Prions

Stability properties of PrP(Sc) from cattle with experimental transmissible spongiform encephalopathies: use of a rapid whole homogenate, protease-free assay

Background

Transmissible Spongiform Encephalopathies (TSEs), including scrapie in sheep, chronic wasting disease (CWD) in cervids, transmissible mink encephalopathy (TME), and bovine spongiform encephalopathy (BSE), are fatal diseases of the nervous system associated with accumulation of misfolded prion protein (PrP^Sc). Different strains of TSEs exist, associated with different PrP^Sc conformations that can be probed by the stability assay, in which PrP^Sc is treated with increasing concentrations of the denaturant guanidine hydrochloride (GdnHCl).

Results

Here, we provide the first comprehensive application of a rapid, protease-free version of the GdnHCl stability assay to brain tissue from cattle experimentally infected with various TSE isolates. Consistent with previous findings from a single Japanese isolate, the L-type isolates of BSE are not distinguishable from classical BSE in this assay. In contrast, H-type isolates of BSE, including our unique isolate of E211K BSE, exhibit higher stability than classical BSE, suggesting that its increased protection against protease digestion at the BSE N-terminus is associated with a higher stability in GdnHCl. While the difference in stability in our version of the assay is likely not large enough for effective use in a diagnostic laboratory setting, the use of alternative experimental conditions may enhance this effect. TSEs from other natural host species that have been passaged in cattle, including CWD and TME, were not distinguishable from classical BSE, while isolates of cattle passaged scrapie exhibited a slight increase in stability as compared to classical BSE.

Conclusions

These results suggest that the core of PrP^Sc, as probed in this assay, has similar stability properties among cattle-passaged TSE isolates and that the conformational differences that lead to changes in the proteinase K cleavage site do not cause large changes in the stability of PrP^Sc from TSE-affected cattle. However, the stability differences observed here will provide a basis of comparison for new isolates of atypical BSE observed in the future and in other geographic locations, especially in the case of H-type BSE.

In vitro prion protein conversion suggests risk of bighorn sheep (Ovis canadensis) to transmissible spongiform encephalopathies

Background

Transmissible spongiform encephalopathies (TSEs) affect both domestic sheep (scrapie) and captive and free-ranging cervids (chronic wasting disease; CWD). The geographical range of bighorn sheep (Ovis canadensis; BHS) overlaps with states or provinces that have contained scrapie-positive sheep or goats and areas with present epizootics of CWD in cervids. No TSEs have been documented in BHS, but the susceptibility of this species to TSEs remains unknown.

Results

We acquired a library of BHS tissues and found no evidence of preexisting TSEs in these animals. The prion protein gene (Prnp) in all BHS in our library was identical to scrapie-susceptible domestic sheep (A¹³⁶R¹⁵⁴Q¹⁷¹ genotype). Using an in vitro prion protein conversion assay, which has been previously used to assess TSE species barriers and, in our study appears to recollect known species barriers in mice, we assessed the potential transmissibility of TSEs to BHS. As expected based upon Prnp genotype, we observed BHS prion protein conversion by classical scrapie agent and evidence for a species barrier between transmissible mink encephalopathy (TME) and BHS. Interestingly, our data suggest that the species barrier of BHS to white-tailed deer or wapiti CWD agents is likely low. We also used protein misfolding cyclic amplification to confirm that CWD, but not TME, can template prion protein misfolding in A¹³⁶R¹⁵⁴Q¹⁷¹ genotype sheep.

Conclusions

Our results indicate the in vitro conversion assay used in our study does mimic the species barrier of mice to the TSE agents that we tested. Based on Prnp genotype and results from conversion assays, BHS are likely to be susceptible to infection by classical scrapie. Despite mismatches in amino acids thought to modulate prion protein conversion, our data indicate that A¹³⁶R¹⁵⁴Q¹⁷¹ genotype sheep prion protein is misfolded by CWD agent, suggesting that these animals could be susceptible to CWD. Further investigation of TSE transmissibility to BHS, including animal studies, is warranted. The lack of reported TSEs in BHS may be attributable to other host factors or a lack of TSE surveillance in this species.

The story of stolen chaperones: how overexpression of Q/N proteins cures yeast prions

Prions are self-seeding alternate protein conformations. Most yeast prions contain glutamine/asparagine (Q/N)-rich domains that promote the formation of amyloid-like prion aggregates. Chaperones, including Hsp104 and Sis1, are required to continually break these aggregates into smaller “seeds.” Decreasing aggregate size and increasing the number of growing aggregate ends facilitates both aggregate transmission and growth. Our previous work showed that overexpression of 11 proteins with Q/N-rich domains facilitates the de novo aggregation of Sup35 into the [PSI⁺] prion, presumably by a cross-seeding mechanism. We now discuss our recent paper, in which we showed that overexpression of most of these same 11 Q/N-rich proteins, including Pin4C and Cyc8, destabilized pre-existing Q/N rich prions. Overexpression of both Pin4C and Cyc8 caused [PSI⁺] aggregates to enlarge. This is incompatible with a previously proposed “capping” model where the overexpressed Q/N-rich protein poisons, or “caps,” the growing aggregate ends. Rather the data match what is expected of a reduction in prion severing by chaperones. Indeed, while Pin4C overexpression does not alter chaperone levels, Pin4C aggregates sequester chaperones away from the prion aggregates. Cyc8 overexpression cures [PSI⁺] by inducing an increase in Hsp104 levels, as excess Hsp104 binds to [PSI⁺] aggregates in a way that blocks their shearing.

Probing early misfolding events in prion protein mutants by NMR spectroscopy

The post-translational conversion of the ubiquitously expressed cellular form of the prion protein, PrPC, into its misfolded and pathogenic isoform, known as prion or PrPSc, plays a key role in prion diseases. These maladies are denoted transmissible spongiform encephalopathies (TSEs) and affect both humans and animals. A prerequisite for understanding TSEs is unraveling the molecular mechanism leading to the conversion process whereby most α-helical motifs are replaced by β-sheet secondary structures. Importantly, most point mutations linked to inherited prion diseases are clustered in the C-terminal domain region of PrPC and cause spontaneous conversion to PrPSc. Structural studies with PrP variants promise new clues regarding the proposed conversion mechanism and may help identify "hot spots" in PrPC involved in the pathogenic conversion. These investigations may also shed light on the early structural rearrangements occurring in some PrPC epitopes thought to be involved in modulating prion susceptibility. Here we present a detailed overview of our solution-state NMR studies on human prion protein carrying different pathological point mutations and the implications that such findings may have for the future of prion research.

