C-terminal fragment of amyloid precursor protein induces astrocytosis

Glycogen Synthase Kinase 3 (GSK3): Its Role and Inhibitors

Glycogen Synthase Kinase 3 (GSK3) is one of the Serine/Threonine protein kinases, which has gained a lot of attention for its role in a variety of pathways. It has two isoforms, GSK3α and GSK3β. However, GSK3β is highly expressed in different areas of the brain and has been implicated in Alzheimer's disease as it is involved in tau phosphorylation. Due to its high specificity concerning substrate recognition, GSK3 has been considered as an important target. In the last decade, several GSK3 inhibitors have been reported and two molecules are in clinical trials. This review collates the information published in the last decade about the role of GSK3 in Alzheimer's disease and progress in the development of its inhibitors. Using this collated information, medicinal chemists can strategize and design novel GSK3 inhibitors that could be useful in the treatment of Alzheimer's disease.

Serum amyloid A1 is involved in amyloid plaque aggregation and memory decline in amyloid beta abundant condition

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by cognitive impairment, progressive neurodegeneration, and amyloid-β (Aβ) lesion. In the neuronal death and disease progression, inflammation is known to play an important role. Our previous study on acute-phase protein serum amyloid A1 (SAA1) overexpressed mice showed that the liver-derived SAA1 accumulated in the brain by crossing the brain blood barrier (BBB) and trigger the depressive-like behavior on mouse. Since SAA1 involved in immune responses in other diseases, we focused on the possibility that SAA1 may exacerbate the neuronal inflammation related to Alzheimer's disease. A APP/SAA overexpressed double transgenic mouse was generated using amyloid precursor protein overexpressed (APP)-c105 mice and SAA1 overexpressed mice to examine the function of SAA1 in Aβ abundant condition. Comparisons between APP and APP/SAA1 transgenic mice showed that SAA1 exacerbated amyloid aggregation and glial activation; which lead to the memory decline. Behavior tests also supported this result. Overall, overexpression of SAA1 intensified the neuronal inflammation in amyloid abundant condition and causes the greater memory decline compared to APP mice, which only expresses Aβ 1-42.

Lysosomal dysfunction in the brain of a mouse model with intraneuronal accumulation of carboxyl terminal fragments of the amyloid precursor protein

Recent data suggest that intraneuronal accumulation of metabolites of the amyloid-β-precursor protein (APP) is neurotoxic. We observed that transgenic mice overexpressing in neurons a human APP gene harboring the APP^E693Q (Dutch) mutation have intraneuronal lysosomal accumulation of APP carboxylterminal fragments (APP-CTFs) and oligomeric amyloid β (oAβ) but no histological evidence of amyloid deposition. Morphometric quantification using the lysosomal marker protein 2 (LAMP-2) immunolabeling showed higher neuronal lysosomal counts in brain of 12-months-old APP^E693Q as compared with age-matched non-transgenic littermates, and western blots showed increased lysosomal proteins including LAMP-2, cathepsin D and LC3. At 24 months of age, these mice also exhibited an accumulation of α-synuclein in the brain, along with increased conversion of LC3-I to LC3-II, an autophagosomal/autolysosomal marker. In addition to lysosomal changes at 12 months of age, these mice developed cholinergic neuronal loss in the basal forebrain, GABAergic neuronal loss in the cortex, hippocampus and basal forebrain and gliosis and microgliosis in the hippocampus. These findings suggest a role for the intraneuronal accumulation of oAβ and APP-CTFs and resultant lysosomal pathology at early stages of Alzheimer's disease-related pathology.

