Prionoses--neurodegenerative diseases caused by prions, offectious proteinaceous molecules

Prionoses are a group of human and animal neurodegenerative diseases caused by prions, infectious pathogens that differ from bacteria, fungi, parasites, viroids, and viruses. Despite intensive searches over the past three decades, no nucleic acid has been found within prions and considerable experimental data argue that prions are composed exclusively of proteins (glycoproteins). Normal prion protein (PrPC) is encoded by a gene present in all nuclear cells of humans and other mammals but is constitutively expressed mainly in neurons. PrPC is protease sensitive and nonpathogenic but it can be modified to the pathological and protease resistant form designated PrPSC which is essential for infectivity. Prion diseases are manifested as infectious, genetic, or sporadic disorders and are also named as transmissible spongiform encephalopathies (TSE). TSE culminate with a progressive and fatal degeneration of the CNS. The human prionoses include Creutzfeldt-Jakob disease (CJD), kuru, Gerstman-Str?ussler-Scheinker syndrome (GSS), and fatal familial insomnia (FFI). In mammals, more than 15 different species have been described to suffer from prion disorders till now. Scrapie of sheep and goats is the oldest and the most studied of the prion diseases. Bovine spongiform encephalopathy (BSE) and transmissible mink encephalopathy are thought to result from the feeding of scrapie-infected animal products, whereas BSE has been identified in transmission to mice, domestic cats, two exotic species of ruminant, and monkey. More than 20 cases of clinically and pathologically atypical form of CJD, referred to as "new variant" CJD (vCJD) have been recognized in unusually young people in the United Kingdom. There is a strong evidence that the same prion strain is involved in both BSE and vCJD. It suggest the breaking of species barrier which results by spreading of BSE to humans, putatively by dietary exposure. Understanding the function of prion proteins and their modification to the pathological form may give new insight into the etiologic and pathogenic mechanisms also other diseases caused by aberrant proteins, including Alzheimer' disease, amyotrophic lateral sclerosis, and Parkinson's disease. (Tab. 4, Fig. 3, Ref. 76.)     

Cardiopulmonary resuscitation: a review for clinicians

Modification of the cellular prion protein has been correlated with the acquisition of several neurodegenerative diseases, including kuru, scrapie, bovine spongiform encephalopathy (BSE), and Creutzfeldt-Jakob disease (CJD). Sequence conservation and amino acid identity are known to influence the efficacy of interspecific transmission. We analyzed patterns of interspecific genetic variation with a view toward identifying features related to disease transmission. The reconstructed gene trees and amino acid tree were compared with the species tree, and all discordances observed were related to the species barrier of disease transmission. The rates of synonymous substitution, nonsynonymous substitution, and nucleotide content were determined for the protein-coding gene. Substitutions implicated in each of the prion diseases were found to occur in regions of the protein that are least variable across all species-opposite to the pattern of variability expected from interaction with an infectious pathogen. Amino acid residues related to the species barrier form a single cluster associated with the first alpha-helical domain of the protein. Residues related to sporadic and hereditary human prion disease form two separate clusters, associated with the second and third alpha-helical domains. Taken together, these results are consistent with the view that prion diseases arise from accidents in protein folding, rather than infection with an undiscovered virus-like particle. We speculate that the differences in disease phenotype between transmissable and hereditary forms could result from interactions between different parts of the protein during propagation.     

Generation of monoclonal antibodies against human prion proteins in PrP0/0 mice

BACKGROUND: Prion diseases belong to a group of neurodegenerative disorders affecting humans and animals. The human diseases include kuru, Creutzfeldt-Jakob disease (CJD), Gerstmann-Str?ussler-Scheinker syndrome (GSS), and fatal familial insomnia (FFI). The pathogenic mechanisms of the prion diseases are not yet understood. Monoclonal antibodies provide valuable tools in the diagnosis, as well as in the basic research, of several diseases; however, monospecific antisera or monoclonal antibodies (mAbs) against human prion proteins were, until now, not available. MATERIALS AND METHODS: We have developed an immunization protocol based on nucleic acid injection into nontolerant PrP0/0 mice. DNA or RNA coding for different human prion proteins including the mutated sequences associated with CJD, GSS, and FFI were injected into muscle tissue. Mice were primarily inoculated with DNA plasmids encoding the prion protein (PRNP) gene and boosted either with DNA, RNA, or recombinant Semliki Forest Virus particles expressing PRNP. Hybridomas were then prepared. RESULTS: Different mAbs against human prion proteins were obtained, and their binding behavior was analyzed by peptide enzyme-linked immunosorbent assay, Western blot, immunofluorescence, and immunoprecipitation. Their cross-reactivity with prion protein from other species was also determined. Our mAbs are directed against four different linear epitopes and may also recognize discontinuous regions of the native prion protein. CONCLUSIONS: These antibodies should allow us to address questions concerning the nature of the prion protein as well as the initiation and progression of prion diseases. Moreover, these mAbs can now be used for the diagnosis of prion diseases of humans and animals.     

