Amyloid Precursor Protein Concentration Research Articles

Butyrate acts as a G-protein-coupled receptor ligand that prevents high glucose-induced amyloidogenesis in N2a cells through the protein kinase B/glycogen synthase kinase-3β pathway.

Butyrate acts as a G-protein-coupled receptor ligand that prevents high glucose-induced amyloidogenesis in N2a cells through the protein kinase B/glycogen synthase kinase-3β pathway.

A Numerical Study of Sensitivity Coefficients for a Model of Amyloid Precursor Protein and Tubulin-Associated Unit Protein Transport and Agglomeration in Neurons at the Onset of Alzheimer's Disease.

Modeling of intracellular processes occurring during the development of Alzheimer's disease (AD) can be instrumental in understanding the disease and can potentially contribute to finding treatments for the disease. The model of intracellular processes in AD, which we previously developed, contains a large number of parameters. To distinguish between more important and less important parameters, we performed a local sensitivity analysis of this model around the values of parameters that give the best fit with published experimental results. We show that the influence of model parameters on the total concentrations of amyloid precursor protein (APP) and tubulin-associated unit (tau) protein in the axon is reciprocal to the influence of the same parameters on the average velocities of the same proteins during their transport in the axon. The results of our analysis also suggest that in the beginning of AD the aggregation of amyloid-β and misfolded tau protein have little effect on transport of APP and tau in the axon, which suggests that early damage in AD may be reversible.

How the formation of amyloid plaques and neurofibrillary tangles may be related: a mathematical modelling study.

We develop a mathematical model that enables us to investigate possible mechanisms by which two primary markers of Alzheimer's disease (AD), extracellular amyloid plaques and intracellular tangles, may be related. Our model investigates the possibility that the decay of anterograde axonal transport of amyloid precursor protein (APP), caused by toxic tau aggregates, leads to decreased APP transport towards the synapse and APP accumulation in the soma. The developed model thus couples three processes: (i) slow axonal transport of tau, (ii) tau misfolding and agglomeration, which we simulated by using the Finke-Watzky model and (iii) fast axonal transport of APP. Because the timescale for tau agglomeration is much larger than that for tau transport, we suggest using the quasi-steady-state approximation for formulating and solving the governing equations for these three processes. Our results suggest that misfolded tau most likely accumulates in the beginning of the axon. The analysis of APP transport suggests that APP will also likely accumulate in the beginning of the axon, causing an increased APP concentration in this region, which could be interpreted as a 'traffic jam'. The APP flux towards the synapse is significantly reduced by tau misfolding, but not due to the APP traffic jam, which can be viewed as a symptom, but rather due to the reduced affinity of kinesin-1 motors to APP-transporting vesicles.

Moderate blast exposure alters gene expression and levels of amyloid precursor protein.

Objective:To explore gene expression after moderate blast exposure (vs baseline) and proteomic changes after moderate- (vs low-) blast exposure.Methods:Military personnel (N = 69) donated blood for quantification of protein level, and peak pressure exposures were detected by helmet sensors before and during a blast training program (10 days total). On day 7, some participants (n = 29) sustained a moderate blast (mean peak pressure = 7.9 psi) and were matched to participants with no/low-blast exposure during the training (n = 40). PAXgene tubes were collected from one training site at baseline and day 10; RNA-sequencing day 10 expression was compared with each participant's own baseline samples to identify genes and pathways differentially expressed in moderate blast-exposed participants. Changes in amyloid precursor protein (APP) from baseline to the day of blast and following 2 days were evaluated. Symptoms were assessed using a self-reported form.Results:We identified 1,803 differentially expressed genes after moderate blast exposure; the most altered network was APP. Significantly reduced levels of peripheral APP were detected the day after the moderate blast exposure and the following day. Protein concentrations correlated with the magnitude of the moderate blast exposure on days 8 and 9. APP concentrations returned to baseline levels 3 days following the blast, likely due to increases in the genetic expression of APP. Onset of concentration problems and headaches occurred after moderate blast.Conclusions:Moderate blast exposure results in a signature biological profile that includes acute APP reductions, followed by genetic expression increases and normalization of APP levels; these changes likely influence neuronal recovery.