Early hyperactivity in lateral entorhinal cortex is associated with elevated levels of AβPP metabolites in the Tg2576 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder which is the most common cause of dementia in the elderly today. One of the earliest symptoms of AD is olfactory dysfunction. The present study investigated the effects of amyloid β precursor protein (AβPP) metabolites, including amyloid-β (Aβ) and AβPP C-terminal fragments (CTF), on olfactory processing in the lateral entorhinal cortex (LEC) using the Tg2576 mouse model of human AβPP over-expression. The entorhinal cortex is an early target of AD related neuropathology, and the LEC plays an important role in fine odor discrimination and memory. Cohorts of transgenic and age-matched wild-type (WT) mice at 3, 6, and 16months of age (MO) were anesthetized and acute, single-unit electrophysiology was performed in the LEC. Results showed that Tg2576 exhibited early LEC hyperactivity at 3 and 6MO compared to WT mice in both local field potential and single-unit spontaneous activity. However, LEC single-unit odor responses and odor receptive fields showed no detectable difference compared to WT at any age. Finally, the very early emergence of olfactory system hyper-excitability corresponded not to detectable Aβ deposition in the olfactory system, but rather to high levels of intracellular AβPP-CTF and soluble Aβ in the anterior piriform cortex (aPCX), a major afferent input to the LEC, by 3MO. The present results add to the growing evidence of AβPP-related hyper-excitability, and further implicate both soluble Aβ and non-Aβ AβPP metabolites in its early emergence.

p53 in neurodegenerative diseases and brain cancers

More than thirty years elapsed since a protein, not yet called p53 at the time, was detected to bind SV40 during viral infection. Thousands of papers later, p53 evolved as the main tumor suppressor involved in growth arrest and apoptosis. A lot has been done but the protein has not yet revealed all its secrets. Particularly important is the observation that in totally distinct pathologies where apoptosis is either exacerbated or impaired, p53 appears to play a central role. This is exemplified for Alzheimer's and Parkinson's diseases that represent the two main causes of age-related neurodegenerative affections, where cell death enhancement appears as one of the main etiological paradigms. Conversely, in cancers, about half of the cases are linked to mutations in p53 leading to the impairment of p53-dependent apoptosis. The involvement of p53 in these pathologies has driven a huge amount of studies aimed at designing chemical tools or biological approaches to rescue p53 defects or over-activity. Here, we describe the data linking p53 to neurodegenerative diseases and brain cancers, and we document the various strategies to interfere with p53 dysfunctions in these disorders.

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.

Microglia function in Alzheimer's disease

Contrary to early views, we now know that systemic inflammatory/immune responses transmit to the brain. The microglia, the resident "macrophages" of the brain's innate immune system, are most responsive, and increasing evidence suggests that they enter a hyper-reactive state in neurodegenerative conditions and aging. As sustained over-production of microglial pro-inflammatory mediators is neurotoxic, this raises great concern that systemic inflammation (that also escalates with aging) exacerbates or possibly triggers, neurological diseases (Alzheimer's, prion, motoneuron disease). It is known that inflammation has an essential role in the progression of Alzheimer's disease (AD), since amyloid-β (Aβ) is able to activate microglia, initiating an inflammatory response, which could have different consequences for neuronal survival. On one hand, microglia may delay the progression of AD by contributing to the clearance of Aβ, since they phagocyte Aβ and release enzymes responsible for Aβ degradation. Microglia also secrete growth factors and anti-inflammatory cytokines, which are neuroprotective. In addition, microglia removal of damaged cells is a very important step in the restoration of the normal brain environment, as if left such cells can become potent inflammatory stimuli, resulting in yet further tissue damage. On the other hand, as we age microglia become steadily less efficient at these processes, tending to become over-activated in response to stimulation and instigating too potent a reaction, which may cause neuronal damage in its own right. Therefore, it is critical to understand the state of activation of microglia in different AD stages to be able to determine the effect of potential anti-inflammatory therapies. We discuss here recent evidence supporting both the beneficial or detrimental performance of microglia in AD, and the attempt to find molecules/biomarkers for early diagnosis or therapeutic interventions.

