Neurotoxic mechanisms by Alzheimer's disease-linked N141I mutant presenilin 2

Presenilin 2 N141I mutation induces hyperactive immune response through the epigenetic repression of REV-ERBα

Hyperimmunity drives the development of Alzheimer disease (AD). The immune system is under the circadian control, and circadian abnormalities aggravate AD progress. Here, we investigate how an AD-linked mutation deregulates expression of circadian genes and induces cognitive decline using the knock-in (KI) mice heterozygous for presenilin 2 N141I mutation. This mutation causes selective overproduction of clock gene-controlled cytokines through the DNA hypermethylation-mediated repression of REV-ERBα in innate immune cells. The KI/+ mice are vulnerable to otherwise innocuous, mild immune challenges. The antipsychotic chlorpromazine restores the REV-ERBα level by normalizing DNA methylation through the inhibition of PI3K/AKT1 pathway, and prevents the overexcitation of innate immune cells and cognitive decline in KI/+ mice. These results highlight a pathogenic link between this AD mutation and immune cell overactivation through the epigenetic suppression of REV-ERBα.

Hyperimmunity is associated with Alzheimer disease. Here the authors show that the Presenilin 2 N141I mutation causes overproduction of clock-controlled cytokines and memory deficits through suppression of REV-ERBα gene by hypermethylation.

Mechanism of oxidative stress in neurodegeneration

Biological tissues require oxygen to meet their energetic demands. However, the consumption of oxygen also results in the generation of free radicals that may have damaging effects on cells. The brain is particularly vulnerable to the effects of reactive oxygen species due to its high demand for oxygen, and its abundance of highly peroxidisable substrates. Oxidative stress is caused by an imbalance in the redox state of the cell, either by overproduction of reactive oxygen species, or by dysfunction of the antioxidant systems. Oxidative stress has been detected in a range of neurodegenerative disease, and emerging evidence from in vitro and in vivo disease models suggests that oxidative stress may play a role in disease pathogenesis. However, the promise of antioxidants as novel therapies for neurodegenerative diseases has not been borne out in clinical studies. In this review, we critically assess the hypothesis that oxidative stress is a crucial player in common neurodegenerative disease and discuss the source of free radicals in such diseases. Furthermore, we examine the issues surrounding the failure to translate this hypothesis into an effective clinical treatment.

Targeting microglia-mediated neurotoxicity: the potential of NOX2 inhibitors

Microglia are key sentinels of central nervous system health, and their dysfunction has been widely implicated in the progressive nature of neurodegenerative diseases. While microglia can produce a host of factors that are toxic to neighboring neurons, NOX2 has been implicated as a common and essential mechanism of microglia-mediated neurotoxicity. Accumulating evidence indicates that activation of the NOX2 enzyme complex in microglia is neurotoxic, both through the production of extracellular reactive oxygen species that damage neighboring neurons as well as the initiation of redox signaling in microglia that amplifies the pro-inflammatory response. More specifically, evidence supports that NOX2 redox signaling enhances microglial sensitivity to pro-inflammatory stimuli, and amplifies the production of neurotoxic cytokines, to promote chronic and neurotoxic microglial activation. Here, we describe the evidence denoting the role of NOX2 in microglia-mediated neurotoxicity with an emphasis on Alzheimer's and Parkinson's disease, describe available inhibitors that have been tested, and detail evidence of the neuroprotective and therapeutic potential of targeting this enzyme complex to regulate microglia.

MOCA is an integrator of the neuronal death signals that are activated by familial Alzheimer's disease-related mutants of amyloid β precursor protein and presenilins

The death of cholinergic neurons in the cerebral cortex and certain subcortical regions is linked to irreversible dementia relevant to AD (Alzheimer's disease). Although multiple studies have shown that expression of a FAD (familial AD)-linked APP (amyloid β precursor protein) or a PS (presenilin) mutant, but not that of wild-type APP or PS, induced neuronal death by activating intracellular death signals, it remains to be addressed how these signals are interrelated and what the key molecule involved in this process is. In the present study, we show that the PS1-mediated (or possibly the PS2-mediated) signal is essential for the APP-mediated death in a γ-secretase-independent manner and vice versa. MOCA (modifier of cell adhesion), which was originally identified as being a PS- and Rac1-binding protein, is a common downstream constituent of these neuronal death signals. Detailed molecular analysis indicates that MOCA is a key molecule of the AD-relevant neuronal death signals that links the PS-mediated death signal with the APP-mediated death signal at a point between Rac1 [or Cdc42 (cell division cycle 42)] and ASK1 (apoptosis signal-regulating kinase 1).

