Prion Strains Research Articles

Species barrier as molecular basis for adaptation of synthetic prions with N-terminally truncated PrP.

Mammalian prions are neurotropic pathogens formed from PrPSc assemblies, a misfolded variant of the host-encoded prion protein PrPC. Multiple PrPSc conformations or strains self-propagate in host populations or mouse models of prion diseases, exhibiting distinct biological and biochemical phenotypes. Constrained interactions between PrPSc and PrPC conformations confer species specificity and regulate cross-species transmission. The pathogenicity of fibrillar assemblies derived from bacterially expressed recombinant PrP (rPrP) has been instrumental in demonstrating the protein-only nature of prions. Yet, their ability to encode different strains and transmit between species remains poorly studied, hampering their use in exploring structure-to-strain relationships. Fibrillar assemblies from rPrP with hamster, mouse, human, and bovine primary structures were generated and tested for transmission and adaptation in tg7 transgenic mice expressing hamster PrPC. All assemblies, except the bovine ones, were fully pathogenic on the primary passage, causing clinical disease, PrPSc brain deposition, and spongiform degeneration. They exhibited divergent adaptation processes and strain properties upon subsequent passage. Assemblies of hamster origin propagated without apparent need for adaptation, those of mouse origin adapted abruptly, and those of human origin required serial passages for optimal fitness. Molecular analyses revealed the presence of endogenously truncated PrPSc species in the resulting synthetic strains that lack the 90-140 amino acid region considered crucial for infectivity. In conclusion, rPrP assemblies provide a facile means of generating novel prion strains with adaptative/evolutive properties mimicking genuine prions. The PrP amino acid backbone is sufficient to encode different strains with specific adaptative properties, offering insights into prion transmission and strain diversity.

Prion diseases disrupt glutamate/glutamine metabolism in skeletal muscle.

In prion diseases (PrDs), aggregates of misfolded prion protein (PrPSc) accumulate not only in the brain but also in extraneural organs. This raises the question whether prion-specific pathologies arise also extraneurally. Here we sequenced mRNA transcripts in skeletal muscle, spleen and blood of prion-inoculated mice at eight timepoints during disease progression. We detected gene-expression changes in all three organs, with skeletal muscle showing the most consistent alterations. The glutamate-ammonia ligase (GLUL) gene exhibited uniform upregulation in skeletal muscles of mice infected with three distinct scrapie prion strains (RML, ME7, and 22L) and in victims of human sporadic Creutzfeldt-Jakob disease. GLUL dysregulation was accompanied by changes in glutamate/glutamine metabolism, leading to reduced glutamate levels in skeletal muscle. None of these changes were observed in skeletal muscle of humans with amyotrophic lateral sclerosis, Alzheimer's disease, or dementia with Lewy bodies, suggesting that they are specific to prion diseases. These findings reveal an unexpected metabolic dimension of prion infections and point to a potential role for GLUL dysregulation in the glutamate/glutamine metabolism in prion-affected skeletal muscle.

The molecular determinants of a universal prion acceptor.

In prion diseases, the species barrier limits the transmission of prions from one species to another. However, cross-species prion transmission is remarkably efficient in bank voles, and this phenomenon is mediated by the bank vole prion protein (BVPrP). The molecular determinants of BVPrP's ability to function as a universal prion acceptor remain incompletely defined. Building on our finding that cultured cells expressing BVPrP can replicate both mouse and hamster prion strains, we systematically identified key residues in BVPrP that permit cross-species prion replication. We found that residues N155 and N170 of BVPrP, which are absent in mouse PrP but present in hamster PrP, are critical for cross-species prion replication. Additionally, BVPrP residues V112, I139, and M205, which are absent in hamster PrP but present in mouse PrP, are also required to enable replication of both mouse and hamster prions. Unexpectedly, we found that residues E227 and S230 near the C-terminus of BVPrP severely restrict prion accumulation following cross-species prion challenge, suggesting that they may have evolved to counteract the inherent propensity of BVPrP to misfold. PrP variants with an enhanced ability to replicate both mouse and hamster prions displayed accelerated spontaneous aggregation kinetics in vitro. These findings suggest that BVPrP's unusual properties are governed by a key set of amino acids and that the enhanced misfolding propensity of BVPrP may enable cross-species prion replication.

