Pathogenesis Of Prion Diseases Research Articles

An overview of animal prion diseases

Prion diseases are transmissible neurodegenerative conditions affecting human and a wide range of animal species. The pathogenesis of prion diseases is associated with the accumulation of aggregates of misfolded conformers of host-encoded cellular prion protein (PrPC). Animal prion diseases include scrapie of sheep and goats, bovine spongiform encephalopathy (BSE) or mad cow disease, transmissible mink encephalopathy, feline spongiform encephalopathy, exotic ungulate spongiform encephalopathy, chronic wasting disease of cervids and spongiform encephalopathy of primates. Although some cases of sporadic atypical scrapie and BSE have also been reported, animal prion diseases have basically occurred via the acquisition of infection from contaminated feed or via the exposure to contaminated environment. Scrapie and chronic wasting disease are naturally sustaining epidemics. The transmission of BSE to human has caused more than 200 cases of variant Cruetzfeldt-Jacob disease and has raised serious public health concerns. The present review discusses the epidemiology, clinical neuropathology, transmissibility and genetics of animal prion diseases.

Gene Knockout of tau Expression Does Not Contribute to the Pathogenesis of Prion Disease

Prion diseases or transmissible spongiform encephalopathies are a group of fatal and transmissible disorders affecting the central nervous system of humans and animals. The principal agent of prion disease transmission and pathogenesis is proposed to be an abnormal protease-resistant isoform of the normal cellular prion protein. The microtubule-associated protein tau is elevated in patients with Creutzfeldt-Jakob disease. To determine whether tau expression contributes to prion disease pathogenesis, tau knockout and control wild-type mice were infected with the M1000 strain of mouse-adapted human prions. Immunohistochemical analysis for total tau expression in prion-infected wild-type mice indicated tau aggregation in the cytoplasm of a subpopulation of neurons in regions associated with spongiform change. Western immunoblot analysis of brain homogenates revealed a decrease in total tau immunoreactivity and epitope-specific changes in tau phosphorylation. No significant difference in incubation period or other disease features were observed between tau knockout and wild-type mice with clinical prion disease. These results demonstrate that, in this model of prion disease, tau does not contribute to the pathogenesis of prion disease and that changes in the tau protein profile observed in mice with clinical prion disease occurs as a consequence of the prion-induced pathogenesis.

Geographic Accumulation of Creutzfeldt-Jakob Disease in Slovakia - Environmental Metal Imbalance as a Possible Cofactor

Slovakia is characterised by an unusually high number of patients affected by genetic Creutzfeldt-Jakob disease (CJD) with E200K mutation at the PRNP gene. Penetrance of the mutation is incomplete (59%). Therefore, for the onset of the clinical manifestation, an influence of other endo- or exogenous factors could not be excluded. Experimental data suggest that copper and manganese levels may play an important role in the pathogenesis of prion diseases. The highest number of Slovak genetic CJD patients originates from Orava - the northern region of central Slovakia. Manganese is a dominant pollutant in Orava. The objective of this study was to clarify a possible exogenous influence of environmental Mn/Cu imbalance on the CJD clustering. Mn and Cu levels were analysed in the brain tissue of genetic CJD cases (from Orava and from control regions of Slovakia), as well as of sporadic CJD patients and controls. Analyses demonstrate i) significantly higher Mn level in focally accumulated, "clustering" genetic CJD cases in comparison to all other groups, ii) Cu status differences between compared groups were without statistical significance; decreased concentrations were found in genetic cases from extrafocal genetic CJD areas, iii) Mn/Cu ratios were increased in all CJD groups in comparison to controls. Metal ratios in clustering gCJD cases were significantly higher in comparison to sporadic cases and also to controls, but not to the extrafocal genetic CJD subgroup. These results indicate that more important than increasing Mn level in pathogenesis of CJD appears to be the role of the Mn/Cu imbalance in the CNS. The imbalance observed in the cluster of genetic CJD cases is probably a result of both: the excessive environmental Mn level and the disturbance of Mn/Cu ratios in the Orava region. Presented findings indicate an environmental Mn/Cu imbalance as a possible exogenous CJD risk co-factor which may, in coincidence with endogenous (genetic) CJD risk, contribute to the focal accumulation (cluster) of genetic CJD in Slovakia.

