Expression of prion protein in mouse erythroid progenitors and differentiating murine erythroleukemia cells

Simple 3D spheroid cell culture model for studies of prion infection

Mouse neuronal CAD 5 cell line effectively propagates various strains of prions. Previously, we have shown that it can also be differentiated into the cells morphologically resembling neurons. Here, we demonstrate that CAD 5 cells chronically infected with prions undergo differentiation under the same conditions. To make our model more realistic, we triggered the differentiation in the 3D culture created by gentle rocking of CAD 5 cell suspension. Spheroids formed within 1 week and were fully developed in less than 3 weeks of culture. The mature spheroids had a median size of ~300 μm and could be cultured for up to 12 weeks. Increased expression of differentiation markers GAP 43, tyrosine hydroxylase, β-III-tubulin and SNAP 25 supported the differentiated status of the spheroid cells. The majority of them were found in the G0/G1 phase of the cell cycle, which is typical for differentiated cells. Moreover, half of the PrPC on the cell membrane was N-terminally truncated, similarly as in differentiated CAD 5 adherent cells. Finally, we demonstrated that spheroids could be created from prion-infected CAD 5 cells. The presence of prions was verified by immunohistochemistry, western blot and seed amplification assay. We also confirmed that the spheroids can be infected with the prions de novo. Our 3D culture model of differentiated CAD 5 cells is low cost, easy to produce and cultivable for weeks. We foresee its possible use in the testing of anti-prion compounds and future studies of prion formation dynamics.

Erythrocyte Indices in Creutzfeldt-Jakob Disease Predict Survival Time

Background

Creutzfeldt–Jakob disease (CJD) is a devastating neurodegenerative disease caused by propagation of abnormally folded prion proteins (PrP^Sc). Some fluid biomarkers have been reported to be associated with disease duration in CJD. Based on studies which have found that prion protein (PrP^C) played a role in erythrocytic hematopoiesis, we evaluated the association between peripheral red blood cell indices and survival time in CJD.

Methods

We retrospectively collected data on peripheral red blood cell indices, including red blood cell (RBC) count, hemoglobin (Hb), hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and red cell distribution width (RDW), from 125 CJD patients. Cox proportional hazard models were generated to determine whether red cell indices correlated with survival time of patients with CJD.

Results

Of the 125 included participants, 70 (56%) were male, and the mean age at diagnosis (SD) was 60.3 (9.5) years. Hemoglobin levels (hazard ratio 1.710, 95% CI 1.124–2.600, p = 0.012) and HCT (hazard ratio 1.689, 95% CI 1.112–2.565, p=0.014) were significantly associated with survival time after controlling for sex, age, and Barthel Index. Red blood cell count, MCV, MCH, MCHC, and RDW were not associated with survival time before or after adjusting for covariates.

Conclusions

Our study found that Hb and HCT were significantly associated with survival time in patients with CJD. These results may inform evaluation of the mechanisms of interaction between prion disease and hematopoiesis, and indicate that Hb and HCT may be potential prognostic biomarkers.

Prion Strains Differ in Susceptibility to Photodynamic Oxidation

Prion disorders, or transmissible spongiform encephalophaties (TSE), are fatal neurodegenerative diseases affecting mammals. Prion-infectious particles comprise of misfolded pathological prion proteins (PrP^TSE). Different TSEs are associated with distinct PrP^TSE folds called prion strains. The high resistance of prions to conventional sterilization increases the risk of prion transmission in medical, veterinary and food industry practices. Recently, we have demonstrated the ability of disulfonated hydroxyaluminum phthalocyanine to photodynamically inactivate mouse RML prions by generated singlet oxygen. Herein, we studied the efficiency of three phthalocyanine derivatives in photodynamic treatment of seven mouse adapted prion strains originating from sheep, human, and cow species. We report the different susceptibilities of the strains to photodynamic oxidative elimination of PrP^TSE epitopes: RML, A139, Fu-1 > mBSE, mvCJD > ME7, 22L. The efficiency of the phthalocyanine derivatives in the epitope elimination also differed (AlPcOH(SO₃)₂ > ZnPc(SO₃)_1-3 > SiPc(OH)₂(SO₃)_1-3) and was not correlated to the yields of generated singlet oxygen. Our data suggest that the structural properties of both the phthalocyanine and the PrP^TSE strain may affect the effectiveness of the photodynamic prion inactivation. Our finding provides a new option for the discrimination of prion strains and highlights the necessity of utilizing range of prion strains when validating the photodynamic prion decontamination procedures.

