Direct observation of the interconversion of normal and toxic forms of α-synuclein

Temperature-Driven Stopped-Flow Experiments for Investigating the Initial Aggregation of the α-Synuclein Amyloid Protein, Focusing on Active and Inactive Phases

The primary objective of this research is to further examine the events occurring during the active or burst phase by focusing on the aggregation of the Syn amyloid protein. Regarding this aspect, it was initially conducted rapid temperature variations using stopped-flow spectrometry and tyrosyl group fluorescence emission detection, within the initial 500 milliseconds in buffered Syn solutions at pH 7, exploring various temperature ranges to investigate protein aggregation. The results obtained were contrasted with results obtained for the Nα-acetyl-L-tyrosinamide (NAYA) parent compound in the same conditions. The utilization of the NAYA compound is suitable as it mimics the peptide bonds in proteins and contains a tyrosyl group resembling the four tyrosyl groups found in the Syn protein structure (the protein has no tryptophan residues). Furthermore, the NAYA compound adopts an intramolecularly hydrogen-bonded structure even in an aqueous solution, similar to the interactions seen in the hydrophilic face of β-sheets. Additionally, the Syn protein system can exhibit the presence of β-sheets as a result of the existence of very low abundant Syn amyloid precursor forms or nuclei during the initial stages of the protein aggregation. Thus, a relationship is present between the molecular processes in the NAYA and Syn protein systems, making the NAYA's application crucial in this research. Moreover, to aid in understanding the results, it was also compared the events during the quiescent or inactive phase (30-500 milliseconds) with those in the burst phase (up to 10 milliseconds) using stopped-flow spectrometry conditions. Steady-state measurements were beneficial in comprehending the occurrences in both the quiescent and burst phases examined. Although protein aggregation and disaggregation were observed during the quiescent phase, determining these processes in the burst phase was more challenging. In the latter case, the aggregation of the Syn protein is actually initiated by the interaction of the intrinsically disordered Syn monomers. In the quiescent phase, first-order rate constants were measured and analysis showed that Syn protein aggregation and disaggregation occur simultaneously. At lower temperatures, early protein disaggregation outweighs protein aggregation whereas at higher temperatures protein disaggregation and aggregation are rather similar. It is also need to highlight that the burst phase, while distinct from the quiescent phase, can be considered as a possible structural phase for obtaining details about the aggregation of this specific disordered protein in solution on a very short timescale.

Circadian disruption promotes the neurotoxicity of oligomeric alpha-synuclein in mice

Circadian disruption often arises prior to the onset of typical motor deficits in patients with Parkinson's disease (PD). It remains unclear whether such a prevalent non-motor manifestation would contribute to the progression of PD. Diffusible oligomeric alpha-synuclein (O-αSyn) is perceived as the most toxic and rapid-transmitted species in the early stages of PD. Exploring the factors that influence the spread and toxicity of O-αSyn should be helpful for developing effective interventions for the disease. The aim of this study was to explore the effects of circadian disruption on PD pathology and parkinsonism-like behaviors in a novel mouse model induced by O-αSyn. We discovered that O-αSyn could enter the brain rapidly following intranasal administration, resulting in the formation of nitrated-αSyn pathology and non-motor symptoms of the mice. Meanwhile, circadian disruption exacerbated the burden of nitrated-αSyn pathology and accelerated the loss of dopaminergic neurons in O-αSyn-treated mice. Subsequent experiments demonstrated that circadian disruption might act via promoting nitrative stress and neuroinflammation. These findings could highlight the circadian rhythms as a potential diagnostic and therapeutic target in early-stage PD.

α-Synuclein species in plasma neuron-derived extracellular vesicles as biomarkers for iRBD

OBJECTIVE

Isolated REM sleep behavior disorder (iRBD) is considered as the strongest predictor of Parkinson's disease (PD). Reliable and accurate biomarkers for iRBD detection and the prediction of phenoconversion are in urgent need. This study aimed to investigate whether α-Synuclein (α-Syn) species in plasma neuron-derived extracellular vesicles (NDEVs) could differentiate between iRBD patients and healthy controls (HCs).

METHODS

Nanoscale flow cytometry was used to detect α-Syn-containing NDEVs in plasma.

RESULTS

A total of 54 iRBD patients and 53 HCs were recruited. The concentrations of total α-Syn, α-Syn aggregates, and phosphorylated α-Syn at Ser129 (pS129)-containing NDEVs in plasma of iRBD individuals were significantly higher than those in HCs (p < 0.0001 for all). In distinguishing between iRBD and HCs, the area under the receiver operating characteristic (ROC) curve (AUC) for an integrative model incorporating the levels of α-Syn, pS129, and α-Syn aggregate-containing NDEVs in plasma was 0.965. This model achieved a sensitivity of 94.3% and a specificity of 88.9%. In iRBD group, the concentrations of α-Syn aggregate-containing NDEVs exhibited a negative correlation with Sniffin' Sticks olfactory scores (r = -0.351, p = 0.039). Smokers with iRBD exhibited lower levels of α-Syn aggregates and pS129-containing NDEVs in plasma compared to nonsmokers (pα-Syn aggregates = 0.014; ppS129 = 0.003).

INTERPRETATION

The current study demonstrated that the levels of total α-Syn, α-Syn aggregates, and pS129-containing NDEVs in the plasma of individuals with iRBD were significantly higher compared to HCs. The levels of α-Syn species-containing NDEVs in plasma may serve as biomarkers for iRBD.

Chitosan-enhanced sensitivity of mercaptoundecanoic acid (MUA)- capped gold nanorod based localized surface plasmon resonance (LSPR) biosensor for detection of alpha-synuclein oligomer biomarker in parkinson's disease

Alpha-synuclein oligomers play a crucial role in the early diagnosis of Parkinson's disease (PD). In this study, a mercaptoundecanoic acid (MUA)-capped gold nanorod (GNR)-coated and chitosan (CH)-immobilized fiber optic probe has shown considerable sensitivity of its detection. The proposed U-shaped fiber optic biosensor based on localized surface plasmon resonance (LSPR) was applied to detect α-syn oligomer (OA) biomarker. By analyzing OA concentrations, the biosensor achieved a limit of detection of (LOD) 11 pM within the concentration range of 10-100 pM and the sensitivity value was found as 502.69 Δλ/RIU. Upon analysis of the CV% (coefficient of variation) and accuracy/recovery values, it is revealed that the sensor successfully fulfilled the criteria for success, displaying accuracy/recovery values within the range of 80%-120% and CV% values below 20%. This sensor presents significant advantages, including high sensitivity, specificity, and ability to detect very low concentrations of OA. In conclusion, the suggested U-shaped fiber optic biosensor has the potential to be valuable in the early detection of PD from a clinical perspective.

A charged tail on anti-α-Synuclein antibodies does not enhance their affinity to α-Synuclein fibrils

The aggregation of α-Synuclein (αSyn) is strongly linked to neuronal death in Parkinson's disease and other synucleinopathies. The spreading of aggregated αSyn between neurons is at least partly dependent on electrostatic interactions between positively charged stretches on αSyn fibrils and the negatively charged heparan sulphate proteoglycans on the cell surface. To date there is still no therapeutic option available that could halt the progression of Parkinson's disease and one of the major limitations is likely the relatively low proportion of αSyn aggregates accessible to drugs in the extracellular space. Here, we investigated whether a negatively charged peptide tail fused to the αSyn aggregate-specific antibodies SynO2 and 9E4 could enhance the antibodies' avidity to αSyn aggregates in order to improve their potential therapeutic effect through inhibiting cell-to-cell spreading and enhancing the clearance of extracellular aggregates. We performed ELISAs to test the avidity to αSyn aggregates of both monovalent and bivalent antibody formats with and without the peptide tail. Our results show that the addition of the negatively charged peptide tail decreased the binding strength of both antibodies to αSyn aggregates at physiological salt conditions, which can likely be explained by intermolecular repulsions between the tail and the negatively charged C-terminus of αSyn. Additionally, the tail might interact with the paratopes of the SynO2 antibody abolishing its binding to αSyn aggregates. Conclusively, our peptide tail did not fulfil the required characteristics to improve the antibodies' binding to αSyn aggregates. Fine-tuning the design of the peptide tail to avoid its interaction with the antibodies' CDR and to better mimic relevant characteristics of heparan sulphates for αSyn aggregate binding may help overcome the limitations observed in this study.

