Inhibition of amyloid-β plaque formation by α-synuclein

Therapeutic potential of Canna edulis RS3-resistant starch in alleviating neuroinflammation and apoptosis in a Parkinson's disease rat model

This study aimed to investigate the effects of Miao medicinal Canna edulis RS3-resistant starch on behavioral performance and substantia nigra neuron apoptosis-related indicators in a rat model of Parkinson's disease (PD). Among the experimental groups, except for the control group, we induced PD rat models by subcutaneous injection of rotenone in the neck and back. After model induction, a 28-day drug intervention was conducted. Various techniques have been employed, including behavioral analysis, Real-time Polymerase Chain Reaction (RT-PCR), western blotting, enzyme-linked immunosorbent assay (ELISA), immunofluorescence, and terminal deoxynucleotidyltransferase-mediated UTP nick-ends. labeling (TUNEL) and Nissl staining to investigate the effect of Canna edulis RS3-resistant starch on the substantia nigra and neuronal apoptosis-related markers in the brains of PD model rats. Our study revealed that Canna edulis RS3, a resistant starch, significantly reduced the climbing time of PD model rats, prolonged their hanging time, lowered the expression levels of the inflammatory factors IL-1β, IL-6, and TNF-α, increased the number of TH-positive neurons in the substantia nigra, and decreased the levels of IL-1β, IL-6, and TNF-α. Furthermore, Canna edulis RS3 elevated the protein expression levels of tyrosine hydroxylase (TH) and Bcl-2 while reducing those of Bax, TLR4, NLRP3,and p-P65, and mitigated apoptosis and morphological changes in dopaminergic neurons in the substantia nigra region. Our results suggest that Canna edulis RS3-resistant starch may offer therapeutic benefits for PD patients with PD by potentially influencing inflammation and apoptosis in the dopaminergic system.

Neuroimaging and fluid biomarkers in Parkinson's disease in an era of targeted interventions

A major challenge in Parkinson's disease is the variability in symptoms and rates of progression, underpinned by heterogeneity of pathological processes. Biomarkers are urgently needed for accurate diagnosis, patient stratification, monitoring disease progression and precise treatment. These were previously lacking, but recently, novel imaging and fluid biomarkers have been developed. Here, we consider new imaging approaches showing sensitivity to brain tissue composition, and examine novel fluid biomarkers showing specificity for pathological processes, including seed amplification assays and extracellular vesicles. We reflect on these biomarkers in the context of new biological staging systems, and on emerging techniques currently in development.

Exploring Structural Insights of Aβ42 and α-Synuclein Monomers and Heterodimer: A Comparative Study Using Implicit and Explicit Solvent Simulations

Protein misfolding, aggregation, and fibril formation play a central role in the development of severe neurological disorders, including Alzheimer's and Parkinson's diseases. The structural stability of mature fibrils in these diseases is of great importance, as organisms struggle to effectively eliminate amyloid plaques. To address this issue, it is crucial to investigate the early stages of fibril formation when monomers aggregate into small, toxic, and soluble oligomers. However, these structures are inherently disordered, making them challenging to study through experimental approaches. Recently, it has been shown experimentally that amyloid-β 42 (Aβ42) and α-synuclein (α-Syn) can coassemble. This has motivated us to investigate the interaction between their monomers as a first step toward exploring the possibility of forming heterodimeric complexes. In particular, our study involves the utilization of various Amber and CHARMM force-fields, employing both implicit and explicit solvent models in replica exchange and conventional simulation modes. This comprehensive approach allowed us to assess the strengths and weaknesses of these solvent models and force fields in comparison to experimental and theoretical findings, ensuring the highest level of robustness. Our investigations revealed that Aβ42 and α-Syn monomers can indeed form stable heterodimers, and the resulting heterodimeric model exhibits stronger interactions compared to the Aβ42 dimer. The binding of α-Syn to Aβ42 reduces the propensity of Aβ42 to adopt fibril-prone conformations and induces significant changes in its conformational properties. Notably, in AMBER-FB15 and CHARMM36m force fields with the use of explicit solvent, the presence of Aβ42 significantly increases the β-content of α-Syn, consistent with the experiments showing that Aβ42 triggers α-Syn aggregation. Our analysis clearly shows that although the use of implicit solvent resulted in too large compactness of monomeric α-Syn, structural properties of monomeric Aβ42 and the heterodimer were preserved in explicit-solvent simulations. We anticipate that our study sheds light on the interaction between α-Syn and Aβ42 proteins, thus providing the atom-level model required to assess the initial stage of aggregation mechanisms related to Alzheimer's and Parkinson's diseases.

Pathological and physiological functional cross-talks of α-synuclein and tau in the central nervous system

α-Synuclein and tau are abundant multifunctional brain proteins that are mainly expressed in the presynaptic and axonal compartments of neurons, respectively. Previous works have revealed that intracellular deposition of α-synuclein and/or tau causes many neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. Despite intense investigation, the normal physiological functions and roles of α-synuclein and tau are still unclear, owing to the fact that mice with knockout of either of these proteins do not present apparent phenotypes. Interestingly, the co-occurrence of α-synuclein and tau aggregates was found in post-mortem brains with synucleinopathies and tauopathies, some of which share similarities in clinical manifestations. Furthermore, the direct interaction of α-synuclein with tau is considered to promote the fibrillization of each of the proteins in vitro and in vivo. On the other hand, our recent findings have revealed that α-synuclein and tau are cooperatively involved in brain development in a stage-dependent manner. These findings indicate strong cross-talk between the two proteins in physiology and pathology. In this review, we provide a summary of the recent findings on the functional roles of α-synuclein and tau in the physiological conditions and pathogenesis of neurodegenerative diseases. A deep understanding of the interplay between α-synuclein and tau in physiological and pathological conditions might provide novel targets for clinical diagnosis and therapeutic strategies to treat neurodegenerative diseases.

Aquaporin-4 and Parkinson's Disease

The water-selective channel aquaporin-4 (AQP4) is implicated in water homeostasis and the functioning of the glymphatic system, which eliminates various metabolites from the brain tissue, including amyloidogenic proteins. Misfolding of the α-synuclein protein and its post-translational modifications play a crucial role in the development of Parkinson's disease (PD) and other synucleopathies, leading to the formation of cytotoxic oligomers and aggregates that cause neurodegeneration. Human and animal studies have shown an interconnection between AQP4 dysfunction and α-synuclein accumulation; however, the specific role of AQP4 in these mechanisms remains unclear. This review summarizes the current knowledge on the role of AQP4 dysfunction in the progression of α-synuclein pathology, considering the possible effects of AQP4 dysregulation on brain molecular mechanisms that can impact α-synuclein modification, accumulation and aggregation. It also highlights future directions that can help study the role of AQP4 in the functioning of the protective mechanisms of the brain during the development of PD and other neurodegenerative diseases.

Co-aggregation of α-synuclein with amyloid-β stabilizes β-sheet-rich oligomers and enhances the formation of β-barrels

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative diseases with markedly different pathological features of β-amyloid (Aβ) plaques and α-synuclein (αS) Lewy bodies (LBs), respectively. However, clinical overlaps in symptoms and pathologies between AD and PD are commonly observed caused by the cross-interaction between Aβ and αS. To uncover the molecular mechanisms behind their overlapping symptoms and pathologies, we computationally investigated the impact of αS on an Aβ monomer and dimerization using atomistic discrete molecular dynamics simulations (DMD). Our results revealed that αS could directly interact with Aβ monomers and dimers, thus forming β-sheet-rich oligomers, including potentially toxic β-barrel intermediates. The binding hotspot involved the second half of the N-terminal domain and NAC region in αS, along with residues 10-21 and 31-42 in Aβ. In their hetero-complex, the binding hotspot primarily assumed a β-sheet core buried inside, which was dynamically shielded by the highly charged, amyloid-resistant C-terminus of αS. Because the amyloid prion region was the same as the binding hotspot being buried, their fibrillization may be delayed, causing the toxic oligomers to increase. This study sheds light on the intricate relationship between Aβ and αS and provides insights into the overlapping pathology of AD and PD.

