Specific T-cell receptor beta-rearrangements of gluten-triggered CD8+ T-cells are enriched in celiac disease patients' duodenal mucosa

Celiac disease (CeD) is an autoimmune disorder affecting the small intestine with gluten as disease trigger. Infections including Influenza A, increase the CeD risk. While gluten-specific CD4+ T-cells, recognizing HLA-DQ2/DQ8 presented gluten-peptides, initiate and sustain the celiac immune response, CD8+ α/β intraepithelial T-cells elicit mucosal damage. Here, we subjected TCRs from a cohort of 56 CeD patients and 22 controls to an analysis employing 749 published CeD-related TCRβ-rearrangements derived from gluten-specific CD4+ T-cells and gluten-triggered peripheral blood CD8+ T-cells. We show, that in addition to TCRs from gluten-specific CD4+ T-cells, TCRs of gluten-triggered CD8+ T-cells are significantly enriched in CeD duodenal tissue samples. TCRβ-rearrangements of gluten-triggered CD8+ T-cells were even more expanded in patients than TCRs from gluten-specific CD4+ T-cells (p < 0.0002) and highest in refractory CeD. Sequence alignments with TCR-antigen databases suggest that a subgroup of these most likely indirectly gluten-triggered TCRs recognize microbial, viral, and autoantigens.

Winner-loser effects improve social network efficiency between competitors with equal resource holding power

Animal societies are structured of dominance hierarchy (DH). DH can be viewed as networks and analyzed by graph theory. We study the impact of state-dependent feedback (winner-loser effect) on the emergence of local dominance structures after pairwise contests between initially equal-ranking members (equal resource-holding-power, RHP) of small and large social groups. We simulated pairwise agonistic contests between individuals with and without a priori higher RHP by Monte-Carlo-method. Random pairwise contests between equal-ranking competitors result in random dominance structures ('Null variant') that are low in transitive triads and high in pass along triads; whereas state-dependent feedback ('Winner-loser variant') yields centralized 'star' structured DH that evolve from competitors with initially equal RHP and correspond to hierarchies that evolve from keystone individuals. Monte-Carlo simulated DH following state-dependent feedback show motif patterns very similar to those of a variety of natural DH, suggesting that state-dependent feedback plays a pivotal role in robust self-organizing phenomena that transcend the specifics of the individual. Self-organization based on state-dependent feedback leads to social structures that correspond to those resulting from pre-existing keystone individuals. As the efficiency of centralized social networks benefits both, the individual and the group, centralization of social networks appears to be an important evolutionary goal.

Microbiome analysis of the skin of sheep that are resistant or susceptible to breech flystrike

Context Breech strike is a serious disease for wool sheep. Skin wrinkle and dags are known predisposing factors for breech strike; however, a large part of the variation among sheep is unknown. Aims We studied the natural diversity and difference in microbial populations in the skin around the breech area in Merino sheep genetically resistant and susceptible to breech strike, by using 16S rRNA gene sequence analysis. Methods The sheep were from the breech strike flocks at the Mount Barker research station in Western Australia and from the CSIRO research station near Armidale in New South Wales. Skin samples were collected from the breech of all 2013-born progeny in both flocks before they were struck. Yearling ewes and rams were then naturally exposed to challenge by Lucilia cuprina blowflies. Breeding values for breech strike were estimated and used with phenotypic data to identify breech strike-resistant and -susceptible sheep. Skin samples of 78 unstruck and 73 struck sheep were selected, their microbiomes were analysed using 16S rRNA meta-barcoding, and operational taxonomic unit counts were analysed. Results The diversity analyses showed that the two flocks in the different environments had different microbiome profiles, but no difference was found between sexes or between breech strike-resistant and -susceptible sheep in either flock. Conclusions The results indicated that microbial differences on the skin of sheep are not associated with differences in susceptibility to breech strike. Implications Microbial differences do not offer opportunities to manage breech strike in Merino sheep.

A non-synonymous SNP in exon 3 of the KIT gene is responsible for the classic grey phenotype in alpacas (Vicugna pacos)

The alpaca classic grey phenotype is of particular interest to the industry. Until now, there were only indirect data suggesting that the KIT gene was involved in the classic grey phenotype. All exons of KIT in three black and three classic silvergrey alpacas were sequenced. Five non-synonymous SNPs were observed. There was only one SNP found that was present only in the silvergrey alpacas, and this was also the only SNP predicted to be damaging. This variant results in a change of a glycine (Gly) to an arginine (Arg) at amino acid position 126 (c.376G>A), occurring in the second Ig-like domain of the extracellular domain of KIT. Basic protein modelling predicted that this variant is likely destabilising. Therefore, an additional 488 alpacas were genotyped for this SNP using the tetra-primer amplification refractory mutation system PCR (Tetra-primer ARMS-PCR). All classic grey alpacas were observed to be heterozygous, and 99.3% of non-grey dark base colour alpacas were found to be homozygous for the wildtype allele in this position. These results confirm that the classic grey phenotype in alpacas is the result of a c.376G>A (p.Gly126Arg) SNP in exon 3 of KIT. These data also support the hypothesis that the grey phenotype is autosomal dominant and that the mutation is most likely homozygous lethal.

Data integration for identification of important transcription factors of STAT6-mediated cell fate decisions

Data integration has become a useful strategy for uncovering new insights into complex biological networks. We studied whether this approach can help to delineate the signal transducer and activator of transcription 6 (STAT6)-mediated transcriptional network driving T helper (Th) 2 cell fate decisions. To this end, we performed an integrative analysis of publicly available RNA-seq data of Stat6-knockout mouse studies together with STAT6 ChIP-seq data and our own gene expression time series data during Th2 cell differentiation. We focused on transcription factors (TFs), cytokines, and cytokine receptors and delineated 59 positively and 41 negatively STAT6-regulated genes, which were used to construct a transcriptional network around STAT6. The network illustrates that important and well-known TFs for Th2 cell differentiation are positively regulated by STAT6 and act either as activators for Th2 cells (e.g., Gata3, Atf3, Satb1, Nfil3, Maf, and Pparg) or as suppressors for other Th cell subpopulations such as Th1 (e.g., Ar), Th17 (e.g., Etv6), or iTreg (e.g., Stat3 and Hif1a) cells. Moreover, our approach reveals 11 TFs (e.g., Atf5, Creb3l2, and Asb2) with unknown functions in Th cell differentiation. This fact together with the observed enrichment of asthma risk genes among those regulated by STAT6 underlines the potential value of the data integration strategy used here. Thus, our results clearly support the opinion that data integration is a useful tool to delineate complex physiological processes.

