Adaptation of the bovine spongiform encephalopathy agent to primates and comparison with Creutzfeldt-- Jakob disease: implications for human health

Lack of Evidence for Transmission of Atypical H-Type Bovine Spongiform Encephalopathy Prions (H-BSE Prions) by Intracranial and Oral Challenges to Nonhuman Primates

Bovine spongiform encephalopathy (BSE) is a prion disease in cattle caused by classical-type (C-), L-type (L-), or H-type (H-) BSE prions. While C-BSE prions are zoonotic agents responsible for variant Creutzfeldt-Jakob disease, L- and H-BSE prions are believed not to be connected to human prion diseases. However, L-BSE prions have been shown to transmit to cynomolgus monkeys (Macaca fascicularis), suggesting they may have zoonotic potential. In the present study, we examined whether H-BSE prions are transmissible to cynomolgus monkeys. The monkeys were injected intracranially (n = 2) or given orally (n = 2) with brain homogenates from a cow infected with H-BSE prions. After asymptomatic observation periods of 4-6 years, the monkeys were euthanized for autopsy. Histological examination of the brain did not reveal any pathological changes. Immunohistochemical and Western blot analyses did not detect disease-associated forms of prion protein (PrPSc) in the brain, peripheral neurons, or lymphatic tissues. The unsuccessful transmission indicates an effective barrier against the transmission of cattle H-BSE prions to cynomolgus monkeys. Based on the results obtained in this nonhuman primate model, we estimated that the potential transmission of H-BSE prions to humans is substantially lower than C- and L-BSE prions.

Chronic Wasting Disease: State of the Science

Chronic wasting disease (CWD) is a prion disease affecting cervid species, both free-ranging and captive populations. As the geographic range continues to expand and disease prevalence continues to increase, CWD will have an impact on cervid populations, local economies, and ecosystem health. Mitigation of this "wicked" disease will require input from many different stakeholders including hunters, landowners, research biologists, wildlife managers, and others, working together. The NC1209 (North American interdisciplinary chronic wasting disease research consortium) is composed of scientists from different disciplines involved with investigating and managing CWD. Leveraging this broad breadth of expertise, the Consortium has created a state-of-the-science review of five key aspects of CWD, including current diagnostic capabilities for detecting prions, requirements for validating these diagnostics, the role of environmental transmission in CWD dynamics, and potential zoonotic risks associated with CWD. The goal of this review is to increase stakeholders', managers', and decision-makers' understanding of this disease informed by current scientific knowledge.

Prion assemblies: structural heterogeneity, mechanisms of formation, and role in species barrier

Prions are proteinaceous pathogens responsible for a wide range of neurodegenerative diseases in animal and human. Prions are formed from misfolded, ß-sheet rich, and aggregated conformers (PrPSc) of the host-encoded prion protein (PrPC). Prion replication stems from the capacity of PrPSc to self-replicate by templating PrPC conversion and polymerization. The question then arises about the molecular mechanisms of prion replication, host invasion, and capacity to contaminate other species. Studying these mechanisms has gained in recent years further complexity with evidence that PrPSc is a pleiomorphic protein. There is indeed compelling evidence for PrPSc structural heterogeneity at different scales: (i) within prion susceptible host populations with the existence of different strains with specific biological features due to different PrPSc conformers, (ii) within a single infected host with the co-propagation of different strains, and (iii) within a single strain with evidence for co-propagation of PrPSc assemblies differing in their secondary to quaternary structure. This review summarizes current knowledge of prion assembly heterogeneity, potential mechanisms of formation during the replication process, and importance when crossing the species barrier.

Glycans are not necessary to maintain the pathobiological features of bovine spongiform encephalopathy

The role of the glycosylation status of PrPC in the conversion to its pathological counterpart and on cross-species transmission of prion strains has been widely discussed. Here, we assessed the effect on strain characteristics of bovine spongiform encephalopathy (BSE) isolates with different transmission histories upon propagation on a model expressing a non-glycosylated human PrPC. Bovine, ovine and porcine-passaged BSE, and variant Creutzfeldt-Jakob disease (vCJD) isolates were used as seeds/inocula in both in vitro and in vivo propagation assays using the non-glycosylated human PrPC-expressing mouse model (TgNN6h). After protein misfolding cyclic amplification (PMCA), all isolates maintained the biochemical characteristics of BSE. On bioassay, all PMCA-propagated BSE prions were readily transmitted to TgNN6h mice, in agreement with our previous in vitro results. TgNN6h mice reproduced the characteristic neuropathological and biochemical hallmarks of BSE, suggesting that the absence of glycans did not alter the pathobiological features of BSE prions. Moreover, back-passage of TgNN6h-adapted BSE prions to BoTg110 mice recovered the full BSE phenotype, confirming that the glycosylation of human PrPC is not essential for the preservation of the human transmission barrier for BSE prions or for the maintenance of BSE strain properties.

Non-human primates in prion diseases

The fascinating history of prion diseases is intimately linked to the use of nonhuman primates as experimental models, which brought so fundamental and founding information about transmissibility, pathogenesis, and resistance of prions. These models are still of crucial need for risk assessment of human health and may contribute to pave a new way towards the moving field of prion-like entities which now includes the main human neurodegenerative diseases (especially Alzheimer's and Parkinson's diseases).

Guijarro L, García-Honduvilla N, Álvarez-Mon M, Buján J, García-Gallego S. Dendrimers and Dendritic Materials: From Laboratory to Medical Practice in Infectious Diseases

Infectious diseases are one of the main global public health risks, predominantly caused by viruses, bacteria, fungi, and parasites. The control of infections is founded on three main pillars: prevention, treatment, and diagnosis. However, the appearance of microbial resistance has challenged traditional strategies and demands new approaches. Dendrimers are a type of polymeric nanoparticles whose nanometric size, multivalency, biocompatibility, and structural perfection offer boundless possibilities in multiple biomedical applications. This review provides the reader a general overview about the uses of dendrimers and dendritic materials in the treatment, prevention, and diagnosis of highly prevalent infectious diseases, and their advantages compared to traditional approaches. Examples of dendrimers as antimicrobial agents per se, as nanocarriers of antimicrobial drugs, as well as their uses in gene transfection, in vaccines or as contrast agents in imaging assays are presented. Despite the need to address some challenges in order to be used in the clinic, dendritic materials appear as an innovative tool with a brilliant future ahead in the clinical management of infectious diseases and many other health issues.

Transgenic mouse models for the study of prion diseases

Prions are unique agents that challenge the molecular biology dogma by transmitting information on the protein level. They cause neurodegenerative diseases that lack of any cure or treatment called transmissible spongiform encephalopathies. The function of the normal form of the prion protein, the exact mechanism of prion propagation between species as well as at the cellular level and neuron degeneration remains elusive. However, great amount of information known for all these aspects has been achieved thanks to the use of animal models and more precisely to transgenic mouse models. In this chapter, the main contributions of these powerful research tools in the prion field are revised.

