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

Cerebrospinal fluid biomarkers profile in scans without evidence of dopaminergic deficits (SWEDD)

Background

A small proportion of patients with clinical parkinsonism have normal transporter-single photon emission computed tomography (DaTSPECT) which is commonly defined as scans without evidence of dopaminergic deficits (SWEDD). A better understanding of SWEDD can improve the current therapeutic options and appropriate disease monitoring.

Aim

We aimed to assess CSF biomarkers levels including α-synuclein (α-syn), amyloid βeta (Aβ1-42), total tau (t-tau), and phosphorylated tau (p-tau) in SWEDD and investigate the longitudinal alteration in the CSF profile.

Methods

In total, 406 early-stage PD, 58 SWEDD, and 187 healthy controls (HCs) were entered into our study from PPMI. We compared the level of CSF biomarkers at baseline, six months, one year, and two years. Furthermore, the longitudinal alteration of CSF biomarkers was explored in each group using linear mixed models.

Results

There was no significant difference in the level of CSF α-syn Aβ1-42, t-tau, and p-tau between HCs and SWEDD at different time points. Investigating the level of CSF α-syn in PD and SWEDD showed a significant difference at one (p = 0.016) and two years (p = 0.006). Also, we observed a significant difference in the level of CSF Aβ1-42 between SWEDD and PD at one year (p = 0.012). Moreover, there was a significant difference in the level of CSF t-tau between SWEDD and PD subjects at one (p = 0.013) and two years (p = 0.017). Furthermore, there was a significant difference in the level of CSF p-tau between SWEDD and PD groups at two years visits (p = 0.030). Longitudinal analysis showed a significant decrease after one (p = 0.029) and two years (p = 0.002) from baseline in the level of CSF α-syn only in the PD group. Also, we observed that the level of CSF Aβ1-42 significantly increased after one year in SWEDD (p = 0.031) and decreased after two years from baseline in PD subjects (p = 0.005). Moreover, there was a significant increase in the level of CSF t-tau after two years (p = 0.036) and CSF p-tau after six months from baseline in SWEDD subjects (p = 0.011).

Conclusion

This finding suggests a faster neurodegeneration process in PD patients compared to SWEDD at least based on these biomarkers. Future studies with longer follow-up duration and more sample sizes are necessary to validate our results.

Potential value of cerebrospinal fluid α-synuclein in the identification of postoperative delirium undergoing knee/hip arthroplasty: The perioperative neurocognitive disorder and biomarker lifestyle study

Objective

Postoperative delirium (POD) is a common postoperative complication, which may be associated with α-synuclein (α-syn). The purpose of this study was to explore the association between the expression level of α-syn in cerebrospinal fluid (CSF) and POD.

Methods

We conducted a prospective observational cohort study, which involved in 740 participants (mean age of 61.86 years, range 40–90 years; 40% female) from the Perioperative Neurocognitive Disorder And Biomarker Lifestyle (PNDABLE) study in the final analysis. POD was diagnosed using the Confusion Assessment Scale (CAM), and its severity was measured using the Memorial Delirium Assessment Scale (MDAS). Enzyme-linked immune-sorbent assay (ELISA) was used to detect the concentrations of α-syn, Aβ40, Aβ42, T-tau, and P-tau in CSF.

Results

The incidence of POD was 11.22% (83/740). The logistic regression analysis showed that the increased concentrations of CSF α-syn (OR = 1.005, 95%CI 1.004–1.006, P < 0.001), P-tau (OR = 1.093, 95%CI 1.071–1.115, P < 0.001), and T-tau (OR = 1.008, 95%CI 1.006–1.009, P < 0.001) were risk factors of POD. Linear regression showed that CSF α-syn had positive correlations with P-tau (β = 0.480, P < 0.001), T-tau (β = 0.334, P < 0.001), while negative correlations with Aβ40 (β = –0.378 P < 0.001), Aβ42 (β = -0.800, P = 0.001) in POD patients. Mediation analyses showed the association between α-syn and POD was partially mediated by tau pathologies (proportion: 16–17%).

Conclusion

CSF α-syn is one of the preoperative risk factors for POD, which may be mediated through tau pathologies.

Clinical trial registration

[www.ClinicalTrials.gov], identifier [ChiCTR20 00033439].

