Retromer binds the FANSHY sorting motif in SorLA to regulate amyloid precursor protein sorting and processing

sorLA is a sorting receptor for amyloid precursor protein (APP) genetically linked to Alzheimer's disease (AD). Retromer, an adaptor complex in the endosome-to-Golgi retrieval pathway, has been implicated in APP transport because retromer deficiency leads to aberrant APP sorting and processing and levels of retromer proteins are altered in AD. Here we report that sorLA and retromer functionally interact in neurons to control trafficking and amyloidogenic processing of APP. We have identified a sequence (FANSHY) in the cytoplasmic domain of sorLA that is recognized by the VPS26 subunit of the retromer complex. Accordingly, we characterized the interaction between the retromer complex and sorLA and determined the role of retromer on sorLA-dependent sorting and processing of APP. Mutations in the VPS26 binding site resulted in receptor redistribution to the endosomal network, similar to the situation seen in cells with VPS26 knockdown. The sorLA mutant retained APP-binding activity but, as opposed to the wild-type receptor, misdirected APP into a distinct non-Golgi compartment, resulting in increased amyloid processing. In conclusion, our data provide a molecular link between reduced retromer expression and increased amyloidogenesis as seen in patients with sporadic AD.     

γ‐Secretase binding sites in aged and Alzheimer's disease human cerebrum: the choroid plexus as a putative origin of CSF Aβ

Deposition of β ‐amyloid (Aβ) peptides, cleavage products of β‐amyloid precursor protein (APP) by β‐secretase‐1 (BACE1) and γ‐secretase, is a neuropathological hallmark of Alzheimer's disease (AD). γ‐Secretase inhibition is a therapeutical anti‐Aβ approach, although changes in the enzyme's activity in AD brain are unclear. Cerebrospinal fluid (CSF) Aβ peptides are thought to derive from brain parenchyma and thus may serve as biomarkers for assessing cerebral amyloidosis and anti‐Aβ efficacy. The present study compared active γ‐secretase binding sites with Aβ deposition in aged and AD human cerebrum, and explored the possibility of Aβ production and secretion by the choroid plexus (CP). The specific binding density of [³H]‐L‐685,458, a radiolabeled high‐affinity γ‐secretase inhibitor, in the temporal neocortex and hippocampal formation was similar for AD and control cases with similar ages and post‐mortem delays. The CP in post‐mortem samples exhibited exceptionally high [³H]‐L‐685,458 binding density, with the estimated maximal binding sites (Bmax) reduced in the AD relative to control groups. Surgically resected human CP exhibited APP, BACE1 and presenilin‐1 immunoreactivity, and β‐site APP cleavage enzymatic activity. In primary culture, human CP cells also expressed these amyloidogenic proteins and released Aβ40 and Aβ42 into the medium. Overall, our results suggest that γ‐secretase activity appears unaltered in the cerebrum in AD and is not correlated with regional amyloid plaque pathology. The CP appears to be a previously unrecognised non‐neuronal contributor to CSF Aβ, probably at reduced levels in AD.     

Amyloid precursor protein truncated at any of the γ-secretase sites is not cleaved to β-amyloid

βA4 secretion occurs upon processing of amyloid protein precursor (APP) by β-secretase (N-terminus of βA4) and γ-secretase (C-terminus). To determine the sequence of these activities and the processing intermediate of βA4, we expressed several truncated APP molecules in human HEK-293 cells. Immunofluorescence and biotinylation studies indicated that full-length APP or APP lacking the cytosolic domain both were located intracellularly, associated with the cell surface and secreted. APPs truncated after amino acid 40, 42, or 43 of βA4 were not inserted into cell membranes, were found intracellularly but not on the cell surface, and were efficiently secreted into the culture medium. The secretion of APP truncated at amino acid 40 of βA4 occurred without proteolytic processing. Neither βA4 nor P3 (the product of the α-secretase) was secreted from any of the APP molecules truncated at the γ-secretase sites. In sharp contrast to this, when the C-terminal 100 amino acids of APP were expressed (APP truncated at the N-terminus of βA4), a robust βA4 secretion was observed. Thus, the C-terminal fragment of APP produced by β-secretase activity is likely to be the processing intermediate of βA4. © 1996 Wiley-Liss, Inc.     

