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K Beyreuther

Publications and source records attributed to K Beyreuther.

At least 19 recordsLinked to original sources
PubMed1992

Alzheimer beta A4-amyloid protein precursor in immunocompetent cells.

The mechanism of proteolytic breakdown of the beta A4-amyloid protein precursor (APP) has attracted much attention because of its relevance for Alzheimer's disease. Apart from the pathological role of APP in the amyloidogenesis, many efforts have been made to identify the functional significance of this widely expressed protein in various biological processes. Employing biochemical techniques, we demonstrate that APP is involved in the initiation of the immune response. Upon stimulation, it is expressed by the major functional types of T-lymphocytes, i.e. CD4+ and CD8+ cells. As was demonstrated for the CD4+ lymphoid cell line H9, APP is predominantly secreted. The remaining COOH-terminal fragments generated upon secretion were highly unstable. Of the APP produced by immunocompetent cells, considerable amounts were shown to be leukocyte-derived APP (L-APP). In addition, we were able to identify the KPI-containing L-APP isoform, L-APP733, as the major expressed L-APP isoform in immunocompetent cells, including rat microglial cells and astrocytes. The L-APP expression pattern of these cells showed high similarity. These findings seem to be indicative of an important function of APP within the immune system. Therefore, APP may be involved in various immunopathogenic conditions of the periphery and in the central nervous system.

Amyloid beta-Peptides↗
PubMed1992

Substitutions of hydrophobic amino acids reduce the amyloidogenicity of Alzheimer's disease beta A4 peptides.

The deposition of amyloid protein aggregates in brain is the main pathological feature of Alzheimer's disease. Their principal constituent is a peptide termed beta A4, which comprises up to 43 amino acid residues. It is highly insoluble under physiological conditions and aggregates into filaments that form very dense clusters in vivo and in vitro. Based on a beta A4 prototype sequence spanning residues 10 to 42 or 43, we have designed analogues in which hydrophobic amino acid residues in position 17 to 20 were substituted by more hydrophilic residues. Depending on the kind of newly introduced amino acids and their position within the sequence, the substitution of only two residues led to variants exhibiting a broad spectrum of different properties. Common to them was a reduced beta-sheet content after solubilization in water and in the solid state. Some of the variants showed significantly reduced amyloidogenicity: although still forming filaments, they did not aggregate into the highly condensed depositions that are typical for amyloid. In addition, they could be solubilized in 200 mM-NaCl and KCl. When mixed with beta A4 peptides bearing the natural sequence, two of the analogues could inhibit the formation of filaments in vitro. These results demonstrate that a well-preserved hydrophobic core around residues 17 to 20 of beta A4 is crucial for the formation of beta-sheet structure and the amyloid properties of beta A4. The introduction of structural alterations within this region may guide the development of reagents for the therapy of Alzheimer's disease.

Alzheimer Disease↗
PubMed1992

Amyloidogenicity of beta A4 and beta A4-bearing amyloid protein precursor fragments by metal-catalyzed oxidation.

Previously we have shown that the COOH-terminal 100 residues (A4CT) of the amyloid protein precursor (APP), which carry the sequence of the amyloid beta A4 protein of Alzheimer's disease at N-terminal position, form highly insoluble aggregates if expressed in the rabbit reticulocyte lysate and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Dyrks, T., Weidemann, A., Multhaup, G., Salbaum, J.M., Lemaire, H.-G., Kang, J., Müller-Hill, B., Masters, C. L., and Beyreuther, K. (1988) EMBO J. 7, 949-957). Here we report that aggregation of this COOH-terminal APP fragment A4CT and also of beta A4 itself depends on additional factors. In contrast to the reticulocyte expression system, expression of A4CT and beta A4 in the wheat germ expression system resulted in only monomeric forms. We have identified the factors which are capable of transforming both soluble A4CT and beta A4 into insoluble and aggregating molecules. Monomeric A4CT or beta A4 expressed in the wheat germ lysate could be transformed into aggregating molecules by the addition of metal-catalyzed oxidation systems. The addition of radical scavengers such as ascorbic acid, trolox, and amino acids prevented the aggregation process induced by the radical initiators. Thus, the aggregation of amyloidogenic APP fragments if analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis requires amino acid oxidation and protein cross-linking induced by radical generation systems.

