Food-borne transmission of prions can lead to infection of the gastrointestinal tract and neuroinvasion via the splanchnic and vagus nerves. Here we report that the transmission of transmissible mink encephalopathy (TME) is 100,000-fold more efficient by inoculation of prions into the tongues of hamsters than by oral ingestion. The incubation period following TME agent (hereinafter referred to as TME) inoculation into the lingual muscles was the shortest among the five nonneuronal routes of inoculation, including another intramuscular route. Deposition of the abnormal isoform of the prion protein, PrP Sc , was first detected in the tongue and submandibular lymph node at 1 to 2 weeks following inoculation of the tongue with TME. PrP Sc deposits in the tongue were associated with individual axons, and the initial appearance of TME in the brain stem was found in the hypoglossal nucleus at 2 weeks postinfection. At later time points, PrP Sc was localized to brain cell groups that directly project to the hypoglossal nucleus, indicating the transneuronal spread of TME. TME PrP Sc entry into the brain stem preceded PrP Sc detection in the rostral cervical spinal cord. These results demonstrate that TME can replicate in both the tongue and regional lymph nodes but indicate that the faster route of brain invasion is via retrograde axonal transport within the hypoglossal nerve to the hypoglossal nucleus. Topical application of TME to a superficial wound on the surface of the tongue resulted in a higher incidence of disease and a shorter incubation period than with oral TME ingestion. Therefore, abrasions of the tongue in livestock and humans may predispose a host to oral prion infection of the tongue-associated cranial nerves. In a related study, PrP Sc was detected in tongues following the intracerebral inoculation of six hamster-adapted prion strains, which demonstrates that prions can also travel from the brain to the tongue in the anterograde direction along the tongue-associated cranial nerves. These findings suggest that food products containing ruminant or cervid tongue may be a potential source of prion infection for humans.Prion diseases are fatal neurodegenerative diseases of humans, livestock, and cervids. The majority of prion diseases have an infectious etiology, and food-borne infection has been linked to the transmission of transmissible mink encephalopathy (TME), bovine spongiform encephalopathy (BSE), and kuru in humans (21,23,58). Indirect evidence suggests that oral infection is involved in the transmission of other prion diseases, such as scrapie in sheep, chronic wasting disease (CWD) in deer and elk, and variant Creutzfeldt-Jakob disease in humans (2,13,26,47,52). The experimental ingestion of high doses of scrapie agent (hereinafter referred to as scrapie) has been used to determine the sites of scrapie replication in peripheral tissues and the routes by which the disease spreads to the peripheral and central nervous systems (24,33,36,38,54).The disease-specific isoform of the prion protein, PrP Sc ...

Prion strains are characterized by differences in the outcome of disease, most notably incubation period and neuropathological features. While it is established that the disease specific isoform of the prion protein, PrPSc, is an essential component of the infectious agent, the strain-specific relationship between PrPSc properties and the biological features of the resulting disease is not clear. To investigate this relationship, we examined the amplification efficiency and conformational stability of PrPSc from eight hamster-adapted prion strains and compared it to the resulting incubation period of disease and processing of PrPSc in neurons and glia. We found that short incubation period strains were characterized by more efficient PrPSc amplification and higher PrPSc conformational stabilities compared to long incubation period strains. In the CNS, the short incubation period strains were characterized by the accumulation of N-terminally truncated PrPSc in the soma of neurons, astrocytes and microglia in contrast to long incubation period strains where PrPSc did not accumulate to detectable levels in the soma of neurons but was detected in glia similar to short incubation period strains. These results are inconsistent with the hypothesis that a decrease in conformational stability results in a corresponding increase in replication efficiency and suggest that glia mediated neurodegeneration results in longer survival times compared to direct replication of PrPSc in neurons.

This disease continues to emerge in cervids in the United States and Canada.

