Growth factor production by Creutzfeldt-Jakob disease cell lines

Involvement of astrocytes in transmissible spongiform encephalopathies: a confocal microscopy study

Astroglial proliferation associated with pathological prion protein (PrPsc) deposition is widely described in Transmissible Spongiform Encephalopathies (TSEs). However, little is known of the actual role played by glia in their pathogenesis. The aim of the study has been to determine whether PrPsc is located exclusively in neurons or in both neurons and glial cells present in the central nervous system in a natural Scrapie model. Samples of cerebellum from 25 Scrapie sheep from various flocks were sectioned. Following epitope retrieval with formic acid, proteinase K and heat treatment, primary antibody L42 and primary antibodies against glial fibrillary acidic protein were applied as prion- and astrocytic-specific markers, respectively. For visualization, a suitable mixture of fluorochrome-conjugated secondary antibodies was used. Relevant controls were processed in the same manner. As determined by confocal microscopy, PrPsc deposits co-localized with glial cells in all samples. Our results suggest that these cells can sustain active prion propagation, in agreement with similar findings from other studies of primary cell cultures and inoculated mice. Furthermore, despite ongoing debate regarding whether varied TSE sources show differences in their tropism for different cell lineages in the brains of affected animals, no differences in co-localization results were seen.

Changes in N-acetylaspartate and myo-inositol detected in the cerebral cortex of hamsters with Creutzfeldt-Jakob disease

The levels of several low-molecular-weight metabolites were measured in 1H nuclear magnetic resonance (NMR) spectra of extracts of Syrian hamster brain infected with Creutzfeldt-Jakob disease (CJD). Metabolite levels were determined in cerebral cortex in CJD-infected and age-matched controls at defined times (40, 65, 85, 105, and 135 days) during the 130- to 135-day incubation period to terminal disease. At 135 days, CJD-infected hamsters showed a significant decrease in N-acetylaspartate of 32% (p < 0.05) and an increase in myo-inositol of 67% (p < 0.001) from age-matched controls. At earlier times (40 to 110 days) levels of N-acetylaspartate and myo-inositol were not significantly different from controls. No significant changes were detected in the cortical levels of glutamate, aspartate, or GABA between 40 and 135 days. The late changes in N-acetylaspartate and myo-inositol in CJD-infected hamsters are similar to those observed in magnetic resonance spectroscopy studies of human CJD. Because they also correspond to the changes found in other dementias, including Alzheimer's disease and HIV dementia, these changes indicate converging pathogenetic pathways involved in many neurodegenerative diseases.

Inducible nitric oxide synthase and nitrotyrosine are found in monocytes/macrophages and/or astrocytes in acute, but not in chronic, multiple sclerosis

We have examined the localization of inducible nitric oxide synthase (iNOS) and nitrotyrosine (the product of nitration of tyrosine by peroxynitrite, a highly reactive derivative of nitric oxide [NO]) in demyelinating lesions from (i) two young adult patients with acute multiple sclerosis (MS), (ii) a child with MS (consistent with diffuse sclerosis), and (iii) five adult patients with chronic MS. Previous reports have suggested a possible correlation between iNOS, peroxynitrite, related nitrogen-derived oxidants, and the demyelinating processes in MS. We have demonstrated iNOS-immunoreactive cells in both acute-MS and diffuse-sclerosis-type lesions. In acute-MS lesions, iNOS was localized in both monocytes/macrophages and reactive astrocytes. However, foamy (myelin-laden) macrophages and the majority of reactive astrocytes were iNOS negative. In specimens from the childhood MS patient, iNOS protein was present only in a subpopulation of reactive or hypertrophic astrocytes. In contrast, no iNOS staining was detected in chronic-MS lesions. Immunohistochemical staining of acute-MS lesions with an antibody to nitrotyrosine revealed codistribution of iNOS- and nitrotyrosine-positive cells, although nitrotyrosine staining was more widespread in cells of the monocyte/macrophage lineage. In diffuse-sclerosis-type lesions, nitrotyrosine staining was present in hypertrophic astrocytes, whereas it was absent in chronic-MS lesions. These results suggest that NO and nitrogen-derived oxidants may play a role in the initiation of demyelination in acute-MS lesions but not in the later phase of the disease.

