Immunohistochemical localization of prion protein in spongiform encephalopathies and normal brain tissue

Kuru Disease: Bridging the Gap Between Prion Biology and Human Health

This article explores the intriguing case of Kuru disease, a rare and fatal prion disease that once afflicted the Fore people of Papua New Guinea. Scientists are still perplexed as to the origins of Kuru because efforts to discover infectious agents like viruses have been ineffective. Initial research revealed similarities between Kuru and scrapie, a neurological disorder that affects sheep, suggesting potential similarities between the two diseases. In further research, experiments in which chimpanzee brain tissue from Kuru patients was implanted led to the development of Kuru-like symptoms in the animals, suggesting a transmissible component to the condition. Furthermore, data collected from epidemiological studies highlights a drop in Kuru transmission, especially after the Fore people stopped engaging in cannibalism, and the disease showed different incubation times that affected persons within particular age groups. Neuropathological tests in the infected brain tissue have found typical intracellular vacuoles, spongiform alterations, and amyloid plaques. According to studies, Kuru susceptibility has been linked genetically to particular PRNP gene variations. Kuru and other prion disorders have few effective treatments currently, underlining the vital need for early identification. Scientists have created sensitive detection techniques to stop the spread of prion diseases and looked into possible inhibitors. Hypochlorous acid, in particular, has shown potential in cleaning processes. Besides making great progress in understanding Kuru, there are still many unresolved issues surrounding its causes, transmission, and management. The terms "kuru disease," "human prion disease," "transmissible spongiform encephalopathies," and "Creutzfeldt-Jakob syndrome" were used to search the studies; papers unrelated to the review article were removed. Eighty-four articles are included in the review text to fully understand the complexities of this puzzling disease and its consequences for prion biology and human health; additional study is essential.

Extracellular Amyloid Deposits in Alzheimer's and Creutzfeldt-Jakob Disease: Similar Behavior of Different Proteins?

Neurodegenerative diseases are characterized by the deposition of specific protein aggregates, both intracellularly and/or extracellularly, depending on the type of disease. The extracellular occurrence of tridimensional structures formed by amyloidogenic proteins defines Alzheimer's disease, in which plaques are composed of amyloid β-protein, while in prionoses, the same term "amyloid" refers to the amyloid prion protein. In this review, we focused on providing a detailed didactic description and differentiation of diffuse, neuritic, and burnt-out plaques found in Alzheimer's disease and kuru-like, florid, multicentric, and neuritic plaques in human transmissible spongiform encephalopathies, followed by a systematic classification of the morphological similarities and differences between the extracellular amyloid deposits in these disorders. Both conditions are accompanied by the extracellular deposits that share certain signs, including neuritic degeneration, suggesting a particular role for amyloid protein toxicity.

Altered distribution, aggregation, and protease resistance of cellular prion protein following intracranial inoculation

Prion protein (PrP^C) is a protease-sensitive and soluble cell surface glycoprotein expressed in almost all mammalian cell types. PrP^Sc, a protease-resistant and insoluble form of PrP^C, is the causative agent of prion diseases, fatal and transmissible neurogenerative diseases of mammals. Prion infection is initiated via either ingestion or inoculation of PrP^Sc or when host PrP^C stochastically refolds into PrP^Sc. In either instance, the early events that occur during prion infection remain poorly understood. We have used transgenic mice expressing mouse PrP^C tagged with a unique antibody epitope to monitor the response of host PrP^C to prion inoculation. Following intracranial inoculation of either prion-infected or uninfected brain homogenate, we show that host PrP^C can accumulate both intra-axonally and within the myelin membrane of axons suggesting that it may play a role in axonal loss following brain injury. Moreover, in response to the inoculation host PrP^C exhibits an increased insolubility and protease resistance similar to that of PrP^Sc, even in the absence of infectious prions. Thus, our results raise the possibility that damage to the brain may be one trigger by which PrP^C stochastically refolds into pathogenic PrP^Sc leading to productive prion infection.

Kuru, the First Human Prion Disease

Kuru, the first human prion disease was transmitted to chimpanzees by D. Carleton Gajdusek (1923–2008). In this review, we summarize the history of this seminal discovery, its anthropological background, epidemiology, clinical picture, neuropathology, and molecular genetics. We provide descriptions of electron microscopy and confocal microscopy of kuru amyloid plaques retrieved from a paraffin-embedded block of an old kuru case, named Kupenota. The discovery of kuru opened new vistas of human medicine and was pivotal in the subsequent transmission of Creutzfeldt–Jakob disease, as well as the relevance that bovine spongiform encephalopathy had for transmission to humans. The transmission of kuru was one of the greatest contributions to biomedical sciences of the 20th century.

Evolutionary implications of metal binding features in different species' prion protein: an inorganic point of view

Prion disorders are a group of fatal neurodegenerative conditions of mammals. The key molecular event in the pathogenesis of such diseases is the conformational conversion of prion protein, PrPC, into a misfolded form rich in β-sheet structure, PrPSc, but the detailed mechanistic aspects of prion protein conversion remain enigmatic. There is uncertainty on the precise physiological function of PrPC in healthy individuals. Several evidences support the notion of its role in copper homeostasis. PrPC binds Cu2+ mainly through a domain composed by four to five repeats of eight amino acids. In addition to mammals, PrP homologues have also been identified in birds, reptiles, amphibians and fish. The globular domain of protein is retained in the different species, suggesting that the protein carries out an essential common function. However, the comparison of amino acid sequences indicates that prion protein has evolved differently in each vertebrate class. The primary sequences are strongly conserved in each group, but these exhibit a low similarity with those of mammals. The N-terminal domain of different prions shows tandem amino acid repeats with an increasing amount of histidine residues going from amphibians to mammals. The difference in the sequence affects the number of copper binding sites, the affinity and the coordination environment of metal ions, suggesting that the involvement of prion in metal homeostasis may be a specific characteristic of mammalian prion protein. In this review, we describe the similarities and the differences in the metal binding of different species' prion protein, as revealed by studies carried out on the entire protein and related peptide fragments.

Kuru: a journey back in time from papua new Guinea to the neanderthals' extinction

Kuru, the first human transmissible spongiform encephalopathy was transmitted to chimpanzees by D. Carleton Gajdusek (1923-2008). In this review, I briefly summarize the history of this seminal discovery along its epidemiology, clinical picture, neuropathology and molecular genetics. The discovery of kuru opened new windows into the realms of human medicine and was instrumental in the later transmission of Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheinker disease as well as the relevance that bovine spongiform encephalopathy had for transmission to humans. The transmission of kuru was one of the greatest contributions to biomedical sciences of the 20th century.

