Localization of the putative precursor of Alzheimer's disease-specific amyloid at nuclear envelopes of adult human muscle

Modifications and Trafficking of APP in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD), the most common neurodegenerative disorder, is the leading cause of dementia. Neuritic plaque, one of the major characteristics of AD neuropathology, mainly consists of amyloid β (Aβ) protein. Aβ is derived from amyloid precursor protein (APP) by sequential cleavages of β- and γ-secretase. Although APP upregulation can promote AD pathogenesis by facilitating Aβ production, growing evidence indicates that aberrant post-translational modifications and trafficking of APP play a pivotal role in AD pathogenesis by dysregulating APP processing and Aβ generation. In this report, we reviewed the current knowledge of APP modifications and trafficking as well as their role in APP processing. More importantly, we discussed the effect of aberrant APP modifications and trafficking on Aβ generation and the underlying mechanisms, which may provide novel strategies for drug development in AD.

High glucose promotes Aβ production by inhibiting APP degradation

Abnormal deposition of neuriticplaques is the uniqueneuropathological hallmark of Alzheimer’s disease (AD).Amyloid β protein (Aβ), the major component of plaques, is generated from sequential cleavage of amyloidβ precursor protein (APP) by β-secretase and γ-secretase complex. Patients with diabetes mellitus (DM), characterized by chronic hyperglycemia,have increased risk of AD development.However, the role of high blood glucose in APP processing and Aβ generation remains elusive. In this study, we investigated the effect of high glucose on APP metabolism and Aβ generation in cultured human cells. We found that high glucose treatment significantly increased APP protein level in both neuronal-like and non-neuronal cells, and promoted Aβ generation. Furthermore, we found that high glucose-induced increase of APP level was not due to enhancement of APP gene transcription but resulted from inhibition of APP protein degradation. Taken together, our data indicated that hyperglycemia could promote AD pathogenesis by inhibiting APP degradation and enhancing Aβ production. More importantly, the elevation of APP level and Aβ generation by high glucose was caused by reduction of APP turnover rate.Thus,our study provides a molecular mechanism of increased risk of developing AD in patients withDMand suggests thatglycemic control might be potentially beneficial for reducing the incidence of AD in diabetic patients and delaying the AD progression.

Alzheimer Abeta peptide induces chromosome mis-segregation and aneuploidy, including trisomy 21: requirement for tau and APP

Chromosome aneuploidy, especially trisomy 21, arises in both familial and sporadic Alzheimer's disease. Expression of FAD genes or exposure to Aβ peptide induces aneuploidy in tg-mice and cultured cells. The requirement for GSK-3β, calpain, and Tau in Aβ-induced chromosome mis-segregation points to MT dysfunction as contributing to AD pathogenesis.

Both sporadic and familial Alzheimer's disease (AD) patients exhibit increased chromosome aneuploidy, particularly trisomy 21, in neurons and other cells. Significantly, trisomy 21/Down syndrome patients develop early onset AD pathology. We investigated the mechanism underlying mosaic chromosome aneuploidy in AD and report that FAD mutations in the Alzheimer Amyloid Precursor Protein gene, APP, induce chromosome mis-segregation and aneuploidy in transgenic mice and in transfected cells. Furthermore, adding synthetic Aβ peptide, the pathogenic product of APP, to cultured cells causes rapid and robust chromosome mis-segregation leading to aneuploid, including trisomy 21, daughters, which is prevented by LiCl addition or Ca²⁺ chelation and is replicated in tau KO cells, implicating GSK-3β, calpain, and Tau-dependent microtubule transport in the aneugenic activity of Aβ. Furthermore, APP KO cells are resistant to the aneugenic activity of Aβ, as they have been shown previously to be resistant to Aβ-induced tau phosphorylation and cell toxicity. These results indicate that Aβ-induced microtubule dysfunction leads to aneuploid neurons and may thereby contribute to the pathogenesis of AD.

Topological proteomics, toponomics, MELK-technology

MELK is an ultrasensitive topological proteomics technology analysing proteins on the single cell level (Multi-Epitope-Ligand-'Kartographie'). It can trace out large scale protein patterns with subcellular resolution, mapping the topological position of many proteins simultaneously in a cell. Thereby, it addresses higher level order in a proteome, referred to as the toponome, coding cell functions by topologically and timely determined webs of interacting proteins. The resulting cellular protein maps provide new structures in the proteome: single combinatorial protein patterns (s-CPP), and combinatorial protein pattern motifs (CPP-motifs), bound to superior units. They are images of functional protein networks, which are specific signatures of tissues, cell types, cell states and diseases. The technology unravels hierarchies of proteins related to particular cell functions or dysfunctions, thus identifying and prioritising key proteins within cell and tissue protein networks. Interlocking MELK with the drug screening machinery provides new clues related to the selection of target proteins, and functionally relevant hits and drug leads. The present chapter summarizes the steps that have contributed to the establishment of the technology.

Expression of the gene encoding the beta-amyloid precursor protein APP in Xenopus laevis

The beta-amyloid precursor protein APP is generally accepted to be directly or indirectly involved in the neurodegenerative disorder Alzheimer's disease and has been extensively studied in a number of mammalian systems. Its normal function remains, however, still elusive. We have used the clawed toad, Xenopus laevis, to study the first non-mammalian APP protein. Screening of a Xenopus laevis intermediate pituitary cDNA library led to the identification of two structurally different APP gene transcripts presumably resulting from duplicated genes. Sequence comparison between the Xenopus and human APP proteins revealed at the amino acid sequence level an identity of 92%. Both Xenopus genes were found to be expressed in all tissues examined, but their expression levels differed among tissues. In addition, as in mammals, alternative splicing was observed and the alternatively spliced APP(695) mRNA variant was expressed predominantly in the brain and the oocyte, while the longer isoforms (APP(751-770)) were predominant in the other tissues examined. Of special interest is the finding that, like human but unlike mouse or rat beta-amyloid (Abeta), the Xenopus peptide contains all amino acid residues implicated in amyloidogenesis. We conclude that Xenopus APP mRNA is ubiquitously expressed and alternatively spliced, and that the highly conserved Xenopus APP protein contains an Abeta peptide with amyloidogenic potency.

