Misfolded protein aggregates represent a continuum with overlapping features in neurodegenerative diseases, but differences in protein components and affected brain regions. The molecular hallmark of synucleinopathies such as Parkinson's disease, dementia with Lewy bodies and multiple system atrophy are megadalton α-synuclein-rich deposits suggestive of one molecular event causing distinct disease phenotypes. Glial α-synuclein (α-SYN) filamentous deposits are prominent in multiple system atrophy and neuronal α-SYN inclusions are found in Parkinson's disease and dementia with Lewy bodies. The discovery of α-SYN assemblies with different structural characteristics or 'strains' has led to the hypothesis that strains could account for the different clinico-pathological traits within synucleinopathies. In this study we show that α-SYN strain conformation and seeding propensity lead to distinct histopathological and behavioural phenotypes. We assess the properties of structurally well-defined α-SYN assemblies (oligomers, ribbons and fibrils) after injection in rat brain. We prove that α-SYN strains amplify in vivo. Fibrils seem to be the major toxic strain, resulting in progressive motor impairment and cell death, whereas ribbons cause a distinct histopathological phenotype displaying Parkinson's disease and multiple system atrophy traits. Additionally, we show that α-SYN assemblies cross the blood-brain barrier and distribute to the central nervous system after intravenous injection. Our results demonstrate that distinct α-SYN strains display differential seeding capacities, inducing strain-specific pathology and neurotoxic phenotypes.

α-Synuclein strains cause distinct synucleinopathies after local and systemic administration

PREFACE The advantages which have been derived from the caution with which hypothetical statements are admitted, are in no instance more obvious than in those sciences which more particularly belong to the healing art. It therefore is necessary, that some conciliatory explanation should be offered for the present publication: in which, it is acknowledged, that mere conjecture takes the place of experiment; and, that analogy is the substitute for anatomical examination, the only sure foundation for pathological knowledge. When, however, the nature of the subject, and the circumstances under which it has been here taken up, are considered, it is hoped that the offering of the following pages to the attention of the medical public, will not be severely censured. The disease, respecting which the present inquiry is made, is of a nature highly afflictive. Notwithstanding which, it has not yet obtained a place in the classification of nosologists; some have regarded its characteristic symptoms as distinct and different diseases, and others have given its name to diseases differing essentially from it; whilst the unhappy sufferer has considered it as an evil, from the domination of which he had no prospect of escape. The disease is of long duration: to connect, therefore, the symptoms which occur in its later stages with those which mark its commencement, requires a continuance of observation of the same case, or at least a correct history of its symptoms, even for several years. Of both these advantages the writer has had the opportunities of availing himself, and has hence been led particularly to observe several other cases in which the disease existed in different stages of its progress. By these repeated observations, he hoped that he had been led to a probable conjecture as to the nature of the malady, and that analogy had suggested such means as might be productive of relief, and perhaps even of cure, if employed before the disease had been too long established. He therefore considered it to be a duty to submit his opinions to the examination of others, even in their present state of immaturity and imperfection. To delay their publication did not, indeed, appear to be warrantable. The disease had escaped particular notice; and the task of ascertaining its nature and cause by anatomical investigation, did not seem likely to be taken up by those who, from their abilities and opportunities, were most likely to accomplish it. That these friends to humanity and medical science, who have already unveiled to us many of the morbid processes by which health and life is abridged, might be excited to extend their researches to this malady, was much desired; and it was hoped, that this might be procured by the publication of these remarks. Should the necessary information be thus obtained, the writer will repine at no censurewhich the precipitate publication of mere conjectural suggestions may incur: but shall think himself fully rewarded by having excited the attention of those, who may point out the most appropriate means of relieving a tedious and most distressing malady.

An Essay on the Shaking Palsy

Distinct tau prion strains propagate in cells and mice and define different tauopathies.

Misfolded α-synuclein amyloid fibrils are the principal components of Lewy bodies and neurites, hallmarks of Parkinson's disease (PD). We present a high-resolution structure of an α-synuclein fibril, in a form that induces robust pathology in primary neuronal culture, determined by solid-state NMR spectroscopy and validated by EM and X-ray fiber diffraction. Over 200 unique long-range distance restraints define a consensus structure with common amyloid features including parallel, in-register β-sheets and hydrophobic-core residues, and with substantial complexity arising from diverse structural features including an intermolecular salt bridge, a glutamine ladder, close backbone interactions involving small residues, and several steric zippers stabilizing a new orthogonal Greek-key topology. These characteristics contribute to the robust propagation of this fibril form, as supported by the structural similarity of early-onset-PD mutants. The structure provides a framework for understanding the interactions of α-synuclein with other proteins and small molecules, to aid in PD diagnosis and treatment.

