Pathophysiology of synuclein aggregation in Lewy body disease

Potential treatment of Parkinson's disease using new-generation carbon nanotubes: a biomolecular in silico study

Background: One of the underlying mechanisms of Parkinson's disease is the aggregation of α-synuclein proteins, including amyloids and Lewy bodies in the brain. Aim: To study the inhibitory effect of doped carbon nanotubes (CNTs) on amyloid aggregation. Materials & methods: Molecular dynamics tools were utilized to simulate the influence of CNTs doped with phosphorus, nitrogen and bromine and nitrogen on the formation of α-synuclein amyloid. Results: The CNTs exhibited strong interactions with α-synuclein, with phosphorus-doped CNTs having the most substantial interactions. Conclusion: Doped-CNTs, especially phosphorus-doped carbon nanotube could effectively prevent α-synuclein amyloid formation, thus, it could be considered as a potential treatment for Parkinson's disease. However, further in vitro and clinical investigations are required.

Proteomic Characterization of the Olfactory Molecular Imbalance in Dementia with Lewy Bodies

Olfactory dysfunction is one of the prodromal symptoms in dementia with Lewy bodies (DLB). However, the molecular pathogenesis associated with decreased smell function remains largely undeciphered. We generated quantitative proteome maps to detect molecular alterations in olfactory bulbs (OB) derived from DLB subjects compared to neurologically intact controls. A total of 3214 olfactory proteins were quantified, and 99 proteins showed significant alterations in DLB cases. Protein interaction networks disrupted in DLB indicated an imbalance in translation and the synaptic vesicle cycle. These alterations were accompanied by alterations in AKT/MAPK/SEK1/p38 MAPK signaling pathways that showed a distinct expression profile across the OB–olfactory tract (OT) axis. Taken together, our data partially reflect the missing links in the biochemical understanding of olfactory dysfunction in DLB.

Fatty Acid-Binding Protein 3 is Critical for α-Synuclein Uptake and MPP+-Induced Mitochondrial Dysfunction in Cultured Dopaminergic Neurons

α-Synuclein is an abundant neuronal protein that accumulates in insoluble inclusions in Parkinson′s disease and other synucleinopathies. Fatty acids partially regulate α-Synuclein accumulation, and mesencephalic dopaminergic neurons highly express fatty acid-binding protein 3 (FABP3). We previously demonstrated that FABP3 knockout mice show decreased α-Synuclein oligomerization and neuronal degeneration of tyrosine hydroxylase (TH)-positive neurons in vivo. In this study, we newly investigated the importance of FABP3 in α-Synuclein uptake, 1-methyl-4-phenylpyridinium (MPP⁺)-induced axodendritic retraction, and mitochondrial dysfunction. To disclose the issues, we employed cultured mesencephalic neurons derived from wild type or FABP3^−/− C57BL6 mice and performed immunocytochemical analysis. We demonstrated that TH⁺ neurons from FABP3^+/+ mice take up α-Synuclein monomers while FABP3^−/− TH⁺ neurons do not. The formation of filamentous α-Synuclein inclusions following treatment with MPP⁺ was observed only in FABP3^+/+, and not in FABP3^−/− neurons. Notably, detailed morphological analysis revealed that FABP^−/− neurons did not exhibit MPP⁺-induced axodendritic retraction. Moreover, FABP3 was also critical for MPP⁺-induced reduction of mitochondrial activity and the production of reactive oxygen species. These data indicate that FABP3 is critical for α-Synuclein uptake in dopaminergic neurons, thereby preventing synucleinopathies, including Parkinson′s disease.

Free-Water Imaging in White and Gray Matter in Parkinson's Disease

This study aimed to discriminate between neuroinflammation and neuronal degeneration in the white matter (WM) and gray matter (GM) of patients with Parkinson’s disease (PD) using free-water (FW) imaging. Analysis using tract-based spatial statistics (TBSS) of 20 patients with PD and 20 healthy individuals revealed changes in FW imaging indices (i.e., reduced FW-corrected fractional anisotropy (FA_T), increased FW-corrected mean, axial, and radial diffusivities (MD_T, AD_T, and RD_T, respectively) and fractional volume of FW (FW) in somewhat more specific WM areas compared with the changes of DTI indices. The region-of-interest (ROI) analysis further supported these findings, whereby those with PD showed significantly lower FA_T and higher MD_T, AD_T, and RD_T (indices of neuronal degeneration) in anterior WM areas as well as higher FW (index of neuroinflammation) in posterior WM areas compared with the controls. Results of GM-based spatial statistics (GBSS) analysis revealed that patients with PD had significantly higher MD_T, AD_T, and FW than the controls, whereas ROI analysis showed significantly increased MD_T and FW and a trend toward increased AD_T in GM areas, corresponding to Braak stage IV. These findings support the hypothesis that neuroinflammation precedes neuronal degeneration in PD, whereas WM microstructural alterations precede changes in GM.

Visual hallucinations, thalamocortical physiology and Lewy body disease: A review

One of the core diagnostic criteria for Dementia with Lewy Bodies (DLB) is the presence of visual hallucinations. The presence of hallucinations, along with fluctuations in the level of arousal and sleep disturbance, point to potential pathological mechanisms at the level of the thalamus. However, the potential role of thalamic dysfunction in DLB, particularly as it relates to the presence of formed visual hallucinations is not known. Here, we review the literature on the pathophysiology of DLB with respect to modern theories of thalamocortical function and attempt to derive an understanding of how such hallucinations arise. Based on the available literature, we propose that combined thalamic-thalamic reticular nucleus and thalamocortical pathology may explain the phenomenology of visual hallucinations in DLB. In particular, diminished α7 cholinergic activity in the thalamic reticular nucleus may critically disinhibit thalamocortical activity. Further, concentrated pathological changes within the posterior regions of the thalamus may explain the predilection for the hallucinations to be visual in nature.

