Ligand Profiling as a Diagnostic Tool to Differentiate Patient-Derived α-Synuclein Polymorphs

Amyloid fibrils are characteristic of many neurodegenerative diseases, including Alzheimer's and Parkinson's diseases. While different diseases may have fibrils formed of the same protein, the supramolecular morphology of these fibrils is disease-specific. Here, a method is reported to distinguish eight morphologically distinct amyloid fibrils based on differences in ligand binding properties. Eight fibrillar polymorphs of α-synuclein (αSyn) were investigated: five generated de novo using recombinant αSyn and three generated using protein misfolding cyclic amplification (PMCA) of recombinant αSyn seeded with brain homogenates from deceased patients diagnosed with Parkinson's disease (PD), multiple system atrophy (MSA), and dementia with Lewy bodies (DLB). Fluorescence binding assays were carried out for each fibril using a toolkit of six different ligands. The fibril samples were separated into five categories based on a binary classification of whether they bound specific ligands or not. Quantitative binding measurements then allowed every fibrillar polymorph to be uniquely identified, and the PMCA fibrils derived from PD, MSA, and DLB patients could be unambiguously distinguished. This approach constitutes a novel and operationally simple method to differentiate amyloid fibril morphologies and to identify disease states using PMCA fibrils obtained by seeding with patient samples.

The advances in the early and accurate diagnosis of Creutzfeldt-Jakob disease and other prion diseases: where are we today?

INTRODUCTION

Before the introduction of MRI diffusion-weighted images (DWI), the diagnosis of Creutzfeldt-Jakob disease (CJD) relied upon nonspecific findings including clinical symptoms, EEG abnormalities, and elevated levels of cerebrospinal fluid 14-3-3 protein. Subsequently, the use of DWI has improved diagnostic accuracy, but it sometimes remains difficult to differentiate CJD from encephalitis, epilepsy, and other dementing disorders. The revised diagnostic criteria include real-time quaking-induced conversion (RT-QuIC), detecting small amounts of CJD-specific prion protein, and clinically sensitive DWI. Combining these techniques has further improved diagnostic accuracy, enabling earlier diagnosis.

AREAS COVERED

Herein, the authors review the recent advances in diagnostic methods and revised diagnostic criteria for sporadic CJD. They also discuss other prion diseases, such as variant CJD and chronic wasting disease, where the emergence of new types is a concern.

EXPERT OPINION

Despite improvements in diagnostic methods and criteria, some subtypes of prion disease are still difficult to diagnose, and even the diagnosis using the most innovative RT-QuIC test remains a challenge in terms of accuracy and standardization. However, these revised criteria can be adapted to the emergence of new types of prion diseases. It is essential to continue careful surveillance and update information on the latest prion disease phenotypes.

Corrigendum: PMCA-based detection of prions in the olfactory mucosa of patients with sporadic Creutzfeldt-Jakob disease

[This corrects the article DOI: 10.3389/fnagi.2022.848991.].

PMCA-Based Detection of Prions in the Olfactory Mucosa of Patients With Sporadic Creutzfeldt-Jakob Disease

