Multi-Arm PEG/Peptidomimetic Conjugate Inhibitors of DR6/APP Interaction Block Hematogenous Tumor Cell Extravasation

The binding of amyloid precursor protein (APP) expressed on tumor cells to death receptor 6 (DR6) could initiate the necroptosis pathway, which leads to necroptotic cell death of vascular endothelial cells (ECs) and results in tumor cells (TCs) extravasation and metastasis. This study reports the first inhibitor of DR6/APP interaction as a novel class of anti-hematogenous metastatic agent. By rationally utilizing three combined strategies including selection based on phage display library, d-retro-inverso modification, and multiple conjugation of screened peptidomimetic with 4-arm PEG, the polymer-peptidomimetic conjugate PEG-tAHP-DRI (tetra-(D-retro-inverso isomer of AHP-12) substitued 4-arm PEG5k ) is obtained as the most promising agent with the strongest binding potency (KD  = 51.12 × 10-9  m) and excellent pharmacokinetic properties. Importantly, PEG-tAHP-DRI provides efficient protection against TC-induced ECs necroptosis both in vitro and in vivo. Moreover, this ligand exhibits prominent anti-hematogenous metastatic activity in serval different metastatic mouse models (B16F10, 4T1, CT26, and spontaneous lung metastasis of 4T1 orthotopic tumor model) and displays no apparent detrimental effects in preliminary safety evaluation. Collectively, this study demonstrates the feasibility of exploiting DR6/APP interaction to regulate hematogenous tumor cells transendothelial migration and provides PEG-tAHP-DRI as a novel and promising inhibitor of DR6/APP interaction for developments of anti-hematogenous metastatic therapies.

Abolishing UCHL1's hydrolase activity exacerbates TBI-induced axonal injury and neuronal death in mice

Ubiquitin (Ub) C-terminal hydrolase L1 (UCHL1) is a multifunctional protein that is expressed in neurons throughout brain at high levels. UCHL1 deletion is associated with axonal degeneration, progressive sensory motor ataxia, and premature death in mice. UCHL1 has been hypothesized to play a role in the pathogenesis of neurodegenerative diseases and recovery after neuronal injury. UCHL1 hydrolyzes Ub from polyubiquitinated (poly-Ub) proteins, but also may ligate Ub to select neuronal proteins, and interact with cytoskeletal proteins. These and other mechanisms have been hypothesized to underlie UCHL1's role in neurodegeneration and response to brain injury. A UCHL1 knockin mouse containing a C90A mutation (C90A) devoid of hydrolase activity was constructed. The C90A mouse did not develop the sensory and motor deficits, degeneration of the gracile nucleus and tract, or premature death as seen in UCHL1 deficient mice. C90A and wild type (WT) mice were subjected to the controlled cortical impact (CCI) model of traumatic brain injury (TBI), and cell death, axonal injury and behavioral outcome were assessed. C90A mice exhibited decreased spared tissue volume, greater loss of CA1 hippocampal neurons and greater axonal injury as detected using anti-amyloid precursor protein (APP) antibody and anti- non-phosphorylated neurofilament H (SMI-32) antibody immunohistochemistry after CCI compared to WT controls. Poly-Ub proteins and Beclin-1 were elevated after CCI in C90A mice compared to WT controls. Vestibular motor deficits assessed using the beam balance test resolved by day 5 after CCI in WT mice but not in C90A mice. These results suggest that the hydrolase activity of UCHL1 does not account for the progressive neurodegeneration and premature death seen in mice that do not express full length UCHL1. The hydrolase activity of UCHL1 contributes to the function of the ubiquitin proteasome pathway (UPP), ameliorates activation of autophagy, and improves motor recovery after CCI. Thus, UCHL1 hydrolase activity plays an important role in acute injury response after TBI.

Knockdown of circAPLP2 Inhibits Progression of Colorectal Cancer by Regulating miR-485-5p/FOXK1 Axis

Background: Circular RNAs (circRNAs) have recently been reported to play essential roles in the progression of various cancers, including colorectal cancer (CRC). However, the roles of circRNA amyloid precursor-like protein 2 (circAPLP2) in CRC and its underlying mechanism have not been investigated. Materials and Methods: The expression levels of circAPLP2, microRNA-485-5p (miR-485-5p), and forkhead-box K1 (FOXK1) were determined by quantitative real-time polymerase chain reaction. Cell proliferation, apoptosis, migration, and invasion were assessed by methylthiazolyldiphenyl-tetrazolium bromide assay, flow cytometry, and transwell assay, respectively. Western blot assay was performed to measure the protein levels of proliferating cell nuclear antigen, Bcl-2, Bax, vimentin, E-cadherin, fibronectin, and FOXK1. The interaction between miR-485-5p and circAPLP2 or FOXK1 was predicted by starBase and verified by dual-luciferase reporter assay. A xenograft tumor model was established to confirm the functions of circAPLP2 in vivo. The lactate production was measured using lactate assay kit. Results: circAPLP2 expression was enhanced in CRC tissues and cells. circAPLP2 knockdown or miR-485-5p overexpression suppressed cell proliferation, migration, and invasion, whereas it promoted apoptosis in CRC cells, which was reversed by upregulating FOXK1. Moreover, miR-485-5p could directly bind to circAPLP2 and its downregulation reversed the suppressive effect of circAPLP2 knockdown on progression of CRC cells. In addition, FOXK1 was a downstream target of miR-485-5p. Furthermore, circAPLP2 modulated FOXK1 expression by sponging miR-485-5p in CRC cells. Besides, interference of circAPLP2 suppressed tumor growth in vivo and inhibited glycolysis in vitro by upregulating miR-485-5p and downregulating FOXK1. Conclusions: circAPLP2 knockdown inhibited CRC progression through regulating miR-485-5p/FOXK1 axis, providing a novel avenue for treatment of CRC.

Early administration of galantamine from preplaque phase suppresses oxidative stress and improves cognitive behavior in APPswe/PS1dE9 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disease that progressively impairs memory and cognition. Deposition of amyloid-β (Aβ) peptides is the most important pathophysiological hallmark of AD. Oxidative stress induced by generation of reactive oxygen species (ROS) is a prominent phenomenon in AD and known to occur early in the course of AD. Several reports suggest a relationship between change in redox status and AD pathology including progressive Aβ deposition, glial cell activation, and inflammation. Galantamine is an acetylcholinesterase inhibitor and has been reported to have an oxidative stress inhibitory function. In the present study, galantamine was administered orally to AD model mice from before the appearance of Aβ plaques (preplaque phase), and in vivo change in redox status of the brain was measured using electron paramagnetic resonance (EPR) imaging. Administration of galantamine from the preplaque phase ameliorated memory decline in Morris water maze test and novel object recognition test. Monitoring of the redox status of the brain using EPR imaging showed that galantamine treatment improved the unbalanced redox state. Additionally, galantamine administration enhanced microglial function to promote Aβ clearance, reducing the Aβ-positive area in the cortex and amount of insoluble Aβ in the brain. In contrast, galantamine treatment from the preplaque phase suppressed the production of proinflammatory cytokines through neurotoxic microglial activity. Therefore, galantamine administration from the preplaque phase may have the potential of clinical application for the prevention of AD. In addition, our results demonstrate the usefulness of EPR imaging for speedy and quantitative evaluation of the efficacy of disease-modifying drugs for AD.

Silymarin's Inhibition and Treatment Effects for Alzheimer's Disease

As a longstanding problem, Alzheimer's disease (AD) has stymied researchers in the medical field with its increasing incidence and enormous treatment difficulty. Silymarin has always been valued by researchers for its good efficacy and safety in treating liver disease. Recent studies have shown that silymarin also has good pharmacological activity in the nervous system, especially for the treatment of AD. Silymarin can control the production of Aβ by inhibiting the precursor substance of Aβ (β-amyloid precursor protein), and it can inhibit the polymerization of Aβ. Silymarin can also increase the acetylcholine content in the nervous system by inhibiting cholinesterase activity. At the same time, it also has the effect of resisting oxidative stress and the inflammatory response of the nervous system. These pharmacological activities contribute to the inhibition of the onset of AD. The good efficacy of silymarin on AD and its high safety and availability give it huge potential for the treatment of AD.

