Strain-specific viral properties of variant Creutzfeldt-Jakob disease (vCJD) are encoded by the agent and not by host prion protein

Decellularized small intestine scaffolds: a potential xenograft for restoration of intestinal perforation

Small intestine perforation is a serious medical condition that requires immediate medical attention. The traditional course of treatment entails resection followed by anastomosis; however, it has complications such as small bowel syndrome (SBS), anastomotic leakage, and fistula formation. Here, a novel strategy is demonstrated, that utilizes the xenogeneic, decellularized goat small intestine as a patch for small intestine regeneration in cases of intestinal perforation. The goat small intestine scaffold underwent sodium dodecyl sulfate decellularization, which revealed consistent, quick, and effective decellularization. Decellularization contributed the least amount of extracellular matrix degradation while maintaining the intestinal architecture. By implanting the decellularized goat small intestine scaffolds (DGSIS) on the chorioallantoic membrane (CAM), no discernible loss of angiogenesis was seen in the CAM region, and this enabled the DGSIS to be evaluated for biocompatibility in ovo. The DGSIS was then xeno-transplanted as a patch on a small intestine perforation rat model. After 30 days post transplant, barium salt used as contrast gastrointestinal X-ray imaging revealed no leakage or obstruction in the small intestine. Histology, scanning electron microscopy, and immunohistochemistry assisted in analyzing the engraftment of host cells into the xeno patch. The xeno-patch expressed high levels of E-cadherin, α-smooth muscle actin (α-SMA), Occludin, Zonnula occluden (ZO-1), Ki 67, and Na+/K+-ATPase. The xeno-patch was consequently recellularized and incorporated into the host without causing an inflammatory reaction. As an outcome, decellularized goat small intestine was employed as a xenograft and could be suitable for regeneration of the perforated small intestine.

Reduced Expression of Prion Protein With Increased Interferon-β Fail to Limit Creutzfeldt-Jakob Disease Agent Replication in Differentiating Neuronal Cells

Immortalized uninfected septal (SEP) neurons proliferate but after physiological mitotic arrest they express differentiated neuronal characteristics including enhanced cell-to-cell membrane contacts and ≥ 8 fold increases in host prion protein (PrP). We compared proliferating uninfected and Creutzfeldt-Jakob Disease (CJD) agent infected cells with their arrested counterparts over 33 days by quantitative mRNA and protein blot analyses. Surprisingly, uninfected arrested cells increased interferon-β (IFN-β) mRNA by 2.5–8 fold; IFN-β mRNA elevations were not previously associated with neuronal differentiation. SEP cells with high CJD infectivity titers produced a much larger 40–68-fold increase in IFN-β mRNA, a classic host anti-viral response that is virucidal for RNA but not DNA viruses. High titers of CJD agent also induced dramatic decreases in host PrP, a protein needed for productive agent replication. Uninfected arrested cells produced large sustained 20–30-fold increases in PrP mRNA and protein, whereas CJD arrested cells showed only transient small 5-fold increases in PrP. A > 10-fold increase in infectivity, but not PrP misfolding, induced host PrP reductions that can limit CJD agent replication. In contrast to neuronal lineage cells, functionally distinct migratory microglia with high titers of CJD agent do not induce an IFN-β mRNA response. Because they have 1/50th of PrP of an average brain cell, microglia would be unable to produce the many new infectious particles needed to induce a large IFN-β response by host cells. Instead, microglia and related cells can be persistent reservoirs of infection and spread. Phase separations of agent-associated molecules in neurons, microglia and other cell types can yield new insights into the molecular structure, persistent, and evasive behavior of CJD-type agents.