Neuronal cell death in Alzheimer's disease and a neuroprotective factor, humanin

Brain atrophy caused by neuronal loss is a prominent pathological feature of Alzheimer's disease (AD). Amyloid beta (Abeta), the major component of senile plaques, is considered to play a central role in neuronal cell death. In addition to removal of the toxic Abeta, direct suppression of neuronal loss is an essential part of AD treatment; however, no such neuroprotective therapies have been developed. Excess amount of Abeta evokes multiple cytotoxic mechanisms, involving increase of the intracellular Ca(2+) level, oxidative stress, and receptor-mediated activation of cell-death cascades. Such diversity in cytotoxic mechanisms induced by Abeta clearly indicates a complex nature of the AD-related neuronal cell death. We have identified a 24-residue peptide, Humanin (HN), which suppresses in vitro neuronal cell death caused by all AD-related insults, including Abeta, so far tested. The anti-AD effect of HN has been further confirmed in vivo using mice with Abeta-induced amnesia. Altogether, such potent neuroprotective activity of HN against AD-relevant cytotoxicity both in vitro and in vivo suggests the potential clinical applications of HN in novel AD therapies aimed at controlling neuronal death.

NOX enzymes in the central nervous system: from signaling to disease

Oxidative stress has been implicated in the pathogenesis of neurologic and psychiatric diseases. The brain is particularly vulnerable to oxidative damage due to high oxygen consumption, low antioxidant defense, and an abundance of oxidation-sensitive lipids. Production of reactive oxygen species (ROS) by mitochondria is generally thought to be the main cause of oxidative stress. However, a role for ROS-generating NADPH oxidase NOX enzymes has recently emerged. Activation of the phagocyte NADPH oxidase NOX2 has been studied mainly in microglia, where it plays a role in inflammation, but may also contribute to neuronal death in pathologic conditions. However, NOX-dependent ROS production can be due to the expression of other NOX isoforms, which are detected not only in microglia, but also in astrocytes and neurons. The physiologic and pathophysiologic roles of such NOX enzymes are only partially understood. In this review, we summarize the present knowledge about NOX enzymes in the central nervous system and their involvement in neurologic and psychiatric diseases.

Dose formulation and analysis of diapocynin

Procedures based on high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection and liquid chromatography-mass spectrometry (LC-MS) are described for analyzing diapocynin. Diapocynin was synthesized by oxidative coupling of two apocynin monomers, through the in situ generation of sulfate radicals. It was purified by washing 3 times each with boiling water, followed by boiling methanol. HPLC was used to determine the concentration of unreacted apocynin and other impurities and the purity of the diapocynin that had been synthesized. Negative-ion, atmospheric pressure chemical ionization (APCI) LC-MS was used to determine the molecular weights of impurities. The method using HPLC with UV detection provided a calibration curve that was linear from 0.16 to 24 microg/mL. The LC-MS method was linear from 0.005 to 2 microg/mL. It was found that diapocynin has low solubility in deionized water and corn oil but is soluble in dimethylsulfoxide (DMSO) and alkaline aqueous solutions. Also, diapocynin is 13 times more lipophilic than apocynin, even though both compounds have the same p K a of 7.4. The log of the octanol/water partition coefficient (log P) was 1.01 for apocynin and 1.82 for diapocynin. A solution of 5.5 mg/mL (16.7 mM) diapocynin in DMSO was found to be stable for at least 30 days when stored at room temperature.

Synaptic localization of a functional NADPH oxidase in the mouse hippocampus

Superoxide has been shown to be critical for hippocampal long-term potentiation (LTP) and hippocampus-dependent memory function. A possible source for the generation of superoxide during these processes is NADPH oxidase. The active oxidase consists of two membrane proteins, gp91phox and p22phox, and four cytosolic proteins, p40phox, p47phox, p67phox, and Rac. Upon stimulation, the cytosolic proteins translocate to the membrane to form a complex with the membrane components, which results in production of superoxide. Here, we determined the presence, localization, and functionality of a NADPH oxidase in mouse hippocampus by examining the NADPH oxidase proteins as well as the production of superoxide. All of the NADPH oxidase proteins were present in hippocampal homogenates and enriched in synaptoneurosome preparations. Immunocytochemical analysis of cultured hippocampal neurons indicated that all NADPH oxidase proteins were localized in neuronal cell bodies as well as dendrites. Furthermore, double labeling analysis using antibodies to p67phox and the presynaptic marker synaptophysin suggest a close association of the NADPH oxidase subunits with synaptic sites. Finally, stimulation of hippocampal slices with phorbol esters triggered translocation of the cytoplasmic NADPH oxidase proteins to the membrane and an increase in superoxide production that was blocked by inhibitors of NADPH oxidase. Taken together, our data suggest that NADPH oxidase is present in mouse hippocampus and might be the source of superoxide production required for LTP and memory function.