Randomized Trial of Verubecestat for Prodromal Alzheimer's Disease

BACKGROUND

Prodromal Alzheimer's disease offers an opportunity to test the effect of drugs that modify the deposition of amyloid in the brain before the onset of dementia. Verubecestat is an orally administered β-site amyloid precursor protein-cleaving enzyme 1 (BACE-1) inhibitor that blocks production of amyloid-beta (Aβ). The drug did not prevent clinical progression in a trial involving patients with mild-to-moderate dementia due to Alzheimer's disease.

METHODS

We conducted a randomized, double-blind, placebo-controlled, 104-week trial to evaluate verubecestat at doses of 12 mg and 40 mg per day, as compared with placebo, in patients who had memory impairment and elevated brain amyloid levels but whose condition did not meet the case definition of dementia. The primary outcome was the change from baseline to week 104 in the score on the Clinical Dementia Rating Scale-Sum of Boxes (CDR-SB; scores range from 0 to 18, with higher scores indicating worse cognition and daily function). Secondary outcomes included other assessments of cognition and daily function.

RESULTS

The trial was terminated for futility after 1454 patients had been enrolled; 485 had been assigned to receive verubecestat at a dose of 12 mg per day (the 12-mg group), 484 to receive verubecestat at a dose of 40 mg per day (the 40-mg group), and 485 to receive placebo. A total of 234 patients, 231 patients, and 239 patients per group, respectively, completed 104 weeks of the trial regimen. The estimated mean change from baseline to week 104 in the CDR-SB score was 1.65 in the 12-mg group, 2.02 in the 40-mg group, and 1.58 in the placebo group (P = 0.67 for the comparison between the 12-mg group and the placebo group and P = 0.01 for the comparison between the 40-mg group and the placebo group), suggesting a worse outcome in the higher-dose group than in the placebo group. The estimated rate of progression to dementia due to Alzheimer's disease was 24.5, 25.5, and 19.3 events per 100 patient-years in the 12-mg group, the 40-mg group, and the placebo group, respectively (hazard ratio for 40 mg vs. placebo, 1.38; 97.51% confidence interval, 1.07 to 1.79, not adjusted for multiple comparisons), favoring placebo. Adverse events were more common in the verubecestat groups than in the placebo group.

CONCLUSIONS

Verubecestat did not improve clinical ratings of dementia among patients with prodromal Alzheimer's disease, and some measures suggested that cognition and daily function were worse among patients who received verubecestat than among those who received placebo. (Funded by Merck Sharp & Dohme; ClinicalTrials.gov number, NCT01953601.).

Oxidatively modified glyceraldehyde-3-phosphate dehydrogenase in neurodegenerative processes and the role of low molecular weight compounds in counteracting its aggregation and nuclear translocation

A number of independent studies have shown the contribution of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the pathogenesis of several neurodegenerative disorders. Indeed, GAPDH aggregates have been found in many post-mortem samples of brains of patients diagnosed with Alzheimer's and Parkinson disease. Currently, it is accepted that GAPDH-mediated cell death pathways in the neurodegenerative processes are associated with apoptosis caused by GAPDH nuclear translocation and excessive aggregation under oxidative stress conditions. Also the role of GAPDH in neurodegenerative diseases is linked to it directly binding to specific amyloidogenic proteins and petides such as β-amyloid precursor protein, β-amyloid peptide and tau protein in Alzheimer's disease, huntingtin in Huntington's disease and α-synuclein in Parkinson disease. One of the latest studies indicated that GAPDH aggregates significantly accelerate amyloidogenesis of the β-amyloid peptide, which implies that aggregates of GAPDH may act as a specific aggregation "seed" in vitro. Previous detailed studies revealed that the active-site cysteine (Cys152) of GAPDH plays an essential role in the oxidative stress-induced aggregation of GAPDH associated with cell death. Furthermore, oxidative modification of this cysteine residue initiates the translocation of the enzyme to the nucleus, subsequently leading to apoptosis. The crystallographic structure of GAPDH shows that the Cys152 residue is located close to the surface of the molecule in a hydrophilic environment, which means that it can react with low molecular weight compounds such as hydroxynonenal or piceatannol. Therefore, it is highly possible that GAPDH may serve as a target for small molecule compounds with the potential to slow down or prevent the progression of neurodegenerative disorders. Recently appearing new evidence has highlighted the significance of low molecular weight compounds in counteracting the oxidation of GAPDH and consequently its aggregation and other unfavourable pathological processes. Hence, this review aims to present all recent findings concerning molecules that are able to interact with GAPDH and counteract its aggregation and translocation to the nucleus.

Manganese causes neurotoxic iron accumulation via translational repression of amyloid precursor protein and H-Ferritin

For more than 150 years, it is known that occupational overexposure of manganese (Mn) causes movement disorders resembling Parkinson's disease (PD) and PD-like syndromes. However, the mechanisms of Mn toxicity are still poorly understood. Here, we demonstrate that Mn dose- and time-dependently blocks the protein translation of amyloid precursor protein (APP) and heavy-chain Ferritin (H-Ferritin), both iron homeostatic proteins with neuroprotective features. APP and H-Ferritin are post-transcriptionally regulated by iron responsive proteins, which bind to homologous iron responsive elements (IREs) located in the 5'-untranslated regions (5'-UTRs) within their mRNA transcripts. Using reporter assays, we demonstrate that Mn exposure repressed the 5'-UTR-activity of APP and H-Ferritin, presumably via increased iron responsive proteins-iron responsive elements binding, ultimately blocking their protein translation. Using two specific Fe2+ -specific probes (RhoNox-1 and IP-1) and ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS), we show that loss of the protective axis of APP and H-Ferritin resulted in unchecked accumulation of redox-active ferrous iron (Fe2+ ) fueling neurotoxic oxidative stress. Enforced APP expression partially attenuated Mn-induced generation of cellular and lipid reactive oxygen species and neurotoxicity. Lastly, we could validate the Mn-mediated suppression of APP and H-Ferritin in two rodent in vivo models (C57BL6/N mice and RjHan:SD rats) mimicking acute and chronic Mn exposure. Together, these results suggest that Mn-induced neurotoxicity is partly attributable to the translational inhibition of APP and H-Ferritin resulting in impaired iron metabolism and exacerbated neurotoxic oxidative stress. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Structural Optimization of Foldamer-Dendrimer Conjugates as Multivalent Agents against the Toxic Effects of Amyloid Beta Oligomers

Alzheimer’s disease is one of the most common chronic neurodegenerative disorders. Despite several in vivo and clinical studies, the cause of the disease is poorly understood. Currently, amyloid β (Aβ) peptide and its tendency to assemble into soluble oligomers are known as a main pathogenic event leading to the interruption of synapses and brain degeneration. Targeting neurotoxic Aβ oligomers can help recognize the disease at an early stage or it can be a potential therapeutic approach. Unnatural β-peptidic foldamers are successfully used against many different protein targets due to their favorable structural and pharmacokinetic properties compared to small molecule or protein-like drug candidates. We have previously reported a tetravalent foldamer-dendrimer conjugate which can selectively bind Aβ oligomers. Taking advantage of multivalency and foldamers, we synthesized different multivalent foldamer-based conjugates to optimize the geometry of the ligand. Isothermal titration calorimetry (ITC) was used to measure binding affinity to Aβ, thereafter 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) based tissue viability assay and impedance-based viability assay on SH-SY5Y cells were applied to monitor Aβ toxicity and protective effects of the compounds. Important factors for high binding affinity were determined and a good correlation was found between influencing the valence and the capability of the conjugates for Aβ binding.

Dyrk1 inhibition improves Alzheimer's disease-like pathology

There is an urgent need for the development of new therapeutic strategies for Alzheimer's disease (AD). The dual-specificity tyrosine phosphorylation-regulated kinase-1A (Dyrk1a) is a protein kinase that phosphorylates the amyloid precursor protein (APP) and tau and thus represents a link between two key proteins involved in AD pathogenesis. Furthermore, Dyrk1a is upregulated in postmortem human brains, and high levels of Dyrk1a are associated with mental retardation. Here, we sought to determine the effects of Dyrk1 inhibition on AD-like pathology developed by 3xTg-AD mice, a widely used animal model of AD. We dosed 10-month-old 3xTg-AD and nontransgenic (NonTg) mice with a Dyrk1 inhibitor (Dyrk1-inh) or vehicle for eight weeks. During the last three weeks of treatment, we tested the mice in a battery of behavioral tests. The brains were then analyzed for the pathological markers of AD. We found that chronic Dyrk1 inhibition reversed cognitive deficits in 3xTg-AD mice. These effects were associated with a reduction in amyloid-β (Aβ) and tau pathology. Mechanistically, Dyrk1 inhibition reduced APP and insoluble tau phosphorylation. The reduction in APP phosphorylation increased its turnover and decreased Aβ levels. These results suggest that targeting Dyrk1 could represent a new viable therapeutic approach for AD.

