Review: Creutzfeldt-Jakob disease: prion protein type, disease phenotype and agent strain

The human transmissible spongiform encephalopathies or human prion diseases are one of the most intensively investigated groups of rare human neurodegenerative conditions. They are generally held to be unique in terms of their complex epidemiology and phenotypic variability, but they may also serve as a paradigm with which other more common protein misfolding disorders might be compared and contrasted. The clinico-pathological phenotype of human prion diseases appears to depend on a complex interaction between the prion protein genotype of the affected individual and the physico-chemical properties of the neurotoxic and transmissible agent, thought to comprise of misfolded prion protein. A major focus of research in recent years has been to define the phenotypic heterogeneity of the recognized human prion diseases, correlate this with molecular-genetic features and then determine whether this molecular-genetic classification of human prion disease defines the biological properties of the agent as determined by animal transmission studies. This review seeks to survey the field as it currently stands, summarize what has been learned, and explore what remains to be investigated in order to obtain a more complete scientific understanding of prion diseases and to protect public health.

The first case of protease-sensitive prionopathy (PSPr) in The Netherlands: a patient with an unusual GSS-like clinical phenotype

An atypical case of prion disease is described in a 54-year-old Dutch man, homozygous for valine at codon 129 of the prion protein gene (PRNP). The clinical phenotype was characterised by progressive dementia, spastic paraplegia and sensorimotor polyneuropathy. The disease duration was 20 months. Genetic analysis of PRNP did not reveal any abnormalities. Neuropathologically, only mild spongiform change and a coarse granular immunohistochemical staining for the abnormal prion protein, PrP(Sc), was observed, with poorly formed plaques in the molecular layer of the cerebellar cortex. However, Western blotting showed low but detectable levels of proteinase K(PK)-resistant PrP(Sc) occurring in an unusual ladder-like profile. These features define a phenotype that corresponds to the recently described protease-sensitive prionopathy (PSPr). Our report on the first Dutch patient with PSPr further expands the spectrum of prionopathies and exemplifies the need to re-evaluate cases of atypical prion disease.

Variant CJD infection in the spleen of a neurologically asymptomatic UK adult patient with haemophilia

SUMMARY

All UK patients with bleeding disorders treated with any UK-sourced pooled factor concentrates between 1980 and 2001 have been informed that they may be at an increased risk of infection with variant Creutzfeldt-Jakob disease (vCJD). We describe a study to detect disease-associated, protease-resistant prion protein (PrP(res)) in 17 neurologically aymptomatic patients with haemophilia considered to be at increased risk of vCJD. Materials from 11 autopsy and seven biopsy cases were analysed for PrP(res). The tissues available from each case were variable, ranging from a single biopsy sample to a wide range of autopsy tissues. A single specimen from the spleen of one autopsy case gave a strong positive result on repeated testing for PrP(res) by Western blot analysis. This tissue came from a 73-year-old male patient with no history of neurological disease, who was heterozygous (methionine/valine) at codon 129 in the prion protein gene. He had received over 9000 units of factor VIII concentrate prepared from plasma pools known to include donations from a vCJD-infected donor, and some 400,000 units not known to include donations from vCJD-infected donors. He had also received 14 units of red blood cells and had undergone several surgical and invasive endoscopic procedures. Estimates of the relative risks of exposure through diet, surgery, endoscopy, blood transfusion and receipt of UK-sourced plasma products suggest that by far the most likely route of infection in this patient was receipt of UK plasma products.

Panencephalopathic Creutzfeldt-Jakob disease in the Netherlands and the UK: clinical and pathological characteristics of nine patients

AIMS

The panencephalopathic type of Creutzfeldt-Jakob disease (PECJD) has extensive abnormalities in cerebral white matter as well as the cortex. PECJD has rarely been described in Caucasians and debate continues on its classification and pathogenesis. We describe our experience of PECJD over a 14-year period of surveillance for CJD in the Netherlands and the UK.

METHODS

Between 1993 and 2006, nine cases of PECJD were identified. Clinical, histological and biochemical characteristics of all patients were analysed and compared; all cases were classified clinically as sporadic CJD.

RESULTS

The median age at onset was 57.8 years and median disease duration was 22 months. The average brain weight was 887 g. Most patients showed a two-stage clinical course with initial rapid deterioration to a state of akinetic mutism, which then persisted over a longer time scale. Neuropathological findings were characterized by severe global atrophy with status spongiosus. Cerebral white matter involvement tended to be associated with either disease duration or severity of cerebral cortical lesions. Five patients could be classified into the MM1 subtype of sporadic CJD, one patient into the MM2 subgroup and another into the MV2 subgroup. Two patients were heterozygous at codon 129 in the prion protein gene and contained both type 1 and type 2 PrP(res) isoforms in the brain.

CONCLUSIONS

We believe that white matter pathology in PECJD represents an end-stage pattern that reflects secondary degeneration due to widespread cortical neuronal loss that occurs in the early part of the disease, rather than representing a primary lesion.

