A Pathogenic Presenilin-1 Deletion Causes Abberrant Aβ42 Production in the Absence of Congophilic Amyloid Plaques
2001; Elsevier BV; Volume: 276; Issue: 10 Linguagem: Inglês
10.1074/jbc.m007183200
ISSN1083-351X
AutoresHarald Steiner, Tamás Révész, Manuela Neumann, Helmut Romig, Melissa G. Grim, Brigitte Pesold, Hans A. Kretzschmar, John Hardy, Janice L. Holton, Ralf Baumeister, Henry Houlden, Christian Haass,
Tópico(s)S100 Proteins and Annexins
ResumoFamilial Alzheimer's disease (FAD) is frequently associated with mutations in the presenilin-1 (PS1) gene. Almost all PS1-associated FAD mutations reported so far are exchanges of single conserved amino acids and cause the increased production of the highly amyloidogenic 42-residue amyloid β-peptide Aβ42. Here we report the identification and pathological function of an unusual FAD-associated PS1 deletion (PS1 ΔI83/ΔM84). This FAD mutation is associated with spastic paraparesis clinically and causes accumulation of noncongophilic Aβ-positive "cotton wool" plaques in brain parenchyma. Cerebral amyloid angiopathy due to Aβ deposition was widespread as were neurofibrillary tangles and neuropil threads, although tau-positive neurites were sparse. Although significant deposition of Aβ42 was observed, no neuritic pathology was associated with these unusual lesions. Overexpressing PS1 ΔI83/ΔM84 in cultured cells results in a significantly elevated level of the highly amyloidogenic 42-amino acid amyloid β-peptide Aβ42. Moreover, functional analysis in Caenorhabditis elegans reveals reduced activity of PS1 ΔI83/ΔM84 in Notch signaling. Our data therefore demonstrate that a small deletion of PS proteins can pathologically affect PS function in endoproteolysis of β-amyloid precursor protein and in Notch signaling. Therefore, the PS1 ΔI83/ΔM84 deletion shows a very similar biochemical/functional phenotype like all other FAD-associated PS1 or PS2 point mutations. Since increased Aβ42 production is not associated with classical senile plaque formation, these data demonstrate that amyloid plaque formation is not a prerequisite for dementia and neurodegeneration. Familial Alzheimer's disease (FAD) is frequently associated with mutations in the presenilin-1 (PS1) gene. Almost all PS1-associated FAD mutations reported so far are exchanges of single conserved amino acids and cause the increased production of the highly amyloidogenic 42-residue amyloid β-peptide Aβ42. Here we report the identification and pathological function of an unusual FAD-associated PS1 deletion (PS1 ΔI83/ΔM84). This FAD mutation is associated with spastic paraparesis clinically and causes accumulation of noncongophilic Aβ-positive "cotton wool" plaques in brain parenchyma. Cerebral amyloid angiopathy due to Aβ deposition was widespread as were neurofibrillary tangles and neuropil threads, although tau-positive neurites were sparse. Although significant deposition of Aβ42 was observed, no neuritic pathology was associated with these unusual lesions. Overexpressing PS1 ΔI83/ΔM84 in cultured cells results in a significantly elevated level of the highly amyloidogenic 42-amino acid amyloid β-peptide Aβ42. Moreover, functional analysis in Caenorhabditis elegans reveals reduced activity of PS1 ΔI83/ΔM84 in Notch signaling. Our data therefore demonstrate that a small deletion of PS proteins can pathologically affect PS function in endoproteolysis of β-amyloid precursor protein and in Notch signaling. Therefore, the PS1 ΔI83/ΔM84 deletion shows a very similar biochemical/functional phenotype like all other FAD-associated PS1 or PS2 point mutations. Since increased Aβ42 production is not associated with classical senile plaque formation, these data demonstrate that amyloid plaque formation is not a prerequisite for dementia and neurodegeneration. Alzheimer's disease familial AD β-amyloid precursor protein transmembrane domain wild type Alzheimer's disease (AD)1 is an age-dependent neurogenerative disorder. Although most AD cases occur sporadically, autosomal dominant inheritance has been recorded in numerous families (1Selkoe D.J. Nature. 