Effect of Aggregated Lysozyme on Fluorescence Properties of Rose Bengal

Protein aggregates cause abnormal states and trigger various diseases, including neurodegenerative disorders. This study examined whether the xanthene dye derivative Rose Bengal could track a series of conformational changes in protein aggregates. Using lysozyme as a model protein, aggregated proteins were prepared by heating under acidic conditions. The absorption spectra, steady-state fluorescence spectra, fluorescence quantum yield, fluorescence lifetime, and phosphorescence lifetime of a solution containing Rose Bengal in the presence of aggregated lysozyme were measured to identify their spectroscopic characteristics. The absorption spectrum of Rose Bengal changed significantly during the formation of agglomerates in heated lysozyme. Additionally, the fluorescence intensity decreased during the initial stages of the aggregation process with an increase in heating time, followed by an increase in intensity along with a red-shift of the peak wavelength. The decrease in quantum yield with a fixed fluorescence lifetime supported the formation of a nonfluorescent ground-state complex between Rose Bengal and the aggregated lysozyme. Based on the characteristic changes in absorption and fluorescence properties observed during the aggregation process, Rose Bengal is considered an excellent indicator for the sensitive discernment of aggregated proteins.

α-Synuclein oligomers form by secondary nucleation

Oligomeric species arising during the aggregation of α-synuclein are implicated as a major source of toxicity in Parkinson's disease, and thus a major potential drug target. However, both their mechanism of formation and role in aggregation are largely unresolved. Here we show that, at physiological pH and in the absence of lipid membranes, α-synuclein aggregates form by secondary nucleation, rather than simple primary nucleation, and that this process is enhanced by agitation. Moreover, using a combination of single molecule and bulk level techniques, we identify secondary nucleation on the surfaces of existing fibrils, rather than formation directly from monomers, as the dominant source of oligomers. Our results highlight secondary nucleation as not only the key source of oligomers, but also the main mechanism of aggregate formation, and show that these processes take place under conditions which recapitulate the neutral pH and ionic strength of the cytosol.

Origin of Secondary Structure Transitions and Peptide Self-Assembly Propensity in Trifluoroethanol-Water Mixtures

Membrane-peptide interactions are key to the formation of helical intermediates in the early stages of amyloidogenesis. Aqueous solutions of 2,2,2-trifluoroethanol (TFE) provide a membrane-mimetic environment capable of promoting and stabilizing local peptide interactions. Uperin 3.5 (U3.5), a 17-residue and amidated antimicrobial peptide, is unstructured in water but self-assembles into fibrils in the presence of salt. Secondary structure transitions linked to U3.5 self-assembly were investigated in TFE/water mixtures, in both the absence and presence of salt, to assess the role of membrane-peptide interactions on peptide self-assembly and amyloid formation. A 5-to-7-fold increase in fibril yield of U3.5 was observed at low TFE concentrations (10% TFE/water v/v) compared with physiological buffer but only in the presence of salt. No aggregation was observed in salt-free TFE/water mixtures. Circular dichroism spectra showed that partial helical structures, initially stabilized by TFE, transitioned to β-sheet-rich aggregates in a saline buffer. Molecular dynamics simulations confirmed that TFE and salt act synergistically to enhance peptide-peptide interactions, resulting in β-sheet-rich U3.5 oligomers at low TFE concentrations. Specifically, TFE stabilized amphipathic, helical intermediates, leading to increased peptide-peptide attraction through hydrophobic interactions. The presence of salt further enhanced the peptide-peptide interactions by screening positively charged residues. Thus, the study revealed the role of a membrane mimic in stabilizing helical intermediates on the pathway to amyloid formation in the antimicrobial U3.5 peptide.

Nuclear aggregates of NONO/SFPQ and A-to-I-edited RNA in Parkinson's disease and dementia with Lewy bodies

Neurodegenerative diseases are commonly classified as proteinopathies that are defined by the aggregation of a specific protein. Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are classified as synucleinopathies since α-synuclein (α-syn)-containing inclusions histopathologically define these diseases. Unbiased biochemical analysis of PD and DLB patient material unexpectedly revealed novel pathological inclusions in the nucleus comprising adenosine-to-inosine (A-to-I)-edited mRNAs and NONO and SFPQ proteins. These inclusions showed no colocalization with Lewy bodies and accumulated at levels comparable to α-syn. NONO and SFPQ aggregates reduced the expression of the editing inhibitor ADAR3, increasing A-to-I editing mainly within human-specific, Alu-repeat regions of axon, synaptic, and mitochondrial transcripts. Inosine-containing transcripts aberrantly accumulated in the nucleus, bound tighter to recombinant purified SFPQ in vitro, and potentiated SFPQ aggregation in human dopamine neurons, resulting in a self-propagating pathological state. Our data offer new insight into the inclusion composition and pathophysiology of PD and DLB.

"Prion-like" seeding and propagation of oligomeric protein assemblies in neurodegenerative disorders

Intra- or extracellular aggregates of proteins are central pathogenic features in most neurodegenerative disorders. The accumulation of such proteins in diseased brains is believed to be the end-stage of a stepwise aggregation of misfolded monomers to insoluble cross-β fibrils via a series of differently sized soluble oligomers/protofibrils. Several studies have shown how α-synuclein, amyloid-β, tau and other amyloidogenic proteins can act as nucleating particles and thereby share properties with misfolded forms, or strains, of the prion protein. Although the roles of different protein assemblies in the respective aggregation cascades remain unclear, oligomers/protofibrils are considered key pathogenic species. Numerous observations have demonstrated their neurotoxic effects and a growing number of studies have indicated that they also possess seeding properties, enabling their propagation within cellular networks in the nervous system. The seeding behavior of oligomers differs between the proteins and is also affected by various factors, such as size, shape and epitope presentation. Here, we are providing an overview of the current state of knowledge with respect to the "prion-like" behavior of soluble oligomers for several of the amyloidogenic proteins involved in neurodegenerative diseases. In addition to providing new insight into pathogenic mechanisms, research in this field is leading to novel diagnostic and therapeutic opportunities for neurodegenerative diseases.

Elucidation of molecular mechanisms by which amyloid β1-42 fibrils exert cell toxicity

Abrupt aggregation of amyloid β1-42 (Aβ1-42) peptide in the frontal lobe is the expected underlying cause of Alzheimer's disease (AD). β-Sheet-rich oligomers and fibrils formed by Aβ1-42 exert high cell toxicity. A growing body of evidence indicates that lipids can uniquely alter the secondary structure and toxicity of Aβ1-42 aggregates. At the same time, underlying molecular mechanisms that determine this difference in toxicity of amyloid aggregates remain unclear. Using a set of molecular and biophysical assays to determine the molecular mechanism by which Aβ1-42 aggregates formed in the presence of cholesterol, cardiolipin, and phosphatidylcholine exert cell toxicity. Our findings demonstrate that rat neuronal cells exposed to Aβ1-42 fibrils formed in the presence of lipids with different chemical structure exert drastically different magnitude and dynamic of unfolded protein response (UPR) in the endoplasmic reticulum (ER) and mitochondria (MT). We found that the opposite dynamics of UPR in MT and ER in the cells exposed to Aβ1-42: cardiolipin fibrils and Aβ1-42 aggregates formed in a lipid-free environment. We also found that Aβ1-42: phosphatidylcholine fibrils upregulated ER UPR simultaneously downregulating the UPR response of MT, whereas Aβ1-42: cholesterol fibrils suppressed the UPR response of ER and upregulated UPR response of MT. We also observed progressively increasing ROS production that damages mitochondrial membranes and other cell organelles, ultimately leading to cell death.

