Prions

Potential for transmission of sporadic Creutzfeldt-Jakob disease through peripheral routes

Five sporadic Creutzfeldt-Jakob disease (CJD) strains have been identified to date, based on differences in clinicopathological features of the patients, the biochemical properties of abnormal prion proteins, and transmission properties. Recent advances in our knowledge about iatrogenic transmission of sporadic CJD have raised the possibility that the infectivity of sporadic CJD strains through peripheral routes is different from that of intracranial infection. To test this possibility, here we assessed systematically the infectivity of sporadic CJD strains through the peripheral route for the first time using a mouse model expressing human prion protein. Although the infectivity of the V2 and M1 sporadic CJD strains is almost the same in intracerebral transmission studies, the V2 strain infected more efficiently than the M1 strain through the peripheral route. The other sporadic CJD strains examined lacked infectivity. Of note, both the V2 and M1 strains showed preference for mice with the valine homozygosity at the PRNP polymorphic codon. These results indicate that the V2 strain is the most infectious sporadic CJD strain for infection through peripheral routes. In addition, these findings raise the possibility that individuals with the valine homozygosity at the PRNP polymorphic codon might have higher risks of infection through peripheral routes compared with the methionine homozygotes. Thus, preventive measures against the transmission of the V2 sporadic CJD strain will be important for the eradication of iatrogenic CJD transmission through peripheral routes.

Neuroprotective effect and potential of cellular prion protein and its cleavage products for treatment of neurodegenerative disorders part II: strategies for therapeutics development

Introduction: The cellular prion protein (PrP^C), some of its derivatives (especially PrP N-terminal N1 peptide and shed PrP), and PrP^C-containing exosomes have strong neuroprotective activities, which have been reviewed in the companion article (Part I) and are briefly summarized here.Areas covered: We propose that elevating the extracellular levels of a protective PrP form using gene therapy and other approaches is a very promising novel avenue for prophylactic and therapeutic treatments against prion disease, Alzheimer's disease, and several other neurodegenerative diseases. We will dissect the pros and cons of various potential PrP-based treatment options and propose a few strategies that are more likely to succeed. The cited references were obtained from extensive PubMed searches of recent literature, including peer-reviewed original articles and review articles.Expert opinion: Concurrent knockdown of celllular PrP expression and elevation of the extracellular levels of a neuroprotective PrP N-terminal peptide via optimized gene therapy vectors is a highly promising broad-spectrum prophylactic and therapeutic strategy against several neurodegenerative diseases, including prion diseases, Alzheimer's disease and Parkinson's disease.

Neuroprotective effect and potential of cellular prion protein and its cleavage products for treatment of neurodegenerative disorders part I. a literature review

INTRODUCTION

The cellular prion protein (PrP^C) is well known for its pathogenic roles in prion diseases, several other neurodegenerative diseases (such as Alzheimer's disease), and multiple types of cancer, but the beneficial aspects of PrP^C and its cleavage products received much less attention.

AREAS COVERED

Here the authors will systematically review the literatures on the negative as well as protective aspects of PrP^C and its derivatives (especially PrP N-terminal N1 peptide and shed PrP). The authors will dissect the current findings on N1 and shed PrP, including evidence for their neuroprotective effects, the categories of PrP^C cleavage, and numerous cleavage enzymes involved. The authors will also discuss the protective effects and therapeutic potentials of PrP^C-rich exosomes. The cited articles were obtained from extensive PubMed searches of recent literature, including peer-reviewed original articles and review articles.

EXPERT OPINION

PrP and its N-terminal fragments have strong neuroprotective activities that should be explored for therapeutics and prophylactics development against prion disease, Alzheimer's disease and a few other neurodegenerative diseases. The strategies to develop PrP-based therapeutics and prophylactics for these neurodegenerative diseases will be discussed in a companion article (Part II).

The Way forward for the Origin of Life: Prions and Prion-Like Molecules First Hypothesis

In this paper the hypothesis that prions and prion-like molecules could have initiated the chemical evolutionary process which led to the eventual emergence of life is reappraised. The prions first hypothesis is a specific application of the protein-first hypothesis which asserts that protein-based chemical evolution preceded the evolution of genetic encoding processes. This genetics-first hypothesis asserts that an “RNA-world era” came before protein-based chemical evolution and rests on a singular premise that molecules such as RNA, acetyl-CoA, and NAD are relics of a long line of chemical evolutionary processes preceding the Last Universal Common Ancestor (LUCA). Nevertheless, we assert that prions and prion-like molecules may also be relics of chemical evolutionary processes preceding LUCA. To support this assertion is the observation that prions and prion-like molecules are involved in a plethora of activities in contemporary biology in both complex (eukaryotes) and primitive life forms. Furthermore, a literature survey reveals that small RNA virus genomes harbor information about prions (and amyloids). If, as has been presumed by proponents of the genetics-first hypotheses, small viruses were present during an RNA world era and were involved in some of the earliest evolutionary processes, this places prions and prion-like molecules potentially at the heart of the chemical evolutionary process whose eventual outcome was life. We deliberate on the case for prions and prion-like molecules as the frontier molecules at the dawn of evolution of living systems.

The aminoglycoside G418 hinders de novo prion infection in cultured cells

The study of prions and the discovery of candidate therapeutics for prion disease have been facilitated by the ability of prions to replicate in cultured cells. Paradigms in which prion proteins from different species are expressed in cells with low or no expression of endogenous prion protein (PrP) have expanded the range of prion strains that can be propagated. In these systems, cells stably expressing a PrP of interest are typically generated via coexpression of a selectable marker and treatment with an antibiotic. Here, we report the unexpected discovery that the aminoglycoside G418 (Geneticin) interferes with the ability of stably transfected cultured cells to become infected with prions. In G418-resistant lines of N2a or CAD5 cells, the presence of G418 reduced levels of protease-resistant PrP following challenge with the RML or 22L strains of mouse prions. G418 also interfered with the infection of cells expressing hamster PrP with the 263K strain of hamster prions. Interestingly, G418 had minimal to no effect on protease-resistant PrP levels in cells with established prion infection, arguing that G418 selectively interferes with de novo prion infection. As G418 treatment had no discernible effect on cellular PrP levels or its localization, this suggests that G418 may specifically target prion assemblies or processes involved in the earliest stages of prion infection.

Unfolded and intermediate states of PrP play a key role in the mechanism of action of an antiprion chaperone

Prion and prion-like diseases involve the propagation of misfolded protein conformers. Small-molecule pharmacological chaperones can inhibit propagated misfolding, but how they interact with disease-related proteins to prevent misfolding is often unclear. We investigated how pentosan polysulfate (PPS), a polyanion with antiprion activity in vitro and in vivo, interacts with mammalian prion protein (PrP) to alter its folding. Calorimetry showed that PPS binds two sites on natively folded PrP, but one PPS molecule can bind multiple PrP molecules. Force spectroscopy measurements of single PrP molecules showed PPS stabilizes not only the native fold of PrP but also many different partially folded intermediates that are not observed in the absence of PPS. PPS also bound tightly to unfolded segments of PrP, delaying refolding. These observations imply that PPS can act through multiple possible modes, inhibiting misfolding not only by stabilizing the native fold or sequestering natively folded PrP into aggregates, as proposed previously, but also by binding to partially or fully unfolded states that play key roles in mediating misfolding. These results underline the likely importance of unfolded states as critical intermediates on the prion conversion pathway.

