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Biomedical subjects

Adriano Aguzzi

Publications and source records attributed to Adriano Aguzzi.

At least 73 records · Page 4Linked to original sources
PubMed2004

Uptake of 18F-fluorocholine, 18F-fluoroethyl-L-tyrosine, and 18F-FDG in acute cerebral radiation injury in the rat: implications for separation of radiation necrosis from tumor recurrence.

UNLABELLED: Differentiation between posttherapy radiation necrosis and recurrent tumor in humans with brain tumor is still a difficult diagnostic task. The new PET tracers (18)F-fluoro-ethyl-l-tyrosine (FET) and (18)F-fluorocholine (N,N-dimethyl-N-(18)F-fluoromethyl-2-hydroxyethylammonium [FCH]) have shown promise for improving diagnostic accuracy. This study assessed uptake of these tracers in experimental radiation injury. METHODS: In a first model, circumscribed lesions were induced in the cortex of 35 rats using proton irradiation of 150 or 250 Gy. After radiation injury developed, uptake of (18)F-FET, (18)F-FCH, and (18)F-FDG was measured using autoradiography and correlated with histology and disruption of the blood-brain barrier as determined with Evans blue. In a second model, uptake of the tracers was assessed in acute cryolesions, which are characterized by the absence of inflammatory cells. RESULTS: Mean (18)F-FET, (18)F-FCH, and (18)F-FDG standardized uptake values in the most active part of the radiation lesion and the contralateral normal cortex (in parentheses) were 2.27 +/- 0.46 (1.42 +/- 0.23), 2.52 +/- 0.42 (0.61 +/- 0.12), and 6.21 +/- 1.19 (4.35 +/- 0.47). The degree of uptake of (18)F-FCH and (18)F-FDG correlated with the density of macrophages. In cryolesions, (18)F-FET uptake was similar to that in radiation lesions, and (18)F-FCH uptake was significantly reduced. CONCLUSION: Comparison of tracer accumulation in cryolesions and radiation injuries demonstrates that (18)F-FET uptake is most likely due to a disruption of the blood-brain barrier alone, whereas (18)F-FCH is additionally trapped by macrophages. Uptake of both tracers in the radiation injuries is generally lower than the published uptake in tumors, suggesting that (18)F-FET and (18)F-FCH are promising tracers for separating radiation necrosis from tumor recurrence. However, the comparability of our data with the literature is limited by factors such as different species and acquisition protocols and modalities. Thus, more studies are needed to settle this issue. Nevertheless, (18)F-FCH and (18)F-FET seem superior to (18)F-FDG for this purpose.

Acute Disease↗
PubMed2003

Extraneural pathologic prion protein in sporadic Creutzfeldt-Jakob disease.

BACKGROUND: In patients with sporadic Creutzfeldt-Jakob disease, pathologic disease-associated prion protein (PrPSc) has been identified only in the central nervous system and olfactory-nerve tissue. Understanding the distribution of PrPSc in Creutzfeldt-Jakob disease is important for classification and diagnosis and perhaps even for prevention. METHODS: We used a highly sensitive method of detection--involving the concentration of PrPSc by differential precipitation with sodium phosphotungstic acid, which increased the sensitivity of Western blot analysis by up to three orders of magnitude--to search for PrPSc in extraneural organs of 36 patients with sporadic Creutzfeldt-Jakob disease who died between 1996 and 2002. RESULTS: PrPSc was present in the brain tissue of all patients. In addition, we found PrPSc in 10 of 28 spleen specimens and in 8 of 32 skeletal-muscle samples. Three patients had PrPSc in both spleen and muscle specimens. Patients with extraneural PrPSc had a significantly longer duration of disease and were more likely to have uncommon molecular variants of sporadic Creutzfeldt-Jakob disease than were patients without extraneural PrPSc. CONCLUSIONS: Using sensitive techniques, we identified extraneural deposition of PrPSc in spleen and muscle samples from approximately one third of patients who died with sporadic Creutzfeldt-Jakob disease. Extraneural PrPSc appears to correlate with a long duration of disease.

Blotting, Western↗
PubMed2003

Games played by rogue proteins in prion disorders and Alzheimer's disease.

The incidence of Alzheimer's disease (AD) and that of prion disorders (PrD) could not be more different. One-third of octogenarians succumb to AD, whereas Creutzfeldt-Jakob disease typically affects one individual in a million each year. However, these diseases have many common features impinging on the metabolism of neuronal membrane proteins: the amyloid precursor protein APP in the case of AD, and the cellular prion protein PrPC in PrD. APP begets the Abeta peptide, whereas PrPC begets the malignant prion protein PrPSc. Both Abeta and PrPSc are associated with disease, but we do not know what triggers their accumulation and neurotoxicity. A great deal has been learned, however, about protein folding, misfolding, and aggregation; an entirely new class of intramembrane proteases has been identified; and unsuspected roles for the immune system have been uncovered. There is reason to expect that prion research will profit from advances in the understanding of AD, and vice versa.