Native Top-Down Mass Spectrometry and Ion Mobility MS for Characterizing the Cobalt and Manganese Metal Binding of α-Synuclein Protein

Structural characterization of intrinsically disordered proteins (IDPs) has been a major challenge in the field of protein science due to limited capabilities to obtain full-length high-resolution structures. Native ESI-MS with top-down MS was utilized to obtain structural features of protein-ligand binding for the Parkinson's disease-related protein, α-synuclein (αSyn), which is natively unstructured. Binding of heavy metals has been implicated in the accelerated formation of αSyn aggregation. Using high-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, native top-down MS with various fragmentation methods, including electron capture dissociation (ECD), collisional activated dissociation (CAD), and multistage tandem MS (MS³), deduced the binding sites of cobalt and manganese to the C-terminal region of the protein. Ion mobility MS (IM-MS) revealed a collapse toward compacted states of αSyn upon metal binding. The combination of native top-down MS and IM-MS provides structural information of protein-ligand interactions for intrinsically disordered proteins. Graphical Abstract ᅟ.

Dementia

Dementia is a syndrome seen most commonly in older people and characterized by a decline in cognitive performance which impacts on the person's ability to function. There are approximately 47 million people worldwide with dementia and there are 10 million new cases every year. It is a major cause of disability and dependence and impacts on the physical, psychologic, and social well-being of families and carers. Alzheimer's disease is the most common form of dementia. Gait and balance impairments are common in people with dementia and contribute to the significantly elevated risk of falls. Older people with dementia are at increased risk of injury, institutionalization, hospitalization, morbidity, and death after a fall. There is preliminary evidence, predominantly from relatively small studies, that falls and disability can be prevented in this population. However, more good-quality research is needed, both to provide some certainty around the existing evidence base as well as to explore alternate approaches to prevention, including combined cognitive-motor training and cognitive pharmacotherapy.

Metabolic connectomics targeting brain pathology in dementia with Lewy bodies

Dementia with Lewy bodies is characterized by α-synuclein accumulation and degeneration of dopaminergic and cholinergic pathways. To gain an overview of brain systems affected by neurodegeneration, we characterized the [18F]FDG-PET metabolic connectivity in 42 dementia with Lewy bodies patients, as compared to 42 healthy controls, using sparse inverse covariance estimation method and graph theory. We performed whole-brain and anatomically driven analyses, targeting cholinergic and dopaminergic pathways, and the α-synuclein spreading. The first revealed substantial alterations in connectivity indexes, brain modularity, and hubs configuration. Namely, decreases in local metabolic connectivity within occipital cortex, thalamus, and cerebellum, and increases within frontal, temporal, parietal, and basal ganglia regions. There were also long-range disconnections among these brain regions, all supporting a disruption of the functional hierarchy characterizing the normal brain. The anatomically driven analysis revealed alterations within brain structures early affected by α-synuclein pathology, supporting Braak's early pathological staging in dementia with Lewy bodies. The dopaminergic striato-cortical pathway was severely affected, as well as the cholinergic networks, with an extensive decrease in connectivity in Ch1-Ch2, Ch5-Ch6 networks, and the lateral Ch4 capsular network significantly towards the occipital cortex. These altered patterns of metabolic connectivity unveil a new in vivo scenario for dementia with Lewy bodies underlying pathology in terms of changes in whole-brain metabolic connectivity, spreading of α-synuclein, and neurotransmission impairment.

Dementia with Lewy Bodies: Molecular Pathology in the Frontal Cortex in Typical and Rapidly Progressive Forms

Objectives

The goal of this study was to assess mitochondrial function, energy, and purine metabolism, protein synthesis machinery from the nucleolus to the ribosome, inflammation, and expression of newly identified ectopic olfactory receptors (ORs) and taste receptors (TASRs) in the frontal cortex of typical cases of dementia with Lewy bodies (DLB) and cases with rapid clinical course (rpDLB: 2 years or less) compared with middle-aged non-affected individuals, in order to learn about the biochemical abnormalities underlying Lewy body pathology.

Methods

Real-time quantitative PCR, mitochondrial enzymatic assays, and analysis of β-amyloid, tau, and synuclein species were used.

Results

The main alterations in DLB and rpDLB, which are more marked in the rapidly progressive forms, include (i) deregulated expression of several mRNAs and proteins of mitochondrial subunits, and reduced activity of complexes I, II, III, and IV of the mitochondrial respiratory chain; (ii) reduced expression of selected molecules involved in energy metabolism and increased expression of enzymes involved in purine metabolism; (iii) abnormal expression of nucleolar proteins, rRNA18S, genes encoding ribosomal proteins, and initiation factors of the transcription at the ribosome; (iv) discrete inflammation; and (v) marked deregulation of brain ORs and TASRs, respectively. Severe mitochondrial dysfunction involving activity of four complexes, minimal inflammatory responses, and dramatic altered expression of ORs and TASRs discriminate DLB from Alzheimer’s disease. Altered solubility and aggregation of α-synuclein, increased β-amyloid bound to membranes, and absence of soluble tau oligomers are common in DLB and rpDLB. Low levels of soluble β-amyloid are found in DLB. However, increased soluble β-amyloid 1–40 and β-amyloid 1–42, and increased TNFα mRNA and protein expression, distinguish rpDLB.

Conclusion

Molecular alterations in frontal cortex in DLB involve key biochemical pathways such as mitochondria and energy metabolism, protein synthesis, purine metabolism, among others and are accompanied by discrete innate inflammatory response.

The possible involvement of mitochondrial dysfunctions in Lewy body dementia: a systematic review

The hallmark of dementia with Lewy bodies (DLB) is the “Lewy body”, an abnormal aggregation of alpha-synuclein found in some areas of the brain. The brain is the organ/system that is most vulnerable to this oxidative damage, and reactive oxygen species can cause neurodegenerative diseases. Different models of mitochondrial deregulation have been compared in DLB. The results are consistent with the hypothesis that alpha-synuclein affects the mitochondria themselves, increasing their sensitivity or leading to cell death through protective (neurosin) and accelerating (cytochrome c) factors. This systematic review suggests that mitochondria play an important role in neurodegeneration and a crucial role in the formation of Lewy bodies. DLB is a disease characterized by abnormal accumulation of alpha-synuclein that could result in the release of cytochrome c and subsequent activation of the apoptotic cascade.

