Structure, function and toxicity of alpha-synuclein: the Bermuda triangle in synucleinopathies

Synthesis and Semi-Synthesis of Alpha-Synuclein: Insight into the Chemical Complexity of Synucleinopathies

The chemical rules governing protein folding have intrigued generations of researchers for decades. With the advent of artificial intelligence (AI), prediction of protein structure has improved tremendously. However, there is still a level of analysis that is only possible through wet laboratory experiments, especially in respect to the investigation of the pathological effect of mutations and posttranslational modifications (PTMs) on proteins of interest. This requires the availability of pure peptides and proteins in sufficient quantities for biophysical, biochemical, and functional studies. In this context, chemical protein synthesis and semi-synthesis are powerful tools in protein research, which help to enlighten the role of protein modification in the physiology and pathology of proteins. A protein of high interest in the field of biomedicine is alpha-synuclein (aSyn), a protein deeply associated with several devastating neurodegenerative disorders such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), or multiple systems atrophy (MSA). Here, we describe several methods and pathways to synthesize native or modified aSyn, and discuss how these approaches enable us to address pathological mechanisms that may open novel perspectives for therapeutic intervention.

Posttranslational Modifications of -Synuclein, Their Therapeutic Potential, and Crosstalk in Health and Neurodegenerative Diseases

α-Synuclein (α-Syn) aggregation in Lewy bodies and Lewy neurites has emerged as a key pathogenetic feature in Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Various factors, including posttranslational modifications (PTMs), can influence the propensity of α-Syn to misfold and aggregate. PTMs are biochemical modifications of a protein that occur during or after translation and are typically mediated by enzymes. PTMs modulate several characteristics of proteins including their structure, activity, localization, and stability. α-Syn undergoes various posttranslational modifications, including phosphorylation, ubiquitination, SUMOylation, acetylation, glycation, O-GlcNAcylation, nitration, oxidation, polyamination, arginylation, and truncation. Different PTMs of a protein can physically interact with one another or work together to influence a particular physiological or pathological feature in a process known as PTMs crosstalk. The development of detection techniques for the cooccurrence of PTMs in recent years has uncovered previously unappreciated mechanisms of their crosstalk. This has led to the emergence of evidence supporting an association between α-Syn PTMs crosstalk and synucleinopathies. In this review, we provide a comprehensive evaluation of α-Syn PTMs, their impact on misfolding and pathogenicity, the pharmacological means of targeting them, and their potential as biomarkers of disease. We also highlight the importance of the crosstalk between these PTMs in α-Syn function and aggregation. Insight into these PTMS and the complexities of their crosstalk can improve our understanding of the pathogenesis of synucleinopathies and identify novel targets of therapeutic potential. SIGNIFICANCE STATEMENT: α-Synuclein is a key pathogenic protein in Parkinson's disease and other synucleinopathies, making it a leading therapeutic target for disease modification. Multiple posttranslational modifications occur at various sites in α-Synuclein and alter its biophysical and pathological properties, some interacting with one another to add to the complexity of the pathogenicity of this protein. This review details these modifications, their implications in disease, and potential therapeutic opportunities.

Research Priorities on the Role of α-Synuclein in Parkinson's Disease Pathogenesis

Various forms of Parkinson's disease, including its common sporadic form, are characterized by prominent α-synuclein (αSyn) aggregation in affected brain regions. However, the role of αSyn in the pathogenesis and evolution of the disease remains unclear, despite vast research efforts of more than a quarter century. A better understanding of the role of αSyn, either primary or secondary, is critical for developing disease-modifying therapies. Previous attempts to hone this research have been challenged by experimental limitations, but recent technological advances may facilitate progress. The Scientific Issues Committee of the International Parkinson and Movement Disorder Society (MDS) charged a panel of experts in the field to discuss current scientific priorities and identify research strategies with potential for a breakthrough. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The degradation of α--synuclein is limited by dynein to drive the AALP pathway through HDAC6 upon paraquat exposure

Lewy body disease (LBD), one of the most common neurodegenerative diseases (NDDs), is characterized by excessive accumulation of α-synuclein (α-syn) in neurons. In recent years, environmental factors such as exposure to herbicides and pesticides have been attributed to the development of this condition. While majority of the studies on neurotoxic effects of paraquat (PQ) have focused on α-syn-mediated neuronal damage in the early stages of α-syn accumulation in neurons, efforts to explore the key target for α-syn degradation are limited. Recent research has suggested that histone deacetylase 6 (HDAC6) might possibly regulate amyloid clearance, and that the metabolism of compounds in neurons is also directly affected by axonal transport in neurons. Dynein predominantly mediates reverse transportation of metabolites and uptake of signal molecules and other compounds at the end of axons, which is conducive to the reuse of cell components. However, the role of interaction of dynein with HDAC6 in metabolites transport is still unclear. Therefore, this study aimed to investigate the role of HDAC6 in α-syn accumulation/clearance in neurons and the associated possible influencing factors. The results revealed that HDAC6 could transport ubiquitinated α-syn, bind to dynein, form an aggresome, and relocate to the center of the microtubule tissue, ultimately reducing abnormal accumulation of α-syn. However, PQ treatment resulted in HDAC6 upregulation, causing abnormal aggregation of α-syn. Taken together, these findings indicated that PQ exposure caused abnormal accumulation of α-syn and decreased effective degradation of α-syn by HDAC6-mediated aggresome-autophagy-lysosome pathway.

Multivalency drives interactions of alpha-synuclein fibrils with tau

Age-related neurodegenerative disorders like Alzheimer's disease (AD) and Parkinson's disease (PD) are characterized by deposits of protein aggregates, or amyloid, in various regions of the brain. Historically, aggregation of a single protein was observed to be correlated with these different pathologies: tau in AD and α-synuclein (αS) in PD. However, there is increasing evidence that the pathologies of these two diseases overlap, and the individual proteins may even promote each other's aggregation. Both tau and αS are intrinsically disordered proteins (IDPs), lacking stable secondary and tertiary structure under physiological conditions. In this study we used a combination of biochemical and biophysical techniques to interrogate the interaction of tau with both soluble and fibrillar αS. Fluorescence correlation spectroscopy (FCS) was used to assess the interactions of specific domains of fluorescently labeled tau with full length and C-terminally truncated αS in both monomer and fibrillar forms. We found that full-length tau as well as individual tau domains interact with monomer αS weakly, but this interaction is much more pronounced with αS aggregates. αS aggregates also mildly slow the rate of tau aggregation, although not the final degree of aggregation. Our findings suggest that co-occurrence of tau and αS in disease are more likely to occur through monomer-fiber binding interactions, rather than monomer-monomer or co-aggregation.

Network proteomics of the Lewy body dementia brain reveals presynaptic signatures distinct from Alzheimer's disease

Lewy body dementia (LBD), a class of disorders comprising Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB), features substantial clinical and pathological overlap with Alzheimer's disease (AD). The identification of biomarkers unique to LBD pathophysiology could meaningfully advance its diagnosis, monitoring, and treatment. Using quantitative mass spectrometry (MS), we measured over 9,000 proteins across 138 dorsolateral prefrontal cortex (DLPFC) tissues from a University of Pennsylvania autopsy collection comprising control, Parkinson's disease (PD), PDD, and DLB diagnoses. We then analyzed co-expression network protein alterations in those with LBD, validated these disease signatures in two independent LBD datasets, and compared these findings to those observed in network analyses of AD cases. The LBD network revealed numerous groups or "modules" of co-expressed proteins significantly altered in PDD and DLB, representing synaptic, metabolic, and inflammatory pathophysiology. A comparison of validated LBD signatures to those of AD identified distinct differences between the two diseases. Notably, synuclein-associated presynaptic modules were elevated in LBD but decreased in AD relative to controls. We also found that glial-associated matrisome signatures consistently elevated in AD were more variably altered in LBD, ultimately stratifying those LBD cases with low versus high burdens of concurrent beta-amyloid deposition. In conclusion, unbiased network proteomic analysis revealed diverse pathophysiological changes in the LBD frontal cortex distinct from alterations in AD. These results highlight the LBD brain network proteome as a promising source of biomarkers that could enhance clinical recognition and management.