A proautophagic antiviral role for the cellular prion protein identified by infection with a herpes simplex virus 1 ICP34.5 mutant

The cellular prion protein (PrP) often plays a cytoprotective role by regulating autophagy in response to cell stress. The stress of infection with intracellular pathogens can stimulate autophagy, and autophagic degradation of pathogens can reduce their replication and thus help protect the infected cells. PrP also restricts replication of several viruses, but whether this activity is related to an effect on autophagy is not known. Herpes simplex virus 1 (HSV-1) effectively counteracts autophagy through binding of its ICP34.5 protein to the cellular proautophagy protein beclin-1. Autophagy can reduce replication of an HSV-1 mutant, Δ68H, which is incapable of binding beclin-1. We found that deletion of PrP in mice complements the attenuation of Δ68H, restoring its capacity to replicate in the central nervous system (CNS) to wild-type virus levels after intracranial or corneal infection. Cultured primary astrocytes but not neurons derived from PrP(-/-) mice also complemented the attenuation of Δ68H, enabling Δ68H to replicate at levels equivalent to wild-type virus. Ultrastructural analysis showed that normal astrocytes exhibited an increase in the number of autophagosomes after infection with Δ68H compared with wild-type virus, but PrP(-/-) astrocytes failed to induce autophagy in response to Δ68H infection. Redistribution of EGFP-LC3 into punctae occurred more frequently in normal astrocytes infected with Δ68H than with wild-type virus, but not in PrP(-/-) astrocytes, corroborating the ultrastructural analysis results. Our results demonstrate that PrP is critical for inducing autophagy in astrocytes in response to HSV-1 infection and suggest that PrP positively regulates autophagy in the mouse CNS.

Gold nanoparticles as a probe for prion determination via resonance light scattering method

Dihydrolipoic acid (DHLA) modified gold nanoparticles (AuNPs) were used as a highly selective probe for the detection of prion proteins. We discovered that AuNPs undergo aggregation selectively in the presence of recombinant prion protein (rPrP), and such selective aggregation enhanced the resonance light scattering (RLS) intensity from AuNPs tremendously. Based on this phenomenon, we established a new assay for rPrP detection. This new assay is label-free, highly selective, and sensitive. The linear range for rPrP detection is from 2.0 × 10(-10) to 2.0 × 10(-8) mol L(-1) with excellent discrimination against other interfering compounds, and the detection limit is 7 × 10(-11) mol L(-1). This assay has been successfully applied for rPrP detection in E. coli lysate, bovine serum samples and human plasma samples. Compared with other methods, the detection approach described here can achieve high selectivity and sensitivity without any complicated labeling or expensive instruments.

Prion seeding activities of mouse scrapie strains with divergent PrPSc protease sensitivities and amyloid plaque content using RT-QuIC and eQuIC

Different transmissible spongiform encephalopathy (TSE)-associated forms of prion protein (e.g. PrP^Sc) can vary markedly in ultrastructure and biochemical characteristics, but each is propagated in the host. PrP^Sc propagation involves conversion from its normal isoform, PrP^C, by a seeded or templated polymerization mechanism. Such a mechanism is also the basis of the RT-QuIC and eQuIC prion assays which use recombinant PrP (rPrP^Sen) as a substrate. These ultrasensitive detection assays have been developed for TSE prions of several host species and sample tissues, but not for murine models which are central to TSE pathogenesis research. Here we have adapted RT-QuIC and eQuIC to various murine prions and evaluated how seeding activity depends on glycophosphatidylinositol (GPI) anchoring and the abundance of amyloid plaques and protease-resistant PrP^Sc (PrP^Res). Scrapie brain dilutions up to 10⁻⁸ and 10⁻¹³ were detected by RT-QuIC and eQuIC, respectively. Comparisons of scrapie-affected wild-type mice and transgenic mice expressing GPI anchorless PrP showed that, although similar concentrations of seeding activity accumulated in brain, the heavily amyloid-laden anchorless mouse tissue seeded more rapid reactions. Next we compared seeding activities in the brains of mice with similar infectivity titers, but widely divergent PrP^Res levels. For this purpose we compared the 263K and 139A scrapie strains in transgenic mice expressing P101L PrP^C. Although the brains of 263K-affected mice had little immunoblot-detectable PrP^Res, RT-QuIC indicated that seeding activity was comparable to that associated with a high-PrP^Res strain, 139A. Thus, in this comparison, RT-QuIC seeding activity correlated more closely with infectivity than with PrP^Res levels. We also found that eQuIC, which incorporates a PrP^Sc immunoprecipitation step, detected seeding activity in plasma from wild-type and anchorless PrP transgenic mice inoculated with 22L, 79A and/or RML scrapie strains. Overall, we conclude that these new mouse-adapted prion seeding assays detect diverse types of PrP^Sc.

The ubiquitin-proteasome system in spongiform degenerative disorders

Spongiform degeneration is characterized by vacuolation in nervous tissue accompanied by neuronal death and gliosis. Although spongiform degeneration is a hallmark of prion diseases, this pathology is also present in the brains of patients suffering from Alzheimer’s disease, diffuse Lewy body disease, human immunodeficiency virus (HIV) infection, and Canavan’s spongiform leukodystrophy. The shared outcome of spongiform degeneration in these diverse diseases suggests that common cellular mechanisms must underlie the processes of spongiform change and neurodegeneration in the central nervous system. Immunohistochemical analysis of brain tissues reveals increased ubiquitin immunoreactivity in and around areas of spongiform change, suggesting the involvement of ubiquitin–proteasome system dysfunction in the pathogenesis of spongiform neurodegeneration. The link between aberrant ubiquitination and spongiform neurodegeneration has been strengthened by the discovery that a null mutation in the E3 ubiquitin–protein ligase mahogunin ring finger-1 (Mgrn1) causes an autosomal recessively inherited form of spongiform neurodegeneration in animals. Recent studies have begun to suggest that abnormal ubiquitination may alter intracellular signaling and cell functions via proteasome-dependent and proteasome-independent mechanisms, leading to spongiform degeneration and neuronal cell death. Further elucidation of the pathogenic pathways involved in spongiform neurodegeneration should facilitate the development of novel rational therapies for treating prion diseases, HIV infection, and other spongiform degenerative disorders.

Physiology of the prion protein

Prion diseases are transmissible spongiform encephalopathies (TSEs), attributed to conformational conversion of the cellular prion protein (PrP(C)) into an abnormal conformer that accumulates in the brain. Understanding the pathogenesis of TSEs requires the identification of functional properties of PrP(C). Here we examine the physiological functions of PrP(C) at the systemic, cellular, and molecular level. Current data show that both the expression and the engagement of PrP(C) with a variety of ligands modulate the following: 1) functions of the nervous and immune systems, including memory and inflammatory reactions; 2) cell proliferation, differentiation, and sensitivity to programmed cell death both in the nervous and immune systems, as well as in various cell lines; 3) the activity of numerous signal transduction pathways, including cAMP/protein kinase A, mitogen-activated protein kinase, phosphatidylinositol 3-kinase/Akt pathways, as well as soluble non-receptor tyrosine kinases; and 4) trafficking of PrP(C) both laterally among distinct plasma membrane domains, and along endocytic pathways, on top of continuous, rapid recycling. A unified view of these functional properties indicates that the prion protein is a dynamic cell surface platform for the assembly of signaling modules, based on which selective interactions with many ligands and transmembrane signaling pathways translate into wide-range consequences upon both physiology and behavior.

