PrP Sc Deposition Research Articles

Aberrance of GAP43/p-GAP43 Closely Associates with the Pathology of Neuron Loss in Prion-Infected Rodent Models.

Prion diseases are fatal neurodegenerative disorders characterized by neuron damage and loss. Growth-associated protein 43 (GAP43) functions in neuronal plasticity and synaptic function, but its role in prion diseases is not fully elucidated. In this study, we investigated the changes of GAP43 in the central nerve system (CNS) of several prion-infected rodent models and explored the potential relationship of GAP43 with PrPSc deposit and neuron loss using various methods. We found that GAP43 levels were significantly decreased in the brain tissues of scrapie-infected rodent models at the terminal stage of the disease. Immunohistochemical analysis showed that GAP43 colocalized with NeuN-positive cells morphologically, indicating the presence of GAP43 in mature neurons. On contrary, the levels of GAP43 and p-GAP43 increased in a prion-infected cell line SMB-S15 in vitro, accompanying with the increase of intracellular calcium. Stimulation of lipopolysaccharide (LPS) upregulated while removal of PrPSc propagation downregulated the level of GAP43 in SMB-S15 cells. Morphological colocalization and molecular interaction between GAP43 and PrPSc have been addressed in the brains of prion-infected rodents and prion-infected cell line. Histological assays of the serial sections of the whole brains of prion-infected mice proposed that the reduced GAP43 level correlated with large amount of PrPSc deposits and notable neuron damage and loss showing cell crumpled and nuclear pyknosis. The impairment of GAP43 signaling and disturbance of calcium homeostasis by aberrance of brain GAP43/p-GAP43 not only reflect but also likely contribute to the pathology of severe neuron loss at the end of prion disease.

Extraneural infection route restricts prion conformational variability and attenuates the impact of quaternary structure on infectivity.

Prions can exist as different strains that consist of conformational variants of the misfolded, pathogenic prion protein isoform PrPSc. Defined by stably transmissible biological and biochemical properties, strains have been identified in a spectrum of prion diseases, including chronic wasting disease (CWD) of wild and farmed cervids. CWD is highly contagious and spreads via direct and indirect transmission involving extraneural sites of infection, peripheral replication and neuroinvasion of prions. Here, we investigated the impact of infection route on CWD prion conformational selection and propagation. We used gene-targeted mouse models expressing deer PrP for intracerebral or intraperitoneal inoculation with fractionated or unfractionated brain homogenates from white-tailed deer, harboring CWD strains Wisc-1 or 116AG. Upon intracerebral inoculation, Wisc-1 and 116AG-inoculated mice differed in conformational stability of PrPSc. In brains of mice infected intraperitoneally with either inoculum, PrPSc propagated with identical conformational stability and fewer PrPSc deposits in most brain regions than intracerebrally inoculated animals. For either inoculum, PrPSc conformational stability in brain and spinal cord was similar upon intracerebral infection but significantly higher in spinal cords of intraperitoneally infected animals. Inoculation with fractionated brain homogenates resulted in lower variance of survival times upon intraperitoneal compared to intracerebral infection. In summary, we demonstrate that extraneural infection mitigates the impact of PrPSc quaternary structure on infection and reduces conformational variability of PrPSc propagated in the brain. These findings provide new insights into the evolution of stable CWD strains in natural, extraneural transmissions.

In Vitro and In Vivo Evidence towards Fibronectin's Protective Effects against Prion Infection.

