Retinal cell types are differentially affected in sheep with scrapie

Differential Accumulation of Misfolded Prion Strains in Natural Hosts of Prion Diseases

Prion diseases, also known as transmissible spongiform encephalopathies (TSEs), are a group of neurodegenerative protein misfolding diseases that invariably cause death. TSEs occur when the endogenous cellular prion protein (PrP^C) misfolds to form the pathological prion protein (PrP^Sc), which templates further conversion of PrP^C to PrP^Sc, accumulates, and initiates a cascade of pathologic processes in cells and tissues. Different strains of prion disease within a species are thought to arise from the differential misfolding of the prion protein and have different clinical phenotypes. Different strains of prion disease may also result in differential accumulation of PrP^Sc in brain regions and tissues of natural hosts. Here, we review differential accumulation that occurs in the retinal ganglion cells, cerebellar cortex and white matter, and plexuses of the enteric nervous system in cattle with bovine spongiform encephalopathy, sheep and goats with scrapie, cervids with chronic wasting disease, and humans with prion diseases. By characterizing TSEs in their natural host, we can better understand the pathogenesis of different prion strains. This information is valuable in the pursuit of evaluating and discovering potential biomarkers and therapeutics for prion diseases.

Prion-induced photoreceptor degeneration begins with misfolded prion protein accumulation in cones at two distinct sites: cilia and ribbon synapses

Accumulation of misfolded host proteins is central to neuropathogenesis of numerous human brain diseases including prion and prion-like diseases. Neurons of retina are also affected by these diseases. Previously, our group and others found that prion-induced retinal damage to photoreceptor cells in mice and humans resembled pathology of human retinitis pigmentosa caused by mutations in retinal proteins. Here, using confocal, epifluorescent and electron microscopy we followed deposition of disease-associated prion protein (PrPSc) and its association with damage to critical retinal structures following intracerebral prion inoculation. The earliest time and place of retinal PrPSc deposition was 67 days post-inoculation (dpi) on the inner segment (IS) of cone photoreceptors. At 104 and 118 dpi, PrPSc was associated with the base of cilia and swollen cone inner segments, suggesting ciliopathy as a pathogenic mechanism. By 118 dpi, PrPSc was deposited in both rods and cones which showed rootlet damage in the IS, and photoreceptor cell death was indicated by thinning of the outer nuclear layer. In the outer plexiform layer (OPL) in uninfected mice, normal host PrP (PrPC) was mainly associated with cone bipolar cell processes, but in infected mice, at 118 dpi, PrPSc was detected on cone and rod bipolar cell dendrites extending into ribbon synapses. Loss of ribbon synapses in cone pedicles and rod spherules in the OPL was observed to precede destruction of most rods and cones over the next 2–3 weeks. However, bipolar cells and horizontal cells were less damaged, indicating high selectivity among neurons for injury by prions. PrPSc deposition in cone and rod inner segments and on the bipolar cell processes participating in ribbon synapses appear to be critical early events leading to damage and death of photoreceptors after prion infection. These mechanisms may also occur in human retinitis pigmentosa and prion-like diseases, such as AD.

Selective neuronal vulnerability is involved in cerebellar lesions of Guinea pigs infected with bovine spongiform encephalopathy (BSE) prions: Immunohistochemical and electron microscopic investigations

The cerebellar lesions of bovine spongiform encephalopathy (BSE)-infected guinea pigs were characterized as severe atrophy of the cerebellar cortex associated with the loss of granule cells, decrease in the width of the molecular layer, and intense protease-resistant prion protein (PrP^Sc ) accumulations that are similar to cerebellar lesions in kuru and the VV2 type of sporadic Creutzfeldt-Jakob disease. The aim of this study is to assess the relationships between the distribution and localization of PrP^Sc and synapses expressing neurotransmitter transporters in order to reveal the pathogenesis of the disease. We used cell-type-specific immunohistochemical makers recognizing glutamatergic and γ-aminobutylic acid (GABA)ergic terminals to identify terminals impaired with PrP^Sc accumulations. The distribution of PrP^Sc accumulations and immunoreactivity of synaptic vesicles were studied throughout the neuroanatomical pathways in cerebellar lesions. Time course study demonstrated that PrP^Sc accumulation showed a tendency to spread from granular layer to molecular layer. The immunoreactivity of vesicular glutamate transporter 1 (VGluT1) was localized in axon terminals of cerebellar granule cells, and decreased in association with the severity of PrP^Sc accumulations and loss of granule cells. Immunoreactivities of vesicular glutamate transporter 2 (VGluT2) and vesicular GABA transporter (VGAT) that exist in axon terminals of inferior olivary neurons and GABAergic synapses of Purkinje cells, respectively, were preserved well in these lesions. In brainstem, VGluT1 immunoreactivity decreased selectively in pontine nuclei that are a component of the pontocerebellar pathway, although other neurotransmitter immunoreactivities were preserved well. Our findings suggest that the selective loss of VGluT1-immunoreactive synapses subsequent to PrP^Sc accumulations can contribute to the pathogenesis of cerebellar lesions of BSE-infected guinea pigs.