Proteasomal Dysfunction and Endoplasmic Reticulum Stress Enhance Trafficking of Prion Protein Aggregates through the Secretory Pathway and Increase Accumulation of Pathologic Prion Protein

A conformational change of the cellular prion protein (PrP(c)) underlies formation of PrP(Sc), which is closely associated with pathogenesis and transmission of prion diseases. The precise conformational prerequisites and the cellular environment necessary for this post-translational process remain to be completely elucidated. At steady state, glycosylated PrP(c) is found primarily at the cell surface, whereas a minor fraction of the population is disposed of by the ER-associated degradation-proteasome pathway. However, chronic ER stress conditions and proteasomal dysfunctions lead to accumulation of aggregation-prone PrP molecules in the cytosol and to neurodegeneration. In this study, we challenged different cell lines by inducing ER stress or inhibiting proteasomal activity and analyzed the subsequent repercussion on PrP metabolism, focusing on PrP in the secretory pathway. Both events led to enhanced detection of PrP aggregates and a significant increase of PrP(Sc) in persistently prion-infected cells, which could be reversed by overexpression of proteins of the cellular quality control. Remarkably, upon proteasomal impairment, an increased fraction of misfolded, fully glycosylated PrP molecules traveled through the secretory pathway and reached the plasma membrane. These findings suggest a novel pathway that possibly provides additional substrate and template necessary for prion formation when protein clearance by the proteasome is impaired.

Molecular Interaction of TPPP with PrP Antagonized the CytoPrP-Induced Disruption of Microtubule Structures and Cytotoxicity

BackgroundTubulin polymerization promoting protein/p25 (TPPP/p25), known as a microtubule-associated protein (MAP), is a brain-specific unstructured protein with a physiological function of stabilizing cellular microtubular ultrastructures. Whether TPPP involves in the normal functions of PrP or the pathogenesis of prion disease remains unknown. Here, we proposed the data that TPPP formed molecular complex with PrP. We also investigated its influence on the aggregation of PrP and fibrillization of PrP106–126 in vitro, its antagonization against the disruption of microtubule structures and cytotoxicity of cytosolic PrP in cells, and its alternation in the brains of scrapie-infected experimental hamsters.Methodology/Principal FindingsUsing pull-down and immunoprecipitation assays, distinct molecular interaction between TPPP and PrP were identified and the segment of TPPP spanning residues 100–219 and the segment of PrP spanning residues 106–126 were mapped as the regions responsible for protein interaction. Sedimentation experiments found that TPPP increased the aggregation of full-length recombinant PrP (PrP23–231) in vitro. Transmission electron microscopy and Thioflavin T (ThT) assays showed that TPPP enhanced fibril formation of synthetic peptide PrP106–126 in vitro. Expression of TPPP in the cultured cells did not obviously change the microtubule networks observed by a tubulin-specific immunofluorescent assay and cell growth features measured by CCK8 tests, but significantly antagonized the disruption of microtubule structures and rescued the cytotoxicity caused by the accumulation of cytosolic PrP (CytoPrP). Furthermore, Western blots identified that the levels of the endogenous TPPP in the brains of scrapie-infected experimental hamsters were significantly reduced.Conclusion/SignificanceThose data highlight TPPP may work as a protective factor for cells against the damage effects of the accumulation of abnormal forms of PrPs, besides its function as an agent for dynamic stabilization of microtubular ultrastructures.