1999; 399: A23-A31Crossref PubMed Scopus (1515) Google Scholar). Mutations in four genes have been mapped to familial AD (FAD). These include the genes encoding the β-amyloid precursor protein (βAPP), presenilin 1 (PS1), PS2 (1Selkoe D.J. Nature. 1999; 399: A23-A31Crossref PubMed Scopus (1515) Google Scholar), and α2-macroglobulin (2Blacker D. Wilcox M.A. Laird N.M. Rodes L. Horvath S.M. Go R.C. Perry R. Watson Jr., B. Bassett S.S. McInnis M.G. Albert M.S. Hyman B.T. Tanzi R.E. Nat. Genet. 1998; 19: 357-360Crossref PubMed Scopus (579) Google Scholar). Functional analysis revealed that βAPP and PS mutations affect endoproteolytic processing of βAPP in a very similar manner. In the amyloidogenic pathway, βAPP is first cleaved at the N terminus of the Aβ domain by the recently identified β-secretase (3Vassar R. Citron M. Neuron. 2000; 27: 419-422Abstract Full Text Full Text PDF PubMed Scopus (267) Google Scholar). This generates a membrane-retained C-terminal fragment, which is the substrate for the γ-secretase. γ-Secretase cleaves its substrate within the membrane, which results in the physiological secretion of Aβ (1Selkoe D.J. Nature. 1999; 399: A23-A31Crossref PubMed Scopus (1515) Google Scholar). About 90% of secreted Aβ terminates at amino acid 40 (Aβ40), while most of the remaining Aβ peptides are elongated by two amino acids (Aβ42). The rare Aβ42 appears to aggregate much faster than Aβ40 (4Lansbury Jr., P.T. Neuron. 1997; 19: 1151-1154Abstract Full Text Full Text PDF PubMed Scopus (149) Google Scholar, 5Teplow D.B. Amyloid. 1998; 5: 121-142Crossref PubMed Scopus (286) Google Scholar) and is therefore the major constituent of senile plaques (6Mann D.M. Iwatsubo T. Cairns N.J. Lantos P.L. Nochlin D. Sumi S.M. Bird T.D. Poorkaj P. Hardy J. Hutton M. Prihar G. Crook R. Rossor M.N. Haltia M. Ann. Neurol. 1996; 40: 149-156Crossref PubMed Scopus (198) Google Scholar, 7Lemere C.A. Lopera F. Kosik K.S. Lendon C.L. Ossa J. Saido T.C. Yamaguchi H. Ruiz A. Martinez A. Madrigal L. Hincapie L. Arango J.C. Anthony D.C. Koo E.H. Goate A.M. Selkoe D.J. Nat. Med. 1996; 2: 1146-1150Crossref PubMed Scopus (433) Google Scholar). FAD-associated mutations found within βAPP, PS1, and PS2 all cause the increased production of this highly amyloidogenic Aβ variant and therefore increase the kinetics of Aβ aggregation and of its deposition in congophilic senile plaques (1Selkoe D.J. Nature. 1999; 399: A23-A31Crossref PubMed Scopus (1515) Google Scholar). PS proteins not only affect the γ-secretase cleavage in FAD cases but are also required for physiological Aβ generation, since a PS1 ablation results in a dramatically reduced Aβ production (8De Strooper B. Saftig P. Craessaerts K. Vanderstichele H. Guhde G. Annaert W. Von Figura K. Van Leuven F. Nature. 1998; 391: 387-390Crossref PubMed Scopus (1532) Google Scholar). 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Biochemistry. 