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Biomedical subjects

Konrad Beyreuther

Publications and source records attributed to Konrad Beyreuther.

At least 19 recordsLinked to original sources
PubMed2006

PAT1a modulates intracellular transport and processing of amyloid precursor protein (APP), APLP1, and APLP2.

Understanding the intracellular transport of the beta-amyloid precursor protein (APP) is a major key to elucidate the regulation of APP processing and thus beta-amyloid peptide generation in Alzheimer disease pathogenesis. APP and its two paralogues, APLP1 and APLP2 (APLPs), are processed in a very similar manner by the same protease activities. A putative candidate involved in APP transport is protein interacting with APP tail 1 (PAT1), which was reported to interact with the APP intracellular domain. We show that PAT1a, which is 99.0% identical to PAT1, binds to APP, APLP1, and APLP2 in vivo and describe their co-localization in trans-Golgi network vesicles or endosomes in primary neurons. We further demonstrate a direct interaction of PAT1a with the basolateral sorting signal of APP/APLPs. Moreover, we provide evidence for a direct role of PAT1a in APP/APLP transport as overexpression or RNA interference-mediated knockdown of PAT1a modulates APP/APLPs levels at the cell surface. Finally, we show that PAT1a promotes APP/APLPs processing, resulting in increased secretion of beta-amyloid peptide. Taken together, our data establish PAT1a as a functional link between APP/APLPs transport and their processing.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Alzheimer's centennial legacy: prospects for rational therapeutic intervention targeting the Abeta amyloid pathway.

It is now 100 years since the nosological definition of Alzheimer's disease emerged. In the first 80 years, very little progress was made in understanding the mechanisms that caused the brain to degenerate in a remarkably specific fashion (amyloid accumulation with neurofibrillary changes). Over the past 20 years, there has been an explosion of knowledge which continues today at an exponential rate. The molecular pathways underlying the synaptic dysfunction in Alzheimer's disease have delivered many validated therapeutic and diagnostic targets. A variety of therapeutic strategies aimed at disease modification are now in clinical development.

Alzheimer Disease↗
PubMed2006

GM1 up-regulates Ubiquilin 1 expression in human neuroblastoma cells and rat cortical neurons.

GM1 ganglioside was reported to mediate the amyloid beta-protein (Abeta) secretion and accumulation in the pathogenesis of Alzheimer's disease (AD). The objective of this project was to comprehend the underlying molecular changes related to amyloid beta-protein precursor (APP) processing pathway induced by GM1. Using suppression subtractive hybridisation (SSH), we detected one prominent sequence with increased expression in human neuroblastoma cells that stably transfected with human APP695 cDNA treated with GM1. This transcript has high identity to human Ubiquilin 1 gene. Differential expression was initially confirmed by dot blot hybridization. This result was further authenticated with quantitative real-time polymerase chain reaction (RT-PCR) analysis. Furthermore, using Western blots, we discovered that GM1 stimulated the expression of Ubiquilin 1 in human neuroblastoma cells and rat cortical neurons while other gangliosides Asialo-GM1 and GD1b did not. Ubiquilin 1 is one of the candidate genes of AD, which have been shown to modulate the gamma-secretase components in the proteolytic processing of APP, and is therefore a putative candidate for further investigation of GM1 mechanisms in the etiology and pathology of AD.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Delineating common molecular mechanisms in Alzheimer's and prion diseases.

The structure of the infectious agent responsible for prion diseases has not been fully characterized, but evidence points to a beta-rich conformer of the host-encoded prion protein. Amyloid-beta peptide (Abeta), a proteolytic fragment generated from the amyloid precursor protein, has been implicated as the toxic molecule involved in the pathogenesis of Alzheimer's disease. The mechanism of Abeta toxicity might be mediated through the coordination of redox-active transition-metal ions such as copper leading to the generation of reactive oxygen species, coupled with the propensity to interact with lipid bilayers. Key sequence and chemical similarities between prion protein (PrP) and Abeta indicate that similar therapeutic strategies might be applicable for the treatment of Alzheimer's and prion diseases.

