Cell Death In Alzheimer's Disease Research Articles

Relationship Between β-Amyloid and Mitochondrial Dynamics.

Mitochondria as dynamic organelles undergo morphological changes through the processes of fission and fusion which are major factors regulating their functions. A disruption in the balance of mitochondrial dynamics induces functional disorders in mitochondria such as failed energy production and the generation of reactive oxygen species, which are closely related to pathophysiological changes associated with Alzheimer's disease (AD). Recent studies have demonstrated a relationship between abnormalities in mitochondrial dynamics and impaired mitochondrial function, clarifying the effects of morphofunctional aberrations which promote neuronal cell death in AD. Several possible signaling pathways have been suggested for a better understanding of the mechanism behind the key molecules regulating mitochondrial morphologies. However, the exact machinery involved in mitochondrial dynamics still has yet to be elucidated. This paper reviews the current knowledge on signaling mechanisms involved in mitochondrial dynamics and the significance of mitochondrial dynamics in controlling associated functions in neurodegenerative diseases, particularly in AD.

The Polyphenol Oleuropein Aglycone Modulates the PARP1-SIRT1 Interplay: AnIn Vitro and In Vivo Study.

Poly(ADP-ribose) polymerase-1 (PARP1) activation contributes to the cascade of events initiated by amyloid-β (Aβ) peptide eventually leading to cell death in Alzheimer's disease brain. A significant accumulation of PAR polymers and increase of PARP1 expression were detected in the cortex at the early (3.5 months) and intermediate (6 months) stage of Aβ deposition in the TgCRND8 mouse model. Our previous data highlighted the beneficial effects of oleuropein aglycone (OLE), the main polyphenol found in the olive oil, against neurodegeneration both in cultured cells and in model organisms. Here we found that 8-week OLE treatment (50 mg/kg of diet) to 6-month-old TgCRND8 mice rescued to control values PARP1 activation and the levels of its product, PAR. In N2a neuroblastoma cells, PARP1 activation and PAR formation upon exposure to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were abolished by pretreatment for 24 h with either OLE (100μM) or PARP inhibitors. A significant reduction of the NAD+ content, compared to controls, was found in N2a cells exposed to MNNG (100μM) for 90 min; the latter was slightly attenuated by cell treatment for 24 h with PJ-34 or with OLE. In vitro and in vivo, the OLE-induced reduction of PARP1 activation was paralleled by the overexpression of Sirtuin1 (SIRT1), and, in vivo, by a decrease of NF-κB and the pro-apoptotic marker p53. In N2a cells, we also found that OLE potentiates the MNNG-induced increase of Beclin1 levels. In conclusion, our data show that OLE treatment counteracts neuronal damage through modulation of the PARP1-SIRT1 interplay.

The levels of 7,8-dihydrodeoxyguanosine (8-oxoG) and 8-oxoguanine DNA glycosylase 1 (OGG1) – A potential diagnostic biomarkers of Alzheimer's disease

Evidence indicates that oxidative stress contributes to neuronal cell death in Alzheimer's disease (AD). Increased oxidative DNA damage l, as measured with 8-oxoguanine (8-oxoG), and reduced capacity of proteins responsible for removing of DNA damage, including 8-oxoguanine DNA glycosylase 1 (OGG1), were detected in brains of AD patients. In the present study we assessed peripheral blood biomarkers of oxidative DNA damage, i.e. 8- oxoG and OGG1, in AD diagnosis, by comparing their levels between the patients and the controls. Our study was performed on DNA and serum isolated from peripheral blood taken from 100 AD patients and 110 controls. For 8-oxoG ELISA was employed. The OGG1 level was determined using ELISA and Western blot technique. Levels of 8-oxoG were significantly higher in DNA of AD patients. Both ELISA and Western blot showed decreased levels of OGG1 in serum of AD patients. Our results show that oxidative DNA damage biomarkers detected in peripheral tissue could reflect the changes occurring in the brain of patients with AD. These results also suggest that peripheral blood samples may be useful to measure oxidative stress biomarkers in AD.