1999; 38: 13602-13609Crossref PubMed Scopus (101) Google Scholar). In all cases, inhibition of PS function not only reduced Aβ generation but also concomitantly increased the corresponding membrane-retained βAPP C-terminal fragments, which are the immediate precursors for Aβ generation. Since two critical aspartate residues are required within the catalytic center of aspartyl proteases and since γ-secretase function can be blocked by aspartyl protease inhibitors (13Wolfe M.S. Xia W. Moore C.L. Leatherwood D.D. Ostaszewski B. Rahmati T. Donkor I.O. Selkoe D.J. Biochemistry. 1999; 38: 4720-4727Crossref PubMed Scopus (306) Google Scholar), it was recently claimed that PS proteins may be identical with the γ-secretase (14Wolfe M.S. De Los Angeles J. Miller D.D. Xia W. Selkoe D.J. Biochemistry. 1999; 38: 11223-11230Crossref PubMed Scopus (183) Google Scholar). 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Roques P. Fuldner R.A. Johnston J. Cowburn R. Forsell C. Axelman K. Lilius L. Houlden H. Karran E. Roberts G.W. Rossor M. Adams M.D. Hardy J. Goate A. Lannfelt L. Hutton M. Neuroreport. 1995; 7: 297-301Crossref PubMed Scopus (236) Google Scholar, 29De Jonghe C. Cruts M. Rogaeva E.A. Tysoe C. Singleton A. Vanderstichele H. Meschino W. Dermaut B. Vanderhoeven I. Backhovens H. Vanmechelen E. Morris C.M. Hardy J. Rubinsztein D.C. St. George-Hyslop P.H. Van Broeckhoven C. Hum. Mol. Genet. 1999; 8: 1529-1540Crossref PubMed Scopus (69) Google Scholar, 30Crook R. Verkkoniemi A. Perez-Tur J. Mehta N. Baker M. Houlden H. Farrer M. Hutton M. Lincoln S. Hardy J. Gwinn K. Somer M. Paetau A. Kalimo H. Ylikoski R. Poyhonen M. Kucera S. Haltia M. Nat. Med. 1998; 4: 452-455Crossref PubMed Scopus (277) Google Scholar, 31Prihar G. Verkkoniemi A. Perez-Tur J. Crook R. Lincoln S. Houlden H. Somer M. Paetau A. Kalimo H. Grover A. Myllykangas L. Hutton M. Hardy J. Haltia M. Nat. Med. 1999; 5: 1090Crossref PubMed Scopus (44) Google Scholar) have been observed so far. However, none of the deletions are directly associated with a pathological function. We have shown previously that the pathological activity of the PS1 Δexon9 splicing mutation (28Perez-Tur J. Froelich S. Prihar G. Crook R. Baker M. Duff K. Wragg M. Busfield F. Lendon C. Clark R.F. Roques P. Fuldner R.A. Johnston J. Cowburn R. Forsell C. Axelman K. Lilius L. Houlden H. Karran E. Roberts G.W. Rossor M. Adams M.D. Hardy J. Goate A. Lannfelt L. Hutton M. Neuroreport. 1995; 7: 297-301Crossref PubMed Scopus (236) Google Scholar) is independent of the large deletion and rather due to a single amino acid exchange at the aberrant splice junction at codon 290 (32Steiner H. Romig H. Grim M.G. Philipp U. Pesold B. Citron M. Baumeister R. Haass C. J. Biol. Chem. 1999; 274: 7615-7618Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar). A genomic deletion of the exon 9-encoded domain (Δexon9 Finn; see below) was reported as well (30Crook R. Verkkoniemi A. Perez-Tur J. Mehta N. Baker M. Houlden H. Farrer M. Hutton M. Lincoln S. Hardy J. Gwinn K. Somer M. Paetau A. Kalimo H. Ylikoski R. Poyhonen M. Kucera S. Haltia M. Nat. Med. 1998; 4: 452-455Crossref PubMed Scopus (277) Google Scholar). However, due to the aberrant splicing of exon 8 with exon 10, the same amino acid exchange is introduced at codon 290 as observed in the original PS1 Δexon9 splicing mutation. Therefore, the amino acid sequence of PS1 Δexon9 Finn is identical to the PS1 Δexon9 splicing mutation. In analogy to the PS1 Δexon9 splicing mutation (32Steiner H. Romig H. Grim M.G. Philipp U. Pesold B. Citron M. Baumeister R. Haass C. J. Biol. Chem. 1999; 274: 7615-7618Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar), it would therefore be expected that this mutation (PS1 Δexon9 Finn) produces Aβ42 independent of the exon 9 deletion. The unusual genomic exon 9 deletion of PS1 in the Finnish pedigree is associated with Alzheimer's disease and spastic paraparesis. In contrast to all other AD cases, these patients as well as the patients with the PS1 Δexon9 splicing mutation develop "cotton wool" plaques, which lack a congophilic dense core and plaque-related neuritic pathology (30Crook R. Verkkoniemi A. Perez-Tur J. Mehta N. Baker M. Houlden H. Farrer M. Hutton M. Lincoln S. Hardy J. Gwinn K. Somer M. Paetau A. Kalimo H. Ylikoski R. Poyhonen M. Kucera S. Haltia M. Nat. Med. 1998; 4: 452-455Crossref PubMed Scopus (277) Google Scholar). 