Humanin: after the discovery

Humanin (HN) is a novel neuroprotective factor that consists of 24 amino acid residues. HN suppresses neuronal cell death caused by Alzheimer's disease (AD)-specific insults, including both amyloid-beta (betaAbeta) peptides and familial AD-causative genes. Cerebrovascular smooth muscle cells are also protected from Abeta toxicity by HN, suggesting that HN affects both neuronal and non-neuronal cells when they are exposed to AD-related cytotoxicity. HN peptide exerts a neuroprotective effect through the cell surface via putative receptor(s). HN activates a cellular signaling cascade that intervenes (at least) in activation of c-Jun N-terminal kinase. The highly selective effect of HN on AD-relevant cell death indicates that HN is promising for AD therapy. Additionally, a recent study showed that intracellularly overexpressed HN suppressed mitochondria-mediated apoptosis by inhibiting Bax activity.

Neuronal RNA oxidation is a prominent feature of familial Alzheimer's disease

An in situ approach was used to identify the oxidized RNA nucleoside 8-hydroxyguanosine (8OHG) in the frontal cortex of familial Alzheimer's disease (FAD) with a mutation in presenilin-1 (PS-1) or amyloid beta protein precursor (AbetaPP) gene (n = 13, age 47-81 years). Neurons with marked 8OHG immunoreaction in the cytoplasm were widely distributed in the superior/middle frontal gyrus of FAD. Relative intensity measurements of neuronal 8OHG immunoreactivity showed that there was a significant increase in FAD compared with controls (n = 15, age 59-81 years), while there was no difference in relative 8OHG between the PS-1 and the AbetaPP FAD. Interestingly, a presymptomatic case carrying a PS-1 mutation showed a considerable level of relative 8OHG, and the increased levels of neuronal 8OHG in FAD were more prominent in cases with a lower percentage area of Abeta42 burden. These results suggest that oxidative stress is an early event involved in the pathological cascade of FAD.

A Rac1/phosphatidylinositol 3-kinase/Akt3 anti-apoptotic pathway, triggered by AlsinLF, the product of the ALS2 gene, antagonizes Cu/Zn-superoxide dismutase (SOD1) mutant-induced motoneuronal cell death

AlsinLF, the product of the ALS2 gene, inhibits Cu/Zn-superoxide dismutase (SOD1) mutant-induced neurotoxicity via its Rho guanine nucleotide-exchanging factor domain. We here identified Rac1, a Rho family small GTPase, as a target for the Rho guanine nucleotide-exchanging factor activity of alsinLF. Rac1 associates with alsinLF. The amount of the GTP form of Rac1 is up-regulated by enforced overexpression of alsinLF. We further found not only that constitutively active Rac1 suppresses motoneuronal cell death induced by SOD1 mutants but also that the neuroprotective activity of alsinLF was completely inhibited by knocking down the endogenous Rac1 expression with small interfering RNA for Rac1, indicating that Rac1 is the major effector for alsinLF-mediated neuroprotection. Such alsinLF/Rac1-mediated neuroprotection occurs specifically against the SOD1 mutant-induced cell death but not against the cell death induced by any other neurotoxic insults in motoneuronal NSC34 cells. We further demonstrated that the alsinLF/Rac1-mediated neuroprotective signal is transmitted to the phosphatidylinositol 3-kinase/Akt anti-apoptotic axis. Among three Akt family proteins, Akt3 is the major downstream mediator for alsinLF/Rac1-mediated neuroprotection, which is specifically effective against SOD1 mutant-induced neurotoxicity.

