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The first case of CWD in a Norwegian red deer was detected by a routine ELISA test and confirmed by western blotting and immunohistochemistry in the brain stem of the animal. Two different western blotting tests were conducted independently in two different laboratories, showing that the red deer glycoprofile was different from the Norwegian CWD reindeer and CWD moose and from North American CWD. The isolate showed nevertheless features similar to the classical BSE (BSE-C) strain. Furthermore, BSE-C could not be excluded based on the PrPSc immunohistochemistry staining in the brainstem and the absence of detectable PrPSc in the lymphoid tissues. Because of the known ability of BSE-C to cross species barriers as well as its zoonotic potential, the CWD red deer isolate was submitted to the EURL Strain Typing Expert Group (STEG) as a BSE-C suspect for further investigation. In addition, different strain typing in vivo and in vitro strategies aiming at identifying the BSE-C strain in the red deer isolate were performed independently in three research groups and BSE-C was not found in it. These results suggest that the Norwegian CWD red deer case was infected with a previously unknown CWD type and further investigation is needed to determine the characteristics of this potential new CWD strain. [ABSTRACT FROM AUTHOR]

Simple Summary: Prions are novel infectious agents that consist only of protein. It is known that in the same host species, different strains of prion can occur that differ by the cells that are infected and killed. The mechanism responsible for these observations is only beginning to be understood. Two main ideas, which are not mutually exclusive, may provide a framework to understand strain targeting. The first possibility is that as prions spread throughout the CNS they reach strain-specific populations of cells that trigger cell death. The second mechanism is that prions exist in two distinct forms, a replicative form that switches to the production of a toxic form that results in the destruction of cells and the eventual onset of clinical signs of disease. Both neurons and glia may participate in both of these possibilities. The relative contributions of each mechanism have yet to be determined. Prion diseases are caused by the disease-specific self-templating infectious conformation of the host-encoded prion protein, PrPSc. Prion strains are operationally defined as a heritable phenotype of disease under controlled conditions. One of the hallmark phenotypes of prion strain diversity is tropism within and between tissues. A defining feature of prion strains is the regional distribution of PrPSc in the CNS. Additionally, in both natural and experimental prion disease, stark differences in the tropism of prions in secondary lymphoreticular system tissues occur. The mechanism underlying prion tropism is unknown; however, several possible hypotheses have been proposed. Clinical target areas are prion strain-specific populations of neurons within the CNS that are susceptible to neurodegeneration following the replication of prions past a toxic threshold. Alternatively, the switch from a replicative to toxic form of PrPSc may drive prion tropism. The normal form of the prion protein, PrPC, is required for prion formation. More recent evidence suggests that it can mediate prion and prion-like disease neurodegeneration. In vitro systems for prion formation have indicated that cellular cofactors contribute to prion formation. Since these cofactors can be strain specific, this has led to the hypothesis that the distribution of prion formation cofactors can influence prion tropism. Overall, there is evidence to support several mechanisms of prion strain tropism; however, a unified theory has yet to emerge. [ABSTRACT FROM AUTHOR]

