Staurosporine-induced activation of caspase-3 is potentiated by presenilin 1 familial Alzheimer's disease mutations in human neuroglioma cells

Protective effects of curcumin and Ginkgo biloba extract combination on a new model of Alzheimer's disease

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative illnesses, and yet, no workable treatments have been discovered to prevent or reverse AD. Curcumin (CUR), the major polyphenolic compound of turmeric (Curcuma longa) rhizomes, and Ginkgo biloba extract (GBE) are natural substances derived from conventional Chinese herbs that have long been shown to provide therapeutic advantages for AD. The uptake of curcumin into the brain is severely restricted by its low ability to cross the blood-brain barrier (BBB). Meanwhile, GBE has been shown to improve BBB permeability. The present study evaluated the neuroprotective effects and pharmacokinetic profile of curcumin and GBE combination to find out whether GBE can enhance curcumin's beneficial effects in AD by raising its brain concentration. Results revealed that CUR + GBE achieved significantly higher levels of curcumin in the brain and plasma after 30 min and 1 h of oral administration, compared to curcumin alone, and this was confirmed by reversed phase high-performance liquid chromatography (RP-HPLC). The effect of combined oral treatment, for 28 successive days, on cognitive function and other AD-like alterations was studied in scopolamine-heavy metal mixtures (SCO + HMM) AD model in rats. The combination reversed at least, partially on the learning and memory impairment induced by SCO + HMM. This was associated with a more pronounced inhibitory effect on acetylcholinesterase (AChE), caspase-3, hippocampal amyloid beta (Aβ1-42), and phosphorylated tau protein (p-tau) count, and pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukine-1beta (IL-1β), as compared to the curcumin alone-treated group. Additionally, the combined treatment significantly decreased lipid peroxidation (MDA) and increased levels of reduced glutathione (GSH), when compared with the curcumin alone. These findings support the concept that the combination strategy might be an alternative therapy in the management/prevention of neurological disorders. This study sheds light on a new approach for exploring new phyto-therapies for AD and emphasizes that more research should focus on the synergic effects of herbal drugs in future.

Tomatidine Represses Invasion and Migration of Human Osteosarcoma U2OS and HOS Cells by Suppression of Presenilin 1 and c-Raf-MEK-ERK Pathway

Osteosarcoma, which is the most prevalent malignant bone tumor, is responsible for the great majority of bone cancer-associated deaths because of its highly metastatic potential. Although tomatidine is suggested to serve as a chemosensitizer in multidrug-resistant tumors, the anti-metastatic effect of tomatidine in osteosarcoma is still unknown. Here, we tested the hypothesis that tomatidine suppresses migration and invasion, features that are associated with metastatic process in human osteosarcoma cells and also investigate its underlying pathway. Tomatidine, up to 100 μM, without cytotoxicity, inhibited the invasion and migration capabilities of human osteosarcoma U2OS and HOS cells and repressed presenilin 1 (PS-1) expression of U2OS cells. After the knockdown of PS-1, U2OS and HOS cells’ biological behaviors of cellular invasion and migratory potential were significantly reduced. While tomatidine significantly decreased the phosphorylation of c-Raf, mitogen/extracellular signal-regulated kinase (MEK), and extracellular signal-regulated protein kinase (ERK)1/2 in U2OS cells, no obvious influences on p-Jun N-terminal kinase, p38, and Akt, including their phosphorylation, were observed. In ERK 1 silencing U2 OS cells, tomatidine further enhanced the decrease of their migratory potential and invasive activities. We conclude that both PS-1 derived from U2OS and HOS cells and the c-Raf–MEK–ERK pathway contribute to cellular invasion and migration and tomatidine could inhibit the phenomenons. These findings indicate that tomatidine might be a potential candidate for anti-metastasis treatment of human osteosarcoma.

A Review of the Familial Alzheimer's Disease Locus PRESENILIN 2 and Its Relationship to PRESENILIN 1

PRESENILIN 1 (PSEN1) and PRESENILIN 2 (PSEN2) genes are loci for mutations causing familial Alzheimer's disease (fAD). However, the function of these genes and how they contribute to fAD pathogenesis has not been fully determined. This review provides a summary of the overlapping and independent functions of the PRESENILINS with a focus on the lesser studied PSEN2. As a core component of the γ-secretase complex, the PSEN2 protein is involved in many γ-secretase-related physiological activities, including innate immunity, Notch signaling, autophagy, and mitochondrial function. These physiological activities have all been associated with AD progression, indicating that PSEN2 plays a particular role in AD pathogenesis.

Biological Hallmarks of Cancer in Alzheimer's Disease

Although Alzheimer's disease (AD) is an international health research priority for our aging population, little therapeutic progress has been made. This lack of progress may be partially attributable to disease heterogeneity. Previous studies have identified an inverse association of cancer and AD, suggesting that cancer history may be one source of AD heterogeneity. These findings are particularly interesting in light of the number of common risk factors and two-hit models hypothesized to commonly drive both diseases. We reviewed the ten hallmark biological alterations of cancer cells to investigate overlap with the AD literature and identified overlap of all ten hallmarks in AD, including (1) potentially common underlying risk factors, such as increased inflammation, deregulated cellular energetics, and genome instability; (2) inversely regulated mechanisms, including cell death and evading growth suppressors; and (3) functions with more complex, pleiotropic mechanisms, some of which may be stage-dependent in AD, such as cell adhesion/contact inhibition and angiogenesis. Additionally, we discuss the recent observation of a biological link between cancer and AD neuropathology. Finally, we address the therapeutic implications of this topic. The significant overlap of functional pathways and molecules between these diseases, some similarly and some oppositely regulated or functioning in each disease, supports the need for more research to elucidate cancer-related AD genetic and functional heterogeneity, with the aims of better understanding AD risk mediators, as well as further exploring the potential for some types of drug repurposing towards AD therapeutic development.

Presenilin Mutation Suppresses Lung Tumorigenesis via Inhibition of Peroxiredoxin 6 Activity and Expression

Some epidemiological studies suggest an inverse correlation between cancer incidence and Alzheimer's disease (AD). In this study, we demonstrated experimental evidences for this inverse relationship. In the co-expression network analysis using the microarray data and GEO profile of gene expression omnibus data analysis, we showed that the expression of peroxiredoxin 6 (PRDX6), a tumor promoting protein was significantly increased in human squamous lung cancer, but decreased in mutant presenilin 2 (PS2) containing AD patient. We also found in animal model that mutant PS2 transgenic mice displayed a reduced incidence of spontaneous and carcinogen-induced lung tumor development compared to wildtype transgenic mice. Agreed with network and GEO profile study, we also revealed that significantly reduced expression of PRDX6 and activity of iPLA2 in these animal models. PS2 mutations increased their interaction with PRDX6, thereby increasing iPLA2 cleavage via increased γ-secretase leading to loss of PRDX6 activity. However, knockdown or inhibition of γ-secretase abolished the inhibitory effect of mutant PSs. Moreover, PS2 mutant skin fibroblasts derived from patients with AD showed diminished iPLA2 activity by the elevated γ-secretase activity. Thus, the present data suggest that PS2 mutations suppress lung tumor development by inhibiting the iPLA2 activity of PRDX6 via a γ-secretase cleavage mechanism and may explain the inverse relationship between cancer and AD incidence.

