Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “AMYLOID”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18Linked to original sources

Calcium-dependent and -independent binding of the pentraxin serum amyloid P component to glycosaminoglycans and amyloid proteins: enhanced binding at slightly acid pH.

Serum amyloid P component (SAP), a member of the pentraxin family of proteins, binds calcium-dependently to several ligands including glycosaminoglycans (GAG's). We have investigated the influence of pH on the Ca2(+)-dependent binding of SAP to solid phase GAG's and amyloid fibril proteins (AA and beta2M) by ELISA. An increase in the dose-dependent binding of SAP to heparan sulfate, AA-protein and beta2M was observed as the pH decreased from 8.0 to 5.0. Furthermore, a lower, but significant Ca2(+)-independent binding of SAP to heparan sulfate, dermatan sulfate, AA protein and the amyloid precursor protein beta2M was observed. This binding was also enhanced at slightly acid pH, most pronounced at pH 5.0. The results of this study indicate that SAP can exhibit both Ca2(+)-dependent and -independent binding to ligands involved in amyloid fibril formation and that the binding is enhanced under conditions of slightly lowered pH.

Amyloid↗

Brain acetylcholinesterase promotes amyloid-beta-peptide aggregation but does not hydrolyze amyloid precursor protein peptides.

It has been suggested that acetylcholinesterase (AChE) has both a putative proteolytic activity against the amyloid precursor protein (APP), and a capacity to accelerate the assembly of amyloid-beta-peptide (Abeta) into Alzheimer's fibrils. Here, we have studied the ability of bovine brain AChE to share both activities. Results indicate that AChE purified through acridinium was able to process the APP peptides, however after further purification by an edrophonium column, the protease activity was lost. Under both conditions the capacity of the enzyme to promote amyloid formation was maintained. Kinetic studies of the Abeta aggregation process using edrophonium-AChE, indicated that the lag phase of the aggregation process was smaller than the one observed with the esterase purified by acridinium alone. Considering that the total amount of amyloid formed, measured by thioflavine-T fluorescence, was similar for both AChE preparations, our results suggest that the edrophonium-AChE possesses an higher intrinsic capacity to stimulate the aggregation of Abeta(1-40) peptide.

Acetylcholinesterase↗

Targeting of cell-surface beta-amyloid precursor protein to lysosomes: alternative processing into amyloid-bearing fragments.

Progressive cerebral deposition of the amyloid beta-peptide is an early and invariant feature of Alzheimer's disease. The beta-peptide is released by proteolytic cleavages from the beta-amyloid precursor protein (beta APP), a membrane-spanning glycoprotein expressed in most mammalian cells. Normal secretion of beta APP involves a cleavage in the beta-peptide region, releasing the soluble extramembranous portion and retaining a 10K C-terminal fragment in the membrane. Because this secretory pathway precludes beta-amyloid formation, we searched for an alternative proteolytic processing pathway that can generate beta-peptide-bearing fragments from full-length beta APP. Incubation of living human endothelial cells with a beta APP antibody revealed reinternalization of mature beta APP from the cell surface and its targeting to endosomes/lysosomes. After cell-surface biotinylation, full-length biotinylated beta APP was recovered inside the cells. Purification of lysosomes directly demonstrated the presence of mature beta APP and an extensive array of beta-peptide-containing proteolytic products. Our results define a second processing pathway for beta APP and suggest that it may be responsible for generating amyloid-bearing fragments in Alzheimer's disease.

Alzheimer Disease↗

Amyloid deposition is delayed in mice with targeted deletion of the serum amyloid P component gene.

The tissue amyloid deposits that characterize systemic amyloidosis, Alzheimer's disease and the transmissible spongiform encephalopathies always contain serum amyloid P component (SAP) bound to the amyloid fibrils. We have previously proposed that this normal plasma protein may contribute to amyloidogenesis by stabilizing the deposits. Here we show that the induction of reactive amyloidosis is retarded in mice with targeted deletion of the SAP gene. This first demonstration of the participation of SAP in pathogenesis of amyloidosis in vivo confirms that inhibition of SAP binding to amyloid fibrils is an attractive therapeutic target in a range of serious human diseases.

