Alternative splicing of the beta A4 amyloid gene of Alzheimer's disease in cortex of control and Alzheimer's disease patients

Primary over-expression of AβPP in muscle does not lead to the development of inclusion body myositis in a new lineage of the MCK-AβPP transgenic mouse

The aim of this study is to determine whether primary over-expression of AβPP in skeletal muscle results in the development of features of inclusion body myositis (IBM) in a new lineage of the MCK-AβPP transgenic mouse. Quantitative histological, immunohistochemical and western blotting studies were performed on muscles from 3 to 18 month old transgenic and wild-type C57BL6/SJL mice. Electron microscopy was also performed on muscle sections from selected animals. Although western blotting confirmed that there was over-expression of full length AβPP in transgenic mouse muscles, deposition of amyloid-β and fibrillar amyloid could not be demonstrated histochemically or with electron microscopy. Additionally, other changes typical of IBM such as rimmed vacuoles, cytochrome C oxidase-deficient fibres, upregulation of MHC antigens, lymphocytic inflammatory infiltration and T cell fibre invasion were absent. The most prominent finding in both transgenic and wild-type animals was the presence of tubular aggregates which was age-related and largely restricted to male animals. Expression of full length AβPP in this MCK-AβPP mouse lineage did not reach the levels required for immunodetection or deposition of amyloid-β as in the original transgenic strains, and was not associated with the development of pathological features of IBM. These negative results emphasise the potential pitfalls of re-deriving transgenic mouse strains in different laboratories.

Genetics of Alzheimer disease

Alzheimer disease (AD) is the most common causes of neurodegenerative disorder in the elderly individuals. Clinically, patients initially present with short-term memory loss, subsequently followed by executive dysfunction, confusion, agitation, and behavioral disturbances. Three causative genes have been associated with autosomal dominant familial AD (APP, PSEN1, and PSEN2) and 1 genetic risk factor (APOEε4 allele). Identification of these genes has led to a number of animal models that have been useful to study the pathogenesis underlying AD. In this article, we provide an overview of the clinical and genetic features of AD.

Functional interactions of APP with the apoE receptor family

The beta-amyloid precursor protein (APP) is central to the pathogenesis of Alzheimer's disease, but its normal functions in the brain are poorly understood. A number of APP-interacting proteins have been identified: intracellularly, APP interacts with adaptor proteins through its conserved NPXY domain; extracellularly, APP interacts with a component of the extracellular matrix, F-spondin. Interestingly, many of these APP-interacting proteins also interact with the family of receptors for apolipoprotein E (apoE), the Alzheimer's disease risk factor. apoE receptors also share with APP the fact that they are cleaved by the same secretase activities. apoE receptors are shed from the cell surface, a cleavage that is regulated by receptor-ligand interactions, and C-terminal fragments of apoE receptors are cleaved by gamma-secretase. Functionally, both APP and apoE receptors affect neuronal migration and synapse formation in the brain. This review summarizes these numerous interactions between APP and apoE receptors, which provide clues about the normal functions of APP.

Key factors in Alzheimer's disease: beta-amyloid precursor protein processing, metabolism and intraneuronal transport

During the last years it has become evident that the beta-amyloid (Abeta) component of senile plaques may be the key molecule in the pathology of Alzheimer's disease (AD). The source and place of the neurotoxic action of Abeta, however, is still a matter of controversy. The precursor of the beta-amyloid peptide is the predominantly neuronal beta-amyloid precursor protein. We, and others, hypothesize that intraneuronal misregulation of APP leads to an accumulation of Abeta peptides in intracellular compartments. This accumulation impairs APP trafficking, which starts a cascade of pathological changes and causes the pyramidal neurons to degenerate. Enhanced Abeta secretion as a function of stressed neurons and remnants of degenerated neurons provide seeds for extracellular Abeta aggregates, which induce secondary degenerative events involving neighboring cells such as neurons, astroglia and macrophages/microglia. Beta-amyloid precursor protein has a pivotal role in Alzheimer's disease.

Estradiol regulates APP mRNA alternative splicing in the mice brain cortex

Alternative splicing of amyloid precursor protein (APP), one of the candidate genes for Alzheimer's disease, yields three major mRNAs, which give rise to APP770, APP751 and APP695 protein isoforms. Out of these three isoforms, APP695 is expressed most predominantly in the brain. The splicing and processing of APP are shown to be influenced by several factors including hormones. In this study, we report the effect of withdrawal and administration of sex steroid hormones on the alternative splicing of APP mRNA during aging in the brain cortex of mice of both sexes. The level of APP695 mRNA isoform was higher in intact adult as compared to old mice of both sexes. Gonadectomy upregulated the APP695 mRNA isoform levels in all groups except in adult female where the level was downregulated. Estradiol supplementation upregulated the level of APP695 mRNA isoform in all groups except in old male where the level was downregulated. Thus these results show that the level of APP695 mRNA changes with age and estradiol may play a key role in the development of Alzheimer's disease by modulating the level of APP mRNA isoforms.

Amyloid-beta deposition in the cerebral cortex in Dementia with Lewy bodies is accompanied by a relative increase in AbetaPP mRNA isoforms containing the Kunitz protease inhibitor

Deposition of amyloid-beta, the fibrillogenic product of the cell surface protein AbetaPP (amyloid-beta protein precursor), occurs in the cerebral cortex of patients with Dementia with Lewy bodies (DLB). Amyloid deposition, basically in the form of senile plaques, occurs not only in the common form (DLBc), which is defined by changes consistent with diffuse Lewy body disease accompanied by Alzheimer's disease (AD), but also in the pure form (DLBp), in which neurofibrillary tangles are absent. The present study analyses the expression of AbetaPP mRNA isoforms with (AbetaPP751 and AbetaPP770) and without (AbetaPP695) the Kunitz-type serine protease inhibitor (KPI) domain, in the cerebral cortex in DLBc (n=4), DLBp (n=4), Parkinson's disease (PD, n=5), AD (n=3 stages I-IIA, and n=4 stage VC of Braak and Braak), amyloid angiopathy (AA, n=2) and progressive supranuclear palsy (PSP, n=4) compared with age-matched controls (n=6). For this purpose, TaqMan RT-PCR assay was used on frozen post-mortem samples of the frontal cortex (area 8) obtained with short post-mortem delays (8.29+/-4.57 h) and strict RNA preservation (A260/280 of 1.78+/-0.15). A 3.66-fold, 6.67-fold, 4.28-fold and 5.24-fold increases, in the (AbetaPP751+AbetaPP770)/AbetaPP695 mRNA ratio were found in DLBc, DLBp, AD stage VC and AA, respectively, when compared with controls. No modifications in the ratio were found in PD, AD stage I-IIA and PSP. These findings suggest that alternative splicing of the AbetaPP mRNA may play a role in betaA4 amyloidogenesis in DLBp, DLBc, AD stage VC and Amyloid angiopathy.