Pro-Resolving Lipid Mediators Improve Neuronal Survival and Increase Aβ42 Phagocytosis

Inflammation in the brain is a prominent feature in Alzheimer's disease (AD). Recent studies suggest that chronic inflammation can be a consequence of failure to resolve the inflammation. Resolution of inflammation is mediated by a family of lipid mediators (LMs), and the levels of these specialized pro-resolving mediators (SPMs) are reduced in the hippocampus of those with AD. In the present study, we combined analysis of LMs in the entorhinal cortex (ENT) from AD patients with in vitro analysis of their direct effects on neurons and microglia. We probed ENT, an area affected early in AD pathogenesis, by liquid chromatography-tandem mass spectrometry (LC-MS-MS), and found that the levels of the SPMs maresin 1 (MaR1), protectin D1 (PD1), and resolvin (Rv) D5, were lower in ENT of AD patients as compared to age-matched controls, while levels of the pro-inflammatory prostaglandin D2 (PGD2) were higher in AD. In vitro studies showed that lipoxin A4 (LXA4), MaR1, resolvin D1 (RvD1), and protectin DX (PDX) exerted neuroprotective activity, and that MaR1 and RvD1 down-regulated β-amyloid (Aβ)42-induced inflammation in human microglia. MaR1 exerted a stimulatory effect on microglial uptake of Aβ42. Our findings give further evidence for a disturbance of the resolution pathway in AD, and indicate that stimulating this pathway is a promising treatment strategy for AD.

Chronic treatment with anesthetic propofol improves cognitive function and attenuates caspase activation in both aged and Alzheimer's disease transgenic mice

There is a need to seek new treatment(s) for Alzheimer's disease (AD). A recent study showed that AD patients may have decreased levels of functional GABA receptors. Propofol, a commonly used anesthetic, is a GABA receptor agonist. We therefore set out to perform a proof of concept study to determine whether chronic treatment with propofol (50 mg/kg/week) can improve cognitive function in both aged wild-type (WT) and AD transgenic (Tg) mice. Propofol was administrated to the WT and AD Tg mice once a week for 8 or 12 weeks, respectively. Morris water maze was used to assess the cognitive function of the mice following the propofol treatment. Activation of caspase-3, caspase-9, and caspase-8 was investigated using western blot analysis at the end of the propofol treatment. In the mechanistic studies, effects of propofol, amyloid-β protein (Aβ), and GABA receptor antagonist flumazenil on caspase-3 activation and opening of the mitochondrial permeability transition pore were assessed in H4 human neuroglioma and mouse neuroblastoma cells by western blot analysis and flow cytometry. Here we showed that the propofol treatment improved cognitive function and attenuated brain caspase-3 and caspase-9 activation in both aged WT and AD Tg mice. Propofol attenuated Aβ-induced caspase-3 activation and opening of the mitochondrial permeability transition pore in the cells, and flumazenil inhibited the propofol's effects. These results suggested that propofol might improve cognitive function via attenuating the Aβ-induced mitochondria dysfunction and caspase activation, which explored the potential that anesthetic propofol could improve cognitive function in elderly and AD patients.

Exploiting the cytoskeletal filaments of neoplastic cells to potentiate a novel therapeutic approach

Although cytoskeletal-directed agents have been a mainstay in chemotherapeutic protocols due to their ability to readily interfere with the rapid mitotic progression of neoplastic cells, they are all microtubule-based drugs, and there has yet to be any microfilament- or intermediate filament-directed agents approved for clinical use. There are many inherent differences between the cytoskeletal networks of malignant and normal cells, providing an ideal target to attain preferential damage. Further, numerous microfilament-directed agents, and an intermediate filament-directed agent of particular interest (withaferin A) have demonstrated in vitro and in vivo efficacy, suggesting that cytoskeletal filaments may be exploited to supplement chemotherapeutic approaches currently used in the clinical setting. Therefore, this review is intended to expose academics and clinicians to the tremendous variety of cytoskeletal filament-directed agents that are currently available for further chemotherapeutic evaluation. The mechanisms by which microfilament directed- and intermediate filament-directed agents damage malignant cells are discussed in detail in order to establish how the drugs can be used in combination with each other, or with currently approved chemotherapeutic agents to generate a substantial synergistic attack, potentially establishing a new paradigm of chemotherapeutic agents.

Loss of presenilin 2 is associated with increased iPLA2 activity and lung tumor development

Presenilins are the enzymatic components of γ-secretase complex that cleaves amyloid precursor protein, Notch and β-catenin, which has critical roles in the development of Alzheimer's disease and cancer cell growth. Therefore, in the present study, we studied the effects and mechanisms of PS2 knockout on lung cancer development and possible mechanisms as a key regulator of lung tumor development. We compared carcinogen-induced tumor growth between PS2 knockout mice and wild-type mice. PS2 knockout mice showed increased urethane (1 mg/g)-induced lung tumor incidence when compared with that of wild-type mice with decreased activity of γ-secretase in the lung tumor tissues. Consequently, iPLA2 activities in lung tumor tissues of PS2 knockout mice were much higher than in tumor tissues of wild-type mice. Furthermore, knockdown of PS2 using PS2 siRNA decreased γ-secretase activity with increased iPLA2 activity in the lung cancer cells (A549 and NCI-H460), leading to increased lung cancer cell growth. PS2 knockout mice and PS2 knockdown lung cancer cells showed increased DNA-binding activities of nuclear factor kappa-beta, signal transducer and activator of transcription 3 (STAT3) and AP-1 which are critical transcriptional factors of iPLA2 than those of PS2 wild-type mice and control lung cancer cells. Taken together, these results suggest that the loss of PS2 could have a critical role in lung tumor development through the upregulation of iPLA2 activity by reducing γ-secretase.

UV-C Exposure Induces an Apoptosis-Like Process in Euglena gracilis

Euglena gracilis is a unicellular, free-living flagellate that inhabits various freshwater environments. Our research shows that exposure to UV-C light can trigger some form of programmed cell death. Cells exposed to UV-C light underwent delayed changes that were strongly reminiscent of apoptosis in mammalian cells, including cell shrinkage and DNA fragmentation that produced the characteristic ladder pattern commonly seen with apoptosis. DNA fragmentation could be inhibited by pretreatment with Z-VAD-FMK and also independently induced by exposure to staurosporine. In addition, Euglena possess proteins that cross-reacted with antibodies raised against human caspases 3 and 9. Given that Euglena are extremely easy to culture and represent a lineage positioned near the base of the eukaryotic tree, they will be an excellent model system for comparative analyses with apoptotic-like death processes in other eukaryotic microbes.

