Molecular basis of phenotypic variability in sporadic Creutzfeldt-Jakob disease

Humanized knock-in mice expressing chimeric prion protein showed varied susceptibility to different human prions

Mice to which human prions efficiently transmit in short incubation periods are valuable not only as research tools of human prions but also as reliable diagnostic tools. We recently produced a line of knock-in mouse expressing a unique human-mouse chimeric PrP (Ki-ChM mouse), which has mouse-specific residues practically only at the C-terminal part after posttranslational modification, and here we attempted transmission of various human prions to assess the susceptibility profile of the mouse. Susceptibility varied considerably depending on prions inoculated: highly susceptible to MM1 and MV1 types of sporadic Creutzfeldt-Jakob disease (CJD), developing disease within approximately 150 days, familial CJD with M232R mutation, and dura graft-associated CJD (dCJD) without amyloid plaque; less susceptible to MM2-type sporadic CJD and variant CJD, with some mice lacking any sign of transmission; and totally resistant to VV2 type sporadic CJD and dCJD with amyloid plaque. The rather short incubation time achieved by Ki-ChM mice suggests new approaches to produce mice that develop prion disease with very short incubation periods. We compared the characteristic susceptibility profile of Ki-ChM with those of other precedent transgenic mice and discussed, including the prospects in developing genetically engineered mice susceptible to human prions.

Prion deposition in olfactory biopsy of sporadic Creutzfeldt-Jakob disease

Currently, definite peripheral markers for the in vivo diagnosis of sporadic Creutzfeldt-Jakob disease (CJD) are not available. Here, we report the presence of pathological prion protein in the olfactory mucosa of a case with sporadic Creutzfeldt-Jakob disease. Prion protein immunoreactivity was detected in an olfactory biopsy performed 45 days after the disease onset, suggesting that the involvement of olfactory epithelium is an early event in sporadic Creutzfeldt-Jakob disease.

Prion protein heterogeneity in sporadic but not variant Creutzfeldt-Jakob disease: U.K. cases 1991-2002

Human prion diseases can occur as an idiopathic disorder (sporadic Creutzfeldt-Jakob disease) or can be acquired, as is the case for variant Creutzfeldt-Jakob disease. These disorders are characterized by the accumulation of a protease-resistant form of the host-encoded prion protein termed PrP(Sc) in the brains of affected individuals. PrP(Sc) has been proposed to be the principal, if not sole, component of the infectious agent, with its accumulation in the central nervous system the primary event leading to neurodegeneration. A major question remains as to whether self-propagating structural differences in PrP(Sc) might account for the clinicopathological diversity evident in Creutzfeldt-Jakob disease and whether different prion protein types underlie the existence of different strains of causative agent. Here, we describe the results of a large-scale biochemical study of PrP(Sc) from autopsy-proved cases of variant Creutzfeldt-Jakob disease (n = 59) and compare these with cases of sporadic Creutzfeldt-Jakob disease (n = 170) in the United Kingdom over the period 1991 to 2002. The results show PrP(Sc) in variant Creutzfeldt-Jakob disease to be remarkably stereotyped. In contrast, considerable heterogeneity in PrP(Sc) exists both between and within cases of sporadic Creutzfeldt-Jakob disease.

Pathology and pathogenesis of bovine spongiform encephalopathy and scrapie

In common with other prion diseases or transmissible spongiform encephalopathies (TSEs), scrapie of sheep and bovine spongiform encephalopathy (BSE) are characterized by grey matter vacuolation and accumulation of an abnormal isoform of the host prion protein (PrP) in the central nervous system (CNS). In apparent contrast with human disease, neither neuronal loss nor gliosis are invariable features of the pathology of domestic food animal TSEs. In sheep, accumulation of abnormal PrP may also occur in the lymphoreticular and peripheral nervous systems where it may be detected within months of birth. The involvement of tissues other than CNS is influenced by dose, PrP genotype of the host and strain of TSE agent. Although many different strains of scrapie agent have been isolated in rodents following serial passage of affected sheep brain tissue, the significance of these murine strains for natural sheep scrapie, and the extent to which different sheep scrapie strains occur naturally are uncertain. Whereas the consistent vacuolar pattern in the brains of BSE-affected cattle suggests a single strain of agent, the patterns of vacuolation in sheep scrapie are highly variable and cannot be easily used to define strain. In sheep scrapie, immunohistochemistry can be used to visualize different morphological types of abnormal PrP within individual brains. These different types of PrP accumulation seem to be associated with different brain cell types and with variation in the processing of abnormal PrP. When assessed in whole brain, different patterns of PrP accumulation are helpful in distinguishing between different sheep scrapie strains and also between ovine BSE and natural sheep scrapie.

Neuropathology and molecular biology of variant Creutzfeldt-Jakob disease

The neuropathological features of human prion diseases are spongiform change, neuronal loss, astrocytic proliferation and the accumulation of PrP(Sc), the abnormal isoform of prion protein (PrP). The pattern of brain involvement is remarkably variable and is substantially influenced by the host PrP genotype and PrP(Sc) isotype. Variant Creutzfeldt-Jakob disease (vCJD) is a novel human prion disease which results from exposure to the bovine spongiform encephalopathy (BSE) agent. The neuropathology of vCJD shows consistent characteristics, with abundant florid and cluster plaques in the cerebrum and cerebellum, and widespread accumulation of PrP(res) on immunocytochemistry. These features are distinct from all other types of human prion disease. Spongiform change is most marked in the basal ganglia, while the thalamus exhibits severe neuronal loss and gliosis in the posterior nuclei. These areas of thalamic pathology correlate with the areas of high signal seen in the thalamus on magnetic resonance imaging (MRI) examination of the brain. Western blot analysis of PrP(Sc) in the brain in vCJD tissue shows a uniform isotype, with a glycoform ratio characterized by predominance of the diglycosylated band, distinct from sporadic CJD. PrP(Sc) accumulation in vCJD is readily detectable outside the brain, in contrast with other forms of human prion disease, particularly in the lymphoid system and in parts of the peripheral nervous system. This has raised concern about the possible iatrogenic transmission of vCJD by contaminated surgical instruments, or blood. All cases of vCJD are methionine homozygotes at codon 129 of the prion protein gene (PRNP). Continued surveillance is required to investigate cases of vCJD in the UK and other countries where BSE has been reported, particularly as cases of 'human BSE' in individuals who are MV or VV at codon 129 of the PrP gene have not yet been identified. Histological, genetic and biochemical techniques are essential tools for the adequate diagnosis and investigation of human prion diseases.