A polymorphism in the YWHAH gene encoding 14-3-3 eta that is not associated with sporadic Creutzfeldt–Jakob disease (CJD)

14-3-3 proteins are abundantly expressed in the brain, particularly neuronal tissue and are thought to serve multiple biological functions involved in neuronal development and cell growth and death. Recent studies have shown associations of 14-3-3 genes with neurodegenerative disorders based on their chromosomal linkage to these diseases and to regulatory functions for the nervous system. Although the role of 14-3-3 proteins in the pathogenesis of prion diseases remains unknown, the detection of altered levels of isoforms of the 14-3-3 protein in the cerebrospinal fluid is considered a biomarker for diagnosis of sporadic Creutzfeldt-Jakob disease (sCJD). To identify other susceptibility genes for prion disease, we examined nucleotide variations in YWHAH, a gene encoding 14-3-3 eta. This case-control study included 182 sCJD patients and 206 healthy Koreans. Polymerase chain reaction was used to amplify open reading frame and some 3'-untranslated region (UTR) in exon 2, and direct sequencing was carried out. One polymorphism, 753 G/A, was detected in the 3'-UTR of exon 2 on the YWHAH. The genotype distribution and allele frequencies of the YWHAH 753 G/A polymorphism were not significantly different between controls and sCJD patients. This finding indicates that YWHAH 753 G/A polymorphism is unlikely to be linked to genetic susceptibility or have a modifying effect in sCJD. On analysis stratified by the prion protein gene 129 or 219 genotype, no significant relation was found in genotype and allele frequencies of the YWHAH 753G/A. This is the first genetic association study of YWHAH with sCJD populations.

Gene Expression Profiling and Association with Prion-Related Lesions in the Medulla Oblongata of Symptomatic Natural Scrapie Animals

The pathogenesis of natural scrapie and other prion diseases remains unclear. Examining transcriptome variations in infected versus control animals may highlight new genes potentially involved in some of the molecular mechanisms of prion-induced pathology. The aim of this work was to identify disease-associated alterations in the gene expression profiles of the caudal medulla oblongata (MO) in sheep presenting the symptomatic phase of natural scrapie. The gene expression patterns in the MO from 7 sheep that had been naturally infected with scrapie were compared with 6 controls using a Central Veterinary Institute (CVI) custom designed 4×44K microarray. The microarray consisted of a probe set on the previously sequenced ovine tissue library by CVI and was supplemented with all of the Ovis aries transcripts that are currently publicly available. Over 350 probe sets displayed greater than 2-fold changes in expression. We identified 148 genes from these probes, many of which encode proteins that are involved in the immune response, ion transport, cell adhesion, and transcription. Our results confirm previously published gene expression changes that were observed in murine models with induced scrapie. Moreover, we have identified new genes that exhibit differential expression in scrapie and could be involved in prion neuropathology. Finally, we have investigated the relationship between gene expression profiles and the appearance of the main scrapie-related lesions, including prion protein deposition, gliosis and spongiosis. In this context, the potential impacts of these gene expression changes in the MO on scrapie development are discussed.

Involvement of the cellular prion protein in the migration of brain microvascular endothelial cells

The conversion of cellular prion protein (PrP C) to its protease-resistant isoform is involved in the pathogenesis of prion disease. Although PrP C is a ubiquitous glycoprotein that is present in various cell types, the physiological role of PrP C remains obscure. The present study aimed to determine whether PrP C mediates migration of brain microvascular endothelial cells. Small interfering RNAs (siRNAs) targeting PrP C were transfected into a mouse brain microvascular endothelial cell line (bEND.3 cells). siPrP1, selected among three siRNAs, reduced mRNA and protein levels of PrP C in bEND.3 cells. Cellular migration was evaluated with a scratch-wound assay. siPrP1 suppressed migration without significantly affecting cellular proliferation. This study provides the first evidence that PrP C may be necessary for brain microvascular endothelial cells to migrate into damaged regions in the brain. This function of PrP C in the brain endothelium may be a mechanism by which the neurovascular unit recovers from an injury such as an ischemic insult.

