Development Of Prion Diseases Research Articles

Novel Single-Nucleotide Polymorphisms (SNPs) and Genetic Studies of the Shadow of Prion Protein (SPRN) in Quails.

Prion diseases are a group of deadly neurodegenerative disorders caused by the accumulation of the normal prion protein (PrPC) into misfolding pathological conformations (PrPSc). The PrP gene is essential for the development of prion diseases. Another candidate implicated in prion pathogenesis is the shadow of the prion protein (SPRN) gene. To date, genetic polymorphisms of the SPRN gene and the structure of the Sho protein have not been explored in quails. We used polymerase chain reaction (PCR) to amplify the SPRN gene sequence and then conducted Sanger DNA sequencing to identify the genetic polymorphisms in quail SPRN. Furthermore, we examined the genotype, allele, and haplotype frequencies, and assessed the linkage disequilibrium among the genetic polymorphisms of the SPRN gene in quails. Additionally, we used in silico programs such as MutPred2, SIFT, MUpro, AMYCO, and SODA to predict the pathogenicity of non-synonymous single-nucleotide polymorphisms (SNPs). Alphafold2 predicted the 3D structure of the Sho protein in quails. The results showed that a total of 13 novel polymorphisms were found in 106 quails, including 4 non-synonymous SNPs. Using SIFT and MUpro in silico programs, three out of the four non-synonymous SNPs (A68T, L74P, and M105I) were predicted to have deleterious effects on quail Sho. Furthermore, the 3D structure of quail Sho was predicted to be similar to that of chicken Sho. To our knowledge, this is the first report to investigate the genetic and structural properties of the quail SPRN gene.

Novel polymorphisms and genetic studies of the shadow of prion protein gene (SPRN) in pheasants.

Prion diseases in mammals are caused by the structural conversion of the natural prion protein (PrPC) to a pathogenic isoform, the "scrapie form of prion protein (PrPSc)." Several studies reported that the shadow of prion protein (Sho), encoded by the shadow of prion protein gene (SPRN), is involved in prion disease development by accelerating the conformational conversion of PrPC to PrPSc. Until now, genetic polymorphisms of the SPRN gene and the protein structure of Sho related to fragility to prion disease have not been investigated in pheasants, which are a species of poultry. Here, we identified the SPRN gene sequence by polymerase chain reaction (PCR) and compared the SPRN gene and Sho protein sequences among various prion disease-susceptible and -resistant species to identify the distinctive genetic features of pheasant Sho using Clustal Omega. In addition, we investigated genetic polymorphisms of the SPRN gene in pheasants and analyzed genotype, allele, and haplotype frequencies, as well as linkage disequilibrium among the genetic polymorphisms. Furthermore, we used in silico programs, namely Mutpred2, MUpro and AMYCO, to investigate the effect of non-synonymous single nucleotide polymorphisms (SNPs). Finally, the predicted secondary and tertiary structures of Sho proteins from various species were analyzed by Alphafold2. In the present study, we reported pheasant SPRN gene sequences for the first time and identified a total of 14 novel SNPs, including 7 non-synonymous and 4 synonymous SNPs. In addition, the pheasant Sho protein sequence showed 100% identity with the chicken Sho protein sequence. Furthermore, amino acid substitutions were predicted to affect the hydrogen bond distribution in the 3D structure of the pheasant Sho protein. To the best of our knowledge, this is the first report of the genetic and structural features of the pheasant SPRN gene.

