The comparative immunoreactivities of brain amyloids in Alzheimer's disease and scrapie

Pathogenesis of amyloid formation in Alzheimer's disease, Down's syndrome and scrapie

Paired helical filaments (PHF) are abnormal fibrous structures found in human nerve cells and their processes. Ultrastructural studies of the proto-filaments that make up the PHF revealed that the individual proto-filaments have a different substructure from normal neurofilaments or any other known fibrous profiles. Studies using immunological and biochemical methods suggested that abnormally phosphorylated tau, ubiquitin and neurofilament peptides are part of the PHF. Deposits of amyloid fibres in Alzheimer's disease and senile dementia of the Alzheimer type (AD/SDAT) are found in meningeal and brain vessels, choroid plexus and neuritic plaques. In 1984 Glenner and Wong reported the sequence of a beta-protein isolated from cerebrovascular amyloid. We used the amino acid sequence of the cerebrovascular amyloid protein to synthesize oligonucleotide probes specific for the gene encoding this amyloid protein. Screening of a human brain cDNA library allowed us to isolate a clone which encodes the amyloid peptide. In situ hybridization studies and Southern blot analysis of a DNA sample isolated from a human-mouse hybrid cell line indicated that the corresponding genomic sequences of this cDNA clone are located on human chromosome 21. Using immunochemical and histochemical methods, we have identified the cells associated with the formation of the amyloid fibres. With immunochemical and biochemical methods we and others also showed that the protein constituting amyloid in AD/SDAT is different from amyloid in unconventional slow virus diseases.

Genes for Prader Willi syndrome/Angelman syndrome and fragile X syndrome are homologous, with genetic imprinting and unstable trinucleotide repeats causing mental retardation, autism and aggression

Genes for Prader Willi syndrome/Angelman syndrome are homologous to genes for fragile X syndrome. Genetic imprinting and expanded trinucleotide repeats cause mental retardation, autism and aggression.

Neuroaxonal dystrophy in experimental Creutzfeldt-Jakob disease: electron microscopical and immunohistochemical demonstration of neurofilament accumulations within affected neurites

Neuroaxonal dystrophy is a feature of neuronal degeneration encountered in all subacute spongiform "virus" encephalopathies, including scrapie and Creutzfeldt-Jakob disease (CJD). By immunohistochemical techniques, the accumulation of 200 kDa neurofilament protein was demonstrated in affected neurites in murine CJD. These neurites exhibited the ultrastructural features of dystrophic neurites encountered in other neurodegenerative disorders, particularly Alzheimer's disease. These findings support the hypothesis that impairment of slow axoplasmic transport is a common pathogenetic mechanism for CJD and many other neurodegenerative conditions.

Beta-amyloid formation by myocytes of leptomeningeal vessels

Ultrastructural study of the leptomeningeal vessels of three subjects with Alzheimer's disease (AD) shows that beta-amyloid deposits in the media of arteries and arterioles are produced by smooth muscle cells. It appears that the soluble beta-protein secreted by sarcolemmal vesicles of the muscle cell polymerizes into amyloid fibrils in basal lamina. Myocytes trapped in amyloid deposits degenerate and die. The most common and severe degeneration of smooth muscle cells is seen in the external and medial zone of the vascular media. In more advanced stages of amyloidotic changes, the internal zone of media is also involved. The media of vessels with severe changes consists of amyloid deposits and cell debris. Amyloid fibrils around the dead myocytes also undergo degradation. They lose their fibrillar appearance and become floccular, granular, amorphous proteinous material; however, this material is continually positive in immunostaining for beta-amyloid. This study suggests that amyloid formation by smooth muscle cells involves a secretory path. Our data indicate that the smooth muscle cell secretes nonfibrillar beta-protein or beta-protein containing peptides and that conversion of nonfibrillar into fibrillar beta-amyloid takes place in the environment of the basement membrane.

