The Effect of Fragmented Pathogenic α-Synuclein Seeds on Prion-like Propagation

Cannabidiol as a multifaceted therapeutic agent: mitigating Alzheimer's disease pathology and enhancing cognitive function

BACKGROUND

Cannabidiol (CBD), the second most abundant phytocannabinoid in Cannabis sativa, has garnered significant interest due to its non-psychoactive nature and diverse receptor interactions.

METHODS

This study employs in vitro and in vivo methodologies to validate CBD's potential as a treatment for Alzheimer's disease (AD) by addressing key hallmarks of the condition and promoting neuroprotective effects on spatial memory.

RESULTS

Our findings demonstrate CBD's ability to decrease pTau and Aβ aggregation and to mitigate their axonal transport between cortical and hippocampal neurons. Moreover, CBD treatment was shown to reduce neuroinflammation, as CBD was able to skew microglia towards a neuroprotective M2 phenotype while attenuating proinflammatory cytokine release in the 5xFAD AD mouse model. Notably, daily CBD injections (10 mg/Kg) for 28 days in 5xFAD mice resulted in significant improvements in both short- and long-term spatial memory. The study also reveals CBD's capacity to partially revert neurite formation loss induced by Aβ, Tau, and pTau proteins, suggesting a potential role in promoting neuronal plasticity. Additionally, CBD treatment led to a reduction in reactive oxygen species (ROS) formation and increased neuronal viability in the presence of AD-associated protein aggregates.

CONCLUSIONS

These multifaceted effects of CBD, ranging from molecular-level modulation to behavioral improvements, underscore its potential as a comprehensive therapeutic approach for AD. The findings not only support CBD's neuroprotective properties but also highlight its ability to target multiple pathological processes simultaneously, offering a promising avenue for future AD treatment strategies.

Intracellular Inclusions Induced by Patient-Derived and Amplified α-Synuclein Aggregates Are Morphologically Indistinguishable

Lewy Body Disease (LBD) and Multiple System Atrophy (MSA) are synucleinopathies with distinct prognoses and neuropathologies, however, with overlapping clinical symptoms. Different disease characteristics are proposed to be determined by distinct conformations of alpha-synuclein (α-Syn) aggregates, which can self-propagate and spread between cells via a prion-like mechanism. The goal of this study is to investigate whether α-syn aggregates amplified from brain and CSF samples of LBD and MSA patients using the Seed Amplification Assay (SAA) maintain α-Syn seeding properties similar to those of α-syn aggregates derived from patients' brains. To address this, SAA-amplified and un-amplified α-Syn aggregates from LBD and MSA patients' brains, as well as SAA-amplified α-Syn aggregates from LBD and MSA patients' CSF samples, were used to treat synuclein biosensor cells, and induced intracellular α-Syn inclusions were analyzed by confocal microscopy. Our data indicate that induced α-Syn aggregates from LBD and MSA patients' brains have similar seeding properties and morphological characteristics in the α-Syn biosensor cells as those amplified from LBD and MSA patients' brains, as well as those amplified from LBD and MSA patients' CSF samples. In this study, we demonstrated that, regardless of the source of aggregates, the seeds from LBD and MSA produce cellular accumulation of α-Syn with distinct morphologies, confirming the presence of different conformational strains of α-Syn in LBD and MSA and allowing us to differentiate synucleinopathies based on the morphology of aggregates and seeding properties.

Fibril-seeded animal models of synucleinopathies: Pathological mechanisms, disease modeling, and therapeutic implications

Accumulating evidence suggests that prion-like spread of misfolded α-Synuclein (αSyn) underlies the pathological progression of Lewy body diseases (LBD). Animal models injected with αSyn preformed fibrils (PFFs) have provided strong evidence for the prion hypothesis in LBD. Moreover, αSyn PFFs can be administered to various hosts and regions, contributing to the elucidation of pathological mechanisms and disease modeling. These models have also been used to identify biomarkers and develop new disease-modifying therapies for LBD. In contrast, it remains unknown how the prion-like properties of αSyn contribute to the pathogenesis of multiple system atrophy (MSA). Recent studies indicate that conformationally distinct αSyn fibrils induce different pathological features in animals, supporting the strain hypothesis, which suggests that conformational variations in αSyn fibrils contribute to the clinicopathological heterogeneity in synucleinopathies. However, the study of disease-specific αSyn fibrils in pathological mechanisms and disease modeling is still in its early stages. This review aims to highlight recent advances in αSyn fibril-seeded animal models with an emphasis on their unique features and utility in exploring pathological mechanisms and identifying novel disease-modifying therapies. In addition, I discuss future directions for refining these models in light of the emerging strain hypothesis in synucleinopathies.

Intrastriatal injection of alpha-synuclein preformed fibrils to rats results in L-DOPA reversible sensorimotor impairments and alterations in non-motor function

Introduction

The alpha-synuclein (α-syn) preformed fibril (PFF) model of Parkinson's disease (PD) is widely used in rodents to understand the mechanisms contributing to progression of pathology and neurodegeneration in the disorder. While the time course of pathology in the α-syn PFF rat model has been well characterized, it has been more challenging to determine reliable and reproducible behavior impairments. This is mainly due to α-syn PFF injections resulting in a partial nigrostriatal lesion that make motor anomalies more subtle and difficult to detect, just as in patients with PD. In the present study we sought to examine the effect of increased striatal distribution and injection quantity of α-syn PFFs in rats on accumulation of phosphorylated α-syn inclusions, nigrostriatal degeneration, sensorimotor behavior, and nonmotor function related to PD.

Methods

Male Fischer 344 rats were injected unilaterally in the striatum with a total of 24μg α-syn PFFs distributed into three sites, or an equal volume of phosphate buffered saline (PBS) as a control condition. Sensorimotor function was assessed using a battery of behavioral tests sensitive to varying degrees of nigrostriatal neurodegeneration. Non-motor testing included assays for olfaction, emotional reactivity, cognitive function, and sleep.

Results

At six months post injection, α-syn PFF rats displayed significant movement and somatosensory asymmetries compared with control rats. Time to initiate a forelimb step and time to contact an adhesive stimulus on the forepaw took significantly longer with the contralateral limb compared with the ipsilateral limb in α-syn PFF rats. Further, hindlimb stepping in the cylinder was significantly reduced in α-syn PFF-injected rats compared with controls. Cognitive function was also affected in the α-syn PFF rats, with investigation time significantly decreased in an object recognition test. Levodopa reversibility was observed in the movement initiation and cylinder tests. Postmortem analysis revealed a 55% loss of nigral tyrosine hydroxylase immunoreactive neurons and a 63% reduction in striatal dopamine content in α-syn PFF-injected rats.

Conclusion

Thus, using the present α-syn PFF surgical parameters, sufficient nigrostriatal degeneration can be achieved to manifest significant motor and non-motor deficits. These rat α-syn PFF surgical parameters will be important for preclinical assessment of novel diseasemodifying therapies.

New prospects for 89Zr-immuno-PET in brain applications - Alpha-synucleinopathies

BACKGROUND

Recently, 89Zr-immuno-PET imaging of therapeutic antibodies, actively transported over the blood-brain-barrier via transferrin-mediated transcytosis, was demonstrated using the chelator DFO*. In these studies, aducanumab targeting amyloid-beta was fused with a transferrin binding unit: a single-chain Fab fragment derived from 8D3 (scFab8D3). Alpha-synuclein is a hallmark protein of several neurodegenerative diseases such as Parkinson's Disease, Lewy-Body-Dementia, and Multiple System Atrophy. 89Zr-immuno-PET imaging of alpha-synuclein can be a valuable tool for image-guided drug development and assessment of target engagement. The goal of this study was to compare two currently used constructs of 8D3 for targeting potential, namely a single moiety of scFab8D3 fused to the alpha-synuclein antibody HLu-3 (HLu-3-scFab8D3) versus HLu-3 fused with two 8D3 single-chain variable fragments (HLu-3-(scFv8D3)2), by 89Zr-immuno-PET in an alpha-synuclein pre-formed fibril (PFF) deposition model. HLu-3 and the HIV-targeting B12-scFab8D3 were used as controls. The best-performing compound was further investigated in an animal model with predominantly intraneural target aggregation.

METHODS

Antibodies were conjugated with DFO* using DFO*-NCS and subsequently radiolabeled with 89Zr. Assessment of binding affinity was done by alpha-synuclein ELISA and with FACS analysis using mTfR1 expressing CHO-S cells. Radioimmunoconjugates were first evaluated in an extracellular alpha-synuclein deposition model established by intracranial injection of non-sonicated PFFs into the left striatum of C57Bl/6 WT mice, whereas saline was injected into the contralateral site as control. PET imaging was performed 1, 3, and 7 days post-injection, followed by ex vivo biodistribution, autoradiography and immunofluorescence analysis. Based on the results from these studies, the better-performing antibody candidate was tested similarly in an alpha-synuclein seeding model. The seeding model has intraneural alpha-synuclein aggregation and was established by intracranial injection of sonicated PFFs into both striata of F28tg mice, which overexpress human wild-type alpha-synuclein. Untreated F28tg and C57Bl/6 WT mice served as controls.

