Visualization of A beta 42(43) and A beta 40 in senile plaques with end-specific A beta monoclonals: evidence that an initially deposited species is A beta 42(43)

Biological markers for the clinical diagnosis of Alzheimer's disease

There is a compelling need to develop biological marker(s) to confirm a clinical diagnosis of Alzheimer's disease (AD) during life in order to unequivocally identify AD patients for emerging therapeutic interventions. This review describes recent advances in the development of diagnostic marker(s) for AD. They include polymorphism of apolipoprotein E (ApoE) and alpha 1-antichymotrypsin as well as cerebrospinal fluid (CSF) tau and CSF-amyloid beta-protein levels, skin biopsy, and pupil dilatation assay by anti-cholinergic agent. In conclusion, ApoE genotyping should not be used as a sole diagnostic test for AD, and that monitoring of CSF-tau appeared to be most promising and reliable diagnostic aid.

G protein-mediated neuronal DNA fragmentation induced by familial Alzheimer's disease-associated mutants of APP

Missense mutations in the 695-amino acid form of the amyloid precursor protein (APP695) cosegregate with disease phenotype in families with dominantly inherited Alzheimer's disease. These mutations convert valine at position 642 to isoleucine, phenylalanine, or glycine. Expression of these mutant proteins, but not of normal APP695, was shown to induce nucleosomal DNA fragmentation in neuronal cells. Induction of DNA fragmentation required the cytoplasmic domain of the mutants and appeared to be mediated by heterotrimeric guanosine triphosphate-binding proteins (G proteins).

The interaction between apolipoprotein E and Alzheimer's amyloid beta-peptide is dependent on beta-peptide conformation

An important feature of Alzheimer's disease (AD) is the cerebral deposition of amyloid. The main component of the amyloid is a 39-44-amino acid residue protein called amyloid beta (A beta), which also exists as a normal protein in biological fluids, known as soluble A beta. A major risk factor for late-onset AD is the inheritance of the apolipoprotein (apo) E4 isotype of apoE. How apoE is involved in the pathogenesis of AD is unclear; however, evidence exists for a direct apoE/A beta interaction. We and others have shown that apoE copurifies with A beta from AD amyloid plaques and that under certain in vitro conditions apoE promotes a beta-sheet structure in A beta peptides. Currently we document the high affinity binding of A beta peptides to both human recombinant apoE3 and -E4 with a KD of 20 nM. This interaction is greatly influenced by the conformational state of the A beta peptide used. Furthermore, we show that the fibril modulating effect of apoE is also influenced by the initial secondary structure of the A beta peptide. The preferential binding of apoE to A beta peptides with a beta-sheet conformation can in part explain the copurification of A beta and apoE from AD amyloid plaques.

Antibodies to amyloid beta protein (A beta) crossreact with glyceraldehyde-3-phosphate dehydrogenase (GAPDH)

In the present study, we characterized the epitope of a monoclonal antibody against purified amyloid plaque cores (Am-3). By immunocytochemical experiments, Am-3 stained cerebrovascular and senile plaque amyloid in brain sections of patients with Alzheimer's disease (AD) in a similar manner to that of antibodies against amyloid beta-protein (A beta). By Western blotting experiments, Am-3 recognized only a 35 kDa protein, which was revealed to be glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and not A beta or beta amyloid precursor protein (beta PP). However, Am-3 recognized both GAPDH and purified native A beta in a dot-binding assay. Therefore, we concluded that Am-3 recognized both GAPDH and native A beta. Other monoclonal antibodies (6C6 and AmT-1) against the synthetic peptide corresponding to residues 1-28 of A beta also recognized these proteins. Because the amino acid sequences of these two proteins are not homologous, we propose that the crossreactivity between A beta and GAPDH is a consequence of their similar conformational epitopes. The possibility of crossreactions would complicate immunochemical and immunocytochemical studies of brain aging, AD and Down's syndrome. The implications of crossreactivity in developing immunological assays and in investigating the amyloid deposits of AD are discussed.

Amyloid probes based on Congo Red distinguish between fibrils comprising different peptides

BACKGROUND

Amyloid plaques, which characterize degenerating tissue in Alzheimer's disease (brain) and type II diabetes (pancreas), were first visualized by staining with the dye Congo Red (CR). The ability of CR to recognize amyloid fibrils comprising diverse proteins suggests that the binding site includes an unidentified structural feature common to all amyloid fibrils. We set out to design and synthesize analogs of CR that could distinguish between fibrils comprising different peptides.

RESULTS

Relative affinities of several CR analogs for two model amyloid fibrils were measured and compared to that of CR. Amyloid fibrils comprising peptides based on the critical carboxyl terminus of the Alzheimer's disease amyloid protein beta1-42 (beta34-42) and the critical region of the type II diabetes pancreatic amyloid protein, IAPP (IAPP20-29) were tested. The ratio of affinities of each individual CR analog for the two amyloid fibrils varied considerably. Complexation of certain metal ions (Cu(II), Zn(II), Ni(II), Cd(II)) by a CR analog did not abolish its affinity for amyloid but changed the affinity ratio significantly.

CONCLUSIONS

This study demonstrates that small organic and organometallic molecules are capable of detecting differences in amyloid fibril structure and/or amyloid protein sequence. Molecules of this type could have utility as neuropathological probes or imaging agents, since they are much easier to prepare and functionalize than antibodies and are specific for the fibrillar form of the amyloid proteins.