Accumulation of amyloid-β by astrocytes result in enlarged endosomes and microvesicle-induced apoptosis of neurons.

BackgroundDespite the clear physical association between activated astrocytes and amyloid-β (Aβ) plaques, the importance of astrocytes and their therapeutic potential in Alzheimer’s disease remain elusive. Soluble Aβ aggregates, such as protofibrils, have been suggested to be responsible for the widespread neuronal cell death in Alzheimer’s disease, but the mechanisms behind this remain unclear. Moreover, ineffective degradation is of great interest when it comes to the development and progression of neurodegeneration. Based on our previous results that astrocytes are extremely slow in degrading phagocytosed material, we hypothesized that astrocytes may be an important player in these processes. Hence, the aim of this study was to clarify the role of astrocytes in clearance, spreading and neuronal toxicity of Aβ.ResultsTo examine the role of astrocytes in Aβ pathology, we added Aβ protofibrils to a co-culture system of primary neurons and glia. Our data demonstrates that astrocytes rapidly engulf large amounts of Aβ protofibrils, but then store, rather than degrade the ingested material. The incomplete digestion results in a high intracellular load of toxic, partly N-terminally truncated Aβ and severe lysosomal dysfunction. Moreover, secretion of microvesicles containing N-terminally truncated Aβ, induce apoptosis of cortical neurons.ConclusionsTaken together, our results suggest that astrocytes play a central role in the progression of Alzheimer’s disease, by accumulating and spreading toxic Aβ species.Electronic supplementary materialThe online version of this article (doi:10.1186/s13024-016-0098-z) contains supplementary material, which is available to authorized users.

Lycopene Inhibits Amyloid‐β25–35‐Induced Apoptosis by Decreasing Intracellular and Mitochondrial ROS Levels in Human Neuronal SH‐SY5Y Cells

Alzheimer's disease (AD) is a major neurodegenerative disorder which is characterized by amyloid‐beta (Aβ) plaque and neurofibrillary tangles. The accumulation of Aβ in the brain is a crucial feature of AD, which causes cell death in AD by evoking a cascade of oxidative damage to neuronal cells. Lycopene, a carotenoid family, has been recognized as an antioxidant to protect oxidative stress‐induced cell damage in several cell lines.In this study, we investigated the effect of lycopene on Aβ25–35‐induced cytotoxicity in human neuronal SH‐SY5Y cells. SH‐SY5Y cells were widely used a typical model for AD.Cell viability was measured by MTT assay, and apoptotic evidence (bax, bcl‐2, and caspase‐3) was assessed by Western blotting.Our results showed that exposure of cells to Aβ25–35 induces apoptotic cell death by increasing Bax/Bcl‐2 ratio and caspase‐3 activation. In addition, Aβ25–35 increased levels of intracellular reactive oxygen species (ROS) and mitochondrial ROS. Lycopene significantly suppressed viability loss and decreased apoptotic indices (increased Bax/Bcl‐2 ratio and caspase‐3 activation) in Aβ25–35 treated cells. Lycopene reduced the levels of intracellular and mitochondrial ROS in the cells, which was evoked by exposure to Aβ25–35.These results suggest that lycopene attenuates the Aβ25–35‐induced apoptosis by decreasing intracellular and mitochondrial ROS levels in neuronal cells. Lycopene supplementation may be beneficial for preventing neuronal cell death of the patients with Alzheimer's disease.

Increased Levels of Extracellular Microvesicle Markers and Decreased Levels of Endocytic/Exocytic Proteins in the Alzheimer's Disease Brain.