Tau pathology and neurodegeneration

The pathway leading from soluble and monomeric to hyperphosphorylated, insoluble and filamentous tau protein is at the centre of many human neurodegenerative diseases, collectively referred to as tauopathies. Dominantly inherited mutations in MAPT, the gene that encodes tau, cause forms of frontotemporal dementia and parkinsonism, proving that dysfunction of tau is sufficient to cause neurodegeneration and dementia. However, most cases of tauopathy are not inherited in a dominant manner. The first tau aggregates form in a few nerve cells in discrete brain areas. These become self propagating and spread to distant brain regions in a prion-like manner. The prevention of tau aggregation and propagation is the focus of attempts to develop mechanism-based treatments for tauopathies.

Prions in variably protease-sensitive prionopathy: an update

Human prion diseases, including sporadic, familial, and acquired forms such as Creutzfeldt-Jakob disease (CJD), are caused by prions in which an abnormal prion protein (PrP^Sc) derived from its normal cellular isoform (PrP^C) is the only known component. The recently-identified variably protease-sensitive prionopathy (VPSPr) is characterized not only by an atypical clinical phenotype and neuropathology but also by the deposition in the brain of a peculiar PrP^Sc. Like other forms of human prion disease, the pathogenesis of VPSPr also currently remains unclear. However, the findings of the peculiar features of prions from VPSPr and of the possible association of VPSPr with a known genetic prion disease linked with a valine to isoleucine mutation at residue 180 of PrP reported recently, may be of great importance in enhancing our understanding of not only this atypical human prion disease in particular, but also other prion diseases in general. In this review, we highlight the physicochemical and biological properties of prions from VPSPr and discuss the pathogenesis of VPSPr including the origin and formation of the peculiar prions.

Attachment of pathogenic prion protein to model oxide surfaces

Prions are the infectious agents in the class of fatal neurodegenerative diseases known as transmissible spongiform encephalopathies, which affect humans, deer, sheep, and cattle. Prion diseases of deer and sheep can be transmitted via environmental routes, and soil is has been implicated in the transmission of these diseases. Interaction with soil particles is expected to govern the transport, bioavailability and persistence of prions in soil environments. A mechanistic understanding of prion interaction with soil components is critical for understanding the behavior of these proteins in the environment. Here, we report results of a study to investigate the interactions of prions with model oxide surfaces (Al2O3, SiO2) using quartz crystal microbalance with dissipation monitoring and optical waveguide light mode spectroscopy. The efficiency of prion attachment to Al2O3 and SiO2 depended strongly on pH and ionic strength in a manner consistent with electrostatic forces dominating interaction with these oxides. The presence of the N-terminal portion of the protein appeared to promote attachment to Al2O3 under globally electrostatically repulsive conditions. We evaluated the utility of recombinant prion protein as a surrogate for prions in attachment experiments and found that its behavior differed markedly from that of the infectious agent. Our findings suggest that prions would tend to associate with positively charged mineral surfaces in soils (e.g., iron and aluminum oxides).

Stress granules as crucibles of ALS pathogenesis

Amyotrophic lateral sclerosis (ALS) is a fatal human neurodegenerative disease affecting primarily motor neurons. Two RNA-binding proteins, TDP-43 and FUS, aggregate in the degenerating motor neurons of ALS patients, and mutations in the genes encoding these proteins cause some forms of ALS. TDP-43 and FUS and several related RNA-binding proteins harbor aggregation-promoting prion-like domains that allow them to rapidly self-associate. This property is critical for the formation and dynamics of cellular ribonucleoprotein granules, the crucibles of RNA metabolism and homeostasis. Recent work connecting TDP-43 and FUS to stress granules has suggested how this cellular pathway, which involves protein aggregation as part of its normal function, might be coopted during disease pathogenesis.

Frontotemporal dementia: implications for understanding Alzheimer disease

Frontotemporal dementia (FTD) comprises a group of behavioral, language, and movement disorders. On the basis of the nature of the characteristic protein inclusions, frontotemporal lobar degeneration (FTLD) can be subdivided into the common FTLD-tau and FTLD-TDP as well as the less common FTLD-FUS and FTLD-UPS. Approximately 10% of cases of FTD are inherited in an autosomal-dominant manner. Mutations in seven genes cause FTD, with those in tau (MAPT), chromosome 9 open reading frame 72 (C9ORF72), and progranulin (GRN) being the most common. Mutations in MAPT give rise to FTLD-tau and mutations in C9ORF72 and GRN to FTLD-TDP. The other four genes are transactive response-DNA binding protein-43 (TARDBP), fused in sarcoma (FUS), valosin-containing protein (VCP), and charged multivesicular body protein 2B (CHMP2B). Mutations in TARDBP and VCP give rise to FTLD-TDP, mutations in FUS to FTLD-FUS, and mutations in CHMP2B to FTLD-UPS. The discovery that mutations in MAPT cause neurodegeneration and dementia has important implications for understanding Alzheimer disease.

Polar substitutions in helix 3 of the prion protein produce transmembrane isoforms that disturb vesicle trafficking

Prion diseases encompass a diverse group of neurodegenerative conditions characterized by the accumulation of misfolded prion protein (PrP) isoforms. Other conformational variants of PrP have also been proposed to contribute to neurotoxicity in prion diseases, including misfolded intermediates as well as cytosolic and transmembrane isoforms. To better understand PrP neurotoxicity, we analyzed the role of two highly conserved methionines in helix 3 on PrP biogenesis, folding and pathogenesis. Expression of the PrP-M205S and -M205,212S mutants in Drosophila led to hyperglycosylation, intracellular accumulation and widespread conformational changes due to failure of oxidative folding. Surprisingly, PrP-M205S and -M205,212S acquired a transmembrane topology (Ctm) previously linked to mutations in the signal peptide (SP) and the transmembrane domain (TMD). PrP-M205,212S also disrupted the accumulation of key neurodevelopmental proteins in lipid rafts, resulting in shortened axonal projections. These results uncover a new role for the hydrophobic domain in promoting oxidative folding and preventing the formation of neurotoxic Ctm PrP, mechanisms that may be relevant in the pathogenesis of both inherited and sporadic prion diseases.

The structure of prion: is it enough for interpreting the diverse phenotypes of prion diseases?