Inorganic mercury prevents the differentiation of SH-SY5Y cells: Amyloid precursor protein, microtubule associated proteins and ROS as potential targets

Exposure to mercury (Hg) occurs through different pathways and forms including methylmecury (MeHg) from seafood and rice, ethylmercury (EtHg), and elemental Hg (Hg⁰) from dental amalgams and artisanal gold mining. Once in the brain all these forms are transformed to inorganic Hg (I-Hg), where it bioaccumulates and remains for long periods. Hg is a well-known neurotoxicant, with its most damaging effects reported during brain development, when cellular key events, such as cell differentiation take place. A considerable number of studies report an impairment of neuronal differentiation due to MeHg exposure, however the effects of I-Hg, an important form of Hg found in brain, have received less attention. In this study, we decided to examine the effects of I-Hg exposure (5, 10 and 20μM) on the differentiation of SH-SY5Y cells induced by retinoic acid (RA, 10μM). We observed extension of neuritic processes and increased expression of neuronal markers (MAP2, tubulin-βIII, and Tau) after RA stimulation, all these effects were decreased by the co-exposure to I-Hg. Interestingly, I-Hg increased the levels of reactive oxygen species (ROS) and nitric oxide (NO) accompanied with increased levels of inducible nitric oxide synthase (iNOS) and, dimethylarginine dimethylaminohydrolase 1 (DDHA1). Remarkably I-Hg decreased levels of nitric oxide synthase neuronal (nNOS). Moreover I-Hg reduced the levels of tyrosine hydroxylase (TH) and amyloid precursor protein (APP) a protein recently involved in neuronal differentiation. These data suggest that the exposure to I-Hg impairs cell differentiation, and point to new potential targets of Hg toxicity such as APP and NO signaling.

MiR-16 regulates cell death in Alzheimer's disease by targeting amyloid precursor protein

OBJECTIVE

The aim of this study was to investigate the role of miR-16 in Alzheimer's disease (AD) and to explore its mechanism of action.

MATERIALS AND METHODS

A cellular AD model using PC12 cells and primary hippocampal neurons was established to evaluate the expression level of miR-16. Transfection of a miR-16 mimic and a miR-16 inhibitor were performed to explore its effect on cell apoptosis and cell viability. In addition, we carried out bioinformatics analysis, luciferase reporting gene assay, and gene expression analyses to identify the potential target of miR-16 and to verify the effect of the target gene on the cellular AD model.

RESULTS

Downregulation of miR-16 was confirmed in the cellular AD model with both PC12 cells (p < 0.05) and primary hippocampal neurons (p < 0.05). Overexpression and inhibition of miR-16 in the cellular AD model with primary hippocampal neurons decreased and increased apoptosis, respectively. The gene encoding amyloid precursor protein (APP) was identified as the target gene of miR-16. Knockdown of APP in primary hippocampal neurons decreased cell apoptosis and increased cell viability in the cellular AD model.

CONCLUSIONS

Our results demonstrate that downregulation of miR-16 in primary hippocampal neurons play an important role in the paracrine effect and might be involved in the development of AD.

Peptides of presenilin-1 bind the amyloid precursor protein ectodomain and offer a novel and specific therapeutic approach to reduce ß-amyloid in Alzheimer's disease

β-Amyloid (Aβ) accumulation in the brain is widely accepted to be critical to the development of Alzheimer's disease (AD). Current efforts at reducing toxic Aβ40 or 42 have largely focused on modulating γ-secretase activity to produce shorter, less toxic Aβ, while attempting to spare other secretase functions. In this paper we provide data that offer the potential for a new approach for the treatment of AD. The method is based on our previous findings that the production of Aβ from the interaction between the β-amyloid precursor protein (APP) and Presenilin (PS), as part of the γ-secretase complex, in cell culture is largely inhibited if the entire water-soluble NH2-terminal domain of PS is first added to the culture. Here we demonstrate that two small, non-overlapping water-soluble peptides from the PS-1 NH2-terminal domain can substantially and specifically inhibit the production of total Aβ as well as Aβ40 and 42 in vitro and in vivo in the brains of APP transgenic mice. These results suggest that the inhibitory activity of the entire amino terminal domain of PS-1 on Aβ production is largely focused in a few smaller sequences within that domain. Using biolayer interferometry and confocal microscopy we provide evidence that peptides effective in reducing Aβ give a strong, specific and biologically relevant binding with the purified ectodomain of APP 695. Finally, we demonstrate that the reduction of Aβ by the peptides does not affect the catalytic activities of β- or γ-secretase, or the level of APP. P4 and P8 are the first reported protein site-specific small peptides to reduce Aβ production in model systems of AD. These peptides and their derivatives offer new potential drug candidates for the treatment of AD.

A γ-secretase inhibitor, but not a γ-secretase modulator, induced defects in BDNF axonal trafficking and signaling: evidence for a role for APP

Clues to Alzheimer disease (AD) pathogenesis come from a variety of different sources including studies of clinical and neuropathological features, biomarkers, genomics and animal and cellular models. An important role for amyloid precursor protein (APP) and its processing has emerged and considerable interest has been directed at the hypothesis that Aβ peptides induce changes central to pathogenesis. Accordingly, molecules that reduce the levels of Aβ peptides have been discovered such as γ-secretase inhibitors (GSIs) and modulators (GSMs). GSIs and GSMs reduce Aβ levels through very different mechanisms. However, GSIs, but not GSMs, markedly increase the levels of APP CTFs that are increasingly viewed as disrupting neuronal function. Here, we evaluated the effects of GSIs and GSMs on a number of neuronal phenotypes possibly relevant to their use in treatment of AD. We report that GSI disrupted retrograde axonal trafficking of brain-derived neurotrophic factor (BDNF), suppressed BDNF-induced downstream signaling pathways and induced changes in the distribution within neuronal processes of mitochondria and synaptic vesicles. In contrast, treatment with a novel class of GSMs had no significant effect on these measures. Since knockdown of APP by specific siRNA prevented GSI-induced changes in BDNF axonal trafficking and signaling, we concluded that GSI effects on APP processing were responsible, at least in part, for BDNF trafficking and signaling deficits. Our findings argue that with respect to anti-amyloid treatments, even an APP-specific GSI may have deleterious effects and GSMs may serve as a better alternative.

RNA silencing of genes involved in Alzheimer's disease enhances mitochondrial function and synaptic activity

An age-dependent increase in mRNA levels of the amyloid precursor protein (APP), the microtubule-associated protein Tau, and voltage-dependent anion channel 1 (VDAC1) genes are reported to be toxic to neurons affected by Alzheimer's disease (AD). However, the underlying toxic nature of these genes is not completely understood. The purpose of our study was to determine the effects of RNA silencing of APP, Tau, and VDAC1 genes in AD pathogenesis. Using human neuroblastoma (SHSY5Y) cells, we first silenced RNA for APP, Tau, and VDAC1 genes, and then performed real-time RT-PCR analysis to measure mRNA levels of 34 genes that are involved in AD pathogenesis. Using biochemical assays, we also assessed mitochondrial function by measuring levels of H2O2 production, lipid peroxidation, cytochrome c oxidase activity, ATP production, and GTPase enzymatic activity. We found that increased mRNA expression of synaptic function and mitochondrial fission genes, and reduced levels of mitochondrial fusion genes in RNA silenced the SHSY5Y cells for APP, Tau and VDAC1 genes relative to the control SHSY5Y cells. In addition, RNA-silenced APP, Tau, and VDAC1 genes in SHSY5Y cells showed reduced levels of H2O2 production, lipid peroxidation, fission-linked GTPase activity, and increased cytochrome oxidase activity and ATP production. These findings suggest that a reduction of human APP, Tau, and VDAC1 may enhance synaptic activity, may improve mitochondrial maintenance and function, and may protect against toxicities of AD-related genes. Thus, these findings also suggest that the reduction of APP, Tau, and VDAC1 mRNA expressions may have therapeutic value for patients with AD.