Amyloid precursor protein mRNA levels in Alzheimer's disease brain

Insoluble beta-amyloid deposits in Alzheimer's disease (AD) brain are proteolytically derived from the membrane bound amyloid precursor protein (APP). The APP gene is differentially spliced to produce isoforms that can be classified into those containing a Kunitz-type serine protease inhibitor domain (K(+), APP(751), APP(770), APRP(365) and APRP(563)), and those without (K(-), APP(695) and APP(714)). Given the hypothesis that Abeta is a result of aberrant catabolism of APP, differential expression of mRNA isoforms containing protease inhibitors might play an active role in the pathology of AD. We took 513 cerebral cortex samples from 90 AD and 81 control brains and quantified the mRNA isoforms of APP with TaqMan real-time RT-PCR. After adjustment for age at death, brain pH and gender we found a change in the ratio of KPI(+) to KPI(-) mRNA isoforms of APP. Three separate probes, designed to recognise only KPI(+) mRNA species, gave increases of between 28% and 50% in AD brains relative to controls (p=0.002). There was no change in the mRNA levels of KPI-(APP 695) (p=0.898). Therefore, whilst KPI-mRNA levels remained stable the KPI(+) species increased specifically in the AD brains.

Identification of a novel alternative splicing isoform of human amyloid precursor protein gene, APP639

Senile plaques, neurofibrillary tangles and amyloid-laden cerebral vessels are characteristic features in the brains of individuals with Alzheimer's disease (AD). The principal component of amyloid in senile plaque and amyloid-laden cerebral vessels is beta-amyloid (Abeta), a peptide proteolytically derived from a large amyloid precursor protein (APP). To date, several alternatively spliced human APP transcripts have been described. Here, we report the identification of a novel alternative splicing isoform of the human APP gene, APP639, which excludes exon 2 as well as exons 7 and 8. RT-PCR and Southern blot analysis show that APP639 mRNA is expressed in many human fetal tissues. In contrast, the APP639 transcript is hardly detected in the aged human cerebral cortex from both pathologically confirmed sporadic AD cases and nondemented controls. However, APP639 mRNA exists in the adult human liver. Western blot analysis shows that the protein product produced from the APP639 cDNA could be recognized by the APP antibody, and it does lack the exon 2 coding region. These results suggest that APP639, a novel alternative splicing isoform of human APP gene, does exist in human tissues in vivo.

The functions of the amyloid precursor protein gene

The amyloid precursor protein (APP) gene and its protein products have multiple functions in the central nervous system and fulfil criteria as neuractive peptides: presence, release and identity of action. There is increased understanding of the role of secretases (proteases) in the metabolism of APP and the production of its peptide fragments. The APP gene and its products have physiological roles in synaptic action, development of the brain, and in the response to stress and injury. These functions reveal the strategic importance of APP in the workings of the brain and point to its evolutionary significance.

Expression of amyloid precursor protein in human astrocytes in vitro: isoform-specific increases following heat shock

The beta-amyloid protein deposited in senile plaques and cerebral blood vessels in the Alzheimer's disease brain is derived from the larger transmembrane spanning amyloid precursor protein. The present study investigates the effects of heat shock on the expression and processing of amyloid precursor protein in a normal human fetal astrocytic cell line CC2565 using reverse transcription-polymerase chain reaction, in situ hybridization histochemistry and western blot analysis. Heat shock led to an increase in the messenger RNA encoding Kunitz protease inhibitor isoforms of amyloid precursor protein, which peaked at 4h post-heat shock. This increase was confined to the messenger RNA encoding amyloid precursor protein-751, with a decrease in amyloid precursor protein-770 and no change in amyloid precursor protein-695. This shift in splicing was accompanied by a significant decrease in secreted amyloid precursor protein and an increase in beta-secretase processing within the cell. These findings demonstrate that astrocytes in vitro demonstrate a striking response to heat shock. This is unlikely to be due to a direct action on the promoter region of the gene, since the response is specific for one splice variant; amyloid precursor protein-751 messenger RNA. This increase in expression is further accompanied by a decrease in secretion of amyloid precursor protein, implying a shift in processing towards an intracellular route, possibly via the actions of the beta-secretase enzyme, which is known to be potentially amyloidogenic. Such a mechanism may contribute to amyloidosis in the intact brain in response to cellular stress, such as head injury.

Amyloid precursor protein gene isoforms in Alzheimer's disease and other neurodegenerative disorders

Differential expression of the amyloid precursor protein gene (APP) may be important in the development of amyloidosis in Alzheimer's disease (AD) and experimentally in the brain's response to injury. Controversial data suggests that APP isoforms containing the Kunitz protease inhibitor isoform (APP KPI+) are over expressed in the brains of patients with AD when compared to the non-Kunitz protease inhibitor containing isoforms (APP KPI-). We have investigated this hypothesis using a quantitative analysis of gene expression on brain tissue collected at post-mortem. In situ hybridization has been used with synthetic oligonucleotide probes labelled with 35S to detect the two principal splice variants of APP: APP 695 (KPI-) and APP 751 (KPI+). A prospective brain bank of frozen brain specimens has been established and includes pathologically proven AD (n=15) and other neurodegenerative disorders as controls (n=18). The controls consist of frontal lobe atrophy (n=4), Huntington's disease (n=5), Parkinson's disease (n=4), motor neuron disease (n=2), multi-infarct dementia (n=1), multisystem atrophy (n=1), and subacute sclerosing panencephalitis (n=1). We have observed no significant differences in the expression of APP 695 KPI- mRNA in frontal lobe: 17.49+/-3.26 optical density (OD) units of mRNA expression in AD vs. 16.13+/-1.76 OD units mRNA in controls (P=0.80, linear regression); or temporal lobe: 14.73+/-2.96 in AD vs. 16.49+/-2.15 in controls (P=0.55). No significant differences have been found in APP 751 KPI+ in frontal lobe: 12.86+/-2.98 in AD vs. 13.70+/-2.88 in controls (P=0.97); and temporal lobe: 13.31+/-4.93 in AD vs. 11.07+/-1.99 in controls (P=0. 65). Analysis of the ratios of APP 751 KPI+ OD units of mRNA to APP 695 KPI- mRNA revealed a trend to an increased ratio which did not reach statistical significance: frontal lobe APP 751 KPI+/APP 695 KPI- 1.92+/-1.04 in AD vs. 0.86+/-0.17 in controls (P=0.54); temporal lobe 2.54+/-1.59 in AD vs. 0.96+/-0.11 controls (P=0.34). Our data has not revealed differential expression of APP mRNA isoforms in AD and supports the hypothesis that post-translational events in APP metabolism are important in amyloidogenesis and the pathogenesis of AD.

