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PubMed2005

Acute phase proteins in dogs and cats: current knowledge and future perspectives.

The acute phase response is a nonspecific inflammatory reaction of the host that occurs shortly after any tissue injury. The response includes changes in the concentration of plasma proteins called acute phase proteins (APPs), some of which decrease in concentration (negative APPs), such as albumin or transferrin, and others of which increase in concentration (positive APPs), such as C-reactive protein, serum amyloid A, haptoglobin, alpha-1-acid glycoprotein, and ceruloplasmin. Most positive APPs are glycoproteins synthesized mainly by hepatocytes upon stimulation by proinflammatory cytokines and released into the bloodstream. The acute phase response and clinical application of monitoring APPs in dogs and cats are reviewed in this article, including biochemical characteristics, assays developed for each individual APP, and preanalytic and analytic factors influencing APP results that should be taken into account for proper and adequate clinical interpretation. In addition, the diagnostic use of APPs and their possible application in monitoring treatment, which can be considered one of the most interesting and promising practical applications of these proteins, will be discussed. Finally, challenges and future developments of APPs in dogs and cats will be considered, because it is expected that new and cheaper automated assays for determination of the main APPs in small animals will contribute to a wider use of these proteins as biomarkers of infection and inflammatory lesions.

Acute-Phase Proteins↗
PubMed2005

Herpes simplex virus interferes with amyloid precursor protein processing.

BACKGROUND: The early events underlying Alzheimer's disease (AD) remain uncertain, although environmental factors may be involved. Work in this laboratory has shown that the combination of herpes simplex virus type 1 (HSV1) in brain and carriage of the APOE-epsilon4 allele of the APOE gene strongly increases the risk of developing AD. The development of AD is thought to involve abnormal aggregation or deposition of a 39-43 amino acid protein--beta amyloid (Abeta)--within the brain. This is cleaved from the much larger transmembranal protein 'amyloid precursor protein' (APP). Any agent able to interfere directly with Abeta or APP metabolism may therefore have the capacity to contribute towards AD. One recent report showed that certain HSV1 glycoprotein peptides may aggregate like Abeta; a second study described a role for APP in transport of virus in squid axons. However to date the effects of acute herpesvirus infection on metabolism of APP in human neuronal-type cells have not been investigated. In order to find if HSV1 directly affects APP and its degradation, we have examined this protein from human neuroblastoma cells (normal and transfected with APP 695) infected with the virus, using Western blotting. RESULTS: We have found that acute HSV1 (and also HSV2) infection rapidly reduces full length APP levels--as might be expected--yet surprisingly markedly increases levels of a novel C-terminal fragment of APP of about 55 kDa. This band was not increased in cells treated with the protein synthesis inhibitor cycloheximide CONCLUSION: Herpes virus infection leads to rapid loss of full length APP from cells, yet also causes increased levels of a novel 55 kDa C-terminal APP fragment. These data suggest that infection can directly alter the processing of a transmembranal protein intimately linked to the aetiology of AD.

Alzheimer Disease↗
PubMed1990

Characterization of the receptors for peptide-YY and avian pancreatic polypeptide in chicken and pig brains.