In vitro BACE1 inhibitory activity of geraniin and corilagin from Geranium thunbergii

Generation of amyloid β peptide through the proteolytic process of amyloid precursor protein by β-secretase and γ-secretase is a main casual factor of Alzheimer's disease, since amyloid β peptide is a major and crucial component of senile plaques in Alzheimer's disease brains. In the process of searching for β-secretase inhibitors from natural resources, the EtOAc soluble fraction of Geranium thunbergii exhibited significant β-secretase inhibitory activity. Two compounds, geraniin and corilagin, isolated from the most active EtOAc fraction of G. thunbergii, exhibited predominant inhibition against β-secretase with IC₅₀ values of 4.0 × 10⁻⁶ M and 3.4 × 10⁻⁵ M, respectively. Dixon plot of geraniin and corilagin demonstrated that the β-secretase inhibition was noncompetitive with the substrate, thus clearly suggesting that these compounds might bind either to the β-secretase subsites or to another regulatory domain with Ki values of 2.8 × 10⁻⁶ M and 7.9 × 10⁻⁵ M, respectively. Both compounds exhibited no significant inhibition against α-secretase and other serine proteases including trypsin and chymotrypsin, showing that they were relatively specific and selective inhibitors of β-secretase. These novel findings suggest that geraniin and corilagin from G. thunbergii may be effective therapeutic agents for further drug development in Alzheimer's disease.

Overexpression of amyloid precursor protein in acute myeloid leukemia enhances extramedullary infiltration by MMP-2

It is known that leukemia patients with extramedullary infiltration (EMI) have a worse prognosis than patients without it. Recent data indicate that the amyloid precursor protein (APP) is involved in cell adhesion, motility, and proliferation. The expression of APP and its prognostic significance in acute myeloid leukemia (AML) have not been studied. Our study shows that AML/ETO(+) leukemia patients that overexpress APP easily get EMI and that their long-term survival rate is lower than patients without overexpression of APP. In an in vitro study, we knocked down APP in Kasumi-1 cells using small interfering RNA (siRNA). Transwell data show that siRNA/APP substantially impairs cell migration, but it does not inhibit cell proliferation. Furthermore, by quantitative real-time polymerase chain reaction and Western blot, we found that siRNA/APP decreases MMP-2 expression in vitro. Our study provides a novel clue that APP is involved in the extramedullary infiltration of leukemia by MMP-2.

Prion protein expression alters APP cleavage without interaction with BACE-1

The prion protein (PrP) and the beta-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE-1) are both copper binding proteins, but are associated with two separate neurodegenerative diseases. The role of BACE-1 in the formation of beta-amyloid has made it a major target in attempts to reduce the formation of beta-amyloid in Alzheimer's diseases. However, the suggestion that PrP, normally associated with prion diseases, binds to BACE-1 and reduces its activity has led to the suggestion that the study of this interaction could be of considerable importance to Alzheimer's disease. We therefore undertook to investigate the possible interaction of these two proteins physically and at the level of transcription, translation and APP cleavage. Our findings suggest that mature PrP and BACE-1 do not physically interact, but that altered PrP expression results in altered BACE-1 protein expression and promoter activity. Additionally, overexpression of PrP results in increased cleavage of APP in contrast to previous datas suggesting a reduction. Our findings suggest that any relation between PrP and BACE-1 is indirect. Altered expression of PrP causes changes in the expression of many other proteins which may be as a result of altered copper metabolism.

Amyloid precursor protein (APP) mediated regulation of ganglioside homeostasis linking Alzheimer's disease pathology with ganglioside metabolism

Gangliosides are important players for controlling neuronal function and are directly involved in AD pathology. They are among the most potent stimulators of Aβ production, are enriched in amyloid plaques and bind amyloid beta (Aβ). However, the molecular mechanisms linking gangliosides with AD are unknown. Here we identified the previously unknown function of the amyloid precursor protein (APP), specifically its cleavage products Aβ and the APP intracellular domain (AICD), of regulating GD3-synthase (GD3S). Since GD3S is the key enzyme converting a- to b-series gangliosides, it therefore plays a major role in controlling the levels of major brain gangliosides. This regulation occurs by two separate and additive mechanisms. The first mechanism directly targets the enzymatic activity of GD3S: Upon binding of Aβ to the ganglioside GM3, the immediate substrate of the GD3S, enzymatic turnover of GM3 by GD3S was strongly reduced. The second mechanism targets GD3S expression. APP cleavage results, in addition to Aβ release, in the release of AICD, a known candidate for gene transcriptional regulation. AICD strongly down regulated GD3S transcription and knock-in of an AICD deletion mutant of APP in vivo, or knock-down of Fe65 in neuroblastoma cells, was sufficient to abrogate normal GD3S functionality. Equally, knock-out of the presenilin genes, presenilin 1 and presenilin 2, essential for Aβ and AICD production, or of APP itself, increased GD3S activity and expression and consequently resulted in a major shift of a- to b-series gangliosides. In addition to GD3S regulation by APP processing, gangliosides in turn altered APP cleavage. GM3 decreased, whereas the ganglioside GD3, the GD3S product, increased Aβ production, resulting in a regulatory feedback cycle, directly linking ganglioside metabolism with APP processing and Aβ generation. A central aspect of this homeostatic control is the reduction of GD3S activity via an Aβ-GM3 complex and AICD-mediated repression of GD3S transcription.

Decrease in the production of β-amyloid by berberine inhibition of the expression of β-secretase in HEK293 cells

BACKGROUND

Berberine (BER), the major alkaloidal component of Rhizoma coptidis, has multiple pharmacological effects including inhibition of acetylcholinesterase, reduction of cholesterol and glucose levels, anti-inflammatory, neuroprotective and neurotrophic effects. It has also been demonstrated that BER can reduce the production of beta-amyloid40/42, which plays a critical and primary role in the pathogenesis of Alzheimer's disease. However, the mechanism by which it accomplishes this remains unclear.

RESULTS

Here, we report that BER could not only significantly decrease the production of beta-amyloid40/42 and the expression of beta-secretase (BACE), but was also able to activate the extracellular signal-regulated kinase1/2 (ERK1/2) pathway in a dose- and time-dependent manner in HEK293 cells stably transfected with APP695 containing the Swedish mutation. We also find that U0126, an antagonist of the ERK1/2 pathway, could abolish (1) the activation activity of BER on the ERK1/2 pathway and (2) the inhibition activity of BER on the production of beta-amyloid40/42 and the expression of BACE.

CONCLUSION

Our data indicate that BER decreases the production of beta-amyloid40/42 by inhibiting the expression of BACE via activation of the ERK1/2 pathway.

Berberine: a potential multipotent natural product to combat Alzheimer's disease

With the accelerated aging of human society Alzheimer's disease (AD) has become one of the most threatening diseases in the elderly. However, there is no efficient therapeutic agent to combat AD. Berberine is a natural isoquinoline alkaloid that possesses a wide range of pharmacological effects. In the present paper, we review the multiple activities of berberine, including antioxidant, acetylcholinesterase and butyrylcholinesterase inhibitory, monoamine oxidase inhibitory, amyloid-b peptide level-reducing and cholesterol-lowering activities, which suggest that berberine may act as a promising multipotent agent to combat AD.

Amyloid-associated nucleic acid hybridisation

Nucleic acids promote amyloid formation in diseases including Alzheimer's and Creutzfeldt-Jakob disease. However, it remains unclear whether the close interactions between amyloid and nucleic acid allow nucleic acid secondary structure to play a role in modulating amyloid structure and function. Here we have used a simplified system of short basic peptides with alternating hydrophobic and hydrophilic amino acid residues to study nucleic acid - amyloid interactions. Employing biophysical techniques including X-ray fibre diffraction, circular dichroism spectroscopy and electron microscopy we show that the polymerized charges of nucleic acids concentrate and enhance the formation of amyloid from short basic peptides, many of which would not otherwise form fibres. In turn, the amyloid component binds nucleic acids and promotes their hybridisation at concentrations below their solution K(d), as shown by time-resolved FRET studies. The self-reinforcing interactions between peptides and nucleic acids lead to the formation of amyloid nucleic acid (ANA) fibres whose properties are distinct from their component polymers. In addition to their importance in disease and potential in engineering, ANA fibres formed from prebiotically-produced peptides and nucleic acids may have played a role in early evolution, constituting the first entities subject to Darwinian evolution.

