Cell Death In Alzheimer's Disease Research Articles

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.

Endoplasmic Reticulum Enrollment in Alzheimer’s Disease

Alzheimer's disease (AD) poses a huge challenge for society and health care worldwide as molecular pathogenesis of the disease is poorly understood and curative treatment does not exist. The mechanisms leading to accelerated neuronal cell death in AD are still largely unknown, but accumulation of misfolded disease-specific proteins has been identified as potentially involved. In the present review, we describe the essential role of endoplasmic reticulum (ER) in AD. Despite the function that mitochondria may play as the central major player in the apoptotic process, accumulating evidence highlights ER as a critical organelle in AD. Stress that impairs ER physiology leads to accumulation of unfolded or misfolded proteins, such as amyloid β (Aβ) peptide, the major component of amyloid plaques. In an attempt to ameliorate the accumulation of unfolded proteins, ER stress triggers a protective cellular mechanism, which includes the unfolded protein response (UPR). However, when activation of the UPR is severe or prolonged enough, the final cellular outcome is pathologic apoptotic cell death. Distinct pathways can be activated in this process, involving stress sensors such as the JNK pathway or ER chaperones such as Bip/GRP94, stress modulators such as Bcl-2 family proteins, or even stress effectors such as caspase-12. Here, we detail the involvement of the ER and associated stress pathways in AD and discuss potential therapeutic strategies targeting ER stress.

Endosymbiotic Actinidic Archaea and Viroids Regulate Cellular Organelle Function, Cell Growth, Cell Differentiation and Cell Death

Background: A hypothesis regarding the role of endosymbiotic actinidic archaea and viroids in the regulation of cell function, cell differentiation, cell proliferation and cell death is discussed. Endomyocardial fibrosis (EMF) along with the root wilt disease of coconut is endemic to Kerala with its radioactive actinide beach sands. Actinides like rutile producing intracellular magnesium deficiency due to rutile-magnesium exchange sites in the cell membrane has been implicated in the etiology of EMF. Organisms like phytoplasmas and viroids have also been demonstrated to play a role in the etiology of these diseases. Actinidic archaea and viroids have been related to the pathogenesis of malignancies and degenerations. The actinidic archaea have a mevalonate pathway and cholesterol catabolism. An actinide dependent shadow biosphere of archaea and viroids regulating the cell cycle is described in the above mentioned disease states. Methods: The following groups were included in the study:- Group A: Non-hodgkin’s B cell lymphoma, multiple myeloma and cns glioma- glioblastoma multiforme. Group B :- Alzheimer’s disease, Parkinson’s disease, Huntington’s disease and Motor neuron disease. There were 10 patients in each group and each patient had an age and sex matched healthy control selected randomly from the general population. Cholesterol substrate was added to the plasma of the patients and the generation of cytochrome F420, free RNA, free DNA, polycyclic aromatic hydrocarbon, hydrogen peroxide, pyruvate, ammonia, glutamate, cytochrome C, hexokinase, ATP synthase, HMG CoA reductase, digoxin and bile acids were studied. The changes with the addition of antibiotics and rutile to the patient’s plasma were also studied. Results: The parameters mentioned above were increased the patient’s plasma with addition of cholesterol substrate. The addition of antibiotics to the patient’s plasma caused a decrease in all the parameters while addition of rutile increased their levels. Conc lus ion: An a c t inide dependent shadow biosphere of archaea and viroids is described in nonhodgkin’s B cell lymphoma, multiple myeloma and CNS glioma- glioblastoma multiforme producing the Warburg phenotype contributing to their pathogenesis. Actinidic archaea and viroids can also contribute to the cell death in Alzheimer’s disease, Parkinson’s disease, Huntington’s disease and Motor neuron disease. The role of actinidic archaea and viroids as well as endogenous digoxin in regulation of cell function, cell differentiation, cell proliferation and cell death is discussed. The endosymbiotic actinidic archaea and viroids can regulate the cell cycle and cellular organelle function. Key words : Archaea; Viroids; Cholesterol; Actinide; Non-Hodgkin’s Lymphoma; Multiple Myeloma; CNS Glioma; Alzheimer’s Disease; Parkinson’s Disease; Huntington’s Disease; Motor Neuron Disease; Cell Cycle; Organelle