Anomalies occurring in lipid profiles and protein distribution in frontal cortex lipid rafts in dementia with Lewy bodies disclose neurochemical traits partially shared by Alzheimer's and Parkinson's diseases

Lipid rafts are highly dynamic membrane microdomains intimately associated with cell signaling. Compelling evidence has demonstrated that alterations in lipid rafts are associated with neurodegenerative diseases such Alzheimer's disease, but at present, whether alterations in lipid raft microdomains occur in other types of dementia such dementia with Lewy bodies (DLB) remains unknown. Our analyses reveal that lipid rafts from DLB exhibit aberrant lipid profiles including low levels of n-3 long-chain polyunsaturated fatty acids (mainly docosahexaenoic acid), plasmalogens and cholesterol, and reduced unsaturation and peroxidability indexes. As a consequence, lipid raft resident proteins holding principal factors of the β-amyloidogenic pathway, including β-amyloid precursor protein, presenilin 1, β-secretase, and PrP, are redistributed between lipid rafts and nonraft domains in DLB frontal cortex. Meta-analysis discloses certain similarities in the altered composition of lipid rafts between DLB and Parkinson's disease which are in line with the spectrum of Lewy body diseases. In addition, redistribution of proteins linked to the β-amyloidogenic pathway in DLB can facilitate generation of β-amyloid, thus providing mechanistic clues to the intriguing convergence of Alzheimer's disease pathology, particularly β-amyloid deposition, in DLB.

DOPAL is transmissible to and oligomerizes alpha-synuclein in human glial cells

INTRODUCTION

Glial cytoplasmic inclusions (GCIs) containing alpha-synuclein (AS) are a neuropathologic hallmark of multiple system atrophy (MSA). Oligomerized AS is thought to be the pathogenic form of the protein. Glial cells normally express little AS, but they can take up AS from the extracellular fluid. 3,4-Dihydroxyphenylacetaldehyde (DOPAL), an obligate intermediate in the intra-neuronal metabolism of dopamine (DA), potently oligomerizes AS. In this study we tested whether DOPAL is taken up by human glial cells and augments intracellular oligomerization of AS.

METHODS

DOPAL (exogenous or endogenous from co-incubation with PC12 cells) and AS (native or A53T mutant form) were added to the incubation medium of glial cells (glioblastoma or MO3.13 oligodendrocytes). Glial cellular contents of DOPAL and its intracellular metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were measured at up to 180 min of incubation. Glial cellular AS oligomers were quantified by Western blotting.

RESULTS

Neither glioblastoma nor MO3.13 cells contained endogenous catecholamines or AS. Co-incubation of the cells with DA-producing PC12 cells produced time-related increases in DOPAL and DOPAC contents. Similarly, glial cellular DOPAL and DOPAC contents increased rapidly after addition of DOPAL to the medium. After addition of native or A53T-AS, intracellular AS also increased. Incubation of glial cells with both DOPAL and AS enhanced the intracellular oligomerization of native and A53T-AS.

CONCLUSIONS

DOPAL is transmissible to glial cells and enhances intracellular oligomerization of AS. An interaction of DOPAL with AS might help explain the formation of CGIs in MSA.

Differential sialylation of serpin A1 in the early diagnosis of Parkinson's disease dementia

The prevalence of Parkinson’s disease (PD) increases with age. Up to 50% of PD show cognitive decline in terms of a mild cognitive impairment already in early stages that predict the development of dementia, which can occur in up to 80% of PD patients over the long term, called Parkinson’s disease dementia (PDD). So far, diagnosis of PD/PDD is made according to clinical and neuropsychological examinations while laboratory data is only used for exclusion of other diseases. The aim of this study was the identification of possible biomarkers in cerebrospinal fluid (CSF) of PD, PDD and controls (CON) which predict the development of dementia in PD. For this, a proteomic approach optimized for CSF was performed using 18 clinically well characterized patients in a first step with subsequent validation using 84 patients. Here, we detected differentially sialylated isoforms of Serpin A1 as marker for differentiation of PD versus PDD in CSF. Performing 2D-immunoblots, all PDD patients could be identified correctly (sensitivity 100%). Ten out of 24 PD patients showed Serpin A1 isoforms in a similar pattern like PDD, indicating a specificity of 58% for the test-procedure. In control samples, no additional isoform was detected. On the basis of these results, we conclude that differentially sialylated products of Serpin A1 are an interesting biomarker to indicate the development of a dementia during the course of PD.

Cognitive status correlates with white matter alteration in Parkinson's disease

Patients with Parkinson's disease (PD) can develop mild cognitive impairment (PD-MCI), frequently progressing to dementia (PDD). Here, we aimed to elucidate the relationship between white matter alteration and cognitive status in PD and dementia with Lewy bodies (DLB) by using diffusion tensor imaging. We also compared the progression patterns of white and gray matter and the cerebral perfusion. We enrolled patients with PD cognitively normal (PD-CogNL, n = 32), PD-MCI (n = 28), PDD (n = 25), DLB (n = 29), and age- and sex-matched healthy control subjects (n = 40). Fractional anisotropy (FA) map of a patient group was compared with that of control subjects by using tract-based spatial statistics. For the patient cohort, intersubject voxel-wise correlation was performed between FA values and Mini-Mental Status Examination (MMSE) scores. We also evaluated the gray matter and the cerebral perfusion by conducting a voxel-based analysis. There were significantly decreased FA values in many major tracts in patients with PD-MCI, PDD, and DLB, but not in PD-CogNL, compared with control subjects. FA values in the certain white matter areas, particularly the bilateral parietal white matter, were significantly correlated with MMSE scores in patients with PD. Patients with PDD and DLB had diffuse gray matter atrophy. All patient groups had occipital and posterior parietal hypoperfusion when compared with control subjects. Our results suggest that white matter damage underlies cognitive impairment in PD, and cognitive impairment in PD progresses with functional alteration (hypoperfusion) followed by structural alterations in which white matter alteration precedes gray matter atrophy.

