A panel of epitope-specific antibodies detects protein domains distributed throughout human alpha-synuclein in Lewy bodies of Parkinson's disease

Analysis of alpha-synuclein harvested from intra-cranial instruments used in deep brain stimulation surgery for Parkinson's disease

Alpha-synuclein (αSyn) forms pathologic aggregates in Parkinson's disease (PD) and is implicated in mechanisms underlying neurodegeneration. While pathologic αSyn has been extensively studied, there is currently no method to evaluate αSyn within the brains of living patients. Patients with PD are often treated with deep brain stimulation (DBS) surgery in which surgical instruments are in direct contact with neuronal tissue; herein, we describe a method by which tissue is purified from DBS surgical instruments in PD and essential tremor (ET) patients and demonstrate that αSyn is robustly detected. 24 patients undergoing DBS surgery for PD (17 patients) or ET (7 patients) were enrolled; from patient samples, 81.2 ± 44.8 µg protein (n=15) is able to be purified, with immunoblot assays specific for αSyn reactive in all tested samples. Light microscopy revealed axons and capillaries as the primary components of purified tissue (n=3). Further analysis was conducted using western blot, demonstrating that truncated αSyn (1-125 αSyn) was significantly increased in PD (n=5) compared to ET (n=3), in which αSyn misfolding is not expected (0.64 ± 0.25 vs. 0.25 ± 0.12, P = 0.046), thus showing that pathologic αSyn can be reliably purified from living PD patients with this method.

Distinct tau and alpha-synuclein molecular signatures in Alzheimer's disease with and without Lewy bodies and Parkinson's disease with dementia

Alpha-synuclein (aSyn) pathology is present in approximately 50% of Alzheimer's disease (AD) cases at autopsy and might impact the age-of-onset and disease progression in AD. Here, we aimed to determine whether tau and aSyn profiles differ between AD cases with Lewy bodies (AD-LB), pure AD and Parkinson's disease with dementia (PDD) cases using epitope-, post-translational modification- (PTM) and isoform-specific tau and aSyn antibody panels spanning from the N- to C-terminus. We included the middle temporal gyrus (MTG) and amygdala (AMY) of clinically diagnosed and pathologically confirmed cases and performed dot blotting, western blotting and immunohistochemistry combined with quantitative and morphological analyses. All investigated phospho-tau (pTau) species, except pT181, were upregulated in AD-LB and AD cases compared to PDD and control cases, but no significant differences were observed between AD-LB and AD subjects. In addition, tau antibodies targeting the proline-rich regions and C-terminus showed preferential binding to AD-LB and AD brain homogenates. Antibodies targeting C-terminal aSyn epitopes and pS129 aSyn showed stronger binding to AD-LB and PDD cases compared to AD and control cases. Two pTau species (pS198 and pS396) were specifically detected in the soluble protein fractions of AD-LB and AD subjects, indicative of early involvement of these PTMs in the multimerization process of tau. Other phospho-variants for both tau (pT212/S214, pT231 and pS422) and aSyn (pS129) were only detected in the insoluble protein fraction of AD-LB/AD and AD-LB/PDD cases, respectively. aSyn load was higher in the AMY of AD-LB cases compared to PDD cases, suggesting aggravated aSyn pathology under the presence of AD pathology, while tau load was similar between AD-LB and AD cases. Co-localization of pTau and aSyn could be observed within astrocytes of AD-LB cases within the MTG. These findings highlight a unique pathological signature for AD-LB cases compared to pure AD and PDD cases.

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.

Truncation or proteolysis of α-synuclein in Parkinsonism

Posttranslational modifications of α-synuclein, such as truncation or abnormal proteolysis, are implicated in Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). A key focus of this article includes the proteases responsible for inducing truncation, the specific sites susceptible to truncation, and the resultant influence of these truncated species on the seeding and aggregation of endogenous α-synuclein. We also shed light on the unique structural attributes of these truncated species, and how these modifications can lead to distinctive forms of synucleinopathies. In addition, we explore the comparative toxic potentials of various α-synuclein species. An extensive analysis of available evidence of truncated α-synuclein species in human-synucleinopathy brains is also provided. Lastly, we delve into the detrimental impact of truncated species on key cellular structures such as the mitochondria and endoplasmic reticulum. Our article discusses enzymes involved in α-synuclein truncation, including 20 S proteasome, cathepsins, asparagine endopeptidase, caspase-1, calpain-1, neurosin/kallikrein-6, matrix metalloproteinase-1/-3, and plasmin. Truncation patterns impact α-synuclein aggregation - C-terminal truncation accelerates aggregation with larger truncations correlated with shortened aggregation lag times. N-terminal truncation affects aggregation differently based on the truncation location. C-terminally truncated α-synuclein forms compact, shorter fibrils compared to the full-length (FL) protein. N-terminally truncated monomers form fibrils similar in length to FL α-synuclein. Truncated forms show distinct fibril morphologies, increased β-sheet structures, and greater protease resistance. Misfolded α-synuclein can adopt various conformations, leading to unique aggregates and distinct synucleinopathies. Fibrils, with prion-like transmission, are potentially more toxic than oligomers, though this is still debated. Different α-synuclein variants with N- and C-terminal truncations, namely 5-140, 39-140, 65-140, 66-140, 68-140, 71-140, 1-139, 1-135, 1-133, 1-122, 1-119, 1-115, 1-110, and 1-103 have been found in PD, DLB, and MSA patients' brains. In Parkinsonism, excess misfolded α-synuclein overwhelms the proteasome degradation system, resulting in truncated protein production and accumulation in the mitochondria and endoplasmic reticulum.

Cellular processing of α-synuclein fibrils results in distinct physiological C-terminal truncations with a major cleavage site at residue Glu 114

α-synuclein (αS) is an abundant, neuronal protein that assembles into fibrillar pathological inclusions in a spectrum of neurodegenerative diseases that include Lewy body diseases (LBD) and Multiple System Atrophy (MSA). The cellular and regional distributions of pathological inclusions vary widely between different synucleinopathies contributing to the spectrum of clinical presentations. Extensive cleavage within the carboxy (C)-terminal region of αS is associated with inclusion formation, although the events leading to these modifications and the implications for pathobiology are of ongoing study. αS preformed fibrils can induce prion-like spread of αS pathology in both in vitro and animal models of disease. Using C truncation-specific antibodies, we demonstrated here that prion-like cellular uptake and processing of αS preformed fibrils resulted in two major cleavages at residues 103 and 114. A third cleavage product (122 αS) accumulated upon application of lysosomal protease inhibitors. In vitro, both 1-103 and 1-114 αS polymerized rapidly and extensively in isolation and in the presence of full-length αS. 1-103 αS also demonstrated more extensive aggregation when expressed in cultured cells. Furthermore, we used novel antibodies to αS cleaved at residue Glu114, to assess x-114 αS pathology in postmortem brain tissue from patients with LBD and MSA, as well as three different transgenic αS mouse models of prion-like induction. The distribution of x-114 αS pathology was distinct from that of overall αS pathology. These studies reveal the cellular formation and behavior of αS C-truncated at residues 114 and 103 as well as the disease dependent distribution of x-114 αS pathology.

New SNCA mutation and structures of α-synuclein filaments from juvenile-onset synucleinopathy

A 21-nucleotide duplication in one allele of SNCA was identified in a previously described disease with abundant α-synuclein inclusions that we now call juvenile-onset synucleinopathy (JOS). This mutation translates into the insertion of MAAAEKT after residue 22 of α-synuclein, resulting in a protein of 147 amino acids. Both wild-type and mutant proteins were present in sarkosyl-insoluble material that was extracted from frontal cortex of the individual with JOS and examined by electron cryo-microscopy. The structures of JOS filaments, comprising either a single protofilament, or a pair of protofilaments, revealed a new α-synuclein fold that differs from the folds of Lewy body diseases and multiple system atrophy (MSA). The JOS fold consists of a compact core, the sequence of which (residues 36-100 of wild-type α-synuclein) is unaffected by the mutation, and two disconnected density islands (A and B) of mixed sequences. There is a non-proteinaceous cofactor bound between the core and island A. The JOS fold resembles the common substructure of MSA Type I and Type II dimeric filaments, with its core segment approximating the C-terminal body of MSA protofilaments B and its islands mimicking the N-terminal arm of MSA protofilaments A. The partial similarity of JOS and MSA folds extends to the locations of their cofactor-binding sites. In vitro assembly of recombinant wild-type α-synuclein, its insertion mutant and their mixture yielded structures that were distinct from those of JOS filaments. Our findings provide insight into a possible mechanism of JOS fibrillation in which mutant α-synuclein of 147 amino acids forms a nucleus with the JOS fold, around which wild-type and mutant proteins assemble during elongation.