Conserved Stress-protective Activity between Prion Protein and Shadoo

Shadoo (Sho) is a neuronally expressed glycoprotein of unknown function. Although there is no overall sequence homology to the cellular prion protein (PrP(C)), both proteins contain a highly conserved internal hydrophobic domain (HD) and are tethered to the outer leaflet of the plasma membrane via a C-terminal glycosylphosphatidylinositol anchor. A previous study revealed that Sho can reduce toxicity of a PrP mutant devoid of the HD (PrPΔHD). We have now studied the stress-protective activity of Sho in detail and identified domains involved in this activity. Like PrP(C), Sho protects cells against physiological stressors such as the excitotoxin glutamate. Moreover, both PrP(C) and Sho required the N-terminal domain for this activity; the stress-protective capacity of PrPΔN as well as ShoΔN was significantly impaired. In both proteins, the HD promoted homodimer formation; however, deletion of the HD had different effects. Although ShoΔHD lost its stress-protective activity, PrPΔHD acquired a neurotoxic potential. Finally, we could show that the N-terminal domain of PrP(C) could be functionally replaced by that of Sho, suggesting a similar function of the N termini of Sho and PrP(C). Our study reveals a conserved physiological activity between PrP(C) and Sho to protect cells from stress-induced toxicity and suggests that Sho and PrP(C) might act on similar signaling pathways.

Expression patterns of prion protein gene in differential genotypes sheep: quantification using molecular beacon real-time RT-PCR

Determination of the transcription level of cellular prion protein (PrP(C)) is essential for understanding its role in organisms and revealing mechanism of susceptibility and resistance to scrapie. However, the expression of prion protein (PrP) mRNA in sheep has not been quantified in great detail in digestive tract which is important during scrapie spread through oral route. Herein, we report on measurement of sheep PrP mRNA using absolute quantitative real-time RT-PCR. Total RNA was isolated from five different regions of the central nervous system (CNS), four regions of lymphoid system, eleven regions of digestive tract, and two reproductive organ tissues of eight sheep of two different genotypes (ARR/ARQ and ARH/ARQ) and PrP mRNA was quantified by real-time RT-PCR using molecular beacon. The results showed that highest levels of PrP mRNA were expressed in thalamus and cerebrum (P<0.01) of CNS examined, followed by cerebellum, spinal cord, and brain stem. In peripheral organs examined, lymph tissue showed moderate level of PrP expression similar to that in digestive tract and reproduction organs. PrP expression levels in the same tissue of different genotype sheep had significant variation. Our study provided the first detail, tissue-specific and genotype-specific data of PrP mRNA expression in sheep for further studies of pathogenesis of prion diseases.

Heat shock protein 104 inhibited the fibrillization of prion peptide 106–126 and disassembled prion peptide 106–126 fibrils in vitro

Amyloid-like fibrils have been associated with the pathogenesis of human prion diseases. Prion peptide of aa 106–126 (PrP106–126) exhibits many PrPSc-like biochemical features, forming amyloid-like fibrils in vitro. Here, we found that the recombinant yeast-derived molecular chaperon Hsp104 inhibited significantly the fibril assembly of the synthetic PrP106–126 peptide by dynamic ThT assays in vitro. EM assays revealed almost no fibril-like structure after incubation of the synthetic PrP106–126 peptides with Hsp104 for 12h. Circular dichroism assays identified that treatment of Hsp104 shifted the secondary structure of PrP106–126 fibrils from β-sheet to a random coil. MTT tests confirmed that interaction of PrP106–126 with Hsp104 maintained the toxicity of PrP106–126 on human neuroblastoma cell line SK-N-SH. Additionally, Hsp104 was able to disassemble the mature PrP106–126 fibrils in vitro, leading to recovering the cytotoxicity of PrP106–126 on SK-N-SH cells. Our study provides the molecular evidences that the yeast-derived Hsp104 can interfere in the fibril assembly and disassembly of human PrP106–126 segment.

Zinc, copper, and carnosine attenuate neurotoxicity of prion fragment PrP106-126

Prion diseases are progressive neurodegenerative diseases that are associated with the conversion of normal cellular prion protein (PrP(C)) to abnormal pathogenic prion protein (PrP(SC)) by conformational changes. Prion protein is a metal-binding protein that is suggested to be involved in metal homeostasis. We investigated here the effects of trace elements on the conformational changes and neurotoxicity of synthetic prion peptide (PrP106-126). PrP106-126 exhibited the formation of β-sheet structures and enhanced neurotoxicity during the aging process. The co-existence of Zn(2+) or Cu(2+) during aging inhibited β-sheet formation by PrP106-126 and attenuated its neurotoxicity on primary cultured rat hippocampal neurons. Although PrP106-126 formed amyloid-like fibrils as observed by atomic force microscopy, the height of the fibers was decreased in the presence of Zn(2+) or Cu(2+). Carnosine (β-alanyl histidine) significantly inhibited both the β-sheet formation and the neurotoxicity of PrP106-126. Our results suggested that Zn(2+) and Cu(2+) might be involved in the pathogenesis of prion diseases. It is also possible that carnosine might become a candidate for therapeutic treatments for prion diseases.