The location and trafficking routes of the neuronal retromer and its role in amyloid precursor protein transport

The retromer complex plays an important role in intracellular transport, is highly expressed in the hippocampus, and has been implicated in the trafficking of the amyloid precursor protein (APP). Nevertheless, the trafficking routes of the neuronal retromer and the role it plays in APP transport in neuronal processes remain unknown. Here we use hippocampal neuronal cultures to address these issues. Using fluorescence microscopy, we find that Vps35, the core element of the retromer complex, is in dendrites and axons, is enriched in endosomes and trans-Golgi network, and is found in APP-positive vesicles. Next, to identify the role the neuronal retromer plays in cargo transport, we infected hippocampal neurons with a lentivirus expressing shRNA to silence Vps35. By live fluorescence imaging, Vps35 deficiency was found to reduce the frequency, but not the kinetics, of long-range APP transport within neuronal processes. Supporting the interpretation that retromer promotes long-range transport, Vps35 deficiency led to increased APP in the early endosomes, in processes but not the soma. Finally, Vps35 deficiency was associated with increased levels of Aβ, a cleaved product of APP, increased colocalization of APP with its cleaving enzyme BACE1 in processes, and caused an enlargement of early endosomes. Taken together, our studies clarify the function of the neuronal retromer, and suggest specific mechanisms for how retromer dysfunction observed in Alzheimer's disease affects APP transport and processing.     

BACE1 Elevation is Involved in Amyloid Plaque Development in the Triple Transgenic Model of Alzheimer’s Disease: Differential Aβ Antibody Labeling of Early-Onset Axon Terminal Pathology

β-amyloid precursor protein (APP) and presenilins mutations cause early-onset familial Alzheimer's disease (FAD). Some FAD-based mouse models produce amyloid plaques, others do not. β-Amyloid (Aβ) deposition can manifest as compact and diffuse plaques; it is unclear why the same Aβ molecules aggregate in different patterns. Is there a basic cellular process governing Aβ plaque pathogenesis? We showed in some FAD mouse models that compact plaque formation is associated with a progressive axonal pathology inherent with increased expression of β-secretase (BACE1), the enzyme initiating the amyloidogenic processing of APP. A monoclonal Aβ antibody, 3D6, visualized distinct axon terminal labeling before plaque onset. The present study was set to understand BACE1 and axonal changes relative to diffuse plaque development and to further characterize the novel axonal Aβ antibody immunoreactivity (IR), using triple transgenic AD (3xTg-AD) mice as experimental model. Diffuse-like plaques existed in the forebrain in aged transgenics and were regionally associated with increased BACE1 labeled swollen/sprouting axon terminals. Increased BACE1/3D6 IR at axon terminals occurred in young animals before plaque onset. These axonal elements were also co-labeled by other antibodies targeting the N-terminal and mid-region of Aβ domain and the C-terminal of APP, but not co-labeled by antibodies against the Aβ C-terminal and APP N-terminal. The results suggest that amyloidogenic axonal pathology precedes diffuse plaque formation in the 3xTg-AD mice, and that the early-onset axonal Aβ antibody IR in transgenic models of AD might relate to a cross-reactivity of putative APP β-carboxyl terminal fragments.     

Decrease in brain soluble amyloid precursor protein β (sAPPβ) in Alzheimer's disease cortex

Amyloid-β peptide (Aβ) is generated by sequential cleavage of the amyloid precursor protein (APP) by β-site amyloid precursor protein cleaving enzyme 1 (β-secretase, or BACE1) and γ-secretase. Several reports demonstrate increased BACE1 enzymatic activity in brain and cerebrospinal fluid (CSF) from Alzheimer's disease (AD) subjects, suggesting that an increase in BACE1-mediated cleavage of APP drives amyloid pathophysiology in AD. BACE1 cleavage of APP leads to the generation of a secreted N-terminal fragment of APP (sAPPβ). To relate BACE1 activity better to endogenous APP processing in AD and control brains, we have directly measured brain sAPPβ levels using a novel APP β-site specific enzyme-linked immunosorbent assay. We demonstrate a significant reduction in brain cortical sAPPβ levels in AD compared with control subjects. In the same brain samples, BACE1 activity was unchanged, full-length APP and sAPPα levels were significantly reduced, and Aβ peptides were significantly elevated. In conclusion, a reduction in cortical brain sAPPβ together with unchanged BACE1 activity suggests that this is due to reduced full-length APP substrate in late-stage AD subjects. These results highlight the need for multiparameter analysis of the amyloidogenic process to understand better AD pathophysiology in early vs. late-stage AD.     

