Chronic wasting disease prion trafficking via the autonomic nervous system.

Chronic wasting disease (CWD) is a fatal spongiform encephalopathy that is efficiently transmitted among members of the mammalian family Cervidae, including deer, elk, and moose. Typical of prion diseases, CWD is characterized by the conversion of the native protease-sensitive protein PrP(C) to a protease-resistant isoform, denoted PrP(RES). In native species, spread of the disease likely results from the ingestion of prion-containing excreta, including urine, saliva, or feces. Although cervid prion protein-expressing transgenic [Tg(CerPrP)] mice have been shown to be effective surrogates of natural CWD, uncertainties remain regarding the mechanisms by which CWD prions traffic in vivo, including the manner by which CWD prions traffic from the gastrointestinal tract to the central nervous system. We used elk prion protein-expressing transgenic [Tg(CerPrP-E)] mice, infected by three different routes of inoculation, and tissue-based IHC to elucidate that centripetal and centrifugal CWD prion transit pathways involve cells and fibers of the autonomic nervous systems, including the enteric nervous system and central autonomic network. Moreover, we identified CWD PrP(RES) associated with the cell bodies and processes of enteric glial cells within the enteric nervous system of CWD-infected Tg(CerPrP-E) mice. The present findings demonstrate the importance of the peripheral and central autonomic networks in CWD neuroinvasion and neuropathogenesis and suggest that enteroglial cells may facilitate the shedding of prions via the intestinal tract.

Orally administered prion protein is incorporated by m cells and spreads into lymphoid tissues with macrophages in prion protein knockout mice.

Transmissible spongiform encephalopathies are fatal neurodegenerative diseases. Infection by the oral route is assumed to be important, although its pathogenesis is not understood. Using prion protein (PrP) knockout mice, we investigated the sequence of events during the invasion of orally administered PrPs through the intestinal mucosa and the spread into lymphoid tissues and the peripheral nervous system. Orally administered PrPs were incorporated by intestinal epitheliocytes in the follicle-associated epithelium and villi within 1 hour. PrP-positive cells accumulated in the subfollicle region of Peyer's patches a few hours thereafter. PrP-positive cells spread toward the mesenteric lymph nodes and spleen after the accumulation of PrPs in the Peyer's patches. The number of PrP molecules in the mesenteric lymph nodes and spleen peaked at 2 days and 6 days after inoculation, respectively. The epitheliocytes in the follicle-associated epithelium incorporating PrPs were annexin V-positive microfold cells and PrP-positive cells in Peyer's patches and spleen were CD11b-positive and CD14-positive macrophages. Additionally, PrP-positive cells in Peyer's patches and spleen were detected in the vicinity of peripheral nerve fibers in the early stages of infection. These results indicate that orally delivered PrPs were incorporated by microfold cells promptly after challenge and that macrophages might act as a transporter of incorporated PrPs from the Peyer's patches to other lymphoid tissues and the peripheral nervous system.

In vivo biodistribution of prion- and GM1-targeted polymersomes following intravenous administration in mice.