Unravelling the role of Humanin

Humanin (HN), a recently identified neuroprotective factor against Alzheimer's disease-related insults, has been reported to function as an anti cell-death factor through multiple mechanisms. One mechanism, revealed in a glioblastoma cell line, involves the apoptosis-inducing protein Bax. This, in addition to the fact that HN is produced in certain normal tissues, such as testis, implies a potential role of HN in oncogenesis. A second mechanism, in neuronal cells, is via a putative cell-surface receptor. It is through this mechanism that HN exhibits its neuroprotective activity.

Cytotoxic mechanisms by M239V presenilin 2, a little-analyzed Alzheimer's disease-causative mutant

Although neurotoxic functions are well characterized in familial Alzheimer's disease (FAD)-linked N141I mutant of presenilin (PS)2, little has been known about M239V-PS2, another established FAD-causative mutant. We found that expression of M239V-PS2 caused neuronal cytotoxicity. M239V-PS2 exerted three forms of cytotoxicity: one was sensitive to both an antioxidant glutathione-ethyl-ester (GEE) and a caspase inhibitor Ac-DEVD-CHO (DEVD); the second was sensitive to GEE but resistant to DEVD; and the third was resistant to both. The GEE/DEVD-sensitive cytotoxicity by M239V-PS2 was likely through NADPH oxidase and the GEE-sensitive/DEVD-resistant cytotoxicity through xanthine oxidase (XO). Both mechanisms by M239V-PS2 were suppressed by pertussis toxin (PTX) and were mediated by Galpha(o), but not by Galpha(i). Although Abeta1-43 itself induced no cytotoxicity, Abeta1-43 potentiated all three components of M239V-PS2 cytotoxicity. As these cytotoxic mechanisms by M239V-PS2 are fully shared with N141I-PS2, they are most likely implicated in the pathomechanism of FAD by PS2 mutations. Notably, cytotoxicity by M239V-PS2 could be inhibited by the combination of two clinically usable inhibitors of superoxide-generating enzymes, apocynin and oxypurinol.

Humanin antagonists: mutants that interfere with dimerization inhibit neuroprotection by Humanin

The 24-residue peptide Humanin (HN) protects neuronal cells from insults of various Alzheimer's disease (AD) genes and Abeta by forming a homodimer. We have previously shown that P3A, S7A, C8A, L9A, L12A, T13A, S14A and P19A mutations nullify the neuroprotective function of HN [Yamagishi, Y., Hashimoto, Y., Niikura, T. & Nishimoto, I. (2003) Peptides, 24, 585-595]. Here we examined whether any of these 'null' mutants could function as dominant-negative mutants. Homodimerization-defective mutants, P3A-, L12A-, S14A- and P19A-HN, specifically blocked neuroprotection by HN, but not by activity-dependent neurotrophic factor. Furthermore, insertion of S7A, the mutation that blocks the homodimerization of HN, but not insertion of G5A abolished the antagonizing function of L12A-HN. While L12A-HN and G5A/L12A-HN actually inhibited HN homodimerization, S7A/L12A-HN had no effect. These data indicate that P3A-, L12A-, S14A- and P19A-HN function as HN antagonists by forming an inactive dimer with HN. This study provides a novel insight into the understanding of the in vivo function of HN, as well as into the development of clinically applicable HN neutralizers.

Alsin, the Product of ALS2 Gene, Suppresses SOD1 Mutant Neurotoxicity through RhoGEF Domain by Interacting with SOD1 Mutants

Mutation of the ALS2 gene encoding alsin is linked to the onset of autosomal recessive motor neuron diseases, including juvenile-onset amyotrophic lateral sclerosis (ALS). Alsin long form (LF) belongs to the family of the guanine nucleotide exchanging factor (GEF) for small GTPases. Expression of alsin LF, but not alsin short form, protected motor neuronal cells from toxicity induced by mutants of the Cu/Zn-superoxide dismutase (SOD1) gene, which cause autosomal dominant ALS. In contrast, expression of alsin did not suppress neurotoxicity by other neurodegenerative insults such as Alzheimer's disease-related genes. Deletion analysis of alsin LF demonstrated that the RhoGEF domain is essential for alsin-mediated neuroprotection. Furthermore, we found that alsin LF bound to SOD1 mutants, but not to wtSOD1, via the RhoGEF domain. Such functional and physical interaction between two ALS-related genes will become a promising clue to clarify the pathogenesis of ALS and other motor neuron diseases.