Convergent generation of atypical prions in knockin mouse models of genetic prion disease.

Most cases of human prion disease arise due to spontaneous misfolding of WT or mutant prion protein, yet recapitulating this event in animal models has proven challenging. It remains unclear whether spontaneous prion generation can occur within the mouse lifespan in the absence of protein overexpression and how disease-causing mutations affect prion strain properties. To address these issues, we generated knockin mice that express the misfolding-prone bank vole prion protein (BVPrP). While mice expressing WT BVPrP (I109 variant) remained free from neurological disease, a subset of mice expressing BVPrP with mutations (D178N or E200K) causing genetic prion disease developed progressive neurological illness. Brains from spontaneously ill knockin mice contained prion disease-specific neuropathological changes as well as atypical protease-resistant BVPrP. Moreover, brain extracts from spontaneously ill D178N- or E200K-mutant BVPrP-knockin mice exhibited prion seeding activity and transmitted disease to mice expressing WT BVPrP. Surprisingly, the properties of the D178N- and E200K-mutant prions appeared identical before and after transmission, suggesting that both mutations guide the formation of a similar atypical prion strain. These findings imply that knockin mice expressing mutant BVPrP spontaneously develop a bona fide prion disease and that mutations causing prion diseases may share a uniform initial mechanism of action.

Propagation of distinct CWD prion strains during peripheral and intracerebral challenges of gene-targeted mice

Since prion diseases result from infection and neurodegeneration of the central nervous system (CNS), experimental characterizations of prion strain properties customarily rely on the outcomes of intracerebral challenges. However, natural transmission of certain prions, including those causing chronic wasting disease (CWD) in elk and deer, depends on propagation in peripheral host compartments prior to CNS infection. Using gene-targeted GtE and GtQ mice, which accurately control cellular elk or deer PrP expression, we assessed the impact that peripheral or intracerebral exposures play on CWD prion strain propagation and resulting CNS abnormalities. Whereas oral and intraperitoneal transmissions produced identical neuropathological outcomes in GtE and GtQ mice and preserved the naturally convergent conformations of elk and deer CWD prions, intracerebral transmissions generated CNS prion strains with divergent biochemical properties in GtE and GtQ mice that were changed compared to their native counterparts. While CWD replication kinetics remained constant during iterative peripheral transmissions and brain titers reflected those found in native hosts, serial intracerebral transmissions produced 10-fold higher prion titers and accelerated incubation times. Our demonstration that peripherally and intracerebrally challenged Gt mice develop dissimilar CNS diseases which result from the propagation of distinct CWD prion strains points to the involvement of tissue-specific cofactors during strain selection in different host compartments. Since peripheral transmissions preserved the natural features of elk and deer prions, whereas intracerebral propagation produced divergent strains, our findings illustrate the importance of experimental characterizations using hosts that not only abrogate species barriers but also accurately recapitulate natural transmission routes of native strains.

Lack of prion transmission barrier in human PrP transgenic Drosophila

While animal prion diseases are a threat to human health, their zoonotic potential is generally inefficient because of interspecies prion transmission barriers. New animal models are required to provide an understanding of these prion transmission barriers and to assess the zoonotic potential of animal prion diseases. To address this goal, we generated Drosophila transgenic for human or non-human primate PrP and determined their susceptibility to known pathogenic prion diseases, namely vCJD and classical BSE, and that with unknown pathogenic potential, namely CWD. Adult Drosophila transgenic for M129 or V129 human PrP, or non-human primate PrP developed a neurotoxic phenotype and showed an accelerated loss of survival after exposure to vCJD, classical BSE, or CWD prions at the larval stage. vCJD prion strain identity was retained after passage in both M129 and V129 human PrP Drosophila. All of the primate PrP fly lines accumulated prion seeding activity and concomitantly developed a neurotoxic phenotype, generally including accelerated loss of survival, after exposure to CWD prions derived from different cervid species, including North American white-tailed deer and muntjac, and European reindeer and moose. These novel studies show that primate PrP transgenic Drosophila lack known prion transmission barriers since, in mammalian hosts, V129 human PrP is associated with severe resistance to classical BSE prions, while both human and cynomolgus macaque PrP are associated with resistance to CWD prions. Significantly, our data suggest that interspecies differences in the amino acid sequence of PrP may not be a principal determinant of the prion transmission barrier.

