65 research outputs found
Co-Infection with the Friend Retrovirus and Mouse Scrapie Does Not Alter Prion Disease Pathogenesis in Susceptible Mice
Prion diseases are fatal, transmissible neurodegenerative diseases of the central nervous system. An abnormally protease-resistant and insoluble form (PrPSc) of the normally soluble protease-sensitive host prion protein (PrPC) is the major component of the infectious prion. During the course of prion disease, PrPSc accumulates primarily in the lymphoreticular and central nervous systems. Recent studies have shown that co-infection of prion-infected fibroblast cells with the Moloney murine leukemia virus (Mo-MuLV) strongly enhanced the release and spread of scrapie infectivity in cell culture, suggesting that retroviral coinfection might significantly influence prion spread and disease incubation times in vivo. We now show that another retrovirus, the murine leukemia virus Friend (F-MuLV), also enhanced the release and spread of scrapie infectivity in cell culture. However, peripheral co-infection of mice with both Friend virus and the mouse scrapie strain 22L did not alter scrapie disease incubation times, the levels of PrPSc in the brain or spleen, or the distribution of pathological lesions in the brain. Thus, retroviral co-infection does not necessarily alter prion disease pathogenesis in vivo, most likely because of different cell-specific sites of replication for scrapie and F-MuLV
The relative abundance of APOE and Aβ1-42 associated with abnormal prion protein differs between Creutzfeldt-Jakob disease subtypes
Aggregated
and protease-resistant mammalian prion protein (PrP<sup>Sc</sup>)
is the primary protein component of infectious prions.
Enriched PrP<sup>Sc</sup> preparations are often used to study the
mechanisms that underly prion disease. However, most enrichment procedures
are relatively nonspecific and tend to yield significant amounts of
non-PrP<sup>Sc</sup> components including various proteins that could
confound functional and structural studies. It is thus important to
identify these proteins and assess their potential relevance to prion
pathogenesis. Following proteinase K treatment and phosphotungstic
acid precipitation of brain homogenate, we have used mass spectrometry
to analyze the protein content of PrP<sup>Sc</sup> isolated from prion-infected
mice, multiple cases of sporadic Creutzfeldt-Jakob disease (sCJD),
and human growth hormone associated cases of iatrogenic CJD (iCJD).
Creatine kinase was the primary protein contaminant in all PrP<sup>Sc</sup> samples, while many of the other proteins identified were
also found in non-CJD controls, which suggests that they are not CJD
specific. Interestingly, the Alzheimer’s disease associated
peptide amyloid β 1–42 (Aβ1–42) was identified
in the majority of the sCJD cases as well as non-CJD age-matched controls,
while apoliprotein E was found in greater abundance in the sCJD cases.
By contrast, while some of the iCJD cases showed evidence of higher
molecular weight Aβ oligomers, monomeric Aβ1–42
peptide was not detected by immunoblot, and only one case had significant
levels of apolipoprotein E. Our data are consistent with the age-associated
deposition of Aβ1–42 in older sporadic CJD and non-CJD
patients and suggest that both apolipoprotein E and Aβ1–42
abundance can differ depending upon the type of CJD
Susceptibilities of Nonhuman Primates to Chronic Wasting Disease
A species barrier may protect humans from this disease
The Distribution of Prion Protein Allotypes Differs Between Sporadic and Iatrogenic Creutzfeldt-Jakob Disease Patients
Sporadic Creutzfeldt-Jakob disease (sCJD) is the most prevalent of the human prion diseases, which are fatal and transmissible neurodegenerative diseases caused by the infectious prion protein (PrP(Sc)). The origin of sCJD is unknown, although the initiating event is thought to be the stochastic misfolding of endogenous prion protein (PrP(C)) into infectious PrP(Sc). By contrast, human growth hormone-associated cases of iatrogenic CJD (iCJD) in the United Kingdom (UK) are associated with exposure to an exogenous source of PrP(Sc). In both forms of CJD, heterozygosity at residue 129 for methionine (M) or valine (V) in the prion protein gene may affect disease phenotype, onset and progression. However, the relative contribution of each PrP(C) allotype to PrP(Sc) in heterozygous cases of CJD is unknown. Using mass spectrometry, we determined that the relative abundance of PrP(Sc) with M or V at residue 129 in brain specimens from MV cases of sCJD was highly variable. This result is consistent with PrP(C) containing an M or V at residue 129 having a similar propensity to misfold into PrP(Sc) thus causing sCJD. By contrast, PrP(Sc) with V at residue 129 predominated in the majority of the UK human growth hormone associated iCJD cases, consistent with exposure to infectious PrP(Sc) containing V at residue 129. In both types of CJD, the PrP(Sc) allotype ratio had no correlation with CJD type, age at clinical onset, or disease duration. Therefore, factors other than PrP(Sc) allotype abundance must influence the clinical progression and phenotype of heterozygous cases of CJD
Cells Expressing Anchorless Prion Protein Are Resistant to Scrapie Infectionâ–¿
