Biomedical subjects

Victoria A Lawson

Publications and source records attributed to Victoria A Lawson.

7 recordsLinked to original sources

PubMed2005

Correlative studies support lipid peroxidation is linked to PrP(res) propagation as an early primary pathogenic event in prion disease.

To assess whether heightened oxidative stress plays an early and primary pathogenic role in transmissible spongiform encephalopathies (TSE), we undertook detailed correlative studies using a mouse-adapted model of human disease. The spatio-temporal evolution of the abnormal, protease-resistant isoform of the prion protein (PrP(res)) and neuropathological changes were correlated with the occurrence and type of oxidative stress. Heightened oxidative stress was demonstrated, but restricted to elevated levels of free aldehydic breakdown products of lipid peroxidation, affecting all brain regions to varying extents. The increase in lipid peroxidation was highest over the mid-incubation period, with the onset showing close temporal and general topographical concordance with the first detection of PrP(res) with both pre-empting the typical neuropathological changes of spongiform change, gliosis and neuronal loss. Further, prion propagation over the disease course was assessed using murine bioassay. This revealed that the initial rapid increase in infectivity titres was contemporaneous with the abrupt onset and maximisation of lipid peroxidation. The present results are an important extension to previous studies, showing that heightened oxidative stress in the form of lipid peroxidation is likely to constitute an early primary pathogenic event in TSE, associated temporally with the integral disease processes of prion propagation and PrP(res) formation, and consistent with causal links between these events and subsequent typical neuropathological changes.

Analysis of Variance↗

PubMed2005

Extended period of asymptomatic prion disease after low dose inoculation: assessment of detection methods and implications for infection control.

We used quantal dose-titration of a mouse-adapted human transmissible spongiform encephalopathy strain (M470) to compare different analytical methods for their ability to detect asymptomatic brain prion infection after low dose inoculation. At a time point approximately 2.5-fold beyond the mean incubation period of high dose inocula, asymptomatic brain infection was commonly observed using histologic examination, Western blot, and "blind" bioassay following intracerebral inoculation with low titer inocula. At this time point, when a clinical end-point titration would usually be determined, evidence of infection was seen in all healthy animals inoculated with up to 100-fold lower inoculation doses than the lowest causing consistent clinical disease. For the assessment of the presence of asymptomatic infection, we compared different Western immunoblot and histopathological methods in relation to "blind" bioassay using transgenic Tga/20 mice overexpressing mouse prion protein (PrP). Sodium phosphotungstic acid (NaPTA) precipitation of protease-resistant PrP isoforms (PrP(res)) prior to Western blotting was found to approach the sensitivity of the Tga/20 bioassay and was superior to conventional Western blot and histopathological methods, wherein infectivity was commonly found when both of the latter were negative. Re-scaling the original titer by incorporating "blind" transmission data from surviving asymptomatic mice revises the estimate two orders of magnitude higher than the value derived using the conventional clinical disease outcome approach. We also found that the sensitivity of the NaPTA Western blot technique, if used with a diluent such as PBS compared with 10% normal brain homogenate, is adversely affected by up to around 20-fold. We postulate that infectious titer estimates based on more sensitive detection systems such as we report provide a more accurate indication of ultimate transmission risk.

Animals↗

PubMed2005

Prion protein glycosylation.

The transmissible spongiform encephalopathies (TSE), or prion diseases are a group of transmissible neurodegenerative disorders of humans and animals. Although the infectious agent (the 'prion') has not yet been formally defined at the molecular level, much evidence exists to suggest that the major or sole component is an abnormal isoform of the host encoded prion protein (PrP). Different strains or isolates of the infectious agent exist, which exhibit characteristic disease phenotypes when transmitted to susceptible animals. In the absence of a nucleic acid genome it has been hard to accommodate the existence of TSE strains within the protein-only model of prion replication. Recent work examining the conformation and glycosylation patterns of disease-associated PrP has shown that these post-translational modifications show strain-specific properties and contribute to the molecular basis of TSE strain variation. This article will review the role of glycosylation in the susceptibility of cellular PrP to conversion to the disease-associated conformation and the role of glycosylation as a marker of TSE strain type.

Animals↗

PubMed2004

Apoptosis induced in synchronized human immunodeficiency virus type 1-infected primary peripheral blood mononuclear cells is detected after the peak of CD4+ T-lymphocyte loss and is dependent on the tropism of the gp120 envelope glycoprotein.

