Amino acid sequence RERMS represents the active domain of amyloid beta/A4 protein precursor that promotes fibroblast growth.

The growth of A-1 fibroblasts depends on exogenous amyloid beta/A4 protein precursor (APP), providing a simple bioassay to study the function of APP. Our preliminary study, testing the activity of a series of fragments derived from the secreted form of APP-695 (sAPP-695) on this bioassay, has shown that at least one of the active sites of sAPP-695 was localized within a 40-mer sequence (APP296-335, Kang sequence; Roch, J.-M., I. P. Shapiro, M. P. Sundsmo, D. A. C. Otero, L. M. Refolo, N. K. Robakis, and T. Saitoh. 1992. J. Biol. Chem. 267:2214-2221). In the present study, to further characterize the growth-promoting activity of sAPP-695 on fibroblasts, we applied a battery of synthetic peptides on this bioassay and found that: (a) the sequence of five amino acids, RERMS (APP328-332), was uniquely required for the growth-promoting activity of sAPP-695; (b) the activity was sequence-specific because the reverse-sequence peptide of the active domain had no activity; and (c) the four-amino-acid peptide RMSQ (APP330-333), which partially overlaps the COOH-terminal side of the active sequence RERMS, could antagonize the activity of sAPP-695. Furthermore, a recombinant protein which lacks this active domain (APP20-591 without 306-335) did not promote fibroblast cell growth, suggesting that this domain is the only site of sAPP-695 involved in the growth stimulation. The availability of these biologically active, short peptides and their antagonists should prove to be an essential step for the elucidation of APP involvement in regulation of cellular homeostasis.

Neurofibrillary tangle-associated alteration of stathmin in Alzheimer's disease.

Stathmin (p19), a 19-kDa cytosolic phosphorotein, plays a key role in converting extracellular signals into intracellular biochemical changes. Antibodies and cDNA specific for stathmin were used to study its levels and localization in normal and Alzheimer's disease (AD) brain tissue. The stathmin protein concentration was reduced in AD neocortex as assessed by Western blotting, whereas the concentration of its mRNA detected by both in situ hybridization and slot blot were increased in AD. The alteration of the stathmin protein concentration was negatively correlated with neurofibrillary tangle numbers but not with plaque numbers. Immunoreactivity was evenly localized to the cytoplasm of neurons in control cortical sections, whereas in AD it was preferentially localized to some of the neurofibrillary tangle-bearing neurons. Numbers of stathmin-positive neurons were inversely correlated with tangle numbers but not with plaque numbers in the frontal cortex of AD patients.

SCG10, a neuron-specific growth-associated protein in Alzheimer's disease.

Neuronal growth-associated proteins (nGAPs) are markers of neuronal process outgrowth and are associated with both degenerative and sprouting responses in Alzheimer's disease (AD) brain. To study possible involvement of SCG10, an nGAP, in AD, we cloned human SCG10 cDNA and analyzed SCG-10 at mRNA and protein levels in control and AD brains. The deduced amino acid sequence of human SCG10 was 69% identical to stathmin, another nGAP. By in situ hybridization, both SCG10 and stathmin mRNAs were detected in selected neuronal populations in aged human brains. Quantitative analysis by RNase protection revealed that levels of neither SCG10 nor stathmin mRNAs were significantly altered in AD. Using an SCG10-specific antibody, Western blot analysis did not reveal any quantitative changes of SCG10 in AD. However, when the concentration of SCG10 protein was plotted against the number of tangles, a positive correlation was found. SCG10 levels did not correlate with plaque numbers. Furthermore, immunohistochemical study revealed that neuronal SCG10 protein accumulated in the cell bodies in AD-affected regions. Thus, SCG10 compartmentalization and metabolism may be altered in AD possibly due to mechanisms related to tangle formation in this disease.

Association of CYP2D microsatellite polymorphism with Lewy body variant of Alzheimer's disease.