The alpha-1,3-galactosyltransferase knockout mouse. Implications for xenotransplantation

BACKGROUND: A conformational change seems to represent the major difference between the scrapie prion protein (PrPSc) and its normal cellular isoform (PrPC). We recently proposed a set of four helix bundle models for the three-dimensional structure of PrPC that are consistent with a variety of spectroscopic and genetic data. RESULTS: We report a plausible model for the three-dimensional structure of a biologically important fragment of PrPSc. The model of residues 108-218 was constructed by an approach that combines computational techniques and experimental data. The proposed structures of this fragment of PrPSc display a four-stranded beta-sheet covered on one face by two alpha-helices. Residues implicated in the prion species barrier are found to cluster on the solvent-accessible surface of the beta-sheet of one of the models. This interface could provide a structural template that would assist the conversion of PrPC to PrPSc and hence direct prion propagation. CONCLUSIONS: Molecular models of the PrP isoforms should prove very useful in developing structural hypotheses about the process by which PrPC is transformed into PrPSc, the mechanisms by which PrP gene mutations give rise to the inherited human prion diseases, and the species barrier that seems to protect humans from animal prions. It seems likely that PrPC represents a kinetically trapped intermediate in PrP folding.     

Ultrastructural studies on scrapie prion protein crystals obtained from reverse micellar solutions

The structural transition from the cellular prion protein (PrPC) that is rich in alpha-helices to the pathological form (PrPSc) that has a high beta-sheet content seems to be the fundamental event underlying the prion diseases. Determination of the structure of PrPSc and the N-terminally truncated PrP 27-30 has been complicated by their insolubility. Here we report the solubilization of PrP 27-30 through a system of reverse micelles that yields monomeric and dimeric PrP. Although solubilization of PrP 27-30 was not accompanied by any recognizable change in secondary structure as measured by FTIR spectroscopy, it did result in a loss of prion infectivity. The formation of small two- and three-dimensional crystals upon exposure to uranyl salts argues that soluble PrP 27-30 possesses considerable tertiary structure. The crystals of PrP 27-30 grown from reverse micellar solutions suggest a novel crystallization mechanism that might be applicable for other membrane proteins. A variety of different crystal lattices diffracted up to 1.85 nm by electron microscopy. Despite the lack of measurable biological activity, the structure of PrP 27-30 in these crystals may provide insight into the structural transition that occurs during PrPSc formation.     

Prion proteins as memory molecules: an hypothesis

Prions are infectious agents widely implicated in a variety of mammalian neurodegenerative diseases generally referred to as transmissible spongiform encephalopathies. Their infectivity is primarily associated with an aberrant conformation of a host-encoded protein, the prion protein, induced by the prion itself in an autocatalytic reaction. The physiological function of this protein is not known. In this paper we suggest that alternative conformations of the prion protein, other than its pathological scrapie state, exist and that the self-sustaining autocatalytic propagation of these states underlies its normal cellular function. In kinetic model calculations we show that the prion protein may constitute a bi-stable molecular switch that can structurally encode and stably store information. A number of cases of prion involvement in normal cellular function and ample molecular detail of pathological prion propagation are cited and correlated to substantiate the implications of this tenet. Our contention is that the prion hypothesis should be extended to a wide variety of physiological processes. We propose that prion proteins are stable determinants of phenotype, operating in diverse functions possibly including memory.     

Species barrier prevents an abnormal isoform of prion protein from accumulating in follicular dendritic cells of mice with Creutzfeldt-Jakob disease

The accumulation of abnormal prion protein in follicular dendritic cells did not occur in mice inoculated with materials from human Creutzfeldt-Jakob disease, whereas it always occurred in mice inoculated with mouse-adapted agents, suggesting an intense expression of the species barrier in the lymphoreticular system.     