Amyloid beta-Protein Precursor↗
PubMed1992

Membrane inserted APP fragments containing the beta A4 sequence of Alzheimer's disease do not aggregate.

Previously we have shown that the COOH-terminal fragment (A4CT) of the Alzheimer amyloid protein precursor (APP), which at the NH2-terminus carries the sequence of the amyloid beta A4 protein, forms highly insoluble aggregates [EMBO J. (1988) 7, 949-957]. Here we report that aggregation is prevented if A4CT is expressed in vitro with a signal sequence at the NH2-terminus (SPA4CT) under conditions which allow membrane insertion. Aggregates from SPA4CT are obtained after removal of membranes by chloroform/methanol extraction or heating.

Alzheimer Disease↗
PubMed1992

Identification and differential expression of a novel alternative splice isoform of the beta A4 amyloid precursor protein (APP) mRNA in leukocytes and brain microglial cells.

The gene for the beta A4-amyloid precursor protein (APP) consists of 19 exons which code for a typical N- and O-glycosylated transmembrane protein with four extracellular domains followed by the transmembrane domain and a short cytoplasmic domain. The beta A4-amyloid sequence is part of exons 16 and 17. Several APP isoforms can be generated by alternative splicing of exons 7 and 8, encoding domains with homologies to Kunitz-type protease inhibitors and the MRC OX-2 antigen, respectively. The mechanism by which the pathological beta A4 is generated is unknown, it is however a critical event in Alzheimer's disease and is distinct from the normally occurring cleavage and secretion of APPs within the beta A4 sequence. We report here for the first time considerable APP mRNA expression by rat brain microglial cells. In addition we showed by S1 nuclease protection and polymerase chain reaction analysis of reverse transcribed RNA (RT-PCR) that T-lymphocytes, macrophages, and microglial cells expressed a new APP isoform by selection of a novel alternative splice site and exclusion of exon 15 of the APP gene. This leads to a transmembrane, beta A4 sequence containing APP variant, lacking 18 amino acid residues close to the amyloidogenic region. The use of this novel alternative splice site alters the structure of APP in close proximity to the beta A4 region and thus may determine a variant, potentially pathogenic processing of leukocyte-derived APP in brain.

Amyloid beta-Protein Precursor↗
PubMed1992

The expression of the amyloid precursor protein (APP) is regulated by two GC-elements in the promoter.

The structure of the promoter of the human APP gene resembles that of housekeeping genes, with the presence of a GC-rich region and the lack of a canonical TATA box. Since analysis of the expression of the APP gene, especially at the transcriptional level, might reveal factors or elements, which influence amyloid formation in Alzheimer's disease, a 5' deletion analysis of the APP promoter was performed, leading to the identification of an activating DNA fragment (Ac), acting also on a heterologous promoter. DNaseI-footprint analysis revealed three protected regions on the Ac fragment. Further gene transfer experiments showed, that at least two elements, designated A and C, confer transcriptional activity in HeLa cells. Whereas the proximal element A is a 19bp long GC-rich DNA sequence, the distal element C is a GC-palindrome with the sequence 5'GCGGCGCCGC.

Amyloid beta-Protein Precursor↗
PubMed1992

Aluminium accumulation in relation to senile plaque and neurofibrillary tangle formation in the brains of patients with renal failure.