Alzheimer Disease↗
PubMed2003

Positioning of follicular dendritic cells within the spleen controls prion neuroinvasion.

Peripheral infection is the natural route of transmission in most prion diseases. Peripheral prion infection is followed by rapid prion replication in lymphoid organs, neuroinvasion and progressive neurological disease. Both immune cells and nerves are involved in pathogenesis, but the mechanisms of prion transfer from the immune to the nervous system are unknown. Here we show that ablation of the chemokine receptor CXCR5 juxtaposes follicular dendritic cells (FDCs) to major splenic nerves, and accelerates the transfer of intraperitoneally administered prions into the spinal cord. Neuroinvasion velocity correlated exclusively with the relative locations of FDCs and nerves: transfer of CXCR5-/- bone marrow to wild-type mice induced perineural FDCs and enhanced neuroinvasion, whereas reciprocal transfer to CXCR5-/- mice abolished them and restored normal efficiency of neuroinvasion. Suppression of lymphotoxin signalling depleted FDCs, abolished splenic infectivity, and suppressed acceleration of pathogenesis in CXCR5-/- mice. This suggests that prion neuroimmune transition occurs between FDCs and sympathetic nerves, and relative positioning of FDCs and nerves controls the efficiency of peripheral prion infection.

Animals↗
PubMed2003

Expression of truncated PrP targeted to Purkinje cells of PrP knockout mice causes Purkinje cell death and ataxia.

PrP knockout mice with disruption of only the PrP-encoding region (Zürich I-type) remain healthy, whereas mice with deletions extending upstream of the PrP-encoding exon (Nagasaki-type) suffer Purkinje cell loss and ataxia, associated with ectopic expression of Doppel in brain, particularly in Purkinje cells. The phenotype is abrogated by co-expression of full-length PrP. Doppel is 25% similar to PrP, has the same globular fold, but lacks the flexible N-terminal tail. We now show that in Zürich I-type PrP-null mice, expression of N-terminally truncated PrP targeted to Purkinje cells also leads to Purkinje cell loss and ataxia, which are reversed by PrP. Doppel and truncated PrP probably cause Purkinje cell degeneration by the same mechanism.

Alleles↗
PubMed2003

Soluble dimeric prion protein binds PrP(Sc) in vivo and antagonizes prion disease.

Conversion of cellular prion protein (PrP(C)) into a pathological conformer (PrP(Sc)) is thought to be promoted by PrP(Sc) in a poorly understood process. Here, we report that in wild-type mice, the expression of PrP(C) rendered soluble and dimeric by fusion to immunoglobulin Fcgamma (PrP-Fc(2)) delays PrP(Sc) accumulation, agent replication, and onset of disease following inoculation with infective prions. In infected PrP-expressing brains, PrP-Fc(2) relocates to lipid rafts and associates with PrP(Sc) without acquiring protease resistance, indicating that PrP-Fc(2) resists conversion. Accordingly, mice expressing PrP-Fc(2) but lacking endogenous PrP(C) are resistant to scrapie, do not accumulate PrP-Fc(2)(Sc), and do not transmit disease to others. These results indicate that various PrP isoforms engage in a complex in vivo, whose distortion by PrP-Fc(2) affects prion propagation and scrapie pathogenesis. The unique properties of PrP-Fc(2) suggest that soluble PrP derivatives may represent a new class of prion replication antagonists.

Animals↗
PubMed2003

Oral prion infection requires normal numbers of Peyer's patches but not of enteric lymphocytes.

Prion pathogenesis following oral exposure is thought to involve gut-associated lymphatic tissue, which includes Peyer's patches (PPs) and M cells. Recruitment of activated B lymphocytes to PPs requires alpha(4)beta(7) integrin; PPs of beta 7(-/-) mice are normal in number but are atrophic and almost entirely devoid of B cells. Here we report that minimal infectious dose and disease incubation after oral exposure to logarithmic dilutions of prion inoculum were similar in beta 7(-/-) and wild-type mice, and PPs of both beta 7(-/-) and wild-type mice contained 3-4 log LD(50)/g prion infectivity > or =125 days after challenge. Despite marked reduction of B cells, M cells were present in beta 7(-/-) mice. In contrast, mice deficient in both tumor necrosis factor and lymphotoxin-alpha (TNF alpha(-/-) x LT alpha(-/-)) or in lymphocytes (RAG-1(-/-), mu MT), in which numbers of PPs are reduced in number, were highly resistant to oral challenge, and their intestines were virtually devoid of prion infectivity at all times after challenge. Therefore, lymphoreticular requirements for enteric and for intraperitoneal uptake of prions differ from each other. Although susceptibility to prion infection following oral challenge correlates with the number of PPs, it is remarkably independent of the number of PP-associated lymphocytes.