Presenilin 1 mutations increase amyloid precursor protein production and proteolysis in Xenopus laevis oocytes

Recent findings suggest that Presenilin 1 (PS1) mutations play a major role in the development of Alzheimer's disease (AD) by increasing the production of the beta amyloid peptide (A beta). The exact mechanism whereby mutations in PS1 lead to this effect is not clear. To examine the question of how PS1 might be involved in amyloid precursor protein (APP) processing, we constructed a chimera of human APP695 fused at the C-terminal to enhanced green fluorescent protein (EGFP). This construct was injected into Xenopus laevis oocytes in the presence of wild type PS1 or one of three PS1 mutations associated with AD. The cellular location of the APP695-EGFP construct was examined by fluorescent confocal microscopy. In addition, membrane fractions of oocytes expressing APP695-EGFP in the presence or absence of wild type or mutant forms of PS1 were evaluated by Western blot analysis. The results show that APP695-EGFP is primarily expressed on the cell surface and undergoes limited cleavage. Specifically, APP695 was cleaved in the A beta domain to generate three distinct C-terminal fragments that correspond in length to stubs expected after cleavage with alpha-, beta- and gamma-secretase, respectively. The presence of wild type PS1 not only increased the production of proteolytic C-terminal fragments of APP, but the production of APP itself. These findings were even more pronounced in the presence of all three PS1 mutations, suggesting that PS1 mutations may lead to over-expression of APP not just increased gamma-secretase activity.     

Restoring Soluble Amyloid Precursor Protein α Functions as a Potential Treatment for Alzheimer's Disease

Soluble amyloid precursor protein α (sAPPα), a secreted proteolytic fragment of nonamyloidogenic amyloid precursor protein (APP) processing, is known for numerous neuroprotective functions. These functions include but are not limited to proliferation, neuroprotection, synaptic plasticity, memory formation, neurogenesis, and neuritogenesis in cell culture and animal models. In addition, sAPPα influences amyloid‐β (Aβ) production by direct modulation of APP β‐secretase proteolysis as well as Aβ‐related or unrelated tau pathology, hallmark pathologies of Alzheimer's disease (AD). Thus, the restoration of sAPPα levels and functions in the brain by increasing nonamyloidogenic APP processing and/or manipulation of its signaling could reduce AD pathology and cognitive impairment. It is likely that identification and characterization of sAPPα receptors in the brain, downstream effectors, and signaling pathways will pave the way for an attractive therapeutic target for AD prevention or intervention. © 2016 Wiley Periodicals, Inc.     

Proteolytic processing of the Alzheimer's disease amyloid precursor protein in brain and platelets

Proteolytic processing of the amyloid precursor protein by beta -and gamma-secretases results in the production of Alzheimer's disease (AD) Abeta amyloid peptides. Modulation of secretase activity is being investigated as a potential therapeutic approach. Recent studies with human brain have revealed that the beta-secretase protein, BACE, is increased in cortex of AD patients. Analysis of betaCTF (or C99), the amyloid precursor protein (APP) product of BACE cleavage that is the direct precursor to Abeta, shows it is also elevated in AD, underlying the importance of beta-secretase cleavage in AD pathogenesis. The C-terminal product of gamma-secretase cleavage of APP, epsilonCTF (or AICD), is enriched in human brain cortical nuclear fractions, a subcellular distribution appropriate for a putative involvement of APP cytosolic domain in signal transduction. Analysis of AD cortex samples, particularly that of a carrier of a familial APP mutation, suggests that processing of APP transmembrane domain generates an alternative CTF product. All these particularities observed in the AD brain demonstrate that APP processing is altered in AD. The transgenic mouse model Tg2576 seems to be a promising laboratory tool to test potential modulators of Abeta formation. Indeed, C-terminal products of alpha-, beta-, and gamma-secretase cleavage are readily detectable in the brain of these transgenic mice. Finally, the finding of the same secretase products in platelets and neurons make platelets a potentially useful and easily accessible clinical tool to monitor effects of novel therapies based on inhibition of beta- or gamma-secretase.     