A distinctive signature of the prion diseases is the accumulation of the pathogenic isoform of the prion protein, PrPSc, in the central nervous system of prion-affected humans and animals. PrPSc is also found in peripheral tissues, raising concerns about the potential transmission of pathogenic prions through human food supplies and posing a significant risk to public health. Although muscle tissues are considered to contain levels of low prion infectivity, it has been shown that myotubes in culture efficiently propagate PrPSc. Given the high consumption of muscle tissue, it is important to understand what factors could influence the establishment of a prion infection in muscle tissue. Here we used in vitro myotube cultures, differentiated from the C2C12 myoblast cell line (dC2C12), to identify factors affecting prion replication. A range of experimental conditions revealed that PrPSc is tightly associated with proteins found in the systemic extracellular matrix, mostly fibronectin (FN). The interaction of PrPSc with FN decreased prion infectivity, as determined by standard scrapie cell assay. Interestingly, the prion-resistant reserve cells in dC2C12 cultures displayed a FN-rich extracellular matrix while the prion-susceptible myotubes expressed FN at a low level. In agreement with the in vitro results, immunohistopathological analyses of tissues from sheep infected with natural scrapie demonstrated a prion susceptibility phenotype linked to an extracellular matrix with undetectable levels of FN. Conversely, PrPSc deposits were not observed in tissues expressing FN. These data indicate that extracellular FN may act as a natural barrier against prion replication and that the extracellular matrix composition may be a crucial feature determining prion tropism in different tissues.

Quantitative analysis of prion disease using an AI-powered digital pathology framework

Prion disease is a fatal neurodegenerative disorder characterized by accumulation of an abnormal prion protein (PrPSc) in the central nervous system. To identify PrPSc aggregates for diagnostic purposes, pathologists use immunohistochemical staining of prion protein antibodies on tissue samples. With digital pathology, artificial intelligence can now analyze stained slides. In this study, we developed an automated pipeline for the identification of PrPSc aggregates in tissue samples from the cerebellar and occipital cortex. To the best of our knowledge, this is the first framework to evaluate PrPSc deposition in digital images. We used two strategies: a deep learning segmentation approach using a vision transformer, and a machine learning classification approach with traditional classifiers. Our method was developed and tested on 64 whole slide images from 41 patients definitively diagnosed with prion disease. The results of our study demonstrated that our proposed framework can accurately classify WSIs from a blind test set. Moreover, it can quantify PrPSc distribution and localization throughout the brain. This could potentially be extended to evaluate protein expression in other neurodegenerative diseases like Alzheimer's and Parkinson's. Overall, our pipeline highlights the potential of AI-assisted pathology to provide valuable insights, leading to improved diagnostic accuracy and efficiency.

Heterogeneity of pathological prion protein accumulation in the brain of moose (Alces alces) from Norway, Sweden and Finland with chronic wasting disease

Prion diseases are a group of neurodegenerative, transmissible, and fatal disorders that affect several animal species. They are characterized by the conformational conversion of the cellular prion protein (PrPC) into the pathological prion protein (PrPSc). In 2016, chronic wasting disease (CWD) gained great importance at European level due to the first disease detection in a wild reindeer (Rangifer tarandus) in Norway. The subsequent intensive CWD surveillance launched in cervids resulted in the detection of CWD in moose (Alces alces), with 11 cases in Norway, 3 in Finland and 4 in Sweden. These moose cases differ considerably from CWD cases in North American and reindeer in Norway, as PrPSc was detectable in the brain but not in lymphoid tissues. These facts suggest the occurrence of a new type of CWD. Here, we show some immunohistochemical features that are clearly different from CWD cases in North American and Norwegian reindeer. Further, the different types of PrPSc deposits found among moose demonstrate strong variations between the cases, supporting the postulation that these cases could carry multiple strains of CWD.

Radotinib Decreases Prion Propagation and Prolongs Survival Times in Models of Prion Disease.

The conversion of cellular prion protein (PrPC) into pathogenic prion isoforms (PrPSc) and the mutation of PRNP are definite causes of prion diseases. Unfortunately, without exception, prion diseases are untreatable and fatal neurodegenerative disorders; therefore, one area of research focuses on identifying medicines that can delay the progression of these diseases. According to the concept of drug repositioning, we investigated the efficacy of the c-Abl tyrosine kinase inhibitor radotinib, which is a drug that is approved for the treatment of chronic myeloid leukemia, in the treatment of disease progression in prion models, including prion-infected cell models, Tga20 and hamster cerebellar slice culture models, and 263K scrapie-infected hamster models. Radotinib inhibited PrPSc deposition in neuronal ZW13-2 cells that were infected with the 22L or 139A scrapie strains and in cerebellar slice cultures that were infected with the 22L or 263K scrapie strains. Interestingly, hamsters that were intraperitoneally injected with the 263K scrapie strain and intragastrically treated with radotinib (100 mg/kg) exhibited prolonged survival times (159 ± 28.6 days) compared to nontreated hamsters (135 ± 9.9 days) as well as reduced PrPSc deposition and ameliorated pathology. However, intraperitoneal injection of radotinib exerted a smaller effect on the survival rate of the hamsters. Additionally, we found that different concentrations of radotinib (60, 100, and 200 mg/kg) had similar effects on survival time, but this effect was not observed after treatment with a low dose (30 mg/kg) of radotinib. Interestingly, when radotinib was administered 4 or 8 weeks after prion inoculation, the treated hamsters survived longer than the vehicle-treated hamsters. Additionally, a pharmacokinetic assay revealed that radotinib effectively crossed the blood-brain barrier. Based on our findings, we suggest that radotinib is a new candidate anti-prion drug that could possibly be used to treat prion diseases and promote the remission of symptoms.

