Identification of synaptic plasma membrane proteins co-precipitated with fibrillar β-amyloid peptide

Glyceraldehyde-3-phosphate dehydrogenase is involved in the pathogenesis of Alzheimer's disease

One of important characteristics of Alzheimer's disease is a persistent oxidative/nitrosative stress caused by pro-oxidant properties of amyloid-beta peptide (Aβ) and chronic inflammation in the brain. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is easily oxidized under oxidative stress. Numerous data indicate that oxidative modifications of GAPDH in vitro and in cell cultures stimulate GAPDH denaturation and aggregation, and the catalytic cysteine residue Cys152 is important for these processes. Both intracellular and extracellular GAPDH aggregates are toxic for the cells. Interaction of denatured GAPDH with soluble Aβ results in mixed insoluble aggregates with increased toxicity. The above-described properties of GAPDH (sensitivity to oxidation and propensity to form aggregates, including mixed aggregates with Aβ) determine its role in the pathogenesis of Alzheimer's disease.

Amyloid precursor protein (APP) and amyloid β (Aβ) interact with cell adhesion molecules: Implications in Alzheimer’s disease and normal physiology

Alzheimer’s disease (AD) is an incurable neurodegenerative disorder in which dysfunction and loss of synapses and neurons lead to cognitive impairment and death. Accumulation and aggregation of neurotoxic amyloid-β (Aβ) peptides generated via amyloidogenic processing of amyloid precursor protein (APP) is considered to play a central role in the disease etiology. APP interacts with cell adhesion molecules, which influence the normal physiological functions of APP, its amyloidogenic and non-amyloidogenic processing, and formation of Aβ aggregates. These cell surface glycoproteins also mediate attachment of Aβ to the neuronal cell surface and induce intracellular signaling contributing to Aβ toxicity. In this review, we discuss the current knowledge surrounding the interactions of cell adhesion molecules with APP and Aβ and analyze the evidence of the critical role these proteins play in regulating the processing and physiological function of APP as well as Aβ toxicity. This is a necessary piece of the complex AD puzzle, which we should understand in order to develop safe and effective therapeutic interventions for AD.

Synaptosome as a tool in Alzheimer's disease research

Synapse dysfunction is an integral feature of Alzheimer's disease (AD) pathophysiology. In fact, prodromal manifestation of structural and functional deficits in synapses much prior to appearance of overt pathological hallmarks of the disease indicates that AD might be considered as a degenerative disorder of the synapses. Several research instruments and techniques have allowed us to study synaptic function and plasticity and their alterations in pathological conditions, such as AD. One such tool is the biochemically isolated preparations of detached and resealed synaptic terminals, the "synaptosomes". Because of the preservation of many of the physiological processes such as metabolic and enzymatic activities, synaptosomes have proved to be an indispensable ex vivo model system to study synapse physiology both when isolated from fresh or cryopreserved tissues, and from animal or human post-mortem tissues. This model system has been tremendously successful in the case of post-mortem tissues because of their accessibility relative to acute brain slices or cultures. The current review details the use of synaptosomes in AD research and its potential as a valuable tool in furthering our understanding of the pathogenesis and in devising and testing of therapeutic strategies for the disease.

An investigation of the correlation between the S-glutathionylated GAPDH levels in blood and Alzheimer's disease progression

