Microglia jointly degrade fibrillar alpha-synuclein cargo by distribution through tunneling nanotubes.

Microglia are the CNS resident immune cells that react to misfolded proteins through pattern recognition receptor ligation and activation of inflammatory pathways. Here, we studied how microglia handle and cope with α-synuclein (α-syn) fibrils and their clearance. We found that microglia exposed to α-syn establish a cellular network through the formation of F-actin-dependent intercellular connections, which transfer α-syn from overloaded microglia to neighboring naive microglia where the α-syn cargo got rapidly and effectively degraded. Lowering the α-syn burden attenuated the inflammatory profile of microglia and improved their survival. This degradation strategy was compromised in cells carrying the LRRK2 G2019S mutation. We confirmed the intercellular transfer of α-syn assemblies in microglia using organotypic slice cultures, 2-photon microscopy, and neuropathology of patients. Together, these data identify a mechanism by which microglia create an "on-demand" functional network in order to improve pathogenic α-syn clearance.

Aptamer binding footprints discriminate α-synuclein fibrillar polymorphs from different synucleinopathies.

Synucleinopathies, including dementia with Lewy bodies (DLB), Parkinson's disease (PD), and multiple system atrophy (MSA), are characterized by the presence of α-synuclein (α-syn) aggregates in the central nervous system. Recent evidence suggests that the heterogeneity of synucleinopathies may be partly explained by the fact that patients may have different α-syn fibrillar polymorphs with structural differences. In this study, we identify nuclease resistant 2'fluoro-pyrimidine RNA aptamers that can differentially bind to structurally distinct α-syn fibrillar polymorphs. Moreover, we introduce a method, AptaFOOT-Seq, designed to rapidly assess the affinity of a mixture of these aptamers for different α-SYN fibrillar polymorphs using next-generation sequencing. Our findings reveal that the binding behavior of aptamers can be very different when they are tested separately or in the presence of other aptamers. In this case, competition and cooperation can occur, providing a higher level of information, which can be exploited to obtain specific 'footprints' for different α-Syn fibrillar polymorphs. Notably, these footprints can distinguish polymorphs obtained from patients with PD, DLB or MSA. This result suggests that aptaFOOT-Seq could be used for the detection of misfolded or abnormal protein conformations to improve the diagnosis of synucleinopathies.

Transmissible long-term neuroprotective and pro-cognitive effects of 1-42 beta-amyloid with A2T icelandic mutation in an Alzheimer's disease mouse model.

The amyloid cascade hypothesis assumes that the development of Alzheimer's disease (AD) is driven by a self-perpetuating cycle, in which ß-amyloid (Aß) accumulation leads to Tau pathology and neuronal damages. A particular mutation (A673T) of the amyloid precursor protein (APP) was identified among Icelandic population. It provides a protective effect against Alzheimer- and age-related cognitive decline. This APP mutation leads to the reduced production of Aß with A2T (position in peptide sequence) change (Aßice). In addition, Aßice has the capacity to form protective heterodimers in association with wild-type Aß. Despite the emerging interest in Aßice during the last decade, the impact of Aßice on events associated with the amyloid cascade has never been reported. First, the effects of Aßice were evaluated in vitro by electrophysiology on hippocampal slices and by studying synapse morphology in cortical neurons. We showed that Aßice protects against endogenous Aß-mediated synaptotoxicity. Second, as several studies have outlined that a single intracerebral administration of Aß can worsen Aß deposition and cognitive functions several months after the inoculation, we evaluated in vivo the long-term effects of a single inoculation of Aßice or Aß-wild-type (Aßwt) in the hippocampus of transgenic mice (APPswe/PS1dE9) over-expressing Aß1-42 peptide. Interestingly, we found that the single intra-hippocampal inoculation of Aßice to mice rescued synaptic density and spatial memory losses four months post-inoculation, compared with Aßwt inoculation. Although Aß load was not modulated by Aßice infusion, the amount of Tau-positive neuritic plaques was significantly reduced. Finally, a lower phagocytosis by microglia of post-synaptic compounds was detected in Aßice-inoculated animals, which can partly explain the increased density of synapses in the Aßice animals. Thus, a single event as Aßice inoculation can improve the fate of AD-associated pathology and phenotype in mice several months after the event. These results open unexpected fields to develop innovative therapeutic strategies against AD.

