Characterization of V642I-A?PP-induced cytotoxicity in primary neurons

The Molecular Structure and Role of Humanin in Neural and Skeletal Diseases, and in Tissue Regeneration

Humanin (HN) belongs to a member of mitochondrial-derived peptides (MDPs) which are encoded by mitochondrial genes. HN shares sequence homology with thirteen HN-like proteins, named MTRNR2L1 to MTRNR2L13, which encompass 24–28 amino acid residues in length. HN mediates mitochondrial status and cell survival by acting via an intracellular mechanism, or as a secreted factor via extracellular signals. Intracellularly, it binds Bcl2-associated X protein (BAX), Bim and tBid, and IGFBP3 to inhibit caspase activity and cell apoptosis. When released from cells as a secreted peptide, HN interacts with G protein-coupled formyl peptide receptor-like 1 (FPRL1/2) to mediate apoptosis signal-regulating kinase (ASK) and c-Jun N-terminal kinase (JNK) signalling pathways. Additionally, it interacts with CNTFR-α/gp130/WSX-1 trimeric receptors to induce JAK2/STA3 signalling cascades. HN also binds soluble extracellular proteins such as VSTM2L and IGFBP3 to modulate cytoprotection. It is reported that HN plays a role in neuronal disorders such as Alzheimer’s disease, as well as in diabetes mellitus, infertility, and cardiac diseases. Its roles in the skeletal system are emerging, where it appears to be involved with the regulation of osteoclasts, osteoblasts, and chondrocytes. Understanding the molecular structure and role of HN in neural and skeletal diseases is vital to the application of HN in tissue regeneration.

Humanin and Alzheimer's disease: The beginning of a new field

BACKGROUND

Humanin (HN) is an endogenous peptide factor and known as a member of mitochondrial-derived peptides. We first found the gene encoding this novel 24-residue peptide in a brain of an Alzheimer's disease (AD) patient as an antagonizing factor against neuronal cell death induced by AD-associated insults.

SCOPE OF REVIEW

This review presents an overview of HN actions in AD-related conditions among its wide range of action spectrum as well as a brief history of the discovery.

MAJOR CONCLUSIONS

HN exhibits multiple intracellular and extracellular anti-cell death actions and antagonizes various AD-associated pathomechanisms including amyloid plaque accumulation.

GENERAL SIGNIFICANCE

This review concisely reflects accumulated knowledge on HN since the discovery focusing on its functions related to AD pathogenesis and provides a perspective to its potential contribution in AD treatments.

Mitochondrial Peptide Humanin Protects Silver Nanoparticles-Induced Neurotoxicity in Human Neuroblastoma Cancer Cells (SH-SY5Y)

The extensive usage of silver nanoparticles (AgNPs) as medical products such as antimicrobial and anticancer agents has raised concerns about their harmful effects on human beings. AgNPs can potentially induce oxidative stress and apoptosis in cells. However, humanin (HN) is a small secreted peptide that has cytoprotective and neuroprotective cellular effects. The aim of this study was to assess the harmful effects of AgNPs on human neuroblastoma SH-SY5Y cells and also to investigate the protective effect of HN from AgNPs-induced cell death, mitochondrial dysfunctions, DNA damage, and apoptosis. AgNPs were prepared with an average size of 18 nm diameter to study their interaction with SH-SY5Y cells. AgNPs caused a dose-dependent decrease of cell viability and proliferation, induced loss of plasma-membrane integrity, oxidative stress, loss of mitochondrial membrane potential (MMP), and loss of ATP content, amongst other effects. Pretreatment or co-treatment of HN with AgNPs protected cells from several of these AgNPs induced adverse effects. Thus, this study demonstrated for the first time that HN protected neuroblastoma cells against AgNPs-induced neurotoxicity. The mechanisms of the HN-mediated protective effect on neuroblastoma cells may provide further insights for the development of novel therapeutic agents against neurodegenerative diseases.

