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Biomedical subjects

A Aguzzi

Publications and source records attributed to A Aguzzi.

At least 91 records · Page 5Linked to original sources
PubMed1999

Human MxA protein protects mice lacking a functional alpha/beta interferon system against La crosse virus and other lethal viral infections.

The human MxA protein is part of the antiviral state induced by alpha/beta interferon (IFN-alpha/beta). MxA inhibits the multiplication of several RNA viruses in cell culture. However, its antiviral potential in vivo has not yet been fully explored. We have generated MxA-transgenic mice that lack a functional IFN system by crossing MxA-transgenic mice constitutively expressing MxA with genetically targeted (knockout) mice lacking the beta subunit of the IFN-alpha/beta receptor (IFNAR-1(-/-) mice). These mice are an ideal animal model to investigate the unique antiviral activity of human MxA in vivo, because they are unable to express other IFN-induced proteins. Here, we show that MxA confers resistance to Thogoto virus, La Crosse virus, and Semliki Forest virus. No Thogoto virus progeny was detectable in MxA-transgenic mice, indicating an efficient block of virus replication at the primary site of infection. In the case of La Crosse virus, MxA restricted invasion of the central nervous system. In contrast, Semliki Forest virus multiplication in the brain was detectable in both MxA-expressing and nonexpressing IFNAR-1(-/-) mice. However, viral titers were clearly reduced in MxA-transgenic mice. Our results demonstrate that MxA does not need the help of other IFN-induced proteins for activity but is a powerful antiviral agent on its own. Moreover, the results suggest that MxA may protect humans from potential fatal infections by La Crosse virus and other viral pathogens.

Alphavirus Infections↗
PubMed1999

Biphasic edema after hypoxic-ischemic brain injury in neonatal rats reflects early neuronal and late glial damage.

Magnetic resonance imaging with diffusion- and T2-weighted imaging and 31P magnetic resonance spectroscopy was used to investigate the relationship between development of brain edema and alterations of the brain energy metabolism after hypoxia-ischemia (HI) brain injury in 7-d-old rats. The results were correlated with histologic examinations at various times during recovery up to 5 d. Moderate HI, induced by right common carotid artery ligation and subsequent exposure to 8% O2 for 90 min, produced a cytotoxic edema of 52+/-9% brain volume and depressed the ratio of phosphocreatine to inorganic phosphate from 1.43+/-0.21 to 0.11+/-0.09. Within 1 h of reoxygenation, the edema decreased to 4+/-2% of brain volume, demarcating the core of the lesion. At 5 h of recovery, a secondary cytotoxic edema together with a newly developing vasogenic edema expanded again, reaching its maximal extent of 45+/-10% brain volume at around 24 h. The ratio of phosphocreatine to inorganic phosphate recovered slowly, reaching 1.12+/-0.27 around 13 h. Thereafter it declined again in a manner analogous to the observations made in human newborns after severe perinatal asphyxia, reaching trough values of 0.48+/-0.22 around 24 h after HI. At the cellular level, the vast majority of neuronal death occurred before 15 h. Subsequently, strong glial activation lasted 2-3 d after HI. At 5 d, a cystic infarction of 35+/-12% brain volume was found. We conclude that the biphasic evolution of brain edema and energy metabolism reflects early neuronal and late glial damage in response to moderate HI injury. Therefore, the secondary energy breakdown reflects glial activation and subsequent glial death.

Animals↗
PubMed1999

The heavy metal-responsive transcription factor-1 (MTF-1) is not required for neural differentiation.

The zinc finger transcription factor MTF-1 is essential for proper response to heavy metal load and other stress conditions in vertebrates, and also contributes to the maintenance of the cellular redox state. Target genes include metallothioneins (MT-I and MT-II) and gamma-glutamylcysteine synthetase (gamma-GCS), an enzyme involved in glutathione biosynthesis. Although MTF-1 is expressed ubiquitously, the primary defect in null mutant mice is hepatocyte necrosis, which results in embryonic lethality around day E14 and prevents the analysis of delayed effects on other organs. To assess the impact of MTF-1 deficiency on the function of the mature central nervous system, we employed the neural grafting strategy. Neuroectodermal brain tissue obtained from transgenic mouse embryos at gestational day 12.5 was transplanted into the caudoputamen of adult wild-type mice. 33 days later, grafts derived from MTF-1 deficient mice consisted of fully differentiated neuroectodermal tissue and showed no differences to heterozygous control grafts. This indicates that MTF-1 is dispensable for the development and differentiation of the nervous system. Such transplants devoid of MTF-1 may provide a useful tool for the further investigation of the effect of cell stress, including oxidative stress.

