Fe65 Stimulates Proteolytic Liberation of the β-Amyloid Precursor Protein Intracellular Domain

Green Tea Polyphenol Epigallocatechin-Gallate in Amyloid Aggregation and Neurodegenerative Diseases

The accumulation of protein aggregates in human tissues is a hallmark of more than 40 diseases called amyloidoses. In seven of these disorders, the aggregation is associated with neurodegenerative processes in the central nervous system such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and Huntington’s disease (HD). The aggregation occurs when certain soluble proteins lose their physiological function and become toxic amyloid species. The amyloid assembly consists of protein filament interactions, which can form fibrillar structures rich in β-sheets. Despite the frequent incidence of these diseases among the elderly, the available treatments are limited and at best palliative, and new therapeutic approaches are needed. Among the many natural compounds that have been evaluated for their ability to prevent or delay the amyloidogenic process is epigallocatechin-3-gallate (EGCG), an abundant and potent polyphenolic molecule present in green tea that has extensive biological activity. There is evidence for EGCG’s ability to inhibit the aggregation of α-synuclein, amyloid-β, and huntingtin proteins, respectively associated with PD, AD, and HD. It prevents fibrillogenesis (in vitro and in vivo), reduces amyloid cytotoxicity, and remodels fibrils to form non-toxic amorphous species that lack seed propagation. Although it is an antioxidant, EGCG in an oxidized state can promote fibrils’ remodeling through formation of Schiff bases and crosslinking the fibrils. Moreover, microparticles to drug delivery were synthesized from oxidized EGCG and loaded with a second anti-amyloidogenic molecule, obtaining a synergistic therapeutic effect. Here, we describe several pre-clinical and clinical studies involving EGCG and neurodegenerative diseases and their related mechanisms.

Lysine acetyltransferase Tip60 acetylates the APP adaptor Fe65 to increase its transcriptional activity

Proteolytic processing of the amyloid precursor protein (APP) releases the APP intracellular domain (AICD) from the membrane. Bound to the APP adaptor protein Fe65 and the lysine acetyltransferase (KAT) Tip60, AICD translocates to the nucleus. Here, the complex forms spherical condensates at sites of endogenous target genes, termed AFT spots (AICD-Fe65-Tip60). We show that loss of Tip60 KAT activity prevents autoacetylation, reduces binding of Fe65 and abolishes Fe65-mediated stabilization of Tip60. Autoacetylation is a prerequisite for AFT spot formation, with KAT-deficient Tip60 retained together with Fe65 in speckles. We identify lysine residues 204 and 701 of Fe65 as acetylation targets of Tip60. We do not detect acetylation of AICD. Mutation of Fe65 K204 and K701 to glutamine, mimicking acetylation-induced charge neutralization, increases the transcriptional activity of Fe65 whereas Tip60 inhibition reduces it. The lysine deacetylase (KDAC) class III Sirt1 deacetylates Fe65 and pharmacological modulation of Sirt1 activity regulates Fe65 transcriptional activity. A second acetylation/deacetylation cycle, conducted by CBP and class I/II KDACs at different lysine residues, regulates stability of Fe65. This is the first report describing a role for acetylation in the regulation of Fe65 transcriptional activity, with Tip60 being the only KAT tested that supports AFT spot formation.

Fe65 is the sole member of its family that mediates transcription regulated by the amyloid precursor protein

The amyloid precursor protein (APP), a central molecule in Alzheimer's disease (AD), has physiological roles in cell adhesion and signaling, migration, neurite outgrowth and synaptogenesis. Intracellular adapter proteins mediate the function of transmembrane proteins. Fe65 (also known as APBB1) is a major APP-binding protein. Regulated intramembrane proteolysis (RIP) by γ-secretase releases the APP intracellular domain (AICD), together with the interacting proteins, from the membrane. We studied the impact of the Fe65 family (Fe65, and its homologs Fe65L1 and Fe65L2, also known as APBB2 and APBB3, respectively) on the nuclear signaling function of the AICD. All Fe65 family members increased amyloidogenic processing of APP, generating higher levels of β-cleaved APP stubs and AICD. However, Fe65 was the only family member supporting AICD translocation to nuclear spots and its transcriptional activity. Using a recently established transcription assay, we dissected the transcriptional activity of Fe65 and provide strong evidence that Fe65 represents a transcription factor. We show that Fe65 relies on the lysine acetyltransferase Tip60 (also known as KAT5) for nuclear translocation. Furthermore, inhibition of APP cleavage reduces nuclear Tip60 levels, but this does not occur in Fe65-knockout cells. The rate of APP cleavage therefore regulates the nuclear translocation of AICD-Fe65-Tip60 (AFT) complexes, to promote transcription by Fe65.

