PET-blot analysis contributes to BSE strain recognition in C57Bl/6 mice

Conventional and State-of-the-Art Detection Methods of Bovine Spongiform Encephalopathy (BSE)

Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative disease that belongs to a group of diseases known as transmissible spongiform encephalopathies (TSEs). It is believed that the infectious agent responsible for prion diseases is abnormally folded prion protein (PrP^Sc), which derives from a normal cellular protein (PrP^C), which is a cell surface glycoprotein predominantly expressed in neurons. There are three different types of BSE, the classical BSE (C-type) strain and two atypical strains (H-type and L-type). BSE is primarily a disease of cattle; however, sheep and goats also can be infected with BSE strains and develop a disease clinically and pathogenically indistinguishable from scrapie. Therefore, TSE cases in cattle and small ruminants require discriminatory testing to determine whether the TSE is BSE or scrapie and to discriminate classical BSE from the atypical H- or L-type strains. Many methods have been developed for the detection of BSE and have been reported in numerous studies. Detection of BSE is mainly based on the identification of characteristic lesions or detection of the PrP^Sc in the brain, often by use of their partial proteinase K resistance properties. The objective of this paper was to summarize the currently available methods, highlight their diagnostic performance, and emphasize the advantages and drawbacks of the application of individual tests.

Bovine adapted transmissible mink encephalopathy is similar to L-BSE after passage through sheep with the VRQ/VRQ genotype but not VRQ/ARQ

Background

Transmissible mink encephalopathy (TME) is a fatal neurologic disease of farmed mink. Evidence indicates that TME and L-BSE are similar and may be linked in some outbreaks of TME. We previously transmitted bovine adapted TME (bTME) to sheep. The present study compared ovine passaged bTME (o-bTME) to C-BSE and L-BSE in transgenic mice expressing wild type bovine prion protein (TgBovXV). To directly compare the transmission efficiency of all prion strains in this study, we considered the attack rates and mean incubation periods. Additional methods for strain comparison were utilized including lesion profiles, fibril stability, and western blotting.

Results

Sheep donor genotype elicited variable disease phenotypes in bovinized mice. Inoculum derived from a sheep with the VRQ/VRQ genotype (o-bTME_VV) resulted in an attack rate, incubation period, western blot profile, and neuropathology most similar to bTME and L-BSE. Conversely, donor material from a sheep with the VRQ/ARQ genotype (o-bTME_AV) elicited a phenotype distinct from o-bTME_VV, bTME and L-BSE. The TSE with the highest transmission efficiency in bovinized mice was L-BSE. The tendency to efficiently transmit to TgBovXV mice decreased in the order bTME, C-BSE, o-bTME_VV, and o-bTME_AV. The transmission efficiency of L-BSE was approximately 1.3 times higher than o-bTME_VV and 3.2 times higher than o-bTME_AV.

Conclusions

Our findings provide insight on how sheep host genotype modulates strain genesis and influences interspecies transmission characteristics. Given that the transmission efficiencies of L-BSE and bTME are higher than C-BSE, coupled with previous reports of L-BSE transmission to mice expressing the human prion protein, continued monitoring for atypical BSE is advisable in order to prevent occurrences of interspecies transmission that may affect humans or other species.

Stability of murine scrapie strain 87V after passage in sheep and comparison with the CH1641 ovine strain

Breed- and prion protein (PRNP) genotype-related disease phenotype variability has been observed in sheep infected with the 87V murine scrapie strain. Therefore, the stability of this strain was tested by inoculating sheep-derived 87V brain material back into VM mice. As some sheep-adapted 87V disease phenotypes were reminiscent of CH1641 scrapie, transgenic mice (Tg338) expressing ovine prion protein (PrP) were inoculated with the same sheep-derived 87V sources and with CH1641. Although at first passage in VM mice the sheep-derived 87V sources showed some divergence from the murine 87V control, all the characteristics of murine 87V infection were recovered at second passage from all sheep sources. These included 100 % attack rates and indistinguishable survival times, lesion profiles, immunohistochemical features of disease-associated PrP accumulation in the brain and PrP biochemical properties. All sheep-derived 87V sources, as well as CH1641, were transmitted to Tg338 mice with identical clinical, pathological, immunohistochemical and biochemical features. While this might potentially indicate that sheep-adapted 87V and CH1641 are the same strain, profound divergences were evident, as murine 87V was unable to infect Tg338 mice but was lethal for VM mice, while the reverse was true for CH1641. These combined data suggest that: (i) murine 87V is stable and retains its properties after passage in sheep; (ii) it can be isolated from sheep showing a CH1641-like or a more conventional scrapie phenotype; and (iii) sheep-adapted 87V scrapie, with conventional or CH1641-like phenotype, is biologically distinct from experimental CH1641 scrapie, despite the fact that they behave identically in a single transgenic mouse line.