Final height, target height and the community

Height varies with age, and it varies with historic time. Final height is determined by endocrine parameters and genetics, by nutrition and health, by environmental factors, by birth weight, early growth, BMI, and developmental tempo. European populations of the 19th century were short, but their shortness did not result from growth impairment at all ages. In those days, shortness was mainly due to a significantly blunted adolescent growth spurt. New modelling approaches suggest an independent regulation of adolescent growth and final height: the target for growth and final height appears to be set by the community. In order to test this hypothesis, we formed a geographic network of Switzerland consisting of 169 nodes (district capitals) and 335 connecting edges (roads), and investigated military conscript data obtained between 2004 and 2009. Average height of Swiss military conscripts was 178.2 cm (SD 6.5 cm). But conscripts from first order neighbouring districts were more similar in height than expected. Short stature districts have short, tall stature districts have tall neighbours. We found significant height correlations between 1st (r=0.58), 2nd (r=0.64), 3rd (r=0.45) and even 4th order neighbours (r=0.42). It appears that tall stature communities generate tall people, short stature communities generate short people, and migrants orientate towards the new height target of their host population (community effect on growth).

Adolescent growth: genes, hormones and the peer group. Proceedings of the 20th Aschauer Soiree, held at Glücksburg castle, Germany, 15th to 17th November 2013

The association between poverty, malnutrition, illness and poor socioeconomic conditions on the one side, and poor growth and short adult stature on the other side, is well recognized. Yet, the simple assumption by implication that poor growth and short stature result from poor living conditions, should be questioned. Recent evidence on the impact of the social network on adolescent growth and adult height further challenges the traditional concept of growth being a mirror of health. Twenty-nine scientists met at Glücksburg castle, Northern Germany, November 15th - 17th 2013, to discuss genetic, endocrine, mathematical and psychological aspects and related issues, of child and adolescent growth and final height.

Association of intraoperative blood pressure instability with adverse outcomes after liver transplantation

BACKGROUND

Blood pressure derangements are common in orthotopic liver transplantation (OLT), and are potentially associated with adverse outcomes if they are sustained. While this concept is often believed to be true, few have rigorously demonstrated the validity of this claim, especially in likely vulnerable OLT patients.

METHODS

We retrospectively investigated 827 patients who underwent OLT to determine the magnitude of these hemodynamic associations with adverse outcomes. The median value of the mean arterial pressure (MAP) and the fractional change in the median MAP between subsequent epochs (FCM) were calculated for every 5-minute epoch intraoperatively. Epochs were classified according to prespecified ranges of MAP and fractional changes in MAP (lability) between epochs. Multivariate stepwise logistic regression was used to model associations of risk factors and epochs of intraoperative blood pressure (BP) instability with primary (30-day mortality and/or graft failure) and secondary adverse outcomes.

RESULTS

Primary adverse outcomes occurred in 10.9% and 12.2% of patients for 30-day mortality and 30-day graft failure, respectively. Independent hemodynamic predictors for 30-day mortality and graft failure included sustained periods of MAP <50 mmHg and BP lability where the MAP changed >25%. All of these values were statistically significant.

CONCLUSION

Although severe intraoperative hypotension and BP lability during OLT are often observed in current practice as consequences of major surgical manipulations and patient vulnerability, these are likely not benign conditions based on this retrospective analysis. Prospective trials are warranted to investigate the possibility that interventions tailored to avoidance of hypotension and BP lability may improve outcomes.

Efficacy and Stability of Integrating Fungicide and Cultivar Resistance to Manage Fusarium Head Blight and Deoxynivalenol in Wheat

Integration of host resistance and prothioconazole + tebuconazole fungicide application at anthesis to manage Fusarium head blight (FHB) and deoxynivalenol (DON) in wheat was evaluated using data from over 40 trials in 12 U.S. states. Means of FHB index (index) and DON from up to six resistance class-fungicide management combinations per trial (susceptible treated [S_TR] and untreated [S_UT]; moderately susceptible treated [MS_TR] and untreated [MS_UT]; moderately resistant treated [MR_TR] and untreated [MR_UT]) were used in multivariate meta-analyses, and mean log response ratios across trials were estimated and transformed to estimate mean percent control ( ) due to the management combinations relative to S_UT. All combinations led to a significant reduction in index and DON (P < 0.001). MR_TR was the most effective combination, with a of 76% for index and 71% for DON, followed by MS_TR (71 and 58%, respectively), MR_UT (54 and 51%, respectively), S_TR (53 and 39%, respectively), and MS_UT (43 and 30%, respectively). Calculations based on the principle of treatment independence showed that the combination of fungicide application and resistance was additive in terms of percent control for index and DON. Management combinations were ranked based on percent control relative to S_UT within each trial, and nonparametric analyses were performed to determine management combination stability across environments (trials) using the Kendall coefficient of concordance (W). There was a significant concordance of management combinations for both index and DON (P < 0.001), indicating a nonrandom ranking across environments and relatively low variability in the within-environment ranking of management combinations. MR_TR had the highest mean rank (best control relative to S_UT) and was one of the most stable management combinations across environments, with low rank stability variance (0.99 for index and 0.67 for DON). MS_UT had the lowest mean rank (poorest control) but was also one of the most stable management combinations. Based on Piepho's nonparametric rank-based variance homogeneity U test, there was an interaction of management combination and environment for index (P = 0.011) but not for DON (P = 0.147), indicating that the rank ordering for index depended somewhat on environment. In conclusion, although the magnitude of percent control will likely vary among environments, integrating a single tebuconazole + prothioconazole application at anthesis with cultivar resistance will be a more effective and stable management practice for both index and DON than either approach used alone.

Baculoviruses expressing the human familial Alzheimer's disease presenilin 1 mutation lacking exon 9 increase levels of an amyloid beta-like protein in Sf9 cells

Presenilin 1 (PS1) plays a pivotal role in the production of the amyloid-beta protein (Abeta) that is central to the pathogenesis of Alzheimer's disease. PS1 regulates the intramembranous proteolysis of a 99-amino-acid C-terminal fragment of the amyloid precursor protein (APP-C99), a cleavage event that releases Abeta following a reaction catalyzed by an enzyme termed 'gamma-secretase'. The molecular mechanism of PS1-mediated, gamma-secretase cleavage remains largely unresolved. In particular, controversy surrounds whether PS1 includes the catalytic site of the gamma-secretase protease or whether instead PS1 mediates gamma-secretase activity indirectly, perhaps by regulating the trafficking or presentation of substrates to the 'authentic' protease, which may be a molecule distinct from PS1. To address this issue, the baculovirus expression system was used to co-express: (i) APP-C99; (ii) a pathogenic, constitutively active mutant form of PS1 lacking exon 9 (PS1DeltaE9); (iii) nicastrin and (iv) tropomyosin in Spodoptera frugiperda (Sf9) cells. Cells infected with APP-C99 alone produced an Abeta-like species, and levels of this species were enhanced by the addition of baculoviruses bearing the PS1DeltaE9 mutation. The addition to APP-C99-infected cells of baculoviruses bearing nicastrin, also a transmembrane protein, had a neutral or inhibitory effect on the reaction; tropomyosin viruses had the same effect as nicastrin viruses. These results suggest that PS1DeltaE9 molecules expressed in Sf9 cells retain the ability to modulate Abeta levels. Baculoviral-expressed PS1DeltaE9 provides a source of microgram quantities of bioactive molecules for use as starting material for purifying and reconstituting gamma-secretase activity from its individual purified component parts.