Transgenic mouse models expressing human and macaque prion protein exhibit similar prion susceptibility on a strain-dependent manner

Cynomolgus macaque has been used for the evaluation of the zoonotic potential of prion diseases, especially for classical-Bovine Spongiform Encephalopathy (classical-BSE) infectious agent. PrP amino acid sequence is considered to play a key role in the susceptibility to prion strains and only one amino acid change may alter this susceptibility. Macaque and human-PrP sequences have only nine amino acid differences, but the effect of these amino acid changes in the susceptibility to dissimilar prion strains is unknown. In this work, the transmissibility of a panel of different prions from several species was compared in transgenic mice expressing either macaque-PrP^C (TgMac) or human-PrP^C (Hu-Tg340). Similarities in the transmissibility of most prion strains were observed suggesting that macaque is an adequate model for the evaluation of human susceptibility to most of the prion strains tested. Interestingly, TgMac were more susceptible to classical-BSE strain infection than Hu-Tg340. This differential susceptibility to classical-BSE transmission should be taken into account for the interpretation of the results obtained in macaques. It could notably explain why the macaque model turned out to be so efficient (worst case model) until now to model human situation towards classical-BSE despite the limited number of animals inoculated in the laboratory experiments.

Bovine Spongiform Encephalopathy - A Review from the Perspective of Food Safety

Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative disease that belongs to transmissible spongiform encephalopathy (TSE). Since the first case was identified in the UK in 1986, BSE spread to other countries including Japan. Its incidence peaked in 1992 in the UK and from 2001 to 2006 in many other countries, but a feed ban aimed at eliminating the recycling of the BSE agent and other control measures aimed at preventing food and feed contamination with the agent were highly effective at reducing the spread of BSE. In 2004, two types of atypical BSE, H-type BSE (H-BSE) and L-type BSE (L-BSE), which differ from classical BSE (C-BSE), were found in France and Italy. Atypical BSE, which is assumed to occur spontaneously, has also been detected among cattle in other countries including Japan. The BSE agent including atypical BSE agent is a unique food-safety hazard with different chemical and biological properties from the microbial pathogens and toxic chemicals that contaminate food. In this review, we summarize the reported findings on the tissue distribution of BSE prions in infected cattle and other aspects of BSE, as well as the control measures against the disease employed in Japan. Topics that require further studies are discussed based on the summarized findings from the perspective of food safety.

Tracking and clarifying differential traits of classical- and atypical L-type bovine spongiform encephalopathy prions after transmission from cattle to cynomolgus monkeys

Classical- (C-) and atypical L-type bovine spongiform encephalopathy (BSE) prions cause different pathological phenotypes in cattle brains, and the disease-associated forms of each prion protein (PrPSc) has a dissimilar biochemical signature. Bovine C-BSE prions are the causative agent of variant Creutzfeldt-Jakob disease. To date, human infection with L-BSE prions has not been reported, but they can be transmitted experimentally from cows to cynomolgus monkeys (Macaca fascicularis), a non-human primate model. When transmitted to monkeys, C- and L-BSE prions induce different pathological phenotypes in the brain. However, when isolated from infected brains, the two prion proteins (PrPSc) have similar biochemical signatures (i.e., electrophoretic mobility, glycoforms, and resistance to proteinase K). Such similarities suggest the possibility that L-BSE prions alter their virulence to that of C-BSE prions during propagation in monkeys. To clarify this possibility, we conducted bioassays using inbred mice. C-BSE prions with or without propagation in monkeys were pathogenic to mice, and exhibited comparable incubation periods in secondary passage in mice. By contrast, L-BSE prions, either with or without propagation in monkeys, did not cause the disease in mice, indicating that the pathogenicity of L-BSE prions does not converge towards a C-BSE prion type in this primate model. These results suggest that, although C- and L-BSE prions propagated in cynomolgus monkeys exhibit similar biochemical PrPSc signatures and consist of the monkey amino acid sequence, the two prions maintain strain-specific conformations of PrPSc in which they encipher and retain unique pathogenic traits.

Unexpected prion phenotypes in experimentally transfused animals: predictive models for humans?

The recently reevaluated high prevalence of healthy carriers (1/2,000 in UK) of variant Creutzfeldt-Jakob Disease (v-CJD), whose blood might be infectious, suggests that the evolution of this prion disease might not be under full control as expected. After experimental transfusion of macaques and conventional mice with blood derived from v-CJD exposed (human and animal) individuals, we confirmed in these both models the transmissibility of v-CJD, but we also observed unexpected neurological syndromes transmissible by transfusion: despite their prion etiology confirmed through transmission experiments, these original cases would escape classical prion diagnosis, notably in the absence of detectable abnormal PrP with current techniques. It is noteworthy that macaques developed an original, yet undescribed myelopathic syndrome associating demyelination and pseudo-necrotic lesions of spinal cord, brainstem and optical tract without affecting encephalon, which is rather evocative of spinal cord disease than prion disease in human medicine. These observations strongly suggest that the spectrum of human prion diseases may extend the current field restricted to the phenotypes associated to protease-resistant PrP, and may notably include spinal cord diseases.

Lack of Transmission of Chronic Wasting Disease to Cynomolgus Macaques

Chronic wasting disease (CWD) is a fatal prion disease that can infect deer, elk, and moose. CWD was first recognized in captive deer kept in wildlife facilities in Colorado from 1967 to 1979. CWD has now been detected in 25 U.S. states, 2 Canadian provinces, South Korea, Norway, and Finland. It is currently unknown if humans are susceptible to CWD infection. Understanding the health risk from consuming meat and/or products from CWD-infected cervids is a critical human health concern. Previous research using transgenic mouse models and in vitro conversion assays suggests that a significant species barrier exists between CWD and humans. To date, reported epidemiologic studies of humans consuming cervids in areas where CWD is endemic have found no evidence to confirm CWD transmission to humans. Previously, we reported data from ongoing cross-species CWD transmission studies using two species of nonhuman primates as models. Squirrel monkeys (SM) and cynomolgus macaques (CM) were inoculated by either the intracerebral or oral route with brain homogenates from CWD-infected deer and elk containing high levels of infectivity. SM were highly susceptible to CWD infection, while CM were not. In the present study, we present new data for seven CWD-inoculated CM euthanized 11 to 13 years after CWD inoculation and eight additional uninoculated control CM. New and archival CM tissues were screened for prion infection by using the ultrasensitive real-time quaking-induced conversion (RT-QuIC) assay, immunohistochemistry, and immunoblotting. In this study, there was no clinical, pathological, or biochemical evidence suggesting that CWD was transmitted from cervids to CM.IMPORTANCE Chronic wasting disease (CWD) is a fatal prion disease found in deer, elk, and moose. Since it was first discovered in the late 1960s, CWD has now spread to at least 25 U.S. states, 2 Canadian provinces, South Korea, Norway, and Finland. Eradication of CWD from areas of endemicity is very unlikely, and additional spread will occur. As the range and prevalence of CWD increase, so will the potential for human exposure to CWD prions. It is currently unknown if CWD poses a risk to human health. However, determining this risk is critical to preventing a scenario similar to that which occurred when mad cow disease was found to be transmissible to humans. In the present study, we used cynomolgus macaque monkeys as a surrogate model for CWD transmission to humans. After 13 years, no evidence for CWD transmission to macaques was detected clinically or by using highly sensitive prion disease-screening assays.