Sporadic Creutzfeldt-Jakob disease (sCJD) is a rare neurodegenerative disorder caused by the conformational conversion of the prion protein (PrP^C) into an abnormally folded form, named prion (or PrP^Sc). The combination of the polymorphism at codon 129 of the PrP gene (coding either methionine or valine) with the biochemical feature of the proteinase-K resistant PrP (generating either PrP^Sc type 1 or 2) gives rise to different PrP^Sc strains, which cause variable phenotypes of sCJD. The definitive diagnosis of sCJD and its classification can be achieved only post-mortem after PrP^Sc identification and characterization in the brain. By exploiting the Real-Time Quaking-Induced Conversion (RT-QuIC) assay, traces of PrP^Sc were found in the olfactory mucosa (OM) of sCJD patients, thus demonstrating that PrP^Sc is not confined to the brain. Here, we have optimized another technique, named protein misfolding cyclic amplification (PMCA) for detecting PrP^Sc in OM samples of sCJD patients. OM samples were collected from 27 sCJD and 2 genetic CJD patients (E200K). Samples from 34 patients with other neurodegenerative disorders were included as controls. Brains were collected from 26 sCJD patients and 16 of them underwent OM collection. Brain and OM samples were subjected to PMCA using the brains of transgenic mice expressing human PrP^C with methionine at codon 129 as reaction substrates. The amplified products were analyzed by Western blot after proteinase K digestion. Quantitative PMCA was performed to estimate PrP^Sc concentration in OM. PMCA enabled the detection of prions in OM samples with 79.3% sensitivity and 100% specificity. Except for a few cases, a predominant type 1 PrP^Sc was generated, regardless of the tissues analyzed. Notably, all amplified PrP^Sc were less resistant to PK compared to the original strain. In conclusion, although the optimized PMCA did not consent to recognize sCJD subtypes from the analysis of OM collected from living patients, it enabled us to estimate for the first time the amount of prions accumulating in this biological tissue. Further assay optimizations are needed to faithfully amplify peripheral prions whose recognition could lead to a better diagnosis and selection of patients for future clinical trials.

PMCA-generated prions from the olfactory mucosa of patients with Fatal Familial Insomnia cause prion disease in mice

Background:

Fatal Familial Insomnia (FFI) is a genetic prion disease caused by the D178N mutation in the prion protein gene (PRNP) in coupling phase with methionine at PRNP 129. In 2017, we have shown that the olfactory mucosa (OM) collected from FFI patients contained traces of PrPSc detectable by Protein Misfolding Cyclic Amplification (PMCA).

Methods:

In this work, we have challenged PMCA-generated products obtained from OM and brain homogenate of FFI patients in BvPrP-Tg407 transgenic mice expressing the bank vole prion protein to test their ability to induce prion pathology.

Results:

All inoculated mice developed mild spongiform changes, astroglial activation, and PrPSc deposition mainly affecting the thalamus. However, their neuropathological alterations were different from those found in the brain of BvPrP-Tg407 mice injected with raw FFI brain homogenate.

Conclusions:

Although with some experimental constraints, we show that PrPSc present in OM of FFI patients is potentially infectious.

Funding:

This work was supported in part by the Italian Ministry of Health (GR-2013-02355724 and Ricerca Corrente), MJFF, ALZ, Alzheimer’s Research UK and the Weston Brain Institute (BAND2015), and Euronanomed III (SPEEDY) to FM; by the Spanish Ministerio de Economía y Competitividad (grant AGL2016-78054-R [AEI/FEDER, UE]) to JMT and JCE; AM-M was supported by a fellowship from the INIA (FPI-SGIT-2015-02).

Preclinical Detection of Prions in Blood of Nonhuman Primates Infected with Variant Creutzfeldt-Jakob Disease

Variant Creutzfeldt-Jakob disease (vCJD) is caused by prion infection with bovine spongiform encephalopathy and can be transmitted by blood transfusion. Protein misfolding cyclic amplification (PMCA) can detect prions in blood from vCJD patients with 100% sensitivity and specificity. To determine whether PMCA enables prion detection in blood during the preclinical stage of infection, we performed a blind study using blood samples longitudinally collected from 28 control macaques and 3 macaques peripherally infected with vCJD. Our results demonstrate that PMCA consistently detected prions in blood during the entire preclinical stage in all infected macaques, without false positives from noninfected animals, when using the optimized conditions for amplification of macaque prions. Strikingly, prions were detected as early as 2 months postinoculation (>750 days before disease onset). These findings suggest that PMCA has the potential to detect vCJD prions in blood from asymptomatic carriers during the preclinical phase of the disease.