Disease progression in human immunodeficiency virus type-1 (HIV-1)-infected individuals is frequently accompanied by declining CD4 cell numbers and the acquisition of a T-tropic (X4) or dual tropic (R5X4) phenotype. Understanding the mechanism of CD4 cell loss in HIV-1 infection is essential for the development of effective therapeutic strategies. In this study, donor populations of peripheral blood mononuclear cells (PBMCs) were selected for their ability to support an equivalent acute infection by both R5 and X4 virus phenotypes. This demonstrated that CD4+ T-lymphocyte loss was due to the gp120 region of Env and was replication independent. Furthermore, apoptosis was only detected in cells infected with an X4 virus after the majority of CD4+ T-lymphocyte loss had occurred. These observations indicate that the CD4+ T-lymphocyte loss in an X4 HIV-1 infection is not directly mediated by apoptosis, although apoptosis may be induced in the remaining cell population as a consequence of this CD4+ T-lymphocyte loss.

Apoptosis↗

PubMed2004

Flexible N-terminal region of prion protein influences conformation of protease-resistant prion protein isoforms associated with cross-species scrapie infection in vivo and in vitro.

Transmissible spongiform encephalopathy (TSE) diseases are characterized by the accumulation in brain of an abnormal protease-resistant form of the host-encoded prion protein (PrP), PrP-res. PrP-res conformation differs among TSE agents derived from various sources, and these conformational differences are thought to influence the biological characteristics of these agents. In this study, we introduced deletions into the flexible N-terminal region of PrP (residues 34-124) and investigated the effect of this region on the conformation of PrP-res generated in an in vitro cell-free conversion assay. PrP deleted from residues 34 to 99 generated 12-16-kDa protease-resistant bands with intact C termini but variable N termini. The variable N termini were the result of exposure of new protease cleavage sites in PrP-res between residues 130 and 157, suggesting that these new cleavage sites were caused by alterations in the conformation of the PrP-res generated. Similarly truncated 12-16-kDa PrP bands were also identified in brain homogenates from mice infected with mouse-passaged hamster scrapie as well as in the cell-free conversion assay using conditions that mimicked the hamster/mouse species barrier to infection. Thus, by its effects on PrP-res conformation, the flexible N-terminal region of PrP seemed to influence TSE pathogenesis and cross-species TSE transmission.

Animals↗

PubMed2004

Transmissible spongiform encephalopathies.

Nosologically, transmissible spongiform encephalopathies (TSE or prion diseases) should be grouped with other neurodegenerative disorders such as Alzheimer's and Parkinson's diseases, which are all caused by toxic gain of function of an aberrant form of a constitutively expressed protein. Failure to clear these proteins from the brain induces neuronal dysfunction. Transmissibility is the property that separates TSE from other neurodegenerative diseases, and this property seems to reside within the structure of the abnormal protein. The human phenotypic range of these encephalopathies includes Creutzfeldt-Jakob disease and its variant form, kuru, Gerstmann-Sträussler-Scheinker syndrome, and fatal familial insomnia. Notwithstanding the generally low incidence of TSE and their limited infectiousness, major epidemics such as bovine spongiform encephalopathy and kuru arise in situations where intraspecies recycling of the abnormal protein is sustained. Moreover, evidence of chronic subclinical infection in animals offers insights into pathogenesis and prompts re-evaluation of the notion of species barriers and present infection control measures. Since case-to-case transmission is the only known mechanism underlying epidemics of TSE, potential reservoirs of infectivity in the tails of epidemics need continued vigilance.

Animals↗

PubMed2002

Adaptive changes after human immunodeficiency virus type 1 transmission.

Primary HIV-1 infection (PHI) is associated with a period of viremia, the resolution of which generally coincides with the development of both humoral and cellular immune responses. In this study replication-competent quasispecies were derived from virus isolated from an individual before and after seroconversion. Virus was also isolated from the presumed donor. Phenotypic and genotypic analysis of biological clones identified transmission of an R5/M-tropic phenotype. However, the ability of clones derived from the recipient to replicate in primary macrophages and PBMCs was restricted after transmission. This apparent selection process was supported by analysis of molecular clones derived from the isolated virus. Analysis of the ratio of synonymous and nonsynonymous substitutions predicted the existence of selective pressure soon after transmission, coincident with the development of HIV-1-specific antibodies. An Env trans-complementation assay demonstrated that the infectivity of a clone derived from the recipient after seroconversion was enhanced in the presence of a selected neutralizing antibody, indicating that the developing humoral immune response may have at least in part contributed to the selective pressure identified.

Adaptation, Physiological↗