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The effect of a cellular prion protein (PrP c ) deficiency on neuroenergetics was primarily analyzed via surveying the expression of genes specifically involved in lactate/pyruvate metabolism, such as monocarboxylate transporters ( MCT1 , MCT2 , MCT4 ). The aim of the present study was to elucidate a potential involvement of PrP c in the regulation of energy metabolism in different brain regions. By using quantitative real-time polymerase chain reaction (qRT-PCR), we observed a marked reduction in MCT1 mRNA expression in the cortex of symptomatic Zürich I Prnp -/- mice, as compared to their wild-type (WT) counterparts. MCT1 downregulation in the cortex was accompanied with significantly decreased expression of the MCT1 functional interplayer, the Na + /K + ATPase α2 subunit. Conversely, the MCT1 mRNA level was significantly raised in the cerebellum of Prnp -/- vs. WT control group, without a substantial change in the Na + /K + ATPase α2 subunit expression. To validate the observed mRNA findings, we confirmed the observed change in MCT1 mRNA expression level in the cortex at the protein level. MCT4, highly expressed in tissues that rely on glycolysis as an energy source, exhibited a significant reduction in the hippocampus of Prnp -/- vs. WT mice. The present study demonstrates that a lack of PrP c leads to altered MCT1 and MCT4 mRNA/protein expression in different brain regions of Prnp -/- vs. WT mice. Our findings provide evidence that PrP c might affect the monocarboxylate intercellular transport, which needs to be confirmed in further studies.

Disrupted sleep is a major feature of Alzheimer's disease (AD), often arising years before symptoms of cognitive decline. Prolonged wakefulness exacerbates the production of amyloid-beta (Aβ) species, a major driver of AD progression, suggesting that sleep loss further accelerates AD through a vicious cycle. However, the mechanisms by which Aβ affects sleep are unknown. We demonstrate in zebrafish that Aβ acutely and reversibly enhances or suppresses sleep as a function of oligomer length. Genetic disruptions revealed that short Aβ oligomers induce acute wakefulness through Adrenergic receptor b2 (Adrb2) and Progesterone membrane receptor component 1 (Pgrmc1), while longer Aβ forms induce sleep through a pharmacologically tractable Prion Protein (PrP) signaling cascade. Our data indicate that Aβ can trigger a bi-directional sleep/wake switch. Alterations to the brain's Aβ oligomeric milieu, such as during the progression of AD, may therefore disrupt sleep via changes in acute signaling events., Competing Interests: GÖ, SL, PL, WA, JR No competing interests declared, (© 2020, Özcan et al.)

Prions are highly resistant to the decontamination procedures normally used to inactivate conventional pathogens. This is a challenging problem not only in the medical and veterinary fields for minimizing the risk of transmission from potentially infective sources but also for ensuring the safe disposal or subsequent use of animal by-products. Specific pressure autoclaving protocols were developed for this purpose, but different strains of prions have been reported to have differing resistance patterns to established prion decontamination procedures, and as additional TSE strains are identified it is necessary to determine the effectiveness of such procedures. In this study we assessed the efficacy of sterilization using the EU recommended autoclave procedure for prions (133°C, 3 Bar for 20 min) on the atypical or Nor98 (AS/Nor98) scrapie strain of sheep and goats. Using a highly sensitive murine mouse model (tg338) that overexpresses ovine PrP C , we determined that this method of decontamination reduced the infectivity titre by 10 10 . Infectivity was nonetheless still detected after applying the recommended autoclaving protocol. This shows that AS/Nor98 can survive the designated legislative decontamination conditions, albeit with a significant decrease in titre. The infectivity of a classical scrapie isolate subjected to the same decontamination conditions was reduced by 10 6 suggesting that the AS/Nor98 isolate is less sensitive to decontamination than the classical scrapie source., (© 2019 Blackwell Verlag GmbH.)

