Pathologic prion protein spreading in the peripheral nervous system of a patient with sporadic Creutzfeldt-Jakob disease

The Use of Real-Time Quaking-Induced Conversion for the Diagnosis of Human Prion Diseases

Prion diseases are rapidly progressive, invariably fatal, transmissible neurodegenerative disorders associated with the accumulation of the amyloidogenic form of the prion protein in the central nervous system (CNS). In humans, prion diseases are highly heterogeneous both clinically and neuropathologically. Prion diseases are challenging to diagnose as many other neurologic disorders share the same symptoms, especially at clinical onset. Definitive diagnosis requires brain autopsy to identify the accumulation of the pathological prion protein, which is the only specific disease biomarker. Although brain post-mortem investigation remains the gold standard for diagnosis, antemortem clinical, instrumental, and laboratory tests showing variable sensitivities and specificity, being surrogate disease biomarkers, have been progressively introduced in clinical practice to reach a diagnosis. More recently, the ultrasensitive Real-Time Quaking-Induced Conversion (RT-QuIC) assay, exploiting, for the first time, the detection of misfolded prion protein through an amplification strategy, has highly improved the “in-vitam” diagnostic process, reaching in cerebrospinal fluid (CSF) and olfactory mucosa (OM) around 96% sensitivity and close to 100% specificity. RT-QuIC also improved the detection of the pathologic prion protein in several peripheral tissues, possibly even before the clinical onset of the disease. The latter aspect is of great interest for the early and even preclinical diagnosis in subjects at genetic risk of developing the disease, who will likely be the main target population in future clinical trials. This review presents an overview of the current knowledge and future perspectives on using RT-QuIC to diagnose human prion diseases.

Clinical Use of Improved Diagnostic Testing for Detection of Prion Disease

Prion diseases are difficult to recognize as many symptoms are shared among other neurologic pathologies and the full spectra of symptoms usually do not appear until late in the disease course. Additionally, many commonly used laboratory markers are non-specific to prion disease. The recent introduction of second-generation real time quaking induced conversion (RT-QuIC) has revolutionized pre-mortem diagnosis of prion disease due to its extremely high sensitivity and specificity. However, RT-QuIC does not provide prognostic data and has decreased diagnostic accuracy in some rarer, atypical prion diseases. The objective of this review is to provide an overview of the current clinical utility of fluid-based biomarkers, neurodiagnostic testing, and brain imaging in the diagnosis of prion disease and to suggest guidelines for their clinical use, with a focus on rarer prion diseases with atypical features. Recent advancements in laboratory-based testing and imaging criteria have shown improved diagnostic accuracy and prognostic potential in prion disease, but because these diagnostic tests are not sensitive in some prion disease subtypes and diagnostic test sensitivities are unknown in the event that CWD transmits to humans, it is important to continue investigations into the clinical utility of various testing modalities.

Prion-related peripheral neuropathy in sporadic Creutzfeldt-Jakob disease

OBJECTIVE

To assess whether the involvement of the peripheral nervous system (PNS) belongs to the phenotypic spectrum of sporadic Creutzfeldt-Jakob disease (sCJD).

METHODS

We examined medical records of 117 sCJDVV2 (ataxic type), 65 sCJDMV2K (kuru-plaque type) and 121 sCJDMM(V)1 (myoclonic type) subjects for clinical symptoms, objective signs and neurophysiological data. We reviewed two diagnostic nerve biopsies and looked for abnormal prion protein (PrP^Sc) by western blotting and real-time quaking-induced conversion (RT-QuIC) in postmortem PNS samples from 14 subjects.

RESULTS

Seventy-five (41.2%) VV2-MV2K patients, but only 11 (9.1%) MM(V)1, had symptoms or signs suggestive of PNS involvement occurring at onset in 18 cases (17 VV2-MV2K, 9.3%; and 1 MM(V)1, 0.8%) and isolated in 6. Nerve biopsy showed a mixed predominantly axonal and demyelinating neuropathy in two sCJDMV2K. Electromyography showed signs of neuropathy in half of the examined VV2-MV2K patients. Prion RT-QuIC was positive in all CJD PNS samples, whereas western blotting detected PrP^Sc in the sciatic nerve in one VV2 and one MV2K.

CONCLUSIONS

Peripheral neuropathy, likely related to PrP^Sc deposition, belongs to the phenotypic spectrum of sCJDMV2K and VV2 and may mark the clinical onset. The significantly lower prevalence of PNS involvement in typical sCJDMM(V)1 suggests that the PNS tropism of sCJD prions is strain dependent.