We have previously identified the peptide-YY (PYY) receptor on porcine brain membranes as a 50-kDa protein after chemical cross-linking. PYY receptors are discretely distributed in the brain of various mammals, to which neuropeptide-Y (NPY), but not pancreatic polypeptide (PP), bind with great specificity. The present study was carried out in order 1) to identify and characterize the PYY receptor in the avian brain, 2) to compare it with the APP receptor that had been demonstrated in the cerebellum, and 3) to examine [125I]APP-binding activity in the porcine brain. [125I]PYY was bound to chicken brain membranes via high affinity (Kd = 2.19 x 10(-10) M) and low affinity (Kd = 1.93 x 10(-7) M) components. The binding sites were highly specific for PYY and APP as well as for NPY and PPP, coupled to a guanine nucleotide regulatory protein, and distributed in various brain areas, including the cerebellum. The C-terminal fragments of PYY, PYY-(17-36) and PYY-(24-36), exhibited low potency in inhibiting binding, but behaved like full agonists. Porcine brain membranes, on the other hand, possessed two orders of the APP-binding sites, a high affinity component (Kd = 4.24 x 10(-9) M) and a low affinity component (Kd = 3.08 x 10(-7) M). APP binding showed a high specificity for APP, but not for PPP, NPY, or PYY. The binding activity was highest in the pituitary gland, followed by the hippocampus, amygdala, cerebral cortex, hypothalamus, and cerebellum. Guanosine 5'-O-thiotriphosphate, a nonhydrolyzable GTP analog, did not inhibit the binding of [125I]APP to porcine or chicken brain membranes, which ran counter to the results of PYY receptors in both species. Cross-linking studies have demonstrated that receptor-bound [125I]APP is cross-linked to a protein of 67 kDa without disulfide-linked subunits in both porcine and chicken brain membranes. In the latter species, [125I]PYY and [125I]NPY were also cross-linked to the same 67-kDa proteins, which were different from the receptor proteins (50 kDa) in mammalian species. These results indicate that chicken brain has receptors specific for PYY and NPY, as was found in mammalian brains, and that PYY, NPY, and PP act in the brain through interaction at multiple receptor sites, which are similar to and shared by other members of the PP family. Furthermore, the finding that APP-binding sites in porcine brain are more specific than those in avian brain suggests that an endogenous peptide similar to APP may exist in porcine brain.

Animals↗
PubMed2002

Advances in the cellular and molecular biology of the beta-amyloid protein in Alzheimer's disease.

Alzheimer's disease (AD) is a progressive senile dementia characterized by deposition of a 4 kDa peptide of 39-42 residues known as amyloid beta-peptide (Abeta) in the form of senile plaques and the microtubule associated protein tau as paired helical filaments. Genetic studies have identified mutations in the Abeta precursor protein (APP) as the key triggers for the pathogenesis of AD. Other genes such as presenilins 1 and 2 (PS1/2) and apolipoprotein E (APOE) also play a critical role in increased Abeta deposition. Several biochemical and molecular studies using transfected cells and transgenic animals point to mechanisms by which Abeta is generated and aggregated to trigger the neurodegeneration that may cause AD. Three important enzymes collectively known as "secretases" participate in APP processing. An enzymatic activity, beta-secretase, cleaves APP on the amino side of Abeta producing a large secreted derivative, sAPPbeta, and an Abeta-bearing membrane-associated C-terminal derivative, CTFbeta, which is subsequently cleaved by the second activity, gamma-secretase, to release Abeta. Alternatively, a third activity, alpha-secretase, cleaves APP within Abeta to the secreted derivative sAPPalpha and membrane-associated CTFalpha. The predominant secreted APP derivative is sAPPalpha in most cell-types. Most of the secreted Abeta is 40 residues long (Abeta40) although a small percentage is 42 residues in length (Abeta42). However, the longer Abeta42 aggregates more readily and was therefore considered to be the pathologically important form. Advances in our understanding of APP processing, trafficking, and turnover will pave the way for better drug discovery for the eventual treatment of AD. In addition, APP gene regulation and its interaction with other proteins may provide useful drug targets for AD. The emerging knowledge related to the normal function of APP will help in determining whether or not the AD associated changes in APP metabolism affect its function. The present review summarizes our current understanding of APP metabolism and function and their relationship to other proteins involved in AD.

Aged↗
PubMed2005

The fetal basis of amyloidogenesis: exposure to lead and latent overexpression of amyloid precursor protein and beta-amyloid in the aging brain.

The fetal basis of adult disease (FeBAD) hypothesis states that many adult diseases have a fetal origin. According to FeBAD, injury or environmental influences occurring at critical periods of organ development could result in "programmatic" changes via alterations in gene expression or gene imprinting that may result in functional deficits that become apparent later in life. Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized by excessive deposits of aggregated beta-amyloid (Abeta) peptides, which are snippets of the beta-amyloid precursor protein (APP). The predominantly sporadic nature of AD suggests that the environment must play a role in neurodegeneration. To examine latent responses to an environmental agent, we exposed rodents to lead and monitored the lifetime expression of the APP gene. We observed that APP mRNA expression was transiently induced in neonates, but exhibited a delayed overexpression 20 months after exposure to Pb had ceased. This upregulation in APP mRNA expression was commensurate with a rise in activity of the transcription factor Sp1, one of the regulators of the APP gene. Furthermore, the increase in APP gene expression in old age was accompanied by an elevation in APP and its amyloidogenic Abeta product. In contrast, APP expression, Sp1 activity, as well as APP and Abeta protein levels were unresponsive to Pb exposure during old age. These data suggested that environmental influences occurring during brain development predetermined the expression and regulation of APP later in life, potentially altering the course of amyloidogenesis.

