Peripheral administration of nanomicelle-encapsulated anti-Aß oligomer fragment antibody reduces various toxic Aß species in the brain.

BACKGROUND: Although a large amount of evidence has revealed that amyloid ß (Aß), especially Aß oligomers, protofibrils, and pyroglutamated Aßs, participate primarily in the pathophysiological processes of Alzheimer's disease, most clinical trials of anti-Aß antibody therapy have never acquired successful efficacy in human clinical trials, partly because peripheral administration of antibody medications was unable to deliver sufficient amounts of the molecules to the brain. Recently, we developed polymeric nanomicelles capable of passing through the blood-brain barrier that function as chaperones to deliver larger amounts of heavy molecules to the brain. Herein, we aimed to evaluate the efficacy of newly developed antibody 6H4 fragments specific to Aß oligomers encapsulated in polymeric nanomicelles on the development of Alzheimer's disease pathology in Alzheimer's disease model mice at the age of emergence of early Alzheimer's disease pathology. RESULTS: During the 10-week administration of 6H4 antibody fragments in polymeric nanomicelles, a significant reduction in the amounts of various toxic Aß species, such as Aß oligomers, toxic Aß conformers, and pyroglutamated Aßs in the brain was observed. In addition, immunohistochemistry indicated inhibition of diameters of Aß plaques, Aß-antibody immunoreactive areas, and also plaque core formation. Behavioral analysis of the mice model revealed that the 6H4 fragments-polymeric nanomicelle group was significantly better at maintaining long-term spatial reference memory in the probe and platform tests of the water maze, thereby indicating inhibition of the pathophysiological process of Alzheimer's disease. CONCLUSIONS: The results indicated that the strategy of reducing toxic Aß species in early dementia owing to Alzheimer's disease by providing sufficient antibodies in the brain may modify Alzheimer's disease progression.

Soluble APP-α and APP-ß in cerebrospinal fluid as potential biomarkers for differential diagnosis of mild cognitive impairment.

OBJECTIVES: Concentrations of soluble amyloid precursor proteins-α (sAPPα) and -ß (sAPPß) in cerebrospinal fluid (CSF) may reflect the neuropathology of Alzheimer's disease (AD). We previously reported that the concentrations of both sAPPα and sAPPß were significantly higher in patients with mild cognitive impairment (MCI) due to AD (MCI-AD) than in control subjects without cognitive impairment. The present study analyzed whether these sAPPs are useful in the differential diagnosis of MCI. METHODS: A modified and sensitive method was used to analyze concentrations of sAPPα and sAPPß in CSF of patients with MCI-AD (n = 30) and MCI due to other causes (MCI-others) (n = 24). Phosphorylated tau (p-tau) and amyloid ß-protein 42 (Aß42) were also analyzed using standard methods. RESULTS: CSF concentrations of sAPPα and sAPPß were significantly higher in the MCI-AD than in the MCI-others group (p < 0.001). Furthermore, concentrations of both sAPPα and sAPPß were highly correlated with the concentration of p-tau, consistent with our previous report. CONCLUSIONS: Measurement of both sAPPs in CSF using sensitive methods can be helpful in the precise differential diagnosis of patients with MCI.

[Euglycemic Diabetic Ketoacidosis Caused by a Sodium-glucose Co-transporter (SGLT) 2 Inhibitor after Coronary Artery Bypass Grafting].

A 65-year-old woman with type Ⅱ diabetes and unstable angina presented with chest pain due to in-stent restenosis. Her regular medication comprised an sodium-glucose co-transporter( SGLT) 2 inhibitor. Because of unstable hemodynamic status, semi-emergency coronary artery bypass grafting (CABG) was performed. Postoperatively, the cardiac and hemodynamic status stabilized, but there was progression of metabolic acidosis. Based on the presence of massive urinary ketone bodies without hyper glycosuria, the patient was diagnosed with euglycemic diabetic ketoacidosis( DKA) caused by an SGLT2 inhibitor. Ketoacidosis without elevated blood glucose( i.e., euglycemic DKA) has been reported to be associated with intake of an SGLT2 inhibitor, which promoted glucose excretion in the urine. Our patient developed euglycemic DKA due to the progression of myocardial ischemia and surgical stress. Guidelines in other countries have stipulated that SGLT2 inhibitor should be stopped 24 hours preoperatively. In our case, euglycemic DKA occurred even when the SGLT2 inhibitor was stopped for more than 24 hours preoperatively. Further studies on the withdrawal of an SGLT2 inhibitor in the appropriate perioperative period are required.