Disease-associated prion protein is not detectable in human systemic amyloid deposits

Cerebral and cardiac amyloid deposits have been reported after scrapie infection in transgenic mice expressing variant prion protein (PrP(C)) lacking the glycophosphatidylinositol anchor. The amyloid fibril protein in the systemic amyloid deposits was not characterized, and there is no clinical or pathological association between prion diseases and systemic amyloidosis in humans. Nevertheless, in view of the potential clinical significance of these murine observations, we tested both human amyloidotic tissues and isolated amyloid fibrils for the presence of PrP(Sc), the prion protein conformation associated with transmissible spongiform encephalopathy (TSE). We also sequenced the complete prion protein gene, PRNP, in amyloidosis patients. No specific immunohistochemical staining for PrP(Sc) was obtained in the amyloidotic cardiac and other visceral tissues of patients with different types of systemic amyloidosis. No protease-resistant prion protein, PrP(res), was detectable by Western blotting of amyloid fibrils isolated from cardiac and other systemic amyloid deposits. Only the complete normal wild-type PRNP gene sequence was identified, including the usual distribution of codon 129 polymorphisms. These reassuringly negative results do not support the idea that there is any relationship of prions or TSE with human systemic amyloidosis, including cardiac amyloid deposition.

In vitro amplification and detection of variant Creutzfeldt–Jakob disease PrPSc

Variant Creutzfeldt-Jakob disease (vCJD) poses a serious risk of secondary transmission and the need to detect infectivity in asymptomatic individuals is therefore of major importance. Following infection, it is assumed that minute amounts of disease-associated prion protein (PrP(Sc)) replicate by conversion of the host cellular prion protein (PrP(C)). Therefore, methods of rapidly reproducing this conversion process in vitro would be valuable tools in the development of such tests. We show that one such technique, protein misfolding cyclic amplification (PMCA), can amplify vCJD PrP(Sc) from human brain tissue, and that the degree of amplification is dependent upon the substrate PRNP codon 129 polymorphism. Both human platelets and transgenic mouse brain are shown to be suitable alternative substrate sources, and amplified PrP(Sc) can be detected using a conformation-dependent immunoassay (CDI), allowing the detection of putative proteinase K sensitive forms of PrP(Sc).

vCJD and the gut: implications for endoscopy

Surveillance for infection by endoscopy for variant CJD and other human prion diseases

Dura mater-associated Creutzfeldt-Jakob disease: experience from surveillance in the UK

Between 1970 and 2003, seven cases of human dura mater-associated Creutzfeldt-Jakob disease (CJD) were identified in the UK. Furthermore, we identified a case of CJD in a porcine dura graft recipient. The mean incubation period of the human dura mater cases was 93 (range 45-177) months. The clinico-pathological features of the cases are described and compared with cases previously reported in the world literature.

Predicting susceptibility and incubation time of human-to-human transmission of vCJD

BACKGROUND

Identification of possible transmission of variant Creutzfeldt-Jakob disease (vCJD) via blood transfusion has caused concern over spread of the disease within the human population. We aimed to model iatrogenic spread to enable a comparison of transmission efficiencies of vCJD and bovine spongiform encephalopathy (BSE) and an assessment of the effect of the codon-129 polymorphism on human susceptibility.

METHODS

Mice were produced to express human or bovine prion protein (PrP) by direct replacement of the mouse PrP gene. Since the human PrP gene has variation at codon 129, with MM, VV, and MV genotypes, three inbred lines with an identical genetic background were produced to express human PrP with the codon-129 MM, MV, and VV genotypes. Mice were inoculated with BSE or vCJD and assessed for clinical and pathological signs of disease.

FINDINGS

BSE was transmitted to the bovine line but did not transmit to the human lines. By contrast, vCJD was transmitted to all three human lines with different pathological characteristics for each genotype and a gradation of transmission efficiency from MM to MV to VV.

INTERPRETATION

Transmission of BSE to human beings is probably restricted by the presence of a significant species barrier. However, there seems to be a substantially reduced barrier for human-to-human transmission of vCJD. Moreover, all individuals, irrespective of codon-129 genotype, could be susceptible to secondary transmission of vCJD through routes such as blood transfusion. A lengthy preclinical disease is predicted by these models, which may represent a risk for further disease transmission and thus a significant public-health issue.

Phenotypic variability in human prion diseases

Human prion diseases are rare neurodegenerative disorders that can occur as sporadic, familial or acquired disorders. Within each of these categories there is a wide range of phenotypic variation that is not encountered in other neurodegenerative disorders. The identification of the prion protein and its key role in the pathogenesis of this diverse group of diseases has allowed a fuller understanding of factors that influence disease phenotype. In particular, the naturally occurring polymorphism at codon 129 in the prion protein gene has a major influence on the disease phenotype in sporadic, familial and acquired prion diseases, although the underlying mechanisms remain unclear. Recent technical advances have improved our ability to study the isoforms of the abnormal prion protein in the brain and in other tissues. This has lead to the concept of molecular strain typing, in which different isoforms of the prion protein are proposed to correspond to individual strains of the transmissible agent, each with specific biological properties. In sporadic Creutzfeldt-Jakob disease there are at least six major combinations of codon 129 genotype and prion protein isotype, which appear to relate to distinctive clinical subgroups of this disease. However, these relationships are proving to be more complex than first considered, particularly in cases with more than a single prion protein isotype in the brain. Further work is required to clarify these relationships and to explain the mechanism of neuropathological targeting of specific brain regions, which accounts for the diversity of clinical features within human prion diseases.