/pdf/solid-state-nmr-structure-of-a-pathogenic-fibril-of-full-33lvilvf6k.pdf

Solid-state NMR structure of a pathogenic fibril of full-length human α-synuclein

The pathological assembly of Aβ, tau, and α-synuclein is at the heart of Alzheimer's and Parkinson's diseases. Extracellular deposits of Aβ and intraneuronal tau inclusions define Alzheimer's disease, whereas intracellular inclusions of α-synuclein make up the Lewy pathology of Parkinson's disease. Most cases of disease are sporadic, but some are inherited in a dominant manner. Mutations frequently occur in the genes encoding Aβ, tau, and α-synuclein. Overexpression of these mutant proteins can give rise to disease-associated phenotypes. Protein assembly begins in specific regions of the brain during the process of Alzheimer's and Parkinson's diseases, from where it spreads to other areas.

http://science.sciencemag.org/content/sci/349/6248/1255555.full.pdf

Alzheimer’s and Parkinson’s diseases: The prion concept in relation to assembled Aβ, tau, and α-synuclein

α-Synuclein aggregation is implicated in a variety of diseases including Parkinson's disease, dementia with Lewy bodies, pure autonomic failure and multiple system atrophy. The association of protein aggregates made of a single protein with a variety of clinical phenotypes has been explained for prion diseases by the existence of different strains that propagate through the infection pathway. Here we structurally and functionally characterize two polymorphs of α-synuclein. We present evidence that the two forms indeed fulfil the molecular criteria to be identified as two strains of α-synuclein. Specifically, we show that the two strains have different structures, levels of toxicity, and in vitro and in vivo seeding and propagation properties. Such strain differences may account for differences in disease progression in different individuals/cell types and/or types of synucleinopathies.

/pdf/structural-and-functional-characterization-of-two-alpha-3qtl5vqbwf.pdf

Structural and functional characterization of two alpha-synuclein strains

Molecular Interaction between the Chaperone Hsc70 and the N-terminal Flank of Huntingtin Exon 1 Modulates Aggregation

The aggregation of Huntingtin (HTT) protein and of its moiety encoded by its Exon1 (HTTExon1) into fibrillar structures inside neurons is the molecular hallmark of Huntington's disease. Prion-like transmission of these aggregates between cells has been demonstrated. The cell-to-cell transmission mechanisms of these protein aggregates and the susceptibility of different kinds of neuronal cells to these toxic assemblies still need assessment. Here we documented the binding to and internalization by differentiated and undifferentiated neuroblastoma cells of exogenous fibrillar HTTExon1 and polyglutamine (polyQ) polypeptides containing the same number of glutamines. We assessed the contribution of endocytosis to fibrillar HTTExon1 uptake, their intracellular localization and fate. We observed that undifferentiated neuroblastoma cells were more susceptible to fibrillar HTTExon1 and polyQ than their differentiated counterparts. Furthermore, we demonstrated that exogenous HTTExon1 aggregates are mainly taken up by endocytosis and directed to lysosomal compartments in both mitotic and quiescent cells. These data suggest that the rates of endocytic processes that differ in mitotic and quiescent cells strongly impact the uptake of exogenous HTTExon1 and polyQ fibrils. This may be either the consequence of distinct metabolisms or distributions of specific protein partners for amyloid-like assemblies at the surface of highly dividing versus quiescent cells. Our results highlight the importance of endocytic processes in the internalization of exogenous HTTExon1 fibrils and suggest that a proportion of those assemblies reach the cytosol where they can amplify by recruiting the endogenous protein after escaping, by yet an unknown process, from the endo-lysosomal compartments.

Binding, internalization and fate of Huntingtin Exon1 fibrillar assemblies in mitotic and nonmitotic neuroblastoma cells.

Background: Hsc70 has an alleviating effect on the toxicity of polyglutamine (polyQ)-containing proteins in vivo. Results: Hsc70 binds specifically the N-terminal flank of huntingtin exon 1. Conclusion: Hsc70 interaction with huntingtin exon 1 N-terminal flank affects the conformation of the resulting assemblies. Significance: We identify the surface interfaces between Hsc70 and huntingtin exon 1, which allows the design of future therapeutic tools. The aggregation of polyglutamine (polyQ)-containing pro- teins is at the origin of nine neurodegenerative diseases. Molec- ular chaperones prevent the aggregation of polyQ-containing proteins. The exact mechanism by which they interact with polyQ-containing, aggregation-prone proteins and interfere with their assembly is unknown. Here we dissect the mechanism of interaction between a huntingtin exon 1 fragment of increas- ing polyQ lengths (HttEx1Qn), the aggregation of which is tightly associated with Huntington's disease, and molecular chaperone Hsc70. We show that Hsc70, together with its Hsp40 co-chaperones, inhibits HttEx1Qn aggregation and modifies the structural, seeding, and infectious properties of the resulting fibrils in a polyQ-independent manner. We demonstrate that Hsc70 binds the 17-residue-long N-terminal flank of HttEx1Qn, and we map Hsc70-HttEx1Qn surface interfaces at the residue level. Finally, we show that this interaction competes with homotypic interactions between the N termini of different HttEx1Qn molecules that trigger the aggregation process. Our results lay the foundations of future therapeutic strategies tar- geting huntingtin aggregation in Huntington disease.

Gemma Ruiz-Arlandis

Papers

Structural and functional characterization of two alpha-synuclein strains

Molecular Interaction between the Chaperone Hsc70 and the N-terminal Flank of Huntingtin Exon 1 Modulates Aggregation

Binding, internalization and fate of Huntingtin Exon1 fibrillar assemblies in mitotic and nonmitotic neuroblastoma cells.

Molecular Interaction between the Chaperone Hsc70 and the N-terminal Flank of Huntingtin Exon 1 Modulates