[Surgical Treatment of Aortic Stenosis Combined with Bilateral Pheochromocytomas in a Dialysis Patient].

We report a case of a dialysis patient with severe aortic stenosis(AS) along with bilateral pheochromocytomas. A 52-year-old man presented with syncope and was diagnosed with severe AS. Although aortic valve replacement(AVR) was scheduled, bilateral pheochromocytomas were found during preoperative examination. There was a high possibility of developing hemodynamical crisis during AVR, and we planned to perform adrenalectomy prior to AVR. To avoid circulatory collapse just after adrenalectomy, balloon aortic valvuloplasty (BAV) was performed beforehand. Two weeks after the adrenalectomy, AVR was performed in a stable condition.

Mitochondria are devoid of amyloid ß-protein (Aß)-producing secretases: Evidence for unlikely occurrence within mitochondria of Aß generation from amyloid precursor protein.

Mitochondrial dysfunction is implicated in the pathological mechanism of Alzheimer's disease (AD). Amyloid ß-protein (Aß), which plays a central role in AD pathogenesis, is reported to accumulate within mitochondria. However, a question remains as to whether Aß is generated locally from amyloid precursor protein (APP) within mitochondria. We investigated this issue by analyzing the expression patterns of APP, APP-processing secretases, and APP metabolites in mitochondria separated from human neuroblastoma SH-SY5Y cells and those expressing Swedish mutant APP. APP, BACE1, and PEN-2 protein levels were significantly lower in crude mitochondria than microsome fractions while those of ADAM10 and the other γ-secretase complex components (presenilin 1, nicastrin, and APH-1) were comparable between fractions. The crude mitochondrial fraction containing substantial levels of cathepsin D, a lysosomal marker, was further separated via iodixanol gradient centrifugation to obtain mitochondria- and lysosome-enriched fractions. Mature APP, BACE1, and all γ-secretase complex components (in particular, presenilin 1 and PEN-2) were scarcely present in the mitochondria-enriched fraction, compared to the lysosome-enriched fraction. Moreover, expression of the ß-C-terminal fragment (ß-CTF) of APP was markedly low in the mitochondria-enriched fraction. Additionally, immunocytochemical analysis showed very little co-localization between presenilin 1 and Tom20, a marker protein of mitochondria. In view of the particularly low expression levels of BACE1, γ-secretase complex proteins, and ß-CTF in mitochondria, we propose that it is unlikely that Aß generation from APP occurs locally within this organelle.

Efficacy and Concurrent Validity of Computerized Brain Training Based on Everyday Living (BTEL) Based on Instrumental Activities of Living for Cognitively Healthy Old Individuals: A Preliminary Study.

Background: Interventions to prevent or attenuate cognitive decline and dementia in older adults are becoming increasingly important. Recently, cognitive training exercise can be via computer or mobile technology for independent or home use. Recent meta-analysis has reported that Computerized Cognitive Training (CCT) is effective at enhancing cognitive function in healthy older and Alzheimer's disease adults, although little is known about individual characteristics of each computerized program. Objective: We developed a new CCT named Brain Training Based on Everyday Living (BTEL) to enhance cognitive capacity for Instrumental Activities of Daily Living (IADL). We aim to evaluate the efficacy of the BTEL among cognitively healthy old individuals and to explore its concurrent validity and construct concept. Methods: We conducted a double-blind study where 106 individuals aged 65 years and older (intervened = 53, control = 53) worked on the active and placebo tasks three times a week over three months (clinical trial: UMIN000048730). The main results were examined using ANCOVA and calculating correlation coefficients. Results: We found no effect on total score of the three tests; however, there was significant effect for the BTEL on: recognition in MMSE, and immediate recall in HDSR. The tasks are associated with prefrontal cortex. In addition, correlations indicated that each BTEL domain had some validity as a cognitive assessment tool. Different from previous CCT, we determined the neuropsychological characteristics of specific cognitive tasks of the BTEL to a certain degree. Conclusions: We found modest efficacy of the BTEL in cognitively healthy old individuals and confirmed its concurrent validity and the conceptual construct.