Valproic acid and its congener propylisopropylacetic acid reduced the amount of soluble amyloid-β oligomers released from 7PA2 cells

The amyloid hypothesis of Alzheimer's disease suggests that synaptic degeneration and pathology is caused by the accumulation of amyloid-β (Aβ) peptides derived from the amyloid precursor protein (APP). Subsequently, soluble Aβ oligomers cause the loss of synaptic proteins from neurons, a histopathological feature of Alzheimer's disease that correlates with the degree of dementia. In this study, the production of toxic forms of Aβ was examined in vitro using 7PA2 cells stably transfected with human APP. We show that conditioned media from 7PA2 cells containing Aβ oligomers caused synapse degeneration as measured by the loss of synaptic proteins, including synaptophysin and cysteine-string protein, from cultured neurons. Critically, conditioned media from 7PA2 cells treated with valproic acid (2-propylpentanoic acid (VPA)) or propylisopropylacetic acid (PIA) did not cause synapse damage. Treatment with VPA or PIA did not significantly affect total Aβ42 concentrations; rather these drugs selectively reduced the concentrations of Aβ42 oligomers in conditioned media. In contrast, treatment significantly increased the concentrations of Aβ42 monomers in conditioned media. VPA or PIA treatment reduced the concentrations of APP within lipid rafts, membrane compartments associated with Aβ production. These effects of VPA and PIA were reversed by the addition of platelet-activating factor, a bioactive phospholipid produced following activation of phospholipase A2, an enzyme sensitive to VPA and PIA. Collectively these data suggest that VPA and PIA reduce Aβ oligomers through inhibition of phospholipase A2 and suggest a novel therapeutic approach to Alzheimer's treatment.

Alteration of Alzheimer Amyloid Precursor Protein after Treatment with Carbamazepine in Colon Cancer

Background: Amyloid precursor protein (APP), which is involved in cell proliferation, is observed to be over expressed in human cancer. Thus, it is crucial to investigate its role in cancer and suggest treatment strategies to alter its effects on cell growth. Objectives: The main purpose of this study was to determine APP concentrations in colon cancer SW480 cell line after treatment with histone deacetylase inhibitors (HDACIs), namely valproic acid (VPA) and carbamazepine (CBZ). Methods: In the present experimental study, carried out during the period 2014 - 2016 in Iran, 1000000 cells were seeded and incubated in a six-well plate for each sample preparation. The cells were then treated with drugs and APP was evaluated. The concentration of this protein was detected using the enzyme-linked immunosorbent assay (ELISA) method. Results: We found that treatment with CBZ (P < 0.001) and VPA (P < 0.001) reduced the APP levels significantly compared to controls. The APP level reduction by CBZ was 41.6% more than that by VPA. Conclusions: The results of this study suggest that APP reduction by HDACIs can apparently play an important role in the treatment of colon cancer.

Citrulline diet supplementation improves specific age-related raft changes in wild-type rodent hippocampus

The levels of molecules crucial for signal transduction processing change in the brain with aging. Lipid rafts are membrane microdomains involved in cell signaling. We describe here substantial biophysical and biochemical changes occurring within the rafts in hippocampus neurons from aging wild-type rats and mice. Using continuous sucrose density gradients, we observed light-, medium-, and heavy raft subpopulations in young adult rodent hippocampus neurons containing very low levels of amyloid precursor protein (APP) and almost no caveolin-1 (CAV-1). By contrast, old rodents had a homogeneous age-specific high-density caveolar raft subpopulation containing significantly more cholesterol (CHOL), CAV-1, and APP. C99-APP-Cter fragment detection demonstrates that the first step of amyloidogenic APP processing takes place in this caveolar structure during physiological aging of the rat brain. In this age-specific caveolar raft subpopulation, levels of the C99-APP-Cter fragment are exponentially correlated with those of APP, suggesting that high APP concentrations may be associated with a risk of large increases in beta-amyloid peptide levels. Citrulline (an intermediate amino acid of the urea cycle) supplementation in the diet of aged rats for 3months reduced these age-related hippocampus raft changes, resulting in raft patterns tightly close to those in young animals: CHOL, CAV-1, and APP concentrations were significantly lower and the C99-APP-Cter fragment was less abundant in the heavy raft subpopulation than in controls. Thus, we report substantial changes in raft structures during the aging of rodent hippocampus and describe new and promising areas of investigation concerning the possible protective effect of citrulline on brain function during aging.