Alpha-synuclein affects certain iron transporters of BV2 microglia cell through its ferric reductase activity

Alpha-synuclein (α-syn) is a major component of Lewy bodies, which is a biomarker of Parkinson's disease (PD). It accumulates in substantia nigra pars compacta (SNpc) to form insoluble aggregates and cause neurotoxicity, which is often accompanied by iron deposition. We compared the iron reductase activity between monomeric α-syn (M-α-syn) and oligomeric α-syn (O-α-syn) and investigated the effect of α-syn on iron metabolism of BV2 microglia cells as well. α-syn had ferric reductase activity, and O-α-syn had stronger enzyme activity than M-α-syn. M-α-syn upregulated iron uptake protein, divalent metal transporter1 (DMT1) expression, and iron influx but did not regulate iron release protein ferroportin1 (FPN1) expression and iron efflux. O-α-syn elevated the expression of both DMT1 and FPN1 and thus increased the iron influx and efflux in BV2 microglial cells, but the expressions of iron regulatory protein1 (IRP1) and hypoxia-inducible factor 2α (HIF-2α) had no significant change. Moreover, both M-α-syn and O-α-syn could increase the mRNA expressions of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in BV2 microglia cells. Both types of α-syn can activate microglia, which leads to increased expressions of proinflammatory factors. α-syn can affect DMT1 and FPN1 expressions in BV2 microglia cells, which might be through its ferric reductase activity.NEW & NOTEWORTHY The effects of monomeric α-syn (M-α-syn) and oligomeric α-syn (O-α-syn) on the iron metabolism of BV2 microglia cells were detected by exogenous α-syn treatment. This study provides a strong experimental basis for α-syn involvement in iron metabolism in microglia.

Statistical Experimental Designs for cLTB-Syn Vaccine Production Using Daucus carota Cell Suspension Cultures

The carrot-made LTB-Syn antigen (cLTB-Syn) is a vaccine candidate against synucleinopathies based on carrot cells expressing the target antigen LTB and syn epitopes. Therefore, the development of an efficient production process is required with media culture optimization to increase the production yields as the main goal. In this study, the effect of two nitrogen sources (urea and glutamate) on callus cultures producing cLTB-Syn was studied, observing that the addition of 17 mM urea to MS medium favored the biomass yield. To optimize the MS media composition, the influence of seven medium components on biomass and cLTB-Syn production was first evaluated by a Plackett-Burman design (PBD). Then, three factors were further analyzed using a central composite design (CCD) and response surface methodology (RSM). The results showed a 1.2-fold improvement in biomass, and a 4.5-fold improvement in cLTB-Syn production was achieved at the shake-flask scale. At the bioreactor scale, there was a 1.5-fold increase in biomass and a 2.8-fold increase in cLTB-Syn yield compared with the standard MS medium. Moreover, the cLTB-Syn vaccine induced humoral responses in BALB/c mice subjected to either oral or subcutaneous immunization. Therefore, cLTB-Syn is a promising vaccine candidate that will aid in developing immunotherapeutic strategies to combat PD and other neurodegenerative diseases without the need for cold storage, making it a financially viable option for massive immunization.

Can exercise benefits be harnessed with drugs? A new way to combat neurodegenerative diseases by boosting neurogenesis

Adult hippocampal neurogenesis (AHN) is affected by multiple factors, such as enriched environment, exercise, ageing, and neurodegenerative disorders. Neurodegenerative disorders can impair AHN, leading to progressive neuronal loss and cognitive decline. Compelling evidence suggests that individuals engaged in regular exercise exhibit higher production of proteins that are essential for AHN and memory. Interestingly, specific molecules that mediate the effects of exercise have shown effectiveness in promoting AHN and cognition in different transgenic animal models. Despite these advancements, the precise mechanisms by which exercise mimetics induce AHN remain partially understood. Recently, some novel exercise molecules have been tested and the underlying mechanisms have been proposed, involving intercommunications between multiple organs such as muscle-brain crosstalk, liver-brain crosstalk, and gut-brain crosstalk. In this review, we will discuss the current evidence regarding the effects and potential mechanisms of exercise mimetics on AHN and cognition in various neurological disorders. Opportunities, challenges, and future directions in this research field are also discussed.

Novel 4-triazole phenyl amide (4-TPA) molecules: Potent promoters of α-synuclein fibril disassembly

Parkinson's disease profoundly compromises patients' daily lives, and the disassembly of α-synuclein aggregates, a primary pathological factor, represents a promising therapeutic approach. In this study, we conducted a systematic screening and optimization process to identify the novel scaffold B37, a 4-triazolyl-phenylamine derivative, exhibiting a potent disassembly activity of 1.1 μM against α-synuclein preformed fibrils. Notably, B37 demonstrated significant neuroprotective effects, ameliorated autophagic dysfunction induced by preformed fibrils, mitigated oxidative stress, and restored the co-localization of preformed fibrils with lysosomes. Transmission electron microscopy corroborated its in vitro disassembly function. Pharmacokinetic profiling revealed favorable parameters with a receptible blood-brain barrier permeability. B37 emerges as a promising lead compound for further optimization, aiming to develop a highly effective agent targeting the disassembly of α-synuclein aggregates to treat neurodegenerative diseases like Parkinson's disease.

Reconsidering red blood cells as the diagnostic potential for neurodegenerative disorders

BACKGROUND

Red blood cells (RBCs) are usually considered simple cells and transporters of gases to tissues.

HYPOTHESIS

However, recent research has suggested that RBCs may have diagnostic potential in major neurodegenerative disorders (NDDs).

RESULTS

This review summarizes the current knowledge on changes in RBC in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and other NDDs. It discusses the deposition of neuronal proteins like amyloid-β, tau, and α-synuclein, polyamines, changes in the proteins of RBCs like band-3, membrane transporter proteins, heat shock proteins, oxidative stress biomarkers, and altered metabolic pathways in RBCs during neurodegeneration. It also highlights the comparison of RBC diagnostic markers to other in-market diagnoses and discusses the challenges in utilizing RBCs as diagnostic tools, such as the need for standardized protocols and further validation studies.

SIGNIFICANCE STATEMENT

The evidence suggests that RBCs have diagnostic potential in neurodegenerative disorders, and this study can pave the foundation for further research which may lead to the development of novel diagnostic approaches and treatments.

The misfolding mystery: α-synuclein and the pathogenesis of Parkinson's disease

Neurodegenerative diseases such as Parkinson's disease (PD) are characterized by the death of neurons in specific areas of the brain. One of the proteins that is involved in the pathogenesis of PD is α-synuclein (α-syn). α-Syn is a normal protein that is found in all neurons, but in PD, it misfolds and aggregates into toxic fibrils. These fibrils can then coalesce into pathological inclusions, such as Lewy bodies and Lewy neurites. The pathogenic pathway of PD is thought to involve a number of steps, including misfolding and aggregation of α-syn, mitochondrial dysfunction, protein clearance impairment, neuroinflammation and oxidative stress. A deeper insight into the structure of α-syn and its fibrils could aid in understanding the disease's etiology. The prion-like nature of α-syn is also an important area of research. Prions are misfolded proteins that can spread from cell to cell, causing other proteins to misfold as well. It is possible that α-syn may behave in a similar way, spreading from cell to cell and causing a cascade of misfolding and aggregation. Various post-translational alterations have also been observed to play a role in the pathogenesis of PD. These alterations can involve a variety of nuclear and extranuclear activities, and they can lead to the misfolding and aggregation of α-syn. A better understanding of the pathogenic pathway of PD could lead to the development of new therapies for the treatment of this disease.

