Alana M. Thackray

Metal imbalance and compromised antioxidant function are early changes in prion disease.

The prion protein (PrP) has been shown to bind copper. In the present study we have investigated whether prion disease in a mouse scrapie model resulted in modification of metal concentrations. We found changes in the levels of copper and manganese in the brains of scrapie-infected mice prior to the onset of clinical symptoms. Interestingly, we noted a major increase in blood manganese in the early stages of disease. Analysis of purified PrP from the brains of scrapie-infected mice also showed a reduction in copper binding to the protein and a proportional decrease in antioxidant activity between 30 and 60 days post-inoculation. We postulate that alterations in trace-element metabolism as a result of changes in metal binding to PrP are central to the pathological modifications in prion disease.

The trigeminal ganglion is a location for equine herpesvirus 1 latency and reactivation in the horse

Four specific pathogen-free ponies were infected intranasally with equine herpesvirus 1 (EHV-1) and two were similarly infected with an EHV-1 thymidine kinase deletion mutant. The primary infections were characterized by a transient fever accompanied by virus shedding into nasal mucus and viraemia. No virus was detected in clinical specimens after 15 days post-infection. Two months later a reactivation stimulus was administered to all six ponies and only the four that had been previously inoculated with wild-type EHV-1 shed virus into nasal mucus (for 10 days), proving the presence of a latent infection. No recurrence of viraemia was observed. The animals were monitored for a further 6 weeks and were consistently shown to be free from infectious virus. Tissues were then obtained postmortem. Co-cultivation of explanted trigeminal ganglia from two out of the four ponies that carried the wild-type virus yielded cultures positive for infectious virus. Apart from nasal epithelium, no infectious virus was recovered from any other tissue. PCR confirmed the presence of virus DNA in the ganglia from all six ponies. Lymphoid tissues also yielded positive signals using this technique. The relevance of virus detection by PCR in lymphoid and neural tissues is discussed in relation to the potential for reactivation of latent virus in the host. However, evidence is presented to show that EHV-1 is neurotropic and, in common with other members of the alpha-herpesvirus subfamily, establishes latency in sensory ganglia from which virus can be reactivated.

Single Protein Molecule Detection by Glass Nanopores

Nanopores can be used to detect and analyze single molecules in solution. We have used glass nanopores made by laser-assisted capillary-pulling, as a high-throughput and low cost method, to detect a range of label-free proteins: lysozyme, avidin, IgG, β-lactoglobulin, ovalbumin, bovine serum albumin (BSA), and β-galactosidase in solution. Furthermore, we show for the first time solid state nanopore measurements of mammalian prion protein, which in its abnormal form is associated with transmissible spongiform encephalopathies. Our approach provides a basis for protein characterization and the study of protein conformational diseases by nanopore detection.

Proteinase K-sensitive disease-associated ovine prion protein revealed by conformation-dependent immunoassay

PrPSc [abnormal disease-specific conformation of PrP (prion-related protein)] accumulates in prion-affected individuals in the form of amorphous aggregates. Limited proteolysis of PrPSc results in a protease-resistant core of PrPSc of molecular mass of 27-30 kDa (PrP27-30). Aggregated forms of PrP co-purify with prion infectivity, although infectivity does not always correlate with the presence of PrP27-30. This suggests that discrimination between PrPC (normal cellular PrP) and PrPSc by proteolysis may underestimate the repertoire and quantity of PrPSc subtypes. We have developed a CDI (conformation-dependent immunoassay) utilizing time-resolved fluorescence to study the conformers of disease-associated PrP in natural cases of sheep scrapie, without using PK (proteinase K) treatment to discriminate between PrPC and PrPSc. The capture-detector CDI utilizes N-terminal- and C-terminal-specific anti-PrP monoclonal antibodies that recognize regions of the prion protein differentially buried or exposed depending on the extent of denaturation of the molecule. PrPSc was precipitated from scrapie-infected brain stem and cerebellum tissue following sarkosyl extraction, with or without the use of sodium phosphotungstic acid, and native and denatured PrPSc detected by CDI. PrPSc was detectable in brain tissue from homozygous VRQ (V136 R154 Q171) and ARQ (A136 R154 Q171) scrapie-infected sheep brains. The highest levels of PrPSc were found in homozygous VRQ scrapie-infected brains. The quantity of PrPSc was significantly reduced, up to 90% in some cases, when samples were treated with PK prior to the CDI. Collectively, our results show that the level of PrPSc in brain samples from cases of natural scrapie display genotypic differences and that a significant amount of this material is PK-sensitive.