Clinical and neurobiological correlates of soluble amyloid precursor proteins in the cerebrospinal fluid

According to a widely accepted hypothesis, the amyloid precursor protein (APP) is processed by two competing pathways: the amyloidogenic β-secretase-mediated pathway or the nonamyloidogenic α-secretase-mediated pathway. APP is cleaved preferentially through the nonamyloidogenic pathway in normal brain, whereas the balance shifts to the amyloidogenic pathway in Alzheimer's disease (AD). The levels of the α-secretase-cleaved soluble APP (sAPPα) and β-secretase-cleaved soluble APP (sAPPβ) in cerebrospinal fluid (CSF) are likely to reflect these competing mechanisms. We investigated the levels and the relationship between sAPPα and sAPPβ in the CSF of 64 patients with mild AD, 76 patients with mild cognitive impairment, and 12 cognitively healthy control subjects, as well as the effect of apolipoprotein E genotype and sex on soluble APP levels. There was a significant positive correlation between sAPPα and sAPPβ levels in all three groups. sAPPα and sAPPβ concentrations were higher in patients with mild cognitive impairment compared with patients with AD. In the AD group, females exhibited higher sAPPα and sAPPβ levels than males. No influence of the apolipoprotein E genotype on soluble APP concentrations was detected. The positive correlation between sAPPα and sAPPβ challenges the hypothesis that AD is caused by an imbalance of the α- and β-secretase APP proteolysis through competing mechanisms. Moreover, the differences in CSF levels of sAPPα and sAPPβ between male and female patients with AD may reflect a "sexual dimorphism" in the activity of the two APP processing pathways in AD.

Quantitative modelling of amyloidogenic processing and its influence by SORLA in Alzheimer's disease

The extent of proteolytic processing of the amyloid precursor protein (APP) into neurotoxic amyloid-β (Aβ) peptides is central to the pathology of Alzheimer's disease (AD). Accordingly, modifiers that increase Aβ production rates are risk factors in the sporadic form of AD. In a novel systems biology approach, we combined quantitative biochemical studies with mathematical modelling to establish a kinetic model of amyloidogenic processing, and to evaluate the influence by SORLA/SORL1, an inhibitor of APP processing and important genetic risk factor. Contrary to previous hypotheses, our studies demonstrate that secretases represent allosteric enzymes that require cooperativity by APP oligomerization for efficient processing. Cooperativity enables swift adaptive changes in secretase activity with even small alterations in APP concentration. We also show that SORLA prevents APP oligomerization both in cultured cells and in the brain in vivo, eliminating the preferred form of the substrate and causing secretases to switch to a less efficient non-allosteric mode of action. These data represent the first mathematical description of the contribution of genetic risk factors to AD substantiating the relevance of subtle changes in SORLA levels for amyloidogenic processing as proposed for patients carrying SORL1 risk alleles.

SorLA/LR11 Regulates Processing of Amyloid Precursor Protein via Interaction with Adaptors GGA and PACS-1

SorLA has been recognized as a novel sorting receptor that regulates trafficking and processing of the amyloid precursor protein (APP) and that represents a significant risk factor for sporadic Alzheimer disease. Here, we investigated the cellular mechanisms that control intracellular trafficking of sorLA and their relevance for APP processing. We demonstrate that sorLA acts as a retention factor for APP in trans-Golgi compartments/trans-Golgi network, preventing release of the precursor into regular processing pathways. Proper localization and activity of sorLA are dependent on functional interaction with GGA and PACS-1, adaptor proteins involved in protein transport to and from the trans-Golgi network. Aberrant targeting of sorLA to the recycling compartment or the plasma membrane causes faulty APP trafficking and imbalance in non-amyloidogenic and amyloidogenic processing fates. Thus, our findings identified altered routing of sorLA as a major cellular mechanism contributing to abnormal APP processing and enhanced amyloid beta-peptide formation.