Synapses do not facilitate prion-like transfer of alpha-synuclein: a quantitative study in reconstructed unidirectional neural networks.

Alpha-synuclein (aSyn) aggregation spreads between cells and underlies the progression of neuronal lesions in the brain of patients with synucleinopathies such as Parkinson's diseases. The mechanisms of cell-to-cell propagation of aggregates, which dictate how aggregation progresses at the network level, remain poorly understood. Notably, while prion and prion-like spreading is often simplistically envisioned as a "domino-like" spreading scenario where connected neurons sequentially propagate protein aggregation to each other, the reality is likely to be more nuanced. Here, we demonstrate that the spreading of preformed aSyn aggregates is a limited process that occurs through molecular sieving of large aSyn seeds. We further show that this process is not facilitated by synaptic connections. This was achieved through the development and characterization of a new microfluidic platform that allows reconstruction of binary fully oriented neuronal networks in vitro with no unwanted backward connections, and through the careful quantification of fluorescent aSyn aggregates spreading between neurons. While this allowed us for the first time to extract quantitative data of protein seeds dissemination along neural pathways, our data suggest that prion-like dissemination of proteinopathic seeding aggregates occurs very progressively and leads to highly compartmentalized pattern of protein seeding in neural networks.

Functional and neuropathological changes induced by injection of distinct alpha-synuclein strains: A pilot study in non-human primates.

The role of alpha-synuclein in Parkinson's disease has been heavily investigated since its discovery as a component of Lewy bodies. Recent rodent data demonstrate that alpha-synuclein strain structure is critical for differential propagation and toxicity. Based on these findings, we have compared, for the first time, in this pilot study, the capacity of two alpha-synuclein strains and patient-derived Lewy body extracts to model synucleinopathies after intra-putaminal injection in the non-human primate brain. Functional alterations triggered by these injections were evaluated in vivo using glucose positron emission tomography imaging. Post-mortem immunohistochemical and biochemical analyses were used to detect neuropathological alterations in the dopaminergic system and alpha-synuclein pathology propagation. In vivo results revealed a decrease in glucose metabolism more pronounced in alpha-synuclein strain-injected animals. Histology showed a decreased number of dopaminergic tyrosine hydroxylase-positive cells in the substantia nigra to different extents according to the inoculum used. Biochemistry revealed that alpha-synuclein-induced aggregation, phosphorylation, and propagation in different brain regions are strain-specific. Our findings show that distinct alpha-synuclein strains can induce specific patterns of synucleinopathy in the non-human primate, changes in the nigrostriatal pathway, and functional alterations that resemble early-stage Parkinson's disease.

Clustering of Tau fibrils impairs the synaptic composition of α3-Na+/K+-ATPase and AMPA receptors.

Tau assemblies have prion-like properties: they propagate from one neuron to another and amplify by seeding the aggregation of endogenous Tau. Although key in prion-like propagation, the binding of exogenous Tau assemblies to the plasma membrane of naïve neurons is not understood. We report that fibrillar Tau forms clusters at the plasma membrane following lateral diffusion. We found that the fibrils interact with the Na+/K+-ATPase (NKA) and AMPA receptors. The consequence of the clustering is a reduction in the amount of α3-NKA and an increase in the amount of GluA2-AMPA receptor at synapses. Furthermore, fibrillar Tau destabilizes functional NKA complexes. Tau and α-synuclein aggregates often co-exist in patients' brains. We now show evidences for cross-talk between these pathogenic aggregates with α-synuclein fibrils dramatically enhancing fibrillar Tau clustering and synaptic localization. Our results suggest that fibrillar α-synuclein and Tau cross-talk at the plasma membrane imbalance neuronal homeostasis.