A fluorescent protein-readout for transcriptional activity reveals regulation of APP nuclear signaling by phosphorylation sites

Signaling pathways that originate at the plasma membrane, including regulated intramembrane proteolysis (RIP), enable extracellular cues to control transcription. We modified the yeast Gal4 transcription system to study the nuclear translocation of transcriptionally active complexes using the fluorescent protein citrine (Cit) as a reporter. This enabled highly sensitive quantitative analysis of transcription in situ at the single cell level. The Gal4/UAS-Cit transcription assay displayed a sigmoidal response limited by the number of integrated reporter cassettes. We validated the assay by analyzing nuclear translocation of the amyloid precursor protein (APP) intracellular domain (AICD) and confirmed the requirement of Fe65 for nuclear translocation of AICD. In addition to the strong on-off effects on transcriptional activity, the results of this assay establish that phosphorylation modifies nuclear signaling. The Y682F mutation in APP showed the strongest increase in Cit expression, underscoring its role in regulating Fe65 binding. Together, we established a highly sensitive fluorescent protein-based assay that can monitor transcriptional activity at the single cell level and demonstrate that AICD phosphorylation affects Fe65 nuclear activity. This assay also introduces a platform for future single cell-based drug screening methods for nuclear translocation.

Immununochemical Markers of the Amyloid Cascade in the Hippocampus in Motor Neuron Diseases

BACKGROUND

Several findings suggest that the amyloid precursor protein (APP) and the amyloid cascade may play a role in motor neuron disease (MND).

OBJECTIVE

Considering that dementia is one of the most frequent non-motor symptoms in amyotrophic lateral sclerosis (ALS) and that hippocampus is one of the brain areas with greater presence of amyloid-related changes in neurodegenerative diseases, our aim was to analyze the molecular markers of the amyloid cascade of APP in pathology studies of the hippocampus of autopsied patients with ALS and ALS-frontotemporal dementia (FTD).

METHODS

We included nine patients with MND and four controls. Immunohistochemical studies and confocal microscopy were used to analyze the expression of APP, TDP-43, pho-TDP-43, Aβ, APP intracellular cytoplasmatic domain (AICD) peptide, Fe65 protein, and pho-TAU in the hippocampus of seven patients with ALS, two patients with ALS-FTD, and four controls. These findings were correlated with clinical data.

RESULTS

Patients displayed increased expression of APP and Aβ peptide. The latter was correlated with cytoplasmic pho-TDP-43 expression. We also found decreased Fe65 expression. A parallel increase in AICD expression was not found. Patients showed increased expression of pho-TAU in the hippocampus. Findings were similar in patients with ALS and those with ALS-FTD, though more marked in the latter group.

CONCLUSION

Post-mortem analyses showed that the amyloid cascade is activated in the hippocampus of patients with MND and correlated with cytoplasmic pho-TDP-43 expression. The number of intracellular or extracellular aggregates of Aβ peptides was not significant.

Phosphorylation of FE65 Ser610 by serum- and glucocorticoid-induced kinase 1 modulates Alzheimer's disease amyloid precursor protein processing

Phosphorylation of FE65 Ser⁶¹⁰ by serum- and glucocorticoid-induced kinase 1 (SGK1) attenuates amyloid precursor protein (APP) processing via regulation of FE65–APP interaction.