Alzheimer Disease↗
PubMed2006

Subcellular trafficking of the amyloid precursor protein gene family and its pathogenic role in Alzheimer's disease.

Changes in the intracellular transport of amyloid precursor protein (APP) affect the extent to which APP is exposed to alpha- or beta-secretase in a common subcellular compartment and therefore directly influence the degree to which APP undergoes the amyloidogenic pathway leading to generation of beta-amyloid. As the presynaptic regions of neurons are thought to be the main source of beta-amyloid in the brain, attention has been focused on axonal APP trafficking. APP is transported along axons by a fast, kinesin-dependent anterograde transport mechanism. Despite the wealth of in vivo and in vitro data that have accumulated regarding the connection of APP to kinesin transport, it is not yet clear if APP is coupled to its specific motor protein via an intracellular interaction partner, such as the c-Jun N-terminal kinase-interacting protein, or by yet another unknown molecular mechanism. The cargo proteins that form a functional complex with APP are also unknown. Due to the long lifespan, and vast extent, of neurons, in particular axons, neurons are highly sensitive to changes in subcellular transport. Recent in vitro and in vivo studies have shown that variations in APP or tau affect mitochondrial and synaptic vesicle transport. Further, it was shown that this axonal dysfunction might lead to impaired synaptic plasticity, which is crucial for neuronal viability and function. Thus, changes in APP and tau expression may cause perturbed axonal transport and changes in APP processing, contributing to cognitive decline and neurodegeneration in Alzheimer's disease.

Alzheimer Disease↗
PubMed2006

Pathways to the discovery of the Abeta amyloid of Alzheimer's disease.

Many participants played a role in discovering the composition and sequence of the Abeta amyloid of Alzheimer's disease. This sequence enabled the cloning of the amyloid precursor protein (APP), which elucidated its proteolytic origin from the membrane of neurons. The proteolytic enzymes which process APP and the Abeta fragment itself are now the prime validated drug targets for therapeutic intervention.

Alzheimer Disease↗
PubMed2005

Homo- and heterodimerization of APP family members promotes intercellular adhesion.

The amyloid precursor protein (APP) plays a central role in Alzheimer's disease, but its physiological function and that of its mammalian paralogs, the amyloid precursor-like proteins 1 and 2 (APLPs), is still poorly understood. APP has been proposed to form dimers, a process that could promote cell adhesion via trans-dimerization. We investigated the dimerization and cell adhesion properties of APP/APLPs and provide evidence that all three paralogs are capable of forming homo- and heterocomplexes. Moreover, we show that trans-interaction of APP family proteins promotes cell-cell adhesion in a homo- and heterotypic fashion and that endogenous APLP2 is required for cell-cell adhesion in mouse embryonic fibroblasts. We further demonstrate interaction of all the three APP family members in mouse brain, genetic interdependence, and molecular interaction of APP and APLPs in synaptically enriched membrane compartments. Together, our results provide evidence that homo- and heterocomplexes of APP/APLPs promote trans-cellular adhesion in vivo.

Amyloid beta-Protein Precursor↗
PubMed2005

Locomotor activity and evoked dopamine release are reduced in mice overexpressing A30P-mutated human alpha-synuclein.

We have generated a transgenic mouse line overexpressing mutated human A30P alpha-synuclein under the control of the prion-related protein promoter. Immunohistology revealed mutated human A30P alpha-synuclein protein in numerous brain areas, but no gross morphological changes, Lewy bodies, or loss of dopaminergic cell bodies. The transgenic mice displayed decreased locomotion, impaired motor coordination, and balance. In vivo voltammetry showed that A30P mice responded to longer stimulation of the ascending dopaminergic pathways with less dopamine release in striatum and had a slower rate of dopamine decline after repeated stimulations or after alpha-methyl-p-tyrosine-HCl treatment. However, dopamine re-uptake or transporter levels were similar in transgenic and control mice. Our data provide evidence that overexpression of mutated human A30P alpha-synuclein in mice leads to a reduced size of the dopamine storage pool. This is in agreement with the previously postulated involvement of alpha-synuclein in the turnover of transmitter vesicles and may explain the observed motor deficits in A30P mice.