The hallmark of transmissible spongiform encephalopathies (TSEs or prion diseases) is the accumulation of an abnormally folded, partially protease-resistant form (PrP-res) of the normal protease-sensitive prion protein (PrP-sen). PrP-sen is attached to the cell membrane by a glycosylphosphatidylinositol (GPI) anchor. In vitro, the anchor and the local membrane environment are important for the conversion of PrP-sen to PrP-res. In vivo, however, the anchor is not necessary because transgenic mice expressing anchorless PrP-sen accumulate PrP-res and replicate infectivity. To clarify the role of the GPI anchor in TSE infection, cells expressing GPI-anchored PrP-sen, anchorless PrP-sen, or both forms of PrP-sen were exposed to the mouse scrapie strain 22L. Cells expressing anchored PrP-sen produced PrP-res after exposure to 22L. Surprisingly, while cells expressing anchorless PrP-sen made anchorless PrP-res in the first 96 h postinfection, no PrP-res was detected at later passes. In contrast, when cells expressing both forms of PrP-sen were exposed to 22L, both anchored and anchorless PrP-res were detected over multiple passes. Consistent with the in vitro data, scrapie-infected cells expressing anchored PrP-sen transmitted disease to mice whereas cells expressing anchorless PrP-sen alone did not. These results demonstrate that the GPI anchor on PrP-sen is important for the persistent infection of cells in vitro. Our data suggest that cells expressing anchorless PrP-sen are not directly infected with scrapie. Thus, PrP-res formation in transgenic mice expressing anchorless PrP-sen may be occurring extracellularly
Recombinant Prion Protein Refolded with Lipid and RNA Has the Biochemical Hallmarks of a Prion but Lacks In Vivo Infectivity
<div><p>During prion infection, the normal, protease-sensitive conformation of prion protein (PrP<sup>C</sup>) is converted via seeded polymerization to an abnormal, infectious conformation with greatly increased protease-resistance (PrP<sup>Sc</sup>). In vitro, protein misfolding cyclic amplification (PMCA) uses PrP<sup>Sc</sup> in prion-infected brain homogenates as an initiating seed to convert PrP<sup>C</sup> and trigger the self-propagation of PrP<sup>Sc</sup> over many cycles of amplification. While PMCA reactions produce high levels of protease-resistant PrP, the infectious titer is often lower than that of brain-derived PrP<sup>Sc</sup>. More recently, PMCA techniques using bacterially derived recombinant PrP (rPrP) in the presence of lipid and RNA but in the absence of any starting PrP<sup>Sc</sup> seed have been used to generate infectious prions that cause disease in wild-type mice with relatively short incubation times. These data suggest that lipid and/or RNA act as cofactors to facilitate the de novo formation of high levels of prion infectivity. Using rPrP purified by two different techniques, we generated a self-propagating protease-resistant rPrP molecule that, regardless of the amount of RNA and lipid used, had a molecular mass, protease resistance and insolubility similar to that of PrP<sup>Sc</sup>. However, we were unable to detect prion infectivity in any of our reactions using either cell-culture or animal bioassays. These results demonstrate that the ability to self-propagate into a protease-resistant insoluble conformer is not unique to infectious PrP molecules. They suggest that the presence of RNA and lipid cofactors may facilitate the spontaneous refolding of PrP into an infectious form while also allowing the de novo formation of self-propagating, but non-infectious, rPrP-res.</p></div
Proteomics Analysis of Amyloid and Nonamyloid Prion Disease Phenotypes Reveals Both Common and Divergent Mechanisms of Neuropathogenesis
Prion
diseases are a heterogeneous group of neurodegenerative disorders
affecting various mammals including humans. Prion diseases are characterized
by a misfolding of the host-encoded prion protein (PrP<sup>C</sup>) into a pathological isoform termed PrP<sup>Sc</sup>. In wild-type
mice, PrP<sup>C</sup> is attached to the plasma membrane by a glycosylphosphatidylinositol
(GPI) anchor and PrP<sup>Sc</sup> typically accumulates in diffuse
nonamyloid deposits with gray matter spongiosis. By contrast, when
mice lacking the GPI anchor are infected with the same prion inoculum,
PrP<sup>Sc</sup> accumulates in dense perivascular amyloid plaques
with little or no gray matter spongiosis. In order to evaluate whether
different host biochemical pathways were implicated in these two phenotypically
distinct prion disease models, we utilized a proteomics approach.
In both models, infected mice displayed evidence of a neuroinflammatory
response and complement activation. Proteins involved in cell death
and calcium homeostasis were also identified in both phenotypes. However,
mitochondrial pathways of apoptosis were implicated only in the nonamyloid
form, whereas metal binding and synaptic vesicle transport were more
disrupted in the amyloid phenotype. Thus, following infection with
a single prion strain, PrP<sup>C</sup> anchoring to the plasma membrane
correlated not only with the type of PrP<sup>Sc</sup> deposition but
also with unique biochemical pathways associated with pathogenesis
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