Cerebral amyloid beta protein deposits and other Alzheimer lesions in non-demented elderly east Africans

There is little knowledge of the existence of Alzheimer disease (AD) or Alzheimer type of dementia in indigenous populations of developing countries. In an effort to evaluate this, we assessed the deposition of amyloid beta (A beta) protein and other lesions associated with AD in brains of elderly East Africans. Brain tissues were examined from 32 subjects, aged 45 to 83 years with no apparent neurological disease, who came to autopsy at two medical Institutions in Nairobi and Dar es Salaam. An age-matched sample from subjects who had died from similar causes in Cleveland was assessed in parallel. Of the 20 samples from Nairobi, 3 (15%) brains exhibited neocortical A beta deposits that varied from numerous diffuse to highly localized compact or neuritic plaques, many of which were also thioflavin S positive. Two of the cases had profound A beta deposition in the prefrontal and temporal cortices and one of these also exhibited moderate to severe cerebral amyloid angiopathy. Similarly, 2 of the 12 samples from Dar es Salaam exhibited diffuse and compact A beta deposits that were also predominantly reactive for the longer A beta 42 species compared to A beta 40. We also noted that A beta plaques were variably immunoreactive for amyloid associated proteins, apolipoprotein E, serum amyloid P and complement C3. Tau protein reactive neurofibrillary tangles (NFT) were also evident in the hippocampus of 4 subjects. By comparison, 4 (20%) of the 20 samples from randomly selected autopsies performed in Cleveland showed A beta deposits within diffuse and compact parenchymal plaques and the vasculature. These observations suggest A beta deposition and some NFT in brains of non-demented East Africans are qualitatively and quantitatively similar to that in age-matched elderly controls from Cleveland. While our small scale study does not document similar prevalence rates of preclinical AD, it suggests that elderly East Africans are unlikely to escape AD as it is known in developed countries.

Brain amyloid--a physicochemical perspective

The ability to form stable cross-beta fibrils is an intrinsic physicochemical characteristic of the human beta-amyloid peptide (A beta), which forms the brain amyloid of Alzheimer's disease (AD). The high amyloidogenicity and low solubility of this hydrophobic approximately 40-mer have been barriers to its study in the past, but the availability of synthetic peptide and new physical methods has enabled many novel approaches in recent years. Model systems for A beta aggregation (relevant to initial nidus formation) and A beta deposition (relevant to plaque growth and maturation) in vitro have allowed structure/activity relationships and kinetics to be explored quantitatively, and established that these processes are biochemically distinct. Different forms of the peptide, with different physiochemical characteristics, are found in vascular and parenchymal amyloid. Various spectroscopic methods have been used to explore the three-dimensional conformation of A beta both in solution and in solid phase, and demonstrated that the peptide adopts a different configuration in each state. A significant conformational transition is essential to the transformation of A beta from solution to fibril. These observations suggest new therapeutic targets for the treatment of AD.

Granules in glial cells of patients with Alzheimer's disease are immunopositive for C-terminal sequences of beta-amyloid protein

Granular structures that are recognized by antibodies specific for the C-terminal but not the N-terminal sequences of the beta-amyloid protein (A beta) fragments are present in a subset of microglia and astrocytes in Alzheimer brain tissue. The immunohistochemical profile indicates that the A beta in these granules is truncated between the residues 17 and 31 and terminates at the residue 42 or 43. Such granule-containing glia occur only in brain areas with the heavy A beta deposits. Whether the intraglial A beta fragments accumulate as a result of phagocytosis of extracellular A beta or are formed intracellularly by glial cells from amyloid precursor protein (APP) remains unknown.

Two-hybrid system as a model to study the interaction of beta-amyloid peptide monomers

The kinetics of amyloid fibril formation by beta-amyloid peptide (Abeta) are typical of a nucleation-dependent polymerization mechanism. This type of mechanism suggests that the study of the interaction of Abeta with itself can provide some valuable insights into Alzheimer disease amyloidosis. Interaction of Abeta with itself was explored with the yeast two-hybrid system. Fusion proteins were created by linking the Abeta fragment to a LexA DNA-binding domain (bait) and also to a B42 transactivation domain (prey). Protein-protein interactions were measured by expression of these fusion proteins in Saccharomyces cerevisiae harboring lacZ (beta-galactosidase) and LEU2 (leucine utilization) genes under the control of LexA-dependent operators. This approach suggests that the Abeta molecule is capable of interacting with itself in vivo in the yeast cell nucleus. LexA protein fused to the Drosophila protein bicoid (LexA-bicoid) failed to interact with the B42 fragment fused to Abeta, indicating that the observed Abeta-Abeta interaction was specific. Specificity was further shown by the finding that no significant interaction was observed in yeast expressing LexA-Abeta bait when the B42 transactivation domain was fused to an Abeta fragment with Phe-Phe at residues 19 and 20 replaced by Thr-Thr (AbetaTT), a finding that is consistent with in vitro observations made by others. Moreover, when a peptide fragment bearing this substitution was mixed with native Abeta-(1-40), it inhibited formation of fibrils in vitro as examined by electron microscopy. The findings presented in this paper suggest that the two-hybrid system can be used to study the interaction of Abeta monomers and to define the peptide sequences that may be important in nucleation-dependent aggregation.

Abeta-peptide length and apolipoprotein E genotype in Alzheimer's disease

Apolipoprotein E (ApoE) epsilon4 allele, a risk factor for the development of Alzheimer's disease (AD), is associated with increased amyloid deposition. We examined cerebral cortex in 68 AD cases using antibodies to beta-amyloid (Abeta) peptides of different length (Abeta1-40 and Abeta1-42) and found that the increased plaque frequency observed with epsilon4 genotypes may be largely attributed to an increase in Abeta1-40-positive plaques. Indeed, both the number of Abeta1-40-positive plaques, as well as the ratio of Abeta1-40/Abeta1-42-positive plaques, increased with epsilon4 dosage. In contrast, the frequency of Abeta1-42-immunoreactive plaques was similar for epsilon3/epsilon3, epsilon3/epsilon4, and epsilon4/epsilon4 genotypes. ApoE may influence Abeta1 length by facilitating Abeta1-40 deposition onto Abeta1-42-seeded plaques or by modulating the activity of a putative carboxypeptidase that forms Abeta1-40 from Abeta1-42 in situ.