OBJECTIVE: To examine the genetic association of CYP2D6 locus with Lewy body variant (LBV) and Parkinson's disease (PD). METHODS: Allelic association was studied in patients with pure AD, LBV, and PD by using the CYP2D microsatellite, the (dG-dT)n dinucleotide repeat (n=16 to 27) located between CYP2D8P and CYP2D7 genes, and the CYP2D6 B and D mutations. RESULTS: We found overrepresentation of the alleles longer than 21 repeat (the long-type alleles) in LBV (allele frequency, 0.313) (odds ratio=1.99, p=0.019 by chi2 test) and in PD (0.298) (odds ratio=1.86, p=0.037), but not in pure AD (0.196), compared with the age-matched control (0.186). Strong association was noted of the long-type alleles with the CYP2D6 B mutation (odds ratio=88.50, p < 0.001 by Fisher's exact test), but not with the D mutation or the deletion of CYP2D6 gene. CONCLUSIONS: The CYP2D locus is closely associated with LBV and PD. The CYP2D6 B mutation may be involved in pathogenesis of LBV and PD in a dominant-negative manner, or in the linkage disequilibrium of the CYP2D microsatellite to another pathogenic gene locus.

Oxidative stress induces amyloid-like aggregate formation of NACP/alpha-synuclein in vitro.

The precursor of non-amyloid beta protein component of Alzheimer's disease amyloid (NACP/alpha-synuclein), found in Lewy bodies of Parkinson's disease (PD), is a presynaptic protein genetically linked to some familial types PD. Mechanisms of abnormal NACP/alpha-synuclein aggregation in neurodegenerative diseases are unclear. Since oxidative stress might play a role in PD pathogenesis, we investigated the role of iron and peroxide in NACP/alpha-synuclein aggregation. Immunoblot analysis showed that human NACP/alpha-synuclein (but not beta-synuclein) aggregated in the presence of ferric ion and was inhibited by the iron chelator deferoxamine. Ferrous ion was not effective by itself, but it potentially aggregated NACP/alpha-synuclein in the presence of hydrogen peroxide. NACP/ alpha-synuclein aggregates displayed strong thioflavine-S and congo-red reactivity, reminiscent of amyloid. This study suggests that NACP/alpha-synuclein aggregation might be closely related to oxidative reactions which may play a critical role in neurodegeneration in disorders with Lewy bodies.

Human recombinant NACP/alpha-synuclein is aggregated and fibrillated in vitro: relevance for Lewy body disease.

The precursor of non-amyloid beta protein component of Alzheimer's disease amyloid (NACP/alpha-synuclein) is aggregated and fibrillated under certain conditions, i.e., increasing time lag, high temperature and low pH. These in vitro aggregates form Thioflavine-S-positive filamentous structures, reminiscent of amyloid-like fibrils. Since some Lewy bodies in Parkinson's disease display Thioflavine-S reactivity, our results may suggest that amyloidogenic properties of NACP/alpha-synuclein may play a crucial role in pathogenesis of disorders with Lewy bodies such as Parkinson's disease.

The synaptic protein NACP is abnormally expressed during the progression of Alzheimer's disease.

NACP, the precursor of non-A beta component of Alzheimer's disease (AD) amyloid (NAC), is a synaptic protein that could potentially be involved in AD. We studied, by dot-blot, NACP levels in the frontal cortex of AD cases staged according to severity of disease and correlated them with cognitive performance and neuropathological markers. Early AD cases showed one fold higher levels of NACP immunoreactivity (IR) compared to moderate and severe AD. Levels of NACP-IR were correlated with tangle counts (r = -0.305, P = 0.04) and Blessed score (r = -0.356, P = 0.01), but not with plaque counts (r = 0.132, P = 0.39). This study suggests that the abnormal accumulation of NACP during the early stages of AD might play an important role in the mechanisms of neurodegeneration and synaptic damage in AD.