Propofol and magnesium attenuate isoflurane-induced caspase-3 activation via inhibiting mitochondrial permeability transition pore

Background

The inhalation anesthetic isoflurane has been shown to open the mitochondrial permeability transition pore (mPTP) and induce caspase activation and apoptosis, which may lead to learning and memory impairment. Cyclosporine A, a blocker of mPTP opening might attenuate the isoflurane-induced mPTP opening, lessening its ripple effects. Magnesium and anesthetic propofol are also mPTP blockers. We therefore set out to determine whether propofol and magnesium can attenuate the isoflurane-induced caspase activation and mPTP opening.

Methods

We investigated the effects of magnesium sulfate (Mg²⁺), propofol, and isoflurane on the opening of mPTP and caspase activation in H4 human neuroglioma cells stably transfected to express full-length human amyloid precursor protein (APP) (H4 APP cells) and in six day-old wild-type mice, employing Western blot analysis and flowcytometry.

Results

Here we show that Mg²⁺ and propofol attenuated the isoflurane-induced caspase-3 activation in H4-APP cells and mouse brain tissue. Moreover, Mg²⁺ and propofol, the blockers of mPTP opening, mitigated the isoflurane-induced mPTP opening in the H4-APP cells.

Conclusion

These data illustrate that Mg²⁺ and propofol may ameliorate the isoflurane-induced neurotoxicity by inhibiting its mitochondrial dysfunction. Pending further studies, these findings may suggest the use of Mg²⁺ and propofol in preventing and treating anesthesia neurotoxicity.

Anesthetic propofol attenuates the isoflurane-induced caspase-3 activation and Aβ oligomerization

Accumulation and deposition of β-amyloid protein (Aβ) are the hallmark features of Alzheimer's disease. The inhalation anesthetic isoflurane has been shown to induce caspase activation and increase Aβ accumulation. In addition, recent studies suggest that isoflurane may directly promote the formation of cytotoxic soluble Aβ oligomers, which are thought to be the key pathological species in AD. In contrast, propofol, the most commonly used intravenous anesthetic, has been reported to have neuroprotective effects. We therefore set out to compare the effects of isoflurane and propofol alone and in combination on caspase-3 activation and Aβ oligomerization in vitro and in vivo. Naïve and stably-transfected H4 human neuroglioma cells that express human amyloid precursor protein, the precursor for Aβ; neonatal mice; and conditioned cell culture media containing secreted human Aβ40 or Aβ42 were treated with isoflurane and/or propofol. Here we show for the first time that propofol can attenuate isoflurane-induced caspase-3 activation in cultured cells and in the brain tissues of neonatal mice. Furthermore, propofol-mediated caspase inhibition occurred when there were elevated levels of Aβ. Finally, isoflurane alone induces Aβ42, but not Aβ40, oligomerization, and propofol can inhibit the isoflurane-mediated oligomerization of Aβ42. These data suggest that propofol may mitigate the caspase-3 activation by attenuating the isoflurane-induced Aβ42 oligomerization. Our findings provide novel insights into the possible mechanisms of isoflurane-induced neurotoxicity that may aid in the development of strategies to minimize potential adverse effects associated with the administration of anesthetics to patients.

RNA interference-mediated silencing of BACE and APP attenuates the isoflurane-induced caspase activation

Background

β-Amyloid protein (Aβ) has been shown to potentiate the caspase-3 activation induced by the commonly used inhalation anesthetic isoflurane. However, it is unknown whether reduction in Aβ levels can attenuate the isoflurane-induced caspase-3 activation. We therefore set out to determine the effects of RNA interference-mediated silencing of amyloid precursor protein (APP) and β-site APP-cleaving enzyme (BACE) on the levels of Aβ and the isoflurane-induced caspase-3 activation.

Methods

H4 human neuroglioma cells stably transfected to express full-length human APP (H4-APP cells) were treated with small interference RNAs (siRNAs) targeted at silencing BACE and APP for 48 hours. The cells were then treated with 2% isoflurane for six hours. The levels of BACE, APP, and caspase-3 were determined using Western blot analysis. Sandwich Enzyme-linked immunosorbent assay (ELISA) was used to determine the extracellular Aβ levels in the conditioned cell culture media.

Results

Here we show for the first time that treatment with BACE and APP siRNAs can decrease levels of BACE, full-length APP, and APP c-terminal fragments. Moreover, the treatment attenuates the Aβ levels and the isoflurane-induced caspase-3 activation. These results further suggest a potential role of Aβ in the isoflurane-induced caspase-3 activation such that the reduction in Aβ levels attenuates the isoflurane-induced caspase-3 activation.

Conclusion

These findings will lead to more studies which aim at illustrating the underlying mechanism by which isoflurane and other anesthetics may affect Alzheimer's disease neuropathogenesis.

Familial Alzheimer's disease mutations in presenilin 1 do not alter levels of the secreted amyloid-beta protein precursor generated by beta-secretase cleavage

Alzheimer's disease (AD) is an insidious and progressive disease with a genetically complex and heterogenous etiology. More than 200 fully penetrant mutations in the amyloid beta-protein precursor (APP), presenilin 1 (or PSEN1), and presenilin 2 (PSEN2) have been linked to early-onset familial AD (FAD). 177 PSEN1 FAD mutations have been identified so far and account for more than approximately 80% of all FAD mutations. All PSEN1 FAD mutations can increase the Abeta42:Abeta40 ratio with seemingly different and incompletely understood mechanisms. A recent study has shown that the 286 amino acid N-terminal fragment of APP (N-APP), a proteolytic product of beta-secretase-derived secreted form of APP (sAPPbeta), could bind the death receptor, DR6, and lead to neurodegeneration. Here we asked whether PSEN1 FAD mutations lead to neurodegeneration by modulating sAPPbeta levels. All four different PSEN1 FAD mutations tested (in three mammalian cell lines) did not alter sAPPbeta levels. Therefore PS1 mutations do not appear to contribute to AD pathogenesis via altered production of sAPPbeta.

Nitrous oxide plus isoflurane induces apoptosis and increases beta-amyloid protein levels

BACKGROUND

Some anesthetics have been suggested to induce neurotoxicity, including promotion of Alzheimer's disease neuropathogenesis. Nitrous oxide and isoflurane are common anesthetics. The authors set out to assess the effects of nitrous oxide and/or isoflurane on apoptosis and beta-amyloid (Abeta) levels in H4 human neuroglioma cells and primary neurons from naïve mice.

METHODS

The cells or neurons were exposed to 70% nitrous oxide and/or 1% isoflurane for 6 h. The cells or neurons and conditioned media were harvested at the end of the treatment. Caspase-3 activation, apoptosis, processing of amyloid precursor protein, and Abeta levels were determined.