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by two aggregates, namely, amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs) of hyperphosphorylated tau protein (tau-p), which are released into the blood in a very small amount and cannot be easily detected. An increasing number of recent studies have suggested that S-glutathionylated glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is highly correlated with Aβ in patients with AD and that S-glutathionylated GAPDH plays a role as a proapoptotic factor in AD. We found that S-glutathionylated GAPDH is abundant in the blood of AD patients, which is unusual because S-glutathionylated GAPDH cannot exist in the blood under normal conditions. The aim of this study was to further explore the correlation between the S-glutathionylated GAPDH levels in blood plasma and AD progression. As controls, we recruited 191 people without AD, which included 111 healthy individuals and 37 patients with depression and insomnia, in the psychosomatic clinic. Moreover, 47 patients with AD (aged 40–89 years) were recruited at the neurology clinic. The blood S-glutathionylated GAPDH levels in the AD patients were significantly (p < 0.001) higher (752.7 ± 301.7 ng/dL) than those in the controls (59.92 ± 122.4 ng/dL), irrespective of gender and age. For AD diagnosis, the criterion blood S-glutathionylated GAPDH level > 251.62 ng/dL exhibited 95.74% sensitivity and 92.67% specificity. In fact, the individuals aged 70–89 years, namely, 37 patients from the psychosomatic clinic and 42 healthy individuals, showed significant blood S-glutathionylated GAPDH levels (230.5 ± 79.3 and 8.05 ± 20.51 ng/dL, respectively). This finding might indicate neurodegenerative AD progression in psychosomatic patients and suggests that the degree of neuronal apoptosis during AD progression might be sensitively evaluated based on the level of S-glutathionylated GAPDH in blood.

Comparison of protective properties of resveratrol and melatonin in the radiation inactivation and destruction of glyceraldehyde-3-phosphate dehydrogenase and lactate dehydrogenase

Purpose: This work investigates the effect of resveratrol and melatonin on structural and functional changes of two enzymes, lactate dehydrogenase (LDH) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), exposed to radiation-induced reactive oxygen species.Materials and methods: Solutions of dehydrogenases with or without antioxidants (resveratrol or melatonin) were irradiated with X-rays under the atmosphere of air and at room temperature (21 ± 2 °C). In order to determine the protective effect of melatonin and resveratrol in radiation-induced damage to GAPDH and LDH spectroscopy and HPLC methods were used. Furthermore, plausible binding sites of melatonin or resveratrol to the GAPDH or LDH molecule were analysed.Results and conclusions: Resveratrol shows better protective properties in the inactivation of GAPDH when compared to melatonin. LDH does not contain ‒SH groups in its active site, and is not inactivated by water radiolysis products other than hydroxyl radicals or the secondary radicals of the studied low-molecular-weight compounds. Resveratrol and melatonin protected the structure of LDH to a greater extent than GAPDH. This difference can be attributed to the fact that LDH potentially binds more resveratrol or melatonin molecules (27 binding sites for resveratrol and 40 for melatonin) than GAPDH (10 binding sites for resveratrol and 18 for melatonin).

Regional hypometabolism in the 3xTg mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive age-related neurodegenerative disease. Although neurofibrillary tangles and amyloid beta are classic hallmarks of AD, the earliest deficits in AD progression may be caused by unknown factors. One suspected factor has to do with brain energy metabolism. To investigate this factor, brain metabolic activity in 3xTg-AD mice and age-matched controls were measured with FDG-PET. Significant hypometabolic changes (p < .01) in brain metabolism were detected in the cortical piriform and insular regions of AD brains relative to controls. These regions are associated with olfaction, which is a potential clinical marker for AD progression as well as neurogenesis. The activity of the terminal component of the mitochondrial respiratory chain (complex IV) and the expression of complex I-V were significantly decreased (p < .05), suggesting that impaired metabolic activity coupled with impaired oxidative phosphorylation leads to decreased mitochondrial bioenergetics and subsequent Neurodegeneration. Although there is an association between neuroinflammatory pathological markers (microglial) and hypometabolism in AD, there was no association found between neuropathological (Aβ, tau, and astrocytes) and functional changes in AD sensitive brain regions, also suggesting that brain hypometabolism occurs prior to AD pathology. Therefore, targeting metabolic mechanisms in cortical piriform and insular regions at early stages may be a promising approach for preventing, slowing, and/or blocking the onset of AD and preserving neurogenesis.

