Neurodegenerative Prion Diseases Research Articles

Current understanding of PrnP Genetics: A tool for Molecular Assisted Selection in Sheep Populations (A review)

Scrapie is a neurodegenerative prion disease of sheep, goats and mouflons, belonging to the group of transmissible spongiform encephalopathies (TSEs), which affects humans as well. Even though classical scrapie has been known for over 250 years, the 1985 BSE crisis related to the advent of new forms of the Creutzfeldt-Jakob disease (vCJD) in humans imposed the implementation of rapid coercive legal measures of prevention, control and eradication of TSEs. According to the prion hypothesis, the transmissible agent is the pathological isoform (PrP Sc ) of cellular prion protein (PrP C ). Specific polymorphisms of the gene that encodes cell prion protein (PrnP) in sheep have been associated with resistance / natural susceptibility to the development and progression of the disease. Combinations of alleles at three adjacent codons (136 [A/V], 154 [H/R], 171 [H/Q/R]) underpin the classification of 15 possible genotypes in risk classes, applicable in selection schemes where the maximum resistance is conferred by ARR allele, and the minimum by the VRQ allele. Although, after applying these programmes, the genetic structure of sheep populations has changed favourably, genotype association studies showed that no genotype is completely resistant to the infection, including homozygote ARR / ARR. With the discovery of atypical scrapie (Nor98), it became evident that the connection between the genetics of prion protein gene polymorphisms and susceptibility to the disease must be re-evaluated individually for each breed. In scrapie monitoring and control programmes, three diagnostic categories of the disease are observed: classical scrapie, atypical scrapie and BSE scrapie in small ruminant. This review shows the chronology of progress in the fight for the eradication of TSEs in sheep, 30 years after the BSE epidemic outburst, focusing especially on the link between the molecular diagnostic forms and the genetics of the disease. Â

REST alleviates neurotoxic prion peptide-induced synaptic abnormalities, neurofibrillary degeneration and neuronal death partially via LRP6-mediated Wnt-β-catenin signaling.

Prion diseases are a group of infectious neurodegenerative diseases characterized by multiple neuropathological hallmarks including synaptic damage, spongiform degeneration and neuronal death. The factors and mechanisms that maintain cellular morphological integrity and protect against neurodegeneration in prion diseases are still unclear. Here we report that after stimulation with the neurotoxic PrP106-126 fragment in primary cortical neurons, REST translocates from the cytoplasm to the nucleus and protects neurons from harmful effects of PrP106-126. Overexpression of REST reduces pathological damage and abnormal biochemical alterations of neurons induced by PrP106-126 and maintains neuronal viability by stabilizing the level of pro-survival protein FOXO1 and inhibiting the permeability of the mitochondrial outer membrane, release of cytochrome c from mitochondria to cytoplasm and the activation of Capase3. Conversely, knockdown of REST exacerbates morphological damage and inhibits the expression of FOXO1. Additionally, by overexpression or knockdown of LRP6, we further show that LRP6-mediated Wnt-β-catenin signaling partly regulates the expression of REST. Collectively, we demonstrate for the first time novel neuroprotective function of REST in prion diseases and hypothesise that the LRP6-Wnt-β-catenin/REST signaling plays critical and collaborative roles in neuroprotection. This signaling of neuronal survival regulation could be explored as a viable therapeutic target for prion diseases and associated neurodegenerative diseases.

Purification and Refolding to Amyloid Fibrils of (His)6-tagged Recombinant Shadoo Protein Expressed as Inclusion Bodies in E. coli.

The Escherichia coli expression system is a powerful tool for the production of recombinant eukaryotic proteins. We use it to produce Shadoo, a protein belonging to the prion family. A chromatographic method for the purification of (His)6-tagged recombinant Shadoo expressed as inclusion bodies is described. The inclusion bodies are solubilized in 8 M urea and bound to a Ni(2+)-charged column to perform ion affinity chromatography. Bound proteins are eluted by a gradient of imidazole. Fractions containing Shadoo protein are subjected to size exclusion chromatography to obtain a highly purified protein. In the final step purified Shadoo is desalted to remove salts, urea and imidazole. Recombinant Shadoo protein is an important reagent for biophysical and biochemical studies of protein conformation disorders occurring in prion diseases. Many reports demonstrated that prion neurodegenerative diseases originate from the deposition of stable, ordered amyloid fibrils. Sample protocols describing how to fibrillate Shadoo into amyloid fibrils at acidic and neutral/basic pHs are presented. The methods on how to produce and fibrillate Shadoo can facilitate research in laboratories working on prion diseases, since it allows for production of large amounts of protein in a rapid and low cost manner.