RESULTS

The radioimmunoconjugate was produced in sufficient radiochemical yields and purity. There was no impairment of binding affinity towards alpha-synuclein, and acceptable binding with negligible losses to mTfR1. PET imaging with [89Zr]Zr-HLu-3-scFab8D3 and [89Zr]Zr-HLu-3-(scFv8D3)2 in the deposition model showed uptake at the site of alpha-synuclein deposits. However, uptake was variable between mice. Reliable PET quantification was hampered due to the small deposition volume (~2 μL). Immunofluorescence revealed specific alpha-synuclein target engagement of both constructs with PFF deposits in the striatum, in contrast to the [89Zr]Zr-B12-scFab8D3 control. Unexpectedly, ex vivo autoradiography showed uptake in some controls ([89Zr]Zr-B12-scFab8D3 in the contralateral striatum without PFFs), potentially related to astrocyte activation at the injection sites. Ex vivo and PET brain uptake was higher for [89Zr]Zr-HLu-3-scFab8D3 when compared to [89Zr]Zr-HLu-3-(scFv8D3)2 and was therefore selected for further testing in the alpha-synuclein seeding model. No significant difference in in vivo and ex vivo brain uptake of [89Zr]Zr-HLu-3-scFab8D3 between PFF-injected F28tg, F28tg and C57Bl/6 mice was observed. Furthermore, ex vivo immunofluorescence and autoradiography showed no specific alpha-synuclein target engagement.

CONCLUSIONS

Successful target engagement of [89Zr]Zr-HLu-3-scFab8D3 and [89Zr]Zr-HLu-3-(scFv8D3)2 with alpha-synuclein was shown in a PFF deposition model. PET imaging showed variable results, and in vivo detection of the depositions was possible in some cases. Due to the better performance in the deposition model, [89Zr]Zr-HLu-3-scFab8D3 was further investigated in an alpha-synuclein seeding model with intraneural Lewy-body pathology, showing no difference between the control groups and PFF-seeded mice. Furthermore, immunostaining of seeded F28tg mice manifested sufficient intraneural alpha-synuclein pathology but no corresponding antibody accumulation. These results underscore the ongoing challenge of imaging intraneural inclusions via immuno-PET.

Mouse α-synuclein fibrils are structurally and functionally distinct from human fibrils associated with Lewy body diseases

The intricate process of α-synuclein aggregation and fibrillization holds pivotal roles in Parkinson's disease (PD) and multiple system atrophy (MSA). While mouse α-synuclein can fibrillize in vitro, whether these fibrils commonly used in research to induce this process or form can reproduce structures in the human brain remains unknown. Here, we report the first atomic structure of mouse α-synuclein fibrils, which was solved in parallel by two independent teams. The structure shows striking similarity to MSA-amplified and PD-associated E46K fibrils. However, mouse α-synuclein fibrils display altered packing arrangements, reduced hydrophobicity, and heightened fragmentation sensitivity and evoke only weak immunological responses. Furthermore, mouse α-synuclein fibrils exhibit exacerbated pathological spread in neurons and humanized α-synuclein mice. These findings provide critical insights into the structural underpinnings of α-synuclein pathogenicity and emphasize a need to reassess the role of mouse α-synuclein fibrils in the development of related diagnostic probes and therapeutic interventions.

SARS-CoV-2 infection exacerbates the cellular pathology of Parkinson's disease in human dopaminergic neurons and a mouse model

While an association between Parkinson's disease (PD) and viral infections has been recognized, the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on PD progression remains unclear. Here, we demonstrate that SARS-CoV-2 infection heightens the risk of PD using human embryonic stem cell (hESC)-derived dopaminergic (DA) neurons and a human angiotensin-converting enzyme 2 (hACE2) transgenic (Tg) mouse model. Our findings reveal that SARS-CoV-2 infection exacerbates PD susceptibility and cellular toxicity in DA neurons pre-treated with human preformed fibrils (hPFFs). Additionally, nasally delivered SARS-CoV-2 infects DA neurons in hACE2 Tg mice, aggravating the damage initiated by hPFFs. Mice infected with SARS-CoV-2 display persisting neuroinflammation even after the virus is no longer detectable in the brain. A comprehensive analysis suggests that the inflammatory response mediated by astrocytes and microglia could contribute to increased PD susceptibility associated with SARS-CoV-2. These findings advance our understanding of the potential long-term effects of SARS-CoV-2 infection on the progression of PD.

Alpha-synuclein inclusion responsive microglia are resistant to CSF1R inhibition

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder that is characterized by the presence of proteinaceous alpha-synuclein (α-syn) inclusions (Lewy bodies), markers of neuroinflammation and the progressive loss of nigrostriatal dopamine (DA) neurons. These pathological features can be recapitulated in vivo using the α-syn preformed fibril (PFF) model of synucleinopathy. We have previously determined that microglia proximal to PFF-induced nigral α-syn inclusions increase in soma size, upregulate major-histocompatibility complex-II (MHC-II) expression, and increase expression of a suite of inflammation-associated transcripts. This microglial response is observed months prior to degeneration, suggesting that microglia reacting to α-syn inclusion may contribute to neurodegeneration and could represent a potential target for novel therapeutics. The goal of this study was to determine whether colony stimulating factor-1 receptor (CSF1R)-mediated microglial depletion impacts the magnitude of α-syn aggregation, nigrostriatal degeneration, or the response of microglial in the context of the α-syn PFF model.

METHODS

Male Fischer 344 rats were injected intrastriatally with either α-syn PFFs or saline. Rats were continuously administered Pexidartinib (PLX3397B, 600 mg/kg), a CSF1R inhibitor, to deplete microglia for a period of either 2 or 6 months.

RESULTS

CSF1R inhibition resulted in significant depletion (~ 43%) of ionized calcium-binding adapter molecule 1 immunoreactive (Iba-1ir) microglia within the SNpc. However, CSF1R inhibition did not impact the increase in microglial number, soma size, number of MHC-II immunoreactive microglia or microglial expression of Cd74, Cxcl10, Rt-1a2, Grn, Csf1r, Tyrobp, and Fcer1g associated with phosphorylated α-syn (pSyn) nigral inclusions. Further, accumulation of pSyn and degeneration of nigral neurons was not impacted by CSF1R inhibition. Paradoxically, long term CSF1R inhibition resulted in increased soma size of remaining Iba-1ir microglia in both control and PFF rats, as well as expression of MHC-II in extranigral regions.

CONCLUSIONS

Collectively, our results suggest that CSF1R inhibition does not impact the microglial response to nigral pSyn inclusions and that CSF1R inhibition is not a viable disease-modifying strategy for PD.

MerTK is a mediator of alpha-synuclein fibril uptake by human microglia

Mer tyrosine kinase (MerTK) is a receptor tyrosine kinase that mediates non-inflammatory, homeostatic phagocytosis of diverse types of cellular debris. Highly expressed on the surface of microglial cells, MerTK is of importance in brain development, homeostasis, plasticity and disease. Yet, involvement of this receptor in the clearance of protein aggregates that accumulate with ageing and in neurodegenerative diseases has yet to be defined. The current study explored the function of MerTK in the microglial uptake of alpha-synuclein fibrils which play a causative role in the pathobiology of synucleinopathies. Using human primary and induced pluripotent stem cell-derived microglia, the MerTK-dependence of alpha-synuclein fibril internalization was investigated in vitro. Relevance of this pathway in synucleinopathies was assessed through burden analysis of MERTK variants and analysis of MerTK expression in patient-derived cells and tissues. Pharmacological inhibition of MerTK and siRNA-mediated MERTK knockdown both caused a decreased rate of alpha-synuclein fibril internalization by human microglia. Consistent with the non-inflammatory nature of MerTK-mediated phagocytosis, alpha-synuclein fibril internalization was not observed to induce secretion of pro-inflammatory cytokines such as IL-6 or TNF, and downmodulated IL-1β secretion from microglia. Burden analysis in two independent patient cohorts revealed a significant association between rare functionally deleterious MERTK variants and Parkinson's disease in one of the cohorts (P = 0.002). Despite a small upregulation in MERTK mRNA expression in nigral microglia from Parkinson's disease/Lewy body dementia patients compared to those from non-neurological control donors in a single-nuclei RNA-sequencing dataset (P = 5.08 × 10-21), no significant upregulation in MerTK protein expression was observed in human cortex and substantia nigra lysates from Lewy body dementia patients compared to controls. Taken together, our findings define a novel role for MerTK in mediating the uptake of alpha-synuclein fibrils by human microglia, with possible involvement in limiting alpha-synuclein spread in synucleinopathies such as Parkinson's disease. Upregulation of this pathway in synucleinopathies could have therapeutic values in enhancing alpha-synuclein fibril clearance in the brain.