Both murine host and inoculum modulate expression of experimental variant Creutzfeldt-Jakob disease

Transmissible spongiform encephalopathies (TSEs) are infections that are experimentally transmissible to laboratory animals. TSE agents (prions) can be serially passaged in the same animal species. The susceptibility of mice to infection with specific TSE agents can be unpredictable and must be established empirically. We challenged wild-type C57BL/6 and RIIIS/J mice and transgenic mice overexpressing bovine prion protein (TgBo110) with a human brain infected with variant Creutzfeldt-Jakob disease (vCJD) agent and pooled brains of macaques experimentally infected with human vCJD agent (first-passage macaque vCJD). The human vCJD brain yielded a wide range of infectivity titres in different mouse models; TgBo110 mice were the most sensitive. In contrast, infectivity titres of macaque vCJD brain were similar in all three murine models. The brains of RIIIS/J mice infected with both human and macaque vCJD had mild or no vacuolation, while infected C57BL/6 and TgBo110 mice had spongiform degeneration with vacuolation. Abnormal prion protein (PrP^TSE) extracted from the brains of vCJD-infected TgBo110 mice displayed different glycosylation profiles and had greater resistance to denaturation by guanidine hydrochloride than PrP^TSE from infected wild-type mice or from either inoculum. Those histopathological features of TSE and physical properties of PrP^TSE in mice with experimental vCJD were intrinsic to the host, even though we also observed differences between wild-type mice infected with either agent, suggesting a modulatory effect of the inoculum. This study compared three widely used mouse models infected with two different vCJD inocula. The results show that the host plays a major role in manifestations of experimental TSEs.

Familial human prion diseases associated with prion protein mutations Y226X and G131V are transmissible to transgenic mice expressing human prion protein

Human familial prion diseases are associated with mutations at 34 different prion protein (PrP) amino acid residues. However, it is unclear whether infectious prions are found in all cases. Mutant PrP itself may be neurotoxic, or alternatively, PrP mutation might predispose to spontaneous formation of infectious PrP isoforms. Previous reports demonstrated transmission to animal models by human brain tissue expressing 7 different PrP mutations, but 3 other mutations were not transmissible. In the present work, we tested transmission using brain homogenates from patients expressing 3 untested PrP mutants: G131V, Y226X, and Q227X. Human brain homogenates were injected intracerebrally into tg66 transgenic mice overexpressing human PrP. Mice were followed for nearly 800 days.

From 593 to 762 dpi, 4 of 8 mice injected with Y226X brain had PrPSc detectable in brain by immunostaining, immunoblot, and PrP amyloid seeding activity assayed by RT-QuIC. From 531 to 784 dpi, 11 of 11 G131V-injected mice had PrPSc deposition in brain, but none were positive by immunoblot or RT-QuIC assay. In contrast, from 529 to 798 dpi, no tg66 mice injected with Q227X brain had PrPSc or PrP amyloid seeding activity detectable by these methods. Y226X is the only one of 4 known PrP truncations associated with familial disease which has been shown to be transmissible. This transmission of prion infectivity from a patient expressing truncated human PrP may have implications for the spread and possible transmission of other aggregated truncated proteins in prion-like diseases such as Alzheimer’s disease, Parkinson’s disease and tauopathies.

Human transmissible spongiform encephalopathies: historic view

The first of several pivotal moments leading to current understanding of human transmissible spongiform encephalopathies (TSEs) occurred in 1959 when veterinary pathologist W.J. Hadlow first recognized several similarities between scrapie-a slow infection of sheep caused by an unusual infectious agent-and kuru, a fatal exotic neurodegenerative disease affecting only people of a single language group in the remote mountainous interior of New Guinea, described two years earlier by D.C. Gajdusek and V. Zigas. Based on the knowledge of scrapie, Gajdusek, C.J. Gibbs, Jr., and M.P. Alpers soon initiated efforts to transmit kuru by inoculating kuru brain tissue into non-human primates, that-although requiring several years-ultimately proved successful. In the same year that Hadlow first proposed that kuru and scrapie might have similar etiology, I. Klatzo noted that kuru's histopathology resembled that of Creutzfeldt-Jakob disease (CJD), another progressive fatal neurodegenerative disease of unknown etiology that A.M. Jakob had first described in 1921. Gajdusek and colleagues went on to demonstrate that not only the more common sporadic form of CJD but also familial CJD and a generally similar familial brain disease (Gerstmann-Sträussler-Scheinker syndrome) were also transmissible, first to non-human primates and later to other animals. (Other investigators later transmitted an even rarer brain disease, fatal familial insomnia, to animals.) Iatrogenic CJD (spread by human pituitary-derived hormones and tissue grafts) was also transmitted to animals. Much later, in 1996, a new variant of CJD was attributed to human infection with the agent of bovine spongiform encephalopathy; vCJD itself caused an iatrogenic TSE spread by blood transfusion (and probably by a human-plasma-derived clotting factor). Starting in the 1930s, the scrapie agent was found to have a unique constellation of physical properties (marked resistance to inactivation by chemicals, heat and radiation), eventually interpreted as suggesting that it might be an unconventional self-replicating pathogen based on protein and containing no nucleic acid. The work of S.B. Prusiner led to the recognition in the early 1980s that a misfolded form of a ubiquitous normal host protein was usually if not always detectable in tissues containing TSE agents, greatly facilitating the diagnosis and TSEs and understanding their pathogenesis. Prusiner proposed that the TSE agent was likely to be composed partly if not entirely of the abnormal protein, for which he coined the term "prion" protein and "prion" for the agent. Expression of the prion protein by animals-while not essential for life-was later found to be obligatory to infect them with TSEs, and a variety of mutations in the protein clearly tracked with TSEs in families, explaining the autosomal dominant pattern of disease and confirming a central role for the protein in pathogenesis. Prusiner's terminology and the prion hypothesis came to be widely though not universally accepted. A popular corollary proposal, that prions arise by spontaneous misfolding of normal prion protein leading to sporadic cases of CJD, BSE, and scrapie, is more problematic and may serve to discourage continued search for environmental sources of exposure to TSE agents.

Detection of prions in blood from patients with variant Creutzfeldt-Jakob disease

Human prion diseases are infectious and invariably fatal neurodegenerative diseases. They include sporadic Creutzfeldt-Jakob disease (sCJD), the most common form, and variant CJD (vCJD), which is caused by interspecies transmission of prions from cattle infected by bovine spongiform encephalopathy. Development of a biochemical assay for the sensitive, specific, early, and noninvasive detection of prions (PrP^Sc) in the blood of patients affected by prion disease is a top medical priority to increase the safety of the blood supply. vCJD has already been transmitted from human to human by blood transfusion, and the number of asymptomatic carriers of vCJD in the U.K. alone is estimated to be 1 in 2000 people. We used the protein misfolding cyclic amplification (PMCA) technique to analyze blood samples from 14 cases of vCJD and 153 controls, including patients affected by sCJD and other neurodegenerative or neurological disorders as well as healthy subjects. Our results showed that PrP^Sc could be detected with 100% sensitivity and specificity in blood samples from vCJD patients. Detection was possible in any of the blood fractions analyzed and could be done with as little as a few microliters of sample volume. The PrP^Sc concentration in blood was estimated to be ~0.5 pg/ml. Our findings suggest that PMCA may be useful for premortem noninvasive diagnosis of vCJD and to identify prion contamination of the blood supply. Further studies are needed to fully validate the technology.