Purification and Refolding to Amyloid Fibrils of (His)<sub>6</sub>-tagged Recombinant Shadoo Protein Expressed as Inclusion Bodies in<em> E. coli</em>

The Escherichia coli expression system is a powerful tool for the production of recombinant eukaryotic proteins. We use it to produce Shadoo, a protein belonging to the prion family. A chromatographic method for the purification of (His)6-tagged recombinant Shadoo expressed as inclusion bodies is described. The inclusion bodies are solubilized in 8 M urea and bound to a Ni2+-charged column to perform ion affinity chromatography. Bound proteins are eluted by a gradient of imidazole. Fractions containing Shadoo protein are subjected to size exclusion chromatography to obtain a highly purified protein. In the final step purified Shadoo is desalted to remove salts, urea and imidazole. Recombinant Shadoo protein is an important reagent for biophysical and biochemical studies of protein conformation disorders occurring in prion diseases. Many reports demonstrated that prion neurodegenerative diseases originate from the deposition of stable, ordered amyloid fibrils. Sample protocols describing how to fibrillate Shadoo into amyloid fibrils at acidic and neutral/basic pHs are presented. The methods on how to produce and fibrillate Shadoo can facilitate research in laboratories working on prion diseases, since it allows for production of large amounts of protein in a rapid and low cost manner.

Prion Infectivity Plateaus and Conversion to Symptomatic Disease Originate from Falling Precursor Levels and Increased Levels of Oligomeric PrPSc Species.

In lethal prion neurodegenerative diseases, misfolded prion proteins (PrP(Sc)) replicate by redirecting the folding of the cellular prion glycoprotein (PrP(C)). Infections of different durations can have a subclinical phase with constant levels of infectious particles, but the mechanisms underlying this plateau and a subsequent exit to overt clinical disease are unknown. Using tandem biophysical techniques, we show that attenuated accumulation of infectious particles in presymptomatic disease is preceded by a progressive fall in PrP(C) level, which constricts replication rate and thereby causes the plateau effect. Furthermore, disease symptoms occurred at the threshold associated with increasing levels of small, relatively less protease-resistant oligomeric prion particles (oPrP(Sc)). Although a hypothetical lethal isoform of PrP cannot be excluded, our data argue that diminishing residual PrP(C) levels and continuously increasing levels of oPrP(Sc) are crucial determinants in the transition from presymptomatic to symptomatic prion disease. Prions are infectious agents that cause lethal brain diseases; they arise from misfolding of a cell surface protein, PrP(C) to a form called PrP(Sc). Prion infections can have long latencies even though there is no protective immune response. Accumulation of infectious prion particles has been suggested to always reach the same plateau in the brain during latent periods, with clinical disease only occurring when hypothetical toxic forms (called PrP(L) or TPrP) begin to accumulate. We show here that infectivity plateaus arise because PrP(C) precursor levels become downregulated and that the duration of latent periods can be accounted for by the level of residual PrP(C), which transduces a toxic effect, along with the amount of oligomeric forms of PrP(Sc).

Cytosolically expressed PrP GPI-signal peptide interacts with mitochondria

We previously reported that PrP GPI-anchor signal peptide (GPI-SP) is specifically degraded by the proteasome. Additionally, we showed that the point mutation P238S, responsible for a genetic form of prion diseases, while not affecting the GPI-anchoring process, results in the accumulation of PrP GPI-SP, suggesting the possibility that PrP GPI-anchor signal peptide could play a role in neurodegenerative prion diseases. We now show that PrP GPI-SP, when expressed as a cytosolic peptide, is able to localize to the mitochondria and to induce mitochondrial fragmentation and vacuolarization, followed by loss in mitochondrial membrane potential, ultimately resulting in apoptosis. Our results identify the GPI-SP of PrP as a novel candidate responsible for the impairment in mitochondrial function involved in the synaptic pathology observed in prion diseases, establishing a link between PrP GPI-SP accumulation and neuronal death.