Cognitive dysfunction in animal models of human lewy-body dementia

Cognitive impairments are a common feature of synucleinopathies such as Parkinson's Disease Dementia and Dementia with Lewy Bodies. These pathologies are characterized by accumulation of Lewy bodies and Lewy neurites as well as neuronal cell death. Alpha-synuclein is the main proteinaceous component of Lewy bodies and Lewy neurites. To model these pathologies in vivo, toxins that selectively target certain neuronal populations or different means of inducing alpha-synuclein aggregation can be used. Alpha-synuclein accumulation can be induced by genetic manipulation, viral vector overexpression or the use of preformed fibrils of alpha-synuclein. In this review, we summarize the cognitive impairments associated with different models of synucleinopathies and relevance to observations in human diseases.

Aggregation-resistant alpha-synuclein tetramers are reduced in the blood of Parkinson's patients

Synucleinopathies such as Parkinson's disease (PD) are defined by the accumulation and aggregation of the α-synuclein protein in neurons, glia and other tissues. We have previously shown that destabilization of α-synuclein tetramers is associated with familial PD due to SNCA mutations and demonstrated brain-region specific alterations of α-synuclein multimers in sporadic PD patients following the classical Braak spreading theory. In this study, we assessed relative levels of disordered and higher-ordered multimeric forms of cytosolic α-synuclein in blood from familial PD with G51D mutations and sporadic PD patients. We used an adapted in vitro-cross-linking protocol for human EDTA-whole blood. The relative levels of higher-ordered α-synuclein tetramers were diminished in blood from familial PD and sporadic PD patients compared to controls. Interestingly, the relative amount of α-synuclein tetramers was already decreased in asymptomatic G51D carriers, supporting the hypothesis that α-synuclein multimer destabilization precedes the development of clinical PD. Our data, therefore suggest that measuring α-synuclein tetramers in blood may have potential as a facile biomarker assay for early detection and quantitative tracking of PD progression.

MicroRNA-124-3p Modulates Alpha-Synuclein Expression Levels in a Paraquat-Induced in vivo Model for Parkinson's Disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and the most common movement disorder. Although PD etiology is not fully understood, alpha (α)-synuclein is a key protein involved in PD pathology. MicroRNAs (miRNA), small gene regulatory RNAs that control gene expression, have been identified as biomarkers and potential therapeutic targets for brain diseases, including PD. In particular, miR-124 is downregulated in the plasma and brain samples of PD patients. Recently we showed that the brain delivery of miR-124 counteracts 6-hydroxydopamine-induced motor deficits. However, its role in α-synuclein pathology has never been addressed. Here we used paraquat (PQ)-induced rat PD model to evaluate the role of miR-124-3p in α-synuclein accumulation and dopaminergic neuroprotection. Our results showed that an intranigral administration of miR-124-3p reduced the expression and aggregation of α-synuclein in the substantia nigra (SN) of rats exposed to PQ. NADPH oxidases (NOX), responsible for reactive oxygen species generation, have been considered major players in the development of α-synuclein pathology. Accordingly, miR-124-3p decreased protein expression levels of NOX1 and its activator, small GTPase Rac1, in the SN of PQ-lesioned rats. Moreover, miR-124-3p was able to counteract the reduced levels of pituitary homeobox 3 (PITX3), a protein required for the dopaminergic phenotype, induced by PQ in the SN. This is the first study showing that miR-124-3p decreases PQ-induced α-synuclein levels and the associated NOX1/Rac1 signaling pathway, and impacts PITX3 protein levels, supporting the potential of miR-124-3p as a disease-modifying agent for PD and related α-synucleinopathies.

Inhibition of fibril formation by polyphenols: molecular mechanisms, challenges, and prospective solutions

Fibril formation is a key feature in neurodegenerative diseases like Alzheimer's, Parkinson's, and systemic amyloidosis. Polyphenols, found in plant-based foods, show promise in inhibiting fibril formation and disrupting disease progression. The ability of polyphenols to break the amyloid fibrils of many disease-linked proteins has been tested in numerous studies. Polyphenols have their distinctive mechanism of action. They behave differently on various events in the aggregation pathway. Their action also differs for different proteins. Some polyphenols only inhibit the formation of fibrils whereas others break the preformed fibrils. Some break the fibrils into smaller species, and some change them to other morphologies. This article delves into the intricate molecular mechanisms underlying the inhibitory effects of polyphenols on fibrillogenesis, shedding light on their interactions with amyloidogenic proteins and the disruption of fibril assembly pathways. However, addressing the challenges associated with solubility, stability, and bioavailability of polyphenols is crucial. The current strategies involve nanotechnology to improve the solubility and bioavailability, thus showing the potential to enhance the efficacy of polyphenols as therapeutics. Advancements in structural biology, computational modeling, and biophysics have provided insights into polyphenol-fibril interactions, offering hope for novel therapies for neurodegenerative diseases and amyloidosis.

Interaction between α-Synuclein and Bioactive Lipids: Neurodegeneration, Disease Biomarkers and Emerging Therapies

The present review provides a comprehensive examination of the intricate dynamics between α-synuclein, a protein crucially involved in the pathogenesis of several neurodegenerative diseases, including Parkinson's disease and multiple system atrophy, and endogenously-produced bioactive lipids, which play a pivotal role in neuroinflammation and neurodegeneration. The interaction of α-synuclein with bioactive lipids is emerging as a critical factor in the development and progression of neurodegenerative and neuroinflammatory diseases, offering new insights into disease mechanisms and novel perspectives in the identification of potential biomarkers and therapeutic targets. We delve into the molecular pathways through which α-synuclein interacts with biological membranes and bioactive lipids, influencing the aggregation of α-synuclein and triggering neuroinflammatory responses, highlighting the potential of bioactive lipids as biomarkers for early disease detection and progression monitoring. Moreover, we explore innovative therapeutic strategies aimed at modulating the interaction between α-synuclein and bioactive lipids, including the development of small molecules and nutritional interventions. Finally, the review addresses the significance of the gut-to-brain axis in mediating the effects of bioactive lipids on α-synuclein pathology and discusses the role of altered gut lipid metabolism and microbiota composition in neuroinflammation and neurodegeneration. The present review aims to underscore the potential of targeting α-synuclein-lipid interactions as a multifaceted approach for the detection and treatment of neurodegenerative and neuroinflammatory diseases.

Internalized α-synuclein fibrils become truncated and resist degradation in neurons while glial cells rapidly degrade α-synuclein fibrils

Parkinson's disease (PD) and other α-synucleinopathies are characterized by the accumulation of α-synuclein (αS) pathology that can spread via the cell-to-cell transmission of αS aggregates. To better understand how various brain cells contribute to the spreading of αS pathology, we examined the metabolism of αS aggreges or pre-formed fibrils (PFFs) in neuronal and glial cells (microglia, astrocytes, and oligodendrocytes). In neurons, while the full-length αS rapidly disappeared following αS PFF uptake, truncated αS accumulated with a half-life of days rather than hours. Epitope mapping and fractionation studies indicate that αS PFF was truncated at the C-terminal region following uptake and remained insoluble/aggregated. In contrast, microglia and astrocytes rapidly metabolized αS PFF as the half-lives of αS PFF in these glial cells were <6 hours. Differential processing of αS by neurons was recapitulated in cell lines as differentiated CLU neuronal cell lines stably accumulate truncated αS while undifferentiated cells rapidly metabolize αS. Immunolocalization and subcellular fractionation studies show that internalized αS PFF is initially localized to endosomes followed by lysosomes. The lysosome is largely responsible for the degradation of internalized αS PFF as the inhibition of lysosomal function leads to the stabilization of αS in all cell types. Significantly, αS PFF causes lysosomal dysfunction in neurons. In summary, we show that neurons are inefficient in metabolizing internalized αS aggregates, partially because αS aggregates cause lysosomal dysfunction, potentially generating aggregation-prone truncated αS. In contrast, glial cells may protect neurons from αS aggregates by rapidly clearing αS aggregates.

