Cross-sequence transmission of sporadic Creutzfeldt-Jakob disease creates a new prion strain

Historical and More Common Nongenetic Movement Disorders From Asia

Nongenetic movement disorders are common throughout the world. The movement disorders encountered may vary depending on the prevalence of certain disorders across various geographical regions. In this paper, we review historical and more common nongenetic movement disorders in Asia. The underlying causes of these movement disorders are diverse and include, among others, nutritional deficiencies, toxic and metabolic causes, and cultural Latah syndrome, contributed by geographical, economic, and cultural differences across Asia. The industrial revolution in Japan and Korea has led to diseases related to environmental toxin poisoning, such as Minamata disease and β-fluoroethyl acetate-associated cerebellar degeneration, respectively, while religious dietary restriction in the Indian subcontinent has led to infantile tremor syndrome related to vitamin B12 deficiency. In this review, we identify the salient features and key contributing factors in the development of these disorders.

A point mutation in GPI-attachment signal peptide accelerates the development of prion disease

A missense variant from methionine to arginine at codon 232 (M232R) of the prion protein gene accounts for ~ 15% of Japanese patients with genetic prion diseases. However, pathogenic roles of the M232R substitution for the induction of prion disease have remained elusive because family history is usually absent in patients with M232R. In addition, the clinicopathologic phenotypes of patients with M232R are indistinguishable from those of sporadic Creutzfeldt-Jakob disease patients. Furthermore, the M232R substitution is located in the glycosylphosphatidylinositol (GPI)-attachment signal peptide that is cleaved off during the maturation of prion proteins. Therefore, there has been an argument that the M232R substitution might be an uncommon polymorphism rather than a pathogenic mutation. To unveil the role of the M232R substitution in the GPI-attachment signal peptide of prion protein in the pathogenesis of prion disease, here we generated a mouse model expressing human prion proteins with M232R and investigated the susceptibility to prion disease. The M232R substitution accelerates the development of prion disease in a prion strain-dependent manner, without affecting prion strain-specific histopathologic and biochemical features. The M232R substitution did not alter the attachment of GPI nor GPI-attachment site. Instead, the substitution altered endoplasmic reticulum translocation pathway of prion proteins by reducing the hydrophobicity of the GPI-attachment signal peptide, resulting in the reduction of N-linked glycosylation and GPI glycosylation of prion proteins. To the best of our knowledge, this is the first time to show a direct relationship between a point mutation in the GPI-attachment signal peptide and the development of disease.

New developments in prion disease research using genetically modified mouse models

While much of what we know about the general principles of protein-based information transfer derives from studies of experimentally adapted rodent prions, these laboratory strains are limited in their ability to recapitulate features of human and animal prions and the diseases they produce. Here, we review how recent approaches using genetically modified mice have informed our understanding of naturally occurring prion diseases, their strain properties, and the factors controlling their transmission and evolution. In light of the increasing importance of chronic wasting disease, the application of mouse transgenesis to study this burgeoning and highly contagious prion disorder, in particular recent insights derived from gene-targeting approaches, will be a major focus of this review.

Extracellular vesicles with diagnostic and therapeutic potential for prion diseases

Prion diseases (PrD) or transmissible spongiform encephalopathies (TSE) are invariably fatal and pathogenic neurodegenerative disorders caused by the self-propagated misfolding of cellular prion protein (PrP^C) to the neurotoxic pathogenic form (PrP^TSE) via a yet undefined but profoundly complex mechanism. Despite several decades of research on PrD, the basic understanding of where and how PrP^C is transformed to the misfolded, aggregation-prone and pathogenic PrP^TSE remains elusive. The primary clinical hallmarks of PrD include vacuolation-associated spongiform changes and PrP^TSE accumulation in neural tissue together with astrogliosis. The difficulty in unravelling the disease mechanisms has been related to the rare occurrence and long incubation period (over decades) followed by a very short clinical phase (few months). Additional challenge in unravelling the disease is implicated to the unique nature of the agent, its complexity and strain diversity, resulting in the heterogeneity of the clinical manifestations and potentially diverse disease mechanisms. Recent advances in tissue isolation and processing techniques have identified novel means of intercellular communication through extracellular vesicles (EVs) that contribute to PrP^TSE transmission in PrD. This review will comprehensively discuss PrP^TSE transmission and neurotoxicity, focusing on the role of EVs in disease progression, biomarker discovery and potential therapeutic agents for the treatment of PrD.

The First Meta-Analysis of the M129V Single-Nucleotide Polymorphism (SNP) of the Prion Protein Gene (PRNP) with Sporadic Creutzfeldt-Jakob Disease

Prion diseases are fatal, chronic, and incurable neurodegenerative diseases caused by pathogenic forms of prion protein (PrP^Sc) derived from endogenous forms of prion protein (PrP^C). Several case–control and genome-wide association studies have reported that the M129V polymorphism of the human prion protein gene (PRNP) is significantly associated with susceptibility to sporadic Creutzfeldt–Jakob disease (CJD). However, since some case–control studies have not shown these associations, the results remain controversial. We collected data that contain the genotype and allele frequencies of the M129V single-nucleotide polymorphism (SNP) of the PRNP gene and information on ethnic backgrounds from sporadic CJD patients. We performed a meta-analysis by collecting data from eligible studies to evaluate the association between the M129V SNP of the PRNP gene and susceptibility to sporadic CJD. We found a very strong association between the M129V SNP of the PRNP gene and susceptibility to sporadic CJD using a meta-analysis for the first time. We validated the eligibility of existing reports and found severe heterogeneity in some previous studies. We also found that the MM homozygote is a potent risk factor for sporadic CJD compared to the MV heterozygote in the heterozygote comparison model (MM vs. MV, odds ratio = 4.9611, 95% confidence interval: 3.4785; 7.0758, p < 1 × 10⁻¹⁰). To the best of our knowledge, this was the first meta-analysis assessment of the relationship between the M129V SNP of the PRNP gene and susceptibility to sporadic CJD.

Potential for transmission of sporadic Creutzfeldt-Jakob disease through peripheral routes

Five sporadic Creutzfeldt-Jakob disease (CJD) strains have been identified to date, based on differences in clinicopathological features of the patients, the biochemical properties of abnormal prion proteins, and transmission properties. Recent advances in our knowledge about iatrogenic transmission of sporadic CJD have raised the possibility that the infectivity of sporadic CJD strains through peripheral routes is different from that of intracranial infection. To test this possibility, here we assessed systematically the infectivity of sporadic CJD strains through the peripheral route for the first time using a mouse model expressing human prion protein. Although the infectivity of the V2 and M1 sporadic CJD strains is almost the same in intracerebral transmission studies, the V2 strain infected more efficiently than the M1 strain through the peripheral route. The other sporadic CJD strains examined lacked infectivity. Of note, both the V2 and M1 strains showed preference for mice with the valine homozygosity at the PRNP polymorphic codon. These results indicate that the V2 strain is the most infectious sporadic CJD strain for infection through peripheral routes. In addition, these findings raise the possibility that individuals with the valine homozygosity at the PRNP polymorphic codon might have higher risks of infection through peripheral routes compared with the methionine homozygotes. Thus, preventive measures against the transmission of the V2 sporadic CJD strain will be important for the eradication of iatrogenic CJD transmission through peripheral routes.

Phenotypic diversity of genetic Creutzfeldt-Jakob disease: a histo-molecular-based classification

The current classification of sporadic Creutzfeldt–Jakob disease (sCJD) includes six major clinicopathological subtypes defined by the physicochemical properties of the protease-resistant core of the pathologic prion protein (PrP^Sc), defining two major PrP^Sc types (i.e., 1 and 2), and the methionine (M)/valine (V) polymorphic codon 129 of the prion protein gene (PRNP). How these sCJD subtypes relate to the well-documented phenotypic heterogeneity of genetic CJD (gCJD) is not fully understood. We analyzed molecular and phenotypic features in 208 individuals affected by gCJD, carrying 17 different mutations, and compared them with those of a large series of sCJD cases. We identified six major groups of gCJD based on the combination PrP^Sc type and codon 129 genotype on PRNP mutated allele, each showing distinctive histopathological characteristics, irrespectively of the PRNP associated mutation. Five gCJD groups, named M1, M2C, M2T, V1, and V2, largely reproduced those previously described in sCJD subtypes. The sixth group shared phenotypic traits with the V2 group and was only detected in patients carrying the E200K-129M haplotype in association with a PrP^Sc type of intermediate size (“i”) between type 1 and type 2. Additional mutation-specific effects involved the pattern of PrP deposition (e.g., a “thickened” synaptic pattern in E200K carriers, cerebellar “stripe-like linear granular deposits” in those with insertion mutations, and intraneuronal globular dots in E200K-V2 or -M”i”). A few isolated cases linked to rare PRNP haplotypes (e.g., T183A-129M), showed atypical phenotypic features, which prevented their classification into the six major groups. The phenotypic variability of gCJD is mostly consistent with that previously found in sCJD. As in sCJD, the codon 129 genotype and physicochemical properties of PrP^Sc significantly correlated with the phenotypic variability of gCJD. The most common mutations linked to CJD appear to have a variable and overall less significant effect on the disease phenotype, but they significantly influence disease susceptibility often in a strain-specific manner. The criteria currently used for sCJD subtypes can be expanded and adapted to gCJD to provide an updated classification of the disease with a molecular basis.