Neuroinflammatory gene expression profiles of reactive glia in the substantia nigra suggest a multidimensional immune response to alpha synuclein inclusions

Parkinson's disease (PD) pathology is characterized by alpha-synuclein (α-syn) aggregates, degeneration of dopamine neurons in the substantia nigra pars compacta (SNpc), and neuroinflammation. The presence of reactive glia correlates with deposition of pathological α-syn in early-stage PD. Thus, understanding the neuroinflammatory response of microglia and astrocytes to synucleinopathy may identify therapeutic targets. Here we characterized the neuroinflammatory gene expression profile of reactive microglia and astrocytes in the SNpc during early synucleinopathy in the rat α-syn pre-formed fibril (PFF) model. Rats received intrastriatal injection of α-syn PFFs and expression of immune genes was quantified with droplet digital PCR (ddPCR), after which fluorescent in situ hybridization (FISH) was used to localize gene expression to microglia or astrocytes in the SNpc. Genes previously associated with reactive microglia (Cd74, C1qa, Stat1, Axl, Casp1, Il18, Lyz2) and reactive astrocytes (C3, Gbp2, Serping1) were significantly upregulated in the SN of PFF injected rats. Localization of gene expression to SNpc microglia near α-syn aggregates identified a unique α-syn aggregate microglial gene expression profile characterized by upregulation of Cd74, Cxcl10, Rt-1a2, Grn, Csf1r, Tyrobp, C3, C1qa, Serping1 and Fcer1g. Importantly, significant microglial upregulation of Cd74 and C3 were only observed following injection of α-syn PFFs, not α-syn monomer, confirming specificity to α-syn aggregation. Serping1 expression also localized to astrocytes in the SNpc. Interestingly, C3 expression in the SNpc localized to microglia at 2- and 4-months post-PFF, but to astrocytes at 6-months post-PFF. We also observed expression of Rt1-a2 and Cxcl10 in SNpc dopamine neurons. Cumulatively our results identify a dynamic, yet reproducible gene expression profile of reactive microglia and astrocytes associated with early synucleinopathy in the rat SNpc.

Transcriptomic profiling of early synucleinopathy in rats induced with preformed fibrils

Examination of early phases of synucleinopathy when inclusions are present, but long before neurodegeneration occurs, is critical to both understanding disease progression and the development of disease modifying therapies. The rat alpha-synuclein (α-syn) preformed fibril (PFF) model induces synchronized synucleinopathy that recapitulates the pathological features of Parkinson's disease (PD) and can be used to study synucleinopathy progression. In this model, phosphorylated α-syn (pSyn) inclusion-containing neurons and reactive microglia (major histocompatibility complex-II immunoreactive) peak in the substantia nigra pars compacta (SNpc) months before appreciable neurodegeneration. However, it remains unclear which specific genes are driving these phenotypic changes. To identify transcriptional changes associated with early synucleinopathy, we used laser capture microdissection of the SNpc paired with RNA sequencing (RNASeq). Precision collection of the SNpc allowed for the assessment of differential transcript expression in the nigral dopamine neurons and proximal glia. Transcripts upregulated in early synucleinopathy were mainly associated with an immune response, whereas transcripts downregulated were associated with neurotransmission and the dopamine pathway. A subset of 29 transcripts associated with neurotransmission/vesicular release and the dopamine pathway were verified in a separate cohort of males and females to confirm reproducibility. Within this subset, fluorescent in situ hybridization (FISH) was used to localize decreases in the Syt1 and Slc6a3 transcripts to pSyn inclusion-containing neurons. Identification of transcriptional changes in early synucleinopathy provides insight into the molecular mechanisms driving neurodegeneration.

Comparison of Prognosis and Cognitive Function of Holistic Neurological Disease: Tochigi Neurological Disease Cohort Study

Background

While many studies focus on the prognosis of individual neurological diseases, very few comprehensively compare and analyze real-world data of these diseases.

Objective

To address this gap in knowledge, in this study, we comprehensively analyzed the real-life data of patients with neurological diseases.

Methods

We prospectively enrolled patients with neurological diseases at three hospitals from December 1, 2016 to September 30, 2020. Neurological diseases were classified into nine groups: Dementia, Cerebrovascular disease, Parkinson's and related, Functional, Spinocerebellar degeneration, Neuroimmune, Epilepsy, Muscle dystrophy disease, and Hypertension. Patients were followed up for three years, and their prognosis and evaluation of their cognitive function served as the endpoint.

Results

A total of 426 patients were finally enrolled. Both mortality and cognitive function differed among the neurological disease categories. After 3 years, mortality was highest in the Dementia (25.5%), Parkinson's and related (21.6%), and Spinocerebellar degeneration (35.3%) groups while the cognitive function of patients in these three groups was significantly lowest.

Conclusions

When the neurological diseases were holistically observed, both mortality and cognitive function of the Dementia, Parkinson's and related, and Spinocerebellar degeneration groups were significantly worse than the remaining diseases.

Ultrastructures of α-Synuclein Filaments in Synucleinopathy Brains and Experimental Models

Intracellular α-synuclein (α-syn) inclusions are a neuropathological hallmark of Lewy body disease (LBD) and multiple system atrophy (MSA), both of which are termed synucleinopathies. LBD is defined by Lewy bodies and Lewy neurites in neurons, while MSA displays glial cytoplasmic inclusions in oligodendrocytes. Pathological α-syn adopts an ordered filamentous structure with a 5-10 nm filament diameter, and this conformational change has been suggested to be involved in the disease onset and progression. Synucleinopathies also exhibit characteristic ultrastructural and biochemical properties of α-syn filaments, and α-syn strains with distinct conformations have been identified. Numerous experimental studies have supported the idea that pathological α-syn self-amplifies and spreads throughout the brain, during which processes the conformation of α-syn filaments may drive the disease specificity. In this review, we summarize the ultrastructural features and heterogeneity of α-syn filaments in the brains of patients with synucleinopathy and in experimental models of seeded α-syn aggregation.

Development and validation of an expanded antibody toolset that captures alpha-synuclein pathological diversity in Lewy body diseases

The abnormal aggregation and accumulation of alpha-synuclein (aSyn) in the brain is a defining hallmark of synucleinopathies. Various aSyn conformations and post-translationally modified forms accumulate in pathological inclusions and vary in abundance among these disorders. Relying on antibodies that have not been assessed for their ability to detect the diverse forms of aSyn may lead to inaccurate estimations of aSyn pathology in human brains or disease models. To address this challenge, we developed and characterized an expanded antibody panel that targets different sequences and post-translational modifications along the length of aSyn, and that recognizes all monomeric, oligomeric, and fibrillar aSyn conformations. Next, we profiled aSyn pathology across sporadic and familial Lewy body diseases (LBDs) and reveal heterogeneous forms of aSyn pathology, rich in Serine 129 phosphorylation, Tyrosine 39 nitration and N- and C-terminal tyrosine phosphorylations, scattered both to neurons and glia. In addition, we show that aSyn can become hyperphosphorylated during processes of aggregation and inclusion maturation in neuronal and animal models of aSyn seeding and spreading. The validation pipeline we describe for these antibodies paves the way for systematic investigations into aSyn pathological diversity in the human brain, peripheral tissues, as well as in cellular and animal models of synucleinopathies.

Photo-oxygenation of histidine residue inhibits α-synuclein aggregation

Aggregation of α-synuclein (α-syn) into amyloid is the pathological hallmark of several neurodegenerative disorders, including Parkinson disease, dementia with Lewy bodies, and multiple system atrophy. It is widely accepted that α-syn aggregation is associated with neurodegeneration, although the mechanisms are not yet fully understood. Therefore, the inhibition of α-syn aggregation is a potential therapeutic approach against these diseases. This study used the photocatalyst for α-syn photo-oxygenation, which selectively adds oxygen atoms to fibrils. Our findings demonstrate that photo-oxygenation using this photocatalyst successfully inhibits α-syn aggregation, particularly by reducing its seeding ability. Notably, we also discovered that photo-oxygenation of the histidine at the 50th residue in α-syn aggregates is responsible for the inhibitory effect. These findings indicate that photo-oxygenation of the histidine residue in α-syn is a potential therapeutic strategy for synucleinopathies.

USP19 deubiquitinase inactivation regulates α-synuclein ubiquitination and inhibits accumulation of Lewy body-like aggregates in mice

The USP19 deubiquitinase is found in a locus associated with Parkinson's Disease (PD), interacts with chaperonins, and promotes secretion of α-synuclein (α-syn) through the misfolding-associated protein secretion (MAPS) pathway. Since these processes might modulate the processing of α-syn aggregates in PD, we inactivated USP19 (KO) in mice expressing the A53T mutation of α-syn and in whom α-syn preformed fibrils (PFF) had been injected in the striatum. Compared to WT, KO brains showed decreased accumulation of phospho-synuclein (pSyn) positive aggregates. This improvement was associated with less activation of microglia and improved performance in a tail-suspension test. Exposure of primary neurons from WT and KO mice to PFF in vitro also led to decreased accumulation of pSyn aggregates. KO did not affect uptake of PFF nor propagation of aggregates in the cultured neurons. We conclude that USP19 instead modulates intracellular dynamics of aggregates. At an early time following PFF injection when the number of pSyn-positive neurons were similar in WT and KO brains, the KO neurons contained less aggregates. KO brain aggregates stained more intensely with anti-ubiquitin antibodies. Immunoprecipitation of soluble proteins from WT and KO brains with antibodies to pSyn showed higher levels of ubiquitinated oligomeric species in the KO samples. We propose that the improved pathology in USP19 KO brains may arise from decreased formation or enhanced clearance of the more ubiquitinated aggregates and/or enhanced disassembly towards more soluble oligomeric species. USP19 inhibition may represent a novel therapeutic approach that targets the intracellular dynamics of α-syn complexes.