Accumulation of beta-amyloid fibrils in pancreas of transgenic mice

Some forms of familial Alzheimer's disease are caused by mutations in the amyloid beta protein precursor (beta APP), and there is excellent evidence that these mutations foster amyloid deposition by increasing secretion of total amyloid beta protein (A beta) or the highly amyloidogenic A beta 1-42 form. These observations provide a powerful rationale for developing an animal model of AD by generating transgenic mice in which cerebral amyloid deposition is induced by A beta overproduction. To produce substantial A beta in vivo, we generated mice expressing the transgene of signal peptide and 99 residues of carboxyl-terminal fragment (CTF) of beta APP under control of the cytomegalovirus enhancer/chicken beta-actin promoter. The transgenic mRNA was detected in many tissues of these mice, but the levels of transgenic mRNA, CTF, and A beta did not correlate well indicating that tissue-specific posttranslational processing may play an important role in determining the amount of A beta that accumulates in various tissues. A beta was detected biochemically in brain, kidney, and pancreas with the largest amount present in pancreas. In transgenic plasma, there was a marked accumulation of human A beta 1-40 and A beta 1-42(43) to levels over 30-times those observed in normal human plasma. Thus, the transgenic mice produce and secrete considerable A beta. Despite this increase in A beta secretion and the elevated A beta in brain, immunohistochemistry revealed no consistent cerebral A beta deposition. In pancreas, however, intracellular A beta deposits were detected immunohistochemically in acinar cells and interstitial macrophages, some of which showed severe degeneration. In addition, examination of these cells by immunoelectron microscopy revealed many putative amyloid fibrils (7-12 nm) that were stained by anti-A beta antibodies. Overall, our findings indicate that tissue-specific posttranslational processing may play a pivotal role in A beta production and amyloid fibril formation in vivo. By carefully analyzing the changes that occur in the transgenic mice described here as compared to the transgenic line that has recently been shown to form extracellular amyloid plaques in brain, it may be possible to gain considerable insight into the factors that determine the location and amount of A beta that accumulates as amyloid.

Artifactual strain-specific signs of incipient brain amyloidosis in APP transgenic mice

In an attempt to generate transgenic mice modeling Alzheimer-type amyloidogenesis, the COOH-terminal 103 residue human APP segment was expressed in brain regions known to be vulnerable in AD. Transfected cells overexpressing this transgene were previously shown to develop intracytoplasmic inclusions that were immunoreactive with antibodies to the APP COOH-terminus. Transgenic C57B6/SJL mice produced transgene-coded mRNA in their brains at levels up to sixfold above endogenous APP, most abundantly within cortical and hippocampal pyramidal neurons. Immunocytochemistry with anti-A beta antibodies revealed occasional structures that resembled diffuse amyloid, but which could not be detected on serial sections. Immunolabeling with antibodies to APP regions NH2-terminal to the transgene-coded domain revealed elevated immunoreactivity within perikarya and neurites in regions expressing the highest transgene and endogenous APP mRNA levels, similar to observations previously reported within vulnerable neurons in AD brain. However, subsequent breeding revealed that this phenotype segregated with the B6/SJL background rather than the transgene, thus emphasizing the importance of genetic background to observations of putative AD-type pathology in transgenic animals.

Carboxy terminal of beta-amyloid deposits in aged human, canine, and polar bear brains

Immunocytochemistry, using antibodies specific for different carboxy termini of beta-amyloid. A beta 40 and A beta 42(43), was used to compare beta-amyloid deposits in aged animal models to nondemented and demented Alzheimer's disease human cases. Aged beagle dogs exhibit diffuse plaques in the absence of neurofibrillary pathology and the aged polar bear brains contain diffuse plaques and PHF-1-positive neurofibrillary tangles. The brains of nondemented human subjects displayed abundant diffuse plaques, whereas the AD cases had both diffuse and mature (cored) neuritic plaques. Diffuse plaques were positively immunostained with an antibody against A beta 42(43) in all examined species, whereas A beta 40 immunopositive mature plaques were observed only in the human brain. Anti-A beta 40 strongly immunolabeled cerebrovascular beta-amyloid deposits in each of the species examined, although some deposits in the polar bear brain were preferentially labeled with anti-A beta 42(43). beta-amyloid deposition was evident in the outer molecular layer of the dentate gyrus in the aged dog, polar bear, and human. Within this layer, A beta 42 was present as diffuse deposits, although these deposits were morphologically distinct in each of the examined animal models. In dogs, A beta 42 was cloud-like in nature; the polar bear demonstrated a more aggregated type of deposition, and the nondemented human displayed well-defined deposits. Alzheimer's disease cases were most frequently marked by neuritic plaques in this region. Taken together, the data indicate that beta-amyloid deposition in aged mammals is similar to the earliest stages observed in human brain. In each species, A beta 42(43) is the initially deposited isoform in diffuse plaques.

Differential effects of a Rab6 mutant on secretory versus amyloidogenic processing of Alzheimer's beta-amyloid precursor protein

The Ras-related GTP-binding protein, Rab6, is localized in late Golgi compartments where it mediates intra-Golgi vesicular trafficking. Herein we report that coexpression of Alzheimer's beta-amyloid precursor protein (beta APP751) with a dominant-negative Rab6 mutant (Rab6N126I) in human embryonal kidney 293 cells causes an increase in secretion of the soluble amino-terminal exodomain (s-APP alpha) derived from non-amyloidogenic processing of beta-APP751 by alpha-secretase. The effect was specific to Rab6N126I, since the corresponding mutation in Rab8 (i.e. Rab8N121I), which has been implicated in protein transport to the plasma membrane, caused a modest reduction in s-APP alpha secretion. While Rab6N126I stimulated secretion of APP alpha, the accumulation of amyloid beta peptide (A beta) in the medium was either moderately reduced or unaffected. Similar differential effects of Rab6N126I on secretion of s-APP alpha versus A beta were observed in cell cultures that were overproducing A beta after transfection with a plasmid encoding Swedish variant of beta APP751. Moreover, assays of medium from the latter cultures revealed a marked increase in secretion of s-APP alpha relative to s-APP beta (the immediate product derived from cleavage of beta APP by beta-secretase). The results indicate that vesicular transport events controlled by Rab6 occur at or near a critical juncture in the trans-Golgi network where beta APP is sorted into either the constitutive alpha-secretase pathway or the amyloidogenic beta-secretase pathway.