Microglial NLRP3 Inflammasome Activation upon TLR2 and TLR5 Ligation by Distinct α-Synuclein Assemblies.

Parkinson's disease (PD) is the second most common age-related neurodegenerative disorder and is characterized by the formation of cellular inclusions inside neurons that are rich in an abnormal form of the protein α-synuclein (α-syn). Microglia are the CNS resident immune cells that react to misfolded proteins through pattern recognition receptor ligation and activation of signaling transduction pathways. Here, we studied activation of primary microglia isolated from wild-type mouse by distinct α-syn forms and their clearance. Internalization of α-syn monomers and oligomers efficiently activated the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome via TLR2 and TLR5 ligation, thereby acting on different signaling checkpoints. We found that primary microglia effectively engulf α-syn but hesitate in its degradation. NLRP3 inhibition by the selective inhibitor CRID3 sodium salt and NLRP3 deficiency improved the overall clearance of α-syn oligomers. Together, these data show that distinct α-syn forms exert different microglial NLRP3 inflammasome activation properties, thereby compromising its degradation, which can be prevented by NLRP3 inhibition.

Disassembly of Tau fibrils by the human Hsp70 disaggregation machinery generates small seeding-competent species.

The accumulation of amyloid Tau aggregates is implicated in Alzheimer's disease (AD) and other tauopathies. Molecular chaperones are known to maintain protein homeostasis. Here, we show that an ATP-dependent human chaperone system disassembles Tau fibrils in vitro We found that this function is mediated by the core chaperone HSC70, assisted by specific cochaperones, in particular class B J-domain proteins and a heat shock protein 110 (Hsp110)-type nucleotide exchange factor (NEF). The Hsp70 disaggregation machinery processed recombinant fibrils assembled from all six Tau isoforms as well as Sarkosyl-resistant Tau aggregates extracted from cell cultures and human AD brain tissues, demonstrating the ability of the Hsp70 machinery to recognize a broad range of Tau aggregates. However, the chaperone activity released monomeric and small oligomeric Tau species, which induced the aggregation of self-propagating Tau conformers in a Tau cell culture model. We conclude that the activity of the Hsp70 disaggregation machinery is a double-edged sword, as it eliminates Tau amyloids at the cost of generating new seeds.

Distinct alpha-Synuclein species induced by seeding are selectively cleared by the Lysosome or the Proteasome in neuronally differentiated SH-SY5Y cells.

A major pathological feature of Parkinson's disease (PD) is the aberrant accumulation of misfolded assemblies of alpha-synuclein (α-Syn). Protein clearance appears as a regulator of the 'α-Syn burden' underlying PD pathogenesis. The picture emerging is that a combination of pathways with complementary roles, including the Proteasome System and the Autophagy-Lysosome Pathway, contributes to the intracellular degradation of α-Syn. This study addresses the mechanisms governing the degradation of α-Syn species seeded by exogenous fibrils in neuronally differentiated SH-SY5Y neuroblastoma cells with inducible expression of α-Syn. Using human α-Syn recombinant fibrils (pre-formed fibrils, PFFs), seeding and aggregation of endogenous Proteinase K (PK)-resistant α-Syn species occurs within a time frame of 6 days, and is still prominent after 12 days of PFF addition. Clearance of α-Syn assemblies in this inducible model was enhanced after switching off α-Syn expression with doxycycline. Lysosomal inhibition led to accumulation of SDS-soluble α-Syn aggregates 6 days after PFF-addition or when switching off α-Syn expression. Additionally, the autophagic enhancer, rapamycin, induced the clearance of α-Syn aggregates 13 days post-PFF addition, indicating that autophagy is the major pathway for aggregated α-Syn clearance. SDS-soluble phosphorylated α-Syn at S129 was only apparent at 7 days of incubation with a higher amount of PFFs. Proteasomal inhibition resulted in further accumulation of SDS-soluble phosphorylated α-Syn at S129, with limited PK resistance. Our data suggest that in this inducible model autophagy is mainly responsible for the degradation of fibrillar α-Syn, whereas the proteasome system is responsible, at least in part, for the selective clearance of phosphorylated α-Syn oligomers.