Beta A4 deposition in the temporal cortex of adults with Down's syndrome

The deposition of beta A4 has been quantified in the temporal cortex of 9 adults (4 male, 5 female) with Down's syndrome (DS), mean age (+/- SD) 54.7 +/- 8.8 years (range 41-67 years) at the time of death. Immunostaining with antibodies, raised to different portions of the beta A4 protein, showed a greater number of deposits than were seen with traditional silver impregnation or amyloid stains. Antibody to beta A4(1-10) identified fewer plaques than the antibody to beta A4(12-28), the mean ratio of beta A4(1-10)/beta A4(12-28) plaques being 0.30 +/- 0.10 (mean +/- SD). Morphologically, 'diffuse' and 'neuritic' deposits could be distinguished but there was no significant difference in the beta A4(1-10)/beta A4(12-28) ratio according to plaque morphology, nor did the ratio change with age. Quantitatively, the beta A4(12-28) load in the temporal cortex of DS patients was high, occupying some 14% of the field area, and it was not related to the age of the subject over the range studied. Similarly, the total beta A4(12-28) plaque count was high and not age-related. The proportion of morphological plaque types visualised by the Glees and Marsland silver impregnation and by beta A4(12-28) immunostaining were compared. In both techniques 'diffuse' plaques (D) were predominant in the younger subjects and the proportion of 'neuritic' plaques (N) increased with age. The relative proportions of cored plaques (Cp) and plaque cores (C) did not change significantly with age.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunolocalization of Alzheimer beta-amyloid peptide precursor to cellular membranes in baculovirus expression system

One characteristic of Alzheimer's disease (A beta disease) is the accumulation of amyloid deposits within the extracellular space of the brain and meninges. A 40 amino acid peptide called beta-peptide or A4 protein is the subunit of the amyloid fibrils found in these deposits. The sequence of beta-peptide is contained within those of a family of larger proteins called the Alzheimer beta-amyloid peptide precursor (APP). These APPs contain, in addition to a signal sequence, a hydrophobic sequence that is believed to span cell membranes. Although biochemical studies indicate that some APPs have properties of integral membrane proteins, morphological confirmation of this has not been reported. We recently described an expression system in which human APP751 cDNA was placed under the transcriptional regulation of the polyhedrin gene promoter in the baculovirus Autographica californica infecting a Spodoptera frugiperda cell line (Ramakrishna et al., Biochem Biophys Res Commun 174:983-989, 1991). As part of a larger biochemical and molecular biological study of APP, we have carried out an immunocytochemical study using antibodies directed against several epitopes within APP to reveal, at both the light and the electron microscopic levels, the cellular localization of APP in the baculovirus expression system. These studies demonstrate that APP751 is abundantly synthesized and inserted into certain of the membrane compartments of the cell. As early as 24 hr postinfection, APP751 is found associated with all membrane compartments excepting mitochondrial membranes. The patterns of immunolabeling are consistent with our biochemical findings that the protein is processed in these cells so as to release the extracellular domain and to retain a transmembrane and intracellular segment. These data provide the first morphological demonstration of the membrane location of APP751, its posttranslational processing to a secreted fragment, and its exclusion from the mitochondrial membranes. This system is especially valuable for identifying conditions under which antibodies raised against APP or appropriate synthetic peptides will react with native APP.

Antibodies raised against different portions of A4 protein identify a subset of plaques in Down's syndrome

Antisera were raised to peptides corresponding to residues 1-10 and 12-28 of the published sequence of A4 protein, a 42/43 amino acid long peptide isolated from the brains of patients with Down's syndrome and Alzheimer's disease. Immunohistochemical studies performed on sections of temporal lobe from 12 cases of Down's syndrome showed that the number of senile plaques in the molecular layer of the dentate gyrus which were identified by antibody to A4(1-10) was only 23% (range 11-53%) of that recognised by antibody to A4(12-28). This observation has important consequences for both the diagnosis and the pathogenesis of Down's syndrome and Alzheimer's disease.