APP/Go protein Gβγ-complex signaling mediates Aβ degeneration and cognitive impairment in Alzheimer's disease models

Deposition of amyloid-β (Aβ), the proteolytic product of the amyloid precursor protein (APP), might cause neurodegeneration and cognitive decline in Alzheimer's disease (AD). However, the direct involvement of APP in the mechanism of Aβ-induced degeneration in AD remains on debate. Here, we analyzed the interaction of APP with heterotrimeric Go protein in primary hippocampal cultures and found that Aβ deposition dramatically enhanced APP-Go protein interaction in dystrophic neurites. APP overexpression rendered neurons vulnerable to Aβ toxicity by a mechanism that required Go-Gβγ complex signaling and p38-mitogen-activated protein kinase activation. Gallein, a selective pharmacological inhibitor of Gβγ complex, inhibited Aβ-induced dendritic and axonal dystrophy, abnormal tau phosphorylation, synaptic loss, and neuronal cell death in hippocampal neurons expressing endogenous protein levels. In the 3xTg-AD mice, intrahippocampal application of gallein reversed memory impairment associated with early Aβ pathology. Our data provide further evidence for the involvement of APP/Go protein in Aβ-induced degeneration and reveal that Gβγ complex is a signaling target potentially relevant for developing therapies for halting Aβ degeneration in AD.

The physiological role of the amyloid precursor protein as an adhesion molecule in the developing nervous system

The amyloid precursor protein (APP) is a type I transmembrane glycoprotein better known for its participation in the physiopathology of Alzheimer disease as the source of the beta amyloid fragment. However, the physiological functions of the full length protein and its proteolytic fragments have remained elusive. APP was first described as a cell-surface receptor; nevertheless, increasing evidence highlighted APP as a cell adhesion molecule. In this review, we will focus on the current knowledge of the physiological role of APP as a cell adhesion molecule and its involvement in key events of neuronal development, such as migration, neurite outgrowth, growth cone pathfinding, and synaptogenesis. Finally, since APP is over-expressed in Down syndrome individuals because of the extra copy of chromosome 21, in the last section of the review, we discuss the potential contribution of APP to the neuronal and synaptic defects described in this genetic condition. Read the Editorial Highlight for this article on page 9. Cover Image for this issue: doi. 10.1111/jnc.13817.

Amyloid Precursor Protein family as unconventional Go-coupled receptors and the control of neuronal motility

Cleavage of the Amyloid Precursor Protein (APP) generates amyloid peptides that accumulate in Alzheimer Disease (AD), but APP is also upregulated by developing and injured neurons, suggesting that it regulates neuronal motility. APP can also function as a G protein-coupled receptor that signals via the heterotrimeric G protein Gαo, but evidence for APP-Gαo signaling in vivo has been lacking. Using Manduca as a model system, we showed that insect APP (APPL) regulates neuronal migration in a Gαo-dependent manner. Recently, we also demonstrated that Manduca Contactin (expressed by glial cells) induces APPL-Gαo retraction responses in migratory neurons, consistent with evidence that mammalian Contactins also interact with APP family members. Preliminary studies using cultured hippocampal neurons suggest that APP-Gαo signaling can similarly regulate growth cone motility. Whether Contactins (or other APP ligands) induce this response within the developing nervous system, and how this pathway is disrupted in AD, remains to be explored.

Role of APP Interactions with Heterotrimeric G Proteins: Physiological Functions and Pathological Consequences

Following the discovery that the amyloid precursor protein (APP) is the source of β-amyloid peptides (Aβ) that accumulate in Alzheimer’s disease (AD), structural analyses suggested that the holoprotein resembles a transmembrane receptor. Initial studies using reconstituted membranes demonstrated that APP can directly interact with the heterotrimeric G protein Gαo (but not other G proteins) via an evolutionarily G protein-binding motif in its cytoplasmic domain. Subsequent investigations in cell culture showed that antibodies against the extracellular domain of APP could stimulate Gαo activity, presumably mimicking endogenous APP ligands. In addition, chronically activating wild type APP or overexpressing mutant APP isoforms linked with familial AD could provoke Go-dependent neurotoxic responses, while biochemical assays using human brain samples suggested that the endogenous APP-Go interactions are perturbed in AD patients. More recently, several G protein-dependent pathways have been implicated in the physiological roles of APP, coupled with evidence that APP interacts both physically and functionally with Gαo in a variety of contexts. Work in insect models has demonstrated that the APP ortholog APPL directly interacts with Gαo in motile neurons, whereby APPL-Gαo signaling regulates the response of migratory neurons to ligands encountered in the developing nervous system. Concurrent studies using cultured mammalian neurons and organotypic hippocampal slice preparations have shown that APP signaling transduces the neuroprotective effects of soluble sAPPα fragments via modulation of the PI3K/Akt pathway, providing a mechanism for integrating the stress and survival responses regulated by APP. Notably, this effect was also inhibited by pertussis toxin, indicating an essential role for Gαo/i proteins. Unexpectedly, C-terminal fragments (CTFs) derived from APP have also been found to interact with Gαs, whereby CTF-Gαs signaling can promote neurite outgrowth via adenylyl cyclase/PKA-dependent pathways. These reports offer the intriguing perspective that G protein switching might modulate APP-dependent responses in a context-dependent manner. In this review, we provide an up-to-date perspective on the model that APP plays a variety of roles as an atypical G protein-coupled receptor in both the developing and adult nervous system, and we discuss the hypothesis that disruption of these normal functions might contribute to the progressive neuropathologies that typify AD.