Chromosome missegregation and trisomy 21 mosaicism in Alzheimer's disease

A connection between Alzheimer's disease (AD) and Down syndrome (trisomy 21) is indicated by the fact that all Down syndrome individuals develop Alzheimer's disease neuropathology by the 4th decade of life. Previous studies have examined the frequency of aneuploidy and other chromosomal defects in cells from familial Alzheimer's disease (FAD) patients, with varying results. To investigate the possibility that a specific type of aneuploidy--trisomy 21 mosaicism--may contribute to Alzheimer's disease, we used quantitative fluorescence in situ hybridization to measure the number of trisomy 21 cells in primary fibroblast cultures from AD and unaffected subjects. The 27 AD cultures, including 15 that were derived from individuals carrying FAD mutations in presenilin 1 or 2, exhibited a significant approximately twofold increase in the number of trisomy 21 cells compared to 13 control cultures. A small double-hybridization experiment suggested that the aneuploidy in AD cells was not limited to chromosome 21 but extended at least to chromosome 18 as well. In a parallel study, the endogenous presenilin proteins in fibroblasts were localized to the centrosomes, the nuclear envelope, and its associated interphase kinetochores. Together these results indicate that the presenilin proteins may be involved in mitosis and that FAD mutations in the presenilin genes may predispose to chromosome missegregation (nondisjunction). The data reported here also suggest that trisomy 21 mosaicism may contribute to other forms of AD that are not caused by a presenilin mutation.

Amyloid myopathy: an underdiagnosed entity

Amyloidosis can involve multiple organs, including kidney, heart, peripheral nerve, skin, joints, and skeletal muscle, but rarely presents as a myopathy. We studied 13 adults with muscle weakness for between 3 months and 4 years in whom the diagnosis of systemic amyloidosis was unsuspected before or until just before the time of the muscle biopsy. All muscle specimens demonstrated congophilic deposits around blood vessels and muscle fibers, some necrotic and regenerating fibers, and signs of mild denervation. Immunostains in 10 patients revealed immunoglobulin amyloidosis in 7 and gelsolin amyloidosis in 1. Apolipoprotein E co-localized with the congophilic deposits in all 10, and a C-terminal epitope of the beta-amyloid precursor protein was detected in 6. The frequency of the diagnosis of amyloid myopathy increased 10-fold when we adopted the fluorescent Congo red stain as a routine procedure in assessing muscle biopsy specimens.

Serine proteinase inhibitors in human skeletal muscle: expression of beta-amyloid protein precursor and alpha 1-antichymotrypsin in vivo and during myogenesis in vitro

The balance of serine proteases and inhibitors in nerve and muscle is altered during programmed- and injury-induced remodeling. A serpin, alpha 1-antichymotrypsin (alpha 1-ACT), and Kunitz-inhibitor containing forms of the beta-amyloid precursor protein (beta APP) may be important components of this balance. In the present study, we analyzed their expression in primary cultures of human myogenic (satellite) cells that mimic myogenic differentiation using Western blotting and immunocytochemistry. In vitro results were compared to in vivo results from normal adult human skeletal muscle biopsies. Using an anti-alpha 1-ACT polyclonal antibody, we detected a 62 kDa immunoreactive band both in cultured human myogenic cells (mononucleated myoblasts as well as multi-nucleated myotubes) and in extracts of human muscle biopsies. With a polyclonal anti-beta APP antibody we found two bands (105 and 120 kDa) in myoblasts and myotubes in culture. However, the same antibody recognized only a single band at 92 kDa in biopsies. By immunocytochemistry, both alpha 1-ACT and beta APP were indistinctly present on localized to the surface of myoblasts in culture. In contrast, these inhibitors were dense on myotube surfaces, where they often formed distinct aggregates and frequently co-localized. In permeabilized muscle cells, alpha 1-ACT and beta APP appeared to be localized to the perikarya of both myoblasts and myotubes. Confirming previous results, both alpha 1-ACT and beta APP were present at the neuromuscular junction in human muscle sections. These developmental changes found during in vitro myogenesis for alpha 1-ACT and beta APP, both serine protease inhibitors, reinforce the hypothesis that regulation of the serine proteases and serine protease inhibitors plays an important role in neuromuscular differentiation.

Role of microglia in senile plaque formation

To assess the role of microglial cells in senile plaque (SP) formation, we examined the density and distribution of microglia in the temporal neocortex of three groups of nondemented individuals, chosen to represent sequential stages of SP formation (no SP, n = 14; diffuse plaques (DP) only, n = 12; both DP and neuritic plaques (NP), n = 14) and patients with Alzheimer's disease (AD, n = 11). The mean density of microglia was significantly greater in the AD group. In nondemented individuals, the presence of NP but not DP was associated with an increased number of microglial cells. Most NP (91%) were focally associated with microglial cells. DP less commonly contained microglia, however, individuals with some NP had microglia within a greater proportion of their DP (47%) than did those with only DP (19%). These findings suggest that: (a) microglia are not involved in the formation of DP; (b) the presence of NP is associated with both an overall increase in microglia and the focal aggregation of cells around NP; (c) microglia may be locally involved in the conversion of DP into NP. This final point represents the most significant aspect of this study, providing the first quantitative evidence to support a specific role for microglia in the formation of NP from DP.