Inhibitors of catalase-amyloid interactions protect cells from beta-amyloid-induced oxidative stress and toxicity

Compelling evidence shows a strong correlation between accumulation of neurotoxic β-amyloid (Aβ) peptides and oxidative stress in the brains of patients afflicted with Alzheimer disease (AD). One hypothesis for this correlation involves the direct and harmful interaction of aggregated Aβ peptides with enzymes responsible for maintaining normal, cellular levels of reactive oxygen species (ROS). Identification of specific, destructive interactions of Aβ peptides with cellular anti-oxidant enzymes would represent an important step toward understanding the pathogenicity of Aβ peptides in AD. This report demonstrates that exposure of human neuroblastoma cells to cytotoxic preparations of aggregated Aβ peptides results in significant intracellular co-localization of Aβ with catalase, an anti-oxidant enzyme responsible for catalyzing the degradation of the ROS intermediate hydrogen peroxide (H(2)O(2)). These catalase-Aβ interactions deactivate catalase, resulting in increased cellular levels of H(2)O(2). Furthermore, small molecule inhibitors of catalase-amyloid interactions protect the hydrogen peroxide-degrading activity of catalase in Aβ-rich environments, leading to reduction of the co-localization of catalase and Aβ in cells, inhibition of Aβ-induced increases in cellular levels of H(2)O(2), and reduction of the toxicity of Aβ peptides. These studies, thus, provide evidence for the important role of intracellular catalase-amyloid interactions in Aβ-induced oxidative stress and propose a novel molecular strategy to inhibit such harmful interactions in AD.

Inhibiting β-secretase activity in Alzheimer's disease cell models with single-chain antibodies specifically targeting APP

The Amyloid-β (Aβ) peptide is produced from the amyloid precursor protein (APP) by sequential proteolytic cleavage of APP first by β-secretase and then by γ-secretase. β-Site APP cleaving enzyme-1 (BACE-1) is the predominant enzyme involved in β-secretase processing of APP and is a primary therapeutic target for treatment of Alzheimer's disease. While inhibiting BACE-1 activity has obvious therapeutic advantages, BACE-1 also cleaves numerous other substrates with important physiological activity. Thus, blanket inhibition of BACE-1 function may have adverse side effects. We isolated a single chain variable fragment (scFv) from a human-based scFv yeast display library that selectively inhibits BACE-1 activity toward APP by binding the APP substrate at the proteolytic site. We selected the iBSEC1 scFv, since it recognizes the BACE-1 cleavage site on APP but does not bind the adjacent highly antigenic N-terminal of Aβ, and thus it will target APP but not soluble Aβ. When added to 7PA2 cells, a mammalian cell line that overexpresses APP, the iBSEC1 scFv binds APP on the cell surface, reduces toxicity induced by APP overexpression, and reduces both intracellular and extracellular Aβ levels by around 50%. Since the iBSEC1 scFv does not contain the antibody F(c) region, this construct does not pose the risk of exacerbating inflammation in the brain as faced with full-length monoclonal antibodies for potential therapeutic applications.

Histone deacetylase inhibitor valproic acid inhibits cancer cell proliferation via down-regulation of the alzheimer amyloid precursor protein

The beta-amyloid precursor protein (APP) represents a type I transmembrane glycoprotein that is ubiquitously expressed. In the brain, it is a key player in the molecular pathogenesis of Alzheimer disease. Its physiological function is however less well understood. Previous studies showed that APP is up-regulated in prostate, colon, pancreatic tumor, and oral squamous cell carcinoma. In this study, we show that APP has an essential role in growth control of pancreatic and colon cancer. Abundant APP staining was found in human pancreatic adenocarcinoma and colon cancer tissue. Interestingly, treating pancreatic and colon cancer cells with valproic acid (VPA, 2-propylpentanoic acid), a known histone deacetylase (HDAC) inhibitor, leads to up-regulation of GRP78, an endoplasmic reticulum chaperone immunoglobulin-binding protein. GRP78 is involved in APP maturation and inhibition of tumor cell growth by down-regulation of APP and secreted soluble APPalpha. Trichostatin A, a pan-HDAC inhibitor, also lowered APP and increased GRP78 levels. In contrast, treating cells with valpromide, a VPA derivative lacking HDAC inhibitory properties, had no effect on APP levels. VPA did not modify the level of epidermal growth factor receptor, another type I transmembrane protein, and APLP2, a member of the APP family, demonstrating the specificity of the VPA effect on APP. Small interfering RNA-mediated knockdown of APP also resulted in significantly decreased cell growth. Based on these observations, the data suggest that APP down-regulation via HDAC inhibition provides a novel mechanism for pancreatic and colon cancer therapy.

Small-molecule aggregation inhibitors reduce excess amyloid in a trisomy 16 mouse cortical cell line

We have previously characterized a number of small molecule organic compounds that prevent the aggregation of the beta-amyloid peptide and its neurotoxicity in hippocampal neuronal cultures. We have now evaluated the effects of such compounds on amyloid precursor protein (APP) accumulation in the CTb immortalized cell line derived from the cerebral cortex of a trisomy 16 mouse, an animal model of Down's syndrome. Compared to a non-trisomic cortical cell line (CNh), CTb cells overexpress APP and exhibit slightly elevated resting intracellular Ca2+ levels ([Ca2+] inverted exclamation mark). Here, we show that the compounds 2,4-dinitrophenol, 3-nitrophenol and 4-anisidine decreased intracellular accumulation of APP in CTb cells. Those compounds were non-toxic to the cells, and slightly increased the basal [Ca2+] inverted exclamation mark. Results indicate that the compounds tested can be leads for the development of drugs to decrease intracellular vesicular accumulation of APP in trisomic cells.

Homer2 and Homer3 interact with amyloid precursor protein and inhibit Abeta production

The study of Amyloid Precursor Protein (APP) processing has been the focus of considerable interest, since it leads to Abeta peptide generation, the main constituent of neuritic plaques found in brains of Alzheimer's disease patients. Therefore, the identification of novel APP binding partners that regulate Abeta peptide production represents a pharmaceutical target aiming at reducing Alphabeta pathology. In this study, we provide evidence that Homer2 and Homer3 but not Homer1 proteins interact specifically with APP. Their expression inhibits APP processing and reduces secretion of Abeta peptides. In addition, they decrease the levels of cell surface APP and inhibit maturation of APP and beta-secretase (BACE1). The effects of Homer2 and Homer3 on APP trafficking to the cell surface and/or on APP and BACE1 maturation could be part of the mechanism by which the expression of these proteins leads to the significant reduction of Abeta peptide production.

Inhibition of amyloid ?-peptide production by blockage of ?-secretase cleavage site of amyloid precursor protein

Amyloid beta-peptide (Abeta) is implicated as the major causative agent in Alzheimer's disease (AD). Abeta is produced by the processing of the amyloid precursor protein (APP) by BACE1 (beta-secretase) and gamma-secretase. Many inhibitors have been developed for the secretases. However, the inhibitors will interfere with the processing of not only APP but also of other secretase substrates. In this study, we describe the development of inhibitors that prevent production of Abeta by specific binding to the beta-cleavage site of APP. We used the hydropathic complementarity (HC) approach for the design of short peptide inhibitors. Some of the HC peptides were bound to the substrate peptide (Sub W) corresponding to the beta-cleavage site of APP and blocked its cleavage by recombinant human BACE1 (rhBACE1) in vitro. In addition, HC peptides specifically inhibited the cleavage of Sub W, and not affecting other BACE1 substrates. Chemical modification allowed an HC peptide (CIQIHF) to inhibit the processing of APP as well as the production of Abeta in the treated cells. Such novel APP-specific inhibitors will provide opportunity for the development of drugs that can be used for the prevention and treatment of AD with minimal side effects.