#4966 CELLULAR PRION PROTEIN ACTIVATES THE TBK1-IRF3 SIGNALING PATHWAY TO AGGRAVATE RENAL FIBROSIS

Abstract Background and Aims Chronic kidney disease (CKD) is an irreversible degenerative disease characterized by gradual loss of renal function, contributing to high morbidity and mortality as well as heavy economic cost to society. Clinically, there are few available strategies to slow CKD progression. Because the uremic phenotypes include many features of aging, CKD is considered as a premature aging syndrome. Neurodegenerative diseases, such as Alzheimer's disease, and Parkinson's disease are extensively studied aging-related diseases, in which cytotoxic proteins misfolding and aggregation in neural cells is the main characteristic. The misfolding and aggregation of the prion protein is tightly linked to the development of prion diseases. Interestingly, a remarkable elevation of cellular prion protein (PrPC) in the urine and plasma of CKD patients was reported. However, the role of PrPC in the pathogenesis of kidney diseases remains largely unknown. The aim of the current study is to investigate the role of PrPC in renal fibrosis. Methods Immunohistochemistry staining was conducted to evaluate the expression of PrPC in renal biopsies from CKD patients. Enzyme linked immunosorbent assay (ELISA) was performed to detect urinary PrPC of CKD patients. Animal model of renal fibrosis was induced by unilateral ureteral occlusion (UUO). Western blot, real time PCR and immunofluorescence staining were performed to evaluate the expression and distribution of PrPC. Proximal tubule specific Prnp knockout mice (PEPCK-Prnp-KO) was constructed to explore the pathogenic role of PrPC in renal fibrosis. Primary proximal tubular epithelial cells (PTCs) overexpressed PrPC were collected for RNA-seq analysis. TBK1 inhibitor amlexanox, and IRF3 siRNA were used to block TBK1-IRF3 pathway in rat tubular epithelial cells (NRK-52E), respectively. Amlexanox was administered orally to UUO mice. H&E, Masson and Sirius red staining were used to estimate renal pathology. Results The protein expression levels of PrPC both in renal biopsies and urine from CKD patients were elevated and significantly correlated with the severity of interstitial fibrosis and the decline of eGFR. PrPC proteins were significantly increased, and aggregated in proximal renal tubules in fibrotic renal tissues induced by UUO. Compared with wild-type littermates, PEPCK-Prnp-KO mice showed reduced extracellular matrix accumulation and interstitial inflammation at day 7 after UUO. PrPC provokes profibrotic response of renal tubular cells via the TBK1-IRF3 pathway. TBK1 inhibitor amlexanox or silencing endogenous IRF3 significantly inhibited PrPC-induced profibrogenic phenotypic transformation in NRK-52 cells. Amlexanox attenuated interstitial fibrosis induced by UUO. Conclusion Our experimental results indicate that PrPC-TBK1-IRF3 pathway plays a detrimental role in profibrogenic transformation of renal tubular cells and thus contributes to interstitial fibrosis. Blocking TBK1 activation is a plausible strategy for therapeutic intervention of chronic kidney disorders.

Mast Cell Proteases Cleave Prion Proteins and a Recombinant Ig against PrP Can Activate Human Mast Cells.

IgE Abs, best known for their role in allergic reactions, have only rarely been used in immunotherapies. Nevertheless, they offer a potential alternative to the more commonly used IgGs. The affinity of IgE Ag binding influences the type of response from mast cells, so any immunotherapies using IgEs must balance Ag affinity with desired therapeutic effect. One potential way to harness differential binding affinities of IgE is in protein aggregation diseases, where low-affinity binding of endogenous proteins is preferred, but enhanced binding of clusters of disease-associated aggregated proteins could target responses to the sites of disease. For this reason, we sought to create a low-affinity IgE against the prion protein (PrP), which exists in an endogenous monomeric state but can misfold into aggregated states during the development of prion disease. First, we determined that mast cell proteases tryptase and cathepsin G were capable of degrading PrP. Then we engineered a recombinant IgE Ab directed against PrP from the V region of a PrP-specific IgG and tested its activation of the human mast cell line LAD2. The αPrP IgE bound LAD2 through Fc receptors. Crosslinking receptor-bound αPrP IgE activated SYK and ERK phosphorylation, caused Fc receptor internalization, and resulted in degranulation. This work shows that a recombinant αPrP IgE can activate LAD2 cells to release enzymes that can degrade PrP, suggesting that IgE may be useful in targeting diseases that involve protein aggregation.

Tailored behavioural tests reveal early and progressive cognitive deficits in M1000 prion disease

Prion diseases are pathogenically linked to the normal cellular prion protein (PrPC) misfolding into abnormal conformers (PrPSc), with PrPSc accumulation underpinning both transmission and neurotoxicity. Despite achieving this canonical understanding, however fundamental questions remain incompletely resolved, including the level of pathophysiological overlap between neurotoxic and transmitting species of PrPSc and the temporal profiles of their propagation. To further investigate the likely time of occurrence of significant levels of neurotoxic species during prion disease development, the well characterised in vivo M1000 murine model was employed. Following intracerebral inoculation, detailed serial cognitive and ethological testing at specified time points suggested subtle transition to early symptomatic disease from ∼50% of the overall disease course. In addition to observing a chronological order for impaired behaviours, different behavioural tests also showed distinctive profiles of evolving cognitive impairments with the Barnes maze demonstrating a relatively simple linear worsening of spatial learning and memory over an extended period while in contrast a conditioned fear memory paradigm previously untested in murine prion disease demonstrated more complex alterations during disease progression. These observations support the likely production of neurotoxic PrPSc from at least just prior to the mid-point of murine M1000 prion disease and illustrate the likely need to tailor the types of behavioural testing across the time course of disease progression for optimal detection of cognitive deficits.