Ultrastructural localization of amyloid protein precursor in the normal and postischemic gerbil brain

Intracellular localization of amyloid protein precursor (APP) in the normal and postischemic gerbil brain was examined by immunoelectron microscopy. In the normal brain, APP immunoreactivity was localized to the multivesicular body, the nuclear membrane, Golgi apparatus and rough endoplasmic reticulum. After ischemia for 5 min and reperfusion for 24 h, some neurons became intensely immunoreactive for APP in the subiculum and CA3 region of the hippocampus and layers III and V/VI of the cerebral cortex. No intense labeling occurred in glial cells. Intensely labeled neurons were characterized by eccentric nuclei and accumulation of cellular organelles in the center of the neuronal perikarya, as well as a strongly immunoreactive nuclear membrane and cisternal structures, which were presumed to be dispersed Golgi apparatus and/or fragmented rough ER. APP immunoreactivity in the multivesicular body suggests re-internalization of APP and its degradation in the endosomal-lysosomal pathway. The ultrastructural features of neurons with intense APP immunoreactivity suggested mild neuronal damage, similar to those found in central chromatolysis. This indicates that accumulation of APP in these neurons is caused by disturbance of axonal transport, although the information does not allow us to exclude the possibility of an increase in APP production.

CDEBP, a site-specific DNA-binding protein of the ‘APP-like’ family, is required during the early development of the mouse

A murine protein, termed CDEBP, was previously shown to bind the double-stranded DNA motif GTCACATG, identical to the yeast centromeric element CDEI. The cDNA sequence showed three domains with extensive similarities to the amyloid beta precursor protein (APP). The protein is homologous over its entire length to the human protein designated APPH. In situ immunofluorescence assays using antibodies raised against distinct parts of CDEBP detected discrete sites of accumulation inside the interphase nucleus, and the bulk of the protein was not associated with mitotic chromosomes. One of the complexes with double-stranded CDEI oligonucleotides detected by gel shift assay was not present when the protein had been selectively removed from nuclear extracts by immunoprecipitation. We reported previously that microinjection into one-cell mouse embryos of DNA fragments including the CDEI sequence results in an early arrest of development with abnormal nuclei containing variable amounts of DNA. The same characteristic figures were observed when embryos were treated with antisense oligonucleotides complementary to parts of the CDEBP coding region. Complexes between the CDEBP protein and CDEI sites in the mouse genome thus appear to play a critical role in the replication/segregation of the embryonic genome.

Senile plaques in temporal lobe epilepsy

Senile plaques (SP) are one of the characteristic pathological lesions of Alzheimer's disease (AD). They are also seen in the brains of some non-demented individuals as an age-related change. Identification of clinical conditions associated with these "incidental" SP could provide insight into AD pathogenesis. We have examined the presence of SP in lobectomy specimens (n = 101) removed in the surgical treatment of temporal lobe epilepsy (TLE). SP were present in 10 specimens from epileptic patients aged 36 to 61 years and the presence of SP correlated positively with patient age. No other significant AD-related pathology was identified and no patients showed any evidence of dementia on neuropsychological testing. When compared with temporal lobe tissue from non-demented, non-epileptic autopsy controls (n = 406), the density and distribution of SP was the same. The age-related incidence of SP however, was significantly greater in the epileptics. This suggests that some aspects of TLE has a positive influence on the formation of SP.

Senile plaques do not progressively accumulate with normal aging

Senile plaques (SP) are one of the pathologic hallmarks of Alzheimer's disease (AD). Models of SP formation, particularly the early stages, could provide valuable insight into AD pathogenesis. One such model may be provided by non-demented elderly individuals in whom some SP are a common incidental finding. This study has examined post-mortem brain tissue from a large number of such neurologically normal patients in an attempt to better understand the temporal sequence of SP formation. SP were identified in modified Bielschowsky-stained sections of mesial temporal lobe in 122 (30%) of 402 cases. The prevalence of SP in the temporal neocortex correlated strongly with patient age. Surprisingly, however, neither the mean nor maximum SP density showed any increase with age. This suggests that SP do not progressively accumulate in normal aging but develop over a limited time period after which their number stabilizes at a constant level. In most cases, all SP were of the diffuse type. In 37 cases (9%), however, some neuritic SP (NP) were also seen. Although the NP density did not show a significant increase with age either, the proportion of SP which were neuritic (NP/SP), did. This suggests that changes in SP morphology may be more important than total SP numbers in normal aging.

Conspicuous accumulation of a single-stranded DNA binding protein in skeletal muscle fibers in inclusion body myositis

In muscle biopsies from patients with inclusion body myositis (IBM), multiple sites were found in many muscle fibers that bound single-stranded but not double-stranded DNA without sequence specificity, as exemplified by several different cDNA probes. This activity was attributable to a protein, because it was abolished by proteases but not by RNAse. Most of the sites of binding were myonuclei, whereas some were rimmed vacuoles, which probably result from nuclear breakdown. No comparable binding was seen in 27 control biopsies. A number of human and viral single-stranded DNA binding proteins exist but our data does not identify the protein responsible for DNA binding in IBM. Our findings reinforce the supposition that nuclear damage plays a basic role in the pathogenesis of IBM.

Lack of variation in the nucleotide sequence corresponding to the transmembrane domain of the beta-amyloid precursor protein in Alzheimer's disease

The nucleotide sequence corresponding to the APP transmembrane domain and flanking regions of charged amino acids was determined for 91 patients with histologically confirmed Alzheimer's disease, 9 patients with dementias of other etiologies, and 14 controls who had no identifiable brain disease. Twenty-eight of the AD patients had a first-degree relative with dementia. No mutations were detected among the 100 demented patients. However, one of the 14 controls exhibited a change in the 3' base of codon 716 which would not be expected to result in an amino acid substitution at this position.