Probing amyloid fibril secondary structures by infrared nanospectroscopy: experimental and theoretical considerations.

Amyloid fibrils are composed of aggregated peptides or proteins in a fibrillary structure with a higher ß-sheet content than their native structure. Attenuated total reflection Fourier transform infrared spectroscopy only provides bulk analysis of a sample therefore it is impossible to discriminate between different aggregated structures. To overcome this limitation, near-field techniques like AFM-IR have emerged in the last twenty years to allow infrared nanospectroscopy. This technique obtains IR spectra with a spatial resolution of ten nanometres, the size of isolated fibrils. Here, we present essential practical considerations to avoid misinterpretations and artefacts during these analyses. Effects of polarization of the incident IR laser, illumination configuration and coating of the AFM probes are discussed, including the advantages and drawbacks of their use. This approach will improve interpretation of AFM-IR spectra especially for the determination of secondary structures of species not accessible using classical ATR-FTIR.

Crucial Role of FABP3 in αSyn-Induced Reduction of Septal GABAergic Neurons and Cognitive Decline in Mice.

In synucleinopathies, while motor symptoms are thought to be attributed to the accumulation of misfolded α-synuclein (αSyn) in nigral dopaminergic neurons, it remains to be elucidated how cognitive decline arises. Here, we investigated the effects of distinct αSyn strains on cognition and the related neuropathology in the medial septum/diagonal band (MS/DB), a key region for cognitive processing. Bilateral injection of αSyn fibrils into the dorsal striatum potently impaired cognition in mice. The cognitive decline was accompanied by accumulation of phosphorylated αSyn at Ser129 and reduction of gamma-aminobutyric acid (GABA)-ergic but not cholinergic neurons in the MS/DB. Since we have demonstrated that fatty acid-binding protein 3 (FABP3) is critical for αSyn neurotoxicity in nigral dopaminergic neurons, we investigated whether FABP3 also participates in αSyn pathology in the MS/DB and cognitive decline. FABP3 was highly expressed in GABAergic but rarely in cholinergic neurons in the MS/DB. Notably, Fabp3 deletion antagonized the accumulation of phosphorylated αSyn, decrease in GABAergic neurons, and cognitive impairment caused by αSyn fibrils. Overall, the present study indicates that FABP3 mediates αSyn neurotoxicity in septal GABAergic neurons and the resultant cognitive impairment, and that FABP3 in this subpopulation could be a therapeutic target for dementia in synucleinopathies.

Atomic Force Microscopy Imaging and Nanomechanical Properties of Six Tau Isoform Assemblies.

The amyloid fibrillar form of the protein Tau is involved in a number of neurodegenerative diseases, also known as tauopathies. In this work, six different fibrillar Tau isoforms were assembled in vitro. The morphological and nanomechanical properties of these isoforms were studied using atomic force microscopy at high resolution in air and buffer. Our results demonstrate that all Tau isoform fibrils exhibit paired-helical-filament-like structures consisting of two protofibrils separated by a shallow groove. Interestingly, whereas the N-terminal inserts do not contribute to any morphological or mechanical difference between the isoforms with the same carboxyl-terminal microtubule-binding domain repeats, isoforms with four microtubule repeats (4R) exhibited a persistence length ranging from 2.0 to 2.8 µm, almost twofold higher than those with three repeats (3R). In addition, the axial Young's modulus values derived from the persistence lengths, as well as their radial ones determined via nanoindentation experiments, were very low compared to amyloid fibrils made of other proteins. This sheds light on the weak intermolecular interaction acting between the paired ß-sheets within Tau fibrils. This may play an important role in their association into high molecular weight assemblies, their dynamics, their persistence, their clearance in cells, and their propagation.