Detailing the ultrastructure's increase of prion protein in pancreatic adenocarcinoma

BACKGROUND

Recent evidences have shown a relationship between prion protein (PrPc) expression and pancreatic ductal adenocarcinoma (PDAC). Indeed, PrPc could be one of the markers explaining the aggressiveness of this tumor. However, studies investigating the specific compartmentalization of increased PrPc expression within PDAC cells are lacking, as well as a correlation between ultrastructural evidence, ultrastructural morphometry of PrPc protein and clinical data. These data, as well as the quantitative stoichiometry of this protein detected by immuno-gold, provide a significant advancement in understanding the biology of disease and the outcome of surgical resection.

AIM

To analyze quantitative stoichiometry and compartmentalization of PrPc in PDAC cells and to correlate its presence with prognostic data.

METHODS

Between June 2018 and December 2020, samples from pancreatic tissues of 45 patients treated with pancreatic resection for a preoperative suspicion of PDAC at our Institution were collected. When the frozen section excluded a PDAC diagnosis, or the nodules were too small for adequate sampling, patients were ruled out from the present study. Western blotting was used to detect, quantify and compare the expression of PrPc in PDAC and control tissues, such as those of non-affected neighboring pancreatic tissue of the same patient. To quantify the increase of PrPc and to detect the subcellular compartmentalization of PrPc within PDAC cells, immuno-gold stoichiometry within specific cell compartments was analyzed with electron microscopy. Finally, an analysis of quantitative PrPc expression according to prognostic data, such as cancer stage, recurrence of the disease at 12 mo after surgery and recurrence during adjuvant chemotherapy was made.

RESULTS

The amount of PrPc within specimen from 38 out of 45 patients was determined by semi-quantitative analysis by using Western blotting, which indicates that PrPc increases almost three-fold in tumor pancreatic tissue compared with healthy pancreatic regions [242.41 ± 28.36 optical density (OD) vs 95 ± 17.40 OD, P < 0.0001]. Quantitative morphometry carried out by using immuno-gold detection at transmission electron microscopy confirms an increased PrPc expression in PDAC ductal cells of all patients and allows to detect a specific compartmentalization of PrPc within tumor cells. In particular, the number of immuno-gold particles of PrPc was significantly higher in PDAC cells respect to controls, when considering the whole cell (19.8 ± 0.79 particles vs 9.44 ± 0.45, P < 0.0001). Remarkably, considering PDAC cells, the increase of PrPc was higher in the nucleus than cytosol of tumor cells, which indicates a shift in PrPc compartmentalization within tumor cells. In fact, the increase of immuno-gold within nuclear compartment exceeds at large the augment of PrPc which was detected in the cytosol (nucleus: 12.88 ± 0.59 particles vs 5.12 ± 0.32, P < 0.0001; cytosol: 7.74. ± 0.44 particles vs 4.3 ± 0.24, P < 0.0001). In order to analyze the prognostic impact of PrPc, we found a correlation between PrPc expression and cancer stage according to pathology results, with a significantly higher expression of PrPc for advanced stages. Moreover, 24 patients with a mean follow-up of 16.8 mo were considered. Immuno-blot analysis revealed a significantly higher expression of PrPc in patients with disease recurrence at 12 mo after radical surgery (360.71 ± 69.01 OD vs 170.23 ± 23.06 OD, P = 0.023), also in the subgroup of patients treated with adjuvant CT (368.36 ± 79.26 OD in the recurrence group vs 162.86 ± 24.16 OD, P = 0.028), which indicates a correlation with a higher chemo-resistance.

CONCLUSION

Expression of PrPc is significantly higher in PDAC cells compared with control, with the protein mainly placed in the nucleus. Preliminary clinical data confirm the correlation with a poorer prognosis.