beta-Amyloid precursor epitopes in muscle fibers of inclusion body myositis

Sporadic inclusion body myositis (IBM) and hereditary inclusion body myopathy (hIBM) are severe and progressive muscle diseases, characterized pathologically by vacuolated muscle fibers that contain 15- to 21-nm cytoplasmic tubulofilaments (CTFs). Those vacuolated muscle fibers also contain abnormally accumulated ubiquitin and beta-amyloid protein (A beta), and they contain amyloid in beta-pleated sheets as indicated by Congo red and crystal violet positivity. Using several well-characterized antibodies, we have now demonstrated that, in addition to A beta, two other epitopes, N-terminal and C-terminal, of the beta-amyloid precursor protein (beta PP) are abnormally accumulated in IBM vacuolated muscle fibers and similarly in hIBM. At the light microscopy level, immunoreactivities of N- and C-epitopes of beta PP closely colocalized with A beta and ubiquitin immunoreactivities. However, by immunogold electronmicroscopy, even though N-, C-, and A beta epitopes of beta PP and ubiquitin colocalized at the amorphous and dense floccular structures, only A beta was localized to the 6- to 10-nm amyloid-like fibrils and only ubiquitin was localized to CTFs. beta PP immunoreactive structures were often in proximity to CTFs, but CTFs themselves never contained beta PP immunoreactivities. The fact that A beta but not C- or N-terminal epitopes of beta PP localized to the 6- to 10-nm amyloid-like fibrils suggests that free A beta might be generated during beta PP processing and, after aggregation, may be responsible for the amyloid present within IBM muscle fibers. Our study demonstrates that three epitopes of beta PP accumulate abnormally in diseased human muscle, and therefore this phenomenon is not unique to Alzheimer's disease, Down's syndrome brain, and Dutch-type cerebrovascular amyloidosis.

Isolation and characterization of APLP2 encoding a homologue of the Alzheimer's associated amyloid beta protein precursor

Familial Alzheimer's disease (FAD) is a genetically heterogeneous disorder that includes a rare early-onset form linked to mutations in the amyloid b protein precursor (APP) gene. Clues to the function of APP derive from the recent finding that it is a member of a highly conserved protein family that includes the mammalian amyloid precursor-like protein (APLP1) gene which maps to the same general region of human chromosome 19 linked to late-onset FAD. Here we report the isolation of the human APLP2 gene. We show that APLP2 is a close relative of APP and exhibits a very similar pattern of expression in the brain and throughout the body. Like APP, APLP2 contains a cytoplasmic domain predicted to couple with the GTP-binding protein G(o) indicating that it may be an additional cell surface activator of this G protein.

An antibody against the Alzheimer's disease amyloid precursor protein recognizes distinct conformational isoforms

The Alzheimer's disease amyloid precursor protein (APP) consists of several isoforms, which are extensively post-translationally modified and processed. A monoclonal antibody, MAbE1, was raised against a synthetic peptide from an extracellular domain that is common to all isoforms of APP. Immunoblots and immunolocalization studies on cells of neuronal and other origins demonstrated that this antibody recognized a subclass of APP isoforms when compared to a monoclonal antibody raised against a bacterial fusion protein of APP, MAb22C11. Prominent protein bands of 71 kDa and 120 kDa were only detected on immunoblots of cell lysates and no immunoreactivity was observed in protein samples obtained from cell conditioned media. Immunofluorescence labelling with MAbE1 revealed predominantly perinuclear staining of cells of neuronal and glial origin. The data suggest that this monoclonal antibody detects distinct conformational isoforms of APP present in intracellular compartments.

Distribution of beta/A4 protein and amyloid precursor protein in hereditary cerebral hemorrhage with amyloidosis-Dutch type and Alzheimer's disease

Brain amyloidosis with abundant beta/A4 protein deposition in plaques and cortical and meningeal vessels is found in Alzheimer's disease (AD) and hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D). In contrast to AD, no neuritic pathology or classical congophilic plaques are found in HCHWA-D. Unlike most AD cases, the congophilic angiopathy in HCHWA-D is very severe. It is still unknown whether beta/A4 deposits in plaques and vessels have the same origin. In this study, we have used frozen cortical tissue of HCHWA-D and AD patients to investigate the beta/A4 amyloid protein and the amyloid precursor protein (APP) in different types of plaques and congophilic angiopathy. Immunohistochemical staining was conducted using antibodies against synthetic beta/A4 proteins and antibodies against APP including MAbP2-1, a monoclonal antibody against purified protease nexin-2, which is the secreted form of APP. In contrast to immunohistochemical studies on formalin-fixed, paraffin-embedded tissue, frozen tissue of HCHWA-D patients revealed a very high number of beta/A4 plaques resembling AD. All plaques were of the diffuse type. Double-staining with MabP2-1 and beta/A4 antisera revealed: 1) the presence of APP immunoreactivity in classical plaques and transitional forms; 2) the absence of APP immunoreactivity in diffuse plaques in HCHWA-D and AD; and 3) pronounced APP immunoreactivity in congophilic vessels in HCHWA-D in contrast to weak APP staining in congophilic vessels in AD. Together these findings suggest that: a) the presence of APP in plaques is related to neuritic changes; b) different processes occur in amyloid formation in plaques and vessels; and c) differences exist between the process of amyloid formation in HCHWA-D and AD.

Molecular and cellular biology of Alzheimer amyloid

Alzheimer's Disease (AD), a disorder of unknown etiology, is the most common form of adult-onset dementia and is characterized by severe intellectual deterioration. The definitive diagnosis of AD is made by postmortem examination of the brain, which reveals large quantities of neurofibrillary tangles (NFT) and senile plaques within the parenchyma. The NFT are composed of paired helical filaments associated with several cytoskeletal proteins. The primary protein component of senile plaques is beta/A4 amyloid, a 42-43 amino acid peptide derived from a much larger molecule, the amyloid precursor protein (APP). Vascular beta/A4 amyloidosis is also prevalent in the disease. The mechanism by which beta/A4 amyloid accumulates in the AD brain is unknown. Recent research has demonstrated that the precursor molecule, APP, is a transmembrane protein with a large extracytoplasmic domain, a membrane spanning region that includes the portion that gives rise to beta/A4 amyloid, and a short intracytoplasmic domain. The precursor has multiple forms among which are those that differ by a variable length insert within the extracytoplasmic domain. The insert has sequence homology to the family of Kunitz protease inhibitor proteins. Cellular and animal models have been developed to study the nature of APP processing and the biological and behavioral consequences of beta/A4 amyloidosis. The results of such studies indicate that the normal processing of APP involves enzymatic cleavage of the molecule within the beta/A4 amyloid region, thus preventing the accumulation of beta/A4 in the normal brain. The factors leading to abnormal processing of APP, and consequent beta/A4 amyloid accumulation within the AD brain, have yet to be identified. In cell culture, the biological effects associated with beta/A4 amyloid include neurotrophic and neurotoxic activities, while the peptide has also been shown to have dramatic behavioral effects in animal models.

