Evidence for biological and structural diversity among scrapie strains

T-Tau and P-Tau in Brain and Blood from Natural and Experimental Prion Diseases

Synaptic abnormalities are prominent in prion disease pathogenesis and are responsible for functional deficits. The microtubule associated protein, Tau, binds to and stabilizes microtubules in axons ensuring axonal transport of synaptic components. Tau phosphorylation reduces its affinity for microtubules leading to their instability and resulting in disrupted axonal transport and synaptic dysfunction. We report on the levels of total Tau (T-Tau) and phosphorylated Tau (P-Tau), measured by highly sensitive laser-based immunoassays, in the central nervous system and biofluids from experimentally transmitted prion disease in mice and natural cases of sporadic Creutzfeldt-Jakob Disease (sCJD) in humans. We found that, in contrast to sCJD where only the levels of T-Tau in brain are increased, both T-Tau and P-Tau are increased in the brains of symptomatic mice experimentally infected with the ME7, 139A and 22L mouse-adapted scrapie strains. The increased levels of T-Tau in sCJD brain, compared to control samples, were also observed in patient plasma. In contrast, there was no detectable increase in T-Tau and P-Tau in plasma from symptomatic experimentally infected mice. Furthermore, our data suggests that in mice showing clinical signs of prion disease the levels and/or ratios of T-Tau and P-Tau are only a useful parameter for differentiating the mouse-adapted scrapie strains that differ in the extent of disease. We conclude that the neuropathogenesis associated with P-Tau and synaptic dysfunction is similar for at least two of the mouse-adapted scrapie strains tested but may differ between sporadic and experimentally transmitted prion diseases.

Prion infection of mouse brain reveals multiple new upregulated genes involved in neuroinflammation or signal transduction

Gliosis is often a preclinical pathological finding in neurodegenerative diseases, including prion diseases, but the mechanisms facilitating gliosis and neuronal damage in these diseases are not understood. To expand our knowledge of the neuroinflammatory response in prion diseases, we assessed the expression of key genes and proteins involved in the inflammatory response and signal transduction in mouse brain at various times after scrapie infection. In brains of scrapie-infected mice at pre- and postclinical stages, we identified 15 previously unreported differentially expressed genes related to inflammation or activation of the STAT signal transduction pathway. Levels for the majority of differentially expressed genes increased with time postinfection. In quantitative immunoblotting experiments of STAT proteins, STAT1α, phosphorylated-STAT1α (pSTAT1α), and pSTAT3 were increased between 94 and 131 days postinfection (p.i.) in brains of mice infected with strain 22L. Furthermore, a select group of STAT-associated genes was increased preclinically during scrapie infection, suggesting early activation of the STAT signal transduction pathway. Comparison of inflammatory markers between mice infected with scrapie strains 22L and RML indicated that the inflammatory responses and gene expression profiles in the brains were strikingly similar, even though these scrapie strains infect different brain regions. The endogenous interleukin-1 receptor antagonist (IL-1Ra), an inflammatory marker, was newly identified as increasing preclinically in our model and therefore might influence scrapie pathogenesis in vivo. However, in IL-1Ra-deficient or overexpressor transgenic mice inoculated with scrapie, neither loss nor overexpression of IL-1Ra demonstrated any observable effect on gliosis, protease-resistant prion protein (PrPres) formation, disease tempo, pathology, or expression of the inflammatory genes analyzed.

IMPORTANCE

Prion infection leads to PrPres deposition, gliosis, and neuroinflammation in the central nervous system before signs of clinical illness. Using a scrapie mouse model of prion disease to assess various time points postinoculation, we identified 15 unreported genes that were increased in the brains of scrapie-infected mice and were associated with inflammation and/or JAK-STAT activation. Comparison of mice infected with two scrapie strains (22L and RML), which have dissimilar neuropathologies, indicated that the inflammatory responses and gene expression profiles in the brains were similar. Genes that increased prior to clinical signs might be involved in controlling scrapie infection or in facilitating damage to host tissues. We tested the possible role of the endogenous IL-1Ra, which was increased at 70 days p.i. In scrapie-infected mice deficient in or overexpressing IL-1Ra, there was no observable effect on gliosis, PrPres formation, disease tempo, pathology, or expression of inflammatory genes analyzed.