Phosphatidylinositol-glycan-phospholipase D is involved in neurodegeneration in prion disease.

PrPSc is formed from a normal glycosylphosphatidylinositol (GPI)-anchored prion protein (PrPC) by a posttranslational modification. Most GPI-anchored proteins have been shown to be cleaved by GPI phospholipases. Recently, GPI-phospholipase D (GPI-PLD) was shown to be a strictly specific enzyme for GPI anchors. To investigate the involvement of GPI-PLD in the processes of neurodegeneration in prion diseases, we examined the mRNA and protein expression levels of GPI-PLD in the brains of a prion animal model (scrapie), and in both the brains and cerebrospinal fluids (CSF) of sporadic and familial Creutzfeldt-Jakob disease (CJD) patients. We found that compared with controls, the expression of GPI-PLD was dramatically down-regulated in the brains of scrapie-infected mice, especially in the caveolin-enriched membrane fractions. Interestingly, the observed decrease in GPI-PLD expression levels began at the same time that PrPSc began to accumulate in the infected brains and this decrease was also observed in both the brain and CSF of CJD patients; however, no differences in expression were observed in either the brains or CSF specimens from Alzheimer’s disease patients. Taken together, these results suggest that the down-regulation of GPI-PLD protein may be involved in prion propagation in the brains of prion diseases.

Genetic evidence for susceptibility and resistance against scrapie in Indian sheep.

Scrapie is a fatal, neurodegenerative disease of sheep and goats (Prusiner 1982). The cause behind the disease is infection by prion proteins (Prusiner 1982). The progression of scrapie is known to be influenced by the amino acid polymorphism of the host prion protein (PRNP) gene (Belt et al. 1995). The present study was carried out on Indian sheep breeds i.e., Karnah, Mandya, Malpura and Garole to identify polymorphisms of the PRNP gene at codons (136, 154 and 171) responsible for the susceptibility and resistance of the scrapie disease in sheep. The known risky allele (ARQ) was found to be the most frequent (77.75%). The most resistant (ARR) and most susceptible (VRQ) alleles were found equally distributed with a frequency of 1.75%. Although, most of the alleles were known to confer susceptibility or partial susceptibility to scrapie, yet so far none of the Indian sheep breeds showed any clinical symptoms of the disease. The possible reason could be genotype–environment interaction, management practices and/or resistance of Indian sheep to scrapie via some other mechanism. Fatal neurodegenerative prion diseases are both genetic and infectious to humans and other mammals (Prusiner 1991). Scrapie is considered as a prototype of various forms of prion diseases that include bovine spongiform encephalopathy (BSE) in cattle and Creutzfeldt–Jakob disease in human (Prusiner 1991). It is characterized by the accumulation of an abnormal isoform of the PRNP in the central nervous system (Prusiner 1991). Scrapie is a rare, contagious, slowly progressive, endemic brain disease in

Creutzfeldt-Jakob disease presented with dizziness, weakness and neuropsychiatric symptoms: 2 Case Reports

Creutzfeldt-Jakob disease (CJD) is among very rare, progressive, untreatable, neurodegenerative prion diseases. While the incidence is reported as 1/1000000 years in European countries, sporadic cases are rarely presented in Turkey. Clinical findings are in the form of rapid progressive dementia, myoclonus, cerebellar, pyramidal and extra pyramidal symptoms. Definitive diagnosis is established by histopathological examination. Our case is a 64-year-old male and 70-year-old female patients admitted with dizziness emerged as sub-acute weakness, nausea, vomiting, insomnia, imbalance and additional neuropsychiatric complaints. Focal activity slowness and common periodic sharp wave activities were observed in EEG. CJD was considered because bilateral symmetrical diffusion limitation was observed at both sides in the basal ganglia level in cranial diffusion MRI’s and 14-3-3 protein was resulted as positive in CSF examinations. CJD, which is a very rare disease in patients presenting with progressive neuropsychiatric symptoms and seizure, is one of the diagnosis to be considered and we wanted to emphasize that there is no treatment for it and preventive measures should be taken.