Relative increase in Alzheimer's disease of soluble forms of cerebral Abeta amyloid protein precursor containing the Kunitz protease inhibitory domain

Although a number of studies have examined amyloid precursor protein (APP) mRNA levels in Alzheimer's disease (AD), no clear consensus has emerged as to whether the levels of transcripts for isoforms containing a Kunitz protease inhibitory (KPI)-encoded region are increased or decreased in AD. Here we compare AD and control brain for the relative amounts of APP protein containing KPI to APP protein lacking this domain. APP protein was purified from the soluble subcellular fraction and Triton X-100 membrane pellet extract of one hemisphere of AD (n = 10), normal (n = 7), and neurological control (n = 5) brains. The amount of KPI-containing APP in the purified protein samples was determined using two independent assay methods. The first assay exploited the inhibitory action of KPI-containing APP on trypsin. The second assay employed reflectance analysis of Western blots. The proportion of KPI-containing forms of APP in the soluble subcellular fraction of AD brains is significantly elevated (p < 0.01) compared with controls. Species containing a KPI domain comprise 32-41 and 76-77% of purified soluble APP from control and AD brains, respectively. For purified membrane-associated APP, 72-77 and 65-82% of control and AD samples, respectively, contain a KPI domain. Since KPI-containing species of APP may be more amyloidogenic (Ho, L., Fukuchi, K., and Yonkin, S. G. (1996) J. Biol. Chem. 271, 30929-30934), our findings support an imbalance of isoforms as one possible mechanism for amyloid deposition in sporadic AD.

The amyloid precursor protein gene: a neuropeptide gene with diverse functions in the central nervous system

The amyloid precursor protein (APP) is a member of a family of proteins found in the central nervous system with a fundamental role in the pathogenesis of Alzheimer's disease. This review describes the experimental evidence that has provided functional insights into this protein and emphasizes the importance of APP in many neurobiological processes.

Presenilin-1, amyloid precursor protein and amyloid precursor-like protein 2 mRNA levels in human superior frontal cortex during aging

The presenilin-1 (PS-1) and amyloid precursor protein (APP) genes carry mutations which co-segregate with early-onset familial Alzheimer's disease. The APP and PS-1 gene products may be involved in the aetiology of the more common late onset form of Alzheimer's disease, where increasing age is a major risk factor. To investigate whether age affected mRNA expression of these genes, we quantified PS-1, total APP, APP containing the kunitz-type protease inhibitor (KPI) domain and amyloid precursor-like protein 2 (APLP2) mRNAs in post-mortem superior frontal cortices from 23 control subjects aged 38 to 89 years using solution hybridisation-RNase protection assays. PS-1, total APP, APP KPI and APLP2 mRNA levels were unchanged over this age range. PS-1 was the least abundant mRNA, at approximately 7% of total APP, the most highly expressed mRNA studied (10.8 copies/pg total RNA). The proportion of total APP encoding the KPI domain (approximately 52%) was unaffected by age. APLP2 mRNA was present at approximately 29% of the total APP mRNA level. Significant positive correlations were present between total APP, APP KPI and APLP2 mRNA levels. These results indicate that the increased prevalence of Alzheimer's disease cannot be attributed to alterations in cortical PS-1, APP and APLP2 mRNA levels or APP KPI splicing during aging.

Cell-specific expression of beta-amyloid precursor protein isoform mRNAs and proteins in neurons and astrocytes

The abnormal accumulation of beta-amyloid (A beta) in senile plaques appears to be a central pathological process in Alzheimer's disease. A beta is formed by proteolysis of beta-amyloid precursor protein (APP) with several isoforms generated by alternative splicing of exons 7, 8 and 15. A semi-quantitative reverse transcription (RT)-polymerase chain reaction (PCR) analysis showed that APP695 mRNA lacking exon 7 and 8 was most abundant in primary cultures of rat neurons, while APP770 and APP751 representing, respectively, the full length and exon 8 lacking isoforms predominated in cultured astroglial cells. Antisera AP-2 and AP-4 were produced by immunizing rabbits with keyhole limpet haemocyanin coupled with synthetic peptides representing KPI region APP301-316 and A beta region APP670-686 of APP770, respectively. These polyclonal antisera were purified against the corresponding peptide using affinity chromatography. Western blot analysis of homogenates of relatively enriched neuronal and astroglial cultures showed that these antibodies discretely stained bands of proteins in a cell-specific manner. Dot-blot analysis using AP-2, AP-4 and 22C11 antibodies indicated that, in comparison with neurons, cultured astrocytes contained 3-fold greater KPI-containing APP isoform proteins. The amount of total APP proteins, which include both KPI-containing and KPI-lacking APP isoforms, was approximately 90% higher in astrocytes than in neurons. Consistent with these in vitro findings in cultured astrocytes, in fimbria-fornix lesioned rat hippocampus, labelling with AP-2 antibody, which specifically reacts with KPI-containing APP proteins, was mainly observed in glial fibrillary acidic protein-positive reactive astrocytes in vivo. The results showed that APP isoforms are expressed in a cell type-specific manner in the brain and, since deposition of A beta is closely associated with the expression of KPI-containing APP isoforms, provide further evidence for the involvement of astrocytes in plaque biogenesis.