The Synthetic Microneurotrophin BNN27 Affects Retinal Function in Rats With Streptozotocin-Induced Diabetes

BNN27, a C17-spiroepoxy derivative of DHEA, was shown to have antiapoptotic properties via mechanisms involving the nerve growth factor receptors (tropomyosin-related kinase A [TrkA]/neurotrophin receptor p75 [p75^NTR]). In this study, we examined the effects of BNN27 on neural/glial cell function, apoptosis, and inflammation in the experimental rat streptozotocin (STZ) model of diabetic retinopathy (DR). The ability of BNN27 to activate the TrkA receptor and regulate p75^NTR expression was investigated. BNN27 (2,10, and 50 mg/kg i.p. for 7 days) administration 4 weeks post-STZ injection (paradigm A) reversed the diabetes-induced glial activation and loss of function of amacrine cells (brain nitric oxide synthetase/tyrosine hydroxylase expression) and ganglion cell axons via a TrkA receptor (TrkAR)-dependent mechanism. BNN27 activated/phosphorylated the TrkA^Y490 residue in the absence but not the presence of TrkAR inhibitor and abolished the diabetes-induced increase in p75^NTR expression. However, it had no effect on retinal cell death (TUNEL⁺ cells). A similar result was observed when BNN27 (10 mg/kg i.p.) was administered at the onset of diabetes, every other day for 4 weeks (paradigm B). However, BNN27 decreased the activation of caspase-3 in both paradigms. Finally, BNN27 reduced the proinflammatory (TNFα and IL-1β) and increased the anti-inflammatory (IL-10 and IL-4) cytokine levels. These findings suggest that BNN27 has the pharmacological profile of a therapeutic for DR, since it targets both the neurodegenerative and inflammatory components of the disease.

The Alzheimer's-related amyloid beta peptide is internalised by R28 neuroretinal cells and disrupts the microtubule associated protein 2 (MAP-2)

Age-related Macular Degeneration (AMD) is a common, irreversible blinding condition that leads to the loss of central vision. AMD has a complex aetiology with both genetic as well as environmental risks factors, and share many similarities with Alzheimer's disease. Recent findings have contributed significantly to unravelling its genetic architecture that is yet to be matched by molecular insights. Studies are made more challenging by observations that aged and AMD retinas accumulate the highly pathogenic Alzheimer's-related Amyloid beta (Aβ) group of peptides, for which there appears to be no clear genetic basis. Analyses of human donor and animal eyes have identified retinal Aβ aggregates in retinal ganglion cells (RGC), the inner nuclear layer, photoreceptors as well as the retinal pigment epithelium. Aβ is also a major drusen constituent; found correlated with elevated drusen-load and age, with a propensity to aggregate in retinas of advanced AMD. Despite this evidence, how such a potent driver of neurodegeneration might impair the neuroretina remains incompletely understood, and studies into this important aspect of retinopathy remains limited. In order to address this we exploited R28 rat retinal cells which due to its heterogeneous nature, offers diverse neuroretinal cell-types in which to study the molecular pathology of Aβ. R28 cells are also unaffected by problems associated with the commonly used RGC-5 immortalised cell-line, thus providing a well-established model in which to study dynamic Aβ effects at single-cell resolution. Our findings show that R28 cells express key neuronal markers calbindin, protein kinase C and the microtubule associated protein-2 (MAP-2) by confocal immunofluorescence which has not been shown before, but also calretinin which has not been reported previously. For the first time, we reveal that retinal neurons rapidly internalised Aβ_1-42, the most cytotoxic and aggregate-prone amongst the Aβ family. Furthermore, exposure to physiological amounts of Aβ_1-42 for 24 h correlated with impairment to neuronal MAP-2, a cytoskeletal protein which regulates microtubule dynamics in axons and dendrites. Disruption to MAP-2 was transient, and had recovered by 48 h, although internalised Aβ persisted as discrete puncta for as long as 72 h. To assess whether Aβ could realistically localise to living retinas to mediate such effects, we subretinally injected nanomolar levels of oligomeric Aβ_1-42 into wildtype mice. Confocal microscopy revealed the presence of focal Aβ deposits in RGC, the inner nuclear and the outer plexiform layers 8 days later, recapitulating naturally-occurring patterns of Aβ aggregation in aged retinas. Our novel findings describe how retinal neurons internalise Aβ to transiently impair MAP-2 in a hitherto unreported manner. MAP-2 dysfunction is reported in AMD retinas, and is thought to be involved in remodelling and plasticity of post-mitotic neurons. Our insights suggest a molecular pathway by which this could occur in the senescent eye leading to complex diseases such as AMD.