Strategies for examination of Alzheimer’s disease amyloid precursor protein isoforms

We describe a proteomics procedure using bioinformatics, immunoprecipitation, two-dimensional gel electrophoresis, Western blotting, in-gel digestion, LC-MS, MALDI-MS, and MS-MS for isolation and identification of amyloid precursor protein (APP) isoforms APP695, APP751, and APP770. Retinoic acid-induced Ntera 2 cell line, derived from a human teratocarcinoma cells, was the in-vitro source of APP. Initial isolation of whole APP was performed by immunoprecipitation, using AB10, a monoclonal antibody raised to amino acids 1-17 of the beta-amyloid peptide sequence, which is present in all three alpha secretase-cleaved isoforms of interest. The next stage was separation of whole APP into its isoform components by two-dimensional gel electrophoresis. Because of low APP concentrations, detection by the usual staining methods, for example Sypro Ruby, able to detect low picomole concentrations, did not enable visualisation of the isoforms. Western analysis, however, enabled primary detection of APP, because of the inherent sensitivity of antibodies raised to specific isoform regions. This initial visualization acted as a template for excision of isoforms from 2D gels, which were then subjected to peptide mass mapping. Initial theoretical digestion of each isoform revealed the presence of specific peptides, which were then used as "tags" for isoform detection.

Amyloid precursor protein (APP) and its derivatives change after cellular energy depletion. An in vitro-study

To study the relationship between the metabolism of amyloid precursor protein (APP) and cellular energy failure, HEK 293 cells stably transfected with betaAPP 695 underwent graded energy failure induced either by i) hypoxia (pO(2) 25 mm Hg), ii) inhibition of the respiratory chain by sodium azide (NaN(3)), or iii) by combined glucose deprivation/hypoxia of different duration and severity. Secreted APP (APPs) and the derivative betaA4 were quantified autoradiographically by immunoprecipitation, and [(35)S] methionine labeling. APP holoprotein (APPh) was determined by Western blot analysis. The concentrations of the energy-rich metabolites ATP, ADP, creatine phosphate (CrP), and adenosine were measured by high performance liquid chromatography. Mild to moderate energy failure after NaN(3) treatment (2h, 4h) and hypoxia (2h, 8h) was characterized by normal ATP concentration but also by a high reduction in CrP. A stress condition indicated by an increased ATP turnover and adenosine increase was obtained. Intracellular APPh increased but its metabolites APPs and betaA4 as measured in the extracellular compartment decreased. These changes may point to a compensatory response of APP but also to a initial disturbance in intracellular APP metabolism. Severe abnormalities in both energy formation and utilization after 8h NaN(3) and hypoxia glucose deprivation were found to be accompanied by a drastic fall in intracellular APPh concentration by at least 50%, paralleled by an accelerating reduction in the extracellular concentrations of both APPs and betaA4.A significant linear correlation between APPh and ATP and between CrP and betaA4 became obvious. The data of the present study indicate that abnormalities in APP metabolism were generated in an energy-dependent manner. The obvious similarities to sporadic Alzheimer s disease are discussed.