RESULTS

Treatment with a combination of 70% nitrous oxide and 1% isoflurane for 6 h induced caspase-3 activation and apoptosis in H4 naïve cells and primary neurons from naïve mice. The 70% nitrous oxide plus 1% isoflurane, but neither alone, for 6 h induced caspase-3 activation and apoptosis, and increased levels of beta-site amyloid precursor protein-cleaving enzyme and Abeta in H4-amyloid precursor protein cells. In addition, the nitrous oxide plus isoflurane-induced Abeta generation was reduced by a broad caspase inhibitor, Z-VAD. Finally, the nitrous oxide plus isoflurane-induced caspase-3 activation was attenuated by gamma-secretase inhibitor L-685,458, but potentiated by exogenously added Abeta.

CONCLUSION

These results suggest that the common anesthetics nitrous oxide plus isoflurane may promote neurotoxicity by inducing apoptosis and increasing Abeta levels. The generated Abeta may further potentiate apoptosis to form another round of apoptosis and Abeta generation. More studies, especially the in vivo confirmation of these in vitro findings, are needed.

The common inhalational anesthetic sevoflurane induces apoptosis and increases beta-amyloid protein levels

OBJECTIVE

To assess the effects of sevoflurane, the most commonly used inhalation anesthetic, on apoptosis and beta-amyloid protein (Abeta) levels in vitro and in vivo. Subjects Naive mice, H4 human neuroglioma cells, and H4 human neuroglioma cells stably transfected to express full-length amyloid precursor protein.

INTERVENTIONS

Human H4 neuroglioma cells stably transfected to express full-length amyloid precursor protein were exposed to 4.1% sevoflurane for 6 hours. Mice received 2.5% sevoflurane for 2 hours. Caspase-3 activation, apoptosis, and Abeta levels were assessed.

RESULTS

Sevoflurane induced apoptosis and elevated levels of beta-site amyloid precursor protein-cleaving enzyme and Abeta in vitro and in vivo. The caspase inhibitor Z-VAD decreased the effects of sevoflurane on apoptosis and Abeta. Sevoflurane-induced caspase-3 activation was attenuated by the gamma-secretase inhibitor L-685,458 and was potentiated by Abeta. These results suggest that sevoflurane induces caspase activation which, in turn, enhances beta-site amyloid precursor protein-cleaving enzyme and Abeta levels. Increased Abeta levels then induce further rounds of apoptosis.

CONCLUSIONS

These results suggest that inhalational anesthetic sevoflurane may promote Alzheimer disease neuropathogenesis. If confirmed in human subjects, it may be prudent to caution against the use of sevoflurane as an anesthetic, especially in those suspected of possessing excessive levels of cerebral Abeta.

Presenilin 1 forms aggresomal deposits in response to heat shock

Aggresomes have been described as cytoplasmic membrane protein aggregates that are induced by proteasome inhibition or overexpression of certain proteins. Here, we characterized aggresomes formed by the Alzheimer's disease-associated presenilin 1 (PS1) protein. Proteasome inhibition induced accumulation of PS1 in the endoplasmic reticulum (ER) and retrotranslocation of the protein from the ER membrane into the cytoplasm. Aggresomes formed by PS1 modified the ER structure whereas proteasomes were inhibited. Therefore, clear visual identification of PS1 aggresomes required removal of the proteasome inhibitor followed by hours of recovery to redistribute the ER throughout the cells. Aggresomes formed by PS1 did not potentiate or attenuate apoptotic cell death induced by staurosporine treatment. Selective presence of the heat-shock proteins Hsp70 and HDJ-2/HSDJ, but not Hsp90, in aggresomes suggested chaperone-mediated transport of PS1 into these structures. Because proteasome inhibition and heat shock are both known to induce expression of heat shock proteins, we also demonstrated that heat shock alone was sufficient to induce PS1 aggresome formation and Hsp70 expression. These results indicate that aggresome formation by PS1 is chaperone-mediated and can be induced in response to heat-shock stress, a common cellular event in neurodegenerative diseases. Malfunctioning of the proteasome or heat-shock stress response in the brains of patients affected by Alzheimer's disease may lead to the accumulation of stable aggresomes of PS1, perhaps contributing to neurodegeneration.

Alterations in presenilin 1 processing by amyloid-beta peptide in the rat retina

Accumulating evidence indicates that mutations in the presenilin 1 (PS1) gene are responsible for most cases of familial Alzheimer's disease (AD). Although its biological functions are not yet fully understood, it appears that PS1 plays a role in the processing and trafficking of the amyloid precursor protein (APP). However, little is known about factors that are involved in regulating the metabolism of PS1 especially in relation to AD pathology. In this study, we have examined the effect of optic nerve crush, intravitreal injection of the inflammatory agent lipopolysaccharide (LPS) or injection of amyloid beta(1-42) (A beta(1-42)) on the expression and processing of PS1 in the rat retina. We found that 48 h after injection of A beta(1-42) there was a dramatic alteration in the banding pattern of PS1 on Western blots, as indicated by marked changes in the levels of expression of some of its C- and N-terminal fragments in retinal homogenates. These results suggest an A beta(1-42)-induced potentiation of a non-specific stress-related but inflammation-independent alteration of processing of PS1 in this in vivo model.

Hypocapnia induces caspase-3 activation and increases Abeta production

BACKGROUND

At least half of all cases of early onset (<60) familial Alzheimer's disease (FAD) are caused by any of over 150 mutations in three genes: the amyloid precursor protein (APP), presenilin 1 (PS1), and presenilin 2 (PS2). Mutant forms of PS1 have been shown to sensitize cells to apoptotic cell death.

OBJECTIVE

We investigated the effects of hypocapnia, a risk factor for both cognitive and neurodevelopment deficits, on caspase-3 activation, apoptosis, and amyloid beta-protein (Abeta) production, and assessed the influence of the PS1Delta9 FAD mutation on these effects.

METHOD

For this purpose, we exposed stably transfected H4 human neuroglioma cells to conditions consistent with hypocapnia (PCO2<40 mm Hg) and hypocapnia plus hypoxia (PO2<21%).

RESULTS

Hypocapnia (20 mm Hg CO2 for 6 h) induced caspase-3 activation and apoptosis; the PS1Delta9 FAD mutation significantly potentiated these effects. Moreover, the combination of hypocapnia (20 mm Hg CO2) and hypoxia (5%O2) induced caspase-3 activation and apoptosis in a synergistic manner. Hypocapnia (5 and 20 mm Hg CO2 for 6 h) also led to an increased Abeta production.

CONCLUSION

The findings suggest that hypocapnia (e.g. during general anesthesia) could exacerbate AD neuropathogenesis.

