Inconsistent detection of PrP in extraneural tissues of cats with feline spongiform encephalopathy

Mountain Lions (Puma concolor) Resist Long-Term Dietary Exposure To Chronic Wasting Disease

For nearly 18 yr, we evaluated susceptibility of captive mountain lions (Puma concolor) to chronic wasting disease (CWD) in the face of repeated exposure associated with consuming infected cervid carcasses. Three mountain lions with a monomorphic prion protein gene (PRNP) sequence identical to that described previously for the species had access to parts of ≥432 infected carcasses during ≥2,013 feeding occasions, conservatively representing >14,000 kg of infected feed material, during May 2002 to March 2020. The proportion of diet in infected carcass material averaged 43% overall but differed from year to year (minimally 11%-74%). Most infected carcasses were mule deer (Odocoileus hemionus; ∼75%). We observed no clinical signs suggestive of progressive encephalopathy or other neurologic disease over the ∼14.5-17.9 yr between first known exposure and eventual death. Histopathology revealed no spongiform changes or immunostaining suggestive of prion infection in multiple sections of nervous and lymphoid tissue. Similarly, none of 133 free-ranging mountain lion carcasses sampled opportunistically during 2004-2020 showed immunostaining consistent with prion infection in sections of brainstem or lymph node. These findings align with prior work suggesting that CWD-associated prions face strong barriers to natural transmission among species outside the family Cervidae.

Detection of Pathognomonic Biomarker PrPSc and the Contribution of Cell Free-Amplification Techniques to the Diagnosis of Prion Diseases

Transmissible spongiform encephalopathies or prion diseases are rapidly progressive neurodegenerative diseases, the clinical manifestation of which can resemble other promptly evolving neurological maladies. Therefore, the unequivocal ante-mortem diagnosis is highly challenging and was only possible by histopathological and immunohistochemical analysis of the brain at necropsy. Although surrogate biomarkers of neurological damage have become invaluable to complement clinical data and provide more accurate diagnostics at early stages, other neurodegenerative diseases show similar alterations hindering the differential diagnosis. To solve that, the detection of the pathognomonic biomarker of disease, PrP^Sc, the aberrantly folded isoform of the prion protein, could be used. However, the amounts in easily accessible tissues or body fluids at pre-clinical or early clinical stages are extremely low for the standard detection methods. The solution comes from the recent development of in vitro prion propagation techniques, such as Protein Misfolding Cyclic Amplification (PMCA) and Real Time-Quaking Induced Conversion (RT-QuIC), which have been already applied to detect minute amounts of PrP^Sc in different matrixes and make early diagnosis of prion diseases feasible in a near future. Herein, the most relevant tissues and body fluids in which PrP^Sc has been detected in animals and humans are being reviewed, especially those in which cell-free prion propagation systems have been used with diagnostic purposes.

Generation of a persistently infected MDBK cell line with natural bovine spongiform encephalopathy (BSE)

Bovine spongiform encephalopathy (BSE) is a zoonotic transmissible spongiform encephalopathy (TSE) thought to be caused by the same prion strain as variant Creutzfeldt-Jakob disease (vCJD). Unlike scrapie and chronic wasting disease there is no cell culture model allowing the replication of proteinase K resistant BSE (PrP^BSE) and the further in vitro study of this disease. We have generated a cell line based on the Madin-Darby Bovine Kidney (MDBK) cell line over-expressing the bovine prion protein. After exposure to naturally BSE-infected bovine brain homogenate this cell line has shown to replicate and accumulate PrP^BSE and maintain infection up to passage 83 after initial challenge. Collectively, we demonstrate, for the first time, that the BSE agent can infect cell lines over-expressing the bovine prion protein similar to other prion diseases. These BSE infected cells will provide a useful tool to facilitate the study of potential therapeutic agents and the diagnosis of BSE.

