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

Molecular determinants of α-synuclein mutants' oligomerization and membrane interactions

Parkinson's disease (PD) is associated with the formation of toxic α-synuclein oligomers that can penetrate the cell membrane. Familial forms of PD are caused by the point mutations A53T, A30P, E46K, and H50Q. Artificial point mutations E35K and E57K also increase oligomerization and pore formation. We generated structural conformations of α-synuclein and the above-mentioned mutants using molecular dynamics. We elucidated four main regions in these conformers contacting the membrane and found that the region including residues 39-45 (Zone2) may have maximum membrane penetration. E57K mutant had the highest rate of interaction with the membrane, followed by A53T, E46K, and E35K mutants and wild type (wt) α-synuclein. The mutant A30P had the smallest percentage of conformers that contact the membrane by Zone 2 than all other mutants and wt α-synuclein. These results were confirmed experimentally in vitro. We identified the key amino acids that can interact with the membrane (Y38, E62, and N65 (first hydrophilic layer); E104, E105, and D115 (second hydrophilic layer), and V15 and V26 (central hydrophobic layer)) and the residues that are involved in the interprotein contacts (L38, V48, V49, Q62, and T64). Understanding the molecular interactions of α-synuclein mutants is important for the design of compounds blocking the formation of toxic oligomers.

β-Amyloid and α-synuclein cooperate to block SNARE-dependent vesicle fusion

Alzheimer's disease (AD) and Parkinson's disease (PD) are caused by β-amyloid (Aβ) and α-synuclein (αS), respectively. Ample evidence suggests that these two pathogenic proteins are closely linked and have a synergistic effect on eliciting neurodegenerative disorders. However, the pathophysiological consequences of Aβ and αS coexistence are still elusive. Here, we show that large-sized αS oligomers, which are normally difficult to form, are readily generated by Aβ42-seeding and that these oligomers efficiently hamper neuronal SNARE-mediated vesicle fusion. The direct binding of the Aβ-seeded αS oligomers to the N-terminal domain of synaptobrevin-2, a vesicular SNARE protein, is responsible for the inhibition of fusion. In contrast, large-sized Aβ42 oligomers (or aggregates) or the products of αS incubated without Aβ42 have no effect on vesicle fusion. These results are confirmed by examining PC12 cell exocytosis. Our results suggest that Aβ and αS cooperate to escalate the production of toxic oligomers, whose main toxicity is the inhibition of vesicle fusion and consequently prompts synaptic dysfunction.

Extracellular α-synuclein alters synaptic transmission in brain neurons by perforating the neuronal plasma membrane

It has been postulated that the accumulation of extracellular α-synuclein (α-syn) might alter the neuronal membrane by formation of 'pore-like structures' that will lead to alterations in ionic homeostasis. However, this has never been demonstrated to occur in brain neuronal plasma membranes. In this study, we show that α-syn oligomers rapidly associate with hippocampal membranes in a punctate fashion, resulting in increased membrane conductance (5 fold over control) and the influx of both calcium and a fluorescent glucose analogue. The enhancement in intracellular calcium (1.7 fold over control) caused a large increase in the frequency of synaptic transmission (2.5 fold over control), calcium transients (3 fold over control), and synaptic vesicle release. Both primary hippocampal and dissociated nigral neurons showed rapid increases in membrane conductance by α-syn oligomers. In addition, we show here that α-syn caused synaptotoxic failure associated with a decrease in SV2, a membrane protein of synaptic vesicles associated with neurotransmitter release. In conclusion, extracellular α-syn oligomers facilitate the perforation of the neuronal plasma membrane, thus explaining, in part, the synaptotoxicity observed in neurodegenerative diseases characterized by its extracellular accumulation. We propose that α-synuclein (α-syn) oligomers form pore-like structures in the plasma membrane of neurons from central nervous system (CNS). We believe that extracellular α-syn oligomers facilitate the formation of α-syn membrane pore-like structures, thus explaining, in part, the synaptotoxicity observed in neurodegenerative diseases characterized by its extracellular accumulation. We think that alterations in ionic homeostasis and synaptic vesicular depletion are key steps that lead to synaptotoxicity promoted by α -syn membrane pore-like structures.

What we can learn from animal models about cerebral multi-morbidity

Late-onset diseases such as Alzheimer's disease, Parkinson's disease, or frontotemporal lobar degeneration are considered to be protein-folding disorders, with the accumulation of protein deposits causing a gain-of-toxic function. Alzheimer's disease is characterized by two histological hallmark lesions: amyloid-β-containing plaques and tau-containing neurofibrillary tangles. However, signature proteins, including α-synuclein, which are found in an aggregated fibrillar form in the Lewy bodies of Parkinson's disease brains, are also frequently found in Alzheimer's disease. This highlights the fact that, although specific aggregates form the basis for diagnosis, there is a high prevalence of clinical overlap between neuropathological lesions linked to different diseases, a finding known as cerebral co- or multi-morbidity. Furthermore, the proteins forming these lesions interact, and this interaction accelerates an ongoing degenerative process. Here, we review the contribution that transgenic animal models have made to a better mechanistic understanding of the causes and consequences of co- or multi-morbidity. We discuss selected vertebrate and invertebrate models as well as the insight gained from non-transgenic senescence-accelerated mouse-prone mice. This article is part of a series on 'Cerebral multi-morbidity of the aging brain'.

Prion-like features of misfolded Aβ and tau aggregates

Recent findings have shown that several misfolded proteins can transmit disease pathogenesis in a prion-like manner by transferring their conformational properties to normally folded units. However, the extent by which these molecule-to-molecule or cell-to-cell spreading processes reflect the entire prion behavior is now subject of controversy, especially due to the lack of epidemiological data supporting inter-individual transmission of non-prion protein misfolding diseases. Nevertheless, extensive research has shown that several of the typical characteristics of prions can be observed for Aβ and tau aggregates when administered in animal models. In this article we review recent studies describing the prion-like features of both proteins, highlighting the similarities with bona fide prions in terms of inter-individual transmission, their strain-like conformational diversity, and the transmission of misfolded aggregates by different routes of administration.

CSF beta-amyloid 1-42 - what are we measuring in Alzheimer's disease?

Objective

To characterize biological and technical factors which influence cerebrospinal fluid (CSF) Alzheimer's disease (AD) biomarker levels, including the presence of apolipoprotein E (APOE) ε4 allele, AD diagnosis, Aβ-binding proteins, sample processing, and preanalytical handling.

