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R Race

Publications and source records attributed to R Race.

At least 19 recordsLinked to original sources
PubMed2001

Long-term subclinical carrier state precedes scrapie replication and adaptation in a resistant species: analogies to bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease in humans.

Cattle infected with bovine spongiform encephalopathy (BSE) appear to be a reservoir for transmission of variant Creutzfeldt-Jakob disease (vCJD) to humans. Although just over 100 people have developed clinical vCJD, millions have probably been exposed to the infectivity by consumption of BSE-infected beef. It is currently not known whether some of these individuals will develop disease themselves or act as asymptomatic carriers of infectivity which might infect others in the future. We have studied agent persistence and adaptation after cross-species infection using a model of mice inoculated with hamster scrapie strain 263K. Although mice inoculated with hamster scrapie do not develop clinical disease after inoculation with 10 million hamster infectious doses, hamster scrapie infectivity persists in brain and spleen for the life span of the mice. In the present study, we were surprised to find a 1-year period postinfection with hamster scrapie where there was no evidence for replication of infectivity in mouse brain. In contrast, this period of inactive persistence was followed by a period of active replication of infectivity as well as adaptation of new strains of agent capable of causing disease in mice. In most mice, neither the early persistent phase nor the later replicative phase could be detected by immunoblot assay for protease-resistant prion protein (PrP). If similar asymptomatic carriers of infection arise after exposure of humans or animals to BSE, this could markedly increase the danger of additional spread of BSE or vCJD infection by contaminated blood, surgical instruments, or meat. If such subclinical carriers were negative for protease-resistant PrP, similar to our mice, then the recently proposed screening of brain, tonsils, or other tissues of animals and humans by present methods such as immunoblotting or immunohistochemistry might be too insensitive to identify these individuals.

Adaptation, Physiological↗
PubMed2000

Opposite effects of dextran sulfate 500, the polyene antibiotic MS-8209, and Congo red on accumulation of the protease-resistant isoform of PrP in the spleens of mice inoculated intraperitoneally with the scrapie agent.

The mode and the site of action of the major antiscrapie drugs have been studied by investigating their effects on the abnormal protease-resistant isoform of PrP (PrPres) and on its accumulation in mouse spleen. Day-by-day PrPres accumulation in the spleen and in other peripheral organs was first monitored to describe the early steps of scrapie pathogenesis. Three phases were identified: the detection of scrapie inoculum on the day of scrapie infection, a clearance phase, and then the peripheral accumulation of PrPres. In a second step, the effects of the polyene antibiotic MS-8209, the polyanion dextran sulfate 500 (DS500), and Congo red were assessed on these phases, after the drugs were coincubated with scrapie inoculum. Highly different mechanisms and sites of action were apparent. MS-8209 had a weak effect on the accumulation of PrPres in spleen, suggesting another site of intervention for this drug. DS500 delayed the beginning of the clearance phase but then blocked PrPres synthesis for a long period of time, probably because of its immunological effects on the spleen. Surprisingly, Congo red suppressed the clearance phase of scrapie inoculum and then increased transiently accumulation of PrPres in spleen. We showed in vitro that this effect was related to a direct enhancement of the protease resistance of PrPres by the drug.

Amphotericin B↗
PubMed2000

Entry versus blockade of brain infection following oral or intraperitoneal scrapie administration: role of prion protein expression in peripheral nerves and spleen.

Naturally occurring transmissible spongiform encephalopathy (TSE) diseases such as bovine spongiform encephalopathy in cattle are probably transmitted by oral or other peripheral routes of infection. While prion protein (PrP) is required for susceptibility, the mechanism of spread of infection to the brain is not clear. Two prominent possibilities include hematogenous spread by leukocytes and neural spread by axonal transport. In the present experiments, following oral or intraperitoneal infection of transgenic mice with hamster scrapie strain 263K, hamster PrP expression in peripheral nerves was sufficient for successful infection of the brain, and cells of the spleen were not required either as a site of amplification or as transporters of infectivity. The role of tissue-specific PrP expression of foreign PrP in interference with scrapie infection was also studied in these transgenic mice. Peripheral expression of heterologous PrP completely protected the majority of mice from clinical disease after oral or intraperitoneal scrapie infection. Such extensive protection has not been seen in earlier studies on interference, and these results suggested that gene therapy with mutant PrP may be effective in preventing TSE diseases.