Amyloid Precursor Proteins Are Dynamically Trafficked and Processed during Neuronal Development

Proteolytic processing of the Amyloid Precursor Protein (APP) produces beta-amyloid (Aβ) peptide fragments that accumulate in Alzheimer's Disease (AD), but APP may also regulate multiple aspects of neuronal development, albeit via mechanisms that are not well understood. APP is a member of a family of transmembrane glycoproteins expressed by all higher organisms, including two mammalian orthologs (APLP1 and APLP2) that have complicated investigations into the specific activities of APP. By comparison, insects express only a single APP-related protein (APP-Like, or APPL) that contains the same protein interaction domains identified in APP. However, unlike its mammalian orthologs, APPL is only expressed by neurons, greatly simplifying an analysis of its functions in vivo. Like APP, APPL is processed by secretases to generate a similar array of extracellular and intracellular cleavage fragments, as well as an Aβ-like fragment that can induce neurotoxic responses in the brain. Exploiting the complementary advantages of two insect models (Drosophila melanogaster and Manduca sexta), we have investigated the regulation of APPL trafficking and processing with respect to different aspects of neuronal development. By comparing the behavior of endogenously expressed APPL with fluorescently tagged versions of APPL and APP, we have shown that some full-length protein is consistently trafficked into the most motile regions of developing neurons both in vitro and in vivo. Concurrently, much of the holoprotein is rapidly processed into N- and C-terminal fragments that undergo bi-directional transport within distinct vesicle populations. Unexpectedly, we also discovered that APPL can be transiently sequestered into an amphisome-like compartment in developing neurons, while manipulations targeting APPL cleavage altered their motile behavior in cultured embryos. These data suggest that multiple mechanisms restrict the bioavailability of the holoprotein to regulate APPL-dependent responses within the nervous system. Lastly, targeted expression of our double-tagged constructs (combined with time-lapse imaging) revealed that APP family proteins are subject to complex patterns of trafficking and processing that vary dramatically between different neuronal subtypes. In combination, our results provide a new perspective on how the regulation of APP family proteins can be modulated to accommodate a variety of cell type-specific responses within the embryonic and adult nervous system.

Apocynin attenuates cholesterol oxidation product-induced programmed cell death by suppressing NF-κB-mediated cell death process in differentiated PC12 cells

Cholesterol oxidation products are suggested to be involved in neuronal degeneration. Apocynin has demonstrated to have anti-inflammatory and anti-oxidant effects. We assessed the effect of apocynin on the cholesterol oxidation product-induced programmed cell death in neuronal cells using differentiated PC12 cells in relation to NF-κB-mediated cell death process. 7-Ketocholesterol and 25-hydroxycholesterol decreased the levels of Bid and Bcl-2, increased the levels of Bax and p53, and induced loss of the mitochondrial transmembrane potential, release of cytochrome c and activation of caspases (-8, -9 and -3). 7-Ketocholesterol caused an increase in the levels of cytosolic and nuclear NF-κB p65, cytosolic NF-κB p50 and cytosolic phospho-IκB-α, which was inhibited by the addition of 0.5 μM Bay11-7085 (an inhibitor of NF-κB activation). Apocynin attenuated the cholesterol oxidation product-induced changes in the programmed cell death-related protein levels, NF-κB activation, production of reactive oxygen species, and depletion of GSH. The results show that apocynin appears to attenuate the cholesterol oxidation product-induced programmed cell death in PC12 cells by suppressing the activation of the mitochondrial pathway and the caspase-8- and Bid-dependent pathways that are mediated by NF-κB activation. The preventive effect appears to be associated with the inhibitory effect on the production of reactive oxygen species and depletion of GSH.