The presence of amyloid kuru plaques is a pathological hallmark of sporadic Creutzfeldt–Jakob disease (sCJD) of the MV2K subtype. Recently, PrP plaques (p) have been described in the white matter of a small group of CJD (p-CJD) cases with the 129MM genotype and carrying resPrPD type 1 (T1). Despite the different histopathological phenotype, the gel mobility and molecular features of p-CJD resPrPD T1 mimic those of sCJDMM1, the most common human prion disease. Here, we describe the clinical features, histopathology, and molecular properties of two distinct PrP plaque phenotypes affecting the gray matter (pGM) or the white matter (pWM) of sCJD cases with the PrP 129MM genotype (sCJDMM). Prevalence of pGM- and pWM-CJD proved comparable and was estimated to be ~ 0.6% among sporadic prion diseases and ~ 1.1% among the sCJDMM group. Mean age at onset (61 and 68 years) and disease duration (~ 7 months) of pWM- and pGM-CJD did not differ significantly. PrP plaques were mostly confined to the cerebellar cortex in pGM-CJD, but were ubiquitous in pWM-CJD. Typing of resPrPD T1 showed an unglycosylated fragment of ~ 20 kDa (T120) in pGM-CJD and sCJDMM1 patients, while a doublet of ~ 21–20 kDa (T121−20) was a molecular signature of pWM-CJD in subcortical regions. In addition, conformational characteristics of pWM-CJD resPrPD T1 differed from those of pGM-CJD and sCJDMM1. Inoculation of pWM-CJD and sCJDMM1 brain extracts to transgenic mice expressing human PrP reproduced the histotype with PrP plaques only in mice challenged with pWM-CJD. Furthermore, T120 of pWM-CJD, but not T121, was propagated in mice. These data suggest that T121 and T120 of pWM-CJD, and T120 of sCJDMM1 are distinct prion strains. Further studies are required to shed light on the etiology of p-CJD cases, particularly those of T120 of the novel pGM-CJD subtype. [ABSTRACT FROM AUTHOR]

Prion diseases are caused by the disease-specific self-templating infectious conformation of the host-encoded prion protein, PrPSc. Prion strains are operationally defined as a heritable phenotype of disease under controlled conditions. One of the hallmark phenotypes of prion strain diversity is tropism within and between tissues. A defining feature of prion strains is the regional distribution of PrPSc in the CNS. Additionally, in both natural and experimental prion disease, stark differences in the tropism of prions in secondary lymphoreticular system tissues occur. The mechanism underlying prion tropism is unknown; however, several possible hypotheses have been proposed. Clinical target areas are prion strain-specific populations of neurons within the CNS that are susceptible to neurodegeneration following the replication of prions past a toxic threshold. Alternatively, the switch from a replicative to toxic form of PrPSc may drive prion tropism. The normal form of the prion protein, PrPC, is required for prion formation. More recent evidence suggests that it can mediate prion and prion-like disease neurodegeneration. In vitro systems for prion formation have indicated that cellular cofactors contribute to prion formation. Since these cofactors can be strain specific, this has led to the hypothesis that the distribution of prion formation cofactors can influence prion tropism. Overall, there is evidence to support several mechanisms of prion strain tropism; however, a unified theory has yet to emerge.

Prions replicate by a self-templating mechanism. Infidelity in the process can lead to the emergence of new infectious structures, referred to as variants or strains. The question of whether prions are prone to mis-templating is not completely answered. Our previous experiments with 23 variants of the yeast [PSI+] prion do not support broad mutability. However, it became clear recently that the heat shock protein Hsp104 can restrict [PSI+] strain variation. This raises the possibility that many transmutable variants of the prion may have been mistaken as faithful-propagating simply because the mutant structure was too sturdy or too frail to take root in the wild-type cell. Here, I alter the strength of Hsp104 in yeast, overexpressing wild-type Hsp104 or expressing the hypo-active Hsp104T160M mutant, and check if the new environments enable the variants to mutate. Two variants hitherto thought of as faithful-propagating are discovered to generate different structures, which are stabilized with the hypo-active chaperone. In contrast, most transmutable variants discovered in cells overexpressing Hsp104 have been correctly identified as such previously in wild-type cells without the overexpression. The majority of transmutable variants only mis-template the structure of VH, VK, or VL, which are the most frequently observed variants and do not spontaneously mutate. There are four additional variants that never give rise to different structures in all cell conditions tested. Therefore, quite a few [PSI+] variants are faithful-propagating, and even the transmutable ones do not freely evolve but can only change to limited structural types. [ABSTRACT FROM AUTHOR]

