Nerve growth factor modulates the expression and secretion of beta-amyloid precursor protein through different mechanisms in PC12 cells

Association between pseudoexfoliation and Alzheimer's disease-related brain atrophy

BACKGROUND/AIMS

Pseudoexfoliation (PEX) syndrome is an age-related disorder characterized by the accumulation of extracellular material in the anterior eye segment. PEX pathogenesis is not fully understood, but amyloid which accumulates in the brain of patients with Alzheimer's disease (AD) is a PEX component. PEX deposition shares features with amyloid aggregation in AD, and brain atrophy is a common AD feature, with β-amyloid accumulation among contributing factors. This study investigated whether PEX syndrome is associated with AD-related brain atrophy.

METHODS

We reviewed the medical records of patients diagnosed with PEX at the Veterans Health Service Medical Center between January 2015 and August 2021. This retrospective cohort study included 48 patients with PEX and 48 healthy age- and sex-matched controls. Patients with PEX were divided into two groups: with and without glaucoma. The main outcome measure was brain atrophy, using a visual rating scale, and AD incidence. Brain atrophy was measured using the Scheltens scale for medial temporal atrophy, the posterior cortical atrophy scale for parietal atrophy, and the Pasquier scale for global cortical atrophy.

RESULTS

The percentage of participants with medial temporal atrophy was 56.3% in the PEX group and 35.4% in the control group. The global cortical atrophy and parietal atrophy scores were significantly higher in the PEX group (P<0.05), whereas the PEX and PEX glaucoma groups showed no difference. Among the 96 participants, 16 and 5 participants in the PEX and control groups, respectively, were diagnosed with dementia. Patients with PEX glaucoma tended to have lower Mini-Mental State Examination scores, indicating impaired cognitive function, than those without glaucoma.

CONCLUSION

PEX is associated with brain atrophy, reflecting the risk of developing AD. Patients with PEX glaucoma may present with advanced AD stages. Our results suggest that PEX may be a predictor of AD.

Network pharmacology identify intersection genes of quercetin and Alzheimer’s disease as potential therapeutic targets

Background

Currently, there are no efficient therapies for Alzheimer’s disease (AD) among the elderly, although it is the most common etiology of dementia among the elderly. Quercetin, which has a variety of therapeutic properties, may pave the way for novel approaches to AD treatment. In the AD patients’ frontal cortex, current study aims to identify the potential mechanisms of quercetin’s pharmacological targets.

Materials and methods

The pharmacological targets of quercetin have been studied from DrugBank and SwissTarget. In order to distinguish AD-associated genes targeted by quercetin (Q-ADGs), we utilized an integrated intersection of gene expressions of the frontal cortex in combination with transcriptome analysis. To detect cortex-related Q-ADGs and immune-related Q-ADGs, a drug screening database and the immune infiltration analysis was utilized. The Q-ADGs were then linked with the AD severity scores (MMSE scores) to find severity-associated Q-ADGs. In addition, the miRNA-seq datasets were examined to identify severity-associated Q-ADG-miRNAs. Twelve genes, more frequently related to AD by previous studies among all the genes identified in the present study, were subjected to the verification of qRT-PCR in AD cell model.

Results

In the frontal lobe of AD, 207 Q-ADGs were discovered and found that axonogenesis, glial differentiation, and other biological processes had been enriched. There were 155 immune-related Q-ADGs (e.g., COX2, NOS2, HMGB1) and 65 cortex-related Q-ADGs (e.g., FOXO1, CXCL16, NOTCH3). Sixteen Q-ADGs (e.g., STAT3, RORA, BCL6) and 28 miRNAs (e.g., miR-142-5p, miR-17-5p) were found to be related to MMSE scores. In the qRT-PCR results, six out of twelve genes were significantly regulated by quercetin. DYRK1A, FOXO1, NOS2, NGF, NQO1, and RORA genes were novel target of quercetin in AD. DYRK1A, NOS2, and NQO1 genes targeted by quercetin have benefits in the treatment of AD. However, FOXO1, NGF, and RORA genes targeted by quercetin might have a negative impact on AD.

Conclusion

The role of quercetin in AD appears to be multifaceted, and it can affect patients’ frontal cortex in a variety of pathways, such as axonogenesis, immune infiltration, and glial cell differentiation. DYRK1A, NOS2, and NQO1 might be potential novel effective drug targets for quercetin in AD.