Amyloid beta 1-42 deposits do not lead to Alzheimer's neuritic plaques in aged dogs

In alzheimer's disease, amyloid beta (A beta) is deposited in senile plaques and amyloid angiopathy. Longer A beta peptides, which extend to residue 42 (A beta 42), have been suggested to be critical for the seeding of amyloid. Aged dogs develop cerebral vessel amyloid and parenchymal preamyloid lesions. Preamyloid in humans is related to senile plaques, whereas in dogs such progression is rare. We evaluated the composition of aged canine vessel amyloid and preamyloid both biochemically and immunohistochemically. The vessel amyloid extended mainly to residue 40 (A beta 40), while preamyloid contained a mixture of A beta 17-42 and A beta 42, with minimal A beta 40. Our results suggest other factors besides A beta 42 are important for neuritic plaque formation.

Amyloid beta protein in rat soleus muscle in chloroquine-induced myopathy using end-specific antibodies for A beta 40 and A beta 42: immunohistochemical evidence for amyloid beta protein

Previous immunohistochemical studies from this laboratory demonstrated that monoclonal antibodies raised against various regions of amyloid precursor protein (APP) (i.e., N-terminus, amyloid beta protein (A beta), and C-terminus) strongly labeled vacuoles in chloroquine-induced myopathy-affected muscle in rats. In this study, we used antibodies end specific for the A beta 40 and A beta 42 species, and a monoclonal antibody to A beta 1-9 which reacts with APP and A beta. Most vacuoles clearly reacted with anti-A beta 1-9, while about half reacted with anti-A beta 42, and only a few reacted with anti-A beta 40. These results demonstrate that vacuoles in chloroquine-induced myopathy-affected muscle contain cleaved A beta, and that distribution of the two major A beta species is similar to what is observed in A beta deposition in Alzheimer's disease (AD)-affected brain. This provides further evidence that chloroquine-induced myopathy in rats provides a suitable model to understand APP processing into A beta, and the role of APP in terms of the pathogenesis of AD.

Amyloid beta-protein ending at Thr43 is a minor component of some diffuse plaques in the Alzheimer's disease brain, but is not found in cerebrovascular amyloid

The distribution of amyloid beta-protein ending at 40 (A beta 40), 42 (A beta 42), and 43 (A beta 43) were immunocytochemically examined in Alzheimer's brains. A large number of diffuse plaques were stained with A beta 42 antibody (S42), but some were weakly labeled with A beta 43 antibody (S43). Immature and mature plaques were labeled with A beta 40 antibody (S40), S42, and S43. Thus, A beta 42 is the major component of diffuse plaques, the initial phase of plaque formation, and A beta 43 is present as a minor component. Only A beta 40 is present in cerebrovascular amyloid.

Carboxyl end-specific monoclonal antibodies to amyloid beta protein (A beta) subtypes (A beta 40 and A beta 42(43)) differentiate A beta in senile plaques and amyloid angiopathy in brains of aged cynomolgus monkeys

Senile plaques (SPs) and cerebral amyloid angiopathy (CAA) in the brains of five aged (20-26 years old) cynomolgus monkeys were investigated immunohistochemically using two monoclonal antibodies (anti-A beta 40 (BA27) and anti-A beta 42(43) (BC05)) that can differentiate the carboxyl termini of amyloid beta protein (A beta) subtypes. In four of five animals, all types of SPs (i.e. diffuse, primitive, and classical plaques; DPs, PPs, and CPs, respectively) were identified by BC05. However, BA27 did not label DPs and stained only about one third of PPs and CPs, mainly labeling granular structures and cored portions, respectively. In CAA, lesions of cortical capillaries reacted to BC05 in four of five cases, but rarely and weakly to BA27 in two of five cases. On the other hand, lesions of parenchymal and meningeal arterioles were stained by both BA27 and BC05. These staining profiles of SPs in cynomolgus monkeys correspond well to those in humans, although there are two remarkable features in cynomolgus monkeys. First, BA27 stained PPs associated with granular structures. Secondly, capillary A beta reacted intensely to BC05 but only slightly to BA27. Despite these unique features, the results suggest that aged cynomolgus monkeys can be used to investigate the pathogenesis of A beta deposition in SPs and CAA.

Inhibition of Alzheimer beta-peptide fibril formation by serum amyloid P component

A 39-43-amino acid residue-long fragment (beta-peptide) from the amyloid precursor protein is the predominant component of amyloid deposits in the brain of individuals with Alzheimer's disease. Serum amyloid P component (SAP) is present in all types of amyloid, including that of Alzheimer's disease. We have used an in vitro model to study the effects of purified SAP on the fibril formation of synthetic Alzheimer beta-peptide 1-42. SAP was found to inhibit fibril formation and to increase the solubility of the peptide in a dose-dependent manner. At a 5:1 molar ratio of A beta 1-42 peptide to SAP, fibril formation was completely inhibited, and approximately 80% of the peptide remained in solution even after 4 days of incubation. At lower SAP concentrations, e.g. at peptide to SAP ratio of 1000:1, short fibrillar like structures, lacking amyloid characteristics, were formed. These structures frequently contained associated SAP molecules, suggesting that SAP binds to the polymerizing peptide in a reaction which prevented further fibril formation.

Structural model for the beta-amyloid fibril based on interstrand alignment of an antiparallel-sheet comprising a C-terminal peptide

Amyloids are a class of noncrystalline, yet ordered, protein aggregates. A new approach was used to provide the initial structural data on an amyloid fibril--comprising a peptide (beta 34-42) from the C-terminus of the beta-amyloid protein--based on measurement of intramolecular 13C-13C distances and 13C chemical shifts by solid-state 13C NMR and individual amide absorption frequencies by isotope-edited infrared spectroscopy. Intermolecular orientation and alignment within the amyloid sheet was determined by fitting models to observed intermolecular 13C-13C couplings. Although the structural model we present is defined to relatively low resolution, it nevertheless shows a pleated antiparallel beta-sheet characterized by a specific intermolecular alignment.