Tackling prion diseases: a review of the patent landscape

Introduction: Prion diseases are a class of rare and fatal neurodegenerative diseases for which no cure is currently available. They are characterized by conformational conversion of cellular prion protein (PrP^C) into the disease-associated 'scrapie' isoform (PrP^Sc). Under an etiological point of view, prion diseases can be divided into acquired, genetic, and idiopathic form, the latter of which are the most frequent.Areas covered: Therapeutic approaches targeting prion diseases are based on the use of chemical and nature-based compounds, targeting either PrP^C or PrP^Sc or other putative player in pathogenic mechanism. Other proposed anti-prion treatments include passive and active immunization strategies, peptides, aptamers, and PrP^C-directed RNA interference techniques. The treatment efficacy has been mainly assessed in cell lines or animal models of the disease testing their ability to reduce prion accumulation.Expert opinion: The assessed strategies focussing on the identification of an efficient anti-prion therapy faced various issues, which go from permeation of the blood brain barrier to immunological tolerance of the host. Indeed, the use of combinatory approaches, which could boost a synergistic anti-prion effect and lower the potential side effects of single treatments and may represent an extreme powerful and feasible way to tackle prion disease.

Canine D163-PrP polymorphic variant does not provide complete protection against prion infection in small ruminant PrP context

E/D₁₆₃ polymorphism of dog prion protein (PrP) has been recently proposed as the variant responsible for canid prion resistance. To further investigate the protective role of this variant against prion replication, the transgenic mouse model OvPrP-Tg532 expressing sheep/goat PrP carrying the substitution D₁₆₂ (equivalent to D₁₆₃ position of dog PrP) was generated and intracranially inoculated with a broad collection of small ruminant prion strains. OvPrP-Tg532 mice showed resistance to classical bovine spongiform encephalopathy (BSE) from sheep and some classical scrapie isolates from sheep and goat but were susceptible to ovine atypical L-BSE and numerous classical scrapie isolates. Strikingly, some of these classical scrapie isolates showed a shift in their prion strain properties. These results suggest that other PrP residues apart from E/D₁₆₃ variant of dog PrP or factors distinct than PrP may participate in prion resistance of canids and that different factors may be required for D₁₆₂ sheep PrP to provide effective protection to sheep against ruminant prions.

Tau strains shape disease

Tauopathies consist of over 25 different neurodegenerative diseases that include argyrophilic grain disease (AGD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Pick’s disease (PiD). Tauopathies are defined by brain accumulation of microtubule-associated protein tau in fibrillar aggregates, whose prevalence strongly correlates with dementia. Dominant mutations in tau cause neurodegenerative diseases, and most increase its aggregation propensity. Pathogenesis of tauopathies may involve pathological tau conformers that serve as templates to recruit native protein into growing assemblies and also move between brain cells to cause disease progression, similar to prions. Prions adopt pathological conformations, termed “strains,” that stably propagate in living systems, and create unique patterns of neuropathology. Data from multiple laboratories now suggest that tau acts as a prion. It propagates unique strains indefinitely in cultured cells, and when these are inoculated into mouse models, they create defined neuropathological patterns, which establish a direct link between conformation and disease. In humans, distinct fibril structures are associated with different diseases, but causality has not been established as in mice. Cryo-EM structures of tau fibrils isolated from tauopathy brains reveal distinct fibril cores across disease. Interestingly, the conformation of the tau monomer unit within different fibril subtypes from the same patient appears relatively preserved. This is consistent with data that the tau monomer samples an ensemble of conformations that act as distinct pathologic templates in the formation of restricted numbers of strains. The propensity of a tau monomer to adopt distinct conformations appears to be linked to defined local motifs that expose different patterns of amyloidogenic amino acid sequences. The prion hypothesis, which predicts that protein structure dictates resultant disease, has proved particularly useful to understand the diversity of human tauopathies. The challenge now is to develop methods to rapidly classify patients according to the structure of the underlying pathological protein assemblies to achieve more accurate diagnosis and effective therapy.

Chronic Wasting Disease Diagnostic Discrepancies: The Importance of Testing Both Medial Retropharyngeal Lymph Nodes

Chronic wasting disease (CWD) of white-tailed deer (Odocoileus virginianus) is a fatal neurologic disease that is spreading across North America. A common surveillance protocol for CWD currently involves screening with an enzyme-linked immunosorbent assay (ELISA) followed by confirmatory testing with immunohistochemistry (IHC). Medial retropharyngeal lymph nodes (MRPLN) are the tissue of choice to diagnose CWD in free-ranging white-tailed deer. We examined left and right MRPLN from 101 ELISA-positive deer harvested from 2015 to 2019 to determine the prevalence of cases in which prion protein was not detected by IHC as well as differences in IHC labeling between contralateral lymph nodes. Prion protein was not detected using IHC in either MRPLN in 5.9% (6/101) of cases. There was a significant but weak positive relationship between the number of IHC-positive follicles and ELISA optical density values (R2=0.08, P=0.039). Mean optical density values in IHC-positive MRPLN were higher than in IHC-negative MRPLN; however, this was not statistically significant (P=0.260). Failure to confirm ELISA diagnoses with IHC may have been because the methods tested different areas of MRPLN, or that there were differences in test sensitivity or antibody affinity. An additional 5.9% (6/101) of cases had one IHC-positive MRPLN, whereas the contralateral MRPLN was IHC negative. Therefore, testing a single MRPLN for CWD may lead to false-negative results, regardless of methodology, which highlights the importance of collecting and testing both MRPLN.

Dynamics of prion proliferation under combined treatment of pharmacological chaperones and interferons

Prions are proteins that cause fatal neurodegenerative diseases. The misfolded conformation adopted by prions can be transmitted to other normally folded proteins. Therapeutics to stop prion proliferation have been studied experimentally; however, it is not clear how the combination of different types of treatments can decrease the growth rate of prions in the brain. In this article, we combine the implementation of pharmacological chaperones and interferons to develop a novel model using a non-linear system of ordinary differential equations and study the quantitative effects of these two treatments on the growth rate of prions. This study aims to identify how the two treatments affect prion proliferation, both individually and in tandem. We analyze the model, and qualitative global results on the disease-free and disease equilibria are proved analytically. Numerical simulations, using parameter values from in vivo experiments that provide a pharmaceutically important demonstration of the effects of these two treatments, are presented here. This mathematical model can be used to identify and optimize the best combination of the treatments within their safe ranges.

Harnessing the Physiological Functions of Cellular Prion Protein in the Kidneys: Applications for Treating Renal Diseases

A cellular prion protein (PrP^C) is a ubiquitous cell surface glycoprotein, and its physiological functions have been receiving increased attention. Endogenous PrP^C is present in various kidney tissues and undergoes glomerular filtration. In prion diseases, abnormal prion proteins are found to accumulate in renal tissues and filtered into urine. Urinary prion protein could serve as a diagnostic biomarker. PrP^C plays a role in cellular signaling pathways, reno-protective effects, and kidney iron uptake. PrP^C signaling affects mitochondrial function via the ERK pathway and is affected by the regulatory influence of microRNAs, small molecules, and signaling proteins. Targeting PrP^C in acute and chronic kidney disease could help improve iron homeostasis, ameliorate damage from ischemia/reperfusion injury, and enhance the efficacy of mesenchymal stem/stromal cell or extracellular vesicle-based therapeutic strategies. PrP^C may also be under the influence of BMP/Smad signaling and affect the progression of TGF-β-related renal fibrosis. PrP^C conveys TNF-α resistance in some renal cancers, and therefore, the coadministration of anti-PrP^C antibodies improves chemotherapy. PrP^C can be used to design antibody-drug conjugates, aptamer-drug conjugates, and customized tissue inhibitors of metalloproteinases to suppress cancer. With preclinical studies demonstrating promising results, further research on PrP^C in the kidney may lead to innovative PrP^C-based therapeutic strategies for renal disease.

