monoclonal antibodies, mAb38F and mAb38E2, with high affinity and strong selectivity for large α-synuclein oligomers were generated. These antibodies, which do not bind amyloid-beta or tau, recognize Lewy body pathology in brains from patients with Parkinson's disease and dementia with Lewy bodies and detect pathology earlier in α-synuclein transgenic mice than linear epitope antibodies. An oligomer-selective sandwich ELISA, based on mAb38F, was set up to analyze brain extracts of the transgenic mice. The overall levels of α-synuclein oligomers/protofibrils were found to increase with age in these mice, although the levels displayed a large interindividual variation. Upon subcellular fractionation, higher levels of α-synuclein oligomers/protofibrils could be detected in the endoplasmic reticulum around the age when behavioral disturbances develop. In summary, our novel oligomer-selective α-synuclein antibodies recognize relevant pathology and should be important tools to further explore the pathogenic mechanisms in Lewy body disorders. Moreover, they could be potential candidates both for immunotherapy and as reagents in an assay to assess a potential disease biomarker.

Effect of α-synuclein on amyloid β-induced toxicity: relevance to Lewy body variant of Alzheimer disease

Alzheimer's disease, the most prevalent age-related neurodegenerative disease, is characterized by the presence of extracellular senile plaques composed of amyloid-beta (Aβ) peptide and intracellular neurofibrillary tangles. More than 50 % of Alzheimer's disease (AD) patients also exhibit abundant accumulation of α-synuclein (α-Syn)-positive Lewy bodies. This Lewy body variant of AD (LBV-AD) is associated with accelerated cognitive dysfunction and progresses more rapidly than pure AD. In addition, it has been suggested that Aβ and α-Syn can directly interact. In this study we investigated the effect of α-Syn on Aβ-induced toxicity in cortical neurons. In order to mimic the intracellular accumulation of α-Syn observed in the brain of LBV-AD patients, we used valproic acid (VPA) to increase its endogenous expression levels. The release of α-Syn from damaged presynaptic terminals that occurs during the course of the disease was simulated by challenging cells with recombinant α-Syn. Our results showed that either VPA-induced α-Syn upregulation or addition of recombinant α-Syn protect primary cortical neurons from soluble Aβ1-42 decreasing the caspase-3-mediated cell death. It was also found that neuroprotection against Aβ-induced toxicity mediated by α-Syn overexpression involves the PI3K/Akt cell survival pathway. Furthermore, recombinant α-Syn was shown to directly interact with Aβ1-42 and to decrease the levels of Aβ1-42 oligomers, which might explain its neuroprotective effect. In conclusion, we demonstrate that either endogenous or exogenous α-Syn can be neuroprotective against Aβ-induced cell death, suggesting a cell defence mechanism during the initial stages of the mixed pathology.

A powerful yeast model to investigate the synergistic interaction of α-synuclein and tau in neurodegeneration

Several studies revealed consistent overlap between synucleinopathies and tauopathies, demonstrating that α-synuclein (ASYN) and tau co-localize in neurofibrillary tangles and in Lewy bodies from Alzheimer’s and Parkinson’s disease patients and corresponding animal models. Additionally, it has been shown that ASYN can act as an initiator of tau aggregation and phosphorylation and that these two proteins directly interact. Despite these evidences, the cellular pathway implicated in this synergistic interaction remains to be clarified. The aim of this study was to create a yeast model where the concomitant expression of ASYN and tau can be used to perform genome wide screenings for the identification of genes that modulate this interaction, in order to shed light into the pathological mechanism of cell dysfunction and to provide new targets for future therapeutic intervention. We started by validating the synergistic toxicity of tau and ASYN co-expression in yeast, by developing episomal and integrative strains expressing WT and mutant forms of both proteins, alone or in combination. The episomal strains showed no differences in growth delay upon expression of ASYN isoforms (WT or A53T) alone or in combination with tau 2N/4R isoforms (WT or P301L). However, in these strains, the presence of ASYN led to increased tau insolubility and correlated with increased tau phosphorylation in S396/404, which is mainly mediated by RIM11, the human homolog of GSK3β in yeast. On the other hand, the integrative strains showed a strong synergistic toxic effect upon co-expression of ASYN WT and tau WT, which was related to high levels of intracellular ASYN inclusions and increased tau phosphorylation and aggregation. Taken together, the strains described in the present study are able to mimic relevant pathogenic features involved in neurodegeneration and are powerful tools to identify potential target genes able to modulate the synergistic pathway driven by ASYN and tau interaction.