Regulation by glycogen synthase kinase-3 of inflammation and T cells in CNS diseases

Elevated markers of neuroinflammation have been found to be associated with many psychiatric and neurodegenerative diseases, such as mood disorders, Alzheimer's disease, and multiple sclerosis (MS). Since neuroinflammation is thought to contribute to the pathophysiology of these diseases and to impair responses to therapeutic interventions and recovery, it is important to identify mechanisms that regulate neuroinflammation and potential targets for controlling neuroinflammation. Recent findings have demonstrated that glycogen synthase kinase-3 (GSK3) is an important regulator of both the innate and adaptive immune systems' contributions to inflammation. Studies of the innate immune system have shown that inhibitors of GSK3 profoundly alter the repertoire of cytokines that are produced both by peripheral and central cells, reducing pro-inflammatory cytokines, and increasing anti-inflammatory cytokines. Furthermore, inhibitors of GSK3 promote tolerance to inflammatory stimuli, reducing inflammatory cytokine production upon repeated exposure. Studies of the adaptive immune system have shown that GSK3 regulates the production of cytokines by T cells and the differentiation of T cells to subtypes, particularly Th17 cells. Regulation of transcription factors by GSK3 appears to play a prominent role in its regulation of immune responses, including of NF-κB, cyclic AMP response element binding protein, and signal transducer and activator of transcription-3. Invivo studies have shown that GSK3 inhibitors ameliorate clinical symptoms of both peripheral and central inflammatory diseases, particularly experimental autoimmune encephalomyelitis, the animal model of MS. Therefore, the development and application of GSK3 inhibitors may provide a new therapeutic strategy to reduce neuroinflammation associated with many central nervous system diseases.

Sphingolipid storage affects autophagic metabolism of the amyloid precursor protein and promotes Abeta generation

Deposition of amyloid β peptides (Aβs) in extracellular amyloid plaques within the human brain is a hallmark of Alzheimer's disease (AD). Aβ derives from proteolytic processing of the amyloid precursor protein (APP) by β- and γ-secretases. The initial cleavage by β-secretase results in shedding of the APP ectodomain and generation of APP C-terminal fragments (APP-CTFs), which can then be further processed within the transmembrane domain by γ-secretase, resulting in release of Aβ. Here, we demonstrate that accumulation of sphingolipids (SLs), as occurs in lysosomal lipid storage disorders (LSDs), decreases the lysosome-dependent degradation of APP-CTFs and stimulates γ-secretase activity. Together, this results in increased generation of both intracellular and secreted Aβ. Notably, primary fibroblasts from patients with different SL storage diseases show strong accumulation of potentially amyloidogenic APP-CTFs. By using biochemical, cell biological, and genetic approaches, we demonstrate that SL accumulation affects autophagic flux and impairs the clearance of APP-CTFs. Thus, accumulation of SLs might not only underlie the pathogenesis of LSDs, but also trigger increased generation of Aβ and contribute to neurodegeneration in sporadic AD.

Neuroinflammatory processes in Alzheimer's disease

Generation of neurotoxic amyloid beta peptides and their deposition along with neurofibrillary tangle formation represent key pathological hallmarks in Alzheimer's disease (AD). Recent evidence suggests that inflammation may be a third important component which, once initiated in response to neurodegeneration or dysfunction, may actively contribute to disease progression and chronicity. Various neuroinflammatory mediators including complement activators and inhibitors, chemokines, cytokines, radical oxygen species and inflammatory enzyme systems are expressed and released by microglia, astrocytes and neurons in the AD brain. Degeneration of aminergic brain stem nuclei including the locus ceruleus and the nucleus basalis of Meynert may facilitate the occurrence of inflammation in their projection areas given the antiinflammatory and neuroprotective action of their key transmitters norepinephrine and acetylcholine. While inflammation has been thought to arise secondary to degeneration, recent experiments demonstrated that inflammatory mediators may stimulate amyloid precursor protein processing by various means and therefore can establish a vicious cycle. Despite the fact that some aspects of inflammation may even be protective for bystander neurons, antiinflammatory treatment strategies should therefore be considered. Non-steroidal anti-inflammatory drugs have been shown to reduce the risk and delay the onset to develop AD. While, the precise molecular mechanism underlying this effect is still unknown, a number of possible mechanisms including cyclooxygenase 2 or gamma-secretase inhibition and activation of the peroxisome proliferator activated receptor gamma may alone or, more likely, in concert account for the epidemiologically observed protection.