2H. Houlden and J. Hardy, unpublished data. 2H. Houlden and J. Hardy, unpublished data.Finally, the deletion produced by the intron 4 mutation of PS1 could not be associated with an increased Aβ42 production (29De Jonghe C. Cruts M. Rogaeva E.A. Tysoe C. Singleton A. Vanderstichele H. Meschino W. Dermaut B. Vanderhoeven I. Backhovens H. Vanmechelen E. Morris C.M. Hardy J. Rubinsztein D.C. St. George-Hyslop P.H. Van Broeckhoven C. Hum. Mol. Genet. 1999; 8: 1529-1540Crossref PubMed Scopus (69) Google Scholar). It rather turned out that a single amino acid insertion, which is generated by aberrant splicing, is responsible for the pathological activity of this mutation (29De Jonghe C. Cruts M. Rogaeva E.A. Tysoe C. Singleton A. Vanderstichele H. Meschino W. Dermaut B. Vanderhoeven I. Backhovens H. Vanmechelen E. Morris C.M. Hardy J. Rubinsztein D.C. St. George-Hyslop P.H. Van Broeckhoven C. Hum. Mol. Genet. 1999; 8: 1529-1540Crossref PubMed Scopus (69) Google Scholar). Therefore, no PS1 deletion has so far been associated with increased Aβ42 generation. We have now analyzed the function of a novel PS1 deletion (PS1 ΔI83/ΔM84; Fig. 1), which is also associated with early onset AD and spastic paraparesis. A potentially pathological function in Aβ generation and Notch signaling was specifically investigated. We found that PS1 ΔI83/ΔM84 causes increased Aβ42 production like all other FAD-associated PS1/PS2 mutations. The PS1 ΔI83/ΔM84 mutation is associated with Aβ deposition in noncongophilic cotton wool plaques, widespread cerebral amyloid angiopathy, neurofibrillary tangles, and neuropil threads, although tau-positive abnormal neurites are rare. Antibody 3926 to synthetic Aβ was described before (33Wild-Bode C. Yamazaki T. Capell A. Leimer U. Steiner H. Ihara Y. Haass C. J. Biol. Chem. 1997; 272: 16085-16088Abstract Full Text Full Text PDF PubMed Scopus (284) Google Scholar). The polyclonal and monoclonal antibodies against amino acids 263–407 of PS1 (3027; BI.3D7) and against amino acids 297–356 of PS2 (3711; BI.HF5c) were described previously (32Steiner H. Romig H. Grim M.G. Philipp U. Pesold B. Citron M. Baumeister R. Haass C. J. Biol. Chem. 1999; 274: 7615-7618Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar). For tau immunohistochemistry, the AT8 antibody (Innogenetics, Belgium) and mouse monoclonal antibody PHF1 (a gift from Peter Davies) were used. An anti-GFAP antibody (Dako, UK) was used for the detection of astrocytosis. The presence of microglia was detected with an antibody against major histocompatibility complex class II proteins (clone CR3/43), which was obtained from Dako, UK. For Aβ immunohistochemistry, N-terminal antibody 6F/3D to Aβ8–17 (Dako, UK) or 6E10 to Aβ1–17 (Senetek) as well as C-terminal specific antisera recognizing Aβ ending at Ala42 (antibody 44-344; Immunogenetics, Belgium) or Val40 (antibody 44-348; Immunogenetics, Belgium) were used. Brains from the patient with the PS1 ΔI83/ΔM84 mutation and from a patient with a PS1 T115C mutation were collected at postmortem and fixed in 10% formalin in phosphate-buffered