Claudio Russo

Presenilin-1 mutations in Alzheimer's disease

Mutations in the gene encoding the protein presenilin-1 are the most common cause of familial Alzheimers disease and they often produce a different disease course from sporadic Alzheimers and another familial form associated with mutations in the gene encoding β-amyloid precursor protein. Here we show that a peculiar form of β-amyloid that is devoid of the first ten amino acids accumulates in the brains of patients carrying presenilin-1 mutations, and is more abundant than in subjects affected by the other types of Alzheimers.

β-Amyloid Is Different in Normal Aging and in Alzheimer Disease

The mechanism of neurodegeneration caused by β-amyloid in Alzheimer disease is controversial. Neuronal toxicity is exerted mostly by various species of soluble β-amyloid oligomers that differ in their N- and C-terminal domains. However, abundant accumulation of β-amyloid also occurs in the brains of cognitively normal elderly people, in the absence of obvious neuronal dysfunction. We postulated that neuronal toxicity depends on the molecular composition, rather than the amount, of the soluble β-amyloid oligomers. Here we show that soluble β-amyloid aggregates that accumulate in Alzheimer disease are different from those of normal aging in regard to the composition as well as the aggregation and toxicity properties.

Heterogeneity of water-soluble amyloid β-peptide in Alzheimer's disease and Down's syndrome brains

Water‐soluble amyloid β‐peptides (sAβ), ending at residue 42, precede amyloid plaques in Downs syndrome (DS). Here we report that sAβ consists of the full‐length Aβ1–42 and peptides truncated and modified by cyclization of the N‐terminal glutamates, Aβ3(pE)–42 and Aβ11(pE)–42. The Aβ3(pE)–42 peptide is the most abundant form of sAβ in Alzheimers disease (AD) brains. In DS, sAβ3(pE)–42 concentration increases with age and the peptide becomes a dominant species in the presence of plaques. Both pyroglutamate‐modified peptides and the full‐length Aβ form a stable aggregate that is water soluble. The findings point to a crucial role of the aggregated and modified sAβ in the plaque formation and pathogenesis of AD.

Identification of Amino-Terminally and Phosphotyrosine-Modified Carboxy-Terminal Fragments of the Amyloid Precursor Protein in Alzheimer's Disease and Down's Syndrome Brain

The carboxy-terminal fragments (CTFs) of the amyloid precursor protein (APP) are considered β-amyloid (Aβ) precursors as well as molecular species possibly amyloidogenic and neurotoxic by themselves in vitro or in animal models. The CTFs role in the pathogenesis of Alzheimers disease (AD) is however relatively unexplored in human brain. In this study, we analyzed brain extracted CTFs in subjects with AD, non-AD control, and Downs syndrome (DS) cases. Our data indicate that: (i) In fetal DS subjects CTFs levels are increased in comparison to age-matched control, suggesting that the enhanced CTFs formation is important for the early occurrence of plaques deposition in DS. No significant difference in CTFs level is present between AD and age-matched control cases. (ii) CTFs modified at their N-terminus are the direct precursors of similarly N-terminally modified Aβ peptides, which constitute the most abundant species in AD and DS plaques. This observation suggests that N-truncated Aβ peptides are formed directly at β-secretase level and not through a progressive proteolysis of full-length Aβ1-40/42. (iii) Among the differently cleaved CTFs, only the 22- and 12.5-kDa CTF polypeptides are tyrosine phosphorylated in both AD and control brain while the full-length APP and the CTFs migrating below the 12.5-kDa marker are not phosphorylated, suggesting that APP and CTFs may be involved in different pathways depending on their length and sequences. This study provides evidence that CTFs constitute in human brain a molecular species directly involved in AD pathogenesis and in the development of the AD-like pathology in DS subjects.

Effect of the E200K Mutation on Prion Protein Metabolism: Comparative Study of a Cell Model and Human Brain

The hallmark of prion diseases is the cerebral accumulation of a conformationally altered isoform (PrP(Sc)) of a normal cellular protein, the prion protein (PrP(C)). In the inherited form, mutations in the prion protein gene are thought to cause the disease by altering the metabolism of the mutant PrP (PrP(M)) engendering its conversion into PrP(Sc). We used a cell model to study biosynthesis and processing of PrP(M) carrying the glutamic acid to lysine substitution at residue 200 (E200K), which is linked to the most common inherited human prion disease. PrP(M) contained an aberrant glycan at residue 197 and generated an increased quantity of truncated fragments. In addition, PrP(M) showed impaired transport of the unglycosylated isoform to the cell surface. Similar changes were found in the PrP isolated from brains of patients affected by the E200K variant of Creutzfeldt-Jakob disease. Although the cellular PrP(M) displayed some characteristics of PrP(Sc), the PrP(Sc) found in the E200K brains was quantitatively and qualitatively different. We propose that the E200K mutation cause the same metabolic changes of PrP(M) in the cell model and in the brain. However, in the brain, PrP(M) undergoes additional modifications, by an age-dependent mechanism that leads to the formation of PrP(Sc) and the development of the disease.