Understanding protein adsorption kinetics to surfaces is of importance for various environmental and biomedical applications. Adsorption of bovine serum albumin to various self-assembled monolayer surfaces including neutral and charged hydrophilic and hydrophobic surfaces was investigated using in-situ combinatorial quartz crystal microbalance with dissipation and spectroscopic ellipsometry. Adsorption of bovine serum albumin varied as a function of surface properties, bovine serum albumin concentration and pH value. Charged surfaces exhibited a greater quantity of bovine serum albumin adsorption, a larger bovine serum albumin layer thickness, and increased density of bovine serum albumin protein compared to neutral surfaces at neutral pH value. The quantity of adsorbed bovine serum albumin protein increased with increasing bovine serum albumin concentration. After equilibrium sorption was reached at pH 7.0, desorption of bovine serum albumin occurred when pH was lowered to 2.0, which is below the isoelectric point of bovine serum albumin. Our data provide further evidence that combinatorial quartz crystal microbalance with dissipation and spectroscopic ellipsometry is a sensitive analytical tool to evaluate attachment and detachment of adsorbed proteins in systems with environmental implications.

Interspecies transmission of the transmissible spongiform encephalopathies (TSEs), or prion diseases, can result in the adaptation and selection of TSE strains with an expanded host range and increased virulence such as in the case of bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease. To investigate TSE strain adaptation, we serially passaged a biological clone of transmissible mink encephalopathy (TME) into Syrian golden hamsters and examined the selection of distinct strain phenotypes and conformations of the disease-specific isoform of the prion protein (PrP Sc ). The long-incubation-period drowsy (DY) TME strain was the predominate strain, based on the presence of its strain-specific PrP Sc following interspecies passage. Additional serial passages in hamsters resulted in the selection of the hyper (HY) TME PrP Sc strain-dependent conformation and its short incubation period phenotype unless the passages were performed with a low-dose inoculum (e.g., 10؊5 dilution), in which case the DY TME clinical phenotype continued to predominate. For both TME strains, the PrP Sc strain pattern preceded stabilization of the TME strain phenotype. These findings demonstrate that interspecies transmission of a single cloned TSE strain resulted in adaptation of at least two strain-associated PrP Sc conformations that underwent selection until one type of PrP Sc conformation and strain phenotype became predominant. To examine TME strain selection in the absence of host adaptation, hamsters were coinfected with hamster-adapted HY and DY TME. DY TME was able to interfere with the selection of the short-incubation HY TME phenotype. Coinfection could result in the DY TME phenotype and PrP Sc conformation on first passage, but on subsequent passages, the disease pattern converted to HY TME. These findings indicate that during TSE strain adaptation, there is selection of a strain-specific PrP Sc conformation that can determine the TSE strain phenotype.

Neurotoxicity in all prion disorders is believed to result from the accumulation of PrP-scrapie (PrPSc), a β-sheet rich isoform of a normal cell-surface glycoprotein, the prion protein (PrPC). Limited reports suggest imbalance of brain iron homeostasis as a significant associated cause of neurotoxicity in prion-infected cell and mouse models. However, systematic studies on the generality of this phenomenon and the underlying mechanism(s) leading to iron dyshomeostasis in diseased brains are lacking. In this report, we demonstrate that prion disease–affected human, hamster, and mouse brains show increased total and redox-active Fe (II) iron, and a paradoxical increase in major iron uptake proteins transferrin (Tf) and transferrin receptor (TfR) at the end stage of disease. Furthermore, examination of scrapie-inoculated hamster brains at different timepoints following infection shows increased levels of Tf with time, suggesting increasing iron deficiency with disease progression. Sporadic Creutzfeldt-Jakob disease (sCJD)–affected human brains show a similar increase in total iron and a direct correlation between PrP and Tf levels, implicating PrPSc as the underlying cause of iron deficiency. Increased binding of Tf to the cerebellar Purkinje cell neurons of sCJD brains further indicates upregulation of TfR and a phenotype of neuronal iron deficiency in diseased brains despite increased iron levels. The likely cause of this phenotype is sequestration of iron in brain ferritin that becomes detergent-insoluble in PrPSc-infected cell lines and sCJD brain homogenates. These results suggest that sequestration of iron in PrPSc–ferritin complexes induces a state of iron bio-insufficiency in prion disease–affected brains, resulting in increased uptake and a state of iron dyshomeostasis. An additional unexpected observation is the resistance of Tf to digestion by proteinase-K, providing a reliable marker for iron levels in postmortem human brains. These data implicate redox-iron in prion disease–associated neurotoxicity, a novel observation with significant implications for prion disease pathogenesis.