New insights into the role of fibroblast growth factors in Alzheimer's disease

Alzheimer's disease (AD), acknowledged as the most common progressive neurodegenerative disorder, is the leading cause of dementia in the elderly. The characteristic pathologic hallmarks of AD-including the deposition of extracellular senile plaques (SP) formation, intracellular neurofibrillary tangles, and synaptic loss, along with prominent vascular dysfunction and cognitive impairment-have been observed in patients. Fibroblast growth factors (FGFs), originally characterized as angiogenic factors, are a large family of signaling molecules that are implicated in a wide range of biological functions in brain development, maintenance and repair, as well as in the pathogenesis of brain-related disorders including AD. Many studies have focused on the implication of FGFs in AD pathophysiology. In this review, we will provide a summary of recent findings regarding the role of FGFs and their receptors in the pathogenesis of AD, and discuss the possible opportunities for targeting these molecules as novel treatment strategies in AD.

Systemic administration of fibroblast growth factor-2 (FGF2) reduces BACE1 expression and amyloid pathology in APP23 mice

There is an emerging evidence that growth factors may have a potential beneficial use in the treatment of Alzheimer's disease (AD) because of their neuroprotective properties and effects on neuronal proliferation. Basic fibroblast growth factor or fibroblast growth factor-2 (FGF2) is an anti-inflammatory, angiogenic, and neurotrophic factor that is expressed in many cell types, including neurons and glial cells. Here, we explored whether subcutaneous administration of FGF2 could have therapeutic effects in the APP 23 transgenic mouse, a model of amyloid pathology. FGF2 treatment attenuated spatial memory deficits, reduced amyloid-β (Aβ) and tau pathologies, decreased inducible nitric oxide synthase expression, and increased the number of astrocytes in the dentate gyrus in APP 23 mice compared with the vehicle-treated controls. The decrease in Aβ deposition was associated with a reduction in the expression of BACE1, the main enzyme responsible for Aβ generation. These results were confirmed in a neuroblastoma cell line, which demonstrated that incubation with FGF2 regulates BACE1 transcription. In addition, and in contrast with what has been previously published, the levels of FGF2 were reduced in postmortem brains from AD patients compared with controls. These data, therefore, suggest that systemic administration of FGF2 could have a potential therapeutic application in AD.

Insights into the physiological function of the β-amyloid precursor protein: beyond Alzheimer's disease

The β-amyloid precursor protein (APP) has been extensively studied for its role as the precursor of the β-amyloid protein (Aβ) of Alzheimer's disease. However, the normal function of APP remains largely unknown. This article reviews studies on the structure, expression and post-translational processing of APP, as well as studies on the effects of APP in vitro and in vivo. We conclude that the published data provide strong evidence that APP has a trophic function. APP is likely to be involved in neural stem cell development, neuronal survival, neurite outgrowth and neurorepair. However, the mechanisms by which APP exerts its actions remain to be elucidated. The available evidence suggests that APP interacts both intracellularly and extracellularly to regulate various signal transduction mechanisms.

This article reviews studies on the structure, expression and post-translational processing of β-amyloid precursor protein (APP), as well as studies on the effects of APP in vitro and in vivo. We conclude that the published data provide strong evidence that APP has a trophic function. APP is likely to be involved in neural stem cell development, neuronal survival, neurite outgrowth and neurorepair. However, the mechanisms by which APP exerts its actions remain to be elucidated. The available evidence suggests that APP interacts both intracellularly and extracellularly to regulate various signal transduction mechanisms.

Is there any relation between pseudoexfoliation syndrome and Alzheimer's type dementia?

PURPOSE

To investigate the frequency of Alzheimer-related dementia in patients with pseudoexfoliation syndrome (PEX).

METHODS

Sixty-seven patients with PEX and 67 age-, gender-, and educational-background-matched control subjects were compared for the presence of Alzheimer-related dementia according to DSM- IV-TR. The effects of cataract, glaucoma, additional ocular and systemic disease on the dementia incidence were also evaluated in patients with PEX and the control group.

RESULTS

The frequency of Alzheimer-related dementia was higher in patients with PEX (p = 0.0001). The frequency of dementia in patients who had cataract was higher than in patients without cataract (p = 0.003). There was also an association between additional ocular disease and dementia (p < 0.05). However, there was no association between systemic disease and dementia (p > 0.05). Furthermore, there was no difference for the frequency of dementia between patients who had glaucoma or not among patients with PEX (p = 0.953).

CONCLUSION

The increased frequency of Alzheimer-related dementia in patients with PEX is important and a possible association between PEX and Alzheimer's disease could be present.