Adaptation of the protein misfolding cyclic amplification (PMCA) technique for the screening of anti-prion compounds.

Prion diseases result from the misfolding of the physiological prion protein (PrPC) to a pathogenic conformation (PrPSc). Compelling evidence indicates that prevention and/or reduction of PrPSc replication are promising therapeutic strategies against prion diseases. However, the existence of different PrPSc conformations (or strains) associated with disease represents a major problem when identifying anti-prion compounds. Efforts to identify strain-specific anti-prion molecules are limited by the lack of biologically relevant high-throughput screening platforms to interrogate compound libraries. Here, we describe adaptations to the protein misfolding cyclic amplification (PMCA) technology (able to faithfully replicate PrPSc strains) that increase its throughput to facilitate the screening of anti-prion molecules. The optimized PMCA platform includes a reduction in sample and reagents, as well as incubation/sonication cycles required to efficiently replicate and detect rodent-adapted and cervid PrPSc strains. The visualization of PMCA products was performed via dot blots, a method that contributed to reduced processing times. These technical changes allowed us to evaluate small molecules with previously reported anti-prion activity. This proof-of-principle screening was evaluated for six rodent-adapted prion strains. Our data show that these compounds targeted either none, all or some PrPSc strains at variable concentrations, demonstrating that this PMCA system is suitable to test compound libraries for putative anti-prion molecules targeting specific PrPSc strains. Further analyses of a small compound library against deer prions demonstrate the potential of this new PMCA format to identify strain-specific anti-prion molecules. The data presented here demonstrate the use of the PMCA technique in the selection of prion strain-specific anti-prion compounds.

Characterisation of European Field Goat Prion Isolates in Ovine PrP Overexpressing Transgenic Mice (Tgshp IX) Reveals Distinct Prion Strains.

After the detection of bovine spongiform encephalopathy (BSE), and a zoonotic transmissible spongiform encephalopathy (TSE) caused by the pathological prion protein (PrPSc) in two goats, the investigation of goat prions became of greater interest. Therefore, a broad collection of European goat TSE isolates, including atypical scrapie, CH1641 and goat BSE as reference prion strains were biochemically characterised and subsequently inoculated into seven rodent models for further analysis (already published results of this comprehensive study are reviewed here for comparative reasons). We report here the histopathological and immunohistochemical data of this goat TSE panel, obtained after the first passage in Tgshp IX (tg-shARQ) mice, which overexpress the ovine prion protein. In addition to the clear-cut discrimination of all reference prion strains from the classical scrapie (CS) isolates, we were further able to determine three categories of CS strains. The investigation further indicates the occurrence of sub-strains that slightly resemble distant TSE strains, such as BSE or CH1641, reinforcing the theory that CS is not a single strain but a mixture of sub-strains, existing at varying extents in one isolate. This study further proved that Tgshp IX is a potent and reliable tool for the in-depth characterisation of prion strains.

Simple 3D spheroid cell culture model for studies of prion infection.