Prion diseases, or transmissible spongiform encephalopathies, are neurodegenerative diseases, which affect human and many species of animals with 100% fatality rate. The most accepted etiology for prion disease is 'prion', which arises from the conversion from cellular PrP(C) to the pathological PrP(Sc). This review discussed the characteristic structure of PrP, including PRNP gene, PrP(C), PrP(Sc), PrP amyloid, and prion strains.

Brain homogenates from human tauopathies induce tau inclusions in mouse brain

Filamentous inclusions made of hyperphosphorylated tau are characteristic of numerous human neurodegenerative diseases, including Alzheimer's disease, tangle-only dementia, Pick disease, argyrophilic grain disease (AGD), progressive supranuclear palsy, and corticobasal degeneration. In Alzheimer's disease and AGD, it has been shown that filamentous tau appears to spread in a stereotypic manner as the disease progresses. We previously demonstrated that the injection of brain extracts from human mutant P301S tau-expressing transgenic mice into the brains of mice transgenic for wild-type human tau (line ALZ17) resulted in the assembly of wild-type human tau into filaments and the spreading of tau inclusions from the injection sites to anatomically connected brain regions. Here we injected brain extracts from humans who had died with various tauopathies into the hippocampus and cerebral cortex of ALZ17 mice. Argyrophilic tau inclusions formed in all cases and following the injection of the corresponding brain extracts, we recapitulated the hallmark lesions of AGD, PSP and CBD. Similar inclusions also formed after intracerebral injection of brain homogenates from human tauopathies into nontransgenic mice. Moreover, the induced formation of tau aggregates could be propagated between mouse brains. These findings suggest that once tau aggregates have formed in discrete brain areas, they become self-propagating and spread in a prion-like manner.

Hsp104 drives "protein-only" positive selection of Sup35 prion strains encoding strong [PSI(+)]

Structurally distinct, self-templating prion "strains" can encode distinct phenotypes and amplify at different rates depending upon the environment. Indeed, prion strain ensembles can evolve in response to environmental challenges, which makes them highly challenging drug targets. It is not understood how the proteostasis network amplifies one prion strain at the expense of another. Here, we demonstrate that Hsp104 remodels the distinct intermolecular contacts of different synthetic Sup35 prion strains in a way that selectively amplifies prions encoding strong [PSI(+)] and simultaneously eliminates prions encoding weak [PSI(+)]. Hsp104 has reduced ability to fragment prions encoding weak [PSI(+)], but readily converts them to nontemplating forms. By contrast, Hsp104 readily fragments prions encoding strong [PSI(+)], but has reduced ability to eliminate their infectivity. Thus, we illuminate direct mechanisms underpinning how the proteostasis network can drive prion strain selection.

Alzheimer's disease and prion protein

Alzheimer's disease (AD) is a devastating neurodegenerative disease with progressive loss of memory and cognitive function, pathologically hallmarked by aggregates of the amyloid-beta (Aβ) peptide and hyperphosphorylated tau in the brain. Aggregation of Aβ under the form of amyloid fibrils has long been considered central to the pathogenesis of AD. However, recent evidence has indicated that soluble Aβ oligomers, rather than insoluble fibrils, are the main neurotoxic species in AD. The cellular prion protein (PrP(C)) has newly been identified as a cell surface receptor for Aβ oligomers. PrP(C) is a cell surface glycoprotein that plays a key role in the propagation of prions, proteinaceous infectious agents that replicate by imposing their abnormal conformation to PrP(C) molecules. In AD, PrP(C) acts to transduce the neurotoxic signals arising from Aβ oligomers, leading to synaptic failure and cognitive impairment. Interestingly, accumulating evidence has also shown that aggregated Aβ or tau possesses prion-like activity, a property that would allow them to spread throughout the brain. In this article, we review recent findings regarding the function of PrP(C) and its role in AD, and discuss potential therapeutic implications of PrP(C)-based approaches in the treatment of AD.

Mechanisms of protein seeding in neurodegenerative diseases

Most age-associated neurodegenerative diseases involve the aggregation of specific proteins within the nervous system. In Alzheimer disease, the insidious pathogenic process begins many years before the symptoms emerge, and the lesions that characterize the disease—senile plaques and neurofibrillary tangles—ramify systematically through the brain. We review evidence that the -amyloid and tau proteins, which aggregate to form senile plaques and neurofibrillary tangles, respectively, are induced to misfold and self-assemble by a process of templated conformational change that amplifies a toxic species. Recent data also indicate that the spread of these lesions from one site to another is mediated by the cellular uptake, transport, and release of endogenous seeds formed by the cognate proteins. This simple pathogenic principle suggests that the formation, trafficking, and metabolism of pathogenic protein seeds are promising therapeutic targets for Alzheimer disease and other neurodegenerative disorders.

Defining the conformational features of anchorless, poorly neuroinvasive prions

Infectious prions cause diverse clinical signs and form an extraordinary range of structures, from amorphous aggregates to fibrils. How the conformation of a prion dictates the disease phenotype remains unclear. Mice expressing GPI-anchorless or GPI-anchored prion protein exposed to the same infectious prion develop fibrillar or nonfibrillar aggregates, respectively, and show a striking divergence in the disease pathogenesis. To better understand how a prion's physical properties govern the pathogenesis, infectious anchorless prions were passaged in mice expressing anchorless prion protein and the resulting prions were biochemically characterized. Serial passage of anchorless prions led to a significant decrease in the incubation period to terminal disease and altered the biochemical properties, consistent with a transmission barrier effect. After an intraperitoneal exposure, anchorless prions were only weakly neuroinvasive, as prion plaques rarely occurred in the brain yet were abundant in extracerebral sites such as heart and adipose tissue. Anchorless prions consistently showed very high stability in chaotropes or when heated in SDS, and were highly resistant to enzyme digestion. Consistent with the results in mice, anchorless prions from a human patient were also highly stable in chaotropes. These findings reveal that anchorless prions consist of fibrillar and highly stable conformers. The additional finding from our group and others that both anchorless and anchored prion fibrils are poorly neuroinvasive strengthens the hypothesis that a fibrillar prion structure impedes efficient CNS invasion.