Animals↗
PubMed1999

Effectiveness of polyene antibiotics in treatment of transmissible spongiform encephalopathy in transgenic mice expressing Syrian hamster PrP only in neurons.

To date very few drugs have favorably influenced the course of transmissible spongiform encephalopathies. In previous studies, the polyene antibiotics amphotericin B (AmB) and MS-8209 prolonged the incubation time in Syrian hamsters of the 263K strain of scrapie, but AmB had no effect against other scrapie strains in Syrian hamsters. In the present experiments using transgenic mice expressing Syrian hamster PrP in neurons only, MS-8209 extended the life spans of animals infected with the 263K strain but not the DY strain. AmB was effective against both 263K and DY and prevented death in 18% of DY-infected animals. The AmB effect against strain 263K was more prominent in mice whose endogenous PrP gene had been inactivated by homologous recombination. It was unclear whether this difference was due to a change in the duration of the disease or to possible interactive effects between the mouse PrP gene and the drugs themselves. The effectiveness of treatment after intracerebral scrapie infection in transgenic mice expressing PrP only in neurons suggested that neurons are important sites of action for these drugs.

Amphotericin B↗
PubMed1998

Scrapie infectivity and proteinase K-resistant prion protein in sheep placenta, brain, spleen, and lymph node: implications for transmission and antemortem diagnosis.

Probable transmission of bovine spongiform encephalopathy to humans has focused intense interest on all of the transmissible spongiform encephalopathies (TSEs) and how they spread. In all TSEs, an abnormal disease-associated, proteinase K-resistant protein referred to as PrP-res or PrPsc accumulates in brain. In some species, PrP-res accumulates in other tissues as well. Sheep placenta, brain, spleen, and lymph node were analyzed in detail for PrP-res and infectivity. Both were detected in all brain and spleen samples and in placenta and lymph nodes of 80% of the scrapie-infected sheep. A perfect correlation was observed between infectivity and PrP-res detection. These results substantiate the probability that placenta plays an important role in natural transmission of scrapie, suggest that analysis of placenta for PrP-res could be the basis for an antemortem test for sheep scrapie, and show that PrP-res, scrapie infectivity, and scrapie disease are closely associated.

Animals↗
PubMed1995

Identification of differentially expressed genes in scrapie-infected mouse neuroblastoma cells.

In vitro cDNA libraries from scrapie-infected and non-infected murine neuroblastoma cell lines were screened with cDNA probes derived by subtractive hybridization from scrapie-infected and uninfected cells to identify genes with altered expression associated with scrapie infection. Eleven independent recombinant clones, whose expression was either increased or decreased in scrapie-infected cells, were identified. Expression of these genes was also analyzed in a panel of scrapie-infected and non-infected cell lines. Five genes had altered mRNA expression in most scrapie-infected neuroblastoma cell clones compared to non-infected clones. These genes were chromogranin B, intracisternal-A particle envelope, ornithine decarboxylase antizyme, heat shock protein 70 and one unidentified gene. None of these alterations in gene expression was uniquely scrapie-specific; however, the skewed association of increased expression with scrapie infection suggested that a causal relationship might exist between scrapie infection and altered expression of these genes in mouse neuroblastoma cells in vitro.

Animals↗
PubMed1993

Foreign PrP expression and scrapie infection in tissue culture cell lines.