Secretin receptor involvement in prion-infected cells and animals

The cellular mechanisms behind prion biosynthesis and metabolism remain unclear. Here we show that secretin signaling via the secretin receptor regulates abnormal prion protein formation in prion-infected cells. Animal studies demonstrate that secretin receptor deficiency slightly, but significantly, prolongs incubation time in female but not male mice. This gender-specificity is consistent with our finding that prion-infected cells are derived from females. Therefore, our results provide initial insights into the reasons why age of disease onset in certain prion diseases is reported to occur slightly earlier in females than males.

TSE strain differentiation in mice by immunohistochemical PrP(Sc) profiles and triplex Western blot

TSE strains are routinely identified by their incubation period and vacuolation profile in the brain after intracerebral inoculation and serial passaging in inbred mouse lines. There are some major drawbacks to this method that are related to the variation in vacuolation that exists in the brains of mice infected with the same TSE strain and to variation between observers and laboratories in scoring vacuolation and determining the final incubation period.

AIM

We investigated the potential of PrP(Sc) immunohistochemistry and triplex Western blotting as possible alternative methods to differentiate between TSE strains.

METHODS

TSE reference strains ME7, 87A/87V, 22A/22C, 79A/79V and 301C/301V were intracerebrally inoculated in RIII or VM inbred mice that differ in their PrP genotype. Immunohistochemical PrP(Sc) profiles were drawn up by scanning light microscopy both on coronal and sagittal sections.

RESULTS

On the basis of the localization of PrP(Sc) in the cerebral cortex, hippocampus, and cerebellar cortex and the overall type of PrP(Sc) staining, all TSE strains could be well differentiated from each other through their typical strain dependent characteristics. In addition, Western blot showed that the combination of glycosylation profile and 12B2 epitope content of PrP(Sc) allowed to distinguish between all reference strains except for ME7 and 22A in VM mice.

CONCLUSION

TSE strains in mice can be identified on the basis of their PrP(Sc) profile alone. The potential to identify TSE strains in ruminants with these PrP(Sc) profiles after a single primary passage in mice will be the topic of future studies.

Early and persistent expression of phosphorylated α-synuclein in the enteric nervous system of A53T mutant human α-synuclein transgenic mice

Alpha-synuclein is a key protein in Parkinson disease (PD) and dementia with Lewy bodies. It is found in Lewy bodies in the brains of PD patients and has been reported in the peripheral nervous system in postmortem tissues from PD patients and in biopsies from patients in the preclinical phase of PD. Here, we used a transgenic mouse model of human synucleinopathies expressing the A53T mutant α-synuclein (TgM83) in which a neurodegenerative process associated with α-synuclein occurs spontaneously and increases with age. In particular, α-synuclein protein phosphorylated at serine 129 (pSer129 α-synuclein) naturally and progressively increases in diseased brains. We examined the time course of pSer129 α-synuclein presence in the gut of these mice between 1.5 and 22 months of age using immunohistochemistry and paraffin-embedded tissue blots. The pSer129 α-synuclein accumulated early (before the onset of motor signs) and persistently in the enteric nervous system and was concomitantly found in the brain. These results suggest that the accumulation of phosphorylated α-synuclein in the enteric and central nervous systems may result from parallel pathologic processes when the disease is linked to a mutation of α-synuclein.

L-type bovine spongiform encephalopathy in genetically susceptible and resistant sheep: changes in prion strain or phenotypic plasticity of the disease-associated prion protein?

BACKGROUND

Sheep with prion protein (PrP) gene polymorphisms QQ171 and RQ171 were shown to be susceptible to the prion causing L-type bovine spongiform encephalopathy (L-BSE), although RQ171 sheep specifically propagated a distinctive prion molecular phenotype in their brains, characterized by a high molecular mass protease-resistant PrP fragment (HMM PrPres), distinct from L-BSE in QQ171 sheep.

METHODS

The resulting infectious and biological properties of QQ171 and RQ171 ovine L-BSE prions were investigated in transgenic mice expressing either bovine or ovine PrP.

RESULTS

In both mouse lines, ovine L-BSE transmitted similarly to cattle-derived L-BSE, with respect to survival periods, histopathology, and biochemical features of PrPres in the brain, as well as splenotropism, clearly differing from ovine classic BSE or from scrapie strain CH1641. Nevertheless and unexpectedly, HMM PrPres was found in the spleen of ovine PrP transgenic mice infected with L-BSE from RQ171 sheep at first passage, reminiscent, in lymphoid tissues only, of the distinct PrPres features found in RQ171 sheep brains.

CONCLUSIONS

The L-BSE agent differs from both ovine classic BSE or CH1641 scrapie maintaining its specific strain properties after passage in sheep, although striking PrPres molecular changes could be found in RQ171 sheep and in the spleen of ovine PrP transgenic mice.