Prion and prion-like diseases in animals

Transmissible spongiform encephalopaties (TSEs) are fatal neurodegenerative diseases characterized by the aggregation and accumulation of the misfolded prion protein in the brain. Other proteins such as β-amyloid, tau or Serum Amyloid-A (SAA) seem to share with prions some aspects of their pathogenic mechanism; causing a variety of so called prion-like diseases in humans and/or animals such as Alzheimer's, Parkinson's, Huntington's, Type II diabetes mellitus or amyloidosis. The question remains whether these misfolding proteins have the ability to self-propagate and transmit in a similar manner to prions. In this review, we describe the prion and prion-like diseases affecting animals as well as the recent findings suggesting the prion-like transmissibility of certain non-prion proteins.

Advances in screening test development for transmissible spongiform encephalopathies

The blood of patients with transmissible spongiform encephalopathy or prion disease can no longer be considered free of infectivity. There have been two recent reports of highly probable transfusion-associated iatrogenic variant Creutzfeldt-Jakob disease infections, and there is supporting experimental evidence of scrapie transmission by the transfusion of blood from sheep with naturally occurring disease. In the absence of a preclinical diagnostic test for transmissible spongiform encephalopathy, the main precautionary measures undertaken by blood agencies employ donor exclusion criteria, ensuring that the number of any further iatrogenic cases will be small. The development of a sensitive, specific and reliable diagnostic test is urgently needed for early identification of infected individuals in order to ensure the safety of blood supplies. During the past 5 years, significant progress has been made in improving the sensitivity and specificity of tests using brain and lymphoreticular tissues to identify Creutzfeldt-Jakob disease-infected individuals. However, the quest for a blood test is still in its infancy and requires extensive further research.

Structure of the β2-α2 loop and interspecies prion transmission

Prions are misfolded, aggregated conformers of the prion protein that can be transmitted between species. The precise determinants of interspecies transmission remain unclear, although structural similarity between the infectious prion and host prion protein is required for efficient conversion to the misfolded conformer. The β2-α2 loop region of endogenous prion protein, PrP(C), has been implicated in barriers to prion transmission. We recently discovered that conversion was efficient when incoming and host prion proteins had similar β2-α2 loop structures; however, the roles of primary vs. secondary structural homology could not be distinguished. Here we uncouple the effect of primary and secondary structural homology of the β2-α2 loop on prion conversion. We inoculated prions from animals having a disordered or an ordered β2-α2 loop into mice having a disordered loop or an ordered loop due to a single residue substitution (D167S). We found that prion conversion was driven by a homologous primary structure and occurred independently of a homologous secondary structure. Similarly, cell-free conversion using PrP(C) from mice with disordered or ordered loops and prions from 5 species correlated with primary but not secondary structural homology of the loop. Thus, our findings support a model in which efficient interspecies prion conversion is determined by small stretches of the primary sequence rather than the secondary structure of PrP.

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.

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.

A molecular switch controls interspecies prion disease transmission in mice

Transmissible spongiform encephalopathies are lethal neurodegenerative disorders that present with aggregated forms of the cellular prion protein (PrPC), which are known as PrPSc. Prions from different species vary considerably in their transmissibility to xenogeneic hosts. The variable transmission barriers depend on sequence differences between incoming PrPSc and host PrPC and additionally, on strain-dependent conformational properties of PrPSc. The beta2-alpha2 loop region within PrPC varies substantially between species, with its structure being influenced by the residue types in the 2 amino acid sequence positions 170 (most commonly S or N) and 174 (N or T). In this study, we inoculated prions from 5 different species into transgenic mice expressing either disordered-loop or rigid-loop PrPC variants. Similar beta2-alpha2 loop structures correlated with efficient transmission, whereas dissimilar loops correlated with strong transmission barriers. We then classified literature data on cross-species transmission according to the 170S/N polymorphism. Transmission barriers were generally low between species with the same amino acid residue in position 170 and high between those with different residues. These findings point to a triggering role of the local beta2-alpha2 loop structure for prion transmissibility between different species.