Prions cause fatal neurodegenerative disease in humans and animals and there is currently no treatment available. The cellular prion protein is normally tethered to the outer leaflet of the plasma membrane by a glycophosphatidyl inositol (GPI) anchor. A rare stop codon mutation in the PRNP gene leads to the production of GPI-anchorless prion protein and the development of familial prion disease, which has been reproduced in mouse models. GPI-anchorless prions in humans or mice form large, dense plaques containing fibrils in the brain that vary from the more common non-fibrillar prion aggregates. Here we investigated the biochemical differences between GPI-anchored and GPI-anchorless prions. We also assessed the capacity of GPI-anchorless prions to spread from entry sites into the central nervous system. We found that infectious GPI-anchorless prions were extraordinarily stable when exposed to protein denaturing conditions. Additionally, we show that GPI-anchorless prions rarely invade the central nervous system and then only after long incubation periods, despite their presence in extraneural tissues including adipose tissue and heart. Our study shows that GPI-anchored prions converted into GPI-anchorless prions become extraordinarily stable, more resistant to enzyme digestion, and are poorly able to invade the nervous system.

PrPC controls via protein kinase A the direction of synaptic plasticity in the immature hippocampus

The cellular form of prion protein PrP(C) is highly expressed in the brain, where it can be converted into its abnormally folded isoform PrP(Sc) to cause neurodegenerative diseases. Its predominant synaptic localization suggests a crucial role in synaptic signaling. Interestingly, PrP(C) is developmentally regulated and its high expression in the immature brain could be instrumental in regulating neurogenesis and cell proliferation. Here, PrP(C)-deficient (Prnp(0/0)) mice were used to assess whether the prion protein is involved in synaptic plasticity processes in the neonatal hippocampus. To this aim, calcium transients associated with giant depolarizing potentials, a hallmark of developmental networks, were transiently paired with mossy fiber activation in such a way that the two events were coincident. While this procedure caused long-term potentiation (LTP) in wild-type (WT) animals, it caused long-term depression (LTD) in Prnp(0/0) mice. Induction of LTP was postsynaptic and required the activation of cAMP-dependent protein kinase A (PKA) signaling. The induction of LTD was presynaptic and relied on G-protein-coupled GluK1 receptor and protein lipase C. In addition, at emerging CA3-CA1 synapses in WT mice, but not in Prnp(0/0) mice, pairing Schaffer collateral stimulation with depolarization of CA1 principal cells induced LTP, known to be PKA dependent. Postsynaptic infusion of a constitutively active isoform of PKA catalytic subunit Cα into CA1 and CA3 principal cells in the hippocampus of Prnp(0/0) mice caused a persistent synaptic facilitation that was occluded by subsequent pairing. These data suggest that PrP(C) plays a crucial role in regulating via PKA synaptic plasticity in the developing hippocampus.

Life is a self-organizing machine driven by the informational cycle of Brillouin

Acquiring information is indisputably energy-consuming and conversely, the availability of information permits greater efficiency. Strangely, the scientific community long remained reluctant to establish a physical equivalence between the abstract notion of information and sensible thermodynamics. However, certain physicists such as Szilard and Brillouin proposed: (i) to give to information the status of a genuine thermodynamic entity (k B T ln2 joules/bit) and (ii) to link the capacity of storing information inferred from correlated systems, to that of indefinitely increasing organization. This positive feedback coupled to the self-templating molecular potential could provide a universal basis for the spontaneous rise of highly organized structures, typified by the emergence of life from a prebiotic chemical soup. Once established, this mechanism ensures the longevity and robustness of life envisioned as a general system, by allowing it to accumulate and optimize microstate-reducing recipes, thereby giving rise to strong nonlinearity, decisional capacity and multistability. Mechanisms possibly involved in priming this cycle are proposed.

Glycoform-selective prion formation in sporadic and familial forms of prion disease

The four glycoforms of the cellular prion protein (PrP(C)) variably glycosylated at the two N-linked glycosylation sites are converted into their pathological forms (PrP(Sc)) in most cases of sporadic prion diseases. However, a prominent molecular characteristic of PrP(Sc) in the recently identified variably protease-sensitive prionopathy (VPSPr) is the absence of a diglycosylated form, also notable in familial Creutzfeldt-Jakob disease (fCJD), which is linked to mutations in PrP either from Val to Ile at residue 180 (fCJD(V180I)) or from Thr to Ala at residue 183 (fCJD(T183A)). Here we report that fCJD(V180I), but not fCJD(T183A), exhibits a proteinase K (PK)-resistant PrP (PrP(res)) that is markedly similar to that observed in VPSPr, which exhibits a five-step ladder-like electrophoretic profile, a molecular hallmark of VPSPr. Remarkably, the absence of the diglycosylated PrP(res) species in both fCJD(V180I) and VPSPr is likewise attributable to the absence of PrP(res) glycosylated at the first N-linked glycosylation site at residue 181, as in fCJD(T183A). In contrast to fCJD(T183A), both VPSPr and fCJD(V180I) exhibit glycosylation at residue 181 on di- and monoglycosylated (mono181) PrP prior to PK-treatment. Furthermore, PrP(V180I) with a typical glycoform profile from cultured cells generates detectable PrP(res) that also contains the diglycosylated PrP in addition to mono- and unglycosylated forms upon PK-treatment. Taken together, our current in vivo and in vitro studies indicate that sporadic VPSPr and familial CJD(V180I) share a unique glycoform-selective prion formation pathway in which the conversion of diglycosylated and mono181 PrP(C) to PrP(Sc) is inhibited, probably by a dominant-negative effect, or by other co-factors.

Towards further reduction and replacement of animal bioassays in prion research by cell and protein misfolding cyclic amplification assays

Laboratory animals have long since been used extensively in bioassays for prions in order to quantify, usually in terms of median infective doses [ID50], how infectious these pathogens are in vivo. The identification of aberrant prion protein as the main component and self-replicating principle of prions has given rise to alternative approaches for prion titration. Such approaches often use protein misfolding cyclic amplification (PMCA) for the cell-free biochemical measurement of prion-associated seeding activity, or cell assays for the titration of in vitro infectivity. However, median seeding and cell culture infective doses (SD50 and CCID50, respectively) of prions are neither formally congruent nor definitely representative for ID50 titres in animals and can be therefore only tentatively translated into the latter. This may potentially impede the acceptance and use of alternative methods to animal bioassays in prion research. Thus, we suggest performing PMCA and cell assays jointly, and to check whether these profoundly different test principles deliver consistent results in order to strengthen the reliability and credibility of prion ID50 assessments by in vitro methods. With regard to this rationale, we describe three pairs of PMCA and glial cell assays for different hamster-adapted prion agents (the frequently used 263K scrapie strain, and 22A-H scrapie and BSE-H). In addition, we report on the adaptation of quantitative PMCA to human variant Creutzfeldt-Jakob disease (vCJD) prions on steel wires for prion disinfection studies. Our rationale and methodology can be systematically extended to other types of prions and used to further reduce or replace prion bioassays in rodents.