Raised CSF phospho-tau concentrations in variant Creutzfeldt-Jakob disease: diagnostic and pathological implications

OBJECTIVE

To investigate whether phosphorylated tau protein (tau-pT181) is increased in variant Creutzfeldt-Jakob disease (vCJD) and if the tau-pT181/tau protein ratio is useful for distinguishing between patients with and without CJD.

METHODS

CSF tau protein and tau-pT181 were measured in 50 patients with sporadic CJD (sCJD), 51 patients with vCJD, 46 sCJD controls, and 37 vCJD controls, using Innotest hTau and Innotest P-Thr181, Innogenetics.

RESULTS

Concentrations of CSF tau protein were increased in sCJD (5120 v 367 pg/ml in controls, p < 0.001) and vCJD (952 v 106 pg/ml, p < 0.001); tau-pT181 was also raised in sCJD (61 v 35 pg/ml in controls, p = 0.002) and vCJD (114 v 33 pg/ml, p < 0.001). Median concentrations of tau-pT181 were higher in vCJD than in sCJD (p < 0.001). The tau-pT181/tau protein ratio was lower than in controls in both sCJD (12 v 128 (p < 0.001)) and vCJD (119 v 279 (p < 0.001)). Mean tau-pT181/tau protein ratio was 10-fold higher in vCJD than in sCJD. Raised CSF tau protein had the highest efficiency for distinguishing sCJD and vCJD from controls.

CONCLUSIONS

CSF tau-pT181 concentrations are raised in vCJD and are higher than in sCJD. Measurement of CSF tau-pT181/tau protein ratio does not improve the diagnostic efficiency of CSF tau protein alone for either vCJD or sCJD. The higher concentration of CSF tau-pT181 found in vCJD suggests that unexplained pathogenic factors influence the phosphorylation of tau protein in vCJD patients.

Abnormal prion protein in the retina of the most commonly occurring subtype of sporadic Creutzfeldt-Jakob disease

BACKGROUND

Involvement of the eye has been reported in patients with variant Creutzfeldt-Jakob disease (vCJD), but there is disagreement on whether retinal involvement occurs in sporadic Creutzfeldt-Jakob disease (sCJD).

METHODS

Western blotting, paraffin embedded tissue blotting, and immunohistochemistry were used to test whether the abnormal form of the prion protein (PrPSc) accumulates to detectable levels in the eye in a case of the most common subtype of sCJD (MM1).

RESULTS

Low levels of PrPSc were detectable in the retina, localised to the plexiform layers of the central retina. PrPSc was not detectable in other ocular tissues.

CONCLUSIONS

The abnormal form of the prion protein is present in the retina in the most common sCJD subtype (MM1), albeit at levels lower than those found previously in vCJD and in sCJD of the VV2 subtype.

Evaluation of urinary PrPSc as a diagnostic test for sporadic, variant, and familial CJD

Previously collected urine specimens from 100 patients referred to the UK National CJD Surveillance Unit as suspected cases of Creutzfeldt-Jakob disease (CJD) were analyzed, testing for abnormal prion protein (PrP(Sc)). In this context, the test had a low sensitivity and was not completely specific for CJD. Additionally, the proteins detected by this assay were not PrP(Sc) but appeared to be immunoglobulins.

Advances in the detection of prion protein in peripheral tissues of variant Creutzfeldt-Jakob disease patients using paraffin-embedded tissue blotting

The accumulation of PrP(Sc), an abnormal and disease-associated form of the normal prion protein (PrP(c)), within the central nervous system (CNS) is a key pathological feature of Creutzfeldt-Jakob disease (CJD). Following limited proteolytic digestion of PrP(Sc), the detection of PrP(res) within lymphoid tissues is a unique characteristic of variant CJD in comparison with other human prion diseases, raising fears of an increased risk of iatrogenic spread. Because levels of PrP(res) in lymphoid tissues are lower than those found in CNS tissue, there is concern that other peripheral tissues may harbour infectivity at levels that current detection systems cannot demonstrate PrP(res). We have modified the paraffin-embedded tissue blot (PET blot), a technique combining immunohistochemistry (IHC), histoblot and Western blotting, for the detection of PrP(res) in paraffin sections in peripheral tissues in variant CJD. Five cases of variant CJD were examined, using a panel of anti-PrP antibodies. In each of these five cases, spleen, tonsil, lymph nodes and dorsal root ganglia showed an increase in the sensitivity and specificity of labelling using the PET blot when compared with optimized PrP(res) IHC methods. Control cases showed no evidence of PrP accumulation in either peripheral or CNS tissues. Autopsy and biopsy brain material from sporadic CJD cases also showed an increased sensitivity of PrP(res) detection with the PET blot, confirming its value as an important diagnostic and research tool in human prion diseases.