Animals↗
PubMed2004

Interference of human and Drosophila APP and APP-like proteins with PNS development in Drosophila.

The view that only the production and deposition of Abeta plays a decisive role in Alzheimer's disease has been challenged by recent evidence from different model systems, which attribute numerous functions to the amyloid precursor protein (APP). To investigate the potential cellular functions of APP and its paralogs, we use transgenic Drosophila as a model. Upon overexpression of the APP-family members, transformations of cell fates during the development of the peripheral nervous system were observed. Genetic analysis showed that APP, APLP1 and APLP2 induce Notch gain-of-function phenotypes, identified Numb as a potential target and provided evidence for a direct involvement of Disabled and Neurotactin in the induction of the phenotypes. The severity of the induced phenotypes not only depended on the dosage and the particular APP-family member but also on particular domains of the molecules. Studies with Drosophila APPL confirmed the results obtained with human proteins and the analysis of flies mutant for the appl gene further supports an involvement of APP-family members in neuronal development and a crosstalk between the APP family and Notch.

Amino Acid Motifs↗
PubMed2004

Tenuigenin treatment decreases secretion of the Alzheimer's disease amyloid beta-protein in cultured cells.

Amyloid beta-protein (A beta) is a pivotal pathological factor in Alzheimer's disease (AD). Tenuigenin, extracted from the Chinese herb Polygala tenuifolia, seems to ameliorate the reduction in cholinergic function on rat models induced by A beta. To examine this therapeutic effect, we tested whether Tenuigenin could inhibit secretion of A beta in neuroblastoma cells stably transfected with two amyloid precursor protein (APP) constructs: the APP695 cDNA (SH-SY5Y APP695) and the C-terminal 99 amino acid residues of APP plus the signal peptide (SH-SY5Y SPA4CT). Tenuigenin inhibited the secretion of A beta and the C-terminal 99 amino acids of APP (C99) in SH-SY5Y APP695 cells, but did not change the A beta and C99 levels in SH-SY5Y SPA4CT cells. Fluorescence Resonance Energy Transfer (FRET) assays showed that Tenuigenin inhibited the proteolytic activities of BACE1 (beta-secretase) on its substrate in vitro. In addition, Tenuigenin did not demonstrate any cytotoxic effects, nor did it affect APP mRNA expression, holoAPP synthesis or sAPP alpha secretion. Our data suggest that Tenuigenin can inhibit the secretion of A beta in SH-SY5Y APP 695 cells via BACE1 inhibition. Taken together, these results suggest that Tenuigenin may be worthy of future study as an anti-AD drug.

Amyloid Precursor Protein Secretases↗
PubMed2004

Tyrosine gated electron transfer is key to the toxic mechanism of Alzheimer's disease beta-amyloid.

Alzheimer's disease (AD) is characterized by the presence of neurofibrillary tangles and amyloid plaques, which are abnormal protein deposits. The major constituent of the plaques is the neurotoxic beta-amyloid peptide (Abeta); the genetics of familial AD support a direct role for this peptide in AD. Abeta neurotoxicity is linked to hydrogen peroxide formation. Abeta coordinates the redox active transition metals, copper and iron, to catalytically generate reactive oxygen species. The chemical mechanism underlying this process is not well defined. With the use of density functional theory calculations to delineate the chemical mechanisms that drive the catalytic production of H2O2 by Abeta/Cu, tyrosine10 (Y10) was identified as a pivotal residue for this reaction to proceed. The relative stability of tyrosyl radicals facilitates the electron transfers that are required to drive the reaction. Confirming the theoretical results, mutation of the tyrosine residue to alanine inhibited H2O2 production, Cu-induced radicalization, dityrosine cross-linking, and neurotoxicity.