Effect of glycans and the glycophosphatidylinositol anchor on strain dependent conformations of scrapie prion protein: improved purifications and infrared spectra

Mammalian prion diseases involve conversion of normal prion protein, PrP(C), to a pathological aggregated state (PrP(res)). The three-dimensional structure of PrP(res) is not known, but infrared (IR) spectroscopy has indicated high, strain-dependent β-sheet content. PrP(res) molecules usually contain a glycophosphatidylinositol (GPI) anchor and large Asn-linked glycans, which can also vary with strain. Using IR spectroscopy, we tested the conformational effects of these post-translational modifications by comparing wild-type PrP(res) with GPI- and glycan-deficient PrP(res) produced in GPI-anchorless PrP transgenic mice. These analyses required the development of substantially improved purification protocols. Spectra of both types of PrP(res) revealed conformational differences between the 22L, ME7, and Chandler (RML) murine scrapie strains, most notably in bands attributed to β-sheets. These PrP(res) spectra were also distinct from those of the hamster 263K scrapie strain. Spectra of wild-type and anchorless 22L PrP(res) were nearly indistinguishable. With ME7 PrP(res), modest differences between the wild-type and anchorless spectra were detected, notably an ∼2 cm(-1) shift in an apparent β-sheet band. Collectively, the data provide evidence that the glycans and anchor do not grossly affect the strain-specific secondary structures of PrP(res), at least relative to the differences observed between strains, but can subtly affect turns and certain β-sheet components. Recently reported H-D exchange analyses of anchorless PrP(res) preparations strongly suggested the presence of strain-dependent, solvent-inaccessible β-core structures throughout most of the C-terminal half of PrP(res) molecules, with no remaining α-helix. Our IR data provide evidence that similar core structures also comprise wild-type PrP(res).

Comparative profiling of highly enriched 22L and Chandler mouse scrapie prion protein preparations

Transmissible spongiform encephalopathies (TSEs) or prion diseases are characterized by the accumulation of an aggregated isoform of the prion protein (PrP). This pathological isoform, termed PrP(Sc), appears to be the primary component of the TSE infectious agent or prion. However, it is not clear to what extent other protein cofactors may be involved in TSE pathogenesis or whether there are PrP(Sc)-associated proteins which help to determine TSE strain-specific disease phenotypes. We enriched PrP(Sc) from the brains of mice infected with either 22L or Chandler TSE strains and examined the protein content of these samples using nanospray LC-MS/MS. These samples were compared with "mock" PrP(Sc) preparations from uninfected brains. PrP was the major component of the infected samples and ferritin was the most abundant impurity. Mock enrichments contained no detectable PrP but did contain a significant amount of ferritin. Of the total proteins identified, 32% were found in both mock and infected samples. The similarities between PrP(Sc) samples from 22L and Chandler TSE strains suggest that the non-PrP(Sc) protein components found in standard enrichment protocols are not strain specific.

Getting a grip on prions: oligomers, amyloids, and pathological membrane interactions

The prion (infectious protein) concept has evolved with the discovery of new self-propagating protein states in organisms as diverse as mammals and fungi. The infectious agent of the mammalian transmissible spongiform encephalopathies (TSE) has long been considered the prototypical prion, and recent cell-free propagation and biophysical analyses of TSE infectivity have now firmly established its prion credentials. Other disease-associated protein aggregates, such as some amyloids, can also have prion-like characteristics under certain experimental conditions. However, most amyloids appear to lack the natural transmissibility of TSE prions. One feature that distinguishes the latter from the former is the glycophosphatidylinositol membrane anchor on prion protein, the molecule that is corrupted in TSE diseases. The presence of this anchor profoundly affects TSE pathogenesis, which involves major membrane distortions in the brain, and may be a key reason for the greater neurovirulence of TSE prions relative to many other autocatalytic protein aggregates.

Prion disease induced alterations in gene expression in spleen and brain prior to clinical symptoms

Prion diseases are fatal neurodegenerative disorders that affect animals and humans. There is a need to gain understanding of prion disease pathogenesis and to develop diagnostic assays to detect prion diseases prior to the onset of clinical symptoms. The goal of this study was to identify genes that show altered expression early in the disease process in the spleen and brain of prion disease-infected mice. Using Affymetrix microarrays, we identified 67 genes that showed increased expression in the brains of prion disease-infected mice prior to the onset of clinical symptoms. These genes function in many cellular processes including immunity, the endosome/lysosome system, hormone activity, and the cytoskeleton. We confirmed a subset of these gene expression alterations using other methods and determined the time course in which these changes occur. We also identified 14 genes showing altered expression prior to the onset of clinical symptoms in spleens of prion disease infected mice. Interestingly, four genes, Atp1b1, Gh, Anp32a, and Grn, were altered at the very early time of 46 days post-infection. These gene expression alterations provide insights into the molecular mechanisms underlying prion disease pathogenesis and may serve as surrogate markers for the early detection and diagnosis of prion disease.