TMEM175: A lysosomal ion channel associated with neurological diseases

Lysosomes are acidic intracellular organelles with autophagic functions that are critical for protein degradation and mitochondrial homeostasis, while abnormalities in lysosomal physiological functions are closely associated with neurological disorders. Transmembrane protein 175 (TMEM175), an ion channel in the lysosomal membrane that is essential for maintaining lysosomal acidity, has been proven to coordinate with V-ATPase to modulate the luminal pH of the lysosome to assist the digestion of abnormal proteins and organelles. However, there is considerable controversy about the characteristics of TMEM175. In this review, we introduce the research progress on the structural, modulatory, and functional properties of TMEM175, followed by evidence of its relevance for neurological disorders. Finally, we discuss the potential value of TMEM175 as a therapeutic target in the hope of providing new directions for the treatment of neurodegenerative diseases.

α-Synuclein Aggregation Is Triggered by Oligomeric Amyloid-β 42 via Heterogeneous Primary Nucleation

An increasing number of cases where amyloids of different proteins are found in the same patient are being reported. This observation complicates diagnosis and clinical intervention. Amyloids of the amyloid-β peptide or the protein α-synuclein are traditionally considered hallmarks of Alzheimer's and Parkinson's diseases, respectively. However, the co-occurrence of amyloids of these proteins has also been reported in patients diagnosed with either disease. Here, we show that soluble species containing amyloid-β can induce the aggregation of α-synuclein. Fibrils formed under these conditions are solely composed of α-synuclein to which amyloid-β can be found associated but not as part of the core of the fibrils. Importantly, by global kinetic analysis, we found that the aggregation of α-synuclein under these conditions occurs via heterogeneous primary nucleation, triggered by soluble aggregates containing amyloid-β.

Naringenin-Functionalized Gold Nanoparticles and Their Role in α-Synuclein Stabilization

Misfolding and self-assembly of several intrinsically disordered proteins into ordered β-sheet-rich amyloid aggregates emerged as hallmarks of several neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Here we show how the naringenin-embedded nanostructure effectively retards aggregation and fibril formation of α-synuclein, which is strongly associated with the pathology of Parkinson's-like diseases. Naringenin is a polyphenolic compound from a plant source, and in our current investigation, we reported the one-pot synthesis of naringenin-coated spherical and monophasic gold nanoparticles (NAR-AuNPs) under optimized conditions. The average hydrodynamic diameter of the produced nanoparticle was ∼24 nm and showed a distinct absorption band at 533 nm. The zeta potential of the nanocomposite was ∼-22 mV and indicated the presence of naringenin on the surface of nanoparticles. Core-level XPS spectrum analysis showed prominent peaks at 84.02 and 87.68 eV, suggesting the zero oxidation state of metal in the nanostructure. Additionally, the peaks at 86.14 and 89.76 eV were due to the Au-O bond, induced by the hydroxyl groups of the naringenin molecule. The FT-IR analysis further confirmed strong interactions of the molecule with the gold nanosurface via the phenolic oxygen group. The composite surface was found to interact with monomeric α-synuclein and caused a red shift in the nanoparticle absorption band by ∼5 nm. The binding affinity of the composite nanostructure toward α-synuclein was in the micromolar range (K_a∼ 5.02 × 10⁶ M^-1) and may produce a protein corona over the gold nanosurface. A circular dichroism study showed that the nanocomposite can arrest the conformational fluctuation of the protein and hindered its transformation into a compact cross-β-sheet conformation, a prerequisite for amyloid fibril formation. Furthermore, it was found that naringenin and its nanocomplex did not perturb the viability of neuronal cells. It thus appeared that engineering of the nanosurface with naringenin could be an alternative strategy in developing treatment approaches for Parkinson's and other diseases linked to protein conformation.

Overexpression of alpha synuclein disrupts APP and Endolysosomal axonal trafficking in a mouse model of synucleinopathy

Mutations or triplication of the alpha synuclein (ASYN) gene contribute to synucleinopathies including Parkinson's disease (PD), Dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Recent evidence suggests that ASYN also plays an important role in amyloid-induced neurotoxicity, although the mechanism(s) remains unknown. One hypothesis is that accumulation of ASYN alters endolysosomal pathways to impact axonal trafficking and processing of the amyloid precursor protein (APP). To define an axonal function for ASYN, we used a transgenic mouse model of synucleinopathy that expresses a GFP-human ASYN (GFP-hASYN) transgene and an ASYN knockout (ASYN-/-) mouse model. Our results demonstrate that expression of GFP-hASYN in primary neurons derived from a transgenic mouse impaired axonal trafficking and processing of APP. In addition, axonal transport of BACE1, Rab5, Rab7, lysosomes and mitochondria were also reduced in these neurons. Interestingly, axonal transport of these organelles was also affected in ASYN-/- neurons, suggesting that ASYN plays an important role in maintaining normal axonal transport function. Therefore, selective impairment of trafficking and processing of APP by ASYN may act as a potential mechanism to induce pathological features of Alzheimer's disease (AD) in PD patients.

Amyloid Protein Cross-Seeding Provides a New Perspective on Multiple Diseases In Vivo

Amyloid protein cross-seeding is a peculiar phenomenon of cross-spreading among different diseases. Unlike traditional infectious ones, diseases caused by amyloid protein cross-seeding are spread by misfolded proteins instead of pathogens. As a consequence of the interactions among misfolded heterologous proteins or polypeptides, amyloid protein cross-seeding is considered to be the crucial cause of overlapping pathological transmission between various protein misfolding disorders (PMDs) in multiple tissues and cells. Here, we briefly review the phenomenon of cross-seeding among amyloid proteins. As an interesting example worth mentioning, the potential links between the novel coronavirus pneumonia (COVID-19) and some neurodegenerative diseases might be related to the amyloid protein cross-seeding, thus may cause an undesirable trend in the incidence of PMDs around the world. We then summarize the theoretical models as well as the experimental techniques for studying amyloid protein cross-seeding. Finally, we conclude with an outlook on the challenges and opportunities for basic research in this field. Cross-seeding of amyloid opens up a new perspective in our understanding of the process of amyloidogenesis, which is crucial for the development of new treatments for diseases. It is therefore valuable but still challenging to explore the cross-seeding system of amyloid protein as well as to reveal the structural basis and the intricate processes.

Oligomerization by co-assembly of β-amyloid and α-synuclein

Aberrant self-assembly of an intrinsically disordered protein is a pathological hallmark of protein misfolding diseases, such as Alzheimer's and Parkinson's diseases (AD and PD, respectively). In AD, the 40-42 amino acid-long extracellular peptide, β-amyloid (Aβ), self-assembles into oligomers, which eventually aggregate into fibrils. A similar self-association of the 140 amino acid-long intracellular protein, α-synuclein (αS), is responsible for the onset of PD pathology. While Aβ and αS are primarily extracellular and intracellular polypeptides, respectively, there is evidence of their colocalization and pathological overlaps of AD and PD. This evidence has raised the likelihood of synergistic, toxic protein-protein interactions between Aβ and αS. This mini review summarizes the findings of studies on Aβ-αS interactions related to enhanced oligomerization via co-assembly, aiming to provide a better understanding of the complex biology behind AD and PD and common pathological mechanisms among the major neurodegenerative diseases.