Alzheimer's disease and post-operative cognitive dysfunction

Alzheimer's disease (AD), an insidious and progressive neurodegenerative disorder accounting for the vast majority of dementia, is characterized by global cognitive decline and the robust accumulation of amyloid deposits and neurofibrillary tangles in the brain. This review article is based on the currently published literature regarding molecular studies of AD and the potential involvement of AD neuropathogenesis in post-operative cognitive dysfunction (POCD). Genetic evidence, confirmed by neuropathological and biochemical studies, indicates that excessive beta-amyloid protein (Abeta) generated from amyloidogenic processing of the beta-amyloid precursor protein (APP) plays a fundamental role in the AD neuropathogenesis. Abeta is produced from APP by beta-secretase, and then gamma-secretase complex, consisting of presenilins, nicastrin (NCSTN), APH-1 and PEN-2. Additionally, Abeta clearance and APP adaptor proteins can contribute to AD neuropathogenesis via affecting Abeta levels. Finally, cellular apoptosis may also be involved in AD neuropathogenesis. Surgery and anesthesia can cause cognitive disorders, especially in elderly patients. Even the molecular mechanisms underlying these disorders are largely unknown; several perioperative factors such as hypoxia, hypocapnia and anesthetics may be associated with AD and render POCD via trigging AD neuropathogenesis. More studies to assess the potential relationship between anesthesia/surgery and AD dementia are, therefore, urgently needed.

Zebrafish lacking Alzheimer presenilin enhancer 2 (Pen-2) demonstrate excessive p53-dependent apoptosis and neuronal loss

Gamma-secretase cleavage, mediated by a complex of presenilin, presenilin enhancer (Pen-2), nicastrin, and Aph-1, is the final proteolytic step in generating amyloid beta protein found in brains of Alzheimer's disease patients and Notch intracellular domain critical for proper neuronal development. Here, we employ the zebrafish model to study the role of Pen-2 in neuronal survival. We found that (i) knockdown of Pen-2 using antisense morpholino led to a reduction of islet-1 positive neurons, (ii) Notch signaling was reduced in embryos lacking Pen-2 or other gamma-secretase components, (iii) neuronal loss in Pen-2 knockdown embryos is not as a result of a lack of neuronal precursor cells or cell proliferation, (iv) absence of Pen-2 caused massive apoptosis in the whole animal, which could be suppressed by simultaneous knockdown of the tumor suppressor p53, (v) loss of islet-1 or acetylated tubulin positive neurons in Pen-2 knockdown embryos could be partially rescued by knockdown of p53. Our results demonstrate that knockdown of Pen-2 directly induces a p53-dependent apoptotic pathway that contributes to neuronal loss and suggest that Pen-2 plays an important role in promoting neuronal cell survival and protecting from apoptosis in vivo.

Effects of RNAi-mediated silencing of PEN-2, APH-1a, and nicastrin on wild-type vs FAD mutant forms of presenilin 1

The gamma-secretase complex consists of PS1/PS2, nicastrin, APH-1a, and PEN-2. PS1 undergoes endoproteolytic processing to yield two fragments: PS1-NTF and PS1-CTF. Changes in PEN-2 levels have been shown previously to affect the endoproteolytic processing of wild-type (wt)-PS1. However, the effects of PEN-2 on the proteolytic processing of familial Alzheimer's disease (FAD) mutant forms of PS1 have not yet been reported. To determine whether PEN-2 affects the proteolytic processing of mutant PS1 in the same manner as that of wt-PS1, we established RNA interference (RNAi) for PEN-2 in H4 human neuroglioma cells stably transfected to express wt or FAD mutant forms of PS1 including L286V, A246E, and that lacking exon 9 (Delta9). As expected, in H4 cells expressing wt-PS1, RNAi for PEN-2 increased levels of PS1-FL and attenuated PS1 endoproteolysis. Likewise, in cells expressing PS1 with the FAD missense mutations, L286V and A246E, RNAi for PEN-2 increased PS1-FL and reduced PS1 endoproteolysis. However, in H4 cells stably transfected to express the FAD-linked Delta9 mutation (PS1 lacking exon 9), RNAi for PEN-2 did not increase but, instead, decreased PS1-FL. In contrast, RNAi for nicastrin and APH-1a decreased PS1-FL in H4 cells expressing either wt-PS1 or Delta9-PS1. In summary, the metabolism of wt-PS1 and FAD-linked Delta9-PS1 is specifically and differentially affected by loss of function of PEN-2.

Interaction of presenilins with FKBP38 promotes apoptosis by reducing mitochondrial Bcl-2

Presenilins 1 and 2 (PS1/2), causative molecules for familial Alzheimer's disease (FAD), are multipass transmembrane proteins localized predominantly in the endoplasmic reticulum (ER) and Golgi apparatus. Heteromeric protein complexes containing PS1/2 are thought to participate in several functions, including intramembrane proteolysis mediated by their gamma-secretase activities. Previous studies have shown that PS1/2 are also involved in the regulation of apoptotic cell death, although the underlying mechanism remains unknown. Here, we demonstrate that FKBP38, an immunophilin family member residing in the mitochondrial membrane, is an authentic PS1/2-interacting protein. PS1/2 and FKBP38 form macromolecular complexes together with anti-apoptotic Bcl-2. PS1/2 promote the degradation of FKBP38 and Bcl-2 and sequester these proteins in the ER/Golgi compartments, thereby inhibiting FKBP38-mediated mitochondrial targeting of Bcl-2 via a gamma-secretase-independent mechanism. Thus, PS1/2 increase the susceptibility to apoptosis by antagonizing the anti-apoptotic function of FKBP38. In contrast, C-terminal fragments of caspase-processed PS1/2 redistribute Bcl-2 to the mitochondria by abrogating the activity of full-length PS1/2, resulting in a dominant-negative anti-apoptotic effect. In cultured cells and mutant PS1-knockin mice brains, FAD-linked PS1/2 mutants enhance the pro-apoptotic activity by causing a more efficient reduction in mitochondrial Bcl-2 than wild-type PS1/2. These results suggest a novel molecular mechanism for the regulation of mitochondria-mediated apoptosis by competition between PS1/2 and FKBP38 for subcellular targeting of Bcl-2. Excessive pro-apoptotic activity of PS1/2 may play a role in the pathogenesis of FAD.

Effects of RNA Interference-mediated Silencing of γ-Secretase Complex Components on Cell Sensitivity to Caspase-3 Activation

Familial Alzheimer's disease mutations in the presenilin 1 gene (PSEN1) have been previously shown to potentiate caspase activation and apoptosis in transfected cells and transgenic mice. However, the mechanism underlying this effect is not known. We set out to determine whether cellular sensitivity to caspase activation could be affected by modulating presenilin 1 (PS1) processing. PS1 processing was altered using RNA interference (RNAi) aimed at silencing the expression of the genes encoding the four components of the gamma-secretase complex, PSEN1, APH-1, PEN-2, and nicastrin. RNAi for these genes was carried out in naive H4 human neuroglioma cells, as well as H4 cell lines overexpressing either wild-type PSEN1 or the Familial Alzheimer's disease mutant PSEN1-Delta9 (PS1-mutant), that were induced to undergo apoptosis. In wild-type PSEN1 cells, RNAi for PEN-2, as expected, increased levels of full-length PS1 (PS1-FL) and decreased PS1 endoproteolysis. This was accompanied by potentiated caspase-3 activation in response to an apoptotic stimulus. In contrast, nicastrin RNAi, which only decreased levels of PS1-amino-terminal fragment and did not affect PS1-FL levels, had no effect on caspase-3 activation during apoptosis. Surprisingly, in the PS1-mutant cells, RNAi for PEN-2 (and APH-1) did not increase but instead reduced the levels of PS1-FL deleted for exon 9. In turn, this was accompanied by attenuated caspase-3 activation in response to an apoptotic stimulus. Finally, in naive H4 cells, PSEN1 RNAi also attenuated caspase-3 activation in response to an apoptotic stimulus. Collectively, these findings indicate that cellular sensitivity to caspase activation correlates with overall PS1 protein levels, particularly with levels of FL-PS1.