Gene expression alterations in brains of mice infected with three strains of scrapie

Background

Transmissible spongiform encephalopathies (TSEs) or prion diseases are fatal neurodegenerative disorders which occur in humans and various animal species. Examples include Creutzfeldt-Jakob disease (CJD) in humans, bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in deer and elk, and scrapie in sheep, and experimental mice. To gain insights into TSE pathogenesis, we made and used cDNA microarrays to identify disease-associated alterations in gene expression. Brain gene expression in scrapie-infected mice was compared to mock-infected mice at pre-symptomatic and symptomatic time points. Three strains of mouse scrapie that show striking differences in neuropathology were studied: ME7, 22L, and Chandler/RML.

Results

In symptomatic mice, over 400 significant gene expression alterations were identified. In contrast, only 22 genes showed significant alteration in the pre-symptomatic animals. We also identified genes that showed significant differences in alterations in gene expression between strains. Genes identified in this study encode proteins that are involved in many cellular processes including protein folding, endosome/lysosome function, immunity, synapse function, metal ion binding, calcium regulation and cytoskeletal function.

Conclusion

These studies shed light on the complex molecular events that occur during prion disease, and identify genes whose further study may yield new insights into strain specific neuropathogenesis and ante-mortem tests for TSEs.

Protein misfolding cyclic amplification for diagnosis and prion propagation studies

Diverse human disorders are thought to arise from the misfolding and aggregation of an underlying protein. Among them, prion diseases are some of the most intriguing disorders that can be transmitted by an unprecedented infectious agent, termed prion, composed mainly (if not exclusively) of the misfolded prion protein. The hallmark event in the disease is the conversion of the native prion protein into the disease-associated misfolded protein. We have recently described a novel technology to mimic the prion conversion process in vitro. This procedure, named protein misfolding cyclic amplification (PMCA), conceptually analogous to DNA amplification by polymerase chain reaction (PCR), has important applications for research and diagnosis. In this chapter we describe the rational behind PMCA and some of the many potential applications of this novel technology. We also describe in detail the technical and methodological aspects of PMCA, as well as its application in automatic and serial modes that have been developed with a view to improving disease diagnosis.

Histopathological changes in the pituitary glands of female hamsters infected with the 139H strain of scrapie

Previous studies in hamsters showed that the 139H strain of scrapie injected intracerebrally caused a generalized endocrinopathy and marked hypoglycaemia and hyperinsulinaemia. The low scrapie infectivity levels in the pancreas suggested that the changes noted in that organ were of neuroendocrine origin. In the current study, female weanling Syrian hamsters were inoculated intracerebrally with scrapie strain 139H or 263K, or with homogenate of normal hamster brain. Coronal sections of the pituitary gland were stained with haematoxylin and eosin, Gomori's one-step trichrome, Congo red, thioflavin-S, and antibodies specific for several pituitary hormones. Sections were examined by light microscopy. The hamsters inoculated with scrapie strain 139H showed extensive pituitary vacuolization. Most vacuoles were located in the ventral or ventrolateral parts of the pars distalis. The pituitary glands of 139H-infected hamsters also showed cellular changes, namely, hypertrophy, atrophy and cytoplasmic vesicles. Nuclear changes such as swelling, vesicle formation, chromatin increase, pyknosis, karyorrhexis and karyolysis also occurred. The cellular and nuclear changes were most pronounced in the regions with vacuolation. Hamsters infected with the 263K strain did not show these changes. Immunocytochemical examination suggested that parenchymal cell types which produce different hormones were affected in areas of vacuolation. The changes produced by 139H were not seen in hamsters infected with strain 263K. This study provides the first evidence of cytopathological changes in the pituitary glands of scrapie-infected animals and suggests a relationship between the pituitary changes and the pathological findings in the pancreas and other endocrine organs of 139H-infected hamsters.

