Creatine Promotes Endometriosis by Inducing Ferroptosis Resistance via Suppression of PrP.

Endometriosis, a chronic inflammatory disease, significantly impairs the quality of life of women in their reproductive years; however, its pathogenesis remains poorly understood. The accumulation of retrograde menstruation and recurrent bleeding fosters a high-iron environment in ectopic lesions, triggering ferroptosis in ectopic endometrial stromal cells (EESCs), thereby hindering the establishment of endometriosis. However, abnormal EESCs demonstrate resistance to ferroptosis in high-iron environments, promoting the progression of this disease. Here, novel findings on the accumulation of creatine, derived from endogenous synthesis, in both peritoneal fluid and EESCs of patients with endometriosis are presented. Creatine supplementation reduces cellular iron concentrations, mitigating oxidative stress and lipid peroxidation, thereby enhancing cell viability and preventing ferroptosis under high-iron conditions. Utilizing the drug affinity-responsive target stabilization (DARTS) assay, prion protein (PrP) as a potential creatine-sensing protein is identified. Mechanistically, creatine binds to the active site of PrP, inhibits the conversion of trivalent iron to divalent iron, and decreases iron uptake, promoting the tolerance of EESCs to ferroptosis. This interaction contributes to the development of endometriosis. The novel association between creatine and ferroptosis provides valuable insights into the role of creatine in endometriosis progression and highlights its potential as a therapeutic target for endometriosis.

Peptide aptamer targeting Aß-PrP-Fyn axis reduces Alzheimer's disease pathologies in 5XFAD transgenic mouse model.

Currently, no effective therapeutics exist for the treatment of incurable neurodegenerative diseases such as Alzheimer's disease (AD). The cellular prion protein (PrPC) acts as a high-affinity receptor for amyloid beta oligomers (AßO), a main neurotoxic species mediating AD pathology. The interaction of AßO with PrPC subsequently activates Fyn tyrosine kinase and neuroinflammation. Herein, we used our previously developed peptide aptamer 8 (PA8) binding to PrPC as a therapeutic to target the AßO-PrP-Fyn axis and prevent its associated pathologies. Our in vitro results indicated that PA8 prevents the binding of AßO with PrPC and reduces AßO-induced neurotoxicity in mouse neuroblastoma N2a cells and primary hippocampal neurons. Next, we performed in vivo experiments using the transgenic 5XFAD mouse model of AD. The 5XFAD mice were treated with PA8 and its scaffold protein thioredoxin A (Trx) at a 14.4 µg/day dosage for 12 weeks by intraventricular infusion through Alzet® osmotic pumps. We observed that treatment with PA8 improves learning and memory functions of 5XFAD mice as compared to Trx-treated 5XFAD mice. We found that PA8 treatment significantly reduces AßO levels and Aß plaques in the brain tissue of 5XFAD mice. Interestingly, PA8 significantly reduces AßO-PrP interaction and its downstream signaling such as phosphorylation of Fyn kinase, reactive gliosis as well as apoptotic neurodegeneration in the 5XFAD mice compared to Trx-treated 5XFAD mice. Collectively, our results demonstrate that treatment with PA8 targeting the AßO-PrP-Fyn axis is a promising and novel approach to prevent and treat AD.

In Vitro Characterization of Protein:Nucleic Acid Liquid-Liquid Phase Separation by Microscopy Methods and Nanoparticle Tracking Analysis.

Uncontrolled assembly/disassembly of physiologically formed liquid condensates is linked to irreversible aggregation. Hence, the quest for understanding protein-misfolding disease mechanism might lie in the studies of protein:nucleic acid coacervation. Several proteins with intrinsically disordered regions as well as nucleic acids undergo phase separation in the cellular context, and this process is key to physiological signaling and is related to pathologies. Phase separation is reproducible in vitro by mixing the target recombinant protein with specific nucleic acids at various stoichiometric ratios and then examined by microscopy and nanotracking methods presented herein. We describe protocols to qualitatively assess hallmarks of protein-rich condensates, characterize their structure using intrinsic and extrinsic dyes, quantify them, and analyze their morphology over time. Analysis by nanoparticle tracking provides information on the concentration and diameter of high-order protein oligomers formed in the presence of nucleic acid. Using the model protein (globular domain of recombinant murine PrP) and DNA aptamers (high-affinity oligonucleotides with 25 nucleotides in length), we provide examples of a systematic screening of liquid-liquid phase separation in vitro.