Mechanistic Insights Behind the Self-Assembly of Human Insulin under the Influence of Surface-Engineered Gold Nanoparticles

Elucidating the underlying principles of amyloid protein self-assembly at nanobio interfaces is extremely challenging due to the diversity in physicochemical properties of nanomaterials and their physical interactions with biological systems. It is, therefore, important to develop nanoscale materials with dynamic features and heterogeneities. In this work, through engineering of hierarchical polyethylene glycol (PEG) structures on gold nanoparticle (GNP) surfaces, tailored nanomaterials with different surface properties and conformations (GNPs-PEG) are created for modulating the self-assembly of a widely studied protein, insulin, under amyloidogenic conditions. Important biophysical studies including thioflavin T (ThT) binding, circular dichroism (CD), surface plasmon resonance (SPR), and atomic force microscopy (AFM) showed that higher-molecular weight GNPs-PEG triggered the formation of amyloid fibrils by promoting adsorption of proteins at nanoparticle surfaces and favoring primary nucleation rate. Moreover, the modulation of fibrillation kinetics reduces the overall toxicity of insulin oligomers and fibrils. In addition, the interaction between the PEG polymer and amyloidogenic insulin examined using MD simulations revealed major changes in the secondary structural elements of the B chain of insulin. The experimental findings provide molecular-level descriptions of how the PEGylated nanoparticle surface modulates protein adsorption and drives the self-assembly of insulin. This facile approach provides a new avenue for systematically altering the binding affinities on nanoscale surfaces by tailoring their topologies for examining adsorption-induced fibrillogenesis phenomena of amyloid proteins. Together, this study suggests the role of nanobio interfaces during surface-induced heterogeneous nucleation as a primary target for designing therapeutic interventions for amyloid-related neurodegenerative disorders.

Single-Molecule Characterization and Super-Resolution Imaging of Alzheimer's Disease-Relevant Tau Aggregates in Human Samples

Hyperphosphorylation and aggregation of the protein tau play key roles in the development of Alzheimer's disease (AD). While the molecular structure of the filamentous tau aggregates has been determined to atomic resolution, there is far less information available about the smaller, soluble aggregates, which are believed to be more toxic. Traditional techniques are limited to bulk measures and struggle to identify individual aggregates in complex biological samples. To address this, we developed a novel single-molecule pull-down-based assay (MAPTau) to detect and characterize individual tau aggregates in AD and control post-mortem brain and biofluids. Using MAPTau, we report the quantity, as well as the size and circularity of tau aggregates measured using super-resolution microscopy, revealing AD-specific differences in tau aggregate morphology. By adapting MAPTau to detect multiple phosphorylation markers in individual aggregates using two-color coincidence detection, we derived compositional profiles of the individual aggregates. We find an AD-specific phosphorylation profile of tau aggregates with more than 80 % containing multiple phosphorylations, compared to 5 % in age-matched non-AD controls. Our results show that MAPTau is able to identify disease-specific subpopulations of tau aggregates phosphorylated at different sites, that are invisible to other methods and enable the study of disease mechanisms and diagnosis.

Mitochondrial dysfunction: mechanisms and advances in therapy

Mitochondria, with their intricate networks of functions and information processing, are pivotal in both health regulation and disease progression. Particularly, mitochondrial dysfunctions are identified in many common pathologies, including cardiovascular diseases, neurodegeneration, metabolic syndrome, and cancer. However, the multifaceted nature and elusive phenotypic threshold of mitochondrial dysfunction complicate our understanding of their contributions to diseases. Nonetheless, these complexities do not prevent mitochondria from being among the most important therapeutic targets. In recent years, strategies targeting mitochondrial dysfunction have continuously emerged and transitioned to clinical trials. Advanced intervention such as using healthy mitochondria to replenish or replace damaged mitochondria, has shown promise in preclinical trials of various diseases. Mitochondrial components, including mtDNA, mitochondria-located microRNA, and associated proteins can be potential therapeutic agents to augment mitochondrial function in immunometabolic diseases and tissue injuries. Here, we review current knowledge of mitochondrial pathophysiology in concrete examples of common diseases. We also summarize current strategies to treat mitochondrial dysfunction from the perspective of dietary supplements and targeted therapies, as well as the clinical translational situation of related pharmacology agents. Finally, this review discusses the innovations and potential applications of mitochondrial transplantation as an advanced and promising treatment.

A Targetable N-Terminal Motif Orchestrates α-Synuclein Oligomer-to-Fibril Conversion

Oligomeric species populated during α-synuclein aggregation are considered key drivers of neurodegeneration in Parkinson's disease. However, the development of oligomer-targeting therapeutics is constrained by our limited knowledge of their structure and the molecular determinants driving their conversion to fibrils. Phenol-soluble modulin α3 (PSMα3) is a nanomolar peptide binder of α-synuclein oligomers that inhibits aggregation by blocking oligomer-to-fibril conversion. Here, we investigate the binding of PSMα3 to α-synuclein oligomers to discover the mechanistic basis of this protective activity. We find that PSMα3 selectively targets an α-synuclein N-terminal motif (residues 36-61) that populates a distinct conformation in the mono- and oligomeric states. This α-synuclein region plays a pivotal role in oligomer-to-fibril conversion as its absence renders the central NAC domain insufficient to prompt this structural transition. The hereditary mutation G51D, associated with early onset Parkinson's disease, causes a conformational fluctuation in this region, leading to delayed oligomer-to-fibril conversion and an accumulation of oligomers that are resistant to remodeling by molecular chaperones. Overall, our findings unveil a new targetable region in α-synuclein oligomers, advance our comprehension of oligomer-to-amyloid fibril conversion, and reveal a new facet of α-synuclein pathogenic mutations.

Macrophages and Natural Killers Degrade α-Synuclein Aggregates

Amyloid oligomers and fibrils are protein aggregates that exert a high cell toxicity. Efficient degradation of these protein aggregates can minimize the spread and progression of neurodegeneration. In this study, we investigate the properties of natural killer (NK) cells and macrophages in the degradation of α-synuclein (α-Syn) aggregates grown in a lipid-free environment and in the presence of phosphatidylserine and cholesterol (PS/Cho), which are lipids that are directly associated with the onset and progression of Parkinson's disease. We found that both types of α-Syn aggregates were endocytosed by neurons, which caused strong damage to cell endosomes. Our results also indicated that PS/Cho vesicles drastically increased the toxicity of α-Syn fibrils formed in their presence compared to the toxicity of α-Syn aggregates grown in a lipid-free environment. Both NK cells and macrophages were able to degrade α-Syn and α-Syn/Cho monomers, oligomers, and fibrils. Quantitative analysis of protein degradation showed that macrophages demonstrated substantially more efficient internalization and degradation of amyloid aggregates in comparison to NK cells. We also found that amyloid aggregates induced the proliferation of macrophages and NK cells and significantly changed the expression of their cytokines and chemokines.

A glimpse into the structural properties of α-synuclein oligomers

α-Synuclein (αS) aggregation is the main neurological hallmark of a group of debilitating neurodegenerative disorders, collectively referred to as synucleinopathies, of which Parkinson's disease is the most prevalent. αS oligomers formed during the initial stages of aggregation are considered key pathogenic drivers of disease onset and progression, standing as privileged targets for therapeutic intervention and diagnosis. However, the structure of αS oligomers and the mechanistic basis of oligomer to fibril conversion are yet poorly understood, thereby precluding the rational formulation of strategies aimed at targeting oligomeric species. In this review, we delve into the recent advances in the structural and mechanistic characterization of αS oligomers. We also discuss how these advances are transforming our understanding of these elusive species and paving the way for oligomer-targeting therapeutics and diagnosis.

Evaluating the Diagnostic Potential of Combined Salivary and Skin Biomarkers in Parkinson's Disease

Oligomeric alpha-synuclein (α-syn) in saliva and phosphorylated α-syn deposits in the skin have emerged as promising diagnostic biomarkers for Parkinson's disease (PD). This study aimed to assess and compare the diagnostic value of these biomarkers in discriminating between 38 PD patients and 24 healthy subjects (HSs) using easily accessible biological samples. Additionally, the study sought to determine the diagnostic potential of combining these biomarkers and to explore their correlations with clinical features. Salivary oligomeric α-syn levels were quantified using competitive ELISA, while skin biopsies were analyzed through immunofluorescence to detect phosphorylated α-syn at Ser129 (p-S129). Both biomarkers individually were accurate in discriminating PD patients from HSs, with a modest agreement between them. The combined positivity of salivary α-syn oligomers and skin p-S129 aggregates differentiated PD patients from HSs with an excellent discriminative ability with an AUC of 0.9095. The modest agreement observed between salivary and skin biomarkers individually suggests that they may reflect different aspects of PD pathology, thus providing complementary information when combined. This study's results highlight the potential of utilizing a multimodal biomarker approach to enhance diagnostic accuracy in PD.