Classical scrapie in small ruminants is caused by at least four different prion strains

The diversity of goat scrapie strains in Europe has recently been studied using bioassays in a wide collection of rodent models, resulting in the classification of classical scrapie into four different categories. However, the sole use of the first passage does not lead to isolate adaptation and identification of the strains involved and might therefore lead to misclassification of some scrapie isolates. Therefore, this work reports the complete transmission study of a wide collection of goat transmissible spongiform encephalopathy (TSE) isolates by intracranial inoculation in two transgenic mouse lines overexpressing either small ruminant (TgGoat-ARQ) or bovine (TgBov) PrP^C. To compare scrapie strains in sheep and goats, sheep scrapie isolates from different European countries were also included in the study. Once the species barrier phenomenon was overcome, an accurate classification of the isolates was attained. Thus, the use of just two rodent models allowed us to fully differentiate at least four different classical scrapie strains in small ruminants and to identify isolates containing mixtures of strains. This work reinforces the idea that classical scrapie in small ruminants is a prion disease caused by multiple different prion strains and not by a single strain, as is the case for epidemic classical bovine spongiform encephalopathy (BSE-C). In addition, the clear dissimilarity between the different scrapie strains and BSE-C does not support the idea that classical scrapie is the origin of epidemic BSE-C.

Amyloid-Mediated Mechanisms of Membrane Disruption

Protein aggregation and amyloid formation are pathogenic events underlying the development of an increasingly large number of human diseases named “proteinopathies”. Abnormal accumulation in affected tissues of amyloid β (Aβ) peptide, islet amyloid polypeptide (IAPP), and the prion protein, to mention a few, are involved in the occurrence of Alzheimer’s (AD), type 2 diabetes mellitus (T2DM) and prion diseases, respectively. Many reports suggest that the toxic properties of amyloid aggregates are correlated with their ability to damage cell membranes. However, the molecular mechanisms causing toxic amyloid/membrane interactions are still far to be completely elucidated. This review aims at describing the mutual relationships linking abnormal protein conformational transition and self-assembly into amyloid aggregates with membrane damage. A cross-correlated analysis of all these closely intertwined factors is thought to provide valuable insights for a comprehensive molecular description of amyloid diseases and, in turn, the design of effective therapies.

Neuropathology of Animal Prion Diseases

Transmissible Spongiform Encephalopathies (TSEs) or prion diseases are a fatal group of infectious, inherited and spontaneous neurodegenerative diseases affecting human and animals. They are caused by the conversion of cellular prion protein (PrP^C) into a misfolded pathological isoform (PrP^Sc or prion- proteinaceous infectious particle) that self-propagates by conformational conversion of PrP^C. Yet by an unknown mechanism, PrP^C can fold into different PrP^Sc conformers that may result in different prion strains that display specific disease phenotype (incubation time, clinical signs and lesion profile). Although the pathways for neurodegeneration as well as the involvement of brain inflammation in these diseases are not well understood, the spongiform changes, neuronal loss, gliosis and accumulation of PrP^Sc are the characteristic neuropathological lesions. Scrapie affecting small ruminants was the first identified TSE and has been considered the archetype of prion diseases, though atypical and new animal prion diseases continue to emerge highlighting the importance to investigate the lesion profile in naturally affected animals. In this report, we review the neuropathology and the neuroinflammation of animal prion diseases in natural hosts from scrapie, going through the zoonotic bovine spongiform encephalopathy (BSE), the chronic wasting disease (CWD) to the newly identified camel prion disease (CPD).

Preclinical Detection of Prions in Blood of Nonhuman Primates Infected with Variant Creutzfeldt-Jakob Disease

Variant Creutzfeldt-Jakob disease (vCJD) is caused by prion infection with bovine spongiform encephalopathy and can be transmitted by blood transfusion. Protein misfolding cyclic amplification (PMCA) can detect prions in blood from vCJD patients with 100% sensitivity and specificity. To determine whether PMCA enables prion detection in blood during the preclinical stage of infection, we performed a blind study using blood samples longitudinally collected from 28 control macaques and 3 macaques peripherally infected with vCJD. Our results demonstrate that PMCA consistently detected prions in blood during the entire preclinical stage in all infected macaques, without false positives from noninfected animals, when using the optimized conditions for amplification of macaque prions. Strikingly, prions were detected as early as 2 months postinoculation (>750 days before disease onset). These findings suggest that PMCA has the potential to detect vCJD prions in blood from asymptomatic carriers during the preclinical phase of the disease.

Wide distribution of prion infectivity in the peripheral tissues of vCJD and sCJD patients

Sporadic Creutzfeldt-Jakob disease (sCJD) is the commonest human prion disease, occurring most likely as the consequence of spontaneous formation of abnormal prion protein in the central nervous system (CNS). Variant Creutzfeldt–Jakob disease (vCJD) is an acquired prion disease that was first identified in 1996. In marked contrast to vCJD, previous investigations in sCJD revealed either inconsistent levels or an absence of PrP^Sc in peripheral tissues. These findings contributed to the consensus that risks of transmitting sCJD as a consequence of non-CNS invasive clinical procedures were low. In this study, we systematically measured prion infectivity levels in CNS and peripheral tissues collected from vCJD and sCJD patients. Unexpectedly, prion infectivity was detected in a wide variety of peripheral tissues in sCJD cases. Although the sCJD infectivity levels varied unpredictably in the tissues sampled and between patients, these findings could impact on our perception of the possible transmission risks associated with sCJD.

Partial Prion Cross-Seeding between Fungal and Mammalian Amyloid Signaling Motifs

Amyloids are β-sheet-rich protein polymers that can be pathological or display a variety of biological roles. In filamentous fungi, specific immune receptors activate programmed cell death execution proteins through a process of amyloid templating akin to prion propagation.

In filamentous fungi, NLR-based signalosomes activate downstream membrane-targeting cell death-inducing proteins by a mechanism of amyloid templating. In the species Podospora anserina, two such signalosomes, NWD2/HET-S and FNT1/HELLF, have been described. An analogous system involving a distinct amyloid signaling motif, termed PP, was also identified in the genome of the species Chaetomium globosum and studied using heterologous expression in Podospora anserina. The PP motif bears resemblance to the RIP homotypic interaction motif (RHIM) and to RHIM-like motifs controlling necroptosis in mammals and innate immunity in flies. We identify here a third NLR signalosome in Podospora anserina comprising a PP motif and organized as a two-gene cluster encoding an NLR and an HELL domain cell death execution protein termed HELLP. We show that the PP motif region of HELLP forms a prion we term [π] and that [π] prions trigger the cell death-inducing activity of full-length HELLP. We detect no prion cross-seeding between HET-S, HELLF, and HELLP amyloid motifs. In addition, we find that, like PP motifs, RHIMs from human RIP1 and RIP3 kinases are able to form prions in Podospora and that [π] and [Rhim] prions partially cross-seed. Our study shows that Podospora anserina displays three independent cell death-inducing amyloid signalosomes. Based on the described functional similarity between RHIM and PP, it appears likely that these amyloid motifs constitute evolutionarily related cell death signaling modules.

Atomic-level differences between brain parenchymal- and cerebrovascular-seeded Aβ fibrils

Alzheimer's disease is characterized by neuritic plaques, the main protein components of which are β-amyloid (Aβ) peptides deposited as β-sheet-rich amyloid fibrils. Cerebral Amyloid Angiopathy (CAA) consists of cerebrovascular deposits of Aβ peptides; it usually accompanies Alzheimer's disease, though it sometimes occurs in the absence of neuritic plaques, as AD also occurs without accompanying CAA. Although neuritic plaques and vascular deposits have similar protein compositions, one of the characteristic features of amyloids is polymorphism, i.e., the ability of a single pure peptide to adopt multiple conformations in fibrils, depending on fibrillization conditions. For this reason, we asked whether the Aβ fibrils in neuritic plaques differed structurally from those in cerebral blood vessels. To address this question, we used seeding techniques, starting with amyloid-enriched material from either brain parenchyma or cerebral blood vessels (using meninges as the source). These amyloid-enriched preparations were then added to fresh, disaggregated solutions of Aβ to make replicate fibrils, as described elsewhere. Such fibrils were then studied by solid-state NMR, fiber X-ray diffraction, and other biophysical techniques. We observed chemical shift differences between parenchymal vs. vascular-seeded replicate fibrils in select sites (in particular, Ala2, Phe4, Val12, and Gln15 side chains) in two-dimensional 13C-13C correlation solid-state NMR spectra, strongly indicating structural differences at these sites. X-ray diffraction studies also indicated that vascular-seeded fibrils displayed greater order than parenchyma-seeded fibrils in the "side-chain dimension" (~ 10 Å reflection), though the "hydrogen-bond dimensions" (~ 5 Å reflection) were alike. These results indicate that the different nucleation conditions at two sites in the brain, parenchyma and blood vessels, affect the fibril products that get formed at each site, possibly leading to distinct pathophysiological outcomes.

