Persistent retroviral infection with MoMuLV influences neuropathological signature and phenotype of prion disease

A fundamental step in pathophysiology of prion diseases is the conversion of the host encoded prion protein (PrP^C) into a misfolded isoform (PrP^Sc) that accumulates mainly in neuronal but also non-neuronal tissues. Prion diseases are transmissible within and between species. In a subset of prion diseases, peripheral prion uptake and subsequent transport to the central nervous system are key to disease initiation. The involvement of retroviruses in this process has been postulated based on the findings that retroviral infections enhance the spread of prion infectivity and PrP^Sc from cell to cell in vitro. To study whether retroviral infection influences the phenotype of prion disease or the spread of prion infectivity and PrP^Sc in vivo, we developed a murine model with persistent Moloney murine leukemia retrovirus (MoMuLV) infection with and without additional prion infection. We investigated the pathophysiology of prion disease in MoMuLV and prion-infected mice, monitoring temporal kinetics of PrP^Sc spread and prion infectivity, as well as clinical presentation. Unexpectedly, infection of MoMuLV challenged mice with prions did not change incubation time to clinical prion disease. However, clinical presentation of prion disease was altered in mice infected with both pathogens. This was paralleled by remarkably enhanced astrogliosis and pathognomonic astrocyte morphology in the brain of these mice. Therefore, we conclude that persistent viral infection might act as a disease modifier in prion disease.     

Quantification of surviving cerebellar granule neurones and abnormal prion protein (PrPSc) deposition in sporadic Creutzfeldt-Jakob disease supports a pathogenic role for small PrPSc deposits common to the various molecular subtypes

B. A. Faucheux, E. Morain, V. Diouron, J.‐P. Brandel, D. Salomon, V. Sazdovitch, N. Privat, J.‐L. Laplanche, J.‐J. Hauw and S. Haïk (2011) Neuropathology and Applied Neurobiology 37, 500–512 Quantification of surviving cerebellar granule neurones and abnormal prion protein (PrP^Sc) deposition in sporadic Creutzfeldt–Jakob disease supports a pathogenic role for small PrP^Sc deposits common to the various molecular subtypes Aims: Neuronal death is a major neuropathological hallmark in prion diseases. The association between the accumulation of the disease‐related prion protein (PrP^Sc) and neuronal loss varies within the wide spectrum of prion diseases and their experimental models. In this study, we investigated the relationships between neuronal loss and PrP^Sc deposition in the cerebellum from cases of the six subtypes of sporadic Creutzfeldt–Jakob disease (sCJD; n = 100) that can be determined according to the M129V polymorphism of the human prion protein gene (PRNP) and PrP^Sc molecular types. Methods: The numerical density of neurones was estimated with a computer‐assisted image analysis system and the accumulation of PrP^Sc deposits was scored. Results: The scores of PrP^Sc immunoreactive deposits of the punctate type (synaptic type) were correlated with neurone counts – the higher the score the higher the neuronal loss – in all sCJD subtypes. Large 5‐ to 50‐µm‐wide deposits (focal type) were found in sCJD‐MV2 and sCJD‐VV2 subtypes, and occasionally in a few cases of the other studied groups. By contrast, the highest scores for 5‐ to 50‐µm‐wide deposits observed in sCJD‐MV2 subtype were not associated with higher neuronal loss. In addition, these scores were inversely correlated with neuronal counts in the sCJD‐VV2 subtype. Conclusions: These results support a putative pathogenic role for small PrP^Sc deposits common to the various sCJD subtypes. Furthermore, the observation of a lower loss of neurones associated with PrP^Sc type‐2 large deposits is consistent with a possible ‘protective’ role of aggregated deposits in both sCJD‐MV2 and sCJD‐VV2 subtypes.     