Amyloid↗

Expression of recombinant human serum amyloid A in mammalian cells and demonstration of the region necessary for high-density lipoprotein binding and amyloid fibril formation by site-directed mutagenesis.

Site-directed mutagenesis of the acute-phase human serum amyloid A (SAA1 alpha) protein was used to evaluate the importance of the N-terminal amino acid residues, namely RSFFSFLGEAF The full-length cDNA clone of SAA1 alpha (pA1.mod.) was used to create two mutations, namely Gly-8 to Asp-8 and an 11 amino acid truncation between Arg-1 and Phe-11 respectively. Wild-type and mutant cDNAs were expressed in Chinese hamster ovary (CHO) cells under the control of the human cytomegalovirus promoter, which resulted in the secretion of the processed proteins into the culture media. Wild-type recombinant human SAA (rSAA) protein was shown to have pI values of 6.0 and 6.4, similar to the human SAA isoform SAA1 alpha and SAA1 alpha desArg found in acute-phase plasma. N-terminal sequencing of 56 residues confirmed its identity with human SAA1 alpha. The total yield of wild-type rSAA measured by ELISA was between 3.5 and 30 mg/l. The two mutations resulted in reduced expression levels of the mutant SAA proteins (3-10 mg/l). Further measurements of rSAA concentration in lipid fractions of culture medium collected at a density of 1.21 g/ml (high-density liporotein; HDL) and 1.063-1.18 g/ml (very-low-density lipoprotein/low-density lipoprotein; VLDL/LDL) showed that 76% of the wild-type protein was found in the HDL fraction and the remaining 24% in the infranatant non-lipid fraction. In contrast the relative concentration of mutant rSAA in HDL and infranatant fractions was reversed. This is consistent with the previously proposed involvement of the 11 amino acid peptide in anchoring. SAA protein on to HDL3 [Turnell, Sarra, Glover, Baum, Caspi, Baltz and Pepys (1986) Mol. Biol. Med. 3, 387-407]. Wild-type rSAA protein was shown to from amyloid fibrils in vitro under acidic conditions as shown by electron microscopy, and stained positive with Congo Red and exhibited apple-green birefringence when viewed under polarized light. Under the same conditions mutSAA(G8D) and mutSAA delta 1-11 did not form amyloid fibrils. In conclusion, replacement of Gly-8 by Asp-8 or deletion of the first 11 amino acid residues at the N-terminus of rSAA diminishes its capacity to bind to HDL and decreases amyloid fibril formation.

Amyloid↗

Congo red inhibits proteoglycan and serum amyloid P binding to amyloid beta fibrils.

Various data suggest that Alzheimer's disease results from the accumulation of amyloid beta (A beta) peptide fibrils and the consequent formation of senile plaques in the cognitive regions of the brain. One approach to lowering senile plaque burden in Alzheimer's disease brain is to identify compounds that will increase the degradation of existing amyloid fibrils. Previous studies have shown that proteoglycans and serum amyloid P (SAP), molecules that localize to senile plaques, bind to A beta fibrils and protect the amyloid peptide from proteolytic breakdown. Therefore, molecules that prevent the binding of SAP and/or proteoglycans to fibrillar A beta might increase plaque degradation and prove useful in the treatment of Alzheimer's disease. The nature of SAP and proteoglycan binding to A beta is defined further in the present study. SAP binds to both fibrillar and nonfibrillar forms of A beta. However, only the former is rendered resistant to proteolysis after SAP association. It is interesting that both SAP and proteoglycan binding to A beta fibrils can be inhibited by glycosaminoglycans and Congo red. Unexpectedly, Congo red protects fibrillar A beta from breakdown, suggesting that this compound and other structurally related molecules are unlikely to be suitable for use in the treatment of Alzheimer's disease.

Amyloid beta-Peptides↗

Cystatin C colocalizes with amyloid-beta and coimmunoprecipitates with amyloid-beta precursor protein in sporadic inclusion-body myositis muscles.

