Showing papers by "Fabrizio Tagliavini published in 1999"

Frontotemporal dementia and corticobasal degeneration in a family with a P301S mutation in tau.

Abstract: The tau gene has been found to be the locus of dementia with rigidity linked to chromosome 17. Exonic and intronic mutations have been described in a number of families. Here we describe a P301S mutation in exon 10 of the tau gene in a new family. Two members of this family were affected. One individual presented with frontotemporal dementia, whereas his son has corticobasal degeneration, demonstrating that the same primary gene defect in tau can lead to 2 distinct clinical phenotypes. Both individuals developed rapidly progressive disease in the third decade. Neuropathologically, the father presented with an extensive filamentous pathology made of hyperphosphorylated tau protein. Biochemically, recombinant tau protein with the P301S mutation showed a greatly reduced ability to promote microtubule assembly.

Sporadic Creutzfeldt-Jakob disease: co-occurrence of different types of PrP(Sc) in the same brain.

Abstract: Phenotypic heterogeneity of sporadic Creutzfeldt-Jakob disease (CJD) has been linked to biochemically distinct types of the protease-resistant form of the prion protein (type 1 and type 2 PrP(Sc)). We investigated 14 cases of sporadic CJD and found that both type 1 and type 2 PrP(Sc) coexisted in 5 subjects. The distinct PrP(Sc) isoforms were associated with different patterns of PrP deposition and severity of spongiform changes, suggesting that the PrP(Sc) type plays a central role in determining the neuropathologic profile of CJD.

Microglial cells respond to amyloidogenic PrP peptide by the production of inflammatory cytokines.

Abstract: The scrapie isoform of the prion protein (PrPres) induces neurodegeneration and gliosis in the central nervous system. These features may be reproduced in vitro on exposure of neuronal and glial cultures to PrPres and the peptide HuPr P106-126. In the present study, we investigated the role of microglial cells and astrocytes in the pathological process by studying their molecular response to PrP 106-126 exposure. PrP 106-126 elicited a specific overproduction of pro-inflammatory cytokines IL1beta and IL6 in microglial cells (but not increased expression of TNFalpha, IL10, and TGFbeta1) and over-expression of GFAP in astrocytes. These effects were strictly dependent on the ability of the peptide to form amyloid fibrils. These data strongly suggest that microglial cells contribute to prion-related neurodegenerative processes by producing proinflammatory cytokines in the brain areas of amyloid PrP deposition.

Molecular determinants of the physicochemical properties of a critical prion protein region comprising residues 106-126.

Abstract: Prion diseases are marked by the cerebral accumulation of conformationally modified forms of the cellular prion protein (PrP(C)), known as PrP(res). The region comprising the residues 106-126 of human PrP seems to have a key role in this conformational conversion, because a synthetic peptide homologous with this sequence (PrP106-126) adopts different secondary structures in different environments. To investigate the molecular determinants of the physicochemical characteristics of PrP106-126, we synthesized a series of analogues including PrP106-126 H(D), PrP106-126 A and PrP106-126 K, with l-His-->d-His, His-->Ala and His-->Lys substitutions respectively at position 111, PrP106-126 NH(2) with amidation of the C-terminus, PrP106-126 V with an Ala-->Val substition at position 117, and PrP106-126 VNH(2) with an Ala-->Val substitution at position 117 and amidation of the C-terminus. The analysis of the secondary structure and aggregation properties of PrP106-126 and its analogues showed the following. (1) His(111) is central to the conformational changes of PrP peptides. (2) Amidation of the C-terminal Gly(126) yields a predominantly random coil structure, abolishes the molecular polymorphism and decreases the propensity of PrP106-126 to generate amyloid fibrils. (3) PrP106-126 V, carrying an Ala-->Val substitution at position 117, does not demonstrate a fibrillogenic ability superior to that of PrP106-126. However, the presence of Val at position 117 increases the aggregation properties of the amidated peptide. (4) Amyloid fibrils are not required for neurotoxicity because the effects of PrP106-126 NH(2) on primary neuronal cultures were similar to those of the wild-type sequence. Conversely, astroglial proliferation is related to the presence of amyloid fibrils, suggesting that astrogliosis in prion encephalopathies without amyloid deposits is a mediated effect rather than a direct effect of disease-specific PrP isoforms.

Determination of solution conformations of PrP106-126, a neurotoxic fragment of prion protein, by 1H NMR and restrained molecular dynamics.

Abstract: Experimental two-dimensional 1H NMR data have been obtained for PrP106–128 under the following solvent conditions: deionized water/2,2,2-trifluoroethanol 50 : 50 (v/v) and dimethylsulfoxide. These data were analyzed by restrained molecular mechanics calculations to determine how changes in solvation affect the conformation of the peptide. In deionized water at pH 3.5, the peptide adopted a helical conformation in the hydrophobic region spanning residues Met112–Leu125, with the most populated helical region corresponding to the Ala115–Ala119 segment (≈ 10%). In trifluoroethanol/H2O, the α-helix increased in population especially in the Gly119–Val122 tract (≈ 25%). The conformation of this region was found to be remarkably sensitive to pH, as the Ala120–Gly124 tract shifted to an extended conformation at pH 7. In dimethylsulfoxide, the hydrophobic cluster adopted a prevalently extended conformation. For all tested solvents the region spanning residues Asn108–Met112 was present in a ‘turn-like’ conformation and included His111, situated just before the starting point of the α-helix. Rather than by conformational changes, the effect of His111 is exerted by changes in its hydrophobicity, triggering aggregation. The amphiphilic properties and the pH-dependent ionizable side-chain of His111 may thus be important for the modulation of the conformational mobility and heterogeneity of PrP106–126.

A βPP Peptide Carboxyl-Terminal to Aβ Is Neurotoxic

Abstract: Extracellular Aβ-amyloid and intraneuronal paired helical filaments (PHFs) composed of tau protein are the neuropathological hallmark of Alzheimer's disease. Aβ is a 39- to 43-residue peptide derived by cleavage of a 695- to 770-amino-acid membrane-associate glycoprotein (termed β-protein precursor, βPP). Following the observation that an antiserum to an epitope located between residues 713 and 723 of βPP 770 (ie, the transmembrane region of the βPP distal to Aβ) labels PHFs and that a synthetic peptide homologous to residues 713 to 730 of βPP 770 (βPP713–730) is highly fibrillogenic and interacts with tau in vitro , it has been hypothesized that βPP fragments other than Aβ may feature in the pathogenesis of Alzheimer's disease concurring with neuronal degeneration. To investigate this issue, we have analyzed the effects of the exposure of primary neuronal cultures to the synthetic peptide βPP713–730. Cultures were prepared from rat hippocampus on embryonic day 17 and incubated with the peptide at 2.5 to 30 μmol/L concentration for 1 to 4 days. Cell viability was compared with that of control cultures exposed to a scrambled sequence of the peptide. A 4-day exposure to 20 μmol/L βPP713–730 resulted in almost complete neuronal loss, whereas no changes were observed with the scrambled peptide. Degenerating neurons showed DNA fragmentation by agarose gel electrophoresis and apoptotic changes by light and electron microscopy. These findings support the view that βPP sequences other than Aβ may play a role in nerve cell degeneration in Alzheimer's disease.