Alzheimer's disease (AD) is a chronic neurodegenerative disorder accounting for more than 50% of all dementia cases. AD neuropathology is characterized by the formation of extracellular plaques and intracellular neurofibrillary tangles consisting of aggregated amyloid-β and tau, respectively. The disease mechanism has only been partially elucidated and is believed to also involve many other proteins. This study intended to perform a proteomic profiling of post mortem AD brains and compare it with control brains as well as brains from other neurological diseases to gain insight into the disease pathology. Here we used label-free shotgun mass spectrometry to analyze temporal neocortex samples from AD, other neurological disorders, and non-demented controls, in order to identify additional proteins that are altered in AD. The mass spectrometry results were verified by antibody suspension bead arrays. We found 50 proteins with altered levels between AD and control brains. The majority of these proteins were found at lower levels in AD. Pathway analyses revealed that several of the decreased proteins play a role in exocytic and endocytic pathways, whereas several of the increased proteins are related to extracellular vesicles. Using antibody-based analysis, we verified the mass spectrometry results for five representative proteins from this group of proteins (CD9, HSP72, PI42A, TALDO, and VAMP2) and GFAP, a marker for neuroinflammation. Several proteins involved in exo-endocytic pathways and extracellular vesicle functions display altered levels in the AD brain. We hypothesize that such changes may result in disturbed cellular clearance and a perturbed cell-to-cell communication that may contribute to neuronal dysfunction and cell death in AD.

RAGE mediated intracellular Aβ uptake contributes to the breakdown of tight junction in retinal pigment epithelium.

Intracellular amyloid beta (Aβ) has been implicated in neuronal cell death in Alzheimer's disease (AD). Intracellular Aβ also contributes to tight junction breakdown of retinal pigment epithelium (RPE) in age-related macular degeneration (AMD). Although Aβ is predominantly secreted from neuronal cells, the mechanism of Aβ transport into RPE remains to be fully elucidated. In this study, we demonstrated that intracellular Aβ was found concomitantly with the breakdown of tight junction in RPE after subretinal injection of Aβ into the mouse eye. We also presented evidence that receptor for advanced glycation end products (RAGE) contributed to endocytosis of Aβ in RPE. siRNA-mediated knockdown of RAGE prevented intracellular Aβ accumulation as well as subsequent tight junction breakdown in RPE. In addition, we found that RAGE-mediated p38 MAPK signaling contributed to endocytosis of Aβ. Blockade of RAGE/p38 MAPK signaling inhibited Aβ endocytosis, thereby preventing tight junction breakdown in RPE. These results implicate that intracellular Aβ contributes to the breakdown of tight junction in RPE via the RAGE/p38 MAPK-mediated endocytosis. Thus, we suggest that RAGE could be a potential therapeutic target for intracellular Aβ induced outer BRB breakdown in AMD.

Abstract 11: Molecular mechanisms of inverse association between cancer and Alzheimer's disease

Abstract Apoptosis has been implicated in both cancer and neurodegenerative disease such as Alzheimer's disease (AD). Defective or inefficient apoptosis is an acquired hallmark of cancer cells, while cytochrome c-dependent apoptosis is a crucial pathway in AD related neuronal cell death. Notably, recent studies have revealed an inverse correlation between development of cancer and AD—AD patients show a reduced risk of cancer, while cancer survivors are less likely to acquire AD. Here we propose that amyloid β (Aβ), a widely accepted pathological culprit of AD, hijacks the intrinsic apoptotic pathway eliciting different symptoms for cancer and AD. By developing an in vitro single-vesicle cytochrome c release assay, we show that even in the absence of death signal the oligomeric form of synthetic Aβ directly interacts with a pro-apoptotic bcl-2 family protein BAK and induces apoptotic pores sufficient for cytochrome c release. Furthermore, Aβ oligomers not only cause neuronal cell death in HT-22 cells but also the apoptotic effect was significantly reduced with suppressed BAK expression via siRNA, further substantiating its apoptotic interaction with BAK. Moreover, a significant reduction of cytochrome c release was also observed with isolated mitochondria from BAK siRNA-treated HT-22 cells which specifically identifies the target machinery. These results demonstrate Aβ oligomers’ efficacy as a potent apoptotic ligand. In collection, we suggest that while Aβ oligomers may cause neuronal cell death in AD it may also ameliorate tumor proliferation in relation to cancer. Thus, providing molecular level evidence for the inverse association reported between cancer and AD patients. Citation Format: Yoosoo Yang, EunJung Lee, In-San Kim. Molecular mechanisms of inverse association between cancer and Alzheimer's disease. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 11. doi:10.1158/1538-7445.AM2015-11

Amyloid-β peptide-induced cytotoxicity and mitochondrial dysfunction in yeast.