Involvement of trace elements in the pathogenesis of prion diseases.

Prion diseases are progressive neurodegenerative diseases that are associated with conformational changes that convert normal cellular prion protein (PrP(C)) into an abnormal pathogenic prion protein (PrP(Sc)). It is widely recognized that prion diseases are forms of transmissible amyloidosis and are considered to be protein-misfolding diseases (conformational diseases), a category that also includes Alzheimer's disease. Trace elements play crucial roles in the conformational change affecting PrP(C), and increasing evidence suggests that PrP(C) is a metal-binding protein that is involved in the homeostasis of Cu, Zn, and Fe. In this article, we review the current understanding of links between trace elements and the conformational change to PrP(Sc), based on our studies using synthetic prion peptides, as well as other new findings. We also focus on PrP(Sc)-induced disruption of Ca homeostasis as a molecular mechanism for neurodegeneration in prion diseases. Possible roles of carnosine (ß-alanyl histidine) as a candidate neuroprotective substance use in prion diseases are also discussed.

Pressure-assisted dissociation and degradation of “proteinase K-resistant” fibrils prepared by seeding with scrapie-infected hamster prion protein

The crucial step for the fatal neurodegenerative prion diseases involves the conversion of a normal cellular protein, PrPC, into a fibrous pathogenic form, PrPSc, which has an unusual stability against heat and resistance against proteinase K digestion. A successful challenge to reverse the reaction from PrPSc into PrPC is considered valuable, as it would give a key to dissolving the complex molecular events into thermodynamic and kinetic analyses and may also provide a means to prevent the formation of PrPSc from PrPC eventually in vivo. Here we show that, by applying pressures at kbar range, the “proteinase K-resistant” fibrils (rHaPrPres) prepared from hamster prion protein (rHaPrP [23–231]) by seeding with brain homogenate of scrapie-infected hamster, becomes easily digestible. The result is consistent with the notion that rHaPrPres fibrils are dissociated into rHaPrP monomers under pressure and that the formation of PrPSc from PrPC is thermodynamically controlled. Moreover, the efficient degradation of prion fibrils under pressure provides a novel means of eliminating infectious PrPSc from various systems of pathogenic concern.

Deletion of the prion gene Prnp affects offensive aggression in mice

Prion protein (Prp(c)) is involved in the etiology of prion neurodegenerative diseases in mammals. The biological functions of Prp(c) are still largely unknown despite many studies in recent years. Different studies have shown impairment in locomotion, emotional/social behaviors, sleep disorders and memory impairment in mice lacking the prion gene Prnp (Prnp(-/-)) but its exact functions in the brain are still unclear. In the present study, Zurich I Prnp(-/-) and their littermate wild type (WT) control male mice were behaviorally characterized for offensive aggressive behavior in a resident-intruder paradigm with the aim to establish the possible function of Prp(c) in the regulation of offensive aggressive behavior. Prnp(-/-) mice showed reduced latencies to the first attack and bite, higher percentage of mice biting and higher frequencies of attacks of stimulus males. These results show that Prnp(-/-) mice exhibit altered aggressive behavior in comparison to their WT controls and therefore suggest that lack of the Prnp either directly or indirectly affects brain circuitry responsible for the regulation of offensive aggressive behavior.

Neural Stem Cell Differentiation and Prion Infection

Prion diseases are transmissible, fatal, neurodegenerative diseases in human and animals. The molecular basis of neurodegeneration in prion diseases is largely unclear. Developing a cellular model capable of monitoring prion-induced cytotoxicity would be a promising approach for better understanding the prion pathogenesis. One candidate cellular assay is a model based on neurospheres, which contains neural stem cells (NSCs). Both undifferentiated and differentiated NSCs have been demonstrated to be permissive to prion infection, and prion-induced cytopathic changes in differentiated neruosphere cultures were reported (Iwamaru et al., 2013). This protocol describes the procedure to induce differentiation of NSCs from transgenic mice overexpressing prion protein (tga20 mice) into cultures susceptible for prion infection.