Cystatin C (CC), an endogenous cysteine protease inhibitor, is accumulated within amyloid-beta (A beta) amyloid deposits in Alzheimer's disease (AD) brain and was proposed to play a role in the AD pathogenesis. Because the chemo-morphologic muscle phenotype of sporadic inclusion-body myositis (s-IBM) has several similarities with the phenotype of AD brain, including abnormal accumulation of A beta deposits, we studied expression and localization of CC in muscle biopsies of 10 s-IBM, and 16 disease- and five normal-control muscle biopsies. Physical interaction of CC with amyloid-beta precursor protein (A beta PP) was studied by a combined immunoprecipitation/immunoblotting technique in the s-IBM muscle biopsies and in A beta PP-overexpressing cultured human muscle fibers. In all s-IBM muscle biopsies, CC-immunoreactivity either colocalized with, or was adjacent to, the A beta-immunoreactive inclusions in 80-90% of the vacuolated muscle fibers, mostly in non-vacuolated regions of their cytoplasm. Ultrastructurally, CC immunoreactivity-colocalized with A beta on 6-10 nm amyloid-like fibrils and floccular material. By immunoblotting, CC expression was strongly increased in IBM muscle as compared to the controls. By immunoprecipitation/immunoblotting experiments, CC coimmunoprecipitated with A beta PP, both in s-IBM muscle and in A beta PP-overexpressing cultured normal human muscle fibers. Our studies (i) demonstrate for the first time that CC physically associates with A beta PP, and (ii) suggest that CC may play a novel role in the s-IBM pathogenesis, possibly by influencing A beta PP processing and A beta deposition.

Amyloid beta-Peptides↗

Familial amyloid polyneuropathy type I (Portuguese): distribution and characterization of renal amyloid deposits.

Renal amyloidosis has been considered rare and late in the evolution of the transthyretin (TTR) familial amyloid polyneuropathy (FAP) of the Portuguese type (type I). Renal biopsy has been performed systematically in 14 patients with FAP type I before liver transplantation. In all patients, TTR Met30 mutation was shown. Seven had proteinuria or abnormal microalbuminuria, whereas seven others had no urinary abnormalities. All had renal amyloid deposition predominantly in the medulla. Glomerular and vascular involvement was more prominent in patients with urinary abnormalities. Patients with the most extensive renal lesions represented a subgroup with a low score of polyneuropathy disability, a high prevalence of nephropathy in the proband generation, or a late onset for relatives with nephropathy. Immunohistochemistry studies showed that the amyloid substance corresponded to transthyretin. We have shown that renal TTR-derived amyloid deposition is common in patients with FAP type I, even in the absence of urinary abnormalities. The clinical presentation of nephropathy is not a late occurrence in the disease.

Adult↗

Islet amyloid, islet-amyloid polypeptide, and diabetes mellitus.

Islet-amyloid deposits, which are a common feature of Type II diabetes mellitus, are derived from the polymerization of a putative hormone identified as IAPP. IAPP is synthesized by normal islet beta cells and probably is cosecreted with insulin. Although the physiologic function of IAPP and its role in the pathogenesis of Type II diabetes mellitus are just beginning to be unraveled, IAPP may play an important part in the development of this most common form of diabetes mellitus by opposing the action of insulin in peripheral tissues. The polymerization of IAPP to form extracellular islet-amyloid deposits may further contribute to the development of Type II diabetes mellitus by destroying islet cells and by disrupting the passage of glucose and hormones to and from them. Substantial evidence indicates that the propensity of IAPP to polymerize and form extracellular amyloid deposits in only certain species (e.g., humans, cats, and raccoons) is directly associated with an intrinsically amyloidogenic part of the molecule--i.e., positions 20 through 29 of IAPP. The inherent amyloidogenicity of IAPP in these species may be further facilitated by increased beta-cell production of IAPP, leading to a high local concentration that predisposes to polymerization. The latter possibility is supported by studies demonstrating that IAPP production by islet beta cells is increased in normoglycemic cats with impaired glucose tolerance. Although increased production of IAPP may initially cause insulin resistance, prolonged overproduction of IAPP may ultimately impair insulin secretion by leading to the progressive deposition of insoluble islet amyloid, a finding apparent in most subjects with overt diabetes. If, as these studies suggest, increased IAPP production is linked to the development of Type II diabetes mellitus, further studies must address the genetic and nongenetic factors that influence this important biologic change in humans and some animal species.