Protein-lipid interactions and protein anchoring modulate the modes of association of the globular domain of the Prion protein and Doppel protein to model membrane patches.

The Prion protein is the molecular hallmark of the incurable prion diseases affecting mammals, including humans. The protein-only hypothesis states that the misfolding, accumulation, and deposition of the Prion protein play a critical role in toxicity. The cellular Prion protein (PrPC) anchors to the extracellular leaflet of the plasma membrane and prefers cholesterol- and sphingomyelin-rich membrane domains. Conformational Prion protein conversion into the pathological isoform happens on the cell surface. In vitro and in vivo experiments indicate that Prion protein misfolding, aggregation, and toxicity are sensitive to the lipid composition of plasma membranes and vesicles. A picture of the underlying biophysical driving forces that explain the effect of Prion protein - lipid interactions in physiological conditions is needed to develop a structural model of Prion protein conformational conversion. To this end, we use molecular dynamics simulations that mimic the interactions between the globular domain of PrPC anchored to model membrane patches. In addition, we also simulate the Doppel protein anchored to such membrane patches. The Doppel protein is the closest in the phylogenetic tree to PrPC, localizes in an extracellular milieu similar to that of PrPC, and exhibits a similar topology to PrPC even if the amino acid sequence is only 25% identical. Our simulations show that specific protein-lipid interactions and conformational constraints imposed by GPI anchoring together favor specific binding sites in globular PrPC but not in Doppel. Interestingly, the binding sites we found in PrPC correspond to prion protein loops, which are critical in aggregation and prion disease transmission barrier (ß2-α2 loop) and in initial spontaneous misfolding (α2-α3 loop). We also found that the membrane re-arranges locally to accommodate protein residues inserted in the membrane surface as a response to protein binding.

Following the Aggregation of Human Prion Protein on Heparin Functionalized Gold Surface in Real Time.

The aggregation of the prion protein (PrP) plays a key role in the development of prion diseases and is believed to be an autocatalytic process with a very high kinetic barrier. Intensive studies have focused on overcoming the kinetic barriers under extremely nonphysiological in vitro conditions by altering the pH of PrP solution on solid surfaces, such as gold, mica, and a lipid bilayer. Importantly, sulfated glycosaminoglycans (GAGs), including heparin, were found to be associated with PrP misfolding and aggregation, suggesting GAGs have catalytic roles in PrP aggregation processes. However, the exact role and details of GAGs in the PrP aggregation are not clear and need a thorough perusal. Here, we investigate the PrP aggregation process on a heparin functionalized gold surface by in situ, real-time monitoring of the atomic scale details of the whole aggregation process by single molecule atomic force microscopy (AFM), combining simultaneous topographic and recognition (TREC) imaging and single molecule force spectroscopy (SMFS). We observed the whole aggregation process for full-length human recombinant PrP (23-231) aggregation on the heparin modified gold surface, from the formation of oligomers, to the assembly of protofibrils and short fibers, and the formation of elongated mature fibers. Heparin is found to promote the PrP aggregation by facilitating the formation of oligomers during the early nucleation stage.

Amyloid precursor protein (APP) and amyloid ß (Aß) interact with cell adhesion molecules: Implications in Alzheimer's disease and normal physiology.

Alzheimer's disease (AD) is an incurable neurodegenerative disorder in which dysfunction and loss of synapses and neurons lead to cognitive impairment and death. Accumulation and aggregation of neurotoxic amyloid-ß (Aß) peptides generated via amyloidogenic processing of amyloid precursor protein (APP) is considered to play a central role in the disease etiology. APP interacts with cell adhesion molecules, which influence the normal physiological functions of APP, its amyloidogenic and non-amyloidogenic processing, and formation of Aß aggregates. These cell surface glycoproteins also mediate attachment of Aß to the neuronal cell surface and induce intracellular signaling contributing to Aß toxicity. In this review, we discuss the current knowledge surrounding the interactions of cell adhesion molecules with APP and Aß and analyze the evidence of the critical role these proteins play in regulating the processing and physiological function of APP as well as Aß toxicity. This is a necessary piece of the complex AD puzzle, which we should understand in order to develop safe and effective therapeutic interventions for AD.