Development of decellularization protocol for caprine small intestine submucosa as a biomaterial

Decellularized animal tissues have been proven to be promising biomaterials for various tissue engineering (TE) applications. Among various animal tissues, small intestine submucosa (SIS) has gained attention of many researchers due to its easy availability from the abattoir waste, excellent physicochemical and biological characteristics of a good biomaterial. In this study, Caprine SIS was decellularized to get decellularized caprine SIS (DG-SIS). For decellularization, several physical, chemical and enzymatic protocols have been described in the literature. To optimize the decellularization of caprine SIS, several decellularization protocol (DP), including an in-house developed by us, had been attempted, and effect of the different DPs on the obtained DG-SIS were assessed in terms of decellularization, physiochemical and biological properties. All the DPs differ in terms of decellularization, but three DPs where ionic detergent like sodium dodecyl sulphate (SDS) has been used, largely affect the native composition (e.g. glycosaminoglycans (GAGs)), biological properties and other physiochemical properties of the G-SIS as compared to the DP that uses hypertonic solution of potassium iodide (KI) and non-ionic detergent (TritonX-100). The obtained DG-SISs were fibrous, hemocompatible, biocompatible, hydrophilic, biodegradable and exhibited significant antibacterial activity. Therefore, the DG-SIS will be a prospective biomaterial for TE applications.

Curcumin in decellularized goat small intestine submucosa for wound healing and skin tissue engineering

Biomaterials derived from extracellular matrices (ECMs) were extensively used for skin tissue engineering and wound healing. ECM is a complex network of biomolecules (e.g., proteins), which provide organizational support to cells for growth. Thus, ECM could be an ideal biomaterial for fabricating the scaffold. However, oxidative stress and biofilm formation at the wound site remains a major challenge that could be neutralized using herbal ingredients (e.g., curcumin). In this study, ECM was extracted from the biowaste of the goat abattoir by using decellularization. The goat small intestine submucosa (G-SIS) is decellularized to obtain the decellularized G-SIS (DG-SIS) and curcumin (in different concentrations) was incorporated in the DG-SIS to fabricate curcumin-embedded DG-SIS scaffolds. Changes brought by increasing the concentrations of the curcumin in DG-SIS were observed in various properties, including free radical scavenging and antibacterial properties. Results depicted that the scaffolds are porous, biodegradable, biocompatible, antibacterial, and hydrophilic and showed sustained release of curcumin. Besides, it showed free radicals scavenging property. The porosity and hydrophilicity of the scaffolds were decreased with an increase in the curcumin content. However, biodegradability, free radical scavenging, biocompatibility, and antibacterial properties of the scaffolds increased with an increase in the curcumin content. The DG-SIS scaffold containing 1 wt % of curcumin may be a potential biomaterial for wound-healing and skin tissue engineering.

Decellularization of caprine esophagus using fruit pericarp extract of Sapindus mukorossi

Biological detergents like sodium deoxycholate, sodium dodecyl sulphate and Triton X-100 impairs the collagenous and non-collagenous proteins, glycosaminoglycans and growth factors. Further, certain chemical and enzymes are responsible for residual cytotoxicity in the decellularized extracellular matrix. The main focus of this study was to explore the decellularization property of soap nut pericarp extract (SPE) for development of decellularized tubular esophageal scaffold. For this 2.5, 5.0 and 10% concentrations of SPE were used for decellularization of caprine esophageal tissues. Histological analysis of hematoxylin and eosin and Masson's trichrome stained tissue samples confirmed decellularization with preservation of extracellular matrix microarchitecture. Scanning electron microscopic images of luminal surface of decellularized esophageal matrix showed randomly oriented collagen fibres with large interconnected pores and cells were absent. However, the external surface was more textured with fibrous structures and collagen fibres were well preserved. DAPI stained decellularized tissues revealed complete removal of nuclear components, verified by DNA content measurement and SDS-PAGE. The FTIR spectra of decellularized esophagus shows absorption peaks of amide A, B, I, II and III. Elastic modulus of the decellularized esophagus scaffolds increased (P > 0.05) as compared to native tissues. Histological and scanning electron microscopic evaluation of in vitro seeded scaffolds showed attachment and growth of primary chicken embryo fibroblasts over and within the decellularized scaffolds. It was concluded that 5% SPE is ideal for preparation of cytocompatible decellularized caprine esophageal scaffold with well-preserved extracellular matrix architecture and, may be used as an alternative to biological detergents and other chemicals.