Variant Creutzfeldt-Jakob disease: risk of transmission by blood and blood products

Variant Creutzfeldt-Jakob disease (CJD) is a novel acquired human prion disease apparently resulting from exposure to the bovine spongiform encephalopathy (BSE) agent. Variant CJD differs from other human prion diseases in that the disease-associated form of the prion protein and infectivity are readily detectable in lymphoid tissues throughout the body. Lymphoid tissues and lymphocytes are implicated in the peripheral pathogenesis of prion diseases (where infectivity may be detected during the preclinical phase of the illness), giving rise to concerns that blood and blood products may also contain infectious particles, representing a possible source of iatrogenic spread of variant CJD. This concern has been reinforced following the experimental transmission of BSE in a sheep model by transfusion of blood and buffy coat from animals in the preclinical phase of the illness, and the recent identification of a UK case of variant CJD in a patient who had received packed red blood cells that had been donated by an individual who subsequently died from variant CJD. Studies in animal models suggest that most prion infectivity in blood may be cell-associated, with lower levels in the plasma, and there is evidence to suggest that any infectivity present may be reduced during the process of plasma fractionation. However, the possibility that plasma or blood products could transmit the disease cannot be excluded. Further studies are required to develop more sensitive means to detect disease-associated prion protein in blood; such techniques could be employed for screening purposes to reduce exposure to contaminated products and to assist with risk management in potentially exposed individuals.

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.

Neuropathology and molecular biology of variant Creutzfeldt-Jakob disease

The neuropathological features of human prion diseases are spongiform change, neuronal loss, astrocytic proliferation and the accumulation of PrP(Sc), the abnormal isoform of prion protein (PrP). The pattern of brain involvement is remarkably variable and is substantially influenced by the host PrP genotype and PrP(Sc) isotype. Variant Creutzfeldt-Jakob disease (vCJD) is a novel human prion disease which results from exposure to the bovine spongiform encephalopathy (BSE) agent. The neuropathology of vCJD shows consistent characteristics, with abundant florid and cluster plaques in the cerebrum and cerebellum, and widespread accumulation of PrP(res) on immunocytochemistry. These features are distinct from all other types of human prion disease. Spongiform change is most marked in the basal ganglia, while the thalamus exhibits severe neuronal loss and gliosis in the posterior nuclei. These areas of thalamic pathology correlate with the areas of high signal seen in the thalamus on magnetic resonance imaging (MRI) examination of the brain. Western blot analysis of PrP(Sc) in the brain in vCJD tissue shows a uniform isotype, with a glycoform ratio characterized by predominance of the diglycosylated band, distinct from sporadic CJD. PrP(Sc) accumulation in vCJD is readily detectable outside the brain, in contrast with other forms of human prion disease, particularly in the lymphoid system and in parts of the peripheral nervous system. This has raised concern about the possible iatrogenic transmission of vCJD by contaminated surgical instruments, or blood. All cases of vCJD are methionine homozygotes at codon 129 of the prion protein gene (PRNP). Continued surveillance is required to investigate cases of vCJD in the UK and other countries where BSE has been reported, particularly as cases of 'human BSE' in individuals who are MV or VV at codon 129 of the PrP gene have not yet been identified. Histological, genetic and biochemical techniques are essential tools for the adequate diagnosis and investigation of human prion diseases.

Investigation of PrPres in dental tissues in variant CJD

OBJECTIVES

To study the distribution of disease-associated prion protein (PrP) in oral and dental tissues in variant CJD.

DESIGN

Prospective single centre autopsy based study.

SETTING

Within the National CJD Surveillance Unit, UK, 2000-2002.

MATERIALS AND METHODS

Patients with suspected variant CJD undergoing autopsy where permission to remove tissues for research purposes had been obtained from the relatives. Fixed and frozen autopsy tissues from the brain, trigeminal ganglion, alveolar nerve, dental pulp, gingiva, salivary gland, tongue and tonsils were studied by Western blot, PET blot and immunocytochemistry to detect disease-associated PrP.

RESULTS

Disease-associated PrP was only detected in the brain, trigeminal ganglia and tonsils.

CONCLUSIONS

The failure to detect disease-associated PrP in most dental and oral tissues will help inform ongoing risk assessments for dental surgery in relation to the possible iatrogenic transmission of variant CJD via dental instruments.

Variant Creutzfeldt-Jakob disease and its transmission by blood

Variant Creutzfeldt-Jakob disease (vCJD) is a novel acquired human prion disease resulting from human exposure to the agent causing bovine spongiform encephalopathy (BSE). vCJD differs from all other human prion diseases in that the disease-associated form of the prion protein and infectivity are present in lymphoid tissues throughout the body. Lymphoid tissues and lymphocytes are implicated in the peripheral pathogenesis of prion diseases (where infectivity may be detected during the preclinical phase of the illness), giving rise to concerns that blood and blood products may also contain infectivity, thus representing a possible source of iatrogenic spread of vCJD. These concerns have been reinforced by the recent transmission of BSE in an experimental sheep model by blood transfusion from an infected animal in the preclinical phase of the illness. Studies in other animal models suggest that most infectivity in blood may be cell-associated, with lower levels in the plasma, and there is evidence to indicate that any infectivity present may be reduced during the process of plasma fractionation. At present, the attempts to detect disease-associated prion protein and infectivity in buffy coat from vCJD patients have been negative, but these studies have been limited in size and in the sensitivity of the detection systems employed. Further studies are required to develop more sensitive means of detection of disease-associated prion protein in blood; such techniques could also be employed for screening purposes, both individually and to help ascertain more precisely the likely numbers of future cases of vCJD.

Variant Creutzfeldt-Jakob disease

Variant CJD is a novel human prion disease that represents the first known occasion in which animal prion diseases have been transmitted to humans. There are many uncertainties concerning vCJD, including the mechanism of transmission between species, the extent of human exposure to the BSE agent, the infectious dose for humans, and the future burden of human disease. It is hoped that continuing scientific research may lead to answers to some of these questions and that further understanding of the mechanism of prion replication may lead to the development of effective treatment. Indeed a recent publication has suggested that the drugs quinacrine or chloropromazine may be candidates for the treatment of human prion diseases [42].