PrP expression and scrapie infectivity was studied in a group of tissue culture cell lines from mice, hamsters, rats and humans. Cell surface PrP protein was detected in seven of ten cell lines from a variety of tissues and showed both cell surface and cytoplasmic perinuclear distributions. Mouse N2a neuroblastoma cells could be persistently infected with scrapie in vitro, but OBL-21 mouse neuroma cells were never successfully infected. Foreign PrP molecules including hamster PrP, mutant hamster PrP with leucine at amino acid 102, and mutant mouse PrP expressing a hamster-encoded PrP antigen epitope were expressed in mouse N2a cells. However, none of these cell lines could be successfully infected with the 263K hamster scrapie agent. Furthermore, expression of these foreign PrP molecules did not lead to spontaneous generation of protease-resistant PrP or a transmissible scrapie-like agent in vitro.

Animals↗
PubMed1992

Diagnostic implications of detection of proteinase K-resistant protein in spleen, lymph nodes, and brain of sheep.

Brain, spleen, and selected lymph nodes from sheep with clinical signs of scrapie were analyzed for presence of proteinase K-resistant protein (PrP-res). Diagnosis of scrapie on the basis of detection of PrP-res was compared with diagnosis on the basis of histologic evaluation of the brain from clinically affected or exposed sheep. Proteinase K-resistant protein was found in every brain that was histologically positive for scrapie, and in addition, was found in the brain of several clinically positive sheep that were not diagnosed as scrapie-positive by histologic evaluation. Proteinase K-resistant protein was also found in 87% of the spleens and lymph nodes from sheep that had PrP-res detected in brain homogenates. Therefore, analysis of sheep brain, spleen, or lymph nodes for PrP-res provided a diagnostic approach that was superior to histologic examination alone for detection of naturally scrapie agent-infected sheep.

Animals↗
PubMed1991

Neuropathological changes in scrapie and Alzheimer's disease are associated with increased expression of apolipoprotein E and cathepsin D in astrocytes.

With the rationale that the neuropathological similarities between scrapie and Alzheimer's disease reflect convergent pathological mechanisms involving altered gene expression, we set out to identify molecular events involved in both processes, using scrapie as a model to study the time course of these changes. We differentially screened a cDNA library constructed from scrapie-infected mice to identify mRNAs that increase or decrease during disease and discovered in this way two mRNAs that are increased in scrapie and Alzheimer's disease. These mRNAs were subsequently shown by sequence analysis to encode apolipoprotein E and cathepsin D (EC 3.4.23.5). Using in situ hybridization and immunocytochemistry to define the cellular and anatomic pathology of altered gene expression, we found that in both diseases the increase in apolipoprotein E and cathepsin D mRNAs and proteins occurred in activated astrocytes. In scrapie, the increase in gene expression occurred soon after the amyloid-forming abnormal isoform of the prion protein has been shown to accumulate in astrocytes. In Alzheimer's disease, the increased expression of cathepsin D also occurred in association with beta-amyloid. These studies reveal some of the molecular antecedents of neuropathological changes in scrapie and Alzheimer's disease and accord new prominence to the role of astrocytes in neurodegenerative conditions.

Aged↗
PubMed1989

Comparative sequence analysis, in vitro expression and biosynthesis of mouse PrP.

A number of studies have indicated that an endogenous brain protein, PrP, is associated with transmissible agents causing spongiform encephalopathies such as scrapie, kuru, and Creutzfeldt-Jakob disease. It has been proposed that PrP derived from scrapie brain is the scrapie agent itself. To test directly whether the PrP mRNA in scrapie brain tissue can encode the scrapie agent, we expressed PrP cDNA cloned from scrapie-infected mouse brain in vitro. The expressed PrP did not transmit scrapie to susceptible mice. Thus either PrP is not the scrapie agent, or the expressed PrP requires additional modification to be infectious. The normal function of PrP is unknown, however, comparison of the amino acid sequences of PrP from mouse, hamster, and human revealed that many structural features of potential functional significance have been conserved during evolution. To learn about normal PrP and whether it is altered by scrapie infection in vitro, we have performed studies of PrP biosynthesis in normal and scrapie-infected mouse neuroblastoma tissue culture cells. The major PrP species were glycoproteins anchored at the cell surface by covalent linkage to phosphatidylinositol. No scrapie-associated modifications of PrP biosynthesis were observed, and, none of the metabolically labeled PrP observed in either scrapie-infected normal cells was resistant to proteinase K.