Alzheimer's disease (AD) is the most common neurodegenerative disease, characterized by deposits of amyloid-β (Aβ) peptides. However, the underlying molecular mechanisms of neuron cell dysfunction and cell death in AD still remain poorly understood. Yeast Saccharomyces cerevisiae shares many conserved biological processes with all eukaryotic cells, including human neurons. Thanks to relatively simple and quick genetic and environmental manipulations, the large knowledge base and data collections, this organism has become a valuable tool to unravel fundamental intracellular mechanisms underlying neurodegeneration. In this study, we have used yeast as a model system to study the effects of intracellular Aβ peptides and we found that cells constitutively producing native Aβ directed to the secretory pathway exhibited a lower growth rate, lower biomass yield, lower respiratory rate, increased oxidative stress, hallmarks of mitochondrial dysfunction and ubiquitin-proteasome system dysfunction. These findings are relevant for better understanding the role of Aβ in cell stress and cell damage.

Heat-shock protein HSP70 protects neuroblastoma cells SK-N-SH from the neurotoxic effects hydrogen peroxide and the β-amyloid peptide

Neuronal cell death in Alzheimer's disease is associated with the development of oxidative stress caused by the reactive oxygen species (ROS), which can be generated as a result of the effect of beta-amyloid peptides. One of the sources of ROS is hydrogen peroxide, inducing the apoptosis and necrosis of neural tissue cells. The mechanism of hydrogen peroxide apoptotic action includes launching signaling pathways that involve protein kinases PI3K, p38MAPK, JNK and ERK. Oxidative stress leads to increased synthesis of heat-shock proteins in the cells including HSP70. It was shown that the exogenous HSP70 could reduce generation of ROS in cells. In this study, we determined how HSP70 affected apoptosis and necrosis in human neuroblastoma cells SK-N-SH, induced by hydrogen peroxide and β-amyloid peptide Aβ(1-42). It was shown that HSP70 reduces the cytotoxic effects of hydrogen peroxide and beta-amyloid, and protein kinases PI3K and JNK play an important role in the mechanism of HSP70 protective effect on the peroxide induced apoptosis in SK-N-SH cells.

Influence of Sequence and Lipid Type on Membrane Perturbation by Human and Rat Amyloid β-Peptide (1-42)

The hallmark characteristics of plaque formation and neuronal cell death in Alzheimer's disease (AD) are caused principally by the amyloid β-peptide (Aβ). Current research focuses on understanding the interactions between Aβ and neuronal cell membranes, given the relationship between membrane perturbation and neurotoxicity. Aβ sequence and lipid composition are essential variables to consider when elucidating the impact of the biological membrane on Aβ structure and the effect of Aβ on membrane integrity. Atomistic molecular dynamics simulations testing two Aβ sequences (Human Aβ1-42) (HAβ) and Rat Aβ(1-42) (RAβ)), five lipid types, and totaling 9 μs in simulation time, were performed in order to explain the effect of these variables on membrane perturbation. All metrics used to assess membrane perturbation agree insomuch that it can be concluded that HAβ and RAβ contribute to membrane perturbation by causing a more rigid, gel-like lipid phase. The presence of cholesterol in a model raft membrane was found to moderate the amount of perturbation caused by HAβ and RAβ. Differences between HAβ and RAβ were seen based on lipid headgroup charge and hydrogen bond capacity. The position of arginine in the N-terminal region was determined to be the mediating factor in these differences in lipid affinity and disruption between HAβ and RAβ. Overall, this work rationalizes the influence of sequence and lipid type on Aβ-membrane interactions, providing mechanistic insight into the etiology of AD.