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Molecular basis of complex retinopathies such as AMD is incompletely understood.

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The Alzheimer's-related Aβ peptides are rapidly internalised by retinal neurons.

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Internalised Aβ is retained within neurons and transiently impairs MAP-2.

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Subretinally injected Aβ mimics its naturally-occurring distribution in aged retinas.

The transmissible spongiform encephalopathies of livestock

Prion diseases or transmissible spongiform encephalopathies (TSEs) are fatal protein-misfolding neurodegenerative diseases. TSEs have been described in several species, including bovine spongiform encephalopathy (BSE) in cattle, scrapie in sheep and goats, chronic wasting disease (CWD) in cervids, transmissible mink encephalopathy (TME) in mink, and Kuru and Creutzfeldt-Jakob disease (CJD) in humans. These diseases are associated with the accumulation of a protease-resistant, disease-associated isoform of the prion protein (called PrP(Sc)) in the central nervous system and other tissues, depending on the host species. Typically, TSEs are acquired through exposure to infectious material, but inherited and spontaneous TSEs also occur. All TSEs share pathologic features and infectious mechanisms but have distinct differences in transmission and epidemiology due to host factors and strain differences encoded within the structure of the misfolded prion protein. The possibility that BSE can be transmitted to humans as the cause of variant Creutzfeldt-Jakob disease has brought attention to this family of diseases. This review is focused on the TSEs of livestock: bovine spongiform encephalopathy in cattle and scrapie in sheep and goats.

Transplantation of Neuro2a Cells into the Developing Postnatal Mouse Eye

The present study aimed to investigate the influence of the host retinal microenvironment on cell migration and differentiation using Neuro2a (N2a) cells transduced with green fluorescent protein. N2a cells were transplanted into the vitreous cavities of developing mouse eyes (C57BL/6) on postnatal days 1, 5, and 10 (P1, 5, and 10). To analyze the effects of the host microenvironment on neural differentiation of N2a cells in vitro, cells were treated with a conditioned medium (CM) collected from retinal cells cultured at each developmental stage. We observed that numerous cells transplanted into P5 mice eyes migrated into all layers of the host retina, and the presence of processes indicated morphological differentiation. Some transplanted N2a cells expressed several neural markers. However, cells transplanted into the P1 and 10 mice eyes only proliferated within the vitreous cavity. Neurite length increased in N2a cells treated with CM collected from the cultured retinal cells from P5 and 10 mice, while western blotting revealed that the levels of proteins related to neural differentiation were not significantly altered in N2a cells treated with CM. We show that the migration and differentiation capacities of transplanted cells were differentially influenced by the microenvironment of the retinal postnatal ontogeny.

Changes in retinal function and morphology are early clinical signs of disease in cattle with bovine spongiform encephalopathy

Bovine spongiform encephalopathy (BSE) belongs to a group of fatal, transmissible protein misfolding diseases known as transmissible spongiform encephalopathies (TSEs). All TSEs are caused by accumulation of misfolded prion protein (PrPSc) throughout the central nervous system (CNS), which results in neuronal loss and ultimately death. Like other protein misfolding diseases including Parkinson's disease and Alzheimer's disease, TSEs are generally not diagnosed until the onset of disease after the appearance of unequivocal clinical signs. As such, identification of the earliest clinical signs of disease may facilitate diagnosis. The retina is the most accessible part of the central nervous system, and retinal pathology in TSE affected animals has been previously reported. Here we describe antemortem changes in retinal function and morphology that are detectable in BSE inoculated animals several months (up to 11 months) prior to the appearance of any other signs of clinical disease. We also demonstrate that differences in the severity of these clinical signs reflect the amount of PrPSc accumulation in the retina and the resulting inflammatory response of the tissue. These results are the earliest reported clinical signs associated with TSE infection and provide a basis for understanding the pathology and evaluating therapeutic interventions.