Experimental transfusion of variant CJD-infected blood reveals previously uncharacterised prion disorder in mice and macaque

Exposure of human populations to bovine spongiform encephalopathy through contaminated food has resulted in <250 cases of variant Creutzfeldt-Jakob disease (vCJD). However, more than 99% of vCJD infections could have remained silent suggesting a long-term risk of secondary transmission particularly through blood. Here, we present experimental evidence that transfusion in mice and non-human primates of blood products from symptomatic and non-symptomatic infected donors induces not only vCJD, but also a different class of neurological impairments. These impairments can all be retransmitted to mice with a pathognomonic accumulation of abnormal prion protein, thus expanding the spectrum of known prion diseases. Our findings suggest that the intravenous route promotes propagation of masked prion variants according to different mechanisms involved in peripheral replication.

Modeling Variant Creutzfeldt-Jakob Disease and Its Pathogenesis in Non-human Primates

In the early 90s', Europe was shaken by the fear that the prions from "mad cow disease" (bovine spongiform encephalopathy) would transmit the disease to humans via beef products. In 1996, the first variant Creutzfeldt-Jakob (vCJD) patients were described, and the same year our Bovine Spongiform Encephalopathy (BSE) transmission studies to cynomolgus macaques demonstrated that the BSE prion was highly infectious for primates, inducing brain lesions identical to those observed in vCJD patients. These studies provided the first experimental evidence that vCJD was BSE in humans. Subsequent studies established the BSE/vCJD-infected cynomolgus macaque as a robust model to study the pathogenesis of vCJD. We showed rapid adaptation of BSE prions to primates upon subsequent passage, and their distribution in peripheral tissues and blood. Some key studies are summarized in the present paper.

Assessment of the PrPc Amino-Terminal Domain in Prion Species Barriers

Chronic wasting disease (CWD) in cervids and bovine spongiform encephalopathy (BSE) in cattle are prion diseases that are caused by the same protein-misfolding mechanism, but they appear to pose different risks to humans. We are interested in understanding the differences between the species barriers of CWD and BSE. We used real-time, quaking-induced conversion (RT-QuIC) to model the central molecular event in prion disease, the templated misfolding of the normal prion protein, PrP^c, to a pathogenic, amyloid isoform, scrapie prion protein, PrP^Sc We examined the role of the PrP^c amino-terminal domain (N-terminal domain [NTD], amino acids [aa] 23 to 90) in cross-species conversion by comparing the conversion efficiency of various prion seeds in either full-length (aa 23 to 231) or truncated (aa 90 to 231) PrP^c We demonstrate that the presence of white-tailed deer and bovine NTDs hindered seeded conversion of PrP^c, but human and bank vole NTDs did the opposite. Additionally, full-length human and bank vole PrP^cs were more likely to be converted to amyloid by CWD prions than were their truncated forms. A chimera with replacement of the human NTD by the bovine NTD resembled human PrP^c The requirement for an NTD, but not for the specific human sequence, suggests that the NTD interacts with other regions of the human PrP^c to increase promiscuity. These data contribute to the evidence that, in addition to primary sequence, prion species barriers are controlled by interactions of the substrate NTD with the rest of the substrate PrP^c molecule.

IMPORTANCE

We demonstrate that the amino-terminal domain of the normal prion protein, PrP^c, hinders seeded conversion of bovine and white-tailed deer PrP^cs to the prion forms, but it facilitates conversion of the human and bank vole PrP^cs to the prion forms. Additionally, we demonstrate that the amino-terminal domain of human and bank vole PrP^cs requires interaction with the rest of the molecule to facilitate conversion by CWD prions. These data suggest that interactions of the amino-terminal domain with the rest of the PrP^c molecule play an important role in the susceptibility of humans to CWD prions.

PrP aggregation can be seeded by pre-formed recombinant PrP amyloid fibrils without the replication of infectious prions

Mammalian prions are unusual infectious agents, as they are thought to consist solely of aggregates of misfolded prion protein (PrP). Generation of synthetic prions, composed of recombinant PrP (recPrP) refolded into fibrils, has been utilised to address whether PrP aggregates are, indeed, infectious prions. In several reports, neurological disease similar to transmissible spongiform encephalopathy (TSE) has been described following inoculation and passage of various forms of fibrils in transgenic mice and hamsters. However, in studies described here, we show that inoculation of recPrP fibrils does not cause TSE disease, but, instead, seeds the formation of PrP amyloid plaques in PrP-P101L knock-in transgenic mice (101LL). Importantly, both WT-recPrP fibrils and 101L-recPrP fibrils can seed plaque formation, indicating that the fibrillar conformation, and not the primary sequence of PrP in the inoculum, is important in initiating seeding. No replication of infectious prions or TSE disease was observed following both primary inoculation and subsequent subpassage. These data, therefore, argue against recPrP fibrils being infectious prions and, instead, indicate that these pre-formed seeds are acting to accelerate the formation of PrP amyloid plaques in 101LL Tg mice. In addition, these data reproduce a phenotype which was previously observed in 101LL mice following inoculation with brain extract containing in vivo-generated PrP amyloid fibrils, which has not been shown for other synthetic prion models. These data are reminiscent of the "prion-like" spread of aggregated forms of the beta-amyloid peptide (Aβ), α-synuclein and tau observed following inoculation of transgenic mice with pre-formed seeds of each misfolded protein. Hence, even when the protein is PrP, misfolding and aggregation do not reproduce the full clinicopathological phenotype of disease. The initiation and spread of protein aggregation in transgenic mouse lines following inoculation with pre-formed fibrils may, therefore, more closely resemble a seeded proteinopathy than an infectious TSE disease.

Emergence of two prion subtypes in ovine PrP transgenic mice infected with human MM2-cortical Creutzfeldt-Jakob disease prions

Introduction

Mammalian prions are proteinaceous pathogens responsible for a broad range of fatal neurodegenerative diseases in humans and animals. These diseases can occur spontaneously, such as Creutzfeldt-Jakob disease (CJD) in humans, or be acquired or inherited. Prions are primarily formed of macromolecular assemblies of the disease-associated prion protein PrP^Sc, a misfolded isoform of the host-encoded prion protein PrP^C. Within defined host-species, prions can exist as conformational variants or strains. Based on both the M/V polymorphism at codon 129 of PrP and the electrophoretic signature of PrP^Sc in the brain, sporadic CJD is classified in different subtypes, which may encode different strains. A transmission barrier, the mechanism of which remains unknown, limits prion cross-species propagation. To adapt to the new host, prions have the capacity to ‘mutate’ conformationally, leading to the emergence of a variant with new biological properties. Here, we transmitted experimentally one rare subtype of human CJD, designated cortical MM2 (129 MM with type 2 PrP^Sc), to transgenic mice overexpressing either human or the VRQ allele of ovine PrP^C.

Results

In marked contrast with the reported absence of transmission to knock-in mice expressing physiological levels of human PrP, this subtype transmitted faithfully to mice overexpressing human PrP, and exhibited unique strain features. Onto the ovine PrP sequence, the cortical MM2 subtype abruptly evolved on second passage, thereby allowing emergence of a pair of strain variants with distinct PrP^Sc biochemical characteristics and differing tropism for the central and lymphoid tissues. These two strain components exhibited remarkably distinct replicative properties in cell-free amplification assay, allowing the ‘physical’ cloning of the minor, lymphotropic component, and subsequent isolation in ovine PrP mice and RK13 cells.