Due to the aging of the population, the incidence of neurodegenerative diseases, such as Parkinson's and Alzheimer's, is expected to grow and, hence, the demand for adequate treatment modalities. However, the delivery of medicines into the brain for the treatment of brain-related diseases is hampered by the presence of a tight layer of endothelial cells that forms the blood-brain barrier (BBB). Furthermore, most conventional drugs lack stability and/or bioavailability. These obstacles can be overcome by the application of nanocarriers, in which the therapeutic entity has been incorporated, provided that they are effectively targeted to the brain endothelial cell layer. Drug nanocarriers decorated with targeting ligands that bind BBB receptors may accumulate efficiently at/in brain microvascular endothelium and hence represent a promising tool for brain drug delivery. Following the accumulation of drug nanocarriers at the brain vasculature, the drug needs to be transported across the brain endothelial cells into the brain. Transport across brain endothelial cells can occur via passive diffusion, transport proteins, and the vesicular transport pathways of receptor-mediated and adsorptive-mediated transcytosis. When a small lipophilic drug is released from its carrier at the brain vasculature, it may enter the brain via passive diffusion. On the other hand, the passage of intact nanocarriers, which is necessary for the delivery of larger and more hydrophilic drugs into brain, may occur via active transport by means of transcytosis. In previous work we identified GM1 ganglioside and prion protein as potential transcytotic receptors at the BBB. GM1 is a glycosphingolipid that is ubiquitously present on the endothelial surface and capable of acting as the transcytotic receptor for cholera toxin B. Likewise, prion protein has been shown to have transcytotic capacity at brain endothelial cells. Here we determine the transcytotic potential of polymersome nanocarriers functionalized with GM1- and prion-targeting peptides (G23, P50 and P9), that were identified by phage display, in an in vitro BBB model. In addition, the biodistribution of polymersomes functionalized with either the prion-targeting peptide P50 or the GM1-targeting peptide G23 is determined following intravenous injection in mice. We show that the prion-targeting peptides do not induce efficient transcytosis of polymersomes across the BBB in vitro nor induce accumulation of polymersomes in the brain in vivo. In contrast, the G23 peptide is shown to have transcytotic capacity in brain endothelial cells in vitro, as well as a brain-targeting potential in vivo, as reflected by the accumulation of G23-polymersomes in the brain in vivo at a level comparable to that of RI7217-polymersomes, which are targeted toward the transferrin receptor. Thus the G23 peptide seems to serve both of the requirements that are needed for efficient brain drug delivery of nanocarriers. An unexpected finding was the efficient accumulation of G23-polymersomes in lung. In conclusion, because of its combined brain-targeting and transcytotic capacity, the G23 peptide could be useful in the development of targeted nanocarriers for drug delivery into the brain, but appears especially attractive for specific drug delivery to the lung.

Defining the pathway of worm-like amyloid fibril formation by the mouse prion protein by delineation of the productive and unproductive oligomerization reactions.

Aggregation reactions of proteins leading to amyloid fibril formation are often characterized by early transient accumulation of a heterogeneous population of soluble oligomers differing in size and structure. Delineating the kinetic roles of the different oligomeric forms in fibril formation has been a major challenge. The aggregation of the mouse prion protein to form worm-like amyloid fibrils at low pH is known to proceed via a ß-rich oligomer ensemble, which is shown here to be comprised of two subpopulations of oligomers that differ in size and internal structure. The relative populations of the two oligomers can be tuned by varying the concentration of NaCl present. By demonstrating that the apparent rate constant for the formation of fibrils is dependent linearly on the concentration of the larger oligomer and is independent of the concentration of the smaller oligomer, we show that the larger oligomer is a productive intermediate that accumulates on the direct pathway of aggregation from monomer to worm-like fibrils. The smaller oligomer is shown to be populated off the pathway of the larger oligomer and, hence, is not directly productive for fibril formation. The relative populations of the two oligomers can also be tuned by single-amino acid residue changes in the sequence of the protein. The different protein variants yield worm-like fibrils of different lengths, and the apparent rate of formation of the fibrils by the mutant variants is also shown to be dependent on the concentration of the larger but not of the smaller oligomer formed.

Small-molecule aggregates inhibit amyloid polymerization.

Many amyloid inhibitors resemble molecules that form chemical aggregates, which are known to inhibit many proteins. Eight known chemical aggregators inhibited amyloid formation of the yeast and mouse prion proteins Sup35 and recMoPrP in a manner characteristic of colloidal inhibition. Similarly, three known anti-amyloid molecules inhibited beta-lactamase in a detergent-dependent manner, which suggests that they too form colloidal aggregates. The colloids localized to preformed fibers and prevented new fiber formation in electron micrographs. They also blocked infection of yeast cells with Sup35 prions, which suggests that colloidal inhibition may be relevant in more biological milieus.

Prions adhere to soil minerals and remain infectious.

