Prion Strains and Transmission Barrier Phenomena

Several experimental evidences show that prions are non-conventional pathogens, which physical support consists only in proteins. This finding raised questions regarding the observed prion strain-to-strain variations and the species barrier that happened to be crossed with dramatic consequences on human health and veterinary policies during the last 3 decades. This review presents a focus on a few advances in the field of prion structure and prion strains characterization: from the historical approaches that allowed the concept of prion strains to emerge, to the last results demonstrating that a prion strain may in fact be a combination of a few quasi species with subtle biophysical specificities. Then, we will focus on the current knowledge on the factors that impact species barrier strength and species barrier crossing. Finally, we present probable scenarios on how the interaction of strain properties with host characteristics may account for differential selection of new conformer variants and eventually species barrier crossing

High-Pressure Response of Amyloid Folds

The abnormal protein aggregates in progressive neurodegenerative disorders, such as Alzheimer’s, Parkinson’s and prion diseases, adopt a generic structural form called amyloid fibrils. The precise amyloid fold can differ between patients and these differences are related to distinct neuropathological phenotypes of the diseases. A key focus in current research is the molecular mechanism governing such structural diversity, known as amyloid polymorphism. In this review, we focus on our recent work on recombinant prion protein (recPrP) and the use of pressure as a variable for perturbing protein structure. We suggest that the amyloid polymorphism is based on volumetric features. Accordingly, pressure is the thermodynamic parameter that fits best to exploit volume differences within the states of a chemical reaction, since it shifts the equilibrium constant to the state that has the smaller volume. In this context, there are analogies with the process of correct protein folding, the high pressure-induced effects of which have been studied for more than a century and which provides a valuable source of inspiration. We present a short overview of this background and review our recent results regarding the folding, misfolding, and aggregation-disaggregation of recPrP under pressure. We present preliminary experiments aimed at identifying how prion protein fibril diversity is related to the quaternary structure by using pressure and varying protein sequences. Finally, we consider outstanding questions and testable mechanistic hypotheses regarding the multiplicity of states in the amyloid fold

Heterogeneity and Architecture of Pathological Prion Protein Assemblies: Time to Revisit the Molecular Basis of the Prion Replication Process?

Prions are proteinaceous infectious agents responsible for a range of neurodegenerative diseases in animals and humans. Prion particles are assemblies formed from a misfolded, β-sheet rich, aggregation-prone isoform (PrPSc) of the host-encoded cellular prion protein (PrPC). Prions replicate by recruiting and converting PrPC into PrPSc, by an autocatalytic process. PrPSc is a pleiomorphic protein as different conformations can dictate different disease phenotypes in the same host species. This is the basis of the strain phenomenon in prion diseases. Recent experimental evidence suggests further structural heterogeneity in PrPSc assemblies within specific prion populations and strains. Still, this diversity is rather seen as a size continuum of assemblies with the same core structure, while analysis of the available experimental data points to the existence of structurally distinct arrangements. The atomic structure of PrPSc has not been elucidated so far, making the prion replication process difficult to understand. All currently available models suggest that PrPSc assemblies exhibit a PrPSc subunit as core constituent, which was recently identified. This review summarizes our current knowledge on prion assembly heterogeneity down to the subunit level and will discuss its importance with regard to the current molecular principles of the prion replication process

Quel impact à long terme des antibiotiques persistants apportés au sol lors de l’épandage de lisiers ?

Quel impact à long terme des antibiotiques persistants apportés au sol lors de l’épandage de lisiers ?. 4ème Séminaire d’Ecotoxicologie de l’INR

Stability analysis of a steady state of a model describing Alzheimer’s disease and interactions with prion proteins

International audienceAlzheimer's disease (AD) is a neuro-degenerative disease affecting more than 46 million people worldwide in 2015. AD is in part caused by the accumulation of Aβ peptides inside the brain. These can aggregate to form insoluble oligomers or fibrils. Oligomers have the capacity to interact with neurons via membrane receptors such as prion proteins (PrP C). This interaction leads PrP C to be misfolded in oligomeric prion proteins (PrP ol), transmitting a death signal to neurons. In this work, we propose a new mathematical model bringing together different mechanisms: Aβ polymerization, including formation of oligomers and fibrils, and interaction between Aβ oligomers and prion proteins. The model is based on Becker-Döring equations for the polymer-ization process, with delayed differential equations accounting for Aβ/PrP C interactions. We analyse the well-posedness of the model and show existence, uniqueness and non-negativity of 2 Helal et al. solutions. Moreover, we demonstrate that this model admits a non-trivial steady state, which is found to be globally stable thanks to a Lyapunov function. We finally present numerical simulations and discuss the impact of model parameters on the whole dynamics, which could constitute the main targets for pharmaceutical industry

Quel impact à long terme des antibiotiques apportés au sol lors de l’épandage de lisiers ? L’exemple de la ciprofloxacine