Alzheimer's disease (AD) is a fatal neurodegenerative disease affecting 36 million people worldwide. Genetic and biochemical research indicate that the excessive generation of amyloid-β peptide (Aβ) from amyloid precursor protein (APP), is a major part of AD pathogenesis. FE65 is a brain-enriched adaptor protein that binds to APP. However, the role of FE65 in APP processing and the mechanisms that regulate binding of FE65 to APP are not fully understood. In the present study, we show that serum- and glucocorticoid-induced kinase 1 (SGK1) phosphorylates FE65 on Ser⁶¹⁰ and that this phosphorylation attenuates FE65 binding to APP. We also show that FE65 promotes amyloidogenic processing of APP and that FE65 Ser⁶¹⁰ phosphorylation inhibits this effect. Furthermore, we found that the effect of FE65 Ser⁶¹⁰ phosphorylation on APP processing is linked to a role of FE65 in metabolic turnover of APP via the proteasome. Thus FE65 influences APP degradation via the proteasome and phosphorylation of FE65 Ser⁶¹⁰ by SGK1 regulates binding of FE65 to APP, APP turnover and processing.

LINGO-1 promotes lysosomal degradation of amyloid-β protein precursor

Sequential proteolytic cleavages of amyloid-β protein precursor (AβPP) by β-secretase and γ-secretase generate amyloid β (Aβ) peptides, which are thought to contribute to Alzheimer's disease (AD). Much of this processing occurs in endosomes following endocytosis of AβPP from the plasma membrane. However, this pathogenic mode of processing AβPP may occur in competition with lysosomal degradation of AβPP, a common fate of membrane proteins trafficking through the endosomal system. Following up on published reports that LINGO-1 binds and promotes the amyloidogenic processing of AβPP we have examined the consequences of LINGO-1/AβPP interactions. We report that LINGO-1 and its paralogs, LINGO-2 and LINGO-3, decrease processing of AβPP in the amyloidogenic pathway by promoting lysosomal degradation of AβPP. We also report that LINGO-1 levels are reduced in AD brain, representing a possible pathogenic mechanism stimulating the generation of Aβ peptides in AD.

Neprilysin and Aβ Clearance: Impact of the APP Intracellular Domain in NEP Regulation and Implications in Alzheimer's Disease

One of the characteristic hallmarks of Alzheimer's disease (AD) is an accumulation of amyloid β (Aβ) leading to plaque formation and toxic oligomeric Aβ complexes. Besides the de novo synthesis of Aβ caused by amyloidogenic processing of the amyloid precursor protein (APP), Aβ levels are also highly dependent on Aβ degradation. Several enzymes are described to cleave Aβ. In this review we focus on one of the most prominent Aβ degrading enzymes, the zinc-metalloprotease Neprilysin (NEP). In the first part of the review we discuss beside the general role of NEP in Aβ degradation the alterations of the enzyme observed during normal aging and the progression of AD. In vivo and cell culture experiments reveal that a decreased NEP level results in an increased Aβ level and vice versa. In a pathological situation like AD, it has been reported that NEP levels and activity are decreased and it has been suggested that certain polymorphisms in the NEP gene result in an increased risk for AD. Conversely, increasing NEP activity in AD mouse models revealed an improvement in some behavioral tests. Therefore it has been suggested that increasing NEP might be an interesting potential target to treat or to be protective for AD making it indispensable to understand the regulation of NEP. Interestingly, it is discussed that the APP intracellular domain (AICD), one of the cleavage products of APP processing, which has high similarities to Notch receptor processing, might be involved in the transcriptional regulation of NEP. However, the mechanisms of NEP regulation by AICD, which might be helpful to develop new therapeutic strategies, are up to now controversially discussed and summarized in the second part of this review. In addition, we review the impact of AICD not only in the transcriptional regulation of NEP but also of further genes.