γ-Secretase Activity of Presenilin 1 Regulates Acetylcholine Muscarinic Receptor-mediated Signal Transduction

Familial Alzheimer's disease (FAD) presenilin 1 (PS1) mutations give enhanced calcium responses upon different stimuli, attenuated capacitative calcium entry, an increased sensitivity of cells to undergo apoptosis, and increased gamma-secretase activity. We previously showed that the FAD mutation causing an exon 9 deletion in PS1 results in enhanced basal phospholipase C (PLC) activity (Cedazo-Minguez, A., Popescu, B. O., Ankarcrona, M., Nishimura, T., and Cowburn, R. F. (2002) J. Biol. Chem. 277, 36646-36655). To further elucidate the mechanisms by which PS1 interferes with PLC-calcium signaling, we studied the effect of two other FAD PS1 mutants (M146V and L250S) and two dominant negative PS1 mutants (D257A and D385N) on basal and carbachol-stimulated phosphoinositide (PI) hydrolysis and intracellular calcium concentrations ([Ca2+]i) in SH-SY5Y neuroblastoma cells. We found a significant increase in basal PI hydrolysis in PS1 M146V cells but not in PS1 L250S cells. Both PS1 M146V and PS1 L250S cells showed a significant increase in carbachol-induced [Ca2+]i as compared with nontransfected or wild type PS1 transfected cells. The elevated carbachol-induced [Ca2+]i signals were reversed by the PLC inhibitor neomycin, the ryanodine receptor antagonist dantrolene, the general aspartyl protease inhibitor pepstatin A, and the specific gamma-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester. The cells expressing either PS1 D257A or PS1 D385N had attenuated carbachol-stimulated PI hydrolysis and [Ca2+]i responses. In nontransfected or PS1 wild type transfected cells, N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester and pepstatin A also attenuated both carbachol-stimulated PI hydrolysis and [Ca2+]i responses to levels found in PS1 D257A or PS1 D385N dominant negative cells. Our findings suggest that PS1 can regulate PLC activity and that this function is gamma-secretase activity-dependent.

Mitochondrial glutaminase enhances extracellular glutamate production in HIV-1-infected macrophages: linkage to HIV-1 associated dementia

Dysfunction in mononuclear phagocyte (MP, macrophages and microglia) immunity is thought to play a significant role in the pathogenesis of HIV-1 associated dementia (HAD). In particular, elevated extracellular concentrations of the excitatory neurotransmitter glutamate, produced by MP as a consequence of viral infection and immune activation, can induce neuronal injury. To determine the mechanism by which MP-mediated neuronal injury occurs, the concentration and rates of production of extracellular glutamate were measured in human monocyte-derived macrophage (MDM) supernatants by reverse phase high-performance liquid chromatography (RP-HPLC). Measurements were taken of supernatants from MDM infected with multiple HIV-1 strains including ADA and DJV (macrophage tropic, M-tropic), and 89.6 (dual tropic). High levels of glutamate were produced by MDM infected with M-tropic viruses. AZT, an inhibitor of HIV-1 replication, inhibited glutamate generation, demonstrating a linkage between HIV-1 infection and enhanced glutamate production. In our culture system, glutamate production was dependent upon the presence of glutamine and was inhibited by 6-diazo-5-oxo-L-norleucine, a glutaminase inhibitor. Supernatants collected from HIV-1-infected MP generated more glutamate following glutamine addition than supernatants isolated from uninfected MP. These findings implicate the involvement of a glutamate-generating enzyme, such as phosphate-activated mitochondrial glutaminase (PMG) in MP-mediated glutamate production.

Overexpression of wild-type presenilin 2 or its familial Alzheimer's disease-associated mutant does not induce or increase susceptibility to apoptosis in different cell lines

Programmed cell death, or apoptosis, has been implicated in Alzheimer's disease. Mutations in the presenilin (PS) genes, PS1 and PS2, are a major cause of early-onset familial Alzheimer's disease (FAD). Previous studies have suggested that the PS play a role in apoptosis. However, the mechanisms whereby presenilins affect apoptosis and the relationship of FAD-associated presenilin mutants to the apoptotic effect have not been elucidated. In the present study, in an attempt to further explore the effect of PS2 on apoptosis we examined whether overexpression of wild-type or mutant PS2 can directly induce apoptosis or increase cell susceptibility to apoptosis in various cell lines, such as N2a, CHO, and HEK 293T. Wild-type or mutant PS2 was transiently transfected into these cell lines and the viability of the transfected cells was evaluated by their morphology, DNA fragmentation and condensation, appearance of sub-G(1/0) cells, and caspase activation. We also examined the susceptibility of the PS2-transfected cells to apoptosis induced by the apoptotic inducers staurosporine and H(2)O(2). Our results showed that overexpression of either wild type or mutant PS2 in these cell lines did not directly induce apoptosis or increase the susceptibility to apoptosis induced by staurosporine or H(2)O(2). Taken together, these results suggest that overexpression of PS2 does not cause pro-apoptotic effects, at least not in the cellular systems and conditions employed in this study, and therefore it seems unlikely that apoptosis plays a prominent role in the neuropathological effects of PS2 in Alzheimer's disease.

Enhanced long-term potentiation in the hippocampus of rats expressing mutant presenillin-1 is age related

Electrophysiological recordings were made from Fischer rats engineered to express the human presenilin 1 gene carrying the M146V mutation. Extracellular recordings of field excitatory post-synaptic potential (EPSPs) were made to investigate EPSP properties, paired pulse responses, posttetanic potentiation, and long-term potentiation in the stratum radiatum and dentate gyrus of hippocampal slices maintained in vitro. Transgenic rats aged approximately 6 months showed no differences from their wild-type littermates in any of these properties. However, at 18 months, long-term potentiation in the CA1 was facilitated in the transgenic rats with a different pattern of synaptic enhancement. No changes were observed in paired pulse facilitation (PPF) or post-tetanic potentiation (PPT) and no changes were seen in the dentate gyrus. Field potential amplitudes were significantly greater and PPF was enhanced in the CA1 of all older rats. Intracellular recordings from CA1 pyramidal cells of the older group of rats revealed no differences in the passive or active membrane properties of cells in the two groups, but intracellularly recorded EPSPs were significantly longer.