Functional genomics screen identifies proteostasis targets that modulate prion protein (PrP) stability.

Prion protein (PrP) adopts either a helical conformation (PrPC) or an alternative, beta sheet-rich, misfolded conformation (PrPSc). The PrPSc form has the ability to "infect" PrPC and force it into the misfolded state. Accumulation of PrPSc is associated with a number of lethal neurodegenerative disorders, including Creutzfeldt-Jacob disease (CJD). Knockout of PrPC protects cells and animals from PrPSc infection; thus, there is interest in identifying factors that regulate PrPC stability, with the therapeutic goal of reducing PrPC levels and limiting infection by PrPSc. Here, we assembled a short-hairpin RNA (shRNA) library composed of 25+ shRNA sequences for each of 133 protein homeostasis (aka proteostasis) factors, such as molecular chaperones and co-chaperones. This Proteostasis shRNA Library was used to identify regulators of PrPC stability in HEK293 Hu129M cells. Strikingly, the screen identified a number of Hsp70 family members and their co-chaperones as putative targets. Indeed, a chemical pan-inhibitor of Hsp70s reduced PrPC levels and limited conversion to PrPSc in N2a cells. These results implicate specific proteostasis sub-networks, especially the Hsp70 system, as potential new targets for the treatment of CJD. More broadly, the Proteostasis shRNA Library might be a useful tool for asking which proteostasis factors are important for a given protein.

2,3,5,6-Tetramethylpyrazine protects retinal photoreceptors against endoplasmic reticulum stress by modulating ATF4-mediated inhibition of PRP aggregation.

Endoplasmic reticulum (ER) stress is a common threat to photoreceptors during the pathogenesis of chronic retinopathies and often results in irreversible visual impairment. 2,3,5,6-Tetramethylpyrazine (TMP), which possesses many beneficial pharmacological activities, is a potential drug that could be used to protect photoreceptors. In the present study, we found that the cellular growth rate of 661 W cells cultured under low glucose conditions was lower than that of control cells, while the G2/M phase of the cell cycle was longer. We further found that the mitochondrial membrane potential (ΔΨm) was lower and that ER stress factor expression was increased in 661 W cells cultured under low glucose conditions. TMP reversed these trends. Visual function and cell counts in the outer nuclear layer (ONL) were low and the TUNEL-positive rate in the ONL was high in a C3H mouse model of spontaneous retinal degeneration. Similarly, visual function was decreased, and the TUNEL-positive rate in the ONL was increased in fasted C57/BL6j mice compared with control mice. On the other hand, ER stress factor expression was found to be increased in the retinas of both mouse models, as shown by reverse transcription real-time PCR (RT-qPCR) and western blotting. TMP reversed the physiological and molecular biological variations observed in both mouse models, and ATF4 expression was enhanced again. Further investigation by using western blotting illustrated that the proportion of insoluble prion protein (PRP) versus soluble PRP was reduced both in vitro and in vivo. Taken together, these results suggest that TMP increased the functions of photoreceptors by alleviating ER stress in vitro and in vivo, and the intrinsic mechanism was the ATF4-mediated inhibition of PRP aggregation. TMP may potentially be used clinically as a therapeutic agent to attenuate the functional loss of photoreceptors during the pathogenesis of chronic retinopathies. KEY MESSAGES: • Already known: TMP is a beneficial drug mainly used in clinic to enhance organ functions, and the intrinsic mechanism is still worthy of exploring. • New in the study: We discovered that TMP ameliorated retinal photoreceptors function via ER stress alleviation, which was promoted by ATF4-mediated inhibition of PRP aggregation. • Application prospect: In prospective clinical practices, TMP may potentially be used in the clinic as a therapeutic agent to attenuate the photoreceptors functional reduction in chronic retinopathies.

Evidence for aggregation-independent, PrPC-mediated Aß cellular internalization.