Potential repurposing of oncology drugs for the treatment of Alzheimer's disease.

Alzheimer's disease (AD) is the most common form of neurodegenerative dementia, affecting about 30 million people worldwide. Despite recent advances in understanding its molecular pathology, no mechanism-based drugs are currently available that can halt the progression of AD. Because amyloid-ß-peptide (Aß), a primary component of senile plaques, is thought to be a central pathogenic culprit, several disease-modifying therapies are being developed, including inhibitors of Aß-producing proteases and immunotherapies with anti-Aß antibodies. Drug repositioning or repurposing is regarded as a complementary and reasonable approach to identify new drug candidates for AD. This commentary will discuss the clinical relevance of an attractive candidate compound reported in a recent paper by Hayes et al. (BMC Medicine 2013) as well as perspectives regarding the possible repositioning of oncology drugs for the treatment of AD. See related research article here http://www.biomedcentral.com/1741-7015/11/81.

Abnormal cross-talk between mutant presenilin 1 (I143T, G384A) and glycosphingolipid biosynthesis.

Mutations in the presenilin 1 (PS1) gene are associated with early onset familial Alzheimer's disease (FAD). In this study, we found that the expression of mutant-PS1 in stable transfectants of SH-SY5Y neuroblastoma cells results in a reduction of the biosynthesis and steady-state levels of glucosylceramide. As an in vivo corroboration of these data, there was a significant reduction of brain glucosylceramide and gangliosides in an animal model of FAD. In mutant-PS1-transfectants (I143T, G384A), immunocytochemistry disclosed a remarkable reduction of glucosylceramide synthase (GlcT-1)-like immunoreactivity in the cells when compared with those of mock- and wild-PS1 transfectants. Immunoprecipitation of GlcT-1 protein from mutant-PS1 transfectants demonstrated a marked reduction in GlcT-1 protein, but there was no reduction in the levels of GlcT-1 mRNA. Both coprecipitation and γ-secretase inhibition experiments suggest that mutant-PS1 seems to form a complex with GlcT-1 protein and to be involved in GlcT-1 degradation, which was never found in other cell types. Thus, mutations in the PS1 gene result in profound glycosphingolipids abnormalities by abnormal molecular interaction with GlcT-1.

Statins reduce amyloid ß-peptide production by modulating amyloid precursor protein maturation and phosphorylation through a cholesterol-independent mechanism in cultured neurons.

Statins, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors, have been reported to attenuate amyloid-ß peptide (Aß) production in various cellular models. However, the mechanisms by which statins affect neuronal Aß production have not yet been clarified. Here, we investigated this issue in rat primary cortical neurons using two statins, pitavastatin (PV) and atorvastatin (AV). Treatment of neurons with 0.2-2.5 µM PV or AV for 4 days induced a concentration- and time-dependent reduction in the secretion of both Aß40 and Aß42. Moreover, Western blot analyses of cell lysates showed that treatment with PV or AV significantly reduced expression levels of the mature form of amyloid precursor protein (APP) and Thr668-phosphorylated APP (P-APP), but not immature form of APP; the decreases in P-APP levels were more notable than those of mature APP levels. The statin treatment did not alter expression of BACE1 (ß-site APP-cleaving enzyme 1) or γ-secretase complex proteins (presenilin 1, nicastrin, APH-1, and PEN-2). In neurons overexpressing APP via recombinant adenoviruses, PV or AV similarly reduced Aß secretion and the levels of mature APP and P-APP. Statins also markedly reduced cellular cholesterol content in neurons in a concentration-dependent manner. Co-treatment with mevalonate reversed the statin-induced decreases in Aß secretion and mature APP and P-APP levels, whereas co-treatment with cholesterol did not, despite recovery of cellular cholesterol levels. Finally, cell-surface biotinylation experiments revealed that both statins significantly reduced the levels of cell-surface P-APP without changing those of cell surface mature APP. These results suggest that statins reduce Aß production by selectively modulating APP maturation and phosphorylation through a mechanism independent of cholesterol reduction in cultured neurons.