Cell biology of prion infection

The development of multiple cell culture models of prion infection over the last two decades has led to a significant increase in our understanding of how prions infect cells. In particular, new techniques to distinguish exogenous from endogenous prions have allowed us for the first time to look in depth at the earliest stages of prion infection through to the establishment of persistent infection. These studies have shown that prions can infect multiple cell types, both neuronal and nonneuronal. Once in contact with the cell, they are rapidly taken up via multiple endocytic pathways. After uptake, the initial replication of prions occurs almost immediately on the plasma membrane and within multiple endocytic compartments. Following this acute stage of prion replication, persistent prion infection may or may not be established. Establishment of a persistent prion infection in cells appears to depend upon the achievement of a delicate balance between the rate of prion replication and degradation, the rate of cell division, and the efficiency of prion spread from cell to cell. Overall, cell culture models have shown that prion infection of the cell is a complex and variable process which can involve multiple cellular pathways and compartments even within a single cell.

What Makes a Prion: Infectious Proteins From Animals to Yeast

While philosophers in ancient times had many ideas for the cause of contagion, the modern study of infective agents began with Fracastoro's 1546 proposal that invisible "spores" spread infectious disease. However, firm categorization of the pathogens of the natural world would need to await a mature germ theory that would not arise for 300 years. In the 19th century, the earliest pathogens described were bacteria and other cellular microbes. By the close of that century, the work of Ivanovsky and Beijerinck introduced the concept of a virus, an infective particle smaller than any known cell. Extending into the early-mid-20th century there was an explosive growth in pathogenic microbiology, with a cellular or viral cause identified for nearly every transmissible disease. A few occult pathogens remained to be discovered, including the infectious proteins (prions) proposed by Prusiner in 1982. This review discusses the prions identified in mammals, yeasts, and other organisms, focusing on the amyloid-based prions. I discuss the essential biochemical properties of these agents and the application of this knowledge to diseases of protein misfolding and aggregation, as well as the utility of yeast as a model organism to study prion and amyloid proteins that affect human and animal health. Further, I summarize the ideas emerging out of these studies that the prion concept may go beyond proteinaceous infectious particles and that prions may be a subset of proteins having general nucleating or seeding functions involved in noninfectious as well as infectious pathogenic protein aggregation.

CJD and Scrapie Require Agent-Associated Nucleic Acids for Infection

Unlike Alzheimer's and most other neurodegenerative diseases, Transmissible Spongiform Encephalopathies (TSEs) are all caused by actively replicating infectious particles of viral size and density. Different strain-specific TSE agents cause CJD, kuru, scrapie and BSE, and all behave as latent viruses that evade adaptive immune responses and can persist for years in lymphoreticular tissues. A foreign viral structure with a nucleic acid genome best explains these TSE strains and their endemic and epidemic spread in susceptible species. Nevertheless, it is widely believed that host prion protein (PrP), without any genetic material, encodes all these strains. We developed rapid infectivity assays that allowed us to reproducibly isolate infectious particles where >85% of the starting titer separated from the majority of host components, including PrP. Remarkably, digestion of all forms of PrP did not reduce brain particle titers. To ask if TSE agents, as other viruses, require nucleic acids, we exposed high titer FU-CJD and 22L scrapie particles to potent nucleases. Both agent-strains were propagated in GT1 neuronal cells to avoid interference by complex degenerative brain changes that can impede nuclease digestions. After exposure to nucleases that are active in sarkosyl, infectivity of both agents was reproducibly reduced by ≥99%. No gold-stained host proteins or any form of PrP were visibly altered by these nucleases. In contrast, co-purifying protected mitochondrial DNA and circular SPHINX DNAs were destroyed. These findings demonstrate that TSE agents require protected genetic material to infect their hosts, and should reopen investigation of essential agent nucleic acids. J. Cell. Biochem. 117: 1947-1958, 2016. © 2016 Wiley Periodicals, Inc.

