Identification of the probable structure of the sAPPα-GABABR1a complex and theoretical solutions for such cases.

Amyloid precursor protein (APP) is the core of the pathogenesis of Alzheimer's disease (AD). Existing studies have shown that the soluble secreted APP (sAPPα) fragment obtained from the hydrolysis of APP by α-secretase has a synaptic function. Thereinto, a nine-residue fragment (APP9mer) of the extension domain region of sAPPα can bind directly and selectively to the N-terminal sushi1 domain (SD1) of the γ-aminobutyric acid type B receptor subunit 1a (GABABR1a) protein, which can influence synaptic transmission and plasticity by changing the GABABR1a conformation. APP9mer is a highly flexible, disordered region, and as such it is difficult to experimentally determine the optimal APPmer-SD1 binding complex. In this study we constructed two types of APP9mer-SD1 complexes through molecular docking and molecular dynamics simulation, aiming to explore the recognition function and mechanism of the specific binding of APP9mer with SD1, from which the most probable APPmer-SD1 model conformation is predicted. All the data from the analyses of RMSD, RMSF, PCA, DCCM and MM/PBSA binding energy as well as comparison with the experimental dissociation constant Kd suggest that 2NC is the most likely conformation to restore the crystal structure of the experimental APP9mer-SD1 complex. Of note, the key recognition residues of APP9mer are D24, D25, D27, W29 and W30, which mainly act on the 9-45 residue domain of SD1 (consisting of two loops and three short ß-chains at the N-terminus of SD1). The mini-model with key residues identified establishes the molecular basis with deep insight into the interaction between APP and GABABR1a and provides a target for the development of therapeutic strategies for modulating GABABR1a-specific signaling in neurological and psychiatric disorders. More importantly, the study offers a theoretical solution for how to determine a biomolecular structure with a highly flexible, disordered fragment embedded within. The flexible fragment involved in a protein structure has to be deserted usually during the structural determination with experimental methods (e.g. X-ray crystallography, etc.).

Rapid evolution of mammalian APLP1 as a synaptic adhesion molecule.

Amyloid precursor protein (APP) family members are involved in essential neuronal development including neurite outgrowth, neuronal migration and maturation of synapse and neuromuscular junction. Among the APP gene family members, amyloid precursor-like protein 1 (APLP1) is selectively expressed in neurons and has specialized functions during synaptogenesis. Although a potential role for APLP1 in neuronal evolution has been indicated, its precise evolutionary and functional contributions are unknown. This study shows the molecular evolution of the vertebrate APP family based on phylogenetic analysis, while contrasting the evolutionary differences within the APP family. Phylogenetic analysis showed 15 times higher substitution rate that is driven by positive selection at the stem branch of the mammalian APLP1, resulting in dissimilar protein sequences compared to APP/APLP2. Docking simulation identified one positively selected site in APLP1 that alters the heparin-binding site, which could affect its function, and dimerization rate. Furthermore, the evolutionary rate covariation between the mammalian APP family and synaptic adhesion molecules (SAMs) was confirmed, indicating that only APLP1 has evolved to gain synaptic adhesion property. Overall, our results suggest that the enhanced synaptogenesis property of APLP1 as one of the SAMs may have played a role in mammalian brain evolution.

Selenomethionine Attenuates the Amyloid-ß Level by Both Inhibiting Amyloid-ß Production and Modulating Autophagy in Neuron-2a/AßPPswe Cells.

Alzheimer's disease (AD) is a complex and progressive neurological disorder, and amyloid-ß (Aß) has been recognized as the major cause of AD. Inhibiting Aß production and/or enhancing the clearance of Aß to reduce its levels are still the effective therapeutic strategies pursued in anti-AD research. In previous studies, we have reported that selenomethionine (Se-Met), a major form of selenium in animals and humans with significant antioxidant capacity, can reduce both amyloid-ß (Aß) deposition and tau hyperphosphorylation in a triple transgenic mouse model of AD. In this study, a Se-Met treatment significantly decreased the Aß levels in Neuron-2a/AßPPswe (N2asw) cells, and the anti-amyloid effect of Se-Met was attributed to its ability to inhibit Aß generation by suppressing the activity of BACE1. Furthermore, both the LC3-II/LC3-I ratio and the number of LC3-positive puncta were significantly decreased in Se-Met-treated cells, suggesting that Se-Met also promoted Aß clearance by modulating the autophagy pathway. Subsequently, Se-Met inhibited the initiation of autophagy through the AKT-mTOR-p70S6K signaling pathway and enhanced autophagic turnover by promoting autophagosome-lysosome fusion and autophagic clearance. Our results further highlight the potential therapeutic effects of Se-Met on AD.