Animals↗
PubMed2003

Prions and the immune system: a journey through gut, spleen, and nerves.

For more than two decades it has been contended that prion infection does not elicit immune responses: transmissible spongiform encephalopathies do not go along with conspicuous inflammatory infiltrates, and antibodies to the prion protein are typically undetectable. Why is it, then, that prions accumulate in lymphoid organs, and that various states of immune deficiency prevent peripheral prion infection? This review revisits the current evidence of the involvement of the immune system in prion diseases, while attempting to trace the elaborate mechanisms by which peripherally administered prions invade the brain and ultimately cause damage. The investigation of these questions leads to unexpected detours, including the neurophysiology of lymphoid organs, and even the function of a prion protein homolog in male fertility.

Animals↗
PubMed2003

Genetic ablation of the tumor suppressor menin causes lethality at mid-gestation with defects in multiple organs.

Patients suffering from multiple endocrine neoplasia type 1 (MEN1) are predisposed to multiple endocrine tumors. The MEN1 gene product, menin, is expressed in many embryonic, as well as adult tissues, and interacts with several proteins in vitro and in vivo. However, the biological function of menin remains largely unknown. Here we show that disruption of the Men1 gene in mice causes embryonic lethality at E11.5-E13.5. The Men1 null mutant embryos appeared smaller in size, frequently with body haemorrhages and oedemas, and a substantial proportion of them showed disclosure of the neural tube. Histological analysis revealed an abnormal development of the nervous system and heart hypotrophy in some Men1 null embryos. Furthermore, Men1 null livers generally displayed an altered organization of the epithelial and hematopoietic compartments associated with enhanced apoptosis. Chimerism analysis of embryos generated by injection of Men1 null ES cells, showed that cells lacking menin do not seem to have a general cell-autonomous defect. However, primary Men1 null embryonic fibroblasts entered senescence earlier than their wild-type counterparts. Despite normal proliferation ability, Men1 null ES cells exhibited a deficiency to form embryoid bodies, suggesting an impaired differentiation capacity in these cells. The present study demonstrates that menin plays an important role in the embryonic development of multiple organs in addition to its proposed role in tumor suppression.

Alleles↗
PubMed2003

Human prion diseases: epidemiology and integrated risk assessment.

Human prion diseases are devastating and incurable, but are very rare. Fears that the bovine spongiform encephalopathy epizootic would lead to a large epidemic of its presumed human counterpart, variant Creutzfeldt-Jakob disease (vCJD), have not been realised. Yet a feeling of uncertainty prevails in the general public and in the biomedical world. The lack of data on the prevalence of asymptomatic carriers of vCJD compounds this uncertainty. In addition to this problem, Switzerland is currently faced with another issue of major public concern: a recent rise in the incidence of CJD. Here we examine the plausibility of several scenarios that may account for the increase in CJD incidence, including ascertainment bias due to improved reporting of CJD, iatrogenic transmission, and transmission of a prion zoonosis. In addition, we present the design and current status of a Swiss population-wide study of subclinical vCJD prevalence.

Creutzfeldt-Jakob Syndrome↗
PubMed2003

Prion pathogenesis in the absence of Toll-like receptor signalling.

To reach the brain from peripheral sites, prions must colonize various cell types within the lymphoreticular compartment. However, no prion entry receptors are yet known. Toll-like receptors (TLRs) are pattern-recognition receptors that bind a multitude of pathogens and are therefore candidates as effectors of prion entry. Moreover, injection of unmethylated CpG oligodinucleotides, which stimulate TLR9, has been reported to delay peripherally initiated scrapie. We therefore studied prion infection in MyD88(-/-) mice, which are defective in TLR signalling. Despite subtle defects in splenic microarchitecture, MyD88(-/-) mice challenged intraperitoneally or intracerebrally were fully susceptible to disease and died of scrapie after similar incubation times to those of wild-type mice. Splenic infectivity titres rose to similar levels with the same kinetics, and brains showed similar histopathological changes. TLR signalling therefore does not have any major role in prion pathogenesis, and the protective effect of TLR stimulation is unlikely to result from direct interactions with prions.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Immune system and peripheral nerves in propagation of prions to CNS.