Neuronal and astrocytic responses involving the serotonergic system in human spongiform encephalopathies

The relationships between the degree of cortical prion protein (PrP) deposition, tissue vacuolation and astrocytosis were studied in the frontal cortex of 27 cases of human spongiform encephalopathy, encompassing 13 cases of sporadic Creutzfeldt-Jakob disease (sCJD), four cases of familial CJD (fCJD) (one owing to E200K mutation, one owing to 144 bp insertion, one owing to P102L mutation and one owing to A117V mutation), five cases of iatrogenic CJD (iCJD) owing to growth hormone therapy and five cases of variant CJD (vCJD). The size and number of tryptophan hydroxylase (TPH) positive cells in the dorsal raphe were determined as an index of the function of the brain's serotonergic system. The amount of PrP deposited in frontal cortex in vCJD was significantly greater than that in both sCJD and iCJD, which did not differ significantly from each other. The extent of grey matter deposition of PrP correlated with that of white matter deposition. Deposition of PrP as plaques was greater in cases of sCJD bearing valine at codon 129 of PrP gene, especially when homozygous. However, all cases of vCJD displayed florid plaque formation yet these were homozygous for methionine at codon 129. Prion protein deposition as plaques was greater in cases of sCJD with 2A PrP isotype than those with 1 PrP isotype, similar to that seen in cases of vCJD all of which are 2B PrP isotype. There were no significant differences in the extent of astrocytosis between the different aetiological groups, in either grey or white matter, as visualized with glial fibrillary acidic protein (GFAP) or 5HT-2A receptor (5HT-2AR) immunostaining, although there was a strong correlation between the severity of 5HT-2AR and GFAP reactions within both grey and white matter. The extent of PrP deposition within the grey, but not white, matter correlated with the degree of astrocytosis for both GFAP and 5HT-2AR and the extent of tissue vacuolation in grey and white matter, although the latter did not correlate with degree of astrocytosis for either GFAP or 5HT-2AR. Astrocytes may be responding directly to the presence of PrP within the tissue, rather than the vacuolar damage to neurones. Although S100beta immunoreactivity was present in astrocytes in control cases, no S100beta staining was seen in astrocytes in either grey or white matter in most CJD cases. There were no differences in the number of TPH-positive cells between CJD and control cases, although the mean TPH-positive cell size was significantly greater, and cells were more intensely stained, in CJD compared to controls, suggesting a pathological overactivity of the brain's serotonergic system in CJD. This may result in excessive release of 5HT within the brain triggering increased 5HT-2AR expression within activated astrocytes leading to release and depletion of S100beta protein from such cells. The clinical symptoms of fluctuating attention and arousal could be mediated, at least in part, by such alterations in function of the serotonergic system.

Extraneural pathologic prion protein in sporadic Creutzfeldt-Jakob disease

BACKGROUND

In patients with sporadic Creutzfeldt-Jakob disease, pathologic disease-associated prion protein (PrPSc) has been identified only in the central nervous system and olfactory-nerve tissue. Understanding the distribution of PrPSc in Creutzfeldt-Jakob disease is important for classification and diagnosis and perhaps even for prevention.

METHODS

We used a highly sensitive method of detection--involving the concentration of PrPSc by differential precipitation with sodium phosphotungstic acid, which increased the sensitivity of Western blot analysis by up to three orders of magnitude--to search for PrPSc in extraneural organs of 36 patients with sporadic Creutzfeldt-Jakob disease who died between 1996 and 2002.

RESULTS

PrPSc was present in the brain tissue of all patients. In addition, we found PrPSc in 10 of 28 spleen specimens and in 8 of 32 skeletal-muscle samples. Three patients had PrPSc in both spleen and muscle specimens. Patients with extraneural PrPSc had a significantly longer duration of disease and were more likely to have uncommon molecular variants of sporadic Creutzfeldt-Jakob disease than were patients without extraneural PrPSc.

CONCLUSIONS

Using sensitive techniques, we identified extraneural deposition of PrPSc in spleen and muscle samples from approximately one third of patients who died with sporadic Creutzfeldt-Jakob disease. Extraneural PrPSc appears to correlate with a long duration of disease.

Identification of novel proteinase K-resistant C-terminal fragments of PrP in Creutzfeldt-Jakob disease

The central event in the pathogenesis of prion diseases, a group of fatal, transmissible neurodegenerative disorders including Creutzfeldt-Jakob disease (CJD) in humans, is the conversion of the normal or cellular prion protein (PrPC) into the abnormal or scrapie isoform (PrPSc). The basis of the PrPC to PrPSc conversion is thought to involve the diminution of alpha-helical domains accompanied by the increase of beta structures within the PrP molecule. Consequently, treatment of PrPSc with proteinase K (PK) generates a large PK-resistant C-terminal core fragment termed PrP27-30 that in human prion diseases has a gel mobility of approximately 19-21 kDa for the unglycosylated form, and a ragged N terminus between residues 78 and 103. PrP27-30 is considered the pathogenic and infectious core of PrPSc. Here we report the identification of two novel PK-resistant, but much smaller C-terminal fragments of PrP (PrP-CTF 12/13) in brains of subjects with sporadic CJD. PrP-CTF 12/13, like PrP27-30, derive from both glycosylated as well as unglycosylated forms. The unglycosylated PrPCTF 12/13 migrate at 12 and 13 kDa and have the N terminus at residues 162/167 and 154/156, respectively. Therefore, PrP-CTF12/13 are 64-76 amino acids N-terminally shorter than PrP27-30 and are about half of the size of PrP27-30. PrP-CTF12/13 are likely to originate from a subpopulation of PrPSc distinct from that which generates PrP27-30. The finding of PrP-CTF12/13 in CJD brains widens the heterogeneity of the PK-resistant PrP fragments associated with prion diseases and may provide useful insights toward the understanding of the PrPSc structure and its formation.