Patients with isolated REM-sleep behavior disorder have elevated levels of alpha-synuclein aggregates in stool

Misfolded and aggregated α-synuclein is a neuropathological hallmark of Parkinson's disease (PD). Thus, α-synuclein aggregates are regarded as a biomarker for the development of diagnostic assays. Quantification of α-synuclein aggregates in body fluids is challenging, and requires highly sensitive and specific assays. Recent studies suggest that α-synuclein aggregates may be shed into stool. We used surface-based fluorescence intensity distribution analysis (sFIDA) to detect and quantify single particles of α-synuclein aggregates in stool of 94 PD patients, 72 isolated rapid eye movement sleep behavior disorder (iRBD) patients, and 51 healthy controls. We measured significantly elevated concentrations of α-synuclein aggregates in stool of iRBD patients versus those of controls (p = 0.024) or PD patients (p < 0.001). Our results show that α-synuclein aggregates are excreted in stool and can be measured using the sFIDA assay, which could support the diagnosis of prodromal synucleinopathies.

Specific Detection of Physiological S129 Phosphorylated α-Synuclein in Tissue Using Proximity Ligation Assay

BACKGROUND

Synucleinopathies are a group of neurodegenerative disorders that are pathologically characterized by intracellular aggregates called Lewy bodies. Lewy bodies are primarily composed of α-synuclein (asyn) protein, which is mostly phosphorylated at serine 129 (pS129) when aggregated and therefore used as a marker for pathology. Currently commercial antibodies against pS129 asyn stain aggregates well but in healthy brains cross react with other proteins, thus making it difficult to specifically detect physiological pS129 asyn.

OBJECTIVE

To develop a staining procedure that detects endogenous and physiological relevant pS129 asyn with high specificity and low background.

METHODS

We used the fluorescent and brightfield in situ proximity ligation assay (PLA) to specifically detect pS129 asyn in cell culture, mouse, and human brain sections.

RESULTS

The pS129 asyn PLA specifically stained physiological and soluble pS129 asyn in cell culture, mouse brain sections, and human brain tissue without significant cross-reactivity or background signal. However, this technique was not successful in detecting Lewy bodies in human brain tissue.

CONCLUSION

We successfully developed a novel PLA method that can, in the future, be used on in vitro and in vivo samples as a tool to explore and better understand the cellular localization and function of pS129 asyn in health and disease.

Optical pulse labeling studies reveal exogenous seeding slows α-synuclein clearance

The accumulation of α-synuclein (α-syn) in intracellular formations known as Lewy bodies (LBs) is associated with several neurodegenerative diseases including Parkinson's disease and Lewy Body Dementia. There is still limited understanding of how α-syn and LB formation is associated with cellular dysfunction and degeneration in these diseases. To examine the clearance and production dynamics of α-syn we transduced organotypic murine brain slice cultures (BSCs) with recombinant adeno-associated viruses (rAAVs) to express Dendra2-tagged human wild-type (WT) and mutant A53T α-syn, with and without the addition of exogenous α-syn fibrillar seeds and tracked them over several weeks in culture using optical pulse labeling. We found that neurons expressing WT or mutant A53T human α-syn show similar rates of α-syn turnover even when insoluble, phosphorylated Ser129 α-syn has accumulated. Taken together, this data reveals α-syn aggregation and overexpression, pSer129 α-syn, nor the A53T mutation affect α-syn dynamics in this system. Prion-type seeding with exogenous α-syn fibrils significantly slows α-syn turnover, in the absence of toxicity but is associated with the accumulation of anti-p62 immunoreactivity and Thiazin Red positivity. Prion-type induction of α-syn aggregation points towards a potential protein clearance deficit in the presence of fibrillar seeds and the ease of this system to explore precise mechanisms underlying these processes. This system facilitates the exploration of α-syn protein dynamics over long-term culture periods. This platform can further be exploited to provide mechanistic insight on what drives this slowing of α-syn turnover and how therapeutics, other genes or different α-syn mutations may affect α-syn protein dynamics.

Development of an α-synuclein fibril and oligomer specific tracer for diagnosis of Parkinson's disease, dementia with Lewy bodies and multiple system atrophy

The development of specific disease-associated PET tracers is one of the major challenges, the realization of which in neurodegenerative diseases would enable not only the efficiency of diagnosis but also support the development of disease-modifying therapeutics. Parkinson's disease (PD) is the most common neurodegenerative movement disorder and is characterized by neuronal fibrillary inclusions composed of aggregated α-synuclein (α-syn). However, these deposits are not only found in PD, but also in other related diseases such as multiple system atrophy (MSA) and dementia with Lewy bodies (DLB), which are grouped under the term synucleinopathies. In this study, we used NGS-guided phage display selection to identify short peptides that bind aggregated α-syn. By surface plasmon resonance (SPR)-based affinity screening, we identified the peptide SVLfib-5 that recognizes aggregated α-syn with high complex stability and sequence specificity. Further analysis SPR showed that SVLfib-5 is not only specific for aggregated α-syn, but in particular recognizes fibrillary and oligomeric structures. Moreover, fluorescence microscopy of human brain tissue sections from PD, MSA, and DLB patients with SVLfib-5 allowed specific recognition of α-syn and a clear discrimination between diseased and non-diseased samples. These findings provide the basis for the further development of an α-syn PET tracer for early diagnosis and monitoring of disease progression and therapy progress.

Structures of α-synuclein filaments from human brains with Lewy pathology

Parkinson's disease (PD) is the most common movement disorder, with resting tremor, rigidity, bradykinesia and postural instability being major symptoms¹. Neuropathologically, it is characterized by the presence of abundant filamentous inclusions of α-synuclein in the form of Lewy bodies and Lewy neurites in some brain cells, including dopaminergic nerve cells of the substantia nigra². PD is increasingly recognised as a multisystem disorder, with cognitive decline being one of its most common non-motor symptoms. Many patients with PD develop dementia more than 10 years after diagnosis³. PD dementia (PDD) is clinically and neuropathologically similar to dementia with Lewy bodies (DLB), which is diagnosed when cognitive impairment precedes parkinsonian motor signs or begins within one year from their onset⁴. In PDD, cognitive impairment develops in the setting of well-established PD. Besides PD and DLB, multiple system atrophy (MSA) is the third major synucleinopathy⁵. It is characterized by the presence of abundant filamentous α-synuclein inclusions in brain cells, especially oligodendrocytes (Papp-Lantos bodies). We previously reported the electron cryo-microscopy structures of two types of α-synuclein filament extracted from the brains of individuals with MSA⁶. Each filament type is made of two different protofilaments. Here we report that the cryo-electron microscopy structures of α-synuclein filaments from the brains of individuals with PD, PDD and DLB are made of a single protofilament (Lewy fold) that is markedly different from the protofilaments of MSA. These findings establish the existence of distinct molecular conformers of assembled α-synuclein in neurodegenerative disease.

Autophagy mediates the clearance of oligodendroglial SNCA/alpha-synuclein and TPPP/p25A in multiple system atrophy models

Accumulation of the neuronal protein SNCA/alpha-synuclein and of the oligodendroglial phosphoprotein TPPP/p25A within the glial cytoplasmic inclusions (GCIs) represents the key histophathological hallmark of multiple system atrophy (MSA). Even though the levels/distribution of both oligodendroglial SNCA and TPPP/p25A proteins are critical for disease pathogenesis, the proteolytic mechanisms involved in their turnover in health and disease remain poorly understood. Herein, by pharmacological and molecular modulation of the autophagy-lysosome pathway (ALP) and the proteasome we demonstrate that the endogenous oligodendroglial SNCA and TPPP/p25A are degraded mainly by the ALP in murine primary oligodendrocytes and oligodendroglial cell lines under basal conditions. We also identify a KFERQ-like motif in the TPPP/p25A sequence that enables its effective degradation via chaperone-mediated autophagy (CMA) in an in vitro system of rat brain lysosomes. Furthermore, in a MSA-like setting established by addition of human recombinant SNCA pre-formed fibrils (PFFs) as seeds of pathological SNCA, we thoroughly characterize the contribution of CMA and macroautophagy in particular, in the removal of the exogenously added and the seeded oligodendroglial SNCA pathological assemblies. We also show that PFF treatment impairs autophagic flux and that TPPP/p25A exerts an inhibitory effect on macroautophagy, while at the same time CMA is upregulated to remove the pathological SNCA species formed within oligodendrocytes. Finally, augmentation of CMA or macroautophagy accelerates the removal of the engendered pathological SNCA conformations further suggesting that autophagy targeting may represent a successful approach for the clearance of pathological SNCA and/or TPPP/p25A in the context of MSA.Abbreviations: 3MA: 3-methyladenine; ACTB: actin, beta; ALP: autophagy-lysosome pathway; ATG5: autophagy related 5; AR7: atypical retinoid 7; CMA: chaperone-mediated autophagy; CMV: cytomegalovirus; CTSD: cathepsin D; DAPI: 4',6-diamidino-2-phenylindole; DMEM: Dulbecco's modified Eagle's medium; Epox: epoxomicin; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GCIs: glial cytoplasmic inclusions; GFP: green fluorescent protein; HMW: high molecular weight; h: hours; HSPA8/HSC70: heat shock protein 8; LAMP1: lysosomal-associated membrane protein 1; LAMP2A: lysosomal-associated membrane protein 2A; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; mcherry: monomeric cherry; MFI: mean fluorescence intensity; mRFP: monomeric red fluorescent protein; MSA: multiple system atrophy; OLN: oligodendrocytes; OPCs: oligodendroglial progenitor cells; PBS: phosphate-buffered saline; PC12: pheochromocytoma cell line; PD: Parkinson disease; PFFs: pre-formed fibrils; PIs: protease inhibitors; PSMB5: proteasome (prosome, macropain) subunit, beta type 5; Rap: rapamycin; RFP: red fluorescent protein; Scr: scrambled; SDS: sodium dodecyl sulfate; SE: standard error; siRNAs: small interfering RNAs; SNCA: synuclein, alpha; SQSTM1: sequestosome 1; TPPP: tubulin polymerization promoting protein; TUBA: tubulin, alpha; UPS: ubiquitin-proteasome system; WT: wild type.