Microsatellite analysis of genetic diversity in wild and farmed Emus (Dromaius novaehollandiae)

The emu (Dromaius novaehollandiae) occupies most regions of the Australian continent and in recent times has been farmed for meat, oil, and leather. Very little is known about the genetic structure of natural or farmed populations of these birds. We report a preliminary study of genetic variation in emus undertaken by typing birds from five farms and two natural populations at five polymorphic microsatellite loci. Genetic diversity was high for all populations and there was little evidence of inbreeding, with most populations conforming to Hardy-Weinberg equilibrium for most loci. Significant heterozygote deficiencies at one locus in a number of populations were detected and may indicate the presence of null alleles. Comparisons of allele frequencies showed little evidence of genetic differentiation either among farmed populations or between farmed and natural populations.

Decreased MK-801 binding in discrete hippocampal regions of prion-infected mice

The neurochemical alterations associated with neurodegeneration in prion diseases are not well defined. It is therefore of interest to study the influence of prion infection on messenger molecules and their receptors. In the present study we have analyzed the possible involvement of NMDA receptors in prion-infected mice using ligand binding autoradiography and iodinated MK-801, a noncompetitive NMDA antagonist. The results show a reduced binding of MK-801 in discrete regions of hippocampus at 110 days after infection, that is before the appearance of behavioral symptoms. In addition, early transient increases in MK-801 binding were observed in several layers. The exact neuroanatomical correlate of these changes in MK-801 binding, as well as its functional significance in relation to prion symptomatology, remain to be analyzed.

Cryptic epitopes in N-terminally truncated prion protein are exposed in the full-length molecule: dependence of conformation on pH

Prion diseases are diseases of protein conformation. Structure-dependent antibodies have been sought to probe conformations of the prion protein (PrP) resulting from environmental changes, such as differences in pH. Despite the absence of such antibodies for full-length PrP, a recombinant Fab (D13) and a Fab derived from mAb 3F4 showed pH-dependent reactivity toward epitopes within the N-terminus of N-terminally truncated PrP(90-231). Refolding and maintaining this protein at pH > or =5.2 before immobilization on an ELISA plate inhibited reactivity relative to protein exposed to pH < or =4.7. The reactivity was not affected by pH changes after immobilization, showing retention of conformation after binding to the plate surface, although guanidine hydrochloride at 1.5-2 M was able to expose the cryptic epitopes after immobilization at pH > or =5.2. The alpha-helical CD spectrum of PrP(90-231) refolded at pH 5.5 was reduced somewhat by these pH changes, with a minor shift toward beta-sheet at pH 4 and then toward coil at pH 2. No covalent changes were caused by the pH differences. This pH dependence suggests titration of an acidic region that might inhibit the N-terminal epitopes. A similar pH dependence for a monoclonal antibody reactive to the central region identified an acidic region incorporating Glu152 as a significant participant.

Efficiency and toxicity of liposome-mediated gene transfer to corneal endothelial cells

Gene transfer to corneal endothelial cells could be an important advance to modulate functions of these critical cells and is a field of current investigations. The development of gene transfer methods is a prerequisite for gene therapy to realize its full potential. We attempted to investigate and optimize the efficacy and safety of cationic liposome mediated gene transfer into corneal endothelial cells using different lipid formulations. Mono- and polycationic lipids and the neutral helper lipid dioleolphosphotidyl-ethanolamine (DOPE) were used for preparation of cationic liposomes. Six liposomal formulations containing DAC/DOPE 30/70 (DAC 30), DOSGA/DOPE 30/70 (DOSGA 30), DOSGA 100, DMRIE/DOPE 50/50 (DMRIE 50) and SP/DOPE 20/80 (SP 20) were complexed with the pUT 651-plasmid, encoding the E. coli beta-galactosidase gene. Subconfluent primary and passaged bovine corneal endothelial cells (BCEC) were transfected with different amounts of liposomes and DNA or uncomplexed free DNA as control. Quantitative expression of beta-galactosidase was measured using a colorimetric assay. In order to assess the effects on cell viability and growth, a modified acidic phosphatase assay was employed. Differences were detected using these various liposome preparations. Transfection experiments demonstrated the highest gene expression using SP 20> DMRIE 50 ranging at approximately 3 mU per beta-gal per well. Low expression of beta-galactosidase was achieved using DAC 30, DOSGA 30 and DOSGA 100. No beta-galactosidase expression was found in control dishes. There was no difference seen following transfection of primary or subsequent passages of BCEC. As indicated by the acid phosphatase assay, no significant toxicity was detected for the most efficient lipids used. Of the preparations studied, SP 20 appeared as the optimal vehicle for plasmid-mediated transfection of BCEC. The ability to deliver genes to BCEC via liposomes could be valuable, since the use of other vectors for transfection may be limited by undesired effects.

Copper-catalyzed oxidation of the recombinant SHa(29-231) prion protein

Metal-catalyzed oxidation may result in structural damage to proteins and has been implicated in aging and disease, including neurological disorders such as Alzheimer's disease and amyotrophic lateral sclerosis. The selective modification of specific amino acid residues with high metal ion affinity leads to subtle structural changes that are not easy to detect but may have dramatic consequences on physical and functional properties of the oxidized protein molecules. PrP contains a histidine-rich octarepeat domain that binds copper. Because copper-binding histidine residues are particularly prone to metal-catalyzed oxidation, we investigated the effect of this reaction on the recombinant prion protein SHaPrP(29-231). Using Cu2+/ascorbate, we oxidized SHaPrP(29-231) in vitro. Oxidation was demonstrated by liquid chromatography/mass spectrometry, which showed the appearance of protein species of higher mass, including increases in multiples of 16, characteristic of oxygen incorporation. Digestion studies using Lys C indicate that the 29-101 region, which includes the histidine-containing octarepeats, is particularly affected by oxidation. Oxidation was time- and copper concentration-dependent and was evident with copper concentrations as low as 1 microM. Concomitant with oxidation, SHaPrP(29-231) suffered aggregation and precipitation, which was nearly complete after 15 min, when the prion protein was incubated at 37 degrees C with a 6-fold molar excess of Cu2+. These findings indicate that PrP, a copper-binding protein, may be particularly susceptible to metal-catalyzed oxidation and that oxidation triggers an extensive structural transition leading to aggregation.