Inflammation and Programmed Cell Death in Alzheimer’s Disease: Comparison of the Central Nervous System and Peripheral Blood

Although the central nervous system (CNS) has been defined as a privileged site in Alzheimer's disease (AD), periphery can be more than simply witness of events leading to neurodegeneration. The CNS and peripheral blood can mutually communicate through cells and factors trafficking from the circulation into the brain and vice versa. A number of articles have reviewed inflammatory profiles and programmed cell death (PCD) in AD, separately in the CNS and at the peripheral level. This review does not provide an exhaustive account of what has been published on inflammation and PCD in AD. Rather, the aim of this review is to focus on possible linkages between the central and the peripheral compartments during AD progression, by critically analyzing, in a comparative manner, phenomena occurring in the CNS as well as the peripheral blood. In fact, growing evidence suggests that CNS and peripheral inflammation might present common features in the disease. Microarrays and metabolomics revealed that dysfunction of the glycolytic and oxidative pathways is similar in the brain and in the periphery. Moreover, dysregulated autophagosome/lysosomal molecular machinery, both at the CNS and the peripheral level, in AD-related cell damage, has been observed. Possible implications of these observations have been discussed.

Transcriptional signaling pathways inversely regulated in Alzheimer's disease and glioblastoma multiform

Convincing epidemiological data suggest an inverse association between cancer and neurodegeneration, including Alzheimer's disease (AD). Since both AD and cancer are characterized by abnormal, but opposing cellular behavior, i.e., increased cell death in AD while excessive cell growth occurs in cancer, this motivates us to initiate the study into unraveling the shared genes and cell signaling pathways linking AD and glioblastoma multiform (GBM). In this study, a comprehensive bioinformatics analysis on clinical microarray datasets of 1,091 GBM and 524 AD cohorts was performed. Significant genes and pathways were identified from the bioinformatics analyses – in particular ERK/MAPK signaling, up-regulated in GBM and Angiopoietin Signaling pathway, reciprocally up-regulated in AD – connecting GBM and AD (P < 0.001), were investigated in details for their roles in GBM growth in an AD environment. Our results showed that suppression of GBM growth in an AD background was mediated by the ERK-AKT-p21-cell cycle pathway and anti-angiogenesis pathway.

Type-1 interferon signaling mediates neuro-inflammatory events in models of Alzheimer's disease

A neuro-inflammatory response has been implicated in human patients and animal models of Alzheimer's disease (AD). Type-1 interferons are pleiotropic cytokines involved in the initiation and regulation of the pro-inflammatory response; however, their role in AD is unknown. This study investigated the contribution of type-1 IFN signaling in the neuro-inflammatory response to amyloid-beta (Aβ) in vitro and in the APP/PS1 transgenic mouse model of AD. Enzyme-linked immunosorbent assay confirmed a 2-fold increase in IFNα in APP/PS1 brains compared with control brains. Quantitative polymerase chain reaction also identified increased IFNα and IFNβ expression in human pre-frontal cortex from AD patients. In vitro studies in primary neurons demonstrated Aβ-induced type-1 IFN expression preceded that of other classical pro-inflammatory cytokines, IL1-β, and IL-6. Significantly, ablation of type-1 interferon-α receptor 1 expression in BE(2)M17 neuroblastoma cells and primary neurons afforded protection against Aβ-induced toxicity. This study supports a role for type-1 interferons in the pro-inflammatory response and neuronal cell death in AD and suggests that blocking type-1 interferon-α receptor 1 maybe a therapeutic target to limit the disease progression.

Knockout of Toll-like receptor 2 attenuates Aβ25–35-induced neurotoxicity in organotypic hippocampal slice cultures