Effect of haloperidol and risperidone on amyloid precursor protein levels in vivo

The neurotoxic β-amyloid peptide of Alzheimer’s disease is formed from the amyloid precursor protein (APP), which is a member of an evolutionarily highly conserved gene family with significant functional importance. Because behavioral and psychiatric symptoms treated with antipsychotics may influence the course of the disease, we have investigated traditional and atypical antipsychotic drugs, administered through the intraperitoneal route, for their effects on rat cortical APP. Western-immunoblotting was utilized for semi-quantitative evaluation of APP levels. Treatment with haloperidol resulted in an acute elevation of cortical APP both in therapeutic and toxic doses, however, it had no significant chronic impact on APP. Atypical antipsychotic risperidone did not change cortical APP concentration. These results indicate that both haloperidol and risperidone are considered to be relatively safe with respect to APP metabolism. Possible mechanisms, including involvement of calcium and APP itself as a receptor, are discussed.

The effect of insulin and glucose on the plasma concentration of Alzheimer's amyloid precursor protein

The deposition of beta amyloid is a critical event in the pathogenesis of Alzheimer's disease. This peptide is a metabolite of the amyloid precursor protein. Recent research suggests that there is a correlation between plasma insulin and glucose concentrations and memory performance in Alzheimer's disease sufferers. Additionally, in vitro evidence suggests that both insulin and glucose may affect the metabolism of amyloid precursor protein and therefore the production of beta amyloid—however, to our knowledge no in vivo data have yet been published. We investigated the effect of elevated plasma levels of glucose and insulin on the plasma concentration of amyloid precursor protein in non-Alzheimer's disease subjects. As would be expected following ingestion of a glucose drink, blood insulin and glucose levels significantly increased. Interestingly, however, plasma amyloid precursor protein concentration decreased. Whilst no correlation was observed between insulin or glucose levels and plasma amyloid precursor protein concentration, the decrease in plasma amyloid precursor protein concentration was affected by the apolipoprotein E genotype of the subject. Possession of an ϵ4 allele resulted in a reduced decrease in plasma amyloid precursor protein in response to glucose ingestion when compared to non-ϵ4 subjects. We conclude that glucose ingestion, and the subsequent elevation of plasma levels of glucose and insulin leads to a decrease in plasma amyloid precursor protein concentration. Further studies are required to determine the clinical significance of these physiological changes in plasma amyloid precursor protein and the implications for Alzheimer's disease pathogenesis.

Effect of propentofylline on hippocampal brain energy state and amyloid precursor protein concentration in a rat model of cerebral hypoperfusion.

An animal model of graded cerebral hypoperfusion achieved by way of 2- and 4-brain vessel occlusion (vo) was used to test the effect of chronic propentofylline (PPF) administration on hippocampal energy state and amyloid precursor protein (APP) concentration. For this purpose, forty adult rats were subjected to stepwise and permanent 2 vo and 4 vo and PPF in a dose of 25 mg/day per kilogram body weight was continuously administered intraperitoneally for 1 week or 3 weeks, respectively. During the final steady-state experiment arterial blood parameters and blood gases (mean arterial blood pressure, PO2, pCO2, pH, hematocrit, hemoglobin, body temperature) were measured. Brain tissue concentrations of adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine were measured in rat hippocampus by high-pressure liquid chromatography (HPLC) analysis; APP concentration was determined using Western blot techniques. In adult rat brain, long-term PPF treatment induced a striking increase in hippocampal ATP concentration which was paralleled by an enhancement of the ATP/ADP-ratio. Specifically, after 2 vo with 1 week of PPF treatment the ATP concentration in hippocampus was enhanced by 18% when compared with 2 vo without PPF treatment, whereas after 3 weeks PPF administration with 4 vo the concentration of ATP was enhanced by 31%. Furthermore, PPF reduced the tissue concentration of adenosine from 17.75 +/- 2.79 to 8.83 +/- 3.68 pmol/mg wet weight during 4 vo if compared with animals without PPF. In addition, the APP concentration was enhanced by 35% after 1 week PPF administration when compared with non PPF treated animals. In summary, the results demonstrated that chronic administration of PPF induced an enhancement in ATP concentration in adult rat hippocampus under conditions of long-term brain vessel occlusion. Interestingly, 1 week PPF seems to have a stimulating effect on APP which may act neuroprotectively. Thus, PPF may protect hippocampal neurons from chronic ischemic damage. In conclusion, PPF may have some beneficial effects and could be used in the treatment of patients with chronic cerebrovascular disorders or neurodegenerative diseases such as vascular dementia.