Evidence linking amyloid beta (Aß) cellular uptake and toxicity has burgeoned, and mechanisms underlying this association are subjects of active research. Two major, interconnected questions are whether Aß uptake is aggregation-dependent and whether it is sequence-specific. We recently reported that the neuronal uptake of Aß depends significantly on peptide chirality, suggesting that the process is predominantly receptor-mediated. Over the past decade, the cellular prion protein (PrPC) has emerged as an important mediator of Aß-induced toxicity and of neuronal Aß internalization. Here, we report that the soluble, nonfibrillizing Aß (1-30) peptide recapitulates full-length Aß stereoselective cellular uptake, allowing us to decouple aggregation from cellular, receptor-mediated internalization. Moreover, we found that Aß (1-30) uptake is also dependent on PrPC expression. NMR-based molecular-level characterization identified the docking site on PrPC that underlies the stereoselective binding of Aß (1-30). Our findings therefore identify a specific sequence within Aß that is responsible for the recognition of the peptide by PrPC, as well as PrPC-dependent cellular uptake. Further uptake stereodifferentiation in PrPC-free cells points toward additional receptor-mediated interactions as likely contributors for Aß cellular internalization. Taken together, our results highlight the potential of targeting cellular surface receptors to inhibit Aß cellular uptake as an alternative route for future therapeutic development for Alzheimer's disease.

Characterization of brain-derived extracellular vesicles reveals changes in cellular origin after stroke and enrichment of the prion protein with a potential role in cellular uptake.

Extracellular vesicles (EVs) are important means of intercellular communication and a potent tool for regenerative therapy. In ischaemic stroke, transient blockage of a brain artery leads to a lack of glucose and oxygen in the affected brain tissue, provoking neuronal death by necrosis in the core of the ischaemic region. The fate of neurons in the surrounding penumbra region depends on the stimuli, including EVs, received during the following hours. A detailed characterization of such stimuli is crucial not only for understanding stroke pathophysiology but also for new therapeutic interventions. In the present study, we characterize the EVs in mouse brain under physiological conditions and 24 h after induction of transient ischaemia in mice. We show that, in steady-state conditions, microglia are the main source of small EVs (sEVs), whereas after ischaemia the main sEV population originates from astrocytes. Brain sEVs presented high amounts of the prion protein (PrP), which were further increased after stroke. Moreover, EVs were enriched in a proteolytically truncated PrP fragment (PrP-C1). Because of similarities between PrP-C1 and certain viral surface proteins, we studied the cellular uptake of brain-derived sEVs from mice lacking (PrP-KO) or expressing PrP (WT). We show that PrP-KO-sEVs are taken up significantly faster and more efficiently than WT-EVs by primary neurons. Furthermore, microglia and astrocytes engulf PrP-KO-sEVs more readily than WT-sEVs. Our results provide novel information on the relative contribution of brain cell types to the sEV pool in murine brain and indicate that increased release of sEVs by astrocytes together with elevated levels of PrP in sEVs may play a role in intercellular communication at early stages after stroke. In addition, amounts of PrP (and probably PrP-C1) in brain sEVs seem to contribute to regulating their cellular uptake.

Case Report: Histopathology and Prion Protein Molecular Properties in Inherited Prion Disease With a De Novo Seven-Octapeptide Repeat Insertion.

The insertion of additional 168 base pair containing seven octapeptide repeats in the prion protein (PrP) gene region spanning residues 51-91 is associated with inherited prion disease. In 2008, we reported the clinical features of a novel de novo seven-octapeptide repeat insertion (7-OPRI) mutation coupled with codon 129 methionine (M) homozygosity in the PrP gene of a 19-year-old man presenting with psychosis and atypical dementia, and 16-year survival. Here, we describe the histopathological and PrP molecular properties in the autopsied brain of this patient. Histopathological examination revealed widespread brain atrophy, focal spongiform degeneration (SD), cortical PrP plaques, and elongated PrP formations in the cerebellum. Overall, these histopathological features resemble those described in a Belgian pedigree with 7-OPRI mutation except for the presence of PrP plaques in our case, which are morphologically different from the multicore plaques described in some OPRI mutations and in Gerstmann-Sträussler-Scheinker (GSS) syndrome. The comparative characterization of the detergent-soluble and detergent-insoluble PrP in our patient and in sporadic Creutzfeldt-Jakob disease (CJD) revealed distinct molecular signatures. Proteinase K digestion of the pathogenic, disease-associated PrP (PrPD) revealed PrPD type 1 in the cerebral cortex and mixed PrPD types 1 and 2 in the cerebellum. Altogether, the present study outlines the importance of assessing the phenotypical and PrP biochemical properties of these rare conditions, thereby widening the spectrum of the phenotypic heterogeneity of the 7-OPRI insertion mutations. Further studies are needed to determine whether distinct conformers of PrPD are associated with two major clinico-histopathological phenotypes in prion disease with 7-OPRI.