Acetylated tau, a novel pathological signature in Alzheimer's disease and other tauopathies

The microtubule-binding protein, tau, is the major component of neurofibrillary inclusions characteristic of Alzheimer's disease and related neurodegenerative tauopathies. When tau fibrillizes, it undergoes abnormal post-translational modifications resulting in decreased solubility and altered microtubule-stabilizing properties. Recently, we reported that the abnormal acetylation of tau at lysine residue 280 is a novel, pathological post-translational modification. Here, we performed detailed immunohistochemistry to further examine acetylated-tau expression in Alzheimer's disease and other major tauopathies. Immunohistochemistry using a polyclonal antibody specific for acetylated-tau at lysine 280 was conducted on 30 post-mortem central nervous system regions from patients with Alzheimer's disease (10 patients), corticobasal degeneration (5 patients), and progressive supranuclear palsy (5 patients). Acetylated-tau pathology was compared with the sequential emergence of other tau modifications in the Alzheimer's disease hippocampus using monoclonal antibodies to multiple well-characterized tau epitopes. All cases studied showed significant acetylated-tau pathology in a distribution pattern similar to hyperphosphorylated-tau. Acetylated-tau pathology was largely in intracellular, thioflavin-S-positive tau inclusions in Alzheimer's disease, and also thioflavin-S-negative pathology in corticobasal degeneration and progressive supranuclear palsy. Acetylated-tau was present throughout all stages of Alzheimer's disease pathology, but was more prominently associated with pathological tau epitopes in moderate to severe-stage cases. These temporal and morphological immunohistochemical features suggest acetylation of tau at this epitope is preceded by early modifications, including phosphorylation, and followed by later truncation events and cell death in Alzheimer's disease. Acetylation of tau at lysine 280 is a pathological modification that may contribute to tau-mediated neurodegeneration by both augmenting losses of normal tau properties (reduced solubility and microtubule assembly) as well as toxic gains of function (increased tau fibrillization). Thus, inhibiting tau acetylation could be a disease-modifying target for drug discovery target in tauopathies.

Effect of Mutations on Aβ Monomer Flexibility: Implications for Peptide Association

Aggregates of the amyloid beta peptide (Aβ) are thought to trigger brain cell death in Alzheimer's disease patients. The current hypothesis is that Aβ aggregation occurs after the peptide is released from the cell membrane to the aqueous environment. Two different types of Aβ aggregates have been identified: soluble and insoluble. Soluble aggregates are formed in early stages of peptide association, whereas insoluble aggregates are the final state of aggregation. Interestingly, it is the soluble aggregates, not the insoluble ones, which correlate with disease progression. Despite the relevance of soluble aggregates as a target for Alzheimer's disease, their mechanism of formation is unknown. The formation of soluble aggregates in solution is strongly affected by mutations in the Aβ sequence. The role of local flexibility in protein function has recently received attention: in this study we ask whether local flexibility plays a similar role in soluble aggregate formation. To answer this question, we perform all-atom molecular dynamics simulations of the wild-type Aβ(1-40) monomer in water, and two mutated forms (Q15L & D23Y) that vary in their ability to form soluble aggregates. Our results show that the flexibility of the monomer is linked to the quantity of soluble aggregates formed: the more flexible peptide, D23Y, displays fewer soluble aggregates. Its enhanced flexibility could allow the peptide to more easily access the conformations most favorable to association and nucleation. Since Aβ aggregation and toxicity increase with peptide length, we compare monomer flexibility for the Aβ(1-40) peptides with their respective Aβ(1-42) analogues. The dynamic patterns are not conserved between the Aβ(1-40) and Aβ(1-42) versions; this suggests that mutations may affect Aβ monomer flexibility differently depending on its length.