Amino Acid Sequence↗
PubMed1988

In vitro expression of cloned PrP cDNA derived from scrapie-infected mouse brain: lack of transmission of scrapie infectivity.

A cDNA for the prion protein (PrP) derived from scrapie-infected mouse brain was expressed in C127 mouse cells in vitro under the control of the mouse metallothionein promoter. PrP synthesis was detected by immunoprecipitation using a rabbit antibody specific for a 15 amino acid PrP peptide. Homogenates of cells expressing the cloned PrP cDNA inoculated into weanling mice failed to induce clinical scrapie during 190 days of observation. We conclude that either PrP is not the transmissible agent of scrapie or the PrP is not processed appropriately in this cell system to create the infectious agent.

Animals↗
PubMed1987

The molecular pathogenesis of astrogliosis in scrapie and Alzheimer's disease.

In slow infections caused by scrapie and other unconventional agents, and in Alzheimer's disease (AD), the formation of neuritic plaques and the increase in astrocytes and astrocyte-specific protein, glial fibrillary acidic protein (GFAP), are pathological changes common to both conditions. With the rationale that these parallels imply convergent pathogenetic mechanisms, we identified a gene whose expression increases in both. We now report the results of a more extensive analysis of this gene and show that by sequence analysis it is highly homologous and likely identical to GFAP. GFAP mRNA accumulates late in the course of scrapie in subpial and periventricular astrocytes and in cells in foci in the hippocampus. The increased abundance of GFAP mRNA is accompanied by an increase in the corresponding protein. GFAP mRNA is localized by in situ hybridization to the cell body and processes of astrocytes. In AD, the latter pattern predominates, consistent with induction of GFAP mRNA in the sites of synthesis in glial processes in the neuritic plaque.

Alzheimer Disease↗
PubMed1986

Molecular cloning and complete sequence of prion protein cDNA from mouse brain infected with the scrapie agent.

The prion protein (PrP) is a scrapie-associated fibril protein that accumulates in the brains of hamsters and mice infected with the scrapie agent, and also in the brains of persons affected with kuru or Creutzfeldt-Jakob disease. It has been previously proposed that PrP could be either the primary transmissible agent of scrapie or a secondary component involved in the pathogenesis of scrapie. At present, the second possibility seems more likely, for the PrP-specific mRNA is present in both infected and uninfected brains. We have isolated and sequenced the complete PrP-specific cDNA from mRNA isolated from infected mouse brains. Comparison of the mouse PrP with the hamster PrP reveals a high homology in the amino acid sequence and the presence of a conserved octapeptide repeated four times, whose function is unknown at present. Structural features are discussed and compared with other proteins. Except for its homology with the hamster PrP, mouse PrP has no significant homology to any known protein sequence, including neurofilaments, neuropeptides, and amyloid proteins of Alzheimer disease. Some features of the PrP, however, are similar to structures found in aggregating proteins, such as the wheat glutenin, keratin, and collagen.

Amino Acid Sequence↗
PubMed1985

Cloning of a gene whose expression is increased in scrapie and in senile plaques in human brain.

A complementary DNA library was constructed from messenger RNA's extracted from the brains of mice infected with the scrapie agent. The library was differentially screened with the objectives of finding clones that might be used as markers of infection and finding clones of genes whose increased expression might be correlated with the pathological changes common to scrapie and Alzheimer's disease. A gene was identified whose expression is increased in scrapie. The complementary DNA corresponding to this gene hybridized preferentially and focally to cells in the brains of scrapie-infected animals. The cloned DNA also hybridized to the neuritic plaques found with increased frequency in brains of patients with Alzheimer's disease.

Alzheimer Disease↗