Dysregulation of hypoxia-inducible factor by presenilin/γ-secretase loss-of-function mutations

Presenilin (PSEN) 1 and 2 are the catalytic components of the γ-secretase complex, which cleaves a variety of proteins, including the amyloid precursor protein (APP). Proteolysis of APP leads to the formation of the APP intracellular domain (AICD) and amyloid β that is crucially involved in the pathogenesis of Alzheimer's disease. Prolyl-4-hydroxylase-domain (PHD) proteins regulate the hypoxia-inducible factors (HIFs), the master regulators of the hypoxic response. We previously identified the FK506 binding protein 38 (FKBP38) as a negative regulator of PHD2. Genetic ablation of PSEN1/2 has been shown to increase FKBP38 protein levels. Therefore, we investigated the role of PSEN1/2 in the oxygen sensing pathway using a variety of genetically modified cell and mouse lines. Increased FKBP38 protein levels and decreased PHD2 protein levels were found in PSEN1/2-deficient mouse embryonic fibroblasts and in the cortex of forebrain-specific PSEN1/2 conditional double knock-out mice. Hypoxic HIF-1α protein accumulation and transcriptional activity were decreased, despite reduced PHD2 protein levels. Proteolytic γ-secretase function of PSEN1/2 was needed for proper HIF activation. Intriguingly, PSEN1/2 mutations identified in Alzheimer patients differentially affected the hypoxic response, involving the generation of AICD. Together, our results suggest a direct role for PSEN in the regulation of the oxygen sensing pathway via the APP/AICD cleavage cascade.

FE65 regulates and interacts with the Bloom syndrome protein in dynamic nuclear spheres – potential relevance to Alzheimer's disease

The intracellular domain of the amyloid precursor protein (AICD) is generated following cleavage of the precursor by the γ-secretase complex and is involved in membrane to nucleus signaling, for which the binding of AICD to the adapter protein FE65 is essential. Here we show that FE65 knockdown causes a down regulation of the protein BLM and the MCM protein family and that elevated nuclear levels of FE65 result in stabilization of the BLM protein in nuclear mobile spheres. These spheres are able to grow and fuse, and potentially correspond to the nuclear domain 10. BLM plays a role in DNA replication and repair mechanisms and FE65 was also shown to play a role in the cell's response to DNA damage. A set of proliferation assays in our work revealed that FE65 knockdown cells exhibit reduced cell replication in HEK293T cells. On the basis of these results, we hypothesize that nuclear FE65 levels (nuclear FE65/BLM containing spheres) may regulate cell cycle re-entry in neurons due to increased interaction of FE65 with BLM and/or an increase in MCM protein levels. Thus, FE65 interactions with BLM and MCM proteins may contribute to the neuronal cell cycle re-entry observed in Alzheimer disease brains.

The physiology of the β-amyloid precursor protein intracellular domain AICD

The amyloid-β precursor protein (βAPP) undergoes several cleavages by enzymatic activities called secretases. Numerous studies aimed at studying the biogenesis and catabolic fate of Aβ peptides, the proteinaceous component of the senile plaques that accumulate in Alzheimer's disease-affected brains. Relatively recently, another secretase-mediated β-APP-derived catabolite called APP IntraCellular Domain (AICD) entered the game. Whether AICD corresponded to a biologically inert by-pass product of βAPP processing or whether it could harbor its own function remained questionable. In this study, we review the mechanisms by which AICD is generated and how its production is regulated. Furthermore, we discuss the degradation mechanism underlying its rapid catabolic fate. Finally, we review putative AICD-related functions and more particularly, the numerous studies indicating that AICD could translocate to the nucleus and control at a transcriptional level, the expression of a series of proteins involved in various functions including the control of cell death and Aβ degradation.