Generation of human chronic wasting disease in transgenic mice

Chronic wasting disease (CWD) is a cervid prion disease caused by the accumulation of an infectious misfolded conformer (PrP^Sc) of cellular prion protein (PrP^C). It has been spreading rapidly in North America and also found in Asia and Europe. Although bovine spongiform encephalopathy (i.e. mad cow disease) is the only animal prion disease known to be zoonotic, the transmissibility of CWD to humans remains uncertain. Here we report the generation of the first CWD-derived infectious human PrP^Sc by elk CWD PrP^Sc-seeded conversion of PrP^C in normal human brain homogenates using in vitro protein misfolding cyclic amplification (PMCA). Western blotting with human PrP selective antibody confirmed that the PMCA-generated protease-resistant PrP^Sc was derived from the human PrP^C substrate. Two lines of humanized transgenic mice expressing human PrP with either Val or Met at the polymorphic codon 129 developed clinical prion disease following intracerebral inoculation with the PMCA-generated CWD-derived human PrP^Sc. Diseased mice exhibited distinct PrP^Sc patterns and neuropathological changes in the brain. Our study, using PMCA and animal bioassays, provides the first evidence that CWD PrP^Sc can cross the species barrier to convert human PrP^C into infectious PrP^Sc that can produce bona fide prion disease when inoculated into humanized transgenic mice.

Understanding Intra-Species and Inter-Species Prion Conversion and Zoonotic Potential Using Protein Misfolding Cyclic Amplification

Prion diseases are fatal neurodegenerative disorders that affect humans and animals, and can also be transmitted from animals to humans. A fundamental event in prion disease pathogenesis is the conversion of normal host prion protein (PrP^C) to a disease-associated misfolded form (PrP^Sc). Whether or not an animal prion disease can infect humans cannot be determined a priori. There is a consensus that classical bovine spongiform encephalopathy (C-type BSE) in cattle transmits to humans, and that classical sheep scrapie is of little or no risk to human health. However, the zoonotic potential of more recently identified animal prion diseases, such as atypical scrapie, H-type and L-type BSE and chronic wasting disease (CWD) in cervids, remains an open question. Important components of the zoonotic barrier are (i) physiological differences between humans and the animal in question, (ii) amino acid sequence differences of the animal and human PrP^C, and (iii) the animal prion strain, enciphered in the conformation of PrP^Sc. Historically, the direct inoculation of experimental animals has provided essential information on the transmissibility and compatibility of prion strains. More recently, cell-free molecular conversion assays have been used to examine the molecular compatibility on prion replication and zoonotic potential. One such assay is Protein Misfolding Cyclic Amplification (PMCA), in which a small amount of infected tissue homogenate, containing PrP^Sc, is added as a seed to an excess of normal tissue homogenate containing PrP^C, and prion conversion is accelerated by cycles of incubation and ultrasonication. PMCA has been used to measure the molecular feasibility of prion transmission in a range of scenarios using genotypically homologous and heterologous combinations of PrP^Sc seed and PrP^C substrate. Furthermore, this method can be used to speculate on the molecular profile of PrP^Sc that might arise from a zoonotic transmission. We discuss the experimental approaches that have been used to model both the intra- and inter-species molecular compatibility of prions, and the factors affecting PrP^c to PrP^Sc conversion and zoonotic potential. We conclude that cell-free prion protein conversion assays, especially PMCA, are useful, rapid and low-cost approaches for elucidating the mechanisms of prion propagation and assessing the risk of animal prions to humans.

Adaptive selection of a prion strain conformer corresponding to established North American CWD during propagation of novel emergent Norwegian strains in mice expressing elk or deer prion protein

Prions are infectious proteins causing fatal, transmissible neurodegenerative diseases of animals and humans. Replication involves template-directed refolding of host encoded prion protein, PrP^C, by its infectious conformation, PrP^Sc. Following its discovery in captive Colorado deer in 1967, uncontrollable contagious transmission of chronic wasting disease (CWD) led to an expanded geographic range in increasing numbers of free-ranging and captive North American (NA) cervids. Some five decades later, detection of PrP^Sc in free-ranging Norwegian (NO) reindeer and moose marked the first indication of CWD in Europe. To assess the properties of these emergent NO prions and compare them with NA CWD we used transgenic (Tg) and gene targeted (Gt) mice expressing PrP with glutamine (Q) or glutamate (E) at residue 226, a variation in wild type cervid PrP which influences prion strain selection in NA deer and elk. Transmissions of NO moose and reindeer prions to Tg and Gt mice recapitulated the characteristic features of CWD in natural hosts, revealing novel prion strains with disease kinetics, neuropathological profiles, and capacities to infect lymphoid tissues and cultured cells that were distinct from those causing NA CWD. In support of strain variation, PrP^Sc conformers comprising emergent NO moose and reindeer CWD were subject to selective effects imposed by variation at residue 226 that were different from those controlling established NA CWD. Transmission of particular NO moose CWD prions in mice expressing E at 226 resulted in selection of a kinetically optimized conformer, subsequent transmission of which revealed properties consistent with NA CWD. These findings illustrate the potential for adaptive selection of strain conformers with improved fitness during propagation of unstable NO prions. Their potential for contagious transmission has implications for risk analyses and management of emergent European CWD. Finally, we found that Gt mice expressing physiologically controlled PrP levels recapitulated the lymphotropic properties of naturally occurring CWD strains resulting in improved susceptibilities to emergent NO reindeer prions compared with over-expressing Tg counterparts. These findings underscore the refined advantages of Gt models for exploring the mechanisms and impacts of strain selection in peripheral compartments during natural prion transmission.

Prions cause fatal, transmissible neurodegenerative diseases in animals and humans. They are composed of an infectious, neurotoxic protein (PrP) which replicates by imposing pathogenic conformations on its normal, host-encoded counterpart. Chronic wasting disease (CWD) is a contagious prion disorder threatening increasing numbers of free-ranging and captive North American deer, elk, and moose. While CWD detection in Norwegian reindeer and moose in 2016 marked the advent of disease in Europe, its origins and relationship to North American CWD were initially unclear. Here we show, using mice engineered to express deer or elk PrP, that Norwegian reindeer and moose CWD are caused by novel prion strains with properties distinct from those of North American CWD. We found that selection and propagation of North American and Norwegian CWD strains was controlled by a key amino acid residue in host PrP. We also found that particular Norwegian isolates adapted during their propagation in mice to produce prions with characteristics of the North American strain. Our findings defining the transmission profiles of novel Norwegian prions and their unstable potential to produce adapted strains with improved fitness for contagious transmission have implications for risk analyses and management of emergent European CWD.

Characterization of Sporadic Creutzfeldt-Jakob Disease and History of Neurosurgery to Identify Potential Iatrogenic Cases

We previously reported a phenotype of Creutzfeldt-Jakob disease (CJD), CJD-MMiK, that could help identify iatrogenic CJD. To find cases mimicking CJD-MMiK, we investigated clinical features and pathology of 1,155 patients with diagnosed sporadic CJD or unclassified CJD with and without history of neurosurgery. Patients with history of neurosurgery more frequently had an absence of periodic sharp-wave complexes on electroencephalogram than patients without a history of neurosurgery. Among 27 patients with history of neurosurgery, 5 had no periodic sharp-wave complexes on electroencephalogram. We confirmed 1 case of CJD-MMiK and suspected another. Both had methionine homozygosity at codon 129 of the prion protein gene and hyperintensity lesions in the thalamus on magnetic resonance images of the brain, which might be a clinical marker of CJD-MMiK. A subgroup with a history of neurosurgery and clinical features mimicking dura mater graft-associated CJD might have been infected during neurosurgery and had symptoms develop after many years.

Two distinct conformers of PrPD type 1 of sporadic Creutzfeldt-Jakob disease with codon 129VV genotype faithfully propagate in vivo

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 (PrP^D). 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 PrP^D (resPrP^D). We recently reported that the sCJDVV1 subtype (129VV homozygosity paired with PrP^D type 1, T1) shows an electrophoretic profile where the resPrP^D 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 resPrP^D 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 resPrP^D represent distinct human prion strains associated with partially overlapping histotypes.