Bovine spongiform encephalopathy induces misfolding of alleged prion-resistant species cellular prion protein without altering its pathobiological features

Bovine spongiform encephalopathy (BSE) prions were responsible for an unforeseen epizootic in cattle which had a vast social, economic, and public health impact. This was primarily because BSE prions were found to be transmissible to humans. Other species were also susceptible to BSE either by natural infection (e.g., felids, caprids) or in experimental settings (e.g., sheep, mice). However, certain species closely related to humans, such as canids and leporids, were apparently resistant to BSE. In vitro prion amplification techniques (saPMCA) were used to successfully misfold the cellular prion protein (PrP(c)) of these allegedly resistant species into a BSE-type prion protein. The biochemical and biological properties of the new prions generated in vitro after seeding rabbit and dog brain homogenates with classical BSE were studied. Pathobiological features of the resultant prion strains were determined after their inoculation into transgenic mice expressing bovine and human PrP(C). Strain characteristics of the in vitro-adapted rabbit and dog BSE agent remained invariable with respect to the original cattle BSE prion, suggesting that the naturally low susceptibility of rabbits and dogs to prion infections should not alter their zoonotic potential if these animals became infected with BSE. This study provides a sound basis for risk assessment regarding prion diseases in purportedly resistant species.

The interpretation of disease phenotypes to identify TSE strains following murine bioassay: characterisation of classical scrapie

Mouse bioassay can be readily employed for strain typing of naturally occurring transmissible spongiform encephalopathy cases. Classical scrapie strains have been characterised historically based on the established methodology of assessing incubation period of disease and the distribution of disease-specific vacuolation across the brain following strain stabilisation in a given mouse line. More recent research has shown that additional methods could be used to characterise strains and thereby expand the definition of strain “phenotype”. Here we present the phenotypic characteristics of classical scrapie strains isolated from 24 UK ovine field cases through the wild-type mouse bioassay. PrP^Sc immunohistochemistry (IHC), paraffin embedded tissue blots (PET-blot) and Western blotting approaches were used to determine the neuroanatomical distribution and molecular profile of PrP^Sc associated with each strain, in conjunction with traditional methodologies. Results revealed three strains isolated through each mouse line, including a previously unidentified strain. Moreover IHC and PET-blot methodologies were effective in characterising the strain-associated types and neuroanatomical locations of PrP^Sc. The use of Western blotting as a parameter to define classical scrapie strains was limited. These data provide a comprehensive description of classical scrapie strain phenotypes on isolation through the mouse bioassay that can provide a reference for further scrapie strain identification.

Transmissibility of caprine scrapie in ovine transgenic mice

Background

The United States control program for classical ovine scrapie is based in part on the finding that infection is typically spread through exposure to shed placentas from infected ewes. Transmission from goats to sheep is less well described. A suitable rodent model for examining the effect of caprine scrapie isolates in the ovine host will be useful in the ovine scrapie eradication effort. In this study, we describe the incubation time, brain lesion profile, glycoform pattern and PrP^Sc distribution patterns in a well characterized transgenic mouse line (Tg338) expressing the ovine VRQ prion allele, following inoculation with brain from scrapie infected goats.

Results

First passage incubation times of caprine tissue in Tg338 ovinized mice varied widely but second passage intervals were shorter and consistent. Vacuolation profiles, glycoform patterns and paraffin-embedded tissue blots from terminally ill second passage mice derived from sheep or goat inocula were similar. Proteinase K digestion products of murine tissue were slightly smaller than the original ruminant inocula, a finding consistent with passage of several ovine strains in previous reports.

Conclusions

These findings demonstrate that Tg338 mice propagate prions of caprine origin and provide a suitable baseline for examination of samples identified in the expanded US caprine scrapie surveillance program.

Paraffin-embedded tissue blot as a sensitive method for discrimination between classical scrapie and experimental bovine spongiform encephalopathy in sheep

The paraffin-embedded tissue (PET) blot was modified for use as a tool to differentiate between classical scrapie and experimental bovine spongiform encephalopathy (BSE) in sheep. Medulla (obex) from 21 cases of classical scrapie and 6 cases of experimental ovine BSE were used to develop the method such that it can be used as a tool to differentiate between BSE and scrapie in the same way that differential immunohistochemistry (IHC) has been used previously. The differential PET blot successfully differentiated between all of the scrapie and ovine BSE cases. Differentiation was permitted more easily with PET blot than by differential IHC, with accurate observations possible at the macroscopic level. At the microscopic level, sensitivity was such that discrimination by the differential PET blot could be made with more confidence than with differential IHC in cases where the immunohistochemical differences were subtle. The differential PET blot makes use of harsh epitope demasking conditions, and, because of the differences in the way prion protein is processed in different prion diseases, it can serve as a new, highly sensitive method to discriminate between classical scrapie and experimental BSE in sheep.