Oxidatively modified glyceraldehyde-3-phosphate dehydrogenase in neurodegenerative processes and the role of low molecular weight compounds in counteracting its aggregation and nuclear translocation

A number of independent studies have shown the contribution of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the pathogenesis of several neurodegenerative disorders. Indeed, GAPDH aggregates have been found in many post-mortem samples of brains of patients diagnosed with Alzheimer's and Parkinson disease. Currently, it is accepted that GAPDH-mediated cell death pathways in the neurodegenerative processes are associated with apoptosis caused by GAPDH nuclear translocation and excessive aggregation under oxidative stress conditions. Also the role of GAPDH in neurodegenerative diseases is linked to it directly binding to specific amyloidogenic proteins and petides such as β-amyloid precursor protein, β-amyloid peptide and tau protein in Alzheimer's disease, huntingtin in Huntington's disease and α-synuclein in Parkinson disease. One of the latest studies indicated that GAPDH aggregates significantly accelerate amyloidogenesis of the β-amyloid peptide, which implies that aggregates of GAPDH may act as a specific aggregation "seed" in vitro. Previous detailed studies revealed that the active-site cysteine (Cys152) of GAPDH plays an essential role in the oxidative stress-induced aggregation of GAPDH associated with cell death. Furthermore, oxidative modification of this cysteine residue initiates the translocation of the enzyme to the nucleus, subsequently leading to apoptosis. The crystallographic structure of GAPDH shows that the Cys152 residue is located close to the surface of the molecule in a hydrophilic environment, which means that it can react with low molecular weight compounds such as hydroxynonenal or piceatannol. Therefore, it is highly possible that GAPDH may serve as a target for small molecule compounds with the potential to slow down or prevent the progression of neurodegenerative disorders. Recently appearing new evidence has highlighted the significance of low molecular weight compounds in counteracting the oxidation of GAPDH and consequently its aggregation and other unfavourable pathological processes. Hence, this review aims to present all recent findings concerning molecules that are able to interact with GAPDH and counteract its aggregation and translocation to the nucleus.

Somatostatin binds to the human amyloid β peptide and favors the formation of distinct oligomers

The amyloid β peptide (Aβ) is a key player in the etiology of Alzheimer disease (AD), yet a systematic investigation of its molecular interactions has not been reported. Here we identified by quantitative mass spectrometry proteins in human brain extract that bind to oligomeric Aβ1-42 (oAβ1-42) and/or monomeric Aβ1-42 (mAβ1-42) baits. Remarkably, the cyclic neuroendocrine peptide somatostatin-14 (SST14) was observed to be the most selectively enriched oAβ1-42 binder. The binding interface comprises a central tryptophan within SST14 and the N-terminus of Aβ1-42. The presence of SST14 inhibited Aβ aggregation and masked the ability of several antibodies to detect Aβ. Notably, Aβ1-42, but not Aβ1-40, formed in the presence of SST14 oligomeric assemblies of 50 to 60 kDa that were visualized by gel electrophoresis, nanoparticle tracking analysis and electron microscopy. These findings may be relevant for Aβ-directed diagnostics and may signify a role of SST14 in the etiology of AD.

DOI:http://dx.doi.org/10.7554/eLife.28401.001

Treating Alzheimer’s disease and related dementias is one of the major challenges currently facing healthcare providers worldwide. A hallmark of the disease is the formation of large deposits of a specific molecule, known as amyloid beta (Aβ), in the brain. However, more and more research suggests that smaller and particularly toxic amyloid beta clumps – often referred to as oligomeric Aβ – appear as an early sign of Alzheimer’s disease.

To understand how the formation of these smaller amyloid beta clumps triggers other aspects of the disease, it is important to identify molecules in the human brain that oligomeric Aβ binds to. To this end, Wang et al. attached amyloid beta or oligomeric Aβ molecules to microscopically small beads. The beads were then exposed to human brain extracts in a test tube, which allowed molecules in the extracts to bind to the amyloid beta or oligomeric Aβ. The samples were then spun at high speed, meaning that the beads and any other molecules bound to them sunk and formed pellets at the bottom of the tubes. Each pellet was then analyzed to see which molecules it contained.

The experiments identified more than a hundred human brain proteins that can bind to amyloid beta. One of them, known as somatostatin, selectively binds to oligomeric Aβ. Wang et al. were able to determine the structural features of somatostatin that control this binding.