Analysis of Protein Conformational Strains-A Key for New Diagnostic Methods of Human Diseases

α-Synuclein is a naturally unfolded protein which easily aggregates and forms toxic inclusions and deposits. It is associated with several neurodegenerative diseases, including Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). These diseases, called synucleinopathies, have overlapping symptoms but require different methods of treatment. There are no reliable approaches for early diagnoses of these diseases, and as a result, the treatment begins late, and the disorders are often misdiagnosed. Recent studies revealed that α-synuclein forms distinctive spatial structures or strains at the early steps of these diseases, which may be used for early diagnosis. One of these early diagnostic methods called PMCA (protein misfolding cyclic amplification) allows identification of the distinct α-synuclein strains specific for different human diseases. The method is successfully used for differential diagnosis of patients with PD and MSA.

Two distinct prions in fatal familial insomnia and its sporadic form

Fatal familial insomnia is a genetic prion disease, which is associated with the aspartic acid to asparagine substitution at codon 178 of the prion protein gene. Although the hallmark pathological feature is thalamic and olivary degeneration, there is a patient with an atypical fatal familial insomnia without the hallmark feature. The cause of the pathological variability is unclear. We analysed a Japanese fatal familial insomnia kindred and compared one atypical clinicopathological fatal familial insomnia phenotype case and typical fatal familial insomnia phenotype cases with transmission studies using multiple lines of knock-in mice and with protein misfolding cyclic amplification. We also analysed the transmissibility and the amplification properties of sporadic fatal insomnia. Transmission studies revealed that the typical fatal familial insomnia with thalamic and olivary degeneration showed successful transmission only using knock-in mice expressing human-mouse chimeric prion protein gene. The atypical fatal familial insomnia with spongiform changes showed successful transmission only using knock-in mice expressing bank vole prion protein gene. Two sporadic fatal insomnia cases with thalamic and olivary degeneration showed the same transmissibility as the typical fatal familial insomnia phenotype. Interestingly, one sporadic fatal insomnia case with thalamic/olivary degeneration and spongiform changes showed transmissibility of both the typical and atypical fatal familial insomnia phenotypes. Protein misfolding cyclic amplification could amplify both typical fatal familial insomnia cases and sporadic fatal insomnia cases but not the atypical fatal familial insomnia phenotype or other sporadic Creutzfeldt-Jakob disease subtypes. In addition to clinical findings and neuropathological features, the transmission properties and the amplification properties were different between the typical and atypical fatal familial insomnia phenotypes. It is suggested that two distinct prions were associated with the diversity in the fatal familial insomnia phenotype, and these two prions could also be detected in sporadic fatal insomnia.

Susceptibility of Human Prion Protein to Conversion by Chronic Wasting Disease Prions

Chronic wasting disease (CWD) is a contagious and fatal neurodegenerative disease and a serious animal health issue for deer and elk in North America. The identification of the first cases of CWD among free-ranging reindeer and moose in Europe brings back into focus the unresolved issue of whether CWD can be zoonotic like bovine spongiform encephalopathy. We used a cell-free seeded protein misfolding assay to determine whether CWD prions from elk, white-tailed deer, and reindeer in North America can convert the human prion protein to the disease-associated form. We found that prions can convert, but the efficiency of conversion is affected by polymorphic variation in the cervid and human prion protein genes. In view of the similarity of reindeer, elk, and white-tailed deer in North America to reindeer, red deer, and roe deer, respectively, in Europe, a more comprehensive and thorough assessment of the zoonotic potential of CWD might be warranted.

Diagnosis of Methionine/Valine Variant Creutzfeldt-Jakob Disease by Protein Misfolding Cyclic Amplification

A patient with a heterozygous variant of Creutzfeldt-Jakob disease (CJD) with a methionine/valine genotype at codon 129 of the prion protein gene was recently reported. Using an ultrasensitive and specific protein misfolding cyclic amplification–based assay for detecting variant CJD prions in cerebrospinal fluid, we discriminated this heterozygous case of variant CJD from cases of sporadic CJD.

Baseline concentration of misfolded α-synuclein aggregates in cerebrospinal fluid predicts risk of cognitive decline in Parkinson's disease

BACKGROUND

The prognostic significance of misfolded α-synuclein (α-Syn) aggregates in Parkinson's disease (PD) has not been well investigated. The aim of this study was to reveal the relationship between misfolded α-Syn aggregate concentration in cerebrospinal fluid (CSF) and cognitive decline risk in PD.