The protein-only hypothesis predicts that infectious mammalian prions are composed solely of PrPSc, a misfolded conformer of the normal prion protein, PrPC. However, protein-only PrPSc preparations lack significant levels of prion infectivity, leading to the alternative hypothesis that cofactor molecules are required to form infectious prions. Here, we show that prions with parental strain properties and full specific infectivity can be restored from protein-only PrPSc in vitro. The restoration reaction is rapid, potent, and requires bank vole PrPC substrate, post-translational modifications, and cofactor molecules. To our knowledge, this represents the first report in which the essential properties of an infectious mammalian prion have been restored from pure PrP without adaptation. These findings provide evidence for a unified hypothesis of prion infectivity in which the global structure of protein-only PrPSc accurately stores latent infectious and strain information, but cofactor molecules control a reversible switch that unmasks biological infectivity., Competing Interests: The authors have declared that no competing interests exist.

Prion diseases are rapidly progressive, incurable neurodegenerative disorders caused by misfolded, aggregated proteins known as prions, which are uniquely infectious. Remarkably, these infectious proteins have been responsible for widespread disease epidemics, including kuru in humans, bovine spongiform encephalopathy in cattle, and chronic wasting disease in cervids, the latter of which has spread across North America and recently appeared in Norway and Finland. The hallmark histopathological features include widespread spongiform encephalopathy, neuronal loss, gliosis, and deposits of variably sized aggregated prion protein, ranging from small, soluble oligomers to long, thin, unbranched fibrils, depending on the disease. Here, we explore recent advances in prion disease research, from the function of the cellular prion protein to the dysfunction triggering neurotoxicity, as well as mechanisms underlying prion spread between cells. We also highlight key findings that have revealed new therapeutic targets and consider unanswered questions for future research.

Mammalian prions propagate by template-directed misfolding and aggregation of normal cellular prion related protein PrPC as it converts into disease-associated conformers collectively referred to as PrPSc. Mammalian species may be permissive for prion disease because these hosts have co-evolved specific co-factors that assist PrPC conformational change and prion propagation. We have tested this hypothesis by examining whether faithful prion propagation occurs in the normally PrPC-null invertebrate host Drosophila melanogaster. Ovine PrP transgenic Drosophila exposed at the larval stage to ovine scrapie showed a progressive accumulation of transmissible prions in adult flies. Strikingly, the biological properties of distinct ovine prion strains were maintained during their propagation in Drosophila. Our observations show that the co-factors necessary for strain-specific prion propagation are not unique to mammalian species. Our studies establish Drosophila as a novel host for the study of transmissible mammalian prions.

Prion diseases include a number of progressive neuropathies involving conformational changes in cellular prion protein (PrPc) that may be fatal sporadic, familial or infectious. Pathological evidence indicated that neurons affected in prion diseases follow a dying-back pattern of degeneration. However, specific cellular processes affected by PrPc that explain such a pattern have not yet been identified. Results from cell biological and pharmacological experiments in isolated squid axoplasm and primary cultured neurons reveal inhibition of fast axonal transport (FAT) as a novel toxic effect elicited by PrPc. Pharmacological, biochemical and cell biological experiments further indicate this toxic effect involves casein kinase 2 (CK2) activation, providing a molecular basis for the toxic effect of PrPc on FAT. CK2 was found to phosphorylate and inhibit light chain subunits of the major motor protein conventional kinesin. Collectively, these findings suggest CK2 as a novel therapeutic target to prevent the gradual loss of neuronal connectivity that characterizes prion diseases.