Finally, in further experiments performed in test tubes, Wang et al. noticed that smaller oligomeric Aβ clumps were more likely to form than larger amyloid beta deposits when somatostatin was present. This could signify a previously unrecognized role of somatostatin in the development of Alzheimer’s disease.

Further studies are now needed to confirm whether the presence of somatostatin in the brain favors the formation of smaller, toxic oligomeric Aβ clumps over large innocuous amyloid beta deposits. If so, new treatments could be developed that aim to reduce oligomeric Aβ levels in the brain by preventing somatostatin from interacting with amyloid beta molecules. Wang et al. also suggest that somatostatin could be used in diagnostic tests to detect abnormal levels of oligomeric Aβ in the brain or body fluids of people who have Alzheimer’s disease.

DOI:http://dx.doi.org/10.7554/eLife.28401.002

Assessment of GAPDH expression by quantitative real time PCR in blood of Moroccan AD cases

INTRODUCTION

Neuroproteomics studies have showed the high affinity interactions between GAPDH - β-amyloid in Alzheimer disease. The aim of our study is to complete our previous studies by assessing the mechanism responsible of decreased expression of GAPDH protein in the blood of Moroccan AD cases probably due to an alteration at the transcriptional level or at the post translational level.

METHODS

The mRNA expression of GAPDH was assessed by quantitative real time PCR in AD cases and healthy controls.

RESULTS

Our result revealed a significant difference of mRNA expression level of GAPDH in AD cases as compared to healthy controls (P<0.05).

CONCLUSION

This data is consistent with several studies by showing the direct involvement of GAPDH in amyloid aggregation by undergoing several modifications, which influence its chemical structure and its biological activity.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and Alzheimer's disease

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a ubiquitous enzyme that catalyzes the sixth step of glycolysis and thus, serves to break down glucose for energy production. Beyond the traditional aerobic metabolism of glucose, recent studies have highlighted additional roles played by GAPDH in non-metabolic processes, such as control of gene expression and redox post-translational modifications. Neuroproteomics have revealed high affinity interactions between GAPDH and Alzheimer's disease-associated proteins, including the β-amyloid, β-amyloid precursor protein and tau. This neuronal protein interaction may lead to impairment of the GAPDH glycolytic function in Alzheimer's disease and may be a forerunner of its participation in apoptosis. The present review examines the crucial implication of GAPDH in neurodegenerative processes and clarifies its role in apoptotic cell death.

A proteomic approach for the involvement of the GAPDH in Alzheimer disease in the blood of Moroccan FAD cases

Several articles have highlighted the potential involvement of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in neurodegeneration by showing a non-glycolytic activity of GAPDH specifically in the brains of subjects with Alzheimer's disease (AD). The novel aim of this study was to elucidate the critical role of GAPDH and its interaction with β-amyloid in the blood of Moroccan patients with familial AD (FAD) carrying presenilin mutations and in sporadic late onset AD (LOAD). Our results show a significant decrease in the activity of GAPDH in blood samples from patients with FAD as compared to sporadic cases and healthy controls. The expression level of GAPDH in brain specimens from mutant tau transgenic mice and patients with FAD was unchanged as compared to healthy controls. In contrast, the expression level of GAPDH in blood samples from mutant tau transgenic mice and patients with FAD was decreased as compared to sporadic cases and healthy controls. Moreover, there is an accumulation of β-amyloid aggregates in the blood samples of patients with FAD and an increase in amyloid fibrils in both the blood and brain samples of these patients. Our study adds new insight to previous ones by showing the involvement of GAPDH in AD, which may influence the pathogenesis of this neurodegenerative disease.