Pro-apoptotic effect of presenilin 2 (PS2) overexpression is associated with down-regulation of Bcl-2 in cultured neurons

Presenilin 2 (PS2) is a polytopic membrane protein that is mutated in some cases of familial Alzheimer's disease (AD). The normal functions of PS2 and its pathogenic role in AD remain unclear. We investigated the biological role of this protein in neurons, using adenovirus-mediated transduction of the PS2 gene into rat primary cortical neurons. Immunocytochemical analyses demonstrated increased PS2 immunoreactivity in most neurons infected with recombinant adenoviruses expressing PS2. Neurons infected with wild-type or mutant (N141I) PS2-expressing adenoviruses showed a significant increase in basal cell death, compared with those infected with control beta-galactosidase-expressing adenovirus. Moreover, PS2 overexpression markedly increased neuronal susceptibility to staurosporine-induced apoptosis. Mutant PS2 was more effective in enhancing apoptosis than its wild-type counterpart. Staurosporine-induced death was significantly inhibited by a specific caspase 3 inhibitor. Western analyses revealed that Bcl-2 protein expression was specifically down-regulated in neurons overexpressing PS2, which temporally corresponded to the accumulation of C- and N-terminal fragments of PS2. Additionally, expression of mutant, but not wild-type PS2, increased the production of beta-amyloid protein (Abeta) 42. These data collectively suggest that the pro-apoptotic effect of PS2 is mediated by down-regulation of Bcl-2. PS2 mutations may increase the susceptibility of neurons to apoptotic stimuli by perturbing the regulation of cell death.

The multifaceted roles of glycogen synthase kinase 3beta in cellular signaling

Glycogen synthase kinase-3beta (GSK3beta) is a fascinating enzyme with an astoundingly diverse number of actions in intracellular signaling systems. GSK3beta activity is regulated by serine (inhibitory) and tyrosine (stimulatory) phosphorylation, by protein complex formation, and by its intracellular localization. GSK3beta phosphorylates and thereby regulates the functions of many metabolic, signaling, and structural proteins. Notable among the signaling proteins regulated by GSK3beta are the many transcription factors, including activator protein-1, cyclic AMP response element binding protein, heat shock factor-1, nuclear factor of activated T cells, Myc, beta-catenin, CCAAT/enhancer binding protein, and NFkappaB. Lithium, the primary therapeutic agent for bipolar mood disorder, is a selective inhibitor of GSK3beta. This raises the possibility that dysregulation of GSK3beta and its inhibition by lithium may contribute to the disorder and its treatment, respectively. GSK3beta has been linked to all of the primary abnormalities associated with Alzheimer's disease. These include interactions between GSK3beta and components of the plaque-producing amyloid system, the participation of GSK3beta in phosphorylating the microtubule-binding protein tau that may contribute to the formation of neurofibrillary tangles, and interactions of GSK3beta with presenilin and other Alzheimer's disease-associated proteins. GSK3beta also regulates cell survival, as it facilitates a variety of apoptotic mechanisms, and lithium provides protection from many insults. Thus, GSK3beta has a central role regulating neuronal plasticity, gene expression, and cell survival, and may be a key component of certain psychiatric and neurodegenerative diseases.

Caspase cleavage of exon 9 deleted presenilin-1 is an early event in apoptosis induced by calcium ionophore A 23187 in SH-SY5Y neuroblastoma cells

Presenilins (PSs) are mutated in a majority of familial Alzheimer disease (FAD) cases. Mutated PSs may cause FAD by a number of pro-apoptotic mechanisms, or by regulating gamma-secretase activity, a protease involved in beta-amyloid precursor protein processing to the neurotoxic beta-amyloid peptide. Besides their normal endoproteolytic processing, PSs are substrates for caspases, being cleaved to alternative N-terminal and C-terminal fragments. So far little is known about the role of PSs cleavage in the apoptotic machinery. Here, we used SH-SY5Y neuroblastoma cells stably transfected with wild-type or exon 9 deleted presenilin 1 (PS1) in a time-course study after the exposure to the calcium ionophore A23187. During and after exposure to A 23187, intracellular calcium levels were higher in exon 9 deleted PS1 cells as compared with non-transfected and wild-type PS1 transfected cells. Cell death and the enrichment of apoptotic cells after A23187 exposure were increased by overexpression of exon 9 deleted PS1 as compared with the control cell lines. Wild-type PS1 cells were compared with exon 9 deleted PS1 cells and the temporal relationship between PS1 and other caspase substrates cleavages was analyzed. Exon 9 deleted PS1 cells exhibited a higher caspase-3 activation and a greater cleavage of PS1 and poly(ADP-ribose) polymerase (PARP) compared with wild-type PS1 cells. Exon 9 deleted PS1 cleavage occurred earlier than other caspase substrate cleavages (i.e., PARP and gelsolin), simultaneous with minimum detectable caspase-3 activation. Therefore, alternative cleavage of PS1 may play an important role for the regulation of the proteolytic cascade activated during apoptosis.

Detection of the presenilin 1 COOH-terminal fragment in the extracellular compartment: a release enhanced by apoptosis

Mutations in gene encoding presenilin 1 (PS1) are responsible for the majority of familial Alzheimer's disease (FAD) cases. We studied PS1 localization in HEK293 cells and in primary neurons obtained from rat cortex and hippocampus. We first demonstrated that PS1-CTF, but neither PS1-FL nor PS1-NTF, is released into the medium as a soluble and membrane-associated form. After induction of apoptosis with staurosporine (Sts), we observed a dramatic increase in the level of PS1-CTF in the medium, both in HEK293 and in primary neurons. Immunocytochemical analysis suggested that the release of PS1-CTF might occur via membrane shedding. Abeta(1-42) treatment reduced PS1-CTF extracellular levels. This decrease was strongly associated to an impaired secretion of sAPP fragments, thus suggesting a role of PS1-CTF in the control of trafficking and generation of APP fragments.

Calsenilin is a substrate for caspase-3 that preferentially interacts with the familial Alzheimer's disease-associated C-terminal fragment of presenilin 2