Regional Differences in Neuroinflammation-Associated Gene Expression in the Brain of Sporadic Creutzfeldt-Jakob Disease Patients

Neuroinflammation is an essential part of neurodegeneration. Yet, the current understanding of neuroinflammation-associated molecular events in distinct brain regions of prion disease patients is insufficient to lay the ground for effective treatment strategies targeting this complex neuropathological process. To address this problem, we analyzed the expression of 800 neuroinflammation-associated genes to create a profile of biological processes taking place in the frontal cortex and cerebellum of patients who suffered from sporadic Creutzfeldt-Jakob disease. The analysis was performed using NanoString nCounter technology with human neuroinflammation panel+. The observed gene expression patterns were regionally and sub-regionally distinct, suggesting a variable neuroinflammatory response. Interestingly, the observed differences could not be explained by the molecular subtypes of sporadic Creutzfeldt-Jakob disease. Furthermore, analyses of canonical pathways and upstream regulators based on differentially expressed genes indicated an overlap between biological processes taking place in different brain regions. This suggests that even smaller-scale spatial data reflecting subtle changes in brain cells' functional heterogeneity and their immediate pathologic microenvironments are needed to explain the observed differential gene expression in a greater detail.

MicroRNAs as Biomarkers for Animal Health and Welfare in Livestock

MicroRNAs (miRNAs) are small and highly conserved non-coding RNA molecules that orchestrate a wide range of biological processes through the post-transcriptional regulation of gene expression. An intriguing aspect in identifying these molecules as biomarkers is derived from their role in cell-to-cell communication, their active secretion from cells into the extracellular environment, their high stability in body fluids, and their ease of collection. All these features confer on miRNAs the potential to become a non-invasive tool to score animal welfare. There is growing interest in the importance of miRNAs as biomarkers for assessing the welfare of livestock during metabolic, environmental, and management stress, particularly in ruminants, pigs, and poultry. This review provides an overview of the current knowledge regarding the potential use of tissue and/or circulating miRNAs as biomarkers for the assessment of the health and welfare status in these livestock species.

Methionine oxidation within the prion protein

Prion diseases are characterized by the self-templated misfolding of the cellular prion protein (PrPC) into infectious aggregates (PrPSc). The detailed molecular basis of the misfolding and aggregation of PrPC remains incompletely understood. It is believed that the transient misfolding of PrPC into partially structured intermediates precedes the formation of insoluble protein aggregates and is a critical component of the prion misfolding pathway. A number of environmental factors have been shown to induce the destabilization of PrPC and promote its initial misfolding. Recently, oxidative stress and reactive oxygen species (ROS) have emerged as one possible mechanism by which the destabilization of PrPC can be induced under physiological conditions. Methionine residues are uniquely vulnerable to oxidation by ROS and the formation of methionine sulfoxides leads to the misfolding and subsequent aggregation of PrPC. Here, we provide a review of the evidence for the oxidation of methionine residues in PrPC and its potential role in the formation of pathogenic prion aggregates.

Cloning and analysis of PRNP gene of Vulpes corsac in Qinghai plateau, China

PRNP gene encodes PrP protein, which is conservative among different species and associates with the susceptibility of prion disease. In this report, we cloned and sequenced the full-length PRNP gene of Vulpes corsac in Qinghai plateau, China. The amino acid sequence of Vulpes corsac PrP showed 100% homology with those of the other three species of foxes. The taxa relationship of Vulpes corsac PrP with other species of animals, including human, canine, bovine, cervus, capra, ovis, camelus, felis, Mustela, mouse and hamster were also analysed.

Improving the Predictive Value of Prion Inactivation Validation Methods to Minimize the Risks of Iatrogenic Transmission With Medical Instruments

Prions are pathogenic infectious agents responsible for fatal, incurable neurodegenerative diseases in animals and humans. Prions are composed exclusively of an aggregated and misfolded form (PrP^Sc) of the cellular prion protein (PrP^C). During the propagation of the disease, PrP^Sc recruits and misfolds PrP^C into further PrP^Sc. In human, iatrogenic prion transmission has occurred with incompletely sterilized medical material because of the unusual resistance of prions to inactivation. Most commercial prion disinfectants validated against the historical, well-characterized laboratory strain of 263K hamster prions were recently shown to be ineffective against variant Creutzfeldt-Jakob disease human prions. These observations and previous reports support the view that any inactivation method must be validated against the prions for which they are intended to be used. Strain-specific variations in PrP^Sc physico-chemical properties and conformation are likely to explain the strain-specific efficacy of inactivation methods. Animal bioassays have long been used as gold standards to validate prion inactivation methods, by measuring reduction of prion infectivity. Cell-free assays such as the real-time quaking-induced conversion (RT-QuIC) assay and the protein misfolding cyclic amplification (PMCA) assay have emerged as attractive alternatives. They exploit the seeding capacities of PrP^Sc to exponentially amplify minute amounts of prions in biospecimens. European and certain national medicine agencies recently implemented their guidelines for prion inactivation of non-disposable medical material; they encourage or request the use of human prions and cell-free assays to improve the predictive value of the validation methods. In this review, we discuss the methodological and technical issues regarding the choice of (i) the cell-free assay, (ii) the human prion strain type, (iii) the prion-containing biological material. We also introduce a new optimized substrate for high-throughput PMCA amplification of human prions bound on steel wires, as translational model for prion-contaminated instruments.

Unbelievable but True: Epigenetics and Chromatin in Fungi

Evolutionary innovations in chromatin biology have been recently discovered through the study of fungi. In Saccharomyces cerevisiae, a prion form of a deacetylase complex assembles over subtelomeric domains that produces a heritable gene expression state that enables resistance to stress. In Candida albicans, stress triggers adaptive chromosome destabilization via erasure a centromeric histone H3, CENP-A; a process that cooperates with a newly evolved H2A variant lacking a mitotic phosphorylation site. Finally, in Cryptococcus neoformans, the loss of a cytosine DNA methyltransferase at least 50 million years ago has enabled the Darwinian evolution of methylation patterns over geological timescales. These studies reveal a remarkable genetic and epigenetic evolutionary plasticity of the chromatin fiber, despite the highly conserved structure of the nucleosome.