Large Platelet and Endothelial Extracellular Vesicles in Cord Blood of Preterm Newborns: Correlation with the Presence of Hemolysis

Different biomarkers are investigated to detect the causes of severe complications in preterm infants. Extracellular vesicles (EVs) are recognized as an important part of cell-to-cell communication, and their increased levels were reported in numerous pathological states. We aimed to increase our knowledge about the incidence of platelet and endothelial EVs in cord blood of preterm newborns using conventional flow cytometry. The presence of platelet (CD36+CD41+), activated platelet (CD41+CD62+), and endothelial (CD31+CD105+) EVs was analyzed. Immune electron microscopy was used to confirm the presence of EVs and the specificity of their labeling. The size of detected extracellular vesicles was in the range 400-2000 nm. The differences in the counts of EVs between the preterm and control group were not significant and no correlation of EVs count with gestation age was recorded. Cord blood plasma samples with free hemoglobin level > 1 mg/mL had more than threefold higher counts of CD36+CD41+ and CD41+CD62+ EVs (p < 0.001), while the count of CD31+CD105+ EVs was only moderately increased (p < 0.05). Further studies utilizing cytometers with improved sensitivity are needed to confirm that the analysis of large platelet and endothelial EVs mirrors the quantitative situation of their whole plasma assemblage.

Detection of Prions in Brain Homogenates and CSF Samples Using a Second-Generation RT-QuIC Assay: A Useful Tool for Retrospective Analysis of Archived Samples

The possibilities for diagnosing prion diseases have shifted significantly over the last 10 years. The RT-QuIC assay option has been added for neuropsychiatric symptoms, supporting biomarkers and final post-mortem confirmation. Samples of brain homogenates used for final diagnosis, archived for many years, provide the possibility for retrospective studies. We used a second-generation RT-QuIC assay to detect seeding activity in different types of sporadic and genetic prion diseases in archival brain homogenates and post-mortem CSF samples that were 2 to 15 years old. Together, we tested 92 archival brain homogenates: 39 with definite prion disease, 28 with definite other neurological disease, and 25 with no signs of neurological disorders. The sensitivity and specificity of the assay were 97.4% and 100%, respectively. Differences were observed in gCJD E200K, compared to the sporadic CJD group. In 52 post-mortem CSF samples-24 with definite prion disease and 28 controls-we detected the inhibition of seeding reaction due to high protein content. Diluting the samples eliminated such inhibition and led to 95.8% sensitivity and 100% specificity of the assay. In conclusion, we proved the reliability of archived brain homogenates and post-mortem CSF samples for retrospective analysis by RT-QuIC after long-term storage, without changed reactivity.

The occurrence of prion protein in surgically resected pancreatic adenocarcinoma

BACKGROUND

Among the several new targets for the comprehension of the biology of pancreatic ductal adenocarcinoma (PDAC), Prion proteins (PrPc) deserve particular mention, since they share a marked neurotropism. Actually, PrPc could have also a role in tumorigenesis, as recently demonstrated. However, only few in vitro studies in cell cultures showed the occurrence of PrPc in PDAC cells. We aim to evaluate the presence of PrPc in vivo in PDAC tissues as a potential new biomarker.

METHODS

Samples from tumors of 23 patients undergone pancreatic resections from July 2018 to May 2020 at our institution were collected and analyzed. Immunohistochemistry and western blotting of PDAC tissues were compared with control tissues. Immunohistochemistry was used also to evaluate the localization of PrPc and of CD155, a tumoral stem-cell marker.

RESULTS

All cases were moderately differentiated PDAC, with perineural invasion (PNI) in 19/23 cases (83%). According to western-blot analysis, PrPc was markedly expressed in PDAC tissues (273.5 ± 44.63 OD) respect to controls (100 ± 28.35 OD, p = 0.0018). Immunohistochemistry confirmed these findings, with higher linear staining of PrPc in PDAC ducts (127.145 ± 7.56 μm vs 75.21 ± 5.01 μm, p < 0.0001). PrPc and CD155 exactly overlapped in ductal tumoral cells, highlighting the possible relationship of PrPc with cancer stemness. Finally, PrPc expression related with cancer stage and there was a potential correspondence with PNI.

CONCLUSIONS

Our work provides evidence for increased levels of PrPc in PDAC. This might contribute to cancer aggressiveness and provides a potentially new biomarker. Work is in progress to decipher clinical implications.

Expression and functions of cellular prion proteins in immunocytes

Prion diseases are fatal neurodegenerative processes caused by the accumulation of the pathological prion protein, PrP^Sc . While pathological lesions are limited to the central nervous system (CNS), disease-specific proteins accumulate and replicate in secondary lymphoid organs prior to neuroinvasion, and their replication there depends on the abundance of cellular prion protein (PrP^C ). PrP^C is expressed in both central and peripheral lymphoid tissues, and up- or downregulates innate and adaptive immune responses. In addition to prion diseases, PrP^C is also immunologically involved in other neurological disorders and infectious diseases, including Alzheimer's disease and human immunodeficiency virus infection. Herein, we summarize the expression and functions of PrP^C in various immunocytes, as well as its immunological and pathological roles in neurodegeneration and infection.