Abnormal Activation of Microglia Accompanied with Disrupted CX3CR1/CX3CL1 Pathway in the Brains of the Hamsters Infected with Scrapie Agent 263K

Microglial cells are resident mononuclear phagocytes of the central nervous system (CNS). Active proliferation of microglia in the brain has been identified in neurodegenerative disorders, including some kinds of prion disease. However, the detailed regional distribution between microglia and PrP^Sc deposition has not been presented, and investigation of fractalkine signaling which is involved in the regulation of activation of microglia in prion disease is not well documented. In this study, the disease phenomenon of microglial accumulation in the CNS was thoroughly analyzed using a scrapie-infected experimental model. Western blots of microglia-specific markers Iba1 and CD68, immunohistochemical and immunofluorescent assays demonstrated obviously activation of microglia in almost whole brain regions in the infected animals. Under the dynamic analysis on hallmarks of activation of microglia, a time-dependent increase of Iba1 and CD68 was detected, accompanied by accumulation of PrP^Sc and progression of neurodegenerative symptoms. With serial brain sections and double staining of Iba1 and PrP^Sc, we observed that the microglia distributed around PrP^Sc deposits in 263K-infected hamsters’ brains, proposing PrP^Sc phagocytosis. Flow cytometry assays with the single-cell suspensions prepared from the cortical region of the infected brains verified an activation of microglial population. ELISA assays of the cytokines in brain homogenates revealed significant upregulations of interleukin (IL)-1β, IL-6 and TNF-α when infected. Evaluation of fractalkine signaling in the infected hamsters’ brains showed progressively downregulation of CX3CL1 during the incubation. Prion peptide PrP106-126 also disrupted fractalkine and evoked microglial activation in rat primary neuron–glia mixed cultures. Our data here demonstrate an activated status of microglia in CNS tissues of infectious prion disease, possibly through fractalkine signaling deficiency.     

Accumulation of prion protein in the vagus nerve in creutzfeldt–jakob disease

Disease‐associated proteins are thought to propagate along neuronal processes in neurodegenerative diseases. To detect disease‐associated prion protein (PrP^Sc) in the vagus nerve in different forms and molecular subtypes of Creutzfeldt–Jakob disease (CJD), we applied 3 different anti‐PrP antibodies. We screened the vagus nerve in 162 sporadic and 30 genetic CJD cases. Four of 31 VV‐2 type sporadic CJD and 7 of 30 genetic CJD cases showed vagal PrP^Sc immunodeposits with distinct morphology. Thus, PrP^Sc in CJD affects the vagus nerve analogously to α‐synuclein in Parkinson disease. The morphologically diverse deposition of PrP^Sc in genetic and sporadic CJD argues against uniform mechanisms of propagation of PrP^Sc. Ann Neurol 2019;85:782–787     

Sporadic fatal insomnia with spongiform degeneration in the thalamus and widespread PrPSc deposits in the brain

We report a case of human prion disease of 29 months duration in a 74‐year‐old Japanese man. The disease started with progressive sleeplessness and dementia. MRI showed gradually progressive cerebral atrophy. Neuronal loss, spongiform change and gliosis were evident in the thalamus and cerebral cortex, as well as in the striatum and amygdaloid nucleus. In the cerebellar cortex, mild‐to‐moderate depletion of Pukinje cells and spongiform change were observed. Mild neuronal loss in the inferior olivary nucleus was also seen. Immunohistochemistry revealed widespread perivacuolar deposits of abnormal prion protein (PrP^Sc) in the cerebral cortex, thalamus, basal ganglia, and brainstem, and minimal plaque‐like deposits of PrP^Sc in the cerebellar cortex. In the cerebellar plaque‐like deposits, the presence of amyloid fibrils was confirmed ultrastructurally. The entire pathology appeared to lie halfway between those of CJD and fatal insomnia, and further demonstrated the relationship between spongiform degeneration and PrP^Sc deposits, especially in the diseased thalamus. By immunoblotting, the thalamus was shown to contain the lowest amount of PrP^SC among the brain regions examined. The PrP^Sc of type 2, in which the ratio of the three glycoforms was compatible with that of sporadic fatal insomnia (MM2‐thalamic variant) reported previously, was also demonstrated. Analysis of the prion protein gene (PRNP) showed no mutation, and homozygosity for methionine at codon 129. In conclusion, we considered that this patient had been suffering from sporadic, pathologically atypical fatal insomnia.     