Diffusion-weighted magnetic resonance imaging in dura mater graft-associated Creutzfeldt-Jakob disease

PURPOSE

To elucidate the extension patterns of the hyperintense areas on diffusion-weighted magnetic resonance imaging (DW-MRI) in patients with dura mater graft-associated Creutzfeldt-Jakob disease (dCJD).

METHODS

We collected the DW-MRI of dCJD cases identified by the CJD Surveillance Committee in Japan, between April 1999 and February 2018. The dCJD cases were classified into non-plaque and plaque-types. The relationship among the abnormal signals, the pathological classification, and the sites of grafting were analyzed.

RESULTS

We collected DW-MRI of 11 patients with dCJD, all of whom were methionine homozygous at codon 129 of the prion protein gene. The age at onset was 41 (26-76) [median (range)] years, the age at dural grafting was 19 (10-53) years, and the incubation period was 22 (16-29) years. Eight dCJD cases were classified as non-plaque-type and three cases were plaque-type. Five of the non-plaque-type cases and all the plaque-type cases were pathologically confirmed. Brain DW-MRI was performed 3 (1-22) months after the onset. Most of the non-plaque-type cases showed brighter hyperintensity in the cerebral cortex and basal ganglia on the side of dural grafting. Subsequent DW-MRI showed widespread hyperintense lesions in the brain. Regarding the plaque-type cases, initial scans showed hyperintensity in the basal ganglia and the thalamus in one patient. Another patient's lesion was confined to the basal ganglia. The third patient showed no abnormalities seven months post-onset; however, serial images showed a hyperintensity confined to the thalamus.

CONCLUSIONS

Non-plaque and plaque-types demonstrated different patterns of propagation of distinct prion strains.

Two distinct prions in fatal familial insomnia and its sporadic form

Fatal familial insomnia is a genetic prion disease, which is associated with the aspartic acid to asparagine substitution at codon 178 of the prion protein gene. Although the hallmark pathological feature is thalamic and olivary degeneration, there is a patient with an atypical fatal familial insomnia without the hallmark feature. The cause of the pathological variability is unclear. We analysed a Japanese fatal familial insomnia kindred and compared one atypical clinicopathological fatal familial insomnia phenotype case and typical fatal familial insomnia phenotype cases with transmission studies using multiple lines of knock-in mice and with protein misfolding cyclic amplification. We also analysed the transmissibility and the amplification properties of sporadic fatal insomnia. Transmission studies revealed that the typical fatal familial insomnia with thalamic and olivary degeneration showed successful transmission only using knock-in mice expressing human-mouse chimeric prion protein gene. The atypical fatal familial insomnia with spongiform changes showed successful transmission only using knock-in mice expressing bank vole prion protein gene. Two sporadic fatal insomnia cases with thalamic and olivary degeneration showed the same transmissibility as the typical fatal familial insomnia phenotype. Interestingly, one sporadic fatal insomnia case with thalamic/olivary degeneration and spongiform changes showed transmissibility of both the typical and atypical fatal familial insomnia phenotypes. Protein misfolding cyclic amplification could amplify both typical fatal familial insomnia cases and sporadic fatal insomnia cases but not the atypical fatal familial insomnia phenotype or other sporadic Creutzfeldt-Jakob disease subtypes. In addition to clinical findings and neuropathological features, the transmission properties and the amplification properties were different between the typical and atypical fatal familial insomnia phenotypes. It is suggested that two distinct prions were associated with the diversity in the fatal familial insomnia phenotype, and these two prions could also be detected in sporadic fatal insomnia.

Primary structural differences at residue 226 of deer and elk PrP dictate selection of distinct CWD prion strains in gene-targeted mice

Our gene-targeting strategy addresses several critical issues relating to chronic wasting disease (CWD), a contagious, lethal neurodegenerative prion disease affecting wild as well as captive cervids, which poses an uncertain risk to humans. First, we show that residue 226, the sole primary structural difference between deer and elk prion protein, dictates the selection and propagation of different CWD strains. Because the strain properties of prions affect their host-range potential, these findings suggest that CWD from elk and deer pose distinct risks to humans and other species. Second, we show that these gene-targeted mice offer an unprecedented means to address distinctive aspects of CWD peripheral pathogenesis and horizontal transmission that are not afforded by previously generated transgenic mouse models.

Although the unifying hallmark of prion diseases is CNS neurodegeneration caused by conformational corruption of host prion protein (PrP) to its infective counterpart, contagious transmission of chronic wasting disease (CWD) results from shedding of prions produced at high titers in the periphery of diseased cervids. While deer and elk PrP primary structures are equivalent except at residue 226, which is glutamate in elk and glutamine in deer, the effect of this difference on CWD pathogenesis is largely unknown. Using a gene-targeting approach where the mouse PrP coding sequence was replaced with elk or deer PrP, we show that the resulting GtE226 and GtQ226 mice had distinct kinetics of disease onset, prion conformations, and distributions of prions in the brains of diseased mice following intracerebral CWD challenge. These findings indicate that amino acid differences at PrP residue 226 dictate the selection and propagation of divergent strains in deer and elk with CWD. Because prion strain properties largely dictate host-range potential, our findings suggest that prion strains from elk and deer pose distinct risks to sympatric species or humans exposed to CWD. GtE226 and GtQ226 mice were also highly susceptible to CWD prions following intraperitoneal and oral exposures, a characteristic that stood in stark contrast to previously produced transgenic models. Remarkably, disease transmission was effective when infected mice were cohoused with naïve cagemates. Our findings indicate that gene-targeted mice provide unprecedented opportunities to accurately investigate CWD peripheral pathogenesis, CWD strains, and mechanisms of horizontal CWD transmission.

Understanding Prion Strains: Evidence from Studies of the Disease Forms Affecting Humans

Prion diseases are a unique group of rare neurodegenerative disorders characterized by tissue deposition of heterogeneous aggregates of abnormally folded protease-resistant prion protein (PrPSc), a broad spectrum of disease phenotypes and a variable efficiency of disease propagation in vivo. The dominant clinicopathological phenotypes of human prion disease include Creutzfeldt⁻Jakob disease, fatal insomnia, variably protease-sensitive prionopathy, and Gerstmann⁻Sträussler⁻Scheinker disease. Prion disease propagation into susceptible hosts led to the isolation and characterization of prion strains, initially operatively defined as "isolates" causing diseases with distinctive characteristics, such as the incubation period, the pattern of PrPSc distribution, and the regional severity of neuropathological changes after injection into syngeneic hosts. More recently, the structural basis of prion strains has been linked to amyloid polymorphs (i.e., variant amyloid protein conformations) and the concept extended to all protein amyloids showing polymorphic structures and some evidence of in vivo or in vitro propagation by seeding. Despite the significant advances, however, the link between amyloid structure and disease is not understood in many instances. Here we reviewed the most significant contributions of human prion disease studies to current knowledge of the molecular basis of phenotypic variability and the prion strain phenomenon and underlined the unsolved issues from the human disease perspective.

Recent advances in the histo-molecular pathology of human prion disease

Prion diseases are progressive neurodegenerative disorders affecting humans and other mammalian species. The term prion, originally put forward to propose the concept that a protein could be infectious, refers to PrP^Sc , a misfolded isoform of the cellular prion protein (PrP^C ) that represents the pathogenetic hallmark of these disorders. The discovery that other proteins characterized by misfolding and seeded aggregation can spread from cell to cell, similarly to PrP^Sc , has increased interest in prion diseases. Among neurodegenerative disorders, however, prion diseases distinguish themselves for the broader phenotypic spectrum, the fastest disease progression and the existence of infectious forms that can be transmitted through the exposure to diseased tissues via ingestion, injection or transplantation. The main clinicopathological phenotypes of human prion disease include Creutzfeldt-Jakob disease, by far the most common, fatal insomnia, variably protease-sensitive prionopathy, and Gerstmann-Sträussler-Scheinker disease. However, clinicopathological manifestations extend even beyond those predicted by this classification. Because of their transmissibility, the phenotypic diversity of prion diseases can also be propagated into syngenic hosts as prion strains with distinct characteristics, such as incubation period, pattern of PrP^Sc distribution and regional severity of histopathological changes in the brain. Increasing evidence indicates that different PrP^Sc conformers, forming distinct ordered aggregates, encipher the phenotypic variants related to prion strains. In this review, we summarize the most recent advances concerning the histo-molecular pathology of human prion disease focusing on the phenotypic spectrum of the disease including co-pathologies, the characterization of prion strains by experimental transmission and their correlation with the physicochemical properties of PrP^Sc aggregates.