Amino Acid Sequence↗

Proteolysis of chimeric beta-amyloid precursor proteins containing the Notch transmembrane domain yields amyloid beta-like peptides.

gamma-Secretase is an unusual intramembranous protease that has been reported to cleave the beta-amyloid precursor protein (APP) near the middle of its transmembrane domain (TMD) but cleave Notch near the cytoplasmic end of its TMD. To ascertain whether the TMD sequence of the substrate determines where gamma-secretase cleaves and whether the region just before the TMD participates in recognition by the enzyme, we expressed chimeric human APP molecules containing either the TMD or pre-TMD regions of Notch or other transmembrane proteins. APP chimeras bearing either the Notch or the amyloid precursor-like protein-2 TMD released similar amounts of approximately 4-kDa amyloid beta-peptide (Abeta)-like peptides as did intact APP. Mass spectrometry revealed that the principal Abeta-like peptide ended at residue 40, indicating cleavage at the middle of the Notch TMD in the chimera. Generation of Abeta-like peptides was significantly decreased when the APP TMD was replaced by those of SREBP-1 or human epithelial growth factor receptor 3. Replacement of the APP pre-TMD region (Abeta 10-28) with that of SREBP-1 increased generation of Abeta-like peptides, while those of human epithelial growth factor receptor 3 or amyloid precursor-like protein-2 decreased it. We conclude that gamma-secretase can cleave near the middle of the Notch TMD, that Abeta-like peptides may arise during Notch processing, and that the pre-TMD sequence of the substrate influences recognition or binding by the enzyme.

Amino Acid Sequence↗

Antagonistic effects of beta-site amyloid precursor protein-cleaving enzymes 1 and 2 on beta-amyloid peptide production in cells.

The deposition of extracellular beta-amyloid peptide (A beta) in the brain is a pathologic feature of Alzheimer's disease. The beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), an integral membrane aspartyl protease responsible for cleavage of amyloid precursor protein (APP) at the beta-site, promotes A beta production. A second integral membrane aspartyl protease related to BACE1, referred to as beta-site amyloid precursor protein cleaving enzyme 2 (BACE2) has also been demonstrated to cleave APP at the beta-cleavage site in transfected cells. The role of endogenous BACE2 in A beta production remains unresolved. We investigated the role of endogenous BACE2 in A beta production in cells by selective inactivation of its transcripts using RNA interference. We are able to reduce steady state levels for mRNA for each enzyme by >85%, and protein amounts by 88-94% in cells. Selective inactivation of BACE1 by RNA interference results in decreased beta-cleaved secreted APP and A beta peptide secretion from cells, as expected. Selective inactivation of BACE2 by RNAi results in increased beta-cleaved secreted APP and A beta peptide secretion from cells. Simultaneous targeting of both enzymes by RNA interference does not have any net effect on A beta released from cells. Our observations of changes in APP metabolism and A beta are consistent with a role of BACE2 in suppressing A beta production in cells that co-express both enzymes.

Amyloid Precursor Protein Secretases↗

Ceramide stabilizes beta-site amyloid precursor protein-cleaving enzyme 1 and promotes amyloid beta-peptide biogenesis.

The lipid second messenger ceramide regulates several biochemical events that occur during aging. In addition, its level is highly elevated in the amyloid-burdened brains of Alzheimer's disease patients. Here, we analyzed the impact of aberrant ceramide levels on amyloid beta-peptide (Abeta) generation by using a cell-permeable analog of ceramide, C6-ceramide, and several biochemical inhibitors of the sphingomyelin/glycosphingolipid biosynthetic pathway. We found that C6-ceramide increased the biogenesis of Abeta by affecting beta-but not gamma-cleavage of the amyloid precursor protein. Similarly to C6-ceramide, increased levels of endogenous ceramide induced by neutral sphingomyelinase treatment also promoted the biogenesis of Abeta. Conversely, fumonisin B1, which inhibits the biosynthesis of endogenous ceramide, reduced Abeta production. Exogenous C6-ceramide restored both intracellular ceramide levels and Abeta generation in fumonisin B1-treated cells. These events were specific for amyloid precursor protein and were not associated with apoptotic cell death. Pulse-chase and time-course degradation experiments showed that ceramide post-translationally stabilizes the beta-secretase BACE1. Taken together, these data indicate that the lipid second messenger ceramide, which is elevated in the brains of Alzheimer's disease patients, increases the half-life of BACE1 and thereby promotes Abeta biogenesis.