saline. Blocks from the major anatomical areas, including the hippocampal formation, were processed in paraffin wax. Tissue sections were stained with hematoxylin and eosin and Bielschowsky's silver impregnation methods. Congo red and thioflavine S methods were used to detect Aβ deposits in β-sheet conformation. For immunohistochemistry, 4-, 7-, or 20-μm sections were deparaffinized in xylene and rehydrated using graded alcohols. For PHF1, AT8, and CR3/43 immunohistochemistry, sections were pretreated in a microwave oven in sodium citrate buffer for 20 min, for GFAP immunohistochemistry in trypsin for 10 min, and for Aβ, Aβ40, and Aβ42 immunohistochemistry in formic acid for 10 min followed by treatment in a pressure cooker in citrate buffer for 10 min. After washes in phosphate-buffered saline and 10% milk, sections were incubated with the PHF1 antibody at 4 °C or with the GFAP, AT8, CR3/43, Aβ, Aβ40, and Aβ42 antibodies at room temperature. Detection of antibody binding was either performed with the ABC or the alkaline phosphatase anti-alkaline phosphatase system (DAKO) according to the manufacturer's instructions. Either diaminobenzidine/H2O2 or neufuchsin was used as chromogen. Genomic DNA and mRNA were extracted from blood and frozen brain, respectively. All exons of the PS1 gene were analyzed by polymerase chain reaction amplification of genomic DNA and Big Dye sequencing. Sequence analyses of PS1 exon 4 revealed a heterozygous deletion of ATCATG at codons 83 and 84 (isoleucine-methionine) of the gene. The corresponding cDNA encoding PS1 ΔI83/ΔM84 was cloned into pcDNA3.1-zeo(+) expression vector (Invitrogen). Human embryonic kidney 293 cells (K293) were cultured in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum, 1% penicillin/streptomycin, 200 μg/ml G418 (to select for βAPP expression), and 200 μg/ml zeocin (to select for presenilin expression). K293 cells stably expressing PS1 ΔI83/ΔM84 were generated by transfection of K293 cells stably expressing βAPP containing the Swedish mutation (34Citron M. Oltersdorf T. Haass C. McConlogue L. Hung A.Y. Seubert P. Vigo-Pelfrey C. Lieberburg I. Selkoe D.J. Nature. 1992; 360: 672-674Crossref PubMed Scopus (1514) Google Scholar). K293 cells stably coexpressing Swedish βAPP695 and wt PS1 or PS1 Δexon9 were described previously (35Citron M. Westaway D. Xia W. Carlson G. Diehl T. Levesque G. Johnson-Wood K. Lee M. Seubert P. Davis A. Kholodenko D. Motter R. Sherrington R. Perry B. Yao H. Strome R. Lieberburg I. Rommens J. Kim S. Schenk D. Fraser P. St. George Hyslop P. Selkoe D.J. Nat. Med. 1997; 3: 67-72Crossref PubMed Scopus (1148) Google Scholar, 36Steiner H. Capell A. Pesold B. Citron M. Kloetzel P.M. Selkoe D.J. Romig H. Mendla K. Haass C. J. Biol. Chem. 1998; 273: 32322-32331Abstract Full Text Full Text PDF PubMed Scopus (181) Google Scholar). Cell lysates from stably transfected K293 cells were prepared and subjected to immunoprecipitation using the polyclonal antibody 3027 to PS1 or 3711 to PS2 (32Steiner H. Romig H. Grim M.G. Philipp U. Pesold B. Citron M. Baumeister R. Haass C. J. Biol. Chem. 1999; 274: 7615-7618Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar). Following gel electrophoresis, immunoprecipitated PS proteins were identified by immunoblotting using the monoclonal antibody BI.3D7 (PS1) or BI.HF5c (PS2) (32Steiner H. Romig H. Grim M.G. Philipp U. Pesold B. Citron M. Baumeister R. Haass C. J. Biol. Chem. 1999; 274: 7615-7618Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar). Bound antibodies were detected by enhanced chemiluminescence (ECL; Amersham Pharmacia Biotech). Conditioned