Aging↗
PubMed1999

Thrombin induces surface and intracellular secretion of amyloid precursor protein from human endothelial cells.

Thrombin, a major coagulant and inflammatory mediator, was shown to regulate amyloid precursor protein (APP) secretion. APP is the protein from which the amyloid beta peptide (A(beta)) is derived. A(beta) forms the core of vascular and cerebral plaques in Alzheimer's disease (AD). In this study, human umbilical vein endothelial cells (HUVEC) were used to examine the effects of thrombin on APP expression. Cell supernatants from thrombin-treated HUVEC were immunoblotted to measure secreted APP. Thrombin-induced secretion of APP peaks at approximately 30 min post-treatment. Immunohistochemical analysis found that APP is not colocalized with or secreted through the same pathway as coagulation factor VIII. The secretion of APP is thrombin receptor-mediated, since it is inhibited by the thrombin antagonist N-Acetyl-D-Phe-Pro-1-Amido-4-Guanidino-Butyl-1-Boronic Acid. It also is induced by treatment with a calcium ionophore. Moreover, APP secretion is protein kinase C (PKC)-dependent because it is blocked by the PKC inhibitor bisindolylmaleimide. APP secretion also occurs from the cell surface, possibly through direct cleavage by thrombin. Immunoreactivity on the surface of HUVEC decreased after thrombin treatment but not after treatment with a non-proteolytic thrombin receptor activator. These data suggest that thrombin induces APP secretion through a PKC-dependent mechanism, as well as from the cell surface. Our results are consistent with thrombin playing a role in AD pathology.

Amyloid beta-Protein Precursor↗
PubMed2001

Demonstration by fluorescence resonance energy transfer of two sites of interaction between the low-density lipoprotein receptor-related protein and the amyloid precursor protein: role of the intracellular adapter protein Fe65.

Amyloid-beta, the major constituent of senile plaques in Alzheimer's disease, is derived from the amyloid precursor protein (APP) by proteolysis. Kunitz protease inhibitor (KPI) containing forms of APP (APP751/770) interact with a multifunctional endocytic receptor, the low-density lipoprotein receptor-related protein (LRP), which modulates its proteolytic processing affecting production of amyloid-beta. We used fluorescence resonance energy transfer (FRET) using labeled LRP and APP in H4 cell line to examine the subcellular localization and the molecular domains involved in the APP-LRP interaction. KPI-containing forms of APP (APP770) demonstrated FRET with LRP that was sensitive to the LRP inhibitor receptor-associated protein (RAP), suggesting an interaction between the extracellular domains of APP770 and LRP. APP695 also interacts with LRP to lesser degree (as measured by extracellular domain probes), and this ectodomain interaction is not altered by RAP. By using C-terminally tagged LRP and APP, we demonstrate a second site of interaction between the C termini of both APP695 and APP770 and the C terminus of LRP, and that the interactions at these regions are not sensitive to RAP. We next examined the possibility that the C-termini APP-LRP interaction was mediated by Fe65, an adaptor protein that interacts with the cytoplasmic tails of LRP and APP. FRET studies confirmed a close proximity between the amino Fe65 phosphotyrosine binding (PTB) domain and LRP cytoplasmic domain and between the carboxyl Fe65 PTB domain and the APP cytoplasmic domain. These findings demonstrate that LRP interaction with APP occurs via both extracellular and intracellular protein interaction domains.

Amyloid beta-Protein Precursor↗
PubMed1992

Characterization of platelet-releasable forms of beta-amyloid precursor proteins: the effect of thrombin.