Mouse neuronal CAD 5 cell line effectively propagates various strains of prions. Previously, we have shown that it can also be differentiated into the cells morphologically resembling neurons. Here, we demonstrate that CAD 5 cells chronically infected with prions undergo differentiation under the same conditions. To make our model more realistic, we triggered the differentiation in the 3D culture created by gentle rocking of CAD 5 cell suspension. Spheroids formed within 1 week and were fully developed in less than 3 weeks of culture. The mature spheroids had a median size of ~300 μm and could be cultured for up to 12 weeks. Increased expression of differentiation markers GAP 43, tyrosine hydroxylase, β-III-tubulin and SNAP 25 supported the differentiated status of the spheroid cells. The majority of them were found in the G0/G1 phase of the cell cycle, which is typical for differentiated cells. Moreover, half of the PrPC on the cell membrane was N-terminally truncated, similarly as in differentiated CAD 5 adherent cells. Finally, we demonstrated that spheroids could be created from prion-infected CAD 5 cells. The presence of prions was verified by immunohistochemistry, western blot and seed amplification assay. We also confirmed that the spheroids can be infected with the prions de novo. Our 3D culture model of differentiated CAD 5 cells is low cost, easy to produce and cultivable for weeks. We foresee its possible use in the testing of anti-prion compounds and future studies of prion formation dynamics.

A multiverse of α-synuclein: investigation of prion strain properties with carboxyl-terminal truncation specific antibodies in animal models

Synucleinopathies are a group of neurodegenerative disorders characterized by the presence of misfolded α-Synuclein (αSyn) in the brain. These conditions manifest with diverse clinical and pathophysiological characteristics. This disease diversity is hypothesized to be driven by αSyn strains with differing biophysical properties, potentially influencing prion-type propagation and consequentially the progression of illness. Previously, we investigated this hypothesis by injecting brain lysate (seeds) from deceased individuals with various synucleinopathies or human recombinant αSyn preformed fibrils (PFFs) into transgenic mice overexpressing either wild type or A53T human αSyn. In the studies herein, we expanded on these experiments, utilizing a panel of antibodies specific for the major carboxyl-terminally truncated forms of αSyn (αSynΔC). These modified forms of αSyn are found enriched in human disease brains to inform on potential strain-specific proteolytic patterns. With monoclonal antibodies specific for human αSyn cleaved at residues 103, 114, 122, 125, and 129, we demonstrate that multiple system atrophy (MSA) seeds and PFFs induce differing neuroanatomical spread of αSyn pathology associated with host specific profiles. Overall, αSyn cleaved at residue 103 was most widely present in the induced pathological inclusions. Furthermore, αSynΔC-positive inclusions were present in astrocytes, but more frequently in activated microglia, with patterns dependent on host and inoculum. These findings support the hypothesis that synucleinopathy heterogeneity might stem from αSyn strains with unique biochemical properties that include proteolytic processing, which could result in dominant strain properties.

Therapeutic targeting of cellular prion protein: toward the development of dual mechanism anti-prion compounds.

PrP Sc , a misfolded, aggregation-prone isoform of the cellular prion protein (PrP C ), is the infectious prion agent responsible for fatal neurodegenerative diseases of humans and other mammals. PrP Sc can adopt different pathogenic conformations (prion strains), which can be resistant to potential drugs, or acquire drug resistance, posing challenges for the development of effective therapies. Since PrP C is the obligate precursor of any prion strain and serves as the mediator of prion neurotoxicity, it represents an attractive therapeutic target for prion diseases. In this minireview, we briefly outline the approaches to target PrP C and discuss our recent identification of Zn(II)-BnPyP, a PrP C -targeting porphyrin with an unprecedented bimodal mechanism of action. We argue that in-depth understanding of the molecular mechanism by which Zn(II)-BnPyP targets PrP C may lead toward the development of a new class of dual mechanism anti-prion compounds.

Molecular signatures in prion disease: altered death receptor pathways in a mouse model.