Pharmacokinetics and distribution of clioquinol in golden hamsters

Clioquinol (5-chloro-7-iodo-8-quinolinol) is a zinc and copper chelator that can dissolve amyloid deposits and may be beneficial in Alzheimer's disease. Prion diseases are also degenerative CNS disorders characterised by amyloid deposits. The pharmacokinetics and tissue distribution of drugs active against prions may clarify their targets of action. We describe the pharmacokinetics of clioquinol in hamster plasma, spleen and brain after single and repeated oral or intraperitoneal administration (50 mg kg(-1)), as well as after administration with the diet. A single intraperitoneal administration led to peak plasma clioquinol concentrations after 15 min (Tmax), followed by a decay with an apparent half-life of 2.20 +/- 1.1 h. After oral administration, Tmax was reached after 30 min and was followed by a similar process of decay; the AUC(0-last) was 16% that recorded after intraperitoneal administration. The Cmax and AUC values in spleen after a single administration were about 65% (i.p.) and 25% (p.o.) those observed in blood; those in liver were 35% (p.o.) those observed in blood and those in brain were 20% (i.p.) and 10% (p.o.) those observed in plasma. After repeated oral doses, the plasma, brain and spleen concentrations were similar to those observed at the same times after a single dose. One hour after intraperitoneal dosing, clioquinol was also found in the ventricular CSF. Clioquinol was also given with the diet; its morning and afternoon concentrations were similar, and matched those after oral administration. No toxicity was found after chronic administration. Our results indicate that clioquinol, after oral administration with the diet, reaches concentrations in brain and peripheral tissues (particularly spleen) that can be considered effective in preventing prion accumulation, but are at least ten times lower than those likely to cause toxicity.

Determination of 5-chloro-7-iodo-8-quinolinol (clioquinol) in plasma and tissues of hamsters by high-performance liquid chromatography and electrochemical detection

This paper describes a method of determining clioquinol levels in hamster plasma and tissue by means of HPLC and electrochemical detection. Clioquinol was separated on a Nucleosil C18 300 mm x 3.9 mm i.d. 7 microm column at 1 ml/min using a phosphate/citrate buffer 0.1M (400 ml) with 600 ml of a methanol:acetonitrile (1:1, v/v) mobile phase. The retention times of clioquinol and the IS were, respectively, 11.6 and 8.1 min; the quantitation limit (CV>8%) was 5 ng/ml in plasma and 10 ng/ml in tissues. The intra- and inter-assay accuracies of the method were more than 95%, with coefficients of variation between 3.0 and 7.7%, and plasma and tissue recovery rates of 72-77%. There was a linear response to clioquinol 5-2000 ng/ml in plasma, and 10-1000 ng/g in tissues. The method is highly sensitive and selective, makes it possible to study the pharmacokinetics of plasma clioquinol after oral administration and the distribution of clioquinol in tissues, and could be used to monitor plasma clioquinol levels in humans.

Immunohistochemistry for the prion protein: comparison of different monoclonal antibodies in human prion disease subtypes

Demonstration of the abnormal form of the prion protein (PrP) in the brain confirms the diagnosis of human prion disease (PrD). Using immunohistochemistry, we have compared ten monoclonal antibodies in PrD subtypes including sporadic and variant Creutzfeldt-Jakob disease (CJD), fatal familial insomnia, Alzheimer's disease (AD), and control brains. CJD subgroups were determined using Western blot analysis for the protease-resistant PrP type in combination with sequencing to determine the genotype at the methionine/valine polymorphism at codon 129 of the prion protein gene. None of the antibodies labeled given subgroups exclusively, but the intensity of immunoreactivity varied among morphologically distinct types of deposit. Fine granular or synaptic PrP deposits stained weakly or not at all with antibodies against the N-terminus of PrP, and were visible in one case only with 12F10 and SAF54. Coarser and plaque type deposits were immunolabeled with all antibodies. The immunostaining patterns appear characteristic for the disease subgroups. Labeling of certain neurons in all cases irrespective of disease, and staining at the periphery and/or throughout the senile plaques of AD patients were also noted. Antibodies such as 6H4 and 12F10 failed to give this type of labeling and are therefore less likely to recognise non-pathological PrP material in immunohistochemistry.

Visualization of prion infection in transgenic mice expressing green fluorescent protein-tagged prion protein

Tg(PrP-EGFP) mice express an enhanced green fluorescent protein (EGFP)-tagged version of the prion protein (PrP) that behaves like endogenous PrP in terms of its posttranslational processing, anatomical localization, and functional activity. In this study, we describe experiments in which Tg(PrP-EGFP) mice were inoculated intracerebrally with scrapie prions. Although PrP-EGFP was incapable of sustaining prion infection in Tg(PrP-EGFP)/Prn-p(0/0) mice, it acted as a dominant-negative inhibitor that bound to, and fluorescently marked, deposits of PrPSc generated from endogenous PrP in Tg(PrP-EGFP)/Prn-p(+/+) mice. Scrapie infection of these latter animals caused a progressive accumulation of fluorescent PrP-EGFP aggregates in neuropil, axons, and prominently in the Golgi apparatus of neurons. Our results provide an entirely new picture of PrPSc localization during the course of prion infection, and they identify for the first time intracellular sites of PrPSc formation that are not well visualized with conventional immunohistochemical techniques.

Expression of PrP(C) in the rat brain and characterization of a subset of cortical neurons

The cellular prion protein (PrP(C)) is a membrane-bound glycoprotein mainly present in the CNS. The scrapie prion protein (PrP(Sc)) is an isoform of PrP(C), and it is responsible for transmissible spongiform encephalopathies (TSEs), a group of neurodegenerative diseases affecting both humans and animals. The presence of the cellular form is necessary for the establishment and further evolution of prion diseases. Here, we map the regional distribution of PrP(C) in the rat brain and study the chemical nature of these immunopositive neurons. Our observations are congruent with retrograde transport of prions, as shown by the ubiquitous distribution of PrP(C) throughout the rat brain, but especially in the damaged areas that send projections to primarily affected nuclei in fatal familial insomnia. On the other hand, the presence of the cellular isoform in a subset of GABAergic neurons containing calcium-binding proteins suggests that PrP(C) plays a role in the metabolism of calcium. The lack of immunostaining in neurons ensheathed by perineuronal nets indicates that prions do not directly interact with components of these nets. The destruction of these nets is more likely to be the consequence of a factor needed for prions during the early stages of TSEs. This would cause destruction of these nets and death of the surrounded neurons. Our results support the view that destruction of this extracellular matrix is caused by the pathogenic effect of prions and not a primary event in TSEs.

Generation and characterisation of monoclonal antibodies to Rainbow trout (Oncorhynchus mykiss) prion protein

We report the production and characterisation of three monoclonal antibodies to the prion protein (PrP) of Rainbow trout (Oncorhynchus mykiss), a piscine protein with characteristic structural features common to mammalian prion protein. All of the antibodies were used to detect PrP in ELISA, Western blot and by immunohistochemistry. The antibodies showed specificity for certain genera of the Salmonidae, binding to PrP of Rainbow trout and Atlantic salmon (Salmo salar) but not to that from Arctic char (Salvelinus alpinus). Using the immunoreagents in Western blots, we demonstrated that O. mykiss PrP protein is a 64 kDa protein present in brain, spinal chord and optic nerve. PrP was not detected in a range of peripheral tissues: eye, heart, stomach, intestine, liver, kidney, spleen, muscle and skin. Furthermore, PrP could be detected in all brain regions studied: optic lobe, cerebrum/olfactory lobe, cerebellum, hypothalamus/pituitary and medulla oblongata and was widespread within these tissues as determined by immunohistochemistry. These immunoreagents provide specific tools to study the biology of Rainbow trout and Atlantic salmon PrP and any possible transmissible spongiform encephalopathy-like disease of these economically important fish species.