Activated platelets release a potent inhibitor of factor XIa previously identified as a Kunitz proteinase inhibitor domain-containing form of the beta-amyloid precursor proteins (beta APP). Two carboxy-terminal truncated forms of the beta APP, beta APP-751 and beta APP-770, are shown to be the predominant isoforms secreted by platelets. The release of beta APP from platelets is responsible for the higher concentration of beta APP in serum compared with plasma, and thrombin dose-response data show that release of beta APP is most consistent with alpha granule localization within the platelet. Thrombin induces a limited and specific proteolysis of platelet-secreted beta APP, resulting in loss of a carboxy-terminal fragment. This phenomena is dependent on both thrombin concentration and duration of incubation and is inhibited by the thrombin-specific inhibitor hirudin, characteristics that can be duplicated in a mixture of purified recombinant beta APP-751 and thrombin. A similar effect of thrombin on full-length transmembrane forms of beta APP would result in a membrane-bound remnant containing the intact beta-amyloid protein.

Alternative Splicing↗
PubMed2006

[Effect of antitachycardia pacemaker on atrial tachyarrhythmia detection, prevention and termination].

OBJECTIVE: The present study retrospectively evaluated the reliability of detecting atrial tachyarrhythmias (ATA), the efficacy of automatic atrial antitachycardia pacing (ATP) and the performance of atrial preventive pacing (APP) algorithms in an implanted antitachycardia DDDRP pacemaker for patients with sick sinus syndrome and paroxysmal ATA. METHODS: In all 24 patients, a DDDRP pacemaker (Medtronic AT500/AT501) was implanted. APP algorithms were switched on at the implanting physician's discretion. During each pacemaker follow-up, information was saved to disk and the ATA burden between those patients with APP algorithms switched "ON" and "OFF" were compared. Reliability of ATA detection was determined by reviewing the stored electrograms and ATP efficacy was also reviewed. Both the pacemaker memory data and manual EGM retrieval were used for the analysis. RESULTS: Complication-free survival at (17.63 +/- 8.79) months was 100%. In 12 patients APP was not turned "ON" until the latest follow-up, in 6 patients APP was switched "ON" at their first visit after implantation, and in another 6 patients APP was switched "ON" after a median follow-up of 9.29 months. There were 97 367 episodes of ATA detected by the devices, of those with stored atrial electrograms the correct classification of ATA was (76.77 +/- 20.52)%. The percentage of atrial pacing with APP algorithms turned on was (87.95 +/- 20.93)%, which was significantly higher than that in patients with APP "OFF" (50.73 +/- 34.46)% (P < 0.01). ATP efficacy was (50.27 +/- 19.29)%. However, the ATA burden (14.73% vs 16.52%, or 7.52 hours vs 6.58 hours per week, P > 0.05) and the longest duration of single ATA episode (27.27 hours vs 20.75 hours, P > 0.05) were not significantly different between those patients with APP "ON" and "OFF". No proarrhythmic effect or major cardiovascular event was observed. CONCLUSIONS: The antitachycardia DDDRP pacemaker correctly detects and diagnoses about 75% of the ATA episodes, while the ATP therapy successfully terminates atrial tachycardia or flutter in about 50% of attacks. However, there is no difference in ATA burden with the APP algorithms and high incidence of atrial pacing. As a non-curative therapy strategy, this high-cost device may only be used in strictly selected indication patients in addition to other treatments of ATA.

Aged↗
PubMed1989

Isolation and expression of multiple forms of beta amyloid protein precursor cDNAs.

Alzheimer's disease (AD) is associated with the extra-normal accumulation of a 42 amino acid (aa) beta-amyloid peptide (BAP) in amyloid plaques and cerebrovascular deposits. Though BAP is deposited exclusively in brains of AD and Down syndrome patients, the mRNA encoding the putative precursor to BAP is found in the brain and in peripheral tissues. Using an HL 60 cDNA library, we have isolated two Amyloid Peptide Precursor (APP) cDNAs with sequences that code for proteins containing 751 and 770 aa (APP 751 and APP 770). These longer forms of APP encode a novel region of 56 aa which is homologous to the Kunitz domain of serine protease inhibitors which is not found in the 695 aa form (APP 695) isolated from brain (1). We have examined APP expression at the RNA level using Northern blots and S1 nuclease protection studies in which the lengths, distributions and relative abundances of APP RNAs were assayed. We find that brain, WA 17 cells and NG 108-15 cells contain all three forms of APP RNAs while HL 60 cells, TMT3 cells and AB-1 cells contain predominantly the APP 751 and APP 770 RNAs.