Pre-plaque conformational changes in Alzheimer's disease-linked Aß and APP.

Reducing levels of the aggregation-prone Aß peptide that accumulates in the brain with Alzheimer's disease (AD) has been a major target of experimental therapies. An alternative approach may be to stabilize the physiological conformation of Aß. To date, the physiological state of Aß in brain remains unclear, since the available methods used to process brain tissue for determination of Aß aggregate conformation can in themselves alter the structure and/or composition of the aggregates. Here, using synchrotron-based Fourier transform infrared micro-spectroscopy, non-denaturing gel electrophoresis and conformational specific antibodies we show that the physiological conformations of Aß and amyloid precursor protein (APP) in brain of transgenic mouse models of AD are altered before formation of amyloid plaques. Furthermore, focal Aß aggregates in brain that precede amyloid plaque formation localize to synaptic terminals. These changes in the states of Aß and APP that occur prior to plaque formation may provide novel targets for AD therapy.

Familial Alzheimer's Disease Mutations within the Amyloid Precursor Protein Alter the Aggregation and Conformation of the Amyloid-ß Peptide.

Most cases of Alzheimer's disease (AD) are sporadic, but a small percentage of AD cases, called familial AD (FAD), are associated with mutations in presenilin 1, presenilin 2, or the amyloid precursor protein. Amyloid precursor protein mutations falling within the amyloid-ß (Aß) sequence lead to a wide range of disease phenotypes. There is increasing evidence that distinct amyloid structures distinguished by amyloid conformation-dependent monoclonal antibodies have similarly distinct roles in pathology. It is possible that this phenotypic diversity of FAD associated with mutations within the Aß sequence is due to differences in the conformations adopted by mutant Aß peptides, but the effects of FAD mutations on aggregation kinetics and conformational and morphological changes of the Aß peptide are poorly defined. To gain more insight into this possibility, we therefore investigated the effects of 11 FAD mutations on the aggregation kinetics of Aß, as well as its ability to form distinct conformations recognized by a panel of amyloid conformation-specific monoclonal antibodies. We found that most FAD mutations increased the rate of aggregation of Aß. The FAD mutations also led to the adoption of alternative amyloid conformations distinguished by monoclonal antibodies and resulted in the formation of distinct aggregate morphologies as determined by transmission electron microscopy. In addition, several of the mutant peptides displayed a large reduction in thioflavin T fluorescence, despite forming abundant fibrils indicating that thioflavin T is a probe of conformational polymorphisms rather than a reliable indicator of fibrillization. Taken together, these results indicate that FAD mutations falling within the Aß sequence lead to dramatic changes in aggregation kinetics and influence the ability of Aß to form immunologically and morphologically distinct amyloid structures.

Nanolithography of Amyloid Precursor Protein Cleavage with ß-Secretase by Atomic Force Microscopy.

Cleavage of the amyloid precursor protein (APP) by secretases is critical in neural cell processes including the pathway for neural cell proliferation and that underlying the pathogenesis of Alzheimer's disease (AD). Understanding the mechanism of APP cleavage and development of a convenient tool for the accurate evaluation of APP cleavage intensity by secretases are very important in the development of new AD therapeutic targets. In this study, we developed a sophisticated technology to evaluate the APP cleavage mechanism at the nano-molecular level by atomic force microscopic (AFM) nanolithography. APP was modified on a glass substrate; nanolithography of APP cleavage by ß-secretase-modified AFM probe scanning was achieved. APP cleavage was verified by the AFM imaging and the fluorescent immunostaining. The present method will be very useful in understanding the molecular level of the APP cleavage mechanism by ß-secretase in vitro; this method will facilitate inhibitor screening for the therapeutic target of AD.

Synaptic changes in the dentate gyrus of APP/PS1 transgenic mice revealed by electron microscopy.