Expression of cellular prion protein in the frontal and occipital lobe in Alzheimer's disease, diffuse Lewy body disease, and in normal brain: an immunohistochemical study

Cellular prion protein (PrP(c)) is a glycoprotein expressed at low to moderate levels within the nervous system. Recent studies suggest that PrP(c) may possess neuroprotective functions and that its expression is upregulated in certain neurodegenerative disorders. We investigated whether PrP(c) expression is altered in the frontal and occipital cortex in two well-characterized neurodegenerative disorders--Alzheimer's disease (AD) and diffuse Lewy body disease (DLBD)--compared with that in normal human brain using immunohistochemistry and computerized image analysis. The distribution of PrP(c) was further tested for correlation with glial reactivity. We found that PrP(c) was localized mainly in the gray matter (predominantly in neurons) and expressed at higher levels within the occipital cortex in the normal human brain. Image analysis revealed no significant variability in PrP(c) expression between DLBD and control cases. However, blood vessels within the white matter of DLBD cases showed immunoreactivity to PrP(c). By contrast, this protein was differentially expressed in the frontal and occipital cortex of AD cases; it was markedly overexpressed in the former and significantly reduced in the latter. Epitope specificity of antibodies appeared important when detecting PrP(c). The distribution of PrP(c) did not correlate with glial immunoreactivity. In conclusion, this study supports the proposal that regional changes in expression of PrP(c) may occur in certain neurodegenerative disorders such as AD, but not in other disorders such as DLBD.

GFP-tagged prion protein is correctly localized and functionally active in the brains of transgenic mice

Prion diseases result from conversion of PrPC, a neuronal membrane glycoprotein of unknown function, into PrPSc, an abnormal conformer that is thought to be infectious. To facilitate analysis of PrP distribution in the brain, we have generated transgenic mice in which a PrP promoter drives expression of PrP-EGFP, a fusion protein consisting of enhanced green fluorescent protein inserted adjacent to the glycolipid attachment site of PrP. We find that PrP-EGFP in the brain is glycosylated and glycolipid-anchored and is localized to the surface membrane and the Golgi apparatus of neurons. Like endogenous PrP, PrP-EGFP is concentrated in synapse-rich regions and along axon tracts. PrP-EGFP is functional in vivo, since it ameliorates the cerebellar neurodegeneration induced by a truncated form of PrP. These observations clarify uncertainties in the cellular localization of PrPC in brain, and they establish PrP-EGFP transgenic mice as useful models for further studies of prion biology.

Prion protein (PrPc) immunocytochemistry and expression of the green fluorescent protein reporter gene under control of the bovine PrP gene promoter in the mouse brain

Expression of the cellular prion protein (PrP(c)) by host cells is required for prion replication and neuroinvasion in transmissible spongiform encephalopathies. As a consequence, identification of the cell types expressing PrP(c) is necessary to determine the target cells involved in the cerebral propagation of prion diseases. To identify the cells expressing PrP(c) in the mouse brain, the immunocytochemical localization of PrP(c) was investigated at the cellular and ultrastructural levels in several brain regions. In addition, we analyzed the expression pattern of a green fluorescent protein reporter gene under the control of regulatory sequences of the bovine prion protein gene in the brain of transgenic mice. By using a preembedding immunogold technique, neuronal PrP(c) was observed mainly bound to the cell surface and presynaptic sites. Dictyosomes and recycling organelles in most of the major neuron types also exhibited PrP(c) antigen. In the olfactory bulb, neocortex, putamen, hippocampus, thalamus, and cerebellum, the distribution pattern of both green fluorescent protein and PrP(c) immunoreactivity suggested that the transgenic regulatory sequences of the bovine PrP gene were sufficient to promote expression of the reporter gene in neurons that express immunodetectable endogenous PrP(c). Transgenic mice expressing PrP-GFP may thus provide attractive murine models for analyzing the transcriptional activity of the Prnp gene during prion infections as well as the anatomopathological kinetics of prion diseases.

Pharmacokinetics and distribution of sodium 3,4-diaminonaphthalene-1-sulfonate, a Congo Red derivative active in inhibiting PrP(res) replication

Sodium 3,4-diaminonaphthalene-1-sulfonate (CRA) is a compound, synthesised by our group from Congo Red (CR), that is active in preventing the pathological conversion of normal prion protein (PrP). As the precise mechanisms controlling the ways in which prions are distributed and infect the brain and other organs are not fully understood, studying the pharmacokinetics of drugs that are active against prions may clarify their targets and their means of inhibiting prion infection. This paper describes the pharmacokinetics of CRA in plasma, spleen and brain after single or repeated intraperitoneal or subcutaneous administration, as determined by means of specific and sensitive fluorimetric HPLC. A single intraperitoneal administration led to peak plasma CRA concentrations after 15 min, followed by biphasic decay with an apparent half-life of 4.3 h. After subcutaneous administration, T(max) was reached after 30 min, and was followed by a similar process of decay: Cmax and the AUC0-last were 25% those recorded after intraperitoneal administration. The mean peak concentrations and AUCs of CRA after a single intraperitoneal or subcutaneous administration in peripheral tissue (spleen) were similar to those observed in blood, whereas brain concentrations were about 2% those in plasma. After repeated intraperitoneal or subcutaneous doses, the Cmax values in plasma, brain and spleen were similar to those observed at the same times after a single dose. After repeated intraperitoneal doses, CRA was also found in the ventricular cerebrospinal fluid at concentrations of 1.8 +/- 0.2 microg(-1) mL, which is similar to, or slightly higher than, those found in brain. Brain concentrations may be sufficient to explain the activity of CRA on PrP reproduction in the CNS. However, peripheral involvement cannot be excluded because the effects of CRA are more pronounced after intraperitoneal than after intracerebral infection.

Cytosolic prion protein in neurons

Localizing the cellular prion protein (PrPC) in the brain is necessary for understanding the pathogenesis of prion diseases. However, the precise ultrastructural localization of PrPC still remains enigmatic. We performed the first quantitative study of the ultrastructural localization of PrPC in the mouse hippocampus using high-resolution cryoimmunogold electron microscopy. PrPC follows the standard biosynthetic trafficking pathway with a preferential localization in late endosomal compartments and on the plasma membrane of neurons and neuronal processes. PrPC is found with the same frequency within the synaptic specialization and perisynaptically, but is almost completely excluded from synaptic vesicles. Unexpectedly, PrP is also found in the cytosol in subpopulations of neurons in the hippocampus, neocortex, and thalamus but not the cerebellum. Cytosolic PrP may have altered susceptibility to aggregation, suggesting that these neurons might play a significant role in the pathogenesis of prion diseases, in particular those mammals harboring mutant PrP genes.