Comparison of efficacies of famciclovir and valaciclovir against herpes simplex virus type 1 in a murine immunosuppression model.

A mouse model of herpes simplex virus type 1 infection in an immunocompromised host was established by using cyclosporin-A to impair T-cell function. Following inoculation of herpes simplex virus type 1 into the skin of the ear pinna, cyclosporin-A prolonged virus replication in the skin and neural tissues compared with that in immunocompetent mice. This model was used to investigate the activity of famciclovir (FCV) and valaciclovir (VACV), which are oral products of the antiherpesvirus agents penciclovir and acyclovir, respectively. Both prodrugs gave similar blood profiles of the antiherpesvirus agents in normal and cyclosporin-treated mice. The compounds were administered by the oral route at 50 mg/kg per dose twice daily for 5 days. Both compounds were very effective at clearing infectious virus from the tissues despite the immunosuppression; FCV-treated animals cleared virus from the ear pinna more rapidly than VACV-treated animals. The areas under the concentration-time curve (AUC) for virus replication with time were reduced to 50 and 30% of control values for ear pinna and brain stem, respectively, with VACV therapy and to < 5% in both tissues by FCV. When treatment was continued to day 10, the reductions in AUC for ear and brain stem, respectively, were to 33 and 26% of control values with VACV and to < 3 and < 5% with FCV. However, on cessation of the antiviral treatment, there was a reproducible recurrence of infectious virus in the tissues obtained from VACV-treated mice. The recurrence of infectious virus was also evident after 10 days of treatment with VACV. In mice which had received FCV for 10 or 5 days, these was no resumption of virus replication in the ear pinna or brain stem. When dosing was reduced to once per day, both compounds were less effective at controlling the infection. Nevertheless, no recurrence of infectious virus was observed on cessation of FCV therapy.

Accelerated Prion Disease in the Absence of Interleukin-10

ABSTRACT The identity of pro- and anti-inflammatory cytokines in the neuropathogenesis of prion diseases remains undefined. Here we have investigated the role of anti-inflammatory cytokines on the progression of prion disease through the use of mice that lack interleukin-4 (IL-4), IL-10, IL-13, or both IL-4 and IL-13. Collectively our data show that among these anti-inflammatory cytokines, IL-10 plays a prominent role in the regulation of prion disease. Mice deficient in IL-10 are highly susceptible to the development of prion disease and show a markedly shortened incubation time. In addition, we have correlated cytokine gene expression in prion-inoculated IL-10−/− mice to wild-type-inoculated animals. Our experiments show that in the absence of IL-10 there is an early expression of tumor necrosis factor alpha (TNF-α). In wild-type prion-inoculated mice, the expression of TNF-α mRNA occurs at a later time point that correlates with the extended incubation time for terminal disease development in these animals compared to those that lack IL-10. Elevated levels of IL-13 mRNA are found at early time points in the central nervous system of prion-inoculated IL-10−/− mice. At terminal disease, the brains of wild-type mice inoculated with RML or ME7 are characterized by elevated levels of mRNA for the proinflammatory cytokines TNF-α and IL-1β, together with the anti-inflammatory cytokines IL-10, IL-13, and transforming growth factor beta. Our data are consistent with a role for proinflammatory cytokines in the initiation of pathology during prion disease and an attempt by anti-inflammatory cytokines to regulate the ensuing, invariably fatal pathology.

Emergence of multiple prion strains from single isolates of ovine scrapie

The infectious agent associated with prion diseases such as ovine scrapie shows strain diversity. Ovine prion strains have typically been identified by their transmission properties in wild-type mice. However, strain typing of ovine scrapie isolates in wild-type mice may not reveal properties of the infectious prion agent as they exist in the original host. This could be circumvented if ovine scrapie isolates are passaged in ovine prion protein (PrP)-transgenic mice. This study used incubation time, lesion profile, immunohistochemistry of the disease-associated PrP (PrP(Sc)) and molecular profile to compare the range of ovine prion strains that emerged from sheep scrapie isolates following serial passage in wild-type and ovine PrP transgenic mice. It was found that a diverse range of ovine prion strains emerged from homozygous ARQ and VRQ scrapie isolates passaged in wild-type and ovine PrP transgenic mice. However, strain-specific PrP(Sc) deposition and PrP27-30 molecular profile patterns were identified in ovine PrP transgenic mice that were not detected in wild-type mice. Significantly, it was established that the individual mouse brain selected for transmission during prion strain typing had a significant influence on strain definition. Serial passage of short- and long-incubation-time animals from the same group of scrapie-inoculated mice revealed different prion strain phenotypes. These observations are consistent with the possibility that some scrapie isolates contain more than one prion strain.