Interactions of pathological hallmark proteins: tubulin polymerization promoting protein/p25, beta-amyloid, and alpha-synuclein

The disordered tubulin polymerization promoting protein (TPPP/p25) was found to be co-enriched in neuronal and glial inclusions with α-synuclein in Parkinson disease and multiple system atrophy, respectively; however, co-occurrence of α-synuclein with β-amyloid (Aβ) in human brain inclusions has been recently reported, suggesting the existence of mixed type pathologies that could result in obstacles in the correct diagnosis and treatment. Here we identified TPPP/p25 as an interacting partner of the soluble Aβ oligomers as major risk factors for Alzheimer disease using ProtoArray human protein microarray. The interactions of oligomeric Aβ with proteins involved in the etiology of neurological disorders were characterized by ELISA, surface plasmon resonance, pelleting experiments, and tubulin polymerization assay. We showed that the Aβ(42) tightly bound to TPPP/p25 (K(d) = 85 nm) and caused aberrant protein aggregation by inhibiting the physiologically relevant TPPP/p25-derived microtubule assembly. The pair-wise interactions of Aβ(42), α-synuclein, and tubulin were found to be relatively weak; however, these three components formed soluble ternary complex exclusively in the absence of TPPP/p25. The aggregation-facilitating activity of TPPP/p25 and its interaction with Aβ was monitored by electron microscopy with purified proteins by pelleting experiments with cell-free extracts as well as by confocal microscopy with CHO cells expressing TPPP/p25 or amyloid. The finding that the interaction of TPPP/p25 with Aβ can produce pathological-like aggregates is tightly coupled with unusual pathology of the Alzheimer disease revealed previously; that is, partial co-localization of Aβ and TPPP/p25 in the case of diffuse Lewy body disease with Alzheimer disease.

Lipid raft proteome reveals that oxidative phosphorylation system is associated with the plasma membrane

Although accumulating proteomic analyses have supported the fact that mitochondrial oxidative phosphorylation (OXPHOS) complexes are localized in lipid rafts, which mediate cell signaling, immune response and host-pathogen interactions, there has been no in-depth study of the physiological functions of lipid-raft OXPHOS complexes. Here, we show that many subunits of OXPHOS complexes were identified from the lipid rafts of human adipocytes, C2C12 myotubes, Jurkat cells and surface biotin-labeled Jurkat cells via shotgun proteomic analysis. We discuss the findings of OXPHOS complexes in lipid rafts, the role of the surface ATP synthase complex as a receptor for various ligands and extracellular superoxide generation by plasma membrane oxidative phosphorylation complexes.

Proteomic identification of protein targets for 15-deoxy-Δ(12,14)-prostaglandin J2 in neuronal plasma membrane

15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)) is one of factors contributed to the neurotoxicity of amyloid β (Aβ), a causative protein of Alzheimer's disease. Type 2 receptor for prostaglandin D(2) (DP2) and peroxysome-proliferator activated receptorγ (PPARγ) are identified as the membrane receptor and the nuclear receptor for 15d-PGJ(2), respectively. Previously, we reported that the cytotoxicity of 15d-PGJ(2) was independent of DP2 and PPARγ, and suggested that 15d-PGJ(2) induced apoptosis through the novel specific binding sites of 15d-PGJ(2) different from DP2 and PPARγ. To relate the cytotoxicity of 15d-PGJ(2) to amyloidoses, we performed binding assay [(3)H]15d-PGJ(2) and specified targets for 15d-PGJ(2) associated with cytotoxicity. In the various cell lines, there was a close correlation between the susceptibilities to 15d-PGJ(2) and fibrillar Aβ. Specific binding sites of [(3)H]15d-PGJ(2) were detected in rat cortical neurons and human bronchial smooth muscle cells. When the binding assay was performed in subcellular fractions of neurons, the specific binding sites of [(3)H]15d-PGJ(2) were detected in plasma membrane, nuclear and cytosol, but not in microsome. A proteomic approach was used to identify protein targets for 15d-PGJ(2) in the plasma membrane. By using biotinylated 15d-PGJ(2), eleven proteins were identified as biotin-positive spots and classified into three different functional proteins: glycolytic enzymes (Enolase2, pyruvate kinase M1 (PKM1) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH)), molecular chaperones (heat shock protein 8 and T-complex protein 1 subunit α), cytoskeletal proteins (Actin β, F-actin-capping protein, Tubulin β and Internexin α). GAPDH, PKM1 and Tubulin β are Aβ-interacting proteins. Thus, the present study suggested that 15d-PGJ(2) plays an important role in amyloidoses not only in the central nervous system but also in the peripheral tissues.