Pathological diagnosis of variant Creutzfeldt-Jakob disease

The neuropathological and biochemical features of the 89 histologically confirmed cases of variant Creutzfeldt-Jakob disease (vCJD) diagnosed up to the end of October 2001 in the UK are reviewed. Histology of the central nervous system, lymphoid tissues and other organs was accompanied by immunocytochemistry and Western blot analysis of the disease-associated form of the prion protein (PrP(RES)). All patients with vCJD were methionine homozygotes at codon 129 of the PrP gene. The pathology of vCJD showed relatively uniform morphological and immunocytochemical characteristics, which were distinct from other forms of CJD. PrP(RES) accumulation was widespread in lymphoid tissues in vCJD, but was not identified in other non-neural tissues. PrP(RES) in vCJD brain tissue showed a uniform glycotype pattern distinct from sporadic CJD. Given the increasingly widespread occurrence of bovine spongiform encephalopathy in Europe and Asia, there is a major need for widespread CJD surveillance. This should be accompanied by a multidisciplinary laboratory approach to the investigation and diagnosis of all forms of CJD, with the need to investigate autopsy tissues from suspected cases by the histological and biochemical techniques described herein.

Sporadic Creutzfeldt-Jakob disease in a young Dutch valine homozygote: atypical molecular phenotype

A case of sporadic Creutzfeldt-Jakob disease (sCJD) is described in a young Dutch protein prion gene (PRNP) codon 129 valine homozygote. Certain clinical and molecular features of this case overlap those of variant CJD. The case highlights possible difficulties in the differential diagnosis of vCJD and the more rare sCJD subtypes based on molecular features alone.

Clinicopathological phenotype of codon 129 valine homozygote sporadic Creutzfeldt-Jakob disease

The naturally occurring polymorphism at codon 129 of the human prion protein gene (PRNP) influences susceptibility to sporadic Creutzfeldt-Jakob Disease (CJD); the majority of the patients are methionine homozygotes at this locus, while valine homozygotes represent only 10% of cases. The aim was to study the clinical and neuropathological phenotype of sporadic CJD in valine homozygotes, to estimate the reliability of current clinical diagnostic criteria, and to identify any consistent and distinct features. Twelve cases of sporadic CJD with a codon 129 valine homozygote genotype were identified at the National CJD Surveillance Unit in Edinburgh. In addition to a retrospective clinical analysis, tissue blocks were stained by conventional techniques and by immunocytochemistry for prion protein. Frozen brain tissue was available from five cases for Western blot analysis of PrPRES, which in all cases showed a type 2 mobility. The cases included four males and eight females, average age 63.6 years, with a mean duration of illness of 6 months. Eleven patients presented with ataxia, and none had the characteristic EEG changes found in sporadic CJD. The neuropathological phenotype comprised spongiform change and prion protein immunopositivity most marked in the subcortical grey matter and cerebellum, prion protein positive plaque-like deposits in all regions, laminar deposition of prion protein in the cerebral cortex, and hippocampal involvement (which is seldom reported in sporadic CJD). In conclusion, these cases exhibited a fairly uniform phenotype, which is relatively distinct from sporadic CJD in methionine homozygotes, and thus diagnosis may be difficult using existing clinical criteria.

Genetic influence on the structural variations of the abnormal prion protein

Prion diseases are characterized by the presence of the abnormal prion protein PrP(Sc), which is believed to be generated by the conversion of the alpha-helical structure that predominates in the normal PrP isoform into a beta-sheet structure resistant to proteinase K (PK). In human prion diseases, two major types of PrP(Sc), type 1 and 2, can be distinguished based on the difference in electrophoretic migration of the PK-resistant core fragment. In this study, protein sequencing was used to identify the PK cleavage sites of PrP(Sc) in 36 cases of prion diseases. We demonstrated two primary cleavage sites at residue 82 and residue 97 for type 1 and type 2 PrP(Sc), respectively, and numerous secondary cleavages distributed along the region spanning residues 74-102. Accordingly, we identify three regions in PrP(Sc): one N-terminal (residues 23-73) that is invariably PK-sensitive, one C-terminal (residues 103-231) that is invariably PK-resistant, and a third variable region (residues 74-102) where the site of the PK cleavage, likely reflecting the extent of the beta-sheet structure, varies mostly as a function of the PrP genotype at codon 129.

Small heat shock proteins, the cytoskeleton, and inclusion body formation

Since first being implicated in central nervous system disease 10 years ago, much has been learned concerning the regulation and function of the small heat shock protein alpha B-crystallin. Neuropathological, cellular and molecular studies all now point to a functional relationship between alpha B-crystallin and intermediate filaments. alpha B-crystallin accumulation marks reactive astrocytes in general in a wide variety of disorders and specifically intermediate filament-based glial inclusion bodies such as Rosenthal fibres found in astrocytes in Alexander's disease. In vitro, alpha B-crystallin expression suppresses intermediate filament aggregation and can prevent or reverse experimentally induced glial inclusion body formation. Conversely, dysregulation of glial fibrillary acidic protein expression in vivo results in Rosenthal fibre formation and upregulation of endogenous alpha B-crystallin expression. These data and those from studies recently carried out on other tissues strongly suggest that one function of this small heat shock protein is to modulate intermediate filament organization under conditions of physiological stress and neurodegenerative disease.