Amyloid-beta precursor-like protein APLP1 is a novel p53 transcriptional target gene that augments neuroblastoma cell death upon genotoxic stress

The tumor suppressor p53 is a key modulator of the cellular stress response, inducing cell-cycle arrest, apoptosis, senescence and cell differentiation. To evaluate further the molecular mechanism underlying p53 function, the transcriptional profiles of proliferating and senescent WI-38 cells, both wild-type p53 expressers and counterparts with an inactivated p53, were compared by DNA microarray analysis. In particular, the amyloid-beta precursor-like protein 1 (APLP1) is induced in senescent cells in a p53-dependent manner. APLP1 was confirmed to be a novel transcriptional target of p53 by in vivo and in vitro characterization of a p53 responsive element found in the first intron of the APLP1 gene locus. APLP1 knockdown experiments demonstrate that APLP1 is required for the proliferation of fibroblastic and epithelial cells. Moreover, depletion of APLP1 expression diminishes stress-induced apoptosis of neural cells, whereas ectopic APLP1 expression augments apoptosis. Based on these data, a mechanism is proposed whereby p53-dependent induction of APLP1 is involved in neural cell death, and which may exacerbate neuronal cell loss in some acute or chronic neurodegenerative disorders.

Immunotherapy against APP β-Secretase Cleavage Site Improves Cognitive Function and Reduces Neuroinflammation in Tg2576 Mice without a Significant Effect on Brain Aβ Levels

BACKGROUND/OBJECTIVES

Active and passive immunization methodologies against amyloid-beta (Abeta) are employed to clear and reduce cerebral Abetatowards treatment of Alzheimer's disease (AD) patients. The therapeutic potential of these antibodies in AD patients is limited because of adverse inflammatory reactions and cerebral hemorrhage, which are associated with the treatment. We propose a novel approach to inhibit Abeta production via antibodies against the beta-secretase cleavage site of the amyloid precursor protein (APP). Such an approach limits APP processing by beta-secretase, mainly through the endocytic pathway, and overcomes some of the limitations of BACE inhibition. Anti-APP beta-site antibodies, tested in a cellular model expressing wild-type APP, were found to bind full-length APP, internalize into the cells and interfere with BACE activity, inhibiting both intra- and extracellular Abeta peptide formation.

METHODS

We investigated the effect of anti-beta-site antibodies in an AD animal model regarding antibody efficacy, as well as possible adverse effects in the brain and periphery that may result from antibody treatment.

RESULTS/CONCLUSIONS

Here, we show that long-term systemic administration of anti-APP beta-site antibodies to Tg2576 transgenic mice improved mouse cognitive functions associated with a reduction in both brain inflammation and the incidence of microhemorrhage. Furthermore, antibody treatment did not induce any peripheral autoimmunity responses. In spite of the beneficial effects observed in antibody-treated mice, brain Abeta levels were not altered as a result of antibody treatment.

Inhibition of Aβ production by NF-κB inhibitors

The transcription factor nuclear factor kappaB (NF-kappaB) is widely expressed in the nervous system and increased NF-kappaB immunoreactivity has been observed in Alzheimer's disease (AD) brains in the nuclei of neurons within the vicinity of diffuse beta-amyloid plaques. Beta-amyloid (Abeta) peptides are the main constituent of senile plaques and are known to stimulate NF-kappaB activity. In the present study, we investigated the effect of various NF-kappaB inhibitors on the production of Abeta1-40, Abeta1-42, secreted APP (sAPPbeta and sAPPalpha) and APP C-terminal fragments (APP-CTF) using CHO cells overexpressing the beta-amyloid precursor protein (APP). Our data show that NF-kappaB inhibitors decrease both Abeta1-40 and Abeta1-42 production. In addition, we show that some NF-kappaB inhibitors decrease sAPPbeta and APP-CTFbeta suggesting that they reduce the beta-secretase cleavage of APP. Altogether our data suggest that NF-kappaB inhibitors may be of therapeutic importance for the treatment of AD pathology not only by blocking inflammatory processes but also by directly inhibiting the production of Abeta peptides.

Effect of mycelial extract of Clavicorona pyxidata on the production of amyloid beta-peptide and the inhibition of endogenous beta-secretase activity in vitro

Amyloid beta-peptide (Abeta), which is a product of the proteolytic effect of beta-secretase (BACE) on an amyloid precursor protein, is closely associated with Alzheimer's disease (AD) pathogenesis. There is sufficient evidence to suggest that a BACE inhibitor may reduce Abeta levels, thus decreasing the risk of AD. In a previous study, an extract of Clavicorona pyxidata DGUM 29005 mycelia was found to inhibit the production of a soluble beta-amyloid precursor protein (sbetaAPP), Abeta, and BACE in neuronal cell lines. We sought to determine whether this mycelial extract exerts the same effect in human rhabdomyosarcoma A-204 and rat pheochromocytoma PC-12 cells. We found that the production of Abeta decreased in a dose-dependent manner in the presence of the mycelial extract and that the concentration of Abeta never exceeded 50 microg/ml. The presence of sAPP was detected in every culture medium to which the mycelial extract had been added and its concentration remained the same, regardless of the concentration of the extract used. Endogenous beta-secretase activity in A-204 and PC-12 cellular homogenates also decreased in the presence of this extract. These cells, in culture, were not susceptible to the cytotoxic activity of the mycelial extract.

Suppression of beta-amyloid precursor protein signaling into the nucleus by estrogens mediated through complex formation between the estrogen receptor and Fe65

The C-terminal fragment of the beta-amyloid precursor protein produced after cleavage by gamma-secretase, namely, APPct or AICD, has been shown to form a multimeric complex with the adaptor protein Fe65 and to regulate transcription through the recruitment of the histone acetyltransferase Tip60. The present study shows that 17beta-estradiol inhibits the transcriptional and apoptotic activities of the APPct complex by a process involving the interaction of estrogen receptor alpha (ERalpha) with Fe65. ERalpha-Fe65 complexes were detected both in vitro and in the mouse brain, and recruitment of ERalpha to the promoter of an APPct target gene (KAI1) was demonstrated. Our studies reveal a novel mechanism of estrogen action, which may explain the well-known neuroprotective functions of estrogens as well as the complex role of this female hormone in the pathogenesis of neuronal degeneration diseases.

The novel gamma secretase inhibitor N-[cis-4-[(4-chlorophenyl)sulfonyl]-4-(2,5-difluorophenyl)cyclohexyl]-1,1,1-trifluoromethanesulfonamide (MRK-560) reduces amyloid plaque deposition without evidence of notch-related pathology in the Tg2576 mouse

There is a substantial body of evidence indicating that beta-amyloid peptides (Abeta) are critical factors in the onset and development of Alzheimer's disease (AD). One strategy for combating AD is to reduce or eliminate the production of Abeta through inhibition of the gamma-secretase enzyme, which cleaves Abeta from the amyloid precursor protein (APP). We demonstrate here that chronic treatment for 3 months with 3 mg/kg of the potent, orally bioavailable and brain-penetrant gamma-secretase inhibitor N-[cis-4-[(4-chlorophenyl)-sulfonyl]-4-(2,5-difluorophenyl)cyclohexyl]-1,1,1-trifluoromethanesulfonamide (MRK-560) attenuates the appearance of amyloid plaques in the Tg2576 mouse. These reductions in plaques were also accompanied by a decrease in the level of reactive gliosis. The morphometric and histological measures agreed with biochemical analysis of Abeta(40) and Abeta(42) in the cortex. Interestingly, the volume of the plaques across treatment groups did not change, indicating that reducing Abeta levels does not significantly alter deposit growth once initiated. Furthermore, we demonstrate that these beneficial effects can be achieved without causing histopathological changes in the ileum, spleen, or thymus as a consequence of blockade of the processing of alternative substrates, such as the Notch family of receptors. This indicates that in vivo a therapeutic window between these substrates seems possible--a key concern in the development of this approach to AD. An understanding of the mechanisms whereby MRK-560 shows differentiation between the APP and Notch proteolytic pathway of gamma-secretase should provide the basis for the next generation of gamma-secretase inhibitors.

N-Substituted carbazolyloxyacetic acids modulate Alzheimer associated gamma-secretase

N-Sulfonylated and N-alkylated carbazolyloxyacetic acids were investigated for the inhibition and modulation of the Alzheimer's disease associated gamma-secretase. The introduction of a lipophilic substituent, which may vary from arylsulfone to alkyl, turned 2-carbazolyloxyacetic acids into potent gamma-secretase modulators. This resulted in the selective reduction of Abeta(42) and an increase of the less aggregatory Abeta(38) fragment by several compounds (e.g., 7d and 8c). Introduction of an electron donating group at position 6 and 8 of N-substituted carbazolyloxyacetic acids either decreased the activity or inversed modulation. The most active compounds displayed activity on amyloid precursor protein (APP) overexpressing cell lines in the low micromolar range and little or no effect on the gamma-secretase cleavage at the epsilon-site.