Conclusions

Here, we provide in-depth assessment of the transmissibility and evolution of one rare subtype of sporadic CJD upon homologous and heterologous transmission. The notion that the environment or matrix where replication is occurring is key to the selection and preferential amplification of prion substrain components raises new questions on the determinants of prion replication within and between species. These data also further interrogate on the interplay between animal and human prions.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-016-0284-9) contains supplementary material, which is available to authorized users.

Transmission of scrapie prions to primate after an extended silent incubation period

Classical bovine spongiform encephalopathy (c-BSE) is the only animal prion disease reputed to be zoonotic, causing variant Creutzfeldt-Jakob disease (vCJD) in humans and having guided protective measures for animal and human health against animal prion diseases. Recently, partial transmissions to humanized mice showed that the zoonotic potential of scrapie might be similar to c-BSE. We here report the direct transmission of a natural classical scrapie isolate to cynomolgus macaque, a highly relevant model for human prion diseases, after a 10-year silent incubation period, with features similar to those reported for human cases of sporadic CJD. Scrapie is thus actually transmissible to primates with incubation periods compatible with their life expectancy, although fourfold longer than BSE. Long-term experimental transmission studies are necessary to better assess the zoonotic potential of other prion diseases with high prevalence, notably Chronic Wasting Disease of deer and elk and atypical/Nor98 scrapie.

A prion reduction filter does not completely remove endogenous prion infectivity from sheep blood

BACKGROUND

Variant Creutzfeldt-Jakob disease (vCJD) is a transmissible spongiform encephalopathy affecting humans, acquired initially through infection with bovine spongiform encephalopathy (BSE). A small number of vCJD cases have been acquired through the transfusion of blood from asymptomatic donors who subsequently developed vCJD. Filter devices that selectively bind the infectious agent associated with prion disease have been developed for removal of infection from blood. This study independently assessed one such filter, the P-CAPT filter, for efficacy in removing infectivity associated with the BSE agent in sheep blood. The sheep BSE model has previously been used to evaluate the distribution of infectivity in clinically relevant blood components. This is the first study to assess the ability of the P-CAPT filter to remove endogenous infectivity associated with blood components prepared from a large animal model.

STUDY DESIGN AND METHODS

Paired units of leukoreduced red blood cells (LR-RBCs) were prepared from donors at the clinical stage of infection and confirmed as having BSE. One cohort of recipients was transfused with LR-RBCs alone, whereas a parallel cohort received LR and P-CAPT-filtered RBCs (LR-RBCs-P-CAPT).

RESULTS

Of 14 recipients, two have been confirmed as having BSE. These sheep had received LR-RBCs and LR-RBCs-P-CAPT from the same donor.

CONCLUSIONS

The results indicate that, after leukoreduction and P-CAPT filtration, there can still be sufficient residual infectivity in sheep RBCs to transmit infection when transfused into a susceptible recipient.

Evaluation of the protection of primates transfused with variant Creutzfeldt-Jakob disease-infected blood products filtered with prion removal devices: a 5-year update

BACKGROUND

Analysis of archived appendix samples reveals that one in 2000 individuals in the United Kingdom may carry the infectious prion protein associated with variant Creutzfeldt-Jakob disease (vCJD), raising questions about the risk of transfusion transmission from apparently healthy carriers. Blood leukoreduction shows limited efficiency against prions. Therefore, in absence of antemortem diagnostic tests, prion removal filters, including the P-Capt filter were designed to improve blood transfusion safety.

STUDY DESIGN AND METHODS

We evaluated the performances of two filters, the P-Capt and one prototype (PMC#005), with blood-borne infectivity in two independent experiments. Blood was drawn twice from prion-infected macaques. Corresponding RBCCs were prepared according to two different procedures: in Study A, the leukoreduction step was followed by the filtration through the P-Capt. In Study B, the leukoreduction and prion removal were performed simultaneously through the PMC#005. For each study, two groups of three animals were transfused twice with samples before or after filtration.

RESULTS

Among the six macaques transfused with nonfiltered samples, five developed neurologic signs but only four exhibited peripheral detectable protease-resistant prion protein (PrPres) accumulation. In Study A, the three animals transfused with P-Capt-filtered samples remain asymptomatic and devoid of PrPres in lymph node biopsies 6 years after the transfusion. In Study B, one animal transfused with PMC#005-filtered samples developed vCJD.

CONCLUSION

After 5 to 6 years of progress, this ongoing study provides encouraging results on the prion blood removal performances of the P-Capt filter in macaques, an utmost relevant model for human prion diseases.

Prions in the urine of patients with variant Creutzfeldt-Jakob disease

BACKGROUND

Prions, the infectious agents responsible for transmissible spongiform encephalopathies, consist mainly of the misfolded prion protein (PrP(Sc)). The unique mechanism of transmission and the appearance of a variant form of Creutzfeldt-Jakob disease, which has been linked to consumption of prion-contaminated cattle meat, have raised concerns about public health. Evidence suggests that variant Creutzfeldt-Jakob disease prions circulate in body fluids from people in whom the disease is silently incubating.

METHODS

To investigate whether PrP(Sc) can be detected in the urine of patients with variant Creutzfeldt-Jakob disease, we used the protein misfolding cyclic amplification (PMCA) technique to amplify minute quantities of PrP(Sc), enabling highly sensitive detection of the protein. We analyzed urine samples from several patients with various transmissible spongiform encephalopathies (variant and sporadic Creutzfeldt-Jakob disease and genetic forms of prion disease), patients with other degenerative or nondegenerative neurologic disorders, and healthy persons.

RESULTS

PrP(Sc) was detectable only in the urine of patients with variant Creutzfeldt-Jakob disease and had the typical electrophoretic profile associated with this disease. PrP(Sc) was detected in 13 of 14 urine samples obtained from patients with variant Creutzfeldt-Jakob disease and in none of the 224 urine samples obtained from patients with other neurologic diseases and from healthy controls, resulting in an estimated sensitivity of 92.9% (95% confidence interval [CI], 66.1 to 99.8) and a specificity of 100.0% (95% CI, 98.4 to 100.0). The PrP(Sc) concentration in urine calculated by means of quantitative PMCA was estimated at 1×10(-16) g per milliliter, or 3×10(-21) mol per milliliter, which extrapolates to approximately 40 to 100 oligomeric particles of PrP(Sc) per milliliter of urine.

CONCLUSIONS

Urine samples obtained from patients with variant Creutzfeldt-Jakob disease contained minute quantities of PrP(Sc). (Funded by the National Institutes of Health and others.).

Ultrasensitive detection of PrP(Sc) in the cerebrospinal fluid and blood of macaques infected with bovine spongiform encephalopathy prion

Prion diseases are characterized by the prominent accumulation of the misfolded form of a normal cellular protein (PrP(Sc)) in the central nervous system. The pathological features and biochemical properties of PrP(Sc) in macaque monkeys infected with the bovine spongiform encephalopathy (BSE) prion have been found to be similar to those of human subjects with variant Creutzfeldt-Jakob disease (vCJD). Non-human primate models are thus ideally suited for performing valid diagnostic tests and determining the efficacy of potential therapeutic agents. In the current study, we developed a highly efficient method for in vitro amplification of cynomolgus macaque BSE PrP(Sc). This method involves amplifying PrP(Sc) by protein misfolding cyclic amplification (PMCA) using mouse brain homogenate as a PrP(C) substrate in the presence of sulfated dextran compounds. This method is capable of amplifying very small amounts of PrP(Sc) contained in the cerebrospinal fluid (CSF) and white blood cells (WBCs), as well as in the peripheral tissues of macaques that have been intracerebrally inoculated with the BSE prion. After clinical signs of the disease appeared in three macaques, we detected PrP(Sc) in the CSF by serial PMCA, and the CSF levels of PrP(Sc) tended to increase with disease progression. In addition, PrP(Sc) was detectable in WBCs at the clinical phases of the disease in two of the three macaques. Thus, our highly sensitive, novel method may be useful for furthering the understanding of the tissue distribution of PrP(Sc) in non-human primate models of CJD.