1-Indanone and 1,3-indandione Derivatives as Ligands for Misfolded α-Synuclein Aggregates

The development of imaging agents for in vivo detection of alpha-synuclein (α-syn) pathologies faces several challenges. A major gap in the field is the lack of diverse molecular scaffolds with high affinity and selectivity to α-syn fibrils for in vitro screening assays. Better in vitro scaffolds can instruct the discovery of better in vivo agents. We report the rational design, synthesis, and in vitro evaluation of a series of novel 1-indanone and 1,3-indandione derivatives from a Structure-Activity Relationship (SAR) study centered on some existing α-syn fibril binding ligands. Our results from fibril saturation binding experiments show that two of the lead candidates compounds 8 and 32 bind α-syn fibrils with binding constants (K_d ) of 9.0 and 18.8 nM, respectively, and selectivity of greater than 10× for α-syn fibrils compared with amyloid-β (Aβ) and tau fibrils. Our results demonstrate that the lead ligands avidly label all forms of α-syn on PD brain tissue sections, but only the dense core of senile plaques in AD brain tissue, respectively. These results are corroborated by ligand-antibody colocalization data from Syn211, which shows immunoreactivity toward all forms of α-syn aggregates, and Syn303, which displays preferential reactivity toward mature Lewy pathology. Our results reveal that 1-indanone derivatives have desirable properties for the biological evaluation of α-synucleinopathies.

Influence of curcumin and rosmarinic acid on disrupting the general properties of Alpha-Synuclein oligomer: Molecular dynamics simulation

Alpha-Synuclein (αS) is a protein involved in Parkinson's disease (PD) and is probably the main cause of the pathology of the disease. During pathogenesis, αS monomers aggregate, leading to the formation of a variety of oligomeric species. Recent research studies suggest that the oligomeric toxic species may be one of the main processes for pathology and disease. Here, we studied influence of two natural polyphenolic compounds, Curcumin (CUR) and Rosmarinic acid (RA), on disrupting the general properties of αS oligomer by molecular dynamics (MD) simulation method. The hydrophobic central domain of αS (NAC), is the most essential district responsible for protein self-aggregation; so, in this study, our systems have been developed to form a quintuplet NAC region of αS called 5mer; they have 10 and 20 CUR and RA molecules and a 5mer with no ligand. The several important and efficient analyzes were performed to investigate the effect of ligands on the structural properties of αS oligomers. The results indicated that both ligands can be successful in disrupting the original structure of αS oligomers; therefore, they can be considered suitable candidates for designing Parkinson's drugs.

The subcellular arrangement of alpha-synuclein proteoforms in the Parkinson's disease brain as revealed by multicolor STED microscopy

Various post-translationally modified (PTM) proteoforms of alpha-synuclein (aSyn)-including C-terminally truncated (CTT) and Serine 129 phosphorylated (Ser129-p) aSyn-accumulate in Lewy bodies (LBs) in different regions of the Parkinson's disease (PD) brain. Insight into the distribution of these proteoforms within LBs and subcellular compartments may aid in understanding the orchestration of Lewy pathology in PD. We applied epitope-specific antibodies against CTT and Ser129-p aSyn proteoforms and different aSyn domains in immunohistochemical multiple labelings on post-mortem brain tissue from PD patients and non-neurological, aged controls, which were scanned using high-resolution 3D multicolor confocal and stimulated emission depletion (STED) microscopy. Our multiple labeling setup highlighted a consistent onion skin-type 3D architecture in mature nigral LBs in which an intricate and structured-appearing framework of Ser129-p aSyn and cytoskeletal elements encapsulates a core enriched in CTT aSyn species. By label-free CARS microscopy we found that enrichments of proteins and lipids were mainly localized to the central portion of nigral aSyn-immunopositive (aSyn+) inclusions. Outside LBs, we observed that 122CTT aSyn+ punctae localized at mitochondrial membranes in the cytoplasm of neurons in PD and control brains, suggesting a physiological role for 122CTT aSyn outside of LBs. In contrast, very limited to no Ser129-p aSyn immunoreactivity was observed in brains of non-neurological controls, while the alignment of Ser129-p aSyn in a neuronal cytoplasmic network was characteristic for brains with (incidental) LB disease. Interestingly, Ser129-p aSyn+ network profiles were not only observed in neurons containing LBs but also in neurons without LBs particularly in donors at early disease stage, pointing towards a possible subcellular pathological phenotype preceding LB formation. Together, our high-resolution and 3D multicolor microscopy observations in the post-mortem human brain provide insights into potential mechanisms underlying a regulated LB morphogenesis.

The molecular and cellular basis of copper dysregulation and its relationship with human pathologies

Copper (Cu) is an essential micronutrient required for the activity of redox-active enzymes involved in critical metabolic reactions, signaling pathways, and biological functions. Transporters and chaperones control Cu ion levels and bioavailability to ensure proper subcellular and systemic Cu distribution. Intensive research has focused on understanding how mammalian cells maintain Cu homeostasis, and how molecular signals coordinate Cu acquisition and storage within organs. In humans, mutations of genes that regulate Cu homeostasis or facilitate interactions with Cu ions lead to numerous pathologic conditions. Malfunctions of the Cu⁺ -transporting ATPases ATP7A and ATP7B cause Menkes disease and Wilson disease, respectively. Additionally, defects in the mitochondrial and cellular distributions and homeostasis of Cu lead to severe neurodegenerative conditions, mitochondrial myopathies, and metabolic diseases. Cu has a dual nature in carcinogenesis as a promotor of tumor growth and an inducer of redox stress in cancer cells. Cu also plays role in cancer treatment as a component of drugs and a regulator of drug sensitivity and uptake. In this review, we provide an overview of the current knowledge of Cu metabolism and transport and its relation to various human pathologies.

Ncx3-Induced Mitochondrial Dysfunction in Midbrain Leads to Neuroinflammation in Striatum of A53t-α-Synuclein Transgenic Old Mice

The exact mechanism underlying selective dopaminergic neurodegeneration is not completely understood. The complex interplay among toxic alpha-synuclein aggregates, oxidative stress, altered intracellular Ca²⁺-homeostasis, mitochondrial dysfunction and disruption of mitochondrial integrity is considered among the pathogenic mechanisms leading to dopaminergic neuronal loss. We herein investigated the molecular mechanisms leading to mitochondrial dysfunction and its relationship with activation of the neuroinflammatory process occurring in Parkinson’s disease. To address these issues, experiments were performed in vitro and in vivo in mice carrying the human mutation of α-synuclein A53T under the prion murine promoter. In these models, the expression and activity of NCX isoforms, a family of important transporters regulating ionic homeostasis in mammalian cells working in a bidirectional way, were evaluated in neurons and glial cells. Mitochondrial function was monitored with confocal microscopy and fluorescent dyes to measure mitochondrial calcium content and mitochondrial membrane potential. Parallel experiments were performed in 4 and 16-month-old A53T-α-synuclein Tg mice to correlate the functional data obtained in vitro with mitochondrial dysfunction and neuroinflammation through biochemical analysis. The results obtained demonstrated: 1. in A53T mice mitochondrial dysfunction occurs early in midbrain and later in striatum; 2. mitochondrial dysfunction occurring in the midbrain is mediated by the impairment of NCX3 protein expression in neurons and astrocytes; 3. mitochondrial dysfunction occurring early in midbrain triggers neuroinflammation later into the striatum, thus contributing to PD progression during mice aging.