A point mutation in GPI-attachment signal peptide accelerates the development of prion disease.

A missense variant from methionine to arginine at codon 232 (M232R) of the prion protein gene accounts for ~ 15% of Japanese patients with genetic prion diseases. However, pathogenic roles of the M232R substitution for the induction of prion disease have remained elusive because family history is usually absent in patients with M232R. In addition, the clinicopathologic phenotypes of patients with M232R are indistinguishable from those of sporadic Creutzfeldt-Jakob disease patients. Furthermore, the M232R substitution is located in the glycosylphosphatidylinositol (GPI)-attachment signal peptide that is cleaved off during the maturation of prion proteins. Therefore, there has been an argument that the M232R substitution might be an uncommon polymorphism rather than a pathogenic mutation. To unveil the role of the M232R substitution in the GPI-attachment signal peptide of prion protein in the pathogenesis of prion disease, here we generated a mouse model expressing human prion proteins with M232R and investigated the susceptibility to prion disease. The M232R substitution accelerates the development of prion disease in a prion strain-dependent manner, without affecting prion strain-specific histopathologic and biochemical features. The M232R substitution did not alter the attachment of GPI nor GPI-attachment site. Instead, the substitution altered endoplasmic reticulum translocation pathway of prion proteins by reducing the hydrophobicity of the GPI-attachment signal peptide, resulting in the reduction of N-linked glycosylation and GPI glycosylation of prion proteins. To the best of our knowledge, this is the first time to show a direct relationship between a point mutation in the GPI-attachment signal peptide and the development of disease.

Following the Aggregation of Human Prion Protein on Heparin Functionalized Gold Surface in Real Time.

The aggregation of the prion protein (PrP) plays a key role in the development of prion diseases and is believed to be an autocatalytic process with a very high kinetic barrier. Intensive studies have focused on overcoming the kinetic barriers under extremely nonphysiological in vitro conditions by altering the pH of PrP solution on solid surfaces, such as gold, mica, and a lipid bilayer. Importantly, sulfated glycosaminoglycans (GAGs), including heparin, were found to be associated with PrP misfolding and aggregation, suggesting GAGs have catalytic roles in PrP aggregation processes. However, the exact role and details of GAGs in the PrP aggregation are not clear and need a thorough perusal. Here, we investigate the PrP aggregation process on a heparin functionalized gold surface by in situ, real-time monitoring of the atomic scale details of the whole aggregation process by single molecule atomic force microscopy (AFM), combining simultaneous topographic and recognition (TREC) imaging and single molecule force spectroscopy (SMFS). We observed the whole aggregation process for full-length human recombinant PrP (23-231) aggregation on the heparin modified gold surface, from the formation of oligomers, to the assembly of protofibrils and short fibers, and the formation of elongated mature fibers. Heparin is found to promote the PrP aggregation by facilitating the formation of oligomers during the early nucleation stage.

Methionine homozygosity for PRNP polymorphism and susceptibility to human prion diseases

BackgroundNo studies have assessed the independent association of methionine homozygosity at codon 129 with the susceptibility to prion diseases, controlling for the effects of the codon 219 polymorphisms and other...

MicroRNA-146a as abiomarker for transmissible spongiform encephalopathy.