Strain-Dependent Morphology of Reactive Astrocytes in Human- and Animal-Vole-Adapted Prions.

Reactive astrogliosis is one of the pathological hallmarks of prion diseases. Recent studies highlighted the influence of several factors on the astrocyte phenotype in prion diseases, including the brain region involved, the genotype backgrounds of the host, and the prion strain. Elucidating the influence of prion strains on the astrocyte phenotype may provide crucial insights for developing therapeutic strategies. Here, we investigated the relationship between prion strains and astrocyte phenotype in six human- and animal-vole-adapted strains characterized by distinctive neuropathological features. In particular, we compared astrocyte morphology and astrocyte-associated PrPSc deposition among strains in the same brain region, the mediodorsal thalamic nucleus (MDTN). Astrogliosis was detected to some extent in the MDTN of all analyzed voles. However, we observed variability in the morphological appearance of astrocytes depending on the strain. Astrocytes displayed variability in thickness and length of cellular processes and cellular body size, suggesting strain-specific phenotypes of reactive astrocytes. Remarkably, four out of six strains displayed astrocyte-associated PrPSc deposition, which correlated with the size of astrocytes. Overall, these data show that the heterogeneous reactivity of astrocytes in prion diseases depends at least in part on the infecting prion strains and their specific interaction with astrocytes.

Experimental bovine spongiform encephalopathy infection in rabbits

The aim of our work was to determine the sensitivity of rabbits to the C-BSE pathogen in the first passage, to obtain a laboratory model on rabbits to study the C-BSE pathogen. The results of the experiments showed that with intracerebral infection of rabbits with the causative agent of classical spongiform encephalopathy of cows (C-BSE) they are 100% sensitive to the pathogen with an incubation period of 570 to 1842 days. The disease proceeds with the development of a clinical picture typical of prion diseases, the development of pathomorphological changes in the central nervous system in the form of vacuolization of neurons and neuropiles in various parts of the brain and massive deposition of prion protein PrPSc both in brain tissues and in peripheral lymphoid tissue (spleen). The laboratory model on rabbits is a highly sensitive model for studying the prion of bovine spongiform encephalopathy (C-BSE) and probably the causative agent of v-CJD.

Experimental infection of bovine spongi-form encephalopathy in guinea pigs: clinical symptoms, pathohistology and immunohistochemistry

Prion diseases are infectious neurodegenerative diseases affecting humans and animals that are invariably fatal and have no currently available prevention or treatment methods. These diseases are also known as transmissible spongiform encephalopathies (TSE), characterized by similar neurological disorders, vacuolization of the neuroparenchyma, accumulation of the pathogenic isoform of the prion protein in it, the absence of an immunological response to the pathogen, and the inevitable death. The most famous of them is the classic bovine spongiform encephalopathy, because. has unprecedented social and economic consequences. C-BSE of cattle is also dangerous for humans, causing one of the forms of Creutzfeldt-Jakob disease, leading to a gradual progression of irreversible C-BSE lesions, leading to the death of a sick person. Laboratory animal models make a huge contribution to the study of the biological properties of prions and the diseases they cause. Thus, mouse models of prion infections have played a major role in deciphering fundamental questions of prion biology and assessing the potential transmissibility of neurodegenerative diseases. However, despite the economic acceptability and other positive properties of this model, it has a number of disadvantages. It produces low-volume tissue samples, and it is very difficult to obtain the required volume of serum and cerebrospinal fluid for many studies. Therefore, the search for and study of the disease in new models of laboratory animals sensitive to bovine C-BSE is of great scientific importance in the study of prion diseases. This work shows that during experimental intracerebral infection of guinea pigs with the causative agent of classical bovine spongiform encephalopathy, they are 100% sensitive to the pathogen. The clinical picture of the disease, developing severe pathomorphological changes in all parts of the brain with vacuolization of neurons and neropil and massive deposition of the prion protein PrPSc are described. Guinea pigs can be a highly sensitive object for laboratory study of the causative agent of bovine spongiform encephalopathy.

