APP Level Research Articles

Oxidative stress, amyloid metabolism and Alzheimer's pathogenesis: Extrapolation of a cell-based study

Sporadic Alzheimer's disease (AD) is multifactorial in origin, but the key elements of the pathogenic process are mitochondrial dysfunction, oxidative stress, inflammatory response, protein aggregation. The molecular links among these potential pathogenic mechanisms are not fully elucidated, but oxidative stress because of its ability to alter cell signaling, gene expression, membrane properties, enzyme and receptor functions is most likely to influence the cross-talk among the probable pathogenic processes of AD. In an ongoing study in the lab we have observed that the age-related oxidative stress alters amyloid peptide metabolism in rat brain which is prevented by long-term dietary supplementation. This study has attempted to explore the role of oxidative stress in triggering and propagating amyloid peptide pathology in a cell based model. PC 12 cells have been subjected to an oxidative insult by exposure to H202 (100-400 μM) or t-butylhydroperoxide (100-400 μM) in the presence or absence of radical scavengers and antioxidants. The altered metabolism of amyloid peptide has been monitored by measuring the expression levels of APP, the intracellular and extra cellular level of Aß-42, the activities/ levels of ß secretase, δ secretase as well as the degrading enzymes of Aß-42 namely neprilysin and insulin degrading enzyme (IDE). Oxidative damage markers, protein aggregation and cell death have also been measured in this experimental model. Significant alterations in APP expression and intracellular content of Aß-42 have been observed along with accumulation of oxidative damage markers and conspicuous cell death in PC 12 cells exposed to oxidative stress. Conclusions: When extrapolated to in vivo situation, our results imply that oxidative stress present in aged brain can be a major factor in triggering and promoting altered APP metabolism leading to the genesis of sporadic AD. The study shows oxidative stress mediated Amyloid precursor protein metabolism alteration as also accumulation of Aß-42 in cell. This study has clear implications in understanding the common mechanisms of brain aging and AD.

GRK5 Deficiency Accelerates β-Amyloid Accumulation in Tg2576 Mice via Impaired Cholinergic Activity

Membrane G protein-coupled receptor kinase 5 (GRK5) deficiency is linked to Alzheimer disease, yet its precise roles in the disease pathogenesis remain to be delineated. We have previously demonstrated that GRK5 deficiency selectively impairs desensitization of presynaptic M2 autoreceptors, which causes presynaptic M2 hyperactivity and inhibits acetylcholine release. Here we report that inactivation of one copy of Grk5 gene in transgenic mice overexpressing β-amyloid precursor protein (APP) carrying Swedish mutations (Tg2576 or APPsw) resulted in significantly increased β-amyloid (Aβ) accumulation, including increased Aβ(+) plaque burdens and soluble Aβ in brain lysates and interstitial fluid (ISF). In addition, secreted β-APP fragment (sAPPβ) also increased, whereas full-length APP level did not change, suggesting an alteration in favor of β-amyloidogenic APP processing in these animals. Reversely, perfusion of methoctramine, a selective M2 antagonist, fully corrected the difference between the control and GRK5-deficient APPsw mice for ISF Aβ. In contrast, a cholinesterase inhibitor, eserine, although significantly decreasing the ISF Aβ in both control and GRK5-deficient APPsw mice, failed to correct the difference between them. However, combining eserine with methoctramine additively reduced the ISF Aβ further in both animals. Altogether, these findings indicate that GRK5 deficiency accelerates β-amyloidogenic APP processing and Aβ accumulation in APPsw mice via impaired cholinergic activity and that presynaptic M2 hyperactivity is the specific target for eliminating the pathologic impact of GRK5 deficiency. Moreover, a combination of an M2 antagonist and a cholinesterase inhibitor may reach the maximal disease-modifying effect for both amyloid pathology and cholinergic dysfunction.