Changes in cellular prion protein expression, processing and localisation during differentiation of the neuronal cell line CAD 5

BACKGROUND INFORMATION

Cellular prion protein (PrP^C ) is infamous for its role in prion diseases. The physiological function of PrP^C remains enigmatic, but several studies point to its involvement in cell differentiation processes. To test this possibility, we monitored PrP^C changes during the differentiation of prion-susceptible CAD 5 cells, and then we analysed the effect of PrP^C ablation on the differentiation process.

RESULTS

Neuronal CAD 5 cells differentiate within 5 days of serum withdrawal, with the majority of the cells developing long neurites. This process is accompanied by an up to sixfold increase in PrP^C expression and enhanced N-terminal β-cleavage of the protein, which suggests a role for the PrP^C in the differentiation process. Moreover, the majority of PrP^C in differentiated cells is inside the cell, and a large proportion of the protein does not associate with membrane lipid rafts. In contrast, PrP^C in proliferating cells is found mostly on the cytoplasmic membrane and is predominantly associated with lipid rafts. To determine the importance of PrP^C in cell differentiation, a CAD 5 PrP^-/- cell line with ablated PrP^C expression was created using the CRISPR/Cas9 system. We observed no considerable difference in morphology, proliferation rate or expression of molecular markers between CAD 5 and CAD 5 PrP^-/- cells during the differentiation initiated by serum withdrawal.

CONCLUSIONS

PrP^C characteristics, such as cell localisation, level of expression and posttranslational modifications, change during CAD 5 cell differentiation, but PrP^C ablation does not change the course of the differentiation process.

SIGNIFICANCE

Ablation of PrP^C expression does not affect CAD 5 cell differentiation, although we observed many intriguing changes in PrP^C features during the process. Our study does not support the concept that PrP^C is important for neuronal cell differentiation, at least in simple in vitro conditions.

Prion protein deficiency impairs hematopoietic stem cell determination and sensitizes myeloid progenitors to irradiation

Highly conserved among species and expressed in various types of cells, numerous roles have been attributed to the cellular prion protein (PrPC). In hematopoiesis, PrPC regulates hematopoietic stem cell self-renewal but the mechanisms involved in this regulation are unknown. Here we show that PrPC regulates hematopoietic stem cell number during aging and their determination towards myeloid progenitors. Furthermore, PrPC protects myeloid progenitors against the cytotoxic effects of total body irradiation. This radioprotective effect was associated with increased cellular prion mRNA level and with stimulation of the DNA repair activity of the Apurinic/pyrimidinic endonuclease 1, a key enzyme of the base excision repair pathway. Altogether, these results show a previously unappreciated role of PrPC in adult hematopoiesis, and indicate that PrPC-mediated stimulation of BER activity might protect hematopoietic progenitors from the cytotoxic effects of total body irradiation.

Cellular prion protein controls stem cell-like properties of human glioblastoma tumor-initiating cells

Prion protein (PrP^C) is a cell surface glycoprotein whose misfolding is responsible for prion diseases. Although its physiological role is not completely defined, several lines of evidence propose that PrP^C is involved in self-renewal, pluripotency gene expression, proliferation and differentiation of neural stem cells. Moreover, PrP^C regulates different biological functions in human tumors, including glioblastoma (GBM). We analyzed the role of PrP^C in GBM cell pathogenicity focusing on tumor-initiating cells (TICs, or cancer stem cells, CSCs), the subpopulation responsible for development, progression and recurrence of most malignancies. Analyzing four GBM CSC-enriched cultures, we show that PrP^C expression is directly correlated with the proliferation rate of the cells. To better define its role in CSC biology, we knocked-down PrP^C expression in two of these GBM-derived CSC cultures by specific lentiviral-delivered shRNAs. We provide evidence that CSC proliferation rate, spherogenesis and in vivo tumorigenicity are significantly inhibited in PrP^C down-regulated cells. Moreover, PrP^C down-regulation caused loss of expression of the stemness and self-renewal markers (NANOG, Sox2) and the activation of differentiation pathways (i.e. increased GFAP expression). Our results suggest that PrP^C controls the stemness properties of human GBM CSCs and that its down-regulation induces the acquisition of a more differentiated and less oncogenic phenotype.