Numerous studies have reported widespread synaptic dysfunction or loss in early stages of both Alzheimer disease (AD) patients and animal models; it is widely accepted that synapse loss is the major structural correlate of cognitive dysfunction. Elucidation of the changes that may affect synapses is crucial for understanding the pathogenic mechanisms underlying AD, but ultrastructural preservation of human postmortem brain tissue is often poor, and classical methods for quantification of synapses have significant technical limitations. We previously observed changes in dendritic spines in plaque-free regions of the neuropil of the dentate gyrus of double-transgenic APP/PS1 (amyloid precursor protein/presenilin 1) model mice by light microscopy. Here, we used electron microscopy to examine possible synaptic alterations in this region. We used standard stereologic techniques to determine numbers of synapses per volume. We were able to reconstruct and analyze thousands of synapses and their 3-dimensional characteristics using a focused ion beam/scanning electron microscope and 3-dimensional reconstruction software (EspINA), which performs semiautomated segmentation of synapses. Our results show that both numbers of synapses per volume and synaptic morphology are affected in plaque-free regions of APP/PS1 mice. Therefore, changes in the number and morphology of synapses seem to be widespread alterations in this animal model.

Ultrastructural studies in APP/PS1 mice expressing human ApoE isoforms: implications for Alzheimer's disease.

Alzheimer's disease is characterized in part by extracellular aggregation of the amyloid-ß peptide in the form of diffuse and fibrillar plaques in the brain. Electron microscopy (EM) has made an important contribution in understanding of the structure of amyloid plaques in humans. Classical EM studies have revealed the architecture of the fibrillar core, characterized the progression of neuritic changes, and have identified the neurofibrillary tangles formed by paired helical filaments (PHF) in degenerating neurons. Clinical data has strongly correlated cognitive impairment in AD with the substantial synapse loss observed in these early ultrastructural studies. Animal models of AD-type brain amyloidosis have provided excellent opportunities to study amyloid and neuritic pathology in detail and establish the role of neurons and glia in plaque formation. Transgenic mice overexpressing mutant amyloid precursor protein (APP) alone with or without mutant presenilin 1 (PS1), have shown that brain amyloid plaque development and structure grossly recapitulate classical findings in humans. Transgenic APP/PS1 mice expressing human apolioprotein E isoforms also develop amyloid plaque deposition. However no ultrastructural data has been reported for these animals. Here we show results from detailed EM analysis of amyloid plaques in APP/PS1 mice expressing human isoforms of ApoE and compare these findings with EM data in other transgenic models and in human AD. Our results show that similar to other transgenic animals, APP/PS1 mice expressing human ApoE isoforms share all major cellular and subcellular degenerative features and highlight the identity of the cellular elements involved in Aß deposition and neuronal degeneration.

Imaging amyloid precursor protein in vivo: an axonal transport assay.

Fusion of fluorescent probes to axonally transported proteins represents an established approach that enables live imaging of axonal transport. In this approach, in vivo examination of fluorescent particle dynamics provides information about the length, directionality, and the velocity by which axonally transported proteins travel along axons. Analysis of these parameters provides information about the distribution of axonal proteins and their dynamics in and between different subcellular compartments. Establishing the movement behavior of amyloid precursor protein within axons indicated that live imaging approaches offer the opportunity to significantly enhance our understanding of the biology as well as pathology of axonal transport. This chapter provides a fluorescence-based procedure for measuring axonal transport of APP in cultured newborn mouse hippocampal neurons.

Aß(39-42) modulates Aß oligomerization but not fibril formation.

Recently, certain C-terminal fragments (CTFs) of Aß42 have been shown to be effective inhibitors of Aß42 toxicity. Here, we examine the interactions between the shortest CTF in the original series, Aß(39-42), and full-length Aß. Mass spectrometry results indicate that Aß(39-42) binds directly to Aß monomers and to the n = 2, 4, and 6 oligomers. The Aß42:Aß(39-42) complex is further probed using molecular dynamics simulations. Although the CTF was expected to bind to the hydrophobic C-terminus of Aß42, the simulations show that Aß(39-42) binds at several locations on Aß42, including the C-terminus, other hydrophobic regions, and preferentially in the N-terminus. Ion mobility-mass spectrometry (IM-MS) and electron microscopy experiments indicate that Aß(39-42) disrupts the early assembly of full-length Aß. Specifically, the ion-mobility results show that Aß(39-42) prevents the formation of large decamer/dodecamer Aß42 species and, moreover, can remove these structures from solution. At the same time, thioflavin T fluorescence and electron microscopy results show that the CTF does not inhibit fibril formation, lending strong support to the hypothesis that oligomers and not amyloid fibrils are the Aß form responsible for toxicity. The results emphasize the role of small, soluble assemblies in Aß-induced toxicity and suggest that Aß(39-42) inhibits Aß-induced toxicity by a unique mechanism, modulating early assembly into nontoxic hetero-oligomers, without preventing fibril formation.

Neuropathology of the recessive A673V APP mutation: Alzheimer disease with distinctive features.