Understanding Creutzfeldt-Jackob disease from a viewpoint of amyloidogenic evolvability.

Creutzfeldt-Jackob disease (CJD), the most common human prion disorder, is frequently accompanied by ageing-associated neurodegenerative conditions, such as Alzheimer's disease and Parkinson's disease. Although cross-seeding of amyloidogenic proteins (APs), including amyloid ß and α-synuclein, may be critical in the co-morbidity of neurodegenerative disorders, the direct interaction of APs with prion protein (PrP), the central molecule involved in the pathogenesis of CJD, is unlikely. Currently, the nature of this biological interaction and its significance remain obscure. In this context, the objective of the present study is to discuss such interactions from the perspective of amyloidogenic evolvability, a putative function of APs. Hypothetically, both hereditary- and sporadic CJD might be attributed to the role of PrP in evolvability against multiple stressors, such as physical stresses relevant to concussions, which might be manifest through the antagonistic pleiotropy mechanism in ageing. Furthermore, accumulating evidence suggests that PrP- and other APs evolvability may negatively regulate each other. Provided that increased APs evolvability might be beneficial for acquired CJD in young adults, a dose-reduction of α-synuclein, a natural inhibitor of αS aggregation, might be therapeutically effective in upregulating APs evolvability. Collectively, a better understanding of amyloidogenic evolvability may lead to the development of novel therapies for CJD.

Prion protein-Semisynthetic prion protein (PrP) variants with posttranslational modifications.

Deciphering the pathophysiologic events in prion diseases is challenging, and the role of posttranslational modifications (PTMs) such as glypidation and glycosylation remains elusive due to the lack of homogeneous protein preparations. So far, experimental studies have been limited in directly analyzing the earliest events of the conformational change of cellular prion protein (PrPC ) into scrapie prion protein (PrPSc ) that further propagates PrPC misfolding and aggregation at the cellular membrane, the initial site of prion infection, and PrP misfolding, by a lack of suitably modified PrP variants. PTMs of PrP, especially attachment of the glycosylphosphatidylinositol (GPI) anchor, have been shown to be crucially involved in the PrPSc formation. To this end, semisynthesis offers a unique possibility to understand PrP behavior invitro and invivo as it provides access to defined site-selectively modified PrP variants. This approach relies on the production and chemoselective linkage of peptide segments, amenable to chemical modifications, with recombinantly produced protein segments. In this article, advances in understanding PrP conversion using semisynthesis as a tool to obtain homogeneous posttranslationally modified PrP will be discussed.

Combustion- and friction-derived magnetic air pollution nanoparticles in human hearts.

Air pollution is a risk factor for cardiovascular and Alzheimer's disease (AD). Iron-rich, strongly magnetic, combustion- and friction-derived nanoparticles (CFDNPs) are abundant in particulate air pollution. Metropolitan Mexico City (MMC) young residents have abundant brain CFDNPs associated with AD pathology. We aimed to identify if magnetic CFDNPs are present in urbanites' hearts and associated with cell damage. We used magnetic analysis and transmission electron microscopy (TEM) to identify heart CFDNPs and measured oxidative stress (cellular prion protein, PrPC), and endoplasmic reticulum (ER) stress (glucose regulated protein, GRP78) in 72 subjects age 23.8 ±â€¯9.4y: 63 MMC residents, with Alzheimer Continuum vs 9 controls. Magnetite/maghemite nanoparticles displaying the typical rounded crystal morphologies and fused surface textures of CFDNPs were more abundant in MMC residents' hearts. NPs, ∼2-10 × more abundant in exposed vs controls, were present inside mitochondria in ventricular cardiomyocytes, in ER, at mitochondria-ER contact sites (MERCs), intercalated disks, endothelial and mast cells. Erythrocytes were identified transferring 'hitchhiking' NPs to activated endothelium. Magnetic CFDNP concentrations and particle numbers ranged from 0.2 to 1.7 µg/g and ∼2 to 22 × 109/g, respectively. Co-occurring with cardiomyocyte NPs were abnormal mitochondria and MERCs, dilated ER, and lipofuscin. MMC residents had strong left ventricular PrPC and bi-ventricular GRP78 up-regulation. The health impact of up to ∼22 billion magnetic NPs/g of ventricular tissue are likely reflecting the combination of surface charge, ferrimagnetism, and redox activity, and includes their potential for disruption of the heart's electrical impulse pathways, hyperthermia and alignment and/or rotation in response to magnetic fields. Exposure to solid NPs appears to be directly associated with early and significant cardiac damage. Identification of strongly magnetic CFDNPs in the hearts of children and young adults provides an important novel layer of information for understanding CVD pathogenesis emphasizing the urgent need for prioritization of particulate air pollution control.