Insight into the regulation by second messenger molecules of the permeability of the blood-brain barrier

Recent advances in our knowledge of the blood-brain barrier have in part been made by studying the properties and function of cerebral endothelial cells in vitro. After an era of working with a fraction, enriched in cerebral microvessels by centrifugation, the next generation of in vitro blood-brain barrier model systems was introduced, when the conditions for routinely culturing the endothelial cells were established. This review summarizes the results obtained mainly from this in vitro approach. Different elements of the intracellular signaling messenger systems have been detected in the course of our studies in the cerebral endothelial cells. It has been shown that the synthesizing enzymes of and substrate proteins for the second messenger molecules are present in the cerebral endothelial cells, and their activity and/or amount can change in pathological circumstances, i.e., during the formation of brain oedema. Pharmacological treatments interfering with the second messenger systems proved to be effective in the prevention of brain oedema formation.     

Polymerization of human prion peptide HuPrP 106-126 to amyloid in nucleic acid solution

The human prion peptide PrP106-126 polymerizes in the presence of DNA both in its circular and linearized forms under solution conditions where the peptide alone does not polymerize. The polymerization process has been monitored by the increase in the fluorescence of anilino naphthalene sulfonic dye which detects the availability of the hydrophobic surface(s) in the aggregate as a consequence of polymerization. The polymerization is a nucleation dependent phenomenon as is evidenced from an existence of a lag period before the onset of the polymerization and a strong dependence of the polymerization on the prion peptide concentrations. The reaction is dependent on the pH as seen from rapid polymerization at pH 5 compared to the reaction at neutral pH where no polymerization is observed after a relatively long period of incubation. The polymer has been characterized as amyloid by using new absorbing and emitting species resulting from the interaction of the polymer with the amyloid specific fluorescent dye, Thioflavine S. This is probably the first demonstration that an endogenous macromolecule can influence the polymerization of a prion peptide. We have previously shown that there is a conformational change in the nucleic acid as a consequence of this interaction. This prion peptide is considered as a model to understand prion diseases as is evidenced from its toxicity towards primary brain cells in culture. The peptide encompasses one of the important amyloidogenic regions of the normal cellular prion protein. Demonstration of nucleic acid induced polymerization of the normal and scrapie prion isoforms accompanying a change in the nucleic acid conformation can establish a possible role of nucleic acid in prion disease.     

Transgenic and knockout mice in research on prion diseases

Since the discovery of the prion protein (PrP) gene more than a decade ago, transgenetic investigations on the PrP gene have shaped the field of prion biology in an unprecedented way. Many questions regarding the role of PrP in susceptibility of an organism exposed to prions have been elucidated. For example mice with a targeted disruption of the PrP gene have allowed the demonstration that an organism that lacks PrPc is resistant to infection by prions. Reconstitution of these mice with mutant PrP genes allowed investigations on the structure-activity relationship of the PrP gene with regard to scrapie susceptibility. Unexpectedly, transgenic mice expressing PrP with specific amino-proximal truncations spontaneously develop a neurologic syndrome presenting with ataxia and cerebellar lesions. A distinct spontaneous neurologic phenotype was observed in mice with internal deletions in PrP. Using ectopic expression of PrP in PrP knockout mice has turned out to be a valuable approach towards the identification of host cells that are capable of replicating prions. Transgenic mice have also contributed to our understanding of the molecular basis of the species barrier for prions. Finally, the availability of PrP knockout mice and transgenic mice overexpressing PrP allows selective reconstitution experiments aimed at expressing PrP in neurografts or in specific populations of hemato- and lymphopoietic cells. Such studies have shed new light onto the mechanisms of prion spread and disease pathogenesis.     