Mutations of three different genes, encoding ß-amyloid precursor protein (APP), presenilin 1 and presenilin 2 are associated with familial Alzheimer's disease (AD). Recently, the APP mutation A673V has been identified that stands out from all the genetic defects previously reported in these three genes, since it causes the disease only in the homozygous state (Di Fede et al. in Science 323:1473-1477, 2009). We here provide the detailed neuropathological picture of the proband of this family, who was homozygous for the APP A673V mutation and recently came to death. The brain has been studied by histological and immunohistochemical techniques, at the optical and ultrastructural levels. Cerebral Aß accumulation and tau pathology were severe and extensive. Peculiar features were the configuration of the Aß deposits that were of large size, mostly perivascular and exhibited a close correspondence between the pattern elicited by amyloid stainings and the labeling obtained with immunoreagents specific for Aß40 or Aß42. Moreover, Aß deposition spared the neostriatum while deeply affecting the cerebellum, and therefore was not in compliance with the hierarchical topographical sequence of involvement documented in sporadic AD. Therefore, the neuropathological picture of familial AD caused by the APP recessive mutation A673V presents distinctive characteristics compared to sporadic AD or familial AD inherited as a dominant trait. Main peculiar features are the morphology, structural properties and composition of the Aß deposits as well as their topographic distribution in the brain.

Human pro-islet amyloid polypeptide (ProIAPP(1-48)) forms amyloid fibrils and amyloid spherulites in vitro.

Deposition of beta sheets of islet amyloid polypeptide (IAPP) in pancreatic tissue is implicated in the aetiology of type 2 diabetes mellitus (T2DM). IAPP is cleaved from its precursor protein, pro-islet amyloid polypeptide (ProIAPP) and incomplete cleavage results in ProIAPP(1-48), which is found co-deposited with IAPP. Cu(II) prevents IAPP from forming amyloid and herein we investigated if it would also prevent ProIAPP(1-48) from forming beta sheets. Excess Cu(II) prevented ProIAPP(1-48) from forming amyloid and additionally reversed the formation of beta sheets in pre-formed fibrils of the peptide. The latter was also true for ProIAPP(1-48) fibrils formed in the presence of Al(III). An unexpected finding was the formation of spherulites of ProIAPP(1-48) which were only observed in preparations which included Al(III). The spherulites were 40-100 microm in diameter and stained positively for Al(III) suggesting a role for this metal in their formation. The abolition by Cu(II) of the propensity of ProIAPP(1-48) to form amyloid may have important implications for the treatment of T2DM. The immediate significance for diabetes of the equally novel observation of spherulites of ProIAPP(1-48) is unknown though, as with spherulites of Abeta(42) in Alzheimer's disease, there may be implications for the aetiology of the disease.

Degradation of soluble and fibrillar amyloid beta-protein by matrix metalloproteinase (MT1-MMP) in vitro.

The progressive accumulation of beta-amyloid (Abeta) in senile plaques and in the cerebral vasculature is the hallmark of Alzheimer's disease and related disorders. Degradation of Abeta by specific proteolytic enzymes is an important process that regulates its levels in brain. Matrix metalloproteinase 2 (MMP2) was shown to be expressed in reactive astrocytes surrounding amyloid plaques and may contribute to Abeta degradation. Membrane type 1 (MT1) MMP is the physiological activator for the zymogen pro-MMP2. Here, we show that, in addition to MMP2, its activator MT1-MMP is also expressed in reactive astrocytes in regions with amyloid deposits in transgenic mice. Using a Cos-1 cell expression system, we demonstrated that MT1-MMP can degrade exogenous Abeta40 and Abeta42. A purified soluble form of MT1-MMP degraded both soluble and fibrillar Abeta peptides in a time-dependent manner, yielding specific degradation products. Mass spectrometry analysis identified multiple MT1-MMP cleavage sites on soluble Abeta40 and Abeta42. MT1-MMP-mediated Abeta degradation was inhibited with the general MMP inhibitor GM6001 or the specific MT1-MMP inhibitor tissue inhibitor of metalloproteinases 2. Furthermore, in situ experiments showed that purified MT1-MMP degraded parenchymal fibrillar amyloid plaques that form in the brains of Abeta precursor protein transgenic mice. Together, these findings indicate that MT1-MMP possesses Abeta degrading activity in vitro.

Amyloidogenesis abolished by proline substitutions but enhanced by lipid binding.