Amyloid Precursor Protein Secretases↗

A different amyloid formation mechanism: de novo oculoleptomeningeal amyloid deposits after liver transplantation.

BACKGROUND: Liver transplantation has served as a treatment for patients with familial amyloidotic polyneuropathy (FAP) because variant transthyretin (TTR), the pathogenic protein of FAP, is predominantly produced by the liver. However, the effect on amyloid formation of TTR that is synthesised by the retina and the choroid plexus remains to be elucidated in FAP patients with liver transplants. OBJECTIVE: To investigate changes in ocular tissues and the central nervous system (CNS) of FAP patients after liver transplantation. DESIGN: Clinical study. SETTING: Graduate School of Medical Sciences, Kumamoto University, Japan. INTERVENTION: Transplantation of livers from cadaveric or living donors. MEASUREMENTS: Preoperative measures and postoperative (16-108 months) follow-up of clinical data, including routine ophthalmologic, neurologic, and laboratory evaluations. RESULTS: In 22 patients with FAP related to the amyloidogenic TTR (ATTR) Val30Met and 3 patients with FAP ATTR Tyr114Cys, after liver transplantation, 3 patients began to show evidence of de novo glaucoma, and 1 had vitreous opacity that was caused by the variant TTR. Another three patients showed new amyloid deposits in the pupillary margin, which could lead to glaucoma and vitreous opacity. As for changes in the CNS and levels of total protein and TTR in cerebrospinal fluid (CSF), after liver transplantation, two FAP ATTR Tyr114Cys patients exhibited de novo amyloid deposition in the leptomeninges, and total protein and TTR levels in CSF were significantly increased. CONCLUSIONS: Oculoleptomeningeal involvement in FAP was not prevented by liver transplantation because variant TTR produced by the retina and the choroid plexus forms amyloid fibrils in situ.

Adult↗

Murine tissue macrophages synthesize and secrete amyloid proteins different to amyloid A (AA).

We recently demonstrated that serum amyloid A (SAA) gene expression can be induced in extrahepatic sites with exception of the brain. Furthermore we demonstrated that tissue macrophages express SAA-gene constitutively and that SAA-gene expression can be increased by endotoxin. Until now the protein corresponding to the SAA-specific mRNA contained in macrophages has not been identified. We compared proteins precipitated from endogenously labelled samples by three antisera against amyloid A (AA) raised in different laboratories. Radiolabelled samples were derived from murine hepatocyte cultures, from cell-free translation of acute phase liver RNA or hepatocytes RNA and from peritoneal macrophages as well as Kupffer cells. All three antisera recognize a protein of 12.5 kDa Mr produced by hepatocytes (SAA), and a major protein of 14.3 kDa Mr contained in the cell-free translation products; this is the precursor of the mature SAA as demonstrated by cleavage experiments with canine pancreas microsomal enzymes. The antisera also recognize two proteins--a major one of 14.5 kDa Mr and a second of 12.5 kDa Mr contained in the supernatants and cell lysates of liver and peritoneal macrophages. New antisera raised against the two proteins do not recognize any protein, either of hepatocyte or of cell-free translation samples; they specifically precipitate two proteins from macrophage samples with the same molecular mass as that of the proteins precipitated by the anti SAA antisera. Murine acute phase sera do not react with the new antisera. However, amyloid deposits of amyloidotic mice specifically react with the new antisera. We describe two new components of murine amyloid produced by tissue macrophages.

Acute-Phase Proteins↗

Cathepsin B generates the most common form of amyloid A (76 residues) as a degradation product from serum amyloid A.

Amyloid A protein (AA), the chief constituent of reactive amyloid deposits, is derived from serum amyloid A (SAA) and most commonly corresponds to the amino-terminal 76 residues (AA76). Digestion of recombinant human SAA1 with a lysosomal thiol protease, cathepsin B, and analysis of the products by SDS-PAGE and amino-terminal sequencing revealed that AA76 was generated as a minor and transient degradation product. Digestion with neutrophil elastase generated intermediates different from AA76. This finding suggests that cathepsin B may play an important role in amyloid fibrilogenesis by converting SAA to AA.