Lymphocyte content of amyloid precursor protein is increased in Down's syndrome and aging

We quantified cellular amyloid precursor protein (APP) in ethanol-permeabilized peripheral lymphocytes from 13 subjects with Alzheimer's disease (AD), 11 subjects with Down's syndrome (DS), and 13 healthy elderly and 31 healthy young controls. APP content was analyzed by indirect immunofluorescence and flow cytometry, using the 22C11 monoclonal antibody (mAb) directed against an N-terminal domain of APP. Authenticity of 22C11 APP signal was confirmed by immunoblotting and flow cytometry studies with the mAb 6E10, directed against the A beta domain of APP. Consistent with gene dosage, patients with DS had 1.51-fold higher lymphocyte APP signal than age-matched normal young subjects (corrected p < 0.05). Both AD patients and elderly control groups had significantly increased lymphocyte APP signal compared to young controls (either comparison corrected p < 0.01). Indeed, increasing age in non-DS subjects was significantly correlated with lymphocyte APP (r = 0.508, p < 0.0001), such that APP immunoreactivity more than doubled from 20 to 80 years. Lymphocyte APP was nonsignificantly higher in AD vs. aged controls in this small sample. Increased cellular APP content in DS and aging may correspond to generalized alterations in expression or processing of this molecule, and suggests a novel determinant for the timing of AD onset.

A new quantitative solution hybridisation-RNase protection assay for APP and APLP2 mRNA

Amyloid precursor protein (APP) and amyloid precursor-like protein 2 (APLP2) are members of a multigene family of proteins implicated in the pathogenesis of Alzheimer's disease. We describe the development of an RNA-RNA solution hybridisation-RNase protection assay to quantify APP mRNA. APP mRNA splice forms containing the Kunitz-type protease inhibitor (KPI) insert, and APLP2 mRNA in total nucleic acid extracts from a range of tissue types. Solution hybridisation-RNase protection assay enables absolute quantification of target mRNA, by conversion of the hybridisation signal to pg mRNA using a standard curve. The assay is sensitive, capable of detecting 1 pg target mRNA, and reproducible, with an inter-assay variability of less than 10% and an intra-assay variability of 3-4%. We quantified APP and APLP2 mRNA in cell lines and post-mortem human brain tissue samples. To test whether we could detect physiological differences in APP mRNA levels, a fibroblast cell line with a paternal chromosome 21 deletion of the region including the APP gene was analysed and found to express half as much APP mRNA as control fibroblasts. In addition, a reversible, approx. 30% increase in APP mRNA levels was detected in human lymphoblastoid cell lines following heat shock, a physical stimulus previously shown to increase APP expression. Regional differences in the expression of APP and APLP2 were seen in human post-mortem cerebral cortex and cerebellum. Levels of APP and APLP2 mRNA were highest in the temporal cortex, slightly lower in frontal and occipital cortices, and lowest in the cerebellum. The highest proportion of KPI-containing APP was seen in the frontal and temporal cortices. The ratio of APP:APLP2 mRNA was 1:0.3 in the cortical tissue and 1:0.8 in the cerebellum. In conclusion, quantitative solution hybridisation-RNase protection assay of total APP. APP KPI and APLP2 mRNA provides a new tool to improve the resolution of studies of potentially subtle alterations in the expression of these genes in both cell culture model systems and Alzheimer's disease post-mortem human brain tissue.

Quantification of APP and APLP2 mRNA in APOE genotyped Alzheimer's disease brains

Amyloid precursor protein (APP) is metabolised to produce A beta, a peptide found aggregated in Alzheimer's disease neuritic plaques. APP is a member of a multigene protein family which includes amyloid precursor-like protein 2 (APLP2). Since A beta accumulation can be triggered by factors acting up- or downstream of APP processing, we investigated whether APP mRNA expression was altered in Alzheimer's disease post-mortem cerebral cortex. In addition, we characterised cortical APLP2 mRNA levels. Quantitative RNA-RNA solution hybridisation-RNase protection was used to assay total APP. APP containing the Kunitz-type protease inhibitor (KPI) insert and APLP2 mRNA in mid-temporal and superior frontal cortices from apolipoprotein E-genotyped subjects with Alzheimer's disease, other neurological diseases and non-demented controls. Approximately 3 times more APP than APLP2 mRNA was detected and about 70% of total APP mRNA contained the KPI insert in the control subjects. Total APP and APLP2 mRNA levels were significantly reduced in Alzheimer's disease mid-temporal, but not superior frontal cortex, suggesting that regional reductions in these mRNA correlate with severity of disease pathology. A small significant increase in the proportion of APP KPI mRNA was seen in both cortical regions in Alzheimer's disease. Apolipoprotein E genotype did not influence cortical levels of total APP, APP KPI or APLP2 mRNA. Alzheimer's disease-related increases in tissue DNA content were seen in both regions studied, while tissue RNA levels were reduced in the positive disease controls. In summary, these results indicate that Alzheimer's disease is not associated with over-expression of either APP or APLP2 mRNA. Our findings reveal a disease-associated increase in the proportion of APP KPI-containing isoforms, and further investigation should clarify whether this predisposes affected individuals to A beta production and aggregation, or reflects later events such as gliosis and neuronal cell death.

Changes in expression of lymphocyte amyloid precursor protein mRNA isoforms in normal aging and Alzheimer's disease

We measured, by employing a quantitative reverse-transcriptase PCR procedure, the relative (to beta-actin) levels of amyloid precursor protein APP751 and APP770 mRNA isoforms in lymphocytes obtained from 64 cognitively intact subjects ranging in ages from 20 to 91 years and in 19 patients with sporadic Alzheimer's disease. A positive correlation was observed between the relative lymphocyte APP751 mRNA levels and subject age for the cognitively intact cohort. No difference in lymphocyte APP751 mRNA levels was observed between Alzheimer's disease patients and their age-matched controls (> 55 years of age). However, the ratio of lymphocyte APP751:APP770 mRNA levels was significantly lower in Alzheimer's disease subjects compared to the > 55-year-old cohort. This decreased ratio is most likely due to an average 31% increase in the lymphocyte APP770 isoform in Alzheimer's disease patients compared to 12% in the > 55-year-old cognitively intact group. Marked individual differences in amount of APP mRNA isoforms were encountered among all the subject groups and in the < or = 55-year-old cohort, a 10-fold variation in individual APP751 mRNA levels was observed. The relevance of these findings in lymphocytes to the pathogenesis of Alzheimer's disease is discussed.