Inducible nitric oxide synthase in Theiler's murine encephalomyelitis virus infection

We investigated the role of inducible nitric oxide synthase (iNOS) in Theiler's murine encephalomyelitis virus (TMEV) infection of susceptible (SJL) and resistant (C57BL/6 [B6]) strains of mice. TMEV is an excellent model of virus-induced demyelinating disease, such as multiple sclerosis (MS). Previous studies of others have suggested that NO may play a role in the pathogenesis of demyelinating disease. The presence and level of iNOS were determined in the brains and spinal cords of SJL and B6 TMEV-infected mice by the following methods: (i) PCR amplification of iNOS transcripts, followed by Southern blotting with an iNOS-specific probe, and (ii) immunohistochemical staining with an anti-iNOS-specific affinity-purified rabbit antibody. iNOS-specific transcripts were determined in the brains and spinal cord of both SJL and B6 TMEV-infected mice on days 0 (control), days 3, 6, and 10 (encephalitic stage of disease), and days 39 to 42, 66, and 180 (demyelinating phase) postinfection (p.i.). iNOS-specific transcripts were found in the brains and spinal cords of both SJL and B6 TMEV-infected mice at 6, 10, and 39 (SJL) days p.i., but they were absent in mock-infected mice and in TMEV-infected SJL and B6 mice at 0, 3, 66, and 180 days p.i. Immunohistochemical staining confirmed the presence of iNOS protein in both TMEV-infected SJL and B6 mice at days 6 and 10 p.i., but not at days 0, 3, 66, and 180 days p.i. Weak iNOS staining was also observed in TMEV-infected SJL mice at 42 days p.i. iNOS-positive staining was found in reactive astrocytes surrounding areas of necrotizing inflammation, particularly in the midbrain. Weak iNOS staining was also observed in cells of the monocyte/macrophage lineage in areas of parenchymal inflammation and necrosis (mesencephalon) and in leptomeningeal and white matter perivascular infiltrates of the spinal cord. Rod-shaped microglia-like cells and foamy macrophages (myelin-laden) were iNOS negative. These results suggest that NO does not play a direct role in the late phase of demyelinating disease in TMEV-infected mice.

A neurotoxic prion protein fragment induces rat astroglial proliferation and hypertrophy

Prion-related encephalopathies are characterized by the accumulation of an abnormal prion protein isoform (PrPSc) and the deposition of PrP amyloid in the brain. This process is accompanied by neuronal loss and astrogliosis. We recently showed that a synthetic peptide corresponding to residues 106-126 of human PrP is amyloidogenic and causes neuronal death by apoptosis in vitro. In the present study we investigated the effects of 1- and 14-day exposures of rat astroglial cultures to micromolar concentrations of this peptide as well as peptides homologous to other portions of PrP, a peptide corresponding to residues 25-35 of amyloid-beta protein, and a scrambled sequence of PrP 106-126. No significant changes were observed after 1-day exposure of cultures to any peptide. Conversely, 14-day treatment with PrP 106-126 (50 microM) resulted in a 5-fold increase in glial fibrillary acidic protein (GFAP) expression, as evaluated by Northern and Western blot analyses, and a 1.5-fold increment in cell number. Light and electron microscopy immunohistochemistry showed an enlargement in size and density of astroglial processes, and an increase in GFAP-immunoreactive intermediate filaments. These changes were not observed after 14-day treatment of cultures with the other peptides, including PrP 106-126 scrambled. The increase in GFAP expression of astroglial cultures exposed to PrP 106-126 was quantitatively similar to that found in scrapie-infected hamster brains.(ABSTRACT TRUNCATED AT 250 WORDS)

Dementias, neurodegeneration, and viral mechanisms of disease from the perspective of human transmissible encephalopathies