SNCA genetic lowering reveals differential cognitive function of alpha-synuclein dependent on sex

Antisense oligonucleotide (ASO) therapy for neurological disease has been successful in clinical settings and its potential has generated hope for Alzheimer's disease (AD). We previously described that ablating SNCA encoding for α-synuclein (αSyn) in a mouse model of AD was beneficial. Here, we sought to demonstrate whether transient reduction of αSyn expression using ASOSNCA could be therapeutic in a mouse model of AD. The efficacy of the ASOSNCA was measured via immunocytochemistry, RT-qPCR and western blotting. To assess spatial learning and memory, ASOSNCA or PBS-injected APP and non-transgenic (NTG) mice, and separate groups of SNCA-null mice, were tested on the Barnes circular maze. Hippocampal slice electrophysiology and transcriptomic profiling were used to explore synaptic function and differential gene expression between groups. Reduction of SNCA transcripts alleviated cognitive deficits in male transgenic animals, but surprisingly, not in females. To determine the functional cause of this differential effect, we assessed memory function in SNCA-null mice. Learning and memory were intact in male mice but impaired in female animals, revealing that the role of αSyn on cognitive function is sex-specific. Transcriptional analyses identified a differentially expressed gene network centered around EGR1, a central modulator of learning and memory, in the hippocampi of SNCA-null mice. Thus, these novel results demonstrate that the function of αSyn on memory differs between male and female brains.

Influence of TiO2 and ZnO Nanoparticles on α-Synuclein and β-Amyloid Aggregation and Formation of Protein Fibrils

The most common neurological disorders, i.e., Parkinson's disease (PD) and Alzheimer's disease (AD), are characterized by degeneration of cognitive functions due to the loss of neurons in the central nervous system. The aggregation of amyloid proteins is an important pathological feature of neurological disorders.The aggregation process involves a series of complex structural transitions from monomeric to the formation of fibrils. Despite its potential importance in understanding the pathobiology of PD and AD diseases, the details of the aggregation process are still unclear. Nanoparticles (NPs) absorbed by the human circulatory system can interact with amyloid proteins in the human brain and cause PD. In this work, we report the study of the interaction between TiO₂ nanoparticles (TiO₂-NPs) and ZnO nanoparticles (ZnO-NPs) on the aggregation kinetics of β-amyloid fragment 1-40 (βA) and α-synuclein protein using surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS). The characterizations of ZnO-NPs and TiO₂-NPs were evaluated by X-ray diffraction (XRD) spectrum, atomic force microscopy (AFM), and UV-Vis spectroscopy. The interaction of nanoparticles with amyloid proteins was investigated by SERS. Our study showed that exposure of amyloid protein molecules to TiO₂-NPs and ZnO-NPs after incubation at 37 °C caused morphological changes and stimulated aggregation and fibrillation. In addition, significant differences in the intensity and location of active Raman frequencies in the amide I domain were found. The principal component analysis (PCA) results show that the effect of NPs after incubation at 4 °C does not cause changes in βA structure.

Seed-induced Aβ deposits in the corpus callosum disrupt white matter integrity in a mouse model of Alzheimer’s disease

Neuropathologically, Alzheimer’s disease (AD) is characterized by the accumulation of amyloid-beta peptide (Aβ) and subsequent formation of the so-called Aβ plaques. Along with neuronal loss, previous studies report white matter anomalies and corpus callosum (CC) atrophy in AD patients. Notably, perturbations in the white matter can be observed years before expected disease onset, suggesting that early stages of disease progression play a role in AD-associated loss of myelin integrity. Through seed-induced deposition of Aβ, we are able to examine alterations of central nervous system (CNS) integrity during the initial stages of plaque formation. In this study, we investigate the impact of Aβ seeding in the CC utilizing various imaging techniques as well as quantitative gene expression analysis and demonstrate that Aβ deposits result in an imbalance of glial cells in the CC. We found increased amounts of phagocytic microglia and reactive astrocytes, while oligodendrocyte progenitor cell (OPC) numbers were reduced. Moreover, white matter aberrations adjacent to the Aβ seeding were observed together with an overall decline in callosal myelination. This data indicate that the initial stages of plaque formation induce oligodendrocyte dysfunction, which might ultimately lead to myelin loss.

Update on new trend and progress of the mechanism of polysaccharides in the intervention of Alzheimer's disease, based on the new understanding of relevant theories: A review

Alzheimer's disease (AD), a neurodegenerative disease with insidious onset and progressive progression, is the main type of dementia. Currently, there is no specific cure for the disease. At the same time, a series of drug developments based on the classic theory, the Aβ cascade hypothesis, have not completed phase III clinical trials, challenging the hypothesis. Polysaccharides obtained from natural products can be used in the treatment of AD, which has attracted academic attention due to its advantages of multi-target, multi-channel, no or modest side effects. The TCM syndrome type of AD is mainly "qi and blood deficiency, kidney essence deficiency", and the medicine is mainly used to replenish qi and blood, kidney and bone marrow. Thus, there has been extensive and in-depth research on polysaccharides obtained from tonic Chinese herbal medicine in China. Based on this background, this paper evaluated the effects and mechanisms of natural polysaccharides on AD by combing and screening English and related literature in recent 5 years and summarized the extraction process and structure-activity relationship of polysaccharides.

Immunohistochemical Demonstration of the pGlu79 α-Synuclein Fragment in Alzheimer’s Disease and Its Tg2576 Mouse Model

The deposition of β-amyloid peptides and of α-synuclein proteins is a neuropathological hallmark in the brains of Alzheimer’s disease (AD) and Parkinson’s disease (PD) subjects, respectively. However, there is accumulative evidence that both proteins are not exclusive for their clinical entity but instead co-exist and interact with each other. Here, we investigated the presence of a newly identified, pyroglutamate79-modified α-synuclein variant (pGlu79-aSyn)—along with the enzyme matrix metalloproteinase-3 (MMP-3) and glutaminyl cyclase (QC) implicated in its formation—in AD and in the transgenic Tg2576 AD mouse model. In the human brain, pGlu79-aSyn was detected in cortical pyramidal neurons, with more distinct labeling in AD compared to control brain tissue. Using immunohistochemical double and triple labelings and confocal laser scanning microscopy, we demonstrate an association of pGlu79-aSyn, MMP-3 and QC with β-amyloid plaques. In addition, pGlu79-aSyn and QC were present in amyloid plaque-associated reactive astrocytes that were also immunoreactive for the chaperone heat shock protein 27 (HSP27). Our data are consistent for the transgenic mouse model and the human clinical condition. We conclude that pGlu79-aSyn can be generated extracellularly or within reactive astrocytes, accumulates in proximity to β-amyloid plaques and induces an astrocytic protein unfolding mechanism involving HSP27.