The pro-inflammatory, innate-immune system ribonucleic acid mediator microRNA-146a, constitutively expressed in the brain and central nervous system (CNS) of both the mouse and the human, is pathologically up-regulated in multiple transmissible spongiform encephalopathies (TSEs) to several times its basal level. miRNA-146a: (i) exists as a ~22-ribonucleotide (nt) single-stranded non-coding RNA (sncRNA) whose sequence is unique and highly selected over evolution; (ii) is brain-, CNS- and lymphoid-tissue enriched and exhibits a 100% RNA sequence homology between the mouse and the human; (iii) has been repeatedly shown to play critical immunological and pro-inflammatory roles in the onset and propagation of several human CNS disorders including progressive, incapacitating, and lethal neurological syndromes that include prion disease (PrD) and Alzheimer's disease (AD); (iv) is a fascinating molecular entity because it is representative of the smallest class of soluble, information-carrying, amphipathic sncRNA yet described; (v) has capability to be induced by cellular stressors and the pro-inflammatory transcription factor NF-kB (p50/p65); (vi) has capability to post-transcriptionally regulate multiple mRNAs and cellular processes in neurological health and disease; (vii) is upregulated in human host cells after viral invasion by single-stranded RNA (ssRNA) or double-stranded DNA (dsDNA) neurotropic viruses; and (viii) has an immense potential in neuro-degenerative disease therapeutics via anti-NF-kB and/or anti-miRNA-146a treatment strategies. In this short communication we provide for the first time evidence that miRNA-146a is a prominent sncRNA species in experimental murine prion disease, progressively increasing in the pre-symptomatic stages in C57BL/6J, SJL/J or Swiss Albino murine scrapie prion models. The highest miRNA-146a levels were quantified in these three different murine scrapie models exhibiting full symptomology of prion infection. The results suggest that miRNA-146a levels in the brain may be useful as an accessory diagnostic, prognostic or response-to-treatment biomarker to monitor the onset and development of PrD in experimental murine models that may also be extrapolated to be a relevant adjunct biomarker in human TSEs.

Structure of prion β-oligomers as determined by short-distance crosslinking constraint-guided discrete molecular dynamics simulations.

The conversion of the native monomeric cellular prion protein (PrPC) into an aggregated pathological β‐oligomeric form (PrPβ) and an infectious form (PrPSc) is the central element in the development of prion diseases. The structure of the aggregates and the molecular mechanisms of the conformational changes involved in the conversion are still unknown. We applied mass spectrometry combined with chemical crosslinking, hydrogen/deuterium exchange, limited proteolysis, and surface modification for the differential characterization of the native and the urea+acid‐converted prion β‐oligomer structures to obtain insights into the mechanisms of conversion and aggregation. For the determination of the structure of the monomer and the dimer unit of the β‐oligomer, we applied a recently‐developed approach for de novo protein structure determination which is based on the incorporation of zero‐length and short‐distance crosslinking data as intra‐ and inter‐protein constraints in discrete molecular dynamics simulations (CL‐DMD). Based on all of the structural‐proteomics experimental data and the computationally predicted structures of the monomer units, we propose the potential mode of assembly of the β‐oligomer. The proposed β‐oligomer assembly provides a clue on the β‐sheet nucleation site, and how template‐based conversion of the native prion molecule occurs, growth of the prion aggregates, and maturation into fibrils may occur.

Deletion of Kif5c Does Not Alter Prion Disease Tempo or Spread in Mouse Brain

In prion diseases, the spread of infectious prions (PrPSc) is thought to occur within nerves and across synapses of the central nervous system (CNS). However, the mechanisms by which PrPSc moves within axons and across nerve synapses remain undetermined. Molecular motors, including kinesins and dyneins, transport many types of intracellular cargo. Kinesin-1C (KIF5C) has been shown to transport vesicles carrying the normal prion protein (PrPC) within axons, but whether KIF5C is involved in PrPSc axonal transport is unknown. The current study tested whether stereotactic inoculation in the striatum of KIF5C knock-out mice (Kif5c−/−) with 0.5 µL volumes of mouse-adapted scrapie strains 22 L or ME7 would result in an altered rate of prion spreading and/or disease timing. Groups of mice injected with each strain were euthanized at either pre-clinical time points or following the development of prion disease. Immunohistochemistry for PrP was performed on brain sections and PrPSc distribution and tempo of spread were compared between mouse strains. In these experiments, no differences in PrPSc spread, distribution or survival times were observed between C57BL/6 and Kif5c−/− mice.