The only known difference between the cellular (PrP C ) and scrapie-specific (PrP Sc ) isoforms of the prion protein is conformational. Because disruption of PrP Sc structure decreases scrapie infectivity, restoration of the disease-specific conformation should restore infectivity. In this study, disruption of PrP Sc (as monitored by the loss of proteinase K resistance) by guanidine hydrochloride (GdnHCl) resulted in decreased infectivity. Upon dilution of the GdnHCl, protease resistance of PrP was restored and infectivity was regained. The addition of copper facilitated restoration of both infectivity and protease resistance of PrP in a subset of samples that did not renature by the simple dilution of the GdnHCl. These data demonstrate that loss of scrapie infectivity can be a reversible process and that copper can enhance this restoration of proteinase K resistance and infectivity. PrP1 is a highly conserved, host-encoded sialoglycoprotein that may play a role in normal synaptic function and circadian rhythms (1, 2). This host protein (PrP C ) is present in the brain and other tissues and is sensitive to proteinase K (PK) digestion (3). During the course of a scrapie infection, PrP C undergoes a post-translational modification to a disease-specific isoform (PrP Sc ) that has increased resistance to limited PK digestion. This modification appears to be solely conformational with PrP Sc having a higher ␤-sheet content than PrP C (4 -7). In vitro cell culture studies have demonstrated that PrP C is the precursor to PrP Sc (8, 9). Inhibition of the migration of PrP C to the cell surface blocks the formation of PrP Sc , confirming that PrP Sc arises via alternate or misprocessing of PrP Sc (8). PrP Sc is resistant to limited PK digestion (10, 11), but upon treatment with GdnHCl, the PrP denatures (12) and becomes sensitive to protease digestion (13). The loss of PK resistance correlates well with loss of infectivity of the PrP Sc -enriched preparation. In this study, we examined the ability of GdnHCl-denatured, PrP Sc -enriched preparations to renature. Renaturation was monitored by Western blot analysis for the presence of PK-resistant PrP and animal bioassay for infectivity. The capacity of PrP to bind copper led us to determine the effect of this transition metal on the renaturation process. EXPERIMENTAL PROCEDURESDenaturation/Renaturation Reactions-Brains were removed from clinically affected hamsters infected with the 263K strain of hamsteradapted scrapie agent, flash frozen, and stored at Ϫ80°C. PrP Sc -enriched fractions were prepared to the P4 pellet step following a modification of Bolton et al. (14) that excludes the PK digestion. The P4 pellet was resuspended in buffered saline containing glycerol (10 mM Tris, pH 7.4, 130 mM NaCl, 5% glycerol), and the protein concentration was determined by the BCA protein assay (Pierce). The reaction conditions for the denaturation and subsequent renaturation were based upon the cell-free conversion reactions described by Kocisko et al. (13). PrP Sc -enriched preparat...

Chronic wasting disease (CWD), a member of the transmissible spongiform encephalopathies (TSEs), was first identified in captive mule and black-tail deer in 1967. Due to the failure to transmit CWD to rodents, we investigated the use of ferrets (Mustela putorius furo) as a small animal model of CWD. The inoculation of CWD into ferrets resulted in an incubation period of 17-21 months on primary passage that shortened to 5 months by the third ferret passage. The brain tissue of animals inoculated with ferret-passaged CWD exhibited spongiform degeneration and reactive astrocytosis. Western blot analysis of ferret-passaged CWD demonstrated the presence of PrP-res. Unlike mule deer CWD, ferret-passaged CWD was transmissible to Syrian golden hamsters (Mesocricetus auratus). Increasing the passage number of CWD in ferrets increased the pathogenicity of the agent for hamsters. This increase in host range of a field isolate on interspecies transmission emphasizes the need for caution when assessing the potential risk of transmission of TSEs, such as bovine spongiform encephalopathy, to new host species.