Changes in properties of serine 129 phosphorylated α-synuclein with progression of Lewy-type histopathology in human brains

Modifications of α-synuclein resulting in changes in its conformation are considered to be key pathological events for Lewy body diseases (LBD), which include Parkinson's disease (PD) and dementia with Lewy bodies (DLB). We have previously described a histopathological Unified Staging System for LBD that classifies the spread of α-synuclein phosphorylated at serine 129 (pS129-α-synuclein) from olfactory bulb to brainstem or limbic regions, and finally neocortex. Lewy bodies and Lewy neurites are highly enriched in pS129-α-synuclein. Increased formation of pS129-α-synuclein changes its solubility properties enhancing its tendency to aggregate and disrupt normal function. As in vitro and animal studies have shown that inhibiting formation of pS129-α-synuclein can prevent toxic consequences, this has become one of the therapeutic targets for LBD. However, detailed biochemical descriptions of the changes in pS129-α-synuclein properties in diseased human brains are needed to further our understanding of how these might contribute to molecular pathogenesis. In this study, we used 130 separate brain samples from cingulate cortex (limbic cortex) and 131 from temporal cortex (neocortex) that had been staged according to our Unified Staging System to examine progressive changes in properties of pS129-α-synuclein with the formation of progressively more severe histological Lewy-type pathology. The brain samples from these staged cases had been separated into cytosol-enriched, membrane-enriched (detergent soluble) and insoluble (ureas/SDS soluble) fractions. We also characterized the nature and appearance of higher molecular weight forms of pS129-α-synuclein. The major species was the 16 kD monomeric form; this accumulated with increasing stage with a large increase in Stage IV samples. By comparing two brain regions, we showed higher accumulation of insoluble pS129-α-synuclein in cingulate cortex, where histological deposits occur first, than in temporal cortex in samples with advanced (stage IV) LB pathology.

Molecular chaperones and co-chaperones in Parkinson disease

Parkinson disease, a progressive neurodegenerative disorder, is caused by the pathological accumulation of proteins, including the ubiquitous presynaptic protein α-synuclein. Alterations in the metabolism of α-synuclein have clearly been linked to neurodegeneration, and early steps in the pathological sequence of this protein include the formation of oligomers, fibrils, and small aggregates. Targeting these early steps of oligomerization is one of the main therapeutic approaches in the quest to develop disease-modifying agents. Molecular chaperones, molecules that can mediate the proper folding and refolding of client proteins, are vital to cell function and survival and thus have been explored as potential therapeutic agents. Important to Parkinson disease, chaperones are capable of preventing α-synuclein misfolding, oligomerization, and aggregate formation as shown in vitro and in Parkinson disease animal models. Furthermore, chaperones and associated co-chaperones are closely linked to pathways of protein degradation, like the ubiquitin-proteasome system and autophagy, and are thus able to remove irreversibly misfolded proteins. In this review, we summarize the role of molecular chaperones in Parkinson disease models and discuss the importance of preserving protein homeostasis to prevent neurodegeneration. We also review the growing number of exciting studies that have targeted molecular chaperone function as a novel therapeutic approach.