Parkinson’s disease: diagnostic relevance of elevated levels of soluble α-synuclein oligomers in cerebrospinal fluid

Evaluation of: Tokuda T, Qureshi MM, Ardah MT et al.: Detection of elevated levels of α-synuclein oligomers in CSF from patients with Parkinson disease. Neurology 75, 1766–1772 (2010). This study measured the cerebrospinal fluid (CSF) levels of total and oligomeric α-synuclein (the principal component of Lewy bodies and Lewy neuritis and is characteristic of Lewy body dementias, including Parkinson’s disease [PD]). The authors used quantitative ELISA assays to detect these two types of α-synuclein in PD and control groups, as well as α-synuclein oligomers in PD, progressive supranuclear palsy (PSP), Alzheimer’s disease (AD) and control subjects. All patients fulfilled the well-established clinical criteria for AD, PD and PSP. The PD group had highly elevated α-synuclein oligomers in relation to those detected in the control group (p < 0.0001; sensitivity 75% and specificity 87.5%; area under the curve of 0.859). Greater sensitivity and specificity (89.3 and 90.6%, respectively), with an area under the curve of 0.948, was obtained when the CSF oligomers:total α-synuclein ratio was used. The CSF α-synuclein oligomers and ratio measures were not influenced by age, disease duration and/or clinical symptomatology, including dementia and motor disability in the PD subjects. Interestingly, subjects with mild and early PD had significantly higher α-synuclein oligomer levels and ratios compared with control subjects. In the accompanying cross-sectional study, the CSF α-synuclein oligomer measures were significantly elevated in PD in comparison with AD (p < 0.001), PSP (p < 0.05) and control subjects (p < 0.05). The increased levels of CSF α-synuclein oligomers, even in patients with mild and early PD, suggest their potential use in diagnosing even presymptomatic PD. However, further work is now needed to establish whether these α-synuclein measures can differentiate PD from other α-synucleinopathies (e.g., dementia with Lewy bodies, multiple system atrophy, neurodegeneration with brain iron accumulation), as well as neurological diseases characterized by Parkinsonism but not α-synuclein aggregates (so-called ‘non-α-synucleinopathies’, including a number of taupathies characterized by Parkinsonism [e.g., PSP, corticobasal degeneration, frontotemporal dementia and Parkinsonism linked to chromosome 17 or dementia pugilistica]).

Cerebrospinal fluid biomarkers for dementia with lewy bodies

More than 750,000 of the UK population suffer from some form of cognitive impairment and dementia. Of these, 5–20% will have Dementia with Lewy Bodies (DLB). Clinico-pathological studies have shown that it is the low frequency of DLB clinical core features that makes the DLB diagnosis hardly recognisable during life, and easily misdiagnosed for other forms of dementia. This has an impact on the treatment and long-term care of the affected subjects. Having a biochemical test, based on quantification of a specific DLB biomarker within Cerebrospinal Fluid (CSF) could be an effective diagnostic method to improve the differential diagnosis. Although some of the investigated DLB CSF biomarkers are well within the clinical criteria for sensitivity and specificity (>90%), they all seem to be confounded by the contradictory data for each of the major groups of biomarkers (α-synuclein, tau and amyloid proteins). However, a combination of CSF measures appear to emerge, that may well be able to differentiate DLB from other dementias: α-synuclein reduction in early DLB, a correlation between CSF α-synuclein and Aβ42 measures (characteristic for DLB only), and t-tau and p-tau181 profile (differentiating AD from DLB).

Modelling the role of UCH-L1 on protein aggregation in age-related neurodegeneration

Overexpression of the de-ubiquitinating enzyme UCH-L1 leads to inclusion formation in response to proteasome impairment. These inclusions contain components of the ubiquitin-proteasome system and α-synuclein confirming that the ubiquitin-proteasome system plays an important role in protein aggregation. The processes involved are very complex and so we have chosen to take a systems biology approach to examine the system whereby we combine mathematical modelling with experiments in an iterative process. The experiments show that cells are very heterogeneous with respect to inclusion formation and so we use stochastic simulation. The model shows that the variability is partly due to stochastic effects but also depends on protein expression levels of UCH-L1 within cells. The model also indicates that the aggregation process can start even before any proteasome inhibition is present, but that proteasome inhibition greatly accelerates aggregation progression. This leads to less efficient protein degradation and hence more aggregation suggesting that there is a vicious cycle. However, proteasome inhibition may not necessarily be the initiating event. Our combined modelling and experimental approach show that stochastic effects play an important role in the aggregation process and could explain the variability in the age of disease onset. Furthermore, our model provides a valuable tool, as it can be easily modified and extended to incorporate new experimental data, test hypotheses and make testable predictions.

Astrocytes in the amygdala

The amygdala has received considerable attention because of its established role in specific behaviors and disorders such as anxiety, depression, and autism. Studies have revealed that the amygdala is a complex and dynamic brain region that is highly connected with other areas of the brain. Previous works have focused on neurons, demonstrating that the amygdala in rodents is highly plastic and sexually dimorphic. However, our more recent work explores sex differences in nonneuronal cells, joining a rich literature concerning glia in the amygdala. Prior investigation of glia in the amygdala can generally be divided into disease-related and hormone-related categories, with both areas of research producing interesting findings concerning glia in this important brain region. Despite a wide range of research topics, the collected findings make it clear that glia in the amygdala are sensitive and plastic cells that respond and develop in a highly region specific manner.

A pathologic cascade leading to synaptic dysfunction in alpha-synuclein-induced neurodegeneration

Several neurodegenerative diseases are typified by intraneuronal alpha-synuclein deposits, synaptic dysfunction, and dementia. While even modest alpha-synuclein elevations can be pathologic, the precise cascade of events induced by excessive alpha-synuclein and eventually culminating in synaptotoxicity is unclear. To elucidate this, we developed a quantitative model system to evaluate evolving alpha-synuclein-induced pathologic events with high spatial and temporal resolution, using cultured neurons from brains of transgenic mice overexpressing fluorescent-human-alpha-synuclein. Transgenic alpha-synuclein was pathologically altered over time and overexpressing neurons showed striking neurotransmitter release deficits and enlarged synaptic vesicles; a phenotype reminiscent of previous animal models lacking critical presynaptic proteins. Indeed, several endogenous presynaptic proteins involved in exocytosis and endocytosis were undetectable in a subset of transgenic boutons ("vacant synapses") with diminished levels in the remainder, suggesting that such diminutions were triggering the overall synaptic pathology. Similar synaptic protein alterations were also retrospectively seen in human pathologic brains, highlighting potential relevance to human disease. Collectively the data suggest a previously unknown cascade of events where pathologic alpha-synuclein leads to a loss of a number of critical presynaptic proteins, thereby inducing functional synaptic deficits.