Clinical and pathologic features of H-type bovine spongiform encephalopathy associated with E211K prion protein polymorphism

The majority of bovine spongiform encephalopathy (BSE) cases have been ascribed to the classical form of the disease. H-type and L-type BSE cases have atypical molecular profiles compared to classical BSE and are thought to arise spontaneously. However, one case of H-type BSE was associated with a heritable E211K mutation in the prion protein gene. The purpose of this study was to describe transmission of this unique isolate of H-type BSE when inoculated into a calf of the same genotype by the intracranial route. Electroretinograms were used to demonstrate preclinical deficits in retinal function, and optical coherence tomography was used to demonstrate an antemortem decrease in retinal thickness. The calf rapidly progressed to clinical disease (9.4 months) and was necropsied. Widespread distribution of abnormal prion protein was demonstrated within neural tissues by western blot and immunohistochemistry. While this isolate is categorized as BSE-H due to a higher molecular mass of the unglycosylated PrP^Sc isoform, a strong labeling of all 3 PrP^Sc bands with monoclonal antibodies 6H4 and P4, and a second unglycosylated band at approximately 14 kDa when developed with antibodies that bind in the C-terminal region, it is unique from other described cases of BSE-H because of an additional band 23 kDa demonstrated on western blots of the cerebellum. This work demonstrates that this isolate is transmissible, has a BSE-H phenotype when transmitted to cattle with the K211 polymorphism, and has molecular features that distinguish it from other cases of BSE-H described in the literature.

Experimental interspecies transmission studies of the transmissible spongiform encephalopathies to cattle: comparison to bovine spongiform encephalopathy in cattle

Prion diseases or transmissible spongiform encephalopathies (TSEs) of animals include scrapie of sheep and goats; transmissible mink encephalopathy (TME); chronic wasting disease (CWD) of deer, elk and moose; and bovine spongiform encephalopathy (BSE) of cattle. The emergence of BSE and its spread to human beings in the form of variant Creutzfeldt-Jakob disease (vCJD) resulted in interest in susceptibility of cattle to CWD, TME and scrapie. Experimental cross-species transmission of TSE agents provides valuable information for potential host ranges of known TSEs. Some interspecies transmission studies have been conducted by inoculating disease-causing prions intracerebrally (IC) rather than orally; the latter is generally effective in intraspecies transmission studies and is considered a natural route by which animals acquire TSEs. The "species barrier" concept for TSEs resulted from unsuccessful interspecies oral transmission attempts. Oral inoculation of prions mimics the natural disease pathogenesis route whereas IC inoculation is rather artificial; however, it is very efficient since it requires smaller dosage of inoculum, and typically results in higher attack rates and reduces incubation time compared to oral transmission. A species resistant to a TSE by IC inoculation would have negligible potential for successful oral transmission. To date, results indicate that cattle are susceptible to IC inoculation of scrapie, TME, and CWD but it is only when inoculated with TME do they develop spongiform lesions or clinical disease similar to BSE. Importantly, cattle are resistant to oral transmission of scrapie or CWD; susceptibility of cattle to oral transmission of TME is not yet determined.

Transplantation of bone marrow-derived mesenchymal stem cells into the developing mouse eye

Mesenchymal stem cells (MSCs) have been studied widely for their potential to differentiate into various lineage cells including neural cells in vitro and in vivo. To investigate the influence of the developing host environment on the integration and morphological and molecular differentiation of MSCs, human bone marrow-derived mesenchymal stem cells (BM-MSCs) were transplanted into the developing mouse retina. Enhanced green fluorescent protein (GFP)-expressing BM-MSCs were transplanted by intraocular injections into mice, ranging in ages from 1 day postnatal (PN) to 10 days PN. The survival dates ranged from 7 days post-transplantation (DPT) to 28DPT, at which time an immunohistochemical analysis was performed on the eyes. The transplanted BM-MSCs survived and showed morphological differentiation into neural cells and some processes within the host retina. Some transplanted cells expressed microtubule associated protein 2 (MAP2ab, marker for mature neural cells) or glial fibrillary acid protein (GFAP, marker for glial cells) at 5PN 7DPT. In addition, some transplanted cells integrated into the developing retina. The morphological and molecular differentiation and integration within the 5PN 7DPT eye was greater than those of other-aged host eye. The present findings suggest that the age of the host environment can strongly influence the differentiation and integration of BM-MSCs.