O-GlcNAcase Inhibitor ASN90 is a Multimodal Drug Candidate for Tau and α-Synuclein Proteinopathies

Neurodegenerative proteinopathies are characterized by the intracellular formation of insoluble and toxic protein aggregates in the brain that are closely linked to disease progression. In Alzheimer's disease and in rare tauopathies, aggregation of the microtubule-associated tau protein leads to the formation of neurofibrillary tangles (NFT). In Parkinson's disease (PD) and other α-synucleinopathies, intracellular Lewy bodies containing aggregates of α-synuclein constitute the pathological hallmark. Inhibition of the glycoside hydrolase O-GlcNAcase (OGA) prevents the removal of O-linked N-acetyl-d-glucosamine (O-GlcNAc) moieties from intracellular proteins and has emerged as an attractive therapeutic approach to prevent the formation of tau pathology. Like tau, α-synuclein is known to be modified with O-GlcNAc moieties and in vitro these have been shown to prevent its aggregation and toxicity. Here, we report the preclinical discovery and development of a novel small molecule OGA inhibitor, ASN90. Consistent with the substantial exposure of the drug and demonstrating target engagement in the brain, the clinical OGA inhibitor ASN90 promoted the O-GlcNAcylation of tau and α-synuclein in brains of transgenic mice after daily oral dosing. Across human tauopathy mouse models, oral administration of ASN90 prevented the development of tau pathology (NFT formation), functional deficits in motor behavior and breathing, and increased survival. In addition, ASN90 slowed the progression of motor impairment and reduced astrogliosis in a frequently utilized α-synuclein-dependent preclinical rodent model of PD. These findings provide a strong rationale for the development of OGA inhibitors as disease-modifying agents in both tauopathies and α-synucleinopathies. Since tau and α-synuclein pathologies frequently co-exist in neurodegenerative diseases, OGA inhibitors represent unique, multimodal drug candidates for further clinical development.

α-synuclein-assisted oligomerization of β-amyloid (1-42)

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative disorders, characterized by aggregation of amyloid polypeptides, β-amyloid (Aβ) and α-synuclein (αS), respectively. Aβ and αS follow similar aggregation pathways, starting from monomers, to soluble toxic oligomeric assemblies, and to insoluble fibrils. Various studies have suggested overlaps in the pathologies of AD and PD, and have shown Aβ-αS interactions. Unfortunately, whether these protein-protein interactions lead to self- and co-assembly of Aβ and αS into oligomers - a potentially toxic synergistic mechanism - is poorly understood. Among the various Aβ isoforms, interactions of Aβ containing 42 amino acids (Aβ (1-42), referred to as Aβ42) with αS are of most direct relevance due to the high aggregation propensity and the strong toxic effect of this Aβ isoform. In this study, we carefully determined molecular consequences of interactions between Aβ42 and αS in their respective monomeric, oligomeric, and fibrillar forms using a comprehensive set of experimental tools. We show that the three αS conformers, namely, monomers, oligomers and fibrils interfered with fibrillization of Aβ42. Specifically, αS monomers and oligomers promoted oligomerization and stabilization of soluble Aβ42, possibly via direct binding or co-assembly, while αS fibrils hindered soluble Aβ42 species from converting into insoluble aggregates by the formation of large oligomers. We also provide evidence that the interactions with αS were mediated by various parts of Aβ42, depending on Aβ42 and αS conformers. Furthermore, we compared similarities and dissimilarities between Aβ42-αS and Aβ40-αS interactions. Overall, the present study provides a comprehensive depiction of the molecular interplay between Aβ42 and αS, providing insight into its synergistic toxic mechanism.

Seed-induced Aβ deposition alters neuronal function and impairs olfaction in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-β (Aβ) which ultimately forms plaques. These Aβ deposits can be induced in APP transgenic mouse models by prion-like seeding. It has been widely accepted that anosmia and hyposmia occur during the early stages of AD, even before cognitive deficits are present. In order to determine the impact of seed-induced Aβ deposits on olfaction, we performed intracerebral injections of seed-competent brain homogenate into the olfactory bulb of young pre-depositing APP transgenic mice. Remarkably, we observed a dramatic olfactory impairment in those mice. Furthermore, the number of newborn neurons as well as the activity of cells in the mitral cell layer was decreased. Notably, exposure to an enriched environment reduced Aβ seeding, vivified neurogenesis and most importantly reversed olfactory deficits. Based on our findings, we conclude that altered neuronal function as a result of induced Aβ pathology might contribute to olfactory dysfunction in AD.

Revisit the Cellular Transmission and Emerging Techniques in Understanding the Mechanisms of Proteinopathies

Alzheimer’s and Parkinson’s diseases (AD and PD) are amongst top of the prevalent neurodegenerative disease. One-third of PD patients are diagnosed with dementia, a pre-symptom of AD, but the underlying mechanism is elusive. Amyloid beta (Aβ) and α-synuclein are two of the most investigated proteins, whose pathological aggregation and spreading are crucial to the pathogenesis of AD and PD, respectively. Transcriptomic studies of the mammalian central nervous system shed light on gene expression profiles at molecular levels, regarding the complexity of neuronal morphologies and electrophysiological inputs/outputs. In the last decade, the booming of the single-cell RNA sequencing technique helped to understand gene expression patterns, alternative splicing, novel transcripts, and signal pathways in the nervous system at single-cell levels, providing insight for molecular taxonomy and mechanistic targets of the degenerative nervous system. Here, we re-visited the cell-cell transmission mechanisms of Aβ and α-synuclein in mediating disease propagation, and summarized recent single-cell transcriptome sequencing from different perspectives and discussed its understanding of neurodegenerative diseases.

Microglia contribute to the propagation of Aβ into unaffected brain tissue

Microglia appear activated in the vicinity of amyloid beta (Aβ) plaques, but whether microglia contribute to Aβ propagation into unaffected brain regions remains unknown. Using transplantation of wild-type (WT) neurons, we show that Aβ enters WT grafts, and that this is accompanied by microglia infiltration. Manipulation of microglia function reduced Aβ deposition within grafts. Furthermore, in vivo imaging identified microglia as carriers of Aβ pathology in previously unaffected tissue. Our data thus argue for a hitherto unexplored mechanism of Aβ propagation.

This study shows that Aβ from transgenic host tissue is able to enter and deposit within wild-type grafts via microglia, thus identifying microglia as carriers of Aβ deposition into previously unaffected brain tissue.

Distinct Aβ pathology in the olfactory bulb and olfactory deficits in a mouse model of Aβ and α-syn co-pathology

Several degenerative brain disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Dementia with Lewy bodies (DLB) are characterized by the simultaneous appearance of amyloid‐β (Aβ) and α‐synuclein (α‐syn) pathologies and symptoms that are similar, making it difficult to differentiate between these diseases. Until now, an accurate diagnosis can only be made by postmortem analysis. Furthermore, the role of α‐syn in Aβ aggregation and the arising characteristic olfactory impairments observed during the progression of these diseases is still not well understood. Therefore, we assessed Aβ load in olfactory bulbs of APP‐transgenic mice expressing APP695^KM670/671NL and PSEN1^L166P under the control of the neuron‐specific Thy‐1 promoter (referred to here as APPPS1) and APPPS1 mice co‐expressing SNCA^A30P (referred to here as APPPS1 × [A30P]aSYN). Furthermore, the olfactory capacity of these mice was evaluated in the buried food and olfactory avoidance test. Our results demonstrate an age‐dependent increase in Aβ load in the olfactory bulb of APP‐transgenic mice that go along with exacerbated olfactory performance. Our study provides clear evidence that the presence of α‐syn significantly diminished the endogenous and seed‐induced Aβ deposits and significantly ameliorated olfactory dysfunction in APPPS1 × [A30P]aSYN mice.