Astrocytosis and amyloid deposition in scrapie-infected hamsters

In scrapie infection, prion protein (PrP^Sc) is localized in areas where there is neurodegeneration and astrocytosis. It is thought that PrP^Sc is toxic to neurons and trophic for astrocytes. In our study, paraffin sections from scrapie infected (263K and 139H) and control hamsters were examined with histological and immunocytochemical staining. We found that PrP^Sc was present in the ependymal cells of both 263K- and 139H-infected hamsters. In 139H-infected hamsters, PrP^Sc was found in the cytoplasm of neurons in cerebral cortex and in hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. In contrast, neuronal cytoplasm and nuclei, were positive for PrP^Sc in most areas such as cortex, hippocampus, and thalamus in 263K-infected hamsters. Many aggregations of PrP^Sc could be seen in the cortex, hippocampus, substantia nigra and around the Pia mater, corpus callosum, fimbria, ventricles, and blood vessels in sections from 139H- and/or 263K-positive animals. Furthermore, PrP^Sc was also co-localized with glial fibrillary acidic protein (GFAP) in many reactive astrocytes (approximately 90%) in certain areas such as the hippocampus in 263K-infected hamsters, but not 139H-infected hamsters. The patterns of astrocytosis and PrP^Sc formation were different between 139H- and 263K-infected hamsters, which may be used for a diagnosis purpose. Our results suggest a hypothesis that multiple cell-types are capable of PrP^Sc production. Our results also confirm that reactive astrocytes can produce and/or accumulate PrP^Sc during some scrapie strain infections. The findings suggest a `snowball effect', that is: astrocytosis might play an important role in amyloidosis, while amyloidosis may induce further astrocytosis at least in 263K-infected hamsters.     

Molecular biology and pathology of prion strains in sporadic human prion diseases

Prion diseases are believed to propagate by the mechanism involving self-perpetuating conformational conversion of the normal form of the prion protein, PrP^C, to the misfolded, pathogenic state, PrP^Sc. One of the most intriguing aspects of these disorders is the phenomenon of prion strains. It is believed that strain properties are fully encoded in distinct conformations of PrP^Sc. Strains are of practical relevance to human prion diseases as their diversity may explain the unusual heterogeneity of these disorders. The first insight into the molecular mechanisms underlying heterogeneity of human prion diseases was provided by the observation that two distinct disease phenotypes and their associated PrP^Sc conformers co-distribute with distinct PrP genotypes as determined by the methionine/valine polymorphism at codon 129 of the PrP gene. Subsequent studies identified six possible combinations of the three genotypes (determined by the polymorphic codon 129) and two common PrP^Sc conformers (named types 1 and 2) as the major determinants of the phenotype in sporadic human prion diseases. This scenario implies that each 129 genotype–PrP^Sc type combination would be associated with a distinct disease phenotype and prion strain. However, notable exceptions have been found. For example, two genotype–PrP^Sc type combinations are linked to the same phenotype, and conversely, the same combination was found to be associated with two distinct phenotypes. Furthermore, in some cases, PrP^Sc conformers naturally associated with distinct phenotypes appear, upon transmission, to lose their phenotype-determining strain characteristics. Currently it seems safe to assume that typical sporadic prion diseases are associated with at least six distinct prion strains. However, the intrinsic characteristics that distinguish at least four of these strains remain to be identified.     

Prion infection in cells is abolished by a mutated manganese transporter but shows no relation to zinc

The cellular prion protein has been identified as a metalloprotein that binds copper. There have been some suggestions that prion protein also influences zinc and manganese homeostasis. In this study we used a series of cell lines to study the levels of zinc and manganese under different conditions. We overexpressed either the prion protein or known transporters for zinc and manganese to determine relations between the prion protein and both manganese and zinc homeostasis. Our observations supported neither a link between the prion protein and zinc metabolism nor any effect of altered zinc levels on prion protein expression or cellular infection with prions. In contrast we found that a gain of function mutant of a manganese transporter caused reduction of manganese levels in prion infected cells, loss of observable PrP^Sc in cells and resistance to prion infection. These studies strengthen the link between manganese and prion disease.     

Subtyping of human cellular prion proteins and their differential solubility

A human form of a prion disorder is the Creutzfeldt-Jakob disease. A hallmark of the disease is the accumulation of misfolded prion proteins (PrP^Sc), which exist as heterogeneous subtypes. PrP^Sc is formed by protein conversion from the host-encoded cellular prion (PrP^C), which is expressed and modified to various isoforms. Little is known about variation in PrP^C; however, it is assumed that PrP^C types play important roles in the formation of PrP^Sc. In this study, we separated distinct human PrP^C subtypes on the basis of differential protein solubilities in detergent solutions. Single and sequential application of the detergents Triton X-100, octyl-glucopyranoside and CHAPS facilitated high solubility of glycosylated PrP^C isoforms, whereas high proportions of nonglycosylated PrP^C remained non-soluble. Most proteins became highly soluble with laurylsarcosine and sodium dodecyl sulphate. Our findings demonstrate that the solubility characteristics of heterogeneous PrP^C overlap in human brains and convey distinct solubility subtypes. Differentiation by solubility experiments can therefore provide valuable information on prion protein composition, facilitate the separation of subtypes, and offer new prospects for conversion specificity of distinct isoforms.     