Susceptibility of GT1-7 cells to mouse-passaged field scrapie isolates with a long incubation

A typical feature of scrapie in sheep and goats is the accumulation of disease-associated prion protein. Scrapie consists of many strains with different biological properties. Nine natural sheep scrapie cases were transmitted to wild-type mice and mouse-passaged isolates were classified into 2 types based on incubation time: short and long. These 2 types displayed a distinct difference in their pathology. We attempted to transmit these mouse-passaged isolates to 2 murine cell lines (GT1–7 and L929) to compare their properties. All of the isolates were transmitted to L929 cells. However, only mouse-passaged field isolates with a long incubation time were transmitted to GT1–7 cells. This specific susceptibility of GT1–7 cells was also confirmed with a primary-passaged isolate that was not completely adapted to the new host species. Characterization of the mechanisms of the specific susceptibility of GT1–7 cells to isolates with a long incubation time may lead to a greater understanding of the differences among prion strains.

Proteomic analysis of host brain components that bind to infectious particles in Creutzfeldt-Jakob disease

Transmissible encephalopathies (TSEs), such as Creutzfeldt-Jakob disease (CJD) and scrapie, are caused by infectious agents that provoke strain-specific patterns of disease. Misfolded host prion protein (PrP-res amyloid) is believed to be the causal infectious agent. However, particles that are stripped of PrP retain both high infectivity and viral proteins not detectable in uninfected mouse controls. We here detail host proteins bound with FU-CJD agent infectious brain particles by proteomic analysis. More than 98 proteins were differentially regulated, and 56 FU-CJD exclusive proteins were revealed after PrP, GFAP, C1q, ApoE, and other late pathologic response proteins were removed. Stripped FU-CJD particles revealed HSC70 (144× the uninfected control), cyclophilin B, an FU-CJD exclusive protein required by many viruses, and early endosome-membrane pathways known to facilitate viral processing, replication, and spread. Synaptosomal elements including synapsin-2 (at 33×) and AP180 (a major FU-CJD exclusive protein) paralleled the known ultrastructural location of 25 nm virus-like TSE particles and infectivity in synapses. Proteins without apparent viral or neurodegenerative links (copine-3), and others involved in viral-induced protein misfolding and aggregation, were also identified. Human sCJD brain particles contained 146 exclusive proteins, and heat shock, synaptic, and viral pathways were again prominent, in addition to Alzheimer, Parkinson, and Huntington aggregation proteins. Host proteins that bind TSE infectious particles can prevent host immune recognition and contribute to prolonged cross-species transmissions (the species barrier). Our infectious particle strategy, which reduces background sequences by >99%, emphasizes host targets for new therapeutic initiatives. Such therapies can simultaneously subvert common pathways of neurodegeneration.

Acinetobacter phage genome is similar to Sphinx 2.36, the circular DNA copurified with TSE infected particles

While analyzing plasmids of Acinetobacter sp. DS002 we have detected a circular DNA molecule pTS236, which upon further investigation is identified as the genome of a phage. The phage genome has shown sequence similarity to the recently discovered Sphinx 2.36 DNA sequence co-purified with the Transmissible Spongiform Encephalopathy (TSE) particles isolated from infected brain samples collected from diverse geographical regions. As in Sphinx 2.36, the phage genome also codes for three proteins. One of them codes for RepA and is shown to be involved in replication of pTS236 through rolling circle (RC) mode. The other two translationally coupled ORFs, orf106 and orf96, code for coat proteins of the phage. Although an orf96 homologue was not previously reported in Sphinx 2.36, a closer examination of DNA sequence of Sphinx 2.36 revealed its presence downstream of orf106 homologue. TEM images and infection assays revealed existence of phage AbDs1 in Acinetobacter sp. DS002.

Infectious particles, stress, and induced prion amyloids: a unifying perspective

Transmissible encephalopathies (TSEs) are believed by many to arise by spontaneous conversion of host prion protein (PrP) into an infectious amyloid (PrP-res, PrP (Sc) ) without nucleic acid. Many TSE agents reside in the environment, with infection controlled by public health measures. These include the disappearance of kuru with the cessation of ritual cannibalism, the dramatic reduction of epidemic bovine encephalopathy (BSE) by removal of contaminated feed, and the lack of endemic scrapie in geographically isolated Australian sheep with susceptible PrP genotypes. While prion protein modeling has engendered an intense focus on common types of protein misfolding and amyloid formation in diverse organisms and diseases, the biological characteristics of infectious TSE agents, and their recognition by the host as foreign entities, raises several fundamental new directions for fruitful investigation such as: (1) unrecognized microbial agents in the environmental metagenome that may cause latent neurodegenerative disease, (2) the evolutionary social and protective functions of different amyloid proteins in diverse organisms from bacteria to mammals, and (3) amyloid formation as a beneficial innate immune response to stress (infectious and non-infectious). This innate process however, once initiated, can become unstoppable in accelerated neuronal aging.