Molecular and Transmission Characteristics of Primary-Passaged Ovine Scrapie Isolates in Conventional and Ovine PrP Transgenic Mice

ABSTRACT A more complete assessment of ovine prion strain diversity will be achieved by complementing biological strain typing in conventional and ovine PrP transgenic mice with a biochemical analysis of the resultant PrPSc. This will provide a correlation between ovine prion strain phenotype and the molecular nature of different PrP conformers associated with particular prion strains. Here, we have compared the molecular and transmission characteristics of ovine ARQ/ARQ and VRQ/VRQ scrapie isolates following primary passage in tg338 (VRQ) and tg59 (ARQ) ovine PrP transgenic mice and the conventional mouse lines C57BL/6 (Prnpa), RIII (Prnpa), and VM (Prnpb). Our data show that these different genotypes of scrapie isolates display similar incubation periods of >350 days in conventional and tg59 mice. Facilitated transmission of sheep scrapie isolates occurred in tg338 mice, with incubation times reduced to 64 days for VRQ/VRQ inocula and to ≤210 days for ARQ/ARQ samples. Distinct genotype-specific lesion profiles were seen in the brains of conventional and tg59 mice with prion disease, which was accompanied by the accumulation of more conformationally stable PrPSc, following inoculation with ARQ/ARQ compared to VRQ/VRQ scrapie isolates. In contrast, the lesion profiles, quantities, and stability of PrPSc induced by the same inocula in tg338 mice were more similar than in the other mouse lines. Our data show that primary transmission of different genotypes of ovine prions is associated with the formation of different conformers of PrPSc with distinct molecular properties and provide the basis of a molecular approach to identify the true diversity of ovine prion strains.

Mouse-Adapted Ovine Scrapie Prion Strains Are Characterized by Different Conformers of PrPSc

ABSTRACT The agent responsible for prion disease may exist in different forms, commonly referred to as strains, with each carrying the specific information that determines its own distinct biological properties, such as incubation period and lesion profile. Biological strain typing of ovine scrapie isolates by serial passage in conventional mice has shown some diversity in ovine prion strains. However, this biological diversity remains poorly supported by biochemical prion strain typing. The protein-only hypothesis predicts that variation between different prion strains in the same host is manifest in different conformations adopted by PrPSc. Here we have investigated the molecular properties of PrPSc associated with two principal Prnpa mouse-adapted ovine scrapie strains, namely, RML and ME7, in order to establish biochemical prion strain typing strategies that may subsequently be used to discriminate field cases of mouse-passaged ovine scrapie isolates. We used a conformation-dependent immunoassay and a conformational stability assay, together with Western blot analysis, to demonstrate that RML and ME7 PrPSc proteins show distinct biochemical and physicochemical properties. Although RML and ME7 PrPSc proteins showed similar resistance to proteolytic digestion, they differed in their glycoform profiles and levels of proteinase K (PK)-sensitive and PK-resistant isoforms. In addition, the PK-resistant core (PrP27-30) of ME7 was conformationally more stable following exposure to guanidine hydrochloride or Sarkosyl than was RML PrP27-30. Our data show that mouse-adapted ovine scrapie strains can be discriminated by their distinct conformers of PrPSc, which provides a basis to investigate their diversity at the molecular level.

Subclinical Prion Disease Induced by Oral Inoculation

ABSTRACT Natural transmission of prion disease is believed to occur by peripheral infection such as oral inoculation. Following this route of inoculation, both the peripheral nervous system and the lymphoreticular system may be involved in the subsequent neuroinvasion of the central nervous system by prions, which may not necessarily result in clinical signs of terminal disease. Subclinical prion disease, characterized by the presence of infectivity and PrPSc in the absence of overt clinical signs, may occur. It is not known which host factors contribute to whether infection with prions culminates in a terminal or subclinical disease state. We have investigated whether the level of host PrPc protein expression is a factor in the development of subclinical prion disease. When RML prion inoculum was inoculated by either the i.c. or intraperitoneal route, wild-type and tga20 mice both succumbed to terminal prion disease. In contrast, orally inoculated tga20 mice succumbed to terminal prion disease, whereas wild-type mice showed no clinical signs. However, wild-type mice sacrificed 375 or 525 days after oral inoculation harbored significant levels of brain PrPSc and infectivity. These data show that same-species transmission of prions by the oral route in animals that express normal levels of PrPc can result in subclinical prion disease. This indicates that the level of host PrPc protein expression is a contributing factor to the regulation of development of terminal prion disease. Events that increase PrPc expression may predispose a prion-infected animal to the more deleterious effects of prion pathology.