Functions of the Prion Protein

Although initially disregarded compared to prion pathogenesis, the functions exerted by the cellular prion protein PrP^C have gained much interest over the past two decades. Research aiming at unraveling PrP^C functions started to intensify when it became appreciated that it would give clues as to how it is subverted in the context of prion infection and, more recently, in the context of Alzheimer's disease. It must now be admitted that PrP^C is implicated in an incredible variety of biological processes, including neuronal homeostasis, stem cell fate, protection against stress, or cell adhesion. It appears that these diverse roles can all be fulfilled through the involvement of PrP^C in cell signaling events. Our aim here is to provide an overview of our current understanding of PrP^C functions from the animal to the molecular scale and to highlight some of the remaining gaps that should be addressed in future research.

Prion Protein-Hemin Interaction Upregulates Hemoglobin Synthesis: Implications for Cerebral Hemorrhage and Sporadic Creutzfeldt-Jakob Disease

Hemin is known to induce endocytosis of prion-protein (PrP(C)) from the neuronal plasma membrane, potentially limiting propagation of the disease causing PrP-scrapie (PrP(Sc)) isoform. Hemin is therefore an attractive disease-modifying option for sporadic Creutzfeldt-Jakob disease (sCJD), a human prion disorder with no effective treatment. The hemin-PrP(C) interaction is also of interest in cerebral-hemorrhage (CH), a condition where potentially toxic hemin molecules come in contact with neuronal PrP(C). Interestingly, PrP(C) is upregulated in penumbric neurons surrounding CH and is known to confer neuroprotection in a dose-dependent manner. The underlying mechanism, however, is not clear. Here, we report that hemin binds PrP(C) on diverse cell lines, resulting in its aggregation or degradation in a cell-type specific manner. Surprisingly, the hemin-PrP(C) interaction upregulates Hb synthesis in hematopoietic cells, a response reversed by deleting the hemin-binding octa-peptide repeat region of PrP(C). A similar response is noted in brain organotypic cultures where exposure to hemin induces significantly more α-globin in wild-type (PrP(+/+)) relative to PrP-knock-out (PrP(-/-)) samples. Furthermore, red blood cells and brain tissue from PrP(-/-) mice show significantly less α-globin relative to PrP(+/+) controls, indicating a positive effect of PrP(C) on Hb synthesis under physiological conditions as well. Surprisingly, levels of α-globin are significantly higher in sCJD brain tissue relative to controls, suggesting compensatory upregulation of Hb synthesis by surviving neurons or misregulation in diseased brains. These observations reveal a unique function of PrP(C) that is likely to impact the therapeutic management of CH and sCJD.

Multifaceted Role of Sialylation in Prion Diseases

Mammalian prion or PrP(Sc) is a proteinaceous infectious agent that consists of a misfolded, self-replicating state of a sialoglycoprotein called the prion protein, or PrP(C). Sialylation of the prion protein N-linked glycans was discovered more than 30 years ago, yet the role of sialylation in prion pathogenesis remains poorly understood. Recent years have witnessed extraordinary growth in interest in sialylation and established a critical role for sialic acids in host invasion and host-pathogen interactions. This review article summarizes current knowledge on the role of sialylation of the prion protein in prion diseases. First, we discuss the correlation between sialylation of PrP(Sc) glycans and prion infectivity and describe the factors that control sialylation of PrP(Sc). Second, we explain how glycan sialylation contributes to the prion replication barrier, defines strain-specific glycoform ratios, and imposes constraints for PrP(Sc) structure. Third, several topics, including a possible role for sialylation in animal-to-human prion transmission, prion lymphotropism, toxicity, strain interference, and normal function of PrP(C), are critically reviewed. Finally, a metabolic hypothesis on the role of sialylation in the etiology of sporadic prion diseases is proposed.

Expression of the cellular prion protein affects posttransfusion recovery and survival of red blood cells in mice

BACKGROUND

Cellular prion protein (PrP(C) ) is expressed on various cell types including red blood cells (RBCs). The PrP(C) plays a key role in the pathogenesis of prion diseases, but its physiologic function remains unclear. PrP(C) is expressed on CD34+ hematopoietic stem cells and its expression is regulated during blood cell differentiation including the erythroid line.