Ras signal triggers β-amyloid precursor protein (APP) expression

It has recently been discovered that the Drosophila β-amyloid protein precursor like (Appl) gene, the ortholog of the human β-Amyloid Precursor Protein (APP) gene, is transcriptionally activated by receptor tyrosine kinase activity that involves Ras/MAPK signaling in vivo. This regulation is specifically controlled in photoreceptor neurons of the Drosophila retina. This suggests that some cases of Alzheimer disease, those which have been associated with high expression of the APP gene, may involve Ras signal transduction.

β amyloid protein precursor-like (Appl) is a Ras1/MAPK-regulated gene required for axonal targeting in Drosophila photoreceptor neurons

In a genome-wide expression profile search for genes required for Drosophila R7 photoreceptor development we found β amyloid protein precursor-like (Appl), the ortholog of human APP, which is a key factor in the pathogenesis of Alzheimer's disease. We analyzed Appl expression in the eye imaginal disc and found that is highly accumulated in R7 photoreceptor cells. The R7 photoreceptor is responsible for UV light detection. To explore the link between high expression of Appl and R7 function, we have analyzed Appl null mutants and found reduced preference for UV light, probably because of mistargeted R7 axons. Moreover, axon mistargeting and inappropriate light discrimination are enhanced in combination with neurotactin mutants. R7 differentiation is triggered by the inductive interaction between R8 and R7 precursors, which results in a burst of Ras1/MAPK, activated by the tyrosine kinase receptor Sevenless. Therefore, we examined whether Ras1/MAPK is responsible for the high Appl expression. Inhibition of Ras1 signaling leads to reduced Appl expression, whereas constitutive activation drives ectopic Appl expression. We show that Appl is directly regulated by the Ras/MAPK pathway through a mechanism mediated by PntP2, an ETS transcription factor that specifically binds ETS sites in the Appl regulatory region. We also found that zebrafish appb expression increased after ectopic fgfr activation in the neural tube of zebrafish embryos, suggesting a conserved regulatory mechanism.

Effects of nerve growth factor and nitric oxide synthase inhibitors on amyloid precursor protein mRNA levels and protein stability

We determined previously that nitric oxide (NO) modulates the nerve growth factor (NGF)-mediated increases in amyloid precursor protein (APP) levels in PC12 cells. To elucidate potential mechanisms, the effects of NGF and NO synthase (NOS) inhibitors on APP mRNA levels and protein stability were evaluated. Surprisingly, treatment of PC12 cells with NGF resulted in decreased levels of APP695 and APP751/770 mRNA. Therefore, the effect of NGF on APP protein stability was examined using the translation inhibitor, cycloheximide. Under these conditions, NGF did not alter the rate of APP degradation, suggesting that NGF may be enhancing the translation rate of APP. Since NOS inhibitors attenuate the NGF-mediated increase in APP levels, their effect on APP mRNA levels and protein stability was also assessed. S-methylisothiourea (S-MIU), selective for inducible NOS, decreased both APP695 and APP751/770 mRNA levels while the non-selective NOS inhibitor, N(ω)-nitro-L-arginine methylester (L-NAME) had no effect. In both control and NGF-treated PC12 cells, S-MIU increased the half-life of APP, with the greatest effect observed with the APP695 isoform. Based on these data we propose that in PC12 cells, NGF increases APP levels through enhanced translation rate and that NO, which modulates the NGF-induced increase in APP protein, also regulates APP mRNA levels and could play a role in APP processing.

Increased secreted amyloid precursor protein-α (sAPPα) in severe autism: proposal of a specific, anabolic pathway and putative biomarker

Autism is a neurodevelopmental disorder characterized by deficits in verbal communication, social interactions, and the presence of repetitive, stereotyped and compulsive behaviors. Excessive early brain growth is found commonly in some patients and may contribute to disease phenotype. Reports of increased levels of brain-derived neurotrophic factor (BDNF) and other neurotrophic-like factors in autistic neonates suggest that enhanced anabolic activity in CNS mediates this overgrowth effect. We have shown previously that in a subset of patients with severe autism and aggression, plasma levels of the secreted amyloid-β (Aβ) precursor protein-alpha form (sAPPα) were significantly elevated relative to controls and patients with mild-to-moderate autism. Here we further tested the hypothesis that levels of sAPPα and sAPPβ (proteolytic cleavage products of APP by α- and β-secretase, respectively) are deranged in autism and may contribute to an anabolic environment leading to brain overgrowth. We measured plasma levels of sAPPα, sAPPβ, Aβ peptides and BDNF by corresponding ELISA in a well characterized set of subjects. We included for analysis 18 control, 6 mild-to-moderate, and 15 severely autistic patient plasma samples. We have observed that sAPPα levels are increased and BDNF levels decreased in the plasma of patients with severe autism as compared to controls. Further, we show that Aβ1-40, Aβ1-42, and sAPPβ levels are significantly decreased in the plasma of patients with severe autism. These findings do not extend to patients with mild-to-moderate autism, providing a biochemical correlate of phenotypic severity. Taken together, this study provides evidence that sAPPα levels are generally elevated in severe autism and suggests that these patients may have aberrant non-amyloidogenic processing of APP.