Strong immunoreactivity of beta-amyloid precursor protein, including the beta-amyloid protein sequence, at human neuromuscular junctions

At the postsynaptic domain of the human neuromuscular junction (NMJ), we have demonstrated strong concentrations of the N-terminus 45-62, C-terminus 676-695 and beta-amyloid protein sequences of beta-amyloid precursor protein (beta APP). We used well-characterized monoclonal and polyclonal antibodies for co-localization with three other postsynaptic proteins, applying double and triple fluorescence labeling. Strong immunoreactivity of all three beta APP sequences was found at all NMJs identified by bound alpha-bungarotoxin (alpha BT), where they co-localized with alpha BT and with immunoreactive desmin and dystrophin, which are postsynaptic proteins of human NMJs. This appears to be the first demonstration of beta APP sequences concentrated postsynaptically at human NMJs. beta APP may have a role in normal junction biology and possibly in some diseases affecting NMJs.

Alzheimer's disease. Beta-amyloid precursor protein expression in the nucleus basalis of Meynert

The nucleus basalis of Meynert (nbM) was examined using immunocytochemistry for beta-amyloid precursor protein (beta APP) expression in Alzheimer's disease (AD). In mild AD cases, light labeling of the cell body and proximal processes was observed, and small intracellular structures were labeled rarely. In the more severe cases, intense cytoplasmic beta APP labeling was seen, often along with small beta APP-positive structures. Double-labeling experiments demonstrated that in the more severe cases these small structures were also decorated by a neurofibrillary tangle (NFT) antiserum. Other neurons in the severe cases showed incorporation of beta APP into large inclusions, which were also labeled with the NFT antiserum. However, some large inclusions in the severe cases were labeled by the NFT antiserum but contained no beta APP. Extraneuronal NFTs did not show beta APP labeling and did not react with an antibody to the beta-amyloid peptide. These results suggest that increased expression of beta APP coincides with intracellular NFT formation in the nbM, but that the formation of extraneuronal NFTs results in a loss of beta APP immunoreactivity.

Immunohistochemical localization of the proteinase inhibitor region of amyloid precursor proteins in the neocortex of Alzheimer's disease and aged controls

The immunohistochemical localization of the proteinase inhibitor region of amyloid protein precursors (APPI) in the postmortem human neocortex was studied using a polyclonal antibody raised against a purified recombinant human APPI derivative produced by COS-1 cells. APPI-like immunoreactivity (APPI-LI) was found diffusely in the human neocortex. APPI-LI appeared as irregularly shaped granular structures. The size of the APPI-LI structures was 1-4 microns in diameter. APPI-LI usually formed a cluster of 10- to 20-microns diameter in the cortical gray matter and 20- to 40-microns diameter in the subcortical white matter. Double staining for APPI and glial fibrillary acidic protein indicated that APPI-LI in the white matter and molecular layer was localized exclusively in the fibrillary astrocytes. In contrast, APPI-LI was found in neurons as well as in the fibrillary astrocytes in layers II through to VI. Under fluorescence microscopy, APPI-LI in both neurons and fibrillary astrocytes were found in close association with lipofuscin. The present observations indicate that APPI is localized in neurons and astrocytes in the human neocortex and that APPI may be associated with lipofuscin or lysosome in the human neocortex.

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.

Expression patterns of beta-amyloid precursor protein (beta-APP) in neural and nonneural human tissues from Alzheimer's disease and control subjects

Both neural and nonneural human tissues from patients with or without Alzheimer's disease (AD) were surveyed to detect the presence of the beta-amyloid protein and its precursors. This was accomplished using polyclonal and monoclonal antibodies to epitopes in the 695 amino acid long beta-APP (i.e., beta-APP695), as well as in related beta-APPs. Immunoreactivity in beta-APP in brain was prominent in senile plaques, extraneuronal tangles, and neurons. Outside the brain, beta-APP staining was seen in neurons and satellite glial cells of the dorsal root, enteric and trigeminal ganglia, the adeno- and neurohypophysis, megakaryocytes, and adrenal gland in samples from patients with AD and those without AD. Western blots of neocortex revealed three major proteins with apparent molecular masses of 105, 115, and 125 kDa in the insoluble membrane-associated fractions, while two broad bands with a molecular weight centered at about 100 and 120 kDa were detected in soluble fractions. In addition, the pituitary and adrenal glands as well as cardiac muscle revealed prominent immunobands in membrane-associated fractions. Notably, other nonneural tissues were devoid of beta-APP immunoreactivity. Thus, the beta-APPs are detectable only in a limited number of nonneural tissues. Taken together, these data suggest that beta-APPs produced in the brain are sources of beta-APP peptides that accumulate as senile plaques in AD.

Alzheimer's disease amyloid beta-clipping enzyme (APP secretase): identification, purification, and characterization of the enzyme

Alzheimer's disease (AD) is the most frequent cause of dementia, although no genetic abnormality has been identified. Recent studies have elucidated the molecular defect in AD, including the abnormal deposition of amyloid beta peptide (beta/A4) in senile plaques of affected individuals. Normal brain contains the enzyme, APP secretase, which cleaves inside the beta/A4 portion of the precursor protein (APP); abnormal processing of APP occurs in AD brain. Until now, no evidence has been provided that APP secretase is an intracellular proteinase. We have now prepared two synthetic substrates of APP secretase, both of which contain the cleavage point and are much more sensitive than substrates previously available to identify APP secretase. Using these substrates, we found an intracellular proteinase that has APP secretase activity. This proteinase has been identified as cathepsin B.