Association of an 11–12 kDa protease-resistant prion protein fragment with subtypes of dura graft-associated Creutzfeldt–Jakob disease and other prion diseases

Creutzfeldt–Jakob disease can develop in subjects given a cadaveric dura mater graft (dCJD). This disease has a phenotypic heterogeneity despite the lack of genetic variation. Numerous plaque-type prion protein (PrP) deposits are found in the brain of some but not all subjects; hence, there may be two subtypes of this clinical entity. To validate dCJD subtypes further, we carried out a larger-scale clinicopathological analysis and typing of protease-resistant PrP (PrPSc) in dCJD cases. Cases with plaque-type PrP deposits (p-dCJD) were shown to be distinct from those without PrP plaques (np-dCJD), from several clinicopathological aspects. Analysis of PrPSc revealed that, while the major PrPSc species from both subtypes was of 21 kDa after deglycosylation (type 1 PrPSc), a C-terminal PrP fragment of 11–12 kDa (fPrP11–12) was associated with np-dCJD but not with p-dCJD. The disease type-specific association of fPrP11–12 was also observed in subjects with other prion diseases. An fPrP11–12-like C-terminal PrP fragment was detected in brain lysates from patients associated with fPrP11–12, but not from patients or normal subjects unassociated with fPrP11–12. Results indicated that fPrP was produced by CJD-associated processes in vivo. The present data provide several lines of evidence that support the need for subtyping of dCJD and contribute to the understanding of the processing of disease-specific PrP species. The unique relationship of fPrP11–12 with CJD phenotype supports the view that the phenotypic heterogeneity of CJD is related to the formation of different types of disease-specific PrP and fragments thereof.

The sympathetic nervous system is involved in variant Creutzfeldt-Jakob disease

Prion epizoonoses spread from animals consumed by humans raise the question of which pathways lead to prion neuroinvasion after oral exposure of humans. Here we show that neurons of sympathetic ganglia of patients with variant Creutzfeldt-Jakob disease (vCJD) accumulate the abnormal isoform of the protein prion. This observation shows the involvement of the sympathetic nervous system in the pathogenesis of vCJD and suggests a role for GUT-associated sympathetic neurons in prion propagation in humans after oral contamination.

Variant Creutzfeldt-Jakob disease: pathology, epidemiology, and public health implications

Prion diseases, or transmissible spongiform encephalopathies, include Creutzfeldt-Jakob disease (CJD) in humans and scrapie and bovine spongiform encephalopathy (BSE) in animals. These neurodegenerative diseases are invariably fatal and can be transmitted by inoculation or dietary exposure. They are associated with the accumulation of an altered, disease-associated form of the normal prion protein. Pathologically, prion diseases result in neuronal cell death and a characteristic spongiform appearance of the brain tissue. The emergence of a variant form of CJD (vCJD) in the United Kingdom in 1996 has been causally and experimentally linked to the UK BSE epidemic in the 1980s and early 1990s. The finding that BSE is transmissible to different animal species, unlike previously characterized prion diseases such as sheep scrapie, has raised enormous public health concerns worldwide. Although it is not yet possible to gauge the size of a potential vCJD epidemic, preliminary data indicate a significant dietary exposure to BSE-infected material in Britain and wider implications of the transmissibility of prion diseases. The threat to public health has intensified research efforts to understand the molecular basis of prion diseases, understand their transmission between species, improve methods of diagnosis, and develop therapeutic strategies for treatment and prevention of disease. In this review, we summarize current data on the pathology of BSE and vCJD and the epidemiology of vCJD, and we outline public health implications based on these data, emphasizing preventative measures and areas of research for screening and diagnosis.

Creutzfeldt-Jakob disease with florid plaques after cadaveric dura mater graft

A patient with dura-associated Creutzfeldt-Jakob disease (D-CJD) which occurred about 15 years after a dura mater graft is reported in the present study. The prion protein gene analysis disclosed no mutation. The D-CJD was atypical in: (i), the long interval between the onset of ataxia and the occurrence of dementia; (ii), the presence of transient myoclonus; and (iii), the presence of florid plaques in the brain. The electron-microscopic findings showed bundles of amyloid filaments which radiated from the center of the plaques without degenerating neurites. This case of D-CJD may belong to a new subtype of D-CJD.

Molecular classification of sporadic Creutzfeldt-Jakob disease

According to the protein-only hypothesis of prion propagation, an abnormal isoform (designated PrP(Sc)) of the cellular prion protein (PrP(C)) is the principal or sole component of transmissible prions. However, the existence of multiple prion strains has been difficult to accommodate within this hypothesis. We have previously reported the identification of four types of human PrP(Sc) associated with sporadic and acquired human prion diseases. These PrP(Sc) types are distinguished by differing molecular mass of fragments following limited proteinase K digestion and by differing ratios of di-, mono- and unglycosylated PrP(Sc). That these discrete biochemical features of PrP(Sc) are serially transmissible to human PrP in transgenic mice following experimental transmission suggests that they may be responsible for encoding prion strain diversity. Here we present detailed clinical, pathological and molecular data from a large number of sporadic Creutzfeldt-Jakob disease (CJD) cases. We show that PrP(Sc) types are associated with codon 129 status, duration of illness and neuropathological phenotype. A novel PrP(Sc) type is presented, illustrating further heterogeneity in CJD, and suggesting that further molecular subtypes of CJD may exist at lower frequencies. A molecular classification of sporadic CJD is proposed.

Extensive cortical damage in a case of Creutzfeldt-Jacob disease: clinicoradiological correlations

MRI demonstrated extensive cortical involvement in a patient with pathologically proven Creutzfeldt-Jacob disease. The whole brain was atrophic; some of the supratentorial cortex, putamen and caudate nucleus gave high signal on T2-weighted images; the changes were more extensive on diffusion-weighted images (DWI). Comparison of the history, and the sites of atrophy and signal change suggested that the latter predominates in regions with long-lasting damage and prevalent gliosis, while high signal on DWI indicate current neuronal loss. This case widens the range of MRI findings in patients with Creutzfeldt-Jacob disease, and suggests that some information about the progression of the disease can be extracted from single MRI study.