Prions are not only unique in the way they replicate. Also the sequence of events triggered by peripheral prion infection, generically termed 'peripheral pathogenesis', sets prions aside from all other known pathogens. Whereas most bacteria, parasites, and viruses trigger innate and adaptive immune responses, the mammalian immune system appears to be remarkably oblivious to prions. Transmissible spongiform encephalopathies (TSEs) do not go along with inflammatory infiltrates, and antibodies to the prion protein are not typically raised during the course of the disease. On the other hand, there is conspicuous involvement of lymphoid organs, which accumulate sizeable concentrations of the infectious agent early during disease. Moreover, various states of immune deficiency can abolish peripheral pathogenesis and prevent 'take' of infection when prions are administered to peripheral sites. Here, we critically re-visit the current evidence for an involvement of the immune system in prion diseases, and will attempt to trace the elaborate mechanisms by which prions, upon entry into the body from peripheral sites, reach the brain.

Amyloid↗
PubMed2003

No superoxide dismutase activity of cellular prion protein in vivo.

Prion diseases are characterized by the deposition of PrP(Sc), an abnormal form of the cellular prion protein PrP(C), which is encoded by the Prnp gene. PrP(C) is highly expressed on neurons and its function is unknown. Recombinant PrP(C) was claimed to possess superoxide dismutase (SOD) activity, and it was hypothesized that abrogation of this function may contribute to neurodegeneration in prion diseases. We tested this hypothesis in vivo by studying copper/zinc and manganese SOD activity in genetically defined crosses of mice lacking the Sod1 gene with mice lacking PrP(C), and with hemizygous or homozygous tga20 transgenic mice overexpressing various levels of PrP(C). We failed to detect any influence of the Prnp genotype and gene dosage on SOD1 or SOD2 activity in heart, spleen, brain, and synaptosome-enriched brain fractions. Control experiments included crosses of mice lacking or overexpressing PrPc with mice overexpressing human Cu2+/Zn2+-superoxide dismutase, and confirmed that SOD enzymatic activity correlated exclusively with the gene dosage of bona fide human or murine SOD. We conclude that PrP(C) in vivo does not discernibly contribute to total SOD activity and does not possess an intrinsic dismutase activity.

Animals↗
PubMed2003

Stimulation of plasminogen activation by recombinant cellular prion protein is conserved in the NH2-terminal fragment PrP23-110.

The cellular prion protein (PrP(c)), tissue-type plasminogen activator (t-PA) and plasminogen are expressed in synaptic membranes in vivo. In the central nervous system the fibrinolytic system is associated with excitotoxin-mediated neurotoxicity and Alzheimer's disease. Recently binding of the disease associated isoform of the prion protein (PrP(Sc)) to plasminogen and stimulation of t-PA activity have been reported. In this study the interaction of PrP(c) and plasminogen was investigated using chromogenic assays in vitro. We found that plasmin is able to cleave recombinant PrP(c) at lysine residue 110 generating an NH(2)-terminal truncated molecule that has previously been described as a major product of PrP(c) metabolism. We further characterized the proteolytic fragments with respect to their ability to stimulate plasminogen activation in vitro. Our results show that the NH(2)-terminal part of PrP(c) spanning amino acids 23-110 (PrP23-110) together with low molecular weight heparin stimulates t-PA mediated plasminogen activation in vitro. The apparent rate constant was increased 57 fold in the presence of 800 nM PrP23-110. Furthermore, we compared the stimulation of t-PA activity by PrP(c) and beta-amyloid peptide (1-42). While the activity of the beta-amyloid was independent of low molecular weight heparin, PrP23-110 was approximately 4- and 37 fold more active than beta-amyloid in the absence or presence of low molecular weight heparin. In summary, plasmin cleaves PrP(c) in vitro and the liberated NH(2)-terminal fragment accelerates plasminogen activation. Cleavage of PrP c has previously been reported. Thus cleavage of PrP(c) enhancing plasminogen activation at the cell surface could constitute a regulatory mechanism of pericellular proteolysis.

Amino Acid Sequence↗
PubMed2002

Unhampered prion neuroinvasion despite impaired fast axonal transport in transgenic mice overexpressing four-repeat tau.

Transmissible spongiform encephalopathies often are caused by peripheral uptake of infectious prions, and the peripheral nervous system is involved in prion spread to the brain. Although the cellular prion protein is subjected to fast axonal transport, the mechanism of intranerval transport of infectious prions is unclear. Here we administered prions intranervally to transgenic mice overexpressing the four-repeat human tau protein, which exhibit defective fast axonal transport. These mice showed unaltered neuroinvasion, suggesting that transport mechanisms distinct from fast axonal transport effect prion neuroinvasion along peripheral nerves. Surprisingly, scrapie-sick tau transgenic mice accumulated intraneuronal deposits of hyperphosphorylated tau protein. The coincidence of tau and prion pathology resembled Gerstmann-Sträussler-Scheinker syndrome. These findings identify tau pathology as a possible end stretch of prion-induced neurodegeneration.

Animals↗