Levels and alternative splicing of amyloid beta protein precursor (APP) transcripts in brains of APP transgenic mice and humans with Alzheimer's disease

Abnormal expression of human amyloid precursor protein (hAPP) gene products may play a critical role in Alzheimer's disease (AD). Recently, a transgenic model was established in which platelet-derived growth factor (PDGF) promoter-driven neuronal expression of an alternatively spliced hAPP minigene resulted in prominent AD-type neuropathology (Games, D., Adams, D., Alessandrini, R., Barbour, R., Berthelette, P., Blackwell, C., Carr, T., Clemens, J., Donaldson, T., Gillespie, F., Guido, T., Hagopian, S., Johnson-Wood, K., Khan, K., Lee, M., Leibowitz, P., Lieberburg, I., Little, S., Masliah, E., McConlogue, L., Montoya-Zavala, M., Mucke, L., Paganini, L., and Penniman, E. (1995) Nature 373, 523-527). Here we compared the levels and alternative splicing of APP transcripts in brain tissue of hAPP transgenic and nontransgenic mice and of humans with and without AD. PDGF-hAPP mice showed severalfold higher levels of total APP mRNA than did nontransgenic mice or humans, whereas their endogenous mouse APP mRNA levels were decreased. This resulted in a high ratio of mRNAs encoding mutated hAPP versus wild-type mouse APP. Modifications of hAPP introns 6, 7, and 8 in the PDGF-hAPP construct resulted in a prominent change in alternative splice site selection with transcripts encoding hAPP770 or hAPP751 being expressed at substantially higher levels than hAPP695 mRNA. Frontal cortex of humans with AD showed a subtle increase in the relative abundance of hAPP751 mRNA compared with normal controls. These data identify specific intron sequences that may contribute to the normal neuronspecific alternative splicing of APP pre-mRNA in vivo and support a causal role of hAPP gene products in the development of AD-type brain alterations.

Beta APP mRNA transcription is increased in cultured fibroblasts from the familial Alzheimer's disease-1 family

Familial (autosomal dominant) Alzheimer's disease (FAD) is a genetically heterogeneous disorder. Mutations in exons 16 and 17 of the amyloid beta-protein precursor (beta PP) gene currently account for less than 2% of FAD kindreds. No known defect in beta PP quantity, structure, or processing accounts for disease-associated beta-amyloid deposition in the majority of early-onset FAD kindreds. Only two out of a sample of 48 pedigrees (particularly the early onset FAD 4 kindred) contributed noticeably to evidence of linkage at the D21S16/13 and S1/S11 loci in the chromosomal region 21q21 [75]. Many early onset FAD pedigrees (including the FAD 1 and FAD 4 kindreds) show strong evidence of linkage to markers in the chromosome 14q24.3 region. Patients with trisomy 21 (Down's syndrome, DS) virtually always develop a histopathological phenotype indistinguishable from FAD, presumably on the basis of increased beta PP gene dosage and transcription. Whereas no beta PP gene duplication has been found in FAD, other mechanisms that augment beta PP production by effects at the transcriptional level could explain some FAD cases. Here, we report that cultured fibroblasts from affected members of the FAD 1 pedigree show a approximately 1.9 fold increase (P = 0.007) in beta PP mRNA levels compared to unaffected members when the cells are grown under stressed conditions in 0.5% serum. The elevated levels of beta PP mRNA in cells cultured in 0.5% serum also cosegregate with haplotypes in the 14q24.3 region when analyzed by linkage methods (LOD score = 3.26 at theta = 0.001). This is the chromosomal region to which FAD in this family has previously been mapped. As expected, fibroblasts from patients with DS used as a control show a similar beta PP mRNA increase. Fibroblasts from the FAD 4 pedigree did not show this defect under the conditions utilized here. beta PP and A beta protein levels were determined quantitatively after metabolic labeling and immunoprecipitation and found to increase 2.0 and 2.5 fold, respectively, in the fibroblasts from affected FAD 1 members. Finally, transient transfections of a beta PP promoter/chloramphenicol acetyl transferase reporter gene construct demonstrated a approximately 3-4 fold increase in beta PP promoter activity in affected fibroblasts from the FAD 1 but not the FAD 4 pedigree. Taken together, these data raise the possibility that an increase in beta PP transcription may underlie the AD phenotype in at least some of the chromosome 14-linked FAD families.

Gene expression in Alzheimer neocortex as a function of age and pathologic severity

Previous studies have shown a marked decline in neuronal and an increase in glial gene expression in Alzheimer's disease (AD) neocortex. Severity of pathologic changes may be greater in presenile AD (PAD) than in senile AD (SAD). We evaluated whether changes in transcript expression were altered as a function of age or pathologic severity. Northern analysis revealed a marked (> 50%) decline in expression of transcripts for the neurofilament light subunit and the major amyloid precursor protein (APP) isoforms in both PAD and SAD. Expression of these neuronal transcripts declined as a function of age in AD and control cases. Expression of the glial fibrillary acidic protein (GFAP) transcript was increased in AD, particularly in the presenile group. AD cases with larger numbers of neurofibrillary tangles had higher levels of GFAP transcript; AD cases with larger numbers of senile plaques had higher levels of APP695 transcript. We conclude that the neuronal mRNA decrements of AD are superimposed on an age-related decline. Age-related shift in expression of certain genes may account for the differences in pathologic severity of PAD and SAD.

Amyloid precursor protein gene expression in neural cell lines: influence of DNA cytosine methylation

Transcription of the gene encoding amyloid precursor protein (APP) varies in a cell-specific and developmentally regulated manner. The 5' region of this gene possesses a high frequency of CpG dinucleotides as well as copies of a GC-rich sequence, a potential trans factor binding element. These findings raise the possibility that DNA cytosine methylation could participate in the regulation of APP gene expression. We examined APP mRNA/18S rRNA ratio in three neural cell lines (N18TG2, SN6, SN17) cultured in 5-azacytidine (5-AZA), an inhibitor of maintenance methylase which results in loss of cytosine methylation in proliferating cells. Culture in 5-AZA globally reduced methylation in genomic DNA as assessed by an increase in HpaII restriction sites, reduced cytosine methylation in the APP gene as assessed by Southern blotting of HpaII digests, and increased APP mRNA steady state abundance in all studied cell lines. Cell lines re-acquired APP gene methylation 48 h after removal of 5-AZA from media. These results indicate that in vitro alteration of DNA methylation can affect APP gene expression, and suggest that the APP gene in neuronal cell lines may be rapidly inactivated in vitro, perhaps to neutralize its potential toxicity.