The influence of lipid molecules on the aggregation of a highly amyloidogenic segment of human islet amyloid polypeptide, hIAPP20-29, and the corresponding sequence from rat has been studied by all-atom replica exchange molecular dynamics (REMD) simulations with explicit solvent model. hIAPP20-29 fragments aggregate into partially ordered beta-sheet oligomers and then undergo large conformational reorganization and convert into parallel/antiparallel beta-sheet oligomers in mixed in-register and out-of-register patterns. The hydrophobic interaction between lipid tails and residues at positions 23-25 is found to stabilize the ordered beta-sheet structure, indicating a catalysis role of lipid molecules in hIAPP20-29 self-assembly. The rat IAPP variants with three proline residues maintain unstructured micelle-like oligomers, which is consistent with non-amyloidogenic behavior observed in experimental studies. Our study provides the atomic resolution descriptions of the catalytic function of lipid molecules on the aggregation of IAPP peptides.

Autophagy, amyloidogenesis and Alzheimer disease.

Autophagy is the sole pathway for organelle turnover in cells and is a vital pathway for degrading normal and aggregated proteins, particularly under stress or injury conditions. Recent evidence has shown that the amyloid beta peptide is generated from amyloid beta precursor protein (APP) during autophagic turnover of APP-rich organelles supplied by both autophagy and endocytosis. Abeta generated during normal autophagy is subsequently degraded by lysosomes. Within neurons, autophagosomes and endosomes actively form in synapses and along neuritic processes but efficient clearance of these compartments requires their retrograde transport towards the neuronal cell body, where lysosomes are most concentrated. In Alzheimer disease, the maturation of autophagolysosomes and their retrograde transport are impeded, which leads to a massive accumulation of ;autophagy intermediates' (autophagic vacuoles) within large swellings along dystrophic and degenerating neurites. The combination of increased autophagy induction and defective clearance of Abeta-generating autophagic vacuoles creates conditions favorable for Abeta accumulation in Alzheimer disease.

Presenilin-1-mediated retention of APP derivatives in early biosynthetic compartments.

Processing of the amyloid precursor protein (APP) leads to the production of amyloid-beta (Abeta), the major component of extracellular plaques in the brains of Alzheimer's disease (AD) patients. Presenilin-1 (PS-1) plays a key role in the final step of Abeta formation, the gamma-secretase cleavage. Previously, we showed that PS-1 is retained in pre-Golgi compartments by incorporation into COPI-coated membranes of the vesicular tubular clusters (VTCs) between endoplasmic reticulum (ER) and Golgi complex. Here, we show that PS-1 also mediates the retention of the beta-cleavage-derived APP-C-terminal fragment (CTFbeta) and/or Abeta in pre-Golgi membranes. Overexpression of PS-1 increased the percentage of CTFbeta and/or Abeta in VTCs as well as their distribution to COPI-coated VTC membranes. By contrast, overexpression of the dominant-negative aspartate mutant PS-1(D257A) or PS-knockout decreased incorporation of these APP derivatives into COPI-coated membranes. Sorting of APP derivatives to COPI-coated VTC membranes was not depending on the APP cytosolic tail. In post-Golgi compartments, PS-1 expression enhanced the association of full-length APP/APPs with endosomal compartments at the expense of plasma membrane-bound APP. We conclude that PS-1, in addition to its role in gamma-secretase cleavage, is also required for the subcellular routing of APP and its derivatives. Malfunctioning of PS-1 in this role may have important consequences for the progress of AD.

Structural role of glycine in amyloid fibrils formed from transmembrane alpha-helices.

Amyloid fibrils associated with diseases such as Alzheimer's are often derived from the transmembrane helices of membrane proteins. It is known that the fibrils have a cross-beta-sheet structure where main chain hydrogen bonding occurs between beta-strands in the direction of the fibril axis. However, the structural basis for how the membrane-spanning helix is converted into a beta-sheet or how protofibrils associate into fibrils is not known. Here, we use a model peptide corresponding to a portion of the single transmembrane helix of glycophorin A to investigate the structural role of glycine in amyloid-like fibrils formed from transmembrane helices. Glycophorin A contains a GxxxG motif that is found in many transmembrane sequences including that of the amyloid precursor protein and prion protein. We propose that glycine, which mediates helix interactions in membrane proteins, also provides key packing motifs when it occurs in beta-sheets. We show that glycines in the glycophorin A transmembrane helix promote extended beta-strand formation when the helix partitions into aqueous environments and stabilize the packing of beta-sheets in the formation of amyloid-like fibrils. We demonstrate that fibrillization can be disrupted with a new class of inhibitors that target the molecular grooves created by glycine.