Prion Protein Protects Cancer Cells against Endoplasmic Reticulum Stress Induced Apoptosis.

Unfolded protein response (UPR) is an adaptive reaction for cells to reduce endoplasmic reticulum (ER) stress. In many types of cancers, such as lung cancer and pancreatic cancer, cancer cells may harness ER stress to facilitate their survival and growth. Prion protein (PrP) is a glycosylated cell surface protein that has been shown to be up-regulated in many cancer cells. Since PrP is a protein prone to misfolding, ER stress can result in under-glycosylated PrP, which in turn may activate ER stress. To assess whether ER stress leads to the production of under-glycosylated PrP and whether under-glycosylated PrP may contribute to ER stress thus leading to cancer cell apoptosis, we treated different cancer cells with brefeldin A (BFA), thapsigargin (Thps), and tunicamycin (TM). We found that although BFA, Thps, and TM treatment activated UPR, only ATF4 was consistently activated by these reagents, but not other branches of ER stress. However, the canonical PERK-eIF2α-ATF4 did not account for the observed activation of ATF4 in lung cancer cells. In addition, BFA, but neither Thps nor TM, significantly stimulated the expression of cytosolic PrP. Finally, we found that the levels of PrP contributed to anti-apoptosis activity of BFA-induced cancer cell death. Thus, the pathway of BFA-induced persistent ER stress may be targeted for lung and pancreatic cancer treatment.

Detection of tau in Gerstmann-Sträussler-Scheinker disease (PRNP F198S) by [18F]Flortaucipir PET.

This study aimed to determine the pattern of [18F]flortaucipir uptake in individuals affected by Gerstmann-Sträussler-Scheinker disease (GSS) associated with the PRNP F198S mutation. The aims were to: 1) determine the pattern of [18F]flortaucipir uptake in two GSS patients; 2) compare tau distribution by [18F]flortaucipir PET imaging among three groups: two GSS patients, two early onset Alzheimer's disease patients (EOAD), two cognitively normal older adults (CN); 3) validate the PET imaging by comparing the pattern of [18F]flortaucipir uptake, in vivo, with that of tau neuropathology, post-mortem. Scans were processed to generate standardized uptake value ratio (SUVR) images. Regional [18F]flortaucipir SUVR was extracted and compared between GSS patients, EOADs, and CNs. Neuropathology and tau immunohistochemistry were carried out post-mortem on a GSS patient who died 9 months after the [18F]flortaucipir scan. The GSS patients were at different stages of disease progression. Patient A was mildly to moderately affected, suffering from cognitive, psychiatric, and ataxia symptoms. Patient B was moderately to severely affected, suffering from ataxia and parkinsonism accompanied by psychiatric and cognitive symptoms. The [18F]flortaucipir scans showed uptake in frontal, cingulate, and insular cortices, as well as in the striatum and thalamus. Uptake was greater in Patient B than in Patient A. Both GSS patients showed greater uptake in the striatum and thalamus than the EOADs and greater uptake in all evaluated regions than the CNs. Thioflavin S fluorescence and immunohistochemistry revealed that the anatomical distribution of tau pathology is consistent with that of [18F]flortaucipir uptake. In GSS patients, the neuroanatomical localization of pathologic tau, as detected by [18F]flortaucipir, suggests correlation with the psychiatric, motor, and cognitive symptoms. The topography of uptake in PRNP F198S GSS is strikingly different from that seen in AD. Further studies of the sensitivity, specificity, and anatomical patterns of tau PET in diseases with tau pathology are warranted.