Differential Membrane Binding and Seeding of Distinct α-Synuclein Fibrillar Polymorphs.

The aggregation of the protein α-synuclein (α-Syn) leads to different synucleinopathies. We recently showed that structurally distinct fibrillar α-Syn polymorphs trigger either Parkinson's disease or multiple system atrophy hallmarks in vivo. Here, we establish a structural-molecular basis for these observations. We show that distinct fibrillar α-Syn polymorphs bind to and cluster differentially at the plasma membrane in both primary neuronal cultures and organotypic hippocampal slice cultures from wild-type mice. We demonstrate a polymorph-dependent and concentration-dependent seeding. We show a polymorph-dependent differential synaptic redistribution of α3-Na+/K+-ATPase, GluA2 subunit containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, and GluN2B-subunit containing N-methyl-D-aspartate receptors, but not GluA1 subunit containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and metabotropic glutamate receptor 5 receptors. We also demonstrate polymorph-dependent alteration in neuronal network activity upon seeded aggregation of α-Syn. Our findings bring new, to our knowledge, insight into how distinct α-Syn polymorphs differentially bind to and seed monomeric α-Syn aggregation within neurons, thus affecting neuronal homeostasis through the redistribution of synaptic proteins.

Tunneling nanotubes spread fibrillar α-synuclein by intercellular trafficking of lysosomes.

Synucleinopathies such as Parkinson's disease are characterized by the pathological deposition of misfolded α-synuclein aggregates into inclusions throughout the central and peripheral nervous system. Mounting evidence suggests that intercellular propagation of α-synuclein aggregates may contribute to the neuropathology; however, the mechanism by which spread occurs is not fully understood. By using quantitative fluorescence microscopy with co-cultured neurons, here we show that α-synuclein fibrils efficiently transfer from donor to acceptor cells through tunneling nanotubes (TNTs) inside lysosomal vesicles. Following transfer through TNTs, α-synuclein fibrils are able to seed soluble α-synuclein aggregation in the cytosol of acceptor cells. We propose that donor cells overloaded with α-synuclein aggregates in lysosomes dispose of this material by hijacking TNT-mediated intercellular trafficking. Our findings thus reveal a possible novel role of TNTs and lysosomes in the progression of synucleinopathies.

Interaction of the chaperones alpha B-crystallin and CHIP with fibrillar alpha-synuclein: Effects on internalization by cells and identification of interacting interfaces.

The spread of fibrillar alpha-synuclein from affected to naïve neuronal cells is thought to contribute to the progression of synucleinopathies. The binding of fibrillar alpha-synuclein to the plasma membrane is key in this process. We and others previously showed that coating fibrillar alpha-synuclein by the molecular chaperone Hsc70 affects fibrils properties. Here we assessed the effect of the two molecular chaperones alpha B-crystallin and CHIP on alpha-synuclein fibrils uptake by Neuro-2a cells. We demonstrate that both chaperones diminish fibrils take up by cells. We identify through a cross-linking and mass spectrometry strategy the interaction interfaces between alpha-synuclein fibrils and alpha B-crystallin or CHIP. Our results open the way for designing chaperone-derived polypeptide binders that interfere with the propagation of pathogenic alpha-synuclein assemblies.

Dipeptide repeat derived from C9orf72 hexanucleotide expansions forms amyloids or natively unfolded structures in vitro.