Protective effects of Humanin and calmodulin-like skin protein in Alzheimer's disease and broad range of abnormalities

Humanin is a 24-amino acid, secreted bioactive peptide that prevents various types of cell death and improves some types of cell dysfunction. Humanin inhibits neuronal cell death that is caused by a familial Alzheimer's disease (AD)-linked gene via binding to the heterotrimeric Humanin receptor (htHNR). This suggests that Humanin may play a protective role in AD-related pathogenesis. Calmodulin-like skin protein (CLSP) has recently been identified as a physiological agonist of htHNR with 10(5)-fold more potent anti-cell death activity than Humanin. Humanin has also shown to have protective effects against some metabolic disorders. In this review, the broad range of functions of Humanin and the functions of CLSP that have been characterized thus far are summarized.

Humanin and age-related diseases: a new link?

Humanin (HN) is 24-amino acid mitochondria-associated peptide. Since its initial discovery over a decade ago, a role for HN has been reported in many biological processes such as apoptosis, cell survival, substrate metabolism, inflammatory response, and response to stressors such as oxidative stress, ischemia, and starvation. HN and its potent analogs have been shown to have beneficial effects in many age-related diseases including Alzheimer's disease, stroke, diabetes, myocardial ischemia and reperfusion, atherosclerosis, amyotrophic lateral sclerosis, and certain types of cancer both in vitro and in vivo. More recently, an association between HN levels, growth hormone/insulin-like growth factor-1 (GH/IGF axis), and life span was demonstrated using various mouse models with mutations in the GH/IGF axis. The goal of this review is to summarize the current understanding of the role of HN in aging and age-related diseases.

Amyloid β precursor protein as a molecular target for amyloid β--induced neuronal degeneration in Alzheimer's disease

A role of amyloid β (Aβ) peptide aggregation and deposition in Alzheimer's disease (AD) pathogenesis is widely accepted. Significantly, abnormalities induced by aggregated Aβ have been linked to synaptic and neuritic degeneration, consistent with the "dying-back" pattern of degeneration that characterizes neurons affected in AD. However, molecular mechanisms underlying the toxic effect of aggregated Aβ remain elusive. In the last 2 decades, a variety of aggregated Aβ species have been identified and their toxic properties demonstrated in diverse experimental systems. Concurrently, specific Aβ assemblies have been shown to interact and misregulate a growing number of molecular effectors with diverse physiological functions. Such pleiotropic effects of aggregated Aβ posit a mayor challenge for the identification of the most cardinal Aβ effectors relevant to AD pathology. In this review, we discuss recent experimental evidence implicating amyloid β precursor protein (APP) as a molecular target for toxic Aβ assemblies. Based on a significant body of pathologic observations and experimental evidence, we propose a novel pathologic feed-forward mechanism linking Aβ aggregation to abnormalities in APP processing and function, which in turn would trigger the progressive loss of neuronal connectivity observed early in AD.

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).

The neuroprotective effects of apocynin

The recognition of health benefits of phytomedicines and herbal supplements lead to an increased interest to understand the cellular and molecular basis of their biological activities. Apocynin (4-hydroxy-3-methoxy-acetophenone) is a constituent of the Himalayan medicinal herb Picrorhiza kurroa which is regarded as an inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase, a superoxide-producing enzyme. NADPH oxidase appears to be especially important in the modulation of redox-sensitive signaling pathways and also has been implicated in neuronal dysfunction and degeneration, and neuroinflammmation in diseases ranging from stroke, Alzheimer's and Parkinson's diseases to psychiatric disorders. In this review, we aim to give an overview of current literature on the neuroprotective effects of apocynin in the prevention and treatment of neurodegenerative disorders. Particular attention is given to in vivo studies.

Cognitive impairment in humanized APP×PS1 mice is linked to Aβ(1-42) and NOX activation

Cognitive impairment in Alzheimer's disease (AD) is strongly associated with both extensive deposition of amyloid β peptides and oxidative stress, but the exact role of these indices in the development of dementia is not clear. This study was designed to determine the relationship between cognitive impairment, activation of the free radical producing enzyme NADPH oxidase (NOX), and progressive changes in Aβ deposition and solubility in humanized APP×PS1 knock-in mice of increasing age. Data show that cognitive performance and expression of key synaptic proteins were progressively decreased in aging APP×PS1 mice. Likewise, NOX activity and expression of the specific NOX subunit NOX4 were significantly increased in APP×PS1 mice in an age-dependent manner, and NOX activity and cognitive impairment shared a significant linear relationship. Data further show that age-dependent increases in Aβ(1-42) had a significant linear relationship with both NOX activity and cognitive performance in APP×PS1 knock-in mice. Collectively, these data show that NOX expression and activity are significantly upregulated with age in this humanized model of Aβ pathogenesis, and suggest that NOX-associated redox pathways are intimately linked to both the loss of cognitive function and the deposition of Aβ(1-42).