Continuous production of prions after infectious particles are eliminated: implications for Alzheimer's disease

Rat septal cells, induced to enter a terminal differentiation-like state by temperature shift, produce prion protein (PrP) levels 7x higher than their proliferative counterparts. Host PrP accumulates on the plasma membrane, newly elaborated nanotubes, and cell-to-cell junctions, important conduits for viral spread. To find if elevated PrP increased susceptibility to FU-CJD infection, we determined agent titers under both proliferating and arresting conditions. A short 5 day arrest and a prolonged 140 day arrest increased infectivity by 5x and 122x (>2 logs) respectively as compared to proliferating cells. Total PrP rapidly increased 7x and was even more elevated in proliferating cells that escaped chronic arrest conditions. Amyloid generating PrP (PrP-res), the “infectious prion” form, present at ∼100,000 copies per infectious particle, also increased proportionately by 140 days. However, when these highly infectious cells were switched back to proliferative conditions for 60 days, abundant PrP-res continued to be generated even though 4 logs of titer was lost. An identical 4 log loss was found with maximal PrP and PrP-res production in parallel cells under arresting conditions. While host PrP is essential for TSE agent spread and replication, excessive production of all forms of PrP can be inappropriately perpetuated by living cells, even after the initiating infectious agent is eliminated. Host PrP changes can start as a protective innate immune response that ultimately escapes control. A subset of other neurodegenerative and amyloid diseases, including non-transmissible AD, may be initiated by environmental infectious agents that are no longer present.

High CJD infectivity remains after prion protein is destroyed

The hypothesis that host prion protein (PrP) converts into an infectious prion form rests on the observation that infectivity progressively decreases in direct proportion to the decrease of PrP with proteinase K (PK) treatment. PrP that resists limited PK digestion (PrP-res, PrP(sc)) has been assumed to be the infectious form, with speculative types of misfolding encoding the many unique transmissible spongiform encephalopathy (TSE) agent strains. Recently, a PK sensitive form of PrP has been proposed as the prion. Thus we re-evaluated total PrP (sensitive and resistant) and used a cell-based assay for titration of infectious particles. A keratinase (NAP) known to effectively digest PrP was compared to PK. Total PrP in FU-CJD infected brain was reduced to ≤0.3% in a 2 h PK digest, yet there was no reduction in titer. Remaining non-PrP proteins were easily visualized with colloidal gold in this highly infectious homogenate. In contrast to PK, NAP digestion left 0.8% residual PrP after 2 h, yet decreased titer by >2.5 log; few residual protein bands remained. FU-CJD infected cells with 10× the infectivity of brain by both animal and cell culture assays were also evaluated. NAP again significantly reduced cell infectivity (>3.5 log). Extreme PK digestions were needed to reduce cell PrP to <0.2%, yet a very high titer of 8 logs survived. Our FU-CJD brain results are in good accord with the only other report on maximal PrP destruction and titer. It is likely that one or more residual non-PrP proteins may protect agent nucleic acids in infectious particles.

Mouse-adapted scrapie strains 139A and ME7 overcome species barrier to induce experimental scrapie in hamsters and changed their pathogenic features

BACKGROUND

Transmissible spongiform encephalopathy (TSE) diseases are known to be zoonotic diseases that can infect different kinds of animals. The transmissibility of TSE, like that of other infectious diseases, shows marked species barrier, either being unable to infect heterologous species or difficult to form transmission experimentally. The similarity of the amino acid sequences of PrP among species is believed to be one of the elements in controlling the transmission TSE interspecies. Other factors, such as prion strains and host's microenvironment, may also participate in the process.