Identification of NLR-associated Amyloid Signaling Motifs in Bacterial Genomes

In filamentous fungi, amyloid signaling sequences allow Nod-like receptors (NLRs) to activate downstream cell-death inducing proteins with HeLo and HeLo-like (HELL) domains and amyloid RHIM and RHIM-related motifs control immune defense pathways in mammals and flies. Herein, we show bioinformatically that analogous amyloid signaling motifs exist in bacteria. These short motifs are found at the N terminus of NLRs and at the C terminus of proteins with a domain we term BELL. The corresponding NLR and BELL proteins are encoded by adjacent genes. We identify 10 families of such bacterial amyloid signaling sequences (BASS), one of which (BASS3) is homologous to RHIM and a fungal amyloid motif termed PP. BASS motifs occur nearly exclusively in bacteria forming multicellular structures (mainly in Actinobacteria and Cyanobacteria). We analyze experimentally a subset of seven of these motifs (from the most common BASS1 family and the RHIM-related BASS3 family) and find that these sequences form fibrils in vitro. Using a fungal in vivo model, we show that all tested BASS-motifs form prions and that the NLR-side motifs seed prion-formation of the corresponding BELL-side motif. We find that BASS3 motifs show partial prion cross-seeding with mammalian RHIM and fungal PP-motifs and that proline mutations on key positions of the BASS3 core motif, conserved in RHIM and PP-motifs, abolish prion formation. This work expands the paradigm of prion amyloid signaling to multicellular prokaryotes and suggests a long-term evolutionary conservation of these motifs from bacteria, to fungi and animals.

Pathophysiology of Parkinson's disease: Mitochondria, alpha-synuclein and much more…

Parkinson's disease (PD) is a complex, age-related, neurodegenerative disease whose pathogenesis remains incompletely understood. Here, we give an overview of the progress that has been made over the past four decades in our understanding of this disorder. We review the role of mitochondria, environmental toxicants, alpha-synuclein and neuroinflammation in the development of PD. We also discuss more recent data from genetics, which strongly support the endosomal-lysosomal pathways and mitophagy as being central to PD. Finally, we discuss the emerging role of the gut-brain axis as a modulator of PD progression. This article is intended to provide a comprehensive, general and practical review of PD pathogenesis for the general neurologist.

Amyloid Signaling in Filamentous Fungi and Bacteria

Amyloids are implicated in many protein misfolding diseases. Amyloid folds, however, also display a range of functional roles particularly in the microbial world. The templating ability of these folds endows them with specific properties allowing their self-propagation and protein-to-protein transmission in vivo. This property, the prion principle, is exploited by specific signaling pathways that use transmission of the amyloid fold as a way to convey information from a receptor to an effector protein. I describe here amyloid signaling pathways involving fungal nucleotide binding and oligomerization domain (NOD)-like receptors that were found to control nonself recognition and programmed cell death processes. Studies on these fungal amyloid signaling motifs stem from the characterization of the fungal [Het-s] prion protein and have led to the identification in fungi but also in multicellular bacteria of several distinct families of signaling motifs, one of which is related to RHIM [receptor-interacting protein (RIP) homotypic interaction motif], an amyloid motif regulating mammalian necroptosis.

The utility of bank voles for studying prion disease

The transmission of prions between species is typically an inefficient process due to the species barrier, which represents incompatibility between prion seed and substrate molecules. Bank voles (Myodes glareolus) are an exception to this rule, as they are susceptible to a diverse range of prion strains from many different animal species. In particular, bank voles can be efficiently infected with most types of human prions and have played a critical role in validating variably protease-sensitive prionopathy (VPSPr) and certain forms of Gerstmann-Sträussler-Scheinker (GSS) disease as bona fide prion disorders rather than non-transmissible proteinopathies. The bank vole prion protein (BVPrP) confers a "universal prion acceptor" phenotype when expressed in mice and when used as a substrate for in vitro prion amplification assays, indicating that the unique prion transmission properties of bank voles are mediated by BVPrP. Over-expression of BVPrP in mice can also promote the spontaneous development of prion disease, indicating that BVPrP is intrinsically prone to both spontaneous and template-directed misfolding. Here, we discuss the utility of bank voles and BVPrP for prion research and how they have provided new tools for establishing rapid animal bioassays, modeling spontaneous prion disease, standardizing prion diagnostics, and understanding the molecular basis of the species barrier.

Insight From Animals Resistant to Prion Diseases: Deciphering the Genotype - Morphotype - Phenotype Code for the Prion Protein

Prion diseases are a group of neurodegenerative diseases endemic in humans and several ruminants caused by the misfolding of native prion protein (PrP) into pathological conformations. Experimental work and the mad-cow epidemic of the 1980s exposed a wide spectrum of animal susceptibility to prion diseases, including a few highly resistant animals: horses, rabbits, pigs, and dogs/canids. The variable susceptibility to disease offers a unique opportunity to uncover the mechanisms governing PrP misfolding, neurotoxicity, and transmission. Previous work indicates that PrP-intrinsic differences (sequence) are the main contributors to disease susceptibility. Several residues have been cited as critical for encoding PrP conformational stability in prion-resistant animals, including D/E159 in dog, S167 in horse, and S174 in rabbit and pig PrP (all according to human numbering). These amino acids alter PrP properties in a variety of assays, but we still do not clearly understand the structural correlates of PrP toxicity. Additional insight can be extracted from comparative structural studies, followed by molecular dynamics simulations of selected mutations, and testing in manipulable animal models. Our working hypothesis is that protective amino acids generate more compact and stable structures in a C-terminal subdomain of the PrP globular domain. We will explore this idea in this review and identify subdomains within the globular domain that may hold the key to unravel how conformational stability and disease susceptibility are encoded in PrP.

C. elegans Models to Study the Propagation of Prions and Prion-Like Proteins

A hallmark common to many age-related neurodegenerative diseases, such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS), is that patients develop proteinaceous deposits in their central nervous system (CNS). The progressive spreading of these inclusions from initially affected sites to interconnected brain areas is reminiscent of the behavior of bona fide prions in transmissible spongiform encephalopathies (TSEs), hence the term prion-like proteins has been coined. Despite intensive research, the exact mechanisms that facilitate the spreading of protein aggregation between cells, and the associated loss of neurons, remain poorly understood. As population demographics in many countries continue to shift to higher life expectancy, the incidence of neurodegenerative diseases is also rising. This represents a major challenge for healthcare systems and patients’ families, since patients require extensive support over several years and there is still no therapy to cure or stop these diseases. The model organism Caenorhabditis elegans offers unique opportunities to accelerate research and drug development due to its genetic amenability, its transparency, and the high degree of conservation of molecular pathways. Here, we will review how recent studies that utilize this soil dwelling nematode have proceeded to investigate the propagation and intercellular transmission of prions and prion-like proteins and discuss their relevance by comparing their findings to observations in other model systems and patients.

Amyloidogenic Intrinsically Disordered Proteins: New Insights into Their Self-Assembly and Their Interaction with Membranes

Aβ, IAPP, α-synuclein, and prion proteins belong to the amyloidogenic intrinsically disordered proteins’ family; indeed, they lack well defined secondary and tertiary structures. It is generally acknowledged that they are involved, respectively, in Alzheimer’s, Type II Diabetes Mellitus, Parkinson’s, and Creutzfeldt–Jakob’s diseases. The molecular mechanism of toxicity is under intense debate, as many hypotheses concerning the involvement of the amyloid and the toxic oligomers have been proposed. However, the main role is represented by the interplay of protein and the cell membrane. Thus, the understanding of the interaction mechanism at the molecular level is crucial to shed light on the dynamics driving this phenomenon. There are plenty of factors influencing the interaction as mentioned above, however, the overall view is made trickier by the apparent irreproducibility and inconsistency of the data reported in the literature. Here, we contextualized this topic in a historical, and even more importantly, in a future perspective. We introduce two novel insights: the chemical equilibrium, always established in the aqueous phase between the free and the membrane phospholipids, as mediators of protein-transport into the core of the bilayer, and the symmetry-breaking of oligomeric aggregates forming an alternating array of partially ordered and disordered monomers.

Sporadic Creutzfeldt-Jakob Disease among Physicians, Germany, 1993-2018

sCJD patients were significantly more likely than the general population to be physicians.