A role for FE65 in controlling GnRH-1 neurogenesis

Gonadotropin-releasing hormone-1 (GnRH-1) neurons migrate from the nasal placode to the forebrain where they control gonadal function via the hypothalamic-pituitary-gonadal axis. The birth of GnRH-1-expressing neurons is one of the first neurogenic events in the developing nasal placode. By gene expression screening on single GnRH-1 neurons, amyloid precursor binding protein-1 (FE65) was identified in migratory GnRH-1 neurons. FE65 has been shown to modulate β1-integrin dynamics, actin cytoskeleton, cell motility, and FE65/amyloid precursor protein signaling has been described in neuro/glial cell fate determination as well as in modulating neurogenesis. Analysis of two mouse lines, one deficient for the 97 kDa FE65 isoform and a second deficient for the 97 and 60 kDa forms of FE65, showed overlapping phenotypes. In both lines, no migratory defects of the GnRH-1 neurons were observed, but a 25% increase in GnRH-1 neuronal number during embryonic development was found. Bromodeoxyuridine birth tracing and spatiotemporal tracking of GnRH-1 cell precursors demonstrated that the lack of the N-terminal portion of FE65, which includes part of the functional nuclear translocation/gene transcription domain of FE65 (WW domain), extends the timing of GnRH-1 neurogenesis in the developing nasal placode without affecting proliferation of GnRH-1 neuronal progenitors or cell death. The observed changes in the dynamics of GnRH-1 neurogenesis highlight a unique role for the 97 kDa isoform of FE65 and suggest that GnRH-1 cells, which have a short neurogenic window, originate from multipotent progenitors able to generate distinct cell types as GnRH-1 neurogenesis declines in response to environmental changes.

Transcriptional regulation of human FE65, a ligand of Alzheimer's disease amyloid precursor protein, by Sp1

FE65 is a neuronal-enriched adaptor protein that binds to the Alzheimer's disease amyloid precursor protein (APP). FE65 forms a transcriptionally active complex with the APP intracellular domain (AICD). The precise gene targets for this complex are unclear but several Alzheimer's disease-linked genes have been proposed. Additionally, evidence suggests that FE65 influences APP metabolism. The mechanism by which FE65 expression is regulated is as yet unknown. To gain insight into the regulatory mechanism, we cloned a 1.6 kb fragment upstream of the human FE65 gene and found that it possesses particularly strong promoter activity in neurones. To delineate essential regions in the human FE65 promoter, a series of deletion mutants were generated. The minimal FE65 promoter was located between -100 and +5, which contains a functional Sp1 site. Overexpression of the transcription factor Sp1 potentiates the FE65 promoter activity. Conversely, suppression of the FE65 promoter was observed in cells either treated with an Sp1 inhibitor or in which Sp1 was knocked down. Furthermore, reduced levels of Sp1 resulted in downregulation of endogenous FE65 mRNA and protein. These findings reveal that Sp1 plays a crucial role in transcriptional control of the human FE65 gene.

Phenylbutyric acid rescues endoplasmic reticulum stress-induced suppression of APP proteolysis and prevents apoptosis in neuronal cells

BACKGROUND

The familial and sporadic forms of Alzheimer's disease (AD) have an identical pathology with a severe disparity in the time of onset [1]. The pathological similarity suggests that epigenetic processes may phenocopy the Familial Alzheimer's disease (FAD) mutations within sporadic AD. Numerous groups have demonstrated that FAD mutations in presenilin result in 'loss of function' of gamma-secretase mediated APP cleavage [2], [3], [4], [5]. Accordingly, ER stress is prominent within the pathologically impacted brain regions in AD patients [6] and is reported to inhibit APP trafficking through the secretory pathway [7], [8]. As the maturation of APP and the cleaving secretases requires trafficking through the secretory pathway [9], [10], [11], we hypothesized that ER stress may block trafficking requisite for normal levels of APP cleavage and that the small molecular chaperone 4-phenylbutyrate (PBA) may rescue the proteolytic deficit.

METHODOLOGY/PRINCIPAL FINDINGS

The APP-Gal4VP16/Gal4-reporter screen was stably incorporated into neuroblastoma cells in order to assay gamma-secretase mediated APP proteolysis under normal and pharmacologically induced ER stress conditions. Three unrelated pharmacological agents (tunicamycin, thapsigargin and brefeldin A) all repressed APP proteolysis in parallel with activation of unfolded protein response (UPR) signaling-a biochemical marker of ER stress. Co-treatment of the gamma-secretase reporter cells with PBA blocked the repressive effects of tunicamycin and thapsigargin upon APP proteolysis, UPR activation, and apoptosis. In unstressed cells, PBA stimulated gamma-secretase mediated cleavage of APP by 8-10 fold, in the absence of any significant effects upon amyloid production, by promoting APP trafficking through the secretory pathway and the stimulation of the non-pathogenic alpha/gamma-cleavage.