Microglial cells and amyloid beta protein (A beta) deposition; association with A beta 40-containing plaques

Two distinct species of amyloid beta protein (A beta) with different carboxyl termini, A beta 40 and A beta 42(43), are deposited in plaques in the brains of patients with Alzheimer's disease and Down's syndrome. The relationship between these two forms of A beta and microglial cells was investigated in 16 subjects with Down's syndrome ranging in age from 31 to 64 years. The amount of A beta 40 in plaques was low in persons under 50 years of age, even though high amounts of A beta 42(43) were present. Microglia were observed most commonly in plaques containing both A beta 40 and A beta 42(43) but less commonly in those with A beta 42(43) alone. The presence of microglial cells in plaques may be associated with the accumulation of A beta 40 and these cells may have a role in the production or processing of this particular molecular species.

Amino-terminal deletions enhance aggregation of beta-amyloid peptides in vitro

beta-Amyloid protein, which assembles into pathological aggregates deposited in Alzheimer's disease brain tissue, exhibits N-terminal heterogeneity both in vitro and in vivo. To investigate the effects of this N-terminal heterogeneity on the assembly characteristics and biophysical properties of beta-amyloid, we synthesized a series of peptides with progressively shortened N termini (initial residues at positions beta 1, beta 4, beta 8, beta 12, and beta 17) and C termini extending to residue beta 40 or beta 42. We report that peptides with N-terminal deletions exhibit enhanced peptide aggregation relative to full-length species, as quantitatively assessed by sedimentation analyses. Overall, sedimentation levels were greater for peptides terminating at residue beta 42 than for those terminating at residue beta 40. To determine if established biophysical features of the full-length protein were maintained in the truncated peptides, structural and bioactive properties of these peptides were examined and compared. Full-length and truncated peptides exhibiting aggregation showed circular dichroism spectra consistent with predominant beta-sheet conformation, fibrillar morphology under transmission electron microscopy, and significant toxicity in cultures of rat hippocampal neurons. These data demonstrate that N-terminal deletions enhance aggregation of beta-amyloid into neurotoxic, beta-sheet fibrils and suggest that such peptides may initiate and/or nucleate the pathological deposition of beta-amyloid.

Reduction of beta-amyloid peptide42 in the cerebrospinal fluid of patients with Alzheimer's disease

In this clinical study the cerebrospinal fluid (CSF) level of a novel form of the beta-amyloid peptide (A beta) extending to position 42 (A beta 42) was determined in patients with Alzheimer's disease (AD) as well as controls. In addition to measurement of CSF A beta 42 levels, total A beta peptides, microtubule-associated protein tau, and apolipoprotein E (ApoE) genotype were also assessed. It is interesting that CSF A beta 42 levels were found to be significantly lower in AD patients relative to controls, whereas total A beta levels were not. A beta 42 has recently been shown to preferentially deposit in the brain tissue of patients with AD, suggesting that diminished clearance may account for its reduction in CSF. As previously reported, tau levels were increased in AD patients; however, neither A beta 42 nor tau levels were apparently influenced by the ApoE genotype.

GM1 ganglioside-bound amyloid beta-protein (A beta): a possible form of preamyloid in Alzheimer's disease

The earliest event so far known that occurs in the brain affected with Alzheimer's disease (AD) is the deposition and fibril formation of amyloid beta-protein (A beta). A beta is cleaved from a glycosylated membrane protein, called beta-amyloid protein precursor, and normally secreted into the extracellular space. Here we report on the presence of membrane-bound A beta that tightly binds GM1 ganglioside. This suggests that this novel A beta species, rather than secreted A beta, may act as a 'seed' for amyloid and further that intracellular abnormalities in the membrane recycling already exist at the stage of amyloidogenesis.

The toxicity in vitro of beta-amyloid protein

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Brain cathepsin B but not metalloendopeptidases degrade rAPP751 with production of amyloidogenic fragments. Comparison with synthetic peptides emulating beta- and gamma-secretase sites

Lysosomal cathepsin B but not L degraded rAPP751 to yield C-terminal 19-25 kDa fragments containing beta A4, reinforcing the view that acidic proteases participate in endosomal-lysosomal processing to yield amyloidogenic fragments in situ. This mechanism is consistent with fragmentation of endogenous APPs within clathrin-coated vesicles (CVs) by vesicular hydrolases, with the appearance of C-terminal amyloidogenic fragments following incubation at pH 6.5. A neutral endopeptidase resembling NEP 24.11 (PS-NEP) purified from detergent extracts of human brain degraded rAPP751; however, breakdown was not blocked robustly by metal chelators or phosphoramidon, suggesting the presence of an alternative processing enzyme. Effects of other inhibitors showed that breakdown was mediated by serine-protease-like component(s). A phosphoramidon-insensitive metalloendopeptidase (PI-NEP) partially purified from rat brain P2 using detergents, and resembling NEP 24.15, showed no activity towards rAPP751. Peptides containing putative beta- or gamma-secretase sites were synthesized for purposes of examining their metabolism by the brain enzymes. Those containing beta-secretase sites were hydrolysed at one or more sites by the four enzymes, but only PI- and PS-NEP acted at the Met-Asp site of Ac-Val-Lys-Met-Asp-Ala-Glu-Phe-Arg.NH2. In the case of substrates containing the gamma-site, these two categories of enzymes were the only ones degrading N-Ac-Ile-Ala.NH2. These data imply that the brain metalloendopeptidases, while inactive towards intact precursors, may be involved in turnover of intermediates containing beta- or gamma-sites.

Amyloid beta-proteins 1-40 and 1-42(43) in the soluble fraction of extra- and intracranial blood vessels

To investigate the process of amyloid beta-protein (A beta) accumulation in cerebral amyloid angiopathy (CAA), the levels of A beta were determined in the soluble fraction of extra- and intracranial blood vessels and leptomeninges obtained at autopsy. Two enzyme immunoassays were employed that are known to sensitively and specifically quantify two A beta species, A beta 1-40 and 1-42(43). A beta was detectable in the intracranial blood vessels and leptomeninges with the latter containing the highest levels, while it was undetectable in the extracranial blood vessels. Thus the levels of soluble A beta correlated well with the predilection sites for CAA. Among individuals aged 20 to 90, the A beta levels in the leptomeninges increased sharply in those aged 50 to 70 and thereafter tended to decline. However, only slight degrees of CAA were detected by immunocytochemistry, even when those leptomeninges contained high levels of A beta comparable with those in Alzheimer's disease. The level of A beta 1-42 was almost always severalfold that of A beta 1-40 in the soluble fraction of leptomeninges. This is in good agreement with the immunocytochemical result showing the presence of A beta 40-negative, A beta 42(43)-positive meningeal vessels. These results indicate that A beta 1-42 is the initially deposited species in CAA and that the disruption of A beta homeostasis precedes A beta deposition in the meningeal vessels.