METHODS

A total of 278 patients with PD were retrospectively included. They were diagnosed between 2011 and 2013. The end-point was 2016, and the follow-up period was 54.3 ± 10.0 months. Cognitive decline was defined as a 4-point decrease in the Mini-Mental State Examination score during follow-up. Misfolded α-Syn aggregate concentration in baseline CSF was measured using the protein misfolding cyclic amplification (PMCA) technique. Time to reach 50% of the maximum fluorescence value was recorded.

RESULTS

The PMCA technique successfully detected the level of misfolded α-Syn aggregates in CSF with a sensitivity of 85.3% and a specificity of 91.4%. The time to reach 50% of the maximum fluorescence value was shorter in the patients with cognitive decline than in the patients without cognitive decline (190.7 ± 40.1 h vs. 240.8 ± 45.6 h, P < 0.001). Multifactorial Cox regression analysis revealed that reaching 50% of the maximum fluorescence value in ≤219 h at baseline was associated with increased risk of cognitive decline during the follow-up (HR: 4.90, 95% CI: 2.75-8.74, P < 0.001).

CONCLUSION

Baseline concentration of misfolded α-Syn aggregates in CSF measured by the PMCA technique predicts risk of cognitive decline in PD.

Distribution and Quantitative Estimates of Variant Creutzfeldt-Jakob Disease Prions in Tissues of Clinical and Asymptomatic Patients

In the United-Kingdom, ≈1 of 2,000 persons could be infected with variant Creutzfeldt-Jakob disease (vCJD). Therefore, risk of transmission of vCJD by medical procedures remains a major concern for public health authorities. In this study, we used in vitro amplification of prions by protein misfolding cyclic amplification (PMCA) to estimate distribution and level of the vCJD agent in 21 tissues from 4 patients who died of clinical vCJD and from 1 asymptomatic person with vCJD. PMCA identified major levels of vCJD prions in a range of tissues, including liver, salivary gland, kidney, lung, and bone marrow. Bioassays confirmed that the quantitative estimate of levels of vCJD prion accumulation provided by PMCA are indicative of vCJD infectivity levels in tissues. Findings provide critical data for the design of measures to minimize risk for iatrogenic transmission of vCJD.

Prion protein amplification techniques

Protein amplification techniques exploit the ability of PrP^TSE to induce a conformational change in prion protein (PrP) in a continuous fashion, so that the small amount of PrP^TSE found in tissues and biologic fluids in prion diseases can be amplified to a point where they are detectable by conventional laboratory techniques. The most widely used protein aggregation assays are protein misfolding cyclic amplification assay (PMCA) and real-time quaking-induced conversion (RT-QuIC). These assays have been used extensively in both animal and human prion disease in studies ranging from the development of diagnostics, understanding disease transmission potential, to investigating mechanisms underlying neurodegeneration. In human prion disease, cerebrospinal fluid (CSF) RT-QuIC analysis has been shown to be a highly sensitive and specific test for sporadic Creutzfeldt-Jakob disease (sCJD) and has now been included in the diagnostic criteria. It is also a useful investigation for some genetic forms of prion disease where other cerebrospinal fluid tests may be negative. PMCA shows great potential for the diagnosis of variant CJD (vCJD) and has the ability to distinguish vCJD from sCJD, which may become increasingly important with emergence of a patient with neuropathologically confirmed vCJD associated with PRNP codon129MV, which indicates that a new wave of vCJD cases is likely and that these may be difficult to distinguish from sCJD.