Characterization of lysosomes and lysosomal enzymes from Chediak-Higashi-syndrome cultured fibroblasts.

Chediak-Higashi-syndrome cultured skin fibroblasts were used to study the possible involvement of lysosomal enzymes and lysosomal dysfunction in this disorder. Our evidence indicated that Chediak-Higashi fibroblasts displayed a significant decrease in the specific activity of the acidic alpha-D-mannosidase (pH 4.2) compared with normal controls. Additional studies revealed a small, but significant, decrease in the rate of degradation of 125I-labelled beta-D-glucosidase that had been endocytosed into Chediak-Higashi cells.

Decreased adhesiveness of Alzheimer's disease fibroblasts: is amyloid beta-protein precursor involved?

The adhesiveness of fibroblasts derived from Alzheimer's disease (AD) patients to a plastic substratum was assessed as the proportion of cells attached to a plastic dish bottom after a 30-minute incubation in culture medium of cells dissociated in ethylenediaminetetraacetic acid and was compared with the adhesiveness of normal fibroblasts from non-AD controls. It was found that the normal fibroblasts adhered better to plastic than did AD cells. This reduced adhesiveness was observed in fibroblasts derived from both sporadic and familial AD patients. Because of the possible involvement of amyloid beta-protein precursor (ABPP) in the process of cellular adhesion, the amount of ABPP messenger RNA was measured in these fibroblasts and was found to be decreased in the familial AD fibroblasts, although not in cells from sporadic AD patients. Furthermore, there were fewer molecules detected by an anti-ABPP antibody in conditioned media from familial AD fibroblasts as compared with media from control fibroblasts. Therefore, although it is possible that the reduced adhesiveness of familial AD fibroblasts may result from genetic deficits in ABPP gene expression, the reduced adhesiveness of sporadic AD fibroblasts most likely results from certain deficits in molecules other than the ABPP.

Abnormal accumulation of NACP/alpha-synuclein in neurodegenerative disorders.

The precursor of the non-Abeta component of Alzheimer's disease amyloid (NACP) (also known as a-synuclein) is a presynaptic terminal molecule that accumulates in the plaques of Alzheimer's disease. Recent studies have shown that a mutation in NACP is associated with familial Parkinson's disease, and that Lewy bodies are immunoreactive with antibodies against this molecule. To clarify the patterns of accumulation and differences in abnormal compartmentalization, we studied NACP immunoreactivity using double immunolabeling and laser scanning confocal microscopy in the cortex of patients with various neurodegenerative disorders. In Lewy body variant of Alzheimer's disease, diffuse Lewy body disease, and Parkinson's disease, NACP was found to immunolabel cortical Lewy bodies, abnormal neurites, and dystrophic neurites in the plaques. Double-labeling studies showed that all three of these neuropathological structures also contained ubiquitin, synaptophysin, and neurofilament (but not tau) immunoreactivity. In contrast, neurofibrillary tangles, neuropil threads, Pick bodies, ballooned neurons, and glial tangles (most of which were tau positive) were NACP negative. These results support the view that NACP specifically accumulates in diseases related to Lewy bodies such as Lewy body variant of Alzheimer's disease, diffuse Lewy body disease, and Parkinson's disease and suggests a role for this synaptic protein in the pathogenesis of neurodegeneration.

Secreted form of amyloid beta protein precursor is involved in the growth regulation of fibroblasts.

Fibroblasts that harbor an antisense construct of amyloid beta protein precursor (ABPP) cDNA, A-1, produced less ABPP mRNA and ABPP and grew poorly. Normal growth was restored when either parent cell conditioned medium (CM) or purified ABPP was provided. The capacity of the CM to restore cell growth was abolished by passage through an anti-ABPP immunoaffinity column; the activity was in the bound fraction. A Mr 90,000 protein recognized by the anti-ABPP antibody was diminished in the CM of A-1. CM from ABPP cDNA-transfected cells expressing high levels of ABPP was more potent than that from non-transfected parent cells in restoring A-1 growth. These results indicate that ABPP is released from cells into the medium and has an autocrine function in growth regulation.