Aluminum neurotoxicity in mammals

Although aluminum comprises a large percentage of the Earth's crust, it is excluded from body tissues, and especially from the central nervous system. When aluminum is experimentally introduced to the central nervous system, several neurotoxic effects are observed:i.e. neurofibrillary changes, behavioral and cognitive deficits and enzymatic and neurotransmitter changes, as well as certain types of epileptic seizures.The localization of relatively high levels of aluminum in Alzheimer disease, Guamanian amyotrophic lateral sclerosis and Parkinsonism-dementia has led to the implication of aluminum as a pathogenic factor in these diseases. Recent studies have shown that microtubule-associated proteins are part of the paired helical filaments which make up the intraneuronal neurofibrillary tangle. Other studies have identified the protein making the vascular and neuritic (senile) plaque amyloid and located the gene responsible for this protein to chromosome 21.Our electron microprobe analysis studies have not found the levels of aluminum or silicon in either the neurofibrillary tangles or amyloid cores reported elsewhere, nor have the levels of aluminum been elevated in approximately one half of the tangles and plaque cores examined to date.

Microanalysis of Alzheimer disease NFT and plaques

Electron probe energy dispersive microanalysis of isolated andin situ neurofibrillary tangles (NFT) and neuritic (senile) plaque cores have been done to investigate the levels of Al, Si, Ca and Fe in the leading lesions of Alzheimer disease neuropathology. Varying levels of Si and Al, and to a lesser extent Ca, have been co-localized in about one half of the NFT and plaques examined using X-ray mapping. The variability of detection and the low levels of Al present indicates that aluminum is not required for the formation of the NFT and that aluminosilicates are not involved in the formation of the plaque core.

Cytoskeletal protein pathology and the formation of beta-amyloid fibers in Alzheimer's disease

Discovery of the abnormally phosphorylated tau in paired helical filaments, its accumulation preceding the formation of the tangles and the in vitro microtubule assembly defect suggest that an abnormality in the protein phosphorylation/dephosphorylation system is involved in the pathogenesis of Alzheimer cytoskeletal pathology. The levels of mRNA for the beta-amyloid precursor protein (beta APP) in the brain suggest that only a small deficiency in the processing of the precursor would be sufficient to account for the accumulation of beta-amyloid in Alzheimer brain. Identification of reticuloendothelial system cells responsible for the production/processing of beta-amyloid will help to elucidate the pathogenesis of the brain amyloidosis. The disproportionate accumulation of paired helical filaments and amyloid within the same affected brain and from disease to disease raises the possibility of different etiologies for each of these lesions coexisting in Alzheimer's disease.

Amyloid protein and neurofibrillary tangles coexist in the same neuron in Alzheimer disease

In Alzheimer disease, paired helical filaments accumulate in the neuron, and amyloid fibers are found in the extracellular space in the neuropil and brain vessels. Amyloid and paired helical filaments are morphologically distinct. Although messenger RNA that encodes the amyloid has also been shown in several tissues, including brain, the intracellular expression of the protein has not been observed. By using monoclonal antibodies to a synthetic amyloid beta peptide, the present study demonstrates that amyloid reactivity is present in both Alzheimer patients and normal individuals in different types of neurons, including the neurons with the neurofibrillary tangles, but not in the tangle itself.

Immunoreactivity of neuronal lipofuscin with monoclonal antibodies to the amyloid beta-protein

Monoclonal antibodies generated against a synthetic peptide corresponding to amino acids 1 to 24 of cerebrovascular amyloid beta-protein do not only stain amyloidotic blood vessels and the amyloid deposits of the (senile) neuritic plaques, but also the neuronal pigment lipofuscin. Staining of lipofuscin is observed in both cerebral and cerebellar cortices, subcortical nuclei as well as the brain stem, and is identical in Alzheimer and normal control brain. Western blots of a lipofuscin enriched fraction show an anti-beta-protein reactive polypeptide migrating at approximately 31 kDa position on SDS-polyacrylamide gel electrophoresis. These results suggest that this polypeptide is associated with lipofuscin and is most likely derived from the predicted amyloid precursor protein. This implicates that, unlike in Alzheimer's disease where this protein is also processed extraneuronally in a manner to release an amyloid fiber forming fragment, the end point of its processing in the nerve cell seems to accumulate on a lipopigment characteristic for normal aging.