Inhibition of complex glycosylation increases the formation of PrPsc

N-linked glycans with complex structure have a major role in the biological activity of a wide variety of cell surface and secreted glycoproteins. Here, we show that geldanamycin, an inhibitor of Hsp90, interferes with the formation of complex glycosylated mammalian prion protein (PrPC). Similarly to inhibitors of alpha-mannosidases, geldanamycin stabilized a high mannose PrPC glycoform and prevented the subsequent processing into complex structures. Moreover, a PrP/Grp94 complex could be isolated from geldanamycin-treated cells, suggesting that Grp94 might play a role in the processing of PrPC in the endoplasmic reticulum. Inhibition of complex glycosylation did not interfere with the glycosylphosphatidylinositol (GPI) anchor attachment and cellular trafficking of high mannose PrPC to the outer leaflet of the plasma membrane. In scrapie-infected neuroblastoma cells, however, high mannose PrPC glycoforms were preferred substrates for the formation of PrP-scrapie (PrPSc). Our study reveals that complex glycosylation is dispensable for the cellular trafficking of PrPC, but modulates the formation of PrPSc.

Determinants of the in vivo folding of the prion protein. A bipartite function of helix 1 in folding and aggregation

Misfolding of the mammalian prion protein (PrP) is implicated in the pathogenesis of prion diseases. We analyzed wild type PrP in comparison with different PrP mutants and identified determinants of the in vivo folding pathway of PrP. The complete N terminus of PrP including the putative transmembrane domain and the first beta-strand could be deleted without interfering with PrP maturation. Helix 1, however, turned out to be a major determinant of PrP folding. Disruption of helix 1 prevented attachment of the glycosylphosphatidylinositol (GPI) anchor and the formation of complex N-linked glycans; instead, a high mannose PrP glycoform was secreted into the cell culture supernatant. In the absence of a C-terminal membrane anchor, however, helix 1 induced the formation of unglycosylated and partially protease-resistant PrP aggregates. Moreover, we could show that the C-terminal GPI anchor signal sequence, independent of its role in GPI anchor attachment, mediates core glycosylation of nascent PrP. Interestingly, conversion of high mannose glycans to complex type glycans only occurred when PrP was membrane-anchored. Our study indicates a bipartite function of helix 1 in the maturation and aggregation of PrP and emphasizes a critical role of a membrane anchor in the formation of complex glycosylated PrP.

Familial primary progressive aphasia

Primary progressive aphasia (PPA) is a neurodegenerative disease presenting with isolated, progressive, language dysfunction. After at least 2 years, dementia may develop, but the aphasia predominates. Few families with hereditary PPA have been reported; some have autosomal dominance. A chromosome 17 mutation in tau exon 13 has been found in one family, and a few have linkage to chromosome 17. However, early appearance of prominent memory, behavior, and motor impairments differentiates these patients from typical PPA. The objective was to report clinical features, pathology, and genetic analysis of a family with typical PPA. We report three siblings with the typical clinical syndrome of PPA. Each presented with word-finding difficulties and early anomia. Ages at onset were 60, 61, and 65 years. Aphasia was the only symptom for at least 2 years. A nonaffected brother is 75 years of age. Family history review found no other affected relatives. Neuropathology in one patient demonstrated "dementia lacking distinctive histopathology" with ubiquitin-positive cortical neurons. DNA analysis of the proband did not detect any known mutation in tau exons 1-5, 7, or 9-13. To our knowledge, this is the first family presenting with hereditary aphasia in which typical PPA occurs in all affected members.

Potent inhibition of scrapie prion replication in cultured cells by bis-acridines

Prion diseases are characterized by an accumulation of PrP(Sc), a misfolded isoform of the normal cellular prion protein, PrP(C). We previously reported the bioactivity of acridine-based compounds against PrP(Sc) replication in scrapie-infected neuroblastoma cells and now report the improved potency of bis-acridine compounds. Bis-acridines are characterized by a dimeric motif, comprising two acridine heterocycles tethered by a linker. A library of bis-(6-chloro-2-methoxy-acridin-9-yl) and bis-(7-chloro-2-methoxy-benzo[b][1,5]naphthyridin-10-yl) analogs was synthesized to explore the effect of structurally diverse linkers on PrP(Sc) replication in scrapie-infected neuroblastoma cells. Structure-activity analysis revealed that linker length and structure are important determinants for inhibition of prion replication in cultured scrapied cells. Three bis-acridine analogs, (6-chloro-2-methoxy-acridin-9-yl)-(3-[4-[3-(6-chloro-2-methoxy-acridin-9-ylamino)-propyl]-piperazin-1-yl]-propyl)-amine, N,N'-bis-(6-chloro-2-methoxy-acridin-9-yl)-1,8-diamino-3,6-dioxaoctane, and (1-[[4-(6-chloro-2-methoxy-acridin-9-ylamino)-butyl]-[3-(6-chloro-2-methoxy-acridin-9-ylamino)-propyl]-carbamoyl]-ethyl)-carbamic acid tert-butyl ester, showed half-maximal inhibition of PrP(Sc) formation at 40, 25, and 30 nM, respectively, and were not cytotoxic to uninfected neuroblastoma cells at concentrations of 500 nM. Our data suggest that bis-acridine analogs may provide a potent alternative to the acridine-based compound quinacrine, which is currently under clinical evaluation for the treatment of prion disease.

Variant Creutzfeldt-Jakob disease

Variant CJD is a novel human prion disease that represents the first known occasion in which animal prion diseases have been transmitted to humans. There are many uncertainties concerning vCJD, including the mechanism of transmission between species, the extent of human exposure to the BSE agent, the infectious dose for humans, and the future burden of human disease. It is hoped that continuing scientific research may lead to answers to some of these questions and that further understanding of the mechanism of prion replication may lead to the development of effective treatment. Indeed a recent publication has suggested that the drugs quinacrine or chloropromazine may be candidates for the treatment of human prion diseases [42].