Low copper and high manganese levels in prion protein plaques

Accumulation of aggregates rich in an abnormally folded form of the prion protein characterize the neurodegeneration caused by transmissible spongiform encephalopathies (TSEs). The molecular triggers of plaque formation and neurodegeneration remain unknown, but analyses of TSE-infected brain homogenates and preparations enriched for abnormal prion protein suggest that reduced levels of copper and increased levels of manganese are associated with disease. The objectives of this study were to: (1) assess copper and manganese levels in healthy and TSE-infected Syrian hamster brain homogenates; (2) determine if the distribution of these metals can be mapped in TSE-infected brain tissue using X-ray photoelectron emission microscopy (X-PEEM) with synchrotron radiation; and (3) use X-PEEM to assess the relative amounts of copper and manganese in prion plaques in situ. In agreement with studies of other TSEs and species, we found reduced brain levels of copper and increased levels of manganese associated with disease in our hamster model. We also found that the in situ levels of these metals in brainstem were sufficient to image by X-PEEM. Using immunolabeled prion plaques in directly adjacent tissue sections to identify regions to image by X-PEEM, we found a statistically significant relationship of copper-manganese dysregulation in prion plaques: copper was depleted whereas manganese was enriched. These data provide evidence for prion plaques altering local transition metal distribution in the TSE-infected central nervous system.

Functional genomics approach for identification of molecular processes underlying neurodegenerative disorders in prion diseases

Prion diseases or transmissible spongiform encephalopathies (TSEs) are infectious neurodegenerative disorders leading to death. These include Cresutzfeldt-Jakob disease (CJD), familial, sporadic and variant CJD and kuru in humans; and animal TSEs include scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) of mule deer and elk, and transmissible mink encephalopathy. All these TSEs share common pathological features such as accumulation of mis-folded prion proteins in the central nervous system leading to cellular dysfunction and cell death. It is important to characterize the molecular pathways and events leading to prion induced neurodegeneration. Here we discuss the impact of the functional genomics approaches including microarrays, subtractive hybridization and microRNA profiling in elucidating transcriptional cascades at different stages of disease. Many of these transcriptional changes have been observed in multiple neurodegenerative diseases which may aid in identification of biomarkers for disease. A comprehensive characterization of expression profiles implicated in neurodegenerative disorders will undoubtedly advance our understanding on neuropathology and dysfunction during prion disease and other neurodegenerative disorders. We also present an outlook on the future work which may focus on analysis of structural genetic variation, genome and transcriptome sequencing using next generation sequencing with an integrated approach on animal and human TSE related studies.

Acquisition of drug resistance and dependence by prions

We have reported that properties of prion strains may change when propagated in different environments. For example, when swainsonine-sensitive 22L prions were propagated in PK1 cells in the presence of swainsonine, drug-resistant variants emerged. We proposed that prions constitute quasi- populations comprising a range of variants with different properties, from which the fittest are selected in a particular environment. Prion populations developed heterogeneity even after biological cloning, indicating that during propagation mutation-like processes occur at the conformational level. Because brain-derived 22L prions are naturally swainsonine resistant, it was not too surprising that prions which had become swa sensitive after propagation in cells could revert to drug resistance. Because RML prions, both after propagation in brain or in PK1 cells, are swainsonine sensitive, we investigated whether it was nonetheless possible to select swainsonine-resistant variants by propagation in the presence of the drug. Interestingly, this was not possible with the standard line of PK1 cells, but in certain PK1 sublines not only swainsonine-resistant, but even swainsonine-dependent populations (i.e. that propagated more rapidly in the presence of the drug) could be isolated. Once established, they could be passaged indefinitely in PK1 cells, even in the absence of the drug, without losing swainsonine dependence. The misfolded prion protein (PrP(Sc)) associated with a swainsonine-dependent variant was less rapidly cleared in PK1 cells than that associated with its drug-sensitive counterpart, indicating that likely structural differences of the misfolded PrP underlie the properties of the prions. In summary, propagation of prions in the presence of an inhibitory drug may not only cause the selection of drug-resistant prions but even of stable variants that propagate more efficiently in the presence of the drug. These adaptations are most likely due to conformational changes of the abnormal prion protein.

Levels of the Mahogunin Ring Finger 1 E3 ubiquitin ligase do not influence prion disease

Prion diseases are rare but invariably fatal neurodegenerative disorders. They are associated with spongiform encephalopathy, a histopathology characterized by the presence of large, membrane-bound vacuolar structures in the neuropil of the brain. While the primary cause is recognized as conversion of the normal form of prion protein (PrP^C) to a conformationally distinct, pathogenic form (PrP^Sc), the cellular pathways and mechanisms that lead to spongiform change, neuronal dysfunction and death are not known. Mice lacking the Mahogunin Ring Finger 1 (MGRN1) E3 ubiquitin ligase develop spongiform encephalopathy by 9 months of age but do not become ill. In cell culture, PrP aberrantly present in the cytosol was reported to interact with and sequester MGRN1. This caused endo-lysosomal trafficking defects similar to those observed when Mgrn1 expression is knocked down, implicating disrupted MGRN1-dependent trafficking in the pathogenesis of prion disease. As these defects were rescued by over-expression of MGRN1, we investigated whether reduced or elevated Mgrn1 expression influences the onset, progression or pathology of disease in mice inoculated with PrP^Sc. No differences were observed, indicating that disruption of MGRN1-dependent pathways does not play a significant role in the pathogenesis of transmissible spongiform encephalopathy.

Single-molecule approaches to prion protein misfolding

The structural conversion of the prion protein PrP into a transmissible, misfolded form is the central element of prion disease, yet there is little consensus as to how it occurs. Key aspects of conversion into the diseased state remain unsettled, from details about the earliest stages of misfolding such as the involvement of partially- or fully-unfolded intermediates to the structure of the infectious state. Part of the difficulty in understanding the structural conversion arises from the complexity of the underlying energy landscapes. Single molecule methods provide a powerful tool for probing complex folding pathways as in prion misfolding, because they allow rare and transient events to be observed directly. We discuss recent work applying single-molecule probes to study misfolding in prion proteins, and what it has revealed about the folding dynamics of PrP that may underlie its unique behavior. We also discuss single-molecule studies probing the interactions that stabilize non-native structures within aggregates, pointing the way to future work that may help identify the microscopic events triggering pathogenic conversion. Although single-molecule approaches to misfolding are relatively young, they have a promising future in prion science.