An unidentified environmental reservoir of infectivity contributes to the natural transmission of prion diseases (transmissible spongiform encephalopathies [TSEs]) in sheep, deer, and elk. Prion infectivity may enter soil environments via shedding from diseased animals and decomposition of infected carcasses. Burial of TSE-infected cattle, sheep, and deer as a means of disposal has resulted in unintentional introduction of prions into subsurface environments. We examined the potential for soil to serve as a TSE reservoir by studying the interaction of the disease-associated prion protein (PrP(Sc)) with common soil minerals. In this study, we demonstrated substantial PrP(Sc) adsorption to two clay minerals, quartz, and four whole soil samples. We quantified the PrP(Sc)-binding capacities of each mineral. Furthermore, we observed that PrP(Sc) desorbed from montmorillonite clay was cleaved at an N-terminal site and the interaction between PrP(Sc) and Mte was strong, making desorption of the protein difficult. Despite cleavage and avid binding, PrP(Sc) bound to Mte remained infectious. Results from our study suggest that PrP(Sc) released into soil environments may be preserved in a bioavailable form, perpetuating prion disease epizootics and exposing other species to the infectious agent.

Fate of prions in soil: trapped conformation of full-length ovine prion protein induced by adsorption on clays.

Studying the mechanism of retention of ovine prion protein in soils will tackle the environmental aspect of potential dissemination of scrapie infectious agent. We consider the surface-induced conformational changes that the recombinant ovine prion protein (ovPrP) may undergo under different pH conditions when interacting with soil minerals of highly adsorptive capacities such as montmorillonite. The conformational states of the full-length ovine prion protein adsorbed on the electronegative clay surface are compared to its solvated state in deuterated buffer in the pD range 3.5-9, using FTIR spectroscopy. The in vitro pH-induced conversion of the alpha-helical monomer of ovPrP into oligomers of beta-like structure prone to self-aggregation does not occur when the protein is adsorbed on the clay surface. The conformation of the trapped ovPrP molecules on montmorillonite is pH-independent and looks like that of the ovPrP solvated state at pD higher than 7, suggesting the major role of Arg and Lys residues in the electrostatic origin of adsorption. The uneven distribution of positively and negatively charged residues of the ovPrP protein would promote a favored orientation of the protein towards the clay, so that not only the basic residues embedded in the N-terminal flexible part but also external basic residues in the globular part of the protein might participate to the attractive interaction. From these results, it appears unlikely that the interaction of normal prions (PrP(C)) with soil clay surfaces could induce a change of conformation leading to the pathogenic form of prions (PrP(Sc)).

Prions and the blood and immune systems.

Prion diseases take a number of forms in animals and humans. They are caused by conformational change in widely expressed prion protein leading to the formation of intracellular aggregates. Although the main focus of disease is the central nervous system, it is known that involvement of the immune system occurs in peripherally transmitted disease in particular. Animal experiments suggest that in some prion diseases follicular dendritic cells in the germinal centers are a major site of initial accumulation, and that abnormal prion protein and infectivity are detectable in peripheral lymphoid tissue from the earliest phase of disease. This raises the possibility that in a human peripherally transmitted prion disease like variant Creutzfeldt-Jakob disease, further transmission could occur through blood or tissue products or contamination of surgical instrumentation. Indeed two recent reports confirm that this disease has been transmitted by blood, raising significant public health concerns.

Organ distribution of prion proteins in variant Creutzfeldt-Jakob disease.

In this article we give an overview of the transmissible spongiform encephalopathies, with emphasis on the evidence for the distribution of abnormal prions in tissues. The normal prion protein is distributed ubiquitously throughout human body tissues. Endogenous expression of the normal prion protein, as well as auxiliary proteins, plays a part in accumulation of the abnormal prion protein. As exemplified by variant Creutzfeldt-Jakob disease (vCJD) the abnormal prion protein can accumulate in the host lymphoid system, in particular the follicular dendritic cells. The route for the disease-related prion neuroinvasion is likely to involve the peripheral nervous system. An alternative route may involve blood constituents. Both animal studies and studies on vCJD patients suggest a potential for abnormal prion distribution in several peripheral tissues other than the lymphoreticular system. In human beings the abnormal prion has been reported in the brain, tonsils, spleen, lymph node, retina, and proximal optic nerve. Infectivity, although present in peripheral tissues, is at lower levels than in the central nervous system (CNS). Animal models suggest that the growth of infectivity in the CNS is likely to be gradual with maximum values during the clinical phase of disease. That tissues may harbour the abnormal prion, at different levels of infectivity, during the incubation period of the disease raises concerns of iatrogenic transmission of the disease either after surgery, blood transfusion, or accidental organ transplantation from donors in the preclinical phase of the disease.