Endocytic intermediates involved with the intracellular trafficking of a fluorescent cellular prion protein

We have investigated the intracellular traffic of PrP(c), a glycosylphosphatidylinositol (GPI)-anchored protein implicated in spongiform encephalopathies. A fluorescent functional green fluorescent protein (GFP)-tagged version of PrP(c) is found at the cell surface and in intracellular compartments in SN56 cells. Confocal microscopy and organelle-specific markers suggest that the protein is found in both the Golgi and the recycling endosomal compartment. Perturbation of endocytosis with a dynamin I-K44A dominant-negative mutant altered the steady-state distribution of the GFP-PrP(c), leading to the accumulation of fluorescence in unfissioned endocytic intermediates. These pre-endocytic intermediates did not seem to accumulate GFP-GPI, a minimum GPI-anchored protein, suggesting that PrP(c) trafficking does not depend solely on the GPI anchor. We found that internalized GFP-PrP(c) accumulates in Rab5-positive endosomes and that a Rab5 mutant alters the steady-state distribution of GFP-PrP(c) but not that of GFP-GPI between the plasma membrane and early endosomes. Therefore, we conclude that PrP(c) internalizes via a dynamin-dependent endocytic pathway and that the protein is targeted to the recycling endosomal compartment via Rab5-positive early endosomes. These observations indicate that traffic of GFP-PrP(c) is not determined predominantly by the GPI anchor and that, different from other GPI-anchored proteins, PrP(c) is delivered to classic endosomes after internalization.

A marked disparity between the expression of prion protein and its message by neurones of the CNS

Expression of the normal cellular form of prion protein is both necessary and rate-limiting in the spread of prion disease, yet its cellular expression in vivo is poorly understood. To optimise immunohistochemical labelling of this protein in mouse brain, we have developed novel antibodies that recognise cellular prion protein in glutaraldehyde-fixed tissue. Expression was found to be predominantly neuronal, and to differ between different classes of neurone. Thus, neurones immunoreactive for GABA expressed very high levels of normal prion protein; most projection neurones expressed much lower levels, particularly on their axons in the major fibre tracts, and some neurones (e.g. those positive for dopamine) displayed no detectable prion protein. In marked contrast, all neurones, even those that were immunonegative, expressed high levels of message for prion protein, shown by non-radioactive in situ hybridisation. Glia expressed very low levels of message, and undetectable levels of prion protein. We conclude that the steady-state level of prion protein, which differs so markedly between different neuronal types, is primarily controlled post-transcriptionally, possibly by differences in protein trafficking or degradation. These marked differences in the way different neurones produce and/or degrade their normal cellular prion protein may influence the selective spread and neurotoxic targeting of prion diseases within the CNS.

Internalization of mammalian fluorescent cellular prion protein and N-terminal deletion mutants in living cells

The cellular prion protein (PrP(c)) is a glycosylphosphatidylinositol (GPI)-anchored plasma membrane protein whose conformational altered forms (PrP(sc)) are known to cause neurodegenerative diseases in mammals. In order to investigate the intracellular traffic of mammalian PrP(c) in living cells, we have generated a green fluorescent protein (GFP) tagged version of PrP(c). The recombinant protein was properly anchored at the cell surface and its distribution pattern was similar to that of the endogenous PrP(c), with labeling at the plasma membrane and in an intracellular perinuclear compartment. Comparison of the steady-state distribution of GFP-PrP(c) and two N-terminal deletion mutants (Delta32-121 and Delta32-134), that cause neurological symptoms when expressed in PrP knockout mice, was carried out. The mutant proteins accumulated in the plasma membrane at the expense of decreased labeling in the perinuclear region when compared with GFP-PrP(c). In addition, GFP-PrP(c), but not the two mutants, internalized from the plasma membrane in response to Cu2+ treatment and accumulated at a perinuclear region in SN56 cells. Our data suggest that GFP-PrP(c) can be used to follow constitutive and induced PrP(c) traffic in living cells.

Cellular and subcellular morphological localization of normal prion protein in rodent cerebellum

Normal cellular prion protein, a necessary protagonist in fatal neurodegenerative prion diseases, was mapped in rodent cerebellum to establish its cellular and ultrastuctural localization. Existing morphological data about native prion protein distribution in brain tissues remain, indeed, contradictory and do not fit with biochemical and cell biological results. Using ultrastructural preembedding immunocytochemistry and a monoclonal anti-mouse prion protein antibody, this report shows that cellular prion protein is present in all cortico-cerebellar and deep nuclei neuronal cell types, as well as in all glial cell types. The heaviest expression appears on parallel fibres and astrocytic processes. The protein is exclusively located on the outer cell membrane and in Golgi and endosomal intracytoplasmic organelles, with no cytoplasmic or synaptic vesicle labelling. Most important, and in contrast with previous ultrastructural data, cellular prion protein is shown to be distributed on all portions of neurons, without any preferential synaptic targeting. The present morphological report shows, for the first time in vivo, that the cellular prion protein is present on the entire cell surface membrane of all neuronal and glial cell types of the rat cerebellum. This ubiquitous presence supports the notion that prion protein has a generalized cellular function in brain tissue rather than a specialized role restricted to synaptic transmission.

Synaptic prion protein immuno-reactivity in the rodent cerebellum

The cellular prion protein PrP(c) is a neurolemmal glycoprotein essential for the development of the transmissible spongiform encephalopathies. In these neurodegenerative diseases, host PrP(c) is converted to infectious protease-resistant isoforms PrP(res) or prions. Prions provoque predictable and distinctive patterns of PrP(res) accumulation and neurodegeneration depending on the prion strain and on regional cell-specific properties modulating PrP(c) affinity for infectious PrP(res) in the host brain. Synaptolysis and synaptic accumulation of PrP(res) during PrP-related diseases suggests that the synapses could be primary sites able to propagate PrP(res) and neurodegeneration in the central nervous system. In the rodent cerebellum, the present light and electron microscopic immuno-cytochemical analysis shows that distinct types of synapses display differential expression of PrP(c), suggesting that synapse-specific parameters could influence neuroinvasion and neurodegeneration following cerebral infection by prions. Although the physiological functions of PrP(c) remain unknown, the concentration of PrP(c) almost exclusively at the Purkinje cell synapses in the cerebellum suggests its critical involvement in the synaptic relationships between cerebellar neurons in agreement with their known vulnerability to PrP deficiencies.

Prion protein immunoreactivity in brain samples from an unselected autopsy population: findings in 200 consecutive cases

Immunostaining for prion protein (PrP) using the KG9 monoclonal antibody was undertaken on brain sections from an unselected group of 200 post-mortem cases. One case of clinically diagnosed vCJD was confirmed and showed widespread abundant PrP immunostaining with KG9 and somewhat less abundant PrP with another monoclonal antibody, 3F4. PrP immunostaining seen with KG9 was insensitive to proteinase K pretreatment in sections from this case of vCJD. Among the remaining 199 cases, sections from 84 (42%) showed small amounts of PrP immunoreactivity with the KG9 antibody, mainly localized to neurones, neural processes and argyrophilic plaques of the type seen in ageing and Alzheimer's disease. Purkinje cells, swollen (ischaemic) axons, macrophages and microglials cells were also occasionally labelled with this antibody in non-CJD cases. Pre-treatment of adjacent sections from non-CJD cases with positive KG9 staining abolished this staining, indicating that it represented the cellular form of PrP. There were differences in age, sex and cause of death in non-CJD cases with some PrP immunostaining patterns compared with cases lacking any staining. Specifically, a younger mean age, more females and fewer cardiac deaths were found among those with neuronal PrP staining patterns. Staining of some features was also significantly associated. These findings need to be taken into account when PrP immunostaining is used to diagnose prion diseases. They may indicate that cellular PrP is increased in the human brain under some circumstances and provide insight into the handling of this protein by human brain cells.