Histopathological studies of "CH1641-like" scrapie sources versus classical scrapie and BSE transmitted to ovine transgenic mice (TgOvPrP4)

The possibility of the agent causing bovine spongiform encephalopathy (BSE) infecting small ruminants is of serious concern for human health. Among scrapie cases, the CH1641 source in particular appears to have certain biochemical properties similar to the BSE strain. In France, several natural scrapie cases were identified as “CH1641-like” natural scrapie isolates in sheep and goats. The Tg(OvPrP4) mouse line expressing the ovine prion protein is a sensitive model for studying and identifying strains of agents responsible for scrapie and BSE. This model is also very useful when studying specific scrapie source CH1641, known to be not transmissible to wild-type mice despite the similarity of some of its biochemical properties to those of the BSE strain. As it is important to be able to fully distinguish CH1641 from BSE, we herein report the histopathological data from CH1641 scrapie transmission experiments compared to specific cases of “CH1641-like” natural scrapie isolates in sheep, murine scrapie strains and BSE. In addition to the conventional vacuolar lesion profile approach and PrP^d brain mappings, an innovative differential PET-blot analysis was introduced to classify the different strains of agent and revealed the first direct concordance between ways of grouping strains on the basis of PrP^d biochemical characteristics.

Transmission of prion strains in a transgenic mouse model overexpressing human A53T mutated α-synuclein

There is a growing interest in the potential roles of misfolded protein interactions in neurodegeneration. To investigate this issue, we inoculated 3 prion strains intracerebrally into transgenic (TgM83) mice that overexpress human A53T α-synuclein. In comparison to nontransgenic controls, there was a striking decrease in the incubation periods of scrapie, classic and H-type bovine spongiform encephalopathies(C-BSE and H-BSE), with conservation of the histopathologic and biochemical features characterizing these 3 prion strains. TgM83 mice died of scrapie or C-BSE prion diseases before accumulating the insoluble and phosphorylated forms of α-synuclein specific to late stages of synucleinopathy. In contrast, the median incubation time for TgM83 mice inoculated with H-BSE was comparable to that observed when these mice were uninfected, thereby allowing the development of molecular alterations of α-synuclein. The last 4 mice of this cohort exhibited early accumulations of H-BSE prion protein along with α-synuclein pathology. The results indicate that a prion disease was triggered concomitantly with an overt synucleinopathy in some transgenic mice overexpressing human A53T α-synuclein after intracerebral inoculation with an H-BSE prion strain.

PrPSc spreading patterns in the brain of sheep linked to different prion types

Scrapie in sheep and goats has been known for more than 250 years and belongs nowadays to the so-called prion diseases that also include e.g. bovine spongiform encephalopathy in cattle (BSE) and Creutzfeldt-Jakob disease in humans. According to the prion hypothesis, the pathological isoform (PrP^Sc) of the cellular prion protein (PrP^c) comprises the essential, if not exclusive, component of the transmissible agent. Currently, two types of scrapie disease are known - classical and atypical/Nor98 scrapie. In the present study we examine 24 cases of classical and 25 cases of atypical/Nor98 scrapie with the sensitive PET blot method and validate the results with conventional immunohistochemistry. The sequential detection of PrP^Sc aggregates in the CNS of classical scrapie sheep implies that after neuroinvasion a spread from spinal cord and obex to the cerebellum, diencephalon and frontal cortex via the rostral brainstem takes place. We categorize the spread of PrP^Sc into four stages: the CNS entry stage, the brainstem stage, the cruciate sulcus stage and finally the basal ganglia stage. Such a sequential development of PrP^Sc was not detectable upon analysis of the present atypical/Nor98 scrapie cases. PrP^Sc distribution in one case of atypical/Nor98 scrapie in a presumably early disease phase suggests that the spread of PrP^Sc aggregates starts in the di- or telencephalon. In addition to the spontaneous generation of PrP^Sc, an uptake of the infectious agent into the brain, that bypasses the brainstem and starts its accumulation in the thalamus, needs to be taken into consideration for atypical/Nor98 scrapie.

Emergence of classical BSE strain properties during serial passages of H-BSE in wild-type mice

Background

Two distinct forms of atypical spongiform encephalopathies (H-BSE and L-BSE) have recently been identified in cattle. Transmission studies in several wild-type or transgenic mouse models showed that these forms were associated with two distinct major strains of infectious agents, which also differed from the unique strain that had been isolated from cases of classical BSE during the food-borne epizootic disease.

Methodology/Principal Findings

H-BSE was monitored during three serial passages in C57BL/6 mice. On second passage, most of the inoculated mice showed molecular features of the abnormal prion protein (PrP^d) and brain lesions similar to those observed at first passage, but clearly distinct from those of classical BSE in this mouse model. These features were similarly maintained during a third passage. However, on second passage, some of the mice exhibited distinctly different molecular and lesion characteristics, reminiscent of classical BSE in C57Bl/6 mice. These similarities were confirmed on third passage from such mice, for which the same survival time was also observed as with classical BSE adapted to C57Bl/6 mice. Lymphotropism was rarely detected in mice with H-BSE features. In contrast, PrP^d was detectable, on third passage, in the spleens of most mice exhibiting classical BSE features, the pattern being indistinguishable from that found in C57Bl/6 mice infected with classical BSE.

Conclusion/Significance

Our data demonstrate the emergence of a prion strain with features similar to classical BSE during serial passages of H-BSE in wild-type mice. Such findings might help to explain the origin of the classical BSE epizootic disease, which could have originated from a putatively sporadic form of BSE.