Transport of prion protein across the blood-brain barrier.

The cellular form of the prion protein (PrP(c)) is necessary for the development of prion diseases and is a highly conserved protein that may play a role in neuroprotection. PrP(c) is found in both blood and cerebrospinal fluid and is likely produced by both peripheral tissues and the central nervous system (CNS). Exchange of PrP(c) between the brain and peripheral tissues could have important pathophysiologic and therapeutic implications, but it is unknown whether PrP(c) can cross the blood-brain barrier (BBB). Here, we found that radioactively labeled PrP(c) crossed the BBB in both the brain-to-blood and blood-to-brain directions. PrP(c) was enzymatically stable in blood and in brain, was cleared by liver and kidney, and was sequestered by spleen and the cervical lymph nodes. Circulating PrP(c) entered all regions of the CNS, but uptake by the lumbar and cervical spinal cord, hypothalamus, thalamus, and striatum was particularly high. These results show that PrP(c) has bidirectional, saturable transport across the BBB and selectively targets some CNS regions. Such transport may play a role in PrP(c) function and prion replication.

Blood clearance of the prion protein introduced by intravenous route in sheep is influenced by host genetic and physiopathologic factors.

BACKGROUND: The risk of transmissible spongiform encephalopathy (TSE) transmission by blood transfusion is dependent on the blood concentrations of the pathologic isoform of prion protein (PrPsc) but may also be influenced by blood concentrations of cellular PrP (PrPc). These concentrations are controlled by the blood clearance of PrP, which has never been evaluated. STUDY DESIGN AND METHODS: The blood (actually plasma) clearance of ovine purified prokaryote recombinant PrP (rPrP) was measured in genotyped and in nephrectomized sheep. The exposure to proteinase K-resistant fragments of PrP (PrPres) after intravenous (IV) administration of scrapie-associated fibrils (SAFs) was also investigated in a sheep. RESULTS: The ARR variant of rPrP was eliminated more rapidly than its VRQ counterpart. The PrPc plasma concentrations in homozygous highly susceptible VRQ sheep were greater than in homozygous ARR-resistant sheep, suggesting that clearance of the ARR variant of PrPc was higher than that of the VRQ variant. The plasma clearance of rPrP was decreased by 52 percent after a bilateral nephrectomy indicating the significant contribution of the kidneys in eliminating rPrP. PrPres was shown to be slowly eliminated after IV administration of scrapie-associated fibrils. CONCLUSION: PrP host genotype and physiopathologic factors could influence the risk of TSE transmission by modulating blood PrP clearance. This risk was increased by the sustained exposure to PrPres after IV administration. It should be noted that although the materials that have been administered (rPrP and SAFs) were not the actual species of interest, they can be of value as probes for investigating PrP clearance mechanisms.

Transportation of prion protein across the intestinal mucosa of scrapie-susceptible and scrapie-resistant sheep.