Differential solubility of prions is associated in manifold phenotypes

The main feature of prion diseases is the accumulation of infectious proteins (PrP^Sc). Since PrP^Sc results from conversion of cellular prion proteins (PrP^C), differential expressed PrP^C types may play an important role in the formation and conversion efficiency to specific PrP^Sc forms. However, little is known about the PrP^C expression, regulation and differentiation. Here, we demonstrate a new type of differentiation of overlapping PrP^C isoforms in brain homogenates using differential SDS solubility. Low and highly soluble PrP^C were detected along with various types of protein which are present in the brain of non-infected humans, sheep and cattle. Our findings provide evidence for the existence of several overlapping PrP^C proteins exhibiting distinct glycotypes. The selection of defined PrP^C types offers new possibilities for identifying highly efficient converting proteins and provides the potential for disease control.     

Cellular and sub-cellular pathology of animal prion diseases: relationship between morphological changes,accumulation of abnormal prion protein and clinical disease

The transmissible spongiform encephalopathies (TSEs) or prion diseases of animals are characterised by CNS spongiform change, gliosis and the accumulation of disease-associated forms of prion protein (PrP^d). Particularly in ruminant prion diseases, a wide range of morphological types of PrP^d depositions are found in association with neurons and glia. When light microscopic patterns of PrP^d accumulations are correlated with sub-cellular structure, intracellular PrP^d co-localises with lysosomes while non-intracellular PrP^d accumulation co-localises with cell membranes and the extracellular space. Intracellular lysosomal PrP^d is N-terminally truncated, but the site at which the PrP^d molecule is cleaved depends on strain and cell type. Different PrP^d cleavage sites are found for different cells infected with the same agent indicating that not all PrP^d conformers code for different prion strains. Non-intracellular PrP^d is full-length and is mainly found on plasma-lemmas of neuronal perikarya and dendrites and glia where it may be associated with scrapie-specific membrane pathology. These membrane changes appear to involve a redirection of the predominant axonal trafficking of normal cellular PrP and an altered endocytosis of PrP^d. PrP^d is poorly excised from membranes, probably due to increased stabilisation on the membrane of PrP^d complexed with other membrane ligands. PrP^d on plasma-lemmas may also be transferred to other cells or released to the extracellular space. It is widely assumed that PrP^d accumulations cause neurodegenerative changes that lead to clinical disease. However, when different animal prion diseases are considered, neurological deficits do not correlate well with any morphological type of PrP^d accumulation or perturbation of PrP^d trafficking. Non-PrP^d-associated neurodegenerative changes in TSEs include vacuolation, tubulovesicular bodies and terminal axonal degeneration. The last of these correlates well with early neurological disease in mice, but such changes are absent from large animal prion disease. Thus, the proximate cause of clinical disease in animal prion disease is uncertain, but may not involve PrP^d.     

EP24.15 is associated with lipid rafts

Metalloendopeptidase EC 3.4.24.15 (EP24.15, thimet oligopeptidase) is a neuropeptide-metabolizing peptidase expressed throughout the body, but primarily in the brain, gonads, and pituitary. For EP24.15 to have its greatest effect upon peptides in the periphery, it must be targeted and released into the extracellular space. Western blot analysis of fractions taken from discontinuous sucrose density gradients carried out on crude plasma membrane fractions from AtT-20 cells reveals colocalization of EP24.15 and flotillin-1, a known lipid raft marker. Further analysis revealed that an intracellular membrane marker and non-lipid raft, plasma membrane marker, failed to colocalize, supporting EP24.15/lipid raft association. Furthermore, EP24.15 immunoreactivity in lipid raft fractions generated from cells treated with methyl beta-cyclodextrin (MbetaCD) was greatly reduced. Finally, treatment with MbetaCD resulted in the accumulation of EP24.15 in the media of drug-treated cells over vehicle-treated cells, suggesting that a large percentage of EP24.15 associating with lipid rafts resides on the extracellular surface of the plasma membrane. With this exofacial localization, EP24.15 could have ample access to neuropeptides not only in the immediate microenvironment, but the ability to degrade or modify peptides bound for receptor interaction.     