Mammalian prion diseases are infectious neurodegenerative diseases caused by the self-templating form of the prion protein PrP Sc . Much evidence supports the hypothesis that prions exist as a mixture of a dominant strain and minor prion strains. While it is known that prions can infect new species, the relative contribution of the dominant prion strain and minor strains in crossing the species barrier is unknown. We previously identified minor prion strains from a biologically cloned drowsy (DY) strain of hamster-adapted transmissible mink encephalopathy (TME). Here we show that these minor prion strains have increased infection efficiency to rabbit kidney epithelial cells that express hamster PrP C compared to the dominant strain DY TME. Using protein misfolding cyclic amplification (PMCA), we found that the dominant strain DY TME failed to convert mouse PrP C to PrP Sc , even after several serial passages. In contrast, the minor prion strains isolated from biologically cloned DY TME robustly converted mouse PrP C to PrP Sc in the first round of PMCA. This observation indicates that minor prion strains from the mutant spectra contribute to crossing the species barrier. Additionally, we found that the PMCA conversion efficiency for the minor prion strains tested was significantly different from each other and from the short-incubation period prion strain HY TME. This suggests that minor strain diversity may be greater than previously anticipated. These observations further expand our understanding of the mechanisms underlying the species barrier effect and has implications for assessing the zoonotic potential of prions., Importance: Prions from cattle with bovine spongiform encephalopathy have transmitted to humans, whereas scrapie from sheep and goats likely has not, suggesting that some prions can cross species barriers more easily than others. Prions are composed of a dominant strain and minor strains, and the contribution of each population to adapt to new replicative environments is unknown. Recently, minor prion strains were isolated from the biologically cloned prion strain DY TME, and these minor prion strains differed in properties from the dominant prion strain, DY TME. Here we found that these minor prion strains also differed in conversion efficiency and host range compared to the dominant strain DY TME. These novel findings provide evidence that minor prion strains contribute to interspecies transmission, underscoring the significance of minor strain components in important biological processes.

Abstract Current classifications of sporadic Creutzfeldt–Jakob disease (sCJD) identify five subtypes associated with different disease phenotypes. Most of these histopathological phenotypes (histotypes) co-distribute with distinct pairings of methionine (M)/valine (V) genotypes at codon 129 of the prion protein (PrP) gene and the type (1 or 2) of the disease-associated PrP (PrPD). Types 1 and 2 are defined by the molecular mass (~ 21 kDa and ~ 19 kDa, respectively) of the unglycosylated isoform of the proteinase K-resistant PrPD (resPrPD). We recently reported that the sCJDVV1 subtype (129VV homozygosity paired with PrPD type 1, T1) shows an electrophoretic profile where the resPrPD unglycosylated isoform is characterized by either one of two single bands of ~ 20 kDa (T120) and ~ 21 kDa (T121), or a doublet of ~ 21–20 kDa (T121−20). We also showed that T120 and T121 in sCJDVV have different conformational features but are associated with indistinguishable histotypes. The presence of three distinct molecular profiles of T1 is unique and raises the issue as to whether T120 and T121 represent distinct prion strains. To answer this question, brain homogenates from sCJDVV cases harboring each of the three resPrPD profiles, were inoculated to transgenic (Tg) mice expressing the human PrP-129M or PrP-129V genotypes. We found that T120 and T121 were faithfully replicated in Tg129V mice. Electrophoretic profile and incubation period of mice challenged with T121−20 resembled those of mice inoculated with T121 and T120, respectively. As in sCJDVV1, Tg129V mice challenged with T121 and T120 generated virtually undistinguishable histotypes. In Tg129M mice, T121 was not replicated while T120 and T121−20 generated a ~ 21–20 kDa doublet after lengthier incubation periods. On second passage, Tg129M mice incubation periods and regional PrP accumulation significantly differed in T120 and T121−20 challenged mice. Combined, these data indicate that T121 and T120 resPrPD represent distinct human prion strains associated with partially overlapping histotypes.