To determine the mechanisms of intestinal transport of infection, and early pathogenesis, of sheep scrapie, isolated gut-loops were inoculated to ensure that significant concentrations of scrapie agent would come into direct contact with the relevant ileal structures (epithelial, lymphoreticular, and nervous). Gut loops were inoculated with a scrapie brain pool homogenate or normal brain or sucrose solution. After surgery, animals were necropsied at time points ranging from 15 min to 1 month and at clinical end point. Inoculum-associated prion protein (PrP) was detected by immunohistochemistry in villous lacteals and in sub-mucosal lymphatics from 15 min to 3.5 h post-challenge. It was also detected in association with dendritic-like cells in the draining lymph nodes at up to 24 h post-challenge. Replication of infection, as demonstrated by the accumulation of disease-associated forms of PrP in Peyer's patches, was detected at 30 days and sheep developed clinical signs of scrapie at 18-22 months post-challenge. These results indicate discrepancies between the routes of transportation of PrP from the inoculum and sites of de novo-generated disease-associated PrP subsequent to scrapie agent replication. When samples of homogenized inoculum were incubated with alimentary tract fluids in vitro, only trace amounts of protease-resistant PrP could be detected by western blotting, suggesting that the majority of both normal and abnormal PrP within the inoculum is readily digested by alimentary fluids.

Prion distribution in hamster lung and brain following intraperitoneal inoculation.

Prion titres were measured in the lungs and brains of Syrian hamsters after intraperitoneal inoculation with sucrose gradient-purified 263K prions (approximately 10(8) LD50). Prions were detected in the lung of one hamster on day 7, but were not detected in the lungs of any other hamster until day 71. Prions were detected in the lungs of all hamsters sampled thereafter but titres remained low through day 127. Prions were first detected in the brain on day 35 and brain titres increased exponentially until day 127 with a doubling time of about 4.5 days. On day 133, titres averaged 10(8.0) LD50/g in brain and 10(5.0) LD50/g in lung. Two out of the five remaining hamsters were clinically normal but prion titres were not significantly different from those in the clinically affected hamsters. Thus, significant prion titres may be found outside the CNS in clinically normal hamsters.

Novel biological activity of the region (106-126) on human prion sequence.

We report that the synthetic peptide Prp106-126 (KTNMKHMAGAAAAGAVVGGLG-COOH) and the reversed peptide Prp126-106 (GLGGVVAGAAAAGAMHKMNTK-COOH) of human prion (hPrp) can express the decarboxylase activity for oxaloacetate in the presence of trifluoroethanol, similar to that of Oxaldie 1 (LAKLLKALAKLLKK-CONH2) reported previously. The degree of the relative activity of Prp106-126 and Prp126-106 to Oxaldie 1 is 0.47 and 0.21, respectively. Based on this experimental result, we applied the informational system method (ISM) developed by Veljkovic et al. to the amino acid sequence of Prp106-126 and Prp126-106 to extract a common factor. The same spectra were obtained, indicating that the same periodicity may be conserved on their sequences, as a necessary factor for expressing the same biological activity, irrespective of the orientation of the primary sequence.

Cellular uptake of the prion protein fragment PrP106-126 in vitro.

The aetiological agent of prion disease is proposed to be an aberrant isoform of the cell surface glycoprotein known as the prion protein (PrP(c)). This pathological isoform (PrP(Sc)) is abnormally deposited in the extracellular space of diseased CNS. Neurodegeneration in these disease has been shown to be associated with accumulation of PrP(Sc) in affected tissue. To investigate the possible uptake mechanisms that may be required for PrP(Sc)-induced neurodegeneration we studied the cellular trafficking of the neurotoxic fragment, PrP106-126. We were able to detect, by fluorescence microscopy, PrP106-126 inclusions in murine neurones, astrocytes and microglia in vitro. These inclusions were abundant after 24 hour exposure and still present 48h post-exposure. Shorter exposure times yielded only occasional cells with inclusions. Large extracellular aggregates of PrP106-126 could also be detected, which appeared in a time dependent manner. The appearance of inclusions or aggregates was not dependent on PrP(c) expression as determined by exposure of peptides from PrP-null mice. Using transmission electron microscopy and gold particle detection, positively labelled osmiophilic inclusions of peptide could be detected in the cytoplasm of exposed cells. These results demonstrate that cultured cells are capable of sequestering PrP106-126 and may indicate uptake pathways for PrP(Sc) in various cell types. Toxicity of PrP106-126 may thus be mediated via a sequestration pathway that is not effective for this peptide in PrP-null cells.