media (2 ml) were collected from confluent K293 cells in six-well dishes for 24 h. The media were assayed for Aβ40 and Aβ42 according to a previously described enzyme-linked immunosorbent assay (36Steiner H. Capell A. Pesold B. Citron M. Kloetzel P.M. Selkoe D.J. Romig H. Mendla K. Haass C. J. Biol. Chem. 1998; 273: 32322-32331Abstract Full Text Full Text PDF PubMed Scopus (181) Google Scholar). To construct a new sel-12 expression vector, a 3.0-kilobase pair fragment of cosmid C08A12 was amplified by polymerase chain reaction using primers CCC GGC TGC AGC TCA ATT ATT CTA GTA AGC and GTC TCC ATG GAT CCG AAT TCT GAA ACG TTC AAA TAA C and cloned into pPD49.26 (37Fire A. Harrison S.W. Dixon D. Gene ( Amst. ). 1990; 93: 189-198Crossref PubMed Scopus (526) Google Scholar). The resulting plasmid contains only nontranscribed sequences from the 5′ region of the C. elegans sel-12 gene. PS1 derivatives were cloned into this vector as aBamHI/SalI fragment. Transgenic lines were established by microinjection of plasmid DNA mixtures into the C. elegans germ line to create extrachromosomal arrays (26Baumeister R. Leimer U. Zweckbronner I. Jakubek C. Grunberg J. Haass C. Genes Funct. 1997; 1: 149-159Crossref PubMed Scopus (185) Google Scholar). Four independent lines from the progeny of F2 generation animals were established. Since the sel-12(ar171) animals never lay eggs (26Baumeister R. Leimer U. Zweckbronner I. Jakubek C. Grunberg J. Haass C. Genes Funct. 1997; 1: 149-159Crossref PubMed Scopus (185) Google Scholar), rescue of the sel-12 defect can be quantified by scoring egg-laying behavior in transgenic animals (26Baumeister R. Leimer U. Zweckbronner I. Jakubek C. Grunberg J. Haass C. Genes Funct. 1997; 1: 149-159Crossref PubMed Scopus (185) Google Scholar). 50 transgenic animals of each line were analyzed for their ability to lay eggs. The numbers of eggs laid by individual transgenic animals were counted and placed into four categories: Egl+++, robust egg laying, more than 30 eggs laid; Egl++, 15–30 eggs laid; Egl+, 5–15 eggs laid; Egl−, 0–5 eggs laid. Several families were identified by Houlden et al. (38Houlden H. Baker M. McGowan E. Lewis P. Hutton M. Crook R. Wood N.W. Kumar-Singh S. Geddes J. Swash M. Scaravilli F. Holton J.L. Lashley T. Tomita T. Hashimoto T. Verkkoniemi A. Kalimo H. Somer M. Paetau A. Martin J.-J. Van Broeckhoven C. Golde T. Hardy J. Haltia M. Revesz T. Ann. Neurol. 2000; 48: 806-808Crossref PubMed Scopus (109) Google Scholar) with autosomal dominant early onset AD with spastic paraparesis. Here we present the detailed pathological, biochemical, and functional analysis of one of these families. Neuropathological examination of a large Scottish family (Fig.1 A) revealed the presence of large cotton wool plaques (see below) similar to those seen in the Finnish family (30Crook R. Verkkoniemi A. Perez-Tur J. Mehta N. Baker M. Houlden H. Farrer M. Hutton M. Lincoln S. Hardy J. Gwinn K. Somer M. Paetau A. Kalimo H. Ylikoski R. Poyhonen M. Kucera S. Haltia M. Nat. Med. 1998; 4: 452-455Crossref PubMed Scopus (277) Google Scholar, 39Verkkoniemi A. Somer M. Rinne J.O. Myllykangas L. Crook R. Hardy J. Viitanen M. Kalimo H. Haltia M. Neurology. 2000; 54: 1103-1109Crossref PubMed Scopus (65) Google Scholar). Sequencing revealed the presence of an exon 4 deletion (ATC-ATG; isoleucine-methionine) of codons 83 and 84 of the PS1 gene. The mutation was not present in 100 controls. The PS1 ΔI83/ΔM84 deletion occurs within TM1 of PS1 (Fig. 1 B). TM1 may be functionally important, since other mutations were previously located in that region. Interestingly, the PS1 ΔI83/ΔM84 deletion is located immediately C-terminal to the V82L mutation (40Campion D. Flaman J.M. Brice A. Hannequin D. Dubois B. Martin C. Moreau V. Charbonnier F. Didierjean O. Tardieu S. Penet C. Puel M. Pasquier F. Ledoze F. Bellis G. Calenda A. Heilig R. Martinez M. Mallet J. Bellis M. Clergetdarpoux F. Agid Y. Frebourg T. Hum. Mol. Genet. 