PRNP Val129 homozygosity increases risk for early-onset Alzheimer's disease

We analyzed the PRNP M129V polymorphism in a Dutch population-based early-onset Alzheimer's disease sample. We observed a significant association between early-onset Alzheimer's disease and homozygosity of M129V (odds ratio [OR], 1.9; 95% confidence interval [CI], 1.1-3.3; p = 0.02) with the highest risk for V homozygotes (OR, 3.2; 95% CI, 1.4-7.1; p < 0.01). In patients with a positive family history, these risks increased to 2.6 (95% CI, 1.3-5.3; p < 0.01) and 3.5 (95% CI, 1.3-9.3; p = 0.01), respectively.

Perspectives on prion biology, prion disease pathogenesis, and pharmacologic approaches to treatment

The main goals of this article have been to summarize our current understanding of the biology of PrP, the propagation of prions, and the etiology and pathogenesis of each form of prion disease (familial, sporadic, and infectious); and to review current rational pharmacologic strategies for treatment of prion diseases. Each of these subjects is presented primarily from the perspective of investigations performed by the prion disease research laboratories at the University of California in San Francisco and by its many collaborators in the United States and abroad. This review focuses on key results from the hundreds of transgenic mouse lines expressing different PrP constructs that have been used to determine the roles played by different PrPSc and PrPC domains in prion propagation and the prion disease phenotype.

Hereditary Creutzfeldt-Jakob disease and fatal familial insomnia

Studies on hereditary CJD and FFI have contributed greatly to the understanding of all forms of prion disease. Most importantly, they have provided strong support for the prion hypothesis [2]. The linkage of pathogenic PRNP mutations to human prion disease strengthens the notion that a change in PrP conformation is a key event that triggers the development of the disease. Although hereditary CJD and FFI account for only 10% of all cases of human prion disease, they provide a unique opportunity for studying disease pathogenesis initiated by perturbation in the PrP structure. An understanding of the events that accompany a change in PrP conformation has far-reaching implications for sCJD (the most common form of the disease) and for sporadic fatal insomnia. A wealth of available evidence indicates that a common pathway in disease pathogenesis may be shared by both the sporadic and the hereditary forms of prion disease, except that the initiating events are stochastic in the former, rather than predetermined by the presence of a germ-line mutation. In addition, investigations of hereditary CJD and FFI have provided plausible mechanisms of phenotypic heterogeneity in prion disease, a phenomenon analogous to the "prion strain" diversity in animal prion disease. Although many other neurodegenerative diseases such as Alzheimer's disease, amyotrophic lateral sclerosis, and Huntington's chorea are fairly homogeneous in disease phenotype, prion disease includes many clinically and pathologically distinct disease entities. In hereditary prion disease, the disease phenotype is likely to be determined by the combined effect of pathogenic mutations, codon 129 polymorphism, and the type of PrPSc. The pathogenic mutations include point mutations that are located mostly in the central and C-terminal region of PrP, and deletion and insertion mutations that are located in the N-terminal region. It is conceivable that these distinct types of mutations may result in differential changes in conformation or stability of PrP. The codon 129 polymorphism plays a twofold role in modulating the disease outcome. On the mutant allele, it determines the basic features of the disease phenotype--as in the case of FFI and CJD178--that result respectively from the coupling of M or V at codon 129 with the D178N mutation. On the normal allele, it may modulate the severity of the phenotype. A PrPSc subtype is encoded by the PRNP haplotype, and subsequently is generated by a conformational conversion process that transforms the cellular isoform to the pathogenic protein. The site for the formation of a specific PrPSc conformer and its accumulation in different brain regions are likely to contribute to the clinical features and pathologic lesions. The phenotypic homogeneity in other neurologic diseases, including Alzheimer's disease, may be due, in part, to the lack of a powerful genetic modifier such as the codon 129 polymorphism in the PrP gene, and the lack of the ability of affected gene products such as PrP to assume multiple protein conformations. Clearly, the remaining issue in the understanding of pathogenesis of prion disease is a detailed and accurate knowledge of the in vivo processes and conditions for the formation of PrPSc that inevitably lead to the development and expression of the disease. This knowledge will enable the development of a rational and effective strategy for therapeutic intervention.

Diagnosis of prion diseases

This article reviews the various techniques and methodologies for the recognition and diagnosis of clinical and neuropathologic variants of human prion diseases.

Detection of pathologic prion protein in the olfactory epithelium in sporadic Creutzfeldt-Jakob disease

BACKGROUND

Olfactory cortexes and the olfactory tracts are involved in sporadic Creutzfeldt-Jakob disease. We examined peripheral regions of the olfactory sensory pathway, including the olfactory mucosa, to assess whether pathologic infectious prion protein (PrPSc) is deposited in the epithelium lining the nasal cavity.

METHODS

We studied nine patients with neuropathologically confirmed sporadic Creutzfeldt-Jakob disease. We obtained the brain, the cribriform plate with the attached olfactory mucosa, and the surrounding respiratory epithelium at autopsy. Control samples of nasal mucosa were obtained post mortem or at biopsy from age-matched control subjects and from control patients with other neurodegenerative diseases. The olfactory and respiratory mucosa and the intracranial olfactory system were analyzed by light microscopy, immunohistochemistry, and Western blotting for pathological changes and for deposition of PrPSc.

RESULTS

In all nine patients with sporadic Creutzfeldt-Jakob disease, PrPSc was found in the olfactory cilia and central olfactory pathway but not in the respiratory mucosa. No PrPSc was detected in any of the tissue samples from the 11 controls.

CONCLUSIONS

Our pathological and biochemical studies show that PrPSc is deposited in the neuroepithelium of the olfactory mucosa in patients with sporadic Creutzfeldt-Jakob disease, indicating that olfactory biopsy may provide diagnostic information in living patients. The olfactory pathway may represent a route of infection and a means of spreading prions.

Sporadic Creutzfeldt-Jakob disease with MM1-type prion protein and plaques

The authors report a 75-year-old woman with atypical sporadic Creutzfeldt-Jakob disease (CJD) characterized by MM1-type prion protein (PrP) (methionine homozygosity at codon 129 in the PrP gene and type-1 protease-resistant PrP) and PrP plaques. This patient is the first case of sporadic CJD with plaque-forming MM1-type PrP, suggesting either a shared prion strain with the plaque-forming subset of dural graft-associated CJD or shared host genetic factors that are unrelated to the PrP genotype.