Proteolytic cleavage of the Alzheimer's disease amyloid A4 precursor protein

Amyloid A4 protein (beta-protein) is deposited in the brain of a patient with Alzheimer's disease (AD) as one of the main components of extracellular cerebrovascular amyloid, as well as neurofibrillary tangles. It is derived from a precursor protein, and its formation has been considered to be a rate-limiting step for brain degeneration in AD. In this article, proteolytic cleavage events that can degrade amyloid precursor protein are reviewed with respect to how the topographical distribution of the proteinase and its substrates disturbs normal processing steps in AD brain.

Synthesis and secretion of Alzheimer amyloid beta A4 precursor protein by stimulated human peripheral blood leucocytes

Alzheimer amyloid precursor proteins (APP) are actively secreted by stimulated human peripheral mononuclear blood leucocytes (PMBLs). Induction of APP transcription, translation and secretion was observed with several T cell mitogens but was highest with phytohemagglutinin. The time course of induction is similar to that reported for IL-2 and IL-2 receptor. We suggest that APP may play an important role in the construction of the immunological network and the differentiation of T cells.

Hepatic aging as an etiological factor in the development of Alzheimer's disease

Alzheimer's disease is a frequent cause of dementia in the elderly. The prevalence and incidence increase with aging. It is hypothesised that the age related decline in liver size and lysosomal function results in decreased clearance as well as decreased or altered proteolysis of the Alzheimer precursor protein, and results in the deposition of A4 protein in cerebral blood vessels and brain with congophilic angiopathy and senile/amyloid plaque formation.

Ultrastructural localization of the putative precursors of the A4 amyloid protein associated with Alzheimer's disease

Any explanation of the causes of Alzheimer's disease and of its unique cerebral pathologic features must take into account the distribution and ultrastructural localization of the pre-A4 amyloid proteins in tissues and organs. The authors have analyzed the expression of the pre-A4 amyloid proteins in several tissues by immunogold electron microscopy and by immunofluorescence. For this purpose, they have used a mouse monoclonal antibody and a guinea pig antiserum raised against two synthetic peptides corresponding to two different sequences common to all the full-length forms of the A4 amyloid precursors. They observed a tissue-specific distribution of the secreted and the transmembrane form of the precursors. The authors could determine that the secreted form is generated in vivo within the cytoplasm. In the salivary glands and in the adenohypophysis, all the immunoreactivity is associated with the process of secretion, whereas in the muscle, a staining pattern compatible with the presence of the pre-A4 amyloid proteins in the sarcoplasmic reticulum has been observed. This difference in the localization may reflect tissue-specific processing pathways and suggests that posttranslational modifications such as proteolytic removal of the transmembrane and cytoplasmic domains contribute to the structural and thus functional diversity of the A4 amyloid precursors.

Characterization of beta-amyloid precursor proteins with or without the protease-inhibitor domain using anti-peptide antibodies

Alternative splicing of the transcript encoding the beta-amyloid precursor protein (BAPP) of Alzheimer's disease produces multiple mRNA species. Translation of these mRNAs predicts protein products of 770, 751, and 695 amino acids. The difference arises from the inclusion in BAPP-770/751 of a 56-residue insert region which is homologous to Kunitz-type protease inhibitors. We have prepared and affinity-purified anti-peptide antibodies that react specifically with either BAPP-770/751 (insert-specific) or BAPP-695 (junction-specific). A detectable level of the mRNA corresponding to the BAPP-770/751 protein was found in all cell lines tested. Immunoprecipitation of 35S-labeled proteins from these cell lines showed them to contain one or two Mr 105,000 bands reactive with the insert-specific serum, i-291. In contrast, only cos-7 cells and the human neuroblastoma cell line, IMR-32, contained mRNA species that encode the BAPP-695 protein, as shown by Northern analysis with a junction-spanning oligonucleotide probe. A band of Mr 95,000 was immunoprecipitated specifically from these two cell lines using the junction-specific serum, J-284. Indirect immunofluorescence labeling of cells corroborated these findings. All cells reacted with the insert-specific antibodies, i-291 and i-324. Only cos-7 and IMR-32 cells reacted with the junction-specific antibody, J-284. These results demonstrate the usefulness of anti-peptide antibodies for the differential detection of the BAPP-695 and BAPP-770/751 proteins.

Amyloid beta-protein precursor (APP) of cultured cells: secretory and non-secretory forms of APP

Overproduction or aberrant catabolism of the predicted amyloid beta-protein precursor (APP) is suspected as the cause of amyloid deposition in Alzheimer's disease and Down's syndrome brains. For possible in vitro experiments of amyloid formation, we have examined the expression of APP in various cultured cells. We found two types of APP producing cell lines. PC12h (rat pheochromocytoma) and HL-60 (human acute promyelocytic leukemia) cells produce a secretory form that is released into the culture medium, while Bu-17 (human glioma) cells synthesize only a non-secretory form that accumulates at the cell surface. APP immunoreactivity on the latter cells was detected at the tips of cell processes or growth cones. These observations indicate that the nonsecretory form of APP may play a role in cell contact or adhesion.

Heterogenic mRNAs with an identical protein-coding region of the human embryonic myosin alkali light chain in skeletal muscle cells

The formation of human myotubes in culture is accompanied by the induction of developmentally regulated, muscle-specific genes. We have studied the expression of human myosin light chain proteins and mRNAs during myogenesis in culture, in particular the skeletal embryonic myosin light chain 1 (MC1emb), which is indistinguishable from MLC1 of adult atrial cardiac muscle (MLC1A) as has been shown for rodent and bovine MLC1emb. We have identified distinct MLC1emb/MLC1A mRNAs in cultured human skeletal muscle cells that differ in their 5' and 3' untranslated regions but contain identical protein-coding regions. The alternative 3' untranslated region is detectable also in RNA of human atria. The different MLC1emb RNAs are likely to be encoded by one gene. It appears that the two MLC1emb 5' untranslated regions of the human gene are specific for man. In the mouse, only one 5' untranslated region of the MLC1emb gene has been detected.