Strain-specified relative conformational stability of the scrapie prion protein

Studies of prion biology and diseases have elucidated several new concepts, but none was more heretical than the proposal that the biological properties that distinguish different prion strains are enciphered in the disease-causing prion protein (PrP(Sc)). To explore this postulate, we examined the properties of PrP(Sc) from eight prion isolates that propagate in Syrian hamster (SHa). Using resistance to protease digestion as a marker for the undenatured protein, we examined the conformational stabilities of these PrP(Sc) molecules. All eight isolates showed sigmoidal patterns of transition from native to denatured PrP(Sc) as a function of increasing guanidine hydrochloride (GdnHCl) concentration. Half-maximal denaturation occurred at a mean value of 1.48 M GdnHCl for the Sc237, HY, SHa(Me7), and MT-C5 isolates, all of which have approximately 75-d incubation periods; a concentration of 1.08 M was found for the DY strain with a approximately 170-d incubation period and approximately 1.25 M for the SHa(RML) and 139H isolates with approximately 180-d incubation periods. A mean value of 1.39 M GdnHCl for the Me7-H strain with a approximately 320-d incubation period was found. Based on these results, the eight prion strains segregated into four distinct groups. Our results support the unorthodox proposal that distinct PrP(Sc) conformers encipher the biological properties of prion strains.

Quantitative trait loci affecting prion incubation time in mice

Although the gene encoding prion protein (PrP) is the major determinant of susceptibility to prion disease, other genes also affect prion incubation time in mice and may be involved in prion replication. Scrapie incubation time was analyzed as a quantitative trait using crosses between SJL/J and CAST/Ei mice; these mouse strains encode identical PrP molecules but have different incubation periods. Our analysis revealed loci on Chromosomes 9 and 11 that affect prion susceptibility.

Optimization of nonviral gene transfer of vascular smooth muscle cells in vitro and in vivo

Gene therapy strategies for the prevention of restenosis postangioplasty are promising. Nonviral gene transfer to the arterial wall in vivo has so far been limited by poor efficiency. This study aimed to optimize transfection of primary vascular smooth muscle cells using cationic nonviral formulations based on cholesterol derivates (DC-, DAC-, DCQ-, and Sp-Chol), double-chained amphiphils (LipofectAMINE, DOTMA, DOSGA, DOSPER, and DOCSPER), or heterogeneous reagents (Superfect, Effectene, and Tfx-50). Estimation of transfection efficiencies was performed using galactosidase assays at different ratios of transfection reagent to plasmid DNA with reporter gene. Toxicity was monitored by analyzing cell metabolism. Transfer efficiency and safety were determined in a porcine restenosis model for local gene therapy using morphometry, histology, galactosidase assays, and reverse-transcriptase polymerase chain reaction. The highest in vitro transfection efficiency was achieved using the recently developed DOCSPER liposomes, with transfer rates of at least 20% in vascular smooth muscle cells. Transfer efficiency was further enhanced up to 20% by complexing with poly-L-lysine. Transfection efficiency in vivo in a porcine restenosis model was up to 15% of adventitial cells using DOCSPER versus 0.1% using LipofectAMINE. Toxicity in vivo and in vitro was lowest using DOCSPER. Increased biological effects were demonstrated following optimization of transfer conditions.

Self-assembly of recombinant prion protein of 106 residues

The central event in the pathogenesis of prion diseases is a profound conformational change of the prion protein (PrP) from an alpha-helical (PrP(C)) to a beta-sheet-rich isoform (PrP(Sc)). The elucidation of the mechanism of conformational transition has been complicated by the challenge of collecting high-resolution biophysical data on the relatively insoluble aggregation-prone PrP(Sc) isoform. In an attempt to facilitate the structural analysis of PrP(Sc), a redacted chimeric mouse-hamster PrP of 106 amino acids (MHM2 PrP106) with two deletions (Delta23-88 and Delta141-176) was expressed and purified from Escherichia coli. PrP106 retains the ability to support PrP(Sc) formation in transgenic mice, implying that it contains all regions of PrP that are necessary for the conformational transition into the pathogenic isoform [Supattapone, S., et al. (1999) Cell 96, 869-878]. Unstructured at low concentrations, recombinant unglycosylated PrP106 (rPrP106) undergoes a concentration-dependent conformational transition to a beta-sheet-rich form. Following the conformational transition, rPrP106 possesses properties similar to those of PrP(Sc)106, such as high beta-sheet content, defined tertiary structure, resistance to limited digestion by proteinase K, and high thermodynamic stability. In GdnHCl-induced denaturation studies, a single cooperative conformational transition between the unstructured monomer and the assembled beta-oligomer was observed. After proteinase K digestion, the oligomers retain an intact core with unusually high beta-sheet content (>80%). Using mass spectrometry, we discovered that the region of residues 134-215 of rPrP106 is protected from proteinase K digestion and possesses a solvent-independent propensity to adopt a beta-sheet-rich conformation. In contrast to the PrP(Sc)106 purified from the brains of neurologically impaired animals, multimeric beta-rPrP106 remains soluble, providing opportunities for detailed structural studies.

A synthetic peptide initiates Gerstmann-Sträussler-Scheinker (GSS) disease in transgenic mice

The molecular basis of the infectious, inherited and sporadic forms of prion diseases is best explained by a conformationally dimorphic protein that can exist in distinct normal and disease-causing isoforms. We identified a 55-residue peptide of a mutant prion protein that can be refolded into at least two distinct conformations. When inoculated intracerebrally into the appropriate transgenic mouse host, 20 of 20 mice receiving the beta-form of this peptide developed signs of central nervous system dysfunction at approximately 360 days, with neurohistologic changes that are pathognomonic of Gerstmann-Sträussler-Scheinker disease. By contrast, eight of eight mice receiving a non-beta-form of the peptide failed to develop any neuropathologic changes more than 600 days after the peptide injections. We conclude that a chemically synthesized peptide refolded into the appropriate conformation can accelerate or possibly initiate prion disease.

Transmissible and genetic prion diseases share a common pathway of neurodegeneration

Prion diseases can be infectious, sporadic and genetic. The infectious forms of these diseases, including bovine spongiform encephalopathy and Creutzfeldt-Jakob disease, are usually characterized by the accumulation in the brain of the transmissible pathogen, an abnormally folded isoform of the prion protein (PrP) termed PrPSc. However, certain inherited PrP mutations appear to cause neurodegeneration in the absence of PrPSc, working instead by favoured synthesis of CtmPrP, a transmembrane form of PrP. The relationship between the neurodegeneration seen in transmissible prion diseases involving PrPSc and that associated with ctmPrP has remained unclear. Here we find that the effectiveness of accumulated PrPSc in causing neurodegenerative disease depends upon the predilection of host-encoded PrP to be made in the ctmPrP form. Furthermore, the time course of PrPSc accumulation in transmissible prion disease is followed closely by increased generation of CtmPrP. Thus, the accumulation of PrPSc appears to modulate in trans the events involved in generating or metabolising CtmPrP. Together, these data suggest that the events of CtmPrP-mediated neurodegeneration may represent a common step in the pathogenesis of genetic and infectious prion diseases.