Aggregation and phase separation of α-synuclein in Parkinson's disease

The deposition of α-synuclein (α-Syn) in Lewy bodies serves as a prominent pathological hallmark of Parkinson's disease (PD). Recent research has revealed that α-Syn can undergo liquid-liquid phase separation (LLPS) during its fibrillization. Over time, the maturation of the resulting condensates leads to a liquid-to-solid phase transition (LSPT) ultimately resulting in the amyloid deposition in cells which is linked to the pathogenesis and development of PD. Herein, we summarize the understanding of α-Syn aggregation which can be described by nucleation and elongation steps to obtain insights into the correlation of protein aggregation, structural polymorphism, and PD progression. Additionally, we discuss the LLPS phenomena of α-Syn and heterotypic cross-amyloid interactions with a focus on aberrant LSPT in the aggregation process. Exploring the underlying mechanisms and interplay between α-Syn aberrant aggregation, pathological phase transitions, and PD pathogenesis will shed light on potential therapeutic interventions.

Amyloid, Crohn's disease, and Alzheimer's disease - are they linked?

Crohn's disease (CD) is a chronic inflammatory disease that most frequently affects part of the distal ileum, but it may affect any part of the gastrointestinal tract. CD may also be related to systemic inflammation and extraintestinal manifestations. Alzheimer's disease (AD) is the most common neurodegenerative disease, gradually worsening behavioral and cognitive functions. Despite the meaningful progress, both diseases are still incurable and have a not fully explained, heterogeneous pathomechanism that includes immunological, microbiological, genetic, and environmental factors. Recently, emerging evidence indicates that chronic inflammatory condition corresponds to an increased risk of neurodegenerative diseases, and intestinal inflammation, including CD, increases the risk of AD. Even though it is now known that CD increases the risk of AD, the exact pathways connecting these two seemingly unrelated diseases remain still unclear. One of the key postulates is the gut-brain axis. There is increasing evidence that the gut microbiota with its proteins, DNA, and metabolites influence several processes related to the etiology of AD, including β-amyloid abnormality, Tau phosphorylation, and neuroinflammation. Considering the role of microbiota in both CD and AD pathology, in this review, we want to shed light on bacterial amyloids and their potential to influence cerebral amyloid aggregation and neuroinflammation and provide an overview of the current literature on amyloids as a potential linker between AD and CD.

Genetic variation and pesticide exposure influence blood DNA methylation signatures in females with early-stage Parkinson's disease

Although sex, genetics, and exposures can individually influence risk for sporadic Parkinson's disease (PD), the joint contributions of these factors to the epigenetic etiology of PD have not been comprehensively assessed. Here, we profiled sex-stratified genome-wide blood DNAm patterns, SNP genotype, and pesticide exposure in agricultural workers (71 early-stage PD cases, 147 controls) and explored replication in three independent samples of varying demographics (n = 218, 222, and 872). Using a region-based approach, we found more associations of blood DNAm with PD in females (69 regions) than in males (2 regions, Δβadj| ≥0.03, padj ≤ 0.05). For 48 regions in females, models including genotype or genotype and pesticide exposure substantially improved in explaining interindividual variation in DNAm (padj ≤ 0.05), and accounting for these variables decreased the estimated effect of PD on DNAm. The results suggested that genotype, and to a lesser degree, genotype-exposure interactions contributed to variation in PD-associated DNAm. Our findings should be further explored in larger study populations and in experimental systems, preferably with precise measures of exposure.

4-Oxo-2-Nonenal- and Agitation-Induced Aggregates of α-Synuclein and Phosphorylated α-Synuclein with Distinct Biophysical Properties and Biomedical Applications

α-Synuclein (α-syn) can form oligomers, protofibrils, and fibrils, which are associated with the pathogenesis of Parkinson's disease and other synucleinopathies. Both the lipid peroxidation product 4-oxo-2-nonenal (ONE) and agitation can induce aggregation of α-syn and phosphorylated α-syn. Thus, clarification of the characteristics of different α-syn species could help to select suitable aggregates for diagnosis and elucidate the pathogenesis of diseases. Here, we characterized ONE-induced wild-type (WT) α-syn aggregates (OW), ONE-induced phosphorylated α-syn (p-α-syn) aggregates (OP), agitation-induced α-syn preformed fibrils (PFF), and agitation-induced p-α-syn preformed fibrils (pPFF). Thioflavin T (ThT) dying demonstrated that OW and OP had fewer fibrils than the PFF and pPFF. Transmission electron microscopy revealed that the lengths of PFF and pPFF were similar, but the diameters differed. OW and OP had more compact structures than PFF and pPFF. Aggregation of p-α-syn was significantly faster than WT α-syn. Furthermore, OW and OP were more sodium dodecyl sulfate-stable and proteinase K-resistant, suggesting greater stability and compactness, while aggregates of PFF and pPFF were more sensitive to proteinase K treatment. Both ONE- and agitation-induced aggregates were cytotoxic when added exogenously to SH-SY5Y cells with increasing incubation times, but the agitation-induced aggregates caused cell toxicity in a shorter time and more p-α-syn inclusions. Similarly, p-proteins were more cytotoxic than non-p-proteins. Finally, all four aggregates were used as standard antigens to establish sandwich enzyme-linked immunosorbent assay (ELISA). The results showed that the recognition efficiency of OW and OP was more sensitive than that of PFF and pPFF. The OW- and OP-specific ELISA for detection of p-α-syn and α-syn in plasma samples of Thy1-α-syn transgenic mice showed that the content of aggregates could reflect the extent of disease. ONE and agitation induced the formation of α-syn aggregates with distinct biophysical properties and biomedical applications.

Immunotherapy with an antibody against CD1d modulates neuroinflammation in an α-synuclein transgenic model of Lewy body like disease

The neuroinflammatory process in synucleinopathies of the aging population such as Parkinson's disease (PD) and dementia with Lewy bodies (DLB) involves microglial activation as well as infiltration of the CNS by T cells and natural killer T cells (NKTs). To evaluate the potential of targeting NKT cells to modulate neuroinflammation, we treated α-syn transgenic (tg) mice (e.g.: Thy1 promoter line 61) with an antibody against CD1d, which is a glycoprotein expressed in antigen presenting cells (APCs). CD1d-presented lipid antigens activate NKT cells through the interaction with T cell receptor in NKTs, resulting in the production of cytokines. Thus, we hypothesized that blocking the APC-NKT interaction with an anti-CD1d antibody might reduce neuroinflammation and neurodegeneration in models of DLB/PD. Treatment with the anti-CD1d antibody did not have effects on CD3 (T cells), slightly decreased CD4 and increased CD8 lymphocytes in the mice. Moreover, double labeling studies showed that compared to control (IgG) treated α-syn tg mice, treatment with anti-CD1d decreased numbers of CD3/interferon γ (IFN γ)-positive cells, consistent with NKTs. Further double labeling studies showed that CD1d-positive cells co-localized with the astrocytes marker GFAP and that anti-CD1d antibody reduced this effect. While in control α-syn tg mice CD3 positive cells were near astrocytes, this was modified by the treatment with the CD1d antibody. By qPCR, levels of IFN γ, CCL4, and interleukin-6 were increased in the IgG treated α-syn tg mice. Treatment with CD1d antibody blunted this cytokine response that was associated with reduced astrocytosis and microgliosis in the CNS of the α-syn tg mice treated with CD1d antibody. Flow cytometric analysis of immune cells in α-syn tg mice revealed that CD1d-tet + T cells were also increased in the spleen of α-syn tg mice, which treatment with the CD1d antibody reduced. Reduced neuroinflammation in the anti-CD1d-treated α-syn tg mice was associated with amelioration of neurodegenerative pathology. These results suggest that reducing infiltration of NKT cells with an antibody against CD1d might be a potential therapeutical approach for DLB/PD.