Experimental models of gut-first Parkinson's disease: A systematic review

BACKGROUND

There is strong support from studies in humans and in animal models that Parkinson's disease (PD) may begin in the gut. This brings about a unique opportunity for researchers in the field of neurogastroenterology to contribute to advancing the field and making contributions that could lead to the ability to diagnose and treat PD in the premotor stages. Lack of familiarity with some of the aspects of the experimental approaches used in these studies may present a barrier for neurogastroenterology researchers to enter the field. Much remains to be understood about intestinal-specific components of gut-first PD pathogenesis and the field would benefit from contributions of enteric and central nervous system neuroscientists.

PURPOSE

To address these issues, we have conducted a systematic review of the two most frequently used experimental models of gut-first PD: transneuronal propagation of α-synuclein preformed fibrils and oral exposure to environmental toxins. We have reviewed the details of these studies and present methodological considerations for the use of these models. Our aim is that this review will serve as a framework and useful reference for neuroscientists, gastroenterologists, and neurologists interested in applying their expertise to advancing our understanding of gut-first PD.

Phosphorylation of α-synuclein at T64 results in distinct oligomers and exerts toxicity in models of Parkinson's disease

α-Synuclein accumulates in Lewy bodies, and this accumulation is a pathological hallmark of Parkinson's disease (PD). Previous studies have indicated a causal role of α-synuclein in the pathogenesis of PD. However, the molecular and cellular mechanisms of α-synuclein toxicity remain elusive. Here, we describe a novel phosphorylation site of α-synuclein at T64 and the detailed characteristics of this post-translational modification. T64 phosphorylation was enhanced in both PD models and human PD brains. T64D phosphomimetic mutation led to distinct oligomer formation, and the structure of the oligomer was similar to that of α-synuclein oligomer with A53T mutation. Such phosphomimetic mutation induced mitochondrial dysfunction, lysosomal disorder, and cell death in cells and neurodegeneration in vivo, indicating a pathogenic role of α-synuclein phosphorylation at T64 in PD.

α-Synuclein Conformational Strains as Drivers of Phenotypic Heterogeneity in Neurodegenerative Diseases

The synucleinopathies, which include Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy, are a class of human neurodegenerative disorders unified by the presence of α-synuclein aggregates in the brain. Considerable clinical and pathological heterogeneity exists within and among the individual synucleinopathies. A potential explanation for this variability is the existence of distinct conformational strains of α-synuclein aggregates that cause different disease manifestations. Like prion strains, α-synuclein strains can be delineated based on their structural architecture, with structural differences among α-synuclein aggregates leading to unique biochemical attributes and neuropathological properties in humans and animal models. Bolstered by recent high-resolution structural data from patient brain-derived material, it has now been firmly established that there are conformational differences among α-synuclein aggregates from different human synucleinopathies. Moreover, recombinant α-synuclein can be polymerized into several structurally distinct aggregates that exhibit unique pathological properties. In this review, we outline the evidence supporting the existence of α-synuclein strains and highlight how they can act as drivers of phenotypic heterogeneity in the human synucleinopathies.

α-synuclein build-up is alleviated via ESCRT-dependent endosomal degradation brought about by p38MAPK inhibition in cells expressing p25α

α-synucleinopathy is driven by an imbalance of synthesis and degradation of α-synuclein (αSyn), causing a build up of αSyn aggregates and post-translationally modified species, which not only interfere with normal cellular metabolism but also by their secretion propagates the disease. Therefore, a better understanding of αSyn degradation pathways is needed to address α-synucleinopathy. Here, we used the nerve growth factor–differentiated catecholaminergic PC12 neuronal cell line, which was conferred α-synucleinopathy by inducible expression of αSyn and tubulin polymerization-promoting protein p25α. p25α aggregates αSyn, and imposes a partial autophagosome–lysosome block to mimic aspects of lysosomal deficiency common in neurodegenerative disease. Under basal conditions, αSyn was degraded by multiple pathways but most prominently by macroautophagy and Nedd4/Ndfip1-mediated degradation. We found that expression of p25α induced strong p38MAPK activity. Remarkably, when opposed by inhibitor SB203580 or p38MAPK shRNA knockdown, endolysosomal localization and degradation of αSyn increased, and αSyn secretion and cytotoxicity decreased. This effect was specifically dependent on Hsc70 and the endosomal sorting complex required for transport machinery, but different from classical microautophagy, as the αSyn Hsc70 binding motif was unnecessary. Furthermore, in a primary neuronal (h)-αSyn seeding model, p38MAPK inhibition decreased pathological accumulation of phosphorylated serine-129-αSyn and cytotoxicity. In conclusion, p38MAPK inhibition shifts αSyn degradation from various forms of autophagy to an endosomal sorting complex required for transport–dependent uptake mechanism, resulting in increased αSyn turnover and cell viability in p25α-expressing cells. More generally, our results suggest that under conditions of autophagolysosomal malfunction, the uninterrupted endosomal pathway offers a possibility to achieve disease-associated protein degradation.

Direct Demonstration of Seed Size-Dependent α-Synuclein Amyloid Amplification

The size of amyloid seeds is known to modulate their autocatalytic amplification and cellular toxicity. However, the seed size-dependent secondary nucleation mechanism, toxicity, and disease-associated biological processes mediated by α-synuclein (α-Syn) fibrils are largely unknown. Using the cellular model and in vitro reconstitution, we showed that the size of α-Syn fibril seeds dictates not only their cellular internalization and associated cell death but also the distinct mechanisms of fibril amplification pathways involved in the pathological conformational change of α-Syn. Specifically, small fibril seeds showed elongation possibly through monomer addition at the fibril termini, whereas longer fibrils template the fibril amplification by surface-mediated nucleation as demonstrated by super-resolution microscopy. The distinct mechanism of fibril amplification and cellular uptake along with toxicity suggest that breakage of fibrils into seeds of different sizes determines the underlying pathological outcome of synucleinopathies.

Quantum-dot-labeled synuclein seed assay identifies drugs modulating the experimental prion-like transmission

Synucleinopathies are neurodegenerative disorders including Parkinson disease (PD), dementia with Lewy body (DLB), and multiple system atrophy (MSA) that involve deposits of the protein alpha-synuclein (α-syn) in the brain. The inoculation of α-syn aggregates derived from synucleinopathy or preformed fibrils (PFF) formed in vitro induces misfolding and deposition of endogenous α-syn. This is referred to as prion-like transmission, and the mechanism is still unknown. In this study, we label α-syn PFF with quantum dots and visualize their movement directly in acute slices of brain tissue inoculated with α-syn PFF seeds. Using this system, we find that the trafficking of α-syn seeds is dependent on fast axonal transport and the seed spreading is dependent on endocytosis and neuronal activity. We also observe pharmacological effects on α-syn seed spreading; clinically available drugs including riluzole are effective in reducing the spread of α-syn seeds and this effect is also observed in vivo. Our quantum-dot-labeled α-syn seed assay system combined with in vivo transmission experiment reveals an early phase of transmission, in which uptake and spreading of seeds occur depending on neuronal activity, and a later phase, in which seeds induce the propagation of endogenous misfolded α-syn.

Analysis of hemisphere-dependent effects of unilateral intrastriatal injection of α-synuclein pre-formed fibrils on mitochondrial protein levels, dynamics, and function

Genetic and neuropathological evidence strongly implicates aberrant forms of α-synuclein in neurodegeneration. Antibodies specific for α-synuclein phosphorylated at serine 129 (pS129) are selective for the pathological protein aggregates that are characteristic of Parkinson's disease (PD) and other synucleinopathies, such as dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Although the etiology of most synucleinopathies remains uncertain, a large body of evidence points to mitochondrial dysfunction. The recent development of animal models based on intracranial injection of α-synuclein pre-formed fibrils (PFFs) has provided a valuable experimental system in which to study the spread and neurotoxicity of α-synuclein aggregates, yet the effects of PFF-induced protein aggregates on mitochondrial function and dynamics have not been rigorously examined in vivo. To help fill this knowledge gap, we injected the striatum of mice unilaterally with well-characterized small length (< 30 nm) PFFs or monomeric α-synuclein control and measured the distribution and extent of pS129 α-synuclein-immunoreactive aggregates, the loss of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra, the abundance of mitochondrial proteins, and the activity of mitochondrial respiratory chain components at 3 months and 6 months post injection. Intrastriatal injection of small length PFFs, but not monomeric α-synuclein control, induced robust pS129 α-synuclein immunoreactive inclusions in the cortex, ventral midbrain, and striatum, as well as in rarely reported brain regions, such as the hippocampus, as early as 3 months post injection. Significant loss of nigral tyrosine hydroxylase-immunoreactive neurons was observed in the PFF-injected hemisphere at 3 months and 6 months post injection. The unilateral striatal injection of small length PFFs also caused hemisphere-dependent and treatment-dependent changes in the cortical levels of mitochondrial proteins such as VDAC1, COX-IV, and DRP-1, as well as functional changes in mitochondrial complex I activity in the contralateral striatum. Together, these data demonstrate that intrastriatal injection of mice with small length PFFs induces extensive bilateral protein aggregates, significant unilateral nigral cell loss, and altered contralateral levels of mitochondrial proteins and respiratory chain activity. Our data suggest this animal model may be useful for studying the role of mitochondrial dysfunction in α-synucleinopathies, for studying the hemisphere-dependent effects of α-synuclein aggregates, and for testing neuroprotective therapies that target mitochondrial dysfunction and protein aggregation.