Alpha-synuclein aggregation involves a bafilomycin A 1-sensitive autophagy pathway

Synucleinopathies like Parkinson disease and dementia with Lewy bodies (DLB) are characterized by α-synuclein aggregates within neurons (Lewy bodies) and their processes (Lewy neurites). Whereas α-synuclein has been genetically linked to the disease process, the pathological relevance of α-synuclein aggregates is still debated. Impaired degradation is considered to result in aggregation of α-synuclein. In addition to the ubiquitin-proteasome degradation, the autophagy-lysosomal pathway (ALP) is involved in intracellular degradation processes for α-synuclein. Here, we asked if modulation of ALP affects α-synuclein aggregation and toxicity. We have identified an induction of the ALP markers LAMP-2A and LC3-II in human brain tissue from DLB patients, in a transgenic mouse model of synucleinopathy, and in a cell culture model for α-synuclein aggregation. ALP inhibition using bafilomycin A 1 (BafA1) significantly potentiates toxicity of aggregated α-synuclein species in transgenic mice and in cell culture. Surprisingly, increased toxicity is paralleled by reduced aggregation in both in vivo and in vitro models. The dichotomy of effects on aggregating and nonaggregating species of α-synuclein was specifically sensitive to BafA1 and could not be reproduced by other ALP inhibitors. The present study expands on the accumulating evidence regarding the function of ALP for α-synuclein degradation by isolating an aggregation specific, BafA1-sensitive, ALP-related pathway. Our data also suggest that protein aggregation may represent a detoxifying event rather than being causal for cellular toxicity.

Intracerebral inoculation of pathological α-synuclein initiates a rapidly progressive neurodegenerative α-synucleinopathy in mice

The accumulation of misfolded proteins is a fundamental pathogenic process in neurodegenerative diseases. However, the factors that trigger aggregation of α-Synuclein (α-Syn), the principal component of the intraneuronal inclusions known as Lewy bodies (LBs), and Lewy neurites (LNs), which characterize Parkinson's disease (PD) and dementia with LBs (DLB), are poorly understood. We show here that in young asymptomatic α-Syn transgenic (Tg) mice, intracerebral injections of brain homogenates derived from older Tg mice exhibiting α-Syn pathology accelerate both the formation of intracellular LB/LN-like inclusions and the onset of neurological symptoms in recipient animals. Pathological α-Syn propagated along major central nervous system (CNS) pathways to regions far beyond injection sites and reduced survival with a highly reproducible interval from injection to death in inoculated animals. Importantly, inoculation with α-Syn amyloid fibrils assembled from recombinant human α-Syn induced identical consequences. Furthermore, we show for the first time that synthetic α-Syn fibrils are wholly sufficient to initiate PD-like LBs/LNs and to transmit disease in vivo. Thus, our data point to a prion-like cascade in synucleinopathies whereby cell-cell transmission and propagation of misfolded α-Syn underlie the CNS spread of LBs/LNs. These findings open up new avenues for understanding the progression of PD and for developing novel therapeutics.

The role of α-synuclein in neurodegeneration — An update

Genetic, neuropathological and biochemical evidence implicates α-synuclein, a 140 amino acid presynaptic neuronal protein, in the pathogenesis of Parkinson’s disease and other neurodegenerative disorders. The aggregated protein inclusions mainly containing aberrant α-synuclein are widely accepted as morphological hallmarks of α-synucleinopathies, but their composition and location vary between disorders along with neuronal networks affected. α-Synuclein exists physiologically in both soluble and membran-bound states, in unstructured and α-helical conformations, respectively, while posttranslational modifications due to proteostatic deficits are involved in β-pleated aggregation resulting in formation of typical inclusions. The physiological function of α-synuclein and its role linked to neurodegeneration, however, are incompletely understood. Soluble oligomeric, not fully fibrillar α-synuclein is thought to be neurotoxic, main targets might be the synapse, axons and glia. The effects of aberrant α-synuclein include alterations of calcium homeostasis, mitochondrial dysfunction, oxidative and nitric injuries, cytoskeletal effects, and neuroinflammation. Proteasomal dysfunction might be a common mechanism in the pathogenesis of neuronal degeneration in α-synucleinopathies. However, how α-synuclein induces neurodegeneration remains elusive as its physiological function. Genome wide association studies demonstrated the important role for genetic variants of the SNCA gene encoding α-synuclein in the etiology of Parkinson’s disease, possibly through effects on oxidation, mitochondria, autophagy, and lysosomal function. The neuropathology of synucleinopathies and the role of α-synuclein as a potential biomarker are briefly summarized. Although animal models provided new insights into the pathogenesis of Parkinson disease and multiple system atrophy, most of them do not adequately reproduce the cardinal features of these disorders. Emerging evidence, in addition to synergistic interactions of α-synuclein with various pathogenic proteins, suggests that prionlike induction and seeding of α-synuclein could lead to the spread of the pathology and disease progression. Intervention in the early aggregation pathway, aberrant cellular effects, or secretion of α-synuclein might be targets for neuroprotection and disease-modifying therapy.