Chronological Changes in the Expression Pattern of Hippocampal Prion Proteins During Disease Progression in Sporadic Creutzfeldt-Jakob Disease MM1 Subtype.

The differential effects of sporadic Creutzfeldt-Jakob disease (sCJD) on the hippocampus and other neocortical areas are poorly understood. We aimed to reveal the histological patterns of cellular prion protein (PrPC) and abnormal prion protein (PrPSc) in hippocampi of sCJD patients and normal controls (NCs). Our study examined 18 postmortem sCJD patients (MM1, 14 cases; MM1 + 2c, 3 cases; MM1 + 2t, 1 case) and 12 NCs. Immunohistochemistry was conducted using 4 primary antibodies, of which 3 targeted the N-terminus of the prion protein (PrP), and 1 (EP1802Y) targeted the C-terminal domain. PrPC expression was abundant in the hippocampus of NCs, and the distribution of PrPC at CA3/4 was reminiscent of synaptic complexes. In sCJD cases with a disease history of <2 years, antibodies against the N-terminus could not detect synapse-like PrP expression at CA4; however, EP1802Y could characterize the synapse-like expression. PrPSc accumulation and spongiform changes became evident after 2 years of illness, when PrPSc deposits were more noticeably detected by N-terminal-specific antibodies. Our findings highlighted the chronology of histopathological alterations in the CA4 region in sCJD patients.

Sporadic Creutzfeldt-Jakob disease VM1: phenotypic and molecular characterization of a novel subtype of human prion disease

The methionine (M)—valine (V) polymorphic codon 129 of the prion protein gene (PRNP) plays a central role in both susceptibility and phenotypic expression of sporadic Creutzfeldt-Jakob diseases (sCJD). Experimental transmissions of sCJD in humanized transgenic mice led to the isolation of five prion strains, named M1, M2C, M2T, V2, and V1, based on two major conformations of the pathological prion protein (PrPSc, type 1 and type 2), and the codon 129 genotype determining susceptibility and propagation efficiency. While the most frequent sCJD strains have been described in codon 129 homozygosis (MM1, MM2C, VV2) and heterozygosis (MV1, MV2K, and MV2C), the V1 strain has only been found in patients carrying VV. We identified six sCJD cases, 4 in Catalonia and 2 in Italy, carrying MV at PRNP codon 129 in combination with PrPSc type 1 and a new clinical and neuropathological profile reminiscent of the VV1 sCJD subtype rather than typical MM1/MV1. All patients had a relatively long duration (mean of 20.5 vs. 3.5 months of MM1/MV1 patients) and lacked electroencephalographic periodic sharp-wave complexes at diagnosis. Distinctive histopathological features included the spongiform change with vacuoles of larger size than those seen in sCJD MM1/MV1, the lesion profile with prominent cortical and striatal involvement, and the pattern of PrPSc deposition characterized by a dissociation between florid spongiform change and mild synaptic deposits associated with coarse, patch-like deposits in the cerebellar molecular layer. Western blot analysis of brain homogenates revealed a PrPSc type 1 profile with physicochemical properties reminiscent of the type 1 protein linked to the VV1 sCJD subtype. In summary, we have identified a new subtype of sCJD with distinctive clinicopathological features significantly overlapping with those of the VV1 subtype, possibly representing the missing evidence of V1 sCJD strain propagation in the 129MV host genotype.

Synthesis and Biological Evaluation of Novel 2-(Benzofuran-2-yl)-chromone Derivatives for In Vivo Imaging of Prion Deposits in the Brain.