Oxidatively modified glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and Alzheimer's disease: many pathways to neurodegeneration

Recently, the oxidoreductase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), has become a subject of interest as more and more studies reveal a surfeit of diverse GAPDH functions, extending beyond traditional aerobic metabolism of glucose. As a result of multiple isoforms and cellular locales, GAPDH is able to come in contact with a variety of small molecules, proteins, membranes, etc., that play important roles in normal and pathologic cell function. Specifically, GAPDH has been shown to interact with neurodegenerative disease-associated proteins, including the amyloid-beta protein precursor (AbetaPP). Studies from our laboratory have shown significant inhibition of GAPDH dehydrogenase activity in Alzheimer's disease (AD) brain due to oxidative modification. Although oxidative stress and damage is a common phenomenon in the AD brain, it would seem that inhibition of glycolytic enzyme activity is merely one avenue in which AD pathology affects neuronal cell development and survival, as oxidative modification can also impart a toxic gain-of-function to many proteins, including GAPDH. In this review, we examine the many functions of GAPDH with respect to AD brain; in particular, the apparent role(s) of GAPDH in AD-related apoptotic cell death is emphasized.

Genome-wide identification of new Wnt/beta-catenin target genes in the human genome using CART method

Background

The importance of in silico predictions for understanding cellular processes is now widely accepted, and a variety of algorithms useful for studying different biological features have been designed. In particular, the prediction of cis regulatory modules in non-coding human genome regions represents a major challenge for understanding gene regulation in several diseases. Recently, studies of the Wnt signaling pathway revealed a connection with neurodegenerative diseases such as Alzheimer's. In this article, we construct a classification tool that uses the transcription factor binding site motifs composition of some gene promoters to identify new Wnt/β-catenin pathway target genes potentially involved in brain diseases.

Results

In this study, we propose 89 new Wnt/β-catenin pathway target genes predicted in silico by using a method based on multiple Classification and Regression Tree (CART) analysis. We used as decision variables the presence of transcription factor binding site motifs in the upstream region of each gene. This prediction was validated by RT-qPCR in a sample of 9 genes. As expected, LEF1, a member of the T-cell factor/lymphoid enhancer-binding factor family (TCF/LEF1), was relevant for the classification algorithm and, remarkably, other factors related directly or indirectly to the inflammatory response and amyloidogenic processes also appeared to be relevant for the classification. Among the 89 new Wnt/β-catenin pathway targets, we found a group expressed in brain tissue that could be involved in diverse responses to neurodegenerative diseases, like Alzheimer's disease (AD). These genes represent new candidates to protect cells against amyloid β toxicity, in agreement with the proposed neuroprotective role of the Wnt signaling pathway.

Conclusions

Our multiple CART strategy proved to be an effective tool to identify new Wnt/β-catenin pathway targets based on the study of their regulatory regions in the human genome. In particular, several of these genes represent a new group of transcriptional dependent targets of the canonical Wnt pathway. The functions of these genes indicate that they are involved in pathophysiology related to Alzheimer's disease or other brain disorders.

Protection against beta-amyloid-induced apoptosis by peptides interacting with beta-amyloid