The effects of long-term exposure to aluminium on the development of Alzheimer-type neuropathological changes have been studied post-mortem in patients with chronic renal failure who did not have dialysis encephalopathy. Administration of aluminium-containing phosphate binding compounds appears to be a major factor in the accumulation of aluminium in the brain of dialysis patients. The mean serum aluminium concentrations determined during life and brain aluminium concentrations determined post-mortem correlated with both the duration and total amount of aluminium hydroxide administered to these patients. No correlation was found between the presence of bone aluminium and either the mean serum or brain aluminium concentration. Longitudinal monitoring of serum aluminium concentrations may provide a more reliable index than bone biopsy of brain aluminium concentrations in dialysis patients. Dynamic secondary ion mass spectrometry revealed focal accumulations of aluminium associated with cortical pyramidal neurones. The majority of patients also showed immunostaining in pyramidal neurones with an antibody to the N-terminal region of the beta/A4 amyloid precursor protein, while staining was absent in age-matched control cases. One-third of the patients exhibited beta/A4-positive amorphous senile plaques in the cerebral cortex. However, there was no clear correlation between either the presence and intensity of beta/A4 amyloid precursor immunostaining or the presence of senile plaques and the concentration of aluminium in the cerebral cortex. Cortical neurofibrillary tangles were not observed in any of the dialysis patients. These data suggest that it is unlikely that aluminium plays any major role in neurofibrillary tangle formation and that its putative role in senile plaque formation is likely to be only part of a complex cascade of changes.

Aluminum↗
PubMed1992

Beta A4 amyloid protein and its precursor in Alzheimer's disease.

The beta A4 amyloid protein is now understood to play a pivotal role in the development of Alzheimer's disease. This protein is generated by the abnormal processing of the amyloid protein precursor, a large membrane glycoprotein. Insights into the mechanisms of this abnormal processing will give information relevant to the design of new therapeutic strategies for Alzheimer's disease.

Alzheimer Disease↗
PubMed1992

Primary structure and alternative splice variants of gephyrin, a putative glycine receptor-tubulin linker protein.

A 93 kd polypeptide associated with the mammalian inhibitory glycine receptor (GlyR) is localized at central synapses and binds with high affinity to polymerized tubulin. This protein, named gephyrin (from the Greek gamma epsilon phi upsilon rho alpha, bridge), is thought to anchor the GlyR to subsynaptic microtubules. Here we report its primary structure deduced from cDNA and show that corresponding transcripts are found in all rat tissues examined. In brain, at least five different gephyrin mRNAs are generated by alternative splicing. Expression of gephyrin cDNAs in 293 kidney cells yields polypeptides reactive with a gephyrin-specific antibody, which coprecipitate with polymerized tubulin. Thus, gephyrin may define a novel type of microtubule-associated protein involved in membrane protein-cytoskeleton interactions.

Amino Acid Sequence↗
PubMed1992

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.

Alzheimer Disease↗
PubMed1992

Human brain beta A4 amyloid protein precursor of Alzheimer's disease: purification and partial characterization.

The major component of the amyloid deposition that characterizes Alzheimer's disease is the 4-kDa beta A4 protein, which is derived from a much larger amyloid protein precursor (APP). A procedure for the complete purification of APP from human brain is described. The same amino terminal sequence of APP was found in two patients with Alzheimer's disease and one control subject. Two major forms of APP were identified in human brain with apparent molecular masses of 100-110 kDa and 120-130 kDa. Soluble and membrane fractions of brain contained nearly equal amounts of APP in both humans and rats. Immunoprecipitation with carboxyl terminus-directed antibodies indicates that the soluble forms of APP are truncated. Carboxyl terminus truncation of membrane-associated forms of human brain APP was also found to occur during postmortem autolysis. The availability of purified human brain APP will facilitate the investigation of its normal function and the events that lead to its abnormal cleavage in patients with Alzheimer's disease.

Aged↗
PubMed1992

Association and release of the amyloid protein precursor of Alzheimer's disease from chick brain extracellular matrix.