Immunohistochemical study of PrP(Sc) distribution in neural and extraneural tissues of two cats with feline spongiform encephalopathy

Background

Two domestic shorthair cats presenting with progressive hind-limb ataxia and increased aggressiveness were necropsied and a post mortem diagnosis of Feline Spongiform Encephalopathy (FSE) was made. A wide spectrum of tissue samples was collected and evaluated histologically and immunohistologically for the presence of PrP^Sc.

Results

Histopathological examination revealed a diffuse vacuolation of the grey matter neuropil with the following areas being most severely affected: corpus geniculatum medialis, thalamus, gyrus dentatus of the hippocampus, corpus striatum, and deep layers of the cerebral and cerebellar cortex as well as in the brain stem. In addition, a diffuse glial reaction involving astrocytes and microglia and intraneuronal vacuolation in a few neurons in the brain stem was present.

Heavy PrP^Sc immunostaining was detected in brain, retina, optic nerve, pars nervosa of the pituitary gland, trigeminal ganglia and small amounts in the myenteric plexus of the small intestine (duodenum, jejunum) and slightly in the medulla of the adrenal gland.

Conclusion

The PrP^Sc distribution within the brain was consistent with that described in other FSE-affected cats. The pattern of abnormal PrP in the retina corresponded to that found in a captive cheetah with FSE, in sheep with scrapie and was similar to nvCJD in humans.

Neuropathology of italian cats in feline spongiform encephalopathy surveillance

Feline spongiform encephalopathy (FSE) is a transmissible spongiform encephalopathy associated with the consumption of feedstuffs contaminated with tissue from bovine spongiform encephalopathy-affected cattle and characterized by the accumulation in the central nervous system of an abnormal isoform of the prion protein (PrP(sc)). Clinically, it presents as a progressive fatal neurologic syndrome that is not easily distinguished from other feline neurologic conditions. Most cases of FSE have been reported in England, where it was first detected in 1990, but a few cases have been reported from other European countries. To identify possible cases of FSE in Italy, the Italian Ministry of Health funded a 2-year surveillance project during which the brains from 110 domestic cats with neurologic signs were evaluated histologically for spongiform encephalopathy and immunohistochemically to detect PrP(sc). Although no cases of FSE were found, the study proved useful in monitoring the Italian cat population for other neurologic diseases: neoplasia (21.8%), toxic-metabolic encephalopathy (18.2%), granulomatous encephalitis (15.5%), suppurative encephalitis (4.6%), trauma (3.6%), circulatory disorders (3.6%), degeneration (2.7%), nonsuppurative encephalitis (2.7%), and neuromuscular diseases (1.8%). No histologic lesions were found in 20% of the brains, and samples from 5.5% of the cats were rejected as unsuitable.

Occurrence and cellular localization of PrPd in kidneys of scrapie-affected sheep in the absence of inflammation

Following a preliminary description of disease-associated prion protein (PrPd) deposition in the kidneys of scrapie-affected sheep, detailed studies have been undertaken in order to evaluate the factors that could account for such PrPd accumulation and to determine the precise location of PrPd in the renal papillae. Immunohistochemical (IHC) examinations for PrPd were conducted in kidneys collected at post-mortem from 30 naturally and 37 experimentally infected sheep. In addition, PrPd detection by western blot analysis (WB) and ultrastructural examination was carried out in a selection of kidneys. PrPd-specific, multifocal IHC labelling with antibody R145 was achieved in the kidneys of 44% and 51% of the naturally and experimentally infected sheep, respectively. The specificity of these results was confirmed by further IHC and WB using several PrP antibodies raised to different amino acid sequences, and by examination of control tissues. PrPd was shown to accumulate in the interstitium of the renal papillae, in association with the cell membrane and lysosomes of fibroblast-like cells, or extracellularly, in close contact with collagen and basal membranes. These deposits were unrelated to inflammatory changes in the kidney as shown by routine histology and by IHC for different immune cell markers. PrPd accumulated in the kidney of sheep that showed widespread PrPd deposition in the lymphoreticular system and had long incubation periods; these findings argue for a haematogenous origin of renal PrPd, although the precise site and mechanism-glomerular filtration and reabsorption at Henle's loop, or extravasation from vasa recta capillaries, or both-by which PrPd leaves the blood to accumulate in the interstitium of renal papillae remain to be determined. Either of these pathogenetic mechanisms could lead to environmental contamination via urine.