The paradoxical cell biology of alpha-Synucle

Synucleinopathies are a group of neurodegenerative diseases characterized by accumulation and aggregation of the protein alpha-synuclein in neuronal perikarya and processes. In contrast to the proximal localization of alpha-synuclein in diseased states, under physiologic conditions, the bulk of alpha-synuclein is present in distant presynaptic terminals. Thus, pathologic conditions lead to mislocalization and aggregation of alpha-synuclein in neuronal cell bodies, and an outstanding question relates to the cell-biological mechanisms that can lead to such mislocalization. Like most other synaptic proteins, alpha-synuclein is synthesized in the neuronal perikarya and then transported into axons and synaptic domains. Accordingly, it has been hypothesized that disturbances in biogenesis/axonal transport or presynaptic targeting of alpha-synuclein can lead to its mislocalization in diseased states. In this chapter, key observations that lead to this hypothesis are presented in addition to a review of some recent literature that has directly addressed this issue. Finally, conflicting results that have resulted from such studies are also highlighted, and a view is offered to reconcile these controversies.

Pink1 suppresses α-synuclein-induced phenotypes in a Drosophila model of Parkinson’s disease

Parkinson’s disease (PD) is the most prevalent human neurodegenerative movement disorder and is characterized by a selective and progressive loss of the dopaminergic neurons. Mutations in the genes parkin and PTEN-induced putative kinase 1 (PINK1) result in autosomal recessive forms of PD. It has been suggested that parkin and Pink1 function in the same pathway in Drosophila , with Pink1 acting upstream of parkin. Previous work in our laboratory has shown the ability of parkin to rescue an α-synuclein-induced PD-like phenotype in Drosophila. To investigate the ability of Pink1 to protect against α-synuclein-induced toxicity, we have performed longevity, mobility, and histological studies to determine whether Drosophila Pink1 can rescue the α-synuclein phenotypes. We have found that overexpression of Pink1 results in the rescue of the α-synuclein-induced phenotype of premature loss of climbing ability, suppression of degeneration of the ommatidial array, and the suppression of α-synuclein-induced developmental defects in the Drosophila eye. These results mark the first demonstration of Pink1 counteracting PD phenotypes in a protein toxicity animal model, and they show that Pink1 is able to impart protection against potentially harmful proteins such as α-synuclein that would otherwise result in cellular stress.

Pathologic modifications of alpha-synuclein in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated squirrel monkeys

alpha-Synuclein expression is increased in dopaminergic neurons challenged by toxic insults. Here, we assessed whether this upregulation is accompanied by pathologic accumulation of alpha-synuclein and protein modifications (i.e. nitration, phosphorylation, and aggregation) that are typically observed in Parkinson disease and in other synucleinopathies. A single injection of the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to squirrel monkeys caused a buildup of alpha-synuclein but not of beta-synuclein or synaptophysin within nigral dopaminergic cell bodies. Immunohistochemistry and immunoelectron microscopy also revealed large numbers of dystrophic axons labeled with alpha-synuclein. Antibodies that recognize nitrated and phosphorylated (at serine 129) alpha-synuclein stained neuronal cell bodies and dystrophic axons in the midbrain of MPTP-treated animals. After toxicant exposure, alpha-synuclein deposition occurred at the level of neuronal axons in which amorphous protein aggregates were observed by immunoelectron microscopy. In a subset of these axons, immunoreactivity for alpha-synuclein was still evident after tissue digestion with proteinase K, further indicating the accumulation of insoluble protein. These data indicate that toxic injury can induce alpha-synuclein modifications that have been implicated in the pathogenesis of human synucleinopathies. The findings are also consistent with a pattern of evolution of alpha-synuclein pathology that may begin with the accumulation and aggregation of the protein within damaged axons.

[Near a biological diagnosis of Alzheimer's disease and related disorders]

PURPOSE

To review the current concepts in the biological diagnosis of Alzheimer's disease (AD) and related disorders.

CURRENT KNOWLEDGE AND KEY POINTS

As new therapeutics specific of AD may be available soon, early diagnosis of AD in the context of mild cognitive impairment (MCI) or dementia appears to be challenging. The high amount of atypical clinical forms of AD leads to develop new tools allowing in vivo diagnosis. New CerebroSpinal Fluid (CSF) biomarkers seem to reflect specific aspects of deep neuropathological changes observed in AD, i.e. amyloid deposits and neurofibrillary tangles. Amyloid beta-peptide 1-42 (Abeta(1-42)) and hyperphosphorylated tubulin associated unit (tau) isoforms appear to be the most sensitive and specific CSF biomarkers, the combination of these biomarkers depicting the best diagnosis value for AD. These molecules are also efficient in the prediction of the conversion from the MCI state to the dementia state of AD. Combined to clinical and neuro-imaging information, CSF biomarkers appear thus to be highly relevant in improving the early etiological diagnosis of dementia.

FUTURE PROSPECTS AND PROJECTS

The current research focalises on the development of new molecules coming from Abeta and tau protein families, in the CSF and in the serum, as well as molecules reflecting other pathological metabolism changes, as alpha-synuclein in Lewy Body Disease. The diagnosis value of CSF biological markers is so promising that they have been recently included in the research diagnosis criteria of AD.

Molecular pathways and genetic aspects of Parkinson's disease: from bench to bedside

Idiopathic Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by dopaminergic neuronal loss within the substantia nigra. The incidence and prevalence of PD is rising with an increasing aging population. PD is a slowly progressive condition and patients can develop debilitating motor and functional impairment. Current research has implicated oxidative stress, alpha-synucleinopathy and dysfunction of the ubiquitin-proteasome system in the pathogenesis of PD. A number of gene mutations have also been linked to the development of PD. The elucidation of these new molecular pathways has increased our knowledge of PD pathophysiology. This article reviews important molecular mechanisms and genetic causes implicated in the pathogenesis of PD, which has led to new areas of therapeutic drug research.