Case report of homozygous E200D mutation of PRNP in apparently sporadic Creutzfeldt-Jakob disease

BackgroundInherited prion diseases are rare autosomal dominant disorders associated with diverse clinical presentations. All are associated with mutation of the gene that encodes prion protein (PRNP). Homozygous mutations with atypical clinical phenotypes have been described but are extremely rare.Case presentationA Chinese patient presented with a rapidly progressive cognitive and motor disorder in the clinical spectrum of sCJD. Investigations strongly suggested a diagnosis of CJD. He was found to carry a homozygous mutation at PRNP codon 200 (E200D), but there was no known family history of the disorder. The estimated allele frequency of E200D in East Asian populations is incompatible with it being a highly penetrant mutation in the heterozygous state.ConclusionIn our view the homozygous PRNP E200D genotype is likely to be causal of CJD in this patient. Homotypic PrP interactions are well known to favour the development of prion disease. The case is compatible with recessively inherited prion disease.

The interplay between a GC-rich oligonucleotide and copper ions on prion protein conformational and phase transitions

The prion protein (PrP) misfolding to its infectious form is critical to the development of prion diseases, whereby various ligands are suggested to participate, such as copper and nucleic acids (NA). The PrP globular domain was shown to undergo NA-driven liquid-liquid phase separation (LLPS); this latter may precede pathological aggregation. Since Cu(II) is a physiological ligand of PrP, we argue whether it modulates phase separation altogether with nucleic acids. Using recombinant PrP, we investigate the effects of Cu(II) (at 6 M equivalents) and a previously described PrP-binding GC-rich DNA (equimolarly to protein) on PrP conformation, oligomerization, and phase transitions using a range of biophysical techniques. Raman spectroscopy data reveals the formation of the ternary complex. Microscopy suggests that phase separation is mainly driven by DNA, whereas Cu(II) has no influence. Our results show that DNA can be an adjuvant, leading to the structural conversion of PrP, even in the presence of an endogenous ligand, copper. These results provide new insights into the role of Cu(II) and NA on the phase separation, structural conversion, and aggregation of PrP, which are critical events leading to neurodegeneration.

The Prion-like Properties of Amyloid-beta Peptide and Tau: Is there Any Risk of Transmitting Alzheimer's Disease During Neurosurgical Interventions?

Recent studies have recognized similarities between the peptides involved in the neuropathology of Alzheimer's disease and prions. The Tau protein and the Amyloid β peptide represent the theoretical pillars of Alzheimer's disease development. It is probable that there is a shared mechanism for the transmission of these substances and the prion diseases development; this presumption is based on the presentation of several cases of individuals without risk factors who developed dementia decades after a neurosurgical procedure. This article aims to present the role of Aβ and Tau, which underlie the pathophysiologic mechanisms involved in the AD and their similarities with the prion diseases infective mechanisms by means of the presentation of the available evidence at molecular (in-vitro), animal, and human levels that support the controversy on whether these diseases might be transmitted in neurosurgical interventions, which may constitute a wide public health issue.

Goats naturally devoid of PrPC are resistant to scrapie

Prion diseases are progressive and fatal, neurodegenerative disorders described in humans and animals. According to the “protein-only” hypothesis, the normal host-encoded prion protein (PrPC) is converted into a pathological and infectious form (PrPSc) in these diseases. Transgenic knockout models have shown that PrPC is a prerequisite for the development of prion disease. In Norwegian dairy goats, a mutation (Ter) in the prion protein gene (PRNP) effectively blocks PrPC synthesis. We inoculated 12 goats (4 PRNP+/+, 4 PRNP+/Ter, and 4 PRNPTer/Ter) intracerebrally with goat scrapie prions. The mean incubation time until clinical signs of prion disease was 601 days post-inoculation (dpi) in PRNP+/+ goats and 773 dpi in PRNP+/Ter goats. PrPSc and vacuolation were similarly distributed in the central nervous system (CNS) of both groups and observed in all brain regions and segments of the spinal cord. Generally, accumulation of PrPSc was limited in peripheral organs, but all PRNP+/+ goats and 1 of 4 PRNP+/Ter goats were positive in head lymph nodes. The four PRNPTer/Ter goats remained healthy, without clinical signs of prion disease, and were euthanized 1260 dpi. As expected, no accumulation of PrPSc was observed in the CNS or peripheral tissues of this group, as assessed by immunohistochemistry, enzyme immunoassay, and real-time quaking-induced conversion. Our study shows for the first time that animals devoid of PrPC due to a natural mutation do not propagate prions and are resistant to scrapie. Clinical onset of disease is delayed in heterozygous goats expressing about 50% of PrPC levels.