Amino Acid Sequence↗

In vitro degradation of serum amyloid A by cathepsin D and other acid proteases: possible protection against amyloid fibril formation.

The effects of acid proteases on degradation of serum amyloid A protein (SAA) were investigated in vitro. Human recombinant SAA1 (rSAA1), when incubated with human spleen extracts at pH 3.2, was degraded in the amino-terminal portion of the molecule. This reaction was inhibited by an acid protease inhibitor, pepstatin. The degraded SAA molecules lacking nine or more amino-terminal residues, when exposed to in vitro fibril-forming conditions, failed to form Congo red positive precipitates and did not show amyloid fibril-like structure by electron microscopy. This suggests that the amino-terminal portion of SAA is essential for fibril formation. Cathepsin D, one of the lysosomal enzymes, also initiated degradation of rSAA1 at the amino-terminus. Cathepsin D immunoreactivity was detected in marginal areas of amyloid deposits in spleens from patients with reactive amyloidosis. These findings suggest that cathepsin D or similar acid proteases may be involved in SAA catabolism and may protect against amyloid formation.

Amyloid↗

Production of amyloid beta protein from normal amyloid beta-protein precursor (beta APP) and the mutated beta APPS linked to familial Alzheimer's disease.

The approximately 4 kD (39-43 amino acid) polypeptide (amyloid beta protein, A beta) deposited as amyloid in Alzheimer's disease (AD) is derived from a set of 695-770 residue precursor proteins collectively referred to as the amyloid beta-protein precursor (beta APP). Using immunoblotting techniques, metabolic labeling, and sequencing we have analyzed beta APP derivatives in medium conditioned by: (1) human mononuclear leukemic (K562) cells expressing a model beta AP-bearing carboxyl-terminal beta APP derivative (2) human neuroblastoma (M17) cells transfected with constructs expressing full length beta APP and (3) M17 cells expressing only endogenous beta APP. In each case, we observed the release of a approximately 4 kD beta APP derivative essentially identical to the A beta found in AD amyloid. A similar, if not identical, beta APP fragment was readily detected in CSF from both Alzheimer's disease patients and controls. These observations indicate that the A beta is produced and released by normal processing of the beta APP. To determine if the production of A beta or A beta-tearing COOH-terminal beta APP derivatives is altered in cells expressing the mutant beta APPs linked to familial AD, we have compared M17 cells expressing wild type beta APP with those expressing mutant beta APPs (beta APP delta I or beta APP delta NL). After continuous metabolic labeling for 8 hours, cells expressing the beta APP delta NL mutant showed a 5-fold increase in the relative amount of an approximately 11.4 kD A beta-bearing carboxyl-terminal beta APP derivative, and they released 6-fold more 4 kD A beta into the medium. These observations provide strong evidence that: (1) the pathway producing A beta in cultured cells is highly relevant to AD and (2) the beta APP delta NL mutant causes AD because its processing is altered in a way that releases increased amounts of A beta.

Alzheimer Disease↗

Plasma beta-amyloid peptide, transforming growth factor-beta 1, and risk for cerebral amyloid angiopathy.

Despite the documented association between apolipoprotein E genotype and cerebral amyloid angiopathy (CAA), a substantial proportion of CAA-related hemorrhages occur in patients without known risks for this disorder. Two other factors implicated in the pathogenesis of CAA are the amyloid-beta peptide (preferentially deposited in vessels as a 40-amino acid species) and the multifunctional cytokine transforming growth factor-beta 1 (a specific promoter of vascular amyloid deposition in transgenic models). We measured plasma concentrations of these factors in a series of 25 patients diagnosed with probable or definite CAA-related hemorrhage and compared them with 21 patients with hemorrhage due to probable hypertensive vasculopathy and 42 elderly control subjects without hemorrhage. We found no differences among the groups in concentrations of the 40- or 42-amino acid species of beta-amyloid or either the active or latent form of transforming growth factor-beta 1. While the data do not exclude important roles for these molecules as risks for CAA, they indicate that plasma measurements are not useful in its diagnosis.

Aged↗