Cerebrospinal fluid α-synuclein predicts neurodegeneration and clinical progression in non-demented elders

Background

Accumulating reports have suggested that α-synuclein is involved in the pathogenesis of Alzheimer’s disease (AD). As the cerebrospinal fluid (CSF) α-synuclein has been suggested as a potential biomarker of AD, this study was set out to test whether CSF α-synuclein is associated with other AD biomarkers and could predict neurodegeneration and clinical progression in non-demented elders.

Methods

The associations between CSF α-synuclein and other AD biomarkers were investigated at baseline in non-demented Chinese elders. The predictive values of CSF α-synuclein for longitudinal neuroimaging change and the conversion risk of non-demented elders were assessed using linear mixed effects models and multivariate Cox proportional hazard models, respectively, in the Alzheimer’s disease Neuroimaging Initiative (ADNI) database.

Results

The CSF α-synuclein levels correlated with AD-specific biomarkers, CSF total tau and phosphorylated tau levels, in 651 Chinese Han participants (training set). These positive correlations were replicated in the ADNI database (validation set). Using a longitudinal cohort from ADNI, the CSF α-synuclein concentrations were found to increase with disease severity. The CSF α-synuclein had high diagnostic accuracy for AD based on the “ATN” (amyloid, tau, neurodegeneration) system (A + T+ versus A − T − control) (area under the receiver operating characteristic curve, 0.84). Moreover, CSF α-synuclein predicted longitudinal hippocampus atrophy and conversion from MCI to AD dementia.

Conclusions

CSF α-synuclein is associated with CSF tau levels and could predict neurodegeneration and clinical progression in non-demented elders. This finding indicates that CSF α-synuclein is a potentially useful early biomarker for AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-020-00222-1.

Regulation of Alzheimer's disease-associated proteins during epileptogenesis

Clinical evidence and pathological studies suggest a bidirectional link between temporal lobe epilepsy and Alzheimer's disease (AD). Data analysis from omic studies offers an excellent opportunity to identify the overlap in molecular alterations between the two pathologies. We have subjected proteomic data sets from a rat model of epileptogenesis to a bioinformatics analysis focused on proteins functionally linked with AD. The data sets have been obtained for hippocampus (HC) and parahippocampal cortex samples collected during the course of epileptogenesis. Our study confirmed a relevant dysregulation of proteins linked with Alzheimer pathogenesis. When comparing the two brain areas, a more prominent regulation was evident in parahippocampal cortex samples as compared to the HC. Dysregulated protein groups comprised those affecting mitochondrial function and calcium homeostasis. Differentially expressed mitochondrial proteins included proteins of the mitochondrial complexes I, III, IV, and V as well as of the accessory subunit of complex I. The analysis also revealed a regulation of the microtubule associated protein Tau in parahippocampal cortex tissue during the latency phase. This was further confirmed by immunohistochemistry. Moreover, we demonstrated a complex epileptogenesis-associated dysregulation of proteins involved in amyloid β processing and its regulation. Among others, the amyloid precursor protein and the α-secretase alpha disintegrin metalloproteinase 17 were included. Our analysis revealed a relevant regulation of key proteins known to be associated with AD pathogenesis. The analysis provides a comprehensive overview of shared molecular alterations characterizing epilepsy development and manifestation as well as AD development and progression.

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

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

Insights into the Molecular Mechanisms of Alzheimer's and Parkinson's Diseases with Molecular Simulations: Understanding the Roles of Artificial and Pathological Missense Mutations in Intrinsically Disordered Proteins Related to Pathology