Glycosylation differences between the normal and pathogenic prion protein isoforms

Prion protein consists of an ensemble of glycosylated variants or glycoforms. The enzymes that direct oligosaccharide processing, and hence control the glycan profile for any given glycoprotein, are often exquisitely sensitive to other events taking place within the cell in which the glycoprotein is expressed. Alterations in the populations of sugars attached to proteins can reflect changes caused, for example, by developmental processes or by disease. Here we report that normal (PrP(C)) and pathogenic (PrP(Sc)) prion proteins (PrP) from Syrian hamsters contain the same set of at least 52 bi-, tri-, and tetraantennary N-linked oligosaccharides, although the relative proportions of individual glycans differ. This conservation of structure suggests that the conversion of PrP(C) into PrP(Sc) is not confined to a subset of PrPs that contain specific sugars. Compared with PrP(C), PrP(Sc) contains decreased levels of glycans with bisecting GlcNAc residues and increased levels of tri- and tetraantennary sugars. This change is consistent with a decrease in the activity of N-acetylglucosaminyltransferase III (GnTIII) toward PrP(C) in cells where PrP(Sc) is formed and argues that, in at least some cells forming PrP(Sc), the glycosylation machinery has been perturbed. The reduction in GnTIII activity is intriguing both with respect to the pathogenesis of the prion disease and the replication pathway for prions.

Necrotizing fasciitis due to appendicitis

Necrotizing fasciitis, although rare, is one of the more serious, life-threatening complications of missed acute appendicitis. Patients who are predisposed to developing necrotizing fasciitis, regardless of the cause, are typically immunocompromised. We present a case of a 49-year-old immunocompetent female whose diagnosis of acute appendicitis was missed and who subsequently developed necrotizing fasciitis of the abdominal wall and flank. She recovered 1 month after admission due to aggressive surgical and medical therapy.

Solution structure of Syrian hamster prion protein rPrP(90-231)

NMR has been used to refine the structure of Syrian hamster (SHa) prion protein rPrP(90-231), which is commensurate with the infectious protease-resistant core of the scrapie prion protein PrPSc. The structure of rPrP(90-231), refolded to resemble the normal cellular isoform PrPC spectroscopically and immunologically, has been studied using multidimensional NMR; initial results were published [James et al. (1997) Proc. Natl. Acad. Sci. U.S.A. 94, 10086-10091]. We now report refinement with better definition revealing important structural and dynamic features which can be related to biological observations pertinent to prion diseases. Structure refinement was based on 2778 unambiguously assigned nuclear Overhauser effect (NOE) connectivities, 297 ambiguous NOE restraints, and 63 scalar coupling constants (3JHNHa). The structure is represented by an ensemble of 25 best-scoring structures from 100 structures calculated using ARIA/X-PLOR and further refined with restrained molecular dynamics using the AMBER 4.1 force field with an explicit shell of water molecules. The rPrP(90-231) structure features a core domain (residues 125-228), with a backbone atomic root-mean-square deviation (RMSD) of 0.67 A, consisting of three alpha-helices (residues 144-154, 172-193, and 200-227) and two short antiparallel beta-strands (residues 129-131 and 161-163). The N-terminus (residues 90-119) is largely unstructured despite some sparse and weak medium-range NOEs implying the existence of bends or turns. The transition region between the core domain and flexible N-terminus, i.e., residues 113-128, consists of hydrophobic residues or glycines and does not adopt any regular secondary structure in aqueous solution. There are about 30 medium- and long-range NOEs within this hydrophobic cluster, so it clearly manifests structure. Multiple discrete conformations are evident, implying the possible existence of one or more metastable states, which may feature in conversion of PrPC to PrPSc. To obtain a more comprehensive picture of rPrP(90-231), dynamics have been studied using amide hydrogen-deuterium exchange and 15N NMR relaxation times (T1 and T2) and 15N{1H} NOE measurements. Comparison of the structure with previous reports suggests sequence-dependent features that may be reflected in a species barrier to prion disease transmission.

Eight prion strains have PrP(Sc) molecules with different conformations

Variations in prions, which cause different incubation times and deposition patterns of the prion protein isoform called PrP(Sc), are often referred to as 'strains'. We report here a highly sensitive, conformation-dependent immunoassay that discriminates PrP(Sc) molecules among eight different prion strains propagated in Syrian hamsters. This immunoassay quantifies PrP isoforms by simultaneously following antibody binding to the denatured and native forms of a protein. In a plot of the ratio of antibody binding to denatured/native PrP graphed as a function of the concentration of PrP(Sc), each strain occupies a unique position, indicative of a particular PrP(Sc) conformation. This conclusion is supported by a unique pattern of equilibrium unfolding of PrP(Sc) found with each strain. Our findings indicate that each of the eight prion strains has a PrP(Sc) molecule with a unique conformation and, in accordance with earlier results, indicate the biological properties of prion strains are 'enciphered' in the conformation of PrP(Sc) and that the variation in incubation times is related to the relative protease sensitivity of PrP(Sc) in each strain.

Identification of a prion protein epitope modulating transmission of bovine spongiform encephalopathy prions to transgenic mice

There is considerable concern that bovine prions from cattle with bovine spongiform encephalopathy (BSE) may have been passed to humans (Hu), resulting in a new form of Creutzfeldt-Jakob disease (CJD). We report here the transmission of bovine (Bo) prions to transgenic (Tg) mice expressing BoPrP; one Tg line exhibited incubation times of approximately 200 days. Like most cattle with BSE, vacuolation and astrocytic gliosis were confined in the brainstems of these Tg mice. Unexpectedly, mice expressing a chimeric Bo/Mo PrP transgene were resistant to BSE prions whereas mice expressing Hu or Hu/Mo PrP transgenes were susceptible to Hu prions. A comparison of differences in Mo, Bo, and Hu residues within the C terminus of PrP defines an epitope that modulates conversion of PrPC into PrPSc and, as such, controls prion transmission across species. Development of susceptible Tg(BoPrP) mice provides a means of measuring bovine prions that may prove critical in minimizing future human exposure.

Structure of the recombinant full-length hamster prion protein PrP(29-231): the N terminus is highly flexible

The prion diseases seem to be caused by a conformational change of the prion protein (PrP) from the benign cellular form PrPC to the infectious scrapie form PrPSc; thus, detailed information about PrP structure may provide essential insights into the mechanism by which these diseases develop. In this study, the secondary structure of the recombinant Syrian hamster PrP of residues 29-231 [PrP(29-231)] is investigated by multidimensional heteronuclear NMR. Chemical shift index analysis and nuclear Overhauser effect data show that PrP(29-231) contains three helices and possibly one short beta-strand. Most striking is the random-coil nature of chemical shifts for residues 30-124 in the full-length PrP. Although the secondary structure elements are similar to those found in mouse PrP fragment PrP(121-231), the secondary structure boundaries of PrP(29-231) are different from those in mouse PrP(121-231) but similar to those found in the structure of Syrian hamster PrP(90-231). Comparison of resonance assignments of PrP(29-231) and PrP(90-231) indicates that there may be transient interactions between the additional residues and the structured core. Backbone dynamics studies done by using the heteronuclear [1H]-15N nuclear Overhauser effect indicate that almost half of PrP(29-231), residues 29-124, is highly flexible. This plastic region could feature in the conversion of PrPC to PrPSc by template-assisted formation of beta-structure.