Is the presence of abnormal prion protein in the renal glomeruli of feline species presenting with FSE authentic?

In a recent paper written by Hilbe et al (BMC vet res, 2009), the nature and specificity of the prion protein deposition in the kidney of feline species affected with feline spongiform encephalopathy (FSE) were clearly considered doubtful. This article was brought to our attention because we published several years ago an immunodetection of abnormal prion protein in the kidney of a cheetah affected with FSE. At this time we were convinced of its specificity but without having all the possibilities to demonstrate it. As previously published by another group, the presence of abnormal prion protein in some renal glomeruli in domestic cats affected with FSE is indeed generally considered as doubtful mainly because of low intensity detected in this organ and because control kidneys from safe animals present also a weak prion immunolabelling. Here we come back on these studies and thought it would be helpful to relay our last data to the readers of BMC Vet res for future reference on this subject.

Here we come back on our material as it is possible to study and demonstrate the specificity of prion immunodetection using the PET-Blot method (Paraffin Embedded Tissue - Blot). It is admitted that this method allows detecting the Proteinase K (PK) resistant form of the abnormal prion protein (PrPres) without any confusion with unspecific immunoreaction. We re-analysed the kidney tissue versus adrenal gland and brain samples from the same cheetah affected with TSE using this PET-Blot method. The PET-Blot analysis revealed specific PrPres detection within the brain, adrenal gland and some glomeruli of the kidney, with a complete identicalness compared to our previous detection using immunohistochemistry. In conclusion, these new data enable us to confirm with assurance the presence of specific abnormal prion protein in the adrenal gland and in the kidney of the cheetah affected with FSE. It also emphasizes the usefulness for the re-examination of any available tissue blocks with the PET-Blot method as a sensitive complementary tool in case of doubtful PrP IHC results.

The synaptic pathology of alpha-synuclein aggregation in dementia with Lewy bodies, Parkinson's disease and Parkinson's disease dementia

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are usually associated with loss of dopaminergic neurons. Loss of substantia nigra neurons and presence of Lewy body inclusions in some of the remaining neurons are the hallmark pathology seen in the final stages of the disease. Attempts to correlate Lewy body pathology to either cell death or severity of clinical symptoms, however, have not been successful. While the pathophysiology of the neurodegenerative process can hardly be explained by Lewy bodies, the clinical symptoms do indicate a degenerative process located at the presynapse resulting in a neurotransmitter deficiency. Recently it was shown that 90% or even more of alpha-synuclein aggregates in DLB cases were located at the presynapses in the form of very small deposits. In parallel, dendritic spines are retracted, whereas the presynapses are relatively preserved, suggesting a neurotransmitter deprivation. The same alpha-synuclein pathology can be demonstrated for PD. These findings give rise to the notion that not cell death but rather alpha-synuclein aggregate-related synaptic dysfunction causes the neurodegeneration. This opens new perspectives for understanding PD and DLB. If presynaptic alpha-synuclein aggregation, not neuronal loss, is the key issue of the neurodegenerative process, then PD and DLB may eventually be treatable in the future. The disease may progress via trans-synaptical spread, suggesting that stem cell transplants are of limited use. Future therapies may focus on the regeneration of synapses.

Biochemical and immunohistochemical characterization of feline spongiform encephalopathy in a German captive cheetah

Feline spongiform encephalopathy (FSE) is a transmissible spongiform encephalopathy that affects domestic cats (Felis catus) and captive wild members of the family Felidae. In this report we describe a case of FSE in a captive cheetah from the zoological garden of Nuremberg. The biochemical examination revealed a BSE-like pattern. Disease-associated scrapie prion protein (PrP(Sc)) was widely distributed in the central and peripheral nervous system, as well as in the lymphoreticular system and in other tissues of the affected animal, as demonstrated by immunohistochemistry and/or immunoblotting. Moreover, we report for the first time the use of the protein misfolding cyclic amplification technique for highly sensitive detection of PrP(Sc) in the family Felidae. The widespread PrP(Sc) deposition suggests a simultaneous lymphatic and neural spread of the FSE agent. The detection of PrP(Sc) in the spleen indicates a potential for prion infectivity of cheetah blood.

Paraffin-embedded tissue (PET) blot method: application to Alzheimer disease

Traditionally, immunohistochemistry, immunoblotting, and histoblot have been used to detect protein in tissue samples. However, each of these techniques has a number of disadvantages. The sensitivity of protein detection in immunohistochemistry is lost due to fixation or paraffin embedding methods that modify antigenic sites. The anatomical resolution and specific cellular involvement are lost in immunoblotting. Histoblot, a hybrid of these two techniques, is able to resolve these issues, but it cannot be applied to formalin-fixed tissues. A recent technique, paraffin-embedded tissue (PET) blot, retains the superior protein detection and anatomical resolution of histoblot and is applicable to formalin-fixed tissues. Unfortunately, a major obstacle to the widespread application of PET is the lack of a detailed methodological description. In this paper, we describe a PET blotting method that was formulated from our own empirical and experimental research in Alzheimer disease and a systematic review of the current literature. From this, we conclude that PET can be applied to a variety of conditions with a wide spectrum of pathology.