Margination and diapedesis of inflammatory cells in the islets of Langerhans in hamsters infected with the 139H strain of scrapie

The islets of Langerhans in hamsters infected with the 139H strain of scrapie contain large masses of red blood cells not surrounded by the usual arterial, venous or capillary wall cells. We have referred to these structures as "blood vessel cores" (BVCs). BVCs were almost always centrally located within the islets and surrounded by pancreatic B cells. Margination and diapedesis of inflammatory cells were observed at the BVC walls in 139H-infected hamsters. The cells consisted of the following types: single or clustered lymphocytes; and mixtures of lymphocytes and macrophages or neutrophils. Interaction observed between groups of inflammatory cells and B cells at the BVC walls and inside the islets of Langerhans indicated an inflammatory process. We refer to this interaction as the "linkage-reaction", and to the inflammatory cells as "linkage-inflammatory cells". These phenomena were not observed in other organs (adrenal, uterus, ovary, spleen, liver, kidney, oesophagus, trachea, intestine or pituitary) in 139H-affected hamsters or in the islets of Langerhans of animals infected with other scrapie strains (263K-infected hamsters; 139A-, ME7- and 22L-infected SJL mice). This appears to represent the first clear evidence of an inflammatory reaction in any organ in scrapie-infected animals.

Concentration and distribution of infectivity and PrPSc following partial denaturation of a mouse-adapted and a hamster-adapted scrapie strain

PrPSc is a specific protein marker for slow infectious diseases known as the transmissible subacute spongiform encephalopathies. Although PrPSc is closely associated with infectivity, it is not known if it is the infectious agent itself, a component of the agent or merely adventitiously associated with infectivity. In the present study we demonstrate that the resistance of PrPSc to partial denaturation and of infectivity to inactivation differs markedly for two scrapie strains. Proteinase K treatment or electrophoretic analysis of partially denatured PrPSc preparations reveal a dissociation between infectivity and demonstrable PrPSc. Our findings support other evidence that not all PrPSc is required for infectivity. Our studies combined with previous biological analyses suggest that PrPSc cannot be the sole component associated with the infectious agent.

Effect of infection with the 139H scrapie strain on the number, area and/or location of hypothalamic CRF- and VP-immunostained neurons

Scrapie is a transmissible neurodegenerative disease which shares some characteristics with Alzheimer disease (AD). Recent studies show abnormal enlargement of the adrenal glands and kidneys in 139H-affected hamsters. Using immunocytochemical techniques with antibodies to corticotropin-releasing factor (CRF) and vasopressin (VP), we observed the following: (1) a significantly higher number of CRF-immunostained neurons in the preoptic nucleus of hypothalamus of 139H-affected hamsters than controls; (2) the area of VP-immunostained (ir-VP) neurons in the lateral hypothalamus, which includes the internuclear group of magnocellular neurons and the nucleus circularis, was significantly lower for 139H-affected hamsters than for controls; and (3) no significant difference between 139H-affected and control hamsters with regard to the number of ir-VP neurons in the dorsal-medial hypothalamus (DMH), including the paraventricular hypothalamus, or the supraoptic nuclei. However, the population of ir-VP neurons in the DMH shifted to the anterior part of the hypothalamus in 139H-affected hamsters. Three-dimensional models of the immunostaining were prepared and these provide clear depictions of the changes noted. The changes in the CRF and VP systems in 139H-affected hamsters suggest that the neuroendocrine system can be affected by unconventional slow infections.

Histopathological changes in the islets of Langerhans in scrapie 139H-affected hamsters

Previous studies showed that the 139H strain of scrapie injected into hamsters caused obesity, a marked hypertrophy of the islets of Langerhans, generalized endocrinopathy and marked hypoglycaemia-hyperinsulinaemia. In the current study, female weanling Syrian hamsters (LVG/LAK strain) were inoculated intracerebrally with scrapie strain 139H or 263K, or with normal hamster brain. Sections of the pancreas stained with haematoxylin and eosin or Gomori's one-step trichrome were examined by light microscopy. The 139H-affected hamsters showed extensive vacuolization, cellular hypertrophy, cellular atrophy, cytoplasmic vesicles and nuclear pathological changes in the islets of Langerhans. Also observed were abnormal structures, termed blood vessel cores, in the islets of 139H-affected hamsters. These structures were almost always centrally located within islets and were surrounded by B cells, some of which were abnormally elongated. None of these pathological changes were seen in the islets of Langerhans in control or 263K-affected hamsters. The level of scrapie-specific protease resistant protein (PrPSc) in pancreas was much lower than that in brain, a finding consistent with previous data showing low scrapie infectivity titres in pancreas.