Amyloid-β and α-synuclein are intrinsically disordered proteins (IDPs), which are at the center of Alzheimer's and Parkinson's disease pathologies, respectively. These IDPs are extremely flexible and do not adopt stable structures. Furthermore, both amyloid-β and α-synuclein can form toxic oligomers, amyloid fibrils and other type of aggregates in Alzheimer's and Parkinson's diseases. Experimentalists face challenges in investigating the structures and thermodynamic properties of these IDPs in their monomeric and oligomeric forms due to the rapid conformational changes, fast aggregation processes and strong solvent effects. Classical molecular dynamics simulations complement experiments and provide structural information at the atomic level with dynamics without facing the same experimental limitations. Artificial missense mutations are employed experimentally and computationally for providing insights into the structure-function relationships of amyloid-β and α-synuclein in relation to the pathologies of Alzheimer's and Parkinson's diseases. Furthermore, there are several natural genetic variations that play a role in the pathogenesis of familial cases of Alzheimer's and Parkinson's diseases, which are related to specific genetic defects inherited in dominant or recessive patterns. The present review summarizes the current understanding of monomeric and oligomeric forms of amyloid-β and α-synuclein, as well as the impacts of artificial and pathological missense mutations on the structural ensembles of these IDPs using molecular dynamics simulations. We also emphasize the recent investigations on residual secondary structure formation in dynamic conformational ensembles of amyloid-β and α-synuclein, such as β-structure linked to the oligomerization and fibrillation mechanisms related to the pathologies of Alzheimer's and Parkinson's diseases. This information represents an important foundation for the successful and efficient drug design studies.

Genetic association between RAGE polymorphisms and Alzheimer's disease and Lewy body dementias in a Japanese cohort: a case-control study

BACKGROUND/AIMS

Interaction of receptor for advanced glycation end products (RAGE) with amyloid-β increases amplification of oxidative stress and plays pathological roles in Alzheimer's disease (AD). Oxidative stress leads to α-synuclein aggregation and is also a major contributing factor in the pathogenesis of Lewy body dementias (LBDs). Therefore, we aimed to investigate whether RAGE gene polymorphisms were associated with AD and LBDs.

METHODS

Four single nucleotide polymorphisms (SNPs)-rs1800624, rs1800625, rs184003, and rs2070600-of the gene were analyzed using a case-control study design comprising 288 AD patients, 76 LBDs patients, and 105 age-matched controls.

RESULTS

Linkage disequilibrium (LD) examination showed strong LD from rs1800624 to rs2070600 on the gene (1.1 kb) in our cases in Japan. Rs184003 was associated with an increased risk of AD. Although there were no statistical associations for the other three SNPs, haplotypic analyses detected genetic associations between AD and the RAGE gene. Although relatively few cases were studied, results from the SNPs showed that they did not modify the risk of developing LBDs in the Japanese population.

CONCLUSION

Our findings suggested that polymorphisms in the RAGE gene are involved in genetic susceptibility to AD. Copyright © 2016 John Wiley & Sons, Ltd.

Amyloid β-peptides 1-40 and 1-42 form oligomers with mixed β-sheets

Two main amyloid-β peptides of different length (Aβ₄₀ and Aβ₄₂) are involved in Alzheimer's disease. Their relative abundance is decisive for the severity of the disease and mixed oligomers may contribute to the toxic species. However, little is know about the extent of mixing. To study whether Aβ₄₀ and Aβ₄₂ co-aggregate, we used Fourier transform infrared spectroscopy in combination with ¹³C-labeling and spectrum calculation and focused on the amide I vibration, which is sensitive to backbone structure. Mixtures of monomeric labeled Aβ₄₀ and unlabeled Aβ₄₂ (and vice versa) were co-incubated for ∼20 min and their infrared spectrum recorded. The position of the main ¹³C-amide I' band shifted to higher wavenumbers with increasing admixture of ¹²C-peptide due to the presence of ¹²C-amides in the vicinity of ¹³C-amides. The results indicate that Aβ₄₀ and Aβ₄₂ form mixed oligomers with a largely random distribution of Aβ₄₀ and Aβ₄₂ strands in their β-sheets. The structures of the mixed oligomers are intermediate between those of the pure oligomers. There is no indication that one of the peptides forces the backbone structure of its oligomers on the other peptide when they are mixed as monomers. We also demonstrate that isotope-edited infrared spectroscopy can distinguish aggregation modulators that integrate into the backbone structure of their interaction partner from those that do not. As an example for the latter case, the pro-inflammatory calcium binding protein S100A9 is shown not to incorporate into the β-sheets of Aβ₄₂.

Neuropsychiatric Disturbances in Alzheimer's Disease: What Have We Learned from Neuropathological Studies?