Methods

CSF was collected from 140 subjects with normal cognition, mild cognitive impairment, AD, and non-AD dementia. CSF levels of beta-amyloid 1–42 (Aβ42), total Tau (t-Tau), and Tau phosphorylated at threonine 181 (p-Tau181) were analyzed following the standard and modified protocols. CSF levels of apoJ, apoE, albumin, and α-synuclein were measured in a subgroup (n = 69), and their effects on measured AD biomarker levels were also determined in vitro using human CSF samples.

Results

CSF Aβ42 levels measured using the AD Neuro-imaging Initiative (ADNI) protocol (which we call suspended Aβ42 or susAβ) were lower than total measurable CSF Aβ42 in all groups, and on average represents 57% of the latter. Logistic regression analysis showed this proportion (% susAβ) to be directly correlated with CSF Aβ42 and apoJ levels, but inversely correlated with CSF t-Tau levels. Finally, we showed in vitro that increasing apoE and apoJ levels directly increased % susAβ.

Conclusion

CSF susAβ levels are influenced by biological and technical factors, and may represent a marker of Aβ susceptible to lipoprotein-mediated clearance. Clinical trials should include total measurable Aβ42 and susAβ to better inform outcomes.

Structural diversity of Alzheimer's disease amyloid-β dimers and their role in oligomerization and fibril formation

Alzheimer's disease (AD) is associated with the formation of toxic amyloid-β (Aβ)42 oligomers, and recent evidence supports a role for Aβ dimers as building blocks for oligomers. Molecular dynamics simulation studies have identified clans for the dominant conformations of Aβ42 forming dimers; however, it is unclear if a larger spectrum of dimers is involved and which set(s) of dimers might evolve to oligomers verse fibrils. Therefore, for this study we generated multiple structural conformations of Aβ42, using explicit all-atom molecular dynamics, and then clustering the different structures based on key conformational similarities. Those matching a selection threshold were then used to model a process of oligomerization. Remarkably, we showed a greater diversity in Aβ dimers than previously described. Depending on the clan family, different types of Aβ dimers were obtained. While some had the tendency to evolve into oligomeric rings, others formed fibrils of diverse characteristics. Then we selected the dimers that would evolve to membranephilic annular oligomers. Nearly one third of the 28 evaluated annular oligomers had the dimer interfaces between the neighboring Aβ42 monomers with possible salt bridges between the residue K28 from one side and either residue E22 or D23 on the other. Based on these results, key amino acids were identified for point mutations that either enhanced or suppressed the formation and toxicity of oligomer rings. Our studies suggest a greater diversity of Aβ dimers. Understanding the structure of Aβ dimers might be important for the rationale design of small molecules that block formation of toxic oligomers.

Cerebrospinal fluid biomarkers in parkinsonian conditions: an update and future directions

Parkinsonian diseases comprise a heterogeneous group of neurodegenerative disorders, which show significant clinical and pathological overlap. Accurate diagnosis still largely relies on clinical acumen; pathological diagnosis remains the gold standard. There is an urgent need for biomarkers to diagnose parkinsonian disorders, particularly in the early stages when diagnosis is most difficult. In this review, several of the most promising cerebrospinal fluid candidate markers will be discussed. Their strengths and limitations will be considered together with future developments in the field.

ESCRT-mediated uptake and degradation of brain-targeted α-synuclein single chain antibody attenuates neuronal degeneration in vivo

Parkinson's disease and dementia with Lewy bodies are neurodegenerative disorders characterized by accumulation of α-synuclein (α-syn). Recently, single-chain fragment variables (scFVs) have been developed against individual conformational species of α-syn. Unlike more traditional monoclonal antibodies, these scFVs will not activate or be endocytosed by Fc receptors. For this study, we investigated an scFV directed against oligomeric α-syn fused to the LDL receptor-binding domain from apolipoprotein B (apoB). The modified scFV showed enhanced brain penetration and was imported into neuronal cells through the endosomal sorting complex required for transport (ESCRT) pathway, leading to lysosomal degradation of α-syn aggregates. Further analysis showed that the scFV was effective at ameliorating neurodegenerative pathology and behavioral deficits observed in the mouse model of dementia with Lewy bodies/Parkinson's disease. Thus, the apoB modification had the effect of both increasing accumulation of the scFV in the brain and directing scFV/α-syn complexes for degradation through the ESCRT pathway, leading to improved therapeutic potential of immunotherapy.

Cross dimerization of amyloid-β and αsynuclein proteins in aqueous environment: a molecular dynamics simulations study

Self-assembly of the intrinsically unstructured proteins, amyloid beta (Aβ) and alpha synclein (αSyn), are associated with Alzheimer's Disease, and Parkinson's and Lewy Body Diseases, respectively. Importantly, pathological overlaps between these neurodegenerative diseases, and the possibilities of interactions between Aβ and αSyn in biological milieu emerge from several recent clinical reports and in vitro studies. Nevertheless, there are very few molecular level studies that have probed the nature of spontaneous interactions between these two sequentially dissimilar proteins and key characteristics of the resulting cross complexes. In this study, we have used atomistic molecular dynamics simulations to probe the possibility of cross dimerization between αSyn1-95 and Aβ1-42, and thereby gain insights into their plausible early assembly pathways in aqueous environment. Our analyses indicate a strong probability of association between the two sequences, with inter-protein attractive electrostatic interactions playing dominant roles. Principal component analysis revealed significant heterogeneity in the strength and nature of the associations in the key interaction modes. In most, the interactions of repeating Lys residues, mainly in the imperfect repeats 'KTKEGV' present in αSyn1-95 were found to be essential for cross interactions and formation of inter-protein salt bridges. Additionally, a hydrophobicity driven interaction mode devoid of salt bridges, where the non-amyloid component (NAC) region of αSyn1-95 came in contact with the hydrophobic core of Aβ1-42 was observed. The existence of such hetero complexes, and therefore hetero assembly pathways may lead to polymorphic aggregates with variations in pathological attributes. Our results provide a perspective on development of therapeutic strategies for preventing pathogenic interactions between these proteins.

New α- and γ-synuclein immunopathological lesions in human brain

Introduction

Several neurodegenerative diseases are classified as proteopathies as they are associated with the aggregation of misfolded proteins. Synucleinopathies are a group of neurodegenerative disorders associated with abnormal deposition of synucleins. α-Synucleinopathies include Parkinson’s disease, dementia with Lewy bodies, and multiple system atrophy. Recently accumulation of another member of the synuclein family- γ−synuclein in neurodegenerative diseases compelled the introduction of the term γ−synucleinopathy. The formation of aggregates and deposits of γ−synuclein is facilitated after its oxidation at methionine 38 (Met³⁸).