Determination of RNA content in postischemic gerbil brain by in situ hybridization

Brief periods of cerebral ischemia result in prolonged inhibition of protein synthesis. In CA1 sector of hippocampus inhibition is irreversible, leading to delayed death of pyramidal neurons. In order to study the possible role of gene transcription in this process, expression of four individual RNAs was investigated in the gerbil brain after 5 min of global cerebral ischemia by in situ hybridization with the following nucleic acid probes: plasmid pMr100 (ribosomal RNA sequences), plasma pAG82 (cytochrome c oxidase sequences), plasmid p629 (amyloid A4 precursor protein of Alzheimer's disease, pre-A4 protein), and plasmid pHF beta A-1 (beta-actin sequences). Cytochrome c oxidase mRNA and ribosomal RNA did not show any changes in expression up to 48 hr after ischemia. After longer recirculation times they gradually declined in the CA1 sector of hippocampus in parallel with the morphological manifestation of delayed neuronal death. The pre-A4 mRNA transiently decreased after 8 hr of recirculation of the CA1 sector but then recovered before it finally disappeared in parallel with delayed neuronal death. The beta-actin mRNA transiently appeared to increase after 8 hr of recirculation in the stratum radiatum of hippocampus but then also declined and disappeared when CA1 neurons began to disintegrate. The possible significance of these changes in the pathogenesis of ischemic neuronal damage is discussed.

Putative N-terminal splitting enzyme of amyloid A4 peptides is the multicatalytic proteinase, ingensin, which is widely distributed in mammalian cells

The main characteristic changes observed in Alzheimer's disease (AD) are the presence of neurofibrillary tangles and the deposition of amyloid A4 peptides. The most abundant amyloid A4 peptide species in AD (which we tentatively named A4') is composed of 39 amino acids, which is devoid of the 3 N-terminal amino acids, Asp-Ala-Glu, of the originally reported A4 peptide. We synthesized a model peptide substrate, Suc-Ala-Glu-methylcoumarinamide (MCA), to identify the proteinase that splits the A4' peptide. DEAE-cellulose column chromatography of rat liver and porcine brain extracts showed that only one peak material digested the synthetic substrate at pH 8. The results for the final preparation indicate that the Suc-Ala-Glu-MCA-degrading enzyme is a high-molecular-mass proteinase, with a molecular mass of above 500,000, and is composed of several low-molecular-mass subunits. These results suggest that a non-lysosomal multicatalytic proteinase (we named this enzyme ingensin (ingens = large in Latin). Ishiura, S. et al. (1985) FEBS Lett. 189, 119-123) catalyzes the above reaction. Antiserum against the purified multicatalytic proteinase, ingensin, crossreacted with the purified Suc-Ala-Glu-MCA-degrading proteinase. It is likely that ingensin shows a similar action toward amyloid precursor protein (APP) in vivo.

Amyloid A4 protein and its precursor in Down's syndrome and Alzheimer's disease

In patients with Alzheimer's disease, amyloid fibrils that are aggregates of A4 protein subunits are deposited in the brain. A similar process occurs at an earlier age in persons with Down's syndrome. To investigate the deposition of amyloid in these diseases, we used a radioimmunoassay to measure levels of the amyloid precursor (PreA4) in the serum of 17 patients with Down's syndrome, 15 patients with Alzheimer's disease, and 33 normal elderly controls. The mean (+/- SD) concentration of serum PreA4 was increased 1.5-fold in patients with Down's syndrome (2.49 +/- 1.13 nmol per liter) as compared with that in controls (1.68 +/- 0.49 nmol per liter; P less than 0.007); the levels in patients with Alzheimer's disease were similar to those in controls (1.83 +/- 0.78; P less than 0.98). We also found that the concentration of PreA4 in the brain tissue of two adults with Down's syndrome (100 and 190 pmol per gram) was higher than that in the brain tissue of either 26 patients with Alzheimer's disease (64.4 +/- 17.3 pmol per gram) or 17 elderly controls with neurologic disease (68.5 +/- 26.3 pmol per gram). Immunocytochemical studies of brain tissue from 26 patients with Down's syndrome showed that the deposition of A4 protein amyloid began in these patients approximately 50 years earlier than it began in 127 normal aging subjects studied previously, although the rate of deposition was the same. We conclude that, since the gene for PreA4 is on the long arm of chromosome 21, which is present in triplicate in Down's syndrome, overexpression of this gene may lead to increased levels of PreA4 and amyloid deposition in Down's syndrome. However, since increased levels of PreA4 are not present in Alzheimer's disease, additional factors must account for the amyloid deposition in that disorder.

Identification, biogenesis, and localization of precursors of Alzheimer's disease A4 amyloid protein

To study the putative precursor proteins (PreA4(695), PreA4(751), and PreA4(770] of Alzheimer's disease A4 amyloid protein, polyclonal and monoclonal antibodies were raised against a recombinant bacterial PreA4(695) fusion protein. These antibodies were used to identify the precursors in different cell lines as well as in human brain homogenates and cerebrospinal fluid (CSF). The precursors are tyrosine-sulfated, O- and N-glycosylated membrane proteins and have half-lives of 20-30 min in cells. Cells express the polypeptides at their surface but also secrete C-terminal truncated proteins into the medium. These proteins are also found in CSF of both Alzheimer's disease patients and normal individuals. The proteins are derived from their cognate membrane-associated forms by proteolysis and have apparently lost the cytoplasmic and the transmembrane domains. Since the latter contributes to the A4 amyloid sequence, it seems possible that this proteolytic cleavage represents the first step in the formation of A4 amyloid deposits.