Defective neurite extension is caused by a mutation in amyloid beta/A4 (A beta) protein precursor found in familial Alzheimer's disease.

Clonal central nervous system neuronal cells, B103, do not synthesize detectable endogenous APP or APLP. B103 cells transfected with both wild-type (B103/APP) and mutant APP construct (B103/APP delta NL) secreted comparable amounts of soluble forms of APP (sAPP). B103/APP cells produced sAPP and cleaved at amyloid beta/A4 (A beta) 16, the alpha-secretase site, and B103/APP delta NL cells produced sAPP beta cleaved at A beta 1, the beta-secretase site. B103/APP delta NL cells developed fewer neurites than B103/APP cells in a serum-free defined medium. Neurite numbers of parent B103 cells were increased by the 50% conditioned medium (CM) from B103/APP cells but reduced by the CM from B103/APP delta NL cells. Chemically synthesized A beta at concentration levels higher than 1 nM reduced numbers of neurites from B103 or B103/APP delta NL cells. However, A beta at 1-100 nM could not reduce the neurite number of B103/APP cells. The protective activity against A beta's deleterious effect to reduce neurite numbers was attributed to sAPP alpha in the CM. Although sAPP alpha could block the effect of A beta, sAPP beta could not do so under the identical condition, suggesting the importance of the C-terminal 15-amino acid sequence in sAPP alpha. Nevertheless, sAPP alpha's protective activity required the N-terminal sequence around RERMS, previously identified to be the active domain of sAPP beta. The overall effect of APP mutation which overproduced A beta and sAPP beta and underproduced sAPP alpha was a marked decline in the neurotrophic effect of APP. We suggest that the disruption of balance between the detrimental effect of A beta and the trophic effect of sAPP may be important in the pathogenesis of AD caused by this pathogenic APP mutation.

Immunoreactivity of CD45, a protein phosphotyrosine phosphatase, in Alzheimer's disease.

Both protein kinases and phosphoprotein phosphatases are important components of signal transduction systems in cells. Recent studies in Alzheimer's disease (AD) have shown abnormal protein phosphorylation in the cortex suggesting an alteration in these enzymes. In the present study, an antibody against CD45 was used to analyze the status of this protein phosphotyrosine phosphatase in AD. We studied and quantified the immunohistochemical and immunochemical distribution of this integral membrane protein in control and AD brain. We found that anti-CD45 immunostained the great majority of microglia, both resting and activated. These cells were Ricinus communis agglutinin I positive and glial fibrillary acidic protein and neurofilament negative. The AD frontal cortex showed a 35% (P less than 0.01) increase in the number of anti-CD45 immunoreactive microglia as compared with controls. These results were consistent with the immunoblot quantification of CD45 immunoreactivity following native gel electrophoresis. In AD, 30% of the CD45-immunostained microglia were clustered in the neuritic plaques (about six per plaque) while the remaining 70% were scattered in the neuropil. The AD hippocampus showed an increase in CD45-immunoreactive microglia in the molecular layer of the dentate gyrus. At the ultrastructural level, CD45 immunoreactivity was localized exclusively to the plasma membrane of the microglia. The presence of the anti-CD45 immunoreactivity in microglia suggests the possibility that they may require the presence of CD45 as a cell surface receptor which may regulate cell function through modulation of intracellular signaling.

Bacterial expression, purification, and functional mapping of the amyloid beta/A4 protein precursor.