Discovery of Effective Dual PROTAC Degraders for Neurodegenerative Disease-Associated Aggregates

The aggregation of specific proteins is a histopathological hallmark in various neurodegenerative diseases (NDs), among which Alpha-synuclein (α-Syn) and tau have received increased attention. The targeted protein degradation (TPD) strategy has been studied in the treatment of NDs, but multitarget bifunctional molecules have been ignored. Herein, a series of effective dual PROTAC degraders were developed, which could degrade α-Syn aggregates and total tau simultaneously. The degradation effects were evaluated in vitro, and the results showed that T3 could significantly knockdown α-Syn aggregates and total tau in the degradation efficiency with DC50 of 1.57 ± 0.55 and 4.09 ± 0.90 μM, respectively. Further mechanistic exploration showed that the degradation effect was mediated by the ubiquitin-proteasome system (UPS). Additionally, the therapeutic efficacy of T3 was confirmed in an MPTP-induced PD mouse model. Our results suggest that these dual PROTACs may provide a potential therapeutic strategy for NDs.

Neonatal stress disrupts the glymphatic system development and increases the susceptibility to Parkinson's disease in later life

INTRODUCTION

Neonatal stress disrupts brain development and increases the risk of neurological disorders later in life. However, the impact of neonatal stress on the development of the glymphatic system and susceptibility to Parkinson's disease (PD) remains largely unknown.

METHODS

Neonatal maternal deprivation (NMD) was performed on mice for 14 consecutive days to model chronic neonatal stress. Adeno-associated virus expressing A53T-α-synuclein (α-syn) was injected into the substantia nigra to establish PD model mice. Glymphatic activity was determined using in vivo magnetic resonance imaging, ex vivo fluorescence imaging and microplate assay. The transcription and expression of aquaporin-4 (AQP4) and other molecules were evaluated by qPCR, western blotting, and immunofluorescence. Animal's responses to NMD and α-syn overexpression were observed using behavioral tests.

RESULTS

Glymphatic activity was impaired in adult NMD mice. AQP4 polarization and platelet-derived growth factor B (PDGF-B) signaling were reduced in the frontal cortex and hippocampus of both young and adult NMD mice. Furthermore, exogenous α-syn accumulation was increased and PD-like symptoms were aggravated in adult NMD mice.

CONCLUSION

The results demonstrated that NMD could disrupt the development of the glymphatic system through PDGF-B signaling and increase the risk of PD later in life, indicating that alleviating neonatal stress could be beneficial in protecting the glymphatic system and reducing susceptibility to neurodegeneration.

Network Proteomics of the Lewy Body Dementia Brain Reveals Presynaptic Signatures Distinct from Alzheimer's Disease

Lewy body dementia (LBD), a class of disorders comprising Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB), features substantial clinical and pathological overlap with Alzheimer's disease (AD). The identification of biomarkers unique to LBD pathophysiology could meaningfully advance its diagnosis, monitoring, and treatment. Using quantitative mass spectrometry (MS), we measured over 9,000 proteins across 138 dorsolateral prefrontal cortex (DLPFC) tissues from a University of Pennsylvania autopsy collection comprising control, Parkinson's disease (PD), PDD, and DLB diagnoses. We then analyzed co-expression network protein alterations in those with LBD, validated these disease signatures in two independent LBD datasets, and compared these findings to those observed in network analyses of AD cases. The LBD network revealed numerous groups or "modules" of co-expressed proteins significantly altered in PDD and DLB, representing synaptic, metabolic, and inflammatory pathophysiology. A comparison of validated LBD signatures to those of AD identified distinct differences between the two diseases. Notably, synuclein-associated presynaptic modules were elevated in LBD but decreased in AD relative to controls. We also found that glial-associated matrisome signatures consistently elevated in AD were more variably altered in LBD, ultimately stratifying those LBD cases with low versus high burdens of concurrent beta-amyloid deposition. In conclusion, unbiased network proteomic analysis revealed diverse pathophysiological changes in the LBD frontal cortex distinct from alterations in AD. These results highlight the LBD brain network proteome as a promising source of biomarkers that could enhance clinical recognition and management.

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.

Assessment of the Anti-Amyloidogenic Properties of Essential Oils and Their Constituents in Cells Using a Whole-Cell Recombinant Biosensor

Essential oils exhibit numerous medicinal properties, including antimicrobial, anti-inflammatory and antioxidant effects. Recent studies also indicate that certain essential oils demonstrate anti-amyloidogenic activity against β-amyloid, the protein implicated in Alzheimer's disease. To investigate whether the anti-aggregating properties of essential oils extend to α-synuclein, the protein involved in Parkinson's disease, we constructed and employed a whole-cell biosensor based on the split-luciferase complementation assay. We validated our biosensor by using baicalein, a known inhibitor of α-synuclein aggregation, and subsequently we tested eight essential oils commonly used in food and the hygienic industry. Two of them, citron and sage, along with their primary components, pure linalool (the main constituent in citron essential oil) and pure eucalyptol (1,8-cineole, the main constituent in sage essential oil), were able to reduce α-syn aggregation. These findings suggest that both essential oils and their main constituents could be regarded as potential components in functional foods or incorporated into complementary Parkinson's disease therapies.

4-Arylidene curcumin derivatives in vitro inhibit α-Synuclein aggregation and disaggregate the preformed fibril

This study focuses on the misfolding and aggregation of α-Syn as a central mechanism linking various pathological processes in PD. Maintaining α-Syn proteostasis through suitable inhibitors emerges as an effective approach to prevent PD. A more efficient strategy for PD treatment involves disintegrating neurotoxic oligomers and fibrils into normal functional α-Syn using inhibitors. To this end, a series of 4-arylidene curcumin derivatives were synthesized with a sheet-like conjugated skeleton and higher binding energies with α-Syn residues. Among these derivatives, three candidate compounds exhibited promising α-Syn aggregation inhibitory activities in vitro, with IC50 values as low as 0.61 μM. The inhibitory action extended throughout the entire aggregation process, stabilizing α-Syn proteostasis conformation and preventing β-sheets aggregation. Furthermore, the candidate compounds demonstrated effective disintegration capabilities against preformed α-Syn oligomers and fibrils. Initial mechanistic investigations indicated that the inhibitors may bind to a specific domain within the fibril, inducing fibril instability and subsequent collapse. This process resulted in the formation of a complex system of aggregates with smaller sizes and monomers. Overall, these findings provide valuable insights into the potential of 4-arylidene curcumin derivatives as therapeutic agents for targeting α-Syn aggregation in PD treatment.

Expression profiles of α-synuclein in cortical lesions of patients with FCD IIb and TSC, and FCD rats

Background

Focal cortical dysplasia (FCD) IIb and tuberous sclerosis complex (TSC) are common causes of drug-resistant epilepsy in children. However, the etiologies related to the development of FCD IIb and TSC are not fully understood. α-synuclein (α-syn) is a member of synucleins family that plays crucial roles in modulating synaptic transmission in central nervous system. Here, we explored the expression profiles and potential pathogenic functions of α-syn in cortical lesions of epileptic patients with FCD IIb and TSC.

Methods

Surgical specimens from epileptic patients with FCD IIb and TSC, as well as FCD rats generated by in utero X-ray-radiation were adopted in this study and studied with immunohistochemistry, immunofluorescence, western blotting, and co-immunoprecipitation etc. molecular biological techniques.

Result

Our results showed that α-syn expression was reduced in FCD IIb and TSC lesions. Specifically, α-syn protein was intensely expressed in dysplastic neurons (DNs) and balloon cells (BCs) in FCD IIb lesions, whereas was barely detected in DNs and giant cells (GCs) of TSC lesions. Additionally, p-α-syn, the aggregated form of α-syn, was detected in DNs, BCs, GCs, and glia-like cells of FCD IIb and TSC lesions. We previous showed that the function of N-methyl-D-aspartate receptor (NMDAR) was enhanced in FCD rats generated by X-ray-radiation. Here, we found the interaction between α-syn and NMDAR subunits NMDAR2A, NMDAR2B were augmented in cortical lesions of FCD patients and FCD rats.

Conclusion

These results suggested a potential role of α-syn in the pathogenesis of FCD IIb and TSC by interfering with NMDAR.