METHODS

Two mouse-adapted strains 139A and ME7 were cerebrally inoculated to Golden hamsters. Presences of scrapie associate fibril (SAF) and PrPSc in brains of the infected animals were tested by TEM assays and Western blots dynamically during the incubation periods. The pathogenic features of the novel prions in hamsters, including electrophoretic patterns, glycosylating profiles, immunoreactivities, proteinase K-resistances and conformational stabilities were comparatively evaluated. TSE-related neuropathological changes were assayed by histological examinations.

RESULTS

After long incubation times, mouse-adapted agents 139A and ME7 induced experimental scrapie in hamsters, respectively, showing obvious spongiform degeneration and PrPSc deposits in brains, especially in cortex regions. SAF and PrPSc in brains were observed much earlier than the onset of clinical symptoms. The molecular characteristics of the newly-formed PrPSc in hamsters, 139A-ha and ME7-ha, were obviously distinct from the original mouse agents, however, greatly similar as that of a hamster-adapted scrapie strain 263 K. Although the incubation times and main disease signs of the hamsters of 139A-ha and ME7-ha were different, the pathogenic characteristics and neuropathological changes were highly similar.

CONCLUSIONS

This finding concludes that mouse-adapted agents 139A and ME7 change their pathogenic characteristics during the transmission to hamsters. The novel prions in hamsters' brains obtain new molecular properties with hamster-specificity.

Candidate cell substrates, vaccine production, and transmissible spongiform encephalopathies

Transmissible spongiform encephalopathy (TSE) agents have contaminated human tissue-derived medical products, human blood components, and animal vaccines. The objective of this study was to determine the potential susceptibility to infection of 5 cell lines used or proposed for manufacture of biological products, as well as other lines. Cell lines were exposed to the infectious agents of sporadic and variant Creutzfeldt-Jakob disease and bovine spongiform encephalopathy (BSE). Exposed cultures were tested for TSE-associated prion protein (PrP(TSE)) and TSE infectivity by assay in rodents and nonhuman primates. No PrP(TSE) or infectivity has been detected in any exposed cell line under study so far. Animals inoculated with BSE brain homogenate developed typical spongiform encephalopathy. In contrast, animals inoculated with cells exposed to the BSE agent remained asymptomatic. All cell lines we studied resisted infection with 3 TSE agents, including the BSE agent.

Replication and spread of CJD, kuru and scrapie agents in vivo and in cell culture

Transmissible Spongiform Encephalopathy (TSE) agents are defined by their virulence for particular species, their spread in the population, their incubation time to cause disease, and their neuropathological sequelae. Murine adapted human agents, including sporadic CJD (sCJD), New Guinea kuru, and Japanese CJD agents, display particularly distinct incubation times and maximal infectious brain titers. They also induce agent-specific patterns of neurodegeneration. When these TSE agents are transmitted to cultured hypothalamic GT1 cells they maintain their unique identities. Nevertheless, the human kuru (kCJD) and Japanese FU-CJD agents, as well as the sheep 22L and 263K scrapie agents display doubling times that are 8x to 33x faster in cells than in brain, indicating release from complex innate immune responses. These data are most consistent with a foreign viral structure, rather than an infectious form of host prion protein (PrP-res). Profound agent-specific inhibitory effects are also apparent in GT1 cells, and maximal titer plateau in kCJD and FU-CJD differed by 1,000-fold in a cell-based assay. Remarkably, the lower titer kCJD agent rapidly induced de novo PrP-res in GT1 cells, whereas the high titer FU-CJD agent replicated silently for multiple passages. Although PrP-res is often considered to be toxic, PrP-res instead may be part of a primal defense and/or clearance mechanism against TSE environmental agents. Limited spread of particular TSE agents through nanotubes and cell-to-cell contacts probably underlies the long peripheral phase of human CJD.