Laboratory diagnosis of variant Creutzfeldt-Jakob disease

The neuropathological and biochemical features of 33 cases of variant Creutzfeldt-Jakob disease (vCJD) diagnosed up to the end of 1998 are analysed in relation to the 646 cases of suspected CJD referred to the CJD Surveillance Unit laboratory from 1990 to 1998. Morphological studies of the central nervous system, lymphoid tissues and other organs were accompanied by immunocytochemistry; Western blot analysis of PrPRES was performed on frozen brain tissue. The findings were analysed in relation to clinical and genetic data. The pathology of vCJD showed morphological and immunocytochemical characteristics distinct from other cases of CJD. PrP accumulation was widespread in lymphoid tissues in vCJD, but was not identified in other non-neural tissues. PrPRES accumulation in vCJD brain tissue showed a uniform glycotype pattern distinct from sporadic CJD. All analysed cases of vCJD were methionine homozygotes at codon 129 of the PrP gene. No evidence currently exists to suggest that cases of CJD diagnosed in individuals who are MV or VV at codon 129 of the PrP gene represent 'human bovine spongiform encaphalopathy (BSE)'. Continued surveillance is required to further investigate this possibility, with the need to investigate autopsy tissues from suspected cases by histological and biochemical techniques.

AlphaB-crystallin regulates intermediate filament organization in situ

AlphaB-crystallin is a small heat shock protein (hsp) and molecular chaperone that can interact with a wide spectrum of cellular components including intermediate filaments (IF). The significance of these interactions is not currently known. We have tested whether increased alphaB-crystallin expression effects changes in the IF systems in situ. Adenoviral-mediated gene transfer was used to overexpress alphaB-crystallin in primary astrocytes. A positive correlation was observed between overexpression of alphaB-crystallin and diffuse, filigree IF. AlphaB-crystallin did not appear to alter the polymerization state of IF proteins. These data show that an increase in alphaB-crystallin expression in the absence of stress can modify the organizational state of IF and that alphaB-crystallin can function as an IF debundling protein.

Suppression of fibroblast growth factor 2 expression by antisense oligonucleotides inhibits embryonic chick neural retina cell differentiation and survival in vivo

During retinal differentiation, fibroblast growth factor 2 (FGF2) expression increases in retinal neurons following the sequential appearance of the neuronal layers. The function of the developmental increase of endogenous FGF2 in the developing chick retina was investigated by using an antisense strategy, using both optic vesicle cultures and in ovo-intravitreal microinjections. The former model allowed us to study the consequences of FGF2 down-regulation on early ganglion cell differentiation, whereas, in the latter model, subsequent development stages and terminal maturation of the retina were studied. FGF2 inhibition resulted in reduced ganglion cell differentiation, as visualized by the expression of the ganglion cell-specific RA4 and Islet-1 markers in optic vesicle cultures. Eyes intravitreally injected with the FGF2-specific antisense oligonucleotide exhibited profound retinal differentiation defects: thinning of the ganglion and outer nuclear (photoreceptors) cell layers and increased cell death in ganglion cell and inner nuclear layers. These results indicate that the loss of endogenous FGF2 cannot be compensated for in the retina and suggest that, although many other sources of FGF exist in the eye, the main role of the increase in endogenous FGF2 observed during retinal development is to intrinsically stimulate neuron differentiation and to protect neurons against cell death.

Fatal encephalopathy with astrocyte inclusions in GFAP transgenic mice

Increased expression of glial fibrillary acidic protein (GFAP) is a hallmark of gliosis, the astrocytic hypertrophy that occurs during a wide variety of diseases of the central nervous system. To determine whether this increase in GFAP expression per se alters astrocyte function, we generated transgenic mice that carry copies of the human GFAP gene driven by its own promoter. Astrocytes of these mice are hypertrophic, up-regulate small heat-shock proteins, and contain inclusion bodies identical histologically and antigenically to the Rosenthal fibers of Alexander's disease. Mice in the highest expressing lines die by the second postnatal week. The results support the notion that Alexander's disease is a disorder of astrocytes, and provide an animal model for studying the causes and consequences of inclusion body disease.

Macular holes: migratory gaps and vitreous as obstacles to glial closure

PURPOSE

Retinal glia may play an important role in the closure of macular holes. This in vitro study examines whether and how the specific pathoanatomy, including foveal eversion and foveal vitreous, may interfere with glial closure of macular holes.

METHODS

Culture dishes used to grow glial cells were modified by the placement of slopes, vertical steps, and gaps to mimic the in vivo migratory surface in and surrounding macular holes. In separate experiments, defects were made in a rodent glial monolayer. These defects were exposed to hyaluronic acid (HA) and to rabbit (RV) and bovine (BV) vitreous gel. The migratory behavior and completeness of closure of defects were compared to controls.

RESULTS

As expected, glial cells migrated further and in greater numbers on a smooth surface. Slopes and steps were moderate obstacles to migration; gaps in the surface were absolute obstacles. HA modified the pattern of adhesion of cells at the bottom of defects. Defects in the glial monolayer were repaired in 5-7 days. Compared to these controls, repair was inhibited by 11% (n.s.), 28% (P = 0.02), and 58% (P = 0.004) after direct exposure of defects to HA, RV and BV, respectively.