Prions replicate by a self-templating mechanism. Infidelity in the process can lead to the emergence of new infectious structures, referred to as variants or strains. The question of whether prions are prone to mis-templating is not completely answered. Our previous experiments with 23 variants of the yeast [PSI+] prion do not support broad mutability. However, it became clear recently that the heat shock protein Hsp104 can restrict [PSI+] strain variation. This raises the possibility that many transmutable variants of the prion may have been mistaken as faithful-propagating simply because the mutant structure was too sturdy or too frail to take root in the wild-type cell. Here, I alter the strength of Hsp104 in yeast, overexpressing wild-type Hsp104 or expressing the hypo-active Hsp104T160M mutant, and check if the new environments enable the variants to mutate. Two variants hitherto thought of as faithful-propagating are discovered to generate different structures, which are stabilized with the hypo-active chaperone. In contrast, most transmutable variants discovered in cells overexpressing Hsp104 have been correctly identified as such previously in wild-type cells without the overexpression. The majority of transmutable variants only mis-template the structure of VH, VK, or VL, which are the most frequently observed variants and do not spontaneously mutate. There are four additional variants that never give rise to different structures in all cell conditions tested. Therefore, quite a few [PSI+] variants are faithful-propagating, and even the transmutable ones do not freely evolve but can only change to limited structural types.

Abstract Current evidence indicating a role of the human prion protein (PrP) in amyloid-beta (Aβ) formation or a synergistic effect between Aβ and prion pathology remains controversial. Conflicting results also concern the frequency of the association between the two protein misfolding disorders and the issue of whether the apolipoprotein E gene (APOE) and the prion protein gene (PRNP), the major modifiers of Aβ- and PrP-related pathologies, also have a pathogenic role in other proteinopathies, including tau neurofibrillary degeneration. Here, we thoroughly characterized the Alzheimer’s disease/primary age-related tauopathy (AD/PART) spectrum in a series of 450 cases with definite sporadic or genetic Creutzfeldt-Jakob disease (CJD). Moreover, we analyzed: (i) the effect of variables known to affect CJD pathogenesis and the co-occurring Aβ- and tau-related pathologies; (II) the influence of APOE genotype on CJD pathology, and (III) the effect of AD/PART co-pathology on the clinical CJD phenotype. AD/PART characterized 74% of CJD brains, with 53.3% and 8.2% showing low or intermediate-high levels of AD pathology, and 12.4 and 11.8% definite or possible PART. There was no significant correlation between variables affecting CJD (i.e., disease subtype, prion strain, PRNP genotype) and those defining the AD/PART spectrum (i.e., ABC score, Thal phase, prevalence of CAA and Braak stage), and no difference in the distribution of APOE ε4 and ε2 genotypes among CJD subtypes. Moreover, AD/PART co-pathology did not significantly affect the clinical presentation of typical CJD, except for a tendency to increase the frequency of cognitive symptoms. Altogether, the present results seem to exclude an increased prevalence AD/PART co-pathology in sporadic and genetic CJD, and indicate that largely independent pathogenic mechanisms drive AD/PART and CJD pathology even when they coexist in the same brain.