beta-Amyloid peptide produces apoptosis in neurons at micromolar concentrations, but the mechanism by which beta-amyloid exerts its toxic effect is unknown. The normal biological function of beta-amyloid is also unknown. We used phage display, co-precipitation, and mass spectrometry to examine the protein-protein interactions of beta-amyloid in normal rabbit brain in order to identify the biochemical receptors for beta-amyloid. beta-Amyloid was found to bind primarily to proteins involved in low density lipoprotein and cholesterol transport and metabolism, including sortilin, endoplasmic reticulum-Golgi intermediate compartment 2 (ERGIC2), ERGIC-53, steroid 5alpha-reductase, and apolipoprotein B. beta-Amyloid also bound to the C-reactive protein precursor, a protein involved in inflammation, and to 14-3-3, a protein that regulates glycogen synthase kinase-3beta, the kinase involved in tau phosphorylation. Of eight synthetic peptides identified as targets of beta-amyloid, three were found to be effective blockers of the toxic effect of beta-amyloid on cultured neuronal cells. These peptides bound to the hydrophobic region (residues 17-21) or to the nearby protein kinase C pseudo-phosphorylation site (residues 26-30) of beta-amyloid, suggesting that these may be the most critical regions for beta-amyloid effector action and for aggregation. Peptides or other small molecules that bind to this region may protect against beta-amyloid toxic effect by competitively blocking its ability to bind beta-amyloid effector proteins such as sortilin and 14-3-3.

Localizations of endogenous APP/APP-proteolytic products are consistent with microtubular transport

Dementia of the Alzheimer type (DAT) is associated with the accumulation of beta-amyloid (A beta) peptides derived from beta-amyloid precursor protein (APP). Goldstein and coworkers have suggested that APP acts as a cargo receptor connecting post-Golgi vesicles and motor proteins. Sisodia and colleagues have suggested that APP is a passive passenger within the vesicles. Both views predict that one should be able to visualize colocalizations of APP with microtubules, the object of the present investigation. To avoid possible artifacts created by APP overexpression, we studied endogenous expression in a human neuroblastoma cell line (SK-N-SH). Using high resolution fluorescence microscopy and antibodies specific for the amino termini of APP and A beta sequences, we found that endogenous APP and A beta peptide immunoreactivities colocalized with microtubules in interphase cells. Disruption of microtubules, followed by fixation at various time points during repolymerization, allowed us to observe the sequence and timing of these colocalizations in interphase cells. In addition, to our surprise, we found that A beta immunoreactivities colocalize with the mitotic spindle, a bundle of specialized microtubules. Because of the condensed cytoplasm found in neurons, we suggest that SK-N-SH cells might be a more convenient experimental system for exploring the mechanisms that underlie these protein localizations and the pathology that might result from altered APP protein structure and function.

Differential proteomics analysis of synaptic proteins identifies potential cellular targets and protein mediators of synaptic neuroprotection conferred by the slow Wallerian degeneration (Wlds) gene

Non-somatic synaptic and axonal compartments of neurons are primary pathological targets in many neurodegenerative conditions, ranging from Alzheimer disease through to motor neuron disease. Axons and synapses are protected from degeneration by the slow Wallerian degeneration (Wld(s)) gene. Significantly the molecular mechanisms through which this spontaneous genetic mutation delays degeneration remain controversial, and the downstream protein targets of Wld(s) resident in non-somatic compartments remain unknown. In this study we used differential proteomics analysis to identify proteins whose expression levels were significantly altered in isolated synaptic preparations from the striatum of Wld(s) mice. Eight of the 16 proteins we identified as having modified expression levels in Wld(s) synapses are known regulators of mitochondrial stability and degeneration (including VDAC1, Aralar1, and mitofilin). Subsequent analyses demonstrated that other key mitochondrial proteins, not identified in our initial screen, are also modified in Wld(s) synapses. Of the non-mitochondrial proteins identified, several have been implicated in neurodegenerative diseases where synapses and axons are primary pathological targets (including DRP-2 and Rab GDP dissociation inhibitor beta). In addition, we show that downstream protein changes can be identified in pathways corresponding to both Ube4b (including UBE1) and Nmnat1 (including VDAC1 and Aralar1) components of the chimeric Wld(s) gene, suggesting that full-length Wld(s) protein is required to elicit maximal changes in synaptic proteins. We conclude that altered mitochondrial responses to degenerative stimuli are likely to play an important role in the neuroprotective Wld(s) phenotype and that targeting proteins identified in the current study may lead to novel therapies for the treatment of neurodegenerative diseases in humans.