Results

Several types of intracytoplasmic inclusions containing post-translationally modified α- and γ−synucleins are detected. Oxidized Met³⁸-γ-synuclein forms aberrant inclusions in amygdala and substantia nigra. Double staining revealed colocalization of oxidized-γ-synuclein with α-synuclein in the cytoplasm of neurons. Another type of synuclein positive inclusions in the amygdala of dementia with Lewy bodies patients has the appearance of Lewy bodies. These inclusions are immunoreactive when analyzed with antibodies to α-synuclein phosphorylated on serine 129, as well as with antibodies to oxidized-γ-synuclein. Some of these Lewy bodies have doughnut-like shape with round or elongated shape. The separate immunofluorescent images obtained with individual antibodies specific to oxidized-γ-synuclein and phospho-α-synuclein clearly shows the colocalization of these synuclein isoforms in substantia nigra inclusions. Phospho-α-synuclein is present almost exclusively at the periphery of these structures, whereas oxidized-γ-syn immunoreactivity is also located in the internal parts forming dot-like pattern of staining.

We also identified several types of oxidized-γ-syn positive astrocytes with different morphology and examined their immunohistochemical phenotypes. Some of them are compact cells with short processes, others have longer processes. Oxidized-γ-synuclein positive astrocytes may also display mixed morphological and immunocytochemical phenotypes between protoplasmic and fibrous astrocytes.

Conclusions

These results reveal new γ−synuclein positive lesions in human brain. Oxidized-γ-synuclein is colocalized with phospho-α-synuclein in doughnut-like inclusions. Several types of astrocytes with different morphology are immunopositive for oxidized-γ-synuclein.

Amyloid-β oligomers as a template for secondary amyloidosis in Alzheimer's disease

Alzheimer's disease is a complex disease characterized by overlapping phenotypes with different neurodegenerative disorders. Oligomers are considered the most toxic species in amyloid pathologies. We examined human AD brain samples using an anti-oligomer antibody generated in our laboratory and detected potential hybrid oligomers composed of amyloid-β, prion protein, α-synuclein, and TDP-43 phosphorylated at serines 409 and 410. These data and in vitro results suggest that Aβ oligomer seeds act as a template for the aggregation of other proteins and generate an overlapping phenotype with other neuronal disorders. Furthermore, these results could explain why anti-amyloid-β therapy has been unsuccessful.

Dopamine-induced α-synuclein oligomers show self- and cross-propagation properties

Amyloid aggregates of α-synuclein (αS) protein are the predominant species present within the intracellular inclusions called Lewy bodies in Parkinson's disease (PD) patients. Among various aggregates, the low-molecular weight ones broadly ranging between 2 and 30 mers are known to be the primary neurotoxic agents responsible for the impairment of neuronal function. Recent research has indicated that the neurotransmitter dopamine (DA) is one of the key physiological agents promoting and augmenting αS aggregation, which is thought to be a significant event in PD pathologenesis. Specifically, DA is known to induce the formation of soluble oligomers of αS, which in turn are responsible for inducing several important cellular changes leading to cellular toxicity. In this report, we present the generation, isolation, and biophysical characterization of five different dopamine-derived αS oligomers (DSOs) ranging between 3 and 15 mers, corroborating previously published reports. More importantly, we establish that these DSOs are also capable of replication by self-propagation, which leads to the replication of DSOs upon interaction with αS monomers, a process similar to that observed in mammilian prions. In addition, DSOs are also able to cross-propagate amyloid-β (Aβ) aggregates involved in Alzheimer's disease (AD). Interestingly, while self-propagation of DSOs occur with no net gain in protein structure, cross-propagation proceeds with an overall gain in β-sheet conformation. These results implicate the involvement of DSOs in the progression of PD, and, in part, provide a molecular basis for the observed co-existence of AD-like pathology among PD patients.

Targeting the proper amyloid-beta neuronal toxins: a path forward for Alzheimer's disease immunotherapeutics

Levels of amyloid-beta monomer and deposited amyloid-beta in the Alzheimer’s disease brain are orders of magnitude greater than soluble amyloid-beta oligomer levels. Monomeric amyloid-beta has no known direct toxicity. Insoluble fibrillar amyloid-beta has been proposed to be an in vivo mechanism for removal of soluble amyloid-beta and exhibits relatively low toxicity. In contrast, soluble amyloid-beta oligomers are widely reported to be the most toxic amyloid-beta form, both causing acute synaptotoxicity and inducing neurodegenerative processes. None of the amyloid-beta immunotherapies currently in clinical development selectively target soluble amyloid-beta oligomers, and their lack of efficacy is not unexpected considering their selectivity for monomeric or fibrillar amyloid-beta (or both) rather than soluble amyloid-beta oligomers. Because they exhibit acute, memory-compromising synaptic toxicity and induce chronic neurodegenerative toxicity and because they exist at very low in vivo levels in the Alzheimer’s disease brain, soluble amyloid-beta oligomers constitute an optimal immunotherapeutic target that should be pursued more aggressively.

Hippocampal neuronal cells that accumulate α-synuclein fragments are more vulnerable to Aβ oligomer toxicity via mGluR5--implications for dementia with Lewy bodies

BACKGROUND

In dementia with Lewy bodies (DLB) abnormal interactions between α-synuclein (α-syn) and beta amyloid (Aβ) result in selective degeneration of neurons in the neocortex, limbic system and striatum. However, factors rendering these neurons selectively vulnerable have not been fully investigated. The metabotropic glutamate receptor 5 (mGluR5) has been shown to be up regulated in DLB and might play a role as a mediator of the neurotoxic effects of Aβ and α-syn in vulnerable neuronal populations. In this context, the main objective of the present study was to investigate the role of mGluR5 as a mediator of the neurotoxic effects of α-syn and Aβ in the hippocampus.

RESULTS

We generated double transgenic mice over-expressing amyloid precursor protein (APP) and α-syn under the mThy1 cassette and investigated the relationship between α-syn cleavage, Aβ, mGluR5 and neurodegeneration in the hippocampus. We found that compared to the single tg mice, the α-syn/APP tg mice displayed greater accumulation of α-syn and mGluR5 in the CA3 region of the hippocampus compared to the CA1 and other regions. This was accompanied by loss of CA3 (but not CA1) neurons in the single and α-syn/APP tg mice and greater loss of MAP 2 and synaptophysin in the CA3 in the α-syn/APP tg. mGluR5 gene transfer using a lentiviral vector into the hippocampus CA1 region resulted in greater α-syn accumulation and neurodegeneration in the single and α-syn/APP tg mice. In contrast, silencing mGluR5 with a lenti-shRNA protected neurons in the CA3 region of tg mice. In vitro, greater toxicity was observed in primary hippocampal neuronal cultures treated with Aβ oligomers and over-expressing α-syn; this effect was attenuated by down-regulating mGluR5 with an shRNA lentiviral vector. In α-syn-expressing neuronal cells lines, Aβ oligomers promoted increased intracellular calcium levels, calpain activation and α-syn cleavage resulting in caspase-3-dependent cell death. Treatment with pharmacological mGluR5 inhibitors such as 2-Methyl-6-(phenylethynyl)pyridine (MPEP) and 3-((2-Methyl-4-thiazolyl)ethynyl)pyridine (MTEP) attenuated the toxic effects of Aβ in α-syn-expressing neuronal cells.