Experimental chronic wasting disease (CWD) in the ferret

Chronic wasting disease (CWD), a prion disease of North American deer, elk and moose, affects both free-ranging and captive cervids. The potential host range for CWD remains uncertain. The susceptibility of the ferret to CWD was examined experimentally by administering infectious brain material by the intracerebral (IC) or oral (PO) route. Between 15 and 20 months after IC inoculation, ferrets developed neurological signs consistent with prion disease, including polyphagia, somnolence, piloerection, lordosis and ataxia. Upon first sub-passage of ferret-adapted CWD, the incubation period decreased to 5 months. Spongiform change in the neuropil was most marked in the basal ganglia, thalamus, midbrain and pons. The deposition of PrP(CWD) was granular and was occasionally closely associated with, or localized within, neurons. There were no plaque-like or perivascular PrP aggregates as seen in CWD-infected cervids. In western blots, the PrP(CWD) glycoform profile resembled that of CWD in deer, typified by a dominant diglycosylated glycoform. CWD disease in ferrets followed IC but not PO inoculation, even after 31 months of observation. These findings indicate that CWD-infected ferrets share microscopical and biochemical features of CWD in cervids, but appear to be relatively resistant to oral infection by primary CWD inoculum of deer origin.

Intraepithelial and interstitial deposition of pathological prion protein in kidneys of scrapie-affected sheep

Prions have been documented in extra-neuronal and extra-lymphatic tissues of humans and various ruminants affected by Transmissible Spongiform Encephalopathy (TSE). The presence of prion infectivity detected in cervid and ovine blood tempted us to reason that kidney, the organ filtrating blood derived proteins, may accumulate disease associated PrP^Sc. We collected and screened kidneys of experimentally, naturally scrapie-affected and control sheep for renal deposition of PrP^Sc from distinct, geographically separated flocks. By performing Western blot, PET blot analysis and immunohistochemistry we found intraepithelial (cortex, medulla and papilla) and occasional interstitial (papilla) deposition of PrP^Sc in kidneys of scrapie-affected sheep. Interestingly, glomerula lacked detectable signals indicative of PrP^Sc. PrP^Sc was also detected in kidneys of subclinical sheep, but to significantly lower degree. Depending on the stage of the disease the incidence of PrP^Sc in kidney varied from approximately 27% (subclinical) to 73.6% (clinical) in naturally scrapie-affected sheep. Kidneys from flocks without scrapie outbreak were devoid of PrP^Sc. Here we demonstrate unexpectedly frequent deposition of high levels of PrP^Sc in ovine kidneys of various flocks. Renal deposition of PrP^Sc is likely to be a pre-requisite enabling prionuria, a possible co-factor of horizontal prion-transmission in sheep.

Amino acid sequence of the Felis catus prion protein

A new determination of the house cat (Felis catus) prion protein gene sequence (fPrnp), which has so far been subject of controversy, is reported. The newly determined fPrnp sequence is similar to dog (Canis familiaris) and mink (Mustela putorius) Prnp, but differs significantly from both fPrnp sequences that were previously deposited in the GenBank. Comparison of the canine and feline prion protein sequences suggests a set of amino acid replacements relative to bovine PrP that might relate to the observed different susceptibilities of the two species to TSE infection by ingestion of BSE-infected beef.