The miR-124 regulates the expression of BACE1/β-secretase correlated with cell death in Alzheimer's disease

The role of miR-124 on the expression of β-site APP cleaving enzyme 1 (BACE1), an important cleavager of amyloid precursor protein that plays a pivotal role in the β-amyloid production, was studied in this paper using cellular models for Alzheimer’ disease (AD) of cultured PC12 cell lines and primary cultured hippocampal neurons. The aim of the present study was to uncover novel potential miR-124 targets and shed light on its function in the cellular AD model. MiR-124 expression was steadily altered when its mimic and inhibitor were transfected in vitro. The results showed the expression of BACE1, one of the potential functional downstream targets of miR-124, was well correlated with cell death induced by Aβ neurotoxicity, and its expression level could be up- and down-regulated by suppression or over expression of miR-124 level respectively. These findings suggest that miR-124 may work as a basilic regulating factor to alleviate cell death in the process of AD by targeting BACE1, play an essential role in the control of BACE1 gene expression, and might be considered as a novel therapeutic target in treating AD.

Inhibition of Polo-like kinase 1 reduces beta-amyloid-induced neuronal cell death in Alzheimer's disease

Alzheimer's disease (AD) is a progressive and fatal brain disease, but the pathogenesis of AD is still not understood. Aberrant cell-cycle re-entry of neuronal cells is emerging as a potential pathological mechanism in AD. Polo-like kinase 1 (Plk1) is an established regulator of many cell cycle-related events. Interestingly, Plk1 is present in susceptible hippocampal and cortical neurons of AD patients but not age-matched controls. However, whether Plk1 is involved in the pathogenesis of AD remains elusive. In this study, we showed that Plk1 activity is elevated in AD patient brain as indicated by the increased phosphorylation signal of p150Glued, a Plk1-specific substrate. Furthermore, we demonstrated that Plk1 is elevated during the cell-cycle re-entry of neuronal cells in an in vitro cell-culture model. Significantly, inhibition of Plk1 kinase activity or depletion of Plk1 by RNAi reduces β-amyloid (Aβ)-induced neuronal cell death. These results validate Plk1 as a possible target for AD therapy.

Amyloid β-Mediated Cell Death of Cultured Hippocampal Neurons Reveals Extensive Tau Fragmentation without Increased Full-length Tau Phosphorylation

A variety of genetic and biochemical evidence suggests that amyloid β (Aβ) oligomers promote downstream errors in Tau action, in turn inducing neuronal dysfunction and cell death in Alzheimer and related dementias. To better understand molecular mechanisms involved in Aβ-mediated neuronal cell death, we have treated primary rat hippocampal cultures with Aβ oligomers and examined the resulting cellular changes occurring before and during the induction of cell death with a focus on altered Tau biochemistry. The most rapid neuronal responses upon Aβ administration are activation of caspase 3/7 and calpain proteases. Aβ also appears to reduce Akt and Erk1/2 kinase activities while increasing GSK3β and Cdk5 activities. Shortly thereafter, substantial Tau degradation begins, generating relatively stable Tau fragments. Only a very small fraction of full-length Tau remains intact after 4 h of Aβ treatment. In conflict with expectations based on suggested increases of GSK3β and Cdk5 activities, Aβ does not cause any major increases in phosphorylation of full-length Tau as assayed by immunoblotting one-dimensional gels with 11 independent site- and phospho-specific anti-Tau antibodies as well as by immunoblotting two-dimensional gels probed with a pan-Tau antibody. There are, however, subtle and transient increases in Tau phosphorylation at 3-4 specific sites before its degradation. Taken together, these data are consistent with the notion that Aβ-mediated neuronal cell death involves the loss of full-length Tau and/or the generation of toxic fragments but does not involve or require hyperphosphorylation of full-length Tau.

Amyloid Precursor Protein Binding Protein Fe65 Is Cleaved by Caspases during DNA Damage-Induced Apoptosis

Caspases cleave several cellular proteins to execute cell death by apoptosis. The identification of novel substrates of caspases could provide an important clue for elucidation of new apoptosis signaling pathways. In this study, we tested whether an amyloid precursor protein (APP) binding protein Fe65 is proteolytically degraded in neuronal cell death by apoptosis, using a neuron-like cell line, human neuroblastoma SH-SY5Y cells. When treated with DNA damaging agents, etoposide (ETP) and camptothecin (CPT), SH-SY5Y cells underwent apoptosis in a dose-dependent manner. Interestingly, Fe65 (97 kDa) was cleaved to a 65 kDa product during DNA damage-induced apoptosis. Furthermore, the cleavage of Fe65 was accompanied by activation of caspases-9 and -3. The restriction cleavage of Fe65 was completely suppressed by the treatment with a pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(OMe) fluoromethylketone (z-VAD-fmk). These results reveal the restriction cleavage of Fe65 by caspases during DNA damage-induced apoptosis. Since Fe65 has been shown to suppress APP processing to amyloid β (Aβ) production, our findings may provide a new insight into the molecular mechanism by which DNA damage induces Aβ production and subsequent neuronal cell death in Alzheimer's disease (AD).