Nerve growth factor as a paradigm of neurotrophins related to Alzheimer's disease

Converging lines of evidence on the possible connection between NGF signaling and Alzheimer's diseases (AD) are unraveling new facets which could depict this neurotrophin (NTF) in a more central role. AD animal models have provided evidence that a shortage of NGF supply may induce an AD-like syndrome. In vitro experiments, moreover, are delineating a possible temporal and causal link between APP amiloydogenic processing and altered post-translational tau modifications. After NGF signaling interruption, the pivotal upstream players of the amyloid cascade (APP, beta-secretase, and active form of gamma-secretase) are up-regulated, leading to an increased production of amyloid beta peptide (Abeta) and to its intracellular aggregation in molecular species of different sizes. Contextually, the Abeta released pool generates an autocrine toxic loop in the same healthy neurons. At the same time tau protein undergoes anomalous, GSKbeta-mediated, phosphorylation at specific pathogenetic sites (Ser262 and Thr 231), caspase(s) and calpain- I- mediated truncation, detachment from microtubules with consequent cytoskeleton collapse and axonal transport impairment. All these events are inhibited when the amyloidogenic processing is reduced by beta and gamma secretase inhibitors or anti-Abeta antibodies and appear to be causally correlated to TrkA, p75CTF, Abeta, and PS1 molecular association in an Abeta-mediated fashion. In this scenario, the so-called trophic action exerted by NGF (and possibly also by other neurotrophins) in these targets neurons is actually the result of an anti-amyloidogenic activity.

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.

Synaptic degeneration in Alzheimer's disease

Synaptic loss is the major neurobiological substrate of cognitive dysfunction in Alzheimer's disease (AD). Synaptic failure is an early event in the pathogenesis that is clearly detectable already in patients with mild cognitive impairment (MCI), a prodromal state of AD. It progresses during the course of AD and in most early stages involves mechanisms of compensation before reaching a stage of decompensated function. This dynamic process from an initially reversible functionally responsive stage of down-regulation of synaptic function to stages irreversibly associated with degeneration might be related to a disturbance of structural brain self-organization and involves morpho-regulatory molecules such as the amyloid precursor protein. Further, recent evidence suggests a role for diffusible oligomers of amyloid beta in synaptic dysfunction. To form synaptic connections and to continuously re-shape them in a process of ongoing structural adaptation, neurons must permanently withdraw from the cell cycle. Previously, we formulated the hypothesis that differentiated neurons after having withdrawn from the cell cycle are able to use molecular mechanisms primarily developed to control proliferation alternatively to control synaptic plasticity. The existence of these alternative effector pathways within neurons might put them at risk of erroneously converting signals derived from plastic synaptic changes into the program of cell cycle activation, which subsequently leads to cell death. The molecular mechanisms involved in cell cycle activation might, thus, link aberrant synaptic changes to cell death.

Neurotrophic factors in Alzheimer's disease: role of axonal transport

Neurotrophic factors (NTF) are small, versatile proteins that maintain survival and function to specific neuronal populations. In general, the axonal transport of NTF is important as not all of them are synthesized at the site of its action. Nerve growth factor (NGF), for instance, is produced in the neocortex and the hippocampus and then retrogradely transported to the cholinergic neurons of the basal forebrain. Neurodegenerative dementias like Alzheimer’s disease (AD) are linked to deficits in axonal transport. Furthermore, they are also associated with imbalanced distribution and dysregulation of NTF. In particular, brain-derived neurotrophic factor (BDNF) plays a crucial role in cognition, learning and memory formation by modulating synaptic plasticity and is, therefore, a critical molecule in dementia and neurodegenerative diseases. Here, we review the changes of NTF expression and distribution (NGF, BDNF, neurotrophin-3, neurotrophin-4/5 and fibroblast growth factor-2) and their receptors [tropomyosin-related kinase (Trk)A, TrkB, TrkC and p75^NTR] in AD and AD models. In addition, we focus on the interaction with neuropathological hallmarks Tau/neurofibrillary tangle and amyloid-β (Abeta)/amyloid plaque pathology and their influence on axonal transport processes in order to unify AD-specific cholinergic degeneration and Tau and Abeta misfolding through NTF pathophysiology.