RASP: Optimal Single Puncta Detection in Complex Cellular Backgrounds

Super-resolution and single-molecule microscopies have been increasingly applied to complex biological systems. A major challenge of these approaches is that fluorescent puncta must be detected in the low signal, high noise, heterogeneous background environments of cells and tissue. We present RASP, Radiality Analysis of Single Puncta, a bioimaging-segmentation method that solves this problem. RASP removes false-positive puncta that other analysis methods detect and detects features over a broad range of spatial scales: from single proteins to complex cell phenotypes. RASP outperforms the state-of-the-art methods in precision and speed using image gradients to separate Gaussian-shaped objects from the background. We demonstrate RASP's power by showing that it can extract spatial correlations between microglia, neurons, and α-synuclein oligomers in the human brain. This sensitive, computationally efficient approach enables fluorescent puncta and cellular features to be distinguished in cellular and tissue environments, with sensitivity down to the level of the single protein. Python and MATLAB codes, enabling users to perform this RASP analysis on their own data, are provided as Supporting Information and links to third-party repositories.

Surface Modification of Ultrasonic Cavitation by Surfactants Improves Detection Sensitivity of α-Synuclein Amyloid Seeds

The rapid amplification and sensitive detection of α-synuclein (αSyn) seeds is an efficient approach for the early diagnosis of Parkinson's disease. Ultrasonication stands out as a promising method for the rapid amplification of αSyn seeds because of its robust fibril fragmentation capability. However, ultrasonication also induces the primary nucleation of αSyn monomers, deteriorating the seed detection sensitivity by generating seed-independent fibrils. In this study, we show that an addition of surfactants to the αSyn monomer solution during αSyn seed detection under ultrasonication remarkably improves the detection sensitivity of the αSyn seeds by a factor of 100-1000. Chemical kinetic analysis reveals that these surfactants reduce the rate of primary nucleation while promoting the fragmentation of the αSyn fibrils under ultrasonication. These effects are attributed to the modification of the ultrasonic cavitation surface by the surfactants. Our study enhances the utility of ultrasonication in clinical assays targeting αSyn seeds as the Parkinson's disease biomarker.

Influence of Cigarette Aerosol in Alpha-Synuclein Oligomerization and Cell Viability in SH-SY5Y: Implications for Parkinson's Disease

Although cigarette aerosol exposure is associated with various adverse health issues, its impact on Parkinson's disease (PD) remains elusive. Here, we investigated the effect of cigarette aerosol extract (CAE) on SH-SY5Y cells for the first time, both with and without α-synuclein (α-Syn) overexpression. We found that α-Syn aggravates CAE-induced cell death, oxidative stress, and mitochondrial dysfunction. Fluorescence cross-correlation spectroscopy (FCCS) revealed a dual distribution of α-Syn within the cells, with homogeneous regions indicative of monomeric α-Syn and punctated regions, suggesting the formation of oligomers. Moreover, we observed colocalization of α-Syn oligomers with lysosomes along with a reduction in autophagy activity. These findings suggest that α-Syn overexpression exacerbates CAE-induced intracellular cytotoxicity, mitochondrial dysfunction, and autophagy dysregulation, leading to elevated cell mortality. Our findings provide new insights into the pathogenic mechanisms linking exposure to cigarette aerosols with neurodegenerative diseases.

A Relationship between the Structures and Neurotoxic Effects of Aβ Oligomers Stabilized by Different Metal Ions

Oligomeric assemblies of the amyloid β peptide (Aβ) have been investigated for over two decades as possible neurotoxic agents in Alzheimer's disease. However, due to their heterogeneous and transient nature, it is not yet fully established which of the structural features of these oligomers may generate cellular damage. Here, we study distinct oligomer species formed by Aβ40 (the 40-residue form of Aβ) in the presence of four different metal ions (Al3+, Cu2+, Fe2+, and Zn2+) and show that they differ in their structure and toxicity in human neuroblastoma cells. We then describe a correlation between the size of the oligomers and their neurotoxic activity, which provides a type of structure-toxicity relationship for these Aβ40 oligomer species. These results provide insight into the possible role of metal ions in Alzheimer's disease by the stabilization of Aβ oligomers.

A topographical atlas of α-synuclein dosage and cell type-specific expression in adult mouse brain and peripheral organs

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide and presents pathologically with Lewy pathology and dopaminergic neurodegeneration. Lewy pathology contains aggregated α-synuclein (αSyn), a protein encoded by the SNCA gene which is also mutated or duplicated in a subset of familial PD cases. Due to its predominant presynaptic localization, immunostaining for the protein results in a diffuse reactivity pattern, providing little insight into the types of cells expressing αSyn. As a result, insight into αSyn expression-driven cellular vulnerability has been difficult to ascertain. Using a combination of knock-in mice that target αSyn to the nucleus (SncaNLS) and in situ hybridization of Snca in wild-type mice, we systematically mapped the topography and cell types expressing αSyn in the mouse brain, spinal cord, retina, and gut. We find a high degree of correlation between αSyn protein and RNA levels and further identify cell types with low and high αSyn content. We also find high αSyn expression in neurons, particularly those involved in PD, and to a lower extent in non-neuronal cell types, notably those of oligodendrocyte lineage, which are relevant to multiple system atrophy pathogenesis. Surprisingly, we also found that αSyn is relatively absent from select neuron types, e.g., ChAT-positive motor neurons, whereas enteric neurons universally express some degree of αSyn. Together, this integrated atlas provides insight into the cellular topography of αSyn, and provides a quantitative map to test hypotheses about the role of αSyn in network vulnerability, and thus serves investigations into PD pathogenesis and other α-synucleinopathies.

Pyrazolamide derivatives inhibit α-Synuclein aggregation, disaggregate preformed fibers, and reduce inclusion formation in neuron cells

α-Syn fibers, the primary cause and central element of Lewy bodies (LB), play a pivotal role in the development of Parkinson's disease (PD). This research aims to identify more potent inhibitors of α-Syn aggregation. A series of N-aryl-3-aryl-pyrazole-5-carboxamide derivatives were designed and synthesized for this purpose. Among them, four candidate compounds, combining pyrazole and polyphenol blocks, were identified through screening, demonstrating good inhibitory effects with IC50 values in the low micromolar range (1.25-4.29 μM). Two candidates exhibited high permeability through the blood-brain barrier. Mechanistic studies using various methods revealed that the candidates preferentially bind to the aggregation-prone domains-proNAC or NAC domains of α-Syn. This binding hinders the conformational transition from random coil/α-helix to β-sheet, preserving α-Syn proteostasis. As a result, it interferes with α-Syn nuclei formation, prolongs the lag phase, decelerates the elongation phase, and ultimately impedes the formation of α-Syn fibrils. Additionally, the candidates demonstrated promising results in the disaggregation of preformed α-Syn fibers, potentially by binding to specific sites near the β-sheet domain within fibers. This reduces fiber stability, causing rapid collapse and yielding smaller aggregates and monomers. Crucially, the candidate compounds exhibited significant inhibitory efficacy against α-Syn aggregation within nerve cells with low cytotoxicity. This resulted in a notable inhibition of the formation of LB-like α-Syn inclusions. These compounds show considerable promise as potential therapeutic agents for the prevention and treatment of PD.

In situ single-molecule investigations of the impacts of biochemical perturbations on conformational intermediates of monomeric α-synuclein

α-Synuclein aggregation is a common trait in synucleinopathies, including Parkinson's disease. Being an unstructured protein, α-synuclein exists in several distinct conformational intermediates, contributing to both its function and pathogenesis. However, the regulation of these monomer conformations by biochemical factors and potential drugs has remained elusive. In this study, we devised an in situ single-molecule manipulation approach to pinpoint kinetically stable conformational intermediates of monomeric α-synuclein and explore the effects of various biochemical factors and drugs. We uncovered a partially folded conformation located in the non-amyloid-β component (NAC) region of monomeric α-synuclein, which is regulated by a preNAC region. This conformational intermediate is sensitive to biochemical perturbations and small-molecule drugs that influencing α-synuclein's aggregation tendency. Our findings reveal that this partially folded intermediate may play a role in α-synuclein aggregation, offering fresh perspectives for potential treatments aimed at the initial stage of higher-order α-synuclein aggregation. The single-molecule approach developed here can be broadly applied to the study of disease-related intrinsically disordered proteins.