Toll-like receptors (TLRs), which have been implicated in various neuroinflammatory responses, are thought to act in defense mechanisms by inhibiting neuronal cell death in Alzheimer’s disease. In this study, we evaluated the effects of TLR2 on amyloid beta peptide 25–35 (Aβ25–35)-induced neuronal cell death, synaptic dysfunction, and microglial activation in organotypic hippocampal slice cultures (OHSCs) from wild-type (WT) C57BL/6 mice and TLR2-knockout (KO) mice. In WT mice, Aβ25–35 induced β-amyloid aggregation and surrounding TLR2 expression. And, propidium iodide (PI) uptake, which is a measure of cell death, increased in a dose-dependent manner in slices with Aβ25–35 treatment. In the Aβ25–35-treated TLR2-KO OHSCs, the PI uptake was significantly attenuated to the control level, indicating that the cells were less susceptible to Aβ25–35-induced neuronal toxicity. In the ultrastructural analysis, nuclear shrinkage, slightly swollen mitochondria, and degraded organelles were detected in the Aβ25–35-treated slices from WT mice but not in the Aβ25–35-treated slices from TLR2-KO, suggesting the resistance of TLR2-KO to Aβ25–35-induced neurotoxicity. In Aβ25–35-treated OHSCs of WT mice, the levels of phosphorylated tau were increased and the levels of synaptophysin were decreased in a dose-dependent manner, but they were not changed in OHSCs of TLR2-KO mice. In WT mice, Aβ25–35 increased total protein level and immunoreactivity of Iba-1, which was colocalized with TLR2. However, there were no significant changes in the slices of Aβ25–35-treated TLR2-KO mice. These results suggested that TLR2 may play a role in Aβ25–35-induced neuronal cell loss and synaptic dysfunction through the activation of microglia in OHSCs.

Modulation of 5-Lipoxygenase in Proteotoxicity and Alzheimer's Disease

The accumulation of intracellular β amyloid (Aβ) may be one of the factors leading to neuronal cell death in Alzheimer's disease (AD). Using a pyrazole called CNB-001, which was selected for its ability to reduce intracellular Aβ, we show that the activation of the eIF2α/ATF4 arm of the unfolded protein response is sufficient to degrade aggregated intracellular Aβ. CNB-001 is a potent inhibitor of 5-lipoxygenase (5-LOX), decreases 5-LOX expression, and increases proteasome activity. 5-LOX inhibition induces eIF2α and PERK (protein kinase R-like extracellular signal-regulated kinase) phosphorylation, and HSP90 and ATF4 levels. When fed to AD transgenic mice, CNB-001 also increases eIF2α phosphorylation and HSP90 and ATF4 levels, and limits the accumulation of soluble Aβ and ubiquitinated aggregated proteins. Finally, CNB-001 maintains the expression of synapse-associated proteins and improves memory. Therefore, 5-LOX metabolism is a key element in the promotion of endoplasmic reticulum dysfunction, and its inhibition under conditions of stress is sufficient to reduce proteotoxicity both in vivo and in vitro.

Natural Products as Promising Drug Candidates for the Treatment of Alzheimer’s Disease: Molecular Mechanism Aspect

Alzheimer's disease (AD) is the most common neurodegenerative disorder to date, with no curative or preventive therapy. Histopathological hallmarks of AD include deposition of β-amyloid plaques and formation of neurofibrillary tangles. Extent studies on pathology of the disease have made important discoveries regarding mechanism of disease and potential therapeutic targets. Many cellular changes including oxidative stress, disruption of Ca2+ homeostasis, inflammation, metabolic disturbances, and accumulation of unfolded/misfolded proteins can lead to programmed cell death in AD. Despite intensive research, only five approved drugs are available for the management of AD. Hence, there is a need to look at alternative therapies. Use of natural products and culinary herbs in medicine has gained popularity in recent years. Several natural substances with neuroprotective effects have been widely studied. Most of these compounds have remarkable antioxidant properties and act mainly by scavenging free radical species. Some of them increase cell survival and improve cognition by directly affecting amyloidogenesis and programmed cell death pathways. Further studies on these natural products and their mechanism of action, parallel with the use of novel pharmaceutical drug design and delivery techniques, enable us to offer an addition to conventional medicine. This review discussed some natural products with potential neuroprotective properties against Aβ with respect to their mechanism of action.