Downstream effects of polypathology on neurodegeneration of medial temporal lobe subregions

The medial temporal lobe (MTL) is a nidus for neurodegenerative pathologies and therefore an important region in which to study polypathology. We investigated associations between neurodegenerative pathologies and the thickness of different MTL subregions measured using high-resolution post-mortem MRI. Tau, TAR DNA-binding protein 43 (TDP-43), amyloid-β and α-synuclein pathology were rated on a scale of 0 (absent)-3 (severe) in the hippocampus and entorhinal cortex (ERC) of 58 individuals with and without neurodegenerative diseases (median age 75.0 years, 60.3% male). Thickness measurements in ERC, Brodmann Area (BA) 35 and 36, parahippocampal cortex, subiculum, cornu ammonis (CA)1 and the stratum radiatum lacunosum moleculare (SRLM) were derived from 0.2 × 0.2 × 0.2 mm3 post-mortem MRI scans of excised MTL specimens from the contralateral hemisphere using a semi-automated approach. Spearman's rank correlations were performed between neurodegenerative pathologies and thickness, correcting for age, sex and hemisphere, including all four proteinopathies in the model. We found significant associations of (1) TDP-43 with thickness in all subregions (r =  - 0.27 to r =  - 0.46), and (2) tau with BA35 (r =  - 0.31) and SRLM thickness (r =  - 0.33). In amyloid-β and TDP-43 negative cases, we found strong significant associations of tau with ERC (r =  - 0.40), BA35 (r =  - 0.55), subiculum (r =  - 0.42) and CA1 thickness (r =  - 0.47). This unique dataset shows widespread MTL atrophy in relation to TDP-43 pathology and atrophy in regions affected early in Braak stageing and tau pathology. Moreover, the strong association of tau with thickness in early Braak regions in the absence of amyloid-β suggests a role of Primary Age-Related Tauopathy in neurodegeneration.

Kapd Is Essential for Specification of the Dopaminergic Neurogenesis in Zebrafish Embryos

To define novel networks of Parkinson's disease (PD) pathogenesis, the substantia nigra pars compacta of A53T mice, where a death-promoting protein, FAS-associated factor 1 was ectopically expressed for 2 weeks in the 2-, 4-, 6-, and 8-month-old mice, and was subjected to transcriptomic analysis. Compendia of expression profiles and a hierarchical clustering heat map of differentially expressed genes associated with PD were bioinformatically generated. Transcripts level of a particular gene was fluctuated by 20, 60, and 0.75 fold in the 4-, 6-, and 8-month-old mice compared to the 2 months old. Because the gene contained Kelch domain, it was named as Kapd (Kelch-containing protein associated with PD). Biological functions of Kapd were systematically investigated in the zebrafish embryos. First, transcripts of a zebrafish homologue of Kapd, kapd were found in the floor plate of the neural tube at 10 h post fertilization (hpf), and restricted to the tegmentum, hypothalamus, and cerebellum at 24 hpf. Second, knockdown of kapd caused developmental defects of DA progenitors in the midbrain neural keel and midbrain? hindbrain boundary at 10 hpf. Third, overexpression of kapd increased transcripts level of the dopaminergic immature neuron marker, shha in the prethalamus at 16.5 hpf. Finally, developmental consequences of kapd knockdown reduced transcripts level of the markers for the immature and mature DA neurons, nkx2.2, olig2, otx2b, and th in the ventral diencephalon of the midbrain at 18 hpf. It is thus most probable that Kapd play a key role in the specification of the DA neuronal precursors in zebrafish embryos.

GDNF signaling in subjects with minimal motor deficits and Parkinson's disease

The failure of glial cell derived neurotropic factor to be efficacious in blinded clinical trials for Parkinson's disease may be due to alterations in signaling receptors and downstream signaling molecules. To test this hypothesis, brain sections were obtained from older adults with no motor deficit (n = 6), minimal motor deficits (n = 10), and clinical diagnosis of Parkinson's disease (n = 10) who underwent motor examination proximate to death. Quantitative unbiased stereology and densitometry were performed to analyze RET and phosphorylated ribosomal protein S6 expression in nigral neurons. Individuals with no motor deficit had extensive and intense RET and phosphorylated ribosomal protein S6 immunoreactive neurons in substantia nigra. The number and staining intensity of RET-immunoreactive neurons were reduced moderately in subjects with minimal motor deficits and severely reduced in Parkinson's disease relative to no motor deficit group. The number and staining intensity of phosphorylated ribosomal protein S6 was more markedly reduced in both subjects with minimal motor deficits and Parkinson's disease. Reductions in levels of RET and phosphorylated ribosomal protein S6 were recapitulated in a non-human primate genetic Parkinson's disease model based on over-expression of human mutant α-synuclein (A53T). These data indicate that for neurotrophic factors to be effective in patients with minimal motor deficits or PD, these factors would likely have to upregulate RET and phosphorylated ribosomal protein S6 immunoreactive neurons in substantia nigra .

Co-administration of TiO2-nanowired dl-3-n-butylphthalide (dl-NBP) and mesenchymal stem cells enhanced neuroprotection in Parkinson's disease exacerbated by concussive head injury

dl-3-n-butylphthalide (dl-NBP) is a powerful antioxidant compound with profound neuroprotective effects in stroke and brain injury. However, its role in Parkinson's disease (PD) is not well known. Traumatic brain injury (TBI) is one of the key factors in precipitating PD like symptoms in civilians and particularly in military personnel. Thus, it would be interesting to explore the possible neuroprotective effects of NBP in PD following concussive head injury (CHI). In this chapter effect of nanowired delivery of NBP together with mesenchymal stem cells (MSCs) in PD with CHI is discussed based on our own investigations. It appears that CHI exacerbates PD pathophysiology in terms of p-tau, α-synuclein (ASNC) levels in the cerebrospinal fluid (CSF) and the loss of TH immunoreactivity in substantia niagra pars compacta (SNpc) and striatum (STr) along with dopamine (DA), dopamine decarboxylase (DOPAC). And homovanillic acid (HVA). Our observations are the first to show that a combination of NBP with MSCs when delivered using nanowired technology induces superior neuroprotective effects in PD brain pathology exacerbated by CHI, not reported earlier.

How specific are the conformation-specific α-synuclein antibodies? Characterization and validation of 16 α-synuclein conformation-specific antibodies using well-characterized preparations of α-synuclein monomers, fibrils and oligomers with distinct structures and morphology

Increasing evidence suggests that alpha-synuclein (α-syn) oligomers are obligate intermediates in the pathway involved in α-syn fibrillization and Lewy body (LB) formation, and may also accumulate within LBs in Parkinson's disease (PD) and other synucleinopathies. Therefore, the development of tools and methods to detect and quantify α-syn oligomers has become increasingly crucial for mechanistic studies to understand their role in PD, and to develop new diagnostic methods and therapies for PD and other synucleinopathies. The majority of these tools and methods rely primarily on the use of aggregation state-specific or conformation-specific antibodies. Given the impact of the data and knowledge generated using these antibodies on shaping the foundation and directions of α-syn and PD research, it is crucial that these antibodies are thoroughly characterized, and their specificity or ability to capture diverse α-syn species is tested and validated. Herein, we describe an antibody characterization and validation pipeline that allows a systematic investigation of the specificity of α-syn antibodies using well-defined and well-characterized preparations of various α-syn species, including monomers, fibrils, and different oligomer preparations that are characterized by distinct morphological, chemical and secondary structure properties. This pipeline was used to characterize 18 α-syn antibodies, 16 of which have been reported as conformation- or oligomer-specific antibodies, using an array of techniques, including immunoblot analysis (slot blot and Western blot), a digital ELISA assay using single molecule array technology and surface plasmon resonance. Our results show that i) none of the antibodies tested are specific for one particular type of α-syn species, including monomers, oligomers or fibrils; ii) all antibodies that were reported to be oligomer-specific also recognized fibrillar α-syn; and iii) a few antibodies showed high specificity for oligomers and fibrils but did not bind to monomers. These findings suggest that the great majority of α-syn aggregate-specific antibodies do not differentiate between oligomers and fibrils, thus highlighting the importance of exercising caution when interpreting results obtained using these antibodies. Our results also underscore the critical importance of the characterization and validation of antibodies before their use in mechanistic studies and as diagnostic tools or therapeutic agents. This will not only improve the quality and reproducibility of research and reduce costs but will also reduce the number of therapeutic antibody failures in the clinic.

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.