Upregulation of amyloid precursor protein by platelet-derived growth factor in hippocampal precursor cells

Amyloid precursor protein generates the secreted amyloid precursor protein alpha, which protects hippocampal neurons from ischemic injury and facilitates neuronal survival and synaptogenesis in the developing nervous system. Here, we examined whether platelet-derived growth factor regulates the generation of secreted amyloid precursor protein alpha during the neuronal differentiation of hippocampal precursor cells, HiB5. We showed that platelet-derived growth factor promoted amyloid precursor protein production and secreted amyloid precursor protein alpha secretion. These effects of platelet-derived growth factor were diminished by the PI3K-specific inhibitor wortmannin and the protein kinase C-specific inhibitor GF109203X, suggesting the involvement of the PI3K and protein kinase C-signaling pathway. Furthermore, the conditioned media enriched with secreted amyloid precursor protein alpha promoted the survival of HiB5 cells during neuronal differentiation. These results suggest that the neurotrophic effect of platelet-derived growth factor is mediated in part via upregulation of the expression and release of secreted amyloid precursor protein alpha.

Effect of hydrogen sulphide on beta-amyloid-induced damage in PC12 cells

1. Hydrogen sulphide (H(2)S) is a well-known cytotoxic gas. Recently, H(2)S has been shown to protect neurons against oxidative stress caused by glutamate, peroxynitrite and HOCl. Considerably lower H(2)S levels have been reported in the brain of Alzheimer's disease (AD) patients with accumulation of beta-amyloid (A beta). 2. The aim of present study was to explore the cytoprotection by H(2)S against A beta(25-35)-induced apoptosis and the molecular mechanisms underlying this effect in PC12 cells. 3. Our findings indicated that A beta(25-35) significantly reduced cell viability and induced apoptosis of PC12 cells, along with dissipation of the mitochondrial membrane potential (MMP) and overproduction of reactive oxygen species (ROS). 4. Sodium hydrosulphide (NaHS), an H(2)S donor, protected PC12 cells against A beta(25-35)-induced cytotoxicity and apoptosis not only by reducing the loss of MMP, but also by attenuating the increase in intracellular ROS. 5. The results of the present study suggest that the cytoprotection by H(2)S is related to the preservation of MMP and attenuation of A beta(25-35)-induced intracellular ROS generation. These findings could significantly advance therapeutic approaches to the neurodegenerative diseases that are associated with oxidative stress, such as AD.

Involvement of M1-muscarinic acetylcholine receptors, protein kinase C and mitogen-activated protein kinase in the effect of huperzine A on secretory amyloid precursor protein-α

This study is to explore the involvement of muscarinic acetylcholine receptors/protein kinase C cascade and the mitogen-activated protein kinase pathway in the effect of huperzine A on the secretory amyloid precursor protein-alpha. Upregulation of secretory amyloid precursor protein-alpha by huperzine A was attenuated by muscarinic acetylcholine receptor antagonist (specifically by M1-muscarinic acetylcholine receptor antagonist), and markedly blocked (-37.7%) by protein kinase C inhibitor as well. Meanwhile, huperzine A can activate the phosphorylation of mitogen-activated protein kinase and, accordingly, partly restored PD98059-decreased secretory amyloid precursor protein-alpha secretion. In addition, huperzine A largely inhibited (-55.4%) acetylcholinesterase activity of the cell line. Our results suggest that activated M1-muscarinic acetylcholine receptor/protein kinase C pathway and mitogen-activated protein kinase signaling are involved in the process of huperzine A enhancing the secretory amyloid precursor protein-alpha secretion.