Nicotine effects on the regulation of amyloid precursor protein splicing, neurotrophin and glucose transporter RNA levels in aged rats

It has been reported that an inverse relationship exists between nicotine intake and the incidence of Alzheimer's Disease (AD). Although nicotine has been reported to induce c-fos, in the present study it was shown that this induction does not alter the accumulation of a number of transcripts associated with AD. Altered splicing patterns of Amyloid Precursor Protein (APP) and changes in neurotrophin and glucose transporter expression have been implicated in AD and behavioral deficits in rats. The effects of subacute administration of nicotine (12 mg/ml at 2.3 microliters/hr for 14 days) on the abundance levels of APP, glucose transporter (GLUT) and neurotrophin transcripts were determined by rtPCR in the hippocampus, cortex, and striatum of aged (22-24 months) male Wistar rats. No significant differences between saline and nicotine infused rats were detected for APP abundance levels or ratio of the various isoforms. However, both groups had a higher level of APP transcripts containing the Kunitz Protease Inhibitor (KPI) domain in the hippocampus than in either the cortex or striatum. The mean percentages of APP 695 for the two groups were 75% in the hippocampus and 82 and 81% in the cortex and striatum, respectively (P < 0.01). No changes in the abundance of GLUT1, GLUT3, nerve growth factor (NGF) or brain derived neurotrophic factor (BDNF) transcripts were detected. However, since both APP and GLUT1 are thought to be regulated post-transcriptionally, the present results do not rule out a change at the protein level. Further work will be required to determine whether nicotine can influence the expression of these proteins which affect neuronal function.

Alzheimer's disease and transgenic mice

Transgenic mice overexpressing the three major neuronal isoforms of the human amyloid precursor protein (APP), APP695, APP751, APP770 may provide an animal model for the analysis of the mechanisms and risk factors leading to amyloid deposition in Alzheimer's disease (AD) and Downs syndrome (DS). We have therefore generated transgenic mice expressing these isoforms under the control of the strong metallothionin promoter. Although we can demonstrate expression of transgenic APP in several tissues including brain, expression levels never exceeded those of the endogenous mouse APP. So far we have not been able to detect pathological changes resembling those of AD and DS. However we could demonstrate significant changes in spatial navigation tasks and motor behavior in the transgenic mice. The question remains open whether overexpression of APP is sufficient to induce Alzheimer pathology.

Age-related change in the proportion of amyloid precursor protein mRNAs in the gray matter of cerebral cortex

Alternative splicing of a transcript of amyloid precursor protein (APP) gene generates at least three types of mRNA coding for APP770, APP751, and APP695; the former two harbor, while the latter one lacks a Kunitz-type serine protease inhibitor (KPI). We compared, by using the RNase protection technique, APP mRNAs expression between gray and white matters in the frontal lobe, with special reference to Alzheimer's disease (AD) and aging. The proportions (y) of APP770 plus APP751 mRNAs in the white matter were nearly twice as much as those in the gray matter, both in control (non-AD) and AD brains; the difference between the two matters was statistically significant. Furthermore, in the gray matter of control, there was a positive correlation (y = 1.07 x-57.1, r = 0.899) between the age (x) and the proportion (y), but not in the white matter where the proportion varied markedly among individuals. In AD brains, no significant correlation was found in either of the two matters. These results indicated that the APP mRNAs proportion in the gray matter may serve as a molecular index of the brain aging in non-AD persons.

Aberrant proteolysis of the beta-amyloid precursor protein in familial Alzheimer's disease lymphoblastoid cells

Lymphoblastoid cells from patients with early-onset and late-onset familial Alzheimer's disease showed increased expressions of beta-amyloid precursor mRNA and protein as well as interleukin-1 and alpha 1-antichymotrypsin protein. Early-onset and late-onset familial Alzheimer's disease cells had greater production of 16-kDa beta-amyloid C-terminal preamyloid peptides than did normal cells. A pulse-chase experiment indicated that aberrant processing of this peptide resulted in its abnormal accumulation. Furthermore, the peptide prepared from early-onset familial Alzheimer's disease cells using formic acid could be separated into four discrete fragments. The N-terminal amino acid sequencing of each fragment indicated that the 16-kDa peptide was generated by cleavage, principally at the 30 amino acids N-terminal to beta-amyloid. Both the enhanced synthesis and aberrant processing of the beta-amyloid precursor protein, therefore, are basic processes associated with familial Alzheimer's disease lymphoblastoid cells.

Effects of interleukin-1 and interleukin-6 on metallothionein and amyloid precursor protein expression in human neuroblastoma cells. Evidence that interleukin-6 possibly acts via a receptor different from the 80-kDa interleukin-6 receptor

Since immunohistochemical studies indicated the presence of interleukin-6 in the cortices of patients with Alzheimer's disease, we were interested in the eventual biological effects of this cytokine on neuronal cells. We found that interleukin-6 and interleukin-1 induced metallothionein expression in a human neuronal (SH-SY5Y neuroblastoma) cell line. In contrast to metallothionein, amyloid precursor protein expression was unaffected by both cytokines. When searching in the same cell line for the expression of the classical 80-kDa interleukin-6 binding protein, which is part of the dimeric interleukin-6 receptor, we were unable to detect the respective mRNA. Our findings either indicate that the interleukin-6 receptor in these cells is expressed in extremely low levels or that interleukin-6 may act upon neuronal cells via a different, yet unknown neuronal receptor.

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.