CONCLUSIONS

Together, these results support the possibility that vulnerability of hippocampal neurons to α-syn and Aβ might be mediated via mGluR5. Moreover, therapeutical interventions targeting mGluR5 might have a role in DLB.

Differential role of CSF alpha-synuclein species, tau, and Aβ42 in Parkinson's Disease

There is a great interest in developing cerebrospinal fluid (CSF) biomarkers for diagnosis and prognosis of Parkinson's disease (PD). CSF alpha synuclein (α-syn) species, namely total and oligomeric α-syn (t-α-syn and o-α-syn), have shown to be of help for PD diagnosis. Preliminary evidences show that the combination of CSF t-α-syn and classical Alzheimer's disease (AD) biomarkers—β-amyloid 1–42 (Aβ₄₂), total tau (t-tau), phosphorylated tau (p-tau)—differentiate PD patients from controls, and that reduced levels of Aβ₄₂ represent a predictive factor for development of cognitive deterioration in PD. In this prospective study carried out in 44 PD patients and 25 neurological controls we wanted to verify whether the combination of CSF α-synuclein species—t-α-syn and o-α-syn—and classical AD biomarkers may help in differentiating PD from neurological controls, and if these biomarkers may predict cognitive decline. The median of follow-up duration was 3 years (range: 2–6 years). Mini Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) were used for monitoring cognitive changes along time, being administered once a year. Oligo/total α-syn ratio (o/t-α-syn ratio) confirmed its diagnostic value, significantly contributing to the discrimination of PD from neurological controls. A greater diagnostic accuracy was reached when combining o/t-α-syn and Aβ₄₂/tau ratios (Sens = 0.70, Spec = 0.84, AUC = 0.82; PPV = 0.89, NPV = 0.62, LR+ = 4.40, DOR = 12.52). Low CSF Aβ₄₂ level was associated with a higher rate of MMSE and MoCA decline, confirming its role as independent predictive factor for cognitive decline in PD. None of the other biomarkers assessed (t-tau, p-tau, t-α-syn and o-α-syn) showed to have prognostic value. We conclude that combination of CSF o/t-α-syn and Aβ₄₂/tau ratios improve the diagnostic accuracy of PD. PD patients showing low CSF Aβ₄₂ levels at baseline are more prone to develop cognitive decline.

α-Synuclein in cerebrospinal fluid of Alzheimer's disease and mild cognitive impairment

In addition to amyloid-β (Aβ) and tau, α-synuclein, best known for its role in Parkinson's disease (PD), has been suggested to be involved in cognition and pathogenesis of Alzheimer's disease (AD). We investigate the potential of α-synuclein in cerebrospinal fluid (CSF) as a biomarker of cognitive decline in AD, and its prodromal phase, mild cognitive impairment (MCI). Using an established, sensitive Luminex assay, we measured α-synuclein levels in the CSF of a cohort of close to 400 healthy control, MCI, and AD subjects obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI) and factored in APOE genotype in data analysis. CSF α-synuclein levels were significantly higher in the MCI (p = 0.005) and AD (p < 0.001) groups, compared to controls. However, receiver operating characteristic (ROC) curve analysis suggests that CSF α-synuclein level on its own only offered modest sensitivity (65%) and specificity (74%) as a diagnostic marker of AD, with an area under the curve (AUC) value of 0.719 for AD versus controls. The effect of APOE genotype, if any, was quite subtle. However, there was a significant correlation between α-synuclein and cognition (p = 0.001), with increased α-synuclein levels associated with decreased Mini-Mental State Exam scores. Our results support a role for α-synuclein even in MCI, the early phase of AD, in addition to being a potential contributor in MCI and AD diagnosis or monitoring of disease progression.

Mechanisms of transthyretin aggregation and toxicity

Amyloidoses are characterised by the deposition of insoluble protein that occurs in the extracellular compartment of various tissues. One form of amyloidosis is caused by transthyretin (TTR) misfolding and deposition in target tissues. It is clear that many amyloidoses share common features of fibrillogenesis and toxicity. This chapter examines the mechanisms of TTR aggregation with a view to understanding the possible therapeutic interventions in amyloid disease.

Confluence of α-synuclein, tau, and β-amyloid pathologies in dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is pathologically characterized by α-synuclein aggregates in the brain. Most patients with DLB also show cerebral Alzheimer disease-type pathology (i.e. β-amyloid plaques and hyperphosphorylated tau deposits). It is unclear whether this overlap is coincidental or driven by specific regional or cellular interactions. The aims of this study were to investigate the regional convergence of α-synuclein, tau, and β-amyloid and to identify patterns of cellular co-occurrence of tau and α-synuclein in DLB. The study group consisted of 22 patients who met clinical and neuropathologic criteria for DLB. Protein aggregates were assessed semiquantitatively in 17 brain areas. APOE and MAPT genotypes were determined. Cellular co-occurrence of tau and α-synuclein was evaluated by double immunofluorescence. We found that total β-amyloid pathology scores correlated positively with total α-synuclein pathology scores (ρ = 0.692, p = 0.001). The factors that correlated best with the amount of α-synuclein pathology were the severity of β-amyloid pathology and presence of the MAPT H1 haplotype. Tau and α-synuclein frequently colocalized in limbic areas, but no correlation between total pathology scores was observed. This study confirms and extends the role of β-amyloid deposition and the MAPT H1 haplotype as contributing factors in DLB pathogenesis and demonstrates the confluence of multiple agents in neurodegenerative diseases.

Exploratory analysis of neuropsychological and neuroanatomical correlates of progressive mild cognitive impairment in Parkinson's disease

BACKGROUND

Parkinson's disease with mild cognitive impairment (PD-MCI) is a heterogeneous entity in terms of cognitive profiles and conversion to dementia. However, the risk factors for ongoing cognitive decline in patients with PD-MCI are not clearly defined.

METHODS

51 patients with PD-MCI were prospectively followed-up for a minimum of 2 years. Subjects were classified as MCI converters (n=15) or MCI non-converters (n=36) based on whether they were subsequently diagnosed with PD dementia. We explored cognitive profiles and neuroanatomical characteristics of PD-MCI converters using voxel based morphometry (VBM) of grey matter (GM) density and region of interest based volumetric analysis of the substantia innominata (SI).