The Fate of PrP GPI‐Anchor Signal Peptide is Modulated by P238S Pathogenic Mutation

Glycosylphosphatidylinositol (GPI)-anchored proteins are localized to the plasma membrane via a C-terminally linked GPI anchor. The GPI anchor is added concomitantly to the cleavage of the carboxy-terminal GPI-anchor signal sequence, thereby causing the release of a C-terminal hydrophobic peptide, whose fate has not yet been investigated. Here we followed the fate of the GPI-attachment signal of the prion protein (PrP), a protein implicated in various types of transmissible neurodegenerative spongiform encephalopathies (TSE). The PrP GPI-anchor signal sequence shows a remarkable and unusual degree of conservation across the species and contains two point mutations (M232R/T and P238S) that are responsible for genetic forms of prion disorders. We show that the PrP GPI-anchor signal peptide (SP), but not the one from an unrelated GPI-anchored protein (folate receptor), undergoes degradation via the proteasome. Moreover, the P238S point mutation partially protects the PrP GPI-anchor SP from degradation. Our data provide the first attempt to address the fate of a GPI-anchor SP and identify a role for the P238S mutation, suggesting the possibility that the PrP GPI-anchor SP could play a role in neurodegenerative prion diseases.

Splice site SNPs of phospholipase PLCXD3 are significantly associated with variant and sporadic Creutzfeldt-Jakob disease

BackgroundVariant Creutzfeldt-Jakob disease is an infectious, neurodegenerative, protein-misfolding disease, of the prion disease family, originally acquired through ingestion of meat products contaminated with bovine spongiform encephalopathy (BSE). Public health concern was increased by the discovery of human-to-human transmission via blood transfusion. This study has verified a novel genetic marker linked to disease risk.MethodsSNP imputation and association testing indicated those genes that had significant linkage to disease risk and one gene was investigated further with Sanger resequencing. Results from variant Creutzfeldt-Jakob disease were compared with those from sporadic (idiopathic) Creutzfeldt-Jakob disease and published controls.ResultsThe most significant disease risk, in addition to the prion protein gene, was for the phosphatidylinositol-specific phospholipase C, X domain containing 3 (PLCXD3) gene. Sanger resequencing of CJD patients across a region of PLCXD3 with known variants confirmed three SNPs associated with variant and sporadic CJD.ConclusionsThese data provide the first highly significant confirmation of SNP allele frequencies for a novel CJD candidate gene providing new avenues for investigating these neurodegenerative prion diseases. The phospholipase PLCXD3 is primarily expressed in the brain and is associated with lipid catabolism and signal transduction.

Iatrogenic Creutzfeldt-Jakob disease via surgical instruments

Creutzfeldt-Jakob disease (CJD) is a neurodegenerative prion disease that can spread via contaminated neurosurgical instruments previously used on an infected patient. We examine current guidelines on how to recognize, handle, and prevent instrument-related iatrogenic CJD. Despite only four reported patients worldwide implicating contaminated neurosurgical instruments, and none in the past 30years, the public health consequences of potential instrument-related iatrogenic CJD can be far-reaching. Conventional sterilization and disinfection methods are inadequate in reducing prion infectivity of contaminated instruments, and World Health Organization recommendations for disinfection using bleach or sodium hydroxide are often impractical for routine decontamination. Recently, possible CJD exposure via infected surgical instruments was suspected at a large teaching hospital. Although CJD was later disproven, the intervening investigation exposed the difficulty in tracking infected surgical instruments and in protecting subsequent surgical patients from prion infection. To identify patients at risk for iatrogenic CJD, infectivity of instruments after this index patient is estimated using simple scenario modeling, assuming a certain log reduction of infectivity for each cleansing cycle. Scenario modeling predicts that after six cycles of instrument use with conventional cleansing following an index patient, other patients are highly unlikely to be at risk for iatrogenic CJD. Despite its rarity, the threat of iatrogenic CJD transmission via contaminated instruments poses tremendous challenges to neurosurgeons. Basic prevention strategies should be employed for patients with suspected CJD, including use of disposable instruments where possible and quarantining non-disposable instruments until the diagnosis is ascertained, or using special instrument reprocessing methods if CJD is suspected.