Polyethylene glycol treatment after traumatic brain injury reduces beta-amyloid precursor protein accumulation in degenerating axons

Polyethylene glycol (PEG; 2,000 MW; 30% v/v) is a nontoxic molecule that can be injected intravenously and possesses well-documented neuroprotective properties in the spinal cord of the guinea pig. Recent studies have shown that intravenous PEG can also enter the rat brain parenchyma after injury and repair cellular membrane damage in the region of the corpus callosum. Disrupted anterograde axonal transport and resulting beta-amyloid precursor protein (APP) accumulation are byproducts of traumatic axonal injury (TAI) in the brain. APP accumulation indicates axonal degeneration as a result of axotomy, a detriment that can lead to cell death. In this study, we show that PEG treatment can eliminate APP accumulation in specific brain areas of rats receiving TAI. Six areas of the brain were analyzed: the medial cortex, hippocampus, lateral cortex, thalamus, medial lemniscus, and medial longitudinal fasciculus. Increased APP expression after injury was abolished in the thalamus and reduced in the medial longitudinal fasciculus by PEG treatment. In all remaining areas except for the lateral cortex, APP expression was not increased between injured and uninjured brains, indicating that damage was undetected in those brain areas in this study.

Intracellular pathways of folded and misfolded amyloid precursor protein degradation

A number of studies suggest that early events in the maturation of amyloid precursor protein (APP) are important in determining its entry into one of several alternative processing pathways, one of which leads to the toxic protein beta-amyloid (Abeta). In pulse-labeled APP expressing CHO cells two proteolytic systems can degrade newly translated APP: the proteosome and a cysteine protease. When N-glycosylation was inhibited by tunicamycin, the former system is the dominant mechanism of APP degradation. Without tunicamycin present, the cysteine protease is operational: cysteine protease inhibitors completely inhibit APP turnover in cells in which the secretory pathway is interrupted with brefeldin A or when alpha-secretase and endosomal degradation are also pharmacologically blocked. APP immunoprecipitated from cells extracted under mild conditions and labeled in the presence of tunicamycin exhibited greater sensitivity to endoproteinase glu-C (V8) or lys-C than from cells without drug. The V8 fragment missing in tunicamyin treated cells encompassed the KPI inhibitor insertion site but was distinct from the site of N-glycosylation. It is concluded that a conformational change caused by interrupted N-glycosylation shunts newly translated APP into the proteasomal degradation pathway. Pulse-labeled and chased cells showed an additional V8 fragment that was not present in pulsed-labeled cells and was not due to glycosylation since it was also present in cells labeled in the presence of brefeldin. This latter result indicates that an additional, delayed conformational alteration occurs in the endoplasmic reticulum.

Identification of Novel Small Molecule Inhibitors of Amyloid Precursor Protein Synthesis as a Route to Lower Alzheimer's Disease Amyloid-β Peptide

A wealth of independent research with transgenic mice, antibodies, and vaccines has pointed to a causative role of the amyloid-beta peptide (A beta) in Alzheimer's disease (AD). Based on these and earlier associative studies, A beta represents a promising target for development of therapeutics focused on AD disease progression. Interestingly, a cholinesterase inhibitor currently in clinical trials, phenserine, has been shown to inhibit production of both amyloid precursor protein (APP) and A beta. We have shown that this inhibition occurs at the post-transcriptional level with a specific blocking of the synthesis of APP relative to total protein synthesis (Shaw et al., 2001). However, the dose of phenserine necessary to block APP production is far higher than that needed to elicit its anticholinesterase activity, and it is these latter actions that are dose limiting in vivo. The focus of this study was to screen 144 analogs of phenserine to identify additional small molecules that inhibit APP protein synthesis, and thereby A beta production, without possessing potent acetylcholinesterase (AChE) inhibitory activity. An enzyme-linked immunosorbent assay was used to identify analogs capable of suppressing APP production following treatment of human neuroblastoma cells with 20 muM of compound. Eight analogs were capable of dose dependently reducing APP and A beta production without causing cell toxicity in further studies. Several of these analogs had little to no AChE activities. Translation of APP and A beta actions to mice was demonstrated with one agent. They thus represent interesting lead molecules for assessment in animal models, to define their tolerance and utility as potential AD therapeutics.

Amyloid precursor protein is involved in staurosporine induced glial differentiation of neural progenitor cells

Staurosporine (STS) has been reported as not only a pro-apoptotic agent, but also a terminal differentiation inducer in several neuroblastoma cell lines. Here, we report involvement of amyloid precursor protein (APP) in a STS induced astrocytic differentiation of human neural progenitor cells (NT-2/D1). We found that STS-treated NT-2/D1 cells expressed astrocyte-specific glial fibrillary acidic protein (GFAP), aspartate transporter, and glutamate transporter-1 with a distinctive astrocytic morphology. STS treatment increased GFAP promoter activity and increased expression and secretion of APP in NT-2/D1 cell culture. Overexpressed APP enhanced GFAP promoter activity and expression of GFAP, while gene silencing of APP by RNA interference decreased GFAP expression. These results indicate involvement of APP in STS induced astrocytic differentiation of NT-2/D1 cells. Furthermore, suppression of ERK1/2 phosphorylation, which is known to regulate APP expression by a MEK1 inhibitor, PD098059, reduced both APP and GFAP expression in STS treated NT-2/D1 cells. Thus, STS may induce astrocytic differentiation of NT-2/D1 by increasing APP levels associate with activation of ERK pathway.

BACE inhibitor reduces APP-beta-C-terminal fragment accumulation in axonal swellings of okadaic acid-induced neurodegeneration

Emerging evidence suggests that not only beta-amyloid but also other amyloid precursor protein (APP) fragments, such as the beta-C-terminal fragment (betaCTF), might be involved in Alzheimer's disease (AD). Treatment of neurons with okadaic acid (OA), a protein phosphatase-2A inhibitor, has been used to induce tau phosphorylation and neuronal death to create a research model of AD. In this study, we analyzed axonopathy and APP regulation in cultured rat neurons treated with OA. After OA treatment, the neurons presented with axonal swellings filled with vesicles, microtubule fragments, and transport molecules such as kinesin and synapsin-I. Western blotting showed that intracellular APP levels were increased and immunocytochemistry using antibodies against the APP C-terminus showed that APP accumulated in the axonal swellings. This APP C-terminus immunoreactivity disappeared when neurons were cotreated with a beta-secretase inhibitor, but not with alpha- or gamma-secretase inhibitors, indicating that the accumulation was primarily composed of APP-betaCTF. These findings provide the first evidence that APP-betaCTF can accumulate in the axons of OA-treated neurons, and may suggest that APP-betaCTF is involved in the pathogenesis of AD.

The novel beta-secretase inhibitor KMI-429 reduces amyloid beta peptide production in amyloid precursor protein transgenic and wild-type mice

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid plaques and neurofibrillary tangles in the brain. The major component of the plaques, amyloid beta peptide (Abeta), is generated from amyloid precursor protein (APP) by beta- and gamma-secretase-mediated cleavage. Because beta-secretase/beta-site APP cleaving enzyme 1 (BACE1) knockout mice produce much less Abeta and grow normally, a beta-secretase inhibitor is thought to be one of the most attractive targets for the development of therapeutic interventions for AD without apparent side-effects. Here, we report the in vivo inhibitory effects of a novel beta-secretase inhibitor, KMI-429, a transition-state mimic, which effectively inhibits beta-secretase activity in cultured cells in a dose-dependent manner. We injected KMI-429 into the hippocampus of APP transgenic mice. KMI-429 significantly reduced Abeta production in vivo in the soluble fraction compared with vehicle, but the level of Abeta in the insoluble fraction was unaffected. In contrast, an intrahippocampal injection of KMI-429 in wild-type mice remarkably reduced Abeta production in both the soluble and insoluble fractions. Our results indicate that the beta-secretase inhibitor KMI-429 is a promising candidate for the treatment of AD.

siRNA targeted against amyloid precursor protein impairs synaptic activity in vivo

The amyloid precursor protein (APP) plays a central role in Alzheimer's disease (AD) pathogenesis through its cleavage leading to the accumulation of the peptide betaA4. Diffusible oligomeric assemblies of amyloid beta peptide are thought to induce synaptic dysfunction, an early change in AD. We tested the hypothesis that a reduction in presynaptic APP could itself lead to a decrease in synaptic efficacy in vivo. Twenty-four hours after intraocular injection, siRNA targeted against APP accumulated in retinal cells and the APP in retinal terminals in the superior colliculus was significantly reduced. Surprisingly, the amyloid precursor-like protein 2 (APLP2) was reduced as well. Functional imaging experiments in rats during visual stimulation showed that knockdown of presynaptic APP/APLP2 significantly reduced the stimulation-induced glucose utilization in the superior colliculus. Our results suggest that perturbations in the amount of APP/APLP2 axonally transported to, and/or in their turnover in the nerve terminal alter synaptic function and could be a pathogenic mechanism in AD.