Altered levels and splicing of the amyloid precursor protein in the adult rat hippocampus after treatment with DMSO or retinoic acid

Alzheimer's disease and cognitive impairment in rats has been associated with an increase in the percentage of amyloid precursor protein (APP) containing the KPI domain. It has recently been reported that retinoic acid (RA) is capable of increasing the levels and altering the splicing ratio of APP in cultured SH-SY5Y cells. The effects of peripherally administered RA (64 or 640 micrograms/kg; i.p.; q.d.) on the abundance of APP, the ratio of the three major isoforms, and the relative abundance of nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) were determined by rtPCR in the hippocampus of aged rats. Corresponding changes in choline acetyltransferase (ChAT) activity were also measured. Vehicle (DMSO) treated rats exhibited a 2 x (P < 0.01) increase in total APP and an 8 x (P < 0.001) decrease in the cyclophilin transcript. In addition, DMSO increased the percentage of APP 695 from 89% in saline treated rats to 94%. Treatment of RA in DMSO decreased the accumulation of total APP relative to cyclophilin at both the low (6.4 x; P < 0.01) and high (8 x; P < 0.05) dosages when compared to DMSO treated rats. Furthermore, the level of APP-695 decreased to 82% with low dosage of RA and 75% at high dosage of the total APP transcripts. No significant change in either NGF, NT-3, or BDNF transcripts were observed following low or high dosage RA administration relative to cyclophilin RNA nor was a change in ChAT activity detected at either of the dosages tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonisotopic in situ hybridization of amyloid beta protein precursor in Alzheimer's disease: expression in neurofibrillary tangle bearing neurons and in the microenvironment surrounding senile plaques

We have used nonisotopic in situ hybridization techniques with biotinylated junctional oligonucleotide probes to study expression of amyloid precursor protein (APP) 695 and 751 mRNA in the hippocampal formation of Alzheimer's disease. Both mRNAs are strongly expressed in neurons of the hippocampal formation, particularly in the dentate gyrus granule cells and the pyramidal neurons of CA3. The patterns of expression of neither APP695 nor APP751 mRNA correlate well with the stereotyped topography of neurofibrillary tangles or senile plaques, which occur primarily in CA1 and subiculum. We double-labeled in situ sections with immunohistochemical reagents for neurofibrillary tangles or senile plaques. Neurons that contain neurofibrillary tangles continue to express APP mRNA. The level of APP695 and APP751 was measured semiquantitatively by optical density measurements in neurons that were close to (within 25 microns) or father from a senile plaque (more than 100 microns). There was no increase in expression in neurons in the immediate microenvironment of senile plaques. Our results suggest that no major change in distribution or type of APP mRNA accompanies neurofibrillary tangle or senile plaque development.

Age-associated chromosome 21 loss in Down syndrome: possible relevance to mosaicism and Alzheimer disease

We previously observed low level mosaicism (2-4% normal cells) in phytohemagglutinin-stimulated peripheral blood lymphocytes (PBL) in 29% of a small group of elderly persons with Down syndrome (DS). An analysis of cytogenetic data on 154 trisomy 21 cases (age 1 day to 68 years) showed that the proportion of diploid cells in such cultures significantly increased (P < 0.005) with advancing age. Thus, the "occult" mosaicism in PBL of the elderly persons with DS is likely due to the accumulation of cells that have lost a chromosome 21. A consequence of chromosome 21 loss could be uniparental disomy of the 2n cells, a factor that might have significant biological consequences if some chromosome 21 genes are imprinted. Loss of a chromosome 21 from trisomic cells might result in tissue-specific mosaicism and "classical" mosaicism in different age groups. Chromosome 21 loss might also be relevant to the development of Alzheimer-type dementia in DS and in the general population.

NGF deprivation and neuronal degeneration trigger altered beta-amyloid precursor protein gene expression in the rat superior cervical ganglia in vivo and in vitro

In order to study the expression of beta-amyloid precursor protein (APP) isoforms during neuronal degeneration we have used the rat superior cervical ganglia (SCG) as an experimental model. In the neonate these sympathetic ganglia are nerve growth factor (NGF) dependent and in vivo administration of anti-NGF antiserum results in exaggerated neuronal degeneration. Analysis of APP mRNA transcripts in the SCG, following NGF deprivation, revealed a coincident decrease in APP695 and augmentation of APP751/770. These changes were specific to the SCG and were not seen in sensory ganglia. Subsequent in vitro studies, using primary dissociated cultures of sympathetic or cortical neurones, confirmed these changes in APP gene expression during neuronal degeneration. These observations may have important implications for the generation of beta-amyloid in Alzheimer's disease.

Differential regional and cellular distribution of beta-amyloid precursor protein messenger RNAs containing and lacking the Kunitz protease inhibitor domain in the brain of human, rat and mouse

The beta-amyloid precursor protein is the precursor of the main component of senile plaques (the beta-amyloid peptide or beta/A4) found in the brain of aged humans and, in higher amounts, in the brain of Alzheimer's disease and Down's syndrome subjects. Four different forms of beta-amyloid precursor protein messenger RNAs have been described in humans and rodents: beta-amyloid precursor protein 695, beta-amyloid precursor protein 714, beta-amyloid precursor protein 751 and beta-amyloid precursor protein 770 messenger RNAs (numbers corresponding to the number of encoded amino acids). The two latter forms are characterized by containing in their sequence a region with high homology to the Kunitz family of serine protease inhibitors. We have used oligonucleotide probes to study the distribution of the different messenger RNAs encoding each of the four beta-amyloid precursor proteins by in situ hybridization histochemistry in human, rat and mouse brain. We found that beta-amyloid precursor protein 695, beta-amyloid precursor protein 714 and beta-amyloid precursor protein 751 messenger RNAs were widely distributed in the human, rat and mouse brain and that their distribution was roughly similar in most brain areas in these three species. The distribution of beta-amyloid precursor protein 770 messenger RNA was not so wide and differed among the three species studied. beta-amyloid precursor protein 751 and 770 messenger RNAs were the only forms present at significant levels in rodent choroid plexus and meninges, while beta-amyloid precursor protein messenger RNA isoforms containing and lacking the Kunitz domain were detected in the human choroid plexus. We also observed that the relative levels of beta-amyloid precursor protein 751 and 770 messenger RNAs in the rat cerebral white matter as well as in the mouse and human striatum were higher than those of the beta-amyloid precursor protein messenger RNAs lacking the Kunitz domain. While the most abundant beta-amyloid precursor protein messenger RNAs in the brain of all three species under study were, in descending order, beta-amyloid precursor protein 695 and beta-amyloid precursor protein 751 messenger RNAs, the least abundant form was not the same for all species: in human it was beta-amyloid precursor protein 714 messenger RNA and in rat and mouse brain it was beta-amyloid precursor protein 770 messenger RNA. Our results show differences both inter- and intraspecies of the relative abundance and distribution of four beta-amyloid precursor protein messenger RNAs in rat, mouse and human brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Nerve growth factor-induced neuronal differentiation is accompanied by differential induction and localization of the amyloid precursor protein (APP) in PC12 cells and variant PC12S cells

