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

Abstract

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...

Prion protein glycans reduce intracerebral fibril formation and spongiosis in prion disease

“…Prion aggregates accumulate during the conversion of the cellular prion protein, PrP C , into a β-sheet rich multimer known as PrP Sc (12,13). Although the PrP Sc structure has not yet been solved, several lines of evidence suggest that PrP posttranslational modifications (PTMs), a glycophosphatidylinositol (GPI) anchor and 2 N-linked glycans (14)(15)(16)(17)(18), impact the prion conformation (19)(20)(21), species barriers (22,23), and disease progression (24,25). Previous studies have demonstrated that PrP Sc maintains the sialylated glycans (α2,6-linked) (17,26) and that sialylation influences prion conversion and intracellular trafficking (27)(28)(29)(30)(31), yet how these bulky, anionic glycans modify prion assembly and the disease phenotype remains unresolved (32).…”

Lack of Transmission of Chronic Wasting Disease to Cynomolgus Macaques

“…The zoonotic transmission of prion disease from animals to humans appears to vary with different species and prion agents. For example, in spite of likely exposures over the last 200 years, there is little evidence of transmission of scrapie from sheep to humans (5)(6)(7)(8). However, there is strong evidence for the transmission of bovine spongiform encephalopathy (BSE) from cattle to humans albeit at a very low frequency (9)(10)(11).…”

Shedding light on prion disease

“…Generation of prions seems to depend on more than just formation of PrP Sc and likely requires its assembly into unique structures. 99 A recent study described higher infectivity upon prion-challenge in mice expressing anchorless PrP C compared to wild type mice 106. However, since in this study the effect was only seen in recipient mice with dramatic overexpression of PrP C , results cannot be compared to our study where physiological shedding of PrP C is only abolished in a small subset of total brain cells 39.…”