Dietary restriction modulates alpha-synuclein expression in the aging rat cortex and hippocampus

Dietary restriction (DR) is one of the promising environmental interventions known to attenuate aging and decrease risk of age-related neurodegenerative disorders. The aim of this study was to assess the effects of DR on expression of alpha-synuclein, a presynaptic protein involved in pathogenesis of Parkinson's and some other neurodegenerative diseases, in the cortex and hippocampus of adult, middle-aged, late middle-aged, and aged rats. Using Real Time RT-PCR, the authors report that aging regulates the expression of alpha-synuclein in a tissue-specific manner and that long-term DR reverts the late age-related changes of alpha-synuclein expression.

Bioactivity profiling with parallel mass spectrometry reveals an assemblage of green tea metabolites affording protection against human huntingtin and alpha-synuclein toxicity

Aberrant protein aggregation and misfolding are key pathological features of many neurodegenerative disorders, including Huntington's and Parkinson's diseases. Compounds that offer protection from toxicity associated with aggregation-prone neurodegenerative proteins may have applications for the treatment of a multitude of disorders. A high-throughput bioassay system with parallel electrospray ionization mass spectrometry screening has been designed for critical evaluation of milligram quantities of natural product extracts, including dietary substances, for compounds of pharmacological relevance to the treatment of human neurodegenerative diseases. Using Saccharomyces cerevisiae strains engineered to express mutant human huntingtin and alpha-synuclein, we are able to identify extracts and compounds that protect cells from toxicity associated with these proteins. Applying this screening paradigm, we determined that a bioactive green tea extract contains an assemblage of catechins that were individually characterized for their respective protective effects against huntingtin and alpha-synuclein toxicity.

Identification and characterization of a new alpha-synuclein isoform and its role in Lewy body diseases

Alternative splicing is an important mechanism to generate a large number of mRNAs, thus increasing proteome diversity and tissue specificity. Three transcript variants of alpha-synuclein, a neuronal protein mainly involved in synapses, have been described so far. Whereas alpha-synuclein 140 is the whole and main transcript, alpha-synuclein 112 and 126 are short proteins that result from in-frame deletions of exons 3 and 5, respectively. Because the aforesaid alpha-synuclein isoforms show differential expression changes in Lewy body diseases (LBDs), in the present work, we searched for a fourth alpha-synuclein isoform and studied its expression levels in LBD brains. By using isoform-specific primers, isoform co-amplification and direct sequencing, we identified alpha-synuclein 98, which lacks exons 3 and 5. mRNA expression analyses in non-neuronal tissue revealed that alpha-synuclein 98 is a brain-specific splice variant with varying expression levels in different areas of fetal and adult brain. Additionally, we studied alpha-synuclein 98 expression levels by real-time semi-quantitative RT-PCR in the frontal cortices of LBD patients and compared them with those of Alzheimer disease (AD) patients and control subjects. Overexpression of alpha-synuclein 98 in LBD and AD brains would indicate its specific involvement in the pathogenesis of these neurodegenerative disorders.

Development of alpha-synuclein immunoreactive astrocytes in the forebrain parallels stages of intraneuronal pathology in sporadic Parkinson's disease

Astrocytic alpha-synuclein-immunoreactive inclusions have recently been noted to develop in sporadic Parkinson's disease (PD). Here, the presence of immunoreactive astrocytes is reported in 14 autopsy cases with clinically diagnosed PD and a neuropathological stage of 4 or higher. The labeled astrocytes occur preferentially in prosencephalic regions (amygdala, thalamus, septum, striatum, claustrum, and cerebral cortex). They appear first in layers V-VI of the temporal mesocortex, then in the striatum and in thalamic nuclei that project to the cortex. The topographical distribution pattern of these astrocytes closely parallels that of the cortical intraneuronal Lewy neurites and Lewy bodies, which, from their foothold in the mesocortex, gradually encroach upon neocortical association areas and even the primary fields. Thus, labeling of astrocytes appears to accompany the formation of neuronal inclusion bodies. Relatively small immunoreactive cortical pyramidal neurons in layers V-VI probably project to nearby destinations, such as the striatum and thalamus. Inasmuch as the projection neurons of both the striatum and the dorsal thalamus do not develop Lewy bodies, it is suggested that the most likely cause of the astrocytic reaction may be a slightly altered alpha-synuclein molecule that escapes from terminal axons of affected cortico-striatal or cortico-thalamic neurons and is taken up by astrocytes. Other aggregated proteins known to co-occur with PD-associated intraneuronal lesions, e.g., Abeta protein or neurofibrillary changes of the Alzheimer type, do not appear to influence the development of the alpha-synuclein immunoreactive astrocytes.

Alpha-synuclein protects cerebellar granule neurons against 6-hydroxydopamine-induced death

The physiological role of alpha-synuclein, a protein found enriched in intraneuronal deposits characterizing Parkinson's disease, is debated. While its aggregation is usually considered linked to neuropathology, its normal function may be related to fundamental processes of synaptic transmission and plasticity. By using antisense oligonucleotide strategy, we report in this study that alpha-synuclein silencing in cultured cerebellar granule cells results in widespread death of these neurons, thus demonstrating an essential pro-survival role of the protein towards primary neurons. To study alpha-synuclein expression and processing in a Parkinson's disease model of neurotoxicity, we exposed differentiated cultures of cerebellar granule neurons to toxic concentrations of 6-hydroxydopamine (6-OHDA). This resulted in neuronal death accompanied by a decrease of the monomeric form of alpha-synuclein, which was due to both decreased synthesis of the protein and its increased mono-ubiquitination accompanied by nuclear translocation. The essential neuroprotective role of alpha-synuclein was confirmed by the fact that subchronic valproate treatment, which increases alpha-synuclein expression and prevents its nuclear translocation in cerebellar granule cells exposed to 6-OHDA, significantly protected these neurons from 6-OHDA insult. In agreement with the pro-survival role of alpha-synuclein in this model, subtoxic concentrations of alpha-synuclein antisense oligonucleotides, aggravated 6-OHDA toxicity towards granule neurons. Our results demonstrate that normal alpha-synuclein expression is essential for the viability of primary neurons and that its pro-survival role is abolished in 6-OHDA neurotoxic challenge. These results are relevant to more precisely define the role of alpha-synuclein in neuronal cells and to better understand its putative involvement in neurodegeneration.