Alanine↗
PubMed2004

The proteolytic processing of the amyloid precursor protein gene family members APLP-1 and APLP-2 involves alpha-, beta-, gamma-, and epsilon-like cleavages: modulation of APLP-1 processing by n-glycosylation.

Amyloid precursor protein (APP) processing is of major interest in Alzheimer's disease research, since sequential cleavages by beta- and gamma-secretase lead to the formation of the 4-kDa amyloid Abeta protein peptide that accumulates in Alzheimer's disease brain. The processing of APP involves proteolytic conversion by different secretases leading to alpha-, beta-, gamma-, delta-, and epsilon-cleavages. Since modulation of these cleavages represents a rational therapeutic approach to control amyloid formation, its interference with the processing of the members of the APP gene family is of considerable importance. By using C-terminally tagged constructs of APLP-1 and APLP-2 and the untagged proteins, we have characterized their proteolytic C-terminal fragments produced in stably transfected SH-SY5Y cells. Pharmacological manipulation with specific protease inhibitors revealed that both homologues are processed by alpha- and gamma-secretase-like cleavages, and that their intracellular domains can be released by cleavage at epsilon-sites. APLP-2 processing appears to be the most elaborate and to involve alternative cleavage sites. We show that APLP-1 is the only member of the APP gene family for which processing can be influenced by N-glycosylation. Additionally, we were able to detect p3-like fragments of APLP-1 and p3-like and Abeta-like fragments of APLP-2 in the media of stably transfected SH-SY5Y cells.

Amyloid Precursor Protein Secretases↗
PubMed2004

Iron inhibits neurotoxicity induced by trace copper and biological reductants.

The extracellular microenvironment of the brain contains numerous biological redox agents, including ascorbate, glutathione, cysteine and homocysteine. During ischemia/reperfusion, aging or neurological disease, extracellular levels of reductants can increase dramatically owing to dysregulated homeostasis. The extracellular concentrations of transition metals such as copper and iron are also substantially elevated during aging and in some neurodegenerative disorders. Increases in the extracellular redox capacity can potentially generate neurotoxic free radicals from reduction of Cu(II) or Fe(III), resulting in neuronal cell death. To investigate this in vitro, the effects of extracellular reductants (ascorbate, glutathione, cysteine, homocysteine or methionine) on primary cortical neurons was examined. All redox agents except methionine induced widespread neuronal oxidative stress and subsequent cell death at concentrations occurring in normal conditions or during neurological insults. This neurotoxicity was totally dependent on trace Cu (>or=0.4 microM) already present in the culture medium and did not require addition of exogenous Cu. Toxicity involved generation of Cu(I) and H(2)O(2), while other trace metals did not induce toxicity. Surprisingly, administration of Fe(II) or Fe(III) (>or=2.5 microM) completely abrogated reductant-mediated neurotoxicity. The potent protective activity of Fe correlated with Fe inhibiting reductant-mediated Cu(I) and H(2)O(2) generation in cell-free assays and reduced cellular Cu uptake by neurons. This demonstrates a novel role for Fe in blocking Cu-mediated neurotoxicity in a high reducing environment. A possible pathogenic consequence for these phenomena was demonstrated by abrogation of Fe neuroprotection after pre-exposure of cultures to the Alzheimer's amyloid beta peptide (Abeta). The loss of Fe neuroprotection against reductant toxicity was greater after treatment with human Abeta1-42 than with human Abeta1-40 or rodent Abeta1-42, consistent with the central role of Abeta1-42 in Alzheimer's disease. These findings have important implications for trace biometal interactions and free radical-mediated damage during neurodegenerative illnesses such as Alzheimer's disease and old-age dementia.

Animals↗
PubMed2004

APP intracellular domain is increased and soluble Abeta is reduced with diet-induced hypercholesterolemia in a transgenic mouse model of Alzheimer disease.