Effects of cholesterol transport inhibitor U18666A on APP metabolism in rat primary astrocytes

Amyloid β (Aβ) peptides generated from the amyloid precursor protein (APP) play an important role in the degeneration of neurons and development of Alzheimer's disease (AD). Current evidence indicates that high levels of cholesterol—which increase the risk of developing AD—can influence Aβ production in neurons. However, it remains unclear how altered level/subcellular distribution of cholesterol in astrocytes can influence APP metabolism. In this study, we evaluated the effects of cholesterol transport inhibitor U18666A—a class II amphiphile that triggers redistribution of cholesterol within the endosomal–lysosomal (EL) system—on APP levels and metabolism in rat primary cultured astrocytes. Our results revealed that U18666A increased the levels of the APP holoprotein and its cleaved products (α‐/β‐/η‐CTFs) in cultured astrocytes, without altering the total levels of cholesterol or cell viability. The cellular levels of Aβ_1‐40 were also found to be markedly increased, while secretory levels of Aβ_1‐40 were decreased in U18666A‐treated astrocytes. We further report a corresponding increase in the activity of the enzymes regulating APP processing, such as α‐secretase, β‐secretase, and γ‐secretase as a consequence of U18666A treatment. Additionally, APP‐cleaved products are partly accumulated in the lysosomes following cholesterol sequestration within EL system possibly due to decreased clearance. Interestingly, serum delipidation attenuated enhanced levels of APP and its cleaved products following U18666A treatment. Collectively, these results suggest that cholesterol sequestration within the EL system in astrocytes can influence APP metabolism and the accumulation of APP‐cleaved products including Aβ peptides, which can contribute to the development of AD pathology.     

Low-Density Lipoprotein Receptor-Related Protein-1 (LRP1) C4408R Mutant Promotes Amyloid Precursor Protein (APP) α-Cleavage in Vitro

Previous studies have demonstrated that the low-density lipoprotein receptor-related protein-1 (LRP1) plays conflicting roles in Alzheimer’s disease (AD) pathogenesis, clearing β-amyloid (Aβ) from the brain while also enhancing APP endocytosis and resultant amyloidogenic processing. We have recently discovered that co-expression of mutant LRP1 C-terminal domain (LRP1-CT C4408R) with Swedish mutant amyloid precursor protein (APPswe) in Chinese hamster ovary (CHO) cells decreases Aβ production, while also increasing sAPPα and APP α-C-terminal fragment (α-CTF), compared with CHO cells expressing APPswe alone. Surprisingly, the location of this mutation on LRP1 corresponded with the α-secretase cleavage site of APP. Further experimentation confirmed that in CHO cells expressing APPswe or wild-type APP (APPwt), co-expression of LRP1-CT C4408R decreases Aβ and increases sAPPα and α-CTF compared with co-expression of wild-type LRP1-CT. In addition, LRP1-CT C4408R enhanced the unglycosylated form of LRP1-CT and reduced APP endocytosis as determined by flow cytometry. This finding identifies a point mutation in LRP1 which slows LRP1-CT-mediated APP endocytosis and amyloidogenic processing, while enhancing APP α-secretase cleavage, thus demonstrating a potential novel target for slowing AD pathogenesis.     

Effects of Edaravone on Amyloid-β Precursor Protein Processing in SY5Y-APP695 Cells

Previous reports have revealed that reactive oxygen species (ROS) is involved in the development of Alzheimer’s disease (AD), and recent studies indicate that free radical-generating systems can regulate amyloid-β precursor protein (APP) processing. Edaravone is a novel free radical scavenger currently used to reduce cerebral damages after acute cerebral infarction. In the present study, we used SH-SY5Y cells stably transfected with the human “Swedish” APP mutation APP695 (SY5Y-APP695swe) as an in vitro model to investigate the effect of edaravone on APP processing. The result showed that edaravone treatment for 24 h down-regulated β-amyloid (Aβ) production in a dose-dependent manner. Moreover, edaravone modulated APP processing by increasing α-secretase-derived APP fragments and decreasing β-secretase-derived APP fragments. In addition, the mRNA and protein levels of insulin degrading enzyme (IDE) and neprilysin (NEP), two key Aβ degrading enzymes, were not changed after edaravone administration. Taken together, our data suggested that edaravone played an important role in regulating Aβ production by enhancing the non-amyloidogenic pathway and inhibiting the amyloidogenic pathway. Thus, edaravone may be potentially useful for treating Alzheimer’s disease (AD).     