Comparative Analysis of the Relative Fragmentation Stabilities of Polymorphic Alpha-Synuclein Amyloid Fibrils

The division of amyloid fibril particles through fragmentation is implicated in the progression of human neurodegenerative disorders such as Parkinson's disease. Fragmentation of amyloid fibrils plays a crucial role in the propagation of the amyloid state encoded in their three-dimensional structures and may have an important role in the spreading of potentially pathological properties and phenotypes in amyloid-associated diseases. However, despite the mechanistic importance of fibril fragmentation, the relative stabilities of different types or different polymorphs of amyloid fibrils toward fragmentation remain to be quantified. We have previously developed an approach to compare the relative stabilities of different types of amyloid fibrils toward fragmentation. In this study, we show that controlled sonication, a widely used method of mechanical perturbation for amyloid seed generation, can be used as a form of mechanical perturbation for rapid comparative assessment of the relative fragmentation stabilities of different amyloid fibril structures. This approach is applied to assess the relative fragmentation stabilities of amyloid formed in vitro from wild type (WT) α-synuclein and two familial mutant variants of α-synuclein (A30P and A53T) that generate morphologically different fibril structures. Our results demonstrate that the fibril fragmentation stabilities of these different α-synuclein fibril polymorphs are all highly length dependent but distinct, with both A30P and A53T α-synuclein fibrils displaying increased resistance towards sonication-induced fibril fragmentation compared with WT α-synuclein fibrils. These conclusions show that fragmentation stabilities of different amyloid fibril polymorph structures can be diverse and suggest that the approach we report here will be useful in comparing the relative stabilities of amyloid fibril types or fibril polymorphs toward fragmentation under different biological conditions.

Spreading of Aggregated α-Synuclein in Sagittal Organotypic Mouse Brain Slices

The accumulation of α-synuclein (α-syn) in the brain plays a role in synucleinopathies and it is hypothesized to spread in a prion-like fashion between connected brain regions. In the present study, we aim to investigate this spreading in well-characterized sagittal organotypic whole brain slices taken from postnatal wild type (WT) and transgenic mice overexpressing human α-syn under the promoter of proteolipid protein (PLP). Collagen hydrogels were loaded with monomers of human α-syn, as well as human and mouse pre-formed fibrils (PFFs), to allow local application and slow release. The spreading of α-syn was evaluated in different brain regions by immunohistochemistry for total α-syn and α-syn phosphorylated at the serine129 position (α-syn-P). The application of human and mouse PFFs of α-syn caused the aggregation and spreading of α-syn-P in the brain slices, which was pronounced the most at the region of hydrogel application and surrounding striatum, as well as along the median forebrain bundle. The organotypic slices from transgenic mice showed significantly more α-syn pathology than those from WT mice. The present study demonstrates that seeding with α-syn PFFs but not monomers induced intracellular α-syn pathology, which was significantly more prominent in brain slices with α-syn overexpression. This is consistent with the prion-like spreading theory of α-syn aggregates. The sagittal whole brain slices characterized in this study carry the potential to be used as a novel model to study α-syn pathology.

Intermediates of α-synuclein aggregation: Implications in Parkinson's disease pathogenesis

Cytoplasmic deposition of aberrantly misfolded α-synuclein (α-Syn) is a common feature of synucleinopathies, including Parkinson's disease (PD). However, the precise pathogenic mechanism of α-Syn in synucleinopathies remains elusive. Emerging evidence has suggested that α-Syn may contribute to PD pathogenesis in several ways; wherein the contribution of fibrillar species, for exerting toxicity and disease transmission, cannot be neglected. Further, the oligomeric species could be the most plausible neurotoxic species causing neuronal cell death. However, understanding the structural and molecular insights of these oligomers are very challenging due to the heterogeneity and transient nature of the species. In this review, we discuss the recent advancements in understanding the formation and role of α-Syn oligomers in PD pathogenesis. We also summarize the different types of α-Syn oligomeric species and potential mechanisms to exert neurotoxicity. Finally, we address the possible ways to target α-Syn as a promising approach against PD and the possible future directions.

N-Methyl-D-aspartate (NMDA) and cannabinoid CB2 receptors form functional complexes in cells of the central nervous system: insights into the therapeutic potential of neuronal and microglial NMDA receptors

BACKGROUND

The cannabinoid CB2 receptor (CB2R), which is a target to afford neuroprotection, and N-methyl-D-aspartate (NMDA) ionotropic glutamate receptors, which are key in mediating excitatory neurotransmission, are expressed in both neurons and glia. As NMDA receptors are the target of current medication in Alzheimer's disease patients and with the aim of finding neuromodulators of their actions that could provide benefits in dementia, we hypothesized that cannabinoids could modulate NMDA function.

METHODS

Immunocytochemistry was used to analyze the colocalization between CB2 and NMDA receptors; bioluminescence resonance energy transfer was used to detect CB2-NMDA receptor complexes. Calcium and cAMP determination, mitogen-activated protein kinase (MAPK) pathway activation, and label-free assays were performed to characterize signaling in homologous and heterologous systems. Proximity ligation assays were used to quantify CB2-NMDA heteromer expression in mouse primary cultures and in the brain of APPSw/Ind transgenic mice, an Alzheimer's disease model expressing the Indiana and Swedish mutated version of the human amyloid precursor protein (APP).

RESULTS

In a heterologous system, we identified CB2-NMDA complexes with a particular heteromer print consisting of impairment by cannabinoids of NMDA receptor function. The print was detected in activated primary microglia treated with lipopolysaccharide and interferon-γ. CB2R activation blunted NMDA receptor-mediated signaling in primary hippocampal neurons from APPSw/Ind mice. Furthermore, imaging studies showed that in brain slices and in primary cells (microglia or neurons) from APPSw/Ind mice, there was a marked overexpression of macromolecular CB2-NMDA receptor complexes thus becoming a tool to modulate excessive glutamate input by cannabinoids.

CONCLUSIONS

The results indicate a negative cross-talk in CB2-NMDA complexes signaling. The expression of the CB2-NMDA receptor heteromers increases in both microglia and neurons from the APPSw/Ind transgenic mice, compared with levels in samples from age-matched control mice.

Alpha-Synuclein and the Endolysosomal System in Parkinson's Disease: Guilty by Association

Abnormal accumulation of the protein α- synuclein (α-syn) into proteinaceous inclusions called Lewy bodies (LB) is the neuropathological hallmark of Parkinson's disease (PD) and related disorders. Interestingly, a growing body of evidence suggests that LB are also composed of other cellular components such as cellular membrane fragments and vesicular structures, suggesting that dysfunction of the endolysosomal system might also play a role in LB formation and neuronal degeneration. Yet the link between α-syn aggregation and the endolysosomal system disruption is not fully elucidated. In this review, we discuss the potential interaction between α-syn and the endolysosomal system and its impact on PD pathogenesis. We propose that the accumulation of monomeric and aggregated α-syn disrupt vesicles trafficking, docking, and recycling, leading to the impairment of the endolysosomal system, notably the autophagy-lysosomal degradation pathway. Reciprocally, PD-linked mutations in key endosomal/lysosomal machinery genes (LRRK2, GBA, ATP13A2) also contribute to increasing α-syn aggregation and LB formation. Altogether, these observations suggest a potential synergistic role of α-syn and the endolysosomal system in PD pathogenesis and represent a viable target for the development of disease-modifying treatment for PD and related disorders.

A Summary of Phenotypes Observed in the In Vivo Rodent Alpha-Synuclein Preformed Fibril Model

The use of wildtype recombinant alpha-synuclein preformed fibrils (aSyn PFFs) to induce endogenous alpha-synuclein to form pathological phosphorylation and trigger neurodegeneration is a popular model for studying Parkinson's disease (PD) biology and testing therapeutic strategies. The strengths of this model lie in its ability to recapitulate the phosphorylation/aggregation of aSyn and nigrostriatal degeneration seen in PD, as well as its suitability for studying the progressive nature of PD and the spread of aSyn pathology. Although the model is commonly used and has been adopted by many labs, variability in observed phenotypes exists. Here we provide summaries of the study design and reported phenotypes from published reports characterizing the aSyn PFF in vivo model in rodents following injection into the brain, gut, muscle, vein, peritoneum, and eye. These summaries are designed to facilitate an introduction to the use of aSyn PFFs to generate a rodent model of PD-highlighting phenotypes observed in papers that set out to thoroughly characterize the model. This information will hopefully improve the understanding of this model and clarify when the aSyn PFF model may be an appropriate choice for one's research.