Prion diseases are fatal neurodegenerative disorders caused by the deposition of scrapie prion protein aggregates (PrPSc) in the brain. We previously reported that styrylchromone (SC) and benzofuran (BF) derivatives have potential as imaging probes for PrPSc. To further improve their properties, we designed and synthesized 2-(benzofuran-2-yl)-chromone (BFC) derivatives hybridized with SC and BF backbones as novel single-photon emission computed tomography probes for the detection of cerebral PrPSc deposits. Recombinant mouse prion protein (rMoPrP) aggregates and mouse-adapted bovine spongiform encephalopathy (mBSE)-infected mice were used to evaluate the binding properties of BFC derivatives to PrPSc. The BFC derivatives exhibited high binding affinities (equilibrium dissociation constant [Kd] = 22.6-47.7 nM) for rMoPrP aggregates. All BFC derivatives showed remarkable selectivity against amyloid beta aggregates. Fluorescence microscopy confirmed that the fluorescence signals of the BFC derivatives corresponded to the antibody-positive deposits of PrPSc in mBSE-infected mouse brains. Among the BFC derivatives, [125I]BFC-OMe and [125I]BFC-NH2 exhibited high brain uptake and favorable washout from the mouse brain. In vitro autoradiography demonstrated that the distribution of [125I]BFC-OMe in the brain tissues of mBSE-infected mice was colocalized with PrPSc deposits. Taken together, BFC derivatives appear to be promising prion imaging probes.

Minimal change prion retinopathy: Morphometric comparison of retinal and brain prion deposits in Creutzfeldt-Jakob disease

Sporadic Creutzfeldt-Jakob disease (sCJD) is the most commonly diagnosed human prion disease caused by the abnormal misfolding of the ‘cellular’ prion protein (PrPC) into the transmissible ‘scrapie-type’ prion form (PrPSc). Neuropathologic evaluation of brains with sCJD reveals abnormal PrPSc deposits primarily in grey matter structures, often associated with micro-vacuolar spongiform changes in neuropil, neuronal loss, and gliosis. Abnormal PrPSc deposits have also been reported in the retina of patients with sCJD, but few studies have characterized the morphology of these retinal PrPSc deposits or evaluated for any retinal neurodegenerative changes. We performed histopathologic and morphometric analyses of retinal and brain prion deposits in 14 patients with sCJD. Interestingly, we discovered that the morphology of retinal PrPSc deposits generally differs from that of brain PrPSc deposits in terms of size and shape. We found that retinal PrPSc deposits consistently localize to the outer plexiform layer of the retina. Additionally, we observed that the retinal PrPSc deposits are not associated with the spongiform change, neuronal loss, and gliosis often seen in the brain. The stereotypic morphology and location of PrPSc deposits in sCJD retinas may help guide the use of ocular imaging devices in the detection of these deposits for a clinical diagnosis.

Neurogranin and Neurofilament Light Chain as Preclinical Biomarkers in Scrapie.

Prion diseases are diagnosed in the symptomatic stage, when the neuronal damage is spread throughout the central nervous system (CNS). The assessment of biological features that allow the detection of asymptomatic cases is needed, and, in this context, scrapie, where pre-symptomatic infected animals can be detected through rectal biopsy, becomes a good study model. Neurogranin (Ng) and neurofilament light chain (NfL) are proteins that reflect synaptic and axonal damage and have been studied as cerebrospinal fluid (CSF) biomarkers in different neurodegenerative disorders. In this study, we evaluated Ng and NfL both at the protein and transcript levels in the CNS of preclinical and clinical scrapie-affected sheep compared with healthy controls and assessed their levels in ovine CSF. The correlation between these proteins and the main neuropathological events in prion diseases, PrPSc deposition and spongiosis, was also assessed. The results show a decrease in Ng and NfL at the protein and gene expression levels as the disease progresses, and significant changes between the control and preclinical animals. On the contrary, the CSF levels of NfL increased throughout the progression of the disease. Negative correlations between neuropathological markers of prion disease and the concentration of the studied proteins were also found. Although further research is needed, these results suggest that Ng and NfL could act as biomarkers for neurodegeneration onset and intensity in preclinical cases of scrapie.