Complex proteinopathy with accumulations of prion protein, hyperphosphorylated tau, α-synuclein and ubiquitin in experimental bovine spongiform encephalopathy of monkeys

Proteins aggregate in several slowly progressive neurodegenerative diseases called 'proteinopathies'. Studies with cell cultures and transgenic mice overexpressing mutated proteins suggested that aggregates of one protein induced misfolding and aggregation of other proteins as well - a possible common mechanism for some neurodegenerative diseases. However, most proteinopathies are 'sporadic', without gene mutation or overexpression. Thus, proteinopathies in WT animals genetically close to humans might be informative. Squirrel monkeys infected with the classical bovine spongiform encephalopathy agent developed an encephalopathy resembling variant Creutzfeldt-Jakob disease with accumulations not only of abnormal prion protein (PrP(TSE)), but also three other proteins: hyperphosphorylated tau (p-tau), α-synuclein and ubiquitin; β-amyloid protein (Aβ) did not accumulate. Severity of brain lesions correlated with spongiform degeneration. No amyloid was detected. These results suggested that PrP(TSE) enhanced formation of p-tau and aggregation of α-synuclein and ubiquitin, but not Aβ, providing a new experimental model for neurodegenerative diseases associated with complex proteinopathies.

Consumption of bovine spongiform encephalopathy (BSE) contaminated beef and the risk of variant Creutzfeldt-Jakob disease

To date, the variant Creutzfeldt-Jakob disease (vCJD) risk assessments that have been performed have primarily focused on predicting future vCJD cases in the United Kingdom, which underwent a bovine spongiform encephalopathy (BSE) epidemic between 1980 and 1996. Surveillance of potential BSE cases was also used to assess vCJD risk, especially in other BSE-prevalent EU countries. However, little is known about the vCJD risk for uninfected individuals who accidentally consume BSE-contaminated meat products in or imported from a country with prevalent BSE. In this article, taking into account the biological mechanism of abnormal prion PrP(res) aggregation in the brain, the probability of exposure, and the expected amount of ingested infectivity, we establish a stochastic mean exponential growth model of lifetime exposure through dietary intake. Given the findings that BSE agents behave similarly in humans and macaques, we obtained parameter estimates from experimental macaque data. We then estimated the accumulation of abnormal prions to assess lifetime risk of developing clinical signs of vCJD. Based on the observed number of vCJD cases and the estimated number of exposed individuals during the BSE epidemic period from 1980 to 1996 in the United Kingdom, an exposure threshold hypothesis is proposed. Given the age-specific risk of infection, the hypothesis explains the observations very well from an extreme-value distribution fitting of the estimated BSE infectivity exposure. The current BSE statistics in the United Kingdom are provided as an example.

Mother to offspring transmission of chronic wasting disease in reeves' muntjac deer

The horizontal transmission of prion diseases has been well characterized in bovine spongiform encephalopathy (BSE), chronic wasting disease (CWD) of deer and elk and scrapie of sheep, and has been regarded as the primary mode of transmission. Few studies have monitored the possibility of vertical transmission occurring within an infected mother during pregnancy. To study the potential for and pathway of vertical transmission of CWD in the native cervid species, we used a small cervid model-the polyestrous breeding, indoor maintainable, Reeves' muntjac deer-and determined that the susceptibility and pathogenesis of CWD in these deer reproduce that in native mule and white-tailed deer. Moreover, we demonstrate here that CWD prions are transmitted from doe to fawn. Maternal CWD infection also appears to result in lower percentage of live birth offspring. In addition, evolving evidence from protein misfolding cyclic amplification (PMCA) assays on fetal tissues suggest that covert prion infection occurs in utero. Overall, our findings demonstrate that transmission of prions from mother to offspring can occur, and may be underestimated for all prion diseases.

Characterization of variant Creutzfeldt-Jakob disease prions in prion protein-humanized mice carrying distinct codon 129 genotypes

To date, all clinical variant Creutzfeldt-Jakob disease (vCJD) patients are homozygous for methionine at polymorphic codon 129 (129M/M) of the prion protein (PrP) gene. However, the appearance of asymptomatic secondary vCJD infection in individuals with a PRNP codon 129 genotype other than M/M and transmission studies using animal models have raised the concern that all humans might be susceptible to vCJD prions, especially via secondary infection. To reevaluate this possibility and to analyze in detail the transmission properties of vCJD prions to transgenic animals carrying distinct codon 129 genotype, we performed intracerebral inoculation of vCJD prions to humanized knock-in mice carrying all possible codon 129 genotypes (129M/M, 129M/V, or 129V/V). All humanized knock-in mouse lines were susceptible to vCJD infection, although the attack rate gradually decreased from 129M/M to 129M/V and to 129V/V. The amount of PrP deposition including florid/amyloid plaques in the brain also gradually decreased from 129M/M to 129M/V and to 129V/V. The biochemical properties of protease-resistant abnormal PrP in the brain and transmissibility of these humanized mouse-passaged vCJD prions upon subpassage into knock-in mice expressing bovine PrP were not affected by the codon 129 genotype. These results indicate that individuals with the 129V/V genotype may be more susceptible to secondary vCJD infection than expected and may lack the neuropathological characteristics observed in vCJD patients with the 129M/M genotype. Besides the molecular typing of protease-resistant PrP in the brain, transmission studies using knock-in mice carrying bovine PrP may aid the differential diagnosis of secondary vCJD infection, especially in individuals with the 129V/V genotype.

Review: Creutzfeldt-Jakob disease: prion protein type, disease phenotype and agent strain

The human transmissible spongiform encephalopathies or human prion diseases are one of the most intensively investigated groups of rare human neurodegenerative conditions. They are generally held to be unique in terms of their complex epidemiology and phenotypic variability, but they may also serve as a paradigm with which other more common protein misfolding disorders might be compared and contrasted. The clinico-pathological phenotype of human prion diseases appears to depend on a complex interaction between the prion protein genotype of the affected individual and the physico-chemical properties of the neurotoxic and transmissible agent, thought to comprise of misfolded prion protein. A major focus of research in recent years has been to define the phenotypic heterogeneity of the recognized human prion diseases, correlate this with molecular-genetic features and then determine whether this molecular-genetic classification of human prion disease defines the biological properties of the agent as determined by animal transmission studies. This review seeks to survey the field as it currently stands, summarize what has been learned, and explore what remains to be investigated in order to obtain a more complete scientific understanding of prion diseases and to protect public health.

