Spontaneous generation of mammalian prions

Abstract

Prions are transmissible agents that cause lethal neurodegeneration in humans and other mammals. Prions bind avidly to metal surfaces such as steel wires and, when surface-bound, can initiate infection of brain or cultured cells with remarkable efficiency. While investigating the properties of metal-bound prions by using the scrapie cell assay to measure infectivity, we observed, at low frequency, positive assay results in control groups in which metal wires had been coated with uninfected mouse brain homogenate. This phenomenon proved to be reproducible in rigorous and exhaustive control experiments designed to exclude prion contamination. The infectivity generated in cell culture could be readily transferred to mice and had strain characteristics distinct from the mouse-adapted prion strains used in the laboratory. The apparent "spontaneous generation" of prions from normal brain tissue could result if the metal surface, possibly with bound cofactors, catalyzed de novo formation of prions from normal cellular prion protein. Alternatively, if prions were naturally present in the brain at levels not detectable by conventional methods, metal surfaces might concentrate them to the extent that they become quantifiable by the scrapie cell assay.cell culture | scrapie | metal | Creutzfeldt-Jakob disease P rions, the transmissible agents that cause fatal neurodegenerative diseases such as Creutzfeldt-Jakob disease in humans, or bovine spongiform encephalopathy and scrapie in animals, occur in the form of various strains and are composed principally or entirely of aggregates of misfolded cellular prion protein (PrP C ), generally referred to as PrP Sc . Replication comes about by autocatalytic conversion of PrP C to the pathogenic isoform (1).In vitro and in vivo studies using model systems have suggested host-encoded cofactors are required to facilitate the propagation of prions (2-5). A variety of polyanionic compounds, lipids, proteoglycans from brain homogenate or purified protein have been shown to stimulate the conversion of PrP C to PrP Sc in vitro (6-10).Steel wire exposed to scrapie prion-infected brain or brain homogenate acquires an extraordinary infectious potential (11,12). Although the amount of protein bound was undetectable by conventional methods, the wires were as effective in eliciting disease as injection of approximately 10 6 LD 50 units in the form of brain homogenate. We have isolated an N2a neuroblastoma-derived cell line, N2aPK1 (i.e., "PK1") (13), that is highly susceptible to infection by a wide spectrum of murine strains, including RML and 22L, but not ME7 and 301C (13,14). When PK1 cells were grown on RML prion-coated wires, adherent cells became PrP Sc -positive, in contrast to neighboring cells, which remained negative, implying that adherence to the prion-coated surface is a prerequisite for infectivity transfer (15). We exploited these observations to detect prions in RML prion-infected brain homogenates diluted as much as 10 −10 , by adsorbing infectivity to steel wire surfaces and sub...

Spontaneous generation of rapidly transmissible prions in transgenic mice expressing wild-type bank vole prion protein

“…Although infectious prions have been formed spontaneously from WT PrP in vitro (4)(5)(6)(7)(8), there are currently no animal models of sCJD in which expression of WT PrP in the brain leads to spontaneous neurodegeneration. Some lines of transgenic (Tg) or knock-in mice expressing human or mouse PrP containing mutations linked to familial human prion disease develop a spontaneous neurodegenerative illness (9)(10)(11)(12)(13)(14).…”

Pathogenic Mutations within the Hydrophobic Domain of the Prion Protein Lead to the Formation of Protease-Sensitive Prion Species with Increased Lethality

“…Continued passage of infected cells leads to an increase in rPrP Sc levels in MoPrP-and G113V-infected RK13 cells, although rPrP Sc levels remain low in A116V-RK13 cells (data not shown). In contrast, long-term passage of control (noninfected) cells did not result in the spontaneous formation of PrP Sc , as has been reported in other studies (52). No differences in cytotoxicity and cell growth rates were observed in RK13 cells expressing MoPrP or mutants either prior to or following exposure to prions, indicating that the observed reduction in rPrP Sc levels is not due to cell death (data not shown).…”

An Auto-Catalytic Surface for Conformational Replication of Amyloid Fibrils—Genesis of an Amyloid World?

“…There are other interesting examples in the literature where these phenomena have been observed. The activity of surface aligned assemblies of misfolded insulin molecules reported here do resemble the extreme infectivity efficiency (per molecule count) seen in prion diseases where steel wires have been shown to be essentially coated with monolayers of prion protein (Flechsig et al 2001;Edgeworth et al 2010). Surface mediated alignment hence likely allows efficient lowering of the activation energy barrier for protein conformational conversion.…”