The amyloid protein precursor (APP) of Alzheimer's disease was found to bind saturably (Kd = 60 nM) to embryonic chick brain extracellular matrix (ECM). The binding of APP to ECM was not inhibited by 10 micrograms/ml heparin or heparan sulfate. However, pretreatment of cells with 1 mM 4-methylumbelliferyl-beta-D-xyloside, an inhibitor of proteoglycan biosynthesis, reduced the number of APP binding sites on the ECM by 80%. The binding of APP to ECM was also inhibited by pretreatment with chlorate, an inhibitor of glycan sulfation, and heparitinase, which digests the carbohydrate component of heparan sulfate proteoglycans. These results suggest that APP binds with high affinity to one or more heparan sulfate proteoglycans. Acidic and basic fibroblasts growth factor (FGF) also bound to chick ECM. When ECM was incubated with a protease associated with the enzyme AChE (AChE-AP), APP and acidic FGF were released intact from the matrix. The AChE-AP was at least 100-fold more potent in releasing APP from ECM than other trypsin-like proteases (trypsin, plasmin, thrombin). The action of the AChE-AP was inhibited by glia-derived nexin (protease nexin I) and by human brain APP at low nanomolar concentrations. These results suggest that in vivo an AChE-AP may cleave ECM proteins to regulate the availability of soluble APP or other factors bound to the ECM.

Alzheimer Disease↗
PubMed1991

A protease activity associated with acetylcholinesterase releases the membrane-bound form of the amyloid protein precursor of Alzheimer's disease.

Amyloid deposits in the brains of patients with Alzheimer's disease (AD) contain a protein (beta A4) which is abnormally cleaved from a larger transmembrane precursor protein (APP). APP is believed to be normally released from membranes by the action of a protease referred to as APP secretase. Amyloid deposits have also been shown to contain the enzyme acetylcholinesterase (AChE). In this study, a protease activity associated with AChE was found to possess APP secretase activity, stimulating the release of a soluble 100K form of APP from HeLa cells transfected with an APP cDNA. The AChE-associated protease was strongly and specifically inhibited by soluble APP (10 nM) isolated from human brain. The AChE-associated protease cleaved a synthetic beta A4 peptide at the predicted cleavage site. As AChE is decreased in AD, a deficiency of its associated protease might explain why APP is abnormally processed in AD.

Acetylcholinesterase↗
PubMed1991

Localization of Alzheimer beta A4 amyloid precursor protein at central and peripheral synaptic sites.

We have recently shown that the amyloid beta A4 precursor protein (APP) is synthesized in neurons and undergoes fast axonal transport to synaptic sites [Koo et al., Proc. Natl. Acad. Sci. U.S.A., 87 (1990) 1561-1565]. Using immunofluorescence, laser confocal microscopy and immunoelectron microscopy with simultaneous detection of APP and synaptophysin, we now report a preferential localization of APP at synaptic sites of human and rat brain and at neuromuscular junctions. APP is further found on vesicular elements of neuronal perikarya, dendrites and axons. The synaptic localization of APP implies (1) a role of APP in physiological synaptic activity and (2) a potential and early impairment of central synapses when synaptic APP is converted to beta A4 amyloid during the pathological evolution of Alzheimer's disease and Down's syndrome.

Amyloid beta-Protein Precursor↗
PubMed1991

Human and rodent sequence analogs of Alzheimer's amyloid beta A4 share similar properties and can be solubilized in buffers of pH 7.4.

The filamentous amyloid protein aggregates found in the brain of patients affected with Alzheimer's disease principally consist of a peptide termed beta A4, according to its secondary structure of beta-pleated sheets and its molecular mass of about 4 kDa. It has a length of up to 42 or 43 residues. By chemical means, we have synthesized peptide analogs corresponding to the human and rodent beta A4 sequences. We describe structural and functional properties of peptides spanning residues 1-43, 10-23, 1-27 and 4-27 of beta A4. The peptides have been tested for their ability to form filaments in vitro. Their solubilities and secondary structures in solution and in the solid state have been used to detect differences between the properties of human and rodent beta A4 sequences. We show that mouse and rat beta A4 homologs are as amyloidogenic as the human sequence. The absence of amyloid deposits in the brain of aged rats and mice is therefore not due to the three amino acid substitutions identified within the sequence which is homologous to beta A4 of humans. Moreover, peptides corresponding to residues 1-27 of human and rodent beta A4 are solubilized under physiological conditions; thus they are very unlikely to form stable filaments in vivo.

Amino Acid Sequence↗