Propagation of prion strains through specific conformers of the prion protein

Two prion strains with identical incubation periods in mice exhibited distinct incubation periods and different neuropathological profiles upon serial transmission to transgenic mice expressing chimeric Syrian hamster/mouse (MH2M) prion protein (PrP) genes [Tg(MH2M) mice] and subsequent transmission to Syrian hamsters. After transmission to Syrian hamsters, the Me7 strain was indistinguishable from the previously established Syrian hamster strain Sc237, despite having been derived from an independent ancestral source. This apparent convergence suggests that prion diversity may be limited. The Me7 mouse strain could also be transmitted directly to Syrian hamsters, but when derived in this way, its properties were distinct from those of Me7 passaged through Tg(MH2M) mice. The Me7 strain did not appear permanently altered in either case, since the original incubation period could be restored by effectively reversing the series of passages. Prion diversity enciphered in the conformation of the scrapie isoform of PrP (PrP(Sc)) (G. C. Telling et al., Science 274:2079-2082, 1996) seems to be limited by the sequence of the PrP substrates serially converted into PrP(Sc), while prions are propagated through interactions between the cellular and scrapie isoforms of PrP.

Selective neuronal targeting in prion disease

The pattern of scrapie prion protein (PrP(Sc)) accumulation in the brain is different for each prion strain. We tested whether the PrP(Sc) deposition pattern is influenced by the Asn-linked oligosaccharides of PrP(C) in transgenic mice. Deletion of the first oligosaccharide altered PrP(C) trafficking and prevented infection with two prion strains. Deletion of the second did not alter PrP(C) trafficking, permitted infection with one prion strain, and had a profound effect on the PrP(Sc) deposition pattern. Our data raise the possibility that glycosylation can modify the conformation of PrP(C). Glycosylation could affect the affinity of PrP(C) for a particular conformer of PrP(Sc), thereby determining the rate of nascent PrP(Sc) formation and the specific patterns of PrP(Sc) deposition.

Marked decrease of neuropeptide Y Y2 receptor binding sites in the hippocampus in murine prion disease

Using autoradiographic binding methodology with monoiodinated peptide YY together with the agonists neuropeptide Y (NPY) and NPY (13-36), as well as in situ hybridization with oligonucleotide probes complementary to the NPY Y2 receptor (Y2-R) mRNA, we have studied whether or not intracerebral prion inoculation affects Y2-Rs in male CD-1 mice. Monoiodinated peptide YY binding, mainly representing Y2-Rs, was down-regulated by 85% in the CA1 strata oriens and radiatum and by 50-65% in the CA3 stratum oriens 110-140 days postinoculation. In the CA3 stratum radiatum, where the mossy fibers from the dentate granule cells project, there was a significant decrease in PYY binding at 110-120 days. Y2-R mRNA, moderately expressed both in the CA1 and CA3 pyramidal cell layers and the granule cell layer in the dentate gyrus, showed a slight, but not significant, decrease in CA3 neurons 130 days postinoculation. The results indicate that the accumulation of the scrapie prion protein in the CA1-3 region strongly inhibits NPY binding at the Y2-Rs, which, however, is only marginally due to reduced Y2-R mRNA expression. The loss of the ability of NPY to bind to inhibitory Y2-Rs may cause dysfunction of hippocampal circuits and may contribute to the clinical symptoms in mouse scrapie.

Difference between lambs with chronic and mild dermatophilosis in frequency of alleles of CD3 gamma

Southern blots prepared with DNA from 20 Merino lambs that previously had chronic dermatophilosis (chronic) and 20 lambs that previously had mild dermatophilosis lesions (resistant) were hybridised with DNA sequences of the genes for the T-cell receptor-beta (TCR beta), a TCR-associated peptide 'cluster designation 3 gamma chain' (CD3 gamma) and ovine Major Histocompatibility Complex class 1 (ov. MHC class 1). There was a significant difference in the incidence of an allele of CD3 gamma between the chronic and resistant lambs. No significant difference in the incidence of alleles of TCR beta or ov. MHC class 1 was detected.

Solution structure of a 142-residue recombinant prion protein corresponding to the infectious fragment of the scrapie isoform

The scrapie prion protein (PrPSc) is the major, and possibly the only, component of the infectious prion; it is generated from the cellular isoform (PrPC) by a conformational change. N-terminal truncation of PrPSc by limited proteolysis produces a protein of approximately 142 residues designated PrP 27-30, which retains infectivity. A recombinant protein (rPrP) corresponding to Syrian hamster PrP 27-30 was expressed in Escherichia coli and purified. After refolding rPrP into an alpha-helical form resembling PrPC, the structure was solved by multidimensional heteronuclear NMR, revealing many structural features of rPrP that were not found in two shorter PrP fragments studied previously. Extensive side-chain interactions for residues 113-125 characterize a hydrophobic cluster, which packs against an irregular beta-sheet, whereas residues 90-112 exhibit little defined structure. Although identifiable secondary structure is largely lacking in the N terminus of rPrP, paradoxically this N terminus increases the amount of secondary structure in the remainder of rPrP. The surface of a long helix (residues 200-227) and a structured loop (residues 165-171) form a discontinuous epitope for binding of a protein that facilitates PrPSc formation. Polymorphic residues within this epitope seem to modulate susceptibility of sheep and humans to prion disease. Conformational heterogeneity of rPrP at the N terminus may be key to the transformation of PrPC into PrPSc, whereas the discontinuous epitope near the C terminus controls this transition.

Genetic analysis of the freshwater crayfish Cherax tenuimanus

The marron (Cherax tenuimanus) is one of the few species of freshwater crayfish native to Australia that is suitable for aquaculture and occurs only in the southwest of Western Australia. This study describes polymorphic microsatellite markers which differentiate marron populations from several geographically distinct regions (including rivers and streams, dams, and commercial marron farms) throughout Western Australia. Twenty microsatellite loci, primarily of the (CA)n. (GT)n type, were isolated and sequenced from a marron cosmid library. Three of these loci were characterised further. Two loci exhibited extensive polymorphism and one was monomorphic. The polymorphic loci exhibited Mendelian codominant inheritance in the family group comprising two individual parents and approximately 100 offspring bred for this study. These loci permitted differentiation between the five geographically distinct populations studied and thus provide a basis for genetic characterisation of marron stock in Western Australia.

