Article

Crucial Role for Prion Protein Membrane Anchoring in the Neuroinvasion and Neural Spread of Prion Infection

Laboratory of Persistent Viral Diseases, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, Montana 59840, USA.
Journal of Virology (Impact Factor: 4.44). 02/2011; 85(4):1484-94. DOI: 10.1128/JVI.02167-10
Source: PubMed

ABSTRACT

In nature prion diseases are usually transmitted by extracerebral prion infection, but clinical disease results only after
invasion of the central nervous system (CNS). Prion protein (PrP), a host-encoded glycosylphosphatidylinositol (GPI)-anchored
membrane glycoprotein, is necessary for prion infection and disease. Here, we investigated the role of the anchoring of PrP
on prion neuroinvasion by studying various inoculation routes in mice expressing either anchored or anchorless PrP. In control
mice with anchored PrP, intracerebral or sciatic nerve inoculation resulted in rapid CNS neuroinvasion and clinical disease
(154 to 156 days), and after tongue, ocular, intravenous, or intraperitoneal inoculation, CNS neuroinvasion was only slightly
slower (193 to 231 days). In contrast, in anchorless PrP mice, these routes resulted in slow and infrequent CNS neuroinvasion.
Only intracerebral inoculation caused brain PrPres, a protease-resistant isoform of PrP, and disease in both types of mice.
Thus, anchored PrP was an essential component for the rapid neural spread and CNS neuroinvasion of prion infection.

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    • "Previously we showed an association at the time of clinical disease between PrPres amyloid and the ISF drainage system using ISF tracers [29]; however, in this work we did not look at multiple preclinical time-points to determine the localization and pattern of spread of the PrPres amyloid over time. Because of the very poor spread of PrPres in peripheral nerves after intranerval injection of mice expressing anchorless PrP [30], we hypothesized that in brain of tg44 mice PrPres might not spread via neuroanatomical connections as seen in C57 mice. Two possibilities were considered: First, mechanical dissemination of PrPres aggregates capable of seeding new PrPres conversion might occur mostly at the time of intracerebral (i.c.) injection. "
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    ABSTRACT: In 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. To 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. In 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.
    Full-text · Article · Jan 2014
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    • "Homozygous Tg44+/+ mice expressing a transgene encoding mouse prion protein lacking the GPI anchor (anchorless PrP) were described previously [25]. Mice from 4–6 weeks of age were infected with 1% brain homogenate of RML scrapie stock using intracerebral (IC) or intravenous (IV) routes using volumes of 50 μl and 250 μl respectively as previously described [26-28]. Uninfected age-matched Tg44+/+ mice and non-transgenic C57BL/10SnJ mice were also used in some experiments. "
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    ABSTRACT: Background In some prion diseases, misfolded aggregated protease-resistant prion protein (PrPres) is found in brain as amyloid, which can cause cerebral amyloid angiopathy. Small diffusible precursors of PrPres amyloid might flow with brain interstitial fluid (ISF), possibly accounting for the perivascular and intravascular distribution of PrPres amyloid. We previously reported that PrPres amyloid in scrapie-infected transgenic mice appeared to delay clearance of microinjected brain ISF tracer molecules. Results Here we studied distribution of PrPres amyloid on capillaries, arteries and veins to test whether vascular specificity of PrPres corresponded to distribution of ISF tracer molecules. To distinguish PrPres-positive arteries from veins and capillaries, scrapie-infected mouse brains were studied by immunodetection of alpha smooth muscle actin. ISF was studied using fluorescein-labeled ovalbumin microinjected into brain as a tracer. In infected preclinical or clinical mice, PrPres was found mostly on capillaries (73-78%). Lower levels were found on arteries (11-14%) and veins (11-13%). Compared to PrPres, ISF tracer was found at higher levels on capillaries (96-97%), and the remaining tracer was found at a skewed ratio of 4 to 1 on arteries and veins respectively. Conclusions PrPres association with blood vessels suggested that ISF flow might transport diffusible PrPres precursor molecules to perivascular sites. However, the different vascular specificity of PrPres and ISF tracer indicated that ISF flow did not alone control PrPres dissemination. Possibly blood vessel basement membrane (BM) components, such as glucosaminoglycans, might concentrate small PrPres aggregates and serve as scaffolds for PrP conversion on multiple vessel types.
    Full-text · Article · Jun 2013
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    • "The PNS is primarily involved in prion transport to the CNS (reviewed by Heikenwalder et al., 2007) and membrane-anchored PrP C expression within the PNS is required (Blättler et al., 1997; Klingeborn et al., 2011; Race et al., 2000). However, how prions spread along peripheral nerves remains unclear. "
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    ABSTRACT: In naturally acquired transmissible spongiform encephalopathies, the pathogenic agents or prions spread from the sites of initial peripheral uptake or replication to the brain where they cause progressive and fatal neurodegeneration. Routing via the peripheral nervous system is considered as one of the main pathways to attain the central nervous system. Replication of prions in Schwann cells is viewed as a potentially important parameter for efficient prion spread along nerves. Here we used a Cre-loxP mouse transgenetic approach to disrupt PrPC specifically in myelinating Schwann cells. Despite the use of infection routes targeting highly myelinated nerves, there was no alteration in mouse prion pathogenesis, suggesting that conversion-dependent, centripetal spread of prions does not crucially rely on PrPC expressed by myelinating Schwann cells.
    Full-text · Article · Feb 2013 · Journal of General Virology
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