Our transmission experiments with human CJD emphasize the centrality of an exogenous infectious pathogen that can exist in symbiosis with its host for extended periods. Many latent or persistent viruses can cause neurodegenerative disease and may have a role in late onset dementias. There are reasons to believe that CJD infections may share properties with some of these latent viruses in causing dementia, and several retroviral mechanisms may be operative in CJD. In order to clarify viral-like attributes of the CJD agent we have closely followed infectivity and find the following: 1) the CJD agent has a virus-like size and density, and is biochemically separable from most host-encoded prion protein (PrP); 2) Endogenous retroviral IAP RNA sequences of 5,000 bases, as well as several gag-like nucleic acid binding proteins, co-purify with infectivity in preparations treated with high concentrations of anionic detergents and exhaustive nuclease digestion. They signify the purification of true viral cores rather than aggregation artifacts, and diminish claims that there are no protected nucleic acids of > 50 bases in highly purified infectious preparations; 3) In established hamster CJD, temporal studies show the agent has an effective doubling time of approximately 7.5 days in brain, consistent with complex host-viral interactions common to slow viral infections; 4) PrP-res does not correspond to titered levels of infectivity either in a biochemical or an in vivo setting but may function as a viral receptor that can modulate disease expression. Interestingly, functional changes in glial cells occur earlier than PrP-res changes, and indicate an important role for glial cells in evolving infections; 5) Human-rodent transmission studies suggest that CJD, or a CJD-like variant can be a common but latent infection of humans, with relatively infrequent expression of neurological disease. Susceptibility to disease can rest on host attributes and possibly age-related co-factors. Nonetheless, fundamental viral principles are also operative. Agent strain variants, viral burden, and the routes of infection are critical parameters for latency and disease expression. The properties described above have led me to return to the inclusion of CJD (and scrapie) in the panorama of conventional slow viral infections of the brain, as originally proposed by Sigurdsson. Identification of virus-specific molecules are essential for elucidating the role of these agents in the spectrum of human dementias.

Modulation of prion protein gene expression by growth factors in cultured mouse astrocytes and PC-12 cells

The present study was performed on primary cultures of mouse astrocytes and cultures of rat pheochromocytoma PC-12 in order to investigate the regulation of the prion protein (PrP) gene expression in relation to proliferation and differentiation. Treatment of PC-12 cells with interleukin-6 (IL-6) and beta-nerve growth factor (NGF) resulted in induction of neuronal differentiation. Northern blot analysis demonstrated a 4-fold increase of PrP mRNA in relation to cellular differentiation, after 7 days of treatment with either of the two factors. In astrocytes, PrP and glial fibrillary acidic protein (GFAP) mRNA levels were found to be regulated in a similar manner during development in vitro. A 3-fold increase of their mRNAs was observed from 5 to 14 days of culture (proliferation period). Then, their gene expressions showed a slight decrease from 14 to 28 days (maturation period). Treatment of astrocytes with IL-6, basic fibroblast growth factor (bFGF), and epidermal growth factor (EGF) appeared to markedly down-regulate the expression of GFAP mRNAs, which might reflect cell maturation. In contrast, they had no significant effect on the expression of PrP gene. These results suggest that the PrP gene expression is differently regulated in neural cells. In neuronal cells, it is mainly associated with differentiation. On the other hand, in astrocytes, the PrP mRNA level seems to be not only related to the proliferation and differentiation stages.

A transmissible Creutzfeldt-Jakob disease-like agent is prevalent in the human population

The etiology of most human dementias is unknown. Creutzfeldt-Jakob disease (CJD), a relatively uncommon human dementia, is caused by a transmissible virus-like agent. Molecular markers that are specific for the agent have not yet been defined. However, the infectious disease can be transmitted to rodents from both brain and infected buffy coat (blood) samples. To determine whether human CJD infections are more widespread than is apparent from the low incidence of neurological disease, we attempted to transmit CJD from buffy coat samples of 30 healthy volunteers who had no family history of dementing illness. Primary transmissions from 26 of 30 individuals produced CJD-like spongiform changes in the brains of recipient hamsters at 200-500 days postinoculation. This positive evidence of viremia was found for individuals in all age groups (20-30, 40-50, and 61-71 years old), whereas 12 negatively scored brain samples failed to produce similar changes in hamsters observed for > 900 days in the same setting. We suggest that a CJD agent endemically infects humans but only infrequently produces an infectious dementia. Disease expression is likely to be influenced by several host factors in combination with viral variants that have altered neurovirulence.