The Immune System in the Pathogenesis and Prevention of Prion Diseases

Bovine spongiform encephalopathy (BSE) remains a significant threat to both human and animal health in the United States and in particular a threat to the agriculture industry. The diagnosis of BSE in a single cow within the United States in 2003 led to net losses of billions of dollars and additional studies have pointed to significant sociological consequences of BSE cases in Canada, particularly in terms of the dissolution of rural communities. Unlike other infectious diseases, BSE and other prion diseases are caused by a misfolded protein (PrPSc) that is highly resistant to normal nucleic acid-based disinfection and sterilization procedures. Disease progression is linked to the progressive conversion of a normal cellular molecule (PrPC) into the infectious form (PrPSc) mainly on cells of the immune and neurological systems, leading to formation of multimolecular fibrils associated with progressive neurodegeneration and dementia. Due to the unique nature of this infectious particle and the fact that the disease is caused by a misfolded form of a normal self-protein, development of vaccines and other therapeutics have been challenging. The molecular mechanisms behind PrPSc targeting to lymph node germinal centers and the failure of immune recognition, remain unclear. Here, we review the current knowledge of prion disease biology, the role of the immune system in disease transmission and pathogenesis and efforts towards development of therapeutics and vaccines. While feed-based control of BSE has been successful in limiting transmission and spread of the disease, the recent description of apparently spontaneous and/or genetic forms of BSE underlies the importance of continued research into tools to counter this unique disease threat to the world economy as well as animal and human health.

Establishment of the cell line expressing human prion protein on PrP0/0 background

In this work we described preparation of the novel cell lines expressing human prion protein on PrP0/0-background. Prepared cell lines originated from the Nagasaki mice (PrP0/0) and showed a fibroblast phenotype. The expression level of human prion protein in the developed cell lines was comparable to the physiological expression measured in GT1-7 cells. A great advantage of the prepared cell lines was their short doubling time that allowed obtaining of a large amount of cells for the proteomic experiments. Newly established cell lines open a broad spectrum of applications in the prion research. Besides the study of physiological function of the prion protein or its interactome, the new cell lines could be successfully employed as a unique tool for the better understanding of key events in the pathogenesis of prion diseases.

Impairment of Erythropoiesis In Inbred Cellular Prion Protein Deficient Mice.

