Unusual cerebral vascular prion protein amyloid distribution in scrapie-infected transgenic mice expressing anchorless prion protein

acta neuropathol commun

Phillips

et al. 2014

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BackgroundIn humans and animals, prion protein (PrP) is usually expressed as a glycophosphatidylinositol (GPI)-anchored membrane protein, but anchorless PrP may be pathogenic in humans with certain familial prion diseases. Anchored PrP expressed on neurons mediates spread of prions along axons in the peripheral and central nervous systems. However, the mechanism of prion spread in individuals expressing anchorless PrP is poorly understood. Here we studied prion spread within brain of mice expressing anchorless or anchored PrP.ResultsTo create a localized initial point of infection, we microinjected scrapie in a 0.5 microliter volume in the striatum. In this experiment, PrPres and gliosis were first detected in both types of mice at 40 days post-inoculation near the needle track. In mice with anchored PrP, PrPres appeared to spread via neurons to distant connected brain areas by the clinical endpoint at 150 days post-inoculation. This PrPres was rarely associated with blood vessels. In contrast, in mice with anchorless PrP, PrPres spread did not follow neuronal circuitry, but instead followed a novel slower pattern utilizing the drainage system of the brain interstitial fluid (ISF) including perivascular areas adjacent to blood vessels, subependymal areas and spaces between axons in white matter tracts.ConclusionsIn transgenic mice expressing anchorless PrP small amyloid-seeding PrPres aggregates appeared to be transported in the ISF, thus spreading development of cerebral amyloid angiopathy (CAA) throughout the brain. Spread of amyloid seeding by ISF may also occur in multiple human brain diseases involving CAA.

Section: Resultssupporting

confidence: 88%

Distinct patterns of spread of prion infection in brains of mice expressing anchorless or anchored forms of prion protein

Rangel

acta neuropathol commun

Phillips

et al. 2014

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“…Amyloid PrPres, which is fibrillar, is more highly organized than nonamyloid PrPres (6). The lack of a GPI anchor on PrP may favor amyloid formation because the lack of membrane tethering, and the lack of large carbohydrate moieties, might facilitate the protein interactions required for assembly into large organized fibrillar aggregates (49)(50)(51). Thus, the GPI-negative amyloid PrPres derived from infected tg44 mice might also differ from GPI-positive nonamyloid PrPres from C57 mice in its ability to interact with PrPsen to generate new PrPres.…”

mentioning

confidence: 99%

Increased Infectivity of Anchorless Mouse Scrapie Prions in Transgenic Mice Overexpressing Human Prion Protein

Phillips

Meade-White

et al. 2015

J Virol

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Prion protein (PrP) is found in all mammals, mostly as a glycoprotein anchored to the plasma membrane by a C-terminal glycosylphosphatidylinositol (GPI) linkage. Following prion infection, host protease-sensitive prion protein (PrPsen or PrPC) is converted into an abnormal, disease-associated, protease-resistant form (PrPres). Biochemical characteristics, such as the PrP amino acid sequence, and posttranslational modifications, such as glycosylation and GPI anchoring, can affect the transmissibility of prions as well as the biochemical properties of the PrPres generated. Previous in vivo studies on the effects of GPI anchoring on prion infectivity have not examined cross-species transmission. In this study, we tested the effect of lack of GPI anchoring on a species barrier model using mice expressing human PrP. In this model, anchorless 22L prions derived from tg44 mice were more infectious than 22L prions derived from C57BL/10 mice when tested in tg66 transgenic mice, which expressed wild-type anchored human PrP at 8-to 16-fold above normal. Thus, the lack of the GPI anchor on the PrPres from tg44 mice appeared to reduce the effect of the mouse-human PrP species barrier. In contrast, neither source of prions induced disease in tgRM transgenic mice, which expressed human PrP at 2-to 4-fold above normal. IMPORTANCE Prion protein (PrP) is found in all mammals, usually attached to cells by an anchor molecule called GPI. Following prion infection, PrP is converted into a disease-associated form (PrPres). While most prion diseases are species specific, this finding is not consistent, and species barriers differ in strength. The amino acid sequence of PrP varies among species, and this variability affects prion species barriers. However, other PrP modifications, including glycosylation and GPI anchoring, may also influence cross-species infectivity. We studied the effect of PrP GPI anchoring using a mouse-to-human species barrier model. Experiments showed that prions produced by mice expressing only anchorless PrP were more infectious than prions produced in mice expressing anchored PrP. Thus, the lack of the GPI anchor on prions reduced the effect of the mouse-human species barrier. Our results suggest that prion diseases that produce higher levels of anchorless PrP may pose an increased risk for cross-species infection. P rion diseases, also known as transmissible spongiform encephalopathies (TSEs), are fatal neurodegenerative diseases that occur in many mammals, including humans. Central to all prion diseases is the conversion of the normal host prion protein (PrPsen or PrPC) into an abnormal, protease-resistant form (PrPres) associated with disease. In previous studies, PrPres and infectivity were generated concurrently in a cell-free in vitro system, proving that live cells were not required for formation of new prion infectivity in a cell-free in vitro system (1-4), a finding which supported the role of PrPres as the infectious prion agent (5). During the course of prion disease, repeated conversion of P...

“…18 To explain this process we speculated that brain endothelial basement membranes might provide biochemical structures forming a scaffold capable of binding small oligomers of PrPSc and initiating their assembly into larger polymers. 30 These polymers in turn might be able to self-scaffold to mediate further polymerization to account for the spread of the PrPSc amyloid radially away from the blood vessel and into the CNS parenchyma. In contrast, in visceral tissues such as heart, colon and brown fat, PrPSc amyloid was consistently found in interstitial areas, and perivascular amyloid was less prominent than in brain.…”

Section: Discussionmentioning

confidence: 99%

Ultrastructure and pathology of prion protein amyloid accumulation and cellular damage in extraneural tissues of scrapie-infected transgenic mice expressing anchorless prion protein

Jeffrey

McGovern

et al. 2017

Prion

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In most human and animal prion diseases the abnormal disease-associated prion protein (PrPSc) is deposited as non-amyloid aggregates in CNS, spleen and lymphoid organs. In contrast, in humans and transgenic mice with PrP mutations which cause expression of PrP lacking a glycosylphosphatidylinositol (GPI)-anchor, most PrPSc is in the amyloid form. In transgenic mice expressing only anchorless PrP (tg anchorless), PrPSc is deposited not only in CNS and lymphoid tissues, but also in extraneural tissues including heart, brown fat, white fat, and colon. In the present paper, we report ultrastructural studies of amyloid PrPSc deposition in extraneural tissues of scrapie-infected tg anchorless mice. Amyloid PrPSc fibrils identified by immunogold-labeling were visible at high magnification in interstitial regions and around blood vessels of heart, brown fat, white fat, colon, and lymphoid tissues. PrPSc amyloid was located on and outside the plasma membranes of adipocytes in brown fat and cardiomyocytes, and appeared to invaginate and disrupt the plasma membranes of these cell types, suggesting cellular damage. In contrast, no cellular damage was apparent near PrPSc associated with macrophages in lymphoid tissues and colon, with enteric neuronal ganglion cells in colon or with adipocytes in white fat. PrPSc localized in macrophage phagolysosomes lacked discernable fibrils and might be undergoing degradation. Furthermore, in contrast to wild-type mice expressing GPI-anchored PrP, in lymphoid tissues of tg anchorless mice, PrPSc was not associated with follicular dendritic cells (FDC), and FDC did not display typical prion-associated pathogenic changes.