In Memory of Valeria Manetto (1953–1995)

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Gerstmann-Sträussler-Scheinker disease revisited: accumulation of covalently-linked multimers of internal prion protein fragments

Despite their phenotypic heterogeneity, most human prion diseases belong to two broadly defined groups: Creutzfeldt-Jakob disease (CJD) and Gerstmann-Sträussler-Scheinker disease (GSS). While the structural characteristics of the disease-related proteinase K-resistant prion protein (resPrPD) associated with the CJD group are fairly well established, many features of GSS-associated resPrPD are unclear. Electrophoretic profiles of resPrPD associated with GSS variants typically show 6-8 kDa bands corresponding to the internal PrP fragments as well as a variable number of higher molecular weight bands, the molecular nature of which has not been investigated. Here we have performed systematic studies of purified resPrPD species extracted from GSS cases with the A117V (GSSA117V) and F198S (GSSF198S) PrP gene mutations. The combined analysis based on epitope mapping, deglycosylation treatment and direct amino acid sequencing by mass spectrometry provided a conclusive evidence that high molecular weight resPrPD species seen in electrophoretic profiles represent covalently-linked multimers of the internal ~ 7 and ~ 8 kDa fragments. This finding reveals a mechanism of resPrPD aggregate formation that has not been previously established in prion diseases

Chronic Wasting Disease and Potential Transmission to Humans

Chronic wasting disease (CWD) of deer and elk is endemic in a tri-corner area of Colorado, Wyoming, and Nebraska, and new foci of CWD have been detected in other parts of the United States. Although detection in some areas may be related to increased surveillance, introduction of CWD due to translocation or natural migration of animals may account for some new foci of infection. Increasing spread of CWD has raised concerns about the potential for increasing human exposure to the CWD agent. The foodborne transmission of bovine spongiform encephalopathy to humans indicates that the species barrier may not completely protect humans from animal prion diseases. Conversion of human prion protein by CWD-associated prions has been demonstrated in an in vitro cell-free experiment, but limited investigations have not identified strong evidence for CWD transmission to humans. More epidemiologic and laboratory studies are needed to monitor the possibility of such transmissions

Mathematical models for the diffusion magnetic resonance signal abnormality in patients with prion diseases

AbstractIn clinical practice signal hyperintensity in the cortex and/or in the striatum on magnetic resonance (MR) diffusion-weighted images (DWIs) is a marker of sporadic Creutzfeldt–Jakob Disease (sCJD). MR diagnostic accuracy is greater than 90%, but the biophysical mechanisms underpinning the signal abnormality are unknown. The aim of this prospective study is to combine an advanced DWI protocol with new mathematical models of the microstructural changes occurring in prion disease patients to investigate the cause of MR signal alterations. This underpins the later development of more sensitive and specific image-based biomarkers. DWI data with a wide a range of echo times and diffusion weightings were acquired in 15 patients with suspected diagnosis of prion disease and in 4 healthy age-matched subjects. Clinical diagnosis of sCJD was made in nine patients, genetic CJD in one, rapidly progressive encephalopathy in three, and Gerstmann–Sträussler–Scheinker syndrome in two. Data were analysed with two bi-compartment models that represent different hypotheses about the histopathological alterations responsible for the DWI signal hyperintensity. A ROI-based analysis was performed in 13 grey matter areas located in affected and apparently unaffected regions from patients and healthy subjects. We provide for the first time non-invasive estimate of the restricted compartment radius, designed to reflect vacuole size, which is a key discriminator of sCJD subtypes. The estimated vacuole size in DWI hyperintense cortex was in the range between 3 and 10 µm that is compatible with neuropathology measurements. In DWI hyperintense grey matter of sCJD patients the two bi-compartment models outperform the classic mono-exponential ADC model. Both new models show that T2 relaxation times significantly increase, fast and slow diffusivities reduce, and the fraction of the compartment with slow/restricted diffusion increases compared to unaffected grey matter of patients and healthy subjects. Analysis of the raw DWI signal allows us to suggest the following acquisition parameters for optimized detection of CJD lesions: b = 3000 s/mm2 and TE = 103 ms. In conclusion, these results provide the first in vivo estimate of mean vacuole size, new insight on the mechanisms of DWI signal changes in prionopathies and open the way to designing an optimized acquisition protocol to improve early clinical diagnosis and subtyping of sCJD

Effects of different experimental conditions on the PrPSc core generated by protease digestion: implications for strain typing and molecular classification of CJD.