AbstractAbstract 2032Cellular prion protein (PrPc) plays a key role in pathogenesis of prion diseases, however, its physiologic function remains unclear. The involvement of PrPc in hematopoiesis was suggested by importance of its expression for self renewal and survival of long term repopulating hematopoietic stem cells. Prion diseases were shown to deregulate transcription of several erythroid genes and we have demonstrated reduction of erythroid cell and erythropoietin production in FVB PrP-/- (Zurich I) mice in response to acute anemia (Zivny J. et al. Blood Cells Mol Dis. 2008;40:302-307). In this study, we exploited different mouse models with manipulated level of PrPc expression to verify the role of PrPc in erythropoiesis. First set of experiments was carried out on PrP-/- (Zurich I) and Tga20 PrP over-expressing mice on a mixed C57Bl6/129Sv genetic background. Inbred C57Bl6 mice served as a wild type control (WT). Induction of acute anemia by phenylhydrazine (PHZ) in PrP-/- and WT mice (n=18) led to drop in the hematocrit (HCT) from 52.5±1.5 and 49.8±2.5% to 37.9± 1.0 and 41.9±3.0% after 24 h, respectively. The course of anemia was significantly deeper in PrP-/- mice at 72 h, 96 h and 120 h (p < 0.01) after PHZ administration. Plasma levels of erythropoietin (Epo) in response to anemia reached higher maximum levels in PrP-/- than WT mice (2250 vs. 1810 pg/mL) although rose more slowly. The level of Epo mRNA in kidneys increased approximately 30-fold in both, WT and PrP-/- mice, however, in WT mice peaked at 24 h whereas in KO mice at 96 h. We repeated the study with smaller groups of PrP-/- and Tga20 mice (n=9) and analysed samples 24 h and 96 h post anemia induction. Random PrP gene re-introduction in Tga20 mice rescued the animals from severe anemia. Decrease in HCT after PHZ administration was significantly lower in Tga20 comparing to PrP-/- mice and was accompanied by less elevated reticulocyte (RTC) count, plasma Epo level and level of Epo mRNA in kidneys. Next we studied the dynamics of unchallenged erythropoiesis in PrP-/-, Tga20 and WT mice by in vivo labelling of blood cells with NHS-biotin and subsequent flow cytometric analysis of relative numbers of newly produced non-labelled RBC. WT mice had significantly enhanced turnover of RBC with higher counts of non-labelled RBC comparing to PrP-/- during 46 days of chase (p < 0.05). Half- life of labeled RBC in WT mice was 20 days, but 32 and 30 days in PrP-/- and Tga20 mice, respectively. Tga20 mice displayed tendency to increased RBC turnover over PrP-/- mice, but the difference was significant only 2 and 33 days after initiation of the experiment. Having in mind possible limitations of experiments conducted in genetically modified inbred mice we have designed second set of experiments in more stringent animal models. We mated C57Bl6/129Sv PrP-/- mice with inbred C57Bl6 and outbred CD-1 mice. Heterozygotes in F1 generation were mated and their PrP -/-, PrP -/+ and PrP +/+ offspring used in the experiments. Anemia was induced by PHZ and blood was sampled from tail vein at defined time points and HCT and RTC count were analysed. In C57Bl6 crossbreeds we observed significantly higher starting HCT level in PrP-/- mice (p < 0.05) compared to PrP-/+ and PrP+/+ mice reaching 53.2±2.3, 50.0±2.1 and 49±2.9%, respectively. Similar decrease in HCT was observed for all PrP groups 24 h after PHZ administration, however, significant differences between PrP-/- and PrP+/+ mice were recorded at 48 h and 72 h. The recovery to normal HCT was again retarded in PrP-/- mice. RTC counts rose more rapidly in PrP+/+ mice after PHZ administration and declined to basal levels faster than in PrP-/- mice, the difference reached significance at 24 h, 48 h and 96 h. Dynamics of unchallenged erythropoiesis in C57Bl6 crossbreeds was similar in all three PrP genotypes with no significant differences in numbers of newly produced RBC during 57 days of the experiment. In CD-1 crossbreed mice no significant differences in HCT and RTC counts were detected after PHZ induced anemia among PrP-/-, PrP-/+ and PrP+/+ siblings. Also the dynamics of unchallenged erythropoiesis was similar in all PrP genotypes. To sum up, our data confirmed the role of PrPc in stress erythropoiesis in studied inbred mouse models. In outbred model the effect of PrP deletion on erythropoiesis seems to be compensated. (GACR310/08/0878, GAUK86408) Disclosures:No relevant conflicts of interest to declare.

Deletion of the Prion Protein Does not Affect Erythropoiesis in a Mouse Model of Beta-Thalassemia