A domain responsible for spontaneous conversion of bank vole prion protein

Bank vole is a small rodent that shows high susceptibility to infection with diverse prion strains. To determine whether the increased susceptibility of bank voles to prion diseases can be attributed to the intrinsic nature of bank vole prion protein (PrP) or to host factors other than PrP, we produced transgenic mice overexpressing bank vole PrP. These transgenic mice spontaneously developed neurological illness with spongiform changes and the accumulation of abnormal PrP in the brain. Then, we produced transgenic mice overexpressing chimeric mouse/bank vole PrP, which differs from mouse PrP only at two residues located at the C-terminus, to determine the minimum essential domain for the induction of spontaneous generation of abnormal PrP. These transgenic mice also developed spontaneous neurological illness with spongiform changes and the accumulation of abnormal PrP in the brain. In addition, knock-in mice expressing bank vole PrP at the same level as that of wild-type mice did not develop spontaneous disease but showed high susceptibility to infection with diverse prion strains, similarly to bank voles. Taken together, these findings show that bank vole PrP has a high propensity for the conformational conversion both in spontaneous disease and in prion infection, probably due to the characteristic structural properties of the C-terminal domain.

Development of a quick bioassay for the evaluation of transmission properties of acquired prion diseases

Evaluation of transmission properties is important for the differential diagnosis of a subgroup of acquired Creutzfeldt-Jakob disease (CJD) with methionine homozygosity at polymorphic codon 129 of the PRNP gene, an intermediate type abnormal prion protein (PrP), and kuru plaques, denoted as acquired CJD-MMiK. The present study aimed to develop a quick evaluation system of the transmission properties of acquired CJD-MMiK. In the PrP-humanized mice intraperitoneally inoculated with brain homogenates from an acquired CJD-MMiK patient, accumulation of abnormal PrP was observed in follicular dendritic cells of the spleen at 75 days post-inoculation. The transmission properties of acquired CJD-MMiK were quite different from those of sporadic CJD with the same PRNP codon 129 genotype. Moreover, even at 14 days post-inoculation, the characteristic transmission properties of acquired CJD-MMiK could be detected. These findings suggest that the bioassay using follicular dendritic cells of the spleen, named as a FDC assay, can be an easy, time-saving, and useful method to distinguish acquired CJD-MMiK from sporadic CJD.

Iatrogenic Creutzfeldt-Jakob disease

Iatrogenic transmission of Creutzfeldt-Jakob disease (CJD) has occurred through particular medical procedures. Among them, dura mater grafts and pituitary-derived growth hormone obtained from human cadavers undiagnosed as CJD are the most frequent sources of infection. Recent advances in our knowledge about dura mater graft- and human pituitary-derived growth hormone-associated CJD patients have revealed that the combination of the infected CJD strain and the PRNP genotype of the patient determines their clinical, neuropathologic, and biochemical features. In this chapter, we summarize the clinical, neuropathologic, biochemical, and diagnostic features of dura mater graft- and human pituitary-derived growth hormone-associated CJD patients for the appropriate diagnosis of iatrogenic CJD.

UK Iatrogenic Creutzfeldt-Jakob disease: investigating human prion transmission across genotypic barriers using human tissue-based and molecular approaches

Creutzfeldt–Jakob disease (CJD) is the prototypic human prion disease that occurs most commonly in sporadic and genetic forms, but it is also transmissible and can be acquired through medical procedures, resulting in iatrogenic CJD (iCJD). The largest numbers of iCJD cases that have occurred worldwide have resulted from contaminated cadaveric pituitary-derived human growth hormone (hGH) and its use to treat primary and secondary growth hormone deficiency. We report a comprehensive, tissue-based and molecular genetic analysis of the largest series of UK hGH-iCJD cases reported to date, including in vitro kinetic molecular modelling of genotypic factors influencing prion transmission. The results show the interplay of prion strain and host genotype in governing the molecular, pathological and temporal characteristics of the UK hGH-iCJD epidemic and provide insights into the adaptive mechanisms involved when prions cross genotypic barriers. We conclude that all of the available evidence is consistent with the hypothesis that the UK hGH-iCJD epidemic resulted from transmission of the V2 human prion strain, which is associated with the second most common form of sporadic CJD.

Prion disease: experimental models and reality

The understanding of the pathogenesis and mechanisms of diseases requires a multidisciplinary approach, involving clinical observation, correlation to pathological processes, and modelling of disease mechanisms. It is an inherent challenge, and arguably impossible to generate model systems that can faithfully recapitulate all aspects of human disease. It is, therefore, important to be aware of the potentials and also the limitations of specific model systems. Model systems are usually designed to recapitulate only specific aspects of the disease, such as a pathological phenotype, a pathomechanism, or to test a hypothesis. Here, we evaluate and discuss model systems that were generated to understand clinical, pathological, genetic, biochemical, and epidemiological aspects of prion diseases. Whilst clinical research and studies on human tissue are an essential component of prion research, much of the understanding of the mechanisms governing transmission, replication, and toxicity comes from in vitro and in vivo studies. As with other neurodegenerative diseases caused by protein misfolding, the pathogenesis of prion disease is complex, full of conundra and contradictions. We will give here a historical overview of the use of models of prion disease, how they have evolved alongside the scientific questions, and how advancements in technologies have pushed the boundaries of our understanding of prion biology.

Distinctive properties of plaque-type dura mater graft-associated Creutzfeldt-Jakob disease in cell-protein misfolding cyclic amplification

There are two distinct subtypes of dura mater graft-associated Creutzfeldt-Jakob disease (dCJD) with methionine homozygosity at codon 129 of the PRNP gene. The majority of cases is represented by a non-plaque-type (np-dCJD) resembling sporadic CJD (sCJD)-MM1 or -MV1, while the minority by a plaque-type (p-dCJD). p-dCJD shows distinctive phenotypic features, namely numerous kuru plaques and an abnormal isoform of prion protein (PrP(Sc)) intermediate in size between types 1 and 2. Transmission studies have shown that the unusual phenotypic features of p-dCJD are linked to the V2 prion strain that is associated with sCJD subtypes VV2 or -MV2. In this study, we applied protein misfolding cyclic amplification (PMCA) using recombinant human prion protein as a substrate and demonstrated that p-dCJD prions show amplification features that are distinct from those of np-dCJD. Although no amplification of np-dCJD prions was observed with either 129 M or 129 V substrate, p-dCJD prions were drastically amplified with the 129 V substrates, despite the PRNP codon 129 incompatibility between seed and substrate. Moreover, by using a type 2 PrP(Sc)-specific antibody not recognizing PrP(Sc) in p-dCJD, we found that type 2 products are generated de novo from p-dCJD prions during PMCA with the 129 V substrates. These findings suggest that our cell-PMCA is a useful tool for easily and rapidly identifying acquired CJD associated with the transmission of the V2 CJD strain to codon 129 methionine homozygotes, based on the preference for the 129 V substrate and the type of the amplified products.

Sporadic Creutzfeldt-Jakob Disease MM1+2C and MM1 are Identical in Transmission Properties

The genotype (methionine, M or valine, V) at polymorphic codon 129 of the PRNP gene and the type (1 or 2) of abnormal prion protein in the brain are the major determinants of the clinicopathological features of sporadic Creutzfeldt-Jakob disease (CJD), thus providing molecular basis for classification of sporadic CJD, that is, MM1, MM2, MV1, MV2, VV1 or VV2. In addition to these "pure" cases, "mixed" cases presenting mixed neuropathological and biochemical features have also been recognized. The most frequently observed mixed form is the co-occurrence of MM1 and MM2, namely MM1+2. However, it has remained elusive whether MM1+2 could be a causative origin of dura mater graft-associated CJD (dCJD), one of the largest subgroups of iatrogenic CJD. To test this possibility, we performed transmission experiments of MM1+2 prions and a systematic neuropathological examination of dCJD patients in the present study. The transmission properties of the MM1+2 prions were identical to those of MM1 prions because MM2 prions lacked transmissibility. In addition, the neuropathological characteristics of MM2 were totally absent in dCJD patients examined. These results suggest that MM1+2 can be a causative origin of dCJD and causes neuropathological phenotype similar to that of MM1.