Accumulation of prion protein in the vagus nerve in creutzfeldt-jakob disease

Disease‐associated proteins are thought to propagate along neuronal processes in neurodegenerative diseases. To detect disease‐associated prion protein (PrP^Sc) in the vagus nerve in different forms and molecular subtypes of Creutzfeldt–Jakob disease (CJD), we applied 3 different anti‐PrP antibodies. We screened the vagus nerve in 162 sporadic and 30 genetic CJD cases. Four of 31 VV‐2 type sporadic CJD and 7 of 30 genetic CJD cases showed vagal PrP^Sc immunodeposits with distinct morphology. Thus, PrP^Sc in CJD affects the vagus nerve analogously to α‐synuclein in Parkinson disease. The morphologically diverse deposition of PrP^Sc in genetic and sporadic CJD argues against uniform mechanisms of propagation of PrP^Sc. Ann Neurol 2019;85:782–787

Immunohistochemical detection of disease-associated prion protein in the peripheral nervous system in experimental H-type bovine spongiform encephalopathy

H-type bovine spongiform encephalopathy (BSE) has been identified in aged cattle in Europe and North America. To determine the localization of disease-associated prion protein (PrP(Sc)) in the peripheral nerve tissues of cattle affected with H-type BSE, we employed highly sensitive immunohistochemical and immunofluorescence techniques with the tyramide signal amplification (TSA) system. PrP(Sc) deposition was detected in the inferior ganglia, sympathetic nerve trunk, vagus nerve, spinal nerves, cauda equina, and adrenal medulla, using this system. Notably, granular PrP(Sc) deposits were present mainly in the Schwann cells and fibroblast-like cells and occasionally along certain nerve fibers at the surface of the axons. In the adrenal gland, PrP(Sc) immunolabeling was observed within the sympathetic nerve fibers and nerve endings in the adrenal medulla. Although our results were limited to only 3 experimental cases, these results suggest that the TSA system, a highly sensitive immunohistochemical procedure, may help in elucidating the peripheral pathogenesis of H-type BSE.

Molecular diagnosis of human prion disease

INTRODUCTION

Human prion diseases (PrDs) are transmissible fatal nervous system disorders with public health implications. They are characterized by the presence of a disease-associated form of the physiological cellular prion protein. Development of diagnostic procedures is important to avoid transmission, including through blood products. Methods used for the detection of disease-associated PrP have implications for other neurodegenerative diseases.

AREAS COVERED

In this review, the authors discuss recent progress in the understanding of the molecular background of phenotypic variability of human PrDs, and the current concepts of molecular diagnosis. Also, the authors provide a critical summary of the diagnostic methods with regard to the molecular subtypes.

EXPERT OPINION

In spite of a lack of specific tests to detect disease-associated PrP in body fluids, the constellation of clinical symptoms, detection of protein 14-3-3 in cerebrospinal fluid, electroencephalogram, cranial MRI and prion protein gene examinations, together have increased the specificity and sensitivity of in vivo diagnostics. As new forms of PrDs are reported, continuous evaluation of their incidence and the search for their etiology is crucial. Recent studies, suggesting prion-like properties of certain proteinopathies associated with Parkinson's or Alzheimer's disease, have again brought PrDs to the center of interest as a model of diseases with disordered protein processing.

Paracrine diffusion of PrP(C) and propagation of prion infectivity by plasma membrane-derived microvesicles

Cellular prion protein (PrP^c) is a physiological constituent of eukaryotic cells. The cellular pathways underlying prions spread from the sites of prions infection/peripheral replication to the central nervous system are still not elucidated. Membrane-derived microvesicles (MVs) are submicron (0.1–1 µm) particles, that are released by cells during plasma membrane shedding processes. They are usually liberated from different cell types, mainly upon activation as well as apoptosis, in this case, one of their hallmarks is the exposure of phosphatidylserine in the outer leaflet of the membrane. MVs are also characterized by the presence of adhesion molecules, MHC I molecules, as well as of membrane antigens typical of their cell of origin. Evidence exists that MVs shedding provide vehicles to transfer molecules among cells, and that MVs are important modulators of cell-to-cell communication. In this study we therefore analyzed the potential role of membrane-derived MVs in the mechanism(s) of PrP^C diffusion and prion infectivity transmission. We first identified PrP^C in association with the lipid raft components Fyn, flotillin-2, GM1 and GM3 in MVs from plasma of healthy human donors. Similar findings were found in MVs from cell culture supernatants of murine neuronal cells. Furthermore we demonstrated that PrP^Sc is released from infected murine neuronal cells in association with plasma membrane-derived MVs and that PrP^Sc-bearing MVs are infectious both in vitro and in vivo. The data suggest that MVs may contribute both to the intercellular mechanism(s) of PrP^C diffusion and signaling as well as to the process of prion spread and neuroinvasion.