Molecular Mechanism of the Inhibition of EGCG on the Alzheimer Aβ1–42Dimer

Growing evidence supports that amyloid β (Aβ) oligomers are the major causative agents leading to neural cell death in Alzheimer's disease. The polyphenol (-)-epigallocatechin gallate (EGCG) was recently reported to inhibit Aβ fibrillization and redirect Aβ aggregation into unstructured, off-pathway oligomers. Given the experimental challenge to characterize the structures of Aβ/EGCG complexes, we performed extensive atomistic replica exchange molecular dynamics simulations of Aβ1-42 dimer in the present and absence of EGCG in explicit solvent. Our equilibrium Aβ dimeric structures free of EGCG are consistent with the collision cross section from ion-mobility mass spectrometry and the secondary structure composition from circular dichroism experiment. In the presence of EGCG, the Aβ structures are characterized by increased inter-center-of-mass distances, reduced interchain and intrachain contacts, reduced β-sheet content, and increased coil and α-helix contents. Analysis of the free energy surfaces reveals that the Aβ dimer with EGCG adopts new conformations, affecting therefore its propensity to adopt fibril-prone states. Overall, this study provides, for the first time, insights on the equilibrium structures of Aβ1-42 dimer in explicit aqueous solution and an atomic picture of the EGCG-mediated conformational change on Aβ dimer.

Extra-cell cycle regulatory functions of cyclin-dependent kinases (CDK) and CDK inhibitor proteins contribute to brain development and neurological disorders.

In developing brains, neural progenitors exhibit cell cycle-dependent nuclear movement within the ventricular zone [interkinetic nuclear migration (INM)] and actively proliferate to produce daughter progenitors and/or neurons, whereas newly generated neurons exit from the cell cycle and begin pial surface-directed migration and maturation. Dysregulation of the balance between the proliferation and the cell cycle exit in neural progenitors is one of the major causes of microcephaly (small brain). Recent studies indicate that cell cycle machinery influences not only the proliferation but also INM in neural progenitors. Furthermore, several cell cycle-related proteins, including p27kip1, p57kip2, Cdk5, and Rb, regulate the migration of neurons in the postmitotic state, suggesting that the growth arrest confers dual functions on cell cycle regulators. Consistently, several types of microcephaly occur in conjunction with neuronal migration disorders, such as periventricular heterotopia and lissencephaly. However, cell cycle re-entry by disturbance of growth arrest in mature neurons is thought to trigger neuronal cell death in Alzheimer's disease. In this review, we introduce the cell cycle protein-mediated regulation of two types of nuclear movement, INM and neuronal migration, during cerebral cortical development, and discuss the roles of growth arrest in cortical development and neurological disorders.

The N-Methylated Peptide SEN304 Powerfully Inhibits Aβ(1–42) Toxicity by Perturbing Oligomer Formation

Oligomeric forms of β-amyloid (Aβ) have potent neurotoxic activity and are the primary cause of neuronal injury and cell death in Alzheimer's disease (AD). Compounds that perturb oligomer formation or structure may therefore be therapeutic for AD. We previously reported that d-[(chGly)-(Tyr)-(chGly)-(chGly)-(mLeu)]-NH(2) (SEN304) is able to inhibit Aβ aggregation and toxicity, shown primarily by thioflavin T fluorescence and MTT (Kokkoni, N. et al. (2006) N-Methylated peptide inhibitors of β-amyloid aggregation and toxicity. Optimisation of inhibitor structure. Biochemistry 45, 9906-9918). Here we extensively characterize how SEN304 affects Aβ(1-42) aggregation and toxicity, using biophysical assays (thioflavin T, circular dichroism, SDS-PAGE, size exclusion chromatography, surface plasmon resonance, traveling wave ion mobility mass spectrometry, electron microscopy, ELISA), toxicity assays in cell culture (MTT and lactate dehydrogenase in human SH-SHY5Y cells, mouse neuronal cell death and synaptophysin) and long-term potentiation in a rat hippocampal brain slice. These data, with dose response curves, show that SEN304 is a powerful inhibitor of Aβ(1-42) toxicity, particularly effective at preventing Aβ inhibition of long-term potentiation. It can bind directly to Aβ(1-42), delay β-sheet formation and promote aggregation of toxic oligomers into a nontoxic form, with a different morphology that cannot bind thioflavin T. SEN304 appears to work by inducing aggregation, and hence removal, of Aβ oligomers. It is therefore a promising lead compound for Alzheimer's disease.