STUDY DESIGN AND METHODS

We investigated the role of PrP(C) in RBC survival in circulation by transfusing a mix of biotin-labeled RBCs from wild-type (WT) and PrP knockout (KO) mice to groups of recipient mice (WT and KO). The proportion of biotinylated RBCs in peripheral blood was estimated by flow cytometry.

RESULTS

KO RBCs displayed a markedly higher first-day posttransfusion recovery but had a decreased survival in circulation when compared to WT RBCs. Similar results were obtained in all groups of transfused mice, irrespective of RBCs biotinylation level. In addition, we confirmed this finding in an analogous study using Tga20 mice overexpressing PrP(C) and KO mice of a different genetic background.

CONCLUSION

Our results demonstrate that PrP(C) expression affects RBC recovery and survival in circulation.

The cellular form of the prion protein guides the differentiation of human embryonic stem cells into neuron-, oligodendrocyte-, and astrocyte-committed lineages

Prion protein, PrP(C), is a glycoprotein that is expressed on the cell surface beginning with the early stages of embryonic stem cell differentiation. Previously, we showed that ectopic expression of PrP(C) in human embryonic stem cells (hESCs) triggered differentiation toward endodermal, mesodermal, and ectodermal lineages, whereas silencing of PrP(C) suppressed differentiation toward ectodermal but not endodermal or mesodermal lineages. Considering that PrP(C) might be involved in controlling the balance between cells of different lineages, the current study was designed to test whether PrP(C) controls differentiation of hESCs into cells of neuron-, oligodendrocyte-, and astrocyte-committed lineages. PrP(C) was silenced in hESCs cultured under three sets of conditions that were previously shown to induce hESCs differentiation into predominantly neuron-, oligodendrocyte-, and astrocyte-committed lineages. We found that silencing of PrP(C) suppressed differentiation toward all three lineages. Similar results were observed in all three protocols, arguing that the effect of PrP(C) was independent of differentiation conditions employed. Moreover, switching PrP(C) expression during a differentiation time course revealed that silencing PrP(C) expression during the very initial stage that corresponds to embryonic bodies has a more significant impact than silencing at later stages of differentiation. The current work illustrates that PrP(C) controls differentiation of hESCs toward neuron-, oligodendrocyte-, and astrocyte-committed lineages and is likely involved at the stage of uncommitted neural progenitor cells rather than lineage-committed neural progenitors.

PrP(C) from stem cells to cancer

The cellular prion protein PrP(C) was initially discovered as the normal counterpart of the pathological scrapie prion protein PrP(Sc), the main component of the infectious agent of Transmissible Spongiform Encephalopathies. While clues as to the physiological function of this ubiquitous protein were greatly anticipated from the development of knockout animals, PrP-null mice turned out to be viable and to develop without major phenotypic abnormalities. Notwithstanding, the discovery that hematopoietic stem cells from PrP-null mice have impaired long-term repopulating potential has set the stage for investigating into the role of PrP(C) in stem cell biology. A wealth of data have now exemplified that PrP(C) is expressed in distinct types of stem cells and regulates their self-renewal as well as their differentiation potential. A role for PrP(C) in the fate restriction of embryonic stem cells has further been proposed. Paralleling these observations, an overexpression of PrP(C) has been documented in various types of tumors. In line with the contribution of PrP(C) to stemness and to the proliferation of cancer cells, PrP(C) was recently found to be enriched in subpopulations of tumor-initiating cells. In the present review, we summarize the current knowledge of the role played by PrP(C) in stem cell biology and discuss how the subversion of its function may contribute to cancer progression.