Carboxy-terminal truncation and phosphorylation of α-synuclein elongates survival in a prion-like seeding mouse model of synucleinopathy

Pathologic intracellular inclusions formed from polymers of misfolded α-synuclein (αsyn) protein define a group of neurodegenerative diseases termed synucleinopathies which includes Parkinson's disease (PD). Prion-like recruitment of endogenous cellular αsyn has been demonstrated to occur in animal models of synucleinopathy, whereby misfolded αsyn can induce further pathologic αsyn inclusions to form through a prion-like mechanism. It has been suggested that misfolded αsyn may assume differing conformations which lead to varied clinical and pathological manifestations of disease; this phenomenon bears similarities to that of prion strains whereby the same misfolded protein can produce unique diseases. It is unclear what factors influence the development of unique αsyn strains, however post-translational modifications (PTMs) such as phosphorylation and truncation that are present in misfolded αsyn in disease may play a role due to their modulation of biochemical and structural αsyn properties. Herein, we investigate the prion-like properties of misfolded αsyn polymers containing either phosphomimetic (S129E) αsyn, 5 different major carboxy (C)-truncated forms of αsyn (1-115, 1-119, 1-122, 1-125, and 1-129 αsyn), or a mixture of these PTM containing αsyn forms compared to full-length (FL) αsyn in HEK293T cells and M83 transgenic mice overexpressing A53T αsyn. It is demonstrated that upon peripheral intramuscular injection of these C-truncated or S129E αsyn polymers into M83 mice, prion-like progression and time to disease onset in this mouse model is elongated when any of these PTMs are present, demonstrating that common modifications to the C-terminus of αsyn present in disease modulates the prion-like seeding properties of αsyn.

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.

Alpha-synuclein targets GluN2A NMDA receptor subunit causing striatal synaptic dysfunction and visuospatial memory alteration

Parkinson's disease is a progressive neurodegenerative disorder characterized by altered striatal dopaminergic signalling that leads to motor and cognitive deficits. Parkinson's disease is also characterized by abnormal presence of soluble toxic forms of α-synuclein that, when clustered into Lewy bodies, represents one of the pathological hallmarks of the disease. However, α-synuclein oligomers might also directly affect synaptic transmission and plasticity in Parkinson's disease models. Accordingly, by combining electrophysiological, optogenetic, immunofluorescence, molecular and behavioural analyses, here we report that α-synuclein reduces N-methyl-d-aspartate (NMDA) receptor-mediated synaptic currents and impairs corticostriatal long-term potentiation of striatal spiny projection neurons, of both direct (D1-positive) and indirect (putative D2-positive) pathways. Intrastriatal injections of α-synuclein produce deficits in visuospatial learning associated with reduced function of GluN2A NMDA receptor subunit indicating that this protein selectively targets this subunit both in vitro and ex vivo. Interestingly, this effect is observed in spiny projection neurons activated by optical stimulation of either cortical or thalamic glutamatergic afferents. We also found that treatment of striatal slices with antibodies targeting α-synuclein prevents the α-synuclein-induced loss of long-term potentiation and the reduced synaptic localization of GluN2A NMDA receptor subunit suggesting that this strategy might counteract synaptic dysfunction occurring in Parkinson's disease.

Carboxy-terminal truncations of mouse α-synuclein alter aggregation and prion-like seeding

α-synuclein (αsyn) forms pathologic inclusions in several neurodegenerative diseases termed synucleinopathies. The inclusions are comprised of αsyn fibrils harboring prion-like properties. Prion-like activity of αsyn has been studied by intracerebral injection of fibrils into mice, where the presence of a species barrier requires the use of mouse αsyn. Post-translational modifications to αsyn such as carboxy (C)-terminal truncation occur in synucleinopathies, and their implications for prion-like aggregation and seeding are under investigation. Herein, C-truncated forms of αsyn found in human disease are recapitulated in mouse αsyn to study their seeding activity in vitro, in HEK293T cells, in neuronal-glial culture, and in nontransgenic mice. The results show that C-truncation of mouse αsyn accelerates aggregation of αsyn but alters prion-like seeding of inclusion formation.

Nigral overexpression of α-synuclein in a rat Parkinson's disease model indicates alterations in the enteric nervous system and the gut microbiome

BACKGROUND

A hallmark feature of Parkinson's disease (PD) is the build-up of α-synuclein protein aggregates throughout the brain; however α-synuclein is also expressed in enteric neurons. Gastrointestinal (GI) symptoms and pathology are frequently reported in PD, including constipation, increased intestinal permeability, glial pathology, and alterations to gut microbiota composition. α-synuclein can propagate through neuronal systems but the site of origin of α-synuclein pathology, whether it be the gut or the brain, is still unknown. Physical exercise is associated with alleviating symptoms of PD and with altering the composition of the gut microbiota.

METHODS

This study investigated the effects of bilateral nigral injection of adeno-associated virus (AAV)-α-synuclein on enteric neurons, glia and neurochemistry, the gut microbiome, and bile acid metabolism in rats, some of whom were exposed to voluntary exercise.

KEY RESULTS

Nigral overexpression of α-synuclein resulted in significant neuronal loss in the ileal submucosal plexus with no change in enteric glia. In contrast, the myenteric plexus showed a significant increase in glial expression, while neuronal numbers were maintained. Concomitant alterations were observed in the gut microbiome and related bile acid metabolism. Voluntary running protected against neuronal loss, increased enteric glial expression, and modified gut microbiome composition in the brain-injected AAV-α-synuclein PD model.

CONCLUSIONS AND INFERENCES

These results show that developing nigral α-synuclein pathology in this PD model exerts significant alterations on the enteric nervous system (ENS) and gut microbiome that are receptive to modification by exercise. This highlights brain to gut communication as an important mechanism in PD pathology.

Characterization of novel conformation-selective α-synuclein antibodies as potential immunotherapeutic agents for Parkinson's disease

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are progressive neurodegenerative diseases for which there is no disease-modifying treatment. PD and DLB are characterized by aggregation of the synaptic protein α-synuclein, and there is compelling evidence to suggest that progression of these diseases is associated with the trans-cellular spread of pathogenic α-synuclein through the brains of afflicted individuals. Therapies targeting extracellular, pathogenic α-synuclein may therefore hold promise for slowing or halting disease progression. In this regard, it has been suggested that highly-selective antibodies can be administered as therapeutic agents targeting pathogenic proteins. In the current study, we screened a series of antibodies using multiple selection criterion to identify those that selectively bind pathogenic α-synuclein and show potent inhibition of pathology seeding in a neuronal model of α-synucleinopathy. A lead antibody was tested in a mouse model of PD, and it was able to reduce the spread of α-synuclein pathology in the brain and attenuate dopamine reductions in the striatum. This study highlights the therapeutic potential of α-synuclein immunotherapy for the treatment of PD and DLB, and provides a framework for screening of α-synuclein antibodies to identify those with preferred properties.

Dissecting α-synuclein inclusion pathology diversity in multiple system atrophy: implications for the prion-like transmission hypothesis

Synucleinopathies are a group of neurodegenerative diseases characterized by the accumulation of insoluble, aggregated α-synuclein (αS) pathological inclusions. Multiple system atrophy (MSA) presents with extensive oligodendroglial αS pathology and additional more limited neuronal inclusions while most of the other synucleinopathies, such as Parkinson's disease and dementia with Lewy bodies (DLB), develop αS pathology primarily in neuronal cell populations. αS biochemical alterations specific to MSA have been described but thorough examination of these unique and disease-specific protein deposits is further warranted especially given recent findings implicating the prion-like nature of synucleinopathies perhaps with distinct strain-like properties. Taking advantage of an extensive panel of antibodies that target a wide range of epitopes within αS, we investigated the distinct properties of the various types of αS inclusion present in MSA brains with comparison to DLB. Brain biochemical fractionation followed by immunoblotting revealed that the immunoreactive profiles were significantly more consistent for DLB than for MSA. Furthermore, epitope-specific immunohistochemistry varied greatly between different types of MSA αS inclusions and even within different brain regions of individual MSA brains. These studies highlight the importance of using a battery of antibodies for adequate appreciation of the various pathology in this distinct synucleinopathy. In addition, it can be posited that if the spread of pathology in MSA undergoes prion-like mechanisms, "strains" of αS aggregated conformers must be inherently unstable and readily mutable, perhaps resulting in a more stochastic progression process.