Quiescin-sulfhydryl oxidase inhibits prion formation in vitro

Prions are infectious proteins that cause a group of fatal transmissible diseases in animals and humans. The scrapie isoform (PrP^Sc) of the cellular prion protein (PrP^C) is the only known component of the prion. Several lines of evidence have suggested that the formation and molecular features of PrP^Sc are associated with an abnormal unfolding/refolding process. Quiescin-sulfhydryl oxidase (QSOX) plays a role in protein folding by introducing disulfides into unfolded reduced proteins. Here we report that QSOX inhibits human prion propagation in protein misfolding cyclic amplification reactions and murine prion propagation in scrapie-infected neuroblastoma cells. Moreover, QSOX preferentially binds PrP^Sc from prion-infected human or animal brains, but not PrP^C from uninfected brains. Surface plasmon resonance of the recombinant mouse PrP (moPrP) demonstrates that the affinity of QSOX for monomer is significantly lower than that for octamer (312 nM vs 1.7 nM). QSOX exhibits much lower affinity for N-terminally truncated moPrP (PrP89-230) than for the full-length moPrP (PrP23-231) (312 nM vs 2 nM), suggesting that the N-terminal region of PrP is critical for the interaction of PrP with QSOX. Our study indicates that QSOX may play a role in prion formation, which may open new therapeutic avenues for treating prion diseases.

De Novo Generation of a Unique Cervid Prion Strain Using Protein Misfolding Cyclic Amplification

CWD is the only known TSE that affects free-ranging wildlife, specifically cervids such as elk, deer, moose, caribou, and reindeer. CWD has become endemic in both free-ranging and captive herds in North America, South Korea, and, most recently, northern Europe. The prion research community continues to debate the origins of CWD. Original foci of CWD emergence in Colorado and Wyoming coincident with the sheep TSE scrapie suggest that scrapie prions may have adapted to cervids to cause CWD. However, emerging evidence supports the idea that cervid PrP^C may be more prone to misfolding to the pathological isoform. Here we test the hypothesis that cervid PrP^C can spontaneously misfold to create de novo prions. Whether CWD can arise spontaneously as a sporadic TSE or represents a new TSE caused by cervid-adapted scrapie prions profoundly impacts surveillance and mitigation strategies.

Substantial evidence supports the hypothesis that prions are misfolded, infectious, insoluble, and protease-resistant proteins (PrP^RES) devoid of instructional nucleic acid that cause transmissible spongiform encephalopathies (TSEs). Protein misfolding cyclic amplification (PMCA) has provided additional evidence that PrPRes acts as a template that can convert the normal cellular prion protein (PrP^C) present in uninfected normal brain homogenate (NBH) into the infectious misfolded PrP^RES isoform. Human PrP^C has been shown to spontaneously convert to a misfolded pathological state causing sporadic Creutzfeldt-Jakob disease (sCJD). Several investigators have reported spontaneous generation of prions by in vitro assays, including PMCA. Here we tested the rate of de novo generation of cervid prions in our laboratory using our standard PMCA protocol and NBH from transgenic mice expressing cervid PrP^C (TgCerPrP mice). We generated de novo prions in rounds 4, 5, and 7 at low cumulative rates of 1.6, 5.0, and 6.7%, respectively. The prions caused infectious chronic wasting disease (CWD) upon inoculation into normal uninfected TgCerPrP mice and displayed unique biochemical characteristics compared to other cervid prion strains. We conclude that PMCA of cervid PrP^C from normal brain homogenate spontaneously generated a new cervid prion strain. These data support the potential for cervids to develop sporadic CWD.

IMPORTANCE CWD is the only known TSE that affects free-ranging wildlife, specifically cervids such as elk, deer, moose, caribou, and reindeer. CWD has become endemic in both free-ranging and captive herds in North America, South Korea, and, most recently, northern Europe. The prion research community continues to debate the origins of CWD. Original foci of CWD emergence in Colorado and Wyoming coincident with the sheep TSE scrapie suggest that scrapie prions may have adapted to cervids to cause CWD. However, emerging evidence supports the idea that cervid PrP^C may be more prone to misfolding to the pathological isoform. Here we test the hypothesis that cervid PrP^C can spontaneously misfold to create de novo prions. Whether CWD can arise spontaneously as a sporadic TSE or represents a new TSE caused by cervid-adapted scrapie prions profoundly impacts surveillance and mitigation strategies.