We investigated sporadic Creutzfeldt-Jakob disease (sCJD) among physicians in Germany by analyzing occupational information of patients with sCJD recorded by the German CJD Surveillance Unit (1993–2005; 1,250 patients, of whom 4 [0.32%] were physicians) and the National Reference Center for Human Spongiform Encephalopathies (2006–2016; 1,491 patients, of whom 13 [0.87%] were physicians). Among the physicians, we did not identify any neurologists, neurosurgeons, psychiatrists, or pathologists. A cumulative sum test showed an increase in reported physicians over time. Data for 2017–2018 indicated an increased rate of physicians among all notified sCJD cases (5/239 [2.1%]) when we used the total population of Germany as control group. Our data suggest the possibility of an increased risk for sCJD among physicians in Germany. However, we can only speculate about the reasons, and larger multinational studies are needed to replicate the finding and to clarify whether this finding is a general or a country-specific phenomenon.

Novel regulators of PrPC expression as potential therapeutic targets in prion diseases

INTRODUCTION

Prion diseases are rare and fatal neurodegenerative disorders. The key molecular event in these disorders is the misfolding of the physiological form of the cellular prion protein, PrP^C, leading to the accumulation of a pathological isoform, PrP^Sc, with unique features. Both isoforms share the same primary sequence, lacking detectable differences in posttranslational modification, a major hurdle for their biochemical or biophysical independent characterization. The mechanism underlying the conversion of PrP^C to PrP^Sc is not completely understood, so finding an effective therapy to cure prion disorders is extremely challenging.

AREAS COVERED

This review discusses the strategies for decreasing prion replication and throws a spotlight on the relevance of PrP^C in the prion accumulation process.

EXPERT OPINION

PrP^C is the key substrate for prion pathology; hence, the most promising therapeutic approach appears to be the targeting of PrP^C to block the production of the infectious isoform. The use of RNA interference and antisense oligonucleotide technologies may offer opportunities for treatment because of their success in clinical trials for other neurodegenerative diseases.

Global analysis of protein degradation in prion infected cells

Prion diseases are rare, neurological disorders caused by the misfolding of the cellular prion protein (PrP^C) into cytotoxic fibrils (PrP^Sc). Intracellular PrP^Sc aggregates primarily accumulate within late endosomes and lysosomes, organelles that participate in the degradation and turnover of a large subset of the proteome. Thus, intracellular accumulation of PrP^Sc aggregates has the potential to globally influence protein degradation kinetics within an infected cell. We analyzed the proteome-wide effect of prion infection on protein degradation rates in N2a neuroblastoma cells by dynamic stable isotopic labeling with amino acids in cell culture (dSILAC) and bottom-up proteomics. The analysis quantified the degradation rates of more than 4,700 proteins in prion infected and uninfected cells. As expected, the degradation rate of the prion protein is significantly decreased upon aggregation in infected cells. In contrast, the degradation kinetics of the remainder of the N2a proteome generally increases upon prion infection. This effect occurs concurrently with increases in the cellular activities of autophagy and some lysosomal hydrolases. The resulting enhancement in proteome flux may play a role in the survival of N2a cells upon prion infection.

Prions from Sporadic Creutzfeldt-Jakob Disease Patients Propagate as Strain Mixtures

Sporadic Creutzfeldt-Jakob disease (sCJD) cases are currently classified according to the methionine/valine polymorphism at codon 129 of the PRNP gene and the proteinase K-digested abnormal prion protein (PrP^res) isoform identified by Western blotting (type 1 or type 2). Converging evidence led to the view that MM/MV1, VV/MV2, and VV1 and MM2 sCJD cases are caused by distinct prion strains. However, in a significant proportion of sCJD patients, both type 1 and type 2 PrP^res were reported to accumulate in the brain, which raised questions about the diversity of sCJD prion strains and the coexistence of two prion strains in the same patient. In this study, a panel of sCJD brain isolates (n = 29) that displayed either a single or mixed type 1/type 2 PrP^res were transmitted into human-PrP-expressing mice (tgHu). These bioassays demonstrated that two distinct prion strains (M1^CJD and V2^CJD) were associated with the development of sCJD in MM1/MV1 and VV2/MV2 patients. However, in about 35% of the investigated VV and MV cases, transmission results were consistent with the presence of both M1^CJD and V2^CJD strains, including in patients who displayed a "pure" type 1 or type 2 PrP^res The use of a highly sensitive prion in vitro amplification technique that specifically probes the V2^CJD strain revealed the presence of the V2^CJD prion in more than 80% of the investigated isolates, including isolates that propagated as a pure M1^CJD strain in tgHu. These results demonstrate that at least two sCJD prion strains can be present in a single patient.IMPORTANCE sCJD occurrence is currently assumed to result from spontaneous and stochastic formation of a misfolded PrP nucleus in the brains of affected patients. This original nucleus then recruits and converts nascent PrP^C into PrP^Sc, leading to the propagation of prions in the patient's brain. Our study demonstrates the coexistence of two prion strains in the brains of a majority of the 23 sCJD patients investigated. The relative proportion of these sCJD strains varied both between patients and between brain areas in a single patient. These findings strongly support the view that the replication of an sCJD prion strain in the brain of a patient can result in the propagation of different prion strain subpopulations. Beyond its conceptual importance for our understanding of prion strain properties and evolution, the sCJD strain mixture phenomenon and its frequency among patients have important implications for the development of therapeutic strategies for prion diseases.

Enhanced phosphorylation of PERK in primary cultured neurons as an autonomous neuronal response to prion infection

Conversion of cellular prion protein (PrP^C) into the pathogenic isoform of prion protein (PrP^Sc) in neurons is one of the key pathophysiological events in prion diseases. However, the molecular mechanism of neurodegeneration in prion diseases has yet to be fully elucidated because of a lack of suitable experimental models for analyzing neuron-autonomous responses to prion infection. In the present study, we used neuron-enriched primary cultures of cortical and thalamic mouse neurons to analyze autonomous neuronal responses to prion infection. PrP^Sc levels in neurons increased over the time after prion infection; however, no obvious neuronal losses or neurite alterations were observed. Interestingly, a finer analysis of individual neurons co-stained with PrP^Sc and phosphorylated protein kinase RNA-activated-like endoplasmic reticulum (ER) kinase (p-PERK), the early cellular response of the PERK-eukaryotic initiation factor 2 (eIF2α) pathway, demonstrated a positive correlation between the number of PrP^Sc granular stains and p-PERK granular stains, in cortical neurons at 21 dpi. Although the phosphorylation of PERK was enhanced in prion-infected cortical neurons, there was no sign of subsequent translational repression of synaptic protein synthesis or activations of downstream unfolded protein response (UPR) in the PERK-eIF2α pathway. These results suggest that PrP^Sc production in neurons induces ER stress in a neuron-autonomous manner; however, it does not fully activate UPR in prion-infected neurons. Our findings provide insights into the autonomous neuronal responses to prion propagation and the involvement of neuron-non-autonomous factor(s) in the mechanisms of neurodegeneration in prion diseases.

Generation and characterization of two strains of transgene mice expressing chimeric MiniSOG-MusPrP

BACKGROUND

Although the presences of scrapie associated fibril in the brain tissues is a ultrastructural hallmark for prion diseases, the exact morphological structure of prion during the progression of the disease is still unclear. The host prion protein (PrP) is encoded by PrP gene (PRNP) locating on the chromosome 20 in human and the chromosome 2 in mouse. Recently, a novel correlative light and electron microscopy with Mini Singlet Oxygen Generator (miniSOG) was generated. MiniSOG, a small protein of 106 amino acids, can absorb blue light and emit green fluorescence that is detectable under the fluorescence microscope. MiniSOG can also partially catalyze the polymerization of DAB to form black stained structures in the presence of osmium tetroxide, which is able to be observed under transmission electron microscope.