Prion diseases are transmissible and fatal neurodegenerative diseases characterized by accumulation of misfolded prion protein isoform (PrPSc), astrocytosis, microgliosis, spongiosis, and neurodegeneration. Elevated levels of cell membrane associated PrPSc protein and inflammatory cytokines hint towards the activation of death receptor (DR) pathway/s in prion diseases. Activation of DRs regulate, either cell survival or apoptosis, autophagy and necroptosis based on the adaptors they interact. Very little is known about the DR pathways activation in prion disease. DR3 and DR5 that are expressed in normal mouse brain were never studied in prion disease, so also their ligands and any DR adaptors. This research gap is notable and investigated in the present study. C57BL/6J mice were infected with Rocky Mountain Laboratory scrapie mouse prion strain. The progression of prion disease was examined by observing morphological and behavioural abnormalities. The levels of PrP isoforms and GFAP were measured as the marker of PrPSc accumulation and astrocytosis respectively using antibody-based techniques that detect proteins on blot and brain section. The levels of DRs, their glycosylation and ectodomain shedding, and associated factors warrant their examination at protein level, hence western blot analysis was employed in this study. Prion-infected mice developed motor deficits and neuropathology like PrPSc accumulation and astrocytosis similar to other prion diseases. Results from this research show higher expression of all DR ligands, TNFR1, Fas and p75NTR but decreased levels DR3 and DR5. The levels of DR adaptor proteins like TRADD and TRAF2 (primarily regulate pro-survival pathways) are reduced. FADD, which primarily regulate cell death, its level remains unchanged. RIPK1, which regulate pro-survival, apoptosis and necroptosis, its expression and proteolysis (inhibits necroptosis but activates apoptosis) are increased. The findings from the present study provide evidence towards the involvement of DR3, DR5, DR6, TL1A, TRAIL, TRADD, TRAF2, FADD and RIPK1 for the first time in prion diseases. The knowledge obtained from this research discuss the possible impacts of these 16 differentially expressed DR factors on our understanding towards the multifaceted neuropathology of prion diseases and towards future explorations into potential targeted therapeutic interventions for prion disease specific neuropathology.

A Comparison of RML Prion Inactivation Efficiency by Heterogeneous and Homogeneous Photocatalysis.

Prions are proteinaceous pathogens responsible for a variety of devastating diseases in mammals, including scrapie in sheep and goats, chronic wasting disease in cervids, and Creutzfeldt-Jakob disease (CJD) in humans. They are characterized by their exceptional persistence to common inactivation procedures. This applies to all possible sources of prion contamination as prions may be present in the tissues and biological fluids of infected individuals. Hence, efficient prion inactivation procedures are still being sought to minimize the risk of intra- or inter-species transmission. In the past, photocatalytic treatment has been proven to be capable of efficiently oxidizing and inactivating prions. In the present study, the efficacy of homogeneous photo-Fenton-based photocatalysis as well as heterogeneous photocatalysis with TiO2 in reducing RML mouse scrapie infectivity was evaluated. Prion inactivation was assessed by means of a bioassay, and the results were confirmed by in vitro experiments. While the prion infectivity of the RML mouse scrapie was reduced after treatment with the photo-Fenton reagent, the heterogeneous photocatalytic treatment of the same prion strain completely eliminated prion infectivity.

Sigma Receptor Ligands Are Potent Antiprion Compounds that Act Independently of Sigma Receptor Binding.

Prion diseases are invariably fatal neurodegenerative diseases of humans and other animals for which there are no effective treatment options. Previous work from our laboratory identified phenethylpiperidines as a novel class of anti-prion compounds. While working to identify the molecular target(s) of these molecules, we unexpectedly discovered ten novel antiprion compounds based on their known ability to bind to the sigma receptors, σ1R and σ2R, which are currently being tested as therapeutic or diagnostic targets for cancer and neuropsychiatric disorders. Surprisingly, however, knockout of the respective genes encoding σ1R and σ2R (Sigmar1 and Tmem97) in prion-infected N2a cells did not alter the antiprion activity of these compounds, demonstrating that these receptors are not the direct targets responsible for the antiprion effects of their ligands. Further investigation of the most potent molecules established that they are efficacious against multiple prion strains and protect against downstream prion-mediated synaptotoxicity. While the precise details of the mechanism of action of these molecules remain to be determined, the present work forms the basis for further investigation of these compounds in preclinical studies. Given the therapeutic utility of several of the tested compounds, including rimcazole and haloperidol for neuropsychiatric conditions, (+)-pentazocine for neuropathic pain, and the ongoing clinical trials of SA 4503 and ANAVEX2-73 for ischemic stroke and Alzheimer's disease, respectively, this work has immediate implications for the treatment of human prion disease.