The cellular prion protein (PrP C ) whose conformational misfolding leads to the production of deadly prions, has a still-unclarified cellular function despite decades of intensive research. Following our recent finding that PrP C limits Ca 2+ entry via store-operated Ca 2+ channels in neurons, we investigated whether the protein could also control the activity of ionotropic glutamate receptors (iGluRs). To this end, we compared local Ca 2+ movements in primary cerebellar granule neurons and cortical neurons transduced with genetically encoded Ca 2+ probes and expressing, or not expressing, PrP C Our investigation demonstrated that PrP C downregulates Ca 2+ entry through each specific agonist-stimulated iGluR and after stimulation by glutamate. We found that, although PrP-knockout (KO) mitochondria were displaced from the plasma membrane, glutamate addition resulted in a higher mitochondrial Ca 2+ uptake in PrP-KO neurons than in their PrP C -expressing counterpart. This was because the increased Ca 2+ entry through iGluRs in PrP-KO neurons led to a parallel increase in Ca 2+ -induced Ca 2+ release via ryanodine receptor channels. These data thus suggest that PrP C takes part in the cell apparatus controlling Ca 2+ homeostasis, and that PrP C is involved in protecting neurons from toxic Ca 2+ overloads., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2017. Published by The Company of Biologists Ltd.)

We previously showed that baculovirus-derived recombinant prion protein (Bac-PrP) can be converted to the misfolded infectious form (PrP Sc ) by protein misfolding cyclic amplification, an in vitro conversion technique. Bac-PrP, with post-translational modifications, would be useful for various applications such as using PrP as an immunogen for generating anti-PrP antibody, developing anti-prion drugs or diagnostic assays using in vitro conversion systems, and establishing an in vitro prion propagation model. For this purpose, highly purified Bac-PrP with in vitro conversion activity is necessary for use as a PrP C source, to minimize contamination. Furthermore, an exogenous affinity tag-free form is desirable to avoid potential steric interference by the affinity tags during the conversion process. In this study, we established purification methods for the untagged Bac-PrP under native conditions by combining exogenous double-affinity tags, namely, a polyhistidine-tag and a profinity eXact tag, with an octarepeat sequence of the N-terminal region of PrP, which has metal ion-binding affinity. The untagged Bac-PrP with near-homogeneity was obtained by three-step affinity purification, and it was shown that the final, purified Bac-PrP could convert to its pathogenic form. The presented purification procedure could be applied not only to PrP but also to other eukaryotic, recombinant proteins that require high purity and intact physiological activity.

The cellular prion protein (PrPC) has been proposed to play an important role in the pathogenesis of Alzheimer's disease. In cellular models PrPC inhibited the action of the β-secretase BACE1 on wild type amyloid precursor protein resulting in a reduction in amyloid-β (Aβ) peptides. Here we have assessed the effect of genetic ablation of PrPC in transgenic mice expressing human wild type amyloid precursor protein (line I5). Deletion of PrPC had no effect on the α- and β-secretase proteolysis of the amyloid precursor protein (APP) nor on the amount of Aβ38, Aβ40 or Aβ42 in the brains of the mice. In addition, ablation of PrPC did not alter Aβ deposition or histopathology phenotype in this transgenic model. Thus using this transgenic model we could not provide evidence to support the hypothesis that PrPC regulates Aβ production.

Background & Aim: Despite extensive study of the contribution of cell death and apoptosis to radiation-induced acute intestinal injury, our knowledge of the signaling mechanisms involved in epithelial barrier dysfunction remains inadequate. Because PrP(c) plays a key role in intestinal homeostasis by renewing epithelia, we sought to study its role in epithelial barrier function after irradiation., Design: Histology, morphometry and plasma FD-4 levels were used to examine ileal architecture, wound healing, and intestinal leakage in PrP(c)-deficient (KO) and wild-type (WT) mice after total-body irradiation. Impairment of the PrP(c) Src pathway after irradiation was explored by immunofluorescence and confocal microscopy, with Caco-2/Tc7 cells. Lastly, dasatinib treatment was used to switch off the Src pathway in vitro and in vivo., Results: The decrease in radiation-induced lethality, improved intestinal wound healing, and reduced intestinal leakage promoted by PrP(c) deficiency demonstrate its involvement in acute intestinal damage. Irradiation of Cacao2/Tc7 cells induced PrP(c) to target the nuclei associated with Src activation. Finally, the protective effect triggered by dasatinib confirmed Src involvement in radiation-induced acute intestinal toxicity., Conclusion: Our data are the first to show a role for the PrP(c)-Src pathway in acute intestinal response to radiation injury and offer a novel therapeutic opportunity., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