Examining the Toxicity of α-Synuclein in Neurodegenerative Disorders

Simple Summary

Neurodegenerative disorders are complex disorders that display a variety of clinical manifestations. The second-most common neurodegenerative disorder is Parkinson’s disease, and the leading pathological protein of the disorder is considered to be α-synuclein. Nonetheless, α-synuclein accumulation also seems to result in multiple system atrophy and dementia with Lewy bodies. In order to obtain a more proficient understanding in the pathological progression of these synucleinopathies, it is crucial to observe the post-translational modifications of α-synuclein and the conformations of α-synuclein, as well as its role in the dysfunction of cellular pathways.

Abstract

α-synuclein is considered the main pathological protein in a variety of neurodegenerative disorders, such as Parkinson’s disease, multiple system atrophy, and dementia with Lewy bodies. As of now, numerous studies have been aimed at examining the post-translational modifications of α-synuclein to determine their effects on α-synuclein aggregation, propagation, and oligomerization, as well as the potential cellular pathway dysfunctions caused by α-synuclein, to determine the role of the protein in disease progression. Furthermore, α-synuclein also appears to contribute to the fibrilization of tau and amyloid beta, which are crucial proteins in Alzheimer’s disease, advocating for α-synuclein’s preeminent role in neurodegeneration. Due to this, investigating the mechanisms of toxicity of α-synuclein in neurodegeneration may lead to a more proficient understanding of the timeline progression in neurodegenerative synucleinopathies and could thereby lead to the development of potent targeted therapies.

Collusion of α-Synuclein and Aβ aggravating co-morbidities in a novel prion-type mouse model

BACKGROUND

The misfolding of host-encoded proteins into pathological prion conformations is a defining characteristic of many neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and Lewy body dementia. A current area of intense study is the way in which the pathological deposition of these proteins might influence each other, as various combinations of co-pathology between prion-capable proteins are associated with exacerbation of disease. A spectrum of pathological, genetic and biochemical evidence provides credence to the notion that amyloid β (Aβ) accumulation can induce and promote α-synuclein pathology, driving neurodegeneration.

METHODS

To assess the interplay between α-synuclein and Aβ on protein aggregation kinetics, we crossed mice expressing human α-synuclein (M20) with APPswe/PS1dE9 transgenic mice (L85) to generate M20/L85 mice. We then injected α-synuclein preformed fibrils (PFFs) unilaterally into the hippocampus of 6-month-old mice, harvesting 2 or 4 months later.

RESULTS

Immunohistochemical analysis of M20/L85 mice revealed that pre-existing Aβ plaques exacerbate the spread and deposition of induced α-synuclein pathology. This process was associated with increased neuroinflammation. Unexpectedly, the injection of α-synuclein PFFs in L85 mice enhanced the deposition of Aβ; whereas the level of Aβ deposition in M20/L85 bigenic mice, injected with α-synuclein PFFs, did not differ from that of mice injected with PBS.

CONCLUSIONS

These studies reveal novel and unexpected interplays between α-synuclein pathology, Aβ and neuroinflammation in mice that recapitulate the pathology of Alzheimer's disease and Lewy body dementia.

α-Synuclein modulates tau spreading in mouse brains

α-Synuclein (α-syn) and tau aggregates are the neuropathological hallmarks of Parkinson’s disease (PD) and Alzheimer’s disease (AD), respectively, although both pathologies co-occur in patients with these diseases, suggesting possible crosstalk between them. To elucidate the interactions of pathological α-syn and tau, we sought to model these interactions. We show that increased accumulation of tau aggregates occur following simultaneous introduction of α-syn mousepreformed fibrils (mpffs) and AD lysate–derived tau seeds (AD-tau) both in vitro and in vivo. Interestingly, the absence of endogenous mouse α-syn in mice reduces the accumulation and spreading of tau, while the absence of tau did not affect the seeding or spreading capacity of α-syn. These in vivo results are consistent with our in vitro data wherein the presence of tau has no synergistic effects on α-syn. Our results point to the important role of α-syn as a modulator of tau pathology burden and spreading in the brains of AD, PDD, and DLB patients.

Soluble endogenous oligomeric α-synuclein species in neurodegenerative diseases: Expression, spreading, and cross-talk

There is growing recognition in the field of neurodegenerative diseases that mixed proteinopathies are occurring at greater frequency than originally thought. This is particularly true for three amyloid proteins defining most of these neurological disorders, amyloid-beta (Aβ), tau, and alpha-synuclein (αSyn). The co-existence and often co-localization of aggregated forms of these proteins has led to the emergence of concepts positing molecular interactions and cross-seeding between Aβ, tau, and αSyn aggregates. Amongst this trio, αSyn has received particular attention in this context during recent years due to its ability to modulate Aβ and tau aggregation in vivo, to interact at a molecular level with Aβ and tau in vivo and to cross-seed tau in mice. Here we provide a comprehensive, critical, and accessible review about the expression, role and nature of endogenous soluble αSyn oligomers because of recent developments in the understanding of αSyn multimerization, misfolding, aggregation, cross-talk, spreading and cross-seeding in neurodegenerative disorders, including Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, Alzheimer's disease, and Huntington's disease. We will also discuss our current understanding about the relative toxicity of endogenous αSyn oligomers in vivo and in vitro, and introduce potential opportunities to counter their deleterious effects.

The existence of Aβ strains and their potential for driving phenotypic heterogeneity in Alzheimer's disease

Reminiscent of the human prion diseases, there is considerable clinical and pathological variability in Alzheimer's disease, the most common human neurodegenerative condition. As in prion disorders, protein misfolding and aggregation is a hallmark feature of Alzheimer's disease, where the initiating event is thought to be the self-assembly of Aβ peptide into aggregates that deposit in the central nervous system. Emerging evidence suggests that Aβ, similar to the prion protein, can polymerize into a conformationally diverse spectrum of aggregate strains both in vitro and within the brain. Moreover, certain types of Aβ aggregates exhibit key hallmarks of prion strains including divergent biochemical attributes and the ability to induce distinct pathological phenotypes when intracerebrally injected into mouse models. In this review, we discuss the evidence demonstrating that Aβ can assemble into distinct strains of aggregates and how such strains may be primary drivers of the phenotypic heterogeneity in Alzheimer's disease.

Nanoaggregates Derived from Amyloid-beta and Alpha-synuclein Characterized by Sequential Quadruple Force Mapping

Overlapping of Alzheimer's disease and Parkinson's disease is associated with the formation of hetero-oligomers derived from amyloid-beta and alpha-synuclein. However, the structural identity of the hetero-oligomer has yet to be elucidated, particularly at high resolution. Here, with atomic force microscopy, the surface structure of hetero-oligomer was examined with four AFM tips tethering one of the selected antibodies recognizing N-terminus or C-terminus of each peptide. All aggregates were found to be hetero-oligomers, and probability of recognizing the termini is higher than that for the homo-oligomers, suggesting that the termini of the former have a greater tendency to be located at the surface or the termini have more freedom to be recognized, probably through loose packing. The methodology in this study provides us with a new approach to elucidate the structure of such aggregates at the single-molecule level, allowing the exploration of other intrinsically disordered proteins frequently found in nature.