Sporadic and familial CJD: classification and characterisation

Prion diseases are unique transmissible neurodegenerative diseases that have diverse phenotypes and can be familial, sporadic, or acquired by infection. Recent findings indicate that the PrP genotype and the PrP(Sc) type have a major influence on the disease phenotype in both sporadic and familial human prion diseases. This review attempts to classify and characterise sporadic and familial Creutzfeldt-Jakob disease (CJD) as a function of these two disease determinants. Based on the genotype at codon 129 on both PRNP alleles, the size of protease resistant PrP(Sc) fragments and disease phenotype, we divide sporadic CJD into six subtypes: sCJDMM1/sCJDMV1, sCJDVV2, sCJDMV2, sCJDMM2, sCJDVV1, and sporadic fatal insomnia (sFI). Familial CJD is classified into many haplotypes based on the PRNP mutation and codon 129 (and other polymorphic codons) on the mutant allele. The clinical and pathological features are summarised for each sporadic CJD subtype and familial CJD haplotype.

Molecular and clinical classification of human prion disease

While rare in humans, the prion diseases have become an area of intense clinical and scientific interest. The recognition that variant Creutzfeldt-Jakob disease is caused by the same prion strain as bovine spongiform encephalopathy in cattle has dramatically highlighted the need for a precise understanding of the molecular biology of human prion diseases. Detailed clinical, pathological and molecular data from a large number of human prion disease cases have shown that distinct abnormal isoforms of prion protein are associated with prion protein gene polymorphism and neuropathological phenotypes. A molecular classification of human prion diseases seems achievable through characterisation of structural differences of the infectious agent itself.

Prion diseases: pathogenesis and public health concerns

Transmissible spongiform encephalopathy (TSE) agents or prions induce neurodegenerative fatal diseases in humans and in some mammalian species. Human TSEs include Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome, kuru and fatal familial insomnia. In animals, scrapie in sheep and goats, feline spongiform encephalopathy, transmissible mink encephalopathy, chronic wasting disease in wild ruminants, and bovine spongiform encephalopathy (BSE), which appeared in the UK in the mid-1980s [Wells, G.A.H. et al. (1987) Vet. Rec. 121, 419-420], belong to the TSE group. Prions have biological and physicochemical characteristics that differ significantly from those of other microorganisms; for example, they are resistant to inactivation processes that are effective against conventional viruses, including those that alter nucleic acid structure or function. Alternatively, infectivity is highly susceptible to procedures that modify protein conformation. Today, the exact nature of prions remains unknown even though it is likely that they consist of protein only. At the biochemical level, TSEs are characterised by the accumulation, within the central nervous system of the infected individual, of an abnormal isoform of a particular protein from the host, the prion protein [Prusiner, S.B. (1982) Science 216, 136-144]. TSEs are transmissible among their species of origin, but they can also cross the species barrier and induce chronic infection and/or disease in other species. Transmissibility has been proven in natural situations such as the outbreak of CJD among patients treated with pituitary-derived hormones and the appearance of BSE that affected UK cattle in the mid-1980s.

A French cluster of Creutzfeldt-Jakob disease: a molecular analysis

We report the molecular and phenotypic analysis of a French cluster of three cases of Creutzfeldt-Jakob disease (CJD), two of them occurring in 1998 in the same village and the other in 1995 in a neighboring village. Analyses of the occurrence of these events in a close area with less than 3000 inhabitants over the 1992-1999 notification period confirmed that they are rare. This could be explained either by a common source of contamination or by the coincidental occurrence of either sporadic or genetic CJD. We applied genetic analysis and brain PrPres typing to explore these CJD cases. The three patients did not carry any mutation in their prion protein gene coding sequence. All were homozygous for methionine at the polymorphic codon 129. Brain tissue was available from two cases that died in 1998. The two patients showed different PrPres profiles on Western blot and distinct clinico-pathological features. These findings do not support the conclusion that in these three cases, CJD was acquired from a unique source of contamination and suggest that concurrent occurrence of sporadic CJD accounted for this CJD cluster.

The risk of transmission of variant Creutzfeldt–Jakob disease via contact lenses and ophthalmic devices

This review collated the available information regarding the risk of transmission of variant Creutzfeldt-Jakob disease (vCJD) via contact lenses and other ophthalmic devices. The topics examined include: the emerging background science of the unconventional infective agent, the prion, particularly those factors affecting transmission; the estimates of the number of undiagnosed infective individuals; and evidence of infectivity in the external eye. Despite many uncertainties in the literature, we conclude that cross-infection is theoretically possible. An assessment of the extensive search for a complete inactivation procedure resulted in the recommendation of the use of sodium hypochlorite (NaOCl), which does not appear to distort rigid lenses. Further tests are required for other devices.

Brain biopsy in Creutzfeldt-Jakob disease: evolution of pathological changes by prion protein immunohistochemistry

The formation of protease-resistant prion protein (PrPsc) is considered to be an early event in the pathogenesis of Creutzfeldt-Jakob disease (CJD) and hence its demonstration in brain biopsies by immunohistochemistry is considered diagnostic. We analysed eight brain biopsies from the frontal cortex collected from different parts of India from cases diagnosed as CJD on clinical and pathological grounds for the expression of prion protein (PrP). The duration of illness in these cases varied from 2 months to 1 year. Immunohistochemistry was carried out on paraffin sections using two different clones (KG9 and 3F4) of monoclonal antibodies to PrP. Although all eight cases showed classical features of spongiform encephalopathy of varying severity, only five of the eight cases revealed PrP(sc) in the brain tissue. The immunolabelling was focal and all areas with spongiform change were not labelled. A temporal evolution in the staining pattern was evident - particulate diffuse labelling (synaptic type) in early stages (2 months), perivacuolar deposits in intermediate stages (5-6 months), and dense plaques in late stages (12 months).

A journey through the species barrier

The species barrier in prion infectivity is believed to reside in the degree of amino acid sequence heterology between the infectious prion protein, PrP(Sc), of the donor and the normal PrP of the host. bring new evidence that distinct PrP(Sc) species or prion strains may have different conformations even when they have identical amino acid sequence and that the conformation of the exogenous prion strain is a determinant of the species barrier in hosts that have identical PrP genotype.