Animals↗
PubMed1999

Characterization of Tu-2449, a glioma cell line derived from a spontaneous tumor in GFAP-v-src-transgenic mice: comparison with established murine glioma cell lines.

Glial fibrillary acidic protein (GFAP)-v-src transgenic mice develop spontaneous gliomas with a high incidence of malignant progression. We characterize the first glial cell line derived from v-src transgenic mice, Tu-2449 in comparison with a virally induced murine glioma, SRB-10, and a spontaneous murine glioma, P497. Doubling times were lowest, as clonogenicity in soft agar was highest for Tu-2449, and to a lesser degree, Tu-2449 cells formed spheroids and showed migratory behaviour and invaded fetal rat brain aggregates. BCL-2 and BAX expression were lower in Tu-2449 and P497 than in SRB-10 cells. Only Tu-2449 cells accumulated p53 protein in response to genotoxic stress. Tu-2449 and SRB-10 cells that showed low CD95 expression were resistant to CD95 ligand (CD95L)-induced apoptosis unless coexposed to CD95L and inhibitors of RNA or protein synthesis. A chemosensitivity profile revealed Tu-2449 to be rather chemoresistant. Tu-2449 thus displays growth characteristics and patterns of resistance to apoptosis similar to those of other mouse and human glioma cell lines and may therefore become a valuable tool to evaluate new therapies for malignant gliomas in vitro and in vivo.

Animals↗
PubMed1998

Prion protein expression in different species: analysis with a panel of new mAbs.

By immunizing prion knockout mice (Prnp-/-) with recombinant murine prion protein (PrPc), we obtained a panel of mAbs specific for murine PrPc. These mAbs can be applied to immunoblotting, cell surface immunofluorescent staining, and immunohistochemistry at light and electron microscopy. These mAbs recognize both the normal (PrPc) and protease-resistant (PrPres) isoforms of PrP. Some mAbs are species restricted, while others react with PrP from a broad range of mammals including mice, humans, monkeys, cows, sheep, squirrels, and hamsters. Moreover, some of the mAbs selectively recognize different PrP glycoforms as well as the metabolic fragments of PrPc. These newly generated PrPc antibodies will help to explore the biology of PrPc and to establish the diagnosis of prion diseases in both humans and animals.

Animals↗
PubMed1998

A matrix-less measles virus is infectious and elicits extensive cell fusion: consequences for propagation in the brain.

Measles viruses (MV) can be isolated from the brains of deceased subacute sclerosing panencephalitis patients only in a cell-associated form. These viruses are often defective in the matrix (M) protein and always seem to have an altered fusion protein cytoplasmic tail. We reconstituted a cell-free, infectious M-less MV (MV-DeltaM) from cDNA. In comparison with standard MV, MV-DeltaM was considerably more efficient at inducing cell-to-cell fusion but virus titres were reduced approximately 250-fold. In MV-DeltaM-induced syncytia the ribonucleocapsids and glycoproteins largely lost co-localization, confirming the role of M protein as the virus assembly organizer. Genetically modified mice were inoculated with MV-DeltaM or with another highly fusogenic virus bearing glycoproteins with shortened cytoplasmic tails (MV-Delta(tails)). MV-DeltaM and MV-Delta(tails) lost acute pathogenicity but penetrated more deeply into the brain parenchyma than standard MV. We suggest that enhanced cell fusion may also favour the propagation of mutated, assembly-defective MV in human brains.

Amino Acid Sequence↗
PubMed1998

Embryonic lethality and liver degeneration in mice lacking the metal-responsive transcriptional activator MTF-1.