Sporadic Creutzfeldt-Jakob Disease Presenting with Visual Disturbance—A Case Report in China

Creutzfeldt-Jakob disease (CJD) is a rare but fatal neurodegenerative prion disease. Classic CJD comprises a clinical triad of rapidly progressive dementia, myoclonus, and EEG abnormality. At initial presentation, this classic triad is present only in a minority of cases. Visual impairment is one of the predominant manifestations in the course of CJD, especially in Heidenhain variant phenotype. We reported a case presenting with progressive blurred vision, along with other neurological symptoms, who diagnosed as sporadic CJD with cortical blindness in China.

Detection of PrPSc in peripheral tissues of clinically affected cattle after oral challenge with bovine spongiform encephalopathy

Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative prion disease that mainly affects cattle. Transmission of BSE to humans caused a variant form of Creutzfeldt-Jakob disease. Following infection, the protease-resistant, disease-associated isoform of prion protein (PrP(Sc)) accumulates in the central nervous system and in other tissues. Many countries have defined bovine tissues that may contain prions as specified risk materials, which must not enter the human or animal food chains and therefore must be discarded. Ultrasensitive techniques such as protein misfolding cyclic amplification (PMCA) have been developed to detect PrP(Sc) when present in minuscule amounts that are not readily detected by other diagnostic methods such as immunohistochemistry or Western blotting. This study was conducted to determine when and where PrP(Sc) can be found by PMCA in cattle orally challenged with BSE. A total of 48 different tissue samples from four cattle infected orally with BSE at various clinical stages of disease were examined using a standardized PMCA protocol. The protocol used brain homogenate from bovine PrP transgenic mice (Tgbov XV) as substrate and three consecutive rounds of PMCA. Using this protocol, PrP(Sc) was found in the brain, spinal cord, nerve ganglia, optic nerve and Peyer's patches. The presence of PrP(Sc) was confirmed in adrenal glands, as well as in mesenteric lymph nodes - a finding that was reported recently by another group. Interestingly, additional positive results were obtained for the first time in the oesophagus, abomasum, rumen and rectum of clinically affected cattle.

P3‐068: Loss of antioxidant peroxiredoxin 6 protein exacerbates in vivo neurodegeneration in prion disease

P3‐068: Loss of antioxidant peroxiredoxin 6 protein exacerbates <i>in vivo</i> neurodegeneration in prion disease

The association between prion proteins and Aβ1–42 oligomers in cytotoxicity and apoptosis

Misfolding of prion protein (PrP to PrPSc) can cause neurodegenerative prion diseases. As a glycosylphosphatidylinositol (GPI)-anchored membrane protein, the normal form of PrP (PrPC) can function as a receptor for ligands in the extracellular space. PrPC was suggested to be involved in memory, synaptic neuronal communication, and anti-oxidation as a neuroprotective agent. The recently identified interaction between PrPC and Aβ1–42 oligomers suggested another role for PrP as a receptor for Aβ1–42 oligomers, thereby influencing cytotoxicity and apoptosis.Here, the association between PrPC and Aβ1–42 oligomers was investigated by visualizing protein localization in neuronal cells by immunocytochemistry. Aβ1–42 oligomer-induced cytotoxicity was tested in respective expressions of PrPC by using mouse neuroblastoma-2a (N2a) cells, the prion protein overexpressed cells (L2-2B1), and a Prnp-null mouse hippocampal cell line (HpL 3–4). Moreover, apoptotic proteins such as caspase-8 were used to assess the effect of PrPC on Aβ1–42 oligomer-mediated apoptosis. In L2-2B1 and HpL 3–4 cells, the difference in the cytotoxicity of Aβ1–42 oligomers could be clearly distinguished. In addition, Aβ1–42 oligomers induced mitochondria dysfunction, reactive oxygen species (ROS) generation, and calcium influx PrPC-dependently. Apoptosis, related to mitochondria dysfunction, was further investigated to determine the cytotoxic pathway; the results suggest that PrPC could be involved in both the intrinsic and extrinsic apoptotic pathways. Finally, cells with abundant PrPC expression seemed to be more susceptible to Aβ1–42 oligomer toxicity, suggesting the importance of the level of PrPC expression in the induction of apoptosis.