A change in the conformation of prions accompanies the emergence of a new prion strain

To investigate the role of the pathogenic prion protein (PrP(Sc)) in controlling susceptibility to foreign prions, two Syrian hamster (SHa) prion strains, Sc237 and DY, were transmitted to transgenic mice expressing chimeric SHa/mouse PrP genes, Tg(MH2M). First passage of SHa(Sc237) prions exhibited prolonged incubation times, diagnostic of a species barrier. PrP(Sc) of the new MH2M(Sc237) strain possessed different structural properties from those of SHa(Sc237), as demonstrated by relative conformational stability measurements. This change was accompanied by a disease phenotype different from the SHa(Sc237) strain. Conversely, transmission of SHa(DY) prions to Tg(MH2M) mice showed no species barrier, and the MH2M(DY) strain retained the conformational and disease-specific properties of SHa(DY). These results suggest a causal relationship between species barriers, changes in PrP(Sc) conformation, and the emergence of new prion strains.

Heterogeneity of normal prion protein in two- dimensional immunoblot: presence of various glycosylated and truncated forms

The common use of one-dimensional (1-D) immunoblot with a single monoclonal antibody (Mab) engenders the notion that the normal or cellular prion protein (PrP(C) ) comprises few and simple forms. In this study we used two-dimensional (2-D) immunoblot with a panel Mabs to various regions of the prion protein to demonstrate the complexity of the PrP(C) present in human brain. We distinguished over 50 immunoblot spots, each representing a distinct PrP(C) species based on combinations of different molecular weights and isoelectric points (pIs). The PrP(C) heterogeneity is due to the presence of a full-length and two major truncated forms as well as to the diversity of the glycans linked to most of these forms. The two major truncated forms result from distinct cleavage sites located at the N-terminus. In addition, enzymatic removal of sialic acid and lectin binding studies indicate that the glycans linked to the full-length and truncated PrP(C) forms differ in their structure and ratios of the glycoforms. The truncation of PrP(C) and the heterogeneity of the linked glycans may play a role in regulating PrP(C) function. Furthermore, the presence of relatively large quantities of different PrP(C) species may provide additional mechanisms by which the diversity of prion strains could be generated.

Molecular diagnostics of transmissible spongiform encephalopathies

Clinical criteria for the diagnosis of sporadic, iatrogenic and variant Creutzfeldt-Jakob diseases are now available and show an excellent sensitivity and specificity ( approximately 98%). Post-mortem diagnosis, based upon the identification in the brain of the pathological conformer of the prion protein (PrP(Sc)), is also very accurate, and several diagnostic kits are now available that facilitate the immunochemical measurement of PrP(Sc). Several new molecular diagnostic techniques aimed at increasing the sensitivity and specificity of PrP(Sc) detection, and at identifying markers of disease that are other than PrP(Sc), are the subject of ongoing studies. The aim of these studies is to develop preclinical screening tests for the identification of infected, but still healthy, individuals. These tests are also badly needed to check the safety of blood or blood-derived products, and to ensure meat safety in European countries.

Identification of inter-species transmission of prion strains

The concern of the potential transmission of animal spongiform encephalopathies to humans, which arose as soon as the interspecies transmission of these diseases was recognized, has been reinforced with the emergence of bovine spongiform encephalopathy (BSE) in cattle. Recent experimental findings suggest that the infectious agent causing BSE in cattle can lead to the occurrence of a new form of Creutzfeldt-Jakob disease in humans. These findings help us understand how the transmission to humans of an animal disease may be recognized. This can involve an indirect approach through the analysis of neurodegeneration, either in the disease host, or more specifically, in genetically well-defined experimental hosts to which the disease can be transmitted. Recent experimental studies have also shown that the different molecular features of the abnormal form of the prion protein, which accumulates in the infected tissues, can provide important clues to the relationships between different spongiform encephalopathies. However, a better understanding of the molecular features associated with the specific pathogenic behavior of different strains is required. Complex relationships between the infectious agents involved in spongiform encephalopathies and the disease host can make the recognition of a link between animal prion strains and the human disease difficult to establish.

Clinical features of variant Creutzfeldt-Jakob disease

Since 1996, over one hundred cases of variant Creutzfeldt-Jakob disease have appeared, mostly in the United Kingdom. In this review, we summarise the major clinical features of this progressive neurodegenerative condition and compare them with those of sporadic Creutzfeldt-Jakob disease. We emphasise the young age (median 26 years) at presentation and the dominant psychiatric/behavioural features, particularly depression. Sensory symptoms are present initially in half the cases and florid psychiatric symptoms, such as delusions or hallucinations, are also common. Given these symptoms, many patients present in clinical practice initially to a psychiatrist but are referred to neurologists when neurological signs become apparent. Although the definitive diagnosis remains neuropathological, a confident pre-mortem diagnosis is now possible when the 'pulvinar sign' is seen on magnetic resonance imaging studies.

Tau protein and 14-3-3 protein in the differential diagnosis of Creutzfeldt-Jakob disease

BACKGROUND

Diagnosis of Creutzfeldt-Jakob disease (CJD) is made according to the typical clinical picture and can be supported by a positive 14-3-3 CSF immunoblot. Promising results for the diagnostic sensitivity and specificity of tau-protein measurement in CSF already have been described in a smaller group of patients. Both tests in a larger group of patients with the differential diagnosis of CJD were evaluated.

METHODS

CSF of 297 patients under the differential diagnosis of CJD (109 definite, 55 probable, 39 possible; 85 others, 1 iatrogenic, 8 genetic), 23 nondemented control subjects, and 15 non-CJD patients with positive 14-3-3 immunoblots were analyzed. The 14-3-3 immunoblot bands were semiquantitatively rated as strong, medium, and weak. Tau-protein was analyzed using a commercially available ELISA. In addition, patients were neuropathologically classified according to prion protein type and polymorphism at codon 129.

RESULTS

A diagnostic sensitivity of 94%, a diagnostic specificity of 90%, and a positive predictive value of 92% were achieved for tau-protein at a cut-off of 1,300 pg/mL. These results are comparable with those of the 14-3-3 immunoblot. For patients with type II prion protein and methionine/valine or valine/valine polymorphism at codon 129, tau-protein has a higher diagnostic sensitivity than 14-3-3 protein. Tau-protein levels were significantly higher in patients with higher-rated 14-3-3 immunoblot bands.