Alzheimer Disease↗
PubMed1995

The amyloid peptide precursor in Alzheimer's disease.

beta A4, an hydrophobic peptide containing from 39 to 43 amino acids, is the major constituent of the amyloid core of characteristic lesions of Alzheimer's disease (AD) known as senile plaques. By cDNA cloning, it was demonstrated that beta A4 is derived from a much larger precursor named the amyloid peptide precursor or APP. The isolation of cDNA clones and the characterization of their nucleotide sequence has shown that several APP proteins containing from 365 to 770 amino acids are produced by alternative splicing of a single primary transcript. The major APP isoforms contain a large extracellular N-terminal domain and a short intracellular C-terminal end. The beta A4 sequence itself is contained for 15 amino acids in the transmembrane domain while 28 amino acids are protruding into the extracellular space. The gene encoding APP is located on human chromosome 21, which is involved in the autosomal dominant inheritance of some early onset of familial AD (FAD). In a few families, mutations of the APP gene have been described. Although they can explain less than 3% of all FAD cases, these mutations clearly demonstrate that APP metabolism is involved in the development of AD. The overexpression of APP in several cultured cells allowed to characterize two catabolic pathways of the protein. A non amyloidogenic pathway precludes formation of beta A4, because APP is cleaved by an alpha-secretase within the beta A4 sequence, leading to the extracellular release of a C-terminal truncated protein. The amyloidogenic pathway produces soluble extracellular beta A4, by cleavage of APP by beta- and gamma-secretases after endocytosis of the transmembrane protein. Although soluble beta A4 is non toxic, it becomes very neurotoxic as soon as it makes fibrils. It is therefore essential to characterize the different factors which favor the organization of beta A4 into fibrils. They have to be considered as risk factors for AD, as well as targets for new therapies. Another therapeutic approach could consist in developing molecules able to inhibit beta A4 production by stimulating the non amyloidogenic pathway of APP.

Aging↗
PubMed1996

The beta-amyloid domain is essential for axonal sorting of amyloid precursor protein.

We have analysed the axonal sorting signals of amyloid precursor protein (APP). Wild-type and mutant versions of human APP were expressed in hippocampal neurons using the Semliki forest virus system. We show that wild-type APP and mutations implicated in Alzheimer's disease and another brain beta-amyloidosis are sorted to the axon. By analysis of deletion mutants we found that the membrane-inserted APP ectodomain but not the cytoplasmic tail is required for axonal sorting. Systematic deletions of the APP ectodomain identified two regions required for axonal delivery: one encoded by exons 11-15 in the carbohydrate domain, the other encoded by exons 16-17 in the juxtamembraneous beta-amyloid domain. Treatment of the cells with the N-glycosylation inhibitor tunicamycin induced missorting of wild-type APP, supporting the importance of glycosylation in axonal sorting of APP. The data revealed a hierarchy of sorting signals on APP: the beta-amyloid-dependent membrane proximal signal was the major contributor to axonal sorting, while N-glycosylation had a weaker effect. Furthermore, recessive somatodendritic signals, most likely in the cytoplasmic tail, directed the protein to the dendrites when the ectodomain was deleted. Analysis of detergent solubility of APP and another axonally delivered protein, hemagglutinin, demonstrated that only hemagglutinin formed CHAPS-insoluble complexes, suggesting distinct mechanisms of axonal sorting for these two proteins. This study is the first delineation of sorting requirements of an axonally targeted protein in polarized neurons and indicates that the beta-amyloid domain plays a major role in axonal delivery of APP.

Alzheimer Disease↗
PubMed2001

Amyloid precursor protein in platelets of patients with Alzheimer disease: effect of acetylcholinesterase inhibitor treatment.