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.

The pathology of the amyloid A4 precursor of Alzheimer's disease

The A4 amyloid protein is the major subunit present in the amyloid of Alzheimer's disease. It is derived by proteolytic cleavage from a larger precursor (PreA4) which is a neuronal membrane glycoprotein. Whereas in Down's syndrome, over-expression of the gene coding for PreA4 is likely to be responsible for the premature development of cerebral amyloidosis, a similar mechanism is yet to be demonstrated in Alzheimer's disease.

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)

The amyloid percursor protein of Alzheimer disease is expressed as a 130 kDa polypeptide in various cultured cell types

The vascular and parenchymal amyloid deposits in Alzheimer disease (AD), normal aging and Down syndrome are mainly composed of a 4 kDa polypeptide (A4), which derives from a larger precursor protein (APP). There is evidence that APP is a transmembrane glycoprotein present in most tissues, but the characteristics of APP in intact cells are not yet known. In order to investigate this issue, we examined the immunoreactivity of fibroblasts of human and nonhuman cell lines with antisera raised to synthetic peptides corresponding to A4 and to two other domains of the APP. All three antisera recognized a 130 kDa polypeptide (APP-130) in immunoblots from all cell lines. In fibroblasts, an additional polypeptide of 228 kDa (APP-228) was recognized by the antiserum to A4. In immunoblots of two dimensional gels, APP-130 showed a pI of 6.2, while APP-228 failed to focus in the pH range of 4.7-7.0. Sequential extractions of cells with buffer and with Triton X-100 indicate that APP-130 is extractable with nonionic detergents at high ionic strength, whereas 228 kDa APP is a cystolic component. Immunofluorescence staining is consistent with an intracellular perinuclear and plasma membrane localization. It is concluded that APP-130 and APP-228 are two forms of the APP which result from extensive posttranslational modifications of a smaller original gene product. It is likely that APP undergoes similar posttranslational modifications in different cell types.

Immunocytochemical localization of the precursor protein for beta-amyloid in the rat central nervous system

Two rabbit polyclonal antibodies generated against different portions of the amyloid precursor protein were used to localize this protein in normal rat brain. Light and electron microscopic immunohistochemical localizations demonstrate that the protein is widely distributed throughout the neuraxis, with the highest concentrations of immunoreactive neurons occurring in the olfactory bulb, cerebral cortex, septum-diagonal band, globus pallidus, cerebellum, and hippocampus. Immunoreactive astrocytes are also present in the cerebral cortex in relation to both neurons and capillaries. However, immunoreactivity was not observed within the endothelium of the cerebral vasculature. These data demonstrate that the beta-amyloid precursor is widely distributed in the CNS and provide further insight into the cellular elements that may be involved in the neuropathological changes associated with Alzheimer's disease.

Antisera to an amino-terminal peptide detect the amyloid protein precursor of Alzheimer's disease and recognize senile plaques

The cerebral amyloid deposited in Alzheimer's disease (AD) contains a 4.2 kDa beta amyloid polypeptide (beta AP) that is derived from a larger beta amyloid protein precursor (beta APP). Three beta APP mRNAs encoding proteins of 695, 751, and 770 amino acids have previously been identified. In each of these, there is a single membrane-spanning domain close to the carboxyl-terminus of the beta APP, and the 42 amino acid beta AP sequence extends from within the membrane-spanning domain into the large extracellular region of the beta APP. We raised rabbit antisera to a peptide corresponding to amino acids 45-62 near the amino-terminus of the beta APP. We show that these antisera detect the beta APP by demonstrating that they (i) label a set of approximately 120 kDa membrane-associated proteins in human brain previously detected by antisera to the carboxyl-terminus of beta APP and (ii) label a set of approximately 120 kDa membrane-associated proteins that are selectively overexpressed in cells transfected with a full length beta APP expression construct. The beta APP45-62 antisera specifically stain senile plaques in AD brains. This finding, along with the previous demonstration that antisera to the carboxyl-terminus of the beta APP label senile plaques, indicates that both near amino-terminal and carboxyl-terminal domains of the beta APP are present in senile plaques and suggests that proteolytic processing of the full length beta APP molecule into insoluble amyloid fibrils occurs in a highly localized fashion at the sites of amyloid deposition in AD brains.

An antiserum to the C-terminus of the Alzheimer amyloid precursor recognizes a soluble 70 kDa protein

A rabbit antiserum to the C-terminus of the putative brain amyloid precursor was used to probe Western blots of tissue proteins separated by SDS-PAGE. The antiserum specifically labelled a protein of approx. 70 kDa in the Tris buffer-soluble fraction of brain samples from rat, Alzheimer subjects, cases of young and old Down's syndrome, and age-matched controls. The 70 kDa protein was present in low concentrations in human liver and kidney, and was undetectable in human skeletal muscle. The 70 kDa protein may be a metabolite of the amyloid precursor.

Absence of mutation in the beta-amyloid cDNAs cloned from the brains of three patients with sporadic Alzheimer's disease

Using an oligonucleotide probe, we isolated cDNA clones corresponding to the precursor of the beta-amyloid peptide (BAP) from brain libraries of 3 patients with sporadic Alzheimer's disease (AD). DNA sequencing showed that the largest cDNA clone encompasses 83% of the open reading frame proposed by Kang et al. to encode the BAP precursor (APP). cDNA clones from each of the 3 AD brain libraries were identical to the sequence of the APP-cDNAs cloned from normal adult human and fetal brain. An antisense-radiolabeled RNA copy of one of the AD clones detected a pattern of 3 gene transcripts measuring 3.5, 3.2 and 1.6 kilobases (kb) in both normal and AD brain RNAs. These data suggest that there are no mutations in or about the 42 amino acid (aa) sequence of BAP and that the accumulation of amyloid consistently found in AD may result from altered post-translational processing of APP.