The abnormal repetition of the hexanucleotide GGGGCC within the C9orf72 gene is the most common genetic cause of both Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD). Different hypothesis have been proposed to explain the pathogenicity of this mutation. Among them, the production of aberrant proteins called Dipeptide Repeat Proteins (DPR) from the repeated sequence. Those proteins are of interest, as they are toxic and form insoluble deposits in patient brains. In this study, we characterized the structural features of three different DPR encoded by the hexanucleotide repeat GGGGCC, namely poly-GA, poly-GP and poly-PA. We showed that DPR are natively unstructured proteins and that only poly-GA forms in vitro fibrillary aggregates. Poly-GA fibrils are of amyloid nature as revealed by their high content in beta sheets. They neither bind Thioflavin T nor Primuline, the commonly used amyloid fluorescent dyes. Remarkably, not all of the poly-GA primary structure was part of fibrils amyloid core.

Increased Immune Activation by Pathologic α-Synuclein in Parkinson's Disease.

OBJECTIVE: Excessive inflammation in the central nervous system (CNS) and the periphery can result in neurodegeneration and parkinsonism. Recent evidence suggests that immune responses in Parkinson disease patients are dysregulated, leading to an increased inflammatory reaction to unspecific triggers. Although α-synuclein pathology is the hallmark of Parkinson disease, it has not been investigated whether pathologic α-synuclein is a specific trigger for excessive inflammatory responses in Parkinson disease. METHODS: We investigated the immune response of primary human monocytes and a microglial cell line to pathologic forms of α-synuclein by assessing cytokine release upon exposure. RESULTS: We show that pathologic α-synuclein (mutations, aggregation) results in a robust inflammatory activation of human monocytes and microglial BV2 cells. The activation is conformation- dependent, with increasing fibrillation and early onset mutations having the strongest effect on immune activation. We also found that activation of immune cells by extracellular α-synuclein is potentiated by extracellular vesicles, possibly by facilitating the uptake of α-synuclein. Blood extracellular vesicles from Parkinson disease patients induce a stronger activation of monocytes than blood extracellular vesicles from healthy controls. Most importantly, monocytes from Parkinson disease patients are dysregulated and hyperactive in response to stimulation with pathologic α-synuclein. Furthermore, we demonstrate that α-synuclein pathology in the CNS is sufficient to induce the monocyte dysregulation in the periphery of a mouse model. INTERPRETATION: Taken together, our data suggest that α-synuclein pathology and dysregulation of monocytes in Parkinson disease can act together to induce excessive inflammatory responses to α-synuclein. ANN NEUROL 2019;86:593-606.

The structural differences between patient-derived α-synuclein strains dictate characteristics of Parkinson's disease, multiple system atrophy and dementia with Lewy bodies.

Synucleinopathies, such as Parkinson's disease (PD), multiple system atrophy (MSA), and dementia with Lewy bodies (DLB), are defined by the presence of α-synuclein (αSYN) aggregates throughout the nervous system but diverge from one another with regard to their clinical and pathological phenotype. The recent generation of pure fibrillar αSYN polymorphs with noticeable differences in structural and phenotypic traits has led to the hypothesis that different αSYN strains may be in part responsible for the heterogeneous nature of synucleinopathies. To further characterize distinct αSYN strains in the human brain, and establish a structure-pathology relationship, we pursued a detailed comparison of αSYN assemblies derived from well-stratified patients with distinct synucleinopathies. We exploited the capacity of αSYN aggregates found in the brain of patients suffering from PD, MSA or DLB to seed and template monomeric human αSYN in vitro via a protein misfolding cyclic amplification assay. A careful comparison of the properties of total brain homogenates and pure in vitro amplified αSYN fibrillar assemblies upon inoculation in cells and in the rat brain demonstrates that the intrinsic structure of αSYN fibrils dictates synucleinopathies characteristics. We report that MSA strains show several similarities with PD strains, but are significantly more potent in inducing motor deficits, nigrostriatal neurodegeneration, αSYN pathology, spreading, and inflammation, reflecting the aggressive nature of this disease. In contrast, DLB strains display no or only very modest neuropathological features under our experimental conditions. Collectively, our data demonstrate a specific signature for PD, MSA, and DLB-derived strains that differs from previously described recombinant strains, with MSA strains provoking the most aggressive phenotype and more similarities with PD compared to DLB strains.