Evolutionary biologists and disease biologists use the terms strain and adaptation in Chronic Wasting Disease (CWD) research in different ways. In evolutionary biology, a strain is a nascent genetic lineage that can be described by a genealogy, and a phylogenetic nomenclature constructed to reflect that genealogy. Prion strains are described as showing distinct host range, clinical presentation, disease progression, and neuropathological and PrP biochemical profiles, and lack information that would permit phylogenetic reconstruction of their history. Prion strains are alternative protein conformations, sometimes derived from the same genotype. I suggest referring to prion strains as ecotypes, because the variant phenotypic conformations (“strains”) are a function of the interaction between PRNP amino acid genotype and the host environment. In the case of CWD, a prion ecotype in white-tailed deer would be described by its genotype and the host in which it occurs, such as the H95 + ecotype. However, an evolutionary nomenclature is difficult because not all individuals with the same PRNP genotype show signs of CWD, therefore creating a nomenclature reflecting and one-to-one relationship between PRNP genealogy and CWD presence is difficult. Furthermore, very little information exists on the phylogenetic distribution of CWD ecotypes in wild deer populations. Adaptation has a clear meaning in evolutionary biology, the differential survival and reproduction of individual genotypes. If a new prion ecotype arises in a particular host and kills more hosts or kills at an earlier age, it is the antithesis of the evolutionary definition of adaptation. However, prion strains might be transmitted across generations epigenetically, but whether this represents adaptation depends on the fitness consequences of the strain. Protein phenotypes of PRNP that cause transmissible spongiform encephalopathies (TSEs), and CWD, are maladaptive and would not be propagated genetically or epigenetically via a process consistent with an evolutionary view of adaptation. I suggest terming the process of prion strain origination “phenotypic transformation”, and only adaptation if evidence shows they are not maladaptive and persist over evolutionary time periods (e.g., thousands of generations) and across distinct species boundaries (via inheritance). Thus, prion biologists use strain and adaptation, historically evolutionary terms, in quite different ways.

Gorkovskiy et al. observed that many [PSI+] prion isolates, obtained in yeast with the mutant Hsp104T160M chaperone, propagate poorly in wild‐type cells and suggested that Hsp104 is part of the cellular anti‐prion system, curing many nascent [PSI+] variants. Here, we argue that the concept may require reassessment. We induced [PSI+] variants in both the wild‐type and the mutant background. Three new variants were isolated in the T160M background. They exhibited lower thermostability, possessed novel structural features, and were inherently mutable, changing to well‐characterized VH, VK, and VL variants in wild‐type cells. In contrast, VH, VK, and VL of the wild‐type background, could not change freely and were lost in the mutant, due to insufficient chaperone activity. Thus, mutant Hsp104 can impose as much restriction against emerging prion variants as the wild‐type protein. Such restriction conserved the transmutable variants in the T160M background, since new structures mis‐templated from them could not gain a foothold. We further demonstrate excess Hsp104T160M or Hsp104∆2‐147 can eliminate nearly all of the [PSI+] variants in their native background. This finding contradicts the generally held belief that Hsp104‐induced [PSI+] curing requires its N‐terminal domain, and may help settling the current contention regarding how excess Hsp104 cures [PSI+]. [ABSTRACT FROM AUTHOR]

Current classifications of sporadic Creutzfeldt–Jakob disease (sCJD) identify five subtypes associated with different disease phenotypes. Most of these histopathological phenotypes (histotypes) co-distribute with distinct pairings of methionine (M)/valine (V) genotypes at codon 129 of the prion protein (PrP) gene and the type (1 or 2) of the disease-associated PrP (PrPD). Types 1 and 2 are defined by the molecular mass (~ 21 kDa and ~ 19 kDa, respectively) of the unglycosylated isoform of the proteinase K-resistant PrPD (resPrPD). We recently reported that the sCJDVV1 subtype (129VV homozygosity paired with PrPD type 1, T1) shows an electrophoretic profile where the resPrPD unglycosylated isoform is characterized by either one of two single bands of ~ 20 kDa (T120) and ~ 21 kDa (T121), or a doublet of ~ 21–20 kDa (T121−20). We also showed that T120 and T121 in sCJDVV have different conformational features but are associated with indistinguishable histotypes. The presence of three distinct molecular profiles of T1 is unique and raises the issue as to whether T120 and T121 represent distinct prion strains. To answer this question, brain homogenates from sCJDVV cases harboring each of the three resPrPD profiles, were inoculated to transgenic (Tg) mice expressing the human PrP-129M or PrP-129V genotypes. We found that T120 and T121 were faithfully replicated in Tg129V mice. Electrophoretic profile and incubation period of mice challenged with T121−20 resembled those of mice inoculated with T121 and T120, respectively. As in sCJDVV1, Tg129V mice challenged with T121 and T120 generated virtually undistinguishable histotypes. In Tg129M mice, T121 was not replicated while T120 and T121−20 generated a ~ 21–20 kDa doublet after lengthier incubation periods. On second passage, Tg129M mice incubation periods and regional PrP accumulation significantly differed in T120 and T121−20 challenged mice. Combined, these data indicate that T121 and T120 resPrPD represent distinct human prion strains associated with partially overlapping histotypes. [ABSTRACT FROM AUTHOR]