TEMPOL protects human neuroblastoma SH-SY5Y cells against ß-amyloid-induced cell toxicity

Amyloid-β peptide (Aβ) has been implicated in the pathogenesis of Alzheimer's disease (AD). It can cause cell death in Alzheimer's disease by evoking a cascade of oxidative damage to neurons. Antioxidant compounds may help to elucidate and develop a treatment for Alzheimer's disease. In the present study, we investigated the protective effect of TEMPOL (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy), a cyclic nitroxide which is particularly effective at reducing oxidative injury, on Aβ 1–42-induced SH-SY5Y cell toxicity. Exposure of cells to 20 μM Aβ 1–42 for 48 h caused viability loss and apoptotic increase, and pre-treatment with TEMPOL for 24 h significantly reduced the viability loss and apoptotic rate. In addition, TEMPOL inhibited Aβ 1–42-induced superoxide anion generation and hydroxyl radical generation to a striking degree. Based on these results, it is concluded that TEMPOL effectively protects SH-SY5Y cells against β-amyloid-induced damage by suppressing the generation of reactive oxygen species especially, superoxide anion.

Ginkgo biloba extract ameliorates oxidative phosphorylation performance and rescues abeta-induced failure.

BackgroundEnergy deficiency and mitochondrial failure have been recognized as a prominent, early event in Alzheimer's disease (AD). Recently, we demonstrated that chronic exposure to amyloid-beta (Aβ) in human neuroblastoma cells over-expressing human wild-type amyloid precursor protein (APP) resulted in (i) activity changes of complexes III and IV of the oxidative phosphorylation system (OXPHOS) and in (ii) a drop of ATP levels which may finally instigate loss of synapses and neuronal cell death in AD. Therefore, the aim of the present study was to investigate whether standardized Ginkgo biloba extract LI 1370 (GBE) is able to rescue Aβ-induced defects in energy metabolism.Methodology/Principal FindingsWe used a high-resolution respiratory protocol to evaluate OXPHOS respiratory capacity under physiological condition in control (stably transfected with the empty vector) and APP cells after treatment with GBE. In addition, oxygen consumption of isolated mitochondria, activities of mitochondrial respiratory enzymes, ATP and reactive oxygen species (ROS) levels as well as mitochondrial membrane mass and mitochondrial DNA content were determined. We observed a general antioxidant effect of GBE leading to an increase of the coupling state of mitochondria as well as energy homeostasis and a reduction of ROS levels in control cells and in APP cells. GBE effect on OXPHOS was even preserved in mitochondria after isolation from treated cells. Moreover, these functional data were paralleled by an up-regulation of mitochondrial DNA. Improvement of the OXPHOS efficiency was stronger in APP cells than in control cells. In APP cells, the GBE-induced amelioration of oxygen consumption most likely arose from the modulation and respective normalization of the Aβ-induced disturbance in the activity of mitochondrial complexes III and IV restoring impaired ATP levels possibly through decreasing Aβ and oxidative stress level.Conclusions/SignificanceAlthough the underlying molecular mechanisms of the mode of action of GBE remain to be determined, our study clearly highlights the beneficial effect of GBE on the cellular OXPHOS performance and restoration of Aβ-induced mitochondrial dysfunction.

FAD mutations in amyloid precursor protein do not directly perturb intracellular calcium homeostasis.

Disturbances in intracellular calcium homeostasis are likely prominent and causative factors leading to neuronal cell death in Alzheimer's disease (AD). Familial AD (FAD) is early-onset and exhibits autosomal dominant inheritance. FAD-linked mutations have been found in the genes encoding the presenilins and amyloid precursor protein (APP). Several studies have shown that mutated presenilin proteins can directly affect calcium release from intracellular stores independently of Aβ production. Although less well established, there is also evidence that APP may directly modulate intracellular calcium homeostasis. Here, we directly examined whether overexpression of FAD-linked APP mutants alters intracellular calcium dynamics. In contrast to previous studies, we found that overexpression of mutant APP has no effects on basal cytosolic calcium, ER calcium store size or agonist-induced calcium release and subsequent entry. Thus, we conclude that mutated APP associated with FAD has no direct effect on intracellular calcium homeostasis independently of Aβ production.