Cerebrospinal fluid proteins in the diagnosis of disorders of the blood-cerebrospinal fluid barrier in central nervous system diseases

BACKGROUND: Many neurological diseases are connected with the dysfunction of blood-CSF barrier. The quantitative determination of CSF proteins has already been used in the diagnosis of barrier impairments and inflammatory diseases of the central nervous system. PATIENTS: Serum and CSF, totaling 264 samples, were obtained from 15 controls and 117 patients with various diseases of the nervous system. Laurell's electroimmunoassay was used for estimation of albumin and IgG levels in serum and CSF. CSF-protein profile was evaluated according to Reiber's graph for the evaluation of the CSF-protein profile. RESULTS: The graph for the protein profile can be divided into 5 functionally different parts (1--normal range, 2, 3, 4--different types of barrier dysfunctions and 5--local humoral response in CNS without any barrier impairment). There was a good correlation of CSF-protein profiles and neurological diseases in our group of patients. CONCLUSIONS: According to our results, Reiber's graph was helpful for the diagnosis of blood-CSF-barrier dysfunctions. The graph has the following advantages: a) possibility of simultaneous assessment of the functional state of blood-CSF-barrier and the inflammatory response of the CNS, b)sensitivity for the determination of pathological local IgG-production in CNS and c) minimal number of protein assays necessary.     

The human 37-kDa laminin receptor precursor interacts with the prion protein in eukaryotic cells

Prions are thought to consist of infectious proteins that cause transmissible spongiform encephalopathies. According to overwhelming evidence, the pathogenic prion protein PrPSc converts its host encoded isoform PrPC into insoluble aggregates of PrPSc, concomitant with pathological modifications (for review, see refs. 1-3). Although the physiological role of PrPC is poorly understood, studies with PrP knockout mice demonstrated that PrPC is required for the development of prion diseases. Using the yeast two-hybrid technology in Saccharomyces cerevisiae, we identified the 37-kDa laminin receptor precursor (LRP) as interacting with the cellular prion protein PrPC. Mapping analysis of the LRP-PrP interaction site in S. cerevisiae revealed that PrP and laminin share the same binding domain (amino acids 161 to 180) on LRP. The LRP-PrP interaction was confirmed in vivo in insect (Sf9) and mammalian cells (COS-7). The LRP level was increased in scrapie-infected murine N2a cells and in brain and spleen of scrapie-infected mice. In contrast, the LRP concentration was not significantly altered in these organs from mice infected with the bovine spongiform encephalopathic agent (BSE), which have a lower PrPSc accumulation. LRP levels, however, were dramatically increased in brain and pancreas, slightly increased in the spleen and not altered in the liver of crapie-infected hamsters. These data show that enhanced LRP concentrations are correlated with PrPSc accumulation in organs from mice and hamsters. The laminin receptor precursor, which is highly conserved among mammals and is located on the cell surface, may act as a receptor or co-receptor for the prion protein on mammalian cells.     

Detrimental impact of acid and pepsin on the rate of luminal release of transforming growth factor alpha. Its potential pathogenetic role in the development of reflux esophagitis

Little is known about the composition and function of the mosquito peritrophic matrix (PM), a physical barrier that pathogens must traverse to complete their life cycles. Anopheles gambiae and Aedes aegypti PM proteins induced by blood or by a protein-free meal have been characterized by the use of 2-D gel electrophoresis and lectin-binding affinity assays. More than forty proteins have been identified in both species. Over half of the PM proteins of both mosquitoes migrate identically. Many PM proteins appear to be glycosylated, primarily by high mannose N-linked glycosyl groups.     

Early entry of plasma proteins into damaged neurons in brain infarcts. An immunohistochemical study on experimental animals

Entry of plasma proteins into damaged neurons has previously been demonstrated in various pathological conditions, but little is known about brain infarcts in this respect. In the present study, focal ischemic lesions were produced in rats by permanent occlusion of the middle cerebral artery (MCA). The animals were killed from 1 to 48 h postlesion. Leakage of plasma proteins across the blood-brain barrier into the infarcted area was visualized with immunostaining 2-3 h after the occlusion. This is earlier than in most previous reports. Entry of plasma proteins into ischemic neurons was seen 3 h after permanent occlusion of the MCA, while reliable changes were not seen until 12-24 h in sections stained with hematoxylin and eosin (H & E). Ischemic neurons stained for plasma proteins irrespective of their morphological appearance. Even cells that appeared normal with H & E staining were positively labeled. The technique may be used to diagnose very early ischemic lesions.     