CONCLUSIONS/SIGNIFICANCE

ER stress represses gamma-secretase mediated APP proteolysis, which replicates some of the proteolytic deficits associated with the FAD mutations. The small molecular chaperone PBA can reverse ER stress induced effects upon APP proteolysis, trafficking and cellular viability. Pharmaceutical agents, such as PBA, that stimulate alpha/gamma-cleavage of APP by modifying intracellular trafficking should be explored as AD therapeutics.

Pharmacology of epigenetics in brain disorders

Epigenetics is a rapidly growing field and holds great promise for a range of human diseases, including brain disorders such as Rett syndrome, anxiety and depressive disorders, schizophrenia, Alzheimer disease and Huntington disease. This review is concerned with the pharmacology of epigenetics to treat disorders of the epigenome whether induced developmentally or manifested/acquired later in life. In particular, we will focus on brain disorders and their treatment by drugs that modify the epigenome. While the use of DNA methyl transferase inhibitors and histone deacetylase inhibitors in in vitro and in vivo models have demonstrated improvements in disease-related deficits, clinical trials in humans have been less promising. We will address recent advances in our understanding of the complexity of the epigenome with its many molecular players, and discuss evidence for a compromised epigenome in the context of an ageing or diseased brain. We will also draw on examples of species differences that may exist between humans and model systems, emphasizing the need for more robust pre-clinical testing. Finally, we will discuss fundamental issues to be considered in study design when targeting the epigenome.

Synaptic NMDA receptor activation stimulates alpha-secretase amyloid precursor protein processing and inhibits amyloid-beta production

Altered amyloid precursor protein (APP) processing leading to increased production and oligomerization of Abeta may contribute to Alzheimer's disease (AD). Understanding how APP processing is regulated under physiological conditions may provide new insights into AD pathogenesis. Recent reports demonstrate that excitatory neural activity regulates APP metabolism and Abeta levels, although understanding of the molecular mechanisms involved is incomplete. We have investigated whether NMDA receptor activity regulates APP metabolism in primary cultured cortical neurons. We report that a pool of APP is localized to the postsynaptic compartment in cortical neurons and observed partial overlap of APP with both NR1 and PSD-95. NMDA receptor stimulation increased nonamyloidogenic alpha-secretase-mediated APP processing, as measured by a 2.5-fold increase in cellular alpha-C-terminal fragment (C83) levels after glutamate or NMDA treatment. This increase was blocked by the NMDA receptor antagonists d-AP5 and MK801 but not by the AMPA receptor antagonist CNQX or the L-type calcium channel blocker nifedipine, was prevented by chelation of extracellular calcium, and was blocked by the alpha-secretase inhibitor TAPI-1. Cotreatment of cortical neurons with bicuculline and 4-AP, which stimulates glutamate release and activates synaptic NMDA receptors, evoked an MK801-sensitive increase in C83 levels. Furthermore, NMDA receptor stimulation caused a twofold increase in the amount of soluble APP detected in the neuronal culture medium. Finally, NMDA receptor activity inhibited both Abeta1-40 release and Gal4-dependent luciferase activity induced by beta-gamma-secretase-mediated cleavage of an APP-Gal4 fusion protein. Altogether, these data suggest that calcium influx through synaptic NMDA receptors promotes nonamyloidogenic alpha-secretase-mediated APP processing.

Selective vulnerability in Alzheimer's disease: amyloid precursor protein and p75(NTR) interaction

OBJECTIVE

Selective neuronal vulnerability in neurodegenerative diseases is poorly understood. In Alzheimer's disease, the basal forebrain cholinergic neurons are selectively vulnerable, putatively because of their expression of the cell death mediator p75(NTR) (the common neurotrophin receptor), and its interaction with proapoptotic ligands pro-nerve growth factor and amyloid-beta peptide. However, the relation between amyloid precursor protein (APP) and p75(NTR) has not been described previously.