Neuropathology, biochemistry, and biophysics of alpha-synuclein aggregation

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

Differential nigral expression of bcl-2 protein family in the pure and common forms of Dementia with Lewy bodies: relevance for dopaminergic neuronal vulnerability

We investigated whether bcl-2 protein family is involved in the pathogenesis of the dopaminergic neurodegeneration that occurs in Dementia with Lewy bodies (DLB). The expression of the proapoptotic protein bax and the antiapoptotic proteins bcl-2 and bcl-xL was investigated by Western blot in the pars compacta of the substantia nigra of pure and common DLB forms. No changes in the nigral expression levels of bax, bcl-2 and bcl-xL proteins were found between control and DLB pure cases. In the common DLB forms, nigral bcl-xL and bcl-2 proteins levels were significantly decreased in the DLB cases associated with a concomitant severe AD pathology (p < 0.05). An increase in nigral bcl-2 protein expression was observed in the DLB cases with a mild AD-associated pathology (p < 0.05). The present results are in agreement with previous observations indicating that DLB cases with severe AD pathology tend to show severe Lewy pathology suggesting that AD pathology might exacerbate Lewy pathology.

Gamma-synuclein and the progression of cancer

The synucleins are a small, soluble, highly conserved group of neuronal proteins that have been implicated in both neurodegenerative diseases and cancer. The synuclein family consists of alpha-, beta-, and gamma-synucleins (gamma-syn). They are a natively unfolded group of proteins that share sequence homologies and structural properties. So far, the biological functions of the synucleins are still unclear, but their involvement in neurodegenerative diseases and cancer may provide insights into the pathological processes that result from these two groups of debilitating diseases, and present the possibility to use them as potential targets for early diagnosis and treatment. Recently, elevated levels of gamma-syn proteins have been detected in various types of cancer, especially in advanced stages of the disease. Furthermore, studies to date indicate that overexpression of gamma-syn compromises normal mitotic checkpoint controls, resulting in multinucleation as well as faster cell growth. Gamma-syn has also been shown to promote invasion and metastasis in in vitro assays as well as in animal models. Overexpression of gamma-syn also interferes with drug-induced apoptotic responses. These observations raise questions about the involvement of gamma-syn in the process of tumorigenesis and metastasis, and efforts have already been made to use gamma-syn as a marker for assessing breast cancer progression. This review will discuss the involvement of gamma-syn in cancer progression, metastasis and its potential as a marker.

The therapeutic potential of intrabodies in neurologic disorders: focus on Huntington and Parkinson diseases

Single-chain Fv and single-domain antibodies retain the binding specificity of full-length antibodies but they can be cloned, selected, engineered, and manipulated as genes. When expressed intracellularly in mammalian cells these intracellular antibodies, or intrabodies, have the potential to alter the folding, interactions, modifications, or subcellular localization of their targets. These reagents have previously been developed as therapeutics against cancer and HIV. Since misfolded and accumulated intracellular proteins characterize several major neurodegenerative disorders, including Huntington disease (HD) and Parkinson disease, these disorders are prime candidates for intrabody therapy. In this article we review the extension of intrabody technology to the nervous system. Studies of HD have been used to develop the approach and anti-synuclein strategies are in the early stages of development. Such neurodegenerative diseases are therefore poised for engineered antibody approaches, which can provide a pipeline of novel therapeutics and new drug discovery tools.

Cell systems and the toxic mechanism(s) of alpha-synuclein

Mutations in the SNCA gene are causal for familial Parkinson disease/Lewy body disease. alpha-Synuclein is a small acidic protein that binds loosely to the surface of vesicles and may play a role in synaptic dynamics, although its normal function remains somewhat unclear. What is clear is that point mutations or increased expression of wild type alpha-synuclein causes disease. A great deal of literature supports the overall hypothesis that alpha-synuclein is damaging to neurons because it is inherently prone to aggregation; mutations or increased concentration of the protein both increase this tendency. An unproven, but popular, contention is that the toxic species are small oligomers that are relatively soluble, which may react with membranes to damage key processes within the cell. The details of this process, especially in determining the order of events and the requirement of particular processes in cell death, are unclear. Derangements in vesicle processing, including synaptic function, protein turnover, mitochondrial function and oxidative stress, have all been suggested to occur. Whether there is a sequence of events or whether these are interacting effects is unclear, but the outcome is to trigger cell death, by both apoptotic and non-apoptotic mechanisms depending on the system studied. In this article, we develop a framework for thinking about alpha-synuclein in terms of initiating events and secondary processes that are required to trigger neuronal dysfunction and cell death.

Novel perspectives for progesterone in hormone replacement therapy, with special reference to the nervous system

The utility and safety of postmenopausal hormone replacement therapy has recently been put into question by large clinical trials. Their outcome has been extensively commented upon, but discussions have mainly been limited to the effects of estrogens. In fact, progestagens are generally only considered with respect to their usefulness in preventing estrogen stimulation of uterine hyperplasia and malignancy. In addition, various risks have been attributed to progestagens and their omission from hormone replacement therapy has been considered, but this may underestimate their potential benefits and therapeutic promises. A major reason for the controversial reputation of progestagens is that they are generally considered as a single class. Moreover, the term progesterone is often used as a generic one for the different types of both natural and synthetic progestagens. This is not appropriate because natural progesterone has properties very distinct from the synthetic progestins. Within the nervous system, the neuroprotective and promyelinating effects of progesterone are promising, not only for preventing but also for reversing age-dependent changes and dysfunctions. There is indeed strong evidence that the aging nervous system remains at least to some extent sensitive to these beneficial effects of progesterone. The actions of progesterone in peripheral target tissues including breast, blood vessels, and bones are less well understood, but there is evidence for the beneficial effects of progesterone. The variety of signaling mechanisms of progesterone offers exciting possibilities for the development of more selective, efficient, and safe progestagens. The recognition that progesterone is synthesized by neurons and glial cells requires a reevaluation of hormonal aging.