AbstractAbstract 3213The cellular prion protein (PrPc) is a highly conserved GPI-linked cell surface sialoglycoprotein which plays a key role in the pathogenesis of neurodegenerative prion diseases. Although PrPc is conserved across species, its normal function is not clearly understood. PrPc tissue distribution varies by cell type or by level of expression in different species. Circulating red blood cells (RBCs) in humans and mice have similar levels of PrPc and reports in the literature suggest that it has a role in survival of cells under stress conditions. We previously reported that an absence of PrPc in PrPc knock out (Prnp-/-) mice negatively influenced their response to acute anemia induced with phenylhydrazine (PHZ) (Zivny et al. 2008. Blood Cells, Molecules and Diseases. 40: 302–307). Prpn-/- mice displayed a reduction of erythroid cells and erythropoietin production suggesting the importance of PrPc expression for stress erythropoiesis. In order to further explore this observation, we mated chronically anemic β-thalassemic (th3/+) male mice (generously donated by Dr. M Sadelein, NY) with female Prnp-/- mice. Th3/+ mice have a defect in the β chain of hemoglobin and have lower hematocrits (HCT). Their offspring, heterozygous for PrPc (Prnp+/−), were genotyped and anemic th3/+ Prnp+/− males were mated with non-anemic (WT) Prnp+/− females to produce mice for the study. The PrPc genotype of two cohorts of offspring combined (n=127 total), Prnp+/+ (18%), Prpn+/− (56%) and Prnp-/- (26%), did not show significant deviation from a Mendelian distribution. Similarly, the proportion of Prnp-/- genotype among anemic th3/+ offspring (29.5%) was slightly higher than the proportion of Prnp+/+ genotype (18.1%), suggesting that PrPc deletion does not lead to higher in utero mortality of th3/+ mice. Evaluation of the microhematocrit at 12 weeks of age demonstrated decreased HCT levels of th3/+ mice (37.4±5.0% and 35.1±2.9%) in comparison to their WT siblings (51.6±2.5% and 49.1±3.5%). No significant differences were detected among different Prnp genotypes in both th3/+ and WT mice. In order to test if PrPc expression in these mice is important for the recovery from acute anemia, the th3/+ and the WT siblings of all PrPc genotypes (n=6 per group) were injected with PHZ (80 mg/kg). The following parameters were measured over a 7 day period using standard methods: HCT levels, plasma erythropoietin (EPO) levels, peripheral reticulocyte count, percentage of cells in the spleen expressing CD71, and the weight of animals and their spleens at the end of the study. On day 7 after induction of acute anemic stress, plasma EPO levels were higher in th3/+ animals compared to WT animals, 1125±48.4 pg/mL and 338±104.5 pg/mL respectively. The percent of erythroid precursor cells (CD71+) were lower in th3/+ (10.0±0.7%) than in WT (21.8±2.8%) splenocytes but the spleen sizes were larger in the th3/+ mice. Hematocrits were not different with statistical significance between th3/+ (28.8±0.6%) and WT (31.5±0.75%) animals on day 7, but circulating reticulocyte counts were higher in th3/+ (54.2±4.9% vs. 40.9±3.8%) animals. The PrPc genotype (Prnp+/+, Prnp+/− and Prnp-/-) did not affect the results in either the th3/+ or WT animals. Th3/+ animals were chronically anemic and had inefficient erythropoiesis which produced a lower percentage of CD71+ cells, in spite of higher levels of plasma EPO in response to similar levels of hypoxic stress as in the WT mice. However, the overall RBC production of th3/+ mice in response to acute hypoxia was maintained by a large spleen size. The prion protein deletion did not affect the percent of RBC precursors or the final RBC output. Thus, prion protein expression does not appear to influence RBC production in a chronically anemic mouse model. The findings and conclusions in this abstract have not been formally disseminated by the Food and Drug Administration and should not be construed to represent any Agency determination or policy. (GAUK86408, GACR 310/08/0878) Disclosures:No relevant conflicts of interest to declare.

Review: Contribution of transgenic models to understanding human prion disease

J. D. F. Wadsworth, E. A. Asante and J. Collinge (2010) Neuropathology and Applied Neurobiology36, 576–597Contribution of transgenic models to understanding human prion diseaseTransgenic mice expressing human prion protein in the absence of endogenous mouse prion protein faithfully replicate human prions. These models reproduce all of the key features of human disease, including long clinically silent incubation periods prior to fatal neurodegeneration with neuropathological phenotypes that mirror human prion strain diversity. Critical contributions to our understanding of human prion disease pathogenesis and aetiology have only been possible through the use of transgenic mice. These models have provided the basis for the conformational selection model of prion transmission barriers and have causally linked bovine spongiform encephalopathy with variant Creutzfeldt-Jakob disease. In the future these models will be essential for evaluating newly identified potentially zoonotic prion strains, for validating effective methods of prion decontamination and for developing effective therapeutic treatments for human prion disease.