Cholesterol is one of multiple factors, other than familial genetic mutations, that can influence amyloid-beta peptide (Abeta) metabolism and accumulation in Alzheimer disease (AD). The effect of a high-cholesterol diet on amyloid precursor protein (APP) processing in brain has not been thoroughly studied. This study was designed to further investigate the role of cholesterol in the production of Abeta and APP intracellular domain (AICD) in 12-month-old Tg2576 transgenic mice. The mice were maintained on a high-cholesterol diet for 6 weeks. We found that diet-induced hypercholesterolemia increased the APP cytosolic fragment AICD and reduced sAPPalpha in the Tg2576 mice compared to the mice on a control basal diet. In addition, the levels of detergent-extracted Abeta40 were reduced, although no change in guanidine-extracted Abeta levels was observed. Full-length APP, alpha/betaC-terminal fragment (alpha/betaCTF), and beta-secretase (BACE) were not different in the cholesterol-fed mice compared to the control diet-fed mice. This study suggests that a high dietary cholesterol in aged mice may not only influence Abeta metabolism, but also regulate the AICD levels. AICD has a proposed role in signal transduction and apoptosis, hence modulation of AICD production could be an alternative mechanism by which cholesterol contributes to AD pathogenesis.

Alzheimer Disease↗
PubMed2004

Cell-type-specific processing of the amyloid precursor protein by Presenilin during Drosophila development.

The cleavage of proteins within their transmembrane domain by Presenilin (PS) has an important role in different signalling pathways and in Alzheimer's disease. Nevertheless, not much is known about the regulation of PS activity. It has been suggested that substrate recognition by the PS complex depends only on the size of the extracellular domain independent of the amino-acid sequence and that PS activity is constitutive in all cells that express the minimal components of the complex. We report here the development of an in vivo reporter system that allowed us to analyse the processing of human amyloid precursor protein (APP) and the Notch receptor tissue specifically during Drosophila development in the living organism. Using this system, we demonstrate differences between APP and Notch processing and show that PS-mediated cleavage of APP can be regulated in different cell types independent of the size of the extracellular domain.

Amyloid beta-Protein Precursor↗
PubMed2003

Alzheimer beta-amyloid homodimers facilitate A beta fibrillization and the generation of conformational antibodies.

We reported previously that stabilized beta-amyloid peptide dimers were derived from mutant amyloid precursor protein with a single cysteine in the ectodomain juxtamembrane position. In vivo studies revealed that two forms of SDS-stable A beta homodimers exist, species ending at A beta 40 and A beta 42. The phenomenon of the transformation of the initially deposited 42-residue beta-amyloid peptide into the amyloid fibrils of Alzheimer's disease plaques remains to be explained in physical terms, i.e. energetically and structurally. We therefore performed spectroscopic analyses revealing that engineered dimeric peptides ending at residue 42 displayed a much more pronounced beta-structural transition than corresponding monomers. Specifically, the single chemically induced dimerization of A beta peptides significantly increased the beta-sheet content by a factor of 2. The C-terminal residues Ile-41 and Ala-42 of dimeric forms further increased the beta-sheet content by roughly one-third. In contrast to A beta 42, the beta-sheet content of the alpha- and gamma-secretase-generated p3 fragments did not necessarily correlate with the tendency to form fibrils, although p3/17-42 had a pronounced thread forming character with fibril lengths of up to 2.5 microM. Electron microscopic images show that forms of p3/17-42 generated smaller granular particles than forms ending at residue 40. We discuss these findings in terms of A beta 1-42 dimers representing paranuclei, which self-aggregate into ribbon-like ordered fibrils by elongation. Based on A beta 42 dimer-specific titers of a polyclonal antiserum we propose that the A beta homodimer represents a nidus for plaque formation and a well defined novel therapeutic target.

Amyloid beta-Peptides↗
PubMed2003

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.

Alzheimer Disease↗