Detection of classical and atypical/Nor98 scrapie by the paraffin-embedded tissue blot method

The paraffin-embedded tissue (PET) blot method was used to investigate sections of the central nervous system and lymphatic tissues from 24 cases of classical scrapie and 25 cases of atypical/Nor98 scrapie in sheep and four healthy control sheep. The PET blot detected deposits of PrP(Sc) in the brain tissue of all 49 sheep with scrapie but no PrP(Sc) labelling could be detected in the control sheep. By contrast, not all the atypical/Nor98 scrapie cases were detectable by immunohistochemistry. The high sensitivity of the PET blot method made it possible to observe that in some atypical/Nor98 cases, deposits of PrP(Sc) may be restricted to supratentorial brain structures and that the diagnosis may be missed when only testing the obex area, where deposits are common in classical scrapie, and the cerebellar structures, where deposits are considered to be common in atypical/Nor98 cases.

Ultramicroscopy reveals axonal transport impairments in cortical motor neurons at prion disease

The functional imaging of neuronal circuits of the central nervous system is crucial for phenotype screenings or investigations of defects in neurodegenerative disorders. Current techniques yield either low penetration depth, yield poor resolution, or are restricted by the age of the animals. Here, we present a novel ultramicroscopy protocol for fluorescence imaging and three-dimensional reconstruction in the central nervous system of adult mice. In combination with tracing as a functional assay for axonal transport, retrogradely labeled descending motor neurons were visualized with >4 mm penetration depth. The analysis of the motor cortex shortly before the onset of clinical prion disease revealed that >80% neurons have functional impairments in axonal transport. Our study provides evidence that prion disease is associated with severe axonal transport defects in the cortical motor neurons and suggests a novel mechanism for prion-mediated neurodegeneration.

A C-terminal protease-resistant prion fragment distinguishes ovine "CH1641-like" scrapie from bovine classical and L-Type BSE in ovine transgenic mice

The protease-resistant prion protein (PrP(res)) of a few natural scrapie isolates identified in sheep, reminiscent of the experimental isolate CH1641 derived from a British natural scrapie case, showed partial molecular similarities to ovine bovine spongiform encephalopathy (BSE). Recent discovery of an atypical form of BSE in cattle, L-type BSE or BASE, suggests that also this form of BSE might have been transmitted to sheep. We studied by Western blot the molecular features of PrP(res) in four "CH1641-like" natural scrapie isolates after transmission in an ovine transgenic model (TgOvPrP4), to see if "CH1641-like" isolates might be linked to L-type BSE. We found less diglycosylated PrP(res) than in classical BSE, but similar glycoform proportions and apparent molecular masses of the usual PrP(res) form (PrP(res) #1) to L-type BSE. However, the "CH1641-like" isolates differed from both L-type and classical BSE by an abundant, C-terminally cleaved PrP(res) product (PrP(res) #2) specifically recognised by a C-terminal antibody (SAF84). Differential immunoprecipitation of PrP(res) #1 and PrP(res) #2 resulted in enrichment in PrP(res) #2, and demonstrated the presence of mono- and diglycosylated PrP(res) products. PrP(res) #2 could not be obtained from several experimental scrapie sources (SSBP1, 79A, Chandler, C506M3) in TgOvPrP4 mice, but was identified in the 87V scrapie strain and, in lower and variable proportions, in 5 of 5 natural scrapie isolates with different molecular features to CH1641. PrP(res) #2 identification provides an additional method for the molecular discrimination of prion strains, and demonstrates differences between "CH1641-like" ovine scrapie and bovine L-type BSE transmitted in an ovine transgenic mouse model.

Rapid typing of transmissible spongiform encephalopathy strains with differential ELISA

A strain-typing ELISA distinguishes bovine spongiform encephalopathy from other scrapie strains in small ruminants.

The bovine spongiform encephalopathy (BSE) agent has been transmitted to humans, leading to variant Creutzfeldt-Jakob disease. Sheep and goats can be experimentally infected by BSE and have been potentially exposed to natural BSE; however, whether BSE can be transmitted to small ruminants is not known. Based on the particular biochemical properties of the abnormal prion protein (PrPsc) associated with BSE, and particularly the increased degradation induced by proteinase K in the N terminal part of PrPsc, we have developed a rapid ELISA designed to distinguish BSE from other scrapie strains. This assay clearly discriminates experimental ovine BSE from other scrapie strains and was used to screen 260 transmissible spongiform encephalopathy (TSE)–infected small ruminant samples identified by the French active surveillance network (2002/2003). In this context, this test has helped to identify the first case of natural BSE in a goat and can be used to classify TSE isolates based on the proteinase K sensitivity of PrPsc.