Nitric oxide synthase inhibitors modulate nerve growth factor-mediated regulation of amyloid precursor protein expression in PC12 cells

Nerve growth factor (NGF) can regulate nitric oxide synthase (NOS) expression and nitric oxide (NO) can modulate NGF-mediated neurotrophic responses. In this study, the role of NO in NGF-stimulated amyloid precursor protein (APP) levels was studied. PC12 cells were treated with either the non-selective NOS inhibitor N(omega)-nitro-L-arginine methylester (L-NAME) or the inducible NOS selective inhibitor s-methylisothiourea (S-MIU), and the effect on NGF-mediated increases in APP expression was determined. NGF significantly increased total APP protein levels following 96 h of treatment and this increase was prevented in cells pre-treated with S-MIU. Pre-treatment of cells with actinomycin D also blocked this NGF-mediated induction of APP, indicating de novo protein synthesis is necessary. Treatment with NGF increased APP promoter activity; however, this increase was only partially inhibited by pre-treatment with S-MIU and was increased in the presence of L-NAME. This suggests that NO may be modulating other aspects of APP expression in addition to transcription. Inhibition of NGF signaling pathways was also investigated using inhibitors of mitogen-activated protein (MAP) kinase (U0126), Akt (LY294002) and protein kinase C (PKC; U73122 and bisindolylmaleimide 1 (BIS-1)) activation. Inhibition of each of these pathways prevented NGF-mediated increases in APP protein expression; however, only BIS-1 attenuated NGF-mediated increases in promoter activation. This study indicates that NO is involved in the NGF-mediated regulation of APP, in part at the level of APP transcription and could involve the modulation of NGF signal transduction pathways.

Receptor tyrosine kinases positively regulate BACE activity and Amyloid-β production through enhancing BACE internalization

Amyloid-beta (Abeta) peptide, the primary constituent of senile plaques in Alzheimer's disease (AD), is generated by beta-secretase- and gamma-secretase-mediated sequential proteolysis of the amyloid precursor protein (APP). The aspartic protease, beta -site APP cleavage enzyme (BACE), has been identified as the main beta-secretase in brain but the regulation of its activity is largely unclear. Here, we demonstrate that both BACE activity and subsequent Abeta production are enhanced after stimulation of receptor tyrosine kinases (RTKs), such as the receptors for epidermal growth factor (EGF) and nerve growth factor (NGF), in cultured cells as well as in mouse hippocampus. Furthermore, stimulation of RTKs also induces BACE internalization into endosomes and Golgi apparatus. This enhancement of BACE activity and Abeta production upon RTK activation could be specifically inhibited by Src family kinase inhibitors and by depletion of endogenous c-Src with RNAi, and could be mimicked by over-expressed c-Src. Moreover, blockage of BACE internalization by a dominant negative form of Rab5 also abolished the enhancement of BACE activity and Abeta production, indicating the requirement of BACE internalization for the enhanced activity. Taken together, our study presents evidence that BACE activity and Abeta production are under the regulation of RTKs and this is achieved via RTK-stimulated BACE internalization, and suggests that an aberration of such regulation might contribute to pathogenic Abeta production.

Promoter polymorphisms which modulate APP expression may increase susceptibility to Alzheimer's disease

Increasing evidence indicates that variants in promoter of the beta-amyloid precursor protein (APP) gene could up-regulate the APP gene expression and aggravate the amyloid beta protein (A beta) accumulation, thus contributing to the development of Alzheimer's disease (AD). In Chinese Han populations we found three polymorphisms in APP promoter: -877T/C(rs466433), -955A/G(rs364048) and -9G/C. The -877T and -955A alleles were over-represented in 209 sporadic AD (SAD) patients when compared to those in 437 healthy individuals. Furthermore, -877T/C and -955A/G were in strong linkage disequilibrium and they constructed a relatively risky -877T/-955A and a relatively protective -877C/-955G. Luciferase reporter assay indicated -877T/-955A had four times higher transcriptional activity than -877C/-955G. A more marked increase in -877T/-955A transcriptional activity was seen when under A beta(25-35) treatment. As for the -9G/C polymorphism, significant differences between the two alleles were not observed either in genetic evaluation or in functional assay. The present study provides strong evidence that APP promoter polymorphisms that significantly increase APP expression levels are associated with development of SAD.

The significance of the cholinergic system in the brain during aging and in Alzheimer's disease

Acetylcholine is widely distributed in the nervous system and has been implicated to play a critical role in cerebral cortical development, cortical activity, controlling cerebral blood flow and sleep-wake cycle as well as in modulating cognitive performances and learning and memory processes. Cholinergic neurons of the basal forebrain complex have been described to undergo moderate degenerative changes during aging, resulting in cholinergic hypofunction that has been related to the progressing memory deficits with aging. Basal forebrain cholinergic cell loss is also a consistent feature of Alzheimer's disease, which has been suggested to cause, at least partly, the cognitive deficits observed, and has led to the formulation of the cholinergic hypotheses of geriatric memory dysfunction. Impaired cortical cholinergic neurotransmission may also contribute to beta-amyloid plaque pathology and increase phosphorylation of tau protein the main component of neurofibrillar tangles in Alzheimer's disease. Understanding the molecular mechanisms underlying the interrelationship between cortical cholinergic dysfunction, beta-amyloid formation and deposition, and tau pathology in Alzheimer's disease, would allow to derive potential treatment strategies to pharmacologically intervene in the disease-causing signaling cascade.