Biophysical processes underlying cross-seeding in amyloid aggregation and implications in amyloid pathology

Abnormal aggregation of proteins into filamentous aggregates commonly associates with many diseases, such as Alzheimer's disease, Parkinson's disease and type-2 diabetes. These filamentous aggregates, also known as amyloids, can propagate their abnormal structures to either the same precursor molecules (seeding) or other protein monomers (cross-seeding). Cross-seeding has been implicated in the abnormal protein aggregation and has been found to facilitate the formation of physiological amyloids. It has risen to be an exciting area of research with a high volume of published reports. In this review article, we focus on the biophysical processes underlying the cross-seeding for some of the most commonly studied amyloid proteins. Here we will discuss the relevant literature related to cross-seeded polymerization of amyloid-beta, human islet amyloid polypeptide (hIAPP, or also known as amylin) and alpha-synuclein. SEVI (semen-derived enhancer of viral infection) amyloid formation by the cross-seeding between the bacterial curli protein and PAP248-286 is also briefly discussed.

Review on Alzheimer's disease: Inhibition of amyloid beta and tau tangle formation

It is reported that approximately 40 million people are suffering from dementia, globally. Dementia is a group of symptoms that affect neurons and cause some mental disorders, such as losing memory. Alzheimer's disease (AD) which is known as the most common cause of dementia, is one of the top medical care concerns across the world. Although the exact sources of the disease are not understood, is it believed that aggregation of amyloid-beta (Aβ) outside of neuron cells and tau aggregation or neurofibrillary tangles (NFTs) formation inside the cell may play crucial roles. In this paper, we are going to review studies that targeted inhibition of amyloid plaque and tau protein tangle formation, to suppress or postpone AD.

Tau pathology associates with in vivo cortical thinning in Lewy body disorders

OBJECTIVES

To investigate the impact of Alzheimer's disease (AD) co-pathology on an in vivo structural measure of neurodegeneration in Lewy body disorders (LBD).

METHODS

We studied 72 LBD patients (Parkinson disease (PD) = 2, PD-MCI = 25, PD with dementia = 10, dementia with Lewy bodies = 35) with either CSF analysis or neuropathological examination and structural MRI during life. The cohort was divided into those harboring significant AD co-pathology, either at autopsy (intermediate/high AD neuropathologic change) or with CSF signature indicating AD co-pathology (t-tau/Aβ1-42  > 0.3) (LBD+AD, N = 19), and those without AD co-pathology (LBD-AD, N = 53). We also included a reference group of 25 patients with CSF biomarker-confirmed amnestic AD. We investigated differences in MRI cortical thickness estimates between groups, and in the 21 autopsied LBD patients (LBD-AD = 14, LBD+AD = 7), directly tested the association between antemortem MRI and post-mortem burdens of tau, Aβ, and alpha-synuclein using digital histopathology in five representative neocortical regions.

RESULTS

The LBD+AD group was characterized by cortical thinning in anterior/medial and lateral temporal regions (P < 0.05 FWE-corrected) relative to LBD-AD. In LBD+AD, cortical thinning was most pronounced in temporal neocortex, whereas the AD reference group showed atrophy that equally encompassed temporal, parietal and frontal neocortex. In autopsied LBD, we found an inverse correlation with cortical thickness and post-mortem tau pathology, while cortical thickness was not significantly associated with Aβ or alpha-synuclein pathology.

INTERPRETATION

LBD+AD is characterized by temporal neocortical thinning on MRI, and cortical thinning directly correlated with post-mortem histopathologic burden of tau, suggesting that tau pathology influences the pattern of neurodegeneration in LBD.

Medin aggregation causes cerebrovascular dysfunction in aging wild-type mice

Medin is the most common amyloid known in humans, as it can be found in blood vessels of the upper body in virtually everybody over 50 years of age. However, it remains unknown whether deposition of Medin plays a causal role in age-related vascular dysfunction. We now report that aggregates of Medin also develop in the aorta and brain vasculature of wild-type mice in an age-dependent manner. Strikingly, genetic deficiency of the Medin precursor protein, MFG-E8, eliminates not only vascular aggregates but also prevents age-associated decline of cerebrovascular function in mice. Given the prevalence of Medin aggregates in the general population and its role in vascular dysfunction with aging, targeting Medin may become a novel approach to sustain healthy aging.

Mechanisms of Pathogenic Tau and Aβ Protein Spreading in Alzheimer's Disease

Alzheimer’s disease (AD) is pathologically defined by extracellular accumulation of amyloid-β (Aβ) peptides generated by the cleavage of amyloid precursor protein (APP), strings of hyperphosphorylated Tau proteins accumulating inside neurons known as neurofibrillary tangles (NFTs) and neuronal loss. The association between the two hallmarks and cognitive decline has been known since the beginning of the 20th century when the first description of the disease was carried out by Alois Alzheimer. Today, more than 40 million people worldwide are affected by AD that represents the most common cause of dementia and there is still no effective treatment available to cure the disease. In general, the aggregation of Aβ is considered an essential trigger in AD pathogenesis that gives rise to NFTs, neuronal dysfunction and dementia. During the process leading to AD, tau and Aβ first misfold and form aggregates in one brain region, from where they spread to interconnected areas of the brain thereby inducing its gradual morphological and functional deterioration. In this mini-review article, we present an overview of the current literature on the spreading mechanisms of Aβ and tau pathology in AD since a more profound understanding is necessary to design therapeutic approaches aimed at preventing or halting disease progression.

Immunotherapies for Aging-Related Neurodegenerative Diseases-Emerging Perspectives and New Targets

Neurological disorders such as Alzheimer's disease (AD), Lewy body dementia (LBD), frontotemporal dementia (FTD), and vascular dementia (VCID) have no disease-modifying treatments to date and now constitute a dementia crisis that affects 5 million in the USA and over 50 million worldwide. The most common pathological hallmark of these age-related neurodegenerative diseases is the accumulation of specific proteins, including amyloid beta (Aβ), tau, α-synuclein (α-syn), TAR DNA-binding protein 43 (TDP43), and repeat-associated non-ATG (RAN) peptides, in the intra- and extracellular spaces of selected brain regions. Whereas it remains controversial whether these accumulations are pathogenic or merely a byproduct of disease, the majority of therapeutic research has focused on clearing protein aggregates. Immunotherapies have garnered particular attention for their ability to target specific protein strains and conformations as well as promote clearance. Immunotherapies can also be neuroprotective: by neutralizing extracellular protein aggregates, they reduce spread, synaptic damage, and neuroinflammation. This review will briefly examine the current state of research in immunotherapies against the 3 most commonly targeted proteins for age-related neurodegenerative disease: Aβ, tau, and α-syn. The discussion will then turn to combinatorial strategies that enhance the effects of immunotherapy against aggregating protein, followed by new potential targets of immunotherapy such as aging-related processes.

Protein transmission in neurodegenerative disease

Most neurodegenerative diseases are characterized by the intracellular or extracellular aggregation of misfolded proteins such as amyloid-β and tau in Alzheimer disease, α-synuclein in Parkinson disease, and TAR DNA-binding protein 43 in amyotrophic lateral sclerosis. Accumulating evidence from both human studies and disease models indicates that intercellular transmission and the subsequent templated amplification of these misfolded proteins are involved in the onset and progression of various neurodegenerative diseases. The misfolded proteins that are transferred between cells are referred to as 'pathological seeds'. Recent studies have made exciting progress in identifying the characteristics of different pathological seeds, particularly those isolated from diseased brains. Advances have also been made in our understanding of the molecular mechanisms that regulate the transmission process, and the influence of the host cell on the conformation and properties of pathological seeds. The aim of this Review is to summarize our current knowledge of the cell-to-cell transmission of pathological proteins and to identify key questions for future investigation.