Characterisation of new monoclonal antibodies reacting with prions from both human and animal brain tissues

Post-mortem diagnosis of transmissible spongiform encephalopathies (prion diseases) is primarily based on the detection of a protease resistant, misfolded disease associated isoform (PrP(Sc)) of the prion protein (PrP(C)) on neuronal cells. These methods depend on antibodies directed against PrP(C) and capable of reacting with PrP(Sc)in situ (immunohistochemistry on nervous tissue sections) or with the unfolded form of the protein (western and paraffin embedded tissue (PET) blotting). Here, high-affinity monoclonal antibodies (mAbs 1.5D7, 1.6F4) were produced against synthetic PrP peptides in wild-type mice and used for western blotting and immunohistochemistry to detect several types of human prion-disease associated PrP(Sc), including sporadic Creutzfeldt-Jakob Disease (CJD) (subtypes MM1 and VV2), familial CJD and Gerstmann-Sträussler-Scheinker (GSS) disease PrP(Sc) as well as PrP(Sc) of bovine spongiform encephalopathy (bovine brain), scrapie (ovine brain) and experimental scrapie in hamster and in mice. The antibodies were also used for PET-blotting in which PrP(Sc) blotted from brain tissue sections onto a nitrocellulose membrane is visualized with antibodies after protease and denaturant treatment allowing the detection of protease resistant PrP forms (PrP(RES)) in situ. Monoclonal antibodies 1.5D7 and 1.6F4 were raised against the reported epitope (PrP153-165) of the commercial antibody 6H4. While 1.5D7 and 1.6F4 were completely inhibitable by PrP153-165, 6H4 was not, indicating that the specificity of 6H4 is not defined completely by PrP153-165. The two antibodies performed similarly to 6H4 in western blotting with human samples, but showed less reactivity and enhanced background staining with animal samples in this method. In immunohistochemistry 1.5D7 and 1.6F4 performed better than 6H4 suggesting that the binding affinity of 1.5D7 and 1.6F4 with native (aggregated) PrP(Sc)in situ was higher than that of 6H4. On the other hand in PET-blotting, 6H4 reached the same level of reactivity as 1.5D7 and 1.6F4. This shows that 6H4 needs denatured PrP(RES) to reach maximal reactivity, confirming earlier results. As an exception, human PrP(RES) still reacted relatively poorly with 6H4 in PET-blotting, while 1.5D7 and 1.6F4 reacted well with PrP(RES) from most human CJD types. Taken together this implies that the binding epitope of 1.5D7 and 1.6F4 is accessible in the aggregates of undenatured PrP(Sc) (IHC) while the binding site of 6H4 is at least partly inaccessible. In techniques incorporating a denaturing and/or disaggregating step 6H4 showed good binding indicating increased accessibility of the binding site. An exception to this is human samples in PET-blotting suggesting that huPrP(RES) might not be as easily unfolded by denaturation as BSE and scrapie PrP(RES). Also of interest was the ability of 1.5D7 and 1.6F4 to discriminate between two allelic variants of PrP CJD(Sc) (VV vs. MM) in immunohistochemistry as opposed to the normally used antibody 3F4.

Biological and biochemical characterization of L-type-like bovine spongiform encephalopathy (BSE) detected in Japanese black beef cattle

A case of L-type-like atypical bovine spongiform encephalopathy was detected in 14-year-old Japanese black beef cattle (BSE/JP24). To clarify the biological and biochemical properties of the prion in BSE/JP24, we performed a transmission study with wild-type mice and bovinized transgenic mice (TgBoPrP). The BSE/JP24 prion was transmitted to TgBoPrP mice with the incubation period of 199.7 +/- 3.4 days, which was shorter than that of classical BSE (C-BSE) (223.5 +/- 13.5 days). Further, C-BSE was transmitted to wild-type mice with the incubation period of about 409 days, whereas BSE/JP24 prion inoculated mice showed no clinical signs up to 649 days. Severe vacuolation and a widespread and uniform distribution of PrP(Sc) were pathologically observed in the brain of BSE/JP24 prion affected TgBoPrP mice. The molecular weight and glycoform ratio of PrP(Sc) in BSE/JP24 were different from those in C-BSE, and PrP(Sc) in BSE/JP24 exhibited weaker proteinase K resistance than that in C-BSE. These findings revealed that the BSE/JP24 prion has distinct biological and biochemical properties reported for that of C-BSE. Interestingly, a shorter incubation period was observed at the subsequent passage of the BSE/JP24 prion to TgBoPrP mice (152.2 +/- 3.1 days). This result implies that BSE/JP24 prion has newly emerged and showed the possibility that L-type BSE prion might be classified into multiple strains.