Aß Oligomer Toxicity-Reducing Therapy for the Prevention of Alzheimer's Disease: Importance of the Nrf2 and PPARγ Pathways.

Recent studies have revealed that soluble amyloid-ß oligomers (AßOs) play a pathogenetic role in Alzheimer's disease (AD). Indeed, AßOs induce neurotoxic and synaptotoxic effects and are also critically involved in neuroinflammation. Oxidative stress appears to be a crucial event underlying these pathological effects of AßOs. From a therapeutic standpoint, new drugs for AD designed to remove AßOs or inhibit the formation of AßOs are currently being developed. However, it is also worth considering strategies for preventing AßO toxicity itself. In particular, small molecules with AßO toxicity-reducing activity have potential as drug candidates. Among such small molecules, those that can enhance Nrf2 and/or PPARγ activity can effectively inhibit AßO toxicity. In this review, I summarize studies on the small molecules that counteract AßO toxicity and are capable of activating Nrf2 and/or PPARγ. I also discuss how these interrelated pathways are involved in the mechanisms by which these small molecules prevent AßO-induced neurotoxicity and neuroinflammation. I propose that AßO toxicity-reducing therapy, designated ATR-T, could be a beneficial, complementary strategy for the prevention and treatment of AD.

A case with burning mouth syndrome followed by dementia with Lewy bodies: a case report.

Burning mouth syndrome (BMS) is characterized by persistent oral burning sensations without corresponding organic findings. Dementia with Lewy bodies (DLB) is a common type of dementia and generally presents visual hallucination and parkinsonism as motor dysfunction besides cognitive decline. In this case report, we present a case in which DLB emerged during the treatment for BMS, with a relatively positive outcome for BMS. A 74 years-old female complained of burning pain in her mouth and a subsequent decrease in food intake. Following a diagnosis of BMS, pharmacotherapy was initiated. BMS was much improved with mirtazapine 15 mg and aripiprazole 1.0 mg, leading to the restoration of her food intake by day 180. However, BMS flared up again triggered by deteriorating physical condition of herself and that of her husband. With aripiprazole 1.5 mg and amitriptyline 25 mg, her BMS gradually improved by day 482. However, by day 510, an increase in anxiety was noted, accompanied by the occasionally misidentification of her husband on day 566. Her cognitive impairment and disorientation were also reported by her husband on the day 572, she was then immediately referred to a neurologist specialized dementia and diagnosed with DLB on the day 583. Her treatment was adjusted to include the prescription of rivastigmine which was titrated up to 9.0 mg. Considering the potential impact of amitriptyline on cognitive function, it was reduced and switched to mirtazapine; however, her oral sensations slightly got worse. Following the consultation with her neurologist, amitriptyline 10 mg was reintroduced and aripiprazole was discontinued on day 755. Remarkably, BMS gradually improved without deteriorating DLB. This case indicated the reaffirmed necessity of careful interviews for changes in daily life not only with the patients but also with their families through the medical assessments. It highlights the vigilance regarding potential cognitive decline underlying or induced as an adverse event especially when treating elderly patients with BMS. While the interaction between BMS and DLB remains unclear, this case underscores the importance of prudent diagnosis and constructing collaboration with specialists in managing BMS with the early phase of DLB.

ER-stress-inducible Herp, facilitates the degradation of immature nicastrin.

BACKGROUND: Herp is an endoplasmic reticulum (ER)-stress-inducible membrane protein harboring an ubiquitin-like domain (ULD). However, its biological functions are not fully understood. Here, we examined the role of Herp in the degradation of γ-secretase components. METHODS: Effects of ULD-lacking Herp (ΔUb-Herp) expression on the degradation of γ-secretase components were analyzed. RESULTS: The cellular expression of ΔUb-Herp was found to inhibit the degradation of overexpressed immature nicastrin and full-length presenilin. The mechanisms underlying Herp-mediated nicastrin degradation was further analyzed. We found that immature nicastrin accumulates in the ER of ΔUb-Herp overexpressing cells or Herp-deficient cells more than that in the ER of wild-type cells. Further, ΔUb-Herp expression inhibited nicastrin ubiquitination, suggesting that the ULD of Herp is likely involved in nicastrin ubiquitination. Co-immunoprecipitation study showed that Herp as well as ΔUb-Herp potentially interacts with nicastrin, mediating nicastrin interaction with p97, which functions in retranslocation of misfolded proteins from the ER to the cytosol. CONCLUSIONS: Thus, Herp is likely involved in degradation of immature nicastrin by facilitating p97-dependent nicastrin retranslocation and ubiquitination. GENERAL SIGNIFICANCE: We suggest that Herp could play a role in the elimination of the excess unassembled components of a multimeric complex.