Transmissible encephalopathy agents: virulence, geography and clockwork

Transmissible spongiform encephalopathies (TSEs) are caused by infectious agents with stable virulence characteristics that are not encoded by the host. Agent-specific features of virulence include variable disease latency and tissue pathology in a given host, as well as the ability to spread to many species. Such cross-species infections contradict predictions based on the prion hypothesis. Recent transmissions of several human agents to normal mice and to monotypic neural cells in culture, underscore the existence of unique agent clades that are prevalent in particular geographic regions. Examples include the epidemic UK bovine agent (BSE) and the New Guinea kuru agent. The virus-like biology of unique TSE agents, including epidemic spread, mutation, and superinfection, can be used to systematically define features of virulence that distinguish common endemic from newly emerging strains.

Proliferative arrest of neural cells induces prion protein synthesis, nanotube formation, and cell-to-cell contacts

Host prion protein (PrP) is most abundant in neurons where its functions are unclear. PrP mRNA transcripts accumulate at key developmental times linked to cell division arrest and terminal differentiation. We sought to find if proliferative arrest was sufficient to cause an increase in PrP in developing neurons. Rat neuronal precursor cells transduced with the temperature sensitive SV-40 T antigen just before terminal differentiation (permissive at 33 degrees C but not at 37.5 degrees C) were analyzed. By 2 days, T antigen was decreased in all cells at 37.5 degrees C, with few DNA synthesizing (BrdU+) cells. Proliferative arrest induced by 37.5 degrees C yielded a fourfold PrP increase. When combined with reduced serum, a sevenfold increase was found. Within 2 days additional neuritic processes with abundant plasma membrane PrP connected many cells. PrP also concentrated between apposed stationary cells, and on extending growth cones and their filopodia. Stationary cells were maintained for 30 days in their original plate, and they reverted to a proliferating low PrP state at 33 degrees C. Ultrastructural studies confirmed increased nanotubes and adherent junctions between high PrP cells. Additionally, some cells shared cytoplasm and these apparently open regions are likely conduits for the exchange of organelles and viruses that have been observed in living cells. Thus PrP is associated with dynamic recognition and contact functions, and may be involved in the transient formation of neural syncytia at key times in embryogenesis. This system can be used to identify drugs that inhibit the transport and spread of infectious CJD particles through the nervous system.

Fukuoka-1 strain of transmissible spongiform encephalopathy agent infects murine bone marrow-derived cells with features of mesenchymal stem cells

BACKGROUND

The possible risk of iatrogenic transmissible spongiform encephalopathies (TSEs, prion diseases) from transplantation of marrow-derived mesenchymal stem cells (MSCs) is uncertain. While most cell lines resist infection, a few propagate TSE agents.

STUDY DESIGN AND METHODS

We generated MSC-like (MSC-L) cell cultures from bone marrow (BM) of mice inoculated with the human-derived Fukuoka-1 (Fu) strain of TSE agent. Cultured cells were characterized for various markers and cellular prion protein (PrP(C) ) by fluorescence-activated cell sorting and for PrP(C) and its pathologic TSE-associated form (PrP(TSE) ) by Western blotting (WB). Cell cultures were tested for their susceptibility to infection with Fu in vitro. The infectivity of one Fu-infected cell culture was assayed in mice.

RESULTS

BM cells from Fu-infected mice expressed neither PrP(C) nor PrP(TSE) after 3 days in culture as demonstrated by WB. Cells adherent to plastic and maintained under two different culture conditions became spontaneously immortalized and began to express PrP(C) at about the same time. One culture became transformed shortly after exposure to Fu in vitro and remained persistently infected, continuously generating PrP(TSE) through multiple passages; the infectivity of cultured cells was confirmed by intracerebral inoculation of lysates into mice. Both persistently TSE-infected and uninfected cells expressed a number of typical MSC markers.

CONCLUSION

BM-derived MSC-L cells of mice became persistently infected with the Fu agent under certain conditions in culture-conditions that differ substantially from those currently used to develop investigational human stem cell therapies.