CELFish ways to modulate mRNA decay

The CELF family of RNA-binding proteins regulates many steps of mRNA metabolism. Although their best characterized function is in pre-mRNA splice site choice, CELF family members are also powerful modulators of mRNA decay. In this review we focus on the different modes of regulation that CELF proteins employ to mediate mRNA decay by binding to GU-rich elements. After starting with an overview of the importance of CELF proteins during development and disease pathogenesis, we then review the mRNA networks and cellular pathways these proteins regulate and the mechanisms by which they influence mRNA decay. Finally, we discuss how CELF protein activity is modulated during development and in response to cellular signals. We conclude by highlighting the priorities for new experiments in this field. This article is part of a Special Issue entitled: RNA Decay mechanisms.

Global transcriptional profiling of the postmortem brain of a patient with G114V genetic Creutzfeldt-Jakob disease

Familial or genetic Creutzfeldt-Jakob disease (fCJD or gCJD) is an inherent human prion disease caused by mutation of the prion protein gene (PRNP). In the present study, global expression patterns of the parietal cortex from a patient with G114V gCJD were analyzed using the Affymetrix Human Genome U133+ 2.0 chip with a commercial normal human parietal cortex RNA pool as a normal control. In total, 8,774 genes showed differential expression; among them 2,769 genes were upregulated and 6,005 genes were downregulated. The reliability of the results was confirmed using real-time RT-PCR assays. The most differentially expressed genes (DEGs) were involved in transcription regulation, ion transport, transcription, cell adhesion, and signal transduction. The genes associated with gliosis were upregulated and the genes marked for neurons were downregulated, while the transcription of the PRNP gene remained unaltered. A total of 169 different pathways exhibited significant changes in the brain of G114V gCJD. The most significantly regulated pathways included Alzheimer's and Parkinson's disease, oxidative phosphorylation, regulation of actin cytoskeleton, MAPK signaling and proteasome, which have previously been linked to prion diseases. In addition, we found some pathways that have rarely been explored in regards to prion diseases that were also significantly altered in G114V gCJD, such as axon guidance, gap junction and purine metabolism. The majority of the genes in the 10 most altered pathways were downregulated. The data of the present study provide useful insights into the pathogenesis of G114V gCJD and potential biomarkers for diagnostic and therapeutic purposes.

Influence of surface groups on poly(propylene imine) dendrimers antiprion activity

Prion diseases are characterized by the accumulation of PrP(Sc), an aberrantly folded isoform of the host protein PrP(C). Specific forms of synthetic molecules known as dendrimers are able to eliminate protease-resistant PrP(Sc) in both an intracellular and in vitro setting. The properties of a dendrimer which govern this ability are unknown. We addressed the issue by comparing the in vitro antiprion ability of numerous modified poly(propylene-imine) dendrimers, which varied in size, structure, charge, and surface group composition. Several of the modified dendrimers, including an anionic glycodendrimer, reduced the level of protease resistant PrP(Sc) in a prion strain-dependent manner. This led to the formulation of a new working model for dendrimer/prion interactions which proposes dendrimers eliminate PrP(Sc) by destabilizing the protein and rendering it susceptible to proteolysis. This ability is not dependent on any particular charge of dendrimer, but does require a high density of reactive surface groups.

Mapping the prion protein distribution in marsupials: insights from comparing opossum with mouse CNS

The cellular form of the prion protein (PrP^C) is a sialoglycoprotein widely expressed in the central nervous system (CNS) of mammalian species during neurodevelopment and in adulthood. The location of the protein in the CNS may play a role in the susceptibility of a species to fatal prion diseases, which are also known as the transmissible spongiform encephalopathies (TSEs). To date, little is known about PrP^C distribution in marsupial mammals, for which no naturally occurring prion diseases have been reported. To extend our understanding of varying PrP^C expression profiles in different mammals we carried out a detailed expression analysis of PrP^C distribution along the neurodevelopment of the metatherian South American short-tailed opossum (Monodelphis domestica). We detected lower levels of PrP^C in white matter fiber bundles of opossum CNS compared to mouse CNS. This result is consistent with a possible role for PrP^C in the distinct neurodevelopment and neurocircuitry found in marsupials compared to other mammalian species.

Intraneuronal β-amyloid and its interactions with proteins and subcellular organelles

Amyloidogenic aggregation and misfolding of proteins are linked to neurodegeneration. The mechanism of neurodegeneration in Alzheimer's disease, which gives rise to severe neuronal death and memory loss, is not yet fully understood. The amyloid hypothesis remains the most accepted theory for the pathomechanism of the disease. It was suggested that β-amyloid accumulation may play a key role in initiating the neurodegenerative processes. The recent intracellular β-amyloid (iAβ) hypothesis emphasizes the primary role of iAβ to initiate the disease by interaction with cytoplasmic proteins and cell organelles, thereby triggering apoptosis. Sophisticated methods (proteomics, protein microarray, and super resolution microscopy) have been used for studying iAβ interactions with proteins and membraneous structures. The present review summarizes the studies on the origin of iAβ and the base of its neurotoxicity: interactions with cytosolic proteins and several cell organelles such as endoplasmic reticulum, endosomes, lysosomes, ribosomes, mitochondria, and the microtubular system.

Chaperone proteins select and maintain [PIN+] prion conformations in Saccharomyces cerevisiae

Prions are proteins that can adopt different infectious conformations known as "strains" or "variants," each with a distinct, epigenetically inheritable phenotype. Mechanisms by which prion variants are determined remain unclear. Here we use the Saccharomyces cerevisiae prion Rnq1p/[PIN(+)] as a model to investigate the effects of chaperone proteins upon prion variant determination. We show that deletion of specific chaperone genes alters [PIN(+)] variant phenotypes, including [PSI(+)] induction efficiency, Rnq1p aggregate morphology/size and variant dominance. Mating assays demonstrate that gene deletion-induced phenotypic changes are stably inherited in a non-Mendelian manner even after restoration of the deleted gene, confirming that they are due to a bona fide change in the [PIN(+)] variant. Together, our results demonstrate a role for chaperones in regulating the prion variant complement of a cell.