The Effect of Stepwise Cerebral Hypoperfusion on Energy Metabolism and Amyloid Precursor Protein (APP) in Cerebral Cortex and Hippocampus in the Adult Rat

To study the relationship between cerebral blood flow, energy metabolism, and the formation of amyloid precursor protein (APP), an in vivo animal model was established in which stepwise long-term cerebral hypoperfusion states were induced. Adult rats underwent a stepwise chronic cerebral hypoperfusion by crosswise occlusion of the carotid and vertebral arteries with different periods and severity of hypoperfusion until the final steady-state experiment. Investigations of metabolic compounds were done in hippocampus and parietotemporal cerebral cortex. The analysis of energy-rich phosphates and adenosine was examined by HPLC analysis. Substrate concentrations of pyruvate and lactate were measured spectrophotometrically. The APP holoprotein was investigated by immunblot technique. Long-term cerebral hypoperfusion induced a decrease of energy-rich phosphates in the brain areas studied, whereas the concentration of adenosine and the ATP turnover were increased. Pyruvate decreased, and lactate was increased, pointing to a shift in the cytoplasmatic redox state. More severe changes were found in parietotemporal cerebral cortex in comparison to the hippocampus. After 2-vessel occlusion, the concentration of APP decreased, whereas the APP concentration was significantly increased in rat brain after 4-vessel occlusion. It has been demonstrated for the first time in vivo that the reduction in cerebral energy metabolism alters the formation of APP due to cerebral hypoperfusion.

Increased secretion of the amino-terminal fragment of amyloid precursor protein in brains of rats with a constitutive up-regulation of protein kinase C.

Protein kinase C (PKC) activation stimulates release of secreted amyloid precursor protein (APPs) in several cell lines. To ascertain the role of PKC in regulating APP metabolism in vivo, we used an animal model (methylazoxymethanol-treated rats; MAM rats) in which PKC is permanently hyperactivated in selected brain areas, i.e., cortex and hippocampus. A significant decrease in membrane-bound APP concentration was found in synaptosomes derived from cortex and hippocampus of MAM rats, where PKC is up-regulated, with a concomitant increase in APPs production in soluble fractions of the same brain areas. In contrast, in a brain area not affected by MAM treatment (i.e., cerebellum), APP secretion is similar in control and MAM rats, indicating that altered metabolism of APP is restricted to only those areas in which the PKC system is up-regulated. In addition, phorbol esters or H-7 modulate APPs release in hippocampal slices from both control and MAM rats, further supporting an in vivo role for this enzyme in regulating metabolism of mature APP.

Postmortem brains reveal similar but not identical amyloid precursor protein-like immunoreactivity in Alzheimer compared with other dementias

Concentrations of amyloid precursor protein (APP)-like immunoreactivity (APPLIR) have been determined by Western blotting in a soluble fraction and two membrane fractions of two areas of brain cortex from patients with Alzheimer's disease (AD) and other dementias. There were no significant differences between AD and other cases in species with the Kunitz protease inhibitor domain. However, the total soluble APPLIR was higher in AD and it was hypothesized that this relates to cholinergic hypoactivity.

Increase in extracellular NCAM and amyloid precursor protein following induction of long-term potentiation in the dentate gyrus of anaesthetized rats

The extracellular concentrations of the amyloid precursor protein (APP) and neural-cell adhesion molecule (NCAM) in the dentate gyrus of the anaesthetized rat were assayed before and after the induction of long-term potentiation (LTP) in vivo. Levels of high molecular weight neurofilament protein and activity of the lysosomal enzyme arylsulphatase were measured as internal controls and indicators of neuronal damage. Ninety minutes after the induction of LTP, the concentrations of NCAM and APP increased, in an NMDA-dependent manner, in the absence of changes in neurofilament and arylsulphatase levels. The delayed changes in the extracellular concentration of these molecules may reflect events leading to morphological modifications following LTP.