Understanding the effect of the membrane-mimetic micelles on the interplay between α-synuclein and Cu(II)/Cu(I) cations

α-Synuclein (αS) is a presynaptic protein whose aggregates are considered as a hallmark of Parkinson's disease (PD). Although its physiological function is still under debate, it is widely accepted that its functions are always mediated by its interaction with membranes. The association of αS with phospholipid membranes occurs concomitant to its folding from its monomeric, unfolded state towards an antiparallel amphipathic α-helix. Besides this, copper ions can also bind αS and modify its aggregation propensity. The effect of Cu(II) and Cu(I) on the lipid-αS affinity and on the structure of the membrane-bound αS have not yet been studied. This knowledge is relevant to understand the molecular pathogenesis of PD. Therefore, we have here studied the affinities between Cu(II) and Cu(I) and the micelle-bound αS, as well as the effect of these cations on the structure of micelle-bound αS. Cu(II) or Cu(I) did not affect the α-helical structure of the micelle-bound αS. However, while Cu(I) binds at the same sites of αS in the presence or in the absence of micelles, the micelle-bound αS displays different Cu(II) binding sites than unbound αS. In any case, sodium docecyl sulphate -micelles reduce the stability of the αS complexes with both Cu(II) and Cu(I). Finally, we have observed that the micelle-bound αS is still able to prevent the Cu(II)-catalysed oxidation of neuronal metabolites (e.g. ascorbic acid) and the formation of reactive oxygen species, thus this binding does not impair its biological function as part of the antioxidant machinery.

Distinct impacts of alpha-synuclein overexpression on the hippocampal epigenome of mice in standard and enriched environments

Elevated alpha-synuclein (SNCA) gene expression is associated with transcriptional deregulation and increased risk of Parkinson's disease, which may be partially ameliorated by environmental enrichment. At the molecular level, there is emerging evidence that excess alpha-synuclein protein (aSyn) impacts the epigenome through direct and/or indirect mechanisms. However, the extents to which the effects of both aSyn and the environment converge at the epigenome and whether epigenetic alterations underpin the preventive effects of environmental factors on transcription remain to be elucidated. Here, we profiled five DNA and histone modifications in the hippocampus of wild-type and transgenic mice overexpressing human SNCA. Mice of each genotype were housed under either standard conditions or in an enriched environment (EE) for 12 months. SNCA overexpression induced hippocampal CpG hydroxymethylation and histone H3K27 acetylation changes that associated with genotype more than environment. Excess aSyn was also associated with genotype- and environment-dependent changes in non-CpG (CpH) DNA methylation and H3K4 methylation. These H3K4 methylation changes included loci where the EE ameliorated the impacts of the transgene as well as loci resistant to the effects of environmental enrichment in transgenic mice. In addition, select H3K4 monomethylation alterations were associated with changes in mRNA expression. Our results suggested an environment-dependent impact of excess aSyn on some functionally relevant parts of the epigenome, and will ultimately enhance our understanding of the molecular etiology of Parkinson's disease and other synucleinopathies.

Influence of Protonation on the Norepinephrine Inhibiting α-Synuclein 71-82 Oligomerization

The pathogenesis of Parkinson's disease (PD) is closely linked to the massive presence of Lewy vesicles and Lewy axons in the cytoplasm of neurons, mainly consisting of α-synuclein (αS). Norepinephrine (NE), whose secretion can be increased by exercise, has been demonstrated to prevent the fibrillation of αS and to break down the mature αS fibrils. In this work, we focus on the influence of protonation on the inhibitory ability of NE by using amyloid core fragment αS71-82 as a template. All-atom replica-exchange molecular dynamics simulations (accumulating to 33.6 μs) in explicit water were performed to explore the inhibitory effect of protonated and nonprotonated NE on αS oligomerization. Our results show that NE/NE+ can lead to a significant decrease in β-sheet content with increasing temperature, while isolated αS maintains relatively higher β-sheet conformations until 363 K, implying that both NE and NE+ can lower the critical temperature required for αS fibril decomposition. NE and NE+ also lead to the formation of less compact αS oligomers by preventing the backbone hydrogen bonds and the side-chain packing. The protonation would affect the binding affinity, interaction modes, and binding intensity of NE with αS. Interesting, NE and NE+ have a distinct binding free energy in the electrostatic and solvation terms, which mostly counter each other and produce a weak binding intensity with αS. Our work contributes to a better understanding of the inhibitory mechanism of NE and NE+ on αS oligomerization relevant to PD pathogenesis, which may provide clues for the design of antiamyloid medicine.

Unveiling the Effects of Copper Ions in the Aggregation of Amyloidogenic Proteins

Amyloid diseases have become a global concern due to their increasing prevalence. Transition metals, including copper, can affect the aggregation of the pathological proteins involved in these diseases. Copper ions play vital roles in organisms, but the disruption of their homeostasis can negatively impact neuronal function and contribute to amyloid diseases with toxic protein aggregates, oxidative stress, mitochondrial dysfunction, impaired cellular signaling, inflammation, and cell death. Gaining insight into the imbalance of copper ions and its impact on protein folding and aggregation is crucial for developing focused therapies. This review examines the influence of copper ions on significant amyloid proteins/peptides, offering a comprehensive overview of the current understanding in this field.

Synucleinopathies: Intrinsic and Extrinsic Factors

α-Synucleinopathies are a group of neurodegenerative disorders characterized by alterations in α-synuclein (α-syn), a protein associated with membrane phospholipids, whose precise function in normal cells is still unknown. These kinds of diseases are caused by multiple factors, but the regulation of the α-syn gene is believed to play a central role in the pathology of these disorders; therefore, the α-syn gene is one of the most studied genes. α-Synucleinopathies are complex disorders that derive from the interaction between genetic and environmental factors. Here, we offer an update on the landscape of the epigenetic regulation of α-syn gene expression that has been linked with α-synucleinopathies. We also delve into the reciprocal influence between epigenetic modifications and other factors related to these disorders, such as posttranslational modifications, microbiota participation, interactions with lipids, neuroinflammation and oxidative stress, to promote α-syn aggregation by acting on the transcription and/or translation of the α-syn gene.

Nicotine-mediated effects in neuronal and mouse models of synucleinopathy

Introduction

Alpha-synuclein (α-Syn) aggregation, transmission, and contribution to neurotoxicity represent central mechanisms underlying Parkinson's disease. The plant alkaloid "nicotine" was reported to attenuate α-Syn aggregation in different models, but its precise mode of action remains unclear.

Methods

In this study, we investigated the effect of 2-week chronic nicotine treatment on α-Syn aggregation, neuroinflammation, neurodegeneration, and motor deficits in D-line α-Syn transgenic mice. We also established a novel humanized neuronal model of α-Syn aggregation and toxicity based on treatment of dopaminergic neurons derived from human induced pluripotent stem cells (iPSC) with α-Syn preformed fibrils (PFF) and applied this model to investigate the effects of nicotine and other compounds and their modes of action.

Results and discussion

Overall, our results showed that nicotine attenuated α-Syn-provoked neuropathology in both models. Moreover, when investigating the role of nicotinic acetylcholine receptor (nAChR) signaling in nicotine's neuroprotective effects in iPSC-derived dopaminergic neurons, we observed that while α4-specific antagonists reduced the nicotine-induced calcium response, α4 agonists (e.g., AZD1446 and anatabine) mediated similar neuroprotective responses against α-Syn PFF-provoked neurodegeneration. Our results show that nicotine attenuates α-Syn-provoked neuropathology in vivo and in a humanized neuronal model of synucleinopathy and that activation of α4β2 nicotinic receptors might mediate these neuroprotective effects.

Predictive value of α-synuclein expression in peripheral blood of multiple sclerosis patients: A two-dimensional assessment of a selected biomarker

INTRODUCTION

Our study aimed to evaluate whether assessing α-synuclein expression levels in blood samples could provide a reliable and straightforward alternative to existing diagnostic and prognostic methods for neurodegenerative disorders, including multiple sclerosis (MS). We specifically investigated if α-synuclein and IL-6 expression levels from serum and peripheral blood mononuclear cells (PBMCs) could accurately predict MS severity in patients using a two-dimensional approach.