Antibodies against alpha-synuclein: tools and therapies

Synucleinopathies including Parkinson's disease, dementia with Lewy bodies and multiple system atrophy are characterized by the abnormal accumulation and propagation of α-synuclein (α-syn) pathology in the central and peripheral nervous system as Lewy bodies or glial cytoplasmic inclusions. Several antibodies against α-syn have been developed since it was first detected as the major component of Lewy bodies and glial cytoplasmic inclusions. Over the years, researchers have generated specific antibodies that alleviate the accumulation of intracellular aggregated α-syn and associated pathology in cellular and preclinical models of synucleinopathies. So far, antibodies have been the first choice as tools for research and diagnosis and currently, a wide variety of antibody fragments have been developed as an alternative to full-length antibodies for increasing its therapeutic usefulness. Recently, conformation specific antibody-based approaches have been found to be promising as therapeutic strategies, both to block α-syn aggregation and ameliorate the resultant cytotoxicity, and as diagnostic tools. In this review, we summarize different α-syn specific antibodies and provide their usefulness in tackling synucleinopathies. This article is part of the Special Issue "Synuclein".

rAAV-based brain slice culture models of Alzheimer's and Parkinson's disease inclusion pathologies

It has been challenging to produce ex vivo models of the inclusion pathologies that are hallmark pathologies of many neurodegenerative diseases. Using three-dimensional mouse brain slice cultures (BSCs), we have developed a paradigm that rapidly and robustly recapitulates mature neurofibrillary inclusion and Lewy body formation found in Alzheimer's and Parkinson's disease, respectively. This was achieved by transducing the BSCs with recombinant adeno-associated viruses (rAAVs) that express α-synuclein or variants of tau. Notably, the tauopathy BSC model enables screening of small molecule therapeutics and tracking of neurodegeneration. More generally, the rAAV BSC "toolkit" enables efficient transduction and transgene expression from neurons, microglia, astrocytes, and oligodendrocytes, alone or in combination, with transgene expression lasting for many months. These rAAV-based BSC models provide a cost-effective and facile alternative to in vivo studies, and in the future can become a widely adopted methodology to explore physiological and pathological mechanisms related to brain function and dysfunction.

Living in Promiscuity: The Multiple Partners of Alpha-Synuclein at the Synapse in Physiology and Pathology

Alpha-synuclein (α-syn) is a small protein that, in neurons, localizes predominantly to presynaptic terminals. Due to elevated conformational plasticity, which can be affected by environmental factors, in addition to undergoing disorder-to-order transition upon interaction with different interactants, α-syn is counted among the intrinsically disordered proteins (IDPs) family. As with many other IDPs, α-syn is considered a hub protein. This function is particularly relevant at synaptic sites, where α-syn is abundant and interacts with many partners, such as monoamine transporters, cytoskeletal components, lipid membranes, chaperones and synaptic vesicles (SV)-associated proteins. These protein–protein and protein–lipid membrane interactions are crucial for synaptic functional homeostasis, and alterations in α-syn can cause disruption of this complex network, and thus a failure of the synaptic machinery. Alterations of the synaptic environment or post-translational modification of α-syn can induce its misfolding, resulting in the formation of oligomers or fibrillary aggregates. These α-syn species are thought to play a pathological role in neurodegenerative disorders with α-syn deposits such as Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), which are referred to as synucleinopathies. Here, we aim at revising the complex and promiscuous role of α-syn at synaptic terminals in order to decipher whether α-syn molecular interactants may influence its conformational state, contributing to its aggregation, or whether they are just affected by it.

Downregulation of tyrosine hydroxylase phenotype after AAV injection above substantia nigra: Caution in experimental models of Parkinson's disease

Adeno-associated virus (AAV) vector-mediated delivery of human α-synuclein (α-syn) gene in rat substantia nigra (SN) results in increased expression of α-syn protein in the SN and striatum which can progressively degenerate dopaminergic neurons. Therefore, this model is thought to recapitulate the neurodegeneration in Parkinson's disease. Here, using AAV to deliver α-syn above the SN in male and female rats resulted in clear expression of human α-syn in the SN and striatum. The protein was associated with moderate behavioral deficits and some loss of tyrosine hydroxylase (TH) in the nigrostriatal areas. However, the immunohistochemistry results were highly variable and showed little to no correlation with behavior and the amount of α-syn present. Expression of green fluorescent protein (GFP) was used as a control to monitor gene delivery and expression efficacy. AAV-GFP resulted in a similar or greater TH loss compared to AAV-α-syn and therefore an additional vector that does not express a protein was tested. Vectors with double-floxed inverse open reading frame (DIO ORF) encoding fluorescent proteins that generate RNA that is not translated also resulted in TH downregulation in the SN but showed no significant behavioral deficits. These results demonstrate that although expression of wild-type human α-syn can cause neurodegeneration, the variability and lack of correlation with outcome measures are drawbacks with the model. Furthermore, design and control selection should be considered carefully because of conflicting conclusions due to AAV downregulation of TH, and we recommend caution with having highly regulated TH as the only marker for the dopamine system.

Physiological C-terminal truncation of α-synuclein potentiates the prion-like formation of pathological inclusions

α-Synuclein (αsyn) aggregates into toxic fibrils in multiple neurodegenerative diseases where these fibrils form characteristic pathological inclusions such as Lewy bodies (LBs). The mechanisms initiating αsyn aggregation into fibrils are unclear, but ubiquitous post-translational modifications of αsyn present in LBs may play a role. Specific C-terminally (C)-truncated forms of αsyn are present within human pathological inclusions and form under physiological conditions likely in lysosome-associated pathways, but the roles for these C-truncated forms of αsyn in inclusion formation and disease are not well understood. Herein, we characterized the in vitro aggregation properties, amyloid fibril structures, and ability to induce full-length (FL) αsyn aggregation through prion-like mechanisms for eight of the most common physiological C-truncated forms of αsyn (1-115, 1-119, 1-122, 1-124, 1-125, 1-129, 1-133, and 1-135). In vitro, C-truncated αsyn aggregated more readily than FL αsyn and formed fibrils with unique morphologies. The presence of C-truncated αsyn potentiated aggregation of FL αsyn in vitro through co-polymerization. Specific C-truncated forms of αsyn in cells also exacerbated seeded aggregation of αsyn. Furthermore, in primary neuronal cultures, co-polymers of C-truncated and FL αsyn were potent prion-like seeds, but polymers composed solely of the C-truncated protein were not. These experiments indicated that specific physiological C-truncated forms of αsyn have distinct aggregation properties, including the ability to modulate the prion-like aggregation and seeding activity of FL αsyn. Proteolytic formation of these C-truncated species may have an important role in both the initiation of αsyn pathological inclusions and further progression of disease with strain-like properties.

Comparison of the in vivo induction and transmission of α-synuclein pathology by mutant α-synuclein fibril seeds in transgenic mice

Parkinson's disease (PD) is one of many neurodegenerative diseases termed synucleinopathies, neuropathologically defined by inclusions containing aggregated α-synuclein (αS). αS gene (SNCA) mutations can directly cause autosomal dominant PD. In vitro studies demonstrated that SNCA missense mutations may either enhance or diminish αS aggregation but cross-seeding of mutant and wild-type αS proteins appear to reduce aggregation efficiency. Here, we extended these studies by assessing the effects of seeded αS aggregation in αS transgenic mice through intracerebral or peripheral injection of various mutant αS fibrils. We observed modestly decreased time to paralysis in mice transgenic for human A53T αS (line M83) intramuscularly injected with H50Q, G51D or A53E αS fibrils relative to wild-type αS fibrils. Conversely, E46K αS fibril seeding was significantly delayed and less efficient in the same experimental paradigm. However, the amount and distribution of αS inclusions in the central nervous system were similar for all αS fibril muscle injected mice that developed paralysis. Mice transgenic for human αS (line M20) injected in the hippocampus with wild-type, H50Q, G51D or A53E αS fibrils displayed induction of αS inclusion pathology that increased and spread over time. By comparison, induction of αS aggregation following the intrahippocampal injection of E46K αS fibrils in M20 mice was much less efficient. These findings show that H50Q, G51D or A53E can efficiently cross-seed and induce αS pathology in vivo. In contrast, E46K αS fibrils are intrinsically inefficient at seeding αS inclusion pathology. Consistent with previous in vitro studies, E46K αS polymers are likely distinct aggregated conformers that may represent a unique prion-like strain of αS.

α-Synuclein and Polyunsaturated Fatty Acids: Molecular Basis of the Interaction and Implication in Neurodegeneration

α-Synuclein (α-syn) is a 140-amino acid protein, the physiological function of which has yet to be clarified. It is involved in several neurodegenerative disorders, and the interaction of the protein with brain lipids plays an important role in the pathogenesis of Parkinson’s disease (PD). Polyunsaturated fatty acids (PUFA) are highly abundant in the brain where they play critical roles in neuronal membrane fluidity and permeability, serve as energy reserves and function as second messengers in cell signaling. PUFA concentration and composition in the brain are altered with age when also an increase of lipid peroxidation is observed. Considering that PD is clearly correlated with oxidative stress, PUFA abundance and composition became of great interest in neurodegeneration studies because of PUFA’s high propensity to oxidize. The high levels of the PUFA docosahexaenoic acid (DHA) in brain areas containing α-syn inclusions in patients with PD further support the hypothesis of possible interactions between α-syn and DHA. Additionally, a possible functional role of α-syn in sequestering the early peroxidation products of fatty acids was recently proposed. Here, we provide an overview of the current knowledge regarding the molecular interactions between α-syn and fatty acids and the effect exerted by the protein on their oxidative state. We highlight recent findings supporting a neuroprotective role of the protein, linking α-syn, altered lipid composition in neurodegenerative disorders and PD development.