Intra- and extracellular Abeta and PHF in clinically evaluated cases of Alzheimer's disease.

Temporal cortical sections from postmortem brains of individuals without any dementing condition and with different degrees of severity of Alzheimer's disease (AD) evaluated by the Clinical Dementia Rating scale (CDR 0-CDR 3) were analyzed using immunohistochemical procedures. To demonstrate the amyloid-beta-peptide (Abeta) deposition and the neurofibrillary pathology, two monoclonal antibodies were used, a human CERAD Abeta (10D5) antibody raised against the N-terminal region of the Abeta-peptide, and an antibody raised against paired helical filaments (PHF-1). The neuron cell bodies and the glial cells were also recognized by two polyclonal antibodies raised, respectively, against the protein gene peptide (PGP 9.5) and glial fibrillary acidic protein (GFAP). Directly related to severity of AD, progressive deposits of Abeta-peptide were found within cortical pyramidal-like neurons and forming senile plaques. Ultrastructurally, Abeta-peptide deposits were related to neuronal intracytoplasmic organelles, such as the ER, the mitochondria, the Nissl bodies and lipofuscin. We have also found that the intracellular deposition of the Abeta peptide is a neuropathological finding prior to the appearance of PHF-immunoreactive structures. We suggest that the intracellular Abeta deposition in cortical pyramidal neurons is a first neurodegenerative event in AD development and that it is involved in cell dysfunction, neuronal death, and plaque formation.

Origin and turnover of microglial cells in fibrillar plaques of APPsw transgenic mice.

Activated microglial cells are an integral component of fibrillar plaques in brains of subjects with Alzheimer's disease (AD) and in brains of transgenic mice overexpressing amyloidogenic fragments of human amyloid precursor protein (APP). The aim of this ultrastructural study of fibrillar plaques was to characterize the origin of microglial cells involved in cored plaque formation. Computer-aided three-dimensional reconstruction of plaques and microvessels in APPsw transgenic mice shows perivascular development of cored plaques. Perivascular location of almost all examined plaques and the infiltration at the interface between vessels and plaques with cells of monocyte/microglia lineage indicates that plaques are formed by inflammatory cells of blood origin. The increase in the number of microglial cells from 1 or 2 in an early plaque to more than 100 in a several-month-old plaque does not result in plaque degradation, but is associated with amyloid core growth and progression of neuronal degeneration, and suggests that recruitment of inflammatory cells of blood origin sustains plaque growth. Infiltration of the plaque with cells of blood origin and degeneration of 10-46% of inflammatory cells in large plaques, which is especially frequent at the interface between capillary wall and plaque, suggest their accelerated turnover.

Diverse fibrillar peptides directly bind the Alzheimer's amyloid precursor protein and amyloid precursor-like protein 2 resulting in cellular accumulation.

The Alzheimer's disease Abeta peptide can increase the levels of cell-associated amyloid precursor protein (APP) in vitro. To determine the specificity of this response for Abeta and whether it is related to cytotoxicity, we tested a diverse range of fibrillar peptides including amyloid-beta (Abeta), the fibrillar prion peptides PrP106-126 and PrP178-193 and human islet-cell amylin. All these peptides increased the levels of APP and amyloid precursor-like protein 2 (APLP2) in primary cultures of astrocytes and neurons. Specificity was shown by a lack of change to amyloid precursor-like protein 1, tau-1 and cellular prion protein (PrP(c)) levels. APP and APLP2 levels were elevated only in cultures exposed to fibrillar peptides as assessed by electron microscopy and not in cultures treated with non-fibrillogenic peptide variants or aggregated lipoprotein. We found that PrP106-126 and the non-toxic but fibril-forming PrP178-193 increased APP levels in cultures derived from both wild-type and PrP(c)-deficient mice indicating that fibrillar peptides up-regulate APP through a non-cytotoxic mechanism and irrespective of parental protein expression. Fibrillar PrP106-126 and Abeta peptides bound recombinant APP and APLP2 suggesting the accumulation of these proteins was mediated by direct binding to the fibrillated peptide. This was supported by decreased APP accumulation following extensive washing of the cultures to remove fibrillar aggregates. Pre-incubation of fibrillar peptide with recombinant APP18-146, the putative fibril binding site, also abrogated the accumulation of APP. These findings show that diverse fibrillogenic peptides can induce accumulation of APP and APLP2 and this mechanism could contribute to pathogenesis in neurodegenerative disorders.