RESULTS

PD-MCI converters showed more severe cognitive deficits in frontal executive functions, immediate verbal memory and visual recognition memory compared with PD-MCI non-converters. VBM analysis revealed that PD-MCI converters had significantly lower GM density in the left prefrontal areas, left insular cortex and bilateral caudate nucleus compared with that in PD-MCI non-converters. The mean normalised SI volume was significantly smaller in both PD-MCI converters (1.19±0.35, p<0.001) and PD-MCI non-converters (1.52±0.27, p<0.001) compared with that in controls (1.87±0.19). PD-MCI converters had a significantly smaller normalised SI volume than PD-MCI non-converters (p<0.001).

CONCLUSIONS

Our data show that atrophy in the frontostriatal areas and cholinergic structures, as well as frontal lobe associated cognitive performance, may act as predictors of dementia in PD-MCI patients, suggesting distinctive patterns of cognitive profiles and a neuroanatomical basis for progressive PD-MCI.

CSF α-synuclein improves diagnostic and prognostic performance of CSF tau and Aβ in Alzheimer's disease

Alzheimer's disease (AD) and Lewy body diseases (LBD), e.g., Parkinson's disease (PD) dementia and dementia with Lewy bodies (DLB), are common causes of geriatric cognitive impairments. In addition, AD and LBD are often found in the same patients at autopsy; therefore, biomarkers that can detect the presence of both pathologies in living subjects are needed. In this investigation, we report the assessment of α-synuclein (α-syn) in cerebrospinal fluid (CSF) and its association with CSF total tau (t-tau), phosphorylated tau181 (p-tau181), and amyloid beta1-42 (Aβ1-42) in subjects of the Alzheimer's Disease Neuroimaging Initiative (ADNI; n = 389), with longitudinal clinical assessments. A strong correlation was noted between α-syn and t-tau in controls, as well as in patients with AD and mild cognitive impairment (MCI). However, the correlation is not specific to subjects in the ADNI cohort, as it was also seen in PD patients and controls enrolled in the Parkinson's Progression Markers Initiative (PPMI; n = 102). A bimodal distribution of CSF α-syn levels was observed in the ADNI cohort, with high levels of α-syn in the subjects with abnormally increased t-tau values. Although a correlation was also noted between α-syn and p-tau181, there was a mismatch (α-syn-p-tau181-Mis), i.e., higher p-tau181 levels accompanied by lower α-syn levels in a subset of ADNI patients. We hypothesize that this α-syn-p-tau181-Mis is a CSF signature of concomitant LBD pathology in AD patients. Hence, we suggest that inclusion of measures of CSF α-syn and calculation of α-syn-p-tau181-Mis improves the diagnostic sensitivity/specificity of classic CSF AD biomarkers and better predicts longitudinal cognitive changes.

Assessing the causes and consequences of co-polymerization in amyloid formation

How, and why, different proteins form amyloid fibrils is most often studied in vitro using a single purified protein sequence. However, many amyloid diseases involve co-aggregation of different protein species, including proteins with/without post-translational modifications (e.g., different strains of PrP), proteins of different length (e.g., β₂-microglobulin and ΔN6, Aβ40, and Aβ42), sequence variants (e.g., Aβ and Aβ(ARC)), and proteins from different organisms (e.g., bovine PrP and human PrP). The consequences of co-aggregation of different proteins upon the structure, stability, species transmission and toxicity of the resulting amyloid aggregates is discussed here, including the role of co-aggregation in expanding the repertoire of oligomeric and fibrillar structures and how this can affect their biological and biophysical properties.

Structural characteristics of thermostable immunogenic outer membrane protein from Salmonella enterica serovar Typhi

In this work, we explored the acid-induced unfolding pathway of non-porin outer membrane protein (OMP), an immunogenic protein from Salmonella Typhi, by monitoring the conformational changes over a pH range of 1.0-7.0 by circular dichroism, intrinsic fluorescence, ANS binding, acrylamide quenching, and dynamic light scattering. The spectroscopic measurements showed that OMP in its native state at pH 7.0 exists in more stable and compact conformation. In contrast, at pH 2.0, OMP retains substantial amount of secondary structure, disrupted side chain interactions, increased hydrodynamic radii, and nearly four-fold increase in ANS fluorescence with respect to the native state, indicating that MG state exists at pH 2.0. Quenching of tryptophan fluorescence by acrylamide further confirmed the accumulation of a partially unfolded state between native and unfolded state. The effect of pH on the conformation and thermostability of OMP points towards its heat resistance at neutral pH (T m ~ 69 °C at pH 7.0, monitored by change in MRE222 nm). Acid unfolded state was also characterized by the lack of a cooperative thermal transition. All these results suggested that acid-induced unfolded state of OMP at pH 2.0 represented the molten globule state. The chemical denaturation studies with GuHCl and urea as denaturants showed dissimilar results. The chemical unfolding experiments showed that in both far-UV CD and fluorescence measurements, GuHCl is more efficient than urea. GuHCl is characterized by low C m (~1 M), while urea is characterized by high C m (~3 M). The fully unfolded states were reached at 2 M GuHCl and 4 M urea concentration, respectively. This study adds to several key considerations of importance in the development of therapeutic agents against typhoid fever for clinical purposes.

Neuropathological alterations in Alzheimer disease

The neuropathological hallmarks of Alzheimer disease (AD) include "positive" lesions such as amyloid plaques and cerebral amyloid angiopathy, neurofibrillary tangles, and glial responses, and "negative" lesions such as neuronal and synaptic loss. Despite their inherently cross-sectional nature, postmortem studies have enabled the staging of the progression of both amyloid and tangle pathologies, and, consequently, the development of diagnostic criteria that are now used worldwide. In addition, clinicopathological correlation studies have been crucial to generate hypotheses about the pathophysiology of the disease, by establishing that there is a continuum between "normal" aging and AD dementia, and that the amyloid plaque build-up occurs primarily before the onset of cognitive deficits, while neurofibrillary tangles, neuron loss, and particularly synaptic loss, parallel the progression of cognitive decline. Importantly, these cross-sectional neuropathological data have been largely validated by longitudinal in vivo studies using modern imaging biomarkers such as amyloid PET and volumetric MRI.

The many faces of α-synuclein: from structure and toxicity to therapeutic target

Disorders characterized by α-synuclein (α-syn) accumulation, Lewy body formation and parkinsonism (and in some cases dementia) are collectively known as Lewy body diseases. The molecular mechanism (or mechanisms) through which α-syn abnormally accumulates and contributes to neurodegeneration in these disorders remains unknown. Here, we provide an overview of current knowledge and prevailing hypotheses regarding the conformational, oligomerization and aggregation states of α-syn and their role in regulating α-syn function in health and disease. Understanding the nature of the various α-syn structures, how they are formed and their relative contributions to α-syn-mediated toxicity may inform future studies aiming to develop therapeutic prevention and intervention.