The Gtx Homeodomain Transcription Factor Exerts Neuroprotection Using Its Homeodomain

Certain cases of familial Alzheimer's disease are caused by mutants of amyloid-beta precursor protein (AbetaPP), including V642I-AbetaPP, K595N/M596L-AbetaPP (NL-AbetaPP), A617G-AbetaPP, and L648P-AbetaPP. By using an unbiased functional screening with transfection and expression of a human brain cDNA library, we searched for genes that protect neuronal cells from toxicity by V642I-AbetaPP. One protective clone was identical to the human GTX, a neuronal homeobox gene. Human Gtx (hGtx) inhibited caspase inhibitor-sensitive neuronal cell death not only by V642I-AbetaPP but also by L648P-, NL-, A617G-AbetaPP, apolipoprotein E4, and Abeta. The region of hGtx responsible for this rescue function was specified to be its homeodomain (Lys148-His207). The rescue function was shared by DLX4, a distal-less family gene with a homeodomain only 38.3% homologous to that of hGtx, suggesting that this function would be generally shared by homeodomains. The neuroprotective function of hGtx was attributable to hGtx-stimulated production and secretion of insulin-like growth factor-I. This study provides molecular clues to understand how neuronal cells developmentally regulate themselves against cell death as well as to develop reagents effective in curative therapeutics of Alzheimer's disease.

Amino- and carboxyl-terminal mutants of presenilin 1 cause neuronal cell death through distinct toxic mechanisms: Study of 27 different presenilin 1 mutants

Presenilin (PS)1 and its mutants, which consist of the N-terminal and C-terminal fragments, cause certain familial forms of Alzheimer's disease (FAD). Our earlier studies found that FAD-linked M146L-PS1 causes neuronal cell death through nitrogen oxide synthase (NOS) and that FAD-linked N141I-PS2, another member of the PS family, causes neuronal cell death through NADPH oxidase. In this study, we examined 27 different FAD-linked mutants of PS1, and found that PS1 mutants with mutations in the N-terminal fragment caused NOS inhibitor (NOSI)-sensitive neuronal cell death; in contrast, the PS1 mutants with mutations in the C-terminal fragment caused NOSI-resistant neuronal cell death. The former toxicity was resistant to the specific NADPH oxidase inhibitor apocynin and was inhibited by Humanin (HN), a newly identified neuroprotective factor against Alzheimer's disease (AD)-relevant insults, but not by insulin-like growth factor-I (IGF-I). In contrast, the latter toxicity was sensitive to apocynin and inhibited by both IGF-I and HN. This study indicates for the first time that N- and C-terminal fragment PS1 mutants can generate distinct neurotoxic signals, which will provide an important clue to the understanding of the entire array of neurotoxic signals generated by FAD-causative mutations of PS1.

Analysis of neurons created from wild-type and Alzheimer's mutation knock-in embryonic stem cells by a highly efficient differentiation protocol

It is impossible to obtain and amplify live neurons from Alzheimer's disease (AD) patients. To establish the neurons harboring AD abnormality, we constructed mouse embryonic stem (ES) cells, in which the AD-causative V642I mutation was introduced to the endogenous amyloid precursor protein (APP) gene, in combination with a protocol to efficiently differentiate ES cells into postmitotic neurons without using a cell sorter. By this protocol, ES cells differentiated into >90% of the central type of adult postmitotic neurons. Neurons derived from V642I-APP knock-in ES cells were indistinguishable from wild-type ES-derived neurons, as determined by the expression of various markers for neuronal differentiation. Notably, V642I-APP knock-in ES cell-derived neurons exhibited significantly increased secretion of Abeta42 without AD-related hyperphosphorylation of tau, indicating that the direct output of the AD-causative mutation is increased Abeta42 secretion. In this study, we analyze created neurons with wild-type and AD genotypes and propose a new strategy for generating neurons for any dominantly inherited neurodegenerative diseases. The strategy can be applied to create human neurons with AD or any other neurodegenerative disease by using human ES cells.