Multiple system atrophy: a clinical and neuropathological perspective

Multiple system atrophy (MSA) is a neurodegenerative disease involving motor abnormalities that include akinesia, rigidity and postural instability. While improved diagnostic criteria have aided the accurate diagnosis of MSA, our understanding of the neuropathological aspects underlying MSA was bolstered by the identification of α-synuclein (α-syn) as the primary constituent of the abnormal protein aggregates observed in the brains of MSA patients. The generation of transgenic animal models of MSA coupled with an increasing understanding of the biochemical structure and function of α-syn has highlighted a number of key pathological pathways thought to underlie the neurodegeneration observed in MSA. This review summarizes key findings in the field, discusses current areas of debate, and describes current experimental approaches towards disease-modifying therapies.

Identification of novel α-synuclein isoforms in human brain tissue by using an online nanoLC-ESI-FTICR-MS method

Parkinson’s disease (PD) and Dementia with Lewy bodies (DLB) are neurodegenerative diseases that are characterized by intra-neuronal inclusions of Lewy bodies in distinct brain regions. These inclusions consist mainly of aggregated α-synuclein (α-syn) protein. The present study used immunoprecipitation combined with nanoflow liquid chromatography (LC) coupled to high resolution electrospray ionization Fourier transform ion cyclotron resonance tandem mass spectrometry (ESI-FTICR-MS/MS) to determine known and novel isoforms of α-syn in brain tissue homogenates. N-terminally acetylated full-length α-syn (Ac-α-syn_1–140) and two N-terminally acetylated C-terminally truncated forms of α-syn (Ac-α-syn_1–139 and Ac-α-syn_1–103) were found. The different forms of α-syn were further studied by Western blotting in brain tissue homogenates from the temporal cortex Brodmann area 36 (BA36) and the dorsolateral prefrontal cortex BA9 derived from controls, patients with DLB and PD with dementia (PDD). Quantification of α-syn in each brain tissue fraction was performed using a novel enzyme-linked immunosorbent assay (ELISA).

Upregulation of alpha-synuclein expression in the rat cerebellum in experimental hepatic encephalopathy

AIMS

The overexpression of alpha-synuclein has been associated with neurodegenerative diseases, especially when the protein aggregates to form insoluble structures. The present study examined the effect of chronic hyperammonaemia on alpha-synuclein expression in the rat cerebellum following portacaval anastomosis (PCA).

METHODS

Immunohistochemical and western blot determinations were performed 1 month and 6 months after the PCA procedure.

RESULTS

A time-dependent increase in alpha-synuclein expression was seen in the cerebellar grey matter compared with the controls. At 1 month post PCA, alpha-synuclein-immunopositive material was observed in the molecular layer, while the Purkinje cells showed weak alpha-synuclein expression, and alpha-synuclein aggregates were observed throughout the granular layer. At 6 months post PCA, alpha-synuclein expression was significantly increased compared with the controls. alpha-synuclein-immunostained astroglial cells were also found; the Bergmann glial cells showed alpha-synuclein-positive processes in the molecular layer of PCA-exposed rats, and in the granular layer, perivascular astrocytes showed intense alpha-synuclein immunoreactivity, as indicated by colocalization of alpha-synuclein with glial fibrillary acidic protein (GFAP). In addition, ubiquitin-immunoreactive inclusions were present in PCA-exposed rats, although they did not colocalize with alpha-synuclein. Western blotting performed at 6 months post PCA showed a reduction in the level of soluble alpha-synuclein compared with 1 month post PCA and the controls; this reduction was concomitant with an increase in the insoluble form of alpha-synuclein.