Synucleins: are they two-edged swords?

The synuclein family consists of three distinct highly homologous genes, α-synuclein, β-synuclein, and γ-synuclein, which have so far been found only in vertebrates. Proteins encoded by these genes are characterized by an acidic C-terminal region and five or six imperfect repeat motifs (KTKEGV) distributed throughout the highly conserved N-terminal region. Numerous data demonstrate that synucleins are implicated in two groups of the most devastating human disorders, i.e., neurodegenerative diseases (NDDs) and cancer. Mutations in the α-synuclein gene are associated with familial forms of Parkinson's disease (PD), and accumulation of α-synuclein inclusions is a hallmark of this disorder. In breast cancer, increased expression of γ-synuclein correlates with disease progression. Conversely, some results indicate that the members of the synuclein family may have a protective effect. How might these small proteins combine such controversial properties? We present evidence that synuclein's features are basically regulated by two mechanisms, i.e., posttranslational modifications (PTMs) and the level of their expression. We also discuss a new, emerging area of investigation of synucleins, namely, their role in the cell-to-cell propagation of pathology.

In vivo alterations in calcium buffering capacity in transgenic mouse model of synucleinopathy

Abnormal accumulation of α-synuclein is centrally involved in the pathogenesis of many disorders with Parkinsonism and dementia. Previous in vitro studies suggest that α-synuclein dysregulates intracellular calcium. However, it is unclear whether these alterations occur in vivo. For this reason, we investigated calcium dynamics in transgenic mice expressing human WT α-synuclein using two-photon microscopy. We imaged spontaneous and stimulus-induced neuronal activity in the barrel cortex. Transgenic mice exhibited augmented, long-lasting calcium transients characterized by considerable deviation from the exponential decay. The most evident pathology was observed in response to a repetitive stimulation in which subsequent stimuli were presented before relaxation of calcium signal to the baseline. These alterations were detected in the absence of significant increase in neuronal spiking response compared with age-matched controls, supporting the possibility that α-synuclein promoted alterations in calcium dynamics via interference with intracellular buffering mechanisms. The characteristic shape of calcium decay and augmented response during repetitive stimulation can serve as in vivo imaging biomarkers in this model of neurodegeneration, to monitor progression of the disease and screen candidate treatment strategies.

α-Synuclein and neuronal cell death

Parkinson’s disease (PD) is a progressive neurodegenerative disorder affecting ∼1 % of people over the age of 65. Neuropathological hallmarks of PD are prominent loss of dopaminergic (DA) neurons in the substantia nigra and formation of intraneuronal protein inclusions termed Lewy bodies, composed mainly of α-synuclein (αSyn). Missense mutations in αSyn gene giving rise to production of degradation-resistant mutant proteins or multiplication of wild-type αSyn gene allele can cause rare inherited forms of PD. Therefore, the existence of abnormally high amount of αSyn protein is considered responsible for the DA neuronal death in PD. Normally, αSyn protein localizes to presynaptic terminals of neuronal cells, regulating the neurotransmitter release through the modulation of assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex. On the other hand, of note, pathological examinations on the recipient patients of fetal nigral transplants provided a prion-like cell-to-cell transmission hypothesis for abnormal αSyn. The extracellular αSyn fibrils can internalize to the cells and enhance intracellular formation of protein inclusions, thereby reducing cell viability. These findings suggest that effective removal of abnormal species of αSyn in the extracellular space as well as intracellular compartments can be of therapeutic relevance. In this review, we will focus on αSyn-triggered neuronal cell death and provide possible disease-modifying therapies targeting abnormally accumulating αSyn.

Autophagy in dementias

Dementias are a varied group of disorders typically associated with memory loss, impaired judgment and/or language and by symptoms affecting other cognitive and social abilities to a degree that interferes with daily functioning. Alzheimer's disease (AD) is the most common cause of a progressive dementia, followed by dementia with Lewy bodies (DLB), frontotemporal dementia (FTD), (VaD) and HIV-associated neurocognitive disorders (HAND). The pathogenesis of this group of disorders has been linked to the abnormal accumulation of proteins in the brains of affected individuals, which in turn has been related to deficits in protein clearance. Autophagy is a key cellular protein clearance pathway with proteolytic cleavage and degradation via the ubiquitin-proteasome pathway representing another important clearance mechanism. Alterations in the levels of autophagy and the proteins associated with the autophagocytic pathway have been reported in various types of dementias. This review will examine recent literature across these disorders and highlight a common theme of altered autophagy across the spectrum of the dementias.

An extracellular mechanism that can explain the neurotoxic effects of α-synuclein aggregates in the brain

Neurodegenerative diseases, such as Parkinson's disease (PD), Alzheimer's disease (AD), and Dementia with Lewy bodies (DLB), display an accumulation of proteins including α-synuclein aggregates in cortical and subcortical regions of the brain. PD is a complex, progressive disease which involves damage of motor and cognitive brain regions, as well as autonomic and sensory areas. Since α-synuclein is a neuronal cytosolic protein, it is assumed that pathogenic changes induced by α-synuclein aggregates occur only at the cytoplasmic level. However, recent studies have identified the presence of extracellular α-synuclein, suggesting that the pathogenic action of this protein may also occur in the extracellular milieu through an unknown mechanism. One of the hypotheses is that extracellular α-synuclein aggregates or oligomers may directly disrupt the neuronal membrane by the formation of a pore reminiscent to the ones formed by β-amyloid aggregates. Here, we will review some evidence that support this mechanism, analyzing the interactions of α-synuclein with components of the plasma membrane, the formation of pore/perforated structures, and the implications on ionic dyshomeostasis. Furthermore, we will also discuss how this mechanism can be integrated into a general phenomenon that may explain the synaptotoxicity and neurotoxicity observed in different neurodegenerative diseases.

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.