Misfolded protein oligomers: mechanisms of formation, cytotoxic effects, and pharmacological approaches against protein misfolding diseases

The conversion of native peptides and proteins into amyloid aggregates is a hallmark of over 50 human disorders, including Alzheimer's and Parkinson's diseases. Increasing evidence implicates misfolded protein oligomers produced during the amyloid formation process as the primary cytotoxic agents in many of these devastating conditions. In this review, we analyze the processes by which oligomers are formed, their structures, physicochemical properties, population dynamics, and the mechanisms of their cytotoxicity. We then focus on drug discovery strategies that target the formation of oligomers and their ability to disrupt cell physiology and trigger degenerative processes.

Modulation of α-synuclein in vitro aggregation kinetics by its alternative splice isoforms

The misfolding and aggregation of α-synuclein is linked to a family of neurodegenerative disorders known as synucleinopathies, the most prominent of which is Parkinson's disease (PD). Understanding the aggregation process of α-synuclein from a mechanistic point of view is thus of key importance. SNCA, the gene encoding α-synuclein, comprises six exons and produces various isoforms through alternative splicing. The most abundant isoform is expressed as a 140-amino acid protein (αSyn-140), while three other isoforms, αSyn-126, αSyn-112, and αSyn-98, are generated by skipping exon 3, exon 5, or both exons, respectively. In this study, we performed a detailed biophysical characterization of the aggregation of these four isoforms. We found that αSyn-112 and αSyn-98 exhibit accelerated aggregation kinetics compared to αSyn-140 and form distinct aggregate morphologies, as observed by transmission electron microscopy. Moreover, we observed that the presence of relatively small amounts of αSyn-112 accelerates the aggregation of αSyn-140, significantly reducing the aggregation half-time. These results indicate a potential role of alternative splicing in the pathological aggregation of α-synuclein and provide insights into how this process could be associated with the development of synucleinopathies.

Exploration of Resveratrol as a Potent Modulator of α-Synuclein Fibril Formation

The molecular determinants of amyloid protein misfolding and aggregation are key for the development of therapeutic interventions in neurodegenerative disease. Although small synthetic molecules, bifunctional molecules, and natural products offer a potentially advantageous approach to therapeutics to remodel aggregation, their evaluation requires new platforms that are informed at the molecular level. To that end, we chose pulsed hydrogen/deuterium exchange mass spectrometry (HDX-MS) to discern the phenomena of aggregation modulation for a model system of alpha synuclein (αS) and resveratrol, an antiamyloid compound. We invoked, as a complement to HDX, advanced kinetic modeling described here to illuminate the details of aggregation and to determine the number of oligomeric populations by kinetically fitting the experimental data under conditions of limited proteolysis. The misfolding of αS is most evident within and nearby the nonamyloid-β component region, and resveratrol significantly remodels that aggregation. HDX distinguishes readily a less solvent-accessible, more structured oligomer that coexists with a solvent-accessible, more disordered oligomer during aggregation. A view of the misfolding emerges from time-dependent changes in the fractional species across the protein with or without resveratrol, while details were determined through kinetic modeling of the protected species. A detailed picture of the inhibitory action of resveratrol with time and regional specificity emerges, a picture that can be obtained for other inhibitors and amyloid proteins. Moreover, the model reveals that new states of aggregation are sampled, providing new insights on amyloid formation. The findings were corroborated by circular dichroism and transmission electron microscopy.

Helical sulfonyl-γ-AApeptides modulating Aβ oligomerization and cytotoxicity by recognizing Aβ helix

In contrast to prevalent strategies which make use of β-sheet mimetics to block Aβ fibrillar growth, in this study, we designed a series of sulfonyl-γ-AApeptide helices that targeted the crucial α-helix domain of Aβ13-26 and stabilized Aβ conformation to avoid forming the neurotoxic Aβ oligomeric β-sheets. Biophysical assays such as amyloid kinetics and TEM demonstrated that the Aβ oligomerization and fibrillation could be greatly prevented and even reversed in the presence of sulfonyl-γ-AApeptides in a sequence-specific and dose-dependent manner. The studies based on circular dichroism, Two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR) spectra unambiguously suggested that the sulfonyl-γ-AApeptide Ab-6 could bind to the central region of Aβ42 and induce α-helix conformation in Aβ. Additionally, Electrospray ionisation-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS) was employed to rule out a colloidal mechanism of inhibitor and clearly supported the capability of Ab-6 for inhibiting the formation of Aβ aggregated forms. Furthermore, Ab-6 could rescue neuroblastoma cells by eradicating Aβ-mediated cytotoxicity even in the presence of pre-formed Aβ aggregates. The confocal microscopy demonstrated that Ab-6 could still specifically bind Aβ42 and colocalize into mitochondria in the cellular environment, suggesting the rescue of cell viability might be due to the protection of mitochondrial function otherwise impaired by Aβ42 aggregation. Taken together, our studies indicated that sulfonyl-γ-AApeptides as helical peptidomimetics could direct Aβ into the off-pathway helical secondary structure, thereby preventing the formation of Aβ oligomerization, fibrillation and rescuing Aβ induced cell cytotoxicity.

Therapeutic potential of Coumarin-polyphenolic acid hybrids in PD: Inhibition of α-Syn aggregation and disaggregation of preformed fibrils, leading to reduced neuronal inclusion formation

This study focuses on the discovery of new potential drugs for treating PD by targeting the aggregation of α-Syn. A series of hybrids combining Coumarin and phenolic acid were designed and synthesized. Four particularly promising compounds were identified, showing strong inhibitory effects with IC50 values ranging from low micromolar to submicromolar concentrations, as low as 0.63 μM. These compounds exhibited a higher binding affinity to α-Syn residues and effectively hindered the entire aggregation process, maintaining the proteostasis conformation of α-Syn and preventing the formation of β-sheet aggregates. This approach holds significant promise for PD prevention. Additionally, these candidate compounds demonstrated the ability to break down preformed α-Syn oligomers and fibrils, resulting in the formation of smaller aggregates and monomers. Moreover, the candidate compounds showed impressive effectiveness in inhibiting α-Syn aggregation within nerve cells, thereby reducing the likelihood of α-Syn inclusion formation resembling Lewy bodies, which highlights their potential for treating PD.

Frequency of Comorbid Pathologies and Their Clinical Impact in Multiple System Atrophy

BACKGROUND

Mixed pathology is common at autopsy for a number of age-associated neurodegenerative disorders; however, the frequency of comorbid pathologies in multiple system atrophy (MSA) and their clinical correlations are poorly understood.

OBJECTIVE

We determined the frequency of comorbid pathologic processes in autopsy-confirmed MSA and assessed their clinical correlates.

METHODS

This study included 160 neuropathologically established MSA from the Mayo Clinic brain bank. Clinical information, including age at onset or death, clinical subtype, initial symptoms, antemortem clinical diagnosis, and cognitive dysfunction was collected. We assessed comorbid pathologies including Alzheimer's disease neuropathologic change, Lewy-related pathology, argyrophilic grain disease, age-related τ astrogliopathy, transactive DNA-binding protein 43 pathology, cerebral amyloid angiopathy, and cerebrovascular small vessel disease and examined their clinical impact.

RESULTS

The majority of MSA patients (62%) had no significant comorbid pathologies. There was a positive correlation between age at onset or death with the number of comorbid pathologies; however, even in the highest quartile group (average age at death 78 ± 6 years), the average number of comorbid pathologies was <2. Logistic regression analysis revealed that none of the assessed variables, including sex, age at onset, and the presence or absence of each comorbid pathology, were significantly associated with cognitive dysfunction.

CONCLUSIONS

The majority of MSA patients do not have comorbid pathologies, even in advanced age, indicating that MSA is unique among neurodegenerative disorders in this regard. There was minimal clinical impact of comorbid pathologies in MSA. These findings warrant focusing on α-synuclein for the treatment strategy for MSA. © 2023 International Parkinson and Movement Disorder Society.