Humanins, the neuroprotective and cytoprotective peptides with antiapoptotic and anti-inflammatory properties

Humanin (HN) is a newly discovered 24-amino acid peptide, which may suppress neuronal cell death. HN cDNA includes an open reading frame (HN-ORF) of 75 bases located 950 bases downstream of the 5' end of the HN cDNA. It has been demonstrated that HN cDNA is 99% identical to the mitochondrial DNA (mtDNA) sequence. HN homologs have been identified as expressed sequence tags (ESTs) in both rats and nematodes. Certain regions that are homologous to the HN cDNA exist on human chromosomes. HN forms homodimers and multimers and this action seems to be essential for peptide function. HN acts as a ligand for formyl peptide receptor-like 1 (FPRL1) and 2 (FPRL2). It has been demonstrated that HN plays a protective role through its antiapoptotic activity that interferes with Bax activation, which suppresses Bax-dependent apoptosis. HN has also been shown to suppress the c-Jun N-terminal kinase (JNK) and ASK/JNK-mediated neuronal cell death. Several studies have also confirmed that HN could be important in the prevention of angiopathy-associated Alzheimer's disease dementia, diseases related to mitochondrial dysfunction (MELAS), and other types of β-amyloid accumulation-associated neurodegeneration. Avery recent study demonstrated a pluripotent cytoprotective effect and mechanisms of HNs in cells not from the CNS, such as germ cells or pancreatic β-cells, and the potent physiological consequences that result from HN interaction with IGFBP3 and STAT3. In vivo studies suggest that HN may also protect against cognitive impairment due to ischemia/reperfusion injury.

NOX activity in brain aging: exacerbation by high fat diet

This study describes how age and high fat diet affect the profile of NADPH oxidase (NOX). Specifically, NOX activity and subunit expression were evaluated in the frontal cerebral cortex of 7-, 16-, and 24-month old mice following a 4-month exposure to either Western diet (WD, 41% calories from fat) or very high fat lard diet (VHFD, 60% calories from fat). Data reveal a significant effect of age in on NOX activity, and show that NOX activity was only increased by VHFD, and only in 24-month old mice. NOX subunit expression was also increased by diet only in older mice. Quantification of protein carbonyls revealed significant age-related increases in protein oxidation, and indicate that only aged mice respond to high fat diet with enhanced protein oxidation. Histological analyses indicate prominent neuronal localization of both NOX subunits and protein carbonylation. Finally, data indicate that changes in reactive microgliosis, but not astrocytosis, mirror the pattern of diet-induced NOX activation and protein oxidation. Collectively, these data show that both age and dietary fat drive NOX activation, and further indicate that aged mice are preferentially sensitive to the effects of high fat diet. These data also suggest that high fat diets might exacerbate age-related oxidative stress in the brain via increased NOX.

NOX activity is increased in mild cognitive impairment

This study was undertaken to investigate the profile of NADPH oxidase (NOX) in the clinical progression of Alzheimer's disease (AD). Specifically, NOX activity and expression of the regulatory subunit p47phox and the catalytic subunit gp91phox was evaluated in affected (superior and middle temporal gyri) and unaffected (cerebellum) brain regions from a longitudinally followed group of patients. This group included both control and late-stage AD subjects, and also subjects with preclinical AD and with amnestic mild cognitive impairment (MCI) to evaluate the profile of NOX in the earliest stages of dementia. Data show significant elevations in NOX activity and expression in the temporal gyri of MCI patients as compared with controls, but not in preclinical or late-stage AD samples, and not in the cerebellum. Immunohistochemical evaluations of NOX expression indicate that whereas microglia express high levels of gp91phox, moderate levels of gp91phox also are expressed in neurons. Finally, in vitro experiments showed that NOX inhibition blunted the ability of oligomeric amyloid beta peptides to injure cultured neurons. Collectively, these data show that NOX expression and activity are upregulated specifically in a vulnerable brain region of MCI patients, and suggest that increases in NOX-associated redox pathways in neurons might participate in the early pathogenesis of AD.

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.