Interaction between pathogenic proteins in neurodegenerative disorders

The misfolding and progressive aggregation of specific proteins in selective regions of the nervous system is a seminal occurrence in many neurodegenerative disorders, and the interaction between pathological/toxic proteins to cause neurodegeneration is a hot topic of current neuroscience research. Despite clinical, genetic and experimental differences, increasing evidence indicates considerable overlap between synucleinopathies, tauopathies and other protein-misfolding diseases. Inclusions, often characteristic hallmarks of these disorders, suggest interactions of pathological proteins enganging common downstream pathways. Novel findings that have shifted our understanding in the role of pathologic proteins in the pathogenesis of Alzheimer, Parkinson, Huntington and prion diseases, have confirmed correlations/overlaps between these and other neurodegenerative disorders. Emerging evidence, in addition to synergistic effects of tau protein, amyloid-β, α-synuclein and other pathologic proteins, suggests that prion-like induction and spreading, involving secreted proteins, are major pathogenic mechanisms in various neurodegenerative diseases, depending on genetic backgrounds and environmental factors. The elucidation of the basic molecular mechanisms underlying the interaction and spreading of pathogenic proteins, suggesting a dualism or triad of neurodegeneration in protein-misfolding disorders, is a major challenge for modern neuroscience, to provide a deeper insight into their pathogenesis as a basis of effective diagnosis and treatment.

γ-Synuclein: seeding of α-synuclein aggregation and transmission between cells

Protein misfolding and aggregation is a ubiquitous phenomenon associated with a wide range of diseases. The synuclein family comprises three small naturally unfolded proteins implicated in neurodegenerative diseases and some forms of cancer. α-Synuclein is a soluble protein that forms toxic inclusions associated with Parkinson's disease and several other synucleinopathies. However, the triggers inducing its conversion into noxious species are elusive. Here we show that another member of the family, γ-synuclein, can be easily oxidized and form annular oligomers that accumulate in cells in the form of deposits. Importantly, oxidized γ-synuclein can initiate α-synuclein aggregation. Two amino acid residues in γ-synuclein, methionine and tyrosine located in neighboring positions (Met(38) and Tyr(39)), are most easily oxidized. Their oxidation plays a key role in the ability of γ-synuclein to aggregate and seed the aggregation of α-synuclein. γ-Synuclein secreted from neuronal cells into conditioned medium in the form of exosomes can be transmitted to glial cells and cause the aggregation of intracellular proteins. Our data suggest that post-translationally modified γ-synuclein possesses prion-like properties and may induce a cascade of events leading to synucleinopathies.

Exosomes: vehicles for the transfer of toxic proteins associated with neurodegenerative diseases?

Exosomes are small membranous vesicles secreted by a number of cell types including neurons and can be isolated from conditioned cell media or bodily fluids such as urine and plasma. Exosome biogenesis involves the inward budding of endosomes to form multivesicular bodies (MVB). When fused with the plasma membrane, the MVB releases the vesicles into the extracellular environment as exosomes. Proposed functions of these vesicles include roles in cell–cell signaling, removal of unwanted proteins, and the transfer of pathogens between cells. One such pathogen which exploits this pathway is the prion, the infectious particle responsible for the transmissible neurodegenerative diseases such as Creutzfeldt–Jakob disease (CJD) of humans or bovine spongiform encephalopathy (BSE) of cattle. Similarly, exosomes are also involved in the processing of the amyloid precursor protein (APP) which is associated with Alzheimer’s disease. Exosomes have been shown to contain full-length APP and several distinct proteolytically cleaved products of APP, including Aβ. In addition, these fragments can be modulated using inhibitors of the proteases involved in APP cleavage. These observations provide further evidence for a novel pathway in which PrP and APP fragments are released from cells. Other proteins such as superoxide dismutase I and alpha-synuclein (involved in amyotrophic lateral sclerosis and Parkinson’s disease, respectively) are also found associated with exosomes. This review will focus on the role of exosomes in neurodegenerative disorders and discuss the potential of these vesicles for the spread of neurotoxicity, therapeutics, and diagnostics for these diseases.

Examining the mechanisms that link β-amyloid and α-synuclein pathologies

β-amyloid (Aβ) and α-synuclein (α-syn) are aggregation-prone proteins typically associated with two distinct neurodegenerative disorders: Alzheimer's disease (AD) and Parkinson's disease. Yet α-syn was first found in association with AD plaques several years before being linked to Parkinson's disease or Lewy body formation. Nowadays, a large subset of AD patients (~50%) is well recognized to co-exhibit significant α-syn Lewy body pathology. Unfortunately, these AD Lewy body variant patients suffer from additional symptoms and an accelerated disease course. Basic research has begun to show that Aβ and α-syn may act synergistically to promote the aggregation and accumulation of each other. While the exact mechanisms by which these proteins interact remain unclear, growing evidence suggests that Aβ may drive α-syn pathology by impairing protein clearance, activating inflammation, enhancing phosphorylation, or directly promoting aggregation. This review examines the interactions between Aβ and α-syn and proposes potential mechanistic links between Aβ accumulation and α-syn pathogenesis.

Prion infection promotes extensive accumulation of α-synuclein in aged human α-synuclein transgenic mice

In neurodegenerative disorders of the aging population, misfolded proteins, such as PrP(Sc), α-synuclein, amyloid β protein and tau, can interact resulting in enhanced aggregation, cross seeding and accelerated disease progression. Previous reports have shown that in Creutzfeldt-Jakob disease and scrapie, α-synuclein accumulates near PrP(Sc) deposits. However, it is unclear if pre-existing human α-synuclein aggregates modified prion disease pathogenesis, or if PrP(Sc) exacerbates the α-synuclein pathology. Here, we inoculated infectious prions into aged α-synuclein transgenic (tg) and non-transgenic littermate control mice by the intracerebral route. Remarkably, inoculation of RML and mNS prions into α-synuclein tg mice resulted in more extensive and abundant intraneuronal and synaptic α-synuclein accumulation. In addition, infectious prions led to the formation of perineuronal α-synuclein deposits with a neuritic plaque-like appearance. Prion pathology was unmodified by the presence of α-synuclein. However, with the mNS prion strain there was a modest but significant acceleration in the time to terminal prion disease in mice having α-synuclein aggregates as compared with non-tg mice. Taken together, these studies support the notion that PrP(Sc) directly or indirectly promotes α-synuclein pathology.

Integrative analysis of common neurodegenerative diseases using gene association, interaction networks and mRNA expression data

Alzheimer's and Parkinson's diseases (AD and PD) are two common neurodegenerative diseases primarily affecting memory and motor functions, respectively. In this study, we integrated data from various sources, and took a systems-biology approach to compare and contrast the molecular and network based dysregulation associated with AD and PD and we integrated these data with known pathways of drug treatment. First, we identified genes that exhibit consistent prior evidence of association with each disease. Then, we extracted disease-specific sub-networks from a human interactome database using associated genes as seeds. To rank the sub-networks we used existing gene expression data from cases and controls. Comparison of resulting disease-associated genes and networks revealed significant overlap between AD and PD. In addition, the identified sub-networks correlated with known drug interdiction pathways, and suggested new potential targets for intervention.