Phospholipids and Cholesterol Determine Molecular Mechanisms of Cytotoxicity of α-Synuclein Oligomers and Fibrils

Progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta, hypothalamus, and thalamus is a hallmark of Parkinson's disease. Neuronal death is linked to the abrupt aggregation of α-synuclein (α-Syn), a small membrane protein that regulates cell vesicle trafficking. α-Syn aggregation rate, as well as the secondary structure and toxicity of α-Syn fibrils, could be uniquely altered by lipids. However, molecular mechanisms that determine such a remarkable difference in the toxicity of α-Syn fibrils formed in the presence of lipids remain unclear. In this study, we used a set of molecular assays to determine the molecular mechanism by which α-Syn fibrils formed in the presence of phosphatidylcholine (PC), cardiolipin (CL), and cholesterol (Cho) exert cell toxicity. We found that rat dopaminergic cells exposed to α-Syn fibrils formed in the presence of different lipids exert drastically different magnitudes and dynamics of unfolded protein response (UPR) in the endoplasmic reticulum (ER) and mitochondria (MT). Specifically, α-Syn:CL were found to cause the strongest, whereas α-Syn fibrils formed in the absence of lipids had the lowest magnitude of the UPR cell response. We also found the opposite dynamics of the ER- and MT-UPR responses in rat dopaminergic cells exposed to protein aggregates. These results could suggest that facing severe ER stress, dopaminergic cells suppress MT-UPR response, enabling the maximal ATP production to restore their normal physiological function. These findings help to better understand complex mechanisms of cell toxicity of amyloid aggregates and ultimately find neuroprotective drug candidates that will be able to suppress the spread of Parkinson's disease.

From Synaptic Physiology to Synaptic Pathology: The Enigma of α-Synuclein

Alpha-synuclein (α-syn) has gained significant attention due to its involvement in neurodegenerative diseases, particularly Parkinson's disease. However, its normal function in the human brain is equally fascinating. The α-syn protein is highly dynamic and can adapt to various conformational stages, which differ in their interaction with synaptic elements, their propensity to drive pathological aggregation, and their toxicity. This review will delve into the multifaceted role of α-syn in different types of synapses, shedding light on contributions to neurotransmission and overall brain function. We describe the physiological role of α-syn at central synapses, including the bidirectional interaction between α-syn and neurotransmitter systems.

The potential of Rhein's aromatic amines for Parkinson's disease prevention and treatment: α-Synuclein aggregation inhibition and disaggregation of preformed fibers

The aggregation of α-Syn is a pivotal mechanism in Parkinson's disease (PD). Effectively maintaining α-Syn proteostasis involves both inhibiting its aggregation and promoting disaggregation. In this study, we developed a series of aromatic amide derivatives based on Rhein. Two of these compounds, 4,5-dihydroxy-N-(3-hydroxyphenyl)-9,10-dioxo-9,10-dihydroanthracene-2-carboxamide (a5) and 4,5-dihydroxy-N-(2-hydroxy-4-chlorophenyl)-9,10-dioxo-9,10-dihydroanthracene-2-carboxamide (a8), exhibited good binding affinities to α-Syn residues, demonstrating promising inhibitory activity against α-Syn aggregation in vitro, with low IC50 values (1.35 and 1.08 μM, respectivly). These inhibitors acted throughout the entire aggregation process by stabilizing α-Syn's conformation and preventing the formation of β-sheet aggregates. They also effectively disassembled preformed α-Syn oligomers and fibrils. Preliminary mechanistic insights indicated that they bound to the specific domain within fibrils, inducing fibril instability, collapse, and the formation of smaller aggregates and monomeric α-Syn units. This research underscores the therapeutic potential of Rhein's aromatic amides in targeting α-Syn aggregation for PD treatment and suggests broader applications in managing and preventing neurodegenerative diseases.

Distribution of proteinase K-resistant anti-α-synuclein immunoreactive axons in the cardiac plexus is unbiased to the left ventricular anterior wall

Lewy body disease (LBD) is characterized by the appearance of Lewy neurites and Lewy bodies, which are predominantly composed of α-synuclein. Notably, the cardiac plexus (CP) is one of the main targets of LBD research. Although previous studies have reported obvious differences in the frequency of Lewy body pathology (LBP) in the CP, none of them have confirmed whether LBP preferably appears in any part of the CP. Thus, we aimed to clarify the emergence and/or propagation of LBP in the CP. In this study, 263 consecutive autopsy cases of patients aged ≥50 years were included, with one region per case selected from three myocardial perfusion areas (MPAs) and subjected to proteinase K and then immunohistochemically stained with anti-α-synuclein antibodies to assess LBP. We stained all three MPAs in 17 cases with low-density LBP and observed the actual distribution of LBP. LBP were identified in the CP in 20.2% (53/263) of patients. Moreover, we found that LBP may appear in only one region of MPAs, mainly in the young-old group (35.3% (6/17) of patients). These findings suggest that it is possible to underestimate LBP in the CP, especially in the young-old group, by restricting the search to only one of the three MPAs.

Alpha-Synuclein Oligomers Driven T1-T2 Switchable Nanoprobes for Early and Accurate Diagnosis of Parkinson's Disease

The alpha-synuclein (α-syn) oligomers hold a central role in the pathology of Parkinson's disease (PD). Achieving accurate detection of α-syn oligomers in vivo presents a promising avenue for early and accurate diagnosis of PD. Magnetic resonance imaging (MRI), with non-invasion and exceptional tissue penetration, offers a potent tool for visualizing α-syn oligomers in vivo. Nonetheless, ensuring diagnostic specificity remains a formidable challenge. Herein, a novel MRI probe (ASOSN) is introduced, which encompasses highly sensitive antiferromagnetic nanoparticles functionalized with single-chain fragment variable antibodies, endowing it with the capacity for discerning recognition and binding to α-syn oligomers and triggering a switchable T1-T2 MRI signal. Significantly, ASOSN possesses the unique capability to accurately discriminate α-syn oligomers from neuroinflammation in vivo. Moreover, ASOSN facilitates the non-invasive and precise visualizing of endogenous α-syn oligomers in living systems. This innovative design heralds the development of a non-invasive visualization strategy for α-syn oligomers, marking a pivotal advancement for early and accurate diagnosis of PD.

Alpha-Synuclein Contribution to Neuronal and Glial Damage in Parkinson's Disease

Parkinson's disease (PD) is a complex neurodegenerative disease characterized by the progressive loss of dopaminergic neurons in the substantia nigra and the widespread accumulation of alpha-synuclein (αSyn) protein aggregates. αSyn aggregation disrupts critical cellular processes, including synaptic function, mitochondrial integrity, and proteostasis, which culminate in neuronal cell death. Importantly, αSyn pathology extends beyond neurons-it also encompasses spreading throughout the neuronal environment and internalization by microglia and astrocytes. Once internalized, glia can act as neuroprotective scavengers, which limit the spread of αSyn. However, they can also become reactive, thereby contributing to neuroinflammation and the progression of PD. Recent advances in αSyn research have enabled the molecular diagnosis of PD and accelerated the development of targeted therapies. Nevertheless, despite more than two decades of research, the cellular function, aggregation mechanisms, and induction of cellular damage by αSyn remain incompletely understood. Unraveling the interplay between αSyn, neurons, and glia may provide insights into disease initiation and progression, which may bring us closer to exploring new effective therapeutic strategies. Herein, we provide an overview of recent studies emphasizing the multifaceted nature of αSyn and its impact on both neuron and glial cell damage.