α-synuclein oligomers and fibrils: a spectrum of species, a spectrum of toxicities.

This review article provides an overview of the different species that α-synuclein aggregates can populate. It also attempts to reconcile conflicting views regarding the cytotoxic roles of oligomers versus fibrils. α-synuclein, while highly dynamic in the monomeric state, can access a large number of different assembly states. Depending on assembly conditions, these states can interconvert over different timescales. The fibrillar state is the most thermodynamically favored due to the many stabilizing interactions formed between each monomeric unit, but different fibrillar types form at different rates. The end distribution is likely to reflect kinetic partitioning as much as thermodynamic equilibra. In addition, metastable oligomeric species, some of which are on-pathway and others off-pathway, can be populated for remarkably long periods of time. Chemical modifications (phosphorylation, oxidation, covalent links to ligands, etc.) perturb these physical interconversions and invariably destabilize the fibrillar state, leading to small prefibrillar assemblies which can coalesce into amorphous states. Both oligomeric and fibrillar species have been shown to be cytotoxic although firm conclusions require very careful evaluation of particle concentrations and is complicated by the great variety and heterogeneity of different experimentally observed states. The mechanistic relationship between oligomers and fibrils remains to be clarified, both in terms of assembly of oligomers into fibrils and potential dissolution of fibrils into oligomers. While oligomers are possibly implicated in the collapse of neuronal homeostasis, the fibrillar state(s) appears to be the most efficient at propagating itself both in vitro and in vivo, pointing to critical roles for multiple different aggregate species in the progression of Parkinson's disease (https://onlinelibrary.wiley.com/page/journal/14714159/homepage/virtual_issues.htm). This article is part of the Special Issue "Synuclein".

Detection of alpha-synuclein aggregates in gastrointestinal biopsies by protein misfolding cyclic amplification.

Lewy bodies and neurites, the pathological signatures found in the central nervous system of Parkinson's disease (PD) patients, are primarily composed of aggregated alpha-synuclein (aSyn). The observation that aSyn aggregates are also found in the enteric nervous system has prompted several studies aimed at developing a diagnostic procedure based on the detection of pathological aSyn in gastrointestinal (GI) biopsies. The existing studies, which have all used immunohistochemistry for the detection of pathological aSyn, have had conflicting results. In the current survey, we analyzed the seeding propensity of aSyn aggregates from GI biopsies. A total of 29 subjects participated to this study, 18 PD patients and 11 controls. For each patient, 2 to 4 GI biopsies were taken from the same site (antrum, sigmoid colon or rectum) and used to seed the aggregation of recombinant aSyn in an assay inspired from the protein misfolding cyclic amplification (PMCA) method. In a subset of patients and controls (14 and 3, respectively), one or two additional biopsies were analyzed by immunohistochemistry for the presence of phosphorylated aSyn histopathology (PASH) using antibodies against phosphorylated aSyn and PGP 9.5. Except for one subject, none of the control samples seeded aSyn aggregation in PMCA reaction. GI biopsies from patients with PD seeded aSyn aggregation in 10 out of 18 cases (7 from the sigmoid colon, 2 from the antrum and one from the rectum). There was good agreement between PMCA and immunohistochemistry results as, except for two cases, all PMCA-positive PD patients were also PASH-positive. Our findings show that the PMCA method we implemented is capable of detecting aSyn aggregates in routine GI biopsies. They also suggest that rectum biopsies do not contain sufficient amounts of aggregated aSyn to detect seeded assembly by PMCA. While encouraging, our findings indicate that further studies are needed to establish the diagnostic potential of the PMCA method we implemented to detect aSyn aggregates in upper GI biopsies.