A biotechnological method provides access to aggregation competent monomeric Alzheimer's 1-42 residue amyloid peptide

Senile plaques, a neuropathological hallmark of Alzheimer's disease, consist primarily of insoluble aggregates of beta-amyloid peptide (A beta). A 42-residue peptide (A beta 1-42) appears to be the predominant form. In contrast to A beta 1-40, A beta 1-42 is characterized by its extreme tendency to aggregate into fibers or precipitate. A tailored biotechnological method prevents aggregation of A beta 1-42 monomers during its production. The method is based on a protein tail fused to the amino terminus of A beta. This tail leads to a high expression in E. coli, and a histidine affinity tag facilitates purification. Selective cleavage of the fusion tail is performed with cyanogen bromide by immobilizing the fusion protein on a reversed phase chromatography column. Cleavage then occurs only at the methionine positioned at the designed site but not at the methionine contained in the membrane anchor sequence of A beta. Furthermore, immobilization prevents aggregation of cleaved A beta. Elution from the HPLC column and all succeeding purification steps are optimized to preserve A beta 1-42 as a monomer. Solutions of monomeric A beta 1-42 spontaneously aggregate into fibers within hours. This permits the investigation of the transition of monomers into fibers and the correlation of physico-chemical properties with biological activities. Mutations of A beta 1-42 at position 35 influence the aggregation properties. Wild-type A beta 1-42 with methionine at position 35 has similar properties as A beta with a methionine sulfoxide residue. The fiber formation tendency, however, is reduced when position 35 is occupied by a glutamine, serine, leucine, or a glutamic acid residue.

The extent of amyloid deposition in brain in patients with Down's syndrome does not depend upon the apolipoprotein E genotype

The extent of deposition of amyloid beta protein (A beta) was investigated in 20 elderly patients with Down's syndrome, using the end-specific monoclonal antibodies BC05 and BA27 to detect the presence of A beta 42(43) and A beta 40 (respectively), and related to apolipoprotein E (ApoE) genotype. No significant differences in the amount of A beta deposited in the brain, either as A beta 42(43) or A beta 40, were noted in patients possessing an ApoE E4 allele, compared to those without. Patients with an ApoE E4 allele in general died at an earlier age than those with only ApoE E3 alleles, the latter in turn being outlived by those with an ApoE E2 allele. In Down's syndrome therefore, ApoE may influence the timing of onset, or the rate of progression, of disease but without affecting the type or total amount of pathology accumulated.

Deposition of apolipoproteins E and J in senile plaques is topographically determined in both Alzheimer's disease and Down's syndrome brain

The link between the immunolocalization of apolipoproteins E (apo E) and J (apo J) and the different severity of beta-amyloid deposition in various areas of Alzheimer's disease (AD) and Down's syndrome (DS) brain was analyzed. Both apolipoproteins were found in all types of senile plaques (SPs) in the cerebral cortex, which is early and severely involved in beta-amyloidosis, but apo E was seen more often than apo J in diffuse A beta deposits, especially in young DS cases and nondemented elderly persons. In the striatum and cerebellum, which show predominance of diffuse A beta deposits throughout the lifespan, apo J was absent, except for few compact deposits, whereas apo E was more widely distributed, apart from diffuse plaques in the striatum. By immunoelectron microscopy, A beta fibrils were disclosed in diffuse plaques in all brain regions studied, but not all of these early fibrillar deposits, even in the neocortex of young DS cases, showed apo E and apo J labeling. Thus, our data indicate that the immunoreactivity to apo E and J within A beta deposits is topographically determined in both AD and DS brain. Moreover, although it appears that neither of apolipoproteins studied is necessary to initiate A beta fibrillogenesis, disclosed topographic dissimilarities of their distribution within parenchymal A beta deposits suggest that they may be involved in different ways in the pathogenesis of beta-amyloidosis.

Steps towards a mouse model of Alzheimer's disease

Alzheimer's disease, a form of senile dementia, is characterised by two kinds of pathological deposits in the brain, called plaques and tangles. The molecular nature of the deposits has been identified but there is as yet little understanding of the underlying biochemistry and cell biology that lead to their formation. Progress in this area would be greatly aided by a realistic animal model. Two recent papers describe the production of transgenic mice that develop significant aspects of the Alzheimer-like pathology. The mice produced by Games et al.(1) develop plaques while those produced by Götz et al.(2) display the early stages of tangle pathology.

Early amyloid-beta deposits show different immunoreactivity to the amino- and carboxy-terminal regions of beta-peptide in Alzheimer's disease and Down's syndrome brain

That the topography, severity, and progression of beta-amyloid deposition in the brain of Alzheimer's disease (AD) and Down's syndrome (DS) cases is not uniform is well documented. We have addressed at present, the issue of whether the structural composition of beta-peptide (A beta) within the early amyloid deposits might contribute to this phenomenon. The cerebral cortex, the caudate/putamen, and the cerebellum from 10 AD and 8 DS cases were immunostained with antibodies that recognize the 1-17; 17-24 amino acid residues of A beta, and the COOH-terminus of A beta 42 variant, thus to the epitopes of A beta located amino- and carboxy-terminally to the site of the putative alpha-secretase cleavage. We demonstrate that numerous diffuse, early plaques in AD and especially in DS cases show predominance of the carboxy-terminally located epitopes of A beta; the most prominent in the cerebellum, less pronounced in the cerebral cortex, and only marginal, or absent in the striatum, except for some DS cases. These data suggest that the deposition of the carboxy-terminal fragment of A beta truncated at the position of alpha-secretase cleavage or close to it in diffuse plaques may be brain-region-specific, reflecting either dissimilar processing of amyloid precursor protein or the resolution of early A beta deposits, and may substantially contribute to different progression of beta-amyloidosis in various brain regions.