Bovine spongiform encephalopathy (BSE) is a prion disease in cattle and is classified into the classical type (C-BSE) and two atypical BSEs, designated as high type (H-BSE) and low type (L-BSE). These classifications are based on the electrophoretic migration of the proteinase K-resistant core (PrPres) of the disease-associated form of the prion protein (PrPd). In a previous study, we succeeded in transmitting the H-BSE prion from cattle to TgHaNSE mice overexpressing normal hamster cellular PrP (PrPC). Further, Western blot analysis demonstrated that PrPres banding patterns of the H-BSE prion were indistinguishable from those of the C-BSE prion in TgHaNSE mice. In addition, similar PrPres glycoprofiles were detected among H-, C-, and L-BSE prions in TgHaNSE mice. Therefore, to better understand atypical BSE prions after interspecies transmission, H-BSE prion transmission from TgHaNSE mice to hamsters was investigated, and the characteristics of classical and atypical BSE prions among hamsters, wild-type mice, and mice overexpressing bovine PrPC (TgBoPrP) were compared in this study using biochemical and neuropathological methods. Identical PrPres banding patterns were confirmed between TgHaNSE mice and hamsters in the case of all three BSE prion strains. However, these PrPres banding patterns differed from those of TgBoPrP and wild-type mice infected with the H-BSE prion. In addition, glycoprofiles of TgHaNSE mice and hamsters infected with the L-BSE prion differed from those of TgBoPrP mice infected with the L-BSE prion. These data indicate that the PrPC amino acid sequences of new host species rather than other host environmental factors may affect some molecular aspects of atypical BSE prions. Although three BSE prion strains were distinguishable based on the neuropathological features in hamsters, interspecies transmission modified some molecular properties of atypical BSE prions, and these properties were indistinguishable from those of C-BSE prions in hamsters. Taken together, PrPres banding patterns and glycoprofiles are considered to be key factors for BSE strain typing. However, this study also revealed that interspecies transmission could sometimes influence these characteristics.

Abstract Last decade witnessed an enormous progress in generating authentic infectious prions or PrPSc in vitro using recombinant prion protein (rPrP). Previous work established that rPrP that lacks posttranslational modification is able to support replication of highly infectious PrPSc with assistance of cofactors of polyanionic nature and/or lipids. Unexpectedly, previous studies also revealed that seeding of rPrP by brain-derived PrPSc gave rise to new prion strains with new disease phenotypes documenting loss of a strain identity upon replication in rPrP substrate. Up to now, it remains unclear whether prion strain identity can be preserved upon replication in rPrP. The current study reports that faithful replication of hamster strain SSLOW could be achieved in vitro using rPrP as a substrate. We found that a mixture of phosphatidylethanolamine (PE) and synthetic nucleic acid polyA was sufficient for stable replication of hamster brain-derived SSLOW PrPSc in serial Protein Misfolding Cyclic Amplification (sPMCA) that uses hamster rPrP as a substrate. The disease phenotype generated in hamsters upon transmission of recombinant PrPSc produced in vitro was strikingly similar to the original SSLOW diseases phenotype with respect to the incubation time to disease, as well as clinical, neuropathological and biochemical features. Infrared microspectroscopy (IR-MSP) indicated that PrPSc produced in animals upon transmission of recombinant PrPSc is structurally similar if not identical to the original SSLOW PrPSc. The current study is the first to demonstrate that rPrP can support replication of brain-derived PrPSc while preserving its strain identity. In addition, the current work is the first to document that successful propagation of a hamster strain could be achieved in vitro using hamster rPrP.