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Heparan Sulfate and Heparin Promote Faithful Prion Replication in Vitro by Binding to Normal and Abnormal Prion Proteins in Protein Misfolding Cyclic Amplification

The precise mechanism underlying the conversion of normal prion protein (PrP^C) into abnormal prion protein (PrP^Sc) remains unclear. Protein misfolding cyclic amplification (PMCA), an in vitro technique used for amplifying PrP^Sc, results in PrP^Sc replication that preserves the strain-specific characteristics of the input PrP^Sc; thus, PMCA mimics the process of in vivo PrP^Sc replication. Previous work has demonstrated that in PMCA, nucleic acids are critical for PrP^Sc amplification, but little information has been reported on glycosaminoglycan (GAG) participation in PrP^Sc replication in vitro Here, we investigated whether GAGs play a role in the faithful replication of PrP^Sc by using a modified PMCA performed with baculovirus-derived recombinant PrP (Bac-PrP) as a substrate. The addition of heparan sulfate (HS) or its analog heparin (HP) restored the conversion efficiency in PMCA that was inhibited through nucleic acid depletion. Moreover, the PMCA products obtained under these conditions were infectious and preserved the properties of the input PrP^Sc These data suggest that HS and HP play the same role as nucleic acids in facilitating faithful replication of prions in PMCA. Furthermore, we showed that HP binds to both Bac-PrP and Bac-PrP^Sc through the sulfated groups present on HP and that the N-terminal domain of Bac-PrP^Sc might potentially not be involved in the binding to HP. These results suggest that the interaction of GAGs such as HS and HP with PrP^C and/or PrP^Sc through their sulfate groups is critical for the faithful replication of prions.

Multiple affinity purification of a baculovirus-derived recombinant prion protein with in vitro ability to convert to its pathogenic form

We previously showed that baculovirus-derived recombinant prion protein (Bac-PrP) can be converted to the misfolded infectious form (PrP^Sc) by protein misfolding cyclic amplification, an in vitro conversion technique. Bac-PrP, with post-translational modifications, would be useful for various applications such as using PrP as an immunogen for generating anti-PrP antibody, developing anti-prion drugs or diagnostic assays using in vitro conversion systems, and establishing an in vitro prion propagation model. For this purpose, highly purified Bac-PrP with in vitro conversion activity is necessary for use as a PrP^C source, to minimize contamination. Furthermore, an exogenous affinity tag-free form is desirable to avoid potential steric interference by the affinity tags during the conversion process. In this study, we established purification methods for the untagged Bac-PrP under native conditions by combining exogenous double-affinity tags, namely, a polyhistidine-tag and a profinity eXact tag, with an octarepeat sequence of the N-terminal region of PrP, which has metal ion-binding affinity. The untagged Bac-PrP with near-homogeneity was obtained by three-step affinity purification, and it was shown that the final, purified Bac-PrP could convert to its pathogenic form. The presented purification procedure could be applied not only to PrP but also to other eukaryotic, recombinant proteins that require high purity and intact physiological activity.

In vitro amplification of scrapie and chronic wasting disease PrP(res) using baculovirus-expressed recombinant PrP as substrate

Protein misfolding cyclic amplification (PMCA) is an in vitro simulation of prion replication, which relies on the use of normal brain homogenate derived from host species as substrate for the specific amplification of abnormal prion protein, PrP(Sc). Studies showed that recombinant cellular PrP, PrP(C), expressed in Escherichia coli lacks N-glycosylation and an glycophosphatidyl inositol anchor (GPI) and therefore may not be the most suitable substrate in seeded PMCA reactions to recapitulate prion conversion in vitro. In this study, we expressed 2 PRNP genotypes of sheep, V136L141R154Q171 and A136F141R154Q171, and one genotype of white-tailed deer (Q95G96, X132,Y216) using the baculovirus expression system and evaluated their suitability as substrates in seeded-PMCA. It has been reported that host-encoded mammalian RNA molecules and divalent cations play a role in the pathogenesis of prion diseases, and RNA molecules have also been shown to improve the sensitivity of PMCA assays. Therefore, we also assessed the effect of co-factors, such as prion-specific mRNA molecules and a divalent cation, manganese, on protein conversion. Here, we report that baculovirus-expressed recombinant PrP(C) shows a glycoform and GPI-anchor profile similar to mammalian brain-derived PrP(C) and supports amplification of PrP(Sc) and PrP(CWD) derived from prion-affected animals in a single round of seeded PMCA in the absence of exogenous co-factors. Addition of species-specific in vitro transcribed PrP mRNA molecules stimulated the conversion efficiency resulting in increased PrP(Sc) or PrP(CWD) production. Addition of 2 to 20 μM of manganese chloride (MnCl2) to unseeded PMCA resulted in conversion of recombinant PrP(C) to protease-resistant PrP. Collectively, we demonstrate, for the first time, that baculovirus expressed sheep and deer PrP can serve as a substrate in protein misfolding cyclic amplification for sheep and deer prions in the absence of additional exogenous co-factors.