Strain-specific role of RNAs in prion replication

Several lines of evidence suggest that various cofactors may be required for prion replication. PrP binds to polyanions, and RNAs were shown to promote the conversion of PrP(C) into PrP(Sc) in vitro. In the present study, we investigated strain-specific differences in RNA requirement during in vitro conversion and the potential role of RNA as a strain-specifying component of infectious prions. We found that RNase treatment impairs PrP(Sc)-converting activity of 9 murine prion strains by protein misfolding cyclic amplification (PMCA) in a strain-specific fashion. While the addition of RNA restored PMCA conversion efficiency, the effect of synthetic polynucleotides or DNA was strain dependent, showing a different promiscuity of prion strains in cofactor utilization. The biological properties of RML propagated by PMCA under RNA-depleted conditions were compared to those of brain-derived and PMCA material generated in the presence of RNA. Inoculation of RNA-depleted RML in Tga20 mice resulted in an increased incidence of a distinctive disease phenotype characterized by forelimb paresis. However, this abnormal phenotype was not conserved in wild-type mice or upon secondary transmission. Immunohistochemical and cell panel assay analyses of mouse brains did not reveal significant differences between mice injected with the different RML inocula. We conclude that replication under RNA-depleted conditions did not modify RML prion strain properties. Our study cannot, however, exclude small variations of RML properties that would explain the abnormal clinical phenotype observed. We hypothesize that RNA molecules may act as catalysts of prion replication and that variable capacities of distinct prion strains to utilize different cofactors may explain strain-specific dependency upon RNA.

Squirrel monkeys (Saimiri sciureus) infected with the agent of bovine spongiform encephalopathy develop tau pathology

Squirrel monkeys (Saimiri sciureus) were infected experimentally with the agent of classical bovine spongiform encephalopathy (BSE). Two to four years later, six of the monkeys developed alterations in interactive behaviour and cognition and other neurological signs typical of transmissible spongiform encephalopathy (TSE). At necropsy examination, the brains from all of the monkeys showed pathological changes similar to those described in variant Creutzfeldt-Jakob disease (vCJD) of man, except that the squirrel monkey brains contained no PrP-amyloid plaques typical of that disease. Constant neuropathological features included spongiform degeneration, gliosis, deposition of abnormal prion protein (PrP(TSE)) and many deposits of abnormally phosphorylated tau protein (p-Tau) in several areas of the cerebrum and cerebellum. Western blots showed large amounts of proteinase K-resistant prion protein in the central nervous system. The striking absence of PrP plaques (prominent in brains of cynomolgus macaques [Macaca fascicularis] with experimentally-induced BSE and vCJD and in human patients with vCJD) reinforces the conclusion that the host plays a major role in determining the neuropathology of TSEs. Results of this study suggest that p-Tau, found in the brains of all BSE-infected monkeys, might play a role in the pathogenesis of TSEs. Whether p-Tau contributes to development of disease or appears as a secondary change late in the course of illness remains to be determined.

Effect of PrP genotype and route of inoculation on the ability of discriminatory Western blot to distinguish scrapie from sheep bovine spongiform encephalopathy

Procedures for discriminating scrapie from bovine spongiform encephalopathy (BSE) in sheep are relevant to ascertain whether BSE has entered the sheep population. This study was aimed at investigating whether the suitability of an official EU discriminative method is affected by the sheep PrP genotype and route of infection.

Molecular pathology of human prion disease

Human prion diseases are associated with a range of clinical presentations and are classified by both clinicopathological syndrome and aetiology with sub-classification according to molecular criteria. Considerable experimental evidence suggests that phenotypic diversity in human prion disease relates in significant part to the existence of distinct human prion strains encoded by abnormal PrP isoforms with differing physicochemical properties. To date, however, the conformational repertoire of pathological isoforms of wild-type human PrP and the various forms of mutant human PrP has not been fully defined. Efforts to produce a unified international classification of human prion disease are still ongoing. The ability of genetic background to influence prion strain selection together with knowledge of numerous other factors that may influence clinical and neuropathological presentation strongly emphasises the requirement to identify distinct human prion strains in appropriate transgenic models, where host genetic variability and other modifiers of phenotype are removed. Defining how many human prion strains exist allied with transgenic modelling of potentially zoonotic prion strains will inform on how many human infections may have an animal origin. Understanding these relationships will have direct translation to protecting public health.

Atypical prion diseases in humans and animals

Although prion diseases, such as Creutzfeldt-Jakob disease (CJD) in humans and scrapie in sheep, have long been recognized, our understanding of their epidemiology and pathogenesis is still in its early stages. Progress is hampered by the lengthy incubation periods and the lack of effective ways of monitoring and characterizing these agents. Protease-resistant conformers of the prion protein (PrP), known as the "scrapie form" (PrP(Sc)), are used as disease markers, and for taxonomic purposes, in correlation with clinical, pathological, and genetic data. In humans, prion diseases can arise sporadically (sCJD) or genetically (gCJD and others), caused by mutations in the PrP-gene (PRNP), or as a foodborne infection, with the agent of bovine spongiform encephalopathy (BSE) causing variant CJD (vCJD). Person-to-person spread of human prion disease has only been known to occur following cannibalism (kuru disease in Papua New Guinea) or through medical or surgical treatment (iatrogenic CJD, iCJD). In contrast, scrapie in small ruminants and chronic wasting disease (CWD) in cervids behave as infectious diseases within these species. Recently, however, so-called atypical forms of prion diseases have been discovered in sheep (atypical/Nor98 scrapie) and in cattle, BSE-H and BSE-L. These maladies resemble sporadic or genetic human prion diseases and might be their animal equivalents. This hypothesis also raises the significant public health question of possible epidemiological links between these diseases and their counterparts in humans.

Phenotypic variability of sporadic human prion disease and its molecular basis: past, present, and future

Human prion diseases are rare neurodegenerative disorders related to prion protein misfolding that can occur as sporadic, familial or acquired forms. In comparison to other more common neurodegenerative disorders, prion diseases show a wider range of phenotypic variation and largely transmit to experimental animals, a feature that led to the isolation and characterization of different strains of the transmissible agent or prion with distinct biological properties. Biochemically distinct PrP(Sc) types have been demonstrated which differ in their size after proteinase cleavage, glycosylation pattern, and possibly other features related to their conformation. These PrP(Sc) types, possibly enciphering the prion strains, together with the naturally occurring polymorphism at codon 129 in the prion protein gene have a major influence on the disease phenotype. In the sporadic form, the most common but perhaps least understood form of human prion disease, there are at least six major combinations of codon 129 genotype and prion protein isotype, which are significantly related to distinctive clinical-pathological subgroups of the disease. In this review, we provide an update on the current knowledge and classification of the disease subtypes of the sporadic human prion diseases as defined by molecular features and pathological changes. Furthermore, we discuss the molecular basis of phenotypic variability taking into account the results of recent transmission studies that shed light on the extent of prion strain variation in humans.