NEW METHODS

Two kinds of miniSOG-PrP expressing recombinant plasmids were generated. Correlative photooxidation and transmission electron microscope were used to detect these plasmids. The plasmids were microinjected into fertilized FVB/NJ eggs and Tg mice expressing miniSOG-PrP fusion proteins were selected after successive bred withPRNP KO Tg mice.

RESULTS

Those two strains of Tg mice, Tg^SOG23 and Tg^231SOG, developed normally and maintained healthy without detectable abnormality after one-year observation. Western blots and immunohistochemical assays with PrP- and miniSOG-specific antibodies confirmed that the chimeric miniSOG-PrP proteins were expressed in the brain tissues of Tg mice. Digital PCR assays proposed that the copy numbers of the inserted external gene in Tg^SOG23 and Tg^231SOG were 2 and 12, respectively.

COMPARISON WITH EXISTING METHOD(S)

Compared with GFP tag miniSOG is significantly smaller, which makes it easy be operated experimentally and possibly has less influence on the biological function of the labeled protein. Additionally, GFP tag is an ideal marker for immunofluorescent assays, but may not be suitable for ultrastructural assays for prion morphology.

CONCLUSION

Those Tg mice may supply novel and useful experimental animals for further study on the potential morphological structure formation and deposits of prion in the brain tissues during prion infection.

Application of yeast to studying amyloid and prion diseases

Amyloids are fibrous cross-β protein aggregates that are capable of proliferation via nucleated polymerization. Amyloid conformation likely represents an ancient protein fold and is linked to various biological or pathological manifestations. Self-perpetuating amyloid-based protein conformers provide a molecular basis for transmissible (infectious or heritable) protein isoforms, termed prions. Amyloids and prions, as well as other types of misfolded aggregated proteins are associated with a variety of devastating mammalian and human diseases, such as Alzheimer's, Parkinson's and Huntington's diseases, transmissible spongiform encephalopathies (TSEs), amyotrophic lateral sclerosis (ALS) and transthyretinopathies. In yeast and fungi, amyloid-based prions control phenotypically detectable heritable traits. Simplicity of cultivation requirements and availability of powerful genetic approaches makes yeast Saccharomyces cerevisiae an excellent model system for studying molecular and cellular mechanisms governing amyloid formation and propagation. Genetic techniques allowing for the expression of mammalian or human amyloidogenic and prionogenic proteins in yeast enable researchers to capitalize on yeast advantages for characterization of the properties of disease-related proteins. Chimeric constructs employing mammalian and human aggregation-prone proteins or domains, fused to fluorophores or to endogenous yeast proteins allow for cytological or phenotypic detection of disease-related protein aggregation in yeast cells. Yeast systems are amenable to high-throughput screening for antagonists of amyloid formation, propagation and/or toxicity. This review summarizes up to date achievements of yeast assays in application to studying mammalian and human disease-related aggregating proteins, and discusses both limitations and further perspectives of yeast-based strategies.

Influence of Interspecies Transmission of Atypical Bovine Spongiform Encephalopathy Prions to Hamsters on Prion Characteristics

Bovine spongiform encephalopathy (BSE) is a prion disease in cattle and is classified into the classical type (C-BSE) and two atypical BSEs, designated as high type (H-BSE) and low type (L-BSE). These classifications are based on the electrophoretic migration of the proteinase K-resistant core (PrP^res) of the disease-associated form of the prion protein (PrP^d). In a previous study, we succeeded in transmitting the H-BSE prion from cattle to TgHaNSE mice overexpressing normal hamster cellular PrP (PrP^C). Further, Western blot analysis demonstrated that PrP^res banding patterns of the H-BSE prion were indistinguishable from those of the C-BSE prion in TgHaNSE mice. In addition, similar PrP^res glycoprofiles were detected among H-, C-, and L-BSE prions in TgHaNSE mice. Therefore, to better understand atypical BSE prions after interspecies transmission, H-BSE prion transmission from TgHaNSE mice to hamsters was investigated, and the characteristics of classical and atypical BSE prions among hamsters, wild-type mice, and mice overexpressing bovine PrP^C (TgBoPrP) were compared in this study using biochemical and neuropathological methods. Identical PrP^res banding patterns were confirmed between TgHaNSE mice and hamsters in the case of all three BSE prion strains. However, these PrP^res banding patterns differed from those of TgBoPrP and wild-type mice infected with the H-BSE prion. In addition, glycoprofiles of TgHaNSE mice and hamsters infected with the L-BSE prion differed from those of TgBoPrP mice infected with the L-BSE prion. These data indicate that the PrP^C amino acid sequences of new host species rather than other host environmental factors may affect some molecular aspects of atypical BSE prions. Although three BSE prion strains were distinguishable based on the neuropathological features in hamsters, interspecies transmission modified some molecular properties of atypical BSE prions, and these properties were indistinguishable from those of C-BSE prions in hamsters. Taken together, PrP^res banding patterns and glycoprofiles are considered to be key factors for BSE strain typing. However, this study also revealed that interspecies transmission could sometimes influence these characteristics.

Shedding and stability of CWD prion seeding activity in cervid feces

CWD is an emergent prion disease that now affects cervid species on three continents. CWD is efficiently spread in wild and captive populations, likely through both direct animal contact and environmental contamination. Here, by longitudinally assaying in feces of CWD-exposed white-tailed deer by RT-QuIC, we demonstrate fecal shedding of prion seeding activity months before onset of clinical symptoms and continuing throughout the disease course. We also examine the impact of simulated environmental conditions such as repeated freeze-thaw cycles and desiccation on fecal prion seeding activity. We found that while multiple (n = 7) freeze-thaw cycles substantially decreased fecal seeding activity, desiccation had little to no effect on seeding activity. Finally, we examined whether RT-QuIC testing of landscape fecal deposits could distinguish two premises with substantial known CWD prevalence from one in which no CWD-infected animals had been detected. In the above pilot study, this distinction was possible. We conclude that fecal shedding of CWD prions occurs over much of the disease course, that environmental factors influence prion seeding activity, and that it is feasible to detect fecal prion contamination using RT-QuIC.

Cellular models for discovering prion disease therapeutics: Progress and challenges

Prions, which cause fatal neurodegenerative disorders such as Creutzfeldt-Jakob disease, are misfolded and infectious protein aggregates. Currently, there are no treatments available to halt or even delay the progression of prion disease in the brain. The infectious nature of prions has resulted in animal paradigms that accurately recapitulate all aspects of prion disease, and these have proven to be instrumental for testing the efficacy of candidate therapeutics. Nonetheless, infection of cultured cells with prions provides a much more powerful system for identifying molecules capable of interfering with prion propagation. Certain lines of cultured cells can be chronically infected with various types of mouse prions, and these models have been used to unearth candidate anti-prion drugs that are at least partially efficacious when administered to prion-infected rodents. However, these studies have also revealed that not all types of prions are equal, and that drugs active against mouse prions are not necessarily effective against prions from other species. Despite some recent progress, the number of cellular models available for studying non-mouse prions remains limited. In particular, human prions have proven to be particularly challenging to propagate in cultured cells, which has severely hindered the discovery of drugs for Creutzfeldt-Jakob disease. In this review, we summarize the cellular models that are presently available for discovering and testing drugs capable of blocking the propagation of prions and highlight challenges that remain on the path towards developing therapies for prion disease.