CONCLUSIONS

Although the precise mechanism by which alpha-synuclein aggregates in PCA-treated rats remains unknown, the present data suggest an important role for this protein in the onset and progression of hepatic encephalopathy, probably via its expression in astroglial cells.

Accelerated formation of alpha-synuclein oligomers by concerted action of the 20S proteasome and familial Parkinson mutations

A hallmark of Parkinson disease (PD) is the formation of intracellular protein inclusions called Lewy bodies that also contain mitochondria. alpha-Synuclein (alpha Syn) is a major protein component of Lewy bodies, where it is in an amyloid conformation and a significant fraction is truncated by poorly understood proteolytic events. Previously, we demonstrated that the 20S proteasome cleaves alpha Syn in vitro to produce fragments like those observed in Lewy bodies and that the fragments accelerate the formation of amyloid fibrils from full-length alpha Syn. Three point mutations in alpha Syn are associated with early-onset familial PD: A30P, E46K, and A53T. However, these mutations have very different effects on the amyloidogenicity and vesicle-binding activity of alpha Syn, suggesting neither of these processes directly correlate with neurodegeneration. Here, we evaluate the effect of the disease-associated mutations on the fragmentation, conformation, and association reactions of alpha Syn in the presence of the 20S proteasome and liposomes. The 20S proteasome produced the C-terminal fragments from both the mutant and wildtype alpha Syn. These truncations accelerated fibrillization of all alpha-synucleins, but again there was no clear correlation between the PD-associated mutations and amyloid formation in the presence of liposomes. Recent data suggests that cellular toxicity is caused by a soluble oligomeric species, which is a precursor to the amyloid form and is immunologically distinguishable from both soluble monomeric and amyloid forms of alpha Syn. Notably, the rate of formation of the soluble, presumptively cytotoxic oligomers correlated with the disease-associated mutations when both 20S proteasome and liposomes were present. Under these conditions, the wildtype protein was also cleaved and formed the oligomeric structures, albeit at a slower rate, suggesting that 20S-mediated truncation of alpha Syn may play a role in sporadic PD as well. Evaluation of the biochemical reactions of the PD-associated alpha-synuclein mutants in our in vitro system provides insight into the possible pathogenetic mechanism of both familial and sporadic PD.

Brain alpha-synuclein accumulation in multiple system atrophy, Parkinson's disease and progressive supranuclear palsy: a comparative investigation

Alpha-synuclein is a major component of Lewy bodies and glial cytoplasmic inclusions, pathological hallmarks of idiopathic Parkinson's disease and multiple system atrophy, and it is assumed to be aetiologically involved in these conditions. However, the quantitative status of brain alpha-synuclein in different Parkinsonian disorders is still unresolved and it is uncertain whether alpha-synuclein accumulation is restricted to regions of pathology. We compared membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein, both the full-length 17 kDa and high molecular weight species, by western blotting in autopsied brain of patients with Parkinson's disease (brainstem-predominant Lewy body disease: n = 9), multiple system atrophy (n = 11), progressive supranuclear palsy (n = 16), and of normal controls (n = 13). Brain of a patient with familial Parkinsonism-dementia due to alpha-synuclein locus triplication (as positive control) showed increased membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein levels with abundant high molecular weight immunoreactivity. In multiple system atrophy, a massive increase in 17 kDa membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein was observed in highly pathologically affected regions, including putamen (+1760%, range +625-2900%), substantia nigra [+1000% (+356-1850%)], and white matter of internal capsule [+2210% (+430-6830%)] together with numerous high molecular weight species. Levels of 17 kDa membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein were only modestly increased in less affected areas (cerebellar cortex, +95%; caudate, +30%; with both also showing numerous high molecular weight species) and were generally normal in cerebral cortices. In both Parkinson's disease and progressive supranuclear palsy, membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein levels were normal in putamen and frontal cortex whereas a trend was observed for variably increased 17 kDa membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein concentrations [+184% (-60% to +618%)] with additional high molecular weight species in Parkinson's disease substantia nigra. No obvious correlation was observed between nigral membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein accumulation and Lewy body density in Parkinson's disease. Two progressive supranuclear palsy cases had membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein accumulation in substantia nigra similar to multiple system atrophy. Several Parkinson's disease patients had very modest high molecular weight membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein accumulation in putamen. Levels of 17-kDa membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein were generally positively correlated with those of high molecular weight membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein and there was a trend for a positive correlation between striatal dopamine loss and 17-kDa membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein concentrations in multiple system atrophy. Brain membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein accumulations in Parkinson's disease and multiple system atrophy are regionally specific, suggesting that these sporadic alpha-synucleinopathies, unlike familial Parkinsonism-dementia, are not associated with a simple global over-expression of the protein. Despite a similar extent of dopamine depletion, the magnitude of brain membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein changes is disease specific, with multiple system atrophy clearly having the most severe accumulation. Literature discrepancies on alpha-synuclein status in 'Parkinson's disease' might be explained by inclusion of cases not having classic brainstem-predominant Lewy body disease and by variable alpha-synuclein accumulation within this diagnostic classification.