METHODS

We designed a case-control study to analyze the expression of α-synuclein and IL-6 in the peripheral blood of an MS patient group (n = 51) and a control group (n = 51). We statistically evaluated the PBMCs and serum profiles of α-synuclein and IL-6 in MS patients, along with their age of onset, disease duration, tobacco exposure, and Expanded Disability Status Scale (EDSS) score, using SPSS V22.0 software and GraphPad Prism V9.0.

RESULTS

Our findings indicate that α-synuclein production was significantly downregulated in MS patients. Principal component analysis also revealed distinct profiles between MS patients and controls. PBMCs and serum profiles of α-synuclein correlated with the EDSS score, suggesting that disease severity can be predicted using α-synuclein profiles. Moreover, α-synuclein showed a significant correlation with IL-6 and age of onset. Lastly, receiver operating characteristic curves of PBMCs and serum activity of α-synuclein profiles displayed discrimination with area under the curve values of 0.856 and 0.705, respectively.

CONCLUSION

Our results imply that measuring α-synuclein levels in both serum and PBMCs could be a valuable method for diagnosing and predicting MS severity, potentially serving as a non-invasive biomarker for the disease.

Dysfunctional energy and future perspective of low dose H2O2 as protective agent in neurodegenerative disease

The number of people with neurodegenerative disease continues to increase every year. A new perspective is needed to overcome this disease. In this review, researchers collected information about dysfunctional energy in neurodegenerative diseases driven by mitochondria. Mitochondrial dysregulation can cause damage to the neuron system. The increase in the amount and interaction of α-synuclein with SAMM50 and GABARAPL1 in the mitochondria is one of the factors causing neurodegenerative disease. As an energy provider in the body, the existence of harmonization in the regulation of mitochondria, specifically the mitochondrial outer membrane, is important. Low-dose hydrogen peroxide (H₂O₂) has neuroprotective abilities to overcome the impairment function of mitochondria in neurodegenerative patients. Based on computational simulation of this case, it can be used as a basic concept for the development of the role of H₂O₂ in neurodegenerative diseases.

Discovery of Small-Molecule Degraders for Alpha-Synuclein Aggregates

Alpha-synuclein (αSyn) species, especially the oligomers and fibers, are associated with multiple neurodegenerative diseases and cannot be directly targeted under the conventional pharmacological paradigm. Proteolysis-targeting chimera technology confers degradation of various "undruggable" targets; however, hardly any small-molecule degrader for αSyn aggregates has been reported yet. Herein, by using the probe molecule sery308 as a warhead, a series of small-molecule degraders for αSyn aggregates were designed and synthesized. Their degradation effects on αSyn aggregates were evaluated on a modified pre-formed fibril-seeding cell model. Compound 2b exhibited the highest degradation efficiency (DC₅₀ = 7.51 ± 0.53 μM) with high selectivity. Mechanistic exploration revealed that both proteasomal and lysosomal pathways were involved in this kind of degradation. Moreover, the therapeutic effects of 2b were tested on SH-SY5Y (human neuroblastoma cell line) cells and Caenorhabditis elegans. Our results provided a new class of small-molecule candidates against synucleinopathies and broadened the substrate spectrum of PROTAC-based degraders.

The brain on time: links between development and neurodegeneration

Neurodegenerative diseases are characterized by the progressive loss of structure or function of neurons. In this Spotlight, we explore the idea that genetic forms of neurodegenerative disorders might be rooted in neural development. Focusing on Alzheimer's, Parkinson's and Huntington's disease, we first provide a brief overview of the pathology for these diseases. Although neurodegenerative diseases are generally thought of as late-onset diseases, we discuss recent evidence promoting the notion that they might be considered neurodevelopmental disorders. With this view in mind, we consider the suitability of animal models for studying these diseases, highlighting human-specific features of human brain development. We conclude by proposing that one such feature, human-specific regulation of neurogenic time, might be key to understanding the etiology and pathophysiology of human neurodegenerative disease.

Neurodifferentiation and Neuroprotection Potential of Mesenchymal Stromal Cell-Derived Secretome Produced in Different Dynamic Systems

Parkinson's disease (PD) is the second most common neurodegenerative disorder and is characterized by the degeneration of the dopamine (DA) neurons in the substantia nigra pars compacta, leading to a loss of DA in the basal ganglia. The presence of aggregates of alpha-synuclein (α-synuclein) is seen as the main contributor to the pathogenesis and progression of PD. Evidence suggests that the secretome of mesenchymal stromal cells (MSC) could be a potential cell-free therapy for PD. However, to accelerate the integration of this therapy in the clinical setting, there is still the need to develop a protocol for the large-scale production of secretome under good manufacturing practices (GMP) guidelines. Bioreactors have the capacity to produce large quantities of secretomes in a scalable manner, surpassing the limitations of planar static culture systems. However, few studies focused on the influence of the culture system used to expand MSC, on the secretome composition. In this work, we studied the capacity of the secretome produced by bone marrow-derived mesenchymal stromal cells (BMSC) expanded in a spinner flask (SP) and in a Vertical-Wheel™ bioreactor (VWBR) system, to induce neurodifferentiation of human neural progenitor cells (hNPCs) and to prevent dopaminergic neuron degeneration caused by the overexpression of α-synuclein in one Caenorhabditis elegans model of PD. Results showed that secretomes from both systems were able to induce neurodifferentiation, though the secretome produced in the SP system had a greater effect. Additionally, in the conditions of our study, only the secretome produced in SP had a neuroprotective potential. Lastly, the secretomes had different profiles regarding the presence and/or specific intensity of different molecules, namely, interleukin (IL)-6, IL-4, matrix metalloproteinase-2 (MMP2), and 3 (MMP3), tumor necrosis factor-beta (TNF-β), osteopontin, nerve growth factor beta (NGFβ), granulocyte colony-stimulating factor (GCSF), heparin-binding (HB) epithelial growth factor (EGF)-like growth factor (HB-EGF), and IL-13. Overall, our results suggest that the culture conditions might have influenced the secretory profiles of cultured cells and, consequently, the observed effects. Additional studies should further explore the effects that different culture systems have on the secretome potential of PD.

Molecular-level interplay between intrinsically disordered clients and Hsp90

Proteostasis is maintained by a network of molecular chaperones, a prominent member of which is the 90-kilodalton heat shock protein Hsp90. The chaperone function of Hsp90 has been extensively reviewed previously, emphasizing its ATPase activity and remodeling of folded client proteins. Experimental evidence implicating Hsp90 in neurodegenerative diseases has bolstered interest in the noncanonical chaperoning of intrinsically disordered protein (IDPs), however the interplay between Hsp90 and its disordered clients remains poorly understood. In this review we describe recent advances that have contributed to our understanding of the intricate mechanisms characterizing Hsp90-mediated chaperoning of the IDPs tau and α-synuclein and survey emerging insights into the modulation of the chaperone-client interplay in the context of neurodegeneration.

Interaction Between the Glymphatic System and α-Synuclein in Parkinson's Disease

The glymphatic system contributes to the clearance of amyloid-β from the brain and is disrupted in Alzheimer's disease. However, whether the system is involved in the removal of α-synuclein (α-syn) and whether it is suppressed in Parkinson's disease (PD) remain largely unknown. In mice receiving the intranigral injection of recombinant human α-syn, we found that the glymphatic suppression via aquaporin-4 (AQP4) gene deletion or acetazolamide treatment reduced the clearance of injected α-syn from the brain. In mice overexpressing the human A53T-α-syn, we revealed that AQP4 deficiency accelerated the accumulation of α-syn, facilitated the loss of dopaminergic neurons, and accelerated PD-like symptoms. We also found that the overexpression of A53T-α-syn reduced the expression/polarization of AQP4 and suppressed the glymphatic activity of mice. The study demonstrates a close interaction between the AQP4-mediated glymphatic system and parenchymal α-syn, indicating that restoring the glymphatic activity is a potential therapeutic target to delay PD progression.