The most significant pathological feature of Parkinson's disease (PD) is the progressive degeneration of dopaminergic (DA) neurons in the substantia nigra. Currently, available treatments for PD cannot prevent the loss of DA neurons. Tyrosine hydroxylase (TH) expressed in substantia nigra neurons catalyzes the conversion of tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA), which is the rate-limiting step of DA biosynthesis. Major reasons for PD occurrence include decreased TH activity in the substantia nigra and secondary DA suppression. Decreased TH activity and the resulting suppression of DA synthesis (or neurotransmission) in the substantia nigra are key factors underlying the development of PD. Cellular prion protein (PRP) is a membrane glycoprotein expressed in the central nervous system. Although the sequence of PRP is highly conserved, its physiological function is unclear. The purpose of this study was to investigate the effect of PRP-targeted small interfering RNA (siRNA) on TH expression in a rat model of PD. Thirty male Wistar rats were injected with 6-hydroxydopamine (6-OHDA) to generate a model of PD. The rats then received injections of PRP-siRNA or nonsense siRNA in the lateral ventricles. Substantia nigra samples were collected for quantification of PRP and TH expression using real-time polymerase chain reaction and western blotting. PRP-siRNA decreased PRP expression in the substantia nigra. TH expression was decreased in PD model rats but was increased after PRP silencing. We conclude that PRP-siRNA may increase TH expression in vivo and may therefore exert protective effects on neurons in a model of PD.

Prions are a self-templating amyloidogenic state of normal cellular proteins, such as prion protein (PrP). They have been identified as the pathogenic agents, contributing to a number of diseases of the nervous system. However, the discovery that the neuronal RNA-binding protein, cytoplasmic polyadenylation element-binding protein (CPEB), has a prion-like state that is involved in the stabilization of memory raised the possibility that prion-like proteins can serve normal physiological functions in the nervous system. Here, we review recent experimental evidence of prion-like properties of neuronal CPEB in various organisms and propose a model of how the prion-like state may stabilize memory., (Copyright © 2016 Cold Spring Harbor Laboratory Press; all rights reserved.)

Since its discovery the cellular prion protein (encoded by the Prnp gene) has been associated with a large number of functions. The proposed functions rank from basic cellular processes such as cell cycle and survival to neural functions such as behavior and neuroprotection, following a pattern similar to that of Moore's law for electronics. In addition, particular interest is increasing in the participation of Prnp in neurodegeneration. However, in recent years a redefinition of these functions has begun, since examples of previously attributed functions were increasingly re-associated with other proteins. Most of these functions are linked to so-called "Prnp-flanking genes" that are close to the genomic locus of Prnp and which are present in the genome of some Prnp mouse models. In addition, their role in neuroprotection against convulsive insults has been confirmed in recent studies. Lastly, in recent years a large number of models indicating the participation of different domains of the protein in apoptosis have been uncovered. However, after more than 10 years of molecular dissection our view is that the simplest mechanistic model in PrP(C)-mediated cell death should be considered, as Ockham's razor theory suggested.

The coalescence of proteins into highly ordered aggregates is a hallmark of protein misfolding disorders (PMDs), which, when affecting the central nervous system, lead to progressive neurodegeneration. Although the chemical identity and the topology of each culprit protein are unique, the principles governing aggregation and propagation are strikingly stereotypical. It is now clear that such protein aggregates can spread from cell to cell and eventually affect entire organ systems - similarly to prion diseases. However, because most aggregates are not found to transmit between individuals, they are not infectious sensu strictiori. Therefore, they are not identical to prions and we prefer to define them as 'prionoids'. Here we review recent advances in understanding the toxicity of protein aggregation affecting the brain., (Copyright © 2015 Elsevier Ltd. All rights reserved.)