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.

Polymorphisms Modulate Sheep Prion Protein Susceptibility to Misfolding by Altering the Residue Network of Interactions

The autocatalytic misfolding of the cellular form of the prion protein, PrPC, to the infectious form, PrPSc, is critical to the development of prion diseases. Though the mechanism for this misfolding is not well understood, previous research recognizes the role of genetic mutations in varying susceptibilities to prion diseases in sheep. Using structural bioinformatics techniques, our study examines the residue interactions in three different sheep PrPC structures. These structures contain different point mutations and have different levels of susceptibility to scrapie prion disease. We will discuss our results in relation to the role of mutations on networks of interaction, and propose a mechanism for the primary misfolding of the a-helical rich PrPC into the b-sheet rich PrPSc. This work was made possible partly by grants from the National Institute for General Medical Science (NIGMS) (5P20GM103427), a component of the National Institutes of Health (NIH), and its contents are the sole responsibility of the authors and do not necessarily represent the official views of NIGMS or NIH.

GPI-anchor signal sequence influences PrPC sorting, shedding and signalling, and impacts on different pathomechanistic aspects of prion disease in mice.

The cellular prion protein (PrPC) is a cell surface glycoprotein attached to the membrane by a glycosylphosphatidylinositol (GPI)-anchor and plays a critical role in transmissible, neurodegenerative and fatal prion diseases. Alterations in membrane attachment influence PrPC-associated signaling, and the development of prion disease, yet our knowledge of the role of the GPI-anchor in localization, processing, and function of PrPC in vivo is limited We exchanged the PrPC GPI-anchor signal sequence of for that of Thy-1 (PrPCGPIThy-1) in cells and mice. We show that this modifies the GPI-anchor composition, which then lacks sialic acid, and that PrPCGPIThy-1 is preferentially localized in axons and is less prone to proteolytic shedding when compared to PrPC. Interestingly, after prion infection, mice expressing PrPCGPIThy-1 show a significant delay to terminal disease, a decrease of microglia/astrocyte activation, and altered MAPK signaling when compared to wild-type mice. Our results are the first to demonstrate in vivo, that the GPI-anchor signal sequence plays a fundamental role in the GPI-anchor composition, dictating the subcellular localization of a given protein and, in the case of PrPC, influencing the development of prion disease.

Valuing the investigation of Prion diseases in Ethiopia

Cellular Prion proteins have a wide variety of function from the birth of a cell to its programmed death. Prion protein can be the cause for a number of lethal animal and human diseases when misfolded. Furthermore, prion infection is transmissible. Polymorphisms of prion gene at different loci are associated with prion diseases development, the onset of symptoms and incubation period. Indel polymorphism in the promoter region of PRNP gene is found to be accoaited to BSE in cattle while the haplotype ARR at positions 136,154 and 171 is resistant to scrapie in sheep. Taking into account the severity of prion disease and its potential entrance to the food chain, genetic and clinical studies continued to be conducted in a different course of time in many countries.

Direct observation of prion protein oligomer formation reveals an aggregation mechanism with multiple conformationally distinct species.

The aggregation of the prion protein (PrP) plays a key role in the development of prion diseases. In the past decade, a similar process has been associated with other proteins, such as Aβ, tau, and α-synuclein, which participate in other neurodegenerative diseases. It is increasingly recognized that the small oligomeric species of aggregates can play an important role in the development of prion diseases. However, determining the nature of the oligomers formed during the aggregation process has been experimentally difficult due to the lack of suitable methods capable of the detection and characterization of the low level of oligomers that may form. To address this problem, we have utilized single-aggregate methods to study the early events associated with aggregation of recombinant murine PrP in vitro to approach the bona fide process in vivo. PrP aggregation resulted in the formation of thioflavin T (ThT)-inactive and ThT-active species of oligomers. The ThT-active oligomers undergo conversion from a Proteinase K (PK)-sensitive to PK-resistant conformer, from which mature fibrils can eventually emerge. Overall, our results show that single-aggregate methods can provide structural and mechanistic insights into PrP aggregation, identify the potential species that mediates cytotoxicity, and reveal that a range of distinct oligomeric species with different properties is formed during prion protein aggregation.