NADPH oxidase immunoreactivity in the mouse brain

Superoxide production via NADPH oxidase has been shown to play a role in neurotoxicity, ischemic stroke, and possibly Parkinson's and Alzheimer's diseases. In addition, NADPH oxidase-dependent production of superoxide may be necessary for normal brain functions, including neuronal differentiation and neuronal plasticity. To improve our understanding of NADPH oxidase in the brain, we studied the localization of the various protein components of NADPH oxidase in the central nervous system of the adult mouse using immunohistochemistry. We detected staining for the cytoplasmic NADPH proteins, p40(phox), p47(phox), and p67(phox), as well as the membrane-associated NADPH oxidase proteins, p22(phox) and gp91(phox) in neurons throughout the mouse brain. Staining of each of the NADPH oxidase proteins was observed in neurons in all regions of the neuraxis, with particularly prominent localizations in the hippocampus, cortex, amygdala, striatum, and thalamus. The expression of NADPH oxidase proteins in neurons suggests the possibility that enzymatic production of superoxide by a NADPH oxidase may play a role in both normal neuronal function as well as neurodegeneration in the brain.

Characterization of the toxic mechanism triggered by Alzheimer's amyloid-beta peptides via p75 neurotrophin receptor in neuronal hybrid cells

Neuronal pathology of the brain with Alzheimer's disease (AD) is characterized by numerous depositions of amyloid-beta peptides (Abeta). Abeta binding to the 75-kDa neurotrophin receptor (p75NTR) causes neuronal cell death. Here we report that Abeta causes cell death in neuronal hybrid cells transfected with p75NTR, but not in nontransfected cells, and that p75NTR(L401K) cannot mediate Abeta neurotoxicity. We analyzed the cytotoxic pathway by transfecting pertussis toxin (PTX)-resistant G protein alpha subunits in the presence of PTX and identified that Galpha(o), but not Galpha(i), proteins are involved in p75NTR-mediated Abeta neurotoxicity. Further investigation suggested that Abeta neurotoxicity via p75NTR involved JNK, NADPH oxidase, and caspases-9/3 and was inhibited by activity-dependent neurotrophic factor, insulin-like growth factor-I, basic fibroblast growth factor, and Humanin, as observed in primary neuron cultures. Understanding the Abeta neurotoxic mechanism would contribute significantly to the development of anti-AD therapies.

The cytoplasmic domain of Alzheimer's amyloid-beta protein precursor causes sustained apoptosis signal-regulating kinase 1/c-Jun NH2-terminal kinase-mediated neurotoxic signal via dimerization

The biological function of full-length amyloid-beta protein precursor (AbetaPP), the precursor of Abeta, is not fully understood. Multiple laboratories have reported that antibody binding to cell surface AbetaPP causes neuronal cell death. Here we examined whether induced dimerization of the cytoplasmic domain of AbetaPP (AbetaPPCD) triggers neuronal cell death. In neurohybrid cells expressing fusion constructs of the epidermal growth factor (EGF) receptor with AbetaPPCD (EGFR/AbetaPP hybrids), EGF drastically enhanced neuronal cell death in a manner sensitive to acetyl-l-aspartyl-l-glutamyl-l-valyl-l-aspartyl-aldehyde (Ac-DEVD-CHO; DEVD), GSH-ethyl ester (GEE), and pertussis toxin (PTX). Dominant-negative apoptosis signal-regulating kinase 1 (ASK1) blocked this neuronal cell death, but not alpha-synuclein-induced cell death. Constitutively active ASK1 (caASK1) caused DEVD/GEE-sensitive cell death in a manner resistant to PTX and sensitive to Humanin, which also suppressed neuronal cell death by EGFR/AbetaPP hybrid. ASK1 formed a complex with AbetaPPCD via JIP-1b, the c-Jun N-terminal kinase (JNK)-interacting protein. EGFR/AbetaPP hybrid-induced and caASK1-induced neuronal cell deaths were specifically blocked by SP600125 (anthra[1,9-cd]pyrazol-6(2H)-one), a specific JNK inhibitor. Combined with our earlier study, these data indicate that dimerization of AbetaPPCD triggers ASK1/JNK-mediated neuronal cell death. We also noticed a potential role of ASK1/JNK in sustaining the activity of this mechanism after initial activation by AbetaPP, which allows for the achievement of cell death by short-term anti-AbetaPP antibody treatment. Understanding the function of AbetaPPCD and its downstream pathway should lead to effective anti-Alzheimer's disease therapeutics.