Gene regulatory network analysis supports inflammation as a key neurodegeneration process in prion disease

Background

The activation of immune cells in the brain is believed to be one of the earliest events in prion disease development, where misfolded PrionSc protein deposits are thought to act as irritants leading to a series of events that culminate in neuronal cell dysfunction and death. The role of these events in prion disease though is still a matter of debate. To elucidate the mechanisms leading from abnormal protein deposition to neuronal injury, we have performed a detailed network analysis of genes differentially expressed in several mouse prion models.

Results

We found a master regulatory core of genes related to immune response controlling other genes involved in prion protein replication and accumulation, and neuronal cell death. This regulatory core determines the existence of two stable states that are consistent with the transcriptome analysis comparing prion infected versus uninfected mouse brain. An in silico perturbation analysis demonstrates that core genes are individually capable of triggering the transition and that the network remains locked once the diseased state is reached.

Conclusions

We hypothesize that this locking may be the cause of the sustained immune response observed in prion disease. Our analysis supports the hypothesis that sustained brain inflammation is the main pathogenic process leading to neuronal dysfunction and loss, which, in turn, leads to clinical symptoms in prion disease.

Regulation of chaperone effects on a yeast prion by cochaperone Sgt2

Yeast prions, based on self-seeded highly ordered fibrous aggregates (amyloids), serve as a model for human amyloid diseases. Propagation of yeast prions depends on the balance between chaperones of the Hsp100 and Hsp70 families. The yeast prion [PSI(+)] can be eliminated by an excess of the chaperone Hsp104. This effect is reversed by an excess of the chaperone Hsp70-Ssa. Here we show that the actions of Hsp104 and Ssa on [PSI(+)] are modulated by the small glutamine-rich tetratricopeptide cochaperone Sgt2. Sgt2 is conserved from yeast to humans, has previously been implicated in the guided entry of tail-anchored proteins (GET) trafficking pathway, and is known to interact with Hsps, cytosolic Get proteins, and tail-anchored proteins. We demonstrate that Sgt2 increases the ability of excess Ssa to counteract [PSI(+)] curing by excess Hsp104. Deletion of SGT2 also restores trafficking of a tail-anchored protein in cells with a disrupted GET pathway. One region of Sgt2 interacts both with the prion domain of Sup35 and with tail-anchored proteins. Sgt2 levels are increased in response to the presence of a prion when major Hsps are not induced. Our data implicate Sgt2 as an amyloid "sensor" and a regulator of chaperone targeting to different types of aggregation-prone proteins.

Atypical H-type bovine spongiform encephalopathy in a cow born after the reinforced feed ban on meat-and-bone meal in Europe

The significance of atypical bovine spongiform encephalopathies (BSE) in cattle for controlling the BSE epidemic is poorly understood. Here we report a case of atypical H-type BSE in a cow born after the implementation of the reinforced feed ban in Europe. This supports an etiology of H-type BSE unrelated to that of classical BSE.

Molecular chaperones, α-synuclein, and neurodegeneration

Parkinson's disease (PD) is a devastating neurological condition that affects about 1 % of people older than 65 years of age. In PD, dopaminergic neurons in the mid-brain slowly accumulate cytoplasmic inclusions (Lewy bodies, LBs) of the protein alpha-synuclein (α-syn) and then gradually lose function and die off. Cell death is thought to be causally linked to the aggregation/fibrillization of α-syn. This review focuses on new findings about the structure of α-syn, about how α-syn cooperates with Hsp70 and Hsp40 chaperones to promote neurotransmitter release, and about cell-to-cell transfer of pathogenic forms of α-syn and how Hsp70 might protect against this disease process.

Early structural features in mammalian prion conformation conversion

The conversion to a disease-associated conformer (PrP(Sc)) of the cellular prion protein (PrP(C)) is the central event in prion diseases. Wild-type PrPC converts to PrP(Sc) in the sporadic forms of the disorders through an unknown mechanism. These forms account for up to 85% of all human (Hu) occurrences; the infectious types contribute for less than 1%, while genetic incidence of the disease is about 15%. Familial Hu prion diseases are associated with about forty point mutations of the gene coding for the PrP denominated PRNP. Most of the variants associated with these mutations are located in the globular domain of the protein. In a recent work in collaboration with the German Research School for Simulation Science, in Jülich, Germany, we performed molecular dynamics simulations for each of these mutants to investigate their structure in aqueous solution. Structural analysis of the various point mutations present in the globular domain unveiled common folding traits that may allow to a better understanding of the early conformational changes leading to the formation of monomeric PrP(Sc). Recent experimental data support these findings, thus opening novel approaches to determine initial structural determinants of prion formation.

Prions in yeast

The concept of a prion as an infectious self-propagating protein isoform was initially proposed to explain certain mammalian diseases. It is now clear that yeast also has heritable elements transmitted via protein. Indeed, the "protein only" model of prion transmission was first proven using a yeast prion. Typically, known prions are ordered cross-β aggregates (amyloids). Recently, there has been an explosion in the number of recognized prions in yeast. Yeast continues to lead the way in understanding cellular control of prion propagation, prion structure, mechanisms of de novo prion formation, specificity of prion transmission, and the biological roles of prions. This review summarizes what has been learned from yeast prions.

Influence of Mabs on PrP(Sc) formation using in vitro and cell-free systems

PrP^Sc is believed to serve as a template for the conversion of PrP^C to the abnormal isoform. This process requires contact between the two proteins and implies that there may be critical contact sites that are important for conversion. We hypothesized that antibodies binding to either PrP^cor PrP^Sc would hinder or prevent the formation of the PrP^C–PrP^Sc complex and thus slow down or prevent the conversion process. Two systems were used to analyze the effect of different antibodies on PrP^Sc formation: (i) neuroblastoma cells persistently infected with the 22L mouse-adapted scrapie stain, and (ii) protein misfolding cyclic amplification (PMCA), which uses PrP^Sc as a template or seed, and a series of incubations and sonications, to convert PrP^C to PrP^Sc. The two systems yielded similar results, in most cases, and demonstrate that PrP-specific monoclonal antibodies (Mabs) vary in their ability to inhibit the PrP^C–PrP^Sc conversion process. Based on the numerous and varied Mabs analyzed, the inhibitory effect does not appear to be epitope specific, related to PrP^C conformation, or to cell membrane localization, but is influenced by the targeted PrP region (amino vs carboxy).