Prion-like mechanisms in neurodegenerative disease: Implications for Huntington's disease therapy

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG repeat expansions in the huntingtin gene resulting in the synthesis of a misfolded form of the huntingtin protein (mHTT) which is toxic. The current treatments for HD are only palliative. Some of the potential therapies for HD include gene therapy (using antisense oligonucleotides and clustered regularly interspaced short palindromic repeats-Cas9 system) and stem-cell-based therapies. Various types of stem cell transplants, such as mesenchymal stem cells, neural stem cells, and reprogrammed stem cells, have the potential to either replace the lost neurons or support the existing neurons by releasing trophic factors. Most of the transplants are xenografts and allografts; however, recent reports on HD patients who received grafts suggest that the mHTT aggregates are transferred from the host neurons to the grafted cells as well as to the surrounding areas of the graft by a "prion-like" mechanism. This observation seems to be true for autotransplantation paradigms, as well. This article reviews the different types of stem cells that have been transplanted into HD patients and their therapeutic efficacy, focusing on the transfer of mHTT from the host cells to the graft. Autotransplants of reprogramed stem cells in HD patients are a promising therapeutic option. However, this needs further attention to ensure a better understanding of the transfer of mHTT aggregates following transplantation of the gene-corrected cells back into the patient.

Deciphering Copper Coordination in the Mammalian Prion Protein Amyloidogenic Domain

Prions are pathological isoforms of the cellular prion protein that is responsible for transmissible spongiform encephalopathies (TSE). Cellular prion protein interacts with copper, Cu(II), through octarepeat and nonoctarepeat (non-OR) binding sites. The molecular details of Cu(II) coordination within the non-OR region are not well characterized yet. By the means of small angle x-ray scattering and x-ray absorption spectroscopic methods, we have investigated the effect of Cu(II) on prion protein folding and its coordination geometries when bound to the non-OR region of recombinant prion proteins (recPrP) from mammalian species considered resistant or susceptible to TSE. As the prion resistant model, we used ovine recPrP (OvPrP) carrying the protective polymorphism at residues A136, R154, and R171, whereas as TSE-susceptible models, we employed OvPrP with V136, R154, and Q171 polymorphism and bank vole recPrP. Our analysis reveals that Cu(II) affects the structural plasticity of the non-OR region, leading to a more compacted conformation. We then identified two Cu(II) coordination geometries: in the type 1 coordination observed in OvPrP at residues A136, R154, and R171, the metal is coordinated by four residues; conversely, the type 2 coordination is present in OvPrP with V136, R154, and Q171 and bank vole recPrP, where Cu(II) is coordinated by three residues and by one water molecule, making the non-OR region more exposed to the solvent. These changes in copper coordination affect the recPrP amyloid aggregation. This study may provide new insights into the molecular mechanisms governing the resistance or susceptibility of certain species to TSE.

Changes in cellular prion protein expression, processing and localisation during differentiation of the neuronal cell line CAD 5

BACKGROUND INFORMATION

Cellular prion protein (PrP^C ) is infamous for its role in prion diseases. The physiological function of PrP^C remains enigmatic, but several studies point to its involvement in cell differentiation processes. To test this possibility, we monitored PrP^C changes during the differentiation of prion-susceptible CAD 5 cells, and then we analysed the effect of PrP^C ablation on the differentiation process.

RESULTS

Neuronal CAD 5 cells differentiate within 5 days of serum withdrawal, with the majority of the cells developing long neurites. This process is accompanied by an up to sixfold increase in PrP^C expression and enhanced N-terminal β-cleavage of the protein, which suggests a role for the PrP^C in the differentiation process. Moreover, the majority of PrP^C in differentiated cells is inside the cell, and a large proportion of the protein does not associate with membrane lipid rafts. In contrast, PrP^C in proliferating cells is found mostly on the cytoplasmic membrane and is predominantly associated with lipid rafts. To determine the importance of PrP^C in cell differentiation, a CAD 5 PrP^-/- cell line with ablated PrP^C expression was created using the CRISPR/Cas9 system. We observed no considerable difference in morphology, proliferation rate or expression of molecular markers between CAD 5 and CAD 5 PrP^-/- cells during the differentiation initiated by serum withdrawal.

CONCLUSIONS

PrP^C characteristics, such as cell localisation, level of expression and posttranslational modifications, change during CAD 5 cell differentiation, but PrP^C ablation does not change the course of the differentiation process.

SIGNIFICANCE

Ablation of PrP^C expression does not affect CAD 5 cell differentiation, although we observed many intriguing changes in PrP^C features during the process. Our study does not support the concept that PrP^C is important for neuronal cell differentiation, at least in simple in vitro conditions.

Unique Structural Features of Mule Deer Prion Protein Provide Insights into Chronic Wasting Disease

Chronic wasting disease (CWD) is a highly infectious prion disease of cervids. Accumulation of prions, the disease-specific structural conformers of the cellular prion protein (PrP^C), in the central nervous system, is the key pathological event of the disorder. The analysis of cervid PrP^C sequences revealed the existence of polymorphism at position 226, in which deer PrP contains glutamine (Q), whereas elk PrP contains glutamate (E). The effects of this polymorphism on CWD are still unknown. We determined the high-resolution nuclear magnetic resonance structure of the mule deer prion protein that was compared to previously published PrP structures of elk and white-tailed deer. We found that the polymorphism Q226E could influence the long-range intramolecular interactions and packing of the β2-α2 loop and the C-terminus of the α3 helix of cervid PrP structures. This solvent-accessible epitope is believed to be involved in prion conversion. Additional differences were observed at the beginning of the well-defined C-terminus domain, in the α2-α3 region, and in its interactions with the α1 helix. Here, we highlight the importance of the PrP structure in prion susceptibility and how single amino acid differences might influence the overall protein folding.

Aberrant Decrease of the Endogenous SIRT3 and Increases of Acetylated Proteins in Scrapie-Infected Cell Line SMB-S15 and in the Brains of Experimental Mice

The linkage between mitochondrial dysfunction and neurodegenerative diseases including prion diseases has been frequently reported. As the major deacetylase in mitochondria, SIRT3 plays a crucial part in regulating the function of many mitochondrial proteins. Although SIRT3 was reported to be linked to several neurodegenerative diseases, it is still unknown if SIRT3 is involved in prion diseases. In this study, we have presented a substantially declined status of mitochondrial SIRT3 in both the levels of cultured cells and an experimental rodent model during scrapie prion replication and infection. Such decreased SIRT3 activity led to a decreased deacetylating activity, resulting in increases of the acetylated forms of some substrates of SIRT3 in cells, such as SOD2 and ATP5β. Declined SOD2 and ATP5β activities subsequently caused an increase of intracellular ROS and a reduction of ATP. Furthermore, we have also proposed evidence that the activity of cellular SIRT3 is partially recovered when abnormal prion propagation in the cultured cells is removed by resveratrol. Those data emphasize a close connection between the prion replication and mitochondrial deacetylation due to SIRT3, thereby partially explaining mitochondrial dysfunction in prion diseases.

Sporadic Creutzfeldt-Jakob Disease in a Woman Married Into a Gerstmann-Sträussler-Scheinker Family: An Investigation of Prions Transmission via Microchimerism

This is the first report of presumed sporadic Creutzfeldt-Jakob disease (sCJD) and Gerstmann-Sträussler-Scheinker disease (GSS) with the prion protein gene c.305C>T mutation (p.P102L) occurring in one family. The father and son were affected with GSS and the mother had a rapidly progressive form of CJD. Diagnosis of genetic, variant, and iatrogenic CJD was ruled out based on the mother's clinical history, genetic tests, and biochemical investigations, all of which supported the diagnosis of sCJD. However, given the low incidence of sCJD and GSS, their co-occurrence in one family is extraordinary and challenging. Thus, a hypothesis for the transmission of infectious prion proteins (PrPSc) via microchimerism was proposed and investigated. DNA from 15 different brain regions and plasma samples of the CJD patient was subjected to PCR and shallow sequencing for detection of a male sex-determining chromosome Y (chr. Y). However, no trace of chr. Y was found. A long CJD incubation period or presumed small concentrations of chr. Y may explain the obtained results. Further studies of CJD and GSS animal models with controlled genetic and proteomic features are needed to determine whether maternal CJD triggered via microchimerism by a GSS fetus might present a new PrPSc transmission route.