Alzheimer Aβ1−42 Monomer Adsorbed on the Self-Assembled Monolayers

Amyloid-beta (Abeta) peptide aggregation on the cell membranes is a key pathological event responsible for neuron cell death in Alzheimer's disease (AD). We present a collection of molecular docking and molecular dynamics simulations to study the conformational dynamics and adsorption behavior of Abeta monomer on the self-assembled monolayer (SAM), in comparison to Abeta structure in bulk solution. Two distinct Abeta conformations (i.e., alpha-helix and beta-hairpin) are selected as initial structures to mimic different adsorption states, whereas four SAM surfaces with different end groups in hydrophobicity and charge distribution are used to examine the effect of surface chemistry on Abeta structure and adsorption. Simulation results show that alpha-helical monomer displays higher structural stability than beta-hairpin monomer on all SAMs, suggesting that the preferential conformation of Abeta monomer could be alpha-helical or random structure when bound to surfaces. Structural stability and adsorption behavior of Abeta monomer on the SAMs originates from competitive interactions between Abeta and SAM and between SAM and interfacial water, which involve the conformation of Abeta, the surface chemistry of SAM, and the structure and dynamics of interfacial waters. The relative net binding affinity of Abeta with the SAMs is in the favorable order of COOH-SAM > NH(2)-SAM > CH(3)-SAM > OH-SAM, highlighting the importance of electrostatic and hydrophobic interactions for driving Abeta adsorption at the SAMs, but both interactions contribute differently to each Abeta-SAM complex. This work provides parallel insights into the understanding of Abeta structure and aggregation on cell membrane.

Lysosomal Proteolysis and Autophagy Require Presenilin 1 and Are Disrupted by Alzheimer-Related PS1 Mutations

Macroautophagy is a lysosomal degradative pathway essential for neuron survival. Here, we show that macroautophagy requires the Alzheimer's disease (AD)-related protein presenilin-1 (PS1). In PS1 null blastocysts, neurons from mice hypomorphic for PS1 or conditionally depleted of PS1, substrate proteolysis and autophagosome clearance during macroautophagy are prevented as a result of a selective impairment of autolysosome acidification and cathepsin activation. These deficits are caused by failed PS1-dependent targeting of the v-ATPase V0a1 subunit to lysosomes. N-glycosylation of the V0a1 subunit, essential for its efficient ER-to-lysosome delivery, requires the selective binding of PS1 holoprotein to the unglycosylated subunit and the Sec61alpha/oligosaccharyltransferase complex. PS1 mutations causing early-onset AD produce a similar lysosomal/autophagy phenotype in fibroblasts from AD patients. PS1 is therefore essential for v-ATPase targeting to lysosomes, lysosome acidification, and proteolysis during autophagy. Defective lysosomal proteolysis represents a basis for pathogenic protein accumulations and neuronal cell death in AD and suggests previously unidentified therapeutic targets.

Evidence for the Involvement of Apoptosis-Inducing Factor–Mediated Caspase-Independent Neuronal Death in Alzheimer Disease

Accumulating evidence suggests the involvement of caspase-dependent and -independent mechanisms in neuronal cell death in Alzheimer disease (AD). The apoptosis-inducing factor (AIF) is a mitochondrial oxido-reductase originally characterized as a mediator of caspase-independent programmed cell death (PCD). In this postmortem study, we investigated the distribution of AIF and its possible morphological association with pathological features in the hippocampus, as well as entorhinal and medial gyrus of temporal cortices of late stage AD, dementia with Lewy bodies (DLB), and control subjects. In comparison with controls, a significant increase in neuronal AIF immunoreactivity (AIF-ir) was observed in the hippocampus and the superficial layers of entorhinal and medial gyrus of temporal cortices in AD--but not DLB--samples. AIF-ir in neuronal nuclei was also significantly more widespread in AD compared with control and DLB samples. Furthermore, AIF-ir was found to be colocalized with neurofibrillary tangles (NFTs) in AD brains. Interestingly, a significant positive correlation was seen between nuclear AIF-ir and Braak stage in CA1 of the hippocampus as well as in entorhinal and temporal cortices in AD samples. These data show for the first time: (1) the nuclear localization of AIF in the AD brain and (2) its colocalization with NFTs, suggesting a possible involvement of AIF-mediated caspase-independent PCD, at least in the late stage of this neuropathology.