Co-occurrence of different prion strains into the same host has been recognized as a natural phenomenon for several sporadic Creutzfeldt-Jakob disease (sCJD) patients and natural scrapie cases. The final outcome of prion coinfection is not easily predictable. In addition to the usual factors that influence prion conversion, the replication of one strain may entail positive or negative consequences to the other. The main aim of this study was to gain insights into the prion coinfection and interference concepts and their potential therapeutic implications. Here, different mouse models were challenged with several combinations of prion strains coupled on the basis of the lengths of their incubation periods and the existence/absence of a species barrier in the tested animal model. We found that nontransmissible strains can interfere the replication of fully transmissible strains when there is a species transmission barrier involved, as happened with the combination of a mouse (22L) and a human (sCJD) strain. However, this phenomenon seems to be strain dependent, since no interference was observed when the human strain coinoculated was vCJD. For the other combinations tested in this study, the results suggest that both strains replicate independently without effect on the replication of one over the other. It is common that the strain with more favorable conditions (e.g., a higher speed of disease development or the absence of a species barrier) ends being the only one detectable at the terminal stage of the disease. However, this does not exclude the replication of the least favored strain, leading to situations of the coexistence of prion strains. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In 2007, we reported a patient with an atypical form of Creutzfeldt- Jakob disease (CJD) heterozygous for methionine-valine (MV) at codon 129 who showed a novel pathological prion protein (PrPTSE) conformation with an atypical glycoform (AG) profile and intraneuronal PrP deposition. In the present study, we further characterize the conformational properties of this pathological prion protein (PrPTSE MVAG), showing that PrPTSE MVAG is composed of multiple conformers with biochemical properties distinct from those of PrPTSE type 1 and type 2 of MV sporadic CJD (sCJD). Experimental transmission of CJD-MVAG to bank voles and genetargeted transgenic mice carrying the human prion protein gene (TgHu mice) showed unique transmission rates, survival times, neuropathological changes, PrPTSE deposition patterns, and PrPTSE glycotypes that are distinct from those of sCJD-MV1 and sCJD-MV2. These biochemical and experimental data suggest the presence of a novel prion strain in CJD-MVAG. IMPORTANCE Sporadic Creutzfeldt-Jakob disease is caused by the misfolding of the cellular prion protein, which assumes two different major conformations (type 1 and type 2) and, together with the methionine/valine polymorphic codon 129 of the prion protein gene, contribute to the occurrence of distinct clinical-pathological phenotypes. Inoculation in laboratory rodents of brain tissues from the six possible combinations of pathological prion protein types with codon 129 genotypes results in the identification of 3 or 4 strains of prions. We report on the identification of a novel strain of Creutzfeldt-Jakob disease isolated from a patient who carried an abnormally glycosylated pathological prion protein. This novel strain has unique biochemical characteristics, does not transmit to humanized transgenic mice, and shows exclusive transmission properties in bank voles. The identification of a novel human prion strain improves our understanding of the pathogenesis of the disease and of possible mechanisms of prion transmission. [ABSTRACT FROM AUTHOR]

Prion diseases or Transmissible Spongiform Encephalopathies (TSEs) are a group of fatal neurodegenerative disorders affecting several mammalian species. Its causative agent, disease-associated prion protein (PrP d ), is a self-propagating β-sheet rich aberrant conformation of the cellular prion protein (PrP C ) with neurotoxic and aggregation-prone properties, capable of inducing misfolding of PrP C molecules. PrP d is the major constituent of prions and, most importantly, is the first known example of a protein with infectious attributes. It has been suggested that similar molecular mechanisms could be shared by other proteins implicated in diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis or systemic amyloidoses. Accordingly, several terms have been proposed to collectively group all these disorders. Through the stringent evaluation of those aspects that characterise TSE-causing prions, in particular propagation and spread, strain variability or transmissibility, we will discuss whether terms such as “prion”, “prion-like”, “prionoid” or “propagon” can be used when referring to the aetiological agents of the above other disorders. Moreover, it will also be discussed whether the term “infectious”, which defines a prion essential trait, is currently misused when referring to the other misfolded proteins. [ABSTRACT FROM AUTHOR]