Grp78 destabilization of infectious prions is strain-specific and modified by multiple factors including accessory chaperones and pH

Lethal neurodegenerative prion diseases result from the continuous accumulation of infectious and variably protease-resistant prion protein aggregates (PrPD) which are misfolded forms of the normally detergent soluble and protease-sensitive cellular prion protein. Molecular chaperones like Grp78 have been found to reduce the accumulation of PrPD, but how different cellular environments and other chaperones influence the ability of Grp78 to modify PrPD is poorly understood. In this work, we investigated how pH and protease-mediated structural changes in PrPD from twomouse-adapted scrapie prion strains, 22L and 87V, influenced processing by Grp78 in the presence or absence of chaperones Hsp90, DnaJC1, and Stip1. We developed a cell-free invitro system to monitor chaperone-mediated structural changes to, and disaggregation of, PrPD. For both strains, Grp78 was most effective at structurally altering PrPD at low pH, especially when additional chaperones were present. While Grp78, DnaJC1, Stip1, and Hsp90 were unable to disaggregate the majority of PrPD from either strain, pretreatment of PrPD with proteases increased disaggregation of 22L PrPD compared to 87V, indicating strain-specific differences in aggregate structure were impacting chaperone activity. Hsp90 also induced structural changes in 87V PrPD as indicated by an increase in the susceptibility of its n-terminus to proteases. Our data suggest that, while chaperones like Grp78, DnaJC1, Stip1, and Hsp90 disaggregate only a small fraction of PrPD, they may still facilitate its clearance by altering aggregate structure and sensitizing PrPD to proteases in a strain and pH-dependent manner.

Interactions between Cytokines and the Pathogenesis of Prion Diseases: Insights and Implications.

Transmissible Spongiform Encephalopathies (TSEs), including prion diseases such as Bovine Spongiform Encephalopathy (Mad Cow Disease) and variant Creutzfeldt-Jakob Disease, pose unique challenges to the scientific and medical communities due to their infectious nature, neurodegenerative effects, and the absence of a cure. Central to the progression of TSEs is the conversion of the normal cellular prion protein (PrPC) into its infectious scrapie form (PrPSc), leading to neurodegeneration through a complex interplay involving the immune system. This review elucidates the current understanding of the immune response in prion diseases, emphasizing the dual role of the immune system in both propagating and mitigating the disease through mechanisms such as glial activation, cytokine release, and blood-brain barrier dynamics. We highlight the differential cytokine profiles associated with various prion strains and stages of disease, pointing towards the potential for cytokines as biomarkers and therapeutic targets. Immunomodulatory strategies are discussed as promising avenues for mitigating neuroinflammation and delaying disease progression. This comprehensive examination of the immune response in TSEs not only advances our understanding of these enigmatic diseases but also sheds light on broader neuroinflammatory processes, offering hope for future therapeutic interventions.

Targeting Neuroinflammation by Pharmacologic Downregulation of Inflammatory Pathways Is Neuroprotective in Protein Misfolding Disorders.