Detection of bovine spongiform encephalopathy-specific PrP(Sc) by treatment with heat and guanidine thiocyanate

The conversion of a ubiquitous cellular protein (PrP(C)), an isoform of the prion protein (PrP), to the pathology-associated isoform PrP(Sc) is one of the hallmarks of transmissible spongiform encephalopathies such as bovine spongiform encephalopathy (BSE). Accumulation of PrP(Sc) has been used to diagnose BSE. Here we describe a quantitative enzyme-linked immunosorbent assay (ELISA) that involves antibodies against epitopes within the protease-resistant core of the PrP molecule to measure the amount of PrP in brain tissues from animals with BSE and normal controls. In native tissue preparations, little difference was found between the two groups. However, following treatment of the tissue with heat and guanidine thiocyanate (Gh treatment), the ELISA discriminated BSE-specific PrP(Sc) from PrP(C) in bovine brain homogenates. PrP(Sc) was identified by Western blot, centrifugation, and protease digestion experiments. It was thought that folding or complexing of PrP(Sc) is most probably reversed by the Gh treatment, making hidden antigenic sites accessible. The digestion experiments also showed that protease-resistant PrP in BSE is more difficult to detect than that in hamster scrapie. While the concentration of PrP(C) in cattle is similar to that in hamsters, PrP(Sc) sparse in comparison. The detection of PrP(Sc) by a simple physicochemical treatment without the need for protease digestion, as described in this study, could be applied to develop a diagnostic assay to screen large numbers of samples.

Evidence of presynaptic location and function of the prion protein

The prion protein (PrP(C)) is a copper-binding protein of unknown function that plays an important role in the etiology of transmissible spongiform encephalopathies. Using morphological techniques and synaptosomal fractionation methods, we show that PrP(C) is predominantly localized to synaptic membranes. Atomic absorption spectroscopy was used to identify PrP(C)-related changes in the synaptosomal copper concentration in transgenic mouse lines. The synaptic transmission in the presence of H(2)O(2), which is known to be decomposed to highly reactive hydroxyl radicals in the presence of iron or copper and to alter synaptic activity, was studied in these animals. The response of synaptic activity to H(2)O(2) was found to correlate with the amount of PrP(C) expression in the presynaptic neuron in cerebellar slice preparations from wild-type, Prnp(0/0), and PrP gene-reconstituted transgenic mice. Thus, our data gives strong evidence for the predominantly synaptic location of PrP(C), its involvement in the regulation of the presynaptic copper concentration, and synaptic activity in defined conditions.

Expression of the prion protein in the rat forebrain--an immunohistochemical study

The cellular prion protein (PrP(C)) is crucial for the development of transmissible spongiform encephalopathies (TSEs), where the pathogenic scrapie isoform (PrP(Sc)) of the same protein, is considered to be the principal or sole infectious agent. Here, we report findings on PrP(C) expression in the rat forebrain, using immunohistochemical techniques on free floating sections of 60 microm thickness. Along with neurons and astrocytes in the gray matter, PrP(c) was detected for the first time in glial cells of the white matter and in cells of circumventricular organs. PrP(C) positive cellular processes were also found to be closely associated with intraparenchymal blood vessels, often in the form of end feet. Interestingly, PrP(C) expression was observed in areas where PrP(Sc) deposition in late stages of infection has been earlier reported in the rat and other species.

Astrocytosis and amyloid deposition in scrapie-infected hamsters

In scrapie infection, prion protein (PrPSc) is localized in areas where there is neurodegeneration and astrocytosis. It is thought that PrPSc 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 PrPSc was present in the ependymal cells of both 263K- and 139H-infected hamsters. In 139H-infected hamsters, PrPSc 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 PrPSc in most areas such as cortex, hippocampus, and thalamus in 263K-infected hamsters. Many aggregations of PrPSc 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, PrPSc 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 PrPSc 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 PrPSc production. Our results also confirm that reactive astrocytes can produce and/or accumulate PrPSc 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.

Transmissible spongiform encephalopathies in food animals. Human food safety and animal feed safety concerns for veterinarians

This article presents a brief overview of transmissible spongiform encephalopathies (TSEs) using examples of diseases that provide evidence supporting oral transmission of the agent. Agent theories are described briefly in general terms. Scrapie, bovine spongiform encephalopathy (BSE), chronic wasting disease, and transmissible mink encephalopathy are discussed to improve disease recognition by the food animal practitioner. Control programs for scrapie and BSE are described and the role of the veterinarian in animal feed and human food safety is related to TSEs.

In situ hybridization and immunohistochemistry for prion protein (PrP) in bovine spongiform encephalopathy (BSE)

In about 5% of the cows showing clinical signs of bovine spongiform encephalopathy (BSE) the histopathological examination is not conclusive. In order to rule out BSE in these cases, additional methods are necessary. For that reason, non-radioactive in situ hybridization (ISH) was performed using a riboprobe against the messenger RNA coding for the prion protein (PrP). In addition, a polyclonal antibody for immunohistochemistry (IHC) was generated against a synthetic peptide derived from bovine PrP. ISH and IHC were used to analyse brain sections of cattle suffering from BSE and various neurological diseases including four cows with clinically suspect but histologically unconfirmed BSE. ISH revealed no differences in localization, distribution and neuronal levels of PrP mRNA between BSE positive and negative cattle. However, there was a BSE-specific staining pattern in IHC allowing to exclude BSE the four suspected cases. Additionally, IHC for PrP is an elegant alternative to search for scrapie associated fibrils by electron microscopy.

Immunohistochemical detection and localization of prion protein in brain tissue of sheep with natural scrapie

A converted form of the normal cellular prion protein (PrP) accumulates in the brains of sheep with scrapie. We describe an immunohistochemical method for identifying scrapie-associated PrP (PrPSc) in periodate-lysine-paraformaldehyde-fixed brain tissue, which provides adequate preservation of tissue morphology. After pretreatment of tissue sections with formic acid and hydrated autoclaving, we located PrPSc in the brains of 50 sheep with natural scrapie by use of antipeptide antisera raised against ovine PrP. No PrP was seen in 20 sheep without histopathologic signs of scrapie. PrPSc that did not stain for amyloid was present in the cytoplasm and at the cell membrane of both neurons and astrocytes. Large amounts of PrPSc were seen at the cell membrane of neurons in the medulla oblongata and pons, whereas PrPSc accumulated at the cell membrane of astrocytes of the glial limitans in all brain regions. PrPSc that stained for amyloid was located in the walls of blood vessels and perivascularly in the brains of 32 (64%) of 50 sheep, mainly in the thalamus and never in the pons or medulla oblongata. No apparent topographic relationship existed between PrPSc that stained for amyloid and PrPSc accumulation associated with neurons or astrocytes. In all scrapie-affected sheep, PrPSc was present in brain regions with vacuolation, but it could also be detected in regions with minimal or no vacuolation. We conclude that the immunohistochemical detection of PrP can be an important confirmative test in scrapie diagnosis.

