Modification of blood cell PrP epitope exposure during prion disease

Bovine spongiform encephalopathy: A review of current knowledge and challenges

Bovine spongiform encephalopathy (BSE), also referred to as mad cow disease, is a chronic degenerative disease that affects the central nervous system. BSE is caused by a misfolded isoform of the prion protein, a widely expressed glycoprotein. The illness is referred to as Variant Creutzfeldt-Jakob disease (vCJD) in humans. In the United Kingdom (UK), BSE in cattle was first discovered in 1986. Based on epidemiological data, it appears that animal feed containing tainted meat and bone meal (MBM) as a source of meat protein is the common cause of the BSE outbreak in the UK. Clinical indicators in cows include irregular body posture, incoordination, difficulty in standing, weight loss, and temperamental changes, including agitation and hostility. Feeding livestock MBM obtained from BSE-infected livestock contaminated with BSE prions is the only known risk factor for BSE development. Strong evidence linking BSE to human transmission and a variant type of CJD has brought the disease to the attention of many countries. Screening living animals for BSE is challenging. In most cases, suspected animals are usually killed. Typically, the central nervous system is examined for prions to diagnose this illness. There is currently no robust treatment for BSE. The prevention of BSE can be achieved by avoiding the feeding of susceptible animals with ruminant tissues that might carry prions.

Bovine spongiform encephalopathy: A review of current knowledge and challenges

Bovine spongiform encephalopathy (BSE), also referred to as mad cow disease, is a chronic degenerative disease that affects the central nervous system. BSE is caused by a misfolded isoform of the prion protein, a widely expressed glycoprotein. The illness is referred to as Variant Creutzfeldt-Jakob disease (vCJD) in humans. In the United Kingdom (UK), BSE in cattle was first discovered in 1986. Based on epidemiological data, it appears that animal feed containing tainted meat and bone meal (MBM) as a source of meat protein is the common cause of the BSE outbreak in the UK. Clinical indicators in cows include irregular body posture, incoordination, difficulty in standing, weight loss, and temperamental changes, including agitation and hostility. Feeding livestock MBM obtained from BSE-infected livestock contaminated with BSE prions is the only known risk factor for BSE development. Strong evidence linking BSE to human transmission and a variant type of CJD has brought the disease to the attention of many countries. Screening living animals for BSE is challenging. In most cases, suspected animals are usually killed. Typically, the central nervous system is examined for prions to diagnose this illness. There is currently no robust treatment for BSE. The prevention of BSE can be achieved by avoiding the feeding of susceptible animals with ruminant tissues that might carry prions.

Prion protein E219K polymorphism: from the discovery of the KANNO blood group to interventions for human prion disease

KANNO is a new human blood group that was recently discovered. The KANNO antigen shares the PRNP gene with the prion protein and the prion protein E219K polymorphism determines the presence or absence of the KANNO antigen and the development of anti-KANNO alloantibodies. These alloantibodies specifically react with prion proteins, which serve as substrates for conversion into pathological isoforms in some prion diseases and may serve as effective targets for resisting prion infection. These findings establish a potential link between the KANNO blood group and human prion disease via the prion protein E219K polymorphism. We reviewed the interesting correlation between the human PRNP gene's E219K polymorphism and the prion proteins it expresses, as well as human red blood cell antigens. Based on the immune serological principles of human blood cells, the prion protein E219K polymorphism may serve as a foundation for earlier molecular diagnosis and future drug development for prion diseases.

Effects of heme-PrP complex on cell-free conversion and peroxidase-linked immunodetection of prions in blood-based assays

Prion protein (PrP) binding to natural and synthetic porphyrins has been previously demonstrated but the effects of endogenous heme interactions with PrP remain uncertain. This study investigated implications of this interaction in blood-based peroxidase-linked prion immunodetection and seeded conversion of cellular prion (PrP(C)) into disease associated form (PrP(Sc)). Heme binding to recombinant PrP(C) enhanced intrinsic peroxidase activity (POD) by 2.5-fold and POD inherent to denatured blood accounted for over 84% of luminol-based substrate oxidation in a prion immunodetection assay. An immuno-capture assay showed that 75-98% of blood POD was attributable to binding of PrP(C) with endogenous heme. Additionally, 10 μM heme inhibited (P<0.05) the seeded conversion of PrP(C) to PrP(Sc) through the protein misfolding cycling amplification assay. We conclude that the observed effects can interfere with cell-free conversion and peroxidase-linked immunodetection of prions in blood-based assays. These results indicate that heme-PrP interactions could modulate intrinsic POD and protect PrP(C) from conversion into PrP(Sc).