The discovery of molecular subtypes of the pathological prion protein PrPSc has provided the basis for a novel classification of human transmissible spongiform encephalopathies (TSEs) and a potentially powerful method for strain typing. However, there is still a significant disparity regarding the understanding and nomenclature of PrPSc types. In addition, it is still unknown whether a specific PrPSc type is associated with each TSE phenotypic variant. In sporadic Creutzfeldt-Jakob disease (sCJD), five disease phenotypes are known, but only two major types of PrPSc, types 1 and 2, have been consistently reproduced. We further analyzed PrPSc properties in sCJD and variant CJD using a high resolution gel electrophoresis system and varying experimental conditions. We found that pH varies among CJD brain homogenates in standard buffers, thereby influencing the characteristics of protease-treated PrPSc. We also show that PrPSc type 1 and type 2 are heterogeneous species which can be further distinguished into five molecular subtypes that fit the current histopathological classification of sCJD variants. Our results shed light on previous disparities in PrPSc typing, provide a refined classification of human PrPSc types, and support the notion that the pathological TSE phenotype is related to PrPSc structure

Detection of Prions in the Urine of Patients Affected by Sporadic Creutzfeldt-Jakob Disease

OBJECTIVE: Currently, it is unknown whether infectious prions are present in peripheral tissues and biological fluids of patients affected by sporadic Creutzfeldt-Jakob disease (sCJD), the most common prion disorder in humans. This represents a potential risk for inter-individual prion infection. The main goal of this study was to evaluate the presence of prions in urine of patients suffering from the major subtypes of sCJD. METHODS: Urine samples from sCJD patients spanning the six major subtypes were tested. As controls, we used urine samples from people affected by other neurological or neurodegenerative diseases as well as healthy controls. These samples were analyzed blinded. The presence of prions was detected by a modified version of the PMCA technology, specifically optimized for high sensitive detection of sCJD prions. RESULTS: The PMCA assay was first optimized to detect low quantities of prions in diluted brain homogenates from patients affected by all subtypes of sCJD spiked into healthy urine. Twenty-nine of the 81 patients affected by sCJD analyzed in this study were positive by PMCA testing, whereas none of the 160 controls showed any signal. These results indicate a 36% sensitivity and 100% specificity. The subtypes with the highest positivity rate were VV1 and VV2, which combined account for about 15-20% of all sCJD cases, and no detection was observed in MV1 and MM2. INTERPRETATION: Our findings indicate that potentially infectious prions are secreted in urine of some sCJD patients, suggesting a possible risk for inter-individual transmission. Prion detection in urine might be used as a noninvasive preliminary screening test to detect sCJD

Bank Vole Prion Protein As an Apparently Universal Substrate for RT-QuIC-Based Detection and Discrimination of Prion Strains

Prions propagate as multiple strains in a wide variety of mammalian species. The detection of all such strains by a single ultrasensitive assay such as Real Time Quaking-induced Conversion (RT-QuIC) would facilitate prion disease diagnosis, surveillance and research. Previous studies have shown that bank voles, and transgenic mice expressing bank vole prion protein, are susceptible to most, if not all, types of prions. Here we show that bacterially expressed recombinant bank vole prion protein (residues 23-230) is an effective substrate for the sensitive RT-QuIC detection of all of the different prion types that we have tested so far--a total of 28 from humans, cattle, sheep, cervids and rodents, including several that have previously been undetectable by RT-QuIC or Protein Misfolding Cyclic Amplification. Furthermore, comparison of the relative abilities of different prions to seed positive RT-QuIC reactions with bank vole and not other recombinant prion proteins allowed discrimination of prion strains such as classical and atypical L-type bovine spongiform encephalopathy, classical and atypical Nor98 scrapie in sheep, and sporadic and variant Creutzfeldt-Jakob disease in humans. Comparison of protease-resistant RT-QuIC conversion products also aided strain discrimination and suggested the existence of several distinct classes of prion templates among the many strains tested

Clinicopathological Correlates in a PRNP P102L Mutation Carrier with Rapidly Progressing Parkinsonism-dystonia

Parkinsonism-dystonia is rare in carriers of PRNP P102L mutation. Severity and distribution of prion protein (PrP) deposition may influence the clinical presentation. We present such clinic-pathological correlation in a 56-year-old male with a PRNP P102L mutation associated with a phenotype characterized by rapidly progressing parkinsonism-dystonia. The patient was studied clinically (videotaped exams, brain MRIs); molecular genetically (gene sequence analysis); and neuropathologically (histology, immunohistochemistry) during his 7-month disease course. The patient had parkinsonism, apraxia, aphasia, and dystonia, which progressed rapidly. Molecular genetic analysis revealed PRNP P102L mutation carrier status. Brain MRIs revealed progressive global volume loss and T2/FLAIR hyperintensity in neocortex and basal ganglia. Postmortem examination showed neuronal loss, gliosis, spongiform changes, and PrP deposition in the striatum. PrP immunohistochemistry revealed widespread severe PrP deposition in the thalamus and cerebellar cortex. Based on the neuropathological and molecular-genetic analysis, the rapidly progressing parkinsonism-dystonia correlated with nigrostriatal, thalamic, and cerebellar pathology