Basal forebrain cholinergic dysfunction in Alzheimer's disease--interrelationship with beta-amyloid, inflammation and neurotrophin signaling

Alzheimer's disease, the most common neurodegenerative disorder of senile dementia, is characterized by two major morpho-pathological hallmarks. Deposition of extracellular neuritic, beta-amyloid peptide-containing plaques (senile plaques) in cerebral cortical regions of Alzheimer patients is accompanied by the presence of intracellular neurofibrillary tangles in cerebral pyramidal neurons. Basal forebrain cholinergic dysfunction is also a consistent feature of Alzheimer's disease, which has been suggested to cause, at least partly, the cognitive deficits observed in patients with Alzheimer's disease. Impaired cortical cholinergic neurotransmission may also contribute to beta-amyloid plaque pathology in Alzheimer's disease by affecting expression and processing of the beta-amyloid precursor protein (APP). Vice versa, low level of soluble beta-amyloid has been observed to inhibit cholinergic synaptic function. Deposition of beta-amyloid plaques in Alzheimer's disease is also accompanied by a significant plaque-associated glial up-regulation of interleukin-1, which has been attributed to affect expression and metabolism of APP and to interfere with cholinergic transmission. Understanding the molecular mechanisms underlying the interrelationship between cortical cholinergic dysfunction, beta-amyloid formation and deposition, as well as local inflammatory upregulation, would allow to derive potential treatment strategies to pharmacologically intervene in the disease-causing signaling cascade.

Increased expression of amyloid precursor protein in oral squamous cell carcinoma

In our previous study, we identified amyloid precursor protein (APP) in an oral squamous cell carcinoma (OSCC)-enriching subtractive hybridization library. Our present study attempts to define the significance of APP expression in the genesis of OSCC. RT-PCR analysis showed increase in APP mRNA expression for more than 2-fold in 76% of OSCC (n = 55) relative to corresponding non-cancerous matched tissues (NCMT). The majority of esophageal SCCs also had increase in APP mRNA expression. OSCC patients exhibiting increase in APP mRNA expression had significantly lower survival rate compared to patients exhibiting the opposite status. Western blotting analysis identified APP751 and APP770 as the major APP isoforms in oral keratinocytes. A high correlation between mRNA and protein expressions of APP was noted in OSCC/NCMT pairs. Immunohistochemistry further showed a remarkable increase of APP in OSCC tissue relative to NCMT. Treatment with an antisense oligonucleotide against APP reduced cellular and secreted APP as well as growth in an OSCC cell line. Our study provides novel clues that APP expression is involved in the proliferation and carcinogenesis of OSCC. Correlated with such pathogenesis was the survival of its victims. The degree of APP expression could serve as an invaluable marker for oral carcinogenesis.

Induction of tyrosine kinase receptor b by retinoic acid allows brain-derived neurotrophic factor-induced amyloid precursor protein gene expression in human SH-SY5Y neuroblastoma cells

Retinoic acid (RA) is a potent regulator of morphogenesis, growth and cell differentiation. Incubation with RA causes arrest of proliferation and neurite extension in SH-SY5Y cells, a neuroblastoma cell line of human origin. In these cells, RA regulates the expression of the beta-amyloid precursor protein. The retinoid increases the levels of intracellular and secreted forms of APP (amyloid precursor protein), APP-mRNA levels and the activity of the APP promoter in transient transfection studies. These responses require long periods of exposition to the ligand, thus suggesting a nondirect effect of the RA receptors on the APP gene. Also in these cells, RA induces the expression of TrkB, the tyrosine kinase receptor for brain-derived neurotrophic factor (BDNF), and 4 days of pretreatment with retinoic acid confers BDNF responsiveness to the APP promoter.