Misfolded amyloid-β strains and their potential roles in the clinical and pathological variability of Alzheimer's disease.

Misfolded amyloid-β strains and their potential roles in the clinical and pathological variability of Alzheimer's disease.

Distinctive Toll-like Receptors Gene Expression and Glial Response in Different Brain Regions of Natural Scrapie.

Prion diseases are chronic and fatal neurodegenerative diseases characterized by the accumulation of disease-specific prion protein (PrPSc), spongiform changes, neuronal loss, and gliosis. Growing evidence shows that the neuroinflammatory response is a key component of prion diseases and contributes to neurodegeneration. Toll-like receptors (TLRs) have been proposed as important mediators of innate immune responses triggered in the central nervous system in other human neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. However, little is known about the role of TLRs in prion diseases, and their involvement in the neuropathology of natural scrapie has not been studied. We assessed the gene expression of ovine TLRs in four anatomically distinct brain regions in natural scrapie-infected sheep and evaluated the possible correlations between gene expression and the pathological hallmarks of prion disease. We observed significant changes in TLR expression in scrapie-infected sheep that correlate with the degree of spongiosis, PrPSc deposition, and gliosis in each of the regions studied. Remarkably, TLR4 was the only gene upregulated in all regions, regardless of the severity of neuropathology. In the hippocampus, we observed milder neuropathology associated with a distinct TLR gene expression profile and the presence of a peculiar microglial morphology, called rod microglia, described here for the first time in the brain of scrapie-infected sheep. The concurrence of these features suggests partial neuroprotection of the hippocampus. Finally, a comparison of the findings in naturallyinfected sheep versus an ovinized mouse model (tg338 mice) revealed distinct patterns of TLRgene expression.

Synthesis and Characterization of Hydroxyethylamino- and Pyridyl-Substituted 2-Vinyl Chromone Derivatives for Detection of Cerebral Abnormal Prion Protein Deposits.

Prion diseases are fatal neurodegenerative diseases characterized by the deposition of abnormal prion protein aggregates (PrPSc) in the brain. In this study, we developed hydroxyethylamino-substituted styrylchromone (SC) and 2-(2-(pyridin-3-yl)vinyl)-4H-chromen-4-one (VPC) derivatives for single-photon emission computed tomography (SPECT) imaging of PrPSc deposits in the brain. The binding affinity of these compounds was evaluated using recombinant mouse prion protein (rMoPrP) aggregates, which resulted in the inhibition constant (Ki) value of 61.5 and 88.0 nM for hydroxyethyl derivative, (E)-2-(4-((2-hydroxyethyl)amino)styryl)-6-iodo-4H-chromen-4-one (SC-NHEtOH) and (E)-2-(4-((2-hydroxyethyl)(methyl)amino)styryl)-6-iodo-4H-chromen-4-one (SC-NMeEtOH), respectively. However, none of the VPC derivatives showed binding affinity for the rMoPrP aggregates. Fluorescent imaging demonstrated that the accumulation pattern of SC-NHEtOH matched with the presence of PrPSc in the brain slices from mouse-adapted bovine spongiform encephalopathy-infected mice. A biodistribution study of normal mice indicated low initial brain uptake of [125I]SC-NHEtOH (0.88% injected dose/g (% ID/g) at 2 min) despite favorable washout from the brain (0.26% ID/g, at 180 min) was displayed. [125I]SC-NHEtOH exhibited binding affinities to both artificial prion aggregates as well as prion deposits in the brain. However, significant improvement in the binding affinity for PrPSc and blood-brain barrier permeability is necessary for the development of successful in vivo imaging probes for the detection of cerebral PrPSc in the brain.

Circulation of Nor98 Atypical Scrapie in Portuguese Sheep Confirmed by Transmission of Isolates into Transgenic Ovine ARQ-PrP Mice.