Neuropathological and biochemical criteria to identify acquired Creutzfeldt-Jakob disease among presumed sporadic cases

As an experimental model of acquired Creutzfeldt-Jakob disease (CJD), we performed transmission studies of sporadic CJD using knock-in mice expressing human prion protein (PrP). In this model, the inoculation of the sporadic CJD strain V2 into animals homozygous for methionine at polymorphic codon 129 (129 M/M) of the PRNP gene produced quite distinctive neuropathological and biochemical features, that is, widespread kuru plaques and intermediate type abnormal PrP (PrP(Sc) ). Interestingly, this distinctive combination of molecular and pathological features has been, to date, observed in acquired CJD but not in sporadic CJD. Assuming that these distinctive phenotypic traits are specific for acquired CJD, we revisited the literature and found two cases showing widespread kuru plaques despite the 129 M/M genotype, in a neurosurgeon and in a patient with a medical history of neurosurgery without dura mater grafting. By Western blot analysis of brain homogenates, we revealed the intermediate type of PrP(Sc) in both cases. Furthermore, transmission properties of brain extracts from these two cases were indistinguishable from those of a subgroup of dura mater graft-associated iatrogenic CJD caused by infection with the sporadic CJD strain V2. These data strongly suggest that the two atypical CJD cases, previously thought to represent sporadic CJD, very likely acquired the disease through exposure to prion-contaminated brain tissues. Thus, we propose that the distinctive combination of 129 M/M genotype, kuru plaques, and intermediate type PrP(Sc) , represents a reliable criterion for the identification of acquired CJD cases among presumed sporadic cases.

Transmissibility of H-Type Bovine Spongiform Encephalopathy to Hamster PrP Transgenic Mice

Two distinct forms of atypical bovine spongiform encephalopathies (H-BSE and L-BSE) can be distinguished from classical (C-) BSE found in cattle based on biochemical signatures of disease-associated prion protein (PrP^Sc). H-BSE is transmissible to wild-type mice—with infected mice showing a long survival period that is close to their normal lifespan—but not to hamsters. Therefore, rodent-adapted H-BSE with a short survival period would be useful for analyzing H-BSE characteristics. In this study, we investigated the transmissibility of H-BSE to hamster prion protein transgenic (TgHaNSE) mice with long survival periods. Although none of the TgHaNSE mice manifested the disease during their lifespan, PrP^Sc accumulation was observed in some areas of the brain after the first passage. With subsequent passages, TgHaNSE mice developed the disease with a mean survival period of 220 days. The molecular characteristics of proteinase K-resistant PrP^Sc (PrP^res) in the brain were identical to those observed in first-passage mice. The distribution of immunolabeled PrP^Sc in the brains of TgHaNSE mice differed between those infected with H-BSE as compared to C-BSE or L-BSE, and the molecular properties of PrP^res in TgHaNSE mice infected with H-BSE differed from those of the original isolate. The strain-specific electromobility, glycoform profiles, and proteolytic cleavage sites of H-BSE in TgHaNSE mice were indistinguishable from those of C-BSE, in which the diglycosylated form was predominant. These findings indicate that strain-specific pathogenic characteristics and molecular features of PrP^res in the brain are altered during cross-species transmission. Typical H-BSE features were restored after back passage from TgHaNSE to bovinized transgenic mice, indicating that the H-BSE strain was propagated in TgHaNSE mice. This could result from the overexpression of the hamster prion protein.

Iatrogenic CJD due to pituitary-derived growth hormone with genetically determined incubation times of up to 40 years

Cases of iatrogenic CJD still occur in the UK 30 years after administration of human pituitary-derived growth hormone ceased. Rudge et al. report a change over time in genotype profile at polymorphic codon 129 of the human prion protein gene in UK patients, distinct from that seen in other countries.

Patients with iatrogenic Creutzfeldt-Jakob disease due to administration of cadaver-sourced growth hormone during childhood are still being seen in the UK 30 years after cessation of this treatment. Of the 77 patients who have developed iatrogenic Creutzfeldt-Jakob disease, 56 have been genotyped. There has been a marked change in genotype profile at polymorphic codon 129 of the prion protein gene (PRNP) from predominantly valine homozygous to a mixed picture of methionine homozygous and methionine-valine heterozygous over time. The incubation period of iatrogenic Creutzfeldt-Jakob disease is significantly different between all three genotypes. This experience is a striking contrast with that in France and the USA, which may relate to contamination of different growth hormone batches with different strains of human prions. We describe the clinical, imaging, molecular and autopsy features in 22 of 24 patients who have developed iatrogenic Creutzfeldt-Jakob disease in the UK since 2003. Mean age at onset of symptoms was 42.7 years. Gait ataxia and lower limb dysaesthesiae were the most frequent presenting symptoms. All had cerebellar signs, and the majority had myoclonus and lower limb pyramidal signs, with relatively preserved cognitive function, when first seen. There was a progressive decline in neurological and cognitive function leading to death after 5–32 (mean 14) months. Despite incubation periods approaching 40 years, the clinical duration in methionine homozygote patients appeared to be shorter than that seen in heterozygote patients. MRI showed restricted diffusion in the basal ganglia, thalamus, hippocampus, frontal and the paracentral motor cortex and cerebellar vermis. The electroencephalogram was abnormal in 15 patients and cerebrospinal fluid 14-3-3 protein was positive in half the patients. Neuropathological examination was conducted in nine patients. All but one showed synaptic prion deposition with numerous kuru type plaques in the basal ganglia, anterior frontal and parietal cortex, thalamus, basal ganglia and cerebellum. The patient with the shortest clinical duration had an atypical synaptic deposition of abnormal prion protein and no kuru plaques. Taken together, these data provide a remarkable example of the interplay between the strain of the pathogen and host prion protein genotype. Based on extensive modelling of human prion transmission barriers in transgenic mice expressing human prion protein on a mouse prion protein null background, the temporal distribution of codon 129 genotypes within the cohort of patients with iatrogenic Creutzfeldt-Jakob disease in the UK suggests that there was a point source of infecting prion contamination of growth hormone derived from a patient with Creutzfeldt-Jakob disease expressing prion protein valine 129.

The influence of PRNP polymorphisms on human prion disease susceptibility: an update

Two normally occurring polymorphisms of the human PRNP gene, methionine (M)/valine (V) at codon 129 and glutamic acid (E)/lysine (K) at codon 219, can affect the susceptibility to prion diseases. It has long been recognized that 129M/M homozygotes are overrepresented in sporadic Creutzfeldt-Jakob disease (CJD) patients and variant CJD patients, whereas 219E/K heterozygotes are absent in sporadic CJD patients. In addition to these pioneering findings, recent progress in experimental transmission studies and worldwide surveillance of prion diseases have identified novel relationships between the PRNP polymorphisms and the prion disease susceptibility. For example, although 219E/K heterozygosity confers resistance against the development of sporadic CJD, this genotype is not entirely protective against acquired forms (iatrogenic CJD and variant CJD) or genetic forms (genetic CJD and Gerstmann-Sträussler-Scheinker syndrome) of prion diseases. In addition, 129M/V heterozygotes predispose to genetic CJD caused by a pathogenic PRNP mutation at codon 180. These findings show that the effects of the PRNP polymorphisms may be more complicated than previously thought. This review aims to summarize recent advances in our knowledge about the influence of the PRNP polymorphisms on the prion disease susceptibility.

Acquired transmissibility of sheep-passaged L-type bovine spongiform encephalopathy prion to wild-type mice

L-type bovine spongiform encephalopathy (L-BSE) is an atypical form of BSE that is transmissible to cattle and several lines of prion protein (PrP) transgenic mice, but not to wild-type mice. In this study, we examined the transmissibility of sheep-passaged L-BSE prions to wild-type mice. Disease-associated prion protein (PrP^Sc) was detected in the brain and/or lymphoid tissues during the lifespan of mice that were asymptomatic subclinical carriers, indicating that wild-type mice were susceptible to sheep-passaged L-BSE. The morphological characteristics of the PrP^Sc of sheep-passaged L-BSE included florid plaques that were distributed mainly in the cerebral cortex and hippocampus of subsequent passaged mice. The PrP^Sc glycoform profiles of wild-type mice infected with sheep-passaged L-BSE were similar to those of the original isolate. The data indicate that sheep-passaged L-BSE has an altered host range and acquired transmissibility to wild-type mice.