Calsenilin is a member of the recoverin family of neuronal calcium-binding proteins that we have previously shown to interact with presenilin 1 (PS1) and presenilin 2 (PS2) holoproteins. The expression of calsenilin can regulate the levels of a proteolytic product of PS2 (Buxbaum, J. D., Choi, E. K., Luo, Y., Lilliehook, C., Crowley, A. C., Merriam, D. E., and Wasco, W. (1998) Nat. Med. 4, 1177-1181) and reverse the presenilin-mediated enhancement of calcium signaling (Leissring, M. A., Yamasaki, T. R., Wasco, W., Buxbaum, J. D., Parker, I., and LaFerla, F. M. (2000) Proc. Natl. Acad. Sci. U. S. A. 97, 8590-8593). Here, we have used cultured mammalian cells that transiently or stably express calsenilin to extend the characterization of calsenilin and of the calsenilin-PS2 interaction. We have found that calsenilin has the ability to interact with endogenous 25-kDa C-terminal fragment (CTF) that is a product of regulated endoproteolytic cleavage of PS2 and that the presence of the N141I PS2 mutation does not significantly alter the interaction of calsenilin with PS2. Interestingly, when the 25-kDa PS2 CTF and the 20-kDa PS2 CTF are both present, calsenilin preferentially interacts with the 20-kDa CTF. Increases in the 20-kDa fragment are associated with the presence of familial Alzheimer's disease-associated mutations (Kim, T., Pettingell, W. H., Jung, Y., Kovacs, D. M., and Tanzi, R. E. (1997) Science 277, 373-376). However, the finding that the production of the 20-kDa fragment is regulated by the phosphorylation of PS2 (Walter, J., Schindzielorz, A., Grunberg, J., and Haass, C. (1999) Proc. Natl. Acad. Sci. U. S. A. 96, 1391-1396) suggests that it is a regulated physiological event that also occurs in the absence of the familial Alzheimer's disease-associated mutations in PS2. Finally, we have demonstrated that calsenilin is a substrate for caspase-3, and we have used site-directed mutagenesis to map the caspase-3 cleavage site to a region that is proximal to the calcium binding domain of calsenilin.

Elevated vulnerability to oxidative stress-induced cell death and activation of caspase-3 by the Swedish amyloid precursor protein mutation

The Swedish double mutation (KM670/671NL) of amyloid precursor protein (APPsw) is associated with early-onset familial Alzheimer's disease (FAD) and results in from three- to sixfold increased beta-amyloid production. The goal of the present study was to elucidate the effects of APPsw on mechanisms of apoptotic cell death. Therefore, PC12 cells were stably transfected with human APPsw. Here we report that the vulnerability of APPsw-bearing PC12 cells to undergo apoptotic cell death was significantly enhanced after exposure to hydrogen peroxide compared to human wild-type APP-bearing cells, empty vector-transfected cells, and parent untransfected cells. In addition, we have analyzed the potential influence of several mechanisms that can interfere with the execution of the apoptotic cell death program: the inhibition of cell death by the use of caspase inhibitors and the reduction of oxidative stress by the use of (+/-)-alpha-tocopherol (vitamin E). Interestingly, oxidative stress-induced cell death was significantly attenuated in APPsw PC12 cells by pretreatment with caspase-3 inhibitors but not with caspase-1 inhibitors. In parallel, caspase-3 activity was markedly elevated in APPsw PC12 after stimulation with hydrogen peroxide for 6 hr, whereas caspase-1 activity was unaltered. In addition, oxidative stress-induced cell death could be reduced after pretreatment of APPsw cells with (+/-)-alpha-tocopherol. The protective potency of (+/-)-alpha-tocopherol was even greater than that of caspase-3 inhibitors. Our findings further emphasize the role of mutations in the amyloid precursor protein in apoptotic cell death and may provide the fundamental basis for further efforts to elucidate the underlying processes caused by FAD-related mutations.

GSK3 beta forms a tetrameric complex with endogenous PS1-CTF/NTF and beta-catenin. Effects of the D257/D385A and FAD-linked mutations

We have previously shown that the endogenous C-terminal fragment of presenilin 1 co-immunoprecipitates with endogenous beta-catenin. Since PS1 has been suggested to be involved in beta-catenin stabilization, we further investigated whether GSK3 beta, responsible for beta-catenin phosphorylation and degradation, is part of the PS1/beta-catenin complex. In naïve H4 and CHO cells, PS1 co-immunoprecipitated with both endogenous beta-catenin and GSK3 beta. In addition, GSK3 beta endogenously binds to the PS1-CTF/NTF complex and beta-catenin in naïve CHO cells. GSK3 beta also co-immunoprecipitated with PS1 full length in CHO cell lines overexpressing PS1 wild type. Given that it has been recently shown that PS1 mutations of aspartate 257 or 385 result in prevention of PS1 endoproteolysis and inhibition of gamma-secretase activity, we also tested whether PS1 endoproteolysis is required for beta-catenin/GSK3 beta/PS1 binding and whether PS1 FAD-linked mutations affect GSK3 beta recruitment in the PS1/beta-catenin complex. GSK3 beta was detected in PS1 immunoprecipitates from H4 cell lines overexpressing PS1 wild type, delta E10, A286E, L246V and in CHO cell lines overexpressing aspartate or M146L mutations. The latter data show that the absence of PS1 endoproteolysis (D257A/D385A and delta E10) or the presence of PS1-FAD mutations does not interfere with beta-catenin/GSK3 beta/PS1 complex formation.

Neurons bearing presenilins: weapons for defense or suicide?

Apoptotic machinery designed for cell's organized self-destruction involve different systems of proteases which cleave vital proteins and disassemble nuclear and cytoplasmic structures, committing the cell to death. The most studied apoptotic proteolytic system is the caspase family, but calpains and the proteasome could play important roles as well. Alzheimer's disease associated presenilins showed to be a substrate for such proteolytic systems, being processed early in several apoptotic models, and recent data suggest that alternative presenilin fragments could regulate cell survival. Mutations in genes encoding presenilins proved to sensitize neurons to apoptosis by different mechanisms e.g. increased caspase-3 activation, oxyradicals production and calcium signaling dysregulation. Here we review the data involving presenilins in apoptosis and discuss a possible role of presenilins in the regulation of apoptotic biochemical machinery.

Par-4 induces cholinergic hypoactivity by suppressing ChAT protein synthesis and inhibiting NGF-inducibility of ChAT activity

Profound reductions in choline acetyl-transferase (ChAT) activity are reliable markers for cholinergic hypoactivity associated with cognitive function deficit in Alzheimer's disease (AD). Par-4 (prostate apoptosis response-4) is a novel mediator of neuronal apoptosis associated with the pathogenesis of AD. Par-4 contains a leucine zipper domain (Leu.zip) that presumably mediates protein-protein interactions critical for its functions in apoptosis. Par-4 activity can be effectively blocked by overexpression of Leu. zip because it exerts a dominant negative action possibly by competitively blocking the interaction of Par-4 with other proteins. Whether Par-4 participates in regulation of cholinergic signaling has not been determined. We report that overexpression of Par-4 results in apoptotic and non-apoptotic reductions in ChAT activity in transfected PC12 cells following exposure to a toxic concentration (50 microM) of aggregated amyloid beta peptide 1-42 (Abeta 1-42) and a non-toxic concentration (1 microM) of soluble Abeta 1-42, respectively. Non-apoptotic reduction in ChAT activity induced by Par-4 can be completely blocked by co-overexpression of Leu.zip, indicating that enhanced Par-4 activity is a necessary event for cholinergic hypoactivity in PC12 cells. Further studies found that Par-4 induces non-apoptotic reduction in ChAT activity by: (1) reducing ChAT protein levels following exposure to non-toxic concentration of Abeta, and (2) blocking the cellular capability to increase ChAT activity following exposure to nerve growth factor (NGF). The role of Par-4 in inducing cholinergic hypoactivity may have significant implications in the understanding and the treatment of memory impairment in AD.