Neuroglia in neurodegeneration

Neuroglial cells are fundamental for control of brain homeostasis and they represent the intrinsic brain defence system. All forms in neuropathology therefore inevitably involve glia. The neurodegenerative diseases disrupt connectivity within brain circuits affecting neuronal-neuronal, neuronal-glial and glial-glial contacts. In addition neurodegenerative processes trigger universal and conserved glial reactions represented by astrogliosis and microglial activation. The complex of recently acquired knowledge allows us to regard the neurodegenerative diseases as primarily gliodegenerative processes, in which glial cells determine the progression and outcome of neuropathological process.

Glycogen synthase kinase-3 (GSK3): inflammation, diseases, and therapeutics

Deciphering what governs inflammation and its effects on tissues is vital for understanding many pathologies. The recent discovery that glycogen synthase kinase-3 (GSK3) promotes inflammation reveals a new component of its well-documented actions in several prevalent diseases which involve inflammation, including mood disorders, Alzheimer's disease, diabetes, and cancer. Involvement in such disparate conditions stems from the widespread influences of GSK3 on many cellular functions, with this review focusing on its regulation of inflammatory processes. GSK3 promotes the production of inflammatory molecules and cell migration, which together make GSK3 a powerful regulator of inflammation, while GSK3 inhibition provides protection from inflammatory conditions in animal models. The involvement of GSK3 and inflammation in these diseases are highlighted. Thus, GSK3 may contribute not only to primary pathologies in these diseases, but also to the associated inflammation, suggesting that GSK3 inhibitors may have multiple effects influencing these conditions.

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.

Human brain astrocytes mediate TRAIL-mediated apoptosis after treatment with IFN-gamma

TNF-related apoptosis inducing ligand (TRAIL) expressions were studied in primary human brain astrocytes in response to pro-inflammatory cytokines. When astrocytes were treated with IL-1beta, TNF-alpha or IFN-gamma, TRAIL was induced in cultured fetal astrocytes. In particular, IFN-gamma induced the highest levels of TRAIL in cultured astrocytes. When astrocytes were pre-treated with IFN-gamma, they induced apoptosis in TRAIL-sensitive Peer cells. Our results suggest that IFN-gamma modulates the expression of TRAIL in astrocytes, which may enhance cytotoxic sensitivity of infiltrating immune cells or brain cells other than astrocytes during inflammation of brain.

Contribution of inflammatory processes to Alzheimer's disease: molecular mechanisms

There is compelling evidence that Alzheimer's disease (AD) amyloid-beta (Abeta) deposition is associated with a local inflammatory response, which is initiated by the activation of microglia and the recruitment of astrocytes. These cells secrete a number of cytokines and neurotoxic products that may contribute to neuronal degeneration and cell death. It has been documented that long-term intake of non-steroidal anti-inflammatory drugs (NSAIDs) decrease the risk for developing AD and delay the onset of the disease. The mechanism behind these NSAIDs is still controversial and several hypotheses have been raised, including changes in the amyloid precursor protein (APP) metabolism, in Abeta aggregation and a decrease in inflammatory mediators. Recently, it was proposed that some NSAIDs might activate the peroxisome proliferator-activated receptor-gamma (PPAR-gamma). PPAR-gamma belongs to a family of nuclear receptors that are able to regulate the transcription of pro-inflammatory molecules, such as iNOS. The activation of PPAR-gamma has been recently reported to reduce Abeta levels in cell culture and AD animal models. The implication of PPAR-gamma in the control of Abeta-induced inflammation suggests a new target for AD therapy and emphasize the contribution of neuroinflammatory mechanisms to the pathogenesis of AD.