Manganese-induced α-synuclein overexpression promotes the accumulation of dysfunctional synaptic vesicles and hippocampal synaptotoxicity by suppressing Rab26-dependent autophagy in presynaptic neurons

Manganese (Mn) overexposure induces learning and memory impairments in mice by disrupting the functions of synapses and synaptic vesicles (SVs) in the hippocampus, which is associated with α-synuclein (α-Syn) overexpression. Rab26-dependent autophagy is a key signaling step required for impaired SV clearance; however, it is unclear whether Mn-induced α-Syn overexpression is linked to dysregulated Rab26-dependent autophagy in presynaptic neurons. In this study, we developed manganism models in male C57BL/6 mice and hippocampal primary neurons to observe the associations between Mn-induced α-Syn overexpression and impaired SV accumulation. The results of the in vivo experiments showed that 100 and 200 μmol/kg Mn exposure significantly impaired memory and synaptic plasticity in the mice, which was related to the accumulation of impaired SVs in the hippocampus. Consistent with the in vivo outcomes, the level of in vitro injured SVs in the 50 and 100 μmol/L Mn-exposed neuron group were higher than that in the control group. Moreover, 100 μmol/L Mn suppressed the initiation of Rab26-dependent autophagy at the synapse. Then, we transfected neurons with LV-α-Syn short hairpin RNA (shRNA) and exposed the neurons to Mn for an additional 24 h. Surprisingly, the area of colocalization between Rab26 and Atg16L1 and the expression level of LC3II-positive SVs were both higher in Mn-exposed LV-α-Syn shRNA-transfected neurons than those in Mn-treated normal or Mn-treated LV-scrambled shRNA-transfected neurons. Thus, Mn-induced α-Syn overexpression was responsible for the dysregulation of Rab26-dependent autophagy, thereby promoting the accumulation of injured SVs, and causing synaptotoxicity and cognitive and memory deficits in mice.

Searching for Biomarkers in the Blood of Patients at Risk of Developing Parkinson's Disease at the Prodromal Stage

Parkinson's disease (PD) is diagnosed many years after its onset, under a significant degradation of the nigrostriatal dopaminergic system, responsible for the regulation of motor function. This explains the low effectiveness of the treatment of patients. Therefore, one of the highest priorities in neurology is the development of the early (preclinical) diagnosis of PD. The aim of this study was to search for changes in the blood of patients at risk of developing PD, which are considered potential diagnostic biomarkers. Out of 1835 patients, 26 patients were included in the risk group and 20 patients in the control group. The primary criteria for inclusion in a risk group were the impairment of sleep behavior disorder and sense of smell, and the secondary criteria were neurological and mental disorders. In patients at risk and in controls, the composition of plasma and the expression of genes of interest in lymphocytes were assessed by 27 indicators. The main changes that we found in plasma include a decrease in the concentrations of l-3,4-dihydroxyphenylalanine (L-DOPA) and urates, as well as the expressions of some types of microRNA, and an increase in the total oxidative status. In turn, in the lymphocytes of patients at risk, an increase in the expression of the DA D3 receptor gene and the lymphocyte activation gene 3 (LAG3), as well as a decrease in the expression of the Protein deglycase DJ-1 gene (PARK7), were observed. The blood changes we found in patients at risk are considered candidates for diagnostic biomarkers at the prodromal stage of PD.

Mitochondrial and Endoplasmic Reticulum Stress Trigger Triglyceride Accumulation in Models of Parkinson's Disease Independent of Mutations in MAPT

The metabolic basis of Parkinson's disease pathology is poorly understood. However, the involvement of mitochondrial and endoplasmic reticulum stress in dopamine neurons in disease aetiology is well established. We looked at the effect of rotenone- and tunicamycin-induced mitochondrial and ER stress on the metabolism of wild type and microtubule-associated protein tau mutant dopamine neurons. Dopamine neurons derived from human isolated iPSCs were subjected to mitochondrial and ER stress using RT and TM, respectively. Comprehensive metabolite profiles were generated using a split phase extraction analysed by reversed phase lipidomics whilst the aqueous phase was measured using HILIC metabolomics. Mitochondrial and ER stress were both shown to cause significant dysregulation of metabolism with RT-induced stress producing a larger shift in the metabolic profile of both wild type and MAPT neurons. Detailed analysis showed that accumulation of triglycerides was a significant driver of metabolic dysregulation in response to both stresses in both genotypes. Whilst the consequence is similar, the mechanisms by which triglyceride accumulation occurs in dopamine neurons in response to mitochondrial and ER stress are very different. Thus, improving our understanding of how these mechanisms drive the observed triglyceride accumulation can potentially open up new therapeutic avenues.

The Consequences of GBA Deficiency in the Autophagy-Lysosome System in Parkinson's Disease Associated with GBA

GBA gene variants were the first genetic risk factor for Parkinson's disease. GBA encodes the lysosomal enzyme glucocerebrosidase (GBA), which is involved in sphingolipid metabolism. GBA exhibits a complex physiological function that includes not only the degradation of its substrate glucosylceramide but also the metabolism of other sphingolipids and additional lipids such as cholesterol, particularly when glucocerebrosidase activity is deficient. In the context of Parkinson's disease associated with GBA, the loss of GBA activity has been associated with the accumulation of α-synuclein species. In recent years, several hypotheses have proposed alternative and complementary pathological mechanisms to explain why lysosomal enzyme mutations lead to α-synuclein accumulation and become important risk factors in Parkinson's disease etiology. Classically, loss of GBA activity has been linked to a dysfunctional autophagy-lysosome system and to a subsequent decrease in autophagy-dependent α-synuclein turnover; however, several other pathological mechanisms underlying GBA-associated parkinsonism have been proposed. This review summarizes and discusses the different hypotheses with a special focus on autophagy-dependent mechanisms, as well as autophagy-independent mechanisms, where the role of other players such as sphingolipids, cholesterol and other GBA-related proteins make important contributions to Parkinson's disease pathogenesis.

Rapid Scan Electron Paramagnetic Resonance Spectroscopy Is a Suitable Tool to Study Intermolecular Interactions of Intrinsically Disordered Protein

Intrinsically disordered proteins (IDPs) are involved in most crucial cellular processes. However, they lack a well-defined fold hampering the investigation of their structural ensemble and interactions. Suitable biophysical methods able to manage their inherent flexibility and broad conformational ensemble are scarce. Here, we used rapid scan (RS) electron paramagnetic resonance (EPR) spectroscopy to study the intermolecular interactions of the IDP α-synuclein (aS). aS aggregation and fibril deposition is the hallmark of Parkinson's disease, and specific point mutations, among them A30P and A53T, were linked to the early onset of the disease. To understand the pathological processes, research intensively investigates aS aggregation kinetics, which was reported to be accelerated in the presence of ethanol. Conventional techniques fail to capture these fast processes due to their limited time resolution and, thus, lose kinetic information. We have demonstrated that RS EPR spectroscopy is suitable for studying aS aggregation by resolving underlying kinetics and highlighting differences in fibrillization behavior. RS EPR spectroscopy outperforms traditional EPR methods in terms of sensitivity by a factor of 5 in our case while significantly reducing data acquisition time. Thus, we were able to sample short time intervals capturing single events taking place during the aggregation process. Further studies will therefore be able to shed light on biological processes proceeding on fast time scales.

Monitoring α-synuclein aggregation

Synucleinopathies, including Parkinson's disease (PD), dementia with Lewy Bodies (DLB), and multiple system atrophy (MSA), are characterized by the misfolding and subsequent aggregation of alpha-synuclein (α-syn) that accumulates in cytoplasmic inclusions bodies in the cells of affected brain regions. Since the seminal report of likely-aggregated α-syn presence within the Lewy bodies by Spillantini et al. in 1997, the keyword "synuclein aggregation" has appeared in over 6000 papers (Source: PubMed October 2022). Studying, observing, describing, and quantifying α-syn aggregation is therefore of paramount importance, whether it happens in tubo, in vitro, in post-mortem samples, or in vivo. The past few years have witnessed tremendous progress in understanding aggregation mechanisms and identifying various polymorphs. In this context of growing complexity, it is of utmost importance to understand what tools we possess, what exact information they provide, and in what context they may be applied. Nonetheless, it is also crucial to rationalize the relevance of the information and the limitations of these methods for gauging the final result. In this review, we present the main techniques that have shaped the current views about α-syn structure and dynamics, with particular emphasis on the recent breakthroughs that may change our understanding of synucleinopathies.