Modulation of Amyloid Precursor Protein Cleavage by Cellular Sphingolipids

Lipid rafts and their component, cholesterol, modulate the processing of beta-amyloid precursor protein (APP). However, the role of sphingolipids, another major component of lipid rafts, in APP processing remains undetermined. Here we report the effect of sphingolipid deficiency on APP processing in Chinese hamster ovary cells treated with a specific inhibitor of serine palmitoyltransferase, which catalyzes the first step of sphingolipid biosynthesis, and in a mutant LY-B strain defective in the LCB1 subunit of serine palmitoyltransferase. We found that in sphingolipid-deficient cells, the secretion of soluble APPalpha (sAPPalpha) and the generation of C-terminal fragment cleaved at alpha-site dramatically increased, whereas beta-cleavage activity remained unchanged, and the epsilon-cleavage activity decreased without alteration of the total APP level. The secretion of amyloid beta-protein 42 increased in sphingolipid-deficient cells, whereas that of amyloid beta-protein 40 did not. All of these alterations were restored in sphingolipid-deficient cells by adding exogenous sphingosine and in LY-B cells by transfection with cLCB1. Sphingolipid deficiency increased MAPK/ERK activity and a specific inhibitor of MAPK kinase, PD98059, restored sAPPalpha level, indicating that sphingolipid deficiency enhances sAPPalpha secretion via activation of MAPK/ERK pathway. These results suggest that not only the cellular level of cholesterol but also that of sphingolipids may be involved in the pathological process of Alzheimer's disease by modulating APP cleavage.

Clinical and experimental study of effect on acute phase protein of multiple organ dysfunction syndrome treated with Dachengqi Decoction

To investigate the level of acute phase protein level (APP) synthesized in hepatocytes in pathogenic process of multiple organ dysfunction syndrome (MODS) and the effect of Dachengqi Decoction (DCQD) on it. The levels of C-reactive protein (CRP), alpha 1-acid glycoprotein (alpha 1-AGP), alpha 1-antitrypsin total (alpha 1-AT), alpha 2-macroglobulin (alpha 2-MG), ceruloplasmine (Cp), hepatoglobin (Hp) and transferrin (Tf) synthesis were determined in 32 cases of MODS patients and rat models of MODS induced by acute infective peritonitis and mesenterial artery ischemia-reperfusion. The serum APP level in MODS patients was increased and higher than that in the control group (P < 0.01). After 3 days of DCQD treatment, it reduced significantly (P < 0.05). Serum APP level in MODS model was also increased significantly, and after 3 days of DCQD treatment, it reduced significantly (P < 0.05). The APP secreting level of rat hepatocytes cultured in vitro raised after stimulated and activated by lipopolysacchride, which was reduced after cultured with rabbits' serum containing different concentration of effective ingredients of DCQD. The APP inhibiting effect of DCQD was dose dependent. Purgation therapy with DCQD could reduce the stimulation of pathogenic factors on hepatocytes, protect the tissues and organs from injury caused by excessive inflammatory reaction.

Apolipoprotein E genotype, Alzheimer's pathologies and related gene expression in the aged population

We have investigated the effect of genotypes of apolipoprotein E (ApoE) on the pathologies found in Alzheimer's disease (AD) and its related gene expression in 38 aged human brains obtained from consecutive autopsied cases. ApoE2/3, -3/3, -3/4, and -4/4 were typed in those aged brains, with ApoE3/3 being most prevalent. The AD pathologies were undetectable in ApoE2/3 brains, but were frequently observed in the other ApoE groups. In ApoE3/3 brains, 55%, 34%, and 24% of the cortical sections examined showed senile plaques (SPs), neurofibrillary tangles (NFTs), and cerebral amyloid angiopathy (CAA), respectively. In ApoE4/4 brains, the SP formation was significantly higher. The ApoE genotype neither affected ApoE, APP, or tau mRNA level, nor the differential expression of the latter two. These results suggest that ApoE4/4 accelerates and ApoE2/3 decelerates the development of the AD pathologies in the aged brain, but this is not through alterations of the APP and tau gene expression.

Influence of cholecystokinin, vasoactive intestinal peptide and secretin on plasma concentration of avian pancreatic polypeptide in laying hens

1. 1. The influence of saline infusion (i.v.) followed by infusion of either cholecystokinin, vasoactive intestinal peptide, or secretin on plasma concentration of avian pancreatic polypeptide (aPP) was studied in sixteen 18–26-week old Single Comb White Leghorn hens. 2. 2. Three concentrations were used for each hormone. Blood was drawn after both saline and hormone infusions and assayed for aPP content. 3. 3. No significant influence of any of the three hormones on plasma aPP level was found in either fed or fasted hens.