Peptide and protein-based nanotubes for nanobiotechnology

The development of biologically relevant nanosystems such as biomolecular probes and sensors requires systems that effectively interface specific biochemical environments with abiotic architectures. The most widely studied nanomaterial, carbon nanotubes, has proven challenging in their adaptation for biomedical applications despite their numerous advantageous physical and electrochemical properties. On the other hand, development of bionanosystems through adaptation of existing biological systems has several advantages including their adaptability through modern recombinant DNA strategies. Indeed, the use of peptides, proteins and protein assemblies as nanotubes, scaffolds, and nanowires has shown much promise as a bottom-up approach to the development of novel bionanosystems. We highlight several unique peptide and protein systems that generate protein nanotubes (PNTs) that are being explored for the development of biosensors, probes, bionanowires, and drug delivery systems.

Enzymatic degradation of PrPSc by a protease secreted from Aeropyrum pernix K1

Background

An R30 fraction from the growth medium of Aeropyrum pernix was analyzed for the protease that can digest the pathological prion protein isoform (PrP^Sc) from different species (human, bovine, deer and mouse).

Methodology/Principal Findings

Degradation of the PrP^Sc isoform by the R30 fraction and the purified protease was evaluated using the 6H4 anti-PrP monoclonal antibody. Fragments from the N-terminal and C-terminal of PrP^Sc were also monitored by Western blotting using the EB8 anti-PrP monoclonal antibody, and by dot blotting using the C7/5 anti-PrP monoclonal antibody, respectively. For detection of smaller peptides from incomplete digestion of PrP^Sc, the EB8 monoclonal antibody was used after precipitation with sodium phosphotungstate. Characterization of the purified active protease from the R30 fraction was achieved, through purification by fast protein liquid chromatography, and identification by tandem mass spectrometry the serine metalloprotease pernisine. SDS-PAGE and zymography show the purified pernisine plus its proregion with a molecular weight of ca. 45 kDa, and the mature purified pernisine as ca. 23 kDa. The purified pernisine was active between 58°C and 99°C, and between pH 3.5 and 8.0. The temperature and pH optima of the enzymatic activity of the purified pernisine in the presence of 1 mM CaCl₂ were 105°C ±0.5°C and pH 6.5±0.2, respectively.

Conclusions/Significance

Our study has identified and characterized pernisine as a thermostable serine metalloprotease that is secreted from A. pernix and that can digest the pathological prion protein PrP^Sc.

Purified and synthetic Alzheimer's amyloid beta (Aβ) prions

The aggregation and deposition of amyloid-β (Aβ) peptides are believed to be central events in the pathogenesis of Alzheimer's disease (AD). Inoculation of brain homogenates containing Aβ aggregates into susceptible transgenic mice accelerated Aβ deposition, suggesting that Aβ aggregates are capable of self-propagation and hence might be prions. Recently, we demonstrated that Aβ deposition can be monitored in live mice using bioluminescence imaging (BLI). Here, we use BLI to probe the ability of Aβ aggregates to self-propagate following inoculation into bigenic mice. We report compelling evidence that Aβ aggregates are prions by demonstrating widespread cerebral β-amyloidosis induced by inoculation of either purified Aβ aggregates derived from brain or aggregates composed of synthetic Aβ. Although synthetic Aβ aggregates were sufficient to induce Aβ deposition in vivo, they exhibited lower specific biological activity compared with brain-derived Aβ aggregates. Our results create an experimental paradigm that should lead to identification of self-propagating Aβ conformations, which could represent novel targets for interrupting the spread of Aβ deposition in AD patients.

Protein aggregation: mechanisms and functional consequences

Understanding the mechanisms underlying protein misfolding and aggregation has become a central issue in biology and medicine. Compelling evidence show that the formation of amyloid aggregates has a negative impact in cell function and is behind the most prevalent human degenerative disorders, including Alzheimer's Parkinson's and Huntington's diseases or type 2 diabetes. Surprisingly, the same type of macromolecular assembly is used for specialized functions by different organisms, from bacteria to human. Here we address the conformational properties of these aggregates, their formation pathways, their role in human diseases, their functional properties and how bioinformatics tools might be of help to study these protein assemblies.

Disease-associated prion protein in neural and lymphoid tissues of mink (Mustela vison) inoculated with transmissible mink encephalopathy

Transmissible spongiform encephalopathies (TSEs) are diagnosed by immunodetection of disease-associated prion protein (PrP(d)). The distribution of PrP(d) within the body varies with the time-course of infection and between species, during interspecies transmission, as well as with prion strain. Mink are susceptible to a form of TSE known as transmissible mink encephalopathy (TME), presumed to arise due to consumption of feed contaminated with a single prion strain of ruminant origin. After extended passage of TME isolates in hamsters, two strains emerge, HY and DY, each of which is associated with unique structural isoforms of PrP(TME) and of which only the HY strain is associated with accumulation of PrP(TME) in lymphoid tissues. Information on the structural nature and lymphoid accumulation of PrP(TME) in mink is limited. In this study, 13 mink were challenged by intracerebral inoculation using late passage TME inoculum, after which brain and lymphoid tissues were collected at preclinical and clinical time points. The distribution and molecular nature of PrP(TME) was investigated by techniques including blotting of paraffin wax-embedded tissue and epitope mapping by western blotting. PrP(TME) was detected readily in the brain and retropharyngeal lymph node during preclinical infection, with delayed progression of accumulation within other lymphoid tissues. For comparison, three mink were inoculated by the oral route and examined during clinical disease. Accumulation of PrP(TME) in these mink was greater and more widespread, including follicles of rectoanal mucosa-associated lymphoid tissue. Western blot analyses revealed that PrP(TME) accumulating in the brain of mink is structurally most similar to that accumulating in the brain of hamsters infected with the DY strain. Collectively, the results of extended passage in mink are consistent with the presence of only a single strain of TME, the DY strain, capable of inducing accumulation of PrP(TME) in the lymphoid tissues of mink but not in hamsters. Thus, mink are a relevant animal model for further study of this unique strain, which ultimately may have been introduced through consumption of a TSE of ruminant origin.

The amyloid state of proteins in human diseases

Amyloid fibers and oligomers are associated with a great variety of human diseases including Alzheimer's disease and the prion conditions. Here we attempt to connect recent discoveries on the molecular properties of proteins in the amyloid state with observations about pathological tissues and disease states. We summarize studies of structure and nucleation of amyloid and relate these to observations on amyloid polymorphism, prion strains, coaggregation of pathogenic proteins in tissues, and mechanisms of toxicity and transmissibility. Molecular studies have also led to numerous strategies for biological and chemical interventions against amyloid diseases.