Transmission Properties of Human PrP 102L Prions Challenge the Relevance of Mouse Models of GSS

Inherited prion disease (IPD) is caused by autosomal-dominant pathogenic mutations in the human prion protein (PrP) gene (PRNP). A proline to leucine substitution at PrP residue 102 (P102L) is classically associated with Gerstmann-Sträussler-Scheinker (GSS) disease but shows marked clinical and neuropathological variability within kindreds that may be caused by variable propagation of distinct prion strains generated from either PrP 102L or wild type PrP. To-date the transmission properties of prions propagated in P102L patients remain ill-defined. Multiple mouse models of GSS have focused on mutating the corresponding residue of murine PrP (P101L), however murine PrP 101L, a novel PrP primary structure, may not have the repertoire of pathogenic prion conformations necessary to accurately model the human disease. Here we describe the transmission properties of prions generated in human PrP 102L expressing transgenic mice that were generated after primary challenge with ex vivo human GSS P102L or classical CJD prions. We show that distinct strains of prions were generated in these mice dependent upon source of the inoculum (either GSS P102L or CJD brain) and have designated these GSS-102L and CJD-102L prions, respectively. GSS-102L prions have transmission properties distinct from all prion strains seen in sporadic and acquired human prion disease. Significantly, GSS-102L prions appear incapable of transmitting disease to conventional mice expressing wild type mouse PrP, which contrasts strikingly with the reported transmission properties of prions generated in GSS P102L-challenged mice expressing mouse PrP 101L. We conclude that future transgenic modeling of IPDs should focus exclusively on expression of mutant human PrP, as other approaches may generate novel experimental prion strains that are unrelated to human disease.

Inherited prion disease (IPD) is caused by pathogenic mutations in the human prion protein (PrP) gene leading to the formation of lethal prions in the brain. To-date the properties of prions causing IPD and their similarities to prions causing other forms of human prion disease remain ill-defined. In the present study we have investigated the properties of prions seen in patients with Gerstmann-Sträussler-Scheinker (GSS) disease associated with the substitution of leucine for proline at amino acid position 102 (GSS P102L). We examined the ability of these prions to infect transgenic mice expressing human mutant 102L PrP, human wild-type PrP or wild-type mice. We found that GSS-102L prions have properties distinct from other types of human prions by showing that they can only infect transgenic mice expressing human PrP carrying the same mutation. Mice expressing wild-type human PrP or wild-type mouse PrP were entirely resistant to infection with GSS-102L prions. We conclude that accurate modeling of inherited prion disease requires the expression of authentic mutant human PrP in transgenic models, as other approaches may generate results that do not mirror the human disease.

Transmission properties of atypical Creutzfeldt-Jakob disease: a clue to disease etiology?

The genotype at polymorphic codon 129 of the PRNP gene has a profound influence on both phenotypic expression and prion strain susceptibility in humans. For example, while the most common sporadic Creutzfeldt-Jakob disease (CJD) subtype, sporadic CJD-MM1 (M1 strain), induces a single phenotype after experimental transmission regardless of the codon 129 genotype of the recipient animal, the phenotype elicited by sporadic CJD-VV2 (V2 strain), the second most common subtype, varies according to the host codon 129 genotype. In particular, the propagation of the V2 strain in codon 129 methionine homozygotes has been linked only to acquired forms of CJD such as plaque-type dura mater graft-associated CJD (dCJD), a subgroup of iatrogenic CJD with distinctive phenotypic features, but has never been observed in sporadic CJD cases. In the present report, we describe atypical CJD cases carrying codon 129 methionine homozygosity, in a neurosurgeon and in a patient with a medical history of neurosurgery without dural grafting, showing the distinctive phenotypic features and transmission properties of plaque-type dCJD. These findings raise the possibility that the two cases, previously thought to represent sporadic CJD, might actually represent acquired CJD caused by infection with the V2 strain. Thus, careful analyses of phenotypic features and transmission properties in atypical cases may be useful to distinguish acquired from sporadic cases of CJD.

IMPORTANCE

Susceptibility to and phenotypic expression of Creutzfeldt-Jakob disease (CJD) depend on both the prion strain and genotype at polymorphic codon 129 of the PRNP gene. For example, propagation of the second most common sporadic CJD strain (V2 strain) into codon 129 methionine homozygotes has been linked to plaque-type dura mater graft-associated CJD (dCJD), a subgroup of iatrogenic CJD with distinctive phenotypic features, but has never been observed in sporadic CJD. In the present report, we describe atypical CJD cases in a neurosurgeon and in a patient with a medical history of neurosurgery without dural grafting, showing the distinctive phenotypic features and transmission properties of plaque-type dCJD. These findings raise the possibility that the two cases, previously considered to represent sporadic CJD, might actually represent acquired CJD caused by infection with the V2 strain.

Infectious prion diseases in humans: cannibalism, iatrogenicity and zoonoses

In contrast with other neurodegenerative disorders associated to protein misfolding, human prion diseases include infectious forms (also called transmitted forms) such as kuru, iatrogenic Creutzfeldt-Jakob disease and variant Creutzfeldt-Jakob disease. The transmissible agent is thought to be solely composed of the abnormal isoform (PrP(Sc)) of the host-encoded prion protein that accumulated in the central nervous system of affected individuals. Compared to its normal counterpart, PrP(Sc) is β-sheet enriched and aggregated and its propagation is based on an autocatalytic conversion process. Increasing evidence supports the view that conformational variations of PrP(Sc) encoded the biological properties of the various prion strains that have been isolated by transmission studies in experimental models. Infectious forms of human prion diseases played a pivotal role in the emergence of the prion concept and in the characterization of the very unconventional properties of prions. They provide a unique model to understand how prion strains are selected and propagate in humans. Here, we review and discuss how genetic factors interplay with strain properties and route of transmission to influence disease susceptibility, incubation period and phenotypic expression in the light of the kuru epidemics due to ritual endocannibalism, the various series iatrogenic diseases secondary to extractive growth hormone treatment or dura mater graft and the epidemics of variant Creutzfeldt-Jakob disease linked to dietary exposure to the agent of bovine spongiform encephalopathy.

Distinct origins of dura mater graft-associated Creutzfeldt-Jakob disease: past and future problems

Dura mater graft-associated Creutzfeldt-Jakob disease (dCJD) can be divided into two subgroups that exhibit distinct clinical and neuropathological features, with the majority represented by a non-plaque-type of dCJD (np-dCJD) and the minority by a plaque-type of dCJD (p-dCJD). The two distinct phenotypes of dCJD had been considered to be unrelated to the genotype (methionine, M or valine, V) at polymorphic codon 129 of the PRNP gene or type (type 1 or type 2) of abnormal isoform of prion protein (PrPSc) in the brain, while these are major determinants of clinicopathological phenotypes of sporadic CJD (sCJD). The reason for the existence of two distinct subgroups in dCJD had remained elusive. Recent progress in research of the pathogenesis of dCJD has revealed that two distinct subgroups of dCJD are caused by infection with different PrPSc strains from sCJD, i.e., np-dCJD caused by infection with sCJD-MM1/MV1, and p-dCJD caused by infection with sCJD-VV2 or -MV2. These studies have also revealed previously unrecognized problems as follows: (i) the numbers of p-dCJD patients may increase in the future, (ii) the potential risks of secondary infection from dCJD, particularly from p-dCJD, may be considerable, and (iii) the effectiveness of the current PrPSc decontamination procedures against the PrPSc from p-dCJD is uncertain. To prevent secondary infection from p-dCJD, the establishment of effective decontamination procedures is an urgent issue. In this review, we summarize the past and future problems surrounding dCJD.

Deciphering the pathogenesis of sporadic Creutzfeldt-Jakob disease with codon 129 M/V and type 2 abnormal prion protein

Background

Sporadic Creutzfeldt-Jakob disease is classified according to the genotype at polymorphic codon 129 (M or V) of the prion protein (PrP) gene and the type (1 or 2) of abnormal isoform of PrP (PrP^Sc) in the brain. The most complicated entity in the current classification system is MV2, since it shows wide phenotypic variations, i.e., MV2 cortical form (MV2C), MV2 with kuru plaques (MV2K), or a mixed form (MV2K + C). To resolve their complicated pathogenesis, we performed a comprehensive analysis of the three MV2 subgroups based on histopathological, molecular, and transmission properties.

Results

In histopathological and molecular analyses, MV2C showed close similarity to MM2 cortical form (MM2C) and could be easily discriminated from the other MV2 subgroups. By contrast, MV2K and MV2K + C showed the same molecular type and the same transmission type, and the sole difference between MV2K and MV2K + C was the presence of cortical pathology characteristic of MV2C/MM2C. The remarkable molecular feature of MV2K or MV2K + C was a mixture of type 2 PrP^Sc and intermediate type PrP^Sc, which shows intermediate electrophoretic mobility between types 1 and 2 PrP^Sc. Modeling experiments using PrP-humanized mice indicated that MV2K contains a mixture of intermediate type PrP^Sc with the 129M genotype (Mi PrP^Sc) and type 2 PrP^Sc with the 129V genotype (V2 PrP^Sc) that originated from V2 PrP^Sc, whereas MV2C + K may also contain type 2 PrP^Sc with the 129M genotype and cortical pathology (M2C PrP^Sc) that lacks infectivity to the PrP-humanized mice in addition to Mi and V2 PrP^Sc.