Intracerebral seeding of amyloid-β and tau pathology in mice: Factors underlying prion-like spreading and comparisons with α-synuclein

Alzheimer's disease (AD) is characterized neuropathologically by progressive neurodegeneration and by the presence of amyloid plaques and neurofibrillary tangles. These plaques and tangles are composed, respectively, of amyloid-beta (Aβ) and tau proteins. While long recognized as hallmarks of AD, it remains unclear what causes the formation of these insoluble deposits. One theory holds that prion-like templated misfolding of Aβ and tau induces these proteins to form pathological aggregates, and propagation of this misfolding causes the stereotyped progression of pathology commonly seen in AD. Supporting this theory, numerous studies have been conducted in which aggregated Aβ, tau, or α-synuclein is injected intracerebrally into pathology-free host animals, resulting in robust formation of pathology. Here, we review this literature, focusing on in vivo intracerebral seeding of Aβ and tau in mice. We compare the results of these experiments to what is known about the seeding and spread of α-synuclein pathology, and we discuss how this research informs our understanding of the factors underlying the onset, progression, and outcomes of proteinaceous pathologies.

Amyloid-Beta (Aβ) Plaques Promote Seeding and Spreading of Alpha-Synuclein and Tau in a Mouse Model of Lewy Body Disorders with Aβ Pathology

Studies have shown an overlap of Aβ plaques, tau tangles, and α-synuclein (α-syn) pathologies in the brains of Alzheimer's disease (AD) and Parkinson's disease (PD) with dementia (PDD) patients, with increased pathological burden correlating with severity of cognitive and motor symptoms. Despite the observed co-pathology and concomitance of motor and cognitive phenotypes, the consequences of the primary amyloidogenic protein on the secondary pathologies remain poorly understood. To better define the relationship between α-syn and Aβ plaques, we injected α-syn preformed fibrils (α-syn mpffs) into mice with abundant Aβ plaques. Aβ deposits dramatically accelerated α-syn pathogenesis and spread throughout the brain. Remarkably, hyperphosphorylated tau (p-tau) was induced in α-syn mpff-injected 5xFAD mice. Finally, α-syn mpff-injected 5xFAD mice showed neuron loss that correlated with the progressive decline of cognitive and motor performance. Our findings suggest a "feed-forward" mechanism whereby Aβ plaques enhance endogenous α-syn seeding and spreading over time post-injection with mpffs.

FG-nucleoporins caught in the act of liquid-liquid phase separation

The interior of nuclear pore complexes (NPCs) is densely filled with FG-nucleoporins that form a permeability barrier of a still-obscure nature. Celetti et al. (2019. J. Cell Biol.https://doi.org/10.1083/jcb.201907157) now reveal that FG-nucleoporins can undergo liquid-liquid phase separation and form liquid droplets that mimic permeability barrier properties of intact NPCs.

The liquid state of FG-nucleoporins mimics permeability barrier properties of nuclear pore complexes

Nuclear pore complexes (NPCs) regulate all cargo traffic across the nuclear envelope. The transport conduit of NPCs is highly enriched in disordered phenylalanine/glycine-rich nucleoporins (FG-Nups), which form a permeability barrier of still elusive and highly debated molecular structure. Here we present a microfluidic device that triggered liquid-to-liquid phase separation of FG-Nups, which yielded droplets that showed typical properties of a liquid state. On the microfluidic chip, droplets were perfused with different transport-competent or -incompetent cargo complexes, and then the permeability barrier properties of the droplets were optically interrogated. We show that the liquid state mimics permeability barrier properties of the physiological nuclear transport pathway in intact NPCs in cells: that is, inert cargoes ranging from small proteins to large capsids were excluded from liquid FG-Nup droplets, but functional import complexes underwent facilitated import into droplets. Collectively, these data provide an experimental model of how NPCs can facilitate fast passage of cargoes across an order of magnitude in cargo size.

Lentivirus-mediated downregulation of α-synuclein reduces neuroinflammation and promotes functional recovery in rats with spinal cord injury

BACKGROUND

The prognosis of spinal cord injury (SCI) is closely related to secondary injury, which is dominated by neuroinflammation. There is evidence that α-synuclein aggregates after SCI and that inhibition of α-synuclein aggregation can improve the survival of neurons after SCI, but the mechanism is still unclear. This study was designed to investigate the effects of α-synuclein on neuroinflammation after SCI and to determine the underlying mechanisms.

METHOD

A T3 spinal cord contusion model was established in adult male Sprague-Dawley rats. An SNCA-shRNA-carrying lentivirus (LV-SNCA-shRNA) was injected into the injury site to block the expression of α-synuclein (forming the SCI+KD group), and the SCI and sham groups were injected with an empty vector. Basso-Beattie-Bresnahan (BBB) behavioural scores and footprint analysis were used to detect motor function. Inflammatory infiltration and myelin loss were measured in the spinal cord tissues of each group by haematoxylin-eosin (HE) and Luxol Fast Blue (LFB) staining, respectively. Immunohistochemistry, Western blot analysis, and RT-qPCR were used to analyse protein expression and transcription levels in the tissues. Immunofluorescence was used to determine the morphology and function of glial cells and the expression of matrix metalloproteinase-9 in the central canal of the spinal cord. Finally, peripheral serum cytokine levels were determined by enzyme-linked immunosorbent assay.

RESULTS

Compared with the SCI group, the SCI+KD group exhibited reduced inflammatory infiltration, preserved myelin, and functional recovery. Specifically, the early arrest of α-synuclein inhibited the pro-inflammatory factors IL-1β, TNF-α, and IL-2 and increased the expression of the anti-inflammatory factors IL-10, TGF-β, and IL-4. The neuroinflammatory response was regulated by reduced proliferation of Iba1+ microglia/macrophages and promotion of the shift of M1-polarized Iba1+/iNOS+ microglia/macrophages to M2-polarized Iba1+/Arg1+ microglia/macrophages after injury. In addition, compared with the SCI group, the SCI+KD group also exhibited a smaller microglia/astrocyte (Iba1/GFAP) immunostaining area in the central canal, lower MMP-9 expression, and improved cerebrospinal barrier function.

CONCLUSION

Lentivirus-mediated downregulation of α-synuclein reduces neuroinflammation, improves blood-cerebrospinal barrier function, promotes functional recovery, reduces microglial activation, and promotes the polarization of M1 microglia/macrophages to an M2 phenotype to confer a neuroprotective immune microenvironment in rats with SCI.

Aβ Seeding as a Tool to Study Cerebral Amyloidosis and Associated Pathology

Misfolded proteins can form aggregates and induce a self-perpetuating process leading to the amplification and spreading of pathological protein assemblies. These misfolded protein assemblies act as seeds of aggregation. In an in vivo exogenous seeding model, both the features of seeds and the position at which seeding originates are precisely defined. Ample evidence from studies on intracerebal injection of amyloid-beta (Aβ)-rich brain extracts suggests that Aβ aggregation can be initiated by prion-like seeding. In this mini-review article, we will summarize the past and current literature on Aβ seeding in mouse models of AD and discuss its implementation as a tool to study cerebral amyloidosis and associated pathology.