Humanin and the receptors for humanin

Alzheimer's disease (AD) is a prevalent dementia-causing neurodegenerative disease. Neuronal death is closely linked to the progression of AD-associated dementia. Accumulating evidence has established that a 24-amino-acid bioactive peptide, Humanin, protects neurons from AD-related neuronal death. A series of studies using various murine AD models including familial AD gene-expressing transgenic mice have shown that Humanin is effective against AD-related neuronal dysfunction in vivo. Most recently, it has been shown that Humanin inhibits neuronal cell death and dysfunction by binding to a novel IL-6-receptor-related receptor(s) on the cell surface involving CNTFRalpha, WSX-1, and gp130. These findings suggest that endogenous Humanin [or a Humanin-like substance(s)] may suppress the onset of AD-related dementia by inhibiting both AD-related neuronal cell death and dysfunction.

Humanin inhibits neuronal cell death by interacting with a cytokine receptor complex or complexes involving CNTF receptor alpha/WSX-1/gp130

Humanin (HN) inhibits neuronal death induced by various Alzheimer's disease (AD)-related insults via an unknown receptor on cell membranes. Our earlier study indicated that the activation of STAT3 was essential for HN-induced neuroprotection, suggesting that the HN receptor may belong to the cytokine receptor family. In this study, a series of loss-of-function tests indicated that gp130, the common subunit of receptors belonging to the IL-6 receptor family, was essential for HN-induced neuroprotection. Overexpression of ciliary neurotrophic factor receptor alpha (CNTFR) and/or the IL-27 receptor subunit, WSX-1, but not that of any other tested gp130-related receptor subunit, up-regulated HN binding to neuronal cells, whereas siRNA-mediated knockdown of endogenous CNTFR and/or WSX-1 reduced it. These results suggest that both CNTFR and WSX-1 may be also involved in HN binding to cells. Consistent with these results, loss-of-functions of CNTFR or WSX-1 in neuronal cells nullified their responsiveness to HN-mediated protection. In vitro-reconstituted binding assays showed that HN, but not the other control peptide, induced the hetero-oligomerization of CNTFR, WSX-1, and gp130. Together, these results indicate that HN protects neurons by binding to a complex or complexes involving CNTFR/WSX-1/gp130.

Thrombin-induced oxidative stress contributes to the death of hippocampal neurons: role of neuronal NADPH oxidase

The present study investigated whether thrombin can induce the production of reactive oxygen species (ROS) through activation of neuronal NADPH oxidase and whether this contributes to oxidative damage and consequently to neurodegeneration. Immunocytochemical and biochemical evidence demonstrated that, in neuron-enriched hippocampal cultures, thrombin induces neurodegeneration in a dose-dependent manner. In parallel, ROS production was evident as assessed by analyzing DCF and hydroethidine. Real-time PCR analysis, at various time points after thrombin treatment, also demonstrated that expression of NADPH oxidase subunits (p47(phox) and p67(phox)) occurs. In addition, Western blot analysis and double-label immunocytochemistry showed an up-regulation in the expression of cytosolic components (Rac 1 and p67(phox)), the translocation of cytosolic proteins (p47(phox) and p67(phox)) to the membrane, and the localization of gp91(phox) or p47(phox) expression in hippocampal neurons of cultures and CA1 layer. The thrombin-induced ROS production, protein oxidation, and loss of cultured hippocampal neurons were partially attenuated by an NADPH oxidase inhibitor and/or by several antioxidants. Collectively, the present study is the first to demonstrate that, in cultured hippocampal neurons, thrombin-induced neurotoxicity is, at least in part, caused by neuronal NADPH oxidase-mediated oxidative stress. This strongly suggests that thrombin can act as an endogenous neurotoxin, and inhibitors of thrombin and/or antioxidants can be useful agents for treating oxidative stress-mediated hippocampal neurodegenerative diseases, such as Alzheimer's disease.