Prion protein regulates iron transport by functioning as a ferrireductase

Prion protein (PrPC) is implicated in the pathogenesis of prion disorders, but its normal function is unclear. We demonstrate that PrPC is a ferrireductase (FR), and its absence causes systemic iron deficiency in PrP knock-out mice (PrP-/-). When exposed to non-transferrin-bound (NTB) radioactive-iron (59FeCl3) by gastric-gavage, PrP-/- mice absorb significantly more 59Fe from the intestinal lumen relative to controls, indicating appropriate systemic response to the iron deficiency. Chronic exposure to excess dietary iron corrects this deficiency, but unlike wild-type (PrP+/+) controls that remain iron over-loaded, PrP-/- mice revert back to the iron deficient phenotype after 5 months of chase on normal diet. Bone marrow (BM) preparations of PrP-/- mice on normal diet show relatively less stainable iron, and this phenotype is only partially corrected by intraperitoneal administration of excess iron-dextran. Cultured PrP-/- BM-macrophages incorporate significantly less NTB-59Fe in the absence or presence of excess extracellular iron, indicating reduced uptake and/or storage of available iron in the absence of PrPC. When expressed in neuroblastoma cells, PrPC exhibits NAD(P)H-dependent cell-surface and intracellular FR activity that requires the copper-binding octa-peptide-repeat region and linkage to the plasma membrane for optimal function. Incorporation of NTB-59Fe by neuroblastoma cells correlates with FR activity of PrPC, implicating PrPC in cellular iron uptake and metabolism. These observations explain the correlation between PrPC expression and cellular iron levels, and the cause of iron imbalance in sporadic-Creutzfeldt-Jakob-disease brains where PrPC accumulates as insoluble aggregates.

The cellular form of the prion protein is involved in controlling cell cycle dynamics, self-renewal, and the fate of human embryonic stem cell differentiation

Prion protein (PrP(C) ), is a glycoprotein that is expressed on the cell surface. The current study examines the role of PrP(C) in early human embryogenesis using human embryonic stem cells (hESCs) and tetracycline-regulated lentiviral vectors that up-regulate or suppresses PrP(C) expression. Here, we show that expression of PrP(C) in pluripotent hESCs cultured under self-renewal conditions induced cell differentiation toward lineages of three germ layers. Silencing of PrP(C) in hESCs undergoing spontaneous differentiation altered the dynamics of the cell cycle and changed the balance between the lineages of the three germ layers, where differentiation toward ectodermal lineages was suppressed. Moreover, over-expression of PrP(C) in hESCs undergoing spontaneous differentiation inhibited differentiation toward lineages of all three germ layers and helped to preserve high proliferation activity. These results illustrate that PrP(C) is involved in key activities that dictate the status of hESCs including regulation of cell cycle dynamics, controlling the switch between self-renewal and differentiation, and determining the fate of hESCs differentiation. This study suggests that PrP(C) is at the crossroads of several signaling pathways that regulate the switch between preservation of or departure from the self-renewal state, control cell proliferation activity, and define stem cell fate.

Deletion of protease-activated receptor 2 prolongs survival of scrapie-inoculated mice

Proteinase-activated receptor 2 (PAR2) has recently been identified to be a possible modulator of neurodegeneration. To investigate whether PAR2 plays a role in prion infection, we inoculated PAR2-deficient (PAR2−/−) and wild-type (WT) mice intracerebrally with the Rocky Mountain Laboratory strain of scrapie. PAR2−/− mice demonstrated a delayed onset of clinical symptoms, including weight loss, and demonstrated moderate but highly significant prolongation of survival over WT controls. Concomitantly, no apparent differences in brain pathology, infectivity or features of brain prion protein between deceased WT and PAR2−/− mice were found. Our study suggests that PAR2 deletion modulates dynamics of the disease without gross perturbation of its pathogenesis.

PrPC displays an essential protective role from oxidative stress in an astrocyte cell line derived from PrPC knockout mice

The PrP(C) protein, which is especially present in the cellular membrane of nervous system cells, has been extensively studied for its controversial antioxidant activity. In this study, we elucidated the free radical scavenger activity of purified murine PrP(C) in solution and its participation as a cell protector in astrocytes that were subjected to treatment with an oxidant. In vitro and using an EPR spin-trapping technique, we observed that PrP(C) decreased the oxidation of the DMPO trap in a Fenton reaction system (Cu(2+)/ascorbate/H(2)O(2)), which was demonstrated by approximately 70% less DMPO/OH(). In cultured PrP(C)-knockout astrocytes from mice, the absence of PrP(C) caused an increase in intracellular ROS (reactive oxygen species) generation during the first 3h of H(2)O(2) treatment. This rapid increase in ROS disrupted the cell cycle in the PrP(C)-knockout astrocytes, which increased the population of cells in the sub-G1 phase when compared with cultured wild-type astrocytes. We conclude that PrP(C) in solution acts as a radical scavenger, and in astrocytes, it is essential for protection from oxidative stress caused by an external chemical agent, which is a likely condition in human neurodegenerative CNS disorders and pathological conditions such as ischemia.