Nuclease resistant circular DNAs copurify with infectivity in scrapie and CJD

In transmissible encephalopathies (TSEs), it is commonly believed that the host prion protein transforms itself into an infectious form that encodes the many distinct TSE agent strains without any nucleic acid. Using a Ф29 polymerase and chromatography strategy, highly infectious culture and brain preparations of three different geographic TSE agents all contained novel circular DNAs. Two circular "Sphinx" sequences, of 1.8 and 2.4 kb, copurified with infectious particles in sucrose gradients and, as many protected viruses, resisted nuclease digestion. Each contained a replicase ORF related to microviridae that infect commensal Acinetobacter. Infectious gradient fractions also contained nuclease-resistant 16 kb mitochondrial DNAs and analysis of >4,000 nt demonstrated a 100% identity with their species-specific sequences. This confirmed the fidelity of the newly identified sequences detailed here. Conserved replicase regions within the two Sphinx DNAs were ultimately detected by PCR in cytoplasmic preparations from normal cells and brain but were 2,500-fold less than in parallel-infected samples. No trace of the two Sphinx replicases was found in enzymes, detergents, or other preparative materials using exhaustive PCR cycles. The Sphinx sequences uncovered here could have a role in TSE infections despite their apparently symbiotic, low-level persistence in normal cells and tissues. These, as well as other cryptic circular DNAs, may cause or contribute to neurodegeneration and infection-associated tumor transformation. The current results also raise the intriguing possibility that mammals may incorporate more of the prokaryotic world in their cytoplasm than previously recognized.

Agent-specific Shadoo responses in transmissible encephalopathies

Transmissible spongiform encephalopathies (TSE) are neurodegenerative diseases caused by an infectious agent with viral properties. Host prion protein (PrP), a marker of late stage TSE pathology, is linked to a similar protein called Shadoo (Sho). Sho is reduced in mice infected with the RML scrapie agent, but has not been investigated in other TSEs. Although PrP is required for infection by TSE agents, it is not known if Sho is similarly required. Presumably Sho protects cells from toxic effects of misfolded PrP. We compared Sho and PrP changes after infection by very distinct TSE agents including sporadic CJD, Asiatic CJD, New Guinea kuru, vCJD (the UK epidemic bovine agent) and 22L sheep scrapie, all passaged in standard mice. We found that Sho reductions were agent-specific. Variable Sho reductions in standard mice could be partly explained by agent-specific differences in regional neuropathology. However, Sho did not follow PrP misfolding in any quantitative or consistent way. Tga20 mice with high murine PrP levels revealed additional agent-specific differences. Sho was unaffected by Asiatic CJD yet was markedly reduced by the kuru agent in Tga20 mice; in standard mice both agents induced the same Sho reductions. Analyses of neural GT1 cells demonstrated that Sho was not essential for TSE infections. Furthermore, because all infected GT1 cells appeared as healthy as uninfected controls, Sho was not needed to protect infected cells from their "toxic" burden of abundant abnormal PrP and intracellular amyloid.

The kuru infectious agent is a unique geographic isolate distinct from Creutzfeldt-Jakob disease and scrapie agents

Human sporadic Creutzfeldt-Jakob disease (sCJD), endemic sheep scrapie, and epidemic bovine spongiform encephalopathy (BSE) are caused by a related group of infectious agents. The new U.K. BSE agent spread to many species, including humans, and clarifying the origin, specificity, virulence, and diversity of these agents is critical, particularly because infected humans do not develop disease for many years. As with viruses, transmissible spongiform encephalopathy (TSE) agents can adapt to new species and become more virulent yet maintain fundamentally unique and stable identities. To make agent differences manifest, one must keep the host genotype constant. Many TSE agents have revealed their independent identities in normal mice. We transmitted primate kuru, a TSE once epidemic in New Guinea, to mice expressing normal and approximately 8-fold higher levels of murine prion protein (PrP). High levels of murine PrP did not prevent infection but instead shortened incubation time, as would be expected for a viral receptor. Sporadic CJD and BSE agents and representative scrapie agents were clearly different from kuru in incubation time, brain neuropathology, and lymphoreticular involvement. Many TSE agents can infect monotypic cultured GT1 cells, and unlike sporadic CJD isolates, kuru rapidly and stably infected these cells. The geographic independence of the kuru agent provides additional reasons to explore causal environmental pathogens in these infectious neurodegenerative diseases.