Detection of elevated levels of soluble alpha-synuclein oligomers in post-mortem brain extracts from patients with dementia with Lewy bodies

A number of neurodegenerative diseases including Parkinson's disease, dementia with Lewy bodies (DLB) and multiple system atrophy are characterized by the formation and intraneuronal accumulation of fibrillar aggregates of alpha-synuclein (alpha-syn) protein in affected brain regions. These and other findings suggest that the accumulation of alpha-syn in the brain plays an important role in the pathogenesis of these diseases. However, more recently it has been reported that early amyloid aggregates or 'soluble oligomers' are the pathogenic species that lead to neurodegeneration and neuronal cell death rather than the later 'mature fibrils'. In this study, we investigated the presence of alpha-syn oligomers in brain lysates prepared from frozen post-mortem brains of normal, Alzheimer's disease and DLB patients. The brain extracts were subjected to high speed centrifugation, to remove insoluble alpha-syn aggregates, followed by specific detection of soluble oligomers in the supernatants by employing FILA-1, an antibody that specifically binds to alpha-syn aggregates, but not to alpha-syn monomers, or to tau or beta-amyloid aggregates. Using this novel enzyme-linked immunosorbent assay (ELISA) method to quantify the amounts of alpha-syn oligomers in the brain extracts, our data clearly show an increase in the levels of soluble oligomers of alpha-syn in the DLB brains compared to those with Alzheimer's disease and the controls (P < 0.0001). Our findings provide strong evidence to support the contention that elevated soluble oligomers of alpha-syn are involved in the pathogenesis of DLB. Furthermore, these findings establish FILA-1 as a very sensitive tool for the detection of oligomeric forms of alpha-syn in human brain lysates.

alpha-Synucleinopathy models and human neuropathology: similarities and differences

Point mutations and genomic multiplications in the alpha-synuclein (alphaSYN) gene cause autosomal-dominant Parkinson's disease. Moreover, alphaSYN fibrils are the major component of Lewy bodies, the neuropathological hallmarks of Parkinson's disease and dementia with Lewy bodies as well as of glial cytoplasmic inclusions in multiple system atrophy. These diseases are collectively referred to as alpha-synucleinopathies. Cellular mechanisms regulating alphaSYN fibril formation and toxicity are intensely studied in vitro, and in cell culture and diverse animal models. Specific neuropathology was achieved in transgenic mouse models using several promoters to express human wild-type and mutant alphaSYN in brain regions affected by the various alpha-synucleinopathies. Somatodendritic accumulation of the transgenic alphaSYN with neuritic distortions was a common finding. The nigrostriatal dopaminergic projections were surprisingly resistant to alpha-synucleinopathy in transgenic mice, although they tended to be more vulnerable to neurotoxins. In a few mouse models, alphaSYN aggregated in an age-dependent manner into genuine fibrillar amyloid. Brain region selective alphaSYN neuropathology correlated with specific behavioral impairments, such as locomotor dysfunction and cognitive decline. Thus, the alphaSYN fibrillization process is tightly linked to neuropathology. The role and thus therapeutic potential of post-translational modifications (ubiquitinylation, oxidation, phosphorylation, truncation) and modifier genes on alphaSYN neuropathology can now be assessed in valid transgenic mouse models of alpha-synucleinopathies.