Chronic stress accelerates learning and memory impairments and increases amyloid deposition in APPV717I-CT100 transgenic mice, an Alzheimer's disease model

Although chronic stress is known to be linked with memory and other neurological disorders, little is known about the relationship between chronic stress and the onset or development of Alzheimer's disease (AD). In this study, we investigated the effects of long-term stress on the onset and severity of cognitive deficits and pathological changes in APPV717I-CT100 mice overexpressing human APP-CT100 containing the London mutation (V717I) after exposure to immobilization stress. We found that chronic immobilization stress accelerated cognitive impairments, as accessed by the Passive avoidance and the Social Transfer of Food Preference (STFP) tests. Moreover, the numbers and densities of vascular and extracellular deposits containing amyloid beta peptide (Abeta) and carboxyl-terminal fragments of amyloid precursor protein (APP-CTFs), which are pathologic markers of AD, were significantly elevated in stressed animals, especially in the hippocampus. Moreover, stressed animals, also showed highly elevated levels of neurodegeneration and tau phosphorylation and increased intraneuronal Abeta and APP-CTFs immunoreactivities in the hippocampus and in the entorhinal and piriform cortex. This study provides the first evidence that chronic stress accelerates the onset and severity of cognitive deficits and that these are highly correlated with pathological changes, which thus indicates that chronic stress may be an important contributor to the onset and development of AD.

Production of nerve growth factor by β-amyloid-stimulated astrocytes induces p75NTR-dependent tau hyperphosphorylation in cultured hippocampal neurons

Reactive astrocytes surround amyloid depositions and degenerating neurons in Alzheimer's disease (AD). It has been previously shown that beta-amyloid peptide induces inflammatory-like responses in astrocytes, leading to neuronal pathology. Reactive astrocytes up-regulate nerve growth factor (NGF), which can modulate neuronal survival by signaling through TrkA or p75 neurotrophin receptor (p75NTR). Here, we analyzed whether soluble Abeta peptide 25-35 (Abeta) stimulated astrocytic NGF expression, modulating the survival of cultured embryonic hippocampal neurons. Hippocampal astrocytes incubated with Abeta up-regulated NGF expression and release to the culture medium. Abeta-stimulated astrocytes increased tau phosphorylation and reduced the survival of cocultured hippocampal neurons. Neuronal death and tau phosphorylation were reproduced by conditioned media from Abeta-stimulated astrocytes and prevented by caspase inhibitors or blocking antibodies to NGF or p75NTR. Moreover, exogenous NGF was sufficient to induce tau hyperphosphorylation and death of hippocampal neurons, a phenomenon that was potentiated by a low steady-state concentration of nitric oxide. Our findings show that Abeta-activated astrocytes potently stimulate NGF secretion, which in turn causes the death of p75-expressing hippocampal neurons, through a mechanism regulated by nitric oxide. These results suggest a potential role for astrocyte-derived NGF in the progression of AD.

Beta-amyloid-induced apoptosis is associated with cyclooxygenase-2 up-regulation via the mitogen-activated protein kinase-NF-kappaB signaling pathway

Inflammatory cell death as well as oxidative stress has been implicated in some neurodegenerative disorders such as Alzheimer's disease (AD). Expression of cyclooxygenase-2 (COX-2) and production of prostaglandins have been frequently elevated in AD. In this study, we have investigated the molecular mechanisms underlying inflammatory cell death induced by beta-amyloid (Abeta), a neurotoxic peptide that accumulates in senile plaques formed in the brains of AD patients. Rat pheochromocytoma (PC12) cells treated with Abeta exhibited increased mRNA and protein expression of COX-2 and production of prostaglandin E(2) (PGE(2)) and underwent apoptotic death as determined by positive in situ terminal end-labeling, decreased mitochondrial membrane potential, increased Bax/Bcl-X(L) ratio, activation of c-Jun N-terminal kinase, and cleavage of poly(ADP-ribose)polymerase. Pretreatment with celecoxib, a selective COX-2 inhibitor, attenuated Abeta-induced cell death, which was aggravated by addition of the COX-2 product PGE(2). Abeta transiently induced activation of redox-sensitive transcription factor NF-kappaB, and pretreatment of PC12 cells with NF-kappaB inhibitors abolished the Abeta-induced COX-2 expression. Pharmacologic inhibition of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38 MAPK) and dominant-negative mutation of both enzymes suppressed not only Abeta-induced NF-kappaB transactivation but also COX-2 expression and PGE(2) production. The above findings suggest that Abeta-induced apoptosis in PC12 cells is associated with COX-2 up-regulation through activation of NF-kappaB, which is mediated by upstream kinases including ERK and p38 MAPK.