Characterization of a transmissible growth-promoting agent derived from CSF of schizophrenic patients which is active on human neuroblastoma cells

A growth-promoting agent for the human neuroblastoma cell line SK-N-SH(EP) (SH-EP) has been detected in human cerebrospinal fluid (CSF) derived from schizophrenic patients. Following treatment with the CSF, a number of properties of the SH-EP cells changed permanently. These included an accelerated rate of growth, an increased cell density at confluence, a change of cell shape, and an increased ability to form colonies in soft agar. All of these changes are consistent with further cellular transformation of the SH-EP cells. Once the cells' properties had changed following CSF treatment, the growth-promoting activity was found to be present in freeze-thawed cell extracts and in the culture medium, and could be passed to untreated SH-EP cells. The activity could be detected in culture media diluted as high as 10(8). It was inactivated by proteinases, chloroform, or heat but passed through a 0.22-micron filter. The growth-promoting activity can be banded on a Percoll gradient, suggesting that it is particulate rather than a soluble growth factor.

The biology and molecular biology of scrapie-like diseases

The transmissible spongiform encephalopathies (TSE's) are degenerative diseases of the central nervous system which naturally affect man (Creutzfeldt-Jakob disease [CJD], Gerstmann-Sträussler syndrome [GSS], kuru), sheep and goats (scrapie), cattle (bovine spongiform encephalopathy [BSE]), mink (transmissible mink encephalopathy), mule deer, elk and antelope (chronic wasting disease). Spongiform encephalopathies have also been diagnosed in captive species of zoo antelope and in domestic cats. Much has been written about these maladies in the wake of the BSE outbreak, the tragic cases of CJD in recipients of cadaver-derived human growth hormone, sex hormones or dura mater and this has stimulated a continuing public health debate about the transmissibility, prevalence and clinical variability of scrapie, CJD and related ("prion") diseases. Prions (Weissmann, Liautard, this volume) and the human (Kretzschmar, this volume) and cattle (Wilesmith, Marsh, this volume) diseases are described in more detail elsewhere. This article presents a brief overview of the biology and molecular cell biology of scrapie and rodent models of these diseases.

The scrapie fibril protein and its cellular isoform

Proteins need help to fold and attain their functional conformation (Ellis and Hemmingsen 1989), and mechanisms have evolved to prevent the accumulation of misfolded protein aggregates within cells (Pelham 1988). These mechanisms fail to prevent the formation of protease-resistant, misfolded forms of PrP (ScPrP) during the development of scrapie and other transmissible spongiform encephalopathies, and ScPrP is a biochemical marker of these diseases. Much is now known about the structure and expression of the PrP gene, but the physiological function of the PrP protein and the mechanism by which the TDE pathogen replicates and specifically interferes with PrP metabolism remain a mystery--a mystery which will entertain prion-ophiliacs for some time yet.

Cellular isoform of the scrapie agent protein participates in lymphocyte activation

The scrapie agent protein (Sp33-37 or PrPSc) is the disease-associated isoform of a normal cellular membrane protein (Cp33-37 or PrPC) of unknown function. We report that normal human lymphocytes and lymphoid cell lines, but not erythrocytes or granulocytes, express PrPC mRNA and protein. PrPC is detectable on the surface of lymphocytes; the surface immunoreactivity is sensitive to phosphatidylinositol-specific phospholipase C, indicating glycosyl-phosphatidylinositol membrane anchorage. Lymphocyte PrPC surface abundance is increased by cell activation, and polyclonal antibodies to PrPC suppress mitogen-induced activation. We conclude that PrPC is a lymphocyte surface molecule that may participate in cell activation.