Creutzfeldt-Jakob disease with Alzheimer-type A beta-reactive amyloid plaques

Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheinker syndrome are classified as transmissible cerebral amyloidoses, in contrast to the non-transmissible amyloidoses of Alzheimer's disease type. While the aetiologies of Creutzfeldt-Jakob disease and Alzheimer's disease and the molecular composition of their amyloids are different, similar basic pathogenetic mechanisms operate in both diseases through synthesis and processing of amyloid precursor proteins, to produce an accumulation of amyloid deposits. We report here a case of Creutzfeldt-Jakob disease exhibiting numerous diffuse A beta immunoreactive plaques, thus presenting features of both Creutzfeldt-Jakob disease and Alzheimer's disease. The existence of such cases underlines the existence of a 'grey' area between the two types of amyloidoses.

Pathology of the transmissible spongiform encephalopathies with special emphasis on ultrastructure

The transmissible spongiform encephalopathies are a group of genetic and infectious disorders which are exemplified by scrapie in animals and Creutzfeldt-Jakob disease in humans. The spongiform encephalopathies are characterized by symmetrical vacuolation of neurons and neuropil. Amyloid plaque formation similar to that found in Alzheimer's disease is conspicuous in many, but not all, of these diseases. The sub-cellular pathology features of the spongiform encephalopathies have been studied by conventional transmission electron microscopy, scanning electron microscopy, freeze fracture, negative staining and most recently by application of immunogold labelling methods. Although these studies have revealed many unusual structures, convincing virus-like particles have not been demonstrated. Considerable data, including important transgenic mouse studies, now suggest that a single cellular protein, designated prion protein, is necessary for infection. Ultrastructural immunogold studies have shown that prion protein is released from the surface of neurons and neurites, diffuses through the extracellular space around infected cells where it accumulates and finally becomes aggregated as amyloid fibrils. It is likely that the accumulation of prion protein within the extracellular space is instrumental in causing nerve cell dysfunction and, ultimately, neurological disease.

The nosology of Creutzfeldt-Jakob disease and conditions related to the accumulation of PrPCJD in the nervous system

Although typical cases of Creutzfeldt-Jakob disease are readily recognized pathologically and clinically, variant forms often pose a diagnostic challenge. From the 1920's, when this disease was first characterized, until quite recently diagnosis relied heavily on morphologic changes. New advances in immunoassays and PrP gene analysis now provide important adjuncts in recognizing the spectrum of disorders of PrP metabolism associated with these transmissible encephalopathies.

Correlative light and electron microscopy studies of PrP localisation in 87V scrapie

The transmissible neurodegenerative diseases, of which scrapie is the archetype, are caused by unconventional infectious agents. Prion protein (PrP), a widespread host coded, cell surface sialoglycoprotein, is thought to be an essential or, controversially, sole component of these agents. During infection, disease specific accumulations of PrP may be observed in immunostained brain sections of mice infected with the 87V scrapie strain as amyloid plaques or as diffuse or granular foci within the neuropil. Using serial light and electron microscopical preparations we determined immunocytochemically that infection specific PrP is present in amyloid fibrils, and accumulates on the plasmalemma of neurites at the periphery of plaques and in the neuropil, irrespective of the morphological form of PrP accumulation when viewed by light microscopy. In some brain areas with dense granular PrP expression complete disruption of neuropil with loss of neurites was associated with fibrils lying free in expanded extracellular space. These results suggest that normal PrP may be converted to its pathological form at the neuronal plasmalemma or in the extracellular space and, furthermore, that amyloid fibrils are formed following the accumulation and aggregation of subunit proteins at these sites.

Prion protein immunocytochemistry: reliable protocols for the investigation of Creutzfeldt-Jakob disease

Current criteria for the histological diagnosis of Creutzfeldt-Jakob disease (CJD) include features such as spongiform change, neuronal loss and reactive gliosis which are shared to a varying extent with other neuro-degenerative disorders. Reliable visualization of prion protein (PrP) has substantial potential value in diagnostic practice and as a research tool, since accumulation of the disease-associated isoform of this protein is apparently specific for spongiform encephalopathies. A number of antisera against PrP have previously been employed in conjunction with a range of pre-treatments designed to optimize the specificity of immunostaining; such varied usage makes the comparison and interpretation of results difficult. This study was undertaken to identify optimal combinations of each of three PrP antisera and five pre-treatments designed to specifically demonstrate disease-specific PrP in a series of seven CJD cases, six cases of Alzheimer-type dementia and six non-demented control cases. Specific staining of amyloid plaques, spongiform neuropil, neurons and, occasionally, astrocytes was achieved in CJD cases. Alzheimer and control cases were unstained. Use of formic acid with guanidine thiocyanate, and hydrolytic autoclaving with IB3 and SP30 antisera proved most effective and can be recommended for future immunocytochemical studies. PrP immunocytochemistry revealed a greater extent of subcortical neural involvement than routine histological techniques in CJD; the relationship between classical neuropathology in CJD and PrP accumulation as revealed by immunocytochemistry is not clear cut and requires further investigation. These findings may help to broaden our understanding of human spongiform encephalopathies, and have implications for diagnostic practices in neuropathology.

Scrapie-associated PrP accumulation and its inhibition: revisiting the amyloid-glycosaminoglycan connection

An abnormal protease-resistant isoform of the protein PrP accumulates in the brain of hosts with transmissible spongiform encephalopathies (TSEs) and appears to be centrally involved in TSE pathogenesis. Studies with scrapie-infected tissue culture cells have indicated that this abnormal PrP is formed from an apparently normal precursor on the plasma membrane or along an endocytic pathway to the lysosomes. Inhibitors of protease-resistant PrP accumulation might serve as tools for studying the basic mechanism of protease-resistant PrP formation and as potential drugs for TSE therapy. Using scrapie-infected neuroblastoma cells to screen for such compounds in vitro, we found that the amyloid binding dye Congo red and certain sulfated glycans potently inhibited the accumulation of protease-resistant PrP in scrapie-infected cells without apparent effects on the metabolism of the normal isoform. The relative potencies of the sulfated glycans corresponded with their previously determined anti-scrapie activities in vivo, suggesting that the prophylactic effects of sulfated polyanions may be due to inhibition of protease-resistant PrP accumulation. Since protease-resistant PrP amyloid is known to contain sulfated glycosaminoglycans, as do other naturally derived amyloids, we hypothesize that these sulfated inhibitors competitively block binding between PrP and endogenous glycosaminoglycans that is important for its accumulation in a protease-resistant, potentially amyloidogenic state. Drugs which interfere with this (pre)amyloid-glycosaminoglycan interaction may be useful for treating a variety of amyloidoses.