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Improving the Predictive Value of Prion Inactivation Validation Methods to Minimize the Risks of Iatrogenic Transmission With Medical Instruments

International audiencePrions are pathogenic infectious agents responsible for fatal, incurable neurodegenerative diseases in animals and humans. Prions are composed exclusively of an aggregated and misfolded form (PrPSc) of the cellular prion protein (PrPC). During the propagation of the disease, PrPSc recruits and misfolds PrPC into further PrPSc. In human, iatrogenic prion transmission has occurred with incompletely sterilized medical material because of the unusual resistance of prions to inactivation. Most commercial prion disinfectants validated against the historical, well-characterized laboratory strain of 263K hamster prions were recently shown to be ineffective against variant Creutzfeldt-Jakob disease human prions. These observations and previous reports support the view that any inactivation method must be validated against the prions for which they are intended to be used. Strain-specific variations in PrPSc physico-chemical properties and conformation are likely to explain the strain-specific efficacy of inactivation methods. Animal bioassays have long been used as gold standards to validate prion inactivation methods, by measuring reduction of prion infectivity. Cell-free assays such as the real-time quaking-induced conversion (RT-QuIC) assay and the protein misfolding cyclic amplification (PMCA) assay have emerged as attractive alternatives. They exploit the seeding capacities of PrPSc to exponentially amplify minute amounts of prions in biospecimens. European and certain national medicine agencies recently implemented their guidelines for prion inactivation of non-disposable medical material; they encourage or request the use of human prions and cell-free assays to improve the predictive value of the validation methods. In this review, we discuss the methodological and technical issues regarding the choice of (i) the cell-free assay, (ii) the human prion strain type, (iii) the prion-containing biological material. We also introduce a new optimized substrate for high-throughput PMCA amplification of human prions bound on steel wires, as translational model for prion-contaminated instruments

Quaternary structural convergence and structural diversification of prion assemblies at the early replication stage

Abstract Aggregation of misfolded forms from host-encoded proteins is key to the pathogenesis of a number of neurodegenerative disorders, including prion diseases, Alzheimer’s disease and Parkinson’s disease. In prion diseases, the cellular prion protein PrP C can misfold into PrP Sc and auto-organize into conformationally distinct assemblies or strains. A plethora of observations reports the existence of PrP Sc structural heterogeneity within prion strains, suggesting the emergence and coevolution of structurally distinct PrP Sc assemblies during prion replication in controlled environment. Such PrP Sc diversification processes remain poorly understood. Although central to prion host-adaptation, structural diversification of PrP Sc assemblies is also a key issue for the formation of PrP conformers involved in neuronal injury. Here, we characterized the evolution of the PrP Sc quaternary structure during prion replication in vivo and in bona fide cell-free amplification assays. Regardless of the strain studied, the early replication stage conduced to the preferential formation of small PrP Sc oligomers, thus highlighting a quaternary structural convergence phenomenon. Their evolutionary kinetics revealed the existence of a PrP C -dependent secondary templating pathway in concert with a structural rearrangement. This secondary templating pathway provides, for the first time, a mechanistic explanation for prion structural diversification during replication, a key determinant for prion adaptation on further transmission, including to other host species. The uncovered processes are also key for a better understanding of the accumulation mechanisms of other misfolded assemblies believed to propagate by a prion-like process

Crossing Species Barriers Relies on Structurally Distinct Prion Assemblies and Their Complementation

International audiencePrion replication results from the autocatalytic templated assisted conversion of the host-encoded prion protein PrPC into misfolded, polydisperse PrPSc conformers. Structurally distinct PrPSc conformers can give rise to multiple prion strains. Within and between prion strains, the biological activity (replicative efficacy and specific infectivity) of PrPSc assemblies is size dependent and thus reflects an intrinsic structural heterogeneity. The contribution of such PrPSc heterogeneity across species prion adaptation, which is believed to be based on fit adjustment between PrPSc template(s) and host PrPC, has not been explored. To define the structural-to-fitness PrPSc landscape, we measured the relative capacity of size-fractionated PrPSc assemblies from different prion strains to cross mounting species barriers in transgenic mice expressing foreign PrPC. In the absence of a transmission barrier, the relative efficacy of the isolated PrPSc assemblies to induce the disease is like the efficacy observed in the homotypic context. However, in the presence of a transmission barrier, size fractionation overtly delays and even abrogates prion pathogenesis in both the brain and spleen tissues, independently of the infectivity load of the isolated assemblies. Altering by serial dilution PrPSc assembly content of non-fractionated inocula aberrantly reduces their specific infectivity, solely in the presence of a transmission barrier. This suggests that synergy between structurally distinct PrPSc assemblies in the inoculum is requested for crossing the species barrier. Our data support a mechanism whereby overcoming prion species barrier requires complementation between structurally distinct PrPSc assemblies. This work provides key insight into the “quasispecies” concept applied to prions, which would not necessarily rely on prion substrains as constituent but on structural PrPSc heterogeneity within prion populatio