The secreted form of Alzheimer amyloid beta/A4 protein precursor (APP) has been shown to be involved in cell growth regulation (Saitoh, T., Sundsmo, M., Roch, J.-M., Kimura, N., Cole, G., Schubert, D., Oltersdorf, T., and Schenk, D.B. (1989) Cell 58, 615-622). Using a strong prokaryotic expression system, we expressed, in Escherichia coli, peptide fragments covering different regions of the secreted form of APP-695. The longest of these fragments (KB75, 572 amino acids from Val-20 to Ile-591), which contained neither the Kunitz-type protease inhibitor (KPI) domain nor the amyloid beta/A4-protein domain, was purified and shown to be biologically active in terms of growth regulation. Two other APP fragments (KB48, 316 amino acids from Val-20 to Met-335; and RB17, 150 amino acids from Thr-296 to Pro-445), overlapping by only 40 amino acids at a close site C-terminal to the KPI insertion site, were also active. Furthermore, a chemically synthesized 40-residue peptide corresponding to this region of overlap also stimulated the growth of A-1 fibroblasts. These results establish the presence of growth-promoting activity in the secreted form of APP-695 and suggest that the site of this activity of APP-695 lies within a 40-amino acid domain next to the KPI insertion site.

NACP, a synaptic protein involved in Alzheimer's disease, is differentially regulated during megakaryocyte differentiation.

Non-amyloid-beta component precursor (NACP) is a presynaptic protein which may play a role in amyloidogenesis in Alzheimer's disease (AD). Since an abnormal function of platelets has been demonstrated in AD, platelets could be used as a model to investigate the role of NACP in this disease. We characterized the patterns of NACP and beta-synuclein expression in a megakaryocyte-platelet system (K562). In this hematopoietic cell line, NACP expression was up-regulated during phorbol ester-induced megakaryocytic differentiation, while beta-synuclein was down-regulated. Consistent with this, NACP but not beta-synuclein was abundantly expressed in platelets. Immunogold electron microscopy of platelets showed that NACP is loosely associated with the plasma membrane, the endomembrane system and, occasionally, with the membrane of secretory alpha-granules. These findings suggest that coordinate expression of the synuclein family members may play a critical role during hematopoietic cell differentiation. Additionally, expression of the synuclein family members may be developmentally regulated during neural differentiation.

Increase of synaptic density and memory retention by a peptide representing the trophic domain of the amyloid beta/A4 protein precursor.

The secreted form (sAPP) of the Alzheimer amyloid beta/A4 protein precursor (APP) has been shown to be involved in the in vitro regulation of fibroblast growth and neurite extension from neuronal cells. The active site of sAPP responsible for these functions is within a small domain just C-terminal to the Kunitz-type protease inhibitor (KPI) insertion site. We report here that a 17-mer peptide, containing this active domain of sAPP, can induce cellular and behavioral changes when infused into rat brains. After 2 weeks of APP 17-mer peptide infusion, the animals were tested for reversal learning and memory retention and were sacrificed for morphological examination of brains. We found that administration of the APP 17-mer peptide resulted in an 18% increase in the number of presynaptic terminals in the frontoparietal cortex. At the behavioral level, 17-mer-infused animals with nonimpaired learning capability showed an increased memory retention that seemed to interfere with reversal learning performance. This APP 17-mer effect on memory retention was not observed in animals with impaired initial learning capacity. These results suggest that APP is involved in memory retention through its effect on synaptic structure.

Genetic studies in Alzheimer's disease with an NACP/alpha-synuclein polymorphism.

The non-Abeta component of Alzheimer's disease amyloid (NAC) is copurified with amyloid from the brain tissue of Alzheimer's disease victims and is immunohistochemically localized to amyloid fibrils. NAC is a hydrophobic peptide fragment from the NAC precursor protein (NACP/alpha-synuclein) that is localized to presynaptic terminals. We used a polymorphic dinucleotide repeat sequence in a genomic clone of NACP for genetic association and linkage studies. Screening of Alzheimer's disease families failed to establish linkage between NACP and Alzheimer's disease. Nevertheless, one of the NACP polymorphisms (NACP allele 2) was shown to have significant association with healthy elderly control individuals with apolipoprotein E risk. This may indicate a possible protective function of the allele.