Measurements of auto-antibodies to α-synuclein in the serum and cerebral spinal fluids of patients with Parkinson's disease

Biomarkers for α-synuclein are needed for diagnosis and prognosis in Parkinson's disease (PD). Endogenous auto-antibodies to α-synuclein could serve as biomarkers for underlying synucleinopathy, but previous assessments of auto-antibodies have shown variability and inconsistent clinical correlations. We hypothesized that auto-antibodies to α-synuclein could be diagnostic for PD and explain its clinical heterogeneity. To test this hypothesis, we developed an enzyme-linked immunosorbent assay for measuring α-synuclein auto-antibodies in human samples. We evaluated 69 serum samples (16 healthy controls (HC) and 53 PD patients) and 145 CSF samples (52 HC and 93 PD patients) from our Institution. Both serum and CSF were available for 24 participants. Males had higher auto-antibody levels than females in both fluids. CSF auto-antibody levels were significantly higher in PD patients as compared with HC, whereas serum levels were not significantly different. CSF auto-antibody levels did not associate with amyloid-β_1-42 , total tau, or phosphorylated tau. CSF auto-antibody levels correlated with performance on the Montreal Cognitive Assessment, even when controlled for CSF amyloidβ_1-42 . CSF hemoglobin levels, as a proxy for contamination of CSF by blood during lumbar puncture, did not influence these observations. Using recombinant α-synuclein with N- and C-terminal truncations, we found that CSF auto-antibodies target amino acids 100 through 120 of α-synuclein. We conclude that endogenous CSF auto-antibodies are significantly higher in PD patients as compared with HC, suggesting that they could indicate the presence of underlying synucleinopathy. These auto-antibodies associate with poor cognition, independently of CSF amyloidβ_1-42 , and target a select C-terminal region of α-synuclein. Read the Editorial Highlight for this article on page 433.

[A rational approach to obtaining high-specific polyclonal antibodies against recombinant alpha-synuclein]

The approach for the quick and efficient production ofpolyclonal antibodies tothe target antigen alpha-synuclein has been proposed. Two methods have been employed to purify specific rabbit polyclonal antibodies against recombinant human alpha-synuclein, produced by subcutaneous immunization with complete Freund's adjuvant. It was shown that purification on CNBr-activated Sepharose with immobilized alpha-synuclein resulted in antibody preparation with rabbit serum histidine-rich glycoprotein as a contaminant. Two-stage antibody purification procedure first on Sepharose with immobilized protein G, and then on alpha-synuclein immobilized column helps to avoid contamination and to obtain homogenous antibody preparation. Antibodies recognize different conformations of alpha-synuclein and can be used in a variety of immunochemical approaches, including immunocytochemistry.

Partial loss of ATP13A2 causes selective gliosis independent of robust lipofuscinosis

Loss-of-function mutations in ATP13A2 are associated with three neurodegenerative diseases: a rare form of Parkinson's disease termed Kufor-Rakeb syndrome (KRS), a lysosomal storage disorder termed neuronal ceroid lipofuscinosis (NCL), and a form of hereditary spastic paraplegia (HSP). Furthermore, recent data suggests that heterozygous carriers of mutations in ATP13A2 may confer risk for the development of Parkinson's disease, similar to the association of mutations in glucocerebrosidase (GBA) with both Parkinson's disease and Gaucher's disease, a lysosomal storage disorder. Mutations in ATP13A2 are generally thought to be loss of function; however, the lack of human autopsy tissue has prevented the field from determining the pathological consequences of losing functional ATP13A2. We and others have previously neuropathologically characterized mice completely lacking murine Atp13a2, demonstrating the presence of lipofuscinosis within the brain - a key feature of NCL, one of the diseases to which ATP13A2 mutations have been linked. To determine if loss of one functional Atp13a2 allele can serve as a risk factor for disease, we have now assessed heterozygous Atp13a2 knockout mice for key features of NCL. In this report, we demonstrate that loss of one functional Atp13a2 allele leads to both microgliosis and astrocytosis in multiple brain regions compared to age-matched controls; however, levels of lipofuscin were only modestly elevated in the cortex of heterozygous Atp13a2 knockout mice over controls. This data suggests the possibility that partial loss of ATP13A2 causes inflammatory changes within the brain which appear to be independent of robust lipofuscinosis. This study suggests that heterozygous loss-of-function mutations in ATP13A2 are likely harmful and indicates that glial involvement in the disease process may be an early event that positions the CNS for subsequent disease development.

Oleuropein aglycone stabilizes the monomeric α-synuclein and favours the growth of non-toxic aggregates

α-synuclein plays a key role in the pathogenesis of Parkinson’s disease (PD); its deposits are found as amyloid fibrils in Lewy bodies and Lewy neurites, the histopathological hallmarks of PD. Amyloid fibrillation is a progressive polymerization path starting from peptide/protein misfolding and proceeding through the transient growth of oligomeric intermediates widely considered as the most toxic species. Consequently, a promising approach of intervention against PD might be preventing α-synuclein build-up, misfolding and aggregation. A possible strategy involves the use of small molecules able to slow down the aggregation process or to alter oligomer conformation favouring the growth of non-pathogenic species. Here, we show that oleuropein aglycone (OleA), the main olive oil polyphenol, exhibits anti-amyloidogenic power in vitro by interacting with, and stabilizing, α-synuclein monomers thus hampering the growth of on-pathway oligomers and favouring the growth of stable and harmless aggregates with no tendency to evolve into other cytotoxic amyloids. We investigated the molecular basis of such interference by both biophysical techniques and limited proteolysis; aggregate morphology was monitored by electron microscopy. We also found that OleA reduces the cytotoxicity of α-synuclein aggregates by hindering their binding to cell membrane components and preventing the resulting oxidative damage to cells.

Animal Toxins as Therapeutic Tools to Treat Neurodegenerative Diseases

Neurodegenerative diseases affect millions of individuals worldwide. So far, no disease-modifying drug is available to treat patients, making the search for effective drugs an urgent need. Neurodegeneration is triggered by the activation of several cellular processes, including oxidative stress, mitochondrial impairment, neuroinflammation, aging, aggregate formation, glutamatergic excitotoxicity, and apoptosis. Therefore, many research groups aim to identify drugs that may inhibit one or more of these events leading to neuronal cell death. Venoms are fruitful natural sources of new molecules, which have been relentlessly enhanced by evolution through natural selection. Several studies indicate that venom components can exhibit selectivity and affinity for a wide variety of targets in mammalian systems. For instance, an expressive number of natural peptides identified in venoms from animals, such as snakes, scorpions, bees, and spiders, were shown to lessen inflammation, regulate glutamate release, modify neurotransmitter levels, block ion channel activation, decrease the number of protein aggregates, and increase the levels of neuroprotective factors. Thus, these venom components hold potential as therapeutic tools to slow or even halt neurodegeneration. However, there are many technological issues to overcome, as venom peptides are hard to obtain and characterize and the amount obtained from natural sources is insufficient to perform all the necessary experiments and tests. Fortunately, technological improvements regarding heterologous protein expression, as well as peptide chemical synthesis will help to provide enough quantities and allow chemical and pharmacological enhancements of these natural occurring compounds. Thus, the main focus of this review is to highlight the most promising studies evaluating animal toxins as therapeutic tools to treat a wide variety of neurodegenerative conditions, including Alzheimer’s disease, Parkinson’s disease, brain ischemia, glaucoma, amyotrophic lateral sclerosis, and multiple sclerosis.

Reduction of Immunoreactivity Against the C-Terminal Region of the Intracellular α-Synuclein by Exogenous α-Synuclein Aggregates: Possibility of Conformational Changes

BACKGROUND

The formation of intracellular aggregates containing α-synuclein (α-syn) is a main pathological feature of Parkinson disease. The propagation of α-syn aggregation via cell-to-cell transmission has been implicated in the progression of Parkinson disease.

OBJECTIVE

Our aim is to clarify the molecular mechanisms underlying the formation of intracellular aggregation by extracellular α-syn.

METHODS

We investigated the effects of exogenous α-syn aggregates on intracellular α-syn immunoreactivity in α-syn-overexpressing SH-SY5Y cells using two antibodies to distinct epitopes of α-syn. To obtain α-syn aggregates, α-syn solution was aged with continuous agitation.

RESULTS

Immunoreactivity against the acidic C-terminal domain of the intracellular α-syn was reduced by exposure to agedα-syn, whereas that against the hydrophobic non-amyloid component region was not changed. The reduction in immunoreactivity was not suppressed by protease inhibitors but was mimicked by neutralization of the negative charges on the C-terminal of the intracellular α-syn induced by spermine or extracellular acidification.

CONCLUSIONS

These results suggest that the reduction in immunoreactivity is attributed not to proteolytic cleavage but to a conformational change at the C-terminus of the intracellular α-syn. The conformational change at the C-terminus of the intracellular α-syn might be involved in an initial step of fibril formation by exogenous α-syn aggregates.