Neuropsychiatric symptoms (NPS) are an integral part of the dementia syndrome and were therefore recently included in the core diagnostic criteria of dementia. The near universal prevalence of NPS in Alzheimer's disease (AD), combined with their disabling effects on patients and caregivers, is contrasted by the fact that few effective and safe treatments exist, which is in part to be attributed to our incomplete understanding of the neurobiology of NPS. In this review, we describe the pathological alterations typical for AD, including spreading and evolution of burden, effect on the molecular and cellular integrity, functional consequences and atrophy of NPS-relevant brain regions and circuits in correlation with specific NPS assessments. It is thereby clearly established that NPS are fundamental expressions of the underlying neurodegenerative brain disease and not simply reflect the patients' secondary response to their illness. Neuropathological studies, moreover, include a majority of end-stage patient samples, which may not correctly represent the pathophysiological environment responsible for particular NPS that may already be present in an early stage, or even prior to AD diagnosis. The burdensome nature and high prevalence of NPS, in combination with the absence of effective and safe pharmacotherapies, provide a strong incentive to continue neuropathological and neurochemical, as well as imaging and other relevant approaches to further improve our apprehension of the neurobiology of NPS.

Genetic Association between Presenilin 2 Polymorphisms and Alzheimer's Disease and Dementia of Lewy Body Type in a Japanese Population

Background/Aims

Mutations in the presenilin 2 (PSEN2) gene cause familial Alzheimer's disease (AD). Common polymorphisms affect gene activity and increase the risk of AD. Nonsynonymous polymorphisms in the PSEN2 gene showed Lewy body dementia (LBD) phenotypes clinically. Therefore, we aimed to investigate whether PSEN2 gene polymorphisms were associated with AD or LBD.

Methods

Seven single nucleotide polymorphisms (SNPs) of the gene were analyzed using a case-control study design comprising 288 AD patients, 76 LBD patients, and 105 age-matched controls.

Results

Linkage disequilibrium (LD) examination showed strong LD from rs1295645 to rs8383 on the gene in our cases from Japan. There were no associations between the SNPs studied here and AD onset, and haplotypic analyses did not detect genetic associations between AD and the PSEN2 gene. Although the number of the cases was small, the SNPs studied did not modify the risk of developing LBD in a Japanese population.

Conclusion

The common SNPs of the PSEN2 gene did not affect the risk of AD or LBD in a Japanese population. Because genetic variability of the PSEN2 gene is associated with behavioral and psychological symptoms of dementia (BPSD) in AD and LBD, further detailed analyses considering BPSD of both diseases would be required.

Cerebrospinal Fluid Aβ42 Levels: When Physiological Become Pathological State

Impaired amyloid beta (Aβ) metabolism is currently considered central to understand the pathophysiology of Alzheimer's disease (AD). Measurements of cerebrospinal fluid Aβ levels remain the most useful marker for diagnostic purposes and to individuate people at risk for AD. Despite recent advances criticized the direct role in neurodegeneration of cortical neurons, Aβ is considered responsible for synaptopathy and impairment of neurotransmission and therefore remains the major trigger of AD and future pharmacological treatment remain Aβ oriented. However, experimental and clinical findings showed that Aβ peptides could have a wider range of action responsible for cell dysfunction and for appearance of clinico-pathological entities different from AD. Such findings may induce misunderstanding of the real role played by Aβ in AD and therefore strengthen criticism on its centrality and need for CSF measurements. Aim of this review is to discuss the role of CSF Aβ levels in light of experimental, clinical pathologic, and electrophysiological results in AD and other pathological entities to put in a correct frame the value of Aβ changes.

Activation of Mitochondrial Complex II-Dependent Respiration Is Beneficial for α-Synucleinopathies

Parkinson’s disease and dementia with Lewy bodies are major challenges in research and clinical medicine world-wide and contribute to the most common neurodegenerative disorders. Previously, specific mitochondrial polymorphisms have been found to enhance clearance of amyloid-β from the brain of APP-transgenic mice leading to beneficial clinical outcome. It has been discussed whether specific mitochondrial alterations contribute to disease progression or even prevent toxic peptide deposition, as seen in many neurodegenerative diseases. Here, we investigated α-synuclein-transgenic C57BL/6J mice with the A30P mutation, and a novel A30P C57BL/6J mouse model with three mitochondrial DNA polymorphisms in the ND3, COX3 and mtRNA^Arg genes, as found in the inbred NOD/LtJ mouse strain. We were able to detect that the new model has increased mitochondrial complex II-respiration which occurs in parallel to neuronal loss and improved motor performance, although it exhibits higher amounts of high molecular weight species of α-synuclein. High molecular weight aggregates of different peptides are controversially discussed in the light of neurodegeneration. A favourable hypothesis states that high molecular weight species are protective and of minor importance for the pathogenesis of neurodegenerative disorders as compared to the extreme neurotoxic monomers and oligomers. Summarising, our results point to a potentially protective and beneficial effect of specific mitochondrial polymorphisms which cause improved mitochondrial complex II-respiration in α-synucleinopathies, an effect that could be exploited further for pharmaceutical interventions.