Autoreactive-Aß antibodies promote APP ß-secretase processing.

Several prior investigations of Alzheimer's disease (AD) patients have indicated naturally occurring autoantibodies against amyloid-ß (Aß) species are produced. Although many studies have focused on the relative concentrations or binding affinities of autoantibodies against Aß-related proteins in AD and aging, data regarding their functional properties are limited. It is generally believed that these antibodies act to aid in clearance of Aß. However, as antibodies which bind to Aß also typically bind to the parent amyloid precursor protein (APP), we reasoned that certain Aß-targeting autoantibodies may bind to APP thereby altering its conformation and processing. Here we show for the first time, that naturally occurring Aß-reactive autoantibodies isolated from AD patients, but not from healthy controls, promote ß-secretase activity in cultured cells. Furthermore, using monoclonal antibodies to various regions of Aß, we found that antibodies generated against the N-terminal region, especially Aß(1-17) , dose dependently promoted amyloidogenic processing of APP viaß-secretase activation. Thus, this property of certain autoantibodies in driving Aß generation could be of etiological importance in the development of sporadic forms of AD. Furthermore, future passive or active anti-Aß immunotherapies must consider potential off-target effects resulting from antibodies targeting the N-terminus of Aß, as co-binding to the corresponding region of APP may actually enhance Aß generation.

Protection against Amyloid-ß Oligomer Neurotoxicity by Small Molecules with Antioxidative Properties: Potential for the Prevention of Alzheimer's Disease Dementia.

Soluble oligomeric assemblies of amyloid ß-protein (Aß), called Aß oligomers (AßOs), have been recognized as primary pathogenetic factors in the molecular pathology of Alzheimer's disease (AD). AßOs exert neurotoxicity and synaptotoxicity and play a critical role in the pathological progression of AD by aggravating oxidative and synaptic disturbances and tau abnormalities. As such, they are important therapeutic targets. From a therapeutic standpoint, it is not only important to clear AßOs or prevent their formation, it is also beneficial to reduce their neurotoxicity. In this regard, recent studies have reported that small molecules, most with antioxidative properties, show promise as therapeutic agents for reducing the neurotoxicity of AßOs. In this mini-review, we briefly review the significance of AßOs and oxidative stress in AD and summarize studies on small molecules with AßO-neurotoxicity-reducing effects. We also discuss mechanisms underlying the effects of these compounds against AßO neurotoxicity as well as their potential as drug candidates for the prevention and treatment of AD.

Amyloid-ß oligomers interact with NMDA receptors containing GluN2B subunits and metabotropic glutamate receptor 1 in primary cortical neurons: Relevance to the synapse pathology of Alzheimer's disease.

Recent evidence suggests that soluble amyloid-ß oligomers (AßOs) act as a key factor in the pathogenetic mechanism of Alzheimer's disease (AD). AßOs induce neurotoxic and synaptotoxic effects probably through binding to certain receptors, however it remains unclarified which receptors are most critically involved. In addition, dysregulation in glutamatergic signaling is implicated in AD. In this study, we used a rat primary cortical neuron model to investigate AßO-induced aberrations of synaptic proteins and binding of extracellular AßOs to candidate receptors in the glutamatergic system. Immunocytochemical analyses showed that both presynaptic (SNAP-25, synapsin I) and postsynaptic (spinophilin, homer 1b/c) proteins appeared to aberrantly dislocate from synapses upon AßO treatment. Double immunofluorescence staining of AßO-treated neurons without permeabilization pretreatment revealed that extracellular AßOs exist over neuronal soma and neurites and clearly colocalized with GluN1 and GluN2B subunits of NMDA receptors and metabotropic glutamate receptor 1 (mGluR1), but not with NMDA GluN2A subunits and mGluR5. AßO treatment altered neither total protein levels nor intracellular localizations of these receptors. These results suggest that extracellular AßOs specifically bind to both NMDA receptors containing GluN2B subunits and mGluR1. It is likely that binding of AßOs to these receptors induces various pathological responses, consequently leading to synaptic disruptions. Our study thus highlights the important roles of GluN2B-containing NMDA receptors and mGluR1 receptors in the synapse pathology in AD.