Single molecule profiling of tau gene expression in Alzheimer's disease

Tau is a microtubule-associated protein that is important for establishing and maintaining neuronal morphology. In addition to its role in normal cells, tau protein is involved in many neurodegenerative diseases, e.g. Alzheimer's disease (AD) and frontotemporal dementia, as the main component of intraneuronal aggregates. Alternative splicing of tau gene in the brain can give rise to at least six protein variants. A causative role of skewed tau exon 10 inclusion has been defined in frontotemporal dementia; however, no link was established between the aberrant splicing of tau and AD. Here, we applied a single-molecule-based technology, polymerase colony or polony, to simultaneously monitor tau splicing variant and haplotype profile in sporadic AD and normal brains. We found that the coordinated expression of tau exons 2 and 10 is altered in AD. Additional investigations of cis and trans mechanisms of this observation revealed a decreased protein expression of a known tau splicing factor, htra2-beta-1 in AD, thereby implicating a trans mechanism. Our results demonstrate that dysregulation of combinatorial splicing might serve as a signature for aging-related diseases, and the polony assay could be widely adapted for the study of other tauopathies. Furthermore, splicing-based therapeutics is an emerging area of drug development, and a well-defined and quantitative assay for monitoring single-gene transcriptome will be relevant for such development.

Dopaminergic neuron loss and up-regulation of chaperone protein mRNA induced by targeted over-expression of alpha-synuclein in mouse substantia nigra

Several transgenic mouse lines with altered alpha-synuclein expression have been developed that show a variety of Parkinson's disease-like symptoms without specific loss of dopaminergic neurons. Targeted over-expression of human alpha-synuclein using viral-vector mediated gene delivery into the substantia nigra of rats and non-human primates leads to dopaminergic cell loss and the formation of alpha-synuclein aggregates reminiscent of Lewy bodies. In the context of these recent findings, we used adeno-associated virus (AAV) to over-express wild type human alpha-synuclein in the substantia nigra of mice. We hypothesized that this over-expression would recapitulate pathological hallmarks of Parkinson's disease, creating a mouse model to further characterize the disease pathogenesis. Recombinant AAV expressing alpha-synuclein was stereotaxically injected into the substantia nigra of mice, leading to a 25% reduction of dopaminergic neurons after 24 weeks of transduction. Furthermore, examination of mRNA levels of stress-related proteins using laser capture microdissection and quantitative PCR revealed a positive correlation of Hsp27 expression with the extent of viral transduction at 4 weeks and a positive correlation of Hsp40, Hsp70 and caspase 9 with the extent of viral transduction at 24 weeks. Taken together, our findings suggest that targeted over-expression of alpha-synuclein can induce pathology at the gross anatomical and molecular level in the substantia nigra, providing a mouse model in which upstream changes in Parkinson's disease pathogenesis can be further elucidated.

Brain CHIP: removing the culprits in neurodegenerative disease

A factor that is common to the most-frequent neurodegenerative diseases is the accumulation of abnormal proteins that are associated with cellular dysfunction. Contrary to years of speculation, recent evidence suggests that soluble intermediates--not the visible pathological aggregates associated with disease--are the cause of neurotoxicity. These findings suggest that aggregate formation might be an adaptive stress response that is facilitated by neuronal protein triage molecules. In particular, the molecular co-chaperone CHIP (C terminus of HSC70-interacting protein) has been linked to several of these disorders, serving as a crucial catalyst for the ubiquitination of several heat shock protein (HSP)70 client proteins that are involved in neurodegenerative disease. Therefore, understanding the mechanisms that are involved in CHIP-mediated protein trafficking might provide invaluable clues to neuronal function, both in normal and diseased conditions.