Pathophysiological roles of amyloidogenic carboxy-terminal fragments of the beta-amyloid precursor protein in Alzheimer's disease

Several lines of evidence suggest that some of the neurotoxicity in Alzheimer's disease (AD) is attributed to proteolytic fragments of amyloid precursor protein (APP) and beta-amyloid (Abeta) may not be the sole active component involved in the pathogenesis of AD. The potential effects of other cleavage products of APP need to be explored. The CTFs, carboxy-terminal fragments of APP, have been found in AD patients' brain and reported to exhibit much higher neurotoxicity in a variety of preparations than Abeta. Furthermore CTFs are known to impair calcium homeostasis and learning and memory through blocking LTP, triggering a strong inflammatory reaction through MAPKs- and NF-kappaB-dependent astrocytosis and iNOS induction. Recently, it was reported that CTF translocated into the nucleus, binding with Fe65 and CP2, and in turn, affected transcription of genes including glycogen synthase kinase-3beta, which results in the induction of tau-rich neurofibrillary tangles and subsequently cell death. Spatial memory of transgenic (Tg) mice overexpressing CT100 was significantly impaired and CTFs were detected in the neurons as well as in plaques of the Tg mice and double Tg mice carrying CT100 and mutant tau. In this review, we summarize observations indicating that both CTF and Abeta may participate in the neuronal degeneration in the progress of AD by differential mechanisms.

Chlamydia pneumoniae induces Alzheimer-like amyloid plaques in brains of BALB/c mice

Amyloid deposits resembling plaques found in Alzheimer's disease (AD) brains were formed in the brains of non-transgenic BALB/c mice following intranasal infection with Chlamydia pneumoniae. The mice were infected at 3 months of age with C. pneumoniae isolated from an AD brain. Infection was confirmed by light and electron microscopy in olfactory tissues of the mice. C. pneumoniae was still evident in these tissues 3 months after the initial infection indicating that a persistent infection had been established. Amyloid beta (Abeta) 1-42 immunoreactive deposits were identified in the brains of infected BALB/c mice up to 3 months post-infection with the density, size, and number of deposits increasing as the infection progressed. A subset of deposits exhibited thioflavin-s labeling. Intracellular Abeta1-42 labeling was observed in neuronal cells. Experimental induction of amyloid deposition in brains of non-transgenic BALB/c mice following infection with C. pneumoniae may be a useful model for furthering our understanding of mechanisms, linked to infection, involved in the initiation of the pathogenesis of sporadic AD.

No alterations of hippocampal neuronal number and synaptic bouton number in a transgenic mouse model expressing the beta-cleaved C-terminal APP fragment

Previous studies in the literature have resulted in conflicting reports on the potential neurotoxicity of the beta-cleaved Alzheimer's disease C-terminal fragment (beta-CTF) of beta-amyloid precursor protein in vivo. To readdress this question by rigorous quantitative methods, we analyzed transgenic mice expressing human beta-CTF with the I45F mutation (SPA4CT) under control of the prion protein promoter by stereological techniques. The transgene was expressed in hippocampus and cortex in large pyramidal neurons and in dentate gyrus granule cells. Proteolytic processing of beta-CTF released Abeta. However, most of it remained uncleaved. Neurodegeneration was evaluated by investigating the numbers of hippocampal pyramidal and granule neurons, as well as the number of synaptophysin-immunopositive presynaptic boutons in the hippocampus of 15-month-old SPA4CT mice with design-based stereological techniques. The analyses showed that a fourfold higher expression of the transgene compared to murine APP levels had no effect on the numbers of both neurons and synaptophysin-immunopositive presynaptic boutons. These data implicate that expression of beta-CTF per se is not neurotoxic, and that other mechanisms are responsible for the neurotoxic events in Alzheimer's disease brain.