Preclinical deposition of pathological prion protein in muscle of experimentally infected primates

Prion diseases are transmissible fatal neurodegenerative disorders affecting humans and animals. A central step in disease progression is the accumulation of a misfolded form (PrP^Sc) of the host encoded prion protein (PrP^C) in neuronal and non-neuronal tissues. The involvement of peripheral tissues in preclinical states increases the risk of accidental transmission. On the other hand, detection of PrP^Sc in non-neuronal easy-accessible compartments such as muscle may offer a novel diagnostic tool. Primate models have proven invaluable to investigate prion diseases. We have studied the deposition of PrP^Sc in muscle and central nervous system of rhesus monkeys challenged with sporadic Creutzfeldt-Jakob disease (sCJD), variant CJD (vCJD) and bovine spongiform encephalopathy (BSE) in preclinical and clinical stage using biochemical and morphological methods. Here, we show the preclinical presence of PrP^Sc in muscle and central nervous system of rhesus monkeys experimentally infected with vCJD.

Agent strain variation in human prion disease: insights from a molecular and pathological review of the National Institutes of Health series of experimentally transmitted disease

Six clinico-pathological phenotypes of sporadic Creutzfeldt-Jakob disease have been characterized which correlate at the molecular level with the type (1 or 2) of the abnormal prion protein, PrP(TSE), present in the brain and with the genotype of polymorphic (methionine or valine) codon 129 of the prion protein gene. However, to what extent these phenotypes with their corresponding molecular combinations (i.e. MM1, MM2, VV1 etc.) encipher distinct prion strains upon transmission remains uncertain. We studied the PrP(TSE) type and the prion protein gene in archival brain tissues from the National Institutes of Health series of transmitted Creutzfeldt-Jakob disease and kuru cases, and characterized the molecular and pathological phenotype in the affected non-human primates, including squirrel, spider, capuchin and African green monkeys. We found that the transmission properties of prions from the common sporadic Creutzfeldt-Jakob disease MM1 phenotype are homogeneous and significantly differ from those of sporadic Creutzfeldt-Jakob disease VV2 or MV2 prions. Animals injected with iatrogenic Creutzfeldt-Jakob disease MM1 and genetic Creutzfeldt-Jakob disease MM1 linked to the E200K mutation showed the same phenotypic features as those infected with sporadic Creutzfeldt-Jakob disease MM1 prions, whereas kuru most closely resembled the sporadic Creutzfeldt-Jakob disease VV2 or MV2 prion signature and neuropathology. The findings indicate that two distinct prion strains are linked to the three most common Creutzfeldt-Jakob disease clinico-pathological and molecular subtypes and kuru, and suggest that kuru may have originated from cannibalistic transmission of a sporadic Creutzfeldt-Jakob disease of the VV2 or MV2 subtype.

Iron content of ferritin modulates its uptake by intestinal epithelium: implications for co-transport of prions

The spread of Chronic Wasting Disease (CWD) in the deer and elk population has caused serious public health concerns due to its potential to infect farm animals and humans. Like other prion disorders such a sporadic Creutzfeldt-Jakob-disease of humans and Mad Cow Disease of cattle, CWD is caused by PrP-scrapie (PrP^Sc), a β-sheet rich isoform of a normal cell surface glycoprotein, the prion protein (PrP^C). Since PrP^Sc is sufficient to cause infection and neurotoxicity if ingested by a susceptible host, it is important to understand the mechanism by which it crosses the stringent epithelial cell barrier of the small intestine. Possible mechanisms include co-transport with ferritin in ingested food and uptake by dendritic cells. Since ferritin is ubiquitously expressed and shares considerable homology among species, co-transport of PrP^Sc with ferritin can result in cross-species spread with deleterious consequences. We have used a combination of in vitro and in vivo models of intestinal epithelial cell barrier to understand the role of ferritin in mediating PrP^Sc uptake and transport. In this report, we demonstrate that PrP^Sc and ferritin from CWD affected deer and elk brains and scrapie from sheep resist degradation by digestive enzymes, and are transcytosed across a tight monolayer of human epithelial cells with significant efficiency. Likewise, ferritin from hamster brains is taken up by mouse intestinal epithelial cells in vivo, indicating that uptake of ferritin is not limited by species differences as described for prions. More importantly, the iron content of ferritin determines its efficiency of uptake and transport by Caco-2 cells and mouse models, providing insight into the mechanism(s) of ferritin and PrP^Sc uptake by intestinal epithelial cells.

The kuru infectious agent is a unique geographic isolate distinct from Creutzfeldt-Jakob disease and scrapie agents

Human sporadic Creutzfeldt-Jakob disease (sCJD), endemic sheep scrapie, and epidemic bovine spongiform encephalopathy (BSE) are caused by a related group of infectious agents. The new U.K. BSE agent spread to many species, including humans, and clarifying the origin, specificity, virulence, and diversity of these agents is critical, particularly because infected humans do not develop disease for many years. As with viruses, transmissible spongiform encephalopathy (TSE) agents can adapt to new species and become more virulent yet maintain fundamentally unique and stable identities. To make agent differences manifest, one must keep the host genotype constant. Many TSE agents have revealed their independent identities in normal mice. We transmitted primate kuru, a TSE once epidemic in New Guinea, to mice expressing normal and approximately 8-fold higher levels of murine prion protein (PrP). High levels of murine PrP did not prevent infection but instead shortened incubation time, as would be expected for a viral receptor. Sporadic CJD and BSE agents and representative scrapie agents were clearly different from kuru in incubation time, brain neuropathology, and lymphoreticular involvement. Many TSE agents can infect monotypic cultured GT1 cells, and unlike sporadic CJD isolates, kuru rapidly and stably infected these cells. The geographic independence of the kuru agent provides additional reasons to explore causal environmental pathogens in these infectious neurodegenerative diseases.

Prion strain discrimination based on rapid in vivo amplification and analysis by the cell panel assay

Prion strain identification has been hitherto achieved using time-consuming incubation time determinations in one or more mouse lines and elaborate neuropathological assessment. In the present work, we make a detailed study of the properties of PrP-overproducing Tga20 mice. We show that in these mice the four prion strains examined are rapidly and faithfully amplified and can subsequently be discriminated by a cell-based procedure, the Cell Panel Assay.

Strain-specific viral properties of variant Creutzfeldt-Jakob disease (vCJD) are encoded by the agent and not by host prion protein

Human CJD, endemic sheep scrapie, epidemic bovine spongiform encephalopathy (BSE), and other transmissible spongiform encephalopathies (TSEs), are caused by a group of related but molecularly uncharacterized infectious agents. The UK-BSE agent infected many species, including humans where it causes variant CJD (vCJD). As in most viral infections, different TSE disease phenotypes are determined by both the agent strain and the host species. TSE strains are most reliably classified by incubation time and regional neuropathology in mice expressing wild-type (wt) prion protein (PrP). We compared vCJD to other human and animal derived TSE strains in both mice and neuronal cultures expressing wt murine PrP. Primary and serial passages of the human vCJD agent, as well as the highly selected mutant 263K sheep scrapie agent, revealed profound strain-specific characteristics were encoded by the agent, not by host PrP. Prion theory posits that PrP converts itself into the infectious agent, and thus short incubations require identical PrP sequences in the donor and recipient host. However, wt PrP mice injected with human vCJD brain homogenates showed dramatically shorter primary incubation times than mice expressing only human PrP, a finding not in accord with a PrP species barrier. All mouse passage brains showed the vCJD agent derived from a stable BSE strain. Additionally, both vCJD brain and monotypic neuronal cultures produced a diagnostic 19 kDa PrP fragment previously observed only in BSE and vCJD primate brains. Monotypic cultures can be used to identify the intrinsic, strain-determining molecules of TSE infectious particles.