Specificity of lymphoreticular accumulation of prion protein for variant Creutzfeldt-Jakob disease

BACKGROUND

Immunocytochemical accumulation of prion protein (PrP) in lymphoid tissues is a feature of variant Creutzfeldt-Jakob disease (vCJD) that has been used both to aid in the diagnosis of patients and as a basis of large scale screening studies to assess the prevalence of preclinical disease in the UK. However, the specificity of this approach is unknown.

AIM

To assess the specificity of lymphoreticular accumulation of PrP for vCJD by examining a range of human diseases.

METHODS

Paraffin wax embedded lymphoreticular tissues from patients with several reactive conditions (58 cases), tumours (27 cases), vCJD (54 cases), and other human prion diseases (56 cases) were assessed. PrP accumulation was assessed by immunocytochemistry using two different monoclonal anti-PrP antibodies and a sensitive detection system.

RESULTS

All cases of vCJD showed widespread lymphoreticular accumulation of PrP; however, this was not seen in the other conditions examined.

CONCLUSION

Lymphoreticular accumulation of PrP, as assessed by immunocytochemistry, appears to be a highly specific feature of vCJD.

Resistance of domestic cats to a US sheep scrapie agent by intracerebral route

Feline spongiform encephalopathy (FSE) is thought to have resulted from consumption of food contaminated with bovine spongiform encephalopathy and the latter is believed to result from the consumption of food contaminated with scrapie. However, no direct experimental documentation exists to indicate that the scrapie agent is capable of amplifying in cats, and, therefore, crossing the species barrier. During 1979, 6 cats ranging in age from 3.5 to 18 months were intracerebrally inoculated with sheep scrapie (inoculum G-639-PP) and were observed for an extended period. Inoculated cats did not develop neurologic disease, and microscopic lesions of spongiform encephalopathy were not evident. Immunohistochemistry and Western blot techniques failed to detect the abnormal form of prion protein (PrP(res)). These results indicate that the sheep scrapie agent (G-639-PP) used in this study was not capable of amplifying in cats and therefore was unable to cross the species barrier to produce FSE.

First case of feline spongiform encephalopathy in a captive cheetah born in France: PrP(sc) analysis in various tissues revealed unexpected targeting of kidney and adrenal gland

Feline spongiform encephalopathy (FSE), affecting domestic and captive feline species, is a prion disease considered to be related to bovine spongiform encephalopathy. Here we report an immunohistological analysis of the first FSE-affected cheetah born in France. The duration of clinical signs, of which ataxia was the main one, was about 8 weeks. The distribution of abnormal prion protein (PrP(sc)) was studied by immunohistochemistry within 27 different tissues. Different antibodies were used to visualise abnormal PrP deposits in situ. PrP(sc )accumulation was detected in the central nervous system (cerebral cortex, cerebellum, brain stem, spinal cord, retina), in peripheral nerves and in lymphoid organs. PrP(sc) deposits were not observed within the enteric nervous system nor in several other organs, such as pancreas, ovary, liver and muscle. More interestingly, unusual PrP(sc )deposits were observed within the zona fasciculata/reticularis of the adrenal gland and within some glomeruli of the kidney raising the question of possible PrP(sc) excretion. The sympathetic innervation of these two organs was visualised and compared to the distribution of PrP(sc) deposits. Our results suggest the possibility that the infectious agent is spread by both haematogenous and nervous pathways.

Other animal prion diseases

In addition to bovine spongiform encephalopathy (BSE) of cattle and scrapie of sheep and goats, a few other animal prion diseases have been reported. These include feline spongiform encephalopathy of zoological and domestic cats (FSE) and transmissible spongiform encephalopathy (TSE) of zoological ruminants and non-human primates, as well as chronic wasting disease of deer and elk (CWD) and transmissible mink encephalopathy of farmed mink (TME). The origins of TSE in cats, zoo bovids, and non-human primates are clearly linked to the BSE epidemic; however, the origins of CWD and TME are less clear, but are not epidemiologically linked to the BSE epidemic. Here we review the epidemiology, transmission, clinical features and pathology of these other animal prion diseases.