Two serine residues distinctly regulate the rescue function of Humanin, an inhibiting factor of Alzheimer's disease-related neurotoxicity: functional potentiation by isomerization and dimerization

The 24-residue peptide Humanin (HN), containing two Ser residues at positions 7 and 14, protects neuronal cells from insults of various Alzheimer's disease (AD) genes and A beta. It was not known why the rescue function of (S14G)HN is more potent than HN by two to three orders of magnitude. Investigating the possibility that the post-translational modification of Ser14 might play a role, we found that HN with D-Ser at position 14 exerts neuroprotection more potently than HN by two to three orders of magnitude, whereas D-Ser7 substitution does not affect the rescue function of HN. On the other hand, S7A substitution nullified the HN function. Multiple series of experiments indicated that Ser7 is necessary for self-dimerization of HN, which is essential for neuroprotection by this factor. These findings indicate that the rescue function of HN is quantitatively modulated by d-isomerization of Ser14 and Ser7-relevant dimerization, allowing for the construction of a very potent HN derivative that was fully neuroprotective at 10 pM against 25 microM A beta1-43. This study provides important clues to the understanding of the neuroprotective mechanism of HN, as well as to the development of novel AD therapeutics.

Involvement of c-Jun N-terminal kinase in amyloid precursor protein-mediated neuronal cell death

Amyloid precursor protein (APP), the precursor of Abeta, has been shown to function as a cell surface receptor that mediates neuronal cell death by anti-APP antibody. The c-Jun N-terminal kinase (JNK) can mediate various neurotoxic signals, including Abeta neurotoxicity. However, the relationship of APP-mediated neurotoxicity to JNK is not clear, partly because APP cytotoxicity is Abeta independent. Here we examined whether JNK is involved in APP-mediated neuronal cell death and found that: (i) neuronal cell death by antibody-bound APP was inhibited by dominant-negative JNK, JIP-1b and SP600125, the specific inhibitor of JNK, but not by SB203580 or PD98059; (ii) constitutively active (ca) JNK caused neuronal cell death and (iii) the pharmacological profile of caJNK-mediated cell death closely coincided with that of APP-mediated cell death. Pertussis toxin (PTX) suppressed APP-mediated cell death but not caJNK-induced cell death, which was suppressed by Humanin, a newly identified neuroprotective factor which inhibits APP-mediated cytotoxicity. In the presence of PTX, the PTX-resistant mutant of Galphao, but not that of Galphai, recovered the cytotoxic action of APP. These findings demonstrate that JNK is involved in APP-mediated neuronal cell death as a downstream signal transducer of Go.

[Neuronal cell death by Alzheimer's disease-relevant insults and its rescue]

Neuronal cell death accounts for the clinical manifestations in Alzheimer's disease (AD). To establish the curative therapy of AD, neuroprotection is one of the primary therapeutic targets, and the elucidation of the mechanism of neuronal cell death is mandatory. Detailed characterization of neuronal cell death caused by familial AD (FAD)-linked mutant genes revealed that different cell death pathways are evoked by different types of mutants. Humanin (HN), a newly identified neuroprotective peptide, suppresses neuronal cell death caused by all known FAD mutants and A beta, while it has no effect on neuronal cell death caused by AD-irrelevant insults. The functional target of HN is the antagonism to neuronal death, not the modulation of A beta production, suggesting that HN-based medication can be combined with other remedies targeting A beta. HN is a promising seed for a novel therapy aiming at complete cure of AD through the suppression of neuronal loss.

Death and survival of neuronal cells exposed to Alzheimer's insults

Neuronal cell death is the central abnormality occurring in brains suffering from Alzheimer's disease (AD). The notion that AD is a disease caused by loss of neurons points toward suppression of neuronal death as the most important therapeutic target. Nevertheless, the mechanisms for neuronal death in AD are still relatively unclear. Three known mutant genes cause familial AD (FAD): amyloid precursor protein, presenilin 1, and presenilin 2. Detailed analysis of cytotoxic mechanisms of the FAD-linked mutant genes reveals that they cause neuronal cell death at physiologically low expression levels. Unexpectedly, cytotoxic mechanisms vary depending on the type of mutations and genes, suggesting that various mechanisms for neuronal cell death are involved in AD patients. In support of this, activity-dependent neurotrophic factor, basic fibroblast growth factor, and insulin-like growth factor-I can completely protect neurons from beta-amyloid (A beta) cytotoxicity but exhibit incomplete or little effect on cytotoxicity by FAD mutant genes. By contrast, Humanin, a newly identified 24-residue peptide, suppresses neuronal cell death by various FAD mutants and A beta, whereas this factor has no effect on cytotoxicity from AD-irrelevant insults. Studies investigating death and survival of neuronal cells exposed to AD insults will open a new horizon in developing therapy aimed at neuroprotection.