Mini review: linkage between α-Synuclein protein and cognition

α-synuclein is a protein that plays important roles in cognitive function in the normal brain, although its exact role is not fully understood. However, current studies reveal that defects in α-synuclein function could contribute to various neurodegenerative disorders, such as Parkinson’s disease (PD), a disease with symptomatic progression of deterioration in motor and cognitive function. Recent studies show that the level of α -synuclein in cerebrospinal fluid (CSF) is highly correlated with speed of cognitive decline, suggesting a potential role of α-synuclein in cognitive function. In this mini review, we will be focus on literatures of α-synuclein in cognitive function in the non-diseased brain, as well as the impact that defective α-synuclein has on cognition in disease brain. This will be accomplished by assessing the effects of soluble α-synuclein, α-synuclein oligomers, and extracellular α-synuclein transport, on neurodegeneration.

Amyloid β oligomers in Alzheimer's disease pathogenesis, treatment, and diagnosis

Protein aggregation is common to dozens of diseases including prionoses, diabetes, Parkinson's and Alzheimer's. Over the past 15 years, there has been a paradigm shift in understanding the structural basis for these proteinopathies. Precedent for this shift has come from investigation of soluble Aβ oligomers (AβOs), toxins now widely regarded as instigating neuron damage leading to Alzheimer's dementia. Toxic AβOs accumulate in AD brain and constitute long-lived alternatives to the disease-defining Aβ fibrils deposited in amyloid plaques. Key experiments using fibril-free AβO solutions demonstrated that while Aβ is essential for memory loss, the fibrillar Aβ in amyloid deposits is not the agent. The AD-like cellular pathologies induced by AβOs suggest their impact provides a unifying mechanism for AD pathogenesis, explaining why early stage disease is specific for memory and accounting for major facets of AD neuropathology. Alternative ideas for triggering mechanisms are being actively investigated. Some research favors insertion of AβOs into membrane, while other evidence supports ligand-like accumulation at particular synapses. Over a dozen candidate toxin receptors have been proposed. AβO binding triggers a redistribution of critical synaptic proteins and induces hyperactivity in metabotropic and ionotropic glutamate receptors. This leads to Ca(2+) overload and instigates major facets of AD neuropathology, including tau hyperphosphorylation, insulin resistance, oxidative stress, and synapse loss. Because different species of AβOs have been identified, a remaining question is which oligomer is the major pathogenic culprit. The possibility has been raised that more than one species plays a role. Despite some key unknowns, the clinical relevance of AβOs has been established, and new studies are beginning to point to co-morbidities such as diabetes and hypercholesterolemia as etiological factors. Because pathogenic AβOs appear early in the disease, they offer appealing targets for therapeutics and diagnostics. Promising therapeutic strategies include use of CNS insulin signaling enhancers to protect against the presence of toxins and elimination of the toxins through use of highly specific AβO antibodies. An AD-dependent accumulation of AβOs in CSF suggests their potential use as biomarkers and new AβO probes are opening the door to brain imaging. Overall, current evidence indicates that Aβ oligomers provide a substantive molecular basis for the cause, treatment and diagnosis of Alzheimer's disease.

The synergistic effect between β-amyloid(1-42) and α-synuclein on the synapses dysfunction in hippocampal neurons

OBJECTIVE

This study was to explore the molecular mechanisms underpinning the synergetic effect between β-amyloid (Aβ) and α-synuclein (α-syn) on synapses dysfunction during the development of neurodegenerative disorders including Parkinson's disease (PD), dementia with Lewy bodies (DLB) and Alzheimer disease (AD).