Scrapie-associated PrP accumulation and agent replication: effects of sulphated glycosaminoglycan analogues

An abnormally protease-resistant and apparently neuropathogenic form of PrP accumulates in the brains of hosts with scrapie and related transmissible spongiform encephalopathies. Studies with scrapie-infected neuroblastoma cells have highlighted dramatic differences in the metabolism of the normal (protease-sensitive) and scrapie-associated (protease-resistant) isoforms of PrP. Furthermore, this model has been useful in identifying inhibitors of protease-resistant PrP accumulation and scrapie agent replication which are valuable as potential therapeutic agents and as probes of the mechanism of protease-resistant PrP formation. These inhibitors include the amyloid stain Congo red and certain sulphated glycans which are glycosaminoglycans themselves or glycosaminoglycan analogues. The relative potencies of various sulphated glycans correlate with their previously determined anti-scrapie activities in vivo, suggesting that the prophylactic effects of sulphated polyanions is due to inhibition of protease-resistant PrP accumulation. These and other observations suggest that an interaction of PrP with endogenous sulphated glycosaminoglycans or proteoglycans is important in protease-resistant PrP accumulation, and raise the possibility that therapies for transmissible spongiform encephalopathies and other amyloidoses could be based on blocking (pre)amyloid-glycosaminoglycan interactions.

Characterisation of antisera raised against species-specific peptide sequences from scrapie-associated fibril protein and their application for post-mortem immunodiagnosis of spongiform encephalopathies

Transmissible spongiform encephalopathies (TSE), such as scrapie or Creutzfeldt-Jakob disease (CJD), are fatal neurodegenerative diseases of the central nervous system caused by a yet unidentified virus. They are accompanied by a brain specific amyloidosis, during which a host coded protein irreversibly aggregates to form the scrapie-associated fibrils. The diagnosis of TSE relies on histopathological detection of spongiform lesions, on electron microscopical detection of fibrils, or on the immunological detection of SAF protein, which is the most specific diagnostic marker. In order to improve the diagnosis of TSE, we developed a protocol for rapid tissue fractionation and enrichment of SAF protein which subsequently allows the specific detection of SAF protein by western blotting and immunodetection. Using some new antisera raised against synthetic peptides with sequences specific for the hamster, sheep, cattle and human SAF protein, several samples can be diagnosed for TSE within 24 hours, starting with only 10-100 mg of brain tissue from different species.

Transmissible cerebral amyloidoses as a model for Alzheimer's disease. An ultrastructural perspective

Alzheimer's disease, a prototypic nontransmissible cerebral amyloidosis, has no adequate experimental model. Several pathogenetic events, however, may be modeled and accurately studied in the transmissible cerebral amyloidoses of kuru, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker disease, and scrapie. The common neuropathological denominator in both types of cerebral amyloidoses is the presence of stellate kuru plaques, senile plaques, and pure neuritic plaques. These amyloid plaques consist of amyloid fibers, dystrophic neurites, and reactive astrocytes in different proportions. Microglial cells, which are regarded as amyloid producer/processor cells in Alzheimer's disease, may play the same function in the transmissible cerebral amyloidoses. In both transmissible and nontransmissible amyloidoses, the impairment of axonal transport leads to accumulation of abnormally phosphorylated cytoskeleton proteins (such as neurofilament proteins and microtubule-associated protein tau), which eventually produce dystrophic neurites observed as parts of plaque or as isolated pathological structures.

Immunohistochemical detection of prion protein in sheep with scrapie

Prion protein (PrP), which is involved in the pathogenesis of scrapie, occurs in 2 forms. The form extracted from scrapie brain is protease resistant (PrP-res), whereas PrP from normal brain is protease sensitive (PrP-sen). This study examined whether PrP-res could be detected in brains of sheep with scrapie by immunohistochemistry (IHC). A suitable IHC procedure was developed using brain tissue from hamsters that had been inoculated with the transmissible mink encephalopathy agent. Tissue samples were fixed in PLP (periodate, lysine, paraformaldehyde) that contained paraformaldehyde at a concentration of 0.125%. Before application of the IHC technique, tissue sections were deparaffinized and treated with formic acid to simultaneously enhance PrP-res immunoreactivity and degrade PrP-sen. Primary antibody was obtained from a rabbit immunized to PrP-res extracted from brains of mice with experimentally induced scrapie. Brain from 21 sheep with histopathologically confirmed scrapie were examined by IHC. In all 21 brains, PrP-res was widely distributed throughout the brain stem. Staining was particularly intense in neuronal cell bodies and around blood vessels. The IHC technique successfully detected PrP-res in brain samples that had been frozen or that were severely autolyzed before fixation in PLP. Brains from 11 scrapie-suspect sheep that were not considered histologically positive were also examined by IHC. PrP-res was found in 4 of these brains. Sections of brains from 14 clinically normal sheep did not have detectable PrP-res. Results of this study indicate that IHC detection of PrP-res is equivalent, and perhaps superior, to histopathology for the diagnosis of scrapie in sheep. Furthermore, IHC is applicable to tissues that have autolytic changes or processing artifacts that prevent satisfactory histopathologic evaluation for lesions of scrapie.

Quantitative assessment of the astrocytic response in natural scrapie of sheep

Scrapie of sheep and goats belongs to the spongiform encephalopathies, a term derived from the characteristic vacuolar degeneration in the central nervous system. Astrocytosis has been described, but a systematic quantitative study has not been made. Such a study is important in resolving the still controversial issues as to whether the astrocytic response is caused directly by the infectious agent or represents a secondary reaction to tissue damage. In this study the numbers of astrocytes in 12 sheep with scrapie and 12 healthy sheep of a similar age were assessed and compared. Sections from eight planes of the brain were immunostained with anti-glial fibrillary acidic protein (GFAP) for astrocytes and their numbers counted in 40 areas of 1 mm2. The main findings were as follows. (1) A significant increase of astrocytes was detected in sheep with scrapie. (2) Astrocytosis was not usually related to the severity of the characteristic vacuolar lesions, indicating that it was at least partly due to a direct effect of the infectious agent but was not a secondary response to the neuronal damage. (3) The astrocytic response varied considerably between individual affected sheep; this may have been due to differences in agent strains, host response, or both.

Human prion diseases (spongiform encephalopathies)

Prion diseases (spongiform encephalopathies) in humans are Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome (GSS), and kuru. Clinically, they are characterized by an inexorably progressing neurological illness with dementia and ataxia as the most prominent signs. The classical neuropathological changes are limited to the central nervous system and consist of spongiform degeneration, amyloid plaques, astrocytic gliosis, and nerve cell loss. The human spongiform encephalopathies, which for many years were considered neurodegenerative disorders of unknown etiology, were finally recognized as transmissible diseases similar to scrapie in sheep in the late 1960's. The infectious agent appears to consist of protein devoid of functional nucleic acid and has been termed prion to distinguish it from viruses. The prion hypothesis has gained wide acceptance through the finding that mutations of the prion protein gene are associated with heritable human prion disease. Different mutations appear to cause prion disease with a distinct pattern of clinical and pathological features in a great number of families. Certain mutations of the PrP gene have been shown to be associated with clinical and neuropathological changes not typical of any variant of human prion disease known to date. A new classification of prion diseases based on the molecular biology and biochemistry of the prion protein is likely to emerge.