Physical studies of conformational plasticity in a recombinant prion protein

PrP(Sc) is known to be the major, if not the only, component of the infectious prion. Limited proteolysis of PrP(Sc) produces an N-terminally truncated polypeptide of about 142 residues, designated PrP 27-30. Recently, a recombinant protein (rPrP) of 142 residues corresponding to the Syrian hamster PrP 27-30 was expressed in Escherichia coli and purified (Mehlhorn et al., 1996). rPrP has been refolded into both alpha-helical and beta-sheet structures as well as various intermediates in aqueous buffers. The beta-sheet state and two pH-dependent alpha-helical states were characterized by CD and NMR. The alpha-helical conformation occurred only after the formation of an intramolecular disulfide bond, whereas the beta-sheet form was accessible either with or without the disulfide. Of the different alpha-helical forms studied, only those refolded in the pH range 5-8 were substantially soluble at physiological pH, exhibiting similar conformations and monomeric analytical sedimentation profiles throughout the above pH range. Furthermore, refolded alpha-rPrP showed NMR chemical shift dispersion typical of proteins with native conformations, although 2D NMR indicated large segments of conformational flexibility. It displayed a cooperative thermal denaturation transition; at elevated temperatures, it converted rapidly and irreversibly to the thermodynamically more stable beta-sheet form. Unfolding of alpha-rPrP by GdnHCl revealed a two-phase transition with a relatively stable folding intermediate at 2 M GdnHCl. The deltaG values were estimated to be 1.9 +/- 0.4 kcal/mol for the first phase and 6.5 +/- 1.2 kcal/mol for the second, consistent with a folding core surrounded by significant segments of flexible conformation. By NMR, alpha-rPrP(acid) isolated at pH 2 without refolding exhibited heterogeneous line widths, consistent with an acid-denatured molten globular state. We conclude that to the extent that rPrP constitutes a relevant folding domain of PrP(C), the various conformations exhibited by rPrP suggest that the PrP sequence may be intrinsically plastic in its conformations; indeed, portions of PrP(C) may possess a relatively open conformation which makes it susceptible to conversion into PrP(Sc) under appropriate conditions.

Failure to transmit disease from gray tremor mutant mice

Mice homozygous for mutant alleles at the gray tremor (gt) locus develop a marked non-intention tremor beginning at 8 days of age. Most homozygous mice die by 3 months. Homozygotes exhibit intense vacuolation of the central nervous system gray matter and vacuolation and hypomyelination of some white matter tracts. Based on neuropathological similarities with scrapie, other investigators inoculated wild-type mice with gray tremor brain homogenates to test the hypothesis of transmissibility. Published reports indicated that spongiform encephalopathy (R. L. Sidman, H. C. Kinney, and H. O. Sweet, Proc. Natl. Acad. Sci. USA 82:253-257, 1985) and disease, including hind limb paralysis in NFS mice (P. M. Hoffman, R. G. Rohwer, C. MacAuley, J. A. Bilello, J. W. Hartley, and H. C. Morse III, Proc. Natl. Acad. Sci. USA 84:3866-3870, 1987), were transmitted by inoculation of gt/gt brain homogenates. In our hands, however, no NFS/NCr animals inoculated intracerebrally with gt/gt or +/+ brain preparations showed any signs of disease or pathological changes in the brain. Positive transmission by other investigators may reflect the microbiological status of their donor or recipient mice.

Aberrant induction of neuropeptide Y mRNA in hippocampal CA3 pyramidal neurones in scrapie-infected mice

The neurochemical alterations preceding neurological dysfunction and neuronal death in prion diseases are not well characterized. Here we examined, using in situ hybridization histochemistry, the expression of neuropeptide Y (NPY), an inducible and abundant neuropeptide in mammalian brain with known neuroregulatory functions, and glial fibrillary acidic protein (GFAP), a marker for astroglial activation, in the hippocampus at different time points following intracerebral prion inoculation in male CD-1 mice. Between 110 and 140 days postinoculation NPY mRNA expression was specifically up-regulated in CA3 pyramidal neurones, whereas expression of NPY in hilar neurones remained unaltered. Up-regulation of GFAP mRNA was observed in the CA1 stratum radiatum at 60 days, and spread throughout the hippocampus, cortex and thalamus between 110 and 140 days, suggesting early accumulation of scrapie prion protein in these regions. The clinical symptoms were first manifested 120 days postinoculation. Aberrant induction of NPY mRNA in the hippocampal CA3 pyramidal neurones preceded the onset of neurological symptoms, and may be involved in the regulation of glutamate release at the Schaffer collateral-CA1 synapses in scrapie-infected mice.

High-level expression and characterization of a purified 142-residue polypeptide of the prion protein

The major, and possible only, component of the infectious prion is the scrapie prion protein (PrPSc); the protease resistant core of PrPSc is PrP 27-30, a protein of approximately 142 amino acids. PrPSc is derived from the cellular PrP isoform (PrPC) by a post-transliatonal process in which a profound conformational change occurs. Syrian hamster (SHa) PrP genes of varying length ranging from the N- and C- terminally truncated 90-228 up to the full-length mature protein 23-231 were inserted into various secretion and intracellular expression vectors that were transformed into Escherichia coli deficient for proteases. Maximum expression was obtained for a truncated SHaPrP containing residues 90-231, which correspond to the sequence of PrP 27-30; disruption of the bacteria using a microfluidizer produced the highest yields of this protein designated rPrP. After solubilization of rPrP in 8 M GdnHC1, it was purified by size exclusion chromatography and reversed phase chromatography. During purification the recovery was approximately 50%, and from each liter of E. coli culture, approximately 50 mg of purified rPrP was obtained. Expression of the longer species containing the basic N-terminal region was less successful and was not pursued further. The primary structure of rPrP was verified by Edman sequencing and mass spectrometry, and secondary structure determined by circular dichroism and Fourier transform infrared spectroscopy. When rPrP was purified under reducing conditions, it had a high beta-sheet content and relatively low solubility similar to PrPSc, particularly at pH values > 7. Refolding of rPrP by oxidation to form a disulfide bond between the two Cys residues of this polypeptide produced a soluble protein with a high alpha-helical content similar to PrPC. These multiple conformations of rPrP are reminiscent of the structural plurality that characterizes the naturally occurring PrP isoforms. The high levels of purified rPrP which can now be obtained should facilitate determination of the multiple tertiary structures that Prp can adopt.