Prion protein-specific antibodies that detect multiple TSE agents with high sensitivity

This paper describes the generation, characterisation and potential applications of a panel of novel anti-prion protein monoclonal antibodies (mAbs). The mAbs were generated by immunising PRNP null mice, using a variety of regimes, with a truncated form of recombinant ovine prion protein spanning residues 94-233. Epitopes of specific antibodies were mapped using solid-phase Pepscan analysis and clustered to four distinct regions within the PrP molecule. We have demonstrated the utility of these antibodies by use of Western blotting and immunohistochemistry in tissues from a range of different species affected by transmissible spongiform encephalopathy (TSE). In comparative tests against extensively-used and widely-published, commercially available antibodies, similar or improved results can be obtained using these new mAbs, specifically in terms of sensitivity of detection. Since many of these antibodies recognise native PrPC, they could also be applied to a broad range of immunoassays such as flow cytometry, DELFIA analysis or immunoprecipitation. We are using these reagents to increase our understanding of TSE pathogenesis and for use in potential diagnostic screening assays.

Prion-induced toxicity in PrP transgenic Drosophila

Prion diseases are fatal transmissible neurodegenerative diseases of humans and various vertebrate species. In their natural hosts these conditions are characterised by prolonged incubation times prior to the onset of clinical signs of terminal disease. Accordingly, tractable models of mammalian prion disease are required in order to better understand the mechanisms of prion replication and prion-induced neurotoxicity. Transmission of prion diseases can occur across a species barrier and this is facilitated in recipients transgenic for the same PrP gene as the individual from which the infectious prions are derived. Here we have tested the hypothesis that exogenous ovine prions can induce neurotoxicity in Drosophila melanogaster transgenic for ovine PrP. Drosophila that expressed ovine PrP pan neuronally and inoculated with ovine prions at the larval stage by oral exposure to scrapie-infected sheep brain homogenate showed markedly accelerated locomotor and survival defects. ARQ PrP transgenic Drosophila exposed to scrapie-infected brain homogenate showed a significant and progressive reduction in locomotor activity compared to similar flies exposed to normal sheep brain homogenate. The prion-induced locomotor defect was accompanied by the accumulation of potentially misfolded PrP in the brains of prion-inoculated flies. VRQ PrP transgenic Drosophila, which expressed less ovine PrP than ARQ flies, showed a reduced median survival compared to similar flies exposed to normal sheep brain homogenate. These prion-induced phenotypic effects were PrP-mediated since ovine prions were not toxic in non-PrP transgenic control flies. Our observations provide the basis of an invertebrate model of transmissible mammalian prion disease.

In vitro amplification of PrPSc derived from the brain and blood of sheep infected with scrapie

Scrapie is a fatal, naturally transmissible, neurodegenerative prion disease that affects sheep and goats and is characterized by the accumulation of a misfolded protein, PrPSc, converted from host-encoded PrPc, in the central nervous system of affected animals. Highly efficient in vitro conversion of host PrPc to PrPSc has been achieved in models of scrapie and in natural prion diseases by protein misfolding cyclic amplification (PMCA). Here, we demonstrate amplification, by serial PMCA, of PrPSc from individual sources of scrapie-infected sheep. Efficiency of amplification was affected by the pairing of the source of PrPSc with the control brain substrate of different genotypes of PrP. In line with previous studies, efficiency of amplification was greatly enhanced with the addition of a synthetic polyanion, polyadenylic acid (PolyA), facilitating rapid detection of low levels of PrPSc from body fluids such as blood. To this end PrPSc was amplified, in a 3 day PMCA assay, from blood leukocyte preparations from VRQ/VRQ scrapie-affected sheep at clinical end point. While PolyA-assisted PMCA resulted in spontaneous conversion of PrPc, we were able to distinguish blood samples from unaffected and affected sheep under controlled conditions. This study demonstrates that highly efficient amplification of PrPSc can be achieved for ovine scrapie from both brain and blood from naturally infected sheep and shows potential applications for improvements in current diagnostics and pre-mortem testing.