Causative and susceptibility genes for Alzheimer's disease: a review

Alzheimer's disease (AD) is the most common type of dementia in the elderly population. Three genes have been identified as responsible for the rare early-onset familial form of the disease: the amyloid precursor protein (APP) gene, the presenilin 1 (PSEN1) gene and the presenilin 2 (PSEN2) gene. Mutations in these genes, however, account for less than 5% of the total number of AD cases. The remaining 95% of AD patients are mostly sporadic late-onset cases, with a complex aetiology due to interactions between environmental conditions and genetic features of the individual. In this paper, we review the most important genes supposed to be involved in the pathogenesis of AD, known as susceptibility genes, in an attempt to provide a comprehensive picture of what is known about the genetic mechanisms underlying the onset and progression of AD. Hypotheses about the role of each gene in the pathogenic pathway are discussed, taking into account the functions and molecular features, if known, of the coded protein. A major susceptibility gene, the apolipoprotein E (APOE) gene, found to be associated with sporadic late-onset AD cases and the only one, whose role in AD has been confirmed in numerous studies, will be included in a specific chapter. As the results reported by association studies are conflicting, we conclude that a better understanding of the complex aetiology that underlies AD may be achieved likely through a multidisciplinary approach that combines clinical and neurophysiological characterization of AD subtypes and in vivo functional brain imaging studies with molecular investigations of genetic components.

Alzheimer's peptide and serine proteinase inhibitors in glaucoma and exfoliation syndrome

The occurrence of inflammation with accompanying amyloid formation in pseudoexfoliation syndrome (PEX) resembles other inflammation-associated amyloidoses such as Alzheimer's disease (AD). To test whether the same proteins can be identified in PEX as in AD, we qualitatively analysed for Alzheimer's peptide (Abeta1-42) and the proteinase inhibitors alpha1-antichymotrypsin (ACT) and alpha-antitrypsin (AAT) in the aqueous humor of patients with and without PEX material. Ninety aqueous humor samples were collected from patients in the age group between 46 and 95 during cataract surgery. Protein profiles in samples were analysed by electrophoresis followed by Western blotting. Blots were developed using specific antibodies against Abeta1-42, AAT and ACT and peroxidase-conjugated IgG as a second antibody. At least one of the analysed proteins was found in 68.8% of 90 cases studied. Abeta1-42 peptide was found in 22.2% of all cases, among them in seven cases with PEX (total n =16) and in four with glaucoma (total n = 10). ACT and AAT were detected in 17.8 and 28.9% of all cases, respectively. In addition, female patients had significantly higher frequencies of detected ACT and AAT, compared to males. Abeta1-42, ACT and AAT were also found in 17.6, 14.7 and 23.5% of the control (non-XF and non-glaucoma) samples (n = 68). Alzheimer's peptide is present in the aqueous humor of patients with PEX and glaucoma suggesting that these diseases may share common features in the biochemistry and etiologies with AD. The presence of Abeta and inflammation-associated proteins in aqueous from cataract cases without detectable PEX raises the possibility that these proteins may reflect early amyloid-related changes in the eye.

Brain-derived neurotrophic factor stimulates beta-amyloid gene promoter activity by a Ras-dependent/AP-1-independent mechanism in SH-SY5Y neuroblastoma cells

The beta-amyloid peptide, the major component of Alzheimer-associated plaques, derives from a larger beta-amyloid precursor protein (APP), that is expressed in both neural and non-neural cells. Overexpression of APP actively contributes to the development of senile plaques and is considered a risk factor for the disease. APP expression is regulated by a variety of cellular mediators, among them ligands of tyrosine kinase receptors. In this study, we present evidence that brain-derived neurotrophic factor (BDNF) modulates, in a dose- and time-dependent fashion, APP promoter activity in SH-SY5Y neuroblastoma cells transiently expressing the receptor TrkB. The APP promoter contains two potential AP-1 sites, and we examined whether or not protein kinase C (PKC) and the AP-1 sites of the promoter mediate the BDNF-induced stimulation of APP. Stimulation of APP promoter activity by BDNF was not affected by the PKC inhibitor bisindolylmaleimide, or by dominant negative mutants of the AP-1 components Fos and Jun, which, however, blocked the response to phorbol esters. These results suggest that activation of the APP promoter by BDNF is largely independent of PKC and AP-1. In contrast, activated Ras increased APP promoter activity in SH-SY5Y cells, and a dominant negative mutant of Ras abolished BDNF-mediated promoter stimulation. Taken together, our results suggest a mechanism that involves activation of the Ras/MAP kinase signaling pathway, and phosphorylation of as yet unidentified effectors which in turn can activate response elements within the APP promoter.