Disruption of prion rods generates 10-nm spherical particles having high alpha-helical content and lacking scrapie infectivity

An abnormal isoform of the prion protein (PrP) designated PrPSc is the major, or possibly the only, component of infectious prions. Structural studies of PrPSc have been impeded by its lack of solubility under conditions in which infectivity is retained. Among the many detergents examined, only treatment with the ionic detergent sodium dodecyl sulfate (SDS) or Sarkosyl followed by sonication dispersed prion rods which are composed of PrP 27-30, an N-terminally truncated form of PrPSc. After ultracentrifugation at 100,000 x g for 1 h, approximately 30% of the PrP 27-30 and scrapie infectivity were found in the supernatant, which was fractionated by sedimentation through 5 to 20% sucrose gradients. Near the top of the gradient, spherical particles with an observed sedimentation coefficient of approximately 6S, approximately 10 mm in diameter and composed of four to six PrP 27-30 molecules, were found. The spheres could be digested with proteinase K and exhibited little, if any, scrapie infectivity. When the prion rods were disrupted in SDS and the entire sample was fractionated by sucrose gradient centrifugation, a lipid-rich fraction at the meniscus composed of fragments of rods and heterogeneous particles containing high levels of prion infectivity was found. Fractions adjacent to the meniscus also contained spherical particles. Circular dichroism of the spheres revealed 60% alpha-helical content; addition of 25% acetonitrile induced aggregates high in beta sheet but remaining devoid of infectivity. Although the highly purified spherical oligomers of PrP 27-30 lack infectivity, they may provide an excellent substrate for determining conditions of renaturation under which prion particles regain infectivity.

Serial transmission in rodents of neurodegeneration from transgenic mice expressing mutant prion protein

Two lines of transgenic (Tg) mice expressing high (H) levels of the mutant P101L prion protein (PrP) developed a neurologic illness and central nervous system pathology indistinguishable from experimental murine scrapie; these mice were designated Tg(MoPrP-P101L)H. Brain homogenates from Tg(MoPrP-P101L)H mice were inoculated intracerebrally into CD-1 Swiss mice, Syrian hamsters, and Tg196 mice, Tg mice expressing the MoPrP-P101L transgene at low levels. None of the CD-1 mice developed central nervous system dysfunction, whereas approximately 10% of hamsters and approximately 40% of the Tg196 mice manifested neurologic signs between 117 and 639 days after inoculation. Serial transmission of neurodegeneration in Tg196 mice and Syrian hamsters was initiated with brain extracts, producing incubation times of approximately 400 and approximately 75 days, respectively. Although the Tg(MoPrP-P101L)H mice appear to accumulate only low levels of infections prions in their brains, the serial transmission of disease to inoculated recipients argues that prion formation occurs de novo in the brains of these uninoculated animals. These Tg mouse studies, taken together with similar findings in humans dying of inherited prion diseases, provide additional evidence that prions lack a foreign nucleic acid.

Prion isolate specified allotypic interactions between the cellular and scrapie prion proteins in congenic and transgenic mice

Different prion isolates, often referred to as "strains," present an enigma because considerable evidence argues that prions are devoid of nucleic acid. To investigate prion diversity, we inoculated three "strains" of prions into congenic and transgenic mice harboring variable numbers of two different alleles, designated a and b, of the prion protein (PrP) structural gene, Prn-p. The length of the incubation time was inversely related to the number of Prn-p(a) genes in mice inoculated with the Rocky Mountain Laboratory (RML) prion strain. Results with mice lacking this locus (Prn-p0/0) and transgenic mice argue that long incubation times are not a dominant trait as thought for many years, but rather they are due to reduced levels of the substrate PrPC-A (cellular isoform of PrP, allotype A) in (Prn-p(a) x Prn-pb)F1 mice. In contrast, the Prn-p(a) gene extended incubation times in mice inoculated with the 87V and 22A prion strains, whereas the Prn-pb gene was permissive. Experiments with the 87V isolate suggest that a genetic locus distinct from Prn-p controls deposition of the scrapie isoform of PrP (PrPSc) and attendant neuropathology. Each prion isolate produced distinguishable patterns of PrPSc accumulation in brain; of note, the patterns in Prn-p(a) and Prn-pb congenic mice inoculated with RML prions were more different than those in congenic Prn-pb mice with RML or 22A prions. Our results suggest that scrapie "strain-specific" incubation times can be explained by differences in the relative efficiency of allotypic interactions that lead to conversion of PrPC into PrPSc.

Spectroscopic characterization of conformational differences between PrPC and PrPSc: an alpha-helix to beta-sheet transition

Although no chemical modifications have been found to distinguish the cellular prion protein PrPC from its infectious analogue PrPSc, spectroscopic methods such as Fourier transform infrared (FTIR) spectroscopy reveal a major conformational difference. PrPC is rich in alpha-helix but is devoid of beta-sheet, whereas PrPSc is high in beta-sheet. N-terminal truncation of PrPSc by limited proteolysis does not destroy infectivity but it increases the beta-sheet content and shifts the FTIR absorption to lower frequencies, typical of the cross beta-pleated sheets of amyloids. Thus the formation of PrPSc from PrPC involves a conformational transition in which one or more alpha-helical regions of the protein is converted to beta-sheet. This transition is mimicked by synthetic peptides, allowing predictions of domains of PrP involved in prion diseases.

The neuropathological phenotype in transgenic mice expressing different prion protein constructs

Neuropathologic examination of transgenic (Tg) mice which express different prion protein (PrP) constructs is essential because spongiform (vacuolar) degeneration of neurons, the distribution of PrPSc and whether PrP amyloid plaques form are the phenotypes of prion diseases. In Tg models of experimental scrapie, it was found that all of the parameters that define prion isolates ('strains') can be manipulated by changing the structure of PrP. In those studies, further evidence that PrPSc causes scrapie neuropathology and determines scrapie incubation time was obtained. In addition, the distribution of PrPSc in the brain was unique for each prion isolate. The implications of these findings are first, that prion isolates target different neuron populations for synthesis of nascent pathogenic PrPSc and, secondly, that prion isolate diversity is determined by neurons. In Tg mice which express mutated PrP mimicking human prion protein gene mutations linked to familial prion diseases, the neuropathological changes have been faithfully reproduced. A new age-related, neuromuscular disorder has also been identified in uninfected Tg mice which overexpress wild-type PrPc. All of the findings with different PrP constructs plus the absence of scrapie pathology in PrP null mice are the strongest argument that the prion protein is the main etiologic and pathogenic factor of prion disorders.

Degeneration of skeletal muscle, peripheral nerves, and the central nervous system in transgenic mice overexpressing wild-type prion proteins

Prion diseases of humans and animals are known to be caused by infection with prions containing PrPSc or mutation of the prion protein (PrP) gene. During transgenetic studies, we discovered that uninoculated older mice harboring high copy numbers of wild-type (wt) PrP transgenes derived from Syrian hamsters (SHa), sheep (She), and PrP-B mice developed truncal ataxia, hindlimb paralysis, and tremors. These transgenic (Tg) mice exhibited a profound necrotizing myopathy involving skeletal muscle, a demyelinating polyneuropathy, and focal vacuolation of the central nervous system. Development of disease was dependent on transgene dosage. For example, half of all Tg(SHaPrP+/+)7 mice homozygous for the SHaPrP transgene array developed disease by approximately 460 days of age, while no hemizygous Tg(SHaPrP+/o)7 mice became ill before 650 days. The novel neurologic syndrome found in older Tg(wtPrP) mice implies that overexpression of wtPrPC is pathogenic and widens the spectrum of prion diseases.