Illuminating amyloid fibrils: Fluorescence-based single-molecule approaches

The aggregation of proteins into insoluble filamentous amyloid fibrils is a pathological hallmark of neurodegenerative diseases that include Parkinson's disease and Alzheimer's disease. Since the identification of amyloid fibrils and their association with disease, there has been much work to describe the process by which fibrils form and interact with other proteins. However, due to the dynamic nature of fibril formation and the transient and heterogeneous nature of the intermediates produced, it can be challenging to examine these processes using techniques that rely on traditional ensemble-based measurements. Single-molecule approaches overcome these limitations as rare and short-lived species within a population can be individually studied. Fluorescence-based single-molecule methods have proven to be particularly useful for the study of amyloid fibril formation. In this review, we discuss the use of different experimental single-molecule fluorescence microscopy approaches to study amyloid fibrils and their interaction with other proteins, in particular molecular chaperones. We highlight the mechanistic insights these single-molecule techniques have already provided in our understanding of how fibrils form, and comment on their potential future use in studying amyloid fibrils and their intermediates.

Mechanistic basis for receptor-mediated pathological α-synuclein fibril cell-to-cell transmission in Parkinson's disease

The spread of pathological α-synuclein (α-syn) is a crucial event in the progression of Parkinson's disease (PD). Cell surface receptors such as lymphocyte activation gene 3 (LAG3) and amyloid precursor-like protein 1 (APLP1) can preferentially bind α-syn in the amyloid over monomeric state to initiate cell-to-cell transmission. However, the molecular mechanism underlying this selective binding is unknown. Here, we perform an array of biophysical experiments and reveal that LAG3 D1 and APLP1 E1 domains commonly use an alkaline surface to bind the acidic C terminus, especially residues 118 to 140, of α-syn. The formation of amyloid fibrils not only can disrupt the intramolecular interactions between the C terminus and the amyloid-forming core of α-syn but can also condense the C terminus on fibril surface, which remarkably increase the binding affinity of α-syn to the receptors. Based on this mechanism, we find that phosphorylation at serine 129 (pS129), a hallmark modification of pathological α-syn, can further enhance the interaction between α-syn fibrils and the receptors. This finding is further confirmed by the higher efficiency of pS129 fibrils in cellular internalization, seeding, and inducing PD-like α-syn pathology in transgenic mice. Our work illuminates the mechanistic understanding on the spread of pathological α-syn and provides structural information for therapeutic targeting on the interaction of α-syn fibrils and receptors as a potential treatment for PD.

Differential seeding and propagating efficiency of α-synuclein strains generated in different conditions

BACKGROUND

Accumulation of alpha-synuclein (α-syn) is a main pathological hallmark of Parkinson's and related diseases, which are collectively known as synucleinopathies. Growing evidence has supported that the same protein can induce remarkably distinct pathological progresses and disease phenotypes, suggesting the existence of strain difference among α-syn fibrils. Previous studies have shown that α-syn pathology can propagate from the peripheral nervous system (PNS) to the central nervous system (CNS) in a "prion-like" manner. However, the difference of the propagation potency from the periphery to CNS among different α-syn strains remains unknown and the effect of different generation processes of these strains on the potency of seeding and propagation remains to be revealed in more detail.

METHODS

Three strains of preformed α-syn fibrils (PFFs) were generated in different buffer conditions which varied in pH and ionic concentrations. The α-syn PFFs were intramuscularly (IM) injected into a novel bacterial artificial chromosome (BAC) transgenic mouse line that expresses wild-type human α-syn, and the efficiency of seeding and propagation of these PFFs from the PNS to the CNS was evaluated.

RESULTS

The three strains of α-syn PFFs triggered distinct propagation patterns. The fibrils generated in mildly acidic buffer led to the most severe α-syn pathology, degeneration of motor neurons and microgliosis in the spinal cord.

CONCLUSIONS

The different α-syn conformers generated in different conditions exhibited strain-specific pathology and propagation patterns from the periphery to the CNS, which further supports the view that α-syn strains may be responsible for the heterogeneity of pathological features and disease progresses among synucleinopathies.

Preformed fibrils generated from mouse alpha-synuclein produce more inclusion pathology in rats than fibrils generated from rat alpha-synuclein

BACKGROUND

Alpha-synuclein (α-syn) preformed fibril (PFF)-induced pathology can be used to study the features and progression of synucleinopathies, such as Parkinson's disease. Intrastriatal injection of mouse α-syn PFFs produce accumulation of α-syn pathology in both mice and rats. Previous studies in mice have revealed that greater sequence homology between the α-syn amino acid sequence used to produce PFFs with that of the endogenous host α-syn increases α-syn pathology in vivo.

NEW METHODS

Based on the prediction that greater sequence homology will result in more α-syn pathology, PFFs generated from recombinant rat α-syn (rPFFs) were used instead of PFFs produced from recombinant mouse α-syn (mPFFs), which are normally used in the model. Rats received unilateral intrastriatal injections of either rPFFs or mPFFs and accumulation of α-syn phosphorylated at serine 129 (pSyn) was examined at 1-month post-surgery.

RESULTS

Rats injected with mPFFs exhibited abundant accumulation of α-syn inclusions in the substantia nigra and cortical regions, whereas in rats injected with rPFFs had significantly fewer SNpc neurons containing pSyn inclusions (≈60% fewer) and little, if any, pSyn inclusions were observed in the cortex.

CONCLUSIONS

Our results suggest that additional factors beyond the degree of sequence homology between host α-syn and injected recombinant α-syn impact efficiency of seeding and subsequent inclusion formation. More practically, these findings caution against the use of rPFFs in the rat preformed fibril model.

Human tauopathy-derived tau strains determine the substrates recruited for templated amplification

Tauopathies are a subset of neurodegenerative diseases characterized by abnormal tau inclusions. Specifically, three-repeat tau and four-repeat tau in Alzheimer’s disease, three-repeat tau in Pick’s disease (PiD) and four-repeat tau in progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) form amyloid-like fibrous structures that accumulate in neurons and/or glial cells. Amplification and cell-to-cell transmission of abnormal tau based on the prion hypothesis are believed to explain the onset and progression of tauopathies. Recent studies support not only the self-propagation of abnormal tau, but also the presence of conformationally distinct tau aggregates, namely tau strains. Cryogenic electron microscopy analyses of patient-derived tau filaments have revealed disease-specific ordered tau structures. However, it remains unclear whether the ultrastructural and biochemical properties of tau strains are inherited during the amplification of abnormal tau in the brain. In this study, we investigated template-dependent amplification of tau aggregates using a cellular model of seeded aggregation. Tau strains extracted from human tauopathies caused strain-dependent accumulation of insoluble filamentous tau in SH-SY5Y cells. The seeding activity towards full-length four-repeat tau substrate was highest in CBD-tau seeds, followed by PSP-tau and Alzheimer’s disease (AD)-tau seeds, while AD-tau seeds showed higher seeding activity than PiD-tau seeds towards three-repeat tau substrate. Abnormal tau amplified in cells inherited the ultrastructural and biochemical properties of the original seeds. These results strongly suggest that the structural differences of patient-derived tau strains underlie the diversity of tauopathies, and that seeded aggregation and filament formation mimicking the pathogenesis of sporadic tauopathy can be reproduced in cultured cells. Our results indicate that the disease-specific conformation of tau aggregates determines the tau isoform substrate that is recruited for templated amplification, and also influences the prion-like seeding activity.

Seeded assembly in vitro does not replicate the structures of α-synuclein filaments from multiple system atrophy

The propagation of conformational strains by templated seeding is central to the prion concept. Seeded assembly of α‐synuclein into filaments is believed to underlie the prion‐like spreading of protein inclusions in a number of human neurodegenerative diseases, including Parkinson's disease, dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). We previously determined the atomic structures of α‐synuclein filaments from the putamen of five individuals with MSA. Here, we used filament preparations from three of these brains for the in vitro seeded assembly of recombinant human α‐synuclein. We find that the structures of the seeded assemblies differ from those of the seeds, suggesting that additional, as yet unknown, factors play a role in the propagation of the seeds. Identification of these factors will be essential for understanding the prion‐like spreading of α‐synuclein proteinopathies.

Reverse engineering Lewy bodies: how far have we come and how far can we go?

Lewy bodies (LBs) are α-synuclein (α-syn)-rich intracellular inclusions that are an important pathological hallmark of Parkinson disease and several other neurodegenerative diseases. Increasing evidence suggests that the aggregation of α-syn has a central role in LB formation and is one of the key processes that drive neurodegeneration and pathology progression in Parkinson disease. However, little is known about the mechanisms underlying the formation of LBs, their biochemical composition and ultrastructural properties, how they evolve and spread with disease progression, and their role in neurodegeneration. In this Review, we discuss current knowledge of α-syn pathology, including the biochemical, structural and morphological features of LBs observed in different brain regions. We also review the most used cellular and animal models of α-syn aggregation and pathology spreading in relation to the extent to which they reproduce key features of authentic LBs. Finally, we provide important insights into molecular and cellular determinants of LB formation and spreading, and highlight the critical need for more detailed and systematic characterization of α-syn pathology, at both the biochemical and structural levels. This would advance our understanding of Parkinson disease and other neurodegenerative diseases and allow the development of more-reliable disease models and novel effective therapeutic strategies.