METHODS

The primary cultured hippocampal neurons prepared from the fetal tissue of mice were divided into six groups and treated with DMSO, Aβ(42-1), α-syn, Aβ(1-42), α-syn plus Aβ(42-1) and α-syn plus Aβ(1-42), respectively. After incubation for 24 h, the synapsin I content was calculated by immunofluorescence and the synaptic vesicle recycling was monitored by FM1-43 staining. Furthermore, the expression of cysteine string protein-α (CSPα) detected by western blot was also conducted.

RESULTS

Either Aβ(1-42) or α-syn alone could induce a significant synapses dysfunction through reducing the content of synapsin I, inhibiting the synaptic vesicle recycling as well as down-regulating the expression of CSPα compared with the controls (P<0.05). However, simultaneous intervention with both α-syn and Aβ(1-42) aggravated these effects in cultured hippocampal neurons compared with the treatment with α-syn (synapsin I content: P<0.001; synaptic vesicle recycling: P=0.007; CSPα expression: P<0.001) or Aβ(1-42) (synapsin I number: P<0.001; synaptic vesicle recycling: P=0.007 CSPα expression: P<0.001) alone.

CONCLUSION

There was synergistic effect between Aβ and α-syn on synapses dysfunction through reducing the synapsin I content, inhibiting the synaptic vesicle recycling and down-regulating the expression of CSPα in several neurodegenerative diseases.

Inconsistencies and controversies surrounding the amyloid hypothesis of Alzheimer's disease

The amyloid hypothesis has driven drug development strategies for Alzheimer's disease for over 20 years. We review why accumulation of amyloid-beta (Aβ) oligomers is generally considered causal for synaptic loss and neurodegeneration in AD. We elaborate on and update arguments for and against the amyloid hypothesis with new data and interpretations, and consider why the amyloid hypothesis may be failing therapeutically. We note several unresolved issues in the field including the presence of Aβ deposition in cognitively normal individuals, the weak correlation between plaque load and cognition, questions regarding the biochemical nature, presence and role of Aβ oligomeric assemblies in vivo, the bias of pre-clinical AD models toward the amyloid hypothesis and the poorly explained pathological heterogeneity and comorbidities associated with AD. We also illustrate how extensive data cited in support of the amyloid hypothesis, including genetic links to disease, can be interpreted independently of a role for Aβ in AD. We conclude it is essential to expand our view of pathogenesis beyond Aβ and tau pathology and suggest several future directions for AD research, which we argue will be critical to understanding AD pathogenesis.

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.

Ginsenoside Rg5 improves cognitive dysfunction and beta-amyloid deposition in STZ-induced memory impaired rats via attenuating neuroinflammatory responses

Neuroinflammatory responses play a crucial role in the pathogenesis of Alzheimer's disease (AD). Ginsenoside Rg5 (Rg5), an abundant natural compound in Panax ginseng, has been found to be beneficial in treating AD. In the present study, we demonstrated that Rg5 improved cognitive dysfunction and attenuated neuroinflammatory responses in streptozotocin (STZ)-induced memory impaired rats. Cognitive deficits were ameliorated with Rg5 (5, 10 and 20mg/kg) treatment in a dose-dependent manner together with decreased levels of inflammatory cytokines TNF-α and IL-1β (P<0.05) in brains of STZ rats. Acetylcholinesterase (AChE) activity was also significantly reduced by Rg5 whereas choline acetyltransferase (ChAT) activity was remarkably increased in the cortex and hippocampus of STZ-induced AD rats (P<0.05). In addition, Congo red and immunohistochemistry staining results showed that Rg5 alleviated Aβ deposition but enhanced the expressions of insulin-like growth factors 1 (IGF-1) and brain derived neurophic factor (BDNF) in the hippocampus and cerebral cortex (P<0.05). Western blot analysis also demonstrated that Rg5 increased remarkably BDNF and IGF-1 expressions whereas decreased significantly Aβ deposits (P<0.05). Furthermore, it was observed that the expressions of COX-2 and iNOS were significantly up-regulated in STZ-induced AD rats and down-regulated strongly (P<0.05) by Rg5 compared with control rats. These data demonstrated that STZ-induced learning and memory impairments in rats could be improved by Rg5, which was associated with attenuating neuroinflammatory responses. Our findings suggested that Rg5 could be a beneficial agent for the treatment of AD.