1995; 4: 7-2373Crossref Scopus (254) Google Scholar). Moreover, a third mutation has been observed in TM1, which results in the exchange of valine at position 96 to phenylalanine (41Kamino K. Sato S. Sakaki Y. Yoshiiwa A. Nishiwaki Y. Takeda M. Tanabe H. Nishimura T. Ii K. St. George-Hyslop P.H. Miki T. Ogihara T. Neurosci. Lett. 1996; 208: 195-198Crossref PubMed Scopus (58) Google Scholar). Neuropathological investigation of the PS1 ΔI83/ΔM84 case by hematoxylin/eosin staining, Bielschowsky's silver staining, and Aβ immunohistochemistry revealed the presence of widespread cotton wool plaques (Figs. 2 and3). These plaques were most frequently found in the neocortex, hippocampus, and striatum. Cotton wool plaques appeared in the neuropil as round, eosinophilic, and strongly Aβ-positive structures often larger than 100 μm in diameter. These frequently seemed to displace other elements such as neurons, a finding readily noticeable in the hippocampus (Fig. 2, A andB). Cotton wool plaques did not generally contain amyloid, since they were negative or occasionally very weakly stained by Congo red and weakly positive with thioflavine S (Fig. 2,C–E). Cerebral amyloid angiopathy was widespread, capillaries having thickened walls, which, together with the affected arterioles, showed apple green birefringence following Congo red staining and strong fluorescence with thioflavine S (Fig. 2,C–E). Bielschowsky silver staining (Fig.2 B) and tau immunohistochemistry (Fig. 2, F andH) revealed that neurofibrillary tangle pathology was widespread in the neocortex and hippocampal formation, although the dentate fascia was spared. Fine neuropil threads were a prominent feature within the cortices, and AT8 as well as PHF1 immunohistochemistry also revealed that the cotton wool plaques contained many thread-like processes but were only rarely associated with abnormal neurites (Fig. 2, F and H). In contrast, numerous tau (Fig. 2 G) and silver-positive abnormal neurites (data not shown) were seen in association with the classical plaques found in the control case with a PS1 T115C mutation (42Cruts M. Van Broeckhoven C. Hum. Mutat. 1998; 11: 183-190Crossref PubMed Scopus (174) Google Scholar) (Fig. 2 G). GFAP immunostaining demonstrated a relatively sparse astrocytic response to the cotton wool plaques (Fig.2 I). Furthermore, no significant microglial activation (CR3/43 immunostaining) was observed in association with cotton wool plaques (Fig. 2 J), in contrast to widespread activated microglia that were clustered mostly around the amyloid plaques in the PS1 T115C case (Fig. 2 K).Figure 3Cotton wool plaques associated with the PS1 ΔI83/ΔM84 mutation contain Aβ42. A andB, Aβ positive cotton wool plaques and blood vessels (arrow) in the neocortex (A, 6F/3D immunohistochemistry, × 115; B, 6E10 immunohistochemistry, × 120). The cotton wool plaques are weakly positive for Aβ40 (44-348 immunohistochemistry, × 50) (C) but strongly positive for Aβ42 (44-344 immunohistochemistry, × 115) (D).View Large Image Figure ViewerDownload Hi-res image Download (PPT) Deposition of Aβ species ending at position 42 is believed to be closely associated with neuritic plaque formation in previously reported cases wit
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