BACKGROUND: Amyloid precursor protein (APP) forms with apparent molecular weights of 130, 110, and 106 kd are present in human platelets. It has been demonstrated that Alzheimer disease (AD) is specifically associated with a decreased APP forms ratio in platelets. OBJECTIVE: To investigate whether acetylcholinesterase (AChE) inhibitor treatment modifies the ratio of platelet APP forms in patients with AD. PATIENTS AND METHODS: From a large sample of patients with probable AD, 30 with mild to moderate AD were selected. Each patient underwent a clinical evaluation including the Mini-Mental State Examination (MMSE) and platelet APP forms analysis at baseline and after 30 days. During this interval, 20 of 30 patients with AD were treated with donepezil hydrochloride (5 mg/d), a piperidine phosphate-based cholinesterase inhibitor. Platelets were subjected to Western blot analysis using monoclonal antibody (22C11). The ratio between the immunoreactivity of the higher-molecular-weight APP form (130 kd) and the lower forms (106 and 110 kd) was measured. RESULTS: All patients taking donepezil completed the 30 days of treatment without adverse effects. The platelet APP forms ratio at baseline did not differ between the 2 AD groups (mean +/- SD optical density ratio: untreated AD, 0.47 +/- 0.12; treated AD, 0.38 +/- 0.18), whereas a significant difference was found at follow-up (mean +/- SD optical density ratio: untreated AD, 0.45 +/- 0.17; treated AD, 0.77 +/- 0.29; P<.001). A significant improvement in MMSE scores in treated AD patients was observed from baseline (16.9 +/- 3.8) to 30 days (18.9 +/- 4.42) (P<.009, 30 days vs baseline), but no significant correlation was found in treated AD patients between MMSE score improvement and APP forms/ratio increase (P =.09). CONCLUSIONS: Administration of AChE inhibitors increases the ratio of APP forms in platelets of patients with AD, suggesting a potential effect of AChE inhibitors on APP trafficking or processing in a peripheral cell.

Aged↗
PubMed2000

Neurohormonal signalling pathways and the regulation of Alzheimer beta-amyloid metabolism.

Alzheimer's disease (AD) is characterized by the intracranial accumulation of the 4 kDa amyloid beta peptide (A beta), following proteolysis of a approximately 700 amino acid, integral membrane precursor, the amyloid beta precursor protein (APP). The best evidence causally linking APP to AD has been provided by the discovery of mutations within the APP coding sequence that segregate with disease phenotypes in autosomal dominant forms of familial AD (FAD). Though FAD is rare (< 10% of all AD), the hallmark features--amyloid plaques, neurofibrillary tangles, synaptic and neuronal loss, neurotransmitter deficits, dementia--are indistinguishable when FAD is compared with typical, common, 'non-familial', or sporadic AD (SAD). Studies of some clinically relevant mutant APP molecules from FAD families have yielded evidence that APP mutations can lead to enhanced generation or aggregability of A beta, consistent with a pathogenic role in AD. Other genetic loci for FAD have been discovered which are distinct from the immediate regulatory and coding regions of the APP gene, indicating that defects in molecules other than APP can also specify cerebral amyloidogenesis and FAD. To date, all APP and non-APP FAD mutations can be demonstrated to have the common feature of promoting amyloidogenesis of A beta. Epidemiological studies indicate that postmenopausal women on oestrogen hormone replacement therapy (HRT) have their relative risk of developing SAD diminished by about one-third as compared with age-matched women not receiving HRT. Because of the key role of cerebral A beta accumulation in initiating AD pathology, it is most attractive that oestradiol might modulate SAD risk or age-at-onset by inhibiting A beta accumulation. A possible mechanistic basis for such a scenario is reviewed here.

Alzheimer Disease↗
PubMed2003

Enhanced production of amyloid precursor protein mRNA by peripheral mononuclear blood cell in Alzheimer's disease.

Previous studies have suggested the involvement of amyloid precursor protein (APP) in Alzheimer's disease (AD), as exons 16 and 17 of the APP gene mutations have been found in some familial AD patients. Furthermore, overexpression and deposition of the beta amyloid peptide, a proteolytic product of APP, have been considered as a pathological hallmark of Alzheimer's disease. Therefore, it is of particular interest to determine the expression of APP gene at the transcription level for better understanding of the roles of APP gene in AD pathogenesis. In this work, we employed the quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) to quantify APP mRNA transcripts in the peripheral mononuclear blood cells (PMBC) of 52 Alzheimer's patients, 28 vascular dementia (VD) patients, and 60 healthy elderly controls. The results showed that the amount (mean +/- SEM) of APP transcripts per microgram of total cDNA was 4.05 +/- 0.27, 2.73 +/- 0.33, and 2.59 +/- 0.27 amole in AD, VD, and healthy controls, respectively. There was a significant increase (P < 0.05) in the expression of APP mRNA transcripts in AD compared with that in VD or in healthy controls. Thus, our data indicated that variation of APP gene expression in PMBC might be a pathogenic source of Alzheimer's disease.