Role of α-synuclein penetration into the membrane in the mechanisms of oligomer pore formation

Parkinson's disease (PD) and dementia with Lewy bodies are common disorders of the aging population and characterized by the progressive accumulation of α-synuclein (α-syn) in the central nervous system. Aggregation of α-syn into oligomers with a ring-like appearance has been proposed to play a role in toxicity. However, the molecular mechanisms and the potential sequence of events involved in the formation of pore-like structures are unclear. We utilized computer modeling and cell-based studies to investigate the process of oligomerization of wild-type and A53T mutant α-syn in membranes. The studies suggest that α-syn penetrates the membrane rapidly, changing its conformation from α-helical towards a coiled structure. This penetration facilitates the incorporation of additional α-syn monomers in the complex, and the subsequent displacement of phospholipids and the formation of oligomers in the membrane. This process occurred more rapidly, and with a more favorable energy of interaction, for mutant A53T compared with wild-type α-syn. After 4 ns of simulation of the protein-membrane model, α-syn had penetrated through two-thirds of the membrane. By 9 ns, the penetration of the annular α-syn oligomers can result in the formation of pore-like structures that fully perforate the lipid bilayer. Experimental incubation of recombinant α-syn in synthetic membranes resulted in the formation of similar pore-like complexes. Moreover, mutant (A53T) α-syn had a greater tendency to accumulate in neuronal membrane fractions in cell cultures, resulting in greater neuronal permeability, as demonstrated with the calcein efflux assay. These studies provide a sequential molecular explanation for the process of α-syn oligomerization in the membrane, and support the role of formation of pore-like structures in the pathogenesis of the neurodegenerative process in PD.

Oligomeric intermediates in amyloid formation: structure determination and mechanisms of toxicity

Oligomeric intermediates are non-fibrillar polypeptide assemblies that occur during amyloid fibril formation and that are thought to underlie the aetiology of amyloid diseases, such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Focusing primarily on the oligomeric states formed from Alzheimer's disease β-amyloid (Aβ) peptide, this review will make references to other polypeptide systems, highlighting common principles or sequence-specific differences. The covered topics include the structural properties and polymorphism of oligomers, the biophysical mechanism of peptide self-assembly and its role for pathogenicity in amyloid disease. Oligomer-dependent toxicity mechanisms will be explained along with recently emerging possibilities of interference.

α-Synuclein aggregation and modulating factors

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

Cell-to-cell transmission of α-synuclein aggregates

It is now recognized that the cell-to-cell transmission of misfolded proteins such as α-synuclein contributes to the neurodegenerative phenotype in neurological disorders such as idiopathic Parkinson's disease, Dementia with Lewy bodies, and Parkinson's disease dementia. Thus, establishing cell-based models for the transmission of α-synuclein is of importance to understand the mechanisms of neurodegeneration in these disorders and to develop new therapies. Here we describe methods to study the neuron-to-neuron propagation of α-synuclein in an in vitro setting that also has in vivo applications.

Cerebrospinal fluid amyloid β and tau in LRRK2 mutation carriers

OBJECTIVE

The goal of the current investigation was to examine a cohort of symptomatic and asymptomatic LRRK2 mutation carriers, in order to address whether the reported alterations in amyloid β (Aβ) and tau species in the CSF of patients with sporadic Parkinson disease (PD) are a part of PD pathogenesis, the aging process, or a comorbid disease in patients with PD, and to explore the possibility of Aβ and tau as markers of early or presymptomatic PD.

METHODS

CSF Aβ42, total tau, and phosphorylated tau were measured with Luminex assays in 26 LRRK2 mutation carriers, who were either asymptomatic (n = 18) or had a phenotype resembling sporadic PD (n = 8). All patients also underwent PET scans with 18F-6-fluoro-l-dopa (FD), 11C-(±)-α-dihydrotetrabenazine (DTBZ), and 11C-d-threo-methylphenidate (MP) to measure dopaminergic function in the striatum. The levels of CSF markers were then compared to each PET measurement.

RESULTS

Reduced CSF Aβ42 and tau levels correlated with lower striatal dopaminergic function as determined by all 3 PET tracers, with a significant association between Aβ42 and FD uptake. When cases were restricted to carriers of the G2019S mutation, the most common LRRK2 variant in our cohort, significant correlations were also observed for tau.

CONCLUSIONS

The disposition of Aβ and tau is likely important in both LRRK2-related and sporadic PD, even during early phases of the disease. A better understanding of their production, aggregation, and degradation, including changes in their CSF levels, may provide insights into the pathogenesis of PD and the potential utility of these proteins as biomarkers.

Effect of melatonin on α-synuclein self-assembly and cytotoxicity

α-Synuclein (αS) assembly has been implicated as a critical step in the development of Lewy body diseases such as Parkinson's disease and dementia with Lewy bodies. Melatonin (Mel), a secretory product of the pineal gland, is known to have beneficial effects such as an antioxidant function and neuroprotection. To elucidate whether Mel has an antiassembly effect, here we used circular dichroism spectroscopy, photoinduced crosslinking of unmodified proteins, thioflavin S fluorescence, size exclusion chromatography, electron microscopy and atomic force microscopy to examine the effects of Mel on the αS assembly. We also examined the effects of Mel on αS-induced cytotoxicity by assaying 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide metabolism in αS-treated, primary neuronal cells. Initial studies revealed that Mel blocked αS fibril formation as well as destabilizing preformed αS fibrils. Subsequent evaluation of the assembly-stage specificity of the effect showed that Mel was able to inhibit protofibril formation, oligomerization, and secondary structure transitions. Importantly, Mel decreased αS-induced cytotoxicity. These data suggest a mechanism of action for Mel, inhibition of assembly of toxic polymers and protection of neurons from their effect.

PESCADOR, a web-based tool to assist text-mining of biointeractions extracted from PubMed queries

Background

Biological function is greatly dependent on the interactions of proteins with other proteins and genes. Abstracts from the biomedical literature stored in the NCBI's PubMed database can be used for the derivation of interactions between genes and proteins by identifying the co-occurrences of their terms. Often, the amount of interactions obtained through such an approach is large and may mix processes occurring in different contexts. Current tools do not allow studying these data with a focus on concepts of relevance to a user, for example, interactions related to a disease or to a biological mechanism such as protein aggregation.

Results

To help the concept-oriented exploration of such data we developed PESCADOR, a web tool that extracts a network of interactions from a set of PubMed abstracts given by a user, and allows filtering the interaction network according to user-defined concepts. We illustrate its use in exploring protein aggregation in neurodegenerative disease and in the expansion of pathways associated to colon cancer.

Conclusions

PESCADOR is a platform independent web resource available at: http://cbdm.mdc-berlin.de/tools/pescador/