Wild type TDP-43 induces neuro-inflammation and alters APP metabolism in lentiviral gene transfer models

The transactivation DNA-binding protein (TDP-43) pathology is associated with fronto-temporal lobar dementia (FTLD) with ubiquitinated inclusions and some cases of Alzheimer's disease (AD). Proteolytic fragments of β-amyloid precursor protein (βAPP) are detected in AD as well as the cerebrospinal fluid (CSF) from FTLD and Amyotrophic Lateral Sclerosis (ALS) patients, suggesting alteration in APP processing. Because of the overlap in TDP-43 pathology between FTLD and AD, we sought to determine whether there is a relationship between TDP-43 and APP metabolism. We generated gene transfer models using lentiviral delivery of human TDP-43 and Aβ(1-42) into the rat primary motor cortex and examined their role 2 weeks post-injection. Expression of TDP-43 and/or Aβ(1-42) increase pro-inflammatory markers, including Interleukin (IL)-6, tumor necrosis factor (TNF-α), glial neurofibrillary proteins (GFAP) and ionized calcium binding adaptor molecule 1 (IBA-1). Lentiviral Aβ(1-42) up-regulates endogenous TDP-43 and promotes its phosphorylation, aggregation and cleavage into 35 kDa fragments. Inversely, lentiviral TDP-43 expression increases the levels and activity of β-secretase (BACE), accelerating production of APP C-terminal fragments (C99) and Aβ(1-40). Here we show that TDP-43 up-regulates APP metabolism and suggest a mechanistic link between TDP-43 and BACE.     

Clioquinol reduces zinc accumulation in neuritic plaques and inhibits the amyloidogenic pathway in AβPP/PS1 transgenic mouse brain

Metal dyshomeostasis in the brain helps promote amyloid-β (Aβ) deposition in Alzheimer's disease (AD). Therefore, targeting the interactions between metal and Aβ is a potential therapeutic approach for AD. The metal chelator, clioquinol (CQ), is thought to reduce Aβ deposits in the AD transgenic mouse brain, and attenuate the clinical symptoms of AD patients. However, whether oral administration of CQ reduces zinc accumulation in Aβ plaques and inhibits the amyloidogenic pathway have not been properly established in AD transgenic mice. By means of autometallographic analysis, we show for the first time that both the number and size of the zinc-containing plaques were significantly reduced in the brain of amyloid-β protein precursor (AβPP)/presenilin 1 (PS1) double transgenic mice treated with CQ (30 mg/kg/day) orally for 2 months. This was accompanied by a reduction in Aβ burden in the CQ-treated mouse brain. Furthermore, CQ treatment markedly reduced the expression levels of AβPP protein, the β-site of AβPP cleaving enzyme 1 (BACE1), PS1, and the secreted β-secretase-derived fragments of AβPP (sAβPPβ). The present data indicate that CQ is able to reduce zinc accumulation in the neuritic plaques and inhibit amyloidogenic AβPP processing in the AβPP/PS1 mouse brain.     

Production and increased detection of amyloid β protein and amyloidogenic fragments in brain microvessels,meningeal vessels and choroid plexus in Alzheimer's disease

Recent advances indicate soluble amyloid β (Aβ) protein is produced constitutively during normal metabolism of the amyloid precursor protein (APP). This has not been directly examined in human brain vascular tissues. Using a panel of well-characterized antibodies, here we show that increased amounts of soluble Aβ were found in isolated vascular tissues from AD subjects compared to age-matched controls without significant Alzheimer pathology. Immunocytochemical analyses of isolated vessel preparations showed characteristic transverse patterns of Aβ deposits in large vessels with smooth muscle, however, fine Aβ deposits were apparent even in capillaries. A proportion of such Aβ protein and potentially amyloidogenic carboxyl terminal fragments were released by solubilization and disruption of the vascular basement membrane by collagenase treatments. We further demonstrated by in vitro metabolic labelling that soluble Aβ or an Aβ-like peptide is associated and produced by cerebral microvessels, meningeal vessels and the choroid plexus isolated postmortem from human as well as rat brain. Compared to those from young rats, cerebral microvessels from aging rats showed increased release of carboxyl terminal fragments of APP and Aβ-like peptide. Our observations provide the first direct demonstration that human vascular tissues produce soluble Aβ, a product of the secretory pathway in APP processing. Our findings also suggest that aging associated alterations in the basement membranes are a factor in Aβ accumulation that results in vascular amyloid deposition, the principal feature of cerebral amyloid angiopathy.     