Elevated manganese levels in blood and CNS in human prion disease

Prion disease or transmissible spongiform encephalopathies are neurodegenerative disorders of humans and other mammals. They are fatal and difficult to diagnose. Previous studies have suggested that some prion diseases cause elevation of manganese in the blood and brain. In the current study we analysed blood and brain samples from humans to determine whether elevation in manganese is a specific characteristic of Creutzfeldt-Jakob disease, the most common form of human prion disease. Analysis of manganese in the blood of normal humans showed that concentrations vary little with age or sex. Analysis of other diseases, including other neurodegenerative disease showed that only CJD showed an elevation in manganese and copper. Other diseases that showed elevated manganese included blood-brain barrier disorders and haemochromatosis. However, CJD could be easily distinguished from these diseases. This implies that increased blood manganese in prion disease is a highly specific characteristic of the disease.

Three-colour flow cytometric detection of PrP in ovine leukocytes

PrP(c) (cellular prion protein, CD230) expression by subpopulations of lymphoid cells has been widely investigated in a variety of species, possibly because of the possible link between transmissible spongiform encephalopathies (TSE) transmission and blood transfusion. However, the role of the immune cells in the transmission of the disease is still unclear. Here we describe the optimisation and standardisation of a three-colour staining procedure to detect PrP in association with phenotypic and activation markers in ovine immune cells. We demonstrate a reproducible, flexible and sensitive method and that the combination of isotype-specific antibodies and Fab fragments is feasible. To our knowledge, this is the first report of such labelling of ovine cells. Using this method, we were able to detect differences in levels of PrP expression between blood and lymph node cells of the same animal, and considerable variability between animals. Moreover, we were able to explore possible associations between PrP expression and cellular activation and to identify cell subsets with different labelling patterns. We are currently employing this approach to evaluate variations in immunological parameters during experimental infection in sheep.

Ovine plasma prion protein levels show genotypic variation detected by C-terminal epitopes not exposed in cell-surface PrPC

Ovine PBMCs (peripheral blood mononuclear cells) express PrP(C) [cellular PrP (prion-related protein)] and have the potential to harbour and release disease-associated forms of PrP during scrapie in sheep. Cell-surface PrP(C) expression by PBMCs, together with plasma PrP(C) levels, may contribute to the regulatory mechanisms that determine susceptibility and resistance to natural scrapie in sheep. Here, we have correlated cell-surface PrP(C) expression on normal ovine PBMCs by FACS with the presence of PrP(C) in plasma measured by capture-detector immunoassay. FACS showed similar levels of cell-surface PrP(C) on homozygous ARR (Ala136-Arg154-Arg171), ARQ (Ala136-Arg154-Gln171) and VRQ (Val136-Arg154-Gln171) PBMCs. Cell-surface ovine PrP(C) showed modulation of N-terminal epitopes, which was more evident on homozygous ARR cells. Ovine plasma PrP(C) levels showed genotypic variation and the protein displayed C-terminal epitopes not available in cell-surface PrP(C). Homozygous VRQ sheep showed the highest plasma PrP(C) level and homozygous ARR animals the lowest. For comparison, similar analyses were performed on normal bovine PBMCs and plasma. PrP(C) levels in bovine plasma were approx. 4-fold higher than ovine homozygous ARQ plasma despite similar levels of PBMC cell-surface PrP(C) expression. Immunoassays using C-terminal-specific anti-PrP monoclonal antibodies as capture and detector reagents revealed the highest level of PrP(C) in both ovine and bovine plasma, whilst lower levels were detected using N-terminal-specific monoclonal antibody FH11 as the capture reagent. This suggested that a proportion of plasma PrP(C) was N-terminally truncated. Our results indicate that the increased susceptibility to natural scrapie displayed by homozygous VRQ sheep correlates with a higher level of plasma PrP(C).