Single-Molecule Detection of α-Synuclein Oligomers in Parkinson's Disease Patients Using Nanopores

α-Synuclein (α-Syn) is an intrinsically disordered protein whose aggregation in the brain has been significantly implicated in Parkinson's disease (PD). Beyond the brain, oligomers of α-Synuclein are also found in cerebrospinal fluid (CSF) and blood, where the analysis of these aggregates may provide diagnostic routes and enable a better understanding of disease mechanisms. However, detecting α-Syn in CSF and blood is challenging due to its heterogeneous protein size and shape, and low abundance in clinical samples. Nanopore technology offers a promising route for the detection of single proteins in solution; however, the method often lacks the necessary selectivity in complex biofluids, where multiple background biomolecules are present. We address these limitations by developing a strategy that combines nanopore-based sensing with molecular carriers that can specifically capture α-Syn oligomers with sizes of less than 20 nm. We demonstrate that α-Synuclein oligomers can be detected directly in clinical samples, with minimal sample processing, by their ion current characteristics and successfully utilize this technology to differentiate cohorts of PD patients from healthy controls. The measurements indicate that detecting α-Syn oligomers present in CSF may potentially provide valuable insights into the progression and monitoring of Parkinson's disease.

Two-color coincidence single-molecule pulldown for the specific detection of disease-associated protein aggregates

Protein misfolding and aggregation is a characteristic of many neurodegenerative disorders, including Alzheimer's and Parkinson's disease. The oligomers generated during aggregation are likely involved in disease pathogenesis and present promising biomarker candidates. However, owing to their small size and low concentration, specific tools to quantify and characterize aggregates in complex biological samples are still lacking. Here, we present single-molecule two-color aggregate pulldown (STAPull), which overcomes this challenge by probing immobilized proteins using orthogonally labeled detection antibodies. By analyzing colocalized signals, we can eliminate monomeric protein and specifically quantify aggregated proteins. Using the aggregation-prone alpha-synuclein protein as a model, we demonstrate that this approach can specifically detect aggregates with a limit of detection of 5 picomolar. Furthermore, we show that STAPull can be used in a range of samples, including human biofluids. STAPull is applicable to protein aggregates from a variety of disorders and will aid in the identification of biomarkers that are crucial in the effort to diagnose these diseases.

Conformational dynamics of α-synuclein and study of its intramolecular forces in the presence of selected compounds

Protein misfolding and aggregation play crucial roles in amyloidogenic diseases through the self-assembly of intrinsically disordered proteins (IDPs) in type II diabetes (T2D), Alzheimer's disease (AD) and Parkinson's disease (PD). PD is the most common neurodegenerative disorder after AD, and is associated with the loss of dopaminergic signaling, which causes motor and nonmotor signs and symptoms. Lewy bodies and Lewy neurites are common pathological hallmarks of PD that are mainly composed of aggregates of disordered α-synuclein (α-Syn). There have been many efforts to develop chemical compounds to prevent aggregation or facilitate disruption of the aggregates. Furthermore, the roles and interactions of many compounds have yet to be revealed at the atomistic level, especially their impacts on the dynamics and chain-chain interactions of the oligomers, which are of interest in this study. The conformational diversity and detailed interactions among homo-oligomer chains of α-Syn are not fully discovered; identifying these might help uncover a practical approach to developing a potent therapy. In this study, we used an in-silico investigation to address the conformational diversity of α-Syn oligomer. The roles of several point mutations in protein aggregation in PD are known; we take this further by evaluating the interaction energies and contributions of all residues in stability and residue-chain interactions. In this study, we docked chemical derivatives of three compounds with high drug-likeness properties to evaluate the roles of our ligands in the conformational dynamicity of the oligomers, with emphasis on intramolecular forces. Free energy evaluation of the modeled inter and intramolecular interactions through MD simulation shows effective interaction and binding between α-Syn and our compounds. However, we find that they do not significantly disrupt the chain-chain interactions, compared to unliganded simulation.

α-Synuclein oligomers and fibrils: partners in crime in synucleinopathies

The misfolding and aggregation of α-synuclein is the general hallmark of a group of devastating neurodegenerative pathologies referred to as synucleinopathies, such as Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. In such conditions, a range of different misfolded aggregates, including oligomers, protofibrils, and fibrils, are present both in neurons and glial cells. Growing experimental evidence supports the proposition that soluble oligomeric assemblies, formed during the early phases of the aggregation process, are the major culprits of neuronal toxicity; at the same time, fibrillar conformers appear to be the most efficient at propagating among interconnected neurons, thus contributing to the spreading of α-synuclein pathology. Moreover, α-synuclein fibrils have been recently reported to release soluble and highly toxic oligomeric species, responsible for an immediate dysfunction in the recipient neurons. In this review, we discuss the current knowledge about the plethora of mechanisms of cellular dysfunction caused by α-synuclein oligomers and fibrils, both contributing to neurodegeneration in synucleinopathies.

The Effects of Lipids on α-Synuclein Aggregation In Vitro

The small neuronal protein α-synuclein (αS) is found in pre-synaptic terminals and plays a role in vesicle recycling and neurotransmission. Fibrillar aggregates of αS are the hallmark of Parkinson's disease and related neurodegenerative disorders. In both health and disease, interactions with lipids influence αS's structure and function, prompting much study of the effects of lipids on αS aggregation. A comprehensive collection (126 examples) of aggregation rate data for various αS/lipid combinations was presented, including combinations of lipid variations and mutations or post-translational modifications of αS. These data were interpreted in terms of lipid structure to identify general trends. These tabulated data serve as a resource for the community to help in the interpretation of aggregation experiments with lipids and to be potentially used as inputs for computational models of lipid effects on aggregation.

Extracellular high molecular weight α-synuclein oligomers induce cell death by disrupting the plasma membrane

α-Synuclein (αS), the causative protein of Parkinson's disease and other α-synucleinopathies, aggregates from a low molecular weight form (LMW-αS) to a high molecular weight αS oligomer (HMW-αSo). Aggregated αS accumulates intracellularly, induces intrinsic apoptosis, is released extracellularly, and appears to propagate disease through prion-like spreading. Whether extracellular αS aggregates are cytotoxic, damage cell wall, or induce cell death is unclear. We investigated cytotoxicity and cell death caused by HMW-αSo or LMW-αS. Extracellular HMW-αSo was more cytotoxic than LMW-αS and was a crucial factor for inducing plasma membrane damage and cell death. HMW-αSo induced reactive oxygen species production and phospholipid peroxidation in the membrane, thereby impairing calcium homeostasis and disrupting plasma membrane integrity. HMW-αSo also induced extrinsic apoptosis and cell death by activating acidic sphingomyelinase. Thus, as extracellular HMW-αSo causes neuronal injury and death via cellular transmission and direct plasma membrane damage, we propose an additional disease progression pathway for α-synucleinopathies.

Computational investigation on the effect of the peptidomimetic inhibitors (NPT100-18A and NPT200-11) on the α-synuclein and lipid membrane interactions

Parkinson's disease (PD) is associated with α-synuclein (α-Syn), a presynaptic protein that binds to cell membranes. The molecular pathophysiology of PD most likely begins with the binding of α-Syn to membranes. Recently, two peptidomimetic inhibitors (NPT100-18A and NPT200-11) were identified to potentially interact with α-Syn and affect the interaction of α-Syn with the membrane. In this study, the effect of the two peptidomimetic inhibitors on the α-Syn-membrane interaction was demonstrated. DFT calculations were performed for optimization of the two inhibitors, and the nucleophilicity (N) and electrophilicity (ω) of NPT100-18A and NPT200-11 were calculated to be 3.90 and 3.86 (N); 1.06 and 1.04 (ω), respectively. Using the docking tool (CB-dock2), the two α-Syn-peptidomimetic inhibitor complexes (α-Syn-NPT100-18A and α-Syn-NPT200-11) have been prepared. Then all-atom molecular dynamics (MD) simulation was carried out on the α-Syn (control), α-Syn-NPT100-18A and α-Syn-NPT200-11 complex systems in presence of DOPE: DOPS: DOPC (5:3:2) lipid bilayer. From the conformational dynamics analysis, the 3-D structure of α-Syn was found to be stable, and the helices present in the regions (1-37) and (45-95) of α-Syn were found to be retained in the presence of the two peptidomimetic inhibitors. The electron density profile analysis revealed the binding modes of NAC and C-terminal region of α-Syn (in the presence of NPT200-11 inhibitor) with lipid membrane are in the close vicinity from the lipid bilayer centre. Our findings in this study on α-Syn-membrane interactions may be useful for developing a new therapeutic approach for treating PD and other neurodegenerative disorders.Communicated by Ramaswamy H. Sarma.