Prion-like transmission of α-synuclein pathology in the context of an NFL null background

Neurofilaments are a major component of the axonal cytoskeleton in neurons and have been implicated in a number of neurodegenerative diseases due to their presence within characteristic pathological inclusions. Their contributions to these diseases are not yet fully understood, but previous studies investigated the effects of ablating the obligate subunit of neurofilaments, low molecular mass neurofilament subunit (NFL), on disease phenotypes in transgenic mouse models of Alzheimer's disease and tauopathy. Here, we tested the effects of ablating NFL in α-synuclein M83 transgenic mice expressing the human pathogenic A53T mutation, by breeding them onto an NFL null background. The induction and spread of α-synuclein inclusion pathology was triggered by the injection of preformed α-synuclein fibrils into the gastrocnemius muscle or hippocampus in M83 versus M83/NFL null mice. We observed no difference in the post-injection time to motor-impairment and paralysis endpoint or amount and distribution of α-synuclein inclusion pathology in the muscle injected M83 and M83/NFL null mice. Hippocampal injected M83/NFL null mice displayed subtle region-specific differences in the amount of α-synuclein inclusions however, pathology was observed in the same regions as the M83 mice. Overall, we observed only minor differences in the induction and transmission of α-synuclein pathology in these induced models of synucleinopathy in the presence or absence of NFL. This suggests that NFL and neurofilaments do not play a major role in influencing the induction and transmission of α-synuclein aggregation.

A novel panel of α-synuclein antibodies reveal distinctive staining profiles in synucleinopathies

Synucleinopathies are a spectrum of neurodegenerative diseases characterized by the intracellular deposition of the protein α-synuclein leading to multiple outcomes, including dementia and Parkinsonism. Recent findings support the notion that across the spectrum of synucleinopathies there exist diverse but specific biochemical modifications and/or structural conformations of α-synuclein, which would give rise to protein strain specific prion-like intercellular transmission, a proposed model that could explain synucleinopathies disease progression. Herein, we characterized a panel of antibodies with epitopes within both the C- and N- termini of α-synuclein. A comprehensive analysis of human pathological tissue and mouse models of synucleinopathy with these antibodies support the notion that α-synuclein exists in distinct modified forms and/or structural variants. Furthermore, these well-characterized and specific tools allow the investigation of biochemical changes associated with α-synuclein inclusion formation. We have identified several antibodies of interest with diverse staining and epitope properties that will prove useful in future investigations of strain specific disease progression and the development of targeted immunotherapeutic approaches to synucleinopathies.

Novel conformation-selective alpha-synuclein antibodies raised against different in vitro fibril forms show distinct patterns of Lewy pathology in Parkinson's disease

AIMS

The aim of this study was to test the hypothesis that different conformations of misfolded α-synuclein (α-syn) are present in Parkinson's disease (PD) brain.

METHODS

Using two previously characterized conformations of α-syn fibrils, we generated new conformation-selective α-syn monoclonal antibodies (mAbs). We then interrogated multiple brain regions in a well-characterized autopsy cohort of PD patients (n = 49) with these mAbs, Syn7015 and Syn9029.

RESULTS

Syn7015 detects Lewy bodies (LBs) and Lewy neurites (LNs) formed by pathological α-syn in all brain regions tested, and is particularly sensitive to LNs and small Lewy dots, inclusions believed to form early in the disease. Further, we observed colocalization between Syn7015 and an early marker of α-syn pathology formation, phospho-Ser129-α-syn, and a lack of extensive colocalization with markers of more mature pathology. In comparison, Syn9029 detects Lewy pathology in all regions examined, but indicates significantly fewer LNs than Syn7015. In addition, colocalization of Syn9029 with later markers of α-syn pathology maturation (ubiquitin and P62) suggests that the pathology detected by Syn9029 is older. Semiquantitative scoring of both LN and LB pathology in nine brain regions further established this trend, with Syn7015 LN scores consistently higher than Syn9029 LN scores.

CONCLUSIONS

Our data indicate that different conformations of α-syn pathology are present in PD brain and correspond to different stages of maturity for Lewy pathology. Regional analysis of Syn7015 and Syn9029 immunostaining also provides support for the Braak hypothesis that α-syn pathology advances through the brain.

Brain-to-stomach transfer of α-synuclein via vagal preganglionic projections

Detection of α-synuclein lesions in peripheral tissues is a feature of human synucleinopathies of likely pathogenetic relevance and bearing important clinical implications. Experiments were carried out to elucidate the relationship between α-synuclein accumulation in the brain and in peripheral organs, and to identify potential pathways involved in long-distance protein transfer. Results of this in vivo study revealed a route-specific transmission of α-synuclein from the rat brain to the stomach. Following targeted midbrain overexpression of human α-synuclein, the exogenous protein was capable of reaching the gastric wall where it was accumulated into preganglionic vagal terminals. This brain-to-stomach connection likely involved intra- and inter-neuronal transfer of non-fibrillar α-synuclein that first reached the medulla oblongata, then gained access into cholinergic neurons of the dorsal motor nucleus of the vagus nerve and finally traveled via efferent fibers of these neurons contained within the vagus nerve. Data also showed a particular propensity of vagal motor neurons and efferents to accrue α-synuclein and deliver it to peripheral tissues; indeed, following its midbrain overexpression, human α-synuclein was detected within gastric nerve endings of visceromotor but not viscerosensory vagal projections. Thus, the dorsal motor nucleus of the vagus nerve represents a key relay center for central-to-peripheral α-synuclein transmission, and efferent vagal fibers may act as unique conduits for protein transfer. The presence of α-synuclein in peripheral tissues could reflect, at least in some synucleinopathy patients, an ongoing pathological process that originates within the brain and, from there, reaches distant organs innervated by motor vagal projections.

Treadmill exercise alleviates nigrostriatal dopaminergic loss of neurons and fibers in rotenone-induced Parkinson rats

Parkinson disease is one of the common brain diseases caused by dopaminergic neuronal loss in the substantia nigra and dopaminergic fiber loss in the striatum. In the present study, the effects of treadmill exercise on motor performance, dopaminergic loss of neurons and fibers, and α-synuclein expression in the nigrostriatum were evaluated using rotenone-induced Parkinson rats. For the induction of Parkinson rats, 3-mg/kg rotenone was injected, once a day for 14 consecutive days. Treadmill running was conducted for 30 min once a day during 14 consecutive days. Rota-rod test for motor balance and coordination and immunohistochemistry for tyrosine hydroxylase and α-synuclein in the nigrostriatum were performed. In the present study, motor balance and coordination was disturbed by induction of rotenone-induced Parkinson disease, in contrast, treadmill exercise alleviated motor dysfunction in the rotenone-induced Parkinson rats. Nigrostriatal dopaminergic loss of neurons and fibers was occurred by induction of rotenone-induced Parkinson disease, in contrast, treadmill exercise alleviated nigrostriatal dopaminergic loss of neurons and fibers in the rotenone-induced Parkinson rats. α-Synuclein expression in the nigrostriatum was enhanced by induction of rotenone-induced Parkinson disease, in contrast, treadmill exercise suppressed α-synuclein expression in the rotenone-induced Parkinson rats. Treadmill exercise improved motor function through preservation of nigrostriatal dopaminergic neurons and fibers and suppression of nigrostriatal formation of Lewy bodies in rotenone-induced Parkinson rats.

Mapping of Surface-Exposed Epitopes of In Vitro and In Vivo Aggregated Species of Alpha-Synuclein

Aggregated alpha-synuclein is the main component of Lewy bodies, intraneuronal deposits observed in Parkinson’s disease and dementia with Lewy bodies. The objective of the study was to identify surface-exposed epitopes of alpha-synuclein in vitro and in vivo formed aggregates. Polyclonal immunoglobulin Y antibodies were raised against short linear peptides of the alpha-synuclein molecule. An epitope in the N-terminal region (1–10) and all C-terminal epitopes (90–140) were found to be exposed in an indirect enzyme-linked immunosorbent assay (ELISA) using recombinant monomeric, oligomeric, and fibrillar alpha-synuclein. In a phospholipid ELISA, the N-terminus and mid-region of alpha-synuclein (i.e., 1–90) were associated with phosphatidylserine and thus occluded from antibody binding. The antibodies that reacted most strongly with epitopes in the in vitro aggregates (i.e., 1–10 and epitopes between positions 90–140) also labeled alpha-synuclein inclusions in brains from transgenic (Thy-1)-h[A30P] alpha-synuclein mice and Lewy bodies and Lewy neurites in brains of patients with alpha-synucleinopathies. However, differences in reactivity were observed with the C-terminal antibodies when brain tissue from human and transgenic mice was compared. Taken together, the study shows that although similar epitopes are exposed in both in vitro and in vivo formed alpha-synuclein inclusions, structural heterogeneity can be observed between different molecular species.