Apoptotic Cell Death and Amyloid Precursor Protein Signaling in Neuroblastoma SH‐SY5Y Cells

Abstract: We have recently shown that the amyloid precursor protein (APP) and a subset of its C‐terminal fragments (CTFs) are tyrosine phosphorylated in human brain and in cultured cells. Tyrosine phosphorylation generates a substrate that is sequentially bound by the adaptor proteins ShcA and Grb2, and this interaction is significantly enhanced in Alzheimers disease brains. Here we have studied the APP/CTFs phosphorylation and ShcA activation in a human neuroblastoma cell line, SH‐SY5Y, under basal and apoptotic conditions. To commit these cells to apoptosis, we used staurosporin, a well‐known apoptotic inducer and protein kinase C blocker. Our data suggest the following: (1) in normally proliferating SH‐SY5Y cells, full‐length APP is complexed with Grb2[Q3], likely through its SH2 domain; (2) upon induction of apoptosis, APP is degraded and ShcA‐Grb2 coimmunoprecipitates with CTFs recognized by anti‐APP antibodies; and (3) caspase inhibitors partially block the degradation of APP and the coprecipitation of CTFs with ShcA‐Grb2 adaptors. In summary, our data suggest that in SH‐SY5Y cells, tyrosine‐phosphorylated APP is involved in a complex with ShcA‐Grb2 adaptors that is disrupted during apoptosis. The abnormal degradation of APP and consequent increased levels of CTFs (as has been observed in Alzheimers disease and Downs syndrome) generate a complex between tyrosine‐phosphorylated CTFs and intracellular adaptors. The signaling through APP and its CTFs may have significant relevance for apoptotic cell death in Alzheimers disease.

reply: Alzheimer's disease: Molecular consequences of presenilin-1 mutation

Gandy et al. compare our results with their 1994 findings that the amino-terminally truncated amyloid Aβ11–42 was relatively abundant in two cases of familial Alzheimers disease involving two distinct mutations in β-APP. However, four important differences should be borne in mind: the authors compare Aβ11–42 with Aβ1–42 and ignore Aβ1–40, although both Aβ1–40 and Aβ1–42 are generated by β-secretase/BACE cleavage at residue Asp 1 (ref. 3); their data are not correlated with features related to disease severity, such as age at onset and duration; they did not examine brains with PS1 mutations (these were not known at that time); and their characterization was based on the use of size-exclusion chromatography and electrospray mass spectrometry to quantify formic-acid-extracted Aβ, whereas we used quantitative analysis of immunoprecipitated water-soluble Aβ on western blots, mass spectrometry to identify Aβ variants, and immunohistochemistry to reveal amino-truncated Aβ peptides in plaques.

Mechanisms of phenotypic heterogeneity in prion, Alzheimer and other conformational diseases

Department of Physiology, East Carolina University,Greenville, NC 27858, USA1. IntroductionOneof thechallengesfacedbyclinicians andpathol-ogistsis dealingwiththevariabilityoftheclinicalsignsandofthepathologicalchangesthatareassociatedwithdiseases. The truism that two patients with the samedisease are never identical poses no serious diagnosticproblems under most circumstances. However, therearediseasesthatpresentconsiderablevariabilityintheirclinical and pathological phenotype, which not onlymakes the diagnosis difficult but also raises the issue ofthe mechanisms that regulate it.While phenotypically Alzheimer disease, amy-otrophic lateral sclerosis and Huntington chorea havebeenconsideredfairlyhomogenousdiseases, priondis-eases include several clinically and pathologically dis-tinct conditions (Table 1) [33]. Until a few years ago,the sporadic form of prion diseases included only theCreutzfeldt-Jakobdisease(CJD)phenotype. Theinher-ited form included familial CJD, fatal familial insom-nia (FFI), and Gerstmann-Straussler-Scheinkerdisease¨(GSS). These three phenotypes are quite different andhave very unique features. In addition, a fourth sub-typeoffamilialpriondiseases associatedwithinsertionmutationshas eithera mixedphenotypewhichincludesfeatures of both CJD and GSS or a pathological phe-notype with no distinctive features. The form acquiredby infection consists of three phenotypes that are alsoquite distinct, namely the iatrogenic CJD, kuru, andthe new variant CJD reported almost exclusively in theUnited Kingdom.A major interest of our group has been the studyof the mechanisms that regulate the phenotypic het-erogeneity. The understanding of these mechanismsmay lead to a classification of prion diseases based onthe causes rather than the effects of this heterogene-ity. Such classification is likely to be more accurateand may result in a wider detection and more precisediagnosis of these diseases.2. Molecular, cell biology and pathology of theprion proteinThematurenormalorcellularprionprotein(PrP