CONCLUSION

The elevated and everted margins of macular holes represent slope, step, and gap-like obstacles to the migration of glial cells and hence to the healing of defects. The defect allows extension of extracellular matrix into it and the subretinal space. Our results indicate that gaps in the migratory surface caused and aggravated by eversion and the presence of vitreous present obstacles to glial migration and closure of macular holes.

Transcription regulation of alpha B-crystallin in astrocytes: analysis of HSF and AP1 activation by different types of physiological stress

The coordinated cellular responses to physiological stress are known to be effected in part by the activation of heat-shock factor 1, a transcriptional activator protein capable of binding to, and inducing transcription from genes containing heat shock elements. Other stress responsive signal transduction pathways also exist including the stress activated protein kinase cascade that regulates the activity of the transcription factor AP1. We have examined the expression of the low molecular stress proteins, heat shock protein 27 and alpha B-crystallin in astrocytes in response to physiological stress of different types and asked what component of this induction is effected at the transcriptional level and whether activation of heat shock factor 1 and AP1 might account for these events. We have found that stress regulated induction of alpha B-crystallin has a strong transcriptional component and that it may be effected by at least two different transcriptional mechanisms. In one set of phenomena, represented here by cadmium exposure, alpha B-crystallin and heat shock protein 27 are coordinately regulated and this occurs in the presence of activated heat shock factor 1. In the second series of phenomena, represented here by hypertonic stress, alpha B-crystallin is induced in the absence of heat shock factor activation and in the absence of any corresponding change in heat shock protein 27 expression. Although hypertonic stress does activate an AP1-like binding activity, the AP1 consensus binding site in the alpha B-crystallin promoter does not appear to be a target for this hypertonic stress inducible activity. These data suggest that the hypertonic stress response is effected through a heat shock factor independent mechanism and that hypertonic stress regulated induction of alpha B-crystallin does not directly depend on the SAPK pathway and AP1 activity.

Expression of the chicken cysteine-rich fibroblast growth factor receptor (CFR) during embryogenesis and retina development

The expression of the chicken cysteine-rich fibroblast growth factor receptor (CFR) during organogenesis and specifically during retina formation was studied by Northern blotting and a sensitive in situ hybridization. At days 2 and 4 of embryonic development (E2 and E4), CFR mRNA was present in a wide variety of developing organs; it was abundantly expressed in nervous structures, particularly in the retina. The levels of CFR transcripts were high during the proliferation and the subsequent differentiation phases of retinal neurogenesis, reached a maximum around E11 during the onset of the major period of retinal cell death, and then declined progressively. CFR mRNA was not detected at late stages when the final arrangement of retinal cell layers has been established. In prolonged primary cell cultures of chicken embryo retina, CFR expression showed a similar down-regulation to that seen with increasing age in vivo. It was up-regulated either directly or indirectly by its ligands. The CFR expression pattern in the developing retina was complementary to that of two other fibroblast growth factor (FGF) receptors, namely FGF-R1 and FGF-R2. In regard to a progressive increase in the expression of their ligands during retinal development, we suggest that CFR may have a role distinct from that of the tyrosine kinase FGF receptors during retinogenesis. Finally, the comparison of CFR expression with those of the other high affinity receptors indicates a regulation of the FGF function at the receptor level during neural retina development.

Beta B2-crystallin in the mammalian retina

beta-crystallins are abundant lens proteins in most, if not all vertebrate species. We have previously reported the presence of low levels of beta-crystallins in chick non-lens tissues, both ocular and extra-ocular, including the expression of beta B2-crystallin in the retina. Here we report that extralenticular beta-crystallin expression is also found in mammals. beta B2-crystallin is expressed in mouse and cat neural and pigmented retinas and in cat iris. Although present at levels lower than those found in the lens, the appearance and accumulation of beta B2-crystallin in the neural retina coincides with the functional maturation of this tissue.

Coordinate and independent regulation of alpha B-crystallin and hsp27 expression in response to physiological stress

alpha-Crystallins share structural and functional properties with the stress protein hsp27. These polypeptides are expressed at low constitutive levels in many tissues including brain, and alpha B-crystallin and hsp27 can accumulate in central nervous system glia in a variety of neurological conditions. We report here that heat shock and exposure to transition metals result in an increase in the steady state mRNA level of alpha B-crystallin and hsp27 in primary cultures of rat forebrain astrocytes. Both exposure to tumour necrosis factor-alpha and hypertonic conditions result in alpha B-crystallin mRNA accumulation but no change in the hsp27 mRNA level. Under some of these conditions increased synthesis and accumulation of alpha B-crystallin and hsp27 protein are also evident. We are unable to detect alpha A-crystallin mRNA in resting or stressed astrocytes. A novel phenomenon involving a transitory change in stress protein mRNA mobility in Northern blots during induction is reported, which is stress type and cell type independent. The results demonstrate multiple stress regulation of alpha B-crystallin and hsp27 in cultured astrocytes, suggesting that they can legitimately be regarded as stress proteins in the central nervous system.