Prion formation, but not clearance, is supported by protein misfolding cyclic amplification

Prion diseases are fatal transmissible neurodegenerative disorders that affect animals including humans. The kinetics of prion infectivity and PrP(Sc) accumulation can differ between prion strains and within a single strain in different tissues. The net accumulation of PrP(Sc) in animals is controlled by the relationship between the rate of PrP(Sc) formation and clearance. Protein misfolding cyclic amplification (PMCA) is a powerful technique that faithfully recapitulates PrP(Sc) formation and prion infectivity in a cell-free system. PMCA has been used as a surrogate for animal bioassay and can model species barriers, host range, strain co-factors and strain interference. In this study we investigated if degradation of PrP(Sc) and/or prion infectivity occurs during PMCA. To accomplish this we performed PMCA under conditions that do not support PrP(Sc) formation and did not observe either a reduction in PrP(Sc) abundance or an extension of prion incubation period, compared to untreated control samples. These results indicate that prion clearance does not occur during PMCA. These data have significant implications for the interpretation of PMCA based experiments such as prion amplification rate, adaptation to new species and strain interference where production and clearance of prions can affect the outcome.

Lack of prion transmission by sexual or parental routes in experimentally infected hamsters

Prion diseases are a group of neurodegenerative disorders affecting humans as well as captive and wild animals. The mechanisms and routes governing the natural spread of prions are not completely understood and several hypotheses have been proposed. In this study, we analyzed the effect of gender in prion incubation period, as well as the possibility of prion transmission by sexual and parental contact using 263K infected hamsters as a model. Our results show that males have significantly longer incubation periods compared with females when exposed to the same quantity of infectious material. Importantly, no evidence of sexual or parental prion transmission was found, even 500 d after sexual contact or birth, respectively. Western blotting and PMCA were unable to detect sub-clinical levels of PrP(Sc) in experimental subjects, suggesting a complete absence of prion transmission by these routes. Our results show that sexual and parental transmission of prions does not occur in this model. It remains to be studied whether this conclusion is valid also for other prion strains and species.

Changes in prion replication environment cause prion strain mutation

Interspecies prion transmission often leads to stable changes in physical and biological features of prion strains, a phenomenon referred to as a strain mutation. It remains unknown whether changes in the replication environment in the absence of changes in PrP primary structure can be a source of strain mutations. To approach this question, RNA content was altered in the course of amplification of hamster strains in serial protein misfolding cyclic amplification (sPMCAb). On adaptation to an RNA-depleted environment and then readaptation to an environment containing RNA, strain 263K gave rise to a novel PrP(Sc) conformation referred to as 263K(R+), which is characterized by very low conformational stability, high sensitivity to proteolytic digestion, and a replication rate of 10(6)-fold/PMCAb round, which exceeded that of 263K by almost 10(4)-fold. A series of PMCAb experiments revealed that 263K(R+) was lacking in brain-derived 263K material, but emerged de novo as a result of changes in RNA content. A similar transformation was also observed for strain Hyper, suggesting that this phenomenon was not limited to 263K. The current work demonstrates that dramatic PrP(Sc) transformations can be induced by changes in the prion replication environment and without changes in PrP primary structure.