Intracellular A beta 1-42 aggregates stimulate the accumulation of stable, insoluble amyloidogenic fragments of the amyloid precursor protein in transfected cells

We have analyzed the effect of internalized amyloid beta-protein (A beta) 1-42 aggregates on the metabolism of the amyloid precursor protein (APP) in stably transfected 293 cells. The amount of potentially amyloidogenic fragments of APP immunoprecipitated by anti-carboxyl-terminal APP and anti-A beta antibodies is dramatically enhanced by the treatment of the cells with A beta 1-42, which is resistant to degradation, but not A beta 1-28, which does not accumulate in cells. This accumulation of amyloidogenic carboxyl-terminal fragments is specific, since there is relatively little effect of A beta 1-42 on the amount of the nonamyloidogenic alpha-secretase carboxyl-terminal fragment. The amyloidogenic fragments accumulate in the same nonionic detergent-insoluble fraction of the cell that contains the internalized A beta 1-42. Western analysis indicates that a subset of the amyloidogenic fragments react with antibodies that recognize a conformation of A beta that is specifically associated with aggregated forms of A beta, suggesting that the adoption of this aggregation-related conformation may be an early event which precedes the final processing that produces A beta. Pulse-chase analysis of the [35S]Met-labeled 16-kDa amyloidogenic fragment indicates that it is relatively stable in A beta 1-42-treated cells, with a half-life of approximately 50 h. This fragment is degraded with a half-life of 30 min in control cells treated with A beta 1-28. In contrast, the turnover of the nonamyloidogenic alpha-secretase product is not significantly altered by the presence of A beta 1-42. The continuous uptake of A beta 1-42 from the medium is not required for the stimulation of amyloidogenic fragment accumulation, suggesting that the presence of intracellular A beta 1-42 aggregates establishes a new pathway for APP catabolism in cells which leads to the long term stability of the fragments. If these amyloidogenic fragments of APP ultimately give rise to A beta, then the production of A beta may be an autocatalytic, "runaway" process in cells containing A beta 1-42 nuclei. It is conceivable that the accumulation of insoluble APP and amyloidogenic fragments of APP in response to A beta 1-42 aggregates may mimic the pathophysiology of dystrophic neurites, where the accumulation of intracellular APP and APP fragments has been documented by immunohistochemistry.

Amyloid beta protein 1-42/43 (A beta 1-42/43) in cerebellar diffuse plaques: enzyme-linked immunosorbent assay and immunocytochemical study

Diffuse plaques are immature and amorphous senile plaques and believed to be in the initial phase of plaque formation. In contrast to amyloid angiopathy and the plaque core amyloid, diffuse plaques failed to be purified in preserved forms from the brain. Here, we studied the diffuse plaques in the cerebellar region of the Alzheimer's disease brain based on immunocytochemistry and ELISA using two different monoclonal antibodies specifically recognizing the carboxyl termini of A beta molecules (BA27 for A beta 1-40 and BC05 for A beta 1-42/43). We found that the amount of A beta 1-40 was in proportion to the staining degree on amyloid angiopathy by immunohistochemistry. We found that A beta 1-42/43 comprised diffuse plaques as the major component in the cerebella of AD brains. Taking these findings into consideration, diffuse plaques, the earliest pathological change in the brain with AD, are concluded to be composed mainly of A beta 1-42/43, implicating the critical importance of this kind of A beta species deposition in the pathogenesis of AD.

Amyloid beta protein (A beta) in Alzheimer's disease brain. Biochemical and immunocytochemical analysis with antibodies specific for forms ending at A beta 40 or A beta 42(43)

Biochemical and immunocytochemical analyses were performed to evaluate the composition of the amyloid beta protein (A beta) deposited in the brains of patients with Alzheimer's disease (AD). To quantitate all A beta s present, cerebral cortex was homogenized in 70% formic acid, and the supernatant was analyzed by sandwich enzyme-linked immunoabsorbent assays specific for various forms of A beta. In 9 of 27 AD brains examined, there was minimal congophilic angiopathy and virtually all A beta (96%) ended at A beta 42(43). The other 18 AD brains contained increasing amounts of A beta ending at A beta 40. From this set, 6 brains with substantial congophilic angiopathy were separately analyzed. In these brains, the amount of A beta ending at A beta 42(43) was much the same as in brains with minimal congophilic angiopathy, but a large amount of A beta ending at A beta 40 (76% of total A beta) was also present. Immunocytochemical analysis with monoclonal antibodies selective for A beta s ending at A beta 42(43) or A beta 40 confirmed that, in brains with minimal congophilic angiopathy, virtually all A beta is A beta ending at A beta 42(43) and showed that this A beta is deposited in senile plaques of all types. In the remaining AD brains, A beta 42(43) was deposited in a similar fashion in plaques, but, in addition, widely varying amounts of A beta ending at A beta 40 were deposited, primarily in blood vessel walls, where some A beta ending at A beta 42(43) was also present. These observations indicate that A beta s ending at A beta 42(43), which are a minor component of the A beta in human cerebrospinal fluid and plasma, are critically important in AD where they deposit selectively in plaques of all kinds.

The core Alzheimer's peptide NAC forms amyloid fibrils which seed and are seeded by beta-amyloid: is NAC a common trigger or target in neurodegenerative disease?

BACKGROUND

NAC is a 35-amino-acid peptide which has been isolated from the insoluble core of Alzheimer's disease (AD) amyloid plaque. It is a fragment of alpha-synuclein (or NACP), a neuronal protein of unknown function. We noted a striking sequence similarity between NAC, the carboxyl terminus of the beta-amyloid protein, and a region of the scrapie prion protein (PrP) which has been implicated in amyloid formation.