Aged↗
PubMed1994

Cell cycle-dependent regulation of the phosphorylation and metabolism of the Alzheimer amyloid precursor protein.

Accumulation of the amyloid A beta peptide, which is derived from a larger precursor protein (APP), and the formation of plaques, are major events believed to be involved in the etiology of Alzheimer's disease. Abnormal regulation of the metabolism of APP may contribute to the deposition of plaques. APP is an integral membrane protein containing several putative phosphorylation sites within its cytoplasmic domain. We report here that APP is phosphorylated at Thr668 by p34cdc2 protein kinase (cdc2 kinase) in vitro, and in a cell cycle-dependent manner in vivo. At the G2/M phase of the cell cycle, when APP phosphorylation is maximal, the levels of mature APP (mAPP) and immature APP (imAPP) do not change significantly. However, imAPP is altered qualitatively. Furthermore, the level of the secreted extracellular N-terminal domain (APPS) is decreased and that of the truncated intracellular C-terminal fragment (APPCOOH) is increased. These findings suggest the possibility that phosphorylation-dependent events occurring during the cell cycle affect the metabolism of APP. Alterations in these events might play a role in the pathogenesis of Alzheimer's disease.

Alzheimer Disease↗
PubMed2004

Inhibition of histone deacetylation enhances the neurotoxicity induced by the C-terminal fragments of amyloid precursor protein.

The AICD (APP intracellular Domain) and C31, caspase-cleaved C-terminal fragment of APP, have been found in Alzheimer's disease (AD) patients' brains and have been reported to induce apoptosis in neuronal cells. In recent, the C-terminal fragments of amyloid precursor protein (APP-CTs) have been reported to form a complex with Fe65 and the histone acetyltransferase Tip60 and are thought to be involved in gene transcription. In this study, based on the hypothesis that APP-CTs might exert neurotoxicity by inducing some gene transcription, we investigated the effects of APP-CTs on histone acetylation which indicates that transcription is actively going on and also on the relationship between histone acetylation and the cytotoxicity induced by APP-CTs in nerve growth factor (NGF)-differentiated PC12 cells and rat primary cortical neurons. Here we demonstrate that the expression of APP-CTs [C31, AICD (C59) and C99] induces increases in acetylation of histone 3 and histone 4 and that treatment with sodium butyrate, an inhibitor of histone deacetylase, significantly enhances the cytotoxicity induced by APP-CTs. The acetylation of histone plays an important role in allowing regulatory proteins to access DNA and is likely to be a major factor in the regulation of gene transcription. Taken together, our results suggest that APP-CTs exert neurotoxicity by transcription-dependent mechanisms and this might contribute to the pathogenesis of AD.

Acetylation↗
PubMed1990

The Alzheimer's amyloid precursor protein is produced by type I astrocytes in primary cultures of rat neuroglia.

The production of beta-amyloid precursor protein (beta APP) by primary mixed glial cell cultures from cerebral cortex of 2-3 day postnatal rats was examined by Northern and Western blotting and by immunocytochemistry. A single 3.5 kb beta APP RNA transcript was detected using probes recognizing all forms of beta APP messenger RNA. No signal was detected with a probe specific for the alternately spliced Kunitz protease inhibitor (KPI) region. In Western blot analysis of protein extracts, antisera specific for either the cytoplasmic or extracellular parts of beta APP detected several proteins ranging from 105 to 140 kDa. None of these were recognized by an antiserum specific to the KPI insert of the beta APP. Multicolor immunofluorescence showed beta APP immunoreactivity in type I (GFAP+ A2B5-) astrocytes, distributed in a fibrillar pattern like that of glial fibrillary acidic protein (GFAP). No beta APP immunoreactivity was detected in oligodendrocytes (GC+) or in A2B5+ progenitor cells. Moreover, no cultured cells showed immunostaining with an antiserum specific for the KPI sequence of beta APP. We conclude that type I astrocytes in primary culture produce amyloid precursor protein, but that oligodendrocytes and their precursors do not. Moreover, type I astrocytes produce predominantly the beta APP subtypes which lacks the KPI sequence.

Amyloid↗