Down patients: extracellular preamyloid deposits precede neuritic degeneration and senile plaques

Using anti-SP28 (a polyclonal antibody to a 28 residue synthetic peptide homologous to the NH2-terminal region of the Alzheimer amyloid beta-protein) to investigate the cerebral cortex of 6 Down patients aged 6-55 y, we found that, besides senile plaques and congophilic vessels, extracellular deposits unrelated to degenerating neurites, tangle-bearing neurons or congophilic vessels were labelled. These deposits were similar to the extracellular deposits previously observed in the cerebral cortex of Alzheimer patients and non-demented individuals. The material accumulated in the deposits did not react with Congo red, thioflavine S or, on some occasions, silver salts and therefore might have been constituted by beta-protein precursors lacking the molecular conformation of amyloid fibrils. Age-related analysis of the cortical lesions in Down patients suggested that such extracellular deposits precede degenerating neurites and evolve into senile plaques.

Relationships among the cerebral amyloid peptides and their precursors

Alzheimer's disease is characterized by deposits of amyloid in cerebral blood vessels and neuropil. Qualitative analyses of partially purified preparations of these amyloid deposits revealed the presence of a unique polypeptide now often called "beta peptide". This peptide is 40 residues long and it exhibits some amino terminal heterogeneity, which may result from the isolation procedure. The major amyloid peptide comprises at least 30% of the dry mass and 70% of the protein of washed neuritic plaque cores. These results indicate that the major peptide is the predominant proteinaceous component of cores; furthermore, they demonstrate that although cores may contain other substances such as aluminum silicate, polysaccharides, and lipids, amyloid peptide is a major component. More careful analysis reveals that the core amyloid peptide differs significantly from cerebrovascular amyloid peptide. Although the core amyloid peptide is constructed of the same backbone as the cerebrovascular amyloid peptide, it contains modifications that render the amino terminal region uncleavable by Edman degradation or by trypsin. It is unknown whether the lower solubility of core amyloid is related to these modifications. The original impetus for characterizing the differences between the core and cerebrovascular amyloid peptides arose from the question of whether both amyloid peptides were formed by a sequential pathway. Our results showing that core amyloid peptide is more extensively modified than vascular amyloid leads us to conclude that if a sequential pathway exists, vascular amyloid peptide must precede core amyloid peptide. Nevertheless, the discovery that amyloid precursor mRNA is widely and abundantly distributed throughout most tissues tends to discourage such a simple account of the relationship between these forms of amyloid.(ABSTRACT TRUNCATED AT 250 WORDS)

Preamyloid deposits in the cerebral cortex of patients with Alzheimer's disease and nondemented individuals

A polyclonal antibody to a 28 residue synthetic peptide, homologous to the NH2 terminal region of amyloid beta-protein, was employed in a study of the frontal and temporal cortex of 8 Alzheimer patients and 13 non-demented individuals aimed to define the relationship of immunolabelled to argyrophilic, congophilic and thioflavine S-positive cortical lesions. In Alzheimer patients, this antiserum labelled not only senile plaques and congophilic angiopathy, but also cortical deposits that were neither argyrophilic, congophilic nor thioflavine S-positive and were unrelated to degenerating neurites, tangle-bearing neurons or congophilic angiopathy. Similar lesions were observed in 4 of 13 non-demented individuals, in the absence of tangles, plaques or congophilic angiopathy, and in one in association with plaques. Such deposits might have been due to amyloid precursors still lacking the beta-pleated sheet molecular conformation responsible for amyloid tinctorial and optical properties.