CONCLUSION

The differential diagnostic significance of the 14-3-3 immunoblot is similar to that of the tau-protein ELISA. The advantage of the tau-protein ELISA is that it is easy to use in routine laboratories. Patients with a negative 14-3-3 immunoblot already have measurable tau-protein levels. This increases information on 14-3-3-negative patients with CJD and especially on patients with other diseases.

Two-dimensional mapping of three phenotype-associated isoforms of the prion protein in sporadic Creutzfeldt-Jakob disease

Transmissible spongiform encephalopathies (TSE), or prion diseases, are mammalian neurodegenerative disorders characterized by a conformational modification of the host-encoded prion protein (PrP(C)) into an isoform which is detergent-insoluble and partially resistant to protease treatment (PrP(Sc)). Distinct types of PrP(Sc), differing in conformation and variation in the relative amount of their glycoforms, have been associated with different phenotypes of TSE. In sporadic Creutzfeldt-Jakob disease (sCJD), two major types of PrP(Sc), with proteinase K (PK)-resistant fragments of 21 and 19 kDa, have been described. No consensus exists, however, on the molecular classification of PrP(Sc) in sCJD, since further heterogeneity within PrPSc conformers has been reported. We studied 19 subjects with dementia or dementia/ataxia at onset and 12 subjects with ataxia at onset. Following two-dimensional gel electrophoresis, we characterized PrP(C) and PrP(Sc) species in normal and sCJD brains by immunoblotting with antibodies recognizing N-terminal and C-terminal PrP regions. Three types of PrP(Sc) were detected in detergent-insoluble fractions from sCJD brains, mainly consisting of full-length PrP(Sc) in subjects with rapidly progressive dementia, and two different sets of amino-truncated PrP(Sc) glycoforms in subjects with dementia/ataxia and ataxia at onset. Examination of the PrP(Sc) core fragment, following PK treatment and deglycosylation, confirmed the existence of three distinctive patterns. These findings have immediate implications for the molecular classification of sCJD.

Propagation of Adenoviral Vectors

This chapter discusses the production systems of adenoviral vectors. Particular attention is paid to the generation and use of complementation cell lines that carry the El genes and emphasizes on the PER.C6 cell line, which was developed to prevent generation of replication-competent adenovirus (RCA) during propagation of El-deleted adenoviral vectors. Further, safety issues with respect to the use of the cell line for making clinical grade material are also addressed in this chapter. The PER.C6 cell line is the best substrate for the production of adenoviral vectors for gene therapy or vaccines. PER.C6 permits extensive analysis for adventitial agents and other safety concerns and thus is less hazardous than short-lived primary cell cultures for which testing must be repeated for each newly established culture.

Effects of agent strain and host genotype on PrP accumulation in the brain of sheep naturally and experimentally affected with scrapie

Different cellular and neuroanatomical types of disease-specific prion protein (PrP(d)) accumulation in the brain were identified in sheep of different breeds and PrP genotypes exposed to experimental or natural scrapie infection. Immunohistochemical examination of the brains of 43 sheep with clinical signs compatible with scrapie revealed 12 different PrP(d)types, which were subjectively quantified in eight different brain regions. The PrP(d)types were grouped into four PrP(d)patterns, the relative magnitude of which provided the PrP(d)profile of each sheep examined. The analysis of the differences in magnitude and relative proportion of each of these PrP(d)types and patterns indicated (1) an effect of the scrapie strain on the PrP(d)profile, and (2) a possible effect of the host genotype on the magnitude of PrP(d)accumulation in the brain, apparently related to the incubation period. Furthermore, intraneuronal deposition of PrP(d)was the type most closely associated with the development of clinical disease. We conclude that different scrapie strains can be distinguished by PrP immunohistochemical examination of brains of affected animals.

Clinical diagnosis and differential diagnosis of CJD and vCJD. With special emphasis on laboratory tests

The most widely distributed form of transmissible spongiform encephalopathy, sporadic Creutzfeldt-Jakob disease, typically affects patients in their sixties. Rapidly progressive dementia is usually followed by focal neurological signs and typically myoclonus. The disease duration in sporadic CJD is shorter than in variant CJD (6 months and 14 months, respectively). The clinical diagnosis in sporadic CJD is supported by the detection of periodic sharp and slow wave complexes in the electroencephalogram, hyperintense signals in basal ganglia on magnetic resonance imaging and elevated levels of neuronal proteins in the cerebrospinal fluid (such as 14-3-3). In contrast to the sporadic form, hyperintense signals in the posterior thalamus ("pulvinar sign") are seen in variant CJD. Following recent developments in diagnostic premortem techniques, clinical criteria for probable sporadic and probable variant CJD were established. Clinicopathological studies on sporadic CJD revealed different phenotypes which are characterized by neuropathological lesion profile, clinical syndrome, codon 129 genotype and type of proteinase K-resistant core of the prion protein. Alzheimer's disease and Lewy body dementia are the most frequent differential diagnoses in sporadic CJD in elderly patients, whereas chronic inflammatory disorders of the central nervous system have to be considered in younger patients.

Familial Creutzfeldt-Jakob disease associated with a point mutation at codon 210 of the prion protein gene

Creutzfeldt-Jakob disease (CJD), the most known human prion disease, is usually sporadic but approximately 15% of the cases are familial. To date, seven CJD cases with codon 210 mutation (GTT to ATT) have been reported in the literature. We describe a case of a 57 year-old woman who presented gait disturbances and rapidly progressive dementia, leading to death four months after onset. Electroencephalogram revealed periodic activity, diffusion-weighted magnetic resonance imaging showed hypersignal in basal ganglia, and test for 14-3-3 protein was strongly positive in the CSF. The complete prion protein gene coding region was sequenced after PCR amplification, showing a point mutation in codon 210. This is the first case of CJD with codon 210 mutation diagnosed in Brazil. We emphasize the role of genetic search for prion protein gene mutation, even in patients presenting clinical features resembling sporadic CJD.