Structure analysis of activity-dependent neurotrophic factor 9 by circular dichroism and sedimentation equilibrium

Activity-dependent neurotrophic factor (ADNF) is a glia-derived neurotrophic peptide, which protects neurons from tetrodoxin treatment and Alzheimer's disease-related and amyotrophic-lateral-sclerosis-related insults at femto-molar concentrations. However, the mechanism of the femto-molar neuroprotection by the peptide has not been elucidated. The characterization of the peptide structure in solution at molecular level should shed light in the mechanism of such extremely high biological activity. From that point of view, the secondary and quaternary structure analysis of ADNF9, an active core fragment peptide of ADNF, was performed by circular dichroism (CD) and sedimentation equilibrium. ADNF9 has also been shown to exhibit a neurotrophic activity in femto-molar concentrations; in this study it showed sub-pM neuroprotective activity against V642I-APP-induced cytotoxity in the mouse primary cortical neuron. CD analysis showed that the secondary structure of ADNF9 is identical in water and phosphate-buffered saline (PBS) and is independent of the peptide concentration. The CD spectra appear to be characterized most likely as disordered. The sedimentation equilibrium experiments demonstrated monomeric structure of the protein over the wide range of peptide concentration. There is a slight enhancement of CD intensity at 37 degrees C relative to 20 degrees C, suggesting a possible hydrophobic association of the peptide. There is no change in the secondary structure in PBS upon freeze-thaw treatment, which has previously been suggested to cause activity loss.

Critical role of methionine-722 in the stimulation of human brain G-proteins and neurotoxicity induced by London familial Alzheimer's disease (FAD) mutated V717G-APP(714-723)

We have demonstrated earlier that V717G-APP(714-723), the membrane fragment of the V717G ("London") familial Alzheimer's disease (FAD) mutant of amyloid precursor protein (APP), is a potent stimulator of G-proteins in human brain membranes. In this study, we tested the hypothesis that Met-722 in the V717G-APP(714-723) peptide (P2) plays a critical role in the P2-induced oxidative stimulation of G-proteins in the human temporal cortex membranes and in the neurotoxicity of the peptide in differentiated PC12 and cerebellar granular cells. We found that 10 microM P3, the Met-722 sulfoxide analog of P2, produced a twofold lower stimulation of G-proteins ([(35)S]-GTPgammaS binding) in control temporal cortex membranes compared with 10 microM P2. The stimulatory effect of 10 microM P4, the Met-722 sulfone analog of P2, was 2.5-fold lower than the effect of P2. In Alzheimer's disease (AD) temporal cortex, the P3 and P4 stimulation of G-proteins was slightly weaker than the P2 stimulation. Substitution of the Met-722 S-atom in P2 by -CH(2)- group (P5) led to the disappearance of P2 stimulatory effect on G-proteins. Glutathione (GSH), melatonin (Mel), desferrioxamine (DFO) and 17-beta-estradiol (17betaE) significantly reduced P2 stimulatory effect on G-proteins in human brain. Only DFO and Mel were able to reduce the moderate stimulation of G-proteins by P3, whereas none of the tested antioxidants influenced the weak stimulation by P4. P2 at 100 microM induced a 40% decrease in PC12 cell viability as revealed by MTT assay, the effect being significantly higher than that of P3 or P4, whereas P1 (wild-type APP(714-723)) did not affect cell viability. Trypan Blue exclusion assay demonstrated that 10 microM P2 and P3 induced 3.8- and 3.5-fold death in the cerebellar granular cells as compared with the respective control values. P1 and P4 at 10 microM induced 1.7- and 2.3-fold increase in cell death, respectively. Treatment of the cerebellar granular cells with pertussis toxin decreased the high neurotoxicity of P2 and P3, whereas the low toxicity of P1 and P4 was not influenced. These results support the hypothesis that the G-protein stimulatory effect and neurotoxicity of "London"-mutated V717G-APP(714-723) (P2) and its Met-722 oxidized analogs involve oxidative-dependent and oxidative-independent mechanisms and the oxidation state of Met-722 plays a critical role in determining the mechanism.

Humanin and colivelin: neuronal-death-suppressing peptides for Alzheimer's disease and amyotrophic lateral sclerosis

Humanin (HN), a 24-amino-acid neuroprotective peptide, was originally found in the occipital lobe of an autopsied Alzheimer's disease (AD) patient. HN inhibits neuronal death by binding to its specific receptor on the cell membrane and triggering a Jak2/STAT3 prosurvival pathway. The activation of this pathway may represent a therapeutic approach to AD. HN also exhibits neuroprotective activity against toxicity by familial amyotrophic lateral sclerosis (ALS)-related mutant superoxide dismutase (SOD1). Recent investigations established that AGA-(C8R)-HNG17, a 17-amno-acid derivative of HN, is 10(5) times more potent as a neuroprotective than HN; at 10-picomolar and higher concentrations in vitro it completely suppresses neuronal death. Moreover, a 26-amino-acid peptide colivelin (CL), composed of activity-dependent neurotrophic factor (ADNF) C-terminally fused to AGA-(C8R)-HNG17, provides complete neuroprotection at 100-femtomolar or higher concentrations in vitro. A series of experiments using mouse AD and ALS models further established the efficacy of HN derivatives, including CL, against these diseases in vivo. HN and CL can be viewed as drug candidates for neuronal death suppression therapy in AD or ALS.