Portugal was among the first European countries to report cases of Atypical Scrapie (ASc), the dominant form of Transmissible Spongiform Encephalopathy (TSE) in Portuguese small ruminants. Although the diagnostic phenotypes observed in Portuguese ASc cases seem identical to those described for Nor98, unequivocal identification requires TSE strain-typing using murine bioassays. In this regard, we initiated characterization of ASc isolates from sheep either homozygous for the ARQ genotype or the classical scrapie-resistant ARR genotype. Isolates from such genotypes were transmitted to TgshpXI mice expressing ovine PrPARQ. Mean incubation periods were 414 ± 58 and 483 ± 107 days in mice inoculated with AL141RQ/AF141RQ and AL141RR/AL141RR sheep isolates, respectively. Both isolates produced lesion profiles similar to French ASc Nor98 ‘discordant cases’, where vacuolation was observed in the hippocampus (G6), cerebral cortex at the thalamus (G8) level, cerebellar white matter (W1) and cerebral peduncles (W3). Immunohistochemical PrPSc deposition was observed in the hippocampus, cerebellar cortex, cerebellar white matter and cerebral peduncles in the form of aggregates and fine granules. These findings were consistent with previously reported cases of ASc Nor98 transmitted to transgenic TgshpXI mice, confirming that the ASc strain present in Portuguese sheep corresponds to ASc Nor98.

Les maladies à prions ou encéphalopathies spongiformes transmissibles

Prion diseases or transmissible spongiform encephalopathies (TSEs) are human and animal diseases naturally or experimentally transmissible with a long incubation period and a fatal course without remission. The nature of the transmissible agent remains debated but the absence of a structure evoking a conventional microorganism led Stanley B. Prusiner to hypothesize that it could be an infectious protein (proteinaceous infectious particle or prion). The prion would be the abnormal form of a normal protein, cellular PrP (PrPc) which will change its spatial conformation and be converted into scrapie prion protein (PrPsc) with properties of partial resistance to proteases, aggregation and insolubility in detergents. No inflammatory or immune response are detected in TSEs which are characterized by brain damage combining spongiosis, neuronal loss, astrocytic gliosis, and deposits of PrPsc that may appear as amyloid plaques. Although the link between the accumulation of PrPsc and the appearance of lesions remains debated, the presence of PrPsc is constant during TSE and necessary for a definitive diagnosis. Even if they remain rare diseases (2 cases per million), the identification of kuru, at the end of the 1950s, of iatrogenic cases in the course of the 1970s and of the variant of Creutzfeldt-Jakob disease (CJD) in the mid-1990s explain the interest in these diseases but also the fears they can raise for public health. They remain an exciting research model because they belong both to the group of neurodegenerative diseases with protein accumulation (sporadic CJD), to the group of communicable diseases (iatrogenic CJD, variant of CJD) but also to the group of genetic diseases with a transmission Mendelian dominant (genetic CJD, Gerstmann-Straussler-Scheinker syndrome, fatal familial insomnia).

PMCA-generated prions from the olfactory mucosa of patients with Fatal Familial Insomnia cause prion disease in mice

Fatal Familial Insomnia (FFI) is a genetic prion disease caused by the D178N mutation in the prion protein gene (PRNP) in coupling phase with methionine at PRNP 129. In 2017, we have shown that the olfactory mucosa (OM) collected from FFI patients contained traces of PrPSc detectable by Protein Misfolding Cyclic Amplification (PMCA). In this work, we have challenged PMCA-generated products obtained from OM and brain homogenate of FFI patients in BvPrP-Tg407 transgenic mice expressing the bank vole prion protein to test their ability to induce prion pathology. All inoculated mice developed mild spongiform changes, astroglial activation, and PrPSc deposition mainly affecting the thalamus. However, their neuropathological alterations were different from those found in the brain of BvPrP-Tg407 mice injected with raw FFI brain homogenate. Although with some experimental constraints, we show that PrPSc present in OM of FFI patients is potentially infectious. This work was supported in part by the Italian Ministry of Health (GR-2013-02355724 and Ricerca Corrente), MJFF, ALZ, Alzheimer's Research UK and the Weston Brain Institute (BAND2015), and Euronanomed III (SPEEDY) to FM; by the Spanish Ministerio de Economía y Competitividad (grant AGL2016-78054-R [AEI/FEDER, UE]) to JMT and JCE; AM-M was supported by a fellowship from the INIA (FPI-SGIT-2015-02).