Clinical, electroretinographic and histomorphometric evaluation of the retina in sheep with natural scrapie

Background

The retina is part of the diencephalon in a peripheral location and may be involved in prion diseases. Retinal function and structural changes were assessed in naturally scrapie-affected red face Manech ewes presenting the classical signs of the disease, and clinically healthy age-matched subjects for controls. Ophthalmic examination was done prior to electroretinography (ERG), which was carried out under conditions that allowed photopic and scotopic activities to be assessed. Histomorphometry of the inner and outer retinal layers was performed post-mortem, and retinas were also examined for evidence of abnormal prion protein (PrP^Sc) accumulation and glial fibrillary acidic protein (GFAP) upregulation as a marker of gliosis. Scrapie status was determined by examination of brain tissue

Results

Ocular reflexes and ophthalmoscopy did not reveal any difference between scrapie affected and control animals. Although the light-and dark-adapted ERG responses of both rod-and cone-mediated functions had a similar waveform in scrapie-affected and control sheep, a significant reduction in the amplitude of the ERG a-and b-waves was observed in affected animals compared to controls. These functional alterations were correlated with a substantial loss of cells in the outer nuclear layer (ONL), lengthening and disorganization in photoreceptor segments, and substantial reduction in cellularity and thickness of the inner nuclear layer (INL). The degenerative changes in the INL and ONL were most marked in the central and paracentral areas of the scrapie retinas, and were accompanied in all scrapie retinas by PrP^Sc deposition in the ganglion cell and synaptic layers. GFAP immunoreactivity was mainly increased in the ganglion cell and inner plexiform layers.

Conclusions

No appreciable fundoscopic changes were observed in the scrapie-affected ewes although reproducible changes in retinal function as measured by ERG were observed in these animals. The alterations in the receptoral and post-receptoral pathways corresponded to the degenerative lesions observed in the ONL and INL of the scrapie retinas. The retinal degeneration was associated with prion protein infectivity which presumably spread via the optic nerve.

Fluorescence spectroscopy of the retina for diagnosis of transmissible spongiform encephalopathies

The feasibility of exploiting fluorescence spectra of the eye for diagnosis of transmissible spongiform encephalopathies (TSEs) was examined. Retinas from scrapie-positive sheep were compared with scrapie-negative sheep using fluorescence spectroscopy, and distinct differences in the fluorescence intensity and spectroscopic signatures were observed. The characteristic fluorescent signatures are thought to be the result of an accumulation of lipofuscin in the retina. It appears that the eye, in particular the retina, is a useful tissue for noninvasive examination of some neurological pathologies such as scrapie. The development of procedures based on examinations of the eye that permit the detection of neurological disorders in animals holds great promise.

Microcebus murinus retina: a new model to assess prion-related neurotoxicity in primates

No effective treatment currently exists for prion diseases and therefore the development of experimental non-human primate models of prion neurotoxicity, to better understand the underlying mechanism and to test new treatments relevant to humans, represents an urgent medical need. However, the establishment of such models is challenging due to animal welfare and cost considerations. We describe here the use of Microcebus murinus retina, in primary cultures and in vivo, as a new experimental primate model to rapidly examine the effects in the central nervous system of PrP(106-126), a neurotoxic fragment of the human prion protein. We demonstrate that PrP(106-126) triggered rod photoreceptor cell loss by apoptosis and a change in morphology of microglial cells in mixed neuronal-glial cultures of retinal cells. In addition, 2days after intravitreal injection of PrP(106-126), retinas showed a significant increase in the number of apoptotic nuclei, mainly in the ganglion cell layer.