Sialylated and O‐glycosidically linked glycans in prion protein deposits in a case of Gerstmann‐Sträussler‐Scheinker disease

Prion diseases are caused by an abnormal form of the prion protein (PrP^Sc). We identified, with lectins, post‐translational modifications of brain proteins due to glycosylation in a Gerstmann‐Sträussler‐Scheinker (GSS) patient. The lectin Amaranthus leucocarpus (ALL), specific for mucin type O‐glycosylated structures (Galß1,3 GalNAcα1,0 Ser/Thr or GalNAcα1,0 Ser/Thr), and Sambucus nigra agglutinin (SNA), specific for Neu5Acα2,6 Gal/GalNAc, showed positive labeling in all the prion deposits and in the core of the PrP^Sc deposits, respectively, indicating specific distribution of O‐glycosylated and sialylated structures. Lectins from Maackia amurensis (MAA, Neu5Acα2,3), Macrobrachium rosenbergii (MrL, Neu5,9Ac2‐specific) and Arachis hypogaea (PNA, Gal‐specific) showed low staining of prion deposits. Immunohistochemistry colocalization with prion antibody indicated that all lectins stained prion protein deposits. These results show that specific modifications in the glycosylation pattern are closely related to the hallmark lesions and might be an early event in neuronal degeneration in GSS disease.     

On the biology of prions

Summary Prions cause scrapie and Creutzfeldt-Jakob disease (CJD); these infectious pathogens are composed largely, if not entirely, of protein molecules. No prion-specific polynucleotide has been identified. Purified preparations of scrapie prions contain high titers (10^9.5 ID₅₀/ml), one protein (PrP 27-30) and amyloid rods (10–20 nm in diameter ×100–200 nm in length). Considerable evidence indicates that PrP 27-30 is required for and inseparable from scrapie infectivity. PrP 27-30 is encoded by a cellular gene and is derived from a larger protein, denoted PrP^Sc or PrP 33-35^Sc, by protease digestion. A cellular isoform, designated PrP^C or PrP 33-35^C, is encoded by the same gene as PrP^Sc and both proteins appear to be translated from the same 2.1 kb mRNA. Monoclonal antibodies to PrP 27-30, as well as antisera to PrP synthetic peptides, specifically react with both PrP^C and PrP^Sc, establishing their relatedness. PrP^C is digested by proteinase K, while PrP^Sc is converted to PrP 27-30 under the same conditions. Prion proteins are synthesized with signal peptides and are integrated into membranes. Detergent extraction of microsomal membranes isolated from scrapie-infected hamster brains solubilizes PrP^C but induces PrP^Sc to polymerize into amyloid rods. This procedure allows separation of the two prion protein isoforms and the demonstration that PrP^Sc accumulates during scrapie infection, while the level of PrP^C does not change. The prion amyloid rods generated by detergent extraction are identical morphologically, except for length, to extracellular collections of prion amyloid filaments which form plaques in scrapie- and CJD-infected brains. The prion amyloid plaques stain with antibodies to PrP 27-30 and PrP peptides. PrP 33-35^C does not accumulate in the extracellular space. Prion rods composed of PrP 27-30 can be dissociated into phospholipid vesicles with full retention of scrapie infectivity. The murine PrP gene (Prn-p) is linked to thePrn-i gene which controls the length of the scrapie incubation period. Prolonged incubation times are a cardinal feature of scrapie and CJD. While the central role of PrP^Sc in scrapie pathogenesis is well established, the chemical as well as conformational differences between PrP^C and PrP^Sc are unknown but probably arise from post-translational modifications.Supported by research grants from the National Institutes of Health (AG 02132 and NS 14069) and a Senator Jacob Javits Center of Excellence in Neuroscience (NS 22786) as well as by gifts from RJR-Nabisco, Inc. and Sherman Fairchild FoundationThis review is based upon a plenary lecture entitled Biology and Neuropathology of Prions presented at the Xth International Congress of Neuropathology, Stockholm, Sweden, September 11, 1986, and is dedicated to the memory of Peter Wilhelm Lampert (1929–1986)     