Prions exist as different strains exhibiting distinct disease phenotypes. Currently, the identification of prion strains is still based on biological strain typing in rodents. However, it has been shown that prion strains may be associated with distinct PrPSc biochemical types. Taking advantage of the availability of several prion strains adapted to a novel rodent model, the bank vole, we investigated if any prion strain was actually associated with distinctive PrPSc biochemical characteristics and if it was possible to univocally identify strains through PrPSc biochemical phenotypes. We selected six different vole-adapted strains (three human-derived and three animal-derived) and analyzed PrPSc from individual voles by epitope mapping of protease resistant core of PrPSc (PrPres) and by conformational stability and solubility assay. Overall, we discriminated five out of six prion strains, while two different scrapie strains showed identical PrPSc types. Our results suggest that the biochemical strain typing approach here proposed was highly discriminative, although by itself it did not allow us to identify all prion strains analyzed.

Bovine spongiform encephalopathy (BSE) and BSE-related disorders have been associated with a single major prion strain. Recently, 2 atypical, presumably sporadic forms of BSE have been associated with 2 distinct prion strains that are characterized mainly by distinct Western blot profiles of abnormal protease-resistant prion protein (PrPres), named high-type (BSE-H) and low-type (BSE-L), that also differed from classical BSE. We characterized 5 atypical BSE-H isolates by analyzing their molecular and neuropathologic properties during transmission in transgenic mice expressing homologous bovine prion protein. Unexpectedly, in several inoculated animals, strain features emerged that were highly similar to those of classical BSE agent. These findings demonstrate the capability of an atypical bovine prion to acquire classical BSE–like properties during propagation in a homologous bovine prion protein context and support the view that the epidemic BSE agent could have originated from such a cattle prion.

Prions are infectious proteins where the same protein may express distinct strains. The strains are enciphered by different misfolded conformations. Strain-like phenomena have also been reported in a number of other amyloid-forming proteins. One of the features of amyloid strains is the ability to self-propagate, maintaining a constant set of physical properties despite being propagated under conditions different from those that allowed initial formation of the strain. Here we report a cross-seeding experiment using strains formed under different conditions. Using high concentrations of seeds results in rapid elongation and new fibrils preserve the properties of the seeding fibrils. At low seed concentrations, secondary nucleation plays the major role and new fibrils gain properties predicted by the environment rather than the structure of the seeds. Our findings could explain conformational switching between amyloid strains observed in a wide variety of in vivo and in vitro experiments.

Neurodegeneration is a common neuropathological feature of prion diseases. Although evidence of apoptosis was found in natural and experimental prion diseases, the precise mechanisms by which neurons die are poorly understood. The pro-apoptotic BAX protein, a key factor of the mitochondrial pathway, plays a central role in the regulation of neuronal apoptosis. Recently, BAX was implicated in neuronal death in a transgenic model of inherited prion disease. Nevertheless, whether neurodegeneration occurs by similar mechanisms in other prion diseases remains unknown. Here, using mice knocked out for the Bax gene, we investigated BAX implication in neuronal death induced by a prion disease of infectious origin. A mouse-adapted prion strain of bovine spongiform encephalopathy (BSE) was inoculated intracerebrally into Bax−/− mice and their wild-type littermates. We found that Bax inactivation did not alter the development of the disease. Clinical illness was not prevented. PrPres deposition and astrogliosis occurred to the usual extent. Neuronal integrity was not maintained, and neurons in hippocampus and thalamus were not protected. These results demonstrated that BAX is not necessary for neuron death induced by the BSE strain. They suggest the existence of multiple molecular death pathways in prion diseases.