Conclusions

Taken together, the present study suggests that the phenotypic heterogeneity of MV2 stems from their different PrP^Sc origin(s).

Insight into the frequent occurrence of dura mater graft-associated Creutzfeldt-Jakob disease in Japan

OBJECTIVE

More than 60% of patients worldwide with Creutzfeldt-Jakob disease (CJD) associated with dura mater graft (dCJD) have been diagnosed in Japan. The remarkable frequency of dura mater grafts in Japan may possibly contribute to the elevated incidence of dCJD, but reasons for the disproportionate use of this procedure in Japan remain unclear. We investigated differences between dCJD patients in Japan and those elsewhere to help explain the more frequent use of cadaveric dura mater and the high incidence of dCJD in Japan.

METHODS

We obtained data on dCJD patients in Japan from the Japanese national CJD surveillance programme and on dCJD patients in other countries from the extant literature. We compared the demographic, clinical and pathological features of dCJD patients in Japan with those from other countries.

RESULTS

Data were obtained for 142 dCJD patients in Japan and 53 dCJD patients elsewhere. The medical conditions preceding dura mater graft transplantation were significantly different between Japan and other countries (p<0.001); in Japan, there were more cases of cerebrovascular disease and hemifacial spasm or trigeminal neuralgia. Patients with dCJD in Japan received dura mater graft more often for non-life-threatening conditions, such as meningioma, hemifacial spasm and trigeminal neuralgia, than in other countries.

CONCLUSIONS

Differences in the medical conditions precipitating dura mater graft may contribute to the frequent use of cadaveric dura mater and the higher incidence of dCJD in Japan.

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.

Atypical neuropathological sCJD-MM phenotype with abundant white matter Kuru-type plaques sparing the cerebellar cortex

We describe an atypical neuropatholgical phenotype of sporadic Creutzfeldt-Jakob disease (sCJD) in a 64-year-old man presenting with a 5-month history of rapidly progressive dementia, comprising behavioral disturbances, memory complaints, disorientation and language alterations. MRI showed diffuse atrophy and hyperintensities in parietal, occipital, temporal and frontal cortices and left caudate nucleus on T2-weighted and fluid-attenuated inversion recovery images. No typical EEG alterations were observed. Repeated 14-3-3 assay was positive after a first negative test. Neuropathology showed classical CJD changes with small cortical foci of large confluent vacuoles and relatively well-preserved cerebellar cortex. The most striking feature was the presence of abundant Kuru-type plaques in both cerebral cortex and subcortical white matter. Sparse Kuru-type plaques were also seen in cerebellum, although only in white matter. Immunohistochemistry showed, in addition to unicentric plaques, diffuse synaptic and patchy perivacuolar, as well as plaque-like and periaxonal pathological prion protein deposits (PrP(res) ). Western blot studies demonstrated the co-occurrence of PrP(res) types 1 and 2 in frontal cortex and a relatively weak type 2 signal in cerebellum. PRNP genotyping revealed methionine homozygosity at codon 129 and excluded mutations. This case shows a previously undescribed combination of histopathological features which preclude its classification according to the current phenotypic and molecular sCJD classification. The observation demonstrates that Kuru-type amyloid plaques mainly involving the cerebral white matter may also occur in sCJD cases with short clinical course and the co-existence of PrP(res) types 1 and 2. This case further highlights the complexity of the correlations between histopathological phenotype and PrP(res) isotype in prion diseases.

Identification of I137M and other mutations that modulate incubation periods for two human prion strains

We report here the transmission of human prions to 18 new transgenic (Tg) mouse lines expressing 8 unique chimeric human/mouse prion proteins (PrP). Extracts from brains of two patients, who died of sporadic Creutzfeldt-Jakob disease (sCJD), contained either sCJD(MM1) or sCJD(VV2) prion strains and were used for inocula. Mice expressing chimeric PrP showed a direct correlation between expression level and incubation period for sCJD(MM1) prions irrespective of whether the transgene encoded methionine (M) or valine (V) at polymorphic residue 129. Tg mice expressing chimeric transgenes encoding V129 were unexpectedly resistant to infection with sCJD(VV2) prions, and when transmission did occur, it was accompanied by a change in strain type. The transmission of sCJD(MM1) prions was modulated by single amino acid reversions of each human PrP residue in the chimeric sequence. Reverting human residue 137 in the chimeric transgene from I to M prolonged the incubation time for sCJD(MM1) prions by more than 100 days; structural analyses suggest a profound change in the orientation of amino acid side chains with the I→M mutation. These findings argue that changing the surface charge in this region of PrP greatly altered the interaction between PrP isoforms during prion replication. Our studies contend that strain-specified replication of prions is modulated by PrP sequence-specific interactions between the prion precursor PrP(C) and the infectious product PrP(Sc).

Biochemical and strain properties of CJD prions: complexity versus simplicity

Prions, the agents responsible for transmissible spongiform encephalopathies, are infectious proteins consisting primarily of scrapie prion protein (PrP(Sc)), a misfolded, β-sheet enriched and aggregated form of the host-encoded cellular prion protein (PrP(C)). Their propagation is based on an autocatalytic PrP conversion process. Despite the lack of a nucleic acid genome, different prion strains have been isolated from animal diseases. Increasing evidence supports the view that strain-specific properties may be enciphered within conformational variations of PrP(Sc). In humans, sporadic Creutzfeldt-Jakob disease (sCJD) is the most frequent form of prion diseases and has demonstrated a wide phenotypic and molecular spectrum. In contrast, variant Creutzfeldt-Jakob disease (vCJD), which results from oral exposure to the agent of bovine spongiform encephalopathy, is a highly stereotyped disease, that, until now, has only occurred in patients who are methionine homozygous at codon 129 of the PrP gene. Recent research has provided consistent evidence of strain diversity in sCJD and also, unexpectedly enough, in vCJD. Here, we discuss the puzzling biochemical/pathological diversity of human prion disorders and the relationship of that diversity to the biological properties of the agent as demonstrated by strain typing in experimental models.

Heparin enhances the cell-protein misfolding cyclic amplification efficiency of variant Creutzfeldt-Jakob disease

Highly sensitive in vitro screening tests are required to prevent the iatrogenic spread of variant Creutzfeldt-Jakob disease (vCJD). Protein misfolding cyclic amplification (PMCA) is a candidate for such a test, but the sensitivity of this method is insufficient. Polyanions were reported to enhance PMCA efficiency, but their effects on vCJD are unclear. We developed a cell-PMCA of vCJD, wherein cell lysate containing exogenously expressed human PrP was used as substrates, to investigate the effects of various sulfated polysaccharides on amplification efficiency. PrP(res) amounts after cell-PMCA were analyzed by western blotting. Heparin, dermatan sulfate, and dextran sulfate (average molecular weight [MW] 1400kDa) enhanced efficiency, but dextran sulfate (average MW 8kDa) and a heparin pentasaccharide analog had no effect. Pentosan polysulfate inhibited cell-PMCA reaction. The amplification efficiency of cell-PMCA of vCJD increased to >100-fold per round with heparin. The enhancing effects of heparin on cell-PMCA were seed dependent: it was high for vCJD, low for sporadic Creutzfeldt-Jakob disease, and low to negligible for hamster-adapted scrapie-derived 263K. In multi-round PMCA, signals were detected at earlier rounds with heparin than without heparin, and PrP(Sc) in 10(-10) diluted vCJD brain was detected by the sixth round. Heparin-assisted cell-PMCA of vCJD represents a significant step toward detecting very minute amounts of PrP(Sc) in the body fluids of asymptomatic vCJD patients.

Review: contribution of transgenic models to understanding human prion disease

Transgenic mice expressing human prion protein in the absence of endogenous mouse prion protein faithfully replicate human prions. These models reproduce all of the key features of human disease, including long clinically silent incubation periods prior to fatal neurodegeneration with neuropathological phenotypes that mirror human prion strain diversity. Critical contributions to our understanding of human prion disease pathogenesis and aetiology have only been possible through the use of transgenic mice. These models have provided the basis for the conformational selection model of prion transmission barriers and have causally linked bovine spongiform encephalopathy with variant Creutzfeldt-Jakob disease. In the future these models will be essential for evaluating newly identified potentially zoonotic prion strains, for validating effective methods of prion decontamination and for developing effective therapeutic treatments for human prion disease.

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.