Method for the determination of the levels of β-amyloid peptide in the CSF sampled from freely moving rats

INTRODUCTION

In the present study, a model was developed to determine the effect of secretase inhibition on beta-amyloid peptide (Abeta) levels in the cerebrospinal fluid (CSF) of freely moving adult rats.

METHODS

Rats were chronically implanted with a cannula into the cisterna magna and CSF samples were collected at different time points from the same animal without anaesthesia. The levels of CSF Abeta were measured by a sandwich ELISA assay.

RESULTS

Administration of DAPT, a functional gamma-secretase inhibitor, resulted in a substantial reduction of Abeta40 and Abeta42, confirming the in vivo functionality of the CSF as a biomarker source for endogenous APP processing modulation by secretase inhibitors.

DISCUSSION

Thus, the present work provides clear evidence for the usefulness of CSF sampling from the freely moving rat model for testing the effectiveness of small molecule inhibitors of Abeta production.

Familial Alzheimer's disease mutations inhibit gamma-secretase-mediated liberation of beta-amyloid precursor protein carboxy-terminal fragment

Cleavage of the beta-secretase processed beta-amyloid precursor protein by gamma-secretase leads to the extracellular release of Abeta42, the more amyloidogenic form of the beta-amyloid peptide, which subsequently forms the amyloid-plaques diagnostic of Alzheimer's disease. Mutations in beta-amyloid precursor protein (APP), presenilin-1 and presenilin-2 associated with familial Alzheimer's disease (FAD) increase release of Abeta42, suggesting that FAD may directly result from increased gamma-secretase activity. Here, we show that familial Alzheimer's disease mutations clustered near the sites of gamma-secretase cleavage actually decrease gamma-secretase-mediated release of the intracellular fragment of APP (CTFgamma). Concordantly, presenilin-1 mutations that result in Alzheimer's disease also decrease the release of CTFgamma. Mutagenesis of the epsilon cleavage site in APP mimicked the effects of the FAD mutations, both decreasing CTFgamma release and increasing Abeta42 production, suggesting that perturbation of this site may account for the observed decrement in gamma-secretase-mediated proteolysis of APP. As CTFgamma has been implicated in transcriptional activation, these data indicate that decreased signaling and transcriptional regulation resulting from FAD mutations in beta-amyloid precursor protein and presenilin-1 may contribute to the pathology of Alzheimer's disease.

Inhibition of amyloid precursor protein processing by beta-secretase through site-directed antibodies

Amyloid-beta peptide (AbetaP) that accumulates in the Alzheimer's diseased brain is derived from proteolytic processing of the amyloid precursor protein (APP) by means of beta- and gamma-secretases. The beta-secretase APP cleaving enzyme (BACE), which generates the N terminus of AbetaP, has become a target of intense research aimed at blocking the enzyme activity, thus reducing AbetaP and, subsequently, plaque formation. The search for specific inhibitors of beta-secretase activity as a possible treatment for Alzheimer's disease intensified with the discovery that BACE may be involved in processing other non-APP substrates. The presence of the APP-BACE complex in early endosomes highlights the cell surface as a potential therapeutic target, suggesting that interference in APP-BACE interaction at the cell surface may affect amyloid-beta production. We present here a unique approach to inhibit AbetaP production by means of antibodies against the beta-secretase cleavage site of APP. These antibodies were found to bind human APP overexpressed by CHO cells, and the formed immunocomplex was visualized in the early endosomes. Indeed, blocking of the beta-secretase site by these antibodies interfered with BACE activity and inhibited both intracellular and extracellular AbetaP formation in these cells.

Structural role of glycine in amyloid fibrils formed from transmembrane alpha-helices

Amyloid fibrils associated with diseases such as Alzheimer's are often derived from the transmembrane helices of membrane proteins. It is known that the fibrils have a cross-beta-sheet structure where main chain hydrogen bonding occurs between beta-strands in the direction of the fibril axis. However, the structural basis for how the membrane-spanning helix is converted into a beta-sheet or how protofibrils associate into fibrils is not known. Here, we use a model peptide corresponding to a portion of the single transmembrane helix of glycophorin A to investigate the structural role of glycine in amyloid-like fibrils formed from transmembrane helices. Glycophorin A contains a GxxxG motif that is found in many transmembrane sequences including that of the amyloid precursor protein and prion protein. We propose that glycine, which mediates helix interactions in membrane proteins, also provides key packing motifs when it occurs in beta-sheets. We show that glycines in the glycophorin A transmembrane helix promote extended beta-strand formation when the helix partitions into aqueous environments and stabilize the packing of beta-sheets in the formation of amyloid-like fibrils. We demonstrate that fibrillization can be disrupted with a new class of inhibitors that target the molecular grooves created by glycine.

beta-site specific intrabodies to decrease and prevent generation of Alzheimer's Abeta peptide

Endoproteolysis of the β-amyloid precursor protein (APP) by β- and γ-secretases generates the toxic amyloid β-peptide (Aβ), which accumulates in the brain of Alzheimer's disease (AD) patients. Here, we established a novel approach to regulate production of Aβ based on intracellular expression of single chain antibodies (intrabodies) raised to an epitope adjacent to the β-secretase cleavage site of human APP. The intrabodies rapidly associated, within the endoplasmic reticulum (ER), with newly synthesized APP. One intrabody remained associated during APP transport along the secretory line, shielded the β-secretase cleavage site and facilitated the alternative, innocuous cleavage operated by α-secretase. Another killer intrabody with an ER retention sequence triggered APP disposal from the ER. The first intrabody drastically inhibited and the second almost abolished generation of Aβ. Intrabodies association with specific substrates rather than with enzymes, may modulate intracellular processes linked to disease with highest specificity and may become instrumental to investigate molecular mechanisms of cellular events.

Pilot Study of the Reducing Effect on Amyloidosis In Vivo by Three FDA Pre-Approved Drugs Via the Alzheimers APP 5Untranslated Region

A pilot study was conducted employing a well known mouse model for Alzheimer's disease to evaluate the anti-amyloid efficacy of three FDA pre-approved drugs. Paroxetine (SSRI and APP 5'UTR directed lead compound), N-acetyl cysteine (antioxidant), and erythromycin (macrolide antibiotic) were provided to the drinking water of TgCRND8 mice for three months. This report provides data that measured the steady-state levels of amyloid Abeta-40 and Abeta-42 Abeta as pmol Abeta per gram of mouse brain cortex in drug treated and placebo animals. The relative levels of Abeta peptide levels were reduced after exposure of mice to paroxetine (N=5), NAC (N=7), and erythromycin (N=7) relative to matched placebo counterparts. These results demonstrated proof-of concept for a strategy to further screen the APP 5'UTR target to identify novel drugs that exhibit anti-amyloid efficacy in vivo. These data also demonstrated a statistically significant anti-amyloid trend for paroxetine, NAC and erythromycin. The potential for conducting further studies with these compounds using larger cohorts of TgCRND8 mice is discussed.

Effect of Active Fraction of Cerebral on Expression of Caspase-3 and β-Amyloid Precursor Protein during Therapy of Hemorrhagic Stroke in the Acute and Delayed Periods

Active anti-stroke fraction of Cerebral preparation (extract of water-soluble molecules from brain tissue of animals with hemorrhagic stroke) decreased caspase-3 expression and improved survival of experimental animals in the acute period after hemorrhagic stroke.