Enhancement of phagocytotic activity by prion protein in PrP-deficient macrophage cells

Macrophages, especially follicular dendritic cells, contribute to the pathogenesis of prion diseases by accumulating an abnormal isoform of prion protein (PrPSc), which is converted from the cellular isoform of prion protein (PrPC). As information on the function of PrPC in macrophages is limited, we have established a prion protein (PrP) gene (Prnp)-deficient macrophage cell line from the bone marrow of ZrchI Prnp-/- mice. These cells expressed macrophage specific proteins (F4/80 and MOMA-2) and displayed phagocytotic properties. The Prnp-/- macrophage cell line (MplZ) showed shorter pseudopodium extension and less phagocytotic activity than a Prnp+/+ macrophage cell line (MWF). In addition, the MplZ cells were more sensitive to serum deprivation than the MWF cells and underwent apoptotic cell death in these conditions. These findings suggest that PrPC enhances the incorporation of materials possibly including PrPSc and decreases the sensitivity of cells to oxidative stress, which may be induced by PrPSc accumulation.

Pro-prion Binds Filamin A, Facilitating Its Interaction with Integrin β1, and Contributes to Melanomagenesis

Filamin A (FLNA) is an integrator of cell mechanics and signaling. The spreading and migration observed in FLNA sufficient A7 melanoma cells but not in the parental FLNA deficient M2 cells have been attributed to FLNA. In A7 and M2 cells, the normal prion (PrP) exists as pro-PrP, retaining its glycosylphosphatidyl-inositol (GPI) anchor peptide signal sequence (GPI-PSS). The GPI-PSS of PrP has a FLNA binding motif and binds FLNA. Reducing PrP expression in A7 cells alters the spatial distribution of FLNA and organization of actin and diminishes cell spreading and migration. Integrin β1 also binds FLNA. In A7 cells, FLNA, PrP, and integrin β1 exist as two independent, yet functionally linked, complexes; they are FLNA with PrP or FLNA with integrin β1. Reducing PrP expression in A7 cells decreases the amount of integrin β1 bound to FLNA. A PrP GPI-PSS synthetic peptide that crosses the cell membrane inhibits A7 cell spreading and migration. Thus, in A7 cells FLNA does not act alone; the binding of pro-PrP enhances association between FLNA and integrin β1, which then promotes cell spreading and migration. Pro-PrP is detected in melanoma in situ but not in melanocyte. Invasive melanoma has more pro-PrP. The binding of pro-PrP to FLNA, therefore, contributes to melanomagenesis.

Role of the Highly Conserved Middle Region of Prion Protein (PrP) in PrP−Lipid Interaction

Converting normal prion protein (PrP(C)) to the pathogenic PrP(Sc) isoform is central to prion disease. We previously showed that, in the presence of lipids, recombinant mouse PrP (rPrP) can be converted into the highly infectious conformation, suggesting a crucial role of lipid-rPrP interaction in PrP conversion. To understand the mechanism of lipid-rPrP interaction, we analyzed the ability of various rPrP mutants to bind anionic lipids and to gain lipid-induced proteinase K (PK) resistance. We found that the N-terminal positively charged region contributes to electrostatic rPrP-lipid binding but does not affect lipid-induced PK resistance. In contrast, the highly conserved middle region of PrP, consisting of a positively charged region and a hydrophobic domain, is essential for lipid-induced rPrP conversion. The hydrophobic domain deletion mutant significantly weakened the hydrophobic rPrP-lipid interaction and abolished the lipid-induced C-terminal PK resistance. The rPrP mutant without positive charges in the middle region reduced the amount of the lipid-induced PK-resistant rPrP form. Consistent with a critical role of the middle region in lipid-induced rPrP conversion, both disease-associated P105L and P102L mutations, localized between lysine residues in the positively charged region, significantly affected lipid-induced rPrP conversion. The hydrophobic domain-localized 129 polymorphism altered the strength of hydrophobic rPrP-lipid interaction. Collectively, our results suggest that the interaction between the middle region of PrP and lipids is essential for the formation of the PK-resistant conformation. Moreover, the influence of disease-associated PrP mutations and the 129 polymorphism on PrP-lipid interaction supports the relevance of PrP-lipid interaction to the pathogenesis of prion disease.