[Prion disease surveillance in Japan: analysis of 1,241 patients]

The Creutzfeldt-Jakob Disease (CJD) Surveillance Committee has identified 1,241 patients with prion diseases during 1999-2009, including 953 with sporadic CJD (sCJD) (76.8%), 207 with genetic prion diseases (16.7%), 78 with environmentally acquired prion diseases (6.3%), and 3 with unclassified CJD. Among atypical cases of sCJD, most common was MM2 type including the cortical and thalamic forms. The genetic cases included 84 with a PrP V180I mutation (40.6%), 37 with a P102L mutation (17.9%), 34 with a E200K mutation (16.4%), 32 with a M232R mutation (15.5%), 4 with a P105L mutation (1.9%), and so on. The environmentally acquired cases included 77 with dura mater graft-associated CJD (dCJD) and one with variant CJD (vCJD). Combined with the results by the previous surveillance systems, a total number of dCJD in Japan was 135. The vCJD patient had a history of short stay in the UK and presented with periodic electroencephalogram in the late stage. Although there was no evidence of association of surgical procedures or blood transfusion with sCJD, 4.5% of the sCJD patients underwent operations after the onset of sCJD, including neurosurgical for 0.8% and ophthalmic for 1.9%, requiring more attention on prion diseases to reduce the iatrogenic risk.

Experimental verification of a traceback phenomenon in prion infection

The clinicopathological phenotypes of sporadic Creutzfeldt-Jakob disease (sCJD) correlate with the allelotypes (M or V) of the polymorphic codon 129 of the human prion protein (PrP) gene and the electrophoretic mobility patterns of abnormal prion protein (PrP(Sc)). Transmission of sCJD prions to mice expressing human PrP with a heterologous genotype (referred to as cross-sequence transmission) results in prolonged incubation periods. We previously reported that cross-sequence transmission can generate a new prion strain with unique transmissibility, designated a traceback phenomenon. To verify experimentally the traceback of sCJD-VV2 prions, we inoculated sCJD-VV2 prions into mice expressing human PrP with the 129M/M genotype. These 129M/M mice showed altered neuropathology and a novel PrP(Sc) type after a long incubation period. We then passaged the brain homogenate from the 129M/M mouse inoculated with sCJD-VV2 prions into other 129M/M or 129V/V mice. Despite cross-sequence transmission, 129V/V mice were highly susceptible to these prions compared to the 129M/M mice. The neuropathology and PrP(Sc) type of the 129V/V mice inoculated with the 129M/M mouse-passaged sCJD-VV2 prions were identical to those of the 129V/V mice inoculated with sCJD-VV2 prions. Moreover, we generated for the first time a type 2 PrP(Sc)-specific antibody in addition to type 1 PrP(Sc)-specific antibody and discovered that drastic changes in the PrP(Sc) subpopulation underlie the traceback phenomenon. Here, we report the first direct evidence of the traceback in prion infection.

Live cell fluorescence resonance energy transfer predicts an altered molecular association of heterologous PrPSc with PrPC

Prion diseases result from the accumulation of a misfolded isoform (PrP(Sc)) of the normal host prion protein (PrP(C)). PrP(Sc) propagates by templating its conformation onto resident PrP(C) to generate new PrP(Sc). Although the nature of the PrP(Sc)-PrP(C) complex is unresolved, certain segments or specific residues are thought to feature critically in its formation. The polymorphic residue 129 is one such site under considerable study. We combined transmission studies with a novel live cell yeast-based fluorescence resonance energy transfer (FRET) system that models the molecular association of PrP in a PrP(Sc)-like state, as a way to explore the role of residue 129 in this process. We show that a reduction in efficiency of prion transmission between donor PrP(Sc) and recipient PrP(C) that are mismatched at residue 129 correlates with a reduction in FRET between PrP-129M and PrP-129V in our yeast model. We further show that this effect depends on the different secondary structure propensities of Met and Val, rather than the specific amino acids. Finally, introduction of the disease-associated P101L mutation (mouse- equivalent) abolished FRET with wild-type mouse PrP, whereas mutant PrP-P101L displayed high FRET with homologous PrP-P101L, as long as residue 129 matched. These studies provide the first evidence for a physical alteration in the molecular association of PrP molecules differing in one or more residues, and they further predict that the different secondary structure propensities of Met and Val define the impaired association observed between PrP(Sc) and PrP(C) mismatched at residue 129.

Incidence and spectrum of sporadic Creutzfeldt-Jakob disease variants with mixed phenotype and co-occurrence of PrPSc types: an updated classification

Six subtypes of sporadic Creutzfeldt-Jakob disease with distinctive clinico-pathological features have been identified largely based on two types of the abnormal prion protein, PrP(Sc), and the methionine (M)/valine (V) polymorphic codon 129 of the prion protein. The existence of affected subjects showing mixed phenotypic features and concurrent PrP(Sc) types has been reported but with inconsistencies among studies in both results and their interpretation. The issue currently complicates diagnosis and classification of cases and also has implications for disease pathogenesis. To explore the issue in depth, we carried out a systematic regional study in a large series of 225 cases. PrP(Sc) types 1 and 2 concurrence was detected in 35% of cases and was higher in MM than in MV or VV subjects. The deposition of either type 1 or 2, when concurrent, was not random and always characterized by the coexistence of phenotypic features previously described in the pure subtypes. PrP(Sc) type 1 accumulation and related pathology predominated in MM and MV cases, while the type 2 phenotype prevailed in VVs. Neuropathological examination best identified the mixed types 1 and 2 features in MMs and most MVs, and also uniquely revealed the co-occurrence of pathological variants sharing PrP(Sc) type 2. In contrast, molecular typing best detected the concurrent PrP(Sc) types in VV subjects and MV cases with kuru plaques. The present data provide an updated disease classification and are of importance for future epidemiologic and transmission studies aimed to identify etiology and extent of strain variation in sporadic Creutzfeldt-Jakob disease.

Unique clinicopathological features and PrP profiles in the first autopsied case of dura mater graft-associated Creutzfeldt-Jakob disease with codon 219 lysine allele observed in Japanese population

Polymorphism at codon 219 lysine in prion protein (PrP) is considered to affect the clinicopathological features of prion diseases including Creutzfeldt-Jakob disease (CJD) and to have an inhibiting effect on the pathogenesis of these diseases. We describe the first autopsied case of dura mater graft-associated CJD (dCJD) with heterozygosity of lysine at codon 219 in PrP observed in a Japanese subject. Although this case demonstrated the non-plaque type of dCJD and MM1 subgroup of CJD pathologically and biochemically, the patient demonstrated a long incubation period (19.3 years), atypical periodic sharp-wave complexes with a dominant rhythm on EEG, partially scattered small deposits of plaque-like PrP along with synaptic type deposits of PrP on immunohistochemistry and an atypical MM1 glycosylation pattern with a relatively increased diglycosylated isoform of proteinase-resistant PrP on western blot analysis (i.e. "MM1 variant" pattern). These findings in this case were atypical of the non-plaque type of dCJD and MM1 subgroup of CJD. Thus, these findings can be unique to dCJD with codon 219 lysine allele, and this allele may influence the clinicopathological features and PrP profiles in dCJD.

A traceback phenomenon can reveal the origin of prion infection

The transmission of prions to animals with incongruent prion protein (PrP) gene (referred to as cross-sequence transmission) results in a relatively long incubation period and can generate a new prion strain with unique transmissibility designated as a traceback phenomenon. For example, cross-sequence transmission of bovine spongiform encephalopathy (BSE) prions to human generated variant Creutzfeldt-Jakob disease (vCJD) prions which retained the transmissibility to mice expressing bovine PrP. This finding suggests that traceback studies could enable us to identify the origin of prions. There are two distinct phenotypes in dura mater graft-associated Creutzfeldt-Jakob disease (dCJD), with the majority represented by a non-plaque-type of dCJD (np-dCJD) and the minority by a plaque-type of dCJD (p-dCJD). To identify the origin of p-dCJD, we performed a traceback study using mice expressing human PrP with methionine homozygosity (129M/M) or valine homozygosity (129V/V) at polymorphic codon 129. The characteristics of p-dCJD such as the accumulation of abnormal isoform of PrP (PrP(Sc)) intermediate in size between type 1 and type 2, and plaque-type PrP deposition in the brain were maintained after transmission to the 129M/M mice. Furthermore, the 129V/V mice were more susceptible to p-dCJD prions than the 129M/M mice and produced type 2 PrP(Sc) that were identical in size to those from the 129V/V mice inoculated with sporadic CJD prions from a patient with 129V/V and type 2 PrP(Sc) (sCJD-VV2). In addition, we performed intracerebral transmission of sCJD-VV2 prions to the 129M/M mice as an experimental model for p-dCJD. These 129M/M mice showed the accumulation of the intermediate type PrP(Sc) and plaque-type PrP deposition in the brain. These results suggest that p-dCJD could be caused by cross-sequence transmission of sCJD-VV2 prions to individuals with the 129M/M genotype.