METHODS

APP and p75(NTR) were assayed for interaction by coimmunoprecipitation in vitro and in vivo, yeast two-hybrid assay, bioluminescence resonance energy transfer, and confocal microscopy. Effects on APP processing and signaling were studied using immunoblotting, enzyme-linked immunosorbent assays, and luciferase reporter assays.

RESULTS

The results of this study are as follows: (1) p75(NTR) and APP interact directly; (2) this interaction is modified by ligands nerve growth factor and beta-amyloid; (3) APP and p75(NTR) colocalization in vivo is modified in Alzheimer's model transgenic mice; (4) APP processing is altered by p75(NTR), and to a lesser extent, p75(NTR) processing is altered by the presence of APP; (5) APP-dependent transcription mediated by Fe65 is blocked by p75(NTR); and (6) coexpression of APP and p75(NTR) triggers cell death.

INTERPRETATION

These results provide new insight into the emerging signaling network that mediates the Alzheimer's phenotype and into the mechanism of basal forebrain cholinergic neuronal selective vulnerability. In addition, the results argue that the interaction between APP and p75(NTR) may represent a therapeutic target in Alzheimer's disease.

Neuronal protein trafficking associated with Alzheimer disease: from APP and BACE1 to glutamate receptors

Aberrant and/or cumulative amyloid-beta (Abeta) production, resulting from proteolytic processing of the amyloid precursor protein (APP) by beta and gamma-secretases, have been postulated to be a main etiological basis of Alzheimer disease (AD). A number of proteins influence the subcellular trafficking itinerary of APP and the beta-site APP-cleaving enzyme (BACE1) between the cell surface, endosomes and the trans-Golgi network (TGN). Available evidence suggests that co-residence of APP and BACE1 in the endosomal compartments promotes amyloidogenesis. Retrograde transport of APP out of the endosome to the TGN reduces Abeta production, while APP routed to and kept at the cell surface enhances its non-amyloidogenic, alpha-secretase-mediated processing. Changes in post-Golgi membrane trafficking in aging neurons that may influence APP processing is particularly relevant to late-onset, idiopathic AD. Dystrophic axons are key features of AD pathology, and impaired axonal transport could play crucial roles in the pathogenesis of idiopathic AD. Recent evidence has also indicated that Abeta-induced synaptic defects and memory impairment could be explained by a loss of both AMPA and NMDA receptors through endocytosis. Detail understanding of factors that influence these neuronal trafficking processes will open up novel therapeutic avenues for preventing or delaying the onset of symptomatic AD.

Association of amyloid precursor protein-binding protein, family B, member 1 with nicotine dependence in African and European American smokers

Although epidemiological studies reveal that cigarette smoking is inversely associated with Alzheimer's disease (AD) and Parkinson's disease (PD), the underlying mechanism remains largely unknown. Considering the facts that amyloid precursor protein-binding protein, family B, member 1 (APBB1) is mapped to a suggestive linkage region on chromosome 11 for nicotine dependence (ND), and has been implicated in the pathogenesis of AD and PD, it represents a plausible candidate for genetic study of ND. Five single nucleotide polymorphisms (SNPs) within APBB1 were genotyped in a sample consisting of 2,037 participants of either African-American (AA) or European-American (EA) origin, and examined their associations with ND assessed by three commonly used measures: Smoking Quantity (SQ), the Heaviness of Smoking Index (HSI), and the Fagerström Test for ND (FTND). Individual SNP-based association analysis showed that all five SNPs are associated with at least one ND measure in one of the three samples; however, only the association of SNP rs4758416 with SQ and HSI remained significant after correction for multiple testing in the pooled sample. Haplotype analysis demonstrated three major haplotypes significantly associated with ND after Bonferroni correction. Formed by rs4758416-rs10839562-rs1079199, haplotype C-C-T showed positive association with FTND in the AA and pooled samples, and conversely, haplotype G-C-T showed negative association with SQ and HSI in AA and EA samples. Another haplotype, C-T-G, formed by rs10839562-rs1079199-rs8164, was significantly associated with HSI in the EA sample. Based on these findings, we conclude that APBB1 represents an important candidate gene in the genetic study on ND and neurodegenerative diseases and warrants further investigation in future.