Beyond the synucleinopathies: alpha synuclein as a driving force in neurodegenerative comorbidities

The fundamental role that alpha-synuclein (aSyn) plays in the pathogenesis of neurodegenerative synucleinopathies, including Parkinson’s disease, dementia with Lewy bodies, and multiple system atrophy, is a well-accepted fact. A wealth of experimental evidence has linked this relatively small but ubiquitously expressed protein to a plethora of cytopathologic mechanisms and suggests that aSyn may be capable of seeding the progressive spread of synucleinopathy throughout the brain. Beyond the synucleinopathies, the abnormal deposition of aSyn is frequently seen in a variety of other neurodegenerative proteinopathies including Alzheimer’s disease. In spite of the fact that the frequency of concomitant aSyn pathology in these disorders is such that it can be considered the rule rather than the exception, the potential role that aSyn may have in these disorders has received relatively little attention.

In this article we postulate that aSyn may in fact be a key protein in driving the pathogenic processes in neurodegenerative comorbidities. In addition to reviewing the frequency of concomitant deposition of aSyn in the neurodegenerative proteinopathies, we also consider our current understanding of the interaction of aSyn with other neurodegenerative disease-associated proteins, including tau, TDP-43, amyloid-β and prion protein, in the context of neuropathologic studies describing the anatomical sites of potential concomitant pathology. We conclude that a growing body of evidence, encompassing neuropathology studies in human brain, animal models of concomitant proteinopathies and studies employing sophisticated methods of probing protein-protein interaction, cumulatively suggest that aSyn is well positioned to exert a strong influence on the pathogenesis of the neurodegenerative comorbidities.

We hope to stimulate research in this emerging field and consider that future studies exploring the contribution of aSyn to the pathogenic processes in neurodegenerative comorbidities may provide critical information pertaining to diagnosis and the development of vital disease modifying treatments for these devastating diseases.

Effects of single and combined immunotherapy approach targeting amyloid β protein and α-synuclein in a dementia with Lewy bodies-like model

INTRODUCTION

Immunotherapeutic approaches targeting amyloid β (Aβ) protein and tau in Alzheimer's disease and α-synuclein (α-syn) in Parkinson's disease are being developed for treating dementia with Lewy bodies. However, it is unknown if single or combined immunotherapies targeting Aβ and/or α-syn may be effective.

METHODS

Amyloid precursor protein/α-syn tg mice were immunized with AFFITOPEs® (AFF) peptides specific to Aβ (AD02) or α-syn (PD-AFF1) and the combination.

RESULTS

AD02 more effectively reduced Aβ and pTau burden; however, the combination exhibited some additive effects. Both AD02 and PD-AFF1 effectively reduced α-syn, ameliorated degeneration of pyramidal neurons, and reduced neuroinflammation. PD-AFF1 more effectively ameliorated cholinergic and dopaminergic fiber loss; the combined immunization displayed additive effects. AD02 more effectively improved buried pellet test behavior, whereas PD-AFF1 more effectively improved horizontal beam test; the combined immunization displayed additive effects.

DISCUSSION

Specific active immunotherapy targeting Aβ and/or α-syn may be of potential interest for the treatment of dementia with Lewy bodies.

Reaction of Amyloid-β Peptide Antibody with Different Infectious Agents Involved in Alzheimer's Disease

As early as the 1980s, molecular virologist Ruth Itzhaki began to investigate if there was a causal connection between infections and neurodegenerative disorder. Although the theory has yet to be universally embraced, in 2016 Itzhaki and 33 other scientists from all over the world published a review article in this very journal presenting evidence for the causal role of pathogens in Alzheimer's disease (AD). Exactly how and in what way pathogens affect the induction of AD has yet to be determined, but one possible answer may involve the cross-reactivity of different pathogens with amyloid-β (Aβ). Aβ autoantibodies have been detected in the serum and cerebrospinal fluid of AD patients and in some healthy individuals. In the present study our major goal was to investigate whether antibodies made against Aβ would react both with other brain proteins as well as pathogens associated with AD as a result of molecular mimicry or the binding of bacterial toxins to Aβ42. Our study used a specific monoclonal antibody made against Aβ42, which not only reacted strongly with Aβ42, tau protein, and α-synuclein, but also had from weak to strong reactions with 25 different pathogens or their molecules, some of which have been associated with AD. The homology between peptide stretches of microbial origin and proteins involved in AD could be a mechanism by which antibodies to homologous peptides mount attacks against autoantigens in AD. We concluded that bacterial molecules bind to Aβ protein, forming small oligomers, then encasing pathogens and their molecules to form amyloid plaques, the tell-tale markers of AD. Conversely, these same Aβ peptides induce the production of antibodies to both Aβ42 and bacterial molecules, which may inhibit bacterial pathogenesis, but in the process may promote amyloid plaque formation.

Neuropathology and pathogenesis of extrapyramidal movement disorders: a critical update-I. Hypokinetic-rigid movement disorders

Extrapyramidal movement disorders include hypokinetic rigid and hyperkinetic or mixed forms, most of them originating from dysfunction of the basal ganglia (BG) and their information circuits. The functional anatomy of the BG, the cortico-BG-thalamocortical, and BG-cerebellar circuit connections are briefly reviewed. Pathophysiologic classification of extrapyramidal movement disorder mechanisms distinguish (1) parkinsonian syndromes, (2) chorea and related syndromes, (3) dystonias, (4) myoclonic syndromes, (5) ballism, (6) tics, and (7) tremor syndromes. Recent genetic and molecular-biologic classifications distinguish (1) synucleinopathies (Parkinson's disease, dementia with Lewy bodies, Parkinson's disease-dementia, and multiple system atrophy); (2) tauopathies (progressive supranuclear palsy, corticobasal degeneration, FTLD-17; Guamian Parkinson-dementia; Pick's disease, and others); (3) polyglutamine disorders (Huntington's disease and related disorders); (4) pantothenate kinase-associated neurodegeneration; (5) Wilson's disease; and (6) other hereditary neurodegenerations without hitherto detected genetic or specific markers. The diversity of phenotypes is related to the deposition of pathologic proteins in distinct cell populations, causing neurodegeneration due to genetic and environmental factors, but there is frequent overlap between various disorders. Their etiopathogenesis is still poorly understood, but is suggested to result from an interaction between genetic and environmental factors. Multiple etiologies and noxious factors (protein mishandling, mitochondrial dysfunction, oxidative stress, excitotoxicity, energy failure, and chronic neuroinflammation) are more likely than a single factor. Current clinical consensus criteria have increased the diagnostic accuracy of most neurodegenerative movement disorders, but for their definite diagnosis, histopathological confirmation is required. We present a timely overview of the neuropathology and pathogenesis of the major extrapyramidal movement disorders in two parts, the first one dedicated to hypokinetic-rigid forms and the second to hyperkinetic disorders.

Aβ oligomers trigger and accelerate Aβ seeding

Aggregation of amyloid‐β (Aβ) that leads to the formation of plaques in Alzheimer's disease (AD) occurs through the stepwise formation of oligomers and fibrils. An earlier onset of aggregation is obtained upon intracerebral injection of Aβ‐containing brain homogenate into human APP transgenic mice that follows a prion‐like seeding mechanism. Immunoprecipitation of these brain extracts with anti‐Aβ oligomer antibodies or passive immunization of the recipient animals abrogated the observed seeding activity, although induced Aβ deposition was still evident. Here, we establish that, together with Aβ monomers, Aβ oligomers trigger the initial phase of Aβ seeding and that the depletion of oligomeric Aβ delays the aggregation process, leading to a transient reduction of seed‐induced Aβ deposits. This work extends the current knowledge about the role of Aβ oligomers beyond its cytotoxic nature by pointing to a role in the initiation of Aβ aggregation in vivo. We conclude that Aβ oligomers are important for the early initiation phase of the seeding process.