Electron Microscopic Analysis of α-Synuclein Fibrils

α-Synuclein (α-syn) is a major component of abnormal protein deposits observed in the brains of patients with synucleinopathies, including Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy (MSA). The synaptic protein α-syn is water-soluble under normal physiological conditions, but in these patients' brains, we see accumulation of insoluble amyloid-like α-syn fibrils with prion-like properties. Intracerebral accumulation of these fibrils is correlated with disease onset and progression. Recombinant α-syn protein also forms amyloid-like fibrils that are structurally akin to those extracted from patients' brains. Recent cryo-electron microscopic studies have identified the core structures of synthetic α-syn fibrils and α-syn fibrils extracted from the brains of patients with MSA at the atomic level. In this chapter, we describe negative staining and immunoelectron microscopy protocols for ultrastructural characterization of synthetic α-syn fibrils and pathological α-syn fibrils.

Identification and Evaluation of Bisquinoline Scaffold as a New Candidate for α-Synuclein-PET Imaging

α-Synuclein (α-syn) aggregates are pathologically associated with the hallmarks found in brains affected by synucleinopathies such as Parkinson's disease (PD) and multiple system atrophy (MSA). Therefore, the in vivo detection of α-syn aggregates using radiolabeled probes is useful for the comprehension of and medical intervention for synucleinopathies. In the present study, we identified a bisquinoline scaffold as a new promising structure for targeting α-syn aggregates by a screening assay. Then, based on the scaffold, novel bisquinoline derivatives, BQ1 and BQ2, were designed and synthesized, and we evaluated their utilities as α-syn imaging probes. Both compounds showed high affinity for recombinant α-syn aggregates in binding assays in vitro and clearly detected α-syn aggregates in human brain sections. BQ2 showed higher affinity for α-syn aggregates than BQ1, leading to performing ¹⁸F-labeling to obtain [¹⁸F]BQ2. In a biodistribution study using normal mice, [¹⁸F]BQ2 displayed moderate uptake (1.59% ID/g at 2 min postinjection) into but subsequent retention (1.35% ID/g at 60 min postinjection) in the brain. The results of this study suggest that a bisquinoline derivative may be a new candidate as an α-syn-PET imaging probe after appropriate structure modification for further improvement in the pharmacokinetics.

Structures of α-synuclein filaments from multiple system atrophy

Synucleinopathies, which include multiple system atrophy (MSA), Parkinson's disease, Parkinson's disease with dementia and dementia with Lewy bodies (DLB), are human neurodegenerative diseases1. Existing treatments are at best symptomatic. These diseases are characterized by the presence of, and believed to be caused by the formation of, filamentous inclusions of α-synuclein in brain cells2,3. However, the structures of α-synuclein filaments from the human brain are unknown. Here, using cryo-electron microscopy, we show that α-synuclein inclusions from the brains of individuals with MSA are made of two types of filament, each of which consists of two different protofilaments. In each type of filament, non-proteinaceous molecules are present at the interface of the two protofilaments. Using two-dimensional class averaging, we show that α-synuclein filaments from the brains of individuals with MSA differ from those of individuals with DLB, which suggests that distinct conformers or strains characterize specific synucleinopathies. As is the case with tau assemblies4-9, the structures of α-synuclein filaments extracted from the brains of individuals with MSA differ from those formed in vitro using recombinant proteins, which has implications for understanding the mechanisms of aggregate propagation and neurodegeneration in the human brain. These findings have diagnostic and potential therapeutic relevance, especially because of the unmet clinical need to be able to image filamentous α-synuclein inclusions in the human brain.

Copper and iron ions accelerate the prion-like propagation of α-synuclein: A vicious cycle in Parkinson's disease

Protein fibrils drive the onset and progression of many diseases in a prion-like manner, i.e. they transcellular propagate through the extracellular space to health cells to initiate toxic aggregation as seeds. The conversion of native α-synuclein into filamentous aggregates in Lewy bodies is a hallmark of Parkinson's disease (PD). Copper and iron ions accumulate in PD brains, however, whether they influence the prion-like propagation of α-synuclein remain unclear. Here, we reported that copper/iron ions accelerate prion-like propagation of α-synuclein fibrils by promoting cellular internalization of α-synuclein fibrils, intracellular α-synuclein aggregation and the subsequent release of mature fibrils to the extracellular space to induce further propagation. Mechanistically, copper/iron ions enhanced α-synuclein fibrils internalization was mediated by negatively charged membrane heparan sulfate proteoglycans (HSPGs). α-Synuclein fibrils formed in the presence of copper/iron ions were more cytotoxic, causing increased ROS production, cell apoptosis, and shortened the lifespan of a C. elegans PD model overexpressing human α-synuclein. Notably, these deleterious effects were ameliorated by two clinically used chelators, triethylenetetramine and deferiprone. Together, our results suggest a new role for heavy metal ions, e.g. copper and iron, in the pathogenesis of PD through accelerating prion-like propagation of α-synuclein fibrils.

Developmental exposure to the organochlorine pesticide dieldrin causes male-specific exacerbation of α-synuclein-preformed fibril-induced toxicity and motor deficits

Human and animal studies have shown that exposure to the organochlorine pesticide dieldrin is associated with increased risk of Parkinson's disease (PD). Previous work showed that developmental dieldrin exposure increased neuronal susceptibility to MPTP toxicity in male C57BL/6 mice, possibly via changes in dopamine (DA) packaging and turnover. However, the relevance of the MPTP model to PD pathophysiology has been questioned. We therefore studied dieldrin-induced neurotoxicity in the α-synuclein (α-syn)-preformed fibril (PFF) model, which better reflects the α-syn pathology and toxicity observed in PD pathogenesis. Specifically, we used a "two-hit" model to determine whether developmental dieldrin exposure increases susceptibility to α-syn PFF-induced synucleinopathy. Dams were fed either dieldrin (0.3 mg/kg, every 3-4 days) or vehicle corn oil starting 1 month prior to breeding and continuing through weaning of pups at postnatal day 22. At 12 weeks of age, male and female offspring received intrastriatal α-syn PFF or control saline injections. Consistent with the male-specific increased susceptibility to MPTP, our results demonstrate that developmental dieldrin exposure exacerbates PFF-induced toxicity in male mice only. Specifically, in male offspring, dieldrin exacerbated PFF-induced motor deficits on the challenging beam and increased DA turnover in the striatum 6 months after PFF injection. However, male offspring showed neither exacerbation of phosphorylated α-syn aggregation (pSyn) in the substantia nigra (SN) at 1 or 2 months post-PFF injection, nor exacerbation of PFF-induced TH and NeuN loss in the SN 6 months post-PFF injection. Collectively, these data indicate that developmental dieldrin exposure produces a male-specific exacerbation of synucleinopathy-induced behavioral and biochemical deficits. This sex-specific result is consistent with both previous work in the MPTP model, our previously reported sex-specific effects of this exposure paradigm on the male and female epigenome, and the higher prevalence and more severe course of PD in males. The novel two-hit environmental toxicant/PFF exposure paradigm established in this project can be used to explore the mechanisms by which other PD-related exposures alter neuronal vulnerability to synucleinopathy in sporadic PD.

Pathogenic Mutations Differentially Regulate Cell-to-Cell Transmission of α-Synuclein

Recent studies suggest that the cell-to-cell spread of pathological α-synuclein (α-syn) plays important roles in the development of Parkinson's disease (PD). PD patients who carry α-syn gene mutations often have an earlier onset and more severe clinical symptoms and pathology than sporadic PD cases who carry the wild-type (WT) α-syn gene. However, the molecular mechanism by which α-syn gene mutations promote PD remains unclear. Here, we hypothesized that pathogenic mutations facilitate the intercellular transfer and cytotoxicity of α-syn, favoring an early disease onset and faster progression. We investigated the effects of eight known pathogenic mutations in human α-syn (A18T, A29S, A30P, E46K, H50Q, G51D, A53E, and A53T) on its pathological transmission in terms of secretion, aggregation, intracellular level, cytotoxicity, seeding, and induction of neuroinflammation in SH-SY5Y neuroblastoma cells, cultured rat neurons, and microglia, and the rat substantia nigra pars compacta. We found that 2 of the 8 mutations (H50Q and A53T) significantly increased α-syn secretion while 6 mutations (A18T, A29S, A30P, G51D, A53E, and E46K) tended to enhance it. In vitroα-syn aggregation experiments showed that H50Q promoted while G51D delayed aggregation most strongly. Interestingly, 3 mutations (E46K, H50Q, and G51D) greatly increased the intracellular α-syn level when cultured cells were treated with preformed α-syn fibrils (PFFs) compared with the WT, while the other 5 had no effect. We also demonstrated that H50Q, G51D, and A53T PFFs, but not E46K PFFs, efficiently seeded in vivo and acutely induced neuroinflammation in rat substantia nigra pars compacta. Our data indicate that pathogenic mutations augment the prion-like spread of α-syn at different steps and blockade of this pathogenic propagation may serve as a promising therapeutic intervention for PD.