Evidence that the Amyloid beta Precursor Protein-intracellular domain lowers the stress threshold of neurons and has a "regulated" transcriptional role

Background

Regulated intramembrane proteolysis of the β-amyloid precursor protein by the γ-secretase yields two peptides. One, amyloid-β, is the major component of the amyloid plaques found in Alzheimer's disease patients. The other, APP IntraCellular Domain, has been involved in regulation of apoptosis, calcium flux and gene transcription. To date, a few potential target genes transcriptionally controlled by AID, alone or complexed with Fe65/Tip60, have been described. Although the reports are controversial: these include KAI1, Neprilysin, p53, EGFR, LRP and APP itself. Furthermore, p53 has been implicated in AID mediated susceptibility to apoptosis. To extend these findings, and assess their in vivo relevance, we have analyzed the expression of the putative target genes and of the total brain basal transriptoma in transgenic mice expressing AID in the forebrain. Also, we have studied the susceptibility of primary neurons from such mice to stress and pro-apoptotic agents.

Results

We found that AID-target genes and the mouse brain basal transcriptoma are not influenced by transgenic expression of AID alone, in the absence of Fe65 over-expression. Also, experiments conducted on primary neurons from AID transgenic mice, suggest a role for AID in sensitizing these cells to toxic stimuli. Overall, these findings hint that a role for AID, in regulating gene transcription, could be induced by yet undefined, and possibly stressful, stimuli in vivo.

Conclusion

Overall, these data suggest that the release of the APP intracellular domain may modulate the sensitivity of neuronal cells to toxic stimuli, and that a transcriptional role of AID could be inscribed in signaling pathways thatare not activated in basal conditions.

The Yin and Yang of YY1 in the nervous system

The transcription factor Yin Yang 1 (YY1) is a multifunctional protein that can activate or repress gene expression depending on the cellular context. YY1 is ubiquitously expressed and highly conserved between species. However, its role varies in diverse cell types and includes proliferation, differentiation, and apoptosis. This review will focus on the function of YY1 in the nervous system including its role in neural development, neuronal function, developmental myelination, and neurological disease. The multiple functions of YY1 in distinct cell types are reviewed and the possible mechanisms underlying the cell specificity for these functions are discussed.

Fibrillar prion peptide PrP(106-126) treatment induces Dab1 phosphorylation and impairs APP processing and Abeta production in cortical neurons

Alzheimer's disease and prion diseases (e.g., Creutzfeldt-Jakob disease) display profound neural lesions associated with aberrant protein processing and extracellular amyloid deposits. However, the intracellular events in prion diseases and their relation with the processing of the amyloid precursor protein (APP) and beta-amyloid generation are unknown. The adaptor protein Dab1 may regulate intracellular trafficking and secretase-mediated proteolysis in APP processing. However, a putative relationship between prion diseases and Dab1/APP interactions is lacking. Thus, we examined, in inoculated animals, whether Dab1 and APP processing are targets of the intracellular events triggered by extracellular exposure to PrP(106-126) peptide. Our in vitro results indicate that PrP(106-126) peptide induces tyrosine phosphorylation of Dab1 by activated members of the Src family of tyrosine kinases (SFK), which implies further Dab1 degradation. We also corroborate these results in Dab1 protein levels in prion-inoculated hamsters. Finally, we show that fibrillar prion peptides have a dual effect on APP processing and beta-amyloid production. First, they block APP trafficking at the cell membrane, thus decreasing beta-amyloid production. In parallel, they reduce Dab1 levels, which also alter APP processing. Lastly, neuronal cultures from Dab1-deficient mice showed severe impairment of APP processing with reduced sAPP secretion and A beta production after prion peptide incubation. Taken together, these data indicate a link between intracellular events induced by exposure to extracellular fibrillar peptide or PrP(res), and APP processing and implicate Dab1 in this link.