RESULTS

NAC was prepared by chemical synthesis and was found to form amyloid fibrils via a nucleation-dependent polymerization mechanism. NAC amyloid fibrils effectively seed beta 1-40 amyloid formation. Amyloid fibrils comprising peptide models of the homologous beta and PrP sequences were also found to seed amyloid formation by NAC.

CONCLUSIONS

The in vitro model studies presented here suggest that seeding of NAC amyloid formation by the beta-amyloid protein, or seeding of amyloid fibrils of the beta-amyloid protein by NAC, may occur in vivo. Accumulation of ordered NAC aggregates in the synapse may be responsible for the neurodegeneration observed in AD and the prion disorders. Alternatively, neurodegeneration may be caused by the loss of alpha-synuclein (NACP) function.

Amyloid beta protein (A beta) deposition: A beta 42(43) precedes A beta 40 in Down syndrome

The chronological relationship regarding deposition of amyloid beta protein (A beta) species, A beta 40 and A beta 42(43), was investigated in 16 brains from Down syndrome patients aged 31 to 64 years. The frontal cortex was probed with two end-specific monoclonals that recognize A beta 40 or A beta 42(43). All senile plaques detected with an authentic beta monoclonal were also A beta 42(43) positive, but only a varying proportion was A beta 40 positive. In young (< or = 50 years old) brains there were many A beta 42(43)-positive, A beta 40-negative diffuse plaques, but only few A beta 40-positive senile plaques (mean, 6.3% of total number of senile plaques). The 2 youngest Down syndrome brains showed only diffuse plaques that were all A beta 42(43) positive but A beta 40 negative. Old (> 50 years old) brains contained many mature senile plaques with amyloid cores in addition to diffuse and immature plaques and the proportion of A beta 40-positive senile plaques was increased (mean, 42% of total). Cerebral amyloid angiopathy was more abundant in old Down syndrome brains and was positive for both A beta 40 and A beta 42(43). In cerebral amyloid angiopathy, A beta 40 predominated over A beta 42(43) in both staining intensity and number of positive vessels. These results indicate that (1) the A beta species initially deposited in the brain as senile plaques is A beta 42(43) and A beta 40 only appears a decade later, and (2) in cerebral amyloid angiopathy A beta 40 appears as early as A beta 42(43).

Human neurons that constitutively secrete A beta do not induce Alzheimer's disease pathology following transplantation and long-term survival in the rodent brain

Since cultured neurons secrete beta-amyloid (A beta) peptides, and A beta forms amyloid deposits in the Alzheimer's disease (AD) brain, transplanted neurons may induce the deposition of A beta in the host brain. To assess this possibility, we studied grafted human neurons (NT2N cells) and their progenitors (NT2 cells) in the rodent brain. Although NT2N cells secrete more A beta than the NT2 cells in vitro, no A beta deposits or other AD lesions were induced in the rodent brain by grafts that survived days (NT2 and NT2N cells) to 46 weeks (NT2N cells). Thus, neither the deposition of A beta nor the induction of other AD lesions are obligatory consequences of the transplantation and long-term survival of human neurons or their progenitors in the rodent brain.

Dominant and differential deposition of distinct beta-amyloid peptide species, A beta N3(pE), in senile plaques

We analyzed an amino-terminal modification of beta-amyloid (A beta) peptide in brain, using anti-A beta antibodies that distinguish distinct molecular species. Examination of cortical sections from 28 aged individuals with a wide range in senile plaque density revealed that a molecular species distinct from the standard A beta is deposited in the brain in a dominant and differential manner. This modified A beta peptide (A beta N3(pE)) starts at the 3rd aminoterminal residue of the standard A beta, glutamate, converted to pyroglutamate through intramolecular dehydration. Because plaques composed of A beta N3(pE) are present in equivalent or greater densities than those composed of standard A beta bearing the first amino-terminal residue (A beta N1) and because deposition of the former species appears to precede deposition of the latter, as confirmed with specimens from Down's syndrome patients, the processes involved in A beta N3(pE) production and retention may play an early and critical role in senile plaque formation.

Polyclonals to beta-amyloid(1-42) identify most plaque and vascular deposits in Alzheimer cortex, but not striatum

Alzheimer's beta-peptides (A beta) aggregation rates depend on A beta length. We made synthetic peptide antisera to A beta 34-40 and 37-42. Purified anti-34-40 preferentially recognizes beta 1-40, vascular amyloid and a subset of plaques while purified anti-37-42 recognizes A beta 1-42 and not A beta 1-40 in dot and Western blots and immunoprecipitates; 37-42 precipitates a small percentage of fibroblast secreted A beta and strongly stains all deposits identified by monoclonals to A beta on adjacent sections from frontal cortex, but not in dorsal striatum.

Amyloid-associated proteins alpha 1-antichymotrypsin and apolipoprotein E promote assembly of Alzheimer beta-protein into filaments

The protease inhibitor alpha 1-antichymotrypsin and the lipid transport protein apolipoprotein E (apoE) are intimately associated with the 42-amino-acid beta-peptide (A beta) in the filamentous amyloid deposits of Alzheimer's disease. We report here that these two amyloid-associated proteins serve a strong stimulatory role in the polymerization of A beta into amyloid filaments. Addition of either alpha 1-anti-chymotrypsin or apoE to the A beta peptide promoted a 10- to 20-fold increase in filament formation, with apoE-4, the isoform recently linked to the development of late-onset Alzheimer's disease, showing the highest catalytic activity. These and other experiments suggest that Alzheimer amyloid deposits arise when A beta is induced to form filaments by amyloid-promoting factors (pathological chaperones) expressed in certain brain regions.

Research on Alzheimer's disease in Japan: a personal view on history and present status

Research on Alzheimer's disease (AD) in Japan is briefly reviewed based mainly on our work. Paired helical filaments (PHF) have been extensively investigated for their components and phosphorylation. Their analysis has no yet provided important insights into the mechanism of neuronal death in AD brain. In beta-amyloidogenesis, the carboxyl extent of amyloid beta-protein (Abeta) is now highlighted. Abeta42, not Abeta40, is the initially deposited species. Future investigations should elucidate why Abeta42 is deposited in the brain parenchyma and how the Abeta deposition leads to PHF formation.