PC12 cells and the morphological variant PC12S cells in culture were examined by immunochemical methods for the presence of the amyloid precursor protein (APP), before and after treatment with the nerve growth factor (NGF). In untreated PC12, untreated PC12S and in NGF-treated PC12 cells, APP was localized in the cytoplasm, whereas in NGF-treated PC12S cells, APP was localized at growth cones, processes and cytoplasm. In PC12 cells, three major forms of APP (695 and 751/770) were detected by Western blot. After NGF treatment, only the level of APP 695 was increased. Immunoprecipitation studies in PC12 cells revealed six protein species, corresponding to immature and mature forms of each of the three APP 695, 751 and 770 proteins. Addition of NGF increased the synthesis of the immature and mature forms of APP695. In PC12S cells, only the higher molecular weight forms of APP (751/770) were detected by both Western blot and immunoprecipitation. Addition of NGF had no effect on their levels. In both cell types, the level of the secreted form of APP showed a significant transient increase after NGF treatment. These results suggest that NGF can differentially regulate the molecular forms of APP and the localization of APP within the cell.

Amyloid precursor protein mRNA encoding the Kunitz protease inhibitor domain is increased by kainic acid-induced seizures in rat hippocampus

A 168-nucleotide exon, found in alternatively spliced amyloid precursor protein (APP) mRNAs, encodes a Kunitz protease inhibitor (KPI) domain. Kainic acid (ip) caused a selective increase of KPI mRNA in rat hippocampus. By in situ hybridization, KPI mRNA was induced in the neuronal layers of the hippocampus 11-12 h after the onset of kainate-induced seizures. The kainate-induced elevation of the KPI-containing APP-770 mRNA was blocked by pretreatment with the anticonvulsant pentobarbital. These data suggest that kainate-induced seizures cause alterations in APP RNA stability and/or processing in rat hippocampal neurons.

Expression of amyloid precursor protein mRNAs in endothelial, neuronal and glial cells: modulation by interleukin-1

The origin of beta-amyloid deposited in senile plaques in Alzheimer's disease (AD) is not known. We compared the expression of protein precursor of beta-amyloid (APP) in the cell types involved in plaque formation. The levels of APP mRNA were determined in primary rat neurons and glial cells in culture, human endothelial cells and in a murine brain-derived endothelial cell line. Northern blot analysis was performed using an APP cDNA probe to detect the general APP sequence and an oligonucleotide (40 mer) complementary to the sequence of the Kunitz protease inhibitor (APP-KPI). The APP mRNA transcripts were abundant in all three cell types. The highest level of APP, normalized to beta-actin mRNA content, was expressed in neurons, followed by glial cells, where the APP expression was similar (94%) while in endothelial cells was lower (53%). The proportion between APP-KPI mRNA and total APP mRNA was high in endothelial, intermediate in glial and low in neuronal cells. We compared the effects of exposure to interleukin-1 (IL-1), a cytokine involved in several biological processes and elevated in AD, on APP mRNA expression in neuronal, glial and endothelial cells. In human endothelial and in brain-derived murine endothelial cells we observed a similar increase (50%) of total APP mRNA or APP-KPI mRNA after treatment with human recombinant IL-1 beta. In neuronal cells, IL-1 (200 ng/ml) substantially increased APP mRNA (175%), detected with both probes. In glial cells, the expression of APP mRNA did not appear to be altered by IL-1 (50-400 ng/ml). The results suggest a role of IL-1 in the neuronal mechanisms related to beta-amyloid protein deposition in AD.

Age-related changes in the proportion of amyloid precursor protein mRNAs in Alzheimer's disease and other neurological disorders

In the human brain, alternative splicing of amyloid precursor protein (APP) gene transcript generates at least three types of mRNA coding for APP770, APP751 and APP695. The former two types harbor, but the latter one lacks a domain of Kunitz-type serine protease inhibitor (KPI). We studied, by using the RNase protection technique, the expression of APP mRNAs in brains of Alzheimer's disease (AD) and other neurological disorders with special reference to aging. We found that the ratio of (APP770 mRNA+APP751 mRNA)/APP695 mRNA in the frontal cortex increased approximately 1.5-fold in AD compared with other neurodegenerative or cerebrovascular disorders. The ratio in other neurological disorders did not change significantly from control even in their affected brain regions. On the other hand, we found a positive correlation between the ratio and age; the ratio (y) increased gradually with the advance of age (x) as expressed by y = 0.005x + 0.014 (r = 0.372) for the AD group, and y = 0.004x -0.037 (r = 0.486) for the non-AD group. These correlations indicate that the AD brain reached the same ratio of KPI-harboring to lacking APP mRNAs a few decades earlier than the non-AD brain in senescence. This finding of AD-specific and age-related change led us to the idea that a relative increase in KPI-harboring APPs over a KPI-lacking APP may perturb normal degradation of APPs, thereby leading to deposition of beta A4 protein as amyloid.

Amyloidogenesis in Alzheimer's disease: basic biology and animal models

A principal neuropathological hallmark of Alzheimer's disease is deposition of beta-amyloid, composed primarily of a 4 kD peptide, A beta. This peptide is derived from larger amyloid precursor proteins. The mechanisms that are responsible for A beta formation in vivo are unknown. Recently, transgenic strategies have been employed to test several hypothetical mechanisms in order to reproduce Alzheimer's disease-specific pathology in rodents.

The amyloid protein precursor of Alzheimer's disease is a mediator of the effects of nerve growth factor on neurite outgrowth

The beta A4 protein, the major component of the amyloid deposition characterizing Alzheimer's disease, derives from the amyloid protein precursor (APP), an integral membrane protein with soluble derivatives. The function of APP is unknown. Both soluble and membrane-associated human brain APP (10(-10) M) significantly increased (P less than 0.025) neurite length and branching in pheochromocytoma PC12 cells, but did not affect the number of neurites per cell. At higher concentrations, APP was cytotoxic, with a half-maximal concentration of 5 x 10(-9) M. Nerve growth factor (NGF) is known to affect APP expression in vivo and in vitro. Antibodies to APP specifically diminished the effects of NGF on neurite length and branching. Thus APP may act to mediate neurite outgrowth promotion by NGF.