Detection of the abnormal isoform of the prion protein associated with chronic wasting disease in the optic pathways of the brain and retina of Rocky Mountain elk (Cervus elaphus nelsoni)

Eyes and nuclei of the visual pathways in the brain were examined in 30 Rocky Mountain elk (Cervus elaphus nelsoni) representing 3 genotypes of the prion protein gene PRNP (codon 132: MM, ML, or LL). Tissues were examined for the presence of the abnormal isoform of the prion protein associated with chronic wasting disease (PrP(CWD)). Nuclei and axonal tracts from a single section of brain stem at the level of the dorsal motor nucleus of the vagus nerve were scored for intensity and distribution of PrP(CWD) immunoreactivity and degree of spongiform degeneration. This obex scoring ranged from 0 (elk with no PrP(CWD) in the brain stem) to 10 (representing elk in terminal stage of disease). PrP(CWD) was detected in the retina of 16 of 18 (89%) elk with an obex score of > 7. PrP(CWD) was not detected in the retina of the 3 chronic wasting disease-negative elk and 9 elk with an obex score of < 6. PrP(CWD) was found in the nuclei of the visual pathways in the brain before it was found in the retina. Within the retina, PrP(CWD) was first found in the inner plexiform layer, followed by the outer plexiform layer. Intracytoplasmic accumulation of PrP(CWD) was found in a few neurons in the ganglion cell layer in the PRNP 132ML elk but was a prominent feature in the PRNP 132LL elk. Small aggregates of PrP(CWD) were present on the inner surface of the outer limiting membrane in PRNP 132LL elk but not in PRNP 132MM or 132ML elk. This study demonstrates PrP(CWD) accumulation in nuclei of the visual pathways of the brain, followed by PrP(CWD) in the retina.

Retinal Function and Morphology Are Altered in Cattle Infected with the Prion Disease Transmissible Mink Encephalopathy

Transmissible spongiform encephalopathies (TSEs) are a group of diseases that result in progressive and invariably fatal neurologic disease in both animals and humans. TSEs are characterized by the accumulation of an abnormal protease-resistant form of the prion protein in the central nervous system. Transmission of infectious TSEs is believed to occur via ingestion of prion protein–contaminated material. This material is also involved in the transmission of bovine spongiform encephalopathy (“mad cow disease”) to humans, which resulted in the variant form of Creutzfeldt-Jakob disease. Abnormal prion protein has been reported in the retina of TSE-affected cattle, but despite these observations, the specific effect of abnormal prion protein on retinal morphology and function has not been assessed. The objective of this study was to identify and characterize potential functional and morphologic abnormalities in the retinas of cattle infected with a bovine-adapted isolate of transmissible mink encephalopathy. We used electroretinography and immunohistochemistry to examine retinas from 10 noninoculated and 5 transmissible mink encephalopathy–inoculated adult Holstein steers. Here we show altered retinal function, as evidenced by prolonged implicit time of the electroretinogram b-wave, in transmissible mink encephalopathy–infected cattle before the onset of clinical illness. We also demonstrate disruption of rod bipolar cell synaptic terminals, indicated by decreased immunoreactivity for the alpha isoform of protein kinase C and vesicular glutamate transporter 1, and activation of Müller glia, as evidenced by increased glial fibrillary acidic protein and glutamine synthetase expression, in the retinas of these cattle at the time of euthanasia due to clinical deterioration. This is the first study to identify both functional and morphologic alterations in the retinas of TSE-infected cattle. Our results support future efforts to focus on the retina for the development of new strategies for the diagnosis of TSEs.

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.

Neuroglobin and prion cellular localization: investigation of a potential interaction

Neuroglobin (Ngb) and the cellular prion protein (PrP(c)), proteins of unknown function in the nervous system, are known to be expressed in the retina and have been observed in different rat retinal cells. The retina is the site of the highest concentration for Ngb, a heme protein of similar size and conformation to myoglobin. In this study, we demonstrated by immunohistochemical analysis of retinal colocalization of Ngb and PrP(c) in the ganglion cell layer. Considering for these two a common protective role in relation to oxidative stress and a possible transient contact during migration of PrP(c) through the eye or upon neuronal degradation, we undertook in vitro studies of the interaction of the purified proteins. Mixing these two proteins leads to rapid aggregation, even at submicromolar concentrations. As observed with the use of dynamic light scattering, particles comprising both proteins evolve to hundreds of nanometers within several seconds, a first report showing that PrP(c) is able to form aggregates without major structural changes. The main effect would then appear to be a protein-protein interaction specific to the surface charge of the Ngb protein with PrP(c) N-terminal sequence. A dominant parameter is the solvent ionic force, which can significantly modify the final state of aggregation. PrP(c), normally anchored to the cell membrane, is toxic in the cytoplasm, where Ngb is present; this could suggest an Ngb function of scavenging proteins capable of forming deleterious aggregates considering a charge complementarity in the complex.