ER Stress-Mediated Apoptotic Pathway Induced by Aβ Peptide Requires the Presence of Functional Mitochondria

Amyloid-beta (Abeta) peptide plays a significant role in the pathogenesis of Alzheimer's disease (AD). Previously we found that Abeta induces both mitochondrial and endoplasmic reticulum (ER) dysfunction leading to apoptosis, and now we address the relevance of ER-mitochondria crosstalk in apoptotic cell death triggered by Abeta peptide. Using mitochondrial DNA-depleted rho0 cells derived from the human NT2 teratocarcinoma cell line, characterized by the absence of functional mitochondria, and the parental rho+ cells, we report here that treatment with the synthetic Abeta1-40 peptide, or the classical ER stressors thapsigargin or brefeldin A, increases GRP78 expression levels and caspase activity, two ER stress markers, and also depletes ER calcium stores. Significantly, we show that the presence of functional mitochondria is required for ER stress-mediated apoptotic cell death triggered by toxic insults such as Abeta. We found that the increase in the levels of the pro-apoptotic transcription factor GADD153/CHOP, which mediates ER stress-induced cell death, as well as caspase-9 and -3 activation and increased number of TUNEL-positive cells, occurs in treated parental rho+ cells but is abolished in rho0 cells. Our results strongly support the close communication between ER and mitochondria during apoptotic cell death induced by the Abeta peptide and provide insights into the molecular cascade of cell death in AD.

Differential Effects of ApoE Isoforms on Dendritic SpinesIn Vivo: Linking an Alzheimer's Disease Risk Factor with Synaptic Alterations

The e4 allele of apolipoprotein E (APOE) is the strongest genetic risk factor for the development of Alzheimer's disease (AD). Accumulation of amyloid-β (Aβ) is hypothesized to initiate synaptic and neuronal dysfunction that ultimately lead to neuronal cell death in AD, and several lines of

The Connecdenn DENN Domain: A GEF for Rab35 Mediating Cargo-Specific Exit from Early Endosomes

The DENN domain is an evolutionarily ancient protein module. Mutations in the DENN domain cause developmental defects in plants and human diseases, yet the function of this common module is unknown. We now demonstrate that the connecdenn/DENND1A DENN domain functions as a guanine nucleotide exchange factor (GEF) for Rab35 to regulate endosomal membrane trafficking. Loss of Rab35 activity causes an enlargement of early endosomes and inhibits MHC class I recycling. Moreover, it prevents early endosomal recruitment of EHD1, a common component of tubules involved in endosomal cargo recycling. Our data reveal an enzymatic activity for a DENN domain and demonstrate that distinct Rab GTPases can recruit a common protein machinery to various sites within the endosomal network to establish cargo-selective recycling pathways.

Cystatin C protects neuronal cells from amyloid-beta-induced toxicity.

Multiple studies suggest that cystatin C (CysC) has a role in Alzheimer's disease (AD) and a decrease in CysC secretion is linked to the disease in patients with a polymorphism in the CysC gene. CysC binds amyloid-beta (Abeta) and inhibits formation of Abeta fibrils and oligomers both in vitro and in mouse models of amyloid deposition. Here we studied the effect of CysC on cultured primary hippocampal neurons and a neuronal cell line exposed to either oligomeric or fibrillar cytotoxic forms of Abeta. The extracellular addition of the secreted human CysC together with preformed either oligomeric or fibrillar Abeta increased cell survival. While CysC inhibits Abeta aggregation, it does not dissolve preformed Abeta fibrils or oligomers. Thus, CysC has multiple protective effects in AD, by preventing the formation of the toxic forms of Abeta and by direct protection of neuronal cells from Abeta toxicity. Therapeutic manipulation of CysC levels, resulting in slightly higher concentrations than physiological could protect neuronal cells from cell death in AD.