Nuclear factor kappa-B p50 and p65 subunits expression in dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is the second most common cause of neurodegenerative dementia after Alzheimer's disease (AD). Parkinsonism in DLB is mainly caused by neuronal loss with Lewy bodies (LBs) in the substantia nigra, thereby inducing degeneration of the nigrostriatal dopaminergic pathway similar to that in Parkinson's disease (PD). To clarify the pathogenesis of DLB, it is important to investigate the mechanisms involved in the degenerative process of LB-bearing neurones. Several reports suggest a role for nuclear factor kappa-B (NFkappaB) in the manifestation of neurodegenerative conditions such as AD and PD. The aim of the present study was to investigate whether NFkappaB subunits are involved in the pathogenesis of neurodegeneration in DLB by measuring tyrosine hydroxylase (TH), NFkappaB p65 and p50 protein expression in frontal cortex and substantia nigra pars compacta of DLB and control human brains. An increase, although not statistically significant, in nigral TH expression in DLB cases was observed. There were no differences in the cortical and nigral expression levels of NFkappaB p65 subunit between control and DLB cases. Western blots of the frontal cortex showed no differences in the expression levels of NFkappaB p50 subunit. However, NFkappaB p50 levels were significantly decreased (P < 0.05) in the pars compacta of the substantia nigra in the DLB cases in comparison with controls. The decrease in the expression of the p50 subunit in the substantia nigra of DLB cases achieved in the present study may increase the vulnerability of the dopaminergic neurones to a possible neurotoxic effect of p65 subunit. Thus, normal levels of NFkappaB p65 might be toxic in neurones with a low expression of the NFkappaB p50 subunit.

Diagnosis and treatment of Parkinson disease: molecules to medicine

Parkinson disease (PD) is a relatively common disorder of the nervous system that afflicts patients later in life with tremor, slowness of movement, gait instability, and rigidity. Treatment of these cardinal features of the disease is a success story of modern science and medicine, as a great deal of disability can be alleviated through the pharmacological correction of brain dopamine deficiency. Unfortunately these therapies only provide temporary, though significant, relief from early symptoms and do not halt disease progression. In addition, pathological changes outside of the motor system leading to cognitive, autonomic, and psychiatric symptoms are not sufficiently treated by current therapies. Much as the discovery of dopamine deficiency led to powerful treatments for motor symptoms, recent discoveries concerning the role of specific genes in PD pathology will lead to the next revolution in disease therapy. Understanding why and how susceptible cells in motor and nonmotor regions of the brain die in PD is the first step toward preventing this cell death and curing or slowing the disease. In this review we discuss recent discoveries in the fields of diagnosis and treatment of PD and focus on how a better understanding of disease mechanisms gained through the study of monogenetic forms of PD has provided novel therapeutic targets.

Paraquat exposure as an etiological factor of Parkinson's disease

Parkinson's disease (PD) is a multifactorial chronic progressive neurodegenerative disease influenced by age, and by genetic and environmental factors. The role of genetic predisposition in PD has been increasingly acknowledged and a number of relevant genes have been identified (e.g., genes encoding alpha-synuclein, parkin, and dardarin), while the search for environmental factors that influence the pathogenesis of PD has only recently begun to escalate. In recent years, the investigation on paraquat (PQ) toxicity has suggested that this herbicide might be an environmental factor contributing to this neurodegenerative disorder. Although the biochemical mechanism through which PQ causes neurodegeneration in PD is not yet fully understood, PQ-induced lipid peroxidation and consequent cell death of dopaminergic neurons can be responsible for the onset of the Parkinsonian syndrome, thus indicating that this herbicide may induce PD or influence its natural course. PQ has also been recently considered as an eligible candidate for inducing the Parkinsonian syndrome in laboratory animals, and can therefore constitute an alternative tool in suitable animal models for the study of PD. In the present review, the recent evidences linking PQ exposure with PD development are discussed, with the aim of encouraging new perspectives and further investigation on the involvement of environmental agents in PD.

Copper(ii) binding by fragments of α-synuclein containing M1-D2- and -H50-residues; a combined potentiometric and spectroscopic study

Stability constants and ligand donor sets of the copper(II) complexes of the NH2-29-56(L1)(AA30GKTKEGVLYV40GSKTKEGVVH50GVATVA56-NH2), NH2-M29-D30-56(L2) and Ac-M29-D30-56(L3) fragments of alpha-synuclein were determined in aqueous solution for 1 : 1 metal-to-ligand molar ratio in the pH range 2.5-10.5. The tyrosine residue in the 39th position of the alpha-synuclein fragments does not take part in the coordination of the metal ion. The potentiometric and spectroscopic data (UV-Vis, CD, EPR) show that acetylation of the amino terminal group induces significant changes in the coordination properties of the L3 fragment compared to that of the L2 peptide. When the amino group is blocked (L3) the imidazole nitrogen of the histidine residue acts as an anchoring site and at higher pH the 3N {N(Im),2N-} and 4N {N(Im),3N-} complexes are formed. The L1 peptide at physiological pH forms in equilibrium 3N {NH2,N-,CO,N(Im)} and 4N {NH2,2N-,N(Im)} complexes. For the L2 peptide the coordination of the copper(II) ions starts from the N-terminal Met residue and with increasing of pH the Asp residue in second position of amino acid sequence coordinates and stabilizes significantly the 2N complex as a result of chelation through the beta-carboxylate group. At physiological pH the 3N {NH2,N-,beta-COO-,N(Im)} coordination mode dominates. At pH above 6 the results for the L2 fragment suggest the formation of 3N and 4N complexes (in equatorial plane) and the involvement of the lateral NH2 group of Lys residue in the axial coordination of Cu(II) ion. In CD spectra sigma (epsilon-NH2-Lys) --> Cu(II) charge transfer transition is observed. The stability constants for the L2 fragment of alpha-synuclein of the 4N {NH2,2N-,N(Im)} and {NH2,3N-} complexes are higher about 1.5 and 0.7 orders of magnitude, respectively, by comparison to those of the L1 peptide. This increase may be explained by the involvement of the epsilon-NH2 group of Lys residue in the coordination sphere of metal ion.