Overexpression and abnormal modification of the stress proteins alpha B-crystallin and HSP27 in Alexander disease

Alexander disease is a leukodystrophy characterized by the presence of numerous Rosenthal fibers, inclusion bodies in astrocytes. A major component of Rosenthal fibers is alpha B-crystallin, some of which is ubiquitinated. In this report, we show that Alexander central nervous system (CNS) tissues contain elevated messenger RNA and protein levels of both alpha B-crystallin and the related small heat shock protein, hsp27, and that Rosenthal fibers contain hsp27. The alpha B-crystallin and hsp27 polypeptide isoform patterns of Alexander disease CNS are also distinct from those of control samples, suggesting that postranslational modifications may be involved in Rosenthal fiber formation. We advance the hypothesis that Rosenthal fibers may be regarded as stress protein inclusions formed in astrocytes as part of a chronic stress response to an as yet unknown stimulus in the CNS of Alexander patients.

Localization of delta-crystallin RNA during lens morphogenesis and differentiation in the normal and talpid3 chick embryo

Embryonic lens fiber cell differentiation in the chick is marked by the accumulation of delta-crystallin protein. The levels of delta-crystallin RNA are shown here to rise dramatically in the cells of the posterior lens pit prior to their elongation and differentiation as lens fibers. This increase correlates with regional proximity to the underlying optic cup (future retina). This accumulation of delta-crystallin RNA during lens induction operates selectively on the delta 1-crystallin transcripts whereas delta 2-crystallin/argininsosuccinate lyase RNA is detectable at lower levels in all developing ocular tissues throughout this period. The talpid3 mutant forms a flat "bridge" of thickened placode-like cells in the head epithelium between the two lens placodes, and this bridge also accumulates delta 1-crystallin RNA, suggesting that the selective increase in delta 1-crystallin RNA levels over those of delta 2-crystallin represents an early event in cellular commitment to lens fiber differentiation in the chick. The significance of the sequence of temporal changes in inductive sources for lens fiber formation is discussed, and we propose that the role of the optic cup is to provide, bound to its extra-cellular material (ECM), a high local concentration of the same growth factors which act as fiber inducers in the older eye.

Evidence for the extralenticular expression of members of the beta-crystallin gene family in the chick and a comparison with delta-crystallin during differentiation and transdifferentiation

The beta-crystallins are major water soluble proteins of vertebrate lens fibre cells and have previously been regarded as lens-specific proteins: however beta B2-and beta A3/A1-crystallin RNAs are transcribed and beta-crystallin polypeptides are detectable in the developing chick retina. The beta-crystallin RNA is transcribed in a subpopulation of retina cells and the number of transcribing cells and the level of beta-crystallin polypeptides increase during the differentiation of the retina. Several tissues express beta-crystallin polypeptides, but individual tissues are characterised by qualitative and quantitative differences in the beta- and delta-crystallin polypeptides expressed. The expression of beta-crystallins appears to be non-random as defined by tissue distribution, cellular localisation and ontogeny, implying a function for extralenticular beta-crystallins and a complex mechanism for the regulation of their expression.

Independent regulation of two coexpressed delta-crystallin genes in chick lens and nonlens tissues

It is known that delta-crystallin is super-abundant in the early chick lens, but it is found at lower levels in certain other tissues. Ninety-nine percent of the lens delta-crystallin poly(A)+ RNA is from the delta 1-crystallin gene. We report here that the delta 1- and delta 2-crystallin genes are both transcribed in the chick lens and retina throughout embryonic development and that both RNAs are found in embryo adenohypophysis and epiphysis and in day-old posthatch chick tibiofemoral chondrocytes and striated muscle. delta 1-crystallin RNA is more abundant in lens tissues, while delta 2-crystallin RNA is more abundant in all nonlens tissues. However, delta 1-crystallin RNA is processed more efficiently than delta 2-crystallin RNA in all early embryonic tissues examined. A comparison of lens epithelium and fibers established that levels of delta 2-crystallin RNA are the same but those of delta 1-crystallin RNA are over 100-fold higher in fibers compared to epithelial cells. The evidence implies independent regulation both of transcription and of post-transcriptional events for these two genes.

Ageing in the chick lens: in vitro studies

In principle, ageing may be due to the interaction of several factors, including the accumulation of random changes both genomic and non-genomic, secondary changes in a tissue contingent upon the changing function of other tissues, and programmed non-random changes in the tissue-specific expression of various genes. The use of a single tissue comprising one cell type only, in which the major gene products are well defined, in which there is a well attested series of developmental and age-related changes in cell properties and gene expression and which can be studied and compared in vivo and in vitro, offers advantages for investigation of these questions. The vertebrate eye lens possesses these advantages. The crystallins (proteins expressed at super-abundant levels in the lens) are well characterised. The lens epithelial cells (LEC) grow readily and can differentiate into the lens fibre cells in vitro, and, finally, such terminally differentiated cells may also be derived, by a process of transdifferentiation, from neural retina cells (NRC) in vitro. Thus the effect on ageing changes of the tissue of origin may also be studied. This article reviews our previous studies on long-term changes in growth potential, differentiation capacity and crystallin expression of chick lens cells in ageing cultures, their overall similarity to events in vivo and the effect on ageing changes of genotypes affecting the growth rate. It presents new information on these genetic aspects, and on crystallin expression in long-term ageing cultures of transdifferentiated neural retina, and compares the behaviour of ageing chick lens cells with that reported for mammals.