Alpha-synuclein: a pathological factor with Aβ and tau and biomarker in Alzheimer's disease

BACKGROUND

Alpha-synuclein (α-syn) is considered the main pathophysiological protein component of Lewy bodies in synucleinopathies. α-Syn is an intrinsically disordered protein (IDP), and several types of structural conformations have been reported, depending on environmental factors. Since IDPs may have distinctive functions depending on their structures, α-syn can play different roles and interact with several proteins, including amyloid-beta (Aβ) and tau, in Alzheimer's disease (AD) and other neurodegenerative disorders.

MAIN BODY

In previous studies, α-syn aggregates in AD brains suggested a close relationship between AD and α-syn. In addition, α-syn directly interacts with Aβ and tau, promoting mutual aggregation and exacerbating the cognitive decline. The interaction of α-syn with Aβ and tau presented different consequences depending on the structural forms of the proteins. In AD, α-syn and tau levels in CSF were both elevated and revealed a high positive correlation. Especially, the CSF α-syn concentration was significantly elevated in the early stages of AD. Therefore, it could be a diagnostic marker of AD and help distinguish AD from other neurodegenerative disorders by incorporating other biomarkers.

CONCLUSION

The overall physiological and pathophysiological functions, structures, and genetics of α-syn in AD are reviewed and summarized. The numerous associations of α-syn with Aβ and tau suggested the significance of α-syn, as a partner of the pathophysiological roles in AD. Understanding the involvements of α-syn in the pathology of Aβ and tau could help address the unresolved issues of AD. In particular, the current status of the CSF α-syn in AD recommends it as an additional biomarker in the panel for AD diagnosis.

The Hidden Cell-to-Cell Trail of α-Synuclein Aggregates

The progressive accumulation of insoluble aggregates of the presynaptic protein alpha-synuclein (α-Syn) is a hallmark of neurodegenerative disorders including Parkinson's disease (PD), Multiple System Atrophy, and Dementia with Lewy Bodies, commonly referred to as synucleinopathies. Despite considerable progress on the structural biology of these aggregates, the molecular mechanisms mediating their cell-to-cell transmission, propagation, and neurotoxicity remain only partially understood. Numerous studies have highlighted the stereotypical spatiotemporal spreading of pathological α-Syn aggregates across different tissues and anatomically connected brain regions over time. Experimental evidence from various cellular and animal models indicate that α-Syn transfer occurs in two defined steps: the release of pathogenic α-Syn species from infected cells, and their uptake via passive or active endocytic pathways. Once α-Syn aggregates have been internalized, little is known about what drives their toxicity or how they interact with the endogenous protein to promote its misfolding and subsequent aggregation. Similarly, unknown genetic factors modulate different cellular responses to the aggregation and accumulation of pathogenic α-Syn species. Here we discuss the current understanding of the molecular phenomena associated with the intercellular spreading of pathogenic α-Syn seeds and summarize the evidence supporting the transmission hypothesis. Understanding the molecular mechanisms involved in α-Syn aggregates transmission is essential to develop novel targeted therapeutics against PD and related synucleinopathies.

Essential collective dynamics analysis reveals nonlocal interactions of alpha-synuclein38-95 monomers with fibrillar seeds

Alpha-synuclein (α-syn) is a cytoplasmic protein commonly found in the nervous system. In solution, α-syn adopts disordered unfolded conformations, although it can also form α-helices upon binding to lipid membranes. Under conditions that are not yet fully understood, α-syn can misfold and aggregate, giving rise to β-sheet rich amyloid fibrils, which then tend to accumulate in degenerating neurons. This leads to Parkinson's disease (PD) and several other conditions collectively termed synucleinopathies. Development of disease-modifying treatments requires detailed understanding of structure and dynamics of α-syn's misfolded aggregates. We have employed 1000 ns long, all-atom molecular dynamics simulations to investigate the interaction of monomeric α-syn_38-95 fragments, which contain the most important amyloidogenic regions, with preformed fibrillar seeds composed of staggered, β-sheet rich α-syn chains of matching length. The simulations indicate that α-syn_38-95 monomers tend to form aggregates with the fibrillar seeds, although we have not observed alignment of the monomeric chains with β-strands of the fibril. To analyze the stability of these aggregates, we have employed the essential collective dynamics method, which allows making accurate assessment of dynamical coupling across individual atoms in macromolecules and supramolecular complexes. The analysis revealed extensive dynamical coupling across initially monomeric α-syn chains and the fibrillar seeds including distal regions thereof that did not contact the monomer directly. We have discussed structural origins of these long-range interactions, their impacts for the stability of α-syn aggregates, and potential implications for the development of anti-PD treatments.

Environmental Neurotoxin β-N-Methylamino-L-alanine (BMAA) as a Widely Occurring Putative Pathogenic Factor in Neurodegenerative Diseases

In the present review we have discussed the occurrence of β-N-methylamino-L-alanine (BMAA) and its natural isomers, and the organisms and sample types in which the toxin(s) have been detected. Further, the review discusses general pathogenic mechanisms of neurodegenerative diseases, and how modes of action of BMAA fit in those mechanisms. The biogeography of BMAA occurrence presented here contributes to the planning of epidemiological research based on the geographical distribution of BMAA and human exposure. Analysis of BMAA mechanisms in relation to pathogenic processes of neurodegeneration is used to critically assess the potential significance of the amino acid as well as to identify gaps in our understanding. Taken together, these two approaches provide the basis for the discussion on the potential role of BMAA as a secondary factor in neurodegenerative diseases, the rationale for further research and possible directions the research can take, which are outlined in the conclusions.

Human pericytes degrade diverse α-synuclein aggregates

Parkinson's disease (PD) is a progressive, neurodegenerative disorder characterised by the abnormal accumulation of α-synuclein (α-syn) aggregates. Central to disease progression is the gradual spread of pathological α-syn. α-syn aggregation is closely linked to progressive neuron loss. As such, clearance of α-syn aggregates may slow the progression of PD and lead to less severe symptoms. Evidence is increasing that non-neuronal cells play a role in PD and other synucleinopathies such as Lewy body dementia and multiple system atrophy. Our previous work has shown that pericytes-vascular mural cells that regulate the blood-brain barrier-contain α-syn aggregates in human PD brains. Here, we demonstrate that pericytes efficiently internalise fibrillar α-syn irrespective of being in a monoculture or mixed neuronal cell culture. Pericytes cleave fibrillar α-syn aggregates (Fibrils, Ribbons, fibrils65, fibrils91 and fibrils110), with cleaved α-syn remaining present for up to 21 days. The number of α-syn aggregates/cell and average aggregate size depends on the type of strain, but differences disappear within 5 five hours of treatment. Our results highlight the role brain vasculature may play in reducing α-syn aggregate burden in PD.

Exploring the Role of Lipid-Binding Proteins and Oxidative Stress in Neurodegenerative Disorders: A Focus on the Neuroprotective Effects of Nutraceutical Supplementation and Physical Exercise

The human brain is primarily composed of lipids, and their homeostasis is crucial to carry on normal neuronal functions. In order to provide an adequate amount of lipid transport in and out of the central nervous system, organisms need a set of proteins able to bind them. Therefore, alterations in the structure or function of lipid-binding proteins negatively affect brain homeostasis, as well as increase inflammation and oxidative stress with the consequent risk of neurodegeneration. In this regard, lifestyle changes seem to be protective against neurodegenerative processes. Nutraceutical supplementation with antioxidant molecules has proven to be useful in proving cognitive functions. Additionally, regular physical activity seems to protect neuronal vitality and increases antioxidant defenses. The aim of the present review was to investigate mechanisms that link lipid-binding protein dysfunction and oxidative stress to cognitive decline, also underlining the neuroprotective effects of diet and exercise.