Rapid diagnosis of human prion disease using streptomycin with tonsil and brain tissues

The use of streptomycin in the pathological prion protein (PrP(sc)) detection procedures represents a new and attractive way for diagnostic purpose. With this agent, western blot readily detected PrP(sc) in 263K scrapie hamster and C57Bl/6 wild-type mice challenged with C506M3 scrapie strain. Our aim was to evaluate this new diagnosis procedure in the field of human transmissible spongiform encephalopathies (TSEs). First, we had confirmed the ability of streptomycin to precipitate PrP(res) from human brain of Creutzfeldt-Jakob disease (CJD) patient. Second, we compared the detection of PrP(res) with streptomycin against three other protocols using other precipitations. Then we assessed PrP(res) detection with streptomycin in 98 brain tissue samples from various aetiologies of human TSEs and 52 brain samples from other dementia. Finally, we applied this protocol for tonsils examination of five patients suspected of variant CJD (v-CJD). Sensitivity and specificity obtained with the streptomycin protocol were both 100% on brain tissue. For tonsil tissues, PrP(res) was clearly identified in the two post-mortem confirmed v-CJD cases, whereas no characteristic three-band pattern was seen in the three confirmed non-v-CJD samples. In this study, streptomycin demonstrated its efficiency to detect PrP(res) both in the central nervous system and in the lymphoid tissue without practical difficulty and with rapid preparation. Because of its ability to act as a good agent for PrP(sc) examination in different tissues, recovery of PrP(sc) in biological fluids using streptomycin should open further perspectives of applications in CJD diagnostics. Streptomycin effects in vivo might thus also be questioned.

Prions in the peripheral nerves of bovine spongiform encephalopathy-affected cattle

With the use of increasingly sensitive methods for detection of the abnormal isoform of prion protein (PrPSc) and infectivity in prion diseases, it has recently been shown that parts of the peripheral nervous system (PNS) of bovine spongiform encephalopathy (BSE)-affected cattle may become infected. It has been reported that prions spread to the central nervous system (CNS) via the PNS in sheep scrapie, but the pathogenesis of BSE in cattle is less well understood. To determine whether parts of the PNS other than those implicated directly in the hypothetical pathogenetic spread of agent from the intestine to the CNS become involved before or after the CNS is affected, PrPSc distribution was investigated by a highly sensitive Western blotting technique in dorsal root ganglia, stellate ganglion, phrenic, radial and sciatic nerves, adrenal gland and CNS of cattle that were inoculated orally with BSE-affected brain and culled sequentially. In experimentally BSE-affected cattle, PrPSc was first detected in the CNS and dorsal root ganglia; subsequently, PrPSc accumulation was detected in the peripheral nerve trunks. PrPSc was also detected in the adrenal glands of cattle that showed clinical signs. No PrPSc was detected in the PNS of BSE-negative cattle. This study shows that, with respect to dorsal root ganglia, a paravertebral sympathetic ganglion and the somatic nerves examined, PrPSc is detected in the PNS during the disease course at the same time as, or after, it accumulates in the CNS.

Managing the risk of transmission of variant Creutzfeldt Jakob disease by blood products

Whereas plasma-derived clotting factor concentrates now have a very good safety record for not being infectious for lipid enveloped viruses, concern has arisen about the possibility that prion diseases might be transmitted by blood products. There is epidemiological evidence that classical sporadic Creutzfeld Jakob disease (CJD) is not transmitted by blood transfusion. There is now good evidence that the abnormal prion associated with variant CJD can be transmitted by transfusion of fresh blood components and infect recipients. To reduce the risk of the pathological prion in the UK infecting recipients of clotting factor concentrates, these are now only manufactured from imported plasma collected from countries where there has not been bovine spongiform encephalopathy (BSE) in cattle and the risk of variant CJD in the population is, therefore, considered negligible. The safety of these concentrates is also enhanced because prion protein is, to an appreciable extent, excluded by the manufacturing process from the final product. To help reduce the chance of prion transmission by fresh blood products, donations are leucodepleted, there is increasing use of imported fresh frozen plasma (especially for treating children) and potential donors, who have been recipients of blood since 1980 (the beginning of the BSE epidemic in cattle) are deferred.

Neuropathologic characteristics of spinal cord lesions in sporadic Creutzfeldt-Jakob disease

We investigated the neuropathologic features of spinal cord lesions in 23 patients with sporadic Creutzfeldt-Jakob disease (sCJD), paying particular attention to neuronal loss and gliosis, pyramidal tract degeneration and prion protein (PrP) deposition. The study included 9 cases of subacute spongiform encephalopathy, 13 cases of panencephalopathic-type sCJD and 1 case of sporadic fatal insomnia (sFI). In the spinal gray matter, although gliosis was present in some patients with disease of relatively long duration, the number of neurons, including large motor neurons, was well preserved regardless of disease duration. Pyramidal tract degeneration was observed in some patients with disease lasting more than 14 months but not in the patient with sFI. PrP deposition was present in the spinal cord of all sCJD patients, and was identified predominantly in the posterior horn, particularly in the substantia gelatinosa, regardless of disease duration or disease classification based on cerebral pathology. Relatively prominent PrP deposition was also observed in Clarke's column. The density of PrP deposition in the sCJD spinal cord was not associated with disease duration or neuronal degeneration. Our results indicate that PrP deposition in the spinal cord is an early pathologic event in sCJD and may remain to the end stage. Although no VV1, VV2 or MV2 cases were included in our study, we suggest that stereotypic accumulation of PrP is a consistent pathologic feature of sCJD and that the spinal cord remains relatively resistant to the pathologic process of sCJD, at least in patients with MM1 sCJD.