α-Synuclein filaments from transgenic mouse and human synucleinopathy-containing brains are major seed-competent species

Assembled α-synuclein in nerve cells and glial cells is the defining pathological feature of neurodegenerative diseases called synucleinopathies. Seeds of α-synuclein can induce the assembly of monomeric protein. Here, we used sucrose gradient centrifugation and transiently transfected HEK 293T cells to identify the species of α-synuclein from the brains of homozygous, symptomatic mice transgenic for human mutant A53T α-synuclein (line M83) that seed aggregation. The most potent fractions contained Sarkosyl-insoluble assemblies enriched in filaments. We also analyzed six cases of idiopathic Parkinson's disease (PD), one case of familial PD, and six cases of multiple system atrophy (MSA) for their ability to induce α-synuclein aggregation. The MSA samples were more potent than those of idiopathic PD in seeding aggregation. We found that following sucrose gradient centrifugation, the most seed-competent fractions from PD and MSA brains are those that contain Sarkosyl-insoluble α-synuclein. The fractions differed between PD and MSA, consistent with the presence of distinct conformers of assembled α-synuclein in these different samples. We conclude that α-synuclein filaments are the main driving force for amplification and propagation of pathology in synucleinopathies.

Immunotherapies in Huntington's disease and α-Synucleinopathies

Modulation of immune activation using immunotherapy has attracted considerable attention for many years as a potential therapeutic intervention for several inflammation-associated neurodegenerative diseases. However, the efficacy of single-target immunotherapy intervention has shown limited or no efficacy in alleviating disease burden and restoring functional capacity. Marked immune system activation and neuroinflammation are important features and prodromal signs in polyQ repeat disorders and α-synucleinopathies. This review describes the current status and future directions of immunotherapies in proteinopathy-induced neurodegeneration with emphasis on preclinical and clinical efficacies of several anti-inflammatory compounds and antibody-based therapies for the treatment of Huntington's disease and α-synucleinopathies. The review concludes with how disease modification and functional restoration could be achieved by using targeted multimodality therapy to target multiple factors.

A simple, versatile and robust centrifugation-based filtration protocol for the isolation and quantification of α-synuclein monomers, oligomers and fibrils: Towards improving experimental reproducibility in α-synuclein research

Increasing evidence suggests that the process of alpha‐synuclein (α‐syn) aggregation from monomers into amyloid fibrils and Lewy bodies, via oligomeric intermediates plays an essential role in the pathogenesis of different synucleinopathies, including Parkinson's disease (PD), multiple system atrophy and dementia with Lewy bodies (DLB). However, the nature of the toxic species and the mechanisms by which they contribute to neurotoxicity and disease progression remain elusive. Over the past two decades, significant efforts and resources have been invested in studies aimed at identifying and targeting toxic species along the pathway of α‐syn fibrillization. Although this approach has helped to advance the field and provide insights into the biological properties and toxicity of different α‐syn species, many of the fundamental questions regarding the role of α‐syn aggregation in PD remain unanswered, and no therapeutic compounds targeting α‐syn aggregates have passed clinical trials. Several factors have contributed to this slow progress, including the complexity of the aggregation pathways and the heterogeneity and dynamic nature of α‐syn aggregates. In the majority of experiment, the α‐syn samples used contain mixtures of α‐syn species that exist in equilibrium and their ratio changes upon modifying experimental conditions. The failure to quantitatively account for the distribution of different α‐syn species in different studies has contributed not only to experimental irreproducibility but also to misinterpretation of results and misdirection of valuable resources. Towards addressing these challenges and improving experimental reproducibility in Parkinson's research, we describe here a simple centrifugation‐based filtration protocol for the isolation, quantification and assessment of the distribution of α‐syn monomers, oligomers and fibrils, in heterogeneous α‐syn samples of increasing complexity. The protocol is simple, does not require any special instrumentation and can be performed rapidly on multiple samples using small volumes. Here, we present and discuss several examples that illustrate the applications of this protocol and how it could contribute to improving the reproducibility of experiments aimed at elucidating the structural basis of α‐syn aggregation, seeding activity, toxicity and pathology spreading. This protocol is applicable, with slight modifications, to other amyloid‐forming proteins.

Correlation between Cellular Uptake and Cytotoxicity of Fragmented α-Synuclein Amyloid Fibrils Suggests Intracellular Basis for Toxicity

Aggregation and intracellular deposition of the protein α-synuclein is an underlying characteristic of Parkinson's disease. α-Synuclein assemblies also undergo cell-cell spreading, facilitating propagation of their cellular pathology. Understanding how cellular interactions and uptake of extracellular α-synuclein assemblies depend on their physical attributes is therefore important. We prepared fragmented fluorescently labeled α-synuclein amyloid fibrils of different average lengths (∼80 nm to >1 μm) and compared their interactions with SH-SY5Y cells. We report that fibrils of all lengths, but not monomers, bind avidly to the cell surface. Their uptake is inversely dependent on their average size, occurs via a heparan sulfate dependent endocytic route, and appears to have a size cutoff of ∼400 nm. The uptake of α-synuclein fibrils, but not monomers, correlates with their cytotoxicity as measured by reduction in metabolic activity, strongly suggesting an intracellular basis for α-synuclein fibril toxicity, likely involving endolysosomes.

Measurement of length distribution of beta-lactoglobulin fibrils by multiwavelength analytical ultracentrifugation

The whey protein beta-lactoglobulin is the building block of amyloid fibrils which exhibit a great potential in various applications. These include stabilization of gels or emulsions. During biotechnological processing, high shear forces lead to fragmentation of fibrils and therefore to smaller fibril lengths. To provide insight into such processes, pure straight amyloid fibril dispersions (prepared at pH 2) were produced and sheared using the rotor stator setup of an Ultra Turrax. In the first part of this work, the sedimentation properties of fragmented amyloid fibrils sheared at different stress levels were analyzed with mulitwavelength analytical ultracentrifugation (AUC). Sedimentation data analysis was carried out with the boundary condition that fragmented fibrils were of cylindrical shape, for which frictional properties are known. These results were compared with complementary atomic force microscopy (AFM) measurements. We demonstrate how the sedimentation coefficient distribution from AUC experiments is influenced by the underlying length and diameter distribution of amyloid fibrils.

In the second part of this work, we show how to correlate the fibril size reduction kinetics with the applied rotor revolution and the resulting energy density, respectively, using modal values of the sedimentation coefficients obtained from AUC. Remarkably, the determined scaling laws for the size reduction are in agreement with the results for other material systems, such as emulsification processes or the size reduction of graphene oxide sheets.

Increased Dynamics of α-Synuclein Fibrils by β-Synuclein Leads to Reduced Seeding and Cytotoxicity

Alpha-synuclein (αS) fibrils are toxic to cells and contribute to the pathogenesis and progression of Parkinson's disease and other synucleinopathies. β-Synuclein (βS), which co-localizes with αS, has been shown to provide a neuroprotective effect, but the molecular mechanism by which this occurs remains elusive. Here we show that αS fibrils formed in the presence of βS are less cytotoxic, exhibit reduced cell seeding capacity and are more resistant to fibril shedding compared to αS fibrils alone. Using solid-state NMR, we found that the overall structure of the core of αS fibrils when co-incubated with βS is minimally perturbed, however, the dynamics of Lys and Thr residues, located primarily in the imperfect KTKEGV repeats of the αS N-terminus, are increased. Our results suggest that amyloid fibril dynamics may play a key role in modulating toxicity and seeding. Thus, enhancing the dynamics of amyloid fibrils may be a strategy for future therapeutic targeting of neurodegenerative diseases.

Limited spread of pathology within the brainstem of α-synuclein BAC transgenic mice inoculated with preformed fibrils into the gastrointestinal tract

Parkinson's disease (PD) is pathologically characterized by intraneuronal α-synuclein (α-Syn) aggregates called Lewy bodies (LBs) as well as the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). On the basis of autopsy studies, Braak et al. hypothesized that Lewy pathology initially occurs in the enteric nervous system, subsequently spreading to the dorsal motor nucleus of the vagus nerve (dmX) and then ascending in the brainstem to the SNpc. However, this hypothetical progression lacks adequate experimental evidence. We previously reported that inoculation of α-Syn preformed fibrils (PFFs) into the gastric wall of wild-type (WT) mice induced LB-like α-Syn aggregates in the dmX via the vagus nerve. However, α-Syn pathology did not spread beyond the dmX up to 12 months postinoculation. In the present study, we inoculated α-Syn PFFs into the gastric wall of bacterial artificial chromosome (BAC) transgenic mice harboring the human α-Syn gene with an A53 T mutation and analyzed the pathology. The transgenic mice had ∼1.5-fold overexpression of α-Syn in the brains and ∼6-fold overexpression of α-Syn in the stomach compared with WT mice. After inoculation of α-Syn PFFs, the transgenic mice developed a higher number of phosphorylated α-Syn (p-α-Syn)-positive neurons in the dmX compared with similarly inoculated WT mice. However, the number of p-α-Syn-positive neurons in the dmX decreased over time, and α-Syn pathology was not observed in other brain regions except in the ambiguous nucleus up to 8 months postinoculation. Taken together, BAC transgenic expression of α-Syn facilitated induction of α-Syn pathology in the brainstem, but not subsequent caudo-rostral spread in accordance with Braak's hypothesis.