Neuroinflammation plays a crucial role in the development of neurodegenerative protein misfolding disorders. This category of progressive diseases includes, but is not limited to, Alzheimer's disease, Parkinson's disease, and prion diseases. Shared pathogenesis involves the accumulation of misfolded proteins, chronic neuroinflammation, and synaptic dysfunction, ultimately leading to irreversible neuronal loss, measurable cognitive deficits, and death. Presently, there are few to no effective treatments to halt the advancement of neurodegenerative diseases. We hypothesized that directly targeting neuroinflammation by downregulating the transcription factor, NF-κB, and the inflammasome protein, NLRP3, would be neuroprotective. To achieve this, we used a cocktail of RNA targeting therapeutics (SB_NI_112) shown to be brain-penetrant, nontoxic, and effective inhibitors of both NF-κB and NLRP3. We utilized a mouse-adapted prion strain as a model for neurodegenerative diseases to assess the aggregation of misfolded proteins, glial inflammation, neuronal loss, cognitive deficits, and lifespan. Prion-diseased mice were treated either intraperitoneally or intranasally with SB_NI_112. Behavioral and cognitive deficits were significantly protected by this combination of NF-κB and NLRP3 downregulators. Treatment reduced glial inflammation, protected against neuronal loss, prevented spongiotic change, rescued cognitive deficits, and significantly lengthened the lifespan of prion-diseased mice. We have identified a nontoxic, systemic pharmacologic that downregulates NF-κB and NLRP3, prevents neuronal death, and slows the progression of neurodegenerative diseases. Though mouse models do not always predict human patient success and the study was limited due to sample size and number of dosing methods utilized, these findings serve as a proof of principle for continued translation of the therapeutic SB_NI_112 for prion disease and other neurodegenerative diseases. Based on the success in a murine prion model, we will continue testing SB_NI_112 in a variety of neurodegenerative disease models, including Alzheimer's disease and Parkinson's disease.

Change in the molecular properties of CH1641 prions after transmission to wild-type mice: Evidence for a single strain.

CH1641 was discovered in 1970 as a scrapie isolate that was unlike all other classical strains of scrapie isolated so far. We performed bio-assays of CH1641 in mice in order to further characterise this specific isolate. We inoculated the original CH1641 isolate into ovine and bovine prion protein (PrP) transgenic mice as well as wild-type mice. In addition, we performed cross- and back passages between the various mouse lines to examine if one identical prion strain was isolated in all mouse lines or whether multiple prion strains exist in CH1641. We report the first successful transmission of CH1641 to wild-type RIII mice and via RIII mice to wild-type VM mice. Unexpectedly, analysis of the protease-resistant prion protein (PrPres ) in wild-type mice showed a classical scrapie banding pattern differing from the banding pattern of the original CH1641 isolate. Cross- and back passages of CH1641 between the various mouse lines confirmed that the same prion strain had been isolated in all mouse lines. The CH1641 isolate consists of a single prion strain but its molecular banding pattern of PrPres differs between wild-type mice and PrP transgenic mice. Consequently, molecular banding patterns of PrPres should be used with caution in strain typing since they do not solely depend on the properties of the prion strain but also on the host prion protein.

Multiple steps of prion strain adaptation to a new host.

The transmission of prions across species is a critical aspect of their dissemination among mammalian hosts, including humans. This process often necessitates strain adaptation. In this study, we sought to investigate the mechanisms underlying prion adaptation while mitigating biases associated with the history of cross-species transmission of natural prion strains. To achieve this, we utilized the synthetic hamster prion strain S05. Propagation of S05 using mouse PrPC in Protein Misfolding Cyclic Amplification did not immediately overcome the species barrier. This finding underscores the involvement of factors beyond disparities in primary protein structures. Subsequently, we performed five serial passages to stabilize the incubation time to disease in mice. The levels of PrPSc increased with each passage, reaching a maximum at the third passage, and declining thereafter. This suggests that only the initial stage of adaptation is primarily driven by an acceleration in PrPSc replication. During the protracted adaptation to a new host, we observed significant alterations in the glycoform ratio and sialylation status of PrPSc N-glycans. These changes support the notion that qualitative modifications in PrPSc contribute to a more rapid disease progression. Furthermore, consistent with the decline in sialylation, a cue for "eat me" signaling, the newly adapted strain exhibited preferential colocalization with microglia. In contrast to PrPSc dynamics, the intensity of microglia activation continued to increase after the third passage in the new host. In summary, our study elucidates that the adaptation of a prion strain to a new host is a multi-step process driven by several factors.

The role of α-synuclein prion strains in Parkinson's disease and multiple system atrophy.

The role of α-synuclein prion strains in Parkinson's disease and multiple system atrophy.