Lemur tail kinase 1 (LMTK1) regulates the endosomal localization of ß-secretase BACE1.

Lemur tail kinase 1 (LMTK1), previously called apoptosis-associated tyrosine kinase (AATYK), is an endosomal Ser/Thr kinase. We recently reported that LMTK1 regulates axon outgrowth, dendrite arborization and spine formation via Rab11-mediated vesicle transport. Rab11, a small GTPase regulating recycling endosome trafficking, is shown to be associated with late-onset Alzheimer's disease (LOAD). In fact, genome-wide association studies identified many proteins regulating vesicle transport as risk factors for LOAD. Furthermore, LMTK1 has been reported to be a risk factor for frontotemporal dementia. Then, we hypothesized that LMTK1 contributes to AD development through vesicle transport and examined the effect of LMTK1 on the cellular localization of AD-related proteins, amyloid precursor protein (APP) and ß-site APP cleaving enzyme 1 (BACE1). The ß-cleavage of APP by BACE1 is the initial and rate-limiting step in Aß generation. We found that LMTK1 accumulated BACE1, but not APP, to the perinuclear endosomal compartment, whereas the kinase-negative(kn) mutant of LMTK1A did not. The ß-C-terminal fragment was prone to increase under overexpression of LMTK1A kn. Moreover, the expression level of LMTK1A was reduced in AD brains. These results suggest the possibility that LMTK1 is involved in AD development through the regulation of the proper endosomal localization of BACE1.

Human CRB2 inhibits gamma-secretase cleavage of amyloid precursor protein by binding to the presenilin complex.

Drosophila Crumbs has been reported to attenuate Notch signaling by inhibition of gamma-secretase cleavage at the wing margins. gamma-Secretase is an intramembrane protease that is responsible for the generation of amyloid-beta (Abeta) peptides from the beta-amyloid precursor protein (APP). Here, we re-examined gamma-secretase inhibition by human CRB2, which is the most abundant Crumbs ortholog in the brain. Transfected CRB2 inhibited proteolytic production of Abeta and APP intracellular domains from APP C-terminal fragments in HEK293 and SH-SY5Y cells. Conversely, knockdown of endogenous CRB2 increased gamma-secretase cleavage products in SH-SY5Y cells. CRB2 inhibition of gamma-cleavage was also detected in cell-free assays. CRB2 interacted with the gamma-secretase complex, but was not a competitive substrate for gamma-cleavage. The transmembrane domain of CRB2 was indispensable for inhibition of Abeta generation and mediated CRB2 binding with the gamma-secretase complex. In addition, the cytoplasmic domain appeared to play a supportive role in gamma-secretase inhibition, whereas mutational disruption of the two protein-binding motifs involved in the formation of cell adhesion complexes did not affect gamma-secretase inhibition. Co-overexpression of presenilin-1 or APH-1 abrogated gamma-secretase inhibition probably through prevention of the incorporation of CRB2 into the gamma-secretase complex. Our results suggest that CRB2 functions as an inhibitory binding protein that is involved in the formation of a mature but inactive pool of the gamma-secretase complex.

Prostaglandin E2 stimulates the production of amyloid-beta peptides through internalization of the EP4 receptor.