Thrombin-induced oxidative stress contributes to the death of hippocampal neurons in vivo: role of microglial NADPH oxidase

The present study investigated whether thrombin, a potent microglial activator, can induce reactive oxygen species (ROS) generation through activation of microglial NADPH oxidase and if this may contribute to oxidative damage and consequent neurodegeneration. Seven days after intrahippocampal injection of thrombin, Nissl staining and immunohistochemistry using the neuronal-specific nuclear protein NeuN revealed a significant loss in hippocampal CA1 neurons. In parallel, thrombin-activated microglia, assessed by OX-42 and OX-6 immunohistochemistry, and ROS production, assessed by hydroethidine histochemistry, were observed in the hippocampal CA1 area in which degeneration of hippocampal neurons occurred. Reverse transcription-PCR at various time points after thrombin administration demonstrated an early and transient expression of inducible nitric oxide synthase (iNOS) and several proinflammatory cytokines. Western blot analysis and double-label immunohistochemistry showed an increase in the expression of and the localization of iNOS within microglia. Additional studies demonstrated that thrombin induced the upregulation of membrane (gp91(phox)) and cytosolic (p47(phox) and p67(phox)) components, translocation of cytosolic proteins (p47(phox), p67(phox), and Rac1) to the membrane, and p67(phox) expression of the NADPH oxidase in microglia in the hippocampus in vivo, indicating the activation of NADPH oxidase. The thrombin-induced oxidation of proteins and loss of hippocampal CA1 neurons were partially inhibited by an NADPH oxidase inhibitor and by an antioxidant. To our knowledge, the present study is the first to demonstrate that thrombin-induced neurotoxicity in the hippocampus in vivo is caused by microglial NADPH oxidase-mediated oxidative stress. This suggests that thrombin inhibition or enhancing antioxidants may be beneficial for the treatment of neurodegenerative diseases, such as Alzheimer's disease, that are associated with microglial-derived oxidative damage.

Transforming growth factor beta2 is a neuronal death-inducing ligand for amyloid-beta precursor protein

APP, amyloid beta precursor protein, is linked to the onset of Alzheimer's disease (AD). We have here found that transforming growth factor beta2 (TGFbeta2), but not TGFbeta1, binds to APP. The binding affinity of TGFbeta2 to APP is lower than the binding affinity of TGFbeta2 to the TGFbeta receptor. On binding to APP, TGFbeta2 activates an APP-mediated death pathway via heterotrimeric G protein G(o), c-Jun N-terminal kinase, NADPH oxidase, and caspase 3 and/or related caspases. Overall degrees of TGFbeta2-induced death are larger in cells expressing a familial AD-related mutant APP than in those expressing wild-type APP. Consequently, superphysiological concentrations of TGFbeta2 induce neuronal death in primary cortical neurons, whose one allele of the APP gene is knocked in with the V642I mutation. Combined with the finding indicated by several earlier reports that both neural and glial expression of TGFbeta2 was upregulated in AD brains, it is speculated that TGFbeta2 may contribute to the development of AD-related neuronal cell death.

Inhibition of thrombin-induced microglial activation and NADPH oxidase by minocycline protects dopaminergic neurons in the substantia nigra in vivo

The present study shows that activation of microglial NADPH oxidase and production of reactive oxygen species (ROS) is associated with thrombin-induced degeneration of nigral dopaminergic neurons in vivo. Seven days after thrombin injection in the rat substantia nigra (SN), tyrosine hydroxylase immunocytochemistry showed a significant loss of nigral dopaminergic neurons. This cell death was accompanied by localization of terminal deoxynucleotidyl transferase-mediated fluorecein UTP nick-end labelling (TUNEL) staining within dopaminergic neurons. This neurotoxicity was antagonized by the semisynthetic tetracycline derivative, minocycline, and the observed neuroprotective effects were associated with the ability of minocycline to suppress NADPH oxidase-derived ROS production and pro-inflammatory cytokine expression, including interleukin-1beta and inducible nitric oxide synthase, from activated microglia. These results suggest that microglial NADPH oxidase may be a viable target for neuroprotection against oxidative damage.

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.