Bovine Spongiform Encephalopathy in Sweden: An H-Type Variant

Bovine spongiform encephalopathy (BSE) had never been detected in Sweden until 2006, when the active surveillance identified a case in a 12-year-old cow. The case was an unusual form, because several molecular features of the protease-resistant prion protein (PrPres) were different from classical BSE. The differences included higher susceptibility for proteinase K, higher molecular weight of the PrPres bands, affinity to the N-terminus-specific antibodies 12B2 and P4, and peculiar banding pattern with antibody SAF84 showing an additional band at the 14 kDa position. The molecular characteristics were in accordance to previous descriptions of H-type BSE. This report shows that a range of Western blot techniques and antibodies can be applied to confirm H-type BSE and further describes that the ratio of the amounts of PrPres#1 and PrPres#2, after deglycosylation, depends on the antibody used during processing. Immunohistochemistry on sections of medulla at the level of the obex applying antibodies with epitopes covering a broad range of the PrP sequence showed accumulation of disease-specific PrP (PrP d ) in the gray matter. Fine punctate deposition in the neuropil was the most predominant type and was more severe in BSE target nuclei. The types of PrP d deposition are described in comparison with classical BSE. PrP-gene sequencing showed 6 copy octarepeat alleles and no abnormalities. It is postulated that the disease had a spontaneous origin, rather than having had been acquired in the BSE epidemic.

Prion strain discrimination in cell culture: the cell panel assay

Prions are thought to consist mainly or entirely of misfolded PrP, a constitutively expressed host protein. Prions associated with the same PrP sequence may occur in the form of different strains; the strain phenotype is believed to be encoded by the conformation of the PrP. Some cell lines can be persistently infected by prions and, interestingly, show preference for certain strains. We report that a cloned murine neuroblastoma cell population, N2a-PK1, is highly heterogeneous in regard to its susceptibility to RML and 22L prions. Remarkably, sibling subclones may show very different relative susceptibilities to the two strains, indicating that the responses can vary independently. We have assembled four cell lines, N2a-PK1, N2a-R33, LD9 and CAD5, which show widely different responses to prion strains RML, 22L, 301C, and Me7, into a panel that allows their discrimination in vitro within 2 weeks, using the standard scrapie cell assay (SSCA).

Molecular discrimination of atypical bovine spongiform encephalopathy strains from a geographical region spanning a wide area in Europe

Transmissible spongiform encephalopathy strains can be differentiated by their behavior in bioassays and by molecular analyses of the disease-associated prion protein (PrP) in a posttranslationally transformed conformation (PrPSc). Until recently, isolates from cases of bovine spongiform encephalopathy (BSE) appeared to be very homogeneous. However, a limited number of atypical BSE isolates have recently been identified upon analyses of the disease-associated proteinase K (PK) resistance-associated moiety of PrPSc (PrPres), suggesting the existence of at least two additional BSE PrPres variants. These are defined here as the H type and the L type, according to the higher and lower positions of the nonglycosylated PrPres band in Western blots, respectively, compared to the position of the band in classical BSE (C-type) isolates. These molecular PrPres variants, which originated from six different European countries, were investigated together. In addition to the migration properties and glycosylation profiles (glycoprofiles), the H- and L-type isolates exhibited enhanced PK sensitivities at pH 8 compared to those of the C-type isolates. Moreover, H-type BSE isolates exhibited differences in the binding of antibodies specific for N- and more C-terminal PrP regions and principally contained two aglycosylated PrPres moieties which can both be glycosylated and which is thus indicative of the existence of two PrPres populations or intermediate cleavage sites. These properties appear to be consistent within each BSE type and independent of the geographical origin, suggesting the existence of different BSE strains in cattle. The choice of three antibodies and the application of two pHs during the digestion of brain homogenates provide practical and diverse tools for the discriminative detection of these three molecular BSE types and might assist with the recognition of other variants.

Atypical transmissible spongiform encephalopathies (TSEs) in ruminants

Transmissible spongiform encephalopathies (TSEs) are associated with the accumulation in infected tissues of a disease-associated form of a host-encoded protein, the prion protein (PrP). Contrary to the normal form of the protein, this form of PrP is partially resistant to protease digestion (PrP(res)). Detailed characterisation of PrP(res) has been intensively investigated in recent years to try and decipher the diversity of TSEs in human and animals. This considerably and unexpectedly enlarged our knowledge about such diseases in ruminants. Previously, such a diversity was essentially shown by the demonstration that scrapie from sheep and goats could have different biological behaviours following transmission of the disease in mice, unlike bovine spongiform encephalopathy from cattle (BSE) which showed a distinct and unique behaviour. The properties of the BSE agent were also demonstrated to be very stable, following transmission to a variety of different species. Molecular studies of PrP(res), followed by transmission studies to mice, gave the first evidence for the accidental transmission of the BSE agent to humans where it induced a variant form of the fatal Creutzfeldt-Jakob disease (CJD) and also to different animal species including a goat in France. This last case was found among a few unusual cases of TSEs in small ruminants that showed some molecular similarities with BSE and which are currently under investigation by transmission studies in mice. The application of the molecular methods to characterise PrP(res) has most recently led to the unexpected discovery of deviant BSE forms in a few affected cattle in Europe and in the United States, which raises the question of a possible different origin at least of some cases of BSE in cattle. Finally, considerable numbers of a new TSE form in small ruminants, referred to as "atypical scrapie" or "Nor98", have meanwhile been identified in most European countries by TSE rapid testing using an assay which recognizes also comparatively less PK resistant PrP(res).