Effective antigen-retrieval method for immunohistochemical detection of abnormal isoform of prion proteins in animals

For immunohistochemistry of the prion diseases, several pretreatment methods to enhance the immunoreactivity of human and animal abnormal proteinase-resistant prion protein (PrP^Sc) on the tissue sections have been employed. The method of 121°C hydrated autoclaving pretreatment or the combination method of 121°C hydrated autoclaving with a certain chemical reagent (formic acid or proteinase K, etc) are now widely used. We found that an improved hydrated autoclaving method at 135°C, more effectively enhanced PrP^Sc immunoreactivity for the antibodies recognizing the linear epitope. In addition, this method was more effective for the long-term fixation samples as compared with other previous methods. However, this modified method could not retrieve PrP^Sc antigenic epitopes composed of conformational structures or several discontinuous epitopes. We describe the comparative studies between our improved method and other antigen-retrieval procedures reported previously. Based on the differences of reaction among the antibodies, we also discuss the mechanisms of the hydrated autoclaving methods to retrieve PrP^Sc immunoreactivity.     

Recombinant prion protein induces a new transmissible prion disease in wild-type animals

Prion disease is a neurodegenerative malady, which is believed to be transmitted via a prion protein in its abnormal conformation (PrP^Sc). Previous studies have failed to demonstrate that prion disease could be induced in wild-type animals using recombinant prion protein (rPrP) produced in Escherichia coli. Here, we report that prion infectivity was generated in Syrian hamsters after inoculating full-length rPrP that had been converted into the cross-β-sheet amyloid form and subjected to annealing. Serial transmission gave rise to a disease phenotype with highly unique clinical and neuropathological features. Among them were the deposition of large PrP^Sc plaques in subpial and subependymal areas in brain and spinal cord, very minor lesioning of the hippocampus and cerebellum, and a very slow progression of disease after onset of clinical signs despite the accumulation of large amounts of PrP^Sc in the brain. The length of the clinical duration is more typical of human and large animal prion diseases, than those of rodents. Our studies establish that transmissible prion disease can be induced in wild-type animals by inoculation of rPrP and introduce a valuable new model of prion diseases.     

Neurodevelopmental expression and localization of the cellular prion protein in the central nervous system of the mouse

Transmissible spongiform encephalopathies (TSEs) are neurodegenerative disorders caused by PrP^Sc, or prion, an abnormally folded form of the cellular prion protein (PrP^C). The abundant expression of PrP^C in the central nervous system (CNS) is a requirement for prion replication, yet despite years of intensive research the physiological function of PrP^C still remains unclear. Several routes of investigation point out a potential role for PrP^C in axon growth and neuronal development. Thus, we undertook a detailed analysis of the spatial and temporal expression of PrP^C during mouse CNS development. Our findings show regional differences of the expression of PrP, with some specific white matter structures showing the earliest and highest expression of PrP^C. Indeed, all these regions are part of the thalamolimbic neurocircuitry, suggesting a potential role of PrP^C in the development and functioning of this specific brain system. J. Comp. Neurol. 518:1879–1891, 2010. © 2010 Wiley‐Liss, Inc.     

Prion infection of mice transgenic for human APPSwe: increased accumulation of cortical formic acid extractable Aβ(1–42) and rapid scrapie disease development

Neuropathological, epidemiological and experimental data indicate a potential interrelationship between Alzheimer's disease and prion diseases. Proteolytic processing of amyloid precursor protein (APP) by β-secretase was recently suggested to be controlled by prion protein expression. Here, we characterized the prion infection of Tg2576 mice, which overexpress the human APP_Swe protein. Prion infection of Tg2576-mice led to an early death of the animals, which was preceded by a relatively short symptomatic stage. However, disease-associated gliosis and deposition of misfolded prion protein PrP^Sc were identical in infected Tg2576-mice and non-transgenic littermate controls. To analyze the effect of prion infection on APP processing and generation of β-amyloid we determined cortical levels of SDS- and formic acid (FA)-extractable forms of β-amyloid (1–40) and (1–42) by ELISA. Formic acid-extractable Aβ (1–42) levels were 10-fold higher in infected versus uninfected Tg2576 mice whereas other forms of Aβ were essentially unaffected by the prion infection. Hence, the experimental model demonstrates that a prion infection of the CNS promotes selectively formation of FA-extractable Aβ(1–42) in Tg2576 mice.     

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.