Amyloid-beta (Abeta) peptides, generated by the proteolysis of beta-amyloid precursor protein by beta- and gamma-secretases, play an important role in the pathogenesis of Alzheimer disease. Inflammation is also important. We recently reported that prostaglandin E(2) (PGE(2)), a strong inducer of inflammation, stimulates the production of Abeta through EP(2) and EP(4) receptors, and here we have examined the molecular mechanism. Activation of EP(2) and EP(4) receptors is coupled to an increase in cellular cAMP levels and activation of protein kinase A (PKA). We found that inhibitors of adenylate cyclase and PKA suppress EP(2), but not EP(4), receptor-mediated stimulation of the Abeta production. In contrast, inhibitors of endocytosis suppressed EP(4), but not EP(2), receptor-mediated stimulation. Activation of gamma-secretase was observed with the activation of EP(4) receptors but not EP(2) receptors. PGE(2)-dependent internalization of the EP(4) receptor was observed, and cells expressing a mutant EP(4) receptor lacking the internalization activity did not exhibit PGE(2)-stimulated production of Abeta. A physical interaction between the EP(4) receptor and PS-1, a catalytic subunit of gamma-secretases, was revealed by immunoprecipitation assays. PGE(2)-induced internalization of PS-1 and co-localization of EP(4), PS-1, and Rab7 (a marker of late endosomes and lysosomes) was observed. Co-localization of PS-1 and Rab7 was also observed in the brain of wild-type mice but not of EP(4) receptor null mice. These results suggest that PGE(2)-stimulated production of Abeta involves EP(4) receptor-mediated endocytosis of PS-1 followed by activation of the gamma-secretase, as well as EP(2) receptor-dependent activation of adenylate cyclase and PKA, both of which are important in the inflammation-mediated progression of Alzheimer disease.

Oxidative stress up-regulates presenilin 1 in lipid rafts in neuronal cells.

Oxidative stress is associated with beta-amyloid peptide (A beta) accumulation in the brains of Alzheimer's disease patients. A beta is generated upon the sequential proteolytic cleavage of transmembrane amyloid precursor protein (APP) by two membrane-bound proteases, beta-secretase (BACE1) and the gamma-secretase complex comprising presenilin 1 (PS1), nicastrin, APH-1 and PEN-2. Recent evidence suggests that significant amounts of BACE1 and gamma-secretase components localize in the cholesterol-rich region of membranes known as lipid rafts, where A beta production occurs preferentially. In this study, we investigated the effects of oxidative stress on the BACE1 and gamma-secretase components in lipid rafts using human neuroblastoma SH-SY5Y cells exposed to ethacrynic acid (EA), a compound that induces cellular glutathione depletion. Following exposure of cells to EA, heme oxygenase-1, a marker protein of oxidative stress, was strongly induced. Moreover, treatment with EA resulted in a significant increase in PS1 protein levels, but not those of nicastrin, APH-1, PEN-2 or BACE1, in both cell lysates and the lipid raft fraction. This increase in PS1 protein expression was prevented by co-treatment with an antioxidant, N-acetylcysteine (NAC). EA additionally induced a significant increase in PS1 mRNA expression, which was inhibited by NAC. Finally, EA treatment was found to promote A beta secretion from cells expressing Swedish mutant APP. It appears that in our cell culture model, oxidative stress enhances PS1 protein levels in lipid rafts via up-regulation of PS1 transcription, which may constitute the mechanism underlying the oxidative stress-associated promotion of A beta production.

IGF-1 promotes beta-amyloid production by a secretase-independent mechanism.

Beta-amyloid peptide (Abeta) is generated via the sequential proteolysis of beta-amyloid precursor protein (APP) by beta- and gamma-secretases, and plays a crucial role in the pathogenesis of Alzheimer's disease (AD). Here, we sought to clarify the role of insulin-like growth factor-1 (IGF-1), implicated in the AD pathomechanism, in the generation of Abeta. Treatment of neuroblastoma SH-SY5Y cells expressing AD-associated Swedish mutant APP with IGF-1 did not alter cellular levels of APP, but significantly increased those of beta-C-terminal fragment (beta-CTF) and secreted Abeta. IGF-1 also enhanced APP phosphorylation at Thr668. Treatment of beta-CTF-expressing cells with IGF-1 increased the levels of beta-CTF and secreted Abeta. The IGF-1-induced augmentation of beta-CTF was observed in the presence of gamma-secretase inhibitors, but not in cells expressing beta-CTF with a Thr668 to alanine substitution. These results suggest that IGF-1 promotes Abeta production through a secretase-independent mechanism involving APP phosphorylation.