Species barriers in a model for specific prion protein dimerisation

It has been proposed that the most highly conserved sequence segment within the prion protein (PrP) may be involved in dimer formation within both the normal (PrPC) and misfolded (PrPSc) forms. This hypothesis is now examined in the context of amino acids known to be involved in species barriers or in disease modifying polymorphisms, and the structure of a mouse PrP fragment. These locations can be plausibly explained on the basis of the specific dimer model, so that a potential role for a conserved dimerisation element in prion disease progression cannot be excluded.     

Genetics of prion diseases and prion diversity in mice

Linkage of the prion protein (PrP) and scrapie incubation time genes in mice provided strong evidence for the central role of PrP in determining susceptibility to prion disorders. Considerable evidence now argues that the prion protein and incubation time genes are identical. The mouse prion protein gene (Prn-p) may act both quantitatively and qualitatively in modulating prion incubation time. Differences at positions 108 and 189 between PrP-A and PrP-B allotypes can place constraints on interaction between the normal cellular and the scrapie-specific isoforms of PrP (PrPC and PrPSc), although the supply of PrPC available for post-translational conversion to PrPSc can also influence incubation time. Results using transgenic (Tg) mice in studies on scrapie 'strains' or isolates suggest that incubation time characteristics of scrapie isolates can be explained by these two properties of PrP. The final section of this report discusses the novel finding that uninoculated Tg mice overexpressing wild-type (wt) PrP transgenes spontaneously develop a late-onset degenerative neuromyopathy, broadening the spectrum of prion diseases and providing new information on PrP function in both normal and pathological states.     

Interaction of prion peptide HuPrP106-126 with nucleic acid

Synthetic prion peptide PrP106-126 has been used as a model to understand prion diseases. The conformation of the peptide depends on the environmental conditions and it forms amyloid in vitro. The potential of this prion peptide to interact with nucleic acids has been studied using a fluorescent labelled nucleic acid by kinetic and equilibrium methods. A decrease in the fluorescence of the labelled DNA induced by the peptide with time is observed which is pH, ionic strength and temperature dependent. The activation energy of the reactions is approximately 100 kJ mol-1. Lysine tripeptide and spermidine, carrying the same number of positive charges as the prion peptide, do not show an appreciable effect on the DNA. The binding constant between the prion peptide and DNA has a value of > 10(6) M-1 in phosphate buffer, pH 8 which is of the same order of magnitude as the binding of a retroviral protein, p10, with model nucleic acids. It is tempting to speculate that this interaction might play a role in the prion diseases.     

BSE: can we predict the future?

Prion diseases are transmissible neurodegenerative disorders of humans and animals. The prion protein (PrPc) gene is expressed to some extent in many cell types but principally in neurons. Normal PrPc may contribute in the protection of neurons and are protease sensitive. Abnormal prions consist of a post-translationally modified form of PrP, PrPsc, which is partly protease resistant. PrPsc is a protein with high resistance to inactivation by irradiation, heat and harsh chemical treatments. It is currently proposed that PrPsc is an infectious protein that propagates by inducing the normal PrPc to become the abnormal PrPsc. PrPsc cause transmissible spongiform encephalopathies (TSE), an unusual group of degenerative brain diseases that can be transmitted by inoculation or ingestion of diseased brain or other tissues. The human diseases occur in an inherited, acquired and sporadic forms. Transmission of prion diseases between species is limited by a species barrier, determined in part by the degree of sequence homology between the host PrP and inoculated PrPsc. The epidemic of bovine spongiform encephalopathy (BSE) in the United Kingdom is a new disease that has affected over 160,000 cattle and has presumably arisen from dietary exposure to PrPsc from sheep with scrapie. Until shown otherwise we must assume that oral consumption of infectious BSE protein is a new factor for Creutzfeldt-Jakob (CJD) disease in man. This disease is a new variant of CJD (nvCJD) and has a different clinical picture. Early diagnostic markers to facilitate the diagnosis and screen blood and organ donors are not available. The control of the disease relies on the measures to eradicate the spread of BSE by banning the use of ruminant tissues in ruminant feed and slaughter and rendering procedures to ensure inactivation of prions of all infected animals. The control of nvCJD is based on reduction of exposure to BSE by banning a variety of tissues for consumption. A surveillance worldwide is increased for both BSE and nv-CJD and the WHO update regularly recommendations to limit the risk of transmitting the disease. The extent and size of the nvCJD will depend on different factors among others the dose of infectious material, the route of infection, the genetic susceptibility of the person. Therefore is not possible to predict how important the disease will be.