Monitoring of early diagnosis of Alzheimer's disease using the cellular prion protein and poly(pyrrole-2-carboxylic acid) modified electrode.

Amyloid-beta oligomers (AßΟ) are considered to be reliable biomarkers for the diagnosis of Alzheimer' disease (AD), and the cellular prion protein (PrPC) is identified as a receptor for AßO. We demonstrated a label and antibody-free electrochemical biosensor for the selective detection of AßO using an electrically conductive poly(pyrrole-2-carboxylic acid) (PPyCOOH) linking agent and PrPC receptor. In the fabrication of the biosensor, each step was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The developed PrPc/PPyCOOH biosensor exhibited extremely low detection limit of 10-4 pM with high sensitivity which is desirable for the early diagnosis of AD. The sensing performance was further confirmed by the mice infected with AD. The proposed sensor emerged as a promising tool for the early detection of AßO.

Interaction of Peptide Aptamers with Prion Protein Central Domain Promotes α-Cleavage of PrPC.

Prion diseases are infectious and fatal neurodegenerative diseases affecting humans and animals. Transmission is possible within and between species with zoonotic potential. Currently, no prophylaxis or treatment exists. Prions are composed of the misfolded isoform PrPSc of the cellular prion protein PrPC. Expression of PrPC is a prerequisite for prion infection, and conformational conversion of PrPC is induced upon its direct interaction with PrPSc. Inhibition of this interaction can abrogate prion propagation, and we have previously established peptide aptamers (PAs) binding to PrPC as new anti-prion compounds. Here, we mapped the interaction site of PA8 in PrP and modeled the complex in silico to design targeted mutations in PA8 which presumably enhance binding properties. Using these PA8 variants, we could improve PA-mediated inhibition of PrPSc replication and de novo infection of neuronal cells. Furthermore, we demonstrate that binding of PA8 and its variants increases PrPC α-cleavage and interferes with its internalization. This gives rise to high levels of the membrane-anchored PrP-C1 fragment, a transdominant negative inhibitor of prion replication. PA8 and its variants interact with PrPC at its central and most highly conserved domain, a region which is crucial for prion conversion and facilitates toxic signaling of Aß oligomers characteristic for Alzheimer's disease. Our strategy allows for the first time to induce α-cleavage, which occurs within this central domain, independent of targeting the responsible protease. Therefore, interaction of PAs with PrPC and enhancement of α-cleavage represent mechanisms that can be beneficial for the treatment of prion and other neurodegenerative diseases.

Hepatitis C virus-induced prion protein expression facilitates hepatitis C virus replication.

Hepatitis C virus (HCV) infects approximately 180 million people worldwide. Significant progress has been made since the establishment of in vitro HCV infection models in cells. However, the replication of HCV is complex and not completely understood. Here, we found that the expression of host prion protein (PrP) was induced in an HCV replication cell model. We then showed that increased PrP expression facilitated HCV genomic replication. Finally, we demonstrated that the KKRPK motif on the N-terminus of PrP bound nucleic acids and facilitated HCV genomic replication. Our results provided important insights into how viruses may harness cellular protein to achieve propagation.

Neurotoxicity of Prion Peptides on Cultured Cerebellar Neurons.

Prion neurotoxicity has been modeled in vitro using synthetic peptides derived from the PrPC sequence. The major region of neurotoxicity has been localized to the hydrophobic domain located in the middle of the PrP protein. Neurotoxicity assays are typically performed on cultured mouse cerebellar neurons derived from neonatal pups, and cell viability can be monitored by assays including MTT or MTS, cell death by LDH release, or apoptosis by caspase cleavage assays. These neurotoxicity studies have been useful in identifying cofactors, such as PrPC and metals, as modulators of PrP peptide-mediated neurotoxicity. Given the biosafety issues associated with handling and purifying infectious prions, the use of synthetic peptides, which display a dependence upon PrPC expression for toxicity, as per the PrPSc agent for infectivity, supports the relevance of using these synthetic peptides for understanding PrP-mediated neurotoxicity.