Positive-negative epitope-tagging of beta amyloid precursor protein to identify inhibitors of A beta processing

In this report, a novel positive-negative epitope tagging approach was developed to study the cellular processing of beta amyloid precursor protein (beta APP). Amino acids centered around the alpha-secretase cleavage site within the A beta sequence were replaced with residues comprising an epitope for which high-affinity monoclonal antibodies are commercially available. The resulting mutant beta APP cDNAs were expressed in human embryonic kidney cells (HEK 293). Cleavage of labeled beta APP by beta- and gamma-secretase(s) results in the release of an epitope-tagged A beta peptide, whereas cleavage by alpha-secretase results in destruction of the epitope. Highly sensitive and specific immunoassays were developed to study processing of this labeled beta APP via the amyloidogenic pathway. Secretion of epitope-tagged A beta was prevented by MDL 28170, a previously described gamma-secretase inhibitor. Confocal microscopic studies revealed that processing and cellular trafficking of epitope-tagged beta APP was not different from wild-type beta APP. These results suggest that positive-negative epitope-tagged beta APP is normally processed within the cell and may be used to identify secretase inhibitors as therapeutics for Alzheimer's disease.     

Cross-Linking of Cell Surface Amyloid Precursor Protein Leads to Increased β-Amyloid Peptide Production in Hippocampal Neurons: Implications for Alzheimer's Disease

The accumulation of the β-amyloid peptide (Aβ) in Alzheimer's disease (AD) is thought to play a causative role in triggering synaptic dysfunction in neurons, leading to their eventual demise through apoptosis. Aβ is produced and secreted upon sequential cleavage of the amyloid precursor protein (APP) by β-secretases and γ-secretases. However, while Aβ levels have been shown to be increased in the brains of AD patients, little is known about how the cleavage of APP and the subsequent generation of Aβ is influenced, or whether the cleavage process changes over time. It has been proposed that Aβ can bind APP and promote amyloidogenic processing of APP, further enhancing Aβ production. Proof of this idea has remained elusive because a clear mechanism has not been identified, and the promiscuous nature of Aβ binding complicates the task of demonstrating the idea. To work around these problems, we used an antibody-mediated approach to bind and cross-link cell-surface APP in cultured rat primary hippocampal neurons. Here we show that cross-linking of APP is sufficient to raise the levels of Aβ in viable neurons with a concomitant increase in the levels of the β-secretase BACE1. This appears to occur as a result of a sorting defect that stems from the caspase-3-mediated inactivation of a key sorting adaptor protein, namely GGA3, which prevents the lysosomal degradation of BACE1. Together, our data suggest the occurrence of a positive pathogenic feedback loop involving Aβ and APP in affected neurons possibly allowing Aβ to spread to nearby healthy neurons.     

β-amyloid precursor protein fragments and lysosomal dense bodies are found in rat brain neurons after ventricular infusion of leupeptin

Infusion of the serine and thiol protease inhibitor, leupeptin, is known to cause a reduction of fast axoplasmic transport, and accumulation of lysosomal dense bodies in neuronal perikarya. We have found these dense bodies in hippocampal and cerebellar neurons contain ubiquitin conjugated proteins. We now demonstrate that these accumulated neuronal lysosomes are labeled by antisera to the cytoplasmic, transmembrane and extracellular domains of β-amyloid precursor protein (APP) and also that lysosomal APP is fragmented. This in vivo model confirms that neurons can process APP via a lysosomal pathway and that neuronal lysosomes in vivo contain both N-terminal and potentially amyloidogenic C-terminal fragments of APP. We also show that increased APP immunoreactivity after leupeptin treatment is seen first in neurons and later in astrocytes. On recovery from infusion, APP N-terminal immunoreactivity diminishes whilst C-terminal reactivity remains in neurons. These findings are consistent with production in whole brain of potentially amyloidogenic fragments of APP within neuronal lysosomes in perikarya and dendrites implying that neurons may play a role in forming the β-amyloid of plaques.     

Amyloid precursor protein gene analysis in familial Alzheimer's disease cases: a lack of mutations in exons 16 and 17

The beta-amyloid precursor protein (APP) gene (on chromosome 21), Presenilin 1 (PS1) gene (on chromosome 14) and Presenilin 2 (PS2) gene (on chromosome 1) are responsible for autosomal dominant early-onset Alzheimer's disease (EOAD). Missense mutations in these genes cause abnormal APP processing with subsequent overproduction of amyloidogenic and toxic A beta (42 peptide. A mutational analysis of APP, PS1, and PS2 genes can be used for both symptomatic and presymptomatic genetic testing and counselling in familial Alzheimer's disease (FAD). To contribute to our knowledge on genetic background of Alzheimer's disease in Poland, we screened APP mutations in a sample of familial EOAD cases from Poznan region. We did not find pathogenic mutations within exons 16 and 17 of the APP gene. Our study confirmed that APP gene mutations account only for a very small portion of FAD.