We have shown previously that the heavy metal-responsive transcriptional activator MTF-1 regulates the basal and heavy metal-induced expression of metallothioneins. To investigate the physiological function of MTF-1, we generated null mutant mice by targeted gene disruption. Embryos lacking MTF-1 die in utero at approximately day 14 of gestation. They show impaired development of hepatocytes and, at later stages, liver decay and generalized edema. MTF-1(-/-) embryos fail to transcribe metallothionein I and II genes, and also show diminished transcripts of the gene which encodes the heavy-chain subunit of the gamma-glutamylcysteine synthetase, a key enzyme for glutathione biosynthesis. Metallothionein and glutathione are involved in heavy metal homeostasis and detoxification processes, such as scavenging reactive oxygen intermediates. Accordingly, primary mouse embryo fibroblasts lacking MTF-1 show increased susceptibility to the cytotoxic effects of cadmium or hydrogen peroxide. Thus, MTF-1 may help to control metal homeostasis and probably cellular redox state, especially during liver development. We also note that the MTF-1 null mutant phenotype bears some similarity to those of two other regulators of cellular stress response, namely c-Jun and NF-kappaB (p65/RelA).

Animals↗
PubMed1998

Expression of amino-terminally truncated PrP in the mouse leading to ataxia and specific cerebellar lesions.

The physiological role of prion protein (PrP) remains unknown. Mice devoid of PrP develop normally but are resistant to scrapie; introduction of a PrP transgene restores susceptibility to the disease. To identify the regions of PrP necessary for this activity, we prepared PrP knockout mice expressing PrPs with amino-proximal deletions. Surprisingly, PrP lacking residues 32-121 or 32-134, but not with shorter deletions, caused severe ataxia and neuronal death limited to the granular layer of the cerebellum as early as 1-3 months after birth. The defect was completely abolished by introducing one copy of a wild-type PrP gene. We speculate that these truncated PrPs may be nonfunctional and compete with some other molecule with a PrP-like function for a common ligand.

Alleles↗
PubMed1998

A strain-independent postnatal neurodegeneration in mice lacking the EGF receptor.

Mice lacking the epidermal growth factor receptor (EGFR) exhibit strain-dependent phenotypes ranging from placental to postnatal skin, lung and brain defects. After birth, all mutant mice develop a progressive neurodegeneration in the frontal cortex, olfactory bulb and thalamus, characterized by massive apoptosis and upregulation of c-fos. These defects occur in a strain-independent manner, since neither rescue of the placental phenotype by aggregation of diploid 129/Sv EGFR mutant and tetraploid wild-type embryos, nor promotion of lung maturation by transplacental dexamethasone administration alters the course of neurodegeneration. VEGF is not induced during the degenerative process, excluding hypoxia and ischemia as causes of cell death. A migratory disorder is detected in the hippocampus with nests of ectopic neurons, which are also apoptotic. Cerebral cortices from EGFR mutants contain lower numbers of GFAP positive astrocytes, which display reduced proliferation in vitro. Since EGFR is expressed in the affected cell-types, these results define a specific function for EGFR in the proliferation and/or differentiation of astrocytes and in the survival of postmitotic neurons.

Animals↗
PubMed1998

PrP expression in B lymphocytes is not required for prion neuroinvasion.

Prion diseases are typically initiated by infection of peripheral sites, as in the case of bovine spongiform encephalopathy, new variant Creutzfeldt-Jakob disease, kuru and most cases of iatrogenic Creutzfeldt-Jakob disease. In mouse scrapie, prion infectivity accumulates in lymphoid organs, and the absence of mature B lymphocytes prevents peripherally administered prions from inducing central nervous system disease. We have now assessed whether expression of the cellular prion protein, PrPc, is required for B lymphocytes to mediate neuroinvasion. We found that repopulation of SCID and Rag-1(-/-) mice with fetal liver cells from either PrP-expressing or PrP-deficient mice and from T-cell deficient mice, but not from B-cell deficient mice, is equally efficient in restoring neuroinvasion after intraperitoneal inoculation of scrapie prions. These results indicate that cells whose maturation depends on B cells or their products, such as follicular dendritic cells, may enhance neuroinvasion. Alternatively, B cells may transport prions to the nervous system by a PrP-independent mechanism.