Novel cognitive improving and neuroprotective activities of Polygala tenuifolia Willdenow extract, BT-11

We carried out this study to search a new active constituent that had cognitive enhancing activity and low side effects from natural source. We found that the extract of dried root of Polygala tenuifolia Willdenow (BT-11, 10 mg/kg, i.p.) could significantly reverse scopolamine-induced cognitive impairments in rat, using a passive avoidance and a water maze test. We also investigated the effects of BT-11 on neurotoxicity induced by glutamate (Glu) and toxic metabolites of amyloid precursor protein (APP) such as amyloid beta protein (A beta) and C-terminal fragment of APP (CT) in primary cultured neurons of rat. The pretreatment of BT-11 (0.5, 3, and 5 micro g/ml) significantly reduced cell death induced by Glu (1 mM), A beta (10 micro M) and CT105 (10 micro M) in a dose-dependent manner. In addition, BT-11 inhibited acetylcholinesterase (AChE) activity in a dose-dependent and non-competitive manner (IC(50) value; 263.7 micro g/ml). Our novel findings suggest the possibility that this extract may have some protective effects against neuronal death and cognitive impairments in Alzheimer's disease (AD), or other neurodegenerative diseases related to excitotoxicity and central cholinergic dysfunction.

Effects of intrahippocampal CT105, a carboxyl terminal fragment of beta-amyloid precursor protein, alone/with inflammatory cytokines on working memory in rats

In this study, we examined the effects of a 105 amino acid carboxyl terminal fragment of beta-amyloid precursor protein (CT105) and inflammatory cytokines on working memory in rats, by using a three-panel runway set-up. CT105 at 10 nmol/side significantly impaired working memory when it was administered bilaterally into the hippocampus. Furthermore, to elucidate the interaction of CT105 with inflammatory cytokines, we co-administered tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in combination with CT105. Concurrent injections of CT105 (1.0 nmol/side) and TNF-alpha (100 ng/side) produced a synergistic deficit of working memory, whereas IL-1beta (100 ng/side) combined with CT105 (1.0 nmol/side) did not affect the working memory performance. These results indicate that the CT105-induced impairment of working memory is strongly aggravated by an increase in the level of the inflammatory cytokine TNF-alpha, which may occur in the brains of patients with Alzheimer's disease.

Carboxyl-terminal peptide of beta-amyloid precursor protein blocks inositol 1,4,5-trisphosphate-sensitive Ca2+ release in Xenopus laevis oocytes

The effects of Alzheimer's disease-related amyloidogenic peptides on inositol 1,4,5-trisphosphate receptor-mediated Ca(2+) mobilization were examined in Xenopus laevis oocytes. Intracellular Ca(2+) was monitored by electrophysiological measurement of the endogenous Ca(2+)-activated Cl(-) current. Application of a hyperpolarizing pulse released intracellular Ca(2+) in oocytes primed by pre-injection of a non-metabolizable inositol 1,4,5-trisphosphate analogue. The carboxyl terminus of the amyloid precursor protein inhibited inositol 1,4,5-trisphosphate receptor-mediated intracellular Ca(2+) release in a dose-dependent manner. Equimolar beta-amyloid peptides Abeta(1-40) or Abeta(1-42) had no effect, and whereas a truncated carboxyl terminus lacking the Abeta domain was equipotent to the full-length one, a carboxyl terminus fragment lacking the NPTY sequence was less effective than the full-length fragment. The inhibition induced by the carboxyl terminus was not associated with the block of the Ca(2+)-dependent Cl(-) channel itself or compromised Ca(2+) influx. We conclude that the carboxyl terminus of the amyloid precursor protein inhibits inositol 1,4,5-trisphosphate-sensitive Ca(2+) release and could thus disrupt Ca(2+) homeostasis and that the carboxyl terminus is much more effective than the beta-amyloid fragments used. By perturbing the coupling of inositol 1,4,5-trisphosphate and Ca(2+) release, the carboxyl terminus of the amyloid precursor protein can potentially be involved in inducing the neural toxicity characteristic of Alzheimer's disease.