Animals↗
PubMed1998

Hypersensitivity to seizures in beta-amyloid precursor protein deficient mice.

Secreted forms of the beta-amyloid precursor protein (beta-APP) have neuroprotective properties in vitro and may be involved in the containment of neuronal excitation. To test whether loss of secreted forms of beta-APP (sAPPs) may enhance excitotoxic responses, we injected mice homozygous for a targeted mutation of the beta-APP gene (beta-APPDelta/Delta) intraperitoneally with kainic acid. We found that in these mice, kainic acid induced seizures initiated earlier, and acute mortality was enhanced compared to isogenic wild-type mice independently from the callosal agenesis phenotype observed to occur at increased frequency in APP mutant mice. Expression of c-fos in cortex and cingulate gyrus was enhanced in beta-APPDelta/Delta mice, although the amount of structural damage and apoptosis in the hippocampal pyramidal cell layer and cortex was similar to that of controls. When cerebellar granule cell cultures and cortical neuronal cultures were challenged with glutamate receptor agonists, the rates of cell death and apoptosis of beta-APPDelta/Delta mice were indistinguishable from those of controls. Therefore, deficiency of sAPPs causes facilitation of seizure activity in the absence of enhanced cell death. Since enhanced seizures were observed also in mice homozygous for a deletion of the entire beta-APP gene, this phenotype results from a loss of APP rather than from a dominant effect of APPDelta.

Amyloid beta-Protein Precursor↗
PubMed1998

Use of brain grafts to study the pathogenesis of prion diseases.

For the study of prion neurotoxicity, we used neural-grafting techniques: mice devoid of the normal host prion protein (Prnp% mice) received a neural graft and were intracerebrally infected with mouse prions. The growth and differentiation properties of neural grafts were defined. Growth of embryonic neuroectodermal tissue was optimal at gestational days 12.5-13.5. The blood-brain barrier is reconstituted after 7 weeks in most animals. Scrapie-infected PrPC-expressing grafts develop a severe spongiform encephalopathy and contain proteinase-resistant protein and infectivity. Infected grafts deliver high amounts of prions to the host brain without eliciting disease. Infected grafts show a progressive disruption of the blood-brain barrier. Following intraocular prion inoculation of a transplanted Prnp% mouse, prions do not reach the intracerebral graft, indicating that PrP expression is required for propagation along the optic tract.

Animals↗
PubMed1998

Prion diseases.

Although the nature of the infectious agent causing prion diseases is still debated, several of its molecular characteristics have been clarified in remarkable detail. The transmissibility of bovine spongiform encephalopathy to humans dramatically highlights the need for research focused at interference with prion replication and spread, and at prevention of brain damage. Precondition to achieving these goals is a thorough understanding of prion biology, and in particular of its protein chemistry.

Animals↗
PubMed1998

Degeneration of the cerebellar granule cell layer in transgenic mice expressing genes of human foamy virus.

Transgenic mice expressing various combinations of structural and regulatory genes of human foamy virus (HFV) develop a neurodegenerative syndrome. delta gpe transgenic mice (which express the auxiliary bel-1 and bet genes along with truncated forms of gag, pol, and env) develop a severe neurological syndrome consisting mainly of spastic tetraparesis and blindness, and show neuronal loss in the hippocampus and cerebral cortex. In addition, mice in two of eight delta gpe lines developed an ataxic gait. Here we studied the phenotype of these two lines, and show that these mice exhibit progressive degeneration of their cerebellar granule cells beginning at 4-8 weeks of age. Transgenic mRNA and HFV proteins accumulate in cerebellar granule cells immediately before the onset of degeneration. The Purkinje cell layer is largely unaffected by this pathological process. Probably due to the loss of granule cell processes, the cerebellar molecular layer is narrowed in the late stages of the disease. These findings indicate that HFV gene products can be neurotoxic for cerebellar granule cells.

Animals↗